Susumu Morioka1, Yoshinobu Sawada1, Katsuhisa Sugimoto2 and Tôji Katô2
1Department of Metallurgy, Faculty of Engineering, Tohoku University, Sendai
Effects of Al2O3 content, worked structure and heat treatment on the corrosion resistance of SAP containing 1.2∼15.5%Al2O3 in pure water at elevated temperatures of 200°∼300°C were studied by measuring the weight gain. Surface corrosion products were analysed by means of electron diffraction and infrared absorption spectra and further observed by electron microscopy. The results obtained are summarized as follows:
(1) The corrosion resistance of the rolled SAP and the pressed SAP varied with the Al2O3 content and was worst at 3.5∼6.8%Al2O3, while that of the extruded SAP was not affected with its Al2O3 content and was best of the three. (2) The corrosion resistance of the rolled SAP was improved by annealing, while that of pressed SAP could not be improved. (3) The surface film on SAP produced by corrosion was made up mostly with α-Al2O(OH)2 (boehmite) and contained a small amount of γ-Al2O3 resulting from the SAP matrix. (4) The grain size of the surface film was fine for SAP of good corrosion resistance but coarse for that of less corrosion resistance.
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