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Highlights: [•] A mass of amorphous carbon nanotubes have been synthesized. [•] The Fe76Si9B10P5 particles were employed as both the catalyst and support. [•] C2H2 and Ar were employed as carbon precursor and carrier gas, respectively. [ABSTRACT FROM AUTHOR]

Abstract: The initial stage growth of bamboo-shaped carbon nanotubes (CNTs) synthesized by catalytic decomposition of methane is investigated. A special experimental procedure has been developed to stop the process after short durations (0s to 3min). It has found that during the early stages (60s), carbon cluster-encapsulated nanoparticles are formed. With prolonging synthesis time (3min), some CNTs coexisted with carbon cluster-encapsulated nanoparticles are formed. HRTEM observations show that these CNTs display multi-walled and bamboo structure and the encapsulated catalytic particles are quasi-cone morphologies. At the same time, the catalytic particles only encapsulated with carbon clusters present quasi-sphere structures. For growth up to 60min, two kinds of bamboo mode structures are observed: conical, and cylindrical, which are developed by quasi-cone and quasi-sphere catalytic particles, respectively. Moreover, the early stage growth mode of the CNTs is predominantly of the base growth mode according to TEM observations. [Copyright &y& Elsevier]

Abstract: Carbon onions with diameters ranging from 5 to 50nm and carbon-coated nickel nanoparticles with diameters ranging from 10 to 60nm have been synthesized on a large scale over Ni/Al catalyst by chemical vapor deposition. The approximate ratio of Ni-filled to empty onions as observed by TEM is 1:3.5. In order to eliminate the nickel nanoparticle and obtain pure hollow carbon onions, HNO3 acid was used to dissolve the nickel from the carbon-coated nickel nanoparticles. The carbon onion particles thus obtained have hollow cores and are mainly composed of well-crystallized graphite, as characterized by high-resolution TEM and Raman spectroscopy. In addition, we proposed a simple purification mechanism for Ni-filled carbon onions based on TEM observations. [Copyright &y& Elsevier]

As one of the most efficient trace element to improve the mechanical properties of alloys, scandium (Sc) has attracted much attention for aluminum alloys in recent years. In this study, a new kind of Al–Zn–Mg–Cu–Sc–Zr alloy has been designed, and the evolution of microstructure and properties during the processes including homogenization, hot extrusion, solid solution and aging has been investigated. The alloy aged at 120 °C reveals a dual-peak aging phenomenon which is attributed to the overlap of the formation of Guinier–Preston (GP) zones and η′ phases. Consequently, excellent mechanical properties can be obtained (UTS = 747 MPa, YS = 721 MPa and EI = 10.9%) when the alloy is aged at 120 °C for 15 h. The improvement of the mechanical performance is mainly attributed to the grain refinement by the primary Al 3 (Sc, Zr) and the dispersion strengthening of the secondary Al 3 (Sc, Zr). Thus, the combined additions of Sc and Zr play an important role for the strengthening of the alloy. [ABSTRACT FROM AUTHOR]

The segregation of alien solute atoms at grain boundaries (GBs) in nanocrystalline materials can dramatically affect their macroscopic properties. As important solutes in Al alloys, Mg and Cu atoms have been experimentally observed to segregate at GBs, which would render a significant impact on the material. In this work, first-principles calculations were used to conduct a systematic and comprehensive investigation to reveal the segregation behavior of Mg and Cu atoms at Al Σ5 (310) and Σ9 (221) GBs and its effect on GB properties. The negative segregation energy demonstrates that both Mg and Cu have a strong tendency to segregate to the Al GBs. Moreover, the segregation of Mg and Cu atoms can reduce the GB energy, indicating an increased thermodynamic stability of the GBs. Mechanical properties are explored by a combination of canonical Griffith fracture model with ab-initio tensile test method. Results reveal that the doped Mg will embrittle both GBs due to the elongation of interatomic bonds and depletion of charge density across the GBs. Contrarily, the segregated Cu contributes greatly to enhancing the GB strength by creating strong Cu-Al bonds with surrounding Al at GBs. Besides, the increased tensile separation displacement of GBs with Cu segregation also suggests an improved resistance to fracture, especially the Σ9 (221) GB. This work provides a theoretical understanding for the changes in microscopic properties of Al GBs caused by Mg and Cu segregation from an atomic and electronic level. [Display omitted] • Mg/Cu solutes have strong segregation tendency toward Ʃ5 (310) and Ʃ9 (221) GBs in Al alloys. • Mg/Cu segregation thermodynamically stabilizes the Ʃ5 (310) and Ʃ9 (221) GBs. • Mg doping causes embrittlement of Al GBs while Cu segregation will enhance the GB cohesion. [ABSTRACT FROM AUTHOR]

