CHEMICAL RESISTANCE OF FAST-FIRED RAW GLAZES IN SOLUTIONS CONTAINING CLEANING AGENTS, ACIDS OR BASES

Chemical resistance of fast-fired raw glazes were tested in several solutions containing
acids, bases or cleaning agents. The testing was done by a visual comparison according to a
standard method used in tile manufacture. The surfaces were also examined with SEM for
detailed information of the chemical effects of the test solutions on the glassy and crystalline
phases. The visual examination fails in some cases to reveal a corrosion attack clearly seen on
SEM analysis. Wollastonite and pseudowollastonite crystals were found to corrode in the test
solutions. If these crystals are very small, the holes left in the surfaces after the dissolution are
equally small and do not correlate with the visual experience of the surface. The corrosion of
the glassy phase, especially in acidic solutions, is also seen better in the SEM examination.
Cleaning agents often contain chelating compounds, which were found to affect the dissolution
of the glassy phase in theglazes. The corrosion of theglassy phase was also found to bestrongly
dependent on the acidity of the test solution