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The effect of temperature, growth kinetics, and substrate on the microstructure of RF off-axis sputter deposited YBa{sub 2}Cu{sub 3}O{sub 7} thin films

Description: YBa{sub 2}Cu{sub 3}O{sub 7} (YBCO) thin films were grown on single crystal substrates by RF off-axis sputter deposition under different growth condition, systematically varied to change the kinetic and thermodynamic processes that determine both the film microstructure and its crystallographic orientation. The effect of substrate temperature, position, and material, total chamber pressure, and RF power on the final film structure was examined. The growth matrix was bounded by temperatures from 640 to 780C, pressures from 50 to 200 mtorr, and power from 50 to 100 watts. Higher growth rates were achieve by increasing the power setting, lowering the total pressure, and moving the substrate farther into the plasma. Care was taken to stay within these parametric stability limits defining the 123-YBCO growth regime. The resulting films were characterized, primarily, by scanning tunneling and atomic force microscopy, x-ray diffraction, and eddy-current measurements. At the extremes of the growth conditions used in this study, ex-situ examination of the films revealed that they spanned the extremes from all c-axis normal to all a-axis normal material, with mixed a-/c-axis normal material in between extremes in deposition parameter limits, with the mixed films containing a-axis material overlaying a c-axis layer. Smooth single orientation films, suitable for multilayer device structure, could be routinely obtained by controlled growth. Highest surface roughness measurements were usually due to incomplete or non uniform a-axis coverage on c-axis films. Combined data obtained from different studies showed that lower temperatures and higher rates favored a-axis growth under the conditions used in these studies. The YBCO films were more unstable to a cross-over from c-axis to a-a-axis growth when deposited on NdGaO{sub 3} and LaAIO{sub 3} than on SrTiO{sub 3}. Under conditions favoring c-axis perpendicular growth, higher temperatures and rates resulted in rounder islands.
Date: July 1, 1995
Creator: Hawley, M.; Houlton, R.J.; Garzon, F.H. & Raistrick, I.D.
Partner: UNT Libraries Government Documents Department

Partial reduction of re-oxidation processing of Y-Ba-Cu-O sputtered thin films

Description: Thin films of Y--Ba--Cu--O were produced by rf sputtering of YBa{sub 2}Cu{sub 3}O{sub 7-x} ceramic targets, using a variety of plasma compositions, rf power levels, and substrate temperatures. Post annealing of these films in oxygen produced superconducting films with T{sub c} values between 40--60 K, broad transition widths and semiconductor-like electrical behavior above T{sub c}. Subsequent annealing at 850{degree}C in an inert gas with a residual oxygen partial pressure of {le}10 ppM followed by an oxygen anneal produced high quality thin films: T{sub c} > 85 K with narrow transition widths. The structure and morphology of these films during reduction-oxidation processing were monitored using x-ray diffraction and electron microscopy. 8 refs., 4 figs.
Date: January 1, 1989
Creator: Garzon, F.H.; Beery, J.G.; Wilde, D.K. & Raistrick, I.D.
Partner: UNT Libraries Government Documents Department

Electrochemical studies of perovskite mixed conductors

Description: Research into the growth of high-quality single crystal thin films of high transition temperature {Tc} superconductors have stimulated interest in other perovskite metal oxides with a variety of physical properties. Thin films of perovskite materials are among the major focal research areas for optical, sensor, electronic, and superconducting applications. Two lanthanum-based oxygen/electronic conducting perovskite oxides of particular interest for high temperature fuel cell electrodes and interconnects and for other electrochemical applications such as oxygen separation devices are La{sub 1{minus}x}Sr{sub x}MnO{sub 3{minus}y} and La{sub 1{minus}x}Sr{sub x}CoO{sub 3{minus}y}. The La-based perovskites are valuable for these technologies because they reduce interfacial resistances by eliminating the need for a three phase contact area (gas, metal electrode, electrolyte). In addition, these oxides may also serve a valuable role as novel catalysts or catalytic supports; however, little is known about what catalytic properties they may possess. Fundamental study of the electrochemical, diffusional oxygen transport, and surface catalytic properties of these materials can be greatly simplified if the complications associated with the presence of grain boundaries and multiple crystallite orientations can be avoided. Therefore, single crystals of these La-based perovskites become highly desirable. In this work, the authors report the structural and electrical properties of highly oriented thin films of La{sub 0.84}Sr{sub 0.16}MnO{sub 3} and La{sub 0.8}Sr{sub 0.2}CoO{sub 3} grown on single crystal Y-ZrO{sub 2} substrates. An addition, the authors have demonstrated growing, in situ, epitaxial multilayer perovskite/fluorite/perovskite configurations for fundamental fuel cell modeling.
Date: December 1, 1994
Creator: Brosha, E. L.; Chung, B. W. & Garzon, F. H.
Partner: UNT Libraries Government Documents Department

The Evolution of High Temperature Gas Sensors.

