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Thermodynamics of Cr2O3, FeCr2O4, ZnCr2O4 and CoCr2O4

Description: High temperature heat capacity measurements were obtained for Cr{sub 2}O{sub 3}, FeCr{sub 2}O{sub 4}, ZnCr{sub 2}O{sub 4} and CoCr{sub 2}O{sub 4} using a differential scanning calorimeter. These data were combined with previously-available, overlapping heat capacity data at temperatures up to 400 K and fitted to 5-parameter Maier-Kelley C{sub p}(T) equations. Expressions for molar entropy were then derived by suitable integration of the Maier-Kelley equations in combination with recent S{sup o}(298) evaluations. Finally, a database of high temperature equilibrium measurements on the formation of these oxides was constructed and critically evaluated. Gibbs energies of Cr{sub 2}O{sub 3}, FeCr{sub 2}O{sub 4} and CoCr{sub 2}O{sub 4} were referenced by averaging the most reliable results at reference temperatures of 1100, 1400 and 1373 K, respectively, while Gibbs energies for ZnCr{sub 2}O{sub 4} were referenced to the results of Jacob [Thermochim. Acta 15 (1976) 79-87] at 1100 K. Thermodynamic extrapolations from the high temperature reference points to 298.15 K by application of the heat capacity correlations gave {Delta}{sub f}G{sup o}(298) = -1049.96, -1339.40, -1428.35 and -1326.75 kJ mol{sup -1} for Cr{sub 2}O{sub 3}, FeCr{sub 2}O{sub 4}, ZnCr{sub 2}O{sub 4} and CoCr{sub 2}O{sub 4}, respectively.
Date: January 9, 2007
Creator: Ziemniak SE, Anovitz LM, Castelli RA, Porter WD
Partner: UNT Libraries Government Documents Department

Multiple ordered phases in the filled skutterudite compound PrOs4As12

Description: Magnetization, specific heat, and electrical resistivity measurements were made on single crystals of the filled skutterudite compound PrOs{sub 4}As{sub 12}. Specific heat measurements indicate an electronic specific heat coefficient {gamma} {approx} 50-200 mJ/mol K{sup 2} at temperatures 10 K {le} T {le} 18 K, and {approx} 1 J/mol K{sup 2} for t {le} 1.6 K. Magnetization, specific heat, and electrical resistivity measurements reveal the presence of two, or possibly three, ordered phases at temperatures below {approx} 2.3 K and in fields below {approx} 3 T. The low temperature phase displays antiferromagnetic characteristics, while the nature of the ordering in the other phase(s) has yet to be determined.
Date: March 20, 2006
Creator: Yuhasz, W M; Butch, N P; Sayles, T A; Ho, P; Jeffries, J R; Yanagisawa, T et al.
Partner: UNT Libraries Government Documents Department

Phenomenological two-gap model for the specific heat of MgB2

Description: The authors show that the specific heat of the superconductor MgB{sub 2} in zero field, for which significant non-BCS features have been reported, can be fitted, essentially within experimental error, over the entire range of temperature to T{sub c} by a phenomenological two-gap model. The resulting gap parameters agree with previous determinations from band-structure calculations, and from various spectroscopic experiments. The determination from specific heat, a bulk property, shows that the presence of two superconducting gaps in MgB{sub 2} is a volume effect.
Date: June 22, 2001
Creator: Bouquet, F.; Wang, Y.; Fisher, R.A.; Hinks, D.G.; Jorgensen, J.D.; Junod, A. et al.
Partner: UNT Libraries Government Documents Department

Is U3Ni3Sn4 best described as near a quantum critical point?

