A Study of Al2O3/TiO2 Coatings by Plasma-Sprayed for High Dielectric Application
|Keywords:||電漿熔射;氧化鋁;氧化鈦;雷射重熔;靜電挾持;介電;崩潰電壓;plasma-sprayed;alumina;titania;laser-remelting;Electrostatic Chuck (ESC);dielectric;breakdown voltage|
The purpose of the research is to obtain ceramic coating with higher dielectric constant. The major application is used in the equipment of electrics static chuck (ESC). Basic structure of ESC includes an electrode layer and a dielectric layer. In order to have enough chuck strength, the dielectric material must have high dielectric constant, high dielectric strength and high electric resistance. Four coating powders including Al2O3、Al2O3+3%TiO2、Al2O3+ 13%TiO2、Al2O3+40%TiO2 were employed on the substrate of Alloy 6061. The result of this experiment shows that the bound stresses of four coatings are between 5595 psi and 8505 psi. The density of Al2O3+TiO2 coating is higher then that of Al2O3. Using high temperature plasma-spray, the brown Al2O3+TiO2 powder becomes blue-black coating. This blue- black coating is a conductive material. Therefore, both Al2O3+13%TiO2 and Al2O3+40%TiO2 become conductive. Since Al2O3+3%TiO2 only has fewer blue-black components, the influence of conductive is small. Since Al2O3+3%TiO2 has a higher density, the breakdown is higher than that of pure Al2O3 about 19.8% and dielectric constant is higher than that of pure Al2O3 about 16.9%. In the high temperature condition, Al2O3+3%TiO2 has greater value of breakdown. Because of the instability of Ti+, the tendency of breakdown decreases clearly. After plasma-spraying, laser remelting was used to reduce defect of porosity. Because the ceramic coating and base metal have different thermal conductive constant and thermal expansion constant, cracks were occurred. Because the preheat temperature has not been enough, the porosity can’t be reduced effectively. Therefore, if stainless steel is chose as the base metal, a higher preheat temperature is needed to reduce porosity.
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