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1

Nanoalloying bulk-immiscible iridium and palladium inhibits hydride formation and promotes catalytic performances  

NASA Astrophysics Data System (ADS)

The hydrogen sorption properties of oxide-supported Ir-Pd nanoalloys have been determined for the first time, and correlated with their catalytic behavior. The addition of Ir to Pd suppresses hydride formation and leads to improved catalytic performances with respect to pure metals in the preferential oxidation of CO in H2 excess (PROX).The hydrogen sorption properties of oxide-supported Ir-Pd nanoalloys have been determined for the first time, and correlated with their catalytic behavior. The addition of Ir to Pd suppresses hydride formation and leads to improved catalytic performances with respect to pure metals in the preferential oxidation of CO in H2 excess (PROX). Electronic supplementary information (ESI) available: Detailed catalyst preparation procedure, additional TEM-EDX results, XRD data, and additional sorption and catalysis results. See DOI: 10.1039/c4nr02836h

Zlotea, C.; Morfin, F.; Nguyen, T. S.; Nguyen, N. T.; Nelayah, J.; Ricolleau, C.; Latroche, M.; Piccolo, L.

2014-08-01

2

Stability and dynamic processes in 16VE iridium(III) ethyl hydride and rhodium(I) ?-ethane complexes: experimental and computational studies.  

PubMed

Iridium(I) and rhodium(I) ethyl complexes, (PONOP)M(C2H5) (M = Ir (1-Et), Rh (2-Et)) and the iridium(I) propyl complex (PONOP)Ir(C3H7) (1-Pr), where PONOP is 2,6-(tBu2PO)2C5H3N, have been prepared. Low-temperature protonation of the Ir complexes yields the alkyl hydrides, (PONOP)Ir(H)(R) (1-(H)(Et)(+) and 1-(H)(Pr)(+)), respectively. Dynamic (1)H NMR characterization of 1-(H)(Et)(+) establishes site exchange between the Ir-H and Ir-CH2 protons (?G(exH)(‡)(-110 °C) = 7.2(1) kcal/mol), pointing to a ?-ethane intermediate. By dynamic (13)C NMR spectroscopy, the exchange barrier between the ? and ? carbons ("chain-walking") was measured (?G(exC)(‡)(-110 °C) = 8.1(1) kcal/mol). The barrier for ethane loss is 17.4(1) kcal/mol (-40 °C), to be compared with the reported barrier to methane loss in 1-(H)(Me)(+) of 22.4 kcal/mol (22 °C). A rhodium ?-ethane complex, (PONOP)Rh(EtH) (2-(EtH)(+)), was prepared by protonation of 2-Et at -150 °C. The barrier for ethane loss (?G(dec)(‡)(-132 °C) = 10.9(2) kcal/mol) is lower than for the methane complex, 2-(MeH)(+), (?G(dec)(‡)(-87 °C) = 14.5(4) kcal/mol). Full spectroscopic characterization of 2-(EtH)(+) is reported, a key feature of which is the upfield signal at -31.2 ppm for the coordinated CH3 group in the (13)C NMR spectrum. The exchange barrier of the hydrogens of the coordinated methyl group is too low to be measured, but the chain-walking barrier of 7.2(1) kcal/mol (-132 °C) is observable by (13)C NMR. The coordination mode of the alkane ligand and the exchange pathways for the Rh and Ir complexes are evaluated by DFT studies. On the basis of the computational studies, it is proposed that chain-walking occurs by different mechanisms: for Rh, the lowest energy path involves a ?(2)-ethane transition state, while for Ir, the lowest energy exchange pathway proceeds through the symmetrical ethylene dihydride complex. PMID:24053635

Walter, Marc D; White, Peter S; Schauer, Cynthia K; Brookhart, Maurice

2013-10-23

3

Iridium in natural waters  

SciTech Connect

Iridium, commonly used as a tracer of extraterrestrial material, was measured in rivers, oceans, and an estuarine environment. The concentration of iridium in the oceans ranges from 3.0 ({+-}1.3) x 10{sup 8} to 5.7 ({+-}0.8) x 10{sup 8} atoms per kilogram. Rivers contain from 17.4 ({+-}0.9) x 10{sup 8} to 92.9 ({+-}2.2) x 10{sup 8} atoms per kilogram and supply more dissolved iridium to the oceans than do extraterrestrial sources. In the Baltic Sea, {approximately}75% of riverine iridium is removed from solution. Iron-manganese oxyhydroxides scavenge iridium under oxidizing conditions, but anoxic environments are not a major sink for iridium. The ocean residence time of iridium is between 2 x 10{sup 3} and 2 x 10{sup 4} years. 32 refs., 3 figs., 1 tab.

Anbar, A.D.; Wasserburg, G.J.; Papanastassiou, D.A. [California Institute of Technology, Pasadena, CA (United States)] [and others

1996-09-13

4

Processing of Iridium and Iridium Alloys  

SciTech Connect

Iridium and its alloys have been considered to be difficult to fabricate due to their high melting temperatures, limited ductility, sensitivity to impurity content, and chemical properties. The variety of processing methods used for iridium and its alloys are reviewed, including purification, melting, forming, joining, and powder metallurgy techniques. Also included are coating and forming by the methods of electroplating, chemical and physical vapor deposition, and melt particle deposition.

Ohriner, Evan Keith [ORNL

2008-01-01

5

The IRIDIUM communications system  

Microsoft Academic Search

A description is given of the IRIDIUM communication system, so-called because the system design originally consisted of 77 networked satellites, and the element iridium has the atomic number 77. The goal is to make instant global communications a reality. The system design now consists of 60 satellites, a system control facility, gateways, and subscriber units. Each of these components is

R. J. Leopold; A. Miller

1993-01-01

6

Hydride compositions  

DOEpatents

A composition for use in storing hydrogen, and a method for making the composition. The composition comprises a mixture of two or more hydrides, each hydride having a different series of hydrogen sorption isotherms that contribute to the overall isotherms of the mixture. The hydrides are chosen so that the isotherms of the mixture have regions wherein the hydrogen equilibrium pressure increases with increasing hydrogen, preferably linearly. The isotherms of the mixture can be adjusted by selecting hydrides with different isotherms and by varying the amounts of the individual hydrides, or both. Preferably, the mixture is made up of hydrides that have isotherms with substantially flat plateaus and in nearly equimolar amounts. The composition is activated by degassing, exposing to hydrogen and then heating at a temperature below the softening temperature of any of the. constituents so that their chemical and structural integrity is preserved. When the composition is used to store hydrogen, its hydrogen content can be found simply by measuring P.sub.H.sbsb.2 and determining H/M from the isothermic function of the composition.

Lee, Myung W. (North Augusta, SC)

1995-01-01

7

Mononuclear Iridium Dinitrogen Complexes Bonded to Zeolite HY.  

PubMed

The adsorption of N2 on structurally well-defined dealuminated HY zeolite-supported iridium diethylene complexes was investigated. Iridium dinitrogen complexes formed when the sample was exposed to N2 in H2 at 298?K, as shown by infrared spectra recorded with isotopically labeled N2 . Four supported species formed in various flowing gases: Ir(N2 ), Ir(N2 )(N2 ), Ir(C2 H5 )(N2 ), and Ir(H)(N2 ). Their interconversions are summarized in a reaction network, showing, for example, that, in the presence of N2 , Ir(N2 ) was the predominant dinitrogen species at temperatures of 273-373?K. Ir(CO)(N2 ) formed transiently in flowing CO, and in the presence of H2 , rather stable iridium hydride complexes formed. Four structural models of each iridium complex bonded at the acidic sites of the zeolite were employed in a computational investigation, showing that the calculated vibrational frequencies agree well with experiment when full calculations are done at the level of density functional theory, independent of the size of the model of the zeolite. PMID:25381885

Yang, Dong; Chen, Mingyang; Martinez-Macias, Claudia; Dixon, David A; Gates, Bruce C

2014-11-01

8

High-Pressure Synthesis and Characterization of Iridium Trihydride  

NASA Astrophysics Data System (ADS)

We have performed in situ synchrotron x-ray diffraction studies of the iridium-hydrogen system up to 125 GPa. At 55 GPa, a phase transition in the metal lattice from the fcc to a distorted simple cubic phase is observed. The new phase is characterized by a drastically increased volume per metal atom, indicating the formation of a metal hydride, and substantially decreased bulk modulus of 190 GPa (383 GPa for pure Ir). Ab initio calculations show that the hydrogen atoms occupy the face-centered positions in the metal matrix, making this the first known noninterstitial noble metal hydride and, with a stoichiometry of IrH3, the one with the highest volumetric hydrogen content. Computations also reveal that several energetically competing phases exist, which can all be seen as having distorted simple cubic lattices. Slow kinetics during decomposition at pressures as low as 6 GPa suggest that this material is metastable at ambient pressure and low temperatures.

Scheler, Thomas; Marqués, Miriam; Konôpková, Zuzana; Guillaume, Christophe L.; Howie, Ross T.; Gregoryanz, Eugene

2013-11-01

9

Method for refining contaminated iridium  

DOEpatents

Contaminated iridium is refined by alloying it with an alloying agent selected from the group consisting of manganese and an alloy of manganese and copper, and then dissolving the alloying agent from the formed alloy to provide a purified iridium powder.

Heshmatpour, Bahman (Waltham, MA); Heestand, Richard L. (Oak Ridge, TN)

1983-01-01

10

Method for refining contaminated iridium  

DOEpatents

Contaminated iridium is refined by alloying it with an alloying agent selected from the group consisting of manganese and an alloy of manganese and copper, and then dissolving the alloying agent from the formed alloy to provide a purified iridium powder.

Heshmatpour, B.; Heestand, R.L.

1982-08-31

11

Solar abundance of iridium  

PubMed Central

By a method of spectrum synthesis, which yields log gfA, where g is the statistical weight of the lower level, f is the oscillator strength, and A is the abundance, an attempt is made to deduce the solar iridium abundance from one relatively unblended, but fairly weak IrI line, ? 3220.78 Å. If the Corliss-Bozman f-value for this line is adopted, we find log A(Ir) = 0.82 on the scale log A(H) = 12.00. The discordance with the value found from carbonaceous chondrites may arise from faulty f-values or from difficulties arising from line blending in this far ultraviolet domain of the solar spectrum. PMID:16578735

Drake, Stephen; Aller, Lawrence H.

1976-01-01

12

IRIDIUM(R) aeronautical satellite communications  

Microsoft Academic Search

The ever-increasing demand to stay in touch, to be able to communicate anywhere and anytime, has created a market for Low Earth Orbit (LEG) satellite communications services such as the Iridium System. The Iridium satellite communications network is being developed to support the needs of the passenger, the cabin crew and the flight crew. Iridium Communications LLC owns a network

P. W. Lemme; S. M. Glenister; A. W. Miller

1998-01-01

13

Multistage metal hydride compressor  

SciTech Connect

Metal hydride compressors can compress hydrogen to high pressures without using mechanical moving parts. They are particularly suited for tritium applications because they require minimal maintenance. A three-stage metal hydride compressor which can compress hydrogen from 14.7 to 20,000 psia has been demonstrated. The design principle and experimental results are presented.

Heung, L.K.

1986-01-01

14

Hysteresis in Metal Hydrides.  

ERIC Educational Resources Information Center

This paper describes a reproducible process where the irreversibility can be readily evaluated and provides a thermodynamic description of the important phenomenon of hysteresis. A metal hydride is used because hysteresis is observed during the formation and decomposition of the hydride phase. (RH)

Flanagan, Ted B., And Others

1987-01-01

15

Hydridomethyl iridium complex  

DOEpatents

A process for functionalizing methane comprising: (a) reacting methane with a hydridoalkyl metal complex of the formula: CpIr[P(R.sub.1).sub.3 ]H(R.sub.2) wherein Cp represents a cyclopentadienyl or alkylcyclopentadienyl radical having from 1 to 5 carbon atoms; Ir represents an iridium atom; P represents a phosphorus atom; R.sub.1 represents an alkyl group; R.sub.2 represents an alkyl group having at least two carbon atoms; and H represents a hydrogen atom, in the presence of a liquid alkane R.sub.3 H having at least three carbon atoms to form a hydridomethyl complex of the formula: CpIr[P(R.sub.1).sub.3 ]HMe where Me represents a methyl radical. (b) reacting said hydridomethyl complex with an organic halogenating agent such as a tetrahalomethane or a haloform of the formulas: CX'X"X'"X"" or CHX'X"X'"; wherein X', X", X"', and X"" represent halogens selected from bromine, iodine and chlorine, to halomethyl complex of step (a) having the formula: CpIr[P(R.sub.1).sub.3 ]MeX: (c) reacting said halomethyl complex with a mercuric halide of the formula HgX.sub.2 to form a methyl mercuric halide of the formula HgMeX; and (d) reacting said methyl mercuric halide with a molecular halogen of the formula X.sub.2 to form methyl halide.

Bergman, Robert G. (P.O. Box 7141, San Francisco, CA 94120-7141); Buchanan, J. Michael (P.O. Box 7141, San Francisco, CA 94120-7141); Stryker, Jeffrey M. (P.O. Box 7141, San Francisco, CA 94120-7141); Wax, Michael J. (P.O. Box 7141, San Francisco, CA 94120-7141)

1989-01-01

16

Hydrogen recovery with metal hydrides  

Microsoft Academic Search

Air Products pursued hydride technology because hydrides first came to our attention as a unique technology which could safely store hydrogen. The preliminary economics for using available hydrides to store hydrogen in motor vehicles were not encouraging at that time. However, the possibilities for using hydrides to selectively separate hydrogen from other components occurred to us. The authors obtained a

J. G. Santangelo; G. T. Chen

1982-01-01

17

Iridium-Catalyzed Allylic Substitution  

NASA Astrophysics Data System (ADS)

Iridium-catalyzed asymmetric allylic substitution has become a valuable method to prepare products from the addition of nucleophiles at the more substituted carbon of an allyl unit. The most active and selective catalysts contain a phosphoramidite ligand possessing at least one arylethyl substituent on the nitrogen atom of the ligand. In these systems, the active catalyst is generated by a base-induced cyclometalation at the methyl group of this substituent to generate an iridium metalacycle bound by the COD ligand of the [Ir(COD)Cl]2 precursor and one additional labile dative ligand. Such complexes catalyze the reactions of linear allylic esters with alkylamines, arylamines, phenols, alcohols, imides, carbamates, ammonia, enolates and enolate equivalents, as well as typical stabilized carbon nucleophiles generated from malonates and cyanoesters. Iridium catalysts for enantioselective allylic substitution have also been generated from phosphorus ligands with substituents bound by heteroatoms, and an account of the studies of such systems, along with a description of the development of iridium catalysts is included.

Hartwig, John F.; Pouy, Mark J.

18

Analytical Characterization of Microlithographically Fabricated Iridium-Based Ultramicroelectrode Arrays  

E-print Network

Analytical Characterization of Microlithographically Fabricated Iridium-Based Ultramicroelectrode Final version: October 31, 1997 Abstract The analytical performance of several mercury-coated iridiumUMEA surfaces. Keywords: Mercury-coated iridium ultramicroelectrode arrays, Stripping voltammetry

Kounaves, Samuel P.

19

IRIDIUM LINER FOR NASA 5 LBF CLASS MATERIAL TEST CHAMBER IRIDIUM LINER FOR ATLANTIC RESEARCH CORPORA  

NASA Technical Reports Server (NTRS)

IRIDIUM LINER FOR NASA 5 LBF CLASS MATERIAL TEST CHAMBER IRIDIUM LINER FOR ATLANTIC RESEARCH CORPORATION 5 LBF CLASS ROCKET CHAMBER 25 LBF CLASS 75 HFC 25 TAC CERAMIC COMPOSITE ROCKET CHAMBER FROM REFRACTURY COMPOSITES INC. PURCHASE ORDER C-551941-

1995-01-01

20

Iridium(R) aeronautical satellite communications  

Microsoft Academic Search

The ever-increasing demand to stay in touch, to be able to communicate anywhere and anytime, has created a market for low Earth orbit (LEO) satellite communications services such as the Iridium system. The Iridium satellite communications network is being developed to support the needs of the passenger, the cabin crew and the flight crew for: aeronautical public correspondence (APC); aeronautical

P. W. Lemme; S. M. Glenister; A. W. Miller

1999-01-01

21

Boron hydride polymer coated substrates  

DOEpatents

A method is disclosed for coating a substrate with a uniformly smooth layer of a boron hydride polymer. The method comprises providing a reaction chamber which contains the substrate and the boron hydride plasma. A boron hydride feed stock is introduced into the chamber simultaneously with the generation of a plasma discharge within the chamber. A boron hydride plasma of ions, electrons and free radicals which is generated by the plasma discharge interacts to form a uniformly smooth boron hydride polymer which is deposited on the substrate.

Pearson, R.K.; Bystroff, R.I.; Miller, D.E.

1986-08-27

22

TCP Performance Enhancement Over Iridium  

NASA Technical Reports Server (NTRS)

In support of iNET maturation, NASA-JPL has collaborated with NASA-Dryden to develop, test and demonstrate an over-the-horizon vehicle-to-ground networking capability, using Iridium as the vehicle-to-ground communications link for relaying critical vehicle telemetry. To ensure reliability concerns are met, the Space Communications Protocol Standards (SCPS) transport protocol was investigated for its performance characteristics in this environment. In particular, the SCPS-TP software performance was compared to that of the standard Transmission Control Protocol (TCP) over the Internet Protocol (IP). This paper will report on the results of this work.

Torgerson, Leigh; Hutcherson, Joseph; McKelvey, James

2007-01-01

23

Determining the Altitude of Iridium Flares  

NASA Technical Reports Server (NTRS)

Iridium flares have nothing to do with the element iridium. Iridium is also the name of a telecommunications company that has been launching satellites into low orbits around the Earth. These satellites are being used for a new type of wireless phone and paging service. Flares have been observed coming from these satellites. These flares have the potential, especially when the full fleet of satellites is in orbit, to disrupt astronomical observations. The paper reviews using simple trigonometry how to calculate the altitude of one of these satellites.

Foster, James; Owe, Manfred

1999-01-01

24

Method for preparing porous metal hydride compacts  

DOEpatents

A method for preparing porous metallic-matrix hydride compacts which can be repeatedly hydrided and dehydrided without disintegration. A mixture of a finely divided metal hydride and a finely divided matrix metal is contacted with a poison which prevents the metal hydride from dehydriding at room temperature and atmospheric pressure. The mixture of matrix metal and poisoned metal hydride is then compacted under pressure at room temperature to form porous metallic-matrix hydride compacts.

Ron, M.; Gruen, D.M.; Mendelsohn, M.H.; Sheft, I.

1980-01-21

25

17. VIEW OF HYDRIDING SYSTEM IN BUILDING 881. THE HYDRIDING ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

17. VIEW OF HYDRIDING SYSTEM IN BUILDING 881. THE HYDRIDING SYSTEM WAS PART OF THE FAST ENRICHED URANIUM RECOVERY PROCESS. (11/11/59) - Rocky Flats Plant, General Manufacturing, Support, Records-Central Computing, Southern portion of Plant, Golden, Jefferson County, CO

26

Dimensionally stable metallic hydride composition  

DOEpatents

A stable, metallic hydride composition and a process for making such a composition. The composition comprises a uniformly blended mixture of a metal hydride, kieselguhr, and a ballast metal, all in the form of particles. The composition is made by subjecting a metal hydride to one or more hydrogen absorption/desorption cycles to disintegrate the hydride particles to less than approximately 100 microns in size. The particles are partly oxidized, then blended with the ballast metal and the kieselguhr to form a uniform mixture. The mixture is compressed into pellets and calcined. Preferably, the mixture includes approximately 10 vol. % or more kieselguhr and approximately 50 vol. % or more ballast. Metal hydrides that can be used in the composition include Zr, Ti, V, Nb, Pd, as well as binary, tertiary, and more complex alloys of La, Al, Cu, Ti, Co, Ni, Fe, Zr, Mg, Ca, Mn, and mixtures and other combinations thereof. Ballast metals include Al, Cu and Ni.

Heung, Leung K. (Aiken, SC)

1994-01-01

27

Subporphyrinato Boron(III) Hydrides.  

PubMed

Subporphyrinato boron(III) hydrides were prepared by reduction of subporphyrinato boron(III) methoxides with diisobutylaluminum hydride (DIBAL-H) in good yields. The authenticity of the B-H bond has been unambiguously confirmed by a (1)H NMR signal that appears as a broad quartet at -2.27 ppm with a large coupling constant with the central (11)B, characteristic B-H infrared stretching frequencies, and single crystal X-ray diffraction analysis. Red shifts in the corresponding absorption and fluorescence profiles are accounted for in terms of the electron-donating nature of the B-hydride. The hydridic character of subporphyrinato boron(III) hydrides has been demonstrated by the production of H2 via reaction with water or HCl, and controlled reductions of aromatic aldehydes and imines in the presence of a catalytic amount of Ph3C[B(C6F5)4]. PMID:25563966

Tsurumaki, Eiji; Sung, Jooyoung; Kim, Dongho; Osuka, Atsuhiro

2015-01-28

28

Effect of ultrasound sonication on electroplating of iridium.  

PubMed

Effect of ultrasound sonication was examined on the electroplating of iridium in aqueous hexabromoiridate(III) solution. The electrodeposits were evaluated by observing the defects of the iridium deposits by means of voltammetry, in which the current-potential curves of the iridium deposits on copper were measured. Applying ultrasound sonication to the electroplating of iridium decreased the defects including the cracks in the deposit whenever the glycerol as the additives was contained or not in the electrolyte. PMID:18164231

Ohsaka, Takashi; Isaka, Motohiro; Hirano, Katsuhiko; Ohishi, Tomoji

2008-04-01

29

Use metal hydrides to recover hydrogen  

Microsoft Academic Search

This article demonstrates the technical feasibility of a hydride separation process from the idea stage through a pilot unit operated on-site on an ammonia purge-gas stream. The proposed hydrogen separation process makes use of the reversible and selective absorption capability of metal hydrides. Attrition (powder formation) of the hydride material, heat management, and deactivation of the hydride by certain contaminants

J. G. Santangelo; G. T. Chen

1983-01-01

30

IRIDIUM (R): A Lockheed transition to commercial space  

NASA Technical Reports Server (NTRS)

At Lockheed Missiles & Space Company, the IRIDIUM commercial space program is dramatically revolutionizing spacecraft development and manufacturing processes to reduce cost while maintaining quality and reliability. This report includes the following sections: an overview of the IRIDIUM system, the Lockheed IRIDIUM project and challenges; cycle-time reduction through production reorganization; and design for manufacturing and quality.

Tadano, Thomas N.

1995-01-01

31

Electrodeposited iridium oxide for neural stimulation and recording electrodes  

Microsoft Academic Search

Iridium oxide films formed by electrodeposition onto noniridium metal substrates are compared with activated iridium oxide films (AIROFs) as a low impedance, high charge capacity coating for neural stimulation and recording electrodes. The electrodeposited iridium oxide films (EIROFs) were deposited on Au, Pt, PtIr, and 316 LVM stainless steel substrates from a solution of IrCl 4, oxalic acid, and K

Ross D. Meyer; Stuart F. Cogan; Trung H. Nguyen; R. David Rauh

2001-01-01

32

"Globalstar, Iridium and other Satellite-Based Mobile Phone  

E-print Network

1 "Globalstar, Iridium and other Satellite-Based Mobile Phone Systems: How Do they Work and Where formed in the early 90's ­ Iridium [LEO, intersatellite links] ­ Globalstar [LEO, satellite diversity in their Flying Machines Iridium LEO Polar TDMA Globalstar LEO Inclined CDMA ICO MEO Inclined Custom Constellation

33

Iridium Anomaly Approximately Synchronous with Terminal Eocene Extinctions  

Microsoft Academic Search

An iridium anomaly has been found in coincidence with the known microtektite level in cores from Deep Sea Drilling Project site 149 in the Caribbean Sea. The iridium was probably not in the microtektites but deposited simultaneously with them; this could occur if the iridium was deposited from a dust cloud resulting from a bolide impact, as suggested for the

Walter Alvarez; Frank Asaro; Helen V. Michel; Luis W. Alvarez

1982-01-01

34

Complex Hydrides for Hydrogen Storage  

SciTech Connect

This report describes research into the use of complex hydrides for hydrogen storage. The synthesis of a number of alanates, (AIH4) compounds, was investigated. Both wet chemical and mechano-chemical methods were studied.

Slattery, Darlene; Hampton, Michael

2003-03-10

35

Electrochemical behavior of metal hydrides  

Microsoft Academic Search

.   Metal hydride electrodes are of particular interest owing to their potential and practical application in batteries. A large\\u000a number of hydrogen storage materials has been characterized so far. This paper deals with the effect of the chemical nature\\u000a and stoichiometry of specific alloy families (AB5, A2B, AB\\/AB2 and AB2) on the hydride stability, hydrogen storage capacity and kinetics of

J. Kleperis; G. Wójcik; A. Czerwinski; J. Skowronski; M. Kopczyk; M. Beltowska-Brzezinska

2001-01-01

36

Low density metal hydride foams  

DOEpatents

Disclosed is a low density foam having a porosity of from 0 to 98% and a density less than about 0.67 gm/cc, prepared by heating a mixture of powered lithium hydride and beryllium hydride in an inert atmosphere at a temperature ranging from about 455 to about 490 K for a period of time sufficient to cause foaming of said mixture, and cooling the foam thus produced. Also disclosed is the process of making the foam.

Maienschein, Jon L. (Oakland, CA); Barry, Patrick E. (Pleasant Hill, CA)

1991-01-01

37

Decomposition kinetics of plutonium hydride  

Microsoft Academic Search

Kinetic data for decomposition of PuH⁠ââ provides insight into a possible mechanism for the hydriding and dehydriding reactions of plutonium. The fact that the rate of the hydriding reaction, K\\/sub H\\/, is proportional to P¹² and the rate of the dehydriding process, K\\/sub D\\/, is inversely proportional to P¹² suggests that the forward and reverse reactions proceed by opposite

J. M. Haschke; J. L. Stakebake

1979-01-01

38

Physics of hydride fueled PWR  

Microsoft Academic Search

The first part of the work presents the neutronic results of a detailed and comprehensive study of the feasibility of using hydride fuel in pressurized water reactors (PWR). The primary hydride fuel examined is U-ZrH1.6 having 45w\\/o uranium: two acceptable design approaches were identified: (1) use of erbium as a burnable poison; (2) replacement of a fraction of the ZrH1.6

Francesco Ganda

2008-01-01

39

Experimental and theoretical mechanistic investigation of the iridium-catalyzed dehydrogenative decarbonylation of primary alcohols.  

PubMed

The mechanism for the iridium-BINAP catalyzed dehydrogenative decarbonylation of primary alcohols with the liberation of molecular hydrogen and carbon monoxide was studied experimentally and computationally. The reaction takes place by tandem catalysis through two catalytic cycles involving dehydrogenation of the alcohol and decarbonylation of the resulting aldehyde. The square planar complex IrCl(CO)(rac-BINAP) was isolated from the reaction between [Ir(cod)Cl]2, rac-BINAP, and benzyl alcohol. The complex was catalytically active and applied in the study of the individual steps in the catalytic cycles. One carbon monoxide ligand was shown to remain coordinated to iridium throughout the reaction, and release of carbon monoxide was suggested to occur from a dicarbonyl complex. IrH2Cl(CO)(rac-BINAP) was also synthesized and detected in the dehydrogenation of benzyl alcohol. In the same experiment, IrHCl2(CO)(rac-BINAP) was detected from the release of HCl in the dehydrogenation and subsequent reaction with IrCl(CO)(rac-BINAP). This indicated a substitution of chloride with the alcohol to form a square planar iridium alkoxo complex that could undergo a ?-hydride elimination. A KIE of 1.0 was determined for the decarbonylation and 1.42 for the overall reaction. Electron rich benzyl alcohols were converted faster than electron poor alcohols, but no electronic effect was found when comparing aldehydes of different electronic character. The lack of electronic and kinetic isotope effects implies a rate-determining phosphine dissociation for the decarbonylation of aldehydes. PMID:25545272

Olsen, Esben P K; Singh, Thishana; Harris, Pernille; Andersson, Pher G; Madsen, Robert

2015-01-21

40

Iridium emissions from Hawaiian volcanoes  

NASA Technical Reports Server (NTRS)

Particle and gas samples were collected at Mauna Loa volcano during and after its eruption in March and April, 1984 and at Kilauea volcano in 1983, 1984, and 1985 during various phases of its ongoing activity. In the last two Kilauea sampling missions, samples were collected during eruptive activity. The samples were collected using a filterpack system consisting of a Teflon particle filter followed by a series of 4 base-treated Whatman filters. The samples were analyzed by INAA for over 40 elements. As previously reported in the literature, Ir was first detected on particle filters at the Mauna Loa Observatory and later from non-erupting high temperature vents at Kilauea. Since that time Ir was found in samples collected at Kilauea and Mauna Loa during fountaining activity as well as after eruptive activity. Enrichment factors for Ir in the volcanic fumes range from 10,000 to 100,000 relative to BHVO. Charcoal impregnated filters following a particle filter were collected to see if a significant amount of the Ir was in the gas phase during sample collection. Iridium was found on charcoal filters collected close to the vent, no Ir was found on the charcoal filters. This indicates that all of the Ir is in particulate form very soon after its release. Ratios of Ir to F and Cl were calculated for the samples from Mauna Loa and Kilauea collected during fountaining activity. The implications for the KT Ir anomaly are still unclear though as Ir was not found at volcanoes other than those at Hawaii. Further investigations are needed at other volcanoes to ascertain if basaltic volcanoes other than hot spots have Ir enrichments in their fumes.

Finnegan, D. L.; Zoller, W. H.; Miller, T. M.

1988-01-01

41

Iridium-Coated Rhenium Combustion Chamber  

NASA Technical Reports Server (NTRS)

Iridium-coated rhenium combustion chamber withstands operating temperatures up to 2,200 degrees C. Chamber designed to replace older silicide-coated combustion chamber in small rocket engine. Modified versions of newer chamber could be designed for use on Earth in gas turbines, ramjets, and scramjets.

Schneider, Steven J.; Tuffias, Robert H.; Rosenberg, Sanders D.

1994-01-01

42

Determining the Altitude of Iridium Flares  

NSDL National Science Digital Library

This series of example calculations applies basic trigonometry to to calculate the altitude of satellites and Iridium satellite flares. This resource is from PUMAS - Practical Uses of Math and Science - a collection of brief examples created by scientists and engineers showing how math and science topics taught in K-12 classes have real world applications.

43

Iridium-192 Production for Cancer Treatment  

SciTech Connect

The purpose of this work is to settle a laboratory for Iridium -192 sources production, that is, to determine a wire activation method and to build a hot cell for the wires manipulation, quality control and packaging. The paper relates, mainly, the wire activation method and its quality control. The wire activation is carried out in our nuclear reactor, IEA- R1m.

Rostelato, M.E.C.M.; Silva, C.P.G.; Rela, P.R.; Zeituni, C.A.; Lepki, V.; Feher, A.

2004-10-05

44

Fundamental experiments on hydride reorientation in zircaloy  

NASA Astrophysics Data System (ADS)

In the current study, an in-situ X-ray diffraction technique using synchrotron radiation was used to follow directly the kinetics of hydride dissolution and precipitation during thermomechanical cycles. This technique was combined with conventional microscopy (optical, SEM and TEM) to gain an overall understanding of the process of hydride reorientation. Thus this part of the study emphasized the time-dependent nature of the process, studying large volume of hydrides in the material. In addition, a micro-diffraction technique was also used to study the spatial distribution of hydrides near stress concentrations. This part of the study emphasized the spatial variation of hydride characteristics such as strain and morphology. Hydrided samples in the shape of tensile dog-bones were used in the time-dependent part of the study. Compact tension specimens were used during the spatial dependence part of the study. The hydride elastic strains from peak shift and size and strain broadening were studied as a function of time for precipitating hydrides. The hydrides precipitate in a very compressed state of stress, as measured by the shift in lattice spacing. As precipitation proceeds the average shift decreases, indicating average stress is reduced, likely due to plastic deformation and morphology changes. When nucleation ends the hydrides follow the zirconium matrix thermal contraction. When stress is applied below the threshold stress for reorientation, hydrides first nucleate in a very compressed state similar to that of unstressed hydrides. After reducing the average strain similarly to unstressed hydrides, the average hydride strain reaches a constant value during cool-down to room temperature. This could be due to a greater ease of deforming the matrix due to the applied far-field strain which would compensate for the strains due to thermal contraction. Finally when hydrides reorient, the average hydride strains become tensile during the first precipitation regime and remain constant in the tensile direction during the second precipitation regime. This could be due to the fact that the face of reoriented hydride platelet is in compression once these platelets have grown to a sufficient size. The second goal of this study was to perform a spatially resolved study of the effect of a stress concentration such as a notch or a crack on hydride reorientation. Using SEM and image analysis, it was found that a sharp crack induces a different hydride microstructure than a blunt notch. In the case of sharp crack, hydrides are more localized and align more with the defect than for blunt notches. The hydride connectivity also increases close to a stress concentration which will assist in crack propagation during DHC. Using TEM, the microstructure of hydrides grown near crack tips were observed to be similar to that of circumferential hydrides grown in the bulk. The orientation relationship studied with SEM and micro-X-ray diffraction was found to be in most cases ?(111)// ?(0002) for hydrides grown both near and far from stress concentrations. Using the same micro-X-ray diffraction technique local hydride and matrix elastic strains were measured and observed to vary significantly from grain to grain. It was however observed that hydrides grown close to the stress concentration are in tension in the face of the platelet, similar to reoriented hydrides, while those grown far from the stress concentration are in tension, similar to circumferential hydrides. The orders of magnitude of the measured strains in the hydrides and the zirconium matrix compared well to those predicted by finite element models. This study shows that it is possible to study hydride dissolution and precipitation in-situ using time-dependent techniques. It was found that the precipitation temperature is lowered by hydride reorientation. The evolution of hydride strains during precipitation was found to be different for unstressed, stressed and reoriented hydrides. The reoriented hydride fraction and connectivity increase with number of cycles which could lead to mor

Colas, Kimberly B.

45

Physics of hydride fueled PWR  

NASA Astrophysics Data System (ADS)

The first part of the work presents the neutronic results of a detailed and comprehensive study of the feasibility of using hydride fuel in pressurized water reactors (PWR). The primary hydride fuel examined is U-ZrH1.6 having 45w/o uranium: two acceptable design approaches were identified: (1) use of erbium as a burnable poison; (2) replacement of a fraction of the ZrH1.6 by thorium hydride along with addition of some IFBA. The replacement of 25 v/o of ZrH 1.6 by ThH2 along with use of IFBA was identified as the preferred design approach as it gives a slight cycle length gain whereas use of erbium burnable poison results in a cycle length penalty. The feasibility of a single recycling plutonium in PWR in the form of U-PuH2-ZrH1.6 has also been assessed. This fuel was found superior to MOX in terms of the TRU fractional transmutation---53% for U-PuH2-ZrH1.6 versus 29% for MOX---and proliferation resistance. A thorough investigation of physics characteristics of hydride fuels has been performed to understand the reasons of the trends in the reactivity coefficients. The second part of this work assessed the feasibility of multi-recycling plutonium in PWR using hydride fuel. It was found that the fertile-free hydride fuel PuH2-ZrH1.6, enables multi-recycling of Pu in PWR an unlimited number of times. This unique feature of hydride fuels is due to the incorporation of a significant fraction of the hydrogen moderator in the fuel, thereby mitigating the effect of spectrum hardening due to coolant voiding accidents. An equivalent oxide fuel PuO2-ZrO2 was investigated as well and found to enable up to 10 recycles. The feasibility of recycling Pu and all the TRU using hydride fuels were investigated as well. It was found that hydride fuels allow recycling of Pu+Np at least 6 times. If it was desired to recycle all the TRU in PWR using hydrides, the number of possible recycles is limited to 3; the limit is imposed by positive large void reactivity feedback.

Ganda, Francesco

46

APEX telescope observations of hydrides  

NASA Astrophysics Data System (ADS)

Hydrides are key ingredients of interstellar chemistry since they are the initial products of chemical networks that lead to the formation of more complex molecules. The fundamental rotational transitions of light hydrides fall into the submillimeter wavelength range. Using the APEX telescope, we observed the long sought hydrides SH+ and OH+ in absorption against the strong continuum source Sagittarius B2(M). Both, absorption from Galactic center gas as well as absorption from diffuse clouds in intervening spiral arms in a large velocity range are observed. The detected absorption of a continuous velocity range on the line-of-sight shows these hydrides to be an abundant component of diffuse clouds. In addition, we used the strongest submillimeter dust continuum sources in the inner Galaxy to serve as background candles for a systematic census of these hydrides in diffuse clouds and massive star forming regions of our Galaxy and initial results of this survey are presented. For this survey, the CHAMP+ array receiver as well as the MPIfR THz receiver was used. We will discuss the scientific potential of the first THz atmospheric window from 1.0 to 1.1 THz for observations from the Chajnantor high site.

Wyrowski, F.; Menten, K.; Gusten, R.; Belloche, A.; Klein, T.; Leinz, C.

2011-05-01

47

Application of the Iridium Satellite System to Aeronautical Communications  

NASA Technical Reports Server (NTRS)

The next generation air transportation system will require greater air-ground communications capacity to accommodate more air traffic with increased safety and efficiency. Communications will remain primarily terrestrially based, but satellite communications will have an increased role. Inmarsat s aeronautical services have been approved and are in use for aeronautical safety communications provided by geostationary satellites. More recently the approval process for the Iridium low earth orbit constellation is nearing completion. The current Iridium system will be able to provide basic air traffic services communications suitable for oceanic, remote and polar regions. The planned second generation of the Iridium system, called Iridium NEXT, will provide enhanced capabilities and enable a greater role in the future of aeronautical communications. This paper will review the potential role of satellite communications in the future of air transportation, the Iridium approval process and relevant system testing, and the potential role of Iridium NEXT.

Kerczewski, Robert J.; Meza, Mike; Gupta, Om

2008-01-01

48

Vanadium hydride deuterium-tritium generator  

DOEpatents

A pressure controlled vanadium hydride gas generator to provide deuterium-tritium gas in a series of pressure increments. A high pressure chamber filled with vanadium-deuterium-tritium hydride is surrounded by a heater which controls the hydride temperature. The heater is actuated by a power controller which responds to the difference signal between the actual pressure signal and a programmed pressure signal.

Christensen, Leslie D. (Livermore, CA)

1982-01-01

49

Hydrogen, lithium, and lithium hydride production  

DOEpatents

A method of producing high purity lithium metal is provided, where gaseous-phase lithium metal is extracted from lithium hydride and condensed to form solid high purity lithium metal. The high purity lithium metal may be hydrided to provide high purity lithium hydride.

Brown, Sam W; Spencer, Larry S; Phillips, Michael R; Powell, G. Louis; Campbell, Peggy J

2014-03-25

50

THE RADIOCHEMISTRY OF IRIDIUM--NAS-NS 3045  

E-print Network

------..--------- !546.8 L472ra .c.8 THE RADIOCHEMISTRY OF IRIDIUM-- NAS-NS 3045 +- -:, G. W The Rctdiochemistry of Iridium #12;COMNll~EE ON. NUCLEAR SCIENCE L.F. CURTffS, CM~ " ROBLEY D.EVAiil%Vk8 Ckzi;c-TRY The Radiochemistry of Iridium G. W. LEDDI~ W Ridge Ndioml Lduwulwy Ckz&Ridge, T-&?See Chb3ber

51

The Cretaceous/ Tertiary Boundary At Iridium Hill, Garfield County, Montana  

NSDL National Science Digital Library

The goal of this virtual field trip to Iridium Hill, Montana is to investigate the disappearance of dinosaur fossils above the Cretaceous/ Tertiary boundary. The site provides rock outcrop photos of Cretaceous and Tertiary strata (Hell Creek and Fort Union Formations), stratigraphic sections and supporting text for this classic iridium-bearing locality. Topics include the K/T boundary, iridium concentrations, stratigraphy, sedimentology and, fluvial and lacustrine depositional environments.

Limited, Athro

52

Iridium-coated rhenium thrusters by CVD  

NASA Technical Reports Server (NTRS)

Operation of spacecraft thrusters at increased temperature reduces propellant requirements. Inasmuch as propellant comprises the bulk of a satellite's mass, even a small percentage reduction makes possible a significant enhancement of the mission in terms of increased payload. Because of its excellent high temperature strength, rhenium is often the structural material of choice. It can be fabricated into free-standing shapes by chemical vapor deposition (CVD) onto an expendable mandrel. What rhenium lacks is oxidation resistance, but this can be provided by a coating of iridium, also by CVD. This paper describes the process used by Ultramet to fabricate 22-N (5-lbf) and, more recently, 445-N (100-lbf) Ir/Re thrusters; characterizes the CVD-deposited materials; and summarizes the materials effects of firing these thrusters. Optimal propellant mixture ratios can be employed because the materials withstand an oxidizing environment up to the melting temperature of iridium, 2400 C (4350 F).

Harding, J. T.; Kazaroff, J. M.; Appel, M. A.

1989-01-01

53

Iridium-coated rhenium thrusters by CVD  

NASA Technical Reports Server (NTRS)

Operation of spacecraft thrusters at increased temperature reduces propellant requirements. Inasmuch as propellant comprises the bulk of a satellite's mass, even a small percentage reduction makes possible a significant enhancement of the mission in terms of increased payload. Because of its excellent high temperature strength, rhenium is often the structural material of choice. It can be fabricated into free-standing shapes by chemical vapor deposition (CVD) onto an expendable mandrel. What rhenium lacks is oxidation resistance, but this can be provided by a coating of iridium, also by CVD. This paper describes the process used by Ultramet to fabricate 22-N (5-lbf) and, more recently, 445-N (100-lbf) Ir/Re thrusters; characterizes the CVD-deposited materials; and summarizes the materials effects of firing these thrusters. Optimal propellant mixture ratios can be employed because the materials withstand an oxidizing environment up to the meltimg temperature of iridium, 2400 C (4350 F).

Harding, John T.; Kazaroff, John M.; Appel, Marshall A.

1988-01-01

54

Mechanical and Electronic Properties of Iridium Nitride  

NASA Astrophysics Data System (ADS)

Based on the structures of known transition metal compounds, the phase stabilities and mechanical properties of iridium nitride (IrN) in nine structures are explored by using ab initio calculations. The calculation results show that MnP-structured IrN (MnP—IrN) is not only the most energetically stable, but also mechanically and dynamically stable at the ground state. The hardness is estimated to be 12 GPa.

Liu, Qiang; Peng, Wei-Min; Peng, Feng

2014-08-01

55

Cyclometallated Iridium and Platinum Complexes with Noninnocent Bhavna Hirani,  

E-print Network

Cyclometallated Iridium and Platinum Complexes with Noninnocent Ligands Bhavna Hirani, Jian Li of the cyclometalated (CN) complexes of iridium and platinum metals with a catechol ligand have been studied-tert- butylcatechol (DTBCat) ligand with the prepared cyclometalated metal complex was carried out in air

Goddard III, William A.

56

Variation of iridium in a differentiated tholeiitic dolerite  

USGS Publications Warehouse

Iridium has been determined in a drill core from the Great Lake (Tasmania) dolerite sheet. Iridium decreases systematically from the mafic dolerites (0.25 ppb) to the granophyres (0.006 ppb). The trend with differentiation closely parallels that of chromium. ?? 1971.

Greenland, L.P.

1971-01-01

57

A determination iridium distribution in rocks from terrestrial impact craters  

Microsoft Academic Search

A neutron activation technique was used to determine the iridium content in rocks from terrestrial impact craters in Ianisiarvi, Karelia, and Elgygytgyn, Chukhotka, USSR. The data are combined with iridium distribution values obtained from rocks in 16 other craters, and analyzed together. The analysis shows that impact cratering does not introduce significant amounts of meteorite matter into the impact crushing

A. T. Bazilevskii; V. I. Feldman; I. G. Kapustkina; G. M. Kolesov

1984-01-01

58

Microstructure of surface cerium hydride growth sites  

SciTech Connect

Samples of cerium were exposed to hydrogen under controlled conditions causing cerium hydride sites to nucleate and grow on the surface. The hydriding rate was measured in situ, and the hydrides were characterised using secondary ion mass spectrometry, scanning electron microscopy, and optical microscopy. The results show that the hydriding rate proceeded more quickly than earlier studies. Characterisation confirmed that the hydrogen is confined to the sites. The morphology of the hydrides was confirmed to be oblate, and stressed material was observed surrounding the hydride, in a number of cases lathlike features were observed surrounding the hydride sites laterally with cracking in the surface oxide above them. It is proposed that during growth the increased lattice parameter of the CeH{sub 2} induces a lateral compressive stress around the hydride, which relieves by the ca. 16% volume collapse of the ?-Ce to ?-Ce pressure induced phase transition. Cracking of the surface oxide above the laths reduces the diffusion barrier to hydrogen reaching the metal/oxide interface surrounding the hydride site and contributes to the anisotropic growth of the hydrides.

Brierley, Martin, E-mail: martin.brierley@awe.co.uk [Atomic Weapons Establishment, Aldermaston, Berkshire, RG7 4PR, United Kingdom and The School of Materials, University of Manchester, Manchester, M13 9PL (United Kingdom); Knowles, John; Montgomery, Neil [Atomic Weapons Establishment, Aldermaston, Berkshire, RG7 4PR (United Kingdom); Preuss, Michael [The School of Materials, University of Manchester, Manchester, M13 9PL (United Kingdom)

2014-05-15

59

Rechargeable metal hydrides for spacecraft application  

NASA Technical Reports Server (NTRS)

Storing hydrogen on board the Space Station presents both safety and logistics problems. Conventional storage using pressurized bottles requires large masses, pressures, and volumes to handle the hydrogen to be used in experiments in the U.S. Laboratory Module and residual hydrogen generated by the ECLSS. Rechargeable metal hydrides may be competitive with conventional storage techniques. The basic theory of hydride behavior is presented and the engineering properties of LaNi5 are discussed to gain a clear understanding of the potential of metal hydrides for handling spacecraft hydrogen resources. Applications to Space Station and the safety of metal hydrides are presented and compared to conventional hydride storage. This comparison indicates that metal hydrides may be safer and require lower pressures, less volume, and less mass to store an equivalent mass of hydrogen.

Perry, J. L.

1988-01-01

60

Metal hydride composition and method of making  

DOEpatents

A dimensionally stable hydride composition and a method for making such a composition. The composition is made by forming particles of a metal hydride into porous granules, mixing the granules with a matrix material, forming the mixture into pellets, and sintering the pellets in the absence of oxygen. The ratio of matrix material to hydride is preferably between approximately 2:1 and 4:1 by volume. The porous structure of the granules accommodates the expansion that occurs when the metal hydride particles absorb hydrogen. The porous matrix allows the flow of hydrogen therethrough to contact the hydride particles, yet supports the granules and contains the hydride fines that result from repeated absorption/desorption cycles.

Congdon, James W. (Aiken, SC)

1995-01-01

61

Iridium/Rhenium Parts For Rocket Engines  

NASA Technical Reports Server (NTRS)

Oxidation/corrosion of metals at high temperatures primary life-limiting mechanism of parts in rocket engines. Combination of metals greatly increases operating temperature and longevity of these parts. Consists of two transition-element metals - iridium and rhenium - that melt at extremely high temperatures. Maximum operating temperature increased to 2,200 degrees C from 1,400 degrees C. Increases operating lifetimes of small rocket engines by more than factor of 10. Possible to make hotter-operating, longer-lasting components for turbines and other heat engines.

Schneider, Steven J.; Harding, John T.; Wooten, John R.

1991-01-01

62

Iridium Interfacial Stack - IrIS  

NASA Technical Reports Server (NTRS)

Iridium Interfacial Stack (IrIS) is the sputter deposition of high-purity tantalum silicide (TaSi2-400 nm)/platinum (Pt-200 nm)/iridium (Ir-200 nm)/platinum (Pt-200 nm) in an ultra-high vacuum system followed by a 600 C anneal in nitrogen for 30 minutes. IrIS simultaneously acts as both a bond metal and a diffusion barrier. This bondable metallization that also acts as a diffusion barrier can prevent oxygen from air and gold from the wire-bond from infiltrating silicon carbide (SiC) monolithically integrated circuits (ICs) operating above 500 C in air for over 1,000 hours. This TaSi2/Pt/Ir/Pt metallization is easily bonded for electrical connection to off-chip circuitry and does not require extra anneals or masking steps. There are two ways that IrIS can be used in SiC ICs for applications above 500 C: it can be put directly on a SiC ohmic contact metal, such as Ti, or be used as a bond metal residing on top of an interconnect metal. For simplicity, only the use as a bond metal is discussed. The layer thickness ratio of TaSi2 to the first Pt layer deposited thereon should be 2:1. This will allow Si from the TaSi2 to react with the Pt to form Pt2Si during the 600 C anneal carried out after all layers have been deposited. The Ir layer does not readily form a silicide at 600 C, and thereby prevents the Si from migrating into the top-most Pt layer during future anneals and high-temperature IC operation. The second (i.e., top-most) deposited Pt layer needs to be about 200 nm to enable easy wire bonding. The thickness of 200 nm for Ir was chosen for initial experiments; further optimization of the Ir layer thickness may be possible via further experimentation. Ir itself is not easily wire-bonded because of its hardness and much higher melting point than Pt. Below the iridium layer, the TaSi2 and Pt react and form desired Pt2Si during the post-deposition anneal while above the iridium layer remains pure Pt as desired to facilitate easy and strong wire-bonding to the SiC chip circuitry.

Spry, David

2012-01-01

63

Iridium Film For Charge-Coupled Device  

NASA Technical Reports Server (NTRS)

Usability extended to different environments. Application of thin film of iridium to back surface of back-surface-illuminated charge-coupled device expected to increase and stabilize quantum efficiency at wavelengths less than 4,500 Angstrom. Enhances quantum efficiency according to principle discussed in "Metal Film Increases CCD Output" (NPO-16815). Does not react with hydrogen, so device need not be kept in oxygen: Advantage where high absorption of ultraviolet light by oxygen undesirable; for example, when device used to make astronomical observations from high altitudes.

Hecht, Michael H.

1990-01-01

64

Magnetic Properties of Plutonium Hydride and Deuteride  

Microsoft Academic Search

Magnetic investigations on plutonium hydride (PuH2.74) and deuteride (PuD2.74) have shown these compounds to be either ferromagnetic, like the corresponding uranium compounds, or ferrimagnetic. The Curie temperatures of plutonium hydride and deuteride are the same, within experimental error, and are 107°K. The magnetic moment for the hydride and deuteride are greater than 0.24 and 0.13 Bohr magnetons per mole of

C. E. Olsen; T. A. Sandenaw; B. T. MATTHIAst

1963-01-01

65

Inhibited solid propellant composition containing beryllium hydride  

NASA Technical Reports Server (NTRS)

An object of this invention is to provide a composition of beryllium hydride and carboxy-terminated polybutadiene which is stable. Another object of this invention is to provide a method for inhibiting the reactivity of beryllium hydride toward carboxy-terminated polybutadiene. It was found that a small amount of lecithin inhibits the reaction of beryllium hydride with the acid groups in carboxy terminated polybutadiene.

Thompson, W. W. (inventor)

1978-01-01

66

Use of reversible hydrides for hydrogen storage  

NASA Technical Reports Server (NTRS)

The addition of metals or alloys whose hydrides have a high dissociation pressure allows a considerable increase in the hydrogenation rate of magnesium. The influence of temperature and hydrogen pressure on the reaction rate were studied. Results concerning the hydriding of magnesium rich alloys such as Mg2Ca, La2Mg17 and CeMg12 are presented. The hydriding mechanism of La2Mg17 and CeMg12 alloys is given.

Darriet, B.; Pezat, M.; Hagenmuller, P.

1980-01-01

67

Vanadium hydride deuterium-tritium generator  

DOEpatents

A pressure controlled vanadium hydride gas generator was designed to provide deuterium-tritium gas in a series of pressure increments. A high pressure chamber filled with vanadium-deuterium-tritium hydride is surrounded by a heater which controls the hydride temperature. The heater is actuated by a power controller which responds to the difference signal between the actual pressure signal and a programmed pressure signal.

Christensen, L.D.

1980-03-13

68

Ab initio treatment of electron correlations in polymers: Lithium hydride chain and beryllium hydride polymer  

E-print Network

Ab initio treatment of electron correlations in polymers: Lithium hydride chain and berylliumH and beryllium hydride Be2H4 . First, employing a Wannier-function-based approach, the systems are studiedH and the beryllium hydride polymer Be2H4 . As a simple, but due to its ionic character, non- trivial model polymer

Birkenheuer, Uwe

69

Lightweight hydrides for automotive storage of hydrogen  

NASA Astrophysics Data System (ADS)

The primary objectives of the considered investigations are related to the reduction of the dissociation temperature of lightweight materials, and the development of new lightweight hydrides containing little, if any, critical material. Attention is given to the characteristics of metal hydrides, the characteristics of a magnesium-base alloy which is to be employed in hydrogen storage systems for automobiles, aspects of alloy development, and the evaluation of magnesium hydride alloys with the aid of a hydride cycling rig. New information concerning the effect of cycling on magnesium alloys is discussed.

Rohy, D. A.; Nachman, J. F.; Argabright, T. A.

70

Diminiode thermionic conversion with 111-iridium electrodes  

NASA Technical Reports Server (NTRS)

Preliminary data indicating thermionic-conversion potentialities for a 111-iridium emitter and collector spaced 0.2 mm apart are presented. These results comprise output densities of current and of power as functions of voltage for three sets of emitter, collector, and reservoir temperatures: 1553, 944, 561 K; 1605, 898, 533 K; and 1656, 1028, 586 K. For the 1605 K evaluation, estimates produced work-function values of 2.22 eV for the emitter and 1.63 eV for the collector with a 2.0-eV barrier index (collector work function plus interelectrode voltage drop) corresponding to the maximum output of 5.5 W/sq cm at 0.24 volt. The current, voltage curve for the 1656 K 111-iridium diminiode yields a 6.2 W/sq cm maximum at 0.25 volt and is comparable with the 1700 K envelope for a diode with an etched-rhenium emitter and a 0.025-mm electrode gap made by TECO and evaluated by NASA.

Koeger, E. W.; Bair, V. L.; Morris, J. F.

1976-01-01

71

Oxidation of a thin samarium film on iridium  

NASA Astrophysics Data System (ADS)

Thermal desorption spectroscopy has been used to study the interaction of oxygen with a thin (<1 nm) samarium film deposited onto a textured iridium ribbon. Desorption of Sm atoms from Ir surface takes place from various states (chemisorbed, condensed, from compound with iridium, and oxide). The formation of samarium oxide is observed already at room temperature. As the temperature increases to T = 1100 K, a compound of samarium with iridium is formed at the first stage and then oxygen interacts with Sm atoms from this compound and "slow" (compared to the first process) growth of samarium oxide takes place.

Afanas'eva, E. Yu.

2014-06-01

72

PLATINUM-GROUP METALS (Platinum, palladium, rhodium, ruthenium, iridium, osmium)  

E-print Network

126 PLATINUM-GROUP METALS (Platinum, palladium, rhodium, ruthenium, iridium, osmium) (Data,000 Rhodium 12,400 8,630 12,000 13,200 14,000 Ruthenium 8,170 9,890 15,900 18,800 24,000 Iridium 3,110 2,100 2.00 Rhodium 1,600.00 838.88 530.28 983.24 2,000.00 Ruthenium 130.67 66.33 35.43 64.22 70.00 Iridium 415.25 294

73

Kinetics of hydride front in Zircaloy-2 and H release from a fractional hydrided surface  

SciTech Connect

The authors study the hydriding process on commercial nuclear fuel claddings from their inner surface using an ultrahigh vacuum method. The method allows determining the incubation and failure times of the fuel claddings, as well as the dissipated energy and the partial pressure of the desorbed H{sub 2} from the outer surface of fuel claddings during the hydriding process. The correlation between the hydriding dissipated energy and the amount of zirconium hydride (formed at different stages of the hydriding process) leads to a near t{sup 1/2} potential law corresponding to the time scaling of the reaction for the majority of the tested samples. The calibrated relation between energy and hydride thickness allows one to calculate the enthalpy of the {delta}-ZrH{sub 1.5} phase. The measured H{sub 2} desorption from the external surface is in agreement with a proposed kinetic desorption model from the hydrides precipitated at the surface.

