L'objectif de ce travail est de comprendre le processus d'altération des calcaires oolithiques et d'estimer leur cinétique d'altération en fonction des conditions climatiques présentes en France. Pour y répondre, des cycles de vieillissement accéléré, basés sur les paramètres issus de l'étude bibliographique et sur les données de température et de précipitations réelles, ont été définis. Ensuite, des lots d'échantillons de deux calcaires oolithiques ont subis ces vieillissements. Les mesures réalisées pour déterminer l'endommagement ont été choisies en fonction de leurs caractéristiques métrologiques et de leur pertinence. Les résultats obtenus ont été comparés avec les mêmes mesures réalisées sur des calcaires altérés de façon naturelle prélevés sur site. Ainsi, les liens entre le processus d'altération des calcaires et les caractéristiques mécaniques, physiques et surtout microstructurales des calcaires ont été établis. Cette analyse a également abouti à des cinétiques d'altération. Les résultats ont été validés par l'étude d'un autre calcaire oolithique sous d'autres conditions climatiques. Enfin, l'influence de changements climatiques éventuels sur les cinétiques d'altération a été déterminée à l'aide d'un outil statistique

Malaria is a parasitic disease claiming one million lives worldwide annually. Unfortunately, malaria-endemic countries in need of good quality medicines are also overwhelmed with counterfeit or substandard medicine. This results in treatment inefficacy, resistance towards treatment and death. Counterfeit or substandard quinine sulfate tablets are known to have infiltrated the market, however at this point in time, treatment efficacy of quinine sulfate has fortunately not yet been significantly impaired by resistance, but immediate action is required to prevent it from becoming obsolete. Validated analytical methods with justified specifications are effective in controlling the quality of medicines and to minimise the effect of poor quality medicines. Pharmacopoeia specifies analytical quality control procedures and accompanying specifications to standardise acceptable levels of product quality. Understandably, different monographs of different pharmacopoeias are developed by different independent laboratories and therefore their respective test procedures/specifications for the same FPP may differ from each other. Institutions such as the Pharmacopoeial Dicussion Group (PDG) aim to harmonise pharmacopoeia in order to synchronise final outcomes. This study evaluated the relevancy of differences in analytical procedures, results and specifications for quinine sulfate tablets set by the United States Pharmacopoeia (USP), British Pharmacopoeia (BP) and International Pharmacopoeia (Ph.Int.) in an aim to ensure that these different methods all provide with similar final outcomes and that they be effective in successfully evaluating the quality of quinine sulfate tablets. Four quinine sulfate tablet products were obtained from different manufacturers and were subjected to the tests of all three pharmacopoeia – BP, USP and Ph.Int. The results from identification, assay and related substance testing concluded that the outcomes were the same between the pharmacopoeia despite their differences in techniques/procedures/specifications. The assay, identification and related substances methods and specifications set by each respective monograph were deemed appropriate to evaluate the quality of quinine sulfate tablets. Even with differences in methodology, quantitative techniques and specifications, the USP and BP dissolution methods for quinine sulfate tablets shared the same final outcome at the first stage of dissolution, whereas none of the products achieved a compliant outcome using the Ph.Int. dissolution method. Possible reasons for the poor dissolution (when using the Ph.Int. method) were identified and investigated. Investigation into the solubility of quinine sulfate found the Ph.Int. dissolution method conditions to be too stringent, as the solubility of quinine sulfate in phosphate buffer pH 6.8 (dissolution medium specified by the Ph.Int.) was found to be much less than in acidic media (as proposed by the BP and USP dissolution methods). Several adapted dissolution methods (called developmental studies) were investigated to serve as potential alternatives for the Ph.Int. dissolution method. The developmental studies investigated an alternative dissolution medium, agitation rates (50 rpm, 75 rpm, 100 rpm) and medium volumes (500 ml, 750 ml, 900 ml and 1000 ml). Developmental study 6 was proposed as an alternative dissolution method. Developmental study 6 stipulates the use of the same medium as the original Ph.Int. method, as it was deemed the medium of choice for its discriminatory ability. To address the impaired solubility of quinine sulfate in phosphate buffer, the medium volume and agitation were increased (in reference to the original method) to 900 ml and 100 rpm respectively. The same analytical quantitation technique (UV-Vis spectroscopy) is proposed for Developmental study 6. The newly proposed method provided with final outcomes comparable to that of the USP and BP, however having more discriminatory power than the USP and BP. / MSc (Pharmaceutics), North-West University, Potchefstroom Campus, 2014

