Corrosion of the crystalline phases of matte glazes in aqueous solutions

Chemical durability was determined for fast and conventionally fired matte raw glazes in acidic to alkaline aqueous solutions. According to XRD, the main crystalline phases in the glazes were diopside, plagioclase, anorthite, wollastonite, and pseudowollastonite. SEM-EDXA and whitelight confocal microscopy were used to analyze the surfaces after immersion in the aqueous solutions. The ionic concentrations in selected solutions after immersion were determined by ICP-AES. Diopside was not attacked by the test solutions. Plagioclase started to corrode along the crystal interfaces in the most acidic environments. Wollastonite crystals with different crystal habitus and slightly different chemical composition formed depending on firing cycle and composition of the glaze. In fast firing, tiny columnar wollastonite crystals were formed. These crystals were attacked in acidic to slightly alkaline environments. In conventionally fired glazes the wollastonite crystals were dendritic. These crystals were attacked only by acidic solutions. Pseudowollastonite with poor chemical resistance formed only in magnesia-free glazes.