Microchemistry and microstructure of some opaque glaze/tile interfaces in relation to their physical properties

Abstract

Physical properties of some double- and once-fired glazed tiles were assessed in the light of the microchemistry and microstructure of their interfaces as investigated using a computer-controlled electron-probe microanalyzer. The properties investigated are melting temperatures and thermal expansion of glazes, as well as crazing resistance and gloss of glaze surfaces. The double- and once-fired glaze layers are strongly bound to their ceramic tiles, as indicated by high resistance to crazing. The application of zircon-ZnO opacifying mixtures in the presence of 5.0–8.0 wt% B 2O 3 leads to maximizing the gloss of glaze surfaces. Increasing B 2O 3 content enhances bubble formation whereas a mat layer results at the surface of once-fired glazes containing higher zircon and ZnO contents at the expense of B 2O 3. The recrystallization of silicate phases, especially in double-fired glazes, is hindered by minimizing the lime and alkali oxides content in the presence of up to 10wt% ZnO.