| 研究実績の概要 |
A new processing concept for production of Ti metal powder via TiSx (1<x<2) and TiN from ilmenite (FeTiO3) has been proposed. TiN or TiOxCyNz was synthesized by carbothermal reduction and nitridation (CTRN) of FeTiO3.
The preparation of clean TiS2 from TiN plays a key role in production of high-purity Ti powders. Either CS2 or S2 gas could be used for synthesis of titanium sulfides from TiOxCyNz or FeTiO3. However, CS2 gas stream leads to contamination of the samples. A dual-zone furnace specially manufactured gradually evaporated the sulfur and could control the partial pressure of S2 gas. The carbon contamination was remarkably suppressed using S2 gas.
TiN was thus transformed to the single phase of Ti2.45S4 and TiS2 at 1473 K for 3.6 and 10.8 ks, respectively. Nitrogen content of the sulfide was reduced to <0.005 mass% N when the sample was sulfurized at 1473 K for 10.8 ks. Then, the sulfide was reduced to Ti metal powder by the electrochemical OS process in molten CaCl2 with a small addition of CaS. The carbon impurity decreased to 0.01 mass% C for the sulfide and <0.1 mass% C for the Ti powder samples.
Sulfidation of TiC was also studied and pure TiS2 samples with carbon content of <0.025 mass% C were prepared at 1473 K for 18 ks, which is applicable for producing Ti powder. We successfully produced Ti powders with spherical morphology consisted of the foil-like Ti sheets with < 0.15 wt% O from TiN or TiC by the electrochemical reduction in molten CaCl2-0.5 mol% CaS. Using this proposal, Ta and Nb powders could be prepared via their sulfides.
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