The isothermal, endothermic, stepwise decomposition of ammonium metavanadate (AMV) in inert (argon or nitrogen), oxidising (air or oxygen) and reducing (ammonia) atmospheres as well as under high vacuum (pressure < IOn bar) conditions has been investigated. The reverse reaction, the isothermal recombination of V₂ 0₅ with ammonia and water vapour has also been investigated. The decomposition and recombination reactions were followed by continuously recording the mass loss of the sample with time using a Cahn R.G. Automatic Electrobalance. This enabled small samples ( ~ lOmg) to be used and consequently any self cooling of the sample during the decomposition was minimized. The intermediates and final products formed have been characterized by chemical analysis, X-ray powder diffraction studies, infrared spectroscopy and the mass loss involved in their formation. The changes in the physical properties of the samples during decomposition and recombination have been investigated by surface area measurements (using the BET method and krypton adsorption) and eIectron microscopy. Values for the enthalpy changes involved in the decomposition have been obtained by differential scanning calorimetry. The stoichiometry of the isothermal decomposition of ammonium metavanadate, under the various conditions of surrounding atmosphere has been discussed. Except for the later stages of the decomposition in ammonia, the results correspond well to the gradual reduction of the ratio of "(NH₄)₂ 0" to "V₂0₅" units from the original 1:1 ratio in ammonium metavanadate to pure "V₂0₅" with ammonia and water being evolved throughout the decomposition in the mole ratio of 2:1. The final product of the decomposition in vacuum, argon and air is "V₂0₅" and in ammonia, below 360°, V0₂. The kinetic parameters for each of the stages of the decomposition of AMV in each of the atmospheres studied have been determined. The mechanism of the first stage of the decomposition under the different conditions of surrounding atmosphere has been discussed from both the kinetic and the thermodynamic points of view. The absolute reaction rate theory has been applied to the decomposition in inert atmospheres enabling the formulae of the activated complexes formed during each stage to be calculated. It has also been shown that the detailed atomic movements occurring during the first stage of the decomposition in ammonia can be predicted from a knowledge of the stoichiometry of the reaction and of the detailed crystal structures of the starting and product materials. The kinetics and mechanism of the recombination of "V₂0₅" with ammonia and water vapour to form AMV have also been discussed in detail.

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The principal aim of this work was the development of a novel conductivity probe for measuring solids concentrations in slurries. The relevance of the thesis to this probe is that it requires rapid transport of aqueous electrolyte through a porous disc to an internal conductivity cell.

A number of solid substances ware examined by nuclear magnetic resonance methods with a view to investigating possible molecular motion. The possibility of using the adiabatic rapid passage technique as a method for investigating the molecular motion in the solid state was studied. Two systems, namely benzene and furan were studied. It was found that spin-lattice relaxation times and in some cases, second moments could be obtained using the adiabatic rapid passage technique; the results obtained were in good agreement with values obtained using standard techniques. Also it was found that the presence of a certain type of molecular motion severely affects the shape and amplitude of the adiabatic rapid passage signal. A number of charge-transfer complexes were investigated using standard broadline (1)H and (19)F nuclear magnetic resonance techniques. Some strong charge-transfer complexes studied in this manner include: a number of amine complexes of BF(3) and some halogen complexes of trimethylamine. Second moment and linewidth changes with temperature were interpreted in terms of reorientations of molecular groups within the complexes. Also studied were a number of weak complexes of benzene. Linewidth, second moment, and also spin-lattice relaxation time measurements showed that the benzene rings were reorientating about their hexad axes at frequencies greater than about 10(5) sec.(-1) at temperatures above 120°K. The activation energies for this motion depended strongly on the environment of the benzene ring in the complex. A study of some arene-chromium-tricarbonyl compounds indicated that the motional properties of the arene rings in the complexes resembled very much the motional properties of the free ring compounds; this suggests that specific bonding effects are relatively inimportant. Finally, linewidth, second moment and spin-lattice relaxation time measurements are reported for some soap systems, the alkali metal stearates and oleates. Transition temperatures observed could in some cases be correlated with values obtained by different methods. Some motional models were suggested in order to explain decreases in linewidths and second moments with increasing temperature. It was shown that methyl group rotation provides a relaxation mechanism in the low temperature phase for all the soaps studied. Activation energies found for this process ranged from 1.8-2.5 Kcal/mole. The effect of thermal history on phase transitions in the alkali metal stearates was also investigated. Thermograms were obtained using samples with different thermal histories using a differential scanning calorimeter. It was found that the thermal history of a sample may affect transition temperatures, and also the absence of presence of some transitions. / Science, Faculty of / Chemistry, Department of / Graduate

