Poly(vinylidene fluoride)-based dielectric materials are prospective candidates for high power density electric storage applications because of their ferroelectric nature, high dielectric breakdown ...strength and superior processability. However, obtaining a polar phase with relaxor-like behavior in poly(vinylidene fluoride), as required for high energy storage density, is a major challenge. To date, this has been achieved using complex and expensive synthesis of copolymers and terpolymers or via irradiation with high-energy electron-beam or γ-ray radiations. Herein, a facile process of pressing-and-folding is proposed to produce β-poly(vinylidene fluoride) (β-phase content: ~98%) with relaxor-like behavior observed in poly(vinylidene fluoride) with high molecular weight > 534 kg mol
, without the need of any hazardous gases, solvents, electrical or chemical treatments. An ultra-high energy density (35 J cm
) with a high efficiency (74%) is achieved in a pressed-and-folded poly(vinylidene fluoride) (670-700 kg mol
), which is higher than that of other reported polymer-based dielectric capacitors to the best of our knowledge.
High-entropy compounds with compositional complexity can be designed as new thermoelectric materials. Here a data-driven model was developed, which chose suitable elements to reduce the enthalpy of ...formation and hence to increase the chance of single phase formation. Using this model, two high-entropy sulfides were designed, metallic Cu5SnMgGeZnS9 and semiconducting Cu3SnMgInZnS7. They were then successfully fabricated as single-phase dense ceramics with homogeneously distributed cations, and their phase stability and atomic local structures were investigated using density functional theory calculations. Finally, a zT value of 0.58 at 773 K was obtained for Cu5Sn1.2MgGeZnS9, where additional Sn was used to tune the carrier concentration. This work provides a simple approach to find new high-entropy functional materials in the largely unexplored multielement chemical space.
Flash sintering (FS) is an energy efficient sintering technique involving electrical Joule heating, which allows very rapid densification (<60 s) of particulate materials. Since the first publication ...on flash-sintered zirconia (3YSZ) in 2010, it has been intensively researched and applied to a wide range of materials. Going back more than a century ago, we have found a close similarity between FS of oxides and Nernst glowers developed in 1897. This review provides a comprehensive overview of FS and is based on a literature survey consisting of 88 papers and seven patents. It correlates processing parameters (i.e. electric field magnitude, current density, waveforms (AC, DC) and frequency, furnace temperature, electrode materials/configuration, externally applied pressure and sintering atmosphere) with microstructures and densification mechanisms. Theorised mechanisms driving the rapid densification are substantiated by modelling work, advanced in situ analysis techniques and by established theories applied to electric current assisted/activated sintering techniques. The possibility of applying FS to a wider range of materials and its implementation in industrial scale processes are discussed.
Abbreviations: ECAS: Electric Current Assisted/Assisted Sintering; FS: flash sintering; SPS: spark plasma sintering; FSPS: flash spark plasma sintering; HIP: hot isostatic press; HP: hot press; T
F
: furnace temperature; T
Onset
: onset temperature; E: electrical field; T
S
: sample temperature; T
Soft
: softening temperature for glasses; T
m
: melting temperature; PTC or NTC: positive or negative temperature coefficient of electrical resistance; IS: impedance spectroscopy; OES: optical emission spectroscopy; AES: atomic emission spectroscopy; DBS: Dog-bone shape, L: length, W: width, T: thickness, D: diameter, H: height, R: rectangular, CS: cross-section; P: particle size; C: crystallite size; 3YSZ: 3 mol-% yttria-stabilised zirconia; I: ion, H: hole, V: vacancy, E: electron, P: proton
Bulk polycrystalline high-entropy carbides are a newly developed group of materials that increase the limited compositional space of ultra-high temperature ceramics, which can withstand extreme ...environments exceeding 2000 °C in oxidizing atmospheres. Since the deformability of grains plays an important role in macromechanical performance, in this work we studied the strength and slip behaviour of grains of a spark-plasma sintered (Hf-Ta-Zr-Nb)C high-entropy carbide in a specific orientation during micropillar compression. For comparison, identical measurements were carried out on the monocarbides HfC and TaC. It was revealed that (Hf-Ta-Zr-Nb)C had a significantly enhanced yield and failure strength compared to the corresponding base monocarbides, while maintaining a similar ductility to the least brittle monocarbide (TaC) during the operation of Formula: see text slip systems. Additionally, it was concluded that the crystal orientation and stress conditions determine the operation of slip systems in mono- and high-entropy carbides at room temperature.