Diaz, M.; Gonzalez-Gonzalez, A.; Moya, J. S.; Remartinez, B.; Perez, S.; Sacedon, J. L. [Instituto de Ciencia de Materiales de Madrid (CSIC), Sor Juana Ines de la Cruz 3, Cantoblanco, 28049 Madrid (Spain); Iberdrola, Tomas Redondo 3, 28033 Madrid (Spain); Instituto de Ciencia de Materiales de Madrid (CSIC), Sor Juana Ines de la Cruz 3, Cantoblanco, 28049 Madrid (Spain)

2009-07-15

74

Erbium hydride thermal desorption : controlling kinetics.  

SciTech Connect

Thermal desorption spectroscopy (TDS) is used to study the decomposition kinetics of erbium hydride thin films. The TDS results presented in this report show that hydride film processing parameters directly impact thermal stability. Issues to be addressed include desorption kinetics for dihydrides and trihydrides, and the effect of film growth parameters, loading parameters, and substrate selection on desorption kinetics.

Ferrizz, Robert Matthew

2007-08-01

75

Phase control of iridium and iridium oxide thin films in atomic layer deposition  

SciTech Connect

The atomic layer deposition of iridium (Ir) and iridium oxide (IrO{sub 2}) films was investigated using an alternating supply of (ethylcyclopentadienyl)(1,5-cyclooctadiene) iridium and oxygen gas at temperatures between 230 and 290 deg. C. The phase transition between Ir and IrO{sub 2} occurred at the critical oxygen partial pressure during the oxygen injection pulse. The oxygen partial pressure was controlled by the O{sub 2}/(Ar+O{sub 2}) ratio or deposition pressures. The resistivity of the deposited Ir and IrO{sub 2} films was about 9 and 120 {mu}{omega} cm, respectively. In addition, the critical oxygen partial pressure for the phase transition between Ir and IrO{sub 2} was increased with increasing the deposition temperature. Thus, the phase of the deposited film, either Ir or IrO{sub 2}, was controlled by the oxygen partial pressure and the deposition temperature. However, the formation of a thin Ir layer was detected between the IrO{sub 2} and SiO{sub 2} substrate. To remove this interfacial layer, the oxygen partial pressure is increased to a severe condition. And the impurity contents were below the detection limit of Auger electron spectroscopy in both Ir and IrO{sub 2} films.

Kim, Sung-Wook; Kwon, Se-Hun; Kwak, Dong-Kee; Kang, Sang-Won [Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, 373-1 Guseong-dong, Yuseong-gu, Daejeon 305-701 (Korea, Republic of)

2008-01-15

76

Iridium anomaly approximately synchronous with terminal eocene extinctions.  

PubMed

An iridium anomaly has been found in coincidence with the known microtektite level in cores from Deep Sea Drilling Project site 149 in the Caribbean Sea. The iridium was probably not in the microtektites but deposited simultaneously with them; this could occur if the iridium was deposited from a dust cloud resulting from a bolide impact, as suggested for the anomaly associated with the Cretaceous-Tertiary boundary. Other workers have deduced that the microtektites are part of the North American strewn tektite field, which is dated at about 34 million years before present, and that the microtektite horizon in deep-sea cores is synchronous with the extinction of five radiolarian species. Mass extinctions also occur in terrestrial mammals within 4 million years of this time. The iridium anomaly and the tektites and microtektites are supportive of a major bolide impact about 34 million years ago. PMID:17819180

Alvarez, W; Asaro, F; Michel, H V; Alvarez, L W

1982-05-21

77

Iridium anomaly approximately synchronous with terminal eocene extinctions  

SciTech Connect

An iridium anomaly has been found in coincidence with the known microtektite level in cores from Deep Sea Drilling Project site 149 in the Caribbean Sea. The iridium was probably not in the microtektites but deposited simultaneously with them; this could occur if the iridium was deposited from a dust cloud resulting from a bolide impact, as suggested for the anomaly associated with the Cretaceous-Tertiary boundary. Other workers have deduced that the microtektites are part of the North American strewn tektite field, which is dated at about 34 million years before present, and that the microtektite horizon in deep-sea cores is synchronous with the extinction of five radiolarian species. Mass extinctions also occur in terrestrial mammals within 4 million years of this time. The iridium anomaly and the tektites and microtektites are supportive of a major bolide impact about 34 million years ago.

Alvarez, W. (Univ. of California, Berkeley); Asaro, F.; Michel, H.V.; Alvarez, L.W.

1982-05-21

78

pH sensor properties of electrochemically grown iridium oxide  

Microsoft Academic Search

The open-circuit potential of an electrochemically grown iridium oxide film is measured and shows a pH sensitivity between ?60 and ?80 mV\\/pH. This sensitivity is found to depend on the state of oxidation of the iridium oxide film; for a higher state of oxidation (or more of the oxide in the high valence state), the sensitivity is also higher. This

W. Olthuis; M. A. M. Robben; P. Bergveld; M. Bos; Linden van der W. E

1990-01-01

79

Synthesis and characterization of nitrides of iridium and palladiums  

SciTech Connect

We describe the synthesis of nitrides of iridium and palladium using the laser-heated diamond anvil cell. We have used the in situ techniques of x-ray powder diffraction and Raman scattering to characterize these compounds and have compared our experimental findings where possible to the results of first-principles theoretical calculations. We suggest that palladium nitride is isostructural with pyrite, while iridium nitride has a monoclinic symmetry and is isostructural with baddeleyite.

Crowhurst, Jonathan C.; Goncharov, Alexander F.; Sadigh, B.; Zaug, J.M.; Aberg, D.; Meng, Yue; Prakapenka, Vitali B. (LLNL); (CIW); (UC)

2008-08-14

80

Iridium{reg_sign} worldwide personal communication system  

SciTech Connect

The IRIDIUM system is a personal worldwide communication system designed to support portable, low power subscriber units through the use of a constellation of satellites in low earth polar orbit. The satellites are networked together to form a system which provides continuous line-of-sight communications between the IRIDIUM system and any point within 30 km of the earth{close_quote}s surface. The system architecture and operation are described. {copyright} {ital 1997 American Institute of Physics.}

Helm, J. [Senior Systems Engineer Motorola Mobile Satellite Systems Division 1600 W. Chandler Blvd., Suite 150 Chandler, Arizona85224 (United States)

1997-01-01

81

CCMR: New Iridium Complexes for the Dehydrogenation of Alkanes  

NSDL National Science Digital Library

To introduce small variations on the previously investigated iridium P-C-P pincer complexes. The variations include substitution of cyclohexyl groups for the tert-butyl and the iso-propyl groups found on the phosphines.Thus, synthesis of these new iridium P-C-P pincer complexes was performed with the aim of improved catalytic dehydrogenation activity as well as a better understand of the influence that ligand sterics and electronics have on the active species.

Wang, David

2004-08-17

82

Zirconium hydride containing explosive composition  

DOEpatents

An improved explosive composition is disclosed and comprises a major portion of an explosive having a detonation velocity between about 1500 and 10,000 meters per second and a minor amount of a donor additive comprising a non-explosive compound or mixture of non-explosive compounds which when subjected to an energy fluence of 1000 calories/cm.sup.2 or less is capable of releasing free radicals each having a molecular weight between 1 and 120. Exemplary donor additives are dibasic acids, polyamines and metal hydrides.

Walker, Franklin E. (18 Shadow Oak Rd., Danville, CA 94526); Wasley, Richard J. (4290 Colgate Way, Livermore, CA 94550)

1981-01-01

83

Activated aluminum hydride hydrogen storage compositions and uses thereof  

DOEpatents

In one aspect, the invention relates to activated aluminum hydride hydrogen storage compositions containing aluminum hydride in the presence of, or absence of, hydrogen desorption stimulants. The invention particularly relates to such compositions having one or more hydrogen desorption stimulants selected from metal hydrides and metal aluminum hydrides. In another aspect, the invention relates to methods for generating hydrogen from such hydrogen storage compositions.

Sandrock, Gary (Ringwood, NJ); Reilly, James (Bellport, NY); Graetz, Jason (Mastic, NY); Wegrzyn, James E. (Brookhaven, NY)

2010-11-23

84

CO adsorption on neutral iridium clusters  

E-print Network

The adsorption of carbon monoxide on neutral iridium clusters in the size range of n = 3 to 21 atoms is investigated with infrared multiple photon dissociation spectroscopy. For each cluster size only a single v(CO) band is present with frequencies in the range between 1962 cm-1 (n = 8) and 1985 cm-1 (n = 18) which can be attributed to an atop binding geometry. This behaviour is compared to the CO binding geometries on clusters of other group 9 and 10 transition metals as well as to that on extended surfaces. The preference of Ir for atop binding is rationalized by relativistic effects on the electronic structure of the later 5d metals.

Kerpal, Christian; Meijer, Gerard; Fielicke, André

2010-01-01

85

Interstellar Hydride Spectroscopy with Herschel  

NASA Astrophysics Data System (ADS)

The Herschel satellite is now giving access with unprecedented sensitivity to the THz spectral range. In particular ground state lines of simple neutral and ionized hydrides have been detected in a wide range of interstellar environments, leading to a renewed understanding of the formation processes of interstellar molecules in the diffuse interstellar medium. In this talk, I will present recent results obtained with the Herschel HIFI and PACS instruments on the carbon, oxygen and nitrogen hydrides. I will discuss how CH and HF can be used as tracers of molecular hydrogen in the diffuse interstellar matter, the new diagnostic capabilities of the cosmic ray ionization rate opened by the OH^+ and H_2O^+ molecular ions, and the role of the dissipation of turbulence in the production of the CH^+ and SH^+ reactive ions. Figure 1: Example of Herschel/HIFI spectra towards the massive star forming region G10.6--0.4. The diffuse interstellar matter along the line of sight towards this massive object is producing multiple absortion features from ˜ 6 to˜ 50 km/s while the emission or absortion signals between -20 to 5 km/s are caused by the massive source itself.

Gerin, Maryvonne

2011-06-01

86

Hydrogen-storing hydride complexes  

DOEpatents

A ternary hydrogen storage system having a constant stoichiometric molar ratio of LiNH.sub.2:MgH.sub.2:LiBH.sub.4 of 2:1:1. It was found that the incorporation of MgH.sub.2 particles of approximately 10 nm to 20 nm exhibit a lower initial hydrogen release temperature of 150.degree. C. Furthermore, it is observed that the particle size of LiBNH quaternary hydride has a significant effect on the hydrogen sorption concentration with an optimum size of 28 nm. The as-synthesized hydrides exhibit two main hydrogen release temperatures, one around 160.degree. C. and the other around 300.degree. C., with the main hydrogen release temperature reduced from 310.degree. C. to 270.degree. C., while hydrogen is first reversibly released at temperatures as low as 150.degree. C. with a total hydrogen capacity of 6 wt. % to 8 wt. %. Detailed thermal, capacity, structural and microstructural properties have been demonstrated and correlated with the activation energies of these materials.

Srinivasan, Sesha S. (Tampa, FL); Niemann, Michael U. (Venice, FL); Goswami, D. Yogi (Tampa, FL); Stefanakos, Elias K. (Tampa, FL)

2012-04-10

87

Trapping of hydride forming elements within miniature electrothermal devices. Part 2. Investigation of collection of arsenic and selenium hydrides on a surface and in a cavity of a graphite rod  

NASA Astrophysics Data System (ADS)

The interaction of arsenic and selenium hydrides with bare and modified graphite was investigated by atomic absorption spectrometry and by radiotracer technique using 75Se radionuclide in a laboratory made brass cylindrical chamber equipped with a vertical quartz tube torch for supporting miniature hydrogen diffusion flame atomizer. Strong interaction was observed at elevated temperatures above 800 °C. In contrast to the very often-reported data for conventional graphite tube atomizers, this high temperature interaction was also accompanied by a pronounced trapping of analytes at elevated temperatures close to 1100-1200 °C when modified graphite was used. Comparing modifiers tested (Ir, Pt and Rh), iridium appeared the only useful permanent modifier. Among various graphite-rod traps designed, the most efficient trapping of analytes was achieved in a graphite cavity. The net selenium trapping efficiencies of approximately 53% and 70% were found by radiotracer technique for the iridium-treated graphite surface and the iridium-treated graphite cavity, respectively. In contrast to the molybdenum surface, bare graphite did not exhibit any significant trapping effect. Trapping isotherms obtained at different temperatures displayed non-linear course in the range up to the upper limit of the analytical relevance of 100 ng of an analyte, indicating a limited trapping capacity of the modified graphite surface and the same trapping mechanism at low and elevated temperatures applied (300-1300 °C). Radiography experiments with 75Se radiotracer showed that a major part of selenium was collected within the small cavity of the graphite rod and that selenium was also deposited after the trapping and vaporization steps in the trap chamber and on the quartz tube wall of the burner. Complementary experiments performed with the conventional transversally heated graphite tube and with bare and thermally shielded injection capillaries for hydride introduction, showed that the pronounced trapping effect could not be observed at elevated temperatures in conventional systems equipped with the bare capillary. The losses of analytes in the non-shielded bare introduction capillary exposed to the heat decrease the transport efficiency of hydrides into the graphite tube, and consequently they cause reduction of the overall trapping efficiency at elevated temperatures.

Do?ekal, Bohumil

2004-04-01

88

Iridium NEXT: A Global access for your sensor needs  

NASA Astrophysics Data System (ADS)

The operational Iridium constellation is comprised of 66 satellites, used to primarily provide worldwide voice and data coverage to satellite phones, pagers and integrated transceivers. The satellites are in low Earth orbit at 781 km and inclination of 86.4 deg, resulting in unprecedented 24/7 coverage and real-time visibility of the entire globe. Recently, through funding from the National Science Foundation (NSF), Iridium has been utilized by the Johns Hopkins University Applied Physics Laboratory (APL), with help from The Boeing Company, as an infrastructure for a comprehensive network for space environment measurements. Known as the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE), the Iridium-based system provides real-time magnetic field measurements using the satellites as part of a new observation network to forecast weather in space. In February 2007, Iridium announced Iridium NEXT, a novel design for a second-generation satellite constellation. Anticipated to begin launching in 2015, Iridium NEXT will maintain the existing Iridium constellation architecture of 66 cross-linked satellite LEO covering 100 percent of the globe. In the spirit of AMPERE, for commercial, government, and scientific organizations Iridium NEXT also plans to offer new earth and space observation opportunities through hosted hosted payloads on the 66 Iridium NEXT satellite network. To provide seamless support and access to this latest innovation in payload transportation, Iridium NEXT has teamed with Space Dynamics Laboratory - Utah State University which has delivered thousands of successful sensors and subsystems for over 400 space borne and aircraf based payloads. One such innovation called SensorPOD will offer unique benefits such as unprecedented spatial and temporal coverage, real-time relay of data to and from up to 5 Kg payloads in space, and access to space at a fraction of the cost of a dedicated missions such as 3U or larger Cubesats. In this paper we will present the specifications, and various options that have been developed to meet the varying needs of the geosciences and space weather community.

Gupta, O. P.; Fish, C. S.

2010-12-01

89

Liquid suspensions of reversible metal hydrides  

DOEpatents

The reversibility of the process M + x/2 H/sub 2/ ..-->.. MH/sub x/, where M is a metal hydride former that forms a hydride MH/sub x/ in the presence of H/sub 2/, generally used to store and recall H/sub 2/, is found to proceed under a liquid, thereby to reduce contamination, provide better temperature control and provide in situ mobility of the reactants. Thus, a slurry of particles of a metal hydride former with an inert solvent is subjected to temperature and pressure controlled atmosphere containing H/sub 2/, to store hydrogen (at high pressures) and to release (at low pressures) previously stored hydrogen. The direction of the flow of the H/sub 2/ through the liquid is dependent upon the H/sub 2/ pressure in the gas phase at a given temperature. When the former is above the equilibrium absorption pressure of the respective hydride the reaction proceeds to the right, i.e., the metal hydride is formed and hydrogen is stored in the solid particle. When the H/sub 2/ pressure in the gas phase is below the equilibrium dissociation pressure of the respective hydride the reaction proceeds to the left, the metal hydride is decomposed and hydrogen is released into the gas phase.

Reilly, J.J.; Grohse, E.W.; Winsche, W.E.

1983-12-08

90

DETERMINATION OF HETEROGENEOUS ELECTRON TRANSFER RATE CONSTANTS AT MICROFABRICATED IRIDIUM ELECTRODES. (R825511C022)  

EPA Science Inventory

There has been an increasing use of both solid metal and microfabricated iridium electrodes as substrates for various types of electroanalysis. However, investigations to determine heterogeneous electron transfer rate constants on iridium, especially at an electron beam evapor...

91

DOI: 10.1002/adsc.200700546 Iridium-Catalyzed Asymmetric Hydrogenation of Vinyl Ethers  

E-print Network

DOI: 10.1002/adsc.200700546 Iridium-Catalyzed Asymmetric Hydrogenation of Vinyl Ethers Ye Zhua,P-ligated iridium complexes in asymmetric hydrogenations of the silyl and methyl enol ethers D and E, but complex

Burgess, Kevin

92

Activation of Sulfur-and Nitrogen-Containing Heterocycles by a Dinuclear Iridium Complex  

E-print Network

Activation of Sulfur- and Nitrogen-Containing Heterocycles by a Dinuclear Iridium Complex David A Of relevance to the present work, the dinuclear iridium complex [Cp*IrH3]2 (1) was previously found to react

Jones, William D.

93

Hydrodesulfurization of Thiophene and Benzothiophene to Butane and Ethylbenzene by a Homogeneous Iridium  

E-print Network

Iridium Complex David A. Vicic and William D. Jones* Department of Chemistry, University of Rochester such as benzothiophene. This led us to explore the reactivity of the bis(µ-hydrido)- bis[chloro(pentamethylcyclopentadienyl)]iridium

Jones, William D.

94

Computational Modeling of Uranium Hydriding and Complexes  

SciTech Connect

Uranium hydriding is one of the most important processes that has received considerable attention over many years. Although many experimental and modeling studies have been carried out concerning thermochemistry, diffusion kinetics and mechanisms of U-hydriding, very little is known about the electronic structure and electronic features that govern the U-hydriding process. Yet it is the electronic feature that controls the activation barrier and thus the rate of hydriding. Moreover the role of impurities and the role of the product UH{sub 3} on hydriding rating are not fully understood. An early study by Condon and Larson concerns with the kinetics of U-hydrogen system and a mathematical model for the U-hydriding process. They proposed that diffusion in the reactant phase by hydrogen before nucleation to form hydride phase and that the reaction is first order for hydriding and zero order for dehydriding. Condon has also calculated and measures the reaction rates of U-hydriding and proposed a diffusion model for the U-hydriding. This model was found to be in excellent agreement with the experimental reaction rates. From the slopes of the Arrhenius plot the activation energy was calculated as 6.35 kcal/mole. In a subsequent study Kirkpatrick formulated a close-form for approximate solution to Condon's equation. Bloch and Mintz have proposed the kinetics and mechanism for the U-H reaction over a wide range of pressures and temperatures. They have discussed their results through two models, one, which considers hydrogen diffusion through a protective UH{sub 3} product layer, and the second where hydride growth occurs at the hydride-metal interface. These authors obtained two-dimensional fits of experimental data to the pressure-temperature reactions. Kirkpatrick and Condon have obtained a linear solution to hydriding of uranium. These authors showed that the calculated reaction rates compared quite well with the experimental data at a hydrogen pressure of 1 atm. Powell et al. have studied U-hydriding in ultrahigh vacuum and obtained the linear rate data over a wide range of temperatures and pressures. They found reversible hydrogen sorption on the UH{sub 3} reaction product from kinetic effects at 21 C. This demonstrates restarting of the hydriding process in the presence of UH{sub 3} reaction product. DeMint and Leckey have shown that Si impurities dramatically accelerate the U-hydriding rates. We report our recent results of relativistic computations that vary from complete active space multi-configuration interaction (CAS-MCSCF) followed by multi-reference configuration interaction (MRSDCI) computations that included up to 50 million configurations for modeling of uranium-hydriding with cluster models will be presented.

Balasubramanian, K; Siekhaus, W J; McLean, W

2003-02-03

95

Mixed N-Heterocyclic Carbene-Bis(oxazolinyl)borato Rhodium and Iridium Complexes in Photochemical and Thermal Oxidative Addition Reactions  

SciTech Connect

In order to facilitate oxidative addition chemistry of fac-coordinated rhodium(I) and iridium(I) compounds, carbene–bis(oxazolinyl)phenylborate proligands have been synthesized and reacted with organometallic precursors. Two proligands, PhB(OxMe2)2(ImtBuH) (H[1]; OxMe2 = 4,4-dimethyl-2-oxazoline; ImtBuH = 1-tert-butylimidazole) and PhB(OxMe2)2(ImMesH) (H[2]; ImMesH = 1-mesitylimidazole), are deprotonated with potassium benzyl to generate K[1] and K[2], and these potassium compounds serve as reagents for the synthesis of a series of rhodium and iridium complexes. Cyclooctadiene and dicarbonyl compounds {PhB(OxMe2)2ImtBu}Rh(?4-C8H12) (3), {PhB(OxMe2)2ImMes}Rh(?4-C8H12) (4), {PhB(OxMe2)2ImMes}Rh(CO)2 (5), {PhB(OxMe2)2ImMes}Ir(?4-C8H12) (6), and {PhB(OxMe2)2ImMes}Ir(CO)2 (7) are synthesized along with ToMM(?4-C8H12) (M = Rh (8); M = Ir (9); ToM = tris(4,4-dimethyl-2-oxazolinyl)phenylborate). The spectroscopic and structural properties and reactivity of this series of compounds show electronic and steric effects of substituents on the imidazole (tert-butyl vs mesityl), effects of replacing an oxazoline in ToM with a carbene donor, and the influence of the donor ligand (CO vs C8H12). The reactions of K[2] and [M(?-Cl)(?2-C8H14)2]2 (M = Rh, Ir) provide {?4-PhB(OxMe2)2ImMes?CH2}Rh(?-H)(?-Cl)Rh(?2-C8H14)2 (10) and {PhB(OxMe2)2ImMes}IrH(?3-C8H13) (11). In the former compound, a spontaneous oxidative addition of a mesityl ortho-methyl to give a mixed-valent dirhodium species is observed, while the iridium compound forms a monometallic allyl hydride. Photochemical reactions of dicarbonyl compounds 5 and 7 result in C–H bond oxidative addition providing the compounds {?4-PhB(OxMe2)2ImMes?CH2}RhH(CO) (12) and {PhB(OxMe2)2ImMes}IrH(Ph)CO (13). In 12, oxidative addition results in cyclometalation of the mesityl ortho-methyl similar to 10, whereas the iridium compound reacts with the benzene solvent to give a rare crystallographically characterized cis-[Ir](H)(Ph) complex. Alternatively, the rhodium carbonyl 5 or iridium isocyanide {PhB(OxMe2)2ImMes}Ir(CO)CNtBu (15) reacts with PhSiH3 in the dark to form the silyl compound {PhB(OxMe2)2ImMes}RhH(SiH2Ph)CO (14) or {PhB(OxMe2)2ImMes}IrH(SiH2Ph)CNtBu (17). These examples demonstrate the enhanced thermal reactivity of {PhB(OxMe2)2ImMes}-supported iridium and rhodium carbonyl compounds in comparison to tris(oxazolinyl)borate, tris(pyrazolyl)borate, and cyclopentadienyl-supported compounds.

Xu, Songchen [Ames Laboratory; Manna, Kuntal [Ames Laboratory; Ellern, Arkady [Ames Laboratory; Sadow, Aaron D [Ames Laboratory

2014-12-08

96

Method of recovering the constituents of catalysts comprising an aluminous carrier, platinum and iridium  

Microsoft Academic Search

A method is described for the recovery of the constituents of catalysts containing platinum and iridium. They are recovered by substantially totally solubilizing the catalysts with an oxidizing solution of hydrochloric acid, and by extracting the precious metals with an anionic resin from which the iridium is selectively washed out. This method enables the platinum and iridium to be completely

J. Grosbois; M. Thomas

1976-01-01

97

Adsorptive Stripping Analysis of Trace Nickel at Iridium-Based Ultramicroelectrode Arrays  

E-print Network

Adsorptive Stripping Analysis of Trace Nickel at Iridium-Based Ultramicroelectrode Arrays Joseph: July 27, 1999 Abstract Lithographically fabricated iridium-based mercury microelectrode arrays the iridium-based microelectrode array very attractive for on-site measurements of trace metals that cannot

Kounaves, Samuel P.

98

Synthesis of Metallic Iridium Oxide Nanowires via Metal Organic Chemical Vapor Deposition Fengyan ZHANG  

E-print Network

Synthesis of Metallic Iridium Oxide Nanowires via Metal Organic Chemical Vapor Deposition Fengyan, U.S.A. (Received December 9, 2004; accepted February 3, 2005; published March 4, 2005) Iridium oxide) iridium (I) as the precursor on Si or SiO2 substrate with and without metal nanoparticles as catalysts

Wang, Deli

99

Chiral Proline-Based Ligands for Iridium-Catalyzed Asymmetric Hydrogenation  

E-print Network

Chiral Proline-Based Ligands for Iridium-Catalyzed Asymmetric Hydrogenation Inauguraldissertation. Parts of this work have been previously published: ,,Proline-Based P,O Ligands/Iridium Complexes in Iridium-Catalyzed Asymmetric Hydrogenation: New Catalysts, Substrates and Applications in Total Synthesis

Amrhein, Valentin

100

Electrodeposition of highly ordered macroporous iridium oxide through self-assembled colloidal templates  

E-print Network

Electrodeposition of highly ordered macroporous iridium oxide through self-assembled colloidal as an Advance Article on the web 24th April 2009 DOI: 10.1039/b900279k Iridium oxide electrodeposited through devices. Introduction Iridium oxide (IrOx) films are well known for their applications in electrochromism

Steiner, Ullrich

101

Deposition and Stripping Properties of Mercury on Iridium S. P. Kounaves*'1 and J. Buffle  

E-print Network

Deposition and Stripping Properties of Mercury on Iridium Electrodes S. P. Kounaves*'1 and J ABSTRACT The reduction of mercury on a fresh iridium surface is reversible with a half-wave potential documented in the literature, the same cannot be said for iridium. During the past 30 years, only a few

Kounaves, Samuel P.

102

Copyright c 2008 IEEE. Reprinted from Ujjwal Deep Dahal, Brent R. Petersen and Julian Meng, "Iridium  

E-print Network

, "Iridium communication system for data telemetry of renewable distributed generation system," in 2008 24th, you agree to all provisions of the copyright laws protecting it. #12;Iridium Communication System for the required telemetry. The Iridium satellite system is able to provide global communications at a reasonable

Petersen, Brent

103

Heterolytic CH Activation and Catalysis by an O-Donor Iridium-Hydroxo Complex  

E-print Network

Notes Heterolytic CH Activation and Catalysis by an O-Donor Iridium-Hydroxo Complex William J. Tenn, Pasadena, California 91125 ReceiVed July 21, 2006 Summary: A well-defined, O-donor ligated iridium-R and H2O. Specifically, we report the preparation of the O-donor iridium- (III) hydroxide complex (acac

Goddard III, William A.

104

Goals: Reduction of IridiumGoals: Reduction of Iridium--usage; ASV Collaboration under Constraints; Online Datausage; ASV Collaboration under Constraints; Online Data--streamingstreaming CoastalCoastal FreewaveFreewave network; Hierarchical Control Scheme  

E-print Network

Goals: Reduction of IridiumGoals: Reduction of Iridium--usage; ASV Collaboration under Constraints endurance (~4 wks) + Collaborative robotic sensing - Slow moving (Iridium is expensive (>$2500 instead of Iridium whenever in range. o Network should support multiple gliders simultaneously to enable

Smith, Ryan N.

105

Heat transfer enhancement in metal hydride systems  

NASA Astrophysics Data System (ADS)

An attempt has been made to enhance the heat transfer of hydrogen storage metal hydride systems by the addition of small fraction of high conductivity materials in various configurations. Results indicate that the form of the enhancement material rather than its composition is the more critical factor. The addition of over 6% aluminum foam enhances the effective thermal conductivity of a hydride bed by a factor of 2.6.

Rosso, M. J., Jr.; Strickland, G.

106

Hydriding combustion synthesis of TiFe  

Microsoft Academic Search

Titanium iron (TiFe) is one of the most attractive metal hydrides because of abundant and low cost raw materials and moderate conditions for hydrogenation and dehydrogenation; however, it has not been practically used due to time-consuming and energy-consuming activation treatment. Aiming to improve the initial activity of TiFe, we applied hydriding combustion synthesis (HCS), which has attractive advantages for the

I. Saita; M. Sato; H. Uesugi; T. Akiyama

2007-01-01

107

Red and blue shifted hydridic bonds.  

PubMed

By performing MP2/aug-cc-pVTZ ab initio calculations for a large set of dimer systems possessing a R-H hydridic bond involved in diverse types of intermolecular interactions (dihydrogen bonds, hydride halogen bonds, hydride hydrogen bonds, and charge-assisted hydride hydrogen bonds), we show that this is rather an elongation than a shortening that a hydride bond undergoes on interaction. Contrary to what might have been expected on the basis of studies in uniform electric field, this elongation is accompanied by a blue instead of red shift of the R-H stretching vibration frequency. We propose that the "additional" elongation of the R-H hydridic bond results from the significant charge outflow from the sigma bonding orbital of R-H that weakens this bond. The more standard red shift obtained for stronger complexes is explained by means of the Hermansson's formula and the particularly strong electric field produced by the H-acceptor molecule. PMID:25043253

Jab?o?ski, Miros?aw

2014-09-15

108

[Biomonitoring of iridium in a urban population].  

PubMed

Iridium (Ir) is one of the six elements collectively known as the platinum group metals. For its excellent catalytic properties, Ir was recently introduced into DeNOx, a new generation of automotive catalysts. The aim of our study was to evaluate urinary Ir levels in an urban population. A total of 122 healthy male subjects of Rome (Italy) were studied. Ir quantification in the urine samples of these subjects was carried out by sector field inductively coupled plasma mass spectrometry. The mean urinary Ir level was 10.41 ng/g creatinine (standard deviation: 9.67; 25th-75th percentile: 3,62-12,74 ng/g creatinine). The scientific community should respond to a potential increase in environmental exposure to Ir, due to its growing use as a catalyst, with very careful evaluation of the biological levels of this metal and monitoring of airborne particulate present in the life environment. Further investigation will enable researchers to confirm and integrate the findings of our present study undertaken in the context of surveillance. PMID:16805466

Iavicoli, I; Bocca, B; Caimi, S; Alimonti, A; Carelli, G; Bergamaschi, A

2006-01-01

109

Experimental determination of the solubility of iridium in silicate melts: Preliminary results  

NASA Technical Reports Server (NTRS)

Little is known of the geochemical behavior of iridium. Normally this element is taken to be chalcophile and/or siderophile so that during planetary differentiation processes, e.g., core formation, iridium is extracted from silicate phases into metallic phases. Experimental determination of the metal/silicate partition coefficient of iridium is difficult simply because it is so large. Also there are no data on the solubility behavior of iridium in silicate melts. With information on the solubility of iridium in silicate melts it is possible, in combination with experimental data for Fe-Ir alloys, to calculate the partition coefficient between a metallic phase and a silicate melt.

Borisov, Alexander; Dingwell, Donald B.; Oneill, Hugh ST.C.; Palme, Herbert

1992-01-01

110

METALLIC HYDRIDES. Magnetic properties of laves-phase rare earth hydrides  

E-print Network

METALLIC HYDRIDES. Magnetic properties of laves-phase rare earth hydrides J. J. Rhyne and G. E on the rare earth site. The rare earth spins disorder at a temperature lower than the bulk Tc in ErFe2 H3 5 per formula unit assuming complete occupation of 3 tetrahedral sites. The heavy rare earth (RFe2

Boyer, Edmond

111

Iridium oxide-polymer nanocomposite electrode materials for water oxidation.  

PubMed

Nanocomposite anode materials for water oxidation have been readily synthesized by electrodeposition of iridium oxide nanoparticles into poly(pyrrole-alkylammonium) films, previously deposited onto carbon electrodes by oxidative electropolymerization of a pyrrole-alkylammonium monomer. The nanocomposite films were characterized by electrochemistry, transmission electron microscopy, and atomic force microscopy. They showed an efficient electrocatalytic activity toward the oxygen evolution reaction. Data from Tafel plots have demonstrated that the catalytic activity of the iridium oxide nanoparticles is maintained following their inclusion in the polymer matrix. Bulk electrolysis of water at carbon foam modified electrodes have shown that the iridium oxide-polymer composite presents a higher catalytic activity and a better operational stability than regular oxide films. PMID:25045786

Lattach, Youssef; Rivera, Juan Francisco; Bamine, Tahya; Deronzier, Alain; Moutet, Jean-Claude

2014-08-13

112

mer-Hydridotris(tri­methyl­phosphane-?P)(d-valinato-?2 N,O)iridium hexa­fluorido­phosphate di­chloro­methane 0.675-solvate  

PubMed Central

The title compound, [Ir(C5H10NO2)H(C3H9P)3]PF6·0.675CH2Cl2, an iridium compound with a meridional arrangement of PMe3 groups, O,N-bidentate coordination of d-valine and with a hydride ligand trans to the N atom is compared with the l-valine complex reported previously. As expected, the complexes from the corresponding l and d isomers of valine crystallize in enanti­omorphic space groups (P43 and P41, respectively). In the crystal, N—H?O and N—H?F hydrogen bonding is observed, the N—H to carbonyl oxygen hydrogen bond producing a helical motif that proceeds along the 41 screw of the c axis. PMID:24764947

Merola, Joseph S.; Slebodnick, Carla; Berg, Michael; Ritchie, Melissa K.

2014-01-01

113

PLATINUM-GROUP METALS (Platinum, palladium, rhodium, ruthenium, iridium, osmium)  

E-print Network

120 PLATINUM-GROUP METALS (Platinum, palladium, rhodium, ruthenium, iridium, osmium) (Data,600 11,200 12,800 13,100 13,000 Ruthenium 49,800 21,200 14,100 13,200 12,500 Iridium 2,550 1,520 3,530 2.12 265.65 530.61 738.51 650.00 Rhodium 6,533.57 1,591.32 2,459.07 2,204.35 1,300.00 Ruthenium 324.60 97

114

PLATINUM-GROUP METALS (Platinum, palladium, rhodium, ruthenium, iridium, osmium)  

E-print Network

124 PLATINUM-GROUP METALS (Platinum, palladium, rhodium, ruthenium, iridium, osmium) (Data,000 Rhodium 10,300 18,200 12,400 9,890 8,630 Ruthenium 11,400 20,900 8,170 10,800 9,940 Iridium 2,270 2,700 3,598.67 838.88 750.25 Ruthenium 40.70 129.76 130.67 66.33 55.60 Employment, mine, number 954 1,290 1,320 1

115

PLATINUM-GROUP METALS (Platinum, palladium, rhodium, ruthenium, iridium, osmium)  

E-print Network

126 PLATINUM-GROUP METALS (Platinum, palladium, rhodium, ruthenium, iridium, osmium) (Data,000 Rhodium 12,000 13,200 13,600 15,900 18,000 Ruthenium 15,900 18,800 23,200 36,000 37,000 Iridium 2,200 3.00 232.93 203.54 322.93 360.00 Rhodium 530.28 983.24 2,059.73 4,561.06 6,060.00 Ruthenium 35.43 64.22 74

116

PLATINUM-GROUP METALS (Platinum, palladium, rhodium, ruthenium, iridium, osmium)  

E-print Network

120 PLATINUM-GROUP METALS (Platinum, palladium, rhodium, ruthenium, iridium, osmium) (Data,600 12,600 11,200 12,800 12,000 Ruthenium 48,700 49,800 21,200 14,100 15,000 Iridium 3,410 2,550 1,520 3.34 355.12 265.65 530.61 730.00 Rhodium 6,203.09 6,533.57 1,591.32 2,459.07 2,030.00 Ruthenium 573.74 324

117

PLATINUM-GROUP METALS (Platinum, palladium, rhodium, ruthenium, iridium, osmium)  

E-print Network

122 PLATINUM-GROUP METALS (Platinum, palladium, rhodium, ruthenium, iridium, osmium) (Data,000 Palladium 127,000 139,000 119,000 113,000 107,000 Rhodium 13,200 13,600 15,900 16,600 16,000 Ruthenium 18,059.73 4,561.06 6,203.09 7,260.00 Ruthenium 64.22 74.41 193.09 573.74 340.00 Iridium 185.33 169.51 349

118

PLATINUM-GROUP METALS (Platinum, palladium, rhodium, ruthenium, iridium, osmium)  

E-print Network

126 PLATINUM-GROUP METALS (Platinum, palladium, rhodium, ruthenium, iridium, osmium) (Data,800 Rhodium 13,500 10,300 18,200 12,400 7,560 Ruthenium 8,880 11,400 20,900 8,170 10,800 Iridium 1,950 2,270 2,990.00 1,598.67 750.75 Ruthenium 47.95 40.70 129.76 130.67 60.00 Employment, mine, number 620 954 1,290 1

119

PLATINUM-GROUP METALS (Platinum, palladium, rhodium, ruthenium, iridium, osmium)  

E-print Network

120 PLATINUM-GROUP METALS (Platinum, palladium, rhodium, ruthenium, iridium, osmium) (Data,000 Rhodium 11,200 12,800 13,100 12,800 11,000 Ruthenium 21,200 14,100 13,300 10,200 13,000 Iridium 1,520 3,511.00 Palladium 265.65 530.61 738.51 649.27 736.00 Rhodium 1,591.32 2,459.07 2,204.35 1,274.98 1,095.00 Ruthenium

120

PLATINUM-GROUP METALS (Platinum, palladium, rhodium, ruthenium, iridium, osmium)  

E-print Network

120 PLATINUM-GROUP METALS (Platinum, palladium, rhodium, ruthenium, iridium, osmium) (Data,600 12,600 11,200 13,000 Ruthenium 36,000 48,700 49,800 21,200 14,000 Iridium 2,800 3,410 2,550 1,520 3.12 265.65 500 Rhodium 4,561.06 6,203.09 6,533.57 1,591.32 2,500 Ruthenium 193.09 573.74 324.60 97.28 198

121

PLATINUM-GROUP METALS (Platinum, palladium, rhodium, ruthenium, iridium, osmium)  

E-print Network

122 PLATINUM-GROUP METALS (Platinum, palladium, rhodium, ruthenium, iridium, osmium) (Data,000 Rhodium 8,630 12,000 13,200 13,600 17,000 Ruthenium 9,890 15,900 18,800 23,200 30,000 Iridium 2,100 2.00 232.93 203.54 330.00 Rhodium 838.88 530.28 983.24 2,059.73 4,300.00 Ruthenium 66.33 35.43 64.22 74

122

PLATINUM-GROUP METALS (Platinum, palladium, rhodium, ruthenium, iridium, osmium)  

E-print Network

120 PLATINUM-GROUP METALS (Platinum, palladium, rhodium, ruthenium, iridium, osmium) (Data,900 16,600 12,600 10,200 Ruthenium 23,200 36,000 48,700 49,800 21,600 Iridium 3,010 2,800 3,410 2,550 1.34 355.12 254.00 Rhodium 2,059.73 4,561.06 6,203.09 6,533.57 1,468.00 Ruthenium 74.41 193.09 573.74 324

123

Hydride dissociation energies of six-membered heterocyclic organic hydrides predicted by ONIOM-G4Method.  

PubMed

Hydride dissociation energy is of great importance in understanding the hydride-donating abilities of organic hydrides. Although the hydride dissociation energies of some organic hydrides have been experimentally measured, much less attention has been focused on the investigation of these quantities from the first principles of physics. Herein, we developed an ONIOM-G4 method and carefully benchmarked this new method against 48 experimental hydride dissociation energies of diverse bulky molecules. It was found that with the combined methods of the HF/6-31+G(d,p)//IEFPCM/Bondi1.15 solvation model, the ONIOM-G4 method can predict the hydride dissociation energies with an error bar of only 1.7 kcal/mol. With the newly developed ONIOM-G4 method, we then systematically studied the hydride dissociation energies of six categories of biologically and pharmaceutically important six-membered heterocyclic organic hydrides, namely, the organic hydrides containing 1,4-dihydropyridine, 1,4-dihydropyrazine, 1,4-oxazine, 1,4-thiazine, 4H-pyran, and 4H-thiopyran ring structures. An extensive hydride dissociation energy scale containing over 100 six-memebered heterocyclic organic hydrides has been established, which may find applications in both synthetic organic chemistry and mechanistic studies of various chemical or biological processes involving transferring of the hydride anion. PMID:22146106

Shi, Jing; Huang, Xiong-Yi; Wang, Hua-Jing; Fu, Yao

2012-01-23

124

Thin-film metal hydrides.  

PubMed

The goal of the medieval alchemist, the chemical transformation of common metals into nobel metals, will forever be a dream. However, key characteristics of metals, such as their electronic band structure and, consequently, their electric, magnetic and optical properties, can be tailored by controlled hydrogen doping. Due to their morphology and well-defined geometry with flat, coplanar surfaces/interfaces, novel phenomena may be observed in thin films. Prominent examples are the eye-catching hydrogen switchable mirror effect, the visualization of solid-state diffusion and the formation of complex surface morphologies. Thin films do not suffer as much from embrittlement and/or decrepitation as bulk materials, allowing the study of cyclic absorption and desorption. Therefore, thin-metal hydride films are used as model systems to study metal-insulator transitions, for high throughput combinatorial research or they may be used as indicator layers to study hydrogen diffusion. They can be found in technological applications as hydrogen sensors, in electrochromic and thermochromic devices. In this review, we discuss the effect of hydrogen loading of thin niobium and yttrium films as archetypical examples of a transition metal and a rare earth metal, respectively. Our focus thereby lies on the hydrogen induced changes of the electronic structure and the morphology of the thin films, their optical properties, the visualization and the control of hydrogen diffusion and on the study of surface phenomena and catalysis. PMID:18980236

Remhof, Arndt; Borgschulte, Andreas

2008-12-01

125

Thermal hydraulic analysis of hydride fuels in BWR's  

E-print Network

This thesis contributes to the hydride nuclear fuel project being completed by UC Berkeley and MIT to assess the possible benefits of using hydride fuel in light water nuclear reactors (LWR's). More specifically, this ...

Creighton, John Everett

2005-01-01

126

Homogeneous and heterogenized iridium water oxidation catalysts  

NASA Astrophysics Data System (ADS)

The development of an efficient catalyst for the oxidative splitting of water into molecular oxygen, protons and electrons is of key importance for producing solar fuels through artificial photosynthesis. We are facing the problem by means of a rational approach aimed at understanding how catalytic performance may be optimized by the knowledge of the reaction mechanism of water oxidation and the fate of the catalytic site under the inevitably harsh oxidative conditions. For the purposes of our study we selected iridium water oxidation catalysts, exhibiting remarkable performance (TOF > 5 s-1 and TON > 20000). In particular, we recently focused our attention on [Cp*Ir(N,O)X] (N,O = 2-pyridincarboxylate; X = Cl or NO3) and [IrCl(Hedta)]Na water oxidation catalysts. The former exhibited a remarkable TOF whereas the latter showed a very high TON. Furthermore, [IrCl(Hedta)]Na was heterogenized onto TiO2 taking advantage of the presence of a dandling -COOH functionality. The heterogenized catalyst maintained approximately the same catalytic activity of the homogeneous analogous with the advantage that could be reused many times. Mechanistic studies were performed in order to shed some light on the rate-determining step and the transformation of catalysts when exposed to "oxidative stress". It was found that the last oxidative step, preceding oxygen liberation, is the rate-determining step when a small excess of sacrificial oxidant is used. In addition, several intermediates of the oxidative transformation of the catalyst were intercepted and characterized by NMR, X-Ray diffractometry and ESI-MS.

Macchioni, Alceo

2014-10-01

127

High H? ionic conductivity in barium hydride  

NASA Astrophysics Data System (ADS)

With hydrogen being seen as a key renewable energy vector, the search for materials exhibiting fast hydrogen transport becomes ever more important. Not only do hydrogen storage materials require high mobility of hydrogen in the solid state, but the efficiency of electrochemical devices is also largely determined by fast ionic transport. Although the heavy alkaline-earth hydrides are of limited interest for their hydrogen storage potential, owing to low gravimetric densities, their ionic nature may prove useful in new electrochemical applications, especially as an ionically conducting electrolyte material. Here we show that barium hydride shows fast pure ionic transport of hydride ions (H?) in the high-temperature, high-symmetry phase. Although some conductivity studies have been reported on related materials previously, the nature of the charge carriers has not been determined. BaH2 gives rise to hydride ion conductivity of 0.2 S cm?1 at 630 °C. This is an order of magnitude larger than that of state-of-the-art proton-conducting perovskites or oxide ion conductors at this temperature. These results suggest that the alkaline-earth hydrides form an important new family of materials, with potential use in a number of applications, such as separation membranes, electrochemical reactors and so on.

Verbraeken, Maarten C.; Cheung, Chaksum; Suard, Emmanuelle; Irvine, John T. S.

2015-01-01

128

High H(-) ionic conductivity in barium hydride.  

PubMed

With hydrogen being seen as a key renewable energy vector, the search for materials exhibiting fast hydrogen transport becomes ever more important. Not only do hydrogen storage materials require high mobility of hydrogen in the solid state, but the efficiency of electrochemical devices is also largely determined by fast ionic transport. Although the heavy alkaline-earth hydrides are of limited interest for their hydrogen storage potential, owing to low gravimetric densities, their ionic nature may prove useful in new electrochemical applications, especially as an ionically conducting electrolyte material. Here we show that barium hydride shows fast pure ionic transport of hydride ions (H(-)) in the high-temperature, high-symmetry phase. Although some conductivity studies have been reported on related materials previously, the nature of the charge carriers has not been determined. BaH2 gives rise to hydride ion conductivity of 0.2 S cm(-1) at 630 °C. This is an order of magnitude larger than that of state-of-the-art proton-conducting perovskites or oxide ion conductors at this temperature. These results suggest that the alkaline-earth hydrides form an important new family of materials, with potential use in a number of applications, such as separation membranes, electrochemical reactors and so on. PMID:25485988

Verbraeken, Maarten C; Cheung, Chaksum; Suard, Emmanuelle; Irvine, John T S

2015-01-01

129

Reactivity of yttrium carboxylates toward alkylaluminum hydrides.  

PubMed

Yttrocene-carboxylate complex [Cp*2Y(OOCAr(Me))] (Cp*=C5Me5, Ar(Me) =C6H2Me3-2,4,6) was synthesized as a spectroscopically versatile model system for investigating the reactivity of alkylaluminum hydrides towards rare-earth-metal carboxylates. Equimolar reactions with bis-neosilylaluminum hydride and dimethylaluminum hydride gave adduct complexes of the general formula [Cp*2Y(?-OOCAr(Me))(?-H)AlR2] (R=CH2SiMe3, Me). The use of an excess of the respective aluminum hydride led to the formation of product mixtures, from which the yttrium-aluminum-hydride complex [{Cp*2Y(?-H)AlMe2(?-H)AlMe2(?-CH3)}2] could be isolated, which features a 12-membered-ring structure. The adduct complexes [Cp*2Y(?-OOCAr(Me))(?-H)AlR2] display identical (1)J(Y,H) coupling constants of 24.5 Hz for the bridging hydrido ligands and similar (89)Y NMR shifts of ?=-88.1 ppm (R=CH2SiMe3) and ?=-86.3 ppm (R=Me) in the (89)Y DEPT45 NMR experiments. PMID:24151216

Schädle, Christoph; Fischbach, Andreas; Herdtweck, Eberhardt; Törnroos, Karl W; Anwander, Reiner

2013-11-25

130

Sealed metal-hydride batteries for aerospace applications  

Microsoft Academic Search

Nickel and silver-metal hydride batteries are being developed for aerospace applications by Eagle-Picher. Metal hydride batteries offer a number of advantages over other aerospace battery systems. Nickel-metal hydride batteries have twice the gravimetric energy density of nickel-cadmium batteries and twice the volumetric energy density of nickel-hydrogen batteries. Silver-metal hydride batteries have the potential of three times the energy density of

Dwaine Coates; R. D. Wright

1992-01-01

131

Hydrides versus competing options for storing hydrogen in energy systems  

SciTech Connect

Metal hydrides present many possibilities for energy storage because of their ability to store hydrogen safely and at modest pressure. We have compared hydrogen storage in metal hydrides to other forms of hydrogen storage. Comparisons have been made using technical performance, cost, and safety as the criteria. Hydrides applications and alternatives for vehicular applications, chemical heat pumps, engines, peak shaving, and others are discussed.

Swisher, J.H.; Johnson, E.D.

1980-04-07

132

Gold Hydride Complexes DOI: 10.1002/anie.200803842  

E-print Network

Gold Hydride Complexes DOI: 10.1002/anie.200803842 Reactions of a Stable Monomeric Gold(I) Hydride Complex** Emily Y. Tsui,* Peter Müller, and Joseph P. Sadighi Gold hydride complexes have been postulated as intermediates in a number of homogeneous gold- catalyzed reactions,[1] but relatively little is known about

Müller, Peter

133

PLATINUM-GROUP METALS (Platinum, palladium, rhodium, ruthenium, iridium, osmium)  

E-print Network

126 PLATINUM-GROUP METALS (Platinum, palladium, rhodium, ruthenium, iridium, osmium) (Data,000 Palladium 78,900 92,500 124,000 146,000 95,000 Rhodium 7,210 7,820 9,600 9,650 7,000 Ruthenium 4,490 9,880 7

134

PLATINUM-GROUP METALS (Platinum, palladium, rhodium, ruthenium, iridium, osmium)  

E-print Network

128 PLATINUM-GROUP METALS (Platinum, palladium, rhodium, ruthenium, iridium, osmium) (Data,000 Palladium 92,500 124,000 146,000 148,000 151,000 Rhodium 7,820 9,600 9,650 14,400 8,600 Ruthenium 9,880 7

135

A comparison of the IRIDIUM and AMPS systems  

Microsoft Academic Search

A brief history of progress made in the mobile telecommunications industry is presented. This article compares the IRIDIUM system (which uses satellite operating in the 22.55 to 23.55 GHz range) to the existing Advanced Phone System (AMPS) cellular system. It is concluded that although the two systems' architectures, services provided, and subscriber number formats vary enormously, the methods used for

Yvette C. Hubbel

1997-01-01

136

A unique six-membered chelated iridium complex.  

PubMed

The reaction of 2-(3-methylbiphenyl-2-yl)pyridine with IrCl(3).nH(2)O in the presence of water incorporates a tightly bonded CO at the iridium center; in the subsequent reaction with picolinic acid a complex revealing an unusual CH activation of a methyl group is formed. PMID:18688425

Ammermann, Sven; Daniliuc, Constantin; Jones, Peter G; du Mont, Wolf-Walther; Kowalsky, Wolfgang; Johannes, Hans-Hermann

2008-08-21

137

Iridium Aluminide Coats For Protection Against Ox idation  

NASA Technical Reports Server (NTRS)

Iridium aluminide coats investigated for use in protecting some metallic substrates against oxidation at high temperatures. Investigation prompted by need for cost-effective anti-oxidation coats for walls of combustion chambers in rocket engines. Also useful in special terrestrial applications like laboratory combustion chambers and some chemical-processing chambers.

Kaplan, Richard B.; Tuffias, Robert H.; La Ferla, Raffaele; Jang, Qin

1996-01-01

138

The Iridium (tm) system: Personal communications anytime, anyplace  

NASA Technical Reports Server (NTRS)

The Iridium system is designed to provide handheld personal communications between diverse locations around the world at any time and without prior knowledge of the location of the personal units. This paper provides an overview of the system, the services it provides, its operation, and an overview of the commercial practices and relatively high volume satellite production techniques which will make the system cost effective. A constellation of 66 satellites will provide an orbiting, spherical-shell, infrastructure for this global calling capability. The satellites act as tall cellular towers and allow convenient operation for portable handheld telephones. The system will provide a full range of services including voice, paging, data, geolocation, and fax capabilities. Motorola is a world leader in the production of high volume, high quality, reliable telecommunications hardware. One of Iridium's goals is to apply these production techniques to high reliability space hardware. Concurrent engineering, high performance work teams, advanced manufacturing technologies, and improved assembly and test methods are some of the techniques that will keep the Iridium system cost effective. Mobile, global, flexible personal communications are coming that will allow anyone to call or receive a call from/to anyplace at anytime. The Iridium system will provide communications where none exist today. This connectivity will allow increased information transfer, open new markets for various business endeavors, and in general increase productivity and development.

Hatlelid, John E.; Casey, Larry

1993-01-01

139

Utilization of Low Bandwidth Iridium Modems for Polar Seismology  

NASA Astrophysics Data System (ADS)

Transmission of realtime seismic data is a desirable goal when a rapid response is needed. However, for many science applications sample waveform data, system state of health, and the ability to command and control the seismic station are operationally adequate. Determining the optimal telemetry requirements for a remote polar seismic experiment requires balancing science objective against the expensive, over-subscribed support available in the polar environments? For example there is a significant difference in the resources needed for a permanent "monitoring" effort versus a short-term experiment. We will describe IRIS/PASSCAL's successful approach to utilizing Iridium telemetry for short-term seismic experiments and suggest viable use of an Iridium RUDICs system for higher data-rate, permanent seismic stations such as a monitoring scenario. Most seismic stations are configured to record at a rate that exceeds twice the data rate of a single Iridium Internet modem. The power requirement to run continuous Iridium telemetry better than doubles that of a standalone seismic station. Doubling station power roughly doubles station logistics by requiring an increased number of support flights for installation and service. The tradeoffs between desirable and adequate telemetry requirements and the ramifications these requirements have on support services must be considered for a successful seismic station. We describe two Iridium telemetry systems, developed by the IRIS/PASSCAL Polar Program, for use with seismic stations in Antarctica and the Arctic. The first system uses an inexpensive Iridium 9602 modem based device and short burst data (SBD) transmission to monitor station performance, provide some command and control, and return a small amount of representative seismic data. Power requirements for this SBD system are approximately 10Ah per year for a daily message. The second system uses an Iridium 9522b modem based device the DOD RUDICs system for a 2400 Baud Internet connection. Returning 1 megabyte of data per day requires approximately 1Ah and can return all of the low sample rate (1sps) seismic data and the SOH data each day.

Parker, T.

2012-12-01

140

Multiple hydride reduction pathways in isoflavonoids  

PubMed Central

Background Isoflavonoids are of interest owing to their appearance in metabolic pathways of isoflavones, and their estrogenic and other physiological properties, making them promising lead compounds for drug design. Results The reduction of isoflavones by various hydride reagents occurs by a 1,4-pathway in contrast to ordinary ?-alkoxy-?,?-unsaturated ketones. Isoflavan-4-ones, cis- and trans-isoflavan-4-ols, ?-methyldeoxybenzoins or 1,2-diphenylprop-2-en-1-ols are obtained depending on the hydride reagent, mostly in good yields. The stereoselective reduction of isoflavan-4-ones is also discussed. Conclusion The work described in this paper shows that most structural types of reduced isoflavonoids are now reliably available in satisfactory or good yields by hydride reductions to be used as authentic reference compounds in analytical and biological studies. PMID:16934147

Salakka, Auli K; Jokela, Tuija H; Wähälä, Kristiina

2006-01-01

141

Delayed hydride cracking of zirconium alloys  

SciTech Connect

High-strength zirconium alloys are susceptible to a mechanism for crack initiation and propagation termed delayed hydride cracking (DHC). In these alloys, it is possible to generate a large enough stress gradient so that hydrogen moves to the highly stressed areas. Therefore, hydrides precipitate and grow in these areas. When the tensile stress is sufficiently great, crack initiation starts at some of these hydrides. Crack propagation occurs by repeating the same process at the crack tip. Of concern for the chemical process industries is the DHC of Zr-2.5Nb welds. Results of long-term tests and case histories indicate that stress relieving is one of the major measures for preventing DHC, provided that ASME mechanical requirements are met.

Yau, T.L. [Teledyne Wah Chang, Albany, OR (United States); Webster, R.T. [Webster (R.T.), Scio, OR (United States)

1995-10-01

142

Mechanisms of hydride abstractions by quinones.  

