NaCl and Na2SO4 solution effect on weathering steel visual appearance when the ambient temperature changes cyclically

Abstract

Visual appearance—colour and texture variation—of weathering steel was compared by testing weathering steel samples in aggressive and non-aggressive conditions, and cyclical changes of ambient temperature. This paper introduces a new method for determining visual appearance of weather-resistant steel in different environmental conditions. Weathering steel samples were tested in H2O, 3% NaCl and 3% Na2SO4 solutions under ambient temperature changing from +20°C to −20°C per day. The structure of steel surface viewed under optical microscope revealed corrosion products in all steel samples. X-ray diffraction analysis of corrosion products revealed the presence of oxy-hydroxides, such as lepidocrocite (ɣ-FeO(OH)), goethite (α-FeO(OH)) and magnetite (Fe3O4) in different environment. Optical microscopy images of corroded surfaces had different visual appearance and orange, yellow, sandy, black or anthracite colours, which indicate that the corrosion products primarily contain lepidocrocite (ɣ-FeO(OH)), goethite (α-FeO(OH)) and magnetite (Fe3O4). EDS analysis revealed that the rust of samples kept in 3% NaCl solution had the highest amount of iron ions.

Keywords

• weathering steel
• nacl and na2so4 solution
• visual appearance
• xrd analysis
• eds analysis