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An engineering and economic evaluation of the methane de-NOX{sup SM} technology (open access)

An engineering and economic evaluation of the methane de-NOX{sup SM} technology

The Institute of Gas Technology (IGT) and Ogden Martin Systems, Inc. (OMS) are conducting joint engineering and economic evaluation of IGT`s METHANE de-NOX{sup SM} technology for its application to new, as well as retrofit, municipal waste combustors (MWCs). It is anticipated that this new technology offers a technically and economically attractive alternative to existing selective noncatalytic reduction (SNCR) systems for new facilities, as well as in retrofit applications. Consequently, IGT and OMS are considering pursuing a long-term demonstration of this technology on an OMS MWC. The METHANE de-NOX approach was developed based on extensive full-scale MWC infurnace characterization and pilot-scale testing using simulated combustion products. The approach involves injection of natural gas, together with recirculated flue gases (for mixing), above the grate to provide oxygen-deficient combustion conditions that promote the destruction of NO{sub x} precursors, as well as NO{sub x}. Extensive pilot-scale testing, using both simulated combustion products and actual municipal waste (MW), showed that significant NO{sub x} reduction could be achieved. The results were used to define the key operating parameters for a field evaluation of the process. A full-scale METHANE de-NOX system was designed and retrofitted to a 100-ton/day Riley/Takuma mass burn system at the Olmsted County Waste-to-Energy …
Date: December 31, 1993
Creator: Abbasi, H. A.; Khinkis, M. J. & Scherrer, R.
Object Type: Report
System: The UNT Digital Library
Stabilization of spent sorbents from coal gasification. Final technical report, September 1, 1992--August 31, 1993 (open access)

Stabilization of spent sorbents from coal gasification. Final technical report, September 1, 1992--August 31, 1993

The objective of this investigation was to determine the rates of reactions involving partially sulfided dolomite and oxygen, which is needed for the design of the reactor system for the stabilization of sulfide-containing solid wastes from gasification of high sulfur coals. To achieve this objective, samples of partially sulfided dolomite were reacted with oxygen at a variety of operating conditions in a fluidized-bed reactor. The effect of external diffusion was eliminated by using small quantities of the sorbent and maintaining a high flow rate of the reactant gas. The reacted sorbents were analyzed to determine the extent of conversion as a function of operating variables including sorbent particle size, reaction temperature and pressure, and oxygen concentration. The results of sulfation tests indicate that the rate of reaction increases with increasing temperature, increasing oxygen partial pressure, and decreasing sorbent particle size. The rate of the sulfation reaction can be described by a diffuse interface model where both chemical reaction and intraparticle diffusion control the reaction rate. The kinetic model of the sulfation reaction was used to determine the requirements for the reactor system, i.e., reactor size and operating conditions, for successful stabilization of sulfide-containing solid wastes from gasification of high sulfur …
Date: December 31, 1993
Creator: Abbasian, J.; Hill, A. H.; Rue, D. M. & Wangerow, J. R.
Object Type: Report
System: The UNT Digital Library
The role of catalyst precursor anions in coal gasification. Eighth quarterly report, [July--September 1993] (open access)

The role of catalyst precursor anions in coal gasification. Eighth quarterly report, [July--September 1993]

This project investigates the roles of various aqueous soluble catalyst precursor anions, specifically acetate, chloride, nitrate, sulfate, and carbonate anions on the surface electrical properties of coal and seeks to understand the effects of these anions on the adsorption, dispersion and activities of calcium and potassium. The effects of the various anions on coal char gasification is currently under investigation. The influence of acetate, chloride and nitrate ions, when using the corresponding potassium compounds, are discussed in this report. The thermograms for the char preparation in nitrogen show that rapid devolatilization of moisture and other volatile materials occurs in the first 30 min. The rate of weight loss decreases significantly thereafter up to about 70 min. when char preparation was complete. Introduction of carbon dioxide after this time resulted in only a small amount of carbon gasification of the unloaded, demineralized coal. However, the chars containing the acetate, chloride or nitrate of potassium gave reactivities of 24.8, 30.4 or 24.3 %wt., respectively. The catalysts were ion-exchanged with the salt solutions and the corresponding potassium content were 2.9, 2.6 and 2.3 %wt. The higher reactivities of the catalyzed chars compared to the unloaded char correlates the high degree of demineralization and …
Date: December 31, 1993
Creator: Abotsi, G. M. K.
Object Type: Report
System: The UNT Digital Library
Performance of CVR coatings for PBR fuels (open access)

