Crystallization of the Kob-Andersen binary Lennard-Jones liquid

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气泡形核 bubble nucleation ,growth and coalescence

Bubble nucleation,growth and coalescence during the 1997Vulcanian explosions of Soufrière Hills Volcano,MontserratT.Giachetti a ,b ,c ,⁎,T.H.Druitt a ,b ,c ,A.Burgisser d ,L.Arbaret d ,C.Galven eaClermont Université,UniversitéBlaise Pascal,Laboratoire Magmas et Volcans,BP 10448,F-63000Clermont-Ferrand,France bCNRS,UMR 6524,LMV,F-63038Clermont-Ferrand,France cIRD,R 163,LMV,F-63038Clermont-Ferrand,France dInstitut des Sciences de la Terre d'Orléans,Universitéd'Orléans,1A,rue de la Férollerie,45071Orléans Cedex 2,France eLaboratoire des Oxydes et Fluorures,Facultédes Sciences et Techniques,Universitédu Maine,Avenue Olivier Messiaen,72085Le Mans Cedex 9,Francea b s t r a c ta r t i c l e i n f o Article history:Received 29July 2009Accepted 5April 2010Available online 13April 2010Keywords:Vulcanian explosions Soufrière Hills vesiculationbubble nucleation bubble growth coalescenceamphibole boudinageSoufrière Hills Volcano had two periods of repetitive Vulcanian activity in 1997.Each explosion discharged the contents of the upper 0.5–2km of the conduit as pyroclastic ﬂows and fallout:frothy pumices from a deep,gas-rich zone,lava and breadcrust bombs from a degassed lava plug,and dense pumices from a transition zone.Vesicles constitute 1–66vol.%of breadcrust bombs and 24–79%of pumices,all those larger than a few tens of µm being interconnected.Small vesicles (b few tens of µm)in all pyroclasts are interpreted as having formed syn-explosively,as shown by their presence in breadcrust bombs formed from originally non-vesicular magma.Most large vesicles (N few hundreds of µm)in pumices are interpreted as pre-dating explosion,implying pre-explosive conduit porosities up to 55%.About a sixth of large vesicles in pumices,and all those in breadcrust bombs,are angular voids formed by syn-explosive fracturing of amphibole phenocrysts.An intermediate-sized vesicle population formed by coalescence of the small syn-explosive bubbles.Bubble nucleation took place heterogeneously on titanomagnetite,number densities of which greatly exceed those of vesicles,and growth took place mainly by decompression.Development of pyroclast vesicle textures was controlled by the time interval between the onset of explosion –decompression and surface quench in contact with va-plug fragments entered the air quickly after fragmentation (∼10s),so the interiors continued to vesiculate once the rinds had quenched,forming breadcrust bombs.Deeper,gas-rich magma took longer (∼50s)to reach the surface,and vesiculation of resulting pumice clasts was essentially complete prior to surface quench.This accounts for the absence of breadcrusting on pumice clasts,and for the textural similarity between pyroclastic ﬂow and fallout pumices,despite different thermal histories after leaving the vent.It also allowed syn-explosive coalescence to proceed further in the pumices than in the breadcrust bombs.Uniaxial boudinage of amphibole phenocrysts in pumices implies signi ﬁcant syn-explosive vesiculation even prior to magma fragmentation,probably in a zone of steep pressure gradient beneath the descending fragmentation front.Syn-explosive decompression rates estimated from vesicle number densities (N 0.3–6.5MPa s −1)are consistent with those predicted by previously published numerical models.©2010Elsevier B.V.All rights reserved.1.IntroductionExplosive volcanic eruptions are driven by the nucleation,growth and coalescence of gas bubbles,followed by fragmentation of the magmatic foam into a suspension of pyroclasts and gas that is discharged at high velocities into the atmosphere.Studies of pyroclast textures,coupled with experimental and numerical approaches,have advanced understanding of these processes (Lensky et al.2004;Spieler et al.2004b;Adams et al.2006;Toramaru 2006;Gardner 2007;Cluzel et al.2008;Koyaguchi et al.2008and references therein),but many questions remain.One concerns the relative importance of homogeneous versus heterogeneous nucleation.Homogeneous nu-cleation requires gas supersaturations of at least several tens of MPa (Mangan and Sisson 2000;Mourtada-Bonnefoi and Laporte 2002;2004;Mangan et al.2004),whereas heterogeneous nucleation requires lower supersaturations (Hurwitz and Navon 1994;Gardner 2007;Cluzel et al.,2008).The degree of equilibrium between gas and melt during bubble growth also has an effect.Equilibrium degassing requires ef ﬁcient volatile diffusion coupled with melt viscosity low enough to allow free gas expansion (Lyakhovsky et al.,1996;Liu and Zhang,2000;Lensky et al.,2004).High degrees of disequilibrium favour short-lived eruptions,whereas equilibrium allows more sustained fragmentation (Melnik and Sparks,2002;Mason et al.,2006).Another issue concerns the timing of bubble growth andJournal of Volcanology and Geothermal Research 193(2010)215–231⁎Corresponding author.Clermont Université,UniversitéBlaise Pascal,Laboratoire Magmas et Volcans,BP 10448,F-63000Clermont-Ferrand,France.E-mail address:giachettithomas@club-internet.fr (T.Giachetti).0377-0273/$–see front matter ©2010Elsevier B.V.All rights reserved.doi:10.1016/j.jvolgeores.2010.04.001Contents lists available at ScienceDirectJournal of Volcanology and Geothermal Researchj o u r n a l h o me p a g e :w w w.e l s ev i e r.c o m/l o c a t e /j vo l g e o r e scoalescence relative to fragmentation and eruption.Some authors postulate little growth following fragmentation(Klug and Cashman, 1991)whereas others envisage signiﬁcant post-fragmentation growth(Thomas et al.1994;Kaminski and Jaupart,1997).Post-fragmentation bubble growth is largely controlled by melt viscosity, being important in maﬁc melts and less so in silicic melts with viscosities N108–109Pa s(Thomas et al.,1994;Gardner et al.,1996; Kaminski and Jaupart,1997).Bubble coalescence and connections control permeability acquisition and the ability of magma to outgas during ascent.Vesicle size distributions provide information on magma vesicu-lation history.Pumices commonly contain multiple vesicle popula-tions covering a large range of sizes(Klug and Cashman,1996;Klug et al.,2002;Adams et al.,2006)that may result from coalescence following a single nucleation event(Orsi et al.,1992;Klug and Cashman,1994,1996;Klug et al.,2002;Burgisser and Gardner,2005). Alternatively,each population may represent a distinct nucleation event,consistent with some ascent models which predict multiple events for viscous magma(Witham and Sparks,1986;Proussevitch and Sahagian,1996;Blower et al.,2001;Massol and Koyaguchi,2005). Small vesicles are commonly attributed to syn-explosive vesiculation that generates an exponential size distribution(Mangan et al.,1993; Klug and Cashman,1996;Klug et al.,2002;Adams et al.,2006).Size distributions of larger populations typically obey power laws usually attributed to coalescence(Klug et al.,2002;Houghton et al.,2003; Gurioli et al.,2005;Adams et al.,2006;Klug and Cashman,1996), although multiple nucleation events also generate power-law distributions(Blower et al.,2001).Magma decompression rates can be estimated from vesicle number densities assuming a unique and brief nucleation event(Toramaru,2006;Cluzel et al.,2008).Detailed studies of eruptive products are required to address these questions and provide ground truth for models.Most vesiculation studies to date have concerned Plinian eruptions.In this paper we study vesiculation during a sequence of well documented Vulcanian explo-sions at Soufrière Hills Volcano in1997.The explosions have been previously described(Druitt et al.,2002;Cole et al.,2002)and modelled (Melnik and Sparks,2002,Clarke et al.,2002;Formenti et al.,2003;Diller et al.,2006;Mason et al.,2006),and their products studied texturally (Formenti and Druitt,2003;Clarke et al.,2007)and chemically(Harford et al.,2003).A key feature was the eruption of pyroclasts of a wide range of types,including dense lava fragments,breadcrust bombs and pumices of different densities.Textural analysis,including a set of high-resolution vesicle-size distributions,enables us to recognize populations of vesicles formed by explosion decompression,quantify bubble nucleation mechanisms and decompression rates,and constrain the timing of bubble nucleation,growth and coalescence during,and immediately following,a typical explosion.In a companion paper we present measurements of groundmass water contents and reconstruct the state of the pre-explosion conduit(Burgisser et al.,in press).2.The1997Vulcanian explosions of the Soufrière Hills VolcanoThe eruption of Soufrière Hills Volcano(Fig.1)began phreatically in July1995;extrusion of lava began in November of the same year and continued intermittently until the time of writing.The explosions in 1997occurred every3–63h(mean of∼10h)in two periods:thirteen between4and12August,and seventyﬁve between22September and 21October(Druitt et al.,2002).Each consisted of an initial high-intensity phase lasting a few tens of seconds,followed by a waning phase lasting1–3h.Multiple jets were ejected at40–140m s−1during theﬁrst10–20s of each explosion,then collapsed back to form pumiceous pyroclasticﬂows that travelled up to6km from the crater (Formenti et al.,2003).Fallout of pumice and ash occurred from high (3–15km)buoyant plumes that developed above the collapsing fountains.Fallout andﬂow took place at the same time from individual explosions.Each explosion discharged on average8×108kg of magma,about two-thirds as pyroclasticﬂows and one-third as fallout, representing a conduit drawdown of0.5–2km(Druitt et al.,2002). Studies of quench pressures using microlite contents and glass water contents support a maximum drawdown of∼2km(Clarke et al.,2007; Burgisser et al.,in press).Each explosion started when magma overpressure exceeded the strength of an overlying degassed plug and a fragmentation front propagated down the conduit at a few tens of m s−1 (Druitt et al.,2002;Clarke et al.,2002;Melnik and Sparks,2002;Spieler et al.,2004a;Diller et al.,2006;Mason et al.,2006).After each explosion, magma rose up the conduit before the onset of a new explosion.The Soufrière Hills andesite contains phenocrysts of plagioclase, hornblende,orthopyroxene,magnetite,ilmenite and quartz set in rhyolitic glass.The pre-eruptive temperature was∼850°C(Devine et al., 2003).3.MethodolgyField work was carried out in2006and2008at three sites(Fig.1): sites1and2are situated on the fans of overlapping pyroclasticﬂow lobes from the explosions,and site3is a composite layer of fallout pumice from many explosions.Fallout pumices were also collected at a fourth site(site4;Fig.1)during an explosion in August1997.Field descriptions were made using a rock saw to cut perpendicular to any ﬂow banding and parallel to any crystal fabric,and over100 representative pyroclasts were taken for laboratory study.Abundances of isolated and connected vesicles were measured on 2–5cm cubes cut from30breadcrust bombs and34ﬂow and fall pumices using a Multivolume1305Helium Pycnometer and the method of Formenti and Druitt(2003),which is explained in the Supplementary electronic material.Separate measurements were made on the rims and cores of22 breadcrust bombs.Twenty-six of the pumice clasts ranged from lapilli to block size,all being b20cm in diameter.Measurements were also made on multiple core-to-rim samples from eight pumices N30cm in diameter. Texturally or compositionally banded pyroclasts were not included.Microscopic observations were made on the broken surfaces of pyroclast fragments using a Jeol JSM-591LV Scanning Electron Micro-scope(SEM)at an acceleration of15kV,and on polished epoxy-impregnated thin sections using the SEM and a stereomicroscope.Six samples representative(in terms of vesicularity and texture)of the pyroclast assemblage were chosen for high-resolution analysis of vesicle and crystal size distributions.Banded clasts,and those with a signiﬁcant fraction of non-spherical vesicles,were excluded,thereby justifying use of a single,randomly oriented thin section for each sample.Vesicle and crystal size distributions were measured by image analysis in two dimensions(Toramaru,1990;Mangan et al.,1993; Klug and Cashman1994,1996;Klug et al.,2002;Adams et al.,2006;Shea et al.,2010).The technique,described fully in Appendix A,allowed objects as small as∼1µm to be measured.Differential epoxy penetration enabled us to distinguish interconnected from isolated vesicles.To represent the state of the magma immediately prior to the last discernible stage of coalescence,we manually‘decoalesced’neighbouring vesicles separated by a partially retracted wall.Volume distributions were assumed to equal area distributions(Klug et al.,2002).Volumetric number densities(N v)were calculated from area number densities(N a) using both the methods of Cheng and Lemlich(1983)and of Sahagian and Proussevitch(1998),which yield very similar values(Table1).Values of N v presented in this paper are those obtained using theﬁrst method,for reasons discussed in the Appendix A.4.Field descriptionsThe pyroclast assemblage consists predominantly of pumices of different colours,vesicularities and textures,with less than a few percent of breadcrust bombs and dense glassy lava clasts.Pyroclasts of all types were present in the pyroclasticﬂow deposits,although the216T.Giachetti et al./Journal of Volcanology and Geothermal Research193(2010)215–231relative proportions varied from lobe to lobe,while dense lava and breadcrust bombs were absent in the fallout.The samples described below come from several different explosions,and cannot be assigned to speci ﬁc dates/times owing to the complex superposition of ﬂow and fallout lobes from the many events.They represent the products of an ‘average ’explosion,as justi ﬁed by (1)the ﬁrst-order similarity of all the explosions (Druitt et al.,2002),and (2)the presence of the entire pyroclast spectrum in all pyroclastic ﬂow lobes we examined.Pumices in the pyroclastic-ﬂow deposits occur as lapilli and blocks up to N 1m in diameter with subangular-to-rounded shapes due to abrasion during transport.They range from beige,well vesiculated varieties,to grey,brown or black denser varieties (Fig.2a –b).A pink colouration affects the surfaces of many blocks,but rarely pervades the interiors.While the majority of pumices are texturally homoge-neous in hand specimen,some denser ones are ﬂow banded with phenocryst alignment in the plane of banding.Rare compositional banding de ﬁned by trails of disintegrated ma ﬁc inclusions also occurs.All pumice clasts (as distinguished from breadcrust bombs)lack surface breadcrusting.This probably cannot be explained by abrasion,because breadcrust fragments are not observed in the ﬂow matrices.All pumices smaller than ∼30cm lack radial gradients in vesicle abundance or size.However,some blocks larger than this exhibit visibly obvious radial gradients in vesicle size,with an outer 3–7-cm-thick rind with vesicles up to several mm,and a more coarsely vesicular interior containing vesicles up to an order of magnitude larger (Fig.2c).In some cases a crude cm-scale radial jointing affects the rind.The rind is inferred to represent the initial textural state of the pumice,while the interior records vesicle coarsening that took place during or after emplacement.The possibility that the interior represents the initial state,and that the rind developed by compaction during rolling in the pyroclastic ﬂow,is not favoured because (1)the rinds texturally resemble the majority of smaller pumice blocks and lapilli,whereas vesicles in the interiors are abnormally coarse,and (2)no circumferential ﬂattening of rind vesicles is observed.Many blocks also contain large voids up to several cm across,including anastamosing vesicle pipes and channels,ductile tears in the plane of ﬂow banding,and curviplanar tears and cracks subparallel to clast margins (Fig.2d),which together account for b 10%of the total vesicularity.Fallout pumices are up to several cm in size and most preserve their original eruption –fragmentation shapes,unmodi ﬁed by abrasion in pyroclastic ﬂows or breakage on ground impact.They range in colour from white to brown and in shape from spheroidal to tabular,the latter comprising about three-quarters of the sample suite.Again,no surface breadcrusting is observed.Breadcrust bombs occur from a few cm to over a metre in diameter.They have vesicular interiors surrounded by darker,less vesicular b 10mm glassy rinds.A continuous range of textural varieties are observed between two endmembers.Coarsely breadcrusted bombs are relatively dense,with well de ﬁned,dark-grey-to-black,poorly-to-non-vesicular rinds,broad,deep surface fractures de ﬁning large polygons,and grey-to-brown vesicular interiors (Fig.2e –f).Finely breadcrusted bombs are less dense,with diffuse,pale vesicular rinds,ﬁner polygonal networks of narrower,shallower surface fractures,and paler,commonly ﬂow-banded interiors (Fig.2g –h).Some bombs that broke during eruption exhibit two generations of breadcrusting,the breakage surface being more ﬁnely breadcrusted than the original,outer surface of the bomb.Breakage is inferred to have exposed the already vesicular interior,which then developed a second generation of ﬁner breadcrust-ing.Bombs were abraded during transport in the pyroclastic ﬂows;most lack completely preserved breadcrust surfaces with sharp edges and corners,and partial rind removal,rounding of polygon edges,and abrasion of vesicular interiors are common.Clasts of black,essentially nonvesicular lava resembling the glassy rinds of the coarsely breadcrust bombs are interpreted as an integral component of the explosion-pyroclast suite.On the other hand,grey-to-brown holocrystalline lava and cinderblock clasts resembling typical dome rock are probably derived either from the crater walls or from earlier block-and-ash ﬂow deposits traversed by the explosion pyroclastic ﬂows.Fig.1.Map of Montserrat showing Soufrière Hills Volcano and sampling locations.Grey:pyroclastic ﬂow deposits of the 1997Vulcanian explosions.217T.Giachetti et al./Journal of Volcanology and Geothermal Research 193(2010)215–231Fig.2.Pumices and breadcrust bombs from the explosions.a)Dark brown pumice with 60%vesicularity,b)Pale pumice with 76%vesicularity,c)Large grey pumice exhibiting a radial gradient in vesicularity,line marks the outer surface of the clast,d)Curviplanar tears and cracks subparallel to clast margins in a dense pumice,e –f)Exterior and cross section of a coarsely breadcrust-bomb,g –h)Exterior and cross section of a ﬁnely breadcrusted bomb.219T.Giachetti et al./Journal of Volcanology and Geothermal Research 193(2010)215–2315.Pyroclast vesicularitiesVesicularities of texturally homogenous pumice lapilli and blocks range from24to79vol.%(Fig.3)and correlate with colour,being lowest in darker pumices and higher in paler ones.The fraction of isolated vesicles(isolated divided by total vesicularity)is universally low(b0.25,with85%b0.1).Flow pumices cover the entire vesicularity range and have isolated fractions of0–0.13,whereas fallout pumices have vesicularities of43–72vol.%and isolated fractions of0.04–0.14,a single sample having0.25(Fig.3).No variation of either vesicularity or isolated vesicle fraction with clast size is observed.Vesicularity proﬁles across eight N30cm pumice blocks are shown in Fig.4.Four of these appeared homogeneous in theﬁeld,and four had visually obvious radial gradients in vesicle size.The four homogeneous blocks(SHV4–12–13–22)lack signiﬁcant gradients in vesicularity from core to rim,as anticipated from inspection.The four vesicle-size-graded blocks(SHV2–14–23–25),on the other hand, exhibit vesicularity gradients,but these vary from sample to sample and no systematic decrease in vesicularity from core to rim is evident.The coarse interiors of these pumices are no more vesicular than the moreﬁnely vesicular rims.Textural coarsening in the interiors therefore took place without inﬂation,as consistent with the absence of surface breadcrusting.Breadcrust-bombs differ from pumices in that(1)their vesicular-ity range(20–66vol.%most lying between35and55%,Fig.3)is smaller,and highly vesicular(N66%)samples are not observed;and (2)the fraction of isolated pores(0.05–0.33,N80%being0.1–0.2) is higher than in pumices of similar vesicularity.Bomb rinds contain 1–25vol.%vesicles,most of which are isolated.Rind and interior vesicularities are broadly correlated(Fig.5).Coarsely breadcrusted bombs have the lowest vesicularities,both in rinds and interiors,and ﬁnely breadcrusted bombs are more vesicular.It is the existence of vesicular rinds onﬁnely breadcrusted bombs that gives these bombs their pale colours and make distinction between rind and interior less clear than in the coarsely breadcrusted bombs.Full tables of vesicularity data are provided as Supplementary electronic material.6.Microscopic vesicle texturesThe pyroclasts contain vesicles with a broad range of sizes set in microlite-bearing groundmass.In this section we focus on vesicles less than a few mm in diameter present in hand specimens,and distinguish three populations:small(less than a few tens ofµm),intermediate(few tens to a few hundreds ofµm)and large(few hundreds ofµm to a few mm).It is shown later that these three populations also have genetic signiﬁcance.Vesicle textures in fallout andﬂow pumices are very similar and are described together.The large vesicles form interconnected networks with curved,scalloped walls indicative of rge vesicles in the more vesicular pumices are quasi-spherical to elliptical in shape. Those in dense pumices commonly have more ragged,ﬁssure-like shapes,suggesting that perhaps they already existed prior to explosion. About15%of the large vesicles are angular voids associated with fractured amphibole phenocrysts(Fig.6a).Intermediate-sized vesicles in all pumices have variably rounded to ragged shapes and,like the large ones,form interconnected networks in three dimensions.In contrast, small vesicles are commonly spherical and many are isolated;they either form a‘matrix’in which the intermediate vesicles are dispersed (Fig.6b),or are situated in the walls separating the latter.In some samples the smallest isolated vesicles form sub-spherical clusters several tens of microns in diameter that protrude with bulbous, cauliform shapes into larger vesicles(Fig.6c;Formenti and Druitt, 2003).There is textural evidence that many vesicles of intermediate size formed by coalescence of the small vesicles(rather than pre-existing them),the process commonly being preserved quenched in progress (Fig.6d).The sizes of some intermediate vesicles appear to be inherited from the clusters of small vesicles when the latter coalesced while preserving the overall sub-spherical form of the cluster.Vesicles in pumices are commonly observed in spatial association with rge,angular voids are associated with fractured amphiboles,and have two endmember types:(1)voids in amphiboles boudinaged uniaxially in the plane ofﬂow foliation,with well deﬁned length-perpendicular fractures(Fig.7);(2)voids in amphiboles that are fractured both perpendicular and parallel to length,and the fragments dispersed around the vesicle margins in a manner suggestive of more isotropic expansion.In both types,crystal fragments arecommonlyFig.3.Plot of connected versus total vesicularity for all the samples of this vasamples from dome collapses at Soufrière Hills Volcano are also shown(Formenti andDruitt,2003).As connected vesicularities could not be determined for breadcrustbombs rinds,we just show the range of bulk vesicularities obtained(thick blackline).Fig.4.Vesicularity as a function of relative position inside large pumices(N30cm).Filled diamonds with solid lines are those pumices that were judged in theﬁeld to betexturally homogeneous;squares with dashed lines are those that had larger vesicles inthe interior than in therind.Fig.5.Relationships between rind and interior vesicularities of breadcrust bombs,including both coarsely andﬁnely breadcrusted types.220T.Giachetti et al./Journal of Volcanology and Geothermal Research193(2010)215–231connected by thin,delicate threads of glass generated either by the bursting of melt inclusions,or by the pulling-out of thin,pre-existing melt ﬁlms in incipient cracks.A single type of amphibole-associated void is commonly dominant within a given pumice block.Type 1is observed in ∼45%of pumices and type 2in ∼35%,the remaining ∼20%of pumices lacking voids associated with amphibole.Another common texture involves radial arrangements of stretched vesicles around phenocrysts of plagioclase or amphibole (Fig.6e).This is attributed to expansion of a magmatic foam around a rigid crystal;it cannot be due to heterogeneous bubble nucleation because in each case the vesicles are separated from the crystal by a thin glass ﬁlm,showing that the crystal was not wetted by gas.Only in the case of titanomagnetite is it common to see vesicles in direct contact with crystals without intervening glass,suggesting that titanomagnetite provided nucleation sites for bubbles (Fig.8).There is abundant evidence that bubble coalescence was ongoing at all scales larger than a few µm at the time of sample quench:ovoid,neck-like connections with partially retracted walls between neighbouring vesicles (Fig.6d),wrinkling of thin vesicle walls (Fig.6f),the occurrence of thin glass ﬁbres,and the interconnection of all but a fraction of the smallest vesicles.Minimum observed vesicle wall thicknesses are b 1µm.Breadcrust bomb rinds contain small,mostly isolated,vesicles that are irregularly distributed,being most abundant near rind-penetratingsurface fractures and around phenocrysts (Fig.9a,c).Areas of vesicle-free groundmass occur in the rinds of coarsely breadcrusted bombs,but not in those of the ﬁnely breadcrusted bombs.The lower limit of the rind is commonly marked by string-like networks of small vesicles,which then merge to form the more uniformly distributed vesicle population of the interior.The interiors of all bombs contain distinct large and small vesicle rge vesicles are invariably associated with fractured amphiboles,like those in the pumices.However,well developed uniaxial boudinage is never observed in breadcrust bombs,and the voids are mostly of the more isotropic type 2.Small vesicles are uniformly distributed throughout the bomb interiors (Fig.9b,d);they are mostly isolated,with quasi-spherical forms,and commonly occur in strings and clusters around crystals and large vesicles.Evidence for vesicle coalescence is abundant in bomb interiors,although less so than in pumices.7.Size distributions of vesicles and crystalsThe six samples chosen for analysis of vesicle and crystal size distributions were a coarsely breadcrusted bomb (BCP1),a ﬁnely breadcrusted bomb (BCP43),three pyroclastic-ﬂow pumices (AMO29,AMO36and PV3),and a fallout pumice (R2).SeparatemeasurementsFig.6.SEM images of broken surfaces (a –d)and thin sections (e –f)of pumices.a)Angular void in a fractured amphibole phenocryst,the fragments being connected by thin glass ﬁbres (white arrows),b)Visual evidence for three different size populations (large,intermediate and small)of vesicles in pumices,c)Cauliform-shaped clusters of small vesicles protruding into intermediate ones,d)Evidence for coalescence of small vesicles to form intermediate-sized ones,e)Microphenocryst of plagioclase surrounded by radiating,elongated vesicles,f)Wrinkling of vesicle wall indicative of the onset of rupture (white arrow).221T.Giachetti et al./Journal of Volcanology and Geothermal Research 193(2010)215–231。

