Search

Compositional screening is an important strategy to improve the oxidation resistance of high‐entropy diborides (HEB2), yet the related studies are limited. Here, we report a rare‐earth (RE) element compositional screening strategy to improve the oxidation resistance of HEB2. To be specific, the single‐phase (Hf0.28Zr0.28Ta0.28RE0.16)B2 (HEB2‐RE) samples with 12 different RE elements are fabricated via ultrafast ultrahigh‐temperature synthesis and spark plasma sintering techniques, and their oxidation resistance is explored by isothermal oxidation tests. The results show that the as‐obtained HEB2‐Sc samples possess the best oxidation resistance among all the as‐fabricated HEB2‐RE samples. Such outstanding oxidation resistance is ascribed to the enhanced viscosity of the generated B2O3 glass originating from the solid solution of (Zr, Me)0.84Sc0.16O2 complex oxides, as confirmed by transmission electron microscope observations and first‐principles calculations. [ABSTRACT FROM AUTHOR]

Estimating the synthesizability is the prerequisite to discovering novel high‐entropy ceramics with exotic properties. Herein, combined with the high‐throughput experiments and machine learning (ML) methods, the synthesizability of high‐entropy hexaborides (HEB6) is investigated. To construct the database, 100 equimolar quinary HEB6 samples synthesized using a self‐developed high‐throughput solid‐state reaction technique and 20 potential synthesizability descriptors calculated from fundamental parameters of constituent precursors are simultaneously collected. By employing the ML and the genetic algorithms, an optimal model consisting of five synthesizability descriptors (l¯$\bar{l}$, δl${\delta }_l$, δχP${\delta }_{{\chi }^{\mathrm{P}}}$, δI1${\delta }_{{I}_1}$, and δEF${\delta }_{{E}_{\mathrm{F}}}$) is determined for predicting the synthesizability of equimolar HEB6 with a high validation accuracy (93.0%), and 7 005 new equimolar quinary HEB6 are then proposed. Moreover, the applicability of our established model on non‐equimolar HEB6 is explored by the prediction of 30 synthesizability diagrams of non‐equimolar quinary HEB6. A high accuracy of 90.9% is further validated by the synthesis experiments of 11 non‐equimolar HEB6 candidates. Our work establishes an effective ML model for assessing the synthesizability of both equimolar and non‐equimolar HEB6 and paves a promising way to accelerate the discovery of new synthetic accessible high‐entropy ceramics. [ABSTRACT FROM AUTHOR]

The synthesis of high‐quality nanopowders is crucial to developing high‐performance, high‐entropy rare‐earth silicates (HERESs). Herein, we report the synthesis of HERES nanopowders, including high‐entropy rare‐earth monosilicates (HEREMs) and high‐entropy rare‐earth disilicates (HEREDs), via a simple chemical co‐precipitation method for the first time. By rationally optimizing the synthesis conditions, monoclinic HEREM nanopowders can be well synthesized with highly uniform element distributions. The formation of HEREM nanoparticles is governed by the production of the precursor from the co‐precipitation reactions between rare‐earth hydroxide and silicic acid at the atomic scale, followed by the dehydration of precursor skeletons. Furthermore, the validation of using this approach to prepare HERED nanopowders is also confirmed. This research will open up a new research area in synthesizing HERES nanopowders. [ABSTRACT FROM AUTHOR]

Due to the huge composition space, composition screening is of great importance to the optimization of high‐entropy diborides (HEBs) with exceptional oxidation resistance. However, related studies are lacking. Here, a novel rapid, effective strategy to fully screen the compositions on the oxidation resistance of HEBs is proposed. Specifically, the synthesis of the equiatomic 1‐ to 9‐cation multicomponent diborides of the IVB, VB, and VIB groups in seconds via an ultrafast ultrahigh‐temperature synthesis technique is realized. Subsequently, combined with the thermogravimetric analysis and first‐principles calculations, the roles of incorporated elements are systematically explored. The results show that Zr, Cr, Ta, Nb, and W elements are the key to the improved oxidation resistance of HEBs, while Ti, Mo, and V elements are destructive. In particular, the positive roles of metal elements are mainly attributed to the partial dissolution of the generated metal oxides into the generated B2O3 glass, which can improve the viscosity of B2O3 and thus enhance its high‐temperature stability and reduce the oxygen diffusion rate, as confirmed by the first‐principles calculations. This study paves a way to rapidly screen the elements in HEBs, which can be a guide for further anti‐oxidation designs. [ABSTRACT FROM AUTHOR]

