•Evaluation of the Coefficients of Linear Thermal Expansion (CLTE) of flax fibre.•Evaluation from an experimentally inverse approach using two micromechanical models.•The flax CLTE were -1.2 and 75 × ...10−6 /K in longitudinal and transverse directions.•Prediction of internal stresses from a model based on classical laminate theory.•Choosing symmetric cross-ply laminate was more interesting than antisymmetric one.
This work aims at evaluating the coefficients of linear thermal expansion (CLTE) of flax/green epoxy unidirectional composites and the CLTE of flax fibre. This required using high precision measuring instrument to experimentally evaluate the CLTE of unidirectional composites with various fibre contents. The flax fibre CLTE were first estimated using an inverse approach with two micromechanical models. From the longitudinal and transverse CLTE, the internal stresses of various symmetric and antisymmetric laminates, due to temperature variation, were then predicted by a 2D analytical model based on classical laminate theory. The inverse approach results showed that the transverse CLTE of flax fibre was positive and estimated at 75 ± 5 × 10−6 /K whereas the longitudinal CLTE was negative and equal to -1.2 ± 0.1 × 10−6 /K, highlighting the high anisotropy of flax fibres. The internal stress analysis in flax fibre laminates showed that the stacking sequence had a significant effect on the internal stresses, whatever the temperature variation. Regarding stacking the layers, choosing symmetric cross-ply laminate was more interesting than antisymmetric one for minimising the internal stresses. The normal stresses reached their maximum absolute values for the cross-ply laminates, whereas the maximum shear stress occurred in the 0/60s and 0/60/0/60 stacking. This study highlighted the importance of choosing an optimised stacking sequence, such as the 0/30° oriented laminates, and a relevant curing cycle prior to the manufacturing process, in order to obtain flax fibre laminates with low internal stresses.
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In this work, a new supplementary formula was introduced to modify the Kerner model. This supplementary formula enable the Kerner model to predict the thermal expansion coefficient of multi-phase ...reinforced composites by normalization of the thermal expansion coefficient, bulk modulus, and shear modulus of the reinforcements. For comparison, the modified Kerner model as well as modified Schapery, the rule of mixtures, and Turner models were used to predict the thermal expansion coefficient of multi-phase reinforced composites 6092 Aluminum Alloy/silicon carbide/β-eucryptite. The results confirm the robustness of the modified Kerner model for predicting the thermal expansion coefficient of composites with multi-phase near-spherical inclusions. It may provide a fine selection to predict the thermal expansion coefficient of multi-phase reinforced metal matrix composites which cannot predict efficiently before.
•An FCC CoCrFeMnNi high-entropy alloy (HEA) was cast and processed by swaging.•Recrystallization resulted in homogenous microstructure (grain size 15μm).•The HEA is nearly untextured after swaging ...(60% reduction) and recrystallization.•First report of the thermal expansion coefficient between 300 and 1270K.•Elastic moduli measured between 200 and 1000K are reported for the first time.
The equiatomic CoCrFeMnNi alloy is now regarded as a model face-centered cubic single-phase high-entropy alloy. Therefore, determination of its intrinsic properties such as the temperature dependencies of elastic moduli and thermal expansion coefficient are important to improve understanding of this new class of material. These temperature dependencies were measured over a large temperature range (200–1270K) in this study.
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High-temperature thermal barrier coating (TBC) materials are desired for the development of high-efficient gas turbines and diesel engines. Herein, to meet up with this requirement, a new class of ...high-entropy fluorite-type oxides (HEFOs) has been synthesized via a solid-state reaction method. Comparing to La2Ce2O7, a promising TBC material, the HEFOs exhibit similar high thermal expansion coefficients (TECs) of 11.92×10−6∼12.11×10−6 K-1 at temperatures above 673 K but a better TEC matching performance at the temperature range of 473–673 K. It is also found that through tuning the average A-site cation radius, the TEC of the HEFOs could be tailored efficiently. The HEFOs also possess low thermal conductivities of 1.52-1.55 W∙m-1∙K-1 at room temperature, which is much lower than that of La2Ce2O7 and comparable to pyrochlores as Gd2Zr2O7. Moreover, the HEFOs display good sintering resistance and phase stability even at temperatures as high as 1873 K. The combination of these fascinating properties makes the HEFOs good candidates for thermal barrier coating and thermal insulating materials.
