Thermal properties of paramagnetic solid helium-3

It was shown in recent work that over a limited molar volume range and at asymptotically high temperatures the thermal modulations of the pressure along isochores of paramagnetic solid³He could be accounted for through the formalism of the Heisenberg model of an antiferromagnetically interacting localized spin-1/2 system. The internal consistency of this formalism requires the characteristic exchange-interaction parameter of the model derived from pressure modulation data to be identical with that appearing in the other thermal properties of this quantum solid. In a restricted temperature region where the spin excitations are the dominant thermal excitations of the solid, heat capacity data yield exchange-interaction parameters in fair agreement with those derived from pressures along isochores of larger molar volume. At higher temperatures, within well-defined limitations, thermal excitations involve both spin and phonon excitations. Here, because of the opposite temperature variations of the spin and phonon heat capacity components, the ensuing heat capacity minimum determines exactly the exchange-energy parameter and the relevant limiting Debye temperature as a function of the measured temperature location and value of the heat capacity extremum along the experimentally explored isochore. The exchange-energy parameters so derived display larger deviations from their predicted pressure-based values than those resulting from the lower temperature but still asymptotic spin-only heat capacities. At the present time, ambiguities in the experimental determinations of the characteristic Weiss temperatures of the asymptotic paramagnetic susceptibilities prevent one from deriving exchange-energy parameters with them. The present work leads to the prediction, within the limitations of the model formalism, of thermal properties of magnetized solid³He. Experimental investigations of these properties offer new approaches for probing the validity of the model formalism applied to paramagnetic solid³He.     

Thermal properties of liquid and solid metals

New generalized expressions for compressibility and thermal expansion of liquid and solid metals are presented.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 50, No. 6, pp. 979–983, June, 1986.     

Thermal stabilization of aluminium titanate and properties of aluminium titanate solid solutions

Aluminium titanate has a near zero thermal expansion coefficient (=0.8×10^–6 °C^–1) in the range 20 to 1000 °C, nevertheless it decomposes below 1200 °C.The thermal stabilization of Al₂TiO₅ without altering its thermal expansion has been considered by partial substitution in the structure compound of Al³⁺ ions by Fe³⁺ ions.The solid solutions prepared by solid state reaction are in agreement with the general formula Al(1–x)₂Fe_2x TiO₅(0<x<0.2)The iron ions present in the crystal structure of Al₂TiO₅ act on its lattice parameters and bring about a catalytic effect in the formation of materials.Solid solutions show a strong thermal stability and a thermal expansion coefficient specially for the solid solution (x=0.1) which is not far from the Al₂TiO₅ value even after annealing for 300 h at 1000 °C.The mechanical properties of such materials corresponding to that solid solution present strength values lower than Al₂TiO₅ ones. After annealing, however, these are improved later due to a microcrystallization.     

Thermal behavior and dissolution properties of naproxen from binary and ternary solid dispersions

Solid dispersions of 10% w/w naproxen (NAP) in poly(ethylene glycol) (PEG) (4000, 6000, or 20,000) as a carrier with or without incorporation of anionic (sodium dodecyl sulfate; SDS) or nonionic (Tween 80; Tw80) surfactant were prepared by the melting method. Physicochemical characteristics were determined by differential scanning calorimetry (DSC) and X-ray diffraction analysis. The results of dissolution studies showed that drug dissolution properties were better from ternary systems than from binary systems since in the former the wetting and solubilizing effects of surfactant and polymer were additive. No influence of the PEG molecular weight was found. The best performance given by anionic surfactant has been attributed to several factors, such as higher hydrophilicity, better solubilizing power, and most facile interaction with both drug and PEG. No important changes in solid-state characteristics or in drug dissolution properties were found after 30 months storage for dispersions with or without surfactant. Only a slight decrease in initial drug dissolution rate was observed at the highest concentration (10% w/w) of SDS.     

Magnetic properties of solid 3He at finite temperature

The Peierls inequality combined with a classical Monte Carlo evaluation of the free energy has been applied as a variational technique to the magnetic spin Hamiltonian of ³He. We find unexpectedly good agreement with the experimental phase diagram and other measured quantities.     

