Influence of heat treatment on tribological behaviors of novel wrought aluminum bronze

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Effect of heat treatment on microstructure and properties of

Abstract: The effect of heat treatment on the microstructure and properties of a hot-extruded nickel-aluminum bronze was investigated. Experimental materials were heat treated through different processes, including quenching, normalizing, aging and annealing, and their microstructure, corrosion resistance and mechanical properties were characterized. It is found that quenching causes all p phase transformed into p’ phase, however, normalizing causes p phase transformed into p’, a and K phases. When the quenched sample is aged, fine K phase is precipitated from the as-quenched microstructure of p’ phase. Annealing causes the transformation of p’ into a and K phases. The results of mechanical property tests show that quenching, normalizing and aging improve the tensile strength and hardness of the experimental material, with a corresponding fall in elongation. Annealing raises the elongation but reduces the tensile strength and hardness. Furthermore, corrosion resistance of nickel-aluminum bronze ranks from worse to better in the following order: aged, quenched, normalized, hot-extruded and annealed. However, with the exposure time of corrosion test increasing, the difference of average corrosion rate between those nickel-aluminum bronzes turns small.

A review of heat treatment on polyacrylonitrile fiber

Review articleA review of heat treatment on polyacrylonitrile ﬁberM.S.A.Rahaman,A.F.Ismail *,A.MustafaMembrane Research Unit (MRU),Faculty of Chemical and Natural Resources Engineering,Universiti Teknologi Malaysia,Skudai 81310,Johor,MalaysiaReceived 23January 2007;accepted 23March 2007Available online 14April 2007AbstractDeveloping carbon ﬁber from polyacrylonitrile (PAN)based ﬁber is generally subjected to three processes namely stabilization,carboniza-tion,and graphitization under controlled conditions.The PAN ﬁber is ﬁrst stretched and simultaneously oxidized in a temperature range of 200e 300 C.This treatment converts thermoplastic PAN to a non-plastic cyclic or a ladder compound.After oxidation,the ﬁbers are carbonized at about 1000 C in inert atmosphere which is usually nitrogen.Then,in order to improve the ordering and orientation of the crystallites in the direction of the ﬁber axis,the ﬁber must be heated at about 1500e 3000 C until the polymer contains 92e 100%.High temperature process generally leads to higher modulus ﬁbers which expel impurities in the chain as volatile by-products.During heating treatment,the ﬁber shrinks in diameter,builds the structure into a large structure and upgrades the strength by removing the initial nitrogen content of PAN precursor and the timing of nitrogen.With better-controlled condition,the strength of the ﬁber can achieve up to 400GPa after this pyrolysis process.Ó2007Published by Elsevier Ltd.Keywords:Polyacrylonitrile;Heat treatment;Stabilization;Carbonization;Carbon ﬁber1.IntroductionIt has been documented that the majority of all carbon ﬁ-bers used today are made from PAN precursor,which is a form of acrylic ﬁber.PAN which is a polymer with a chain of carbon connected to one another (Fig.1)is hard,horny,rel-atively insoluble,and a high-melting material [1].It has been established that PAN-based carbon ﬁber is stronger than other type of precursor-based carbon ﬁber [2].PAN-based ﬁbers also have been found to be the most suitable precursors for produc-ing high performance carbon ﬁbers (compared to pitch,rayon,etc.)generally because of its higher melting point and greater carbon yield (>50%of the original precursor mass)[3e 7].Although carbon ﬁber can be from pitch precursor,the pro-cessing and purifying it to the ﬁber form is very expensive and generally,they are more expensive than PAN-based ﬁbers [8].PAN with molecular formula [C 3H 3N]n can produce car-bon ﬁber of relatively high carbon yield giving rise toa thermally stable,extremely oriented molecular structure when subjected to a low temperature treatment [9].PAN ﬁber was also preferred to be the precursor because of its fast rate in pyrolysis without changing its basic structure [9].Optimizing the pyrolysis of PAN precursor ﬁber would ideally result in en-hanced performance of the resulting carbon ﬁber.Recent study has established that PAN ﬁbers were used on a large scale in textile industry and one of the most suitable and widely applied for making high performance carbon ﬁbers [10e 13].Most PAN-based carbon ﬁbers extensively applied in last two decades were used in the composite technology [14].They are highly desirable for high performance composites for automotive and aerospace technologies due to their enhanced physical and mechanical characteristics [9].Fitzer [15]and Chen and Harrison [16]believed that the optimization of PAN ﬁber would ideally result in high performance for use in aerospace application.Hence PAN-based ﬁber that leads to a good balance in properties can be used in structural appli-cations and provide high strength [2].Year by year there will be an improvement on performance as well as strength and modulus of PAN-based carbon ﬁber*Corresponding author.Tel.:þ6075535592;fax:þ6075581463.E-mail address:afauzi@utm.my (A.F.Ismail).0141-3910/$-see front matter Ó2007Published by Elsevier Ltd.doi:10.1016/j.polymdegradstab.2007.03.023Polymer Degradation and Stability 92(2007)1421e1432[17].Traceski[18]stated that the total worldwide production of PAN-based carbonﬁber was19million lbs per year for 1989and increased up to26million lbs per year.In addition, the worldwide outlook for the demand of PAN carbonﬁbers is currently amounting to a nearly$6billion pound per year worldwide effort[19,20].So,the wide availability of PAN pre-cursor had triggered the production of carbonﬁber.1.1.Heat treatmentHeat treatment is a process that converts the PANﬁber pre-cursor to carbonﬁber.Currently90%of all commercial carbon or graphiteﬁbers are produced by the thermal conversion of a PAN precursor,which is a form of acrylicﬁber.The successful conversion of PAN to high strength,high modulusﬁbers depend in part upon the understanding of the oxidative and thermal treatment.Liu et al.[21]listed the three steps for the conversion of precursor of PAN-basedﬁber to carbon,which are as follows.i.Oxidative stabilization,which forms ladder structure toenable them to undergo processing at higher temperatures. ii.High temperature carbonization,(1600 C)to keep out noncarbon atoms and yield a turbostatic structure.iii.Further heat up to2000 C to improve the orientation of the basal planes and the stiffness ofﬁbers,which is called graphitization.2.Precursor stabilizationAmong the conversion processes shown in Fig.2,an essen-tial and time-consuming step in the conversion of PANﬁbers to high performance carbonﬁber is the oxidative stabilization step[7].This can be explained by chemical reactions that are involved in this process,which are cyclization,dehydrogena-tion,aromatization,oxidation and crosslinking which can re-sult in the formation of the conjugated ladder structure [22,23].The oxidative stabilization stage is one of the most complicated stages,since different chemical reactions take place and the structure of the carbonﬁber is set in this stage.Stabilization process,which is done in atmosphere can change chemical structure of theﬁber and cause them to become thermally stable and so melting will not reoccur[24].Recently, the stabilization process is found to play an important role in converting PANﬁber to an infusible stable ladder polymer that converts C^N bonds to C]N bonds[25]and to develop crosslink between molecules of PAN[26]which tend to operate at high temperatures,with minimum volatilization of carbona-ceous material.The thermal stability of the stabilizedﬁber is at-tributed to the formation of the ladder structure due to cyclization of the nitrile groups in acrylic molecule.Setnescu et al.[27]observed that CH2and CN groups disappeared com-pletely due to elimination,cyclization and aromatization reac-tions and formed C]C,C]N and]C e H groups.Typically, during the course of stabilization,the PAN-based precursorﬁber undergoes a change in colour from white through shades of yel-low and browns to ultimately a black stabilizedﬁber.The mech-anism for colouration is not fully understood.However,the appearance of black colour is believed to be due to the formation of ladder ring structure[28,29].In this process,the required temperature is the important factor that would affect the heating treatment of PANﬁber. Heat treatment involved in stabilization of PANﬁber is carried out usually at the region of180e300 C[24,30].When tem-perature exceeds180 C,the molecular chains will unfold and move around.But some researchers found that heating temperature within200e300 C are usually used to stabilize theﬁber[7,23,25,31e34].Fitzer et al.[35]suggested that in producing best performance carbonﬁber,the best stabilized temperature is270 C.However,other researchers[36e38] found that heating treatment needs higher than300 C to com-plete the stabilization.Mathur et al.[39]also proposed that PANﬁber does not get preferred stability at270 C but needs higher temperature up to400 C.It was known that PANﬁber with optimum stabilization condition can produce higher mod-ulus carbonﬁber than unstablizedﬁber or thanﬁber which is prepared at high temperature stabilization process[31].If the temperature is too high,theﬁbers can overheat and fuse or even burn.However,if the temperature is too low,the reac-tions are slow and incomplete stabilization can be resulted, yielding poor carbonﬁberproperties.Previously two important reactions occur during stabiliza-tion process which can change the chemistry of PAN structure [40].They are dehydrogenation and cyclization reactions as illustrated in Fig.3.Both are important to form ladder polymer structure which was thermally stable and might be able to withstand high temperature during pyrolysis process.In addi-tion,stabilization process also could be present in oxidation reaction which gives an insight about diffusion of oxygen through the reacting polymer [41].2.1.Oxidation reactionThe oxidation reaction during PAN-based precursor stabili-zation is the least reaction and is the step which most precur-sors mercially,stabilization of PAN ﬁber is done in an ‘oxidizing’medium which is typically air.The reaction exotherm when PAN is stabilized in air is partly due to reac-tion with oxygen.Although stabilization could be done in an inert atmosphere,a polymer back-bone containing oxygen-bearing groups that evolves in PAN ladder structure (Fig.4)provides greater stability to sustain high temperature carbon-ization treatment [42].Fitzer and Muller [43]have concluded that the activation energy and the frequency factor were greater in air than in ni-trogen (inert gas).This indicates that oxygen is an initiator for the formation of activated center for cyclization because of the increase in the activation energy.Consequently,various struc-tures of oxidized PAN that account for the presence of oxygen have been proposed including those containing bridging ether links,those containing carbonyl groups,and those in which each nitrogen atom donates its lone pair of electron to an oxygen (as shown in Fig.5)[5,44].2.2.Dehydrogenation processDehydrogenation is the formation of double bonds that sta-bilizes carbon chain and cyclization is the process by whichthe rings are formed.The dehydrogenation reactions have at least two elementary steps,with oxidation in the ﬁrst step and elimination of water in the second.Studies have shown that either the original PAN polymer or cyclized ladder poly-mer can undergo dehydrogenation [43].As a conclusion from Fig.3,the reactions are usually written in the form of Fig.6.Since oxygen is required for the reaction to proceed,dehydro-genation does not occur in inert atmosphere.This is different from the cyclization reaction.The double bond or unsaturated bond that formed in the reaction improves the polymer’s ther-mal stability and reduces chain scission during carbonization [45].2.3.Cyclization reactionThe last reaction that would be discussed is cyclization which is the most important reaction in the stabilization of PAN ﬁber.Cyclization is the reaction of the nitrile groups in the precursor polymer with adjacent groups to form a stable,ladder polymer and could be described by ﬁrst order kinetic equation [43].Cyclization is the most important reaction in stabilization process.The cyclization of the nitrile groups is an exothermic reaction and that the evolution of gaseous prod-ucts accompanies this reaction [46].The reaction is necessary to hold molecules in ﬁber together and increases the stiffness [47e 50].In addition,the idea of cyclization was conceivedbyHoutz [51]in 1950from his observation that PAN stabilization led to change in colouration.During the stabilization process,the PAN structure un-dergoes cyclization reaction and converts the triple bond struc-ture (e.g.C ^N)to double bond structure (e.g.C ]N),resulting in a six-membered cyclic pyridine ring proposed by Houtz [51]as illustrated in Fig.7and changes the aliphatic to cyclic structure prior to the formation of ladder polymer.Referring to this ﬁgure (Fig.7),cyclization reactions can pro-ceed in either an inert atmosphere or in the presence of oxy-gen.In other words,oxygen is not involved in the reaction mechanism of cyclization.When the temperature rises up to 600 C,the cyclized structure undergoes dehydrogenation and links up in lateral direction,producing a graphite-likelayer or ribbon structure (shown in Fig.8)consisting of three hexagons in the lateral direction and bounded by nitrogen atom [52].The initiation of the cyclization reaction has been attributed to several sources:(1)impurities such as catalyst fragments,re-sidual polymerization products,inhibitors,etc.