Soft regime modification of plasma electrolytic oxidation on aluminum alloy surface and the origin of n-type and p-type oxide semiconductor

• Main Authors: Guan-Wei Chen, 陳冠崴
• Other Authors: Dah-Shyang Tsai
• Format: Others
• Language: zh-TW
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/t35yuh

碩士 === 國立臺灣科技大學 === 化學工程系 === 106 === 　　We set the electrical parameters let the plasma electrolytic oxidation (PEO) enter soft sparking(or soft regime) which can be utilized to dismiss the intrinsic porosity problem of PEO coatings on aluminum alloy, since this type of surface treatment generates a dense inner layer. The results show that a typical two-layer structure of soft sparking is generated under different current ratios and frequencies. However, the stratified structure will be generated when the pulse rest time is short, because the micro arc state undergoing extinctions and re-ignitions more than once. Analysis of V-I transients in the anodic pulse of bipolar current reveals the decline in RC time constant is a forerunner. For those experiments developing the feature of dense inner layer, the time constant R2C2 will rises up to a plateau value, then falls. The R2C2 fall occurs before the soft sparking transition as well. For those experiments that end up with a stratified microstructure, the fluctuation of R2C2 synchronizes with stratification, that is, R2C2 can mirror the variation of micro arc state and growth rate. In contrast, the voltage drop in power supply readings is an indirect signal, since the decline is an action of feedback circuitry in response to resistance decrease of the interface dielectric. 　　Through Mott-Schottky analysis, we know the alumina layer of PEO demonstrates both n-type and p-type behavior. Through heating the anodized aluminum oxide layer to 150,200,250,300, and 400°C for 1hr .it only n-type behavior can be observed when the oxide layer was not heated. But the p-type behavior will emerge when it has been heated. Therefore, we show that the p-type behavior is due to the effect of heat.