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In-situ synthesis of mullite-SiCw composite ceramics in Li2O-Al2O3-SiO2 ternary system for solar heat transmission pipeline
摘要： Nano-SiC whiskers (nano-SiCw) were in-situ synthesized in Li2O-Al2O3-SiO2 ternary system for preparing highly densified mullite-SiCw composite ceramics used for solar heat transmission pipeline. Mechanisms on the in-situ synthesis of nano-SiCw in the ternary system were investigated and the impact of nano-SiCw on the performances of the composites had been studied. Results showed that the growth processes of nano-SiC whiskers in Li2O-Al2O3-SiO2 ternary system were dominated by liquid-solid (LS) mechanism and the Li2CO3 additive could improve the SiCw yield through increasing the content of liquid phase and lowering the liquid viscosity. Sample BS3 (with 2.22 wt% Li2CO3 additive) sintered at 1440 °C obtained the highest SiC content of 47.9%. Nano-SiC whiskers with a diameter of 20e30 nm were interlocking with rod-like mullite crystals to improve the mechanical properties of the composites, and sample BS1 sintered at 1420 °C showed the highest bending strength of 115.4 MPa. The in-situ synthesized SiCw also shew significant effects on improving the thermophysical properties of the composites and sample BS1 exhibited a 3.6 times higher thermal conductivity than that of blank sample B1 without the introduction of nano-SiCw.
关键词： Li2O-Al2O3-SiO2 ternary system,Thermal conductivity,Mullite-SiCw composite ceramics,Solar heat transmission pipeline,SiC whiskers
更新于2025-09-23 15:23:52
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Berry phase in strained InSb whiskers
摘要： Strain influence on the longitudinal magnetoresistance for the n-type conductivity InSb whiskers doped by Sn to concentrations 6·1016–6·1017 сm–3 were studied at temperatures from 4.2 to 50 K and magnetic field up to 10 T. The Shubnikov–de Haas oscillations at low temperatures were revealed in the strained and unstrained samples with all range doping concentration. Some peaks of the longitudinal magnetoresistance split as a doublet in the InSb whiskers with doping concentration in the vicinity to metal-insulator transition. Taking into account peak splitting giant g-factor from 30 to 60 was defined for strained and unstrained samples. The magnetoresistance oscillation period of the InSb whiskers doesn’t differ under strain for all doping concentration, but Fermi energy increases and electron effective mass mс decreases and consists 0.02 m0. Berry phase presence was also revealed in strained n-InSb whiskers that shows their transition under a strain to topological insulator phase.
关键词： Berry phase,topological insulator,strained InSb whiskers,Shubnikov–de Haas oscillations,magnetoresistance
更新于2025-09-23 15:21:21
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Synthesis of Y2BaCuO5 nano-whiskers by a solution blow spinning technique and their successful introduction into single-grain, YBCO bulk superconductors
摘要： The ability of single grain Y-Ba-Cu-O (YBCO) bulk superconductors to trap large magnetic fields is due generally to the presence of embedded, non-superconducting Y2BaCuO5 (Y-211) phase particles, in optimum amount, in the superconducting YBa2Cu3O7-δ (Y-123) phase matrix, which increases flux pinning and, hence, critical current density of the bulk material. The presence of smaller particles of Y-211 could be expected to improve further the superconducting properties of single grain, bulk YBCO samples, although the smallest Y-211 particles that have been engineered to date within the bulk microstructure are around 800 nm in size. It is extremely challenging to reduce the Y-211 particle size any further due to problems of particle agglomeration that originate, inevitably, from the effects of surface energy and reactivity at relatively high processing temperatures. In this work, we report a novel approach to the fabrication of Y-211 pinning centres in bulk YBCO superconductors in the form of nano-whiskers manufactured by a solution blow spinning technique. The Y-211 nano-whiskers, of which 62% were smaller than 500 nm, were added to the YBCO precursor powders to produce a single grain bulk sample by the buffer-aided top-seeded melt growth (BA-TSMG) processing technique. The resulting YBCO single grain, of diameter 20 mm, was able to trap a magnetic field of 0.63 T at 77 K with an associated critical current density of 3.9 X 104 A/cm2 in self-field. The results of this study demonstrate clearly that the use of Y-211 nano-whiskers is a promising route for enhancing flux pinning in bulk YBCO single-grains, which is potentially significant for the development of high field engineering applications.
