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Sample records for neptunium borides

  1. Neptunium

    NASA Astrophysics Data System (ADS)

    Yoshida, Zenko; Johnson, Stephen G.; Kimura, Takaumi; Krsul, John R.

    The first report on the discovery of neptunium was in 1940 by McMillan and Abelson (1940), although McMillan did the preliminary work in 1939 and published his findings (McMillan, 1939). He did not claim that a new element had been discovered until confirmatory measurements had been undertaken in the following year. The production of neptunium was accomplished by placing a layer of uranium trioxide on paper with several aluminum or paper foils and then exposing this to neutrons from a cyclotron. Examination of the uranium paper sample containing the non-recoiling fraction displayed that two new radioactive components had been created. One component displayed a 23 min half-life, later identified as U-239, while the second exhibited a 2.3 day half-life. Both components decayed via β particle emission. Preliminary chemical analysis was performed to determine the behavior of the 2.3 day component and resulted in the contradictory assignment of this component as that exhibiting an atomic number of 93, but not being transuranic in nature (Segrè, 1939). Segrè noted in his paper that his conclusions were contradictory. However, the following quotation is from his paper, “The necessary conclusion seems to be that the 23 minute uranium decays into a very long-lived 93 and that transuranic elements have not yet been observed.” The primary stumbling block to the proper assignment of the material as transuranic in nature was the lack of observation of any alpha decay activity that would emanate from the daughter product of the beta decay of this new material with an atomic number 93. It was this work by Segrè (1939) that led McMillan and Abelson to revisit the chemical analysis and determine its properties in greater depth.

  2. NEPTUNIUM SOLVENT EXTRACTION PROCESS

    DOEpatents

    Dawson, L.R.; Fields, P.R.

    1959-10-01

    The separation of neptunium from an aqueous solution by solvent extraction and the extraction of neptunium from the solvent solution are described. Neptunium is separated from an aqueous solution containing tetravalent or hexavalent neptunium nitrate, nitric acid, and a nitrate salting out agent, such as sodium nitrate, by contacting the solution with an organic solvent such as diethyl ether. Subsequently, the neptunium nitrate is extracted from the organic solvent extract phase with water.

  3. Gradient boride layers formed by diffusion carburizing and laser boriding

    NASA Astrophysics Data System (ADS)

    Kulka, M.; Makuch, N.; Dziarski, P.; Mikołajczak, D.; Przestacki, D.

    2015-04-01

    Laser boriding, instead of diffusion boriding, was proposed to formation of gradient borocarburized layers. The microstructure and properties of these layers were compared to those-obtained after typical diffusion borocarburizing. First method of treatment consists in diffusion carburizing and laser boriding only. In microstructure three zones are present: laser borided zone, hardened carburized zone and carburized layer without heat treatment. However, the violent decrease in the microhardness was observed below the laser borided zone. Additionally, these layers were characterized by a changeable value of mass wear intensity factor thus by a changeable abrasive wear resistance. Although at the beginning of friction the very low values of mass wear intensity factor Imw were obtained, these values increased during the next stages of friction. It can be caused by the fluctuations in the microhardness of the hardened carburized zone (HAZ). The use of through hardening after carburizing and laser boriding eliminated these fluctuations. Two zones characterized the microstructure of this layer: laser borided zone and hardened carburized zone. Mass wear intensity factor obtained a constant value for this layer and was comparable to that-obtained in case of diffusion borocarburizing and through hardening. Therefore, the diffusion boriding could be replaced by the laser boriding, when the high abrasive wear resistance is required. However, the possibilities of application of laser boriding instead of diffusion process were limited. In case of elements, which needed high fatigue strength, the substitution of diffusion boriding by laser boriding was not advisable. The surface cracks formed during laser re-melting were the reason for relatively quickly first fatigue crack. The preheating of the laser treated surface before laser beam action would prevent the surface cracks and cause the improved fatigue strength. Although the cohesion of laser borided carburized layer was

  4. ELECTRODEPOSITION OF NEPTUNIUM

    DOEpatents

    Seaborg, G.T.; Wahl, A.C.