Malaria is a parasitic disease claiming one million lives worldwide annually. Unfortunately, malaria-endemic countries in need of good quality medicines are also overwhelmed with counterfeit or substandard medicine. This results in treatment inefficacy, resistance towards treatment and death. Counterfeit or substandard quinine sulfate tablets are known to have infiltrated the market, however at this point in time, treatment efficacy of quinine sulfate has fortunately not yet been significantly impaired by resistance, but immediate action is required to prevent it from becoming obsolete. Validated analytical methods with justified specifications are effective in controlling the quality of medicines and to minimise the effect of poor quality medicines. Pharmacopoeia specifies analytical quality control procedures and accompanying specifications to standardise acceptable levels of product quality. Understandably, different monographs of different pharmacopoeias are developed by different independent laboratories and therefore their respective test procedures/specifications for the same FPP may differ from each other. Institutions such as the Pharmacopoeial Dicussion Group (PDG) aim to harmonise pharmacopoeia in order to synchronise final outcomes. This study evaluated the relevancy of differences in analytical procedures, results and specifications for quinine sulfate tablets set by the United States Pharmacopoeia (USP), British Pharmacopoeia (BP) and International Pharmacopoeia (Ph.Int.) in an aim to ensure that these different methods all provide with similar final outcomes and that they be effective in successfully evaluating the quality of quinine sulfate tablets. Four quinine sulfate tablet products were obtained from different manufacturers and were subjected to the tests of all three pharmacopoeia – BP, USP and Ph.Int. The results from identification, assay and related substance testing concluded that the outcomes were the same between the pharmacopoeia despite their differences in techniques/procedures/specifications. The assay, identification and related substances methods and specifications set by each respective monograph were deemed appropriate to evaluate the quality of quinine sulfate tablets. Even with differences in methodology, quantitative techniques and specifications, the USP and BP dissolution methods for quinine sulfate tablets shared the same final outcome at the first stage of dissolution, whereas none of the products achieved a compliant outcome using the Ph.Int. dissolution method. Possible reasons for the poor dissolution (when using the Ph.Int. method) were identified and investigated. Investigation into the solubility of quinine sulfate found the Ph.Int. dissolution method conditions to be too stringent, as the solubility of quinine sulfate in phosphate buffer pH 6.8 (dissolution medium specified by the Ph.Int.) was found to be much less than in acidic media (as proposed by the BP and USP dissolution methods). Several adapted dissolution methods (called developmental studies) were investigated to serve as potential alternatives for the Ph.Int. dissolution method. The developmental studies investigated an alternative dissolution medium, agitation rates (50 rpm, 75 rpm, 100 rpm) and medium volumes (500 ml, 750 ml, 900 ml and 1000 ml). Developmental study 6 was proposed as an alternative dissolution method. Developmental study 6 stipulates the use of the same medium as the original Ph.Int. method, as it was deemed the medium of choice for its discriminatory ability. To address the impaired solubility of quinine sulfate in phosphate buffer, the medium volume and agitation were increased (in reference to the original method) to 900 ml and 100 rpm respectively. The same analytical quantitation technique (UV-Vis spectroscopy) is proposed for Developmental study 6. The newly proposed method provided with final outcomes comparable to that of the USP and BP, however having more discriminatory power than the USP and BP. / MSc (Pharmaceutics), North-West University, Potchefstroom Campus, 2014

