DIRECT ANALYSIS OF SILICON-CARBIDE POWDER BY TOTAL-REFLECTION X-RAY-FLUORESCENCE SPECTROMETRY

Three silicon carbide powders having different grain size distribution s were analyzed by total reflection X-ray fluorescence (TXRF) spectrom etry with the application of slurry sampling, For the elements investi gated (Fe, Ti, V, Cu, Ni, and Ca) the line-to-background ratios show a maximum value at a surface concentration of 12.5 mu g/mm(2). For the realization of this surface concentration, a 25-mu L aqueous slurry wi th a concentration of 1% (m/V) and pH of 10 was dropped onto the hydro phobic quartz carrier plate. For quantification of the intensity data, gallium was added as an internal standard to the slurries, Under thes e experimental conditions, the analytical data of the fine-grained pow ders (80-90% of the powder particles were less than 1.5 mu m) are in g ood agreement with concentrations determined in various laboratories b y inductively coupled plasma atomic emission spectrometry (ICP-AES), I CP mass spectroscopy (MS), electrothermal vaporization- (ETV)-ICP-AES, slurry sampling graphite furnace atomic absorption spectroscopy (GF-A AS), and neutron activation methods, Powders with a mean grain size gr eater than 1.5 mu m deviate much more from the reference data, Calcula ted limits of detection (LODs) range from 2 to 25 mu g/g, The precisio n expressed as relative standard deviation (RSD) varies between 4 and 14% for Fe, Ti, and V, whose concentrations in the fine-grained silico n carbide samples exceed by a minimum of tenfold their limits of detec tion; however the precision is very poor for Cu (66.6%) and Ni (62.3%) , which have concentrations near the limits of the detection.