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This work addresses the problem of obtaining of Ca 3 Co 4 O 9+δ -based ceramics with enhanced thermoelectric performance. Phase-inhomogeneous layered calcium cobaltite ceramics with cationic nonstoichiometry were prepared by solid-state reactions method and a field assisted sintering technology (FAST). Comprehensive experimental characterizations were conducted on the prepared bulk samples, focusing on their phase composition, as well as thermal (including thermal expansion, thermal diffusivity, and thermal conductivity), electrical (encompassing electrical conductivity and the Seebeck coefficient), and functional properties (such as power factor and figure-of-merit). The FAST technique allowed to obtain ceramics with low porosity and high electrical conductivity, which increased as the Ca:Co ratio within the samples decreased, while sample phase inhomogeneity considerably increased the Seebeck coefficient. The best thermoelectric performance was demonstrated for cationic nonstoichiometric Ca 3 Co 4.4 O 9+δ , which power factor and figure-of-merit values at 825 °C reached 427 μW⋅m−1⋅K−2 and 0.146, respectively. • Ca 3 Co 4 O 9+δ -based ceramics prepared by field assisted sintering technology possessed low porosity and high conductivity. • Electrical conductivity of bulk samples increased at decreasing Ca:Co ratio. • Phase inhomogeneity of prepared ceramics increased the Seebeck coefficient. • Ca 3 Co 4.4 O 9+δ ceramics showed the best thermoelectric performance. [ABSTRACT FROM AUTHOR]

The thermal barrier coatings (TBCs) system, a pivotal technology for advanced aviation engines and ground gas turbines, mitigates direct interaction between high-temperature gas and high-temperature alloy substrates. In this investigation, a series of high-entropy Eu 2 B 2 O 7 (where B = Y, Yb, Ce, Zr, Hf, Ta, and Nb) oxides were synthesized through solid-state reactions. By manipulating B-site cations and introducing substantial atomic size disparities, as well as mass and charge disorder, we synthesized a highly disordered high-entropy Eu 2 B 2 O 7 oxide. This oxide exhibits a disordered fluorite structure and commendable thermal insulation attributes. The observed thermal conductivity of Eu 2 (Y 0.2 Yb 0.2 Zr 0.2 Nb 0.2 Ta 0.2) 2 O 7 ranges from 0.94 to 1.13 W·m–1·K–1, which can be ascribed to amplified lattice anharmonicity and disorder causing supplementary phonon scattering. In addition, It also shows the thermal expansion coefficient of 10.52 × 10−6 K−1 and high-temperature stability. These results denote that the high-entropy Eu 2 B 2 O 7 oxide may become a prospective contender for thermal barrier coatings and thermal insulators. [ABSTRACT FROM AUTHOR]

It is well accepted that the intrinsic thermal conductivity is extremely important in achieving excellent thermal conductivity composite and can be improved via incorporation of mesogens. In this work, an azomethine type liquid crystal epoxy (LCE) with aliphatic ether was designed and synthesized with expected structure, and the liquid crystal epoxy resin (LCER), together with KH‐550‐modified boron nitride (K‐BN)/LCER composites, has been obtained. Results show an increase of 31.6% in the thermal conductivity of the matrix, which could result in an enhancement of 57.7% for the composites when compared with E‐51. Additionally, the coefficient of thermal expansion (CTE), dielectric properties, and shear strength of LCER and K‐BN/LCER composites were assessed across a broad temperature range. Remarkably, the 30 wt% K‐BN/LCER composites showed a maximum decrease of 37.8% in CTE, while maintaining adequate shear strength to fulfill the bonding requirement and high thermal conductivity at both RT and −196°C. [ABSTRACT FROM AUTHOR]

The properties of rare-earth (RE) monosilicates can be regulated by solid solution engineering based on the mixture rule. The combination and number of RE principals are critical factors for better performances. In the present study, four single-phase equimolar multicomponent RE-monosilicate solid solutions including (Dy 1/3 Er 1/3 Yb 1/3) 2 SiO 5 , (Ho 1/3 Er 1/3 Yb 1/3) 2 SiO 5 , (Y 1/4 Er 1/4 Tm 1/4 Lu 1/4) 2 SiO 5 and (Dy 1/4 Er 1/4 Tm 1/4 Yb 1/4) 2 SiO 5 were synthesized by solid-state reaction and hot-pressing method. The microstructures, thermal and mechanical properties, and corrosion resistance to high-temperature water vapor were systematically investigated. Compared to the single-principal and ternary RE-monosilicates, the quaternary RE-monosilicates exhibited lower thermal conductivity of 1.32 Wm−1K−1 at 400 °C, matched thermal expansion coefficients (3.3 × 10−6/oC ∼ 5.8 × 10−6/oC from 200 °C to 1000 °C) with SiC, and much lower weight loss during water vapor corrosion. The results indicate that the increase of the RE element number can promote the grain growth, lower the thermal conductivity and thermal expansion coefficient, and enhance corrosion resistance. [ABSTRACT FROM AUTHOR]

Pr doped La 2 Zr 2 O 7 (LPZ) TBCs have been deposited by electron beam physical vapor deposition. This work concentrates on the thermophysical properties and microstructure evolution of LPZ/YSZ duplex TBCs before and after thermal cyclic so as to probe into the merit and the application feasibility. The thermal expansion, thermal conductivity and phase structure have been measured and analyzed in comparison to other classical TBCs materials. Typical feathery microstructure and intra-columnar gaps did not provide desired thermal cyclic counts for LPZ/YSZ TBCs. Two principal categories of degradation mechanism limited the cyclic lifetime. The first principal degradation mode is the pulverization of LPZ after thermal cyclic due to the Pr rare earth elements modification in lanthanum Zirconates. Pr instability created the pulverization degradation mode instead of spalling. The second degradation mode is the cracks extension paralleled to interface inside TGO due to the brittle spinel generated by excessive oxidation. This study of thermal properties and degradation mechanism might offer thought and inspiration for other advanced TBCs. [ABSTRACT FROM AUTHOR]

The effect of T4 and T6 treatment on the microstructures, precipitates, thermal expansion and thermal conductivity properties of Mg-2Nd-4Zn alloys was systemically investigated. The number of NdZn2 phase increased subjected to T6 treatment. The coherent relationship between the NdZn2 phase and Mg matrix was observed in the Mg-2Nd-4Zn alloys, which plays a great influence on improving the thermal expansion, thermal conductivity and mechanical properties of Mg-2Nd-4Zn alloys. The decrease in the coefficient of thermal expansion (CTE) and the thermal conductivity of Mg alloys were ascribed to the existence of solute atoms in alloys after the T4 treatment. It was also found that the T6-treated alloy has smaller area of the hysteresis loop, which has better thermal stability. Therefore, the high performance was mainly due to T6 treatment, the thermal conductivity of T6-treated Mg-2Nd-4Zn alloy is 124.4 K·m−1·K−1 at room temperature, and TYS of 235.5 MPa, CYS of 393.7 MPa, elongation of tension and compression are 31 and 27%, respectively. [ABSTRACT FROM AUTHOR]

