Melting Apparatus for the Synthesis of Bulk ZrF4‐Based Fluoride Glass

Abstract

Heavy‐metal fluoride glasses are currently prepared by melting of the solid fluoride precursors. We have constructed a melting facility for the synthesis of ZrF4‐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 SF6 or Cl2. It was found that of the latter two halogenating species only Cl2 prevents effectively the formation of black inclusions in the melt (ZrF3 and ZrF2 particles). With this melting apparatus we have routinely melted 250‐g batches of optically clear ZrF4–BaF2–LaF3–AlF3–NaF glass samples.