Proton exchange membrane fuel cells (PEMFC) are attractive energy sources for power trains in vehicles because of their low operating temperature that enables fast start-up and high power densities. Cost reduction and durability are the key issues to be solved before PEMFCs can be successfully commercialized. The major portion of fuel cell cost is associated with the catalyst layer which is typically comprised of carbon-supported Pt and ionomer. The degradation of the catalyst layer is one of the major failure modes that can cause voltage degradation and limit the service life of the fuel cell stack during operation. To develop a highly durable and better performing catalyst layer, topics such as the causes for the degradation, modes of failure, different mechanisms and effect of degradation on fuel cell performance must be studied thoroughly. Key degradation modes of catalyst layer are carbon corrosion and Pt dissolution. These two modes change the electrode structure in the membrane electrode assembly (MEA) and result in catalyst layer thinning, CO2 evolution, Pt deposition in the membrane and Pt agglomeration. Alteration of the electrode morphology can lead to voltage degradation. Accelerated stress tests (ASTs) which simulate the conditions and environments to which fuel cells are subject, but which can be completed in a timely manner, are commonly used to investigate the degradation of the various components. One of the current challenges in employing these ASTs is to relate the performance loss under a given set of conditions to the various life-limiting factors and material changes. In this study, various degradation modes of the cathode catalyst layer are isolated to study their relative impact on performance loss ‗Fingerprints‘ of identifiable performance losses due to carbon corrosion are developed for MEAs with 0.4 mg cm−2 cathode platinum loadings. The fingerprint is used to determine the extent of performance loss due to carbon corrosion and Pt dissolution in cases where both mechanisms operate. This method of deconvoluting the contributions to performance loss is validated by comparison to the measured performance losses when the catalyst layer is subjected to an AST in which Pt dissolution is predominant. The limitations of this method iv are discussed in detail. The developed fingerprint suggests that carbon loss leading to CO2 evolution during carbon corrosion ASTs contributes to performance loss of the cell. A mechanistic model for carbon corrosion of the cathode catalyst layer based on one appearing in the literature is developed and validated by comparison of the predicted carbon losses to those measured during various carbon corrosion ASTs. Practical use of the model is verified by comparing the predicted and experimentally observed performance losses. Analysis of the model reveals that the reversible adsorption of water and subsequent oxidation of the carbon site onto which water is adsorbed is the main cause of the current decay during ASTs. Operation of PEM fuel cells at higher cell temperatures and lower relative humidities accelerates Pt dissolution in the catalyst layer during ASTs. In this study, the effects of temperature and relative humidity on MEA degradation are investigated by applying a newly developed AST protocol in which Pt dissolution is predominant and involves the application of a potentiostatic square-wave pulse with a repeating pattern of 3s at 0.6 V followed by 3s at 1.0 V. This protocol is applied at three different temperatures (40°C, 60°C and 80°C) to the same MEA. A diagnostic signature is developed to estimate kinetic losses by making use of the effective platinum surface area (EPSA) obtained from cyclic voltammograms. The analysis indicates that performance degradation occurs mainly due to the loss of Pt in electrical contact with the support and becomes particularly large at 80°C. This Pt dissolution AST protocol is also investigated at three different relative humidities (100%, 50% and 0%). Electrochemical impedance spectroscopy measurements of the MEAs show an increase in both the polarization and ohmic resistances during the course of the AST. Analysis by cyclic voltammetry shows a slight increase in EPSA when the humidity increases from 50% to 100%. The proton resistivity of the ionomer measured by carrying out impedance measurements on MEAs with H2 being fed on the anode side and N2 on the cathode side is found to increase by the time it reaches its end-of-life state when operated under 0 % RH conditions.