Performance of CVR coatings for PBR fuels

As part of the component development process for the particle bed reactor (PBR), it is necessary to develop coatings for fuel particles which will be time and temperature stable. These coatings must not only protect the particle from attack by the hydrogen coolant, but must also help to maintain the bed in a coolable geometry and mitigate against fission product release. In order to develop these advanced coatings, a process to produce chemical vapor reaction (CVR) coatings on fuel for PBRs has been developed. The initial screening tests for these coatings consisted of testing in flowing hot hydrogen at one atmosphere. Surrogate fuel particles consisting of pyrolytic graphite coated graphite particles have been heated in flowing hydrogen at constant temperature. The carbon loss from these particles was measured as a function of time. Exposure temperatures ranging from 2,500 to 3,000 K were used and samples were exposed for up to 14 minutes in a cyclical fashion, cooling to room temperature between exposures. The rate of weight loss measured as a function of time is compared to that from other tests of coated materials under similar conditions. Microscopic examination of the coatings before and after exposure was also conducted and these …
Date: December 31, 1993
Creator: Adams, J. W.; Barletta, R. E.; Svandrlik, J. & Vanier, P. E.
Object Type: Report
System: The UNT Digital Library
Critical Protection Item Classification for a waste processing facility at Savannah River Site. Revision 1 (open access)

Critical Protection Item Classification for a waste processing facility at Savannah River Site. Revision 1

As a part of its compliance with the Department of Energy requirements for safety of nuclear facilities at the Savannah River Site (SRS), Westinghouse Savannah River Company (WSRC) assigns functional classifications to structures, systems and components (SSCs). As a result, changes in design, operations, maintenance, testing, and inspections of SSCs are performed and backfit requirements are established. This paper describes the Critical Protection Item (CPI) Classification for waste processing facility (WPF) at SRS. The descriptions of the WPF and the processes considered are provided elsewhere. The proposed CPI classification methodology includes the evaluation of the onsite radiological consequences, and the onsite and offsite non-radiological consequences from postulated accidents at the WPF, and comparison of these consequences with allowable frequency-dependent limits. When allowable limits are exceeded, CPIs are identified for accident mitigation.
Date: December 31, 1993
Creator: Ades, M. J. & Garrett, R. J.
Object Type: Article
System: The UNT Digital Library
Development of a cost-effective environmental compliance technology for stripper well brines. Quarterly report, October 1, 1993--December 31, 1993 (open access)

Development of a cost-effective environmental compliance technology for stripper well brines. Quarterly report, October 1, 1993--December 31, 1993

In order to demonstrate to the EPA that brines from both stripper oil and marginal gas wells in the Appalachian Basin are capable of being treated and disposed of by discharge to streams in an environmentally safe manner, the existing research effort on stripper oil well brines will be continued and expanded to examine the range of brines produced from marginal gas wells. The specific object of the research is to demonstrate that the characteristics of wastewater from stripper oil wells and marginal gas wells are sufficiently similar to be treated under a standardized treatment methodology, that the environmental impacts of the discharge of treated brines from both stripper oil and marginal gas wells can be adequately regulated, and that the inclusion of marginal gas wells in the same category as stripper oil wells is appropriate, especially for wells operating in the Appalachian Basin.
Date: December 31, 1993
Creator: Adewumi, M. A. & Watson, R. W.
Object Type: Report
System: The UNT Digital Library
Gas hydrate detection and mapping on the US east coast (open access)

