Mechanical reinforcement while remaining electrical insulation of glass fibre/polymer composites using core–shell CNT@SiO2 hybrids as fillers

Carbon nanotubes (CNTs) have been widely used as mechanical reinforcement agents of composites. However, their aggregations, weak interfacial interaction with polymer, as well as high electrical conductivity limit their use in some especial applications. In this paper, the silicon oxide (SiO₂)-coated (CNT@SiO₂) core–shell hybrids with different SiO₂ thickness were prepared and employed to reinforce glass fibre-reinforced bismaleimide–triazine (BT) resin (GFRBT) composites. The results indicated the mechanical properties, including tensile strength and Young’s modulus increased with the increase of SiO₂ thickness and CNT@SiO₂ loading. Such enhanced mechanical properties were mainly attributed to the intrinsically nature of CNTs, homogeneous dispersion of the hybrids, as well as improved interfacial interaction. Meanwhile, the composites remained high electrical insulation (9.63 × 10¹² Ω cm) due to the existence of SiO₂ layer on CNT surface. This study will guide the design of functionalized CNTs and the construction of high-performance composites.     

MoS2 nanosheet functionalized with Cu nanoparticles and its application for glucose detection

For the first time, Cu nanoparticles were evenly decorated on MoS₂ nanosheet by chemical reduction. The as-prepared Cu-MoS₂ hybrid was characterized by atomic force microscope (AFM), Raman spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD) and then used to fabricate a non-enzymatic glucose sensor. The performance of our sensor was investigated by cyclic voltammetry and amperometric measurement in alkaline media. Electrochemical tests showed that Cu-MoS₂ hybrid exhibited synergistic electrocatalytic activity on the oxidation of glucose with a high sensitivity of 1055 μA mM⁻¹ cm⁻² and a linear range up to 4 mM.     

Structural characterization of β-SiC nanowires synthesized by direct heating method

Crystal structure of β-SiC nanowires was investigated using Raman spectroscopy, FT-IR, XRD, transmission electron microscopy and selected area electron diffraction. Cubic β-SiC nanowires were synthesized by heating NiO catalyzed Si substrates with WO₃ and graphite mixed powders in the growth temperature of 1000–1100 °C. HRTEM image showed atomic arrangements of the grown SiC nanowires with a main growth direction of [111]. Raman spectra showed two characteristic peaks at 796 cm^− 1 and 968 cm^− 1, which are corresponding to transversal optic mode and longitudinal optic mode of β-SiC, respectively. Also, FT-IR absorption spectroscopy showed a SiC characteristic absorption band at ∼792 cm^− 1.     

One step synthesis of Bi@Bi2O3@carboxylate-rich carbon spheres with enhanced photocatalytic performance

Bi@Bi₂O₃@carboxylate-rich carbon core-shell nanosturctures (Bi@Bi₂O₃@CRCSs) have been synthesized via a one-step method. The core–shell nanosturctures of the as-prepared samples were confirmed by X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and Raman spectroscopy. The formation of Bi@Bi₂O₃@CRCSs core–shell nanosturctures should attribute to the synergetic roles of different functional groups of sodium gluconate. Bi@Bi₂O₃@CRCSs exhibits significant enhanced photocatalytic activity under visible light irradiation (λ > 420 nm) and shows an O₂-dependent feature. According to trapping experiments of radicals and holes, hydroxyl radicals were not the main active oxidative species in the photocatalytic degradation of MB, but O₂⁻ are the main active oxidative species.     

Influence of aluminum ions implanted on corrosion behavior of zirconium in 1 M H2SO4

In order to study the effect of aluminum ion implantation on the aqueous corrosion behavior of zirconium, specimens were implanted with aluminum ions with fluence ranging from 1 × 10¹⁶ to 1 × 10¹⁷ ions/cm², using a metal vapor vacuum arc source (MEVVA) at an extraction voltage of 40 kV. The valence states and depth distributions of elements in the surface layer of the samples were analyzed by X-ray photoelectron spectroscopy (XPS) and auger electron spectroscopy (AES), respectively. Transmission electron microscopy (TEM) was used to examine the microstructure of the aluminum-implanted samples. Glancing angle X-ray diffraction (GAXRD) was employed to examine the phase transformation due to the aluminum ion implantation. The potentiodynamic polarization technique was employed to evaluate the aqueous corrosion resistance of implanted zirconium in a 1 M H₂SO₄ solution. It was found that a significant improvement was achieved in the aqueous corrosion resistance of zirconium implanted with aluminum ions. Finally, the mechanism of the corrosion behavior of aluminum-implanted zirconium was discussed.     

