Abstract

The microstructure of refractory materials exhibit grains with a very large size distribution, from some µm to some mm. This prevents automatic, fast and accurate description of the whole microstructure from microscopic observations. However, today, it exist automatic methods allowing image analysis, which are currently used in some other scientific subject such as biology. Optical microscopy allows the observation of large particles (aggregates), however electronic microscopy is suitable to observe finer particles (matrix or bonding phase). Moreover, due to similar composition, it exist few contrast between grains and grain boundaries are not clearly defined. This also prevents thresholding which is necessary to automatically detect grains with the aid of an image analysis method. Actually, it doesn’t exist method allowing the quantitative description and the control of the refractory materials whole microstructure. 

In this work, different complementary methods were used to describe as well as possible the whole microstructure of refractory castables. A skill was developed to obtain special large size samples. They were prepared by drilling, cutting, surface machining and polishing. This large size allows including a lot of large whole particles (aggregates) in the samples and to reduce the “cut” ones at the edge. Optical and scanning electronic microscopy where used for picture acquisition at different magnification. Optical microscopy was used for aggregates observation whereas electronic microscopy was used for fine particles observation. “Panorama” software was used for pictures assembly leading to larger pictures showing a “sufficient” number of particles with high accuracy. Some artefacts such as ink impregnation were used to enhance contrast between different phases and to promote grains recognition by image analysis software. Method was applied to different castables with different particle size distributions. Results show that it is possible to obtain a description of the microstructure including a “particle size distribution”. Today, the progress of the work leads to a finger print of the materials which could be used to check and to compare materials.