Average Linear Thermal Expansion Coefficient Research Articles

Studies on thermal expansion and XPS of urania–thoria solid solutions

The thermal expansion characteristics of polycrystalline (U y Th 1− y )O 2 solid solutions with y=0.13, 0.55 and 0.91 were determined in the temperature range from 298 to 1973 K by means of X-ray diffraction technique. For these temperatures, the average linear thermal expansion coefficients for (U 0.13Th 0.87)O 2, (U 0.55Th 0.45)O 2 and (U 0.91Th 0.09)O 2 are 1.033×10 −5, 1.083×10 −5 and 1.145×10 −5 K −1 , respectively. The measured thermal expansion values were compared with those calculated by applying the equations for linear thermal expansion of pure urania and thoria. It was shown that the stoichiometric (U, Th)O 2 solid solutions are almost ideal at least up to 2000 K. The binding energies of U 4f 7/2 and Th 4f 7/2 electrons of (U 0.1Th 0.9)O 2, (U 0.25Th 0.75)O 2, (U 0.50Th 0.50)O 2, (U 0.75Th 0.25)O 2 and (U 0.90Th 0.10)O 2 were experimentally determined by X-ray photoelectron spectroscopy. The result showed the presence of only U 4+ and Th 4+ chemical states in the stoichiometric urania–thoria solid solutions.

Bulk and lattice thermal expansion of Th 1− xCe xO 2

Bulk and lattice thermal expansion studies on Th 1 − x Ce x O 2 ( x=0.0, 0.04, 0.08 and 1.0) were carried out by dilatometry and high-temperature XRD from room temperature to 1123 K and to 1473 K, respectively. The average linear thermal expansion coefficients, α ̄ , of ThO 2, Th 0.96Ce 0.04O 2, Th 0.92Ce 0.08O 2 and CeO 2 were found to be 9.04×10 −6, 9.35×10 −6, 9.49×10 −6 and 11.58×10 −6 K −1, respectively, between 293 and 1123 K. The average lattice thermal expansion coefficients, α ̄ a , were 9.54×10 −6, 9.85×10 −6, 10.01×10 −6 and 12.06×10 −6 K −1 , respectively, between 293 and 1473 K in this series of compounds. The substitution of 4 and 8 mol% Ce 4+ at Th 4+ sites in ThO 2 has a noticeable influence on the thermal expansion behavior.

Combustion synthesis and bulk thermal expansion studies of Ba and Sr thorates

Nanocrystalline BaThO 3 and SrThO 3 powders have been prepared at a relatively low calcination temperature by a gel combustion technique using citric acid as a fuel and the nitrate as an oxidizer. These powders resulted in highly dense (sintered density > 90% of th.d.) pellets on sintering at 1923 K. The orthorhombic lattice parameters of BaThO 3 were found to be as a=0.635(1), b=0.6387(9) and c=0.8995(9) nm whereas SrThO 3 was monoclinic with a=0.6319(4), b=0.3240(1), c=0.4928(3) nm and β=117.38(5)°. It was observed that the average linear thermal expansion coefficients, α ̄ , for BaThO 3, SrThO 3 and ThO 2 are 11.09×10 −6,10.49×10 −6 and 9.10×10 −6 K −1 , respectively, which are about 21.9% and 15.3%, respectively, higher than that of pure ThO 2 between room temperature and 1123 K.

Thermal‐Expansion Behaviors and Mechanisms for Ca‐ or Sr‐Doped Lanthanum Manganite Perovskites under Oxidizing Atmospheres

The thermal expansion behavior and mechanism of A‐site‐deficient lanthanum manganite perovskites, , and alkaline earth metal (AE)‐doped lanthanum manganite perovskites, , under oxidizing atmospheres have been investigated. The average linear thermal expansion coefficients of the AE‐doped lanthanum manganites decreased with increasing Ca content up to 20 mol % and with increasing Sr content up to 10 mol %, and then increased. During the thermal cycle measurement, the perovskite samples and the perovskites (0 ≤ x ≤ 0.3) shrank, while no anomalous shrinkage behavior was observed for the samples. From the results of high‐temperature X‐ray diffraction analysis, no dependency of cell volume of the perovskites on aging time at selected temperatures and on thermal cycles was observed. © 2000 The Electrochemical Society. All rights reserved.

