Chemical durability of glazed surfaces

Chemical durability of glazes is previously mostly studied as corrosion of the glassy phase. In this work the focus is on corrosion tendency of the typical crystalline phases in raw glazes. Fifteen experimental glazes were ball-milled of commercial raw materials. After fast-firing in industrial kiln and traditional firing in laboratory furnace the glazes were immersed in aqueous solutions of different pH. Changes in the phase composition of the surfaces were analysed with visual examination, XRD and SEM/EDX applying a procedure allowing to study the same crystal both before and after immersion. The results indicate that wollastonite type crystals were attacked in all but the most alkaline solutions. Diopside, quartz and corundum crystals did not show any marked attack. The interfacial layer around feldspar crystals as well as the glassy phase in the glazes corroded in the most acidic and alkaline environments.