Long Xia

Metal–semiconductor Zn/ZnO core–shell nanocables: facile and large-scale fabrication, growth mechanism, oxidation behavior, and microwave absorption performance

A new and facile synthetic route has been developed for the fabrication of metal–semiconductor Zn/ZnO core–shell nanocables on a large scale. Zn/ZnO nanocables were grown by heating a ball-milled mixture of boron and ZnO powders at 1300 °C under ammonia atmosphere. The structure and chemical composition of the as-prepared products were characterized by a variety of techniques including powder X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy. The nanocables were approximately 30–200 nm in diameter and tens of microns in length. The core was a Zn single crystal and the shell was an epitaxially grown ZnO layer of 3–10 nm thickness. It was found that the Zn/ZnO nanocables transformed into mace-like nanostructures or ZnO nanotubes when oxidized at 300 °C in air. The formation mechanism of the Zn/ZnO nanocables as well as the oxidized products has been clarified based on the experimental observations. The Zn/ZnO nanocable–paraffin composites showed good microwave absorption properties, and the reflection loss could reach −23 dB at 13.22 GHz. The mechanism for the enhanced absorption performance is discussed.

Enhanced microwave absorption properties of ferroferric oxide/graphene composites with a controllable microstructure

Fe3O4/graphene composites were synthesized as an advanced electromagnetic wave absorption material by a solvothermal method in a system of ethylene glycol. The Fe3O4 nanoparticles were homogeneously anchored on the graphene sheets and the structures of the nanoparticles could be experimentally controlled from ring-like spheres, flower-like spheres to solid spheres by changing the concentration of the oxide graphene. Microwave absorption tests demonstrated that the structures of the nanoparticles had a positive influence on the microwave absorption properties. Especially, for the Fe3O4/graphene composite with a flower-like structure, the minimum reflection loss value (RL) could reach −53.2 dB and the bandwidth of RL less than 10 dB (90% absorption) ranged from 8.1 to 16 GHz at a thickness of 2.5 mm, which is among the best-reported performances of Fe3O4/graphene materials, showing a huge potential to be used as a candidate for microwave absorbing materials.

Effect of alkali treatments on apatite formation of microarc-oxidized coating on titanium alloy surface

Abstract Alkali treatments with three concentrations were used to modify a microarc-oxidized (MAO) coating on titanium alloy surface in order to further improve its surface bioactivity. Morphology, chemical compositions and phase constitues, roughness, contact angle and apatite induction of the alkali-treated coatings were studied and compared. Scanning electron microscope (SEM) was applied to observe the morphologies, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were used to detect the phase constitutes and chemical compositions, a surface topography profilometer was used to analyze the surface roughness, and contact angle was measured by liquid drop method. Alkali treatements result in the formation of Na 2 Ti 6 O 13 and Na 2 Ti 3 O 7 phase on the MAO coating, which leads to the increase of surface roughness and the decrease of contact angle. Experimental results showed that the apatite induction of the alkali-treated coatings was dependent on the applied alkali concentrations during treatments, and Na + concentration can promote the formation of apatite phase.

Facile fabrication of carbon microspheres decorated with B(OH) 3 and α-Fe 2 O 3 nanoparticles: superior microwave absorption

We demonstrate that novel three-dimensional (3D) B(OH)3 and α-Fe2O3 nanoparticles decorated carbon microspheres (B(OH)3/α-Fe2O3-CMSs) can be fabricated via a facile thermal treatment process. The carbon microspheres with diameter of 1-3μm and decorated B(OH)3 and α-Fe2O3 nanoparticles with diameters of several to tens of nanometers are successfully fabricated. These novel 3D B(OH)3/α-Fe2O3-CMS composites exhibit enhanced microwave absorption with tunable strong absorption wavebands in the frequency range of 2-18GHz. They have a minimum reflection loss (RL) value of -52.69dB at a thickness of 3.0mm, and the effective absorption bandwidth for RL less than -10dB is as large as 5.64GHz. The enhanced microwave absorption performance arises from the synergy of the impedance matching caused by the B(OH)3 nanoparticles, dielectric loss as well as the enhancement of multiple reflection among 3D α-Fe2O3 nanocrystals. These results provide a new strategy to tune electromagnetic properties and enhance the capacity of high-efficient microwave absorbers.

Porous-carbon-nanotube decorated carbon nanofibers with effective microwave absorption properties

Carbon nanofibers decorated with porous carbon nanotubes were prepared by electrospinning and annealing methods. The microwave reflection loss of the products was investigated in the frequency range of 2-18 GHz. The bandwidth with a reflection loss less than -10 dB covers a wide frequency, ranging from 7.0 to 14.1 GHz with thickness of 3.0-5.5 mm, and the minimum reflection loss is -44.5 dB at 10.7 GHz with thickness of 2.0 mm. The large reflection loss and wide reflection band reveal that the products could be a promising candidate for microwave absorption.

