1 - Phase Chemistry in the Development of Transparent Polycrystalline Oxides

Abstract

Polycrystalline oxides have been available for optical applications since the early 1960s when Coble invented translucent Al203. Before this, it was thought that porosity, with its inherent light scattering property, was a necessary consequence of the ceramic fabrication process. Translucent Al203 is a key element in high-pressure sodium lamps manufactured all over the world. Although it is not clear that Coble made extensive use of phase diagrams in his original development, phase relations are important to the success of translucent Al203, and subsequent researchers seeking to sinter other oxides to transparency have found phase relations important to their success in achieving their ultimate goal in sintering: elimination of residual porosity. A number of oxides have been developed for optical applications in which glass, because of refractoriness, chemical compatibility, or limitations on bandwidth, typically cannot compete. These oxides are Al203, MgAl204, ALON, and Y2O3. Although other oxides have been sintered or hot pressed to transparency, these four are considered to be the prime candidates to extend optical applications.