    1960-08-30

    A process of electrodepositing neptunium from solutions is given which comprises conducting the electrodeposition from an absolute alcohol bath containing a neptunium nitrate and lanthanum nitrate at a potential of approximately 50 volts and a current density of between about 1.8 and 4.7 ma/dm/ sup 2/.

  5. NEPTUNIUM OXIDE PROCESSING

    SciTech Connect

    Jordan, J; Watkins, R; Hensel, S

    2009-05-27

    The Savannah River Site's HB-Line Facility completed a campaign in which fifty nine cans of neptunium oxide were produced and shipped to the Idaho National Laboratory in the 9975 shipping container. The neptunium campaign was divided into two parts: Part 1 which consisted of oxide made from H-Canyon neptunium solution which did not require any processing prior to conversion into an oxide, and Part 2 which consisted of oxide made from additional H-Canyon neptunium solutions which required processing to purify the solution prior to conversion into an oxide. The neptunium was received as a nitrate solution and converted to oxide through ion-exchange column extraction, precipitation, and calcination. Numerous processing challenges were encountered in order make a final neptunium oxide product that could be shipped in a 9975 shipping container. Among the challenges overcome was the issue of scale: translating lab scale production into full facility production. The balance between processing efficiency and product quality assurance was addressed during this campaign. Lessons learned from these challenges are applicable to other processing projects.

  6. Neptunium storage at Hanford

    SciTech Connect

    Alderman, C.J.; Shiraga, S.S.; Schwartz, R.A.; Smith, R.J.; Wootan, D.W.

    1993-06-01

    A decision must be made regarding whether the United State`s stockpile of neptunium should be discarded into the waste stream or kept for the production of Pu-238. Although the cost of long term storage is not inconsequential, to dispose of the material means the closing of our option to maintain control over our Pu-238 stockpile. Within the Fuels and Materials Examination Facility at Hanford there exists a remotely operated facility that can be converted for neptunium storage. This paper describes the facility and the anticipated handling requirements.

  7. METHOD OF SEPARATING NEPTUNIUM

    DOEpatents

    Seaborg, G.T.

    1961-10-24

    plutonium in an aqueous solution containing sulfate ions. The process consists of contacting the solution with an alkali metal bromate, digesting the resulting mixture at 15 to 25 deg C for a period of time not more than that required to oxidize the neptunium, adding lanthanum ions and fluoride ions, and separating the plutonium-containing precipitate thus formed from the supernatant solution. (AEC)

  8. SOLVENT EXTRACTION OF NEPTUNIUM

    DOEpatents

    Butler, J.P.

    1958-08-12

    A process is described for the recovery of neptuniunn from dissolver solutions by solvent extraction. The neptunium containing solution should be about 5N, in nitric acid.and about 0.1 M in ferrous ion. The organic extracting agent is tributyl phosphate, and the neptuniunn is recovered from the organic solvent phase by washing with water.

  9. Borides in Thin Film Technology

    NASA Astrophysics Data System (ADS)

    Mitterer, Christian

    1997-10-01

    The borides of transition and rare-earth metals are considered for application as wear- and corrosion-resistant, decorative or thermionic coatings. After a review of physical vapor deposition (PVD) techniques used for the deposition of these coatings, a survey of investigations to apply these coatings is given. As a result of the strong directionality of covalent boron-boron bonds, boride coatings show an increasing tendency to amorphous film growth with increasing B/Meatomic ratio and, for rare-earth hexaborides, with decreasing metallic radius of the rare-earth metal. Mechanical and optical properties are strongly influenced by the crystallographic structure of the boride phase. Because of their high hardness combined with good adhesion, crystalline films based on the diborides of transition metals seem to be promising candidates for wear resistant coatings on cutting tools. Alloying of these films with nitrogen by reactive PVD processes results in the formation of extremely fine-grained multiphase hard coatings with excellent tribological and corrosion behavior, thus offering new applications in the coating of engineering components. Because of their distinct colorations, some of the hexaborides of rare-earth elements may be used as decorative coatings on consumer products like wristwatch casings or eyeglass frames. Another promising field is the development of thermionic coatings based on rare-earth hexaborides, which may offer the possibility of the production of inexpensive and simple high emission filaments.

  10. Results of Neptunium Disposal Testing

    SciTech Connect

    Walker, D.D.

