<p>The local corrosion of refractories at the slag/gas interface is a serious problem that limits the life of the refractories.Although, there have been several studies focused on understanding the Marangoni effect on the refractory dissolution process, there is little quantifiable analysis available. The aim of this study is to establish a better fundamental understanding of refractory dissolution mechanisms, and develop appropriate models for predicting the extent and rate of slag-line dissolution.</p> <p>In the first part of this research, experimental studies using a high temperature dip technique were performed: MgO refractory in SiO₂-CaO-FeO_x-MgO slag and Al₂O₃- SiO₂-CaO-FeO_x-MgO. The experiments were conducted at varies temperature. There was significant evidence of a spinel phase formed at the slag/refractory interface for slags containing 20wt.% Al₂O₃. This existence of the spinel seems to have retarded the dissolution of the refractory. The decrease in erosion rate in the presence of spinel is in proportion to the decrease in the equilibrium MgO concentration at the slag/solid interface. The activation energy is calculated from the relationship of effective mass transfer coefficient vs. temperature and found in the range of mass transfer activation energy.</p> <p>The second part of this search is developing a numerical model to predict the slag-line dissolution. An effective algorithm for analysis of unsteady Marangoni convection in refractory slag line dissolution has been developed. The results show that the Marangoni effect plays a very important role in slag-line erosion at this condition; both the moving boundary condition and curved surface condition have significant effects on the slag-line erosion rate. The comparison of experimental and numerical results shows that the model can predict the refractory maximum corrosion distance caused by Marangoni flow at the slag line. However, the eroded material volume was predicted within 20~30% deviation</p> / Doctor of Philosophy (PhD)

<p>Solidification of Nb-microalloyed HSLA steels may result in the precipitation of niobium carbonitrides, which is hardly surprising in view of their extreme thermodynamic stability. Recently, it was proposed in literature that coarse Nb-rich particles found along the centerline of continuously cast HSLA steels originated from ferroniobium additions during ladle metallurgy. In particular, it was hypothesized that thermally stable phases formed during manufacturing of ferroniobium were released into the melt once the ferroniobium had partially fused. In this contribution, Scheil–Gulliver formalism is employed to predict the phase portrait of ferroniobium in an attempt to simulate the manufacturing process of ferroniobium.</p> <p>To corroborate the predictions, the microstructure of ferroniobium is characterized to determine if thermally stable particles exist in ferroniobium. Further, a model is developed to predict the dissolution rate of thermally stable phases that were observed in ferroniobium as well as in the centerline region of as-cast HSLA steel. Finally, a sample near the centreline region of a Nb-microalloyed HSLA steel is characterized and centreline compositions are measured. Based on experimental evidences, an alternative explanation to the origin of thermally stable particles found near the centreline of HSLA steels is proposed.</p> / Master of Materials Science and Engineering (MMatSE)

Dealloying is a corrosion process in which one or more elements are selectively removed from an alloy leading to a 3-dimensional porous structure of the more noble element(s). These porous structures have been known to cause stress corrosion cracking in noble metal alloy systems but more recent interest in using the corrosion process to produce porous metals has developed. Applications for these structures range from high surface area electrodes for biomedical sensors to use as skeletal structures for fundamental studies (e.g. low temperature heat exchangers or sensitivity of surface diffusivity to chemical environment). In this work we will review our current understanding of alloy corrosion including our most recent results demonstrating a more accurate method for calculating alloy critical potential based on potential hold experiments. The critical potentials calculated through the potential hold method were â 0.030VMSE, 0.110VMSE, and 0.175VMSE for Cu80Pt20, Cu75Pt25 Cu71Pt29 respectively. We will present the use of porous metals for making surface diffusivity measurements in the Pt systems as a function of chemical environment. A review of the use of small angle neutron scattering to make accurate measurements of pore size is presented and the sensitivity of pore size to electrolyte, electrolyte composition, applied potential and temperature will be explained. The production of porous Pt with pore sizes ranging from 2-200nm is demonstrated. / Ph. D.

