Synthesis of Nanocrystalline Barium Ferrite in Ethanol/Water Media

J. Mater. Sci. Technol, Vol.25 No.4, 2009465Synthesis of Nanocrystalline Barium Ferritein Ethanol/Water MediaM. Montazeri- Pour and A. AtaietSchool of Metallurgy and Materials Engineering, University of Tehran, Tehran, IranManuscript received December 21, 2007, in revised form October 26, 2008]Nanocrytalline particles of barium ferrite magnetic material have been prepared by co-precipitation routeusing aqueous and non-aqueous solutions of iron and barium chlorides with a Fe/Ba molar ratio of 11 andsubsequent drying-annealing treatment. Water and ethanol/water mixture with volume ratio of 3:1 were usedas solvents in the process. Coprecipitated powders were annealed at various temperatures for 1 h. F TIR(Fourier transform infrared spectroscopy), XRD (X ray diffraction), DTA/TGA (differential thermal analy-sis/thermogravimetric analysis) and SEM (scanning electron microscopy) techniques were used to evaluatepowder particle characteristics. DTA/TGA results confirmed by those obtained from XRD indicated that theformation of barium frrite occurs in sample synthesized in ethanol/water solution at a relatively low temper-ature of 631°C. Nano-size particles of barium ferrite with mean particle size of almost 75 and 100 nm wereobserved in the SEM micrographs of the samples synthesized in ethanol/water solution after annealing at 700and 800°C for 1 h, respectively.KEY WORDS: Magnetic materials; Hard ferrites; Coprecipitation1. Introductionsolvents, ethanol (CHgCH2OH) is nontoxic and thecheapest9l.Barium ferrite magnetic material (BaO-6Fe2O3)Lisjak and Drofenik(10) claimed that replacing wa-has signifcant potential for applications such as per-ter with ethanol in the processing of barium hexafer-manent magnets and microwave absorbing coatings,rite, in which the solubility of CO2 from air is neg-because of the adequate combination of low cost, rel-ligible, suppresses the BaCO3 formation and henceatively high Curie temperature (450°C), high intrinsicdecreases the formation temperature of barium hexa-coercivity (6700 Oe), chemical stability and resistanceferrite.to corrosionl. In the past decade, there has been anIn the present study, the infuences of coprecipita-increasing. interest in methods for the preparation oftion media on the characteristics of the products, e.g.fine particles of barium ferrite, because of its emerg-phase constitution, crystallite size, thermal behavioring application in perpendicular magnetic recordingand morphology were investigated in more details.media. .The fabrication of bulk barium ferrite requires2. Experimentalpowders with outstanding characteristics in terms ofparticle size, morphology, composition uniformity, pu-FeCl3-6H2O (Merck, >99%) and BaCl2.2H2Ority and magnetic propertiesl2. Finer starting pow-(Merck,≥99%) with a Fe/Ba molar ratio of 11 wereders exhibit a superior sintering behavior, resulting indissolved in water and a mixture of ethanol/ waterlower sintering temperature and denser ceramicslbl. Itwith a volume ratio of 3:1. The molar ratio of Fe/Bashould be noted that powder particle characteristicswas 11 to maintain the stoichiometry of the productare infuenced significantly by the synthesis method.due to the poor solubility of Ba+2 cations in water.Barium ferrite is produced mainly by a con-Two prepared solutions were coprecipitated by ad-ventional mixed oxide ceramic method, which in-dition of NaOH with OH- /C1- molar ratio of 2 atvolves the calcining of BaCO3 and a-Fe2O3 mix-room temperature. The samples synthesized in wa-tures at around 1200°C. However, in order to improveter and ethanol/water solutions were washed by dis-the material properties， several non-conventionaltilled water and ethanol, respectively and dried atroutes such as coprecipitation4a, hydrothermal5,70°C for 15 h. The dried powders were then annealedmicro-emulsion!6, glass crysallization7l and sol-gelat various temperatures for 1 h in air to obtain bar-methods(8] have also been employed to synthesize bar-ium ferrite magnetic phase. The samples synthesizedium ferrite. Among these methods, coprecipitation isin ethanol/water and water solutions are named forthe most attractive one due to simple operation andbrevity“EtOH”and“W", respectively.ease of mass production.The nhase jdentification of the specimens was per-The use of a mixed solvent is a new approach informe中国煤化工RD) on a Philipssynthesis and processing of nanomaterials. The or- PW3: CoK a radiation.ganic solvents play an important role in controllingThe nfYHC N M H G2019 powders an-the nucleation and growth of nanocrystalline mate-nealed at various temperatures was calculated fromrials. On the other hand, among various organicthe X-ray peak broadening of three difraction peaksrelated to (107), (114) and (220) planes using the clas-↑Corresponding author. Ph.D;E-mail address: aataie@ut.ac.ir (A. Ataie)..466J. Mater. Sci. Technol, Vol.25 No.4, 2009100-一10a)284535~3143w|7言35 t)108。