Showing papers on "Thermal expansion published in 1979"

Electrical resistivity of copper, gold, palladium, and silver

Abstract: In this work, recommended values for the electrical resistivity as a function of temperature from the cryogenic region to well beyond the melting point are given for bulk pure copper, gold, palladium, and silver. In addition to the total electrical resistivity values for the solid state, intrinsic electrical resistivity values are presented from cryogenic temperatures to the melting point. The values are corrected for the change in geometry due to thermal expansion. The recommendations are based on theoretical considerations and on the experimental data found in the open literature. That available experimental data together with information pertaining to the specimen characterization and measurement conditions are included in this work. The methods of data evaluation and other considerations used in arriving at the recommendations are described. For the solid state, an interpolation scheme is given to aid in the determination of values between those supplied in the tables; for the liquid state, equations ...

Thermal expansion of crystals

Abstract: FOR crystals with trigonal structure, such as h~ematite, the linear thermal expansion coefficient is not independent of the direction in the lattice as in the case of isotropic crystals. The expansion of the lattice can, however, be calculated from a knowledge of two indepcndent coefficients a,, and ax, which refer respectively to the directions parallel and perpendicular to the principal trigonal axis; the corresponding expansion coefficient, ae, is in accordance with the relation stated by Voigt (1910), a 0 ---a,, cos20 + a~ sin20.

Accurate X-ray determination of the lattice parameters and the thermal expansion coefficients of VO2 near the transition temperature

Abstract: Accurate lattice parameters and thermal expansion coefficients of the low- and high-temperature phases of VO2 have been determined from measurements on single crystals with the Bond method [Acta Cryst. (1960), 13, 814–818]. The transition from a semi-conducting to a metallic phase occurs over a temperature range of 0.1 K with a corresponding volume change of 0.044%.

Properties of iron at high pressures and the state of the core

Abstract: Shock-wave (Hugoniot) data for initially porous and nonporous samples of iron are inverted to yield values of the Gruneisen parameter (γ), adiabatic bulk modulus (Ks), and coefficient of thermal expansion (α) along the Hugoniot to pressures of about 150 GPa (1.5 Mbar). This represents the first reliable estimate of thermal properties (e.g., α) to such high pressures based directly on experimental data. The values of γ fit the conventional function γ = γ0(V/V0)n but with n significantly larger than 1, while extrapolation formulas suggested to date for α appear not to provide the best fit to the data. The present analysis yields values of γ between about 1.4 and 1.0 (essentially temperature independent) and α between about 1.0 and 0.4×10−5 K−1 throughout the earth's core, therefore implying that simple dynamical models of the core are quite viable. These results provide experimental confirmation of the Vaschenko-Zubarev/Irvine-Stacey (or ‘free-volume’) formulation for γ of iron at high pressures, as well as support for Stacey's recent model of the thermal state of the core. The data on density, sound speed, and bulk modulus of iron are extrapolated and corrected to pressures and temperatures existing throughout the earth's core, and compared with current seismological information. This leads to the following conclusions: (1) both densities and bulk moduli in the outer core are less than those of Fe under equivalent conditions (by about 10 and 12%, respectively) but (2) their gradients through the outer core are consistent with gross chemical homogeneity (i.e., uniform intermixing of Fe and a lighter, more compressible element or compound); (3) both densities and bulk moduli for the inner core are compatible with those of iron, suggesting that (4) the inner core-outer core boundary is likely to be a compositional as well as a phase boundary. Assuming that the outer core consists of Fe and a lighter element or compound, X, the constraints on density, bulk modulus and mass fration of X which must be simultaneously satisfied are given.

Thermal expansion of .GAMMA.-Mg2SiO4.

Abstract: Thermal expansion of γ-Mg2SiO4 was measured with X-ray powder diffraction method up to 750°C at atmospheric pressure. The data are analyzed in terms of Gruneisen's theory of thermal expansion and Gruneisen's parameter is obtained to be 1.27. Volume thermal expansion coefficient is 19 at 20°C and 27 at 500°C in unit of 10-6/K. These values are compared with those of γ-Fe2SiO4, MgAl2O4 and other spinel type compounds, and it is suggested that the anharmonic properties of γ-(Mg, Fe)2SiO4 may be very close to those of MgAl2O4.

Thermal expansion of single-crystal manganosite

Abstract: Thermal expansion of manganosite MnO at temperatures between 20°C and 850°C has been carefully determined by a dilatometric technique. The theory of thermal expansion by Gruneisen is improved and the acquired data are analyzed to derive the harmonic and anharmonic parameters of MnO. Gruneisen's parameter γ is 1.56, Debye temperature is 441 K, and pressure derivative of bulk modulus is 7. The volume expansion coefficient is 34.3×10-6/K at 20°C and 47.1×10-6/K at 850°C; almost the same in magnitude to those of MgO and FeO.

