在鋁合金6061上進行微弧氧化層著色並研究其膜層結構，我們添加氧化鉻膠體於電解液。使用平均粒徑69 nm合成氧化鉻粉末，和平均粒徑351 nm GN-M商用氧化鉻粉末進行鍍製，雖然兩種粉末都屬於高度缺氧相的氧化鉻(oxygen deficient, Cr2O3-δ)剛玉 (Corundum type)晶體結構，但完成著色的綠色膜層會氧化成接近組成比的六方晶相Cr2O3。由於粒徑大小不同，所鍍製出來之膜層不同，粒徑大的GN-M氧化鉻商用粉末只在膜層表面反應，而粒徑小的合成氧化鉻粉末進入到膜層內部反應。透過微結構知道，微弧放電會發生在氧化鉻與氧化鋁之界面層，故粒徑小之合成粉末會引發微弧放電深入膜層內部造成孔洞及破壞，因此孔洞深入膜層，緻密層近乎消失；而粒徑大之GN-M商用粉末會將微弧放電引至表面，而使得孔洞及破壞發生在外層，使內部緻密層保存完整。
利用阻抗分析儀(EIS)之電容量測，判斷氧化鋁為N型半導體氧化物，經由Mott-Schottky theory計算出載子流密度(carrier density)，判斷在不同時間下，其氧空位之多寡。由暫態電壓電流圖可以推測氧化鉻屬於P型半導體氧化物。進而推測氧化鉻與氧化鋁界面層吸引微弧放電是因為含有兩種半導體氧化物特性之材料結合。

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.

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