Showing papers on "Thermal expansion published in 1992"
TL;DR: In this paper, an estimate of the volume coefficient of thermal expansion for Mg-perovskite at deep-mantle conditions is made, including plots of the numerical values of γ over a wide T and V range.
Abstract: The high-temperature measurements of elastic constants and related temperature derivatives of nine minerals of interest to geophysical and geochemical theories of the Earth's interior are reviewed and discussed. A number of correlations between these parameters, which have application to geophysical problems, are also presented. Of especial interest is α, the volume coefficient of thermal expansion, and a section is devoted to this physical property. Here we show how α can be estimated at very high temperatures and how it varies with density. An estimate of α for Mg-perovskite at deep-mantle conditions is made. The formula for the Gruneisen ratio γ as a function of V and T is presented, including plots of the numerical values of γ over a wide T and V range. An example calculation of γ for MgO is made. The high-T-high-P values of γ calculated here agree well with results from the ab initio method of calculation for MgO. The use of the thermoelastic parameters is reviewed, showing application to the understanding of thermal pressure, thermal expansivity, enthalpy, and entropy. We review an extrapolation formula to determine Ks, the adiabatic bulk modulus, at very high T. We show that the thermal pressure is quite linear with T up to high temperatures (∼1800 K), and, as a consequence, the anharmonic contribution to the Helmholtz free energy is sufficiently small, so that it can and should be ignored in thermodynamic calculations for mantle conditions.
280 citations
TL;DR: In this article, the relaxation process of the thermal strain in a GaN film due to the thermal expansion coefficient difference in the GaN(0001)/α-Al2O3(0001) heterostructure is studied by varying the film thickness of GaN in a wide range from 1 to 1200 µm.
Abstract: The relaxation process of the thermal strain in a GaN film due to the thermal expansion coefficient difference in the GaN(0001)/α-Al2O3(0001) heterostructure is studied by varying the film thickness of GaN in a wide range from 1 to 1200 µm. The lattice constant c has a large value of 5.191 A at a film thickness less than a few microns, while it decreases to about 150 µm, and becomes constant above 150 µm, indicating that the strain is almost completely relaxed. The intrinsic lattice constants of wurtzite GaN free from the strain, a0 and c0, are determined to be 3.1892±0.0009 and 5.1850±0.0005 A, respectively.
232 citations
TL;DR: In this article, two analytical methods have been developed that can predict the stress transfer between the 0 and 90° plies in a 0°-90°-0° cross-ply laminate containing transverse cracks.
Abstract: Two new analytical methods have been developed that can predict the stress transfer between the 0 and 90° plies in a 0°—90°—0° cross-ply laminate containing transverse cracks. Account is taken of thermal residual stresses arising from a mismatch in thermal expansion coefficients of the 0 and 90° plies. The first method is based on a 2-D model which assumes that generalised plane strain conditions prevail. The theoretical approach retains all relevant stress and displacement components, and satisfies exactly the equilibrium equations, the interface conditions, and other boundary conditions involving stresses. The stress—strain—temperature relations are satisfied either exactly or in an average sense. The 2-D representation can be used to predict the stress and displacement fields for a laminate containing parallel transverse cracks. In this paper the solutions are used to estimate the dependence of the longitudinal values of Young's modulus, Poisson's ratio, and thermal expansion coefficient on the density of transverse cracks. The second analytical method extends the 2-D model so that it can apply to 3-D problems which arise, for example, when edge effects or orthogonal cracking are to be taken into account. For the special case of very large laminate widths the 2- and 3-D models predict results which are very close to each other for both glass fibre/epoxy and carbon fibre/epoxy laminates. It is shown how the 3-D model can be used to predict the transverse Young's modulus and thermal expansion coefficient. Theoretical predictions of the dependence of Poisson's ratio on transverse crack density indicate that experimental measurements can be sensitive to the strain measurement technique used, and to specimen width when using a transverse extensometer. Theoretical predictions, for glass fibre/epoxy and carbon fibre/epoxy laminates, of the dependence of Young's modulus and Poisson's ratio on the crack density are compared with some experimental results.
