Sintering process and grain growth of Mn-Zn ferrite nanoparticles

RARE METALS .Vol. 25 , Spec. Issue , Oct 2006 ,p. 526Sintering process and grain growth of Mn-Zn ferrite nanoparticlesWANG Xin , CUI Ynfang , WANG Yongming , HAO Shunli , and LIU ChunjingSchool of Material Science and Engineering , Hebei University of Technology , Tianjin 300130 , China( Received 2006-06-30 )Abstract :The density , microstructure and magnetic properties of non-doped Mn-Zn ferrite nanoparticles sintered compactswere investigated. The compacts of non-doped Mn-Zn ferrite nanoparticles were sintered by segmented-sintering process atlower sintering temperature. The density of sintered samples was measured by Archimedes method , and the phase compo-sition and microstructure were examined by XRD and SEM. The sintered Mn-Zn ferrite magnetic measurements were car-ried out with Vibrating Sample. The results show that the density of sintered compacts increases with the rising of sinteringtemperature , achieving 4.8245 g° cm-3 when sintered at 900 C , which is the optimal density of Mn-Zn functional ferriteneeded and from the fractured surface of sintered samples ,it can be seen that the grain grows well with small grain sizeand homogeneous distribution.Key words : Mn-Zn ferrite ; sintering temperature ; grain growth ; density ; magnetic properties[ This work was financially supported by the Natural Science Fund of Hebei Province , China ( No. E20000027 ) ,and theNatural Science Foundation of Tianjin , China ( No.06YFJM,JC02400) ]of Mn-Zn ferrite nanoparticles ，more attention has1. Introductionbeen paid to the study of sintering behavior of nanop-articles oxide powder compacts. There are many sinte-Mn-Zn ferrites possess high saturation magnetiza-ring processes of nanaoparticles , such as dry isostatiction , high initial permeability and low magnetic loss atpressing , wet isostatic pressing , slip casting , injectionhigh frequencies compared to other soft magnetic memolding , extrusion casting and tape casting[ 4-9 ]tallic materials , so they have been widely used in e-However , these sintering processes have many disad-lectronic applications ，such as magnetic recordingvantages such as expensive equipment ，high cost ofheads , transformers , choke coils , and noise filter[ 1-production and hardly to produce on a large scale.2 ] It is well known that the sintering behavior of Mn-The grain growth of sintered compacts was studiedZn ferrites is one of the most important processes forin this article , which sintered at different temperaturethe preparation of Mn-Zn ferrites , which mostly de-by segmented-sintering process at lower sintering tem-pends on magnetic properties and mechanical proper-perature. The optimal density of sintered compacts isties of Mn-Zn ferrite materials. The reason is that the4.8245 g. cm -3 sintered at 900 C. The sinteringsintering behavior directly depend on the microstruc-temperature( 900 C ) is 450 C lower than that of con-ture of Mn-Zn ferrite materials , including grain size ,vent中国煤化工50 C ). In this way ,ithomogeneous distribution , sintering density , and soca:YHCNMHG*on , which are the key points to make good Mn-Zn fer-rite material[ 3 ]2. ExperimentalRecently , with the development of the synthesis、Correspondin! WANG Xin E-mail : wangxin022@ 263. netWang x. et al. ,Sintering process and grain growth of Mn-Zn frrite nanoparticles5272.1. Sintering process of Mn-Zn ferrite nanopar-samples was measured by Archimedes method. Duringticlesthe density measurement experiments , it was foundNon-doped Mn-Zn frrite nanoparticles of compo-that there were lots of air bubbles when putting thesition Mna ,Zno ,Fe2.O2 was prepared by improved co-compacts sintered under 800 C into water. So Archi-precipitatior[ 10 ] The powders were granulated withmedes method does not fit for measuring the density of3wt. % poly-vinyl alcohol( PVA ) and 5% ( PEG )these samples. At lower sintering temperature , sin-and uniaxially pressed into toroidal samples of 21 mmtered samples may be in primary stage. In this stage ,out diameter ,9 mm inner diameter and 5.7 mm thick-the moisture , binder and some impurities of the greenness ,with a standard density