scholarly journals Oxygen adsorption on (100) surfaces in Fe–Cr alloys

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Matti Ropo ◽  
Marko Punkkinen ◽  
Pekko Kuopanportti ◽  
Muhammad Yasir ◽  
Sari Granroth ◽  
...  
Keyword(s):  
Density Functional ◽  
Oxygen Affinity ◽  
Surface Oxidation ◽  
Oxygen Adsorption ◽  
Adsorption Site ◽  
Atomic Scale ◽  
Comprehensive Understanding ◽  
Surface Layers ◽  
Subsurface Layers ◽  
Theoretical Results

AbstractThe adsorption of oxygen on bcc Fe–Cr(100) surfaces with two different alloy concentrations is studied using ab initio density functional calculations. Atomic-scale analysis of oxygen–surface interactions is indispensable for obtaining a comprehensive understanding of macroscopic surface oxidation processes. Up to two chromium atoms are inserted into the first two surface layers. Atomic geometries, energies and electronic properties are investigated. A hollow site is found to be the preferred adsorption site over bridge and on-top sites. Chromium atoms in the surface and subsurface layers are found to significantly affect the adsorption properties of neighbouring iron atoms. Seventy-one different adsorption geometries are studied, and the corresponding adsorption energies are calculated. Estimates for the main diffusion barriers from the hollow adsorption site are given. Whether the change in the oxygen affinity of iron atoms can be related to the chromium-induced charge transfer between the surface atoms is discussed. The possibility to utilize the presented theoretical results in related experimental research and in developing semiclassical potentials for simulating the oxidation of Fe–Cr alloys is addressed.

scholarly journals Deciphering atomistic mechanisms of the gas-solid interfacial reaction during alloy oxidation

2020 ◽  
Vol 6 (17) ◽  
pp. eaay8491
Author(s):  
Langli Luo ◽  
Liang Li ◽  
Daniel K. Schreiber ◽  
Yang He ◽  
Donald R. Baer ◽  
...  
Keyword(s):  
Interfacial Reaction ◽  
Oxidation Reaction ◽  
Density Functional ◽  
Surface Oxidation ◽  
Atomic Scale ◽  
Al Alloy ◽  
Initial Surface ◽  
Ion Diffusion ◽  
Alloy Oxidation ◽  
Interfacial Strain

Gas-solid interfacial reaction is critical to many technological applications from heterogeneous catalysis to stress corrosion cracking. A prominent question that remains unclear is how gas and solid interact beyond chemisorption to form a stable interphase for bridging subsequent gas-solid reactions. Here, we report real-time atomic-scale observations of Ni-Al alloy oxidation reaction from initial surface adsorption to interfacial reaction into the bulk. We found distinct atomistic mechanisms for oxide growth in O2 and H2O vapor, featuring a “step-edge” mechanism with severe interfacial strain in O2, and a “subsurface” one in H2O. Ab initio density functional theory simulations rationalize the H2O dissociation to favor the formation of a disordered oxide, which promotes ion diffusion to the oxide-metal interface and leads to an eased interfacial strain, therefore enhancing inward oxidation. Our findings depict a complete pathway for the Ni-Al surface oxidation reaction and delineate the delicate coupling of chemomechanical effect on gas-solid interactions.

scholarly journals InP and AlInP(001)(2 × 4) Surface Oxidation from Density Functional Theory

ACS Omega ◽  
2021 ◽  
Author(s):  
Isaac Azahel Ruiz Alvarado ◽  
Marsel Karmo ◽  
Erich Runge ◽  
Wolf Gero Schmidt
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Surface Oxidation ◽  
Functional Theory

scholarly journals Theoretical insight on the treatment of β-hexachlorocyclohexane waste through alkaline dehydrochlorination

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Alicia Bescós ◽  
Clara I. Herrerías ◽  
Zoel Hormigón ◽  
José Antonio Mayoral ◽  
Luis Salvatella
Keyword(s):  
Density Functional ◽  
Kinetic Studies ◽  
Alkaline Treatment ◽  
Functional Study ◽  
Reaction Intermediates ◽  
Preferential Formation ◽  
Reaction Intermediate ◽  
Rate Determining Step ◽  
Dehydrochlorination Reaction ◽  
Theoretical Results