Description: Although most known non-Fermi liquid (NFL) materials are structurally or chemically disordered, the role of this disorder remains unclear. In particular, very few systems have been discovered that may be stoichiometric and well ordered. To test whether U{sub 3}Ni{sub 3}Sn{sub 4} belongs in this latter class, we present measurements of the x-ray absorption fine structure (XAFS) of polycrystalline and single-crystal U{sub 3}Ni{sub 3}Sn{sub 4} samples that are consistent with no measurable local atomic disorder. We also present temperature-dependent specific heat data in applied magnetic fields as high as 8 T that show features that are inconsistent with the antiferromagnetic Griffiths' phase model, but do support the conclusion that a Fermi liquid/NFL crossover temperature increases with applied field. These results are inconsistent with theoretical explanations that require strong disorder effects, but do support the view that U{sub 3}Ni{sub 3}Sn{sub 4} is a stoichoiometric, ordered material that exhibits NFL behavior, and is best described as being near an antiferromagnetic quantum critical point.
Date: April 8, 2003
Creator: Booth, C. H.; Shlyk, L.; Nenkov, K.; Huber, J. G. & De Long, L. E.
Partner: UNT Libraries Government Documents Department

The Solid-State Heat-Capacity Laser

Description: Heat-capacity operation of a laser is a novel method by which high average powers can be generated. In this paper, we present the principles behind heat-capacity operation, in addition to describing the results of recent experiments.
Date: December 8, 2003
Creator: Rotter, M D; Dane, C B; Gonzales, S A; Merrill, R D; Mitchell, S C; Parks, C W et al.
Partner: UNT Libraries Government Documents Department

A COMPUTATIONAL STUDY OF PHYSICAL AND CHEMICAL INHIBITION IN A PERFECTLY STIRRED REACTOR

Description: This paper reports a set of modeling studies that were undertaken to acquire a more detailed knowledge of combustion inhibition mechanisms. Mixtures of H{sub 2}/O{sub 2}/Ar reacting in the idealized perfectly stirred reactor were investigated. Three H{sub 2}/O{sub 2} kinetic mechanisms were considered, differing from one another by the number of HO{sub 2} reactions included. Two physical inhibitors, Ar and N{sub 2}, and one chemical inhibitor, HBr, were investigated. Additional parameters considered were pressure, equivalence ratio, inhibitor concentration and rate coefficient variation. The most effective inhibitor was HBr which acted chemically and caused substantial reduction in radical concentrations in the mixtures considered. The molecules Ar and N{sub 2} acted as physical diluents with N{sub 2}, the more effective of the two due to its larger heat capacity.
Date: May 1, 1980
Creator: Brown, Nancy J. & Schefer, Robert W.
Partner: UNT Libraries Government Documents Department

Disorder and size effects on Kondo interactions and magneticcorrelations in CePt2 nanoscrystals

Description: The evolution of the Kondo effect and magnetic correlations with size reduction in CePt{sub 2} nanoparticles (3.1-26 nm) is studied by analysis of the temperature-dependent specific heat and magnetic susceptibility. The antiferromagnetic correlations diminish with size reduction. The Kondo effect predominates at small particle size with trivalent, small Kondo temperature (T{sub K}) magnetic regions coexisting with strongly mixed valent, large T{sub K} nonmagnetic regions. We discuss the role of structural disorder, background density of states and the electronic quantum size effect on the results.
Date: December 12, 2006
Creator: Chen, Y.Y.; Huang, P.H.; Ou, M.N.; Wang, C.R.; Yao, Y.D.; Lee,T.K. et al.
Partner: UNT Libraries Government Documents Department

Measurement of Specific Heat Capacity Using Differential Scanning Calorimeter

Description: This document describes the process used at the Idaho National Laboratory’s (INL) High Temperature Test Laboratory (HTTL) for measuring specific heat capacity using a differential scanning calorimeter (DSC). The document is divided into four sections: Approach, in which the technique is described; Setup, in which the physical system is described; Procedure, in which the testing steps are listed and detailed; and Example Test, in which a typical test is outlined following the steps listed in the Procedure section. Example data, results, photos, and curves are provided throughout the document to assist other users of this system.
Date: November 1, 2008
Creator: Daw, J. E.
Partner: UNT Libraries Government Documents Department

