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Hibbs M.R.,Sandia National Laboratories
Journal of Polymer Science, Part B: Polymer Physics | Year: 2013

Anion exchange membranes comprised of a poly(phenylene) backbone and one of five different cationic head-groups are prepared, briefly characterized, and tested for stability in 4 M KOH at 90 °C. The two membranes with resonance-stabilized cations (benzyl pentamethylguanidinium and benzyl N-methylimidazolium) show large (>25%) decreases in both conductivity and ion exchange capacity (IEC) after just one day of testing. The membrane with benzyl trimethylammonium cations shows a 33% loss of conductivity (14% decrease in IEC) after 14 days while the membrane with trimethylammonium cations attached by a hexamethylene spacer shows the least degradation: a 5% loss of conductivity over 14 days with no accompanying loss in IEC. A similar membrane which has a six-carbon spacer and a ketone adjacent to the phenyl ring shows much lower stability, suggesting that the ketone takes part in degradation reactions. © 2012 Wiley Periodicals, Inc. Source

Leung K.,Sandia National Laboratories
Journal of Physical Chemistry C | Year: 2012

Density functional theory and ab initio molecular dynamics simulations are applied to investigate the initial steps of ethylene carbonate (EC) decomposition on spinel Li 0.6Mn 2O 4(100) surfaces. EC is a key component of the electrolyte used in lithium ion batteries. We predict a slightly exothermic EC bond-breaking event on this oxide facet, which facilitates subsequent EC oxidation and proton transfer to the oxide surface. Both the proton and the partially decomposed EC fragment weaken the Mn-O ionic bonding network. Implications for an interfacial film made of decomposed electrolyte on cathode surfaces, and Li xMn 2O 4 dissolution during power cycling, are discussed. © 2012 American Chemical Society. Source

Bishop J.E.,Sandia National Laboratories
International Journal for Numerical Methods in Engineering | Year: 2014

A displacement-based continuous-Galerkin finite element formulation for general polyhedra is presented for applications in nonlinear solid mechanics. The polyhedra can have an arbitrary number of vertices or faces. The faces of the polyhedra can have an arbitrary number of edges and can be nonplanar. The polyhedra can be nonconvex with only the mild restriction of star convexity with respect to the vertex-averaged centroid. Conforming shape functions are constructed using harmonic functions defined on the undeformed configuration, thus requiring the use of a total-Lagrangian finite element formulation in large deformation applications. For nonlinear applications with computationally intensive constitutive models, it is important to minimize the number of element quadrature points. For this reason, an integration scheme is adopted in which the number of quadrature points is equal to the number of vertices. As a first step toward verifying the element behavior in the general nonlinear setting, several linear verification examples are presented using both random Voronoi meshes and distorted hexahedral meshes. For the hexahedral meshes, results for the polyhedral formulation are compared to those of the standard trilinear hexahedral formulation. The element behavior in the nearly incompressible regime is also examined. © 2013 John Wiley & Sons, Ltd. Source

Sheps L.,Sandia National Laboratories
Journal of Physical Chemistry Letters | Year: 2013

We present the time-resolved UV absorption spectrum of the B̃ ( 1A′) ← X̃ (1A′) electronic transition of formaldehyde oxide, CH2OO, produced by the reaction of CH2I radicals with O2. In contrast to its UV photodissociation action spectrum, the absorption spectrum of formaldehyde oxide extends to longer wavelengths and exhibits resolved vibrational structure on its low-energy side. Chemical kinetics measurements of its reactivity establish the identity of the absorbing species as CH2OO. Separate measurements of the initial CH2I radical concentration allow a determination of the absolute absorption cross section of CH2OO, with the value at the peak of the absorption band, 355 nm, of σabs = (3.6 ± 0.9) × 10-17 cm2. The difference between the absorption and action spectra likely arises from excitation to long-lived B̃ (1A′) vibrational states that relax to lower electronic states by fluorescence or nonradiative processes, rather than by photodissociation. © 2013 American Chemical Society. Source

Pitz W.J.,Lawrence Livermore National Laboratory | Mueller C.J.,Sandia National Laboratories
Progress in Energy and Combustion Science | Year: 2011

There has been much recent progress in the area of surrogate fuels for diesel. In the last few years, experiments and modeling have been performed on higher molecular weight components of relevance to diesel fuel such as n-hexadecane (n-cetane) and 2,2,4,4,6,8,8-heptamethylnonane (iso-cetane). Chemical kinetic models have been developed for all the n-alkanes up to 16 carbon atoms. Also, there has been experimental and modeling work on lower molecular weight surrogate components such as n-decane and n-dodecane that are most relevant to jet fuel surrogates, but are also relevant to diesel surrogates where simulation of the full boiling point range is desired. For two-ring compounds, experimental work on decalin and tetralin recently has been published. For esters, kinetic mechanisms for compounds of lower molecular weights but similar to those found in typical biodiesel blendstocks also have been published. For multi-component surrogate fuel mixtures, recent work on modeling of these mixtures and comparisons to real diesel fuel is reviewed. Detailed chemical kinetic models for surrogate fuels are very large in size, so it is noteworthy that significant progress also has been made in improving the mechanism reduction tools that are needed to make these large models practicable in multi-dimensional reacting flow simulations of diesel combustion. Nevertheless, major research gaps remain. In the case of iso-alkanes, there are experiments and modeling work on only one of relevance to diesel: iso-cetane. Also, the iso-alkanes in diesel are lightly branched and no detailed chemical kinetic models or experimental investigations are available for such compounds. More components are needed to fill out the iso-alkane boiling point range. For the aromatic class of compounds, there has been little work for compounds in the boiling point range of diesel. Most of the new work has been on alkyl aromatics that are of the range C7-C9, below the C10-C20 range that is needed. For the chemical classes of cycloalkanes and esters, experiments and modeling on higher molecular weight components are warranted. Finally for multi-component surrogates needed to treat real diesel, the inclusion of higher molecular weight components is needed in models and experimental investigations. Source

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