Preparation of novel calcia-stabilized TZP ceramics

The preparation of tetragonal zirconia polycrystal (TZP) ceramics stabilized by the addition of calcia is presented. These novel ceramics were obtained by means of a fast-firing treatment applied to compacts of nanocrystalline powders with a composition of ZrO₂ — 4 mol% CaO. Powders were synthesized by a nitrate-citrate gel-combustion process and they exhibited the tetragonal phase at room temperature due to their small crystallite size (12–13 nm). These powders were compacted by uniaxial pressing and fired at 1400–1500 °C for 3–5 min, obtaining fine-grained, dense ceramics, which also retained the metastable tetragonal phase. Longer heat treatments increased the average grain size leading to large amounts of the monoclinic phase. It was also found that the critical grain size for the tetragonal-to-monoclinic transformation is about 150 nm for this composition. This small value explains the necessity of a fast-firing treatment of the samples, allowing densification but avoiding a significant grain growth.