Gas hydrate detection and mapping on the US east coast

Project objectives are to identify and map gas hydrate accumulations on the US eastern continental margin using remote sensing (seismic profiling) techniques and to relate these concentrations to the geological factors that-control them. In order to test the remote sensing methods, gas hydrate-cemented sediments will be tested in the laboratory and an effort will be made to perform similar physical tests on natural hydrate-cemented sediments from the study area. Gas hydrate potentially may represent a future major resource of energy. Furthermore, it may influence climate change because it forms a large reservoir for methane, which is a very effective greenhouse gas; its breakdown probably is a controlling factor for sea-floor landslides; and its presence has significant effect on the acoustic velocity of sea-floor sediments.
Date: December 31, 1993
Creator: Ahlbrandt, T. S. & Dillon, W. P.
Object Type: Report
System: The UNT Digital Library
(j,0) {circle_plus} (0,j) representation space: Majorana-like construct (open access)

(j,0) {circle_plus} (0,j) representation space: Majorana-like construct

This is second of the two invited lectures presented at the ``XVII International School of Theoretical Physics: Standard Model and Beyond` 93.`` The text is essentially based on a recent publication by the present authors. Here, after briefly reviewing the (j, 0) {circle_plus} (0, j) Dirac-like construct in the front form, we present a detailed construction of the (j, 0) {circle_plus} (0, j) Majorana-like fields.
Date: December 31, 1993
Creator: Ahluwalia, D. V.; Goldman, T. & Johnson, M. B.
Object Type: Article
System: The UNT Digital Library
(j,0){circle_plus}(0,j) representation space: Dirac-like construct (open access)

(j,0){circle_plus}(0,j) representation space: Dirac-like construct

This is first of the two invited lectures presented at the ``XVII International School of Theoretical Physics: Standard Model and Beyond 1993.`` The text is essentially based on a recent publication by the present authors. Here we show that the Dirac-like construct in the (j,0){circle_plus}(0,j) representation space support a Bargmann-Wightman-Wigner type quantum field theory.
Date: December 31, 1993
Creator: Ahluwalia, D. V.; Johnson, M. B. & Goldman, T.
Object Type: Article
System: The UNT Digital Library
Space-time symmetries: P and CP violation (open access)

Space-time symmetries: P and CP violation

We begin with a few remarks on an explicit construction of a Bargmann-Wightman-Wigner-type quantum field theory in which bosons and antibosons have opposite relative intrinsic parities. We then construct (1,0) {circle_plus} (0,1) Majorana (CP self conjugate) and Majorana-like (CT{sup 5} self conjugate, {Gamma}{sup 5} = chirality operator) fields. We point out that this new structure in the space time symmetries may be relevant to P and CP violation.
Date: December 31, 1993
Creator: Ahluwalia, D. V.; Johnson, M. B. & Goldman, T.
Object Type: Article
System: The UNT Digital Library
A computational model for coal transport and combustion. Quarterly technical progress report, June 1, 1993--August 31, 1993 (open access)

A computational model for coal transport and combustion. Quarterly technical progress report, June 1, 1993--August 31, 1993

The objective of this project is to develop an accurate model describing turbulent flows of coal slurries, rapid flows of granular coal-air mixtures, and turbulent coal combustion processes. The other main objective is to develop a computer code incorporating the new model. Experimental verification of the foundation of the model is also included in the study. In this report the thermodynamically consistent, rate dependent model for turbulent two-phase flows analysis was used and the phasic fluctuation energy dissipation rates are evaluated. Further progress on the application of the kinetic model for rapid flows of granular materials including the frictional energy losses were made. The velocity, the fluctuation energy and the solid volume fraction profiles for granular flows down a vertical channel were obtained. The results were compared with the molecular dynamic simulations of Savage and good agreement was obtained. The computational model was used and the rapid granular flows around a rectangular block in a channel were analyzed. The effect of bumpy wall on flow of granular materials was analyzed. The special case of Couette flow was studied. The preliminary results obtained is quite encouraging. Further progress was made in the experimental study of mono-layer simple shear flow device. Preliminary …
Date: December 31, 1993
Creator: Ahmadi, G.
Object Type: Report
System: The UNT Digital Library
A Computational Model for Coal Transport and Combustion. Quarterly Technical Progress Report, September 1, 1993--November 30, 1993 (open access)