Fabrication and characterization of 3-D Cf/ZrC composites by low-temperature liquid metal infiltration

Three-dimensional braided carbon fiber-reinforced ZrC matrix composite, 3-D C_f/ZrC, were prepared by liquid metal infiltration process at 1200 °C using a Zr₂Cu intermetallic compound as infiltrator. The microstructure and properties of the composites were investigated. The results indicated that ZrC with a yield of 35.2 ± 1.8 vol.% was certified as the major phase of the composites. The formation of ZrC was controlled by a solution-precipitation mechanism. The obtained composites exhibited good mechanical properties, with a flexural strength of 293.0 ± 12.1 MPa, a flexural modulus of 82.7 ± 6.4 GPa and a fracture toughness of 9.8 ± 0.9 MPa m^1/2. The mass and linear ablation rates of the composites exposed to oxyacetylene torch were 0.0013 ± 0.0005 g s⁻¹ and −0.0009 ± 0.0003 mm s⁻¹, respectively. The formation of a dense ZrO₂ protective layer and the evaporation of residual Cu contributed mainly to the excellent ablation resistance.     

Influence of Ga3+ ions on spectroscopic and dielectric features of multi component lithium lead boro bismuth silicate glasses doped with manganese ions

Multi-component glasses of the chemical composition 19.5Li₂O–20PbO–20B₂O₃–30SiO–(10 − x)Bi₂O₃–0.5MnO:xGa₂O₃ with 0 ≤ x ≤ 5.0 have been synthesized. Spectroscopic (optical absorption, IR, Raman and ESR) and dielectric properties were investigated. Optical absorption and ESR spectral studies have indicated that managanese ions do exist in Mn³⁺ state in addition to Mn²⁺ state in the samples containing low concentration of Ga₂O₃. The IR and Raman studies indicated increasing degree of disorder in the glass network with the concentration of Ga₂O₃ up to 3.0 mol%. The dielectric constant, loss and ac conductivity are observed to increase with the concentration of Ga₂O₃ up to 3.0 mol%. The quantitative analysis of the results of dielectric properties has indicated an increase in the insulating strength of the glasses as the concentration of Ga₂O₃ is raised beyond 3.0 mol%. This has been attributed to adaption of gallium ions from octahedral to tetrahedral coordination.     

The AMWCNTs supported porous nanocarbon composites for high-performance supercapacitor

The porous nanocarbons supported by acid-treated multiwall carbon nanotubes (PC@ACNTs) were prepared by the combination of the hydrothermal polymerization of glucose on ACNTs, carbonization under N₂ protection and final activation with ZnCl₂. The materials were characterized by transmission electron microscopy, X-ray powder diffraction and Raman spectra. The results indicated that the ACNTs distributed uniformly into the framework of the porous carbon. The composites showed the high BET specific surface area up to 1712 m² g⁻¹ and good conductivity. The electrochemical measurements indicated that the composites processed good performances for electrochemical energy storage (210 F g⁻¹ at 0.5 A g⁻¹), and high stability (>99.9%), much higher than the corresponding ACNTs, porous carbons and the samples prepared by using raw MWCNTs as source. The good performance of PC@ACNTs composites was relative with the synergy of good conductivity of ACNTs and large specific surface areas of PC.     

Structure property relation of hybrid biocomposites based on jute,viscose and polypropylene: The effect of the fibre content and the length on the fracture toughness and the fatigue properties

In the present study, the extent of jute and viscose fibre breakage during the extrusion process on the fracture toughness and the fatigue properties was investigated. The composite materials were manufactured using direct long fibre thermoplastic (D-LFT) extrusion, followed by compression moulding. The fracture toughness (K_IC) and the fracture energy (G_IC) of the PP–J30 composites were significantly improved (133% and 514%, respectively) with the addition of 10 wt% viscose fibres, indicating hindered crack propagation. The addition of viscose fibres resulted in three times higher fatigue life compared with that of the unmodified jute composites. Further, with the addition of (2 wt%) MAPP, the PP–J30–V10 resulted in a higher average viscose fibre length of 8.1 mm, and the fracture toughness and fracture energy increased from 9.1 to 10.0 MPa m^1/2 and 28.9 to 31.2 kJ/m², respectively. Similarly, the fatigue life increased 51% compared with the PP–J30–V10, thus demonstrating the increased work energy due to hindrance of the propagation of cracks.     