关键词： Solution Blow Spinning,nano-Y2BaCuO5,nano-whiskers,Bulk YBCO,High temperature superconductor,Single-grain superconductor,YBa2Cu3O7-x
更新于2025-09-10 09:29:36
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Photocatalytic performance of K2Ti6O13 whiskers to H2 evolution and CO2 photo-reduction
摘要： K 2 Ti 6 O 13 whiskers were synthesized by conventional sol-gel method, sono-chemical assisted and microwave assisted sol-gel method in order to obtain catalysts with different particle sizes and to modify their optical, textural and electrochemical properties. These modifications improved their photocatalytic activity for H 2 evolution and CO 2 photo-reduction. Long K 2 Ti 6 O 13 whiskers prepared by ultrasound assisted sol-gel method are the most active photocatalysts for the hydrogen evolution reaction using pure water as reactant (U-SG, 10,065 μmol g ?1 ). In contrast, an opposite behavior was observed using a mixture of ethanol-water, where the highest activity was achieved by the shortest and less crystalline K 2 Ti 6 O 13 whiskers (C-SG, h32871 μmol g ?1 ). In case of CO 2 photo-reduction, long whiskers that were also prepared by the sono-chemical assisted sol-gel method were the most active to transform CO 2 to formaldehyde, methane, methanol and hydrogen. The E FB value of this catalyst is located very close to the potential for formaldehyde production and favors the selectivity to this organic product.
关键词： Sol-gel,Whiskers,Hydrogen evolution,K 2 Ti 6 O 13,CO 2 reduction
更新于2025-09-10 09:29:36
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A new design of the YIG/MTC joint brazed by bismuth-based glass
摘要： The paper uncovers an underlined mechanism of joining Yttrium Iron Garnet (YIG) and Magnesium Titanate Ceramic (MTC) with a bismuth-based glass braze. The proposed joint design has not been investigated until present. The central hypothesis is as follows. The brazed bismuth-based glass microstructure and the resulting mechanical strength of a YIG/MTC joint design support favorably a good bonding of the interface domains. The supporting evidence includes the following: (i) the bismuth-based glass features good wettability on YIG and MTC, (ii) the sequence of the coefficients of thermal expansions (YIG, bismuth-based glass, MTC) is in a favorable succession. The study reveals that the interface reactions form: (i) a lamellar phase and YBO3 whiskers at the YIG/Bi25 interface, (ii) both MgFe2O4, and Bi4Ti3O12 whiskers in addition to Zn2Ti3O8 reaction layer at the MTC/Bi25 interface, and (iii) Fe2O3 phase along the brazing seam. The mechanical integrity of joints has been studied as well.
关键词： Magnesium titanate ceramic,Whiskers,Microstructure,Bismuth-based glass braze,Yttrium iron garnet ferrite
更新于2025-09-04 15:30:14
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[IEEE 2018 IEEE 38th International Conference on Electronics and Nanotechnology (ELNANO) - Kiev (2018.4.24-2018.4.26)] 2018 IEEE 38th International Conference on Electronics and Nanotechnology (ELNANO) - Spin-Dependent Transport of Charge Carriers in Silicon Microcrystals Doped with Boron and Diluted with Nickel
摘要： Negative magnetoresistance of Si p-type whiskers with different impurity concentration 1018 – 5×1018 (cid:619)m-3 which corresponds to the transition of a metal-dielectric in silicon and diluted with nickel were studied in longitudinal magnetic field 0 – 14 T in the temperature range 4.2 – 77 K. The large negative magnetoresistance values correspond to hopping conductance on the twice occupied by electrons impurity states. It is established that in order to predict the magnetoresistance of crystals, it is necessary to take into account the polarization component due to the nature of the hopping conductance at low temperatures
关键词： negative magnetoresistance,spin,whiskers,hopping conductance,cryogenic temperatures
更新于2025-09-04 15:30:14