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Continuous tungsten fiber-reinforced tungsten-zirconium carbide-copper (Wf/W-ZrC-Cu) composites have been prepared by infiltrating Zr14Cu51 and 40 wt.% Zr-Cu molten alloys into porous Wf/W + WC preforms at 1200°C. The Zr-Cu infiltrants reducted most WC into W and ZrC. Residual Cu was advantageous to the extrinsic energy dissipation mechanisms of undamaged Wf by friction/interface de-bonding between Wf and W-ZrC matrix. Flexural strength and fracture toughness of the composites reached 571 MPa and 7.85 MPa m1/2, respectively. The composites with ~ 4 vol.% continuous Wf presented a pseudo-plastic-type fracture behavior and exhibited superior fracture work (~ 103 J m−2). The hybrid strengthening and toughening effects of Wf and in situ-formed submicron-sized ZrC particles have made the Wf/W-ZrC-Cu composites better combination properties than reactive melt-infiltrated W-ZrC-Cu composites. [ABSTRACT FROM AUTHOR]

B4C-45vol.% (TiZrHfNbTa) B2 composite was prepared by in-situ reactive spark plasma sintering at 2000°C using powders of transition metal carbides and amorphous boron as raw materials. The composite reached a relative density of over 97% Within 6 min. The simultaneously generated B4C and (TiZrHfNbTa) B2 phases had homogeneous microstructures with particle sizes ~ 1 μm, and Nb segregations in (TiZrHfNbTa) B2 grains were detected. The composite obtained a high three-point bending strength of 422 MPa, a Vickers hardness of 20.9 GPa and a fracture toughness of 5.48 MPa m1/2, respectively. The fine grain and solid solution effects are the main reasons for the improved properties. The crack deflection, branching, and bridging mechanisms observed are also helpful for an improved fracture toughness of the composite. This work provides a fast, convenient method of preparing novel B4C high-entropy boride composite ceramics with enhanced properties. [ABSTRACT FROM AUTHOR]

Zn has attracted widely attention in energy storage systems due to its characteristics of being highly safe, low-price, and environmentally friendly. Besides, the high ionic conductivity of aqueous electrolytes is beneficial for achieving high power output. Herein, the aqueous zinc-ion hybrid capacitors (ZHCs) are constructed by the multi-layered carbon nanosheets (MLCNs), Zn foil, and 1 M ZnSO4 solution as cathode, anode, and electrolyte, respectively. Of which, MLCN is prepared for the first time from a chemical by-product by a confined-tailored strategy of potassium bicarbonate. The MLCN displays well-developed mesoporous structures with high surface area of 1947.2 m2 g−1 and abundant cavities, which play a decisive role in enhancing charge storage and ion diffusion kinetics. As cathode for ZHC, the MLCN displays appealing Zn storage capability, such as high specific capacity of 128.7 mAh g−1 at 0.1 A g−1, excellent rate performance of 88.1 mA h g−1 at 20 A g−1, large energy/power density of 102.1 Wh kg−1/16.9 kW kg−1, and outstanding cycle stability with 1.3% loss after 10,000 cycles. This work will inspire the synthesis of new carbon cathode materials from chemical by-products for Zn ion storage. [ABSTRACT FROM AUTHOR]

Nitrogen and sulfur co-doped hierarchical porous carbon has gained enormous attention in energy storage field owing to its high capacitance and chemical stability. Herein, nitrogen and sulfur co-doped hierarchical porous carbon derived from ginkgo leaves is fabricated via carbonization followed by a facile composite-hydroxide-activation (CHA) strategy for supercapacitors application. The resultant carbon features sheet-like structures with hierarchical pores, possessing specific surface area (1975 m2 g−1), micropore volume (0.62 cm3 g−1), and higher heteroatom content up to 1.88% (N element) and 1.87% (S element). Due to its compositional and structural advantages, the nitrogen and sulfur co-doped hierarchically porous carbon exhibits a high specific capacitance of 333.4 F g−1 (at 0.1 A g−1) and an excellent rate capability (277.5 F g−1 at 20 A g−1). A superior cycling stability can be obtained as well with 94.4% capacitance retention after 10,000 cycles at 5 A g−1. In addition, the XPS result confirms that CHA strategy could be effective to fix heteroatoms into the primarily aromatic carbon backbone. The present study demonstrates an effective and universal strategy to develop high-performance hierarchical porous carbon from biomass for energy storage devices. [ABSTRACT FROM AUTHOR]