AbstractThe occurrence of 4.8–7.2 million tons of hexachlorocyclohexane (HCH) isomers stocked in dumpsites around the world constitutes a huge environmental and economical challenge because of their toxicity and persistence. Alkaline treatment of an HCH mixture in a dehydrochlorination reaction is hampered by the low reactivity of the β-HCH isomer (HCl elimination unavoidably occurring through syn H–C–C–Cl arrangements). More intriguingly, the preferential formation of 1,2,4-trichlorobenzene in the β-HCH dehydrochlorination reaction (despite the larger thermodynamical stability of the 1,3,5-isomer) has remained unexplained up to now, though several kinetic studies had been reported. In this paper, we firstly show a detailed Density Functional study on all paths for the hydroxide anion-induced elimination of β-HCH through a three-stage reaction mechanism (involving two types of reaction intermediates). We have now demonstrated that the first reaction intermediate can follow several alternative paths, the preferred route involving abstraction of the most acidic allylic hydrogen which leads to a second reaction intermediate yielding only 1,2,4-trichlorobenzene as the final reaction product. Our theoretical results allow explaining the available experimental data on the β-HCH dehydrochlorination reaction (rate-determining step, regioselectivity, instability of some reaction intermediates).

First-Principles Study of Triangle Terarylene as a Possible Optical Molecular Switch

2011 ◽  
Vol 311-313 ◽  
pp. 526-529
Author(s):  
Cai Juan Xia ◽  
Han Chen Liu ◽  
Ji Xin Yin
Keyword(s):  
First Principles ◽  
Density Functional ◽  
Molecular Switch ◽  
Optical Switches ◽  
Functional Theory ◽  
Closed Ring ◽  
Potential Applications ◽  
Homo Lumo ◽  
Non Equilibrium Green’S Function ◽  
Theoretical Results

Using non-equilibrium Green’s function formalism combined with first-principles density functional theory, we investigate the electronic transport properties of a triangle terarylene(open- and closed-ring forms) optical molecular switch. The influence of the HOMO-LUMO gaps and the spatial distributions of molecular orbitals on the quantum transport through the molecular device is discussed. Theoretical results show that the conductance of the closed-ring is 3-8 times larger than that of open-ring, which expect that this system can be one of good candidates for optical switches due to this unique advantage, and may have some potential applications in future molecular circuit.

Atomic scale surface engineering of micro- to nano-sized pharmaceutical particles for drug delivery applications

Nanoscale ◽  
2017 ◽  
Vol 9 (32) ◽  
pp. 11410-11417 ◽  
Author(s):  
D. Zhang ◽  
M. J. Quayle ◽  
G. Petersson ◽  
J. R. van Ommen ◽  
S. Folestad
Keyword(s):  
Drug Delivery ◽  
Atomic Layer Deposition ◽  
Surface Engineering ◽  
Atomic Layer ◽  
Atomic Scale ◽  
Ambient Conditions ◽  
Surface Layers ◽  
Layer Deposition ◽  
Atomic Surface ◽  
Scale Surface

Few atomic surface layers via atomic layer deposition under near ambient conditions significantly altered dissolution and dispersion of pharmaceutical particles.

Photocatalytic application of Graphene oxide-ZnO nanocomposite for the reduction of methylene blue dye

2021 ◽  
Author(s):  
Bansura Banu ◽  
Mercy Jennifer ◽  
Udith Ferdila
Keyword(s):  
Methylene Blue ◽  
Graphene Oxide ◽  
Charge Transfer ◽  
Density Of States ◽  
Density Functional ◽  
Basis Sets ◽  
Blue Dye ◽  
Layer Spacing ◽  
Photocatalytic Application ◽  
Theoretical Results

