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(1 - 11 of 11)
- Title
- PLASMA PROCESSING FOR RETENTION OF NANOSTRUCTURES.
- Creator
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Venkatachalapathy, Viswanathan, Seal, Sudipta, University of Central Florida
- Abstract / Description
-
Plasma spray processing is a technique that is used extensively in thermal barrier coatings on gas and steam turbine components, biomedical implants and automotive components. Many processing parameters are involved to achieve a coating with certain functionality. The coating could be required to function as thermal barrier, wear resistant, corrosion resistant or a high temperature oxidation resistant coating. Various parameters, such as, nozzle and electrode design, powder feeding system,...
Show morePlasma spray processing is a technique that is used extensively in thermal barrier coatings on gas and steam turbine components, biomedical implants and automotive components. Many processing parameters are involved to achieve a coating with certain functionality. The coating could be required to function as thermal barrier, wear resistant, corrosion resistant or a high temperature oxidation resistant coating. Various parameters, such as, nozzle and electrode design, powder feeding system, spray distances, substrate temperature and roughness, plasma gas flow rates and others can greatly alter the coating quality and resulting performance. Feedstock (powder or solution precursor) composition and morphology are some of the important variables, which can affect the high end coating applications. The amount of heat a plasma plume has to offer to the particles being processed as a coating depends primarily on the dissociation of the atoms of gaseous mixtures being used to create the plasma and the residence time required for the particle to stay in the flame. The parameters that are conducive for nanostructured retention could be found out if the residence time of the particles in the flame and the available heat in the plume for various gas combinations could be predicted. If the feedstock is a liquid precursor instead of a powder feedstock, the heat that has to be offered by the plasma could be increased by suitable gas combination to achieve a good quality coating. Very little information is available with regard to the selection of process parameters and processing of nano materials feedstock to develop nanostructured coatings using plasma spray. In this study, it has been demonstrated that nano ceramics or ceramic composites either in the form of coatings or bulk free form near net components could be processed using DC plasma spray. For powder feedstock, analytical heat transfer calculations could predict the particle states for a given set of parameters by way of heat input from the plasma to the particles. The parameter selection is rendered easier by means of such calculations. Alumina nano ceramic particles are processed as a coating. During Spray drying, a process of consolidation of nano alumina particles to spherical agglomerates, parameter optimization for complete removal of moisture has been achieved. The parameters are tested for alumina nanoparticles with a plasma torch for the veracity of calculations. The amount of heat transfer from the surface of the agglomerates to the core has been quantified as a function of velocity of particles. Since preparation of nanostructured feedstock for plasma spray is expensive and cumbersome, alternative solution precursor route for direct pyrolysis of precursor to coating has been studied in case of nanocrystalline rare earth oxides. Thus, it has also been shown by this research that nanostructured coatings could be either from a powder feedstock or a solution precursor feedstock. MoSi2-Si3N4, Ni-Al2O3, W-HfC nano ceramic composite systems have been processed as a bulk free form nanocomposite with 60-70% retained nanostructures. The importance of selection of substrates, roughness and the substrate temperature for development of free form bulk components has been highlighted. The improvement in mechanical and high temperature properties associated with having such nanostructured coatings or bulk nanocomposites are revealed. These nanostructured coatings are known for their low thermal conductivity, high wear resistance and can be potentially used as steam and gas turbines coatings for improved thermal efficiency. In summary, bulk nanocomposite through plasma spray processing is a viable alternative to conventional processes such as sintering, HIP for high fracture toughness and hardness applications.
Show less - Date Issued
- 2007
- Identifier
- CFE0001680, ucf:47203
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001680
- Title
- COMPARATIVE STUDY OF ETHANOL AND METHANOL ELECTRO-OXIDATION ON A PLATINUM/CERIA COMPOSITE ELECTRODE IN ALKALINE AND ACID SOLUTIONS: ELECTRO-CATALYTIC PERFORMANCE AND REACTION KINETICS.