201 citations
15 May 1992-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: Physical and mechanical properties of high melting point Ti5Si3 and TiSi2 intermetallics with hexagonal D88 and orthorhombic C54 structure have been investigated as mentioned in this paper.
Abstract: Physical and mechanical properties of high melting point Ti5Si3 and TiSi2 intermetallics with hexagonal D88 and orthorhombic C54 structure have been investigated. Young's moduli of about 160 GPa (Ti5Si3) and 250 GPa (TiSi2) were recorded at room temperature. At 1000°C the elastic moduli are 143 and 215 GPa respectively. Flow stresses of about 1050 MPa for Ti5Si3 and 230 MPa for TiSi2 at 1000°C were measured. With increasing temperature an exponential decrease of the flow stresses occurs. The low density of 4.3 g cm−3 and the pronounced creep resistance are important for high temperature applications of this material.
127 citations
TL;DR: Nanocrystalline (nc) metals show significant differences in their thermodynamic properties, such as specific heat at constant pressure and thermal expansion, in comparison to polycrystalline metals, according to a macroscopic analysis.
Abstract: Nanocrystalline (nc) metals show significant differences in their thermodynamic properties, such as specific heat at constant pressure and thermal expansion, in comparison to polycrystalline metals These properties are explained in terms of a macroscopic analysis Based on a quasiharmonic approximation, the thermodynamic quantities are calculated as functions of the excess volume of the grain-boundary component in nc metals The enhancements of the specific heat and the thermal expansion coefficient are accompanied by a reduction of the Debye temperature The results show good agreement with experimental data
125 citations
TL;DR: In this paper, the authors investigated the rheological behavior of polymers in the neighborhood of the glass transition in the framework of the free volume theory of nonlinear viscoelastic behavior.
Abstract: The rheological behavior of polymers in the neighborhood of the glass transition is investigated in the framework of the free volume theory of nonlinear viscoelastic behavior. Free volume theory as normally applied above the glass transition is modified to account for the effect of the residual volume of vacancies below the glass transition; this modification is accomplished by modeling the changes in the state of the polymer as the sum of viscoelastic changes and a random disturbance deriving from the thermal collisions between molecule segments. The changes in mechanical properties in passing across the glass transition follow from the freezing-in of relaxation mechanisms and of free volume; the model, which also incorporates a time-dependent coefficient of thermal expansion under isobaric conditions, does not require additional parameters other than those characterizing the rubbery state. The pressure dependence of the glass transition is found to be in qualitiative agreement with measurements on PVAc, while the ratio of the glassy and rubbery heat capacities is found to coincide with the ratio of the equilibrium bulk compliances in the glassy and rubbery domains.
125 citations
TL;DR: In this article, the elastocaloric effect, electrical resistivity and thermal expansion have been investigated in a quenched sample of Fe 49 Rh 51 alloy and the giant negative temperature change resulting from a tensile stress of 529 MN/m 2 applied to the sample, is found to be 5.17 K.
115 citations
TL;DR: In this article, the phases of HMX and their transitions were investigated by thermal analysis using X-ray diffraction, and the thermal expansion coefficients and the colume changes at the transitions were extracted from the diffraction series.
Abstract: The phases of HMX and their transitions were investigated by thermal analysis using X-ray diffraction. Series of diffraction pattern were measured, while the samples were heated and cooled. The thermal expansion coefficients and the colume changes at the transitions were extracted from the diffraction series. A contraction of β-HMX was found before changing into δ-HMX resulting in a high volume difference during the transition. On cooling, the reconversion of the high temperature phase requires days. It is further slowed down by decomposition products, which are formed at temperatures beyond 490 K. The final reconversion results in mixtures of α-and βHMX.
