168 Matching Results

Search Results

Advanced search parameters have been applied.

Electrically Conductive, Corrosion-Resistant Coatings Through Defect Chemistry for Metallic Interconnects

Description: The principal objective of this work was to develop oxidation protective coatings for metallic interconnect based on a defect chemistry approach. It was reasoned that the effectiveness of a coating is dictated by oxygen permeation kinetics; the slower the permeation kinetics, the better the protection. All protective coating materials investigated to date are either perovskites or spinels containing metals exhibiting multiple valence states (Co, Fe, Mn, Cr, etc.). As a result, all of these oxides exhibit a reasonable level of electronic conductivity; typically at least about {approx}0.05 S/cm at 800 C. For a 5 micron coating, this equates to a maximum {approx}0.025 {Omega}cm{sup 2} area specific resistance due to the coating. This suggests that the coating should be based on oxygen ion conductivity (the lower the better) and not on electronic conductivity. Measurements of ionic conductivity of prospective coating materials were conducted using Hebb-Wagner method. It was demonstrated that special precautions need to be taken to measure oxygen ion conductivity in these materials with very low oxygen vacancy concentration. A model for oxidation under a protective coating is presented. Defect chemistry based approach was developed such that by suitably doping, oxygen vacancy concentration was suppressed, thus suppressing oxygen ion transport and increasing effectiveness of the coating. For the cathode side, the best coating material identified was LaMnO{sub 3} with Ti dopant on the Mn site (LTM). It was observed that LTM is more than 20 times as effective as Mn-containing spinels. On the anode side, LaCrO3 doped with Nb on the Cr site (LNC) was the material identified. Extensive oxidation kinetics studies were conducted on metallic alloy foils with coating {approx}1 micron in thickness. From these studies, it was projected that a 5 micron coating would be sufficient to ensure 40,000 h life.
Date: December 31, 2006
Creator: Virkar, Anil V.
Partner: UNT Libraries Government Documents Department

Electronic/ionic conductivity and oxygen diffusion coefficient of Sr-Fe-Co-O system

Description: Oxides in the system Sr-Fe-Co-O exhibit both electronic and ionic conductivities. Recently, Sr-Fe-Co-O system attracted great attention because of the potential to be used for oxygen permeable membranes that can operate without the electrodes or external electrical circuitry. Electronic and ionic conductivities at various temperatures have been measured on two compositions in Sr-Fe-Co-O system named SFC-1 and SFC-2. The electronic transference number is much greater than the ionic transference number in SFC-1 sample, while the electronic and ionic transference numbers are very close in SFC-2 sample. At 800{degrees}C, the electronic conductivity and ionic conductivity are {approx}76 S{center_dot}cm-1 and =4 S-cm-1, respectively, for SFC-1. While, for SFC-2, the electronic and ionic conductivities are =10 S-cm-1 and {approx}7 S-cm-1, respectively. By a local fitting to {sigma}{center_dot}T = A exp(-E{sub {alpha}}/{kappa}{Tau}), we found that the oxide ion activation energies are 0.92 eV and 0.37 eV respectively for SFC-1 and SFC-2 samples. Oxygen diffusion coefficient of SFC-2 is {approx}{times}10{sup {minus}7} cm{sup 2}/sec at 900C.
Date: March 1, 1995
Creator: Ma, B.; Park, J.H.; Balachandran, U. & Segre, C.U.
Partner: UNT Libraries Government Documents Department

Ionic conductivities of lithium phosphorus oxynitride glasses, polycrystals, and thin films

Description: Various lithium phosphorus oxynitrides have been prepared in the form of glasses, polycrystals, and thin films. The structures of these compounds were investigated by X-ray and neutron diffraction, X-ray photoelectron spectroscopy (XPS), and high-performance liquid chromatography (HPLC). The ac impedance measurements indicate a significant improvement of ionic conductivity as the result of incorporation of nitrogen into the structure. In the case of polycrystalline Li{sub 2.88}PO{sub 3.73}N{sub 0.14} with the {gamma}-Li{sub 3}PO{sub 4} structure, the conductivity increased by several orders of magnitude on small addition of nitrogen. The highest conductivities in the bulk glasses and thin films were found to be 3.0 {times} 10{sup -7} and 8.9 {times} 10{sup -7} S{center_dot}cm{sup -1} at 25{degrees}C, respectively.
Date: November 1, 1994
Creator: Wang, B.; Bates, J.B.; Chakoumakos, B.C.; Sales, B.C.; Kwak, B.S.; Zuhr, R.A. et al.
Partner: UNT Libraries Government Documents Department

