Influence of zirconia CeO2 lattice stabilizing agent on bioglaze coating

The aim of this research is to study in detail the behaviur of glassy bioactive coatings (Bioglazes) on zirconia substrates with different stabilising agents. In the acse of tetragonal Ce-PSZ, some phenomena arose by applying a glaze coating. The stabilising CeO2 undergoes to an - even partially reversible - autoredox process (CeO3 - Ce2O3), caused by migration of oxygen during the glazing process (ZrO2 is known as a proton and oxygen radical conducer at high temperatures), with a macroscopic effect of a grey-green colouring of the Ce-PSZ substrate below the coated surface ("affected volume"). The migration of oxygen can assume an extent for which at the glazing temperature, about 1300°C, it is possible the chemical equilibrium shifts towards formation of Ce2O3. Grey-green is the own colour of Ce2O3. By eliminating the sealing action of the glaze towards atmosphere, oxygen can diffuse back inside Ce-PSZ lattice, recovering the chemical and thermodynamic equilibrium conditions with CeO2 and Ce2O3 and inducing a decolouring effect in the Ce-PSZ ceramic back to a light colour. The bioactive glass utilised to produce the coatings is a calcium-silicophosphatic one, coded AP40.