A Computational Model for Coal Transport and Combustion. Quarterly Technical Progress Report, September 1, 1993--November 30, 1993

In the period of September 1, 1993 to November 30, 1993, further progress was made of the theoretical and computational modeling of turbulent two-phase flows, as well as granular flows. The effect of bumpy wall on flow of granular materials was also analyzed. The special case of Couette flow was studied. Further progress was made in the experimental study of mono-layer simple shear flow device. Preliminary data concerning the sharing of 12 mm multi-color glass particles are obtained. The preliminary experimental data show the expected variation. A detailed progress report for project review was also prepared which includes the recent development. The description of this report is given.
Date: December 31, 1993
Creator: Ahmadi, Goodarz
Object Type: Report
System: The UNT Digital Library
Dislocation Loops in Spinel Crystals Irradiated Successively With Deep and Shallow Ion Implants (open access)

Dislocation Loops in Spinel Crystals Irradiated Successively With Deep and Shallow Ion Implants

This study examines the influence of microstructural defects on irradiation damage accumulation in the oxide spinel. Single crystals of the compound MgAl{sub 2}O{sub 4} with surface normal [111] were irradiated under cryogenic temperature (100K) either with 50 keV Ne ions (fluence 5.0 {times} 10{sup 12}/cm{sup 2}), 400 keV Ne ions (fluence 6.7 {times} 10{sup 13}/cm{sup 2}) or successively with 400 keV Ne ions followed by 50 keV Ne ions. The projected range of 50 keV Ne ions in spinel is {approximately}50 mn (``shallow``) while the projected range of 400 keV Ne ions is {approximately}500 mn (``deep``). Transmission electron microscopy (TEM) was used to examine dislocation loops/defect clusters formed by the implantation process. Measurements of the dislocation loop size were made using weak-beam imaging technique on cross-sectional TEM ion-implanted specimens. Defect clusters were observed in both deep and shallow implanted specimens, while dislocation loops were observed in the shallow implanted sample that was previously irradiated by 400 keV Ne ions. Cluster size was seen to increase for shallow implants in crystals irradiated with a deep implant (size {approximately}8.5 nm) as compared to crystals treated only to a shallow implant (size {approximately}3.1 nm).
Date: December 31, 1993
Creator: Ai, R. X.; Cooper, E. A.; Sickafus, K. E.; Nastasi, M.; Bordes, N. & Ewing, R. C.
Object Type: Article
System: The UNT Digital Library
MEG studies of human vision: Retinotopic organization of V1 (open access)

MEG studies of human vision: Retinotopic organization of V1

A primary goal of noninvasive studies of human vision is to identify and characterize multiple visual areas in the human brain analogous to those identified in studies of nonhuman primates. By combining functional MEG measurements with images of individual anatomy derived from MRI, the authors hope to determine the location and arrangement of multiple visual areas in human cortex and to probe their functional significance. The authors have identified several different visual areas thus far which appear to be topographically organized. This paper focuses on the retinotopic characterization of the primary visual area (V1) in humans.
Date: December 31, 1993
Creator: Aine, C.; George, J.; Ranken, D.; Best, E.; Tiee, W.; Vigil, V. et al.
Object Type: Article
System: The UNT Digital Library
Characterization of explosive devices in luggage: Initial results of the ART-IIC test series (open access)

Characterization of explosive devices in luggage: Initial results of the ART-IIC test series

Characteristics and damage associated with exploded luggage aboard aircraft are presented in this paper. Plastic-sided suitcases filled with typical travel possessions were exploded inside the fuselage of decomissioned B-52 aircraft. Multilayered shield panels, mounted to one side of the fuselage, served to protect the aircraft body and flight system components from both the blast wave and exploded fragments. The resulting damage produced by the explosions was characterized and the absorbing characteristics of the shielding were evaluated. In addition, the energy of the luggage fragments was estimated.
Date: December 31, 1993
Creator: Akerman, M. A.; Kass, M. D. & Clough, B. T.
Object Type: Article
System: The UNT Digital Library
Fischer Tropsch synthesis in supercritical fluids. Quarterly technical progress report, July 1, 1993--September 30, 1993 (open access)