PubMed

The kinetics of the hydride abstractions by 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) from 13 C-H hydride donors (acyclic 1,4-dienes, cyclohexa-1,4-dienes, dihydropyridines), tributylstannane, triphenylstannane, and five borane complexes (amine-boranes, carbene-boranes) have been studied photometrically in dichloromethane solution at 20 °C. Analysis of the resulting second-order rate constants by the correlation log k2(20 °C) = sN(E + N) ( J. Am. Chem. Soc. 2001 , 123 , 9500 ) showed that the hydride abstractions from the C-H donors on one side and the Sn-H and B-H hydride donors on the other follow separate correlations, indicating different mechanisms for the two reaction series. The interpretation that the C-H donors transfer hydrogen to the carbonyl oxygen of DDQ while Sn-H and B-H hydride donors transfer hydride to a cyano-substituted carbon of DDQ is supported by quantum-chemical intrinsic reaction coordinate calculations and isotope labeling experiments of the reactions of D8-cyclohexa-1,4-diene, Bu3SnD, and pyridine·BD3 with 2,5-dichloro-p-benzoquinone. The second-order rate constants of the reactions of tributylstannane with different quinones correlate linearly with the electrophilicity parameters E of the quinones, which have previously been derived from the reactions of quinones with ?-nucleophiles. The fact that the reactions of Bu3SnH with quinones and benzhydrylium ions are on the same log k2 vs E (electrophilicity) correlation shows that both reaction series proceed by the same mechanism and illustrates the general significance of the reactivity parameters E, N, and sN for predicting rates of polar organic reactions. PMID:25196576

Guo, Xingwei; Zipse, Hendrik; Mayr, Herbert

2014-10-01

143

Atomistic potentials for palladium-silver hydrides  

NASA Astrophysics Data System (ADS)

New embedded-atom method potentials for the ternary palladium-silver-hydrogen system are developed by extending a previously developed palladium-hydrogen potential. The ternary potentials accurately capture the heat of mixing and structural properties associated with solid solution alloys of palladium-silver. Stable hydrides are produced with properties that smoothly transition across the compositions. Additions of silver to palladium are predicted to alter the properties of the hydrides by decreasing the miscibility gap and increasing the likelihood of hydrogen atoms occupying tetrahedral interstitial sites over octahedral interstitial sites.

Hale, L. M.; Wong, B. M.; Zimmerman, J. A.; Zhou, X. W.

2013-06-01

144

Geoneutrino and Hydridic Earth model. Version 2  

E-print Network

Uranium, Thorium and Potassium-40 abundances in the Earth were calculated in the frame of Hydridic Earth model. Terrestrial heat producton from U, Th and K40 decays was calculated also. We must admit the existance of Earth expansion process to understand the obtained large value of terrestrial heat producton. The geoneutrino detector with volume more than 5 kT (LENA type) must be constructed to definitely separate between Bulk Silicat Earth model and Hydridic Earth model. In second version of the article we assume that K40 concentration distributes in the Earth uniformly.

Leonid Bezrukov

2014-02-12

145

1. VIEW OF A PORTION OF THE HYDRIDE PROCESSING LABORATORY. ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

1. VIEW OF A PORTION OF THE HYDRIDE PROCESSING LABORATORY. OPERATIONS IN THE GLOVE BOX IN THE BACKGROUND OF THE PHOTOGRAPH INCLUDED HYDRIDING OF PLUTONIUM AND HYDRIDE SEPARATION. IN THE FOREGROUND, THE VACUUM MONITOR CONTROL PANEL MEASURED TEMPERATURES WITHIN THE GLOVEBOX. THE CENTER CONTROL PANEL REGULATED THE FURNACE INSIDE THE GLOVE BOX USED IN THE HYDRIDING PROCESSES. THIS EQUIPMENT WAS ESSENTIAL TO THE HYDRIDING PROCESS, AS WELL AS OTHER GLOVE BOX OPERATIONS. - Rocky Flats Plant, Plutonium Laboratory, North-central section of industrial area at 79 Drive, Golden, Jefferson County, CO

146

Effect of yttrium on nucleation and growth of zirconium hydrides  

NASA Astrophysics Data System (ADS)

Addition of yttrium in zirconium causes precipitates of yttrium, which form two types of particles and are oxidized upon heat treatment. One type of particles with sub-micrometer scale sizes has a low population, whereas the other with nano scale sizes has a high population and cluster distribution. Owing to strong affinity of yttrium to hydrogen, the nanoparticles, mostly within the grains of the Zr-Y alloy, attract nucleation of hydrides at the clusters of the nanoparticles and cause preferential distribution of intragranular hydrides. In comparison with that of Zr, additional nanoparticles in the Zr-Y alloy impede further growth of hydride precipitates during hydriding. It is deduced that the impediment of growing hydride precipitates by the nanoparticles is developed during an auto-catalytic nucleation process, which leads to formation of thin and intragranular hydrides, favorable to mitigation of hydride embrittlement.

Li, Changji; Xiong, Liangyin; Wu, Erdong; Liu, Shi

2015-02-01

147

Simulation of dose distribution for iridium-192 brachytherapy source type-H01 using MCNPX  

NASA Astrophysics Data System (ADS)

Dosimetric data for a brachytherapy source should be known before it used for clinical treatment. Iridium-192 source type H01 was manufactured by PRR-BATAN aimed to brachytherapy is not yet known its dosimetric data. Radial dose function and anisotropic dose distribution are some primary keys in brachytherapy source. Dose distribution for Iridium-192 source type H01 was obtained from the dose calculation formalism recommended in the AAPM TG-43U1 report using MCNPX 2.6.0 Monte Carlo simulation code. To know the effect of cavity on Iridium-192 type H01 caused by manufacturing process, also calculated on Iridium-192 type H01 if without cavity. The result of calculation of radial dose function and anisotropic dose distribution for Iridium-192 source type H01 were compared with another model of Iridium-192 source.

Purwaningsih, Anik

2014-09-01

148

Effects of ?-hydride precipitation at a crack tip on crack propagation in delayed hydride cracking of Zircaloy-2  

NASA Astrophysics Data System (ADS)

Delayed hydride cracking (DHC) of Zircaloy-2 is one possible mechanism for the failure of boiling water reactor fuel rods in ramp tests at high burnup. Analyses were made for hydrogen diffusion around a crack tip to estimate the crack velocity of DHC in zirconium alloys, placing importance on effects of precipitation of ?-hydride. The stress distribution around the crack tip is significantly altered by precipitation of hydride, which was strictly analyzed using a finite element computer code. Then, stress-driven hydrogen diffusion under the altered stress distribution was analyzed by a differential method. Overlapping of external stress and hydride precipitation at a crack tip induces two stress peaks; one at a crack tip and the other at the front end of the hydride precipitate. Since the latter is larger than the former, more hydrogen diffuses to the front end of the hydride precipitate, thereby accelerating hydride growth compared with that in the absence of the hydride. These results indicated that, after hydride was formed in front of the crack tip, it grew almost steadily accompanying the interaction of hydrogen diffusion, hydride growth and the stress alteration by hydride precipitation. Finally, crack velocity was estimated from the calculated hydrogen flux into the crack tip as a function of temperature, stress intensity factor and material strength. There was qualitatively good agreement between calculation results and experimental data. The stress distribution around the crack tip is significantly altered by precipitation of hydride. Overlapping of external stress and hydride precipitation at a crack tip induces two stress peaks; one at a crack tip and the other at the front end of the hydride precipitate. Since the latter is larger than the former, more hydrogen diffuses to the front end of the hydride precipitate, thereby accelerating hydride growth compared with that in the absence of the hydride. These results indicated that, after hydride was formed in front of the crack tip, it grew almost steadily accompanying the interaction of hydrogen diffusion, hydride growth and the stress alteration by hydride precipitation. Crack velocity was estimated from the calculated hydrogen flux into the crack tip as a function of temperature, stress intensity factor and material strength. There was qualitatively good agreement between calculation results and experimental data. Macroscopic stress, ?c in a fiber reinforced composite with fibers aligned in a loading direction can be expressed as follows: ?c = ?fVf + ?m (1 - Vf), where suffices f, m and c refer to fiber, matrix and composite, respectively, and Vf is volume fraction of fibers.

Kubo, T.; Kobayashi, Y.

2013-08-01

149

Hydride Reorientation and Delayed Hydride Cracking of Spent Fuel Rods in Dry Storage  

NASA Astrophysics Data System (ADS)

The aim of this work is to investigate the effect of thermal creep during vacuum drying of spent fuel rods on hydride reorientation and their delayed hydride cracking (DHC) susceptibility. To these ends, we analyzed Tsai’s thermal creep results of irradiated Zircaloy-4 cladding segments from two pressurized water reactors and Simpson and Ells’ observation where zirconium alloy cladding tube failed during long-term storage at room temperature. On cooling under 190 MPa, the spent fuel rods crept to 3.5 pct strain during vacuum drying showed large radial hydrides, while the ones crept to 0.35 pct strain had very fine radial hydrides. Thus, it is suggested that prior creep deformation promotes hydride reorientation in spent fuel rods on cooling after vacuum drying. Evidence for this suggestion is provided by a model experiment. Considering Kim’s DHC model and experimental facts showing precipitation of hydrides even at room temperature at stress raisers, we suggest that spent fuel rods would fail by DHC in dry storage if stress raisers are present inside the cladding on cooling to below 180 °C, and then axial splits of the failed spent fuel rods would occur by DHC due to fuel expansion by UO2 oxidation.

Kim, Young S.

2009-12-01

150

Metal hydride fuel storage and method thereof  

DOEpatents

Disclosed herein is a metal hydride fuel storage cartridge having integrated resistive heaters that can be used in conjunction with fuel cells such as MEMS-based fuel cells. The cartridge is fabricated using micromachining methods and thin/thick film materials synthesis techniques.

Morse, Jeffrey D. (Martinez, CA); Jankowski, Alan F. (Livermore, CA); Yu, Conrad (Antioch, CA)

2006-10-17

151

Metal hydride fuel storage and method thereof  

DOEpatents

Disclosed herein is a metal hydride fuel storage cartridge having integrated resistive heaters that can be used in conjunction with fuel cells such as MEMS-based fuel cells. The cartridge is fabricated using micromachining methods and thin/thick film materials synthesis techniques.

Morse, Jeffrey D [Martinez, CA; Jankowski, Alan F [Livermore, CA; Yu, Conrad [Antioch, CA

2009-05-05

152

Hydride fuel for LWRs—Project overview  

Microsoft Academic Search

This special issue of Nuclear Engineering and Design consists of a dozen papers that summarize the research accomplished in the DOE NERI Program sponsored project NERI 02-189 entitled “Use of Solid Hydride Fuel for Improved Long-Life LWR Core Designs”. The primary objective of this project was to assess the feasibility of improving the performance of pressurised water reactor (PWR) and

E. Greenspan; M. Fratoni; F. Ganda; F. Ginex; D. Olander; N. Todreas; P. Diller; P. Ferroni; J. Malen; A. Romano; C. Shuffler; J. Trant; B. Petrovic; H. Garkisch

2009-01-01

153

Meteoric smoke fallout over the Holocene epoch revealed by iridium and platinum in Greenland ice  

Microsoft Academic Search

An iridium anomaly at the Cretaceous\\/Tertiary boundary layer has been attributed to an extraterrestrial body that struck the Earth some 65million years ago. It has been suggested that, during this event, the carrier of iridium was probably a micrometre-sized silicate-enclosed aggregate or the nanophase material of the vaporized impactor. But the fate of platinum-group elements (such as iridium) that regularly

Paolo Gabrielli; Carlo Barbante; John M. C. Plane; Anita Varga; Sungmin Hong; Giulio Cozzi; Vania Gaspari; Frédéric A. M. Planchon; Warren Cairns; Christophe Ferrari; Paul Crutzen; Paolo Cescon; Claude F. Boutron

2004-01-01

154

Ductility Evaluation of As-Hydrided and Hydride Reoriented Zircaloy-4 Cladding under Simulated Dry-Storage Condition  

SciTech Connect

Pre-storage drying-transfer operations and early stage storage expose cladding to higher temperatures and much higher pressure-induced tensile hoop stresses relative to normal operation in-reactor and pool storage under these conditions. Radial hydrides could precipitate during slow cooling and provide an additional embrittlement mechanism as the cladding temperature decreases below the ductile-to-brittle transition temperature. As a means of simulating this behavior, unirradiated hydrided Zircaloy-4 samples were fabricated by a gas charging method to levels that encompass the range of hydrogen concentrations observed in current used fuel. Mechanical testing was carried out by the ring compression test (RCT) method at various temperatures to evaluate the sample s ductility for both as-hydrided and post-hydride reorientation treated specimens. As-hydrided samples with higher hydrogen concentration (>800 ppm) resulted in lower strain before fracture and reduced maximum load. Increasing RCT temperatures resulted in increased ductility of the as-hydrided cladding. A systematic radial hydride treatment was conducted at various pressures and temperatures for the hydrided samples with H content around 200 ppm. Following the radial hydride treatment, RCTs on the hydride reoriented samples were conducted and exhibited lower ductility compared to as-hydrided samples.

Yan, Yong [ORNL] [ORNL; Plummer, Lee K [ORNL] [ORNL; Ray, Holly B [ORNL] [ORNL; Cook, Tyler S [ORNL] [ORNL; Bilheux, Hassina Z [ORNL] [ORNL

2014-01-01

155

Synthesis, characterization, and reactivity studies of iridium complexes bearing the ligand diphenylphosphidoboratabenzene  

E-print Network

The synthesis, structure, and reactivity properties of three iridium square planar complexes bearing the anionic phosphine ligand diphenylphosphidoboratabenzene (DPB) are described. Reactivity studies show a rate enhancement ...

Arizpe, Luis (Luis Alfredo)

2011-01-01

156

Bismuth determination in environmental samples by hydride generation-electrothermal atomic absorption spectrometry.  

PubMed

A hydride generation procedure, via flow injection, coupled to electrothermal atomic absorption spectrometry was optimised for Bi determination in sea water and hot-spring water and acid extracts from coal, coal fly ash and slag samples. The effects of several variables such as hydrochloric acid and sodium tetrahydroborate concentrations, hydrochloric acid and sodium tetrahydroborate flow rates, reaction coil length, trapping and atomisation temperatures, trapping time and the Ar flow rate have been investigated by using a 2(9)*3/128 Plackett-Burman design. From these studies, certain variables (sodium tetrahydroborate concentration and trapping time) showed up as significant, and they were optimised by a 2(2)+star central composite design. In addition, a study of the bismuthine trapping and atomisation efficiency from graphite tubes (GTs) permanently treated with uranium, tantalum, lanthanum oxide, niobium, beryllium oxide, chromium oxide and tantalum carbide were investigated. The results obtained were compared with those achieved by iridium and zirconium-treated GTs. The best analytical performances, with characteristic mass of 35 pg and detection limit of 70 ng l(-1), were achieved by using U-treated GTs. Accuracy were checked using several reference materials: 1643d (Trace Elements in Water), TM-24 (Reference Water), GBW-07401 (Soil) and 1632c (Trace Elements in Coal). PMID:18969227

Moscoso-Pérez, Carmen; Moreda-Piñeiro, Jorge; López-Mah??a, Purificación; Muniategui-Lorenzo, Soledad; Fernández-Fernández, Esther; Prada-Rodr??guez, Dar??o

2003-12-01

157

Received 21 Jul 2013 | Accepted 7 Jan 2014 | Published 3 Feb 2014 Iridium oxide nanotube electrodes for  

E-print Network

ARTICLE Received 21 Jul 2013 | Accepted 7 Jan 2014 | Published 3 Feb 2014 Iridium oxide nanotube- rodes of a new geometry, namely nanotubes of iridium oxide. When cardiomyocytes are cultured upon those

Cui, Yi

158

Iridium-Doped Ruthenium Oxide Catalyst for Oxygen Evolution  

NASA Technical Reports Server (NTRS)

NASA requires a durable and efficient catalyst for the electrolysis of water in a polymer-electrolyte-membrane (PEM) cell. Ruthenium oxide in a slightly reduced form is known to be a very efficient catalyst for the anodic oxidation of water to oxygen, but it degrades rapidly, reducing efficiency. To combat this tendency of ruthenium oxide to change oxidation states, it is combined with iridium, which has a tendency to stabilize ruthenium oxide at oxygen evolution potentials. The novel oxygen evolution catalyst was fabricated under flowing argon in order to allow the iridium to preferentially react with oxygen from the ruthenium oxide, and not oxygen from the environment. Nanoparticulate iridium black and anhydrous ruthenium oxide are weighed out and mixed to 5 18 atomic percent. They are then heat treated at 300 C under flowing argon (in order to create an inert environment) for a minimum of 14 hours. This temperature was chosen because it is approximately the creep temperature of ruthenium oxide, and is below the sintering temperature of both materials. In general, the temperature should always be below the sintering temperature of both materials. The iridium- doped ruthenium oxide catalyst is then fabricated into a PEM-based membrane- electrode assembly (MEA), and then mounted into test cells. The result is an electrolyzer system that can sustain electrolysis at twice the current density, and at the same efficiency as commercial catalysts in the range of 100-200 mA/sq cm. At 200 mA/sq cm, this new system operates at an efficiency of 85 percent, which is 2 percent greater than commercially available catalysts. Testing has shown that this material is as stable as commercially available oxygen evolution catalysts. This means that this new catalyst can be used to regenerate fuel cell systems in space, and as a hydrogen generator on Earth.

Valdez, Thomas I.; Narayan, Sri R.; Billings, Keith J.

2011-01-01

159

Iridium in marine organisms from the Gulf of Mexico  

E-print Network

the scientific and popular literature of possible causes of the Iridium (Ir) enrichment in Cretaceous-Tertiary (K-T) boundary sediments and the concomitant biological extinctions (65 m. y. BP). No published data exist for Ir in marine biota, therefore... organisms from all parts of the marine food web were analyzed for Ir by radiochemical neutron activation analysis (RNAA) to characterize the levels present, to estimate the size of the marine biological Ir reservoir, and to compare it to the Ir inventory...

Wells, Mona Cara

1987-01-01

160

Chronic neural stimulation with thin-film, iridium oxide electrodes  

Microsoft Academic Search

Experiments were conducted to assess the effect of chronic stimulation on the electrical properties of the elec- trode-tissue system, as measured using electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). Silicon, mi- cromachined probes with multiple iridium oxide stimulating electrodes (400-1600 m ) were implanted in guinea pig cortex. A 10-17 day post-operative recovery period was followed by five days

James D. Weiland; David J. Anderson

2000-01-01

161

Mono- and bis-tolylterpyridine iridium(III) complexes  

SciTech Connect

The first structure report of trichlorido[4'-(p-tolyl)-2,2':6',2{double_prime}-terpyridine]iridium(III) dimethyl sulfoxide solvate, [IrCl{sub 3}(C{sub 22}H{sub 17}N{sub 3})] {center_dot} C{sub 2}H{sub 6}OS, (I), is presented, along with a higher-symmetry setting of previously reported bis[4'-(p-tolyl)-2,2':6',2{double_prime}-terpyridine]iridium(III) tris(hexafluoridophosphate) acetonitrile disolvate, [Ir(C{sub 22}H{sub 17}N{sub 3})2](PF{sub 6}){sub 3} {center_dot} 2C{sub 2}H{sub 3}N, (II) [Yoshikawa, Yamabe, Kanehisa, Kai, Takashima & Tsukahara (2007). Eur. J. Inorg. Chem. pp. 1911-1919]. For (I), the data were collected with synchrotron radiation and the dimethyl sulfoxide solvent molecule is disordered over three positions, one of which is an inversion center. The previously reported structure of (II) is presented in the more appropriate C2/c space group. The iridium complex and one PF{sub 6}{sup -} anion lie on twofold axes in this structure, making half of the molecule unique.

Hinkle, Lindsay M.; Young, Jr., Victor G.; Mann, Kent R. (UMM)

2012-01-20

162

A Cost-effective Microcontroller-based Iridium Satellite Communication Architecture for a Remote Renewable Energy Source  

E-print Network

A Cost-effective Microcontroller-based Iridium Satellite Communication Architecture for a Remote, 2008 #12;ii DEDICATION This thesis is dedicated to my parents. #12;iii ABSTRACT The Iridium Satellite (SBD) transceiver for data communications. A cost-effective microcontroller-based Iridium SBD satellite

Petersen, Brent

163

Effects of Electrodeposition Conditions and Protocol on the Properties of Iridium Oxide pH Sensor Electrodes  

E-print Network

Effects of Electrodeposition Conditions and Protocol on the Properties of Iridium Oxide pH Sensor of California, Berkeley, Berkeley, California 94720-1460, USA The properties of iridium oxide pH sensors substrates with iridium oxide. Increasing the film thickness beyond the full coverage did not further

Majda, Marcin

164

A Combined Ab Initio and Bond-Order Potentials Study of Cohesion in Iridium Marc J. Cawkwell1  

E-print Network

A Combined Ab Initio and Bond-Order Potentials Study of Cohesion in Iridium Marc J. Cawkwell1 , Duc and excellent resistance to oxidation and corrosion offered by iridium suggest numerous applications since highlighted iridium as worthy of significant industrial interest and academic study. Owing to its

Vitek, Vaclav

165

Adsorption and desorption of samarium atoms on the surface of pure iridium and iridium covered with a graphite monolayer  

NASA Astrophysics Data System (ADS)

Methods of thermionic emission and thermodesorption spectroscopy (TDS) have been used to study the adsorption and condensation of samarium on the surface of pure iridium and iridium covered with a graphite monolayer (valence-saturated neutral substrate) Ir(111)-C. It is shown that at temperatures of 700 < T a < 1200 K the work function ? decreases monotonically from 5.8 to 2.7 eV and during the subsequent deposition of samarium grows slowly to 2.9 eV. It has been found that in all TDS peaks there were observed several phases of samarium. The deposition of samarium onto an Ir-C surface at 700 < T < 1700 K led to a very weak change in the thermionic current in comparison with pure iridium. At temperatures above ˜700 K, samarium is not condensed on the surface of Ir-C, but it is condensed at lower temperatures. By the method of temperature modulation, the heat of samarium desorption was determined to be E ˜ 1.9 eV upon the desorption from an Ir-C surface (at a small coverage) and ˜6 eV upon the desorption from pure Ir.

Orudzhov, A. K.; Dashdemirov, A. O.

2009-01-01

166

HYDRIDE-INDUCED EMBRITTLEMENT IN METALS - STRESS AND TEMPERATURE EFFECTS  

Microsoft Academic Search

A robust mathematical model for the hydrogen embrittlement of hydride forming metals has been developed. The model takes into account the coupling of the operating physical processes, namely: (i) hydrogen diffusion, (ii) hydride precipitation, (iii) non-mechanical energy flow, and (iv) hydride\\/solid-solution deformation. Crack growth is simulated by using a new version of de-cohesion model with time-dependent energy of de-cohesion due

A. G. Varias; A. R. Massih

167

HYDRIDE-RELATED DEGRADATION OF SNF CLADDING UNDER REPOSITORY CONDITIONS  

SciTech Connect

The purpose and scope of this analysis/model report is to analyze the degradation of commercial spent nuclear fuel (CSNF) cladding under repository conditions by the hydride-related metallurgical processes, such as delayed hydride cracking (DHC), hydride reorientation and hydrogen embrittlement, thereby providing a better understanding of the degradation process and clarifying which aspects of the process are known and which need further evaluation and investigation. The intended use is as an input to a more general analysis of cladding degradation.

K. McCoy

2000-12-12

168

Dissipative hydride precipitates in superconducting niobium cavities  

SciTech Connect

We report the first direct observation of the microstructural features exhibiting RF losses at high surface magnetic fields of above 100 mT in field emission free superconducting niobium cavities. The lossy areas were identified by advanced thermometry. Surface investigations using different techniques were carried out on cutout samples from lossy areas and showed the presence of dendritic niobium hydrides. This finding has possible implications to the mechanisms of RF losses in superconducting niobium at all field levels.

Romanenko, A.; Cooley, L.D.; /Fermilab; Ciovati, G.; / /Jefferson Lab; Wu, G.; /Argonne

2011-10-01

169

Metal hydride characteristics by Zr and Ti  

Microsoft Academic Search

Hydrogen absorption experiments were carried out using zirconium (Zr) and titanium (Ti) in the form of a metal sponge, strip\\u000a and rod to investigate the metal hydride characteristics. The Zr and Ti sponges showed a high hydrogen absorption capacity\\u000a despite a low reaction temperature. The H\\/M, which indicates the capacity of hydrogen absorption, was measured at 2.0 for\\u000a the Zr\\/Ti

Sung Ho Lee; Jae Hyung Yoo; Hongsuk Chung

2001-01-01

170

NMR study of the plutonium hydride system  

Microsoft Academic Search

An NMR study was conducted on protons in the nonstoichiometric plutonium hydride system, PuHx. The following compositions were studied: x=1.78, 2.35, 2.65, and 2.78. The line shapes, Knight shifts (K), spin-spin relaxation times (T2), and spin-lattice relaxation times (T1) were measured in the temperature range of 77-300 K. The results indicate the existence of paramagnetic phases at high temperatures, with

G. Cinader; D. Zamir; Z. Hadari

1976-01-01

171

Nickel metal hydride LEO cycle testing  

NASA Technical Reports Server (NTRS)

The George C. Marshall Space Flight Center is working to characterize aerospace AB5 Nickel Metal Hydride (NiMH) cells. The cells are being evaluated in terms of storage, low earth orbit (LEO) cycling, and response to parametric testing (high rate charge and discharge, charge retention, pulse current ability, etc.). Cells manufactured by Eagle Picher are the subjects of the evaluation. There is speculation that NiMH cells may become direct replacements for current Nickel Cadmium cells in the near future.

Lowery, Eric

1995-01-01

172

Hydrogen and deuterium diffusion in lithium hydride  

NASA Astrophysics Data System (ADS)

Hydrogen is considered a promising candidate to achieve an alternative source to overcome future energy supply problems. Very recently, an ab initio molecular dynamics study of the hydrogen diffusion in sodium and lithium hydrides appeared by Ramzan and Ahuja [J. Appl. Phys. 106, 016104 (2009)]. Here, we alternatively report the calculation of the temperature dependence of the diffusion coefficients of hydrogen and deuterium in LiH in terms of a thermodynamical model. The resulting values agree fairly well with experimental data.

Dologlou, Elisabeth

2010-04-01

173

Development and Testing of High Surface Area Iridium Anodes for Molten Oxide Electrolysis  

NASA Technical Reports Server (NTRS)

Processing of lunar regolith into oxygen for habitat and propulsion is needed to support future space missions. Direct electrochemical reduction of molten regolith is an attractive method of processing, because no additional chemical reagents are needed. The electrochemical processing of molten oxides requires high surface area, inert anodes. Such electrodes need to be structurally robust at elevated temperatures (1400-1600?C), be resistant to thermal shock, have good electrical conductivity, be resistant to attack by molten oxide (silicate), be electrochemically stable and support high current density. Iridium with its high melting point, good oxidation resistance, superior high temperature strength and ductility is the most promising candidate for anodes in high temperature electrochemical processes. Several innovative concepts for manufacturing such anodes by electrodeposition of iridium from molten salt electrolyte (EL-Form? process) were evaluated. Iridium electrodeposition to form of complex shape components and coating was investigated. Iridium coated graphite, porous iridium structure and solid iridium anodes were fabricated. Testing of electroformed iridium anodes shows no visible degradation. The result of development, manufacturing and testing of high surface, inert iridium anodes will be presented.

Shchetkovskiy, Anatoliy; McKechnie, Timothy; Sadoway, Donald R.; Paramore, James; Melendez, Orlando; Curreri, Peter A.

2010-01-01

174

Development and Testing of High Surface Area Iridium Anodes for Molten Oxide Electrolysis  

NASA Technical Reports Server (NTRS)

Processing of lunar regolith into oxygen for habitat and propulsion is needed to support future space missions. Direct electrochemical reduction of molten regolith is an attractive method of processing, because no additional chemical reagents are needed. The electrochemical processing of molten oxides requires high surface area, inert anodes. Such electrodes need to be structurally robust at elevated temperatures (1400-1600 C), be resistant to thermal shock, have good electrical conductivity, be resistant to attack by molten oxide (silicate), be electrochemically stable and support high current density. Iridium with its high melting point, good oxidation resistance, superior high temperature strength and ductility is the most promising candidate for anodes in high temperature electrochemical processes. Several innovative concepts for manufacturing such anodes by electrodeposition of iridium from molten salt electrolyte (EL-Form process) were evaluated. Iridium electrodeposition to form of complex shape components and coating was investigated. Iridium coated graphite, porous iridium structure and solid iridium anodes were fabricated. Testing of electroformed iridium anodes shows no visible degradation. The result of development, manufacturing and testing of high surface, inert iridium anodes will be presented.

Shchetkovskiy, Anatoliy; McKechnie, Timothy; Sadoway, Donald R.; Paramore, James; Melendez, Orlando; Curreri, Peter A.

2010-01-01

175

Inadequacy of iridium implant as sole radiation treatment for operable breast cancer  

Microsoft Academic Search

In order to avoid a prolonged course of external irradiation as part of breast conservation therapy, 27 patients received an iridium implant to the primary tumour bed as sole radiation treatment. Surgery was standardised comprising tumourectomy and axillary clearance. Using a rigid implant afterloading with iridium192 wires, 55 Gy was delivered on a continuous basis over 5 days. After 6

I. S. Fentiman; C. Poole; D. Tong; P. J. Winter; W. M. Gregory; H. M. O. Mayles; P. Turner; M. A. Chaudary; R. D. Rubens

1996-01-01

176

An overview of the IRIDIUM (R) low Earth orbit (LEO) satellite system  

Microsoft Academic Search

This paper provides a tutorial overview of the IRIDIUM(R) low earth orbit (LEO) satellite system. Section I contains an introduction to the IRIDIUM(R) network as well as the system specifications. Section II discusses the satellite constellation design, orbital parameters, and horizontal pointing angles between satellites. Section III introduces the idea of time dependent connectivity in a mobile network, and analyzes

Carl E. Fossa; Richard A. Raines; Gregg H. Gunsch; Michael A. Temple

1998-01-01

177

Anodically Electrodeposited Iridium Oxide Films (AEIROF) from Alkaline Solutions for Electrochromic Display Devices  

Microsoft Academic Search

Anodically electrodeposited iridium oxide films from alkaline solutions were investigated for application to electrochromic devices. Micro-crystalline (diameter: 15Å) films obtained by the electrolysis of aqueous alkaline solutions containing iridium chloride, oxalic acid and potassium carbonate showed good electrochromic reaction reversibility. The coloration efficiency of the films was about one third that of typical evaporated tungsten oxide films, and the response

Kazusuke Yamanaka

1989-01-01

178

Real-Time Characterization of Formation and Breakup of Iridium Clusters in Highly Dealuminated Zeolite Y  

SciTech Connect

The chemistry of formation of iridium clusters from mononuclear iridium diethylene complexes anchored in dealuminated Y zeolite, and their subsequent breakup -- all including changes in the metal-metal, metal-support, and metal-ligand interactions -- is demonstrated by time-resolved EXAFS, XANES, and IR spectroscopy.

Uzun, Alper; Gates, Bruce C. (UCD)

2009-01-15

179

Fe induced hydride formation in ZrPd2  

SciTech Connect

We show via first-principles calculations that the electronic structure of ZrPd{sub 2}, which does not form a hydride, can be modified by partial substitution of Fe for Pd, leading to a material that forms a hydride. We also show that PdZr{sub 2}, which forms a very stable hydride, can also be modified by Fe addition to lower the enthalpy of hydride formation. These results are explained in terms of electronic structure, specifically electronegativity, charge transfer, and s-d bonding, and clearly have implications in the search of new materials for hydrogen storage.

Gupta, Michele [Universite Paris Sud, Orsay, France; Gupta, Raju [CEA, Saclay, France; Singh, David J [ORNL

2008-01-01

180

Storing hydrogen in the form of light alloy hydrides  

NASA Technical Reports Server (NTRS)

Different hydrides are investigated to find a system with a sufficiently high storage density (at least 3%). The formation of hydrides with light alloys is examined. Reaction kinetics for hydride formation were defined and applied to the systems Mg-Al-H, Mg-Al-Cu-H, Ti-Al-H, Ti-Al-Cu-H, and Ti-Al-Ni-H. Results indicate that the addition of Al destabilizes MgH2 and TiH2 hydrides while having only a limited effect on the storage density.

Freund, E.; Gillerm, C.

1981-01-01

181

Initial stages of the interaction with oxygen of samarium thin films grown on the iridium surface  

NASA Astrophysics Data System (ADS)

The interaction of thin (<1 nm) samarium films deposited on a textured iridium ribbon has been investigated by thermal desorption spectrometry. Samarium atoms deposited at T = 300 K desorb in three phases associated with the formation of a submonolayer samarium coverage on iridium, a compound of samarium with iridium, and a multilayer samarium film. The interaction with oxygen leads to the appearance of a new desorption phase, which is associated with the formation of samarium oxide. Oxidation of samarium is observed during exposure in oxygen already at room temperature. An increase in temperature of the iridium ribbon, at which exposure in oxygen occurs, to T = 1100 K leads to the formation of the compound of samarium with iridium. Further, the film of the compound decomposes in the course of interaction with oxygen, and samarium oxide grows on the Ir surface.

Afanas'eva, E. Yu.

2014-08-01

182

Development of Hydride Absorber for Fast Reactor—Application of Hafnium Hydride to Control Rod of Large Fast Reactor—  

Microsoft Academic Search

The application of hafnium hydride (Hf-hydride) to a control rod for a large fast reactor where the B4C control rod is originally employed is studied. Three types of Hf-hydride control rods are designed. The control rod worth and its change during the burnup are evaluated for different hydrogen-to-hafnium ratios and are compared with those of the original B4C control rod.

Tomohiko IWASAKI; Kenji KONASHI

2009-01-01

183

Investigation of counterion influence on an octahedral IrH6-complex in the solid state hydrides AAeIrH6 (A = Na, K and Ae = Ca, Sr, Ba, and Eu) with a new structure type.  

PubMed

A number of new quaternary iridium based hydrides and deuterides AAeIrH/D(6) (where A = Na and K; Ae = Ca, Ba, Sr, and Eu) have been synthesized by direct combination of the alkali, alkaline earth or europium binary hydrides/deuterides and iridium powder. The crystal structures were determined by Guinier-Hägg X-ray and neutron powder diffraction and a new cubic structure type was found. The structure is described in space group F43m, but related to the K(2)PtCl(6) type structure. The new structure can be described as consisting of cubes of A(+) and Ae(2+) ions, where the A(+) and Ae(2+) ions alternates so that they occupy opposite corners in the cube. Every second cube contains a regular octahedral [Ir(III)H(6)](-3)-complex and the adjacent is empty. Solid-state IR spectroscopy was used to determine the Ir-allowed stretching and bending frequencies for the [Ir(III)H(6)](-3) complex with different counterions. These were also compared with the corresponding stretching frequencies for Fe(II)H(6), Ru(II)H(6), Os(II)H(6), and Ir(II)H(5) complexes in similar solid state hydrides, which increased when going from Fe through Ru, Os to Ir. The frequencies scaled almost linearly with the inverse of size of the cube surrounding the complexes but showed no significant dependence of the formal oxidation state or the experimentally obtained Ir-D distances. However, this was mainly because of difficulties in obtaining enough accurate atomic positions. The ab initio DFT calculations could reproduce the stretching frequencies within a few 10 cm(-1), indicating that experimental vibrational frequencies offer a sensitive test of DFT results. PMID:22035072

Kadir, K; Moser, D; Münzel, M; Noréus, D

2011-12-01

184

Mechanistically Driven Development of Iridium Catalysts for Asymmetric Allylic Substitution  

PubMed Central

Conspectus Enantioselective allylic substitution reactions comprise some of the most versatile methods for preparing enantiomerically enriched materials. These reactions form products that contain multiple functionalities by creating carbon–nitrogen, carbon–oxygen, carbon–carbon, and carbon–sulfur bonds. For many years, the development of catalysts for allylic substitution focused on palladium complexes. However, studies of complexes of other metals have revealed selectivities that often complement those of palladium systems. Most striking is the observation that reactions with unsymmetrical allylic electrophiles that typically occur with palladium catalysts at the less hindered site of an allylic electrophile occur at the more hindered site with catalysts based on other metals. In this Account, we describe an iridium precursor and a phosphoramidite ligand that catalyze reactions with a particularly broad scope of nucleophiles. The active form of this iridium catalyst is not generated by the simple binding of the phosphoramidite ligand to the metal precursor. Instead, the initial phosphoramidite and iridium precursor react in the presence of base to form a metallacyclic species that is the active catalyst. This species is generated either in situ or separately in isolated form by reactions with added base. The identification of the structure of the active catalyst led to the development of simplified catalysts as well as the most active form of the catalyst now available, which is stabilized by a loosely bound ethylene. Most recently, this structure was used to prepare intermediates containing allyl ligands, the structures of which provide a model for the enantioselectivities discussed here. Initial studies from our laboratory on the scope of iridium-catalyzed allylic substitution showed that reactions of primary and secondary amines, including alkylamines, benzylamines, and allylamines, and reactions of phenoxides and alkoxides occurred in high yields, with high branched-to-linear ratios and high enantioselectivities. Parallel mechanistic studies had revealed the metallacyclic structure of the active catalyst, and subsequent experiments with the purposefully formed metallacycle increased the reaction scope dramatically. Aromatic amines, azoles, ammonia, and amides and carbamates as ammonia equivalents all reacted with high selectivities and yields. Moreover, weakly basic enolates (such as silyl enol ethers) and enolate equivalents (such as enamines) also reacted, and other research groups have used this catalyst to conduct reactions of stabilized carbon nucleophiles in the absence of additional base. One hallmark of the reactions catalyzed by this iridium system is the invariably high enantioselectivity, which reflects a high stereoselectivity for formation of the allyl intermediate. Enantioselectivity typically exceeds 95%, regioselectivity for formation of branched over linear products is usually near 20:1, and yields generally exceed 75% and are often greater than 90%. Thus, the development of iridium catalysts for enantioselective allylic substitution shows how studies of reaction mechanism can lead to a particularly active and a remarkably general system for an enantioselective process. In this case, a readily accessible catalyst effects allylic substitution, with high enantioselectivity and regioselectivity complementary to that of the venerable palladium systems. PMID:20873839

Hartwig, John F.; Stanley, Levi M.

2010-01-01

185

Iridium: Global OTH data communications for high altitude scientific ballooning  

NASA Astrophysics Data System (ADS)

While the scientific community is no stranger to embracing commercially available technologies, the growth and availability of truly affordable cutting edge technologies is opening the door to an entirely new means of global communications. For many years high altitude ballooning has provided science an alternative to costly satellite based experimental platforms. As with any project, evolution becomes an integral part of development. Specifically in the NSBF ballooning program, where flight durations have evolved from the earlier days of hours to several weeks and plans are underway to provide missions up to 100 days. Addressing increased flight durations, the harsh operational environment, along with cumbersome and outdated systems used on existing systems, such as the balloon vehicles Support Instrumentation Package (SIP) and ground-based systems, a new Over-The-Horizon (OTH) communications medium is sought. Current OTH equipment planning to be phased-out include: HF commanding systems, ARGOS PTT telemetry downlinks and INMARSAT data terminals. Other aspects up for review in addition to the SIP to utilize this communications medium include pathfinder balloon platforms - thereby, adding commanding abilities and increased data rates, plus providing a package for ultra-small experiments to ride aloft. Existing communication systems employed by the National Scientific Balloon Facility ballooning program have been limited not only by increased cost, slow data rates and "special government use only" services such as TDRSS (Tracking and Data Relay Satellite System), but have had to make special provisions to geographical flight location. Development of the Support Instrumentation Packages whether LDB (Long Duration Balloon), ULDB (Ultra Long Duration Balloon) or conventional ballooning have been plagued by non-standard systems configurations requiring additional support equipment for different regions and missions along with a myriad of backup for redundancy. Several beneficial points provided by the Iridium platform include pure global accessibility (as well as polar), cost effectiveness because it is available as a COTS (Commercially Off The Shelf) technology, reliability in that the equipment must operate in extreme conditions (near space), integration and development time into current systems must be minimized. As a bonus Motorola and NAL Research Corporation are developing SBD (Short Burst Data) into the Iridium network. This may lead the way to a global IP (Internet Protocol) node based ballooning platform. The Iridium satellite data modems employ the Iridium Low-Earth Orbit (LEO) satellite network. The scope of this paper is to introduce an OTH communications alternative, albeit not necessarily a primary one, to existing ballooning platforms using COTS based emerging technologies. Design aspects, characteristics, actual flight testing statistics, principles of the Iridium modems and communication paths are described including payload and support instrumentation interfacing. Not limited to high altitude ballooning, the Iridium communications platform opens a new era in remote commanding and data retrieval.

Denney, A.

186

Iridium-catalyzed reductive nitro-mannich cyclization.  

PubMed

A new chemoselective reductive nitro-Mannich cyclization reaction sequence of nitroalkyl-tethered lactams has been developed. Relying on the rapid and chemoselective iridium(I)-catalyzed reduction of lactams to the corresponding enamine, subsequent nitro-Mannich cyclization of tethered nitroalkyl functionality provides direct access to important alkaloid natural-product-like structures in yields up to 81?% and in diastereoselectivities that are typically good to excellent. An in-depth understanding of the reaction mechanism has been gained through NMR studies and characterization of reaction intermediates. The new methodology has been applied to the total synthesis of (±)-epi-epiquinamide in four steps. PMID:25399919

Gregory, Alex W; Chambers, Alan; Hawkins, Alison; Jakubec, Pavol; Dixon, Darren J

2015-01-01

187

Determination of iridium in mafic rocks by atomic absorption  

USGS Publications Warehouse

Iridium is determined in mineralized mafic rocks by atomic absorption after fire-assay concentration into a gold bead. Interelement interferences in the atomic-absorption determination are removed and Ir sensitivity is increased by buffering the solutions with a mixture of copper and sodium sulphates. Substantial amounts of Ag, Al, Au, Bi, Ca, Cd, Co, Cr, Fe, Ho, Hg, K, La, Mg, Mn, Mo, Ni, Pb, Te, Ti, V, Y, Zn and platinum metals can be tolerated in the atomic-absorption determination. The sensitivity and detection limits are 3.2 and 0.25 ppm of Ir, respectively. ?? 1970.

Grimaldi, F.S.; Schnepfe, M.M.

1970-01-01

188

Luminescent cyclometallated iridium(III) complexes having acetylide ligands  

DOEpatents

The present invention relates to phosphorescent (triplet-emitting) organometallic materials. The phosphorescent materials of the present invention comprise Ir(III)cyclometallated alkynyl complexes for use as triplet light-emitting materials. The Ir(III)cyclometallated alkynyl complexes comprise at least one cyclometallating ligand and at least one alkynyl ligand bonded to the iridium. Also provided is an organic light emitting device comprising an anode, a cathode and an emissive layer between the anode and the cathode, wherein the emissive layer comprises a Ir(III)cyclometallated alkynyl complex as a triplet emitting material.

Thompson, Mark E.; Bossi, Alberto; Djurovich, Peter Ivan

2014-09-02

189

PLATINUM-GROUP METALS (Platinum, palladium, rhodium, ruthenium, iridium, osmium)  

E-print Network

124 PLATINUM-GROUP METALS (Platinum, palladium, rhodium, ruthenium, iridium, osmium) (Data,000 105,000 119,000 Rhodium 18,200 12,400 9,890 12,000 10,000 Ruthenium 20,900 8,170 10,800 15,900 13.00 Rhodium 1,990.00 1,598.67 838.88 530.28 736.00 Ruthenium 129.76 130.67 66.33 35.43 57.00 Employment, mine

190

The solubility of hydrogen in rhodium, ruthenium, iridium and nickel.  

NASA Technical Reports Server (NTRS)

The temperature variation of the solubility of hydrogen in rhodium, ruthenium, iridium, and nickel in equilibrium with H2 gas at 1 atm pressure has been measured by a technique involving saturating the solvent metal with hydrogen, quenching, and analyzing in resultant solid solutions. The solubilities determined are small (atom fraction of H is in the range from 0.0005 to 0.00001, and the results are consistent with the simple quasi-regular model for dilute interstitial solid solutions. The relative partial enthalpy and excess entropy of the dissolved hydrogen atoms have been calculated from the solubility data and compared with well-known correlations between these quantities.

Mclellan, R. B.; Oates, W. A.

1973-01-01

191

PLATINUM-GROUP METALS (Platinum, palladium, rhodium, ruthenium, iridium, osmium)  

E-print Network

124 PLATINUM-GROUP METALS (Platinum, palladium, rhodium, ruthenium, iridium, osmium) (Data,000 Palladium 148,000 176,000 189,000 181,000 220,000 Rhodium 14,400 13,500 10,300 18,200 11,000 Ruthenium 11 184.14 289.76 363.20 691.84 770.00 Rhodium 298.00 619.83 904.35 1,990.00 1,800.00 Ruthenium 40.51 47

192

Measurements of the hard-x-ray reflectivity of iridium  

SciTech Connect

In connection with the design of a hard-x-ray telescope for the Constellation X-Ray Observatory we measured the reflectivity of an iridium-coated zerodur substrate as a function of angle at 55, 60, 70, and 80 keV at the National Synchrotron Light Source of Brookhaven National Laboratory. The optical constants were derived from the reflectivity data. The real component of the index of refraction is in excellent agreement with theoretical values at all four energies. However, the imaginary component, which is related to the mass attenuation coefficient, is 50% to 70% larger at 55, 60, and 70 keV than theoretical values.

Romaine, S.; Bruni, R.; Gorenstein, P.; Zhong, Z

2007-01-10

193

Metal Hydride Thermal Storage: Reversible Metal Hydride Thermal Storage for High-Temperature Power Generation Systems  

SciTech Connect

HEATS Project: PNNL is developing a thermal energy storage system based on a Reversible Metal Hydride Thermochemical (RMHT) system, which uses metal hydride as a heat storage material. Heat storage materials are critical to the energy storage process. In solar thermal storage systems, heat can be stored in these materials during the day and released at night—when the sun is not out—to drive a turbine and produce electricity. In nuclear storage systems, heat can be stored in these materials at night and released to produce electricity during daytime peak-demand hours. PNNL’s metal hydride material can reversibly store heat as hydrogen cycles in and out of the material. In a RHMT system, metal hydrides remain stable in high temperatures (600- 800°C). A high-temperature tank in PNNL’s storage system releases heat as hydrogen is absorbed, and a low-temperature tank stores the heat until it is needed. The low-cost material and simplicity of PNNL’s thermal energy storage system is expected to keep costs down. The system has the potential to significantly increase energy density.

None

2011-12-05

194

Safety aspects of tritium storage in metal hydride form  

Microsoft Academic Search

Air or nitrogen ingress accident scenarios into JET tritium storage containers, filled with uranium or intermetallic compound (IMC) hydrides, are discussed based on the experimentally determined kinetics of the reaction of these hydrides with air, Oâ and Nâ. Reaction of uranium with air can occur at room temperature. For the initiation of the reactions of uranium with Nâ or of

A. N. Perevezentsev; A. C. Bell; R. Lasser; L. A. Rivkis

1995-01-01

195

A nickel metal hydride battery for electric vehicles  

Microsoft Academic Search

Widespread use of electric vehicles can have significant impact on urban air quality, national energy independence, and international balance of trade. An efficient battery is the key technological element to the development of practical electric vehicles. The science and technology of a nickel metal hydride battery, which stores hydrogen in the solid hydride phase and has high energy density, high

S. R. Ovshinsky; M. A. Fetcenko; J. Ross

1993-01-01

196

The two-stage metal hydride heat transformer  

Microsoft Academic Search

Metal hydrides can be utilized as working materials in different types ofprocesses in the field of energy technology. Among others, thermally driven heat transformationdevices are very promising solutions for the rational use of energy. Main applications forthermodynamic metal hydride machines are the heat transformer for generation of hightemperatures, or the heat pump\\/refrigerator for generation of both high and low temperatures.Such

E Willers; M Groll

1999-01-01

197

Local-spectrum-modified fast reactor cores with hydrides  

Microsoft Academic Search

the application of different hydride materials to core components except for the driver fuel assembly is studied to achieve high core performances for fast reactor by reducing neutron energy and increasing reaction rates locally. The mixtures of absorber materials such as Gd and Zr-hydride are employed to control materials to increase reactivity worth. An optimized composition and layout of the

Yokoyama Tsugio; Konashi Kenji; Iwasaki Tomohiko; Terai Takayuki; Yamawaki Michio

2006-01-01

198

Method of making crack-free zirconium hydride  

DOEpatents

Crack-free hydrides of zirconium and zirconium-uranium alloys are produced by alloying the zirconium or zirconium-uranium alloy with beryllium, or nickel, or beryllium and scandium, or nickel and scandium, or beryllium and nickel, or beryllium, nickel and scandium and thereafter hydriding.

Sullivan, Richard W. (Denver, CO)

1980-01-01

199

Recent advances in metal hydrides for clean energy applications  

SciTech Connect

Metal hydrides are a fascinating class of materials that can be utilized for a surprising variety of clean energy applications, including smart solar collectors, smart windows, sensors, thermal energy storage, and batteries, in addition to their traditional application for hydrogen storage. Over the past decade, research on metal hydrides for hydrogen storage increased due to global governmental incentives and an increased focus on hydrogen storage research for polymer electrolyte membrane fuel cell operation. Tremendous progress has been made in so-called complex metal hydrides for hydrogen storage applications with the discovery of many new hydrides containing covalently bound complex anions. Many of these materials have applications beyond hydrogen storage and are being investigated for lithium-ion battery separator and anode materials. In this issue of MRS Bulletin , we present the state of the art of key evolving metal-hydride-based clean energy technologies with an outlook toward future needs.

Ronnebro, Ewa; Majzoub, Eric H.

2013-06-01

200

Modular hydride beds for mobile applications  

SciTech Connect

Design, construction, initial testing and simple thermal modeling of modular, metal hydride beds have been completed. Originally designed for supplying hydrogen to a fuel cell on a mobile vehicle, the complete bed design consists of 8 modules and is intended for use on the Palm Desert Vehicle (PDV) under development at the Schatz Energy Center, Humbolt State University. Each module contains approximately 2 kg of a commercially available, low temperature, hydride-forming metal alloy. Waste heat from the fuel cell in the form of heated water is used to desorb hydrogen from the alloy for supplying feed hydrogen to the fuel cell. In order to help determine the performance of such a modular bed system, six modules were constructed and tested. The design and construction of the modules is described in detail. Initial testing of the modules both individually and as a group showed that each module can store {approximately} 30 g of hydrogen (at 165 PSIA fill pressure, 17 C), could be filled with hydrogen in 6 minutes at a nominal, 75 standard liters/min (slm) fueling rate, and could supply hydrogen during desorption at rates of 25 slm, the maximum anticipated hydrogen fuel cell input requirement. Tests made of 5 modules as a group indicated that the behavior of the group run in parallel both in fueling and gas delivery could be directly predicted from the corresponding, single module characteristics by using an appropriate scaling factor. Simple thermal modeling of a module as an array of cylindrical, hydride-filled tubes was performed. The predictions of the model are in good agreement with experimental data.

Malinowski, M.E.; Stewart, K.D.

1997-08-01

201

Metal hydride fuel storage and method thereof  

DOEpatents

An apparatus having a first substrate having (1) a cavity, (2) one or more resistive heaters, and (3) one or more coatings forming a diffusion barrier to hydrogen; a second substrate having (1) an outlet valve comprising a pressure relief structure and (2) one or more coatings forming a diffusion barrier to hydrogen, wherein said second substrate is coupled to said first substrate forming a sealed volume in said cavity; a metal hydride material contained within said cavity; and a gas distribution system formed by coupling a microfluidic interconnect to said pressure relief structure. Additional apparatuses and methods are also disclosed.

Morse, Jeffrey D. (Martinez, CA); Jankowski, Alan F. (Livermore, CA); Yu, Conrad (Antioch, CA)

2010-08-10

202

Development of a Potential Surface for Simulation of Proton and Hydride Transfer Reactions in Solution: Application to NADH Hydride Transfer  

E-print Network

Development of a Potential Surface for Simulation of Proton and Hydride Transfer Reactions that incorporates significant quantum mechanical effects for proton and hydride transfer reactions in solution to that of the product during the reaction. Moreover, in order to incorporate changes in bond order and hybridization

Hammes-Schiffer, Sharon

203

Iridium and tantalum foils for spaceflight neutron dosimetry.  

NASA Technical Reports Server (NTRS)

Description of a two-foil system of iridium and tantalum which can measure thermal and intermediate energy neutrons at flux densities of 1 neutron/sq cm-sec over a ten-day lunar mission (1,000,000 neutrons/sq cm). The foils are chemically inert and nontoxic, weigh less than 1 g each, and require only routine gamma pulse height analysis for activation measurement. Detection of fluences below 1,000,000 neutrons/sq cm are achieved for counts of foil activity made as late as two months following neutron exposure. Tantalum foils flown in Apollo 11 indicated a mean dose equivalent to the astronauts of less than 16 mrem from thermal plus intermediate energy neutrons, while nuclear emulsion track analysis indicated approximately 17 mrem from neutrons of energy greater than 0.6 MeV. Iridium foils flown on Apollo 12 indicated dose equivalents of 1.8 to 2.8 mrem from thermal neutrons, excluding tissue thermalized SNAP-27 neutrons.

English, R. A.; Liles, E. D.

1972-01-01

204

Carboranes tuning the phosphorescence of iridium tetrazolate complexes.  

PubMed

New iridium tetrazolate complexes containing o-, m-, or p-carboranyl substitution in different positions of a phenylpyridine ligand have been prepared. The carborane isomers and the effect of their substitution position in the tuning of optical properties have been examined. The neutral complexes with the carboranyl substituent on the phenyl ring in meta position relative to the metal exhibit redshifted emission bands in contrast to blueshifts for those with carboranyl in para position. All cationic complexes display evidently blueshifted dual-peak emission compared with the carborane-free complex (c-TZ) with a broad single-peak emission. Introduction of carborane leads to a blueshift over 70?nm relative to c-TZ. Carboranes also significantly improve phosphorescence efficiency (?P ) and lifetime (?), that is, ?P =0.64 versus 0.21 (c-TZ) and ?=880?ns versus 241?ns (c-TZ). The unique hydrophilic nido-carborane-based Ir(III) complex nido-o-1 shows the largest phosphorescence efficiency (abs ?P =0.57) among known water-soluble iridium complexes, long emission lifetime (?=4.38??s), as well as varying emission efficiency and lifetime with O2 content in aqueous solution. Therefore, nido-o-1 has been used as an excellent oxygen-sensitive phosphor for intracellular O2 sensing and hypoxia imaging. PMID:25352530

Shi, Chao; Tu, Deshuang; Yu, Qi; Liang, Hua; Liu, Yahong; Li, Zhihong; Yan, Hong; Zhao, Qiang; Huang, Wei

2014-12-01

205

Analysis and Consequences of the Iridium 33-Cosmos 2251 Collision  

NASA Technical Reports Server (NTRS)

The collision of Iridium 33 and Cosmos 2251, on 10 February 2009, was the first known unintentional hypervelocity collision in space of intact satellites. Iridium 33 was an active commercial telecommunications satellite, while Cosmos 2251 was a derelict communication satellite of the Strela-2M class. The collision occurred at a relative velocity of 11.6 km/s at an altitude of approximately 790 km over the Great Siberian Plain and near the northern apex of Cosmos 2251 s orbit. This paper describes the physical and orbital characteristics of the relevant spacecraft classes and reports upon our analysis of the resulting debris clouds size, mass, area-to-mass ratio, and relative velocity/directionality distributions. We compare these distributions to those predicted by the NASA breakup model and notable recent fragmentation events; in particular, we compare the area-to-mass ratio distribution for each spacecraft to that exhibited by the FY-1C debris cloud for the purpose of assessing the relative contribution of modern aerospace materials to debris clouds resulting from energetic collisions. In addition, we examine the long-term consequences of this event for the low Earth orbit (LEO) environment. Finally, we discuss "lessons learned", which may be incorporated into NASA s environmental models.

