Twinning plays an important role in governing the balance between strength and ductility in hexagonal-close-packed (HCP) metals. Here, we report a combined experimental and theoretical study of twin nucleation from a single dislocation in HCP crystals. Specifically, high-resolution transmission electron microscopy has been used to identify {112¯1} twin nuclei in HCP rhenium, providing evidence of their nucleation from a dislocation. The favorability of this dislocation-based nucleation mechanism is rationalized by an anisotropic elasticity model of dislocation dissociation, parametrized by density functional theory calculations, which suggests the conditions for disconnection nucleation and propagation, under which this {112¯1} twinning mechanism is expected to be effective. The analysis serves to advance our understanding of the origin of the unique predominance of {112¯1} twinning in rhenium, which correlates with the high strength and ductility featured by this metal. It also provides new insights into design strategies that may be effective in activating this twinning mode and enhancing the balance between strength and ductility in HCP alloys more broadly.

We herein report a simple two-step procedure for fabricating tetragonal CoMn2O4 spinel nanocrystals on carbon fibers. The battery-type behavior of these composite fibers arises from the redox activity of CoMn2O4 in an alkaline aqueous solution, which, in combination with the carbon fibers, endows good electrochemical performance and long-term stability. The C@CoMn2O4 electrode exhibited high specific capacity, up to 62 mA h g-1 at 1 A g-1 with a capacity retention of around 90% after 4000 cycles. A symmetrical coin-cell device assembled with the composite electrodes delivered a high energy density of 7.3 W h kg-1 at a power density of 0.1 kW kg-1, which is around 13 times higher than that of bare carbon electrodes. The coin cell was cycled for 5000 cycles with 96.3% capacitance retention, at a voltage of up to 0.8 V, demonstrating excellent cycling stability.

We report a mesoporous composite system consisting of carbon fiber cores surrounded with Co1.5Mn1.5O4 spinel nanocrystal shells, synthesized by a simple two-step process involving single-nozzle co-electrospinning and subsequent calcination. Benefiting from the obtained core-shell structure, this composite has exhibited high specific capacitance in the two-electrode configuration, up to 384 F g(-1) at 0.28 A g(-1), with no capacitance loss after 2000 cycles at 50 mV s(-1). The incorporation of spinel nanocrystals improved the capacitive performances of composite fibers due to a synergistic effect of redox-active shells and the conductive cores, making this novel material promising for symmetrical supercapacitors.

The controllable synthesis of rutile TiO2 single crystal particles with the preferential orientation of {111} facets still remains a scientific and technological challenge. Here, we developed a facile route for fabrication of rutile TiO2 nanorod crystals (RTiO(2)NRs) having high ratios of oxidative {111} to reductive {110} surfaces. RTiO(2)NRs were synthesized using a peroxo-titanium complex (PTC) approach, which was controlled by changing the Ti/H2O2 ratio. The thus obtained RTiO(2)NRs revealed a high tendency to agglomerate through orientation-dependent attachment along the {110} facets. This resulted in an increased {111}/{110} surface ratio and led to a markedly improved photocatalytic activity of RTiO2NR aggregates. The reported findings illustrate the rich potential of the herein proposed facile and energy-efficient synthesis of nanostructured rutile TiO2-based photocatalysts.

Structural defects such as stacking faults and twins, observed in many face-centered cubic (FCC) structured metals and alloys with low stacking fault energies, in general, play an important role in microstructure evolution, and in particular, in nucleation and crystal growth, morphology development, and phase transformations during synthesis as well as post-synthesis processes.

Low loading PtAu nanoparticles supported on high area carbon were synthesized by water-in-oil microemulsion method and examined for formic acid and methanol oxidation. Prepared catalyst powder was characterized by Xray diffraction (XRD), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). These techniques revealed that the catalyst contains rather agglomerated quasi-spherical particles, similar to 4 nm diameter, composed of a solid solution of Pt and Au with only similar to 4 at% of Au. In spite of such low Au content, both onset and peak potentials for CO oxidation are shifted some 150 mV to more positive values in comparison to Pt synthesized in the same manner due to stronger binding of CO as a result of notable electronic effect. It is important that this small quantity of Au also significantly influences oxidation of formic acid promoting direct path and suppressing indirect path in formic acid oxidation in a degree as expected by a much larger quantity of Au. Such improvement could be due exclusively by ensemble effect of high number of small Pt domains which formation could be possible only by very fine dispersion of such low Au quantity. High number of small Pt domains is corroborated by lower activity for methanol oxidation in comparison to Pt catalyst synthesized by the same procedure. These results emphasize the importance of the Au dispersion on the surface of Pt over its quantity in PtAu catalyst with regards to both, the ensemble and the electronic effects.