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Ceramic materials with negative and close-to-zero coefficients of thermal expansion may open the avenue to the technologies that have so far been constrained by physical limitations concerned with ...the thermal stress or with the insufficient structural stability. Two important characteristics of NTE materials which could be used for the evaluation of the possible area and limitations of the sphere of application for negative thermal expansion (NTE) materials are the linear thermal expansion coefficient and the transition temperature from monoclinic to orthorhombic phase. In this study, the machine learning methods were involved in the analysis of experimental data for NTE oxide ceramics of A2M3O12 family (where M is Mo6+, W6+, V5+ or P5+ while A position may be accommodated by the wide range of metal cations). The models are characterized by the following statistical coefficients: the determination coefficient R2 = 0.81 and prediction error RMSE = 1.170 for linear thermal expansion coefficient; the corresponding parameters for the phase transition temperature were assessed as 0.81 and 82.239, respectively. Ionic conductivity in this class of compounds has been discussed as a tandem functional characteristic, emphasizing the role of anharmonicity in both characteristics. The role of synthesis route and defect chemistry in NTE was analyzed. A conclusion on the expected enhancement of NTE resulted from the intentional introduction of cation A vacancies has been made. The principal possibility of combining two functional characteristics, - an ion conductor and a phase with negative thermal expansion, with some compromise in the characteristics of each of them is substantiated.
•The influence of synthesis route and defect chemistry on NTE was discussed.•Ionic conductivity was discussed as a tandem functional characteristic providing with the parallels with NASICON-type solid electrolytes.•The role of anharmonicity in both characteristics, the negative thermal expansion and the ionic conductivity, has been analyzed and discussed.•A conclusion on the expected enhancement of NTE due to the intentional introduction of cation vacancies has been made.•Modeling of key functional characteristics for NTE compounds of A2M3O12 family has provided with descriptor contribution.
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Cu2O nanostructured films were prepared by the dip-coating method with average crystallite size of 10 ± 1 nm. The photoluminescence of Cu2O was studied for different temperatures in the 70–300 K ...interval. The range of wavelengths analyzed was 360–1000 nm. Two photoluminescence systems were used, with an excitation line of 325 nm He–Cd and 488 nm Ar laser, at different power. Several interband and excitonic transitions at energies in the 1.8–2.8 eV interval were identified for Cu2O where an intensity shift toward lower energies was observed as the temperature was increased. The difference of the thermal expansion coefficients (α) between the Cu2O and the soda-lime substrate induces change from compressive to tensile stress within the 70–300 K interval. This change is a consequence that α value for Cu2O is negative and for soda lime is positive in that temperature region. Raman spectra as a function of temperature, show a frequency shift for all modes studied and α values of thin film Cu2O were estimated from these shifts at 77 and 280 K. The stress (σ) on the Cu2O film was calculated considering the decrease of the temperature in this interval. The effect of this stress on the energy band structure is related to the shift of the PL bands.
•Photoluminescence of Cu2O nanostructured-thin-film in the 1.8 to 2.8 eV range.•Anomalous behavior of low-T photoluminescence emissions of stressed Cu2O films.•Thermal properties of Cu2O film and substrate affect the luminescence of the film.•Thermal expansion coefficient of Cu2O film is calculated from Raman spectroscopy.
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Lead halogen perovskites, and particularly methylammonium lead iodine, CH3NH3PbI3, have recently attracted considerable interest as alternative solar cell materials, and record solar cell ...efficiencies have now surpassed 20%. Concerns have, however, been raised about the thermal stability of methylammonium lead iodine, and a phase transformation from a tetragonal to a cubic phase has been reported at elevated temperature. Here, this phase transition has been investigated in detail using temperature-dependent X-ray diffraction measurements. The phase transformation is pinpointed to 54 °C, which is well within the normal operating range of a typical solar cell. The cell parameters were extracted as a function of the temperature, from which the thermal expansion coefficient was calculated. The latter was found to be rather high (αv = 1.57 × 10–4 K–1) for both the tetragonal and cubic phases. This is 6 times higher than the thermal expansion coefficient for soda lime glass and CIGS and 11 times larger than that of CdTe. This could potentially be of importance for the mechanical stability of perovskite solar cells in the temperature cycling experienced under normal day–night operation. The experimental knowledge of the thermal expansion coefficients and precise determination of the cell parameters can potentially also be valuable while conducting density functional theory simulations on these systems in order to deliver more accurate band structure calculations.
