Inductively-coupled plasma optical emission spectroscopic determination of trace impurities in zirconium oxide-powder

Abstract

Because of their extraordinary properties, advanced ceramic materials, e.g. ZrO2 , offer new possibilities to science and technology in such important areas as microelectronics, high temperature applications in reactors and motors and also medicine. Due to these, Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) has been used for the determination of the most significant impurities (Cr, Fe, U and Th) in high-purity refractory powders of ZrO2 without matrix(Zr) separation. ZrO2 powders were decomposed by fusion with a 10-fold excess of NH4HSO4 and subsequent dissolution of the melt in either HNO3 or HF. ZrO2 samples were fused and dissolved in both HNO3 and HF. The results in the two acids were evaluated with respect to detection limits, blank values, interferences, accuracy and precision. The solution was then directly analyzed by ICP-OES, which was optimized for each independent analytical line. The calibration was performed by standard addition and matrix matching was not necessary. The detection limits in Zr02 in the two acids varied from 1.73μg/l(Fe) to 50μg/l(U). The standard deviations obtained were 1-10 % depending on the element and its concentration in the sample. There was no significant difference on the interferences and accuracy obtained in the two acids. The precision of the results in HN03 was poor as the results were not reproducible day after day due to precipitation. Except for Fe and Cr, the blank values encountered in HF were lower than in HNO3, but generally they were below the detection limits of the metals investigated. It was concluded that HF is the best acid to dissolve the fused ZrO2 powders as it results in stable sample solution. It was further investigated whether the presence of mineral acids, viz. HCl, HNO3 and H2SO4, at 0-50% (v/v) concentration has significant influence on the emission signal of Fe as one of the impurities determined in ZrO2. A number of solutions containing 1, 5, 10, 20 and 50μg/ml of Fe in acid concentrations of Oto 50% (v/v) were used. It has been found that HNO3 and HCl enhances the emission signal at low levels of Fe whereas H2SO4 depresses the emission signal of Fe at all levels. These effects are neither caused by the change in aerosol flow-rate nor the amount of aerosol reaching the plasma.