scholarly journals Defect segregation facilitates oxygen transport at fluorite UO 2 grain boundaries

2019 ◽  
Vol 377 (2152) ◽  
pp. 20190026 ◽  
Author(s):  
A. R. Symington ◽  
M. Molinari ◽  
N. A. Brincat ◽  
N. R. Williams ◽  
S. C. Parker
Keyword(s):  
Grain Boundaries ◽  
Oxygen Transport ◽  
Fission Products ◽  
Strong Interactions ◽  
Low Carbon ◽  
Energy Materials ◽  
Energy Applications ◽  
Oxygen Defects ◽  
Important Challenge ◽  
Dynamics Simulations

An important challenge for modelling transport in materials for energy applications is that in most applications they are polycrystalline, and hence it is critical to understand the properties in the presence of grain boundaries. Moreover, most grain boundaries are not pristine stoichiometric interfaces and hence dopants are likely to play a significant role. In this paper, we describe our recent work on using atomistic molecular dynamics simulations to model the effect of doped grain boundaries on oxygen transport of fluorite structured UO 2 . UO 2 , much like other fluorite grain boundaries, are found to be sinks for oxygen vacancy segregation relative to the grain interior, thus facilitating oxygen transport. Fission products further enhance diffusivity via strong interactions between the impurities and oxygen defects. Doping produces a striking structural alteration in the Σ 5 class of grain boundaries that enhances oxygen diffusivity even further. This article is part of a discussion meeting issue ‘Energy materials for a low carbon future’.

scholarly journals A Comparative Study of Acicular Ferrite Transformation Behavior between Surface and Interior in a Low C–Mn Steel by HT-LSCM

Metals ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 699
Author(s):  
Xiaojin Liu ◽  
Guo Yuan ◽  
Raja. Devesh Kumar Misra ◽  
Guodong Wang
Keyword(s):  
Grain Boundaries ◽  
Cooling Rate ◽  
Acicular Ferrite ◽  
Laser Scanning ◽  
Sample Surface ◽  
Surface Microstructure ◽  
In Situ Observation ◽  
Low Carbon ◽  
Transformation Behavior ◽  
Ferrite Transformation

In this study, the acicular ferrite transformation behavior of a Ti–Ca deoxidized low carbon steel was studied using a high-temperature laser scanning confocal microscopy (HT-LSCM). The in situ observation of the transformation behavior on the sample surface with different cooling rates was achieved by HT-LSCM. The microstructure between the surface and interior of the HT-LSCM sample was compared. The results showed that Ti–Ca oxide particles were effective sites for acicular ferrite (AF) nucleation. The start transformation temperature at grain boundaries and intragranular particles decreased with an increase in cooling rate, but the AF nucleation rate increased and the surface microstructure was more interlocked. The sample surface microstructure obtained at 3 °C/s was dominated by ferrite side plates, while the ferrite nucleating sites transferred from grain boundaries to intragranular particles when the cooling rate was 15 °C/s. Moreover, it was interesting that the microstructure and microhardness of the sample surface and interior were different. The AF dominating microstructure, obtained in the sample interior, was much finer than the sample surface, and the microhardness of the sample surface was much lower than the sample interior. The combined factors led to a coarse size of AF on the sample surface. AF formed at a higher temperature resulted in the coarse size. The available particles for AF nucleation on the sample surface were quite limited, such that hard impingement between AF plates was much weaker than that in the sample interior. In addition, the transformation stress in austenite on the sample surface could be largely released, which contributed to a coarser AF plate size. The coarse grain size, low dislocation concentration and low carbon content led to lower hardness on the sample surface.

scholarly journals Carbon Substitution on N24Cages: Crossover between Triangular and Hexagonal Structures

2013 ◽  
Vol 2013 ◽  
pp. 1-6
Author(s):  
Carrie Sanders ◽  
Douglas L. Strout
Keyword(s):  
Theoretical Calculations ◽  
High Energy ◽  
Energy Materials ◽  
Cylindrical Structures ◽  
High Energy Materials ◽  
Energy Applications ◽  
Carbon Substitution ◽  
Complex Forms ◽  
The Stability ◽  
Carbon Inclusion

Complex forms of nitrogen are of interest for their potential as high-energy materials, but many all-nitrogen systems lack the stability for practical high-energy applications. Inclusion of carbon atoms in an otherwise all-nitrogen structure can increase stability. Nitrogen cages are known for energetically preferring cylindrical structures with triangular endcaps, but carbon cages prefer the pentagon-hexagon structure of the fullerenes. Previous calculations on N22C2have shown that carbon inclusion narrows the gap between triangular and fullerene-like structures. In the current study, three isomers of N24are used as frameworks for carbon substitution. Theoretical calculations are carried out on isomers of N20C4, N18C6, and N16C8, with the goal of determining what level of carbon substitution causes the carbon fullerene-like structures to become energetically preferred.

