FTIR and MAS NMR study of the zinc aluminosilicate ceramic glazes

Raw glazes in the SiO2Al2O3CaOMgONa2OK2OZnO system with ZnO additions (0, 5, 10, 15 and 20 wt%) were synthesized and thermally treated at 1230 °C. Diopside (MgCaSi2O6), β-quartz (the low-temperature form), gahnite (ZnAl2O4) and α-willemite (Zn2SiO4) were the main crystalline phases identified by X-ray investigations in glazes. An increase of the ZnO content from 10 to 20 wt% into the chemical composition of glazes trigged crystallization of the macroscopically visible α-willemite (Zn2SiO4) crystals. Microstructure and structure of the glazes were determined by SEM-EDS, FTIR and 29Si and 27Al MAS NMR spectroscopy. Analysis of MAS NMR spectra showed that silicon (Si4+) and aluminum (Al3+) ions occurred only in tetrahedral coordination in a glassy matrix of all resulting glazes (glass-network ions). The zinc ions (Zn2+) depolymerized the glassy matrix of glazes (network-modifying ions).