Showing papers on "Thermal expansion published in 1982"

Characterization of drained and undrained response of thermally loaded repository rocks

Abstract: The fluid pressure and mechanical response of a potential repository rock to heating is shown to be characterized by the isothermal parameters of the classic stress-strain theory for a porous medium, in combination with some nonisothermal parameters describing the fluid, solid, and pore volume expansivities. The isothermal coefficients are described in terms of easily interpretable parameters by noting that the fluid response can be formulated within the limits of drained and undrained behavior. The low permeability-high thermal conductivity environment generally considered to be ideal for nuclear waste storage would appear to favor an undrained response, at least within the isolated pores and cracks of a fractured rock medium. Several cases are presented that provide a qualitatively correct demonstration of the effects of heating in this environment. These include fluid pressure increases in excess of temperature-induced increases in in situ stress, elastic strain and the potential for inelastic crack propagation, and porosity-permeability augmentation. If the rocks are dry, or of a high permeability such that fluid flow takes place at constant fluid pressure, similar rock material alterations are possible. This follows from the fact that when the temperature is raised to some high value, say 80° or 90°C, and then decreased to its ambient value, the final volume of a polycrystalline substance will generally be greater than the initial one. Hence the effect of temperature is irreversible because of the differential thermal expansion of the composite mineral grains and the generation of new grain boundaries. The increase in porosity during such a heating episode is calculable and empirically related to increases in permeability.

Measurement of Stress Due to Thermal Expansion Anisotropy in Al2O3

Abstract: The stress due to thermal expansion anisotropy in polycrystalline Al2O3 was measured. The broadening of spectroscopic R lines (692 and 693 nm, due to Cr3+ impurities) was used to measure the stresses (at 77 K) in samples with grain sizes of 50 to 150 μm that had been cooled, from 2150 K, at constant rates from 0.1 to 100 K/min. The maximum stress was found to vary from 80 to 100 MPa, depending on the thermal history of the sample. The results are compared to the predictions of a model based on stress relaxation by diffusional creep and are in good agreement for the dependence on cooling rate. No effect due to grain-size changes was observed due to the limited range of grain sizes accessible in this study.

Crystal structure and thermal expansion of α‐quartz SiO2 at low temperatures

Abstract: The crystal structure of α‐SiO2 (low quartz) has been refined at 296, 78, and 13 K from time‐of‐flight neutron powder diffraction data. The major effect of temperature from 296 to 78 K is a nearly rigid body rotation of the SiO4 tetrahedra. Below 78 K, tetrahedral rotation is substantially reduced giving rise to a much smaller thermal expansion. A comparison of the volume dependence of the Si‐O‐Si angle, the rotation angle for SiO4 tetrahedra and the c/a ratio suggests that the mechanism for expansion may be changing from tetrahedral rotation to tetrahedral distortion at the lowest temperatures. The inverse linear relation between the mean Si‐O bond distance and −sec(Si‐O‐Si) which has been observed for silica minerals at both ambient and high‐temperature conditions appears to be consistent with the structural variations that occur at low temperatures.

Effects of humidity on stress in thin silicon dioxide films

Abstract: The stresses of thermally grown as well as chemically vapor deposited (CVD) silicon dioxide were measured by the cantilever beam technique using x‐ray diffraction. Thermally grown oxide shows reversible stress changes upon heating or cooling of the films. The linear thermal expansion of such films is similar to that of bulk vitreous silica, 5×10−7 °C−1, the biaxial elastic modulus was found to be 6.3×1011 dyn/cm2. CVD oxides show extensive hysteresis in the stress‐temperature curves when tested in ambient air. From stress measurements of such films, deposited on Si and GaAs, it was concluded that their average linear thermal expansion coefficient in the temperature range of −170–115 °C is 4×10−6 °C−1, much higher than that of thermally grown oxide, while their biaxial elastic modulus is only 4.6–5.1×1011 dyn/cm2. The stress in such films was found to increase when the films were exposed to a dry ambient or vacuum. The time constant for this change was found to be several minutes at room temperature.

Thermal conductivity and density of toluene in the temperature range 273–373 K at pressures up to 250 MPa

Abstract: New experimental data on the thermal conductivity and the density of liquid toluene are presented in the temperature range 0–100°C at pressures up to 250 MPa. The measurements of thermal conductivity were performed with a transient hot-wire apparatus on an absolute basis with an inaccuracy less than 1.0%. The density was measured with a high-pressure burette method with an uncertainty within 0.1%. The experimental results for both properties are represented satisfactorily by the Tait-type equations, as well as empirical polynomials, covering the entire ranges of temperature and pressure. Furthermore, it is found that simple relations exist between the temperature dependence of thermal conductivity and the thermal expansion coefficient, and also between the pressure dependence of thermal conductivity and the isothermal compressibility, as are suggested theoretically.

