Corrosion Behavior of Alumina Ceramics in Caustic Alkaline Solutions at High Temperatures

Abstract

The corrosion rate and changes in the microstructure and fracture strength of alumina ceramics (93.0% A1203 and 99.5% A I 2 0 , j were studied in O.lm to 25m NaOH solutions at 150°C to 200"C, where m = mol/(kg of H20j. The attack of the caustic alkaline solution started at the grain boundaries. Consequently, the corrosion resistance increased with decreasing SiO, content in Al2O3 ceramics, and the corrosion resistance of 99.5% pure A1203 was similar to that of Si3N4 ceramics. Since large pits are formed by corrosion, the surface area increased first and the apparent corrosion rate increased with time in the initial stage of the corrosion. The corrosion rate of A1203 increased linearly with increasing NaOH concentration, and the activation energy was 102 kJ/mol. The fracture strength of corroded AIZO3 decreased monotonically as the degree of dissolution of alumina increased. [

Corrosion of Ceramic Materials

“…Studies of the corrosion resistance of Si 3 N 4 materials revealed a strong relationship between the stability of the grain boundary and the corrosion resistance of the ceramic material (Galuskova et al, 2011b;Herrmann & Schilm, 2009;Herrmann et al, 2006;Herrmann, 2005;Herrmann, 2012;Kitaoka et al, 1994;Kleebe et al, 1993;Nagae, Koyama, et al, 2006;Sato Figure 14 Potential effect of corrosion on the integrity of zirconia components (after Chevalier et al, 2009Chevalier et al, ). et al, 1988aChevalier et al, , 1988bSato et al, 1992;Schilm et al, 2003;Schilm et al, 2004a;Schilm et al, 2006;Schilm et al, 2007;Schilm, 2004;Seipel & Nickel, 2003;Shimada & Sato, 1989;Somiya, 2001).…”

“…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).…”

“…Besides the described zirconia ceramics, several composites are used, with the most prominent being zirconia-toughened alumina containing 10-20 vol% ZrO 2 (ZTA) and alumina-toughened zirconia (ATZ). Y-TZP is widely used in cutting applications and dental implants and hence the hydrothermal stability of this material has been & Yoshimura, 1996;Sato et al, 1988b;Sato, Sato, Tamura, & Okuwaki, 1992;Sato, Tokunaga, Endo, et al, 1988a, 1988bSchilm et al, 2006;Schilm et al, 2007;Schilm, 2004;Schilm, Herrmann, & Michael, 2004a, 2004bSeipel & Nickel, 2003;Sharkawy & El-Aslabi, 1998;Shimada & Sato, 1989 Figure 12 Strengths of different ceramic materials after corrosion in 1 N NaOH, H 2 SO 4 and water at elevated temperatures (temperature is given in the graph) after 200h .…”

Corrosion of Si3N4-ceramics in aqueous solutions

“…5,7,8 The proposed mechanism of the formation of a stable hydrated SiO 2 -rich network is also in agreement with the different corrosion behaviour of Si 3 N 4 ceramics in HF and under hydrothermal conditions. 4,11,15,[24][25][26][27] The process of formation of a stable passivating SiO 2 network in the ceramics is strongly accelerated by an increasing concentration of SiO 2 in the grain boundary of the ceramics (Fig. 13).…”

“…Linear corrosion kinetics are generally explained by the interfacial controlled dissolution of the grain boundary phase. [24][25][26][27] The corrosion rate can be explained based on the stability of the oxynitride glassy grain boundary phase and can be directly related to the corrosion rate of the oxynitride glasses with the same composition as the grain boundary (see part 1). 1 For high corrosion depth and geometries like balls or bending bars the shrinking core effect has to be taken into account.…”