Slags are crystalline to vitreous by-product materials generated in many high temperature industrial processes. This study presents a general technique for the identification of the phases present in petroleum coke gasification slags. documents the phase assemblages and textures, and finally determines the dissolution of vanadium from these slags as part of the considerations of potential resource reclamation. The general identification procedure utilizes (1) recognition of separate phases using optical microscopy and scanning electron microscopy; (2) electron probe microanalysis (EPM) of chemical compositions of individual phases; (3) statistical analysis of the EPM data to eliminate spurious data; (4) estimation of valence states of transition metals using thermodynamic and computational methods; (5) derivation of chemical formulae for the phases using computational methods and chemistry of ionic substitutions; (6) verification of phase identity using X-ray diffraction analysis. More than twenty phases were determined in petroleum coke slags including oxides, silicates. vanadates, sulfate. sulfides and alloys. The reduced slags are rich in V₂>0₃ with silicates and minor amounts of sulfides and native metals whereas the oxidized slags are composed of V₂>0₄, nickel aluminum spinels. various vanadates and glass. Textural analysis provided information on the crystallization process, reaction with gasifier refractory lining materials, sulfide exsolution processes, glass devitrification. and the development of chemical zonation in some spinels. This information offers some perspectives on the potential of resource reclamation. Resource reclamation for petroleum coke slags is best assessed with a knowledge of phases, phase assemblages, textures and dissolution behavior of the material. The dissolution of vanadium. the most significant element. was examined using long term dissolution experiments. These demonstrate that vanadium concentrations are pH dependent ranging from 1500 ppm to 5000 ppm with a minimum concentration near pH 6. Vanadium dissolution rates range from L28xlO⁴ mol m² sec⁻¹ to 3.08xlO^-6 mol m² sec⁻¹. In view of the strategic nature of vanadium and the fact that the concentration of vanadium in slags is almost two orders of magnitude higher than the current mining grades, petroleum coke slags offer significant potential to serve as resources for vanadium. / Ph. D.

Silver nanoparticles (nanosilver) are gaining significant attention from the academic and regulatory communities, not only because of their antimicrobial effects and subsequent product applications, but also because of their potential health and environmental impacts. Although some human health effects of silver nanoparticles have been reported, realistic exposure levels from the use of consumer products are still largely unknown. The objective of this work was to characterize the release of silver and silver- containing particles during the normal use of silver nanotechnology consumer products. Specific objectives were to review the environmental and human health risks of airborne, engineered nanoparticles, to characterize aerosol emissions from nanosilver spray products, and to characterize nanosilver that may be released from childrenʼs consumer products under conditions of normal use. We identified possible routes of aerosolization of nanosilver from the production, use, and disposal of consumer products and estimated that about 14% of silver nanotechnology products that have been inventoried could potentially release silver particles into the air during use. The spray products investigated emitted 0.24 – 56 ng of silver in aerosols per spray action, and the plurality of aerosols were 1 – 2.5 μm in diameter, easily inhaled, for two products. Both the products' liquid characteristics and the bottles' spraying mechanisms played roles in determining the aerosol size distributions, but the size of silver-containing aerosols was largely independent of the liquid phase size distributions. We compiled an inventory of 82 children's consumer products that claim to contain nanosilver, of which 13 products were examined for presence of silver and tested for release of silver into liquid media and air, and onto skin. All products contained some form of silver, but silver-containing particles were observed in only four products, with sizes ranging from nanoscale up to 10 μm in size. Silver leached preferably into synthetic biological media with higher chloride concentrations, such as sweat and urine. We determined that levels of silver to which children would be exposed during normal use of these products are likely to be low, and bioavailable silver is expected to be in ionic rather than particulate form. / Ph. D.

A brief investigation was made of various enzymes such as urease in conjunction with a wetting agent, ficin, steapsin, and hyaluronidase as aides in the :in vitro" dissolution of calculi in "G"⁷ solution. This investigation indicated that a more effective solvent was needed. / Master of Science

