Showing papers on "Thermal expansion published in 1972"

Equations of state and phase equilibria of stishovite and a coesitelike phase from shock‐wave and other data

Abstract: Shock-wave, static-compression (X ray), ultrasonic, thermal expansion, and thermodynamic data are simultaneously inverted to determine the equations of state of stishovite and a coesitelike SiO2 phase. All the stishovite data except the thermal expansion data are satisfied by a Mie-Gruneisen-type equation of state having a zero pressure bulk modulus K of about 3.50 ± 0.1 Mb, a pressure derivative dK/dP of 3.3 ± 1, and a Gruneisen parameter, initially 1.25 ± 0.1, that decreases slowly with compression. The volume coefficient of thermal expansion at ambient conditions is found to be 13 ± 1 × 10−6/°K, in comparison with 16.4 ± 1.3 measured by Weaver. Some Hugoniot data of Trunin et al. for very porous quartz have densities very close to the density of coesite. However, a calculation of the coesite-stishovite phase line shows that the coesitelike phase persists to about twice the predicted transition pressure at 10,000°K. It is suggested that the discrepancy can be explained if this phase is interpreted as a liquid of about coesite density.

The thermal expansion behaviour of the framework silicates

Abstract: This paper gives a revision and expansion of an earlier interpretation of the thermal expansion behaviour of the framework silicates. The partially-collapsed and ideal fully-expanded structures of quartz, cristobalite, and sodalite are characterized by the geometric relationship between the angle of rotation of their tetrahedra from the ideal fully-expanded state, their cell parameters, and the length of the tetrahedron edge. Their thermal expansion behaviour is interpreted as due mainly to the effect of the rotation of the tetrahedra towards the fully-expanded state modified by anisotropic thermal motion of the framework oxygens and distortion of the tetrahedra from a regular form. With the leucite and sodalite groups the significance of the interframework cations is discussed.

Thermal Expansion, Compressibility, and Polymorphism in Hafnium and Zirconium Titanates

Abstract: Using X-ray diffraction techniques, thermal expansion and compressibility were measured on the orthorhombic compounds HfTiO4, Hf1.26Ti0.74O4, and ZrTiO4 (both quenched and cooled slowly from 1300°C). The thermal expansion of HfTiO4 is highly anisotropic; the thermal expansion coefficients along the crystallographic axes are αa=+(8.7±0.5)×10−6°C−1, αb=−(5.2±0.5)×10−6°C−1, and αc=+ (5.3±0.5)×10−6°C−1. The thermal expansion of Hf1.26Ti0.74O4 was similar to that of HfTiO4 but that of ZrTiO4 was markedly less anisotropic. The compressibilities of HfTiO4 and ZrTiO4 also differed markedly. All compounds investigated, however, behaved similarly in exhibiting a polymorphic transition to a high-pressure phase having the monoclinic baddeleyite (ZrO2) structure. The polymorphism can be explained qualitatively on the basis of crystal structure.

Effect of Crystallization on the Mechanical Properties of Li2O‐SiO2 Glass‐Ceramics

Abstract: Variations in the thermal expansion coefficients, elastic moduli, and fracture strengths of Li2O-SiO2 glass-ceramics were determined as a function of nucleation treatment and volume fraction of crystals present. Strength enhancement was attributed to a decrease in the mean free path between crystals as crystallization proceeds. It is postulated that the eventual reduction in strength in some glass-ceramics is caused by the development of localized cracks at the crystal-glass interface as a result of the volumetric changes which occur during crystallization.

Thermal Expansion of Nb2O5

Abstract: The high-temperature thermal expansion of monoclinic Nb2O5 was studied with X-ray and dilatometric techniques. The X-ray axial thermal expansion was anisotropic; the mean coefficients in the a, b, and c directions, respectively, were 5.3, 0, and 5.9×10−6°C-1 from room temperature to 1000°C. It is proposed that this anisotropy causes microcrack formation in sintered polycrystalline samples. The bulk linear thermal expansion of both sintered and hot-pressed samples was determined with a dilatometer from room temperature to 1200°C. A hysteresis effect between heating and cooling data observed for sintered samples was attributed to the occurrence and recombination of internal microcracks.

