塗布型クロメートの乾燥温度による皮膜構造変化

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Structural changes in dry-in-place chromate films at drying temperatures up to 400°C have been investigated using DTA, SIMS, XRD and XPS. DTA of the deposits from a solution containing Cr(VI), Cr(III) and PO43- species showed two distinct peaks due to endothermic (85∼200°C) and exothermic (200∼400°C) reactions. MASS analysis indicated the presence of fragments of high molecular fragments at the final endothermic stage (∼200°C), suggesting that polymerization occurs, but the polymerized films, partially decomposed at the subsequent exothermic stage (around 300°C). XPS analysis disclosed that the deposits consist of CrO3, Cr2O3, Cr(OH)3 and CrPO4 at the exothermic stage. In respect to the ratio of water-insoluble components of the deposits, however, the endothermic reaction caused a decrease in the Cr(III) species (major part) and an increase in the Cr(VI) (minor part), while in the subsequent exothermic reaction, the Cr(VI) decreased, suggesting that a deoxygenation reaction occurs.
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