Carbon-related materials for electrochemical and high-temperature structural applications
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The processing, structure and properties of carbon-related materials for structural and electrochemical applications have been addressed. In relation to the structural materials, a new material, namely a nanostructured ceramic-carbon hybrid that is prepared by hot-pressing organobentonite particles is provided. In addition, carbon-carbon (C/C) composites that have been improved by filler incorporation, with the fillers including organobentonite and fumed alumina, are provided. In relation to the electrochemical electrode materials, which include various types of particulate carbons, a new method of electrical characterization of such materials in the absence of an electric double layer is provided, thereby enabling for these materials the first determination of (i) the relative dielectric constant, (ii) the effect of the electrolyte on the relative dielectric constant and the volumetric electrical resistivity, (iii) the specific capacitance and areal electrical resistivity of the interface between the electrode and its electrical contact, and (iv) the specific capacitance and areal resistivity of the interface between the electrode and the electrolyte. The need for densification (thereby decreasing the fabrication cost) has been reduced by the incorporation of a particulate filler (fumed alumina or organoclay) during the C/C fabrication. Fumed alumina is in the form of aggregates of nanosize alumina particles. Due to this structure, it is highly deformable (squishable). The squishability enables conformability, which is attractive for the filler to fill the space between the carbon fibers in C/C. Partly due to the presence of the organic component in organoclay, it is possible to use the organoclay both as a binder and a reinforcing filler in C/C. Also partly due to the organic component in organoclay, it is possible to consolidate organoclay particles by the application of heat and pressure, thereby forming a monolith in the absence of a binder and providing a new low-cost high-temperature structure material. All prior studies of electrochemical devices have focused on the characterization of the behavior of the electrochemical cell, without decoupling the contributions to the cell performance by the various components in the cell. In contrast, a method for characterizing the dielectric and conduction behavior of electrode materials is provided in this dissertation. The impacts of this dissertation pertain to the following. A new class of high-temperature structural material in the form of a nanostructured ceramic-carbon hybrid is provided. In addition, improved carbon-carbon composites are provided through filler incorporation, with the improvement pertaining to the oxidation resistance and the mechanical properties, and with the consequence that the need for expensive densification is reduced. The science of electrochemical electrodes has been advanced by providing a method for characterizing the dielectric and conduction behavior of the electrode materials.