Hydrothermal Corrosion of Alumina Ceramics

Abstract

The corrosion behavior and strength degradation of alumina ceramics with 99%, 99.9%, and 99.99% Al2O3 were studied in water at 300°C and 8.6 MPa for 1 to 10 d. The weight loss in alumina ceramics was mainly attributed to the dissolution of SiO2 and Na2O grain‐boundary impurities. Intergranular corrosion proceeded in the alumina ceramics by preferential attack at the grain boundaries. The extent of the strength reduction for corroded alumina ceramics was related to the impurity level in the alumina ceramics.

Hydrothermal corrosion of zirconia-toughened alumina (ZTA) at 200°C

“…1 The comparatively high mass loss found for small exposure times (t ≈ 0) indicates a fast solution of a surface layer damaged by grinding and polishing and also of minor impurities. The constant bending strength indicates that this material shows low corrosion effects at these conditions.…”

“…Alumina ceramics have excellent hardness, corrosion resistance and wear properties, but lower strength and toughness than zirconia or zirconia-toughened alumina (ZTA). 1 The corrosion resistance of alumina under hydrothermal conditions decreases with increasing impurity content of the ceramics and is controlled by the dissolution of the amorphous grain boundary phases, which is often dominated by SiO 2 and Na 2 O. 1,2 Tetragonal zirconia ceramics (TZP) show a much higher toughness and bending strength but are known for their low stability under corrosive conditions.…”

“…1 The corrosion resistance of alumina under hydrothermal conditions decreases with increasing impurity content of the ceramics and is controlled by the dissolution of the amorphous grain boundary phases, which is often dominated by SiO 2 and Na 2 O. 1,2 Tetragonal zirconia ceramics (TZP) show a much higher toughness and bending strength but are known for their low stability under corrosive conditions. This general statement is based on investigations of the corrosion behaviour of Al 2 O 3 and Y-TZP (yttria-stabilisedtetragonal-zirconia-polycrystals) in NaOH and acids at 150-300 • C. [2][3][4] The hydrothermal ageing of Y-TZP ceramics is connected with internal stresses due to the cubic/tetragonal to monoclinic (c/t → m) phase transformation of zirconia.…”

Corrosion of Ceramic Materials

“…Even in supercritical water, they exhibit a high-corrosion resistance (Franks & Gan, 2007;Galuskova et al, 2011a;Genthe & Hausner, 1989;Genthe & Hausner, 1992;Hirata et al, 2003;Hoppert, 2010;Kitaoka et al, 1992;Mikeska et al, 2000;Mikeska, 1999;Oda & Yoshio, 1997;Sato et al, 1991). Silica and alkaline additives in alumina often used to reduce the sintering temperature are leached out in acids and under hydrothermal conditions (Figures 9 and 13).…”

PYROMETALLURGICAL METHOD FOR THE RECOVERY OF ALUMINUM FROM Fe2O3/α-Al2O3 CATALYST

“…This method was applied because dissolving alpha alumina with other classical leachants such as HCl or H2SO4 was not effective (Boukerche et al, 2010, Larba et al, 2013. Alumina based ceramics was found to corrode under hydrothermal conditions because of the dissolution of the impurities existing at the grain boundaries such as MgO, CaO, SiO2 and Na2Os (Oda and Yoshio 1997;Genthe and Ausner 1992) while the dissolution of Al 3+ in bulk material was found to be negligible (Curkovic et al, 2008). The alumina support used in this study was a pure product which explains the fact that under moderate conditions (hydrothermal treatments with HCl or H2SO4 solutions) no dissolution was observed and even under drastic conditions like those tested in this work it was not totally dissolved.…”