Low temperature heat capacity and magnetic properties of UF3

The low temperature heat capacity of UF(3) has been measured using an adiabatic low temperature calorimeter in the temperature range from 10 to 350 K. These data are complemented at the lowest temperature region with data obtained with a Quantum Design PPMS-14 device in the temperature range from 0.5 to 20 K. Good agreement between both techniques has been found, and from these experimental results the absolute entropy of UF(3) at 298.15 K has been determined as 126.8 ± 2.5 J K(-1) mol(-1). On the basis of the specific heat data and the magnetization measurements performed on a SQUID device, a transition at 1.59 K attributed to Curie temperature of a ferromagnetic transition has been found in this study. This observation makes UF(3) a unique compound with an unusually low ferromagnetic ordering temperature.     

DTA determination of specific heats of liquids

A method is described for conversion of the experimentally measured total heat capacity of a sample of low-boiling liquid, heated in a closed, pressure-proof pan, to its specific heat.     

Low temperature specific heat calculations for amorphous polystyrene

Numerous attempts have previously been made to explain low temperature specific heat anomalies in glasses. The potential value of low frequency Raman data in interpreting such results is demonstrated here: the density of states for the 60 cm^?1 side-group mode in amorphous polystyrene is calculated from Raman measurements. Using the harmonic approximation, the contribution to the specific heat from this side-group motion is calculated and added to the Debye term. The form of C/T³ between 1.5 and 4 K is shown to be reproduced, although the magnitude of C/T³ is only about 70% of experimental values. This discrepancy and the anomalous behaviour below 1.5 K is believed to the due to lower-lying vibrational states of the system, perhaps not accessible through Raman scattering experiments.     

Low temperature properties of winterized methyl babassu biodiesel

In this work, differential scanning calorimetry and X-ray diffraction techniques were employed to evaluate the influence of the winterization process on the low temperature properties of methyl babassu biodiesel. The results have shown that the crystallization onset temperature for the non-winterized biodiesel is around 266.4 K (?6.6 °C) which is reduced to 263.6 K (?9.4 °C) for the liquid fraction of winterized biodiesel. The 14 % reduction in the amount of saturated fatty acid methyl esters is probably responsible for the improvement of low temperature properties of winterized methyl babassu biodiesel.     

Interfacial properties of thermally oxidized Ta2Si on Si

Many refractory metal silicides have received great attention due to their potential for innovative developments in the silicon‐based microelectronic industry. However, tantalum silicide, Ta₂Si, has remained practically unnoticed since its successful application in silicon carbide technology as a simple route for a high‐k dielectric formation. The thermal oxidation of Ta₂Si produces high‐k dielectric layers, (O? Ta₂Si)‐based on a combination of Ta₂O₅ and SiO₂. In this work, we investigate the interfacial properties of thermally oxidized (850–1050 °C) Ta₂Si on commercial silicon substrates. The implications of diffusion processes in the dielectric properties of an oxidized layer are analyzed. In particular, we observe migration of tantalum pentoxide nanocrystals into the substrate with increasing oxidation temperature. An estimation of the insulator charge and interfacial O? Ta₂Si/Si trap density is also presented. Copyright © 2008 John Wiley & Sons, Ltd.     

Electrical properties of single-crystalline CaAl2Si2

Electrical resistivity and Hall coefficient measurements of single-crystalline CaAl(2)Si(2) revealed that CaAl(2)Si(2) is a metal in which both electrons and holes contribute to the transport properties; its dominant carriers are holes at temperature below 150 K but electrons above that temperature.     

Low temperature solventless synthesis and characterization of Ni and Fe magnetic nanoparticles

We have successfully implemented a facile, one-pot solventless synthesis procedure starting from acetylacetonate salts and CaH(2) to obtain carbon-coated ferromagnetic metallic Ni and Fe nanoparticles at low temperature. The use of CaH(2) as a reductant drastically reduces reaction temperature down to 140 °C.     

Low temperature properties of acetonitrile confined in MCM-41

The effect of confinement on the phase changes and dynamics of acetonitrile in mesoporous MCM-41 was studied by use of adsorption, FT-IR, DSC, and quasi-elastic neutron scattering (QENS) measurements. Acetonitrile molecules in a monolayer interact strongly with surface hydroxyls to be registered and perturb the triple bond in the C[triple bond]N group. Adsorbed molecules above the monolayer through to the central part of the cylindrical pores are capillary condensed molecules (cc-acetonitrile), but they do not show the hysteresis loop in adsorption-desorption isotherms, i.e., second order capillary condensation. FT-IR measurements indicated that the condensed phase is very similar to the bulk liquid. The cc-acetonitrile freezes at temperatures that depend on the pore size of the MCM-41 down to 29.1 A (C14), below which it is not frozen. In addition, phase changes between alpha-type and beta-type acetonitriles were observed below the melting points. Application of the Gibbs-Thomson equation, assuming the unfrozen layer thickness to be 0.7 nm, gave the interface free energy differences between the interfaces, i.e., Deltagamma(l/alpha) = 22.4 mJ m(-2) for the liquid/pore surface (ps) and alpha-type/ps, and Deltagamma(alpha/beta) = 3.17 mJ m(-2) for alpha-type/ps and beta-type/ps, respectively. QENS experiments substantiate the differing behaviors of monolayer acetonitrile and cc-acetonitrile. The monolayer acetonitrile molecules are anchored so as not to translate. The two Lorentzian analysis of QENS spectra for cc-acetonitriles showed translational motion but markedly slowed. However, the activation energy for cc-acetonitrile in MCM-41 (C18) is 7.0 kJ mol(-1) compared to the bulk value of 12.7 kJ mol(-1). The relaxation times for tumbling rotational diffusion of cc-acetonitrile are similar to bulk values.     

