Influence of impurities in phosphoric acid on the corrosion resistance of some commercially produced alloys

Surface Technology Pub Date : 1985-11-01 DOI:10.1016/0376-4583(85)90115-3

Nabil Nassif

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引用次数: 7

Abstract

The influence of Cl⁻, F⁻, S²⁻, SO²⁻₄, SiO²⁻₃, Fe³⁺, Al³⁺, Ca²⁺ and Mg²⁺ ions, in phosphoric acid, on the corrosion behaviour of stainless steels 304 and 316, alloys 825, 625, 230 and Hastelloys C and G was investigated. The alloys were tested in 75% H₃PO₄ in the absence and presence of various concentrations of each of the impurities at 85 °C under reflux and stirring conditions. Chloride ion was the most aggressive of the impurities because of its physicochemical properties. The best corrosion resistance in chloride contaminated H₃PO₄ was shown by the alloy containing the highest molybdenum and tungsten contents as an insoluble protective basic molybdenum and tungsten chloride film is formed. The presence of sulphide ion in H₃PO₄ considerably affected the corrosion rate as a result of the increased electrocatalytic activity of the passive film for oxygen reduction as a result of film contamination. Corrosion resistance was improved in such a sulphide environment by increasing the chromium content of the alloys.

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磷酸中杂质对某些工业生产合金耐腐蚀性的影响

研究了磷酸中Cl−、F−、S2−、SO2−4、SiO2−3、Fe3+、Al3+、Ca2+和Mg2+离子对304和316不锈钢、825、625、230合金和哈氏合金C和G腐蚀行为的影响。合金在75%的H3PO4中，在85°C回流和搅拌条件下，在不存在和存在不同浓度的每种杂质的情况下进行测试。由于氯离子的物理化学性质，它是最具侵蚀性的杂质。钼、钨含量最高的合金在氯化物污染的H3PO4中形成不溶性保护基性氯化钼、钨膜，具有最佳的耐蚀性。H3PO4中硫化物离子的存在极大地影响了腐蚀速率，这是由于膜污染导致钝化膜的氧还原电催化活性增加。在这种硫化物环境中，通过增加合金的铬含量来提高合金的耐腐蚀性。

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Surface Technology

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