Inhibitor efficiencies of n-alkyl trimethylammonium sulphates were determined against iron corrosion in deaerated sulphuric acid by means of a potentiostatic polarisation technique. n-Butyl, n-hexyl, n-octyl, n-dodecyl, and n-hexadecyl trimethylammonium sulphates were used as inhibitors.
All the tested quaternary ammonium sulphates except n-hexadecyl one inhibited the cathodic reaction of iron and were adsorbed in accordance with Langumuir's adsorption isotherm onto the cathodic iron surface. n-Hexadecyl trimethylammonium sulphate inhibited both the anodic and the cathodic reactions and gave the highest inhibitor efficiency among the inhibitors tested. At 3×10^-6 molar concentration of inhibitor, it was shown by a linear free energy relationship represented by Hammett's equation that the adsorption of the inhibitors on the cathodic iron surface became hard, as carbon numbers of the alkyl chain increased, because of the positive inductive effect of n-alkyl chain. But at the limiting inhibitor concentration, given the maximum inhibitor efficiency, the alkyl chain length in the quaternary ammonium ion brought a stabilisation of adsorbed molecules by van der Waals' forces of cohesion between the adsorbed molecules more strongly than a decrease of the positive character on the nitrogen atom by the positive inductive effect of n-alkyl chain.

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The effects of the temperature on the anodic polarization behaviour of SUS 304 and SUS 316 stainless steels were studied in a sodium-chloride solution in the temperature range of -10 to 35°C. The results obtained were summarized as follows. (1) Anodic polarization curves for SUS 304 in NaCl solution at ca. 0°C showed two pitting potentials, namely, the lower and the upper pitting potentials. The anodic loop due to pit-initiation and repassivation was observed between them. (2) The critical temperature below which anodic loop appears shifted in the lower temperature direction with increasing NaCl concentration. (3) Molybdenum in Cr-Ni stainless steel accelerates repassivation of pits formed in NaCl solution at low temperature. (4) Though the anodic polarization curves of SUS 304 and SUS 316 in chloride solution were similar to each other above room temperature, different behaviour was observed as the temperature was lowered to ca. 0°C.

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Effects of alloying elements, Mo, Sn and Ge, on the repassivation potential, E_R, and the initiation potential for crevice corrosion, V_crev, of 25Cr-6Ni duplex steel have been studied by using a nut/nut crevice in 0.5mol/l NaCl solution at 30°C. In this study, cyclic polarization curves to determine E_R were measured by using Tsujikawa et al method. Results obtained are summarized as follows: (1) Potential scan rates and holding time at potential to maximumn current had no influence on E_R values of 25Cr-6Ni steel in 0.5mol/l NaCl solution at 30°C. (2) The alloying of Mo, Sn and Ge, generally moved E_R toward noble potential direction. (3) E_R values of these steels generally coincide with each initiation potential for crevice corrosion, V_crev, except 3% Mo steel in reheated conditions and Sn bearing steels.

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The effects of dissolved oxygen concentration and temperature on the susceptibility to SCC of low alloy steels in pure water have been studied by means of slow strain rate tensile test (SSRT). The results obtained are summarized as follows: 1) The effect of dissolved oxygen on the susceptibility to SCC appears more clearly at the high temperature range from 200 to 288°C, and the susceptibility to SCC decreases with decreasing dissolved oxygen concentration. On the other hand, the susceptibility to SCC in water containing dissolved oxygen concentration from 0.2 to 8ppm becomes almost the same at the low temperature range belows 150°C. 2) The susceptibility to SCC increases with rising temperature in the case of high dissolved oxygen of 8ppm, but passes through a maximum at the temperatures below 288°C in the case of low dissolved oxygen of 0.2 and 2ppm. 3) Pitting corrosion occurs in water containing 0.2, 2 and 8ppm of dissolved oxygen at temperatures ranging from 50 to 288°C. SCC nucleates at corrosion pits, and correlation is found between the susceptibility to SCC and the number of corrosion pits.

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