Increase In Thermal Expansion Coefficient Research Articles

Thermal Expansion Properties of Sr1-xLaxTiO3-δ Perovskites (0

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RBaCuCoO5 + δ (R = Nd, Sm, Gd) layered cuprocobaltites: Synthesis, structure, and properties

Cuprocobaltites RBaCuCoO5 + gd(R = Nd, Sm, Gd) were prepared. Their unit cell parameters were determined, and thermal expansion, electrical conductivity (σ), and Seebeck coefficient (S) were studied in air in the range 300–1100 K. The compounds have tetragonal structures (space group P4/mmm, Z = 1). Their unit cell parameters are a = 0.3906(2) nm, c= 0.7648(7) nm for NdBaCuCoO5.21; a = 0.3904(2) nm, c = 0.7609(6) nm for SmBaCuCoO5.06; and a = 0.3891(2), c = 0.7592(6) nm for GdBaCuCoO5.02. The RBaCuCoO5 + δ cuprocobaltites at room temperature are p-type semiconductors, whose electrical conductivity and linear thermal expansion coefficient (LTEC) increase with increasing R3+ ionic radius, whereas the Seebeck coefficient decreases. The LTECs of RBaCuCoO5 + δ phases in the range 500–575 K increase by a factor of 1.2–1.5 because of the elimination of weakly bound oxygen. S = f(T) curves for RBaCuCoO5 + δ (R = Nd, Sm, Gd) feature maxima at 510 K for R = Sm and 365 K for R = Gd, probably, due to the change in the spin state of cobalt cations in these phases.

The variation of thermoelastic properties under conditions of variation of isotopic composition of diamond

The parameters of interatomic interaction in diamonds of 12C and 13C isotopes are determined. The parameters are determined by two methods, namely, from the elastic modulus (potential no. 1) and from the sublimation energy at T = 0 K (potential no. 2). Based on these parameters, the Debye model is used to calculate the isobaric temperature dependences of the thermoelastic properties for isotopically different diamonds, namely, the coefficient of thermal expansion (CTE), the density, the elastic modulus B T , and the specific heat capacity. It is demonstrated that the best agreement with the experimentally obtained dependences of the foregoing parameters is obtained when potential no. 1 is used in calculations. The values of CTE, density, and heat capacity increase in the case of transition from 12C diamond to 13C diamond. It is demonstrated that the inequality B T (12C) B T (13C). Experimental results are given which confirm this effect. The variation of the properties of isotopically different diamonds with increasing pressure is discussed.

Micron-scale measurements of the coefficient of thermal expansion by time-domain probe beam deflection

We describe a pump-probe optical technique, time-domain probe-beam deflection, that enables measurements of the coefficient of thermal expansion (CTE) with micron-scale spatial resolution. Our quantitative model for the beam deflection includes contributions from thermal expansion of thin films deposited on a substrate, thermal expansion of the substrate, elastic deformation of the substrate, heating of air above the surface of the sample, and the lateral temperature gradient at the surface of the sample. The usefulness of this technique for high-throughput CTE measurement is demonstrated by two experiments: we are able to find the Invar alloy composition directly from a simple Fe–Ni diffusion couple and we find abnormal CTE increase in an ≈100μm region of dentin adjacent to the dentin-enamel junction of a human tooth. Such a CTE abnormality would be difficult to find using other techniques.

Spring-in angle as molding distortion for thermoplastic matrix composite

In this work, the spring-in angle behavior of a U-channel shaped thermoplastic matrix laminate is studied. The consolidation of the U-channel shaped profile having two different corner radii took place in an autoclave. Spring-in angle was measured at room temperature, after cooling in the autoclave, and during subsequent heating at different temperatures and after final cooling to room temperature. Different thermally induced spring-in angle behaviors were observed for the two inner radii of U-specimen. Thermal expansion coefficients in the through the thickness and in-plane directions were measured. Experimental spring-in angle data were then compared with a differential model derived from the Radford model. Some differences between the model results and experimental spring-in data were observed. The differences observed between the two radii and between experimental and model results were attributed to the existence of fibers distortion at the corner, leading to significant fibers misalignment and wrinkling. Consequently, the Radford model was modified to account for the increase of thermal expansion coefficient in the through the thickness direction. Results showed a better agreement with experimental data. Finally, the difference observed in the spring-in angle before and after heating of the composite indicates the relevance of non-thermoelastic effects in thermoplastic matrix composites.

Effect of thermal strain on structure and polarization fatigue of CSD-derived PbZr0.53Ti0.47O3/LaNiO3 hetero-structures

PbZr0.53Ti0.47O3/LaNiO3 (PZT/LNO) hetero-structures have been successfully deposited on MgO, SrTiO3, Al2O3 and Si substrate by chemical solution routes, respectively. The X-ray diffraction measurements show that out-of-plane lattice parameters of PZT increase as increase of thermal expansion coefficient of substrate. Polarization fatigues of Pt/PZT/LNO capacitors are strongly affected by the thermal strain caused by difference of thermal expansion coefficient between PZT and substrate materials. High fatigue resistance of Pt/PZT/LNO can be obtained by using substrate with similar thermal expansion coefficient as PZT.

