With the development of various metal-parts material industry, hardened ceramics powders (titanium carbide(TiC) / titanium nitride(TiN), etc.) based on titanium are utilized as the raw materials of cutting and cermet-tool. Particularly, titanium nitride(TiN) exhibiting unique gold-colors is actively applied to the high value-parts manufacturing such as watch-buckle, jewelry and so on. Among traditional methods for production of TiN powder, carbothermal-reduction nitriding process of TiO2 powder has been commercially known as a good candidate technology in views of the economical and efficient point. However, this process requires high reaction temperatures (1500~2000oC) in accordance with thermodynamic stability of TiO2, which can induce intense sintering accompanied with post-milling process and low quality powder. Therefore, in order to improve these faults, many researches have been focused on producing the TiN powder at a lower temperature. In this study, nitriding heat-treatment applying titanium hydride(TiH2) powder produced by hydrogenation heat-treatment of sponge Ti, was tried at lower temperatures compared with carbothermal-reduction process. Here, the optimized hydrogenation process was firstly established with regard to reaction temperatures and hours, and then nitriding possibility and kinetic behavior according to reaction temperatures and initial particle size of TiH2 powder was thoroughly investigated.
In order to establish the optimized hydrogenation process, sponge titanium was hydrogenated at 623~1223K for 1~3 hours, and then the individual hydride were characterized by XRD, hydrogen elemental analyzer, etc. It was studied experimentally and thermodynamically that hydrogenation reaction perfectly occurred at 973K(2~3hr), 1023K(1~3hr), 1073K(1 hr), appearing TiH1.924 phase corresponding to 3.97~3.98 wt.% of hydrogen content. Therefore, it let us know that the optimized temperature and time of hydrogenation process were 1023K and 1 hour, respectively.
The sponge TiH2 were milled to reduce the particle size to the 2μm and 15μm and then respective TiH2 powders were nitrided at 1023~1423K for 2 hour, and the individual nitride were characterized by XRD, hydrogen/nitrogen elemental analyzer. The observation of N, H-contents let us know that H-contents was decreased, while N-contents was increased with temperature-rises. In particular, according to initial particle size of TiH2 powder, the smaller size(2μm) can be nitride more effectively even at relatively low temperatures, showing the higher N-contents than coarse(15μm) powder in the overall region of reaction temperatures. Therefore, from our careful study of nitriding kinetics, we found the activation energy for nitriding in fine powder to be 17.45kJ/mol, which was much smaller than in coarse powder, 42.15kJ/mol, which confirmed that the nitriding rate in fine powder was faster than that in coarse powder because of the higher surface-area effect.