Investigation of inhomogeneity in ceramic reactor materials using laser-localized emission spectroscopy

Using Laser-localized emission spectroscopy, a method has been developed for the determination of elemental inhomogeneity within the grains of three coarse-grained ceramic materials - the mullite-based Duritals M70 and E90 and the silica-based Masrock -. The method had to be optimized to allow an acceptable detection of the elements to be analyzed in spite of the small quantities of evaporated material. A Laser-produced crater of 100 μm diameter and depth was found to be necessary to produce the required amount of evaporated material, 0,5 to 0,7 μg depending on the material composition. The results for Durital E90 showed that the large grains consisted of very pure mullite (2 Al2O3xSiO2) and the fine grained regions contained small particles of mullite, corundum and binder, the impurities in the binder being concentrated at the grain boundaries. In Durital M70, the coarse and fine grained regions consisted principally of mullite, the impurities introduced during manufacture being evenly distributed in both regions. Analyses of the Masrock material showed a concentration of impurities in the fine grained regions with a very inhomogeneous distribution. The large grains consisted of nearly pure SiO2. The distribution of impurity elements on the fracture surfaces of ceramics tested showed that the fracture behaviour is mainly influenced by the physical properties of the materials and not by the chemical properties of the phases present in the materials, for example, the binding of the large grains to the matrix. (orig./WL)