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Carbon nanotubes (CNTs) can improve the fracture toughness of ceramic composites. It is widely believed that defects in the CNTs will alter key properties that ultimately dictate composite toughening. However, to date there have been no studies that directly correlate these specific properties to controlled defect levels in CNTs. This type of investigation is presented here, using ceramic nanocomposites with a polymer derived ceramic (PDC) matrix, reinforced with multiwalled CNTs. This work includes basic fracture measurements on full composite films, combined with careful testing of individual CNTs embedded in the same PDC matrix. The defect levels in these CNTs were controlled with high energy carbon ions. By using this approach, it was possible to directly correlate defect levels with the interfacial shear strength (IFSS) of the CNT/PDC interface, the CNT fracture strengths, and the pull-out lengths observed after fracture of the full composites. The radiation induced defects led to substantial increases in the IFSS, and only a marginal decrease is observed in the measured fracture strength. Based on this, the shorter pull-out lengths that occurred with higher defect levels were primarily attributed to stronger bonding at the CNT/PDC interface. [ABSTRACT FROM AUTHOR]

Graphene nanoribbons (GNRs) with opened edges and less structural defects are embedded in polyacrylonitrile (PAN)-based carbon nanofibers (CNFs) by electrospinning followed by stabilization and carbonization. GNRs not only can be used as one-dimensional nanofillers, but also act as nanoplatelet template to promote the formation of graphitic carbon in PAN matrix. X-ray diffraction, Raman spectroscopy and N 2 absorption are used to analyze the microstructure of GNR-reinforced CNFs. In situ tensile test using a micromechanical device inside a scanning electron microscope (SEM) is carried out to evaluate the mechanical performance of individual GNR-reinforced CNF. The tensile strength and elastic modulus of CNFs reinforced by 2 wt% GNRs with a diameter of ∼160 nm are 3.52 GPa and 70.07 GPa, respectively, which are higher than those of pristine PAN CNFs with similar size, i.e. 2.44 GPa and 28.97 GPa. The rough fracture surface for all GNR-reinforced CNFs suggests that the GNRs can dramatically toughen the fibers. A sword-in-sheath failure is observed in 4 wt% GNR reinforced CNFs, confirming that GNRs are entirely embedded and well aligned along the fiber axis. This study demonstrates the potential of GNRs as a promising reinforcement to improve the formation of graphitic carbon and mechanical performance of CNFs. [ABSTRACT FROM AUTHOR]

Multi-wall carbon nanotubes (MWCNTs) can be used to create ceramic nanocomposites with improved fracture toughness. In the present work, atomic layer deposition (ALD) was employed to deposit thin oxide layers on MWCNTs. These core-shell structures were then used to create nanocomposites by using a polymer derived ceramic (PDC) to produce the matrix. Variations in both the initial MWCNT structure and the oxide layers led to substantial differences in fiber-pullout behavior. Single tube pullout tests also showed that the oxide coatings led to stronger bonding with the ceramic matrix. With high defect density MWCNTs, this led to shorter pull-out lengths which is consistent with the conventional understanding of fracture in ceramic matrix composites. However, with low defect density MWCNTs longer pullout lengths were observed with the oxide layers. To interpret the different trends that were observed, we believe that the ALD coatings should not be viewed simply as a means of altering the interfacial properties. Instead, the coated MWCNTs should be viewed as more complex core-shell fibers where both interface and internal properties can be controlled with the ALD layers. [ABSTRACT FROM AUTHOR]

Abstracts Oxygen-modified monolayer g-C 3 N 4 materials (abbreviated as O-g-C 3 N 4 ) with high crystallinity in a high yield are prepared via thermal oxidation. The partial oxygenation of g-C 3 N 4 was simultaneously achieved, providing the opportunity to collaboratively affect both structure and electron for photocatalytic hydrogen evolution. The O-g-C 3 N 4 monolayer exhibited a production rate of ~44.37 mmol/g (~8874.7 μmol/h g) for hydrogen evolution leading to the highest external quantum efficiency (EQE) of 13.7% (at 420 nm) of the reported g-C 3 N 4 nanosheets in a 5 h duration under visible light irradiation. More promisingly, the photocatalytic reaction proceeded for more than 25 h without performance degradation. [ABSTRACT FROM AUTHOR]

