Preparation of refractory carbide fibers by thermal decomposition of transition metal (Ti, Zr, Hf, Nb, Ta) alkoxide-cell
- PDF / 296,405 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 83 Downloads / 156 Views
MATERIALS RESEARCH
Welcome
Comments
Help
Preparation of refractory carbide fibers by thermal decomposition of transition metal (Ti, Zr, Hf, Nb, Ta) alkoxide-cellulose precursor gel fibers Y. Kurokawa, S. Kobayashi, and M. Suzuki Faculty of Engineering, Tohoku University, Aoba Sendai 980, Japan
M. Shimazaki and M. Takahashi Faculty of Science, Japan Women’s University, Mejirodai, Bunkyoku, Tokyo 113, Japan (Received 30 May 1996; accepted 30 April 1997)
Gel fibers have been prepared by extruding cellulose acetate spinning solution into transition metal (Ti, Zr, Hf, Nb, Ta) acetone solution as a coagulation bath. Gel formation must be due to the coordination of metal to OH and CO groups on the pyranose ring. The resultant gel fibers have been converted into carbide fibers by pyrolyzing them in Ar and N2 atmospheres at temperatures lower than for powder processing. This precursor gel can give a molecular scale mixture of metal and carbon sources.
I. INTRODUCTION
Carbon fibers are synthesized by the thermal decomposition of PAN- and pitch-based precursor fibers, and SiC and Al2 O3 fibers are similarly synthesized from precursors of organometallic polymers and Al2 O3yPVA composites,1,2 respectively. They have been exclusively studied for reinforcing materials such as metals, ceramic and polymer. However, there are a few studies of the other inorganic fibers. The preparation of TiC fiber has been attempted using an organic compound obtained from the ester exchange reaction of titanium alkoxide and diacetate as a precursor.3 This precursor is not spinnable because it is insoluble in common solvents and decomposes near its melting point. Alginic acid is known to form a gel when in contact with polyvalent cations such as Ca2+ . The alginate gels exchange with titanium ions, and the exchanged gel fibers are thermally decomposed into TiO2 fiber.4 However, the exchange capacity is low and thus the weight loss is large, and the resultant fibers are brittle. SiCyC and TiCyC composite fibers can be prepared by pyrolysis of metal (Si, Ti) alkoxide-impregnated phenolic resin fiber (Kynol).5,6 Similarly, SiC fiber can be prepared by reacting Kynol fiber with silicon monoxide gas under elevated temperature.7 The sol-gel derived oxide fibers have been prepared from spinnable viscous solutions obtained by controlling the hydrolysis and polycondensation of the alkoxide solution.8 TiN fiber has been prepared by heat-treating the sol-gel derived TiO2 fiber in NH3 atmosphere.9 However, continuous spinning is difficult because long periods are required for the sol-gel conversion. Most transition metals of the fourth (Ti, Zr, Hf) or fifth (Nb, Ta) row of the periodic table form carbides and nitrides in these groups with extremely high melting point (3000–4000 ±C), excellent high tem760
http://journals.cambridge.org
J. Mater. Res., Vol. 13, No. 3, Mar 1998
Downloaded: 07 Apr 2015
perature strength, good corrosion and good hardness.10 However, they cannot be produced as fibers by conventional powder melting of fine powderypolymer co
Data Loading...
