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The physical mechanisms which may contribute to the energy and entropy of mixing in oxide systems are identified and discussed. Ionic size, magnetism and electrostatics can all contribute to the configurational energy dependence of transition-metal oxides. While the many sources of substitutional disorder make configurational entropy an essential contribution to the free energy of oxides, electronic and magnetic entropy may be of the same order of magnitude. This is illustrated with some first-principles results on LiCoO2 and LiMnO2.
In this paper, we propose that a p-type transparent conducting oxide (p-TCO) can function as a selective hole contact and corrosion protection layer on photoanodes used for light-driven water oxidation. To prove the concept, NiCo 2 O 4 was used as the p-TCO for n-Si protection in alkaline condition, and we show that this material has the requisite electronic structure, stability, transparency, and hole conductivity to achieve sustained and efficient solar water oxidation. The photoelectrochemical performance demonstrates the attractive combination of transparency and low-resistance hole conductivity in the NiCo 2 O 4 . Long-term testing indicates multi-day stability with minimal decrease in performance or observable corrosion of the Si photoanode. This works suggests that p-TCOs are promising as corrosion protection layers for stable water oxidation photoanodes.
We have carried out a periodic Kohn-Sham density functional theory investigation of the pathways by which carbon-carbon bonds could be formed during the electrochemical reduction of CO2 on Cu(100) using a model that includes the effects of the electrochemical potential, solvent, and electrolyte. The electrochemical potential was set by relating the applied potential to the Fermi energy and then calculating the number of electrons required by the simulation cell for that specific Fermi energy. The solvent was included as a continuum dielectric, and the electrolyte was described using a linearized Poisson-Boltzmann model. The calculated potential of zero charge for a variety of surfaces agrees with experiment to within a mean average error of 0.09 V, thereby validating the assumptions of the model. Analysis of the mechanism for C-C bond formation revealed that at low-applied potential, C-C bond formation occurs through a CO dimer. However, at high applied potentials, a large activation barrier blocks this pathway; therefore, C-C bond formation occurs through reaction of adsorbed CHO and CO. Rate parameters determined from our calculations were used to simulate the kinetics of ethene formation during the electrochemical reduction of CO over a Cu(100) surface. An excellent match was observed between previously reported measurements of the partial current for ethene formation as a function of applied voltage and the variation in the partial current for C-C bond formation predicted by our microkinetic model. The electrochemical model reported here is simple, fairly easy to implement, and involves only a small increase in computational cost over calculations neglecting the effects of the electrolyte and the applied field. Therefore, it can be used to study the effects of applied potential and electrolyte composition on the energetics of surface reactions for a wide variety of electrochemical reactions.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
Low-temperature synthesis of crystalline silicon and silicon-containing nanowires remains a challenge in synthetic chemistry due to the lack of sufficiently reactive Si precursors. We report that colloidal Si nanowires can be grown using tris(trimethylsilyl)silane or trisilane as the Si precursor by a Ga-mediated solution-liquid-solid (SLS) approach at temperatures of about 200 °C, which is more than 200 °C lower than that reported in the previous literature. We further demonstrate that the new Si chemistry can be adopted to incorporate Si atoms into III-V semiconductor lattices, which holds promise to produce a new Si-containing alloy semiconductor nanowire. This development represents an important step toward low-temperature fabrication of Si nanowire-based devices for broad applications.
A micro-mechanistic understanding of bone fracture that encompasses how cracks interact with the underlying microstructure and defines their local failure mode is lacking, despite extensive research n the response of bone to a variety of factors like aging, loading, and/or disease.
The San Cayetano Formation of western Cuba is the thickest and most extensive subaerial exposure of Jurassic siliciclastic rocks between the southeastern United States and northern South America. Previous workers have speculated that siliciclastic rocks of the San Cayetano Formation were derived from one of the following sources: (1) Yucatan Peninsula, (2) Florida, and (3) northern South America. To address the problem of the provenance of the San Cayetano Formation and the Mesozoic position of western Cuba, we present the results of 40Ar/39Ar isotopic dates from 67 single detrital mica grains from four samples of the San Cayetano Formation. These mica grains have ages that fall within the age ranges of well-known Precambrian crustal-age provinces and Paleozoic orogenic belts in eastern North America and the Yucatan Peninsula. The lack of grains with ages in the 700–550 Ma range suggests that Pan African–Brasiliano orogenic belts that exist in northern South America, northwestern Africa, and beneath Florida did not contribute significant amounts of detritus to the San Cayetano basin. We propose that the Late Jurassic San Cayetano basin formed as a post-rift deltaic complex along the southeastern margin of the Yucatan Peninsula and was detached and transported to its present position in western Cuba in Paleogene time by the northeastward migration of the Caribbean arc.
