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Now showing items 1 - 16 of 48

  • Thermophysical properties of (UxAm1-x)O-2 MOX fuel

    Jossou, Ericmoore   Malakkal, Linu   Ranasingh, Jayangani   Szpunar, Barbara   Szpunar, Jerzy  

    The effect of the addition of americium on the thermophysical properties of uranium dioxide (UO2) has been systematically studied by molecular dynamics (MD) simulation technique in the whole concentration range of americium and the temperature range from 300 K to 3200 K. The predicted thermophysical properties for (UxAm1-x)O-2 solid solutions agree well with the available experimental data. The lattice parameters decreased with the increase in americium concentration and obey Vegard's law up to 2000 K. There is no significant change in the enthalpy, heat capacity, lattice expansion, and thermal conductivity as we increased the concentration of americium. Overall, a series of empirical models are derived for the thermophysical properties of (UxAm1-x)O-2 MOX fuel based on the MD data.
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  • Anisotropic thermophysical properties of U3Si2 fuel:An atomic scale study

    Jossou, Ericmoore   Rahman, Md Jahidur   Oladimeji, Dotun   Beeler, Benjamin   Szpunar, Barbara   Szpunar, Jerzy  

    Due to renewed interest in uranium silicide compounds as a candidate for nuclear reactor fuels, there is a need for extensive investigations of their thermophysical properties as a function of temperature. In this work, we calculate the thermophysical properties of the U3Si2 compound within the framework of molecular dynamics (MD) using a semi-empirical modified Embedded-Atom Method (MEAM) potential and density functional theory (DFT). Thermal expansion, thermal conductivity, heat capacity, and elastic properties are presented as a function of temperature from 300 to 1800 K. The thermal conductivity of U3Si2 increases with temperature due to the electronic contribution while the phonon contribution decreases with increasing temperature. The phonon contribution to the thermal conductivity at 300 K is estimated at 2.03 W/mK and 1.41 W/mK using non-equilibrium molecular dynamics (NEMD) and equilibrium molecular dynamics (EMD), respectively. The electronic contribution is estimated to be 8.56 W/mK using the semi-classical Boltzmann transport theory at 300 K. Furthermore, we compared the thermal conductivity in two different crystallographic directions to shed light on the spatial anisotropy using NEMD and EMD methods. The inherent anisotropic thermophysical properties can be used to parametrize phase field models to incorporate anisotropic thermal conductivity and thermal expansion, allowing for a more accurate description of microstructural evolution under variable temperature and irradiation conditions. (c) 2019 Elsevier B.V. All rights reserved.
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  • Thermal conductivity of bulk and porous ThO2:Atomistic and experimental study

    Malakkal, Linu   Prasad, Anil   Jossou, Ericmoore   Ranasinghe, Jayangani   Szpunar, Barbara   Bichler, Lukas   Szpunar, Jerzy  

    Thorium dioxide (ThO2) is proposed to play a vital role in the world's future energy needs and is considered a better and safer alternative to the currently used nuclear fuel, uranium dioxide (UO2). Thermo-physical properties of ThO2 are superior to UO2, but the fundamental physics governing the heat transport in ThO2 is still ambiguous, and the available data for the thermal conductivity (k) of ThO2 was scattered. In this article, a systematic investigation regarding the lattice thermal conductivity (k(L)) of the bulk and porous ThO2 is carried out theoretically and validated with experiments. The phonon transport calculations were done using two different methods; ab-initio calculations combined with the Boltzmann transport equation (BTE) and the equilibrium molecular dynamics (EMD) simulations using Green Kubo (GK) approach. An extensive examination of the phonon mode contribution, available three-phonon scattering phase space modes, Grtineisen parameter, and mean free path (MFP) distributions were analyzed to understand the underlying physics in the thermal transport of ThO2. The effect of porosity on the k(L) by measurements and molecular dynamics (MD) simulations was explored. The measurements were performed on specimens with different porosity, that were prepared by spark plasma sintering (SPS) using the laser flash (LFA) technique. The results obtained demonstrated that the k(L) values predicted by both the BTE and the EMD simulations were in excellent agreement with our experimental measurements. Moreover, the model to simulate the 95% theoretical density (TD) using MD simulations also captured the decrease in thermal conductivity with porosity and agreed well with the measured results for 95% TD dense sintered pellets. (C) 2019 Elsevier B.V. All rights reserved.
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  • The electronic structure of zirconium in hydrided and oxidized states

