Process for making bulk heavy metal fluoride glasses

Abstract

Heavy metal fluoride glasses are made by a process that requires high purity fluoride constituent compounds fluorinated oxides, or premelted glass cullet. The charge is placed in an enclosed furnace chamber having the ability of atmosphere control, heat control and position control of the charge. In particular, an inert, or nonreactive atmosphere or air is used in the furnace chamber as well as an oxygen-scavenging metal therein. The oxygen-scavenging metal at the high temperature produces a controlled oxygen partial pressure so that the air is essentially inert and non-reactive although the presence of a slightly oxidizing atmosphere is still required to produce the glass. The charge is rapidly raised to its fusion temperature and held at the temperature for a short time in proximity to an oxygen-scavenging material. The charge is immediately removed from the heating source and quickly cooled through the critical crystallization region. The total heating and cooling time being less than one hour. The HMFG or (Zr or Hf)F.sub.4 - BaF.sub.2 - LaF.sub.3 - AlF.sub.2 consistently exhibits high optical homogeneity and no absorption due to carbon dioxide along with very reproducible hardness, thermal parameters, and UV and IR edge absorption behavior.