Anz-Meador, P. D.; Liou, Jer-Chi

2010-01-01

206

Analysis of Abrasive Blasting of DOP-26 Iridium Alloy  

SciTech Connect

The effects of abrasive blasting on the surface geometry and microstructure of DOP-26 iridium alloy (Ir-0.3% W-0.006% Th 0.005% Al) have been investigated. Abrasive blasting has been used to control emissivity of components operating at elevated temperature. The effects of abrasive blasting conditions on surface morphology were investigated both experimentally and by numerical modeling. The simplified model, based on finite element analysis of a single angular particle impacting on Ir alloy disk, calculates the surface deformation and residual strain distribution. The experimental results and modeling results both indicate that the surface geometry is not sensitive to the abrasive blast process conditions of nozzle pressure and standoff distance considered in this study. On the other hand, the modeling results suggest that the angularity of the abrasive particle has an important role in determining surface geometry, which in turn, affects the emissivity. Abrasive blasting causes localized surface strains and localized recrystallization, but it does not affect grain size following extended exposure at elevated temperature. The dependence of emissivity of the DOP-26 alloy on mean surface slope follows a similar trend to that reported for pure iridium.

Ohriner, Evan Keith [ORNL; Zhang, Wei [ORNL; Ulrich, George B [ORNL

2012-01-01

207

Iridium catalyzed carbocyclizations: efficient (5+2) cycloadditions of vinylcyclopropanes and alkynes.  

PubMed

Third-row transition metal catalysts remain a largely untapped resource in cycloaddition reactions for the formation of medium-sized rings. Herein, we report the first examples of iridium-catalyzed inter- and intramolecular vinylcyclopropane (VCP)-alkyne (5+2) cycloadditions. DFT modeling suggests that catalysis by iridium(I) proceeds through a mechanism similar to that previously reported for rhodium(I)-catalyzed VCP-alkyne cycloadditions, but a smaller free energy span for iridium enables substantially faster catalysis under favorable conditions. The system is characterized by up to quantitative yields and is amenable to an array of disubstituted alkynes and vinylcyclopropanes. PMID:25413863

Melcher, Michaela-Christina; von Wachenfeldt, Henrik; Sundin, Anders; Strand, Daniel

2015-01-01

208

Iridium anomaly in the Cretaceous section of the Eastern Kamchatka  

NASA Astrophysics Data System (ADS)

The origin of iridium anomalies is widely discussed with regard to massive fauna and flora extinction at several geologic boundaries. Two hypotheses are most popular, cosmogenic and volcanogenic. Anomalies of iridium are known at many stratigraphic levels, both at the geologic series borders and within geologic series. Our studies revealed increased content of iridium in a section of Cretaceous oceanic deposits on the Kamchatsky Mys Peninsula (Eastern Kamchatka, Russia). The investigated section (56°03.353´N, 163°00.376´E) includes interbedded jaspers and siliceous limestones overlaying pillow-basalts. These deposits belong to the Smagin Formation of the Albian-Cenomanian age. In the middle and upper parts of the section two beds of black carbonaceous rocks with sapropelic organic matter were observed. Their formation marked likely episodes of oxygen depletion of oceanic intermediate water (oceanic anoxic events). Our geochemical studies revealed an enrichment of the carbonaceous beds in a number of major and trace elements (Al2O3, TiO2, FeO, MgO, K2O, P2O5, Cu, Zn, Ni, Cr, V, Mo, Ba, Y, Zr, Nb, REE, U, Au, Pt etc.) in comparison with associating jaspers and limestones. There are likely different sources which contributed to the enrichment. It is possible however to correlate the excess of Al, Ti, Zr, Nb with volcanogenic admixture, which is absent in limestones and jaspers. A possible source of the volcanogenic material was local volcanism as suggested by the close association of the investigated section with volcanic rocks (basaltic lavas and hyaloclastites). The basalts of the Smagin Formation were previously proposed to originate during Cretaceous activity of the Hawaiian mantle plume (Portnyagin et al., Geology, 2008). Neutron activation analysis indicated increased up to 9 ppb concentration of Ir at the bottom of the lower carbonaceous bed (inorganic part of the sample was analyzed comprising 46% of the bulk rock). In other samples Ir content was below the detection limit of the technique (< 2 ppb). The iridium anomaly was found for the fist time in sedimentary section in Kamchatka. This anomaly correlates in the studied section with a positive shift of d13C. Taking into account radiolarian age data (Palechek et al., 2010) this allows to correlate the anomaly with the Middle Cenomanian oceanic anoxic event (MCE). In our interpretation, the formation of the carbonaceous beds could be related to local outbreaks of volcanism which resulted in upwelling of deep waters enriched by mineral substances, sharp increase of plankton biological productivity and oxygen depletion of intermediate waters. Anoxic conditions favored enrichment of the sedimentary deposits in PGE sourced from lavas and hyaloclastites. Thus, iridium anomaly which has been found in Cretaceous sediments in Kamchatka, likely originates from a local volcanic source. This work was supported by the Russian-German project KALMAR and RFBR grant No. 10-05-00065.

Savelyev, Dmitry; Savelyeva, Olga

2010-05-01

209

Sub-Chronic Oral Exposure to Iridium (III) Chloride Hydrate in Female Wistar Rats: Distribution and Excretion of the Metal  

PubMed Central

Iridium tissue distribution and excretion in female Wistar rats following oral exposure to iridium (III) chloride hydrate in drinking water (from 1 to 1000 ng/ml) in a sub-chronic oral study were determined. Samples of urine, feces, blood and organs (kidneys, liver, lung, spleen and brain) were collected at the end of exposure. The most prominent fractions of iridium were retained in kidney and spleen; smaller amounts were found in lungs, liver and brain. Iridium brain levels were lower than those observed in other tissues but this finding can support the hypothesis of iridium capability to cross the blood brain barrier. The iridium kidney levels rose significantly with the administered dose. At the highest dose, important amounts of the metal were found in serum, urine and feces. Iridium was predominantly excreted via feces with a significant linear correlation with the ingested dose, which is likely due to low intestinal absorption of the metal. However, at the higher doses iridium was also eliminated through urine. These findings may be useful to help in the understanding of the adverse health effects, particularly on the immune system, of iridium dispersed in the environment as well as in identifying appropriate biological indices of iridium exposure. PMID:22942873

Iavicoli, Ivo; Fontana, Luca; Bergamaschi, Antonio; Conti, Marcelo Enrique; Pino, Anna; Mattei, Daniela; Bocca, Beatrice; Alimonti, Alessandro

2012-01-01

210

New horizons in boron hydride chemistry  

SciTech Connect

Pentaborane and diborane undergo hydrogen isotope exchange with deuterated aromatic hydrocarbons. Lewis acid catalyzed hydrogen isotope exchange between benzene-d/sub 6/ and pentaborane forms exclusively 1-DB/sub 5/H/sub 8/ at ambient temperature. In uncatalyzed exchanges, pentaborane reacts with benzene-d/sub 6/ to produce 1,2,3,4,5-D/sub 5/B/sub 5/H/sub 4/ at +45/sup 0/C, and B/sub 5/D/sub 9/ at + 120/sup 0/C. This thermally induced hydrogen isotope exchange apparently occurs via a reversible hydroboration of the aromatic ring. Halopentaboranes are converted to the parent pentaborane using tributyltin hydride as the halogen reducing agent under mild conditions and in high yields. Tributyltin hydride also reacts with other haloboranes and halometalloboranes. Deuterated pentaboranes are produced from halopentaboranes and tributyltin deuteride. Mechanistic features of this hydrogen-halogen exchange system are discussed. A new aminoborane, bis(dimethylamino)tetraborane, has been synthesized. On the basis of physical and spectroscopic data, a structure having the classical tetraborane framework is proposed, with two bridge hydrogen atoms replaced by dimethylamino groups. Solvent and temperature effects on the /sup 11/B and /sup 1/H NMR spectra of decaborane have been observed. Solvent polarizability is the major factor affecting chemical shifts. /sup 11/B-/sup 1/H/sub bridge/ and /sup 11/B-/sup 11/B coupling in decaborane can be measured at the B position.

Kunz, J.C.

1985-01-01

211

Hot temperatures line lists for metal hydrides  

NASA Astrophysics Data System (ADS)

The ExoMol project is an ERC funded project set up with the purpose of calculating high quality theoretical molecular line list data to facilitate the emerging field of exoplanet and cool star atmospheric haracterisation [1]. Metal hydrides are important building blocks of interstellar physical chemistry. For molecular identification and characterisation in astrophysical sources, one requires accurate and complete spectroscopic data including transitional frequencies and intensities in the form of a line list. The ab initio methods offer the best opportunity for detailed theoretical studies of free diatomic metal hydrides and other simple hydride molecules. In this contribution we present progress on theoretical line lists for AlH, CrH, MgH, NiH, NaH and TiH obtained from first principles, applicable for a large range of temperatures up to 3500 K. Among the hydrides, AlH is of special interest because of a relatively high cosmic abundance of aluminium. The presence of AlH has been detected in the spectra of M-type and S-type stars as well as in sunspots (See [2] and references therein). CrH is a molecule of astrophysical interest; under the classification scheme developed by Kirkpatrick et al [3], CrH is of importance in distinguishing L type brown dwarfs. It has been proposed that theoretical line-lists of CrH and CrD could be used to facilitate a 'Deuterium test' for use in distinguishing planets, brown dwarfs and stars [5] and also it has been speculated that CrH exists in sunspots [4] but a higherquality hot-temperature line-list is needed to confirm this finding. The presence of MgH in stellar spectra is well documented through observation of the A2 ! X 2+ and B0 2+ ! X 2+ transitions. Different spectral features of MgH have been used as an indicator for the magnesium isotope abundances in the atmospheres of different stars from giants to dwarfs including the Sun, to measure the temperature of stars, surface gravity, stars' metal abundance, gravitational, as well as for a deuterium test (see [6] and references therein). MgH is an important part of stellar atmospheric models. NiH is predicted to be the most common nickelbearing molecule [7] and was indentified in sunspot spectra around 15 000 cm-1 (646 cm) over 40 years ago [8]. Knowledge of 58NiH/60NiH isotopologue ratio in stellar spectra is used to test models of supernovae and star formation [9]. The spectra of metal hydrides such can be very complicated due to the large-number of interacting electronic states, to the importance of electron correlation, relativistic and spin-orbit effects and of the various couplings between angular momenta. Via the use of the Born-Oppenheimer approximation, the Schrödinger equation describing the state of a molecule can be factorised into an 'electronic' component and a nuclear (i.e., rotational-vibrational) component. The former is solved using the ab initio quantum chemistry package MOLPRO, yielding potential energy, dipole and transition moment, and spin-orbit curves. The resulting coupled-surface ro-vibronic problem was then solved using the in-house computer program DUO, which is based on expansion in Hund's case (a) wave functions. Potential curves and couplings were then refined semi-empirically using the available experimental spectroscopic data.

Gorman, M.; Lodi, L.; Leyland, P. pC; Hill, C.; Yurchenko, S. N.; Tennyson, J.

2013-09-01

212

Fracture Resistance of a Zirconium Alloy with Reoriented Hydrides  

NASA Astrophysics Data System (ADS)

Zirconium alloy cladding materials typically contain circumferential hydrides that may be reoriented to align along the radial direction when the cladding tubes are heated above and then cooled below the solvus temperature. The objectives of this study were to investigate the critical stress levels required to cause hydride reorientation (HRT) and to characterize the fracture resistance of Zircaloy-2 after hydride reorientation. HRT heat-treatment was performed on hydrogen-charged Zircaloy-2 specimens at 593 K (320 °C) or 623 K (350 °C) for 1 to 2 hours, followed by cooling to 473 K (200 °C). Fracture testing was conducted on hydride-reoriented three-point bend specimens at 473 K (200 °C) using an in situ loading stage inside a scanning electron microscope. Direct observations indicated that the reoriented hydrides, which ranged from ?1 to 22 ?m in lengths, were more prone to fracture at larger sizes (>10 ?m) compared to smaller sizes (<0.5 ?m). The reoriented hydrides reduced fracture resistance through a void nucleation, growth, and coalescence process at the crack tip. The resulting crack-resistance curves for Zircaloy-2 with reoriented hydrides decrease from 38 to 21 MPa(m)1/2 with increasing hydrogen contents from 51 to 1265 wt ppm hydrogen.

Chan, Kwai S.; He, Xihua; Pan, Yi-Ming

2015-01-01

213

Small satellite nickel-hydrogen and nickel-metal hydride power applications  

Microsoft Academic Search

Nickel and silver-metal hydride batteries are being developed for aerospace applications. Metal hydride batteries offer a number of advantages over other aerospace battery systems. Nickel-metal hydride batteries have twice the gravimetric energy density of nickel-cadmium and twice the volumetric energy density of nickel-hydrogen. Silver-metal hydride batteries have the potential of three times the energy density of nickel-metal hydride and exhibit

William Dean Cook; Dwaine Coates

1993-01-01

214

Molecular Rare-Earth-Metal Hydrides in Non-Cyclopentadienyl Environments.  

PubMed

Molecular hydrides of the rare-earth metals play an important role as homogeneous catalysts and as counterparts of solid-state interstitial hydrides. Structurally well-characterized non-metallocene-type hydride complexes allow the study of elementary reactions that occur at rare-earth-metal centers and of catalytic reactions involving bonds between rare-earth metals and hydrides. In addition to neutral hydrides, cationic derivatives have now become available. PMID:25413985

Fegler, Waldemar; Venugopal, Ajay; Kramer, Mathias; Okuda, Jun

2014-11-20

215

Iridium-catalyst-based autonomous bubble-propelled graphene micromotors with ultralow catalyst loading.  

PubMed

A novel concept of an iridium-based bubble-propelled Janus-particle-type graphene micromotor with very high surface area and with very low catalyst loading is described. The low loading of Ir catalyst (0.54?at?%) allows for fast motion of graphene microparticles with high surface area of 316.2?m(2) ?g(-1). The micromotor was prepared with a simple and scalable method by thermal exfoliation of iridium-doped graphite oxide precursor composite in hydrogen atmosphere. Oxygen bubbles generated from the decomposition of hydrogen peroxide at the iridium catalytic sites provide robust propulsion thrust for the graphene micromotor. The high surface area and low iridium catalyst loading of the bubble-propelled graphene motors offer great possibilities for dramatically enhanced cargo delivery. PMID:25293511

Wang, Hong; Sofer, Zden?k; Eng, Alex Yong Sheng; Pumera, Martin

2014-11-10

216

Investigating the recycling of nickel hydride battery scrap  

NASA Astrophysics Data System (ADS)

New nickel hydride alloys have been developed to replace the cadmium-containing negative electrodes of nickel-cadmium batteries. The new, cadmium free alloys promise enhanced electrochemical properties as well as reduced environmental toxicity. Rechargeable batteries using nickel hydride electrodes are strong candidates for electric vehicle applications. The U.S. Bureau of Mines is investigating hydrometallurgical technology that separates and recovers purified metallic components present in nickel hydride battery scrap. A preliminary investigation of acid dissolution and metal recovery techniques using whole batteries and electrode rolls has shown potential options that will allow the successful recycling of much of the battery fabrication scrap.

Lyman, Jane W.; Palmer, Glenn R.

1993-05-01

217

On the kinetics of iridium nanoparticles formation in ionic liquids and olefin hydrogenation  

Microsoft Academic Search

The in situ formation of an iridium nanoparticles dispersion obtained from the reduction of the organometallic precursor [Ir(cod)Cl]2 in 1-n-butyl-3-methyl imidazolium hexafluorophosphate ionic liquid by molecular hydrogen is an autocatalytic process. These nanoparticles possess a small size and a monomodal size distribution of 2.0±0.4nm iridium nanoparticles can be confirmed by TEM and XRD analysis before and after the catalytic process.

Gledison S. Fonseca; Josiel B. Domingos; Faruk Nome; Jairton Dupont

2006-01-01

218

Measurements of iridium and the hypothesis of meteoritic impact as the end of the Cretaceous period  

Microsoft Academic Search

Analysis methods applied for neutron activation and radiochemistry for determination of trace elements, iridium and gold, were utilized in cosmochemistry. The concentrations analyzed were in the parts per billion band. The analysis by neutron activation determined the concentration of 1.5 gram irradiated iridium sample during 32 hours in thermal flux as 10 to the 13th power neutrons\\/sq cm\\/sec. Gamma spectrometry

Francisco Sircillineto

1986-01-01

219

Highly efficient electrochemiluminescence from iridium(iii) complexes with 2-phenylquinoline ligand.  

PubMed

A series of cyclometalated iridium(iii) complexes with 2-phenylquinoline ligand () were designed and synthesized, which were thoroughly investigated by the photophysics, electrochemistry, theoretical calculations and electrochemiluminescence (ECL). By incorporating methyl groups into the 2-phenylquinoline, the corresponding complexes and displayed lower oxidative potential and higher HOMO energy levels. Most importantly, compared with tris(2,2'-bipyridyl)ruthenium(ii) ([Ru(bipy)3](2+)), these iridium(iii) complexes demonstrated more intense ECL in acetonitrile solutions. PMID:25482203

Zhou, Yuyang; Li, Wanfei; Yu, Linpo; Liu, Yang; Wang, Xiaomei; Zhou, Ming

2014-12-23

220

Accretion rate of extraterrestrial matter - Iridium deposited 33 to 67 million years ago  

Microsoft Academic Search

Iridium measured in 149 samples of a continuous 9-meter section of Pacific abyssal clay covering the time span 33 to 67 million years ago shows a well-defined peak only at the Cretaceous\\/Tertiary boundary. In the rest of the section iridium ranges from a minimum concentration near 0.35 nanograms per gram in the Paleocene to a maximum near 1.7 in the

F. T. Kyte; J. T. Wasson

1986-01-01

221

ENVIRONMENTAL REACTIVITY OF SOLID STATE HYDRIDE MATERIALS  

SciTech Connect

In searching for high gravimetric and volumetric density hydrogen storage systems, it is inevitable that higher energy density materials will be used. In order to make safe and commercially acceptable condensed phase hydrogen storage systems, it is important to understand quantitatively the risks involved in using and handling these materials and to develop appropriate mitigation strategies to handle potential material exposure events. A crucial aspect of the development of risk identification and mitigation strategies is the development of rigorous environmental reactivity testing standards and procedures. This will allow for the identification of potential risks and implementation of risk mitigation strategies. Modified testing procedures for shipping air and/or water sensitive materials, as codified by the United Nations, have been used to evaluate two potential hydrogen storage materials, 2LiBH{sub 4} {center_dot} MgH{sub 2} and NH{sub 3}BH{sub 3}. The modified U.N. procedures include identification of self-reactive substances, pyrophoric substances, and gas-emitting substances with water contact. The results of these tests for air and water contact sensitivity will be compared to the pure material components where appropriate (e.g. LiBH{sub 4} and MgH{sub 2}). The water contact tests are divided into two scenarios dependent on the hydride to water mole ratio and heat transport characteristics. Air contact tests were run to determine whether a substance will spontaneously react with air in a packed or dispersed form. In the case of the 2LiBH{sub 4} {center_dot} MgH{sub 2} material, the results from the hydride mixture compared to the pure materials results showed the MgH{sub 2} to be the least reactive component and LiBH{sub 4} the more reactive. The combined 2LiBH{sub 4} {center_dot} MgH{sub 2} resulted in a material having environmental reactivity between these two materials. Relative to 2LiBH{sub 4} {center_dot} MgH{sub 2}, the chemical hydride NH{sub 3}BH{sub 3} was observed to be less environmentally reactive.

Gray, J; Donald Anton, D

2009-04-23

222

Large Deformation Change in Iridium Isotopes from Laser Spectroscopy  

SciTech Connect

Laser spectroscopy measurements have been performed on neutron-deficient iridium isotopes. The hyperfine structure and isotope shift of the optical Ir I transition 5d{sup 7}6s{sup 2} {sup 4}F{sub 9/2} {yields}5d{sup 7}6s6p {sup 6}F{sub 11/2} have been studied for the {sup 182-189}Ir, {sup 186}Ir{sup m} and {sup 191,193}Ir isotopes. The nuclear magnetic and quadrupole moments were obtained from the hyperfine splitting measurements and the changes of the mean square charge radii from the isotope shift measurements. A large deformation change between {sup 187}Ir and {sup 186}Ir and between {sup 186}Ir{sup m} and {sup 186}Ir{sup g} has been observed.

D. Verney; L. Cabaret; J. Crawford; H.T. Duong; J. Genevey; G. Hubert; F. Ibrahim; M. Krieg; F. Le Blanc; J.K.P. Lee; G. Le Scornet; D. Lunney; J. Obert; J. Oms; J. Pinard; J.C. Putaux; B. Roussiere; J. Sauvage; V. Sebastian

1999-12-31

223

Large deformation change in iridium isotopes from laser spectroscopy  

SciTech Connect

Laser spectroscopy measurements have been performed on neutron-deficient iridium isotopes. The hyperfine structure and isotope shift of the optical Ir I transition 5d{sup 7}6s{sup 2} {sup 4}F{sub 9/2}{yields}5d{sup 7}6s6p {sup 6}F{sub 11/2} have been studied for the {sup 182-189}Ir, {sup 180}Ir{sup m} and {sup 191,193}Ir isotopes. The nuclear magnetic and quadrupole moments were obtained from the hyperfine splitting measurements and the changes of the mean square charge radii from the isotope shift measurements. A large deformation change between {sup 187}Ir and {sup 186}Ir and between {sup 186}Ir{sup m} and {sup 186}Ir{sup g} has been observed.

Verney, D.; Le Blanc, F.; Obert, J.; Oms, J.; Putaux, J. C.; Roussiere, B.; Sauvage, J. [Institut de Physique Nucleaire, IN2P3-CNRS, 91406 Orsay Cedex (France); Cabaret, L.; Duong, H. T.; Pinard, J. [Laboratoire Aime Cotton, 91405 Orsay Cedex (France); Crawford, J.; Lee, J. K. P. [Physics Department, Mc Gill University, H3A2T8 Montreal (Canada); Genevey, J.; Ibrahim, F. [Institut des Sciences Nucleaires, IN2P3-CNRS, 38026 Grenoble Cedex (France); Hubert, G.; Krieg, M.; Sebastian, V. [Institut fuer Physik der Univeristaet Mainz (Germany); Le Scornet, G.; Lunney, D. [CSNSM, IN2P3-CNRS, 91405 Orsay Cedex (France)

1999-11-16

224

A new iridium applicator for vaginal vault irradiation.  

PubMed

A new disposable gynecologic applicator designed for postoperative vaginal vault brachytherapy is presented. The applicator is afterloading manually with iridium 192 wire. We have used this new applicator in more than thirty patients and recorded the following advantages: 1) There is no need to install expensive and complicated equipment; 2) Single use applicators are in sterile packages and are ready to use; 3) Applicator is easily and comfortably carried by patient; 4) There is no need for specific training to use the system; 5) There is no need for general anesthesia during application; 6) There is no need for patient immobilization during treatment; 7) There is no need for urinary catheterization during treatment; 8) Dose distribution is homogeneous; 9) Bladder and rectum doses are at acceptable levels; 10) Radioprotective measures needed to be taken are inexpensive. We believe that this new system could easily be used in every radiation oncology unit. PMID:7957330

Töre, G; Aslay, I; Dinçer, M; Kemikler, G

1994-01-01

225

Comparative modelling of chemical ordering in palladium-iridium nanoalloys  

NASA Astrophysics Data System (ADS)

Chemical ordering in "magic-number" palladium-iridium nanoalloys has been studied by means of density functional theory (DFT) computations, and compared to those obtained by the Free Energy Concentration Expansion Method (FCEM) using derived coordination dependent bond energy variations (CBEV), and by the Birmingham Cluster Genetic Algorithm using the Gupta potential. Several compositions have been studied for 38- and 79-atom particles as well as the site preference for a single Ir dopant atom in the 201-atom truncated octahedron (TO). The 79- and 38-atom nanoalloy homotops predicted for the TO by the FCEM/CBEV are shown to be, respectively, the global minima and competitive low energy minima. Significant reordering of minima predicted by the Gupta potential is seen after reoptimisation at the DFT level.

Davis, Jack B. A.; Johnston, Roy L.; Rubinovich, Leonid; Polak, Micha

2014-12-01

226

Iridium-alloy processing experience in FY 1989  

SciTech Connect

Iridium-alloy blanks and foil are produced at the Oak Ridge National Laboratory for use as fuel cladding material in radioisotope thermoelectric generators for space power sources. Until 1984, the material was produced from small 500-g drop castings. A new process has been developed in which consumable electrodes of about 10 kg are arc melted, extruded, and then rolled to produce the sheet products. The work performed during FY 1989 included the arc melting of three electrodes and the extruding and rolling to sheet of three billets. Significant improvements have been made in the extruding and arc-melting processes. Preliminary results show that these improvements have had an important effect in increasing the rate of blank acceptance in nondestructive evaluations. 4 refs., 33 figs., 11 tabs.

Ohriner, E.K.

1990-11-01

227

A Porphyrin-Stabilized Iridium Oxide Water Oxidation Catalyst  

SciTech Connect

Colloidal solutions of iridium oxide hydrate (IrO{sub 2}·NH{sub 2}O) were formed using porphyrin stabilizers bearing malonate-like functional groups at each of the four meso positions of the porphyrin ring. Cyclic voltammetry and monitoring of solution oxygen concentrations under constant applied potential demonstrated the electrochemical catalytic activity of the porphyrin–IrO{sub 2}·NH{sub 2}O complexes for the oxidation of water to oxygen. Quenching of the porphyrin fluorescence in the complex implies strong interaction between the porphyrin and the IrO{sub 2}·NH{sub 2}O. These results mark a step toward developing a porphyrin-based photoanode for use in a photoelectrochemical water-splitting cell.

Sherman, Ben; Pillai, Smitha; Kodis, Gerdenis; Bergkamp, Jesse; Mallouk, Thomas E.; Gust, Devens; Moore, Thomas A.; Moore, Ana L.

2011-01-01

228

Comparative modelling of chemical ordering in palladium-iridium nanoalloys.  

PubMed

Chemical ordering in "magic-number" palladium-iridium nanoalloys has been studied by means of density functional theory (DFT) computations, and compared to those obtained by the Free Energy Concentration Expansion Method (FCEM) using derived coordination dependent bond energy variations (CBEV), and by the Birmingham Cluster Genetic Algorithm using the Gupta potential. Several compositions have been studied for 38- and 79-atom particles as well as the site preference for a single Ir dopant atom in the 201-atom truncated octahedron (TO). The 79- and 38-atom nanoalloy homotops predicted for the TO by the FCEM/CBEV are shown to be, respectively, the global minima and competitive low energy minima. Significant reordering of minima predicted by the Gupta potential is seen after reoptimisation at the DFT level. PMID:25494749

Davis, Jack B A; Johnston, Roy L; Rubinovich, Leonid; Polak, Micha

2014-12-14

229

Iridium abundance maxima in the Upper Cenomanian extinction interval  

NASA Technical Reports Server (NTRS)

Two iridium abundance peaks, both 0.11 ppb (whole-rock basis) over a local background of 0.017 ppb, have been found in Middle Cretaceous marine rocks near Pueblo, Colorado. They occur just below the 92-million-year-old Cenomanian-Turonian (C-T) stage boundary. No other peaks were found in 45 meters of strata (about 2.5 million years of deposition) above and below the boundary interval. The broad lower peak straddles the first in a series of extinctions of benthic and nektonic macrobiota which comprise the C-T extinction event. The sharp upper peak occurs stratigraphically about 1.2 meters above the lower peak. The excess Ir might be from meteoroid impacts.

Orth, C. J.; Attrep, M., Jr.; Mao, X. Y.; Kauffman, E. G.; Diner, R.

1988-01-01

230

Iridium satellites help map electrical currents in space  

NASA Astrophysics Data System (ADS)

The satellite constellation of Iridium LLC, which filed for Chapter 11 bankruptcy in 1999 after it failed to win enough business for its commercial satellite communications services, is still orbiting at an altitude of about 780 kilometers. Now, however, the satellites are helping to write a new chapter in understanding space weather.Magnetometers onboard each of the system's 66 polar-orbiting satellites are working in conjunction with the high-frequency, multinational Super Dual Auroral Radar Network, or SuperDARN, to provide the first continuous measurements of electrical currents between Earth's upper atmosphere and space. These tools also are generating the first global maps of electrical power flowing into the polar upper atmosphere.

Showstack, Randy

231

Process for production of a metal hydride  

SciTech Connect

A process for production of a metal hydride compound MH.sub.x, wherein x is one or two and M is an alkali metal, Be or Mg. The process comprises combining a compound of formula (R.sup.1O).sub.xM with aluminum, hydrogen and at least one metal selected from among titanium, zirconium, hafnium, niobium, vanadium, tantalum and iron to produce a compound of formula MH.sub.x. R.sup.1 is phenyl or phenyl substituted by at least one alkyl or alkoxy group. A mole ratio of aluminum to (R.sup.1O).sub.xM is from 0.1:1 to 1:1. The catalyst is present at a level of at least 200 ppm based on weight of aluminum.

Allen, Nathan Tait; Butterick, III, Robert; Chin, Arthur Achhing; Millar, Dean Michael; Molzahn, David Craig

2014-08-12

232

Electronic structures of silicene fluoride and hydride  

NASA Astrophysics Data System (ADS)

Silicene is the graphene-like silicon nanosheet, which has been synthesized very recently [B. Lalmi, H. Oughaddou, H. Enriquez, A. Kara, S. Vizzini, B. Ealet, and B. Aufray, Appl. Phys. Lett. 97, 223109 (2010)]. Using first-principles calculations, we systematically investigate the structures and properties of fluorinated and hydrogenated silicene, the silicon analogues of graphane. Different from the carbon-counterpart, the fluorination prefers the conformation with a zigzag-line buckling, while the hydrogenation keeps the chair conformation similar to graphane. A direct band gap is opened in the silicene fluoride, and the gap values can be continuously modulated by the strain. While for the hydride, a strain-induced indirect-to-direct band gap transition is found.

Ding, Yi; Wang, Yanli

2012-02-01

233

Zirconium Hydride Space Power Reactor design.  

NASA Technical Reports Server (NTRS)

The Zirconium Hydride Space Power Reactor being designed and fabricated at Atomics International is intended for a wide range of potential applications. Throughout the program a series of reactor designs have been evaluated to establish the unique requirements imposed by coupling with various power conversion systems and for specific applications. Current design and development emphasis is upon a 100 kilowatt thermal reactor for application in a 5 kwe thermoelectric space power generating system, which is scheduled to be fabricated and ground tested in the mid 70s. The reactor design considerations reviewed in this paper will be discussed in the context of this 100 kwt reactor and a 300 kwt reactor previously designed for larger power demand applications.

Asquith, J. G.; Mason, D. G.; Stamp, S.

1972-01-01

234

New yellow-emitting phosphorescent cyclometalated iridium(III) complex  

NASA Astrophysics Data System (ADS)

We have synthesized a new yellow iridium complex Iridium(III) bis[2-phenylbenzothiazolato-N,C2']-(1-phenylicosane-1,3-dionate) (bt)2Ir(bsm), based on the benzothiazole derivative. The synthesized molecule was identified by 1H NMR and elemental analysis. The UV-Visible absorption and photoluminescence (PL) spectra of (bt)Ir2(bsm) in CH2Cl2 solution were found at 273 nm and 559 nm, respectively. The complex was used as a dopant into a hole-transporting layer (HTL) in a multilayered organic light emitting device (OLED) structure: ITO/doped-HTL/EL/ETL/M. ITO was a transparent anode of In2O3:SnO2, M- a metallic Al cathode, HTL- 4,4'-bis(9H-carbazol-9-yl)biphenyl (CBP) incorporated in poly(N-vinylcarbazole) (PVK) matrix, EL- electroluminescent layer of bis(8-hydroxy-2-methylquinoline)-(4-phenylphenoxy)aluminum (BAlq) and ETL- electron-transporting layer of tris(8-hydroxyquinolinato)aluminum (Alq3). The electroluminescent (EL) spectra of OLEDs were basically the sum of the emissions of BAlq at 496 nm and the emission of (bt)2Ir(bsm) at 559 nm. With increasing (bt)2Ir(bsm) concentration, the relative electroluminescent intensity of greenish-blue emission (at 496 nm) decreased, while the yellow (at 559 nm) - increased and CIE coordinates of the device shifted from (0.21, 0.33) at 0 wt % to (0.40, 0.48) at 8 wt % of the dopant. It was found that OLED with 0.5 wt % (bt)2Ir(bsm) had the best performance and stable color chromaticity at various voltages.

Ivanov, P.; Tomova, R.; Petrova, P.; Stanimirov, S.; Petkov, I.

2012-12-01

235

Hydrogen storage in sodium aluminum hydride.  

SciTech Connect

Sodium aluminum hydride, NaAlH{sub 4}, has been studied for use as a hydrogen storage material. The effect of Ti, as a few mol. % dopant in the system to increase kinetics of hydrogen sorption, is studied with respect to changes in lattice structure of the crystal. No Ti substitution is found in the crystal lattice. Electronic structure calculations indicate that the NaAlH{sub 4} and Na{sub 3}AlH{sub 6} structures are complex-ionic hydrides with Na{sup +} cations and AlH{sub 4}{sup -} and AlH{sub 6}{sup 3-} anions, respectively. Compound formation studies indicate the primary Ti-compound formed when doping the material at 33 at. % is TiAl{sub 3} , and likely Ti-Al compounds at lower doping rates. A general study of sorption kinetics of NaAlH{sub 4}, when doped with a variety of Ti-halide compounds, indicates a uniform response with the kinetics similar for all dopants. NMR multiple quantum studies of solution-doped samples indicate solvent interaction with the doped alanate. Raman spectroscopy was used to study the lattice dynamics of NaAlH{sub 4}, and illustrated the molecular ionic nature of the lattice as a separation of vibrational modes between the AlH{sub 4}{sup -} anion-modes and lattice-modes. In-situ Raman measurements indicate a stable AlH{sub 4}{sup -} anion that is stable at the melting temperature of NaAlH{sub 4}, indicating that Ti-dopants must affect the Al-H bond strength.

Ozolins, Vidvuds; Herberg, J.L. (Lawrence Livermore National Laboratories, Livermore, CA); McCarty, Kevin F.; Maxwell, Robert S. (Lawrence Livermore National Laboratories, Livermore, CA); Stumpf, Roland Rudolph; Majzoub, Eric H.

2005-11-01

236

Dehydriding reactions of mixed complex hydrides  

NASA Astrophysics Data System (ADS)

Dehydriding reactions of the mixtures LiBH 4 + 2LiNH 2 and LiAlH 4 + 2LiNH 2 were investigated. The new pathways confirmed for the dehydriding reactions were LiBH 4 + 2LiNH 2 ? Li 3BN 2 + 4H 2 and LiAlH 4 + 2LiNH 2 ? Li 3AlN 2 + 4H 2 in which 11.9 and 9.6 mass% of hydrogen can be desorbed theoretically. The quantities of desorbed hydrogen were deduced experimentally to be approximately 7.9-9.5 and 4.1 mass% for the mixtures of LiBH 4 + 2LiNH 2 and LiAlH 4 + 2LiNH 2, respectively. The dehydriding temperature of LiBH 4 reduces by 150 K by mixing 2 M LiNH 2. An exothermic peak was observed at a slightly higher temperature of the dehydriding reaction; however, this peak might be due to the solidification of the product after the dehydriding reaction and not due to the exothermic dehydriding reaction. Although the first-step dehydriding reaction of LiAlH 4 is exothermic, the mixture of LiAlH 4 + 2LiNH 2 exhibits an endothermic dehydriding reaction. These results suggest that the stability of the dehydriding reactions of complex hydrides can be controlled by introducing new pathways that are produced by mixing. Two criteria for selecting complex hydrides that are mixed together for producing new pathways were proposed from the viewpoints of both the melting/dehydriding temperatures and the products of the dehydriding reactions.

Nakamori, Y.; Ninomiya, A.; Kitahara, G.; Aoki, M.; Noritake, T.; Miwa, K.; Kojima, Y.; Orimo, S.

237

Bipolar Nickel-Metal Hydride Battery Being Developed  

NASA Technical Reports Server (NTRS)

The NASA Lewis Research Center has contracted with Electro Energy, Inc., to develop a bipolar nickel-metal hydride battery design for energy storage on low-Earth-orbit satellites. The objective of the bipolar nickel-metal hydride battery development program is to approach advanced battery development from a systems level while incorporating technology advances from the lightweight nickel electrode field, hydride development, and design developments from nickel-hydrogen systems. This will result in a low-volume, simplified, less-expensive battery system that is ideal for small spacecraft applications. The goals of the program are to develop a 1-kilowatt, 28-volt (V), bipolar nickel-metal hydride battery with a specific energy of 100 watt-hours per kilogram (W-hr/kg), an energy density of 250 W-hr/liter and a 5-year life in low Earth orbit at 40-percent depth-of-discharge.

Manzo, Michelle A.

1998-01-01

238

Artificial exomuscle investigations for applications--metal hydride.  

PubMed

In pursuing the development of bionic devices, Victhom identified a need for technologies that could replace current motorized systems and be better integrated into the human body motion. The actuators used to obtain large displacements are noisy, heavy, and do not adequately reproduce human muscle behavior. Subsequently, a project at Victhom was devoted to the development of active materials to obtain an artificial exomuscle actuator. An exhaustive literature review was done at Victhom to identify promising active materials for the development of artificial muscles. According to this review, metal hydrides were identified as a promising technology for artificial muscle development. Victhom's investigations focused on determining metal hydride actuator potential in the context of bionics technology. Based on metal hydride properties and artificial muscle requirements such as force, displacement and rise time, an exomuscle was built. In addition, a finite element model, including heat and mass transfer in the metal hydride, was developed and implemented in FEMLAB software. PMID:18458414

Crevier, Marie-Charlotte; Richard, Martin; Rittenhouse, D Matheson; Roy, Pierre-Olivier; Bédard, Stéphane

2007-03-01

239

Transient analysis of hydride fueled pressurized water reactor cores  

E-print Network

This thesis contributes to the hydride nuclear fuel project led by U. C. Berkeley for which MIT is to perform the thermal hydraulic and economic analyses. A parametric study has been performed to determine the optimum ...

Trant, Jarrod Michael

2004-01-01

240

Self-Consistent-Field Calculation on Lithium Hydride for Undergraduates.  

ERIC Educational Resources Information Center

Describes a self-consistent-field-linear combination of atomic orbitals-molecular orbital calculation on the valence electrons of lithium hydride using the method of Roothaan. This description is intended for undergraduate physics students.

Rioux, Frank; Harriss, Donald K.

1980-01-01

241

Life test results of hydride compressors for cryogenic refrigerators  

NASA Technical Reports Server (NTRS)

A development status assessment is made, from the viewpoint of system durability, for the hydride compressors used in such cryogenic refrigerators as that of the JPL, which has operated at 29 K for 500 hours and at lower temperatures for over 1000. Attention is given to a novel hydride compressor unit which has operated through 35,000 cycles and exhibits negligible degradation of check valves, hydride particle size, and expansion valves. The power requirement for liquid hydrogen cooling can be halved through the use of recuperative hot water heating methods, making this system comparable in power use to liquid hydrogen refrigeration systems operating on electricity. Due to the lack of moving parts in hydride refrigerator designs, potential service lifetimes of many years, and perhaps decades, are being projected.

Jones, J. A.; Golben, P. M.

1984-01-01

242

The development of lightweight hydride alloys based on magnesium  

SciTech Connect

The development of a magnesium based hydride material is explored for use as a lightweight hydrogen storage medium. It is found that the vapor transport of magnesium during hydrogen uptake greatly influences the surface and hydride reactions in these alloys. This is exploited by purposely forming near-surface phases of Mg{sub 2}Ni on bulk Mg-Al-Zn alloys which result in improved hydrogen adsorption and desorption behavior. Conditions were found where these near-surface reactions yielded a complex and heterogeneous microstructure that coincided with excellent bulk hydride behavior. A Mg-Al alloy hydride is reported with near atmospheric plateau pressures at temperatures below 200{degrees}C. Additionally, a scheme is described for low temperature in-situ fabrication of Mg{sub 2}Ni single phase alloys utilizing the high vapor pressure of Mg.

Guthrie, S.E.; Thomas, G.J.; Yang, N.Y.C.; Bauer, W. [Sandia National Labs., Livermore, CA (United States)

1996-02-01

243

Development of a metal hydride electrode waste treatment process  

SciTech Connect

Manufacturing residues of metal hydride electrodes for nickel - metal hydride batteries were chemically processed to recover the metal part and heat treated for the organic part. Chemical recovery yielded Ni-Co alloy after electrolysis of the solution and hydroxides of other metal, mainly rare earths. The organic part, pyrolyzed at 700 C, led to separation between carbon and fluorinated matter. Infrared coupling at the output of the pyrolysis furnace was used to identify the pyrolysis gases.

Bianco, J.C.; Martin, D.; Ansart, F.; Castillo, S.

1999-12-01

244

Method of selective reduction of halodisilanes with alkyltin hydrides  

DOEpatents

The invention relates to the selective and sequential reduction of halodisilanes by reacting these compounds at room temperature or below with trialkyltin hydrides or dialkyltin dihydrides without the use of free radical intermediates. The alkyltin hydrides selectively and sequentially reduce the Si-Cl, Si-Br or Si-I bonds while leaving intact the Si-Si and Si-F bonds present.

D'Errico, John J. (Fenton, MI); Sharp, Kenneth G. (Midland, MI)

1989-01-01

245

Method of selective reduction of polyhalosilanes with alkyltin hydrides  

DOEpatents

The invention relates to the selective and stepwise reduction of polyhalosilanes by reacting at room temperature or below with alkyltin hydrides without the use of free radical intermediates. Alkyltin hydrides selectively and stepwise reduce the Si--Br, Si--Cl, or Si--I bonds while leaving intact any Si--F bonds. When two or more different halogens are present on the polyhalosilane, the halogen with the highest atomic weight is preferentially reduced.

Sharp, Kenneth G. (Midland, MI); D'Errico, John J. (Fenton, MI)

1989-01-01

246

Hydrogen segregation and lattice reorientation in palladium hydride nanowires  

NASA Astrophysics Data System (ADS)

We study palladium hydride nanowires of different sizes and hydrogen concentrations at 300 K using molecular dynamic simulations. Strong surface segregation of hydrogen with a depletion zone behind is observed in the palladium hydride nanowires. We also show that lattice reorientation is controlled by the hydrogen concentration as well as the nanowire size. The interplay of surface stresses and hydrogen induced stresses is responsible for the observations.

He, J. H.; Knies, D. L.; Hubler, G. K.; Grabowski, K. S.; Tonucci, R. J.; Dechiaro, L. F.

2012-10-01

247

Development of the Low-Pressure Hydride/Dehydride Process  

SciTech Connect

The low-pressure hydride/dehydride process was developed from the need to recover thin-film coatings of plutonium metal from the inner walls of an isotope separation chamber located at Los Alamos and to improve the safety operation of a hydride recovery process using hydrogen at a pressure of 0.7 atm at Rocky Flats. This process is now the heart of the Advanced Recovery and Integrated Extraction System (ARIES) project.

Rueben L. Gutierrez

2001-04-01

248

Development of the Low-Pressure Hydride\\/Dehydride Process  

Microsoft Academic Search

The low-pressure hydride\\/dehydride process was developed from the need to recover thin-film coatings of plutonium metal from the inner walls of an isotope separation chamber located at Los Alamos and to improve the safety operation of a hydride recovery process using hydrogen at a pressure of 0.7 atm at Rocky Flats. This process is now the heart of the Advanced

Rueben L. Gutierrez

2001-01-01

249

Optimization of Hydride Rim Formation in Unirradiated Zr 4 Cladding  

SciTech Connect

The purpose of this work is to build on the results reported in the M2 milestone M2FT 13PN0805051, document number FCRD-USED-2013-000151 (Hanson, 2013). In that work, it was demonstrated that unirradiated samples of zircaloy-4 cladding could be pre-hydrided at temperatures below 400°C in pure hydrogen gas and that the growth of hydrides on the surface could be controlled by changing the surface condition of the samples and form a desired hydride rim on the outside diameter of the cladding. The work performed at Pacific Northwest National Laboratory since the issuing of the M2 milestone has focused its efforts to optimize the formation of a hydride rim on available zircaloy-4 cladding samples by controlling temperature variation and gas flow control during pre-hydriding treatments. Surface conditioning of the outside surface was also examined as a variable. The results of test indicate that much of the variability in the hydride thickness is due to temperature variation occurring in the furnaces as well as how hydrogen gas flows across the sample surface. Efforts to examine other alloys, gas concentrations, and different surface conditioning plan to be pursed in the next FY as more cladding samples become available

Shimskey, Rick W.; Hanson, Brady D.; MacFarlan, Paul J.

2013-09-30

250

Local-spectrum-modified fast reactor cores with hydrides  

SciTech Connect

the application of different hydride materials to core components except for the driver fuel assembly is studied to achieve high core performances for fast reactor by reducing neutron energy and increasing reaction rates locally. The mixtures of absorber materials such as Gd and Zr-hydride are employed to control materials to increase reactivity worth. An optimized composition and layout of the control materials has shown the feature of burnable poison even in the fast reactor where the reaction rate of absorber nuclides is increased enough to annihilate themselves at the end of cycles. The radial blanket made of the mixture of oxide uranium and Zr hydride is examined to decrease the required thickness as well as to achieve a non-proliferation feature in plutonium isotope compositions in discharged fuels. The shielding performance of radial shield made of Zr-hydride is evaluated to decrease the whole core diameter. Special fuel assemblies mixed with minor actinides and Zr-hydride located at the core peripherals are studied to transmute the minor actinides to fissionable materials effectively. The results has indicates that the application of the hydride materials will increase the core performances twice or triple in general. (authors)

Tsugio, Yokoyama [Aitel Corporation, 8 Shinsugita-cho, Isogo-ku, Yokohama, 235-8523 (Japan); Kenji, Konashi [Institute for Materials Research, Tohoku University, Oarai, Ibaraki-ken, 311-1313 (Japan); Tomohiko, Iwasaki [Department of Quantum Science and Energy Engineering, Tohoku Universiyt, Aoba 6-6-01-2, Aramaki, Aoba-ku, Sendai, 980-8579 (Japan); Takayuki, Terai [Department of Nuclear Engineering and Management, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8656 (Japan); Michio, Yamawaki [Department of Applied Science, Tokai University, 1117 Kitakaname, Hiratsuka, Kanagawa 259- 1292 (Japan)

2006-07-01

251

Trialkylborane-Assisted CO2 Reduction by Late Transition Metal Hydrides  

PubMed Central

Trialkylborane additives promote reduction of CO2 to formate by bis(diphosphine) Ni(II) and Rh(III) hydride complexes. The late transition metal hydrides, which can be formed from dihydrogen, transfer hydride to CO2 to give a formate-borane adduct. The borane must be of appropriate Lewis acidity: weaker acids do not show significant hydride transfer enhancement, while stronger acids abstract hydride without CO2 reduction. The mechanism likely involves a pre-equilibrium hydride transfer followed by formation of a stabilizing formate-borane adduct. PMID:21909178

Miller, Alexander J. M.; Labinger, Jay A.; Bercaw, John E.

2011-01-01

252

Spectrophotometric determination of iridium after flotation of ion-associates formed in iridium(III)-tin(II)-chloride-malachite green- or crystal violet systems  

Microsoft Academic Search

Summary The conditions for the formation of iridium(III) ion associates with tin(II) and basic dyes, Malachite Green (MG) and Crystal Violet (CV), in the medium of hydrochloric acid, and their flotation with organic solvents have been examined. The effect of the light on the formation of these ion associates has been observed. Floated compounds, dissolved in polar solvents (methanol, dimethyl

Zygmunt Marczenko; Krzysztof Kalinowski

1983-01-01

253

IEEE SENSORS JOURNAL, VOL. 13, NO. 10, OCTOBER 2013 3857 Sol-Gel Iridium Oxide-Based pH Sensor Array on  

E-print Network

IEEE SENSORS JOURNAL, VOL. 13, NO. 10, OCTOBER 2013 3857 Sol-Gel Iridium Oxide-Based pH Sensor, Mu Chiao, and Jung-Chih Chiao Abstract--Iridium oxide pH sensing film is demonstrated with wide p and less labor-intensive method, to deposit iridium oxide thin films for pH sensing is reported previously

Chiao, Jung-Chih

254

Modulating the luminescence of an iridium(III) complex incorporating a di(2-picolyl)anilino-appended bipyridine ligand with Zn2+  

E-print Network

Modulating the luminescence of an iridium(III) complex incorporating a di(2-picolyl as an Advance Article on the web 1st December 2009 DOI: 10.1039/b9nj00515c A novel iridium complex incorporating and emission, and a shorter luminescence lifetime. Cyclometallated iridium(III) complexes are well known

Boyer, Edmond

255

Influence of uranium hydride oxidation on uranium metal behaviour  

SciTech Connect

This work addresses concerns that the rapid, exothermic oxidation of active uranium hydride in air could stimulate an exothermic reaction (burning) involving any adjacent uranium metal, so as to increase the potential hazard arising from a hydride reaction. The effect of the thermal reaction of active uranium hydride, especially in contact with uranium metal, does not increase in proportion with hydride mass, particularly when considering large quantities of hydride. Whether uranium metal continues to burn in the long term is a function of the uranium metal and its surroundings. The source of the initial heat input to the uranium, if sufficient to cause ignition, is not important. Sustained burning of uranium requires the rate of heat generation to be sufficient to offset the total rate of heat loss so as to maintain an elevated temperature. For dense uranium, this is very difficult to achieve in naturally occurring circumstances. Areas of the uranium surface can lose heat but not generate heat. Heat can be lost by conduction, through contact with other materials, and by convection and radiation, e.g. from areas where the uranium surface is covered with a layer of oxidised material, such as burned-out hydride or from fuel cladding. These rates of heat loss are highly significant in relation to the rate of heat generation by sustained oxidation of uranium in air. Finite volume modelling has been used to examine the behaviour of a magnesium-clad uranium metal fuel element within a bottle surrounded by other un-bottled fuel elements. In the event that the bottle is breached, suddenly, in air, it can be concluded that the bulk uranium metal oxidation reaction will not reach a self-sustaining level and the mass of uranium oxidised will likely to be small in relation to mass of uranium hydride oxidised. (authors)

Patel, N.; Hambley, D. [National Nuclear Laboratory (United Kingdom); Clarke, S.A. [Sellafield Ltd (United Kingdom); Simpson, K.

2013-07-01

256

Evaluation of oxide-coated iridium-rhenium chambers  

NASA Technical Reports Server (NTRS)

Iridium-coated rhenium (Ir-Re) provides long life operation of radiation-cooled rockets at temperatures up to 2200 C. Ceramic oxide coatings could be used to increase Ir-Re rocket lifetimes and allow operation in highly oxidizing environments. Ceramic oxide coatings promise to serve as both thermal and diffusion barriers for the iridium layer. Seven ceramic oxide-coated Ir-Re, 22-N rocket chambers were tested with gaseous hydrogen/gaseous oxygen (GHz/G02) propellants. Five chambers had thick (over 10 mils), monolithic coatings of either hafnia (HfO2) or zirconia (ZrO2). Two chambers had coatings with thicknesses less than 5 mils. One of these chambers had a thin-walled coating of ZrO2 infiltrated with sol gel HfO2. The other chamber had a coating composed of an Ir-oxide composite. The purpose of this test program was to assess the ability of the oxide coatings to withstand the thermal shock of combustion initiation, adhere under repeated thermal cycling, and operate in aggressively oxidizing environments. All of the coatings survived the thermal shock of combustion and demonstrated operation at mixture ratios up to 11. Testing the Ir-oxide composite-coated chamber included over 29 min at mixture ratio 16. The thicker walled coatings provided the larger temperature drops across the oxide layer (up to 570 C), but were susceptible to macrocracking and eventual chipping at a stress concentrator. The cracks apparently resealed during firing, under compression of the oxide layer. The thinner walled coatings did not experience the macrocracking and chipping of the chambers that was seen with the thick, monolithic coatings. However, burn-throughs in the throat region did occur in both of the thin-walled chambers at mixture ratios well above stoichiometric. The burn-throughs were probably the result of oxygen diffusion through the oxide coating that allowed the underlying Ir and Re layers to be oxidized. The results of this test program indicated that the thin-walled oxide coatings are better suited for repeated thermal cycling than the thick-walled coating, while thicker coatings may be required for operation in aggressively oxidizing environments.

Reed, Brian D.

1994-01-01

257

Design, analysis, and fabrication of oxide-coated iridium/rhenium combustion chambers  

NASA Technical Reports Server (NTRS)

Iridium-coated rhenium (Ir/Re) combustion chambers provide high temperature, oxidation-resistant operation for radiation-cooled liquid-fueled rocket engines. A 22-N (5-lb(sub f)) chamber has been operated for 15 hours at 2200 C (4000 F) using nitrogen tetroxide/monomethyl hydrazine (NTO/MMH) propellant, with negligible internal erosion. The oxidation resistance of these chambers could be further increased by the addition of refractory oxide coatings, providing longer life and/or operation in more oxidizing and higher temperature environments. The oxide coatings would serve as a thermal and diffusion barrier for the iridium coating, lowering the temperature of the iridium layer while also preventing the ingress of oxygen and egress of iridium oxides. This would serve to slow the failure mechanisms of Ir/Re chambers, namely the diffusion of rhenium to the inner surface and the oxidation of iridium. Such protection could extend chamber lifetimes by tens or perhaps hundreds of hours, and allow chamber operation on stoichiometric or higher mixture ratio oxygen/hydrogen (O2/H2) propellant. Extensive thermomechanical, thermochemical, and mass transport modeling was performed as a key material/structure design tool. Based on the results of these analyses, several 22-N oxide-coated Ir/Re chambers were fabricated and delivered to NASA Lewis Research Center for hot-fire testing.

Jang, Q.; Tuffias, R. H.; Laferla, R.; Ghoniem, N. M.

1993-01-01

258

Design, analysis, and fabrication of oxide-coated iridium/rhenium combustion chambers  

NASA Astrophysics Data System (ADS)

Iridium-coated rhenium (Ir/Re) combustion chambers provide high temperature, oxidation-resistant operation for radiation-cooled liquid-fueled rocket engines. A 22-N (5-lb(sub f)) chamber has been operated for 15 hours at 2200 C (4000 F) using nitrogen tetroxide/monomethyl hydrazine (NTO/MMH) propellant, with negligible internal erosion. The oxidation resistance of these chambers could be further increased by the addition of refractory oxide coatings, providing longer life and/or operation in more oxidizing and higher temperature environments. The oxide coatings would serve as a thermal and diffusion barrier for the iridium coating, lowering the temperature of the iridium layer while also preventing the ingress of oxygen and egress of iridium oxides. This would serve to slow the failure mechanisms of Ir/Re chambers, namely the diffusion of rhenium to the inner surface and the oxidation of iridium. Such protection could extend chamber lifetimes by tens or perhaps hundreds of hours, and allow chamber operation on stoichiometric or higher mixture ratio oxygen/hydrogen (O2/H2) propellant. Extensive thermomechanical, thermochemical, and mass transport modeling was performed as a key material/structure design tool. Based on the results of these analyses, several 22-N oxide-coated Ir/Re chambers were fabricated and delivered to NASA Lewis Research Center for hot-fire testing.

Jang, Q.; Tuffias, R. H.; Laferla, R.; Ghoniem, N. M.

1993-11-01

259

CRYSTALLOGRAPHIC PROPERTIES AND MECHANICAL BEHAVIOR OF TITANIUM HYDRIDE LAYERS GROWN ON TITANIUM IMPLANTS  

E-print Network

CRYSTALLOGRAPHIC PROPERTIES AND MECHANICAL BEHAVIOR OF TITANIUM HYDRIDE LAYERS GROWN ON TITANIUM, Switzerland Keywords: SLA treated titanium - bone-anchored dental implants - transmission and scanning electron microscopy - titanium hydride sub-surface layer - epitaxy Abstract Commercially pure titanium

Paris-Sud XI, Université de

260

Synthesis and small molecule chemistry of the niobaziridine-hydride functional group  

E-print Network

Chapter 1. Synthesis and Divergent Reactivity of the Niobaziridine-Hydride Functional Group The synthesis, characterization and reactivity of the niobaziridine-hydride complex Nb(H)([eta]²-t- ]Bu(H)C=NAr)(N[Np]Ar)? (la-H; ...