Epoxy resin (EP) is a promising material that exhibits great potential in the fields of packaging and adhesion. However, reducing its brittleness and coefficient of thermal expansion (CTE) at low filler content is still a challenge. To address this problem, three types of MWCNTs nanofluids (MWCNTs NFs) with different shell structures were designed to modify epoxy resin. With the addition of 1 wt% MWCNTs‐M1, the compression, impact, and lap shear strength of the composites increased to 88.97 MPa, 81.39 kJ/m2, 12.69 MPa, respectively, which are 21.7%, 66.1%, and 58.0% higher than pure epoxy. Meanwhile, incorporating MWCNTs NFs also improved the CTE and thermal conductivity, with a 19.7% decrease in CTE and a 40% improvement in thermal conductivity at 2 wt% NFs content. Particularly, the effect of MWCNTs NFs structure on the composite properties was explored, which can be an available reference for designing specific NFs epoxy composites. Highlights: Three types of MWCNTs nanofluids with different structures were designed.The MWCNTs NFs were used in packaging materials for the first time.The impact performance of composite has been improved by 66%.The CTE of composite is 19.7% lower than pure EP.The thermal conductivity of the composite increased by 40%. [ABSTRACT FROM AUTHOR]

As ceramics based on magnesium aluminum oxynitrides solid solutions are promising materials as refractories, windows/armors, phosphors, and so forth, it is essential to explore their thermal and thermomechanical properties, owing to the physical requirements on application. In this study, Mg5xAl23−5xO27+5xN5−5x were chosen for the investigation on composition‐dependent thermal and thermomechanical properties by the theoretical calculations. Though the binary system with octahedral bonds contributes more to the thermal expansion coefficient of Mg5xAl23−5xO27+5xN5−5x, the binary system with tetrahedral bonds plays an important role in the variation of the thermal expansion coefficient. The change of heat capacity with the rise of x is mainly attributed to the variation of covalent character of Mg5xAl23−5xO27+5xN5−5x. Moreover, the thermal conductivity is mainly affected by the scattering from atoms in 8a sites. Both thermal and mechanical properties contribute to the variation of thermomechanical properties of Mg5xAl23−5xO27+5xN5−5x. This study can provide guidance to designing spinel materials with desirable thermal and thermomechanical properties for application. [ABSTRACT FROM AUTHOR]

It is difficult to obtain X2-type rare-earth monosilicates that have the advantages of low thermal conductivity and a thermal expansion coefficient that matches that of ceramic matrix composites, and thus, the efficient use of these materials in extreme environments is challenging. In this study, we developed a novel component regulation method, which significantly reduced thermal conductivity and helped achieve a suitable thermal expansion coefficient for monosilicates. Monosilicates have low thermal diffusion coefficients mainly due to the effect of extrinsic phonon scattering mechanisms. We analyzed different extrinsic phonon scattering mechanisms associated with point defect, disorder, grain boundary, lattice distortion, dislocation, and symmetry. • A variety of monosilicates with suitable coefficients of thermal expansion were synthesized. • The thermal conductivity of monosilicates was significantly reduced. • The various extrinsic phonon scattering mechanisms related to point defect, disorder, and more were analyzed. [ABSTRACT FROM AUTHOR]

The excellent thermal properties of diamond/SiC composites are mainly attributed to the addition of diamond particles. In order to further increase the diamond content, a novel preparation method was used to regulate the distribution of bimodal diamond particles. Moreover, in order to achieve better performance, the effects of particle size ratios on the properties were studied. The results show that with the increase of small diamond particle size, the bimodal diamond packing will change from unmixing mechanism to mixing mechanism, and the critical ratio (small/large) of entrance for 400 µm diamond particles is between 0.37 and 0.5. When the particle size ratio is 0.25, the thermal conductivity reaches the maximum, reaching 812.27 W/mK (break through 800 W/mK for the first time). In addition, the influence of particle size ratio on coefficient of thermal expansion is also discussed. [ABSTRACT FROM AUTHOR]

Heat transport in two dimensions is fundamentally different from that in three dimensions. As a consequence, the thermal properties of 2D materials are of great interest, from both scientific and application points of view. However, few techniques are available for the accurate determination of these properties in ultrathin suspended membranes. Here, we present an optomechanical methodology for extracting the thermal expansion coefficient, specific heat, and thermal conductivity of ultrathin membranes made of 2H-TaS2, FePS3, polycrystalline silicon, MoS2, and WSe2. The obtained thermal properties are in good agreement with the values reported in the literature for the same materials. Our work provides an optomechanical method for determining the thermal properties of ultrathin suspended membranes, which are difficult to measure otherwise. It provides a route toward improving our understanding of heat transport in the 2D limit and facilitates engineering of 2D structures with a dedicated thermal performance. [ABSTRACT FROM AUTHOR]

The development of lightweight composites with desirable thermo‐mechanical properties is progressively increasing. Phthalonitrile (PN) based composites have shown great potential in this regard. However, the basic thermal properties of PN composites required for engineering design are not yet fully understood. In this work, we investigated the thermal stability, thermal expansion behavior and thermal conductivity of PN composites reinforced with carbon fiber (CF) and high silicon fiberglass (HSF) via combined experimental studies and numerical simulations. The results indicated that CF/PN performs better in thermostability than HSF/PN at temperatures below 500°C. Moreover, the incorporation of CF and HSF lowered the coefficient of thermal expansion (CTE) and thermal insulation of PN. At room temperature, the in‐plane CTE of CF/PN and HSF/PN were 1.97E‐6 and 9.24E‐6°C−1, respectively, while the out‐plane thermal conductivities of CF/PN and HSF/PN were 0.65 and 0.34 W/(m K). It is worth noting that an excessively high fiber volume fraction would lead to poor thermal insulation and lightweight properties of the PN composites, while a low fiber volume fraction would result in poor stiffness and thermal dimensional stability. Determined via TOPSIS model, a fiber volume fraction range of 50%–60% was ideal for both composites with comprehensive optimal properties, respectively. [ABSTRACT FROM AUTHOR]

In recent years, the MgO-Nd 2 Zr 2 O 7 composite ceramics inert matrix (IM) was proposed as a candidate for the transmutation of Pu and minor actinides (MA) in light water reactors (LWR) or accelerator driven sub-critical system (ADS). To take full advantage of the pyrochlore structure of Nd 2 Zr 2 O 7 to accommodate different types of MA and Pu, in this work, Y and Ce co-doped ω MgO-(1- ω)(Nd 1- x Y x) 2 (Zr 1- x Ce x) 2 O 7 (M-NYZC) composite ceramics used as a candidate IM for inert matrix fuel were prepared by solid-state one-step sintering method at 1500 °C for 3 h. The phase structure and microstructure of M-NYZC composite ceramics were characterized by XRD and SEM-EDS. Also, the thermal physical properties of M-NYZC composite ceramics including the thermal expansion coefficient and thermal conductivity were investigated systematically. Results from XRD and SEM-EDS showed that the magnesium oxide and NYZC pyrochlore solid solution are intermixed well with each other, and the M-NYZC samples present uniform element distribution with a grain size of about 1 μm. Also, the as-prepared samples possessed well densified microstructure, and the average relative density of all samples could exceed 95 %. Moreover, the thermal expansion coefficient and thermal conductivity of 0.5M-0.5NYZC (x = 0, 0.15, 0.2, 0.5, 0.9) samples were located in the range of 13.4 × 10-6–14.4 × 10-6 K-1 and 16.34–3.70 W·m-1·K-1 respectively. By comparison, the thermal physical properties of 0.5M-0.5NYZC samples are superior to that of traditional UO 2 and MOX fuels. It is suggested that the M-NYZC composite ceramics prepared in this study can meet the thermal physical performances of inert matrix fuel. [ABSTRACT FROM AUTHOR]

