The dependence of drying temperature on changes in the composition of dry-in-place type chromate composed of Cr
3+, Cr
6+ and PO
43-, has been investigated based on the results of thermal analysis assuming its drying process at actual application.
Using a differential thermal analysis, an endothermic reaction was observed between 85°C and 200°C, while an exothermic reaction peaking at 300°C was observed between 200°C and 400°C.
Further, the influence of these endothermic and exothermic reactions on the composition of dry-in-place type chromate has been investigated by XPS analysis.
The thermal reaction has been also analyzed by the separation of chromate into water-insoluble constituents and soluble constituents, assuming the participation of water in the actual corrosion environment.
The water-insoluble constituents form the polymer structures with Cr
3+, Cr
6+ and PO
43- after endothermic reaction.
In the exothermic reaction following the endothermic reaction, decrease of Cr
6+ and increase of Cr
3+, were caused by a reduction of deoxidization.
It is considered that Cr
3+, which is produced by a reduction of deoxidation, forms CrPO
4.
No composite difference is discernible in water-dissoluble constituents before and after the endothermic reaction, and they were composed of CrO
3, CrPO
4, Cr
2O
3 and Cr(OH)
3·
nH
2O.
The composition after the exothermal reaction is a mixture of CrO
3 and small amounts of Cr
2O
3 and Cr(OH)
3·
nH
2O. CrPO
4 was not detected in this case.
It is concluded that increase in PO
43- fixed in water-insoluble constituents follows the increase in Cr
3+ caused by a reduction of deoxidization.
抄録全体を表示