Galvanic Transformation Dynamics in Heterostructured Nanoparticles

Corrosion is a significant problem for the stability of structural metals and potentially for functional nanomaterials in operating environments. When two metals with different electrochemical potentials form a junction, galvanic corrosion occurs, resulting in the sacrificial dissolution of the metal with a higher oxidation potential (lower electrode potential). Here, it is shown that bimetallic hetero-nanostructures composed of phase-segregated metals undergo galvanic corrosion in aqueous environments. Such selective etching of the sacrificial metal in heterojunction particles leads to the formation of unusual and kinetically stabilized half-spheroid particles. By using a fluid cell and in situ scanning transmission electron microscopy, a two-stage corrosion process can be observed where the Cu experiences a fractal breakdown before the Ag corrodes due to the lack of a protective oxide layer. However, when treated with a mild Ar plasma, the stability of these structures against corrosion is enhanced due to the conversion of the amorphous native oxide to a denser, thin layer of CuO on the Cu surface. Taken together, this work highlights the importance of considering the effects of galvanic corrosion on the stability of multicomponent nanoparticles, and it shows how mass transport in a nanoscale system is influenced by redox processes.     

Efficient wave propagation simulation on quadtree meshes using SBFEM with reduced modal basis

We apply a combination of the transient scaled boundary finite element method (SBFEM) and quadtree‐based discretization to model dynamic problems at high frequencies. We demonstrate that the current formulation of the SBFEM for dynamics tends to require more degrees of freedom than a corresponding spectral element discretization when dealing with smooth problems on regular domains. Thus, we improve the efficiency of the SBFEM by proposing a novel approach to reduce the number of auxiliary variables for transient analyses. Based on this improved SBFEM, we present a modified meshing procedure, which creates a quadtree mesh purely based on the geometry and allows arbitrary sizes and orders of elements, as well as an arbitrary number of different materials. The discretization of each subdomain is created automatically based on material parameters and the highest frequency of interest. The transition between regions of different properties is straightforward when using the SBFEM. The proposed approach is applied to image‐based analysis with a particular focus on geological models. Copyright © 2016 John Wiley & Sons, Ltd.     

Macroscopic simulation and experimental measurement of melt pool characteristics in selective electron beam melting of Ti-6Al-4V

Selective electron beam melting of Ti-6Al-4V is a promising additive manufacturing process to produce complex parts layer-by-layer additively. The quality and dimensional accuracy of the produced parts depend on various process parameters and their interactions. In the present contribution, the lifetime, width and depth of the pools of molten powder material are analyzed for different beam powers, scan speeds and line energies in experiments and simulations. In the experiments, thin-walled structures are built with an ARCAM AB A2 selective electron beam melting machine and for the simulations a thermal finite element simulation tool is used, which is developed by the authors to simulate the temperature distribution in the selective electron beam melting process. The experimental and numerical results are compared and a good agreement is observed. The lifetime of the melt pool increases linearly with the line energy, whereby the melt pool dimensions show a nonlinear relation with the line energy.     

Mobility of nanosized cerium dioxide and polymeric capsules in quartz and loamy sands saturated with model and natural groundwaters

The environmental and health risks posed by emerging engineered nanoparticles (ENPs) released into aquatic environments are largely dependent on their aggregation, transport, and deposition behavior. Herein, laboratory-scale columns were used to examine the mobility of polyacrylic acid (PAA)-coated cerium dioxide nanoparticles (nCeO₂) and an analogous nanosized polymeric capsule (nCAP) in water saturated quartz sand or loamy sand. The influence of solution ionic strength (IS) and cation type (Na⁺, Ca²⁺, or Mg²⁺) on the transport potential of these ENPs was examined in both granular matrices and results were also compared to measurements obtained using a natural groundwater. ENP suspensions were characterized using dynamic light scattering and nanoparticle tracking analysis to establish aggregate size, and laser Doppler electrophoresis to determine ENP electrophoretic mobility. Regardless of IS, virtually all nCeO₂ particles suspended in NaNO₃ eluted from the quartz sand-packed columns. In contrast, heightened nCeO₂ and nCAP particle retention and dynamic (time-dependent) transport behavior was observed with increasing concentrations of the divalent salts and in the presence of natural groundwater. Enhanced particle retention was also observed in loamy sand in comparison to the quartz sand, emphasizing the need to consider the nature of the aqueous matrix and granular medium in evaluating contamination risks associated with the release of ENPs in natural and engineered aquatic environments.     

