Structural changes and anti-corrosion properties of dry-in-place chromate coatings at drying temperatures up to 400
oC have been investigated using DTA, SIMS, XPS and SVET. DTA of the deposits from a chromate bath containing Cr
3+, Cr
6+ and PO
43- species showed two distinct peaks due to endothermic (85∼200
oC) and exothermic (200∼400
oC) reactions. SIMS analysis indicated the presence of high molecular fragments at the final endothermic stage (∼200
oC), suggesting that polymerization occurs; however the polymerized coating was partially decomposed at the subsequent exothermic stage (around 300
oC). XPS analysis disclosed that the deposits consist of Cr
3+, Cr
6+ (Cr
2O
72- etc) and PO
43- as polynuclear complexes at the endothermic stage. Furthermore, corrosion resistance of chromated electrogalvanized steel and self-healing effect were investigated. The order of corrosion resistance from the highest to the lowest as evaluated using a salt spray test for three drying temperatures was 200
oC, 85
oC and 300
oC; it was found that the corrosion resistance differed with the differences in the final drying temperature. The self-healing effect was remarkable in the chromate dried up to 200
oC, and high corrosion resistance was measured by SVET.
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