X-ray diffraction microstructure analysis of mullite, quartz and corundum in porcelain insulators

The X-ray diffraction microstructure analysis has been performed on commercial samples of the silica and alumina porcelain insulators obtained at 1300 °C, with the same time of firing. The study was carried out on mullite, corundum and quartz by applying several integral breadth methods (i.e. the Williamson–Hall analysis, the Langford method and the Halder–Wagner approximation) and the Fourier analysis (Warren–Averbach method). The apparent crystallite sizes determined for the mullite are direction-dependent (anisotropic) and within each group of samples, on average, the greatest values are obtained along the direction [0 0 1]. With regard to the microstructure of the corundum and the quartz, there are little differences between the two groups of samples. Considering all samples on average, the crystallite sizes follow the order corundum > mullite > quartz. These microstructural data were related with the mechanical strength and with the chemical and mineralogical composition of the samples. Due to similar conditions of formation of the porcelains studied, the content of corundum seems to be the principal factor influencing their flexural strength, coinciding with small differences of crystalline microstructure.