Thesis (Ph. D.)--Institute of Paper Chemistry, 1969. / Includes bibliographical references (p. 119-122).

This thesis explores the natural forces controlling variability of the tropospheric oxidants on interannual to glacial-interglacial time scales. The oxidants (primarily OH and ozone) determine the lifetime of many trace gases of human interest, including air pollutants and long-lived greenhouse gases such as methane. The oxidants respond to meteorological conditions, precursor emissions (natural and anthropogenic), and surface and overhead stratospheric boundary conditions, all of which have changed since the Last Glacial Maximum (LGM; ~21ka). This dissertation first examines in mechanistic detail the effect of variability in the lightning source of nitrogen oxides \((NO_x)\) precursors on interannual variability (IAV) of the oxidants in the recent past. An optimized technique is presented to constrain the lightning \(NO_x\) source in the GEOS-Chem global chemical transport model (CTM) to time-varying satellite data from the Lightning Imaging Sensor. This constraint improves the ability of the CTM to reproduce observed IAV in 9-year (1998-2006) hindcasts of tropical ozone and OH. IAV in ozone and OH is more sensitive to lightning than to biomass burning, despite greater IAV in \(NO_x\) from the latter source. The sensitivity of OH to lightning reflects positive chemical feedbacks on ozone production, \(HO_x\) recycling, and loss frequencies. This dissertation next introduces an offline-coupled climate-biosphere-chemistry framework for determining oxidant levels at and since the LGM. Detailed simulations of tropospheric composition are performed by GEOS-Chem driven by meteorological fields from the GISS ModelE general circulation model, land cover from the BIOME4-TG global terrestrial equilibrium vegetation model, and fire emissions from the LMfire model. Time slice simulations are presented for the present day, preindustrial, and two different possible representations of the LGM climate. Sensitivity of the results to uncertainty in lightning and biomass burning emissions is tested. Though well-buffered, all simulations find net reduced oxidative capacities relative to the present day. The most important parameters for controlling tropospheric oxidants over glacial-interglacial periods are changes in overhead ozone, tropospheric \(H_2O\), and lightning. The results are discussed in the context of the ice-core record, particularly for methane. / Engineering and Applied Sciences