Low-temperature melting properties of strongly magnetized solid helium-3

Various equilibrium thermal properties of strongly magnetized solid³He at melting are discussed in terms of the asymptotic, isotropic, nearest-neighbor pair-exchange interaction model at temperatures above 3 mK. Experimental verification of the predictions of the model to a limited degree of approximation suggests the possibility of using solid³He, at or near melting, for the production of fractional or small fractional millikelvin temperatures. This requires its adiabatic demagnetization from currently accessible several millikelvin initial temperatures and large magnetic field strengths to final field strengths above but close to its critical magnetic field strength where its paramagnetism still prevails.Work performed under the auspices of U.S. ERDA.     

Thermal expansion of solid methane

Relative length changes in solid methane at its approximate vapor pressure have been measured between 4 and 26 K. The linear-expansion coefficient calculated from these data is found to have a maximum at 19.8 K, 0.6 K lower than the peak found in specific-heat measurements. A negative expansion coefficient has been observed below 8 K. The possibility of nuclear spin-species conversion is discussed in terms of the long equilibration times and the observed length changes below 8 K.Research supported by National Science Foundation.     

Local nanoelectromechanical properties of multiferroics Gd-doped BiFeO3-BaTiO3 solid solution

Bi(1-x-y)GdxBayFe(1-y)TiyO3 (x = 0.1 and y = 0.1, 0.2, 0.3) solid solutions have been prepared via solid state reaction method with the aim to obtaining magnetoelectric coupling (i.e., linear relation between magnetization and electric field) at room temperature. Optimum calcination and sintering strategies for obtaining pure perovskite phase, high density ceramics and homogeneous microstructures have been determined. The maximum ferroelectric transition temperature (Tc) of this system was 150-170 degrees C with the dielectric constant peak of 2300 at 100 kHz for y = 0.1. Well saturated piezoelectric loops were observed for all composition indicating room temperature ferroelectricity. Hardness and Young's modulus decrease with depth and with increasing concentration y.     

Magnetic properties of solid 3He down to 0.3 mK

Nuclear magnetization of solid ³He has been studied by static magnetization measurements from 10 mK down to 0.3 mK for molar volumes ranging from V = 24.14 to 21.02 cm³/mole in the bcc phase and from V= 19.83 to 19.26 cm³/mole in the hcp phase. In the bcc phase, both the antiferromagnetic transition temperature T _N and the reciprocal of the maximum magnetization V _max ^–1 at T _N vary in proportion to V ^16.5±1, and the magnetization below T _N is constant. The magnetization reduced by M _max is found to be represented by a universal function of the reduced temperature T/T _N. In the hcp phase, the magnetization can approximately be represented by Curie's law, and the estimated Weiss temperatures are below 50 K. We also observed that the boundary magnetism of liquid ³He depends considerably on pressure. The transition temperature of solid ³He to the antiferromagnetic phase coexisting with liquid in a restricted geometry is 15% higher than that of the bulk solid on the melting curve.     

X-ray characterization and electrical properties of SrCeO3 — SrZrO3 solid solution

The crystallographic structure of the SrCeO₂-SrZrO₂ solid solution was determined and the crystallographic constants were calculated from X-ray diffractometry data. The specific electrical conductivities were also determined in the temperature range 800° to 1200°C at different oxygen partial pressures. The thermal gap was calculated and related to the lattice parameters.     

Thermal and physico-mechanical properties of antifriction solid lubricant for cold plastic deformation of titanium alloys

The results of the investigations of thermophysical characteristics, thermomechanical and mechanical properties of epoxy-polysiloxane nanocomposites with different contents of modifying additives in the presence of fine-grained antifriction fillers. It is shown that the joint influence of the modifier (polysiloxane particles) and filler (graphite) on the formation of the composite structure during the hardening results in the essential improvement of its physico-mechanical properties. The optimal formulation of a composition to be used as an antifriction solid lubricant for a cold plastic deformation of titanium alloys is determined.     