Negative thermal expansion in Y2W3O12

Neutron diffraction data were collected on polycrystalline Y2W3O12 at seven temperatures from 15 to 1373 K. All three cell edges of orthorhombic Y2W3O12 decrease with increasing temperature, giving an average linear thermal expansion coefficient of −7.0×10−6 K−1. Rietveld refinements of the neutron diffraction data show an apparent decrease in the average W–O distance of 0.05 Å from 15 to 1373 K. This apparent decrease causes the decrease in the cell edges, but it is not an actual decrease of average W–O distances. The apparent shrinkage is instead considered to be caused by the transverse thermal motion of oxygen in the Y–O–W linkages.

Structure and lattice parameters of thin C60 films

The structure and lattice parameters of C60 fullerite films evaporated in vacuum on the (100) cleavage plane of NaCl at the substrate temperature 290–400 K are investigated in the temperature range 300-5 K by electron-optical methods. Fullerite films have an fcc lattice at room temperature. The film structure changes with the temperature of condensation from epitaxial with the (111) orientation to a disordered and highly nanodisperse structure with a grain size of 4–5 nm. The crystallographic conditions of conjugation of the (100) surface of NaCl and epitaxial C60 fullerite films are determined, and the four-position type of their structure is established. The fcc–sc transition temperature and the observed jump in the lattice parameter are close to the corresponding characteristics of bulk fullerite. The temperature dependence of the lattice parameter in the temperature range 100–260 K is used to determine the average linear thermal expansion coefficient α of the films. An increase in α for small thicknesses is a size effect associated with a considerable influence of the surface. A mechanism of formation of the structure of condensed C60 fullerite films is proposed on the basis of the obtained results.

Thermal Expansion Behavior of Ca-, or Sr-Doped Lanthanum Manganites Under Oxidizing Atmospheres

The thermal expansion behavior of alkaline earth metal (AE)-doped lanthanum manganite perovskites, La1−xAExMnO3 (AE = Ca and Sr, 0 ≤ x ≤ 0.4), under oxidizing atmospheres has been investigated. The average linear thermal expansion coefficients of the AE-doped lanthanum manganites decreased with increasing Ca-content up to 20 mol%, and with increasing Sr-content up to 10 mol%, and then increased. During the thermal cycle measurement, the La1−xAExMnO3 perovskite samples with an AE-content of 0 ≤ x ≤ 0.3 shrank, while no anomalous shrinkage behavior was observed for the La0.6AE0.4MnO3 samples. From the results of high-temperature x-ray diffraction analysis, no dependency of cell volume of the perovskites on aging-time at selected temperatures and thermal cycles was observed.

Thermal Expansion of Nickel‐Zirconia Anodes in Solid Oxide Fuel Cells during Fabrication and Operation

The thermal expansion of NiO‐8 mol % ‐stabilized (YSZ) composites and Ni‐YSZ cermets in air and hydrogen have been investigated in the temperature range from 50 to 1000°C. The average linear thermal expansion coefficient (TEC) of NiO‐YSZ composites in air increased with NiO content over the entire composition range. While NiO in the composites was changed to Ni in the stream, their expansions were governed by the reduction of NiO. For reduced, Ni‐YSZ cermets, the TEC increases significantly with Ni content in the composition range >60 vol % Ni. The TEC increased gradually during repeated thermal cycles between room temperature and 1000°C. When cermets were measured in air, the Ni particles were fully oxidized to NiO above 900°C, and many cracks appeared in the samples.

