Preparation of Alumina Ceramics via a Two-Step Sintering Process

This paper investigates grain growth and densification kinetics in alumina ceramics subjected to spark plasma sintering (SPS) and conventional pressureless sintering (CS). The findings reveal that, under both sintering conditions, grain growth primarily occurs after reaching the sintering 'freezing point'. The analysis of densification kinetics indicates that the activation energies of densification of alumina ceramics are 173.6 KJ/mol and 261.2 KJ/mol during the early stage, and 362.2 KJ/mol and 383.7 KJ/mol in the late stage for SPS and CS conditions, respectively. Therefore, a two-step sintering method (TSS) is proposed, where SPS rapidly sinters alumina powder to reach the grain growth 'freezing point', and then, the sintered bodies are subjected to CS to obtain dense alumina ceramics. The results show that the flexural strength of alumina prepared using this TSS can reach 489.6 MPa, about 19% improvement over those processed solely through CS.