[53](2)the chain end groups;[54](3)random initiation by hydrogen atoms a to the nitrile;[55](4)transformation of a nitrile to an azomethine;[56];(5)the presence of a ketonitrile formed by hydrolysis dur-ing polymerization;[28]and (6)hydrolysis of nitriles to acids during polymerization [57].In addition,due to their reaction,cyclization reactions can proceed in either an inert atmosphere or in the presence of oxygen.In other words,oxygen is not in-volved in the reaction mechanism of cyclization.2.4.Miscellaneous types of stabilization processAlthough a wide variety of stabilization processes are described,they have several design objectives in common.1.Runaway reactions from heat must be prevented.2.Stabilization must be completed throughout the ﬁber.3.The shrinkage must be completed throughout the ﬁbers.4.The reactions are slow and accelerations are helpful.When the production volume increased speciﬁc methods of stabilizing the ﬁber were patented.The patents deal with three major areas:batch process,continuous process,and accelera-tion of stabilization reactions.This section provides general example from each of these areas that illustrates common de-sign objectives described above.2.4.1.Batch processThree examples of batch processes are shown in Figs.9e 11.The ﬁrst process blows hot air through a spool precursor loosely wound on a porous core.The air permits heatremovaland provides a source of oxygen.Shrinkage is controlled by the ﬁber itself as it is wound and spool.However,since the air ﬂow is not uniform and the ﬁbers are in contact with one another,a batch process with a method to move the yarn and improve the uniformity was developed as in Fig.10.The ends are tied and the rollers turned to minimize thecontact of the yarn with the rollers.And the shrinkage is con-trolled by adjusting the tension applied to the rack.The ﬁnal process in Fig.11is a step toward continuous process and probably is more expensive to operate than the two processes (Figs.9and 10)described before.The initial stages of stabili-zation are performed continuously in a multiphase oven with the ﬁber restrained from shrinkage by the oven roller.The more stable ﬁnal stages are completed in batch oven where the yarn is wrapped into loose skeins.However,the process is limited in its ability to produce since the yarn in contact with the support will differ from that surrounded by air,and the tension is not uniform in the skein.2.4.2.Continuous processThe continuous processes for stabilizing PAN are all based on the idea of pulling tows through heated boxes.The ﬁrst sketch in Fig.12illustrates the basic heated box with multiple passes.The tow may be oriented horizontally or vertically in the oven and the air in the oven is circulated to control heat and mass transfers.It also patented by Toho Company [61],where the ﬁber passes through the oven,turns on a roller,and re-enters the oven.In addition,the heat is controlled by the yarn moving outside the hot oven every few minutes.Meanwhile Cour-taulds (Fig.13)has patented a stabilization oven which con-tains a number of different temperature zones in a single oven [62].The yarn is wound on long rollers which pass through a series of bufﬂed oven zones.This concept of multi-ple zones with a stage temperature is probably used in all com-mercial processes.An interesting continuous process is shown by the ﬂuidized bed process (Fig.14)[63].Here the ﬁbersareFig.9.Batch stabilization of polyacrylonitrile yarn on the tube [58].Fig.10.Moving rack process by atomic energy authority [59].1425M.S.A.Rahaman et al./Polymer Degradation and Stability 92(2007)1421e 1432passed through a bed of ﬂuidized hollow balls,signiﬁcantly improving the heat and mass transfer rates.This design could allow the use of higher temperatures and still avoid runaway reaction and should allow more rapid dehydrogenation and oxidation.2.4.3.Accelerator processMost accelerators serve as initiators for the cyclization re-actions.An example of this is the introduction of acidic groups like itaconic acids which was claimed by the US patent 4,079,122[64].This monomer contains two acid groups which provide two initiation sites,leaving fewer uncyclized links for later carbonization.Besides,the US patent 4,397,831[61]claimed that by passing the ﬁbers through a bath which con-tains a water-soluble zinc compound and then washes the ﬁber with the water,could result in Lewis acid served to initiate the cyclization reaction.Other than that,an example for accelera-tor process by modifying the stabilization gas is given by the US patent 3,954,947[65].An atmosphere of oxygen and hy-drogen chloride is used,resulting in shorter times for complete stabilization.3.CarbonizationCarbonization was an aromatic growth and polymerization,in which the ﬁber would undergo heating process at a hightemperature up to 800e 3000 C,typically to a 95%carbon content [31].Carbonization at 1000 C will produce carbon ﬁ-ber in low modulus type and intermediate modulus or type II carbon ﬁber will produce at up to 1500 C [13,16,31,66].Trin-quecoste and group [67],also observed that heating process around 1000 C produced high tensile strength ﬁber,and for high modulus ﬁber,higher temperature treatment is needed.Thus,it would change the PAN structure as illustrated Fig.15[68]and Fig.16[69].A few researchers had put in effort to understand the car-bonization step especially in continuous model [21].However,whatever be the technique,the process only occurs in inert at-mosphere condition and usually involves heating the polymer in a nitrogen rich environment (Fig.17)[70].In addition,ten-sile and modulus have shown signiﬁcant increase with carbon-ization treatment under N 2[71].But some researchers proved that argon also can act as inert gas in carbonization process [72e 76].Whereas,carbonizing the stabilized PAN ﬁber in an atmosphere of HCl vapors could enhance the carbon ﬁber yield,subsequently decreasing the amount of hydrogen cya-nide (HCN)by eliminating nitrogen as ammonia.However,Fig.13.Courtaulds furnace for oxidation,carbonization and graphitization [62].1426M.S.A.Rahaman et al./Polymer Degradation and Stability 92(2007)1421e 1432the consumption of argon and HCl was very costly and HCl could make the equipment corrosive[76,77].In carbonization process,there are two steps wherein,the ﬁrst step involves in carbonization process and is the thermal pyrolysis up to600 C.Low heating rate as low as5 C/min was used which could lower the mass transfer because of in-ability of the structure[35].In the second stage,high heating rate for highﬁnal temperature is needed.Unlike theﬁrst stage,the high heating rate had been used in the second stage because of lesser possibility of damage to the structure due to stability of PAN structure[38].Thus,the pro-cess requires only less than10min for the second stage[78]. However,previous study claimed that too high heating rate could cause higher amount of shrinkage[16,35].Some studies stated that PANﬁber that stabilized at temperature fewer than 250 C could not withstand at high heating rate beyond 1700 C and produced a brittleﬁber[38].Hence,the optimum carbonization was required in order to form better properties ofﬁnal carbonﬁber.3.1.Stretching during pyrolysisStretching during pyrolysis process helps to develop high tensile modulus and improvesﬁber strength upon subsequent heat treatment.Some study indicated that the strength of the ﬁber had been restored and could be improved when the high temperatures were accompanied by reasonable degree of stretching[79].Tsai and Lin[80]and Edie[33]also stated that with the requirement of the stretching in this step,ade-quate modulus and strength of carbonﬁber could be produced.Other than that stretching could attenuate amount of shrink-age,which was caused by high heating rate[70].Therefore,if no stretching was applied in the early stage of pyrolysis,then the length shrinkage and the loss of preferred orientation occur and hence deteriorate the mechanical properties of carbon ﬁber[80].4.GraphitizationFor further improvement on the performance,carbonizedﬁ-ber must undergo graphitization process.Graphitization is the transformation of carbon structure into graphite structure by heat treatment as well as thermal decomposition at high tem-perature processing.Actually,the process of production of both carbonﬁber and graphiteﬁber was essentially the same either in carbonization or in graphitization.During graphitiza-tion the temperature does not only rise until1600 C,but ex-ceeds up to3000 C[38,77,81].In other words,graphitization process was a carbonization process at high heating tempera-ture.At this stage,up to99%of PAN polymer was converted to carbon structure.Carbonﬁber which was produced in this condition was in very high modulusﬁber or can be classiﬁed as type I carbonﬁber.5.Functionality gaseousGenerally,carbonizedﬁber can be found when the temper-ature reaches1200 C and above in inert atmosphere[76]. Through the heating process,theﬁber could expel impurities as volatile by-products such as methane(CH4),hydrogen (H2),hydrogen cyanide(HCN),water(H2O),CO2,NH3and various gases[25,33,35,82].Among that gases,HCN,NH3 and CO are the toxic compounds that evolved during pyrolysis [83].But,HCN and NH3are the major toxic gases that evolved from decomposition of PAN.Data pertaining to evo-lution of gases during the carbonization process,from Donnet and Bahl[84],are shown in Fig.18.The other factor that promoted excessively volatile compo-nent was high stabilization temperature.High stabilization temperature promotes over absorption of oxygen in stabilized ﬁber and might form excessive e C]O ually,the ox-ygen in these bonds escapes as water vapor[25].It is known that the decrease of oxygen as water vapor is due to evolution of H2O in the early stages of carbonization in the range be-tween300e500 C.The evolution of H2O results from the crosslinking condensation reactions between two monomer units of the adjacent ladder polymeric molecular chains which is illustrated in Fig.19[85].When the temperature increased up to800 C,hydrogen cyanide and ammonia were the side gases which also evolved and released with water[68].Watt [86]stated that reaction involving chain termination have been stated as the reason for the formation of ammonia. This could be either by the formation of ammonia from active chain ends,or by the end-to-end joining of two ladder struc-ture(Fig.20A).While,the mechanisms for evolution of hy-drogen cyanide by the same author are shown in Fig.20A,B.Meanwhile,the formation of N2has been found to start early at720 C[68]and more nitrogen was eliminated from the bulk than from the surface during this heating process [69].Evolution of nitrogen and hydrogen was explained by Watt[86]with the scheme in Fig.21.This results in nitrogen atoms substituted in the hexagonal lattice of aromatized car-bon,and explains the presence of large amounts of nitrogen in the carbonizedﬁber.Graphitization at higher temperatures reduces the concentration of residual nitrogen to very small levels.An alternate scheme for dehydrogenation and denitro-genation has been proposed by Zhu et al.[68]and is shown in Fig.15.In addition,there is also elimination of CH4,CO2 and CO that occurs at temperature higher than800 C[87].As a result,the gases were removed until theﬁber contains up to50%carbon content and above[9,88,89].Sometimes, when the temperature increased up to1300 C,the carbonized PANﬁber could achieve96%carbon content[31].The in-crease in the carbon would decrease the nitrogen,hydrogen and oxygen content[25,31,69].Table1shows the percentage of nitrogen and hydrogen which was released from theﬁber and the increase of carbon content when the temperature rises. The release of the gases would result in loss in theﬁberweightwithin 55e 60wt%,and likely generate pores [33].Some stud-ies divided the decrease in the weight into two conditions,for about 32%weight loss in the range of 350e 800 C and 13%loss within 900e 1000 C [90].However,no weight loss was observed beyond 1900 C,and the ﬁber contains only carbon [91].Much of the research work has been done either to improve mechanical properties or to decrease the manufacturing cost of carbon ﬁber [4,35,92].The manufacturing of carbon ﬁber is not an easy task due to their strict procedure.The ﬁber also tends to brittle without proper control on optimization process.Therefore,a comprehensive study should be done to ﬁnd the optimum condition for the production of carbon ﬁber with excellent performance that used in advanced materials and becoming worldwide application.6.Effect of heating treatment on PAN-based carbon ﬁber propertiesThe characteristics of PAN-based carbon ﬁber could be measured through infrared spectra.The infrared spectrum would identify whether the PAN ﬁber was stabilized and car-bonized or not.Sometimes the characteristic was measured by physical properties as well as the diameter and the density of the ﬁber.There was a relationship between diameter,densityand performance of carbon ﬁber.Mittal et al.[38]observed that generally when the diameter decreased,the density would be increased.In general,reducing the PAN ﬁber diameter and increasing ﬁber density could make the ﬁber denser and hence improved the performance of carbon ﬁber.The improvement could be done by introducing proper treatment especially heat treatment.6.1.Infrared (IR)characteristicsInfrared (IR)spectra can be used to analyze the chemical structure that exists in the ﬁber.According to IR analyzes,PAN ﬁber showed prominent peaks at 2940cm À1(e CH stretch),2240cm À1(C ^N stretch)and 1452cm À1(e CH 2bend)and for SAF with 1%IA and 6%MA,the carbonyl stretch of comonomer units appeared at 1730cm À1[23].Conley and Beron [93]stated that two dominant peaks,which are at 2940cm À1and 2240cm À1start decreasing at 180 C due to the formation of cyclization reaction.However,Colemen and coworkers [94e 99]suggested thatthedisappearance of 2240cm À1band for the nitrile began as early as 160 C under vacuum.Setnescu et al.[27]observed,through pyrolysis process,that two peaks almost completely disappeared and new peaks appeared around 800cm À1and 1600cm À1.The change in peaks are due to the formation of C ]C,C ]N and ]C e H and results in the formation of car-bon ﬁber structure.6.2.DiameterLarge diameter is one of the limitations of ﬁber strength.As mentioned before,to give uniformity in heat treatment,ﬁbers must have a small diameter.Chen and Harrison [16],stated that small diameter can reduce any gradient temperature across the ﬁber to form uniformity of heat treatment.Commercial PAN ﬁber like Dralon T (DT)and Special Acrylic Fiber (SAF)have diameter in the range of 8e 20m m [23].As stated before,plasticizer is applied in post-spinning modiﬁcation to reduce ﬁber diameter prior to heat treatment.When heat treatment has been applied as well as the rise in the temperature,the diameter of the ﬁber would shrink againand produced small ﬁber diameter.Sometimes a diameter with ten times lower than human hair could be produced [16].The signiﬁcant reduction in diameter has been observed within the carbonization temperature (below 1000 C)[38].Similar trend of the reduction of ﬁber diameter has been found by Liu et al.[21].In other words,the diameter diminished throughout the carbonization treatment.6.3.DensityVarious studies indicated that a signiﬁcant change in the ﬁ-ber density occurred below carbonization temperature [31,81,100].Within the carbonization temperature (300e 1200 C),the changes in the density of the ﬁbers take place up to 800 C [38].Sometimes,it could rapidly change up to 1000 C [31].The density could be changed due to the com-paction of the structure taking place during the early stages of carbonization.It is also due to the presence of the noncar-bon elements in the ﬁber and the ladder polymer structures in-terconnecting with one another [100].However,the density increase was followed by a sharp drop at 1000 C which is due to the conversion of open pores to closed pores [31].As a consequence,the air would be trapped inside the ﬁbers and hence results in low density which could limit the tensile strength of the ﬁnal carbon ﬁber [25].How-ever,Ozbek and Isaac [79]and Sauder et al.[101]observed that heating temperature (HTT),which increases up to 3000 C,can eliminate the effect of open and closed pores.This is because,in this region high heating rate and high tem-perature were used which made the vibrations ofmoleculesTable 1Chemical composition of some pyrolyzed PAN samples found by elemental analysis [27]Pyrolysis temperature ( C)Element content Carbon (%)Nitrogen (%)Hydrogen (%)Initial 66.3326.00 5.4760068.5111.93 3.6990075.466.281.461430M.S.A.Rahaman et al./Polymer Degradation and Stability 92(2007)1421e 1432。

