M.Ing. / Please refer to full text to view abstract

M.Tech. / The mining industry exerts ever increasing demand for components with high wear resistance to the extent that plain ferrous alloys are falling short. Innovative metal-matrix composites nonferrous metals have been widely researched and used. Casting composites based on ferrous alloys pose monumental challenges in casting. Firstly, the density differential results in large resistant forces on the ceramic such that unless a rigid structure is configured, the less dense ceramic floats on the metal stream. Secondly, the poor wetting properties between metal and ceramic will result in inferior bonding of the matrix, hence separation of solids in service.This study presents the feasibility of manufacturing ceramic based metal matrix composites (MMC) for multi-purpose industrial application including wettability and the bonding between the matrix and the composite. The cold rods of alumina positioned in the mould prior to casting cracked as soon as they came in contact with hot metal. Because of the density difference between ceramic and liquid metal the alumina tended to float under the influence of Ferro static pressure. Infiltration of zirconia (ZrO2) and alumina (Al2O3) in ferrous matrix was investigated. Infiltration of liquid metal in ceramic filters increased with porosity of filters i.e. greater infiltration occurred in filters with larger pore volume fraction measured in terms of number of pores per linear inch (ppi). Thus, there was high infiltration in casting with 10ppi followed by 30ppi and there was poor infiltration in 50ppi ceramics. Infiltration increased with increasing temperature of the ceramics. A temperature of 1000oC was found to be superior to 800oC. The wetting behaviour of molten iron on the substrates of Al2O3 was investigated. Titanium in high chromium white cast iron was found to improve the wetting characteristics on alumina. The wetting angle decreased with increased titanium content. The wear properties of ferrous alloys used were not significantly improved by the ceramic used to make the composite. Filters are produced by a deposition process and hence are not densified for the purpose of manufacturing hard composites

M.Ing. (Electrical And Electronic Engineering) / Please refer to full text to view abstract

M.Ing. / Fibre Bragg gratings (FBGs) have been manufactured for the first time in South Africa by means of the phase mask method. It is possible to manufacture not only uniform FBGs, but also chirped FBGs. The optical fibre that is used for imprinting the FBGs can also be hydrogen loaded locally. FBGs with a reflectivity of 99.7% and higher can be written by making use of the experimental setup presented in this thesis. It is possible to manufacture a FBG with a centre wavelength that has any value between the Bragg wavelength and approximately 6 nm lower than the Bragg wavelength. This is done by stretching the optical fibre prior to the writing process. FBGs have been simulated in MATLAB to get an idea of what one may expect during the manufacturing process. The program makes it possible to simulate the effects of changes in grating length, index modulation, pressure, temperature and strain on the centre wavelength of an FBG. Dispersion is explained in detail. Chromatic dispersion, which is part of dispersion as a whole, can be cancelled by making use of an FBG. The different techniques for the measurement of chromatic dispersion is explained. Some insight is given on dispersion (the pulse broadening in the time domain due to the different velocities of different wavelengths from the source's finite optical bandwidth) compensation. An FBG that was manufactured locally has been tested as a dispersion compensator. It was found that an FBG is effective in performing this function.

