| Summary: | 碩士 === 國立臺灣大學 === 化學工程學研究所 === 93 === In this study, we focused on the aluminum electrochemical characteristics and etching behaviors in the phosphoric acid solution, nitric acid and the phosphoric-nitric acid solution, respectively. In the experiments, we measured the etching rates by electrochemical polarization and the interface phenomena by Electrochemical Impedance Spectra (EIS) technique. We also analyzed the surfaces which were etched by different etchants with XPS.
The results showed that the etching behaviors in the phosphoric acid solutions were discussed with three concentration regions: in the low concentration region (< 3M), the surface alumina thickness decreased rapidly; in the middle concentration region (3M~7M), the thickness reached a steady state thickness and kept a constant value; in the high concentration region (>7M), the alumina thickness decreased again and became a very thin alumina film on the surface. Because the alumina on the surface had two different structures, the inner part is dense alumina and the outer part is porous alumina. They showed various etching behaviors in the three concentration regions. We also found out that nitric acid could oxidize the aluminum surface. That is why the etching rate increased rapidly in the high concentration region. In the high phosphoric acid concentration region, the alumina layer became very thin and H+ can etch aluminum to generate the hydrogen bubbles. This is why the bubbles generation in the low phosphoric acid concentration is slow and in the high phosphoric acid concentration region, it is fast.
Finally, we found out the acetic acid is an organic acid which decreased surface resistance and reduced the surface roughness.
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