US 4,047,960 AGranted

Refractory partially crystalline materials with good visible transparency

AssigneeCorning Glass Works

InventorRichard F. Reade

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Abstract

This invention is concerned with the manufacture of refractory articles of a partially crystalline nature, i.e., materials having a substantial crystal content within a glassy matrix, but wherein the crystal phase normally comprises less than about 50% by volume of the materials. The bodies are produced through the heat treatment of glass articles having compositions within the Al.sub.2 O.sub.3 --SiO.sub.2 --TiO.sub.2 --Nb.sub.2 O.sub.5 and/or Ta.sub.2 O.sub.5 system at elevated temperatures, but not in excess of about 1150.degree. C., to cause the in situ growth of crystals. The materials, containing aluminum niobate, aluminum tantalate, or an aluminum niobate-tantalate solid solution as the predominant crystal phase, exhibit a high degree of transparency to visible light, and retain that transparency even after very extended exposures to temperatures up to in excess of 1000.degree. C. That capability has recommended their utility as arc-tubes or as envelopes for high temperature lamps.

Claims3

Dependent claims

A method for making a transparent partially crystalline article containing at least about 20%, but less than about 50%, by volume crystals dispersed within a residual glassy matrix wherein the predomininant crystal phase consists essentially of aluminum niobate, aluminum tantalate, or an aluminum-tantalate solid solution having a crystal size of about 300-500A in diameter, which crystalline article retains its transparency after extended exposures to temperatures up to about 1150.degree. C., comprising the steps of:

a. melting a batch for a glass consisting essentially, in weight percent on the oxide basis, of about 10-20% Al.sub.2 O.sub.3, 59-72% SiO.sub.2, 5-8% TiO.sub.2, and 5-20% Nb.sub.2 O.sub.5 and/or Ta.sub.2 O.sub.5 0 to about 2% K.sub.2 O and/or 0 to about 6% Cs.sub.2 O;
b. simultaneously cooling said melt to a temperature at least within the transformation range and shaping a glass article of a desired configuration therefrom;
c. heating said glass article to a temperature of at least about 1000.degree. c., but not more than about 1150.degree. C., for a period of time sufficient to cause the crystallization of aluminum niobate, aluminum tantalate, and/or an aluminum niobate-tantalate solid solution having a crystal size of about 300-500A to occur in situ to produce a transparent partially crystalline article;
and then
d. cooling said crystallized article to room temperature.

2 more elements

Dependencies are inferred from the claim text.