Figueroa, Joshua S

2005-01-01

261

PREPRINT submitted to Journal of Physics B Electronic structure of the Magnesium hydride  

E-print Network

PREPRINT submitted to Journal of Physics B Electronic structure of the Magnesium hydride molecular: 31.15.AR,31.15.Ct,31.50.Be,31.50.Df #12; Electronic structure of the Magnesium hydride molecular ion

Recanati, Catherine

262

Comparison of the interactions in the rare gas hydride and Group 2 metal hydride anions  

NASA Astrophysics Data System (ADS)

We study both the rare gas hydride anions, RG-H- (RG = He-Rn) and Group 2 (Group IIa) metal hydride anions, MIIaH- (MIIa = Be-Ra), calculating potential energy curves at the CCSD(T) level with augmented quadruple and quintuple basis sets, and extrapolating the results to the basis set limit. We report spectroscopic parameters obtained from these curves; additionally, we study the Be-He complex. While the RG-H- and Be-He species are weakly bound, we show that, as with the previously studied BeH- and MgH- species, the other MIIaH- species are strongly bound, despite the interactions nominally also being between two closed shell species: M(ns2) and H-(1s2). We gain insight into the interactions using contour plots of the electron density changes and population analyses. For both series, the calculated dissociation energy is significantly less than the ion/induced-dipole attraction term, confirming that electron repulsion is important in these species; this effect is more dramatic for the MIIaH- species than for RG-H-. Our analyses lead us to conclude that the stronger interaction in the case of the MIIaH- species arises from sp and spd hybridization, which allows electron density on the MIIa atom to move away from the incoming H-.

Harris, Joe P.; Manship, Daniel R.; Breckenridge, W. H.; Wright, Timothy G.

2014-02-01

263

Chinese puzzle molecule: a 15?hydride, 28?copper atom nanoball.  

PubMed

The syntheses of the first rhombicuboctahedral copper polyhydride complexes [Cu28 (H)15 (S2 CNR)12 ]PF6 (NR=N(n) Pr2 or aza-15-crown-5) are reported. These complexes were analyzed by single-crystal X-ray and one by neutron diffraction. The core of each copper hydride nanoparticle comprises one central interstitial hydride and eight outer-triangular-face-capping hydrides. A further six face-truncating hydrides form an unprecedented bridge between the inner and outer copper atom arrays. The irregular inner Cu4 tetrahedron is encapsulated within the Cu24 rhombicuboctahedral cage, which is further enclosed by an array of twelve dithiocarbamate ligands that subtends the truncated octahedron of 24?sulfur atoms, which is concentric with the Cu24 rhombicuboctahedron and Cu4 tetrahedron about the innermost hydride. For these compounds, an intriguing, albeit limited, H2 evolution was observed at room temperature, which is accompanied by formation of the known ion [Cu8 (H)(S2 CNR)6 ](+) upon exposure of solutions to sunlight, under mild thermolytic conditions, and on reaction with weak (or strong) acids. PMID:24803070

Edwards, Alison J; Dhayal, Rajendra S; Liao, Ping-Kuei; Liao, Jian-Hong; Chiang, Ming-Hsi; Piltz, Ross O; Kahlal, Samia; Saillard, Jean-Yves; Liu, C W

2014-07-01

264

Synthesis and structure of iridium complex with thiocarbamide  

SciTech Connect

A single crystal of the [Ir(Thio){sub 2}Cl{sub 4}][Ir(Thio){sub 4}Cl{sub 2}] compound synthesized by the reaction of K{sub 3}[IrCl{sub 6}] with thiocarbamide (Thio, SC(NH{sub 2}){sub 2}) in a microwave field is investigated using X-ray diffraction. The compound crystallizes in the monoclinic crystal system with space group Cc(C{sub s}{sup 4}). The unit cell parameters are as follows: a = 13.554(1) A, b = 8.251(1) A, c = 24.992(2) A, {beta} = 92.58(1){sup o}, V = 2791.87(10) A{sup 3}, and Z = 4. The compound has an island structure with two crystallographically independent iridium atoms. Thiocarbamide is coordinated to the central atom through the sulfur atom. The coordination sphere of the Ir(1) atom involves two Cl atoms and four S atoms, whereas the coordination sphere of the Ir(2) atom consists of four Cl atoms and two S atoms. The assignment of the bands in the IR absorption spectrum of the synthesized compound is presented. The thermal behavior of the compound in air is investigated.

Buslaeva, T. M., E-mail: buslaevatm@mail.ru; Kravchenko, V. V.; Kopylova, E. V.; Kashiricheva, I. I. [Lomonosov Moscow State Academy of Fine Chemical Technology (Russian Federation); Alekseeva, O. A.; Kazantsev, S. S. [Russian Academy of Sciences, Shubnikov Institute of Crystallography (Russian Federation)

2008-09-15

265

High Strain Rate Tensile Testing of DOP-26 Iridium  

SciTech Connect

The iridium alloy DOP-26 was developed through the Radioisotope Power Systems Program in the Office of Nuclear Energy of the Department of Energy. It is used for clad vent set cups containing radioactive fuel in radioisotope thermoelectric generator (RTG) heat sources which provide electric power for spacecraft. This report describes mechanical testing results for DOP-26. Specimens were given a vacuum recrystallization anneal of 1 hour at 1375 C and tested in tension in orientations parallel and perpendicular to the rolling direction of the sheet from which they were fabricated. The tests were performed at temperatures ranging from room temperature to 1090 C and strain rates ranging from 1 x 10{sup -3} to 50 s{sup -1}. Room temperature testing was performed in air, while testing at elevated temperatures was performed in a vacuum better than 1 x 10{sup -4} Torr. The yield stress (YS) and the ultimate tensile stress (UTS) decreased with increasing temperature and increased with increasing strain rate. Between 600 and 1090 C, the ductility showed a slight increase with increasing temperature. Within the scatter of the data, the ductility did not depend on the strain rate. The reduction in area (RA), on the other hand, decreased with increasing strain rate. The YS and UTS values did not differ significantly for the longitudinal and transverse specimens. The ductility and RA values of the transverse specimens were marginally lower than those of the longitudinal specimens.

Schneibel, Joachim H [ORNL; Carmichael Jr, Cecil Albert [ORNL; George, Easo P [ORNL

2007-11-01

266

Formation, phase analysis and properties of iridium containing perovskite  

SciTech Connect

Perovskite-type oxide Sr{sub 1.3}La{sub 0.7}MnIrO{sub 6} has been synthesized by solid-state reaction in air at various temperatures and structurally characterized by Rietveld refinement of powder X-ray diffraction data. The structure synthesized at 1473K shows orthorhombic symmetry (S.G. Pnma), whereas that synthesized at 1623K shows cubic symmetry (S.G. Pm3-bar m). For the orthorhombic Sr{sub 1.3}La{sub 0.7}MnIrO{sub 6}, the structural phase transition from orthorhombic to cubic was observed near 773K by the high temperature X-ray diffractometry. The electrical conductivity measurement shows semiconducting property above room temperature for both the phases. Breaking of slope in the temperature dependence of the conductivity brings evidence in support of the phase transition for orthorhombic Sr{sub 1.3}La{sub 0.7}MnIrO{sub 6}. At low temperature, the compounds show ferromagnetic behavior. Magnetic susceptibility data show that both the compounds obey Curie-Weiss law in the high temperature region with the effective magnetic moment consistent with an oxidation state of +3 for manganese and +4 for iridium.

Haque, Md. Tahidul [Department of Materials Science, Toyohashi University of Technology, Tempaku-cho, Toyohashi 441-8580 (Japan); Satoh, Hirohisa [Department of Materials Science, Toyohashi University of Technology, Tempaku-cho, Toyohashi 441-8580 (Japan); Kamegashira, Naoki [Department of Materials Science, Toyohashi University of Technology, Tempaku-cho, Toyohashi 441-8580 (Japan)]. E-mail: nkamegas@tutms.tut.ac.jp

2004-12-02

267

STANDARDIZED TESTING PROGRAM FOR EMERGENT CHEMICAL HYDRIDE AND CARBON STORAGE TECHNOLOGIES  

E-print Network

hydride and carbon nanotube systems to date fall slightly short of the DOE energy density goals of 6STANDARDIZED TESTING PROGRAM FOR EMERGENT CHEMICAL HYDRIDE AND CARBON STORAGE TECHNOLOGIES Richard hydride/carbon hydrogen storage systems. The development of a standardized protocol and testing system

268

Investigation of metal hydride materials as hydrogen reservoirs for metal-hydrogen batteries  

NASA Technical Reports Server (NTRS)

The performance and suitability of various metal hydride materials were examined for use as possible hydrogen storage reservoirs for secondary metal-hydrogen batteries. Lanthanum pentanickel hydride appears as a probable candidate in terms of stable hydrogen supply under feasible thermal conditions. A kinetic model describing the decomposition rate data of the hydride has been developed.

ONISCHAK

1976-01-01

269

Hydrogen storage systems based on hydride materials with enhanced thermal conductivity  

Microsoft Academic Search

The reaction of hydrogen gas with a metal to form a metal hydride is exothermic. If the heat released is not removed from the system, the resulting temperature rise of the hydride will reduce the hydrogen absorption rate. Hence, hydrogen storage systems based on hydride materials must include a way to remove the heat generated during the absorption process. The

Hui Wang; Ajay K. Prasad; Suresh G. Advani

270

CO2 hydrogenation on a metal hydride surface.  

PubMed

The catalytic hydrogenation of CO(2) at the surface of a metal hydride and the corresponding surface segregation were investigated. The surface processes on Mg(2)NiH(4) were analyzed by in situ X-ray photoelectron spectroscopy (XPS) combined with thermal desorption spectroscopy (TDS) and mass spectrometry (MS), and time-of-flight secondary ion mass spectrometry (ToF-SIMS). CO(2) hydrogenation on the hydride surface during hydrogen desorption was analyzed by catalytic activity measurement with a flow reactor, a gas chromatograph (GC) and MS. We conclude that for the CO(2) methanation reaction, the dissociation of H(2) molecules at the surface is not the rate controlling step but the dissociative adsorption of CO(2) molecules on the hydride surface. PMID:22433948

Kato, Shunsuke; Borgschulte, Andreas; Ferri, Davide; Bielmann, Michael; Crivello, Jean-Claude; Wiedenmann, Daniel; Parlinska-Wojtan, Magdalena; Rossbach, Peggy; Lu, Ye; Remhof, Arndt; Züttel, Andreas

2012-04-28

271

Composite Materials for Hazard Mitigation of Reactive Metal Hydrides.  

SciTech Connect

In an attempt to mitigate the hazards associated with storing large quantities of reactive metal hydrides, polymer composite materials were synthesized and tested under simulated usage and accident conditions. The composites were made by polymerizing vinyl monomers using free-radical polymerization chemistry, in the presence of the metal hydride. Composites with vinyl-containing siloxane oligomers were also polymerized with and without added styrene and divinyl benzene. Hydrogen capacity measurements revealed that addition of the polymer to the metal hydride reduced the inherent hydrogen storage capacity of the material. The composites were found to be initially effective at reducing the amount of heat released during oxidation. However, upon cycling the composites, the mitigating behavior was lost. While the polymer composites we investigated have mitigating potential and are physically robust, they undergo a chemical change upon cycling that makes them subsequently ineffective at mitigating heat release upon oxidation of the metal hydride. Acknowledgements The authors would like to thank the following people who participated in this project: Ned Stetson (U.S. Department of Energy) for sponsorship and support of the project. Ken Stewart (Sandia) for building the flow-through calorimeter and cycling test stations. Isidro Ruvalcaba, Jr. (Sandia) for qualitative experiments on the interaction of sodium alanate with water. Terry Johnson (Sandia) for sharing his expertise and knowledge of metal hydrides, and sodium alanate in particular. Marcina Moreno (Sandia) for programmatic assistance. John Khalil (United Technologies Research Corp) for insight into the hazards of reactive metal hydrides and real-world accident scenario experiments. Summary In an attempt to mitigate and/or manage hazards associated with storing bulk quantities of reactive metal hydrides, polymer composite materials (a mixture of a mitigating polymer and a metal hydride) were synthesized and tested under simulated usage and accident conditions. Mitigating the hazards associated with reactive metal hydrides during an accident while finding a way to keep the original capability of the active material intact during normal use has been the focus of this work. These composites were made by polymerizing vinyl monomers using free-radical polymerization chemistry, in the presence of the metal hydride, in this case a prepared sodium alanate (chosen as a representative reactive metal hydride). It was found that the polymerization of styrene and divinyl benzene could be initiated using AIBN in toluene at 70 degC. The resulting composite materials can be either hard or brittle solids depending on the cross-linking density. Thermal decomposition of these styrene-based composite materials is lower than neat polystyrene indicating that the chemical nature of the polymer is affected by the formation of the composite. The char-forming nature of cross-linked polystyrene is low and therefore, not an ideal polymer for hazard mitigation. To obtain composite materials containing a polymer with higher char-forming potential, siloxane-based monomers were investigated. Four vinyl-containing siloxane oligomers were polymerized with and without added styrene and divinyl benzene. Like the styrene materials, these composite materials exhibited thermal decomposition behavior significantly different than the neat polymers. Specifically, the thermal decomposition temperature was shifted approximately 100 degC lower than the neat polymer signifying a major chemical change to the polymer network. Thermal analysis of the cycled samples was performed on the siloxane-based composite materials. It was found that after 30 cycles the siloxane-containing polymer composite material has similar TGA/DSC-MS traces as the virgin composite material indicating that the polymer is physically intact upon cycling. Hydrogen capacity measurements revealed that addition of the polymer to the metal hydride in the form of a composite material reduced the inherent hydrogen storage capacity of the material. This

Pratt, Joseph William; Cordaro, Joseph Gabriel; Sartor, George B.; Dedrick, Daniel E.; Reeder, Craig L.

2012-02-01

272

A nickel metal hydride battery for electric vehicles  

NASA Astrophysics Data System (ADS)

An efficient battery is the key technological element to the development of practical electric vehicles. The science and technology of a nickel metal hydride battery, which stores hydrogen in the solid hydride phase and has high energy density, high power, long life, tolerance to abuse, a wide range of operating temperature, quick-charge capability, and totally sealed maintenance-free operation, is described. A broad range of multi-element metal hydride materials that use structural and compositional disorder on several scales of length has been engineered for use as the negative electrode in this battery. The battery operates at ambient temperature, is made of nontoxic materials, and is recyclable. Demonstration of the manufacturing technology has been achieved.

Ovshinsky, S. R.; Fetcenko, M. A.; Ross, J.

1993-04-01

273

Comparative Investigation of Iridium Coating Electrodeposited on Molybdenum, Rhenium and C/C Composite Substrates in Molten Salt in the Air Atmosphere  

NASA Astrophysics Data System (ADS)

Iridium coatings were prepared on molybdenum, rhenium and C/C composite substrates by electrodeposition in molten salt in the air atmosphere, respectively. The iridium coatings on both the molybdenum and C/C substrate are defective and the adhesion is quite poor, while the iridium coating on rhenium substrate is adhesive and compact without any defects. The microscopic surface morphologies of the iridium coatings obtained on different substrates appear highly similar. The preferred growth directions of the iridium coatings on the rhenium and C/C composite substrates are <111> and <311>, respectively, while the iridium coating on molybdenum substrate has a polycrystalline structure without a certain preferred orientation. The adhesion and surface quality differences of iridium coating obtained on the various substrates arise from different corrosion behaviors in molten salt in the air atmosphere and surface characteristics of the various substrates.

Zhu, Li'an; Bai, Shuxin; Zhang, Hong; Ye, Yicong; Tong, Yonggang

274

Electronic structure and optical properties of lightweight metal hydrides  

Microsoft Academic Search

We study the dielectric functions of the series of simple hydrides LiH, NaH, MgH2 , and AlH3 , and of the complex hydrides Li3AlH6 , Na3AlH6 , LiAlH4 , NaAlH4 , and Mg(AlH4)2 , using first-principles density-functional theory and GW calculations. All compounds are large gap insulators with GW single-particle band gaps varying from 3.5eV in AlH3 to 6.6eV in

M. J. van Setten; V. A. Popa; G. A. de Wijs; G. Brocks

2007-01-01

275

Photoelectron spectroscopy of boron aluminum hydride cluster anions.  

PubMed

Boron aluminum hydride clusters are studied through a synergetic combination of anion photoelectron spectroscopy and density functional theory based calculations. Boron aluminum hydride cluster anions, BxAlyHz(-), were generated in a pulsed arc cluster ionization source and identified by time-of-flight mass spectrometry. After mass selection, their photoelectron spectra were measured by a magnetic bottle-type electron energy analyzer. The resultant photoelectron spectra as well as calculations on a selected series of stoichiometries reveal significant geometrical changes upon substitution of aluminum atoms by boron atoms. PMID:24784280

Wang, Haopeng; Zhang, Xinxing; Ko, Yeon Jae; Gantefoer, Gerd; Bowen, Kit H; Li, Xiang; Kiran, Boggavarapu; Kandalam, Anil K

2014-04-28

276

Photoelectron spectroscopy of boron aluminum hydride cluster anions  

SciTech Connect

Boron aluminum hydride clusters are studied through a synergetic combination of anion photoelectron spectroscopy and density functional theory based calculations. Boron aluminum hydride cluster anions, B{sub x}Al{sub y}H{sub z}{sup ?}, were generated in a pulsed arc cluster ionization source and identified by time-of-flight mass spectrometry. After mass selection, their photoelectron spectra were measured by a magnetic bottle-type electron energy analyzer. The resultant photoelectron spectra as well as calculations on a selected series of stoichiometries reveal significant geometrical changes upon substitution of aluminum atoms by boron atoms.

Wang, Haopeng; Zhang, Xinxing; Ko, Yeon Jae; Gantefoer, Gerd; Bowen, Kit H., E-mail: kbowen@jhu.edu, E-mail: kiran@mcneese.edu [Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218 (United States); Li, Xiang [Center for Space Science and Technology, University of Maryland–Baltimore County, Baltimore, Maryland 21250 (United States)] [Center for Space Science and Technology, University of Maryland–Baltimore County, Baltimore, Maryland 21250 (United States); Kiran, Boggavarapu, E-mail: kbowen@jhu.edu, E-mail: kiran@mcneese.edu [Department of Chemistry and Physics, McNeese State University, Lake Charles, Louisiana 70609 (United States)] [Department of Chemistry and Physics, McNeese State University, Lake Charles, Louisiana 70609 (United States); Kandalam, Anil K. [Department of Physics, West Chester University, West Chester, Pennsylvania 19383 (United States)] [Department of Physics, West Chester University, West Chester, Pennsylvania 19383 (United States)

2014-04-28

277

Materials science of Mg-Ni-based new hydrides  

Microsoft Academic Search

.   One of the advantageous functional properties of Mg alloys (or compounds) is to exhibit the reversible hydriding reaction.\\u000a In this paper, we present our systematic studies regarding the relationship between nanometer- or atomistic-scale structures\\u000a and the specific hydriding properties of the Mg-Ni binary system, such as(1) nanostructured (n)-Mg2Ni, (2) a mixture of n-Mg2Ni and amorphous (a)-MgNi,(3) pure a-MgNi, and(4)

S. Orimo; H. Fujii

2001-01-01

278

Method for preparing hydride configurations and reactive metal surfaces  

DOEpatents

A method for preparing reactive metal surfaces, particularly uranium surfaces is disclosed, whereby the metal is immediately reactive to hydrogen gas at room temperature and low pressure. The metal surfaces are first pretreated by exposure to an acid which forms an adherent hydride-bearing composition on the metal surface. Subsequent heating of the pretreated metal at a temperature sufficient to decompose the hydride coating in vacuum or inert gas renders the metal surface instantaneously reactive to hydrogen gas at room temperature and low pressure.

Silver, G.L.

1984-05-18

279

Ab-initio study of transition metal hydrides  

SciTech Connect

We have performed ab initio self consistent calculations based on Full potential linearized augmented plane wave (FP-LAPW) method to investigate the optical and thermal properties of yttrium hydrides. From the band structure and density of states, the optical absorption spectra and specific heats have been calculated. The band structure of Yttrium metal changes dramatically due to hybridization of Y sp orbitals with H s orbitals and there is a net charge transfer from metal to hydrogen site. The electrical resistivity and specific heats of yttrium hydrides are lowered but the thermal conductivity is slightly enhanced due to increase in scattering from hydrogen sites.

Sharma, Ramesh [Dept. of Physics, Feroze Gandhi Insititute of Engineering and Technology, Raebareli-229001 (India); Shukla, Seema, E-mail: sharma.yamini62@gmail.com; Dwivedi, Shalini, E-mail: sharma.yamini62@gmail.com; Sharma, Yamini, E-mail: sharma.yamini62@gmail.com [Theoretical Condensed Matter Physics Laboratory, Dept. of Physics Feroze Gandhi College, Raebareli-229001 (India)

2014-04-24

280

OBSERVATION AND MECHANISM OF HYDRIDE IN ZIRCALOY-4 AND LOCAL HYDRIDE RE-ORIENTATION INDUCED BY HIGH PRESSURE AT HIGH TEMPERATURES  

SciTech Connect

Hydrided Zircaloy-4 samples were produced by a gas charging method to desired amounts of hydrogen. For low hydrogen content samples, the hydrided platelets appear elongated and needle-like, orientated in the circumferential direction. Mechanical testing was carried out by the ring compression method at various temperatures. Samples with higher hydrogen concentration resulted in lower strain before fracture and reduced maximum load. The trend between temperature and ductility was also very clear: increasing temperatures resulted in increased ductility of the hydrided cladding. A single through-wall crack was observed for a hydrided sample having very high hydrogen concentration under ring compression testing. For samples having lower hydrogen concentrations, the fracture surfaces traversed both circumferential and radial directions, and for which voids were observed near the hydrides. Mechanical tests to study hydride reorientation in these samples are under way, and the results will be reported in the near future.

Yan, Yong [ORNL] [ORNL; Blackwell, Andrew S [ORNL] [ORNL; Plummer, Lee K [ORNL] [ORNL; Radhakrishnan, Balasubramaniam [ORNL] [ORNL; Gorti, Sarma B [ORNL] [ORNL; Clarno, Kevin T [ORNL] [ORNL

2013-01-01

281

Hydrogen storage in metal hydrides. Final report, September 1989-March 1990  

SciTech Connect

The primary objective of this program was to develop an economical process for producing a lightweight hydrogen storage medium by the chemical vapor inflitration (CVI) of a metal hydride former into a reticulated foam substrate. An investigation was conducted to determine the most favorable precursors for forming the candidate hydride-forming materials, along with optimization of their transport and deposition parameters. A substrate optimization study was also performed in order to derive the greatest surface area-to-volume ratio from the resulting metal hydride-forming foam. Thermogravimetric analysis (TGA) was performed on a metal foam sample to determine its hydriding capability. Results were inconclusive, showing only slight if any hydriding.

DelaRosa, M.J.

1990-08-01

282

Comparison of the interactions in the rare gas hydride and Group 2 metal hydride anions  

SciTech Connect

We study both the rare gas hydride anions, RG–H{sup ?} (RG = He–Rn) and Group 2 (Group IIa) metal hydride anions, M{sub IIa}H{sup ?} (M{sub IIa} = Be–Ra), calculating potential energy curves at the CCSD(T) level with augmented quadruple and quintuple basis sets, and extrapolating the results to the basis set limit. We report spectroscopic parameters obtained from these curves; additionally, we study the Be–He complex. While the RG–H{sup ?} and Be–He species are weakly bound, we show that, as with the previously studied BeH{sup ?} and MgH{sup ?} species, the other M{sub IIa}H{sup ?} species are strongly bound, despite the interactions nominally also being between two closed shell species: M(ns{sup 2}) and H{sup ?}(1s{sup 2}). We gain insight into the interactions using contour plots of the electron density changes and population analyses. For both series, the calculated dissociation energy is significantly less than the ion/induced-dipole attraction term, confirming that electron repulsion is important in these species; this effect is more dramatic for the M{sub IIa}H{sup ?} species than for RG–H{sup ?}. Our analyses lead us to conclude that the stronger interaction in the case of the M{sub IIa}H{sup ?} species arises from sp and spd hybridization, which allows electron density on the M{sub IIa} atom to move away from the incoming H{sup ?}.

Harris, Joe P.; Manship, Daniel R.; Wright, Timothy G., E-mail: Tim.Wright@nottingham.ac.uk [School of Chemistry, University of Nottingham, University Park, Nottingham NG7 2RD (United Kingdom); Breckenridge, W. H. [Department of Chemistry, University of Utah, Salt Lake City, Utah 84112 (United States)] [Department of Chemistry, University of Utah, Salt Lake City, Utah 84112 (United States)

2014-02-28

283

The influence of hydride on fracture toughness of recrystallized Zircaloy-4 cladding  

NASA Astrophysics Data System (ADS)

In this work, RXA cladding tubes were hydrogen-charged to target hydrogen content levels between 150 and 800 wppm (part per million by weight). The strings of zirconium hydrides observed in the cross sections are mostly oriented in the circumferential direction. The fracture toughness of hydrided RXA Zircaloy-4 cladding was measured to evaluate its hydride embrittlement susceptibility. With increasing hydrogen content, the fracture toughness of hydrided RXA cladding decreases at both 25 °C and 300 °C. Moreover, highly localized hydrides (forming a hydride rim) aggravate the degradation of the fracture properties of RXA Zircaloy-4 cladding at both 25 °C and 300 °C. Brittle features in the form of quasi-cleavages and secondary cracks were observed on the fracture surface of the hydride rim, even for RXA cladding tested at 300 °C.

Hsu, Hsiao-Hung; Chiang, Ming-Feng; Chen, Yen-Chen

2014-04-01

284

Hyperfine structure and Stark effect in the [18.0] 4 - X3?4 transition of iridium hydride, IrH and [18.2] 4 - X3?4 transition of iridium deuteride, IrD  

NASA Astrophysics Data System (ADS)

High resolution spectra of IrH and IrD, with full width at half maximum (FWHM) of ?0.001 cm-1, have shown well resolved hyperfine structure due to the nuclear spin, I = 3/2, of 193Ir and 191Ir. Analysis of the hyperfine structure in the [18.2] 4 - X3?4 transition of 193IrD and 191IrD yielded well defined magnetic and quadrupole Ir hyperfine parameters which showed that the ground X3?4 state originates predominantly from the two open-shell Ir(5d?35d?3) configuration with a significant contribution from the four open-shell Ir(5d?5d?35d?36s?) configuration. Examination of the Stark effect in the [18.0] 4 - X3?4 transition of 193IrH yielded electric dipole moments of 1.23(1) D and 0.76(1) D for the ground and excited states, respectively. The hyperfine constants and the dipole moment of the ground state are seen to follow the trend shown by the isovalent molecules, CoF, CoH and IrF.

Linton, C.; Granger, A. D.; Adam, A. G.; Steimle, T. C.

2014-10-01

285

Hydride formation in a Ni-base superalloy  

NASA Astrophysics Data System (ADS)

X-ray diffraction, optical- and scanning-electron metallographic and microhardness studies have been conducted in pure Ni and a Ni-base alloy (HASTELLOY Alloy C-276) in an effort to determine if hydrides form in the alloy during cathodic charging in the presence of a strong H-recombination poison. The studies indicate that hydrides do form and that the extent of surface damage caused by them is a function of the alloy thermomechanical state. In the annealed alloy, hydrides produce a network of crystallographic cracks. In the 50 pct cold-worked alloy, extensive intergranular blistering and lamellar peeling are observed in addition to the crack network. In the cold-worked and aged alloy, damage similar to, but less extensive than, that of the cold-worked alloy is found. The average depth of damage penetration may be accounted for by the bulk diffusion of H in the alloy. It is not clear whether the observed susceptibility of the cold-worked and aged alloy to H embrittlement can be attributed to hydride formation.

Lunarska-Borowiecka, Ellina; Fiore, Nicholas F.

1981-01-01

286

Hydride generation from the Exide load-leveling cells  

NASA Astrophysics Data System (ADS)

Stibine and arsine evolution from lead-acid cells in a 36-kWh Exide load-leveling module was measured as this module approached 1900 cycles of operation. A gas-collection apparatus enabled us to determine the maximum and average rates for evolution of both toxic hydrides. Hydride generation began once the cell voltage exceeded 2.4 V. The maximum rate for arsine occurred just above 2.5 V and consistently preceded the peak rate for stibine for each sampled cell. The average rates of hydride generation were found to be 175 g/min for stibine and 12.6 g/min for arsine. The former rate proved to be the critical value in determining safe ventilation requirements for cell off-gases. The minimum airflow requirement was calculated to be 340 L/min per cell. Projections for a hypothetical 1-MWh Exide battery without an abatement system indicated that the normal ventilation capacity in the Battery Energy Storage Test facility provides nearly five times the airflow needed for safe hydride removal.

Marr, J. J.; Smaga, J. A.

1987-05-01

287

Process of forming a sol-gel/metal hydride composite  

DOEpatents

An external gelation process is described which produces granules of metal hydride particles contained within a sol-gel matrix. The resulting granules are dimensionally stable and are useful for applications such as hydrogen separation and hydrogen purification. An additional coating technique for strengthening the granules is also provided.

Congdon, James W. (Aiken, SC)

2009-03-17

288

Growth of gallium nitride by hydride vapor-phase epitaxy  

Microsoft Academic Search

This paper reviews the growth of GaN thick films by hydride vapor-phase epitaxy (HVPE). Emphasis is placed on recent developments, including the growth of nondegenerate material, characterization of film properties and suitability of such films for epitaxial device overgrowths. Films up to 74 ?m thick have been deposited on sapphire substrates with no evidence of thermally induced cracking and a

R. J. Molnar; W. Götz; L. T. Romano; N. M. Johnson

1997-01-01

289

Synthesis and optophysical properties of blue-emitting iridium (III) complex bearing oxadiazole-based picolinic acid derivative  

Microsoft Academic Search

An iridium (III) bis[(4,6-difluorophenyl)pyridinato-N, C2][6-(6?-(4?-(5?-phenyl-1?, 3?, 4?-oxadiazole- 2?-yl) phenoxy) hexyloxy picolinate) was synthesized and characterized by 1H NMR and elementary analysis in order to study the effect of ancillary ligand of the oxadiazole-based picolinic acid derivative\\u000a on optophysical properties of its iridium complex, and further to obtain an iridium complex with highly-efficient blue emission.\\u000a The thermal stability, UV absorption and

Zhong-lin Wen; Zheng-yong Hu; Yu Liu; Fang-liang Xiao; Xiao-yun Ma; Mei-xiang Zhu; Wei-guo Zhu

2009-01-01

290

Optimization and electrochemical characterization of RF-sputtered iridium oxide microelectrodes for electrical stimulation  

NASA Astrophysics Data System (ADS)

A reactively sputtered iridium oxide (IrOx) thin film has been developed as electrochemical modification material for microelectrodes to obtain high stability and charge storage capacity (CSC) in functional electrical stimulation. The effect of the oxygen flow and oxygen to argon ratio during sputtering process on the microstructure and electrochemical properties of the IrOx film is characterized. After optimization, the activated IrOx microelectrode shows the highest CSC of 36.15 mC cm-2 at oxygen flow of 25 sccm and oxygen to argon ratio of (2.5:1). Because the deposition process of the reactively sputtered iridium oxide is an exothermic reaction, it is difficult to form film patterning by the lift-off process. The lift-off process was focused on the partially carbonized photoresist (PR) and normal PR. The higher of the carbonization degree of PR reaches, the longer the immersion duration. However, the patterning process of the iridium oxide film becomes feasible when the sputtering pressure is increasing. The experimental results show that the iridium oxide films forms the pattern with the lowest duration of ultrasonic agitation when the deposition pressure is 4.2 Pa and pressure ratio between O2 and Ar pressure is 3:4.

Kang, Xiaoyang; Liu, Jingquan; Tian, Hongchang; Yang, Bin; NuLi, Yanna; Yang, Chunsheng

2014-02-01

291

Anal. Chem. 1993, 65, 375-379 Analytical Utility of the Iridium-Based Mercury  

E-print Network

Anal. Chem. 1993, 65, 375-379 Analytical Utility of the Iridium-Based Mercury over several days use. The applicationof SWASV theory for mercury film electrodes is shown The mercury electrode in ita many forms has been the overwhelmingsubstrate-of-choicefor electrochemistrysince

Kounaves, Samuel P.

292

DOI: 10.1002/adfm.200500523 Amorphous Diphenylaminofluorene-Functionalized Iridium  

E-print Network

- ium,[3] platinum,[4] osmium,[5] and more recently, ruthenium[6] ), IrIII complexes are still the mostDOI: 10.1002/adfm.200500523 Amorphous Diphenylaminofluorene-Functionalized Iridium Complexes on phospho- rescent third-row heavy-metal complexes continue to spark a flurry of research activities

293

Synthesis and characterization of a series of rhodium, iridium, and ruthenium isocyanide complexes  

E-print Network

Synthesis and characterization of a series of rhodium, iridium, and ruthenium isocyanide complexes Ruthenium Isocyanide a b s t r a c t Several new electrophilic metal isocyanide complexes have been fully the correspond- ing complexes with the general formula LM(CNAr)I2. For the analogous ruthenium complexes better

Jones, William D.

294

Sensors and Actuators B 50 (1998) 117124 Failure analysis of microfabricated iridium ultramicroelectrodes in  

E-print Network

Sensors and Actuators B 50 (1998) 117­124 Failure analysis of microfabricated iridium 18 May 1998 Abstract This study investigates the failure mechanisms for an electrochemical sensor wafer. It has been noted that the use of these sensors during voltammetric determination of heavy metal

Kounaves, Samuel P.

295

A pH Sensor Based on a Stainless Steel Electrode Electrodeposited with Iridium Oxide  

ERIC Educational Resources Information Center

A simple procedure to make an iridium oxide (IrO[subscript 2]) electrodeposited pH sensor, that can be used in a chemical, biomedical, or materials laboratory, is presented here. Some exercises, based on this sensor, that can be used to teach important concepts in the field of biomedical, biochemical, tissue, or materials engineering, are also…

Martinez, C. C. M.; Madrid, R. E.; Felice, C. J.

2009-01-01

296

Electrolysis of Molten Iron Oxide with an Iridium Anode: The Role of Electrolyte Basicity  

E-print Network

Electrolysis of Molten Iron Oxide with an Iridium Anode: The Role of Electrolyte Basicity Hojong electrolysis (MOE) is a carbon-free, electrochemical technique to decompose a metal oxide directly into liquid. Electrolysis is being investigated by the steel industry as a carbon-lean route that copes with the potential

Sadoway, Donald Robert

297

Iridium(I) hydroxides in catalysis: rearrangement of allylic alcohols to ketones.  

PubMed

The iridium(I) hydroxide complex [Ir(OH)(COD)(I(i)Pr)] has been shown to be a competent catalyst for the rearrangement of allylic alcohols to ketones. Reactions proceed in short reaction times (1-1.5 h) with microwave heating, in the absence of additives. PMID:25031155

Nelson, David J; Fernández-Salas, José A; Truscott, Byron J; Nolan, Steven P

2014-09-14

298

Syntheses and electronic structures of ?-nitrido bridged pyridine, diimine iridium complexes.  

PubMed

The syntheses and X-ray crystal structures of dinuclear ?-azido and ?-nitrido bridged iridium complexes bearing the pyridine, diimine ligand (PDI) are reported. Their electronic structures and formal oxidation states of the metal centers are analyzed by theoretical and experimental methods, revealing the non-innocence of the PDI and nitrido ligands. PMID:24964384

Angersbach-Bludau, Friedrich; Schulz, Christopher; Schöffel, Julia; Burger, Peter

2014-08-14

299

Tetraphenylborate versus tetraimidazolylborate as counterions for cationic iridium(iii) complexes: enhanced electrochemical stabilities and electroluminescence.  

PubMed

Tetraimidazolylborate is first used as the counterion of two novel ionic iridium complexes, instead of tetraphenylborate. Both the electrochemical stabilities and electroluminescence are sharply improved. Organic light-emitting diodes have been successfully fabricated with a high current efficiency of 9.48 cd A(-1) and a maximum brightness of 5163 cd m(-2). PMID:25437109

Ma, Dongxin; Duan, Lian; Qiu, Yong

2014-12-01

300

An Operational and Performance Overview of the IRIDIUM Low Earth Orbit Satellite System  

Microsoft Academic Search

Today, both the military and commercial sectors are placing an increased emphasis on global communications. This has prompted the development of several low earth orbit satellite systems that promise worldwide connectivity and real-time voice communications. This article provides a tutorial overview of the IRIDIUM low earth orbit satellite system and performance results obtained via simulation. First, it presents an overview

Stephen R. Pratt; Richard A. Raines; Carl E. Fossa Jr.; Michael A. Temple

1999-01-01

301

Determination of platinum and iridium in marine waters, sediments, and organisms  

Microsoft Academic Search

The determination of platinum and iridium at picogram levels in marine samples is based upon an isolation of anionic forms of these elements upon appropriate resins with a subsequent purification by uptake on a single ion exchange bead. All steps are followed by radiotracers, and yields vary between 35 and 90%. Graphite furnace atomic absorption spectrometry is employed as the

Vern. Hodge; Martha. Stallard; Minoru. Koide; Edward D. Goldberg

1986-01-01

302

Potential contributions to space geodesy from the IridiumNEXT constellation  

NASA Astrophysics Data System (ADS)

The IridiumNEXT constellation will soon replace the existing Iridium satellite telecommunication network, with initial launches set to start in 2015. In addition to the primary task of providing global telecommunication services, each IridiumNEXT satellite will also carry a hosted payload that will provide both private and public institutions the opportunity to place an instrument suite on one or all of constellation's satellites. This creates the possibility to gather continuous, global observations of Earth over the entire 15 year projected mission lifetime. Access to such a platform creates the potential to investigate many of Earth's highly dynamic processes at a spatiotemporal resolution that is simply not possible from single-satellite missions. Space geodesy is one the numerous fields that would benefit from such a mission. Precise orbits of the IridiumNEXT satellites derived through an on-board GNSS receiver (plus accelerometers and star cameras) have the potential to observe the large-scale, high-frequency variations in Earth's gravity field at time scales as short as one day. Additional positioning data from ground-based laser ranging stations would help improve the orbit determination, in addition to providing the necessary link to improve estimates of geocenter motion and reference frames. In this presentation, we will analyze the expected geodetic science returns from such a mission and will discuss the instrumental requirements needed to achieve these objectives.

Gunter, B. C.; Encarnação, J.; Ditmar, P.; Klees, R.

2012-12-01

303

The Formal Oxidation States of Iridium Now Run from -III to +IX.  

PubMed

Rarer than a new element: Recently Wang et?al. produced the [(Ir(+IX) )O4 ](+) ion by a pulsed laser vaporization/thermal expansion method and studied it by IR photodissociation spectroscopy. The oxidation state of +IX had been unknown previously. The picture shows the mass spectra for the argon-tagged iridium oxide species. PMID:25515852

Pyykkö, Pekka; Xu, Wen-Hua

2015-01-19

304

Sulfur-resistant carbon-supported iridium catalysts: Cyclohexane dehydrogenation and benzene hydrogenation  

SciTech Connect

Carbon-supported iridium catalysts, with different metal loadings, were prepared by impregnation of a high-purity activated carbon. The dispersion of the metallic phase was studied by hydrogen and carbon monoxide chemisorption and transmission electron microscopy (TEM). The hydrogen chemisorption on the iridium crystallites supported on activated carbon was quite different from the chemisorption on an Ir/alumina catalyst. TEM observations of the catalysts show metal particles as spheres in the former case and as rafts in the latter. The cyclohexane dehydrogenation and the benzene hydrogenation were studied for both catalyst types. Both reactions are insensitive to the iridium dispersion and to the support. The thiotolerance level of the cyclohexane dehydrogenation, the thiotolerance level is affected neither by the support (activated carbon versus alumina) not by the metallic dispersion of the Ir/carbon catalysts. However, in the benzene hydrogenation the carbon-supported iridium catalysts are more resistant toward the poisoning than the Ir/alumina counterpart. This behavior is interpreted as due to the different metallic microstructures produced on the two supports.

Rodriguez-Ramos, I. (Campus Univ. Autonoma, Madrid (Spain)); Guerrero-Ruiz, A. (UNED, Madrid (Spain))

1992-06-01

305

16 CFR 23.7 - Misuse of the words “platinum,” “iridium,” “palladium,” “ruthenium,” “rhodium,” and “osmium.”  

Code of Federal Regulations, 2012 CFR

...may be used for quality marks on articles: “Plat.” or “Pt.” for Platinum; “Irid.” or “Ir.” for Iridium; “Pall.” or “Pd.” for...per thousand and standard chemical abbreviations (e.g., 585 Pt., 415 Co.). Note to § 23.7: Exemptions...

2012-01-01

306

Testing and evaluation of oxide-coated iridium/rhenium chambers  

NASA Technical Reports Server (NTRS)

Iridium-coated rhenium provides long life operation of radiation-cooled rockets at temperatures up to 2200 C. Ceramic oxide coatings could be used to increase iridium/rhenium rocket lifetimes and allow operation in highly oxidizing environments. Ceramic oxide coatings promise to serve as both thermal and diffusion barriers for the iridium layer. Seven ceramic oxide-coated iridium/rhenium, 22 N rocket chambers were tested on gaseous hydrogen/gaseous oxygen propellants. Five chambers had thick (over 10 mils), monolithic coatings of either hafnia or zirconia. Two chambers had coatings with thicknesses less than 5 mils. One of these chambers had a thin-walled coating of zirconia infiltrated with sol gel hafnia. The other chamber had a coating composed of an iridium/oxide composite. The purpose of this test program was to assess the ability of the oxide coatings to withstand the thermal shock of combustion initiation, adhere under repeated thermal cycling, and operate in aggressively oxidizing environments. All of the coatings survived the thermal shock of combustion and demonstrated operation at mixture ratios up to 11. The iridium/oxide composite coated chamber included testing for over 29 minutes at mixture ratio 16. The thicker-walled coatings provided the larger temperature drops across the oxide layer (up to 570 C), but were susceptible to macrocracking and eventual chipping at a stress concentrator. The cracks apparently resealed during firing, under compression of the oxide layer. The thinner-walled coatings did not experience the macrocracking and chipping of the chambers seen with the thick, monolithic coatings. However, burnthroughs in the throat region did occur in both of the thin-walled chambers at mixture ratios well above stochiometric. The burn-throughs were probably the result of oxygen-diffusion through the oxide coating that allowed the underlying iridium and rhenium layers to be oxidized. The results of this test program indicated that the thin-walled oxide coatings are better suited for repeated thermal cycling than the thick-walled coating, while thicker coatings may be required for operation in aggressively oxidizing environments.

Reed, Brian D.

1993-01-01

307

Addition of C-C and C-H bonds by pincer-iridium complexes: a combined experimental and computational study.  

PubMed

We report that pincer-ligated iridium complexes undergo oxidative addition of the strained C-C bond of biphenylene. The sterically crowded species ((tBu)PCP)Ir ((R)PCP = ?(3)-1,3-C6H3(CH2PR2)2) initially reacts with biphenylene to selectively add the C(1)-H bond, to give a relatively stable aryl hydride complex. Upon heating at 125 °C for 24 h, full conversion to the C-C addition product, ((tBu)PCP)Ir(2,2'-biphenyl), is observed. The much less crowded ((iPr)PCP)Ir undergoes relatively rapid C-C addition at room temperature. The large difference in the apparent barriers to C-C addition is notable in view of the fact that the addition products are not particularly crowded, since the planar biphenyl unit adopts an orientation perpendicular to the plane of the (R)PCP ligands. Based on DFT calculations the large difference in the barriers to C-C addition can be explained in terms of a "tilted" transition state. In the transition state the biphenylene cyclobutadiene core is calculated to be strongly tilted (ca. 50°-60°) relative to its orientation in the product in the plane perpendicular to that of the PCP ligand; this tilt results in very short, unfavorable, non-bonding contacts with the t-butyl groups in the case of the (tBu)PCP ligand. The conclusions of the biphenylene studies are applied to interpret computational results for cleavage of the unstrained C-C bond of biphenyl by ((R)PCP)Ir. PMID:25250874

Laviska, David A; Guan, Changjian; Emge, Thomas J; Wilklow-Marnell, Miles; Brennessel, William W; Jones, William D; Krogh-Jespersen, Karsten; Goldman, Alan S

2014-11-21

308

Identification of an iridium-containing compound with a formal oxidation state of IX.  

PubMed

One of the most important classifications in chemistry and within the periodic table is the concept of formal oxidation states. The preparation and characterization of compounds containing elements with unusual oxidation states is of great interest to chemists. The highest experimentally known formal oxidation state of any chemical element is at present VIII, although higher oxidation states have been postulated. Compounds with oxidation state VIII include several xenon compounds (for example XeO4 and XeO3F2) and the well-characterized species RuO4 and OsO4 (refs 2-4). Iridium, which has nine valence electrons, is predicted to have the greatest chance of being oxidized beyond the VIII oxidation state. In recent matrix-isolation experiments, the IrO4 molecule was characterized as an isolated molecule in rare-gas matrices. The valence electron configuration of iridium in IrO4 is 5d(1), with a formal oxidation state of VIII. Removal of the remaining d electron from IrO4 would lead to the iridium tetroxide cation ([IrO4](+)), which was recently predicted to be stable and in which iridium is in a formal oxidation state of IX. There has been some speculation about the formation of [IrO4](+) species, but these experimental observations have not been structurally confirmed. Here we report the formation of [IrO4](+) and its identification by infrared photodissociation spectroscopy. Quantum-chemical calculations were carried out at the highest level of theory that is available today, and predict that the iridium tetroxide cation, with a Td-symmetrical structure and a d(0) electron configuration, is the most stable of all possible [IrO4](+) isomers. PMID:25341786

Wang, Guanjun; Zhou, Mingfei; Goettel, James T; Schrobilgen, Gary J; Su, Jing; Li, Jun; Schlöder, Tobias; Riedel, Sebastian

2014-10-23

309

Identification of an iridium-containing compound with a formal oxidation state of IX  

NASA Astrophysics Data System (ADS)

One of the most important classifications in chemistry and within the periodic table is the concept of formal oxidation states. The preparation and characterization of compounds containing elements with unusual oxidation states is of great interest to chemists. The highest experimentally known formal oxidation state of any chemical element is at present VIII, although higher oxidation states have been postulated. Compounds with oxidation state VIII include several xenon compounds (for example XeO4 and XeO3F2) and the well-characterized species RuO4 and OsO4 (refs 2, 3, 4). Iridium, which has nine valence electrons, is predicted to have the greatest chance of being oxidized beyond the VIII oxidation state. In recent matrix-isolation experiments, the IrO4 molecule was characterized as an isolated molecule in rare-gas matrices. The valence electron configuration of iridium in IrO4 is 5d1, with a formal oxidation state of VIII. Removal of the remaining d electron from IrO4 would lead to the iridium tetroxide cation ([IrO4]+), which was recently predicted to be stable and in which iridium is in a formal oxidation state of IX. There has been some speculation about the formation of [IrO4]+ species, but these experimental observations have not been structurally confirmed. Here we report the formation of [IrO4]+ and its identification by infrared photodissociation spectroscopy. Quantum-chemical calculations were carried out at the highest level of theory that is available today, and predict that the iridium tetroxide cation, with a Td-symmetrical structure and a d0 electron configuration, is the most stable of all possible [IrO4]+ isomers.

Wang, Guanjun; Zhou, Mingfei; Goettel, James T.; Schrobilgen, Gary J.; Su, Jing; Li, Jun; Schlöder, Tobias; Riedel, Sebastian

2014-10-01

310

Determination of selenium by tungsten coil atomic absorption spectrometry using iridium as a permanent chemical modifier  

NASA Astrophysics Data System (ADS)

Permanent chemical modifiers have been shown to prolong graphite tube lifetime while reducing the furnace cycle time, thus improving cost-effectiveness. In this work, iridium is used as a permanent chemical modifier for the first time in the determination of selenium by tungsten-coil atomic absorption spectrometry (W-Coil AAS). The iridium modifier is thermally coated onto the tungsten coil. After coating, the coil can be used for 300-400 firings without further application of the modifier. Thermal treatment with iridium permits operating with higher pyrolysis temperature and coil lifetime is extended up to 1600 firings. The sensitivity and linearity of the method is improved, and the analytical procedure allows the use of analyte solutions containing up to 8% nitric acid. The short-term stability of the absorbance measurements is demonstrated by the reproducibility in the measurements of a Se amount (6 ng) 30 times higher than the limit of detection (0.2 ng). A 7% relative standard deviation (R.S.D.) was observed for 10 consecutive measurements of 6 ng Se. The long-term stability is almost as good: less than 9% R.S.D. over a 3-week period and 1500 firings. The surface of the tungsten-coil treated with iridium is examined before and after intensive use by scanning electron microscopy. Finally, the thermal treatment of the tungsten-coil with iridium appears to delay the appearance of selenium atoms by approximately 0.2 s although the integrated absorbance measurements are unaffected. The magnitude of delay decreases with coil age.

Hou, Xiandeng; Yang, Zheng; Jones, Bradley T.

2001-02-01

311

Iridium and Spherules in Late Eocene Impact Deposits  

NASA Technical Reports Server (NTRS)

We have been independently examining the Ir (FTK) and spherule (SL) contents of recently discovered late Eocene impact deposits from the south Atlantic and western Indian oceans. These include ODP Sites 1090 [14,15], 709 [lo], and 699 [Liu in prep.]. Iridium abundances at these sites are within the typical range reported for late Eocene deposits, with peak concentrations between 100 and 1000 pg/g. In Table 1 we present estimated net Ir fluences (in ng Ir/cm ) for these and nine other sites. Although there are fewer sites than the K/T boundary, the average of 9 ng Ir/cm2 is probably a good estimate of the late Eocene global flux. This is enough Ir for a 6 km comet (assuming 250 ng/g Ir, p=1.5), is sufficient to produce the Popigai or Chesapeake Bay structures, and is 16% of the flux estimated for the K/T boundary (55 ng/cm2 [ 161). Figure 1 shows the relative abundances of Ir, glassy microtektites and cpx-bearing spherules in sediments from Sites 699 and 1090, which are separated by only 3100 km. Although these two sites have similar Ir anomalies, the abundances of spherules are quite different. Site 1090 has well-defined peaks for both types of spherules, with a peak of 562 cpx spheruledg, while Site 699 contains only a few glassy microtektites and no cpx spherules. While the different abundances of spherules may reflect a heterogeneous distribution of spherules on the Earth s surface, an equally likely cause of this difference may be differential preservation of spherules in the sediment. recovered are only a trace residue of the initial impact deposit. Earlier work found 0.22 ng/g Ir in glassy microtektites from Site 689 [17], an insufficient concentration to support 0.16 ng/g in the bulk sediment at this site. We measured 15 ng/g Ir in a group of 95 cpx spherules from Site 1090 with sizes from 63 to -200 pm, a set typical of the size distribution at this site. Although this is a significant concentration it also cannot support the Ir peak. We presently lack quantitative data on the mass concentration of cpx spherules in Site 1090 sediments, but it is certainly <1 mg/g in The impact record in the late Eocene is very different from that at the Cretaceous-Tertiary In contrast, the late Eocene probably experienced multiple impact events.

Kyte, F. T.; Liu, S.

2002-01-01

312

Exploring metal hydrides using autoclave and multi-anvil hydrogenations  

NASA Astrophysics Data System (ADS)

Metal hydride materials have been intensively studied for hydrogen storage applications. In addition to potential hydrogen economy applications, metal hydrides offer a wide variety of other interesting properties. For example, hydrogen-dominant materials, which are hydrides with the highest hydrogen content for a particular metal/semimetal composition, are predicted to display high-temperature superconductivity. On the other side of the spectrum are hydrides with small amounts of hydrogen (0.1 - 1 at.%) that are investigated as viable magnetic, thermoelectric or semiconducting materials. Research of metal hydride materials is generally important to gain fundamental understanding of metal-hydrogen interactions in materials. Hydrogenation of Zintl phases, which are defined as compounds between an active metal (alkali, alkaline earth, rare earth) and a p-block metal/semimetal, were attempted by a hot sintering method utilizing an autoclave loaded with gaseous hydrogen (< 9 MPa). Hydride formation competes with oxidative decomposition of a Zintl phase. The oxidative decomposition, which leads to a mixture of binary active metal hydride and p-block element, was observed for investigated aluminum (Al) and gallium (Ga) containing Zintl phases. However, a new phase Li2Al was discovered when Zintl phase precursors were synthesized. Using the single crystal x-ray diffraction (SCXRD), the Li2Al was found to crystallize in an orthorhombic unit cell (Cmcm) with the lattice parameters a = 4.6404(8) Å, b = 9.719(2) Å, and c = 4.4764(8) Å. Increased demand for materials with improved properties necessitates the exploration of alternative synthesis methods. Conventional metal hydride synthesis methods, like ball-milling and autoclave technique, are not responding to the demands of finding new materials. A viable alternative synthesis method is the application of high pressure for the preparation of hydrogen-dominant materials. Extreme pressures in the gigapascal ranges can open access to new metal hydrides with novel structures and properties, because of the drastically increased chemical potential of hydrogen. Pressures up to 10 GPa can be easily achieved using the multi-anvil (MA) hydrogenations while maintaining sufficient sample volume for structure and property characterization. Gigapascal MA hydrogenations using ammonia borane (BH3

Puhakainen, Kati

313

Enantioselective synthesis of tetrahydroisoquinolines via iridium-catalyzed intramolecular Friedel-Crafts-type allylic alkylation of phenols.  

PubMed

An efficient iridium-catalyzed intramolecular Friedel-Crafts-type allylic alkylation reaction of phenols was developed, affording tetrahydroisoquinolines with moderate to excellent yields, enantioselectivity, and good regioselectivity. PMID:22540154

Xu, Qing-Long; Dai, Li-Xin; You, Shu-Li

2012-05-18

314

12OC-2001-02 New Cu-diffusion Barrier Materials Based on Ruthenium, Iridium and its Oxides  

E-print Network

12OC-2001-02 New Cu-diffusion Barrier Materials Based on Ruthenium, Iridium and its Oxides Advanced-seeding layer is needed to assure good Cu electrofill. Our invention utilizes a new conductive ruthenium/ruthenium

Mohanty, Saraju P.

315

Development of a gamma-ray detector with iridium transition edge sensor coupled to a Pb absorber  

E-print Network

We have recently started to develop a high-resolution gamma-ray spectrometer for material defect analysis. Our gamma-ray detector is a microcalorimeter consisting of an iridium/gold bilayer transition edge sensor (TES) ...

Leman, Steven W.

316

Catalytic functionalization of methyl group on silicon: iridium-catalyzed C(sp3)-H borylation of methylchlorosilanes.  

PubMed

A methyl group of methylchlorosilanes undergoes C-H borylation in an iridium-catalyzed reaction with bis(pinacolato)diboron in cyclohexane at 80 °C, giving (borylmethyl)chlorosilanes selectively. PMID:23043232

Ohmura, Toshimichi; Torigoe, Takeru; Suginome, Michinori

2012-10-24

317

Efficient catalysis by MgCl2 in hydrogen generation via hydrolysis of Mg-based hydride prepared by hydriding combustion synthesis.  

