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, Fe2NiO4 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 Fe2NiO4 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.