M.Tech. / In this study, ethylene vinyl acetate-fly ash (EVA-FA) composites were explored for the removal of phenols from water. The composites were prepared from EVA and untreated and acid treated fly ash via the melt-mixing technique using a rheomixer. The fly ash was characterised by X-ray fluorescence (XRF), X-ray diffraction (XRD) scanning electron microscopy (SEM) and Brunauer, Emmett and Teller (BET) surface area measurement. Fly ash is composed mainly of SiO2, Al2O3, CaO and Fe2O3. Modified fly ash gave a better specific surface area of 0.4180 m2/g, while 0.0710 m2/g was obtained for unmodified fly-ash due to the disintegration of the outer layer which resulted in smaller particles, hence a larger surface area. EVA-FA composites were prepared from fly ash loadings of 3 to 20% and further characterised by XRD, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and SEM. XRD showed successful incorporation of fly ash into the EVA matrix through the appearance of fly ash diffraction peaks on the EVA-FA composite diffraction pattern. The incorporation of fly ash into the EVA matrix resulted in an improvement in the thermal stability of EVA, but did not have an effect on the melting temperature of the composites. However, a decrease in crystallisation temperature was observed. SEM micrographs revealed uniform dispersion of fly ash particles in the polymer matrix. Adsorption studies were performed using p-chlorophenol (PCP), 2,4,6-trichlorophenol (TCP) and p-nitrophenol (PNP) as model pollutants. An increase in adsorption efficiency of EVA-FA composites was observed as fly ash loading was increased from 3 to 10%. Between 10 and 20% fly-ash loading the removal efficiencies remained constant. The effect of contact time, pH and initial concentration was investigated. Polymer composites prepared from unmodified fly ash resulted in a higher adsorption capacity of phenols. The maximum uptake of PCP was 0.18 mg/g and that for TCP was 0.19 mg/g over a pH range of pH 3 to 5 and after contact time of 8 h. However, the adsorption capacity of 0.30 mg/g for PNP was achieved at pH 5 after a period of 10 h. Equilibrium adsorption data were evaluated using Langmuir and Freundlich adsorption isotherm models. There was no significant difference in the correlation coefficients (R2) from both models for the adsorption of PCP and TCP. However, the equilibrium adsorption data for PNP were better described by the Langmuir adsorption isotherm model. The kinetics data were analysed by pseudo-first-order and pseudo-second-order kinetic models. The pseudo-second-order kinetics model gave better correlation coefficients (> 0.9) for the adsorption of the phenols and the amount adsorbed at equilibrium was comparable to that calculated from the pseudo-second-order equation. Desorption studies were performed using NaOH solution with varying concentrations (0.1 to 0.3 M) and the studies revealed that PNP was the most difficult to be desorbed. Approximately 75% of PNP was recovered while 82% of PCP and 84% of TCP were recovered.

Nitrogen-alloyed austenitic stainless steels are becoming increasingly popular, mainly due to their excellent combination of strength and toughness. Nitrogen desorption to the atmosphere during the autogenous welding of these steels is often a major problem, resulting in porosity and nitrogen losses from the weld. In order to counteract this problem, the addition of nitrogen to the shielding gas has been proposed. This study deals with the absorption and desorption of nitrogen during the autogenous arc welding of a number of experimental stainless steels. These steels are similar in composition to type 310 stainless steel, but with varying levels of nitrogen and sulphur. The project investigated the influence of the base metal nitrogen content, the nitrogen partial pressure in the shielding gas and the weld surface active element concentration on the nitrogen content of autogenous welds. The results confirm that Sievert's law is not obeyed during welding. The weld nitrogen content increases with an increase in the shielding gas nitrogen content at low nitrogen partial pressures, but at higher partial pressures a dynamic equilibrium is created where the amount of nitrogen absorbed by the weld metal is balanced by the amount of nitrogen evolved from the weld pool. In alloys with low sulphur contents, this steady-state nitrogen content is not influenced to any significant extent by the base metal nitrogen content, but in high sulphur alloys, an increase in the initial nitrogen concentration results in higher weld nitrogen contents over the entire range of nitrogen partial pressures evaluated. A kinetic model can be used to describe nitrogen absorption and desorption during welding. The nitrogen desorption rate constant decreases with an increase in the sulphur concentration. This is consistent with a site blockage