Direct analysis of Al2O3 powders by total reflection X-ray fluorescence spectrometry
A direct analysis procedure for the determination of trace impurities of Ca, V, Cr, Mn, Fe, Ni, Cu, Zn and Ga in Al2O3 ceramic powders by total reflection X-ray fluorescence spectrometry (TXRF) is described. The powders were analysed in the form of slurries containing 1–10 mg mL−1 of powder. The use of the procedure in the case of powders with differing grain size and for different slurry concentrations was investigated. Three different quantification possibilities were compared, namely the use of Al as a matrix component, the use of Fe as a trace element contained in the sample or of Co added in concentrations of 200 μg g−1 as internal standard. The homogeneity of elemental distributions in sample layers deposited on the TXRF quartz carriers by evaporating 5 μL of the 10 mg mL−1 slurries was studied by scanning the 4- to 5-mm-diameter spots of two samples by synchrotron radiation TXRF at Hasylab. For powders with differing graininess but mainly finer than about a few 10 μm, no systematic influence of the grain size on the accuracy of the determinations of Ca, V, Fe, Ni, Cu and Zn could be observed. The measurement precision, however, seemed to be limited by inhomogeneous distributions of the trace elements in the samples as testified by the synchrotron radiation TXRF scans. Detection limits of the developed TXRF procedure for Ca, V, Cr, Mn, Fe, Ni, Cu, Zn and Ga were found to be in the 0.3–7 μg g−1 range and were shown to increase slightly with the grain size of the samples. Quantification using Al (matrix) as internal standard led to systematically higher values out of the accuracy required, whereas the other two approaches in all cases led to reliable results.
Direct Analysis of Silicon Carbide Powder by Total Reflection X-Ray Fluorescence Spectrometry
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 μg/mm2. For the realization of this surface concentration, a 25-μL 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 μm) are in good agreement with concentrations determined in various laboratories by inductively coupled plasma atomic emission spectrometry (ICP-AES), ICPmass 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 μm deviate much more from the reference data. Calculated limits of detection (LODs) range from 2 to 25 μg/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.
Direct determination of impurities in powdered silicon carbide by electrothermal atomic absorption spectrometry using the slurry sampling technique
A direct method of analysis of powdered silicon carbide for the determination of Al, Cd, Cr, Cu, Fe, Mg, Mn, Ni, Ti, V and Zn based on electrothermal atomic absorption spectrometry (ETAAS) using the slurry sampling technique is described. Possible spectral interferences caused by the refractory matrix components were studied. The technique was optimized with regard to sample preparation, dispensing, thermal pre-treatment and atomization parameters. The accuracy was checked by comparison of the results with those obtained by ETAAS and inductively coupled plasma atomic emission spectrometry involving decomposition of the sample, and by instrumental neutron activation analysis. For most of the elements investigated the achievable limits of detection are at the sub-microgram per gram level.