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Full-Text Articles in Chemical Engineering

Feasibility Of Cathodic Protection In Grouted Post Tensioned Tendons - Exploratory Model Calculations, Jacob Dharma Bumgardner Nov 2015

Feasibility Of Cathodic Protection In Grouted Post Tensioned Tendons - Exploratory Model Calculations, Jacob Dharma Bumgardner

USF Tampa Graduate Theses and Dissertations

Recent corrosion related failures of grouted post tensioned tendons, even after the introduction of improved grouts, have led to renewed interest in supplemental or backup means of corrosion control for these systems. A finite element model is presented to explore feasibility of impressed current cathodic protection of strand in grouted tendons. The model examines polarization evolution as function of service time and includes consideration of anode placement and size, grout porosity, pore water alkalinity, electrochemical species diffusivity and applied voltage on the polarization efficacy and durability of such a system. The exploratory model projections suggested that, within the context of …


An Improved Dynamic Particle Packing Model For Prediction Of The Microstructure In Porous Electrodes, Chien-Wei Chao Sep 2015

An Improved Dynamic Particle Packing Model For Prediction Of The Microstructure In Porous Electrodes, Chien-Wei Chao

Theses and Dissertations

The goal of this work is to develop a model to predict the microstructure of Li-ion batteries, specifically focusing on the cathode component of the batteries. This kind of model has the potential to assist researchers and battery manufacturers who are trying to optimize the capacity, cycle life, and safety of batteries. Two dynamic particle packing (DPP) microstructure models were developed in this work. The first is the DPP1 model, which simulates the final or dried electrode structure by moving spherical particles under periodic boundaries using Newton's laws of motion. The experience derived from developing DPP1 model was beneficial in …


Tin Nanoparticles Encapsulated In Hollow Tio2 Spheres As High Performance Anode Materials For Li-Ion Batteries, Xiang Pan Aug 2015

Tin Nanoparticles Encapsulated In Hollow Tio2 Spheres As High Performance Anode Materials For Li-Ion Batteries, Xiang Pan

Theses and Dissertations

Tin, an anode material with a high capacity for lithium-ion batteries, has poor cyclic performance because of the high volume expansion upon lithiation. Based on a literature review of the applications of lithium-ion batteries and current research progress of the tin-based anode materials for lithium-ion batteries, we developed a method to synthesize hollow TiO2 spheres with tin nanoparticles anchored on the inner surface of the TiO2 shell. Such a unique tin/TiO2 composite alleviates the volume change of tin–based anode materials in charge-discharge processes. SnCl2·2H2O (Tin (II) chloride dihydrate) and titanium (IV) isopropoxide (TIPT) were used as the Sn source and …


The Electroreduction Of Carbon Dioxide On Porous Copper Nanoparticles, Monica Alisa Padilla Jun 2015

The Electroreduction Of Carbon Dioxide On Porous Copper Nanoparticles, Monica Alisa Padilla

Chemical and Biological Engineering ETDs

Copper nanoparticles of porous, controlled structure were synthesized using the sacrificial support method (SSM). The precursor weight percent (wt%) of copper (Cu) and fumed silica (EH-5) was varied to determine the optimum ratio for this material. The precursors were reduced at i) 350°C in a 7% H2 atmosphere and ii) at 250°C in a 100% H2 atmosphere. The specific surface areas of the nanoparticles was measured by Brunauer-Emmett-Teller N2 absorption. The morphologies and widths of the nanoparticles were confirmed by imaging the nanoparticles by scanning electron microscopy (SEM). The bulk composition of the nanoparticles was determined by X-ray diffraction (XRD). …


Oxygen Reduction Reaction By Copper Complex Based Electrocatalysts, Congling Zhang May 2015

Oxygen Reduction Reaction By Copper Complex Based Electrocatalysts, Congling Zhang

Doctoral Dissertations

My research focuses on catalysis of oxygen reduction reaction (ORR) by a series of Cu(II) [copper with positive two valence] -1,2,4-triazole complex-based electrocatalysts at the cathode of PEMFC (polymer electrolyte membrane fuel cell), an efficient and environmental friendly energy conversion system compared to internal combustion engines in use today. The sluggish kinetics of ORR considerably limited the performance of PEMFCs. Understanding of ORR mechanism is important for developing affordable, active and durable ORR catalysts for such devices.