Physical properties of Li ion conducting polyphosphazene based polymer electrolytes

Description: We report a systematic study of the transport properties and the underlying physical chemistry of some polyphosphazene (PPhz)-based polymer electrolytes. We synthesized MEEP and variants which employed mixed combinations of different length oxyethylene side-chains. We compare the conductivity and ion-ion interactions in polymer electrolytes obtained with lithium triflate and lithium bis(trifluoromethanesulfonyl)imide (TFSI) salts added to the polymer. The combination of the lithium imide salt and MEEP yields a maximum conductivity of 8 x 10{sup -5} {Omega}{sup -1} cm{sup -1} at room temperature at a salt loading of 8 monomers per lithium. In one of the mixed side-chain variations, a maximum conductivity of 2 x 10{sup -4} {Omega}{sup -1} cm{sup -1} was measured at the same molar ratio. Raman spectral analysis shows some ion aggregation and some polymer - ion interactions in the PPhz-LiTFSI case but much less than observed with Li CF{sub 3}SO{sub 3}. A sharp increase in the Tg as salt is added corresponds to concentrations above which the conductivity significantly decreases and ion associations appear.
Date: December 31, 1996
Creator: Sanderson, S.; Zawodzinski, T.; Hermes, R.; Davey, J. & Dai, Hongli
Partner: UNT Libraries Government Documents Department

Rietveld neutron powder profile analysis and electrical conductivity of the fast silver-ion conductor (LaO)AgS

Description: Lanthanum silver oxysulfide, (LaO)AgS, exhibits a predominantly ionic conductivity of 10{sup {minus}3} to 10{sup {minus}1} S/cm between 300 K and 770 K. The tetragonal structure consists of alternating (LaO) and (AgS) sheets, their sequence being O-La-S-Ag-S-La-O. The structure suggests that ionic transport arises from migration of silver ions within the AgS layers analogous to sodium ion transport in Na-{beta}-alumina. Neutron powder diffraction data measured at five temperatures between 300 K and 770 K are analyzed using the Rietveld method to determine the distribution and thermal vibration parameters of the mobile silver ions. The structural investigation is accompanied by measurements of the total conductivity in the same temperature range in order to resolve severe discrepancies in the literature data.
Date: November 18, 1999
Creator: Wilmer, D.; Wuensch, B. J. & Jorgensen, J. D.
Partner: UNT Libraries Government Documents Department

Ionic Current Mapping Techniques and Applications to Aluminum-Copper Corrosion

Description: Measurements have been made of the aluminum/metal galvanic couple. A wide range of geometries were investigated varying the areas of anodic and cathodic surfaces and employing specially designed galvanic cells with crevices. In situ ionic current density mapping was used to monitor galvanic corrosion and currents flowing between separated metals was measured.
Date: October 17, 1999
Creator: Isaacs, H. S.; Jeffcoate, C. S.; Missert, N. A. & Barbour, J. C.
Partner: UNT Libraries Government Documents Department

Development of materials for solid state electrochemical sensors and fuel cell applications. Final report, September 30, 1995--December 30, 1995

Description: The intent of this project was two fold: (1) to develop new ionically conducting materials for solid state gas phase sensors and fuel cells and (2) to train students and create an environment conducive to Solid State Ionics research at Southern University. The authors have investigated the electrode-electrolyte interfacial reactions, defect structure and defect stability in some perovoskite type solid electrolyte materials and the effect of electrocatalyst and electrolyte on direct hydrocarbon and methanol/air fuel cell performance using synchrotron radiation based Extended X-ray Absorption Spectroscopy (EXAFS), surface analytical and Impedance Spectroscopic techniques. They have measured the AC impedance and K edge EXAFS of the entire family of rare earth dopants in Cerium Oxide to understand the effect of dopants on the conductivity and its impact on the structural properties of Cerium Oxide. All of the systems showed an increase in the conductivity over undoped ceria with ceria doped Gd, Sm and Y showing the highest values. The conductivity increased with increasing ionic radius of the dopant cation. The authors have measured the K edge of the EXAFS of these dopants to determine the local structural environment and also to understand the nature of the defect clustering between oxygen vacancies and trivalent ions. The analysis and the data reduction of these complex EXAFS spectra is in progress. Where as in the DOWCs, the authors have attempted to explore the impact of catalyst loadings on the performance of direct oxidation of methanol fuel cells. Their initial measurements on fuel cell performance characteristics and EXAFS are made on commercial membranes Pt/Ru/Nafion 115, 117 and 112.
Date: December 31, 1995
Creator: Bobba, R.; Hormes, J.; Young, V. & Baker, J.A.
Partner: UNT Libraries Government Documents Department

