283 research outputs found
Halide substitution in Ca(BH4)(2)
No full textHalide substitution in Ca(BH4)2 has been investigated in ball milled mixtures of Ca(BH4)2 and CaX2 (X 1⁄4 F, Cl, Br) with different molar ratios. In situ synchrotron radiation powder X-ray diffraction measurements of Ca(BH4)2 + CaCl2 with 1 : 0.5, 1 : 1 and 1 : 2 molar ratios reveal that no substitution of Cl for BH4 occurs from the ball milling process. However, substitution readily occurs after the transitions from a- to b-Ca(BH4)2 and from orthorhombic to tetragonal CaCl2 upon heating above 250 C, which is evident from both contraction of the unit cell and changes in the relative Bragg peak intensities, in agreement with theoretical calculations. Rietveld analyses of the obtained b-Ca((BH4)1xClx)2 solid solutions indicate compositions from x 1⁄4 0 to 0.6, depending on the amount of CaCl2 in the parent mixtures. b-Ca((BH4)0.5Cl0.5)2 was investigated by differential scanning calorimetry and has a slightly higher decomposition temperature compared to pure Ca(BH4)2. No substitution with CaF2 or CaBr2 is observed
Thermodynamic Tuning of Calcium Hydride by Fluorine Substitution
No full textFluorine substitution in CaH2 has been studied by means of experimental and theoretical
methods. Samples with various compositions have been prepared by ball milling. In situ X-ray
diffraction analysis has been carried out as a function of temperature by synchrotron radiation
experiments. An increase of mixing has been observed during heating, suggesting that mixing is
thermodynamically favoured but it is kinetically hindered at low temperatures. Ab initio DFT
calculations have been performed to estimate the thermodynamic mixing properties of both
orthorhombic and cubic solid solutions. On the basis of ab initio results and literature
information, a thermodynamic assessment within the CALPHAD framework has been performed
and the pseudo binary CaH2-CaF2 phase diagram has been calculated. The formation of
orthorhombic and cubic terminal solid solutions in the CaH2-CaF2 system is predicted, in good
agreement with experimental findings
Theoretical and Experimental Study of LiBH4-LiCl Solid Solution
No full textAnion substitution is at present one of the pathways to destabilize metal borohydrides for solid state hydrogen storage. In this work, a solid solution of LiBH4 and LiCl is studied by density functional theory (DFT) calculations, thermodynamic modeling, X-ray diffraction, and infrared spectroscopy. It is shown that Cl substitution has minor effects on thermodynamic stability of either the orthorhombic or the hexagonal phase of LiBH4. The transformation into the orthorhombic phase in LiBH4 shortly after annealing with LiCl is for the first time followed by infrared measurements. Our findings are in a good agreement with an experimental study of the LiBH4-LiCl solid solution structure and dynamics. This demonstrates the validity of the adopted combined theoretical (DFT calculations) and experimental (vibrational spectroscopy) approach, to investigate the solid solution formation of complex hydrides
Food Aid and the WTO: Can New Rules Be Effective?
No full textA new Agreement on Agriculture from the Doha Development Agenda negotiations is certain to contain binding rules on food aid shipments. Negotiating parties are concerned that food aid has been used as a form of export competition policy, and they seek the use of coercive WTO legislation to prevent the disposal of surplus agricultural commodities as food aid. Current Uruguay Round food aid guidelines are contrasted with the most recent Doha Development Agenda proposals, and the prospective effectiveness of new rules is assessed. Food aid rules will be difficult to enforce within the WTO’s Dispute Settlement Understanding. Also, exogenous policy changes in donor countries are reducing the relevance of rules that target food aid as a means of surplus disposal. The future of international food aid governance in the event of a Doha Round collapse is also discussed.agricultural trade, development economics, export competition, food aid, WTO, Food Security and Poverty, International Relations/Trade, O13, O19, Q17, F13,
Synthesis and Structural Investigation of Zr(BH4)(4)
No full textZirconium tetraborohydride, Zr(BH4)4, was synthesized by a metathesis reaction between LiBH4 and ZrCl4 using high-energy ball milling. Initially, a white powder was produced, and during storage at −30 °C in a closed vial, transparent rectangular single crystals formed under the lid by vapor deposition. Single-crystal X-ray diffraction data revealed a cubic unit cell (a = 5.8387(4) Å, space group P-43m, determined at T = 100 K), which consists of neutral Zr(BH4)4 molecules. The BH4– anions coordinate to Zr via the tetrahedral faces (η3). The shortest distance between neighboring molecules in the solid is defined by B–H2···H2–B interactions of 2.77 Å. DFT calculations, based on the experimental structure, have been performed with the CRYSTAL code. A phonon instability in the Γ point was observed for space-group symmetry P-43m, which can be eliminated by a symmetry reduction to the cubic space group P23. Computed IR spectra for the two structural models turned out to be very similar. Synthesis and decomposition was further investigated using in situ synchrotron radiation powder X-ray diffraction
The Six Essentials? Minimal Requirements for the Darwinian Bootstrapping of Quality
No full textSelectionism emphasizes carving patterns, memes remind us of minimal replicable patterns, but a full-fledged Darwinian process needs six essential ingredients to keep going, to recursively bootstrap quality from rude beginnings. While there may be situations ("sparse Darwinism") in which a reduced number suffice, another five ingredients, while not essential, greatly enhance the speed and stability of a Darwinian process. While our best examples are drawn from species evolution, the immune response, and evolutionary epistemology, the Darwinian process may well be a major law of the universe, right up there with chemical bonds as a prime generator of interesting combinations that discover stratified stabilities
Hydrothermal sediments record changes in deep water oxygen content in the SE Pacific
No full textThe distribution of redox?sensitive metals in sediments is potentially a proxy for past ocean ventilation and productivity, but deconvolving these two major controls has proved difficult to date. Here we present a 740 kyr long record of trace element concentrations from an archived sediment core collected at ?15°S on the western flank of the East Pacific Rise (EPR) on 1.1 Myr old crust and underlying the largest known hydrothermal plume in the world ocean. The downcore trace element distribution is controlled by a variable diagenetic overprint of the inferred primary hydrothermal plume input. Two main diagenetic processes are operating at this site: redox cycling of transition metals and ferrihydrite to goethite transition during aging. The depth of oxidation in these sediments is controlled by fluctuations in the relative balance of bottom water oxygen and electron donor input (organic matter and hydrothermal sulfides). These fluctuations induce apparent variations in the accumulation of redox?sensitive species with time. Subsurface U and P peaks in glacial age sediments, in this and other published data sets along the southern EPR, indicate that basin?wide changes in deep ocean ventilation, in particular at glacial?interglacial terminations II, III, IV, and V, alter the depth of the oxidation front in the sediments. These basin?wide changes in the deep Pacific have significant implications for carbon partitioning in the ocean?atmosphere system, and the distribution of redox?sensitive metals in ridge crest sediment can be used to reconstruct past ocean conditions at abyssal depths in the absence of alternative proxy records
2006 Author Recognition Bibliography
No full texthttps://scholarworks.gvsu.edu/authorrecognition/1008/thumbnail.jp
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