Growth of 1,3,5‐Triamino‐2,4,6‐trinitrobenzene (TATB) I. Anisotropic thermal expansion

Abstract: Expansion of TATB is studied on a molecular level by means of x-ray crystallography. Continuous monitoring of the cell constants of TATB between 214 K and 377 K allows calculation of a volume change of +5.1% for this molecular system. Expansion of the pure material is almost exclusively a function of a 4% linear increase in the c axis (the perpendicular distance between sheets of hydrogen-bonded TATB). Calculated from these data, the volume coefficient of thermal expansion for crystalline TATB is 30.4 × 10−5 K−1. The structural features of crystalline TATB and its anisotropic thermal-expansion behaviour are compared with those of graphite and boron nitride. Two other crystalline products in the bulk TATB are either actual polymorphs of TATB or impurities.

Calculation of Thermal Expansion, Compressiblity, an Melting in Alkali Halides: NaCl and KCl

Abstract: A parameter-free calculation of the equation of state for KCl and NaCl is presented which gives an accurate prediction of the equilibrium lattice constant over wide-ranging values of pressure and temperature. The results also show a lattice instability which is consistent with melting.

Thermal expansion of amorphous metals

Abstract: The thermal expansion of three commercial amorphous metals has been measured from room temperature to above the crystallization temperature. The results clearly demonstrated the glassy nature of these materials and show the reduction in volume which results from crystallization. The glass transformation temperature is more evident here than on the usual differential scanning calorimeter curves. The activation energies associated with the glass transformation and crystallization are derived from data taken as a function of heating rate. The measured temperatures for the glass transformation and crystallization from the thermal expansion measurements are the same as those obtained from DSC measurements at the same heating rate.

The thermal expansion of 2H-MoS2 and 2H-WSe2 between 10 and 320 K

Abstract: The hexagonal cell dimensions a and c of 2H-MoS2 and 2H-WSe2 have been measured over the temperature range 10 to 320 K. In both compounds a increased linearly and c non-linearly with temperature, the linear coefficient of thermal expansion in the c direction being greater than that in the a direction for 2H-MoS2. In 2H-WSe2 the linear coefficients of thermal expansion in the a and c directions were approximately equal.

Characteristic magnetovolume effects in Invar type Fe-Pt alloys

Abstract: The thermal expansion and the forced volume magnetostriction have been measured for the Invar type Fe-Pt alloys. Derived values of the spontaneous volume magnetostriction are large and the same order of magnitude as those for the Fe-Ni Invar alloys. Their dependence on concentration and chemical ordering can be explained by the change of Fe-Fe atom pairs and their temperature dependence satisfies the empirical relation, omega s(T)=CM2(T). The forced volume magnetostriction observed at 4.2K is about one order smaller than that for Fe-Ni Invar alloys. This suggests the presence of strong ferromagnetism in Fe-Pt Invar alloys, although this contradicts the observation of large values for the high-field susceptibility in these alloys.

The thermal‐expansion parameters of some GaxIn1−xAsyP1−x alloys

Abstract: The coefficient of thermal expansion has been determined in the temperature range 25–400 °C for InP, the ternary alloy Ga0.47In0.53As, and the quaternary alloy Ga0.26In0.74As0.40P0.60 grown on (100) InP by liquid‐phase epitaxy. This parameter is (4.56±0.10) ×10−6/°C for InP, (5.42±0.10) ×10−6/°C for Ga0.26In0.74As0.60P0.40, and (5.66±0.10) ×10−6/°C for Ga0.47In0.53As.

Densities and expansion coefficients of nafion polymers

Abstract: The densities and expansion coefficients of several Nafions in the acid and salt form were measured. For some samples, effects of variations in the equivalent weight, moisture content, and degree of uniaxial orientation were explored. The densities, which show considerable experimental scatter, seem to be independent of the equivalent weight but to be a strong function of the moisture content. Thin films of the as-received, unbacked polymer are strongly uniaxially oriented. After annealing, reproducible values of the expansion coefficient can be obtained. Two distinct breaks in the linear expansion curve are seen; in the salts, the upper one correlates with the glass transition of the material, while the lower one is found in the vicinity of the mechanical β-dispersion of the polymer. The large scatter of the experimental densities is consistent with the hypothesis that the sample is subject either to a microphase separation process which is strongly influenced by the sample history and which affects the density of the material very strongly, or to partial crystallization of the polymer, or both.

Anorthite: Thermal equation of state to high pressures

Abstract: The shock wave (Hugoniot) data on single crystal and porous anorthite (CaAl2Si208) to pressures of 120 GPa are presented. These data are inverted to yield high pressure values of the Grueneisen parameter, adiabatic bulk modulus, and coefficient of thermal expansion over a broad range of pressures and temperatures which in turn are used to reduce the raw Hugoniot data and construct an experimentally based, high pressure thermal equation of state for anorthite. The hypothesis that higher order anharmonic contributions to the thermal properties decrease more rapidly upon compression than the lowest order anharmonicities is supported. The properties of anorthite corrected to lower mantle conditions show that although the density of anorthite is comparable to that of the lower most mantle, its bulk modulus is considerably less, hence making enrichment in the mantle implausible except perhaps near its base.