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTPreface - Symposium on Catalytic Reaction Engineering for Environmentally Benign Processes and US-Russia Workshop on Environmental CatalysisM. Dudukovic, P. Mills, A. Bell, and L. ManzerCite this: Ind. Eng. Chem. Res. 1994, 33, 12, 2885–2886Publication Date (Print):December 1, 1994Publication History Published online22 December 2003Published inissue 1 December 1994https://pubs.acs.org/doi/10.1021/ie00036a600https://doi.org/10.1021/ie00036a600research-articleACS PublicationsRequest reuse permissionsArticle Views81Altmetric-Citations3LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts
Low-ionization nuclear emission-line regions (LINERs), which exist in a large fraction of galaxies, may be the least luminous manifestation of quasar activity. The nature of LINERs has, however, remained controversial because an AGN-like nonstellar continuum source has not been directly observed in them. We report the detection of bright, unresolved (FWHM $\ltorder 0.1''$) point sources of UV ($\sim 2300$ \AA) emission in the nuclei of nine nearby galaxies from a complete sample of 110 nearby galaxies imaged with {\it HST}. Ground-based optical spectroscopy reveals that five of the nuclei are LINERs, three are starburst nuclei, and one is a Seyfert nucleus. The observed UV flux in each of the five LINERs implies an ionizing flux that is sufficient to account for the observed emission lines through photoionization. The detection of a strong UV continuum in the LINERs argues against shock excitation as the source of the observed emission lines, and supports the idea that photoionization excites the lines in at least some objects of this class. Among the Northern-hemisphere galaxies in the sample, 26 are LINERs, of which only the above five LINERs have a detected nuclear UV source. There are no obvious differences in the optical line intensity ratios between the UV-bright and UV-dark LINERs. If all LINERs are photoionized, then the continuum source is unobscured along our line of sight in $5/26\approx 20\%$ of LINERs. Alternatively, spectrally-similar LINERs may be produced by various excitation mechanisms, with photoionization responsible in only about 20\% of the cases. The high angular resolution allows us to set upper limits, typically several parsecs, on the physical size of the compact star-cluster or AGN-type continuum source that is emitting the UV light in these objects.
Abstract Diblock star polymers were synthesized via atom transfer radical polymerization from a palladium porphyrin macroinitiator. The arms of the star polymers had an amphiphilic design, with the central Pd‐porphyrin surrounded by a relatively hydrophobic block of poly(butyl acrylate) and terminated by a hydrophilic block of poly(oligoethyleneglycol monomethylether monomethacrylate). The size of both the interior and exterior blocks of the polymer arms were tuned over a wide range of molecular weights with the exterior block used to solubilize the stars in polar media. The star polymers showed enhanced reactivity in the oxidation of 2‐furaldehyde relative to a small molecule porphyrin, suggesting that the polymer backbone aids with catalytic turnover. Oxygen diffusion studies indicate that the polymer backbone shields the porphyrin excited state from oxygen quenching. Shielding is independent of molecular weight and polymer composition, but it is not pronounced enough to retard the rate of singlet oxygen generation under preparative photooxidation conditions. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4939–4951, 2006
Abstract The great majority of models that have been developed to predict localized corrosion damage are empirical in nature. As such, they lack the ability to effectively predict damage outside of their immediate realm of calibration and generally can only “predict” what is already known. Furthermore, empirical models generally cannot predict new phenomena or relationships. It is shown that it is possible to describe propagation of corrosion damage deterministically, i.e. to describe how the systems evolves from the present state to the future state on the basis of natural laws [conservation of charge, mass-energy, and mass-charge equivalence (Faraday's law), etc. ], subject to constraint by the natural laws. It is clear that deterministic models have much more predictive power than do empirical models. However, in the general case, it is possible to describe the development of localized corrosion damage in terms of the propagation of an ensemble of corrosion events, rather than as individual cavities. Accordingly, the prediction can be made in terms of statistical terms, for example, probability that the deepest pit will exceed the critical dimension that defines failure ( e.g. , thickness of a pipe wall). In doing so, the statistical parameters (mean depth of the deepest pit with its standard deviation, etc. ) can be calculated deterministically. In order to perform such calculations, we must possess deterministic models for every stage of cavity development (pit nucleation, propagation and repassivation, transition pit into crack, crack propagation, and so forth). Some of these models are outlined in the current review. The deterministic theory outlined here has been applied for the predation of localized corrosion damage in important, practical systems, including pitting in oil field components, in low pressure steam turbine blades and discs, and in condensing heat exchangers, to name but a few of the current and past applications, some of which are reviewed in this paper.
