Low-temperature synthesis of nanodispersed titanium, zirconium, and hafnium carbides

Nanosized refractory titanium, zirconium, and hafnium carbides were manufactured from highly dispersed metal dioxide-carbon starting mixtures at moderate temperatures of 1200A degrees C or lower. The products were characterized by powder X-ray diffraction, elemental analysis, and transmission electron microscopy. The average size of particles (in nanometers) manufactured at 1200A degrees C was as follows: for TiC, 13 +/- 4; for ZrC, 17 +/- 3; and for HfC, 16 +/- 3; the average crystallite size (in nanometers) was as follows: for TiC, 8 +/- 2; for ZrC, 5 +/- 2; and for HfC, 8 +/- 3. Thermodynamic modeling was performed for the synthesis of Group IVB carbides via carbothermal reduction of the corresponding oxides. The results show that in the titanium dioxide-carbon system, for example, titanium monocarbide formation is possible at a temperature as low as 850A degrees C (p = 10(-4) MPa). Highly dispersed metal dioxide-carbon starting mixtures were prepared using solgel technology from metal alkoxyacetylacetonates in the presence of a polymeric carbon source.