The heat capacity of 3He adsorbed on Grafoil (exfoilated graphite) preplated with four layers of 4He was measured between 1 and 50mK. The heat capacity was found to be linear up to 4OmK. At 3He surface densities below 4nm-2 two dimensional Fermi liquid behaviour was found and values of the hydrodynamic effective mass and Landau parameter Ff inferred. Subsequent steps in the heat capacity as a function of coverage were taken as evidence of independent 2D Fermi fluids. A low field DC SQUID pulsed NMR spectrometer was developed for future studies of magnetic order in 2D solid 3He films at ultralow temperatures

Parmi les nouvelles technologies pour l'énergie inscrites dans un contexte de développement durable, les piles à combustible à membrane échangeuse de protons (PEMFC) présentent des aspects séduisants. Toutefois, pour rendre cette technologie compatible avec une application à grande échelle, elle doit répondre à des exigences strictes en termes de coût, performance, et durabilité. Alors que les plaques bipolaires métalliques sont pénalisées par leur résistance à la corrosion et celles en graphite par leurs propriétés mécaniques et leur coût (dû aux phases d'usinage des canaux), les plaques bipolaires composites apparaissent attrayantes en raison de leurs propriétés et performances et de leur coût. Cette thèse s'inscrit dans ce cadre, en proposant un matériau composite à matrice organique de type époxy et charges conductrices de graphite. L'objectif de notre étude consiste à mettre au point un matériau thermodurcissable à base d'une formulation époxyde solide (permettant de contrôler sa chimie et plus particulièrement sa réactivité) fortement chargée en graphite. Deux formulations différentes sont étudiées. La première est à base de prépolymère époxy appelé DGEBA et de dicyandiamide (DDA) comme durcisseur. L'autre formulation étudiée est constituée de DGEBA et de durcisseur : le 3,3',4,4'-benzophénone dianhydride tétracarboxylique (BTDA). Ces deux formulations ont la particularité d'être très réactives à haute température (180-200°C) caractérisées par des temps de gel très courts (plus petit que 1min) afin d'avoir un temps de cycle de réticulation court pour une industrialisation de la fabrication. De plus, ces mêmes matrices ont montré une bonne stabilité chimique à température ambiante ainsi qu'une bonne stabilité thermique du système réticulé compatible avec la température d'utilisation des piles en fonctionnement. Concernant les réseaux composites résultant de la polymérisation DGEBA/BTDA et DGEBA/DDA, le module au plateau caoutchoutique est dominé par le taux de charge qui est très élevé (85%), celui-ci est ainsi très proche d'un réseau à l'autre et reste supérieur à 1 GPa. Nous constatons une viscosité relativement élevée pour les systèmes fortement chargés, point à prendre en compte lors du procédé de transformation. Enfin, la dernière partie des travaux réalisés concerne l'étude de mélange constitué de la matrice thermodurcissable (DGEBA/DDA/urée) modifiée par un thermoplastique (PEI). L'originalité et l'intérêt de ce travail résident dans l'incorporation de charges conductrices afin que celles-ci puissent se disperser dans la phase continue ou co-continue époxyde-amine lors de la séparation de phase pour limiter la proportion de charges et ainsi la viscosité des systèmes chargés. L'autre intérêt est d'améliorer les propriétés de résistance à la rupture du réseau époxyde TD final grâce à la présence de la phase thermoplastique séparée.

The purpose of this work is to explore a method that combines both top-down and bottom-up elements to fabricate electronic devices made from graphene, a single sheet of carbon atoms related to carbon nanotubes and graphite. This material has garnered interest in the semiconductor industry for many reasons, including its potential for ballistic conduction, natural ambipolar (both n- and p-type) carrier transport, and impermeability to nearly all elements. However, its lack of a band gap, and a lack of viable options for creating one in the material, suggests a limited future as a silicon replacement material. A solution to this problem is presented that uses a recently-reported technique of creating pre-patterned graphene features from the thermal decomposition of specially-structured silicon carbide (SiC) surfaces. We employ a combination of direct band structure measurements and electrical results to suggest that a semiconducting bent graphene nanostructure exists in this structured SiC system, creating a possible route toward a broad class of future graphene electronics.