Synthesis of ultrafine powders of high‐entropy rare‐earth silicates (HERESs) is critical for expanding their applications. Here, we report the synthesis of ultrafine HERES powders via a simple molten salt method for the first time. The results show that the single‐phase high‐entropy rare‐earth disilicates (HEREDs) and monosilicates (HEREMs) with monoclinic crystal structures can be successfully synthesized at 1073 and 1173 K, with the content ratios of raw rare‐earth oxides to SiO2 of 1:2.4 and 1:0.9, respectively. The average particle sizes of the as‐synthesized HEREDs and HEREMs powders are measured to be 1.32 and 1.64 μm, respectively. Meanwhile, uniform elemental distributions are confirmed in these powders without any element separation or segregation. In addition, a "dissolution–precipitation" mechanism is proposed to clarify the synthesis process of HERESs. This study not only provides a new synthesis methodology for HERES powders but also reveals a new insight into the growth mode for HERES powders. [ABSTRACT FROM AUTHOR]

The carbon vacancy in high‐entropy carbides (HECs) has a significant impact on their physical and chemical properties, yet relevant studies have still been relatively few. In this study, we investigate the surface energies of HECs with variable carbon vacancies through first‐principles calculations. The results show that the surface energy of the (1 0 0) surface of the stoichiometric HECs is significantly lower than that of (1 1 1) surface. With the decrease in carbon stoichiometry, the surface energies of both (1 0 0) and (1 1 1) surfaces increase gradually, which is mainly due to the weakening of covalent bonding and the decrease of metal Hirshfeld‐I (HI) charges. However, the surface energy of (1 0 0) surface increases more quickly than that of (1 1 1) surface and will exceed that of (1 1 1) surface when the carbon stoichiometry decreases to a certain extent, which is primarily attributed to the greater decrease rate of metal HI charges of (1 0 0) surface. [ABSTRACT FROM AUTHOR]

The nanocrystalline (Hf0.25Zr0.25Ta0.25Ti0.25)C high‐entropy carbide ceramics were successfully prepared through high‐pressure sintering of the self‐synthesized nanopowders for the first time. The results showed that the relative density, grain size, hardness, and elastic modulus of all the as‐prepared samples increased gradually with the increase of sintering temperatures from 1200 to 1600°C. The as‐fabricated samples at 1600°C possessed a relative density of 97.1% and a mean grain size of 98 ± 35 nm and simultaneously exhibited good comprehensive mechanical properties with Vickers hardness of 25.7 ± 0.6 GPa and fracture toughness of 4.3 ± 0.4 MPa·m1/2 at room temperature due to the grain refinement strengthening mechanism and microcrack deflection and bridging toughening mechanism. In addition, they showed a linear decrease in high‐temperature Vickers hardness with the increase of the temperature from room temperature to 1000°C, which was determined by the combined effects of the intrinsic softening of HEC‐1 ceramics at elevated temperature and the presence of ZrO2 impurity phase at the grain boundaries. [ABSTRACT FROM AUTHOR]

Herein the ultrafine‐grained (Hf0.2Zr0.2Ta0.2Nb0.2Ti0.2)B2 high‐entropy diboride ceramics were successfully fabricated by high‐pressure sintering technology for the first time. The results showed that the grain size, relative density, and Vickers hardness of the as‐fabricated samples all increased gradually with increasing sintering temperatures from 1373 K to 1973 K. The relative density and mean grain size of the as‐sintered samples at 1973 K were 97.2% and 684 nm, respectively, and simultaneously they exhibited excellent comprehensive mechanical properties, combining a Vickers hardness of 26.2 GPa and a fracture toughness of 5.3 MPa·m1/2, which were primary attributed to the fine grain strengthening mechanism and microcrack deflection toughening mechanism. [ABSTRACT FROM AUTHOR]

