Thermal plasma treatment of titanium carbide powders: Part II. In-flight formation of carbon-site vacancies and subseque
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Thermal plasma treatment of titanium carbide powders: Part II. In-flight formation of carbon-site vacancies and subsequent nitridation in titanium carbide powders during induction plasma treatment Takamasa Ishigakia) and Yusuke Moriyoshib) National Institute for Research in Inorganic Materials, 1-1, Namiki, Tsukuba-shi, Ibaraki 305, Japan
Takayuki Watanabe and Atsushi Kanzawa Department of Chemical Engineering, Tokyo Institute of Technology, O-okayama, Meguro-ku, Tokyo 152, Japan (Received 8 February 1996; accepted 25 April 1996)
The in-flight modification of titanium carbide powders was carried out in radio-frequency (rf) inductively coupled plasmas. The powders were partially melted and evaporated, and then subjected to modifications in morphology, size, and chemical composition. Both the Ar–H2 and Ar–N2 plasma treatments induced the formation of carbon-site vacancies in titanium carbide. The mixing of NH3 to Ar–H2 plasma at the plasma tail, and the Ar–N2 plasma treatment resulted in the partial substitution of carbon by nitrogen. The variation in physical and chemical modification was discussed compared with the predictions by the thermochemical analysis, and the numerically obtained heat transfer of our preceding paper.
I. INTRODUCTION
The thermal plasma with high temperature, above 10,000 K, contains reactive chemical species. Powders injected into a plasma are subjected, in-flight, to modifications of their morphology, chemical composition, and crystal structure in a short time, i.e., of the order of tens of milliseconds. With growing interest in the processing of powders under plasma conditions, it is becoming increasingly important to know of the interaction between the plasma and the powder particles.1 The variation of shape, morphology, chemical composition, and crystal structure in plasma-treated powders reflects the history of powder during the powder processing.2–4 In a previous paper for the in-flight modification of relatively coarse titanium carbide powders of a particle size under 325 mesh (45 mm),4 it was reported that the plasma treatment gave rise to the preferential removal of carbon, i.e., the formation of carbon-site vacancies, and that the elementary distribution in a particle was the unequilibrated one, i.e., the more carbon deficiency at the surface region. Titanium carbide with very high melting temperature, ,3290 K, has excellent properties, such as high electric conductivity, high hardness, and good corrosion resistance and high-temperature strength. The nonstoichiometric range of x in TiCx is very large, i.e., 0.5 , x , 1, and carbon atoms can be substituted by nitrogen and oxygen atoms, that is, the formation a)Author b)
to whom correspondence should be addressed. Present address: Department of Materials Science, Hosei University, Kajino-cho, Koganei-shi, Tokyo 184, Japan. J. Mater. Res., Vol. 11, No. 11, Nov 1996
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of TiCx Ny Oz , while its crystal structure of NaCl-type remains u
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