Effect of Gravity on Titanium Carbide Foams by Self-propagation High-temperature Synthesis
- PDF / 431,653 Bytes
- 8 Pages / 612 x 792 pts (letter) Page_size
- 36 Downloads / 155 Views
MATERIALS RESEARCH
Welcome
Comments
Help
Effect of gravity on titanium carbide foams by self-propagation high-temperature synthesis Yasuhiro Tanabe,a) Takashi Sakamoto, Nobuko Okada, Takashi Akatsu, and Eiichi Yasuda Center for Materials Design, Materials and Structures Laboratory, Tokyo Institute of Technology, 4259, Nagatsuta, Midori, Yokohama 226-8503, Japan
Seiichi Takasu and Takayuki Sabato Developing Section, Production Department, Nichiden Machinery, Ltd., 85, Minami Yamada-cho, Kusatsu, Shiga 525-8511, Japan (Received 19 August 1998; accepted 26 October 1998)
Titanium carbide foams are synthesized by a self-propagation high-temperature synthesis technique using carbon black, which generates gases during the synthesis. The synthesis is performed under terrestrial and microgravity conditions. The effects of gravity on the synthesis are evaluated in this study. The foaming is mainly caused by H2 O and CO gases from the carbon black. The elongation of the products increases with decreasing environmental pressure and increasing amount of generated gases. Since the gas flows out along the direction of the combustion wave propagation, the products expand only along this direction. The propagation velocity of the combustion wave increases with increasing amount of generated gases and environmental pressure, which is due to the amount of molten Ti transporting into the reaction/preheat zone. Under higher environmental pressures, thermal convection of the environmental gases mainly affects the propagation velocity. However, at lower pressures, the behavior of the molten Ti has a great effect compared with the gases surrounding the specimens.
I. INTRODUCTION
Since self-propagation high temperature synthesis (SHS), combustion synthesis, usually does not need furnaces for synthesis,1 it is a promising method for material synthesis under limited environmental conditions of energy and/or space, e.g., in a space station. Products by SHS are usually porous, because the density of the products is different from those of their raw materials. Almost all SHS research has focused on producing high density. Little work has been performed on producing porous ceramic materials by SHS, which have the advantage of being lightweight and are applicable as heat insulators or reinforcements of metal-based composites. Many studies have been done on titanium carbide (TiC) synthesis by SHS as a model material2 because titanium (Ti) and carbon powders are not very expensive and the formation heat of TiC is large (185 kJymol1 ). However, most reports are on no gas formation processes.3–6 Dunmead et al. reported that diffusion of carbon into molten Ti controls the TiC formation rate under 2711 K.3 Propagation velocity of the combustion wave is controlled by the reaction between carbon and molten Ti in a high-temperature, thin layer, reaction zone of less than 1 mm.4 As heat generated in the reaction a)
Address all correspondence to this author.
1516
http://journals.cambridge.org
J. Mater. Res., Vol. 14, No. 4, Apr 1999
Downloaded:
Data Loading...