- Creator
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Hidalgo, Carlos, Diaz, Diego, University of Central Florida
- Abstract / Description
-
A comparative study of the electro-oxidation of ethanol and methanol was carried out on a Pt/ceria composite electrode prepared by electro-deposition. Modification of the Pt electrode was realized by co-deposition from a 1.0 mM K2PtCl6 solution that also contained a 20 mM suspension of ceria. The electro-catalytic activities and stabilities of the Pt/ceria catalyst towards ethanol electro-oxidation reactions (EOR) and methanol electro-oxidation reactions (MOR) were investigated by...
Show moreA comparative study of the electro-oxidation of ethanol and methanol was carried out on a Pt/ceria composite electrode prepared by electro-deposition. Modification of the Pt electrode was realized by co-deposition from a 1.0 mM K2PtCl6 solution that also contained a 20 mM suspension of ceria. The electro-catalytic activities and stabilities of the Pt/ceria catalyst towards ethanol electro-oxidation reactions (EOR) and methanol electro-oxidation reactions (MOR) were investigated by potentiodynamic and potentiostatic methods in 0.5 M sulfuric acid and 1.0 M sodium hydroxide solutions at various concentrations of ethanol and methanol. The kinetics of ethanol and methanol on a Pt/ceria composite electrode were measured in 0.5 M sulfuric acid and 1.0 M sodium hydroxide solutions using a rotating disk electrode (RDE). Cyclic voltammetry was employed in temperatures ranging from 15 to 55°C to provide quantitative and qualitative information on the kinetics of alcohol oxidation. The temperature dependence of the electro-catalytic activities afforded the determination of apparent activation energies for ethanol and methanol oxidation.
Show less - Date Issued
- 2011
- Identifier
- CFE0003628, ucf:48853
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003628
- Title
- Fabrication and Investigation of an enzyme-free, Nanoparticle-based Biosensor for Hydrogen Peroxide determination.
- Creator
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Neal, Craig, Seal, Sudipta, Cho, Hyoung Jin, Florczyk, Stephen, University of Central Florida
- Abstract / Description
-
Electrochemical biosensors often employ enzymes as detection elements. These sensors are highly selective towards target analytes, however the scope of their application is limited by the poor stability of the enzyme. In this study, multi-valent inorganic cerium oxide nanoparticles were used as detection elements for the analysis of hydrogen peroxide. The electrochemical response of the cerium oxide towards hydrogen peroxide analyte is defined through cyclic voltammetry and chronoamperometry....
Show moreElectrochemical biosensors often employ enzymes as detection elements. These sensors are highly selective towards target analytes, however the scope of their application is limited by the poor stability of the enzyme. In this study, multi-valent inorganic cerium oxide nanoparticles were used as detection elements for the analysis of hydrogen peroxide. The electrochemical response of the cerium oxide towards hydrogen peroxide analyte is defined through cyclic voltammetry and chronoamperometry. This response was found to be dependent on nanoparticle Ce3+:Ce4+ redox state ratio and this property is exploited to fabricate a biosensor. As produced, the biosensor demonstrated sensitivity at picomolar analyte concentrations. Further, the sensitivity of the electrode is stable across a range of temperatures and pH's which inhibit the function of standard enzyme-based sensors. Additionally, the produced sensor retained function in sheep serum demonstrating the high selectivity and robustness of the sensor.
Show less - Date Issued
- 2016
- Identifier
- CFE0006362, ucf:51540
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006362
- Title
- DENSITY-FUNCTIONAL THEORY APPLIED TO PROBLEMS IN CATALYSIS AND ELECTROCHEMISTRY.
- Creator
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Kumar, Santosh, Schelling, Patrick, University of Central Florida
- Abstract / Description
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We study the structure and energetics of water molecules adsorbed at ceria (111) surfaces below one monolayer coverage using density-functional theory. The results of this study provide a theoretical framework for interpreting recent experimental results on the redox properties of water at ceria (111) surfaces. In particular, we have computed the structure and energetics of various absorption geometries at stoichiometric ceria (111) surface. In contrast to experiment results, we do not find a...