A comparative study on the failure resistance of thermal barrier coatings

A bi-material structure, representing a single layer thermal barrier coating, containing an interfacial crack and subjected to a cooling shock, is investigated using the finite element method. Numerical tests are performed to study the effect of material properties mismatch, between the coating and the substrate, on the failure resistance of the cracked structure, represented by the strain energy release rate. No special care is taken for taking into consideration the singular nature of near tip temperature and displacement fields. The parametric study is based on a quasi-static uncoupled thermo-elasticity assumption and a crack opening displacement formula for obtaining the strain energy release rate. The methodology that is followed has been validated in a previous article by comparison to an analytic solution. Computational results indicate that the strain energy release rate peak, experienced during the thermal shock, is highly dependent on the thermal conductivity and thermal expansion coefficient mismatch, but almost independent from the Young’s modulus mismatch between the two materials. It is concluded that, the failure resistance of the thermal barrier coating decreases, as the insulation provided by the coating and its thermal expansion coefficient increase in relation to the substrate.

LaSr3Fe3‐yCoyO10‐δ (0 ≤ y ≤ 1.5) Intergrowth Oxide Cathodes for Intermediate Temperature Solid Oxide Fuel Cells.

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Sr3 − xLaxFe2 − yCoyO7 − δ (0.3 ⩽ x ⩽ 0.6 and 0 ⩽ y ⩽ 0.6) Intergrowth Oxide Cathodes for Intermediate Temperature Solid Oxide Fuel Cells

The perovskite-related intergrowth oxides, ( and ), have been investigated as cathode materials for intermediate temperature solid oxide fuel cells. With a given La content , the electrical conductivity, oxide-ion vacancy concentration, and thermal expansion coefficient (TEC) increase with increasing Co content . With a given Co content, while the electrical conductivity increases, the TEC decreases with increasing La content. The electrocatalytic activity and power density measured with (GDC) single cells with a GDC interlayer between the cathode and electrolyte increase with increasing Co and La contents due to an increase in electrical conductivity and oxide ion vacancy concentration. The electrical conductivity, TEC, and electrochemical performance of the cathodes are also compared with those of the intergrowth and perovskite oxides.

LaSr3Fe3-yCoyO10-δ (0 ≤ y ≤ 1.5) Intergrowth Oxide Cathodes for Intermediate Temperature Solid Oxide Fuel Cells

LaSr3Fe3-yCoyO10-δ (0 ≤ y ≤ 1.5) oxides with a perovskite-related intergrowth structure have been investigated as cathode materials for oxygen reduction reaction in intermediate temperature solid oxide fuel cells (SOFC). The electrical conductivity, oxygen vacancy concentration, and thermal expansion coefficient (TEC) increase with increasing Co content y. The electrocatalytic activity and power density measured with the LaSr3Fe3-yCoyO10-δ/La0.8Sr0.2Ga0.8Mg0.2O2.8 (LSGM)/Ni−Ce0.9Gd0.1O1.95 (GDC) single cells with a porous Ce0.9Gd0.1O1.95 (GDC) interlayer between the cathode and the electrolyte to avoid undesired interfacial reactions increase with increasing Co content because of an increase in the electronic and oxide ion conductivities of the cathode. The intergrowth LaSr3Fe3-yCoyO10-δ cathodes offer electrochemical performances comparable to that of the well-known pervskite La0.6Sr0.4CoO3-δ cathode but with an important advantage of significantly lower TEC.

Thermal vibrations and α → β polymorphic transformation in lanthanum

Neutron diffraction was used to determine temperature dependence of the Debye-Waller factor and thermal atomic displacements for two polymorphic modifications of lanthanum, namely, α-La with a double hcp (dhcp) crystal structure and β-La with an fcc crystal structure. No substantial changes in the mean-square thermal atomic displacements were shown to occur; the Debye temperatures of the two polymorphic modifications, α-La and β-La, are equal to 135 and 130 K, respectively. However, the relative (with respect to the lattice parameters) displacements along the axes change substantially. The transition from the anisotropic hexagonal modification to the isotropic cubic modification leads to a decrease in the maximum thermal atomic displacements and a weakening of their temperature dependence because of their redistribution over the crystallographic axes. Upon the α → β transformation, the volume decreases and the anharmonicity increases as demonstrated by a twofold increase in the volumetric thermal expansion coefficient. An analysis of literature data available for the polymorphic transformations shows that the enhancement in the anharmonicity is related to an increase in the specific volume in the course of transition from the low-temperature to the high-temperature modification. The explanation of this phenomenon is suggested.

