ISSN 0862-5468 (Print), ISSN 1804-5847 (online) 

Ceramics-Silikáty 47, (4) 121 - 131 (2003)

Krajewski Adriano 1, Ravaglioli Antonio 1, Mazzocchi Mauro 1, Labanti Martino 2, La Torretta Teresa 2, Bezzi Giovanni 2, Minoccari Gianloris 2
1 ISTEC-CNR , Institute of Science and Technology for Ceramics - Italian National Research Council, Via Granarolo 64, 480 18 Faenza, Italy
2 ENEA, Department of Engineering of Materials and Processes - National Agency for Environment and Energy, Via Ravengana 186, 480 18 Faenza, Italy

Keywords: Bioactive glass, Bioglaze®, Bioactive coating, Stabilised zirconia

The aim of this research is to study in detail the behaviour of glassy bioactive coatings (Bioglazes®) on zirconia substrates with different stabilising agents. In the case of tetragonal Ce-PSZ, some phenomena arose by applying a glaze coating. The stabilising CeO₂ undergoes to an -even partially reversible- autoredox process (CeO₂-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.

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