of3.0g° cm-3. Thesebody are volatilized with the rise of the temperature ,samples were sintered in N2 containing less than 500and then grains begin to approach to each other , theppm O2 at 720 ,790 ,800 ,830 ,850 , 880 , 900 andapproaching area is becoming more and more large.950 C ,at a constant heating rate of250 C. h-' ,inBut ,the grain size and the pore shape do not change ,a computerized box type furnace , and then they werethe relative density of samples changes slightly.subsequently cooled. These samples were noted aTo the compacts sintered over 800 C , sinteredsamplesA ,B,C,D,E,F ,C and H , respectively.samples may be in the second stage at high sinteringtemperature. In this stage , with the neck area becom-ing large and grain interface moving , the grain growsStage-llitle by litle ,so the pore becomes smaller. The rela- .Stage-Itive density of samples will be improved in this way.Additinally ,it is found that the density of these sam-ples can be suessfully measured by Archimedes641method.t/2.2.2 The characterization of sintered samplesFig.1. Sintering process of Mn-Zn ferrite compacts.The phase composition and microstructure of the sin- .tered Mn-Zn ferrite were examined by XRD and SEMIn this study , the compacts of Mn-Zn ferrite nan-at room temperature , and the results are shown in Fig.oparticles were sintered by segmented-sintering3 and Fig.5.process. The sintering process of Mn-Zn ferrite com-2.2.3 The magnetic properties of sintered samplespacts is shown in Fig. 1. At the first sintering stage ,The sintered Mn-Zn ferrite magnetie measurementsthe temperature rises from room temperature to 300-were carried out with Vibrating Sample Magnetometer450 C at a constant heating rate of 250 C. h-',at room temperature , and the results are shown in Ta-soaking some time ; at the second sintering stage thele 2.temperature rises from 300-450 C to the sinteringtemperature，soaking some time again ，and then3. Results and analysescooled to room temperature. The sintered samples with3.1. Density of sintered samplesdifferent sintering temperatures can be gained in thisThe results of the density of sintered samples areway.中国煤化工fdensity of Mn-Zn fer-rite:YHC N M H Gare shown in Fig.2.2.2. Properties measurementFrom Fig. 2 it can be seen clearly that the2.2. 1 Measurement density of sintered samplesdensity of sintered samples inereases graduallyTo study the physical properties of sintered compactsfrom4. 0106 to4. 8245 g* cm -3 , when sinteringof Mn-Zn化五能anoparicles , the density of sintered528RARE METALS , Vol. 25 , Spee. Issue , Oct 2006Table 1.Characteristics of Mn-Zn ferrites sintered at dif-2 , the density of sintered samples increases with theferent temperaturesrising of the sintering temperature , in this study , ran-SinteringSintered GreenDensity ofging from 800 to 900 C.Samplestemperature/ compact/ body/ sintered compac/So it is concluded that 900 C is optimal sinteringCg(g cm-3)8003.7399 3. 33554.0106temperature of non-doped Mn-Zn ferrite nanopowders ,D8303.82503. 57964.1148with good grain size and high relative density.8503.9771 3. 78384.27078803.84013. 57304. 56313.2. Crystal structure of the samples9003.8431 3. 57014.8245H9503.80743. 50944.8742The crystal structure of the samples sintered atdifferent temperature were examined by X-ray diffrac-.0.tion( XRD ).4.8-Fig. 3 is the XRD pattern of the samples sintered4.6-at 800 ,830 ,850 ,880 ,900 and 950 C , respective-ly. The observed diffraction lines are found to corre-4.4-spond to those of the pattern of Mn-Zn ferrite withhardly any extra lines , indicating that all samples havesingle phase spinel structure and no unreacted constit-uents were present in these samples.780 800 820 840 860 880 900 920 940 960From Fig.4 ,it can be seen that the grain size ofSintering temperature/Csintered samples are growing larger and larger with theFig. 2. Variation of density of Mn-Zn ferrite with sinte-sintering temperature rising when the sintering tempera-ring temperature.ture ranges from 800 to 880 C , and the density of thesintered sample are also increasing with the sinteringtemperatures of these samples increase from 800 totemperature rising. When the sintering temperature900 C. However , the density of samples sintered atranges from 880 to 950 C , it has the opposite trend.950 C is4. 