Two-stage master sintering curve applied to two-step sintering of oxide ceramics

Tetragonal (3 mol% Y2O3) and two cubic zirconia (8 mol% Y2O3) as well as alumina green bodies were used for the construction of the Master Sintering Curve (MSC) created from sets of constant-rate-of-heating (CRH) sintering experiments. The activation energies calculated according to the MSC theory were 770 kJ/mol for Al2O3, 1270 kJ/mol for t-ZrO2, 620 kJ/mol and 750 kJ/mol for c-ZrO2. These values were verified by an alternative approach based on an analysis of the densification rate in the intermediate sintering stage. The MSCs established from the Two-Step Sintering (TSS) experiments showed at high densities a significant deflection from those constructed from the CRH experiments. This deflection was explained by lower sintering activation energy in the closed porosity stage. A new two-stage MSC model was developed to reflect the change in sintering activation energy and to describe TSS. The efficiency of TSS of four materials under investigation was correlated with their activation energies during the final sintering stage.