Description: Gas sensor technology based on high temperature solid electrolytes is maturing rapidly. Recent advances in metal oxide catalysis and thin film materials science has enabled the design of new electrochemical sensors. We have demonstrated prototype amperometric oxygen sensors, nernstian potentiometric oxygen sensors that operate in high sulfur environments, and hydrocarbon and carbon monoxide sensing mixed potentials sensors. Many of these devices exhibit part per million sensitivities, response times on the order of seconds and excellent long-term stability.
Date: January 1, 2001
Creator: Garzon, F. H. (Fernando H.); Brosha, E. L. (Eric L.) & Mukundan, R. (Rangachary)
Partner: UNT Libraries Government Documents Department

Characterization of fuel cell electrocatalysts using x-ray methods

Description: High surface area electrocatalysts are critical components of high efficiency low cost polymer membrane fuel cells. The platinum and/or platinum alloy catalysts are typically prepared as nanocrystalline carbon supported and unsupported anode and cathode materials. The choice of catalyst type depends on whether the application is for hydrogen or direct methanol fuel cells (DMFCs). 2 nm crystallite size Pt supported on Vulcan XC-72 carbon is the anode and cathode catalyst most commonly used for hydrogen fuel cells while Pt-Ru alloys of 3-5 nm are currently being used for anode catalysts in DMFC systems. Key parameters for successful catalyst design are average alloy composition, crystal structure, crystallite composition crystallite size and size distribution. All of the aforementioned parameters can be efficently and nondistructively measured using laboratory scale X-ray analysis methods. Recent advances in personal computer technology allow for full profile (Rietveld) and Warren-Averbach Fourier transform X-ray diffraction methods to be performed quickly and routinely. Full profile, also known as whole pattern analysis methods, model the entire X-ray diffraction pattern rather than just peak maxima. Highly overlapped diffraction patterns are very common in nanocrystalline materials due to size related line broadening phenomena. Full profile methods allow for the precise determination of lattice parameters and accurate measurement of individual diffraction line intensities. Phase fractions and percentages of amorphous material can also be estimated using full profile analysis techniques. Warren-Averbach Fourier transform methods allow for the determination of particle size distributions. This method offers advantages in speed and cost over electron microscopic analysis methods to obtain crystallite size distributions. Fundamental parameter X-ray fluorescence spectroscopy methods allows for the rapid accurate determination of catalyst composition and mass loadings on raw materials and membrane electrode assemblies. Another advantage of this method over older empirical standard methods is the elimination of many calibration standards of different compositions. ...
Date: January 1, 2001
Creator: Garzon, F. H. (Fernando H.); Brosha, E. L. (Eric L.); Zawodzinski, C. (Christine) & Ren, X. (Xiaoming)
Partner: UNT Libraries Government Documents Department

Understanding the response behavior of potentiometric gas sensors for non-equilibrium gas mixtures

Description: Many applications of gas sensors require concentration measurements of reactive gases in mixtures that are out of thermodynamic equilibrium. These applications include: hydrogen and hydrocarbon fuel gas sensors operating in ambient air for explosion hazard detection, carbon monoxide detection in ambient air for health protection, combustion efficiency sensors for stoichiometry control, and nitric oxide sensors for air pollution monitoring. Many potentiometric and amperometric electrochemical sensor technologies have been developed for these applications. A class of the potentiometric sensors developed for gas mixtures are the non-Nerstian sensors. This presentation defines a categorization and theoretical analysis of three distinct electrochemical processes that can produce a non-Nernstian sensor response.
Date: January 1, 2002
Creator: Garzon, F. H. (Fernando H.); Mukundan, R. (Rangachary) & Brosha, E. L. (Eric L.)
Partner: UNT Libraries Government Documents Department