Fischer Tropsch synthesis in supercritical fluids. Quarterly technical progress report, July 1, 1993--September 30, 1993

During this quarter we have tested and calibrated six thermocouples of the temperature probe assembly. We obtained additional information on potential supercritical fluids from several vendors. We found out that all three potential supercritical solvents (propane, butane, and hexane) have less than 1 ppM sulfur impurities, whereas the maximum amount of sulfur in the feed should be less than 0.05 ppM. This remains to be a potential problem, since high levels of sulfur in the feed will result in catalyst poisoning. However, this would be the case with all three potential solvents, and thus we have decided to use propane as the supercritical fluid in our reaction studies based on its cost and favorable supercritical properties. In our shake down tests we will not use a catalyst guard bed for sulfur removal. If we experience problems with catalyst deactivation due to sulfur in feed, the guard bed will be installed in the propane feed line. We have ordered 1-tetradecene and will begin measuring diffusion coefficients of this compound in subcritical propane.
Date: December 31, 1993
Creator: Akgerman, A. & Bukur, D. B.
Object Type: Report
System: The UNT Digital Library
Fischer Tropsch synthesis in supercritical fluids. Quarterly technical progress report, October 1, 1993--December 31, 1993 (open access)

Fischer Tropsch synthesis in supercritical fluids. Quarterly technical progress report, October 1, 1993--December 31, 1993

Objectives for the first quarter for Task A, Diffusion Coefficients of F-T Products in Supercritical Fluids, were to measure diffusion coefficients of 1-tetradecene in subcritical propane and the diffusion coefficients of 1-octene and 1-tetradecene in subcritical propane and the diffusion coefficients of 1-octene and 1-tetradecene in subcritical and supercritical ethane. We planned to use ethane as a solvent because its lower critical temperature enabled measurements without modification of the existing unit. Our objective was to investigate the behavior of the diffusion coefficients in crossing from subcritical to supercritical conditions. Objectives for Task B, Fischer Tropsch reaction related studies, were: (1) to install and test the temperature probe and the flammable gas detector: (2) to conduct Fischer-Tropsch experiments at baseline conditions and at a high pressure in order to test the newly constructed fixed bed reactor assembly. Accomplishments and problems, are presented.
Date: December 31, 1993
Creator: Akgerman, A. & Bukur, D. B.
Object Type: Report
System: The UNT Digital Library
Removal of CO{sub 2} from flue gases by algae. Final technical report, September 1, 1992--August 31, 1993 (open access)

Removal of CO{sub 2} from flue gases by algae. Final technical report, September 1, 1992--August 31, 1993

The objective of this research program is to determine the feasibility of the alga Botryococcus braunii as a biocatalyst for the photosynthetic conversion of flue gas CO{sub 2} to hydrocarbons. Free and immobilized cells of Botryococcus braunii were grown in aqueous medium supplemented with nitrogen, phosphorus and mineral nutrients. Air and CO{sub 2} enriched air [10% to 15% (V/V) CO{sub 2}] in the gas phase and 0.2% to 2% NaHCO{sub 3} in the liquid medium served as the carbon source. Growth and hydrocarbon formation characteristics of free and immobilized cultures of Botryococcus braunii were determined in bench-scale photobioreactors. Technical and economic feasibility of the conversion of flue gas CO{sub 2} to hydrocarbons by Botryococcus braunii culture systems was evaluated. In free cell systems, the hexane extractable oil productivity was about 15 to 37 grams of oil per 100 grams of cell dry weight. In immobilized cell systems, the oil production ranged between 5% and 47% at different immobilization systems and immobilized surface locations, with an average of 19% of cell biomass dry weight. The feasibility and economic evaluation estimated the cost of oil produced from flue gas CO{sub 2} by algae to range between $45 and $75 per barrel assuming …
Date: December 31, 1993
Creator: Akin, C.; Maka, A.; Patel, S.; Conrad, J. & Benemann, J.
Object Type: Report
System: The UNT Digital Library
Investigation of syngas interaction in alcohol synthesis catalysts. Quarterly technical progress report, October 1,1995--December 31, 1995 (open access)