Lattice vibrations in noncrystalline solids

Description: The specific heat of noncrystalline solids differs from that predicted by the Debye model by amounts much larger than is known for crystalline solids. This deviation is most pronounced at temperatures below 1 deg K. Near 0.1 deg K. the experimental specific heat approaches a linear temperature dependence and is up to 30 times larger than predicted by the Debye model. This paper describes Brillouin scattering experiments, and also measurements of the thermal conductivity in thin glass fibers. This work is aimed at elucidating the nature of the excitations responsible for this large specific heat. It is concluded that Debye phonons have sufficiently long lifetimes to be considered as good normal modes in noncrystalline solids and also that these phonons are the main carriers of heat at low temperatures. (11 figures. 29 references) (auth)
Date: August 1, 1973
Creator: Pohl, R.O.; Love, W.F. & Stephens, R.B.
Partner: UNT Libraries Government Documents Department

Energetics of Nanomaterials

Description: This project, "Energetics of Nanomaterials," represents a three-year collaboration among Alexandra Navrotsky (UC Davis), Brian Woodfield and Juliana Boerio-Goates (BYU), and Frances Hellman (UC Berkeley). It's purpose has been to explore the differences between bulk materials, nanoparticles, and thin films in term of their thermodynamic properties, with an emphasis on heat capaacities and entropies, as well as enthalpies. the three groups have brought very different expertise and capabilities to the project. Navrotsky is a solid-state chemist and geochemist, with a unique Thermochemistry Facility emphasizing enthalpy of formation measurements by high temperature oxide melt and room temperatue acid solution calorimetry. Boerio-Goates and Woodfield are calorimetry. Hellman is a physicist with expertise in magnetism and heat capacity measurements using microscale "detector on a chip" calorimetric technology that she pioneered. The overarching question of our work is "How does the free energy play out in nanoparticles?", or "How do differences in free energy affect overall nanoparticle behavior?" Because the free energy represents the temperature-dependent balance between the enthalpy of a system and its entropy, there are two separate, but related, components to the experimental investigations: Solution calorimetric measurements provide the energetics and two types of heat capacity measurements the entropy. We use materials that are well characterized in other ways (structurally, magnetically, and chemically), and samples are shared across the collaboration.
Date: January 28, 2005
Creator: Navrotsky, Alexandra; Woodfield, Brian; Boerio-Goates, Juliana & Hellman, Frances
Partner: UNT Libraries Government Documents Department

Thermodynamic data for biomass conversion and waste incineration

Description: The general purpose of this collection of thermodynamic data of selected materials is to make property information available to the engineering community on chemical mixtures, polymers, composite materials, solid wastes, biomass, and materials not easily identifiable by a single stoichiometric formula. More than 700 materials have been compiled covering properties such as specific heat, gross heat of combustion, heat of fusion, heat of vaporization, and vapor pressure. The information was obtained from the master files of the NBS Chemical Thermodynamics Data Center, the annual issues of the Bulletin of Chemical Thermodynamics, intermittent examinations of the Chemical Abstracts subject indexes, individual articles by various authors, and other general reference sources. The compilation is organized into several broad categories; materials are listed alphabetically within each category. For each material, the physical state, information as to the composition or character of the material, the kind of thermodynamic property reported, the specific property values for the material, and citations to the reference list are given. In addition, appendix A gives an empirical formula that allows heats of combustion of carbonaceous materials to be predicted with surprising accuracy when the elemental composition is known. A spread sheet illustrates this predictability with examples from this report and elsewhere. Appendix B lists some reports containing heats of combustion not included in this publication. Appendix C contains symbols, units, conversion factors, and atomic weights used in evaluating and compiling the thermodynamic data.
Date: September 1, 1986
Creator: Domalski, E.S.; Jobe, T.L. Jr & Milne, T.A.
Partner: UNT Libraries Government Documents Department