PubMed

Magnesium chloride efficiently catalyzed the hydrolysis of Mg-based hydride prepared by hydriding combustion synthesis. Hydrogen yield of 1635 mL g(-1) was obtained (MgH(2)), i.e. with 96% conversion in 30 min at 303 K. PMID:22538836

Zhao, Zelun; Zhu, Yunfeng; Li, Liquan

2012-06-01

318

Highly Active Iridium/Iridium Tin/Tin Oxide Heterogeneous Nanoparticles as Alternative Electrocatalysts for the Ethanol Oxidation Reaction  

SciTech Connect

Ethanol is a promising fuel for low-temperature direct fuel cell reactions due to its low toxicity, ease of storage and transportation, high-energy density, and availability from biomass. However, the implementation of ethanol fuel cell technology has been hindered by the lack of low-cost, highly active anode catalysts. In this paper, we have studied Iridium (Ir)-based binary catalysts as low-cost alternative electrocatalysts replacing platinum (Pt)-based catalysts for the direct ethanol fuel cell (DEFC) reaction. We report the synthesis of carbon supported Ir{sub 71}Sn{sub 29} catalysts with an average diameter of 2.7 {+-} 0.6 nm through a 'surfactant-free' wet chemistry approach. The complementary characterization techniques, including aberration-corrected scanning transmission electron microscopy equipped with electron energy loss spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy, are used to identify the 'real' heterogeneous structure of Ir{sub 71}Sn{sub 29}/C particles as Ir/Ir-Sn/SnO{sub 2}, which consists of an Ir-rich core and an Ir-Sn alloy shell with SnO{sub 2} present on the surface. The Ir{sub 71}Sn{sub 29}/C heterogeneous catalyst exhibited high electrochemical activity toward the ethanol oxidation reaction compared to the commercial Pt/C (ETEK), PtRu/C (Johnson Matthey) as well as PtSn/C catalysts. Electrochemical measurements and density functional theory calculations demonstrate that the superior electro-activity is directly related to the high degree of Ir-Sn alloy formation as well as the existence of nonalloyed SnO{sub 2} on surface. Our cross-disciplinary work, from novel 'surfactant-free' synthesis of Ir-Sn catalysts, theoretical simulations, and catalytic measurements to the characterizations of 'real' heterogeneous nanostructures, will not only highlight the intriguing structure-property correlations in nanosized catalysts but also have a transformative impact on the commercialization of DEFC technology by replacing Pt with low-cost, highly active Ir-based catalysts.

Du W.; Su D.; Wang Q.; Saxner D.; Deskins N.A.; Krzanowski J.E.; Frenkel A.I.; Teng X.

2011-08-03

319

Effect of thermo-mechanical cycling on zirconium hydride reorientation studied in situ with synchrotron X-ray diffraction  

NASA Astrophysics Data System (ADS)

The circumferential hydrides normally present in nuclear reactor fuel cladding after reactor exposure may dissolve during drying for dry storage and re-precipitate when cooled under load into a more radial orientation, which could embrittle the fuel cladding. It is necessary to study the rates and conditions under which hydride reorientation may happen in order to assess fuel integrity in dry storage. The objective of this work is to study the effect of applied stress and thermal cycling on the hydride morphology in cold-worked stress-relieved Zircaloy-4 by combining conventional metallography and in situ X-ray diffraction techniques. Metallography is used to study the evolution of hydride morphology after several thermo-mechanical cycles. In situ X-ray diffraction performed at the Advanced Photon Source synchrotron provides real-time information on the process of hydride dissolution and precipitation under stress during several thermal cycles. The detailed study of diffracted intensity, peak position and full-width at half-maximum provides information on precipitation kinetics, elastic strains and other characteristics of the hydride precipitation process. The results show that thermo-mechanical cycling significantly increases the radial hydride fraction as well as the hydride length and connectivity. The radial hydrides are observed to precipitate at a lower temperature than circumferential hydrides. Variations in the magnitude and range of hydride strains due to reorientation and cycling have also been observed. These results are discussed in light of existing models and experiments on hydride reorientation. The study of hydride elastic strains during precipitation shows marked differences between circumferential and radial hydrides, which can be used to investigate the reorientation process. Cycling under stress above the threshold stress for reorientation drastically increases both the reoriented hydride fraction and the hydride size. The reoriented hydride fraction decreases with increasing hydrogen content although the radial hydride content remains constant (for levels above 200 wt.ppm). The precipitation of reoriented hydrides under stress above the threshold stress for reorientation occurs at a lower temperature than the precipitation of in-plane (circumferential) hydrides in unstressed samples. The effects of cycling on the precipitation temperature when precipitating reoriented hydrides are small. When radial hydrides precipitate under stress, during the first precipitation stage at high temperature the hydride strains become tensile in the direction perpendicular to the hydride platelet face. During the second precipitation regime, these strains remain constant in tension. This indicates a different hydride strain state for reoriented hydrides than for circumferential hydrides. The magnitude of the tensile hydride strain in the transverse direction as measured by the change in d-spacing in the reoriented hydride face increases with cycling, potentially because of the increasing reoriented hydride fraction. The analysis of the FWHM confirms the observed 'signature' of hydride reorientation in a mixed population of hydrides as previously observed in the literature. Once the hydride population is fully reoriented, the FWHM decreases due to the fact that a single population of reoriented hydrides is now present. The strain distribution in this single population is smaller than for a mixed population of circumferential and reoriented hydrides.

Colas, Kimberly B.; Motta, Arthur T.; Daymond, Mark R.; Almer, Jonathan D.

2013-09-01

320

FEASIBILITY OF RECYCLING PLUTONIUM AND MINOR ACTINIDES IN LIGHT WATER REACTORS USING HYDRIDE FUEL  

SciTech Connect

The objective of this DOE NERI program sponsored project was to assess the feasibility of improving the plutonium (Pu) and minor actinide (MA) recycling capabilities of pressurized water reactors (PWRs) by using hydride instead of oxide fuels. There are four general parts to this assessment: 1) Identifying promising hydride fuel assembly designs for recycling Pu and MAs in PWRs 2) Performing a comprehensive systems analysis that compares the fuel cycle characteristics of Pu and MA recycling in PWRs using the promising hydride fuel assembly designs identified in Part 1 versus using oxide fuel assembly designs 3) Conducting a safety analysis to assess the likelihood of licensing hydride fuel assembly designs 4) Assessing the compatibility of hydride fuel with cladding materials and water under typical PWR operating conditions Hydride fuel was found to offer promising transmutation characteristics and is recommended for further examination as a possible preferred option for recycling plutonium in PWRs.

Greenspan, Ehud; Todreas, Neil; Taiwo, Temitope

2009-03-10

321

SPECIATION OF ARSENIC COMPOUNDS IN DRINKING WATER BY CAPILLARY ELECTROPHORESIS WITH HYDRODYNAMICALLY MODIFIED ELECTROOSMOTIC FLOW DETECTED THROUGH HYDRIDE GENERATION INDUCTIVELY COUPLED PLASMA MASS...  

EPA Science Inventory

Capillary electrophoresis (CE) was used to speciate four environmentally significant, toxic forms of arsenic: arsenite, arsenate, monomethylarsonic acid and dimethylarsinic acid. Hydride generation (HG) was used to convert the species into their respective hydrides. The hydride s...

322

SPECIATION OF ARSENIC COMPOUNDS IN DRINKING WATER BY CAPILLARY ELECTROPHORESIS WITH HYDRODYNAMICALLY MODIFIED ELECTROOSMOTIC FLOW DETECTED THROUGH HYDRIDE GENERATION INDUCTIVELY COUPLED PLASMA MASS..  

EPA Science Inventory

Capillary electrophoresis (CE) was used to speciate four environmentally significant, toxic forms of arsenic: arsenite, arsenate, monomethylarsonic acid and dimethylarsinic acid. Hydride generation (HG) was used to convert the species into their respective hydrides. The hydride ...

323

Hydriding and dehydriding characteristics of LiBH{sub 4} and transition metals-added magnesium hydride  

SciTech Connect

Graphical abstract: Hydriding reaction curves under 12 bar H{sub 2}, and dehydriding reaction curves under 1.0 bar H{sub 2}, at 593 K at the 1st cycle for MgH{sub 2}–10Ni–2LiBH{sub 4}–2Ti and MgH{sub 2}. Highlights: ? Addition of Ni, LiBH{sub 4}, and Ti to MgH{sub 2} to increase reaction rates. ? Sample preparation by reactive mechanical grinding. ? At n = 2, the sample absorbed 4.05 wt% H for 60 min at 593 K under 12 bar H{sub 2}. ? Analysis of rate-controlling step for dehydriding of the sample at n = 3. - Abstract: In this study, MgH{sub 2} was used as a starting material instead of Mg. Ni, Ti, and LiBH{sub 4} with a high hydrogen-storage capacity of 18.4 wt% were added. A sample with a composition of MgH{sub 2}–10Ni–2LiBH{sub 4}–2Ti was prepared by reactive mechanical grinding. The activation of MgH{sub 2}–10Ni–2LiBH{sub 4}–2Ti was completed after the first hydriding–dehydrding cycle. The hydriding rate decreases as the temperature increases due to the decrease in the driving force for the hydriding reaction. At the 1st cycle, the sample desorbs 1.45 wt% H for 10 min, 2.54 wt% H for 20 min, 3.13 wt% H for 30 min, and 3.40 wt% H for 60 min at 593 K under 1.0 bar H{sub 2}. At the 2nd cycle, the sample absorbs 3.84 wt% H for 5 min, 3.96 wt% H for 10 min, and 4.05 wt% H for 60 min at 593 K under 12 bar H{sub 2}. MgH{sub 2}–10Ni–2LiBH{sub 4}–2Ti after reactive mechanical grinding contained MgH{sub 2}, Mg, Ni, TiH{sub 1.924}, and MgO phases. The reactive mechanical grinding of Mg with Ni, LiBH{sub 4}, and Ti is considered to create defects on the surface and in the interior of Mg (to facilitate nucleation), and to reduce the particle size of Mg (to shorten diffusion distances of hydrogen atoms). The formation of Mg{sub 2}Ni during hydriding–dehydriding cycling increases the hydriding and dehydriding rates of the sample.

Song, Myoung Youp, E-mail: songmy@jbnu.ac.kr [Division of Advanced Materials Engineering, Hydrogen and Fuel Cell Research Center, Engineering Research Institute, Chonbuk National University, 567 Baekje-daero, Deokjin-gu, Jeonju, 561-756 (Korea, Republic of); Kwak, Young Jun; Lee, Seong Ho [Department of Materials Engineering, Graduate School, Chonbuk National University, 567 Baekje-daero, Deokjin-gu, Jeonju, 561-756 (Korea, Republic of); Park, Hye Ryoung [Faculty of Applied Chemical Engineering, Chonnam National University, 300 Yongbongdong, Bukgu, Gwangju, 500-757 (Korea, Republic of)

2013-07-15

324

Electronic structure and optical properties of lightweight metal hydrides  

Microsoft Academic Search

We study the dielectric functions of the series of simple hydrides LiH, NaH, MgH2, and AlH3, and of the complex hydrides Li3AlH6, Na3AlH6, LiAlH4, NaAlH4, and Mg(AlH4)2, using first-principles density-functional theory and GW calculations. All compounds are large gap insulators with GW single-particle band gaps varying from 3.5 eV in AlH3 to 6.6 eV in LiAlH4. Despite considerable differences between

Setten van M. J; V. A. Popa; Wijs de G. A; G. Brocks

2007-01-01

325

Reversible metal-hydride phase transformation in epitaxial films.  

PubMed

Metal-hydride phase transformations in solids commonly proceed with hysteresis. The extrinsic component of hysteresis is the result of the dissipation of energy of internal stress due to plastic deformation and fracture. It can be mitigated on the nanoscale, where plastic deformation and fracture are suppressed and the transformation proceeds through formation and evolution of coherent phases. However, the phase coherency introduces intrinsic thermodynamic hysteresis, preventing reversible transformation. In this paper, it is shown that thermodynamic hysteresis of coherent metal-hydride transformation can be eliminated in epitaxial film due to substrate constraint. Film-substrate interaction leads to formation of heterophase polydomain nanostructure with variable phase fraction which can change reversibly by varying temperature in a closed system or chemical potential in an open system. PMID:25671335

Roytburd, Alexander L; Boyerinas, Brad M; Bruck, Hugh A

2015-03-11

326

Composition and structure of sputter deposited erbium hydride thin films  

SciTech Connect

Erbium hydride thin films are grown onto polished, a-axis {alpha} Al{sub 2}O{sub 3} (sapphire) substrates by reactive ion beam sputtering and analyzed to determine composition, phase and microstructure. Erbium is sputtered while maintaining a H{sub 2} partial pressure of 1.4 x 10{sup {minus}4} Torr. Growth is conducted at several substrate temperatures between 30 and 500 C. Rutherford backscattering spectrometry (RBS) and elastic recoil detection analyses after deposition show that the H/Er areal density ratio is approximately 3:1 for growth temperatures of 30, 150 and 275 C, while for growth above {approximately}430 C, the ratio of hydrogen to metal is closer to 2:1. However, x-ray diffraction shows that all films have a cubic metal sublattice structure corresponding to that of ErH{sub 2}. RBS and Auger electron that sputtered erbium hydride thin films are relatively free of impurities.

ADAMS,DAVID P.; ROMERO,JUAN A.; RODRIGUEZ,MARK A.; FLORO,JERROLD A.; BANKS,JAMES C.

2000-05-10

327

Hydride-induced embrittlement and fracture in metals—e)ect of stress and temperature distribution  

Microsoft Academic Search

A mathematical model for the hydrogen embrittlement of hydride forming metals has been de- veloped. The model takes into account the coupling of the operating physical processes, namely: (i) hydrogen di)usion, (ii) hydride precipitation, (iii) non-mechanical energy 4ow and (iv) hydride=solid-solution deformation. Material damage and crack growth are also simulated by using de-cohesion model, which takes into account the time

A. G. Varias; A. R. Massiha

328

High Temperature Metal Hydrides as Heat Storage Materials for Solar and Related Applications  

PubMed Central

For the continuous production of electricity with solar heat power plants the storage of heat at a temperature level around 400 °C is essential. High temperature metal hydrides offer high heat storage capacities around this temperature. Based on Mg-compounds, these hydrides are in principle low-cost materials with excellent cycling stability. Relevant properties of these hydrides and their possible applications as heat storage materials are described. PMID:19333448

Felderhoff, Michael; Bogdanovi?, Borislav

2009-01-01

329

Internal dynamics of complex hydrides of the LBH 4 type  

Microsoft Academic Search

The internal dynamics of complex hydrides of light alkali metals of the LBH4 type (L = Li, Na) with regard for the transitions of the L+ cation between the four energetically equivalent equilibrium positions with respect to the BH\\u000a 4\\u000a ?\\u000a anion is analyzed on the basis of symmetry-group chain methods. A rigorous model for the description of the energy

A. V. Burenin

2004-01-01

330

On X-ray Emission from Highly Loaded Hydrides  

Microsoft Academic Search

X-ray emission (1-2 keV) has been observed in various experiments using electrolytic or plasma methods for loading of hydride targets such as Pd-D to atom ratios > 0.8. Intensities vary from very low-level emission up to laser-like focused beams, depending on experimental conditions(A.G. Lipson et al, JETP Letters, (submitted)). Bremsstralung during thermalization of energetic alphas\\/protons created by nuclear reactions in

George H. Miley; Heinrich Hora; Nie Luo; Andrei Lipson

2004-01-01

331

Ground-state energy and relativistic corrections for positronium hydride  

SciTech Connect

Variational calculations of the ground state of positronium hydride (HPs) are reported, including various expectation values, electron-positron annihilation rates, and leading relativistic corrections to the total and dissociation energies. The calculations have been performed using a basis set of 4000 thoroughly optimized explicitly correlated Gaussian basis functions. The relative accuracy of the variational energy upper bound is estimated to be of the order of 2x10{sup -10}, which is a significant improvement over previous nonrelativistic results.

Bubin, Sergiy; Varga, Kalman [Department of Physics and Astronomy, Vanderbilt University, Nashville, Tennessee 37235 (United States)

2011-07-15

332

Yttrium and lanthanum hydride films with switchable optical properties  

Microsoft Academic Search

We discovered that yttrium-, lanthanum- and rare earth-hydride films exhibit remarkable optical properties near their metal–insulator transition: the dihydrides are metallic and shiny while the trihydrides are semiconducting and transparent. The transition between the shiny and transparent state is reversible and can simply be induced by changing the H2 gas pressure or the voltage in an electrolytic cell. No deterioration

R Griessen; J. N Huiberts; M Kremers; A. T. M van Gogh; N. J Koeman; J. P Dekker; P. H. L Notten

1997-01-01

333

Pu 2O 3 and the plutonium hydriding process  

Microsoft Academic Search

The role of cubic Pu2O3 in the corrosion of PuO2-coated Pu by H2 was investigated. Experiments were conducted to demonstrate that nucleation of hydriding is promoted by formation of Pu2O3 sites in the oxide layer. The nucleation mechanism based on diffusion of hydrogen through the PuO2 layer was evaluated and an alternative mechanism based on formation of catalytic Pu2O3 sites

L. N. Dinh; J. M. Haschke; C. K. Saw; P. G. Allen; W. McLean

2011-01-01

334

Thermodynamic properties of the cubic plutonium hydride solid solution  

Microsoft Academic Search

Pressure, temperature, and composition data for the cubic solid solution plutonium hydride phase, PuH\\/sub x\\/, have been measured by microbalance methods. Integral enthalpies and entropies of formation have been evaluated for the composition range 1.90 less than or equal to X less than or equal to 3.00. At 550°K, ..delta..H° \\/sub f\\/(PuH\\/sub x\\/(s)) varies linearly from approximately (-38 +- 1)

Haschke

1981-01-01

335

The Reactivity Patterns of Low-Coordinate Iron Hydride Complexes  

PubMed Central

We report a survey of the reactivity of the first isolable iron-hydride complexes with a coordination number less than five. The high-spin iron(II) complexes [(?-diketiminate)Fe(?-H)]2 react rapidly with representative cyanide, isocyanide, alkyne, N2, alkene, diazene, azide, CO2, carbodiimide and Brønsted acid containing substrates. The reaction outcomes fall into three categories: (1) addition of Fe-H across a multiple bond of the substrate, (2) reductive elimination of H2 to form iron(I) products, and (3) protonation of the hydride to form iron(II) products. The products include imide, isocyanide, vinyl, alkyl, azide, triazenido, benzo[c]cinnoline, amidinate, formate, and hydroxo complexes. These results expand the range of known bond transformations at iron complexes. Additionally, they give insight into the elementary transformations that may be possible at the iron-molybdenum cofactor of nitrogenases, which may have hydride ligands on high-spin, low coordinate metal atoms. PMID:18444648

Yu, Ying; Sadique, Azwana R.; Smith, Jeremy M.; Dugan, Thomas R.; Cowley, Ryan E.; Brennessel, William W.; Flaschenriem, Christine J.; Bill, Eckhard; Cundari, Thomas R.; Holland, Patrick L.

2008-01-01

336

Diffusional exchange of isotopes in a metal hydride sphere.  

SciTech Connect

This report describes the Spherical Particle Exchange Model (SPEM), which simulates exchange of one hydrogen isotope by another hydrogen isotope in a spherical metal hydride particle. This is one of the fundamental physical processes during isotope exchange in a bed of spherical metal particles and is thus one of the key components in any comprehensive physics-based model of exchange. There are two important physical processes in the model. One is the entropy of mixing between the two isotopes; the entropy of mixing is increased by having both isotopes randomly placed at interstitial sites on the lattice and thus impedes the exchange process. The other physical process is the elastic interaction between isotope atoms on the lattice. The elastic interaction is the cause for {beta}-phase formation and is independent of the isotope species. In this report the coupled diffusion equations for two isotopes in the {beta}-phase hydride are solved. A key concept is that the diffusion of one isotope depends not only on its concentration gradient, but also on the concentration gradient of the other isotope. Diffusion rate constants and the chemical potentials for deuterium and hydrogen in the {beta}-phase hydride are reviewed because these quantities are essential for an accurate model of the diffusion process. Finally, a summary of some of the predictions from the SPEM model are provided.

Wolfer, Wilhelm G.; Hamilton, John C.; James, Scott Carlton

2011-04-01

337

Superconductive sodalite-like clathrate calcium hydride at high pressures  

PubMed Central

Hydrogen-rich compounds hold promise as high-temperature superconductors under high pressures. Recent theoretical hydride structures on achieving high-pressure superconductivity are composed mainly of H2 fragments. Through a systematic investigation of Ca hydrides with different hydrogen contents using particle-swam optimization structural search, we show that in the stoichiometry CaH6 a body-centered cubic structure with hydrogen that forms unusual “sodalite” cages containing enclathrated Ca stabilizes above pressure 150 GPa. The stability of this structure is derived from the acceptance by two H2 of electrons donated by Ca forming an “H4” unit as the building block in the construction of the three-dimensional sodalite cage. This unique structure has a partial occupation of the degenerated orbitals at the zone center. The resultant dynamic Jahn–Teller effect helps to enhance electron–phonon coupling and leads to superconductivity of CaH6. A superconducting critical temperature (Tc) of 220–235 K at 150 GPa obtained from the solution of the Eliashberg equations is the highest among all hydrides studied thus far. PMID:22492976

Wang, Hui; Tse, John S.; Tanaka, Kaori; Iitaka, Toshiaki; Ma, Yanming

2012-01-01

338

Delayed hydride cracking of spent fuel rods in dry storage  

NASA Astrophysics Data System (ADS)

Failures of zirconium alloy cladding tubes during a long-term storage at room temperature were first reported by Simpson and Ells in 1974, which remains unresolved by the old delayed hydride cracking (DHC) models. Using our new DHC model, we examined failures of cladding tubes after their storage at room temperature. Stress-induced hydride phase transformation from ? to ? at a crack tip creates a difference in hydrogen concentration between the bulk region and the crack tip due to a higher hydrogen solubility of the ?-hydride, which is a driving force for DHC at low temperatures. Accounting for our new DHC model and the failures of zirconium alloy cladding tubes during long-term storage at room temperature, we suggest that the spent fuel rods to be stored either in an isothermal condition or in a slow cooling condition would fail by DHC during their dry storage upon cooling to below 180 °C. Further works are recommended to establish DHC failure criterion for the spent fuel rods that are being stored in dry storage.

Kim, Young Suk

2008-08-01

339

Structure and properties of complex hydride perovskite materials  

NASA Astrophysics Data System (ADS)

Perovskite materials host an incredible variety of functionalities. Although the lightest element, hydrogen, is rarely encountered in oxide perovskite lattices, it was recently observed as the hydride anion H?, substituting for the oxide anion in BaTiO3. Here we present a series of 30 new complex hydride perovskite-type materials, based on the non-spherical tetrahydroborate anion BH4? and new synthesis protocols involving rare-earth elements. Photophysical, electronic and hydrogen storage properties are discussed, along with counterintuitive trends in structural behaviour. The electronic structure is investigated theoretically with density functional theory solid-state calculations. BH4-specific anion dynamics are introduced to perovskites, mediating mechanisms that freeze lattice instabilities and generate supercells of up to 16 × the unit cell volume in AB(BH4)3. In this view, homopolar hydridic di-hydrogen contacts arise as a potential tool with which to tailor crystal symmetries, thus merging concepts of molecular chemistry with ceramic-like host lattices. Furthermore, anion mixing BH4??X? (X?=Cl?, Br?, I?) provides a link to the known ABX3 halides.

Schouwink, Pascal; Ley, Morten B.; Tissot, Antoine; Hagemann, Hans; Jensen, Torben R.; Smr?ok, ?ubomír; ?erný, Radovan

2014-12-01

340

Structure and properties of complex hydride perovskite materials.  

PubMed

Perovskite materials host an incredible variety of functionalities. Although the lightest element, hydrogen, is rarely encountered in oxide perovskite lattices, it was recently observed as the hydride anion H(-), substituting for the oxide anion in BaTiO3. Here we present a series of 30 new complex hydride perovskite-type materials, based on the non-spherical tetrahydroborate anion BH4(-) and new synthesis protocols involving rare-earth elements. Photophysical, electronic and hydrogen storage properties are discussed, along with counterintuitive trends in structural behaviour. The electronic structure is investigated theoretically with density functional theory solid-state calculations. BH4-specific anion dynamics are introduced to perovskites, mediating mechanisms that freeze lattice instabilities and generate supercells of up to 16 × the unit cell volume in AB(BH4)3. In this view, homopolar hydridic di-hydrogen contacts arise as a potential tool with which to tailor crystal symmetries, thus merging concepts of molecular chemistry with ceramic-like host lattices. Furthermore, anion mixing BH4(-)?X(-) (X(-)=Cl(-), Br(-), I(-)) provides a link to the known ABX3 halides. PMID:25490884

Schouwink, Pascal; Ley, Morten B; Tissot, Antoine; Hagemann, Hans; Jensen, Torben R; Smr?ok, Lubomír; Cerný, Radovan

2014-01-01

341

Uranium metal reactions with hydrogen and water vapour and the reactivity of the uranium hydride produced  

SciTech Connect

Within the nuclear industry, metallic uranium has been used as a fuel. If this metal is stored in a hydrogen rich environment then the uranium metal can react with the hydrogen to form uranium hydride which can be pyrophoric when exposed to air. The UK National Nuclear Laboratory has been carrying out a programme of research for Sellafield Limited to investigate the conditions required for the formation and persistence of uranium hydride and the reactivity of the material formed. The experimental results presented here have described new results characterising uranium hydride formed from bulk uranium at 50 and 160 C. degrees and measurements of the hydrolysis kinetics of these materials in liquid water. It has been shown that there is an increase in the proportion of alpha-uranium hydride in material formed at lower temperatures and that there is an increase in the rate of reaction with water of uranium hydride formed at lower temperatures. This may at least in part be attributable to a difference in the reaction rate between alpha and beta-uranium hydride. A striking observation is the strong dependence of the hydrolysis reaction rate on the temperature of preparation of the uranium hydride. For example, the reaction rate of uranium hydride prepared at 50 C. degrees was over ten times higher than that prepared at 160 C. degrees at 20% extent of reaction. The decrease in reaction rate with the extent of reaction also depended on the temperature of uranium hydride preparation.

Godfrey, H. [National Nuclear Laboratory, Workington Laboratory, Havelock Road, Derwent Howe, Cumbria, CA14 3YQ (United Kingdom); Broan, C.; Goddard, D.; Hodge, N.; Woodhouse, G. [National Nuclear Laboratory, Preston Laboratory, Springfields, Salwick, Preston, Lancashire, PR4 0XJ (United Kingdom); Diggle, A. [Sellafield Limited, Sellafield, Seascale, Cumbria, CA20 1PG (United Kingdom); Orr, R. [National Nuclear Laboratory, Central Laboratory, Sellafield, Seascale, Cumbria, CA20 1PG (United Kingdom)

2013-07-01

342

Surface studies of iridium-alloy grain boundaries associated with weld cracking  

SciTech Connect

Plutonium-238 oxide fuel pellets for the General Purpose Heat Source (GPHS) Radioisotopic Thermoelectric Generators to be used on the NASA Galileo Mission to Jupiter and the International Solar Polar Mission are produced and encapsulated in iridium alloy at the Savannah River Plant (SRP). Underbead cracks occasionally occur in the girth weld on the iridium-alloy-clad vent sets in the region where the gas tungsten arc is quenched. Grain-boundary structures and compositions were characterized by scanning electron microscopy/x-ray energy spectroscopy, electron microprobe analysis and scanning Auger microprobe analysis to determine the cause of weld quench area cracking. Results suggest that weld quench area cracking may be caused by gas porosity or liquation in the grain boundaries.

Mosley, W.C.

1982-01-01

343

Near-IR Phosphorescent Ruthenium(II) and Iridium(III) Perylene Bisimide Metal Complexes.  

PubMed

The phosphorescence emission of perylene bisimide derivatives has been rarely reported. Two novel ruthenium(II) and iridium(III) complexes of an azabenz-annulated perylene bisimide (ab-PBI), [Ru(bpy)2 (ab-PBI)][PF6 ]2 1 and [Cp*Ir(ab-PBI)Cl]PF6 2 are now presented that both show NIR phosphorescence between 750-1000?nm in solution at room temperature. For an NIR emitter, the ruthenium complex 1 displays an unusually high quantum yield (?p ) of 11?% with a lifetime (?p ) of 4.2??s, while iridium complex 2 exhibits ?p <1?% and ?p =33??s. 1 and 2 are the first PBI-metal complexes in which the spin-orbit coupling is strong enough to facilitate not only the Sn ?Tn intersystem crossing of the PBI dye, but also the radiative T1 ?S0 transition, that is, phosphorescence. PMID:25504675

Schulze, Marcus; Steffen, Andreas; Würthner, Frank

2015-01-26

344

First Applications of DoD Iridium RUDICS in the NSF Polar Programs  

NASA Astrophysics Data System (ADS)

We will present the first deployment and application of the new Iridium RUDICS service to remote instrumentation projects within the National Science Foundation's polar programs. The rise of automated observing networks has increased the demand for real-time connectivity to remote instruments, not only for immediate access to data, but to also interrogate health and status. Communicating with field sites in the polar regions is complicated by the remoteness from existing infrastructure, low temperatures and limited connection options. Sites located above 78° latitude are not able to see geostationary satellites, leaving the Iridium constellation as the only one that provide a direct connection. Some others, such as Orbcomm, only provide a store-and-forward service. Iridium is often used as a dial up modem to establish a PPP connection to the Internet with data files transferred via FTP. On low-bandwidth, high-latency networks like Iridium (2400bps with ping times of seconds), this approach is time consuming and inefficient. The dial up time alone takes upwards of a minute, and standard TCP/IP and FTP protocols are hampered by the long latencies. Minimizing transmission time is important for reducing battery usage and connection costs. The new Iridium RUDICS service can be used for more efficient transfers. RUDICS is an acronym for "Router-based Unstructured Digital Inter-working Connectivity Solution" and provides a direct connection between an instrument in the field and a server on the Internet. After dialing into the Iridium gateway, a socket connection is opened to a registered port on a user's server. Bytes sent to or from the modem appear at the server's socket. The connection time is reduced to about 10 seconds because the modem training and PPP negotiation stages are eliminated. The remote device does not need to have a full TCP/IP stack, allowing smaller instruments such as data loggers to directly handle the data transmission. Alternative protocols can be deployed that better exploit the characteristics of the Iridium channel. In addition, the setup naturally scales to handle hundreds of remote devices, an important aspect for larger sensor networks. As part of the NSF's Arctic Research Support and Logistics Services, we have deployed RUDICS systems with three different research projects. These are the first NSF RUDICS deployments for projects using the Department of Defense Iridium gateway, which allows for unlimited connection time at a flat monthly rate for US government users. The first project is O-Buoy, an IPY-OASIS project for self-contained, autonomous observations of atmospheric chemical species in the polar marine boundary layer. The second project is collection of low-power instrument towers on Alaska's North Slope at Imnavait Creek, part of the Arctic Observation Network (AON). Lastly, the autonomous instrument platform at Ivotuk, Alaska, uses RUDICS to provide telemetry about the renewable energy systems. A set of real-time web displays allow researchers for each project to monitor their remote sites and access real-time data.

Valentic, T.; Stehle, R.

2008-12-01

345

Phosphorescent Organic Light-Emitting Devices: Working Principle and Iridium Based Emitter Materials  

PubMed Central

Even though organic light-emitting device (OLED) technology has evolved to a point where it is now an important competitor to liquid crystal displays (LCDs), further scientific efforts devoted to the design, engineering and fabrication of OLEDs are required for complete commercialization of this technology. Along these lines, the present work reviews the essentials of OLED technology putting special focus on the general working principle of single and multilayer OLEDs, fluorescent and phosphorescent emitter materials as well as transfer processes in host materials doped with phosphorescent dyes. Moreover, as a prototypical example of phosphorescent emitter materials, a brief discussion of homo- and heteroleptic iridium(III) complexes is enclosed concentrating on their synthesis, photophysical properties and approaches for realizing iridium based phosphorescent polymers. PMID:19325819

Kappaun, Stefan; Slugovc, Christian; List, Emil J. W.

2008-01-01

346

Iridium and ruthenium catalyzed syntheses, hydroborations, and metathesis reactions of alkenyl-decaboranes.  

PubMed

The selective syntheses of new classes of 6,9-dialkenyl- and 6-alkenyl-decaboranes and 6-alkyl-9-alkenyl-decaboranes have been achieved via iridium and ruthenium catalyzed decaborane and 6-alkyl-decaborane alkyne-hydroborations. Reactions employing [Cp*IrCl2]2 and [RuCl2(p-cymene)]2 precatalysts gave ?-E-alkenyl-decaboranes, while the corresponding reactions with [RuI2(p-cymene)]2 gave the ?-alkenyl-decaborane isomers, with the differences in product selectivity suggesting quite different mechanistic steps for the catalysts. The alkenyl-decaboranes were easily converted to other useful derivatives, including coupled-cage and functionally substituted compounds, via iridium-catalyzed hydroborations and ruthenium-catalyzed homo and cross olefin-metathesis reactions. PMID:23859100

Chatterjee, Shahana; Carroll, Patrick J; Sneddon, Larry G

2013-08-01

347

Synthesis and phosphorescent properties of the copolymers of N-vinylcarbazole, methyl methacrylate and iridium complex  

NASA Astrophysics Data System (ADS)

The copolymers containing carbazole unit and iridium complexes, such as (Ir(bpy)2Cl, Ir(mbpy)2Cl and Ir(Brbpy)2Cl, were synthesized via radical copolymerization of N-vinylcarbazole, methyl methacrylate and iridium complex. The synthesized copolymers were characterized by FT-IR, UV-Vis absorption spectroscopy and photoluminescence (PL) spectroscopy, respectively. According to the results, the copolymers (Ir(Brbpy)2Cl/PVK and Ir(mbpy)2Cl/PVK) exhibit yellow phosphorescence with an emission peak at around 553 nm under UV-visible light in the solid state. The results also reveal almost complete energy transfer from the host carbazole segments to the guest Ir complex in the copolymer film when the Ir content reaches 1.0 wt.%. The synthesized copolymers are good candidates as blue or yellow phosphorescent materials for PLED applications.

Wang, Wen; Zhou, Minglu; Liang, Luying; Lin, Meijuan; Ling, Qidan

2014-06-01

348

DEFORMATION MODELING OF IRIDIUM DOP-26 ALLOY TO DETERMINE POTENTIAL FOR SECONDARY RECRYSTALLIZATION  

SciTech Connect

The DOP-26 iridium alloy (Ir-0.3%W-0.006%Th-0.005% Al) contains a distribution of thorium-containing intermetallic particles, typically less than 1 micrometer in size, which serve to pin grain boundaries. The alloy is thus subject to secondary recrystallization during long-term exposure at elevated temperature if prior plastic strains are within a critical range. A finite element method was used to model the deformation and resulting local plastic strains introduced by sizing operations on recrystallized iridium alloy cups. The results of the analysis show that local strains introduced by the deformation of cups are in all cases maintained below 0.025, the lower critical level for secondary recrystallization at 1600 K. The effects of die clearance and applied load on local plastic strain values were also treated.

Ohriner, Evan Keith [ORNL; Sabau, Adrian S [ORNL; Ulrich, George B [ORNL; George, Easo P [ORNL

2008-01-01

349

Iridium-bearing sublimates at a hot-spot volcano (Piton de la Fournaise, Indian Ocean)  

SciTech Connect

Sublimates and incrustations derived upon the cooling of volcanic gases have been collected on various sites (Piton de la Fournaise, Poas, Momotombo, Etna, Ardoukoba and Erta-Ale). They have been analyzed for Ir and other volatile elements (Se, As, Cu, Au, Ag, Pb, Tl) by means of instrumental neutron activation analysis (INAA) and proton induced X-Ray emission (PIXE). Among the investigated volcanoes, only Piton de la Fournaise is found to release detectable amounts of iridium. Ir in Piton de la Fournaise sublimates is associated with F-minerals. This confirms its gaseous transport as a volatile fluoride compound. Iridium seems to be preferentialy released by hot-spot type volcanoes, and its detection in Piton de la Fournaise sublimates provides a positive argument in favor of a volcanic hypothesis to explain the KTB events.

Toutain, J.P. (Observatorio Vesuviano, Napoli (Italy)); Meyer, G.

1989-12-01

350

Preliminary design studies for an iridium rod target at the BNL-AGS  

SciTech Connect

The BNL-AGS is an intense source of 24 GeV protons. It is proposed to explore the potential to use these protons as the driver for a Pulsed Spallation Neutron Source target. The proposed target design is based on an edge cooled iridium rod concept--similar to the anti-proton production target which operated reliably at CERN under similar conditions. Lead, lead fluoride, and beryllium are investigated as possible reflector materials, and ambient temperature light water and 80 K light water ice are proposed as initial moderator materials. Both moderators are decoupled by cadmium containing moderator chamber walls. The small size of the target has the advantage that the moderators can be placed close to the target (resulting in a bright source), and since a large fraction of the radioactive inventory is contained in the iridium rod, removal and disposition of this inventory should be relatively simple and inexpensive.

Ludewig, H.; Hastings, J.; Montanez, P.; Todosow, M.

1998-12-31

351

A Cascade Isomerization/Prins Strategy through Iridium(III)/Brønsted Acid Cooperative Catalysis**  

PubMed Central

A mild and efficient isomerization/protonation sequence involving an appropriately functionalized indole precursor to generate a wide variety of pyran-fused indoles utilizing cooperative catalysis between cationic iridium (III) and bismuth triflate has been developed. Three distinct cyclization manifolds lead to bioactive scaffolds that can be obtained in good yields. In addition, N-substituted indoles can be synthesized enantioselectively via an oxocarbenium• chiral phosphate counterion strategy. PMID:24218144

Lombardo, Vince M.; Thomas, Christopher D.; Scheidt, Karl A.

2014-01-01

352

Highly efficient deep-blue phosphorescence from heptafluoropropyl-substituted iridium complexes.  

PubMed

New deep-blue iridium complexes, consisting of a heptafluoropropyl (HFP) substituent at the 3' position of 2',4''-difluorophenyl, have a deep HOMO level and decreased shoulder electronic transition and inhibit self-quenching due to the sterically hindered group without conjugation. An OLED using (HFP)2Ir(mpic) exhibited a maximum EQE of 21.4% with a CIE of (0.146, 0.165). PMID:25407660

Kim, Jung-Bum; Han, Seung-Hoon; Yang, Kiyull; Kwon, Soon-Ki; Kim, Jang-Joo; Kim, Yun-Hi

2015-01-01

353

An iridium abundance anomaly at the palynological Cretaceous-Tertiary boundary in northern New Mexico  

USGS Publications Warehouse

An iridium abundance anomaly, with concentrations up to 5000 parts per trillion over a background level of 4 to 20 parts per trillion, has been located in sedimentary rocks laid down under freshwater swamp conditions in the Raton Basin of northeastern New Mexico. The anomaly occurs at the base of a coal bed, at the same stratigraphic position at which several well-known species of Cretaceous-age pollen became extinct. Copyright ?? 1981 AAAS.

Orth, C.J.; Gilmore, J.S.; Knight, J.D.; Pillmore, C.L.; Tschudy, R.H.; Fassett, J.E.

1981-01-01

354

Ascent of Dinosaurs Linked to an Iridium Anomaly at the Triassic-Jurassic Boundary  

Microsoft Academic Search

Analysis of tetrapod footprints and skeletal material from more than 70 localities in eastern North America shows that large theropod dinosaurs appeared less than 10,000 years after the Triassic-Jurassic boundary and less than 30,000 years after the last Triassic taxa, synchronous with a terrestrial mass extinction. This extraordinary turnover is associated with an iridium anomaly (up to 285 parts per

P. E. Olsen; D. V. Kent; H.-D. Sues; C. Koeberl; A. Montanari; E. C. Rainforth; S. J. Fowell; M. J. Szajna; B. W. Hartline

2002-01-01

355

A Site-Isolated Iridium Diethylene Complex Supported on Highly Dealuminated Y Zeolite: Synthesis and Characterization  

SciTech Connect

Highly dealuminated Y zeolite-supported mononuclear iridium complexes with reactive ethylene ligands were synthesized by chemisorption of Ir(C2H4)2(C5H7O2). The resultant structure and its treatment in He, CO, ethylene, and H2 were investigated with infrared (IR) and extended X-ray absorption fine structure (EXAFS) spectroscopies. The IR spectra show that Ir(C2H4)2(C5H7O2) reacted readily with surface OH groups of the zeolite, leading to the removal of C5H7O2 ligands and the formation of supported mononuclear iridium complexes, confirmed by the lack of Ir-Ir contributions in the EXAFS spectra. The EXAFS data show that each Ir atom was bonded to four carbon atoms at an average distance of 2.10 Angstroms, consistent with the presence of two ethylene ligands per Ir atom and in agreement with the IR spectra indicating p-bonded ethylene ligands. The EXAFS data also indicate that each Ir atom was bonded to two oxygen atoms of the zeolite at a distance of 2.15 Angstroms . The supported iridium-ethylene complex reacted with H2 to give ethane, and it also catalyzed ethylene hydrogenation at atmospheric pressure and 294 K. Treatment of the sample in CO led to the formation of Ir(CO)2 complexes bonded to the zeolite. The sharpness of the ?CO bands indicates a high degree of uniformity of these complexes on the support. The iridium-ethylene complex on the crystalline zeolite support is inferred to be one of the most nearly uniform supported metal complex catalysts. The results indicate that it is isostructural with a previously reported rhodium complex on the same zeolite; thus, the results are a start to a family of analogous, structurally well-defined supported metal complex catalysts.

Uzun,A.; Bhirud, V.; Kletnieks, P.; Haw, J.; Gates, B.

2007-01-01

356

A mild dihydrobenzooxaphosphole oxazoline/iridium catalytic system for asymmetric hydrogenation of unfunctionalized dialins.  

PubMed

Air-stable P-chiral dihydrobenzooxaphosphole oxazoline ligands were designed and synthesized. When they were used in the iridium-catalyzed asymmetric hydrogenation of unfunctionalized 1-aryl-3,4-dihydronaphthalenes under one atmosphere pressure of H2 , up to 99:1 e.r. was obtained. High enantioselectivities were also observed in the reduction of the exocyclic imine derivatives of 1-tetralones. PMID:25385009

Qu, Bo; Samankumara, Lalith P; Ma, Shengli; Fandrick, Keith R; Desrosiers, Jean-Nicolas; Rodriguez, Sonia; Li, Zhibin; Haddad, Nizar; Han, Zhengxu S; McKellop, Keith; Pennino, Scott; Grinberg, Nelu; Gonnella, Nina C; Song, Jinhua J; Senanayake, Chris H

2014-12-22

357

Polymer phosphorescent light-emitting devices doped with tris(2-phenylpyridine) iridium as a triplet emitter  

Microsoft Academic Search

We have fabricated phosphorescent polymer light-emitting devices with tris(2-phenylpyridine) iridium [Ir(ppy)3] as a triplet emissive dopant in poly(vinylcarbazole) (PVK) host. The device with 8% doping concentration of [Ir(ppy)3] in PVK showed the external quantum efficiency of 1.9% and the peak luminance of 2,500 cd\\/m2. The emission spectrum of the device exhibited no emission from PVK, indicating that the energy transfer

Chang-Lyoul Lee; Kyung Bok Lee; Jang-Joo Kim

2000-01-01

358

Selective catalytic transfer dehydrogenation of alkanes and heterocycles by an iridium pincer complex.  

PubMed

Catalytic alkane dehydrogenation is a reaction with tremendous potential for application. We describe a highly active PSCOP-pincer iridium catalyst for transfer dehydrogenation of cyclic and linear alkanes. The dehydrogenation of linear alkanes occurs under relatively mild conditions with high regioselectivity for ?-olefin formation. In addition, the catalyst system is very effective in the dehydrogenation of heterocycles to form heteroarenes and olefinic products. PMID:24382741

Yao, Wubing; Zhang, Yuxuan; Jia, Xiangqing; Huang, Zheng

2014-01-27

359

Solvent free selective dehydrogenation of indolic and carbazolic molecules with an iridium pincer catalyst.  

PubMed

A previously known iridium POCOP pincer catalyst was found to selectively dehydrogenate the heterocyclic portion of several indolic and carbazolic molecules. These molecules were found to have an "activity window" (172-178 °C) upon which only the heterocyclic ring underwent dehydrogenation. All reactions were run solvent free, yields for selected substrates were excellent, and the products were isolated by either distillation or alumina plug filtration. PMID:24763968

Brayton, Daniel F; Jensen, Craig M

2014-06-01

360

Synthesis of Highly Active Mg-BASED Hydrides Using Hydriding Combustion Synthesis and NbF5 Additives  

NASA Astrophysics Data System (ADS)

Superiority of the hydriding combustion (HC) technique over conventional metallurgical approach to the synthesis of cost-effective Mg based hydrides, which show promise as hydrogen storage materials, is well known. In the present research, we report further improvements in HC prepared Mg-based materials, achieved by optimizing the preparative parameters of HC and by catalytic addition. Mg90-Ni60-C40 composites prepared using optimized processing parameters were ball-milled with NbF5 (10 h) and characterized for their micro-structural and hydriding properties. The ball-milled/catalyzed powder showed decreased crystallinity with CNTs on its surfaces. Surface area of the ball-milled powder decreased to almost half of the as-HC powder, while TG analysis revealed a four-fold decrease in the desorption temperature of the milled powder compared to that of the as-HC prepared powder. Activated samples achieved the maximum absorption/desorption limits (5.3 wt.%) at as low as 100°C, underlining the possibility of the use of these materials in portable hydrogen storage devices.

Chourashiya, M. G.; Park, C. N.; Park, C. J.

2012-09-01

361

A Novel Efficient Red Emitting Iridium Complex for Polymer Light Emitting Diodes  

NASA Astrophysics Data System (ADS)

Photo-physical properties of iridium complexes bis(1-(2',4'-difluorobiphenyl -4-yl)isoquinoline)iridium(III)(5-(4-(bis(4-methoxyphenyl)amino)phenyl)picolinic acid) used as phosphorescent dopant in polymer light-emitting devices with a blend ofpoly(9,9-dioctylfluorene) and 2-tert-butyl-phenyl-5-biphenyl-1,3,4-oxadiazole as a host matrix are investigated. The iridium complex exhibits distinct UV-vis absorption bands around 300-450 nm and intense red photoluminescent emissions peaked at around 618 nm in dichloromethane. The devices display a maximum external quantum efficiency of 4.8% and luminous efficiency of 3.1 cd·A-1 at current density of 3.2 mA·cm-2 with a dominant red emission peak around 620 nm and a shoulder around 660 nm. At 100 mA·cm-2, the devices still display a maximum external quantum efficiency as high as 3.9%.

Hu, Zheng-Yong; Yang, Jian-Kui; Luo, Jing; Liang, Min; Wang, Jing

2012-12-01

362

Rhodium and iridium salts inhibit proliferation and induce DNA damage in rat fibroblasts in vitro.  

PubMed

Environmental concentration of the platinum group elements is increased in the last years due to their use in automobile catalytic converters. Limited data are available on the effects of such elements at a cellular level and on their toxicity, especially for rhodium and iridium which have been more recently introduced in use. The toxic effects of rhodium and iridium salts were analyzed on a normal diploid rat fibroblast cell line in vitro. Both salts halted cell growth in a dose- and time-dependent fashion by inhibiting cell cycle progression, inducing apoptosis and modulating the expression of cell cycle regulatory proteins. In fact, they both caused an accumulation of cells in the G2/M phase of the cell cycle and affected the expression levels of pRb, cyclins D1 and E, p21(Waf1) and p27(Kip1). DNA strand breaks, as assessed by comet test, and an increase in the intracellular levels of reactive oxygen species also occurred in exposed cell cultures. These findings suggest a potential toxicity of both iridium and rhodium salts and emphasize the need for further studies to understand their effects at a cellular level to enable a better assessment of their toxic effects and to identify ways for their modulation and/or prevention. PMID:22521858

Iavicoli, Ivo; Cufino, Valerio; Corbi, Maddalena; Goracci, Martina; Caredda, Emanuele; Cittadini, Achille; Bergamaschi, Antonio; Sgambato, Alessandro

2012-09-01

363

Ultrasonic detection of laminar-type defects in iridium alloy blanks  

SciTech Connect

Encapsulated isotopic heat sources for use in generating electrical power for space applications require flight-quality hardware material. Iridium is the chosen material for such applications, and Oak Ridge National Laboratory has been the prime supplier of iridium alloy forming blanks 52 mm in diameter by 0.66 mm thick (1.0 by 0.026 in.). Prior to the work reported here, these blanks were ultrasonically examined by using 0.9-mm-diam (0.035-in.) simulated flaw standards. However, as a result of this effort, the sensitivity of our ultrasonic pulse-echo test system has been increased. The improved ultrasonic test system permits blank inspection at the 0.5-mm-diam (0.020-in.) simulated flaw detection level. This test system was successfully demonstrated on the initial blanks provided via an improved processing route (consumable arc-melting, extruding, and rolling). The equipment modification and/or selection and the specific focused search unit immersion technique developed to provide this capability are described. The improved flaw detection capability also provides data maps of a common type of defect in iridium (delaminations).

Cook, K.V.; Cunningham, R.A. Jr.; Simpson, W.A. Jr.; McClung, R.W.

1986-07-01

364

Supported Molecular Iridium Catalysts: Resolving Effects of Metal Nuclearity and Supports as Ligands  

SciTech Connect

The performance of a supported catalyst is influenced by the size and structure of the metal species, the ligands bonded to the metal, and the support. Resolution of these effects has been lacking because of the lack of investigations of catalysts with uniform and systematically varied catalytic sites. We now demonstrate that the performance for ethene hydrogenation of isostructural iridium species on supports with contrasting properties as ligands (electron-donating MgO and electron-withdrawing HY zeolite) can be elucidated on the basis of molecular concepts. Spectra of the working catalysts show that the catalytic reaction rate is determined by the dissociation of H{sub 2} when the iridium, either as mono- or tetra-nuclear species, is supported on MgO and is not when the support is the zeolite. The neighboring iridium sites in clusters are crucial for activation of both H{sub 2} and C{sub 2}H{sub 4} when the support is MgO but not when it is the zeolite, because the electron-withdrawing properties of the zeolite support enable even single site-isolated Ir atoms to bond to both C{sub 2}H{sub 4} and H{sub 2} and facilitate the catalysis.

Lu, Jing; Serna, Pedro; Aydin, Cerem; Browning, Nigel D.; Gates, Bruce C. (UCD)

2012-02-07

365

Neutron activation determination of iridium, gold, platinum, and silver in geologic samples  

USGS Publications Warehouse

Low-level methods for the determination of iridium and other noble metals have become increasingly important in recent years due to interest in locating abundance anomalies associated with the Cretaceous and Tertiary (K-T) boundary. Typical iridium anomalies are in the range of 1 to 100 ??g/kg (ppb). Thus methods with detection limits near 0.1 ??g/kg should be adequate to detect K-T boundary anomalies. Radiochemical neutron activation analysis methods continue to be required although instrumental neutron activation analysis techniques employing elaborate gamma-counters are under development. In the procedure developed in this study samples irradiated in the epithermal neutron facility of the U. S. Geological Survey TRIGA Reactor (Denver, Colorado) are treated with a mini-fire assay technique. The iridium, gold, and silver are collected in a 1-gram metallic lead button. Primary contaminants at this stage are arsenic and antimony. These can be removed by heating the button with a mixture of sodium perioxide and sodium hydroxide. The resulting 0.2-gram lead bead is counted in a Compton suppression spectrometer. Carrier yields are determined by reirradiation of the lead beads. This procedure has been applied to the U.S.G.S. Standard Rock PCC-1 and samples from K-T boundary sites in the Western Interior of North America. ?? 1987 Akade??miai Kiado??.

Millard, H.T., Jr.

1987-01-01

366

Flexible Nerve Stimulation Electrode with Iridium Oxide Sputtered on Liquid Crystal Polymer  

PubMed Central

Current electrode designs require flexible substrates that absorb little moisture and provide large charge injection capability. Sputtered iridium oxide films have superior charge injection capabilities versus noble metals and can adhere to various substrates. Liquid crystal polymers (LCP) have very little water absorption compared to other flexible substrates. Therefore, the combination of sputtered iridium oxide film on liquid crystal polymer substrate was studied using 50Hz, 100?s duration, 10mA biphasic current waveforms for 700 hours at 67°C in bicarbonate buffer saline. Scanning electron micrograph (SEM) analysis showed no delamination and approximately 1% of electrode material was lost to the bicarbonate buffer. The charge injection limit and the cathodic charge storage capacity within the water window were 4.6 +/? 1.0mC/cm2 and 31.5 +/? 6.6mC/cm2 respectively. Additional electrochemical analysis revealed significant charge imbalance attributed to oxygen reduction within the water window. These results, along with the flexible, chemically inert, biocompatible substrate, indicate that sputtered iridium oxide films on liquid crystal polymer could become the method of choice for flexible substrate nerve electrodes. PMID:19224713

Wang, Kevin; Liu, Chung-Chiun; Durand, Dominique M.

2009-01-01

367

Flexible nerve stimulation electrode with iridium oxide sputtered on liquid crystal polymer.  

PubMed

Current electrode designs require flexible substrates that absorb little moisture and provide large charge injection capability. Sputtered iridium oxide films have superior charge injection capabilities versus noble metals and can adhere to various substrates. Liquid crystal polymers (LCPs) have very little water absorption compared to other flexible substrates. Therefore, the combination of sputtered iridium oxide film on LCP substrate was studied using 50 Hz, 100 micros duration, and 10 mA biphasic current waveforms for 700 h at 67 degrees C in bicarbonate buffer saline. Scanning electron micrograph analysis showed no delamination and approximately 1% of electrode material was lost to the bicarbonate buffer. The charge injection limit and the cathodic charge storage capacity within the water window were 4.6 +/- 1.0 and 31.5 +/-6.6 mC/cm2, respectively. Additional electrochemical analysis revealed significant charge imbalance attributed to oxygen reduction within the water window. These results, along with the flexible, chemically inert, and biocompatible substrate, indicate that sputtered iridium oxide films on LCP could become the method of choice for flexible substrate nerve electrodes. PMID:19224713

Wang, Kevin; Liu, Chung-Chiun; Durand, Dominique M

2009-01-01

368

IRIDIUM—a program to model reaction of silicate liquid infiltrating a porous solid assemblage  

NASA Astrophysics Data System (ADS)

The migration of silicate liquid through porous rock can give rise to compositional changes in both the liquid and the host solid assemblage that are important in a number of fields of igneous petrology. Ongoing studies in numerical models of crystallization and compaction behavior in layered intrusions by our group have lead to a need to incorporate more realistic silicate crystallization behavior. The computer program IRIDIUM incorporates liquid-mineral equilibria with one-dimensional transport equations for modeling magmatic infiltration-reaction (IR) phenomenon. The program allows calculation of mineral precipitation/dissolution and chromatographic fronts as silicate liquid percolates through a porous solid matrix. The liquid-mineral equilibria part of the IRIDIUM program is based on the free energy minimization algorithm used in the MELTS software algorithm of Ghiorso and coworkers and includes trace element modeling. The IRIDIUM program incorporates both general and compaction-driven thermal and mass transport equations. A simple example involving infiltration metasomatism in olivine cumulates in the Muskox intrusion shows some of the capabilities of the program.

Boudreau, Alan E.

2003-05-01

369

Combining Electronic Structure Methods with the Calculation of Hydrogen Vibrational Wavefunctions: Application to Hydride Transfer in Liver Alcohol Dehydrogenase  

E-print Network

: Application to Hydride Transfer in Liver Alcohol Dehydrogenase Simon P. Webb, Pratul K. Agarwal, and Sharon of benzyl alcohol catalyzed by liver alcohol dehydrogenase (LADH). The hydride transfer from the benzyl

Hammes-Schiffer, Sharon

370

Combined on-board hydride slurry storage and reactor system and process for hydrogen-powered vehicles and devices  

DOEpatents

An on-board hydride storage system and process are described. The system includes a slurry storage system that includes a slurry reactor and a variable concentration slurry. In one preferred configuration, the storage system stores a slurry containing a hydride storage material in a carrier fluid at a first concentration of hydride solids. The slurry reactor receives the slurry containing a second concentration of the hydride storage material and releases hydrogen as a fuel to hydrogen-power devices and vehicles.