Investigation of syngas interaction in alcohol synthesis catalysts. Quarterly technical progress report, October 1,1995--December 31, 1995

Transition metals copper, cobalt, and iron play a significant role in the conversion of syngas to liquid fuels. Several catalytic studies indicate that product selectivity is governed by the inter-metallic ratios and the method of preparation. The catalytic as well as the magnetic character of the catalyst are known to be influenced by the modifications in the metal crystallites. With a view to examine the relations between the magnetic and catalytic properties, a series of Cu/Fe/Zn catalysts were prepared using the co-precipitation method. During this quarter, the magnetic characteristics of the samples before and after adsorption of carbon monoxide and after desorption of CO were investigated. Results are discussed in this report.
Date: December 31, 1993
Creator: Akundi, MA
Object Type: Report
System: The UNT Digital Library
A Quark Model of λλ Production in PP Interactions (open access)

A Quark Model of λλ Production in PP Interactions

A quark model which includes both scalar and vector contributions to the reaction mechanism (SV quark model) is used in a DWBA calculation of {anti {Lambda}}{Lambda} production in {bar p}p interactions. Total and differential cross-sections, polarizations, depolarizations, and spin-correlation coefficients are computed for laboratory momenta from threshold to 1695 MeV/c. The free parameters of the calculation are the scalar and vector strengths, a quark cluster size parameter, and the parameters of the unknown {anti {Lambda}}{Lambda} potentials. Good agreement with experiment is found for constructive interference of the scalar and vector terms, and for {anti {Lambda}}{Lambda} potentials which differ from those suggested by several authors on the basis of SU(3) arguments. The fit to the data is better than that obtained by other quark models, which use only scalar or vector annihilation terms. The agreement with experiment is also better than that found in meson-exchange models. The recent suggestion [1] that measurement of the depolarization parameter D{sub nn} can be used to discriminate between meson-exchange and quark models is examined in detail. We conclude that a measurement of D{sub nn} will provide a test of which of these models, as presently constructed, is the more appropriate description of strangeness production in …
Date: December 31, 1993
Creator: Alberg, M. A.; Henley, E. M.; Wilets, L. & Kunz, P. D.
Object Type: Article
System: The UNT Digital Library
Tensile and impact properties of iron-aluminum alloys (open access)

Tensile and impact properties of iron-aluminum alloys

Tensile and impact tests have been conducted on specimens from a series of five heats of iron-aluminum alloys. These results have been compared to data for the iron aluminide alloy FA-129. The transition temperatures of all of the Fe{sub 3}Al-based alloys were similar, but the simple ternary alloy had a much higher upper-shelf energy. The reduced aluminum alloys [based on Fe-8Al (wt %)] had lower transition temperatures and higher upper-shelf energy levels than the Fe{sub 3}Al-type alloys. The reduced aluminum alloy with yttrium showed excellent tensile properties, with a room temperature total elongation of 40%, and a very high upper-shelf energy level. Despite the high tensile ductility at room temperature, the transition temperature of the yttrium-containing alloy was still about 150 C, compared to approximately 300 C for FA-129. In general, the microstructures were coarse and anisotropic. The fracture processes were dominated by second-phase particles.
Date: December 31, 1993
Creator: Alexander, D. J. & Sikka, V. K.
Object Type: Article
System: The UNT Digital Library
Phase 3 of a Brushless Doubly-Fed Machine System Development Program : Final Technical Report for Period January 1, 1992-June 30, 1993. (open access)

Phase 3 of a Brushless Doubly-Fed Machine System Development Program : Final Technical Report for Period January 1, 1992-June 30, 1993.

