Fluorescent X-Ray Spectrographic Determination of Tantalum in Commercial Niobium Oxides

Abstract

Recent modifications in fluorescent x-ray spectrographic instrumentation permit the resolution of the tantalum Lai line from the usual interfering lines without a prohibitive loss of intensity. Tantalum La¡ line intensities as high as 750 counts per second can be obtained from a sample of 5% tantalum oxide in niobium oxide by the use of a molybdenum target x-ray tube, a quartz analyzing crystal, and a 4-inch Soller slit collimator.The residual tantalum content of "high-purity" niobium oxide was determined by use of standards prepared from tantalum-free zirconium oxide. Hand-mixed samples, when properly prepared, are as suitable as chemically precipitated samples. The effects of possible impurities, such as stannic oxide, ferrous oxide, titanium dioxide, and sodium sulfate on the analysis were calculated from adsorption data and determined experimentally. Only titanium dioxide was found in commercial niobium oxides in amounts that would result in a measurable analytical error.Fluorescent x-ray spectrography is a rapid and reliable method of analysis. It has an accuracy within ±5% of the amount present in the usual concentration range of 0.5 to 10% tantalum oxide and a lower limit of detection of approximately 0.03% tantalum oxide, and requires an average time per analysis of about 10 minutes, after preparation of standards. DURING the past several years the x-ray laboratory of the Eastern Experiment Station, Bureau of Mines, has received numerous requests to determine the tantalum content of commercial grades of niobium oxides. A survey of the literature indicated a need for a suitable method of analyzing such samples.

X-Ray Absorption and Emission

“…Simultaneous observation of standard and unknown, or rapid commutation betweer the two, is desirable. The method is of great value even when these ideal conditions are not realized (35,62,71,88,89). They are not realized, for example, when a working curve is used; yet this method of comparison is satisfactory in many simple analyses.…”

“…(83,35), and this leads to integrands of the form log (o + bx) dx/x, which are more difficult to handle than the simple exponential integrand that underlies Equation 1.In his treatment, Sherman makes use of emission coefficients, r, that perform the function of the empirical ft in Equation 1. Botl: quantities are proportionalVOL.…”

Quantitative determination of tantalum in niobium by neutron activation analysis

“…Quantitative analysis of tantalum-niobium systems is difficult by standard chemical methods. X-ray fluorescence has been used successfully under carefully controlled conditions (2)(3)(4)(5)(6). To avoid potential problems such as matrix effects and the high dependence on the method of sample preparation inherent in this technique neutron activation analysis was chosen for the present work.…”