Control of Fe(O,OH) 6 nano-network structures of rust for high atmospheric-corrosion resistance

A new-type of weathering steel containing 3.0 mass% Ni and 0.4 mass% Cu (“advanced weathering steel”) exhibits good atmospheric-corrosion resistance in an atmosphere containing relatively high air-born salinity. Here, we show that the high performance was successfully achieved by controlling Fe(O,OH) 6 nano-network structures of rust formed on their surfaces. A novel technique using synchrotron radiation has been developed for the in situ observation of rust-formation during wet–dry cycles. It has been revealed that the evolution of Fe(O,OH) 6 nano-network structures of rust formed on the advanced weathering steel was more unique than those of conventional weathering steel and mild steel. At an early stage of reaction, Fe 2NiO 4 and CuO phases precipitate, which provide sites for the nucleation of the Fe(O,OH) 6 nano-network resulting in the formation of rust composed of fine and dense-packed grains. The existence of Fe 2NiO 4 in the nano-network changes the ion-exchanging properties of rust from anion to cation selective. Then, the rust on the advanced weathering steel “breathes out” chloride ions from the rust/steel interface, and protects steel for more than a century by reducing the life cycle maintenance cost in an environment-friendly manner.