    2003-10-07

    Researchers investigated the neutralization of neptunium solution from H-Canyon Tank 16.4 and the properties of the resulting slurry. This work investigated slurry properties from a single neutralization protocol and limited storage times.

  11. Field free, directly heated lanthanum boride cathode

    DOEpatents

    Leung, Ka-Ngo; Moussa, D.; Wilde, S.B.

    1987-02-02

    A directly heated cylindrical lanthanum boride cathode assembly is disclosed which minimizes generation of magnetic field which would interfere with electron emission from the cathode. The cathode assembly comprises a lanthanum boride cylinder in electrical contact at one end with a central support shaft which functions as one electrode to carry current to the lanthanum boride cylinder and in electrical contact, at its opposite end with a second electrode which is coaxially position around the central support shaft so that magnetic fields generated by heater current flowing in one direction through the central support shaft are cancelled by an opposite magnetic field generated by current flowing through the lanthanum boride cylinder and the coaxial electrode in a direction opposite to the current flow in the central shaft.

  12. Field free, directly heated lanthanum boride cathode

    DOEpatents

    Leung, Ka-Ngo; Moussa, David; Wilde, Stephen B.

    1991-01-01

    A directly heated cylindrical lanthanum boride cathode assembly is disclosed which minimizes generation of magnetic fields which would interfere with electron emission from the cathode. The cathode assembly comprises a lanthanum boride cylinder in electrical contact at one end with a central support shaft which functions as one electrode to carry current to the lanthanum boride cylinder and in electrical contact, at its opposite end with a second electrode which is coaxially position around the central support shaft so that magnetic fields generated by heater current flowing in one direction through the central support shaft are cancelled by an opposite magnetic field generated by current flowing through the lanthanum boride cylinder and the coaxial electrode in a direction opposite to the current flow in the central shaft.

  13. Kinetics of electrochemical boriding of low carbon steel

    NASA Astrophysics Data System (ADS)

    Kartal, G.; Eryilmaz, O. L.; Krumdick, G.; Erdemir, A.; Timur, S.

    2011-05-01

    In this study, the growth kinetics of the boride layers forming on low carbon steel substrates was investigated during electrochemical boriding which was performed at a constant current density of 200 mA/cm 2 in a borax based electrolyte at temperatures ranging from 1123 K to 1273 K for periods of 5-120 min. After boriding, the presence of both FeB and Fe 2B phases were confirmed by the X-ray diffraction method. Cross-sectional microscopy revealed a very dense and thick morphology for both boride phases. Micro hardness testing of the borided steel samples showed a significant increase in the hardness of the borided surfaces (i.e., up to (1700 ± 200) HV), while the hardness of un-borided steel samples was approximately (200 ± 20) HV. Systematic studies over a wide range of boriding time and temperature confirmed that the rate of the boride layer formation is strongly dependent on boriding duration and has a parabolic character. The activation energy of boride layer growth for electrochemical boriding was determined as (172.75 ± 8.6) kJ/mol.

  14. Neptunium nitrate solution. Neptunium TiOA - TTA method. Revision 1

    SciTech Connect

    Not Available

    1985-04-01

    An analytical solvent extraction method for separating neptunium from plutonium, americium, curium, uranium, thorium, and fission products using tri-iso-octylamine (TiOA) and thenoyltrifluoroacetone (TTA) is described. Neptunium is separated from the bulk of the plutonium, americium, curium, and fission products by the extraction of neptunium(IV) into RiOA, dissolved in xylene, from an aqueous nitric acid reducing solution. The neptunium bearing organic solution is then scrubbed with a nitric acid reducing solution to achieve further purification. Final purification is obtained by stripping neptunium from tri-iso-octylaminexylene solution into dilute hydrochloric acid and then extracting the neptunium(IV) into TTA dissolved in xylene. A quantitative neptunium measurement is then made by alpha counting and alpha pulse height analysis. Most of the neptunium bearing sample solutions associated with the chemical processing of irradiated uranium are aqueous nitric acid solutions, and with the exception of uranium(IV) are free from interfering materials.