The mechanical sensitivities and the buring rates of the HMX phase were determined. The high sensitivity of δ-HMX against impact together with its slow reconversion creates handling risks when the HMX is exposed to temperatures above 440 K.
103 citations
TL;DR: In this article, the filler-concentration dependence of the room temperature conductivity of epoxy resins filled with various carbon particles is reported: two carbon blacks differing by the particles size and short carbon fibres were used.
Abstract: The filler-concentration dependence of the room temperature conductivity of epoxy resins filled with various carbon particles is reported: two carbon blacks differing by the particles size and short carbon fibres were used. The familiar insulator-to-conductor transitions are evidenced and analysed according to percolation theory predictions. The temperature variations below room temperature of the resistivity of selected samples are studied. Two distinct temperature dependences are shown, and interpreted as being due either to tunnelling of electrons among neighbouring particles, or to differential thermal expansion of the matrix and the particles when the latter touch one another. All these results are consistent with general results of colloidal stability theories when particle size and shearing (achieved during material processing) are taken into account.
73 citations
Patent•
28 Aug 1992TL;DR: In this article, a ceramics rotatable magnetron sputtering cathode target is formed on the outer surface of the target holder, where at least one layer selected from the group consisting of a layer of a metal or alloy having a thermal expansion coefficient of an intermediate level between the thermal expansion coefficients of the Ceramics layer and the holder, and a layer with a temperature coefficient approximating to the Thermal Expansion Coefficient (TEC) of the COC of the layer, is formed as an undercoat.
Abstract: A ceramics rotatable magnetron sputtering cathode target comprising a cylindrical target holder and a ceramics layer as a target to be sputtered, formed on the outer surface of the target holder, wherein at least one layer selected from the group consisting of a layer of a metal or alloy having a thermal expansion coefficient of an intermediate level between the thermal expansion coefficients of the ceramics layer and the target holder, and a layer of a metal or alloy having a thermal expansion coefficient approximating to the thermal expansion coefficient of the ceramics layer, is formed as an undercoat between the ceramics layer and the target holder.
71 citations
TL;DR: Aluminum borate was synthesized by the reaction of stoichiometric amounts of α-Al 2O3 and B2O3 as mentioned in this paper, which was formed into a dense ceramic by pressureless sintering with CaO, MgO, or CaAl2B2O7 additives.
Abstract: Aluminum borate, 9Al2O3·2B2O3 or Al18B4O33, was synthesized by the reaction of stoichiometric amounts of α-Al2O3 and B2O3. The Al18B4O33 material was formed into a dense ceramic by pressureless sintering with CaO, MgO, or CaAl2B2O7 additives. The material was characterized by low bulk density, moderate coefficient of thermal expansion (3 × 10−6/°C to 5 × 10−6/°C), moderate strength (210 to 324 MPa), and low dielectric constant.
TL;DR: In this paper, the available data on thermal expansion and bulk modulus, the calculated and assessed Cν data on 44 oxides and silicates are made internally consistent satisfying the above relationship between the heat capacity at constant pressure and at constant volume, thermal expansion, and Bulk Modulus.
Abstract: Thermochemical and thermophysical data for several oxides and silicates are assessed and refined from the available data on Cp (heat capacity at constant pressure), thermal expansion (α) and compressibility (β) from the relation: Cp = Cν + α2VTT/βT, where Cν (heat capacity at constant volume) at low-temperatures is modelled from Kieffer's (1979a, b, c) model. For five minerals, periclase, forsterite, pyrope, lime, and corundum, high temperature data are available and a comparison between the available and assessed data shows a good match. The available data on thermal expansion and bulk modulus, the calculated and assessed Cν data on 44 oxides and silicates are made internally consistent satisfying the above relationship between the heat capacity at constant pressure and at constant volume, thermal expansion and bulk modulus. These data are useful in phase equilibrium computations.
TL;DR: Thermal expansion changes and exothermic reactions with temperature indicate secondary cure during postcure heating, and thermally-induced decomposition occurs in multiple stages indicating presence of different structural species in the resin matrix.