•High-entropy half-Heusler compounds were synthesized by mechanical alloying combined with spark plasma sintering•Low thermal conductivity of 1.8–1.5 Wm−1K−1 (300–923 K) is achieved in high-entropy ...half-Heusler•Tuning thermoelectric properties by adjusting Fe/Co ratio; maximum zT values of 0.3 (n-type) and 0.25 (p-type) are achieved
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The application of the high-entropy concept has generated many interesting results for both alloys and ceramics. However, there are very few reports on high entropy thermoelectric materials. In this work, a single phase high-entropy half-Heusler compound MFe1-xCoxSb with 6 equimolar elements (Ti, Zr, Hf, V, Nb and Ta) on the M site was successfully synthesized by a simple method of mechanical alloying, and the single phase was maintained after densification by spark plasma sintering. The multi-elements are homogenously distributed in the samples. The samples are stable and there is no phase separation after annealing at 1073 K in argon for 72 h, which could be attributed to their high configurational entropy. Due to the phonon scattering introduced by multi-elements, the lattice thermal conductivity is largely suppressed with a lowest value of ~ 1.8–1.5 Wm−1K−1 (300–923 K) for MCoSb. By adjusting the Fe/Co ratio, the samples can show both n-type and p-type semiconductor behavior. Maximum zT values of 0.3 and 0.25 are achieved for n-type MCoSb and p-type MFe0.6Co0.4Sb, respectively. The results suggest that the high-entropy concept is a promising strategy to extend the composition range and tune the thermoelectric properties for half-Heusler materials, which could potentially be applied in other thermoelectric materials.
Aortic valve interstitial cells have been implicated in the pathogenesis of aortic stenosis. In response to proinflammatory stimuli, aortic valve interstitial cells undergo an osteogenic phenotypic ...change. The purpose of this study was to determine whether the anti-inflammatory effects of statins prevent osteogenic activity in cultured aortic valve interstitial cells.
Human aortic valve interstitial cells were isolated from hearts explanted for cardiac transplantation. To test whether simvastatin down-regulates TLR4-induced osteogenic response, aortic valve interstitial cells were treated with simvastatin with and without TLR4 agonist lipopolysaccharide (LPS), and osteogenic markers were measured. Simvastatin's influence on in vitro calcium deposition was assessed by alizarin red staining. Knockdown of postreceptor signaling proteins (MyD88 and TRIF) was performed to determine which of 2 TLR4-associated pathways mediates the osteogenic response. Expression levels of TLR4-induced nuclear factor kappa light chain enhancer of activated B cells (NF-κB) and TLR4 expression were assessed after treatment with simvastatin. Statistical testing was done by analysis of variance (P < .05).
Simvastatin decreased LPS-induced ALP and Runx2 expression and inhibited in vitro calcium deposition in aortic valve interstitial cells. Knockdown of MyD88 and TRIF attenuated the osteogenic response. Simvastatin attenuated TLR4-dependent NF-κB signaling and down-regulated TLR4 levels.
Simvastatin prevented TLR4-induced osteogenic phenotypic changes in isolated aortic valve interstitial cells via down-regulation of TLR4 and inhibition of NF-κB signaling. These data offer mechanistic insight into a possible therapeutic role for simvastatin in the prevention of aortic stenosis.
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•Isothermal oxidation of high entropy carbides was studied at 800−1100 °C in air.•Multi-element oxides form in the polycrystalline oxide layer.•Oxide layer shows a through thickness distribution of ...the metals.•Amorphous and compact oxycarbide interlayer acts as an oxygen diffusion barrier.
Isothermal oxidation of (Hf-Ta-Zr-Nb)C high entropy carbide (HEC4) was performed using thermo-gravimetric analysis at 800−1100 °C in air. Polycrystalline oxide layers with multi-element oxides were observed, and their thickness increased with increasing oxidation temperature. Particular attention was paid to the microstructure and role of the interface. An amorphous and compact oxycarbide interlayer was observed between the oxide layer and the bulk carbide in oxidized HEC4, providing an effective diffusion barrier during oxidation. There was a through thickness distribution of the metals in the oxide layer, because of the different oxidation rates and outward diffusion of the cations.
Relaxor ferroelectric ceramics are good candidates for capacitor, sensor and actuator applications because of their high dielectric permittivity, high piezoelectric constant and high value of field ...induced strain, respectively. However, their dielectric loss is usually relatively high, which is a problem for actual applications. The introduction of the high entropy concept opens up the possibility of developing new multi-element relaxor-like ferroelectric materials with short-range ordered polar structures having short relaxation times to decrease their loss. Here we present a new high entropy A-site disordered perovskite (Pb0.25Ba0.25Sr0.25Ca0.25)TiO3 relaxor-like ferroelectric. Moreover, the ceramic has low loss (<0.015) from room temperature to 125 °C. The relaxor-like nature of the material is proved by dielectric and ferroelectric measurements. This work demonstrates the great potential of high entropy perovskites as relaxor-like ferroelectrics with a wide compositional window for tuning their properties for different applications.
CVD-SiC coated and uncoated ceramic matrix composites (Cf/SiC and SiCf/SiC) were joined to their counterparts with a pre-sintered Ti3SiC2 foil using Spark Plasma Sintering. For the first time ...pre-sintered Ti3SiC2 foil was used as a joining filler. The joining parameters were carefully selected to avoid the decomposition of Ti3SiC2 and the reaction between the joining filler and the CVD-SiC coating, which would have deteriorated the oxidation protective function of the coating. Conformal behaviour of the Ti3SiC2 foil during the diffusion joining and the infiltration of the joining filler into the surface cracks in the CVD β-SiC coating allowed the filler to be more integrated with the matrix material. While diffusion bonding occurred during joining of the coated composites, a combination of both solid-state reaction and diffusion bonding was observed for the uncoated Cf/SiC composites. This produced the lower shear strength (19.1MPa) when compared to the diffusion bonded CVD-SiC coated Cf/SiC (31.1MPa).
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