Thermal expansion of β-rhombohedral boron

The cell dimensions of β-rhombohedral boron have been measured in the temperature range 10–1273 K, using X-ray diffraction. The linear thermal expansion coefficients ( α l =( l− l 298)/ l 298 ( T− T 298)) were determined along the a and c directions. It was found that β- rhombohedral boron is anisotropic, displaying a significantly larger thermal expansion coefficient in the c direction than in the a direction. The average linear thermal expansion coefficient is 6.4×10 −6 K −1 in the temperature range 293–1023 K.

Solid state synthesis and properties of monoclinic celsian

Monoclinic celsian of Ba0.75Sr0.25Al2Si2O8 (BSAS-1) and Ba0.85Sr0.15Al2Si2O8 (BSAS-2) compositions have been synthesized from metal carbonates and oxides by solid state reaction. A mixture of BaCO3, SrCO3, Al2O3, and SiO2 powders was precalcined at ∼900–940 °C to decompose the carbonates followed by hot pressing at ∼1300 °C. The hot pressed BSAS-1 material was almost fully dense and contained the monoclinic celsian phase, with complete absence of the undesirable hexacelsian as indicated by X-ray diffraction. In contrast, a small fraction of hexacelsian was still present in hot pressed BSAS-2. However, on further heat treatment at 1200 °C for 24 h, the hexacelsian phase was completely eliminated. The average linear thermal expansion coefficients of BSAS-1 and BSAS-2 compositions, having the monoclinic celsian phase, were measured to be 5.28 × 10−6 °C−1 and 5.15 × 10−6 °C−1, respectively, from room temperature to 1200°C. The hot-pressed BSAS-1 celsian showed room temperature flexural strength of 131 MPa, elastic modulus of 96 GPa and was stable in air up to temperatures as high as ∼1500 °C.

Development of Aluminum Titanate-Clay Composites for Infrared Radiator

Sintered aluminum titanate has a very low thermal expansion and an infrared radiative property selectively emitting large amounts of far infrared rays. However, it is weak in mechanical strength. Spectral infrared emittance, thermal expansion coefficient, and mechanical strength of aluminum titanate-clay composites were studied to develop a material for infrared radiators. The composites containing 10 to 50mass% clay has low spectral emittance in the range of 5000 to 2500cm-1 and high emittance in the range of 1500 to 360cm-1. The bending strength of the composite increased with increasing clay content. The composite with a clay content of 30mass% formed by hand pressing using a plaster mold and fired at 1500°C had a large strength for infrared radiators; 80MPa. The average linear thermal expansion coefficient from room temperature to 800°C of the 30mass% clay-containing composite fired at 1500°C was lower than 2.5×10-6/°C.

Linear thermal expansion coefficient and biaxial elastic modulus of diamondlike carbon films

Diamondlike carbon films were deposited on silicon, gallium arsenide and aluminum substrates using ion-assisted chemical vapor deposition. The stress of these films was measured as a function of temperature between 25 and 150 °C. Using the stress-temperature measurements, the average linear thermal expansion coefficient was found to be 2.3 ppm/°C, while the biaxial elastic modulus 1.74×1011 Pa.

Real‐time X‐ray scattering study of thermal expansion of poly(butylene terephthalate)

AbstractReal‐time x‐ray scattering at elevated temperatures has been used to investigate the thermal expansion characteristics of poly(butylene terephthalate), PBT. Changes in the six lattice parameters of the α‐form of PBT were obtained from wide‐angle x‐ray scattering over the temperature range from 35 to 215°C. The linear thermal expansion coefficients relating the unit cell parameters at temperature T to their values at 0°C are found to be The temperature dependence of both the long period and the lamellar thickness of semicrystalline PBT were determined from real‐time small‐angle x‐ray scattering analysis of the one‐dimensional electron density correlation function. The long period, lamellar thickness, and degree of crystallinity increase as the temperature increases. We find an average linear thermal expansion coefficient of the bulk material to be αave = 5.0 × 10−4°C−1. © 1992 John Wiley & Sons, Inc.