Abstract: Summary
Selected commercial and experimental composites and resin systems have been evaluated by thermal analysis techniques of Differential Scanning Calorimetry, Thermogravimetric Analysis and Thermomechanical Analysis. Important thermal data such as heat of cure, coefficient of thermal expansion, dimensional changes over selected temperature ranges, filler weight percent, onset temperature of decomposition, temperature of peak decomposition rate, temperature of the end of decomposition, etc. have been determined. Heat of cure, thermal expansion coefficient and dimensional changes appear to follow an inverse linear regression fit with filler fraction in the composite. Thermal expansion changes and exothermic reactions with temperature indicate secondary cure during postcure heating. The thermally-induced decomposition occurs in multiple stages indicating presence of different structural species in the resin matrix.
TL;DR: In this article, the thermal expansion, specific heat, dielectric constant, and resistivity of L-arginine phosphate monohydrate have been measured as a function of temperature.
Abstract: The thermal expansion, specific heat, dielectric constant, and resistivity of the novel organic nonlinear crystal, L-arginine phosphate monohydrate have been measured as a function of temperature The thermal expansion is highly anisotropic and has been interpreted on the basis of crystal structure The dielectric constant and resistivity exhibit a temperature dependence that is similar to that of an ionic crystal No anomalies are observed in these physical properties from the liquid nitrogen temperature up to its melting point
TL;DR: In this paper, the anisotropies of electrical resistivity and thermal expansion of single-crystal Ti5Si3 have been measured in the temperature ranges 4·2-300K and 300-1273 K respectively.
Abstract: The anisotropies of electrical resistivity and thermal expansion of single-crystal Ti5Si3 have been measured in the temperature ranges 4·2–300K and 300–1273 K respectively. The anisotropy of the thermal component of the resistivity, defined as ρ(273 K)—p(4·2 K), was found to be 1·65 and the anisotropy of the thermal expansion 2·7 at 1273 K. The anisotropies are discussed on the basis of the directionality of the bonding forces.
TL;DR: In this paper, the properties of a nanocrystalline Ni-P alloy and an amorphous alloy of the same chemical composition are experimentally measured and compared, and the results show that the properties are very different from those of the amorphized alloy.
Abstract: Some properties of a nanocrystalline Ni-P alloy and an amorphous alloy of the same chemical composition, including the thermal expansion coefficient, specific heat capacity, electrical resistance and thermal stability, are experimentally measured and compared. The results show that the properties of the nanocrystalline alloy are very different from those of the amorphous alloy.
TL;DR: In this article, a previously developed formulation for modeling the thermomechanical behavior of chemically decomposing, polymeric materials is verified by simulating the response of carbon phenolic specimens during two high temperature tests: restrained thermal growth and free thermal expansion.
TL;DR: In this article, the authors measured the thermal properties of binary tellurite glasses containing rare earth oxides in the form (TeO2)0.9 (AnOm) 0.1 have been measured and found that the coefficient of thermal expansion in the range of 300-500 K and the transformation temperatures were determined to detect local structural changes that might be induced by the modifiers.
Abstract: To obtain quantitative details about the structure of binary tellurite glasses, the thermal properties have been measured. The thermal properties (linear thermal expansion coefficient α and transformation temperature Tg) of a set of tellurite glasses containing rare earth oxides in the form (TeO2)0.9 (AnOm)0.1 have been measured. The vitreous systems containing the rare earth cations are La, Ce, and Sm. The coefficient of thermal expansion in the range of 300–500 K and the transformation temperatures were determined to detect local structural changes that might be induced by the modifiers. The thermal properties α and Tg are discussed in terms of (i) structure, by calculating the volume of structure unit, the average crosslink density, and the average stretching force constant of each glass system; (ii) vibrations, by correlating the mean long wavelength acoustic mode Griineisen parameter γel and the expansion coefficient α.