Carbon nanotubes (CNTs) have been considered an ideal reinforcement for light-weight and high-strength ceramic matrix composites. Understanding the interfacial properties between CNTs and the matrix is crucial for engineering the desired properties in such composites. Here in-situ pull-out experiments with a polymer derived ceramic (PDC) matrix are carried out with both pristine CNTs and CNTs coated with Al 2 O 3 (CNT/Al 2 O 3 ) produced by Atomic Layer Deposition (ALD), using micro-fabricated devices in a scanning electron microscope. This carefully designed comparative study makes it possible to better understand the interfacial interactions between CNTs and PDC matrices. The interfacial shear strength (IFSS) of CNT-PDC is 9.99 ± 2.84 MPa, while the IFSS of (CNT/Al 2 O 3 )/PDC with ∼3 nm Al 2 O 3 coating thickness is 14.52 ± 2.66 MPa, demonstrating a 45.3% improvement. The non-linear failure observed with the coated CNTs is also indicative of energy dissipation mechanisms that promote toughening in ceramic matrix composites. The improved properties in (CNT/Al 2 O 3 )/PDC are believed to originate from increased surface roughness, which leads to mechanical interlocking at the interface during the pull-out process. The combination of special interlayer structures such as ALD Al 2 O 3 and strong CNTs opens up interesting opportunities for improving the mechanical properties of ceramic nanocomposites reinforced by CNTs. [ABSTRACT FROM AUTHOR]

Abstract: In this work, NbC nanowire arrays were successfully synthesized via a facile and cost-effective biotemplate method. Natural bamboo chips were used as both the carbon source and the template for formation of catalyst particles, which significantly simplify the synthesis process of NbC nanowire arrays. Based on the structural, morphological, and elemental analyses, a fluoride-assisted vapor–liquid–solid growth mechanism was proposed. In situ nanoscale three-point bending measurements demonstrated that the Young’s modulus of NbC nanowires was in the range from 281 to 453GPa with an average value of 338±55GPa. The resistivity of NbC nanowires was further investigated by in situ electrical property characterization using a multipoint measurement inside a transmission electron microscope. The resistivity of NbC nanowires was calculated to be 5.02mΩcm. [Copyright &y& Elsevier]

Abstract: A novel approach combining the atomic force microscopy probing of nacre biopolymer strand and the inverse finite element analysis has been used to directly measure the elastic modulus of nacre biopolymer matrix. An elastic modulus of 11±3GPa was determined for the first time from the direct measurement of the nacre biopolymer matrix. This property is essential for a fundamental understanding of the roles that the biopolymer matrix plays in nacre''s strengthening and toughening, and provides guidelines in selecting engineering polymers for biomimetic materials design and fabrication. Such coupled experimental and modeling techniques should find more applications in studying the mechanical behavior of biological materials. [Copyright &y& Elsevier]

Abstract: A chemical vapor infiltration (CVI) technique was used to overcome most of the challenges involved in fabricating exceptionally-tough CNT/SiC composites. Nanotube pullout and sequential breaking and slippage of the walls of the CNTs during failure were consistently observed for all fractured CNT/SiC samples. These energy absorbing mechanisms result in the fracture strength of the CNT/SiC composites about an order of magnitude higher than the bulk SiC. The CVI-fabricated CNT/SiC composites have an strongly-bonded tube/matrix interface and an amorphous, crack-free SiC matrix, enabling the composites to withstand oxidization at 700–1600°C in air. [Copyright &y& Elsevier]

Abstract: Determination of interfacial properties of thermal barrier coatings (TBCs) is very important for designing and evaluating the durability of TBCs. A new method combining a simple shear test and an inverse finite element analysis was developed and applied to measure the interfacial properties of two flame-sprayed yttria-stabilized zirconia TBCs. Nanoindentation testing was performed to determine the mechanical properties of different materials of the TBC systems. Variation of the lateral force during the shear test was recorded and analyzed to obtain the nominal ultimate shear strength of TBCs. The interfacial properties, namely fracture energy and stress intensity factor (mode II), of different TBC systems under both as-deposited and heat-treated conditions were determined through inverse finite element analysis. [Copyright &y& Elsevier]