High-performance ceramics with low thermal conductivity, high mechanical properties, and idea thermal expansion coefficients have important applications in fields such as turbine blades and automotive engines. Currently, the thermal conductivity of ceramics has been significantly reduced by local doping/substitution or further high-entropy reconfiguration of the composition, but the mechanical properties, especially the fracture toughness, are insufficient and still need to be improved. In this work, based on the high-entropy titanate pyrochlore, TiO 2 was introduced for composite toughening and the high-entropy (Ho 0.2 Y 0.2 Dy 0.2 Gd 0.2 Eu 0.2) 2 Ti 2 O 7 -xTiO 2 (x = 0, 0.2, 0.4, 1.0 and 2.0) composites with high hardness (16.17 GPa), Young's modulus (289.3 GPa) and fracture toughness (3.612 MPa·m0.5), low thermal conductivity (1.22 W·m−1·K−1), and thermal expansion coefficients close to the substrate material (9.5 ×10−6/K) were successfully prepared by the solidification method. The fracture toughness of the composite toughened sample is 2.25 times higher than that before toughening, which exceeds most of the current low-thermal conductivity ceramics. • Preparation of high-entropy pyrochlore/TiO 2 composites by rapid melt solidification. • The composite toughened samples have ultrahigh fracture toughness (3.612 MPa·m0.5). • The solidified composites exhibit excellent mechanical and thermal properties. [ABSTRACT FROM AUTHOR]

High‐entropy single‐phase rare earth titanates (RE0.2Gd0.2Ho0.2Er0.2Yb0.2)2Ti2O7 (RE = Sm, Y, Lu) were designed and synthesized successfully, in which their lattice distortion was quantitatively described by mass disorder and size disorder. It is worth mentioning that (Y0.2Gd0.2Ho0.2Er0.2Yb0.2)2Ti2O7 could obtain the low thermal conductivity (1.51 W·m−1·K−1, 1500°C), high thermal expansion coefficient (average, 11.69×10−6 K−1, RT ∼1500°C) and excellent high‐temperature stability. In addition, the relationship between the microstructure and thermal transport behaviors has been studied at the atomic scale. Due to the disorder of A‐site ions, severe lattice distortion occurred in specific crystal planes, and the large mass difference between Y3+ and other RE3+ further causes mass fluctuation and results in lower thermal conductivity. Compared with YSZ, the high‐entropy rare earth titanate (Y0.2Gd0.2Ho0.2Er0.2Yb0.2)2Ti2O7 has lower thermal conductivity, higher thermal expansion coefficient, and excellent high‐temperature stability, which has great potential for application in the thermal protection field. [ABSTRACT FROM AUTHOR]

Hypereutectic Al-x(1.75Fe-1.25Ni) (x=1,2,4,6) alloys were designed and prepared by gravity casting in the present study. Both the microstructure and the thermophysical properties were investigated. The microstructure was significantly transformed from the eutectic phases to the coarse primary phases with the increase in alloying elements. The result of thermal analysis indicated that the solidification behaviors were modified by the increase in alloying elements, which was ascribed to the generation of different phases. The thermal conductivity and thermal expansion properties were also related to the alloy composition. From the variation in the ratio of thermal conductivity/electrical conductivity, it could be inferred the effective medium of heat conduction was changing, which decreased thermal conductivity due to the introduced defects that hindered the transport of electrons and low efficiency heat conducting medium of intermetallic. Meantime, the formation of bulk intermetallic with low thermal expansion coefficient and large volume fractions reduced effectively the thermal expansion of the alloy. The mathematical model was presented to quantify the influence of alloy content on thermophysical properties. [ABSTRACT FROM AUTHOR]

Gas turbines efficiency growth is primarily associated with an increase in the operating temperature of the combustion chamber, which places new stringent requirements on the materials of thermal barrier coatings. Strontium cerate doped with tin SrCe 1- x Sn x O 3 where x = 0.1 ... 0.5, was proposed as a promising material. The research has shown that the lightly doped solid solution SrCe 1-x Sn x O 3 has an orthorhombic Pnma structure at x < 0.3, whereas at a high content of Sn4+ the monoclinic structure P2 1 /m becomes more favorable. Thermogravimetric analysis (TGA) in reducing atmosphere (5%H 2 in Ar) shows no mass lost as a result of unchangeable charge of Ce4+ and Sn4+. An increase in the distortion of the crystal lattice, due to the large difference in the ionic radii of Ce4+ and Sn4+, leads to a deterioration in the symmetry of the crystal lattice, a reduction of thermal conductivity (from 1.9 to 1.4 W m−1 K−1 at 1000 °C) and at the same time, growth of hardness and porosity. The increase in porosity, along with an increase in the required temperature of solid-state synthesis, indicates an enhancement in the melting point of the obtained materials. For the compounds with an orthorhombic structure, the thermal expansion coefficient increases with a growth in the Sn content, achieving a highest point 12.47·10−6 K−1 at 1100 °C for x = 0.3. The combination of the revealed properties and their comparison with advanced refractories makes the solid solution, primarily SrCe 0.5 Sn 0.5 O 3 , a promising material for application as thermal barrier coatings. [ABSTRACT FROM AUTHOR]

In this paper, a novel power sintering technique, named fast hot-pressing sintering (FHP), which is able to achieve an ultrahigh heating rate similar to the spark plasma sintering (SPS) technique, but at a much lower cost, was applied to prepare a series of Al/Si composites with different Si volume ratios (12 vol.% to 70 vol.%) to meet the requirements of advanced packaging materials for electronic devices. In contrast to SPS, the FHP oven possesses a safe and budget-friendly current power supply, rather than a complex and expensive pulse power supply, for its heating power. The optimized sintering parameters (temperature, pressure and holding time) of FHP for preparing Al/Si composites were investigated and determined as 470 °C, 300 MPa and 5 min, respectively. In order to characterize the potential of Al/Si composites as packaging materials, thermal conductivities and coefficients of thermal expansion were studied. The thermal conductivity of the Al-40Si composite sintered by the FHP method is higher than that of the conventional SPS method (139 to 107 W m−1 K−1). With the increase in Si, the thermal conductivities and coefficients of thermal expansion on both decreases. Furthermore, the thermal conductivities obey the Agari model, whereas the coefficient of thermal expansion and Si volume ratios obey additivity. The numeric modeling would help develop required packaging materials based on the thermal performances of the substrate materials, like Si or GaAs semiconductor devices. [ABSTRACT FROM AUTHOR]

