抄録
Powdered alumina (A), magnesia (M) and silica (S) were selected among the metal oxides used in the ceramic industry to study how the bulk density and tensile strength of green body change with heat treatment. It seems that a desorption temperature of the surface hydroxide layer (TOH) and the melting point (Tm), which are inherent to each powder, correlate with the change in green body characteristics. The results are as follows:
1) The tensile strength of green body with the same porosity decreases until 0.3Tm as the heat treatment temperature increases; above this, it increases. This temperature (0.3Tm) is equivalent to the one at which surface diffusion begins.
2) The hydrophilic group of the surface decreases remarkably when the powder is heat-treated over TOH, and the adsorbed water in the powder decreases in the same atmosphere. Therefore, the density and strength of the green body are affected differently by the same humidity condition.
3) The density and strength of A, M and S are not changed in the same way by heat treatment when green bodies are fabricated at the same compression force. This may be because 0.3Tm is lower than TOH for S but higher for A and M, or because the remainder between these two temperatures is different in degree for each powder.
