High-temperature Thermal Expansion Research Articles

High‐Temperature Raman Spectra and Thermal Expansion of Wollastonite

Unpolarized single‐crystal Raman spectra in the temperature interval of 298–1235 K and powder X‐ray diffractometry data from room temperature up to 1295 K have been obtained from a natural triclinic wollastonite of almost‐ideal composition. Room‐temperature spectra, along with the temperature dependencies of nine major Raman modes, are presented. The temperature shifts of the Raman modes indicate a discontinuity in the temperature range of 950–980 K. No corresponding changes are observed in the temperature dependencies of the lattice parameters. Thermal expansion coefficients for the lattice parameters in the temperature range of 298–1295 K are given.

High temperature stability and thermal expansion behavior of molybdenum-chromium M 2C carbides

The thermal expansion of molybdenum-chromium M 2C carbides has been studied over the temperature range from room temperature to 900°C using high-temperature X-ray diffraction. Hyperstoichiometric carbides demonstrated hysteretic thermal expansion/contraction as excess carbon was lost upon heating above 750°C in an inert environment. Coefficients of thermal expansion of both the a and c axes increase linearly with chromium content.

A model for evaluating and predicting high-temperature thermal expansion

In this paper, a new set of experimental data, αVKTV, representing the partial temperature derivative of the work done by the thermal pressure of the solid, is fitted by n terms of a modified Einstein model. Experimental data show that αVKTV, not αVKT, approaches a constant value at high temperature. Based on the observed linear relationship of isothermal bulk modulus with temperature at high temperature, thermal expansion can be evaluated by fitting αVKTV data. Our previous results have shown that at low temperature or for materials with less variable bulk modulus and expansivity, thermal expansion data can be simply approximated by an n term Einstein model. More generally and for many materials, αVKTV data resemble an isochoric specific heat curve. With this method, thermal expansion can be predicted at high temperatures from low and intermediate temperature range data. With accurate thermal expansion data, high temperature bulk moduli can also be predicted.

High-temperature thermal expansion of binary alloys of Ni with Cr, Mo and Re: a comparison with molecular dynamics simulations

In this paper, thermal expansion studies of the fcc binary alloys (M = Cr, Mo, Re) for from ambient temperature to 900 K are reported. The results of the changes in the lattice constant and the coefficient of thermal expansion with x are compared with the recent molecular dynamics (MD) simulations of Mei, Cooper and co-workers providing the first detailed comparison of this type between experiment and theory over an extended temperature and composition range. For NiMo, good agreement is obtained between experiment and theory for the increase in with x, the decrease of with x, and the temperature variation of . For NiCr, the agreement is considered to be fair for the increase of with x, the decrease of with x, and the versus temperature data. For the NiRe alloys, the observed decrease of with x (say near 900 K) is the opposite to the MD simulation prediction of an increase of with x in this system, although the theoretical predictions at higher temperatures (say 1500 K) tend to be in line with the experimental observations at 900 K. It is argued that effects of magnetic ordering are not responsible for the observed departure from the MD simulation prediction in the NiRe system. A rule-of-mixtures equation gives a linear decrease of with x for the alloys, in qualitative agreement with the experimental results.

Atomic-mass effects in phase diagrams and high-temperature thermodynamic properties

In the classical description of the Gibbs energy, phase diagrams are independent of the masses of the constituent atoms, while the quantum mechanical description at low temperatures shows a mass dependence. This paper discusses how the classical result is related to quantum mechanics at intermediate and high temperatures. In multiatom systems, the conventional Debye model of phonons does not reproduce the classical result, even at high temperatures. However, with properly defined Debye temperatures, giving the logarithmic average of phonon frequencies, the phase diagram becomes independent of atomic masses. It also follows that the high-temperature thermal expansion coefficient does not depend on atomic masses. Hydrides and deuterides, having an exceptionally large mass ratio, display quantum effects even close to the melting temperature.