  15. Direct chemical reduction of neptunium oxide to neptunium metal using calcium and calcium chloride

    NASA Astrophysics Data System (ADS)

    Squires, Leah N.; Lessing, Paul

    2016-04-01

    A process of direct reduction of neptunium oxide to neptunium metal using calcium metal as the reducing agent is discussed. After reduction of the oxide to metal, the metal is separated by density from the other components of the reaction mixture and can be easily removed upon cooling. The direct reduction technique consistently produces high purity (98%-99% pure) neptunium metal.

  16. OXIDATIVE METHOD OF SEPARATING PLUTONIUM FROM NEPTUNIUM

    DOEpatents

    Beaufait, L.J. Jr.

    1958-06-10

    A method is described of separating neptunium from plutonium in an aqueous solution containing neptunium and plutonium in valence states not greater than +4. This may be accomplished by contacting the solution with dichromate ions, thus oxidizing the neptunium to a valence state greater than +4 without oxidizing any substantial amount of plutonium, and then forming a carrier precipitate which carries the plutonium from solution, leaving the neptunium behind. A preferred embodiment of this invention covers the use of lanthanum fluoride as the carrier precipitate.

  17. The fracture toughness of borides formed on boronized cold work tool steels

    SciTech Connect

    Sen, Ugur; Sen, Saduman

    2003-06-15

    In this study, the fracture toughness of boride layers of two borided cold work tool steels have been investigated. Boriding was carried out in a salt bath consisting of borax, boric acid, ferro-silicon and aluminum. Boriding was performed at 850 and 950 deg. C for 2 to 7 h. The presence of boride phases were determined by X-ray diffraction (XRD) analysis. Hardness and fracture toughness of borides were measured via Vickers indenter. Increasing of boriding time and temperature leads to reduction of fracture toughness of borides. Metallographic examination showed that boride layer formed on cold work tool steels was compact and smooth.

  18. Phonon dynamics of neptunium chalcogenides

    NASA Astrophysics Data System (ADS)

    Aynyas, Mahendra; Rukmangad, Aditi; Arya, Balwant S.; Sanyal, Sankar P.

    2012-06-01

    We have performed phonon calculations of Neptunium Chalcogenides (NpX) (X= S, Se, Te) based on breathing shell model (BSM) which includes breathing motion of electron of the Np-atoms due to f-d hybridization. The model predicts that the short range breathing phenomenon play a dominant role in the phonon properties. We also report, for the first time specific heat for these compounds.

  19. Radiotoxicity of neptunium(V) and neptunium(V)-nitrilotriacetic acid (NTA) complexes towards Chelatobacter heintzii

    SciTech Connect

    Banaszak, J.E. |; Reed, D.T.; Rittmann, B.E.

    1997-03-10

    The objective of this work was to investigate the toxicity mechanisms of neptunium and the neptunium-NTA complex towards Chelatobacter heintzii. The results show that metal toxicity of aquo NpO{sub 2}{sup +} may significantly limit growth of Cl heintzii at free metal ion concentrations greater than {approx} 10{sup {minus}5} M. However, neptunium concentrations {ge} 10{sup {minus}4} M do not cause measurable radiotoxicity effects in C. heintzii when present in the form of a neptunium-NTA complex or colloidal/precipitated neptunium-phosphate. The neptunium-NTA complex, which is stable under aerobic conditions, is destabilized by microbial degradation of NTA. When phosphate was present, degradation of NTA led to the precipitation of a neptunium-phosphate phase.

  20. Investigation of the fracture mechanics of boride composites

    NASA Technical Reports Server (NTRS)

    Kaufman, L.; Clougherty, E. V.; Nesor, H.

    1971-01-01

    Fracture energies of WC-6Co, Boride 5 (ZrB2+SiC), Boride 8(ZrB2+SiC+C) and Boride 8-M2(ZrB2+SiC+C) were measured by slow bend and impact tests of notched charpy bars. Cobalt bonded tungsten carbide exhibited impact energies of 0.76 ft-lb or 73.9 in-lb/square inch. Boride 5 and the Boride 8 exhibit impact energies one third and one quarter of that observed for WC-6Co comparing favorably with measurements for SiC and Si3N4. Slow bend-notched bar-fracture energies for WC-6Co were near 2.6 in-lb/square inch or 1/20 the impact energies. Slow bend energies for Boride 8-M2, Boride 8 and Boride 5 were 58%, 42% and 25% of the value observed for WC-6Co. Fractograph showed differences for WC-6Co where slow bend testing resulted in smooth transgranular cleavage while samples broken by impact exhibited intergranular failures. By contrast the boride fractures showed no distinction based on testing method. Fabrication studies were conducted to effect alteration of the boride composites by alloying and introduction of graphite cloth.

