Progress in very dense and high purity alumina coatings enabled by a new range of alumina powders

Alumina coatings are widely used for dielectric and wear applications. The state-of-the-art high volume alumina coatings are served mainly by white fused alumina with medium purity. Dielectric strength is directly linked to the density, thickness and purity of the alumina coatings. For wear resistance, it is commonly known that dense coatings provide longer lifetime and delay the release of material that will speed up the abrasion. Poor flowability and broad particle size distributions can limit coating density and impurities can further reduce its dielectric strength. Inconsistencies in porosity and purity can lead to relatively thick coating specifications to ensure dielectric strength targets are met. Precise particle size control coupled with the spherical morphology improves flowability with finer particle size distributions. The enhanced purity combined with higher coating density increases the dielectric strength or safety factor of a specified coating thickness. The increased performance and consistency may also enable a reduction in the required thickness to meet existing specifications. The newly developed high purity spherical alumina powders offer excellent flowability enabling process consistency and helping to provide reliable dense coating. This paper will present the improved powder features and the coating performance afforded by this range of high purity alumina powders.