Kinetics and Mechanism of a Sintering Process for Macroporous Alumina Ceramics by Extrusion

The paper describes an evaluation of kinetic parameters for sintering from the analysis of stepwise isothermal dilatometry data for the pore-forming process of macroporous alpha-Al₂O₃ ceramics fabricated by extrusion. The experimental results demonstrated that isothermal shrinkage data for the sintering process can fit the following rate equation: d Y /d t = nK ( T ) Y (1 - Y )[(1 - Y )/ Y ]^{1/ n} , where Y is the fraction of volume shrinkage. Kinetic parameters, i.e., the average exponent n and the activation energy E for the pore-forming process, were calculated to be 0.232 and 415.5 kJ/mol, respectively, in the temperature range of 1200-1400°C. The results also show the equivalence between isothermal sintering and stepwise sintering in alumina. In the latter case the temperature is increased in steps over a period of time. The equivalence is derived from understanding how the sintering rate changes with porosity. The sintering mechanism in different temperature ranges is discussed, with reference to microstructure development. The bend strengths of porous ceramics with different porosities are also presented.