Effect of heat treatment on microstructure and

Effect of heat treatment on microstructure andtensile properties of A356 alloysPENG Ji-hua1, TANG Xiao-long1, HE Jian-ting1, XU De-ying21. School of Materials Science and Engineering, South China University of Technology,Guangzhou 510640, China;2. Institute of Nonferrous Metal, Guangzhou Jinbang Nonferrous Co. Ltd., Guangzhou 510340, ChinaReceived 17 June 2010; accepted 15 August 2010Abstract: Two heat treatments of A356 alloys with combined addition of rare earth and strontium were conducted. T6 treatment is a long time treatment (solution at 535 °C for 4 h + aging at 150 °C for 15 h). The other treatment is a short time treatment (solution at 550 °C for 2 h + aging at 170 °C for 2 h). The effects of heat treatment on microstructure and tensile properties of the Al-7%Si-0.3%Mg alloys were investigated by optical microscopy, scanning electronic microscopy and tension test. It is found that a 2 h solution at 550 °C is sufficient to make homogenization and saturation of magnesium and silicon in Į(Al) phase, spheroid of eutectic Si phase. Followed by solution, a 2 h artificial aging at 170 °C is almost enough to produce hardening precipitates. Those samples treated with T6 achieve the maximum tensile strength and fracture elongation. With short time treatment (ST), samples can reach 90% of the maximum yield strength, 95% of the maximum strength, and 80% of the maximum elongation.Key words: Al-Si casting alloys; heat treatment; tensile property; microstructural evolution1 IntroductionThe aging-hardenable cast aluminum alloys, such as A356, are being increasingly used in the automotive industry due to their relatively high specific strength and low cost, providing affordable improvements in fuel efficiency. Eutectic structure of A390 can be refined and its properties can be improved by optimized heat treatment [1]. T6 heat treatment is usually used to improve fracture toughness and yield strength. It is reported that those factors influencing the efficiency of heat treatment of Al-Si hypoeutectic alloys include not only the temperature and holding time [2], but also the as-cast microstructure [3í5] and alloying addition [6í8]. Some T6 treatment test method standards of A356 alloys are made in China, USA, and Japan, and they are well accepted. However, they need more than 4 h for solution at 540 °C, and more than 6 h for aging at 150 °C, thus cause substantial energy consumption and low production efficiency. It is beneficial to study a method to cut short the holding time of heat treatment.The T6 heat treatment of Al-7Si-0.3 Mg alloy includes two steps: solution and artificial aging; the solution step is to achieve Į(Al) saturated with Si and Mg and spheroidized Si in eutectic zone, while the artificial aging is to achieve strengthening phase Mg2Si. Recently, it is shown that the spheroidization time of Siis dependant on solution temperature and the original Si particle size [9í11]. A short solution treatment of 30 minat 540 or 550 °C is sufficient to achieve almost the same mechanical property level as that with a solution treatment time of 6 h [12]. From thermal diffusion calculation and test, it is suggested that the optimum solution soaking time at 540 °C is 2 h [13]. The maximum peak aging time was modeled in terms of aging temperature and activation energy [14í15]. According to this model, the peak yield strength of A356 alloy could be reached within 2í4 h when aging at 170 °C. However, few studies are on the effect of combined treatment with short solution and short aging.In our previous study, it was found that the microstructure of A356 alloy could be optimized by the combination of Ti, B, Sr and RE, and the eutecticFoundation item: Project (2008B80703001) supported by Guangdong Provincial Department of Science and Technology, China; Project (09A45031160) supported by Guangzhou Science and Technology Commission, China; Project (ZC2009015) supported by Zengcheng Science andTechnology Bureau, ChinaCorresponding author: PENG Ji-hua; Tel/Fax: +86-20-87113747; E-mail: jhpeng@DOI: 10.1016/S1003-6326(11)60955-2PENG Ji-hua, et al/Trans. Nonferrous Met. Soc. China 21(2011) 1950í1956 1951melting peak temperature was measured to be 574.4 °Cby differential scanning calorimetry (DSC) [16]. In this study, using this alloy modified together with Sr and RE, the effect of different heat treatments on the microstructure and its mechanical properties were investigated.2 ExperimentalCommercial pure aluminum and silicon were melted in a resistance furnace. The alloy was refinedusing Al5TiB master alloy, modified using Al-10Sr andAl-10RE master alloys. The chemical composition ofthis A356 alloy ingot (Table 1) was checked by readingspectrometer SPECTROLAB. Before casting, the hydrogen content of about 0.25 cm 3 per 100 g in the meltwas measured by ELH-III (made in China). Four bars of50 mm×70 mm×120 mm were machined from the sameingot and heat-treated according to Table 2. Followed thesolution, bars were quenched in hot water of 70 °C.Samples cut from the cast ingot and heat-treated barswere ground, polished and etched using 0.5% HF agent.Optical microscope Leica í430 and scanning electricmicroscope LEO 1530 VP with EDS (Inca 300) wereused to examine the microstructure and fractograph. Toquantify the eutectic Si morphology change of differentheat treatments, an image analyzer Image-Pro Plus 6.0 was used, and each measurement included 800í1200 particles. Table 1 Chemical composition of A356 modified with Ti, Sr and RE (mass fraction, %) Si Cu Fe Mn Mg Ti Zn RE Sr 6.85 <0.01 0.19 <0.01 0.370.23 0.03 0.250.012Table 2 Heat treatments in this study Solution Aging Treatment Temperature/ °C Holding time/h Temperature/°C Holdingtime/hST 550r 5 2 170 2T6 535r 5 4 150 15 Tensile specimens were machined from the heat treated bars. The tensile tests were performed using a screw driven Instron tensile testing machine in air at room temperature. The cross-head speed was 1 mm/min. The strain was measured by using an extensometer attached to the sample and with a measuring length of 50mm. The 0.2% proof stress was used as the yield stressof alloys. Three samples were tested for each heat treatment to calculate the mean value.3 Results and discussion3.1 Microstructural characterization of as-cast alloyThe microstructure of as-cast A356 alloy is shown in Fig. 1(a). It is shown that not only the primary Į(Al) dendrite cell is refined, but also the eutectic silicon is modified well. By means of the image analysis, microstructure parameters of as-cast A356 alloy were analyzed statistically as follows: Į(Al) dendrite cell sizeis 76.1 ȝm, silicon particle size is 2.2 ȝm×1.03 ȝm (length×width), and the ratio aspect of silicon is 2.13. The distributions of RE (mish metal rare earth, more than 65% La among them), Ti, Mg, and Sr in the area shown in Fig. 1(b) are presented in Figs. 1(c)í(f)respectively. It is shown that the eutectic silicon particle is usually covered with Sr, which plays a key role in Siparticle modification; Ti and RE present generallyuniform distribution over the area observed, although alittle segregation of RE is observed and shown by arrowin Fig. 1(d). It is suggested that because the refiner TiAl 3and TiB 2 are covered with RE, the refining efficiency isimproved significantly. In the as-cast alloy, some clustersof Mg probably indicate that coarser Mg 2Si phases exist(arrow in Fig. 1(d))).Ti solute can limit the growth of Į(Al) primarydendrite because of its high growth restriction factor [17].The impediment of formation of poisoning Ti-Si compound around TiAl 3 [18] and promotion of Ti(Al 1íx Si x )3 film covering TiB 2 [19] are very important in Al-Si alloy refining. For Al-Si alloys, the effect of RE on the refining efficiency of Ti and B can be contributed to the following causes [20]: preventing refiner phases from poisoning; retarding TiB 2 phase to amass and sink;promoting the Ti(Al, Si)3 compound growth to cover theTiB 2 phase. In this work, with suitable addition of Reand Sr, the microstructure of A356 alloy was optimized. Especially, eutectic Si is modified fully, which isbeneficial to promote Si to spheroidize further duringsolution treatment. 3.2 Microstructural evolution during heat treatmentThe microstructures of A356 alloys treated withsolution at 550 °C for 2 h and ST treatment are presented in Figs. 2(a) and (b) respectively, while those treatedwith solution at 535 °C for 4 h and T6 treatment are presented in Figs. 2(c) and (d), respectively. From Fig. 1 and Fig. 2, after different heat treatments, the primary Į(Al) has been to some extent and the eutectic silicon has been spheroidized further. Both ST and T6 treatmentsproduce almost the same microstructure. The eutectic Si particle distribution and statistical mean aspect ratio of eutectic Si particle are shown in Fig. 3. After onlysolution at 535 °C for 4 h and 550 °C for 2 h, the meanPENG Ji-hua, et al/Trans. Nonferrous Met. Soc. China 21(2011) 1950í19561952Fig. 1 SEM images (a, b), and EDS mapping from (b) for Ti (c), La (d), Mg (e) and Sr (f) in as-cast alloyFig. 2 Microstructure of A356 alloy with different heat treatments: (a) Solution at 550 °C for 2 h; (b) ST treatment; (c) Solution at 535 °C for 4 h; (d) T6 treatmentPENG Ji-hua, et al/Trans. Nonferrous Met. Soc. China 21(2011) 1950í1956 1953Fig. 3 Statistic analysis of eutectic Si in A356 alloy with different heat treatmentsaspect ratios of Si are 1.57 and 1.54 respectively. After being treated by ST and T6, those aspect ratios of Si do not vary greatly, and they are 1.49 and 1.48, respectively. After solution or solution + aging in this study, the friction of eutectic Si particles with aspect ratio of 1.5 is 50%.The eutectic melting onset temperature of Al-7Si-Mg was reported to be more than 560 °C [16, 19]. 550 °C is below the liquid +solid phase zone. During solution, two steps occur simultaneously, i.e., the formation of Al solution saturated with Si and Mg, and spheroidization of fibrous Si particle. The following model predicts that disintegration and spheroidization of eutectic silicon corals are finished at 540 °C after a few minutes (Ĳmax ) [9]:2maxs 32ʌ..ln 9kT D U UW JI I§· ¨¸©¹ (1) where I denotes the atomic diameter of silicon; Ȗ symbolizes the interfacial energy of the Al/Si interface; ȡ is the original radius of fibrous Si; D s is the inter-diffusion coefficient of Si in Al; and T is the solution temperature. When the D s variation at different temperatures is taken into account, it is plausible to suggest that Ĳmax at 550 °C is less than Ĳmax at 540 °C. From Fig. 2(a), it is actually proved that spheroidization of eutectic Si particle could be finished within 2 h when solution at 550 °C.In a selected area of A356 alloy treated with only solution at 550 °C for 2 h (Fig. 4(a)), the distribution of element Mg is presented in Fig. 4(b). Because there is no cluster of Mg in Fig. 4(b), it means a complete dissolution of Si, Mg into Al dendrite during this solution. From the microstructure of A356 alloy treated with T6 (Fig. 5(a)), the distribution of Mg is shown in Fig. 5(b).Fig. 4 SEM image (a) and EDS mapping (b) of Mg distribution in alloy after only solution at 550 °C for 2 hFig. 5 SEM image (a) and EDS mapping of Mg (b) in alloy after heat treatment with T6For A357 alloy with dendrite size of 240 ȝm, uniform diffusion and saturation of Mg in Al could be finished at 540 °C within 2 h [13]. In this study, the cellPENG Ji-hua, et al/Trans. Nonferrous Met. Soc. China 21(2011) 1950í1956 1954size of primary Į(Al) is less than 100 ȝm. It is reasonable that those solutions treated at 535 °C for 4 h and 550 °C for 2 h, can achieve Į(Al) solid solution saturated with Mg and Si because diffusion route is short, even at a higher solution temperature.During aging, Si and Mg2Si phase precipitation happened in the saturated solid solution of Į(Al) according to the sequence in the Al-Mg-Si alloys with excess Si [21]. The needle shaped Mg2Si precipitation was observed to be about 0.5 ȝm in length and less than 50 nm in width, and the silicon precipitates were mainly distributed in Į(Al) dendrites and few of them could be observed in the eutectic region [22]. Because of the small size, these precipitations could not be observed by SEM in this study. However, it is plausible to suggest that the distribution of Mg in dendrite Al cell zone and eutectic zone is uniform (Fig. 4(b) and 5(b)). According to the study by ROMETSCH and SCHAFFER [15], the time to reach peak yield is 2í4 h and 12í14 h at 170 °C and 150 °C, respectively. From 150 to 190 °C of aging temperature, the peak hardness varies between HB110 and HB120. Hence, it is believed that aging at 170 °C for 2 h produces almost the same precipitation hardening as aging at 150 °C for 15 h.3.3 Tensile properties of A356 alloysThe tensile mechanical properties of A356 alloys are given in Table 3. Due to the microstructure optimization of A356 alloy by means of combination of refining and modification, tensile strength and fracture elongation can reach about 210 MPa and 3.7% respectively. Using T6 treatment in this study, strengthand elongation can be improved significantly. For those samples with T6 treatment, the tensile strength and ductility present the maximum values. 90% of the maximum yield strength, 95% of the maximum ultimate strength, and 80% of the maximum elongation can be reached for samples treated by ST treatment. However,T6 treatment spends about 19 h, while ST treatment takes only about 4 h. Fractographs of samples treated with T6 are presented in Fig. 6. The dimple size is almost similar with different heat treatments, indicating that the size and spacing of eutectic silicon particle vary little with different heat treatments. Shrinkage pore, microcrack inside the silicon particle and crack linkage between eutectic silicon particles were observed on the fracture surfaces.Table 3 Tensile properties of A356 alloys with different heat treatmentsHear treatmentıb/MPa ı0.2/MPa į/% As-cast 210 í 3.7 ST 247 178 5.6T6 255 185 7.0Fig. 6 Fractographs of samples with different heat treatments: (a), (b) T6; (c), (d) STPENG Ji-hua, et al/Trans. Nonferrous Met. Soc. China 21(2011) 1950í1956 1955It is well known that shrinkage pores have a great effect on the tensile strength and ductility of A356 alloys. In-situ SEM fracture of A356 alloy indicates the fracture sequence as follows [4]: micro-crack initiation inside silicon particle; formation of slipping band in the Al dendrite; linkage between the macro-crack and micro-crack, and the growth of crack. During tensile strain, inhomogeneous deformation in the microstructure induces internal stresses in the eutectic silicon and Fe-bearing intermetallic particles. Although the full modification of eutectic Si particle was reached in this study, those samples treated with T6 treatment do not perform as well as expected. The main reason is probably due to the higher gas content (0.25 cm3 per 100 g Al). Our next step is to develop a new means to purify the Al-SI alloys to further improve their mechanical properties.4 Conclusions1) The solution at 535 °C for 4 h and the solution at 550 °C for 2 h can reach full spheroidization of Si particle, over saturation of Si and Mg in Į(Al). The heat treatments of T6 and ST produce almost the same microstructure of A356 alloy.2) After both T6 and ST treatments, the aspect ratio of eutectic Si particle will be reduced from 2.13 to less than 1.6, and the friction of eutectic Si particles with aspect ratio of 1.5 is 50%.3) The T6 treatment can make the maximum strength and fracture elongation for A356 alloy. After ST treatment, 90% of the maximum yield strength, 95% of the maximum ultimate strength, and 80% of the maximum elongation can be achieved.References[1]WAN Li, LUO Ji-rong, LAN Guo-dong, LIANG Qiong-hua.Mechanical properties and microstructures of squeezed and casthypereutectic A390 alloy [J]. Journal of Huazhong University ofScience and Technology: Natural Science Edition, 2008, 36(8):92í95. (in Chinese)[2]RAINCON E, LOPEZ H F, CINEROS H. Temperature effects on thetensile properties of cast and heat treated aluminum alloy A319 [J].Mater Sci Eng A, 2009, 519(1í2): 128í140.[3]MANDAL A, CHAKRABORTY M, MURTY B S. Ageingbehaviour of A356 alloy reinforced with in-situ formed TiB2particles [J]. Mater Sci Eng A, 2008, 489(1í2): 220í226.[4]LEE K, KWON Y N, LEE S. Effects of eutectic silicon particles ontensile properties and fracture toughness of A356 aluminum alloysfabricated by low-pressure-casting, casting-forging, and squeeze-casting processes [J]. J Alloys Compounds, 2008, 461(1í2):532í541. [5]VENCL A, BOBIC I, MISKOVIC Z. Effect of thixocasting and heattreatment on the tribological properties of hypoeutectic Al-Si alloy[J]. Wear, 2008, 264 (7í8): 616í623.[6]BIROL Y. Response to artificial ageing of dendritic and globularAl-7Si-Mg alloys [J]. J. Alloys Compounds, 2009, 484(1): 164í167. [7]TOKAJI K. Notch fatigue behaviour in a Sb-modifiedpermanent-mold cast A356-T6 aluminium alloy [J]. Mater Sci Eng A,2005, 396(1í2): 333í340.[8]KLIAUGA A M, VIEIRA E A, FERRANTE M. The influence ofimpurity level and tin addition on the ageing heat treatment of the356 class alloy [J]. Mater Sci Eng A, 2008, 480(1í2): 5í16.[9]OGRIS E, WAHLEN A, LUCHINGER H, UGGOWITZER P J.Onthe silicon spheroidization in Al-Si alloys [J]. J Light Metals, 2002,2(4): 263í269.[10]SJOLANDER E, SEIFEDDINE S. Optimisation of solutiontreatment of cast Al-Si-Cu alloys [J]. Mater Design, 2010, 31(s1):s44ís49.[11]LIU Bin-yi, XUE Ya-jun. Morphology transformation of eutectic Siin Al-Si alloy during solid solution treatment [J]. Special Casting &Nonferrous Alloys, 2006, 26 (12): 802í805. (in Chinese)[12]ZHANG D L, ZHENG L H, STJOHN D H. Effect of a short solutiontreatment time on microstructure and mechanical properties ofmodified Al-7wt.%Si-0.3wt.%Mg alloy [J]. J Light Metals, 2002,2(1): 27í36.[13]YU Z, ZHANG H , SUN B, SHAO G. Optimization of soaking timefor T6 treatment of aluminium alloy [J]. Heat Treatment, 2009, 24(5):17í20. (in Chinese)[14]ESTEY C M, COCKCROFT S L, MAIJER D M, HERMESMANNC. Constitutive behavior of A356 during the quenching operation [J].Mater Sci Eng A, 2004, 383(2): 245í251.[15]ROMETSCH P A, SCHAFFER G B. An age hardening model forAl-7Si-Mg casting alloys [J]. Mater Sci Eng A, 2002, 325(1í2):424í434.[16]TANG Xiao-long, PENG Ji-hua, HUANG Fang-liang, XU De-ying,DU Ri-sheng. Effect of mishmetal RE on microstructures of A356alloy [J]. The Chinese Journal of Nonferrous Metals, 2010, 20(11):2112í2117. (in Chinese)[17]EASTON M A, STJHON D H. A Model of grain refinementincorporation alloy constitution and potency of heterogeneous nucleant particles [J]. Acta Mater, 2001, 49(10): 1867í1878.[18]QIU D, TAYLOR J A, ZHANG M X, KELLY P M. A mechanismfor the poisoning effect of silicon on the grain refinement of Al-Sialloys [J]. Acta Mater, 2007, 55(4): 1447í1456.[19]JUNG H, MANGELINK-NOEL N, BERGMAN C, BILLIA B.Determination of the average nucleation undercooling of primaryAl-phase on refining particles from Al-5.0wt% Ti-1.0wt% B inAl-based alloys using DSC [J]. J Alloys Compounds, 2009, 477(1í2):622í627.[20]LAN Ye-feng, GUO Peng, ZHANG Ji-jun. The effect of rare earthon the refining property of the Al-Ti-B-RE intermediate alloy [J].Foundry Technology, 2005, 26(9): 774í778. (in Chinese)[21]EDWARDS G A, STILLER K, DUNLOP G L, COUPER M J. Theprecipitation sequence in Al-Mg-Si alloys [J]. Acta Mater, 1998,46(11): 3893í3904.[22]RAN G, ZHOU J E, WANG Q G. Precipitates and tensile fracturemechanism in a sand cast A356 aluminum alloy [J]. J Mater ProcessTechnol, 2008, 207(1): 46í52.PENG Ji-hua, et al/Trans. Nonferrous Met. Soc. China 21(2011) 1950í19561956⛁ ⧚ A356䪱䞥㒘㒛㒧㛑ⱘ1ē 1ē 1ē ԃ 21. ⧚ ⾥ Ϣ ⿟䰶ˈ 510640˗2. 䞥䙺㡆䞥䰤㡆䞥 ⷨお ˈ 510340㽕˖⫼ϸ⾡ϡ ⱘ⛁ ⧚ ⿔䬊㓐㒚䋼ⱘA356 䞥䖯㸠 ⧚ˈϔ⾡䭓䯈 ⧚ T6(535 °C ⒊4 h+150 °C 15 h)ˈ ϔ⾡ ⷁ 䯈ⱘ⛁ ⧚ ST(550 °C ⒊2 h+170 °C 2 h)Ǆ䞛⫼ 䬰ǃ ⬉䬰 ⏽ Ԍ 偠ㄝ ↉ ⛁ ⧚ A356 䞥㾖㒘㒛 Ԍ 㛑ⱘ Ǆ㒧㸼 ˖ 550 °Cϟ ⒊2 h ҹ㦋 MgǃSi䖛佅 Ϩ ⱘĮ(Al) ⒊ԧˈ Փ ⸙Ⳍ⧗ ˗ 㒣170 °CҎ 2 h ˈ ҹ䖒 Ӵ㒳T6 ⧚ⱘ Ǆ Ԍ 偠㒧㸼 ˈA356䪱䞥㒣Ӵ㒳T6 ⧚ њ 催ⱘ Ԍ 㺖Ԍ䭓⥛˗䗮䖛STⷁ ⛁ ⧚ ˈ Ԍ ǃ Ԍ䭓⥛ ҹ䖒 T6 ⧚ ⱘ90%ˈ95% 80%Ǆ䬂䆡˖Al-Si 䞥˗⛁ ⧚˗ Ԍ 㛑˗ 㾖㒘㒛ⓨ(Edited by LI Xiang-qun)。

