A Study Of Rust Stabilizing Surface Treatment For Weathering Steel

Exposed to atmosphere, weathering steel its surface can generate a good protective rust layer combined with the substrate. In some environment, it can be used directly without surface protection treatment. But when the weathering steel nakedly used in the natural environment, prior to form stable rust layer, the rust liquid will flowing, suspension and flying in the surface, and the environment will be polluted, and such kind of problem restrictis the development of weathering steel. In order to solve this problem, Japan firstly developed the rust stabilizing surface treatment for weathering steel in 1960 s. This technology can promote formation of the main ingredient of γ-Fe OOH to α-Fe OOH in rust layer and shorten the time of the formation of stable rust. But this technology is not mature in China, therefore the reseach of rust stabilizing surface treatment for weathering steel with low cost and wide application have very high economic value and engineering significance.The technology research mainly includes two aspects. The first is to choose a substance(we named it as stabilizer) that it can promote the weathering steel surface generate a compact and uniform rust layer as soon as possible. The second is to choose an organic coating material that it will be used in rust stabilizing surface treatment for weathering steel. In this dissertation, with low cost Mn Cu P weathering steel as the study steel and the main research is to choose a stabilizer. The dry/wet cyclic corrosion test(CCT), X-ray diffraction(XRD), electrochemical impedance spectroscopy(EIS) and polarization curve measurements are used, and the coastal atmosphere is the simulating environment. The stabilizer of Cr2(SO4)3 and Na NO2 have been choosen to study its effect on the rust layer stabilization process of Mn Cu P weathering steel, and the main contents for this dissertation are as follows:The effect of Cr2(SO4)3 solution on the corrosion evolution of Mn Cu P weathering steel in the simulated coastal atmosphere had been investigated by 60 dry/wet cyclic corrosion tests. The results indicated that adding Cr2(SO4)3 to the coastal atmosphere simulation solution can obviously decrease the corrosion rate of Mn Cu P steel and accelerate the surface rust layer stabilization. The addition of Cr2(SO4)3 solution on Mn Cu P steel corrosion behavior exist concentration phenomenon of extreme value. Under the experimental conditions of this study, When the simulation solution of Cr2(SO4)3 solution concentration is 0.02 mass %, the corrosion weight gain results of Mn Cu P weathering steel is smallest and firstly enters into the stabilization state.The effect of Na NO2 solution on the corrosion evolution of Mn Cu P weathering steel in the simulated coastal atmosphere had been investigated by 60 dry/wet cyclic corrosion tests. The results indicated that adding Na NO2 to the coastal atmosphere simulation solution can obviously decrease the corrosion rate of Mn Cu P weathering steel and accelerate the surface rust layer stabilization. But a high concentration of Na NO2 makes the corrosion rate of Mn Cu P weathering steel is too small, so it is adverse to form a protective rust layer in the steel surface as soon as possible. Under the experimental conditions of this study, When the simulation solution of Na NO2 solution concentration is 0.005 mass %, the corrosion weight gain results of Mn Cu P weathering steel is smallest and the first enter into the state of stabilization.In all the simulation environments, the rust layer on the surface of Mn Cu P weathering steel by α-Fe OOH, β-Fe OOH, γ-Fe OOH and Fe3O4. Adding Cr2(SO4)3 to the simulation solution, on the one hand, the existence of a small amount of Cr2(SO4)3 inhibit the formation of β-Fe OOH, and promote the formation of Fe3O4; on the other hand, the existence of a amount of Cr2(SO4)3 inhibit the reduction of the β-Fe OOH to the Fe3O4. Adding Na NO2 to the simulation solution, the existence of a small amount of Na NO2 promote the formation of Fe3O4, but the existence of a amount of Na NO2 cause weathering steel rust layer is loose, so the content of Fe3O4 gradually reduce in the rust layer.