The Experts below are selected from a list of 294 Experts worldwide ranked by ideXlab platform
Christopher M Wolverton - One of the best experts on this subject based on the ideXlab platform.
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energetics of cobalt alloys and compounds and Solute vacancy binding in fcc cobalt a first principles database
Acta Materialia, 2017Co-Authors: Shahab S Naghavi, Vinay Hegde, Abhinav Saboo, Christopher M WolvertonAbstract:Abstract Using extensive first-principles density functional calculations, we calculate thermodynamic properties of binary fcc cobalt-based alloys with 25 different Solute elements. For each Solute element X , we calculate its (a) nearest- and next-nearest-neighbor Solute–vacancy binding energy, (b) dilute impurity mixing energy with respect to the equilibrium and hypothetical fcc-based reference states of the Solute, (c) enthalpy of formation of cobalt-rich binary ordered compounds in the Co– X system, (d) solubility enthalpy, and other derived quantities. We find that the Solute–vacancy binding energies of all the studied Solutes in fcc cobalt are positive (indicating favorable binding), in contrast to nickel, aluminum, magnesium, and copper-based alloys, where mid 3 d transition metal Solutes have unfavorable Solute–vacancy binding. We study the physical and chemical effects influencing Solute–vacancy binding energy, and find that (a) it correlates broadly with Solute size—larger Solute atoms possess stronger binding with vacancies—and this is understood in terms of strain relief and secondary next-nearest-neighbor interactions, and (b) it follows a parabolic trend as a function of d -occupancy across the transition metal series—falling to a minimum at the middle of the series—and this is understood in terms of a d -band filling effect. We also find this d -band filling effect in other calculated quantities such as the dilute impurity volumes and dilute impurity mixing energies. To aid in building thermodynamic databases, we tabulate all the calculated thermodynamic quantities, and compare them with experimental phase diagrams data and previous literature, and find good agreement where such data is available.
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Solute vacancy binding in aluminum
Acta Materialia, 2007Co-Authors: Christopher M WolvertonAbstract:Abstract Previous efforts to understand Solute–vacancy binding in aluminum alloys have been hampered by a scarcity of reliable, quantitative experimental measurements. Here, we report a large database of Solute–vacancy binding energies determined from first-principles density functional calculations. The calculated binding energies agree well with accurate measurements where available, and provide an accurate predictor of Solute–vacancy binding in other systems. We find: (i) some common Solutes in commercial Al alloys (e.g., Cu and Mg) possess either very weak (Cu), or even repulsive (Mg), binding energies. Hence, we assert that some previously reported large binding energies for these Solutes are erroneous. (ii) Large binding energies are found for Sn, Cd and In, confirming the proposed mechanism for the reduced natural aging in Al–Cu alloys containing microalloying additions of these Solutes. (iii) In addition, we predict that similar reduction in natural aging should occur with additions of Si, Ge and Au. (iv) Even larger binding energies are found for other Solutes (e.g., Pb, Bi, Sr, Ba), but these Solutes possess essentially no solubility in Al. (v) We have explored the physical effects controlling Solute–vacancy binding in Al. We find that there is a strong correlation between binding energy and Solute size, with larger Solute atoms possessing a stronger binding with vacancies. (vi) Most transition-metal 3d Solutes do not bind strongly with vacancies, and some are even energetically strongly repelled from vacancies, particularly for the early 3d Solutes, Ti and V.
Taishung Chung - One of the best experts on this subject based on the ideXlab platform.
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exploration of polyelectrolytes as draw Solutes in forward osmosis processes
Water Research, 2012Co-Authors: Qingchun Ge, Jincai Su, Taishung ChungAbstract:The development of the forward osmosis (FO) process has been constrained by the slow development of appropriate draw solutions. Two significant concerns related to draw solutions are the draw Solute leakage and intensive energy requirement in recycling draw Solutes after the FO process. FO would be much attractive if there is no draw Solute leakage and the recycle of draw Solutes is easy and economic. In this study, polyelectrolytes of a series of polyacrylic acid sodium salts (PAA-Na), were explored as draw Solutes in the FO process. The characteristics of high solubility in water and flexibility in structural configuration ensure the suitability of PAA-Na as draw Solutes and their relative ease in recycle through pressure-driven membrane processes. The high water flux with insignificant salt leakage in the FO process and the high salt rejection in recycle processes reveal the superiority of PAA-Na to conventional ionic salts, such as NaCl, when comparing their FO performance via the same membranes. The repeatable performance of PAA-Na after recycle indicates the absence of any aggregation problems. The overall performance demonstrates that polyelectrolytes of PAA-Na series are promising as draw Solutes, and the new concept of using polyelectrolytes as draw Solutes in FO processes is applicable.
