THE STUDY OF ALUMINUM ANODIZED BY CONSTANT CURRENT AFTER BEING PREDIPPED IN THE SOLUTION OF AMMONIUM MOLYBDATE AND AMMONIUM FLOURIDE

• Main Authors: Bo-Hua Kung, 龔柏鏵
• Other Authors: Hsing-Hsiang Shih
• Format: Others
• Language: en_US
• Published: 2001
• Online Access: http://ndltd.ncl.edu.tw/handle/60080423293629559631

碩士 === 大同大學 === 化學工程研究所 === 89 === The main purpose in this study is to investigate the effects of constant current method, constant voltage method, dipping time and temperature, anodizing temperature on anodic oxide film anodized from a 10wt% of sulfuric acid for 30min after pre-dipping in the solution of ammonium molybdate and ammonium fluoride. Constant current method shows better results, such as hardness and film thickness, than constant voltage method on anodizing procedure based on the same supplied electric charges at 10~50oC. Adequate high dipping temperature is favorable to the growth of molybdic oxyhydroxide film. And when the pH value of dipping solution is 3,the anodic oxide film has higher hardness. Appropriate longer dipping time would be helpful to obtain a good anodic oxide film. But too longer dipping time would make the molybdic oxyhydroxide film exfoliate, and be harmful to the anodic oxide film. Dipping time and dipping concentration will influence the film thickness of molybdic oxyhydroxide film, not the film thickness of anodic oxide film. The more current density used in anodizing, the thicker the anodic oxide film will be, and the less hard the anodic oxide film will be. Using higher current density (14A/dm2), the film thickness will be more than 60 m. Adequately high anodizing temperature seems to be helpful to obtain thicker film. But at 40 or 50oC, the dissolution rate increases, and the film thickness decreases, so does the hardness. From SEM, dipping for longer than 60min and high current density can not make the pores on the anodic film distribute closely and regularly. Based on EDS charts, the molybdenum exists in the anodic film, and it will improve hardness. But dipping for 240minutes will cause the molybdic oxyhydroxide film exfoliate, and its EDS chart is surely unable to detect the existence of molybdenum atoms. Under the dipping conditions: 60min and 50oC, pH=3, and anodizing conditions: 30oC and 2A/dm2, the maximum microhardness of anodic film through dipping is 586 Hv.