Over the years, megasonic energy has been widely used in the semiconductor industry for effective particle removal from surfaces after chemical mechanical planarization (CMP) processes. As a sound wave propagates through a liquid medium, it generates two effects, namely, acoustic streaming and acoustic cavitation. Acoustic streaming refers to time independent motion of liquid due to viscous attenuation, while cavitation arises from the bubble activity generated due to the difference in the pressure field of the propagating wave. Cavitation can be classified into two categories, (1) stable and (2) transient cavitation. When a bubble undergoes continuous oscillations over repeated cycles it is known to exhibit stable cavitation, while a sudden collapse is referred to as transient cavitation. Due to the rapid implosion of the transient cavity, drastic conditions of temperature (5,000-10,000 K) and pressure (hundreds of bars) are generated within and surrounding the bubble. If this phenomenon occurs close to the substrate, it causes damage to the sub-micron features. In this study, emphasis has been laid on understanding acoustic cavitation as it is critical to achieving high cleaning efficiency without any feature damage. The research work described in this dissertation has been divided into three sections. In the first part of the dissertation, the development of a novel sono-electrochemical technique for removal of sub-micron (300 nm) silica particles from conductive surfaces (Ta) has been discussed. The technique employs megasonic field at low pulse time and duty cycle in conjunction with an applied electrical field for achieving superior particle removal efficiency (PRE). In order to demonstrate the effectiveness of the sono-electrochemical technique, cleaning studies were conducted using 300 nm silica particles both in the presence and absence of an applied electrical field in air and argon saturated solutions. In the presence of the megasonic field (0.5 W/cm², 10% duty cycle, 5ms pulse time) alone, about 55% PRE was observed in Ar saturated DI water, while in the presence of the sono-electrochemical field (-1.5V vs Ag/AgCl (sat. KCl)), about 80% PRE was measured. The enhancement in particle removal efficiency was attributed to oscillating hydrogen bubbles formed from water reduction in close vicinity of the tantalum surface, that grow to a resonant size under suitable acoustic conditions and likely cause removal of particles. Interestingly, increasing the applied potential to -2V (vs Ag/AgCl (sat. KCl)) enhanced the particle removal efficiency to about 100%. Investigations were also performed in solutions containing 10 mM potassium chloride (KCl). The results revealed that even at low applied potentials of -1.5V, almost complete particle removal was achieved. This improvement in PRE was attributed to a combined effect of microstreaming and electro-acoustic forces. The results revealed that almost complete removal of particles could be achieved at low power density and duty cycle when a sound field at 1 MHz is used in conjunction with electrochemistry. The second study focuses on the effect of acoustic frequency and transducer power density for the development of a damage-free megasonic cleaning process. Here, an effort was made to characterize cavitation activity at acoustic frequencies of 1, 2 and 3 MHz by means of electrochemical, acoustic emission and fluorescence spectroscopy techniques. Studies conducted with a microelectrode using ferricyanide as an electroactive species showed that at 1 MHz and 2 W/cm², current peaks with a rise and fall time of about 30-50 ms and 80-120 ms were observed, respectively, which were indicative of transient cavitation behavior. Interestingly at higher frequencies (3 MHz), symmetric and oscillatory behavior in the current was observed. The rise and fall times were about 3 orders of magnitude lower at about 50 µs. This oscillatory behavior in the current at 3 MHz was attributed to the presence of stable cavities. Furthermore, hydrophone studies supported the microelectrode studies as they showed a reduction of about two orders of magnitude in the intensity of transient cavitation as frequency was increased from 1 to 3 MHz. Hydroxyl radical (OH*) capture measurements using terephthalate dosimetry corroborated the above results as they illustrated an order of magnitude decrease in OH* generation rate at 3 MHz compared to 1 MHz. These studies suggest that the use of higher megasonic frequencies may be more suitable for damage-free and effective cleaning of patterned surfaces in the semiconductor industry. In the last part of the dissertation, we investigate the effect of solution parameters on cavitation characteristics using a bicarbonate based alkaline chemical cleaning formulation that has been previously demonstrated to be beneficial in achieving effective megasonic cleaning and low damage. The results of this study revealed that in the presence of ammonia (NH₃) or carbonate/bicarbonate ions at concentrations greater than 75 mM or 200 mM respectively, the measured rate of generation of hydroxyl radicals at 1 MHz and 2 W/cm² was significantly reduced. The lower rate of OH· was attributed to scavenging of radicals in these solutions and additionally due to reduced transient cavitation in ammonia solutions. Hydroxyl radical measurements at higher power density of 8 W/cm² showed that carbonate ions were better scavengers of hydroxyl radicals than bicarbonate ions. The study on the effect of bulk solution temperature illustrated that the rate of generation of OH· increased with increase in temperature from 10 to 30 °C suggesting enhanced transient cavitation at higher temperatures (in the investigated range). The use of optimum concentration of ammonia or carbonates ions in cleaning formulation and bulk solution temperature would likely provide desired cleaning with minimum damage.

The process of radiation induced corrosion of copper is not well understood. The most obvious situation where the knowledge of this process is crucial is in a deep repository for high level spent nuclear fuel where the fuel will be sealed inside copper canisters. The radiation will penetrate the canisters and be absorbed by the surrounding environment. In this study gamma irradiations of polished and pre-oxidized copper cubes in anoxic pure water, air of 60-100 % RH and in humid argon were performed. The copper surfaces were examined using IRAS, XPS, cathodic reduction, SEM, AFM, and Raman spectroscopy. The concentration of copper in the reaction solutions was measured using ICP-OES.  Also the formation of oxidative species caused by radiation absorption of water was studied by numerical simulations using MAKSIMA software. The corrosion of copper during gamma irradiation vastly exceeds what is expected. The production of oxidative species caused by radiation absorption of water is hundreds of times too low to explain the amount of oxidized copper. A possible explanation for this mismatch is an enhanced radiation chemical yield of HO· on the copper surface. Another one is an increased surface area due to oxidation of copper. One speculation is that HO· interacting with the copper oxide can cause oxidation of the metal. If the thermodynamic driving force is large enough then electrons can be conducted from the metal through the oxide to the oxidant. A dramatic increase in surface area together with an increased interfacial yield of HO· might explain the radiation enhanced corrosion process. / <p>QC 20151022</p>

No description available.