A major limitation in developing a successful cancer treatment is the need for a distinction between normal and cancerous tissue. For solid tumors, this distinction can be made on a spatial basis, and successful treatments have been developed accordingly; however, many of these treatments cause pathologies in healthy tissue, much to the detriment of patient health. To address this issue for solid tumours, a conceptual approach would be to administer the chemotherapeutic drug locally, such that the intra-tumour concentration was high, while the systemic exposure to the drug remained low, thus, minimizing side effects. The present research focuses on providing proof-of-concept for the electrochemical generation of a toxicant from a prodrug, and subsequent use to elicit cytotoxicity in cancer cells, in attempts to electrochemically mimic monooxygenase-catalyzed bioactivation. Electro-oxidation of acetaminophen and cyclophosphamide substrates at graphite and Ti/RuO2 anodes was successful in generating their respective toxicants; however, the graphite anode was superior with respect to current efficiency and toxicant yield. Electrolyses conducted in batch and flow reactors produced effluents which reduced EMT-6 cell viability to the IC99 level. This thesis provides proof-of-concept for electrochemical prodrug activation as a viable area for further cancer research.

No description available.

Unconformity-type uranium deposits from the Athabasca Basin are considered to be the result of mixing between oxidized basinal brines and basement-derived reduced fluids/gases, and/or reduced basement rocks. Graphite and/or its breakdown products are suggested to be responsible for uranium mineralization by acting as a reductant that could trigger deposition of uranium. Also, graphite is considered to be indicative of basement structures; being often concentrated along structures which can be identified as electromagnetic (EM) conductors. Thus, exploration for uranium deposits is often focused on the search for EM conductors. Underlying the sedimentary rocks of the basin in the Dufferin Lake zone are variably graphitic pelitic schists (VGPS); altered to chlorite and hematite (Red/Green Zone: RGZ), and locally bleached equivalents near the unconformity during paleoweathering or later fluid interactions. These altered zones are texturally similar rocks within “graphite-depleted zones” as the unconformity is approached. Both zones are characterized by a lower concentration of carbon and sulfur, with the bleached zone showing higher concentrations of uranium and boron, the latter corresponding to high dravite content. The major element composition of the graphite-bearing pelitic schists and altered equivalents (RGZ) are similar. Raman analyses indicate that well-ordered carbon species (graphite to semi-graphite) are present in the pelitic schists, with both types more common within shear zones. In contrast, only rare low-ordered carbon species (carbonaceous matter) were detected in the graphite-depleted samples within the RGZ. This variation is interpreted to be the result of graphite consumption by oxidizing fluids migrating downward from the Athabasca Group. This graphite consumption may have resulted in the production of a mobile reductant (gas or fluid), which may have played a subsequent role in the deposition of uranium mineralization. Secondary fluid inclusions (FI) examined in different quartz vein generations using microthermometry and Raman analysis, provide an indication of the fluids that have interacted with these rocks. Monophase vapor are the dominant type of fluid inclusions in the VGPS, whereas aqueous two-phase (L+V) and three-phase (L+V+Halite) FI occur in the RGZ. CH4-dominant and N2-dominant FI identified using Raman could be the result of fluid(s) interaction with the graphitic lithologies. This would have generated the breakdown of graphite to CH4 and associated feldspars/micas to NH4/N2. CH4, N2 and H2 (resulting from the decomposition of NH4+) represent possible reductants of uranium-bearing brines. Two brines in the RGZ: a regional basinal fluid and an evolved fluid possibly related to U mineralization; similar to other nearby deposits, are observed. These suggest that the basinal brines have circulated in the basement rocks and have been able to evolve by interaction with the basement rocks to possibly be related to uranium mineralization.

