Self-propagating high-temperature synthesis of nano-sized titanium carbide powder
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The combustion process of a titanium–carbon system with sodium chloride as an inert diluent was investigated. The combustion laws and microstructure of final products according to diluent content were obtained. It was shown that sodium chloride not only decreases combustion temperature but also makes effective protective shells around primary carbide crystals and keeps this ultrafine structure up to the end of combustion. As a result, nano-sized titanium carbide powders were successfully obtained.
I. INTRODUCTION
Titanium carbide is widely used for manufacturing hard alloys, cutting tools, and carbide steels due to its unique properties such as high melting point, extreme hardness, low density, and high resistance to corrosion and oxidation. Recently, the requirements for powders, including titanium carbide, have changed with the development of modern ceramic engineering. Submicron and nano-sized powders have appeared at the center of scientific attention due to their superior mechanical properties such as strength, toughness, and creep resistance. The basic synthesis methods for titanium carbide powders are melt crystallization, chemical vapor deposition (CVD), laser, carbon reduction, self-propagating hightemperature synthesis (SHS), etc.1,2 However, the synthesis of submicron and nano-sized titanium carbide powders is a complex task, which requires a special approach, independent of the synthesis method. From this point of view, SHS is not an exception, although is widely used for synthesis of both simple and complex ceramic composite powders.3–8 The combustion of titanium with carbon under the SHS mode has been studied in detail.9–12 It has been shown that titanium carbide phase formation proceeds by liquid titanium and solid carbon reaction mechanisms. Two stages of titanium carbide crystallization were found; the initial and the final.13 In the initial stage of crystallization, the size of carbide crystals is comparable to the size of the initial carbon (approximately 0.1 m). However, during the combustion, these crystals grow rapidly, and the carbide crystal size becomes more than 10 m in the final stage. For the preservation of primary titanium carbide structure, various approaches, such as dilution of the initial mixture by the final product and full or partial replacement of carbon by organic polymers J. Mater. Res., Vol. 17, No. 11, Nov 2002
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(polystyrene, polyvinylchloride, polytetrafluoroethylene) have been conducted. 9,14,15 In these, the prevention of particle size growth to submicron size during the combustion of titanium carbide has not been successful. The minimal size of particles obtained ranged between 1–3 m. In this work, we report a process for obtaining nanosized titanium carbide powders, using elemental powders of Ti and C under the combustion mode with sodium chloride addition as an inert diluent.
II. EXPERIMENTAL
The experiments were carried out in a constant pressure reactor, shown schematically in Fig. 1, using cylindrical p
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