Steric effects of branched alkyl chains on the inhibition efficiency of amine inhibitors for the acid corrosion of iron were studied. Corrosion rates were determined on a pure iron electrode in 6.1M HCl solutions with and without the inhibitors at 30°C by polarization measurements. The inhibitors adopted were monoalkyl amines (I), N-ethyl alkyl amines (II), and N-dimethyl alkyl amines (III), of which alkyl groups are branched and unbranched chains. The inhibition efficiency of I and II decreased with an increase in the degree of branching of the alkyl group in the orders, n-butyl>isopropyl group, and n-butyl>isobutyl>sec-butyl>tert-butyl group. However, the efficiency for III decreased in the order, sec-butyl>tert-butyl>isobutyl>n-butyl group. The polarization data were semi-quantitatively analyzed in connection with the molecular coverage areas, the polar and steric substituent constants, and the basicity constants. The steric effect of the branched chain on the adsorption of the free amine increased with increasing the degree of the branching, resulting in lowering the inhibition efficiency for the anodic partial reaction. Further, this effect was enhanced in the order from I to II and markedly to III. The inhibition efficiency of III for the cathodic partial reaction increased with the degree of the branching in the alkyl group. This increase in the efficiency is attributed to the low hydration number for cations of III by the steric hindrance of the branched chain.

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The passive films on iron in neutral boric-borate and phosphate solutions at +0.845V (S. H. E.) for 1 hour have been investigated by using electrochemical, ellipsometric and Auger spectroscopic techniques.
From analyses of iron dissolution and δP-δA curves during galvanostatic cathodic reduction of the film, it was found that the passive films formed in these solutions consisted of a deposit layer and a barrier layer, and that the composition of the two layers was different in different anion solutions. In boric-borate solution, the deposit layer which grows to 26A was in the oxidation state of iron (III) with the optical constant of 2.20-0.10i and the barrier layer growing to 22A was in the same oxidation state of iron (III) with the optical constant of 2.50-0.30i. In phosphate solution, the deposit layer with the optical constant of 2.20-0.14i showed the mean oxidation valency of iron Z_Fe=2.94 at the thickness 32A, whereas the barrier layer was in the mean oxidation state of Z_Fe=2.33 and had the optical constant of 2.50-0.35i at 18A.
It was also found that there were a iron-depletion or oxygen-excess layer at the deposit/barrier interface and a OH radical or O^- adsorption layer at the deposit/solution interface of the passive film formed in boric-borate solution. No specific adsorption or depletion, however, was found in the passive film formed in phosphate solution.
The Auger spectroscopic measurements revealed that both the deposit layer and the barrier layer formed in phosphate solution contained phosphorus ions, whereas the passive film formed in boric-borate solution contained boron ions only in the deposit layer.
The results were explained by assuming an anion selective property for the film formed in boric-borate solution and a cation selective property for the film formed in phosphate solution.

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There are many techniques developed to protect metallic materials against oxidation at elevated temperatures. Among them, there is a thermal spraying method, which is effective to produce coatings for oxidation resistance, wear resistance and heat insulation. The practice, characteristics and application of thermal spraying methods are described to give some suggestions for selecting the good protective coating for high temperature uses.
The most effective coating for heat resistance is a multilayer coating. Magnesium-zirconate multi-layer coating system is, for example, being applied to Hastelloy combustion chamber on jet engine. The first layer is nickel-aluminide powder which is strongly adherent to the substrate. The second layer is 35% nickel-aluminide and 65% magnesium-zirconate, and the top layer is magnesium-zirconate film.

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Recently, AES (Auger Electron Spectroscopy), ESCA (Electron Spectroscopy for Chemical Analysis), APS (Appearance potential Spectroscopy) and ISS (Ion Scattering Spectroscopy) etc. have been developed as powerful tools of the surface analysis of solids. The use of these new methods for analyses of rusts on metallic materials will throw light into the details of corrosion phenomena. This article described the methods for quantitative analyses of rusts, particularly by means of AES with aid of standard materials such as pure metal and metal oxide, and the analytical results of passive films on Fe-Cr alloy were discussed as typical examples. Finally, it was pointed out that these methods were not always almighty and should be used in parallel with other conventional methods.

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