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Effect of solution saturation state and temperature on diopside dissolution

Description: Steady-state dissolution rates of diopside are measured as a function of solution saturation state using a titanium flow-through reactor at pH 7.5 and temperature ranging from 125 to 175 C. Diopside dissolved stoichiometrically under all experimental conditions and rates were not dependent on sample history. At each temperature, rates continuously decreased by two orders of magnitude as equilibrium was approached and did not exhibit a dissolution plateau of constant rates at high degrees of undersaturation. The variation of diopside dissolution rates with solution saturation can be described equally well with a ion exchange model based on transition state theory or pit nucleation model based on crystal growth/dissolution theory from 125 to 175 C. At 175 C, both models over predict dissolution rates by two orders of magnitude indicating that a secondary phase precipitated in the experiments. The ion exchange model assumes the formation of a Si-rich, Mg-deficient precursor complex. Lack of dependence of rates on steady-state aqueous calcium concentration supports the formation of such a complex, which is formed by exchange of protons for magnesium ions at the surface.
Date: March 23, 2007
Creator: Dixit, S & Carroll, S A
Partner: UNT Libraries Government Documents Department

Spectropolarimetry of FIRST 0840 + 3633

Description: We present Keck spectropolarimetry of a rare ``Iron Lo- BALQSO,`` FIRST 0840+3633. The continuum is {approximately}4% polarized near 2000{Angstrom} rest-frame, but falls to {approximately}2% at longer wavelengths, and maintains a relatively constant position angle of 50{degrees}. The emission lines are unpolarized. The polarization increases up to {approximately}8% in the low-ionization absorption troughs of Mg II {lambda}2800 and Al III {lambda}1860. The polarization and its position angle vary in a complicated manner across the metastable Fe II absorption lines, suggesting that more than one mechanism is at work or that the system geometry is complex.
Date: February 1, 1997
Creator: Brotherton, M.S.; Van Breugel, N.; Dey, A. & Antonucci, R.
Partner: UNT Libraries Government Documents Department

Ion implantation of epitaxial GaN films: damage, doping and activation

Description: Single-crystal GaN films grown on AlN buffer layers previously deposited on 6H-SiC(0001) were studied for radiation damage and its recovery using Rutherford backscattering/channeling, photoluminescence, and cross-sectional TEM. The highest fluence of (1e15 cm{sup -2}) 110 keV Mg and 160 keV Si produced little damage at implantation temperature 550 C. RT damage was higher for same fluences compared to 550 C implantation. The damage was partially annealed by RTA at 1000 C, however, this was not enough to recover the PL signal even for the lowest fluence (1e14 cm{sup -2}). XTEM of as-implanted samples revealed small clusters of defects extended beyond the projected ion range. To recover damage completely, perhaps one needs to go either much higher RTA temperature and/or implant samples in a smaller fluence increment and anneal in between implants to recover the damage.
Date: December 31, 1996
Creator: Parikh, N.; Suvkhanov, A.; Lioubtchenko, M.; Carlson, E.; Bremser, M.; Bray, D. et al.
Partner: UNT Libraries Government Documents Department

Soft x-ray spectroscopy measurements of plasma conditions at early times in ICF experiments on OMEGA. Semi-annual report, November 1, 1998--April 30, 1999

Description: Since arrival of FY-99 funding in December, the authors have been preparing for the first series of experiments under this grant on the OMEGA laser facility, which just took place (for one day) on April 27, 1999. The campaign was successful and results will be included in the next progress report following analyses. For the first time, they fielded their Ten Inch Manipulator (TIM-) mounted flat-field, grazing-incidence extreme-ultraviolet (euv) spectrograph with a four-channel gated-stripline microchannel plate (MCP) detector. This spectrograph covers the spectral range of 30--250 {angstrom} (hv = 50--400 eV). As in a previous campaign of May 1998, where the authors used this instrument with time-integrated photographic recording, the spectrograph reached closer to the target than did the previous version mounted on the chamber wall; such that the sensitivity increased by at least a factor-of-10 for viewing weak spectral features. The analysis during this reporting period of the euv spectroscopic results from the October 1998 NLUF/OMEGA campaign of Mg X, XI and XII spectra from n = 3 to n = 2 transitions are shown in Fig. 1 versus time. The data plotted represent a composite between the three most sensitive striplines, delayed relative to each other, for a number of shots. The intended emphasis was on the early portion of the event while the laser intensity is rising to a peak. This measured euv history agrees with that from the x-ray streak spectrographic data shown in Fig. 2 from the same campaign, i.e., the peak period of emission being in the first 1.5 ns.
Date: May 3, 1999
Creator: Griem, H.R. & Elton, R.C.
Partner: UNT Libraries Government Documents Department