Show moreWe study the structure and energetics of water molecules adsorbed at ceria (111) surfaces below one monolayer coverage using density-functional theory. The results of this study provide a theoretical framework for interpreting recent experimental results on the redox properties of water at ceria (111) surfaces. In particular, we have computed the structure and energetics of various absorption geometries at stoichiometric ceria (111) surface. In contrast to experiment results, we do not find a strong coverage dependence of the adsorption energy. For the case of reduced surface, our results show that it may not be energetically favorable for water to oxidize oxygen vacancy site at the surface. Instead, oxygen vacancies tend to result in water more strongly binding to the surface. The result of this attractive water-vacancy interaction is that the apparent concentration of oxygen vacancies at the surface is enhanced in the presence of water. Finally, we discuss this problem with reference to recent experimental and theoretical studies of vacancy clustering at the (111) ceria surface. We also describe the simulation results for the structure and dynamics of liquid water using the SIESTA electronic structure approach. We find that the structure of water depends strongly on the particular basis set used. Applying a systematic approach to varying the basis set, we find that the basis set which results in good agreement with experimental binding energies for isolated water dimers also provides a reasonable description of the radial distribution functions of liquid water. We show that the structure of liquid water varies in a systematic fashion with the choice of basis set. Comparable to many other first-principle studies of liquid water using gradient-corrected density functionals, the liquid is found to be somewhat overstructured. The possibility of further improvements through a better choice of the basis set is discussed. We find that while improvements are likely to be possible, application to large-scale systems will require use of a computational algorithm whose computational cost scales linearly with system size. Finally, we study the molecular and atomic adsorption of oxygen on the gold nano-clusters. We show multiple stable and metastable structures for atomically and molecularly adsorbed oxygen to the gold cluster. We plan to predict the reaction pathway and calculate activation energy barrier for desorption of molecular oxygen from the atomically adsorbed gold cluster which is very important for any catalytic reaction occurring using gold nanoparticles.
Show less - Date Issued
- 2006
- Identifier
- CFE0001211, ucf:46938
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001211
- Title
- THE GENERATION AND SCAVENGING OF RADICALS VIA CERIUM AND NANOCERIA.
- Creator
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Heckert, Eric, self, william, University of Central Florida
- Abstract / Description
-
Cerium is the most abundant of the rare earth metals, found on average at a level of 66 parts per million in the earth's crust. The unique redox properties of cerium and cerium oxide nanoparticles have led to its use in a wide variety of industrial and commercial uses such as oxygen sensors, fertilizers and as a catalyst to remove toxic gases in automobile exhaust. The use of cerium has also garnered interest in the nanotechnology field. Nanoceria has been generated in its oxide form as...
Show moreCerium is the most abundant of the rare earth metals, found on average at a level of 66 parts per million in the earth's crust. The unique redox properties of cerium and cerium oxide nanoparticles have led to its use in a wide variety of industrial and commercial uses such as oxygen sensors, fertilizers and as a catalyst to remove toxic gases in automobile exhaust. The use of cerium has also garnered interest in the nanotechnology field. Nanoceria has been generated in its oxide form as nanoparticles and nanorods. Recently, nanoceria has been shown to protect against oxidative stress in both animal and cell culture models. Although not fully understood, this observed protective effect of nanoceria is believed to be the result of recently identified SOD mimetic activity. Currently there is little understanding as to how nanoceria is capable of scavenging radicals or what properties makes nanoceria an effective SOD mimetic. Our data shows strong evidence that the oxidation state of nanoceria is directly related to its reported SOD mimetic activity. As such, future studies of nanoceria should be mindful of the oxidation state of nanoceria preparations as only nanoceria with a high concentration of cerium (III) have shown effective SOD mimetic activity. In addition to the characterization of nanoceria and its SOD mimetic activity, we have evidence that free cerium is capable of generating radicals and damaging DNA in vitro in the presence of hydrogen peroxide. These data strongly suggests that the rare earth inner-transition metal cerium is capable of generating hydroxyl radicals via a Fenton-like reaction. Based on these results the use of free cerium salts should be monitored to limit environmental exposure to cerium. Altogether our data would suggest that cerium by virtue of its unique redox chemistry is quite capable of accepting and donating electrons from its surroundings. In its free form cerium is able to redox cycle easily and can generate radicals. However, paradoxically nanoceria may not easily redox cycle due to the bound lattice structure of the particle. The unique nature of nanoceria and cerium leads to a unique circumstance where nanoceria is a radical scavenger while free cerium generates radicals. As such, further investigation is needed to insure that leeching or cerium from nanoceria does not abrogate any potential benefit nanoceria may provide.
