Direct coal gasification with simultaneous production of electricity in a novel fused metal anode SOFC: a theoretical approach

Coal gasification in molten metal baths is a relatively new process with important technological advantages. The economics of the process can be made even more attractive if part of the Gibbs energy change of the oxidation reaction is directly converted into electricity through the use of the concept of a solid oxide fuel cell. This combination of fuel cell and fused metal gasifier in a single reactor-cell of the type: C, O₂, fused metal / YSZ / perovskite, O₂ is the distinguishing feature of the new process analyzed in this work. A mathematical model has been developed which describes the steady-state behaviour of this novel fuel cell and discusses the effect of operating conditions upon cell performance. This theoretical approach shows that, under best-case estimates, the electrochemical cell gasifier is capable of producing very high current and power densities. Paper presented at the 6th Euroconference on Solid State Ionics, Cetraro, Calabria, Italy, Sept. 12–19, 1999.     

Assay of caffeoylquinic acids in Baccharis trimera by reversed-phase liquid chromatography

Baccharis trimera commonly named ‘carqueja’, is wide-spread in South America and are used as raw material for herbal medicines. A reversed-phase liquid chromatography (RP-LC) method coupled to diode array detector was developed for the analysis of caffeoylquinic acids (CQAs), the main compounds responsible for its digestive activity. The identity of the quinic acids was established by mass spectrometry and were them: 5-O-[E]-caffeoylquinic acid, 3,4-O-[E]-dicaffeoylquinic acid, 3,5-O-[E]-dicaffeoylquinic acid, 4,5-O-[E]-dicaffeoylquinic acid and a tricaffeoylquinic acid. The RP-LC method for the quantitation of the caffeoylquinic acids was validated according to ICH guidelines, based on the following parameters: linearity, selectivity, robustness, limits of detection and quantification, precision and recovery. Hydroalcoholic extracts were prepared by the maceration of the plant material with ethanol:water 1:1 (v/v) in a 0.1:25 g mL^?1 plant:solvent ratio in a water bath at 40 °C. Validation data indicated that the HPLC method proposed is suitable for the analysis of caffeoylquinic acids in B. trimera raw material. The results of the LOD and LOQ analyses for the 5-CQA were 4.1 μg mL^?1 and 12.5 μg mL^?1, respectively, 1.3 μg mL^?1, 3.9 μg mL^?1 for 4,5-diCQA and 1.7 μg mL^?1, 5.1 μg mL^?1 for triCQA. The levels of total CQAs ranged from 2.1 to 4.0 g% (w/w). The influence of season harvest and site collection was also evaluated and variations were observed in the results and can be related to phonologic phase, different locations, seasons and soil. Long term and photostability of plant material were carried out and was observed a stable behavior during the time of the experiments.     

Structural Diversity and Thermochromic Properties of Iodobismuthate Materials Containing d-Metal Coordination Cations: Observation of a High Symmetry [Bi(3)I(11)](2-) Anion and of Isolated I(-) Anions

Six new inorganic-organic salts, all containing iodobismuthate anions and d-metal coordination cations, were synthesized solvothermally from reactions of bismuth iodide, a transition metal (M) nitrate salt (M = Co, Fe or Zn), and a heterocyclic, chelating organic ligand: 1,10-phenanthroline (1,10-phen), 3,4,7,8-tetramethyl-1,10-phenanthroline (TMphen), or 2,2':6',2'-terpyridine (tpy). All six compounds were structurally analyzed by single crystal X-ray diffraction, including variable temperature crystallographic analysis to monitor for structural changes. Furthermore, those containing novel anions and achieved in high yield were additionally characterized by solid-state UV visible spectroscopy at room temperature. [Co(1,10-phen)(3)][Bi(3)I(11)] (1), [Fe(1,10-phen)(3)][Bi(3)I(11)] (2), and [Zn(1,10-phen)(3)][Bi(3)I(11)] (3) are isostructural. They crystallize in the monoclinic space group P2(1)/n and contain the unprecedented iodobismuthate anion, [Bi(3)I(11)](2-), which exhibits near D(3h) symmetry and has an unusual arrangement of three cis face-sharing BiI(6) octahedra. [Co(TMPhen)(3)](2)[Bi(2)I(9)][I] (4), which crystallizes in the trigonal space group P-31c, and [Co(tpy)(2)](2)[Bi(2)I(9)][I] (5) and [Zn(tpy)(2)](2)[Bi(2)I(9)][I] (6), which are isostructural and crystallize in the monoclinic space group C2/c, contain the discrete binuclear [Bi(2)I(9)](3-) anion, common in previously reported iodobismuthate compounds. In addition they contain unusual isolated I(-) anions, which are rarely encountered in iodobismuthate phases. Compounds 1-6 show constitutional similarities while utilizing different organic ligands and illustrate the sensitive dependence of reaction conditions on the identity of the halometalate anion formed. Additionally, all six compounds and the starting material BiI(3) are thermochromic; the origin of this behavior is spectroscopically and crystallographically investigated.     

