Search

The novel microwave dielectric ceramic EuNbO 4 with monoclinic structure (PDF # 22-1099) was synthesized using the conventional solid-state reaction process. X-ray diffraction and Rietveld refinement were employed to investigate the phase compositions and crystal parameters. Combined with the refinement results, the structure-property relationship was analyzed using the chemical bonds theory of complex crystals. The surface microtopography was characterized using scanning electric microscope, and the dense and homogeneous microstructures could be observed at EuNbO 4 ceramic sintered at 1125 °C. Infrared reflectivity spectra indicated the absorption of structural phonon oscillation might be the main contribution to polarization for EuNbO4 ceramic. The optimal dielectric properties with ε r = 19.1, Q × f = 15,014 GHz, and τ f = −16.42 ppm/°C were achieved in EuNbO 4 ceramic sintered at 1125 °C. [ABSTRACT FROM AUTHOR]

The single-phase of Ce 2 [Zr 1- x (Ba 1/3 Sb 2/3) x ] 3 (MoO 4) 9 (x = 0.01 ∼ 0.10) (CZBS x M) ceramics were synthesized by the classic solid-state route successfully. The influence of (Ba 1/3 Sb 2/3)4+ replacement for Zr4+ on the lattice parameters, microstructure, chemical bonds and dielectric properties were discussed comprehensively. The X-ray diffraction (XRD) indicated that the CZBS x M ceramics are trigonal-type crystal structure with R-3c space group. The lattice parameters of CZBS x M ceramics were obtained via the Rietveld refinement method. The theory of complex crystals chemical bonds (P-V-L theory) was carried out to study the connections between the chemical bond and dielectric properties. The excellent dielectric properties (ɛ r = 10.71, Q×f = 91,798 GHz and τ f = −15.18 ppm/℃) were obtained at 700 ℃ in CZBS 0.02 M ceramic. [Display omitted] • The effects of (Ba 1/3 Sb 2/3)4+ substitution for Zr4+ on dielectric properties in Ce 2 Zr 3 (MoO 4) 9 was discussed by P-V-L theory. • The Q × f value of Ce 2 Zr 3 (MoO 4) 9 ceramic was increased by more than 3.5 times via doping of (Ba 1/3 Sb 2/3)4+ ions. • The optimum microwave dielectric properties (ɛr = 10.71, Q×f = 91,798 GHz, τf = −15.18 ppm/℃) were obtained at x = 0.02. [ABSTRACT FROM AUTHOR]

In this study, Zn 8 B 3 H 3 O 14 nanosheets were synthesized through a one-step coprecipitation process and employed as both a boron source and substrate templates for the fabrication of boron nitride nanosheets (BNNSs), which were synthesized efficiently at low temperatures by the borate nitration method using ammonia as the nitrogen source. The thickness of the synthesized BNNSs ranged from 3 to 10 nm with a flake dimension of about 2.56 μm. The prepared BNNSs using this method realized 98.8% boron source utilization and single batch yields up to gram level. In addition, BNNSs/SiO 2 microwave-transparent composites were prepared to investigate the potential for large-scale applications of the BNNSs produced by using this method. The composites demonstrated a remarkable increase in bending strength and fracture toughness, reaching 122.02 MPa and 2.31 MPa·m1/2, respectively, with the addition of only 0.5 wt% BNNSs. Compared with SiO 2 without BNNSs, the fracture toughness of the composites is increased by 106%. A novel crack plugging strong toughening mechanism of BNNSs is proposed. Simultaneously, the composites exhibit exceptional microwave-transparent properties, with dielectric constants below 4 in the real part and below 0.03 in the imaginary part. Therefore, this study has successfully achieved the low-temperature and efficient synthesis of micron-scale BNNSs, laying the groundwork for their large-scale application. [Display omitted] • Zn 8 B 3 H 3 O 14 nanosheets were used as substrate templates for the synthesis of BNNSs. • BNNSs were synthesized with high efficiency at low temperatures (900 °C). • The single batch yield of BNNSs reached up to the gram level. • The BNNSs/SiO 2 wave-transparent composites with ultrahigh toughness were obtained. • A novel mechanism for strengthening and toughening (BNNSs plugging) is proposed. [ABSTRACT FROM AUTHOR]

