Dynamic porosity variations in ceramics

A silicon carbide disk was sintered from 2090 to 2190 C in 25 C steps. After each sintering step the disk was examined using a precision acoustic scanning system to determine acoustic attenuation and velocity. The bulk density was found to vary nonmonotonically with sintering temperature. During the sintering process, the density varied as much as 10 pct from its value at 2090 C. Local density fluctuations were observed to occur in an organized and history-dependent way. These local density fluctuations varied up to + or - 7 pct of the bulk density and were made visible by acoustic attenuation and velocity mapping.