Low‐temperature properties of CeAl3

Abstract: Specific heat measurements on CeAl3 are described and compared to thermal‐expansion results. At very low temperatures, the Gruneisen parameter reaches giant negative values. Comparisons are made with the properties of 3He and the unstable‐valent 4f compounds (YbCuAl, CeBe13, CeSn3, and CePd3). It is suggested that the magnetic anisotropy may play a major role.

Phase transformation and thermal expansion of MgNi alloys in a hydrogen atmosphere

Abstract: The thermal expansion of the Mg-5.6 wt.% NiH 2 and Mg-55wt.% NiH 2 systems was examined by in situ X-ray powder diffraction using a specially designed apparatus for measurements at 500 °C and a hydrogen pressure of 5 MPa. The temperature dependence of the unit cell parameters of each alloy and hydride phase and the volume change associated with each phase transformation were determined. The thermal expansion data are summarized. The volume expansions of magnesium to MgH 2 , Mg 2 Ni to high temperature Mg 2 NiH 4 and high temperature Mg 2 NiH 4 to low temperature Mg 2 NiH 4 were calculated from these data as 30.4% (0.2%) at 340 °C, 27.8% (0.2%) at 320°C and 0.3% (0.1%) at 234 °C respectively (the standard deviations are given in parentheses).

Anharmonic properties: Ionic model of the effects of compression and coordination change

Abstract: Thermodynamic properties resulting from anharmonicity in minerals decrease with pressure but are expected to increase across high-pressure phase transitions that are characterized by small volume changes and an increase in coordination number. This conclusion is supported by simple ionic models (based on either a molecular approach or crystal-independent potentials applied to the B1(NaCl structure)–B2(CsCl structure) transition), as well as by the available high-pressure data. The enhanced anharmonicity of the high-pressure phase is caused by the increase in first-neighbor interatomic distance with a coordination change. The Gruneisen parameter and coefficient of thermal expansion are expected to increase by factors of order 20 to 50% across transitions involving changes from fourfold to sixfold and from sixfold to eightfold coordination in halides and oxides. Thus, lower mantle phases are expected to exhibit relatively large coefficients of thermal expansion (e.g., perovskite: α ∼ 3 to 4×10−5 K−1 at 300–1000 K and zero pressure), and the driving force for convective heat transfer may be augmented by the occurrence of phase transformations deep within the Earth's mantle.

Low temperature strain behavior of Pb thin films on a substrate

Abstract: The microstructural changes occurring during cooling from 300 to 100 K in a 0.2 μm thick polycrystalline Pb film deposited on a Si3N4 substrate were studied by a combination of transmission electron microscopy and X-ray diffraction technique. The tensile strain induced in the film upon cooling due to the thermal expansion coefficient mismatch between the film and the substrate was observed to be relaxed by dislocation glide. Most of the dislocations were observed to glide across the grains on 111 planes that are inclined at an angle of ∼ 70 deg to the film surface, and on 111 planes that are nearly parallel to the film surface. All the dislocation motions are confined in each grain by the surface oxide, the substrate, and grain boundaries. Some observations suggested that these dislocations emanate from grain boundaries. At 100 K, the density of dislocations introduced in the grains with diameters larger than ∼0.6 μm was found to be roughly constant (about 1010/cm2), while no dislocations were observed in grains smaller than ∼0.6 μm. The observed dislocation density can account for the amount of strain relaxed which was measured by the X-ray diffraction technique. It was also found that almost all the dislocation glide events involved in the thermal cycling process are reversible. This explains a previous X-ray diffraction result that no work hardening effect was observed in Pb films during the thermal cycling at low temperature. The yield stresses of Pb films as determined by the strain measurements are about three times higher than those expected by a simple dislocation pinning model. Based on the dislocation motion observed in this work, the yield stresses of the films were re-evaluated as a function of film thickness and grain size using an energy criterion model. This model took into account the effects of the surface oxide and substrate on dislocation

The thermal expansion of particulate-reinforced composites

Abstract: After describing the development and standardization of interferometric apparatus employed to measure linear thermal expansion coefficients of materials over the approximate temperature range 80 K to 310 K, an account of an investigation of particulate reinforced Ciba-Geigy epoxy resin CY219/HY219/DY219 is given. The successful conclusion of an appraisal of schemes attempting to describe the dependence of the thermal expansion characteristics of a composite upon the volume-fraction of its filler was followed by a search for particle-size effects. No such effects were observed in composites reinforced with silica flour, glass microspheres and copper powder.

