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Thesis (Ph. D.)--University of California, Santa Cruz, 1988. / Typescript. Includes bibliographical references.

Ion exchange of heavy metals with zeolites is important in terms of different application areas. Industrial wastewater treatment and antibacterial applications are two essential areas that have taken great attention. While silver, zinc and copper are well known for their toxicity, they are also used as antibacterial agents in zeolites. The objective of this study is to investigate the single and multicomponent ion exchange behavior of zeolite 4A for silver, zinc, copper and sodium ions. For this purpose Ag+-Na+, Zn2+-Na+, Cu2+-Na+ binary systems and Ag+-Zn2+-Na+, Ag+-Cu2+-Na+, Cu2+-Zn2+-Na+ ternary systems were investigated in batch systems at 25&deg / C and 0.1 N. Binary ion exchange isotherms indicate that zeolite 4A has high selectivity for silver, zinc and copper with respect to sodium. All exchange isotherms lie above the diagonal over the whole range. Using the equilibrium data, the thermodynamic analysis of the binary systems were carried out. The thermodynamic equilibrium constants and the standard free energies of exchange were calculated as 340.9 and -14.5 kJ/mol for silver-sodium system, 40.5 and -4.6 kJ/mol for zinc-sodium system, and 161.2 and -6.3 kJ/mol for copper-sodium system, respectively. From these values, selectivity sequence of zeolite 4A was determined as Ag+ &gt / Cu2+ &gt / Zn2+. This selectivity sequence was also verified by the results of ternary ion exchange experiments. The experimental data were compared with the Langmuir and Freundlich isotherms. While Freundlich model gives a better correlation for Ag+-Na+ and Zn2+-Na+ exchange, Langmuir model represents a better fit to the experimental data of Cu2+-Na+ exchange.

In serial manufacturing processes, localized energy sources (e.g. plasma cutters, arc welders or water jets) induce material geometry transformations that yield a desired product. Simple parameter control of these energy sources does not necessarily ensure an optimal or successful part because of disturbances in the manufacturing process (material and temperature variations, etc). Currently, control in manufacturing is based on statistical process control where large databases for the manufacturing of a fixed process are available and have been compiled over several manufacturing runs. In the absence of a statistical database, and with the increased need for improved monitoring and throughput, there is need for active process control in manufacturing. In this work, Gas Metal Arc Braze-Welding (GMABW) will serve as a test-bed for the implementation of model predictive control (MPC) for a serial manufacturing process. This dissertation investigates the integration of real time modeling of the temperature field with control algorithms to control the evolving temperature field in the ix braze-welded base metal. Fundamental problems involving MPC that are addressed are modeling techniques to calculate temperature fields with reduced computational requirements and control algorithms that utilize the thermal models directly to inform the controller. The dissertation first outlines and compares analytical and computational thermal models and comparison with experimental data are obtained. A thermal model based on a metamodeling approach is used as the plant model for a classical control system and control parameters are found. Various techniques for dealing with signal noise encountered during experimentation are investigated. A proportional controller is implemented in the experimental setup that applies feedback control of the braze –welding process using thermal signals. A novel approach to MPC is explored by using a metamodel as the plant model for the braze-welding process and having the temperature trajectory dictated by the metamodel in the steady state region of the weld. Lastly, future work and extensions of this research are outlined. / text

Depletion in the reserves of fossil fuels, inefficient energy production from these fuels and the negative effect of their usage on atmosphere, and thereby, on human health have accelerated researches on clean energy. Hydrogen produced from ethanol when used in fuel cells not only generates efficient energy but also creates a closed carbon cycle in nature. ZnO and Cu/ZnO catalysts are known with their superior performance in alcohol synthesis. From the principle of microkinetic reversibility they are expected to be superior catalysts for the steam reforming reaction of ethanol as well. ZnO catalysts can be modified by precious, Pd, or non-precious, Cu, metals to enhance hydrogen desorption capability, and dispersed on SiO2 for high surface areas via sol-gel technique. Steam reforming tests over ZnO catalysts revealed that they act only as ethanol dehydrogenation catalysts in the temperature range of 300-500C. Promotion with Pd or Cu decreased hydrogen selectivity due most probably to unreachable closed pores of the catalysts. Autothermal reforming tests over both ZnO/SiO2 and Co/SBA-15 catalysts, on the other hand, gave rise to the formation of several side products.