The crystal structure of the β″ phase in Al–Mg–Si alloys

THE CRYSTAL STRUCTURE OF THE b0PHASE INAl±Mg±Si ALLOYSS.J.ANDERSEN1,2,H.W.ZANDBERGEN2,J.JANSEN2,3,C.TRáHOLT2,U.TUNDAL4and O.REISO41SINTEF Materials Technology,Applied Physics,7034Trondheim,Norway,2National Centre for HREM,Laboratory of Materials Science,Delft University of Technology,Rotterdamseweg137,2628 AL Delft,The Netherlands,3Laboratory for Crystallography,University of Amsterdam,Nieuwe Achtergracht166,1018WV Amsterdam,The Netherlands and4HYDRO Aluminium,Metallurgical Rand D Centre,Sunndalsùra,Norway(Received17November1997)AbstractÐThe crystal structure of b0,one of the strengthening phases in the commercially important Al±Mg±Si alloys,is determined by use of high resolution electron microscopy(HREM)and electron di raction(ED).A trial structure was established from exit wave phase reconstructed HREM images.A least-square re®nement of the model coordinates was done using data from digitally recorded ED patterns.A recently developed computer program(MSLS)was applied,taking into account dynamic scattering.The atomic unit cell contains two units of Mg5Si6.It is C-centred monoclinic,space group C2/m, a=1.51620.002nm,b=0.405nm,c=0.67420.002nm,b=105.320.58.The atomic packing may be regarded as a hard ball packing using clusters,the clusters being(1)centred tetragons of Mg atoms and(2) so-called twin icosacaps where Mg atoms are centred above and below pentagonal rings of four Si atoms an one Mg atom.A growth related stacking fault in the structure is explained by a de®ciency of Mg atoms.A model for the b0/Al interface is given.#1998Acta Metallurgica Inc.1.INTRODUCTION1.1.GeneralThe discovery of the precipitation hardening mech-anism in the beginning of this century in an Al±Cu alloy has had great implications for all technologies requiring light alloys with some strength,and es-pecially for the aerospace and construction technol-ogies.The increase in hardness that the commercial Al alloys achieve upon hardening is usually a factor of2or more.In the Al±Mg±Si(6xxx)alloys such a tremendous increase in strength is caused by pre-cipitates formed from solution,of merely1wt%of Mg and Si that is added to the aluminium.The maximum hardness is achieved when the alloy con-tains a combination of very®ne fully coherent so-called Guinier Preston(GP-I)zones with diameters about2.5nm,and the semicoherent,larger needles, b0(GP-II zones)with a typical size4Â4Â50nm3. The density of these phases is very high.For the b0 needles,a number density in the matrix of about 104/m m3is normal.This is equal to a volume of nearly1%in the material.The6xxx series alloys are not among the strongest aluminium alloys,but they represent a high share of the aluminium pro-ducts in the world(H20%).In1989,about90%of the tonnage extruded in western Europe,was Al±Mg±Si alloys[1].1.2.The precipitation/transformation sequenceThe phases occurring in the Al±Mg±Si alloys have been studied for more than50years due to the commercial importance of these materials.In1948 Geisler and Hill[2]and Gunier and Lambot[3] reported that X-ray Laue pattern zones indicated the formation of small(H2Â2Â10nm3)needles or Guinier Preston(GP)zones,when the temperature was raised to2008C.Further heating caused the zones to thicken into rods,called b',and®nally a large plate-shaped equilibrium phase,b,was seen to form.The latter was known to be of the f.c.c.CaF2 type with a composition Mg2Si.The alloys that were studied were close to the Al±Mg2Si section of the Al±Mg±Si phase diagram;therefore it was assumed that the composition of all the Mg±Si con-taining phases was ter experiments have shown that the precipitation and transformation is quite complicated and that except for the equili-brium phase,b,the phases involved do not have the stoichiometric ratio Mg2Si.In Table1the transformation sequence at low ageing temperatures for alloys near the quasi-binary section Al±Mg2Si of the phase diagram is summar-ised.The range of existence and sizes of the b'rods and b plates depend not only on the heat-treatment, but on several other factors as well,such as cooling rate from homogenisation or extrusion and the number of Al±Fe(+Mn)±Si containing phases (dispersoids)in the material.This will not be dis-cussed in this paper.In the following a discussion of the precipitation/ transformation sequence shown in Table1is given.Acta mater.Vol.46,No.9,pp.3283±3298,1998#1998Acta Metallurgica Inc.Published by Elsevier Science Ltd.All rights reservedPrinted in Great Britain1359-6454/98$19.00+0.00 PII:S1359-6454(97)00493-X32831.2.1.Atomic clusters.After rapid cooling from homogenisation or extrusion the material is super-saturated with Mg and Si.Due to the higher solubi-lity of Mg in Al,when stored at room temperature or heated,Si ®rst goes out of solution and forms small clusters,but there are also some indications of clustering of Mg [5].The nucleation of Si-clusters will occur at quenched-in vacancies at temperatures as low as À508,below which the vacancy movement becomes very low [6].Storing or heating above À508will cause Mg to di use to the clusters,and Mg±Si phases will pre-cipitate.The di usion of Mg to the Si clusters has been veri®ed through APFIM [5,7]where the ratio of Mg/Si in the average cluster was found to increase with time when heated at 708.Since the number of Si clusters formed will be important for the precipitation of the strengthening GP zones,the storing time at a low temperature before arti®cial ageing is important concerning the material proper-ties.1.2.2.GP zones and the b 0phase .The ®rst phase to precipitate on the small clusters is the GP zones.Based on a TEM study of Al±Mg 2Si [8]Thomas proposed a model for these particles;Mg and Si replace Al in such a ratio that the occupied volume is about the same.He proposed a simple substi-tution along 110-directions with strings of atoms in the sequence Mg±Si±Mg±Mg±Si±Mg.Here two di-ameters of Mg (2Â0.32nm)and one of Si (0.235nm)amounts to 0.874nm,as compared with three diameters of Al (0.859nm).In more recent research the evolution of GP zones in several Al±Mg 2Si alloys was studied by calorimetry [6],in 6061by calorimetry and TEM [5],and by atom-probe ®eld-ion microscopy (APFIM)and TEM/HREM [5,7].These works support the view that there are at least two phases in the size range of the GP-zones,called GP-I and GP-II.For the GP-I type the size is in the range 1±3nm.The crystal structure is unknown.The zones are fully coherent and probably have a spherical shape.Dutta and Allen [9]observed by TEM small spot-like features of ``unresolved''shape of about 2.5nm that should be the GP-I zones.Particles investigated by APFIM [5]with comparable dimensions to these zones seem to have Mg/Si ratios usually less than 1.This composition is therefore di erent from that of the model proposed by Thomas [8].The GP-II zone is the same phase as the currently investigated b 0phase.This phase has the shape of ®ne needles,typically about 4Â4Â50nm 3when the material is in the aged-hardened condition [7,10].In this condition the number density of the nee-dles is high;typically 104/m m 3[10].The b 0phase is fully coherent only along the b -axis.Edwards et al.[7]managed to determine the unit cell of the b 0phase by electron di raction.It was found to be a monoclinic C-centred structure with a =0.153420.012nm,b =0.405nm,c =0.68320.015nm,b =10621.58.The b -axis is along the needle-axis.It is the full coherency of GP-I zones,the semi-coherency of the GP-II zones together with their high number densities that introduce in the alu-minium matrix strain and resistance against move-ment of dislocations,that gives the material its mechanical strength.1.2.3.The b 'phase .The next phase in the trans-formation sequence after the GP-I zones and the b 0phase is the b 'phase.This has a lower Mg/Si ratio than the equilibrium b phase.Lynch et al.found by X-ray microanalysis evidence for a ratio of Mg/Si in the b 'rods in an overaged material to be about 1.73[11],while Matsuma et al.[12]later determined the ratio to be about 1.68.For materials with excess silicon relative to Al±Mg 2Si there may be very small precipitates also of the b 'and a so-called B 'phase that is richer in silicon,or even Si particles [4].Because of this such particles with sizes comparable to b 0[7,4]may be mistaken for the b 0phase.The b 'and the B 'phase are reported as having the hexa-gonal unit cells a =0.705nm,c =0.405nm and a =0.104nm,c =0.405nm,respectively.In Refs [7,4]the relative number of b 0as compared with the smallest b '(and B ')particles was not deter-mined.It was recently suggested that b 'is a h.c.p.structure with a =0.405nm,c =0.67nm [12,13].1.2.4.The b phase.The b phase is the equilibrium phase in this system.It is the only phase up to now with a known structure.It is a CaF 2type f.c.c.structure with a =0.639nm having formula Mg 2Si.The structure may be described as strings of three atoms,Mg±Si±Mg,on the corners and faces of a cube,directed along the diagonals.Table 1.The evolution of Mg±Si phases near the quasi-binary section Al±Mg 2Si (top to bottom)Transformation/precipitation sequence Crystal type Size (nm)Composition Clusters of Si and fewer of Mg unknown unknown Si (Mg)Clusters containing Si and Mg unknown unknown Mg/Si <1Coherent spherical GP-I zonesunknown H 1±3Mg/Si H 1Semi-coherent GP-II zones (b 0needles)monoclinic H 4Â4Â50Mg/Si r 1b 'rods (and B 'rods)hexagonal H 20Â20Â500Mg/Si H 1.7b -Mg 2Si platescubicmicronsMg/Si =2The B 'phase is observed with alloys having excess Si relative to Al±Mg 2Si.It contains more Si than b '[4].ANDERSEN et al.:Al±Mg±Si ALLOY32841.3.SummationSumming up the information above,it appears that the phases that evolve from the very®ne Si-clusters into coarser particles take up progressively more magnesium during the coarsening and trans-formation processes,until an equilibrium compo-sition Mg2Si for the b phase®nally is reached.In this paper we report the structure determi-nation of the b0phase,which must be one of the important hardening phases in the commercial6xxx alloys.The technique used in the structure determi-nation is the through focus exit wave reconstruction technique in high resolution electron microscopy,in combination with quantitative electron di raction.2.EXPERIMENTAL2.1.Material and sample preparationThe as-received material was in the shape of extruded sections.It was supplied by HYDRO Aluminium AS(Sunndalsùra).The composition of the material was Al±0.2Fe±0.5Mg±0.53Si±0.01Mn (wt%).The material is from the same batch and extruded sections as investigated in Refs[10,14], there labelled as A and C,respectively.Specimen preparation and location in the extruded section of the samples for TEM are described in Refs[10,14]. Prior to the arti®cial ageing(5h at1858)the ma-terial had undergone a rather standard processing for an extrusion product.After the jet-polishing, specimens were stored in methanol.Most of the TEM experiments were performed within a day after specimen preparation.2.2.TEM equipment and experimental dataAll TEM work was performed using a PHILIPS CM30-ST/FEG electron microscope operated at 300kV.The microscope is equipped with a Photometrix1024Â1024slow scan CCD camera (12bits dynamical range),enabling a linear record-ing of HREM and ED puter control of the CCD camera and the microscope is handled with a Tietz software package.In this way series of 15±20HREM images with focus increments of typi-cally 5.2nm were recorded for each exit wave reconstruction.For the high resolution work suitable aluminium grains were selected and tilted into a h100i zone axis.HREM images were recorded at room tem-perature on as thin areas as possible,typically4±10nm.Needles were selected that could be viewed along their[010]zone axis.In this situation,the needles usually extend through the whole thickness of the specimen,such that no image blurring occurs due to overlap with the matrix.For a single image, the exposure time was usually about1s.For the di raction experiments a small spot-size (5±10nm)was used with exposure times of1±5s. Two zone-axes of the needles were chosen;[010]and[001].For the latter,the aluminium grain was tilted to a h310i zone axis,where statistically one out of six needles is in the correct orientation. Many of the needles contain stacking-faults or sec-ond phases.For a reliable structure determination it is important that the area where a di raction pat-tern is taken is free of defects.Given the resolution of the microscope it should be relatively easy to select single crystalline b0particles.However,to prevent the rapid contamination of the illuminated area that is typical for this kind of specimen at room temperature,the specimen was cooled to about100K.The sample cooling holder has a much poorer mechanical stability resulting in such a loss of resolution that selection of single crystal b0particles was di cult.Because of this ED pat-terns were taken from each particle encountered. Therefore quite many di raction patterns had to be discarded because of streaking and twinning prob-ably caused by the stacking-faults or sometimes extra spots caused by a intergrown phase that was determined to be b'.Five[010]di raction patterns were selected.For the[001]zone axis there is a greater chance of``cross-talk''due to more overlap of the matrix with the crystal,and suitable di rac-tion patterns for the re®nement were more di cult to®nd.Here®ve of the16recorded patterns were from the correct projection or particle.Only two of these patterns could later be re®ned.In addition to the problem with overlap spots from the b'phase, the reason was also the strong interference with the aluminium matrix in this projection that made sub-traction of the background di cult.The thickness of the investigated areas were somewhat larger for the di raction experiments than for the HREM ex-periments.The subsequent re®nements showed that the thickness usually exceeded10nm.In Fig.6, parts of two of the digitally recorded di raction images are shown.This®gure also shows some streaking caused by oversaturation of the CCD camera,which was not equipped with over¯ow pro-tection.The streaks and the aluminium di raction re¯ections were excluded from the images prior to data reduction.The exit wave reconstruction of the HREM focus series were done with a software package based on algorithms developed by Van Dyck and Coene[15±17].Given the coherency of the presently available ®eld emission guns the structural information in ordinary HREM images goes well beyond the point-to-point resolution in the electron microscope. The reconstruction method takes advantage of the knowledge about the transfer function,e.g.how the microscope optics distorts the electron wave after leaving the crystal(the exit wave)on its way to the image plane.This distortion is also a function of defocus.A series of HREM images are recorded at intervals of known defocus.The amplitude and phase information that is mixed up in the HREM images is retrieved through digital processing,andANDERSEN et al.:Al±Mg±Si ALLOY3285corrections for focus and spherical aberration are done.Furthermore,since typically15±20images are used in the reconstruction a considerable reduction in noise is attained.The exit wave is thus independent of various aberrations of the electron microscope, but it is still dependent on the specimen thickness. Only for very small specimen thicknesses is the exit wave very similar to the projected potential,viz.the projected atomic structure.For thicker sections,e.g. more than about10nm for the presently presented exit wave image,the local contrast in the exit wave can be quite di erent from the local scattering poten-tial.Thus,for such thicknesses a higher brightness at a certain point in the phase image of the exit wave as compared to other points,does not have to imply the presence of a locally more strongly scattering atom at this point.The good news is that the positions of the bright dots should correlate well with the location of the atoms.In the presently used electron microscope the res-olution is enhanced from0.20nm to about0.14nm. The HREM images presented in this work are recombined exit wave phase images.See Coene et al.