model, where surface active elements occupy a fraction of the available surface sites. The absorption rate constant is, however, not a strong function of the surface active element concentration. Alloys with higher base metal nitrogen contents require increased levels of supersaturation prior to the onset of nitrogen evolution as bubbles. These increased levels of supersaturation for the higher-nitrogen alloys is probably related to the higher rate of nitrogen removal as N2 the onset of bubble formation. Given that nitrogen bubble formation and detachment require nucleation and growth, it is assumed that a higher nitrogen removal rate would require a higher degree of supersaturation. Nitrogen losses from nitrogen-alloyed stainless steels can be expected during welding in pure argon shielding gas. Small amounts of nitrogen can be added to the shielding gas to counteract this effect, but this should be done with care to avoid bubble formation. Supersaturation before bubble formation does, however, extend the range of shielding gas compositions which can be used. Due to the lower desorption rates associated with higher surface active element concentrations, these elements have a beneficial influence during the welding of high nitrogen stainless steels. Although higher sulphur contents may not be viable in practice, small amounts of oxygen added to the shielding gas during welding will have a similar effect. / Dissertation (PHD)--University of Pretoria, 2004. / Materials Science and Metallurgical Engineering / unrestricted

The purpose of the work presented in this thesis was to explore and understand the mechanisms governing toughness, ductility and ballistic performance in a class of nanostructured carbide-free bainite-austenite steels, sometimes known as ‘superbainite’. The mechanical properties of these alloys have been extensively reported, but their interpretation is not clear. The thesis begins with an introduction to both the relevant nanostructures and some of the difficulties involved in explaining observed properties, alongside a summary of the role of mixed- microstructures in alloy development. An overview of the debate regarding the mechanism of bainite formation is pre- sented in Chapter 2, in the form of a literature survey encompassing the period of explicit recognition of the bainite microstructure. Of note is the role played by the displacive theory of formation in the development of the alloy structures investigated in this thesis. A characterisation of a commonly available bainitic alloy forms the basis for Chapter 4. Observations confirm the nanoscale nature of the structure, although additional phases are found to be present, namely: cementite and martensite. This is explained as resulting from relatively low alloying additions and chem- ical segregation effects, which are modelled using thermodynamic and kinetic approaches. Chapters 5 and 6 contain a comprehensive study of the response of this alloy to the stress concentration present at the notch root of a Charpy impact sample. The work provides evidence of notch root embrittlement due to stress-induced martensite transformation. Results from synchrotron and laboratory X-ray experiments in particular reveal that machining, as well as applied stress, can initiate the austenite-martensite transformation, and methods to mitigate this effect are suggested. An innovative approach is harnessed in Chapter 7, in order to identify exper- imentally the volume fraction at which three-dimensional connectivity (‘percolation’) of austenite is lost in a superbainitic steel. Hydrogen thermal desorption techniques are applied to this problem, inspired by the tendency of such alloys to undergo tensile failure with limited or zero necking. The striking result sheds light on the importance of austenite morphology in restricting the diffusion of hydrogen into a mixed structure. The final set of experimental work is directed towards understanding the damage mechanisms that occur during projectile penetration of a coarser bainitic armour- plate alloy. The formation of adiabatic shear bands is found to be a dominant factor governing the ballistic failure of the plate. The sheared material undergoes severe high-temperature deformation, but does not change phase upon cooling, leading to the proposal of certain methods that could be implemented to improve ballistic resistance of the steel. The totality of the research presented herein is summarised in Chapter 9, which draws attention to new areas of interest that have arisen from the current work, proposing several future directions of investigation. The broader issue of understanding, common to all studies performed thus far, is that of the causes, effects, and extent, of stress-induced transformation to martensite experienced by the retained austenite that is a key feature of superbainite and similar steels.