In this work, a novel (Hf0.2Zr0.2Ta0.2Nb0.2Ti0.2)(N0.5C0.5) high‐entropy nitride‐carbide (HENC‐1) with multi‐cationic and ‐anionic sublattice structure was reported and their thermophysical and mechanical properties were studied for the first time. The results of the first‐principles calculations showed that HENC‐1 had the highest mixing entropy of 1.151R, which resulted in the lowest Gibbs free energy above 600 K among HENC‐1, (Hf0.2Zr0.2Ta0.2Nb0.2Ti0.2)N high‐entropy nitrides (HEN‐1), and (Hf0.2Zr0.2Ta0.2Nb0.2Ti0.2)C high‐entropy carbides (HEC‐1). In this case, HENC‐1 samples were successfully fabricated by hot‐pressing sintering technique at the lowest temperature (1773 K) among HENC‐1, HEN‐1 and HEC‐1 samples. The as‐fabricated HENC‐1 samples showed a single rock‐salt structure of metal nitride‐carbides and high compositional uniformity. Meanwhile, they exhibited high microhardness of 19.5 ± 0.3 GPa at an applied load of 9.8 N and nanohardness of 33.4 ± 0.5 GPa and simultaneously possessed a high bulk modulus of 258 GPa, Young's modulus of 429 GPa, shear modulus of 176 GPa, and elastic modulus of 572 ± 7 GPa. Their hardness and modulus are the highest among HENC‐1, HEN‐1 and HEC‐1 samples, which could be attributed to the presence of mass disorder and lattice distortion from the multi‐anionic sublattice structure and small grain in HENC‐1 samples. In addition, the thermal conductivity of HENC‐1 samples was significantly lower than the average value from the "rule of mixture" between HEC‐1 and HEN‐1 samples in the range of 300‐800 K, which was due to the presence of lattice distortion from the multi‐anionic sublattice structure in HENC‐1 samples. [ABSTRACT FROM AUTHOR]

Powder synthesis is critical for implementing the wide applications of high‐entropy diborides (HEBs). However, the low‐temperature synthesis of HEB powders was rarely reported. Herein, the low‐temperature synthesis of the single‐phase HEB nanopowders via molten salt‐mediated magnesiothermic reduction (MMR) method was reported for the first time. The results showed that the as‐synthesized nanopowders consisted of the single‐phase HEBs and their average particle sizes are in the range of 28‐56 nm. Meanwhile, they possessed the good compositional homogeneity and the low‐content oxygen impurity in the range of 4.13‐6.12 at%. In addition, their formation mechanism could be well interpreted by a classical MMR growth process. [ABSTRACT FROM AUTHOR]

Polymer‐derived ceramic (PDC) route has been widely used to fabricate various ceramics or ceramic‐matrix composites in recent years. However, the synthesis of high‐entropy ceramics via PDC route has rarely been reported until now. Herein, we successfully synthesized a class of high‐entropy carbides, namely (Hf0.25Nb0.25Zr0.25Ti0.25)C (HEC‐1), via PDC route. The polymer‐derived HEC‐1 ceramics consisted of numerous superfine particles with the average particle size ~800 nm. Meanwhile, they possessed a rock‐salt structure of metal carbides and high‐compositional uniformity from nanoscale to microscale. In addition, the as‐obtained HEC‐1 ceramics had a low oxygen impurity content of 0.51% and a low free carbon impurity content of 2.56%. This work will open up a new research field on the fabrication of high‐entropy ceramics or high‐entropy ceramic‐matrix composites via PDC route. [ABSTRACT FROM AUTHOR]

The polymer‐derived‐ceramic (PDC) route has been widely used to fabricate the transition‐metal carbides (TMCs). Previously reported works focused mainly on the synthesis of the single or binary TMCs, while the synthesis of the ternary or more component TMCs was rarely reported. Herein, a class of the ternary TMCs, namely (Nb1/3Zr1/3Ta1/3)C solid‐solution ceramics, was successfully synthesized via PDC route for the first time. The as‐synthesized ceramics exhibited the particle‐like morphology with an average particle size of ~250 nm and showed a single rock‐salt crystal structure of metal carbides. At the same time, they had high compositional uniformity from nanoscale to microscale. In addition, they possessed low‐oxygen impurity content of 0.79 wt% and moderate‐carbon impurity content of 8.98 wt%. Such work provides a novel route to fabricate the ternary or more component TMCs. [ABSTRACT FROM AUTHOR]

Establishing the formation criterion is urgent for accelerating the discovery and design of solid‐solution materials with desirable properties. The previously reported formation criterion mainly focused on solid‐solution alloys, while the formation criterion was rarely established in solid‐solution ceramics. To solve this problem, herein, we take a class of solid‐solution ceramics, namely binary metal diboride ((MxN1‐x)B2) solid solutions, as a prototype. Through combinatorial methods including high‐throughput molten salt syntheses and high‐throughput first‐principles calculations combined with the machine learning approach, the correlation between influential factors, including atomic size difference (δ), mixing enthalpy at 0 K and 0 Pa (ΔHmix0K), doping condition (φ), and valence electron concentration (VEC), and the formation ability of (MxN1‐x)B2 solid solutions was first studied systematically, and then their formation criterion was well established. The results showed that the influential degree of the aforementioned four factors on the formation ability of (MxN1‐x)B2 solid solutions could be described as follows: δ > ΔHmix0K> φ > VEC. In addition, a newly proposed parameter, β, could well reflect the formation ability of (MxN1‐x)B2 solid solutions: when β > 0, the single‐phase (MxN1‐x)B2 solid solutions could be successfully synthesized in our work and vice versa. This study may provide a theoretical guidance in the discovery and design of various solid‐solution ceramics, such as the metal borides, carbides, nitrides, etc, with desirable properties. [ABSTRACT FROM AUTHOR]

