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Electronic and magnetic properties of graphene quantum dots doped with alkali metals

Publication date: March–April 2021

Source: Journal of Materials Research and Technology, Volume 11

Author(s): Waleed Osman, H. Abdelsalam, M. Ali, N.H. Teleb, I.S. Yahia, M.A. Ibrahim, Q. Zhang

Republished by Plato

Published

on


Elsevier
Volume 11, March–April 2021, Pages 1517-1533
Journal of Materials Research and Technology

open access

Abstract

The electronic and magnetic properties of armchair-hexagonal (AHEX) and zigzag-triangular (ZTRI) graphene quantum dots doped with alkali metals are investigated using density functional theory. The binding energy confirms the stability of the undoped systems. Although doping decreases stability of single layer structures, in bilayer ones the binding energy between the layers increases. The former is due to the broken bonds and the deformation at the surface, while the later is due to the chemical bonds formation between the layers. We found that the lowest ground state energy for AHEX/AHEX-doped is the singlet/quadruplet spin state. Therefore, AHEX dots experience transformation from diamagnetic to ferromagnetic state after doping. In addition, the optimized spin state for ZTRI/ZTRI-doped is the quintet/sextet spin-polarized state. In few cases, the doped AHEX/ZTRI dots have doublet/quadruplet spin state due to the strong interaction between the flake atoms that passivates some unpaired electrons. Magnetic properties depend also on stacking, for instance pristine bilayer triangular flakes become antiferromagnetic due to pairing between edge states. The energy gap significantly affected by doping, for instance the gap decreases from ~3.7 eV in hexagonal flakes to 1.5 eV when it is doped with Na in the upper position. Electrons from the broken bonds around the doped metal form orbitals loosely bound to the flake consequently decreasing the energy gap. On the other hand, stacking increases the energy gap in bilayer triangular flakes due to the mutual passivation of the reactive edge states from both the layers. The calculated spin up/down density ratio is high in hexagonal flakes leading to high spin polarization (P), for instance P = 0.64 in hexagonal flakes doped with K atom. The found enhanced spin polarization, in addition to the tunable magnetic properties, makes doped graphene flakes promising candidates for spintronic devices.

Keywords

Graphene quantum dots

DFT

Doping

Alkali metals

Electronic and magnetic properties

Spin polarization

© 2021 The Author(s). Published by Elsevier B.V.

Source: https://www.sciencedirect.com/science/article/pii/S2238785421001198?dgcid=rss_sd_all

Material

Simulation of deformation and fracture initiation during equal channel angular pressing of AZ31 magnesium alloy with covered tube casing

Publication date: Available online 31 March 2021

Source: Journal of Materials Research and Technology

Author(s): A.R. Eivani, S.M. Mirghasemi, S.H. Seyedein, J. Zhou, H.R. Jafarian

Republished by Plato

Published

on


Elsevier

Available online 31 March 2021

Journal of Materials Research and Technology

open access

Abstract

The present research was aimed at lowering the deformation temperature by applying cover tube casing (CTC) to AZ31 magnesium alloy samples subjected to equal channel angular pressing (ECAP) without triggering surface defects and/or fracture. The Cockcroft-Latham (C & L) fracture model was incorporated into finite element simulation and the critical values for a fracture to occur were determined. The fracture was predicted for the samples deformed at 150, 175, and 200 °C without CTC and with CTC having thicknesses of 1 and 4 mm. The predictions of the model were verified with experimental data. It was found that the workability of AZ31 increased with increasing CTC thickness, as a result of a reduction in the maximum principal stress at the top surface, a uniform distribution of strains, and an increase in the critical damage. In practice, the use of CTC led to the possibility of a reduction in deformation temperature by 25 °C. A sound product with a homogeneous grain structure and a mean grain size of 11 μm was achieved at 175 °C. Thus, the ECAP working window for the alloy was enlarged with accompanying benefits in energy consumption, tooling life, and manufacturing costs.

Keywords

Finite element simulation

Equal channel angular pressing

Fracture

Magnesium

Workability

© 2021 Published by Elsevier B.V.

