Study on the Methanol Corrosion of Copper by Electron Diffraction

Corrosion products formed on copper surfaces in methanol were examined by electron diffraction. Two kinds of copper, that is, Japanese and American copper were used in this study. In both cases corrosion products were confirmed from diffraction patterns as copper oxides, which consisted of the cuprous and cupric oxide at the beginning of corrosion, but only of the latter at the final stage of corrosion. The colouring of corrosion was, on the other hand, very different in both cases, namely, Japanese copper suffered heavier corrosion than American one and showed a lead-gray appearance. From the diffraction patterns obtained at the earliest stage of corrosion it was established that the cupric oxide is easily formed after a short period of immersion. In further experiment copper surfaces immersed in dehydrated methanol were examined. The appearances of the surfaces changed scarcely in such dehydrated methanol, though the diffraction test showed the existence of thin layers of oxides. Hence it seems that the corrosion is mainly due to water absorbed by methanol, but from the fact that specimens immersed in water do not suffer such violent corrosion as in methanol, it is considered that unknown impurities, which exist in methanol and are soluble in water, are effective.