電析Zn-7wt%Cr合金めっき皮膜の構造

概要

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Zn-7wt%Cr alloy was electrodeposited from an acidic sulfate bath consisting of Zn, Cr and organic additives. Studies of the structure of the plating layer by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and transmission electron spectroscopy (TEM) indicated that it consisted of metallic Zn, Cr, a small amount of Cr oxide and 0.015 wt% of carbon. XRD pattern obtained from the plating layer showed a broad peak around 2θ=40 degrees. The crystallite size as determined by TEM was 5-20nm. It is concluded that the plating layer consisted of fine crystallites of Zn-Cr alloy phase, whose structure was uncertain. This alloy recrystallized at 195°C and changed into a regular crystal structure 20-50nm in size. The melting point of the alloy was 452°C, which is not same as the melting point of θ-phase Zn-4.7wt%Cr alloy in the Zn-Cr alloy phase diagram.
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