Abstract: Fe(OH)3/Al with different Fe contents was prepared using a new deposition–precipitation reaction. Then mixed oxides were obtained by calcination of these precursors, and their catalytic activities were examined during synthesis of various carbon nanostructures. It was found that carbon nanotubes were synthesized using a Fe/Al2O3 catalyst with 10wt% Fe, while carbon coated metal nanoparticles resulted from Fe/Al2O3 catalyst with 15wt% Fe, but for the Fe/Al2O3 catalyst with 5wt% Fe, only amorphous carbon has been obtained. [Copyright &y& Elsevier]

Abstract: A mass of hollow carbon nanospheres was fabricated by chemical vapor deposition of methane over Ni/Al2O3 catalyst at 600°C. The products were characterized with scanning electron microscope, transmission electron microscope, and high-resolution transmission electron microscope images. The results showed that the external diameter of the hollow carbon nanospheres was 5–90nm and the thickness of the wall was about 15nm. And a possible formation mechanism of the hollow carbon nanospheres was discussed. [Copyright &y& Elsevier]

Abstract: A facile method was proposed to use Ni/Al2O3 as a catalyst to produce metallic nickel filled carbon nanotubes. Multi-walled carbon nanotubes filled with long continuous nickel nanowire length were synthesized through chemical vapor deposition at low temperature (600°C). Furthermore, the multi-walled carbon nanotubes were well-graphitized nanotubes. The analysis of scanning electron microscopy, transmission electron microscopy, selected area electron diffraction and X-ray diffraction revealed that the metallic nickel nanowires encapsulated inside carbon nanotubes existed as a single crystalline with fcc structure. [Copyright &y& Elsevier]

Abstract: A mass of carbon-coated cobalt nanoparticles were successfully synthesized by chemical vapor deposition of methane over Co/Al catalyst at 650°C. The phases found in the as-prepared carbon-coated nanoparticles were fcc-Co. The diameter of these nanoparticles with 2–10nm carbon coating shell was in the range of 5–80nm. However, it is well-known that the Co nanoparticles are suitable for carbon nanotube synthesis, such as Co/Al2O3 and Co/SiO2 catalysts. Here, we speculated that the formation mechanism of carbon-coated cobalt nanoparticles might due to that the formation of carbon nanotubes was inhibited by the catalyst supporter of Al. Compared with Al2O3 and SiO2, Al possesses very low melting point (660°C), very high diffusion coefficient and thermal conductivity, thus the isotropic precipitation of carbon species on the surface of cobalt particles took place, favoring the formation of carbon-coated Co nanoparticles. [Copyright &y& Elsevier]

