Express X-Ray Fluorescence Analysis of Technical-Grade Tantalum and Niobium: from Raw Materials to Products

Abstract

The available approaches to detecting impurities in Ta- and Nb-based materials involve transferring a sample into a solution with subsequent isolation of impurities. This procedure is quite complicated and time-consuming. Therefore, it is interesting to study the possibilities of direct, in particular, X-ray fluorescence (XRF), analysis of solid samples of these materials. The conventional XRF scheme, which involves the experimental construction of calibration characteristics for each element being determined, requires a large number of reference samples containing a very wide range of impurities. In this work, a preliminary characterization of samples of technical tantalum and niobium and products based on them has been carried out. It is shown that, for initial materials, the XRF method can establish only a significant absence of impurities; however, even for sintered niobium hydride and tantalum powder, XRF can be used for the express estimation of the composition. It is proposed to use a Spectroscan MAX-GVM crystal diffraction spectrometer for the analysis and to construct the calibration using the standard software that implements the fundamental parameter method. In this case, the resulting impurity contents can differ from reference values by one to two orders of magnitude. Such accuracy is often sufficient to adjust the technology. The limits of the XRF detection of impurities in Ta- and Nb-based materials have been established. For the elements determined by K-series lines (from Ti to Co), the detection limits range within 30–60 ppm; for the elements determined by M-series lines (Ta), the detection limit is approximately 200 ppm; and for L-series lines (Nb), it is from 100 to 150 ppm.