MICROCHEMISTRY AND MICROSTRUCTURE OF SOME OPAQUE GLAZE TILE INTERFACES IN RELATION TO THEIR PHYSICAL-PROPERTIES

Physical properties of some double- and once-fired glazed tiles were a ssessed 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 a nd thermal expansion of glazes, as well as crazing resistance and glos s of glaze surfaces. The double- and once-fired glaze layers are stron gly bound to their ceramic tiles, as indicated by high resistance to c razing. The application of zircon-ZnO opacifying mixtures in the prese nce of 5.0-8.0 wt% B2O3 leads to maximizing the gloss of glaze surface s. Increasing B2O3 content enhances bubble formation whereas a mat lay er results at the surface of once-fired glazes containing higher zirco n and ZnO contents at the expense of B2O3. The recrystallization of si licate phases, especially in double-fired glazes, is hindered by minim izing the lime and alkali oxides content in the presence of up to 10wt % ZnO.