As a promising architecture reinforcement, the three-dimensional (3D) configuration of nanocarbon holds great prospects in achieving a strength-ductility combination for metal matrix composite (MMCs). However, due to the native deficiency of Al in catalyzing the growth of nanocarbon, constructing a nanocarbon network has been the long-term challenge for Al matrix composites (AMCs). Herein, we develop a new strategy for synthesizing AMCs reinforced by three-dimensional nanocarbon (3D-C) via plasma-enhanced chemical vapor deposition (PECVD) integrated with hot pressing (HP) as well as hot extrusion, demonstrating exceptional mechanical properties. The detailed characterization reveals that the in-situ generation of nanocarbon layers on the surface of Al powders is attributed to the initiation of isolated carbon islands, followed by merging and self-assembly, which is governed by the PECVD-assisted catalysis growth-regime. The subsequent welding of nanocarbon layers during the HP promotes the formation of interlocking 3D-C networks in Al matrix, enhancing the sintered densification of the composite. Such unique nanocarbon distribution configuration not only effectively constrains the coarsening and deformation of Al grains, but also notably accumulates dislocation under high stress conditions. Moreover, 3D-C with a strong interfacial bonding contributes to the toughness through the microcracks, bridging cracks as well deflecting cracks, which accounts for the high toughness of the composite. This work provides new insights into the 3D distribution configuration of reinforcements in AMCs to achieve the optimized mechanical performance of composites. • Three-dimensional nanocarbon network in Al matrix was successfully synthesized. • 3D-C network constrains grain deformation and facilitates dislocation accumulation. • High-coherent 'C-Al 2 O 3 -Al' interface contributes to strength-ductility combination. [ABSTRACT FROM AUTHOR]

Easy agglomeration and poor interface are bottlenecks restricting the effective transfer of internal stress in ceramic nanoparticle-reinforced metal matrix composites (MMCs). In this study, nanosized MgO particles coated by in-situ few-layered graphene (MgO@FLG) were synthesized using methane as carbon source by chemical vapor deposition (CVD) method, then incorporated with Al matrix through powder metallurgy routes. It is demonstrated that MgO@FLG particles in composites were endowed with more significant strengthening contributions in comparison with the counterparts without coating. This is critically attributed to the interlayer van der Waals of FLG promoting the particle dispersion, and the chemical interface, which involves Mg-O-C bonding and moderate Al 4 C 3 nanorods, improving the interfacial bonding. The thermal expansion behaviors and coefficient of thermal expansion (CTE) of composites were investigated by testing thermal cycling ranging from 50 to 400 °C. The hysteresis residual strain of MgO@FLG/Al composites is less than that of MgO/Al composites, indicating a robust interface adhesion to adapt to the changing of internal stress. Furthermore, a low experimental CTE value was obtained for the MgO@FLG/Al composite, and its theoretical CTE value falls into a possible prediction region of Kerner's model. This work provides new insights into the reinforcement modification and interface design of particle-reinforced MMCs, facing the application of structural components with the improved thermal stability and high load-bearing capacity. [Display omitted] • A novel strategy is developed to fabricate Al matrix composites reinforced by MgO particles with in-situ few-layered graphene (FLG) coating. • The FLG coating promotes MgO particles finely dispersing and forming robust interfacial bonding with Al matrix. • MgO particles with FLG coating endow the composites with a well-balanced strength and ductility. • A tight interface cohesion bridged by in-situ FLG coating is responsible for a low thermal expansion property of composites. [ABSTRACT FROM AUTHOR]

New UV–Vis–NIR light responsive Er/Tm/Yb/Y 2 O 3 -SiC composites are designed by coupling different structured Er/Tm/Yb/Y 2 O 3 upconversion luminescence materials (UCLMs) with 3C-SiC ultrafine nanocrystals (NCs) and explored as an efficient photocatalytic material. The Er/Tm/Yb/Y 2 O 3 UCLMs can convert near-infrared (NIR) light into visible light which can be absorbed by 3C-SiC NCs, thus extend the optical responsive range of the photocatalysts to NIR light region. The structure effect of UCLMs on their upconversion luminescence performance is explored, indicating that the chain-like Er/Tm/Yb/Y 2 O 3 UCLMs display much more preferable luminescence activity than flake-like structure. Compared with pure 3C-SiC NCs, both the two hybrid structures offer excellent performance in catalyzing decomposition of methylene blue (MB) under illumination of NIR light as well as UV–Vis–NIR light. Moreover, the photocatalytic activity of chain-like Er/Tm/Yb/Y 2 O 3 -SiC composites is better than that of the flake-like composites, profiting from the high light absorption efficiency induced by the multiple reflection-absorption effect. It is anticipated that this work provides new insights into the fabrication of photocatalysts with excellent light responses to a broader spectral range. [ABSTRACT FROM AUTHOR]

