D.T. Peterson

Electrotransport of interstitial atoms in yttrium

Abstract The electrotransport velocities of carbon, oxygen and nitrogen in yttrium were determined in the temperature range of 1235 to 1460°C. Diffusion coefficients and effective charges were calculated for these elements for the same temperatures. Yttrium metal purified by the electrotransport method showed a decrease in oxygen content from 780 to 90 p.p.m. and an increase in the resistance ratio from 12 to 45.

ELECTROTRANSPORT OF CARBON, NITROGEN, AND OXYGEN IN GADOLINIUM.

Abstract The electrotransport velocities of carbon, nitrogen and oxygen were measured in both the alpha and beta crystalline forms of gadolinium. Measurements were made at 1050, 1125, 1200 and 1265 °C. All three solutes migrated in the same direction as the electron flow but much higher mobilities were observed in the β (b.c.c.) form. Diffusion coefficients and effective valences were calculated for these elements at the same temperatures. Electrotransport was shown to be an effective method of purifying a small amount of gadolinium as indicated by resistance ratio measurements.

Preparation, electrical and superconducting properties of massive Th4H15☆

Abstract Massive specimens of Th 4 H 15 have been prepared by a high pressure, high temperature synthesis. These specimens showed superconducting transitions at 7.5–8.5 K by magnetic and resistance measurements. The transition was narrower than in powdered Th 4 H 15 samples but stiil not isothermal. The electrical resistivity of Th 4 H 15 was measured from 4.2 K to 300 K. This compound is a metallic conductor and has a resistivity minimum near the stoichiometric composition.

Purification of rare-earth metals by electrotransport

Abstract The principles of the electrotransport purification process are described, together with those variables that affect the degree of purity attainable. Experiments on the purification of yttrium, lutetium and gadolinium with respect to carbon, nitrogen and oxygen are described and the results compared with those predicted from theory. Metal purities were evaluated by resistance ratio measurements and chemical analyses.

PREPARATION OF HIGH PURITY THORIUM AND THORIUM SINGLE CRYSTALS.

Abstract Ultra-high purity thorium has been prepared using electrotransport as the refining method. This metal has a total impurity content of less than 50 p.p.m. and a resistance ratio of greater than 1000. A procedure was also developed by which single crystals of the high purity thorium could be prepared by repeated heating of the specimen through its alpha to beta phase transformation followed by prolonged heating just below the transformation temperature.

The composition of ThH2 and diffusion of hydrogen in ThH2

Abstract The composition of thorium dihydride was determined as a function of temperature and pressure. By using this information, the diffusion coefficients of hydrogen in thorium dihydride were calculated from previous measurements of the parabolic reaction-rate constants. The activation energy for diffusion was found to be 2.3 kcal and D 0 was 2.11·10 −4 cm 2 /sec.

THE PREPARATION OF HIGH-PURITY THORIUM BY THE MAGNESIUM REDUCTION OF THORIUM TETRACHLORIDE

Abstract A process is described for preparing high-purity thorium metal in kilogram quantities. Magnesium metal is used to reduce purified ThCl4 and to form a liquid thorium-magnesium intermediate alloy. This alloy is processed to a thorium sponge metal which is consolidated by arc casting and purified by electron-beam melting. Thorium metal containing a total of 250 p.p.m. of impurities has been consistently prepared by this process.

Diffusion of hydrogen in barium metal

Abstract The diffusion coefficients for hydrogen in barium metal were measured from 200 ° to 620 °C. D 0 was found to be 4.0 × 10 −3 and ΔH was 4.5 kcal. The solubility limit of BaH 2 in barium was determined in the same temperature range and was in agreement with previous measurements.

Hydrogen locations, diffusion and the electronic density of states in yttrium dihydrides: A nuclear magnetic resonance investigation☆

Abstract We report results of wide-line and pulsed proton magnetic resonance measurements on yttrium dihydrides, YH x (1.63 ⩽ x ⩽ 1.98), covering the temperature range 140–760 K and yielding information on hydrogen locations, diffusion and the density of states in the dihydride phase. Our principal conclusions are as follows. (1) At x = 1.98, wide-line second moment measurements indicate that 15% of the octahedral (O) sites in the f.c.c. CaF 2 structure are occupied by hydrogen. (2) Spin-lattice relaxation time measurements in the rotating frame ( T 1 ρ versus T ) yield hydrogen jump frequencies ν j showing three distinct regions in which the activation energy E act for hydrogen diffusion increases with T . (3) For x = 1.98 ν j is consistently higher than for x = 1.92, corroborating the partial occupation of O sites for x values below 2.0. (4) At the lower limiting composition ( x ≈ 1.8) E act becomes anomalously large (approximately 1.1 eV atom −1 ), compared with the value 0.5 eV atom −1 at x = 1.92, and the diffusion rate is about 10 3 times smaller. (5) At low temperatures the spin-lattice relaxation rate T −1 1 is dominated by the conduction electron contribution T −1 1 e . The quantity (T 1e T) −1 2 which is proportional to the density of states at the Fermi level, is 0.061 ± 0.002 s −1 2 K −1 2 for the dihydride compositions studied, indicating a constant density of states in the dihydride phase.

Electronic structure studies of metal hydrides

Abstract The electronic structures of representative metal hydrides were examined using photoelectron and optical spectroscopies. The results of these studies are compared with predictions of the one-electron band model for the various metal-hydrogen systems. Generally excellent agreement is found. The discussion emphasizes Nb4H3 and the dihydrides of scandium, yttrium, neodymium, gadolinium, terbium, erbium, lutetium, hafnium and thorium.