The development of a fullerene based hydrogen storage system

Description: This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at Los Alamos National Laboratory (LANL). The project objective was to evaluate hydrogen uptake by fullerene substrates and to probe the potential of the hydrogen/fullerene system for hydrogen fuel storage. As part of this project, the authors have completed and tested a fully automated, computer controlled system for measuring hydrogen uptake that is capable of handling both a vacuum of 1 x 10{sup -6} torr and pressures greater than 200 bars. The authors have first established conditions for significant uptake of hydrogen by fullerenes. Subsequently, hydrogenation and dehydrogenation of pure and catalyst-doped C60 was further studied to probe suitability for hydrogen storage applications. C60 {center_dot} H18.7 was prepared at 100 bar H2 and 400 C, corresponding to hydrogen uptake of 2.6 wt%. Dehydrogenation of C60 {center_dot} H18.7 was studied using thermogravimetric and powder x-ray diffraction analysis. The C60 {center_dot} H18.7 molecule was found to be stable up to 430 C in Ar, at which point the release of hydrogen took place simultaneously with the collapse of the fullerene structure. X-ray diffraction analysis performed on C60 {center_dot} H18.7 samples dehydrogenated at 454 C, 475 C, and 600 C showed an increasing volume fraction of amorphous material due to randomly oriented, single-layer graphine sheets. Evolved gas analysis using gas chromatography and mass spectroscopy confirmed the presence of both H{sub 2} and methane upon dehydrogenation, indicating decomposition of the fullerene. The remaining carbon could not be re-hydrogenated. These results provide the first complete evidence for the irreversible nature of fullerene hydrogenation and for limitations imposed on the hydrogenation/dehydrogenation cycle by the limited thermal stability of the molecular crystal of fullerene.
Date: November 1, 1998
Creator: Brosha, E.L.; Davey, J.R.; Garzon, F.H. & Gottesfeld, S.
Partner: UNT Libraries Government Documents Department

Polymer electrolyte fuel cells for transportation applications

Description: The application of the polymer electrolyte fuel cell (PEFC) as a primary power source in electric vehicles has received incrming attention during the last few years. This increased attention has been fueled by a combination of significant technical advances in this field and by the initiation of some projects for the demonstration of a complete, PEFC-based power system in a bus or in a passenger car. Such demonstration pretieds reflect an increased faith of industry in the potential of this technology for transportation applications, or, at least, in the need for a detailed evaluation of this potential Nevertheless, large scale transportation applications of PEFCs requim a continued concerted effort of research on catalysis, materials and components, combined with the engineering efforts addressing the complete power system. This is required to achieve cost effective, highly performing PEFC stack and power system. We describe in this contribution some recent results of work performed within the Core Research PEFC Program at Los Alamos National Laboratory, which has addressed transportation applications of PEFCs.
Date: January 1, 1993
Creator: Springer, T.E.; Wilson, M.S.; Garzon, F.H.; Zawodzinski, T.A. & Gottesfeld, S.
Partner: UNT Libraries Government Documents Department

Thin film ionic conductors based on cerium oxide

Description: Fluorite and perovskite structure cerium oxide based ceramics are a class of materials that may exhibit good oxygen ion and/or protonic conductivity. The authors have successfully deposited thin films of these materials on a variety of substrates. Interesting orientation relationships were noticed between cerium oxide films and strontium titanate bi-crystal substrates. Near lattice site coincidence theory has been used to study these relationships.
Date: December 1, 1994
Creator: Haridoss, P.; Hellstrom, E.; Garzon, F. H.; Brown, D. R. & Hawley, M.
Partner: UNT Libraries Government Documents Department

Temperature-dependent growth of LaAlO{sub 3} films on YBa{sub 2}Cu{sub 3}O{sub 7} C-axis films for multilayer structures