Synthesis of the powders is critical for achieving the extensive applications of high‐entropy carbides (HECs). Previously reported studies focus mainly on the high‐temperature (>2000 K) synthesis of HEC micro/submicropowder, while the low‐temperature synthesis of HEC nanopowders is rarely studied. Herein we reported the low‐temperature synthesis of HEC nanopowders, namely (Ta0.25Nb0.25Ti0.25V0.25)C (HEC‐1), via molten salt synthesis for the first time. The synthesis possibility of HEC‐1 nanopowders was first theoretically demonstrated by analyzing lattice size difference and chemical reaction thermodynamics based on the first‐principle calculations, and then the angular HEC‐1 nanopowders were successfully synthesized via molten salt synthesis at 1573 K. The as‐synthesized nanopowders possessed the single‐crystal rock‐salt structure of metal carbides and high compositional uniformity from nanoscale to microscale. In addition, their formation mechanism was well interpreted by a classical molten salt‐assisted growth. [ABSTRACT FROM AUTHOR]

Diabetic complications cause significant morbidity and mortality. Dysfunction of vascular endothelial cells (ECs), caused by oxidative stress, is a main mechanism of cellular damage. Oxidative stress accelerates EC senescence and DNA damage. In this study, we examined the role of mitochondrial sirtuins (SIRTs) in glucose‐induced oxidative stress, EC senescence, and their regulation by miRNAs. Human retinal microvascular endothelial cells (HRECs) were exposed to 5 mmol/L (normoglycemia; NG) or 25 mmol/L glucose (hyperglycemia; HG) with or without transfection of miRNA antagomirs (miRNA‐1, miRNA‐19b, and miRNA‐320; specific SIRT‐targeting miRNAs). Expressions of SIRT3, 4 and 5 and their targeting miRNAs were examined using qRT‐PCR and ELISAs were used to study SIRT proteins. Cellular senescence was investigated using senescence‐associated β‐gal stain; while, oxidative stress and mitochondrial alterations were examined using 8‐OHdG staining and cytochrome B expressions, respectively. A streptozotocin‐induced diabetic mouse model was also used and animal retinas and hearts were collected at 2 months of diabetes. In HRECs, HG downregulated the mRNAs of SIRTs, while SIRT‐targeting miRNAs were upregulated. ELISA analyses confirmed such downregulation of SIRTs at the protein level. HG additionally caused early senescence, endothelial‐to‐mesenchymal transition and oxidative DNA damage in ECs. These changes were prevented by the transfection of specific miRNA antagomirs and by resveratrol. Retinal and cardiac tissues from diabetic mice also showed similar reductions of mitochondrial SIRTs. Collectively, these findings demonstrate a novel mechanism in which mitochondrial SIRTs regulate glucose‐induced cellular aging through oxidative stress and how these SIRTs are regulated by specific miRNAs. Identifying such mechanisms may lead to the discovery of novel treatments for diabetic complications. [ABSTRACT FROM AUTHOR]

High‐entropy metal carbides have recently been arousing considerable interest. Nevertheless, their high‐temperature oxidation behavior is rarely studied. Herein the high‐temperature oxidation behavior of (Hf0.2Zr0.2Ta0.2Nb0.2Ti0.2)C high‐entropy metal carbide (HEC‐1) was investigated at 1573‐1773 K in air for 120 minutes. The results showed that HEC‐1 had good oxidation resistance and its oxidation obeyed a parabolic law at 1573‐1673 K, while HEC‐1 was completely oxidized after isothermal oxidation at 1773 K for 60 minutes and thereby its oxidation followed a parabolic‐linear law at 1773 K. An interesting triple‐layered structure was observed within the formed oxide layer at 1673 K, which was attributed to the inward diffusion of O2 and the outward diffusion of Ti element and CO or CO2 gaseous products. [ABSTRACT FROM AUTHOR]

