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No description available.

Carbon nanotubes have received considerable attention since their discovery due to their novel properties. They have potential application areas in physics, chemistry and biology. Arc discharge, laser furnace, chemical vapor deposition and floating catalyst methods are the most commonly used methods to produce carbon nanotubes. Although carbon nanotubes have superior properties compared to other materials, they could not be used widely. The main reasons of this are that continuous and large scale production of carbon nanotubes could not be achieved and impurities have to be removed. To solve these problems more information about formation of carbon nanotubes has to be known. In this study concentration profiles of reactant and byproducts in a cylindrical reactor are investigated during carbon nanotube production. A special probe to collect gas samples along the reactor and samples loops to store the gas samples were designed and constructed. Gas samples were analyzed one by one in GC/MS. Experiments were done with and without catalyst at same experimental conditions. Thus, effects of catalyst on concentration profiles of chemicals were analyzed. To produce carbon nanotubes more acetylene was used compared to amount of acetylene used in pyrolysis. Increasing reaction temperature from 800&deg / C to 875&deg / C caused decomposing more acetylene and producing more carbon nanotubes. It is believed that data accumulation on the reactions involved in the gas phase will lead to large scale production and lower product costs with a large catalyst surface to be produced in the reactor.

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No description available.

The transport in oxides is studied by the use of gas phase analysis (GPA). An experimental method to identify transported species of gases and their contribution to the overall transport of gases in oxides and an experimental method to evaluate the parameters diffusivity, concentration, permeability of gases in oxides and effective pore size in oxides are developed, respectively. Pt has two effects on the thermal oxidation of metals. One is to enhance the oxidation of metals which takes place at the oxide-metal interface by promoting a high concentration gradient of dissociated oxygen across the oxide layer. The other effect is to suppress the oxidation of metals by decreasing the contact area between metal and oxygen. The overall effect of Pt on the oxidation of metals depends on the mechanism of oxide growth in the absence of Pt. It is suggested that an appropriate amount of Pt coating induces a balanced oxide growth resulting from stoichimetrical inward oxygen flux to outward metal flux, which leads to a reduced oxidation rate. The diffusion of diatomic gases in oxides such as vitreous silica and yttria stabilized zirconia (YSZ) takes place in both molecular and dissociated (atomic or/and ionic) form. The fraction of transport of molecular species decreases with temperatures, and the fraction of transport of dissociated species increases with temperatures. Measured permeabilities of diatomic gases in vitreous silica are higher than the expected permeabilities of their molecules, which are explained by diffusion of molecules combined with a retardation of dissociated species in reversible traps. The diffusion of hydrogen in vitreous silica is concentration dependent and increases with local concentration. Transport paths are shared among transported species and gases at all temperatures in YSZ. Helium shares transport path with molecular oxygen and nitrogen at low temperatures; whereas helium shares transport path with dissociated oxygen and also dissociated nitrogen at high temperatures. / QC 20100705