真空碳热还原法制备碳化钛粉末
来源:测品娱乐
Available online at vcc ̄w.sciencedirect.com - 毋 峰・ ScienceDi rect Transactions of Nonferrous Metals Society of China Press Trans.NonferrousMet.Soc.China 21(2011、185—190 Preparation of TiC powders by carbothermal reduction method in vacuum SEN Wei , 一,XU Bao.qiang 一,YANG Bin 一,SUN Hong.yan 一, SONG Jian—xun 一,WAN He.1i 一,DAI Yong.nian , 1.National Engineering Laboratory for Vacuum Metallurgy,Kunming 650093,China; 2.Key Laboratory ofVacuum Metallurgy for Nonferrous Metal ofYurman Province,Kunming 650093,China; 3.Faculty of Materials Science and Engineering,Kunming University of Science and Technology, Kunrning 650093,China Received 28 January 2010;accepted 4 May 2010 Abstract:The preparation of ifne TiC powders by carbotherrnal reduction of TiO,in vacuum was investigated by XRD.SEM.XRF and laser particle sizer.Thermodynamic analysis indicates that it is easy to prepare TiC in vacuum and the formation sequence of products are Ti407(Magneli phase),Ti305,Ti203,TiCxOl-x and TiC with the increase of reaction temperature.Experimental results demonstrate that TiC powders with single phase are obtained with molar ratio ofTiO,to C ranging from l:3-2 tO 1:6 at l 550。C for 4 h when the system pressure is 50 Pa,and TiCl 0 is gained when the molr ratiao of TiO2 to C is l:4 and l:5.In addition,fine TiCl 0 powders(D equals 3.04 wn)with single phase and low impurities are obtained when the molar ratio of TiO,to C is l:4.SEM observation shows that unifo1111 shape,low agglomeration,and loose structure are observed on the surface ofblock product. Key wards:titanium dioxide;titanium carbide;vacuum;carbothermal reduction method carbotherrnal reduction of Tj0,powders is one of the 1 Introduction Titanium carbide,with cubic crystal structure of appropriate routes to produce TiC powders for its inexpensive raw materials and simple process.According to the result of WEIMER[131.the synthesis of TiC bv this method requires high temperature r1 700-2 l 00。C1 NaCl type,ths been widely used in many fields,such as aerospace materials,cutting tools,composite ceramic and long reaction time(1 0—24 h)in argon atmosphere. So it presents the problems of particle agglomeration, materials and wear resistance tools『l1,because of its outstanding properties, including high melting grain growth, non—uniorm partifcle shape and considerable quantities of unreacted titanium dioxide and temperature(3 067。C),high elastic modulus(4 1 0-450 GPa),high Vickers hardness(29—34 GPa),high electrical conductiviy(30x t1 0。S/cm、and high solvency with other carbides[2-3]. The main methods to synthesize TiC powders are as carbon in the product[3].Therefore.for resolving these problems the formation of TiC powders by carbotherlTla1 reduction in vacuum was researched.AFIR et al『14] nvestiigated the Ti—O—C system in a continuous vacuum. In their study the reduction of TiO,by graphite or metallic titanium was monitored in an oven for X-rays observation wih a gtraphite resistance under continuous vacuum.They determined the crystalline characteristies follows:1)carbothern-lal reduction of TiO2 powders using carbon[4-51 or carbonaceous organic material [6—7】;2)carbothermal reduction ofpolymeric precursors obtained from titanium alkoxides and other organic compounds in inert atmosphere[8];3)direct reaction between metallic titanium and carbon by selfpropagation at high temperature for all observed solid phases as well as their composition:TiO2-x,Ti O2 一1 wih 9 ̄n>4,Tit2O3, Ti0,Ti2O,TiC卜 o ,and TiC. In previous study,the possibility of preparing TiC by using carbothermal reduction of TiO々in vacuum was high—temperature synthesis(SHS)or mechanical bal1 milling[9~l 1】;(4)gas phase reaction of TiCl4 and gaseous hydrocarbons[12].Among them the method of Foundation item:Project(u0837604)supported by the