Six rare‐earth tantalate high‐entropy ceramics of (5RE.2)Ta3O9 (RE represents any five elements selected from La, Ce, Nd, Sm, Eu, Gd) were designed and prepared by spark plasma sintering process at 1400°C in this study. The (5RE.2)Ta3O9 ceramics only consist of a single‐phase solid solution with perovskite structure. Their relative densities are all above 90%, and the average grain size is in the range of 1.47–2.92 μm. The thermal conductivity of (5RE.2)Ta3O9 ceramics is in 2.24–1.90 W m−1 K−1 (25°C–500°C), which is much lower than that of yttria‐stabilized zirconia. In six samples, (La.2Nd.2Sm.2Gd.2Eu.2)Ta3O9 possesses a thermal conductivity of 1.90 W m−1 K−1, a thermal expansion coefficient of 3.47 × 10−6 K−1 (500°C), a Vickers hardness of about 7.33 GPa, and a fracture toughness of about 5.20 MPa m1/2, which are suitable for its application as thermal barrier coatings. [ABSTRACT FROM AUTHOR]

Strain inevitably exists in practical GaN-based devices due to the mismatch of lattice structure and thermal expansion brought by heteroepitaxial growth and band engineering, and it significantly influences the thermal properties of GaN. In this work, thermal transport properties of GaN considering the effects from biaxial strain and electron-phonon coupling (EPC) are investigated using the first principles calculation and phonon Boltzmann transport equation. The thermal conductivity of free GaN is 263 and 257 W/mK for in-plane and cross-plane directions, respectively, which are consistent better with the experimental values in the literature than previous theoretical reports and show a nearly negligible anisotropy. Under the strain state, thermal conductivity changes remarkably. In detail, under +5% tensile strain state, average thermal conductivity at room temperature decreases by 63%, while it increases by 53% under the −5% compressive strain, which is mostly attributed to the changes in phonon relaxation time. Besides, the anisotropy of thermal conductivity changes under different strain values, which may result from the weakening effect from strain induced piezoelectric polarization. EPC is also calculated from the first principles method, and it is found to decrease the lattice thermal conductivity significantly. Specifically, the decrease shows significant dependence on the strain state, which is due to the relative changes between phonon-phonon and electron-phonon scattering rates. Under a compressive strain state, the decreases of lattice thermal conductivity are 19% and 23% for in-plane and cross-plane conditions, respectively, comparable with those under a free state. However, the decreases are small under the tensile strain state, because of the decreased electron-phonon scattering rates and increased phonon anharmonicity. [ABSTRACT FROM AUTHOR]

Temperature-dependent thermal and spectroscopic properties of Nd:YVO4 crystal at temperatures ranging from 77 to 300 K are presented. Thermal properties including specific heat, thermal expansion coefficient, and thermal conductivity are investigated. The spectroscopic parameters, such as absorption, fluorescence, lifetime are also studied. The calculated absorption and emission cross-sections together with relevant thermal properties provide important information for designing cryogenically cooled near infrared laser. Furthermore, we experimentally explore continuous wave (CW) laser performances under various cryogenic temperatures. A maximum output power of 2.13 W is obtained at an incident pump power of 3.7 W at 150 K, corresponding to an optical-to-optical conversion efficiency of 57.6%. [ABSTRACT FROM AUTHOR]

Five kinds of multi-component entropy-stabilized oxide ceramics were prepared by a solid-state reaction method for thermal barrier coatings, namely La0.125Y0.125Yb0.125Gd0.125Zr0.5O1.75 (LaYYbGdZr), Y0.125Yb0.125Gd0.125Ta0.125Zr0.5O1.875 (YYbGdTaZr), La0.1Y0.1Yb0.1Gd0.1Ta0.1Zr0.5O1.85 (LaYYbGdTaZr), Y0.125Yb0.125Gd0.125Ta0.125Hf0.25Zr0.25O1.875 (YYbGdTaHfZr), and La0.1Y0.1Yb0.1Gd0.1Ta0.1Hf0.25Zr0.25O1.85 (LaYYbGdTaHfZr). Many properties of the materials were studied, such as their microscopic morphology, crystal structure, thermophysical properties, and ablation resistance. The results show that the oxide ceramics synthesized in this paper have a uniform single-phase defect fluorite structure, and can still maintain this structure after high-temperature treatment at 1500 °C. The YYbGdTaHfZr coatings had the lowest thermal conductivity (0.61~0.89 W·m–1·K–1), which was much lower than that of YSZ. The ceramic blocks also exhibited excellent thermal expansion properties. The thermal expansion coefficient of LaYYbGdTaZr could reach 11.09 × 10−6 K−1 (1400 °C), which was slightly higher than that of 8YSZ (11.0 × 10−6 K−1). The antioxidant ablation results proved that the YYbGdTaHfZr coating showed the best heat-insulating property. All the results showed that the YYbGdTaHfZr coating is a promising thermal barrier coating. [ABSTRACT FROM AUTHOR]

With the increasing service temperature of aeroengines, the development of thermal/environmental barrier coatings (T/EBCs) has been considered to be a great challenge, which requires high‐temperature stability and excellent thermal and mechanical properties. In this work, high‐entropy design was adopted to change the crystal structure of rare‐earth monosilicates used for T/EBCs. The microstructure evolution, thermal and mechanical properties of the plasma‐sprayed (Lu0.25Yb0.25Er0.25Y0.25)2SiO5 and (Lu0.2Yb0.2Er0.2Ho0.2Y0.2)2SiO5 coatings before and after thermal aging at 1350°C for 50 h were investigated. Results showed that the as‐sprayed coatings exhibited dense structure with amorphous and decomposed phases. The change of microstructure like amorphous crystallized and defect healing occurred after thermal aging, which had obvious influence on thermomechanical properties. Compared with single‐component RE2SiO5 (RE = Yb, Er, Y) coatings, the thermal‐aged high‐entropy coatings exhibited lower thermal conductivity, similar thermal expansion coefficient, and better toughness. The work will provide a foundation for the design and application of T/EBCs materials. [ABSTRACT FROM AUTHOR]

InI single crystals are a promising room temperature detector material for X-rays and γ-rays. To improve crystal growth of the material by simulations, knowledge of thermophysical properties is essential, and since InI is orthorhombic, the anisotropy has to be taken into account. The temperature-dependent thermophysical properties have been measured for InI, including the anisotropic thermal expansion, specific heat, and the thermal diffusivity in the b direction. The anisotropic thermal expansion coefficients, determined by X-ray diffraction, were α11 = 1.03 × 10–5 K−1, α22 = 3.77 × 10–5 K−1, and α33 = 6.26 × 10–5 K−1. The specific heat, measured by DSC, was 0.226 J·g−1·K−1 at 335 K, with a temperature dependence of 9.582 × 10–5 J·g−1·K−2. In the course of the X-ray diffraction and DSC measurements, it could also be shown that supposed phase changes, reported in older literature, are actually not phase changes but oxidation effects. The thermal diffusivity in the b direction, measured by the Xenon Flash method, was 0.288 × 10–6 m2·s−1 at RT, decreasing to 0.253 × 10–6 m2·s−1 at 450 K. In addition, the volume increase upon melting and the thermal expansion of the melt have been determined. [ABSTRACT FROM AUTHOR]

