High pressure torsion of nickel powders obtained by electrodeposition

A new synthesis route for the production of bulk nanostructured materials is presented. Fine Ni powder was made by selected appropriate electrolysis conditions. A compact material with an average grain size below 40 nm was obtained by subsequent cold pressing. Then, using the high pressure torsion (HPT) deformation technique dense bulk nanocrystalline Ni was achieved. The detailed structural investigations of the asprepared and HPT deformed Ni powder, including X-ray diffraction (XRD) and transmission electron microscopy (TEM), reveal in both cases the presence of a face centered cubic (FCC) phase without presence of any oxides. Coherently scattering domain size measurements by XRD show a value of 24 nm for the as-deposited powder and an even smaller value of 13.5 nm after HPT deformation. In addition, optical emission spectroscopy was employed to determine the impurity content of the obtained nanostructured material, showing a relatively low content of 0.9 % carbon and oxygen. The microhardness increased after deformation from (1.5 ± 0.08) GPa for the as-deposited Ni powder to (6.6 ± 0.2) GPa for the HPT deformed Ni powder. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/2061

Nanocrystalline Zr3Al Made through Amorphization by Repeated Cold Rolling and Followed by Crystallization

The intermetallic compound Zr3Al is severely deformed by the method of repeated cold rolling. By X-ray diffraction it is shown that this leads to amorphization. TEM investigations reveal that a homogeneously distributed debris of very small nanocrystals is present in the amorphous matrix that is not resolved by X-ray diffraction. After heating to 773 K, the crystallization of the amorphous structure leads to a fully nanocrystalline structure of small grains (10 - 20 nm in diameter) of the non-equilibrium Zr2Al phase. It is concluded that the debris retained in the amorphous phase acts as nuclei. After heating to 973 K the grains grow to about 100 nm in diameter and the compound Zr3Al starts to form, that is corresponding to the alloy composition

Electrochemical approaches to design materials for potential sensing and energy related applications

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Structure and Strength of Dislocation Junctions: An Atomic Level Analysis

The quasicontinuum method is used to simulate three-dimensional Lomer-Cottrell junctions both in the absence and in the presence of an applied stress. The simulations show that this type of junction is destroyed by an unzipping mechanism in which the dislocations that form the junction are gradually pulled apart along the junction segment. The calculated critical stress needed for breaking the junction is comparable to that predicted by line tension models. The simulations also demonstrate a strong influence of the initial dislocation line directions on the breaking mechanism, an effect that is neglected in the macroscopic treatment of the hardening effect of junctions.Comment: 4 pages, 3 figure

Electrochemical approaches in synthesis of high surface area materials

It is the aim of our work to carry out fundamental studies on designing and synthesizing high surface area functionalized foam and ordered structures for their potential sensing and energy related applications. We combine electrochemical synthesis with structural studies on different length scales including transmission electron microscopy. Templates are directly grown by electrodeposition, either by hydrogen bubble formation or by utilizing of ordered structures formed by anodic electrochemical oxidation. [1-3] We employed an elegant approach to obtain open, foam deposits of Ni and Ni alloys, by using electrodeposition at high current densities, to promote hydrogen evolution and bubble templating (cf. Fig.1). [1] In the next step, the high surface area of such materials was funtionalized by Pd utilizing galvanic displacement reaction. Electrochemical testing of the obtained open foam deposits shows promissing catalytical activity for hydrogen evolution in alkaline environments, as well as methanol and ethanol oxidation. In the case of fabrication of nanodendritic Ag simultaneously grown with porous anodic aluminium oxide we accomplished well anchored dendritic Ag nanostructures [2] of long-term stability [3]. 1. L. D. Rafailović, C. Gammer, C. Rentenberger, T. Trišović, C. Kleber, H. P. Karnthaler, Nano Energy, 2 (2012) 523 https://doi.org/10.1016/j.nanoen.2012.12.004 2. L.D. Rafailovic, C. Gammer, C. Rentenberger, T. Trisovic, C. Kleber, H.P. Karnthaler, Adv. Mater. 27 (2015) 6438 https://doi.org/10.1002/adma.201502451 3. L.D. Rafailovic, C. Gammer, J. Srajer, T. Trisovic, J. Rahel, H.P. Karnthaler; RSC Adv., 6 (2016) 33348, https://doi.org/10.1039/c5ra26632

Mesoscopic Analysis of Structure and Strength of Dislocation Junctions in FCC Metals

We develop a finite element based dislocation dynamics model to simulate the structure and strength of dislocation junctions in FCC crystals. The model is based on anisotropic elasticity theory supplemented by the explicit inclusion of the separation of perfect dislocations into partial dislocations bounding a stacking fault. We demonstrate that the model reproduces in precise detail the structure of the Lomer-Cottrell lock already obtained from atomistic simulations. In light of this success, we also examine the strength of junctions culminating in a stress-strength diagram which is the locus of points in stress space corresponding to dissolution of the junction.Comment: 9 Pages + 4 Figure

Non-canonical metabolic pathways in the malaria parasite detected by isotope-tracing metabolomics

The malaria parasite, Plasmodium falciparum, proliferates rapidly in human erythrocytes by actively scavenging multiple carbon sources and essential nutrients from its host cell. However, a global overview of the metabolic capacity of intraerythrocytic stages is missing. Using multiple