Study of multicomponent diffusion and transport phenomena. Technical report, July 1, 1984--June 30, 1995

Description: This progress report summarizes a project to treat the diffusion and transport phenomena in multicomponent systems from an atomistic point of view mainly by means of a kinetic method based on the Cluster Variation Method (CVM)-Path Probability Method (PPM) formalism. As is well known, the CVM has established itself as one of the most systematic methods of statistical thermodynamics, and macroscopic phenomena treated by thermodynamics can thus be investigated atomistically in great detail. The author describes work in a number of different applications, summarized here by the section titles: percolation threshold in electronic conduction {beta}-alumina type solid electrolytes; mixed alkali effect; chemical diffusion problem; soft lattice gas model and rigid lattice gas model; diffusion in semiconductors; diffusion in ordered alloys; kinetics of relaxation process of hopping ionic conduction.
Date: September 1, 1995
Creator: Sato, Hiroshi
Partner: UNT Libraries Government Documents Department

Enhanced ionic conduction at the film/substrate interface in LiI thin films grown on sapphire(0001)

Description: The ionic conductivity of LiI thin films grown on sapphire(0001) substrates has been studied in-situ during deposition as a function of film thickness and deposition conditions. LiI films were produced at room temperature by sublimation in an ultra-high-vacuum system. The conductivity of the LiI parallel to the film/substrate interface was determined from frequency-dependent impedance measurements as a function of film thickness using Au interdigital electrodes deposited on the sapphire surface. The measurements show a conduction of {approximately}5 times the bulk value at the interface which gradually decreases as the film thickness is increased beyond 100 nm. This interfacial enhancement is not stable but anneals out with a characteristic log of time dependence. Fully annealed films have an activation energy for conduction ({sigma}T) of {approximately}0.47{plus_minus}.03 eV, consistent with bulk measurements. The observed annealing behavior can be fit with a model based on dislocation motion which implies that the increase in conduction near the interface is not due to the formation of a space-charge layer as previously reported but to defects generated during the growth process. This explanation is consistent with the behavior exhibited by CaF{sub 2} films grown under similar conditions.
Date: December 1, 1993
Creator: Lubben, D. & Modine, F. A.
Partner: UNT Libraries Government Documents Department

EVALUATION OF PROTON-CONDUCTING MEMBRANES FOR USE IN A SULFUR-DIOXIDE DEPOLARIZED ELECTROLYZER

Description: The chemical stability, sulfur dioxide transport, ionic conductivity, and electrolyzer performance have been measured for several commercially available and experimental proton exchange membranes (PEMs) for use in a sulfur dioxide depolarized electrolyzer (SDE). The SDE's function is to produce hydrogen by using the Hybrid Sulfur (HyS) Process, a sulfur based electrochemical/thermochemical hybrid cycle. Membrane stability was evaluated using a screening process where each candidate PEM was heated at 80 C in 60 wt. % H{sub 2}SO{sub 4} for 24 hours. Following acid exposure, chemical stability for each membrane was evaluated by FTIR using the ATR sampling technique. Membrane SO{sub 2} transport was evaluated using a two-chamber permeation cell. SO{sub 2} was introduced into one chamber whereupon SO{sub 2} transported across the membrane into the other chamber and oxidized to H{sub 2}SO{sub 4} at an anode positioned immediately adjacent to the membrane. The resulting current was used to determine the SO{sub 2} flux and SO{sub 2} transport. Additionally, membrane electrode assemblies (MEAs) were prepared from candidate membranes to evaluate ionic conductivity and selectivity (ionic conductivity vs. SO{sub 2} transport) which can serve as a tool for selecting membranes. MEAs were also performance tested in a HyS electrolyzer measuring current density versus a constant cell voltage (1V, 80 C in SO{sub 2} saturated 30 wt% H2SO{sub 4}). Finally, candidate membranes were evaluated considering all measured parameters including SO{sub 2} flux, SO{sub 2} transport, ionic conductivity, HyS electrolyzer performance, and membrane stability. Candidate membranes included both PFSA and non-PFSA polymers and polymer blends of which the non-PFSA polymers, BPVE-6F and PBI, showed the best selectivity.
Date: November 11, 2009
Creator: Hobbs, D.; Elvington, M. & Colon-Mercado, H.
Partner: UNT Libraries Government Documents Department

