Reaction of NF₃and SF₆with some oxides connected with heavy-metal fluoride glass processing

The fluorinating properties of NF₃and SF₆in heavy-metal fluoride glass processing were investigated between 200 and 1100 °C. Using infrared (IR) absorption spectroscopy the reactions of NF₃with ZrO₂and Al₂O₃and the reactions of SF₆with ZrO₂, SiO₂, and Ni were studied. The reaction of NF₃with zirconia and alumina starts at 300 and 650 °C, respectively (yielding nitrogen oxides, nitrogen oxyfluoride, and presumably the metal fluorides). The reaction of SF₆and zirconia starts at 600 °C, yielding SO₂F₂. Sulfur hexafluoride and silica yield (above 900 °C) SiF₄, SO₂F₂, and SOF₂. Nickel and SF₆react above 700 °C yielding SF₄(and presumably NiF₄). The results indicate that both gases are effective in oxide conversion at typical fluoride glass melting temperatures (800–900 °C). In addition NF₃can be used as a low-temperature fluorinating source for both oxide containing fluoride and pure oxide precursors. This offers great advantages over the use of solid NH₄HF₂, which is typically used and which forms an additional source of contamination.