Investigation of Rust Layer Formed on Weathering Steel Coated with a Surface Treatment Promoting Protective Rust Formation
Takayuki KAMIMURA, Takashi DOI, Kazuyuki KASHIMA, Norio WAGURE, Shuichi HARA, Katsuya NAKAHARA, Ryuichi ANDO and Hideaki MIYUKI
Abstract:The rust layer formed on the weathering steels coated with a surface treatment promoting protective rust formation exposed at a coastal region containing 0.4 mg/dm2/day of air-borne salt particles for 9 years has been investigated by means of X-ray diffraction, Raman spectroscopy, Electron probe micro-analysis and Mossbauer spectroscopy. In the surface treatment, Cr2(SO4)3 is contained to form the protective rust layer. Corrosion loss vs. time curve of surface treated weathering steels follows Y = AXB type function, where X is the exposure duration, Y is the corrosion loss, A and B are the constants. The surface of the treated weathering steels were covered with triple layers; outer rust layer, surface treatment film and inner rust layer. The outer rust layer consisted of mainly ƒÀ-FeOOH, and the inner one mainly ƒ¿-FeOOH. Cr enrichment was observed in the inner rust layer. It can be said that the surface treatment works well to promote the formation of Cr-containing ƒ¿-FeOOH layer formed on weathering steel. Key Words:Weathering steel, Surface treatment, Air-borne salt, Rust layer, ƒ¿-FeOOH, X-ray diffraction, Raman spectroscopy, Mossbauer spectroscopy