Brooks, Kriston P; Holladay, Jamelyn D; Simmons, Kevin L; Herling, Darrell R

2014-11-18

371

Synthesis, Structure, and Electronic Properties of Monomeric and Dimeric Trispyrazolylborate Platinum(II) Hydride Complexes  

E-print Network

Platinum(II) Hydride Complexes Stefan Reinartz, Mu-Hyun Baik, Peter S. White, Maurice Brookhart cationic platinum(II) monohydride complexes of the type [2-((Hpz*)BHpz*2)Pt- (H)(L)][BAr4] [L ) MeCN (4 and spectroscopic features. Dimeric hydride- bridged platinum complexes in particular have been extensively studied

Baik, Mu-Hyun

372

Opening of a Post Doctoral Position Complex hydrides for hydrogen storage applications  

E-print Network

Opening of a Post Doctoral Position Complex hydrides for hydrogen storage applications, Nanotechnology and Microsystems of the National Center for Scientific Research "Demokritos", is seeking on complex hydrides for hydrogen storage applications in connection with the « Fast, reliable and cost

373

FEASIBILITY OF RECYCLING PLUTONIUM AND MINOR ACTINIDES IN LIGHT WATER REACTORS USING HYDRIDE FUEL  

Microsoft Academic Search

The objective of this DOE NERI program sponsored project was to assess the feasibility of improving the plutonium (Pu) and minor actinide (MA) recycling capabilities of pressurized water reactors (PWRs) by using hydride instead of oxide fuels. There are four general parts to this assessment: ;\\u000a1)\\u0009Identifying promising hydride fuel assembly designs for recycling Pu and MAs in PWRs

Ehud Greenspan; Neil Todreas; Temitope Taiwo

2009-01-01

374

Hydrogen storage material and process using graphite additive with metal-doped complex hydrides  

DOEpatents

A hydrogen storage material having improved hydrogen absorbtion and desorption kinetics is provided by adding graphite to a complex hydride such as a metal-doped alanate, i.e., NaAlH.sub.4. The incorporation of graphite into the complex hydride significantly enhances the rate of hydrogen absorbtion and desorption and lowers the desorption temperature needed to release stored hydrogen.

Zidan, Ragaiy (Aiken, SC); Ritter, James A. (Lexington, SC); Ebner, Armin D. (Lexington, SC); Wang, Jun (Columbia, SC); Holland, Charles E. (Cayce, SC)

2008-06-10

375

ANALYSIS OF THE ELECTRON EXCITATION SPECTRA IN HEAVY RARE EARTH METALS, HYDRIDES AND OXIDES  

E-print Network

397 ANALYSIS OF THE ELECTRON EXCITATION SPECTRA IN HEAVY RARE EARTH METALS, HYDRIDES AND OXIDES C thin evaporated foils of heavy rare earths (Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) in three different chemical states (metal, hydride and oxide) exhibit two main peaks due to collective « plasmon » excitations

Boyer, Edmond

376

X-ray spectroscopy of electrochemically deposited iridium oxide films: detection of multiple sites through structural disorder.  

PubMed

We report the results of X-ray absorption spectroscopy studies on electrochemically deposited iridium oxide films. The emphasis of the study is the correlation of X-ray derived structural data with electrochemically controlled charge state. Data were acquired for films subject to redox cycling in neutral and alkaline aqueous media. In both cases, cyclic voltammetric responses show two redox couples, coulometrically of roughly equal magnitude. Assays of the iridium population (based on the iridium L(3) absorption edge amplitude) and the charge injected (based on integration of the voltammetric response) show that overall an average of ca. one electron per iridium atom is transferred. The absorption edge shifts indicate that the formal charge on the iridium changes, on average, from ca. 3.5+ to ca. 4.5+ across the entire process. EXAFS-derived changes in mean Ir-O distance and their mean square variation have been interpreted in terms of a two-site model, in which the two types of site have distinct redox potentials. Variations of local structure and disorder with potential are discussed and a generic model for structural disorder (parameterized via Debye-Waller factor) with diagnostic capability is developed. PMID:21173969

Hillman, A Robert; Skopek, Magdalena A; Gurman, Stephen J

2011-03-28

377

Iridium-catalyzed enantioselective cycloisomerization of nitrogen-bridged 1,6-enynes to 3-azabicylo[4.1.0]heptenes  

Microsoft Academic Search

A cationic iridium complex catalyzes a cycloisomerization of nitrogen-bridged 1,6-enynes to give 3-azabicyclo[4.1.0]heptenes in good to high yield. When an iridium-chiral diphosphine complex is used, the reaction proceeds enantiomerically to give chiral cyclopropanes fused by a six-membered ring system.

Takanori Shibata; Yuka Kobayashi; Shunsuke Maekawa; Natsuko Toshida; Kentaro Takagi

2005-01-01

378

Hydride-phase formation and its influence on fatigue crack propagationbehavior in a Zircaloy-4 alloy  

SciTech Connect

The hydride-phase formation and its influence on the fatigue behavior of a Zircaloy-4 alloy charged with hydrogen gas are investigated. First, the microstructure and fatigue crack propagation rate of the alloy in the as-received condition are studied. Second, the formation and homogeneous distribution of delta zirconium hydride ( -ZrH2) in the bulk, and its effect on the fatigue crack propagation rate are presented. The results show that in the presence of hydrides the zirconium alloy exhibits reduced toughness and enhanced crack growth rates. Finally, the influence of a pre-existing fatigue crack in the specimen and the subsequent hydride formation were investigated. The residual lattice strain profile around the fatigue crack tip was measured using neutron diffraction. The combined effects of residual strains and hydride precipitation on the fatigue behavior are discussed.

Garlea, Elena [University of Tennessee, Knoxville (UTK); Choo, H. [University of Tennessee, Knoxville (UTK); Wang, G Y [University of Tennessee, Knoxville (UTK); Liaw, Peter K [University of Tennessee, Knoxville (UTK); Clausen, B [Los Alamos National Laboratory (LANL); Brown, D. W. [Los Alamos National Laboratory (LANL); Park, Jae-Sung [University of Tennessee, Knoxville (UTK); Rack, P. D. [University of Tennessee, Knoxville (UTK); Kenik, Edward A [ORNL

2010-01-01

379

Analytical and numerical models of uranium ignition assisted by hydride formation  

SciTech Connect

Analytical and numerical models of uranium ignition assisted by the oxidation of uranium hydride are described. The models were developed to demonstrate that ignition of large uranium ingots could not occur as a result of possible hydride formation during storage. The thermodynamics-based analytical model predicted an overall 17 C temperature rise of the ingot due to hydride oxidation upon opening of the storage can in air. The numerical model predicted locally higher temperature increases at the surface; the transient temperature increase quickly dissipated. The numerical model was further used to determine conditions for which hydride oxidation does lead to ignition of uranium metal. Room temperature ignition only occurs for high hydride fractions in the nominally oxide reaction product and high specific surface areas of the uranium metal.

Totemeier, T.C.; Hayes, S.L. [Argonne National Lab., Idaho Falls, ID (United States). Engineering Div.

1996-05-01

380

ALUMINUM HYDRIDE: A REVERSIBLE MATERIAL FOR HYDROGEN STORAGE  

SciTech Connect

Hydrogen storage is one of the greatest challenges for implementing the ever sought hydrogen economy. Here we report a novel cycle to reversibly form high density hydrogen storage materials such as aluminium hydride. Aluminium hydride (AlH{sub 3}, alane) has a hydrogen storage capacity of 10.1 wt% H{sub 2}, 149 kg H{sub 2}/m{sup 3} volumetric density and can be discharged at low temperatures (< 100 C). However, alane has been precluded from use in hydrogen storage systems because of the lack of practical regeneration methods; the direct hydrogenation of aluminium to form AlH{sub 3} requires over 10{sup 5} bars of hydrogen pressure at room temperature and there are no cost effective synthetic means. Here we show an unprecedented reversible cycle to form alane electrochemically, using alkali alanates (e.g. NaAlH{sub 4}, LiAlH{sub 4}) in aprotic solvents. To complete the cycle, the starting alanates can be regenerated by direct hydrogenation of the dehydrided alane and the alkali hydride being the other compound formed in the electrochemical cell. The process of forming NaAlH{sub 4} from NaH and Al is well established in both solid state and solution reactions. The use of adducting Lewis bases is an essential part of this cycle, in the isolation of alane from the mixtures of the electrochemical cell. Alane is isolated as the triethylamine (TEA) adduct and converted to pure, unsolvated alane by heating under vacuum.

Fewox, C; Ragaiy Zidan, R; Brenda Garcia-Diaz, B

2008-12-31

381

ALUMINUM HYDRIDE: A REVERSIBLE MATERIAL FOR HYDROGEN STORAGE  

SciTech Connect

Hydrogen storage is one of the challenges to be overcome for implementing the ever sought hydrogen economy. Here we report a novel cycle to reversibly form high density hydrogen storage materials such as aluminium hydride. Aluminium hydride (AlH{sub 3}, alane) has a hydrogen storage capacity of 10.1 wt% H{sub 2}, 149 kg H{sub 2}/m{sup 3} volumetric density and can be discharged at low temperatures (< 100 C). However, alane has been precluded from use in hydrogen storage systems because of the lack of practical regeneration methods. The direct hydrogenation of aluminium to form AlH{sub 3} requires over 10{sup 5} bars of hydrogen pressure at room temperature and there are no cost effective synthetic means. Here we show an unprecedented reversible cycle to form alane electrochemically, using alkali metal alanates (e.g. NaAlH{sub 4}, LiAlH{sub 4}) in aprotic solvents. To complete the cycle, the starting alanates can be regenerated by direct hydrogenation of the dehydrided alane and the alkali hydride being the other compound formed in the electrochemical cell. The process of forming NaAlH{sub 4} from NaH and Al is well established in both solid state and solution reactions. The use of adducting Lewis bases is an essential part of this cycle, in the isolation of alane from the mixtures of the electrochemical cell. Alane is isolated as the triethylamine (TEA) adduct and converted to pure, unsolvated alane by heating under vacuum.

Zidan, R; Christopher Fewox, C; Brenda Garcia-Diaz, B; Joshua Gray, J

2009-01-09

382

Optical properties of metal-hydride switchable films  

NASA Astrophysics Data System (ADS)

In 1996 we discovered that yttrium-, lanthanum-, and rare-earth-hydride (REHx) films [1] protected by a thin palladium layer, exhibit spectacular changes in their optical properties when the hydrogen concentration x is increased from 2 to 3. For example, a 500 nm thick YH2 film is metallic and shiny while YH3 is yellowish and transparent. The transition is reversible, fast [2, 3], and can simply be induced by adding or removing hydrogen from the gas phase, an electrolyte or from an H containing liquid. The optical switching that occurs near the metal-insulator transition of these hydrides is remarkably robust as it is not affected by structural or compositional disorder. It occurs in polycrystalline and epitaxial films, in alloys with cubic or hexagonal crystal structures,and deuterides [4] switch as well as hydrides. At small length scales epitaxial YHx films exhibit surprising structural properties which open the way to pixel-by-pixel optical switching [5]. Colour-neutral switchable mirrors based on RE-Mg alloys [6] can be used in all-solid-state switchable devices. Newest results for Rare-Earth free switchable mirrors will be presented. [1] J. N. Huiberts, R. Griessen, J. H. Rector, R. J. Wijngaarden, J. P. Dekker, D. G. de Groot and N. J. Koeman, Nature 380 (1996) 231; [2] S. J. van der Molen, J. W. J. Kerssemakers, J. H. Rector, N. J. Koeman, B. Dam, R. Griessen, J. Appl. Phys. 86 (1999) 6107; [3] F. J. A. den Broeder, S. J. van der Molen, et al., Nature 394 (1998)656; [4] A. T. M. van Gogh, E. S. Kooij, R. Griessen, Phys. Rev. Lett. 83 (1999) 4614; [5] J. W. J. Kerssemakers, S. J. van der Molen and R. Griessen, Nature 406 (2000) 489; [6] P. van der Sluis, M. Ouwerkerk and P. A. Duine, Appl. Phys. Lett. 70 (1997) 3356.

Griessen, Ronald

2001-03-01

383

Electrochemical process and production of novel complex hydrides  

DOEpatents

A process of using an electrochemical cell to generate aluminum hydride (AlH.sub.3) is provided. The electrolytic cell uses a polar solvent to solubilize NaAlH.sub.4. The resulting electrochemical process results in the formation of AlH.sub.3. The AlH.sub.3 can be recovered and used as a source of hydrogen for the automotive industry. The resulting spent aluminum can be regenerated into NaAlH.sub.4 as part of a closed loop process of AlH.sub.3 generation.

Zidan, Ragaiy

2013-06-25

384

Pu 2O 3 and the plutonium hydriding process  

NASA Astrophysics Data System (ADS)

The role of cubic Pu 2O 3 in the corrosion of PuO 2-coated Pu by H 2 was investigated. Experiments were conducted to demonstrate that nucleation of hydriding is promoted by formation of Pu 2O 3 sites in the oxide layer. The nucleation mechanism based on diffusion of hydrogen through the PuO 2 layer was evaluated and an alternative mechanism based on formation of catalytic Pu 2O 3 sites via the Pu-PuO 2 reaction is proposed. The possibility of active participation of other impurities and inclusions in the dioxide is also discussed.

Dinh, L. N.; Haschke, J. M.; Saw, C. K.; Allen, P. G.; McLean, W., II

2011-01-01

385

Structural Stability of Complex Hydrides: LiBH4 Revisited  

NASA Astrophysics Data System (ADS)

A systematic approach to study the phase stability of LiBH4 based on ab initio calculations is presented. Three thermodynamically stable phases are identified and a new phase of Cc symmetry is proposed for the first time for a complex hydride. The x-ray diffraction pattern and vibrational spectra of the Cc structure agree well with recently reported experimental data on LiBH4. Calculations of the free energy at finite temperatures suggest that the experimentally proposed P63mc phase is unstable at T>0 K.

?odziana, Zbigniew; Vegge, Tejs

2004-09-01

386

Modeling of Gallium Nitride Hydride Vapor Phase Epitaxy  

NASA Technical Reports Server (NTRS)

A reactor model for the hydride vapor phase epitaxy of GaN is presented. The governing flow, energy, and species conservation equations are solved in two dimensions to examine the growth characteristics as a function of process variables and reactor geometry. The growth rate varies with GaCl composition but independent of NH3 and H2 flow rates. A change in carrier gas for Ga source from H2 to N2 affects the growth rate and uniformity for a fixed reactor configuration. The model predictions are in general agreement with observed experimental behavior.

Meyyappan, Meyya; Arnold, James O. (Technical Monitor)

1997-01-01

387

Ir/PuO/sub 2/ compatibility: transfer of impurities from plutonium dioxide to iridium metal during high temperature aging  

SciTech Connect

Plutonium oxide fuel pellets for powering radioisotopic thermoelectric generators for NASA space vehicles are encapsulated in iridium which has been grain-boundary-stabilized with thorium and aluminum. After aging for 6 months at 1310/sup 0/C under vacuum, enhanced grain growth is observed in the near-surface grains of the iridium next to the PuO/sub 2/. Examination of the grain boundaries by AES and SIMS shows a depletion of thorium and aluminum. Iron, chromium, and nickel from the fuel were found to diffuse into the iridium along the grain boundaries. Enhanced grain growth appears to result from thorium depletion in the grain boundaries of the near-surface grains next to the fuel. However, in one instance grain growth was slowed by the formation of thorium oxide by oxygen diffusing up the grain boundaries.

Taylor, D.H.; Christie, W.H.; Pavone, D.

1984-01-01

388

Theoretical study of the cyclometalated iridium(III) complexes used as chromophores for organic light-emitting diodes.  

PubMed

Time-dependent density functional theory with linear and quadratic response technology is used to calculate electronic structure, spectra, and spin-orbit coupling effects for analysis of the main mechanism for phosphorescence of the recently synthesized iridium complex [bis(2-phenylpyridine)(2-carboxy-4-dimethylaminopyridine)iridium(III)]. This compound exhibits strong green phosphorescence which is used in solution processable organic light-emitting diode devices (OLEDs) to overcome the efficiency limit imposed by the formation of triplet excitons. Attempting to foresee new structure-property relations that can guide an improved design of OLED devices based on phosphorescence of the lowest triplet state, we have conducted a theoretical analysis of the photophysical properties of a series of iridium cyclometalated complexes. PMID:19123853

Minaev, Boris; Minaeva, Valentina; Agren, Hans

2009-01-29

389

The effects of phosphorous donor ligand substitution on the reactivity of anionic group 6 transition metal carbonyl hydrides  

E-print Network

W(p-H)(CO)4{L)(PPh )] Bridging Hydride in THF Solution 35 37 47 A Comparison of Selectivity in the Reduction of Linear and Branched RBr by Anionic Group 6 Metal Hydrides 57 VI GC Yields for Reductions Using Various Acids with the Hydrides PPN HM(CO)4L... region of Na HW(CO)4P(OMe) in THF solution at 22'C Infrared spectrum of the car bonyl region of bridging hydride [AuW(rr-H)(CO)?(P(OMe) }(PPh )] 34 48 CHAPTER I INTRODUCTION The P-donor ligand substituted hydrides of the gnoup 6 transition metals...

Lusk, Richard Jay

2012-06-07

390

Measurement of nuclear fuel pin hydriding utilizing epithermal neutron scattering  

SciTech Connect

The measurement of hydrogen or zirconium hydriding in fuel cladding has long been of interest to the nuclear power industry. The detection of this hydrogen currently requires either destructive analysis (with sensitivities down to 1 {mu}g/g) or nondestructive thermal neutron radiography (with sensitivities on the order of a few weight percent). The detection of hydrogen in metals can also be determined by measuring the slowing down of neutrons as they collide and rapidly lose energy via scattering with hydrogen. This phenomenon is the basis for the {open_quotes}notched neutron spectrum{close_quotes} technique, also referred to as the Hysen method. This technique has been improved with the {open_quotes}modified{close_quotes} notched neutron spectrum technique that has demonstrated detection of hydrogen below 1 {mu}g/g in steel. The technique is nondestructive and can be used on radioactive materials. It is proposed that this technique be applied to the measurement of hydriding in zirconium fuel pins. This paper summarizes a method for such measurements.

Miller, W.H. [Univ. of Missouri, Columbia, MO (United States); Farkas, D.M.; Lutz, D.R. [General Electric Co., Pleasanton, CA (United States)

1996-12-31

391

Method of generating hydrogen-storing hydride complexes  

DOEpatents

A ternary hydrogen storage system having a constant stoichiometric molar ratio of LiNH.sub.2:MgH.sub.2:LiBH.sub.4 of 2:1:1. It was found that the incorporation of MgH.sub.2 particles of approximately 10 nm to 20 nm exhibit a lower initial hydrogen release temperature of 150.degree. C. Furthermore, it is observed that the particle size of LiBNH quaternary hydride has a significant effect on the hydrogen sorption concentration with an optimum size of 28 nm. The as-synthesized hydrides exhibit two main hydrogen release temperatures, one around 160.degree. C. and the other around 300.degree. C., with the main hydrogen release temperature reduced from 310.degree. C. to 270.degree. C., while hydrogen is first reversibly released at temperatures as low as 150.degree. C. with a total hydrogen capacity of 6 wt. % to 8 wt. %. Detailed thermal, capacity, structural and microstructural properties have been demonstrated and correlated with the activation energies of these materials.

Srinivasan, Sesha S; Niemann, Michael U; Goswami, D. Yogi; Stefanakos, Elias K

2013-05-14

392

First-principles modelling of magnesium titanium hydrides.  

PubMed

Mixing Mg with Ti leads to a hydride Mg(x)Ti((1 - x))H(2) with markedly improved (de)hydrogenation properties for x ? 0.8, as compared to MgH(2). Optically thin films of Mg(x)Ti((1 - x))H(2) have a black appearance, which is remarkable for a hydride material. In this paper we study the structure and stability of Mg(x)Ti((1 - x))H(2), x = 0-1 by first-principles calculations at the level of density functional theory. We give evidence for a fluorite to rutile phase transition at a critical composition x(c) = 0.8-0.9, which correlates with the experimentally observed sharp decrease in (de)hydrogenation rates at this composition. The densities of states of Mg(x)Ti((1 - x))H(2) have a peak at the Fermi level, composed of Ti d states. Disorder in the positions of the Ti atoms easily destroys the metallic plasma, however, which suppresses the optical reflection. Interband transitions result in a featureless optical absorption over a large energy range, causing the black appearance of Mg(x)Ti((1 - x))H(2). PMID:21386386

Er, Süleyman; van Setten, Michiel J; de Wijs, Gilles A; Brocks, Geert

2010-02-24

393

ACCEPTABILITY ENVELOPE FOR METAL HYDRIDE-BASED HYDROGEN STORAGE SYSTEMS  

SciTech Connect

The design and evaluation of media based hydrogen storage systems requires the use of detailed numerical models and experimental studies, with significant amount of time and monetary investment. Thus a scoping tool, referred to as the Acceptability Envelope, was developed to screen preliminary candidate media and storage vessel designs, identifying the range of chemical, physical and geometrical parameters for the coupled media and storage vessel system that allow it to meet performance targets. The model which underpins the analysis allows simplifying the storage system, thus resulting in one input-one output scheme, by grouping of selected quantities. Two cases have been analyzed and results are presented here. In the first application the DOE technical targets (Year 2010, Year 2015 and Ultimate) are used to determine the range of parameters required for the metal hydride media and storage vessel. In the second case the most promising metal hydrides available are compared, highlighting the potential of storage systems, utilizing them, to achieve 40% of the 2010 DOE technical target. Results show that systems based on Li-Mg media have the best potential to attain these performance targets.

Hardy, B.; Corgnale, C.; Tamburello, D.; Garrison, S.; Anton, D.

2011-07-18

394

A Colorimetric and Luminescent Dual-Modal Assay for Cu(II) Ion Detection Using an Iridium(III) Complex  

PubMed Central

A novel iridium(III) complex-based chemosensor bearing the 5,6-bis(salicylideneimino)-1,10-phenanthroline ligand receptor was developed, which exhibited a highly sensitive and selective color change from colorless to yellow and a visible turn-off luminescence response upon the addition of Cu(II) ions. The interactions of this iridium(III) complex with Cu2+ ions and thirteen other cations have been investigated by UV-Vis absorption titration, emission titration, and 1H NMR titration. PMID:24927177

Ma, Dik-Lung; He, Hong-Zhang; Chan, Daniel Shiu-Hin; Wong, Chun-Yuen; Leung, Chung-Hang

2014-01-01

395

Multi-scale characterization of nanostructured sodium aluminum hydride  

NASA Astrophysics Data System (ADS)

Complex metal hydrides are the most promising candidate materials for onboard hydrogen storage. The practicality of this class of materials is counter-poised on three critical attributes: reversible hydrogen storage capacity, high hydrogen uptake/release kinetics, and favorable hydrogen uptake/release thermodynamics. While a majority of modern metallic hydrides that are being considered are those that meet the criteria of high theoretical storage capacity, the challenges lie in addressing poor kinetics, thermodynamics, and reversibility. One emerging strategy to resolve these issues is via nanostructuring or nano-confinement of complex hydrides. By down-sizing and scaffolding them to retain their nano-dimensions, these materials are expected to improve in performance and reversibility. This area of research has garnered immense interest lately and there is active research being pursued to address various aspects of nanostructured complex hydrides. The research effort documented here is focused on a detailed investigation of the effects of nano-confinement on aspects such as the long range atomic hydrogen diffusivities, localized hydrogen dynamics, microstructure, and dehydrogenation mechanism of sodium alanate. A wide variety of microporous and mesoporous materials (metal organic frameworks, porous silica and alumina) were investigated as scaffolds and the synthesis routes to achieve maximum pore-loading are discussed. Wet solution infiltration technique was adopted using tetrahydrofuran as the medium and the precursor concentrations were found to have a major role in achieving maximum pore loading. These concentrations were optimized for each scaffold with varying pore sizes and confinement was quantitatively characterized by measuring the loss in specific surface area. This work is also aimed at utilizing neutron and synchrotron x-ray characterization techniques to study and correlate multi-scale material properties and phenomena. Some of the most advanced instruments were utilized for this work and their data collection and analysis are reported. Quasielastic neutron scattering experiments were conducted at NIST Center for Neutron Research to characterize atomic hydrogen diffusion in bulk and nano-confined NaAlH4. It was observed that upon confinement of NaAlH4, a significantly higher fraction of hydrogen atoms were involved in diffusive motion on the pico-second to nano-second timescales. However, the confinement had no impact on the lattice diffusivities (jump/hopping rates) of atomic hydrogen, indicating that the improved hydrogen release rates were not due to any kinetic destabilization effects. Instead, the investigation strongly suggested thermodynamic destabilization as the major effect of nano-confinement. The local interaction of the metal sites in metal organic frameworks with the infiltrated hydride was studied using extended x-ray absorption spectroscopy technique. The experiments were conducted at Center for Advanced Microstructures and Devices at Louisiana State University. The metal sites were found to be chemically un-altered, hence ruling out any catalytic role in the dehydrogenation at room temperatures. The fractal morphology of NaAlH4 was characterized by ultra-small angle x-ray scattering experiments performed at Argonne National Lab. The studies quantitatively estimated the extent of densification in the course of one desorption cycle. The particle sizes were found to increase two-fold during heat treatment. Also, the nano-confinement procedure was shown to produce dense mass fractals as opposed to pristine NaAlH4, exhibiting a surface fractal morphology. Based on this finding, a new method to identify confined material from un-confined material in nano-composites was developed and is presented. Preliminary results of modeling and correlating multi-scale phenomena using a phase-field approach are also presented as the foundation for future work.

NaraseGowda, Shathabish

396

Efficient light harvesting and energy transfer in a red phosphorescent iridium dendrimer.  

PubMed

A series of red phosphorescent iridium dendrimers of the type [Ir(btp)2(pic-PCn)] (Ir-Gn; n = 0, 1, 2, and 3) with two 2-(benzo[b]thiophen-2-yl)pyridines (btp) and 3-hydroxypicolinate (pic) as the cyclometalating and ancillary ligands were prepared in good yields. Dendritic generation was grown at the 3 position of the pic ligand with 4-(9H-carbazolyl)phenyl dendrons connected to 3,5-bis(methyleneoxy)benzyloxy branches (PCn; n = 0, 2, 4, and 8). The harvesting photons on the PCn dendrons followed by efficient energy transfer to the iridium center resulted in high red emissions at ?600 nm by metal-to-ligand charge transfer. The intensity of the phosphorescence gradually increased with increasing dendrimer generation. Steady-state and time-resolved spectroscopy were used to investigate the energy-transfer mechanism. On the basis of the fluorescence quenching rate constants of the PCn dendrons, the energy-transfer efficiencies for Ir-G1, Ir-G2, and Ir-G3 were 99, 98, and 96%, respectively. The energy-transfer efficiency for higher-generation dendrimers decreased slightly because of the longer distance between the PC dendrons and the core iridium(III) complex, indicating that energy transfer in Ir-Gn is a Förster-type energy transfer. Finally, the light-harvesting efficiencies for Ir-G1, Ir-G2, and Ir-G3 were determined to be 162, 223, and 334%, respectively. PMID:25418124

Cho, Yang-Jin; Hong, Seong Ahn; Son, Ho-Jin; Han, Won-Sik; Cho, Dae Won; Kang, Sang Ook

2014-12-15

397

Triplet exciton diffusion in fac-tris(2-phenylpyridine) iridium(III)-cored electroluminescent dendrimers  

NASA Astrophysics Data System (ADS)

We have studied triplet-triplet annihilation in neat films of electrophosphorescent fac-tris(2-phenylpyridine) iridium(III) [Ir(ppy)3]-cored dendrimers containing phenylene- and carbazole-based dendrons with 2-ethylhexyloxy surface groups using time-resolved photoluminescence. From measured annihilation rates, the limiting current densities above which annihilation would dominate in dendrimer light-emitting devices are found to be >1A/cm2. The triplet exciton diffusion length varies in the range of 2-10 nm depending on the dendron size. The distance dependence of the nearest-neighbor hopping rate shows that energy transfer is dominated by the exchange mechanism.

Namdas, Ebinazar B.; Ruseckas, Arvydas; Samuel, Ifor D. W.; Lo, Shih-Chun; Burn, Paul L.

2005-02-01

398

The effects of iridium on the renal function of female Wistar rats.  

PubMed

Despite the widespread use of iridium (Ir) in catalytic converters for improved capacity for reducing carbon monoxide (CO), hydrocarbon (HC) and nitrogen oxide (NO(x)) emissions, there is a lack of studies that have assessed possible toxicological hazards of exposure to Ir. The present investigation indicates that female Wistar rats exposed to Ir in the drinking water for 90 days displayed renal toxicity based on the elevated urinary retinol binding protein (RBP) and albumin. The RBP was more sensitive to albumin, showing significant increases at 0.01 mg/L. PMID:21764451

Iavicoli, Ivo; Fontana, Luca; Marinaccio, Alessandro; Alimonti, Alessandro; Pino, Anna; Bergamaschi, Antonio; Calabrese, Edward J

2011-10-01

399

Palynological and iridium anomalies at Cretaceous-Tertiary boundary, south-central Saskatchewan  

USGS Publications Warehouse

The Cretaceous-Tertiary boundary in south-central Saskatchewan is marked by coincident anomalies in abundance of iridium and fern spores at the extinction level of a suite of Cretaceous pollen taxa. Evidence of disruption of the terrestrial flora includes the fern-spore abundance anomaly and local extinction of as much as 30 percent of angiosperm species. The reorganized earliest Tertiary flora is made up largely of surviving species that assumed new roles of dominance. Persistence of climatically sensitive taxa across the boundary indicates that if paleoclimate was altered by the terminal Cretaceous event, it returned quickly to the pre-event condition.

Nichols, D.J.; Jarzen, D.M.; Orth, C.J.; Oliver, P.Q.

1986-01-01

400

Iridium Catalyzed Hydrocarboxylation of 1,1-Dimethylallene: Byproduct-Free Reverse Prenylation of Carboxylic Acids  

PubMed Central

Exposure of carboxylic acids 1a-12a to commercially available 1,1-dimethylallene in the presence of substoichiometric quantities of an iridium catalyst prepared in situ from [Ir(cod)Cl]2 and BIPHEP provides the corresponding 1,1-dimethylallyl (reverse prenyl) esters 1b-12b in 74–92% isolated yield. This protocol represents the first branch-regioselective allene hydrocarboxylation. Stoichiometric byproducts are not generated in this process and protecting groups are not required for alcohols, phenols and indolic amines. PMID:18181640

Kim, In Su

2010-01-01

401

Enzymatic Determination of Diglyceride Using an Iridium Nano-Particle Based Single Use, Disposable Biosensor  

PubMed Central

A single use, disposable iridium-nano particle contained biosensor had been developed for the determination of diglyceride (DG). In this study hydrogen peroxide, formed through the enzymatic breakdown of DG via lipase, glycerol kinase and glycerol 3-phosphate oxidase, was electrochemically oxidized at an applied potential of +0.5 V versus the Ag/AgCl reference electrode. The oxidation current was then used to quantify the diglyceride concentration. Optimum enzyme concentrations and the surfactant loading used were established for successful sensor response. Good linear performance was observed over a DG concentration range of 0 to 25 ?M in phosphate buffer and bovine serum media. PMID:22219685

Hsu, Shu-Yi; Bartling, Brandon; Wang, Christina; Shieu, Fuh-Sheng; Liu, Chung-Chiun

2010-01-01

402

Iridium(III)-Catalyzed Direct C-7 Amination of Indolines with Organic Azides.  

PubMed

Iridium-catalyzed regioselective C-7 amination of indolines has been achieved with organic azides as a facile nitrogen source. The developed procedure is convenient to perform even at room temperature and applicable to a wide range of substrates with high catalytic activity. Various types of organic azides (sulfonyl, aryl, and alkyl derivatives) were all successfully reacted under the present conditions as the viable reactant. Furthermore, indoline substrates bearing easily removable N-protecting groups such as N-Boc or N-Cbz could readily be employed, highlighting the synthetic utility of this methodology. PMID:25219399

Shin, Kwangmin; Chang, Sukbok

2014-12-19

403

A Site-Isolated Iridium Diethylene Complex Supported on Highly Dealuminated Y Zeolite: Synthesis And Characterization  

SciTech Connect

Highly dealuminated Y zeolite-supported mononuclear iridium complexes with reactive ethylene ligands were synthesized by chemisorption of Ir(C{sub 2}H{sub 4}){sub 2}(C{sub 5}H{sub 7}O{sub 2}). The resultant structure and its treatment in He, CO, ethylene, and H2 were investigated with infrared (IR) and extended X-ray absorption fine structure (EXAFS) spectroscopies. The IR spectra show that Ir(C{sub 2}H{sub 4}){sub 2}(C{sub 5}H{sub 7}O{sub 2}) reacted readily with surface OH groups of the zeolite, leading to the removal of C{sub 5}H{sub 7}O{sub 2} ligands and the formation of supported mononuclear iridium complexes, confirmed by the lack of Ir-Ir contributions in the EXAFS spectra. The EXAFS data show that each Ir atom was bonded to four carbon atoms at an average distance of 2.10 {angstrom}, consistent with the presence of two ethylene ligands per Ir atom and in agreement with the IR spectra indicating {pi}-bonded ethylene ligands. The EXAFS data also indicate that each Ir atom was bonded to two oxygen atoms of the zeolite at a distance of 2.15 {angstrom}. The supported iridium-ethylene complex reacted with H{sub 2} to give ethane, and it also catalyzed ethylene hydrogenation at atmospheric pressure and 294 K. Treatment of the sample in CO led to the formation of Ir(CO){sub 2} complexes bonded to the zeolite. The sharpness of the V{sub CO} bands indicates a high degree of uniformity of these complexes on the support. The iridium-ethylene complex on the crystalline zeolite support is inferred to be one of the most nearly uniform supported metal complex catalysts. The results indicate that it is isostructural with a previously reported rhodium complex on the same zeolite; thus, the results are a start to a family of analogous, structurally well-defined supported metal complex catalysts.

Uzun, A.; Bhirud, V.A.; Kletnieks, P.W.; Haw, J.F.; Gates, B.C.

2009-06-04

404

A colorimetric chemosensor for Cu2+ ion detection based on an iridium(III) complex  

NASA Astrophysics Data System (ADS)

We report herein the synthesis and application of a series of novel cyclometalated iridium(III) complexes 1-3 bearing a rhodamine-linked NˆN ligand for the detection of Cu2+ ions. Under the optimised conditions, the complexes exhibited high sensitivity and selectivity for Cu2+ ions over a panel of other metal ions, and showed consistent performance in a pH value range of 6 to 8. Furthermore, the potential application of this system for the monitoring of Cu2+ ions in tap water or natural river water samples was demonstrated.

Wang, Modi; Leung, Ka-Ho; Lin, Sheng; Chan, Daniel Shiu-Hin; Kwong, Daniel W. J.; Leung, Chung-Hang; Ma, Dik-Lung

2014-10-01

405

The Collision of Iridium 33 and Cosmos 2251: The Shape of Things to Come  

NASA Technical Reports Server (NTRS)

The collision of Iridium 33 and Cosmos 2251 was the most severe accidental fragmentation on record. More than 1800 debris approx. 10 cm and larger were produced. If solar activity returns to normal, half of the tracked debris will reenter within five years. Less than 60 cataloged debris had reentered by 1 October 2009. Some debris from both satellites will remain in orbit through the end of the century. The collision rate of one every five years will increase without future removal of large derelict spacecraft and launch vehicle orbital stages.

Nicholas, Johnson

2009-01-01

406

Evolution of odd A transitional iridium nuclei at the strong deformation limit levels of $\\^{185}$Ir  

E-print Network

A level scheme is proposed for neutron deficient /sup 185/Ir obtained by the decay of /sup 185/Pt produced with the ISOLDE on-line separator (CERN). This level scheme is compared to those of heavier mass iridium nuclei where the negative parity levels had been interpreted in the asymmetric-rotor-plus-particle model. In /sup 185/Ir similar systems of levels appear with a stronger prolate deformation of the nucleus. They seem correctly described by coupling an odd-particle (or a hole) to a symmetric rotor.

Sébille-Schück, C; Genevey-Rivier, J; Höglund, A; Huck, A; Knipper, A; Richard-Serre, Claude; Walter, G

1976-01-01

407

Iridium 192 implantation of T1 and T2 carcinomas of the mobile tongue  

Microsoft Academic Search

Between 1970 and 1986, 166 patients with T1 or T2 epidermoid carcinomas of the mobile tongue were treated by iridium 192 implantation (70 T1N0, 83 T2N0, 13 T1-2 N1-3). Five-year actuarial survival was 52% for T1N0, 44% for T2aN0, and 8% for or T1-2 N1-3. Cause specific survivals were 90%, 71%, and 46%, respectively. Local control was 87% for both

J. J. Mazeron; J. M. Crook; V. Benck; G. Marinello; M. Martin; M. Raynal; E. Haddad; R. Peynegre; J. P. Le Bourgeois; W. Walop

1990-01-01

408

Iridium(III) complex-coated nanosystem for ratiometric upconversion luminescence bioimaging of cyanide anions.  

PubMed

Chromophoric iridium(III) complex-coated NaYF(4): 20%Yb, 1.6%Er, 0.4%Tm nanocrystals are demonstrated as a ratiometric upconversion luminescence (UCL) probe for highly selective detection of cyanide anion and bioimaging of CN(-) in living cells through inhibition of the energy transfer from the UCL of the nanocrystals to the absorbance of the chromophoric complex. The UCL probe provides a very low detection limit of 0.18 ?M CN(-) in the aqueous solution. PMID:21892822

Liu, Jinliang; Liu, Yi; Liu, Qian; Li, Chunyan; Sun, Lining; Li, Fuyou

2011-10-01

409

Triplet Exciton Diffusion and Phosphorescence Quenching in Iridium(III)-Centered Dendrimers  

NASA Astrophysics Data System (ADS)

A study of triplet-triplet exciton annihilation and nonradiative decay in films of iridium(III)-centered phosphorescent dendrimers is reported. The average separation of the chromophore was tuned by the molecular structure and also by blending with a host material. It was found that triplet exciton hopping is controlled by electron exchange interactions and can be over 600 times faster than phosphorescence quenching. Nonradiative decay occurs by weak dipole-dipole interactions and is independent of exciton diffusion, except in very thin films (<20nm) where surface quenching dominates the decay.

Ribierre, J. C.; Ruseckas, A.; Knights, K.; Staton, S. V.; Cumpstey, N.; Burn, P. L.; Samuel, I. D. W.

2008-01-01

410

Relationship between mass extinction and iridium across the Cretaceous-Paleogene boundary in New Jersey  

USGS Publications Warehouse

We directly link iridium (Ir) anomalies in New Jersey to the mass extinction of marine plankton marking the Cretaceous-Paleogene (K-Pg) boundary. We confirm previous reports of an Ir anomaly 20 cm below the extinction of Cretaceous macrofauna (the "Pinna" bed) with new results from a muddy sand section from Tighe Park, Freehold, New Jersey (United States), but we also show that Ir anomalies correlate with marine mass extinctions at three other clay-rich New Jersey sections. Thus, we attribute the anomaly at Freehold to the downward movement of Ir and reaffirm the link between impact and mass extinction. ?? 2010 Geological Society of America.

Miller, K.G.; Sherrell, R.M.; Browning, J.V.; Field, M.P.; Gallagher, W.; Olsson, R.K.; Sugarman, P.J.; Tuorto, S.; Wahyudi, H.

2010-01-01

411

Field desorption microscopy of graphene on iridium in intercalation with alkali metals  

NASA Astrophysics Data System (ADS)

Field-desorption and field-emission electron microscopy methods have been used to study the effect of a strong electric field on the processes of potassium and cesium desorption from the graphene surface on an iridium field emitter. It was found that two phases of field desorption may exist for these alkali metals. In the low-field phase, alkali metal atoms adsorbed on the surface are desorbed. The existence of the high-field phase is attributed to the egress from under the graphene film and ionization of intercalated alkali metal atoms under the action of the electric field.

Bernatskii, D. P.; Pavlov, V. G.

2014-12-01

412

Development of a used fuel cladding damage model incorporating circumferential and radial hydride responses  

NASA Astrophysics Data System (ADS)

At the completion of the fuel drying process, used fuel Zry4 cladding typically exhibits a significant population of ?-hydride inclusions. These inclusions are in the form of small platelets that are generally oriented both circumferentially and radially within the cladding material. There is concern that radially-oriented hydride inclusions may weaken the cladding material and lead to issues during used fuel storage and transportation processes. A high fidelity model of the mechanical behavior of hydrides has utility in both designing fuel cladding to be more resistant to this hydride-induced weakening and also in suggesting modifications to drying, storage, and transport operations to reduce the impact of hydride formation and/or the avoidance of loading scenarios that could overly stress the radial inclusions. We develop a mechanical model for the Zry4-hydride system that, given a particular morphology of hydride inclusions, allows the calculation of the response of the hydrided cladding under various loading scenarios. The model treats the Zry4 matrix material as J2 elastoplastic, and treats the hydrides as platelets oriented in predefined directions (e.g., circumferentially and radially). The model is hosted by the Albany analysis framework, where a finite element approximation of the weak form of the cladding boundary value problem is solved using a preconditioned Newton-Krylov approach. Instead of forming the required system Jacobian operator directly or approximating its action with a differencing operation, Albany leverages the Trilinos Sacado package to form the Jacobian via automatic differentiation. We present results that describe the performance of the model in comparison with as-fabricated Zry4 as well as HB Robinson fuel cladding. Further, we also present performance results that demonstrate the efficacy of the overall solution method employed to host the model.

Chen, Qiushi; Ostien, Jakob T.; Hansen, Glen

2014-04-01

413

Effect of silicon impurities and heat treatment on uranium hydriding rates  

NASA Astrophysics Data System (ADS)

Several experiments were run to identify variables that affect the hydriding rate of depleted uranium. Only two factors affecting hydriding rate were found: temperature (and time) of the final heat treatment, and silicon content. Increasing the time and temperature of alpha-phase anneals increased the reaction rate, and annealing in the beta-phase greatly increased the reaction rate over alpha-phase annealing. Silicon contents of up to 100 wppm cause dramatic increases in the hydride reaction rate for both alpha- and beta-phase annealed samples.

DeMint, A. L.; Leckey, J. H.

2000-10-01

414

The storage of hydrogen in the form of metal hydrides: An application to thermal engines  

NASA Technical Reports Server (NTRS)

The possibility of using LaNi56, FeTiH2, or MgH2 as metal hydride storage sytems for hydrogen fueled automobile engines is discussed. Magnesium copper and magnesium nickel hydrides studies indicate that they provide more stable storage systems than pure magnesium hydrides. Several test engines employing hydrogen fuel have been developed: a single cylinder motor originally designed for use with air gasoline mixture; a four-cylinder engine modified to run on an air hydrogen mixture; and a gas turbine.

Gales, C.; Perroud, P.

1981-01-01

415

The Zr20Nb-H phase diagram and the characterisation of hydrides in ?-Zr  

NASA Astrophysics Data System (ADS)

In this work a combination of synchrotron X-ray diffraction, transmission electron microscopy and differential scanning calorimetry have been used to characterise the Zr20Nb-H phase diagram and hydrides in ?-Zr. A single hydride phase, termed ?' was found to be present in ?-Zr over a wide range of H concentrations up to 1559 wppm. ?'-hydride had an orthorhombic crystal structure with the composition ZrH0.4 ± 0.2, and was found to be stable during heating to 450 °C; it can therefore be considered the equilibrium hydride in ?-Zr. Accompanying hydride nucleation is a volumetric strain of 10.4% that is accommodated elastically and plastically by the ?-Zr. The body-centre cubic to orthorhombic martensitic transformation is analogous to the Au-Cd system where the basal plane in the hydride is constructed from the (0 1 1)? to give the Bain correspondence. There are strong similarities between the Zr20Nb-H and Nb-H phase diagrams with the former having a lower solubility for H at room temperature, ˜130 wppm and ˜290 wppm respectively. The room temperature solubility difference between body-centre cubic Nb and ?-Zr can be attributed to their electron configurations and the reduction in energy associated with the metallic Zr/Nb-H bonding. The hydrides were found to have a plate morphology and consisted of sub-platelets analogous to ?-hydride in ?-Zr. The hydride had an orthorhombic crystal structure and the (0?(0,[0?[0 and [1?[ orientation relationship with the ?-Zr matrix, consistent with the Au-Cd system. gamma;'-hydride formation was accompanied by a volumetric strain of 10.4% that is accommodated elastically and plastically in the matrix. Sympathetic hydride nucleation occurs in the elastic strain field of the parent hydride. In all instances the long axis of the hydride was consistent with the <0 1 1>?. beta;-Zr has a H solubility of 128 ± 5 wppm at room temperature and considerably higher than ?-Zr. The solubility difference between the BCC and HCP structures can be attributed to the size and number of tetrahedral sites within the respective lattices. In the absence of Nb, the H solubility in ?-Zr would be considerably lower. The Zr-20Nb-H and Nb-H phase diagrams are similar. However, BCC-Nb has a higher H solubility than ?-Zr as a result of their different electron configurations. The ?/? + ?' solvus reaches a plateau at a H concentration of ˜1400 wppm; this is consistent with the concentration at which the enthalpy of formation of BCC ZrH becomes negative. Only one hydride phase, ?' was found in the Zr-20Nb-H system. This phase had the composition ZrH0.4±0.2 and was stable at all the temperatures evaluated. It is analogous to the ?-NbH in the Nb-H system. There was a small hysteresis in the TSSd and TSSp temperatures. This can be attributed to the narrow temperature range over which the hydride forms (˜80 °C) and the smaller volumetric strain for the nucleation of ?'-hydride in ?-Zr than ?-hydride in ?-Zr.

Barrow, L.; Barrow, A. T. W.; Almer, J.; Daymond, M. R.

2013-11-01

416

DEVELOPMENT OF A FABRICATION PROCESS FOR SOL-GEL/METAL HYDRIDE COMPOSITE GRANULES  

SciTech Connect

An external gelation process was developed to produce spherical granules that contain metal hydride particles in a sol-gel matrix. Dimensionally stable granules containing metal hydrides are needed for applications such as hydrogen separation and hydrogen purification that require columns containing metal hydrides. Gases must readily flow through the metal hydride beds in the columns. Metal hydrides reversibly absorb and desorb hydrogen and hydrogen isotopes. This is accompanied by significant volume changes that cause the metal hydride to break apart or decrepitate. Repeated cycling results in very fine metal hydride particles that are difficult to handle and contain. Fine particles tend to settle and pack making it more difficult to flow gases through a metal hydride bed. Furthermore, the metal hydrides can exert a significant force on the containment vessel as they expand. These problems associated with metal hydrides can be eliminated with the granulation process described in this report. Small agglomerates of metal hydride particles and abietic acid (a pore former) were produced and dispersed in a colloidal silica/water suspension to form the feed slurry. Fumed silica was added to increase the viscosity of the feed slurry which helped to keep the agglomerates in suspension. Drops of the feed slurry were injected into a 27-foot tall column of hot ({approx}70 C), medium viscosity ({approx}3000 centistokes) silicone oil. Water was slowly evaporated from the drops as they settled. The drops gelled and eventually solidified to form spherical granules. This process is referred to as external gelation. Testing was completed to optimize the design of the column, the feed system, the feed slurry composition, and the operating parameters of the column. The critical process parameters can be controlled resulting in a reproducible fabrication technique. The residual silicone oil on the surface of the granules was removed by washing in mineral spirits. The granules were dried in air at 40 C. The granules were heated to 230 C for 30 minutes in argon to remove the remaining water and organic materials. The resulting product was spherical composite granules (100 to 2000 micron diameter) with a porous silica matrix containing small agglomerates of metal hydride particles. Open porosity in the silica matrix allows hydrogen to permeate rapidly through the matrix but the pores are small enough to contain the metal hydride particles. Additional porosity around the metal hydride particles, induced using abietic acid as a pore former, allows the particles to freely expand and contract without fracturing the brittle sol-gel matrix. It was demonstrated that the granules readily absorb and desorb hydrogen while remaining integral and dimensionally stable. Microcracking was observed after the granules were cycled in hydrogen five times. The strength of the granules was improved by coating them with a thin layer of a micro-porous polymer sol-gel that would allow hydrogen to freely pass through the coating but would filter out metal hydride poisons such as water and carbon monoxide. It was demonstrated that if a thin sol-gel coating was applied after the granules were cycled, the coating not only improved the strength of the granules but the coated granules retained their strength after additional hydrogen cycling tests. This additional strength is needed to extend the lifetime of the granules and to survive the compressive load in a large column of granules. Additional hydrogen adsorption tests are planned to evaluate the performance of coated granules after one hundred cycles. Tests will also be performed to determine the effects of metal hydride poisons on the granules. The results of these tests will be documented in a separate report. The process that was developed to form these granules could be scaled to a production process. The process to form granules from a mixture of metal hydride particles and pore former such as abietic acid can be scaled up using commercial granulators. The current laboratory-scale external gelation column produc

Hansen, E; Eric Frickey, E; Leung Heung, L

2004-02-23

417

Characterization of sputtered iridium oxide thin films on planar and laser micro-structured platinum thin film surfaces for neural stimulation applications  

NASA Astrophysics Data System (ADS)

Electrical stimulation of neurons provides promising results for treatment of a number of diseases and for restoration of lost function. Clinical examples include retinal stimulation for treatment of blindness and cochlear implants for deafness and deep brain stimulation for treatment of Parkinsons disease. A wide variety of materials have been tested for fabrication of electrodes for neural stimulation applications, some of which are platinum and its alloys, titanium nitride, and iridium oxide. In this study iridium oxide thin films were sputtered onto laser micro-structured platinum thin films by pulsed-DC reactive sputtering of iridium metal in oxygen-containing atmosphere, to obtain high charge capacity coatings for neural stimulation applications. The micro-structuring of platinum films was achieved by a pulsed-laser-based technique (KrF excimer laser emitting at lambda=248nm). The surface morphology of the micro-structured films was studied using different surface characterization techniques. In-vitro biocompatibility of these laser micro-structured films coated with iridium oxide thin films was evaluated using cortical neurons isolated from rat embryo brain. Characterization of these laser micro-structured films coated with iridium oxide, by cyclic voltammetry and impedance spectroscopy has revealed a considerable decrease in impedance and increase in charge capacity. A comparison between amorphous and crystalline iridium oxide thin films as electrode materials indicated that amorphous iridium oxide has significantly higher charge capacity and lower impedance making it preferable material for neural stimulation application. Our biocompatibility studies show that neural cells can grow and differentiate successfully on our laser micro-structured films coated with iridium oxide. This indicates that reactively sputtered iridium oxide (SIROF) is biocompatible.

Thanawala, Sachin

418

Picosecond laser micromachining of nitinol and platinum-iridium alloy for coronary stent applications  

NASA Astrophysics Data System (ADS)

The demand for micromachining of coronary stents by means of industrial lasers rises quickly for treating coronary artery diseases, which cause more than one million deaths each year. The most widely used types of laser for stent manufacturing are Nd:YAG laser systems with a wavelength of 1064 nm with pulse lengths of 10-3-10-2 seconds. Considerable post-processing is required to remove heat-affected zones (HAZ), and to improve surface finishes and geometry. Using a third harmonic laser radiation of picosecond laser (6×10-12 s pulse duration) in UV range, the capability of the picosecond laser micromachining of nitinol and platinum-iridium alloy for coronary stent applications are presented. In this study dross-free cut of nitinol and platinum-iridium alloy tubes are demonstrated and topography analysis of the cut surface is carried out. The HAZ characteristics have been investigated by means of microscopic examinations and measurement of micro-hardness distribution near the cut zones.

Muhammad, N.; Whitehead, D.; Boor, A.; Oppenlander, W.; Liu, Z.; Li, L.

2012-03-01

419

Phase diagram and electrical behavior of silicon-rich iridium silicide compounds  

NASA Technical Reports Server (NTRS)

The iridium-silicon phase diagram on the silicon-rich side was investigated by means of X-ray powder diffraction, density, differential thermal analysis, metalography, microprobe analysis, and electrical resistivity. Attempts were made to prepare eight previously reported silicon-rich iridium silicide compounds by arc melting and Bridgman-like growth. However, microprobe analysis identified only four distinct compositions: IrSi, Ir3Si4, Ir3Si5 and IrSi sub about 3. The existence of Ir4Si5 could not be confirmed in this study, even though the crystal structure has been previously reported. Differential thermal analysis (DTA) in conjunction with X-ray powder diffraction confirm polymorphism in IrSi sub about 3, determined to have orthorhombic and monoclinic unit cells in the high and low temperature forms. A eutectic composition alloy of 83 +/- 1 atomic percent silicon was observed between IrSi sub about 3 and silicon. Ir3Si4 exhibits distinct metallic behavior while Ir3Si5 is semiconducting. Both and IrSi and IrSi sub about 3 exhibit nearly temperature independent electrical resistivities on the order of 5-10 x 10 exp -6 ohms-m.

Allevato, C. E.; Vining, Cronin B.

1992-01-01

420

High-Performance Computer Modeling of the Cosmos-Iridium Collision  

SciTech Connect

This paper describes the application of a new, integrated modeling and simulation framework, encompassing the space situational awareness (SSA) enterprise, to the recent Cosmos-Iridium collision. This framework is based on a flexible, scalable architecture to enable efficient simulation of the current SSA enterprise, and to accommodate future advancements in SSA systems. In particular, the code is designed to take advantage of massively parallel, high-performance computer systems available, for example, at Lawrence Livermore National Laboratory. We will describe the application of this framework to the recent collision of the Cosmos and Iridium satellites, including (1) detailed hydrodynamic modeling of the satellite collision and resulting debris generation, (2) orbital propagation of the simulated debris and analysis of the increased risk to other satellites (3) calculation of the radar and optical signatures of the simulated debris and modeling of debris detection with space surveillance radar and optical systems (4) determination of simulated debris orbits from modeled space surveillance observations and analysis of the resulting orbital accuracy, (5) comparison of these modeling and simulation results with Space Surveillance Network observations. We will also discuss the use of this integrated modeling and simulation framework to analyze the risks and consequences of future satellite collisions and to assess strategies for mitigating or avoiding future incidents, including the addition of new sensor systems, used in conjunction with the Space Surveillance Network, for improving space situational awareness.

Olivier, S; Cook, K; Fasenfest, B; Jefferson, D; Jiang, M; Leek, J; Levatin, J; Nikolaev, S; Pertica, A; Phillion, D; Springer, K; De Vries, W

2009-08-28

421

Ligand exchange and redox processes in iridium triazolylidene complexes relevant to catalytic water oxidation.  

PubMed

Iridium(III) complexes containing a bidentate spectator ligand have emerged as powerful catalyst precursors for water oxidation. Here we investigate the initial steps of the transformation at the iridium center when using complex [IrCp*(pyr-trz)Cl] 1 (Cp* = pentamethylcyclopentadienyl, pyr-trz = 4-(2-pyridyl)-1,2,3-triazol-5-ylidene), a potent water oxidation catalyst precursor. Ligand exchange with water is facile and is reversed in the presence of chloride ions, while MeCN substitution is effective only from the corresponding aqua complex. A pKa of 8.3 for the aqua complex was determined, which is in agreement with strong electron donation from the triazolylidene ligand that is comparable to aryl anions. Evaluation of the pH-dependent oxidation process in aqueous media reveals two regimes (pH 4-8.5 and above pH 10.5) where proton-coupled electron transfer processes occur. These investigations will help to further optimize water oxidation catalysts and indicate that MeCN as a cosolvent has adverse effects for initiating water coordination in the oxidation process. PMID:25415556

Petronilho, Ana; Llobet, Antoni; Albrecht, Martin

2014-12-15

422

Dynamic Structural Changes in a Molecular Zeolite-Supported Iridium Catalyst for Ethene Hydrogenation  

SciTech Connect

The structure of a catalyst often changes as a result of changes in the reactive environment during operation. Examples include changes in bulk phases, extended surface structures, and nanoparticle morphologies; now we report real-time characterization of changes in the structure of a working supported catalyst at the molecular level. Time-resolved extended X-ray absorption fine structure (EXAFS) data demonstrate the reversible interconversion of mononuclear iridium complexes and tetrairidium clusters inside zeolite Y cages, with the structure controlled by the C{sub 2}H{sub 4}/H{sub 2} ratio during ethene hydrogenation at 353 K. The data demonstrate break-up of tetrairidium clusters into mononuclear complexes indicated by a decrease in the Ir-Ir coordination number in ethene-rich feed. When the feed composition was switched to first equimolar and then to a H{sub 2}-rich (C{sub 2}H{sub 4}/H{sub 2} = 0.3) feed, the EXAFS spectra show the reformation of tetrairidium clusters as the Ir-Ir coordination number increased again. When the feed composition was cycled from ethene-rich to H{sub 2}-rich, the predominant species in the catalyst cycled accordingly. Evidence confirming the structural change is provided by IR spectra of iridium carbonyls formed by probing of the catalyst with CO. The data are the first showing how to tune the structure of a solid catalyst at the molecular scale by choice of the reactant composition.

Uzun, Alper; Gates, Bruce C.; (UCD)

2009-11-16

423

[Brachytherapy in France: current situation and economic outlook due to the unavailability of iridium wires].  