Biomimetic mineralisation of apatites on Ca2+ activated cellulose templates

We investigated the activation of regenerated cellulose 2D model thin films and 3D fabric templates with calcium dihydroxide. The Langmuir–Blodgett (LB) film technique was applied for manufacturing of the model thin films using a trimethylsilyl derivative of cellulose (TMS-cellulose). Regenerated cellulose films were obtained by treating the TMS-cellulose LB-films with hydrochloric acid vapours. For 3D templates, regenerated cellulose fabrics (Lyocell®) were used. The regenerated cellulose templates were activated with a Ca(OH)₂-suspension and subsequently exposed to 1.5 × SBF to induce the in situ formation of biomimetic calcium phosphate phases. FTIR and Raman spectroscopy showed that the Ca(OH)₂ and calcite present from reaction with HCO₃⁻ on the template surface were dissolved in the initial stage of exposure to the 1.5 × SBF. After 1 day, the formation of apatitic phases in 1.5 × SBF was observed. According to detailed calculations, high supersaturation levels S in close vicinity to the template surface (S > 16) resulting from the Ca²⁺ diffusion induced the formation of biomimetic calcium phosphate. The biomimetic calcium phosphates were identified by FTIR and Raman spectroscopy as highly carbonated apatites (HCA) lacking hydroxyl ions. 3D fabric templates of regenerated cellulose covered with a biomimetic coating of apatite might be of particular interest for novel scaffold architectures in bone repair and tissue engineering.     

Influence of Eu substitution for Gd on the structure and photoluminescent properties of (Gd1−xEux)2Ti2O7 pyrochlore solid solutions

This paper presents a study of the synthesis and structural properties of the pyrochlore-type titanates (Gd_1?xEu_x)₂Ti₂O₇. Six compositions with 0 ≤ x ≤ 1 were prepared by solid-state reaction with thermal treatments at 1000 and 1200 °C under atmospheric pressure conditions. All the products were systematically characterized by X-ray powder diffraction (XRD), Raman spectroscopy, photoluminescence (PL) and photoluminescent excitation spectra (PLE). Structural refinements of X-ray powder diffraction data using Rietveld method show that all compounds of the (Gd_1?xEu_x)₂Ti₂O₇ solid solution crystallize in a pyrochlore structure. The lattice parameters increase linearly with increasing Eu content in agreement with Vegard's rule. PL spectra show that the characteristic peaks correspond to the f–f transition ⁵D₀–⁷F_J (J = 1, 2, 3 and 4) of Eu³⁺. The effect of Eu³⁺ ions concentration on the optical properties, namely, photoluminescence emission, is measured and discussed. The oxides exhibit higher PL intensity with the Eu³⁺ ion concentration and strong orange emission at 589 nm (⁵D₀–⁷F₁) corresponding to the magnetic dipole transition.     

Fabrication and characterization of n-type aluminum-boron co-doped ZnO on p-type silicon (n-AZB/p-Si) heterojunction diodes

In this paper, the growth of n-type aluminum boron co-doped ZnO (n-AZB) on a p-type silicon (p-Si) substrate by sol–gel method using spin coating technique is reported. The n-AZB/p-Si heterojunctions were annealed at different temperatures ranging from 400 to 800 °C. The crystallite size of the AZB nanostructures was found to vary from 28 to 38 nm with the variation in annealing temperature. The band gap of the AZB decreased from 3.29 to 3.27 eV, with increasing annealing temperature from 400 to 700 °C and increased to 3.30 eV at 800 °C probably due to the formation of Zn₂SiO₄ at the interface. The band gap variation is explained in terms of annealing induced stress in the AZB. The n-AZB/p-Si heterojunction exhibited diode behavior. The best rectifying behavior was exhibited at 700 °C.     

