Thermal conductivity of uranium: effects of purity and microstructure

Thermal conductivity curves for polycrystalline uranium are presented for the temperature range below 373$sup 0$K. The curves are for specimens prepared by different fabrication procedures from material of known purity and hardness. Included is a curve for U/2wt percent Mo alloy. Different mechanisms appear to be influencing the thermal conductivity behavior of uranium in well- defined temperature regions: below 37 to 43$sup 0$K, approximately 40 to approximately 80$sup 0$K, 80 to approximately 280$sup 0$K, and from 280$sup 0$K to the $alpha$ $Yields$ $beta$ transformation temperature. Mechanisms responsible for results in one temperature region continue to exert a strong influence in the next higher temperature region. Impurities and initial microstructure seem to influence results at any starting temperature. Evidence is presented for the possibility of imperfection ordering in uranium between approximately 40 and approximately 280$sup 0$K. It is postulated that the type of ordering is capable with a martensite-like behavior and that all physical property results depend on the extent of a modification of the $alpha$-phase on cooling below approximately 280$sup 0$K. (auth

Valence instabilities as a possible source of actinide system inconsistencies

The presence of a mixed-valence state in light actinides appears evident from the crystal structures of certain U, Np, and Pu phases. As supporting evidence, the physical property response of these actinide elements (and some of their alloys) is compared with that of rare-earth metallic compounds known to have an unstable valence. Impurities may stabilize an intermediate (different) valence state locally in rare-earth compounds in the presence of the valence state of the bulk phase. Impurity elements from different periodic table groupings may likewise stabilize different intermediate valence states in light actinide elements, thus contributing to inconsistencies in results reported by different experimentalists. Any model (theory) advanced for explaining the physical property behavior of U, Np, and Pu may also require consideration of a configurational limit. A phenomenological connection could exist between a martensitic transformation and the fluctuation temperature in both rare earth and actinide systems

HEAT CAPACITY OF PLUTONIUM DIOXIDE BELOW 325 K

The low-temperature heat capacity behavior of PuO/sub 2/ was found to be anomalous and irreproducible, changing slightly after every one of seven liquid helium coolings. Data obtained from a second series of liquid helium coolings, made after refiring three of four original FuO/sub 2/ wafers in air, were consistent with the last run of the first series. The final low-temperature heat capacity vs temperature curve was more like that reported for ThO/sub 2/ than it was for similar curves reported for UO/sub 2/ and NpO/sub 2/. A least squares equation relating heat capacity and temperature is given for the low-temperature region. Values of heat capacity, entropy, and enthalpy are listed for several temperatures. (auth

HEAT CAPACITY OF COPPER BELOW 300 K, A TEST OF TWO CALORIMETER DESIGNS

Two designs of adiabatic calorimeterss in which the surroundings follow the temperature of a test specimen at all times from the lowest temperature achieved by cooling up to room temperatures are described. Values for the heat capacity of oxygen-free, high conductivity copper are given in order to show the reliability to be expected from determinations of heat capacity of elements in which the self-heating by radioactive disintegration is appreciable and can be used as the sole source of heating. Equations based on least-squares analysis of data are listed for the OFHC copper. The methods of numerical integration used for thermodynamic properties are described and values of entropy and enthalpy of copper at 298.15 deg K are shown. (auth

Applicability of a valence fluctuation model to the observed physical property response of actinide materials

On montre que le comportement des propriétés physiques des éléments légers des actinides, U, Np, et Pu et certains de leurs alliages, est similaire à celui des composés intermétalliques de terres rares de valence mixte. On déduit que la théorie d'interconfiguration pourrait être aussi applicable aux matériaux d'actinides.It is shown that the physical property behaviour of the light actinide elements, U, Np, and Pu, and certain of their alloys, is like that of known mixed-valence, R.E. metallic compounds. It is inferred that interconfiguration fluctuation (ICF) theory could also be applicable to actinide materials

HEAT CAPACITY OF COPPER BELOW 300 K, A TEST OF TWO CALORIMETER DESIGNS

Two designs of adiabatic calorimeterss in which the surroundings follow the temperature of a test specimen at all times from the lowest temperature achieved by cooling up to room temperatures are described. Values for the heat capacity of oxygen-free, high conductivity copper are given in order to show the reliability to be expected from determinations of heat capacity of elements in which the self-heating by radioactive disintegration is appreciable and can be used as the sole source of heating. Equations based on least-squares analysis of data are listed for the OFHC copper. The methods of numerical integration used for thermodynamic properties are described and values of entropy and enthalpy of copper at 298.15 deg K are shown. (auth

Multiple martensitic transformations, incommensurate/commensurate phases and charge-density-wave states in plutonium metal: Their consequences

Simultaneous measurements of electrical resistivity, elongation and temperature have been made on a Pu metal specimen between {approximately}80K and 733K. This temperature range covers part of the {alpha}-phase range and up through a major portion of the {delta}-phase range. Results are discussed. 7 refs., 3 figs