| Summary: | 碩士 === 高苑科技大學 === 高分子環保材料研究所 === 96 === The pure zinc film was prepared by a simple zinc plating solution. In this work, the pure zinc film was coated trivalent chromium layer to display by passive film. The passive film of trivalent chromium coating was measured tafel plot, cyclic voltammetry, XRD、SEM、EDX and thickness to disclose a trivalent chromium layer with high corrosion resistance.
The composition of trivalent chromium plating solution contains K2Cr2(SO4)6, oxalic acid, NaNO3 and NaCl. The pH values is increased by consuming H+ ions, when the Zn2+ ions and Cr3+ ions are formed as metal hydroxide to lead a rough and bad trivalent chromium layer. For preparing a better trivalent chromium film, some additives ( NaF、InCl3 and SnCl4 ) are added in the trivalent chromium plating solution.
The optimum composition to prepare the trivalent chromium film with blue-color is K2Cr2(SO4)6 32g, oxalic acid 10g, NaNO3 7g, citric acid 10g and CoSO4 2g at pH 2.0 with passive temperature at 30°C; the best composition to prepare the red-color one is K2Cr2(SO4)6 32g, oxalic acid 10g, NaNO3 7g, citric acid 10g, CoSO4 2g and NaCl 5g at pH 2.0 with passive temperature at 60°C.
The anti-corrosion ability of trivalent chromium film is affected by complex agent’s activity. Because the different complex temperature prepare the variable Cr-complex agent, the activity of Cr-complex agent is the most important factor to plate trivalent chromium film. By UV-VIS spectrum, the wave-length ranges from 400 to 600 nm obtain red and purple light to form better Cr-complex agent to plate trivalent chromium film.
Finally, the 0.3 mL NaF in the blue-color electroless plating solution improves the anti-corrosion ability of the trivalent chromium passive film. When 0.03 g/L InCl3 and 0.03 g/L SnCl4 were added in the trivalent chromium plating solution, the surface of trivalent chromium film became a smooth and light layer to raise corrosion resistance.
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