Bifunctional perovskite catalysts with both oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) activity have potential applications in metal-air batteries and regenerative fuel cells etc. Elucidating the microscopic mechanism of the perovskite bifunctionality is of great scientific significance. Here, we studied the effects of oxygen vacancy (V O) on OER and ORR reaction processes on the LaCoO 3 surface based on the first-principles calculations. The results reveal the linear relationship between OER overpotential and the d‐band center of Co active site at the surface, which relates to the covalent component of the bond between the active sites and the oxygen atom in the intermediates. The O 2 desorption is linearly related to the distance between the d‐band center of Co active site and the p-band center of the oxygen atom in the O 2 intermediate. When V O is located at the subsurface, d‐band center of the Co active site and the covalent component of the bond between Co and O increase, and the OER activity of the adsorbate evolution mechanism is significantly enhanced with an overpotential of about 0.50 V. However, the desorption of OH intermediate is too difficult without V O or the adsorption for O 2 with V O is too weak for the reverse ORR reaction to occur. Therefore, the synergistic reaction mechanism involving Co and the adjacent surface V O is proposed for the ORR process with an overpotential of 0.31 V. The reverse OER reaction pathway with the lattice oxygen participation mechanism has an overpotential of 0.25 V, whereas the kinetics are limited because of the difficult desorption of O 2. Therefore, OER and ORR take a non-reverse reaction pathway, and the results can well explain the microscopic mechanism by which LaCoO 3 has excellent intrinsic ORR activity and V O enhances the LaCoO 3 bifunctionality, and provide theoretical basis for understanding the microscopic mechanism of bifunctional materials. [Display omitted] • The covalent component between Co and O determines the OER overpotential. • O 2 adsorption is linearly related to the distance between Co d‐band and O p-band center. • The non-reverse reaction pathways of OER and ORR are determined. • The synergistic reaction mechanism involving Co and surface V O is proposed. • It is suggested that LaCoO 3 with experimental V O reveals excellent bifunctionality. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) reduced graphene oxide (rGO) anchored carbon-coated Fe 2 O 3 core-shell nanoparticles (Fe 2 O 3 @C-rGO) has been developed successfully through a simple one-pot hydrothermal process followed by a further annealing treatment. The 3D Fe 2 O 3 @C-rGO nanocomposite consists of carbon-coated Fe 2 O 3 nanoparticle clusters (Fe 2 O 3 @C) and rGO nanosheets. The homogenously distributed and intercalated Fe 2 O 3 @C nanoparticles between rGO nanosheets form a highly conductive 3D carbon network with rGO, and present a hierarchical pore size structure, enabling fast ion and electron transport, as well as remarkable specific surface area. The electrochemical performance in supercapacitor has been characterized, and the as-prepared Fe 2 O 3 @C-rGO electrode shows a significant high specific capacitance of 211.4 F/g at 0.5 A/g and 177.2 F/g at 20 A/g with no visible performance decay even after 2500 cycles testing. These properties indicate a good potential to achieve high performance electrochemical devices. [ABSTRACT FROM AUTHOR]