PubMed

In 2013, about 6000 patients were treated with brachytherapy, the number diminishing by 2.6% per year since 2008. Prostate, breast and gynecological cancers are the most common types of cancers. Since 2008, the number of brachytherapy facilities has decreased by 18%. In medicoeconomic terms, brachytherapy faces many problems: the coding system is outdated; brachytherapy treatments cost as much as internal radiation; fees do not cover costs; since iridium wire has disappeared from the market, the technique will be transferred to more expensive high-speed or pulse dose rates. The French financing grid based on the national study of costs lags behind changes in such treatments and in the best of cases, hospitals resorting to alternatives such as in-hospital brachytherapy are funded at 46% of their additional costs. Brachytherapy is a reference technique. With intense pressure on hospital pricing, financing brachytherapy facilities will become even more problematic as a consequence of the disappearance of iridium 192 wires. The case of brachytherapy illustrates the limits of the French financing system and raises serious doubts as to its responsiveness. PMID:25195115

Le Vu, B; Boucher, S

2014-10-01

424

Iridium-catalyzed dehydrogenative decarbonylation of primary alcohols with the liberation of syngas.  

PubMed

A new iridium-catalyzed reaction in which molecular hydrogen and carbon monoxide are cleaved from primary alcohols in the absence of any stoichiometric additives has been developed. The dehydrogenative decarbonylation was achieved with a catalyst generated in situ from [Ir(coe)(2)Cl](2) (coe = cyclooctene) and racemic 2,2'-bis(diphenylphosphino)-1,1'-binaphthyl (rac-BINAP) in a mesitylene solution saturated with water. A catalytic amount of lithium chloride was also added to improve the catalyst turnover. The reaction has been applied to a variety of primary alcohols and gives rise to products in good to excellent yields. Ethers, esters, imides, and aryl halides are stable under the reaction conditions, whereas olefins are partially saturated. The reaction is believed to proceed by two consecutive organometallic transformations that are catalyzed by the same iridium(I)-BINAP species. First, dehydrogenation of the primary alcohol to the corresponding aldehyde takes place, which is then followed by decarbonylation to the product with one less carbon atom. PMID:23108889

Olsen, Esben P K; Madsen, Robert

2012-12-01

425

Infrared study of CO and NO adsorption on alumina-supported iridium catalyst  

SciTech Connect

Infrared spectroscopic measurements were performed for NO and CO adsorbed on reduced and oxidized ir supported on ..gamma..-Al/sub 2/O/sub 3/. Adsorption of NO on a reduced sample produced bands at 1900 and 1850 cm/sup -1/. These bands are attributed to NO adsorbed as NO/sup +delta/ on metal atoms of larger iridium crystallites (Site A) and on iridium atoms influenced strongly by the support (Site B), respectively. Spectra of NO adsorbed on an oxidized sample showed only a single band at 1950 cm/sup -1/. This band is assigned as NO/sup +delta/ on partially oxidized ir sites. CO adsorption on a reduced sample produced bands at 2070-2060 and 2020 cm/sup -1/, which are associated with CO linearly bonded to Site A and Site B, respectively. Oxidation of the sample and subsequent adsorption of CO caused a band only at 2060 cm/sup -1/, which is assigned as CO linearly bonded to Site A. Detailed investigations were made on the effect of the pressure, adsorption temperature, and evacuation at different temperatures on the intensities of the above bands. 7 figures, 3 tables.

Solymosi, F.; Rasko, J.

1980-04-01

426

Color tuning by changing the substituent of highly luminescent iridium (III) complexes  

NASA Astrophysics Data System (ADS)

Our investigations refer to highly efficient emitting materials used in organic light-emitting diodes (OLED). We are especially interested in the possibility of shifting the emission wavelength in phosphorescent iridium(III) complexes. Depending on the mesomeric and inductive behavior of different substituents, the emission spectrum can be varied by introducing those substituents at various positions of the chromophoric ligand. Therefore, we synthesized Ir(ppy)3- analogue complexes with nitrile, trifluoromethyl and methoxy groups at different positions of the ligand's phenyl ring to determine the influence of the position and of each substituent on the emission spectrum. To further study the adjustability we prepared several heteroleptic complexes and changed the ancillary ligand therein. In addition, we developed a new and as yet unknown ligand system based on hetero five membered rings, cyclometalated to iridium to generate homo- and heteroleptic complexes. Devices obtained with these emitting materials have shown high luminescence efficiencies of up to 30 lm/W @ 500 cd/m2.

Weinaug, U. J.; Ammermann, S.; Gargouri, H.; Hoping, M.; Erk, P.; Kahle, K.; Lennartz, Ch.; Molt, O.; Münster, I.; Tamm, M.; Kowalsky, W.; Johannes, H.-H.

2008-08-01

427

Disposable amperometric sensor for neurotransmitters based on screen-printed electrodes modified with a thin iridium oxide film.  

PubMed

Potential cycling in the range from -0.2 to +1.2 V is used for the electrodeposition of hydrous iridium oxide films onto a screen-printed electrode from a saturated solution of alkaline iridium(III) solution. The iridium oxide redox couple shows a stable and obvious reversible redox, with the formal potential being pH dependent in the range 1-14. The properties, stability and electrochemical properties of iridium oxide films were investigated by cyclic voltammetry. A modified electrode showed excellent catalytic activity toward the oxidation of neurotransmitters (catecholamines) over a wide pH range (2-8). The electrocatalytic behavior is further exploited as a sensitive detection scheme for adrenaline and dopamine by hydrodynamic amperometry. Under the optimized conditions, the calibration curves are linear in the concentration range 0.1-70 and 0.1-15 microM for dopamine and adrenaline determination, respectively. The detection limit and sensitivity are 30 nM and 30 nA/microM for adrenaline and 15 nM and 80 nA/microM for dopamine. Finally, the analytical performance of the modified electrode was demonstrated for the elimination of interference by uric acid in catecholamines determination when present in a 1000-fold concentration excess. PMID:16317893

Salimi, Abdollah; Alizadeh, Vali; Compton, Richard G

2005-11-01

428

Enhancement of activity of RuSex electrocatalyst by modification with nanostructured iridium towards more efficient reduction of oxygen  

NASA Astrophysics Data System (ADS)

Electrocatalytic activity of carbon (Vulcan XC-72) supported selenium-modified ruthenium, RuSex/C, nanoparticles for reduction of oxygen was enhanced through intentional decoration with iridium nanostructures (dimensions, 2-3 nm). The catalytic materials were characterized in oxygenated 0.5 mol dm-3 H2SO4 using cyclic and rotating ring disk voltammetric techniques as well as using transmission electron microscopy and scanning electron microscopy equipped with X-ray dispersive analyzer. Experiments utilizing gas diffusion electrode aimed at mimicking conditions existing in the low-temperature fuel cell. Upon application of our composite catalytic system, the reduction of oxygen proceeded at more positive potentials, and higher current densities were observed when compared to the behavior of the simple iridium-free system (RuSex/C) investigated under the analogous conditions. The enhancement effect was more pronounced than that one would expect from simple superposition of voltammetric responses for the oxygen reduction at RuSex/C and iridium nanostructures studied separately. Nanostructured iridium acted here as an example of a powerful catalyst for the reduction of H2O2 (rather than O2) and, when combined with such a moderate catalyst as ruthenium-selenium (for O2 reduction), it produced an integrated system of increased electrocatalytic activity in the oxygen reduction process. The proposed system retained its activity in the presence of methanol that could appear in a cathode compartment of alcohol fuel cell.

Dembinska, Beata; Kiliszek, Malgorzata; Elzanowska, Hanna; Pisarek, Marcin; Kulesza, Pawel J.

2013-12-01

429

Site-isolated Iridium Complexes on MgO Powder: Individual Ir Atoms Imaged by Scanning Transmission Electron Microscopy  

SciTech Connect

Iridium complexes were synthesized on MgO powder by adsorption of Ir(C{sub 2}H{sub 4}){sub 2}(acac) [acac = acetonylacetonate]; images determined by aberration-corrected scanning transmission electron microscopy show individual Ir atoms, demonstrating that the supported complexes were site-isolated.

Uzun, A.; Ortalan, V; D. Browning, N; C. Gates , B

2009-01-01

430

Prognostic factors of local outcome for T1, T2 carcinomas of oral tongue treated by iridium 192 implantation  

Microsoft Academic Search

The results of Iridium 192 implantation for 121 node negative T1 or T2 squamous carcinomas of mobile tongue were reviewed to look for predictors of local control and necrosis. Age, sex, total dose, dose rate, linear activity, and intersource spacing were examined. Minimum follow-up was 2 years but no patient with local recurrence or necrosis was excluded. There were 57

J. J. Mazeron; J. M. Crook; G. Marinello; W. Walop; B. Pierquin

1990-01-01

431

Electronic structure and optical properties of lightweight metal hydrides  

Microsoft Academic Search

We study the electronic structures and dielectric functions of the simple\\u000ahydrides LiH, NaH, MgH2 and AlH3, and the complex hydrides Li3AlH6, Na3AlH6,\\u000aLiAlH4, NaAlH4 and Mg(AlH4)2, using first principles density functional theory\\u000aand GW calculations. All these compounds are large gap insulators with GW\\u000asingle particle band gaps varying from 3.5 eV in AlH3 to 6.5 eV in the

M. J. van Setten; V. A. Popa; G. A. de Wijs; G. Brocks

2007-01-01

432

Comparison of delayed hydride cracking behavior of two zirconium alloys  

NASA Astrophysics Data System (ADS)

Delayed hydride cracking (DHC) is an important failure mechanism that may occur in Zr alloys during service in water-cooled reactors. Two conditions must be attained to initiate DHC from a crack: the stress intensity factor must be higher than a threshold value called KIH and, hydrogen concentration must exceed a critical value. Currently the pressure tubes for CANDU reactor are fabricated from Zr-2.5Nb. In this paper the critical hydrogen concentration for DHC and the crack velocity of a developmental pressure tube, Excel, was evaluated and compared with that of Zr-2.5Nb. The DHC velocity values measured in Excel were higher than usually reported in Zr-2.5Nb. Due to the higher hydrogen solubility limits in Excel, its critical hydrogen concentration for DHC initiation is 10-50 wppm over that of Zr-2.5Nb in the range of 150-300 °C.

Ponzoni, L. M. E.; Mieza, J. I.; De Las Heras, E.; Domizzi, G.

2013-08-01

433

Ovonic nickel metal hydride batteries for space applications  

NASA Technical Reports Server (NTRS)

Ovonic nickel-metal hydride (NiMH) rechargeable batteries are easily adaptable to a variety of applications. Small consumer NiMH cells were developed and are now being manufactured by licensees throughout the world. This technology was successfully scaled up in larger prismatic cells aimed at electric vehicle applications. Sealed cells aimed at satellite power applications were also built and cycle tested by OBC and other outside agencies. Prototype batteries with high specific energy (over 80 Wh/kg), high energy density (245 Wh/L), and excellent power capability (400 W/kg) were produced. Ovonic NiMH batteries demonstrated an excellent cycle life of over 10,000 cycles at 30 percent DOD. Presently, Ovonic Battery Company is working on an advanced version of this battery for space applications as part of an SBIR contract from NASA.

Venkatesan, S.; Corrigan, D. A.; Fetcenko, M. A.; Gifford, P. R.; Dhar, S. K.; Ovshinsky, S. R.

1993-01-01

434

Parametrization of a reactive force field for aluminum hydride  

SciTech Connect

A reactive force field, REAXFF, for aluminum hydride has been developed based on density functional theory (DFT) derived data. REAXFF{sub AlH{sub 3}} is used to study the dynamics governing hydrogen desorption in AlH{sub 3}. During the abstraction process of surface molecular hydrogen charge transfer is found to be well described by REAXFF{sub AlH{sub 3}}. Results on heat of desorption versus cluster size show that there is a strong dependence of the heat of desorption on the particle size, which implies that nanostructuring enhances desorption process. In the gas phase, it was observed that small alane clusters agglomerated into a bigger cluster. After agglomeration molecular hydrogen was desorbed from the structure. This thermodynamically driven spontaneous agglomeration followed by desorption of molecular hydrogen provides a mechanism on how mobile alane clusters can facilitate the mass transport of aluminum atoms during the thermal decomposition of NaAlH{sub 4}.

Ojwang, J. G. O. [Schuit Institute of Catalysis, Eindhoven University of Technology, Postbus 513, Den Dolech 2, Eindhoven 5600 MB (Netherlands); Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Rd. NW, Washington D.C. 20012 (United States); Santen, Rutger A. van; Kramer, Gert Jan [Schuit Institute of Catalysis, Eindhoven University of Technology, Postbus 513, Den Dolech 2, Eindhoven 5600 MB (Netherlands); Duin, Adri C. T. van [Department of Mechanical and Nuclear Engineering, Pennsylvania State University, University Park, Pennsylvania 16802 (United States); Goddard, William A. III [Materials and Process Simulation Center (MSC), California Institute of Technology, 1200 East California Boulevard, Pasadena, California 91125 (United States)

2009-07-28

435

Parametrization of a reactive force field for aluminum hydride  

NASA Astrophysics Data System (ADS)

A reactive force field, REAXFF, for aluminum hydride has been developed based on density functional theory (DFT) derived data. REAXFFAlH3 is used to study the dynamics governing hydrogen desorption in AlH3. During the abstraction process of surface molecular hydrogen charge transfer is found to be well described by REAXFFAlH3. Results on heat of desorption versus cluster size show that there is a strong dependence of the heat of desorption on the particle size, which implies that nanostructuring enhances desorption process. In the gas phase, it was observed that small alane clusters agglomerated into a bigger cluster. After agglomeration molecular hydrogen was desorbed from the structure. This thermodynamically driven spontaneous agglomeration followed by desorption of molecular hydrogen provides a mechanism on how mobile alane clusters can facilitate the mass transport of aluminum atoms during the thermal decomposition of NaAlH4.

Ojwang, J. G. O.; van Santen, Rutger A.; Kramer, Gert Jan; van Duin, Adri C. T.; Goddard, William A.

2009-07-01

436

LaNi5 hydride cryogenic refrigerator test results  

NASA Technical Reports Server (NTRS)

A complete LaNi5 hydrogen absorption cryogenic refrigerator system was developed. The system uses low temperature waste heat of approximately 100 C as a power source, and has no moving parts other than self operating valves. The cycle continues automatically by an electronic sequencing timing mechanism for the three compressors which are phased such that a constant supply of high pressure hydrogen gas is provided. It is indicated that with a fully clean hydrogen system, hundreds of thousand cycles should be attainable, even though some degradation may eventually occur. Simple vacuum reactivation of the hydride of moving parts, other than self operating, long life valves, the refrigerators predicted life is extremely long.

Jones, J. A.

1983-01-01

437

Pressure-induced transformations of molecular boron hydride  

NASA Astrophysics Data System (ADS)

Decaborane, a molecular boron hydride, was compressed to 131 GPa at room temperature to explore possible non-molecular phases in this system and their physical properties. Decaborane changed its colour from transparent yellow to orange/red above 50 GPa and then to black above 100 GPa, suggesting some transformations. Raman scattering and infrared (IR) absorption spectroscopy reveal significant structural changes. Above 100 GPa, B-B skeletal, B-H and B-H-B Raman/IR peaks gradually disappeared, which implies a transformation into a non-molecular phase in which conventional borane-type bonding is lost. The optical band gap of the material at 100 GPa was estimated to be about 1.0 eV.

Nakano, Satoshi; Hemley, Russell J.; Gregoryanz, Eugene A.; Goncharov, Alexander F.; Mao, Ho-kwang

2002-11-01

438

Final report for the DOE Metal Hydride Center of Excellence.  

SciTech Connect

This report summarizes the R&D activities within the U.S. Department of Energy Metal Hydride Center of Excellence (MHCoE) from March 2005 to June 2010. The purpose of the MHCoE has been to conduct highly collaborative and multi-disciplinary applied R&D to develop new reversible hydrogen storage materials that meet or exceed DOE 2010 and 2015 system goals for hydrogen storage materials. The MHCoE combines three broad areas: mechanisms and modeling (which provide a theoretically driven basis for pursuing new materials), materials development (in which new materials are synthesized and characterized) and system design and engineering (which allow these new materials to be realized as practical automotive hydrogen storage systems). This Final Report summarizes the organization and execution of the 5-year research program to develop practical hydrogen storage materials for light duty vehicles. Major results from the MHCoE are summarized, along with suggestions for future research areas.

Keller, Jay O.; Klebanoff, Leonard E.

2012-01-01

439

Atomistic modeling of the plutonium-hydride systems  

NASA Astrophysics Data System (ADS)

Thermodynamic solubility data for hydrogen in plutonium and its alloys suggest the formation of vacancy-hydrogen clusters, for less than 2 at.% hydrogen. It is also known that hydrogen induces lattice contraction of the system. These data along with the low melting point of Pu meet the conditions for superabundant vacancies, which can significantly affect material properties and phase stability. Detailed mechanisms for vacancy diffusion and hydrogen trapping at the atomic scale are largely unknown, however. We investigate the equilibrium properties of Pu-hydrides using various techniques of Monte Carlo simulations. Hydrogen solubility and vacancy concentration are computed as a function of temperature. We also discuss effects of the superabundant vacancies on bulk thermal and mechanical properties.

Lee, Tongsik; Baskes, Mike; Lawson, A. C.; Chen, Shaoping; Valone, Steve; Taylor, Chris

2013-03-01

440

Catalytic effect of carbon nanomaterials on light metal hydride systems  

NASA Astrophysics Data System (ADS)

Carbon nanomaterials are becoming recognized for their use in catalyzing hydrogen desorption from light metal hydride systems, in particular complex borohydrides and alanates. For example, it was shown by us that graphene, carbon nanotubes, and especially fullerenes can improve the hydrogen sorption properties of sodium alanate [Nano Lett. 9, 1501 (2009)]. In parallel to ongoing experimental investigations, we have carried out further theoretical studies in order to better understand the underlying catalyzing mechanism. Our most recent work is concentrated on the interaction of lithium borohydride with fullerene where a complete dehydrogenation process was simulated using the cluster approach. Furthermore, the catalytic effect of graphene nanofibres on sodium alanate has been experimentally demonstrated by our collaborators, and we have studied this system from first principles as well, to better understand the origin of its catalytic effect.

Qian, Zhao; Ahuja, Rajeev; Moyses Araujo, C.; Blomqvist, Andreas; Pathak, Biswarup; Scheicher, Ralph H.

2011-03-01

441

Transition Metal Allyls and Hydrides as Chemical Vapor Deposition Precursors.  

NASA Astrophysics Data System (ADS)

Thin films of high purity palladium can be prepared at low temperature (250^circC) metal-organic chemical vapor deposition of bis(allyl)palladium or (cyclopentadienyl)(allyl)palladium. Metal sulfide films may be deposited from the precursors rm Fe_2S_2(CO)_6 and Ti(S-t-Bu)_4 to give thin films of iron sulfide and titanium disulfide at low temperature. CVD of Ti(BH_4)_3(dme) at 200^circC resulted in deposition of thin films of TiB_2. The AES data establish the films as TiB_{2.07 } with less than 5% carbon and oxygen in the film interior. Passage of Zr(BH_4)_4 or Hf(BH_4)_4 through a hot zone at 250^circC resulted in deposition of thin films of MB_2. In order to trap some of the hydride species that may be formed from the CVD of Zr(BH_4)_4 and Hf(BH_4)_4, these precursors were thermolyzed in the presence of small alkyl phosphines. Treatment of the zirconium and hafnium tetrahydroborate complexes M(BH_4)_4 with trimethylphosphine yields crystals of the new polyhydride rm Zr_2H_3(BH_4)_5(PMe _3)_2 and rm Hf_2H _3(BH_4)_5(PMe_3)_2. Single crystal X-ray diffraction studies of the complexes reveal a distinctly asymmetric dinuclear structure bridged by three hydrogen atoms. Treatment of rm Zr(BH_4) _4 or rm Hf(BH_4)_4 with trimethylphosphine for extended reaction times has given two new polyhydrides of stoichiometry rm M_3H_6(BH_4)_6(PMe _3)_4. The variable temperature ^1H, ^{31} P, and ^{11}B NMR data suggest that these trinuclear compounds contain a non-cyclic M(mu-H)_3 M(mu-H)_3M backbone with the phosphine and tetrahydroborate ligands distributed in 2:2:0 and 2:1:3 ratios among the three metal centers. This suggestion has been confirmed by a single crystal X-ray structure. Treatment of the M(BH_4)_4 complexes with the bidentate phosphine 1,2-bis(dimethyl -phosphino)ethane (dmpe) gives mononuclear hydrides of stoichiometry MH(BH_4)_3(dmpe) _2 or rm MH_2(BH_4) _2(dmpe)_2 depending on the conditions. Treatment of the polyhydride complexes rm M_2H_3(BH_4)_5(PMe _3)_2 with dmpe has given two new group 4 polyhydrides of stoichiometry rm M_2H_4(BH_4)_4(dmpe)_2 . The variable temperature NMR data suggest that these dinuclear compounds contain a M(mu -H)_3M backbone with the phosphine and tetrahydroborate ligands distributed in 2:0 and 1:3 ratios among the two metal centers; this has been confirmed by the single crystal X-ray structure. A terminal hydride is positioned in between the two bidentate dmpe ligands. A dynamic process exchanges these hydride environments, and a likely mechanism for this process has been proposed.

Gozum, John Ekrem

442

Modelling zirconium hydrides using the special quasirandom structure approach.  

PubMed

The study of the structure and properties of zirconium hydrides is important for understanding the embrittlement of zirconium alloys used as cladding in light water nuclear reactors. Simulation of the defect processes is complicated due to the random distribution of the hydrogen atoms. We propose the use of the special quasirandom structure approach as a computationally efficient way to describe this random distribution. We have generated six special quasirandom structure cells based on face centered cubic and face centered tetragonal unit cells to describe ZrH(2-x) (x = 0.25-0.5). Using density functional theory calculations we investigate the mechanical properties, stability, and electronic structure of the alloys. PMID:23588997

Wang, H; Chroneos, A; Jiang, C; Schwingenschlögl, U

2013-05-28

443

Capture of liquid hydrogen boiloff with metal hydride absorbers  

NASA Technical Reports Server (NTRS)

A procedure which uses metal hydrides to capture some of this low pressure (,1 psig) hydrogen for subsequent reliquefaction is described. Of the five normally occurring sources of boil-off vapor the stream associated with the off-loading of liquid tankers during dewar refill was identified as the most cost effective and readily recoverable. The design, fabrication and testing of a proof-of-concept capture device, operating at a rate that is commensurate with the evolution of vapor by the target stream, is described. Liberation of the captured hydrogen gas at pressure .15 psig at normal temperatures (typical liquefier compressor suction pressure) are also demonstrated. A payback time of less than three years is projected.

Rosso, M. J.; Golben, P. M.

1984-01-01

444

Results of an Iridium-Based Data Communication System Providing Internet Access to Polar Expeditions  

NASA Astrophysics Data System (ADS)

The Polar Radar for Ice Sheet Measurements (PRISM) Project at the University of Kansas has developed and field-tested a versatile communications system for use by researchers in high-latitude Polar Regions. The PRISM project is developing advanced intelligent remote sensing technology that involves radar systems, an autonomous rover, and communications systems to measure detailed ice sheet characteristics, and to determine bed conditions (frozen or wet) below active ice sheets in both Greenland and Antarctica. We also have a very strong public outreach and educational program aimed at K-12 educators and students that requires data, voice and video feeds from Polar field locations in near real time. Hence, PRISM requires a robust communications system for use in the field between a base camp and the mobile remote sensing system, and from the field back to the University of Kansas and onto the Internet. The communication system that has been developed is truly mobile and is relatively inexpensive. We initially considered various satellite services during the design phase of this project. The two feasible options for high-latitude locations were Iridium, with its low-bit-rate service (2.4 Kb/s), and Inmarsat/Intelsat with broadband service. We selected the Iridium option for testing and development because it provided coverage in both Antarctica and Greenland. To achieve higher capacity communications, the multilink point-to-point protocol (MLPPP) implemented in Linux was tuned to operate efficiently over the Iridium satellite system. This mechanism combines multiple channels to obtain a seamless data connection with a capacity equal to the sum of the individual link rates. We used four Iridium modems to obtain an aggregate capacity of about 9.6 Kb/s. Standard Internet protocols (TCP/IP) were then used to provide end-to-end connectivity. The communications system field experiments were conducted at the NorthGRIP ice core drilling camp in Greenland (75° 06' N, 42° 20' W) from June 23-July 17, 2003. We measured the reliability, throughput and general performance of this system over periods of up to 24 hours. This included delay, loss, throughput, call drops/up-time, relative signal strengths, connection time and number of connection retries. The system was also successfully tested while moving across the ice sheet at speeds of up to 30 km/h. We were successful in uploading and downloading large files (.2MB to 7.2MB) to the Internet. In combination with a modified Wi-Fi deployment, wireless Internet access was also provided to the entire NorthGRIP camp for a few days. The field experiments have shown that standard Internet protocols combined with MLPPP and Iridium modems can provide Internet access for polar expeditions at useful data rates. The 4-modem configuration we tested was observed to be >90 % efficient, e.g., a 2.5 MB video file was transferred in 35 min. at 9.524 Kb/s. The system had an average up-time of over 90 % and thus is stable and suitable for autonomous operation. Mobile performance results were very similar to that of stationary systems. While the end-to-end network architecture developed to provide Internet access worked well, the system round trip time is significant ( ˜ 1.8 seconds), which can impair real time interactions.

Mohammad, A.; Frost, V.; Braaten, D.

2003-12-01

445

Syntheses and structures of asymmetric Bis(silyl) niobocene hydrides.  

PubMed

This paper deals with the preparation and structural investigation of asymmetric bis(silyl) niobocene hydrides, Cp2Nb(SiHMe2)(H)(SiXMe2) (2; X = F (a), Cl (b), Br (c), I (d)) and Cp2Nb(SiXMe2)(H)(SiYMe2) (X,Y= F-I; X not equal Y). Complexes 2a-d were prepared by selective electrophilic activation of the Si-H bond in Cp2Nb(SiHMe2)2(H). The Cp2Nb(SiXMe2)(H)(SiYMe2) complexes were prepared by electrophilic activation of the Si-H bond in 2a-d and, in some cases, by electrophilic exchange of the X halides in Cp2Nb(SiXMe2)2(H) (1) for other halides, Y. The structures of complexes 2b and 2c have been studied by X-ray and neutron diffraction (ND). The ND results unequivocally established that the hydride ligand in 2c is shifted toward the SiBrMe2 ligand and that in 2b is positioned symmetrically between two nonequivalent silyl groups, with the H...SiClMe2 distance being shorter because of the shorter Nb-SiClMe2 bond length. Analysis of the X-ray structures of complexes 2a-d and complexes Cp2Nb(SiXMe2)(H)(SiYMe2) shows that the largest structural distortions are observed for the silyl groups substituted by heavy halogen atoms. These trends are rationalized in terms of stronger interligand hypervalent interactions (IHI) Nb-H...Si-X for heavy atoms X from Group 7. PMID:17198423

Dorogov, Konstantin Yu; Yousufuddin, Muhammed; Ho, Nam-Nhat; Churakov, Andrei V; Kuzmina, Lyudmila G; Schultz, Arthur J; Mason, Sax A; Howard, Judith A K; Lemenovskii, Dmitry A; Bau, Robert; Nikonov, Georgii I

2007-01-01

446

Solid-State Gadolinium-Magnesium Hydride Optical Switch R. Armitage  

E-print Network

magnetron sputtering from an alloy target. The Gd-Mg thickness is 220 nm, and the Pd cap 15 nm. The Gd (ITO), followed by Gd-Mg hydride, Pd, hydrated zirconium oxide electrolyte, H storage layer, and ITO

447

Hydrogen Internal Combustion Engine Two Wheeler with on-board Metal Hydride Storage  

E-print Network

Hydrogen Internal Combustion Engine Two Wheeler with on-board Metal Hydride Storage K. Sapru*, S, as a transition, the hydrogen internal combustion engine can lead the way to a hydrogen economy, allowing

448

Engineering analysis of low enriched uranium fuel using improved zirconium hydride cross sections  

E-print Network

. All of these simulations used improved zirconium hydride cross sections that were provided by Dr. Ayman Hawari at North Carolina State University. The neutronic and thermal analysis showed that the reactor will operate with approximately the same fuel...

Candalino, Robert Wilcox

2006-10-30

449

Concerted proton-coupled electron transfer from a metal-hydride complex  

NASA Astrophysics Data System (ADS)

Metal hydrides are key intermediates in the catalytic reduction of protons and CO2 as well as in the oxidation of H2. In these reactions, electrons and protons are transferred to or from separate acceptors or donors in bidirectional proton-coupled electron transfer (PCET) steps. The mechanistic interpretation of PCET reactions of metal hydrides has focused on the stepwise transfer of electrons and protons. A concerted transfer may, however, occur with a lower reaction barrier and therefore proceed at higher catalytic rates. Here we investigate the feasibility of such a reaction by studying the oxidation–deprotonation reactions of a tungsten hydride complex. The rate dependence on the driving force for both electron transfer and proton transfer—employing different combinations of oxidants and bases—was used to establish experimentally the concerted, bidirectional PCET of a metal-hydride species. Consideration of the findings presented here in future catalyst designs may lead to more-efficient catalysts.

Bourrez, Marc; Steinmetz, Romain; Ott, Sascha; Gloaguen, Frederic; Hammarström, Leif

2015-02-01

450

Solvation dynamics and energetics of intramolecular hydride transfer reactions in biomass conversion.  

PubMed

Hydride transfer changes the charge structure of the reactant and thus, may induce reorientation/reorganization of solvent molecules. This solvent reorganization may in turn alter the energetics of the reaction. In the present work, we investigate the intramolecular hydride transfer by taking Lewis acid catalyzed glucose to fructose isomerization as an example. The C2-C1 hydride transfer is the rate limiting step in this reaction. Water and methanol are used as solvents and hydride transfer is simulated in the presence of explicit solvent molecules, treated quantum mechanically and at a finite temperature, using Car-Parrinello molecular dynamics (CPMD) and metadynamics. Activation free energy barrier for hydride transfer in methanol is found to be 50 kJ mol(-1) higher than that in water. In contrast, in density functional theory calculations, using an implicit solvent environment, the barriers are almost identical. Analysis of solvent dynamics and electronic polarization along the molecular dynamics trajectory and the results of CPMD-metadynamics simulation of the hydride transfer process in the absence of any solvent suggest that higher barrier in methanol is a result of non-equilibrium solvation. Methanol undergoes electronic polarization during the hydride transfer step. However, its molecular orientational relaxation is a much slower process that takes place after the hydride transfer, over an extended timescale. This results in non-equilibrium solvation. Water, on the other hand, does not undergo significant electronic polarization and thus, has to undergo minimal molecular reorientation to provide near equilibrium solvation to the transition state and an improved equilibrium solvation to the post hydride shift product state. Hence, the hydride transfer step is also observed to be exergonic in water and endergonic in methanol. The aforementioned explanation is juxtaposed to enzyme catalyzed charge transfer reactions, where the enhanced solvation of the transition and product states by enzymes, due to electrostatic interactions, reduces the activation free energy barrier and the free energy change of the reaction. Similarly, we suggest that, in the intramolecular hydride shift, improved solvation of the transition state and of the product state by water is achieved due to minimal polarization and reorientation, and (near) equilibrium solvation. PMID:25591500

Mushrif, Samir H; Varghese, Jithin J; Krishnamurthy, Chethana B

2015-02-01

451

Photogeneration of Hydride Donors and Their Use Toward CO2 Reduction  

SciTech Connect

Despite substantial effort, no one has succeeded in efficiently producing methanol from CO2 using homogeneous photocatalytic systems. We are pursuing reaction schemes based on a sequence of hydride-ion transfers to carry out stepwise reduction of CO2 to methanol. We are using hydride-ion transfer from photoproduced C-H bonds in metal complexes with bio-inspired ligands (i.e., NADH-like ligands) that are known to store one proton and two electrons.

Fujita,E.; Muckerman, J.T.; Polyansky, D.E.

2009-06-07

452

Simulation of Operation Heat or Cold-Making Unit with Hydride Heat Pump  

Microsoft Academic Search

The developed earlier mathematical model is applied for calculations of processes in the hydride heat pump (HHP) intended for increase or reduction of a level of temperature. The model set of equations actuates non-stationary one-dimensional equations of thermal balance in hydride sorbers with allowance for of thermal effects at an absorption\\/desorption of hydrogen. In computer calculations the experimental data on

I. Shanin; FSUE SRI SIA

453

THE PREPARATION OF PLUTONIUM POWDER BY A HYDRIDING PROCESS-INITIAL STUDIES  

Microsoft Academic Search

Micron-sized plutonium powder was produced by hydriding massive metal, ;\\u000a then grinding and decomposing the hydride. An apparatus containing clean ;\\u000a plutonium metal was evacuated to a pressure of 10 mu . Dry oxygen-free hydrogen ;\\u000a was introduced and the apparatus placed in a furnace. After the reaction ;\\u000a started, the apparatus was removed from the furnace and hydrogen added

G. L. Stiffler; M. H. Curtis

1960-01-01

454

Reversible hydriding and dehydriding properties of CaSi: Potential of metal silicides for hydrogen storage  

Microsoft Academic Search

We found that CaSi reversibly absorbs and desorbs hydrogen. First-principles calculations theoretically indicated that CaSi hydride is thermodynamically stable. The hydriding and dehydriding properties of CaSi were experimentally determined using pressure-composition (p-c) isotherms and x-ray diffraction analysis. The p-c isotherms clearly demonstrated plateau pressures in a temperature range of 473-573 K. The maximum hydrogen content was 1.9 wt % under

M. Aoki; N. Ohba; T. Noritake; S. Towata

2004-01-01

455

Improving nickel metal hydride batteries through research in negative electrode corrosion control and novel electrode materials  

E-print Network

IMPROVING NICKEL METAL HYDRIDE BATTERIES THROUGH RESEARCH IN NEGATIVE ELECTRODE CORROSION CONTROL AND NOVEL ELECTRODE MATERIALS A Thesis by MICHAEL SCOTT ALEXANDER Submitted to the Office of Graduate Studies of Texas ARM University... in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE December 1997 Major Subject: Chemical Engineering IMPROVING NICKEL METAL HYDRIDE BATTERIES THROUGH RESEARCH IN NEGATIVE ELECTRODE CORROSION CONTROL AND NOVEL ELECTRODE...

Alexander, Michael Scott

1997-01-01

456

Status of highly loaded uranium-zirconium hydride Low Enriched Uranium (LEU) fuel programs  

Microsoft Academic Search

The LEU uranium-zirconium hydride fuel has successfully completed all essential development testing and is offered commercially in both the 20 weight percent and 45 weight percent uranium concentrations for existing TRIGA reactors and as a conversion fuel for plate-type reactors. Several reactor facilities have already begun conversion to LEU uranium-zirconium hydride fuel. Currently, U-ZrH LEU fuel is in use in

1984-01-01

457

Electrochemical selenium hydride generation with in situ trapping in graphite tube atomizers  

NASA Astrophysics Data System (ADS)

A manifold coupling continuous electrolytic hydride generation of volatile hydrides with atomization in graphite tube atomizers after in situ collection was used for Se(IV) determination. Laboratory-made thin-layer flow-through cells with lead wire (cell I) and granular lead (cell II) as the cathode material were used as the electrolytic generators of volatile selenium hydride. The automatic sampling equipment of the graphite atomizer, with an untreated fused silica capillary, was used both for the introduction of volatile hydride into the atomizer and for pretreatment of the graphite furnace surface with a palladium modifier. The influence of the experimental parameters on the analytical signal was studied and optimum conditions for selenium determination were found. The optimum experimental parameters for hydride generation were: catholyte (1 mol l -1 HCl)/anolyte (2 mol l -1 H 2SO 4) flow rate of 2.0 ml min -1; applied generation current of 1.2 A (cell I) and 0.8 A (cell II); and carrier gas flow rate of 40 (cell I) and 70 ml min -1 (cell II). The hydride generated was collected in the graphite tube (pre-treated with 5 ?g of Pd reduced at 800 °C) at a temperature of 400 °C for 30 s. The overall efficiency of H 2Se electrochemical generation, transport and collection was 71±7% for cell I and 80±5% for cell II. The results for electrochemical generation of H 2Se (cell II) (absolute limit of detection 50 pg, 3? criterion) were compared with the original generation of H 2Se using NaBH 4 as a reduction agent (absolute limit of detection 30 pg) and with conventional liquid sampling. The repeatability at the 1.0 ng ml -1 level was better than 2.4% (relative standard deviation) for electrochemical hydride generation and better than 2.8% for chemical hydride generation.

Šíma, Jan; Rychlovský, Petr

2003-05-01

458

Long-term pressure and thermal cycling studies on lithium imide-lithium amide complex hydrides and vanadium-carbon hydrides, and electrochemical hydrogen permeation studies  

NASA Astrophysics Data System (ADS)

Solid-state hydrogen storage is becoming increasingly important for future development of non-polluting vehicular fuels and nuclear technology. Understanding the nature of classical and complex hydrides is of great importance in developing new high gravimetric or volumetric capacity hydrides. Towards the nuclear technology, we have studied vanadium hydrides with lattice impurities for high volumetric capacities and very low pressures. For the vehicular technology, we have studied complex hydrides with emphasis on gaseous impurity effects upon pressure cycling. Another aspect of this work is to understand fundamental hydrogen permeation in materials, for example permeations in steel. In nuclear applications, vanadium hydride has been generally studied at high pressures, but very little work has been done on low pressure hydriding and the effect of impurities. Thermodynamic pressure composition-isotherms and structural studies were performed on V-0.5 at.%C. The addition of carbon did not change the thermodynamics significantly but it had an impact on the decrepitation effects usually observed in metal hydrides. In vehicular applications, high gravimetric capacities are desirable. This study was focused on modern complex hydrides especially Li based imide-amide and binary amide-alanate systems. In this case, the emphasis was on effect of gaseous impurities upon pressure cycling, and other related. These contamination studies are important as candidate materials must have long-term stability under repeated loading of the hydride beds with fresh hydrogen charges. The starting material was Li3N and during hydriding Li2NH (imide) and subsequently, LiNH 2 (amide) phases were formed with a full capacity of ˜10 wt.% hydrogen. The pressure cycling occurred between the imide and amide phases, yielding ˜5.6 wt.% reversible hydrogen. The gaseous contamination effects on the amide-imide system were studied using 100 ppm levels of impurity gases such as O 2, H2O, CH4, CO and NH3 mixed with UHP hydrogen. In addition, commercial-grade industrial hydrogen was also used to simulate the hydrogen purchased from a commercial "Hydrogen gas" station. In the case of industrial hydrogen we found a ˜50% loss (˜2.6 wt% out of ˜5.6 wt% H2) after 1100 pressure cycles. Using the more oxygenated 100ppm O2-UHP H2 mixtures we found a capacity loss of ˜75% (1.4 wt% out of 5.6 wt%) after 560 pressure cycles. Ex-situ x-ray diffraction studies after cycling revealed formation of predominant new Li2O phase along with Li2NH-LiH phases. The addition of H2O, CH4, NH3, and CO showed varying degrees capacity loss. The alanate-imide binary mixed hydridese were also tested for resistance to impurity gases in hydrogen. These samples were obtained from DoE's Metal Hydride Center of Excellence (MHCoE) partner from University of Utah. Thermodynamic measurements were performed by pressure cycling with O2, and thermal aging with CO on the alanate-imide binary mixtures The initial desorption of the material showed ˜7 wt% hydrogen storage, and subsequent hydriding/dehydriding showed 3 wt.% capacity when using a maximum rehydriding pressure of ˜10 bar. The final portion of this work focuses on electrochemical hydrogen permeation experiments performed on steels for nuclear repository service at Yucca Mountain, Nevada. Hydrogen embrittlement and hydrogen induced cracking are common modes of failure when steel is exposed to hydrogen. In this, we studied the diffusion properties of hydrogen in both low and medium carbon steel using the electrochemical Devanathan-Stachurski method. The diffusivities and total hydrogen flux created by galvanostatic charging were measured in both standard 0.1 N NaOH electrolyte and in electrolyte simulating well water taken near Yucca Mountain. Potentiodynamic, potentiostatic permeation electrochemical tests, along with structural and elemental characterization was performed.

Lamb, Joshua H.

459

First-principles calculations of niobium hydride formation in superconducting radio-frequency cavities  

NASA Astrophysics Data System (ADS)

Niobium hydride is suspected to be a major contributor to degradation of the quality factor of niobium superconducting radio-frequency (SRF) cavities. In this study, we connect the fundamental properties of hydrogen in niobium to SRF cavity performance and processing. We modeled several of the niobium hydride phases relevant to SRF cavities and present their thermodynamic, electronic, and geometric properties determined from calculations based on density functional theory. We find that the absorption of hydrogen from the gas phase into niobium is exothermic and hydrogen becomes somewhat anionic. The absorption of hydrogen by niobium lattice vacancies is strongly preferred over absorption into interstitial sites. A single vacancy can accommodate six hydrogen atoms in the symmetrically equivalent lowest energy sites and additional hydrogen in the nearby interstitial sites affected by the strain field: this indicates that a vacancy can serve as a nucleation center for hydride phase formation. Small hydride precipitates may then occur near lattice vacancies upon cooling. Vacancy clusters and extended defects should also be enriched in hydrogen, potentially resulting in extended hydride phase regions upon cooling. We also assess the phase changes in the niobium-hydrogen system based on charge transfer between niobium and hydrogen, the strain field associated with interstitial hydrogen, and the geometry of the hydride phases. The results of this study stress the importance of not only the hydrogen content in niobium, but also the recovery state of niobium for the performance of SRF cavities.

Ford, Denise C.; Cooley, Lance D.; Seidman, David N.

2013-09-01

460

The terminal solid solubility of hydrogen in irradiated Zircaloy-2 and microscopic modeling of hydride behavior  

NASA Astrophysics Data System (ADS)

Differential scanning calorimetry (DSC) has been applied to elucidate the terminal solid solubility (TSS) of hydrogen in Zircaloy-2 cladding tubes and spacer bands irradiated in commercial BWRs. While recovery of irradiation defects during the first heating stage of as-irradiated specimens made the DSC peak of hydride dissolution dull or broader, no significant difference was detected in the TSS between unirradiated and irradiated Zircaloy-2, irrespective of fast neutron fluence. The effect of post-irradiation annealing on TSS was also examined. The results suggest almost no interaction between irradiation defects and dissolved hydrogen or hydrides at temperatures around 300 °C. Using the present TSS data and reported hydrogen- and hydride-related properties, a microscopic analysis code HYMAC for analyzing hydride behavior in cladding tube with textured grains was constructed. Stress-induced preferential precipitation and dissolution of hydrides were reproduced by adopting a TSS sub-model in which the solubilities decrease in proportion to stress normal to the habit plane in grains and to grain faces. Analyzed results by the code were consistent with typical experimental results of hydride behavior.

Une, K.; Ishimoto, S.; Etoh, Y.; Ito, K.; Ogata, K.; Baba, T.; Kamimura, K.; Kobayashi, Y.

2009-06-01

461

Hydride Formation Process for the Powder Metallurgical Recycle of Zircaloy from Used Nuclear Fuel  

NASA Astrophysics Data System (ADS)

A Zircaloy recycle process is being investigated based on the underlying principle that Zr reacts with H2 to form ZrH2, which is the same reaction that produces performance limiting ZrH2 formations in reactor cladding. However, in the proposed application, hydride formation is an enabling phenomenon that will embrittle and crumble Zircaloy as a precursor for milling and dehydration to form Zircaloy metal powder. Hydride formation experiments were performed to quantify the primary process variables of time and temperature. These experiments were performed by hydriding nuclear grade Zircaloy-4 tubes under flowing gas (Ar-5 pct H2) for various times and temperatures. The results were used to create a correlation for the formation of zirconium hydride as a function of time and temperature. Further, it was observed that it was much more effective to hydride the Zircaloy-4 tubes at temperatures below the ?- ?- ? eutectoid temperature of 818 K (545 °C), presumably related to the high hydrogen solubility of ?-Zr. Samples treated below this temperature readily crumbled during the hydride formation reaction and were subsequently easily ground to powder, making this the ideal temperature range for the proposed recycle method. Hydrogen pickup was faster above 818 K (545 °C), but the samples were generally tougher.

Parkison, Adam J.; McDeavitt, Sean M.

2011-01-01

462

Fracture of Hydrided Zircaloy-4 Sheet under Through-Thickness Crack Growth Conditions  

SciTech Connect

The failure of thin-wall components such as fuel cladding may be caused by crack initiation on the component surface and subsequent crack growth through its thickness. This study has determined the fracture toughness of hydrided cold-worked stress relieved Zircaloy-4 sheet subject to through-thickness crack growth at 25 deg. C. The experimental approach utilizes a novel procedure in which a narrow linear strip of brittle hydride blister across the specimen width creates a well-defined pre-crack upon initial loading. The subsequent crack growth resistance is then characterized by four-point bending of the specimen and an elastic-plastic fracture mechanics analysis. At room temperature, the through-thickness fracture toughness (K{sub Q}) is sensitive to the orientation of the hydride platelets, and K{sub Q} {approx_equal} 25 MPavm for crack growth through a mixed in-plane/out-of-plane hydride field. In contrast, K{sub Q} is much higher ({approx_equal} 75 MPavm) when the hydride platelets are oriented predominantly in the plane of the sheet (and therefore normal to both the crack plane and the crack growth direction). The implication of these fracture toughness values to the fracture strain behavior of hydrided Zircaloy-4 under through-thickness crack growth conditions is illustrated. (authors)

Raynaud, P.A.; Koss, D.A. [Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA 16802 (United States); Motta, A.T. [Department of Mechanical and Nuclear Engineering, The Pennsylvania State University, University Park, PA 16802 (United States); Chan, K.S. [Southwest Research Institute, San Antonio, TX 78238 (United States)

2007-07-01

463

Effects of hydride morphology on the embrittlement of Zircaloy-4 cladding  

NASA Astrophysics Data System (ADS)

Spent nuclear fuel claddings discharged from water reactors contain hydrogen up to 800 wppm depending on the burn-up and power history. During long-term dry storage, the cladding temperature slowly decreases with diminishing decay heat and absorbed hydrogen atoms are precipitated in Zr-matrix according to the terminal solid solubility of hydrogen. Under these conditions, hydrides can significantly reduce cladding ductility and impact resistance, especially when the radial hydrides are massively present in the material. In this study, the effects of hydride morphology on the embrittlement of Zircaloy-4 cladding were investigated using a ring compression test. The results show that circumferentially hydrided Zircaloy-4 cladding is brittle at room temperature but its ductility is regained substantially as the temperature goes above 150 °C. On the other hand, radially hydrided cladding remains brittle at 150 °C and micro-cracks developed in the radial hydrides can act as crack propagation paths. Fracture energy analysis shows that ductile to brittle transition temperature is low in between 25 °C and 100 °C in the former case, whereas it lies in between 200 °C and 250 °C in the latter case.

Kim, Ju-Seong; Kim, Tae-Hoon; Kook, Dong-Hak; Kim, Yong-Soo

2015-01-01

464

Hydrogen generation using silicon nanoparticles and their mixtures with alkali metal hydrides  

NASA Astrophysics Data System (ADS)

Hydrogen is a promising energy carrier, for use in fuel cells, engines, and turbines for transportation or mobile applications. Hydrogen is desirable as an energy carrier, because its oxidation by air releases substantial energy (thermally or electrochemically) and produces only water as a product. In contrast, hydrocarbon energy carriers inevitably produce CO2, contributing to global warming. While CO2 capture may prove feasible in large stationary applications, implementing it in transportation and mobile applications is a daunting challenge. Thus a zero-emission energy carrier like hydrogen is especially needed in these cases. Use of H2 as an energy carrier also brings new challenges such as safe handling of compressed hydrogen and implementation of new transport, storage, and delivery processes and infrastructure. With current storage technologies, hydrogen's energy per volume is very low compared to other automobile fuels. High density storage of compressed hydrogen requires combinations of high pressure and/or low temperature that are not very practical. An alternative for storage is use of solid light weight hydrogenous material systems which have long durability, good adsorption properties and high activity. Substantial research has been conducted on carbon materials like activated carbon, carbon nanofibers, and carbon nanotubes due to their high theoretical hydrogen capacities. However, the theoretical values have not been achieved, and hydrogen uptake capacities in these materials are below 10 wt. %. In this thesis we investigated the use of silicon for hydrogen generation. Hydrogen generation via water oxidation of silicon had been ignored due to slow reaction kinetics. We hypothesized that the hydrogen generation rate could be improved by using high surface area silicon nanoparticles. Our laser-pyrolysis-produced nanoparticles showed surprisingly rapid hydrogen generation and high hydrogen yield, exceeding the theoretical maximum of two moles of H2 per mole of Si. We compare our silicon nanoparticles (˜10nm diameter) with commercial silicon nanopowder (<100nm diameter) and ball-milled silicon powder (325 mesh). The increase in rate upon decreasing the particle size to 10 nm was even greater than would be expected based upon the increase in surface area. While specific surface area increased by a factor of 6 in going from <100 nm to ˜10 nm particles, the hydrogen production rate increased by a factor of 150. However, in all cases, silicon requires a base (e.g. NaOH, KOH, hydrazine) to catalyze its reaction with water. Metal hydrides are also promising hydrogen storage materials. The optimum metal hydride would possess high hydrogen storage density at moderate temperature and pressure, release hydrogen safely and controllably, and be stable in air. Alkali metal hydrides have high hydrogen storage density, but exhibit high uncontrollable reactivity with water. In an attempt to control this explosive nature while maintaining high storage capacity, we mixed our silicon nanoparticles with the hydrides. This has dual benefits: (1) the hydride- water reaction produces the alkali hydroxide needed for base-catalyzed silicon oxidation, and (2) dilution with 10nm coating by, the silicon may temper the reactivity of the hydride, making the process more controllable. Initially, we analyzed hydrolysis of pure alkali metal hydrides and alkaline earth metal hydrides. Lithium hydride has particularly high hydrogen gravimetric density, along with faster reaction kinetics than sodium hydride or magnesium hydride. On analysis of hydrogen production we found higher hydrogen yield from the silicon nanoparticle—metal hydride mixture than from pure hydride hydrolysis. The silicon-hydride mixtures using our 10nm silicon nanoparticles produced high hydrogen yield, exceeding the theoretical yield. Some evidence of slowing of the hydride reaction rate upon addition of silicon nanoparticles was observed.

Patki, Gauri Dilip

465

Cyclometalated iridium(III) complexes for phosphorescence sensing of biological metal ions.  

PubMed

Phosphorescence signaling provides a valuable alternative to conventional bioimaging based on fluorescence. The benefits of using phosphorescent molecules include improved sensitivity and capabilities for effective elimination of background signals by time-gated acquisition. Cyclometalated Ir(III) complexes are promising candidates for facilitating phosphorescent bioimaging because they provide synthetic versatility and excellent phosphorescence properties. In this Forum Article, we present our recent studies on the development of phosphorescence sensors for the detection of metal ions based on cyclometalated iridium(III) complexes. The constructs contained cyclometalating (C^N) ligands with the electron densities and band-gap energies of the C^N ligand structures systematically varied. Receptors that chelated zinc, cupric, and chromium ions were tethered to the ligands to create phosphorescence sensors. The alterations in the C^N ligand structures had a profound influence on the phosphorescence responses to metal ions. Mechanistic studies suggested that the phosphorescence responses could be explained on the basis of the modulation of photoinduced electron transfer (PeT) from the receptor to the photoexcited iridium species. The PeT behaviors strictly adhered to the Rehm-Weller principle, and the occurrence of PeT was located in the Marcus-normal region. It is thus anticipated that improved responses will be obtainable by increasing the excited-state reduction potential of the iridium(III) complexes. Femtosecond transient absorption experiments provided evidence for the presence of an additional photophysical mechanism that involved metal-ion-induced alteration of the intraligand charge-transfer (ILCT) transition state. Utility of the mechanism by PeT and ILCT has been demonstrated for the phosphorescence sensing of biologically important transition-metal ions. In particular, the phosphorescence zinc sensor could report the presence of intracellular zinc pools by using confocal laser scanning microscopy and photoluminescence lifetime imaging microscopy techniques. We hope that the significant knowledge gained from our studies will be of great help in the design of new molecules as phosphorescence sensors. PMID:24266501

You, Youngmin; Cho, Somin; Nam, Wonwoo

2014-02-17

466

Complex Hydride Compounds with Enhanced Hydrogen Storage Capacity  

SciTech Connect

The United Technologies Research Center (UTRC), in collaboration with major partners Albemarle Corporation (Albemarle) and the Savannah River National Laboratory (SRNL), conducted research to discover new hydride materials for the storage of hydrogen having on-board reversibility and a target gravimetric capacity of ? 7.5 weight percent (wt %). When integrated into a system with a reasonable efficiency of 60% (mass of hydride / total mass), this target material would produce a system gravimetric capacity of ? 4.5 wt %, consistent with the DOE 2007 target. The approach established for the project combined first principles modeling (FPM - UTRC) with multiple synthesis methods: Solid State Processing (SSP - UTRC), Solution Based Processing (SBP - Albemarle) and Molten State Processing (MSP - SRNL). In the search for novel compounds, each of these methods has advantages and disadvantages; by combining them, the potential for success was increased. During the project, UTRC refined its FPM framework which includes ground state (0 Kelvin) structural determinations, elevated temperature thermodynamic predictions and thermodynamic / phase diagram calculations. This modeling was used both to precede synthesis in a virtual search for new compounds and after initial synthesis to examine reaction details and options for modifications including co-reactant additions. The SSP synthesis method involved high energy ball milling which was simple, efficient for small batches and has proven effective for other storage material compositions. The SBP method produced very homogeneous chemical reactions, some of which cannot be performed via solid state routes, and would be the preferred approach for large scale production. The MSP technique is similar to the SSP method, but involves higher temperature and hydrogen pressure conditions to achieve greater species mobility. During the initial phases of the project, the focus was on higher order alanate complexes in the phase space between alkaline metal hydrides (AmH), Alkaline earth metal hydrides (AeH2), alane (AlH3), transition metal (Tm) hydrides (TmHz, where z=1-3) and molecular hydrogen (H2). The effort started first with variations of known alanates and subsequently extended the search to unknown compounds. In this stage, the FPM techniques were developed and validated on known alanate materials such as NaAlH4 and Na2LiAlH6. The coupled predictive methodologies were used to survey over 200 proposed phases in six quaternary spaces, formed from various combinations of Na, Li Mg and/or Ti with Al and H. A wide range of alanate compounds was examined using SSP having additions of Ti, Cr, Co, Ni and Fe. A number of compositions and reaction paths were identified having H weight fractions up to 5.6 wt %, but none meeting the 7.5 wt%H reversible goal. Similarly, MSP of alanates produced a number of interesting compounds and general conclusions regarding reaction behavior of mixtures during processing, but no alanate based candidates meeting the 7.5 wt% goal. A novel alanate, LiMg(AlH4)3, was synthesized using SBP that demonstrated a 7.0 wt% capacity with a desorption temperature of 150°C. The deuteride form was synthesized and characterized by the Institute for Energy (IFE) in Norway to determine its crystalline structure for related FPM studies. However, the reaction exhibited exothermicity and therefore was not reversible under acceptable hydrogen gas pressures for on-board recharging. After the extensive studies of alanates, the material class of emphasis was shifted to borohydrides. Through SBP, several ligand-stabilized Mg(BH4)2 complexes were synthesized. The Mg(BH4)2*2NH3 complex was found to change behavior with slightly different synthesis conditions and/or aging. One of the two mechanisms was an amine-borane (NH3BH3) like dissociation reaction which released up to 16 wt %H and more conservatively 9 wt%H when not including H2 released from the NH3. From FPM, the stability of the Mg(BH4)2*2NH3 compound was found to increase with the inclusion of NH3 groups in the inner-Mg coordination

Mosher, Daniel A.; Opalka, Susanne M.; Tang, Xia; Laube, Bruce L.; Brown, Ronald J.; Vanderspurt, Thomas H.; Arsenault, Sarah; Wu, Robert; Strickler, Jamie; Anton, Donald L.; Zidan, Ragaiy; Berseth, Polly

2008-02-18

467