Formal treatment of some low-temperature properties of melting solid helium-3

Recent observations of the low-field-strength paramagnetic susceptibility of melting solid ³He indicate its Curie-Weiss-type behavior at temperatures T > 5 mK. These require an identical temperature behavior of the magnetic melting-pressure shift over the same temperature range. Melting-pressure-shift measurements should thus independently confirm the observed temperature behavior of the susceptibility and yield, in addition, the Curie constant of melting solid ³He. Using the theoretical value of this constant in the low- or moderate-field-strength melting-pressure-shift formula, the calculated shifts appear to be currently accessible to measurements with acceptable accuracy at T > 5 mK. The inverse problem of determination of the paramagnetic moment or magnetization of melting solid ³He from melting-pressure shifts may be solved on the basis of a differential magnetothermodynamic relation without significant limitations on the applied external magnetic field strength or on the temperature range. Helium-3 melting-pressure and temperature measurements in the presence of a constant and uniform magnetic field of known strength should enable, within the above formalism, the determination of the magnetic phase diagram of solid ³He at melting down to the lowest experimentally accessible temperatures. This approach may supplement other independent methods of magnetic phase-boundary-line determinations of solid ³He.Work done under the auspices of the U.S. Department of Energy.     

Thermal and optical properties of benzofuran-2-yl 3-phenyl-3-methylcyclobutyl thiosemicarbazone

The thermal degradation of the benzofuran-2-yl 3-phenyl-3-methylcyclobutyl thiosemicarbazone (CBSC) was studied under air atmosphere using DSC and simultaneous TG/DTA at the temperature range 20–500 °C. Thermal melting activation energy which are 308.6 and 307.9 kJ/mol were evaluated using Kissinger method from DSC and DTA curves, respectively. The activation energy of thermal decomposition was calculated using the Ozawa method for two decomposition stages. The experimental results showed that the activation energy of decomposition for non-isothermal behavior are 123.8 and 135.2 kJ/mol for the first (at 5% weight loss) and second (at 20% weight loss) decomposition stages, respectively. By using hot probe method, electrical conduction mechanism of CBSC was found as p-type. The values of thermal activation energy of electrical conduction, E₁ and E₂, as calculated from lnσ=f(1000/T) curves, were found to be 3.90 and 0.36 eV, respectively. Optical absorption studies in the wavelength range 190–900 nm showed that direct optical band gap of the benzofuran-2-yl 3-phenyl-3-methylcyclobutyl thiosemicarbazone is 2.80 eV.     

Transport properties of Sm1-xCaxCr1-yCuyO3 solid solutions

Sm_1-xCa_xCr_1-yCu_yO₃ perovskite solid solutions were prepared, and their properties were studied. The solid solutions, unreactive with a ZrO₂-based solid electrolyte, are candidate electrode and interconnection materials for high-temperature fuel cells     

Magnetic properties of solid solutions between BiCrO3 and BiGaO3 with perovskite structures

Magnetic properties of BiCr_1−xGa_xO₃ perovskite-type solid solutions are reported, and a magnetic phase diagram is established. As-synthesized BiCrO₃ and BiCr_0.9Ga_0.1O₃ crystallize in a monoclinic (m) C2/c structure. The Néel temperature (T_N) decreases from 111 K in BiCrO₃ to 98 K in BiCr_0.9Ga_0.1O₃, and spin-reorientation transition temperature increases from 72 K in BiCrO₃ to 83 K in BiCr_0.9Ga_0.1O₃. o-BiCr_0.9Ga_0.1O₃ with a PbZrO₃-type orthorhombic structure is obtained by heating m-BiCr_0.9Ga_0.1O₃ up to 573 K in air; it shows similar magnetic properties with those of m-BiCr_0.9Ga_0.1O₃. T_N of BiCr_0.8Ga_0.2O₃ is 81 K, and T_N of BiCr_0.7Ga_0.3O₃ is 63 K. Samples with x = 0.4, 0.5, 0.6 and 0.7 crystallize in a polar R3c structure. Long-range antiferromagnetic order with weak ferromagnetism is observed below T_N = 56 K in BiCr_0.6Ga_0.4O₃, T_N = 36 K in BiCr_0.5Ga_0.5O₃ and T_N = 18 K in BiCr_0.4Ga_0.6O₃. BiCr_0.3Ga_0.7O₃ shows a paramagnetic behaviour because the Cr concentration is below the percolation threshold of 31%.     