A Nd3+-doped Ca3Nb(Al0.5Ga0.5)3Si2O14 (Nd:CNAGS) crystal with dimensions 50 × 80 × 16 mm³ was grown for the first time using the Czochralski (Cz) method as a potential material for ultrafast laser application and elastic optical modulators. The thermal expansion coefficients in different directions show a small difference, which means that the crystal expands more uniformly and could reduce the internal stress concentration when the temperature changes. The specific heat of Nd:CNAGS in the temperature range of 25-300 °C was in the range of 0.632-0.988 J g-1 K-1. The thermal conductivity of the crystal is anisotropic, and the thermal conductivity in the z direction increases with the increase of temperature and is obviously greater than that in the x direction. The optical properties of the crystal, including absorption, transmission, and fluorescence spectra, have been systematically analyzed; the strongest absorption peak with a full width at half-maximum (FWHM) of 19 nm is centered at 805 nm wavelength, and the broad emission band with a peak at 1066 nm has an FWHM of 16 nm. The experimental line strength, the calculated spectral line intensities, the spontaneous radiation probability, the fluorescence branching ratio, and the radiation lifetime are obtained using the Judd-Ofelt (J-O) theory. A 1.06 μm continuous-wave (CW) laser output was realized using the Nd:CNAGS crystal. The maximum output power at 1.06 μm wavelength is 1.54 W at an incident pump power of 12.87 W under an output coupler of 5% along the x-axis direction, corresponding to an optical-to-optical conversion efficiency of 11.97% and a slope efficiency η of 12.28%. [ABSTRACT FROM AUTHOR]

Polymer‐derived amorphous SiCN has excellent high‐temperature stability and properties. To reduce the shrinkage during pyrolysis and to improve the high‐temperature oxidation resistance, Y2O3 was added as a filler. In this study, polymer‐derived SiCN–Y2O3 composites were fabricated by mixing a polymeric precursor of SiCN with Y2O3 submicron powders in different ratios. The mixtures were cross‐linked and pyrolyzed in argon. SiCN–Y2O3 composites were processed using field‐assisted sintering technology at 1350°C for 5 min under vacuum. Dense SiCN–Y2O3 composite pellets were successfully made with relative density higher than 98% and homogeneous microstructure. Due to low temperature and short time of the heat‐treatment, the grain growth of Y2O3 was substantially inhibited. The Y2O3 grain size was ∼1 μm after sintering. The composites' heat capacity, thermal diffusivity, and thermal expansion coefficients were characterized as a function of temperature. The thermal conductivity of the composites ceramics decreased as the amount of amorphous SiCN increased and the coefficient of thermal expansion (CTE) of the composites increased with Y2O3 content. However, the thermal conductivity and CTE did not follow the rule of mixture. This is likely due to the partial oxidation of SiCN and the resultant impurity phases such as Y2SiO5, Y2Si2O7, and Y4.67(SiO4)3O. [ABSTRACT FROM AUTHOR]

Rare‐earth (RE) hafnates are promising thermal and environmental barrier coating (TEBC) materials for SiCf/SiC ceramic matrix composites. In this study, pure‐phase and dense δ‐RE4Hf3O12 (RE = Yb, Lu) bulk ceramics have been fabricated via a hot‐pressing method. The crystal structure, microstructure, mechanical, and thermal properties of δ‐RE4Hf3O12 were systematically investigated in order to probe their potential application as TEBCs. The high‐temperature elastic moduli of δ‐Yb4Hf3O12 and δ‐Lu4Hf3O12 are measured to be 185 and 188 GPa at 1673 K, respectively, which are over 85% values of room temperature. The coefficients of thermal expansion are 7.64 × 10−6 and 7.46 × 10−6 K−1 for δ‐Yb4Hf3O12 and δ‐Lu4Hf3O12, respectively. The relatively low coefficient of thermal expansion and thermal conductivity as well as their excellent high‐temperature stability endow these hafnates as potential TEBC candidates. [ABSTRACT FROM AUTHOR]

Electronic packaging materials should integrate with excellent overall performance including thermal, mechanical, and machinability to meet the challenges of the current highly integrated development of the electronics industry. The low-temperature sintering of high-strength 3D-SiC frameworks with equiaxed grains was achieved at 2250 °C by regulating the contents and particle size of coarse and fine powders in bimodal SiC hybrid particles. And 3D-interpenetrated network structures SiC/Al (SiC 3D /Al) composites for electronic packaging were then fabricated using a vacuum/gas pressure infiltration Al alloys process. Results indicated the thermal conductivity (TC), coefficient of thermal expansion (CTE), and thermal deformation parameter (TDP) of the composites were improved with increasing coarse powder size. And SiC 3D /Al with the coarse powder size of 38 μm and the coarse powder content of 60 wt% achieved the compatibility of optimal thermophysical and mechanical properties with flexural strength of 406.14 MPa, CTE of 5.38 × 10−6/K, TC of 230.03 W m−1 K−1, and TDP of 0.023 matching that of Si. A further increased coarse powder particle size to 48 μm and higher 58 μm reduced the mechanical properties by 14% and 22%, respectively. Moreover, the composites maintained stable CTE and TC after 100 thermal cycles, and 3D-SiC framework was free of defects and no interfacial debonding, ensuring long-term service reliability. Integration of distinguished overall performance was primarily implemented by the synergistic effect of the 3D network framework with equiaxed grains mutual strong bonding as well as the clean and well-bonded interface. This technology provides a reference for the design and synthesis of high-performance electronic packaging materials with scalability and tuneability. [ABSTRACT FROM AUTHOR]

Thermal barrier coatings with excellent thermal performance and corrosion resistance are essential for improving the performance of aero-engines. In this paper, (Y 3-x Yb x)(Al 5-x Sc x)O 12 (x = 0, 0.1, 0.2, 0.3) thermal barrier coating materials were synthesized by a combination of sol-gel method and ball milling refinement method. The thermal properties of the (Y 3-x Yb x)(Al 5-x Sc x)O 12 ceramics were significantly improved by increasing Yb and Sc doping content. Among designed ceramics, (Y 2.8 Yb 0.2)(Al 4.8 Sc 0.2)O 12 (YS-YAG) showed the lowest thermal conductivity (1.58 Wm−1K−1, at 800 °C) and the highest thermal expansion coefficient (10.7 × 10−6 K−1, at 1000 °C). In addition, calcium-magnesium- aluminum -silicate (CMAS) corrosion resistance of YS-YAG was further investigated. It was observed that YS-YAG ceramic effectively prevented CMAS corrosion due to its chemical inertness to CMAS as well as its unique and complex structure. Due to the excellent thermal properties and CMAS corrosion resistance, YS-YAG is considered to be prospective material for thermal barrier coatings. [ABSTRACT FROM AUTHOR]

