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Examining the corrosion behaviour of Al2O3 + 10 per cent ZrO2 in aqueous solutions

Untersuchungen zum Korrosionsverhalten von Al2O3 + 10 Prozent ZrO2
: Graas, T.; Hollstein, T.; Pfeiffer, W.; Reckziegel, A.

Ceramic forum international : CFI. Berichte der Deutschen Keramischen Gesellschaft 74 (1997), Nr.11/12, S.723-726 : Ill., Lit.
ISSN: 0173-9913
Fraunhofer IWM ()

The corrosion behaviour of a dispersion ceramic, Al2O3 + 10 mass-per cent ZrO2, is described. The loss of mass, the strength degradation and the phase changes are measured at temperatures between 25 deg C and 100 deg C in concentrated and 1 m acids of phosphor and sulphur and caustics of sodium. Only slight grain boundary attacks occurred, and no attacks on the grains. This is attributed to the very low content of glassy phase, which is below 300 ppm in this material. The dissolution of the glassy phase at 90 deg C leads to a measurable loss of mass, which increases from NaOH over H2SO4 to H3PO4. The partly decreasing and increasing strength values, measured with 4-point bending, can be explained by two different processes. Strength degradation is due to the dissolution of glassy phase resulting in an increase of effective surface flaw size. Simultaneous, the increase of strength takes place due to the dissolution of the stabiliser Y2O3, which initiates a phase change from the tetragon al phase in the mono-clinic phase with an increase of compressive residual stresses. Y2O3 seems to be dissolved also in boiling pure water and possible to be deposited as Y(OH)3 on the surface. This is indicated both by the phase changes and by the gain of mass.