热处理工艺对Mini CSiC复合材料拉伸性能和强度分布的影响

第49卷第9期当代化工 Vol.49，No.9 2020年9月 Contemporary Chemical Industry September，2020基金项目：国家自然科学青年基金(项目编号：51802263)；西安航空学院校级科研基金(项目编号：2017KY0205)；国家自然科学青年基金(项目编号： 51701148) 。

收稿日期：2020-05-25作者简介：孟志新（1979-），男，内蒙古自治区乌兰察布市人，讲师，博士，2013年毕业于西北工业大学材料学专业，研究方向：陶瓷基复合材料强韧化。

E -mail：*******************。

热处理工艺对Mini C/SiC 复合材料拉伸性能和强度分布的影响孟志新1,3，谭志勇2，张毅3，周影影1，吴坤尧1，鲁媛媛1（1. 西安航空学院材料工程学院，西安 710077； 2. 北京临近空间飞行器系统工程研究所，北京100076；3. 西北工业大学超高温结构复合材料重点实验室，西安 710072）摘要：采用5种工艺制备了C 纤维束增韧SiC 陶瓷基复合材料（Mini C/SiC），研究了热处理工艺对不同制备工艺条件下Mini C/SiC 复合材料拉伸性能和强度分布的影响。

实验结果表明：在不进行热处理的Mini C/SiC 复合材料中引入热解炭（PyC）界面相可提高拉伸性能和强度稳定性。

与不进行热处理的Mini C/SiC 复合材料相比，对引入PyC 界面相复合材料的C 纤维束和/或PyC 界面相进行热处理均可提高拉伸性能。

热处理温度小于等于1 700 ℃时，先对C 纤维进行热处理然后再沉积PyC 界面相的Mini C/SiC 复合材料，其拉伸性能最好。

热处理温度为2 000 ℃时，先对C 纤维沉积PyC 界面相然后再进行热处理的Mini C/SiC 复合材料，其拉伸性能最好。

热处理温度对Mini C/SiC 复合材料变形行为有着显著的影响，热处理温度不同时，复合材料表现出了不同的变形行为。

TiAlCN涂层界面扩散机理与结合强度

TiAlCN涂层界面扩散机理与结合强度孔德军;付贵忠;郭皓元【摘要】利用阴极弧离子镀在Cr12MoV钢表面制备了TiAlCN涂层,通过扫描电镜(SEM)、能量分散光谱法(EDS)、X射线衍射术(XRD)等手段分析了TiAlCN涂层的表面-界面形貌、化学元素分布和物相特性,并对其界面结合机理进行了探讨.结果表明,Al原子第一电离能低于Ti原子,容易从靶材上气化电离出来沉积在基体上,使得涂层中Al元素含量较高;涂层中TiN、AlN和AlTiN为硬质相,其中涂层中高含量的Al原子有利于提高抗磨损性能,无定形C原子有利于降低摩擦系数;Ti、Al、C、N等原子在涂层中产生富集现象,在结合界面处发生扩散,是形成冶金结合的主要机制.另外,用划痕法测得涂层界面结合强度为76.9N,具有较高的抗剥落能力.文中的结果为TiAlCN涂层在冷作模具表面改性处理中的应用提供了实验基础.【期刊名称】《光学精密工程》【年(卷),期】2014(022)005【总页数】7页(P1260-1266)【关键词】TiAlCN涂层;阴极弧离子镀;线扫描;面扫描;结合强度【作者】孔德军;付贵忠;郭皓元【作者单位】常州大学机械工程学院,江苏常州213016;常州大学机械工程学院,江苏常州213016;常州大学机械工程学院,江苏常州213016【正文语种】中文【中图分类】TB431 引言过渡金属氮化物涂层通常采用电弧离子镀和物理气相沉积（Physical Vapor Deposition，PVD）方法制备，这类涂层包括TiN、Cr N、Cr CN、Al－TiN等。

TiN涂层的最高工作温度为500℃，硬度达到2 200 Hv［1］，与钢的摩擦系数为0.6，由于其抗氧化温度不高，只能在普通的工作温度下使用，因此，TiN涂层正逐渐被性能更好的Al－TiN涂层所取代。

Al TiN涂层的抗氧化温度高达800℃，硬度达到3 300 Hv，可满足较高工作温度的要求，但由于Al元素的加入提高了Al－TiN涂层的摩擦系数［2］，与钢的摩擦系数上升至0.7，会加剧涂层的磨损。

热处理的英文作文

热处理的英文作文英文：Heat treatment is a process that involves heating and cooling a material to alter its properties. This process is commonly used in the manufacturing industry to improve the strength, hardness, and durability of metals.There are several different types of heat treatment, including annealing, quenching, and tempering. Annealing involves heating the material to a specific temperature and then allowing it to cool slowly, which helps to reduce the internal stress within the material and make it more ductile. Quenching, on the other hand, involves rapidly cooling the material in water or oil, which increases its hardness but also makes it more brittle. Tempering is a process that involves reheating the material after quenching to reduce its brittleness and improve its toughness.I have personally seen the benefits of heat treatment in my work as a machinist. For example, when working with a piece of steel that needs to be machined to a specific shape, it is often necessary to heat treat the materialfirst to ensure that it is strong enough to withstand the machining process. Without heat treatment, the steel may be too soft or brittle, which can lead to problems such as warping or cracking.Overall, heat treatment is an important process in the manufacturing industry that helps to improve the properties of materials and make them more suitable for specific applications.中文：热处理是一种通过加热和冷却材料来改变其性质的过程。

干热干冷地区围护结构热工设计对内表面温度及室内热舒适的影响

116暖通空调HV&AC 2021年第51卷第2期[引用本文]陈洁，罗智星•杨柳.干热干冷地区围护结构热工设计对内表面温度及室内热舒适的影响[J].暖通空调，2021， 51(2)：116-122_干热干冷地区围护结构热工设计对内表面温度及室内热舒适的影响*摘要为了分析干热干冷地区围护结构热工性能对室内热环境的影响，采用物理环境实测结合动态模拟方法对比分析了 2组墙体的保温、蓄热性能对内表面温度的影响，并结合太阳辐射季节变化探究了太阳辐射吸收比对室内热舒适的影响。

研究表明：实测结果与模拟结果吻合较好，对于干热干冷地区，提高围护结构蓄热性能能够降低夏季内表面温度，对冬季内表面温度影响不大；提高围护结构保温性能可以提升冬季内表面温度，同时引起夏季内表面温度升高，对夏季降温产生不利影响；围护结构月平均得热差值与太阳辐射月累计值显著相关，降低外表面太阳辐射吸收比有利于该地区建筑全年热环境的提升。

关键词围护结构热工设计室内热环境内表面温度干热干冷地区辐射吸收比Influence of thermal properties on inner surface temperature and indoor thermal comfort in dry-hot and dry-cold zoneAbstract In order to analyse the thermal performance of building envelope in the dry-hot and dry- cold zone, uses the physical environment measurement combined with dynamic simulation method to compare and analyse the influence of thermal insulation and thermal storage performances of two groups of walls on the inner surface temperature, and combining with the solar radiation seasonal changes, explores the influence of solar radiation absorption ratio on the indoor thermal comfort. The r e s ults show that the measured results are compliant to the simulation r e s u l t s . In dry-hot and dry-cold zone，improving the thermal storage performance of envelope can reduce the inner surface temperature in summer under the same thermal resistance condition, while the inner surface temperature i n winter changes l i t t l e . Under the same thermal storage condition, improving the insulation performance of envelope can improve the inner surface temperature in winter, and cause the inner surface temperature to r i s e in summer, which will have an adverse effect on the cooling i n summer. There i s a significant correlation between the mean monthly heat gain difference of building envelope and the monthly cumulative solar radiation. Reducing the solar radiation absorption ratio of outer surface i s beneficial to the improvement of building thermal environment in a whole year.Keywords building envelope, thermal design, indoor thermal environment, inner surface temperature, dry-hot and dry-cold zone，radiation absorption ratio★ Xi’an University of Architecture and Technology, Xi’an，China西安建筑科技大学陈洁&罗智星杨柳By Chen Jie * , Luo Zhixmg and Yang Liu〇引言寒冷地区建筑供暖能耗在建筑总能耗中占有很大的比例，但在建筑能耗中增长最快的是空调制☆陈洁，女，1986年11月生，在读博士研究生△杨柳(通信作者）710055陕西省西安市碑林区雁塔路13号西安建筑科技大学建筑学院* “十三五”国家重点研发计划项目“建筑节能设计基础参数研究”（编号：2018YFC0704500)E-mail ：yangliu @xauat . edu . cn收稿日期：2019-09-02一次修回：2019-11 一 27 二次修回：2021-01-072021(2)陈洁，等:干热f -冷地R 围护结构热工设it ■对内表面温度及室内热舒适的影响117冷能耗，特别是干热干冷气候地区，降温需求要比其他寒冷地区大得多[1]。