Thermal Expansion of Electrodeposited Nanoscale Multilayers of Invar with Copper

Nanoscaled, compositionally modulated multilayer alloys of NiFe in the Invar range and Cu were electroplated into an array of cylindrical microrecesses in polymethylmethacrylate 100 μm in diameter, 100 μm tall, with a center-to-center spacing of 300 μm. Deposition conditions were determined using a rotating Hull cell and linear sweep voltammetry. The presence of the nanoscale multilayers was confirmed by transmission electron microscopy and the thermal expansion of the multilayer microposts was measured over the range from 25 to 300°C. As deposited, the multilayer alloy exhibited a negative coefficient of thermal expansion (CTE); for a 4.5 nm thick Cu layer the CTE was -3.28 μm/m-°C up to 150°C and more negative for higher temperatures. To the best of the authors' knowledge this is the first observation of a room temperature, negative CTE in multilayered-Invar alloys. After thermal cycling, the alloy had a small positive CTE of 1.75 μm/m-°C up to 175°C, comparable to that of bulk Invar (1.00 μm/m-°C), and no increase of the CTE was observed for temperatures up to 275°C.

Effect of Grain Size on the Thermal Expansion of Isotropic Synthetic Graphites

The relationship is analyzed between the thermal expansion coefficient of synthetic graphites and the grain size of their filler. It is shown by examining a large number of commercial graphites of different classes that their thermal expansion coefficient increases from 2 × 10−6 to (7–8) × 10−6 K−1 as the grain size decreases from 3000 to 1 µm. The strength of synthetic graphites also increases with increasing grain size and correlates with thermal expansion. The likely reason for the increase in thermal expansion coefficient is the better contact between neighboring microvolumes of the material. A model is proposed for the thermal expansion of synthetic graphites which considers microvolumes 0.1 to 0.5 µm in size, with a thermal expansion coefficient on the order of 8.3 × 10−6 K−1, only a fraction of the microvolumes being involved in thermal-expansion transfer. The fraction of such microvolumes decreases with increasing grain size.

Thermal stability and preparation of dense membrane ceramics of BIMEVOX

The thermal stability and sintering conditions of a series of BIMEVOX compounds was studied. Extended annealing at temperature below the γ/γ′ phase transition, revealed the materials doped with a Me V cation are more stable than other BIMEVOXes. A modification of the BIMEVOX doped with a Me II metal was generally observed after annealing at 450 °C for several weeks. In contrast, no evolution was noticed for BISBVOX.15, BINBVOX.25, BITAVOX.20 compositions annealed for 10 weeks at 450 °C and 7 weeks at 500 °C. These latter compositions exhibit higher melting point and require sintering temperatures above 850 °C. Moreover, the increase in thermal expansion coefficient observed in these materials at the transition of phase is smaller (14 K − 1 to 14.5 K − 1 ) than for the other BIMEVOXes which makes them promising candidates as membrane for oxygen separators or catalytic dense membrane reactors.

Ce 4+-modified cordierite ceramics

A dense, low thermal expansion cordierite ceramic was prepared by the co-precipitation method and Ce 4+ addition. Ce 4+ addition can inhibit μ-cordierite crystallization and improve α-cordierite crystallization. Adding 3.2 wt.% Ce 4+ enables density and mechanical strength to reach maximum values with a minor increase in thermal expansion coefficient.

New double-ceramic-layer thermal barrier coatings based on zirconia–rare earth composite oxides

A series of La 2O 3–ZrO 2–CeO 2 composite oxides were synthesized by solid-state reaction. The final product keeps fluorite structure when the molar ratio Ce/Zr ≥ 0.7/0.3, and below this ratio only mixtures of La 2Zr 2O 7 (pyrochlore) and La 2O 3–CeO 2 (fluorite) exist. Averagely speaking, the increase of CeO 2 content gives rise to the increase of thermal expansion coefficient and the reduction of thermal conductivity, but La 2(Zr 0.7Ce 0.3) 2O 7 has the lowest sintering ability and the lowest thermal conductivity which could be explained by the theory of phonon scattering. Based on the large thermal expansion coefficient of La 2Ce 3.25O 9.5, the low thermal conductivities and low sintering abilities of La 2Zr 2O 7 and La 2(Zr 0.7Ce 0.3) 2O 7, double-ceramic-layer thermal barrier coatings were prepared. The thermal cycling tests indicate that such a design can largely improve the thermal cycling lives of the coatings. Since no single material that has been studied so far satisfies all the requirements for high temperature thermal barrier coatings, double-ceramic-layer coating may be an important development direction of thermal barrier coatings.

