Mean Linear Thermal Expansion Coefficients Research Articles

Cation ordering and structural variations with temperature in MgAl2O4spinel: An X-ray single-crystal study

The equilibrium distribution of Mg and Al between the tetrahedral and octahedral sites of a flux grown, stoichiometric MgAl2O4 spinel was investigated between 600 and 1100 °C by single-crystal X-ray diffraction of quenched samples. The cation distribution for both ordering and disordering runs was obtained by minimizing accurate crystallographic parameters and effective ionic radii. Along with the variation of the degree of inversion from 0.18 to 0.29 between 600 and 1100 °C, both unit cell and oxygen positional parameter decreased linearly. Multiple non-linear least-squares fit of our data with the thermodynamic model of O’Neill and Navrotsky (1983) gave α = 23 ± 2 KJ/mol and β = 13 ± 4 KJ/mol. The influence of both cation inversion and thermal expansion on T-O and M-O bond length variation was determined by comparison of our data with previous in situ studies. In the thermal interval investigated, the inversion accounts for change of −0.014 A for T-O and +0.007 A for M-O. Mean linear polyhedral thermal expansion coefficients of 6.5 × 10−6 °C−1 and 8.9 × 10−6 °C−1 were calculated for T and M sites, respectively.

Synthesiss of Cubic Cs2FeSi5O12Powder in Atmosphere and its Thermal Expansion Property.

Cubic Cs2FeSi5O12 powder with the space group Ia-3d was synthesized by heating the powder mixture of Cs2CO3⋅2H2O, Fe3O4 and amorphous SiO2 with the molar ratio of Cs/Fe=2 and Si/Fe=5 at 1273K for 20h under Ar gas flow. The thermal expansion property of cubic Cs2FeSi5O12 powder was investigated in the temperature range from 298 to 1273K using high-temperature X-ray diffraction. The thermal expansion rate of cubic Cs2FeSi5O12 was lower than that of cubic CsFeSi2O6. Consequently, increasing the molar ratio of Si/Fe was effective for decreasing the thermal expansion rate of Cs-Fe-leucite compounds. Cubic Cs2FeSi5O12 showed a lower thermal expansion with the mean linear thermal expansion coefficient of 1.75×10-6K-1 in the range from 573 to 1273K.

Material property correlations for uranium mononitride: I. Physical properties

The experimental data for the lattice parameter ( a), density ( p), and mean linear thermal expansion coefficient (α) of uranium mononitride (UN) have been collected and reviewed. Empirical correlations for these three properties as functions of temperature ( T, in K) were developed and are given as: a( A ̊ ) = 4.879 + 3.264 × 10 −5(T) + 6.889 × 10 −9(T 2) , ρ( g/ cm 3) = 14.42-2.779 × 10 −4( T)−4.897 × 10 −8( T 2), α( K −1) = 7.096 × 10 −6 + 1.409 × 10 −9( T). The lattice parameter correlation was constructed from experimental data in the range of 298 <-, T <- 2523 K. The density and thermal expansion coefficient correlations were derived from the lattice parameter correlation, and are therefore only strictly applicable over the same temperature range. However, all of the correlation forms employed are very stable; thus, application of these correlations to temperatures above 2523 K should yield reasonable estimates for these properties.

Measurements of the thermal expansion coefficient of 1Cr18Ni9Ti stainless steel with a laser scanning microdisplacement detection technique

A laser scanning microdisplacement detection system has been developed to measure the thermal expansion coefficient of materials over the range from room temperature to 1200 K. The measurement apparatus consists of a dynamic heating device, a microdisplacement detection system, and a microcomputerbased high-speed data acquisition system. The specimen is dynamically heated from room temperature to 1200 K by passing a large electrical current through it. The thermal expansion of the specimen is detected by the laser detection system, which records the shift of Fraunhofer diffraction fringes with a photodetector. Measurements of the mean linear thermal expansion coefficient of 1Cr18Ni9Ti stainless steel in the range of 300–1200 K are described. The results are compared with other reported values of the thermal expansion coefficient. The maximum deviation between them is about 2.3% at the highest temperature, 1200 K.

The anisotropy of the thermal expansion in the AgInC2VI chalcopyrite-type compounds from the X-ray diffraction data

The lattice parameters a and c as well as the thermal expansion coefficient for different directions in the AgInS2, AgInSe2, and AgInTe2 chalcoyprite-type compounds are determined as a function of temperature in the range from 80 to about 700 K using a X-ray diffractometry technique. For all three compounds an anisotropy is found between the axial thermal expansion coefficients with the positive coefficient along the a-axis and the negative coefficient along the c-axis. The absolute value of the temperature coefficient αc/a = α∥ – α⊥ of the axial ratio and the mean linear thermal expansion coefficient are the greatest for AgInS2 and the smallest for AgInTe2. [Russian Text Ignored].