热处理专业名词英文翻译

1、整体热处理 bulk heat treatment2、表面热处理 surface heat treatment3、化学热处理 thermo-chemical treatment4、预备热处理 conditioning heat treatment5、局部热处理 local heat treatment6、可控气氛热处理 heat treatment in-controlled atmosphere7、真空热处理 vacuum heat treatment008、离子热处理 ion heat treatment9、高能束热处理high energy density heat treatment10、形变热处理 thermomechanical treatment11、复合热处理 complex heat treatment12、流态床热处理 heat treatment in fluidized beds13、吸热式气氛 endothermic atmosphere14、放热式气氛 exothermic atmosphere15、放热-吸热式气氛 exo-endothermic atmosphere16、滴注式气氛 drip feed atmosphere17、氮基气氛nitrogen-base atmosphere18、合成气氛artificial atmosphere019、直生式气氛 direct prepared atmosphere20、淬火冷却介质 quenching media21、淬火冷却烈度 quenching severity22、淬透性 hardenability23、淬硬性 hardening capacity24、端淬试验Jominy test25、奥氏体化austenitizing26、等温转变isothermal transformation27、连续冷却转变 continuous cooling transformation28、退火 annealing29、完全退火full annealing30、不完全退火 incomplete annealing31、去应力退火 stress relieving annealing32、球化退火spheroidizing033、正火 normalizing34、等温正火isothermal normalizing35、淬火 quenching harding36、等温淬火austempering37、分级淬火martempering38、亚温淬火intercritical hardening39、冷处理 subzero treatment40、深冷处理cryogenic treatment41、马氏体临界冷却速度 critical colding rate42、有效淬硬深度 effective hardening depth043、回火tempering44、低温回火 low temperature tempering045、高温回火high temperature tempering46、自回火 self tempering47、回火脆性temper brittlement48、淬冷畸变quenching distortion49、氢脆 hydrogen embrittlement50、残留应力residual stresses51、热应力 thermal stresses52、相变应力transformation stresses53、固溶处理solution treatment54、时效 ageing055、沉淀硬化precipitation hardening56、氧化 oxidation57、脱碳 decarburizing58、内氧化 internal oxidation59、渗碳 carburizing60、固体渗碳pack carburizing61、气体渗碳gas caiburizing62、液体渗碳liquid carburizing63、真空渗碳vacuum carburizing64、离子渗碳plasma carburizing065、复碳 carbon restoration66、碳势 carbon potential67、露点 dew point68、强渗期 carburizing period69、扩散期 diffusion period70、载气 carrier gas71、富化气 enrich gas72、渗氮 nitriding73、液体渗氮liquid nitriding74、气体渗氮gas nitriding75、离子渗氮ion nitriding076、退氮 denitriding77、渗氮化合物层 compound layer78、氨分解率ammonia dissociation rate79、渗金属 metal cementation80、多元共渗multicomponent cementation81、碳氮共渗carbonitriding082、氮碳共渗nitrocarburizing83、流氮共渗sulpho-nitriding84、氧氮共渗oxynitriding85、化学气象沉淀 chemical vapor deposition86、物理气相沉淀 physical vapor deposition87、相phase88、组织 structure89、晶粒 grain90、晶界 grain boundary91、晶粒度grain size92、晶粒度等级 grain size number93、共晶组织 eutectic-structure094、共析组织 eutectoid structure95、层片状组织 lamellar-structure96、弥散相dispersed phase97、亚组织substructure98、位错 dislocation099、结构 texture机械专业名词金属切削 metal cutting机床 machine tool金属工艺学 technology of metals 刀具 cutter摩擦 friction联结 link传动 drive/transmission轴 shaft弹性 elasticity频率特性 frequency characteristic 误差 error响应 response定位 allocation机床夹具 jig动力学 dynamic运动学 kinematic静力学 static分析力学 analyse mechanics拉伸 pulling压缩 hitting剪切 shear扭转 twist弯曲应力 bending stress强度 intensity三相交流电 three-phase AC磁路 magnetic circles变压器 transformer异步电动机 asynchronous motor几何形状 geometrical精度 precision正弦形的 sinusoid交流电路 AC circuit机械加工余量 machining allowance 变形力 deforming force变形 deformation应力 stress硬度 rigidity热处理 heat treatment退火 anneal正火 normalizing脱碳 decarburization渗碳 carburization电路 circuit半导体元件 semiconductor element 反馈 feedback发生器 generator直流电源 DC electrical source门电路 gate circuit逻辑代数 logic algebra外圆磨削 external grinding内圆磨削 internal grinding平面磨削 plane grinding变速箱 gearbox离合器 clutch绞孔 fraising绞刀 reamer螺纹加工 thread processing螺钉 screw铣削 mill铣刀 milling cutter功率 power工件 workpiece齿轮加工 gear mechining齿轮 gear主运动 main movement主运动方向 direction of main movement进给方向 direction of feed进给运动 feed movement合成进给运动 resultant movement of feed合成切削运动 resultant movement of cutting合成切削运动方向 direction of resultant movement of cutting 切削深度 cutting depth前刀面 rake face刀尖 nose of tool前角 rake angle后角 clearance angle龙门刨削 planing主轴 spindle主轴箱 headstock卡盘 chuck加工中心 machining center车刀 lathe tool车床 lathe钻削镗削 bore车削 turning磨床 grinder基准 benchmark钳工 locksmith锻 forge压模 stamping焊 weld拉床 broaching machine拉孔 broaching装配 assembling铸造 found流体动力学 fluid dynamics流体力学 fluid mechanics加工 machining液压 hydraulic pressure切线 tangent机电一体化 mechanotronics mechanical-electrical integration 气压 air pressure pneumatic pressure稳定性 stability介质 medium液压驱动泵 fluid clutch 液压泵 hydraulic pump阀门 valve失效 invalidation强度 intensity载荷 load应力 stress安全系数 safty factor可靠性 reliability螺纹 thread螺旋 helix键 spline销 pin滚动轴承 rolling bearing 滑动轴承 sliding bearing 弹簧 spring制动器 arrester brake十字结联轴节 crosshead 联轴歧 coupling链 chain皮带 strap精加工 finish machining粗加工 rough machining变速箱体 gearbox casing腐蚀 rust氧化 oxidation磨损 wear耐用度 durability随机信号 random signal离散信号 discrete signal超声传感器 ultrasonic sensor 集成电路 integrate circuit 挡板 orifice plate残余应力 residual stress套筒 sleeve扭力 torsion冷加工 cold machining电动机 electromotor汽缸 cylinder过盈配合 interference fit热加工 hotwork摄像头 CCD camera倒角 rounding chamfer优化设计 optimal design工业造型设计 industrial moulding design有限元 finite element滚齿 hobbing插齿 gear shaping伺服电机 actuating motor铣床 milling machine钻床 drill machine镗床 boring machine步进电机 stepper motor丝杠 screw rod导轨 lead rail组件 subassembly可编程序逻辑控制器 Programmable Logic Controller PLC 电火花加工 electric spark machining电火花线切割加工 electrical discharge wire - cutting 相图 phase diagram热处理 heat treatment固态相变 solid state phase changes有色金属 nonferrous metal合成纤维 synthetic fibre电化学腐蚀 electrochemical corrosion 车架 automotive chassis悬架 suspension转向器 redirector变速器 speed changer板料冲压 sheet metal parts孔加工 spot facing machining车间 workshop工程技术人员 engineer气动夹紧 pneuma lock数学模型 mathematical model画法几何 descriptive geometry机械制图 Mechanical drawing投影 projection视图 view剖视图 profile chart标准件 standard component零件图 part drawing装配图 assembly drawing尺寸标注 size marking技术要求 technical requirements刚度 rigidity内力 internal force位移 displacement截面 section疲劳极限 fatigue limit断裂 fracture塑性变形 plastic distortion脆性材料 brittleness material刚度准则 rigidity criterion垫圈 washer垫片 spacer直齿圆柱齿轮 straight toothed spur gear 斜齿圆柱齿轮 helical-spur gear直齿锥齿轮 straight bevel gear运动简图 kinematic sketch齿轮齿条 pinion and rack蜗杆蜗轮 worm and worm gear虚约束 passive constraint曲柄 crank摇杆 racker凸轮 cams共轭曲线 conjugate curve范成法 generation method定义域 definitional domain值域 range导数\微分 differential coefficient求导 derivation定积分 definite integral不定积菲 indefinite integral曲率 curvature偏微分 partial differential毛坯 rough游标卡尺 slide caliper千分尺 micrometer calipers攻丝 tap二阶行列式 second order determinant 逆矩阵 inverse matrix线性方程组 linear equations概率 probability随机变量 random variable排列组合 permutation and combination 气体状态方程 equation of state of gas 动能 kinetic energy势能 potential energy机械能守恒 conservation of mechanical energy 动量 momentum桁架 truss轴线 axes余子式 cofactor逻辑电路 logic circuit触发器 flip-flop脉冲波形 pulse shape数模 digital analogy液压传动机构 fluid drive mechanism机械零件 mechanical parts淬火冷却 quench淬火 hardening回火 tempering调质 hardening and tempering磨粒 abrasive grain结合剂 bonding agent砂轮 grinding wheel。

Effect of heat treatment on the tensile strength and

Eﬀect of heat treatment on the tensile strength andcreep resistance of advanced SiCﬁbersJ.J.Sha a,*,T.Nozawa b,J.S.Park b,Y.Katoh b,c,A.Kohyama ba Graduate School of Energy Science,Kyoto University,Gokasho,Uji,Kyoto611-0011,Japanb Institute of Advanced Energy,Kyoto University,Gokasho,Uji,Kyoto611-0011,Japanc Metals and Ceramics Division,Oak Ridge National Laboratory,Oak Ridge,TN37831,USAAbstractSiC-basedﬁbers,Hi-Niclaon TM,Hi-Nicalon TM type S and Tyranno TM-SA,were heat treated at1300–1900°C in Ar for1h.After heat treatment,room temperature tensile strength and1-h bend stress relaxation(BSR)at1400°C in Ar were evaluated for theseﬁbers.As a result,excellent strength retention was exhibited after heat treatment at temper-ature up to1780°C for the Hi-Nicalon TM type Sﬁber and up to1900°C for the Tyranno TM-SAﬁber.In contrast, relatively low strength retention was observed for Hi-Nicalon TMﬁber heat-treated above1600°C.Creep resistance of the as-receivedﬁbers was improved by high-temperature heat treatments,especially at temperatures above theﬁber’s processing temperature.The microstructure analysis by means of X-ray diﬀractometer(XRD)and scanning electron microscopy(SEM)indicated that properties of SiCﬁbers at elevated temperatures are controlled by crystallite size as well as by other factors.Ó2004Elsevier B.V.All rights reserved.1.IntroductionSeveral fusion reactor concepts have been proposed that use SiC/SiC composite as the primary structural materials for theﬁrst wall/blanket because of its high irradiation stability and low after-heat[1–4].Acceptable performance of high temperature ceramic matrix com-posites(CMCs)depends upon judicious selection and incorporation of ceramicﬁber reinforcement with the proper chemical,physical and mechanical properties. For high temperature operation,the most desired criti-calﬁber properties are high strength and stiﬀness and the reliable retention of these properties throughout the service life of the application.Creep ofﬁbers could cause the matrix cracks and accelerate sub-critical crack growth in CMCs[5].Recently developed SiC-basedﬁbers with highly crystallized structure and near stoichiometric composi-tion(such as Hi-Nicalon TM type S[6]and Tyranno TM-SA[7]),are promising reinforcement for CMCs fabrication.Theseﬁbers experienced a pyrolysis/sinter-ing process during fabrication and their microstructure and mechanical properties depend on the heat treatment temperature(HTT).On the other hand,the CMCs may be fabricated above theﬁber’s processing temperature [8,9],in which case,the performance ofﬁbers could be changed by high temperature heat treatment.However, the eﬀect of heat treatment eﬀect on theﬁber’s properties in the CMCs requires further investigation to identify the factors which aﬀect the high temperature properties ofﬁber.Thus,for exploring the optimum condition for high performance CMCs fabrication and application, the present investigation was designed to characterize the creep and tensile behavior of advanced SiCﬁbers before and after heat treatment at elevated tempera-tures.Fracture behavior and microstructure also were examined.*Corresponding author.Tel.:+81-774383463;fax:+81-774 383467.E-mail address:shajianj@iae.kyoto-u.ac.jp(J.J.Sha).0022-3115/$-see front matterÓ2004Elsevier B.V.All rights reserved.doi:10.1016/j.jnucmat.2004.04.123/locate/jnucmat Journal of Nuclear Materials329–333(2004)592–5962.Experimental procedure2.1.Materials and heat treatment conditionTheﬁbers examined in this study were Hi-Nicalon TM (HNL),Hi-Nicalon TM Type-S(HNLS)and Tyranno TM SA(TySA).Table1listsﬁbers properties provided by the manufacturers.Theﬁbers were heat treated in Ar under a pressure of104Pa at aﬂow rate of2l/min at20°C/min and held for1h at desired temperature from 1300to1900°C.After heat treatment,the apparent crystalline size of b-SiC was estimated from the half-value width of the(111)peak(d111)by employing the Scherrer formulation.2.2.Measurement ofﬁber tensile properties and BSR creep resistanceTensile strength of the individualﬁlaments was measured at room temperature in ambient atmosphere with an Instron test machine(model5581).The load was applied at a constant strain rate of2·10À4/s and mea-sured by a load-cell of2.5N.The individualﬁlaments had a gage length of25.4mm and were mounted and aligned on cardboardﬁxture as illustrated in previous study[10].The cardboardﬁxture was cut on both sides prior to test.Theﬁber diameters were determined by SEM examination of theﬁber fragment protruding from one of the glued ends.The total number of tests for each ﬁber type varied from20to30.The tensile test generally followed ASTM-recommended procedures[11].After tensile test,FE-SEM was used to characterize the frac-ture surface ofﬁber fragment by a technique similar to that developed by Youngblood[10].Weibull analysis was performed.The two-parameter Weibull theory was applied to characterize the fracture behavior of brittle SiCﬁbers[12].The frequency ofﬁber failure,F i,at the n th ranked sample from a total of N specimens,is ob-tained from the mean rank method as F i¼n=ðNþ1Þ.The creep behavior ofﬁbers was assessed by bend stress relaxation(BSR)method developed by Morscher and Dicarlo[13].In the BSR test,theﬁlament is bent around a mandrel withﬁxed radius and hold at constant strain.The BSR test on the as-receivedﬁbers was carried out at temperatures in the range of1000–1500°C in argon atmosphere for1h.In addition,1-h BSR test at 1400°C was performed on the heat-treatedﬁbers.The BSR parameter m is the average for3–7ﬁbers for each condition.3.Results and discussion3.1.Fiber tensile strengthThe Weibull average strength(r avg)was calculated from the relation r avg¼r0Cð1þ1=mÞ,where Cð1þ1=mÞis a gamma function.The tensile results for three ﬁber types are depicted in Fig.1(a)–(c).Hi-Nicalon TM ﬁbers exhibited degradation in strength at all test temperatures as indicated in Fig.1(a).In contrast,both near-stoichiometricﬁbers(Hi-Nicalon TM Type S and Tyranno TM-SA),retained most of their initial strength up to1780and1900°C as shown in Fig.1(b)and(c), respectively.Also,the Weibull modulus decreased with increasing the HTT for the Hi-Nicalon TMﬁbers sug-gests changes inﬂaw population andﬂaw size by gas evolution from the decomposition of amorphous SiCO phase.A high Weibull modulus implies better repeatability in strength and more uniform fracture behavior.Fig.2shows average room temperature tensile strengths and apparent crystallite sizes for three types of ﬁbers after heat treatment in Ar for1h at temperatures in the range of1300–1900°C.The grain growth has a signiﬁcant eﬀect on the strength of SiC-basedﬁbers. For the Hi-Nicalon TMﬁber,crystallization degraded its strength at all HTT.In both near stoichiometricﬁbers, strength degradations occurred at the temperatures where crystallite size began to increase.The grain coarsening could be attributed to the coalescence of b-SiC nano-crystal during exposure at high temperatures[14].Fibers with larger grain size generally have relatively lower strengths.But it should be noted that Hi-Nicalon TM showed more rapid strength degradation than Hi-Niclaon TM Type S above1400°C heat treatment as shown in Fig.(2).Hi-Nicalon TM has smaller crystal sizes comparing to that of HiNicalon TM Type S.Fiber strength is controlled by criticalﬂaw size. Also,the residual stresses,which were generated from gas evolution during heat treatment at elevated tem-peratures and the mismatch in thermal expansion coef-ﬁcient between excess carbon and SiC grain,could cause strength loss,and the contribution of residual stressesTable1Nominal properties of SiCﬁbers provided by manufacturersSiCﬁber C/Si Oxygen(wt%)Strength(GPa)Modulus(GPa)Density(g/cm3)Diameter(l m) HNL 1.390.5 2.8270 2.7414HNLS 1.050.2 2.6420 3.112TySA 1.07<0.5 2.6400 3.07J.J.Sha et al./Journal of Nuclear Materials329–333(2004)592–596593from the gas evolution to strength loss could increase with increasing the b-SiC grain size.The typical fracture surfaces for as-received the three ﬁber types are shown in Fig.3(a)–(c).For both as-re-ceived Hi-Nicalon TM and Hi-Nicalon TM Type Sﬁbers,the fracture mainly originated from the inner critical ﬂaws as shown in Fig.3(a)and(b).The strength ofﬁber depends on theﬂaw sizes and distribution.The fracture mirror zone is formed during slow crack propagation. Occasionally,no obvious mirror zone was identiﬁed on the fracture surface in either type of Nicalon TMﬁbers. The fracture surfaces for the Tyranno-SAﬁber showed a trans-crystallite fracture behavior(Fig.3(c)).3.2.BSR creep resistanceFig.4shows dependence of1-h BSR creep resistance m on testing temperature for as-receivedﬁbers.The stress relaxation occurred at temperature as low as1000°C.Hi-Nicalon TM type S and Tyranno TM SA exhibited much better creep resistance than Hi-Nicalon TMﬁber as shown in Fig.4.Fig.5shows dependence of1-h BSR creep resistance m on HTT,which was tested at1400°C. Heat treatments of theﬁbers above the processing temperature resulted in improved creep resistance as shown in Fig.5.The creep resistance of heat treated Hi-Nicalon TMﬁber above1400°C was signiﬁcantly im-proved.However,a relatively low tensile strength above 1400°C heat treatment was observed as shown in Fig.2.Fig.3.Typical fracture surface observation in as-received:(a)Hi-Nicalon TM;(b)Hi-Nicalon TM Type S;(c)Tyranno TM-SA.594J.J.Sha et al./Journal of Nuclear Materials329–333(2004)592–596Likely,this could be attributed to the increased grain sizes,high crystallization of b -SiC and more highly crystallized graphitic carbon.Such microstructural changes are expected to inhibit diﬀusion-controlled creep processes.For the 1600°C heat treated Hi-Niclaon TM ﬁber,the creep resistance was better than those of as-received near stoichiometric ﬁbers although the fact that the grain sizes were much smaller than those of the latter ﬁbers.This result indicated that the improved creep resistance depended on the crystallization and grain growth.The excess carbon distributed at the grain boundary for the Hi-Nicalon TM ﬁber inhibits the coalescence of b -SiC,which results in a stable grain boundary structure.This implies that stability of Grain boundaries (GB)plays an important role on the creep resistance of SiC ﬁber.This assumption was also demonstrated by Tyranno TM -SAﬁber.The enhanced creep resistance of the Tyranno TM -SA ﬁber was obtained prior to increase its crystallitesize.As a result of Al addition to Tyranno TM -SA ﬁber,the complex oxide would be formed at GB by heat treatment and they can stabilize the grain boundary to improve the creep resistance.The stability of GB could be aﬀected by GB composition.4.Conclusions(1)Most of initial tensile strength for both near stoichi-ometric ﬁbers (Hi-Niclaon TM Type S and Tyr-anno TM -SA)was retained after heat treatment up to 1780°C.In fact,Tyranno TM -SA ﬁber had excel-lent strength retention after heat treatment at 1900°C.The tensile strength of ﬁbers is extremely sensi-tive to the critical ﬂaw size and distribution.The mechanism for the strength degradation is attributed to a combination of crystal growth of b -SiC and crit-ical ﬂaw/residual stress.(2)The improved creep resistance was obtained for allof ﬁber types after high temperature heat treatment above 1400°C,and is likely attributed to the crystal-lization and grain growth.It appears more likely that improved creep resistance occurs when HTT ex-ceeds ﬁber fabrication temperature.In addition,the creep resistance is associated with GB composition.The GB composition could aﬀect the stability of GB boundaries.AcknowledgementsThis work was supported by the 21st COE researchprogram of Kyoto University on the establishment of sustainable energy system.References[1]A.R.Raﬀray,L.El-Guebaly,S.Gordeev,S.Malang,E.Mogahed,F.Najmabadi,I.Sviatoslavsky,D.K.Sze,M.S.Tillack,X.Wang,Fus.Eng.Des.58&59(2001)549.[2]L.Giancarli,J.P.Bonal,A.Caso,G.Le Marois,N.B.Morley,J.F.Salavy,Fus.Eng.Des.411(1998)165.[3]B.Riccardi,P.Fenici,A.Frias Rebelo,L.Giancarli,G.Le Marois,E.Philippe,Fus.Eng.Des.51&52(2000)11.[4]S.Ueda,S.Nishio,Y.Seki,R.Kurihara,J.Adachi,S.Yamazaki,J.Nucl.Mater.258–263(1998)1589.[5]C.A.Lewinsohn,R.H.Jones,G.E.Youngblood, C.H.Henager Jr.,in:R.H.Jones, A.Kohyama (Eds.),The Third IEA Workshop on SiC–SiC Ceramic Composites for Fusion Structural Applications,Cocoa Beach,FL,29&30January 1999,p.76.[6]H.Ichikawa,Ann.Chim.Sci.Mater.25(2000)523.J.J.Sha et al./Journal of Nuclear Materials 329–333(2004)592–596595[7]T.Ishikawa,Y.Kohtoku,K.Kumagawa,T.Yamamura,T.Nagasawa,Nature391(1998)773.[8]S.Dong,Y.Katoh,A.Kohyama,J.Am.Ceram.Soc.86(1)(2003)26.[9]S.P.Lee,Y.Katoh,J.S.Park,S.Dong,A.Kohyama,S.Suyama,H.K.Yoon,J.Nucl.Mater.289(2001)30. [10]G.E.Yougnblood,C.Lewinsohn,R.H.Jones,A.Kohy-ama,J.Nucl.Mater.289(2001)1.[11]ASTM D3379-75(reapproved1989)Standard test methodfor tensile strength and Young’s modulus for high-modulus single-ﬁlament materials.[12]W.Weibull,J.Appl.Mech.18(1951)293.[13]G.N.Morscher,J.A.Dicarlo,J.Am.Ceram.Soc.75(1)(1992)136.[14]T.Shimoo,I.Tsukada,M.Narisawa,T.Seguchi,K.Okamura,J.Ceram.Soc.Jpn.105(1997)559.596J.J.Sha et al./Journal of Nuclear Materials329–333(2004)592–596。