TL;DR: In this article, a segmented rigid-rod polyimide was synthesized from 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) and 2,2′-bis(trifluoromethyl)-4, 4′-diaminobiphenyl (PFMB) in order to develop new materials for microelectronic applications.
TL;DR: In this paper, temperature dependence of hardness and expansion in icosahedral Al72Pd20Mn8 alloy (i-AlPdMn) was examined in comparison with a cubic Al60Pd25Mn15 alloy (c-alPdmn), and the thermal expansion coefficient was estimated to be ~14.6×10-6 K-1.
Abstract: Temperature dependence of hardness and expansion in icosahedral Al72Pd20Mn8 alloy (i-AlPdMn) are examined in comparison with a cubic Al60Pd25Mn15 alloy (c-AlPdMn). The hardness at room temperature is about 780 kg/mm2 for i-AlPdMn, much greater than that for c-AlPdMn of 420 kg/mm2, and decreases to about 200 kg/mm2 at 973 K. The thermal expansion of i-AlPdMn is found to be linear versus temperature and the thermal expansion coefficient is estimated to be ~14.6×10-6 K-1.
TL;DR: In this article, the residual stresses were determined to be tensile in the Al matrix and compressive in the reinforcement, and a reduction in residual stress magnitudes was observed after the sample was cooled into liquid nitrogen and heated back to room temperature, which was believed to be caused by plastic deformation of the matrix in low temperature treatment.
Abstract: In metal matrix composites (MMCs) residual stresses are unavoidable during cooling from high temperature in fabrication or heat treatment because of the difference in the thermal expansion coefficients between the matrix and the reinforcement. In particle reinforced MMC the residual stresses have been proved to be hydrostatic in this study by both experiments and mathematical analysis. A very slight surface effect on the measured stresses was predicted in the case Cu Kα radiation was used. The residual stresses were determined to be tensile in the Al matrix and compressive in the reinforcement. A reduction in residual stress magnitudes of both the matrix and reinforcement was observed after the sample was cooled into liquid nitrogen and heated back to room temperature, which is believed to be caused by plastic deformation of the matrix in low temperature treatment.
IBM1
TL;DR: In this paper, the authors investigated the residual stress behavior of poly(4,4′-oxydiphenylene pyromellitimide (PMDA-4, 4′-ODA) and poly(amic acid) precursors in the condensed state on Si wafers.
Patent•
28 Oct 1992TL;DR: In this paper, the authors proposed to reduce the generation of heat stress and hold stable optical coupling efficiency by forming heat expansion coefficient difference of a holding member and a converging means at a specified value or below.
Abstract: PURPOSE: To reduce generation of heat stress and to hold stable optical coupling efficiency by forming heat expansion coefficient difference of a holding member and a converging means at a specified value or below CONSTITUTION: A stem 8 has a copper tungsten alloy property which is equivalent to a holding member A semiconductor laser 1 to project laser light is mounted on a submount 2 A plate 6 of copper tungsten alloy (or ceramic) property to bond and fix a spherical lens 5 to collect laser light from the laser 1 by a low melting point glass 7, a monitoring photodiode 3 to monitor laser light projection, and a temperature detecting element 4 to detect a temperature of the stem 8 are mounted on one side of the stem 8 and a cooling side of a heat electron cooling element 9 is connected to the other thereof The spherical lens 5 and the plate 6 are coupled by using a low melting point glass whose thermal expansion coefficient is approximately equal to them A heat expansion coefficient difference is restrained not more than 1×10 -4 /°C COPYRIGHT: (C)1991,JPO&Japio
TL;DR: Optical measurements have been used to study the biaxial tensile strain in heteroepitaxial ZnTe gronw by molecular-beam epitaxy on both GaAs and GaSb substrates, and its effect on the low-temperature photoluminescence spectrum of the material.