Pristine electric arc furnace slag (EAFS) as well as EAFS modified by alkali activation i.e. alkali activated slag (AAS) have found a novel application as adsorbents used in Cu2+ removal from sulfate solutions. The adsorption tests were carried in batch conditions and results have shown that alkali activation of EAFS enhances the Cu2+ adsorption. The adsorption process was found to follow a pseudo second-order kinetic model and occurs via formation of posnjakite (Cu-4(SO4)(OH)(6)center dot H2O) on the surface of both, EAFS and AAS. Enhanced adsorption properties of AAS, compared to EAFS, are attributed to a more porous structure, larger specific surface area and an increased number of surface groups involved in the binding of Cu2+. (C) 2018 Elsevier B.V. All rights reserved.

PtAu systems are recognized as good catalysts for the oxidation of formic acid electrooxidation, which is investigated as a possible anodic reaction in low-temperature fuel cells.In this research, bimetallic PtAu nanoparticles, supported on high area carbon Vulcan XC-72R, were synthesized by water in oil microemulsion method.The precursor reduction process took place in a single microemulsion, simultaneously, in the presence of 35% of HCl in the water phase, as a capping agent.Electrochemical behavior of the PtAu/C catalyst was investigated at as prepared electrodes by cyclic voltammetry in 0.5M H 2 SO 4 as a supporting electrolyte, and also in the oxidation of adsorbed CO.The results were compared to the Pt/C catalyst prepared by the same synthesis procedure.PtAu/C catalyst powder was also characterized by X-Ray Diffraction (XRD), High Resolution Transmission Electron Microscopy (HRTEM) and Energy Dispersive X-Ray Spectroscopy (EDS).Average particle diameter, of 2nm, was calculated from XRD data, which is close to the value of 2.82 nm obtained from TEM images.Compared to identically synthesized Pt nanoparticles, the bimetallic ones are significantly smaller.EDS maps of PtAu/C sample confirm the presence of both elements, and indicate a very fine distribution of Au in the sample.Elemental composition of about 20% Au and 80% Pt was also determined from these maps.Prepared catalyst was tested for formic acid electro-oxidation in terms of its activity and stability over the long term cycling.The voltammograms recorded indicate the change of reaction mechanism and better utilization of the catalyst surface in comparison to Pt/C.

This article focuses on the microscopic mechanism of thermally induced nanoweld formation between silver nanowires (AgNWs) which is a key process for improving electrical conductivity in NW networks employed for transparent electrodes. Focused ion beam sectioning and transmission electron microscopy were applied in order to elucidate the atomic structure of a welded NW including measurement of the wetting contact angle and characterization of defect structure with atomic accuracy, which provides fundamental information on the welding mechanism. Crystal lattice strain, obtained by direct evaluation of atomic column displacements in high resolution scanning transmission electron microscopy images, was shown to be non-uniform among the five twin segments of the AgNW pentagonal structure. It was found that the pentagonal cross-sectional morphology of AgNWs has a dominant effect on the formation of nanowelds by controlling initial wetting as well as diffusion of Ag atoms between the NWs. Due to complete solid-state wetting, at an angle of ∼4.8°, the welding process starts with homoepitaxial nucleation of an initial Ag layer on (100) surface facets, considered to have an infinitely large radius of curvature. However, the strong driving force for this process due to the Gibbs–Thomson effect, requires the NW contact to occur through the corner of the pentagonal cross-section of the second NW providing a small radius of curvature. After the initial layer is formed, the welded zone continues to grow and extends out epitaxially to the neighboring twin segments.

Tungsten based support was prepared by polycondensation of resorcinol and formaldehyde from ammonium metatungstate, in the presence cetyltrimethylammonium bromide (CTABr) surfactant. Pd nanocatalyst on this support was synthesized by borohydride reduction method. The obtained materials were characterized by High Resolution Transmission Electron Microscopy (HRTEM), Electron Energy Loss Spectroscopy (EELS), X-ray Photoelectron Spectroscopy (XPS) and electrochemical measurements. TEM analysis revealed Pd nanoparticles size in the range of a few nanometers, even the clusters of single Pd atoms. X-Ray Photoelectron Spectroscopy was applied to determine surface composition of the substrates. It was found that tungsten based support consisted of W, WC and WO3 species. The presence of metallic palladium - Pd(0) in the Pd/W@WCWO3 catalyst was revealed, as well. The catalytic activity and stability for the oxygen reduction were investigated in acid and alkaline solutions, by cyclic voltammetry and linear sweep voltammetry at the rotating disc electrode. The catalysts' activities were compared to the carbon supported Pd nanoparticles (Vulcan XC 72). WC supported Pd nanoparticles have shown high activity and superior stability, comparable even to Pt based catalysts, especially in alkaline electrolytes. (C) 2017 Elsevier Ltd. All rights reserved.