This thesis focuses on my endeavors to prepare new porous polymeric monoliths that are viable to use as supports in flow-through processes. Polymer monoliths of various porous properties and different chemical properties have been prepared utilizing the thermally induced phase separation (TIPS) phenomenon and step-growth polymerization reactions. The aim has been to find appropriate synthesis routes to produce separation supports with fully controlled chemical, physical and surface properties. This thesis includes preparation of porous monolithic materials from several non-cross-linked commodity polymers and engineering plastics by dissolution/precipitation process (i.e. TIPS). Elevated temperatures, above the upper critical solution temperature (UCST), were used to dissolve the polymers in appropriate solvents that only dissolve the polymers above this critical temperature. After dissolution, the homogeneous and clear polymer-solvent solution is thermally quenched by cooling. A porous material, of three dimensional structure, is then obtained as the temperature crosses the UCST. More than 20 organic solvents were tested to find the most compatible one that can dissolve the polymer above the UCST and precipitate it back when the temperature is lowered. The effect of using a mixture of two solvents or additives (co-porogenic polymer or surfactant) in the polymer dissolution/precipitation process have been studied more in depth for poly(vinylidine difluoride) (PVDF) polymers of two different molecular weight grades. Monolithic materials showing different pore characteristics could be obtained by varying the composition of the PVDF-solvent mixture during the dissolute­ion/precipitation process. Step-growth polymerization (often called polycondensat­ion reaction) combined with sol-gel process with the aid of porogenic polymer and block copolymer surfactant have also been used as a new route of synthesis for production of porous melamine-formaldehyde (MF) monoliths. In general, the meso- and macro-porous support materials, for which the synthesis/preparation is discussed in this thesis, are useful to a wide variety of applications in separation science and heterogeneous reactions (catalysis).

Elemental semiconductors like silicon and germanium have been used since the beginning of the electronics industry. Silicon has dominated research and production and thus silicon based devices can be produced at the lowest cost using the most mature technology. While dopants can be used to tailor the electric properties of the semiconductor within certain limits, more flexibility is gained using compound semiconductors such as silicon-germanium. The electric properties of a compound semiconductor are highly dependant on the composition, which in turn is influenced by the dissolution reaction and flow characteristics during the growth process. Liquid phase diffusion (LPD) is a solution growth technique that has been proposed to grow silicon-germanium seed crystals for other growth techniques. The dissolution of silicon is a limiting factor for the growth rate in LPD and also Bridgman growth techniques. Investigation of the dissolution process is aimed at increasing the growth rate while still maintaining maximum uniformity of the crystal composition. To accomplish this, a static magnetic field was utilized in experiments done by Armour. The experimental results showed that a top seeded configuration without magnetic fields leads to a diffusion driven process and homogeneous dissolution, while the addition of a strong 0.8 Tesla magnetic field resulted in non-uniform and slightly increased dissolution. This work is complementary to the experimental investigation and aims to help understand the influence of magnetic fields on silicon dissolution. For this work, an OpenFOAM magnetohydrodynamics application including heat and species transport and three different magnetic force models has been developed and validated. The simulations done show that an isothermal state is reached within 90 seconds if no temperature gradient is imposed. Additional simulations with a temperature gradient helped to rule out a possible thermal leak in the experimental system, confirming that it must have been close to isothermal. Since the solutal expansion coefficient of has not been measured properly to the Author's knowledge, two possible values for the expansion coefficient have been considered. It has been found that the exact value of the solutal expansion coefficient does not have a great influence on the results of this work.

The Marathon PGM-Cu deposit is hosted by the Coldwell alkaline complex, which consists predominantly of gabbro and syenite and was emplaced at 1108 Ma as part of the Mid-Continent Rift System. Mineralization at the Marathon PGM-Cu deposit is hosted by the Two Duck Lake Gabbro (TDLG), a fresh olivine-bearing gabbro. The Marathon deposit contains several zones of mineralization including the Basal Zone, the Main Zone and the W-Horizon. The W-Horizon is a high-grade PGE zone characterized by low S, low Cu/Pd and high Cu/Ni. The sulphide mineral assemblage is predominantly chalcopyrite and bornite. This contrasts with the Main Zone where the dominant sulphide mineral assemblage is chalcopyrite and pyrrhotite. The Main Zone contains higher S, higher Cu/Pd and shows a decrease in Cu/Pd and pyrrhotite/chalcopyrite from base to top. Four drill holes were selected for detailed analysis to characterize the W-Horizon style of mineralization. Detailed petrographic study of the pristine and largely unaltered TDLG shows that wide spread hydrothermal alteration is not responsible for the mineralization. Detailed outcrop mapping shows that the TDLG intruded as a series of multiple intrusions in a dynamic magmatic system. Geochemical studies through the W-Horizon show that the mineralization is not the result of crystallization