Showing papers on "Thermal expansion published in 1977"

Linear thermal expansion measurements on silicon from 6 to 340 K

Abstract: Linear thermal expansion measurements have been carried out from 6 to 340 K on a high‐purity silicon sample using a linear absolute capacitance dilatometer. The accuracy of the measurements varies from ±0.01×10−8 K−1 at the lowest temperatures to ±0.1×10−8 K−1 or 0.1%, whichever is greater, near room temperature, and is sufficient to establish silicon as a thermal expansion standard for these temperatures. The agreement with previous data is satisfactory at low temperatures and excellent above room temperature where laser‐interferometry data of comparable accuracy exist. Thermal expansions calculated from ultrasonic and heat‐capacity data are preferred below 13 K where experimental problems occurred.

Absolute linear thermal‐expansion measurements on copper and aluminum from 5 to 320 K

Abstract: A linear absolute dilatometer based on a three‐terminal parallel‐plate capacitor design has been used to obtain thermal expansion data for high‐purity copper and aluminum from 5 to 320 K. These data have an absolute accuracy of ±0.1% above 20 K for copper and above 30 K for aluminum, and agree well with published data at the higher temperatures. The disagreement which exists with other data below 5 K for copper and below 15 K for aluminum is believed to be sample dependent, but the mechanism is not known. The aluminum results in this region depend on the state of annealing of the sample.

Thermal Expansion and Chemical Durability of Phosphate Glasses

Abstract: The thermal expansion coefficient and aqueous dissolution rate were measured for alkali phosphate glasses containing a third and fourth component. For a given series, both properties increased monotonically as the radii of the alkali ions increased. The observed expansion coefficients were in the range 99 to 286 × 10−7°C−1. A small mixed-alkali effect was observed for both properties.

Anomalous thermal expansion and magnetostriction of single crystal Tb .27 Dy .73 Fe 2

Abstract: Single crystal magnetostriction and thermal expansion measurements are reported on Tb 27 Dy 73 Fe 2 A spin reorientation at T = 283K causes the sudden onset of a very large magnetostrictive distortion which yields a huge anomalous contribution to the linear thermal expansion The temperature and magnitude of this contribution is field controlled The expansion coefficient d(\Delta\ell/\ell)/dT can be varied from +5 to +115×10-6/°K Normal magnetostrictive behavior is observed above 283K Below this temperature a change in the easy axis from the highly magnetostrictive [111] axis to the weakly magnetostrictive [100] direction causes an anomalous field dependence Here large external fields are required to saturate the moment along [111]

Dimensional Stability of Fused Silica, Invar, and Several Ultra-low Thermal Expansion Materials

Abstract: We have measured length change vs time for several low thermal expansion materials maintained in evacuated environments at constant temperature (near 300 K). Materials were two types of fused silica, Cer-Vit, ULE, Zerodur, Invar, and super Invar. ΔL/L was measured over a period of 170 days to a precision of two to three parts in 109. In addition, we have measured time-dependent changes in optical contact interfaces and have placed an upper limit on drift of optical phase shift on reflection from multilayer dielectric coatings.

The expansivities and the thermal degradation of some layer compounds

Abstract: The thermal expansion coefficients and the decomposition products at high temperatures under vacuum have been determined for a number of layer compounds; SnS2, SnSe2, SnSSe, ZrS2, HfS2 and TiS2, all of which have crystal structures based on that of cadmium iodide, and∈-GaSe. In all compounds the expansion perpendicular to the layers (∥c) is much greater than that parallel to the layers (⊥c). This is ascribed to the effect of the weak van der Waal's bonding between layers. Thermal degradation at high temperatures (up to 900° C) under vacuum usually follows a route via the monochalcogenide or the sub-chalcogenide to the oxide.

The effect of delta T /oxidizing temperature minus cooling temperature/ on oxide spallation

Abstract: Several alloys (one iron base and five nickel base) were cyclically oxidized in a series of tests in which the higher temperature (1100 or 1200 C) of the cycle was fixed at a level to allow ample oxidation in reasonable time and the lower temperature was variable to allow cycle temperature differences of up to 1400 C. For all nickel alloys, as delta T increased the extent of spallation increased. This effect was attributed to thermal expansion mismatches between the oxide and the nickel substrate. The FeCrAl alloy was not sensitive to delta T and resisted spalling at delta T levels to 1400 C. FeCrAl, and the Al2O3 scale which forms on it, have thermal expansion coefficients which are substantially more alike than any of the other oxide-metal combinations tested.

Influence of elastic and thermal mismatch on the local crack-driving force in brittle composites

Abstract: An expression is derived for the change of localK 1 value of a crackfront near circular and spherical inclusions with elastic moduli and thermal expansion coefficient different from those of the matrix. The derivation is based on the concept of an “image stress” which is imposed on the crack, to illustrate the interaction between elastic and thermal stress concentrations developed around inclusions in a composite material and the crack-tip stress field.