TOWARDS CRYSTALLINE ION BEAMS - THE PALLAS(1) RING TRAP.

Description: To experimentally elucidate fundamental issues of crystalline ion beams at low velocities we presently set up PALLAS, a table top circular RF quadrupole storage ring for acceleration and laser cooling of, e.g., {sup 24}Mg{sup +} ions. Employing the smooth approximation to PALLAS we compare its beam dynamics to heavy ion synchrotrons like TSR Heidelberg and thereby demonstrate the necessity of the highly symmetric lattice for the attainment of crystalline structures. Furthermore, dedicated molecular dynamics simulations are presented, affirming the feasibility of beam crystallization in PALLAS.
Date: October 1, 1998
Creator: SCHATZ,T.
Partner: UNT Libraries Government Documents Department

Detection of photon bursts from single 200 eV Mg ions: Progress in photon burst mass spectrometry

Description: Modern atom counting methods, based on advances in laser and accelerator technology, provide a valuable complement to traditional decay counting methods for radioisotope dating and tracer work. Tandem Accelerator Mass Spectrometry (TAMS) has already had a large impact on /sup 14/C dating and is beginning to provide new opportunities with /sup 10/Be and several other isotopes. We report here on progress in the development of a laser-based technique, Photon Burst Mass Spectrometry, which is potentially capable of analyzing many of the elements which are forbidden in TAMS because they do not form negative ions. We are especially interested in the noble gases, which have a variety of potential scientific and environmental applications.
Date: January 1, 1989
Creator: Fairbank, W.M. Jr.; LaBelle, R.D.; Keller, R.A. & Chamberlin, E.P.
Partner: UNT Libraries Government Documents Department

DEVELOPMENT OF A CO2 SEQUESTRATION MODULE BY INTEGRATING MINERAL ACTIVATION AND AQUEOUS CARBONATION

Description: Mineral carbonation provides a potential option for the long-term storage of carbon dioxide. Serpentine has been chosen as the feedstock mineral, due to its abundance and availability. However, the relatively low reactivity of serpentine has warranted research into physical and chemical treatments that have been shown to greatly increase its reactivity. The use of sulfuric acid as an accelerating medium for the removal of magnesium from serpentine has recently been investigated. In addition to the challenges presented by the dissolution of serpentine, another challenge is the subsequent carbonation of the magnesium ions. A stable hydration sphere for the magnesium ion reduces the carbonation kinetics by obstructing the formation of the carbonation products. Accordingly, this research has evaluated the solubility of carbon dioxide in aqueous solution, the interaction between the dissociation products of carbon dioxide, and the carbonation potential of the magnesium ion.
Date: March 25, 2006
Creator: Alexander, George; Maroto-Valer, M. Mercedes; Aksoy, Parvana & Schobert, Harold
Partner: UNT Libraries Government Documents Department

Development of a CO2 Sequestration Module by Integrating Mineral Activation and Aqueous Carbonation

