Showing papers on "Thermal expansion published in 1988"

Calculated thermal properties of metals.

Abstract: The thermal properties of the 14 nonmagnetic cubic metals through the 4d transition series are derived from first-principles electronic-structure calculations coupled with a Debye treatment of the vibrating lattice. Debye temperatures and Gr\"uneisen constants are derived from an analysis of the compressional characteristics of rigid-lattice binding curves and are used to define the contribution of the lattice vibrations to the free energy. A minimization of the resulting free energy with respect to volume yields temperature-dependent lattice separations and coefficients of thermal expansion. Theoretical values of cohesive energies, equilibrium lattice separations, bulk moduli, Debye temperatures, Gr\"uneisen constants, and coefficients of thermal expansion are derived directly from computed electronic-structure results. Good agreement with experiment is found for all computed quantities.

Thermal properties of rocks

Abstract: All the important thermal properties of rocks can be estimated from the graphs and tables in this report. Most of the useful published data are summarized herein to provide fairly accurate evaluations of thermal coefficients and parameters of rocks for many engineering and scientific purposes. Graphs of the published data on common rocks and minerals were prepared to show the relationships of thermal conductivity with decimal solidity (one minus decimal porosity), water or air pore content, content of certain highly conducting minerals, and temperature. Tables are given of pressure effect on thermal conductivity of minerals and rocks, anisotropy of conductivity, thermal expansion, heat transfer, density, heat generation in rocks, and activation energies of conduction mechanisms in single crystals of minerals. A series of graphs show the specific heats of rock-forming minerals as a function of temperature; with these graphs the specific heat of a rock can be calculated from its mode as accurately as it can be measured. Calculations of conductivity, diffusivity, and thermal inertia of a rock from its mode are described. Discussions of radiative thermal conductivity, radioactive heat generation, and heat transfer in rocks are provided.

High-temperature thermal expansion of six metallic elements measured by dilatation method and X-ray diffraction

Abstract: The thermal expansion of silver, gold, copper, nickel, molybdenum and tungsten has been measured by the dilatation method. The thermal expansion values of silver, gold, copper and nickel have also been evaluated from lattice parameter measurements by X-ray diffraction. These six metals were found to exhibit a nearly uniform expansion over the temperature ranges covered. The thermal expansion values obtained by the dilatation method are in good agreement with those determined by X-ray diffraction. The present results appear also to agree well with those reported previously in the literature.

Carbon-carbon - An overview

Abstract: In nonoxidizing high-temperature environments, carbon-carbon composites retain room temperature properties to more than 2225 C; in oxidizing environments, the variety of coatings thus far developed limits maximum operating temperatures to about 1600 C. The high thermal conductivity and low thermal expansion of these composites renders them ideal for applications encountering thermal shocks. In addition, the variety of fibers, weave patterns, and layup procedures that can be used for the composites allows mechanical properties to be carefully tailored over a wide range to fit the application in question.

Principles and Applications of Wafer Curvature Techniques for Stress Measurements in Thin Films

Abstract: Measurement of the curvature induced in a wafer (or other flat plate) by the stress in a thin film has long been used as a convenient and accurate technique for the determination of the stress. Numerous improvements over the years have led to instruments that provide simple and rapid measurements of stress as a function of the time and temperature for any desired thermal history. A computer controlled instrument using laser scanning will be briefly described and its capabilities and limitations discussed. Applications of the technique to a variety of thin film materials will be discussed. In addition to the effects of differences in thermal expansion, stresses associated with various deposition techniques, gain or loss of material, phase transformations and flow will be considered. In aluminum based systems, themal expansion, plastic flow and phase transformation play major roles. Refractory metals show, in addition, large stresses associated with the deposition process. In inorganic dielectric systems thermal expansion effects are usually relatively small; deposition effects and the gain or loss of material are the dominant effects. Silica based glasses formed by chemical vapor deposition, for example, show large stress changes due to gain or loss of water, and plasma deposited silicon nitride films show large effects associated with hydrogen. Overall, determination of the stress as a function of time and temperature is a valuable part of the evaluation of a thin film material for use in a VLSI device.