    Akhiani, Hamed   Hunt, Adrian   Cui, Xiaoyu   Moewes, Alexander   Szpunar, Jerzy  

    Valence band energy shifts for pure zirconium and a model zirconium alloy (Zircaloy-4) in oxidized and hydrided states have been investigated with X-ray photoelectron spectroscopy (XPS) and X-ray Absorption Near-Edge Structure (XANES) technique. With XANES, we show that O/H interactions in oxidized Zr can be detected in the near-edge region of O K. Using density functional theory (DFT) simulations, we have determined where H atoms bond in the monoclinic ZrO2 lattice. The preferred stoichiometry is ZrO2:H, but the O-H bond is weak; increasing H causes the H atoms to form H-2 molecules rather than O-H bonds. These interactions cause energy shifts in the Zr 3d XPS spectra. The results illustrate the complex processes of hydrogen and oxygen interactions at the Zr surface. (C) 2014 Elsevier B.V. All rights reserved.
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  • Characterization of Viscoelasticity and Self-Healing Ability of VHB 4910

    Fan, Fan   Szpunar, Jerzy  

    The mechanisms responsible for the viscoelasticity and self-healing ability of VHB 4910 are studied. The type of chemical bonds is confirmed using Fourier transform infrared and Raman spectroscopy. The tensile tests demonstrate that the material has viscoelastic behavior that depends on the deformation speed and changes in the hysteresis area with different tensile strains. The shear modulus of entangled networks increases with the deformation speed. This behavior confirms that the viscoelasticity is due to the dissociation and re-association of non-covalent bonding. The hydrogen bonding initiates the healing process and the diffusion of molecular chains strengthens the self-healing ability.
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  • Impact of Vanadium Addition on API X100 Steel

    Nafisi, Shahrooz   Arafin, Muhammad   Glodowski, Robert   Collins, Laurie   Szpunar, Jerzy  

    Laboratory heats of an API X100 steel (Mn-Mo-Nb)with two levels of vanadium (0.004% and 0.063%) were melted and control rolled simulating a coiled plate production process. Extensive microstructural analyses were performed, including optical, EBSD and TEM. Texture analyses of the two alloys were also compared. Mechanical properties were determined for various rolling and pipe axis orientations. Only minor differences in microstructure and texture properties were observed between the two alloys. Yet the 0.063% V alloy had from 8 to 14% higher yield and tensile strengths in all directions, while the toughness and ductility measurements were similar for both alloys. Higher strength of the V added pipeline steel was partially due to its smaller grain size and larger fraction of subgrain boundaries. Some, but perhaps not all, of the strength differences could be related to the observed smaller precipitate size of the higher vanadium steel. The vanadium addition was necessary in this alloy to ensure meeting the required strength properties of X100 steel.
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  • Raman spectroscopy of pre-strained VHB 4910 elastomer towards actuator application

    Sahu, Dhananjay   Sahu, Raj Kumar   Patra, Karali   Szpunar, Jerzy  

    Dielectric elastomers are the potential material to configure soft electromechanical actuators and similar modules. But, understanding the relationship between molecular structures and properties of such elastomers in real-time is a powerful and lacking tool, important to consider when properties are targeted to improve by tailoring (macro)molecular arrangement. Here, molecular bonds within VHB 4910 dielectric elastomer are explored using techniques of Raman spectroscopy. Identified bonds are correlated well with electromechanical properties and macromolecular characteristics. Then the effects of pre-strain known to influences material behavior are comprehended in the context of molecular-level structural-adaptation. Intermolecular bonds revealed for hard segments, soft segments and acrylate structure are found certainly sensitive for applied strain, persist ideology of chain entanglement towards strain-induced crystallization. These results are experimentally consistent and the work may help to focus specific structure to adapt user-defined properties.
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  • An improved procedure for acquiring yield curves over a large range of strains

