酸素処理水中におけるクロムめっきの腐食機構

抄録

Our study of chromium plating corrosion in oxgenated water involved three types of chromium plating on SUS 403 (13% chromium-steel): (1) conventional, (2) double-layer chromium-over-nickel plating, and (3) plating sealing with chromium oxide. Specimens were immersed in water (318K) with a 6 to 7ppm concentration of dissolved oxygen for a maximum of 180 days, during which weight changes were measured. After the test, chromium plating surface and cross section were observed. We found that conventional chromium plating corroded at microcracks, but double-layer chromium over-nickel plating and sealing chromium plating did not corrode. We therefore concluded that chromium plating corroded as follows Fe leached from the base metal due to electric potential created by the difference in concentration of dissolved oxygen inside microcracks and surface. Fe ion hydrolysis then produced acid inside microcracks. Chromium plating passivity was compromised by this acid, leaching chromium plating at microcracks.