Effect of MgO Addition on the Deposition of Al2O3 Coating Layer on Pt Wire by the Electrophoretic Deposition and Sintering of the Layer.

Abstract

Deposition behavior of MgO-added Al2O3 coating layers on Pt wires by the electrophoretic deposition and sintering of those coating layers were examined. Electrical conductivity of the bath solution and amount of deposited Al2O3 were increased by adding MgO into the bath. Mg (acac)2 (magnesium-acetylacetonate) formed through the reaction of MgO with acetylacetone, which was thermally decomposed to MgO by calcination above 400°C. Crystalline phases in the coating layers sintered at 1500°C changed from α-Al2O3+MgO to α-Al2O3+spinel (MgAl2O4) or spinel+MgO, with increasing the MgO content. It was found that layer shrinking and crack formation depended on the amount of MgO added to the bath. Crack-free sintered thick layers were obtained when more than 10 mass% MgO was incorporated. Thermal decomposition of Mg (acac)2 to MgO, leaving pores in the layer was considered to be the crucial processes to avoid crack-formation in the sintered coatings.