    Zhong, Jiru   Xu, Tong   Guan, Kaishu   Szpunar, Jerzy  

    Acquiring a full range of yield curves is a long-standing challenge in material science and engineering. Such curves are extremely important for stress analysis using finite element simulation. In this article, we proposed an improved procedure integrating finite element analysis and hybrid particle swarm optimization to extract a post-necking yield curve from a smooth tensile round bar. The investigated material was 3Cr1MoV. The strain range of the yield curve was extended from 0.0681 mm/mm before necking to 1.5 mm/mm. The results revealed that curves obtained through this procedure are reliable and unique. Three notched round bars were designed to investigate the effects of stress triaxiality on the yield curves. We found that stress triaxiality has a significant influence on curves at large plastic strains (strain > 0.3 mm/mm) and has a negligible effect at low plastic strains (strain < 0.3 mm/mm). Studies revealed that the stress triaxiality-dependent yield curves are related to dilatational plasticity arising from nucleation and growth of voids.
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  • First principles calculations of hydrogen storage on Cu and Pd-decorated graphene

    Choudhary, Aditya   Malakkal, Linu   Siripurapu, Ravi Kiran   Szpunar, Barbara   Szpunar, Jerzy  

    Transition metals (TM) such as palladium (Pd) and copper (Cu) atom were introduced on defect-free graphene and graphene with a single vacancy (SV) defect, to investigate their potential hydrogen storage using first principles calculation. All calculations were performed using plane wave based density functional theory (DFT) as implemented in Quantum ESPRESSO (QE). Generalized gradient approximation (GGA) exchange-correlation function as described by Perdew-Burke-Ernzerhof (PBE) was used. The interaction between the valence electron and the ionic core was represented by ultrasoft pseudopotentials. In this study, the structure and geometry of complex hydrides were investigated, and the effect of a SV defect in graphene on hydrogen storage was explored. It was concluded that the introduction of a SV defect prevents the TM atom clustering and enables hydrogen molecule adsorption within the ideal usable range. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
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  • In Situ 3D Synchrotron Imaging of Failure Processes in Engineering Materials

    Rahman, K. M. Mostafijur   Szpunar, Jerzy   Belev, George  

    The micrometer range resolution of Synchrotron Radiation Tomography has developed an important technique for characterizing the three dimensional (3D) microstructure of materials. This technique was used for imaging Aluminum-alumina composites, porous aluminum and AA 6061 alloy under different loading conditions. The experimental set-up was installed at the Biomedical Imaging and Therapy (BMIT)'s 05B1-1 beamline at Canadian Light Source (CLS). The experimental stage has been designed for conducting the in-situ experiments. The unique feature of this experimental stage is that the sample can be rotated torsion free for taking the images for Computed Tomography imaging during any loading conditions. The developed experimental system and technique allows deciphering the internal structures of composites, porous materials, multiphase alloys and to observe the failure processes such as crack initiation, crack propagation, void formation, void coalescence and the fracture process during loading of materials..
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  • H2S adsorption and dissociation on NH-decorated graphene:A first principles study

    Faye, Omar   Eduok, Ubong   Szpunar, Jerzy   Samoura, Almoustapha   Beye, Aboubaker  

    The removal of H2S gas poses an emerging environmental concern because of the lack of knowledge of an efficient adsorbent. A detailed theoretical study of H2S adsorption and dissociation on NH-doped graphene (GNH) has been carried out by means of density theory calculations. Our results reveal that the adsorption of H2S molecule on GNH composite is enhanced by the presence of active site such as the NH radicals. These NH radical sites formed NH-H bonds and increase the charge transfer from H2S to GNH. The dissociation of the adsorbed H2S molecule leads the chemisorption of SH radical via H-transfer to GNH, while the formation of GNH(2) at a weight percent of 3.76 wt% of NH radical is an endothermic process with an energy of 0.299 eV and 0.358 eV for ortho and paraposition respectively. However, at 7.25 wt% NH radical, we observed a complete dissociation of H2S molecule with an energy released of 0.711 eV for the chemisorbed S atom on GN(2)H(4). Moreover, the H-transfer of the second H atom of H2S molecule at 3.76 wt% was energetic unfavorable. The trend of predicted results within this study reveals that NH-doped graphene (GNH) successfully adsorbed and eliminated of H2S molecule; this work unveils definitive theoretical procedures which can be tested and validated experimentally. (C) 2017 Elsevier B.V. All rights reserved.
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  • Production of High-Strength Al/Al2O3/WC Composite by Accumulative Roll Bonding