[17],Zandbergen et al.[18]and Op de Beeck et al.[19]for examples and discussion of the method. The re®nement of the structure was done using the computer programme package MSLS[20].The CCD images with the di raction patterns were cor-rected for the¯at®eld(variation in the pixel sensi-tivity)and over¯ow during read-out of the CCD camera.Spurious X-ray signals and the Al di rac-tion spots were omitted.Automatic indexing and data reduction on the patterns were done.The obtained two-dimensional indices of the images were next transformed into the correct hkl indices so that the di raction data sets could be combined. MSLS was used for re®nement of the trial structure coordinates as obtained from the reconstructed exit wave.This program re®nes coordinates based on the least-squares procedure using the multi-slice al-gorithm to account for the dynamic di raction.The parameters re®ned were the thickness,the scaling factor,the centre of the Laue circle for each of the data sets,and the atomic coordinates and tempera-ture factors.The R-value used as measure of the correctness of the structure is de®ned as R=a(I calcÀI obs)2/a(I obs)2.Only the signi®cant re¯ections(I obs>2s(I obs))were used.R-values between2and6%are being quoted for the most reliably determined structures.3.RESULTS/DISCUSSION3.1.Conventional HREM/TEMConventional TEM shows the interior of the Al grains to mainly contain particles having a®ne nee-dle shape.The needles lay along h100i Al directions. Figure1gives an example.It is a bright®eld image in an Al h100i zone axis where the needles clearly point in two normal directions.The dark spots are needles pointing in the viewing direction.The exper-imental di raction patterns as well as HREM images show that the needle shaped particles mostly are of one kind,the monoclinic phase that is usually referred to as the b0phase.Figure2shows a HREM image with one such needle.Such images show the precipitates to be coherent along the nee-dle direction(their b-axis)with a h100i Al direction. This con®rms that their cell parameter is the same as aluminium,b=0.405nm.Many of the b0precipitates were found to con-tain stacking faults.In some precipitates an inter-growth of b0with another phase was observed.It is most probably the b'phase which has the hexago-nal axis along the needle direction.Sometimes this phase was found to exist alone.The cell parameter a=0.705nm has been con®rmed from exit wave simulated images.These images will be published later.In the same material coarser rods of the b' phase have earlier been investigated;It was reported that they nucleate on®ne Al±Fe±Si particles[14].It may be expected that much of the b'particles nucle-ate on b0since with longer arti®cial ageing times the micro-structure will contain an increasing amount of rods of b'.By selected area electron dif-fraction the coarse b'phase in this material was determined to have a hexagonal structure with a H0.71nm,c H0.41nm.The a-axis therefore®ts well with the phase intergrown with b0.The struc-ture of the small and large b'is therefore probably the same.We did not observe any B'phase in the material.3.2.Elemental analysis of the b0phaseWe performed several X-ray analyses of the small precipitates with the spot along the needle axis. Due to the very thin specimen areas(10±40nm)the spectra obtained should in principle not be signi®-cantly in¯uenced by absorption in the specimen, which is the most important reason for deviations from the actual concentration.In spite of the small size of the spot(1±2nm),there was always an Al peak present in the spectrum,of varying height. This is partly caused by stray electrons travelling down the column of the electron microscope which are not focused with the rest of the electrons in the beam probe and therefore many hit aluminium. Secondly,because during analysis the beam is par-allel to the needle axis,i.e.to the[010]zone axis of b0,this implies an e ective beam broadening by the elastic scattering of some electrons into aluminium. For some of the recordings there is also an e ect of specimen drift during recording.Another e ect is the contamination layer and the(aluminium)oxide layer on the surface of the particle which primarily contains Al.The EDS experiments could therefore not rule out that some Al is contained in the precipitate.As a standard for determining the K-ratios a mineral forsterite was used whose mainANDERSEN et al.:Al±Mg±Si ALLOY 3286components are MgO and SiO 2with a composition so that the Mg/Si atomic ratio is 2.Not taking into account the possible systematic deviations,the EDS experiments indicated that the atomic ratio for Mg/Si was close to or even below 1.The accuracy of these measurements were on the order of 10%.However,they ruled out the earlier accepted ratio of 2for the b 0phase.EDS measurements were also performed on larger particles of the b 'and b -Mg 2Si phases which had been extracted from the alu-minium matrix.These phases gave compositions near the expected,as listed in Table 1.The accuracy here was much better for thin sections since the alu-minium matrix could be avoided entirely.3.3.Exit wave reconstruction3.3.1.The unit cell.Coherency of the b 0phase with the matrix .In Fig.3a reconstructed exit wave (phase)of a b 0particle in the [010]orientation embedded in aluminium is shown.The b 0[010]direction is parallel to a h 100i type aluminium zone axis and is along the needle.Atomic columns in the viewing direction in the image appear as bright dots.The columns in the Al matrix are clearly resolved;in this projection the separation between nearest neighbor columns are 0.2025nm,or half the Al unit cell length.Due to the face centering of alu-minium the nearest neighbor atom columns are also shifted 0.2025nm in the viewing direction relative to each other.In the ®gure circles are drawn that indicate the two di erent height positions of the atoms in the viewing direction.The lattice image of the Al matrix changes over the image due to local variations in tilt.The b 0unit cell is outlined in the particle.Due to the C-centering,the a -axis is twice the apparent periodicity.By calibrating the magni®cation of the image using the aluminium lattice,the unit cell was established to be a =1.51620.002nm,c =0.67420.002nm and b H 105±1068.HREM of other nee-dles lying in the normal direction (Fig.2)have shown that there is a full coherence between the crystal along the b -axis with the same periodicity as the aluminium matrix;therefore b =0.405nm.In the re®nement of di raction images for this zone axis,the monoclinic angle is calculated.It was found to have a mean value b =105.320.58when averaged over 7di raction patterns.The b 0unit cell is closely related to the alu-minium lattice.From di raction patterns (Fig.5)asFig.1.A typical low magni®cation micrograph of b 0needles in a h 001i Al zone axis.Needles are directed along the three h 100i Al directions and appear therefore point-like (dark spots)in the viewing direction.The needles have a mean diameter of about 4nm,and an average length about 50nm.Alarger b 'rod (white appearance)is directed in the viewing direction in the centre of the image.ANDERSEN et al.:Al±Mg±Si ALLOY 3287well as from the exit wave (Fig.3)the following relationship between the phases can be found; 001 Al k 010 b 0,"310 Al k 001 b 0,230 Al k 100 b 0This relationship is the same as found earlier byEdwards et al.[7].A corresponding super cell in aluminium can be de®ned by real vectors ~ab 0 2~a Al 3~b Al ,~b b 0~c Al ,~c b 0 À32~a Al 12~b Alwith respective lengths 1.46,0.405and 0.64nm witha monoclinic angle of 105.38.Half of this super cellis outlined in Fig.3on the left side of the b 0par-ticle.The super cell is also C-centred monoclinicsince two neighbor corners of the half cell along ~ab 0fall on Al atoms in di erent layers.The unit cell for b 0is slightly larger than this Al super cell;3.8%along ~ab 0and 5.3%along ~c b 0.The half super cell (asymmetric unit)contains 11Al atoms.The coherency between b 0and aluminium aids in quantifying the shift of the stacking fault (sf)in the particle that is indicated in Fig.3;By using the Al matrix as reference it can be veri®ed that Al atoms at the left interface,at the upper part (e.g.near the white corners of the unit cell of b 0)are at a di er-ent height relative to similar atoms of b 0on the lower part (here with a black ®ll){.This is illus-trated by the two outlined (half)super cells in the Al matrix that are related to the unit cell of b 0in the upper and lower part of the particle.These super cells are shifted a vector a Al [101]/2relative to each other,which indicates that the shift across the stacking fault in the particle is nearly the same.This shift vector is a Burgers vector of the most common dislocation in aluminium.A model of the fault is given in Section5.Fig.2.Ordinary HREM image of b 0-needle in an h 001i zone axis in Al.The c -axis of the needle is in the plane,and the coherency with h 100i Al in the needle direction is evident.As expected,there is no exact zone axis of b 0along the viewing direction h 001i Al zone axis.The left part of the picture was fourier ®ltered;A high pass ®lter was applied to the upper part and a low pass ®lter to the lower partto extract the periodic information from Al (upper)and the b 0-phase (lower)only.{Alternatively,assume the corners of the outlined unit cells of b 0on each side of the stacking fault to be at thesame heights along ~cb 0.The atoms to the left of Ðand in the matrix outside Ðthese corners must then necessarily have similar heights,since the atomic con®guration and distances to the left of these corners are similar,whether above or below the stacking fault.This assumption must be wrong;When keeping track of the atomic columns in the matrix it leads to the conclusion of an Al atom being at two heights at the same time.Therefore,the corners ofthe unit cells along ~cb 0have di erent heights across the stacking fault.ANDERSEN et al.:Al±Mg±Si ALLOY3288In Fig.4the coherency between the two phases can be studied in more detail.This image is a Fast Fourier Transformation (FFT)of part of Fig.3.Only the lower part of the b 0precipitate is included to reduce streaking caused by the stacking fault.After applying a Fourier ®lter (selecting the con-tents inside the circles superposed on the FFT of Fig.4)the Al re¯ections plus the 610,610,403and 403re¯ections of b 0contribute to the image in Fig.5.The white arrows indicate interface dislo-cations between the particle and matrix.For example,the b 0(601)lattice planes with a spacing d 601=0.211nm are parallel with the Al (200)planes with a spacing of 0.203nm.Therefore,one interface dislocation is expected for each 25Al d 200spacings (normal to the [100]axis in the ®gure).Similarly,for the 403planes,for each 20Al d 020spacing one expects an interface dislocation.The spacings between dislocations observed in Fig.5are di erent from the theoretical ones.The reason for this devi-ation is probably variation in local strain in the particle caused by the stacking fault.Although the exact dislocation is not clear in the image,a matrix dislocation found (marked ``d '')also complicates the situation concerning the mis®t dislocations.This dislocation is found to have a Burgers vector b =0.5a Al [101],as was found when a Burgers vec-tor loop was performed around the particle.This is indicated by the open arrow (d).In Fig.6,two ex-perimental di raction images from the [010]and [001]zone axes are shown.The b 0610and 403re¯ections that coincide with the 200and 020Al matrix re¯ections can also be seen in Fig.6(a).In Fig.6(b)the perfect coherency relation of the (010)lattice planes of the b 0phases with (200)lattice planes can be seen from the overlap of the respect-ive di raction spots.3.3.2.Extraction of the atomic coordinates for b 0from the exit wave images .Figure 7(a)is an increased magni®cation of part of Fig.3.Here the atomic columns are represented as white dots.From this image the atomic positions were esti-mated using the following assumptions:(1)The number of atoms in the unit cell is 22,just as the number of atoms in the similar super cell in aluminium.The number ®ts the apparentnumberFig.3.Phase of an reconstructed exit wave of a typical b 0needle in Al is shown.The needle is viewed head-on along its [010]axis,and along an Al h 001i zone axis.Atomic columns appear white.The b 0unit cell and half the corresponding super cell in Al are outlined.Similarly ®lled circles in the matrix or in the precipitate are atoms (Al or Mg)at the same height.A stacking fault (sf)is indicated.The shiftacross the stacking fault can be determined to be a Al [101]/2.ANDERSEN et al.:Al±Mg±Si ALLOY 3289。