Description: Mineral carbonation is a promising concept for permanent CO{sub 2} sequestration due to the vast natural abundance of the raw materials and the permanent storage of CO{sub 2} in solid form as carbonates. The sequestration of CO{sub 2} through the employment of magnesium silicates--olivine and serpentine--is beyond the proof of concept stage. For the work done in this project, serpentine was chosen as the feedstock mineral due to its abundance and availability. Although the reactivity of olivine is greater than that of serpentine, physical and chemical treatments have been shown to increase greatly the reactivity of serpentine. The primary drawback to mineral carbonation is reaction kinetics. To accelerate the carbonation, aqueous processes are preferred, where the minerals are first dissolved in solution. In aqueous carbonation, the key step is the dissolution rate of the mineral, where the mineral dissolution reaction is likely to be surface-controlled. The relatively low reactivity of serpentine has warranted research into physical and chemical treatments that have been shown to greatly increase its reactivity. The use of sulfuric acid as an accelerating medium for the removal of magnesium from serpentine has been investigated. To accelerate the dissolution process, the mineral can be ground to very fine particle size, <37 {micro}m, but this is a very energy-intensive process. Previous work in our laboratory showed that chemical surface activation helps to dissolve magnesium from the serpentine (of particle size {approx} 100 {micro}m) and that the carbonation reaction can be conducted under mild conditions (20 C and 4.6 MPa) compared to previous studies that required >185 C, >13 MPa, and <37 {micro}m particle size. This work also showed that over 70% of the magnesium can be extracted at ambient temperature, leaving an amorphous silica with surface area of about 330 m{sup 2}/g. The overall objective of this research program ...
Date: August 14, 2006
Creator: Alexander, George; Aksoy, Parvana; Andresen, John; Maroto-Valer, Mercedes & Schobert, Harold
Partner: UNT Libraries Government Documents Department

Nanostructured material for advanced energy storage : magnesium battery cathode development.

Description: Magnesium batteries are alternatives to the use of lithium ion and nickel metal hydride secondary batteries due to magnesium's abundance, safety of operation, and lower toxicity of disposal. The divalency of the magnesium ion and its chemistry poses some difficulties for its general and industrial use. This work developed a continuous and fibrous nanoscale network of the cathode material through the use of electrospinning with the goal of enhancing performance and reactivity of the battery. The system was characterized and preliminary tests were performed on the constructed battery cells. We were successful in building and testing a series of electrochemical systems that demonstrated good cyclability maintaining 60-70% of discharge capacity after more than 50 charge-discharge cycles.
Date: November 1, 2010
Creator: Sigmund, Wolfgang M. (University of Florida, Gainesville, FL); Woan, Karran V. (University of Florida, Gainesville, FL) & Bell, Nelson Simmons
Partner: UNT Libraries Government Documents Department

Analytical electron microscopy of precipitates in ion-implanted MgAl{sub 2}O{sub 4} spinel

Description: Magnesium aluminate spinel (MgAl{sub 2}O{sub 4}) is being considered as an insulator material within proposed fusion reactors where considerable radiation fields are anticipated. Analytical electron microscopy (AEM) has been used to investigate precipitates within MgAl{sub 2}O{sub 4} spinel following implantation of Al{sup +}, Mg{sup +}, or Fe{sup 2+} ions. Combined diffraction experiments, energy dispersive X-ray spectrometry (EDS), electron energy-loss spectrometry (EELS), and energy-filtered imaging were employed to identify and characterize precipitates observed in the implanted ion region. Diffraction studies suggested these are metallic aluminum colloids, although EELS and energy-filtered images revealed this to be the case only for the Al{sup +} and Mg{sup +} implantations, and not for Fe{sup 2+} ion implantations. Multiple-least-squares (MLS) fitting of EELS spectra was employed to quantify the volume fraction of metallic aluminum when present in the implanted ion region. Energy-filtered images of the implanted ion region clearly show the colloid distribution in the Al{sup +} and Mg{sup +} implanted spinel. Energy-filtered images from the Fe {sup 2+} ion implanted spinel indicate that the features visible in diffraction contrast cannot be associated with either metallic aluminum or iron-rich precipitates.
Date: 1994
Creator: Evans, N. D.; Zinkle, S. J. & Bentley, J.
Partner: UNT Libraries Government Documents Department

Towards crystalline ion beams -- the PALLAS ring trap

Description: To experimentally elucidate fundamental issues of crystalline ion beams at low velocities the authors presently set up PALLAS, a table top circular RF quadrupole storage ring for acceleration and laser cooling of, e.g., {sup 24}Mg{sup +} ions. Employing the smooth approximation to PALLAS they compare its beam dynamics to heavy ion synchrotrons like TSR Heidelberg and thereby demonstrate the necessity of the highly symmetric lattice for the attainment of crystalline structures. Furthermore, dedicated molecular dynamics simulations are presented, affirming the feasibility of beam crystallization in PALLAS.
Date: November 1, 1998
Creator: Schaetz, T.; Habs, D.; Podlech, C.; Schramm, U. & Wei, J.
Partner: UNT Libraries Government Documents Department

Doping of GaN by ion implantation: Does It Work?