Thermal properties of metal‐filled epoxies

Abstract: Thermal expansion coefficients and glass transition temperatures for metal–epoxy composites were determined experimentally. Results were in fair agreement with existing theories when certain fundamental assumptions were fulfilled. The effects of filler content and particle size as well as of adhesion between matrix and filler particles were investigated. The latter, in particular, was found to be of cardinal importance for the properties examined in the present work.

Thermal properties of sodium silicate glasses at low temperatures

Abstract: The heat capacity and the thermal expansion coefficient have been measured at low temperatures for vitreous silica containing 0, 10, 20, 30 and 40% soda. The heat capacity per gram is not much affected at 4 K, but is reduced by up to 30% at 10 K by addition of soda. The effect on the expansion coefficient is much greater; the negative values shown by pure silica below 150 K largely disappear with the addition of {10% soda. Below 10 K the coefficient remains negative until 25% soda is added. The Gruneisen function γ(T) is calculated for the various compositions.

Crystal field effect in the thermal expansion of cubic rare earth compounds

Abstract: We report on evidence of crystal-electric-field effects in the low temperature thermal expansion of various rocksalt-type rare earth compounds (PrSb, SmSb, ErSb, TmSb, CeTe, TmTe). From our measurements we deduce the volume dependence of the energy splitting between the lowest crystal field levels and we calculate magnetoelastic coupling parameters involving the volume strain.

Thermal Expansion in K 2 SeO 4

Abstract: Thermal expansion of K 2 SeO 4 single crystals was measured over the temperature range covering the paraelectric, the intermediate incommensurate, and the ferroelectric commensurate phases. Remarkable change was found at the paraelectric-incommensurate phase transition in all lattice parameters a , b and c . The spontaneous strains x 1s and x 2s along the a and b axes show linear temperature dependence, while the spontaneous strain x 3s along the c axis shows a non-linear temperature dependence.

Thermal expansion data for eight optical materials from 60 K to 300 K

Abstract: Coefficients of linear thermal expansion are reported, in the range 60 K to room temperature, for eight optical materials: Polytran potassium chloride and Polytran calcium fluoride—Harshaw; chemical-vapor-deposited (CVD) zinc sulfide and zinc selenide—Raytheon; germanium (single-crystal and polycrystal); crystalline magnesium fluoride, potassium dihydrogen phosphate (KDP), and lithium niobate—Harshaw. The last three are anisotropic crystals; thermal expansion was measured both parallel and perpendicular to the c axis.

Temperature dependence of the elastic shear moduli of the cubic metals

Abstract: A theoretical model for the temperature dependence of the elastic shear moduli of the cubic metals is presented which accounts for the quantitative relationship of these elastic properties to the thermal expansion. The particular phenomenon which the model is concerned with is the extremely rapid temperature variation of the shear moduli, which typically is about 25 times as great as the rate of thermal expansion. The model has the following salient features: (i) The interatomic pair pseudopotential is approximated over the important thermal range by means of a Morse potential; (ii) the thermal expansion is assumed to arise from anharmonic Morse oscillators which are further assumed not to be significantly coupled to each other; (iii) the exact quantum-mechanical solutions for the Morse oscillators are then combined with the Debye model to give an analytic formula for the thermal expansion; (iv) the elastic shear moduli are calculated from this, assuming nearest-neighbor interactions only. The calculated thermal expansions are found to agree quite well with the experimental values, particularly at low temperatures. The rapid temperature variation of the shear moduli is explained by the model in terms of the thermal movement of the nearest neighbors with respect to the interatomic-potential minima. Complete agreement between calculated and experimental shear moduli has been limited, however, by the contributions beyond the nearest neighbors which are not zero, and which have not been included in the formulas.

Thermal expansion in the magnetically ordered phases of holmium

Abstract: High-resolution capacitance dilatometric measurements of the thermal expansion of single-crystal holmium along the a and c axes are reported from 4.2 to 150K with special attention paid to the regions around 20, 90 and 130K. No anomalous behaviour is found around 90K. Both the Curie and Neel transitions are found to be first order, and the existence of a further transition at about 25K is confirmed.

The coefficients of thermal expansion and the Gruneisen functions of trigonal and amorphous selenium in the temperature range between 10K and 300K

Abstract: For trigonal selenium the coefficients of thermal expansion, alpha /sub ///, parallel to the chains, and alpha perpendicular to , perpendicular to the chains, have been calculated from dilatometric measurements in the temperature range 10K to 300K. By means of values of the specific heat cp(T) and the adiabatic elastic constants Cik(T) from literature the Gruneisen functions gamma in and gamma /sub /// have been computed in the quasiharmonic approximation. For vitreous selenium the coefficient of thermal expansion has been measured in the same temperature range. The Gruneisen function has been calculated from data of specific heat and the adiabatic bulk modulus Ks evaluated from ultrasound measurements. For comparing the thermomechanical behaviour of vitreous and trigonal selenium, respectively, the temperature dependent Gruneisen functions are discussed by means of a linear chain model.