Effect of residual carbon on the sintering behavior of MOX pellets

Sintering behavior of MOX compacts containing different amounts of carbon (290–1735 ppm) was investigated at temperatures from 1073 to 2023 K to study the effect of residual carbon. Specimen shrinkages were measured with a non-contact type optical dilatometer during heating. The compact shrinkage at temperatures from 1273 to 1523 K was about six times larger in the two specimens with high residual carbon content than in the two with low content. This behavior could be understood by considering that shrinkage of the former specimens was enhanced in this temperature range by the decrease of O/M ratio due to the evolution of CO gas and consequently the significant increase of the metal ion inter-diffusion coefficient. In the specimens with low residual carbon content, the amount of CO gas evolution was too small to affect the inter-diffusion coefficient. This difference in shrinkage between the two kinds of specimens was also discussed from a theoretical model applied to the initial sintering stage of ceramics.