Electrospinning is a technique, which can be used to produce nanofibrous materials by introducing electrostatic fields into the polymer solution. Due to their intrinsic properties, such as small fiber diameter, small pore size and large surface area, nanofibres are suitable for use in a variety of applications including wound dressing, filtration, composites and tissue engineering. The study demonstrates the successful and optimised production of Poly(ethylene oxide) (PEO) and chitosan nanofibres by electrospinning. The biocidal effects of chitosan, chitosan-silver nanofibres and silver nanoparticles were successfully investigated. To set up a functional electrospinning apparatus, the PEO solution parameters (concentration, molecular weight, solvent, and addition of polyelectrolyte) and applied potential voltage on the structural morphology and diameter of PEO nanofibres were studied. At lower PEO concentrations, the fibres had morphology with a large variation in fibre diameter, whereas at the higher concentrations, the nanofibres exhibited ordinary morphology with uniform but larger fibre diameters. Higher molecular weight showed larger average diameters when compared to that obtained with the same polymer but of a lower molecular weight. The addition of polyelectrolyte to the polymer solution had an influence on the structural morphology of the PEO. Flow simulation studies of an electrically charged polymer solution showed that an increase in the flow rate was associated with an increase in poly(allylamine hydrochloride) (PAH) concentration for the low molecular weight polymer, the shape and size of the Taylor cone increasing with an increase in PAH concentration for the low molecular weight polymer. During optimization of the PEO nanofibres, based on statistical modelling and using the Box and Behnken factorial design, the interaction effect between PAH concentration and the tip-to-collector distance played the most significant role in obtaining uniform diameter of nanofibres, followed by the interaction between the tip-to-collector distance and the applied voltage and lastly by the applied voltage. The production and optimization of chitosan nanofibres indicated that the interactions between electric field strength and the ratio of trifluoroacetic acid (TFA) and dichloromethane (DCM), TFA/DCM solvents as well as between electric field strength and chitosan concentration had the most significant effect, followed by the concentration of chitosan in terms of producing nanofibres with uniform diameters. Chitosan and chitosan-silver nanofibres could be successfully electrospun by controlling the solution properties, such as surface tension and electrical conductivity with the silver nanoparticles in the chitosan solutions affecting the electrospinnability. The silver nanoparticles in the chitosan solution modified the morphological characteristics of the electrospun nanofibres, while the conductivity and the surface tension were elevated. The fibre diameter of the chitosan and chitosan-silver nanoparticles decreased with an increase in the silver content. The electrospun chitosan nanofibres had a smooth surface and round shape as compared to the silver-chitosan nanofibres with a distorted morphology. The chitosan and chitosan-silver nanofibres as well as the silver nanoparticles exhibited antimicrobial or inhibition activity against S. aureus than against E. coli. S. aureus bacterial culture showed good cell adhesion and spreading inwards into the chitosan nanofibrous membrane. The chitosan-silver nanofibres exhibited a greater minimum inhibitory concentration (MIC), followed by silver nanoparticles and then chitosan nanofibres; suggesting a synergistic effect between the chitosan and silver nanoparticles.

The use of natural fibers as reinforcement in thermoplastics presents an interesting alternative for the production of low cost and ecologically friendly composites. One of the advantages of using natural fibres is their low specific weight, resulting in higher specific strength and stiffness when compared to glass reinforced composites. Natural fibres also present safer handling and working conditions. They are non-abrasive to mixing and can contribute to significant cost reduction. This work is divided into two phases: Phase 1 deals with developing nonwoven mats composites from flax/polypropylene (PP) and evaluating their properties. Flax/polypropylene fibres (at different weight ratios) were processed by needle-punching technique in order to form nonwoven mats. The mats were compression-molded at a temperature of 180oC to form composite materials. The mechanical, thermal and viscoelastic properties of the composites were analyzed. Composites (untreated and silane-treated) were also subjected to varying conditions of temperature and humidity and the tensile properties of the conditioned and unconditioned composites were investigated. The mechanical properties (tensile, flexural and impact) of flax/PP composites were found to increase and reach maximum values at 30 per cent fibre loading and then decrease at higher fibre content. Thermal studies revealed that the composites were stable up to 320oC and samples containing 40 per cent flax fibres were found to exhibit greater thermal stability than neat PP. The dynamic mechanical analyses of the composites showed that the incorporation of flax in the composites resulted in an increase of the storage modulus with a maximum value exhibited by composite containing 40 per cent fibre loading. Composites containing chemically modified fibres exhibited low tensile modulus after conditioning. Phase 2 is based on the investigation of the effect of nano-calcium carbonate (CaCO3) on the properties of two types of polymer matrices: recycled PP and virgin PP. In this case, composites were prepared by melt-mixing and injection molding. The mechanical and thermal properties of the composites were characterized. The tensile modulus of the nano-CaCO3 filled PP (virgin and recycled) composites were found to increase and reach maximum at 30 per cent nano-CaCO3 loading, while the tensile strength decreased with increasing filler content. Thermal studies showed that the nano-CaCO3 filled PP samples exhibited a one-step degradation pattern and are thermally stable up to 450oC. The thermal stability of the samples was found to decrease following the addition of nano-CaCO3. SEM micrographs of the tensile fractured surfaces of composites of the nano-CaCO3 filled virgin and recycled PP revealed the presence of nano-CaCO3 agglomeration.