The aim of achieving integration of lightweight, high strength, high‐temperature resistant, and satisfactory electromagnetic (EM) wave absorption was successfully accomplished in the present study by synthesizing TiC–TiB2 fibers reinforced Si3N4 composites, which were pressureless sintered at 1650°C for 2 h. The preparation of TiC–TiB2 fibers was conducted through a chloride‐assisted carbothermic method. This work focused on investigating the effects of incorporating TiC–TiB2 fibers on the mechanical properties and EM wave absorption characteristics of the composites. The 30 wt% TiC–TiB2/Si3N4 composite displayed the bulk density of 1.89 g/cm3, bending strength of 93.11 ± 3.91 MPa, fracture toughness of 1.81 ± 0.10 MPa m1/2, minimum reflection loss of −38.87 dB, and effective absorption bandwidth of 1.43 GHz in the Ku‐band, respectively. The as‐synthesized TiC–TiB2/Si3N4 composites are promising candidates for EM wave absorbing load‐bearing materials due to their outstanding mechanical properties and microwave absorption properties. [ABSTRACT FROM AUTHOR]

Compared with common monoanionic high entropy ceramics, polyanionic high entropy ceramics, with better performance, are more difficult to prepare. Since transition metal carbides have high hardness and transition metal nitrides have good toughness, it is hoped that high entropy carbonitride ceramics can combine the advantages of the two. In this paper, a series of novel (Ti 0.25 Nb 0.25 Hf 0.25 Ta 0.25)C x N 1–x (x = 0.3, 0.4, 0.5, 0.6, and 0.7) high entropy ceramics were successfully synthesized for the first time using spark plasma sintering at 1850 °C with metal carbides and metal nitrides as raw materials. The phase evolution, microstructure, hardness and fracture toughness of high carbonitride entropy ceramics were investigated. X-ray diffraction indicates the ceramics with the single-phase face-centered cubic structure were successfully prepared. It was found that the high entropy ceramics sintered at 1850 °C with four cationic components have excellent performance on fracture toughness (KIC = 7.1746 MPa m1/2). With the increase of carbide proportion, the hardness of the ceramics increased, but the fracture toughness and bending strength decreased slightly. And it was found that the differences of grain size and porosity content were the main reasons for the mechanical properties difference. The excellent hardness properties, good bending strength and outstanding fracture toughness of the high entropy ceramics provide the possibility for the application of high entropy ceramics in aerospace and other applications requiring high performance. [ABSTRACT FROM AUTHOR]

The relationship between the chemical elements of high-entropy boride (HEB) ceramics and their hardness is important for the prediction of high-hardness HEB ceramics. In this work, by designing four HEB ceramics with different chemical elements, the effect of lattice parameter difference factor (δ, represents the difference-degree in lattice parameters among the five individual constitute diborides) on phase composition and lattice-distortion, and the effect of rule of mixture (ROM) average hardness and lattice-distortion on HEB ceramics hardness were studied. The results indicated that, as δ value increases, more severe lattice-distortion occurs inside the HEB ceramics, and a single solid-solution is difficult to be formed. Furthermore, lattice-distortion and the ROM average hardness codetermine the HEB ceramics hardness. The greater lattice-distortion brings about significantly higher hardness for HEB ceramics than their ROM average hardness. Among the four HEBs, (Hf 0.2 Zr 0.2 Ta 0.2 V 0.2 Nb 0.2)B 2 exhibits the high hardness of 26 GPa measured using a load of 9.8 N. [ABSTRACT FROM AUTHOR]