Influence of heat treatment conditions on the structure and magnetic properties of barium ferrite Ba

Materials Chemistry and Physics98(2006)90–94Inﬂuence of heat treatment conditions on the structure and magnetic properties of barium ferrite BaFe12O19hollow microspheres of low densityPing Ren a,b,JianGuo Guan b,∗,XuDong Cheng ba Department of Energy Sources and Environment Engineering,Shanghai University of Electric Power,Shanghai200093,PR Chinab State Key Laboratory of Advanced Technology for Materials Synthesis,Wuhan University of Technology,Wuhan430070,PR ChinaReceived22May2005;received in revised form28August2005;accepted28August2005AbstractBarium ferrite BaFe12O19hollow microspheres of low density(about2.50g cm−3)were synthesized without BaFe2O4or other intermediate phase by spray pyrolysis technique,combined with co-precipitation precursor and followed further heat treatment.The relationships between the microstructure,magnetic properties and the sintering temperature,time were investigated.Hollow microspheres,constituted by nanometer particles,showed a broad particle distribution of2–15␮m.When the sample was sintered at900◦C for3h or at1100◦C for2h,pure BaFe12O19 ferrite was formed.With the increase of the sintering temperature or time,the grain size and preferential growth orientation were inﬂuenced,the saturation magnetization(M s)had a small increase,and the coercive force(H c)decreased obviously.©2005Elsevier B.V.All rights reserved.Keywords:Barium ferrite;Hollow microspheres;Spray pyrolysis;Microstructure;Magnetic properties1.IntroductionBarium ferrite(BaFe12O19)has been well-known for perma-nent magnets since its development by Philips researchers in the beginning of the1950s because of their high-coercivity,high-saturation magnetization,high resistance,low cost,associated with their excellent chemical stability and resistance to corrosion [1–3].In recent years,hexagonal ferrite has also caused wide interest in high-density recording media and radar-absorbing coatings[4,5].Its frequency of resonance absorption in the range of GHz is more than one thousand times as high as that of spinel ferrite.Therefore,it is promising for a kind of absorption mate-rial in theﬁeld of high frequency.However,they are quite heavy, which restricts their applications requiring lightweight mass. Moreover,they have difﬁculties in increasing the permeability in GHz region because of Snoek limit[6,7].As one of the ways to overcome these problems,hollow microspheres of low den-sity are suggested.At the same time hollow microspheres also exhibit different catalytic,optical,electric and magnetic prop-erties and have important applications in materials,chemistry, catalysis and biologyﬁeld[8].It is expected that microwave ∗Corresponding author.Tel.:+862787218832;fax:+862787879468.E-mail address:guanjg@(J.G.Guan).absorbing ability can be improved by adjusting the diameter and wall thickness of hollow microspheres or composition and grain size of ferrite nanometer particles.A number of fabrication methods have been used to produce hollow microspheres which are comprised of polymer,metal and ceramic materials,including nozzle reactor approaches (spray drying or pyrolysis)[9,10],emulsion/phase separation techniques(often combined with sol–gel processing)[11], emulsion/interfacial polymerization strategies[12],deposition method on sacriﬁcial cores[13]and self-assembly process [14,15].Among these routes,spray pyrolysis technique was considered simplest and suitable for the synthesis of inorganic ferrite hollow microspheres,and large quantity production is likely by using the route.In this paper,we synthesized ferrite precursor with co-precipitation method and obtained BaFe12O19 hollow microspheres by spray pyrolysis technique followed fur-ther heat treatment,and reported the inﬂuence of heat treatment conditions on theﬁnal structure and magnetic properties of the samples.2.ExperimentalBarium ferrite hollow microspheres were produced by three steps,the inves-tigated variables were:calcination temperature(T)and calcination time(t). Firstly,an aqueous solution of Fe(NO3)3·6H2O and Ba(NO3)3·2H2O(Fe/Ba0254-0584/$–see front matter©2005Elsevier B.V.All rights reserved. doi:10.1016/j.matchemphys.2005.08.070P.Ren et al./Materials Chemistry and Physics98(2006)90–9491atomic ratio equal to12)was added to a stirring aqueous solution of NaOH and Na2CO3(OH−/CO32−ion ratio equal to5).After they reacted for2h,the resulting precipitates standed for24h,were then washed with deionized water and dried at110◦C.The dry precipitate was grinded in order to obtainﬁne and uniform barium ferrite precursor powder.Secondly,ﬁne barium ferrite precursor powder was atomized into small particles by negative pressure of the FS-4Flame Spray Dryer.At the same time they were heated quickly at the high temperature ﬂame,which was produced by acetylene and oxygen as combustion gas.They passed the different holes of the Flame Spray Dryer respectively,mixed and burnt in the nozzle.Therefore,spherical droplets,caused by surface tension, decomposed to obtain hollow microspheres.Finally,the hollow microspheres were colleted and further calcined to form BaFe12O19phase or promote crystal-lization under air for3h at several different temperatures(600,800,1000,1100, 1200◦C)and at1100◦C for different time(2,3,4h).X-ray diffraction with Cu K␣radiation(XRD)was used for phase analysis. The surface morphology and size of the grains were studied by scanning electron microscope(SEM).The thermal curves were presented by thermo gravimetric analysis(TG)and differential scanning calorimeter(DSC).The magnetic mea-surements are performed using a vibrating sample magnetometer(VSM)to an appliedﬁeld of16000Oe,hysteresis loops are measured at room temperature.3.Results and discussion3.1.Structural analysis of pyrolysis products without heat treatmentFig.1shows the micrograph,phase constitution and the thermal curves for the pyrolyzed sample by SEM,XRD,TG and DSC.Spherical particles with a broad particle distribu-tion of2–15␮m were observed in Fig.1(a).This was prob-ably related to uneven solid ferrite precursor powder from co-precipitation method or the uniform atomization of the equip-ment.It demonstrated microspheres could be formed by spray pyrolysis method.Although hollow structure could not directly be seen in Fig.1(a),the average density of the sample(about 2.50g cm−3),which represented a50%decrease of hollow microspheres compared to solid powder of(about5.31g cm−3), could explain it to some extent.A small number of slight diffrac-tion peaks␣-Fe2O3and BaCO3were observed in Fig.1(b), which indicated the sample was constituted by a mixture of␣-Fe2O3and BaCO3phase of low crystallinity and also implied time of pyrolysis was not long enough to completely decom-pose iron hydroxide and barium carbonate or to form BaFe12O19 phase.Therefore,its necessary for further heat-treatment to form ferrite phase.Fig.1(c)was evident,an endothermic reaction accompanying with5.2%weight loss was observed at the tem-perature between78and138◦C,which showed the precursor did not decompose completely during the pyrolysis process. Between838and938◦C,the sample undergone exothermic reaction without weight loss.At the temperature range by com-paring XRD patterns of the samples after being heated at600 and1200◦C,it revealed that this change could be ascribed to the reaction of oxides to form barium ferrite.3.2.Inﬂuence of the heating temperature on the structureand magnetic propertiesThe phase constitution of the samples heat-treated at differ-ent temperatures for3h with a heating rate of5K min−1was obtained by XRD and is shown in Fig.2.At600◦C,a small number of␣-Fe2O3diffraction peaks and some slight peaks of BaFe12O19phase were observed.Single phase barium fer-rite had started to form by800◦C(except for the only slight peak at2.69˚A which corresponded to␣-Fe2O3).At900◦C,the sample presented a series of peaks all assigned to BaFe12O19 Fig.1.(a)SEM image,(b)XRD pattern and(c)TG and DSC curves of the sample after spray pyrolysis without heat treatment.92P.Ren et al./Materials Chemistry and Physics98(2006)90–94Fig.2.XRD patterns of the samples calcined at different temperature for3h: (a)600◦C,(b)800◦C,(c)900◦C,(d)1100◦C,(e)1200◦C.phase.When the temperature increased further,the values of diffraction peak intensities improved obviously,which could be associated with the amount and grain coarsening of BaFe12O19 phase.There was a slight change between theﬁrst and second strongest peaks at1200◦C due to preferential grain growth.In this work,pure barium ferrite BaFe12O19was formed directly from iron oxides and barium oxides as the onlycomponents Fig.4.Static magnetic properties of the samples calcined at different tempera-tures for3h.detected.Other intermediate phase such as␣-BaFe2O4,␥-Fe2O3 were never observed during the heat treatment.This is consistent with the results obtained in the previous work[16].As expected from XRD data,change in grain morphology with temperature was observed,which is presented in Fig.3. Hollow microspheres had kept intact during the calcination pro-cess.The surface of the sample without heat treatment was relatively smooth.The surface became rougher with the increase of sintering temperature.By1100◦C,the spheres were consti-tuted by crystals for hexagonal like platelet of about several hundred nanometer.These clearly indicated heat treatment was beneﬁcial for ferrite formation and crystallization.Fig.4shows the effect of the sintering temperature on the magnetic properties between600and1200◦C for3h.The sat-uration magnetization(M s)increased obviously from600to 1000◦C,increased slightly between1000and1200◦C,and reached a maximum of55emu g−1at1200◦C.The value is lower than the theoretical limit(72emu g−1)[17],which might be associated with the density and porosity of hollow micro-spheres.A drastic increase of M s between800and1000◦Cwas Fig.3.SEM images of the samples calcined at different temperatures for3h:(a)without heat treatment,(b)800◦C,(c)1000◦C,(d)1100◦C.P .Ren et al./Materials Chemistry and Physics 98(2006)90–9493related to the increasing amount of BaFe 12O 19phase and a small increase from 1000to 1200◦C for grain coarsening according to XRD and SEM results.The hematite formation in the samples reduced the volumetric fraction of barium ferrite and conse-quently reduced M s before 800◦C.This result is in accordance with that previously described in literature [18].The rema-nent magnetization (M r )reached a maximum of 28emu g −1at 1000◦C,decreasing slightly for higher temperature.The intrin-sic coercive force (H c )basically showed a contrary behavior as M s ,increased obviously before 800◦C due to the increas-ing amount of BaFe 12O 19phase,decreased slightly from 3.4to 3.2kOe between 800and 1000◦C which is close to the coer-civity value of typical hard magnetic materials,and decreased drastically from 3.2to 1.3kOe between 1000and 1200◦C owing to grain coarsening.This indicated the coercive force exhibited strong dependency on the sintering temperature.Similar results were reported by Joonghoe et al.[19],who studied effects of the grain boundary on the coercivity of barium ferrite BaFe 12O 19.The results were also supported by Janasi et al.[18]who con-ducted an investigation on the effect of heat treatment conditions and routes on the magnetic properties of co-precipitated ferrite powders.3.3.Inﬂuence of the heating time on the structure and magnetic propertiesFig.5shows XRD patterns of the samples calcined at 1100◦C for different heat treatment times.In all cases,the samples were virtually single phase BaFe 12O 19ferrite.With the extending of sintering time,the relative intensities of diffraction peaks increased.At the same time the average grain size,measured from the full-width at half-maximum (FWHM)of (107)peak using Scherrer formula,was found to increase from about 450nm for the heated powder for 2h,520nm for 3h,to 550nm for 4h.According to the XRD intensity formulaI =I 0λ3e 432πR 3m 2c 4 Vq V 20|F h k l |2 1+cos 22θsin 2θcos θFig.5.XRD patterns of the samples calcined at 1100◦C for different times:(a)2h,(b)3h,(c)4h.Fig.6.Hysteresis curve of the samples calcined at 1100◦C for different time.where V is the grain volume of (h k l )plain-oriented,q thegrain number of (h k l )plain-oriented,V 0the volume of unit cell,the relative intensities of diffraction peaks were consis-tent with the calculated intensities for the powder heat treated at 1100◦C for 3h.However,when the sintering time was 4h,(107)diffraction peak were dominant whereas relative intensity of (114)diffraction peak was diminished because the grain size of (107)plain-oriented increased quicker than that of (114)plain-oriented based on the above formula and Scherrer for-mula.These implicated that preferential grain growth probably occurred when the samples were sintered at long time.Fig.6shows the magnetization hysteresis loops at room tem-perature of the samples sintered at 1100◦C between 2and 4h.All the samples had almost identical saturation magnetization and remanent magnetization values,indicating that M s and M r are independent on the sintering time,because the samples were all pure BaFe 12O 19phase and their densities are basically same.On the other hand,the coercivity was changed with the sinter-ing time,which decreased initially from 3.0kOe for 2h and then recovered to 2.5kOe for 4h and reached the minimum of 1.9kOe for 3h because of grain size and preferential grain growth according to the XRD results in Fig.5.This clearly illus-trated the well-known fact that the coercivity strongly depended on the calcining time.4.ConclusionsWe had prepared barium ferrite BaFe 12O 19hollow micro-spheres mainly distributed between 2and 15␮m by spray pyrolysis technique,combined with co-precipitation precursor and followed further calcinations,and studied the effect of heat treatment conditions.We found that hollow microspheres kept unbroken and the average density nearly kept unchange-able (about 2.50g cm −3)during the heat treatment.When the sample was sintered at 900◦C for 3h or at 1100◦C for 2h,the single phase BaFe 12O 19ferrite was formed,directly by iron oxide and barium oxide without BaFe 2O 4or ␥-Fe 2O 3intermediate phase.Increasing the temperature was beneﬁcial in increasing the crystalline,improving the saturation mag-netization and eliminating the coercive force.The saturation94P.Ren et al./Materials Chemistry and Physics98(2006)90–94magnetization(M s)increased obviously before1000◦C,and increased slightly between1000and1200◦C and reached the maximum of55emu g−1at1200◦C.Increasing the heat treat-ment time inﬂuenced grain size,preferential grain growth ori-entation and magnetic properties.H c reached a minimum of 1.9kOe for3h and a maximum of3.0kOe for2h,whereas M s was little affected.In a conclusive manner we can say that H c was strongly dependent on heat treatment conditions owing to grain size and preferential growth and M s was closely related to the materials composition.Preparation of narrow distribution of smaller hollow microspheres and study of their structure and properties will be our following work.AcknowledgementThis work is supported by863HI-TECH project of China (no.2002AA305302).References[1]J.Smit,H.P.J.Wijn,Ferrites,Philips Technical Library,Eindhoven,1959.[2]T.Fujiwara,IEEE Trans.Magn.21(1985)1480.[3]P.Campbell,Permanent Magnet Materials and their Application,Cam-bridge University Press,Cambridge,1994.[4]N.Ichnose,Super Particle Technology,Springer-Verlag,1992.[5]K.J.Viney,R.M.Jha,Radar Absorbing Materials,Kluwer AcademicPublishers,1996.[6]K.Hatakeyama,T.Inui,IEEE Trans.Magn.20(1984)1261.[7]M.Matsumoto,Y.Miyata,IEEE Trans.Magn.33(1994)4459.[8]D.L.Wilcox,T.Bernat,D.Kellerman,J.K.Cochran,Materials ResearchSociety Proceedings,vol.375,Pittsburgh,1995.[9]M.Iida,T.Sasaki,M.Watanabe,Chem.Mater.10(1998)3780.[10]K´a roly Zolt´a n,Sz´e pv¨o lgyi J´a nos,Powder Technol.132(2/3)(2003)211.[11]T.Z.Ren,Z.Y.Yuan, B.L.Su,Chem.Phys.Lett.374(1/2)(2003)170.[12]J.Hotz,W.Meier,Langmuir14(1998)1031.[13]J.L.Yin,X.F.Qian,J.Yin,M.W.Shi,G.T.Zhou,Mater.Lett.57(24/25)(2003)3859.[14]R.A.Caruso,A.Susha,F.Caruso,Chem.Mater.13(2001)400.[15]F.Caruso,R.A.Caruso,H.Mohwald,Science282(6)(1998)1111.[16]R.C.Pullar,A.K.Bhattacharya,Mater.Lett.57(2002)537–542.[17]B.T.Shirk,W.R.Buessem,J.Appl.Phys.40(1969)1294.[18]S.R.Janasi,M.Emura,ndgraf,D.Rodrigues,J.Magn.Magn.Mater.238(2002)168–172.[19]Joonghoe Dho,E.K.Lee,J.Y.Park,N.H.Hur,J.Magn.Magn.Mater.285(2005)164–168.。