CHARACTERIZATION OF H CANYON CONDUCTIVITY METER INDICATIONS WITH ELEVATED URANIUM IN NITRIC ACID

Description: Solution conductivity data from the 1CU conductivity meter in H-Canyon shows that uranium concentration in the 0 to 30 gram per liter (g/L) range has no statistically significant effect on the calibration of free nitric acid measurement. Based on these results, no additional actions are needed on the 1CU Conductivity Meter prior to or during the processing of uranium solutions in the 0 to 30 g/L range. A model based only on free nitric acid concentration is shown to be appropriate for explaining the data. Data uncertainties for the free acid measurement of uranium-bearing solutions are 8.5% or less at 95% confidence. The analytical uncertainty for calibrating solutions is an order of magnitude smaller only when uranium is not present, allowing use of a more accurate analytical procedure. Literature work shows that at a free nitric acid level of 0.33 M, uranium concentration of 30 g/L and 25 C, solution conductivity is 96.4% of that of a uranium-free solution. The level of uncertainties in the literature data and its fitting equation do not justify calibration changes based on this small depression in solution conductivity. This work supports preparation of H-Canyon processing of Super Kukla fuel; however, the results will be applicable to the processing of any similar concentration uranium and nitric acid solution. Super Kukla fuel processing will increase the uranium concentration above the nominal zero to 10 g/L level, though not above 30 g/L. This work examined free nitric acid levels ranging from 0.18 to 0.52 molar. Temperature ranged from 27.9 to 28.3 C during conductivity testing. The data indicates that sequential order of measurement is not a significant factor. The conductivity meter was thus flushed effectively between measurements as desired.
Date: October 31, 2007
Creator: Nash, C
Partner: UNT Libraries Government Documents Department

FY08 MEMBRANE CHARACTERIZATION REPORT FOR HYBRID SULFUR ELECTROLYZER

Description: This report summarizes results from all of the membrane testing completed to date at the Savannah River National Laboratory (SRNL) for the sulfur dioxide-depolarized electrolyzer (SDE). Several types of commercially-available membranes have been analyzed for ionic resistance and sulfur dioxide transport including perfluorinated sulfonic acid (PFSA), sulfonated polyether-ketone-ketone (SPEKK), and polybenzimidazole membranes (PBI). Of these membrane types, the poly-benzimidazole membrane, Celtec-L, exhibited the best combination of characteristics for use in an SDE. Several experimental membranes have also been analyzed including hydrated sulfonated Diels-Alder polyphenylenes (SDAPP) membranes from Sandia National Laboratory, perfluorosulfonimide (PFSI) and sulfonated perfluorocyclobutyl aromatic ether (S-PFCB) prepared by Clemson University, hydrated platinum-treated PFSA prepared by Giner Electrochemical Systems (GES) and Pt-Nafion{reg_sign} 115 composites prepared at SRNL. The chemical stability, SO{sub 2} transport and ionic conductivity characteristics have been measured for several commercially available and experimental proton-conducting membranes. Commercially available PFSA membranes such as the Nafion{reg_sign} series exhibited excellent chemical stability and ionic conductivity in sulfur dioxide saturated sulfuric acid solutions. Sulfur dioxide transport in the Nafion{reg_sign} membranes varied proportionally with the thickness and equivalent weight of the membrane. Although the SO{sub 2} transport in the Nafion{reg_sign} membranes is higher than desired, the excellent chemical stability and conductivity makes this membrane the best commercially-available membrane at this time. Initial results indicated that a modified Nafion{reg_sign} membrane incorporating Pt nanoparticles exhibited significantly reduced SO{sub 2} transport. Reduced SO{sub 2} transport was also measured with commercially available PBI membrane and several experimental membranes produced at SNL and Clemson. These membranes also exhibit good chemical stability and conductivity in concentrated sulfuric acid solutions and, thus, serve as promising candidates for the SDE. Therefore, we recommend further testing of these membranes including electrolyzer testing to determine if the reduced SO{sub 2} transport eliminates the formation of sulfur-containing films at the membrane/cathode interface. SO{sub ...
Date: September 1, 2008
Creator: Hobbs, D; Hector Colon-Mercado, H & Mark Elvington, M
Partner: UNT Libraries Government Documents Department