The honeycomb-like porous Co 3 O 4 grown on three dimensional graphene networks/nickel foam (3DGN/NF) has been successfully prepared by a facile solution growth process with subsequent annealing treatment, in which the Co-based metal organic framework (ZIF-67) act as the precursor of the metal oxide. The Co 3 O 4 /three-dimensional graphene networks/Ni foam (Co 3 O 4 /3DGN/NF) hybrid as the electrode for supercapacitor can deliver high specific capacitance (321 F g −1 at 1 A g −1 ) and excellent long-cycling stability (88% of the maximum capacitance after 2000 charge-discharge cycles). Furthermore, the Co 3 O 4 /3DGN/NF hybrid exhibits the maximum energy density of 7.5 W h kg −1 with the power density of 794 W kg −1 and remain 4.1 W h kg −1 with the power density of 15 kW kg −1 in the two-electrode system. The enhanced electrochemical properties can be attributed to the unique nanostructure of Co 3 O 4 with admirable pseudocapacitance performance and the intimate integration of graphene with the Co 3 O 4 and the Ni foam matrix, which not only enhances the electron conductivity for fast electron and ion transport but also provides high specific surface area and excellent structural stability. [ABSTRACT FROM AUTHOR]

In this study, a Cu matrix composite is synthesized reinforced by an in-situ three-dimensional graphene network (3D-GN) grown through chemical vapor deposition (CVD). Nano Cu powders and polymethylmethacrylate (PMMA) are employed as matrix and carbon source respectively. PMMA is dispersed on Cu powders after ball-milling. During the CVD process, carbon atoms from pyrolyzed PMMA diffuse and precipitate on Cu powders. By inheriting the morphology of Cu powders, carbon atoms build a 3D-GN in-situ on Cu powders. A bulk 3D graphene/composite with 0.5 wt% graphene is obtained by vacuum hot-press sintering. The favorable interfaces that crucial to the achievement of exceptional mechanical properties of a bulk composite are verified by TEM and SEM characterizations. A yield strength and tensile strength of 290 MPa and 308 MPa respectively are achieved of the composite. The structure of 3D-GN is well preserved in the bulk composite. We demonstrate that the 3D-GN serves as an effective obstacle to the propagation of dislocations by TEM further. [ABSTRACT FROM AUTHOR]

A free-standing Fe 3 O 4 /rebar graphene (FRG) composite film was obtained through solvothermal method. The microstructure, phases, electrochemical performance of the composite used as anode in lithium ion battery have been characterized by SEM, TEM, XRD, Raman, FT-IR and electrochemical measurements. In rebar graphene (RG), the single-wall carbon nanotubes (SWCNTs) and graphene are interconnected via π–π stacking and covalent bonding. SWCNTs can keep the graphene in RG from fracture and maintain the integrity of the composite electrodes during lithiation/delithiation. The absence of additive and conductive agent can enhance electrochemical performance of FRG composite by losing redundant weight. The FRG composite exhibits an outstanding rate capability with an excellent cycling performance (1038 mAh g −1 after 100 cycles at 100 mA g −1 ). [ABSTRACT FROM AUTHOR]

A mass of carbon nanospheres (CNSs) have been synthesized by chemical vapor deposition of C 2 H 2 directly over Fe-based glassy alloy particles (Fe 76 Si 9 B 10 P 5 ) without the addition of an external catalyst. The morphology and microstructure as well as the growth mechanism of the CNSs have been investigated by using scanning and transmission electron microscopy. The results showed that the obtained products consist of hollow CNSs and CNSs with Fe nanoparticles encapsulated. The CNSs with amorphous walls have high purity (>95%) and uniform size distribution (50–150 nm). The possible formation and growth mechanism of the CNSs were discussed on the basis of the investigation on their initial growth stages. [ABSTRACT FROM AUTHOR]

Highlights: [•] Using zwitterionic surfactant to enhance the dispersion of the CNTs on the powder surface. [•] CNTs as carbon source decreased the formation temperature of Ti2AlC. [•] Al2O3 was generated in situ from the oxygen atoms introduced in the drying procedure. [•] Nanosized Ti3Al was precipitated at 1250°C and distribute in the TiAl matrix homogeneously. [•] Ti2AlC–Al2O3/TiAl composite was synthesized in situ by sintering pre-alloy Ti–Al coated with CNTs. [ABSTRACT FROM AUTHOR]

