It is reviewed the contribution of the corrosion engineering for the modern chemical process development in the 20th century through the struggle against corrosion in the chemicals production field and considered how to overcome the corrosion problem in this field.
Investigations on inhibition mechansims of copper corrosion in aqueous solutions by surface-enhanced Raman scattering (SERS) spectroscopy have been reviewed. SERS spectra of species adsorbed on the iron surface can be measured by using an activated silver electrode completely covered with a thin layer of electrodeposited iron. In-situ SERS studies on inhibition mechanisms of iron corrosion in acid solutions are described in this review.
Intergranular corrosion susceptibilities of the dissimilar welds between SUS 444 which is ferritic stainless steel with high corrosion resistance and austenitic stainless steels were investigated. Judging from the 10% oxalic acid etch test results, there are some cases where the welded joints between SUS 444 and SUS 304, SUS 316 have high intergranular corrosion susceptibilities, while the welded joints between SUS 444 and SUS 316L have low intergranular corrosion susceptibilities. Intergranular corrosion susceptibility of the welded joints between SUS 444 and SUS 316 decreases when over 30% martensite phase precipitated with the high penetration ratio of SUS 316. Intergranular corrosion of the dissimilar welds between high purity SUS 444 and austenitic stainless steels is caused by the formation of chromium depleted zone. The countermeasures for the intergranular corrosion of the dissimilar welds are that the martensite phase with high solubility of carbon and nitrogen is forced to precipitate by increasing the penetration ratio of SUS 316 or SUS 316L is applied for austenitic stainless steel.
The anode samples of rolled and casting zinc plate for use as an anti-fouling panel will be installed on the wall of cooling sea water conduits in coastal steam power station were tested to observe the anti-fouling effects and to find out the suitable anode current density. The results are as follows. The two zinc anodes did not permit easy growth of barnacles in varied current density, if they were succeeded to attach, the easy falling off together with corrosion products such as zinc hydroxides were proceeded. The suitable anode current density for anti-fouling on a long term basis is found to be less than 30mA/m2. The anti-fouling mechanism of zinc anodes depends primarily on the physical effect of the corrosion products film which is soft, fragile and unstable. And also biological effect, that is, a film formed by soft organisms such as attaching diatoms and Botylloides sp. on the corrosion products inhibited to growth of calcareous depositing organisms. In view of the fact that organisms adhered to the surface of the anodes were alive and fell off together with corrosion products, it is very unlikely that the anti-fouling effect is dependent on the zinc biocide.
Potential ennoblement for stainless steel in natural seawater was analyzed. Open circuit potentials (OCPs) of platinum, gold, palladium, chromium, titanium and nickel ennobled in natural seawater as well as stainless steel, SUS 304 (18Cr-8Ni). Potential ennoblement is not a specific event to only stainless steel. Marine biofilm clearly caused potential ennoblement. Cathodic polarization curves for the ennobled stainless steel elucidated that there were two distinct reduction current increases. One is the limited diffusion current of dissolved oxygen reduction below -500mV vs. Ag/AgCl (KClsat). The other reduction current around 0mV vs. Ag/AgCl (KClsat) was considered to be hydrogen peroxide reduction current in acidic condition. Synergistic effect of hydrogen peroxide and low pH in artificial seawater carried out high OCP of stainless steel like that in natural seawater. Therefore, we concluded that synergistic effect of hydrogen peroxide production and low pH by marine microorganisms is possible cause for potential ennoblement in natural seawater.
It is important for those concerned with zinc to know what corrosion form of zinc takes in various environments. A pCl-pH diagram for Zn-Cl--H2O system is usually used as an index of corrosion form of zinc in an arbitrary chloride environment. In this report, the mistake of Zn-Cl--H2O system pCl-pH diagram which had been widely used after 1950's was pointed out and revised. The drawing method which used the solubility product of the corrosion products of zinc in this was shown.