Within recent years, allotropic structures of carbon have been produced in the forms of tubes and ribbons which offer the promise of extraordinary electronic and thermal properties. Here we present analyses of oligophenyl and oligoacene systems–infinite, one-dimensional chains of benzene rings linked along the armchair and zigzag directions. These one-dimensional structures, which are amenable to calculation by analytical means, exhibit features very similar to carbon nanotubes and nanoribbons. Using a tight-binding Hamiltonian we analytically determine the density of states, local density of states, and energy-band structure for the phenyl and the acene. We also examine the effect of disorder on the energies and the corresponding states. / Department of Physics and Astronomy

NBG–18 graphite is developed by SGL Carbon for the Pebble Bed Modular Reactor Company (PBMR), and is used as the preferred material for the internal graphite core structures of a high–temperature gas–cooled nuclear reactor (HTR). The NBG–18 graphite is manufactured using pitch coke, and is vibrationally molded. To assess the structural behaviour of graphite many destructive techniques have been performed in the past. Though the destructive techniques are easy and in some cases relative inexpensive to perform, these methods lead to waste material and require cumbersome time consuming sample preparations. To overcome this problem numerous non–destructive testing techniques are available such as sonic resonance, resonant inspection, ultrasonic testing, low and multifrequency Eddy current analysis, acoustic emission and impulse excitation techniques. The Hammer Impulse Excitation technique was used as a method in predicting the fatigue life of NBG–18 graphite by focussing on the application of modal frequency analysis of determined natural frequencies. Moreover, the typical fatigue characteristics of NBG–18 graphite were determined across a comprehensive set of load ranges. In order to be able to correlate modal frequency parameters with fatigue life, suitable uniaxial fatigue test specimen geometry needed to be obtained. The uniaxial fatigue test specimens were manufactured from two NBG–18 graphite sample blocks. The relationship between natural frequencies of uniaxial test specimens, fatigue life, sample positioning and sample orientation was investigated for different principle stress ratios. Load ratios R = –oo and R = +2 tested proved to show the highest r–values for the Pearson correlation coefficients investigated. However, there was no significant trend found between the natural frequency and the fatigue life. / Thesis (M.Ing. (Nuclear Engineering))--North-West University, Potchefstroom Campus, 2011.

NBG–18 graphite is developed by SGL Carbon for the Pebble Bed Modular Reactor Company (PBMR), and is used as the preferred material for the internal graphite core structures of a high–temperature gas–cooled nuclear reactor (HTR). The NBG–18 graphite is manufactured using pitch coke, and is vibrationally molded. To assess the structural behaviour of graphite many destructive techniques have been performed in the past. Though the destructive techniques are easy and in some cases relative inexpensive to perform, these methods lead to waste material and require cumbersome time consuming sample preparations. To overcome this problem numerous non–destructive testing techniques are available such as sonic resonance, resonant inspection, ultrasonic testing, low and multifrequency Eddy current analysis, acoustic emission and impulse excitation techniques. The Hammer Impulse Excitation technique was used as a method in predicting the fatigue life of NBG–18 graphite by focussing on the application of modal frequency analysis of determined natural frequencies. Moreover, the typical fatigue characteristics of NBG–18 graphite were determined across a comprehensive set of load ranges. In order to be able to correlate modal frequency parameters with fatigue life, suitable uniaxial fatigue test specimen geometry needed to be obtained. The uniaxial fatigue test specimens were manufactured from two NBG–18 graphite sample blocks. The relationship between natural frequencies of uniaxial test specimens, fatigue life, sample positioning and sample orientation was investigated for different principle stress ratios. Load ratios R = –oo and R = +2 tested proved to show the highest r–values for the Pearson correlation coefficients investigated. However, there was no significant trend found between the natural frequency and the fatigue life. / Thesis (M.Ing. (Nuclear Engineering))--North-West University, Potchefstroom Campus, 2011.

No description available.