Quercetin is a flavonol with potential health benefits including activities against cardiovascular disease, obesity, and oxidative stress. However, the benefits of quercetin are likely limited by poor bioavailability, primarily attributed to its poor aqueous solubility (due to its hydrophobicity and crystallinity) and extensive phase-II metabolism. Improving the apparent solubility of quercetin has the potential to improve its in vivo bioavailability. Strategies to increase solution concentrations in the small intestinal lumen have the potential to substantially increase quercetin bioavailability, and efficacy. We aimed to achieve this by incorporating quercetin into amorphous solid dispersions (ASDs) with cellulose derivatives, eliminating crystallinity, and selectively releasing amorphous quercetin under simulated intestinal conditions (pH 6.8, 37C). Amorphous quercetin was dispersed in cellulose esters including 6-carboxycellulose acetate butyrate (CCAB), hydroxypropylmethylcellulose acetate succinate (HPMCAS) and cellulose acetate suberate (CASub) to achieve stability and provide pH-triggered release. In addition, polyvinylpyrrolidone (PVP) containing CASub and CCAB blends were prepared to further promote enhanced dissolution. The ASD employing 10% quercetin in 20% PVP:70% CASub was most successful at enhancing the solution concentration of quercetin, providing an 18-fold increase in the area under the concentration/time curve (AUC) compared to quercetin alone. These results warrant in vivo assessment of quercetin-loaded ASDs formulated with CASub and its blend with PVP towards improving the bioavailability of quercetin. / Master of Science in Life Sciences

Reinforced concrete exposed to chlorides is subject to rapid deterioration once the concentration of the chloride ion in the concrete reaches a critical level to cause corrosion of the reinforcing steel. The chloride ion diffuses through concrete according to Fick's Law, which is a function of time, a driving concentration, and a diffusion constant. The diffusion constant varies with temperature and the variety of concrete . The research included determination of diffusion constants for six types of concretes after 8 weeks and 16 weeks of ponding with an NaC1 solution. In addition, one set of these samples was subjected to the outside environment while the other was indoors under controlled conditions. The mixes included water to cement ratios of 0.35, 0.40, 0.45, and 0.50, and two water to cement ratios of 0.45 with 15% cement replacement with pozblan admixtures (silica fume and type'F flY ash). Thus, the effects of temperature, water to cement ratio, and pozzolanic admixtures in regard to the diffusion constant for concrete were found. The method by,which a diffusion constant was found is as 1)X3% solution of-NaC1 is ponded on top of a four inch thick 'specimen of concrete. 2) Powder samples of the paste are taken at specified time at depths of -0.5, 1.0 1,:5, and 2-.5 inches. 3) These samples are analyzed for chloride content by potentiometric titration. 4) The data is fit to Fick's Law by nonlinear regression and an effective diffusion constant determined. / Master of Science

The efficacy of rifapentine, an oral antibiotic used in the treatment of tuberculosis, is reduced due to its degradation at gastric pH and low solubility at intestinal pH. We aimed to improve delivery properties in vitro by incorporating rifapentine into pH-responsive amorphous solid dispersions with cellulose derivatives including: hydroxypropylmethylcellulose acetate succinate (HPMCAS), cellulose acetate suberate (CASub), and 5-carboxypentyl hydroxypropyl cellulose (CHC). Most amorphous solid dispersions reduced rifapentine release at gastric pH, with the best performing polymer CASub showing >31-fold decrease in area under the curve compared to rifapentine alone. Lower solubility at gastric conditions was accompanied by a reduction in the acidic degradation product 3-formylrifamycin, as compared to rifapentine alone. Certain formulations also showed enhanced apparent solubility and stabilization of supersaturated solutions at intestinal pH, with the best performing polymer HPMCAS showing almost a 4-fold increase in total area under the curve compared to rifapentine alone. These in vitro results suggest that delivery of rifapentine via amorphous solid dispersion with cellulose polymers may improve bioavailability in vivo. / Master of Science in Life Sciences

No / A laboratory-based experiment was carried out to examine the dissolution characteristics of testate amoebae (Protozoa: Rhizopoda) under acidic conditions. The results suggest a large degree of variability in the dissolution susceptibility of taxa and no straightforward distinction between the relative robustness of xenosomic and idiosomic test types. Individuals from the genus Euglypha have tests composed of thin-walled siliceous plates, which are prone to severe dissolution. Certain other taxa are relatively unaffected by low pH conditions, including Assulina muscorum, Amphitrema flavum and Trigonopyxis arcula type. Differential preservation of subfossil testate amoebae must be acknowledged as a particular problem for peat-based palaeoclimate studies.