A Melting Apparatus for the Synthesis of Bulk ZrF sub 4 -Based Fluoride Glass.

Heavy metal fluoride glasses are currently prepared by melting of the solid fluoride precursors. We have constructed a melting facility for the synthesis of bulk ZrF sub 4 -based fluoride glass cullet. This stand-alone system provides a controlled (dry and reactive) atmosphere and in-situ quenching of the melts. The glass is melted in a vitreous carbon crucible, which is mounted in a silica tube flow reactor. The reactor is resistively heated with a tube furnace and purged with He and Sf sub 6 or Cl sub 2. It was found that of the latter two halogenating species only Cl sub 2 prevents effectively the formation of black inclusions in the melt (ZrF sub 3 and ZrF sub 2 particles). With this melting apparatus we have routinely melted 250 gram batches of optically clear ZrF sub 4 -BaF sub 2 -LaF sub 3 -AlF sub 3 -NaF glass samples.