240000 800 1000Temp./CFig. 3 DTA/TGA traces of the W sample230 40 5060 70 8020/dg.Fig. 1 X-ray difraction patterns of the coprecipitated3. Results and Discussionprecursors: (a) W and (b) EtOH samplesFigure 1 shows the XRD patterns for the copre-cipitated EtOH and W samples. Analysis of the XRDpatterns confirms that the powders are mainly amor-间phous with some poorly crystallized barium carbon-ate phase. The less distinctive of BaCO3 peaks inEtOH precursor shows the more amorphous nature ofpowders obtained from the ethanol solution.!Figure 2 shows the F TIR spectra of the coprecipi-tated precursors. Although two curves seem different,the positions of their main peaks are almost consis-0tent with each other. It indicates that the ethanolsolution was not able to change the main composi-1650tion of the coprecipitated product. The absence of32821450the characteristic absorption bands of ethanol such1340as 3000- 2900 cm -1 due to C-H stretching and 1160-1070 cm-1 due to C-0 stretching suggests that nofree ethanol remained in the EtOH precursor. Thebroad bands centered at 3211 and 3292 cm- 1 for the4000 3500 3000 2500 2000 1500 1000 500W and EtOH samples, respectively are due to theWavenumber/am'O -H stretching[12). However, the reduced frequencyFig. 2 FTIR spectra of the coprecipitated precursors:and increased broadening of this band for the W sam-(a) W and (b) EtOH samplesple can be attributed to the more hydrogen bandsexisting between the various hydroxyl groups in thissample. The peak, which occurred near 1650 cm-1 issical Scherrer equationl1]:; .assigned to the H-O-H bending vibration. The moredistinctive of this peak for W sample may be due toD=.0.9λmore water present either a8 absorbed water or waterof hydration. The absorption band at 1340 cm~ 1 isβcosθa main characteristic of β-FeOOH phasel3). The ab-sorption bands at 858, 1059 and 1450 cm- 1 resultedwhere D is the average crystallite size in nm, λ is thefrom the carbonate groups[14). Increasing the trans-radiation wavelength (0.17889 nm for CoKa),β is themittance of the characteristic bands of the BaCO3 atcorrected half width and θ represents the diffraction858 and 1450 cm-1 for W sample confirms the morepeak angle.amounts of this composition!t5l. Also, the broaden-Fourier transform infrared spectroscopy (FTIR)ing band 1000- 600 cm-1 indicated a band of metal-spectra of coprecipitated precursors in the IR rangeoxygenl16.of 600- 4000 cm-1 were recorded by Bruker Equinoxrent with the XRD55 spectrometer. Thermal decomposition behaviorresult中国煤化工.sors are mixturesof the samples was examined by simultaneous dif-of BaMYHCNMH(d probably amor-ferential thermal analysis/thermogravimetric analysisphous(DTA/TGA, model STA 1640 Polymer Laboratories,DTA/TGA traces of the W sample are shown inEngland) in air with the heating rate of 100°C/min.Fig.3. The endothermic peak at about 75°C with 7%CamScan MV2300 scanning electron microscope wasweight loss is associated with the loss of water fromused to characterize the particles morphology.the sample. Two weak exothermic peaks at 235 andJ. Mater. Sci. Technol, Vol.25 No.4, 2009467| BaFe,0#BaFe.O.BaFe,O,0Fe,O、Fe20, 0650C750頭↑蓖雹800C司700C| 750C900C8020/deg.305 50Fig.6 X-ray diffraction patterns for EtOH sample an-20/d0g. .nealed at various temperatures for 1 hFig.4 X-ray difraction patterns for W sample annealedated precursor coprecipitated from the water solution,at various temperatures for 1 hwhich retarded the difusion of Ba2+ and hence for-mation of barium ferrite.100sample. As a consequence of removing of morei31ethanol in the drying step, the related endothermic{5peak at 60°C seems to be less distinctive. This is ingood agreement with the FTIR results. The mass lossof almost 16% up to 600°C could be associated withthe loss of water and CO2 during the degradation of9∞0the precursor. The exothermic peak with a minor5weight loss (~1%) at about 631°C could be due tothe formation of barium ferrite.8Analysis of the above results revealed two impor--10tant points. The first one is that in contrary withw sample, the formation of barium monoferrite non-。