Anodic films have been produced on zirconium and zirconium alloys potentiostatically (at either 20 or 40 V) in 0.35 M ammonium fluoride in glycerol, with interest in the addition of small amounts of water (up to 5 vol.%) to the electrolyte on their growth, morphologies and compositions. Scanning and transmission electron microscopies have been employed to analyse morphologies of the films, which appeared to be porous under all the investigated conditions.Rutherford backscattering spectroscopy and nuclear reaction analysis, used as techniques to investigate film compositions, disclosed the presence of zirconium, oxygen, fluorine, carbon and nitrogen in the films. The contents of fluorine and oxygen in the films were found to increase and decrease respectively by decreasing the amount of water added to the electrolyte from 5 to 0 vol.%. Moreover, the content of fluorine increased by decreasing the applied formation voltage, from 40 to 20 V, for films formed in electrolytes containing similar amounts of added water.In order to get information on the distribution of the species in the films, cross-sections of selected specimens were produced by focused ion beam and analysed by analytical transmission electron microscopy. Oxide-rich nanotubes were revealed embedded in a fluoride-rich matrix, suggesting that the mechanism of growth of the anodic films is governed by different migration rates of the anionic species in the film base, with F- ions, being the fastest anions. The relative amounts of the oxide-rich and fluoride-rich materials were related to the composition of the electrolyte, with the fluoride regions being less extensive and the oxide-rich nanotubes being thicker-walled by adding small amounts of water. Moreover, nanotubes are constituted of two shells (an outer one surrounding the pores and an inner one located between the outer shell and the matrix), suggesting differences in the composition in these two regions, presumed to be due to the incorporation of carbon species, being the slowest migrating species, in the outer shell. The fluoride-rich matrix chemically dissolved following 1 h immersion of the specimens in the formation electrolytes, promoting the transition from porous to nanotubular morphologies. Ageing of the specimens in deionized water for similar times did not significantly influence the morphologies and compositions of the anodic films.

A ingestão de dietas com níveis elevados de flúor interfere na mineralização óssea e, conseqüentemente, poderá influenciar nas propriedades mecânicas dos ossos. Este trabalho teve como objetivo estudar e avaliar algumas propriedades mecânicas de fêmures de coelhos submetidos a dietas com diferentes concentrações de flúor, mediante ensaios mecânicos de flexão em três pontos. Foram utilizados os fêmures de 40 coelhos machos, albinos, da raça Nova Zelândia com 1 mês de idade. Durante 40 dias os animais, divididos em 5 grupos, receberam dietas contendo diferentes concentrações de flúor. As propriedades mecânicas da deformação proporcional e resiliência, apresentaram diferença estatisticamente significante. Houve redução nos valores para rigidez, tensão máxima, carga máxima, mas sem diferença estatisticamente significante, para os grupos com maior concentração de flúor. Diante destas considerações e dos achados neste trabalho, fica evidente a necessidade de mais investigações para caracterizar a relação entre o flúor e as propriedades mecânicas. / High levels of fluoride ingestion may interfere with bone mineralization and, therefore, cause modification in the bone mechanical properties. In this investigation we studied the relationship between some mechanical properties of the rabbit femur and different concentration of fluoride in the diets. It was performed the three bending test in forty femurs obtained from New Zealand white rabbits that had been fed with diet with different fluoride concentration during 40 days since they were one month old. The animals were divided into 5 different groups according to the fluoride concentration in diets. The resilience and proportional deformation were higher for the group with the highest fluoride ingestion and there was no difference among the other groups. Rigidity, ultimate load and tension were lower as fluoride concentration increased but with no statistical difference. It was concluded that more investigation is necessary to establish the relationship of the mechanical properties with fluoride intake.

Não consta resumo na publicação. / Abstract not available.

京都大学 / 0048 / 新制・課程博士 / 博士(エネルギー科学) / 甲第22551号 / エネ博第402号 / 新制||エネ||77(附属図書館) / 京都大学大学院エネルギー科学研究科エネルギー基礎科学専攻 / (主査)教授 野平 俊之, 教授 萩原 理加, 教授 佐川 尚 / 学位規則第4条第1項該当 / Doctor of Energy Science / Kyoto University / DGAM

京都大学 / 0048 / 新制・課程博士 / 博士(エネルギー科学) / 甲第22796号 / エネ博第410号 / 新制||エネ||78(附属図書館) / 京都大学大学院エネルギー科学研究科エネルギー基礎科学専攻 / (主査)教授 坂口 浩司, 教授 佐川 尚, 准教授 高井 茂臣 / 学位規則第4条第1項該当 / Doctor of Energy Science / Kyoto University / DFAM