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Keywords: fold-thrust belt; magnetic fabric; sandstone; weak deformation; Arc of Fars; Zagros (Iran)
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美国科学促进会会士科罗拉多州立大学化学教授

美国科学促进会会士科罗拉多州立大学化学教授DEBBIE C.CRANSDebbie C.Crans博士是科罗拉多州立大学化学与分子细胞学教授，于1985年获取哈佛大学博士学位，后于哥本哈根大学就读博士后，随后加入加州大学洛杉矶分校担任讲师。

1988年，她转入科罗拉多州立大学化学系，开始担任该学校化学与分子细胞学的研究和教学与工作。

在她的职业生涯中，Crans博士一直致力于为科罗拉多州的中小学提供最先进的科学实验和担任大学生的榜样。

Debbie C.Crans博士曾获得多项奖项，是英国皇家学会会员以及美国科学促进会会士。

研究重点是生物无机，生物有机和物理有机化学。

此外，Crans博士研究小组还对医学中金属的重要性感兴趣，特别是钒和其他过渡金属及其离子。

I教育经历1985-1986年，于加州大学就读博士后；1985年，毕业于哈佛大学(获博士学位）；1978年，毕业于哥本哈根大学(获学士学位）；II职位成就2017年，担任科罗拉多州立大学跨学科研究奖学金副主席；2015-2017年，担任科罗拉多州立大学自然科学学院教授；1998年至今，担任科罗拉多州立大学化学教授；1991-1998年，担任科罗拉多州立大学化学副教授；1989年至今，担任科罗拉多州立大学细胞与分子生物学项目成员；1987-1991年，担任科罗拉多州立大学化学助理教授；1986年，担任加州大学洛杉矶分校讲师；III荣誉奖项2019年，获ACS杰出服务奖和杰出研究奖；2016年，英国皇家学会会员；2016年，获道尔顿讨论国际团队奖；2015年，获美国化学学会Arthur P.Cope学者奖；2014年，获选美国科学促进会会士（AAAS）；2012年，获日本协调化学学会讲座奖；2011年，获科罗拉多州立大学校友会最佳教师奖；2009年，美国化学学会会员首届获奖者；2005年，获CSU本科生研究指导奖；2004年，获Vanadis奖（第一次颁发此奖项）；2003年，获科罗拉多州立大学Margaret Hazaleus奖；2001年，获日本科学促进会奖学金；1993-1996年，获Alfred P.Sloan研究员奖；1994年，获Alberta传统基金会奖；1990-1992年，获Eli Lilly青年研究员奖；1989-1994年，获美国国立卫生研究院一等奖；1986-1987年，获美国心脏初级奖学金；IV研究领域生物，生物无机，生物有机和生物分析化学。