厄尔尼诺高温英文

厄尔尼诺高温英文El Niño, also known as El Niño-Southern Oscillation (ENSO), is a natural climate phenomenon that occurs every few years in the Pacific Ocean. It refers to a period of unusually warm ocean temperatures along the western coast of South America. El Niño has the power to disrupt weather patterns around the globe, often leading to extreme weather events such as droughts, floods, and hurricanes.El Niño is caused by the weakening of trade winds and the warming of water in the eastern Pacific Ocean. Normally, trade winds blow from east to west, pushing warm surface waters towards the western Pacific. This allows for the upwelling of cold, nutrient-rich water along the coast of South America, supporting a thriving ecosystem. However, during an El Niño event, the trade winds weaken, causing the warm surface waters to move back towards the east. This disrupts the upwelling process and leads to a reduction in the availability of nutrients for marine life.The warming of ocean temperatures during an El Niño event has far-reaching effects on weather patterns. It causes a shift in the location of the Intertropical Convergence Zone (ITCZ), which is a belt of low pressure near the equator where trade winds converge. This shift in the ITCZ brings heavy rainfall to areas that are typically dry, leading to increased precipitation and thepotential for flooding. On the other hand, it can also result in drought conditions in regions that normally receive ample rainfall. These changes in precipitation patterns can have devastating impacts on agriculture, water supplies, and ecosystems.El Niño can also influence the formation and intensity of tropical cyclones. Warmer ocean temperatures provide more energy for storms to develop and strengthen. This can lead to an increase in the number and intensity of hurricanes, typhoons, and cyclones in various regions around the world. For example, during the 1997-1998 El Niño event, the Pacific Ocean experienced the highest number of tropical cyclones ever recorded, causing widespread damage and loss of life.In addition to its immediate impact on weather patterns, El Niño can have long-term effects on climate. It has been linked to changes in global temperature and precipitation patterns. For instance, during an El Niño event, the Pacific Northwest of the United States tends to experience warmer and drier conditions, while the southern part of the country may see increased rainfall. These changes in climate can have significant implications for ecosystems, agriculture, and water resources.Scientists closely monitor El Niño events to better understand their causes and consequences. They use a variety of tools and techniques, including satellites, buoys, and computer models, to gather data on ocean temperature, wind patterns, andother variables. This information helps in predicting the onset of an El Niño event and its potential impacts.In conclusion, El Niño is a complex climate phenomenon that has a profound impact on weather patterns worldwide. Its ability to disrupt normal atmospheric and oceanic conditions can lead to extreme weather events and have long-lasting effects on climate. The study of El Niño is crucial for our understanding of Earth's climate system and for better preparedness to mitigate its consequences.。

Effect of pyrolysis temperature and

holding time on biochar propertiesBiochar is becoming an increasingly popular alternative to traditional methods for managing soil organic matter, improving soil fertility, and sequestering carbon by converting agricultural wastes into a stable and recalcitrant form of carbon. Pyrolysis, the thermal decomposition of organic matter in the absence of oxygen, is widely used to produce biochar. The pyrolysis temperature and holding time are two critical factors that influence the properties of biochar. This article aims to explore the effect of pyrolysis temperature and holding time on biochar properties and their implications for soil management.Pyrolysis temperaturePyrolysis temperature is a important factor that influences the physicochemical properties of biochar. It determines the degree of thermal degradation of the material, leading to the production of different biochar properties. The effect of pyrolysis temperature on biochar properties can be divided into three categories: chemical composition, physical characteristics, and adsorption properties.Chemical compositionPyrolysis temperature has a significant effect on the chemical composition of biochar, including carbon content, ash content, pH, and functional groups. Higher pyrolysis temperatures generally result in higher carbon content, lower ash content, and higher pH. As the temperature increases, volatile components are driven off, leaving behind a more stable and recalcitrant carbon structure. At the same time, the increase in temperature may cause some functional groups, such as carboxyl and hydroxyl groups, to be decomposed, leading to a decrease in surface functional groups and a corresponding increase in hydrophobicity of the biochar.Physical characteristicsPyrolysis temperature also affects the physical characteristics of biochar, including surface area, pore size distribution, and bulk density. High-temperature pyrolysis leads to the formation of a more open pore structure and a higher surface area. However, pore size distribution is affected by both pyrolysis temperature and the type of feedstock, with higher temperatures resulting in a shift towards smaller pore sizes. Meanwhile, an increase in pyrolysis temperature may cause a decrease in bulk density and an increase in particle size.Adsorption propertiesPyrolysis temperature affects the adsorption properties of biochar, including its ability to adsorb nutrients, heavy metals, and other pollutants. High-temperature pyrolysis generally results in biochar with a higher adsorption capacity due to its higher surface area and pore volume. At the same time, the decrease in functional groups may lead to a reduction in the biochar’s ability to adsorb certain types ofpollutants. The specific effect of pyrolysis temperature on the adsorption properties of biochar is determined by the type and concentration of the adsorbate, as well as the properties of the biochar itself.Holding timeHolding time is another important parameter in pyrolysis that affects the properties of biochar. The holding time is the duration of the pyrolysis process at a given temperature. It is an important factor that determines the final carbonization degree and the degree of thermal degradability of the feedstock. The effects of holding time on biochar properties include chemical composition, surface area, and adsorption properties.Chemical compositionIncreasing the holding time can promote the decomposition of organic matter and improve the carbonization degree of the biochar. However, excessive holding time can lead to excessive thermal degradation and a reduction in the carbon content of the final biochar. The chemical composition of biochar can be affected by the holding time either directly or indirectly. Longer holding times can result in greater efforts to remove moisture and volatile organic matter components from the feedstock, leading to higher carbon yield and lower ash content.Surface areaHolding time can also affect the specific surface area of biochar. As the holding time increases, the surface area of the biochar may increase due to an increase in the extent of decomposition and subsequent micropore formation. However, too long a holding time can also lead to a reduction in specific surface area due to excessive carbonization and vaporization of the volatile components.Adsorption propertiesHolding time can also affect the adsorption performance of biochar. An increase in holding time can result in a higher surface area and micropore volume, leading to a greater adsorption capacity for certain types of pollutants such as heavy metals. However, excessive holding times can reduce the number of surface functional groups responsible for adsorption, merely increasing the micropore density in the biochar, and reducing the potential for adsorption of some other pollutants.ConclusionIn conclusion, pyrolysis temperature and holding time are two crucial factors that influence the properties of biochar, which in turn determine its effectiveness in soil applications. High-temperature pyrolysis tends to result in biochar with higher carbon content, larger surface area, and higher adsorption capacity than low-temperature pyrolysis. Longer holding times can also modify biochar properties,although the extent depends on the conditions of the individual pyrolysis process. A well-designed pyrolysis process can thus be tailored to produce biochar with specific properties suitable for a wide range of soil applications, such as improving soil fertility, reducing greenhouse gas emissions, and remediating contaminated soils.。

不同冷却温度添加氯化镁和谷氨酰胺转氨酶对大豆全粉凝胶流变性质的影响

不同冷却温度添加氯化镁和谷氨酰胺转氨酶对大豆全粉凝胶流变性质的影响李君，康昕，蒲雪丽，崔怀田，王胜男，宋虹，朱丹实，刘贺*（渤海大学食品科学与工程学院，生鲜农产品贮藏加工及安全控制技术国家地方联合工程研究中心，辽宁锦州121013）摘要：以超微粉碎技术处理的大豆全粉为原料，利用氯化镁和谷氨酰胺转氨酶（glutamine transaminase，TG）制备大豆全粉凝胶，并探究温度、氯化镁添加量及TG对大豆全粉凝胶的质构特性、流变特性和微观结构的影响规律。

结果表明：全豆豆乳分别冷却至25、15、5 ℃添加氯化镁和TG时，随着冷却温度的降低凝胶强度逐渐变大、凝胶破裂距离变大，不同冷却温度对凝胶强度和破裂距离影响差异显著。

在冷却至5 ℃、添加0.8%氯化镁和1.2 U/g TG诱导时，凝胶强度达到最大56.23 g。

流变特性结果表明，添加TG的体系中储能模量（G’）呈现快速上升趋势，在5 ℃及15 ℃条件下添加TG豆乳凝胶的G’明显大于未添加TG豆乳凝胶，且温度越低，凝胶的G’越大。

通过扫描电子显微镜可以看出5 ℃条件下添加氯化镁和TG所获得的凝胶，其网络结构更加有序且致密。

关键词：大豆全粉；温度；凝胶特性；微观结构Effects of Adding Magnesium Chloride and Glutamine Transaminase after Cooling to Different Temperatures on the Rheological Properties of Heat-induced Gels from Whole Soybean FlourLI Jun, KANG Xin, PU Xueli, CUI Huaitian, WANG Shengnan, SONG Hong, ZHU Danshi, LIU He*(National & Local Joint Engineering Research Center of Storage, Processing and Safety Control Technology for Fresh Agricultural and Aquatic Products, College of Food Science and Technology, Bohai University, Jinzhou 121013, China) Abstract: Heat-induced gels were prepared by boiling ultrafine whole soybean flour in water and then adding magnesium chloride and glutamine transaminase (TGase) after cooking. This study aimed to investigate the effect of cooling temperature, magnesium chloride concentration and TGase concentration on texture, rheological and microstructural properties of heat-induced gels. The results showed that the strength and rupture distance of gels with both added magnesium chloride and TGase increased with decreasing the cooling temperature from 25 to 15 to 5 ℃, and were significantly affected by the different cooling temperatures. The gel strength reached the maximum value of 56.23 g when the temperature was cooled to 5 ℃ and 0.8% magnesium chloride and 1.2 U/g TGase were added. The rheological results showed that the storage modulus (G’) of gels with added TGase showed a rapid upward trend. And the G’ of gels with TGase addition after cooling to 5 and 15 ℃ was significantly larger than that of their counterparts without TGase. The lower the cooling temperature, the larger the G’ of the gel. The scanning electron microscopic (SEM) images showed that the network structure of the gels formed by adding magnesium chloride and TGase after cooling to 5 ℃ was more orderly and denser.Keywords: whole soybean flour; temperature; gel properties; microstructureDOI:10.7506/spkx1002-6630-20191029-315中图分类号：TS214.2 文献标志码：A 文章编号：1002-6630（2021）08-0017-05引文格式：李君, 康昕, 蒲雪丽, 等. 不同冷却温度添加氯化镁和谷氨酰胺转氨酶对大豆全粉凝胶流变性质的影响[J]. 食品科学, 2021, 42(8): 17-21. DOI:10.7506/spkx1002-6630-20191029-315. LI Jun, KANG Xin, PU Xueli, et al. Effects of adding magnesium chloride and glutamine transaminase after cooling to different temperatures on the rheological properties of heat-induced gels from whole soybean flour[J]. Food Science, 2021, 42(8): 17-21. (in Chinese with English abstract) DOI:10.7506/spkx1002-6630-20191029-315. 收稿日期：2019-10-29基金项目：国家自然科学基金面上项目（31972031）第一作者简介：李君（1988—）（ORCID: 0000-0003-3895-7644），女，讲师，硕士，研究方向为粮食、油脂及植物蛋白工程。