Approach to Melting in Ammonia as a Critical Transition

Abstract: The molar volumes of ammonia solid I and solid II were measured from 0.5 to 14.0 kbar and 185 to 320 K. Over regions that extend 3 kbar and 20 K into the solid phases, variations in compressibility and thermal expansion can be described by power laws with exponents similar to those usually associated with critical transitions. It is suggested that breaking of hydrogen bonds may account for the extreme softening of solid ammonia.

Structure sensitive measurements on e-glass fibers

Abstract: The following properties of continuously drawn fibers from a nozzle have been measured over a broad range of drawing parameters (temperature, pressure on the nozzle, drawing speed): density, thermal expansion, contraction, and birefringence. These properties show characteristic changes of the fiber structure as compared with the structure of the bulk glass. The structure of the fibers is influenced mainly by the following parameters: the cooling rate and the drawing stress. The cooling rate, which rises up to 105 K/s causes an isotropic effect on the glass network of the fiber: an open structure which corresponds to a fictive temperature of up to more than 100 K above the usual glass transition temperature of the bulk glass. The drawing stress acting on the jet during the fiber drawing process causes an anisotropic, frozen-in network deformation which approaches the order of the thermal isotropic deformation. Glass fibers which have been produced at different temperatures but with the same drawing stress show an increasing optical anisotropy with increasing temperature. This effect and similar effects for the density and shrinkage may be a direct indication of a structural orientation in the fiber direction. Although this orientation (anisometry) is negligibly small for a three-dimensional network structure of oxide glass fibers, the anisotropic effect for the frozen-in structural strain-stress is considerable, because these values are as much as 1 10 or more of those for the strength of the originating glass fibers.

Glass-Forming Systems Involving GeO2 with Bi2O3, Ti2O, and PbO

Abstract: The previously studied system GeO2-Bi2O3-TI2O was extended with the addition of PbO using air- and water-quenched melted samples. Large areas of glass formation were found in the systems GeO2–Bi2O3–PbO and GeO2–PbO–Tl2O at all but the lowest GeO2 contents. Glasses were examined by powder X-ray diffraction, differential thermal analysis, thermomechanical analysis, and Archimedes’technique to obtain glass transition and crystallization exotherm temperatures, thermal expansion coefficients, and densities, which are presented in diagrams for the GeO2-PbO binary and for the two ternary systems. Based on calculated values of λ0, the wavelength for zero material dispersion, compositions in this system may be useful for construction of ultralow-loss optical waveguides in the μm region.

Physical and Mechanical Properties of High Manganese Non-magnetic Steel and Its Application to Various Products for Commercial Use

Abstract: In order to develop new high manganese non-magnetic steels that can be employed to extensive applications ranging from cryogenic to elevated temperature uses, the effects of C and Mn on their magnetic permeability, thermal expansion coefficient and mechanical properties are investigated.It is found that the relation between thermal expansion coefficient, β, and both C and Mn contents can be expressed by the following linear regression equation: β(×10-6/°C)=17.66+3.82C(%)-0.22Mn(%). Good mechanical properties are exhibited in the wide range of Mn contents between 18% and 30% at room temperature, while there is a tendency that this optimum range of Mn content is narrowed at cryogenic temperature.Then, H-shapes, round bars and deformed bars are manufactured at the workshops using 5t vacuum melted ingots, aiming to establish the conditions for practical processes for final products and to study such various characteristics of the products as their physical and mechanical properties, machinability and weldability. As a result, it is shown that all of those products have excellent properties as non-magnetic steels.In addition, the manufacturing of non-magnetic pinch rolls attached to the electro-magnetic stirring equipment on the continuous casting machine is described in detail as one of the practical applications of the high Mn non-magnetic steels.

Thermal expansion of TiO2SiO2 and TiO2GeO2 glasses

Abstract: The thermal expansion coefficients of TiO2GeO2 glasses containing up to 12.7 mol% TiO2 were determined and compared with those of TiO2SiO2 glasses. The TiO2GeO2 glasses were prepared by a conventional melting technique. The TiO2SiO2 glasses were prepared by heating the gels formed as a result of hydrolysis and polycondensation of the alkoxide solutions consisting of Ti(OC3H7)4 and Si(OC2H5)4. The thermal expansion coefficient of the alkoxy-derived TiO2SiO2 glasses decreased with increasing TiO2 content similarly to the TiO2SiO2 glasses prepared by the flame hydrolysis technique. It was found that the addition of TiO2 markedly decreased the thermal expansion coefficient of the GeO2 glass. It was concluded on the basis of the contribution of the TiO2 component to the expansivity of the glasses that the Ti4+ ions were present in the 4-coordination state with respect to oxygen atoms in both TiO2GeO2 and TiO2SiO2 glasses.