Dense TaTiP 3 O 12 ceramics were synthesized by the solid-state method and spark plasma sintering (SPS) with 6 wt% V 2 O 5 as a sintering aid, and their phase, microstructure, thermal conductivity, hardness, compressive strength, and expansion property and mechanism were investigated. Results show that the pure phase can be achieved by the two methods. In particular, the sample prepared by SPS possesses a relative density of 97.62% and a porosity of 3.07%, and has better properties than that prepared by the solid-state method. The SPS sample has a thermal conductivity at room temperature of 2.03 w/(m · °C), a Vickers hardness of 4.34 GPa and a compressive strength of 175.98 MPa, which are 0.95, 1.49 and 1.59 times greater than those of the sample prepared by the solid-state method, respectively. In addition, the TaTiP 3 O 12 ceramic prepared by SPS exhibits a linear ultralow negative thermal expansion property with a coefficient of thermal expansion of −0.74 × 10−6 °C −1 (-100–400 °C). The negative thermal expansion in TaTiP 3 O 12 is induced by the coupling effect of [Ta(Ti)O 6 ] octahedron and [PO 4 ] tetrahedron caused by the transverse vibration of bridging oxygen atoms. [ABSTRACT FROM AUTHOR]

Natural composites are gaining more attention due to the light weight and low cost characteristics. In the present investigation, an attempt has been made to fabricate the natural composites using natural fibers like Banyan and Cotton. Composites were made by compression molding technique and five types of composites were prepared, namely, B, BC(3:1), BC(1:1), BC(1:3) and C. Mechanical and thermal properties of the composites were tested. Results showed that Banyan composite exhibited the maximum tensile and flexural strength of 75 MPa and 113 MPa, respectively. This was attributed by the placing of high strength and stiffness Banyan fiber. Further, a maximum thermal resistance of 18.1 × 10−3 m²K/W was observed for Banyan composite. Moreover, the Banyan composite displayed the least coefficient of thermal expansion (CTE) of 1.81 × 10−5/°C which indicated the good dimensional stability of composite. Furthermore, a high thermal diffusivity of 8.79 × 10−7 m²/s was achieved for Banyan composites. Based on the experimental results, it is suggested that the Banyan composite could be a suitable candidate for sustainable thermal insulation applications. [ABSTRACT FROM AUTHOR]

Thermal and electrical properties were measured for TiB2 ceramics containing varying CrB2 contents up to 33 mol%. The room‐temperature thermal diffusivity decreased with increasing Cr content from 0.330 ± 0.003 cm2/s for pure TiB2 to 0.060 ± 0.003 cm2/s for (Ti0.66Cr0.33)B2. The amount of anisotropy in the coefficients of thermal expansion increased with increasing Cr content and the c‐axis had the greatest dependence on Cr addition, with an increase of more than 25% in the thermal expansion for 33 mol% CrB2 compared to TiB2, whereas the a‐axis only increased by about 8%. The electrical conductivity was the lowest for (Ti0.66Cr0.33)B2 at ∼8.5 × 103 S/cm compared to ∼106.1 × 103 S/cm for nominally pure TiB2. Overall, the addition of CrB2 as a sintering aid for TiB2 was shown to have a significant effect on the thermal and electrical properties of TiB2 for additions as small as 5 mol% CrB2. [ABSTRACT FROM AUTHOR]

The high-entropy ceramic materials (Zr 0.25 Ce 0.25 Hf 0.25 Y 0.25)O 1.875 (H-0) and (Zr 0.2 Ce 0.2 Hf 0.2 Y 0.2 RE 0.2)O 1.8 (H-RE) (RE = La, Nd and Sm) with fluorite structure and homogeneous element distribution were prepared. With fluorite structure, fine grain size and high density, the H-0 and H-RE ceramics displayed low thermal conductivity, suitable thermal expansion coefficient, high hardness and fracture toughness. The effect of La, Nd and Sm on the mechanical, heat conductivity and heat expansion properties of high entropy ceramics were discussed. The single-phase high-entropy ceramic materials in this work are very suitable for application as thermal barrier materials. [ABSTRACT FROM AUTHOR]

A GaNbO4 single crystal (ϕ = 24 mm) was successfully grown for the first time by the Czochralski (CZ) method, and the thermal and optical properties were systematically studied. The structure parameters were calculated and belong to the monoclinic C2/m space group. The half-peak width of the rocking curve is 26.63 arcsec, indicating that the crystal is of relatively high quality. The specific heat, thermal diffusion coefficient, and thermal conductivity were measured systematically. The thermal expansion coefficients of the GaNbO4 crystal in different directions were obtained and it is proved that the GaNbO4 crystal has negative thermal expansion along the crystallographic b-axis. The orientation relationship between the thermal expansion ellipsoid axis and the crystallographic axis is determined. The UV-vis diffuse reflectance spectra and the transmittance spectra of the GaNbO4 crystal were measured, and the band gap and the orientation relationship between the optical axis and crystallographic axis were confirmed. The chemical composition was analyzed using X-ray photoelectron spectroscopy (XPS). [ABSTRACT FROM AUTHOR]

(Ho 1/4 Er 1/4 Yb 1/4 Lu 1/4) 2 SiO 5 is synthesized and characterized for the application of a promising multifunctional thermal and environmental barrier coating (TEBC) material. X-ray diffraction and scanning electron microscopy analysis indicate that a X2-type multiple-RE silicate (4RE 1/4) 2 SiO 5 is formed with homogeneous distribution of the four rare earth species. Dense bulk sample exhibits excellent phase stability up to 1400 °C. Key properties including Young's modulus, thermal conductivity and thermal expansion coefficient show interesting composition effects. Specially, (Ho 1/4 Er 1/4 Yb 1/4 Lu 1/4) 2 SiO 5 demonstrates higher elastic stiffness, lower thermal conductivity, lower thermal expansion coefficient and good resistances to molten CMAS and water vapor corrosions. These results confirm the strategy of multiple-RE engineering that may provide optimal property of advanced TEBCs. [ABSTRACT FROM AUTHOR]

As various property studies continue to emerge on high entropy and entropy-stabilized ceramics, we seek a further understanding of the property changes across the phase boundary between "high-entropy" and "entropy-stabilized" phases. The thermal and mechanical properties of bulk ceramic entropy stabilized oxide composition Mg0.2Co0.2Ni0.2Cu0.2Zn0.2O are investigated across this critical transition temperature via the transient plane-source method, temperature-dependent x-ray diffraction, and nano-indentation. The thermal conductivity remains constant within uncertainty across the multi-to-single phase transition at a value of ≈2.5 W/mK, while the linear coefficient of thermal expansion increases nearly 24% from 10.8 to 14.1 × 10−6 K−1. Mechanical softening is also observed across the transition. [ABSTRACT FROM AUTHOR]

In this study, the temperature dependence of the carbon/polyamide 410 composite's heat capacity, thermal expansion, density, and thermal conductivity was investigated. The results demonstrated that the specific heat capacity of the C/PA410 composite increases with temperature, with major transitions observed at the glass transition (Tg) and melting (Tm) temperatures. Due to the presence of fibers, the CTE values in the fiber direction of C/PA410 specimens were one order of magnitude smaller than in the transverse direction. The density measurements reveal that as temperature rises, volume increases, causing density to decrease. The heat diffusivity of the C/PA410 composite was measured using the laser flash technique, which was then used to calculate thermal conductivity. The results show that the average thermal conductivity in the fiber direction increases linearly with temperature, while in the transverse direction it increases linearly with temperature up to 50 °C and then becomes constant between 50 °C and 100 °C. [ABSTRACT FROM AUTHOR]