The effects of molybdenum and aluminum on the thermal expansion coefficients of nickel-base alloys

The effects of molybdenum and aluminum on the mean linear thermal expansion coefficients from room temperature to 1050°C were determined for two types of nickel-base alloys. The Solid Solution Alloys were cast and homogenized Ni-Co-Cr-Mo alloys with 0, 312, and 612 nominal wt pct molybdenum concentrations. The Gamma Prime Alloys were wrought and heat-treated Ni-Cr-Mo-Al(Ti) alloys with 0, 2, 5, and 8 nominal wt pct molybdenum in each of four aluminum plus titanium levels (3 pct Al, 412 pct Al, 6 pct Al, or 1 pct Al + 312 pct Ti nominal wt pct). Thermal expansion coefficients were determined on at least two specimens from each alloy. It was found that molybdenum lowers the thermal expansion coefficients of both the cast Ni-Co-Cr solid solutions and the wrought Ni-Cr-Al(Ti) two-phase alloys. Both aluminum and titanium were also observed to decrease expansion coefficients in the two-phase, γ + γ, alloys. Results are discussed in terms of relative melting point effects between solute and solvent elements, and in terms of the volume fraction of the γ phase present.

Lattice expansions of two boron carbides between 12 and 940°C

High-temperature X-ray diffraction methods have been used to determine unit-cell parameters of two boron carbide compositions from 12° to about 940°C. One composition was at the carbon-rich end of the phase field (i.e. B4C), the second at the boron-rich end (5 at. % C by chemical analysis). The lattice expansion of both substances was isotropic in the temperature range studied. The mean linear thermal expansion coefficient for the carbon-rich composition is 5.65 x 10−6°C−1, while that of the boron-rich composition is 5"87 x 10−6°C−1.

Thermal Expansion of Silver Iodide

The linear thermal expansivity of polycrystalline silver iodide has been measured with a "Fused-Quartz Tube" apparatus in the temperature range 170 - 500 °C, the mean linear thermal expansion coefficient being αt 180=(2.607 + 0.00182 t) 10-5 (°C-1). An irregular change in the thermal expansivity was found close to 432 °C where an order-disorder transition has been reported.

The thermal expansion of alkali borate glasses and the boric oxide anomaly

A brief review is presented of the major theories for the so-called “boric-oxide anomaly” in alkali borate glasses, and a comparison is effected with recent published information on the structure of B 2O 3 and alkali borate glasses. These indicate serious shortcomings in current theories. An experimental study is reported of the mean linear thermal expansion coefficients between 25°C and −196°C of a series of glasses, prepared at composition intervals of 2 mole% alkali oxide, in all five alkali borate systems. The thermal expansion versus composition relations are characterized by broad, flat minima, with no single composition being uniquely identifiable with the minimum. It is concluded that the compositional variation of the thermal expansion coefficient of alkali borate glasses is not truly anomalous, but rather seems to vary with structural variations in a generally predictable manner. It is suggested that the term “anomaly” be reserved for the more serious problem of explaining the change in boron coordination with composition.

Lattice parameter anomalies at the Curie point of pure iron

A high-temperature x-ray study of pure iron has shown that a small, but easily detectable, lattice parameter anomaly, representing a decrease in the mean linear thermal expansion coefficient, occurs over a narrow range of temperature (similar 35 degc) about the Curie point. The total volume change associated with the ferromagnetic-paramagnetic transition in pure iron obtained from the experimental measurements gave values in good agreement with those calculated directly from volume magnetostriction data, although for an alternative method of calculation the agreement was poor.

High-Temperature Thermal Expansion of Certain Group IV and Group V Diborides

The thermal expansions of TiB2, ZrB2, HfB2, NbB2, and TaB2 were measured to temperatures above 1600°C by an X-ray method. Lattice constants were measured for each compound; each had the AlB2-type hexagonal structure. The mean linear thermal expansion coefficients were calculated from the data and are compared to the values found in the literature.

Thermal expansion of tungsten and molybdenum disilicides

1. Linear thermal expansion coefficient of molybdenum disilicide was determined by x-ray diffraction. The mean value between 13° and 613°C is 9.2±0.6 · 10−6deg−1. 2. The mean linear thermal expansion coefficient of tungsten disilicide is less than that of MoSi2 by approximately 3%.