Show less - Date Issued
- 2007
- Identifier
- CFE0001892, ucf:47417
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001892
- Title
- SYNTHESIS OF BIOCOMPATIBLE ANTIOIXIDANT POLYMER COATED CERIUM OXIDE NANOPARTICLES, ITS OXIDASE LIKE BEHAVIOR AND CELLULAR UPTAKE STUDIES.
- Creator
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Asati, Atul, Perez, J Manuel, University of Central Florida
- Abstract / Description
-
Cerium oxide nanoparticles have been widely used for various applications such as catalytic converters for automobile exhaust, ultraviolet absorber, and electrolyte in fuel cells. Most recently, cerium oxide nanoparticles (nanoceria) have been employed as potent free-radical scavengers with neuroprotective, radioprotective, and anti-inflammatory properties. These properties of cerium oxide nanoparticles can open new vistas in medicine and biotechnology. The present study utilizes the water...
Show moreCerium oxide nanoparticles have been widely used for various applications such as catalytic converters for automobile exhaust, ultraviolet absorber, and electrolyte in fuel cells. Most recently, cerium oxide nanoparticles (nanoceria) have been employed as potent free-radical scavengers with neuroprotective, radioprotective, and anti-inflammatory properties. These properties of cerium oxide nanoparticles can open new vistas in medicine and biotechnology. The present study utilizes the water-based-wet-chemical method to synthesize biocompatible,stable and highly monodisperse polymer coated cerium oxide nanoparticles. Polymer coated cerium oxide nanoparticles possess all the characteristics of the uncoated cerium oxide nanoparticles. These nanoparticles were found to be effective as pH-dependent antioxidant giving cytoprotection to normal cell lines against hydrogen peroxide and nitric oxide radical but not to cancer cells. Moreover, cerium oxide nanoparticle also exhibits unique oxidase-like activity at acidic pH oxidizing a series of organic compound without the need of hydrogen peroxide. Based on these results, we have designed an immunoassay in which folate-conjugated cerium oxide nanoparticles provide dual functionality by binding to folate expressing cancer cells and facilitating detection by catalytic oxidation of sensitive colorimetric substrates (dyes). Finally, we have shown that the polymer coated cerium oxide nanoparticles shows distinct toxicity depending upon their subcellular localization based on uptake studies using DiI loaded cerium oxide nanoparticles. In these results, we have found that cerium oxide nanoparticles entrapped into lysosomes are more toxic as opposed to when they are localized in the cytoplasm.Overall we propose that the polymer coated cerium oxide nanoparticles displays selective antioxidant property, oxidase-like activity, and cytotoxicity to biological systems depending upon its pH environment.
Show less - Date Issued
- 2009
- Identifier
- CFE0002924, ucf:47998
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0002924
- Title
- PROBING AND TUNING THE SIZE, MORPHOLOGY, CHEMISTRY AND STRUCTURE OF NANOSCALE CERIUM OXIDE.
- Creator
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Kuchibhatla, Satyanarayana, Seal, Sudipta, University of Central Florida
- Abstract / Description
-
Cerium oxide (ceria)-based materials in the nanoscale regime are of significant fundamental and technological interest. Nanoceria in pure and doped forms has current and potential use in solid oxide fuel cells, catalysis, UV- screening, chemical mechanical planarization, oxygen sensors, and bio-medical applications. The characteristic feature of Ce to switch between the +3 and + 4 oxidation states renders oxygen buffering capability to ceria. The ease of this transformation was expected to be...