Abstract The Graphene Oxide (GO) and GO-Zinc Oxide (GO-ZnO) nanocomposite were prepared using simplified techniques with modified Hummer’s and solvothermal methods for photocatalytic application. In a comparative study, the optimized geometries, binding energies, electronic properties, non-linear optical properties and density of states of GO-ZnO were calculated using density functional theory (DFT) calculations with B3LYP method at 6-31G (d,p) and LanL2DZ basis sets to examine the binding site of a methylene blue (MB) dye systematically. The result of Natural bond orbital (NBO) analysis revealed the effective charge transfer and also explained the mechanism and efficiency of the photocatalytic activity of GO-ZnO. Density of states supported the strong interaction of MB with the GO-ZnO leading to the degradation of the MB dye. The attained theoretical results depict the existence of n → σ*, n → n* and σ → σ* interactions, improved charge transfer, reduced band gap which establish the use of GO-ZnO in the visible light photocatalytic performance. Characterization methods such as XRD, FTIR and UV were carried out to support our theoretical results. The XRD results confirmed the particle size of 21 nm with inter layer spacing of 0.87 nm. FTIR spectroscopy indicated the characteristic bands related to the elements in GO-ZnO. The higher electrical conductivity is studied using UV-Vis spectral analysis. The calculated results show good agreements with experimental observations reveal that the GO-ZnO has good photocatalytic behavior.

scholarly journals Designing order–disorder transformation in high-entropy ferritic steels

2021 ◽  
Author(s):  
Prashant Singh ◽  
Duane D. Johnson
Keyword(s):  
Short Range ◽  
Density Functional ◽  
Short Range Order ◽  
Range Order ◽  
Atomic Scale ◽  
Atomic Fraction ◽  
Compositional Variation ◽  
Ferritic Steels ◽  
Chemical Inhomogeneity ◽  
High Entropy

AbstractOrder–disorder transformations hold an essential place in chemically complex high-entropy ferritic steels (HEFSs) due to their critical technological application. The chemical inhomogeneity arising from mixing of multi-principal elements of varying chemistry can drive property altering changes at the atomic scale, in particular short-range order. Using density-functional theory-based linear-response theory, we predict the effect of compositional tuning on the order–disorder transformation in ferritic steels—focusing on Cr–Ni–Al–Ti–Fe HEFSs. We show that Ti content in Cr–Ni–Al–Ti–Fe solid solutions can be tuned to modify short-range order that changes the order–disorder path from BCC-B2 (Ti atomic-fraction = 0) to BCC-B2-L21 (Ti atomic-fraction > 0) consistent with existing experiments. Our study suggests that tuning degree of SRO through compositional variation can be used as an effective means to optimize phase selection in technologically useful alloys. Graphic abstract

scholarly journals Surface modification of AZ91 magnesium alloy using GTAW technology

2017 ◽  
Vol 65 (6) ◽  
pp. 917-926 ◽  
Author(s):  
J. Iwaszko ◽  
M. Strzelecka ◽  
K. Kudła
Keyword(s):  
Magnesium Alloy ◽  
Heat Source ◽  
Cooling System ◽  
Oxygen Affinity ◽  
Inert Gas ◽  
Surface Layers ◽  
Az91 Magnesium Alloy ◽  
Tandem Configuration ◽  
Welding Torch ◽  
Az91 Magnesium

AbstractIn this study, surface remelting treatment of the AZ91 magnesium alloy by means of welding using a non-consumable electrode in an inert gas shield was carried out. Three variants of surface treatment were used, i.e. the single torch variant with a single heat source without cooling down the samples, the single torch variant with a single heat source and a cooling system with liquid nitrogen, and the double welding torch variant with a double heat source in the torches operating in a tandem configuration. Experimental verification of the applied apparatus solutions was based on both macro- and microstructural assessment of the obtained effects. Comparative analysis of the variants used and the obtained microstructural results allowed the authors to indicate the deficiencies and limitations of particular solutions and to single out the best solution that would be useful for modifying the surface layers of magnesium alloys, as well as other materials having a strong oxygen affinity.

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