高温对药物有何影响呢英文

高温对药物有何影响呢英文The Effects of High Temperatures on MedicationsIntroduction: High temperatures can have significant effects on the stability and potency of medications. It is important to understand these effects in order to ensure the safety and efficacy of drugs. This document will discuss the impact of high temperatures on medications and provide recommendations for proper storage and handling under hot conditions.1. Degradation of Active Ingredients: High temperatures can lead to the degradation of active ingredients in medications. Many medications are sensitive to heat and can break down when exposed to elevated temperatures. This degradation can result in a loss of potency or even render the medication ineffective. It is crucial to store medications in a cool and dry place to prevent this degradation.2. Alteration of Physical Properties: In addition to the degradation of active ingredients, high temperatures can also alter the physical properties of medications. Heat can cause changes in the solubility, dissolution rate, and particle size of the drug, which can impact its absorption and bioavailability. This can lead to unpredictable drug responses and potentially compromise patient safety.3. Increased Risk of Contamination: Heat can increase the risk of contamination of medications. High temperatures can promote the growth of microorganisms, such as bacteria and fungi, in drug products. Contaminated medications can lead to serious infections and adverse reactions in patients. It is essential to store medications in a controlled environment to prevent microbial growth and maintain their sterility.4. Potential for Chemical Reactions: Certain medications are prone to undergo chemical reactions when exposed to high temperatures. For example, heat can cause the breakdown of certain drug molecules or facilitate the formation of new compounds, which may be toxic or have unpredictable effects on patients. Proper storage and handling of medications can help minimize the risk of these chemical reactions.5. Specific Medications and their Susceptibility to Heat: While all medications can be affected by high temperatures to some extent, certain drugs are more susceptible than others. For instance, insulin, certain antibiotics, and biologic medications are known to be highly sensitive to heat. It is vital to be aware of the specific storage requirements for each medication and follow the manufacturer's instructions accordingly.Recommendations: To ensure the efficacy and safety of medications, it is essential to follow proper storage and handling practices, especially under high-temperature conditions. Here are some recommendations:1. Store medications in a cool and dry place, away from direct sunlight and sources of heat.2. Avoid exposing medications to extreme temperatures, such as inside hot cars or near heating appliances.3. Check the storage instructions provided by the manufacturer for individual medications and adhere to them.4. If traveling with medications, use insulated containers or cool packs to maintain a constant temperature.5. Dispose of any medications that have been exposed to high temperatures, as their effectiveness may be compromised.Conclusion:High temperatures can cause numerous adverse effects on medications, including active ingredient degradation, alteration of physical properties, increased risk of contamination, and potential chemical reactions. Following proper storage and handling practices is essential to ensure the effectiveness and safety of medications, particularly in hot climates. It is crucial for healthcare professionals and patients to be aware of these effects and take necessary precautions to preserve the quality of medications.。

材料成型及控制工程专业英语--2.-HEAT-TREATMENT-OF-STEEL

材料成型及控制⼯程专业英语--2.-HEAT-TREATMENT-OF-STEELThe role of heat treatment in modern mechanical engineering can not be overestimated.The changes in the properties of metals due to heat treatment are of extremely great significance.热处理在现代机械⼯程中的作⽤不可能评价的过⾼。

由热处理⽽产⽣的性能改变是特别重要的。

2.1.1 temperature and time 温度和时间The purpose of any heat treating process is to produce the desired changes in the structure of metal by heating to a specified temperature and by subsequent cooling.任何热处理的⽬的都是（通过）将⾦属加热到⼀定的温度并(随后)冷却,以使⾦属组织产⽣所需变化。

2.1.1温度和时间Therefore, the main factors acting in heat treatment aretemperature and time, so that any process of heattreatment can be represented in temperature-time ( t-r ) coordinates.因此，热处理的主要因素是温度和时间，所以任何热处理⼯艺都以⽤温度-时间为坐标轴进⾏表⽰。

热处理⼯艺主要有以下⼏个参数：加热温度t max ，既合⾦加热的最⾼温度；在加热温度下的保温时间；加热速率和冷却速率。

Heat treatment conditions are characterized by thefollowing parameters: heating temperature t max , i.e.the maximum temperature to which an alloy metal is heated; time of holding at the heating temperature ; heating rate and cooling rate .如果以不变速率加热或冷却，则温度和时间的关系可以具有不同倾斜⾓的直线。

热解温度对滤泥生物炭结构性质的影响

·2071·0引言【研究意义】广西是我国最大的甘蔗制糖省（区），滤泥作为制糖生产的副产物之一，其产量丰富。

滤泥由于水含量高达70%~75%，不便于运输、保存和收稿日期：2018-12-21基金项目：国家自然科学基金项目（31760469）作者简介：*为通讯作者，周少基（1960-），博士，副教授，主要从事制糖过程强化及副产物利用研究工作，E-mail ：shaojiz1960@ 。

刘法球（1994-），研究方向为制糖副产物利用，E-mail ：397651979@热解温度对滤泥生物炭结构性质的影响刘法球1，2，周少基1*，唐秋平1，向敏1，唐智光1（1广西大学轻工与食品工程学院，南宁530004；2广西农村投资集团农业发展有限公司，南宁530004）摘要：【目的】研究热解温度对滤泥生物炭性质特征的影响，为制糖废弃物处理提供参考依据。

【方法】将滤泥置于200~600℃下热解制备生物炭，对生物炭进行工业分析、pH 和元素含量测定，以及傅里叶红外光谱、扫描电镜、比表面积和碘值吸附分析。

【结果】随着热解温度的升高，生物炭产率和挥发分含量下降、灰分含量上升，pH 不断增加，表面的C-O 和C-O-C 等活性官能团及-CH 3和-CH 2逐渐消失，H/C 、O/C 和（N+O ）/C 的原子比降低，表明生物炭芳香性及稳定性增强，亲水性和极性减弱；生物炭的孔隙结构丰富，随着热解温度的升高，生物炭中孔隙数量增加，比表面积增大，孔径和孔容有所增加，对碘值的吸附能力持续上升，热解温度为500℃时，比表面积、孔容和对碘值吸附量均达最大值，分别为83.71m 2/g 、0.027m 3/g 和170.38mg/g 。

【结论】在500℃下热解制备滤泥生物炭，其产率相对较高，结构更稳定，且比表面积及孔容最大，对碘的吸附效果最佳，可作为一种优异的吸附材料。

关键词：滤泥；生物炭；热解温度；热稳定性；结构中图分类号：S156.2文献标志码：A文章编号：2095-1191（2019）09-2071-07Effects of pyrolysis temperature on structural propertiesof filter mud biocharLIU Fa-qiu 1，2，ZHOU Shao-ji 1*，TANG Qiu-ping 1，XIANG Min 1，TANG Zhi-guang 1（1School of Light Industry and Food Engeering ，Guangxi University ，Nanning 530004，China ；2Guangxi Rural Investment Group Agricultural Development Co.，Ltd.，Nanning 530004，China ）Abstract ：【Objective 】The effects of pyrolysis temperature on the characteristics of the filter mud biochar were stu-died to provide a scientific basis for the treatment of industrial waste.【Method 】In this study ，filter mud was pyrolyzed at200-600℃to prepare biochar.The biochar was analyzed and characterized through proximate analysis ，pH measure-ment ，elemental analysis ，fourier transform infrared spectroscopy （FTIR ）analysis ，scanning electron microscope （SEM ）analysis ，specific surface area analysis and iodine adsorption analysis.【Result 】The experimental results showed that as the pyrolysis temperature increased ，the yield and volatile matter of biochar decreased ，the ash content increased ，the pH value increased continuously ，and the active functional groups such as C-O and C-O-C and the -CH 3and -CH 2disappeared gradually from the surface of biochar and the atomic ratios of H/C ，O/C ，（N+O ）/C were reduced ，which indicating that the aromaticity and the stability of the biochar was increased ，while its hydrophilic and polarity was reduced.The pore structure of biochar was rich.As the pyrolysis temperature increased ，the number of pores in biochar increased ，the specific surface area became larger ，the pore size and pore volume increased ，the adsorption capacity for iodine value continued to rise.When the pyrolysis temperature was 500℃，the specific surface area ，pore volume and iodine adsorption capacity were the maximum ，which were 83.71m 2/g ，0.027m 3/g and 170.38mg/g ，respectively.【Conclusion 】The preparation of biochar at 500℃by pyrolysis has a relatively high yield ，a more stable structure ，the largest specific surface area and pore volume ，and the best adsorption effect on iodine ，which can be used as a good adsorbent material.Key words ：filter mud ；biochar ；pyrolysis temperature ；thermal stability ；structure50卷南方农业学报·2072·使用，长期以来仅用于回田作肥料，但直接回田施用易造成烧秧、板结、发臭等问题，加重环境负担。

211126653_干热处理对藜麦全粉结构及混粉面团流变学特性的影响

周亚丽，游新勇，李晓龙，等. 干热处理对藜麦全粉结构及混粉面团流变学特性的影响[J]. 食品工业科技，2023，44（9）：74−80. doi:10.13386/j.issn1002-0306.2022060035ZHOU Yali, YOU Xinyong, LI Xiaolong, et al. Effect of Dry Heat Treatment on the Structure of Quinoa Flour and Rheological Properties of Dough[J]. Science and Technology of Food Industry, 2023, 44(9): 74−80. (in Chinese with English abstract). doi:10.13386/j.issn1002-0306.2022060035· 研究与探讨 ·干热处理对藜麦全粉结构及混粉面团流变学特性的影响周亚丽，游新勇*，李晓龙，张坤朋，李安华，高靖雯，刘　萍，朱梓瑜（安阳工学院生物与食品工程学院，河南安阳 455000）摘　要：本研究以藜麦全粉为原料，分别进行常温（对照）、110、130、150 ℃干热处理1 h ；将不同处理的藜麦粉15%与小麦粉85%（w/w ）混合制作面包，分析干热处理温度对藜麦粉结构、混粉面团粉质特性、拉伸特性及面包质构特性、体外消化活性的影响。

结果表明：干热处理使藜麦粉颗粒表面的聚集物脱落并出现缺陷，并且随着处理温度的升高，聚集物脱落的程度增加。

干热处理未改变藜麦粉的A 型晶型结构。

与添加常温藜麦粉的面团相比，添加110、130、150 ℃干热处理藜麦全粉混粉面团的吸水率和弱化度分别升高1.79%和43.75%、3.25%和104.17%、4.83%和125.00%；延伸度、最大拉伸阻力和拉伸阻力均呈下降趋势，拉伸比呈现先升高后降低的趋势。

如果很热用英语怎么写作文

If youre tasked with writing an essay in English about the topic of heat,you could approach it from various angles such as the physical sensation of heat,its impact on daily life,or the broader implications of global warming.Heres a sample essay that you could use as a guide:Title:The Intensity of Summer HeatIntroductionAs the sun climbs higher in the sky,the air becomes thick with the weight of the heat. The intensity of summer heat can be both a blessing and a curse,providing warmth and light,yet also bringing discomfort and the potential for danger.This essay will explore the multifaceted nature of heat during the summer months,delving into its physical effects,its influence on our daily routines,and the broader environmental concerns it raises.Body Paragraph1:The Physical Experience of HeatThe sensation of heat is immediate and allencompassing.It wraps around the body like a heavy blanket,making every movement feel laborious.The skin becomes damp with sweat,and the air seems to shimmer with the heats radiance.The heat can be so intense that it alters ones perception of time,making the minutes feel like hours as the sun beats down relentlessly.Body Paragraph2:Impact on Daily LifeThe heats influence extends beyond the physical.It dictates the rhythm of daily life,with many choosing to retreat indoors during the peak heat of the day.Outdoor activities are often scheduled for the cooler hours of the morning or evening.The demand for air conditioning and fans increases,placing a strain on energy resources.Additionally,the heat can affect ones appetite,leading to a preference for lighter,cooler foods over hot meals.Body Paragraph3:Environmental ConcernsThe discussion of heat cannot be separated from the broader issue of climate change.The increasing frequency and intensity of heatwaves are a clear indication of the Earths rising temperatures.This has farreaching consequences,from the melting of polar ice caps tothe disruption of ecosystems and the potential for more severe weather events.The heat serves as a stark reminder of the need for sustainable practices and the urgency of addressing global warming.ConclusionIn conclusion,the experience of heat is a complex interplay of physical sensation,daily life adjustments,and environmental implications.While it is a natural part of the summer season,the growing intensity of heat is a call to action.It is a reminder of our interconnectedness with the environment and the importance of taking steps to mitigate the effects of climate change.As we navigate the sweltering days of summer,let us also consider the steps we can take to ensure a cooler,more sustainable future.Remember,when writing an essay in English,its important to maintain a clear structure, use a variety of sentence structures,and provide specific examples to support your points. Additionally,ensure that your essay is wellorganized and that your ideas flow logically from one paragraph to the next.。

温度冲击英语

温度冲击英语Temperature ShockThe world we live in is a delicate balance of various environmental factors, each playing a crucial role in sustaining the intricate web of life. Among these factors, temperature is one of the most significant, as it directly impacts the physical, chemical, and biological processes that govern the functioning of our planet. Temperature shock, a phenomenon where sudden and extreme changes in temperature occur, can have profound and far-reaching consequences on the natural world, as well as on human societies.At its core, temperature shock is the result of rapid fluctuations in the Earth's temperature, often caused by a combination of natural and anthropogenic factors. Natural events, such as volcanic eruptions, solar activity, and shifts in ocean currents, can trigger sudden temperature changes, leading to dramatic impacts on the environment. Similarly, human activities, such as the burning of fossil fuels, deforestation, and industrial processes, have contributed to the acceleration of global warming, exacerbating the frequency and intensity of temperature shocks.One of the most visible and immediate effects of temperature shock is its impact on the world's ecosystems. Sudden changes in temperature can disrupt the delicate balance of these systems, causing widespread disruption to the intricate web of life. For example, a rapid increase in temperature can lead to the melting of glaciers and sea ice, altering the habitats of countless species and affecting the availability of essential resources, such as freshwater. Conversely, a sudden drop in temperature can result in the freezing of water bodies, leading to the loss of aquatic life and the disruption of vital food chains.The consequences of temperature shock extend far beyond the natural world, as they can also have significant impacts on human societies. Extreme temperature fluctuations can lead to the disruption of agricultural systems, affecting food production and security. Farmers and agricultural communities may be forced to adapt their practices to cope with these changes, often at great personal and financial cost. Additionally, temperature shocks can contribute to the spread of infectious diseases, as changing environmental conditions can alter the range and behavior of disease-carrying organisms, such as mosquitoes and ticks.The impact of temperature shock on human health is another area of concern. Sudden and extreme temperature changes can lead to a range of health issues, from heat-related illnesses, such as heatexhaustion and heat stroke, to the exacerbation of chronic conditions, such as respiratory and cardiovascular diseases. Vulnerable populations, such as the elderly, the very young, and those with pre-existing medical conditions, are particularly at risk.In the face of these challenges, the need for comprehensive and proactive measures to address the issue of temperature shock has become increasingly urgent. Governments, policymakers, and the scientific community must work together to develop strategies that mitigate the causes of temperature fluctuations, while also implementing effective adaptation measures to protect vulnerable populations and ecosystems.One such approach is the promotion of sustainable energy solutions, which aim to reduce the reliance on fossil fuels and the associated greenhouse gas emissions that contribute to global warming. This includes the widespread adoption of renewable energy sources, such as solar, wind, and hydropower, as well as the implementation of energy-efficient technologies and practices in various sectors of the economy.Additionally, efforts to preserve and restore natural habitats, such as forests, wetlands, and coastal ecosystems, can play a crucial role in enhancing the resilience of these systems to temperature shocks. By maintaining the integrity of these natural environments, we can helpto regulate local and regional temperatures, as well as support the continued provision of essential ecosystem services.At the community level, educational initiatives and public awareness campaigns can empower individuals to understand the risks associated with temperature shock and to take proactive steps to protect themselves and their communities. This may include the development of emergency preparedness plans, the implementation of early warning systems, and the promotion of adaptive strategies, such as the use of heat-resistant building materials and the adoption of heat-related illness prevention measures.In conclusion, temperature shock is a complex and multifaceted challenge that requires a comprehensive and collaborative approach to address. By understanding the underlying causes, recognizing the far-reaching consequences, and implementing effective mitigation and adaptation strategies, we can work towards building a more resilient and sustainable future in the face of this pressing environmental issue.。