  1. Fracture Microindentation on boride layers on AISI 1020 steel

    NASA Astrophysics Data System (ADS)

    Prince, M.; Thanu, A. Justin; Arjun, S. L.; Velmurugan, U.; Gopalakrishnan, P.

    2016-02-01

    In this paper, an attempt has been made to enhance the fracture toughness (Kc) of boride layer using multi-component (Ni, Cr and B) laser bonding. The fracture toughness of continuously pack borided, interrupted pack borided and multi-component (Ni, Cr and B) laser borided steel specimens was measured using Vickers microindentation fracture toughness test as per ASTM E384 standard. The fracture toughness of continuously pack borided layer was - 3.3 MPa.m1/2. The fracture toughness of interrupted boride layer was in the range of - 4.9 MPa.m1/2. The fracture toughness of multi-component (Ni, Cr and B) laser borided layer was in the range of 13.8 - 18.3 MPa.m1/2. A significant improvement in fracture toughness of laser treated specimens was observed from the experimental results. This may be due to better distribution of boron, nickel, chromium and other alloying elements due to laser treatment and relatively more uniform boride layer as compared with continuously pack borided layer and interrupted pack borided layer.

  2. Packaging and Transportation of Additional Neptunium Oxide

    SciTech Connect

    Watkins, R.; Jordan, J.; Hensel, S.

    2010-05-05

    The Savannah River Site's HB-Line Facility completed a second neptunium oxide production campaign in which nine (9) additional cans of neptunium oxide were produced and shipped to the Idaho National Laboratory and Oak Ridge National Laboratory in the 9975 shipping container. These additional cans were from a different feed solution than the first fifty (50) cans of neptunium oxide that were previously produced and shipped via a Letter of Amendment to the 9975 Safety Analysis Report for Packaging (SARP) content table. This paper will address the challenges associated with demonstrating the neptunium oxide produced from the additional feed solution was equivalent to the original neptunium oxide and within the content description of the Letter of Amendment.

  3. Electrochemical Evaluation of Corrosion on Borided and Non-borided Steels Immersed in 1 M HCl Solution

    NASA Astrophysics Data System (ADS)

    Mejía-Caballero, I.; Martínez-Trinidad, J.; Palomar-Pardavé, M.; Romero-Romo, M.; Herrera-Hernández, H.; Herrera-Soria, O.; Campos Silva, I.

    2014-08-01

    In this study the corrosion resistances of AISI 1018 and AISI 304 borided and non-borided steels were estimated using polarization resistance and electrochemical impedance spectroscopy (EIS) techniques. Boriding of the steel samples was conducted using the powder-pack method at 1223 K with 6 h of exposure. Structural examinations of the surfaces of the borided steels showed the presence of a Fe2B layer with isolated FeB teeth on the AISI 1018 steel, whereas a compact layer of FeB/Fe2B was formed on the AISI 304 steel. Polarization resistance and EIS of the borided and non-borided steels surfaces were performed in a corrosive solution of 1 M HCl. The EIS data were analyzed during 43 days of exposure to the acid solution. Impedance curves obtained during this period for the borided and non-borided steels were modeled using equivalent electrical circuits. The results of both electrochemical techniques indicated that boride layers formed at the steel surfaces effectively protect the samples from the corrosive effects of HCl. The main corrosion processes observed on the boride layers were pitting and crevice corrosion.

  4. Colloidal nickel boride catalyst for hydrogenation of olefins

    SciTech Connect

    Nakao, Y.; Fujishige, S.