liquid–liquid phase separation

Biophysical Chemistry 109(2004)105–1120301-4622/04/$-see front matter ᮊ2003Elsevier B.V .All rights reserved.doi:10.1016/j.bpc.2003.10.021Cloud-point temperature and liquid–liquid phase separation ofsupersaturated lysozyme solutionJie Lu *,Keith Carpenter ,Rui-Jiang Li ,Xiu-Juan Wang ,Chi-Bun Ching a ,a a b bInstitute of Chemical and Engineering Sciences,Ayer Rajah Crescent 28,࠻02-08,Singapore 139959,Singapore aChemical and Process Engineering Center,National University of Singapore,Singapore 117576,SingaporebReceived 31July 2003;received in revised form 8October 2003;accepted 16October 2003AbstractThe detailed understanding of the structure of biological macromolecules reveals their functions,and is thus important in the design of new medicines and for engineering molecules with improved properties for industrial applications.Although techniques used for protein crystallization have been progressing greatly,protein crystallization may still be considered an art rather than a science,and successful crystallization remains largely empirical and operator-dependent.In this work,a microcalorimetric technique has been utilized to investigate liquid–liquid phase separation through measuring cloud-point temperature T for supersaturated lysozyme solution.The effects of cloud ionic strength and glycerol on the cloud-point temperature are studied in detail.Over the entire range of salt concentrations studied,the cloud-point temperature increases monotonically with the concentration of sodium chloride.When glycerol is added as additive,the solubility of lysozyme is increased,whereas the cloud-point temperature is decreased.ᮊ2003Elsevier B.V .All rights reserved.Keywords:Biocrystallization;Microcalorimetry;Cloud-point temperature;Liquid–liquid phase separation1.IntroductionKnowledge of detailed protein structure is essen-tial for protein engineering and the design of pharmaceuticals.Production of high-quality pro-tein crystals is required for molecular structure determination by X-ray crystallography.Although considerable effort has been made in recent years,obtaining such crystals is still difficult in general,and predicting the solution conditions where pro-*Corresponding author.Tel.:q 65-6874-4218;fax:q 65-6873-4805.E-mail address:lujie@.sg (J.Lu ).teins successfully crystallize remains a significant obstacle in the advancement of structural molecu-lar biology w 1x .The parameters affecting protein crystallization are typically reagent concentration,pH,tempera-ture,additive,etc.A phase diagram can provide the method for quantifying the influence of solu-tion parameters on the production of crystals w 2,3x .To characterize protein crystallization,it is neces-sary to first obtain detailed information on protein solution phase behavior and phase diagram.Recently physics shows that there is a direct relationship between colloidal interaction energy106J.Lu et al./Biophysical Chemistry109(2004)105–112and phase diagram.Gast and Lekkerkerker w4,5x have indicated that the range of attraction between colloid particles has a significant effect on the qualitative features of phase diagram.A similar relationship should hold for biomacromolecules, i.e.the corresponding interaction potentials govern the macromolecular distribution in solution,the shape of the phase diagram and the crystallization process w6x.Many macromolecular crystallizations appear to be driven by the strength of the attractive interactions,and occur in,or close to,attractive regimes w7,8x.Recent intensive investigation has revealed that protein or colloidal solution possesses a peculiar phase diagram,i.e.liquid–liquid phase separation and sol–gel transition exists in general in addition to crystallization w9,10x.The potential responsible for the liquid–liquid phase separation is a rather short range,possibly van der Waals,attractive potential w11,12x.The measurement of cloud-point temperature T can provide useful informationcloudon the net attractive interaction between protein molecules,namely,the higher the cloud-point tem-perature,the greater the net attractive interaction. Herein Taratuta et al.w13x studied the effects of salts and pH on the cloud-point temperature of lysozyme.Broide et al.w14x subsequently meas-ured the cloud-point temperature and crystalliza-tion temperature for lysozyme as a function of salt type and concentration.From these works the cloud-point temperature was found to be typically 15–458C below the crystallization temperature. Furthermore,Muschol and Rosenberger w15x deter-mined the metastable coexistence curves for lyso-zyme through cloud-point measurements,and suggested a systematic approach to promote pro-tein crystallization.In general,an effective way to determine the strength of protein interactions is to study temperature-induced phase transitions that occur in concentrated protein solutions.Liquid–liquid phase separation can be divided into two stages w11x:(1)the local separation stage at which the separation proceeds in small regions and local equilibrium is achieved rapidly;and(2) the coarsening stage at which condensation of these small domains proceeds slowly to reduce the loss of interface free energy w16x.The coexisting liquid phases both remain supersaturated but differ widely in protein concentration.The effect of a metastable liquid–liquid phase separation on crystallization remains ambiguous w17x.Molecular dynamics simulations and analyt-ical theory predict that the phase separation will affect the kinetics and the mechanisms of protein crystal nucleation w18x.tenWolde and Frenkel w19x have demonstrated that the free energy barrier for crystal nucleation is remarkably reduced at the critical point of liquid–liquid phase separation, thus in general,after liquid–liquid phase separa-tion,crystallization occurs much more rapidly than in the initial solution,which is typically too rapid for the growth of single crystal with low defect densities w15x.The determination of the location of liquid–liquid phase separation curve is thus crucial for efficiently identifying the optimum solution conditions for growing protein crystals. Microcalorimetry has the potential to be a useful tool for determining:(1)the metastable-labile zone boundary;(2)the temperature-dependence of pro-tein solubility in a given solvent;and(3)the crystal-growth rates as a function of supersatura-tion w20x.Microcalorimeters can detect a power signal as low as a few microwatts whereas standard calorimeters detect signals in the milliwatt range. Because of this greater sensitivity,samples with small heat effects can be analyzed.In addition, microcalorimetry has the advantage of being fast, non-destructive to the protein and requiring a relatively small amount of material.The present work is concerned with the analysis of the transient heat signal from microcalorimeter to yield liquid–liquid phase separation information for lysozyme solutions at pH4.8.To further examine the role of salt and additive on interprotein interactions, cloud-point temperature T has been determinedcloudexperimentally as a function of the concentrations of salt,protein and glycerol.2.Materials and methods2.1.MaterialsSix times crystallized lysozyme was purchased from Seikagaku Kogyo,and used without further107J.Lu et al./Biophysical Chemistry 109(2004)105–112purification.All other chemicals used were of reagent grade,from Sigma Chemical Co.2.2.Preparation of solutionsSodium acetate buffer (0.1M )at pH 4.8was prepared with ultrafiltered,deionized water.Sodi-um azide,at a concentration of 0.05%(w y v ),was added to the buffer solution as an antimicrobial agent.Protein stock solution was prepared by dissolving protein powder into buffer.To remove undissolved particles,the solution was centrifuged in a Sigma centrifuge at 12000rev.y min for 5–10min,then filtered through 0.22-m m filters (Mil-lex-VV )into a clean sample vial and stored at 48C for further experiments.The concentration of protein solution was determined by measuring the absorbance at 280nm of UV spectroscopy (Shi-madzu UV-2550),with an extinction coefficient of 2.64ml y (mg cm )w 21x .Precipitant stock solution was prepared by dissolving the required amount of sodium chloride together with additive glycerol into buffer.The pH of solutions was measured by a digital pH meter (Mettler Toledo 320)and adjusted by the addition of small volumes of NaOH or HAc solution.2.3.Measurement of solubilitySolubility of lysozyme at various temperatures and precipitant y additive concentrations was meas-ured at pH 4.8in 0.1M acetate buffer.Solid–liquid equilibrium was approached through both crystallization and dissolution.Dissolving lasted 3days,while the period of crystallization was over 2weeks.The supernatant in equilibrium with a macroscopically observable solid was then filtered through 0.1-m m filters (Millex-VV ).The concen-tration of diluted supernatant was determined spec-troscopically and verified by refractive meter(Kruss)until refractive index remained unchanged ¨at equilibrium state.Solubility of each sample was measured in duplicate.2.4.Differential scanning microcalorimetry Calorimetric experiments were performed with a micro-differential scanning calorimeter with anultra sensitivity,micro-DSC III,from Setaram SA,France.The micro-DSC recorded heat flow in microwatts vs.temperature,thus can detect the heat associated with phase transition during a temperature scan.The sample made up of equal volumes of protein solution and precipitant solu-tion was filtered through 0.1-m m filters to remove dust particles further.To remove the dissolved air,the sample was placed under vacuum for 3min while stirring at 500rev.y min by a magnetic stirrer.The degassed sample was placed into the sample cell of 1.0ml,and a same concentration NaCl solution was placed into the reference cell.The solutions in the micro-DSC were then cooled at the rate of 0.28C y min.After every run,the cells were cleaned by sonicating for 10–15min in several solutions in the following order:deionized water,methanol,ethanol,acetone,1M KOH and finally copious amounts of deionized water.This protocol ensured that lysozyme was completely removed from the cells.The cells were then placed in a drying oven for several hours.The rubber gaskets were cleaned in a similar manner except acetone and 1M KOH were omitted and they were allowed to dry at low temperature.3.Results and discussionA typical micro-DSC scanning experiment is shown in Fig.1.The onset of the clouding phe-nomenon is very dramatic and easily detected.The sharp increase in the heat flow is indicative of a liquid–liquid phase separation process producing a latent heat.This is much consistent with many recent investigations of the liquid–liquid phase separation of lysozyme from solution w 22,23x .In fact,such a liquid–liquid phase separation is a phase transition with an associated latent heat of demixing.In this work,the cloud-point tempera-tures at a variety of lysozyme,NaCl and glycerol concentrations are determined by the micro-DSC at the scan rate of 128C y h.3.1.Effect of protein concentrationIn semilogarithmic Fig.2we plot the solid–liquid and liquid–liquid phase boundaries for lyso-108J.Lu et al./Biophysical Chemistry 109(2004)105–112Fig.1.Heat flow of a typical micro-DSC scan of lysozyme solution,50mg y ml,0.1M acetate buffer,pH 4.8,3%NaCl.The scan rate 128C y h is chosen referenced to the experimental results of Darcy and Wiencek w 23x .Note the large deflection in the curve at approximately 4.38C indicating a latent heat resulting from demixing (i.e.liquid–liquid phase separation )process.Fig.2.Cloud-point temperature and solubility determination for lysozyme in 0.1M acetate buffer,pH 4.8:solubility (5%NaCl )(s );T (5%NaCl,this work )(d );T (5%cloud cloud NaCl,the work of Darcy and Wiencek w 23x )(*);solubility (3%NaCl )(h );T (3%NaCl )(j ).cloud Fig.3.Cloud-point temperature determination for lysozyme as a function of the concentration of sodium chloride,50mg y ml,0.1M acetate buffer,pH 4.8.zyme in 0.1M acetate buffer,pH 4.8,for a range of protein concentrations.It is worth noting that,at 5%NaCl,our experimental data of T from cloud micro-DSC are quite consistent with those from laser light scattering and DSC by Darcy and Wiencek w 23x ,with difference averaging at approx-imately 0.88C.This figure demonstrates that liquid–liquid phase boundary is far below solid–liquid phase boundary,which implies that the liquid–liquid phase separation normally takes place in a highly metastable solution.In addition,cloud-point temperature T increases with the cloud concentration of protein.3.2.Effect of salt concentrationFig.3shows how cloud-point temperature changes as the concentration of NaCl is varied from 2.5to 7%(w y v ).The buffer is 0.1M acetate (pH 4.8);the protein concentration is fixed at 50mg y ml.Over the entire range of salt concentrations studied,the cloud-point temperature strongly depends on the ionic strength and increases monotonically with the concentration of NaCl.Crystallization is driven by the difference in chemical potential of the solute in solution and in the crystal.The driving force can be simplified as w 24xf sy Dm s kT ln C y C (1)Ž.eq109J.Lu et al./Biophysical Chemistry 109(2004)105–112Fig.4.The driving force required by liquid–liquid phase sep-aration as a function of the concentration of sodium chloride,50mg y ml lysozyme solution,0.1M acetate buffer,pH 4.8.In the same way,we plot the driving force,f ,required by liquid–liquid phase separation as a function of the concentration of sodium chloride in Fig.4.At the moderate concentration of sodium chloride,the driving force required by liquid–liquid phase separation is higher than that at low or high salt concentration.As shown in Fig.3,with NaCl concentration increasing,the cloud-point temperature increases,which is in accord with the results of Broide et al.w 14x and Grigsby et al.w 25x .It is known that protein interaction is the sum of different potentials like electrostatic,van der Waals,hydrophobic,hydration,etc.The liquid–liquid phase separation is driven by a net attraction between protein molecules,and the stronger the attraction,the higher the cloud-point temperature.Ionic strength is found to have an effect on the intermolecular forces:attractions increase with ionic strength,solubility decreases with ionic strength,resulting in the cloud-point temperature increases with ionic strength.It is worth noting that,the effect of ionic strength on cloud-point temperature depends strongly on the specific nature of the ions w 13x .Kosmotropic ions bind adjacent water molecules more strongly than water binds itself.When akosmotropic ion is introduced into water,the entro-py of the system decreases due to increased water structuring around the ion.In contrast,chaotropes bind adjacent water molecules less strongly than water binds itself.When a chaotrope is introduced into water,the entropy of the system increases because the water structuring around the ion is less than that in salt-free water.This classification is related to the size and charge of the ion.At high salt concentration ()0.3M ),the specific nature of the ions is much more important w 25x .The charges on a protein are due to discrete positively and negatively charged surface groups.In lysozyme,the average distance between thesecharges is approximately 10Aw 26x .As to the salt ˚NaCl used as precipitant,Na is weakly kosmo-q tropic and Cl is weakly chaotropic w 27x .At low y NaCl concentrations,as the concentration of NaCl increases,the repulsive electrostatic charge–charge interactions between protein molecules decrease because of screening,resulting in the increase of cloud-point temperature.While at high NaCl con-centrations,protein molecules experience an attrac-tion,in which differences can be attributed to repulsive hydration forces w 14,25x .That is,as the ionic strength increases,repulsive electrostatic or hydration forces decrease,protein molecules appear more and more attractive,leading to higher cloud-point temperature.At various salt concentra-tions,the predominant potentials reflecting the driving force for liquid–liquid phase separation are different.Fig.4shows that the driving force,f ,is parabolic with ionic strength,while Grigsby et al.w 25x have reported that f y kT is linear with ionic strength for monovalent salts.The possible reasons for that difference include,their model is based on a fixed protein concentration of 87mg y ml,which is higher than that used in our study,yet f y kT is probably dependent on protein concentration,besides the solutions at high protein and salt concentrations are far from ideal solutions.3.3.Effect of glycerolFig.5compares cloud-point temperature data for 50mg y ml lysozyme solutions in absence of glycerol and in presence of 5%glycerol,respec-110J.Lu et al./Biophysical Chemistry109(2004)105–112parison of cloud-point temperatures for lysozyme at different glycerol concentrations as a function of the con-centration of sodium chloride,50mg y ml,0.1M acetate buffer, pH4.8:0%glycerol(s);5%glycerol(j).Fig.6.Cloud-point temperatures for lysozyme at different glycerol concentrations,50mg y ml lysozyme,5%NaCl,0.1M acetate buffer,pH4.8.Fig.7.Cloud-point temperature and solubility determination for lysozyme at different concentrations of glycerol in0.1M acetate buffer,5%NaCl,pH4.8:solubility(0%glycerol)(s); T(0%glycerol)(d);solubility(5%glycerol)(h);cloudT(5%glycerol)(j).cloudtively.Fig.6shows the cloud-point temperature as a function of the concentration of glycerol.The cloud-point temperature is decreased as the addi-tion of glycerol.In semilogarithmic Fig.7we plot the solid–liquid and liquid–liquid phase boundaries at dif-ferent glycerol concentrations for lysozyme in0.1 M acetate buffer,5%NaCl,pH4.8,for a range of protein concentration.This figure demonstrates that liquid–liquid and solid–liquid phase bounda-ries in the presence of glycerol are below those in absence of glycerol,and the region for growing crystals is narrowed when glycerol is added. Glycerol has the property of stabilizing protein structure.As a result,if crystallization occurs over a long period of time,glycerol is a useful candidate to be part of the crystallization solvent and is often included for this purpose w28x.In addition,glycerol is found to have an effect on the intermolecular forces:repulsions increase with glycerol concentra-tion w29x.Our experiment results of solubility and cloud-point temperature can also confirm the finding.The increased repulsions induced by glycerol can be explained by a number of possible mecha-nisms,all of which require small changes in the protein or the solvent in its immediate vicinity.The addition of glycerol decreases the volume of protein core w30x,increases hydration and the size of hydration layer at the particle surface w31,32x. In this work,we confirm that glycerol shifts the solid–liquid and liquid–liquid phase boundaries. The effect of glycerol on the phase diagram strong-111 J.Lu et al./Biophysical Chemistry109(2004)105–112ly depends on its concentration and this canprovide opportunities for further tuning of nuclea-tion rates.4.ConclusionsGrowing evidence suggests protein crystalliza-tion can be understood in terms of an order ydisorder phase transition between weakly attractiveparticles.Control of these attractions is thus keyto growing crystals.The study of phase transitionsin concentrated protein solutions provides one witha simple means of assessing the effect of solutionconditions on the strength of protein interactions.The cloud-point temperature and solubility datapresented in this paper demonstrate that salt andglycerol have remarkable effects on phase transi-tions.The solid–liquid and liquid–liquid bounda-ries can be shifted to higher or lower temperaturesby varying ionic strength or adding additives.Ourinvestigation provides further information upon therole of glycerol used in protein crystallization.Glycerol can increase the solubility,and decreasethe cloud-point temperature,which is of benefit totuning nucleation and crystal growth.In continuingstudies,we will explore the effects of other kindsof additives like nonionic polymers on phasetransitions and nucleation rates.Much more theo-retical work will be done to fully interpret ourexperimental results.AcknowledgmentsThis work is supported by the grant from theNational Natural Science Foundation of China(No.20106010).The authors also thank Professor J.M.Wiencek(The University of Iowa)for kinddiscussion with us about the thermal phenomenaof liquid–liquid phase separation.Referencesw1x A.McPherson,Current approaches to macromolecular crystallization,Eur.J.Biochem.189(1990)1–23.w2x A.M.Kulkarni, C.F.Zukoski,Nanoparticle crystal nucleation:influence of solution conditions,Langmuir18(2002)3090–3099.w3x E.E.G.Saridakis,P.D.S.Stewart,L.F.Lloyd,et al., Phase diagram and dilution experiments in the crystal-lization of 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ork,1953.。

