Preparations of titanium nitride, titanium carbonitride and titanium carbide via a two-step carbothermic reduction method

摘要

Titanium carbide, titanium carbonitride or titanium nitride were synthesized by a two-step carbothermic reduction method. In this method, a single-phase precursor TiCnO1-n was firstly prepared from the reaction between titanium dioxide and carbon black in argon atmosphere. Then, the precursor was used as raw materials to prepare TiN, TiCxN1-x or TiC. For the production of TiN or TiCxN1-x, the precursor was further carbothermally reduced and nitrided in nitrogen gas atmosphere. For the production of TiC, the precursor was further reduced by carbon in vacuum. In the first reduction step, it was hard to determine the precise molar ratio of TiO2:C due to the uncontrollable ratio of gaseous products CO and CO2 from TiO2 to TiCnO1-n. Whereas the second step only took place in the high temperature region and the gaseous products were thermodynamically in favor of CO. Therefore, the expected products can be obtained by precisely controlling the carbon addition after analyzing the contents of carbon and oxygen in TiCnO1-n. High purity products were prepared with good dispersivity, narrow size distribution and controllable atomic ratio of C:N. The effects of reduction temperature, reaction time, ball milling and particle sizes of raw material TiO2 were studied in detail. TiN, TiCxN1-x and TiC could be obtained under the same optimum time and temperature of 1773 K for 4 h in first step and 1873 K for 8 h in second step.