Acoustic and Thermodynamic Properties of Ethanol from 273.15 to 333.1 5 K and up to 280 MPa

Abstract: The velocity of sound in ethanol has been measured in the temperature range between 273.15 and 333.15 K and at pressures up to 280 MPa using the phase comparison pulse-echo method with two reflectors, which has been described previously. The density, isothermal compressibility, isobaric thermal expansion and the specific heat at constant pressure of ethanol have been evaluated from the measured sound velocity, using an improved method of computation.

Thermal expansion studies of the group IV‐VII transition‐metal disilicides

Abstract: The thermal expansions of the group IV‐VII transition‐metal disilicides and Mn15Si26 have been investigated from room temperature to about 1500 K by x‐ray powder‐diffraction techniques. The results are discussed in relation to the structure of the compounds. Most of the disilicides studied exhibit a high degree of thermal expansion isotropy, exceptions being ZrSi2, HfSi2, and CrSi2. The observed linear thermal expansion coefficients are normally in the range 8–9×10−6 K−1 (298 K) to 11–15×10−6 K−1 (1300 K). The most extreme expansion was exhibited by CrSi2 with a linear expansion coefficient of 22×10−6 K−1 for the a axis at 1300 K.

Thermal conductivity and thermal expansion of stainless steels D9 and HT9

Abstract: Renewed interest in the use of metallic fuel in a liquid-metal fast breeder reactor has prompted study of the thermodynamic and transport properties of fuel and cladding materials. Two stainless steels are of particular interest because of their good performance under irradiation. These are D9, an austenitic steel, and HT9, a ferritic steel. Thermal conductivity and thermal expansion data for these cladding alloys are of particular interest in assessing in-reactor behavior. These two properties were measured for the two steels at temperatures to 1200 K. Of particular interest is the influence on these properties of a phase transition in HT9.

Effects of Interfacial Films on Thermal Stresses in Whisker Reinforced Ceramics

Abstract: Toughening of whisker-reinforced (or fiber-reinforced) ceramics by whisker pullout requires debonding at the whisker/matrix interface. Compressive clamping stresses, which would inhibit interface debonding and/or pullout, are expected in composites where the matrix has a higher thermal expansion coefficient than the whisker. Because such mismatch in thermomechanical properties can result in brittle composites, it is important to explore approaches to modify the thermal stresses in composites. As a result, the effects of a film at the whisker/matrix interface on the stresses due to thermal contraction mismatch upon cooling are considered in this study. Analysis of various properties of the film are considered for the whisker/matrix systems, in particular for SiC/Al2O3, SiC/cordierite, and SiC/mullite composites. Reduction of thermomechanical stresses is shown to occur when the interfacial film has a low Young's modulus. Also, when the whisker has a lower thermal expansion coefficient than the matrix (e.g., SiC/Al2O3), the interfacial stresses generated during cooling decrease as the thermal expansion coefficient of the film increases.

Effect of thermal expansion mismatch and fiber coating on the fiber/matrix interfacial shear stress in ceramic matrix composites

Abstract: A modified indentation technique has been used to measure the interfacial shear stress in a number of ceramic matrices containing silicon carbide fibers. It was shown that the frictional component of interfacial stress was essentially zero when matrix thermal expansion was lower than that of the fiber and increased linearly with thermal expansion mismatch when matrix thermal expansion was higher. The interfacial shear stress was lowered when the fibers were coated with BN. Lower matrix shear stresses resulted in a more extensive fiber pullout during the composite fracture.

Determination of thermal strains by moire interferometry

Abstract: An existing method is extended to measure thermal strain distributions on an absolute basis. Free thermal expansion and stress-induced deformations are separated, allowing the determination of coefficients of expansion, stress-induced strains, normal stresses and shear stresses. The method is applicable to many steady-state and transient thermal-strain problems.

