Characterization and identification of local defects in glass

The most relevant defects in glasses are categorized and investigated by appropriate microanalytical techniques. Since these defects very often present a real challenge because of complex chemical and mineralogical properties, a multimethod approach is necessary to supplement or confirm the findings from scanning techniques. The combination of electron probe microanalysis/energy-dispersive x-ray (EPMA/EDX) and laser ablation inductively coupled plasma mass spectroscopy (LA-ICP-MS) allows the determination of element trace concentrations in a knot, a glassy defect, thus finally enabling the identification of a special source of the defect from otherwise nondistinguishable refractories. The type of crystals can be determined exactly by the use of EPMA and x-ray dispersion (XRD), stones (a crystalline agglomerate) are analyzed by EPMA/EDX pointing to a possible source for this defect; results on metallic inclusions, "filled bubbles," and surface defects are reported and defect sources are discussed. Since close cooperation with the production departments and knowledge of production techniques and conditions are necessary for the diagnosis to take appropriate countermeasures, an approach is presented which systematically accumulates all information into a data base. The structure of such "expert systems" is described, which leads to correlation of appearance, analytical data, and source of the defects for even more accurate diagnosis and faster reaction.