Showing papers on "Thermal expansion published in 1983"

Recommended Values for the Thermal Expansivity of Silicon from 0 to 1000 K

Abstract: Silicon, a high melting point, low expansivity, cubic material which can be obtained readily in high purity form, provides an excellent thermal expansion standard. Various absolute determinations of the thermal expansivity of both single crystal and polycrystalline silicon are used to establish a smooth relationship from 90 to 850 K which is believed to be reliable to roughly 10−8 K−1, and which is extrapolated to 1000 K. Values also are suggested for temperatures to absolute zero. Key words: high temperature expansivity; silicon; standard expansivities; thermal expansivity.

In-Plane Thermal Expansion and Thermal Bending Coefficients of Fabric Composites:

Abstract: This paper examines the in-plane thermal expansion coefficients and thermal bend ing coefficients of fabric composites. Three physical models have been adopted. The "mosaic model" provides a simple means for estimating these thermal properties. The one-dimensional "fiber undulation model" and the two-dimensional "bridging model" are suitable in particular for analyzing the thermomechanical behavior of plain weave and satin weave composites, respectively. The experimental results on in-plane thermal expansion coefficients of a 5-harness satin composite agree well with the theory.

Apparatus for measuring the thermal expansion of solids between 1.5 and 380K

Abstract: Describes a device for measuring the thermal expansion of solids in the temperature range from 1.5 to 380K, based on a three-terminal capacitor method. The construction of the expansion cell allows a fast mounting of the sample without dismantling of the cell, the sample shape being unimportant. The relative sensitivity is Delta l/l=10-10 for l=10 mm. The systematic error is in the order of 10-7. The thermal expansion coefficient can be determined with a sensitivity of 10-9 K-1 and an accuracy of +or-2%.

Thermal Expansion of Alkali Borate Glasses

Abstract: The thermal expansion behavior of lithium, sodium, potassium, and rubidium borate glasses was measured. The results indicate that the “borate anomaly” in the thermal expansion coefficient occurs at ∼20 mol% alkali oxide. A maximum in the glass transformation and dilatometric softening temperatures also occurs at ∼27 mol% alkali oxide. No evidence for phase separation was observed in this study. These effects are related to the structural changes reported for these glasses by Bray and coworkers.

Thermophysical properties of liquid copper and aluminum

Abstract: The electrical resistivity and equation of state of liquid copper and aluminum have been measured to temperatures of 4500 and 4000 K, respectively, using the isobaric expansion apparatus. The specific heats for the liquid are in good agreement with extrapolation of the 1973 Hultgren tables. The electrical resistivities are presented both with and without correction for thermal expansion. Both resistivity and thermal expansion results for aluminum are compared with the predictions of pseudopotential calculations. The specific volumes observed for both metals are less than those reported in the literature, apparently because of axial hydrodynamic displacement. In addition, sudden rapid acceleration in sample growth rate with a corresponding rapid rise in resistivity were observed.

Equation of state and thermodynamic properties of liquid methanol from 298 to 489 K and pressures to 1040 bars

Abstract: The PVT properties of liquid methanol have been measured with a direct-weighing PVT apparatus, from 298 to 489 K and pressures to 1040 bar. The apparatus and the method are described. The results have been fitted to a 16-constant equation of state that has been used, together with published data for vapor pressure and saturated-vapor densities, to calculate the following properties of saturated and compressed liquid methanol over the experimental range: specific volume, isothermal compressibility, thermal expansion coefficient, thermal pressure coefficient, enthalpy, entropy, and constant-pressure heat capacity. The calculated properties are presented in tabular form, at round values of P and T.

Thermal expansion and cracking of three confined water-saturated igneous rocks to 800°C

Abstract: Solutions of engineering problems of very deep drilling, geothermal energy production, and high-level nuclear-waste isolation require adequate understanding of the mechanical and transport properties of rocks at relatively low pressures but high temperatures. Accordingly, the thermal expansions of water-saturated Charcoal Granite, Mt. Hood Andesite, and Cuerbio Basalt have been measured at effective confining pressures (P e ) of 5, 50, and 100 MPa to 800° C. The mean coefficient of linear thermal expansion (α) is a function of lithology,P e , temperature (T) and initial porosity (ϕ). For example, for the Charcoal Granite, α increases withT at all pressures. The signature of the alpha-beta transition of quartz is more pronounced at the lower pressures; at 100 MPa α nearly mimics that of a crack-free rock forT<300° C. α for the andesite atP e =5 MPa ranges from 10 to 15×10−6/°C from 200° to 400° C then decreases gradually to 10.1×10−6/°C at 800° C. At 50 MPa α ranges from 11.7×10−6/°C at 100° C to 8.6×10−6 at 200°C, then increases at a much lower rate to 11×10−6 at 600° C. The basalt, however, has an essentially constant α (11×10−6/°C) forT>150°C at the lower pressure and shows but a small increase in α from 6 to 9×10−6 from 100° to 800° C at 50 MPa. The difference between measured values of thermal expansion and those calculated from simple mixture-theory relates to new crack porosity generated as a result of differential thermal expansion at the anisotropic grain scale. For the granite, a two to three order of magnitude increase in permeability (k) is predicted from the relation,k∝φ 3.