Structure, dynamics, and thermodynamics of a family of potentials with tunable softness

We investigate numerically the structure, thermodynamics, and relaxation behavior of a family of (n, 6) Lennard-Jones-like glass-forming binary mixtures interacting via pair potentials with variable softness, fixed well depth, and fixed well depth location. These constraints give rise to progressively more negative attractive tails upon softening, for separations greater than the potential energy minimum. Over the range of conditions examined, we find only modest dependence of structure on softness. In contrast, decreasing the repulsive exponent from n=12 to n=7 causes the diffusivity to increase by as much as two orders of magnitude at fixed temperature and density, and produces mechanically stable packings (inherent structures) with cohesive energies that are, on average, ～1.7 well depths per particle larger than for the corresponding Lennard-Jones (n=12) case. The softer liquids have markedly higher entropies and lower Kauzmann temperatures than their Lennard-Jones (n=12) counterparts, and they remain diffusive down to appreciably lower temperatures. We find that softening leads to a modest increase in fragility.     

Scaled particle theory for hard sphere pairs. I. Mathematical structure

We develop an extension of the original Reiss-Frisch-Lebowitz scaled particle theory that can serve as a predictive method for the hard sphere pair correlation function g(r). The reversible cavity creation work is analyzed both for a single spherical cavity of arbitrary size, as well as for a pair of identical such spherical cavities with variable center-to-center separation. These quantities lead directly to a prediction of g(r). Smooth connection conditions have been identified between the small-cavity situation where the work can be exactly and completely expressed in terms of g(r), and the large-cavity regime where macroscopic properties become relevant. Closure conditions emerge which produce a nonlinear integral equation that must be satisfied by the pair correlation function. This integral equation has a structure which straightforwardly generates a solution that is a power series in density. The results of this series replicate the exact second and third virial coefficients for the hard sphere system via the contact value of the pair correlation function. The predicted fourth virial coefficient is approximately 0.6% lower than the known exact value. Detailed numerical analysis of the nonlinear integral equation has been deferred to the subsequent paper.     

Apparent spin polarization decay in Cu-dusted Co/Al2O3/Co tunnel junctions

Co/Al2O3/Co magnetic tunnel junctions with an interfacial Cu layer have been investigated with in situ growth characterization and ex situ magnetotransport measurements. Cu interlayers grown on Co give an approximately exponential decay of the tunneling magnetoresistance with xi approximately 0.26 nm while those grown on Al2O3 have a decay length of 0.70 nm. The difference in decay lengths can be explained by different growth morphologies, and in this way clarifies a present disagreement in the literature. For monolayer coverage of Cu, we show that the tunneling spin polarization is suppressed by at least a factor of 2 compared to Co and beyond approximately 5 ML it becomes vanishingly small.     

Effects of nonpolar solutes on the thermodynamic response functions of aqueous mixtures

We investigate the effect of adding nonpolar solutes at atmospheric pressure on water's temperature of maximum density, isothermal compressibility, and isobaric heat capacity, using a statistical mechanical model of water solutions [H. S. Ashbaugh, T. M. Truskett, and P. G. Debenedetti, J. Chem. Phys. 116, 2907 (2002)]. We find that the temperature of maximum density increases with solute hydrophobicity, as characterized by its size, and decreases with its van der Waals attractive parameter a, in agreement with experiment. We predict similar trends for the addition of solutes on the isothermal compressibility and isobaric heat capacity: solute hydrophobicity causes an upward shift in water's anomalies, whereas dispersive interactions as measured by the solute's van der Waals attractive parameter shift the anomalies to lower temperatures. The locus along which the competing contributions of solute size sigma and interaction strength a to the shift in water's response functions balance each other obeys the scaling relationship sigma6 approximately a.     

Method for efficient computation of the density of states in water-explicit biopolymer simulations on a lattice

We present a method for fast computation of the density of states of binary systems. The contributions of each of the components to the density of states can be separated based on the conditional independence of the individual components' degrees of freedom. The conditions establishing independence are the degrees of freedom of the interfacial region between the two components. The separate contributions of the components to the density of states can then be calculated using the Wang-Landau algorithm [Wang, F.; Landau, D. P. Phys. Rev. Lett. 2001, 86, 2050]. We apply this method to a 2D lattice model of a hydrophobic homopolymer in water that exhibits protein-like cold, pressure, and thermal unfolding. The separate computation of the protein and water density of states contributions is faster and more accurate than the combined simulation of both components and allows for the investigation of larger systems.