Experimental Methodologies for Assessing the Surface Energy of Highly Hygroscopic Materials: The Case of Nanocrystalline Magnesia

Hayun, Shmuel; Tran, Tien B.; Ushakov, Sergey V.; Thron, Andrew M.; Benthem, Klaus van; Navrotsky, Alexandra; Castro, Ricardo H. R.

doi:10.1021/jp2087434

Cited by 38 publications

(40 citation statements)

References 44 publications

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“…A glass-plate was kept at a constant height (~10 cm) above the sampling point, allowing collecting particles near the generation zone. The general particle properties correspond to those reported for smoke particles in literature 1,[26][27][28][29][30]. …”

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confidence: 83%

Size Effects in MgO Cube Dissolution

et al. 2015

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Stability parameters and dissolution behavior of engineered nanomaterials in aqueous systems are critical to assess their functionality and fate under environmental conditions. Using scanning electron microscopy, transmission electron microscopy, and X-ray diffraction, we investigated the stability of cubic MgO particles in water. MgO dissolution proceeding via water dissociation at the oxide surface, disintegration of Mg(2+)-O(2-) surface elements, and their subsequent solvation ultimately leads to precipitation of Mg(OH)2 nanosheets. At a pH ≥ 10, MgO nanocubes with a size distribution below 10 nm quantitatively dissolve within few minutes and convert into Mg(OH)2 nanosheets. This effect is different from MgO cubes originating from magnesium combustion in air. With a size distribution in the range 10 nm ≤ d ≤ 1000 nm they dissolve with a significantly smaller dissolution rate in water. On these particles water induced etching generates (110) faces which, above a certain face area, dissolve at a rate equal to that of (100) planes.1 The delayed solubility of microcrystalline MgO is attributed to surface hydroxide induced self-inhibition effects occurring at the (100) and (110) microplanes. The present work underlines the importance of morphology evolution and surface faceting of engineered nanomaterials particles during their dissolution.

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confidence: 83%

Size Effects in MgO Cube Dissolution

et al. 2015

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“…The last of the early studies was conducted in 1965 by Gutshall and Gross [22], who cleaved MgO in vacuum at the temperature of liquid nitrogen and obtained γ values of 1.28 and 1.37 J/m 2 from two measurements. More recently, the surface energy of anhydrous MgO nanoparticles was measured by hightemperature oxide melt solution calorimetry and differential scanning calorimetry [23]. The surface energies obtained by these methods were 1.2 ± 0.1 and 1.3 ± J/m 2 , respectively, supporting the results of the early cleavage experiments.…”

supporting

confidence: 60%

Accurate surface energies from first principles

Lazar

Otyepka

2015

Phys. Rev. B

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The absolute values of solids' surface energies are among the least well-known physical quantities, despite their fundamental importance. Experimental values obtained by various methods often differ by over 100%, mostly because the measurements are indirect and complicated. Reliable computational methods for predicting surface energies would therefore be extremely valuable. Here we assess the utility of using exact exchange (EXX) in conjunction with the many-electron perturbation theory extension of density functional theory, i.e., the random phase approximation (RPA), when predicting surface energies. The EXX + RPA approach was used to calculate the surface energies and cleavage properties of LiH, Mg, Pb, MgO, and NiAl, materials for which reliable experimental surface energies are available. The calculated values agreed well with the experimental data in all cases, suggesting that the longstanding problem of reliably predicting surface energies has been solved.The surface energy γ of a solid is one of its fundamental physical parameters. It governs a wide range of processes, such the stress needed for crack growth, the rate of sintering, and the shape and growth of particles. The surface energies and interface energies of interacting surfaces are important in industrial applications including adhesion, protective coating operations, and lubrication. These quantities are also important in printing, because the surface energy affects the wetting of the substrate by the ink as well as the ink's spreading and adhesion. Despite their importance, few accurate surface energy values are available even for common materials because most experimental techniques for determining surface energies are indirect and subject to many systematic errors [1,2].To determine a surface energy, one must in principle induce the formation of a fresh, clean, and perfect surface, which is difficult to achieve. Such surfaces can theoretically be formed by applying a force to a partially pre-split sample in a cleavage experiment [3]. However, this method is only viable for intrinsically brittle materials at low temperature. Many materials, including most metals, are ductile. Consequently, the work needed to split a sample by crack propagation includes the energy of plastic deformation around the crack tip as well as that required to form the two new surfaces.In contrast, surface tensions can be determined rather accurately, and the surface free energy is equal to the surface tension for a one-component liquid. The surface energy data used in compilations of "recommended" surface energy values [4,5] were obtained by extrapolating measured surface tensions for melted solids to absolute zero. However, the surface tension is not equal to the surface energy in solids, and Makkonen [6,7] has recently argued that there is no mathematical connection between the surface tension of a solid material and the energy required to create a new surface. These issues are conceptually difficult and controversial [8]. It should be emphasized that the terms surfa...

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“…The experimentally-determined surface energy is expected to be slightly higher than the calculated value of a pristine surface due to the presence of different crystallographic planes and surface atom vacancies typical of real surfaces. [55][56][57] Three nearly degenerate terminations comprise the stable surfaces of MgO2, Figure 3 bottom panel. Two of these occur on the (111)-oriented facet, and one on the (100) facet.…”

Section: B Surface Stabilitymentioning

confidence: 99%

Theoretical Limiting Potentials in Mg/O₂ Batteries

et al. 2016

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ABSTRACT:A rechargeable battery based on a multi-valent Mg/O2 couple is an attractive chemistry due to its high theoretical energy density and potential for low cost. Nevertheless, metal-air batteries based on alkaline earth anodes have received limited attention and generally exhibit modest performance. In addition, many fundamental aspects of this system remain poorly understood, such as the reaction mechanisms associated with discharge and charging. The present study aims to close this knowledge gap and thereby accelerate the development of Mg/O2 batteries by employing first-principles calculations to characterize electrochemical processes on the surfaces of likely discharge products, MgO and MgO2. Thermodynamic limiting potentials for charge and discharge are calculated for several scenarios, including variations in surface stoichiometry and the presence/absence of intermediate species in the reaction pathway. The calculations indicate that pathways involving oxygen intermediates are preferred, as they generally result in higher discharge and lower charging voltages. In agreement with recent experiments, cells that discharge to MgO exhibit low round-trip efficiencies, which are rationalized by the presence of large thermodynamic overvoltages. In contrast, MgO2-based cells are predicted to be much more efficient: superoxide-terminated facets on MgO2 crystallites enable low overvoltages and round-trip efficiencies approaching 90%. These data suggest that the performance of Mg/O2 batteries can be dramatically improved by biasing discharge towards the formation of MgO2 rather than MgO.

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Experimental Methodologies for Assessing the Surface Energy of Highly Hygroscopic Materials: The Case of Nanocrystalline Magnesia

Cited by 38 publications

References 44 publications

Size Effects in MgO Cube Dissolution

Size Effects in MgO Cube Dissolution

Accurate surface energies from first principles

Theoretical Limiting Potentials in Mg/O₂ Batteries

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Experimental Methodologies for Assessing the Surface Energy of Highly Hygroscopic Materials: The Case of Nanocrystalline Magnesia

Cited by 38 publications

References 44 publications

Size Effects in MgO Cube Dissolution

Size Effects in MgO Cube Dissolution

Accurate surface energies from first principles

Theoretical Limiting Potentials in Mg/O2 Batteries

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Product

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Theoretical Limiting Potentials in Mg/O₂ Batteries