In Situ Synthesis Of TiB₂-TiC Composite Powder By Carbothermal Reduction

Both TiB₂ and TiC ceramics have excellent properties such as high melting point,high hardness,good thermal conductivity,and good electrical conductivity and wear resistance,and they are physically and chemically compatible.Therefore,compared with the single-component ceramics,TiB₂-TiC composite ceramics exhibit better physical and chemical properties,and can be used as protective materials for various high temperature resistant parts and functional parts such as high temperature crucibles and nuclear reactors,which has broad application prospects.Synthesis of TiB₂-TiC composite powders with high purity,high activity,uniform composition and fine grain size is the key to obtain high-density TiB₂-TiC composite ceramics.At present,the synthesis of TiB₂-TiC composite powders are synthesized by mechanical mixing method,that is.,the TiB₂ and TiC powders are directly mixed by ball milling,which leads the obtained TiB₂-TiC composite powder has the problems of uneven mixing of the two phases and high impurity contentThis paper proposes to synthesize TiB₂-TiC composite ceramics powder by one-step carbon thermal reduction reaction using TiO₂ as titanium source to solve the above mentioned problem.Firstly,the reaction mechanism of carbon thermal synthesis was discussed through thermodynamic calculation combined with experiment.The optimization of B₄C powder pretreatment process and the composite powder synthesis process was completed on this basis,and the raw material formula was further adjusted to regulate the two-phase content in the composite powder.The following study results were obtained after analysis:(1)In the ternary system of B₄C-TiO₂-C,the synthesis of TiB₂-TiC composite powder with carbon thermal reduction involves two basic processes:firstly,B₄C and TiO₂ are reduced by C to generate TiC and by-product B₂O₃ at low temperature stage(1150?),and then the TiC and B₂O₃ generated in the previous stage are used as raw materials to further react to synthesize TiB₂ in the high temperature stage(1450?).In addition,there is also a small amount of TiB₂ generated at low temperature for the B₄C-TiO₂ binary solid-phase reaction in the first stage.(2)The B₄C powder ball milling process was optimized by orthogonal experimental design,and the results of analysis of variance show that the ball milling time is the main effect factor.And the grain size of raw materials can be effectively reduced by prolonging the ball milling time,and the comparative experiments show that the uniformity of the mixture is obviously improved after the ball milling pretreatment,which is beneficial to promote the synthesis reaction.(3)Two-stage synthesis processes are adopted for the experiment,and the influence of reaction temperature and reaction time in each stage was discussed.The results show that in the two-stage process,the influence of temperature is particularly significant,it even directly determines the degree of reaction,and the extended time can also promote the process of reaction to some extent,but it will lead to excessive length of grain.At last,the optimum synthesis process for synthesizing TiB₂-TiC composite powder is 1150°C(1.5h)+1450°C(0.5h).(4)In the experiment of formula optimization,increasing the ratio of TiO₂ and C in the reactants can promote the formation of TiC,which can increase the proportion of TiC powder in the obtained composite powder,and realize the regulation of the ratio of TiB₂ and TiC in the composite powder.In summary,the submicron TiB₂-TiC composite powder can be synthesized in one step at lower temperature and shorter reaction time by optimizing the process and formula.The oxygen content in the powder is controlled at a minimum of 1.65%,and the content of TiC can be adjusted in the range of 14.7%-95.2%,which basically realizes the controllability of the both composition.