Showing papers on "Thermal expansion published in 1984"

Precise determination of lattice parameter and thermal expansion coefficient of silicon between 300 and 1500 K

Abstract: The lattice parameter of high‐purity silicon is measured as a function of temperature between 300 and 1500 K, and the linear thermal expansion coefficient is accurately determined. Precise measurements are made by the high‐temperature attachment for Bond’s x‐ray method to a few parts per million. It is found that the temperature dependence of the linear thermal expansion coefficient α(t) is empirically given by α(t)=(3.725{1−exp[−5.88×10−3{(t−124)} +5.548×10−4t)×10−6 (K−1), where t is the absolute temperature ranging from 120 to 1500 K. It is shown that the lattice parameter in the above temperature range can be calculated using α(t) and the lattice parameter at 273.2 K (0.5430741 nm). Measured values of the lattice parameter and the thermal expansion coefficient for high‐purity float‐zoned (100 kΩ cm) and Czochralski‐grown (30 Ω cm) single crystals are uniformly distributed within ±1×10−5 nm and ±2×10−7 K−1 with respect to the values obtained from the above empirical formula.

Metals during rapid heating by dense currents

Abstract: Research on metals, particularly refractory metals, during pulsed heating by high density currents (up to ~ 107 A/cm2) is reported. In particular, studies have been made of the specific heat and thermal expansion of metals in the liquid state, the resistivity in the liquid state as a function of the amount of energy supplied during free and confined expansion generating pressures up to 4·104 atm, the visible emission, the heat effusion, the changes in certain properties upon melting, the dispersal of a metal during an electrical explosion, and the anomalies of the specific heat and electron emission of a metal in the solid state which stem from the high rate of Joule heating. The experimental data reported on liquid metals (Al, Cu, Mo, W) at high temperatures and high pressures (tens of kilobars) are of considerable interest for the theory of liquid metals.

Scaling relations in the equation of state, thermal expansion, and melting of metals

Abstract: A simple and yet quite accurate prediction of volume as a function of pressure for metals and alloys is presented. Thermal expansion coefficients and melting temperatures are predicted by simple, analytic expressions and results compare favorably with experiment for a broad range of metals. All of these predictions are made possible by the discovery of universality in binding energy relations for metals.

Influence of Silane Treatment and Filler Fraction on Thermal Expansion of Composite Resins

Abstract: The coefficient of thermal expansion of experimental composite materials containing either silane-treated or untreated fillers in a triethylene glycol dimethacrylate (TEGDMA) matrix was investigated. The results show that an inverse linear relationship existed between volume fraction filler and coefficient of thermal expansion. No differences were seen between silane-treated and untreated composites, while it was found that repeated heating (aging) caused the thermal expansion to decrease for all material combinations.Reduction in the coefficient of thermal expansion with increased filler fraction of unbonded filler indicates that the polymerization shrinkage of the matrix induces hoop stresses around the fillers.By use of a simplified theoretical model (Appendix), these stresses could be estimated. These estimates revealed that the induced stresses were remarkably high, and that increased filler fraction increased the tensile stress level surrounding the filler particles. Since these tensile stresses cou...

Heat Transfer Enhancement in a Paraffin Wax Thermal Storage System

Abstract: Heat transfer enhancement in a thermal storage system consisting of vertically arranged fins between a heated and cooled horizontal finned-tube arrangement is reported. The high thermal expansion coefficient and low viscosity of paraffin wax, at temperatures above 50/sup 0/C, are utilized to induce natural convection in the liquid phase even at small thicknesses. The experimental data on the rate of production of liquid as a function of time and temperature of the hot surface is presented. The photographs of the melted zone indicate a naturally buoyant flow induced in the neighborhood of the vertical fins causes a rapid melting of the solid wax and a downdraft along the cooler solid phase surface. The heat transfer coefficient at the interface is calculated from experimentally determined instantaneous locations of the moving boundary.

Effect of interlayers in ceramic-metal joints with thermal expansion mismatches

Abstract: The internal stress resulting from the thermal expansion mismatch between alumina and steel with and without an interlayer was evaluated. On the basis of the calculation, alumina and steel were bonded using the interlayer method and hot isostatic pressing at 1273 to 1573 K under 100 MPa for 30 min. When a laminated interlayer (niobiumlmolybdenum) was used, a joint with high bonding strength was obtained.

