Characterisation of reaction layers on copper surfaces formed in aqueous chloride and sulphate ion containing electrolytes

Abstract

Copper is in a passive state in a potential range of 50 mVH to about 300 mVH in contact with an aqueous electrolyte at neutral pH caused by the formation of a thin tarnishing layer consisting of copper(I)‐corrosion products. This layer inhibits more the anodic than the cathodic partial reaction of the corrosion process. The steep threshold in the transpassive range leads to the oxidation of copper and the formation of secondarily formed reaction layers. In sulphate containing electrolytes voluminous reaction layers of crystalline non‐protective copper(I)‐oxide are formed. The manifestation of corrosion is general attack. In chloride containing electrolytes a two‐fold reaction layer is formed, copper(I)‐chloride underneath copper(I)‐oxide. This amorphous copper(I)‐oxide is formed via hydrolysis of copper(I)‐chloride and inhibits anodic metal dissolution. The only observed manifestation of corrosion is repassivating pitting.

Effect of Chlorine Concentration on Natural Pitting of Copper as a Function of Water Chemistry

“…5,6 The reduction of Cu 2 O at −0.9 V SCE was observed only for pH 5 and 6 ESDW solutions, not at pH 7 and higher, which indicates that Cu 2 O is converted either from precipitation reactions of Cu 2+ ͑two steps via Reactions 16 and 17 in Table V͒ 32 or CuCl 2 − ͑Reaction 18 in Table V͒ 4 or the hydrolysis reaction of CuCl ͑Reaction 19 in Table V͒. 33,34 By comparison, the spontaneous passivity formed by the reaction 2Cu + H 2 O ↔ Cu 2 O + 2H + + 2e − at higher pH ͑Ն7͒ is too thin to be observed. The Cu 2 O film formed by precipitation in solutions containing Cu 2+ is much thicker than the Cu 2 O film that is obtained by direct anodic oxidation.…”

General corrosion of copper in domestic drinking water installations: scientific background and mechanistic understanding

“…50,51,69 This hypothesis is supported by experimental findings. 70 When the solid/liquid interface is completely covered with tenorite, the oxidation of copper stops owing to the lack of electrical conductivity of the film. 68 Although these findings support the earlier considerations of Ives and Rawson, their electrochemical model cannot explain the strong effect of carbon dioxide on the corrosion process.…”

Passivity and Pit Stability Behavior of Copper as a Function of Selected Water Chemistry Variables

“…Incipient pits were only observed on passivated copper in pH 8 and 9 synthetic drinking water but not at pH 6.5 and 7, where copper did not exhibit thin-film passivity formed by direct oxidation but instead formed reprecipitated films. 39,[46][47][48][49] However, it has been shown that although Cl − initiates pitting on copper, [50][51][52][53][54] it has a passivating effect after pit initiation, possibly due to the precipitation of CuCl in pits. The effect of each anion on the stability of the passive film on copper has been widely studied in different environments.…”

“…45 Cl − and SO 4 2− are two important anions which are believed to cause copper-pipe pitting problems in potable water systems. 39,[46][47][48][49] However, it has been shown that although Cl − initiates pitting on copper, [50][51][52][53][54] it has a passivating effect after pit initiation, possibly due to the precipitation of CuCl in pits. 38,41,46 In contrast, SO 4 2− only causes active pitting and may be a more potent anion than Cl − .…”