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study of draw Solutes using 2 methylimidazole based compounds in forward osmosis
Journal of Membrane Science, 2010Co-Authors: Farhana Mehnas N Haja, Minglue Su, Kai Yu Wang, Taishung ChungAbstract:2-Methylimidazole-based organic compounds have been studied as draw Solutes in the forward osmosis (FO) application. The good solubility of these draw Solutes allows comparative studies between the neutral and charged compounds to be conducted. The tailor-designed charged draw Solutes 3 and 4 exhibit higher water fluxes performance and lower reverse Solute fluxes than the neutral draw Solutes 1 and 2 based on HTI cellulose triacetate membranes. The Solutes 3 and 4 show comparable water fluxes even though the latter has a higher osmotic pressure. The ionic strength of the draw solutions may appear to be a contributing factor to the performance. The Solute 4 exhibits lower reverse Solute fluxes than Solute 3, which is primarily attributed to its larger molecule size. The larger molecular size may be potential in membrane-based Solute recovery; however, it may induce more internal concentration polarization (ICP) in current porous membrane. We have also demonstrated the potential application and recycling of the designed draw Solutes in the FO–MD integrated process.
Bernard Pettitt - One of the best experts on this subject based on the ideXlab platform.
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the dewetting transition and the hydrophobic effect
Journal of the American Chemical Society, 2007Co-Authors: Niharendu Choudhury, Bernard PettittAbstract:A molecular-level description of the behavior of water in hydrophobic spaces is presented in terms of the coupled effects of Solute size and atomic Solute-solvent interactions. For model Solutes with surface areas near those of protein contacts, we identify three different regions of Solute-water interaction to be associated with three distinctly different structural characteristics of water in the interSolute region: dry, oscillating, and wet. A first orderlike phase transition is confirmed from the wet to dry state bridged by a narrow region with liquid-vapor oscillations in the interSolute region as the strength of the Solute-water attractive dispersion interaction decreases. We demonstrate that the recent idea that cavitation in the interSolute region of nanoscopic Solutes is preceded by the formation of a vapor layer around an individual Solute is not the general case. The appearance of density waves pulled up around and outside of a nanoscopic plate occurs at lower interaction strengths than are required to obtain a wet state between such plates. We further show that chemically reasonable estimates of the interaction strength lead to a microscopically wet state and a hydrophobic interaction characterized by traps and barriers to association and not by vacuum induced collapse.
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Local density profiles are coupled to Solute size and attractive potential for nanoscopic hydrophobic Solutes
Molecular Simulation, 2005Co-Authors: Niharendu Choudhury, Bernard PettittAbstract:We employ constant pressure molecular dynamics simulations to investigate the effects of Solute size and Solute–water dispersion interactions on the solvation behavior of nanoscopic hydrophobic model Solutes in water at normal temperature and pressure. The hydration behavior around a single planar atomic model Solute as well as a pair of such Solutes have been considered. The hydration water structure of a model nanoscopic Solute with standard Lennard-Jones interaction is shown to be significantly different from that of their purely repulsive analogues. The density of water in the first solvation shell of a Lennard-Jones Solute is much higher than that of bulk water and it remains almost unchanged with the increase of the Solute dimensions from one to a few nanometers. On the other hand, for a purely repulsive analogue of the above model, Solute hydration behavior shows a marked Solute size dependence. The contact density of water in this case decreases with the increasing dimension of the Solute. We also...
Xuebang Wu - One of the best experts on this subject based on the ideXlab platform.