The TiB 2 fibers were prepared by a chloride-assisted carbothermic method accompanied with the vapor-liquid-solid (VLS) mechanism. The influences of TiO 2 , B 2 O 3 , C 12 H 22 O 11 , and calcination temperature on the yield of TiB 2 fibers were investigated. In addition, the effects of TiB 2 fibers content on the electromagnetic (EM) parameters and microwave absorption (MA) properties of TiB 2 fibers/paraffin composite was studied in detail. The TiB 2 fibers/paraffin composite showed excellent microwave absorption performance, with an optimized reflection loss (RL) of −46.63 dB at 14 GHz and a thickness of 1.5 mm. Moreover, it exhibited a broad effective absorption bandwidth (EAB) (RL < −10 dB) of 3.9 GHz, ranging from 12 to 15.9 GHz. TiB 2 fibers exhibit promising potential as materials for high-temperature applications in the field of MA. [ABSTRACT FROM AUTHOR]

In this study, Ce 2 [Zr 1− x (Cr 0.5 Ta 0.5) x ] 3 (MoO 4) 9 (x = 0.02–0.10) ceramics were synthesized using the solid-state reaction technique, and the crystalline parameters, sintering behaviors, chemical bond characteristics, infrared reflection spectrum, and dielectric response at microwave and terahertz frequency were examined. X-ray diffraction results demonstrated the crystallization of all ceramics in the trigonal structure (R-3c space group), and additional peaks were not detected. The densification point of ceramic was 875 °C. The addition of (Cr 0.5 Ta 0.5)4+ significantly reduced the dielectric loss in the host ceramic. For Ce 2 [Zr 0.96 (Cr 0.5 Ta 0.5) 0.04 ] 3 (MoO 4) 9 , outstanding microwave properties of ε r = 10.66, Qf = 79,436 GHz, and τ f = −19.07 ppm/°C were obtained at 875 °C. The chemical bond characteristics were also parameterized to explore the relationship between Zr(CrTa)–O and microwave properties. Infrared spectral results further indicate that phonon vibrations lower than 400 cm−1 contribute to 80% of the polarization. In our comparison between the infrared spectrum and terahertz time-domain spectrum, we found that the permittivity extracted by the latter is closer to the observed value. [ABSTRACT FROM AUTHOR]

The ceramics of Li 2 Ti 1- x (Mg 1/3 Ta 2/3) x O 3 (x = 0.00–0.30) (LTMT x) were fabricated via the solid-phase method. The changes in crystal structure of LTMT x ceramics were confirmed by the X-ray diffraction (XRD). The microstructure of LTMT x ceramics was observed by the scanning electron microscope (SEM). The evolution of crystal structure and vibration for chemical bonds of LTMT x ceramics were studied by Raman spectra. The improvement on quality factors (Q × f values) was related to the weakening of asymmetric vibration in Li–O–Li bond. Based on the THz time domain spectrum (THz-TDS), the polarization mechanism and dielectric properties in THz frequency band were discussed. The satisfactory quality factor (80,005 GHz) was acquired in LTMT 0.15 ceramic, and the best resonant frequency temperature coefficient (τ f) value (0 ppm/°C) was achieved at x = 0.25, which firmly improved the application potential of LTMT x ceramics. [ABSTRACT FROM AUTHOR]

