Research On The Effects Of The Synthesis Conditions On The Preparation Of TiB₂ By Carbothermal Reduction Method

The synthesis of TiB₂ by the carbothermal reduction of titania and borium oxides was studied in detail through the method of all-isothermal TG and by means of XRD,SEM,TG-DSC as well as on the basis of thermodynamical analysis in the paper.The mechanism for the carbothermal reduction process was expounded to some extent.The influence of the synthesis conditions on the process was discussed extensely.The reduction in steps of TiO₂ was acclaimed in the process of carbothermal reduction of TiO₂ and B₂O₃ from the thermodynamical analysis.The stable domains for the intermediate oxide phases and products as well as the forming temperature of TiB₂ were related strongly to the synthesis tempreture,and to the partial pressure of carbon monoxide.It is therefore important to control the reaction temperature,the vacuum pressure or the CO partial pressure and so on for the synthesis of high-purity TiB₂ power.The start reaction temperature will be cut down as soon as the CO partial pressur is maintained at lower level.The start temperature can be therefore put down by vacuum the furnace and/or by cutting down the CO partial pressure through ventilating to it.The kinetic data for the carbothernal reduction of TiO₂ and B₂O₃ were obtained by the proposed method of all-isothermal thermogravimetric.The synthesis process of TiB₂ from titanium dioxide and borium oxide as well as graphite in the range from 900 to 1300℃can be divided into two.In the first range,that is the temperature from 900℃to 1100℃,the weightloss on unit area will be increased with time linearly.Therefore the equationâ–³W_t/A_t=K_reat can be used as the dynamical curve,meaning that the total reaction rate is controlled by the chemical reaction rate.In fact the apparent activation energy for the process in this range is as large as 109.467 KJ/mol,the frequency factor 131.76 g²Â·cm^-4·min^-1.While in the second range,that is the temperature from 1100℃to 1300℃,the relationship between the weightloss on the unit area with time can be fitted by the parabolic equation:(â–³W_t/A_t) ²=K_Dt,meaning that the tatal reaction rate is controlled by the diffusion rate of the reaction materials,with the apparent activation energy 22.281 KJ/mol,and the frequency factor 33.35 g²Â·cm^-4·min^-1.As the results of the research into the influence of synthesis conditions on the carbothermal reduction reaction,the following conclusions were approached.(1)The carbon sources are the most important factors for the formation of TiB₂,and exerts an strong influence on the appearance of products.(2)The quantity of the carbon and Boron put into the starting materials sets up an important influence to the synthesis of TiB₂, and has the direct impact on the purity of the product.(3)The mixing time,synthesis temperature and the total pressure in the furnace have also effects on the reaction.The rate of synthesis and the purity of TiB₂ can optimized by the longer mixing time,the higher synthesis tempreture and the lower CO pressure in the furnace.