The behaviour of iodine, before and after annealing, in pyrolytic carbon (PyC) has been studied using the Rutherford backscattering spectrometry (RBS), X-ray diffraction (XRD) and scanning electron microscopy (SEM). PyC is used as a coating material in the design of the nuclear fuels such as the TRISO particles. TRISO particles are used to produce nuclear energy in nuclear reactors such as the PBMR. Iodine is one of the radioactive fission products produced during the production of nuclear energy by the nuclear fuels. The PyC layers in TRISO particles acts as a barrier for fission products. The main aim of this study was to investigate the effectiveness of PyC as a barrier of iodine diffusion. 360 keV iodine ions were implanted into the PyC to a fluence of 1×1015 iodine ions per cm2, at room temperature. After implantation the PyC samples were annealed (in vacuum) isochronally at 900 °C, 1000 °C, 1100 °C and 1200 °C; all for 9 hours. XRD measurements were performed using a cobalt (Co) XRD spectrometer on θ-2θ configuration; before and after the annealing temperatures. In-lens SEM images were also obtained for the PyC samples before and after heat treatment. RBS measurements were performed using a Van de Graaff accelerator and a 1.6 MeV He+ beam. XRD and SEM were used to study the structure of PyC before and after the annealing. Ion implantation and high temperature treatment affected the structure of PyC. Literature has shown that ion implantation caused structural damages in the implanted region of the PyC, reducing the degree of preferred orientation of the graphitic layers of the PyC in that region. The XRD results showed that high temperature annealing caused an increase in the degree of preferred orientation of the graphitic layers in the PyC used which is in agreement with other studies. Comparison of our SEM results to other reports has shown that the PyC used has a structure similar or close to the laminar structures of PyCs, with medium to high degree of preferred orientation. RBS was used to produce the iodine depth profiles, which provided insight on implantation depth of iodine in PyC as well as iodine behaviour after annealing. The results showed that iodine concentration in the implanted profile decreased with increasing annealing temperature. The full width at half maximum (FWHM) of the iodine profiles, obtained using the computer program Genplot, showed that after heat treatments of 900 °C, 1000 °C and 1100 °C more iodine initially diffused deeper into the PyC bulk than towards the PyC surface. At 1200 °C, the diffusion of iodine towards the PyC surface increased. It was proposed that this iodine behaviour was associated with the changes in the PyC structure due to ion implantation and high temperature treatment of the PyC. The obtained iodine profiles and the corresponding FWHM did not show evidence that the diffusion of iodine in both directions could be attributed to Fickian diffusion mechanism; hence no activation energy for the iodine diffusion in laminar PyC was determined. Copyright / Dissertation (MSc)--University of Pretoria, 2012. / Physics / unrestricted

L’essor des matériaux composites à matrice céramique dans les domaines de l’aéronautique, du spatial et du nucléaire force le développement de nouveaux matériaux et procédés associés afin de répondre à l’exigence toujours plus poussée de ces secteurs d’activité. La course à la réduction des coûts de fabrication a notamment contribué à ces développements. Dans cet objectif, le LCTS contribue à développer un moyen original et alternatif pour la synthèse d’interphases et de matrices des CMC par densification du renfort fibreux : le procédé dit « de caléfaction ». Ces travaux de recherche ont pour principal objectif l’étude de précurseurs originaux pour l’élaboration de matériaux pyrocarbone (pyC) et Si-O-C par ce procédé. Ce mémoire s’articule ainsi autour de 2parties expérimentales que sont i) l’élaboration de revêtements pyC à partir de précurseurs alcools et ii)l’élaboration de revêtements Si-O-C à partir de précurseurs organosilylés.Les diverses techniques de caractérisation physico-chimique utilisées, couplées aux nombreuses expériences réalisées dans ces travaux ont permis de relier la structure et/ou la composition chimique des revêtements obtenus aux paramètres expérimentaux utilisés (précurseurs, températures et durées d’élaboration). Des conditions optimales de préparation de PyC de très haute qualité à partir d’alcools ont été obtenues. Quant au système Si-O-C, il est montré que la structure et la composition des dépôts dépendent des conditions. / The growth of ceramic matrix composite (CMC) in the fields of aeronautic, spatial and nuclear pushes the development of new material and associated processes in order to answer to the tough requirements in this business sectors. Fabrication cost savings, in particular, has helped these improvements. In this aim, the LTCS has contributed to develop an original and alternative device for the synthesis of CMC’s interphases and matrices : the “film boiling densification”.This PhD as for key objective the study of original precursors for PyC and Si-O-C fabrication using this process. This manuscript is divided into two experimental parts dedicated to : i) the fabrication of carbon coatings from alcohols and ii) the fabrication of Si-O-C coatings from silylated precursors.The diverse characterization technics coupled to the numerous experiments permitted to connect the coatings structure and/or the chemical composition to the experimental parameters (precursor, temperature,duration). Optimal conditions were found for the preparation of high quality PyC from alcohols.For Si-O-C system, it is show that structure and chemical composition depends on experimental conditions.