The fracture toughness and oxidation resistance are crucial factors affecting the practical applications of high-entropy diboride ceramics (HEBs). In this study, silicon carbide whiskers (SiC w) were introduced as a reinforcement for HEBs for the first time. To achieve a uniform dispersion of SiC w within the HEB powders, a combination of simultaneous ultrasonic dispersion, mechanical agitation, and freeze-drying technology was employed. Consequently, a series of composites, (Hf 0.2 Zr 0.2 Ta 0.2 V 0.2 Nb 0.2)B 2 -nSiC w (n = 0–20 vol%), were densified by spark plasma sintering. The effect of SiC w on the microstructure and mechanical properties of the HEBs were studied, as well as the toughening mechanism involved. The results revealed that the introduction of SiC w led to grain-size refinement in (Hf 0.2 Zr 0.2 Ta 0.2 V 0.2 Nb 0.2)B 2 , along with significant improvements in relative density, hardness, fracture toughness, and oxidation resistance. The relative density, hardness and fracture-toughness of (Hf 0.2 Zr 0.2 Ta 0.2 V 0.2 Nb 0.2)B 2 -SiC w composites exhibited an initial increase followed by a decrease with increasing SiC w content. Specifically, the (Hf 0.2 Zr 0.2 Ta 0.2 V 0.2 Nb 0.2)B 2 –15 vol% SiC w composite simultaneously obtained the highest hardness of 25.6 GPa and fracture-toughness of 4.8 MPa·m1/2, representing a 26% improvement compared to (Hf 0.2 Zr 0.2 Ta 0.2 V 0.2 Nb 0.2)B 2 ceramics. • The effect of SiC w on microstructure, mechanical properties and oxidation resistance of HEBs were studied for the first time. • The K Ic of (Hf 0.2 Zr 0.2 Ta 0.2 V 0.2 Nb 0.2)B 2 ceramic was increased by 26% without loss of hardness by introducing SiC w. • The oxidation resistance of HEBs was greatly enhanced due to the addition of SiC whiskers. [ABSTRACT FROM AUTHOR]

Diabetic cardiomyopathy (DCM) is a worldwide public health concern that continues to display rapid growth trends. This study investigated the function of sirtuin 3 (SIRT3), a primary mitochondrial deacetylase with important roles in antioxidant defense and oxidative metabolism, during high glucose-induced cardiomyocyte (AC16 cell) injury. Peroxisome proliferator-activated receptor-α (PPAR-α) is directly related to the occurrence of DCM. Hence, we further examined the relationship between SIRT3 and PPAR-α. AC16 cells were treated with various concentrations of glucose. Relative mRNA expression and protein levels were detected by RT-qPCR and western blot analysis, respectively. Cell proliferation and apoptosis were assessed using CCK8 and Annexin V-FITC apoptosis detection kits, respectively. DCFH-DA assay was used to measure reactive oxygen species (ROS) accumulation. The results indicated that high glucose treatment reduced the expression of mRNA and protein of SIRT3 and PPAR-α in AC16 cells. Moreover, high glucose inhibited cell proliferation, as well as induced apoptosis, intracellular hydrogen peroxide production, and JNK1/2 phosphorylation. These effects were antagonized by SIRT3 overexpression or treatment with the PPAR-α agonist, Wy14643. Conversely, inhibition of SIRT3 via 3-TYP led to similar phenomena as those induced by high glucose treatment in AC16 cells, which were blocked by Wy14643. Lastly, chromatin immunoprecipitation (ChIP) and luciferase assays demonstrated SIRT3 as a direct target of PPAR-α. Taken together, the results provide evidence for an important role of SIRT3 in high glucose-induced cardiomyocyte injury and regulation of JNK1/2 signaling. Further, SIRT3 is a direct downstream target of PPAR-α. [ABSTRACT FROM AUTHOR]

The crucial issue for fuel cells is to improve the activity and durability of Pt‐based catalysts. Herein, based on the short distance enhancement effects, a novel PtCo@NC catalyst with remarkably enhanced electrocatalytic properties for methanol oxidation reaction (MOR) in acidic electrolytes is developed by shortening the Pt–Co active site distance. In brief, a series of PtCo@NC catalysts with different Pt–Co biatomic arrangement are precisely synthesized by an in situ reduction‐fusion method, achieving Pt–Co structural evolution from a Pt/Co individual monometallic islet (A‐700 °C) to PtCo heterodimer (A‐800 °C) and then a PtCo alloy (A‐900 °C) embedded on nitrogen‐doped carbon matrixes. Compared with the Pt/Co monometallic islet and heterodimer, the PtCo@NC (A‐900 °C) with the shortest Pt–Co active site distance exhibits the highest mass activity of 2.30 A mgPt−1, which is 12.23 times higher than that of commercial Pt/C and exceeds almost all the reported MOR catalysts in acidic electrolytes. Both experiments and density functional theory calculations reveal that the remarkably improved activity stems from the modification of electron distribution around Pt/Co metal centers, thus promoting the rate‐determining methanol dehydrogenation step and CO oxidative removal processes, which are dependent on the distance between bimetallic active sites. [ABSTRACT FROM AUTHOR]