Influences of Ga doping on lattice parameter, microstructure, thermal expansion coefficient and electrical conductivity of La 0.6Sr 0.4CoO 3− y

Lattice parameters, microstructures, thermal expansion coefficients and electrical conductivities of Ga-doped La 0.6Sr 0.4CoO 3− y were investigated in order to characterize influences of interdiffusion of Ga from La(Sr)Ga(Mg)O 3− y electrolyte into La 0.6Sr 0.4CoO 3− y cathode in intermediate temperature solid oxide fuel cell. Unknown phases were formed when the amount of Ga doped was beyond 20% of B-site cation in the perovskite structure. In the single-phase region, the lattice parameters and thermal expansion coefficients were increased with the Ga doping. The thermal expansion coefficient increases were much higher than those of La(Sr)Ga(Mg)O 3− y electrolyte. The electrical conductivities decreased with an increase in the doped amount of Ga, and the electrical conduction changed from metallic to semiconductor-like with the Ga doping. Those results clearly indicate that the interdiffusion of Ga into La 0.6Sr 0.4CoO 3− y cathode has unfavorable influences on the physicochemical properties of La 0.6Sr 0.4CoO 3− y in the intermediate temperature solid oxide fuel cell.

Cooling Enhancements in Thin Films Supported by Flexible Complex Seals in the Presence of Ultrafine Suspensions

Flow and heat transfer inside thin films supported by flexible soft seals having voids of a stagnant fluid possessing a large coefficient of volumetric thermal expansion βT are studied in the presence of suspended ultrafine particles. The study is conducted under periodically varying thermal load conditions. The governing continuity, momentum and energy equations are non-dimensionalized and reduced to simpler forms. The deformation of the seal is related to the internal pressure and lower plate’s temperature based on the theory of linear elasticity and a linearized model for thermal expansion. It is found that enhancements in the cooling are achieved by an increase in the volumetric thermal expansion coefficient, thermal load, thermal dispersion effects, softness of the supporting seals and the thermal capacitance of the coolant fluid. Further, thermal dispersion effects are found to increase the stability of the thin film. The noise in the thermal load is found to affect the amplitude of the thin film thickness, Nusselt number and the lower plate temperature however it has a negligible effect on their mean values.

Spectroscopic investigation of MoO 3–Fe 2O 3–P 2O 5 and SrO–Fe 2O 3–P 2O 5 glasses. Part I

The relationship between the composition, structure and selected properties for four series of iron phosphate glasses containing MoO 3 and SrO has been investigated. The three series of MoO 3–Fe 2O 3–P 2O 5 glasses were prepared with increasing MoO 3 content. In series A the molar Fe/P ratio was constant at 0.67, in series B the O/P ratio was 3.5, whereas, in series C the molar percentages of Fe 2O 3 was fixed at 40 mol%. In the fourth series, M, SrO was added to maintain the Fe/P ratio constant at 0.67. The structural changes in these glasses have been studied by Raman spectroscopy. The Raman spectra show that MoO 3 is incorporated into the phosphate network. However, the structure/properties are strongly influenced by the overall O/P ratio. In glasses with O/P > 3.5 the addition of MoO 3 depolymerized some of the bridging oxygens in pyrophosphate units to form isolated (PO 4) 3− orthophosphate groups. The decrease in glass temperature, T g, and glass density, D, increase in thermal expansion coefficient, α, and glass density, D, for these glasses are attributed to an increase in the number of weaker P–O–Mo bonds connected to both orthophosphate and pyrophosphate units. The replacement of the stronger P–O–P bonds for the weaker Mo–O–P bonds imparts greater covalency to the network and contributes to the lower bond strength as the bond covalence decreases from P–O to Mo–O. The addition of up to 20 mol% SrO does not produce any changes in the Raman spectra and any further disruption of pyrophosphate chains.

Observation of Two Kinds of Structural Phase Transitions in the Ba2In2 O 5 System

Structural phase transitions of at high temperatures were investigated by thermal gravimetric-differential thermal analysis (TG-DTA), dilatometry, and differential scanning calorimetry (DSC). It was revealed that there exist three phases in At ∼910°C, a first-order structural phase transition was observed involving absorption of heat and discrete decrease of volume, which agreed well with the reported order-disorder transition of oxide-ion vacancy. At ∼1070°C, a second-order phase transition involving discrete increase of thermal expansion coefficient was observed. The crystal structures of these three phases of were investigated by means of high-temperature X-ray diffractometry (XRD). The XRD patterns at 900 and 1200°C could be indexed assuming brownmillerite-type orthorhombic and tetragonal crystal structures, respectively. The diffraction pattern obtained at 1000°C could not be explained as ideal cubic perovskite structure with disordered oxide-ion vacancy. High-temperature XRD also revealed that rate of the phase transition at 904°C was low, corresponding to high activation energy of the phase transition estimated by using a Kissinger plot of DTA curves. © 2002 The Electrochemical Society. All rights reserved.