毕业设计论文塑料注射成型

Modeling of morphology evolution in the injection moldingprocess of thermoplastic polymersR.Pantani,I.Coccorullo,V.Speranza,G.Titomanlio* Department of Chemical and Food Engineering,University of Salerno,via Ponte don Melillo,I-84084Fisciano(Salerno),Italy Received13May2005;received in revised form30August2005;accepted12September2005AbstractA thorough analysis of the effect of operative conditions of injection molding process on the morphology distribution inside the obtained moldings is performed,with particular reference to semi-crystalline polymers.The paper is divided into two parts:in the ﬁrst part,the state of the art on the subject is outlined and discussed;in the second part,an example of the characterization required for a satisfactorily understanding and description of the phenomena is presented,starting from material characterization,passing through the monitoring of the process cycle and arriving to a deep analysis of morphology distribution inside the moldings.In particular,fully characterized injection molding tests are presented using an isotactic polypropylene,previously carefully characterized as far as most of properties of interest.The effects of both injectionﬂow rate and mold temperature are analyzed.The resulting moldings morphology(in terms of distribution of crystallinity degree,molecular orientation and crystals structure and dimensions)are analyzed by adopting different experimental techniques(optical,electronic and atomic force microscopy,IR and WAXS analysis).Final morphological characteristics of the samples are compared with the predictions of a simulation code developed at University of Salerno for the simulation of the injection molding process.q2005Elsevier Ltd.All rights reserved.Keywords:Injection molding;Crystallization kinetics;Morphology;Modeling;Isotactic polypropyleneContents1.Introduction (1186)1.1.Morphology distribution in injection molded iPP parts:state of the art (1189)1.1.1.Modeling of the injection molding process (1190)1.1.2.Modeling of the crystallization kinetics (1190)1.1.3.Modeling of the morphology evolution (1191)1.1.4.Modeling of the effect of crystallinity on rheology (1192)1.1.5.Modeling of the molecular orientation (1193)1.1.6.Modeling of theﬂow-induced crystallization (1195)ments on the state of the art (1197)2.Material and characterization (1198)2.1.PVT description (1198)*Corresponding author.Tel.:C39089964152;fax:C39089964057.E-mail address:gtitomanlio@unisa.it(G.Titomanlio).2.2.Quiescent crystallization kinetics (1198)2.3.Viscosity (1199)2.4.Viscoelastic behavior (1200)3.Injection molding tests and analysis of the moldings (1200)3.1.Injection molding tests and sample preparation (1200)3.2.Microscopy (1202)3.2.1.Optical microscopy (1202)3.2.2.SEM and AFM analysis (1202)3.3.Distribution of crystallinity (1202)3.3.1.IR analysis (1202)3.3.2.X-ray analysis (1203)3.4.Distribution of molecular orientation (1203)4.Analysis of experimental results (1203)4.1.Injection molding tests (1203)4.2.Morphology distribution along thickness direction (1204)4.2.1.Optical microscopy (1204)4.2.2.SEM and AFM analysis (1204)4.3.Morphology distribution alongﬂow direction (1208)4.4.Distribution of crystallinity (1210)4.4.1.Distribution of crystallinity along thickness direction (1210)4.4.2.Crystallinity distribution alongﬂow direction (1212)4.5.Distribution of molecular orientation (1212)4.5.1.Orientation along thickness direction (1212)4.5.2.Orientation alongﬂow direction (1213)4.5.3.Direction of orientation (1214)5.Simulation (1214)5.1.Pressure curves (1215)5.2.Morphology distribution (1215)5.3.Molecular orientation (1216)5.3.1.Molecular orientation distribution along thickness direction (1216)5.3.2.Molecular orientation distribution alongﬂow direction (1216)5.3.3.Direction of orientation (1217)5.4.Crystallinity distribution (1217)6.Conclusions (1217)References (1219)1.IntroductionInjection molding is one of the most widely employed methods for manufacturing polymeric products.Three main steps are recognized in the molding:ﬁlling,packing/holding and cooling.During theﬁlling stage,a hot polymer melt rapidlyﬁlls a cold mold reproducing a cavity of the desired product shape. During the packing/holding stage,the pressure is raised and extra material is forced into the mold to compensate for the effects that both temperature decrease and crystallinity development determine on density during solidiﬁcation.The cooling stage starts at the solidiﬁcation of a thin section at cavity entrance (gate),starting from that instant no more material can enter or exit from the mold impression and holding pressure can be released.When the solid layer on the mold surface reaches a thickness sufﬁcient to assure required rigidity,the product is ejected from the mold.Due to the thermomechanical history experienced by the polymer during processing,macromolecules in injection-molded objects present a local order.This order is referred to as‘morphology’which literally means‘the study of the form’where form stands for the shape and arrangement of parts of the object.When referred to polymers,the word morphology is adopted to indicate:–crystallinity,which is the relative volume occupied by each of the crystalline phases,including mesophases;–dimensions,shape,distribution and orientation of the crystallites;–orientation of amorphous phase.R.Pantani et al./Prog.Polym.Sci.30(2005)1185–1222 1186R.Pantani et al./Prog.Polym.Sci.30(2005)1185–12221187Apart from the scientiﬁc interest in understandingthe mechanisms leading to different order levels inside a polymer,the great technological importance of morphology relies on the fact that polymer character-istics (above all mechanical,but also optical,electrical,transport and chemical)are to a great extent affected by morphology.For instance,crystallinity has a pro-nounced effect on the mechanical properties of the bulk material since crystals are generally stiffer than amorphous material,and also orientation induces anisotropy and other changes in mechanical properties.In this work,a thorough analysis of the effect of injection molding operative conditions on morphology distribution in moldings with particular reference to crystalline materials is performed.The aim of the paper is twofold:ﬁrst,to outline the state of the art on the subject;second,to present an example of the characterization required for asatisfactorilyR.Pantani et al./Prog.Polym.Sci.30(2005)1185–12221188understanding and description of the phenomena, starting from material description,passing through the monitoring of the process cycle and arriving to a deep analysis of morphology distribution inside the mold-ings.To these purposes,fully characterized injection molding tests were performed using an isotactic polypropylene,previously carefully characterized as far as most of properties of interest,in particular quiescent nucleation density,spherulitic growth rate and rheological properties(viscosity and relaxation time)were determined.The resulting moldings mor-phology(in terms of distribution of crystallinity degree, molecular orientation and crystals structure and dimensions)was analyzed by adopting different experimental techniques(optical,electronic and atomic force microscopy,IR and WAXS analysis).Final morphological characteristics of the samples were compared with the predictions of a simulation code developed at University of Salerno for the simulation of the injection molding process.The effects of both injectionﬂow rate and mold temperature were analyzed.1.1.Morphology distribution in injection molded iPP parts:state of the artFrom many experimental observations,it is shown that a highly oriented lamellar crystallite microstructure, usually referred to as‘skin layer’forms close to the surface of injection molded articles of semi-crystalline polymers.Far from the wall,the melt is allowed to crystallize three dimensionally to form spherulitic structures.Relative dimensions and morphology of both skin and core layers are dependent on local thermo-mechanical history,which is characterized on the surface by high stress levels,decreasing to very small values toward the core region.As a result,the skin and the core reveal distinct characteristics across the thickness and also along theﬂow path[1].Structural and morphological characterization of the injection molded polypropylene has attracted the interest of researchers in the past three decades.In the early seventies,Kantz et al.[2]studied the morphology of injection molded iPP tensile bars by using optical microscopy and X-ray diffraction.The microscopic results revealed the presence of three distinct crystalline zones on the cross-section:a highly oriented non-spherulitic skin;a shear zone with molecular chains oriented essentially parallel to the injection direction;a spherulitic core with essentially no preferred orientation.The X-ray diffraction studies indicated that the skin layer contains biaxially oriented crystallites due to the biaxial extensionalﬂow at theﬂow front.A similar multilayered morphology was also reported by Menges et al.[3].Later on,Fujiyama et al.[4] investigated the skin–core morphology of injection molded iPP samples using X-ray Small and Wide Angle Scattering techniques,and suggested that the shear region contains shish–kebab structures.The same shish–kebab structure was observed by Wenig and Herzog in the shear region of their molded samples[5].A similar investigation was conducted by Titomanlio and co-workers[6],who analyzed the morphology distribution in injection moldings of iPP. They observed a skin–core morphology distribution with an isotropic spherulitic core,a skin layer characterized by aﬁne crystalline structure and an intermediate layer appearing as a dark band in crossed polarized light,this layer being characterized by high crystallinity.Kalay and Bevis[7]pointed out that,although iPP crystallizes essentially in the a-form,a small amount of b-form can be found in the skin layer and in the shear region.The amount of b-form was found to increase by effect of high shear rates[8].A wide analysis on the effect of processing conditions on the morphology of injection molded iPP was conducted by Viana et al.[9]and,more recently, by Mendoza et al.[10].In particular,Mendoza et al. report that the highest level of crystallinity orientation is found inside the shear zone and that a high level of orientation was also found in the skin layer,with an orientation angle tilted toward the core.It is rather difﬁcult to theoretically establish the relationship between the observed microstructure and processing conditions.Indeed,a model of the injection molding process able to predict morphology distribution in theﬁnal samples is not yet available,even if it would be of enormous strategic importance.This is mainly because a complete understanding of crystallization kinetics in processing conditions(high cooling rates and pressures,strong and complexﬂowﬁelds)has not yet been reached.In this section,the most relevant aspects for process modeling and morphology development are identiﬁed. In particular,a successful path leading to a reliable description of morphology evolution during polymer processing should necessarily pass through:–a good description of morphology evolution under quiescent conditions(accounting all competing crystallization processes),including the range of cooling rates characteristic of processing operations (from1to10008C/s);R.Pantani et al./Prog.Polym.Sci.30(2005)1185–12221189–a description capturing the main features of melt morphology(orientation and stretch)evolution under processing conditions;–a good coupling of the two(quiescent crystallization and orientation)in order to capture the effect of crystallinity on viscosity and the effect ofﬂow on crystallization kinetics.The points listed above outline the strategy to be followed in order to achieve the basic understanding for a satisfactory description of morphology evolution during all polymer processing operations.In the following,the state of art for each of those points will be analyzed in a dedicated section.1.1.1.Modeling of the injection molding processTheﬁrst step in the prediction of the morphology distribution within injection moldings is obviously the thermo-mechanical simulation of the process.Much of the efforts in the past were focused on the prediction of pressure and temperature evolution during the process and on the prediction of the melt front advancement [11–15].The simulation of injection molding involves the simultaneous solution of the mass,energy and momentum balance equations.Theﬂuid is non-New-tonian(and viscoelastic)with all parameters dependent upon temperature,pressure,crystallinity,which are all function of pressibility cannot be neglected as theﬂow during the packing/holding step is determined by density changes due to temperature, pressure and crystallinity evolution.Indeed,apart from some attempts to introduce a full 3D approach[16–19],the analysis is currently still often restricted to the Hele–Shaw(or thinﬁlm) approximation,which is warranted by the fact that most injection molded parts have the characteristic of being thin.Furthermore,it is recognized that the viscoelastic behavior of the polymer only marginally inﬂuences theﬂow kinematics[20–22]thus the melt is normally considered as a non-Newtonian viscousﬂuid for the description of pressure and velocity gradients evolution.Some examples of adopting a viscoelastic constitutive equation in the momentum balance equations are found in the literature[23],but the improvements in accuracy do not justify a considerable extension of computational effort.It has to be mentioned that the analysis of some features of kinematics and temperature gradients affecting the description of morphology need a more accurate description with respect to the analysis of pressure distributions.Some aspects of the process which were often neglected and may have a critical importance are the description of the heat transfer at polymer–mold interface[24–26]and of the effect of mold deformation[24,27,28].Another aspect of particular interest to the develop-ment of morphology is the fountainﬂow[29–32], which is often neglected being restricted to a rather small region at theﬂow front and close to the mold walls.1.1.2.Modeling of the crystallization kineticsIt is obvious that the description of crystallization kinetics is necessary if theﬁnal morphology of the molded object wants to be described.Also,the development of a crystalline degree during the process inﬂuences the evolution of all material properties like density and,above all,viscosity(see below).Further-more,crystallization kinetics enters explicitly in the generation term of the energy balance,through the latent heat of crystallization[26,33].It is therefore clear that the crystallinity degree is not only a result of simulation but also(and above all)a phenomenon to be kept into account in each step of process modeling.In spite of its dramatic inﬂuence on the process,the efforts to simulate the injection molding of semi-crystalline polymers are crude in most of the commercial software for processing simulation and rather scarce in the ﬂeur and Kamal[34],Papatanasiu[35], Titomanlio et al.[15],Han and Wang[36],Ito et al.[37],Manzione[38],Guo and Isayev[26],and Hieber [25]adopted the following equation(Kolmogoroff–Avrami–Evans,KAE)to predict the development of crystallinityd xd tZð1K xÞd d cd t(1)where x is the relative degree of crystallization;d c is the undisturbed volume fraction of the crystals(if no impingement would occur).A signiﬁcant improvement in the prediction of crystallinity development was introduced by Titoman-lio and co-workers[39]who kept into account the possibility of the formation of different crystalline phases.This was done by assuming a parallel of several non-interacting kinetic processes competing for the available amorphous volume.The evolution of each phase can thus be described byd x id tZð1K xÞd d c id t(2)where the subscript i stands for a particular phase,x i is the relative degree of crystallization,x ZPix i and d c iR.Pantani et al./Prog.Polym.Sci.30(2005)1185–1222 1190is the expectancy of volume fraction of each phase if no impingement would occur.Eq.(2)assumes that,for each phase,the probability of the fraction increase of a single crystalline phase is simply the product of the rate of growth of the corresponding undisturbed volume fraction and of the amount of available amorphous fraction.By summing up the phase evolution equations of all phases(Eq.(2))over the index i,and solving the resulting differential equation,one simply obtainsxðtÞZ1K exp½K d cðtÞ (3)where d c Z Pid c i and Eq.(1)is recovered.It was shown by Coccorullo et al.[40]with reference to an iPP,that the description of the kinetic competition between phases is crucial to a reliable prediction of solidiﬁed structures:indeed,it is not possible to describe iPP crystallization kinetics in the range of cooling rates of interest for processing(i.e.up to several hundreds of8C/s)if the mesomorphic phase is neglected:in the cooling rate range10–1008C/s, spherulite crystals in the a-phase are overcome by the formation of the mesophase.Furthermore,it has been found that in some conditions(mainly at pressures higher than100MPa,and low cooling rates),the g-phase can also form[41].In spite of this,the presence of different crystalline phases is usually neglected in the literature,essentially because the range of cooling rates investigated for characterization falls in the DSC range (well lower than typical cooling rates of interest for the process)and only one crystalline phase is formed for iPP at low cooling rates.It has to be noticed that for iPP,which presents a T g well lower than ambient temperature,high values of crystallinity degree are always found in solids which passed through ambient temperature,and the cooling rate can only determine which crystalline phase forms, roughly a-phase at low cooling rates(below about 508C/s)and mesomorphic phase at higher cooling rates.The most widespread approach to the description of kinetic constant is the isokinetic approach introduced by Nakamura et al.According to this model,d c in Eq.(1)is calculated asd cðtÞZ ln2ðt0KðTðsÞÞd s2 435n(4)where K is the kinetic constant and n is the so-called Avrami index.When introduced as in Eq.(4),the reciprocal of the kinetic constant is a characteristic time for crystallization,namely the crystallization half-time, t05.If a polymer is cooled through the crystallization temperature,crystallization takes place at the tempera-ture at which crystallization half-time is of the order of characteristic cooling time t q deﬁned ast q Z D T=q(5) where q is the cooling rate and D T is a temperature interval over which the crystallization kinetic constant changes of at least one order of magnitude.The temperature dependence of the kinetic constant is modeled using some analytical function which,in the simplest approach,is described by a Gaussian shaped curve:KðTÞZ K0exp K4ln2ðT K T maxÞ2D2(6)The following Hoffman–Lauritzen expression[42] is also commonly adopted:K½TðtÞ Z K0exp KUÃR$ðTðtÞK T NÞ!exp KKÃ$ðTðtÞC T mÞ2TðtÞ2$ðT m K TðtÞÞð7ÞBoth equations describe a bell shaped curve with a maximum which for Eq.(6)is located at T Z T max and for Eq.(7)lies at a temperature between T m(the melting temperature)and T N(which is classically assumed to be 308C below the glass transition temperature).Accord-ing to Eq.(7),the kinetic constant is exactly zero at T Z T m and at T Z T N,whereas Eq.(6)describes a reduction of several orders of magnitude when the temperature departs from T max of a value higher than2D.It is worth mentioning that only three parameters are needed for Eq.(6),whereas Eq.(7)needs the deﬁnition ofﬁve parameters.Some authors[43,44]couple the above equations with the so-called‘induction time’,which can be deﬁned as the time the crystallization process starts, when the temperature is below the equilibrium melting temperature.It is normally described as[45]Dt indDtZðT0m K TÞat m(8)where t m,T0m and a are material constants.It should be mentioned that it has been found[46,47]that there is no need to explicitly incorporate an induction time when the modeling is based upon the KAE equation(Eq.(1)).1.1.3.Modeling of the morphology evolutionDespite of the fact that the approaches based on Eq.(4)do represent a signiﬁcant step toward the descriptionR.Pantani et al./Prog.Polym.Sci.30(2005)1185–12221191of morphology,it has often been pointed out in the literature that the isokinetic approach on which Nakamura’s equation (Eq.(4))is based does not describe details of structure formation [48].For instance,the well-known experience that,with many polymers,the number of spherulites in the ﬁnal solid sample increases strongly with increasing cooling rate,is indeed not taken into account by this approach.Furthermore,Eq.(4)describes an increase of crystal-linity (at constant temperature)depending only on the current value of crystallinity degree itself,whereas it is expected that the crystallization rate should depend also on the number of crystalline entities present in the material.These limits are overcome by considering the crystallization phenomenon as the consequence of nucleation and growth.Kolmogoroff’s model [49],which describes crystallinity evolution accounting of the number of nuclei per unit volume and spherulitic growth rate can then be applied.In this case,d c in Eq.(1)is described asd ðt ÞZ C m ðt 0d N ðs Þd s$ðt sG ðu Þd u 2435nd s (9)where C m is a shape factor (C 3Z 4/3p ,for spherical growth),G (T (t ))is the linear growth rate,and N (T (t ))is the nucleation density.The following Hoffman–Lauritzen expression is normally adopted for the growth rateG ½T ðt Þ Z G 0exp KUR $ðT ðt ÞK T N Þ!exp K K g $ðT ðt ÞC T m Þ2T ðt Þ2$ðT m K T ðt ÞÞð10ÞEqs.(7)and (10)have the same form,however the values of the constants are different.The nucleation mechanism can be either homo-geneous or heterogeneous.In the case of heterogeneous nucleation,two equations are reported in the literature,both describing the nucleation density as a function of temperature [37,50]:N ðT ðt ÞÞZ N 0exp ½j $ðT m K T ðt ÞÞ (11)N ðT ðt ÞÞZ N 0exp K 3$T mT ðt ÞðT m K T ðt ÞÞ(12)In the case of homogeneous nucleation,the nucleation rate rather than the nucleation density is function of temperature,and a Hoffman–Lauritzen expression isadoptedd N ðT ðt ÞÞd t Z N 0exp K C 1ðT ðt ÞK T N Þ!exp KC 2$ðT ðt ÞC T m ÞT ðt Þ$ðT m K T ðt ÞÞð13ÞConcentration of nucleating particles is usually quite signiﬁcant in commercial polymers,and thus hetero-geneous nucleation becomes the dominant mechanism.When Kolmogoroff’s approach is followed,the number N a of active nuclei at the end of the crystal-lization process can be calculated as [48]N a ;final Zðt final 0d N ½T ðs Þd sð1K x ðs ÞÞd s (14)and the average dimension of crystalline structures can be attained by geometrical considerations.Pantani et al.[51]and Zuidema et al.[22]exploited this method to describe the distribution of crystallinity and the ﬁnal average radius of the spherulites in injection moldings of polypropylene;in particular,they adopted the following equationR Z ﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃ3x a ;final 4p N a ;final 3s (15)A different approach is also present in the literature,somehow halfway between Nakamura’s and Kolmo-goroff’s models:the growth rate (G )and the kinetic constant (K )are described independently,and the number of active nuclei (and consequently the average dimensions of crystalline entities)can be obtained by coupling Eqs.(4)and (9)asN a ðT ÞZ 3ln 24p K ðT ÞG ðT Þ 3(16)where heterogeneous nucleation and spherical growth is assumed (Avrami’s index Z 3).Guo et al.[43]adopted this approach to describe the dimensions of spherulites in injection moldings of polypropylene.1.1.4.Modeling of the effect of crystallinity on rheology As mentioned above,crystallization has a dramatic inﬂuence on material viscosity.This phenomenon must obviously be taken into account and,indeed,the solidiﬁcation of a semi-crystalline material is essen-tially caused by crystallization rather than by tempera-ture in normal processing conditions.Despite of the importance of the subject,the relevant literature on the effect of crystallinity on viscosity isR.Pantani et al./Prog.Polym.Sci.30(2005)1185–12221192rather scarce.This might be due to the difﬁculties in measuring simultaneously rheological properties and crystallinity evolution during the same tests.Apart from some attempts to obtain simultaneous measure-ments of crystallinity and viscosity by special setups [52,53],more often viscosity and crystallinity are measured during separate tests having the same thermal history,thus greatly simplifying the experimental approach.Nevertheless,very few works can be retrieved in the literature in which(shear or complex) viscosity can be somehow linked to a crystallinity development.This is the case of Winter and co-workers [54],Vleeshouwers and Meijer[55](crystallinity evolution can be drawn from Swartjes[56]),Boutahar et al.[57],Titomanlio et al.[15],Han and Wang[36], Floudas et al.[58],Wassner and Maier[59],Pantani et al.[60],Pogodina et al.[61],Acierno and Grizzuti[62].All the authors essentially agree that melt viscosity experiences an abrupt increase when crystallinity degree reaches a certain‘critical’value,x c[15]. However,little agreement is found in the literature on the value of this critical crystallinity degree:assuming that x c is reached when the viscosity increases of one order of magnitude with respect to the molten state,it is found in the literature that,for iPP,x c ranges from a value of a few percent[15,62,60,58]up to values of20–30%[58,61]or even higher than40%[59,54,57].Some studies are also reported on the secondary effects of relevant variables such as temperature or shear rate(or frequency)on the dependence of crystallinity on viscosity.As for the effect of temperature,Titomanlio[15]found for an iPP that the increase of viscosity for the same crystallinity degree was higher at lower temperatures,whereas Winter[63] reports the opposite trend for a thermoplastic elasto-meric polypropylene.As for the effect of shear rate,a general agreement is found in the literature that the increase of viscosity for the same crystallinity degree is lower at higher deformation rates[62,61,57].Essentially,the equations adopted to describe the effect of crystallinity on viscosity of polymers can be grouped into two main categories:–equations based on suspensions theories(for a review,see[64]or[65]);–empirical equations.Some of the equations adopted in the literature with regard to polymer processing are summarized in Table1.Apart from Eq.(17)adopted by Katayama and Yoon [66],all equations predict a sharp increase of viscosity on increasing crystallinity,sometimes reaching inﬁnite (Eqs.(18)and(21)).All authors consider that the relevant variable is the volume occupied by crystalline entities(i.e.x),even if the dimensions of the crystals should reasonably have an effect.1.1.5.Modeling of the molecular orientationOne of the most challenging problems to present day polymer science regards the reliable prediction of molecular orientation during transformation processes. Indeed,although pressure and velocity distribution during injection molding can be satisfactorily described by viscous models,details of the viscoelastic nature of the polymer need to be accounted for in the descriptionTable1List of the most used equations to describe the effect of crystallinity on viscosityEquation Author Derivation Parameters h=h0Z1C a0x(17)Katayama[66]Suspensions a Z99h=h0Z1=ðx K x cÞa0(18)Ziabicki[67]Empirical x c Z0.1h=h0Z1C a1expðK a2=x a3Þ(19)Titomanlio[15],also adopted byGuo[68]and Hieber[25]Empiricalh=h0Z expða1x a2Þ(20)Shimizu[69],also adopted byZuidema[22]and Hieber[25]Empiricalh=h0Z1Cðx=a1Þa2=ð1Kðx=a1Þa2Þ(21)Tanner[70]Empirical,basedon suspensionsa1Z0.44for compact crystallitesa1Z0.68for spherical crystallitesh=h0Z expða1x C a2x2Þ(22)Han[36]Empiricalh=h0Z1C a1x C a2x2(23)Tanner[71]Empirical a1Z0.54,a2Z4,x!0.4h=h0Zð1K x=a0ÞK2(24)Metzner[65],also adopted byTanner[70]Suspensions a Z0.68for smooth spheresR.Pantani et al./Prog.Polym.Sci.30(2005)1185–12221193。

