抄録
Zirconium carbide was hot-pressed at the temperature ranging from 1450°C to 1950°C in graphite molds with nickel added by the amount of 3-10% in order to improve its sinterability and oxidation resistance.
Density-time relation during hot-pressing obtained by a dilatometric method wass consistent with the rate equation proposed by Murray et al. for hot-pressing ceramics. The equation was dD/dt=3P/4η⋅(1-D). The activation energy for densification of ZrC derived from experiments was calculated to be about 50kcal/mole.
Densification of ZrC compact was strongly accelerated by Ni addition. A body with higher density was formed with increasing amount of Ni addition. Little grain growth was observed in ZrC-Ni compacts. X-ray microanalyzer analysis showed that in specimen hot-pressed with 3% Ni at 1750°C, Ni element was not always limited to be on grainn boundaries, but was distributed rather uniformly through the specimen. Mobility of Ni element in ZrC compact seems to be great. Chemical analysis showed that residual amount of Ni decreased with increasing hot-pressing temperatures in ZrC-10% Ni compact. Nikel metal and zirconium carbide were recognized in specimen by X-ray diffraction, but no other compound of nickel was observed in the diffraction pattern. With optical microscope it was observed that most of pores in compact were distributed in the surface layer which was distinguished from inner layer. The abnormal grain growth and growth of pores in coarse grains were observed. Although open pores decreased easily and almost disappeared at the end of firing process, some of closed pores remained even at the end of the firing process, and this fact was considered to be due to the existence of Ni metal.