The first part of my work focused on improving the ORR performance of Cu(II)-1,2,4-triazole complex-based catalysts in an acidic environment by exploring synthesis …


Mathematical Modeling Of A Primary Zinc/Air Battery, Z. Mao, Ralph E. White Mar 2015

Mathematical Modeling Of A Primary Zinc/Air Battery, Z. Mao, Ralph E. White

Ralph E. White

The mathematical model developed by Sunu and Bennion has been extended to include the separator, precipitation of both solid ZnO and K2Zn(OH)4, and the air electrode, and has been used to investigate the behavior of a primary Zn-Air battery with respect to battery design features. Predictions obtained from the model indicate that anode material utilizationis predominantly limited by depletion of the concentration of hydroxide ions. The effect of electrode thickness on anode material utilization is insignificant, whereas material loading per unit volume has a great effect on anode material utilization; a higher loading lowers both the anode material utilization and …


The Effect Of Particle Size On The Discharge Performance Of A Nickel-Metal Hydride Cell, Jussi M. Heikonen, Harry J. Ploehn, Ralph E. White Mar 2015

The Effect Of Particle Size On The Discharge Performance Of A Nickel-Metal Hydride Cell, Jussi M. Heikonen, Harry J. Ploehn, Ralph E. White

Ralph E. White

We investigate the effect of particle size on the discharge performance of a nickel-metal hydride cell with a mathematical model. Electrodes with uniform as well as with nonuniform particle sizes are studied. With uniform particle size, the dependence of the particle-to-particle resistance on the particle size is taken into account. The optimal particle size depends on the discharge rate. Moreover, we show that under certain conditions it is advantageous to use a nonuniform particle size. In general, the higher the discharge current density, the more the particle size affects the electrode performance.


Effect Of Porosity On The Capacity Fade Of A Lithium-Ion Battery: Theory, Godfrey Sikha, Branko N. Popov, Ralph E. White Mar 2015

Effect Of Porosity On The Capacity Fade Of A Lithium-Ion Battery: Theory, Godfrey Sikha, Branko N. Popov, Ralph E. White

Ralph E. White

A mathematical model is presented to predict the performance of a lithium-ion battery. It includes the changes in the porosity of the material due to the reversible intercalation processes and the irreversible parasitic reaction. The model was also extended to predict the capacity fade in a lithium-ion battery based on the unwanted parasitic reaction that consumes Li+ along with the changes in the porosities of the electrodes with cycling due to the continuous parasitic side reaction. The model can be used to predict the drop in the voltage profile, change in the state of charge, and the effects of charge …


Theoretical Analysis Of Metal Hydride Electrodes: Studies On Equilibrium Potential And Exchange Current Density, Bala S. Haran, Branko N. Popov, Ralph E. White Mar 2015

Theoretical Analysis Of Metal Hydride Electrodes: Studies On Equilibrium Potential And Exchange Current Density, Bala S. Haran, Branko N. Popov, Ralph E. White

Ralph E. White

A theoretical model for the metal hydride electrode has been developed assuming that hydrogen diffusion in the alloy and charge-transfer at the surface control the discharge process. Theoretical equations for the dependence of equilibrium potential and exchange current density on the surface hydrogen concentration have been derived. These parameters have been used to correlate experimental data with the theoretical electrode discharge model. Analysis of both the experimental and theoretical discharge curves reveals a potential plateau determined by the magnitude of the interactions between the hydrogen in the alloy and the unhydrided metal. Neglecting these hydrogen-metal site interactions results in simulations …


A Finite-Difference Method For Pseudo-Two-Dimensional Boundary Value Problems, Z. Mao, Ralph E. White Mar 2015

A Finite-Difference Method For Pseudo-Two-Dimensional Boundary Value Problems, Z. Mao, Ralph E. White

Ralph E. White

A finite-difference method is presented for solving pseudo-two-dimensional boundary-value problems. The sparse and nearly block tridiagonal properties of the matrices generated by using the finite-difference method for problems of this type are fully utilized and maintained, which yields a method that is highly efficient in the use of storage space and computation. An example shows that the central process unit time required by the method is significantly less than that required by an alternative method.


Determination Of Transport And Electrochemical Kinetic Parameters Of Bare And Copper-Coated Lani4.27Sn0.24 Electrodes In Alkaline Solution, G. Zheng, Branko N. Popov, Ralph E. White Mar 2015

Determination Of Transport And Electrochemical Kinetic Parameters Of Bare And Copper-Coated Lani4.27Sn0.24 Electrodes In Alkaline Solution, G. Zheng, Branko N. Popov, Ralph E. White

Ralph E. White

Electrochemical properties of bare and copper-coated LaNi4.27Sn0.24 electrodes were investigated in alkaline solution. The exchange current density, polarization resistance, and equilibrium potential were determined as functions of the state of charge in the electrodes. The symmetry factors for bare and copper-coated electrodes were estimated to be 0.53 and 0.52, respectively. By using a constant current discharge technique, the hydrogen diffusion coefficient in bare and coated LaNi4.27Sn0.24 was estimated to be 6.75 × 10–11 cm2/s.


