Thesis (M.S.)--University of Wisconsin--Madison, 1967. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (M.S.)--Ohio University, March, 2006. / Title from PDF t.p. Includes bibliographical references (p. 57-58)

Thesis (Ph. D.)--Drexel University, 2006. / Includes abstract and vita. Includes bibliographical references (leaves 174-191).

Th. 3e cycle--Instrumentation aux basses températures--Grenoble 1, 1979. N°: 30.

The objectives of the research project were to gain a deeper understanding of the factors influencing the graphite morphology in cast iron; particularly the role of different solute elements in relation to the industrial manufacture of compacted graphite iron. A number of melt treatment processes were assessed for their abilities to produce low nodularity compacted graphite microstructures over a range of casting section thicknesses. In this respect, the magnesium-titanium method was found to be superior to treatment using cerium Mischmetall and calcium additives; and very promising results were obtained with methods using zirconium as a major constituent of the treatment alloy. Scanning electron microscopy, secondary ion mass spectrometry and X-ray microanalysis were used to study the structural characteristics of different cast iron microstructures and the elemental distributions of important solutes between the phases. This information was used to clarify the role of the main solute elements in graphite morphology control and to assess current graphite growth theories.

The integrity of graphite components is critical for their fitness for purpose. Since graphite is a quasi-brittle material the dominant mechanism for loss of integrity is cracking, most specifically the interaction and coalescence of micro-cracks into a critically sized flaw. Including mechanistic understanding at the length scale of local features (meso-scale) can help capture the dependence on microstructure of graphites macro-scale integrity. Lattice models are a branch of discrete, local approach models consisting of nodes connected into a lattice through discrete elements, including springs and beams. Element properties allow the construction of a micro-mechanically based material constitutive law, which will generate the expected non-linear quasi-brittle response. This research focuses on the development of the Site-Bond lattice model, which is constructed from a regular tessellation of truncated octahedral cells. The aim of this research is to explore the Site-Bond model with a view to increasing understanding of deformation and fracture behaviour of nuclear graphite at the length scale of micro-structural features. The methodology (choice of element, appropriate meso length-scale, calibration of bond stiffness constants, microstructure mapping) and results, which include studies on fracture energy and damage evolution, are presented through a portfolio of published work.

The area covered in my diploma work is in the geomorphologic complex of the Šumava Mountains, in the diverse moldanubic zone. This work describes natural conditions of the entire area and its specific locations, including particularly the graphite mines in the surroundings of the village of Černá v Pošumaví and the hamlets of Bližná and Mokrá. These deposits are situated in the former district of Český Krumlov. In the past, mainly in the late 19th century and during the First World War, the mines in this area were without any doubt some of the biggest and richest places of deposit in the world. Numerous graphite vein deposits were discovered in the area with high content of quality material which was exported to many parts of the world. After the First World War mining here was in decline due to gradual growth of costs and increased production of other competing graphite mines worldwide. Another event which contributed to the downfall of mining in some abundant locations was also the construction of Lipno I. dam. In Bližná mining continued until the end of the 20th century when it was terminated in 1998. High quality water is drawn there today. The present work also deals with the methods of graphite processing and its use. A dictionary is attached here for better understanding of some expert geological terms.

In addition to its role as moderator within British nuclear reactors, polycrystalline graphite is also a major structural component of the core, enabling access for control rods, coolant gas and fuel. Aging processes, primarily fast neutron irradiation and radiolytic oxidation lead to distortion of the graphite components and property changes which ultimately reduce the material's effectiveness and can lead to component failure.Despite much research into the material, graphite behaviour under irradiation conditions is not fully understood and has resulted in an overestimation of the extent of component failures in Magnox reactors, and a subsequent underestimation of component failures in the following generation Advanced Gas-cooled Reactors (AGRs). A greater understanding of the material is therefore required in order to make more informed evaluations as part of on-going safety cases. Young's modulus is one property which varies as a complex function of radiolytic oxidation and fast neutron irradiation dose; this work investigates investigate the Young's modulus behaviour of nuclear grade graphites through property measurement and microstructural characterisation. Physical properties are dependent on microstructure, which is in turn a result of the manufacturing processes and raw materials used in its fabrication. Because of this, this thesis begins with a microstructural study of AGR graphite artefacts from varying points during the manufacturing process and post-irradiation, utilising X-ray diffraction to observe changes in crystallinity, microscopy to directly observe the microstructure and pycnometry to gauge porosity variations. Increases in crystallinity towards graphitisation are seen, with a subsequent decrease after irradiation; and significant changes are observed from inspection of optical and scanning electron micrographs. Young's modulus property data are obtained using a combination of static and dynamic techniques to accumulate data from a variety of techniques. An experiment designed to track changes to the speed of sound under compressive load was carried out on Magnox and AGR graphite, showing different behaviour between the grades, and variation with irradiation.A final series of tests combine compressive testing with in-situ microscopy to try and better understand the reasons behind this varied in behaviour and relate microstructural changes to graphite behaviour under compressive loading.

For years, electron beam induced deposition has been used to fabricate electrical contacts for micro and nanostructures. The role of the contact resistance is key to achieve high performance and efficiency in electrical devices. The present thesis reports on the electrical, structural and chemical characterization of electron beam deposited platinum electrodes that are exposed to different steps of thermal annealing and how they are used in four-probe devices of ultrathin graphite (uG) flakes (<100nm thickness). The device integration of liquid phase exfoliated uG is demonstrated, and its performance compared to devices made with analogous mechanically exfoliated uG. For both devices, similar contact resistances of ~2kΩ were obtained. The electrical measurements confirm a 99.5% reduction in contact resistance after vacuum thermal annealing at 300 °C. Parallel to this, Raman characterization confirms the formation of a nanocrystalline carbon structure over the electrode. While this could suggest an enhancement of the electrical transport in the device, an additional thermal annealing step in air at 300 °C, promoted the oxidation and removal of the carbon shell and confirmed that the contact resistance remained the same. Overall this shows that the carbon shell along the electrode has no significant role in the contact resistance. Finally, the challenges based on topographical analysis of the deposited electrodes are discussed. Reduction of the electrode’s height down to one-third of the initial value, increased surface roughness, formation of voids along the electrodes and the onset of platinum nanoparticles near the area of deposition, represent a challenge for future work.

Graphene, a two-dimensional nanomaterial, has been given much attention since it was first isolated in 2004. Driving this intensive research effort are the unique properties of this one atom thick sheet of carbon, in particular its electrical, thermal and mechanical properties. While the technological applications proposed for graphene abound, its low-cost production in large scales is still a matter of interrogation. Simple methods to obtain few-layered graphene flakes of high structural quality are being investigated with the exfoliation of graphite taking a prominent place in this arena. From the many suggested approaches, the most promising involve the use of liquid media assisted by intercalants and shear forces acting on the basal layers of graphite. In this thesis, it is discussed how a novel method was developed to produce flakes with consistent lateral dimensions that are also few-layered and retain the expected structural and chemical characteristics of graphene. Here, the source material was a commercially available graphiteintercalated compound, also known as expandable graphite. Several exfoliation-inducing tools were investigated including the use of blenders, homogenizers, and ultrasonic processors. To aid in this process, various solvents and intercalants were explored under different reactive conditions. The more efficient approach in yielding defect-free thin flakes was the use of thermally expanded graphite in boiling dimethylformamide followed by ultrasonic processing and centrifugation. In parallel, a method to fraction the flakes as a function of their lateral size was developed. Ultimately, it was possible to obtain samples of graphene flakes with a lateral dimension of a few micrometers (<5 μm) and thickness of 1-3 nm (i.e. <10 layers).