Linear thermal expansion coefficients of orthopyroxene to 1000°C

Abstract: The linear thermal expansion coefficients of a bronzite specimen with the approximate molecular formula (Mg.8Fe.2)SiO3 have been measured by an X-ray diffractometer technique in the range 25°–1000°C in an air atmosphere. The linear thermal expansion coefficients determined for the crystallographic a, b, and c directions are α11 =. 0.164 × 10−4 °C−1, α22 = 0.145 × 10−4 °C−1, and α33 = 0.168 × 10−4 °C−1, respectively. No phase changes were observed in the temperature range studied.

Role of the elastic constants in negative thermal expansion of axial solids

Abstract: In cubic solids the elastic properties cannot affect the sign of the thermal expansion, but in axial solids negative thermal expansion can arise not only from anisotropy in the Gruneisen functions, but also from elastic anisotropy. The origin of negative thermal linear expansion is discussed for arsenic, graphite, selenium, tellurium and indium. A negative linear compressibility is neither necessary nor sufficient to ensure negative thermal expansion. The extension of the treatment to solids of lower symmetry is outlined.

Thermal expansion of InxGa1−xP alloys

Abstract: The coefficient of thermal expansion has been determined for a series of InxGa1−xP alloys in the temperature range 15–650 °C. This parameter was found to increase linearly from (4.75±0.1)×10−6/°C for InP to (5.91±0.1)×10−6/°C for GaP.

Thermal expansion of ABO4-compounds with zircon- and scheelite structures

Abstract: The structural relationship between zircon- and scheelite-type compounds is discussed Both structures show identical oxygen coordination of A- and B-ions (8 and 4), the scheelite structure however is more densely packed than the zircon structure and has a layer-like arrangement of the cations This is in agreement with the thermal expansion results which showed that, generally, all scheelite compounds have much higher thermal expansion in the c-direction than corresponding zircon compounds The magnitude of the thermal expansion is determined primarily by the cation valencies Compounds containing uni- or divalent A-ions had much higher thermal expansion than compounds with 4-valent cations The highest thermal expansion coefficients were found for NaIO4(S), CaCrO4(Z) and for the scheelite-type tungstates ThGeO4(Z) had the lowest thermal expansion of all compounds investigated, followed by TaBO4

Synthesis and Thermal Expansion of Polycrystalline Cesium Minerals

Abstract: CsAlSi2O6, CsAlGe2O6, CsFeSi2O6, CsFeGe2O6, and CsBSi2O6 were prepared by reaction of Cs2CO3 and oxides and by a base-exchange method. The compounds were characterized by optical examination and X-ray diffraction. Dilatometric measurements of the linear thermal expansions of the cubic silicate pollucites gave relatively low coefficients, but the expansion of the germanate analogs is considerably higher. Attempts at synthesis of CsCrSi2O6 and CsCrGe2O6 and the special nature of CsBSi2O6 are briefly described.

Physical and Chemical Properties of Aluminum Oxide Film Deposited by AlCl3-CO2-H2 System

Abstract: The changes of structure and physico-chemical properties of aluminum oxide film with deposition and heat treatment temperatures have been investigated by infra-red spectroscopy, X-ray diffraction analysis, electron probe analysis, ellipsometry, microscopy and etch rate measurement. The films have been deposited on a heated silicon substrate in the temperature range of 400~1000°C by AlCl3–CO2–H2 system and heat-treated in H2, O2 and Ar atmospheres between 500°C and 1300°C after deposition. Results show that the composition of the film is affected by the imperfection of reactions. By the heat treatment at high temperature aluminum oxide film crystallizes, and changes of structure and properties of the film depend on the deposition temperature as well as heat treatment procedures, and the film proceeds through various stages to α-alumina. The damage of the surface of the film by heat treatment is explained by the large thermal expansion coefficient of the film, and is also caused by vapor etch by HCl formed by the reaction between H2 gas and chlorine contained in the film deposited at low temperature. The growth of silicon dioxide film underneath aluminum oxide by oxygen heat treatment is limited by the substitutional diffusion of oxydizing species into aluminum oxide and the new formed film, and also depends on the strength of Al–O bond of aluminum oxide.