Chemical structures and properties of low thermal expansion coefficient polyimides

Abstract: The relationships, between chemical structures of various aromatic polyimides and their thermal expansion coefficients, were investigated and the properties of low thermal expansion polyimides were elucidated Such low values were observed for polyimides obtained from pyromellitic dianhydride or 3,3‘4,4‘-biphenyltetracarboxylic dianhydride and aromatic diamines which included only benzene or pyridine rings fused at para-positions without a flexible linkage It was proposed that these low thermal expansion coefficients were related to the lineerity of their polymer molecular skeletons In particular, PIQ-Ll 00 (Hitachi Chemical Co Ltd) is one such low thermal expansion polyimide and, it has excellent mechanical properties, thermal stability, and low absorbed moisture content

Absolute thermal expansion measurements of single-crystal silicon in the range 300–1300 K with an interferometric dilatometer

Abstract: The thermal expansion coefficient of single-crystal silicon has been measured in the range 300–1300 K using an interferometric dilatometer. The measurement system consists of a double-path optical heterodyne interferometer and a radiant image furnace with a quartz vacuum tube, which provides both accuracy and rapidity of measurement. The uncertainties in length and temperature determination are within 4 nm and 0.4 K, respectively. A high-purity dislocation-free FZ silicon single crystal was used in the study. Thermal expansion coefficients of silicon oriented in the [111] direction have been determined over the temperature range from 300 to 1300 K. The standard deviation of the measurement data from the best fitting for the fifth-order polynomial in temperature is 2.1×10−8 K−1. The present value for the thermal expansion coefficient agrees within 9×10−8K−1 with the interferometric measurement of polycrystalline pure silicon by Roberts (1981) between 300 and 800 K and within 1.2 × 10−7 K−1 with the single-crystal X-ray diffractometric measurement by Okada and Tokumaru (1984) between 300 and 1300 K.

Effect of chemical pressure on the magnetism of YMn2: magnetic properties of Y1-xScxMn2 and Y1-xLaxMn2

Abstract: Magnetic susceptibility, thermal expansion and NMR have been measured for the pseudobinary Laves phase intermetallic compounds Y1-xScxMn2 with x

Thermal expansion studies on the group IV-VII transition metal diborides

Abstract: The thermal expansions of the group IV–VII transition metal diborides were studied with the aid of X-ray powder diffraction. The diborides were studied over the temperature range 298–1500 K. All the diborides except for CrB 2 display larger thermal expansion coefficients in the c direction than in the a direction. The expansion coefficients in the c direction decrease with increasing radius of the metal atom, a fact which can be correlated to an increase in metal-boron bond strength. The thermal expansion coefficient in the a direction changes very little with the size of the metal radius, owing to the fact that the bonding strength in the basal plane is determined by the strong B-B bonds within the boron layer. The mean thermal expansion coefficients of the diborides increase linearly with their reciprocal melting points.

Anisotropy of thermal expansion of GaAs on Si(001)

Abstract: We have measured the thermal expansion between 20 and 450 °C of epitaxially grown GaAs thin films on Si(001) as well as of the Si substrate by means of high‐resolution x‐ray scattering. Our results show that the thermal expansion of GaAs in the direction parallel to the film plane follows the thermal expansion of the silicon substrate and is therefore smaller than in bulk GaAs. Furthermore, the thermal expansion perpendicular to the film plane (parallel to the growth direction) exceeds the bulk GaAs value by the Poisson contribution as a result of the in‐plane constraint. The thermal expansion coefficients for GaAs films on Si(001) substrates in the directions parallel and perpendicular to the film plane are αT∥(GaAs) =3.46×10−6/K and αT⊥(GaAs) =8.91×10−6/K, respectively.

Thermal Expansion Coefficients of Unidirectional Fiber-Reinforced Ceramics

Abstract: The influence of internal stresses, due to the thermomechanical mismatch between the fiber and the matrix, on the thermal expansion behavior of unidirectional fiber reinforced ceramics is considered. Using the composite cylinder model, the effective thermal expansion coefficients of the composite are calculated from the total strains, which consist of the strains due to temperature changes and the strains induced by the presence of internal stresses. The results reveal that when the fiber and the matrix have the same elastic constants, the rule of mixtures approach can be used to obtain the thermal expansion coefficients of the composite, as observed in previous analytical solutions. Also, for the case of low volume fractions of fibers with Young's moduli much larger than those of matrices, and the thermal expansion coefficients lower than those of matrices, the transverse thermal expansion coefficient of the composite is higher than that of either the fiber or the matrix. However, unlike previous studies, the present analysis provides a physical basis for this phenomenon in terms of the internal thermal stress state within the composite.

