Abstract
Three silicon carbide powders having different grain size distributions were analyzed by total reflection X-ray fluorescence (TXRF) spectrometry with the application of slurry sampling. For the elements investigated (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/mm2. For the realization of this surface concentration, a 25- mu L aqueous slurry with a concentration of 1% (m/V) and pH of 10 was dropped onto the hydrophobic quartz carrier plate. For quantification of the intensity data, gallium was added as an internal standard to the slurries. Under these experimental conditions, the analytical data of the fine-grained powders (80-90% of the powder particles were less than 1.5 mu m) are in good agreement with concentrations determined in various laboratories by inductively coupled plasma atomic emission spectrometry (ICP-AES), ICP mass spectroscopy (MS), electrothermal vaporization- (ETV)-ICP-AES, slurry sampling graphite furnace atomic absorption spectroscopy (GF-AAS), and neutron activation methods. Powders with a mean grain size greater than 1.5 mu m deviate much more from the reference data. Calculated limits of detection (LODs) range from 2 to 25 mu g/g. The precision expressed as relative standard deviation (RSD) varies between 4 and 14% for Fe, Ti, and V, whose concentrations in the fine-grained silicon carbide samples exceed by a minimum of tenfold their limits of detection; however the precision is very poor for Cu (66.6%) and Ni (62.3%), which have concentrations near the limits of the detection.
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