Thermomechanical behaviors and antiferroelectric superstructures in Pb(Yb1/2Nb1/2)O3–rich Pb(Yb1/2Nb1/2)O3–Pb(Fe1/2Nb1/2)O3solution system

Abstract The phase transition behavior of the pseudo-binary (1-x Pb(Yb1/2Nb1/2)O3–xPb(Fe1/2Nb1/2)O3 solid solution has been investigated by thermal expansion and x-ray diffraction. The deviation from the high temperature thermal expansion at temperature near the paraelectric-antiferoelectric (ferroelectric) transition can be explained by the elastic strain coupling to the dipole moments via the electrostriction. For 0<x<0.11, the transition is characteristically sharp, whereas for 0.14≤x≤0.3 it is diffise. X-ray diffraction of pure Pb(Ybl/2Nb1/2)O3 shows a well-defined antiferroelectric superstructure. With the increasing Pb(Fe1/2Nb1/2)O3 concentration, the order-disorder as well as displacement superstructure is observed to diminish. Such structural manifestation on transition seems to be connected with the dielectric behavior.

High Temperature Thermal Expansion Behavior of Ceramic Matrix Composites

High Temperature Thermal Expansion Behavior of Ceramic Matrix Composites

Thermal expansion and elastic constants

We give a simple, useful relationship between thermal expansion, ΔV/V, and elastic constants. The relationship permits estimation of thermal expansion from only elastic constants (second order and third order) and atomic volume. Elastic-constant temperature dependence is not required. We test the relationship for a variety of crystalline solids. Considering the 0-293 K region, measurement-calculation disagreement ranges from less than 1 to 15%. The model permits extrapolation of high-temperature (near-linear) thermal expansion to zero temperature.

High-temperature thermal expansion of libyan desert glass as compared to that of silica glasses and natural silicates

The thermal expansion behavior of two different Libyan Desert Glasses (LDG), four commercial silica glasses and three natural silicates (agate, flint, opal) was investigated from room temperature up to 1600°C with a dilatometer and heating rates between 1 and 50 K · min−1. LDG and silica glasses have almost the same expansion behavior up to about 1100°C. At higher temperatures the expansion behavior of the silica glasses is governed solely by a viscosity-dependent flow for the conditions used, whereas that of the LDG glasses also shows the influence of a crystallization effect. Differences between different LDG samples and between different parts within one sample may be attributed to differences in the contents of nuclei or crystallites already present, e.g., due to different impurities and/or differences in thermal history. There are no similarities in the expansion behavior between the LDG glasses and the cold-formed non-crystalline or crypto-crystalline silicates. These results are consistent with a high-temperature melting rather than a low-temperature sol-gel-like formation process of the LDG glasses.

The high-temperature thermal expansion of Ni3Al measured by X-ray diffraction and dilation methods

The lattice parameters of Ni3Al have been determined accurately for the temperature range 25 to 594 degrees C by a high-temperature X-ray powder diffraction method. These data are used to evaluate the coefficients of thermal expansion at various temperatures. The thermal expansion of Ni3Al has also been measured from 25 to 1000 degrees C by a dilation method. The thermal expansion values obtained by the dilation method are in good agreement with those determined by the X-ray diffraction method at around room temperature, but the agreement deteriorates with increase in temperature.

High-temperature lattice thermal expansion of some mixed crystals of the CuGe2P3-Cu2GeS3 system

CuGe 2 P 3 est un semi-conducteur type p cristallisant dans F43m; dans la maille elementaire, les atomes de Ge et Cu sont repartis au hasard sur les sites cationiques. Pour Cu 2 GeS 3 , differentes structures ont ete etablies, a temperature ambiante. Dans ces 2 composes, les sites anioniques sont occupes respectivement par des atomes de P et S. Des cristaux mixtes de CuGe 2 P 3 +0,2Cu 2 GeS 3 ont ete obtenus par methode Bridgmann. Les parametres de maille obeissent a une loi du type A+BT+CT 2 ou T est la temperature. Etude de l'influence de la temperature sur les parametres cristallins de systeme CuGe 2 P 3 -xCu 2 GeS 3 et variation du coefficient de dilatation thermique en fonction de la temperature

High-temperature thermal expansion of six metallic elements measured by dilatation method and X-ray diffraction

The thermal expansion of silver, gold, copper, nickel, molybdenum and tungsten has been measured by the dilatation method. The thermal expansion values of silver, gold, copper and nickel have also been evaluated from lattice parameter measurements by X-ray diffraction. These six metals were found to exhibit a nearly uniform expansion over the temperature ranges covered. The thermal expansion values obtained by the dilatation method are in good agreement with those determined by X-ray diffraction. The present results appear also to agree well with those reported previously in the literature.