Strengthened glass-ceramic article and method

Abstract: The glass-ceramic disclosed is characterized by a lithium aluminosilicate crystal phase having a very low coefficient of thermal expansion and a residual glassy phase of substantial amount and higher coefficient of expansion, usually a borosilicate or boroaluminosilicate glass. The two phases form a dilatant system wherein the thermal expansion curve changes markedly in character at a transition point in the range of 500°-750° C., the crystal phase dominating below that temperature and the glass phase controlling at higher temperatures.

Method of evaluating the thermal stability of the pyroelectric properties of polyvinylidene fluoride: Effects of poling temperature and field

Abstract: The ac pyroelectric response of a number of differently poled polyvinylidene fluoride films has been measured while the temperature was varied at a constant rate ∼5 °C/min from room temperature to near the melting temperature. The response first increases with increasing temperature, which is attributed to an increase of the thermal expansion coefficient and eventually decreases due to melting and/or loss of electric dipole orientation. The details of the temperature dependence are influenced in a reproducible manner by the poling variables, especially the poling temperature. The measurement is therefore proposed as a way of evaluating the effect of processing variables on the thermal stability of the piezoelectric and pyroelectric properties.

The anorthoclase structures: the effects of temperature and composition

Abstract: Cell-parameter and structure refinements using single-crystal X-ray diffraction have been carried out on three natural low-Ca anorthoclases (K-analbites), (Or32.5Ab66.7Ano.s, Or22.3Ab7o.sAn69'Orl3.sAbs3.7An2.5),at room temperature and at temperatures above the triclinic/monoclinic symmetry inversion (400°, 510°, and 750° C, respectively). Room temperature cell parameters are consistent with monoclinic Si,AI topochemistry and a high degree of disorder (tt = 0.50 to 0.52 from the b-c plot). A room-temperature inversion composition of Or36 is extrapolated from cos2a* and T-O-T angle plots. Mean M-O bond lengths and T-O-T angles increase with potassium content, whereas their variances decrease, indicating a trend to more regular coordination, as in sanidine. A similar relationship develops with thermal expansion and the structural changes associated with inversion to monoclinic symmetry, but the individual (M-O) values suggest a nonisotropic, ellipsoidal expansion of Na-rich alkali cavities. Examination of dimensional change in the structures due to change in temperature and alkali composition indicates that most of the effect is related to change in M-O bonding, with the aluminosilicate framework responding passively. Anisotropic thermal models for single M sites produce non-positive definite ellipsoids. Modeling with isotropic split-sites yields four parts for the more sodic structures, essentially identical to the models for high albite or analbite. For the more potassic crystals, a separate isotropic K site and an anisotropic Na(Ca) site is indicated.

Residual stress and thermal expansion coefficient of plasma polymerized films

Abstract: The residual stress in plasma polymerized films and its annealing effect were measured by employing the Newton ring method. The plasma polymerized films studied were hexamethyldisiloxane (HMDS), norbornadiene (NBD), and acryronitrile (AN) films. The stress in the film is compressive, and this compressive stress changes into tensile stress by annealing treatment. The ESR measurement indicates that the annealing effect on the stress is due to the trapped radical reaction. From the thermal stress measurement, the thermal expansion coefficient and Young's modulus have also been obtained; Young's modulus is in the order of magnitude of 108g/cm2 with HMDS and NBD films, and the thermal expansion coefficient is in the order of magnitude of 10−5 deg−1 with HMDS and NBD films. These values are much different from those of conventional polymer. This is attributed to the highly crosslinked structure of the films.

Magnetic and thermal expansion properties in hydrided Fe–Zr amorphous alloys

Abstract: The effect of hydrogenation on the Invar‐like thermal expansion anomaly for Fe–Zr amorphous alloys has been investigated. Low temperature magnetization hysteresis has also been examined for the hydrided alloys. The Invar anomaly is changed slightly by hydrogenation only through the increase in the saturation magnetization at 0 K (Mso), since the spontaneous‐volume‐magnetostriction (ωm) for the anomaly increases in proportion to the square of the saturation magnetization (Ms)2. But, the coupling constant between ωm and M2s is not changed by hydrogenation. Field cooling down to 4.2 K makes the magnetization hysteresis asymmetric in the case of the nonhydrided alloys, while no longer any asymmetrical loop has been observed in the hydrided alloys. Thus, the observed large ωm is explained by the simple ferromagnetic effect, rather than by the concept based on a magnetically mixed state.

