Using confocal scanning laser microscopy for the in situ study of high-temperature behaviour of complex ceramic materials

Abstract

The confocal scanning laser microscopy (CSLM) technique has been successful in many metallurgical fields. This paper assesses its applicability to the in situ investigation of the high-temperature behaviour of complex ceramic materials. Magnesia–chromite refractory is selected as a ceramic test material. At room temperature, CSLM images correspond well to typical light optical microscopy (LOM) and backscattered electron (BSE) micrographs. In fact, because of the high axial resolution (short focal depth) and the confocal optics of the CSLM technique, the porosity level of the mirror polished ceramic specimens is more truthfully assessed by the CSLM (2-D) images than by the BSE micrographs (long focal depth). However, at high-temperatures (1550–1650 °C) the observed CSLM (2-D) image quality is slightly poorer. The principal explanation is the in situ roughening of the specimen surface during heating. The roughening has two causes: differential thermal expansion of the two primary phases in the ceramic test material and, to a lesser extent, thermal grooving. Nevertheless, it is shown that the CSLM image quality suffices for an in situ study of the high-temperature behaviour of ceramic materials. This is illustrated for the magnesia–chromite system by examining the dissolution mechanism of secondary (magnesiochromite) spinel into the periclase phase.