Synthesis of high‐purity high‐entropy metal diboride powders is critical to implementing their extensive applications. However, the related studies are rarely reported. Herein we first theoretically studied the synthesis possibility of high‐purity high‐entropy diboride powders, namely (Hf0.25Ta0.25Nb0.25Ti0.25)B2 (HTNTB), via boro/carbothermal reduction by analyzing the thermodynamics of the possible chemical reactions and then successfully synthesized the high‐purity and superfine HTNTB powders via boro/carbothermal reduction for the first time. The as‐prepared powders exhibited low‐oxygen impurity content of 0.49 wt% and small average particle size of 260 nm. Meanwhile, they possessed good single‐crystal hexagonal structure of metal diborides and high‐compositional uniformity from nanoscale to microscale. This work will open up a new research field on the synthesis of high‐purity high‐entropy metal diboride powders. [ABSTRACT FROM AUTHOR]

Dense ZrB2‐SiC‐Al3BC3 ultra‐high temperature ceramic composite was fabricated by hot pressing sintering at 1900°C for 1 hour under a pressure of 20 MPa using Zirconium diboride (ZrB2) as the raw material and a powder mixture of SiC, B4C, Al, and carbon as the sintering additive. Al and B4C underwent in situ reaction with carbon powder to produce Al3BC3, which promoted the densification of ZrB2 ceramic. SiC grains were found to be elongated during sintering. The ZrB2‐SiC‐Al3BC3 composite exhibited excellent mechanical properties, such as high flexural strength of 589 ± 147 MPa and fracture toughness of 7.81 ± 1.09 MPa m1/2. Oxidation behavior of the ZrB2‐SiC‐Al3BC3 composite was studied in air at 1500°C for 1 hour. A continuous layer of oxides consisting of a mixture of SiO2, Al2SiO5, and Al2O3 was formed on the surface of the ZrB2‐SiC‐Al3BC3 composite. This layer of oxides efficiently prevented oxygen from diffusing into the specimens during oxidation, which improved the oxidation resistance of the ZrB2 ceramics. [ABSTRACT FROM AUTHOR]

The synthesis of high‐entropy metal carbide powders is critical for implementing their extensive applications. However, the one‐step synthesis of high‐entropy metal carbide powders is rarely studied. Herein, the synthesis possibility of high‐entropy metal carbide powders, namely (Zr0.25Ta0.25Nb0.25Ti0.25)C (ZTNTC), via one‐step carbothermal reduction was first investigated theoretically by analyzing chemical thermodynamics and lattice size difference based on the first‐principle calculations, and then the ZTNTC powders with particle size of 0.5‐2 μm were successfully synthesized experimentally. The as‐synthesized powders not only had a single rock‐salt crystal structure of metal carbides, but also possessed high‐compositional uniformity from nanoscale to microscale. More interestingly, they exhibited the distinguished coral‐like morphology with the hexagonal step surface, whose growth was governed by a classical screw dislocation growth mechanism. [ABSTRACT FROM AUTHOR]

The synthesis of the multi‐component transition‐metal diboride (MeB2) solid‐solution powders has been recently attracting considerable attentions. However, the synthesis of the ternary or more component MeB2 solid‐solution powders has rarely been reported until now. To fabricate the ternary MeB2 solid‐solution powders, herein we utilized two kinds of the ternary MeB2 solid solutions as prototypes, namely (Hf1/3Zr1/3Ti1/3)B2 (HZTB) and (Ta1/3Nb1/3Ti1/3)B2 (TNTB). The formation possibility of HZTB and TNTB was first analyzed by the first‐principles calculations and then we attempted of fabricated them by a simple molten salt synthesis technique. The first‐principles calculations results showed that the mixing Gibbs free energy at room temperature and lattice size difference at 0 K of HZTB and TNTB were (1.666 kJ/mol and 3.146%) and (−3.030 kJ/mol and 1.254%), respectively. This suggested that TNTB solid solution was more prone to being fabricated than HZTB solid solution. The experimental results showed the high purity TNTB solid‐solution nanopowders were successfully synthesized by the molten salt synthesis technique at 1373 K with 30% excessive B as precursors while the HZTB solid solution was not able to be synthesized by the molten salt synthesis technique. The as‐synthesized TNTB solid‐solution nanopowders exhibited the distinguished nanorod morphology with the diameters of 20‐40 nm and lengths of 100‐200 nm. Meanwhile, they possessed the good single‐crystal hexagonal structure and high compositional uniformity from nanoscale to microscale. In addition, their formation mechanism associated to the possible chemical reactions was well interpreted by the thermodynamics analysis. [ABSTRACT FROM AUTHOR]

