PREPARATION AND MICROSTRUCTURE OF SPHERIC AL COMPOSITES IN THE SYSTEMCARBON-ZIRCONIUM DIBORIDE

In order to prepare carbon-ceramics composites having spherical shape, a powder mixture of carbon and zirconium diboride (ZrB2) was heat-tre ated at 2400, 2600 and 2800 degrees C. Carbon black, calcined pitch co ke and natural graphite were used. Above 2600 degrees C, spherical bod ies of silver color, about 20 mu m-2 mm in diameter, were formed for a ll carbon powders. The spherical body was the spherical composites in the system carbon-ZrB2; the surface was covered with polyhedral graphi te and the inside was composed of small graphite and ZrB2 particles. T he formation process of the spherical composites is considered as foll ows: ZrB2 in contact with carbon fuses in the temperature range of 240 0 to 2600 degrees C, carbon dissolves in the fused ZrB2, the ZrB2 cont aining carbon changes into spheres by surface tension, and the carbon dissolved in ZrB2 separates out as graphite during cooling.