Distribution of carbon contamination in oxide ceramics occurring during spark-plasma-sintering (SPS) processing: II - Effect of SPS and loading temperatures

Carbon contamination during the SPS processing was investigated in the spinel, alumina and zirconia. The carbon contamination changes with the SPS conditions and the target materials. At the high heating rate of 100 °C/min, the contamination occurred over the entire area in the spinel, but only around the surface areas in the alumina and zirconia. For the spinel, the contamination is sensitive to the SPS parameters, such as the heating rate and loading conditions, but less sensitive to the sintering temperature. This suggests that the carbon contamination was caused by evaporation of CO gas from the carbon paper/dies. At the high heating rates, the carbon evaporation is enhanced due to the rapid heating, and then, the evaporated CO gases are encapsulated into the closed pores during the heating process and remain in the matrix. The carbon contamination can be suppressed by a high temperature loading even at the high heating rate.