    1981-04-01

    Colloidal nickel boride was prepared from nickel(II) chloride by reduction with sodium borohydride in the presence of polyvinylpyrrolidone in ethanol. Hydrogenation of various olefins was examined over the colloidal catalyst at 30/sup 0/C and atmospheric pressure. The colloidal nickel boride was much more effective than the precipitated nickel boride prepared in the absence of polyvinylpyrrolidone as a hydrogenation catalyst, especially for isopropenyl compounds. Additional amines and sodium acetate were slightly inhibitive to the colloidal catalyst, while, being strongly promotive to the precipitated catalyst. The colloidal nickel boride was superior to the charcoal-supported metals of the platinum group in catalytic activity for ..cap alpha..-methylstyrene.

  5. Investigation of the diffusion kinetics of borided stainless steels

    NASA Astrophysics Data System (ADS)

    Kayali, Yusuf

    2013-12-01

    In this study, the kinetics of borides formed on AISI 420, AISI 304 and AISI 304L stainless steels was investigated. Boronizing treatment was carried out using Ekabor-II powders at the processing temperatures of 1123, 1173 and 1223 K for 2, 4 and 6 h. The phases of the boride layers of borided AISI 420, AISI 304 and AISI 304L stainless steels were FeB, Fe2B, CrB and NiB, respectively. The thickness of the boride layer formed on the borided steels ranged from 4.6 to 64 μm depending on the boriding temperature, boriding time and alloying elements of the stainless steels. Depending on the chemical composition, temperature and layer thickness, the activation energies of boron in AISI 420, AISI 304 and AISI 304L stainless steels were found to be 206.161, 234.641 and 222.818 kJ/mol, respectively. The kinetics of growth of the boride layers formed on the AISI 420, AISI 304 and AISI 304L stainless steels and the thickness of the boride layers were investigated.

  6. Organometallic neptunium(III) complexes.

    PubMed

    Dutkiewicz, Michał S; Farnaby, Joy H; Apostolidis, Christos; Colineau, Eric; Walter, Olaf; Magnani, Nicola; Gardiner, Michael G; Love, Jason B; Kaltsoyannis, Nikolas; Caciuffo, Roberto; Arnold, Polly L

    2016-08-01

    Studies of transuranic organometallic complexes provide a particularly valuable insight into covalent contributions to the metal-ligand bonding, in which the subtle differences between the transuranium actinide ions and their lighter lanthanide counterparts are of fundamental importance for the effective remediation of nuclear waste. Unlike the organometallic chemistry of uranium, which has focused strongly on U(III) and has seen some spectacular advances, that of the transuranics is significantly technically more challenging and has remained dormant. In the case of neptunium, it is limited mainly to Np(IV). Here we report the synthesis of three new Np(III) organometallic compounds and the characterization of their molecular and electronic structures. These studies suggest that Np(III) complexes could act as single-molecule magnets, and that the lower oxidation state of Np(II) is chemically accessible. In comparison with lanthanide analogues, significant d- and f-electron contributions to key Np(III) orbitals are observed, which shows that fundamental neptunium organometallic chemistry can provide new insights into the behaviour of f-elements. PMID:27442286

  7. Organometallic neptunium(III) complexes

    NASA Astrophysics Data System (ADS)

    Dutkiewicz, Michał S.; Farnaby, Joy H.; Apostolidis, Christos; Colineau, Eric; Walter, Olaf; Magnani, Nicola; Gardiner, Michael G.; Love, Jason B.; Kaltsoyannis, Nikolas; Caciuffo, Roberto; Arnold, Polly L.

    2016-08-01

    Studies of transuranic organometallic complexes provide a particularly valuable insight into covalent contributions to the metal–ligand bonding, in which the subtle differences between the transuranium actinide ions and their lighter lanthanide counterparts are of fundamental importance for the effective remediation of nuclear waste. Unlike the organometallic chemistry of uranium, which has focused strongly on UIII and has seen some spectacular advances, that of the transuranics is significantly technically more challenging and has remained dormant. In the case of neptunium, it is limited mainly to NpIV. Here we report the synthesis of three new NpIII organometallic compounds and the characterization of their molecular and electronic structures. These studies suggest that NpIII complexes could act as single-molecule magnets, and that the lower oxidation state of NpII is chemically accessible. In comparison with lanthanide analogues, significant d- and f-electron contributions to key NpIII orbitals are observed, which shows that fundamental neptunium organometallic chemistry can provide new insights into the behaviour of f-elements.

