XPSによる塗布型クロメートの乾燥温度による組成変化の解析

抄録

The dependence of drying temperature on changes in the composition of dry-in-place type chromate composed of Cr³⁺, Cr⁶⁺ and PO₄^3-, 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 Cr³⁺, Cr⁶⁺ and PO₄^3- after endothermic reaction.
In the exothermic reaction following the endothermic reaction, decrease of Cr⁶⁺ and increase of Cr³⁺, were caused by a reduction of deoxidization.
It is considered that Cr³⁺, which is produced by a reduction of deoxidation, forms CrPO₄.
No composite difference is discernible in water-dissoluble constituents before and after the endothermic reaction, and they were composed of CrO₃, CrPO₄, Cr₂O₃ and Cr(OH)₃·nH₂O.
The composition after the exothermal reaction is a mixture of CrO₃ and small amounts of Cr₂O₃ and Cr(OH)₃·nH₂O. CrPO₄ was not detected in this case.
It is concluded that increase in PO₄^3- fixed in water-insoluble constituents follows the increase in Cr³⁺ caused by a reduction of deoxidization.