The influence of domain state on thermal-mechanical properties of KTN crystal

The average linear thermal expansion coefficients of single-domain and multi-domain tetragonal KTA 1 - x Nb x O 3 ( x = 0.5 and x = 0.48, respectively) crystals were measured in the vicinity of tetragonal-cubic phase transition temperature by using thermal mechanical analysis method. The influence of domain state on thermal mechanical properties of these crystals has been investigated. The possibility of determining the dominant spontaneous polarization direction of a multi-domain crystal by its thermal mechanical properties is discussed.

Crystallization kinetics of binary borosilicate glass composite

Kinetics of cristobalite precipitation in a binary glass composite, containing a low-softening borosilicate (BSG) and a high-softening high silica (HSG) glass, have been investigated. XRD results show that the pure glasses do not crystallize under the sintering conditions used, but when mixed in appropriate proportions the cristobalite gradually precipitates out of the initial amorphous binary glass mixture as the sintering continues at temperatures ranging from 800 to 1000 °C. Average linear thermal expansion coefficient (TCE) results show that the TCE increases significantly with increasing precipitation of cristobalite as a function of sintering time. Comparing the experimental TCE results with those theoretically calculated, it is concluded that the precipitation originates most likely in the HSG rather than in the BSG. The precipitation kinetics follow the Avrami equation, and the results show an apparent activation energy of 82 kJ/mol which is close to those for the diffusion of alkali ions in silicate glasses, suggesting mass-transport controlled kinetics. The values of the Avrami exponent are 1.7–1.8, which could be interpreted as a 3-dimension diffusional growth at zero nucleation rate. The linear growth rates of cristobalite, calculated from the precipitation curve, are in the range of 4–8 × 10−5 μm/min, and show slight temperature dependence from 800 to 1000 °C. The linear growth rates of cristobalite are also calculated theoretically using the equation derived by Turnbull et al.,2 and the data are 0–3 orders of magnitude smaller than those observed experimentally. This disparity is attributed to the catalytic effect of the OH and O in air and in the glass network, as well as the diffusion of alkali ions from BSG to HSG.

Phase diagram and elastic properties of Fe 30% Ni alloy by synchrotron radiation

Diffusionless phase transitions of Fe‐Ni alloy with 30 wt % Ni (Fe30Ni) were studied at high temperature and pressure by synchrotron radiation. Several isothermal runs ranging from 25°C to 600°C were carried out at up to 20–60 GPa to determine the phase relationships and elastic properties of the alloy. The ruby fluorescence method was used for pressure measurements at room temperature. The compressibility of the fcc phase of the alloy, determined up to 48 GPa, has a bulk modulus of 160 ± 15 GPa at room temperature assuming K′0 = 4. The average linear thermal expansion coefficient of the fcc phase of Fe30Ni was estimated to be 10.2 ± 1.5 × 10−6 K−1 between 25°C and 600°C. The pressure at high temperature was calculated using the equation of state of the fcc phase assuming that the compressibility of the alloy at high temperature remains the same as at 25°C. The Fe30Ni alloy has both fcc and bcc structures at ambient conditions. However, the bcc phase disappeared (bcc‐out) after pressure was applied to the sample at various temperatures. The bcc‐out transition boundary has a negative slope of −55° ± 5°C/GPa. The fcc phase transformed to a hexagonal close‐packed phase at high pressure (hcp‐in). The slope of the phase boundary of hcp‐in was determined to be 25 ± 5°C/GPa. This result, combined with our previous investigation (Huang et al., 1988), indicates that the slope of the fcc/hcp phase boundary in Fe‐Ni alloys remains constant with an increase of Ni content up to 30 wt %.