  8. PRECIPITATION METHOD OF SEPARATION OF NEPTUNIUM

    DOEpatents

    Magnusson, L.B.

    1958-07-01

    A process is described for the separation of neptunium from plutonium in an aqueous solution containing neptunium ions in a valence state not greater than +4, plutonium ioms in a valence state not greater than +4, and sulfate ions. The Process consists of adding hypochlorite ions to said solution in order to preferentially oxidize the neptunium and then adding lanthanum ions and fluoride ions to form a precipitate of LaF/sub 3/ carrying the plutonium, and thereafter separating the supernatant solution from the precipitate.

  9. Mechanism of boriding from pastes in a glow discharge

    SciTech Connect

    Isakov, S.A.; Al'tshuler, S.A.

    1987-09-01

    The authors investigate the boridation of steel 45 from the standpoint of the glow-discharge dissociation of a borax paste and the plasma arc spraying of the resulting boron into the steel. The effects of process parameters on the impregnation of boron into the steel and its phase behavior in the boridation process are discussed.

  10. The influence of carbon content in the borided Fe-alloys on the microstructure of iron borides

    SciTech Connect

    Kulka, M. . E-mail: coolka@sol.put.poznan.pl; Pertek, A. . E-mail: pertek@sol.put.poznan.pl; Klimek, L. . E-mail: kemilk@p.lodz.pl

    2006-04-15

    This paper presents the results of Electron Back-Scatter Diffraction (EBSD) analyses of the borided layers produced on substrate of varying carbon content. Two types of materials were investigated: borided Armco iron of very low carbon content and borocarburized chromium- and nickel-based steels of high carbon content beneath iron borides. The tetragonal phase Fe{sub 2}B was identified in all materials studied. It was difficult to obtain an EBSD pattern from iron boride (FeB) because of its presence at low depths below the surface, and because of the rounded corners of the specimens. EBSD provided information on the orientation of Fe{sub 2}B crystals. In case of the low-carbon Armco iron the crystallographic orientation was constant along the full length of the Fe{sub 2}B needle. The EBSPs obtained from borocarburized steel indicate that the crystallographic orientation of the Fe{sub 2}B phase changes along the length of the needle. This is the result of hindered boron diffusion due to boriding of the carburized substrate. The increased resistance to friction wear of borocarburized layers arises from two reasons. One is the decreased microhardness gradient between the iron borides and the substrate, which causes a decrease in the brittleness of the iron borides and an improved distribution of internal stresses in the diffusion layer. The second is the changeable crystallographic orientation of iron borides, which leads to the lower texture and porosity of borided layers. These advantageous properties of the borocarburized layer can be obtained if the carbon content beneath the iron borides is no more than about 1.0-1.2 wt.% C.

  11. Boriding of high carbon high chromium cold work tool steel

    NASA Astrophysics Data System (ADS)

    Muhammad, W.

    2014-06-01

    High-carbon high-chromium cold work tool steels are widely used for blanking and cold forming of punches and dies. It is always advantageous to obtain an increased wear resistant surface to improve life and performance of these steels. In this connection boriding of a high-carbon high-chromium cold work die steel, D3, was conducted in a mixture of 30% B4C, 70% borax at 950 °C for two, four and six hours. Case depth of the borided layer obtained was between 40 to 80 μm. After boriding, the surface hardness achieved was between 1430 to 1544 HV depending upon the process time. X-ray diffraction studies confirmed the formation of a duplex compound layer consisting of FeB and Fe2B. It is generally considered that FeB is undesirable because of its inherent brittleness. Post boriding treatment (homogenization) transformed the compound layer into single-phase layer of Fe2B, while surface hardness decreased to 1345-1430 HV. Pin-on-disc wer test showed that wear resistance of the borided samples was superior as compared to non-borided material and increased with boriding time.