Graphene-like nanomembranes made of the neighboring elements of boron, carbon and nitrogen elements, are well-known of showing outstanding physical properties. Herein, with the aid of density functional theory (DFT) calculations, various atomic configurations of the graphene-like BCN nanosheets are investigated. DFT results reveal that depending on the atomic arrangement, the BCN monolayers may display semimetallic Dirac cone or semiconducting electronic nature. BCN nanosheets are also found to exhibit high piezoelectricity and carrier mobilities with considerable in-plane anisotropy, depending on the atomic arrangement. For the predicted most stable BCN monolayer, thermal and mechanical properties are explored using machine learning interatomic potentials. The room temperature tensile strength and lattice thermal conductivity of the most stable BCN monolayer are estimated to be orientation-dependent and remarkably high, over 78 GPa and 290 W/m.K, respectively. In addition, the thermal expansion coefficient of the monolayer BCN at room temperature is estimated to be −3.2 × 10−6 K−1, which is close to that of the graphene. The piezoelectric response of the herein proposed BCN lattice is also predicted to be close to that of the h-BN monolayer. Presented results highlight outstanding physics of the BCN nanosheets. [Display omitted] [ABSTRACT FROM AUTHOR]

Low-thermal conductivity ceramics play an indispensable role in maximizing the efficiency and durability of hot end components. Pyrochlore, particularly zirconate pyrochlore, is currently a highly promising and widely studied candidate for its extremely low thermal conductivity. However, there are still few pyrochlores that offer both stiffness, insulation, and good thermal expansion properties. In this work, the solidification method was innovatively introduced into the preparation of titanate pyrochlore, and combined it with the compositional design of high-entropy. Through careful composition design and solidification control, the high-density and uniform elements distributed high-entropy titanate pyrochlore ceramics were successfully prepared. These samples possess high hardness (15.88 GPa) and Young's modulus (295.5 GPa), low thermal conductivity (0.947 W·m−1·K−1), excellent thermal expansion coefficient (11.6 ×10−6/K) and an exquisite balance between stiffness and insulation (E/κ, 312.1 GPa·W−1·m·K), in which the E/κ exhibits the highest value among the current reported works. • Propose a new synthesis way for high-entropy ceramics by melt solidification. • Samples possess a record-breaking balance between stiffness and insulation (E/κ). • The obtained ceramics exhibit extremely low thermal conductivity and high hardness. [ABSTRACT FROM AUTHOR]

High-performance thermal storage ceramics can enable utilization of solar thermal power generation plants. In this work, in situ synthesis was used to prepare mullite thermal storage ceramics. Calcined bauxite, talc, and kaolin were used as raw materials. The effects of additives (e.g., SiC, Si 3 N 4 , TiC, and ZrB 2) on the density, mechanical durability, phase components, microstructure, and thermal performance of the mullite ceramics were studied. The results showed that the thermal expansion coefficient, thermal conductivity, and heat storage density of the mullite ceramics were affected by their phase components. SiC and Si 3 N 4 did not decompose during the in situ syntheses, but TiC and ZrB 2 decomposed. With the addition of 10 wt % SiC, the thermal conductivity improved to 2.72 W (m K)−1 (298 K). The heat storage density of this material was 688 kJ kg−1 (273–1073 K). Consequently, the in situ synthesized mullite thermal storage ceramic with added SiC could be a promising candidate material for a compound latent-sensible heat storage system. [ABSTRACT FROM AUTHOR]

A new high-entropy diboride (Hf 0.25 Zr 0.25 Ta 0.25 Sc 0.25)B 2 was designed to investigate the effect of introducing rare-earth metal diboride ScB 2 into high-entropy diborides on its structure and properties. The local mixing enthalpy predicts that (Hf 0.25 Zr 0.25 Ta 0.25 Sc 0.25)B 2 has high enthalpy driving force, which more easily allows the formation of single-phase AlB 2 -type structures between components. The experiments further demonstrate that (Hf 0.25 Zr 0.25 Ta 0.25 Sc 0.25)B 2 possesses excellent phase stability, lattice integrity and nanoscale chemical homogeneity. (Hf 0.25 Zr 0.25 Ta 0.25 Sc 0.25)B 2 showed relatively high hardness (30.7 GPa), elastic modulus (E , G , and B of 522, 231 and 233 GPa, respectively), bending strength (454 MPa), and low thermal conductivity (13.9 W·m−1·K−1). The thermal expansion of (Hf 0.25 Zr 0.25 Ta 0.25 Sc 0.25)B 2 is higher than that of ZrB 2 and HfB 2 due to weakened bonding (M d - B p and M dd bonding) and enhanced anharmonic effects. Thus, incorporating Sc into high-entropy diborides can tailor the properties associated with the bonding, which further expands the compositional space of high-entropy diborides. [ABSTRACT FROM AUTHOR]

The limited efficiency of traditional trial-and-error experiments has impeded the development and application of high-entropy fluorite oxides in thermal insulation coatings. To solve this problem, a novel entropy descriptor based on first principles is presented to help select candidate components for synthesizing high-entropy fluorite structure oxides. Results show that the compatibilities of 10 single-phase high-entropy fluorite oxides can be accurately predicted based on entropy formation ability. In the studied (Zr, Hf, Pr, La, X) O 2-δ system, a correlation between thermal characteristics and size/mass differences was established by designing the size and mass of X. Specifically, we found that the thermal conductivity is more strongly correlated with the difference in atomic mass, while the coefficient of thermal expansion is strongly correlated with the difference in atomic size. X-ray photoelectron spectroscopy (XPS) analysis shows that the concentration of oxygen vacancy can effectively reduce the thermal conductivity of high-entropy fluorite oxides. In addition, the values of hardness, elastic modulus and thermal conductivity of five single-phase fluorite oxides are successfully predicted by first principles calculation, and the differences between these values and the experimental results are small, which provides a prospective significance for the performance prediction of high-entropy fluorite oxides. Our findings provide a strategy for customizing high-entropy fluorite single-phase oxides with suitable properties to meet the performance requirements of thermal barrier coatings (TBCs). • The DFT calculation provides an entropy descriptor to evaluate the comfiability of high-entropy single-phase fluorite oxides based on their entropy formation capacity. • The hardness, elastic modulus and thermal conductivity of the studied sample are obtained by DFT calculation, and the difference between them and the experimental values is small. • In the (Zr, Hf, Pr, La, X)O 2-δ system, the atomic size difference and atomic mass difference of five single-phase samples were quantified, and their thermal conductivity and thermal expansion values were correlated. [ABSTRACT FROM AUTHOR]

In the development for advanced nuclear fuels for LWRs, the focus has traditionally centered on a limited array of materials like doped-UO 2 , UN, and U 3 Si 2 , leaving the vast majority of potential uranium compounds unexplored. To expand the search and expedite the discovery of advanced LWR fuels, we developed a machine learning (ML) classification model dedicated to identifying uranium compounds with excellent thermal conductivity. However, the model's predictive accuracy and the feasibility of such an ML-assisted approach to advanced nuclear fuel discovery have yet to be empirically validated. Therefore, this study examines the thermal properties of two uranium compounds, UFe 3 B 2 and USiNi, that are predicted to outperform UO 2 at high temperatures. Our findings confirm that the model precisely predicted the thermal conductivities of both compounds, thereby adding credibility to its reliability. However, the experimental process unveiled several challenges, such as the fabrication of single-phase USiNi and microcrack-free UFe 3 B 2 samples, which our ML model, focused primarily on thermal conductivity, could not anticipate. These challenges underscore the need for a more comprehensive ML framework that considers the intricacies of sample fabrication. This advancement is crucial for the more efficient development of practical, accident-tolerant, advanced LWR fuels. • Validated ML model's predictions for uranium compounds' thermal conductivity. • First report of UFe 3 B 2 and USiNi thermophysical and mechanical properties. • Identified unforeseen experimental challenges beyond ML prediction. • Emphasized need for comprehensive ML framework for advanced nuclear fuel development. [ABSTRACT FROM AUTHOR]