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interplay of Solute mixed self interstitial atoms and substitutional Solutes with interstitial and substitutional helium atoms in tungsten transition metal alloys
Nuclear Fusion, 2019Co-Authors: Xuebang Wu, Yichun Xu, Tao Zhang, Q F FangAbstract:In a fusion reactor environment, the irradiation of neutrons and helium (He) plasma produces a great number of self-interstitial atoms and vacancies in tungsten (W), which inevitably interact with alloying Solutes to form mixed self-interstitial atoms and substitutional Solutes. The interactions of Solutes with He atoms affect the behaviors of both, and ultimately cause the formation of Solute precipitates and He bubbles; however, the micro-mechanisms of this are still mysterious. In this work, we perform systematic ab initio calculations to study the mutual influence of Solutes and He atoms on their behaviors. It is found that most of the considered Solutes bind tightly with the most stable dumbbells forming mixed or dumbbells. Solute-mixed dumbbells can act as trapping centers for He atoms. Mixed dumbbells bind very tightly with interstitial He atoms and all the binding energies are larger than 1.0 eV. Compared with the energy for the formation of a W Frenkel pair with the presence of He, the energies needed for the formation of most Solute-mixed Frenkel pairs are decreased while titanium, zirconium, niobium, hafnium, and tantalum-mixed Frenkel pairs are exceptions. Similarly, substitutional Solutes can also trap interstitial and substitutional He atoms, and Solutes bind stronger with interstitial He followed by and Solutes while it is the opposite for interactions of substitutional Solutes with substitutional He atoms. The underlying reasons controlling the interactions of mixed dumbbells and substitutional Solutes with interstitial and substitutional He atoms are analyzed.
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Interactions of Solute (3p, 4p, 5p and 6p) with Solute, vacancy and divacancy in bcc Fe
Journal of Nuclear Materials, 2014Co-Authors: Xiang-shan Kong, Xuebang Wu, Qianfeng Fang, Jun Chen, Zhiguang WangAbstract:Abstract Solute–vacancy binding energy is a key quantity in understanding Solute diffusion kinetics and phase segregation, and may help choice of alloy compositions for future material design. However, the binding energy of Solute with vacancy is notoriously difficult to measure and largely unknown in bcc Fe. With first-principles method, we systemically calculate the binding energies of Solute (3 p , 4 p , 5 p and 6 p alloying Solutes are included) with vacancy, divacancy and Solute in bcc Fe. The binding energy of Si with vacancy in the present work is in good consistent with experimental value available. All the Solutes considered are able to form stable Solute–vacancy, Solute–divacancy complexes, and the binding strength of Solute–divacancy is about two times larger than that of Solute–vacancy. Most Solutes could not form stable Solute–Solute complexes except S, Se, In and Tl. The factors controlling the binding energies are analyzed at last.
Q F Fang - One of the best experts on this subject based on the ideXlab platform.
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interplay of Solute mixed self interstitial atoms and substitutional Solutes with interstitial and substitutional helium atoms in tungsten transition metal alloys
Nuclear Fusion, 2019Co-Authors: Xuebang Wu, Yichun Xu, Tao Zhang, Q F FangAbstract:In a fusion reactor environment, the irradiation of neutrons and helium (He) plasma produces a great number of self-interstitial atoms and vacancies in tungsten (W), which inevitably interact with alloying Solutes to form mixed self-interstitial atoms and substitutional Solutes. The interactions of Solutes with He atoms affect the behaviors of both, and ultimately cause the formation of Solute precipitates and He bubbles; however, the micro-mechanisms of this are still mysterious. In this work, we perform systematic ab initio calculations to study the mutual influence of Solutes and He atoms on their behaviors. It is found that most of the considered Solutes bind tightly with the most stable dumbbells forming mixed or dumbbells. Solute-mixed dumbbells can act as trapping centers for He atoms. Mixed dumbbells bind very tightly with interstitial He atoms and all the binding energies are larger than 1.0 eV. Compared with the energy for the formation of a W Frenkel pair with the presence of He, the energies needed for the formation of most Solute-mixed Frenkel pairs are decreased while titanium, zirconium, niobium, hafnium, and tantalum-mixed Frenkel pairs are exceptions. Similarly, substitutional Solutes can also trap interstitial and substitutional He atoms, and Solutes bind stronger with interstitial He followed by and Solutes while it is the opposite for interactions of substitutional Solutes with substitutional He atoms. The underlying reasons controlling the interactions of mixed dumbbells and substitutional Solutes with interstitial and substitutional He atoms are analyzed.