in a layered intrusion. The results of geochemical assays and electron microprobe analysis of olivine grains show that the chemistry through the TDLG hosting the W-Horizon is erratic. This data supports the TDLG intruding as a series of sills in a dynamic conduit environment. The calculated sulphide metal tenors for the W-Horizon are higher than can be explained by closed system R Factor models. Multistage dissolution upgrading in an open system is examined as the process forming the W-Horizon. This model is able to produce the sulphide metal tenors observed in the W-Horizon. Sulphur loss also affects grades and tenors and was examined through geochemical and petrological data. The change in sulphide mineral assemblage from a pyrrhotite and chalcopyrite (S-rich) to chalcopyrite and bornite (S-poor) supports S-loss. Whole rock S and Se contents are also analyzed to investigate S loss, a lower S/Se indicates that sulphur has been removed from the system. Average S/Se values are ~800 for the W-Horizon, ~1980 for the Main Zone and ~1700 in unmineralized samples. The very low S/Se observed within the W-Horizon supports S-loss. Sulphur loss in a dynamic magmatic conduit system is proposed for the formation of the W-Horizon mineralization. In this model sulphur undersaturated basaltic magma interacted with an immiscible sulphide liquid in a magma conduit, resulting in the dissolution of sulphide into the basaltic melt and PGE enrichment.

One of the most important boron minerals, colemanite is reacted with sulfuric acid to produce boric acid. During this reaction, gypsum (calcium sulfate dihydrate) is formed as a byproduct. In this study, the boric acid production was handled both in a batch and four continuously stirred slurry reactors (4-CFSSR&rsquo / s) in series system. In this reaction system there are at least three phases, one liquid and two solid phases (colemanite and gypsum). In a batch reactor all the phases have the same operating time (residence time), whereas in a continuous reactor all the phases may have different residence time distributions. The residence time of both the reactant and the product solids are very important because they affect the dissolution conversion of colemanite and the growth of gypsum crystals. The main aim of this study was to investigate the dynamic behavior of continuous flow stirred slurry reactors. By obtaining the residence time distribution of the solid and liquid components, the non-idealities in the reactors can be found. The experiments performed in the continuous flow stirred slurry reactors showed that the reactors to be used during the boric acid production experiments approached an ideal CSTR in the range of the stirring rate (500-750 rpm) studied. The steady state performance of the continuous flow stirred slurry reactors (CFSSR&rsquo / s) in series was also studied. During the studies, two colemanites having the same origin but different compositions and particle sizes were used. The boric acid production reaction consists of two simultaneous reactions, dissolution of colemanite and crystallization of gypsum. The dissolution of colemanite and the gypsum formation was followed from the boric acid and calcium ion concentrations, respectively. The effect of initial CaO/ SO42- molar ratio (1.00, 1.37 and 2.17) on the boric acid and calcium ion concentrations were searched. Also, at these initial molar ratios the colemanite feed rate was varied (5, 7.5, 10 and 15 g/min) to change the residence time of the slurry. Purity of the boric acid solution was examined in terms of the selected impurities, which were the magnesium and sulfate ion concentrations. The concentrations of them were compared at the initial molar ratios of 1.00 and 1.37 with varying colemanite feed rates. It was seen that at high initial CaO/ SO42- molar ratios the sulfate and magnesium ion concentrations decreased but the calcium ion concentration increased. The gypsum crystals formed in the reaction are in the shape of thin needles. These crystals, mixed with the insolubles coming from the mineral, are removed from the boric acid slurry by filtration. Filtration of gypsum crystals has an important role in boric acid production reaction because it affects the efficiency, purity and crystallization of boric acid. These crystals must grow to an appropriate size in the reactor. The growth process of gypsum crystals should be synchronized with the dissolution reaction. The effect of solid hold-up (0.04&ndash / 0.09), defined as the volume of solid to the total volume, on the residence time of gypsum crystals was investigated and the change of the residence time (17-60 min) on the growth of the gypsum was searched. The residence time at each reactor was kept constant in each experiment as the volumes of the reactors were equal. The growth of gypsum was examined by a laser diffraction particle size analyzer and the volume weighted mean diameters of the gypsum crystals were obtained. The views of the crystals were taken under a light microscope. It was observed that the high residence time had a positive effect on the growth of gypsum crystals. The crystals had volume weighted mean diameters of even 240 &micro / m. The gypsum crystal growth model was obtained by using the second order crystallization reaction rate equation. The residence time of the continuous reactors are used together with the gypsum growth model to simulate the continuous boric acid reactors with macrofluid and microfluid models. The selected residence times (20-240 min) were modeled for different number of CSTR&rsquo / s (1-8) and the PFR. The simulated models were, then verified with the experimental data. The experimentally found calcium ion concentrations checked with the concentrations found from the microfluid model. It was also calculated that the experimental data fitted the microfluid model with a deviation of 4-7%.