Natural Science Foundation ofYunnan Province,China;Project(51004058)supported by he tNational Natural Science Foundation ofChina;Project(20095314110003)supported by Specialized Research Fund for the Doctoral Program of Higher Education Corresponding author:YANG Bin;Tel:+86・871—5161583;E-mail:kgyb2005@126.com DOI:10.1016/S1003-6326(11)60697—3 186 SEN Wei,et al/Trans.Nonferrous Met.Soc.China 21(20l1)185—190 Table 1 Reactions forTi02一C system No. a investigated,and the trace amotmts of TiC in product were observed[15].The main purpose of this work is to produce homogeneous and fine TiC powders through carbothermal reduction in vacuum.For optimizing the process parameters,the effects of different reaction temperature and molar ratio Of Ti0,to C on reaction products are also studied based on thermodynamic analysis. Reaction TiO2(s)+(1/4)C(s)=(1/4)Ti4OT(S)+(1/4)CO(g) TiO2(s)+(1/3)C(s):(1/3)Ti3Os(s)+(1/3)CO(g) TiO2(s)+(1/2)C(s)=(1/2)Ti203(s)+(1/2)CO(g) b c d e TiO2(s)+C(s)=TiO(s)+CO(g) TiO2(s)+3C(s)=TiC(s)+2CO(g) TiO2(s)+2C(s)=Ti(s)+2CO(g) f 2 Experimental he relaTtionship between reaction enthalpy and temperature is shown in Fig.1.which illustrates that the Titania(TIO2_>98.6%,mass fraction)was used as raw materia1 and charcoal(C 89%,mass fraction)as reductant in experiments.The average particle size of TiO2 is 0.1—0.15 【1. For preparing TiC powders,the mixtures of titania and charcoal with certain molar ratio were milled 6-10 h in planetary—type ball milling at the rotating speed of 1 00—400 r/imn.111e mixed powders were compressed into blocks by uni.axial pressing in a hardened steel die under 4-6 NIPa.Then the blocks were removed into crucibles and put into vacuum furnace.The feed was heated to diferent reaction temperatures at a heating rate of 10。C/rain and the temperature was held for 4 h when the systempressurewas 50Pa.Thenthevacuumfurnace power was switched off when products were cooled down to 200。C.The reduced products were obtained, and fine TiC powders were gained via crushing and milling. Lattice parameter and phase composition of the prepared TiC were investigated by X—ray diffraction instrument(D/max一3B)using Cu radiation in the range of 10。一95。(2 with a step of 5(。)/min.The morphology,element content and grain size distribution were studied by scanning electron microscopy(SEM, EPMA一8705),X-ray fluorescence spectrophotometer (XRF,ZSX1 00e)and laser particle sizer(LPS,LS800), respectively. 3 Resuits and discussion 3.1 Thermodynamic analysis According to the data and formula ni Ref.[16],the Gibbs free energy and reaction enthalpy for the carbothermal reduction of TiO2 can be calculated.So the initial reaction temperature at different pressures could be obtained.Some potential reactions between TiO2 and C are listed in 【ble 1.and the following reactions are included in its reaction fb)一fd): 3Ti4O7+C=4Ti3O5+CO (1) 2Ti3O5+C=3Ti203+CO (2) (1/2)Ti305+C=(3/2)Ti0+C0 (3) eaction heat from reaction(a)to reaction(D y.It indicates that reactions can conduct when heat is enough.Therefore,higher temperature nad longer holding time are necessary for preparing large amounts ofTiC. hTe Gibbs free energy of reaction(e)at diferent n Fig.2,which is based on the initial on temperatures of l 271,848,787,71 l,645 and 588。C when the system pressu—I_【og. /^ Ir{es a Q 0 ure 10 ,50,10,1,0.1埒u and 0.01 Pa Pa.respectively.It is apparent htat the initial Temperature/。C Fig.1 Reaction enthalpy of reactions(a)一(f)as function of temperature Temperature/。C Fig.2 Gibbs free energy of reaction(e)at diferent pressure∽ asfunctionoftemperature order of rincrease graduallonly pressures is shown ireactiSEN Wei,et al/Trans.Nonferrous Met.Soc.China 21(2011)185—190 187 reaction temperature of reaction fe)decreases obviously when the system pressure declines.Therefore,the preparation Of TiC in vacuum is easier thall that at atmospheric pressure.What’s more.1arge amounts of TiC form easily for the gas CO escapes fast from raw material(TiO,and C1 in vacuum. 