Show moreCerium oxide (ceria)-based materials in the nanoscale regime are of significant fundamental and technological interest. Nanoceria in pure and doped forms has current and potential use in solid oxide fuel cells, catalysis, UV- screening, chemical mechanical planarization, oxygen sensors, and bio-medical applications. The characteristic feature of Ce to switch between the +3 and + 4 oxidation states renders oxygen buffering capability to ceria. The ease of this transformation was expected to be enhanced in the nanoceria. In most the practical scenarios, it is necessary to have a stable suspension of ceria nanoparticles (CNPs) over longer periods of time. However, the existing literature is confined to short term studies pertaining to synthesis and property evaluation. Having understood the need for a comprehensive understanding of the CNP suspensions, this dissertation is primarily aimed at understanding the behavior of CNPs in various chemical and physical environments. We have synthesized CNPs in the absence of any surfactants at room temperature and studied the aging characteristics. After gaining some understanding about the behavior of this functional oxide, the synthesis environment and aging temperature were varied, and their affects were carefully analyzed using various materials analysis techniques such as high resolution transmission electron microscopy (HRTEM), UV-Visible spectroscopy (UV-Vis), and X-ray photoelectron spectroscopy (XPS). When the CNPs were aged at room temperature in as-synthesized condition, they were observed to spontaneously assemble and evolve as fractal superoctahedral structures. The reasons for this unique polycrystalline morphology were attributed to the symmetry driven assembly of the individual truncated octahedral and octahedral seed of the ceria. HRTEM and Fast Fourier Transform (FFT) analyses were used to explain the agglomeration behavior and evolution of the octahedral morphology. Some of the observations were supported by molecular dynamic simulations. Poly (ethylene glycol) (PEG) and ethylene glycol (EG) were used to control the kinetics of this morphology evolution. The ability to control the agglomeration of CNPs in these media stems from the lower dielectric constant and an increased viscosity of the EG and PEG based solvents. CNPs when synthesized and aged in frozen conditions, i.e. in ice, were found to form one dimensional, high aspect ratio structures. A careful analysis has provided some evidence that the CNPs use the porous channels in ice as a template and undergo oriented attachment to form nanorods. When the aging treatment was done near freezing temperature in solution, the nanorods were not observed, confirming the role of channels in ice. When synthesized in aqueous media such as DI water, PEG and EG; CNPs were observed to exhibit a reversible oxidation state switching between +3 and +4. Band gap values were computed from the optical absorption data. The changes in the band gap values observed were attributed to the changes in the oxidation state of CNPs as opposed to the quantum confinement effects, as expected in other nanoparticle systems. The work presented in this dissertation demonstrates, with evidence, that in order to obtain a comprehensive understanding of the properties of nanoscale materials it is of paramount importance to monitor their behavior over relatively longer periods of time under various ambient environments. While the solution based techniques offer a versatility and low cost route to study the fundamental properties of nanomaterials, they suffer some inherent problems such as precursor contamination and uncontrolled chemical reactions. Especially when analyzing the behavior of ceria-based materials for applications like solid oxide fuel cells, a great control in the density and crystalline quality are desired. In order to achieve this, as a first step pure ceria thin films were synthesized using oxygen plasma assisted molecular beam epitaxy (OPA-MBE). The ceria films were analyzed using various in situ and ex situ techniques to study the crystal structure, growth mode and epitaxial quality of the films. It was observed that the epitaxial orientation of the ceria films could be tuned by varying the deposition rate. When the films were grown at low deposition rate (< 8 Å/min) ceria films with epitaxial (200) orientation were observed where as the films grown at high deposition rates (up to 30 Å/min) showed (111) orientation. Theoretical simulations were used to confirm some of the experimental facts observed in both nanoparticles and thin films.
Show less - Date Issued
- 2008
- Identifier
- CFE0002163, ucf:47499
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0002163
- Title
- INVESTIGATION OF NANOCERIA-MODIFIED PLATINUM-GOLD COMPOSITE ELECTRODES FOR THE ELECTROCHEMICAL REDUCTION OF OXYGEN IN ALKALINE MEDIA.