Bulk thermal expansion studies of BiCaSrCu2O x and Bi2CaSr2Cu2O x

The compounds BiCaSrCu2Ox and Bi2CaSr2Cu2Ox were prepared by ceramic techniques and characterized by X-ray powder diffractometry (XRD) and microthermogravimetry (μTG) and their bulk thermal expansion measurements were carried out using dilatometry in the temperature range 298⩽T⩽1073 K in air. The results have been analyzed and are compared with those obtained earlier for YBa2Cu3O7. The XRD analysis shows that both BiCaSrCu2Ox and Bi2CaSr2Cu2Ox are single phase in nature, having an orthorhombic symmetry. The μTG analysis carried out in oxygen, air, and nitrogen shows negligible weight loss (R~0.1%) on heating to 1073 K, indicating that these two compounds, unlike YBa2Cu3O7, are quite stable. The analysis of bulk thermal expansion data reveals that the average linear thermal expansion coefficient (α1) for both BiCaSrCu2Ox and Bi2CaSr2Cu2Ox is almost the same (α1≈ 10.5×10−6 K−1) and is found to be nearly half of that for YBa2Cu3O7 (α1≈ 18×10−6 K−1), suggesting that the interatomic bonding in both BiCaSrCu2Ox and Bi2CaSr2Cu2Ox is stronger as compared to YBa2Cu3O7.

Thermogravimetric and dilatometric studies of LaBa 2Cu 3− yM yO x(M = Ni, Li; y = 0, 0.1)

Thermogravimetric (TG) and dilatometric studies of the pure compound LaBa 2Cu 3O x and the Ni and Li doped compounds LaBa 2Cu 2.9Ni 0.1O x and LaBa 2Cu 2.9Li 0.1O x were carried out in the temperature range 298 ⩽ T ⩽ 1173 K. The results were analysed and compared with those obtained earlier for YBa 2Cu 3O x . The values of oxygen content x for the compounds LaBa 2Cu 3O x and YBa 2Cu 3O x were obtained from the TO data in 8%H 2-Ar and their behaviour compared with that of pure CuO and NiO under similar conditions. The values of average linear thermal expansion coefficients (α 1) were determined from the dilatometric data for the pure and Ni and Li doped compounds of LaBa 2Cu 3O x . The dilatometric and TG results both suggest that the oxygen ions in the pure compounds LaBa 2Cu 3O x and YBa 2Cu 3, O x are more loosely bound than those in the doped compounds.

Ionic Conductivity of Y<sub>2</sub>O<sub>3</sub> Stabilized ZrO<sub>2</sub>-ZrSiO<sub>4</sub> Ceramics

Two-phase composite ceramics consisting of 8mol% Y2O3 stabilized ZrO2 and 10 to 70wt% of ZrSiO4 were fabricated. The ceramics showed ionic conduction above 500°C. The conductivity of the ceramics decreased with increasing ZrSiO4 content, but the ceramics with 70wt% of ZrSiO4 still had a high conductivity of 3×10-1S·m-1 at 1000°C. The activation energy of conductivity of the ceramics was 104kJ·mol-1, which agreed closely with that of a pure 8mol% Y2O3 stabilized ZrO2. The thermal expansion coefficient of the ceramics decreased with increasing ZrSiO4 content, and the ceramics with 70wt% of ZrSiO4 showed a low average linear thermal expansion coefficient of 5.5×10-6°C-1 between room temperature and 1000°C. The 8mol% Y2O3 stabilized ZrO2-ZrSiO4 ceramics showed higher ionic conductivity than the conventional 8mol% Y2O3 stabilized ZrO2-Al2O3 ceramics, when they have the same thermal expansion coefficients.

Thermal and mechanical properties of aluminumtitanate-mullite composites (part 1)

The thermal expansion, thermal stability and bending strength of aluminumtitanate (AT)-mullite composites prepared from synthesized AT, Newzealand kaolin and aluminum hydroxide were investigated. The results obtained are summarized as follows; (1) The average linear thermal expansion coefficient from 100° to 1100°C increased slightly with increasing amount of AT up to 50wt%, and decreased with further increase in the amount of AT, approaching to be value of fired AT. The average linear thermal expansion coefficients from 1100° to 1400°C in heating and from 1400°C to the turning point in the cooling stage increased monotonously with increasing AT content. (2) The degree of thermal expansion hysteresis decreased with decreasing amount of AT. (3) The bending strength of the composites containing 10-30wt% AT was the highest, and decreased with further increase in the amount of AT. (4) The decomposition of AT in the composites was restrained almost completely.