• Al matrix composite reinforced by uniformly dispersed MgAl 2 O 4 particles was successfully synthesized via shift-speed ball-milling (SSBM) combined with reactive sintering. • The produced MgO as a precursor participates the formation of homogeneously dispersed MgAl 2 O 4 that forms robust interfacial bonding with matrix. • Submicron MgAl 2 O 4 particles remarkably contributes to the strength of composite via the coefficient of thermal expansion (CTE) mismatch strengthening and grain refinement. In-situ synthesized Al matrix composites (AMCs) have drawn lots of interest recently relying on the designability of reinforcement configurations and promising mechanical properties. In this work, a new generation of AMCs reinforced by in-situ MgAl 2 O 4 particles was fabricated based on Al-Mg-ZnO system using shift-speed ball-milling (SSBM) combined with reactive sintering method. The detailed microstructural characterization and comprehensive thermodynamic analysis rationalized the in-situ reaction mechanism, in which the substituted MgO was involved in the formation of homogeneously dispersed MgAl 2 O 4 that forms robust interfacial bonding with matrix. In addition, the coefficient of thermal expansion mismatch strengthening and grain refinement acted in concert to render the impressive mechanical properties, achieving the yield stress of 347 MPa and ultimate tensile stress of 505 MPa. This work can be informative for the fabrication of high-performance in-situ MgAl 2 O 4 reinforced AMCs based on Al-Mg-oxides system. [ABSTRACT FROM AUTHOR]

• High temperature mechanical behavior of MgAlB 4 w/Al was studied. • UTS of 20 wt% MgAlB 4 w/Al composite at 300 °C can reach up to 166 MPa. • The failure behavior changes from the whisker fracture to interfacial debonding. High temperature tensile properties and fracture mechanism of the MgAlB 4 w/Al composites. [Display omitted] Aiming at developing high temperature resistance aluminum matrix composites for both structural and functional purposes, the novel MgAlB 4 whisker reinforced Al matrix composites with directional distributed reinforcement were fabricated using powder metallurgy followed by hot extrusion. The microstructure characterization demonstrated that Al grains exhibited a distinct< 111 > Al texture and MgAlB 4 whiskers aligned along the extrusion direction in the as-extruded composites. The high temperature tests indicate that UTS of the 20 wt% MgAlB 4w /Al composite at 200 °C and 300 °C can reach up to 266 MPa and 166 MPa, respectively, with a CTE of 23.7 × 10−6 K−1 at 300 °C. The whiskers distributed within the grains have a pinning effect on the dislocation movement and the whiskers distributed on the grain boundaries impede the grain boundaries sliding and migration. Additionally, the failure behavior changes from MgAlB 4 whiskers fracture to interfacial debonding of MgAlB 4w -Al matrix as the temperature increases. [ABSTRACT FROM AUTHOR]

Abstract: An approach was developed to fabricate carbon nanotube (CNT)-reinforced Al composites. In a typical process, the Co catalyst was evenly deposited on the surface of Al powder by impregnation route, and then the CNTs were grown in the Al powder by chemical vapor deposition to obtain CNT/Al powders. After ball-milling of the obtained powders for a short time, the CNT/Al composites were fabricated by compacting, sintering and hot extrusion of the ball-milled powders. During this process, the well dispersed CNT reinforcement is deeply embedded in the Al powder forming an effective interface bonding with matrix. As a result, the CNT/Al composites containing 2.5wt.% CNTs exhibit the ultimate tensile strength of 334MPa which is 1.7 times higher than that of unreinforced Al, and good ductility of ∼18% elongation to failure. Thus, well-balanced strength and ductility are achieved in CNT-reinforced Al composites. [Copyright &y& Elsevier]