New Fluorination Reactions of Ammonium Bifluoride

This paper describes a novel route for the production of low-oxygen-containing fluorozirconate glasses. The process involves the use of a hitherto unknown solid-state chemical reaction between ammonium bifluoride and specific anhydrous and hydrated metal fluoride salts. The products are defined as ammonium fluoride–metal fluoride complexes. The kinetics of their formation and subsequent dissociation were followed by thermogravimetric analysis. It was observed that these complexes decompose with the evolution of HF above temperatures at which ammonium bifluoride decomposes and where its supply may be exhausted. These materials have been used to melt fluorozirconate glasses. The oxygen contents of these glasses have been dramatically reduced to approximately 10 ppm. The glass stability, as defined by the lack of devitrification on reheating, also appears to increase with a lowering of the oxygen content. This implies that the mechanism of nucleation and growth is predominantly heterogeneous and not homogeneous nucleation. Furthermore, the production of long lengths of crystal-free fluoride fibers for transcontinental optical communication systems appears to be a realistic goal, especially if the heterogeneities can be eliminated.