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•The simulation model of LZ7C3 was successfully built according to experimental results.•Thermophysical properties of LZ7C3 were studied by experiment together with molecular dynamics ...simulation.•Phase structures of La2(ZrxCe1−x)2O7 serials were studied by MD simulation.
This paper presents structure, thermal expansion coefficient and phase stability of La2(Zr0.7Ce0.3)2O7 (LZ7C3) ceramic by both theoretical and experimental results. It was found out that LZ7C3 powders had a pyrochlore structure after being heat-treated at temperatures higher than 1473 K or higher according to XRD and TEM results. The calculated average thermal expansion coefficient (TEC) was 7.12 × 10−6 K−1, which is a little smaller than experiment result, but changes of calculated average TECs of LZ, YSZ and LZ7C3 had the same trend with experimental results. Finally, the radial distribution function (RDF) was calculated to study the phase stability of LZ7C3.
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In order to obtain the solid oxide fuel cell (SOFC) interconnect coatings with high electrical conductivity, satisfactory protectiveness, and well-fitting thermal expansion, a series of CuxCo3-xO4-δ ...(x = 0, 0.5, 0.8, and 1.0) coatings are prepared by supersonic spraying via subsequent sintering. The chemical composition, lattice and morphological structures, electrical properties, and thermal expansion are characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), area-specific resistance (ASR), and coefficient of thermal expansion (CTE) measurements. The experimental results show that the formation of CuCo2O4 is a reversible and incomplete reaction at the elevated temperature, and the coexistence of CuO, Co3O4, and CuCo2O4 is inevitable in the coatings. The concentration of the chemicals mentioned above is highly related to the coatings’ Cu:Co molar ratio. The correlation between the chemical composition and the properties is comprehensively studied in this research. The CuxCo3-xO4-δ coatings exhibit good electrical conductivity when 0 ≤ x ≤ 0.8, satisfactory protectiveness when 0.5 ≤ x ≤ 1.0, and fitting CTE with remarkable robustness through the quick heating-cooling cycles when 0.8 ≤ x ≤ 1.0. In general, Cu0.8Co2.2O4-δ can be an appropriate candidate to meet the advancing interconnect coating demands with high electrical conductivity, satisfactory protectiveness, and well-fitting thermal expansion properties.
•The formation of CuCo2O4 spinel is a reversible reaction at elevated temperatures.•Higher Cu:Co ratio leads to better fitting CTE and more reliable coating performance.•Higher Cu:Co ratio forms more CuO, which reduces the electrical conductivity.•Cu0.8Co2.2O4-δ balances the conductivity, oxidation resistance, and robustness well.
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LaNb1−xMxO4 oxides with pentavalent elements of different ionic sizes (M=Sb, Ta and V, x=0.05–0.3) were synthesized by the solid state reaction method. Special interest was devoted to the antimony ...substituted lanthanum niobate which is a new material in this group. Rietveld analysis of the X-ray diffraction patterns was used to determine the influence of the material composition on unit cell parameters. On the basis of dilatometric measurements phase transition temperatures and thermal expansion coefficients of the studied materials were determined. It was shown that with increasing concentration of Sb the phase transition temperature decreases. Thermal expansion coefficient of the antimony substituted samples above the transition temperature is in the range from 8.1 to 9.1×10−61/K, whereas below the transition temperature the TEC value is between 14 and 17.3×10−61/K. Influence of Ta, V and Sb substitutions on the microstructure and grain size was studied.
Substitution of niobium by other pentavalent elements in LaNbO4 leads to change in phase transition temperature. In case of Sb substituent a shift of phase transition into the lower temperature region is observed. LaNb0.7Sb0.3O4 substitution allows to achieve material with tetragonal crystal structure at room temperature and no phase transition up to 1000°C. Display omitted
•Antimony doped lanthanum niobate was successfully synthesized by solid state synthesis method.•The structural properties have been investigated by XRD and SEM.•The influence of doping on phase transition temperature has been studied.
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