Vacancy induced anomalies in the Laves phase CeNi2

For the cubic Laves phase CeNi2, pronounced anomalies have been observed in the lattice spacings and micro-hardness values with quenching from elevated temperatures and in the high temperature thermal expansion behaviour. All these effects have been attributed to the production of a high concentration of vacancies at high temperatures. A low vacancy formation energy is indicated by the temperature dependence of the vacancy concentration. The vacancies are thought to be associated with the variable valency state of the cerium atoms, and with the critical electron concentration of the cubic Laves phase.

High Temperature Electrical Resistivity and Thermal Expansion Coefficient of High Dense Carbons and Carbon

High Temperature Electrical Resistivity and Thermal Expansion Coefficient of High Dense Carbons and Carbon

The self-consistent average phonon equation of state for ionic crystals

The self-consistent average phonon (SCAP) approximation was successful in describing the thermodynamic properties of monatomic solids. This formalism was extended to ionic crystals (specifically sodium chloride) at two levels of approximation: (1) the phonon frequencies replaced by a single average frequency, and (2) the phonon frequencies replaced by two average frequencies corresponding to the usual acoustic and optic phonons. In order to compare with earlier calculations and with experiments various forms of the interatomic potential (with polarization neglected) were used. The SCAP calculation is in good agreement with experiment at low and medium temperatures but underestimates the high temperature thermal expansion. It is concluded that the SCAP formalism with polarization included should give a good approximation to the thermodynamic properties of simple ionic crystals over the entire temperature range.

High-temperature thermal expansion study of cadmium stannidiphosphide by an X-ray method

The lattice parameters of the compound cadmium stanni-diphosphide (CdSnP2) have been determined at different temperatures in the range 28 to 536 degrees C. From these data, the thermal expansion and the tetragonal distortion have been evaluated at various temperatures. The linear thermal expansion coefficients along the a and c axes are estimated to be alpha a=6.55*10-6 K-1 and alpha c=2.75*10-6 K-1 respectively and the axial ratio c/a, changes with a coefficient of -3.63*10-6 K-1. This study indicates the anisotropy between the axial expansion coefficients ( alpha a> alpha c) and an increase in the tetragonal distortion, 2-(c/a), with temperature. These results have been interpreted in terms of the thermal expansion of the Cd-P and Sn-P bonds of the CdSnP2 lattice.

ChemInform Abstract: HIGH TEMPERATURE THERMAL EXPANSION STUDIES OF PURE URANIUM DIOXIDE, GADOLINIUM OXIDE AND URANIUM DIOXIDE‐1.5 W O GADOLINIUM OXIDE SOLID SOLUTION

Chemischer InformationsdienstVolume 9, Issue 21 Physical Inorganic Chemistry ChemInform Abstract: HIGH TEMPERATURE THERMAL EXPANSION STUDIES OF PURE URANIUM DIOXIDE, GADOLINIUM OXIDE AND URANIUM DIOXIDE-1.5 W O GADOLINIUM OXIDE SOLID SOLUTION A. C. MOMIN, A. C. MOMINSearch for more papers by this authorM. D. MATHEWS, M. D. MATHEWSSearch for more papers by this author A. C. MOMIN, A. C. MOMINSearch for more papers by this authorM. D. MATHEWS, M. D. MATHEWSSearch for more papers by this author First published: May 23, 1978 https://doi.org/10.1002/chin.197821008Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume9, Issue21May 23, 1978 RelatedInformation

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High temperature thermal expansion of ThO2, MgO and Y2O3 by X-ray diffraction

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The high temperature thermal expansion of graphite parallel to the hexagonal axis

A calculation is made of the effects on the hexagonal axis thermal expansion coefficient of a graphite crystal of the changes in the interlayer forces due to the large interlayer expansions. It is found that the expansion coefficient is significantly increased at temperatures above 800°K and that the magnitudes of the experimental increases up to 3000°K can be readily accounted for.