Microstructure and mechanical properties of hot extruded 6016 aluminum alloy/graphite composites

The incorporation of graphite particles into AA6016 aluminum alloy matrix to fabricate metal/ceramic composites is still a great challenge and various parameters should be considered. In this study, dense AA6016 aluminum alloy/(0-20 wt%) graphite composites have successfully been fabricated by powder metallurgy process. At first, the mixed aluminum and graphite powders were cold compacted at 200 MPa and then sintered at 500 ℃ for 1 h followed by hot extrusion at 450 ℃. The influence of ceramic phases(free graphite and in-situ formed carbides) on microstructure, physical and mechanical properties of the produced composites were finally investigated. The results show that the fabricated composites have a relative density of over 98%. SEM observations indicate that the graphite has a good dispersion in the alloy matrix even at high graphite content. Hardness of all the produced composites was higher than that of aluminum alloy matrix. No cracks were observed at strain less than 23% for all hot extruded materials.Compressive strength, reduction in height, ultimate tensile stress, fracture stress, yield stress, and fracture strain of all Al/graphite composites were determined by high precision second order equations. Both compressive and ultimate tensile strengths have been correlated to microstructure constituents with focusing on the in-situ formed ceramic phases, silicon carbide(SiC) and aluminum carbide(Al_4 C_3). The ductile fracture mode of the produced composites became less dominant with increasing free graphite content and in-situ formed carbides. Wear resistance of Al/graphite composites was increased with increasing graphite content. Aluminum/20 wt% graphite composite exhibited superior wear resistance over that of AA6016 aluminum alloy.     

The cation inversion and magnetization in nanopowder zinc ferrite obtained by soft mechanochemical processing

Two zinc ferrite nanoparticle materials were prepared by the same method – soft mechanochemical synthesis, but starting from different powder mixtures: (1) Zn(OH)₂/α-Fe₂O₃ and (2) Zn(OH)₂/Fe(OH)₃. In both cases a single phase system was obtained after 18 h of milling. The progress of the synthesis was controlled by X-ray diffractometry (XRD), Raman spectroscopy, TEM and magnetic measurements. Analysis of the XRD patterns by Rietveld refinement allowed determination of the cation inversion degree for both obtained single phase ZnFe₂O₄ samples. The sample obtained from mixture (1) has the cation inversion degree 0.3482 and the sample obtained from mixture (2) 0.400. Magnetization measurements were confirmed that the degrees of the inversion were well estimated. Comparison with published data shows that used method of synthesis gives nano powder samples with extremely high values of saturation magnetizations: sample (1) 78.3 emu g⁻¹ and sample (2) 91.5 emu g⁻¹ at T = 4.5 K.     

Preparation,characterization and photocatalytic activity of TiO2 codoped with yttrium and nitrogen

Nanocrystalline photocatalysts of TiO₂ codoped with yttrium and nitrogen were prepared by the sol–gel method and investigated by X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), the Brunauer–Emmett–Teller (BET) surface area measurement, X-ray photoelectron spectroscopy (XPS) and ultraviolet–visible diffuse reflectance spectroscopy (UV–vis DRS), respectively. Slight red-shifts of the Raman peak at 144 cm^?1 were observed in the doped samples after the incorporation of Y³⁺ and N^3? into the lattice of TiO₂. The N doping caused the improvement of visible light absorption because of the formation of the N 2p states isolated above the valence band maximum of TiO₂. Whereas, the absorption property of the pure or N doped TiO₂ was depressed after the introduction of Y. The photocatalytic activities of the samples were evaluated by monitoring the degradation of methylene blue (MB) solution. The codoped sample with N and 0.05 at.% Y exhibited an enhanced photocatalytic efficiency. It is suggested that the charge trapping due to the Y doping and the visible light response due to the N doping are responsible for the enhanced photocatalytic performance in this sample. However, the photocatalytic activity of the codoped TiO₂ was suppressed step by step as the Y doping level increased, which could be attributed to the formation of photogenerated charge carriers recombination centers at the Y substituting sites.     

Fracture behaviour of α-Al2O3 ceramics reinforced with a mixture of single-wall and multi-wall carbon nanotubes

The extraordinary mechanical properties of single-wall carbon nanotubes (SWCNTs) and multi-wall carbon nanotubes (MWCNTs) have generated interest in incorporating them as toughening agents in ceramics. This work describes the fracture behaviour of an alumina (Al₂O₃) ceramic reinforced with a mixture of 0.05 wt% MWCNTs + 0.05 wt% SWCNTs. The CNT/Al₂O₃ nanocomposite was pressureless sintered in air using graphite powder as bed powder at 1520 °C for 1 h. The hardnesses and fracture toughnesses were lower than for pure Al₂O₃ and Al₂O₃ + 0.1 wt% SWCNTs and Al₂O₃ + 0.1 wt% MWCNTs. A predominantly transgranular fracture mode with a decrease in crack deflection and no pull-out was observed in the SWCNT + MWCNT–Al₂O₃ nanocomposite. MWCNTs had to the best reinforcing effect in Al₂O₃ nanocomposite.     

