Ferroelastic RETaO 4 ceramics are promising thermal barrier coatings (TBCs) because of their attractive thermomechanical properties. The influence of crystal structure distortion degree on thermomechanical properties of RETaO 4 is estimated in this work. The relationship between Young's modulus and TECs is determined. The highest TECs (10.7 × 10 −6 K −1 , 1200°C) of RETaO 4 are detected in ErTaO 4 ceramics and are ascribed to its small Young's modulus and low Debye temperature. The intrinsic lattice thermal conductivity (3.94-1.26 W m −1 K −1 , 100-900°C) of RETaO 4 deceases with increasing of temperature due to an elimination in thermal radiation effects. The theoretical minimum thermal conductivity (1.00 W m −1 K −1 ) of RETaO 4 indicates that the experimental value is able to be reduced further. We have delved deeply into the thermomechanical properties of ferroelastic RETaO 4 ceramics and have emphasized their high-temperature applications as TBCs. K E Y W O R D Sband gap, intrinsic lattice thermal conductivity, rare earth tantalates, thermal barrier coatings, thermal expansion performance, Young's modulus

Thermal barrier coatings (TBCs) are one of the most important materials in gas turbine to protect the high temperature components. RETa3O9 compounds have a defect‐perovskite structure, indicating that they have low thermal conductivity, which is the critical property of TBCs. Herein, dense RETa3O9 bulk ceramics were fabricated via solid‐state reaction. The crystal structure was characterized by X‐ray diffraction (XRD) and Raman Spectroscope. Scanning electron microscope (SEM) was used to observe the microstructure. The thermophysical properties of RETa3O9 were studied systematically, including specific heat, thermal diffusivity, thermal conductivity, thermal expansion coefficients, and high‐temperature phase stability. The thermal conductivities of RETa3O9 are very low (1.33‐2.37 W/m·K, 373‐1073 K), which are much lower than YSZ and La2Zr2O7; and the thermal expansion coefficients range from 4.0 × 10−6 K−1 to 10.2×10−6 K−1 (1273 K), which is close to La2Zr2O7 and YSZ. According to the differential scanning calorimetry (DSC) curve there is not phase transition at the test temperature. Due to the high melting point and excellent high‐temperature phase stability with these oxides, RETa3O9 ceramics were promising candidate materials for TBCs.

Thermal barrier coatings (TBCs) can effectively protect the alloy substrate of hot components in aeroengines or land-based gas turbines by the thermal insulation and corrosion/erosion resistance of the ceramic top coat. However, the continuous pursuit of a higher operating temperature leads to degradation, delamination, and premature failure of the top coat. Both new ceramic materials and new coating structures must be developed to meet the demand for future advanced TBC systems. In this paper, the latest progress of some new ceramic materials is first reviewed. Then, a comprehensive spalling mechanism of the ceramic top coat is summarized to understand the dependence of lifetime on various factors such as oxidation scale growth, ceramic sintering, erosion, and calcium-magnesium-aluminium-silicate (CMAS) molten salt corrosion. Finally, new structural design methods for high-performance TBCs are discussed from the perspectives of lamellar, columnar, and nanostructure inclusions. The latest developments of ceramic top coat will be presented in terms of material selection, structural design, and failure mechanism, and the comprehensive guidance will be provided for the development of next-generation advanced TBCs with higher temperature resistance, better thermal insulation, and longer lifetime.

Four high-entropy perovskite (HEP) RETa3O9 samples were fabricated via a spark plasma sintering (SPS) method, and the corresponding thermophysical properties and underlying mechanisms were investigated for environmental/thermal barrier coating (E/TBC) applications. The prepared samples maintained low thermal conductivity (1.50 W·m−1·K−1), high hardness (10 GPa), and an appropriate Young’s modulus (180 GPa), while the fracture toughness increased to 2.5 MPa·m1/2. Nanoindentation results showed the HEP ceramics had excellent mechanical properties and good component homogeneity. We analysed the influence of different parameters (the disorder parameters of the electronegativity, ionic radius, and atomic mass, as well as the tolerance factor) of A-site atoms on the thermal conductivity. Enhanced thermal expansion coefficients, combined with a high melting point and extraordinary phase stability, expanded the applications of the HEP RETa3O9. The results of this study had motivated a follow-up study on tantalate high-entropy ceramics with desirable properties.

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Abundant oxides are studied to replace present thermal barrier coatings (TBCs), yttria-stabilized zirconia (YSZ), to perfect the application performances. 1-8 YSZ displays relatively high thermal conductivity (2.5 W•m −1 •K −1 , 1000°C), high Young's modulus (~230 GPa), low application temperature (≤1200°C), and weak CaO-MgO-Al 2 O 3-SiO 2 corrosion resistance. 1,2,9-12 To conquer the weaknesses, multifarious means are applied to perfect YSZ properties, and diverse oxides are researched as novel TBCs. 3,6,13-20 RE 3 NbO 7 oxides (RE is rare earth) are considered as structural materials, as that they display low thermal conductivity (1.0-2.0 W•m −1 •K −1 , 25-900°C), high thermal expansion coefficients (11 × 10 −6 K −1 , 1200°C), and exceptional corrosion resistance. 16,21 The thermal transport mechanism and mechanical properties of fluorites RE 3 NbO 7 are well documented, and the thermal properties of weberites RE 3 NbO 7 are reported. 16,21,22 Besides thermal properties, hardness, toughness, and modulus are vital, nevertheless, the dominant mechanisms of mechanical properties of weberites RE 3 NbO 7 are not clear. The critical factors of hardness, toughness and modulus of ceramics include lattice distortion degree, bond length, microstructure features, and others. Suitable hardness, toughness, and modulus are demanded, and their mutual relations are connective. 23-26 To obtain TBCs with excellent working performance, the mechanical properties and corresponding dominant mechanisms are of great importance. The correlations among crystal structures, surface appearances and mechanical properties of weberites RE 3 NbO 7 are researched. The influences of bond length, lattice distortion degree, crystal structures and microstructures on mechanical properties are studied. Furthermore, the correlations between thermal and mechanical properties are connected. The dominant

The essential oils (EOs) derived from aromatic plants such as Piper species are considered to play a role in alleviating neuronal ailments that are associated with inhibition of acetylcholinesterase (AChE). The chemical compositions of 23 EOs prepared from 16 Piper spp. were analyzed by both gas chromatography with a flame ionization detector (GC-FID) and gas chromatography-mass spectrometry (GC-MS). A total of 76 compounds were identified in the EOs from the leaves and stems of 19 samples, while 30 compounds were detected in the EOs from the fruits of four samples. Sesquiterpenes and phenylpropanoids were found to be rich in these EOs, of which asaricin, caryophyllene, caryophyllene oxide, isospathulenol, (+)-spathulenol, and β-bisabolene are the major constituents. The EOs from the leaves and stems of Piper austrosinense, P. puberulum, P. flaviflorum, P. betle, and P. hispidimervium showed strong AChE inhibitory activity with IC values in the range of 1.51 to 13.9 mg/mL. A thin-layer chromatography (TLC) bioautography assay was employed to identify active compound(s) in the most active EO from P. hispidimervium. The active compound was isolated and identified as asaricin, which gave an IC value of 0.44 ± 0.02 mg/mL against AChE, comparable to galantamine with an IC 0.15 ± 0.01 mg/mL.

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