Abstract
Glass–ceramics raw glazes in the Na2O–K2O–CaO–Al2O3–ZnO–SiO2 system with low ZrO2 additions (0, 3 and 5wt%), used as nucleating agent, were synthesised and thermally treated at 1250°C. Willemite (Zn2SiO4), sanidine (K0.831 Na0.169Al Si3O8), gahnite (ZnAl2O4) and zircon (Zr2SiO4) were the main crystalline phases identified by X-ray investigations in the resulting glazes. An increase of the ZrO2 content from 0 to 5wt% trigged an increase of the crystallinity degree from 71.34% to 83.73% and gahnite crystallite size from 176 to 336Å. Further, morphological and structural data of these glass–ceramics were supplementary determined by SEM, MAS-NMR of 27Al and 29Si and Raman Spectroscopy. The structural modifications in terms of the glass ceramic compositions, especially small ZrO2 additions to the expense of the SiO2 and the relationship between composition and colour characteristics of the glazes are investigated and presented in this paper.
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