Description: Fabrication of ultra smooth films, free of micro-shorts, is essential to the development of High Temperature Superconducting (HTS) thin film devices. One such example is a SNS junction consisting of two HTS layers separated by a uniformly smooth continuous barrier material. Other schemes under consideration require multilayer structures of up to 5 - 7 epitaxially grown layers of complex oxide material. Successful fabrication of such devices necessitates understanding the epitaxial growth of polycrystalline oxide films on polycrystalline film templates. Toward this end we have developed a set of deposition parameters that produce high quality epitaxial insulating layers suitable for HTS device applications. All films in this study were grown by off-axis RF magnetron sputter deposition. LaAlO{sub 3} films were deposited over MgO grown YBa{sub 2}Cu{sub 3}O{sub 7} (YBCO) c-axis thin films at temperatures ranging from 200 to 700C and on virgin substrates at 600C. Atomic Force Microscopy, eddy current measurements, and x-ray diffraction techniques were used to monitor the effect of growth conditions on the resulting film crystallinity, nanostructure, and electrical properties. Ex-situ interrupted growth characterization of these materials has yielded new insight into the processes that control the growth mechanism and resulting microstructure. All films were polycrystalline. Below 600C, LaAlO{sub 3} films were not epitaxial while films grown at 650C showed some <200> orientation. The shape of the underlying YBCO film is most clearly evident for the film grown at 400C. Surface roughness depended on the appearance of crystals on the film surface. The superconducting properties of the underlying YBCO film required O{sub 2} annealing prior to deposition of the LaAlO{sub 3} layer.
Date: January 1, 1995
Creator: Hawley, M. E.; Houlton, R. J.; Raistrick, I. A. & Garzon, F. H.
Partner: UNT Libraries Government Documents Department

Vapor deposition of thin-film Y-doped ZrO{sub 2} for electrochemical device applications

Description: Solid oxide electrolytes based on yttria-stabilized zirconia (YSZ) are widely used in applications such as oxygen sensors, solid oxide fuel cells, oxygen pumps, electrocatalytic reactors, and electrochemically driven oxygen separation membranes. However, bulk YSZ is used in these applications. This requires high operating temperatures in order to minimize ohmic loss. One alternative of overcoming this problem is to use a thin film of the electrolyte. In the work, the authors have grown polycrystalline thin films of fully stabilized Y-ZrO{sub 2} on thick porous Al{sub 2}O{sub 3} substrates in multilayer La{sub 1{minus}x}Sr{sub x}MEO{sub 3}YSZ/La{sub 1{minus}x}Sr{sub x}MEO{sub 3} (ME = Mn, Co) configurations using a combination of single-target RF magnetron sputtering and electron beam physical vapor deposition techniques. The structure and morphology of these films have been studied using X-ray diffraction, and Scanning Electron Microscopy techniques. The ionic conductivity of the thin films has been measured using AC impedance analysis.
Date: December 1, 1994
Creator: Chung, B. W.; Brosha, E. L.; Brown, D. R. & Garzon, F. H.
Partner: UNT Libraries Government Documents Department

Development of ceramic mixed potential sensors for automotive application

Description: Mixed potential sensors that utilize Gd{sub 0.2}Ce{sub 0.8}O{sub 2} electrolytes and patterned dense 1 {micro}m-thick LaMnO{sub 3} thin films were studied at 600 C and 1%O{sub 2}. The response to C{sub 3}H{sub 6} and CO of two different sensor configurations were studied continuously for 1000 hrs versus an air reference. Although two different current collection schemes and two different metal oxide electrode geometries were employed, the magnitude of the mixed potential generated by both sensors was remarkably similar. From previous work with Au-ceria-Pt mixed potential sensors, this behavior is attributed to precisely controlling the metal oxide electrode/solid electrolyte interface unlike the random interface produced when Au electrodes are used. Although doped ceria is not a suitable electrolyte for automotive exhaust gas applications, this work serves to illustrate design goals for zirconia-based sensors.
Date: January 1, 2001
Creator: Brasha, E. (Eric); Mukundan, R. (Rangachary); Brown, D. R. (David R.); Garzon, F. H. (Fernando H.) & Visser, J. (Jaco)
Partner: UNT Libraries Government Documents Department