Role of structure in ion movement of glasses. Final report, July 1, 1990--December 31, 1995

Description: The ion movement in inorganic glasses is key to their optimum use in various applications such as solid electrolytes, durable nuclear waste form, stable insulation in electronic devices etc. The primary objective of this project was to understand ion movement in relation to the physical structure of inorganic glasses. Five different glass forming systems were selected for systematically varying different aspects of the structure and determining their influence on ion dynamics: (1) binary Rb and K germanate glass series; (2) mixed (Rb, Ag) and (Rb, K) germanate glass series (3) high purity quartz amorphized by neutron irradiation (4) sodium triborate glasses with different melt conditions and (5) heavy metal fluoride glasses. A two-pronged research program was developed: on the one hand dc ionic conductivity and ac relaxation were measured for a variety of oxide and fluoride glasses as a function of composition, temperature and frequency to characterize long and short range ion transport phenomena. The ion movement was also observed in terms of nuclear spin relaxation rate at University of Dortmund, Germany. On the other hand, the structure was characterized by high resolution x-ray photoelectron spectroscopy (XPS) at Lehigh, infra-red (IR) and Raman spectroscopy at National Hellenic Research Foundation, Athens, Greece, and extended x-ray absorption fine structure (EXAFS) experiments at National Synchrotron Light Source, Brookhaven National Laboratory. The most significant results of the project are briefly summarized.
Date: May 1, 1996
Creator: Jain, H.
Partner: UNT Libraries Government Documents Department

Application of the Solubility Parameter Concept to the Design of Chemiresistor Arrays

Description: Arrays of unheated chemically sensitive resistors (chemiresistors) can serve as extremely small, low-power-consumption sensors with simple read-out electronics. We report here results on carbon-loaded polymer composites, as well as polymeric ionic conductors, as chemiresistor sensors. We use the volubility parameter concept to understand and categorize the chemiresistor responses and, in particular, we compare chemiresistors fabricated from polyisobutylene (PIB) to results from PIB-coated acoustic wave sensors. One goal is to examine the possibility that a small number of diverse chemiresistors can sense all possible solvents-the "Universal Solvent Sensor Array". keywords: chemiresistor, volubility parameter, chemical sensor
Date: January 11, 1999
Creator: Eastman, M.P.; Hughes, R.C.; Jenkins, M.W.; Patel, S.V.; Ricco, A.J. & Yelton, G.
Partner: UNT Libraries Government Documents Department

Reinvestigation of ionic motion in amorphous materials: A power law approach to the a.c. conductivity. Progress report

Description: The motion of mobile ions in glassy materials produces a dielectric response that is characteristically non-Debye. This deviation from ideal Debye behavior is evidenced both in the a.c. conductivity, {sigma}(f), which increases anomalously as a power law of the form {sigma}(f) = {sigma}{sub 0}(1+(f/f{sub 0}){sup n}), and in the electric modulus which is better described by a stretched-exponential relaxation of the form {phi}(t) = exp({minus}(t/{tau}){sup {beta}}). The authors have examined the dielectric response of sodium germanate glasses over a wide composition range. In accordance with other studies, they observed substantial narrowing of the electric modulus with decreasing alkali content. However, no changes were evident in the power law response of the a.c. conductivity, and {sigma}(f) could be scaled to a common response curve at all compositions. This result clearly rules out inter-ionic interactions as a source for the non-Debye relaxation. The authors extended the study of sodium germanates to examine also the power law dynamics in the mixed alkali (MA) glass.
Date: January 1, 1999
Partner: UNT Libraries Government Documents Department