Compendium of thermophysical property measurement methods: Vol. 1, survey of measurement techniques

Abstract: This book describes the state-of-the-art methods for the measurement of thermal and electrical conductivity, thermal diffusivity, specific heat, thermal expansion, and thermal radiative properties of solid materials, from room temperature to very high temperatures. Topics considered include axial heat flow methods of measuring thermal conductivity, the analysis of apparatus with radial symmetry for steady-state measurements of thermal conductivity, thermophysical property determinations using direct heating methods, the guarded hot-plate method for thermal conductivity measurements, the hot-wire method for the measurement of the thermal conductivity of refractory materials, the B.S. 1902 panel test method for the measurement of the thermal conductivity of refractory materials, high-temperature measurements of electric conductivity, pulse techniques for thermal diffusivity measurement, temperature wave techniques, adiabatic calorimetry, modulation calorimetry, thermal expansion measurement by interferometry, and certified reference materials for thermophysical properties.

Thermal expansion of polycrystalline aggregates: I. Exact analysis

Abstract: An exact relation is developed between the thermal expansion coefficient and the bulk modulus of statistically isotropic polycrystalline aggregates composed of crystals of hexagonal, tetragonal or trigonal symmetry. This relation is exploited to derive simple close bounds for the thermal expansion coefficient in terms of single crystal properties. Comparison of bounds to experimentally obtained expansion coefficients shows fair to very good agreement.

Fracture of Brittle Solids in the Presence of Thermoelastic Stresses

Abstract: A micromechanical model for strength behavior as a function of grain size in two-phase materials with thermal expansion mismatch and in single-phase materials with thermal expansion anisotropy is presented. The strength vs grain-size plot is interpreted in terms of internal stresses and the ratio of grain to flaw size. The strength of thermally isotropic material is predicted to exhibit a weak grain-size dependence with a negative grain-size exponent normally different from 0.5. In thermally anisotropic poly crystalline solids, before the critical grain size for spontaneous cracking is reached, there will be a region of decreasing strength with increasing grain size due to an increase in the grain-to-flaw size ratio. When a critical grain size is reached, the ratio of grain to flaw size will decrease instantaneously and the strength will decrease in the same fashion. Very good agreement was obtained between predicted and experimentally observed strength behavior for TiO2 and MgO ceramics.

Magnetic contributions to thermal expansion of transition metals: implications for local moments above Tc

Abstract: Most transition-metal magnets, although itinerant in nature, do not undergo large volume contractions on passing from the magnetic to the non-magnetic state Such a contraction might be expected because of the very large internal magnetic pressure which has been calculated to exist in these magnets at zero temperature By developing the theory of the spontaneous magnetovolume effect in greater generality than previously, the authors show that it is the local magnetic moment which dictates the pressure A positive pressure also arises from the energy of disordering the moments at high temperature, and a small net expansion from the coupling of magnetic fluctuations to the anharmonic part of the lattice potential The effects are related to the experimentally measurable specific heat and thermal coefficient of linear expansion They analyse the data to infer root-mean-square values of the atomic magnetic moments above the Curie (Neel) temperature TC(TN) in Fe, Ni and Cr, and find a remarkably small reduction from the saturation values at T=0 Even in the Invar alloys most of the atomic moment remains above Tc

Phase equilibrium, glass-forming, properties and structure of glasses in the TeO2-B2O3 system

Abstract: Phase equilibrium, glass-forming, properties and structure of the glasses in the TeO2-B2O3 system have been investigated. The phase diagram is a simple eutectic-like type without any compound formation. A wide region of stable phase separation has been established. A monotectic temperature at 934 K and nonvariant point at 73.6% TeO2 has been determined. The temperature dependence of the stable phase separation in the system has been studied. Some properties (density, transformation temperature, softening point, coefficient of thermal expansion, hardness, absorption in the UV and VIS region) of the tellurite borate glasses have been investigated. A structural interpretation of the glasses, on the basis of B11 NMR spectra was undertaken and two coordination states of boron atoms have been established. A simple model of two tellurium-boron-oxygen building units is presented.

Multilayered ceramic circuit board

Abstract: A multilayered ceramic circuit board, formed by sintering together a plurality of unit ceramic circuit boards, wherein each unit ceramic circuit board includes a ceramic layer, a patterned electrically conductive layer and through hole conductors formed in the ceramic layer for connecting the patterned electrically conductive layers of the respective unit ceramic circuit boards to form a predetermined wiring circuit. The patterned electrically conductive layers and the through hole conductors have a coefficient of thermal expansion which is greater than the coefficient of thermal expansion of the ceramic layers, wherein the difference between the coefficients of thermal expansion is selected to be less than 100×10-7 /°C., and the through holes have decreased pitch. The conductive layers and conductors can be formed of a metal such as gold, silver or copper, with a low softening point glass filler to reduce the coefficient of thermal expansion of the conductive layers and conductors. The multilayered ceramic circuit board according to the present invention is less sensitive to cracks due to thermal stress.

