Starting from a multicomponent lead phosphate glass composition given in the literature, a glass was developed suitable for the protective overclad of heavy- metal fluoride glass fibers. Besides a low glass transition temperature less than 270 degree C, a high thermal expansion coefficient greater than 18 center dot 10** minus **6 K** minus **1, the phosphate glass material developed had a water resistance at 60 degree C for 10 h comparable to that of commercial container glass. The final composition developed was (in mol%): 54.7 P//2O//5, 19.8 PbO, 18.0 Na//2O, 1.2 MgO, 1.2 BaO, 1.2 CaO, 0.4 V//2O//5, 1.5 Al//2O//3, 2.0 Bi//2O//3. Besides the influences of these different components the action of the melting conditions, especially melting temperature and trace SiO//2 content from the crucible material, have to be taken into account. Fiber drawing experiments including the in-situ application of the phosphate glass overclad were successful. (Author abstract) 20 Refs.
Hartmann, Matthias Bintzer-Schmidt, Sigrid Heinz Frischat, Guenther