3.2 Efleets of reaetion temperature on reacfion products 功e formation ofphase in carbothermal process was studied in temperature range of 1 1 00。C一1 550。C. Figure 3 shows XRD paRems of products prepared at 1 100,1 200,1 300,l 400,1 500 and 1 550。C for 4 h when the molar ratio of TiO,to C is 1:4.It can be seen that Ti305 phase and Magneli phase(Ti407)appear at 1 100。C.At 1 200。C,a largo amount of Ti,O phases form while the peak intensity of Ti O diminishes and Ti4O7 disappears.At the same time,trace amount of solid solution TiCxO1一 is formed easily fr(_om TiC and Ti『IoLu.r)I)1/^ 0co 0o毒∞(O because their lattice parameters are approximately the same[1,14].Al 1 300。C,TiC phase appears and the peak intensities of solid solution TiCxO1一 increase when the peaks of Ti203 diminish and Ti3O5 disappears,which indicates that TiC phase may forid from TiCx0l_ with further reduction.At 1 400。C and 1 500。C,Ti,O peak intensities diminish gradually and TiCxOl-x disappear while TiC peak intensities increase.At 1 550。C.only TiC phase is formed.The results illustrate that the formation sequence ofthe products in vacuum should be Magneli phase(Ti407),Ti305,Ti203,TiC O1 and TiC. Pig.3 XRD paRems of products prepared at diferent temperatures:(a)1 100。C;(b)1 200。C;(c)1 300。C;(d) 1 400。C;(e)1 500。C;(D 1 550。C Furthermore,Gibbs free energy of reactions(a)一m at 50 Pa was calculated and shown in Fig.4.which is based on the initial reaction temperatures of reactions (a)一(D at 666,709,761,926,848 and l 209。C, respectively.The results indicate that the formation sequence of products should be Ti4O7,Ti305,Ti203,TiC, TiO and Ti with increasing reaction temperature.But Ti phase is not detected in experiments owing to the fact that reaction(D needs more reaction heat(Fig.1)and its Gibbs free energy is higher than htat ofreaction(e).On the contrary,TiC can be prepared easily because the Gibbs free energy of reaction(e)is the lowest at higher temperature. 0 Temperature/。C Fig.4 Gibbs free energy of reaction(a)一(f)as function of temperature at 50 Pa The analysis from Fig.3 also implies that Ti203 is the lowest oxide phase before forming TiCxO1-x and TiC when carbon content in raw materials is enough.This is inconsistent with other work concerning Ti305[17—18] and TIP[1 91 as lowest oxide of the system,while consistent with the observation of KOC[31 and BERGER『4]. In fact.carbothermal reduction reaction of TiO,is a continuous process.Based on XRD results in Fig.3 and reaction thermodynamics between TiO,and C,the main reactions rae: TiO2+C==Ti 02 l+CO >4) 4Ti O2 一l+(n-4)C=nTi407+(n-4)CO( >4) 3 Ti407+C一4n3O5+CO 2Ti305+C ̄3Ti2O3+CO Ti2O3+(1+ )C一2Ti O1_x+(1+2x)CO TiC O1-x+(2一 )C—TiC+(1 )C0 3-3 Efleets of different molar ratio of TiO,to C on reaction products Figure 5 shows XRD pattems of the reaction products prepared at l 550。C for 4 h when the molar ratio of TiO,to C ranges from 1:1 to l:6.As seen in parer(a),Ti203 and TiP phase appear when the molar ratio ofTiO2 to C is l:1.In pattern fb),the solid solution TiCxO1-x is formed when Ti2O3 peak intensities diminish and TiP disappears.In pattern(c),TiC phase is formed 1 —、 、188 SEN Wei,et al/Trans.Nonferrous Met.Soc.China 21(2011)185—190 when Ti203 peak intensities decrease and Ti O1 disappears.The results indicate that TiC phase may be formed at the expense of titanium oxides and oxycarbides when the molar ratio of Ti0,to C decreases. Therefore,only TiC phase is observed when the molar ratio of TiO2 to C decreases continually(pat-tern(d)一(g)). But excessive carbon is observed in TiC powders with the molar ratio Of 1:4.1:5 and l:6 when dipped in acid. The excessive carbon is not detected in pattems(e)一(g) since the charcoal powders are amorphous carbon and small amounts of them cannot be detected by XRD instrument.However,the excessive carbon may be separated from TiC powders by combustion method. Therefore.pure TiC powders will be gained in molar ratio range Of 1:3.2 t0 1:6. ● 。