机械化学反应法合成铁酸镍纳米颗粒 (Formation of NiFe2O4 nanoparticles by mechanochemical reaction)

Formation of NiFe 2O 4nanoparticles by mechanochemical reactionHuaming Yang *,Xiangchao Zhang,Weiqin Ao,Guanzhou QiuDepartment of Inorganic Materials,School of Resources Processing and Bioengineering,Central South University,Changsha 410083,ChinaReceived 7July 2003;received in revised form 16November 2003;accepted 3February 2004AbstractPreparation of nanosized NiFe 2O 4particles by mechanochemical reaction(NiO þa -Fe 2O 3)and subsequent thermal treatment was investigated using X-ray diffraction (XRD).Thermal treatment of the as-milled powder at 7008C for 1h led to the formation of NiFe 2O 4nanoparticles with an average crystal size of about 23nm.Effect of thermal treatment temperature on the crystal size of the nanoparticles was studied.The mechanism of nanoparticles growth was primarily discussed.The activation energy of NiFe 2O 4nanoparticle formation during calcination was calculated to be 16.6kJ/mol.#2004Elsevier Ltd.All rights reserved.Keywords:A.Inorganic compounds;A.Nanostructure;B.Crystal growth;C.X-ray diffraction1.IntroductionThe synthesis of ultrafine magnetic particles has been intensively investigated in recent years because of their potential applications in high-density magnetic recording and magnetic fluids.Nanostructured materials exhibit unusual physical and chemical properties,significantly different from those conventional bulk materials due to their extremely small size or large specific surface area [1,2].Nickel ferrite (NiFe 2O 4)is a well-known magnetic material.This property of NiFe 2O 4is significantly affected by the particle size.There are some reports that nanosized NiFe 2O 4particles are beneficial in promoting useful properties [3,4].Several techniques have been developed to prepare NiFe 2O 4nanoparticles,including chemical co-precipitation [5,6],sol–gel method [7],citrate precursor technique[8],shock wave technique [9],mechanical alloying [10],microwave processing [11]and aerosolization[12].But none are fully satisfactory in that nanocrystalline NiFe 2O 4is difficult or inconvenient toobtain.Materials Research Bulletin 39(2004)833–837*Corresponding author.Tel.:þ86-731-8830549;fax:þ86-731-8710804.E-mail address:hmyang@ (H.Yang).0025-5408/$–see front matter #2004Elsevier Ltd.All rights reserved.doi:10.1016/j.materresbull.2004.02.001Mechanochemical processing is a novel method for the production of nanosized materials,where separated nanoparticles can be prepared.Recently,a wide variety of nanoparticles have been synthesized by mechanochemical technique,including ZnS,CdS,LiMn2O4,SiO2,CeO2,Co3O4and SnO2[13–20]. Mechanochemical synthesis is particularly suitable for large-scale production because of its simple process and low cost.In this paper,the synthesis of nanosized NiFe2O4particles by mechanochemical reaction was reported.The NiFe2O4nanoparticles was excellent as high-performance magnetic materials.These results will be reported in a future paper.2.ExperimentalTwo starting materials(NiO and a-Fe2O3)were mixed with a molar ratio of1:1to form the mixture. 10g of the mixture and9stainless steel balls of2.5mm in diameter and40stainless steel balls of 0.4mm in diameter were sealed in a300ml stainless steel vial.Mechanochemical milling was performed with a KM-10type planetary mill for8h at600rpm using a ball-to-powder mass ratio of 20:1.The as-milled powder was subsequently heat-treated at7008C in air for1h to form NiFe2O4.The nanoparticle nature of the product was examined using a D/max-g A diffractometer(Cu K a radiation, l¼0:154056nm).The average crystal size(D)was calculated from diffraction peak half-widths using Scherrer’s equation.3.Results and discussionFig.1shows the XRD patterns of the NiOþa-Fe2O3milled powders:(a)the starting mixture;(b) milled for8h and(c)after calcined at7008C for1h.Only the peaks associated with NiO and a-Fe2O3 were observed in the patterns of the starting materials(a).After8h milling of the mixture,only typical NiFe2O4peaks were detected,indicating that the reaction NiOþa-Fe2O3was complete:NiOþa-Fe2O3!NiFe2O4(1)Fig.1.XRD patterns of the NiOþa-Fe2O3milled powders,(a)the starting mixture;(b)milled for8h;(c)after calcined at 7008C for1h.834H.Yang et al./Materials Research Bulletin39(2004)833–837Standard Gibbs free energy change D G 298calculated in Eq.(1)is À18.3kJ/mol,indicating that the milling kinetically assists the thermodynamically spontaneous reactions to form NiFe 2O 4from the starting mixture when the interface of the solid surface in the mixture is closely contacted and sheared by the continuous milling.It also can be deduced that the crystallization of NiFe 2O 4is initiated in the as-milled powder of the starting materials,consequently,the solid-phase diffusion is promoted by the long-time milling.Thermal treatment of the as-milled powder at 7008C for 1h improved the crystallization of particles and finally resulted in the formation of the NiFe 2O 4nanoparticles.The calculated XRD crystal size of NiFe 2O 4nanoparticle was about 23nm.Fig.2shows the XRD patterns of the NiFe 2O 4nanoparticles synthesized at 600–8008C.With the increase in the calcination temperature,the intensities of the peaks coincident with NiFe 2O 4increased to some degree.Fig.3shows the variation of XRD crystal size (D )of NiFe 2O 4nanoparticles obtained by the thermal treatment of precursor at different temperatures,it can be indicated that the crystal size gradually increased from approximately 19nm at 6008C to $28nm at 8008C.So,the heating temperature has moderate effect on the NiFe 2O 4crystal size.This is directly related to the crystallization ofnanoparticles.Fig.2.XRD patterns of the NiFe 2O 4nanoparticles synthesized at different calcinationtemperatures.Fig.3.Variation of the average crystal size (D )of the NiFe 2O 4nanoparticles with calcination temperature.H.Yang et al./Materials Research Bulletin 39(2004)833–837835A straight line of ln(D )against 1/T (Fig.4)is plotted according to the Scott equation given below under the condition of homogeneous growth of nanoparticle [21],which approximately describes the growth rate of nanoparticle during calcination:D ¼C exp ÀE RT(2)where D is the particle size,C is a constant (¼177.67),E is the activation energy for crystal growth,R is the ideal gas constant and T is the absolute temperature.There exists a good linear relationship.E value could be calculated from the slope of the straight line as E ¼16:6kJ/mol.It can be considered that the crystallite grows primarily by means of an interfacial reaction.It also shows that the growth of the NiFe 2O 4nanocrystallite is easily affected by the calcination temperature,which can be con firmed from Fig.3.4.ConclusionsNiFe 2O 4nanoparticles were successfully prepared by heating the as-milled powder obtained via the mechanochemical reaction of NiO and a -Fe 2O 3.The crystal size was easily affected by the calcination temperature.The activation energy (E )of NiFe 2O 4nanoparticle growth during thermal treatment was calculcated to be 16.6kJ/mol.The calcination temperature has a signi ficant effect on the nanoparticle growth.This simple,low-cost route should be applicable for the synthesis of other functional nanoparticles.AcknowledgementsThis work was supported by the National Nature Science Foundation of China (No.50304014),the Excellent Doctoral Dissertation Foundation of Hunan Province (No.200114)and the Postgraduate Educational Innovation Engineering of Central South University (No.030702).Fig.4.Plot of ln(D )against 1/T for the equation D ¼C exp(ÀE /RT ).836H.Yang et al./Materials Research Bulletin 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