Since the inception of the BDFM development program in 1989, the value of BDFM technology has become apparent. The BDFM provides for adjustable speed, synchronous operation while keeping costs associated with the required power conversion equipment lower than in competing technologies. This provides for an advantage in initial as well as maintenance expenses over conventional drive system. Thus, the BDFM enables energy efficient, adjustable speed process control for applications where established drive technology has not been able to deliver satisfactory returns on investment. At the same time, the BDFM challenges conventional drive technologies in established markets by providing for improved performance at lower cost. BDFM converter rating is kept at a minimum, which significantly improves power quality at the utility interface over competing power conversion equipment. In summary, BDFM technology can be expected to provide significant benefits to utilities as well as their customers. This report discusses technical research and development activities related to Phase 3 of the Brushless Doubly-Fed Machine System Development Program, including work made possible by supplemental funds for laboratory improvement and prototype construction. Market research for the BDFM was provided by the College of Business at Oregon State University; market study results will be discussed in …
Date: December 31, 1993
Creator: Alexander, Gerald C.; Spee, Rene & Wallace, Alan K.
Object Type: Report
System: The UNT Digital Library
Realtime structural electrochemistry of platinum clusters using dispersive XAFS (open access)

Realtime structural electrochemistry of platinum clusters using dispersive XAFS

Chemical reference tables state that the standard potential for the reaction of Pt with water, Pt + 2H{sub 2}O {r_arrow} Pt(OH){sub 2} + 2H{sup +} + 2e{sup {minus}}, is 0.98 V, and electrochemical studies propose that this reaction may occur at potentials as low as 0.8 V. Using dispersive x-ray absorption fine-structure (XAFS) spectroscopy, the authors have directly probed the structural evolution of a Pt catalyst operating in-situ in a polymer electrolyte fuel cell during cyclic voltammetry. The changes in the number of Pt and O nearest-neighbors and the Pt charge demonstrate a close correspondence with features in the voltammogram. Because dispersive XAFS is very sensitive to detecting structural changes, they have been able to detect the presence of chemisorbed oxygen at potentials of 0.6--0.9 V in the anodic sweep. Since double-layer charging is regarded as the only process in this region for bulk Pt, these results may reflect a limitation of previous (indirect) studies on Pt electrochemistry, or they may indicate that these clusters are different from their bulk metal counterparts. Exploiting the time-resolving capability of dispersive XAFS, they also monitored changes in the Pt charge and the number of O and Pt nearest-neighbors during the electrochemical oxidation and …
Date: December 31, 1993
Creator: Allen, P. G.; Conradson, S. D.; Wilson, M. S.; Gottesfeld, S. & Raistrick, I. D.
Object Type: Article
System: The UNT Digital Library
High-efficiency target-ion sources for RIB generation (open access)

High-efficiency target-ion sources for RIB generation

A brief review is given of high-efficiency ion sources which have been developed or are under development at ISOL facilities which show particular promise for use at existing, future, or radioactive ion beam (RIB) facilities now under construction. Emphasis will be placed on those sources which have demonstrated high ionization efficiency, species versatility, and operational reliability and which have been carefully designed for safe handling in the high level radioactivity radiation fields incumbent at such facilities. Brief discussions will also be made of the fundamental processes which affect the realizable beam intensities in target-ion sources. Among the sources which will be reviewed will be selected examples of state-of-the-art electron-beam plasma-type ion sources, thermal-ionization, surface-ionization, ECR, and selectively chosen ion source concepts which show promise for radioactive ion beam generation. A few advanced, chemically selective target-ion sources will be described, such as sources based on the use of laser-resonance ionization, which, in principle, offer a more satisfactory solution to isobaric contamination problems than conventional electromagnetic techniques. Particular attention will be given to the sources which have been selected for initial or future use at the Holifield Radioactive Ion Beam Facility now under construction at the Oak Ridge National Laboratory.
Date: December 31, 1993
Creator: Alton, G. D.
Object Type: Article
System: The UNT Digital Library