The formation possibility of (Hf0.2Zr0.2Ta0.2Nb0.2Ti0.2)C high‐entropy ceramic (HHC‐1) was first analyzed by the first‐principles calculations, and then, it was successfully fabricated by hot‐pressing sintering technique at 2073 K under a pressure of 30 MPa. The first‐principles calculation results showed that the mixing enthalpy and mixing entropy of HHC‐1 were −0.869 ± 0.290 kJ/mol and 0.805R, respectively. The experimental results showed that the as‐prepared HHC‐1 not only had an interesting single rock‐salt crystal structure of metal carbides but also possessed high compositional uniformity from nanoscale to microscale. By taking advantage of these unique features, it exhibited extremely high nanohardness of 40.6 ± 0.6 GPa and elastic modulus in the range from 514 ± 10 to 522 ± 10 GPa and relatively high electrical resistivity of 91 ± 1.3 μΩ·cm, which could be due to the presence of solid solution effects. [ABSTRACT FROM AUTHOR]

High‐purity superfine (HfxZr1‐x)B2 solid‐solution powders with various chemical compositions (x = 0.2, 0.5, and 0.8) were successfully synthesized via molten salt synthesis technique at 1423 K using ZrO2, HfO2, and 20% excessive B as precursors within a KCl/NaCl molten salt for the first time. The results showed that the as‐synthesized solid‐solution powders exhibited the irregular polyhedral morphology with the average particle sizes of 170–185 nm and simultaneously possessed a single‐crystalline hexagonal structure and good compositional uniformity from nanoscale to microscale. In addition, their formation mechanisms were well interpreted by analyzing the thermodynamics of the possible chemical reactions in the molten salt. [ABSTRACT FROM AUTHOR]

A series of (Pr, Ce)‐ZrSiO4 ceramic pigments were synthesized and characterized using XRD, SEM, EDS, XPS, XRF, colorimeter, and a UV‐VIS‐NIR spectrometer. The prepared pigments were mainly composed of the zircon phase and were well crystallized. Only a specific amount of Pr was incorporated into the ZrSiO4 lattice. Compared with Pr, Ce was almost completely incorporated into the ZrSiO4 lattice and was homogeneously distributed within the pigment particles. The dopant Ce reduced the amount of Pr dissolved in the ZrSiO4 lattice and thus caused the b* values of the samples to decrease slightly. Meanwhile, the presence of Ce induced an apparent increase in red tone in the samples. The enhanced red tone resulted primarily from an increase in the absorption of light with wavelengths between 500 and 565 nm. High‐temperature stability analysis demonstrated that it is feasible to improve the tone of Pr‐ZrSiO4 pigment by doping with Ce. [ABSTRACT FROM AUTHOR]

(Zr1/3Nb1/3Ti1/3)C metal carbide solid‐solution ceramic has been successfully fabricated by hot pressing sintering at 2473 K using ZrC, NbC, and TiC powders as raw materials. The results show that the as‐prepared solid‐solution ceramic possesses a single rock‐salt crystal structure of metal carbides and simultaneously exhibits high compositional uniformity from nanoscale to microscale. By taking advantage of these unique features, it shows relatively high hardness of 38.8 ± 4.4 Gpa and elastic modulus of 481.8 ± 31.0 Gpa and relatively low thermal conductivity of 17.1 ± 0.3 W/(m·K) and thermal diffusivity of 6.1 ± 0.1 mm2/s, which may attribute primarily to the presence of solid solution effects. [ABSTRACT FROM AUTHOR]

Abstract: The synthesis of TiB2 nanopowders arouses considerable interests due to its importance for implementing the extensive applications of TiB2 ceramic. Herein, the high‐purity ultrafine TiB2 nanopowders were successfully synthesized via a molten salt assisted borothermal reduction technique at a relatively low temperature of 1173 K using TiO2 and B powders as precursors within a KCl/NaCl salt. The results showed that the as‐obtained TiB2 nanopowders possessed a polycrystallinity structure, and their specific surface area and equivalent average particle size were 33.18 m2/g and 40 nm, respectively. This study provides a new low temperature synthesis technique of TiB2 nanopowders. [ABSTRACT FROM AUTHOR]

Production of excessive transforming growth factor‐beta 1 (TGF‐β1) with elevated TGF‐β1 activity has been implicated in renal fibrosis via renal epithelial cells activation and collagen deposition. As such, attenuating the binding of TGF‐β1 to its receptor TGF‐beta receptor type II (TGF‐βRII) in TGF‐β1‐dependent signaling is an attractive target for the control of renal fibrosis. Here, we verified the interaction between novel truncated human TGF‐βRII (thTβRII, Thr23‐Gln166) and TGF‐β1, prepared thTβRII in Escherichia coli, and assessed the effects of thTβRII on TGF‐β1‐induced human kidney epithelial cells (HK‐2) and unilateral ureteral obstruction (UUO) model of renal fibrosis. Our data showed that thTβRII accounted for up to 20% of the total protein and 40% of the inclusion bodies of whole cell lysates under the optimal conditions (0.8 mM IPTG and 25°C for 6 H). Most of the expressed protein in inclusion body was refolded by dialysis refolding procedures and purified by Ni2+‐IDA affinity chromatography. Furthermore, thTβRII decreased type I collagen and α‐smooth muscle actin protein expression in TGF‐β1‐induced HK‐2 cells, and ameliorated kidney morphology and fibrotic responses in fibrosis animal. These findings indicate that thTβRII holds great promise for developing new treatments for renal fibrosis. [ABSTRACT FROM AUTHOR]

