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The processes of atmospheric corrosion of iron and steel and the properties of corrosion products (rusts) are modeled based on a quantitative evaluation of the chemical reactions pertaining to corrosion to elucidate the conditions with which corrosion-protective rust films form. Based on the model, it is suggested that in the initial stage of corrosion, in the rusts, the pH of the aquatic system is maintained at 9.31 owing to an equilibrium with iron(II) hydroxide and the rate of air-oxidation at this pH is very fast, and that dense, self-repairing rust films form, protecting the underlying iron and steel. However, after corrosion stops, the rust film deteriorates due to the dissolution and shrinkage by aging, and the deteriorated rust film separates the anode and cathode reaction products (Fe 2+ and OH -ions) to cause crevice corrosion. The air-oxidation of iron(II) in anode channels without the presence of OH -ions results in strongly acidic solutions (pH 1.41), causing acid corrosion. It is proposed that good catalysts (e.g.copper(II) and phosphate ions) accelerate the air-oxidation at low pH, delaying the crevice-and acid-corrosion stages. Further, it is argued that iron compounds with negative charges due to the non-stoichiometric proportions of the lattice oxide ions and metal ions (solid oxoanions of iron) exhibit stable cation-selective permeability even with a drop in pH. Rust films including such compounds would stop the passage of aggressive anions and act to protect iron and steel.

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SynopsisCorrelation between the chemical structure of polyamides and the reactivity to hypochlorous acid was investigated to evaluate their chlorine resistance as a membrane material for reverse osmosis. Modes of interaction of polyamides with hypochlorous acid were classified into three; no reaction, reversib!e chlorination at the amide nitrogen, and irreversible chlorination at the aromatic nucleus. These modes of interaction were dependent upon the amine component of polyamide. Secondary amines such as piperazine and N-methylaniline gave amides which were quite stable against hypochlorous acid. Thus, poly(isophthaloy1 piperazine) was most stable among the polyamides investigated in this study. Polyamide derived from aliphatic primary diamines such as polyethyleneisophthalamide gave an N-chlorinated amide, which could be reversibly dechlorinated by the treatment with a reducing agent such as sodium hydrosulfite. Polyamides comprised of aromatic primary diamines such as poly(rn-phenyleneisophthalamide), on the other hand, gave a product with chlorinated rn-phenylene nucleus which could not be dechlorinated by a reducing agent.

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