    Shamanian, Morteza   Mohammadnezhad, Mahyar   Szpunar, Jerzy  

    In this study, Al/Al2O3/WC composites were fabricated via the accumulative roll bonding (ARB) process. Furthermore, the microstructure evolution, mechanical properties, and deformation texture of the composite samples were reported. The results illustrated that when the number of cycles was increased, the distribution of particles in the aluminum matrix improved, and the particles became finer. The microstructure of the fabricated composites after eight cycles of the ARB process showed an excellent distribution of reinforcement particles in the aluminum matrix. Elongated ultrafine grains were formed in the ARB-processed specimens of the Al/Al2O3/WC composite. It was observed that as the strain increased with the number of cycles, the tensile strength, microhardness, and elongation of produced composites increased as well. The results indicated that after ARB process, the overall texture intensity increases and a different-strong texture develops. The main textural component is the Rotated Cube component.
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  • Microstructural Effects on the Oxidation Behavior of Alloy 800HT in Supercritical Water

    Akhiani, Hamed   Nezakat, Majid   Penttila, Sami   Szpunar, Jerzy  

    Alloy 800HT is one promising candidate for use as a fuel cladding material in supercritical water-cooled rectors. In the present study, specific thermomechanical processing (TMP) was used to study the effects of grain size and grain boundary character distribution (GBCD) on the oxidation behavior of alloy 800HT in supercritical water (SCW). The processed samples were exposed to SCW at 600 degrees C and 25 MPa for 100, 300, and 1000 h. The results showed that grain size and grain boundaries are important factors that affect the oxidation behavior of alloy 800HT in SCW. We also found that TMP improves the adhesion and integrity of the oxide scale.
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  • Effect of annealing temperature on the corrosion resistance of MgO coatings on Mg alloy

    Xu, Zhen   Eduok, Ubong   Szpunar, Jerzy  

    MgO coatings were electrodeposited on Mg alloy substrates via cathodic electrolytic technique and annealed at different temperatures. The protective performance of these annealed coatings was investigated, and a correlation drawn between annealing temperature of coatings and their corrosion resistances as well as mechanical hardness. At optimum temperature (250 degrees C), the thermal treatment relieved internal tensile stress leading to crystallization of oxide coating layers with compact and continuous multilayered microstructures. At higher temperatures (around 500 degrees C), phase transformations within the coating microstructure broadened inherent inter-diffusion pathways/microdefects. Surface and bulk evidences of pores and cracks are observed at 500 degrees C as clear evidences of the consequence of over-calcination using scanning electron microscopy. Enhanced corrosion resistance for coatings are achieved at optimum curing temperature judging from electrochemical corrosion results after chloride-induced corrosion tests. The dependence of corrosion resistance on annealing temperature of coatings has also been investigated by potentiodynamic polarization and electrochemical impedance spectroscopic techniques. A modelled curing mechanism, as it relates to barrier performance at low and high thermal conditions, has been illustrated from experimental evidences.
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  • Atomistic and experimental study on thermal conductivity of bulk and porous cerium dioxide

    Malakkal, Linu   Prasad, Anil   Oladimeji, Dotun   Jossou, Ericmoore   Ranasinghe, Jayangani   Szpunar, Barbara   Bichler, Lukas   Szpunar, Jerzy  

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  • Atomistic and experimental study on thermal conductivity of bulk and porous cerium dioxide

    Malakkal, Linu   Prasad, Anil   Oladimeji, Dotun   Jossou, Ericmoore   Ranasinghe, Jayangani   Szpunar, Barbara   Bichler, Lukas   Szpunar, Jerzy  

    Cerium dioxide (CeO2) is a surrogate material for traditional nuclear fuels and an essential material for a wide variety of industrial applications both in its bulk and nanometer length scale. Despite this fact, the underlying physics of thermal conductivity (k(L)), a crucial design parameter in industrial applications, has not received enough attention. In this article, a systematic investigation of the phonon transport properties was performed using ab initio calculations unified with the Boltzmann transport equation. An extensive examination of the phonon mode contribution, available three-phonon scattering phase space, mode Gruneisen parameter and mean free path (MFP) distributions were also conducted. To further augment theoretical predictions of the k(L), measurements were made on specimens prepared by spark plasma sintering using the laser flash technique. Since the sample porosity plays a vital role in the value of measured k(L), the effect of porosity on k(L) by molecular dynamics (MD) simulations were investigated. Finally, we also determined the nanostructuring effect on the thermal properties of CeO2. Since CeO2 films find application in various industries, the dependence of thickness on the in-plane and cross-plane k(L) for an infinite CeO2 thin film was also reported.
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