近年与凝聚态有关的诺贝尔奖

近年与凝聚态有关的诺贝尔奖近年与凝聚态有关的诺贝尔奖2009-03-10 18：202003 AlexeiA.Abrikosov,Vitaly L.Ginzburg,Anthony J.Leggett For pioneering contributions to the theory of superconductors and superfluids对超导体和超流体理论的先驱性贡献2001 Eric A.Cornell,Wolfgang Ketterle,Carl E.Wieman For the achievement of Bose-Einstein condensation in dilute gases of alkali atoms,and for early fundamental studies of the properties of the condensates碱性原子稀薄气体的玻色-爱因斯坦凝聚态和凝聚态物质性质早期基础性研究2000 Zhores I.Alferov,HerbertKroemer,Jack S.Kilby For basic work on information and communication technology For developing semiconductor heterostructures used inhigh-speed-and opto-electronics For his part in the invention of the integrated circuit发明快速晶体管、激光二极管和集成电路2000 AlanJ.Heeger,Alan G.MacDiarmid,Hideki Shirakawa Chemistry Prize For the discovery and development of conductive polymers导电聚合物的发现和发展1998 Ro bert ughlin,Horst L.St&ouml；rmer,Daniel C.Tsui For their discovery of anew form of quantum fluid with fractionally charged excitations发现并解释了电子在强磁场中相互作用而形成一种新粒子,称为准粒子1998 Walter Kohn,John A.Pople Chemistry Prize for his development of the density-functional theory for his development of computational methods in quantum chemistry提出的密度泛函理论对化学作出了巨大的贡献波函数方法1996 David M.Lee,Douglas D.Osheroff,Robert C.Richardson for their discovery of superfluidity in helium-3发现氦-3中的超流动性1994 Bertram N.Brockhouse,Clifford G.Shull for pioneering contributions to the development of neutron scattering techniques for studies of condensed matter中子谱学和中子衍射技术1991 Pierre-Gilles de Gennes for discovering that methods developed for studying order phenomena in simple systems can be generalized to more complex forms of matter,in part icular to liquid crystals and polymers把研究简单系统中有序现象的方法推广到更复杂的物理态,特别是液晶和聚合物1987 J.Georg Bednorz,K.Alex Müller for their important break-through in the discovery of superconductivity in ceramic materials高温超导电性1986 Ernst Ruska,Gerd Binnig,Heinrich Rohrerfor his fundamental work in electron optics,and for the design of the first electron microscope for their design of the scanning tunneling microscope在电光学领域作了基础性工作,并设计了第一架电子显微镜设计出了扫描隧道显微镜1985 Klaus von Klitzing for the discovery of the quantized Hall effect发现量子霍尔效应1982 Kenneth G.Wilson for his theory for critical phenomena in connection with phase transitions表彰他对与相变有关的临界现象所作的理论贡献1978 Pyotr Kapitsa,Arno Penzias,Robert Woodrow Wilson for his basic inventions and discoveries in the area of low-temperature physics for their discovery of cosm ic microwave background radiation表彰他在低温物理学领域的基本发明和发现表彰他们发现了宇宙背景微波辐射1977 PhilipW.Anderson,Sir Nevill F.Mott,John H.van Vleck for their fundamental theoretical investigations of the electronic structure of magnetic and disordered systems表彰他们对磁性和无序系统的电子结构所作的基础理论研究1973 Leo Esaki,Ivar Giaever,Brian D.Josephson for their experimental discoveries regarding tunneling phenomena in semiconductors and superconductors,respectively for his theoretical predictions of the properties of asupercurrent through atunnel barrier,in particular those phenomena which are generally known as the Josephson effects表彰他们分别在有关半导体和超导体中德隧道现象的实验发现表彰他对穿过隧道壁垒的超导电流所作的理论预言，特别是关于普遍称为约瑟夫森效应的那些现象1972 John Bardeen,Leon N.Cooper,Robert Schrieffer for their jointly developed theory ofsuperconductivity,usually called the BCS-theory表彰他们合作发展了通常称为BCS理论的超导电性理论1970 Hannes Alfvén,Louis Néel for fundamental work and discoveries in magneto-hydrodynamics withfruitful applications in different parts of plasma physics for fundamental work and discoveries concerning antiferromagnetism and ferrimagnetism which have led to important applications in solidstate physics表彰他对磁流体动力学的基础工作和发现，及其在等离子体不同部分卓有成效的应用表彰他对反铁磁性和铁氧体磁性所作的基础研究和发现1962 Lev Landau for his pioneering theories for condensedmatter,especially liquid helium表彰他作出了凝聚态特别是液氦的先驱性理论1961 Robert Hofstadter,Rudolf M&ouml；ssbauer for his pioneering studies of electron scattering in atomic nuclei and for his thereby achieved discoveries concerning the stucture of the nucleons for his researches concerning the resonance absorption of gamma radiation and his discovery in this connection of the effect which bears his name表彰他在电子受原子核散射的先驱性研究及由此获得的核子结构的发现研究g辐射的共振吸收并发现了以他的名字命名的穆思堡尔效应1956 WilliamB.Shockley,John Bardeen,Walter H.Brattain for their researches on semiconductors and their discovery of the transistor effect表彰他们对半导体的研究和晶体管效应的发现。

岩石地球化学课件赵志丹

岩石地球化学课件赵志丹
推荐软件和参考书
1.
计算CIPW的软件，Norm3
2.
Geokit, 路远发编写
3.
A TEXTURAL ATLAS OF MINERALS IN THIN SECTION, 软件, 编写者为Daniel J. Schulze,
University of Toronto.
4.
霞石正长岩响岩类
花岗岩 -流纹岩类
SiO2
< 45 %
45-53 %
53-66 %
> 66 %
<3.3 3.3-9 >9 <3.3 3.3-9
>9 <3.3 3.3-9
Na2O+K2O <3.5
>3.5 平均3.6 平均4.6 平均7 平均5.5
平均9
平均 14
平均 6-8
(N2O aK2O2)
代表性岩浆岩的化学成分
SiO2 TiO2 Al2O3 Fe2O3 FeO MnO MgO CaO Na2O K2O H2O+
Total
橄榄岩 42.26 0.63 4.23 3.61 6.58 0.41 31.24 5.05 0.49 0.34 3.91
98.75
玄武岩 49.20 1.84 15.74 3.79 7.13 0.20 6.73 9.47 2.91 1.10 0.95
玄武岩
花岗闪长岩
花岗岩
SiO2饱和度与矿物共生组合的关系
(1) SiO2过饱和——SiO2很多（过多），除形成硅酸盐矿物外，还有剩余—石英， Q就是过饱和矿物，含有Q的岩石，就是SiO2过饱和岩石。
SiO2过饱和岩石

诺贝尔奖得主Brown和Goldstein

Statins uesd as therapy medicine
1975年，一名日本科学家Akira Endo, 发现某些霉菌会合成强烈的抑制HMG CoA还原酶的产物。 Brown 和Goldstein 证实这些抑制剂可以增加狗的肝脏的LDL受体的水平，并且诱导血浆LDL水平的显著降低。随即，这种药物就进入了临床试验，发现能够显著降低人血浆LDL水平，保护心脏病的患者减少心血管事件的发生。这一类药物，统称为他汀，在全世界每天有超过3千万的人在服用他汀药物。
Dr. Michael Brown
Dr. Joseph Goldstein
在美国西南医学中心的两位科学家Brown和Goldstein因为在胆固醇代谢机制研究中的卓越贡献共同获得了1985年的诺贝尔医学和生理学奖。基于他们的发现，一种降脂类药－他汀类药物在临床上的得以广泛应用，据估计，单单在美国，目前就有大约2000万人在服用他汀类药物（年销售额高达260 亿美元），每年有6000~7000 人因此而延长了生命。
Dissecting Receptor Regulation and Its Implications for Statin Therapy
从最初的对LDL受体的研究中， Brown/Goldstein的团队认识到这个受体是可以被调控的。当细胞的胆固醇被去除时，受体的数量增加。相反，当细胞内胆固醇堆积时，受体基因则表达受抑制受体的数量就下降。在体内，肝脏产生了大部分的LDL受体因此肝脏从血中清除了大部分的LDL。 Goldstein和Brown 意识到如果降低肝细胞内的胆固醇则肝脏表达的LDL受体的数量就会增加。这就可以通过摄入低胆固醇和饱和脂肪酸的饮食来达到。也可以通过服用抑制胆固醇合成的药物来实现。也就是抑制胆固醇合成的限速酶3-羟基-3-甲基戊二酰辅酶A还原酶 (HMG CoA 还原酶)。

