Preparation and measurement of green coatings through plasma electrolytic oxidation in electrolytic solutions of chromia inclusions
| Autor: | Chen-Yu Liu, 劉宸侑 |
|---|---|
| Rok vydání: | 2017 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 105 In an effort to color the aluminum alloy surface and study the film structure in green via plasma electrolytic oxidation (PEO), two alkaline solution have been employed with particulate inclusions and sodium aluminate. We use a self-made chromia pigment with a mean size 69 nm and commercially available pigment, GN-M, with a larger particle size 351 nm. Both pigments are oxygen deficient Cr2O3-δ of corundum-type structure before coating, the oxidative environment of PEO converts them into stoichiometric Cr2O3. Due to difference of particle size, resulting in very different microstructure. The GN-M inclusion of large size amasses on top of the coating, while the self-made inclusion of small size goes deep. We could observe the Cr2O3-Al2O3 interface brings the electric microdischarges burns from microstructure. The self-made particulate inclusions bring the electric microdischarges inside the coating and create inner pores and damages. Therefore, the hole into the film and dense layer almost disappeared. On the other hand, the GN-M inclusions bring the electric microdischarges on coating surface and create outer pores and damage. So we can keep the inner dense layer intact. Through the electrochemical impedance spectroscopy (EIS) analysis, we confirm PEO alumina is an N-type semiconductor oxide. We subsequently calculate the carrier density by Mott-Schottky theory and measure the oxygen vacancies at different PEO times. From the transient voltage-current diagram, we infer that chromium oxide belongs to P-type semiconductor oxide. It is further assumed that the Cr2O3-Al2O3 interface brings the electric microdischarges because the two types of semiconductors containing opposite carriers and eliminate each other at their interface. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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