Hot-dip zinc-coated steel sheets are used as an outdoor industrial material, but they corrode because of acid rain. In this study, the corrosion process of hot-dip zinc-coated steel sheets in simulated acid rain solution with in-situ Raman spectroscopy has been studied. The current density of specimen decreased with constant potential holding at −0.6V vs. Ag/AgCl in simulated acid rain solution. And, the main peak, ZnSO4·7H2O was detected with in-situ Raman spectroscopy at the time of decreasing current density. Therefore, it is considered to be the case that the following equation describes the reactions that occurred. Zn2++SO42−+7H2O→ZnSO4·7H2O. The current density was decreased by ZnSO4·7H2O because the growth of ZnSO4·7H2O covered surface area of the specimen. Hot-dip zinc-coated steel sheets showed an anticorrosive effect as a result of the hot-dip zinc-coating layer being dissolved by a sacrificial anode function, and ZnSO4·7H2O was formed in the simulated acid rain solution.
The stability of chromium oxide film in subcritical and supercritical water was studied to clarify the corrosion behavior. Platinum specimen was coated with chromium oxide by metal organic chemical vapor deposition. Time variation of the weight change of the chromium oxide film during immersion in high temperature water was obtained, and the structure of the film was examined by scanning electron microscope, X-ray diffraction, and Raman spectroscopy. It was found that the chromium oxide film on the platinum specimen disappeared after the immersion in the DO (dissolved oxygen)=8000 ppb pure water at 623 K, while the weight and the structure for the specimen were almost unchanged during immersion in deaerated pure water. The loss rate of the chromium oxide film during the immersion in the pure water in the presence of dissolved oxygen at 623 K was much larger than that at 723 K. The crystallinity of the film after immersion in the pure water at 723 K was higher than that before the immersion from X-ray diffraction patterns and Raman spectra. The mechanism of the loss of chromium oxide films was discussed in terms of the dissolved oxygen in subcritical and supercritical water.
It is well known that the adhesion strength of metal plating film on Al substrate should be remarkably improved by introducing double zincate treatment as a pretreatment process for metal plating on Al. At each step of alkaline etching, desmutting, the first zincate treatment, HNO3 dipping, and the second zincate treatment in the double zincate process, depth profiles and the chemical state of the surface elements were extensively measured by XPS. A set of surface structure models in the process was proposed to explain the improvement of the adhesion strength by double zincate treatment. By dipping the first zincate film in HNO3 solution, a granular zinc deposit of about 1 μm thickness, roughly deposited on Al passivation film at the first zincate treatment, was dissolved, and zinc nano-particles were believed to be concurrently formed in the Al passivation film of about 3nm thickness. In the second zincate treatment the nano-particles should be exposed to the second zincate solution to act as nuclei for formation of a highly uniform and thin zinc film. The zinc particles were so close to the metallic Al substrate, that Dipolar coupling such as Alδ+…Oδ&minus…Znδ+ would act to improve the adhesion strength of double zincate film on Al substrate.
Si was sublimated at 1400 degrees in a vacuum, and caused to react with the VGCF. Based on the mixed rate of Si, it became clear that sublimated Si reacts to the VGCF surface partially or fully, and forms the reaction phase of SiC. As a result of evaluating wettability, it became clear that SiC phase causes the molten magnesium alloy to have good wettability.