Abstract: High‐purity Ti0.2Zr0.8B2 solid‐solution nanopowders were successfully synthesized via a molten salt assisted borothermal reduction at 1323‐1373 K using ZrO2, TiO2 and amorphous B as starting materials. The Ti0.2Zr0.8B2 solid‐solution nanopowders synthesized at 1323 K show the largest specific surface area of 12.24 m2/g and the lowest equivalent average particle size of 86 nm. Meanwhile, they exhibit the high compositional uniformity and the good single‐crystal hexagonal structure. This study provides a new method to synthesize the high‐purity solid‐solution nanopowders of the transition‐metal borides. [ABSTRACT FROM AUTHOR]

We numerically predict the microstructure properties of ceramic membranes and the coupling effects of microstructure properties and layer thickness on the strength and permeance of ceramic membranes. It is found that particle size is the most important factor, followed by thickness and finally by microstructure parameters. The general design principle for strength and permeance are [ABSTRACT FROM AUTHOR]

To protect the carbon/carbon (C/C) composites from oxidation, an outer ultra-high-temperature ceramics ( UHTCs) HfB2-SiC coating was prepared on SiC-coated C/C composites by in situ reaction method. The outer HfB2-SiC coating consists of HfB2 and SiC, which are synchronously obtained. During the heat treatment process, the formed fluid silicon melt is responsible for the preparation of the outer HfB2-SiC coating. The HfB2-SiC/SiC coating could protect the C/C from oxidation for 265 h with only 0.41 × 10−2 g/cm2 weight loss at 1773 K in air. During the oxidation process, SiO2 glass and HfO2 are generated. SiO2 glass has a self-sealing ability, which can cover the defects in the coating, thus blocking the penetration of oxygen and providing an effective protection for the C/C substrate. In addition, SiO2 glass can react with the formed HfO2, thus forming the HfSiO4 phase. Owing to the 'pinning effect' of HfSiO4 phase, crack deflecting and crack termination are occurred, which will prevent the spread of cracks and effectively improve the oxidation resistance of the coating. [ABSTRACT FROM AUTHOR]

Single crystal 6 H- SiC nanoribbons were in situ synthesized in large scale on the as-prepared SiC- Si ceramic substrates via a facile heat-treatment approach using ferrocene as catalyst. The as-synthesized nanoribbons were up to several millimeters long, with widths of 200-300 nm and thicknesses of 20-80 nm. A novel combination growth mechanism of vapor-liquid-solid-based and vapor-solid-tip was proposed for the growth mode of the as-synthesized nanoribbons. This study provided not only a new method for synthesizing SiC nanoribbons but also a new insight into the growth mode for SiC nanoribbons. [ABSTRACT FROM AUTHOR]

Large-scale ultra-long 6 H- SiC nanowires were in situ synthesized on the as-prepared SiC- Si ceramic substrate using graphite as the carbon source and substrate as the silicon source via improving the adsorbed O2 content on the graphite precursors using milling technology. The as-grown nanowires were typical single crystal of hexagonal 6 H- SiC with diameters of 50-100 nm and lengths of up to several millimeters (or even centimeters). Vapor-solid mechanism was proposed for the growth mode of the as-grown ultra-long 6 H- SiC nanowires. This study not only provided new insight into the growth mode for in situ synthesizing 6 H- SiC nanowires on silicon-based ceramics, but also suggested a new design methodology for synthesizing ultra-long nanowires. [ABSTRACT FROM AUTHOR]

Improving the SiC- Si/ MAS interface is essential for enhancing the SiC- Si/ MAS joint strength. In this work, well-dispersed SiC nanowires (NWs) were in situ synthesized at the SiC- Si/ MAS interface in the joints as the anchors, which made the fracture feature of the joints change from SiC- Si/ MAS interface fracture to MAS fracture, resulting in an obvious improvement of the shear strength. The results showed that the average shear strength of the joints was increased by 49% by in situ synthesizing SiC NWs, which was primarily attributed to the excellent interface anchoring effects of SiC NWs involving the interfacial bonding anchoring between SiC NWs and SiC- Si layer and the mechanical interlocking anchoring between SiC NWs with the junctions and the surrounding grains. This study may provide new insight into the anchoring mechanisms and suggest a new design methodology for nanowire joints, leading to improved joint strength. [ABSTRACT FROM AUTHOR]