冰淇淋冰晶体再结晶的抑制作用研究进展

薛磊，刘爱国，刘园，等. 冰淇淋冰晶体再结晶的抑制作用研究进展[J]. 食品工业科技，2023，44（23）：394−402. doi:10.13386/j.issn1002-0306.2023030170XUE Lei, LIU Aiguo, LIU Yuan, et al. Research Progress on Inhibition of Recrystallization of Ice Cream Crystals[J]. Science and Technology of Food Industry, 2023, 44(23): 394−402. (in Chinese with English abstract). doi: 10.13386/j.issn1002-0306.2023030170· 专题综述 ·冰淇淋冰晶体再结晶的抑制作用研究进展薛　磊1,2，刘爱国1,2, *，刘　园3，刘立增1,2，强　锋4，曲睿晶1,2（1.天津商业大学生物技术与食品科学学院，天津 300134；2.天津市食品生物技术重点实验室，天津 300134；3.江苏省食品药品监督检验研究院，江苏南京 210008；4.天津天狮学院，天津 301700）摘　要：冰淇淋具有热力学不稳定的特性，在加工、储运和销售过程中，温度波动导致冰晶体发生再结晶现象从而使得平均冰晶体尺寸增大，导致冰淇淋质地粗糙，口感变差。

因此，抑制冰淇淋内冰晶体再结晶现象是保证冰淇淋质量的关键。

本文综述了冷冻过程中冰晶体过冷、成核、生长和再结晶的形成机理及研究进展，冰淇淋原料中的乳化剂、稳定剂、甜味料和蛋白质对冰晶体再结晶的抑制作用，并详细介绍了超声波辅助冷冻技术、磁场辅助冷冻技术、高压辅助冷冻技术和电场辅助冷冻技术等新兴冷冻技术对冰淇淋再结晶的抑制作用，并对其未来的发展方向进行了展望，为适应线上销售趋势，研发新产品，解决冰淇淋冰晶体再结晶难题提供了理论参考。

海藻酸钠水凝胶3D打印效果和流变特征及其相关性分析

钟启明，张佳雨，郭城，等. 海藻酸钠水凝胶3D 打印效果和流变特征及其相关性分析[J]. 食品工业科技，2023，44（23）：21−28.doi: 10.13386/j.issn1002-0306.2023030162ZHONG Qiming, ZHANG Jiayu, GUO Cheng, et al. Correlation Analysis of 3D Printability and Rheological Properties of Sodium Alginate Hydrogels[J]. Science and Technology of Food Industry, 2023, 44(23): 21−28. (in Chinese with English abstract). doi:10.13386/j.issn1002-0306.2023030162· 未来食品 ·海藻酸钠水凝胶3D 打印效果和流变特征及其相关性分析钟启明1，张佳雨1，郭　城1，杨国燕1，贾喜午1，刘玉彪2，金伟平1,*（1.武汉轻工大学食品科学与工程学院，湖北武汉 430000；2.武汉中粮科技食品有限公司，湖北武汉 431400）摘　要：本研究以钙离子诱导海藻酸钠水凝胶为模型，通过稳态剪切、形变扫描、屈服应力等流变学测试，辅以水合分布特征分析海藻酸钠水凝胶网络结构，综合3D 打印产品的形态与Micro-CT 微结构，经Spearman 相关性系数分析，建立流变参数与3D 打印效果之间的关联性。

结果表明，当固定海藻酸钠与Ca 2+质量分数比为24:1，海藻酸钠浓度为4.5%时，凝胶3D 打印产品形态评分最佳，层纹结构清晰，孔隙率为12.21%。

此时凝胶的流变特征参数K 、η1、G'、G"、τ0和τy 分别为255.1 Pa·s n ，2740 Pa·s ，3509 Pa ，673.2 Pa ，261.4 Pa 和51.62 Pa ；凝胶网络内部以毛细管水（约99.20%）为主，表现出强持水力。

QUANTUM_ESPRESSO_a_modular_and_open-source_software_project_for_quantum_simulations_of_materials

2 1
arXiv:0906.2569v1 [cond-mat.mtrl-sci] 14 Jun 2009
Q UANTUM ESPRESSO is an integrated suite of computer codes for electronic-structure calculations and materials modeling, based on density-functional theory, plane waves, and pseudopotentials (norm-conserving, ultrasoft, and projector-augmented wave). Q UANTUM ESPRESSO stands for opEn Source Package for Research in Electronic Structure, Simulation, and Optimization. It is freely available to researchers around the world under the terms of the GNU General Public License. Q UANTUM ESPRESSO builds upon newlyrestructured electronic-structure codes that have been developed and tested by some of the original authors of novel electronic-structure algorithms and applied in the last twenty years by some of the leading materials modeling groups worldwide. Innovation and efﬁciency are still its main focus, with special attention paid to massively-parallel architectures, and a great effort being devoted to user friendliness. Q UANTUM ESPRESSO is evolving towards a distribution of independent and inter-operable codes in the spirit of an open-source project, where researchers active in the ﬁeld of electronic-structure calculations are encouraged to participate in the project by contributing their own codes or by implementing their own ideas into existing codes.

药物结晶中的经典与非经典结晶路径

1897 年,奥斯特瓦尔德提出了著名的奥斯特瓦尔德阶段定律( Ostwald’ s law of stages) [13] ,指出结晶过程中首先出现的是最不稳定晶型,随后出现稳定性依次提高的其他晶型,不同晶型出现的先后顺序与它们自身的稳定性有关。奥斯特瓦尔德阶段定律是在药物结晶实验中常用的指导原则, 是经过一系列实验数据总结得到的一个基本规律,是对晶型成核难易程度的基本判断依据。然而这个规则并不一直有效。例如 CaCO3 各个晶型在模拟体液中的转化并不符合奥斯特瓦尔德阶段定律[14] 。对乙酰氨基酚从水中结晶得到的是稳定晶型 I[15] 。奥斯特瓦尔德时期,由于饱和溶液或者熔体中存在亚稳区间或过冷现象,即热滞后现象,人们由此推断成核存在势垒。直到 Volmer 和 Gibbs 等阐明了决定成核过程的参数,进一步发展了成核
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Liquid crystal element and method for measuring ph

专利名称：Liquid crystal element and method formeasuring physical property of liquid crystalmaterial发明人：木村宗弘,大西仰,佐原良亮申请号：JP2019012716申请日：20190129公开号：JP2020122652A公开日：20200813专利内容由知识产权出版社提供专利附图：摘要：Problem to measure flexoelectric coefficient with high accuracy. The liquid crystal element comprises first substrate 11, second substrate 12, liquid crystal layers15A to C, and electric field applying means.The liquid crystal layer has a uniform orientational domain which is uniform orientation when no electric field is applied, and a strain orientational domain which is strain orientations including the spur deformation and bend deformation when no electric field is applied, and the uniform orientational domain and the strain orientational domain are arranged adjacent to each other and are integrated together It is built.Electric field applying meansA first applying means for applying an electric field in the thickness direction of the liquid crystal layer to a first region, which is at least a portion of the uniform orientation domain, andA second applying means for applying a voltage in the thickness direction of the liquid crystal layer to a second region, which is at least a portion of the strain oriented domain, andA third applying means for applying a voltage in a direction substantially orthogonal to the layer thickness of the liquid crystal layer with respect to a third region, which is at least a portion of the strain oriented domain, is provided.Diagram申请人：国立大学法人長岡技術科学大学地址：新潟県長岡市上富岡町１６０３－１国籍：JP代理人：特許業務法人むつきパートナーズ更多信息请下载全文后查看。

Observation method of protein crystal

专利名称：Observation method of protein crystal发明人：西澤典彦,松村浩由,森勇介,石田周太郎,伊東一良,杉山成,安達宏昭,井上豪,高野和文,村上聡申请号：JP2012535029申请日：20110920公开号：JPWO2012039377A1公开日：20140203专利内容由知识产权出版社提供专利附图：摘要： By observing 3-dimensional real-time non-destructive, the growth process of the protein crystals, and to accurately control the growth of crystals, to provide theobservation technique of the protein crystals allows the production of high quality single crystals. Monitoring method of protein crystals to perform observation of protein crystals produced by the crystallization method with OCT measurement using lightemitted from the ultra-broadband light source, using gel. Ultra-broadband light source is, the observation method of protein crystals is an ultra broadband supercontinuum light source. Center wavelength of the light emitted from the ultra-wideband supercontinuumlight source, method of observing protein crystals is 0.8μm band. Observation of protein crystals, observation method of protein crystals is the observation by in situ measurement.申请人：国立大学法人大阪大学地址：大阪府吹田市山田丘１番１号国籍：JP代理人：上代哲司,神野直美更多信息请下载全文后查看。

高分子材料发展史及诺贝尔奖得主

主要贡献：
利用等活性假设及直接的统计方法，他计算了高分子分子量分布，即最可几分布，并利用动力学实验证实了等活性假设；
引入链转移概念，将聚合物统计理论用于非线性分子，产生了凝胶理论；
Flory-Huggins格子理论； 1948年作出了最重要的贡献，即提出“排除体积”
理论和θ温度概念；
他的著作“Principles of polymer chemistry” （1953）是高分子学科中的Bible。
1955年美国人利用齐格勒-纳塔催化剂聚合异戊二烯，首次用人工方法合成了结构与天然橡胶基本一样的合成天然橡胶。
“for their discoveries in the field of the chemistry and
technology of high polymers ”
1956年Szwarc提出活性聚合概念，高分子进入分子设计时代。1956年发现了在负离子聚合反应过程中可使链终止反应停止进行，从而得到活的高分子负离子。用这个方法可制得多种嵌段共聚物（见嵌段共聚合）、其他“分子设计”成的高分子，以及单分散高分子等。
高分子材料科学
大事记
家庭中的聚乙烯制品碳纤维复合材料
聚丙烯制品
由碳纤维和铝合金制成的赛车底盘
❖1839年美国人 Charles Goodyear 发现天然橡胶与硫磺共热后明显地改变了性能，使它从硬度较低、遇热发粘软化、遇冷发脆断裂的不实用的性质，变为富有弹性、可塑性的材料。
模拟壁虎腿 (Gecko feet)
Dry Adhesive Based on Van der Waals nteraction
a
b
SEM of microfabricated polyimide pillars (diameter 0.5μm, height 2μm, separation between pillars 1.6μm)

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FIG. 1: (a) Particle positions projected onto a plane for the standard Kob-Andersen binary Lennard-Jones liquid (the large (A) particles are green, the small (B) particles are black). The system is shown after 15 µs of simulation (Argon units) at T=0.40 and density 1.2 (dimensionless units). After this simulation time the A particles phase separated and formed a large crystal, as is clear in the second ﬁgure showing the same conﬁguration with all A particles removed.
2 system was simulated at the density 1.2 in dimensionless units [1] at varying temperatures. The standard timereversible leap-frog algorithm [5] was used with a time step of 0.005 (in Argon units: ≈ 10−14 s). The software used has been described elsewhere [6]; it utilizes a double sorting of neighbor particles that makes it possible to simulate 10 µs within 2-3 days of computing on a standard computer. For temperatures above 0.45 no crystallization was detected. In the temperature interval [0.39, 0.45] a suspicious drop in pressure taking place typically after a few billion time steps indicates that something is happening. It turns out that the system phase separates such that the A particles form fairly large regions with no B particles present. Linked to this phase separation is a crystallization of the A particles. Ten simulations were performed in the [0.39, 0.45] temperature interval; after 4 billion time steps eight of these ten simulations phase separated with crystallization of the A particles. Figure 1 shows a representative example of our results, giving the positions of the particles after a simulation time of 15 µs and for T=0.40 (NVT-MD). There is a large region of pure A particles showing clear crystalline order. This is consistent with the results of Fernandez and Harrowell [7], who found that the T = 0 equilibrium phase of the Kob-Andersen BLJ consists of a coexisting A (fcc) and AB (CsCl structure) crystals. We proceed now to make a modiﬁcation of the Kob-Andersen system, with the goal to make it less prone to crystallization. A liquid mixture is stable against crystallization if the composition of the mixture disfavors the creation of a critical nucleus of the crystal when the liquid is cooled down. In the standard Kob and Andersen (KA) system this is achieved by letting the smaller B-particles act as “glue” between the A-particles and thus the LJ-parameters: σAB = 0.8σAA ; σBB = 0.88σAA ; AB = 1.5 AA and BB = 0.5 AA disobeys the Lorentz-Berthelot (LB) mixing rules σAB = (σAA + σBB )/2, AB = ( AA BB )
arXiv:0712.0377v2 [cond-mat.soft] 9 Feb 2008
PACS numbers: 64.70.Pf; 61.20.Lc

As computers get faster, simulations of the highly viscous liquid phase preceding glass formation become increasingly realistic. In this context it is nice to have a standard model system to refer to, just like the Ising model is a standard model for critical phenomena. For several years the Kob-Andersen 80-20 binary Lennard-Jones (BLJ) mixture [1] has served this purpose, because it is easy to simulate and was never found to crystallize. The Kob-Andersen BLJ consists of two types of Lennard-Jones particles, 80% large particles (A) and 20% small particles (B). The BLJ potentials are modiﬁcations of the potentials devised by Weber and Stillinger [2], who constructed the pair potentials for the binary mixture based of physical-chemical data for the Ni80 P20 alloy. The Kob-Andersen potentials do not obey the Lorentz-Berthelot rules for mixture, especially with respect to the A-B attraction that is three times stronger than the B-B attraction. This ensures a non-ideal mixture with large negative mixing enthalpy (and energy), which suppresses phase separation. Recently, Pedersen and co-workers reported crystallization of the Wahnstrom BLJ [3] after lengthy computer runs [4]. The crystal is the MgZn2 phase consisting of particles in the ratio 1:2, diﬀerent from the 1:1 ratio deﬁning the Wahnstrom BLJ. Thus concentration ﬂuctuations precede (or at least correlate with) crystal formation. These ﬁndings inspired us to investigate whether the more widely studied Kob-Andersen BLJ also crystallizes in lengthy computer runs. We performed molecular dynamics simulations of 1000 particles of the standard Kob-Andersen binary LennardJones liquid in the NVE and NVT ensembles (in the latter case using the standard Nose-Hoover thermostat). The