Thermal expansion of organic and inorganic matrix composites - a review of theoretical and experimental studies

Abstract: This paper reviews theoretical and experimental studies conducted in organic, ceramic, and metal matrix composites containing cylindrical, lamellar, and spheroidal inclusions as reinforcements. Mathematical formulations proposed to predict thermal expansion coefficients of fiber, disk, and sphere reinforced organic and inorganic matrix composites have been reviewed. Experimental studies undertaken to confirm theoretical predictions of thermal expansion coefficients of a variety of reinforcement geometry composites have also been discussed. 51 references.

Thermal Expansion Coefficients of High-Tc Superconductors

Abstract: High-Tc superconducting oxides were confirmed to have much higher thermal expansion coefficients than various substrate materials. The difference in thermal expansion between superconductor and substrate materials corresponded well with the crack size formed in the film. Thermal expansion of Ba2YCu3O7-δ abruptly changes at about 350°C and 650°C, which reflects the change of oxygen concentration and the phase transition, respectively. The expansion pattern varied considerably by the substitution of yttrium by ytterbium, suggesting a difference in the kinetics of oxygen uptake and secession between the two superconductors.

A molecular dynamics study of solid and liquid UO2

Abstract: The authors present an extensive series of molecular dynamics simulations of UO2 in the solid and liquid states, in which they calculate the ionic diffusion coefficients and some of the important thermodynamic quantities. The simulations are based on a rigid-ion model derived from the new shell model potentials of Jackson and co-workers (1986) and make use of recently developed constant-pressure and constant-temperature techniques. The simulations confirm that UO2 is an oxygen superionic conductor, as suggested by recent neutron scattering experiments. The temperature of the diffuse transition to the superionic regime is in satisfactory agreement with experiment, as is the melting point of the model system. The thermal expansion coefficient, specific heat and bulk modulus for the solid agree well with experiment below about 2500 K but are less satisfactory near the melting point; they suggest that the differences may be due to the effect of electronic excitations. The volume increase on melting and thermodynamic quantities of the liquid are sensitive to details of the inter-ionic potentials and are in only fair agreement with experiment.

Calculation of the thermal expansion of metals using the embedded-atom method

Abstract: The linear coefficient of thermal expansion of the fcc metals Cu, Ag, Au, Ni, Pd, and Pt are computed using the semiempirical embedded-atom method to determine the energetics. The results are in good agreement with experiment. The importance of including the equation of state in the determination of the empirical functions is discussed.

Molar Volume and Thermodynamics of the Structural Change of Liquid Se-Te System

Abstract: The molar volume of the liquid Se–Te system has been measured using a high energy γ-ray attenuation method. The thermal expansion coefficient, α p , deduced from the dependence on temperature of the molar volume has a minimum which shifts to the higher temperature with Se concentration. It has been shown that α p consists of two parts, one due to the normal expansion effect and the other associated with the structural change in the liquid. The latter has a linear relation with the anomalous part of the specific heat. Discussion is given on a model describing the structural evolution with temperature and/or pressure.

Densities of Pb-Sn alloys during solidification

Abstract: Data for the densities and expansion coefficients of solid and liquid alloys of the Pb-Sn system are consolidated in this paper. More importantly, the data are analyzed with the purpose of expressing either the density of the solid or of the liquid as a function of its composition and temperature. In particular, the densities of the solid and of the liquid during dendritic solidification are derived. Finally, the solutal and thermal coefficients of volume expansion for the liquid are given as functions of temperature and composition.

The temperature dependence of Cr3+ photoluminescence in some garnet crystals

Abstract: The temperature dependence of Cr3+ photoluminescence has been measured in the garnets Y3Ga5O12, Gd3Sc2Al3O12 and Gd3Sc2Ga3O12. The observed intensities in the 2Eg to 4A2g and 4T2g to 4A2g emission transitions are interpreted using a model based on the effects of small changes in unit-cell size on energy level shifts due to variations in the strength of the octahedral crystal field. Such changes in unit-cell length are produced by either crystal non-stoichiometry or thermal expansion. The effect of thermal expansion is to reduce the energy level splitting between 2Eg and 4T2g excited states with increasing temperature. In garnets where this splitting is small, spin-orbit admixture of these levels produces measurable changes in the emission band shape and radiative decay time at low temperatures.