Effect of some oxidizing agents on pitting corrosion of aluminum in neutral water
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Three kinds of dissolved agents are considered to be indispensable for occurrence and propagation of pitting corrosion of aluminum in water. That is, the 1st one is a corrosion inhibitor which reacts with aluminum surface and inhibits the corrosion over the whole surface, the 2nd one is an activator which locally destroys inhibitive action of the 1st one, and the last one is an oxidizing agent which depolarizes cathode and promotes cathodic reaction.In the present study, the effects of oxidizing agents (such as dissolved oxygen, H2O2, free chlorine, K2Cr2O7, and KMnO4) on occurrence and propagation of pitting corrosion of aluminum were investigated for the specimen placed in neutral water containing sulfate or phosphate ions as inhibitors and chloride ions as activators.The results obtained were summarized as follows:(1) In water containing 5ppm of sulfate ions as Na2SO4 and 5ppm of chloride ions as NaCl, the pitting corrosion was not observed for less than 80ppm of dissolved oxygen, but it was distinctly observed at that amount of 150ppm. When the oxygen content was more higher, corrosion occurred over the whole surface to form a boehmite film and no pitting corrosion was observed.(2) The addition of an oxidizing agent such as H2O2 and freechlorine to the water, containing a certain amount of corrosion inhibitors and chloride ions, promoted the occurrence of pitting corrosion of aluminum immersed in the solution. However, the oxidizing agent such as K2Cr2O7 acted as a passivator, by which pitting corrosion was not. (3) Among the corrosion inhibitors, phosphate ion was more active than sulfate ion in provoking and propagating pitting corrosion of aluminum in water containing oxidizing agents. Whereas, fluoride ion had noability for provoking pitting corrosion.(4) These phenomena were discussed in connection with the results of potentiostatic polarization measurements.
- 一般社団法人 軽金属学会の論文
一般社団法人 軽金属学会 | 論文
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