Friction and wear behavior of polytetrafluoroethene composites filled with Ti3SiC2

In this work, polytetrafluoroethylene (PTFE) composites filled with Ti₃SiC₂ or graphite were prepared through powder metallurgy. The effects of different filling components, loads and sliding velocities on the friction performance of Ti₃SiC₂/PTFE composites were studied. Ti₃SiC₂/PTFE composites exhibit better wear resistance than graphite/PTFE composites due to the better mechanical properties of Ti₃SiC₂. The wear resistance was found to improve around 100× over unfilled PTFE with the addition of 1 wt.% Ti₃SiC₂. In addition, the 10 wt.% sample had the lowest wear rate of K = 2.1 × 10⁻⁶ mm³/Nm and the lowest steady friction coefficient with μ = 0.155 at the condition of 90 N–0.4 m/s. Ti₃SiC₂ was proved to promote the formation of a thin and uniform transfer film on counterpart surface and a protection oxide film on worn surface, which are the key roles for improving wear resistance.     

A facile assembly of polyimide/graphene core–shell structured nanocomposites with both high electrical and thermal conductivities

Polyimide/reduced graphene oxide (PI/r-GO) core–shell structured microspheres were fabricated by in-situ reduction of graphene oxide (GO), which was coated on the surface of PI microspheres via hydrogen bonding and π–π stacking interaction. The highly ordered 3D core–shell structure of PI/r-GO microspheres with graphene shell thickness of 3 nm was well characterized by scanning electron microscope (SEM), transmission electron microscopy (TEM) and Raman spectra. The glass transition temperature (T_g) of PI/r-GO microspheres was slightly increased because of the interaction of r-GO and PI matrix while the temperature at 5% weight loss (T_5%) of PI/r-GO microspheres was decreased due to the side effect of reductant hydrazine hydrate. The PI/r-GO nanocomposites exhibited highly electrical conductivity with percolation threshold of 0.15 vol% and ultimate conductivity of 1.4 × 10⁻² S/m. Besides, the thermal conductivity of PI/r-GO nanocomposites with 2% weight content of r-GO could reach up to 0.26 W/m K.     

Experimental study on synthesizing TiO2 nanotube/polyaniline (PANI) nanocomposites and their thermoelectric and photosensitive property characterization

In this paper, TiO₂ nanotube/polyaniline (PANI) nanocomposites were made. The thermoelectric and photosensitive properties of the nanocomposites were studied. The effects of processing time, voltage, concentration of F^? ions and H₃PO₄ on the formation of TiO₂ nanotubes were investigated. The morphologies of the synthesized nanocomposites were revealed by scanning electron microscopy (SEM). The formation of polyaniline was confirmed by both Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR). The optimum conditions for the formation of well-organized TiO₂ nanotubes are at 20 V for 60 min in the electrolyte containing 0.2 M fluorine ions. The highest absolute value of the Seebeck coefficient for the TiO₂ nanotube/polyaniline nanocomposites is 124 μV/K at 30 °C. Pure Ti foil does not show photosensitive property, while the TiO₂ nanotubes have strong photosensitivity.     

Improving mechanical and electrical properties of oriented polymer-free multi-walled carbon nanotube paper by spraying while winding

In this study, a new method is introduced for fabricating carbon nanotube (CNT) paper, in which the solvent is sprayed on the CNT sheet while it is wound on a rotating mandrel. As the solvent evaporated, the capillary force pulls CNT closer together, resulting in a CNT paper with a high degree of alignment and a high packing density. Three batches of multi-walled CNTs with different wall thicknesses, tube diameters and lengths are utilized for synthesizing highly oriented CNT papers. It is found that CNTs with smallest diameter of 8 nm form strongest CNT paper with a tensile strength of 563 MPa and a tensile modulus of 15 GPa, while that made with CNTs of 10 nm diameter shows the highest electrical conductivity of 5.5 × 10⁴ S/m.