• The Zn 8 B 3 H 3 O 14 nanosheets were discovered and efficiently synthesized by the one-step coprecipitate method. • This method is simple, high yield and low cost to prepare Zn 8 B 3 H 3 O 14 nanosheets. • The nanosheets have good thermal stability, and their decomposition temperature reaches 414 °C. With the rapid development of two-dimensional materials, the exploration of new two-dimensional materials has become a research hotspot. In this work, novel Zn 8 B 3 H 3 O 14 nanosheets were efficiently synthesized by the one-step coprecipitate method using the water bath reaction at 70 °C for 24 h. The preparation of Zn 8 B 3 H 3 O 14 nanosheets by this method has the advantages of a simple preparation process, low cost, low equipment requirements, and mass production. The microstructure and morphology of nanosheets were characterized in detail. In addition, the nanosheets have good thermal stability properties, and their decomposition temperature reaches 414 °C. This allows the nanosheets to adopt higher processing and service temperatures when applied to polymer materials. [ABSTRACT FROM AUTHOR]

Abstract Active, stable and low-cost oxygen evolution reaction (OER) catalyst for electrochemical water splitting is key to efficient energy conversion and storage. Here, we report a three-dimensional (3D) nanonetwork as noble-metal-free electrode consisting of nickel cobalt diselenide (NiCoSe 2) nanobrush arrays on Ni foam (NF) through the initial hydrothermal reaction and subsequent thermal selenization process. Introducing ammonium fluoride as surface controller, different NiCoSe 2 hierarchical architecture can be modulated from nanorods, nanobrush to nanosheets. The unique brush-like NiCoSe 2 possesses high surface area for mass transfer, rough surface with rich active sites, 3D nanostructure preventing the accumulation of O 2 bubbles. Compared to NiCoSe 2 nanorods/NF, NiCoSe 2 nanosheets/NF and commercial RuO 2 , NiCoSe 2 nanobrush/NF exhibits an enhanced OER performance in alkaline media to reach a low overpotential of 274 mV at the current density of 10 mA/cm2, small Tafel slope and a long-term stability. The developed 3D nanonetwork highlights the nanoscale engineering and offers a promising alternative to noble metal catalysts for electrochemical water oxidation. [ABSTRACT FROM AUTHOR]

This study synthesized a novel Na 5 Tm(MoO 4) 4 (NTM) ceramic through the solid-state process. A single tetragonal phase of NTM ceramic was formed when sintered at 550 ℃—650 ℃. Raman spectrum studied the lattice dynamics information of NTM ceramic. The influence of multiple chemical bonds in NTM ceramic on the crystal stability and dielectric properties was revealed via the Phillips–van Vechten–Levine (P–V–L) theory. Optimal dielectric properties of ε r = 7.66, Q · f = 67,499 GHz (at 10.11 GHz), and τ f = − 58.85 ppm/℃ were achieved in NTM ceramic sintered at 625 ℃. According to the terahertz time-domain spectrum, the dielectric constant of NTM ceramics in the terahertz band is slightly less than that in the microwave band. Furthermore, the ceramic shows good chemical compatibility with Ag powder and is suitable for low temperature co-fired ceramic (LTCC) applications. The ultra-low sintering temperature, low dielectric constant, and low dielectric loss in the microwave and terahertz frequency bands make it an excellent dielectric material for preparing high-frequency wireless communication devices. [Display omitted] • A novel Na 5 Tm(MoO 4) 4 ceramic with good Q · f was prepared. • The terahertz time-domain spectrum of Na 5 Tm(MoO 4) 4 ceramic was studied. • The lattice vibration of Na 5 Tm(MoO 4) 4 ceramic was analyzed. • Effect of bond characteristics on Na 5 Tm(MoO 4) 4 ceramic were discussed. [ABSTRACT FROM AUTHOR]

