The Kinetics Of TiO₂ Carbothermal Reduction Nitridation Reaction

TiN,TiC,Ti（C,N）have high hardness,high melting point and excellent resistance to molten metal corrosion.They are widely used in metallurgy,aerospace,electronics and machining industries.At present,the effects of furnace atmosphere on product phase and mechanism are less studied when TiN,TiC and Ti（C,N）are prepared by TiO₂carbothermic reduction nitridation.In this paper,based on thermodynamics theory,the macroscopic kinetic mechanism of TiO₂ carbothermal reduction nitridation reaction was studied,and the effects of atmosphere on the phase composition,chemical composition and microstructure of nitriding reaction products were studied.The results show:1.Under the standard state,the theoretical synthesis temperature of TiC and TiN is1499.3K and 1610.9K,respectively.When the temperature over 1892.2K,the mutual conversion between TiC and TiN occurs.TiN and Ti（C,N）will coexist if nitrogen is continuously introduced.If carbon source is added above this temperature,the phase is mainly TiC.2.With the increase of the reaction temperature,the range of partial pressure of N₂,CO in the furnace required for the synthesis of different phases is gradually increased,and the requirements for the partial pressure of each gas in the furnace are lowered.At the same reaction temperature,as the P_N22 increases continuously,the stable region of TiN gradually increases,the conversion temperature of TiN to TiC increases,whereas the increase of P_COO leads to an increase in the synthesis temperature of TiN.3.The influence of carbon source on nitriding reaction is more significant at high temperature,carbon black is more reactive than graphite,nitriding rate is also improved.The change of the atmosphere in the furnace has a certain influence on the product phase of the reaction.When there is no external CO in the reaction,the product phase is mainly TiN.As P_COO increasesin the furnace,the Ti（O,C,N）phase appears.4.The lowest synthesis temperature,the highest nitriding rate and the fastest reaction rate can be obtained by reacting under flowing nitrogen coke-buried condition,which is an efficient and effective treatment to preparation of TiN,TiC and Ti（C,N）.Under this atmosphere,P_N22 and P_COO working together to promote the mass transfer of the reaction as well as reducing the synthesis temperature of titanium non-oxide.5.Under flowing nitrogen coke-buried atmosphere,when graphite is used as carbon source,the sample with n_Ti∶n_C=1∶3 is the optimal precursor in the reaction.Titanium non-oxide such as TiN_0.93,Ti(C_0.4,N_0.6)was synthesised on the surface of the sample with n_Ti∶n_C=1∶3 under flowing nitrogen coke-buried atmosphere.6.When there is H₂O（g）in the reaction atmosphere,the nitridation product will undergo hydration which is carried out from the outside to the inside,hydration is a process of weight gain.When the carbon is excessive,the hot steam in the furnace will first react with the residual carbon powder.When the carbon powder in the sample is completely consumed,the hot water vapor in the furnace reacts with TiN and TiN is oxidized to TiO₂ with time or temperature increases.