The main purpose of the present study was to investigate whether gender, certain relationship characteristics (time elapsed since the dissolution, being the dissolver or the sufferer part, duration of the relationship, sexuality, the broken relationship being the first relationship ever, any present partner, importance of the relationship, importance of the dissolution), problem solving skills, and self- esteem were predictors of psychological distress following a romantic relationship dissolution. It was also aimed to examine the relationships between some relationship characteristics (duration of the relationship, and time elapsed since the dissolution), and psychological distress. The sample consisted of 213 Middle East Technical University students who were out of a romantic relationship within the last year. The data were gathered by administering Problem Solving Inventory, Brief Symptom Inventory, Rosenberg&rsquo / s Self- Esteem Scale, and Demographic Information Form. Multiple hierarchical regression analyses, and analyses of variance were conducted to test the aims of the study. According to the results of the study, the importance of the dissolution, the status of any present partner, time elapsed since the dissolution, impulsive style of problem solving skills, and self- esteem were found as significant predictors of psychological distress following a romantic relationship dissolution. On the other hand, it was found that gender, duration of the relationship, sexuality, being the dissolver or the sufferer, importance of the relationship, the broken relationship being the first relationship ever, and and the remaining five subscales (reflective style, avoidant style, monitoring, problem- solving confidence, planfulness) of problem solving skills did not emerge as significant predictors of psychological distress. In addition, time elapsed since the dissolution yielded significant effect on depression. The findings of the study were discussed in the light of the relevant literature.

Durability of carbon-supported platinum nanoparticle is one of the limiting factors for PEM fuel cell commercial applications. In our research work, we applied both experimental and mathematical simulative tools to study the mechanisms of Pt/C catalyst degradation. An accelerated catalyst degradation protocol by cycling the cathode potential in a square-wave profile was applied to study the losses of cell performances, catalyst ORR activity, and Pt active surface areas. Post-mortem analyses of cathode Pt particle size by X-ray diffraction and platinum distributions in CCMs by SEM/EDS were also conducted. Increased cell temperature and relative humidity was found to accelerate the cathode catalyst degradation. High membrane water contents or abundant water/ionic channels within the polymer electrolyte were believed to accelerate Pt ion transport and cathode degradation. After degradation tests, significant amount of Pt loss into the membrane forming a Pt "band" was observed through cathode platinum dissolution and chemical reduction of soluble Pt ions by permeated hydrogen from the anode. Platinum deposition was confirmed at a location where the permeated hydrogen and oxygen had the complete catalytic combustion over the deposited Pt clusters/particles as the catalyst. A cathode degradation model was built including the processes of platinum oxidation, dissolution/replating, diffusion of Pt ions and Pt band formation in electrolyte. A simplified bi-modal particle size distribution was applied with equal numbers of small and large type particles uniformly distributed in the cathode initially. Processes of Pt mass exchange between two types of particles were demonstrated to cause the overall particle growth. This was due to the particle size effect that platinum dissolution from the small type particles and replating of Pt ions onto the large particles was favored. Parametric study found the increased upper cycling potential was the dominated factor to accelerate the catalyst degradation. Also high frequency of potential cycle and low surface oxide coverage accelerated the degradation rate. Pt dissolution and oxidation processes in perchloric acid were preliminary investigated, and both chemical and electrochemical processes of oxidation and dissolution were believed to be involved under closed-circuit fuel cell conditions with oxygen presence at cathode.