Description: Epitaxially grown GaN by metal organic chemical vapor deposition (MOCVD) on SiC were implanted with 100 keV Si{sup +} (for n-type) and 80 keV Mg{sup +} (for p-type) with various fluences from 1 {times} 10{sup 12} to 7 {times} 10 {sup 15} ions/cm{sup 2} at liquid nitrogen temperature (LT), room temperature (RT), and 700 C (HT). High temperature (1,200 C and 1,500 C) annealing was carried out after capping the GaN with epitaxial AlN by MOCVD to study damage recovery. Samples were capped by a layer of AlN in order to protect the GaN surface during annealing. Effects of implant temperature, damage and dopant activation are critically studied to evaluate a role of ion implantation in doping of GaN. The damage was studied by Rutherford Backscattering/Channeling, spectroscopic ellipsometry and photoluminescence. Results show dependence of radiation damage level on temperature of the substrate during implantation: implantations at elevated temperatures up to 550 C decrease the lattice disorder; hot implants above 550 C can not be useful in doping of GaN due to nitrogen loss from the surface. SE measurements have indicated very high sensitivity to the implantation damage. PL measurements at LT of 80 keV Mg{sup +} (5 {times} 10{sup 14} cm{sup 2}) implanted and annealed GaN showed two peaks: one {approximately} 100 meV and another {approximately} 140 meV away from the band edge.
Date: April 1, 1998
Creator: Suvkhanov, A.; Wu, W.; Price, K.; Parikh, N.; Irene, E.; Hunn, J. et al.
Partner: UNT Libraries Government Documents Department

Influence of Annealing Conditions on Dopant Antirotation of Si+ and Mg+ Implanted GaN

Description: This report reflects the results of heat treatment under various conditions on as-grown and ion implanted GaN. The PL spectrums of as-grown GaN and GaN with 400 A AlN cap were almost identical. This fact allows one to use PL analysis without AlN stripping. As-grown GaN and ion implanted with Mg and Si crystals were annealed at 1300 C for 10 minutes in three different conditions: in flowing argon gas; in flowing ultra high purity nitrogen; and in a quartz capsule sealed with nitrogen gas. The results of PL, RBS, SEM and TEM analysis show an advantage of GaN high temperature annealing in quartz capsules with nitrogen ambient as compared to annealing in argon and nitrogen gas flow. Encapsulation with nitrogen over-pressure prevents the decomposition of the GaN crystal and the AlN capping film, and allows one to achieve optical activation of implanted Mg and Si after 1300 C annealing.
Date: October 12, 1999
Creator: Suvkhanov, A.; Parikh, N.; Usov, I.; Hunn, J.D.; Withrow, S.; Thomson, D. et al.
Partner: UNT Libraries Government Documents Department

A background subtraction routine for enhancing energy-filtered plasmon images of MgAl{sub 2}O{sub 4} implanted with Al{sup +} and Mg{sup +} ions

Description: MgAl{sub 2}O{sub 4}, a candidate fusion reactor material, was irradiated with Al{sup +} or Mg{sup +} ions; electron energy-loss spectra and energy-filtered plasmon images showed that metallic Al colloids are present in the ion-irradiated regions. This paper shows the subtraction of the spinel plasmon component in images using 15-eV-loss electrons in some detail.
Date: June 1995
Creator: Evans, N. D.; Kenik, E. A.; Bentley, J. & Zinkle, S. J.
Partner: UNT Libraries Government Documents Department

Ordered one-component plasmas: Phase transitions, normal modes, large systems, and experiments in a storage ring