80magnetic phase does not take place in EtOH sam-ple. The same result was reported by Pullar andTemp./CBhattacharyal17. The second one is that the forma-tion temperature of barium ferrite dramatically de-Fig.5 DTA/TGA traces. of the EtOH samplecreased from 743°C in W sample to 631°C in EtOHsample.The temperature of 631°C is very close to the2849C most probably correspond to the conversionformation temperature of barium ferrite (634°C)of hydroxides to oxides followed by crystallization ofobtained by coprecipitation/ mechanical millinga-Fe2O3 and 7-Fe2O3. Two pronounced exothermicmethod[18], and is one of the lowest temperatures,peaks with a minor weight loss (~0.5%) also occurredwhich has been reported for formation of bariumat about 661 and 743°C. The first exothermic peakferrite via coprecipitation routel4,10.could be due to the formation of barium monoferriteFigure 6 shows the XRD patterns for the EtOH(BaFe2O4). The second exothermic peak may be at-sample after it was annealed at various temperaturestributed to the formation of barium ferrite.The XRD patterns of the W sample after anneal-for中国煤化工t 650°C indicatesthatSingle phase bar-ing at various temperatures are shown in Fig. 4. Bar-ium:MHC N M H G sample annealedium ferrite became tmajor phase in sample an-at 7(agIcHHICu WIUu u1A/TGAresults, itnealed at 7509C, but some un-reacted intermediate is concluded that using ethanol as a co-solvent alongphases like barium monoferrite and hematite were stillwith water significantly lowered the formation tem-observed. Remaining of phase impurities up to 850°Cperature of magnetic phase.indicates the poor reactivity of the hard agglomer-Table 1 summarizes the mean crystallite size of468J. Mater. Sci. Technol, Vol.25 No.4, 2009Table 1 Mean crystallite size of the W and EtOH samples annealed at various temperaturesSample Temp.7 C Crystallite size calculated fromMean crystallitediferent diffraction peaks/ nmsize/nm(107)(114)(220)75039334W800434038850484641459005549165065031294RAEtOH7003336_3街Fig. 7 SEM micrographs of the: (国) W and (b) EtOH samples both annealed at 800°C for 1hto 75 nm (see Fig. 8).It is noted that different physical and chemicalproperties of ethanol and water can remarkably in-fuence the coprecipitation process.precipitation, water molecules can bridge the sur-face hydroxyl groups of neighboring precipitates toform hard agglomerates by making solid necks between precipitate small particles as long a8 they nucle-ated. Therefore, the powders treated in water preferto form large particles. In contrary, ethanol is pos-tulated to hydrogen bands to surface hydroxyls, butcould not cause particle-particle interaction and henceparticle coarsening. Thus, the powders prepared inethanol/water mixture showed softer agglomerationnature and smaller mean particle size leading the pre-cursor becoming very soft and friable. The above ex-planation also is in agreement with increasing hydro-gen bands in W sample as shown in FTIR analysis.Fig. 8 SEM micrograph of the EtOH sample annealed atModel brought in Fig. 9 describes the function of700°Cfor1hethanol in the weakening hydrogen bands between theadjacent hydroxide particlesl2. It is also suggestedthat the higher surface tension of water compared tothe EtOH and W samples annealed at various tem-ethanol leads to high capillary forces and thus hardperatures. It shows that the mean crystallite size ofagglomerates in powders during dryingl19]. Therefore,barium ferrite for EtOH sample is lower than that ofthese hard agglomerates could be inhibited by wash-W sample in identical annealing temperature.ingt中国煤化工a-nation of bariumFigure 7 shows SEM micrographs of the W andIt.EtOH samples after annealing at 800°C. It seems thatferritelMHCNMHGosition of BaCO3,the particles morphology was affected by the type offerrite formation[20,21]. Since thewhich ..nperature for M-solvent. The mean particle size was measured as 160bonding of amor-and 100 nm for W and EtOH samples, respectively.phous nanoparticles in precursor is rather weak, it isBy decreasing the annealing temperature to 700°C,easier to break these bonds during annealing treat-the mean particle size of the EtOH sample decreasedment.J. Mater. Sci. Technol, Vol.25 No.4, 2009469ability to weakening the hydrogen bands between the|adjacent particles and its low surface tension facilitatethe formation of nano size single phase barium ferrite.,0-H .AcknowledgementThe financial support of this work by the Iranian Nan-HydraodeHydroddeotechnology Initiative was gratefully acknowledged.REFERENCES[1 ] H. Kojima: Ferromagnetic Materials, eds. E.P. Wohl-HHarth, North-Holland, Amsterdam, 1982, 3, 305.[2] G. Benito, MP. Morales, J. Requena, V. Raposo, M.Vazquez and J.S. Moya: J. Magn. Magn. Mater,2001, 234, 65.H号3] M. Rozman and M. Drofenik; J. Am. Ceram. Soc,p-H+-+--1998, 81, 1757.4] A. Ataie, S. Heshmati-Manesh and H. Kazempour: J.Mater. Sci, 2002, 37, 2125.[5] G.V. Duong, r.S. Turtelli, B.D. Thuan, D.V. Linh, N.Hanh and R. Groessinger: J. Non-Cryst. Solids, 2007,Hydroxde. HO-C-C- HHycroide353, 811.1 HH[6] J. Palla, D.O. Shah, P.G. Casillas and JM. Aquino:J. Nanopart. Res, 1999, 1, 215.^o-m[7 ] R. Muller, C. Ulbrich, W. Schuppel, H. 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