Effect of Thermal History on the Properties of a Willemite Glass‐Ceramic

Abstract: The effect of time and temperature on the properties and structure of a willemite glass-ceramic were measured. -0 polymorphs of willemite were found to exist in most of the glass-ceramics. Those properties of the glass-ceramic which depend primarily on the composition of the glassy phase (helium permeation and diffusion, and chemical durability) were found to be strong functions of the thermal history of the samples, whereas those properties which depend on both the compositions and the relative amounts of both the glassy and crystalline phases (thermal expansion coefficient, density, and refractive index) were found to be relatively insensitive to thermal history. The properties of the glass-ceramics could be described by simple mixing models using the properties measured for willemite and for glasses having theoretical residual glass compositions corresponding to varying degrees of crystallinity in the glass-ceramic.

On precipitation in rapidly solidified aluminium-silicon alloys

Abstract: The precipitation of silicon in rapidly solidified AlSi alloys was studied. For alloys with 2.4 and 11.0 wt % Si (2.3 and 10.3 at % Si, respectively) the lattice parameters of the Alrich and of the Si-rich phases were measured after ageing at 397,425 and 448 K. For alloys with 2.6 and 13.0 wt % Si crystallite sizes and lattice strains were determined by analysis of the X-ray diffraction line broadening. After ageing the lattice parameters of the Al-rich and the Si-rich phases were influenced by the difference in thermal expansion between both phases. After correction for this effect the amount of silicon dissolved in the Al-rich phase was estimated as a function of ageing time. Quenched-in (excess) vacancies influenced the precipitation kinetics. Activation energies for precipitation appeared to depend on the extent of transformation. Further, quenched-in vacancies caused anomalous maxima in the lattice parameter curves. The behaviour of the lattice microstrains on ageing was explained as a result of the disappearance of stresses due to quenching and the introduction and subsequent dissipation of stresses due to precipitation. After completed precipitation stresses due to the difference in thermal expansion between both phases still exist at room temperature.

Anomalous components of supercooled water expansivity, compressibility, and heat capacity (Cp and Cv) from binary formamide+water solution studies

Abstract: Recently reported heat capacity studies of N2H4+H2O and H2O2+H2O solutions, from which an anomalous component of the pure water behavior could be extracted by extrapolation, have been extended to a system NH2CHO+H2O which has the chemical stability needed to permit expansivity and compressibility measurements as well. Data accurate to ±2% for each of these properties as well as for the heat capacity are reported. The expansivity data support almost quantitatively an earlier speculative separation of the bulk and supercooled water expansivity into a ‘‘normal’’ (or ‘‘background’’) part and an ‘‘anomalous’’ part, the latter part fitting a critical law αanom=A(T/Ts−1)−γ with exponent γ=1.0. According to the present analysis, the anomalous part of the expansivity which is always negative, yields Ts in the range 225–228, γ in the range 1.28–1.0, depending on the choice of background extrapolation function. The normal contribution to the heat capacity obtained from the present work is intermediate in character t...

Thermal conductivity of minerals at high pressure: The effect of phase transitions

Abstract: Theory predicts and measurements confirm that anharmonic properties such as the lattice thermal resistivity, the Gruneisen parameter, and the coefficient of thermal expansion generally decrease as a function of increasing density upon compression of solids. The Debye-Gruneisen continuum model further predicts a discontinuous decrease of anharmonic properties during a phase transition with a density increase, in contradiction with available experimental data on alkali halides. We present results calculated from a model based on interatomic potentials. This model correctly predicts an increase in anharmonic properties for simple compounds transforming from a six- to an eight-coordinated structure. These results stress the importance of interatomic spacing as well as density in determining changes in thermodynamic properties due to polymorphism. The change in crystal structure across a phase transition also affects the thermal conductivity via Brillouin zone summations over the interacting phonon modes. We have used in the calculations either the bulk sound speed, or the Debye average velocity calculated from the longitudinal and transverse velocities (in both cases, theoretically derived from the interatomic potentials). We have found that the pressure dependence of thermal conductivity determined from the bulk sound speed agrees much better with experimental data for each phase than that determined from the average velocity. Apparently, shear modes contribute less to the change of thermal conductivity with compression than has been thought.