Description: The property of cold one-component plasmas, confined by external forces, to form an ordered array has been known for some time both from simulations and from experiment. The purpose of this talk is to summarize some recent work on simulations and some new experimental results. The author discusses some experimental work on real storage rings, magnetic storage devices in which partials circulate with large kinetic energies and for which laser cooling is used on partially ionized ions to attain temperatures ten or more orders of magnitude lower than their kinetic energies.
Date: December 31, 1994
Creator: Schiffer, J.P.
Partner: UNT Libraries Government Documents Department

Isoelectronic behavior of resonant and intercombination lines in MgI-like ions

Description: Radiative transitions with very different characteristic rates can serve as important diagnostics of local conditions in a plasma. Here, the observed intensity ratio of the 3s{sup 2} {sup 1}S{sub 0} - 3s3p {sup 1}P{sub 1} to the 3s{sup 2} {sup 1}S{sub 0} - 3s3p {sup 3}P{sub 1} transitions in MgI-like ions has always presented those who model plasma spectra with a challenge; the observed intensity of the intercombination line is always several times greater than what simple models predict. The authors offer a model that takes into account the contribution to the MgI-like emission features from autoionizing levels of the adjacent AlI-like charge state. Models in the present work, which include the effects of configuration interaction on ionic wavefunctions, and the contribution of both direct, impact ionization and autoionization channels from the AlI-like ion to the MgI-like ion, give good agreement with the observed resonant/intercombination (R/I) emission ratio only when a departure from ionization equilibrium is assumed. The authors also identify, for the first time, intercombination lines of the form 3s3p {sup 1}P{sub 1} - 3p{sup 2} {sup 3}P{sub 2} in several elements relevant to both astrophysical and magnetically-confined fusion plasmas.
Date: August 1, 1995
Creator: Fournier, K.B.; Goldstein, W.H.; Finkenthal, M.; Bell, R.E. & Terry, J.L.
Partner: UNT Libraries Government Documents Department

Non-alloyed, refractory metal contact optimization with shallow implantations of Zn and Mg

Description: Refractory metal contacts to GaAs show great promise for stability during high-temperature processing and for high-reliability. In this paper the authors report a study of sputtered tungsten and tungsten silicide contacts to ion implanted p-GaAs with both Zn and Mg implantations. This study focused on refractory contacts to shallow implanted contact layers that are suitable for devices such as JFETs and HBTs. The very different energy loss mechanisms of Zn and Mg ions result in different levels of implant damage which is studied by varying anneal temperatures and measuring the effects on contact and sheet resistances with the transmission line method. For the fabrication schemes investigated, specific contact resistivity versus anneal temperature with implant doses from 1 {times} 10{sup 14} to 5 {times} 10{sup 15} cm{sup {minus}2} are found to vary from non-ohmic to 10{sup {minus}7} {Omega}-cm{sup 2}. Low resistance contacts to shallow (<800 {angstrom}) implanted layers are achieved.
Date: March 22, 1994
Creator: Lovejoy, M. L.; Zolper, J. C.; Sherwin, M. E.; Baca, A. G.; Shul, R. J.; Rieger, D. J. et al.
Partner: UNT Libraries Government Documents Department

Cation disorder in high dose neutron irradiated spinel

Description: The crystal structures of MgAl{sub 2}O{sub 4} spinel single crystals irradiated to high neutron fluences (>5{center_dot}10{sup 26} n/m{sup 2} (E{sub n}>0.1 MeV)), were examined by neutron diffraction. Crystal structure refinement of the highest dose sample indicated that the average scattering strength of the tetrahedral crystal sites decreased by {approximately}20% while increasing by {approximately}8% on octahedral sites. Since the neutron scattering length for Mg is considerably larger than for Al, this result is consistent with site exchange between Mg{sup 2+} ions on tetrahedral sites and Al{sup 3+} ions on octahedral sites. Least squares refinements also indicated that in all irradiated samples, at least 35% of Mg{sup 2+} and Al{sup 3+} ions in the crystal experienced disordering replacements. This retained dpa on the cation sublattices is the largest retained damage ever measured in an irradiated spinel material.
Date: June 1, 1994
Creator: Sickafus, K. E.; Larson, A. C.; Yu, N.; Nastasi, M.; Hollenberg, G. W.; Garner, F. A. et al.
Partner: UNT Libraries Government Documents Department

