Tantalum Samples Research Articles

Superconducting Critical Field of Tantalum as a Function of Temperature and Pressure

The results of precise critical field measurements on tantalum samples which show soft superconducting behavior are given along with direct measurements of the pressure effect, ${(\frac{\ensuremath{\partial}{H}_{c}}{\ensuremath{\partial}P})}_{T}$, as a function of temperature. The Bardeen-Cooper-Schrieffer theory is used as a guide in the extrapolation of these data to absolute zero from 1.1\ifmmode^\circ\else\textdegree\fi{}K. The advantages of using an ${H}^{2}$ vs ${T}^{2}$ representation for both the critical-field and pressure-effect data are discussed, and it is shown that if both sets of data can be represented in terms of power series [${H}^{2}$ or ${(\frac{\ensuremath{\partial}{{H}_{c}}^{2}}{\ensuremath{\partial}P})}_{T}$ vs ${T}^{2}$] over a limited range of temperature, it is then possible to write down explicit power series expressions for the differences in the thermodynamic functions between the normal and superconducting states over this same temperature range. The electronic contributions to the specific heats and the thermal expansions for tantalum are calculated from the experimental data.

Differential Paramagnetic Effect in Superconductors

The magnetic moment and the differential magnetic susceptibility of two spherical samples of tin and tantalum have been measured as a function of magnetic field and temperature. The differential paramagnetic effect (DPE) is observed in both ac and dc mutual inductance measurements provided the sample exhibits a good Meissner effect. For a superconducting sample in which the infinite conductivity behavior dominates the Meissner effect, the DPE does not appear in the ac measurements but does, under certain conditions, show up in dc measurements. The results of the dc mutual inductance measurements are used to classify the DPE as reproducible or nonreproducible. The former is of ideal Meissner-type superconductors while the latter is more of superconductors whose macroscopic magnetic properties are dominated by the classical infinite electrical conductivity behavior. The superconducting-to-normal transitions obtained by the three techniques are compared and the data discussed in view of (a) occurrence of the DPE; (b) magnitude of the DPE; (c) ability of these data to give information about the volume participation of the sample; and (d) relation of the characteristic magnetic fields determined by these transitions and the bulk critical field of the sample.

X-ray fluorescence spectrographic determination of impurities and alloying elements in tantalum container materials

X-ray fluorescence methods have been used for determining molybdenum, niobium, thorium, tungsten, yttrium and zirconium as impurities or alloying constituents in tantalum and binary tantalum alloys being investigated as container materials for molten plutonium fuels. Various solvents were tested for dissolving tantalum samples, and hydrofluoric acid was found to be the most suitable. Samples are dissolved in hydrofluoric acid and diluted to a known volume; then the solution is analyzed by means of an X-ray tube with a tungsten target. X-ray tube operating conditions and counting times were selected to give good precision in a minimum time. Effects of impurities and variations in X-ray tube voltage and current, scintillation counter voltage, solvent composition, dilution volume and count rate were determined. Molybdenum, niobium and zirconium as impurities in tantalum within the concentration range of 25–2000 p.p.m. are determined by means of a line-to-background intensity-ratio method with a precision ranging from 17 p.p.m. at the 25–100 p.p.m. level to 43 p.p.m. at the 2000 p.p.m. level. From 0.5 to 10 per cent of tungsten in tantalum-tungsten alloys is determined with an absolute standard deviation of 0.09 per cent by comparing the intensity ratio of the tungsten Lα1 to tungsten LαCompton for the sample with ratios obtained for known standards. Thorium or yttrium in binary alloys is determined in the 0.025 to 10 per cent concentration range, using an internal standard procedure. Thorium is added as an internal standard in the determination of yttrium, and yttrium is added as an internal standard in the determination of thorium. Following sample dissolution, the ThF4, and YF3 precipitates are separated from the tantalum, dissolved in H2SO4and diluted to volume, and the intensity ratio of the thorium to yttrium lines is measured. Relative standard deviations of 7 and 2 per cent, respectively, were obtained in the 0.025–0.1 and 0.1–10 per cent concentration ranges for yttrium, and 12 and 3 per cent for thorium in the 0.025–0.1 and 0.1–10 per cent concentration ranges.

X-ray fluorescence spectrographic determination of impurities and alloying elements in tantalum container materials

X-ray fluorescence methods have been used for determining molybdenum, niobium, thorium, tungsten, yttrium and zirconium as impurities or alloying constituents in tantalum and binary tantalum alloys being investigated as container materials for molten plutonium fuels. Various solvents were tested for dissolving tantalum samples, and hydrofluoric acid was found to be the most suitable. Samples are dissolved in hydrofluoric acid and diluted to a known volume; then the solution is analyzed by means of an X-ray tube with a tungsten target. X-ray tube operating conditions and counting times were selected to give good precision in a minimum time. Effects of impurities and variations in X-ray tube voltage and current, scintillation counter voltage, solvent composition, dilution volume and count rate were determined.Molybdenum, niobium and zirconium as impurities in tantalum within the concentration range of 25–2000 p.p.m. are determined by means of a line-to-background intensity-ratio method with a precision ranging from 17 p.p.m. at the 25–100 p.p.m. level to 43 p.p.m. at the 2000 p.p.m. level. From 0.5 to 10 per cent of tungsten in tantalum-tungsten alloys is determined with an absolute standard deviation of 0.09 per cent by comparing the intensity ratio of the tungsten Lα1 to tungsten LαCompton for the sample with ratios obtained for known standards. Thorium or yttrium in binary alloys is determined in the 0.025 to 10 per cent concentration range, using an internal standard procedure. Thorium is added as an internal standard in the determination of yttrium, and yttrium is added as an internal standard in the determination of thorium. Following sample dissolution, the ThF4, and YF3 precipitates are separated from the tantalum, dissolved in H2SO4and diluted to volume, and the intensity ratio of the thorium to yttrium lines is measured. Relative standard deviations of 7 and 2 per cent, respectively, were obtained in the 0.025–0.1 and 0.1–10 per cent concentration ranges for yttrium, and 12 and 3 per cent for thorium in the 0.025–0.1 and 0.1–10 per cent concentration ranges.

The heat conductivity of superconductors below 1° K

A method for the accurate measurement of thermal conductivity in the temperature region below 1°K has been developed. This method has been used to determine the heat conductivity of very pure samples of lead, tin, indium, thallium, tantalum and columbium between 0·2 and 1°K. The results have been discussed with reference to theory and to the experiments at higher temperatures. The conclusion is reached that the heat conductivity of a superconductive metal near absolute zero is identical with that of a dielectric crystal.