CORRELATED SCANNING AUGER AND X-RAY PHOTOELECTRON SPECTROSCOPIC INVESTIGATIONS OF SILICON-CARBIDE POWDERS

The application of SAM and XPS to the study of powder mixtures composed of silicon carbide and processing additives is presented. The density of sintered SiC specimens has been shown to be related to the surface composition of the freeze-dried mixtures, measured after milling the water slurries and after heating for the removal of binding polymers (dewaxing). Effects of milling and dewaxing on the dispersion of sintering aids, on the formation of residual carbon layers and on the evolution of the surface oxide have been tested by XPS while the spatial distribution of surface carbon species has been tested by SAM. The procedure for the acquisition of Auger spectra and linescans on these powder samples is described. SAM analysis of dewaxed SiC greens, reveals the presence of graphitic carbon agglomerates with an average diameter of roughly 5 mum after 1 h of mixing in attrition mill which decreases to less than 1 mum after 16 h. The study shows that processing parameters such as type and concentration of sintering aid, milling time and dewaxing procedure can be optimized using the information of surface spectroscopies, acquired after each step of processing, for the production of high density specimens.