Click to increase image sizeClick to decrease image sizeKEYWORDS: incoloy 800oxidationhydrogensurface propertiespermeationpermeabilitydeuteriumpressure dependencehigh temperature
Abstract The magnetic susceptibility and electrical resistivity of uranium phosphides and UP-ThP solid solutions were measured. All the uranium phosphides exhibited paramagnetism at room temperature, and followed the Curie-Weiss law. The Néel point TN for UP2 and UP, and the Weiss constant θ were estimated. Ferromagnetic components made their appearance in UP2 and UP, in the temperature range below TN. With UP-ThP solid solutions, the changes according to composition observed in the values of TN and θ indicated that UP is magnetically diluted by ThP, which latter compound is characterized by Pauli paramagnetism, and whose presence contributes to diminish the exchange interactions. The electrical resistivity of UP increased rather rapidly with temperature up to a point corresponding to TN beyond which the tendency changed sharply to a slightly negative coefficient. ThP showed a consistently low value of resistivity, were slowly rising with temperature, and that of UP-ThP solid solutions revealed a behavior intermediate between those of UP and ThP.
The behavior in hydrolysis of uranium monocarbonitrides (UC1-xNx) of various compositions has been studied and compared with the hydrolysis of UN and UC. The products of the hydrolysis were found to be H2, CH4, C2H6, C3H8, NH3, CH3NH2, C2H5NH2 and C3H7NH2, and did not vary qualitatively with the composition (C/N), while quantitatively their relative amounts, and also the temperature of formation were found to be markedly affected by the composition. The more carbon-rich compounds tended to be easily hydrolyzed below 100°C, as in the case of UC, while the amenity to hydrolysis was found significantly weaker with the nitrogen-rich compounds, as with UN. The hydrolysis of carbonitrides is characterized by the formation of amines, which were found particularly abundant in the case of UC0.53N0.47 (C:N≈1:1). To elucidate the mechanism of the reaction under study, a mechanically mixed specimen of UN and UC was hydrolyzed. No amines were observed to be generated in this case. This finding was considered suggestive of two plausible mechanisms, namely, mutual interaction between free radicals located within short distances of each other, and the hydrogenation of skeletons such as C-C-N.
Self-consistent Hartree-Fock-Slater model cluster calculations are carried out in order to investigate the electronic structure of hydrogen chemisorption on transition metal surfaces. Orbital energies and results of Mulliken's population analysis are presented for H·Ni5, H·Ni9, H·Pd9 and H·W9 clusters. The level structures of the clusters are also given by density-of-states (DOS) curves and compared with the experimental UPS and EELS spectra. Hydrogen chemisorption gives rise to bonding levels near the bottom of the valence band and antibonding ones on the top. The energy difference between them in H·Ni9 is in good agreement with that obtained by EELS. It is concluded that not only localized d electrons but also sp electrons play important roles in hydrogen-metal bondings. Details of hydrogen-metal bond formation, electronic charge transfer and their differences with adsorbate metals are also discussed.
Non-relativistic and relativistic band structures of NaCl type uranium compounds were calculated with tight-binding approximation based on the rigid band concept. The calculations revealed that the narrow 5f band played important role, and from the desity of states curve the Fermi levels of these compounds were found to lie on or near the 5f band. Moreover, spin-orbit and crystalline field effects were seen to split the 5f band further into five sub-bands. The Fermi levels proved to be related to the lowest sub-band, in which two states were included, and the width of this sub-band was estimated to be 0.05eV. The validity of the foregoing band structure based on calculation is discussed in reference to specific heat at low temperatures and also to magnetic properties.
The magnetic susceptibility and electrical resistivity of uranium phosphides and UP-ThP solid solutions were measured. All the uranium phosphides exhibited paramagnetism at room temperature, and followed the Curie-Weiss law. The Néel point TN for UP2 and UP, and the Weiss constant θ were estimated. Ferromagnetic components made their appearance in UP2 and UP, in the temperature range below TN. With UP-ThP solid solutions, the changes according to composition observed in the values of TN and θ indicated that UP is magnetically diluted by ThP, which latter compound is characterized by Pauli paramagnetism, and whose presence contributes to diminish the exchange interactions. The electrical resistivity of UP increased rather rapidly with temperature up to a point corresponding to TN beyond which the tendency changed sharply to a slightly negative coefficient. ThP showed a consistently low value of resistivity, were slowly rising with temperature, and that of UP-ThP solid solutions revealed a behavior intermediate between those of UP and ThP.
The band structure of metallic Th and NaCl-type ThX (X=C, N, P, S) compounds were calculated by tight-binding method, with the parametrization improvement. Values of two-center parameters chosen so as to fit the result for Th given by Gupta & Loucks were found to be very close to two-center integrals with a suitable integration range. Applying this method for evaluating parameters, the band structures for ThX compounds were also computed. Population analysis to determine the electron populations in each orbital based on the results obtained by the method indicated that for all compounds calculated the occupied states consist mainly of σ type bonding between metalloid p and Th dr as well as bonding between π and Th dϵ.
Abstract Magnetic susceptibility measurements were carried out on octacoordinated uranium(IV) complexes, such as tetrakis(acetylacetonato)uranium (IV), tetrakis(trifluoroacetylacetonato)uranium (IV), tetrakis(benzoylacetonato)uranium(IV), tetrakis(dibenzoylmethanato)uranium(IV), tetrakis(thenoyltrifluoroacetonato)uranium(IV), tetrakis(cupferronato)uranium(IV), and uranium(IV)tetrachloride, in the temperature range from room temperature to the temperature of liquid nitrogen or liquid helium. The Curie-Weiss law holds above the temperature of liquid nitrogen, with a magnetic moment of 3.5–2.92 BM. For the latter two complexes, a temperature-independent paramagnetism was observed in the low temperature range; the other complexes also seemed to show the same trend. We tried to interpret the magnetic behavior on the basis of the crystal-field model of the square antiprism structure or the dodecahedron structure of the complexes.