Magnetic properties of solid solutions between BiCrO3 and BiGaO3 with perovskite structures

Abstract

Magnetic properties of BiCr_1?xGa_xO₃ perovskite-type solid solutions are reported, and a magnetic phase diagram is established. As-synthesized BiCrO₃ and BiCr_0.9Ga_0.1O₃ crystallize in a monoclinic (m) C2/c structure. The Néel temperature (T_N) decreases from 111 K in BiCrO₃ to 98 K in BiCr_0.9Ga_0.1O₃, and spin-reorientation transition temperature increases from 72 K in BiCrO₃ to 83 K in BiCr_0.9Ga_0.1O₃. o-BiCr_0.9Ga_0.1O₃ with a PbZrO₃-type orthorhombic structure is obtained by heating m-BiCr_0.9Ga_0.1O₃ up to 573 K in air; it shows similar magnetic properties with those of m-BiCr_0.9Ga_0.1O₃. T_N of BiCr_0.8Ga_0.2O₃ is 81 K, and T_N of BiCr_0.7Ga_0.3O₃ is 63 K. Samples with x = 0.4, 0.5, 0.6 and 0.7 crystallize in a polar R3c structure. Long-range antiferromagnetic order with weak ferromagnetism is observed below T_N = 56 K in BiCr_0.6Ga_0.4O₃, T_N = 36 K in BiCr_0.5Ga_0.5O₃ and T_N = 18 K in BiCr_0.4Ga_0.6O₃. BiCr_0.3Ga_0.7O₃ shows a paramagnetic behaviour because the Cr concentration is below the percolation threshold of 31%.     

Thermal analysis of liquid and solid propellants

Kinetic constants from differential scanning calorimetry data using heat evolution and variable heating rate methods were obtained for the thermal decomposition of a liquid monopropellant; good agreement was found between the observed and predicted half-life for the first order decomposition reaction. The rate of volatilization of nitroglycerin in a crosslinked double base propellant was investigated by isothermal and dynamic thermogravimetry and was found to be first order. The effect of sample size, atmospheric environment, aging and crosslink density of the propellant on the volatilization rate was determined. It was observed that the rate increased as (1) the sample was changed from a cylindrical plug to a powdered form, (2) the atmosphere around the sample was changed from nitrogen to helium to vacuum, (3) as the thermal stability of the sample decreased, and (4) the relative crosslink density was changed from a higher to a lower value. A kinetic compensation effect was found for cylindrical plugs but not for powdered samples.     

3D针刺C/SiC-TaC复合材料的热膨胀性能

采用液相加压浸渗法将TaC渗入到三维针刺毡中, 并结合反应熔体渗透法(RMI)制得C/SiC-TaC复合材料。采用热膨胀仪测量了热处理前后复合材料从室温到1400 ℃温度范围内的热膨胀系数(CTE), 发现C/SiC-TaC的CTE数值较C/SiC的高。从材料内部热应力的变化、 制备方法及添加物和基体的性能方面定性地分析了CTE的变化机制。研究表明, C/SiC-TaC复合材料的膨胀性能在各个温度段的变化机制不同, 低温段(1100 ℃以下)CTE的不断上升主要由90°无纬布、 TaC和SiC基体贡献, 该阶段的起伏波动主要由复合材料的结构应力和孔隙分布不均及残余Si产生; 高温段(1100 ℃以上)的热膨胀性能主要由0°无纬布和界面热应力决定。热处理降低了复合材料在1100 ℃以下的CTE, 也改变了高温段的变化规律。      

Thermal shock waves in nonlinear solid media

Heat transfer of the wave character is considered in linear and nonlinear media on the basis of a new law of the heat conduction with allowance not only for the first and second order temporal derivatives of the heat flux, but the higher order derivatives as well. This allowed us to reduce the heat transfer that was studied on the basis of a hyperbolic equation to a task about the heat transfer described by a parabolic equation with a retarded time argument. It is shown that under certain conditions for the heat transfer at free boundaries, the discontinuities of the first kind arising in the temperature distribution in nonlinear media are trans-formed to compression wave heat fluxes. The results obtained here confirm the assumptions made. The results can be used in designing the heat transfer in hypersonic vehicles under conditions of high-intensity aero-gas-dynamic and radiation heating.