The use of hydroxyl radical based reaction (Fenton reaction) for the destruction of organic pollutants has been widely reported in the literature. However, the low pH requirement and rapid hydrogen peroxide consumption rate make the application of conventional Fenton reaction difficult for in-situ treatment. In this study, we conducted a modified Fenton reaction by introducing a chelating agent into the reaction system that could prevent Fe(OH)3 (s) precipitation even at a neutral pH condition and reduce the H2O2 consumption rate by controlling the Fe2+ concentration. A chelating agent (mono-chelate or poly-chelate) combines with Fe2+ or Fe3+ to form stable metal-chelate complexes in solution. This decreases the concentration of Fe2+ in the solution so that reactions can be carried for longer contact times. Experimental results (citrate was the chelating agent) for 2,4,6-trichlorophenol (TCP) showed that TCP degradations were greater than 95% after 2.5 h and 24 h reaction times at fixed pH 5 and 6, respectively. For the same reaction time, the normalized chloride formations were 85% at pH 5 and 88% at pH 6. Several other chlorinated organic compounds were also chosen as the model compounds for detoxification studies because of their chemical structures: trichloroethylene (unsaturated hydrocarbon), carbon tetrachloride (highly oxidized compound), 2,2-dichlorobiphenyl, and biphenyl (a dual-aromatic ring structure). Poly-chelating agents (such as polyacrylic acid-PAA) provide multiple Fe2+/Fe3+ binding sites in the modified Fenton reaction for the oxidation of contaminants (2,2-dichlorobiphenyl, and biphenyl) at a neutral pH environment. Numerical simulation based on the kinetic model developed from the well known Fenton reaction and iron-chelate chemistry fits experiment data well for both standard and chelate modified Fenton reactions. In this dissertation, it was proven that both monomeric (citrate) and polymeric (PAA) chelate modified Fenton reactions were effective for dechlorination of carbon tetrachloride from aqueous phase by the superoxide radical anion. On the other hand, PAA (a poly-chelating agent) can also be used for solid surface modification by polymerization of acrylic acid (monomer). The successful degradations of biphenyl and trichloroethylene by the PAA functionalized silica particles/membrane demonstrate the versatile applications of the chelate modified Fenton reaction.

Radical chemistry has always been a very active area of research. This is due to the fact that radicals are both very numerous in variety and very reactive. A radical is any chemical species that possesses one or more unpaired electrons. These unpaired electrons usually lead to the extremely reactive characteristics of the chemical species. This reactivity can be beneficial; this is true in the case of polymer chemistry. For instance, some plastics are synthesized through a radical chain reaction. In addition, radicals are used in the synthesis of novel organic compounds with the goal of creating new pharmaceuticals. Radical reactivity can be detrimental as well; radicals have been implicated in a number of ailments including heart disease and cancer. One particular view of cancer cells is that their DNA is somehow mutated; a radical could cause this mutation. In fact, one radical species in particular is known to oxidize DNA, the hydroxyl radical.Unfortunately, the electronic structures of most radicals do not lend themselves to direct study by modem spectroscopic methods. Recently, researchers have discovered that hydroxyl radical, being very reactive in nature, easily complexes with other species. If these complexes are spectrosopically active, then we can study the radical reactivity indirectly through a "reporter" molecule. One such approach uses the transient visible absorbance of the complexes of hydroxyl radical with the thiocyanate anion. In addition, there is other experimental evidence that suggests that thiocyanate anion complexes with other radicals as well. These experiments have been very successful in improving our understanding of radical chemistry, but very little is known about the electronic structure or connectivities of these complexes.Our research is comprised of a systematic theoretical study of the structure, vibrational frequencies, and spectroscopic properties of complexes of hydroxyl radical with thiocyanate anion. In addition, we will investigate the structures, vibrational frequencies, and spectroscopic properties of complexes of thiocyanate anion and other radical species.The ultimate goal of our research is to determine the feasibility of utilizing thiocyanate anion as an LFP reporter for radical species other than hydroxyl radical.Our theoretical approach is based in computerized, mathematical models of the properties of the species being studied, based on quantum mechanics and density functional theory as implemented in the computational chemistry software Gaussian 03. Our study includes calculations that provide the energies, optimized geometry, vibrational frequencies, charge and spin densities, and other properties of the various species. This consists of the various isolated radicals and anions, complexes, transitions states, pre-reactive complexes, and structural isomers. / Department of Chemistry

Aerosols of nitrate solutions were irradiated in the presence of radical scavengers in an attempt to measure the yield of hydroxyl radical in both the aqueous phase and the gas phase. Carbon monoxide, benzoic acid, benzene and cyclohexane were used as scavengers to trap hydroxyl radical. The products from the reaction of these scavengers with hydroxyl radical were analysed with High Performance Liquid Chromatography and mass spectrometry. The radiant flux in the chamber was measured via ferrioxalate actinometry, both with bulk liquid and aerosol droplets. Many quantitative results were obtained but several anomalies were found. This suggests that Mie theory is not capable of predicting rates of photochemical reactions within droplets.

Thesis (Ph.D.)--McMaster University (Canada), 1991. / Source: Dissertation Abstracts International, Volume: 53-01, Section: B, page: 0308. Supervisor: John Warkentin.

Thesis (Ph. D.)--University of California, Riverside, 2009. / Includes abstract. Includes bibliographical references. Issued in print and online. Available via ProQuest Digital Dissertations.