Le procédé de galvanisation à chaud se compose d’un recuit continu suivi d’une immersion de la bande d’acier dans un bain de zinc afin de lui conférer une protection contre la corrosion. Au cours de l’étape de recuit de recristallisation des nouveaux aciers, dits à « haute limite élastique », les éléments d’addition, tel que l’aluminium, ségrégent et diffusent en surface où ils forment des îlots voire des films superficiels qui, mal mouillés par le zinc liquide, nuisent à la qualité du produit final. Dans ce cadre, l’étude s’est attachée d’une part à caractériser l’oxydation sélective d’alliages binaires Fe-Al et d’autre part, dans le cas modèle de l’α-alumine (0001), à déterminer les effets de la terminaison de surface sur l’énergie d’adhésion du zinc, à l’aide d’une approche combinant simulations numériques ab initio (théorie de la fonctionnelle de la densité) et expériences sous ultra-vide (réflectivité UV-visible, photoémission et désorption thermique). A l’issu de recuits calqués sur les conditions industrielles les alliages binaires Fe-Al (1,5 et 8% pds.) présentent en surface une couche couvrante d’γ-alumine de plusieurs nanomètres d’épaisseur. Une entrée du flux de gaz focalisée sur l’échantillon aboutit à une croissance vermiculaire des grains d’alumine alors qu’un flux de gaz homogène engendre une croissance plus structurée qui montre que l’approche modèle Zn/α-alumine (0001) est pertinente.Les simulations numériques faites aux premiers stades du dépôt, ont montré que, le zinc interagit faiblement avec la surface stœchiométrique (1x1), ce qui confirme l’expérience. Expérience et calcul convergent sur la valeur de ≈ 0,5 eV de l’énergie d’adsorption. Par contre, un excès de charge de surface peut considérablement renforcer l’adsorption. Deux mécanismes ont été identifiés et décrits en terme de stabilité thermodynamique, en fonction des conditions environnementales (pression, température) : (i) une sous-stœchiométrie surfacique en Al, telle que présente sur la terminaison polaire, (ii) un excès de groupements hydroxyles de surfaces, issus de la dissociation de l’eau, opérationnel aussi bien sur la terminaison polaire que non-polaire de l’alumine. En parallèle avec l’expérience, la simulation montre que le zinc est capable d’interagir fortement avec la surface en en déplaçant l’hydrogène des groupements hydroxyles de surface. L’énergie d’adsorption du zinc ainsi adsorbé, évaluée à 7 eV par le calcul, est du même ordre que la valeur expérimentale de 3,5 eV. L’étude étendue à plusieurs métaux de transition a permis d’identifier le titane comme élément montrant l’interaction la plus forte avec l’alumine et qu’un enrichissement en titane de la surface d’alumine peut fortement améliorer l’adhésion du zinc. / The process of continuous hot galvanization consists in annealing and then diving a steel strip in a zinc bath to confer it a protection against corrosion. During the recrystallization annealing step of the so call “high elastic limit’ steels, the additional elements, such as aluminum, segregate and diffuse towards the surface and form oxide islands or superficial film which degrade the zinc adhesion and harm the final quality. This study attempted, on one hand to characterize the selective oxidation of binary alloys and, on the other hand, to improve adhesion at the zinc/α-Al2O3 (0001) interface taken as a test bed. The originality of the research program is to be based on both numerical ab initio simulation (density functional theory) and experiments (UV-vis reflectivity, photoemission, thermal desorption) to determine the parameters of greater relevance.After annealing based on industrial conditions, binary alloys (1.5%- 8% wt.) are totally covered by γ-alumina layer some nanometers in thickness. Gas flow focused on the sample leads to a ‘worm’ like growth of the alumina grains while an homogeneous flow gives rise to a well- structured growth which shows the relevance of the study of Zn/α-alumina (0001).The numerical simulations of the early stage of deposition show that, zinc interacts weakly on a stoichiometric surface (1x1) what is in agreement with experiments. Experiment and theory converge on 0.5 eV for adhesion energy. On the other hand, an excess of surface charge can considerably reinforce the adsorption. Two mechanisms were identified and described in terms of thermodynamics stability according to the environmental conditions (pressure, temperature): (i) electron deficiency present at polar termination, such as oxygen rich (ii) an excess of surface hydroxyls groups issued from water dissociation. Interestingly, this effect is operational on both polar and non-polar terminations. In parallel with experiments, calculation show zinc is able to spill over the hydroxyls groups and interact strongly with the surface. Adhesion energy is 7 eV which is in a good agreement with the 3.5 eV of experimental value. Extended over the 3d transition metals series, the calculations identify titanium as the element exposing the strongest interaction with alumina. By focusing on the adhesive characteristics at the Zn/alumina interfaces, calculations show that titanium enrichment can indeed improve considerably the adhesion.

