No abstract available

[en] Phase stability of amorphous intermetallic alloys, in terms of both formation and thermal stability, can be related to the alloy chemistry of the crystalline counterpart: the intermetallic compounds. The formation of the amorphous alloys is generally favored by the composition range in which the complex-structured intermetallic compounds and nearby eutectic point are present. The relative thermal stability of the amorphous intermetallic alloys, expressed by the reduced crystallization temperature, T/sub rc/, (T/sub rc/= T/sub c/T/sub m/, where T/sub c/ is the crystallization temperature ⁰K, and T/sub m/ the melting temperature of the crystallized phase ⁰K) increases with the increasing of the structural complexity of the crystalline counterparts. Based on recent data of amorphous intertransiton metal alloys, T/sub rc/ increases rapidly from less than 0.1 for the simple structures of bcc, fcc, or hcp, to nearly 0.4 for more complex structures such as A15, Laves-, sigma- and CaCu₅-phases up to 0.6 for highly complex structures of eta-, delta-, and μ-phases. It can therefore be argued that alloy principles for the equilibrium compounds can be applied to the phase stability of the amorphous intermetallic alloys

No abstract available

[en] This paper shows that simple crystal chemistry rules may be applied to interpret and predict the solubility limit and phase stability of alloys at nonequilibrium conditions. Twenty-nine liquid-quenched metastable hcp solid solutions containing elements with both bcc and hcp allotropic forms were studied. Hcp solid solutions of Group III elements with Ti, Zr, and Hf obtained by splat cooling showed that the metastable solubility limits were semiquantitatively correlated to the size factors and c/a ratios. TEM studies indicated that the extended solubilities results from trapping of extra solute in the α' martensite matrices during L yields beta yields alpha' transformation. Hcp intra-rare earth solid solutions were controlled by the structural metastability, e.g. these hcp phases were all terminated at c/a ratios near 1.597. Thus, the linear correlation of the c/a deviation from ideality and phase stability proposed by Hodges was demonstrated. The solubility limit and structure stability for liquid-quenched metastable hcp phases, as well as the implication for the equilibrium solubility limits, are discussed

[en] The authors report an improved measurement of the semileptonic branching fractions of B mesons. B mesons are produced in the reaction e⁺e^-→Υ(4S)→B bar B, and have been analyzed with the CLEO II detector at the Cornell Electron Storage Ring (CESR). The data sample used for this analysis is substantially larger than has been used for any previous study. Semileptonic branching fractions have been extracted by fitting the inclusive electron and muon spectra to the refined free-quark model, and to the form-factor model. Consistency of the measured spectra with the theoretical models, including D, D*, D**(lv) production fractions, is assessed

[en] Due to the complexity of the structural, microstructural and compositional characteristics of spent fuel, basic leaching and dissolution mechanisms were studied with UO₂ matrix material, specifically with single-crystal UO₂, to isolate individual contributory factors. The effects of oxidation and oxidation-dissolution were investigated in different oxidation conditions, such as in air, oxygenated solutions and deionized water containing H₂O₂. In addition, the effects of temperature on dissolution of UO₂ were studied in autoclaves at 75 and 150⁰C. Also, oxidation and dissolution measurements were investigated via electrochemical methods to determine if those techniques could be applied to the characterization of leaching and dissolution of spent fuel in a hot cell. Finally, the effects of radiation were explored since the radiolysis of water may create a localized oxidizing condition at or near the spent fuel-solution interface, even in neutral or reducing conditions as commonly found in deep geological environments. The oxidation and oxidation-dissolution mechanisms for UO₂ are proposed as follows: The UO₂ surface is first oxidized in solution to form a UO/sub 2+x/ surface layer several angstroms thick. This oxidized surface has a high dissolution rate since the UO/sub 2+x/ reacts with the dissolved O₂, or H₂O₂, to form uranyl complex ions in a U(VI) state. As the uranyl ions exceed the solubility limits in solution, they become hydrolyzed to form solid deposits and suspended particles of UO₃ hydrates. The thickness and porosity of the deposited UO₃ hydrate surface-film is dependent on temperature, pH and deposition time. A long-term dissolution rate is then determined by the nature of the surface film, such as porosity, solubility and mechanical properties

[en] This talk reports the latest CLEO observation of anti D production in b decays, which provides new insight of the QCD interactions in heavy quark systems. The observed B semileptonic branching fraction has been significantly lower than QCD expectations, as was confirmed by recent lepton-lepton correlation studies at various experiments that removed most of the model dependence in previous generation measurements. One possible explanation to accommodate this lepton shortage or a wider hadronic width of B mesons is that the process b → c anti cs contributes at a higher rate than expected. That explanation, however, predicts more charm production in than is observed. Using lepton tags in B events this analysis measures the fraction of b → anti DX in addition to b →DX. The first observation of anti B → anti DDX has profound implications to both experiment and theory

[en] In the course of synthesis of superconductive alloys up to 1 mm thick by high-rate sputter deposition, metastable bcc phases of Nb₃Al, Nb₃Sn, Nb₃Ge, Nb₃(AlGe), and Nb₃Si were obtained. This paper reports our study of the phase transformation of metastable bcc solid solutions by heat treatment. The grain sizes of the as-deposited bcc phases depended on deposition temperature. For depositions made at approximately 10⁰C, large variations of grain size were observed among the materials, e.g. approximately 1000 A for Nb₃Al and Nb₃Sn, approximately 50 A for Nb₃Ge, Nb₃ (AlGe), and Nb₃Si. All bcc phases transformed to the A-15 phase at approximately 650⁰C within 24 hours except for Nb₃Si, which transformed into a tetragonal phase at approximately 750⁰C. The grain size of the A-15 phase was approximately three to five times the initial grain size of the bcc phase. The phase transformations in Nb₃(AlGe) and Nb₃Si were described by tentative time-temperature-transformation diagrams. Transmission electron microscopic investigation of the bcc → A-15 transformation for Nb₃Al shows the presence of both coherent and incoherent type precipitates in the early stages of transformation

[en] The sputtering technique was used to make the following superconductors, for which the phases and deposition kinetics are discussed: Nb₃Ge + GeO₂, Nb₃Al + Al₂O₃, Nb₃Sn + SnO₂, Nb₃Si + Al₂O₃, Nb₃Ge + Al₂O₃

[en] The oxidation and dissolution mechanisms for UO₂ and spent fuel will be quite similar based on this preliminary work with electrochemical leaching of UO₂ and spent fuel. In solutions containing oxygen or other oxidizing species, the UO₂ surface will be rapidly oxidized and dissolved following the transformation of uranium from U(IV) to U(VI). The hydrolysis of dissolved uranyl ions forms solid UO₃ hydrates or related complex compounds deposited onto the UO₂ surface, or other surfaces, as thin or thick coatings. Depending on the pH, temperature, and time, the various kinds of porosity and the mechanical properties of the hydrate coatings will control the dissolution rate. The effects of radiation, in terms of generation of H₂O₂, will enhance the dissolution kinetics. Electrochemical methods may be useful for determining the surface conditions, dissolution rate, and accelerated dissolution behavior for NO₂ and spent fuel. Electrochemial methods can rapidly generate much information in terms of dissolution rate and surface film properties - such as thickness, porosity, and oxidation state - in-situ during the leaching process