A dense oxidation protective SiC- Si ceramic coating with well-dispersion SiC nanowires was prepared on carbon/carbon ( C/ C) composites using a two-step technique consisting of chemical vapor deposition and hot-pressing reactive sintering. The results showed that the toughness and thermal shock resistance of the coating were dramatically improved, resulting in an excellent oxidation protection for the coated C/ C composites, which is attributed primarily to the toughening effects of SiC nanowires in the coating including two special energy dissipation mechanisms involving the super-plasticity deformation of SiC nanowires and the plastic fracture at the interface of the nanowire-matrix, except for nanowire pullout, nanowire bridging, and microcrack deflection. More importantly, a novel oxidation protective failure mechanism of the coated C/ C composites revealed that the presence of Al3+ in the coating, damaged the network structure of SiO2 glass and resulted in the slight oxidation of C/ C composites. [ABSTRACT FROM AUTHOR]

Revealing the hardening mechanisms is crucial for facilitating the design of superhard high‐entropy borides. Taking high‐entropy diborides (HEB2) as the prototype, the hardening mechanisms of high‐entropy borides are thoroughly investigated. Specifically, the equiatomic 4—9‐cation single‐phase HEB2 ceramics (4—9HEB2) are fabricated by an ultra‐fast high‐temperature sintering method. The experimental results show that the hardness of the as‐fabricated 4—9HEB2 samples has an increasing tendency with the increase of metal components. With a combination of first‐principles calculations, machine‐learning‐potential‐based molecular dynamics simulations, and scanning transmission electron microscopy characterizations, lattice distortion is explicitly identified to be essential in hardening HEB2 by increasing strain field fluctuation, enlarging atomic strain energy, and strengthening B─B bonds. The results unravel the hardening mechanisms of HEB2 by intensifying lattice distortion, providing fascinating guidance for developing superhard high‐entropy borides. [ABSTRACT FROM AUTHOR]

This work presents the exploration of a promising thermal environmental barrier coating material by engineering the compositions of (Ho1/4Er1/4Dy1/4X1/4)2Si2O7 high‐entropy rare‐earth disilicates (HERED‐X, X = Gd, Tm, Yb, Lu, Sc, Y). Among all the samples, the as‐fabricated HERED‐Gd samples possess the best CMAS corrosion resistance with a corrosion rate of 8.2 ± 0.14 µm h−1 at 1673 K, which is attributed to the synergistic effects of high chemical reactivity of HERED‐Gd and good stability of the formed apatite in CMAS melt. Moreover, they demonstrate a matched coefficient of thermal expansion (4.6 × 10−6 K−1) with SiCf/SiC composites (4.5–5.5 × 10−6 K−1) and a low thermal conductivity (1.89 W m−1 K−1 at room temperature). [ABSTRACT FROM AUTHOR]

Production of excessive transforming growth factor-beta 1 (TGF-β1) with elevated TGF-β1 activity has been implicated in renal fibrosis via renal epithelial cells activation and collagen deposition. As such, attenuating the binding of TGF-β1 to its receptor TGF-beta receptor type II (TGF-βRII) in TGF-β1-dependent signaling is an attractive target for the control of renal fibrosis. Here, we verified the interaction between novel truncated human TGF-βRII (thTβRII, Thr23-Gln166) and TGF-β1, prepared thTβRII in Escherichia coli, and assessed the effects of thTβRII on TGF-β1-induced human kidney epithelial cells (HK-2) and unilateral ureteral obstruction (UUO) model of renal fibrosis. Our data showed that thTβRII accounted for up to 20% of the total protein and 40% of the inclusion bodies of whole cell lysates under the optimal conditions (0.8 mM IPTG and 25°C for 6 H). Most of the expressed protein in inclusion body was refolded by dialysis refolding procedures and purified by Ni 2+ -IDA affinity chromatography. Furthermore, thTβRII decreased type I collagen and α-smooth muscle actin protein expression in TGF-β1-induced HK-2 cells, and ameliorated kidney morphology and fibrotic responses in fibrosis animal. These findings indicate that thTβRII holds great promise for developing new treatments for renal fibrosis., (© 2018 International Union of Biochemistry and Molecular Biology, Inc.)