Novel carbon-ion fuel cells

Description: This report details acitvities by the Duke University Department of Mechanical Engineering and Material Science on the Novel Carbon-Ion Fuel Cells for the Department of Energy Advanced Coal Research Program grant for the third quarter of 1995.
Date: October 3, 1995
Creator: Cocks, F.H. & LaViers, H.
Partner: UNT Libraries Government Documents Department

Li ion conductors based on laponite/poly(ethylene oxide) composites

Description: Synthesis and characterization of single ion conducting poly(ethylene oxide) (PEO)/Li-laponite nanocomposites are reported. The amount of PEO that can be intercalated into laponite, a synthetic hectorite with high surface area, ranges from about 0.7g/g Li-laponite when the polymer average molecular weight is 1,000 or above, to about 1 g/g for oligomers of average molecular weight 500. The interlayer spacing increases from about 10 {angstrom} in the dry clay to 20--24 {angstrom} in the nanocomposites, depending upon polymer molecular weight, and the average particle size increases proportionally, but is still in the sub-micron range. AC impedance measurements on the clear, slightly brittle, self-supporting films indicate that the nanocomposite conductivity is greatly enhanced over that of the dry clay. A maximum of about 10{sup {minus}6} S/cm at 80 C is obtained for materials containing a slight excess of polymer, and conductivities of nanocomposites containing PEO were generally higher than that of those containing oxymethylene linked polyethylene glycol (amorphous PEOs). Suggestions for further improving conductivity and mechanical properties of these novel materials are presented.
Date: November 1, 1997
Creator: Doeff, M. M. & Reed, J. S.
Partner: UNT Libraries Government Documents Department

Neutron and X-ray scattering experiments on lithium polymer electrolytes

Description: The authors are carrying out structural, dynamical and transport measurements of lithium polymer electrolytes, in order to provide information needed to improve the performance of secondary lithium battery systems. Microscopically, they behave as liquids under conditions of practical interest. Development of batteries based on these materials has focused on rechargeable systems with intercalation/insertion cathodes and lithium or lithium-containing materials as anodes. The electrolytes are generally composites of a polyethylene oxide (PEO) or another modified polyether and a salt such as LiClO{sub 4}, LiAsF{sub 6} or LiCF{sub 3}SO{sub 3}. Research on electrolyte materials for lithium batteries has focused on synthesis, characterization, and development of practical devices. Some characterization work has been carried out to determine the properties of the ion polymer and ion interactions, principally through spectroscopic, thermodynamic and transport measurements. It is generally believed that ionic conduction is a property of the amorphous phase of these materials. It is also believed that ion association, ion polymer interactions and local relaxations of the polymer strongly influence the ionic mobility. However, much about the nature of the charge carriers, the ion association processes, and the ion polymer interactions and the role that these play in the ionic conductivity of the electrolytes remains unknown. The authors have initiated a combined experimental and theoretical study of the structure and dynamics of lithium polymer electrolytes. They plan to investigate the effects of the polymer host on ion solvation and the attendant effects of ion pairing, which affect the ionic transport in these systems.
Date: September 1, 1997
Creator: Saboungi, M.L. & Price, D.L.
Partner: UNT Libraries Government Documents Department

Ion-Conducting Polymer Films as Chemical Sensors

Description: Solid Polymer Electrolytes (SPE) are widely used in batteries and fuel cells because of the high ionic conductivity that can be achieved at room temperature. The ions are usually Li or protons, although other ions can be shown to conduct in these polymer films. There has been very little work on using these films as chemical sensors. We have found that thin films of polymers like polyethyleneoxide (PEO) are very sensitive to low concentrations of volatile organic compounds (VOCS) like common solvents. We will present impedance spectroscopy of PEO films in the frequency range 0.01 Hz to 1 MHz for different concentrations of VOCS. We find that the measurement frequency is important for distinguishing ionic conductivity from the double layer capacitance and parasitic capacitances.
Date: May 3, 1999
Creator: Hughes, R.C.; Patel, S.V.; Pfeifer, K.B. & Yelton, W.G.
Partner: UNT Libraries Government Documents Department

SYNTHESIS OF A NEW FAMILY OF FLUORINATED BORONATE COMPOUNDS AS ANION RECEPTORS AND STUDIES OF THEIR USE AS ADDITIVES IN LITHIUM BATTERY ELECTROLYTES.