There is currently no definitive biomarker for Alzheimer's Disease (AD), confirmation of diagnosis is only possible post-mortem. Magnetic resonance spectroscopy (MRS) has potential in aiding diagnosis, an MRS scan can be performed during an MRI scan, only adding around 10 minutes to scan time. Use of data from the two scans may allow more accurate diagnosis of AD. This thesis investigates a transgenic mouse model of AD, the TASTPM mouse, using in vitro and in vivo MRS as well as matrix assisted laser desorption ionisation mass spectrometry imaging (MALDI MS Imaging). The first aim of the study was to search for a biomarker of AD that may allow better diagnosis or further our understanding of the pathology of the disease. The second aim was to evaluate the TASTPM mouse as a model of AD for use in preclinical testing of amyloid lowering agents. The third aim was to investigate a thalamic pathology in the TASTPM mice using MALDI MS Imaging. Metabolically, we found differences between the brains of TASTPM mice and their wild type base strain in both in vitro and in vivo scans. These differences may be exploited in the preclinical testing of novel amyloid lowering therapies. We also found similarities with human AD and other mouse models, lower N-acetylaspartate, lower glutamate and higher myo-inositol are all observed in human AD, as well as the TASTPM mice in vivo. We also found further evidence of impaired neuronal energy metabolism in TASTPM mice, such as lower succinate. Cerebral hypometabolism is a symptom of human AD. The TASTPM mouse seems to be a fairly good approximation of the human disease, sharing several traits. In our investigation of the thalamic pathology, we discovered a peptide which was strongly localised to the regions of the pathology and isolated it, but were unable to identify it, the work in this area will continue.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Environmental problems have become increasingly acute and frequent in recent decades, mainly due to unrestrained population growth and increased industrial activity. The textile industry merits especial attention in this context, since large volumes of water are used in finishing processes, which results in substantial quantities of liquid effluent. The objective of this work was to determine the optimum conditions for adsorption/desorption of reactive dyes, employing humin in batch experiments and with fixed bed columns where the humin was immobilized on silicate. Immobilization was confirmed by Fourier transform infrared analysis. Adsorption isotherms were constructed, and the kinetic data fitted to literature models. Multiple adsorption/desorption cycles were investigated using the fixed bed column. Results of the batch experiments showed that adsorption of Reactive Red 120 (RR 120) and Reactive Orange 16 (RO 16) by humin was most effective at pH 1.0, while optimum adsorption of Reactive Blue 2 (RB 2) was obtained at pH 2.0. Adsorption equilibria were rapidly achieved for all initial dye concentrations tested. Temperature measurements indicated that all of the processes were exothermic and could be described using a pseudo-second order kinetic model. The Freundlich isotherm provided the best fit for RO 16, while the Langmuir isotherm best described the adsorption of RR 120 and RB 2. In column experiments, adsorption efficiencies of 96.2 %, 62.1 % and 44.6 % were obtained for RR 120, RO 16 and RB 2, respectively, while the corresponding desorption efficiencies for these dyes were 81.4 %, 51.3 % and 23.7 %, respectively. Reductions in retention efficiency of 16 % (RO 16), 21 % (RR 120) and 26 % (RB 2) were observed between the first and second cycles. Reductions between the second and third cycles were of 7 %, 1 % and 1 %, respectively, indicating that the column could be used in further cycles. Overall, the biosorbent showed excellent performance in removal of reactive dyes, with the additional advantage that it could be regenerated and reused. : / Nas últimas décadas, os problemas ambientais têm se tornado cada vez mais críticos e frequentes, principalmente devido ao desmedido crescimento populacional e ao aumento da atividade industrial. A indústria têxtil merece atenção redobrada nesse contexto pela elevada quantidade de água utilizada nos processos de acabamento e geração de grandes volumes de efluentes líquidos. Esse trabalho teve como objetivo determinar as condições ótimas de adsorção / dessorção de corantes reativos utilizando experimentos em bateladas e colunas de leito fixo com humina imobilizada em silicato. A imobilização da humina