The Effect of Waste Package Components on Radionuclides Released from Spent Fuel Under Hydrothermal Conditions

1987 ◽  
Vol 112 ◽  
Author(s):  
Shirley A. Rawson ◽  
William L. Neal ◽  
James R. Burnell
Keyword(s):  
Low Carbon Steel ◽  
Fission Products ◽  
Nuclear Waste Repository ◽  
Low Carbon ◽  
Spent Fuel ◽  
Hydrothermal Conditions ◽  
Waste Package ◽  
Dissolved Species ◽  
Radionuclide Release ◽  
Time Invariant

AbstractThe Basalt Waste Isolation Project has conducted a series of hydrothermal experiments to characterize waste/barrier/rock interactions as a part of its study of the Columbia River basalts as a potential medium for a nuclear waste repository. Hydrothermal tests of 3–15 months duration were performed with light water reactor spent fuel and simulated groundwater, in combination with candidate container materials (low-carbon steel or copper) and/or basalt, in order to evaluate the effect of waste package materials on spent fuel radionuclide release behavior. Solutions were filtered through 400 and 1.8 nm filters to distinguish colloidal from dissolved species. In all experiments, 14C, 129I, and 137Cs occurred only as dissolved species, whereas the actinides occurred in 400 nm filtrates primarily as spent fuel particles. Actinide concentrations in 1.8 nm filtrates were below detection in steel-bearing experiments. In the system spent fuel + copper, apparent time-invariant concentrations of 14C and 137Cs were obtained, but in the spent fuel + steel system, the concentrations of 14C and 137Cs increased gradually throughout the experiments. In experiments containing basalt or steel + basalt, 137Cs concentrations decreased with time. In tests with copper + basalt, 14C and 129I concentrations attained time-invariant values and 137Cs concentrations decreased. Concentrations for the actinides and fission products measured in these experiments were below those calculated from Federal regulations governing radionuclide release.

The Effect of Severe Plastic Deformation on the Brittle-Ductile Transition in Low Carbon Steel

2009 ◽  
Vol 633-634 ◽  
pp. 471-480
Author(s):  
Masaki Tanaka ◽  
Kenji Higashida ◽  
Tomotsugu Shimokawa
Keyword(s):  
Fracture Toughness ◽  
Carbon Steel ◽  
Grain Boundaries ◽  
Three Dimensional ◽  
Low Carbon Steel ◽  
Dislocation Dynamics ◽  
Strain Rates ◽  
Low Carbon ◽  
Dislocation Source ◽  
Brittle Ductile Transition

Brittle-ductile transition (BDT) behaviour was investigated in low carbon steel deformed by an accumulative roll-bonding (ARB) process. The temperature dependence of its fracture toughness was measured by conducting four-point bending tests at various temperatures and strain rates. The fracture toughness increased while the BDT temperature decreased in the specimens deformed by the ARB process. Arrhenius plots between the BDT temperatures and the strain rates indicated that the activation energy for the controlling process of the BDT was not changed by the deformation with the ARB process. It was deduced that the decrease in the BDT temperature by grain refining was not due to the increase in the dislocation mobility controlled by short-range barriers. Quasi-three-dimensional simulations of dislocation dynamics, taking into account of crack tip shielding due to dislocations, were performed to investigate the effect of a dislocation source spacing along a crack front on the BDT. The simulation indicated that the BDT temperature is decreased with decreasing in the dislocation source spacing. Molecular dynamics simulations revealed that moving dislocations were impinged against grain boundaries and were reemitted from there with increasing strain. It indicates that grain boundaries can be new sources in ultra-fine grained materials, which increases toughness at low temperatures.

Crystallographic Texture Control Helps Improve Pipeline Steel Resistance to Hydrogen-Induced Cracking

2010 ◽  
Author(s):  
V. Venegas ◽  
O. Herrera ◽  
F. Caleyo ◽  
J. M. Hallen ◽  
T. Baudin
Keyword(s):  
Grain Boundaries ◽  
Crystallographic Texture ◽  
Pipeline Steel ◽  
Low Carbon Steel ◽  
Rolling Process ◽  
Warm Rolling ◽  
American Petroleum Institute ◽  
Low Carbon ◽  
Steel Rolling ◽  
Hydrogen Induced Cracking

Low-carbon steel specimens, all within API (American Petroleum Institute) specifications, were produced following different thermomechanical paths. After austenization, the samples were rolled and recrystallized. The rolling process was carried out using different reduction-in-thickness degrees and finishing temperatures. The investigated steels showed similar microstructural features but differed considerably in their crystallographic textures and grain boundary distributions. After cathodic hydrogen charging, hydrogen-induced cracking (HIC) was detected in the hot-rolled recrystallized steels, whereas the cold and warm-rolled recrystallized steels proved resistant to this damage. Among the investigated specimens, the HIC-stricken show either the strongest {001}ND texture fiber, the smallest fraction of low-angle grain boundaries, or the weakest {111}ND (γ) texture fiber ({hkl}ND representing crystallographic orientations with {hkl} planes parallel to the steel rolling plane). In contrast, the HIC-resistant steels show the weakest {001}ND texture fiber, the largest fraction of low-angle grain boundaries, and the strongest γ fiber. These results support the hypothesis of this and previous works, that crystallographic texture control, through warm rolling schedules, helps improve pipeline steel resistance to hydrogen-induced cracking.