Thin film techniques for solid state ionic devices

Description: The perovskite of type LaCrO{sub 3} sense electrode for a new type growth and patterning of thin tas been previously shown to be an excellent of mixed potential sensor. Techniques for the film electrodes with stable morphology and reproducible stoichiometry grown on yttria-stabilized zirconia solid electrolyte have therefore become extremely desirable. In this work, thin films of LaCrO{sub 3} and La{sub 0.8}Sr{sub 0.2}Cr0{sub 3} were prepared using RF magnetron sputtering, electron beam evaporation and pulsed laser deposition. Direct growth of the perovskite from oxide targets were usually accompanied by second phases with Cr in valance states higher than 3'. Films prepared by an intermediate fluoride process via offaxis RF magnetron sputtering process produced the highest quality films but the deposition rate was typically low at approximately 1500khr. Stoichiometric films were prepared using an electron beamlthermal evaporation dual source method but not reproducibly. Single-phase lanthanum chromite films could not be prepared using PLD and a fluoride precursor.
Date: January 1, 2003
Creator: Brosha, E. L. (Eric L.); Mukundan, R. (Rangachary); Brown, D. R. (David R.) & Garzon, F. H. (Fernando H.)
Partner: UNT Libraries Government Documents Department

Development of Sensors and Sensing Technology for Hydrogen Fuel Cell Vehicle Applications

Description: One related area of hydrogen fuel cell vehicle (FCV) development that cannot be overlooked is the anticipated requirement for new sensors for both the monitoring and control of the fuel cell's systems and for those devices that will be required for safety. Present day automobiles have dozens of sensors on-board including those for IC engine management/control, sensors for state-of-health monitoring/control of emissions systems, sensors for control of active safety systems, sensors for triggering passive safety systems, and sensors for more mundane tasks such as fluids level monitoring to name the more obvious. The number of sensors continues to grow every few years as a result of safety mandates but also in response to consumer demands for new conveniences and safety features. Some of these devices (e.g. yaw sensors for dynamic stability control systems or tire presure warning RF-based devices) may be used on fuel cell vehicles without any modification. However the use of hydrogen as a fuel will dictate the development of completely new technologies for such requirements as the detection of hydrogen leaks, sensors and systems to continuously monitor hydrogen fuel purity and protect the fuel cell stack from poisoning, and for the important, yet often taken for granted, tasks such as determining the state of charge of the hydrogen fuel storage and delivery system. Two such sensors that rely on different transduction mechanisms will be highlighted in this presentation. The first is an electrochemical device for monitoring hydrogen levels in air. The other technology covered in this work, is an acoustic-based approach to determine the state of charge of a hydride storage system.
Date: January 6, 2010
Creator: Brosha, E L; Sekhar, P K; Mukundan, R; Williamson, T; Garzon, F H; Woo, L Y et al.
Partner: UNT Libraries Government Documents Department

Terahertz emission from YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} thin films via bulk electric quadrupole optical rectification

Description: The authors describe here the first observation of terahertz emission from unbiased YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} (YBCO) thin films. These films are excited by 150 fs, 1.5 eV and 3.0 eV, optical pulses for a range of temperatures, T, 4 K < T < 300 K and for a range of oxygen doping from optimally-doped ({delta} = 0) to insulating ({delta} = 0.8). They demonstrate that this emission is generated by optical rectification due to the bulk electric quadrupole source term, comprising the first observation of such a source term in terahertz emission.
Date: March 1, 1998
Creator: Siders, J.L.W.; Trugman, S.A.; Houlton, R.J.; Garzon, F.H. & Taylor, A.J.
Partner: UNT Libraries Government Documents Department

Electrochemical and XRD characterization of platinum-ruthenium blacks for DMFC anodes.

Description: It is generally accepted that Pt-Ru alloy catalysts with an atomic Pt-to-Ru ratio of 1:1 generate the best anode perform'ance in the direct methanol fuel cell (DMFG). However, at near-ambient cell operating temperatures, Gasteiger et al. reported that a catalyst with significantly lower Ru content, {approx} 10 at %, offers the highest activity towards methanol. Recently, Dinh et al. demonstrated that the activity of different Pt-Ru catalysts with the same Pt-to-Ru atomic ratio in the bulk might vary depending on the actual surface composition, which is often significantly different from that in the bulk phase, In this work, we study several experimental Pt-Ru catalysts (Johnson Matthey) with Pt-to-Ru atomic ratio ranging from 9: 1 to 1 :2. Electrocatalytic activity of these catalysts in methanol oxidation reaction is investigated in a regular DMFC 'and probed using voltammetric stripping of surhce CO.
Date: January 1, 2002
Creator: Eickes, C. (Christian); Brosha, E. L. (Eric L.); Garzon, F. H. (Fernando H.); Purdy, G. M. (Geraldine M.); Zelenay, P. (Piotr); Morita, T. (Takanari) et al.
Partner: UNT Libraries Government Documents Department