Description: Numerous studies have been done on developing new electrolytes for lithium batteries with high ionic conductivity, and good chemical and electrochemical stability. In addition to the research on new salts and solvents, the use of cation receptors to reduce ion pairing in non-aqueous electrolytes has been considered as an approach to improve the properties of electrolytes. Although both cation and anion receptors enhance the dissociation of ion pairs and increase the conductivity of electrolytes, the use of anion receptors is more attractive for a lithium battery electrolyte because anion receptors increase the lithium transference number in the electrolyte. However, most available neutral anion receptors complex with anions through hydrogen binding and cannot be used in lithium batteries. Recently, we have reported on synthesis of a series of new neutral boron compounds as anion receptors based on the idea that electron-deficient boron would complex the anion of the ion pair. The anion complexation effect of these boron compounds was further enhanced by attaching electron-withdrawing groups. Here we report synthesis of another new family of boronate compounds. The effect of these new compounds on conductivity of lithium salts in non-aqueous solution was studied. The molecular weights of these new boronate compounds are lower than our previously reported boron compounds. Therefore, their effects on conductivity enhancement are superior. They also display high electrochemical stability up to 5 V.
Date: June 8, 2001
Creator: MCBREEN,J.; LEE,H.S. & YANG,X.Q.
Partner: UNT Libraries Government Documents Department

Characteristics and Mechanisms in Ion-Conducting Polymer Films as Chemical Sensors

Description: Solid Polymer Electrolytes (SPE) are widely used in batteries and fuel cells because of the high ionic conductivity that can be achieved at room temperature. The ions are usually Li or protons, although other ions can be shown to conduct in these polymer films. There has been very little published work on SPE films used as chemical sensors. The authors have found that thin films of polymers like polyethylene oxide (PEO) are very sensitive to low concentrations of volatile organic compounds (VOCs) such as common solvents. Evidence of a new sensing mechanism involving the percolation of ions through narrow channels of amorphous polymer is presented. They present impedance spectroscopy of PEO films in the frequency range 0.0001 Hz to 1 MHz for different concentrations of VOCs and relative humidity. They find that the measurement frequency is important for distinguishing ionic conductivity from the double layer capacitance and the parasitic capacitance.
Date: July 12, 2000
Creator: Hughes, Robert C.; Yelton, William G.; Pfeifer, Kent B. & Patel, Sanjay V.
Partner: UNT Libraries Government Documents Department

Pressure effect on ionic conductivity in yttrium-oxide-doped single-crystal zirconium oxide

Description: In this study, the authors investigated the effect of pressure on the ionic conductivity of a 9.5 mol% yttria-stabilized zirconia (YSZ) single crystal. The experiment was conducted in the elastic region, and the oxygen ion transport number was unity (t{sub ion} > 0.99999). A conventional four-probe DC method was used to measure the ionic conductivity of the rectangular-shaped sample under uniaxial pressures up to 600 atm at 750 C in air. Measured ionic conductivity decreased as applied pressure increased. Based on henry Eyring`s absolute reaction rate theory, which states that the calculated activation volume has a positive value ({Delta}V{sup 2} = 2.08 cm{sup 3}/mol of O{sup {minus}2}) for oxygen ion transport in the fluoride cubic lattice, they concluded that the results they obtained could be explained by an oxygen ion transport mechanism. This mechanism can explain the fact that the interionic distance increases during oxygen ion transport from one unit cell to neighboring unit cells.
Date: June 1, 1998
Creator: Park, E.T. & Park, J.H.
Partner: UNT Libraries Government Documents Department

Application of ionic and electronic conducting ceramics in solid oxide fuel cells

Description: Solid oxide fuel cells (SOFCs) offer a pollution-free technology to electrochemically generate electricity at high efficiencies. These fuel cells consist of an oxygen ion conducting electrolyte, electronic or mixed electronic and ionic conducting electrodes, and an electronic conducting interconnection. This paper reviews the ceramic materials used for the different cell components, and discusses the performance of cells fabricated using these materials. The paper also discusses the materials and processing studies that are underway to reduce the cell cost, and summarizes the recently built power generation systems that employed state-of-the-art SOFCs.
Date: December 1, 1997
Creator: Singhal, S.C.
Partner: UNT Libraries Government Documents Department