Synthesis, structure, and properties of BaAl2Si2

Single crystals of BaAl2Si2 were grown from an Al molten flux and characterized using single-crystal X-ray diffraction at 10 and 90 K and neutron diffraction at room temperature. BaAl2Si2 crystallizes with the alpha-BaCu2S2 structure type (Pnma), is isostructural with alpha-BaAl2Ge2, and is an open 3D framework compound, where Al and Si form a covalent cagelike network with Ba2+ cations residing in the cages. BaAl2Si2 has a unit cell of a=10.070(3) A, b=4.234(1) A, and c=10.866(3) A, as determined by room-temperature single-crystal neutron diffraction (R1=0.0533, wR2=0.1034). The structure as determined by single-crystal neutron and X-ray diffraction (10 and 90 K) indicates that BaAl2Si2 (Pnma) is strictly isostructural to other (alpha)-BaCu2S2-type structures, requiring site specificity for Al and Si. Unlike BaAl2Ge2, no evidence for an alpha to beta (BaZn2P2-type, I4/mmm) phase transition was observed. This compound shows metallic electronic resistivity and Pauli paramagnetic behavior.     

Influence of synthesis temperature on structural and magnetic properties of magnetoferritin

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Specific heats of guayule and natural rubbers above the glass transition temperature

Heat capacities of guayule and natural rubbers were measured between 228 and 333 K using a DuPont 990 Differential Scanning Calorimeter. Data obtained were fitted to a straight line. We obtained the following equations where C_p is given in cal g^?1 K^?1. For guayule rubber, C_p = 22.6152 × 10^?4T + 0.7731 (correlation factor = 0.99). For natural rubber. C_p = 16.9195 × 10^?4T + 0.9209 (correlation factor = 0.98). Furthermore, some theoretical considerations and instrumental conditions were analyzed so that the determinations of heat capacities could be improved.     

Low temperature heat capacity and magnetic studies on DyCu5

Low temperature heat capacity studies on DyCu₅ revealed a λ-anomaly at 6.55 K. Evaluation of the entropy indicated that the ground state is not (2J + 1) fold degenerate. High field magnetization data yield a moment of 9.28 μ_B at 4.2 K and 120 kOe.     

Structural and magnetic properties of orthorhombic LixMnO2

Rietveld refinement of the crystal and magnetic structures of Li_xMnO₂ (x = 0.98, 1.00, 1.02) are performed using neutron and X-ray measurements. A significant structural disorder due to the presence of manganese ions in lithium positions (Mn_Li) and lithium ions in manganese ones (Li_Mn) is found to be a common feature of Li_0.98MnO₂, Li_1.00MnO₂, and Li_1.02MnO₂.An essential anisotropy of the thermal-expansion coefficients of the lithium manganese oxides is observed in the temperature range of 1.5–300 K. Furthermore, the distortion of the oxygen octahedral environment around the manganese ions decreases when the temperature lowers. This is attributed to the strong exchange interactions between parallel exchange-coupled Mn chains. First-principles calculations of the effective exchange-interaction parameters in Li₁₆Mn₁₆O₃₂ confirm the essential antiferromagnetic interactions between the chains. In addition, a hypothetical (Li₁₅Mn)Mn₁₆O₃₂ structure where a lithium atom located between the Mn double layers is replaced by a manganese atom is considered. The calculations reveal that the presence of such defects results in appearance of a ferromagnetic component that agrees with the magnetic measurements.     

Compressibility and specific heats of heavier condensed rare gases near the liquid-vapor critical point

This study concerns the way to describe some physical properties of simple liquids by using the Bogoliubov-Born-Green-Kirkwood-Yvon hierarchy. It constructively analyzes the recent contribution of Sarkisov [G. N. Sarkisov, J. Chem. Phys. 119, 373 (2003)] on the structural behavior of a simple fluid near the liquid-vapor critical point. His work, already compared with computer simulation studies, is here brought into direct contact for the heavier condensed rare gases Ar, Kr, and Xe with (a) experiment and (b) earlier theoretical investigations. Directions for future studies then emerge.     

Determination of specific heats of some edible oils and fats by differential scanning calorimetry

Measurements of specific heat as a function of temperature were carried out with a differential scanning calorimeter on rape-seed, soybean, sunflower and corn oils and on lard.

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Zusammenfassung Es wurden Messungen der spezifischen Wärme als Funktion der Temperatur von Raps-, Soia-, Sommerblumen- und Mais-ölen und von Schmalz mit Hilfe von einem Dynamische-Differenz-Kalorimeter durchgeführt.

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Automatic estimation of heats of atomization and heats of reaction

Various additivity schemes for estimating heats of atomization have been evaluated to test their usefulness for designing a computer program. The approach is based on the Allen scheme and uses parameters obtained from thermochemical data. In addition, a method has been developed which allows the direct calculation of reaction enthalpies. Only the immediate environment of the bonds involved in the reaction has to be scanned. A program based on this method utilizes thermochemical parameters, too. Computation times with this program are extremely short and independent of the size of the molecules participating in the reaction. The procedure can be applied to a large variety of organic compounds. Examples demonstrate the accuracy of the predicted values.