The hazardous hexavalent chromium formed on trivalent chromium conversion coating: The origin, influence factors and control measures
- 作者：Jinhua Li ; Chenlan Yao ; Yanbiao Liu ; Di Li ; Baoxue Zhou ; zhoubaoxue@sjtu.edu.cn ; Weimin Cai
- 关键词：Hexavalent chromium ; Trivalent chromium conversion coating ; Environmental issue ; Oxidation
- 刊名：Journal of Hazardous Materials
- 出版年：2012
- 期刊代码：50_03043894
- 类别：ce
- 出版时间：30 June, 2012
- 卷：221-222
- 期：Complete
- 页码：56-61
- 文件大小：449 K
摘要
In this paper, the effects of processing parameters and constituents of treating-agent on the presence of hazardous hexavalent chromium on trivalent chromium conversion coating were studied. Results showed that shorter immersion time, lower bath pH value as well as lower working and baking temperatures retarded the presence of hexavalent chromium. In addition, the concentration of hexavalent chromium on conversion coatings prepared by the oxalic acid treating-agent was far greater than those on conversion coatings prepared by formic acid and acetic acid treating-agents. Results also indicated that the concentration of hexavalent chromium on conversion coatings was enhanced due to the addition of bivalent cobalt and nitrate anion in treating-agent, especially for oxalic acid conversion coating. However, the addition of hydroxyl compound d-gluconic acid in treating-agent could reduce the concentration of hexavalent chromium effectively. Moreover, a possible formation mechanism of hexavalent chromium on trivalent conversion coating was proposed. Findings of this study provide a better understanding of the formation of hexavalent chromium on trivalent chromium conversion coating and can facilitate the management of trivalent chromium treating-agents and trivalent chromium fasteners.