Electron Diffraction Study on the Selective Oxidation of Copper-Aluminium Alloys

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Copper-aluminium alloys containing 1〜10 per cent of aluminium were selectively oxidized by the Price's method, and surface films formed on them were examined by electron diffraction. The relations connecting the nature of the films with the treatment-temperature, the aluminium-content and the discolouration-resistance to various acids were elucidated. Diffraction patterns obtained in the range of the high discolouration-resistance did not correspond with the expected γ-Al_2O_3 but with those which Harrington et al had previously obtained from a heated surface of an electropolished aluminium, and they were considered to arise from one of the complicated modifications of aluminium oxide. When the original or heat-treated surfaces were heated in an oxidizing gas flame, the obtained patterns possessed, besides the rings of γ-Al_2O_3, a few extra ones which neither belonged to the f. c. c. lattice nor could be ascribed to reasonable impurities. After detailed considerations this fact led to a con-clusion that the alumina obtained by us had a more complicated symmetry than γ-Al_2O_3 of the ordinary spinel type. When a specimen of 1 per cent aluminium selectively oxidized was subsequently heated in an electric furnace, a break-up of Debye rings took place owing to the refraction effect of electron due to minute crystals of cupric oxide.
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