Express X-ray fluorescent analysis of technical-grade tantalum and niobium: from raw materials to products

Abstract

Determination of impurities in Ta- and Nb-based materials is a necessary operation in supporting technological processes. The existing approaches involve the transfer of a sample into a solution with subsequent isolation of impurities. This procedure is rather complicated and takes a lot of time. For this reason, it is of interest to study the possibilities of direct analysis of solid-phase samples of materials, e.g., X-ray fluorescence analysis (XRF). The usual scheme of X-ray fluorescence analysis, which involves the experimental construction of calibration characteristics for each element to be determined, requires using a large number of reference samples containing a rather wide range of impurities. We present the results of preliminary characterization of samples of technical-grade tantalum and niobium and products on their base. It is shown that for starting materials, only a significant absence of impurities can be determined using XPA, but even for sintered niobium hydride and Ta powder, XPA can be used as a method for rapid assessment of the composition. A SPECTROSCAN MAX GVM crystal-diffraction spectrometer can be used for analysis and a standard software that implements the fundamental parameter method (FPA) can be used for calibration. In this case, the obtained values of the content of impurities may differ by 1 – 2 orders of magnitude from the reference values. However, such an accuracy is often enough to correct technological processes. The limits of detecting impurities by XRF in Ta- and Nb-based materials are revealed: for elements determined by K-series (from Ti to Co), the detection limits lie in the range from 30 to 60 ppm, whereas for the elements determined by M-series (Ta) the detection limit is approximately 200 ppm and for L-series (Nb) the detection limit is in the range from 100 to 150 ppm.