Takashi Sakaki1, Yozyu Shimizu1 and Kazutaka Sakiyama2
1Technology Laboratories, Toyo Soda Manufacturing Co., Ltd., Yamaguchi
The corrosion behaviour of various commercial alloys was studied by measurements of potentio-dynamic polarization curves, the change in corrosion potential with time and the average corrosion rate. The corrodent used was 48%NaOH solution at temperatures between 373 and 473 K, and the following results were obtained. The corrosion resistance of stainless steels was improved by adding nickel and chromium. Especially, immersion tests showed that ferritic stainless steels containing 27--30% chromium and austenitic stainless steels containing nickel more than 20% possessed excellent corrosion resistance. On the other hand, addition of molybdenum and copper to the stainless steels gave no protective effects as to the alkaline corrosion. When the corrodent was a 48%NaOH solution obtained by the diaphragm process, NaClO3 contained in the solution acted as an oxidizer. Its oxidation powder increased somewhat the tendency of the high chromium steels to become passive, but promoted dissolution of nickel.
concentrated alkaline solution, corrosion resistance, effect of NaClO3, austenitic stainless steel, ferritic stainless steel, anodic polarization, immersion test, corrosion chart
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