Shaped press-forged normally frangible inorganic crystals

Abstract

A polycrystalline shaped article useful as a light-transmitting body or scintillation phosphor is formed from an essentially monocrystalline melt-grown macrocrystal ingot by pressing the ingot between opposed surfaces with no radial restraint, at a temperature below its melting point and under sufficient pressure to transform the ingot, in situ, into a fully dense, homogeneous, polycrystalline mass of unrestricted width. A polycrystalline shaped article useful as a light-transmitting and/or light-generating body may also be formed from a fully dense, homogeneous, optically integral polycrystalline mass by pressing the polycrystalline mass between opposed surfaces with no radial constraint, at a temperature below its melting point, but greater than one-half its melting point measured in degrees centigrade, under sufficient pressure to form a relatively larger polycrystalline mass of lesser height. Wherever trace impurities in the order of about one part per million are detrimental, as in a scintillation phosphor, or where it is essential that a theoretically fully dense material, with no voids, be formed, as for example in a laser window, no method, other than press-forging a fully dense crystalline mass will suffice. In particular, windows may be press-forged which permit the transmittance of laser beams with less than 0.1% absorption, or no more absorption than is displayed by the archetype monocrystalline ingot, whichever is greater. In addition, press-forged windows are characterized by several times greater strength than that obtained with essentially single crystal ingots. Similarly, optically integral scintillation phosphors may be formed having large diameters which are theoretically not limited by the size of the largest essentially monocrystalline ingot which may be grown.