*-TIC *--TiO (g) "-Ti203i 1 o:-T (f) 1 i (e) 1 . . (d) ^ . (c) . . _.L ,。 . (b) , l_ _i... .. (a) T j i:I. , ;.。 l0 2O 30 40 50 60 70 80 90 20/(。) Fig.5 XRD paRems of reaction products prepared at 1 550。C with diferent molar ratio ofTiP2 to C:(a)1:l;(b)1:2;(c)1:3; (d)1:3_2;(e)1:4;(D 1:5;(g)1:6 hTe finer the stoichiometric TiC powder particles, the higher the mechanical strength of the consolidated materials obtained.So it is necessary to calculate the lattice parameter for defining the stoichiometry of TiC powders by means of extrapolation technique[20—23] with the following equation: … 12 (COS 20十字 + 10) a=d(^肼)[厅 十七 +, 】 (11) where 0 is the difraction angle.a is the lattice parameter which could be determined by Eq.(1 1).a0 is the true lattice parameter of TiC which could be determined by Eq.f101.In accordance with XRD patterns,we can draw the figure of lattice parameter versus Nelson—Riley function and extrapolateto a0as 0=-90。. The calculated Nelson—Riley extrapolation plots for TiC powders prepared at l 550。C for 4 h when the molar ratio of TiO,to C is 1:3,1:3.2,1:4,l:5, respectively are shown in Fig.6.111e corresponding lattice parameters extrapolated using this method are 0.43 1 45,0.43 1 60.0.432 40 and 0.432 40 nnl, respectively.According to the Intemational Centre for Dirfaction Data(JCPDS.ICDD 2000)Powder Difraction File(PDF)card 65—0242.the relevant lattice parameters of TiC is 0.432 7 nlTI.SO the calculated results indicate that the extrapolated values deviate from the standard value and become close to it when the molar ratio of TiO2 to C decrease,which can be attributed to the reasons as follows.First,the strain and lattice defect are induced by changing reaction temperature.Second, sub—stoichiometric composition exists in the prepared TiC powders for TiC exists over a very wide compositional range according to Ti-C phase diagram[24].The atom ratio of C to Ti varies from 0.49 to 0.95.Therefore,sub.stoichiometric TiCx <1)may exists in TiC powders.However,we may aceeDt TiC powders as TiC10 when the extrapolated values with .molar ratio of1:4 anLd 1:uLu 5 ar苗g窭 (1e slightly i 31蔫 nferiorto standard value. 0.433 5 _一Molar ratio l:3 ・一Molar ratio 1:3-2 0.433 0 ▲一Molar ratio 1:4 ・一Molar ratio l:5 0.432 5 ▲ ● ● 0.4320 :二==== 0.431 5 ● ● 0.43l 0 一 0.430 5 0 0.2 0.4 0.6 0.8 1.0 l-2 1.4 1.6 Nelson—Riley function, 0)/% Fig.6 Nelson-Riley extrapolation plots for TiC powders prepared at 1 550。Cfor4hwithdifferentmolar ratio 3.4 Characterization of fine TiC powders prepared at 1 550。Cfor4h From the above results,TiC powders that are near stoichiometry were prepared at 1 550。C for 4 h when the molar ratio ofTiO,to C is 1:4.Figure 7 shows SEM micrographs of the surface of TiC block.From Figs.7(a)一(c),we can see that the morphology of the surface of TiC block is homogeneous and lpose agglomeration.It can be seen rfom Figs.7(a)and(d)that among TiC crystal grains lots of gas porosities distribute. which are caused by discharged gas CO in carbothernqal reduction process.The results illus仃ate that the increasing contact area between reactants by ball milling should result in a more complete reaction and uniform shape.In addition,loose structure can be formed owing to the gas CO escaping easily in vacuum.Consequently, 190 SENWei,et al/Trans.NonferrousMet.Soc.China 21(2011)185—190 Journal ofAlloys and Compounds 1999,288(1/2):124—140. Bao—qiang,YANG Bin,HE Jin—piang,SEN Wei,DAI Yong-nian, [15] XU LlIJ Da-chun.Study on carbothermic reduction of titanim