L'objectif de cette thèse est de préparer les composites de polyamide avec des fibres naturelles, capables de résister à des températures élevées. La matrice polymère et les fibres traitées doivent être résistants à la température séparément. Pour cette raison, cette thèse se concentre en deux thèmes principaux : le traitement chimique des fibres naturelles et la transformation des composites de ces fibres traitées avec polyamide 6 et 6,6 matrice. Curaua, jute et lin sont des fibres utilisées. Pour supprimer les composantes à basse masse molaire, comme l'hémicellulose et la lignine, des fibres naturelles, un alcalin-traitement a été effectué en utilisant un poids de 5,0.% de solution d'hydroxyde de sodium. Deux techniques de traitement à des environnements différents ont été comparés : à pression ambiante (trois traitements successifs, à 80 ºC, pendant 1h chacun) et haute pression (1,5 MPa et 120 ºC à différents intervalles de temps : 15, 30, 45 et 60 minutes). Une amélioration des propriétés thermiques des fibres naturelles a été observée dans les deux cas par analyse thermogravimétrique (TGA) et, en regardant les différentes réponses des trois fibres étudiées au traitement alcalin à haute pression, il a été décidé de fixer 30 minutes de haute pression mercerisage pour toutes les fibres avant d'effectuer des post-traitements (acétylation et silanisation) et la préparation de composites utilisant polyamide 6 et 6.6 comme matrices. On a utilisé des teneurs en fibres à la fois dans la matrice de polyamide (10, 20 et 30 en poids.%). Par testings de tension et observations au MEB, on a montré une amélioration des propriétés mécaniques des PA 6/ fibres traitées à la proportion 70/30. Pour réduire la température de traitement de PA 6.6, une combinaison de 2,5 en poids. % de LiCl et 2,5 en poids. % de N-butyl benzène sulfonamide (NBBSA) a été définie par conception expérimentale et il a été ajouté au polyamide 6.6 pur. En outre, on a trouvé la plus grande des propriétés mécaniques des composites préparés avec matrice de polyamide et 10 % en poids de fibres alcaline-traitées + silanisées sur polyamide plastifié 6,6. Il était possible de préparer des composites à plus forte teneur en fibres allant jusqu'à 30 en poids. %. Cependant, il est nécessaire d'améliorer les paramètres de compoundage pour améliorer la dispersion des fibres. / The objective of this PhD Thesis is to prepare composites of polyamide with natural fibers, able to withstand high temperatures. The polymeric matrix and treated fibers should be resistant to temperature separately. For this reason, this Thesis is focused in two main topics: chemical treatment of natural fibers and processing of composites of these treated fibers with polyamide 6 and 6.6 matrix. Curauá, jute and flax were the fibers used. To remove low molar mass components, as hemicellulose and lignin, of natural fibers, alkaline-treatment was conducted using a 5.0 wt.% of sodium hydroxide solution. Two treatment techniques at different environments were compared: at room pressure (three successive treatments, at 80 ºC, during 1h each) and high pressure (1.5 MPa and 120 ºC at different time intervals: 15, 30, 45 and 60 minutes). Improvement of thermal properties of natural fibers was observed in both cases by thermogravimetric analysis (TGA) and, looking at the different responses of the three studied fibers to the high pressure alkaline treatment, it was decided to fix 30 minutes of high pressure mercerization for all fibers before performing post-treatments (acetylation and silanization) and preparing composites using polyamide 6 and 6.6 as matrixes. It was employed different fiber contents in both polyamide matrix (10, 20 and 30 wt. %). By tension testings and SEM observations, it was shown improvement of mechanical properties of PA 6 / treated fibers at 70/30 proportion. To reduce the processing temperature of PA 6.6, a combination of 2.5 wt. % of LiCl and 2.5 wt. % of N-butyl benzene sulphonamide (NBBSA) was defined throught experimental design and it was added to pure polyamide 6.6. Moreover, it was found that the highest mechanical properties for composites prepared with polyamide 6.6 matrix was those using 10 wt. % of alkaline-treated + silanized fibers on plasticized polyamide 6.6. It was possible to prepare composites with higher fiber content up to 30 wt. %. However, it is needed an improvement of compounding parameters to enhance fiber dispersion.