This work prepared a new type of Ce 2 [Zr 1- x (Al 1/2 Nb 1/2) x ] 3 (MoO 4) 9 (CZ 1- x (AN) x M) (x = 0.02–0.10) microwave dielectric ceramics through the solid-phase process. CZ 1- x (AN) x M ceramics exhibited low dielectric constant, ultra-low dielectric loss, and near-zero resonant frequency temperature coefficient, which is suitable for 5 G technology. The effects of (Al 1/2 Nb 1/2)4+ replacing Zr4+ on the sintering characteristics, crystal structure, and microwave dielectric properties of Ce 2 Zr 3 (MoO 4) 9 (CZM) ceramics were studied systematically. In this work, CZ 1- x (AN) x M could form a pure crystal structure in the whole doping range according to the X-ray diffraction pattern. The crystal cell parameters of the ceramics were confirmed by Rietveld refinement analysis. Furthermore, the surface morphology of CZ 1- x (AN) x M sintered at the optimum sintering temperature was studied by scanning electron microscopy. Some internal parameters of the ceramics were calculated and analyzed by employing the P-V-L theory. The theoretical loss was acquired by employing an infrared reflection spectrometer. When x was 0.04 and the sintering temperature was 850 ℃, the best properties were achieved, including ε r = 10.54, Q·f = 91,476 GHz (at 9.55 GHz), and τ f = − 8.95 ppm/℃. This work studied the relationship between lattice vibration and microwave dielectric properties and discussed the influence of ion doping on microwave dielectric properties from the perspective of chemical bonds, laying a theoretical foundation for related research. [Display omitted] • The intrinsic factor of the permittivity was analyzed by IR reflectance spectroscopy. • The cell parameters were obtained through the Rietveld refinement method. • The effects of (Al 1/2 Nb 1/2)4+ the properties were explored based on the P-V-L theory. • Excellent properties including, ε r = 10.54, Q·f = 91,476 GHz, and τ f = − 8.95 ppm/℃. [ABSTRACT FROM AUTHOR]

Obstructive sleep apnea (OSA) is highly associated with hypertension. However, the correlation between hypertension and OSA at different levels of severity and the influence of gender on that correlation are unclear. A total of 996 patients (776 males and 190 females) with OSA were recruited. The influence of gender on the correlation between hypertension and OSA at different stratifications of severity, based on the apnea-hypopnea index (AHI), was fully evaluated together with the major health risk factors obesity, age, and diabetes. Females with OSA were significantly older on average than males with OSA. Moreover, females had milder degrees of OSA on average than the extent of severity seen in males. The proportion of females with diabetes or hypertension was higher than that of males. The proportion of males with hypertension and obesity increased significantly with OSA, and age also increased with OSA. The percentage of females with hypertension at different degrees of OSA severity was stable at about 26% in the mild, moderate, and severe OSA groups. Among females, age was increased significantly in the moderate relative to the mild OSA group. Moreover, the proportion of obese subjects was increased significantly in the severe compared with the moderate OSA group. The proportions of males and females with diabetes were not significantly different among all OSA severity groups. An ordinal multivariate logistic regression analysis confirmed that hypertension, age, and obesity were associated with OSA severity in males, whereas only age and obesity were associated with OSA severity in females. Although the proportion of subjects with hypertension was higher in females with OSA than in males with OSA, the proportion of subjects with hypertension increased as the severity of OSA increased in males but not in females. [ABSTRACT FROM AUTHOR]