Thermal expansion and Grüneisen parameters of isotropic and oriented polyethylene

Abstract: The linear thermal expansion coefficients α of three isotropic samples (crystallinity v = 0.42-0.8) and one oriented sample (v = 0.8, draw ratio 11) of polyethylene have been measured between 2 and 100 K. Together with our previous measurements at high temperatures, these data provide general patterns for the crystallinity and orientation dependence over a wide temperature range. α varies only slightly with crystallinity from 50 to 120 K, but at higher and lower temperatures, it increases significantly with decreasing crystallinity. The increase at high temperature arises from segmental motion in the amorphous regions, while the large increase near 5 K is similar to that observed in many glasses. The tranverse expansion coefficient of the oriented sample is 40-100% higher than the values for isotropic polyethylene, but the axial expansion coefficient is much smaller and is negative over the entire temperature range. The values of these coefficients are quite close to those for the polyethylene crystal, a feature readily understood in terms of existing models. However, as a result of the much larger elastic anisotropy of the crystal, the Gruneisen parameters (especially the axial Gruneisen parameters) of these two types of polyethylene have rather different values.

Laser to fiber connection

Abstract: A device for optically coupling a fiber to a solid state laser is taught. Briefly stated, a fiber is held by a pedestal or holder and, after alignment between the fiber and the laser, the holder is attached to the same mounting platform upon which the laser is also mounted. The holding or attachment material exhibits the same thermal properties as the base material, thereby minimizing any thermal expansion or contraction which would cause misalignment between the fiber and the laser.

The structure change of PMN in the diffuse phase transition region

Abstract: The mean square displacements and the thermal expansion coefficient were investigated by means of X-ray diffraction in PMN.

On the Stability of Plane and Curved Flames

Abstract: Theoretical studies on flame stability have generally been based on one of two approaches: (i) the hydrodynamic model which accounts for thermal expansion due to combustion, but ignores flame structure, and (ii) the diffusional-thermal model which considers flame structure in a prescribed constant density flow, thus ignoring thermal expansion. The present study is based on a model we derived, in which both thermal expansion and flame structure are accounted for. The model describes the dynamics of flame fronts including their stability. We discuss the stability of plane and curved flames. In particular we determine the effect of flame stretch, thermal expansion, Lewis number and Prandtl number, on stability.

Anharmonicity in fluoperovskites

Abstract: From an experimental determination of the temperature and pressure dependence of the R25 soft-mode frequency in RbCaF3, KZnF3 and CsCaF3, it is shown that the overall temperature-dependent shift of the soft mode is mainly due to the self-energy (the purely anharmonic effect) whereas the quasi-harmonic contribution (the thermal expansion effect) is one order of magnitude lower.

Thermal expansion uniformity of materials for large telescope mirrors

Abstract: Uniformity of thermal expansion has been measured for fused quartz and borosilicate glass. The variation of expansion coefficient for three melts of TO8E was 5 x 10 to the -9th/K over a temperature range of 300 to 100 K and was found to vary linearly with position in the melt. This spatial gradient averaged 3.5 x 10 to the -11th/K-cm. The room-temperature thermal expansivity variation of Duran (Tempax) glass was about 27 x 10 to the -9th/K, while that of E6 glass was about 52 x 10 to the -9th/K.

A dynamic technique for measurements of thermophysical properties at high temperatures

Abstract: A technique is described for the dynamic measurement of selected thermophysical properties of electrically conducting solids in the range 1500 K to the melting temperature of the specimen. The technique is based on rapid resistive selfheating of the specimen from room temperature to any desired high temperature in less than 1 s by the passage of an electrical current pulse through it and on measuring the pertinent quantities, such as current, voltage, and temperature, with millisecond resolution. The technique was applied to the measurement of heat capacity, electrical resistivity, hemispherical total emissivity, normal spectral emissivity, thermal expansion, temperature and energy of solid-solid phase transformations, melting temperature, and heat of fusion. Two possible options for the extension of the technique to measurements above the melting temperature of the specimen are briefly discussed. These options are: (1) submillisecond heating of the specimen and performance of the measurements with microsecond resolution, and (2) performance of the experiments in a near-zero-gravity environment with millisecond resolution.

Glass compositions having low expansion and dielectric constants

Abstract: Glass fibers having suitable properties for reinforcing electrical laminates have a defined viscosity-liquidus relationship, a low coefficient of thermal expansion, a high elastic modulus, and a low dielectric constant.

Metallizable, essentially isotropic polymeric substrates well adopted for printed circuits

Abstract: Essentially isotropic metallizable polymeric substrates having very low coefficients of thermal expansion are well adopted for printed circuits, are facilely prepared by papermaking technique and hot pressing, and are comprised of a fibrous polymer matrix, advantageously an aramide non-woven batt, bonded together with a cured imido prepolymer, and include particulate filler material, advantageously electrically insulating metal oxide particles, distributed therethrough.