Preparation of polymeric alkaline earth metaphosphate glasses

Abstract

Polymeric metaphosphate glasses, [M(PO.sub.3).sub.b ].sub.n, having chemical durabilities at least 40-400 times greater than those of the prior art are provided. In the formula, M is selected from the group consisting of Al, Be, Mg, Ca, Sr, Ba, Cd and Zn, and 'b' has a value of 3 for Al and 2 for the other cations. The high durabilities of the glasses are achieved by controlled preparation of the precursor compounds in specific stoichiometric proportion, by heating the precursors in a controlled thermal cycle to induce preliminary polymerization of the intermediates, by thereafter melting said intermediates, and by subsequently holding said melt for a time to complete the polymerization. The melt is then cast to form the glass which is then annealed in the normal manner. The disclosure involves in particular single high purity compound precursors which form single phase glasses. Each system is subject to mutual phase separation if mixtures are used; even impurities become segregated because each single-phase-glass system rejects said impurities during polymerization. Single phases are necessary because mixtures of glass phases are found to be less stable than the single phase glass of the present invention and cannot be prepared free from striae for use in optical or other applications.