- Creator
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Hegishte, Rahul, Diaz, Diego, University of Central Florida
- Abstract / Description
-
Platinum-gold and nanoceria-modified platinum-gold electrodes were prepared on a platinum surface via electrochemical reduction of solutions of platinum and gold salts in the dispersion of nanoceria. The molar ratios of Pt and Au were varied in both PtAu and PtAu/CeO2 electrodes while the total concentration of the metals was maintained at 2 x 10-3M and the concentration of nanoceria was maintained constant at 5 x 10-3M. The electrodes were characterized by their cyclic voltammetry curves in...
Show morePlatinum-gold and nanoceria-modified platinum-gold electrodes were prepared on a platinum surface via electrochemical reduction of solutions of platinum and gold salts in the dispersion of nanoceria. The molar ratios of Pt and Au were varied in both PtAu and PtAu/CeO2 electrodes while the total concentration of the metals was maintained at 2 x 10-3M and the concentration of nanoceria was maintained constant at 5 x 10-3M. The electrodes were characterized by their cyclic voltammetry curves in 0.5M sulfuric acid solution. The electrochemically active area of the electrodes was determined using the copper underpotential deposition method. The linear sweep voltammograms of the PtAu and PtAu/CeO2 electrodes were plotted from -1V to 0V vs. Ag/AgCl, 3M KCl reference electrode using the rotating disk electrodes for the rotation speeds from 200 to 3600rpm in an oxygen saturated 0.1M sodium hydroxide solution. The values of the kinetic controlled current density were determined from the rotating disk voltammetry. The values of the limiting current density for each rotation speed were used to plot the Koutecky-Levich plots for the electrodes. The rate constants were obtained from the Koutecky-Levich plots for each composition of the electrode. The values of kinetic current density and the rate constants indicated that the addition of Au enhances the ORR rates in both the PtAu and the PtAu/CeO2 electrodes. The values of the kinetic current densities of the PtAu/CeO2 were lower than that of the PtAu electrodes owing to the poor electrical conductivity of ceria. The Koutecky-Levich plots for the PtAu and the PtAu/CeO2 electrodes are linear for the four-electron reduction of oxygen in the alkaline media, which indicates that the overall reaction follows the first order kinetics. The electron transfer rate constants obtained from the Koutecky-Levich plots for the PtAu and the PtAu/CeO2 electrodes both were found to increase in values with the addition of Au. The Tafel plots were plotted for the PtAu and PtAu/CeO2 electrodes and the values of Tafel slopes were found to be in a small range for lower amounts of Au which indicated that the ORR rates were enhanced in lower amounts of Au. The values of Tafel slopes were found to be much higher for the ceria-modified PtAu electrodes as compared to the PtAu electrodes, which indicate the lower rates of ORR after the modification with ceria. Also, the ORR rates for the electrodes with smaller amounts of Au in PtAu/CeO2 were higher than those in the larger amounts of Au.
Show less - Date Issued
- 2011
- Identifier
- CFE0003639, ucf:48860
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003639
- Title
- Development of Novel Redox Sensors and Processes Towards Biological Applications.
- Creator
-
Patel, Jigna, Yestrebsky, Cherie, Clausen, Christian, Hampton, Michael, Harper, James, Diaz, Diego, University of Central Florida
- Abstract / Description
-
Research on the cure and early detection of diseases such as diabetes, Alzheimer's, and Parkinson's is becoming of great interest due to the increasing number of people affected by them every year. An accurate and quick detection of various damaging species is highly critical in treatments of such diseases not only for exploring possible cures but also for early detection. If these diseases are detected during the initial stages than the possibility of curing them is much higher. Motivated by...