Acicular mullite-reinforced porous self-bonded ceramics were fabricated using mullite powders as principal raw materials, alumina and silicon dioxide powders as starting synthetic source of self-bonded mullite phase, and 2 wt% AlF3·3H2O as an accelerant. The influences of self-bonded mullite weight percent on the phase composition, microstructures, mechanical performance and thermal conductivities of acicular mullite-reinforced porous self-bonded samples were investigated. As self-bonded mullite weight percent varied between 0 and 50 wt%, linear shrinkage, bulk density and thermal conductivities of fired porous self-bonded mullite samples reduced, whereas their porosity increased. Addition of appropriate amounts of self-bonded mullite decreased the mean pore size and window size in porous sample, and enhanced the mechanical strength. When self-bonded mullite weight percent reached 50 wt%, the compressive and flexural strength of acicular mullite-reinforced porous self-bonded ceramics was, respectively, kept as 19.9 MPa and 8.8 MPa, with a porosity of 74.7%, a diminutive mean pore size of 159 μm and a window size of 44 μm. Moreover, the linear shrinkage and thermal conductivity of the materials at 50 °C were only 7.4% and 0.23 W m K−1, respectively. [ABSTRACT FROM AUTHOR]

Silico-ferrite of calcium (SFC) was synthesized through a solid-state route. The phase purity of the sample was characterized by means of X-ray diffraction (XRD) and field-emission scanning electron microscopy (FESEM). X-ray absorption fine structure (XAFS) spectroscopic analysis was used to determine the structure, and the results showed that SFC possesses more Fe–O tetrahedral structure than similarly structured silico-ferrites of calcium and aluminum (SFCA) and verified the existence of a small amount of Fe2+ in SFC. Ac impedance spectroscopy was used to evaluate the electrical properties of SFC, and the results showed that SFC had the properties of a negative temperature coefficient (NTC) thermosensitive material, and indicated that Si4+ donor doping leads to free electrons during the synthesis of SFC. The correlated barrier hopping (CBH) mechanism was proposed for the ac conduction mechanism of SFC, and Si4+ donor-doped SFC exhibited high electronic conductivity at temperatures greater than 102 °C. [ABSTRACT FROM AUTHOR]

Elongated mullite was synthesized via an in situ solid-phase reaction using α-Al2O3 and SiO2 as the raw materials and TiO2 as an additive, and characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM). On the basis of thermodynamic analysis of the reaction process, the effects of TiO2 content and reaction temperature on the phase composition, phase contents, and microstructure of the synthesized samples were investigated. The results showed that elongated mullite with a length of about 8.0 μm was formed for the sample with 7 mass-% TiO2 at 1873 K. The dosage of TiO2 exceeded its solid solubility limit in mullite which resulted in the anisotropic growth of mullite grains. [ABSTRACT FROM AUTHOR]

Crystallized FeB and Fe2B powders were synthesized by a molten salt method with elemental Fe and B powders as starting materials. The results indicated that the presence of molten NaCl/KCl salts and the excess of Fe or B powders were essential to obtain pure FeB or Fe2B powders. The formation mechanism of iron borides was investigated by examining the phase compositions of the obtained products with different molar ratio of Fe/B. It was found that Fe powders firstly reacted with B powders to form Fe2B phase, and FeB phase formed from the reaction between Fe2B and excessive B. The as-synthesized FeB and Fe2B powders had a uniform short-rod and plate like morphology, respectively. Both FeB and Fe2B exhibited typical soft magnetic behavior. The saturation magnetization and the coercivity were 36.4 emu/g and 15.5 kA/m for FeB, 126.9 emu/g and 6.1 kA/m for Fe2B, respectively. The electrochemical performances of the as-synthesized FeB powders were evaluated by cyclic voltammetry, galvanostatic charge–discharge and electrochemical impedance test. [ABSTRACT FROM PUBLISHER]

Water-soluble cores are an effective solution for complex inner cavity castings due to its excellent ability of leaching out in water. Compared with the rapid development of 3D printing sand mold/core, the water-soluble core additive manufacturing technology is limited by its material properties because water-soluble inorganic salt materials tend to agglomerate and are transparent for the visible and near-infrared lasers. In this study, a process based on direct jetting potassium carbonate solution onto powder bed mix with ceramic sand and bentonite followed with post-treatment was proposed to prepare the water-soluble sand core. The mechanical property of the core was detected in different stages of the forming process, and the mechanism of strength and collapse was analyzed with the aid of phase diagram and scanning electron microscopy. The results show that the strength of binder jetting core exceeds 2 MPa after sintering at 900 °C for 10 min via pre-sintering and soaking, and the residual strength of the core decreases to 0.12 MPa, which guarantees the leachability of the core out of a casting under a slight vibration. Liquid bridge between sand grains built up in the process of binder jetting transforms into K2CO3 bonding bridge during the heating process, and a reticular structure of KAlSimOn grows up with the increase of sintering temperature and the extension of time, which explains the pre-sintered core maintains the original shape in K2CO3 solution and the sintered core has a low strength after soaking in water. What is more, a casting trial of tee pipe was conducted to verify the suitability of the developed cores for aluminum alloy castings with complex internal cavities. [ABSTRACT FROM AUTHOR]