Rheological properties and irreversible dispersion changes in carbon nanotube/epoxy systems

We report on the rheological properties of semidilute carbon nanotube (CNT)/epoxy suspensions with varying filler content prepared with different dispersion methods. We show that dispersion techniques can be distinguished by means of the rheological response. It was found that the suspensions undergo a lasting dispersion changes during the first shear sweep measurement. Shear‐induced changes within the suspension can also be visualized optically. Our results demonstrate that the rheological properties are strongly influenced by the measurement procedure, which has to be known in order to guarantee reproducible and comparable results. Finally, it does not seem possible to completely reset the sample history by shear treatment. POLYM. ENG. SCI., 2011. ©2011 Society of Plastics Engineers     

Furan in heat‐treated foods: Formation,exposure, toxicity,and aspects of risk assessment

Furan is formed in a variety of heat‐treated foods through thermal degradation of natural food constituents. Relatively high levels of furan contamination are found in ground roasted coffee, instant coffee, and processed baby foods. European exposure estimates suggest that mean dietary exposure to furan may be as high as 1.23 and 1.01 μg/kg bw/day for adults and 3‐ to 12‐month‐old infants, respectively. Furan is a potent hepatotoxin and hepatocarcinogen in rodents, causing hepatocellular adenomas and carcinomas in rats and mice, and high incidences of cholangiocarcinomas in rats at doses ≥2 mg/kg bw. There is therefore a relatively low margin of exposure between estimated human exposure and doses that cause a high tumor incidence in rodents. Since a genotoxic mode of action cannot be excluded for furan‐induced tumor formation, the present exposures may indicate a risk to human health and need for mitigation. This review summarizes the current knowledge on mechanisms of furan formation in food, human dietary exposure to furan, and furan toxicity, and highlights the need to establish the risk resulting from the genotoxic and carcinogenic properties of furan at doses lower than 2 mg/kg bw.     

Organization of knowledge about a relationship partner: Implications for liking and loving.

In close relationships, the association between negative beliefs about a partner and loving was found to be moderated by how that negative knowledge was organized. In general, evaluatively integrative organization (i.e., categorizing positive and negative beliefs together) was associated with more positive thoughts, feelings, and behaviors toward the partner when the negative content of beliefs was high and relationships were relatively long. Additional evidence suggests that compartmentalization (i.e., organizing positive and negative beliefs in separate categories) may be an effective strategy for handling negative beliefs about a partner in a new relationship. Findings for behavioral closeness raise the possibility that the nature of shared activities, as well as an individual's cognitive processes, may influence how knowledge about a relationship partner is organized. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Investigating the prospects of bacterial biosurfactants for metal nanoparticle synthesis – a comprehensive review

Establishing biological synthesis of nanoparticles is increasing nowadays in the field of nanotechnology. The search for an optimal source with durability, stability, capacity to withstand higher environmental conditions with excellent characteristics is yet to meet. Consequently, there is need to create an eco‐friendly strategy for metal nanoparticle synthesis. One approach investigated in this review is the use of biosurfactants to enhance the synthesis biologically. In comparison with the other technologies, biosurfactants are less toxic and exhibit higher properties. This method is different from the conventional practice like physical and chemical methods. Several research studies represented that the biosurfactant influences the production of nanoparticles about 2–50 nm. In this manner, the research towards the biosurfactant has raised. This review also addressed the feasibility of biosurfactant and their benefits in the synthesis of metallic nanoparticles. The findings from this review can recommend a conceivable use of biosurfactant as a source for metal nanoparticle synthesis.Inspec keywords: nanoparticles, microorganisms, nanotechnology, biotechnology, nanofabrication, durability, surfactants, reviewsOther keywords: biological synthesis, bacterial biosurfactants, environmental conditions, metallic nanoparticles synthesis, nanotechnology, durability, review, stability, size 2.0 nm to 50.0 nm     

Revealing the Dynamics of Hybrid Metal Halide Perovskite Formation via Multimodal In Situ Probes

The exploration of the synthetic space of halide perovskites hinges on an enormous number of parameters requiring time‐consuming experimentation to decouple and optimize. Here, the formation of the prototype material CH₃NH₃PbI₃ (MAPbI₃) is investigated at different time and length scales using multimodal in situ measurements to monitor the evolution of crystalline phases, morphology, and photoluminescence as a function of the lead precursors. Kinetically fast formation of crystalline precursor phases already during the spin‐coat deposition is observed using lead iodide (PbI₂) or lead chloride (PbCl₂) routes. These precursor phases most likely template final MAPbI₃ film morphology. In particular, the emergence of the “needle‐like” structure is shown to appear before film annealing. In situ photoluminescence measurements suggest nanoscale nucleation followed by rapid nuclei densification and growth. Using this multimodal in situ approach, different formation pathways can be identified either via precursor phases in the PbI₂ and PbCl₂ routes or direct perovskite formation from molecular building blocks as observed in the lead acetate (PbAc₂) route. Correlation of in situ results with photovoltaic device performance demonstrates the power of in situ multimodal techniques, paves the way to a fast screening of synthetic parameters, and ultimately leads to controlled synthetic procedures that yield high‐efficiency devices.