In this paper, we propose a multiple amplify-and-forward (AF) relays based cooperative orthogonal frequency division multiplexing (OFDM) with quadrature index modulation (C-OFDM-QIM) system to enhance the spectral efficiency and the transmission reliability, where two independent subcarrier subsets are activated to convey the real and imaginary symbol vectors, respectively, and the per-subcarrier relay selection (RS) scheme is adopted to select the relay with the maximum end-to-end signal-to-noise ratio (SNR) for each active subcarrier. Both fixed-gain AF and variable-gain AF protocols are investigated at the selected relays. Based on the order statistics and the max-flow min-cut theory, the closed-form average outage probability (AOP) and the average capacity are derived, respectively. Numerical results demonstrate that the theoretical AOP is correct and accurate and the proposed C-OFDM-QIM system outperforms the traditional cooperative OFDM with index modulation (C-OFDM-IM) system in the spectral efficiency, the outage performance, and the average capacity. [ABSTRACT FROM AUTHOR]

Protonic ceramic electrochemical cells (PCECs) have the potential in reducing the energy input and carbon emissions in ethylene production from ethane dehydrogenation. The performance of conventional perovskite-based anode materials for ethane conversion in PCECs is limited by their low active surface area and proneness to coke deposition. In this work, for the first time, we demonstrate the use of aligned carbon nanotube forests (CNTFs) as a novel anode material for an ethane fueled PCEC to co-produce ethylene and electricity. The CNTF electrode was grown on the electrolyte by the chemical vapor deposition (CVD) method. Highly dispersed iron carbide nanoparticles are formed in situ on the CNTFs during the CVD process, acting as highly active catalysts for ethane dehydrogenation. The novel PCECs show superior catalytic and electrochemical performances to that using conventional perovskite-based anodes. The cell also exhibits excellent durability and anti-coking abilities within 100 h test. This work showcases the promising application of nanostructured carbon, a new class of non-perovskite materials, as the multifunctional electrode materials for PCECs. [Display omitted] • CNTF can be integrated into PCEC as electrode and catalyst support by CVD method. • CNTF is a promising non-perovskite candidate electrode material for PCEC. • CNTF shows superior electrochemical and catalytic performance than SFM. • Carburized Fe species on CNTF are the active species for EDH reaction. [ABSTRACT FROM AUTHOR]

Abstract: Robust Gd–La codoped TiO2 microspheres with diameter of 2∼3 μm were successfully synthesized via a hydrothermal method using poly(ethylene glycol)-block–poly(propylene glycol)-block–poly(ethylene glycol) as a template. The photocatalytic activity of the Gd–La codoped TiO2 microspheres evaluated by photodegrading methyl orange (MO) has been significantly enhanced compared to that of undoped TiO2 microspheres. Ti4+ may substitute for La3+ and Gd3+ in the lattices of rare earth oxides to create abundant oxygen vacancies and surface defects for electron trapping and dye adsorption, accelerating the separation of photogenerated electron–hole pairs and MO photodegradation. The formation of an exciton energy level below the conduction band of TiO2 from the binding of electrons and oxygen vacancies decreases the excitation energy of Gd–La codoped TiO2 microspheres, resulting in robust photocatalysts. The results suggest that Gd–La codoped TiO2 microspheres calcined at 350 °C are very promising for enhancing the photocatalytic activity of photocatalysts. [Copyright &y& Elsevier]