udioxide and carbon black叨.Internationa1 Jouma1 of Refractory Metals and Hard Materials,l992,3f1):3-15. e of some technological [5] MAITRE A.TETARD D.LEFORT P Rolparameters during carburizing titanium dioxide们.Journal of the in vacuum[C]//Ba De・ehun.Proceeding of 9th Vacuum Metallury gnd Surfaace Engineering Conference.Beijing:Electronics Industry ress,2009:499—505.P European Ceramic Society,2000,2(1):15_22. Y C.KANG H J.KIM D J.Formation ofTiC particle during [6】 WOO carbothermal reduction ofTiO2 fJ】.Journal ofthe European Ceramic Society,2007,27(2/3):719—722. [7】 KOC R,MENG C,SWlFT G A.Sintering properties of submicron 【16] YE Da—in,HU Jihan—hua.Practical data handbook of ino ̄anic thermodynamics【M].2nd edition.Beijing:Metallrgiucal Industry Press,2002:6-25,48-62.(in Chinese) [17] KOC R.Kinetics and phase evolution during carbothermal synthesis oftitanim ucarbide rfom carbon—coated titania powder[J1_Journal of TiC powders from carbon coated titania precursor[J].Journal of Materials Science,2000,35(12):313l一3141. [8] PREISSH,BERGERLM,SCHULTZED.Studies on carbothermal he tEuropean Ceramic Society,1997,17(1 1):1309—1315. 【18】 OUENSANGA A.Thermodynamic study of the Ti—C—O system in preparation of titanim caurbide from diferent gel preeurous[J]l Journal ofthe European Ceramic Society,1999,19(2):195—206. [9】 ZHU xin—kun,ZHAO Kun—yu,CHENG Bao—chang,LIN Qiu-shi, he ttemperature range 1 400一l 600 K[J】.Journal of Less—Common Metals,1979,63(2):225-235. zHANG Xiu—qing,cHEN Tie-li,SHU Yun—sheng,YONG QI-long. Fabrication of nanocrystalline TiC powder by high—energy ball [19] LYUBIMOV V D,ALYAMOVSKⅡS I,SHVEIK1N G E Mechanism of the rducteion of titanim oxiudes by carbon[JJ. milling[J】.1’be Chinese Journal ofNonfeITOUS Metals,2001,ll(2): 269—272.(in Chinese) hesis of high temperature materials by [1O】 MUNIR Z A.Syntself-propagating combustion metho ̄[J].American Ceramic Soeiety Bulletin,1988,67(2):56—63. BAVBANDE D V MISHRA R,JUNEJA J M.Studies on the kinetics of sntyhesis of TiC by calciothermic reduction of Ti02 in presence of Russian Journal ofInorganic Chemistry,1981,26(9):1243—1247. YANG Yu-xing,QI Rui.X-ray difraction analysis[M】.Shanghai: [2O】 Shanghai Jiao-tong Universiy tPress,1994:129.(n iChinese) LI Shu—tang.Base of c ̄stallology about X—ray diffraction[M]. 【21] Beijing:Metallurgical Industry ress,1990:154—155.(Pn iChinese) [22] RAZAVI M.RAHIMIPOUR M I乙KABOLI R.Synthesis of TiC nanocomposite powder from impure TiO2 and carbon black by carbon[JJ_Journal of Thermal Analysis and Calorimetry,2004,78(3) 775-780. mechanically activatd sientering [J]l Journal of Alloys and Compounds,2008,460(1/2):694-698. ect of starting [23] LOHSE B H.CALKA A.WEXLER D.Efrcomposiiton on the synthesis ofnanocrysaltline TiC during milling of D W.ALEXANDR0VSKⅡS,K工M B K.Mg.thermal reduction [12] LEE of TiCh+C ̄Ch solution for producing ultrafine titanium carbide[J】. Materials Chemistry and Physics,2Oo4,88(1):23—26. MER A [13] WEICarbide.nitride and boride materials.synthesis and titanim aund carbon【J].Journal of Alloys and Compounds,2005, 394(1/2):148—151. 【24] DAI Yong—nin.Bianary alloy phase diagrams[M】.Beijing:Science Press,2009:254.(in Chinese) fEdited by LAI Hai-hui) processing[M].London:Chapman&Hall,1997. [14] AFIR A,ACHOUR M,SAOULA N.X—ray difraction study 0f Ti—O—C system at high temperature and in a contniuous vacuuln[J】. 真空碳热还原法制备碳化钛粉末 森维 , 一,徐宝强 一,杨斌 一,孙红燕 ,宋建勋 一,万贺利1,2戴永年 , 1.真空冶金国家工程实验室,昆明650093; 2.云南省有色金属真空冶金重点实验室,昆明650093; 3.昆明理工大学材料科学与工程学院,昆明650093 摘要:采用XRD、SEM、XRF以及激光粒度分析仪等分析手段,研究真空条件下碳热还原TiO2制备的碳化钛 粉末。热力学计算和实验结果表明:真空条件下容易获得碳化钛,且随温度逐渐升高得到的产物顺序为:Magneli 相(Ti4O7)、Ti3O5、Ti2O3、TiCxO1 和TiC。当物料配比为1:3.2—1:6时,在1 550。C保温4 h的条件下可获得单相 TiC粉末;物料配比为1:4和1:5时,产物粉末为标准化学计量的TiC1 0粉末;物料配比为l:4时,得到的产物为 单相低杂质超细碳化钛粉末(D5o为3.04 0m)、SEM观察表明在产物块体表面存在分布均匀、团聚小、结构疏松的 结构。 关键词:二氧化钛;碳化钛:真空;碳热还原方法