New strategies for trace analyses of ZrO2, SiC and Al2O3 ceramic powders

The progress possible in the analysis of refractory powders such as ZrO2, SiC and Al2O3 by the use of new sample preparation, processing and introduction techniques elaborated for AAS, ICP-OES and ICP-MS with low and high mass resolution is demonstrated. For optimized sample preparation techniques based on dissolution of ZrO2, e.g. fusion with (NH4)2SO4, it is shown to what extent impurities present in (NH4)2SO4 determine the detection limit. Hydraulic high pressure nebulization with and without matrix removal by complexing the impurities with dithiocarbamates (Cu, Co, Cr and Ni) or oxine (Fe, Mn and Mo) and fixing them on a C18 solid phase for subsequent solid phase extraction coupled with flame atomic absorption was used to determine Fe, Cu, Cr, Mn, Ni, Co and Mo impurities in (NH4)2SO4 in the 10–100 ng/g range. Further a method to synthesize (NH4)2SO4 with higher purity than some commercially available high-purity (NH4)2SO4 with respect to Fe, Cu, Cr and Mn using high-purity NH3 and chlorosulphonic acid is shown. Reliable determinations of Fe and Al at the 100 μg/g level in ZrO2 with ICP-OES with matrix removal as well as with ICP-MS without matrix removal are reported. For the direct analysis of Al2O3 powders, slurry nebulization ICP-MS sample introduction is shown to improve detection limits and to reduce sample preparation, if the leachable and non-leachable fractions are analyzed separately. For powders such as SiC, the matrix or solvents can cause spectral interferences. Matrix removal is shown to be useful to improve detection limits for the interfered elements. High resolution ICP-MS can be used to control the completeness of matrix removal techniques and to overcome limitations due to spectral interferences even in case of complex materials.