foi verificada utilizando-se a técnica de espectroscopia de infravermelho com transformada de Fourrier. Isotermas de adsorção foram construídas e os dados cinéticos foram ajustados aos modelos encontrados na literatura. Resultados dos experimentos em batelada mostraram que a adsorção de Reactive Red 120 e Reactive Orange 16 por humina foi mais efetiva em pH 1,0 e pH 2 para o RB 2. E múltiplos ciclos de adsorção/dessorção foram testados nos experimentos em coluna de leito fixo com humina imobilizada em silicato. Os equilíbrios de adsorção foram alcançados rapidamente para todas as concentrações iniciais de corante utilizadas. Medições da temperatura indicaram que o processo foi exotérmico e descrito por um modelo cinético de pseudo-segunda ordem para todos os corantes. A isoterma de Freundlich se ajustou melhor para o RO 16, enquanto que a isoterma de Langmuir descreveu melhor a adsorção de RR 120 e do RB 2. Experimentos em coluna mostraram eficiências de adsorção de 96,2; 62,1 e 44,6% para o RR120, RO 16 e RB 2, respectivamente, bem como boa eficiência de dessorção de 81,4; 51,3 e 23,7% para os mesmos corantes, respectivamente. Uma diminuição da eficiência de retenção foi observada entre o primeiro e o segundo ciclo para o RO 16, RR 120 e RB 2 de aproximadamente 16, 21 e 26%, respectivamente. Entre o segundo e o terceiro ciclo de 7, 1 e 1% para os mesmos corantes. O que mostra a possibilidade de utilização da coluna em ciclos adicionais. O biossorvente apresenta um excelente desempenho na remoção de corantes reativos, com a vantagem que pode ser regenerado e reutilizado.

abstract: Limited access to clean water due to natural or municipal disasters, drought, or contaminated wells is driving demand for point-of-use and humanitarian drinking water technologies. Atmospheric water capture (AWC) can provide water off the centralized grid by capturing water vapor in ambient air and condensing it to a liquid. The overarching goal of this dissertation was to define geographic and thermodynamic design boundary conditions for AWC and develop nanotechnology-enabled AWC technologies to produce clean drinking water. Widespread application of AWC is currently limited because water production, energy requirement, best technology, and water quality are not parameterized. I developed a geospatial climatic model for classical passive solar desiccant-driven AWC, where water vapor is adsorbed onto a desiccant bed at night, desorbed by solar heat during the day, and condensed. I concluded passive systems can capture 0.25–8 L/m2/day as a function of material properties and climate, and are limited because they only operate one adsorption-desorption-condensation cycle per day. I developed a thermodynamic model for large-scale AWC systems and concluded that the thermodynamic limit for energy to saturate and condense water vapor can vary up to 2-fold as a function of climate and mode of saturation. Thermodynamic and geospatial models indicate opportunity space to develop AWC technologies for arid regions where solar radiation is abundant. I synthesized photothermal desiccants by optimizing surface loading of carbon black nanoparticles on micron-sized silica gel desiccants (CB-SiO2). Surface temperature of CB-SiO2 increased to 60oC under solar radiation and water vapor desorption rate was 4-fold faster than bare silica. CB-SiO2 could operate >10 AWC cycles per day to produce 2.5 L/m2/day at 40% relative humidity, 3-fold more water than a conventional passive system. Models and bench-scale experiments were paired with pilot-scale experiments operating electrical desiccant and compressor dehumidifiers outdoors in a semi-arid climate to benchmark temporal water production, water quality and energy efficiency. Water quality varied temporally, e.g, dissolved organic carbon concentration was 3 – 12 mg/L in the summer and <1 mg/L in the winter. Collected water from desiccant systems met all Environmental Protection Agency standards, while compressor systems may require further purification for metals and turbidity. / Dissertation/Thesis / Doctoral Dissertation Civil, Environmental and Sustainable Engineering 2020