Modification Of Newman's Band(J) Subroutine To Multi-Region Systems Containing Interior Boundaries: Mband, D. Fan, Ralph E. White Mar 2015

Modification Of Newman's Band(J) Subroutine To Multi-Region Systems Containing Interior Boundaries: Mband, D. Fan, Ralph E. White

Ralph E. White

Newman's BAND(J) subroutine, which has been used widely to solve models of various electrochemical systems, is extended to solve a system of coupled, ordinary differential equations with interior boundary conditions. A set of coupled, linear ordinary differential equations is used to demonstrate the solution procedure. The results show that the extended technique has the same accuracy as that of using pentadiagonal BAND(J), but the execution speed is about five times faster than that of pentadiagonal BAND(J). Using sparse matrix solver Y12MAF to solve the same set of equations takes even longer time than pentadiagonal BAND(J).


Estimation Of Electrode Kinetic Parameters Of The Lithium/Thionyl Chloride Cell Using A Mathematical Model, T. I. Evans, Ralph E. White Mar 2015

Estimation Of Electrode Kinetic Parameters Of The Lithium/Thionyl Chloride Cell Using A Mathematical Model, T. I. Evans, Ralph E. White

Ralph E. White

A one-dimensional mathematical model for the lithium/thionyl chloride primary cell is used in conjunction with a parameter estimation technique, in order to estimate the electrode kinetic parameters of this electrochemical system. The electrode kinetic parameters include the anodic transfer coefficient and exchange current density of the lithium oxidation, a,1 and i0,1,ref; the cathodic transfer coefficient and the effective exchange current density of the thionyl chloride reduction, c,4 and a0i0,4,ref, and a morphology parameter, . The parameter estimation is performed on simulated data first in order to gain confidence in the method. Data reported in the literature for a high-rate discharge …


Simple Models For Diaphragm-Type Chlorine/Caustic Cells Ii. Effect Of Acidic Anolyte On Steady-State Caustic Yield, John Van Zee, Ralph E. White Mar 2015

Simple Models For Diaphragm-Type Chlorine/Caustic Cells Ii. Effect Of Acidic Anolyte On Steady-State Caustic Yield, John Van Zee, Ralph E. White

Ralph E. White

A simple steady-state model of a diaphragm-type chlorine/caustic cell in which the diaphragm is divided into two regions by a homogeneous acid-base reaction is presented. The location of the reaction affects significantly the caustic yield and effluent concentration. The model is used to predict the location of this reaction as a function of the operating variables, the physical constants, and three measurable properties of the diaphragm. These measurable properties are the MacMullin number or resistivity ratio of electrolyte-filled diaphragm relative to the electrolyte, the Darcy's law diaphragmpermeability, and the diaphragm thickness. The model is used to predict a maximum in …


A Mathematical Model Of Electrochemical Reactions Coupled With Homogeneous Chemical Reactions, Ken-Ming Yen, Taewhan Yeu, Ralph E. White Mar 2015

A Mathematical Model Of Electrochemical Reactions Coupled With Homogeneous Chemical Reactions, Ken-Ming Yen, Taewhan Yeu, Ralph E. White

Ralph E. White

The zinc/bromine (Zn/Br2) flow battery has received considerable
attention in recent years [e.g., (2-4)]. Although it
is agreed that the solution chemistry is important in the
system, most of the work that has been done is concentrated
on the design variables. In this note the basic mass
transfer-solution and surface kinetics are studied to furnish
a better understanding of the system.


A Comparison Of Newman's Numerical Technique And Deboor's Algorithm, D. A. Curtis, T. I. Evans, Ralph E. White Mar 2015

A Comparison Of Newman's Numerical Technique And Deboor's Algorithm, D. A. Curtis, T. I. Evans, Ralph E. White

Ralph E. White

Newman's numerical technique (1-4) has been used extensivelyto solve two-point boundary value problems consistingof coupled, ordinary differential equations#12;. Unfortunately,his method does not always yield a solution to asystem of independent equations#12;. Sometimes his algorithm(BAND) signals incorrectly that the coefficientmatrix is singular (e.g., DETERMINANT = 0 AT J = 2),and no solution is obtained to the system of equations#12;.This problem sometimes occurs when one tries to useBAND to solve a two-point boundary value problemwhich consists of a set of mixed order ordinary differentialequations. For example, the battery model equations presentedrecently by Evans and White (5) are representativeof this type of equation …


Electrochemical Processes In Microfluidics Systems Under Ac Electric Fields, Ran An Jan 2015

Electrochemical Processes In Microfluidics Systems Under Ac Electric Fields, Ran An

Dissertations, Master's Theses and Master's Reports - Open

Alternating current (AC) electric signal has been widely applied in microfluidic systems to induce AC electrokinetic behavior. AC electrokinetic phenomena including AC electrophoresis, AC dielectrophoresis, AC electroosmosis flow and AC electrothermal flow are widely applied in (bio)particle sorting, separation and concentration and micropumps. However, numbers of non-ideal AC electrokinetic behaviors have been reported: human erythrocyte deformation in AC dielectrophoresis system has been observed; flow reversal in AC electroosmosis flow pumps has also been reported. In this dissertation, a systematic study on human erythrocyte crenation in AC dielectrophoresis system was firstly conducted. Multiple possible physical mechanisms inducing cell crenation including temperature, …