Highlights • A double perovskite PBFN is synthesized and characterized. • The nature of mixed electronic and ionic conductor benefits catalysis. • High power densities are achieved at 800 °C in H 2 and CH 4. • The anode exhibits stable performance in dry methane. • The anode shows strong redox stability. Abstract A novel A-site deficient ceramic oxide (PrBa) 0.95 (Fe 0.9 Nb 0.1) 2 O 5+δ with layered perovskite structure has been investigated as an anode material for a direct-hydrocarbon fueled solid oxide fuel cell. Promising performance of this anode is achieved by stabilizing the material with Nb doping at B sites, which shows excellent chemical stability and high catalytic activity in the reducing fuel condition. The button cell based on lanthanum gallate electrolyte exhibits peak power density of 1.05 W cm−2 in H 2 , 0.64 W cm−2 in CH 4 (∼3% H 2 O) and 0.57 W cm−2 in dry CH 4 at 800 °C, respectively. When the temperature is decreased to as low as 600 °C, the cell still reaches 0.18 W cm−2 in hydrogen. The anode is highly resistant against redox cycling with capability of rapid recovery from oxidizing condition. Based on a series of performance durability tests under various fuel conditions, this anode material has been demonstrated to be feasible for long-term operation in dry CH 4 without observable degradation. The results demonstrate a new technical route to develop highly active and stable ceramic anode by doping high-valence rare-earth elements into B sites of perovskite material. [ABSTRACT FROM AUTHOR]

Abstract In this study, well-aligned single-walled carbon nanotube (SWCNT) films were utilized as lamellae to prepare a multifunctional nanocomposite by a feasible 'layer-by-layer' preparation method. This structural design can not only dramatically reduce the agglomeration effect of SWCNTs, but also achieve high in-plane stiffness. It was found that the well-aligned SWCNT films contribute to the high stress-transfer between CNTs and present good wettability with epoxy matrix, thereby improving the mechanical enhancement. Interestingly, this laminated structure possesses distinct electrical behaviors under different loading conditions. The electrical resistance linearly increases with the increase of in-plane tensile strain but is insensitive to bending. This work could provide in-depth understanding on the mechanical and electrical properties of CNT-based laminated nanocomposites. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

In this paper, we take the spatial and delay-Doppler dimensions into account and propose a novel transmission scheme combining quadrature spatial modulation (QSM) and orthogonal time frequency space (OTFS) to improve the spectral efficiency, achieve the diversity gains, and resist strong Doppler effect in high-mobility scenes. The system model and the specific signal transmission process of the OTFS with QSM (QSM-OTFS) scheme are presented first. Then, the theoretical average bit error rate (ABER) analysis for QSM-OTFS system is provided. Additionally, a linear enhanced minimum mean square error (EMMSE) detection is investigated to reduce the detection complexity in the QSM-OTFS system. Numerical results illustrate that the QSM-OTFS system is able to obtain an improved ABER performance compared with the typical spatial modulation (SM) based OTFS (SM-OTFS) and that the proposed EMMSE detection outperforms the other linear detection algorithms under the same spectral efficiency. [ABSTRACT FROM AUTHOR]

Cellulose nanomaterials (CNMs) naturally exist in plant biomass. The success of extraction of CNMs opened up a new era of using plant biomass for innovative industrial applications. Because CNMs are abundant, renewable, biodegradable, transparent, light weight and low in cost, they are ideal materials for large volume applications such as packaging, automotive, building and infrastructure. In many potential application areas, CNM-enabled products appear in a composite form, mostly polymer composites. The industrial-scale manufacturing of CNM/thermoplastic composites remains as a set of unsolved problems for academia and industry. A prime challenge in applications is the nanoscale dispersion of CNMs in thermoplastic matrices during melt processing. Both bench-scale and pilot-scale studies have been conducted to solve the dispersion issue of CNMs. In this article, research related to the dispersion of CNMs in thermoplastic matrices during melt processing were critically reviewed. All research papers were classified into three groups: chemically-aided dispersion, physically-aided dispersion and mechanically-aided dispersion. Numerous factors affect the CNM dispersion and the mechanical performance of its nanocomposites. There are material-related factors, including CNM types and forms, polymer matrices, surface modification, coupling agents, etc. Extrusion processing parameters also play a significant role, covering screw rotation speed, extrusion barrel temperature settings and screw design. In addition, the material-related factors interact with the processing-related factors. Understanding all factors and their interactions are important for moving CNM nanocomposites research a step further towards industrial-relevant production, which is the final ambitious goal of this manuscript. Image 1 [ABSTRACT FROM AUTHOR]