Abstract: Optical measurements have been used to study the biaxial tensile strain in heteroepitaxial ZnTe gronw by molecular-beam epitaxy on both GaAs and GaSb substrates, and its effect on the low-temperature photoluminescence (PL) spectrum of the material. The observed strain (0.92×10 -3 for ZnTe/GaAs and 0.45×10 -3 for ZnTe/GaSb) agrees with that expected for differential thermal contraction from the growth temperature to low temperature, based on the difference in thermal expansion coefficients
TL;DR: In this article, a combination of a carbon coatings on the fibers and an interfacial gap due to the thermal expansion mismatch in the composite can significantly lower the effective thermal diffusivity in the direction transverse to the fiber.
Abstract: Experiments were carried out on samples of reaction-bonded silicon nitride uniaxially reinforced by SiC monofilaments with and without a 3-micron-thick carbon-rich coating. It is found that a combination of a carbon coatings on the fibers and an interfacial gap due to the thermal expansion mismatch in the composite can significantly (by a factor of 2) lower the effective thermal diffusivity in the direction transverse to the fiber. At atmospheric pressure, gaseous conduction across the interfacial gap makes a significant contribution to the heat transfer across the interface, indicated by significantly lower values of the effective thermal diffusivity under vacuum than in nitrogen or helium at atmospheric pressure.
20 Feb 1992-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, residual thermal strains and stresses that developed during cooling of a silicon-carbide-fiber-reinforced titanium matrix high-temperature composite were determined by an experimental neutron diffraction technique.
Abstract: Residual thermal strains and stresses that developed during cooling of a silicon-carbide-fiber-reinforced titanium matrix high-temperature composite were determined by an experimental neutron diffraction technique. The results were compared with those obtained by finite element analysis. The study was conducted over the temperature range 20–950 °C. As a result of thermal expansion mismatch, compressive residual strains and stresses were generated in the fibers during cool-down. The axial residual strains and stresses were highly tensile in the matrix, and the matrix underwent plastic deformation. Average transverse residual strains in the matrix were compressive. The measured data compare fairly well with finite element method predictions. The effects of fabrication procedures and thermal processing, such as liquid nitrogen dipping and thermal cycling, on the residual strains were also studied.
TL;DR: In this paper, high temperature X-ray investigations of CeO2 films gave a linear thermal expansion coefficient of 11.6 × 10−6 K−1, corresponding to a temperature dependence of the lattice parameter of a 0 = (5.4067 + T × 6.37 × 10 −5 ) A.
TL;DR: In this paper, the lattice parameter of synthetic diamond single crystals has been measured in the range 4.2-320 K by the X-ray diffraction method and the thermal expansion coefficient α calculated from the experimental results is very small (of the order of 10-7 or less).
Abstract: The lattice parameter of synthetic diamond single crystals has been measured in the range 4.2-320 K by the X-ray diffraction method. The lattice parameter is found to be nearly constant between 4.2 and 90 K. The thermal expansion coefficient α calculated from the experimental results is very small (of the order of 10-7 or less) and no definite evidence of the negative thermal expansion is found within our relative experimental accuracy of the order of ±1×10-6.
TL;DR: In this paper, hot isostatic pressing (HIPing) was found to increase the thermal diffusivity/conductivity of uniaxial silicon carbide fiber-reinforced reaction-bonded silicon nitride (RBSN) matrix composites.
Abstract: Hot isostatic pressing (HIPing) was found to increase the thermal diffusivity/conductivity of uniaxial silicon carbide fibre-reinforced reaction-bonded silicon nitride (RBSN) matrix composites, as the result of the densification of the matrix, the increase in the grain size of the silicon carbide and the improved thermal contact between the fibres and the matrix Transverse to the fibre direction the thermal diffusivity/conductivity was found to be a function of the surrounding gaseous atmosphere due to the access of the gas phase to the fibre-matrix interface, which was facilitated by the existence of an interfacial gap due to the thermal expansion mismatch between the fibres and the matrix The interfacial conductance was found to exhibit a strong positive temperature dependence as the result of the closure of the interfacial gap with increasing temperature