DETERMINATION OF IMPURITIES IN SILICON-CARBIDE POWDERS

The analysis of SiC powders used for the production of high-performance ceramics was investigated by combined procedures as well as by a direct technique including atomic spectrometric detection. For the combined chemical procedure, SiC powders (0.25 g) were completely dissolved in a mixture of HNO3, HF and fuming H2SO4 in an autoclave at 240-degrees-C within 8 to 20 h. In the final 0.5% w/v solution 13 elements were determined by electrothermal atomic absorption spectrometry (ETAAS) and by inductively coupled plasma atomic emission spectrometry (ICP-AES). With acid decomposition the detection limits for Ca, Cd, Cr, Cu, Mg, Mn and Zn were found to be in the range of 0.1-1-mu-g/g; those for Al, B, Fe, Ni, Ti and V are at the 1-5-mu-g/g level. With a Babington-type nebulizer 1% slurries of SiC can be directly analyzed by ICP-AES. Calibration was performed by standard addition of aqueous solutions of the elements to be determined and the detection limits are close to those of ETAAS subsequent to pressure decomposition. The required analysis time was reduced from approx. 24 h to 30 min. First results for Ca, Cr, Cu, Mg, Mn, Ti and V as well as the needs to overcome systematic errors of this method, e. g. for Fe, are communicated.