The pitting corrosion of copper in cold water containing inhibitors composed of amino trimethylene phosphonic acid (ATMP), benzotriazole (BTA) and zinc sulfate (ZnSO4) has been studied by the immersion test and electrochemical measurements. The results obtained are summarized as follows: 1) the pitting corrosion of copper did not occur in cold water containing ATMP, ATMP+BTA and ATMP+ZnSO4, respectively. Pitting occurred in cold water containing both ATMP+BTA+ZnSO4 and ATMP+BTA+Na2SO4. The pH value of water lowered to 3. The presence of SO42- in ATMP+BTA solution is essential for the occurrence of pitting corrosion in copper. 2) In the immersion test, pitting corrosion of copper occurred under the presence of SO42- more than 0.6ppm in ATMP+BTA solution. 3) The pitting corrosion easily occurred and the number of pits increased, corrosion potential and breakdown potential became less noble with increase in SO42- concentration from 0 to 180ppm.
The autonomous oscillation of the electrode potential of iron immersed in oxidative solution has been studied by many workers. In this paper, the mechanism of this phenomenon in phosphoric acid solutions containing hydrogen peroxide was analysed by appling the pulsed current to the oscillatory systems. The threshold potential required to activate the passive surface of iron was found. It was confirmed that this threshold potential was the same as the Flade potential.
Effect of Cl- and dissolved oxygen on galvanic corrosion of 5182 aluminum alloy coupled with steel can stocks were investigated in 0.2% citric acid solutions containing various amounts of Cl- by electrochemical polarization and galvanic current measurements. In all solutions, 5182 alloy was anodic as expected from the fact that the alloy is less noble than the steel. It was found that galvanic current density is strongly dependent on the amount of dissolved oxygen and on the area in steel can stocks where coating is locally damaged and iron is exposed. In the solution containing 100ppm of Cl-, galvanic current density was of the order of a few μA/cm2, but it could be higher than 100μA/cm2 in the solution containing 5000ppm of Cl-. In the case where 5182 aluminum is coupled with 3004 alloy used for all aluminum can body stocks, on the other hand, galvanic current density was less than 5μA/cm2 even in the solution containing 5000ppm of Cl-. These results indicate that aluminum-steel bi-metal cans are not suitable for beverages containing higher concentrations of Cl-, because of latent problem of galvanic attack and also of higher self-corrosion rates of steel cans. Even for beverages containing lower concentrations of Cl-, there still arises a potential problem of galvanic corrosion if the inside coatings of steel can stocks are locally damaged and iron is locally exposed. Thus, it is considered that all aluminum cans are more preferable to steel cans for the cases where beverages are expected to contain higher concentrations of Cl-.
An anodic dissolution behavior of oxide films formed on the SUS 430 and 304 stainless steels during annealing process was studied in acidic Na2SO4 solution using electrochemical techniques. Structural analyses of the films at various stages of the electrolysis process were also carried out by X-ray diffraction, Grow Discharge Spectroscopy (GDS) and ESCA techniques. Dissolution rate of the oxide was accelerated with anodic polarization, although it was not affected by the solution pH. It was found that major compounds of the oxide films of SUS 430 and SUS 304 stainless steels were (Fe, Cr)2O3 and SiO2, and (Fe, Cr)2O3, FeCr2O4 and SiO2, respectively. By electrolyzing in the transpassive region Cr was dissolved whereas Fe and Si oxides remained on the surface of the stainless steels.
Corrosion resistance of sintered SiC ceramics, which were prepared using defferent sintering methods, crystal structures and sintering aids, were tested in pure water, 0.1kmol·m-3 H2SO4, and 0.1kmol·m-3 LiOH at 300°C for 50h. It was found that the corrosion resistance of SiC ceramics prepared using pressureless sintering, β-SiC powder, and sintering aids of B and C is better than those prepared using reaction sintering, α-SiC powder, and the aids of Al2O3. The corrosion rate of SiC ceramics in high temperature solutions increased with increasing concentration of oxidizing reagents in the solutions, and this suggests the corrosion proceeds in electrochemical reactions. The XPS analysis of specimen surfaces before and after the corrosion tests revealed that SiO2 films formed on SiC ceramics in air dissolved in high temperature solutions and no films grew in such solutions.
Application of Laser Raman spectroscopy to corrosion study was introduced. The spectroscopy can detect the composition of surface layers on corroded metals under in-situ conditions. Examples for in-situ measurements of corrosion surfaces in gaseous environment and in aqueous solution were presented.