Environmental effects on surface devitrification of fluorozirconate glasses

Surface devitrification of fluorozirconate glasses has a dominant role in preform drawing and highly depends on environmental conditions. The effects of different atmospheres (N 2, SF 6, CF 4, CHF 3, CHCIF 2, CHCl 2F, CCl 2F 2, CBrF 3, C 2F 6, C 2ClF 5, C 2Cl 2F 4, C 3F 8, air) and different materials (platinum, gold, graphite, Teflon ® PTFE, aluminum) normally used in glass processing were analysed. The devitrification phenomenon, occuring on the surface and into the bulk after sample reheating at drawing temperature, was checked by several analysis techniques and the kinetic parameters were calculated by DSC analysis to evaluate effects induced by different materials. Surface devitrification of glasses treated under CF 4 atmosphere is less evident than for samples treated under other gases. Moreover it was found that platinum should be avoided for glass processing equipments, because of its tendency to induce crystallization.