Electronic and Phase Stability Properties of V-X (X=Pd, Rh, Ru) Alloys

Description: In this work, we focus on the ordered structures of V-X systems, where X=Ru, Rh, Pd, and relate the variation in the difference of the numbers of valence electrons of the alloy constituents to the information contained in the constitution phase diagrams, and the electronic and stability properties. The electronic properties deduced from the low-temperature specific heat studies are presented for the V-Ru and V-Rh systems and compared with those of the V-Pd alloys for which new experimental results are also included. The theoretical analysis based on first-principles electronic structure calculations confirms the measured variation of the electronic specific heat coefficients with alloy composition, and predicts specific ordering trends in the V-X systems. The superconducting properties are described for the V-X disordered alloys, the ordered V{sub 1}-{sub x}Rh{sub X} and V{sub 1}-{sub x}Ru{sub x} systems, and related to their structural instability.
Date: April 21, 2004
Creator: Turchi, P A; Waterstrat, R M; Kuentzler, R; Drchal, V & Kudrnovsky, J
Partner: UNT Libraries Government Documents Department

Synthesis and properties of bulk metallic glasses in Pd-Ni-P and Pd-Cu-P alloys

Description: Bulk amorphous Pd-Ni-P and Pd-Cu-P alloy rods with diameters 7-25 mm were synthesized over a wide composition range using a fluxing technique. For most bulk amorphous Pd-Ni-P alloys, the difference {Delta}T=T{sub x}-T{sub g} between the crystallization temperature T{sub x} and the glass transition temperature T{sub g} is larger than 90 K, while for bulk amorphous Pd-Cu-P alloys, {Delta}T varies from 27 to 73 K. Pd{sub 40}Ni{sub 40}P{sub 20} has the highest glass formability, and 300-g bulk amorphous cylinders, 25mm dia and 50mm long, can be easily produced. This size is not an upper limit. The paper presents the glass formation ranges for both ternary alloy systems and data on the thermal stability of the amorphous alloys, as well as their specific heat, density, and elastic properties.
Date: November 1, 1996
Creator: He, Y. & Schwarz, R.B.
Partner: UNT Libraries Government Documents Department

Cell asymmetry correction for temperature modulated differential scanning calorimetry

Description: The quality of measurement of heat capacity by differential scanning calorimetry (DSC) is based on strict symmetry of the twin calorimeter, which is important for temperature-modulated DSC. Heat capacities for sapphire-filled and empty aluminium calorimeters (pans) under designed cell imbalance caused by different pan-masses were measured. In addition, positive and negative signs of asymmetry were explored by analyzing the phase-shift between temperature and heat flow for sapphire and empty runs. The phase shifts change by more than 18{degree} depending on asymmetry sign. Once the asymmetry sign is determined, the asymmetry correction for modulated DSC can be made.
Date: December 31, 1996
Creator: Ishikiriyama, K. & Wunderlich, B.
Partner: UNT Libraries Government Documents Department

Magnetocaloric effect of Gd{sub 4}(Bi{sub x}Sb{sub 1{minus}x}){sub 3} alloy series

Description: Alloys from the Gd{sub 4}(Bi{sub x}Sb{sub 1{minus}x}){sub 3} series were prepared by melting a stoichiometric amounts of pure metals in an induction furnace. The crystal structure is of the anti-Th{sub 3}P{sub 4} type (space group I{bar 4}3d) for all the compounds tested. The linear increase of the lattice parameters with Bi concentration is attributed to the larger atomic radius of Bi than that of Sb. Magnetic measurements show that the alloys order ferromagnetically from 266K to 330K, with the ordering temperature increasing with decreasing Bi concentration. The alloys are soft ferromagnets below their Curie temperatures, and follow the Curie-Weiss law above their ordering temperatures. The paramagnetic effective magnetic moments are low compared to the theoretical value for a free Gd{sup 3+}, while the ordered magnetic moments are close to the theoretical value for Gd. The alloys exhibit a moderate magnetocaloric effect (MCE) whose maxima are located between 270K and 338K and have relatively wide peaks. The peak MCE temperature decreases with decreasing Bi concentration while the peak height increases with decreasing Bi concentration. The Curie temperatures determined from inflection points of heat capacity are in good agreement with those obtained from the magnetocaloric effect. The MCE results obtained from the two different methods (magnetization and heat capacity) agree quite well with each other for all of the alloys in the series.
Date: December 1, 1999
Creator: Niu, Xuejun
Partner: UNT Libraries Government Documents Department