Orientador: Jorge de Lucas Junior / Banca: Gener Tadeu Pereira / Banca: Luiz Augusto do Amaral / Banca: Ana Carolina Amorim Orrico / Banca: Mônica Sarolli Silva de Mendonça Costa / Resumo: Objetivou-se avaliar a melhor diluição para dejetos de suínos, aves de postura, ovinos, caprinos, bovinos de corte e bovinos de leite para o abastecimento de biodigestores, bem como a influência da separação de sólidos desses mesmos dejetos na produção e qualidade do biogás, no potencial de produção de biogás e redução de sólidos. Para o teste de diluições os dejetos foram diluídos em água nas proporções: 1:4, 1:5, 1:6, 1:7 e 1:8 (kg de dejeto por kg de água) e adotado o processo físico de peneiramento (peneiras com malhas quadradas de 0,75, 1,00 e 1,50 mm) para separação dos sólidos. Para o ensaio de biodigestão anaeróbia (biodigestores tipo batelada e semi-contínuos) a separação dos sólidos foi feita com peneira de malha de 1mm e substratos com cerca de 4% de sólidos totais. Teste de diluição: embora os resultados tenham variado entre os tipos de dejeto, de modo geral a peneira de malha 1,50 mm permitiu a maior passagem de sólidos. Mas em relação a diluição cada tipo de dejeto apresentou uma resposta. Ensaio de biodigestão anaeróbia (biodigestores tipo batelada): embora para cada dejeto o processo de biodigestão anaeróbia tenha tido uma resposta diferente, de modo geral a separação de sólidos proporcionou melhor qualidade de biogás, porém não foi eficiente para aumentar o potencial de produção de biogás e reduzir sólidos do substrato. Ensaio de biodigestão anaeróbia (biodigestores do tipo semi-contínuo): para os dejetos utilizados (aves de postura e bovinos de leite) a separação de sólidos proporcionou melhor qualidade de biogás, menor produção de biogás, maior redução de sólidos e, para os potenciais de produção de biogás os resultados foram quase sempre positivos. Conclui-se que para o teste de diluição e peneiras os resultados não permitiram uma conclusão geral para todos os dejetos avaliados, pois cada um apresentou características individuais e, para a ... / Abstract: This trial aimed to evaluate the best dilution for pig, laying hens, sheep, goats, beef cattle and dairy cattle manure to supply digesters, as well as the influence of the solids separation in those same wastes on the production and quality of biogas, on the potential of biogas production and solids reduction. For the dilution test the wastes were diluted with water in the proportions 1:4, 1:5, 1:6, 1:7 and 1:8 (kg of manure per kg of water) and adopted the physical process of screening (sieve with square meshes of 0.75, 1.00 and 1.50 mm) for separation of solids. When tested for anaerobic digestion (batch and semi-continuous digesters) separation of solids was made with 1 mm mesh sieve and substrates of about 4% total solids. Dilution test: although the results varied among the types of manure, generally a 1.50 mm mesh sieve allowed greater flow of solids. But in relation to the dilution used each type of waste had a different response. Testing of anaerobic digestion (batch digesters): although for each manure the process of anaerobic digestion has had a different result, generally solids separation provided better biogas quality, but it was not efficient to increase the potential of biogas production and reduce solids of substrate. Testing of anaerobic digestion (semi-continuous digesters): for the wastes (laying hens and dairy cattle) used the solids separation provided better quality of biogas, lower biogas production, greater reduction of solids and in regards to the potential of biogas production the results were almost always positive. It was concluded that for dilution and sieves test results did not allow a general conclusion for all waste reviews, because each one had individual characteristics and, the separation of solids is an efficient method to enhance the quality of the biogas produced, but in relation to the potential of biogas production and solids reduction of the substrate ... / Doutor

In field experiments conducted in northern Virginia during 1998, oils reduced photosynthesis, fruit maturity, and crop yield. Three applications of a 1.5% (v/v) oil/water emulsion were made to Chardonnay and Cabernet Sauvignon vine canopies at 6200 L/ha (Chardonnay) and 2440 L/ha (Cabernet Sauvignon). Net assimilation rate (NAR), soluble solids concentration (SSC), and berry size were reduced by oil treatments when compared to an untreated control. Also in 1998, a 1.5% (v/v) oil/water emulsion at 5550 L/ha and 4680 L/ha was applied to 23 wine grape cultivars. Eleven cultivars had significant foliar injury but injury was not related to reductions in fruit maturity. Experiments conducted in 1999 determined if reduced spray volumes or applications to only the fruit zone minimize reductions in NAR and SSC. Chardonnay and Cabernet Sauvignon were treated with JMS Stylet oil (1.5%) using 5600 L/ha or 1870 L/ha applied to the whole canopy or 930 L/ha applied to the fruit zone. The NAR of 5600 L/ha treated Cabernet Sauvignon was significantly lower than the NAR of control and other oil treatments on three measurement dates. The NAR of Chardonnay in the 5600 L/ha treatment was significantly lower than the NAR of control treatments in three measurements. Cabernet Sauvignon SSC was reduced by the 5600 L/ha and 1870 L/ha treatments, relative to the water treated control, on three sample dates but not at harvest. The SSC of Chardonnay in the 5600 L/ha treatment was reduced at harvest as compared to all other treatments. The SSC of Chardonnay in the 1870 and 930 L/ha treatments was reduced relative to the water control. Low volumes of oil caused less reduction in NAR and SSC; however, there are concerns about the efficacy of oils used at low volumes due to poor coverage. / Master of Science

