Microstructural determination in some SiC based hot gas filter materials

Insufficient reliability of hot gas filter materials is among the main obstacles to the replacement of traditional power generation processes with advanced, more efficient coal or biomass based routes. Knowledge of the effects of water vapour and thermal transients on microstructure and its relation to the mechanical properties of filter materials is important for understanding the material degradation process in complex operating environments, for lifetime prediction and for further materials development. In the present study, the microstructure of two advanced, commercially available SiC based clay bonded filters was characterised by scanning electron microscopy (SEM) and a quantitative X-ray diffraction (XRD) method. Porosity, density and thermal expansion coefficient of the materials were determined. The quantitative XRD method specially developed for the materials studied is described in detail. Apparent densities and coefficients of thermal expansion calculated from the determined phase compositions of the two filters were in agreement with measured values.