Mechanics of Metals with Phase Changes

Description: New experimental data is presented on some exotic metals that exhibit phase changes at cryogenic temperatures. The types of phase changes that were detected in the specific heat data range from martensitic (diffusion less) transitions to superconducting transitions. In addition, the charge density wave (CDW) state in uranium metal was detected in the specific heat. Specific-heat measurements were made in zero-magnetic field using an apparatus capable of obtaining temperatures as low as 0.4 K. Calibration performed on this apparatus, using a single-crystal copper sample, show its accuracy to be 0.50%, while the resolution was better than 0.1%. Our measurements demonstrate that similar high precision and accurate specific-heat measurements can be obtained on milligram-scale samples. In Chapters 2 and 3, specific-heat measurements are presented for the B2 (CsCl structure) alloy AuZn and for {alpha}-uranium (orthorhombic symmetry). The AuZn alloy exhibits a continuous transition at 64.75 K and an entropy of transition of ({Delta}S{sub tr}) 2.02 J K{sup {minus}1} mol{sup {minus}1}. Calculation of the Debye temperature, by extrapolating of the high temperature phase elastic constants to T = 0 K yields a value of 207 K ({+-}2 K), in favorable agreement with the calorimetric value of 219 K ({+-}0.50 K), despite the intervening martensitic transition. Reported results for single-crystal {alpha}-U show a low-temperature limiting {Theta}{sub D} of 256 K ({+-}0.50 K) and four low-temperature anomalies: a superconducting transition below 1 K, an electronic transition at 22 K, and two anomalies at 38 K and at 42 K indicative of the CDW state. In order to continue the study of the actinide series of elements, a program was initiated to first purify and then grow single crystals of plutonium. Accordingly, the focus of Chapters 4 through 6 will be a description of plutonium sample preparation. In this program plutonium metal was purified via ...
Date: January 1, 2001
Creator: Lashley, J.C.
Partner: UNT Libraries Government Documents Department

Heat Capacity Measurements in Pulsed Magnetic Fields

Description: The new NHMFL 60T quasi-continuous magnet produces a flat-top field for a period of 100 ms at 60 Tesla, and for longer time at lower fields, e.g. 0.5 s at 45 Tesla. We have developed for the first time the capability to measure heat capacity at very high magnetic fields in the NHMFL 60T quasi-continuous magnet at LANL, using a probe built out of various plastic materials. The field plateau allows us to utilize a heat-pulse method to obtain heat capacity data. Proof-of-principle heat capacity experiments were performed on a variety of correlated electron systems. Both magnet performance characteristics and physical properties of various materials studied hold out a promise of wide application of this new tool.
Date: October 23, 1998
Creator: Jaime, M.; Movshovich, R.; Sarrao, J.L.; Kim, J.; Stewart, G.; Beyermann, W.P. et al.
Partner: UNT Libraries Government Documents Department

Utilization of sensitivity coefficients to guide the design of a thermal battery

Description: Equations are presented to describe the sensitivity of the temperature field in a heat-conducting body to changes in the volumetric heat source and volumetric heat capacity. These sensitivity equations, along with others not presented, are applied to a thermal battery problem to compute the sensitivity of the temperature field to 19 model input parameters. Sensitivity coefficients, along with assumed standard deviation in these parameters, are used to estimate the uncertainty in the temperature prediction. From the 19 parameters investigated, the battery cell heat source and volumetric heat capacity were clearly identified as being the major contributors to the overall uncertainty in the temperature predictions. The operational life of the thermal battery was shown to be very sensitive to uncertainty in these parameters.
Date: August 1, 1998
Creator: Blackwell, B.F.; Dowding, K.J.; Cochran, R.J. & Dobranich, D.
Partner: UNT Libraries Government Documents Department