ISOLEUCYL-tRNA-SYNTHETASE A FLUORESCENCE STUDY OP THE BINDINGPROPERTIES OF THE SYNTHETASE FROM ESCHERICHIA COLI

Description: Fluorescence properties of purified isoleucyl-tRNA-synthetase isolated from E. coli B have been studied. No changes in the quantum yield, energy or polarization of the emission were detected in the presence (either individually or in combinations) of the substrates and cofactors required for activation of L-isoleucine. In 2.5 M urea enzyme activity and intrinsic fluorescence intensity (at 340 nm) each decrease with time, showing similar kinetics and rate constants. The rate of this decay is reduced in the presence of ligands which can bind to the enzyme and the effect has been used to measure dissociation constants for enzyme-ligand complexes. Values have been obtained for the complexes between enzyme and L-isoleucine (K{sub diss} = 2.5 x 10{sup -5} M), L-valine (K{sub diss} = 3.0 x 10{sup -4} M), ATP (K{sub diss} = 1.5 x 10{sup -4} M) and PP{sub i} (K{sub diss} = 2.0 x 10{sup -4} M) at 25{sup o}. The effects of ionic strength, and the temperature dependence and urea concentration dependence of L-isoleucine binding have also been studied. Magnesium ions, which are required for catalysis, do not greatly affect the binding of single substrates, but changes are seen in the presence of ATP and L-isoleucine together. The magnesium ion concentration dependence of this effect (half-point about 2 x 10{sup -4} M) and the equilibrium constant for L-isoleucine activation (2 x 10{sup -6} M) have both been measured. The reliability of the methods has been discussed. Results have been interpreted in terms of current theories of amino acid activation. The binding parameters are sufficient to explain the stability of enzyme bound L-isoleucylarenylate without invoking conformation changes. This is consistent with the absence of substrate induced fluorescence changes. Magnesium effects are explained in terms of reduced electrostatic repulsion between reactants bearing like charges.
Date: November 1, 1970
Creator: Penzer, Geoffrey R.; Bennett, Edward L. & Calvin, Melvin.
Partner: UNT Libraries Government Documents Department

III-Nitride ion implantation and device processing

Description: Ion implantation doping and isolation has played a critical role in realizing high performance photonic and electronic devices in all mature semiconductor materials; this is also expected for binary III-Nitride materials (InN, GaN, AlN) and their alloys as epitaxy improves and more advanced device structures fabricated. This paper reports on recent progress in ion implantation doping of III-Nitride materials that has led to the first demonstration of a GaN JFET (junction field effect transistor). The JFET was fabricated with all ion implantation doping; in particular, p-type doping of GaN with Ca has been demonstrated with an estimated acceptor ionization energy of 169 meV. O-implantation has also been studied and shown to yield n-type conduction with an ionization energy of {similar_to}29 meV. Neither Ca or O display measurable redistribution during a 1125 C, 15 s activation anneal which sets an upper limit on their diffusivity at this temperature of 2.7{times}10{sup {minus}13}cm{sup 2}/s.
Date: June 1, 1996
Creator: Zolper, J.C.; Shul, R.J.; Baca, A.G.; Pearton, S.J.; Abernathy, C.R.; Wilson, R.G. et al.
Partner: UNT Libraries Government Documents Department

Implant activation and redistribution of dopants in GaN

Description: GaN and related III-Nitride materials (IN, an) have recently been the focus of extensive research for photonic and electronic device applications. As this material system matures, ion implantation doping and isolation is expected to play an important role in advance device demonstrations. To this end, we report the demonstration of implanted p-type doping with Mg+P and Ca as well as n-type doping with Si in GaN. These implanted dopants require annealing 105 approximately1100 {degrees}C to achieve electrical activity, but demonstrate limited redistribution at this temperature. The redistribution of other potential dopants in GaN (such as Be, Zn, and Cd) will also be reported. Results for a GaN junction field effect transistor (JFET), the first GaN device to use implantation doping, will also be presented.
Date: July 1, 1996
Creator: Zolper, J.C.; Pearton, S.J.; Wilson, R.G. & Stall, R.A.
Partner: UNT Libraries Government Documents Department

