XPS Analysis of the Dependence of Drying Temperature on Changes in the Composition of Dry-in-place Type Chromate

• Published in: Hyōmen gijutsu Vol. 43; no. 3; pp. 211 - 215
• Main Authors: SUDA, Arata, OGINO, Takao, TANAKA, Shigeo, MAEDA, Shigeyoshi
• Format: Journal Article
• Language: English; Japanese
• Published: Tokyo The Surface Finishing Society of Japan 01.03.1992; Hyomen Gijutsu Kyokai; Japan Science and Technology Agency
• Subjects: Dry-in-place Type Chromate; Drying Temperature; Thermal Analysis; X-ray Photoelectron Spectroscopy
• ISSN: 0915-1869; 1884-3409
• DOI: 10.4139/sfj.43.211

The dependence of drying temperature on changes in the composition of dry-in-place type chromate composed of Cr3+, Cr6+ and PO43-, 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 PO43- 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 PO43- fixed in water-insoluble constituents follows the increase in Cr3+ caused by a reduction of deoxidization.