Many basal forebrain and mesopontine tegmental cholinergic projection systems tend to overlap in their origins. This raises the possibility that these projection systems are collateralized to innervate divergent areas. In experiment one, the degree to which basal forebrain and mesopontine tegmental neurons that innervate the reticular thalamic nucleus have axons that collateralize to innervate the cortex as well was examined with a retrograde fluorescence labeling method combined with immunohistochemistry. A significant portion of the labeled neurons in the region of the nucleus basalis magnocellularis and pedunculopontine tegmental nucleus projecting to the reticular thalamic nucleus were observed to be also labeled (double-labeled) following intracortical tracer injections. Many of these double-labeled neurons displayed choline acetyltransferase choline acetyltransferase immunoreactivity. It was also shown that numerous basal forebrain neurons that innervated the reticular thalamic nucleus contained the calcium-binding protein, parvalbumin. These neurons tended to be located more rostrally than the ChAT immunoreactive neurons; primarily in the region of the ventral pallidum. There was some indication that parvalbumin-containing neurons in the basal forebrain that innervate the reticular thalamic nucleus also have axons that branch to innervate the cortex. Finally, none of the basal forebrain neurons innervating the reticular thalamic nucleus was found to contain somatostatin. In experiment two, the degree to which basal forebrain neurons have axons that collateralize to innervate the interpeduncular nucleus and hippocampus was examined with retrograde fluorescence labeling methods. Labeled neurons projecting to both of these limbic structures were observed only occasionally. Comparison of the distribution of single labeled neurons innervating each of these structures revealed that within the region of origin, in the horizontal limb of the diagonal band, neurons innervating the interpeduncular nucleus tended to be located dorsally to those innervating the hippocampus. The results of these experiments are discussed in relation to their anatomical and functional implications toward a greater understanding of the basal forebrain and mesopontine cholinergic and non-cholinergic projection systems. / Medicine, Faculty of / Graduate

D.Ing. / This thesis studies the application of newer generation engineering materials, specifically carbon fibre reinforced polymers, as bone plates in cases of fractured bones. The application of bone plates subsequent to bone fracture is a very old orthopaedic technique that has always rendered some problems. The rigidity of the bone plate, and thus the plated system as a whole, is of advantage during the healing phase, but of disadvantage later. Bone remodels itself to most efficiently perform the load bearing required of it. In a plated system, the load is born primarily by the plate and therefore protects the underlying bone, leading to osteoporosis and eventual atrophy. All bone plates are made of a material that is totally foreign to the body, and in most cases these are removed after some healing of the bone had occurred. The majority of current research programmes with respect to bone plates are directed towards biodegradable bone plates that reduces in mechanical strength at approximately the same rate as bone gains in its ability to sustain loads. The principle of stimulating bone growth in cases of delayed union and non-union has been studied since the early 1960's. The studies revealed that bone healing can in fact be enhanced by the introduction of a very small electric current to the fracture site. Variations to the mechanisms and position of application of the current, alternating or direct, are well documented. Although the physiological healing process associated with electrical stimulus remains largely unknown, the principle is well established. The phenomenon of galvanic corrosion has been known since the tum of the century. Where two dissimilar materials are in the presence of a conducting media, the more "reactive" of the two materials will react as an anode or electron donor to the other material. An electric current thus will flow from the one material to the other. Having three existing and known phenomena, namely bone plating, bone healing stimulation and galvanic corrosion raises the question of whether these can be combined to yield a solution superior to any current plating mechanism - a plate that would render sufficient mechanical support but act as an electron source and thus as a bone healing stimulus. The purpose of this study is to assess the biological criteria determining the choice of bone plates (inclusive of mechanical, physiological and electrical criteria) and thereafter selecting a material suitable for this dynamic requirement.

M.Ing. / Please refer to full text to view abstract