Interaction of Pb-Cd-Al-Li fluoride glass with water

Abstract

Fluoride glasses based on high atomic weight metals are being actively investigated for use as ultralow-loss mid-IR optical fiber. In addition to stability, formability and strength, resistance to degradation by water is an important selection criterion. CLAP glass, based on PbF2 and CdF2 has been suggested as a more resistant alternative to fluorozirconate glasses, which are based on ZrF4 and BaF2. For this study, high optical quality CLAP glass has been prepared, exposed to distilled water at room temperature and closely observed. Visible effects of reaction were observed as line etching in a gridlike network and dulling of the surface within 1–1/2 min. Transmissivity was severely impaired within one hr and excrescence had developed at a number of locations by the end of the 18-hr test. The character of alteration appears to depend upon whether the surface is pristine (original) or nascent (formed by fracture). The pristine surface formed a coherent layer containing pores and sporadic, nondescript cellular outgrowths, whereas the nascent surface developed a network of fissures which nucleated and sustained growth of an abundance of crystalline, hexagonal platelet clusters. These results indicate that attack by water is most disruptive on surfaces such as those created in cleaving an optical fiber for splicing. Hermeticity, particularly at connectors, must be assured in order to prevent degradation of fiber and function in glasses of this type.