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Source: https://www.sciencedirect.com/science/article/pii/S2238785421003239?dgcid=rss_sd_all

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Material

Preparation, characterization, and nonlinear optical properties of graphene oxide thin film doped with low chirality metallic SWCNTs

Publication date: Available online 31 March 2021

Source: Journal of Materials Research and Technology

Author(s): Asmaa M. Abozied, Ayman M. Mostafa, A. Abouelsayed, A.F. Hassan, A.A. Ramadan, Emad A. Al-Ashkar, Badawi Anis

Republished by Plato

Published

on


Elsevier

Available online 31 March 2021

Journal of Materials Research and Technology

open access

Abstract

We present non-linear optical properties of graphene oxide (GO) doped with low chirality metallic single walled carbon nanotubes (m-SWCNTs) thin films. The weight percentage of the m-SWCNTs was 5, 10, and 20 wt%. High-resolution transmission electron microscope (HRTEM), high resolution scanning electron microscope (HRSEM), Raman, and UV-vis spectroscopy were used to characterize the prepared samples. We have investigated their nonlinear optical properties using open and closed Z-scan technique at Nd:YAG laser at 1064 nm laser pulses (7 ns, 10 Hz). The nonlinear absorption coefficient β, nonlinear refractive index n2, and third order nonlinear susceptibility χ3 were calculated. The results show that all samples exhibit reverse saturable absorption (RSA) because of increasing metallicity and/or partial reduction of GO during laser illumination. The nonlinearity response of the GO/m-SWCNT films increase as the m-SWCNTs percentage increases. The high non-linear optical parameters of the GO/m-SWCNTs films make them as superior candidates for near-infrared (NIR) laser protection applications.

Keywords

Graphene Oxide

low chirality metallic-SWCNTs

NLO

thin film

Z-scan

© 2021 The Author(s). Published by Elsevier B.V.

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Source: https://www.sciencedirect.com/science/article/pii/S2238785421003161?dgcid=rss_sd_all

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Material

Selective room-temperature leaching of copper from mechanically activated copper smelter slag

Publication date: Available online 1 April 2021

Source: Journal of Materials Research and Technology

Author(s): Lyazzat Mussapyrova, Rashid Nadirov, Peter Baláž, Michal Rajňák, Radovan Bureš, Matej Baláž

Republished by Plato

Published

on


Elsevier

Available online 1 April 2021

Journal of Materials Research and Technology

open access

Abstract

Herein, the room-temperature sulfuric acid leaching of copper smelter slag powder in the presence of potassium dichromate was investigated, resulting in the selective extraction of copper with its separation from zinc and iron. To enhance the extraction of copper, mechanical activation in the planetary ball mill and attritor was used. The Taguchi method was applied to determine the optimal conditions for both mechanical activation and leaching. For mechanical activation in the attritor, a rotation speed of 1200 rpm, ball-to-powder ratio of 40 and milling time of 75 min were ideal. Under these conditions, the specific surface area (SBET) could be increased from 1.7 m2/g, for the starting slag, to 59.4 m2/g. According to ANOVA, the most important factor is the rotation speed. For comparison, the slag was subjected also to planetary ball milling using the same conditions and a specific surface area of 116 m2/g was obtained. Leaching conditions that maximize copper recovery and, independently, copper selectivity, were also found. The maximum copper recovery was 87.3%, while the maximum copper selectivity was 97.9%. The most influential parameters in leaching were the concentration of K2Cr2O7 and the liquid-to-solid ratio. The copper selectivity is attributed to better solubility of chalcopyrite (CuFeS2) in comparison with zinc ferrite (ZnFe2O4) and fayalite (FeSiO4) containing the other metals. This study provides a statistical approach for planning the experiments of pretreatment and leaching to efficiently obtain valuable metals from secondary raw resources in an environmentally interesting fashion by using low concentrations of leaching agents and mechanical pretreatment.

Graphical abstract

Keywords

copper smelter slag

copper recovery

mechanical activation

selective leaching

© 2021 The Author(s). Published by Elsevier B.V.

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Source: https://www.sciencedirect.com/science/article/pii/S2238785421003173?dgcid=rss_sd_all

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