Moisture and Thermal Expansion Properties of Unidirectional Composite Materials and the Epoxy Matrix

Abstract: Experimental techniques are presented for determining the moisture- and thermal- expansion coefficients of polymers and polymer-matrix composite materials. Materials tested included Hercules 3501-6...

The lattice thermal expansion of hydroxyapatite

Abstract: La dilatation thermique le long des axes α et c du Ca 10 (PO 4 ) 6 (OH) 2 est determinee, entre 22 et 1000°C a l'aide de la diffraction RX a haute temperature

Thermal properties of Na2O·3SiO2 glasses with high water content

Abstract: Na 2 O·3SiO 2 glasses with various water contents (up to ∼8wt%) were prepared under high pressure, hydrothermal conditions and their thermal properties, were analyzed by DTA and dilatometry. The glass transition temperature (Tg) determined by the two methods agreed reasonably well. Exsolution of dissolved water occurs at temperature above Tg and is accompanied by foaming. Both the glass transition temperature and the foaming temperature decrease with increasing water content, while the thermal expansion coefficient increases with increasing water content. The change of the glass transition temperature with water content was compared with equations applicable to polymer plasticizers, and was found to be best described by an equation which takes the different contribution of hydroxyl ions and molecular water into account. It was concluded that the hydroxyl ions lower Tg drastically while the molecular water lowers it only slightly by merely diluting the glasses.

Clad metal lead frame substrates

Abstract: An integrated circuit casing assembly 22,52 for electrical applications is disclosed which includes a lead frame formed from a composite structure 10, 60, 70. Depending upon the specific composite structure a desired coefficient of thermal expansion and thermal conductivity of the assembly can be achieved.

An analysis of the process of recrystallization of silicon thin films with either a scanning laser or strip heater

Abstract: An analysis of the temperature, stress distribution, and crystal growth was made to model the process of recrystallization of silicon thin films with either a scanning laser or strip heater. The temperature distribution of a wafer with one or more thin film layers was calculated using both Green’s function and Fourier series methods. With increasing velocity, the temperature profile becomes asymmetric and the maximum temperature decreases. Heat flow is influenced by the applied heat profile, the layer thicknesses, thermal properties, heat transfer coefficient between the wafer and substrate, and the velocity of the heat zone. If the heat zone is wider than the wafer thickness the temperature profile may be approximated using a one‐dimensional model. Thermal stresses are generated by either a nonuniform temperature or differential thermal expansion between layers. Temperature differences along the film that are greater than 10 °C may plastically deform the silicon film. To crystallize cell‐free single‐crys...

Density of liquid Hg1−xCdxTe

Abstract: Negative thermal expansion has been established in liquid Hg1−xCdx for x<0.2 employing a pycnometric method. Pure HgTe increases in density from its melting point at 670 °C to a maximum value at ∼750 °C, where normal thermal expansion progressively resumes. The dependence of density on temperature for liquid Hg1−xCdxTe arises almost exclusively from the HgTe portion of the melt, while CdTe acts as a diluent. The temperature corresponding to the maximum density changes slightly with composition, increasing by about 5 °C for x=0.1.

Stress relief of basal orientation zinc oxide thin films by isothermal annealing

Abstract: The effect of isothermal annealing on residual strain in the lattice of as‐deposited basal crystallographic orientation zinc oxide was studied. Films were prepared by rf diode sputter deposition from a zinc oxide target and annealed in air for 5 to 1995 min at 300 or 500 °C. The change in crystallography as a result of annealing was determined by x‐ray diffraction. The results show that as‐deposited films have a residual tensile strain along the c axis with an average value of +0.62%. Strain relaxation begins to occur after 5 min at 300 °C. The small activation energy, ∼0.2 eV, suggests that interstitial diffusion assisted by local plastic strain may be the process by which strain relaxation initiates. Annealing at 500 °C for longer than 5 min causes a compressive strain to develop along the c axis upon cooling. This effect is attributed to the difference in the coefficient of thermal expansion of zinc oxide and silicon. Comparison with other annealing studies suggest that the magnitude of this effect is ...

Study of structural relaxation of Ni78Si8B14 metallic glass by electrical resistivity and thermal expansion measurements

Abstract: Electrical resistivity and thermal expansion measurements were made to elucidate the structural relaxation of Ni 78 Si 8 B 14 metallic glass, especially, the topological short range ordering. The decrease of the resistivity and the increase of its temperature coefficient were observed, and these changes due to the structural relaxation were discussed on the basis of the extended Ziman theory for metallic glasses proposed by Nagel. The densification of about 0.25% and the decrease of 4% in the thermal expansion coefficient were observed in the considerably relaxed sample. The topological short range ordering in Ni 78 Si 8 B 14 metallic glass occurs rapidly at the annealing temperature above 200°C.