Fine Titanium Nitride Powders by the Vapor Phase Reaction of TiCl<sub>4</sub>-NH<sub>3</sub>-H<sub>2</sub>-N<sub>2</sub> System

Abstract

The formation of fine titanium-nitride powders by the vapor phase reaction of TiCl4-NH3-H2-N2 system was investigated between 700° and 1500°C with emphasis on the effects of reaction conditions on the properties of the nitride powders. The following results were obtained.1) Mixing temperature of TiCl4 and NH3 gave a remarkable influence on the properties of the titanium nitride powders produced. When the mixing temperature was about 250°C (method (A)), the nitride powders produced had a wide distribution of particle size from 0.01 to 0.4μ. BET surface area (SBET) of the nitride powders by method (A) was larger than the surface area estimated from the particle size distribution based on the electron micrographs (SEM). On the other hand, when the mixing temperature was above 700°C (method (B)), the nitride powders produced were finer than those by method (A) and had a narrow distribution of particle size from 0.03 to 0.2μ. In the case of method (B), the particle size can be controlled with reaction conditions (mainly with reaction temperature); it decreased with the increase of reaction temperature. SBET of the nitridepowders by method (B) was nearly equal to SEM.2) These titanium nitrides showed a wide range of nonstoichiometry with an excess nitrogen; atomic ratio N/Ti=1.1-1.4. The N/Ti ratio decreased with the elevation of reaction temperature. X-ray diffraction patterns of all nitride samples showed NaCl-structure. It was found that these titanium nitrides contained Ti vacancies equivalent to the excess nitrogen.3) For the formation process of titanium nitride particles, it was proposed that the process in method (A) consisted of the formation of TiCl4-NH3 adduct powders and the subsequent thermal decomposition into nitride, and that the process in method (B) consisted of the formation of TiN nuclei and its growth into nitride particles.