Energy-filtered plasmon images of MgAl{sub 2}O{sub 4} implanted with Al{sup +} and Mg{sup +} ions

Description: Magnesium aluminate spinel (MgAl{sub 2}O{sub 4}) is a candidate material for specialized applications in proposed fusion reactors, and previously, has been irradiated with Al{sup +} or Mg{sup +} ions to assess the effects of high-dose irradiation. Electron energy-loss spectrometry (EELS) has been used to confirm the identity of metallic aluminum colloids located in the ion-implanted region of the spinel because electron diffraction experiments were inconclusive for phase identification. In the present study, energy-filtered plasmon images of the ion-implanted region have been obtained to reveal this colloid distribution.
Date: June 1, 1995
Creator: Evans, N.D.; Bentley, J. & Zinkle, S.J.
Partner: UNT Libraries Government Documents Department

Direct catalytic decomposition of nitric oxide. Quarterly technical progress report No. 4, July--September 1992

Description: This project investigates a suitable catalyst system for direct NO decomposition in post-combustion NO{sub x} control. Since the process does not use a reductant, it is a greatly simplified process basically involving passing the flue gas through a catalytic converter. Catalysts are prepared by incorporating metal cations into zeolite supports by ion exchange. Catalysts of primary interest include Cu, Pd, Ag, and Ni exchanged zeolites. Particular emphasis is given on promoted Cu-exchanged zeolites, especially the catalyst system Mg/Cu-ZSM-5 and a few others, which are promising for NO conversion to nitrogen at typical flue gas O{sub 2} and NO levels and over the temperature range of 723--873K. Effects of zeolite modification, Cu exchange level and catalyst preparation conditions on the catalyst activity are studied in a packed-bed microreactor. Temperature-programmed desorption and reduction experiments will be carried out in a thermogravimetric analyzer and a single-particle electrodynamic balance. Kinetic studies of NO and O{sub 2} interaction with catalysts over a wide temperature range as well as catalyst structural investigations are planned.
Date: December 31, 1992
Creator: Flytzani-Stephanopoulos, M.; Sarofim, A. F. & Zhang, Y.
Partner: UNT Libraries Government Documents Department

Resonant coherent excitation of N{sup 6+} and Mg{sup 11+} in planar channeling: Anisotropies in ionization probabilities and x-ray emission

Description: The thrust of the conference in which this paper is presented is toward inelastic interactions of ions with surfaces. The work described in this paper deals with inelastic interactions of ions in planar channeling inside the crystal. The authors are, however, not too far off the mark because the planar channeling potential is made up from the sum of two (sheet) surface potentials. For the nitrogen experiment, a beam of N{sup 6+} ions at an energy of 3.25 MeV/amu was supplied by the ORNL EN Tandem accelerator. After suitable collimation, it was passed through an Au crystal (1,800 {angstrom} thick). The emergent charge-state distribution was analyzed by electrostatic deflection followed by a solid-state position-sensitive detector. Charge states 5, 6 and 7 were simultaneously detected. In the case of Mg{sup 11+} the beam was supplied at an energy of 25 MeV/amu by the CSCC Tandem Cyclotron Facility at Chalk River, Canada, and passed through an Ni crystal 4,000 {angstrom} thick which was epitaxially grown with the surface parallel to a (100) plane. The beam was charge state analyzed by a Q3D magnetic analyzer in which charges 11+ and 12+ were registered. At the energy in question, almost no 10+ fraction is visible. Two Si(Li) X-ray detectors aimed at 90{degree} and 45{degree} recorded the emission of Mg{sup 11+} Ly{alpha} (n = 2 {yields} 1) X-rays. In conclusion, there is strong evidence that once a given ionic state is excited, a large fraction of the ions remain in that state and are either ionized or radiate from that state. The result is counter to the expectation that electron-ion collisions in the channel would have a large enough cross section to destroy the alignment before either of these two events could take place. At this point, the reasons for the observed retention of anisotropy ...
Date: December 31, 1994
Creator: Datz, S.; Dittner, P. F.; Krause, H. F.; Vane, C. R.; Crawford, O. H.; Forster, J. S. et al.
Partner: UNT Libraries Government Documents Department