Solid-liquid phase equilibria studies were used to investigate possible compound formation in solutions of (i) N,N-dimethylformamide (DMF) and (ii) N,N-dimethylacetamide (DMA) with a series of halogenated hydrocarbons that were selected to give a wide range of acceptor properties. Solid 1:1 intermolecular compounds were identified from solutions of (i) DMF and (ii) DMA with CCl_4, CBrCl_3, and C_6H_5CCl_3. The intermolecular compounds (DMF)_2•CCl_4 and (DMF)_2•CBrCl_3 were also found. The results suggest charge transfer from DMF or DMA to the chlorine atoms of the acceptor molecule as the process for compound formation. Thermal methods were used to determine with high precision the solid-liquid phase equilibria diagram for the sodium-cesium system. Results differ greatly from those of earlier workers, especially near the eutectic composition where differences in melting points as large as 35°K occur. Although not conclusive, results support the proposal that the peritectic halt results from the formation of an Na_2Cs intermetallic compound by a very sluggish reaction. Thermal methods were also used to determine the mesophase transition temperatures for cholesteryl formate.

In the usual thermal stress analysis of a body, the stresses are found for a predetermined temperature distribution. In problems involving composite materials, thermal contact resistance between materials can significantly affect the temperature distribution. The contact resistance is normally a function of the contact pressure and thermally induced stresses can affect the temperature distribution. Thus in composite bodies the thermal stress problem and the heat transfer problem may be coupled and require a simultaneous solution of both problems.

El texto completo de este trabajo no está disponible en el Repositorio Académico UPC por restricciones de la casa editorial donde ha sido publicado. / The present investigation focuses on the mathematical concept of convexity, as the main tool for the graphic construction of bounded surfaces explicitly and implicitly described, as well as the construction of unconventional solids using GeoGebra. Two cases are presented in which the importance of the concept of convexity is highlighted, in the first situation the convexity is used in the argument of the surface command together with the curves that delimit it to graph a bounded surface, while in the second situation the convexity is evidenced by expressing the coordinates of the surface in parametric form. On the other hand, the 3D graphic view combined with the GeoGebra AR tool allows one to visualize, manipulate, understand and improve the abstraction of mathematical objects that are built in three-dimensional space in a dynamic and friendly environment. These constructions in three-dimensional space that are complex when sketching them with pencil and paper are easier when linking the mathematical definitions with free software such as GeoGebra. / Revisón por pares

Room temperature elastic properties of thin supported TiC films, deposited on silicon and silicon carbide substrates and of single Rh-based alloy crystals, Rh3Nb and Rh3Zr, are investigated by the Surface Brillouin Scattering (SBS) technique. Velocity dispersion curves of surface acoustic waves in TiC films of various thicknesses, deposited on each substrate (Si and SiC) were obtained from SBS spectra. Simulations of SBS spectra of TiC thin hard films on germanium, silicon, diamond and silicon substrates have been carried out over a range of film thickness from 5 nm to 700 nm. The simulations are based on the elastodynamic Green's functions method that predicts the surface displacement amplitudes of acoustic phonons. These simulations provide information essential for analysis of experimental data emerging from SBS experiments. There are striking differences in both the simulated and experimental SBS spectra depending on the respective elastic properties of the film and the substrate. In fast on slow systems (e.g. TiC on silicon), the Rayleigh mode is accompanied by both broad and sharp resonances; in slow on fast systems (e.g TiC on SiC), several orders of Sezawa modes are observed together with the Rayleigh mode. The velocity dispersion of the modes has been obtained experimentally for both situations, allowing the elastic constants of the films to be determined. Effects of two deposition conditions, RF power and substrate bias, on the properties of the films are also considered. Platinum metal group alloys are promising candidates for future ultra high temperatures gas turbines materials due to their excellent high-temperature properties. In the present work, room temperature elastic properties of single crystals of Rh3Nb and Rh3Zr are investigated. SBS spectra for a range of wave vector directions from the (001) surface have been acquired in order to determine the angular variation of the surface acoustic wave velocities and the longitudinal wave threshold within the Lamb shoulder. The elastic stiffnesses of the specimens were determined using two approaches; one approach involves a least-square fit of the experimental data to calculated results and the other is an analytical approach which involves the 2 c minimization of secular equations for the Rayleigh surface acoustic wave and the longitudinal wave threshold velocities in the [100] and [110] directions on the (001) surface of a cubic crystal. Results from the two methods were in good agreement.