Interaction of NF3 with melt confinement materials in fluoride glass processing

Abstract

Nitrogen trifluoride (NF3) was recently used by others as a reactive atmosphere during the melting of heavy metal fluoride glasses. This compound fluorinates oxide impurities, dehydrates the melt, and controls the oxidation state of both glassformer and impurity cations. The reaction of NF3 with nickel, silica, platinum, and vitreous carbon between 200 and 1100°C using IR absorption spectroscopy was investigated. This is an important issue, since reaction products (impurities) from the crucible and containment vessel walls may be incorporated in the melt. All materials, except for nickel, reacted below 600°C yielding corresponding fluorides (and oxides in the case of silica). The results indicate that, directly heated, vitreous carbon crucibles are preferred for melting of fluoride glasses in a NF3 atmosphere.