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, some of which are further refined by sublimation. Handling occurs in a protective atmosphere such as argon. The charge is placed in a sealed modified optical growth furnace having the ability of atmosphere control, heat control and position control of the charge. The charge is firstly raised to its fusion temperature, then to an admixture temperature, and finally to a higher temperature. The charge is immediately removed from the heating source and quickly cooled through the critical crystallization region. The total heating and cooling time being about one to two hours. The resulting glass ingot is partially annealed. The HMFG of (Zr or Hf)F.sub.4 -BaF.sub.2 -LaF.sub.3 -AlF.sub.2 consistently exhibits low levels of both light scattering and bulk OH contact, along with very reproducible hardness, thermal parameters, and UV and IR edge absorption behavior.