The surface film produced on tinplate by chromate treatment was examined by Auger electron spectroscopy iAES) and photoelectron spectroscopy (ESCA), and the effect of the film composition on lacquer adhesion was investigated.The passivation film consists of a large amount of chromium oxide and a small amount of metallic chromium and contains small amounts of impurities such as sulphur, chlorine and calcium. The chromium oxide is hydrated oxide in the outer layer and dehydrated oxide in the inner layer. Assuming that the composition of the outer layer is αCr_2O_3.nH_2O (1-α)SnO_2 (hence a is the covering rate), the hydration degree of the oxide was determined by the atomic concentration of Cr, 0 and Sn obtained by AES. The n-values were from 2.9 to 4.4, which varied with different production lines and the amount of charge (applied current density) in a cathodic treatment. The n-va/ue was in good agreement with the "oxolation degree" defined by the chemical effect of 0 and Cr in AES, which also corresponded roughly to the ratio of O/Cr obtained by ESCA for the outermost layer.
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