Facile approach to fabricate BCN/Fe x (B/C/N) y nano-architectures with enhanced electromagnetic wave absorption

Carbon-based materials have excited extensive interest for their remarkable electrical properties and low density for application in electromagnetic (EM) wave absorbents. However, the processing of heteroatoms doping in carbon nanostructures is an insuperable challenge for attaining effective reflection loss and EM matching. Herein, a facile method for large-scale synthesis of boron and nitrogen doped carbon nanotubes decorated by ferrites particles is proposed. The BCN nanotubes (50-100 nm in diameter) imbedded with nanosized Fe x (B/C/N) y (10-20 nm) are successfully constructed by two steps of polymerization and carbonthermic reduction. The product exhibits an outstanding reflection loss (RL) performance, in that the minimum RL is -47.97 dB at 11.44 GHz with a broad bandwidth 11.2 GHz (from 3.76 to 14.9 GHz) below -10 dB indicating a competitive absorbent in stealth materials. Crystalline and theoretical studies of the absorption mechanism indicate a unique dielectric dispersion effect in the absorbing bandwidth.

A free-standing, flexible and bendable lithium-ion anode materials with improved performance

Bendable, flexible and self-supported anode materials with excellent electrochemical properties have highly attractive for the high performance lithium-ion batteries (LIBs). We report a simple process to prepare a three dimension structure composed of carbon and SnO2 nanoparticles (CGN/SnO2). The non-woven cotton covered with conducting graphene is selected as a flexible and bendable skeleton. Ultrasmall SnO2 nanoparticles with a size of several nanometers uniformly anchor on both the graphene sheets and cotton fibers. The CGN/SnO2 composites exhibited a higher Li-battery performance than carbonized cotton/SnO2 (C/SnO2) and carbonized cotton covered by glucose/SnO2 (CG/SnO2). Especially, the CGN/SnO2 composites after bending 1000 times can maintain the same lithium storage property as before. Combining with this unique flexible, bendable structure, and the outstanding electrical and electrochemical performance, we demonstrate the great potential of CGN/SnO2 composites in high performance Li-ion battery field and the flexible, foldable and stretchable conductors application.

Enhanced mechanical properties of carbon fibre/lithium aluminosilicate composites modified by SiB6 addition

ABSTRACT Carbon fibre-reinforced lithium aluminosilicate matrix composites (Cf/LAS) with different SiB6 contents were prepared by the hot pressing method to assess their mechanical properties and oxidation resistance. Composite that was incorporated with 2 wt-% SiB6 exhibited the highest flexural strength of 500 ± 22.3 MPa. Weight loss and residual strength of Cf/LAS modified by SiB6 were analysed. The results indicated that the addition of SiB6 had a remarkable effect on improving the oxidation resistance for Cf/LAS. To establish a direct relationship among interfacial microstructure, mechanical and oxidation behaviour of the studied composites, their connection was examined and discussed.

Interactions between carbon species and β-spodumene by first principles calculation

First principles calculations were carried out to study the interactions between carbon species and a β-spodumene matrix. Stabilities of low-index surfaces of β-spodumene with different terminations were firstly evaluated by surface energy calculations and results indicate that the Si–O–Li terminated (100) surface is the most stable surface with the lowest surface energy among the considered surfaces. The adsorption of carbon on the surface of β-spodumene and the formability of carbon-β-spodumene species are studied to clarify the interaction properties between them. The carbon species will be easily doped into or adsorbed on the surface of β-spodumene. The electronic structures reveal weak bonding interactions between the carbon layer and β-spodumene matrix, while these interactions can be strengthened by the adsorption of Li atoms on the carbon layer resulting in strong bonding interactions between them and therefore increasing the charge transfer between the carbon layer and β-spodumene matrix. Therefore the appearance of Li in the carbon species will improve the binding properties between the carbon species and β-spodumene matrix.

Reaction Hot-Pressed Sintering of Grain-Refined TiB2-TiC Composites by AlN-SiC Solid Solution

Grain-refined TiB2-TiCx composites were designed and fabricated by reaction hot pressing under 30 MPa at 1800 °C choosing 4.8 Ti-B4C material system with Al, C and Si3N4 as additives. The microstructure of the resultant was homogeneously grain-refined TiB2-TiCx matrix reinforced by AlN-SiC solid solution particles that were embedding tiny TiB2-TiCx crystals. The obtained specimen showed relative high flexural strength of 860±30 MPa and fracture toughness of 13.6±0.3 MPa·m1/2, which can be explained by several toughening mechanisms.