Show moreResearch on the cure and early detection of diseases such as diabetes, Alzheimer's, and Parkinson's is becoming of great interest due to the increasing number of people affected by them every year. An accurate and quick detection of various damaging species is highly critical in treatments of such diseases not only for exploring possible cures but also for early detection. If these diseases are detected during the initial stages than the possibility of curing them is much higher. Motivated by this, many researchers today have developed numerous types of sensing devices that can detect various physiological and biological compounds. However, most of these sensors are enzyme based. They have several setbacks such as the lack of sensitivity, restricted selectivity, short shelf life, and biological fouling. To overcome these obstacles, we examine the use of nanoceria modified Pt and Au electrodes for the detection of glucose and reactive oxygen species such as hydrogen peroxide. Amperometric detection of glucose and hydrogen peroxide is critical for biological applications for diabetes and possible Alzheimer's and Parkinson's patients. This dissertation focuses on the exploration of non-enzymatic detection of glucose and reactive oxygen species which has the prospective to be used for biological applications, in addition to an investigation of an odor control technology that uses these reactive oxygen species for the treatment of wastewater plants. The combination of bi-metallic composites with nanoceria showed increased oxidation ability towards glucose and hydrogen peroxide. The following dissertation expands on the relationship between bi-metallic nanoceria composite materials and its electro-oxidation of glucose and hydrogen peroxide towards biological sensing along with an investigation of an odor control technology that utilizes generates hydroxyl radical fine particle mist for the degradation of hydrogen sulfide odor in wastewater treatment plants.
Show less - Date Issued
- 2013
- Identifier
- CFE0005227, ucf:50585
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005227
- Title
- Scandia and ceria stabilized zirconia based electrolytes and anodes for intermediate temperature solid oxide fuel cells: Manufacturing and properties.
- Creator
-
Chen, Yan, Orlovskaya, Nina, An, Linan, Chen, Quanfang, Sohn, Yongho, Raghavan, Seetha, Huang, Xinyu, University of Central Florida
- Abstract / Description
-
Scandia and ceria stabilized zirconia (10 mol% Sc2O3 (-) 1 mol% CeO2 (-) ZrO2, SCSZ) has superior ionic conductivity in the intermediate temperature range for the operation of solid oxide fuel cells, but it does not exhibit good phase stability in comparison with yttria stabilized zirconia (8 mol% Y2O3 (-) ZrO2, YSZ). To maintain high ionic conductivity and improve the stability of the electrolyte, layered structures with YSZ outer layers and SCSZ inner layers were designed, along with the...
Show moreScandia and ceria stabilized zirconia (10 mol% Sc2O3 (-) 1 mol% CeO2 (-) ZrO2, SCSZ) has superior ionic conductivity in the intermediate temperature range for the operation of solid oxide fuel cells, but it does not exhibit good phase stability in comparison with yttria stabilized zirconia (8 mol% Y2O3 (-) ZrO2, YSZ). To maintain high ionic conductivity and improve the stability of the electrolyte, layered structures with YSZ outer layers and SCSZ inner layers were designed, along with the referential electrolytes containing pure SCSZ or YSZ. The electrolytes were manufactured by tape casting, laminating, and pressureless sintering techniques. After sintering, while the thickness of YSZ outer layers remained constant at ~30 ?m, the thickness of inner layers of SCSZ for the 3-, 4- and 6-layer designs varied at ~30, ~60 and ~120 ?m, respectively. Selected characterizations were employed to study the structure, morphology, impurity content and the density of the electrolytes. Furthermore, in situ X-ray diffraction, neutron diffraction and Raman scattering were carried out to study the phase transition and lattice distortion during long-term annealing at 350 (&)deg;C and 275 (&)deg;C for SCSZ and YSZ, respectively, where the dynamic damping occurred when Young's modulus was measured.In YSZ/SCSZ electrolytes, thermal residual stresses and strains were generated due to the mismatch of coefficients of thermal expansion from each layer of different compositions. They could be adjusted by varying the thickness ratios of each layer in different designs of laminates. The theoretical residual stresses have been calculated for different thickness ratios. The effect of thermal residual stress on the biaxial flexural strength was studied in layered electrolytes. The biaxial flexure tests of electrolytes with various layered designs were performed using a ring-on-ring method at both room temperature and 800 (&)deg;C. The maximum principal stress during fracture indicated an increase of flexural strength in the electrolytes with layered structure at both temperatures in comparison with the electrolytes without compositional gradient. Such an increase of strength is the result of the existence of residual compressive stresses in the outer YSZ layer. In addition, Weibull statistics of the strength values were built for the layered electrolytes tested at room temperature, and the effect of thermal residual stresses on Weibull distribution was established. The calculation of residual stress present at the outer layers was verified. The high ionic conductivity was maintained with layered electrolyte designs in the intermediate temperature range. It was also established that the ionic conductivity of layered electrolytes exhibited 7% (-) 11% improvement at 800 (&)deg;C due to the stress/strain effects, and the largest improvements in a certain electrolyte was found to nearly coincide with the largest residual compressive strain in the outer YSZ layer.In addition to the study of layered electrolytes, mechanical properties of porous Ni/SCSZ cermet were studied. The anode materials were reduced by 65 wt% NiO (-) 35 wt% SCSZ (N65) and 50 wt% NiO (-) 50 wt% SCSZ (N50) porous ceramics in the forming gas. Young's modulus as well as strength and fracture toughness of non-reduced and reduced anodes has been measured, both at room and high temperatures. High temperature experiments were performed in the reducing environment of forming gas. It was shown that while at 700 (&)deg;C and 800 (&)deg;C the anode specimens exhibited purely brittle deformation, a brittle-to-ductile transition occurred at 800 (-) 900 (&)deg;C, and the anode deformed plastically at 900 (&)deg;C. Fractography of the anode specimens were studied to identify the fracture modes of the anodes tested at different temperatures.