scholarly journals A Possible Mechanism of Graphene Oxide to Enhance Thermostability of D-Psicose 3-Epimerase Revealed by Molecular Dynamics Simulations

2021 ◽  
Vol 22 (19) ◽  
pp. 10813
Author(s):  
Congcong Li ◽  
Zhongkui Lu ◽  
Min Wang ◽  
Siao Chen ◽  
Lu Han ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Thermal Stability ◽  
Graphene Oxide ◽  
Md Simulations ◽  
Strong Interactions ◽  
Limiting Factor ◽  
Active Site Residues ◽  
Detailed Mechanism ◽  
Dynamics Simulations ◽  
Thermal Stability Of

Thermal stability is a limiting factor for effective application of D-psicose 3-epimerase (DPEase) enzyme. Recently, it was reported that the thermal stability of DPEase was improved by immobilizing enzymes on graphene oxide (GO) nanoparticles. However, the detailed mechanism is not known. In this study, we investigated interaction details between GO and DPEase by performing molecular dynamics (MD) simulations. The results indicated that the domain (K248 to D268) of DPEase was an important anchor for immobilizing DPEase on GO surface. Moreover, the strong interactions between DPEase and GO can prevent loop α1′-α1 and β4-α4 of DPEase from the drastic fluctuation. Since these two loops contained active site residues, the geometry of the active pocket of the enzyme remained stable at high temperature after the DPEase was immobilized by GO, which facilitated efficient catalytic activity of the enzyme. Our research provided a detailed mechanism for the interaction between GO and DPEase at the nano–biology interface.

scholarly journals Formation of a single quasicrystal upon collision of multiple grains

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Insung Han ◽  
Kelly L. Wang ◽  
Andrew T. Cadotte ◽  
Zhucong Xi ◽  
Hadi Parsamehr ◽  
...  
Keyword(s):  
Grain Boundaries ◽  
Large Scale ◽  
Thin Film Deposition ◽  
Film Deposition ◽  
Decagonal Quasicrystal ◽  
Bulk Crystal Growth ◽  
Computational Discovery ◽  
Dynamics Simulations ◽  
Novel Applications ◽  
Small Misorientation

AbstractQuasicrystals exhibit long-range order but lack translational symmetry. When grown as single crystals, they possess distinctive and unusual properties owing to the absence of grain boundaries. Unfortunately, conventional methods such as bulk crystal growth or thin film deposition only allow us to synthesize either polycrystalline quasicrystals or quasicrystals that are at most a few centimeters in size. Here, we reveal through real-time and 3D imaging the formation of a single decagonal quasicrystal arising from a hard collision between multiple growing quasicrystals in an Al-Co-Ni liquid. Through corresponding molecular dynamics simulations, we examine the underlying kinetics of quasicrystal coalescence and investigate the effects of initial misorientation between the growing quasicrystalline grains on the formation of grain boundaries. At small misorientation, coalescence occurs following rigid rotation that is facilitated by phasons. Our joint experimental-computational discovery paves the way toward fabrication of single, large-scale quasicrystals for novel applications.

Anomalous diffusion of water molecules at grain boundaries in ice Ih

2018 ◽  
Vol 20 (20) ◽  
pp. 13944-13951 ◽  
Author(s):  
Pedro Augusto Franco Pinheiro Moreira ◽  
Roberto Gomes de Aguiar Veiga ◽  
Ingrid de Almeida Ribeiro ◽  
Rodrigo Freitas ◽  
Julian Helfferich ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Molecular Dynamics Simulations ◽  
Grain Boundaries ◽  
Anomalous Diffusion ◽  
First Principles ◽  
Water Molecules ◽  
Diffusive Behavior ◽  
Classical Molecular Dynamics ◽  
Dynamics Simulations

First-principles and classical molecular dynamics simulations show that diffusion of water molecules at pre-melted grain boundaries in ice is glassy-like, showing sub-diffusive behavior.

Molecular Dynamics Simulation Based Cohesive Zone Representation of Intergranular Fracture Processes in Bicrystalline Graphene

2020 ◽  
Author(s):  
MD Imrul Reza Shishir ◽  
Alireza Tabarraei
Keyword(s):  
Molecular Dynamics ◽  
Grain Boundaries ◽  
Cohesive Zone ◽  
Cohesive Zone Model ◽  
Dynamics Simulation ◽  
Zone Model ◽  
Zone Method ◽  
Simulation Based ◽  
Dynamics Simulations ◽  
Fracture Processes

Abstract The fracture properties of various grain boundaries in graphene are investigated using the cohesive zone method (CZM). Molecular dynamics simulations are conducted using REBO2+S potential in order to develop a cohesive zone model for graphene grain boundaries using a double cantilever bicrystalline graphene sheet. The cohesive zone model is used to investigate the traction–separation law to understand the separation-work and strength of grain boundaries.

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