The chemical speciation of trace metals controls their potential bioavailability and therefore toxicity to exposed organisms. Despite previous studies demonstrating the ameliorative effects of dissolved organic carbon (DOC) on metal toxicity, the effectiveness of ligands from varying sources and of potentially variable composition in controlling speciation has not been studied in detail in estuarine waters. In addition, the effect of DOC on radionuclide contaminants in combination with trace metals has not been investigated in any waters. This is of particular interest in the estuarine environment, where both anthropogenic and natural ligands, and contaminants that pose a potential threat to ecosystem health, can be present. Competitive ligand exchange adsorptive cathodic stripping voltammetry (CLE-AdCSV) with complexation capacity titrations was employed to determine the speciation of dissolved Cu and Zn, two metals that possess revised environmental quality standards (EQS) which now account for potential metal bioavailability. Dissolved metal concentrations in the < 0.4 and < 0.2 μm filter fractions of samples from the Tamar Estuary were determined during seasonal transects made over a calendar year. Samples were taken over a full salinity range (0-35) and from locations thought to contain DOC from a variety of sources (e.g. terrigenous, biogenic, sewage). No seasonal trends in metal speciation were identified, but a semi-quantitative assessment of DOC type using 3-D fluorimetry showed domination of humic and fulvic type ligands in the upper estuary, and biogenic-type ligands in the lower estuary, the former appearing the most important in controlling Cu and Zn complexation. Filter size fraction differences showed a major portion of the dissolved metal is associated with the 0.2 ≥ 0.4 μm fraction, indicating an importance of larger molecule ligands in controlling potentially bioavailable metal. Sample ligand concentrations ([L_x]) ranged from 1-372 nM (Cu) and 3-412 nM (Zn), and metal-ligand conditional stability constants (log K_(ML_x )) from 10.5-13.5 (Cu) and 7.5-10 (Zn), which are similar to reported literature. Calculated free metal ion concentrations ([M2+]) of 0.3 – 109 nM (Zn) and 1.4 x 10-13 – 7.3 x 10-11 M (Cu) compared well (92% showed no significant differences (P = 0.02)) with direct measurements of [Zn2+] made for the first time in estuarine waters using “Absence of Gradients and Nernst Equilibrium Stripping” (AGNES) after optimisation for estuarine waters. AGNES fully complements CLE-AdCSV in terms of analytical capability and shows that methods are now available that are capable of directly determining [Zn2+] in estuarine waters for use in environmental monitoring studies. Calculations made using the chemical equilibrium speciation programme Visual MINTEQ (VM) showed [Cu2+] and [Zn2+] could be predicted to within one order of magnitude of measured values when log K_(ML_x ) and [L_x] are determined and input into the model. This was in contrast to poor agreement between measured and predicted [M2+] when VM was used with the NICA-Donnan complexing model, which assumes a set portion of the total DOC concentration input is fulvic acid that actively complexes metals. These results corroborate a lack of identification of a relationship between metal speciation in the Tamar samples and DOC concentration, highlighting that knowledge of DOC type, log K_(ML_x )and L_x are important when assessing environmental risk, setting EQSs and for accurate modeling of [Cu2+]. Finally, a combined chemical and biological study investigating the effects of mixtures of DOC, Zn and the radionuclide tritium (3H) on the marine mussel presents the first evidence of a protective effect of Zn on DNA damage caused by 3H. The association of 3H with DOC remains elusive and an assessment of DOC type is recommended for future research, but the study emphasises the importance of investigating mixture effects in order to avoid inaccurate risk assessment and potentially costly site remediation.