Biotribology, the study of lubrication, wear and friction within the body, has become a topic of high importance in recent times as we continue to encounter debilitating diseases and trauma that destroy function of the joints. A highly successful surgical procedure to replace the joint with an artificial equivalent alleviates dysfunction and pain. However, the wear of the bearing surfaces in prosthetic joints is a significant clinical problem and more patients are surviving longer than the life expectancy of the joint replacement. Revision surgery is associated with increased morbidity and mortality and has a far less successful outcome than primary joint replacement. As such, it is essential to ensure that everything possible is done to limit the rate of revision surgery. Past experience indicates that the survival rate of the implant will be influenced by many parameters, of primary importance, the material properties of the implant, the composition of the synovial fluid and the method of lubrication. In prosthetic joints, effective boundary lubrication is known to take place. The interaction of the boundary lubricant and the bearing material is of utmost importance. The identity of the vital active ingredient within synovial fluid (SF) to which we owe the near frictionless performance of our articulating joints has been the quest of researchers for many years. Once identified, tribo tests can determine what materials and more importantly what surfaces this fraction of SF can function most optimally with. Surface-Active Phospholipids (SAPL) have been implicated as the body’s natural load bearing lubricant. Studies in this thesis are the first to fully characterise the adsorbed SAPL detected on the surface of retrieved prostheses and the first to verify the presence of SAPL on knee prostheses. Rinsings from the bearing surfaces of both hip and knee prostheses removed from revision operations were analysed using High Performance Liquid Chromatography (HPLC) to determine the presence and profile of SAPL. Several common prosthetic materials along with a novel biomaterial were investigated to determine their tribological interaction with various SAPLs. A pin-on-flat tribometer was used to make comparative friction measurements between the various tribo-pairs. A novel material, Pyrolytic Carbon (PyC) was screened as a potential candidate as a load bearing prosthetic material. Friction measurements were also performed on explanted prostheses. SAPL was detected on all retrieved implant bearing surfaces. As a result of the study eight different species of phosphatidylcholines were identified. The relative concentrations of each species were also determined indicating that the unsaturated species are dominant. Initial tribo tests employed a saturated phosphatidylcholine (SPC) and the subsequent tests adopted the addition of the newly identified major constituents of SAPL, unsaturated phosphatidylcholine (USPC), as the test lubricant. All tribo tests showed a dramatic reduction in friction when synthetic SAPL was used as the lubricant under boundary lubrication conditions. Some tribopairs showed more of an affinity to SAPL than others. PyC performed superior to the other prosthetic materials. Friction measurements with explanted prostheses verified the presence and performance of SAPL. SAPL, in particular phosphatidylcholine, plays an essential role in the lubrication of prosthetic joints. Of particular interest was the ability of SAPLs to reduce friction and ultimately wear of the bearing materials. The identification and knowledge of the lubricating constituents of SF is invaluable for not only the future development of artificial joints but also in developing effective cures for several disease processes where lubrication may play a role. The tribological interaction of the various tribo-pairs and SAPL is extremely favourable in the context of reducing friction at the bearing interface. PyC is highly recommended as a future candidate material for use in load bearing prosthetic joints considering its impressive tribological performance.