In this report, we demonstrate a simple fabrication route for polyvinyl butyral (PVB)‐based nanocomposites with carbon nanotubes and graphene. In spite of insufficient percolation threshold due to low concentration of carbonaceous nanofillers, in the amount of 1 wt%, significant improvement of electrical and mechanical properties with negligible deterioration of optical properties for the polymer PVB matrix can be achieved. Both hardness and modulus increase and electrical resistivity and transmittance decrease in this order: PVB + multi‐wall carbon nanotubes (MWCNT) ⇒ PVB + single‐wall carbon nanotubes (SWCNT) ⇒ PVB + graphene. The largest values of reduced modulus and hardness are observed for the PVB + graphene nanocomposite, obtained by nanoindentation. Transmittance is ∼84%, 86%, 89%, and 91% at 370 nm, and at 550 nm is ∼84%, 88%, 90%, and 92%, for PVB + graphene, PVB + MWCNT, PVB + SWCNT, and pure PVB, respectively. The highest resistivity of 4 × 104 Ωcm is exhibited by the PVB + MWCNT nanocomposite while the lowest, 1.9 × 103 Ωcm, is exhibited by the PVB + graphene. Nanocomposite films are fabricated by a simple processing route using ultrasonic mixing and spin coating. POLYM. COMPOS., 38:E490–E497, 2017. © 2016 Society of Plastics Engineers

Geopolymeric binders (GB) were produced using fly ash (FA) and electric arc furnace slag (EAFS). The slag has been added in the range of 0–40%. The effects of slag content on the strength, microstructure and thermal resistance were evaluated. It was found that the amount of EAFS up to 30% positively affects the strength evolution of GB. The main reaction product of FA/EAFS blends was amorphous N–(C)–A–S–H gel along with geopolymer-type gel (N–A–S–H). Thermal resistance of GB was considered from the standpoint of their mechanical and dimensional stability after heating in the temperature interval of 600–800°C. The changes in mechanical and thermal properties of GB after heating are attributed to the changes in their structure. The results have shown that EAFS negatively affects the thermal resistance of GB above 600°C due to the phase transition and morphological transformation of the amorphous gel phase.

In this manuscript a survey of the contemporary research related to platinum nanocatalysts on metal oxide based supports for low temperature fuel cell applications is presented. Different carbon based supports, used as state of the art materials, are listed and discussed, as well. Although carbon based materials possess many desirable properties, such as high surface area, high conductivity and relatively low cost and easy synthesis, the large scale commercialization is limited by instability under accelerated stability testing, simulating real fuel cell operating conditions. To overcome these disadvantages of carbon supports, different metal oxide based ones have been studied and promising results are referenced. The most often used oxide based supports for low temperature fuel cell applications are presented in this review. Suitable discussion and future research related remarks are given, as well.

1 Sandia National Laboratories, Livermore, CA, USA 2 Materials Science and Engineering, Stanford University, Stanford, CA, USA 3 Sandia National Laboratories, Albuquerque, NM, USA 4 Lawrence Livermore National Laboratory, Livermore, CA, USA 5 Materials Science and Engineering, University of CA, Berkeley, CA, USA 6 Nanotechnology and Functional Materials Center, University of Belgrade, Belgrade, Serbia

The dissolution of electric arc furnace steel slag (EAFSS) in highly alkaline MOH solution (M=alkali metal Na or K) has been investigated with emphases on the influence of the initial alkali concentration, solid to liquid (S/L) ratio and temperature on the kinetics of Si and Al dissolution from EAFSS. The shrinking core model (SCM) was used to analyze experimental data and the results have shown that the Si and Al dissolution from EAFSS was greatly influenced by MOH concentration, alkaline ion type and temperature. The dissolution process was controlled by the bulk diffusion through the product layer crystals. The activation energy for Si and Al dissolution was 55.27kJ/mol and 48.05kJ/mol in NaOH solution and 90.68kJ/mol and 33.62kJ/mol in KOH solution, respectively.