Show less - Date Issued
- 2013
- Identifier
- CFE0005090, ucf:50750
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005090
- Title
- The Behavior of Cerium Oxide Nanoparticles in Polymer Electrolyte Membranes in Ex-Situ and In-Situ Fuel Cell Durability Tests.
- Creator
-
Pearman, Benjamin, Hampton, Michael, Blair, Richard, Clausen, Christian, Seal, Sudipta, Campiglia, Andres, Yestrebsky, Cherie, Mohajeri, Nahid, University of Central Florida
- Abstract / Description
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Fuel cells are known for their high efficiency and have the potential to become a major technology for producing clean energy, especially when the fuel, e.g. hydrogen, is produced from renewable energy sources such as wind or solar. Currently, the two main obstacles to wide-spread commercialization are their high cost and the short operational lifetime of certain components.Polymer electrolyte membrane (PEM) fuel cells have been a focus of attention in recent years, due to their use of...
Show moreFuel cells are known for their high efficiency and have the potential to become a major technology for producing clean energy, especially when the fuel, e.g. hydrogen, is produced from renewable energy sources such as wind or solar. Currently, the two main obstacles to wide-spread commercialization are their high cost and the short operational lifetime of certain components.Polymer electrolyte membrane (PEM) fuel cells have been a focus of attention in recent years, due to their use of hydrogen as a fuel, their comparatively low operating temperature and flexibility for use in both stationary and portable (automotive) applications.Perfluorosulfonic acid membranes are the leading ionomers for use in PEM hydrogen fuel cells. They combine essential qualities, such as high mechanical and thermal stability, with high proton conductivity. However, they are expensive and currently show insufficient chemical stability towards radicals formed during fuel cell operation, resulting in degradation that leads to premature failure. The incorporation of durability improving additives into perfluorosulfonic acid membranes is discussed in this work.Cerium oxide (ceria) is a well-known radical scavenger that has been used in the biological and medical field. It is able to quench radicals by facilely switching between its Ce(III) and Ce(IV) oxidation states.In this work, cerium oxide nanoparticles were added to perfluorosulfonic acid membranes and subjected to ex-situ and in-situ accelerated durability tests.The two ceria formulations, an in-house synthesized and commercially available material, were found to consist of crystalline particles of 2 (-) 5 nm and 20 (-) 150 nm size, respectively, that did not change size or shape when incorporated into the membranes.At higher temperature and relative humidity in gas flowing conditions, ceria in membranes is found to be reduced to its ionic form by virtue of the acidic environment. In ex-situ Fenton testing, the inclusion of ceria into membranes reduced the emission of fluoride, a strong indicator of degradation, by an order of magnitude with both liquid and gaseous hydrogen peroxide. In open-circuit voltage (OCV) hold fuel cell testing, ceria improved durability, as measured by several parameters such as OCV decay rate, fluoride emission and cell performance, over several hundred hours and influenced the formation of the platinum band typically found after durability testing.
Show less - Date Issued
- 2012
- Identifier
- CFE0004789, ucf:49731
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004789