The purpose of this study is to investigate the direct effect of using a blowing agent of siloxane (1, 1, 3, 3-tetramethydisiloxane) on the thermo-physical properties of the foamed epoxy. These properties are: density, glass-transition temperature, thermal conductivity and thermal expansion. The work has been conducted experimentally by manufacturing several specimens with different siloxane contents as: 0, 5, 10, 15 and 20 wt%. The properties of the specimens have tested under suitable conditions using different reliable instruments: differential scanning calorimetry, Lee-discs apparatus, and push rod dilatometer. Scanning electron microscope was used as well to analysis the morphological characteristics of the epoxy with respect to the pores generated by the blowing agent. In general, the foamed epoxy has shown different sizes of pores and extra crosslinking which leads to increase the glass-transition temperature of the material. Results show that the addition of 20% siloxane to the neat epoxy (as maximum) leads to: decreasing by 50% in bulk density, increasing by 20% in glass-transition temperature, decreasing by 30% in thermal conductivity, and decreasing by 75% in thermal expansion. [ABSTRACT FROM AUTHOR]

ZrW2O8 is known as a negative coefficient of thermal expansion (CTE) material. In contrast, the studies of other properties than the CTE of ZrW2O8, such as thermal conductivity and mechanical properties, are limited. Herein, a highly dense bulk sample (%T.D. > 95%) of ZrW2O8 from very fine powder (D50 0.3 μm) with a crystalline size of 31 nm using a spark plasma sintering (SPS) technique is synthesized. It is revealed that ZrW2O8 exhibits the lowest level of thermal conductivity among various oxides in a wide temperature range from 300 to 823 K. Furthermore, various physical properties such as a peculiar CTE, elastic constant, and Grüneisen parameter are reported. Owing to its exceptional thermal properties, ZrW2O8 is expected to be used in various thermal management areas. [ABSTRACT FROM AUTHOR]

Past work has focused on the thermal properties of microscale/nanoscale suspended/supported graphene. However, for the thermal design of graphene-based devices, the thermal properties of giant-scale (~mm) graphene, which reflects the effect of grains, must also be investigated and are critical. In this work, the thermal conductivity variation with temperature of giant-scale chemical vapor decomposition (CVD) graphene supported by poly(methyl methacrylate) (PMMA) is characterized using the differential transient electrothermal technique (diff-TET). Compared to the commonly used optothermal Raman technique, diff-TET employs joule heating as the heating source, a situation under which the temperature difference between optical phonons and acoustic phonons is eased. The thermal conductivity of single-layer graphene (SLG) supported by PMMA was measured as 743 ± 167 W/(m·K) and 287 ± 63 W/(m·K) at 296 K and 125 K, respectively. As temperature decreased from 296 K to 275 K, the thermal conductivity of graphene was decreased by 36.5%, which can be partly explained by compressive strain buildup in graphene due to the thermal expansion mismatch. [ABSTRACT FROM AUTHOR]

As a promising candidate for accident tolerant fuels, the UO 2 –Mo composite with continuous Mo channel gains a distinct improvement in the thermal conductivity (TC) of UO 2 fuels to enhance the safety and economy of reactors. However, due to a large difference between the coefficient of thermal expansion (CTE) of UO 2 matrix and Mo channel, microcracks induced by thermal stress usually occur in the matrix of the UO 2 –Mo composite with a high Mo content. In this paper, it is proved that adding Nb into Mo channel could significantly modify the CTE, hence reduce the thermal stress of matrix (MTS). However, under the constant proportion of additive materials, increasing Nb simultaneously decreases the TC of the whole composite due to its lower TC than that of Mo. To balance this contradiction and search an optimizing composition range, a bi-objective optimization method for material properties was proposed. Two models for predicting TC and MTS of the UO 2 –Mo–Nb composite were constructed using Gaussian Process Regression, based on the dataset with uncertainty built by finite element simulation. Leveraging the two models and NSGA-II method, an optimizing composition range of the UO 2 –Mo–Nb composite was obtained. According to the range, a UO 2 composite containing 3 vol% Mo and 1 vol% Nb was fabricated, which exhibited a TC around 30% higher than that of UO 2 at 1000 °C and no microcracks due to the moderate MTS. [ABSTRACT FROM AUTHOR]

Searching for new oxides with low thermal conductivity and high thermal expansion coefficients (TECs) as thermal barrier coatings (TBCs) is vital for the development of highly efficient gas turbines and aeroengines. We report the densification sintering, high TECs, and low thermal conductivity of A 4 Ta 2 O 9 (A = Ca, Mg) tantalates. The best sintering temperature of dense A 4 Ta 2 O 9 ceramics was determined via an optical contact angle tester, and samples with a relative density of 99.8% were synthesized via spark plasma sintering (SPS). The hardness (9–10 GPa), Young's modulus (172.7–211.8 GPa) and fracture toughness (1.5–1.6 MPa m1/2) of the A 4 Ta 2 O 9 ceramics are primarily affected by the bonding strength. Furthermore, we studied the thermal transport properties of A 4 Ta 2 O 9. The low thermal conductivity (1.78–1.93 W m−1 K−1 at 900 °C), extraordinary phase stability, and high TECs (11.4–11.8 × 10−6 K−1 at 1200 °C) of A 4 Ta 2 O 9 ceramics make them candidate TBCs with high operating temperatures. [ABSTRACT FROM AUTHOR]

We prepared the novel high‐entropy (xRE1/x)2Si2O7 (RE = Y, Yb, Er, Sc, Gd and Eu, x = 2–6) ceramics by a two‐step method for the application of thermal environmental barrier coatings (TEBCs), and the effect of configuration entropy and lattice distortion on microstructures and thermal properties at high temperature were investigated. The results showed that the configuration entropy resulted from mass disorder can only contribute to the stability of thermal properties and microstructure. Lattice distortion should be responsible for reduction in thermal properties, which may be due to the enhancement of atomic nonharmonic vibration, resulting in intensified phonon scattering and hindering atomic amplitude oscillation. As‐prepared high‐entropy (Y1/6Yb1/6Er1/6Sc1/6Gd1/6Eu1/6)2Si2O7 ceramic exhibited the relatively low thermal diffusivity, thermal conductivity and coefficient of thermal expansion, which were 0.89–0.50 mm2 s–1, 1.99–2.50 W m–1 K–1 and (3.01–3.78) × 10–6 K–1 in the temperature range of 293–1373 K, respectively. This work provides a solid guarantee for the application of TEBC materials. [ABSTRACT FROM AUTHOR]