In a push towards more environmentally friendly pyrotechnics, new greener pyrotechnic compositions need to be developed. A primary goal is to replace components such as lead, barium, and chromium in pyrotechnic compositions. Fused Deposition Modelling (FDM) is a 3D printing/additive manufacturing method whereby a thin filament is passed through a heated nozzle, and extruded onto a substrate in successive layers. This method of manufacturing could be used to produce pyrotechnic time delays based on suitable “green” polymer/fuel mixtures. Fluoropolymers are an attractive oxidising system for pyrotechnic use as fluorine is highly reactive and reacts relatively easily with common metallic fuels such as aluminium and magnesium to release a large amount of energy. Fluoropolymers are already in use as oxidisers and binders, especially in infrared decoy flares. PTFE has found wide use in the pyrotechnics industry, but is not melt-processible. A similar fluoropolymer, poly(chloro-trifluoroethylene) (PCTFE) was considered instead. PCTFE differs from PTFE in that one of the fluorine atoms in the TFE monomer has been replaced by a chlorine atom. The larger chlorine atom interferes with the packing of the polymer chains during polymerisation and, as such, may make it easier to process than PTFE. It was found that pure PCTFE degraded heavily during processing and was therefore precluded from any further study. Melt-processible copolymers containing PCTFE are available from industry. These copolymers contain vinylidene fluoride (VDF) in addition to the CTFE i.e. poly(CTFE-co-VDF). Two grades of copolymer were obtained from 3M: FK-800® resin and Dyneon® 31508 resin. These two polymers contain different ratios of CTFE to VDF. FK-800® resin was successfully extruded and showed minimal signs of degradation. Pyrotechnic films, containing aluminium powder as the fuel, were cast with both polymers using solvent techniques. Differential thermal analysis (DTA) was used to determine the ignition points of the compositions. All of the FK-800®-based compositions ignited at approximately 450 °C whilst all the Dyneon® 31508-based compositions ignited at approximately 400 °C. The energy output of the compositions was determined using bomb calorimetry. The experimental energy outputs of the FK-800®-based compositions correlated well with the predictions from the thermodynamic simulations. The maximum energy output, ~7.0 MJ∙kg1, occurred at a fuel loading between 30 – 35 wt.%. Except for one composition, the Dyneon® 31508-based compositions did not ignite in the bomb calorimeter. FK-800® was successfully extruded into a filament and showed minimal signs of degradation. In order to assess the impact of adding a solid filler on the mechanical properties and extrudability of the polymer, magnesium hydroxide was used as inactive model compound in place of aluminium. A filament of FK-800® and Mg(OH)2 was successfully compounded and produced using a filler loading of 30 wt.%. Compounding of the Dyneon 31508® with the magnesium hydroxide was unsuccessful. Addition of LFC-1® liquid fluoroelastomer improved the processibility of the Dyneon 31508® by lowering the melt viscosity. / Dissertation (MEng)--University of Pretoria, 2017. / Chemical Engineering / MEng / Unrestricted

Pelchem NF3 plant produces an ammonium acid fluoride waste stream. The material of construction for the piping and stirrer fabrication in the plant is Monel. As a predominantly nickel-copper alloy, with minute quantities of carbon, manganese, silicon, sulfur and iron, these may leach into process fluids involved. The two biggest constituents of Monel contaminate the ammonium acid fluoride waste stream. Despite being the lesser of the two in terms of the composition of the Monel, copper is higher in concentration than nickel in the waste stream: the solubility of copper (II) cation in ammonium fluoride is higher than that of nickel (II) cation. Additionally, the ammonium acid fluoride is stored in steel barrels because of the relatively high process temperature that preclude the use of polymeric drums. This results in the leaching of iron from the steel drum to the solution. Pelchem expressed an interest in a suitable method of purification of ammonium fluoride, with specific interest of removing nickel (II) cation, copper (II) cation as well as iron (II) cation. The constraints to consider when selecting the appropriate methods are operating costs as well as the capital costs, but the most important factor to consider is the effectiveness of the method in removing the contaminant. In this regard, cationic exchange resins are very suitable, and they are very practical for industrial applications. In its simplest form, ammonium fluoride solutions are prepared by bubbling ammonia gas through solutions of hydrofluoric acid. Quite a few interesting uses of ammonium fluoride are available, these include as a chemical modifier in lead analysis, synthesis of beta zeolites, etc. The most prominent use is as a technical grade etchant in the electronics industry. The main aim of this research was to investigate ion exchange as a method of removing contaminants from Pelchem ammonium acid fluoride. Static equilibrium/selectivity experiments reveal that Purolite S930 Plus and Lewatit TP207 show a great affinity for the copper cation. For the limiting step of the reaction, the analysis includes apparent kinetics modelling contrasted with mass transfer modelling. In the case of reaction kinetics, Arrhenius and Van’t hoff equations were used to determine reaction parameters: the activation energies are 14 368 J∙mol-1 and 24 116 J∙mol-1, for Purolite and Lewatit respectively. The pre-exponential constants are 2 213 and 269 682 L2∙min-1∙mol-2 for Purolite and Lewatit in that order. The heats of reaction are -26 555 and -4 696 J∙mol-1 for Purolite and Lewatit respectively. Whilst the equilibrium pre-exponential constants are 75 057and 150 for Purolite and Lewatit respectively. Diffusivities for the two resins were found to be in reasonable agreement with those recorded in literature. They follow a temperature dependency trajectory. Weisz-Prater analysis of the observed reaction rate and the diffusion rate, in the two resins, reveals that intraparticle diffusion is the limiting step in the reaction. / Dissertation (MEng)--University of Pretoria, 2017. / Chemical Engineering / MEng / Unrestricted