Stable bonded barrier layer-telluride thermoelectric device

Abstract: A stable, highly efficient, low resistance bonded thermoelectric device in which a barrier layer is disposed between an electrode and a thermoelement, the barrier layer being impermeable to diffusing contaminants from the electrode while having a coefficient of thermal expansion substantially different from that of the electrode and thermoelements. The barrier is constructed such that it will deform with the electrode and thermoelement when subjected to temperature variations rather than cause thermal stress failure of the bonded assembly.

High-temperature X-ray study of rare-earth silicides

Abstract: The structures of AlB 2 and Mn 5 Si 3 -type hexagonal and Cr 5 B 3 and ThCr 2 Si 2 type tetragonal rare-earth silicides have been investigated by a high-temperature X-ray diffraction method in the temperature range 20 °–1200 °C. Thermal expansion coefficients and transition products of the different compounds are given.

Coefficient of thermal expansion of pentaerythritol tetranitrate and hexahydro-1,3,5-trinitro-s-triazine (RDX)

Abstract: T h e thermal expansion coefficient is a second-order symmetric tensor and hence contains six independent constants for a triclinic crystal. This number is reduced for crystals with higher symmetry. Hexahydro-l,3,5-trinitro-s-triazine (RDX, C3H6N606) crystallizes with orthorhombic symmetry, and its thermal expansion is expressed by three coefficients of linear expansion measured along the principal crystallographic axes. Pentaerythritol tetranitrate (PETN, CSHsK4012) is tetragonal, and two coefficients, one along the unique crystallographic axis and one perpendicular to it, describe the thermal expansion, The direction of measurement of the coefficient of linear thermal expansion is indicated by a subscript giving the crystal face normal to the direction of measurement-e.g., C U ( ~ Z O \ is measured in a direction perpendicular to the (120) crystal face. It happens, for these materials, that a(1oo) is measured parallel to the a crystallographic axis, and similarly ~ ~ ( 0 1 0 ) and

Anomalous thermal expansion with infrared spectroscopy.

Abstract: Anomalous thermal expansion is treated through an analytical approach, based on the anharmonic behavior of lattice vibrations of the solids CuCl and CuBr of which complete ir spectroscopic data were available for the low temperature region In the two cases examined here, anomalous thermal expansion as well as change of anharmonic factor, as a function of temperature, show a mirrorlike proportionality In addition, drastic changes of ir energy absorption take place within the temperature region of re-expansion, suggesting a substantial increase of the ionic fraction of binding, coupled with a corresponding decrease of the covalent fraction, within the re-expansion period These striking events appear to be the basic reason for the re-expansion phenomenon, since the sum value of the ionic radii of the compounds in question is greater than the sum value of the covalent radii, thus enlarging the interatomic distance, instead of contracting it

Thermal Expansion of Iridium at High Temperatures

Abstract: The linear thermal expansion of iridium was measured in the range 891–2221 °C. The following equation was found to fit selected earlier results and the present results over the temperature range 30–2221 °C: 100(Lt−L0)/L0=616.7×10−6t+151.9×10−9t2−28.16×10−12t3+14.63×10−15t4 for t expressed in °C. Thermal expansion coefficients and average coefficients of expansion were calculated.

Thermal Expansion of Platinum from 293 to 1900 K

Abstract: Measurements on the thermal expansion of three samples of high‐purity platinum were made with a Fizeau interferometer in the range below 1000 K and with a twin‐microscope method in the high temperature range. The results obtained indicate that the expansion of the three samples are in excellent agreement with one another and with some of the data in the literature. From 293 to 1900 K the linear thermal expansion of the three samples is given by LT−L293L293×106 = −2279+6.117T+8.251×10−3T2−1.1187×10−5T3+9.1523×10−9T4−3.6754×10−12T5+5.893×10−16T6.