Defects in glasses examined by backscattered electron imaging and by x‐ray wavelength and energy dispersive spectroscopy

Abstract

AbstractTypical optical defects in glasses with a high lead content were examined by backscattered electron imaging (BSI), quantitative energy‐dispersive x‐ray spectroscopy (EDS) and windowless EDS (WEDS) in a scanning electron microscope (SEM) and by quantitative wavelength‐dispersive spectroscopy (WDS) in an electron probe micro‐analyser (EPMA). Most of the images were obtained by using a backscattered electron (BSE) detector of high efficiency and excellent atomic number (Z) resolution (ΔZ = 0.3). The observations showed the presence of cords of varying shape, diameter (10–200 μm) and composition, spherical inclusions and fractures; the fractures were found to be associated with regions of materials of low Z which have developed gas under electron beam irradiation. Quantitative WDS and EDS microanalyses performed on the cords showed the presence of about 3 wt.% of Al2O3 and 2 wt.% of ZrO2, originating from the interaction, at the interface, of the glass and the refractory material used to hold the melted glass, and a lead content lower than the matrix. A high lead content was found, however, in the spherical inclusions. WDS and WEDS showed the presence of carbonates in the low‐Z regions, which probably developed CO2 under electron beam irradiation. These morphological and microchemical results are of great importance in clarifying the origin, and hence finding the means of avoidance, of defect formation.