M. Tech (Department of Chemistry, Faculty of Applied and Computer Sciences) Vaal University of Technology. / Persisting challenges associated with remediation of heavy metals from aqueous media have stirred the need for enhancement of current technologies. Cellulosic agro waste materials (AWM) as well as ion-imprinted polymers (IIP) have received ardent attention from researchers. These materials are often employed in the following industries: water and wastewater treatment, medical, pharmaceutical and packaging. Applications in water and wastewater treatment have gained significant interest due to desirable features they possess. In the case of AWM, these features include a tuneable surface area and poor porosity, basic surface functional groups and chemical stability. Some desired features in IIP include adsorption sites compatible for the ion imprint obtained after leaching with suitable reagents, rigidity and reusability. The efficacy of employing AWM and IIP for the remediation of toxic chromium from aqueous solution was explored. The current study is made up of part A and B. In part A, Macadamia nutshell powder was treated using HNO3, NaOH, as well as Fenton’s reagent. The three materials underwent a new modification which involved reacting treated adsorbents with cetyltrimethylammonium chloride (CTAC), followed by immobilization of 1,5' diphenylcarbazide (DPC) ligand. The adsorbents were ultimately washed, dried and stored for Cr(VI) batch adsorption experiments. Part B involved a synthesis of IIP and their non-imprinted polymer counterpart (NIP) for Cr(VI) sequestration in aqueous solution. This was done by precipitation polymerization of functional monomers, crosslinker and DPC-Cr(VI) complex as a template. Non-imprinted polymers were fashioned in a manner like that of IIP but with the exclusion of Cr(VI) ion template. Characterizations of the adsorbents were done using Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), X-ray fluorescence (XRF), and carbon, hydrogen, nitrogen and sulphur (CHNS) analyzer. Batch adsorption experiments were done and parameters such as solution pH, adsorbent dosage, initial Cr(VI) concentration and contact time were optimized. Working solutions were analyzed using ultraviolet-visible (UV-Vis) and atomic absorption (AA) spectroscopy. Adsorption parameters found to be optimum for DPC immobilized cellulosic adsorbents were pH 1.4, adsorbent mass of 0.1 g, 100 mg/L initial concentration and 125 minutes of contact time. The adsorption parameters determined to be optimum for IIP and NIP were pH 2.6, 0.2 g adsorbent mass, 80 mg/L initial concentration and 240 minutes of contact time. Reusability studies demonstrated the potential of adsorbents to remove Cr(VI) ions from aqueous media after successive adsorption-desorption cycles. Selectivity studies indicated that DPC immobilized adsorbents as well as IIP were able to selectively adsorb Cr(VI) ions from aqueous media in the presence of Zn(II), Cu(II), Co(II) and NI(II) ions. Kinetic models revealed that DPC immobilized cellulosic adsorbents and synthetic IIP were most fitting for pseudo-second order and pseudo first order, respectively. On the other hand, adsorption isotherm studies demonstrated that DPC immobilized cellulosic adsorbents and synthetic polymers were best fit for Freundlich and Langmuir adsorption isotherm, respectively.

This diploma thesis deals with the solution of ammonia separation from waste raw materials of agricultural production. It focuses on determining the efficiency of desorption from an experimental stripping device depending on the measurement temperature. Ammonia water solutions and liquid digestate samples from technical practice were used to verify the functionality of the equipment. Increasing separation efficiency with increasing temperature has been demonstrated. The device was gradually improved during the measurement for a better profitability of the separation process. The results of the experiments are discussed concerning the theoretical assumptions and compared with other methods of ammonia separation.

Thermal desorption (TD), a remediation method used to remove hydrocarbons from contaminated soils, may cause changes in soil properties that threaten soil function and plant productivity. The goal of this research is to better understand the effect that TD treatment has on soils intended for agricultural use. A series of soil phosphorus (P) sorption and desorption experiments were conducted on soils before and after TD treatment to determine P availability for plant uptake and risk for run-off. TD-treated soils retained more P, likely due to mineral transformations of Fe- and Al-oxides. In addition, a three-year field study using mixtures of topsoil (A), crude-contaminated soil (SP), and TD-treated soils (TDU) was conducted. Yields were significantly greater in plots that included A in the mixture compared to SP and TDU soils alone. TD-treated soils can be a replacement for topsoil, but the addition of topsoil will reduce the time to successful reclamation.