<p>The clogging of filtration membrane by particles otherwise known as fouling is a major concern in membrane filtration technology due reduction of flux, membrane lifespan and system performance, with an associated increase in process and operating costs in industries that utilize membrane in their production process. Cleaning or replacement of a fouled membrane requires production to be interrupted or the entire system to be shut down. This is because the cleaning or replacement of the fouled membrane requires production to be interrupted for the cleaning process or the entire system to be shut down for the replacement process to take place, leading to great losses to the industries involved. Many approaches have been devised over the years to tackle this problem, of which not only undermine the performance of the filtration membrane but also contribute to great losses to industries that apply them. Cheaper and more efficient means of fouling control remains the key to solving this problem. </p> <p> </p> <p>A water filtration system is proposed that uses piezoelectric crystals attached on a tubular polyvinylidene fluoride (PVDF) membrane to increase flux and delay the clogging of the pores of the filtration membrane (by particles). Filtration tests with mud solution showed that the membrane vibrated with piezoelectrics reduced the clogging of the pores and increased permeate flux of the filtration process as compared to the non-vibrated membrane. To optimize the permeate flux production of the system and fouling reduction, the effects of voltage, concentration and location of piezoelectric crystals<a> were investigated. An equation to best fit the experimental data was developed which can help in the optimization of the variables.</a></p> <p> </p> <p> </p> <p> </p> <p> </p> <p> </p>

With the increase of population every year, fresh water scarcity has rapidly increased and it is reaching a risky level, particularly in Africa and the Middle East. Desalination of seawater is an essential process for fresh water generation. One of the methods for desalination is membrane distillation (MD). MD process separates an aqueous liquid feed across a porous hydrophobic membrane to produce pure water via evaporation. Polyvinlidene fluoride (PVDF) membranes reinforced with a polyester fabric were fabricated as potential candidates for MD. Non-solvent induced phase separation coupled with steam treatment was used to prepare the PVDF membranes. A portion of the prepared membrane was coated with Teflon (AF2400) to increase its hydrophobicity. In the first study, the fabricated membranes were characterized using scanning electron microscopy and other techniques, and they were evaluated using direct contact MD (DCMD). The fabricated membranes showed a porous sponge-like structure with some macrovoids. The macrovoid formation and the spongy structure in the membrane cross-sections contributed significantly to a high permeate flux as they provide a large space for vapor water transport. The modified PVDF membranes with steaming and coating exhibited a permeate flux of around 40 L/h m2 (i.e. 27-30% increase to the control PVDF membrane) at temperatures of 60 °C (feed) and 20 °C (permeate). This increase in the permeate flux for the modified membranes was mainly attributed to its larger pore size on the bottom surface. In the second study, the control PVDF membrane was tested in two different module designs (i.e. semi-circular pipe and rectangular duct module designs). The semi-circular module design (turbulent regime) exhibited a higher permeate flux, 3-fold higher than that of the rectangular duct module design (laminar regime) at feed temperature of 60 °C. Furthermore, a heat energy balance was performed for each module design to determine the temperature polarization coefficients (TPC). The turbulent module design showed higher TPC (0.5-0.58) than the laminar module (0.1-0.14) (i.e. a poor module design). This indicates that the effect of temperature polarization on the laminar flow was significant, which is below the reported TPC range of 0.4-0.70.

No description available.