8742 g' cm -3 , with lttle rise. Addition-ally , from Table 1 ,it can be seen that the grain size3.3. Microstructure of Mn-Zn ferrite sinteredgrows largely with the rising of sintering temperaturefrom 800-850 C. Sample sintered at 900 C has goodsamplesdensity and small grain size. These observations are ofThe fractured surface of sintered samples sin-significant importance as it makes it possible for thesetered at 900 C is shown in Fig. 5. The grainferrites to be sintered at 900 C.15厂(311)800 C830 CThese phenomena can be explained as follows.850 C客880 CAt lower sintering temperature , the moisture , binder900 C(440)and some impurities of green body are volatilized.(220)(511)Grains begin to approach to each other and the ap-中国煤化工90)(422)proaching area is becoming more and more large. WithYHCNMHGthe rising of sintering temperature , the interface ol020 30grains moves within a neck area , the grain grows lttle201(°)by lttle , the pore becomes smaller and the relativeFig. 3. XRD pattern of the sintered samples.density of5a布限抵will be improved. As shown in Fig.Wang X. et al. , Sintering process and grain growth of Mn-Zn ferrite nanoparticles529Table 2. Magnetic properties of MnZn power ferrites sin-tered5--BSinteringM./M,/B,/ H./xo一--C45-Sample temper-ature/C.( emu. g'Oemu* g~') GG35-1C80048. 8664.4372 265. 69 75. 887D83083. 8372.8160 145.61 35.9215-50-85086.7242. 6034140. 3233. 849154588080.364.1.6693 95.718 27.77140-35-90080. 5892. 1800 132. 1729. 95330-95081.8091. 549694. 9I9 25. 209251780 0082080808000920940960Sintering temperature/rCThe density of the sintered samples and grain growthFig.4. Variation of grain size( B ) and density( C) ofwere investigated. The optimal density (4. 8 g.Mn-Zn ferrite with sintering temperature.cm-3 ) can be gotten by segemented-sintering processand sintered at 900 C. From the fractured surfaces ofsintered samples sintered at 900 C( Fig.5 ),it canbe seen that the grain grows well and homogeneously.From Table.1 ,it is found that the density of sinteredsample is4. 8245 g° cm”, which is the optimal den-sity of Mn-Zn ferrite needed. It is concluded that the3 μmoptimal sintering temperature of non-doped Mn-Zn fer-rite nanoparticles is 900 9C , when sintered by segmen-Fig.5. Fractured surface of samples sintered at 900 C.ted - sintering process. Additionally , the samples sin-tered at 850 C have better magnetic properties.size , distribution and pore shape can be seen clearly.Additionally , the relative density of sintered compactReferencesis high. From the relations of the density and grain[1] Tsay C. Y. ,LiuK.s. ,and LinI. Nan. ,Co-firing pro-size of sintered samples shown in Fig.4 ,it is conclu-cress using conventional and microwave sintering tech-ded that 900 C is the optimal sintering temperature innologies for Mn-Zn and Ni-Zn ferrites. Euro. Ceram.this study ,and the sample sintered at 900 C has goodSoc. ,2001 ,21 :1937.grain size and high relative density.[2] Ken H. , Tatsuji A. , Sinsuke E. ,et al. , Microstrue-tures and magnetic and electric properties of low -temper-3.4. Magnetic properties of sintered samplesature sintering Mn-Zn ferrites without and with additionof lithium borosilicate glass. Magn. Magn. Mater.From Table2 ,it can be seen that the sample sin-1999 , 205 :283.tered at 850 C has better magnetic properties.[3] Ott G. , Wrba J. , and Lucke R. , Reenet developmentspermeability applications.4. Conclusions中国煤化工, 254 -255 :535..MYHCNMH Gj. ,interorging of nano-The compacts of non-doped Mn -Zn ferritecrytaline zirconia : I , experimental. J. Am. Ceram.nanoparticles were sintered at different sinteringSoc. , 1997 ,80 :149.temperature by segmented - sintering process[5] Allen A.J. , Krueger S. , Skandan G. ,et al. , Micro-.structural evolution during the sintering of nanostructured530RARE METALS , Vol. 25 ,Spec. Issue , Oct 2006ceramic oxides. J. Am. Ceram. Soc. , 1996 , 79( 5 ):behavior of nanocrystalline zirconia doped with alumina1201.prepared by chemical vapor synthesis. J. Am. Ceram.[6] Chen P. L. ,and Chen I. 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