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Thesis (Ph.D.)--Lehigh University, 2009. / Adviser: Hugo Caram.

Particle size distribution (PSD) plays a key role in fluidization behavior. The effect of PSD in fluidized, gas-solid mixtures is elucidated by considering two types of bimodal particle mixtures. In the first case, a mixture of "large" particles, which engage in particle-particle collisions, and "small" particles or fines, which follow the fluid streamlines, are considered. In this case, one net effect of the fines is to decrease the pressure drop required to convey a given solids flux in a riser. In the second case, a mixture of two sizes of larger particles in which collisions between like and unlike particles occur are considered. In this case, a reduction in particle phase stress in the bimodal mixture as compared to a monosized particle mixture with the same mean particle diameter is predicted. For dilute flow, this stress reduction is minimal but increases in significance as the suspension becomes more concentrated.

As semiconductor devices get faster and more compact, the equivalent gate dielectric thickness is reduced aggressively. This makes them highly sensitive to contamination. Contamination from organics can degrade the performance of ultra-thin silicon oxide gate dielectric films used in current generation devices. The current understanding of how organic contaminants cause defects in gate oxides is limited. The objective of this research is to perform a fundamental investigation of the kinetics and mechanisms of the interactions of organic contaminants on silicon wafers during thermal oxidation for the growth of ultra-thin gate oxide. The role of moisture, a universal contaminant, in attracting organic impurities is also studied. The adsorption properties of butyl hydroxy toluene (BHT) and isopropyl alcohol (IPA), representing high and low-molecular weight polar organic compounds respectively, on wafer surfaces were characterized. A new experimental system that allowed pre-gate oxidation cleaning of silicon wafers, controlled exposure to organic contaminants and thermal oxidation was developed. A method based on catalytic oxidation of organics was also developed for detection of the kinetics of outgassing of organic contaminants during thermal oxidation. Gate oxide quality was determined by a combination of surface and electrical analytical techniques such as Auger depth profiling, Tunneling Atomic Force Microscopy and Gate Oxide Integrity. Processing conditions such as the type of pre-gate oxidation cleaning, the ambient used for ramp-up to the oxidation temperature, the ramp rates as well as the nature of the organic molecule were found to be important factors affecting the quality of ultra-thin gate oxides. Theoretical models were proposed to determine the kinetic constants and activation energies governing the interactions of contaminants on wafer surfaces under various conditions. Air-borne molecular contamination can be expected to cause similar problems for high-k gate dielectrics expected to replace silicon oxide. The energetics and kinetics of the adsorption of trace-level moisture and organic contaminants on zirconium oxide, a promising high-k candidate, were investigated and compared with that on silicon oxide. Zirconium oxide was found to have a much greater attraction for moisture as well as polar organic impurities. This can be a concern for its adaptation as the gate dielectric.

The objective of this work was to provide a solution to the problem of toxic metal emissions from high temperature combustion processes. Multi-metal as well as single-metal interactions were investigated to provide an understanding of mechanisms that exist in industrial furnaces, where multiple metals are present. Specifically, multiple toxic metals, lead and cadmium, and a common non-toxic metal, sodium, were investigated. Sodium capture by kaolinite was found to exhibit a negative activation energy (between 1100 and 1300°C) similar to that shown previously for lead, due to a catastrophic deactivating melt initiated by the metal oxide/kaolinite reaction product. In addition, an overall sodium/kaolinite reaction rate (soluble + insoluble) was determined. It was also discovered that a larger percentage of sodium/kaolinite reaction product was water soluble when formed at lower equivalence ratios than at high equivalence ratios. The majority of the initially formed sodium/kaolinite reaction products were probably insoluble sodium aluminosilicates. However, at high sorbent utilizations (low equivalence ratios), the meta-kaolinite structure probably broke down to form sodium silicates and aluminates, thus enabling at least twice as much sodium capture as the sodium aluminosilicate products. The cadmium/kaolinite reaction rate was highly activated between 1100°C and 1300°C, due to a self-enhancing melt, which occurred at the high but not low temperature condition. For the Cd/Pb multi-metal system, cadmium capture was enhanced by a melt initiated by the lead/kaolinite reaction product. Also, cadmium enhanced lead capture by reducing the extent of catastrophic melt caused by the lead/kaolinite product. The formation of an optimum eutectic melt accounts for the enhancement of total bimetal capture by kaolinite at high and low temperatures (1100°C to 1300°C). Sodium capture by kaolinite completely dominated over lead capture from a bimetal system. On the other hand, sodium was found to behave similar to lead in terms of enhancing cadmium capture by kaolinite at the low temperature condition. In addition to kaolinite, hydrated lime was found to be effective at capturing cadmium, and CDEM sorbent, composed of calcium carbonate, lime, and kaolinite, was effective at capturing cadmium and a mixture of cadmium and lead.