Manufacture of semiconductor device

Abstract: PURPOSE:To protect a semiconductor substrate against the influence of a thermal strain and to stabilize a thermal diffusion method by performing the temperature rise to a target diffusing temperature via the diffusing treatment to the temperature fall from the diffusing temperature in the same heat treating unit when a conductive type deciding impurity is diffused by the thermal diffusion method CONSTITUTION:A diffusion preventive layer 3 is formed for selective diffusion on a GaAs substrate 2 grown in gas phase for GaAsP crystal 2 the layer 3 as a mask an impurity is diffused in the substrate 1 to produce a P-N junction 4 in an arbitrary depth At this time, a spike 5 might occur due to an abnormal diffusion to the slip line in the crystal 2 due to the difference of lattice constant between the substrate 1 and the crystal 2 A strain is produced at the side of the crystal 2 due to the difference of the thermal expansion coefficient between the layer 3 and the crystal 2 at the end of the layer 3, and an abnormal diffused region 6 might be produced similarly Accordingly, the temperature in the furnace is reduced to approx 450 degC, the substrate and the impurity are filled in the furnace, and are secured at approx 800 degC, and are maintained at the same heat treating unit until they are lowered to 450 degC

Insulated conductor with ceramic-connected elements

Abstract: Electrical articles are provided in which an electrical conductor having a particular coefficient of thermal expansion is bonded to an electrical insulator having substantially the particular coefficient of thermal expansion. The bonding is provided by a ceramic material having substantially the particular coefficient of thermal expansion. By "substantially" is meant a close approximation to the particular coefficient of thermal expansion. The electrical conductor may be made from platinum or titanium or a titanium alloy and the electrical insulator may be made from an alloy of magnesium oxide, silica and aluminum oxide designated as Fosterite. The ceramic material may be partially amorphous and partially crystalline. The bonding may be accomplished by disposing the ceramic material between the electrical conductor and the electrical insulator and by subjecting the ceramic material to a controlled amount of heat. The heat may be applied by a laser beam for an instant such as a fraction of a second. The controlled application of heat causes the ceramic material to flow in the space between the electrical conductor and the electrical insulator and to bond the electrical conductor and the electrical insulator.

X-Ray Study of Thermal Expansion and Transition of Crystalline Cellulose

Abstract: For the cellulose crystals I and II, the spacings and intensities of some typical X-ray reflections were measured over a range of temperature from room temperature to 200°C. The spacing vs. temperature curve for each reflection exhibited a distinct break at about 150°C for Cell I and at about 100°C for Cell II. The thermal expansion coefficients estimated from this curve for the (101) reflection of Cell I were 5.1×10−5 K−1 below 150°C and 1.6×10−4 K−1 above 150°C. The intensity vs. temperature curve for each reflection also exhibited a break at the same temperature as that for the break of the corresponding spacing vs. temperature curve. The reason for the appearance of these breaks is not yet clear.

Low thermal expansion modified cordierites

Abstract: A modified cordierite (2MgO.2Al 2 O 3 .5SiO 2 ) composition in which at least a portion of the silicon dioxide is replaced with germanium oxide. These compositions have low thermal expansion, excellent formability and thermal shock resistance making them especially suitable for the manufacture of mirror substrates to be used at elevated temperatures. By selecting the proportion of germanium oxide according to the intended operating temperature, substantially zero thermal expansion can be achieved between room temperature and the selected operating temperature. Methods of manufacturing the material and of selecting the thermal expansion characteristics are also disclosed.

Thermal potential, mechanical instability, and melting entropy

Abstract: The concept of the thermal potential, introduced in earlier publications in connection with calculations of elastic properties, thermal expansion, and melting temperatures, is shown to be a unifying principle connecting the thermodynamic properties of the solid and molten states. Recently discovered extrapolations connecting the thermodynamic properties of the solid and molten states are demonstrated to be governed by the characteristics of the thermal potential. A simple model of the melting entropy is presented and combined with previously derived expressions involving parameters of the thermal potential to quantitatively connect the heat of fusion with the volume change at melting. The melting entropy is calculated for a group of cubic crystals with the use of the derived expressions, and good agreement is found with observed values. A principal conclusion of this work is that the shear modulus, heat content, and volume, which are discontinuous at the melting temperature, are continuous functions of each other and related through the parameters of the thermal potential.