Control of Fe(O,OH)6 nano-network structures of rust for high atmospheric-corrosion resistance
Masao Kimura, Hiroshi Kihira, Noriaki Ohta, Misao Hashimoto, Takehide Senuma : Corrosion Science, 47 (2005) 2499–2509
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.
Fig. 2. Geometry of the generalized grazing-incidence-angle X-ray scattering (G-GIXS). Intensities with scattering angles (2θa, 2θb, . . .) in a wide area are measured simultaneously by controlling the incidenceangle (αi) independently.
Fig. 3. Parts of the Debye-rings of XRD from the specimen during the 1st wet–dry cycle: (a) t = 0, (b) t = 30 min, and (c) t = 90 min. The horizontal lines show the locations and intensities calculated from the reference material.
Fig. 4. Schematic diagram of the evolution of the Fe(O,OH)6 nano-network of rust formed on the advanced weathering steel in an atmosphere containing relatively high air-born salinity (above), which is compared to conventional weathering steel (middle) and mild steel (below) exposed in milder conditions.