Neutron measurements in search of cold fusion

Description: We have conducted a research for neutron emission from cold fusion systems of the electrochemical type and, to a lesser extent, the high-pressure gas cell type. Using a high-efficiency well counter and an NE 213 scintillator, the experiments were conducted on the earth's surface and in a shielded cave approximately 50 ft underground. After approximately 6500 h of counting time, we have obtained no evidence for cold fusion processes leading to neutron production. However, we have observed all three types of neutron data that have been presented as evidence for cold fusion: large positive fluctuations in the neutron counting rate, weak peaks near 2.5 MeV in the neutron energy spectrum, and bursts of up to 145 neutrons in 500-{mu}s intervals. The data were obtained under circumstances that clearly show our results to be data encountered as a part of naturally occurring neutron background, which is due primarily to cosmic rays. Thus, observing these types of data does not, of itself, provide evidence for the existence of cold fusion processes. Artifacts in the data that were due to counter misbehavior were also to lead to long-term neutron bursts'' whose time duration varied from several hours to several days. We conclude that any experiments which attempt to observe neutron emission must include strong steps to ensure that the experiments deal adequately with both cosmic-ray processes and counter misbehavior. 13 refs., 14 figs.
Date: January 1, 1990
Creator: Anderson, R.E.; Goulding, C.A.; Johnson, M.W.; Butterfield, K.B.; Gottesfeld, S.; Baker, D.A. et al.
Partner: UNT Libraries Government Documents Department

Microstructure and properties of in-situ rf sputtered YBa sub 2 Cu sub 3 O sub 7 thin films for microwave applications

Description: The residual surface resistance of a number of films of YBa{sub 2}Cu{sub 3}O{sub 7}, prepared by off-axis sputtering onto MgO substrates, has been measured using parallel-plate resonator technique. Deposition conditions were kept constant, apart from the substrate temperature. There is no correlation between surface resistance and other important microscopic parameters, such as T{sub c} and c-axis lattice parameter. There is, however, a trend to higher R{sub s} with increasing volume fraction of in-plane misoriented material, although the correlation is not perfect. Furthermore, we have found that most of the misoriented material is localized at the film substrate interface and therefore is probably not responsible for most of the RF losses. The data suggest that at higher deposition temperatures, there is an increasing tendency for 45{degrees}-misoriented material to appear in the films, and it may be that a significant fraction of this material is present closer to the free film surface. STM qualitatively supports this conclusion.
Date: January 1, 1992
Creator: Reagor, D.W.; Houlton, R.J.; Garzon, F.H.; Hawley, M.; Raistrick, I.D. (Los Alamos National Lab., NM (United States)) & Piza, M.E. (Massachusetts Inst. of Tech., Cambridge, MA (United States). Dept. of Materials Science)
Partner: UNT Libraries Government Documents Department

Technical progress in the development of zero emission coal technologies.

Description: We present an update on the development of technologies required for the Zero Emission Carbon (ZEC) concept being pursued by ZECA Corporation. The concept has a highly integrated design involving hydrogasification, a calcium oxide driven reforming step that includes simultaneous C02 separation, coal compatible fuel cells for electricity production and heat recovery, and a closed loop gas system in which coal contaminants are removed either as liquids or solids. The process does not involve any combustion and as such has neither smokestack nor air emissions. An independent assessment of the concept by Nexant, a Bcchtel affiliated company, suggests a net efficiency of approximately 70% for conversion of the higher heat value fuel energy into electrical output. This is even after the penalties of carbon dioxide separation and pressurization to 1000 psi are taken into account. For carbon dioxide sequestration a variety of options are being considered, which include enhanced oil recovery in the near-term and mineral carbonation as a long-term approach. We report on our early results in the development of sulfur tolerant anode materials for solid oxide fuel cells; a critical analysis of the calcium oxide - calcium carbonate cycle; trace element removal; and the recent results of hydrogasification tests.
Date: January 1, 2002
Creator: Ziock, H. J. (Hans-Joachim); Anthony, E. J.; Brosha, E. L. (Eric L.); Garzon, F. H. (Fernando H.); Guthrie, G. D. (George D.); Johnson, A. A. (Alan A.) et al.
Partner: UNT Libraries Government Documents Department