Thermal expansion and a new phase transition in pyroelectric LiKSO4

Abstract: Single crystal macroscopic thermal expansion coefficient measurements have been made on uniaxial lithium potassium sulphate crystal both along and normal to the six fold axis, employing Fizeau’s interferometer method. Measurements were made in the range of −120°C to 500°C. The results show that lithium potassium sulphate exhibits two major anomalies in its expansion coefficients around −95°C and 422°C respectively, the one at −95°C has been observed for the first time. The nature of dimensional changes of the crystal at the upper and lower transition points are opposite in nature. The crystal shows considerable lattice anisotropy. Megaw’s tilt concept has been invoked to explain the relative magnitudes of expansion coefficients alonga andc directions. Structural features responsible for the absence of ferroelectricity in this crystal have been pointed out.

The Thermal Expansion Behavior of Unidirectional and Bidirectional Kevlar/Epoxy Composites

Abstract: The coefficients of thermal expansion, α, of unidirectionally and bi directionally reinforced Kevlar 49/PR-286 composites are reported for the temperature range 25-150°C. Composite thermal expansion is shown to be highly anisotropic with the variation in α considerably greater for multi- axially reinforced composites than for unidirectional composites. Compar ison with data for HTS graphite/epoxy composites demonstrates that the thermal expansion behavior of Kevlar/epoxy composites is considerably more anisotropic.Elastic properties are also reported and coupled with the thermal expan sion data, calculations based on various models for predicting thermal expansion behavior are presented. It is shown that calculated values of thermal expansion are in close agreement with those measured.

The response of a confined gas to a thermal disturbance. I - Slow transients

Abstract: The response of a perfect gas confined in a slot to a monotonically varying temperature disturbance at the boundaries is considered. On the acoustic-time scale of the slot the solution is described in terms of.a thin expanding conduction boundary layer adjacent to the slot wall and an isentropic core in which a continuous system of acoustic waves propagate. The equations describing the heat transfer process on thelonger conduction-time scale are found to include nonlinear convection and pressure work terms. Strong coupling exists between the induced velocity field arising from thermal expansion of the gas and the variation of thermodynamical variables. A weak acoustic field is found to be propagating in a spatially anisotropic system varying slowly in time. Solutions are developed by a variety of perturbation methods based on a small parameter which is the ratio of the acoustic to conduction time in the system.

Relations between melting point, glass transition temperature, and thermal expansion for inorganic crystals and glasses

Abstract: Thermal expansion coefficients correlate with a number of physical properties of crystals. Cubic ionic insulators that have two completely filled sets of lattice sites have a maximum value for the product of the coefficient and melting point. Expansion is diminished by the presence of various internal degrees of freedom, singly or in combination. These factors depend upon the array, band gap, bond length, and character and coupling between orbital sets. For screwlike chain structures and glasses αT 2m is a constant.

Low expansion copper aluminosilicate glasses

Abstract: The thermal expansion coefficients of Cu2OAl2O3SiO2 glasses have been measured. These glasses have very low expansion coefficients similar to that for SiO2 glass, but their liquids temperatures are much lower. It was possible to reduce the liquids temperature by the addition of 2 mol% of Na2O while maintaining low expansivity. In order to explain the low expansivity, the effects of cation size, valence, the Cu2+/Cu+ ratio, bond strength and phase separation were examined. Phase separation was observed in these glasses which probably consisted of a copper-rich dispersed phase and a network former-rich matrix phase. It was concluded that the overall expansion coefficients of the glasses were governed by the low expansion matrix phase.

Physical properties of BeAl2O4 single crystals

Abstract: Physical properties of Czochralski-grown single crystal BeAl2O4 are reported. Data on hardness, thermal expansion, thermal conductivity, and elastic constants are tabulated as a function of crystallographic orientation. Results indicate that the properties of BeAl2O4 compare favourably with those of Al2O3.

An elevated temperature X-ray study of synthetic disordered Na-K alkali feldspars

Abstract: The temperature dependence of cell parameters for three disordered, synthetic alkali feldspars (Or19, Or38, and Or100) has been determined up to 1,000 °C. The samples show no change in composition or degree of Si-Al disorder during the experiments. The triclinic-monoclinic inversion in the sample of composition Or19 occurs at 560 °±10 °C and is accompanied by changes in the rates of expansion of a, b and c; the rate for a increases and those for b and c decrease above the inversion. The b and c parameters in Or100 show small decreases with increasing temperature and this may be due to thermal motion effects causing a contraction of cell directions that are fully expanded at room temperature. Calculation of the thermal expansion ellipsoids for the monoclinic phases shows that the major expansion coefficients (α1) for all three samples are more than an order of magnitude greater than the intermediate (α2) and minor (α3) coefficients. Thus the thermal expansion of these phases is dominated by that of α1 which makes an angle of 22 ± 4 ° with+a; this orientation is parallel to that of the short M-OA2 bonds. The thermal expansion mechanism for monoclinic, disordered alkali feldspars may involve tilting within the framework releasing compression along this direction and allowing the M-OA2 bonds to show high expansion rates. The stretching of the crankshaft units, which are parallel to a, may only play a subordinate role in controlling the expansion of the feldspar framework.