Pd-Ni/C catalyst was synthesized employing a borohydride reduction method. The high area Ni was first dispersed on the carbon support and then modified by Pd nanoparticles. Transmission electron microscopy confirmed relatively even distribution of Ni across the carbon support with discrete palladium particles of about 3.3 nm mean diameter on it. Cyclic voltammetry confirmed the presence of Ni on the catalyst surface. The activity of the Pd-Ni/C catalysts for ethanol oxidation reaction (EOR) in alkaline solution was tested under the potentiodynamic and potentiostatic conditions and the results were compared to those obtained on the Pd/C catalyst. It was found that Pd-Ni/C is more active for the EOR compared to Pd/C by a factor up to 3, depending on the type of experiments and whether specific activity or mass activity are considered. During the potentiodynamic stability test an interesting phenomenon of activation of Pd-Ni/C catalyst was observed. It was found that maximum activity is attained after fifty cycles with the positive potential limit of 1.2 V, regardless of whether they were performed in the electrolyte with or without ethanol. It was postulated that potential cycling of the Pd-Ni surface causes reorganization of the catalyst surface bringing Pd and Ni sites to a more suitable arrangement for the efficient ethanol oxidation. (C) 2016 Elsevier B.V. All rights reserved.

In this research, a water-in-oil microemulsion method with HCl as a capping agent was applied to synthesize carbon supported Pt catalysts. Varying the concentration of HCl caused changes in the shape of obtained nanoparticles, i.e. preferential growth of certain facets. Addition of catalyst support in the synthesis process facilitated the cleaning procedures necessary to remove the surfactant residues. Prepared catalyst powders were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). XRD analysis indicated the influence of HCl addition on the crystallite size and crystal habit. TEM revealed that addition of higher amounts of the capping agent led to the formation of a noticable amount of particles with concave cubic or branched-like structures. Influence of the catalyst particles shape on its electrochemical properties was tested in the oxidations of COads, ammonia and formic acid. The latter one was examined in terms of both activity and stability of as prepared and oxide-annealed (electrochemically treated) catalysts. The results clearly demonstrate that even small changes in the nanoparticle surface structure give rise to distinct modifications in their properties. Concave cubic particles, in comparison to other catalysts, show improved catalytic properties and the contribution of their preferentially oriented {100} facets is electrochemically detectable. (C) 2016 Elsevier B.V. All rights reserved.

Detailed defect structure of dendrite formation was studied in order to connect the mesoscopic with the atomistic structure. It was demonstrated that twinning and stacking fault formation play a central role in the growth of electrodeposited Ag dendrites. The broad faces of Ag dendrites and the main trunk growth direction were found to be ((1) over bar 11) and [(1) over bar1 (2) over bar], respectively. Dendrite branches also formed and grew from the main trunk parallel to the [12 (1) over bar] and [(211) over bar] crystallographic directions. Twins and stacking faults were found to reside on the {111} crystallographic planes, as expected for a face centered cubic (FCC) Ag crystal. Using electron back scattered diffraction (EBSD) we found two variants of in-plane 60 degrees rotational twin domains in the ((1) over bar 11) broad dendrite surface plane. The intersections of twins and stacking faults with dendrite arm surfaces are perpendicular to the (112) arm growth directions. However, occasionally twins on the {111} planes parallel to the (112) arm growth directions were also observed. Although defect assisted dendrite growth is facilitated by twinning and stacking fault formation on {111} planes, the growth directions of the trunk and branches are not of the (111) type, but rather close to (112). The (112) growth directions are maintained by breaking dendrite facets into thermodynamically stable 111 and 200 steps and structural ledges of different length.

Pt nanoparticles supported on Vulcan XC-72R were synthesized by water-in-oil microemulsion method. By incorporating different amounts of HCl as a capping agent in the precursor-containing water phase, nanoparticle shape was varied. Influencing the growth of certain facets leads to the changes of the particle shape depending on the preferential facets. As a result, nanoparticles exhibit some of the electrochemical features typical for single crystals. Commonly employed synthesis procedure for water-in-oil microemulsion method was altered with the addition of catalyst support in the system and changing the catalyst cleaning steps. Prepared catalysts were characterized by thermogravimetric analysis (TGA), transmission electron microscopy (TEM) and electrochemical methods. Activity and stability for methanol oxidation reaction (MOR), a structure-sensitive reaction, were tested. Electrochemical results reveal the influence of particle size, shape and exposed facets on the electrochemical processes. TEM investigations confirm electrochemical findings, while TGA verifies Pt loading in catalyst powder. Based on the results, optimal HCl concentration for cubic particle formation is determined, and structural effect on MOR activity and stability was tested. Cuboidal NPs show very good reaction activity and fair stability under applied experimental conditions.