  12. Method of making an icosahedral boride structure

    DOEpatents

    Hersee, Stephen D.; Wang, Ronghua; Zubia, David; Aselage, Terrance L.; Emin, David

    2005-01-11

    A method for fabricating thin films of an icosahedral boride on a silicon carbide (SiC) substrate is provided. Preferably the icosahedral boride layer is comprised of either boron phosphide (B.sub.12 P.sub.2) or boron arsenide (B.sub.12 As.sub.2). The provided method achieves improved film crystallinity and lowered impurity concentrations. In one aspect, an epitaxially grown layer of B.sub.12 P.sub.2 with a base layer or substrate of SiC is provided. In another aspect, an epitaxially grown layer of B.sub.12 As.sub.2 with a base layer or substrate of SiC is provided. In yet another aspect, thin films of B.sub.12 P.sub.2 or B.sub.12 As.sub.2 are formed on SiC using CVD or other vapor deposition means. If CVD techniques are employed, preferably the deposition temperature is above 1050.degree. C., more preferably in the range of 1100.degree. C. to 1400.degree. C., and still more preferably approximately 1150.degree. C.

  13. Synthesis and properties of nanoscale titanium boride

    NASA Astrophysics Data System (ADS)

    Efimova, K. A.; Galevskiy, G. V.; Rudneva, V. V.

    2015-09-01

    This work reports the scientific and technological grounds for plasma synthesis of titanium diboride, including thermodynamic and kinetic conditions of boride formation when titanium and titanium dioxide are interacting with products resulting from boron gasification in the nitrogen - hydrogen plasma flow, and two variations of its behavior using the powder mixtures: titanium - boron and titanium dioxide - boron. To study these technology variations, the mathematical models were derived, describing the relation between element contents in the synthesized products of titanium and free boron and basic parameters. The probable mechanism proposed for forming titanium diboride according to a "vapour - melt - crystal" pattern was examined, covering condensation of titanium vapour in the form of aerosol, boriding of nanoscale melt droplets by boron hydrides and crystallization of titanium - boron melt. The comprehensive physical - chemical certification of titanium diboride was carried out, including the study of its crystal structure, phase and chemical composition, dispersion, morphology and particle oxidation. Technological application prospects for use of titanium diboride nanoscale powder as constituent element in the wettable coating for carbon cathodes having excellent physical and mechanical performance and protective properties.

  14. Pack-boriding of Fe-Mn binary alloys: Characterization and kinetics of the boride layers

    SciTech Connect

    Bektes, M.; Calik, A.; Ucar, N.; Keddam, M.

    2010-02-15

    In this work, the boronizing of Fe-Mn binary alloys at 0.42, 0.76 and 0.94 wt.% Mn was carried out in a solid medium using the powder pack method. In this method, commercial Ekabor-II boron source and activator (ferro-silicon) were thoroughly mixed to form the boriding medium. The samples were boronized in an electrical resistance furnace for exposure times of 2, 4, 6 and 8 h at 1173 K under atmospheric pressure and a series of boronized samples in the temperature range 1073-1373 K for 3 h. After the furnace process, boronized samples were removed from the furnace and cooled in air. Afterwards, the boride layers generated by the pack-boronizing process were characterized by optical microscopy, scanning electron microscopy, XRD analysis, Vickers microhardness and tensile testing. The generated boride layers, showing a saw-tooth morphology, had a surface microhardness in the range 1400-1270 HV0.1. It was shown that the values of yield stresses and ultimate tensile stresses were increased as the Mn content increases in the boronized Fe-Mn binary alloys. In contrast, the values of elongations determined from the stress-strain curves were decreased. Furthermore, it was found that the calculated mean value of the activation energy of boron diffusion was close to 119 J/mol.

  15. PACKAGING AND TRANSPORTATION OF NEPTUNIUM OXIDE

    SciTech Connect

    Watkins, R; Steve Hensel, S; Jeffrey Jordan, J

    2009-03-03

    The Savannah River Site's HB-Line Facility completed a campaign in which fifty (50) cans of neptunium oxide were produced and shipped to the Idaho National Laboratory in the 9975 shipping container. This shipping campaign involved the addition of neptunium oxide to the 9975 Safety Analysis Report for Packaging (SARP) as a new content and subsequently a Letter of Amendment to the SARP content table. This paper will address the proper steps which should be taken to add a new content table to a SARP. It will also address the importance of product sampling and understanding the material shipping requirements of a SARP.

  16. Dehydration of plutonium or neptunium trichloride hydrate

    DOEpatents

    Foropoulos, Jr., Jerry; Avens, Larry R.; Trujillo, Eddie A.

    1992-01-01

    A process of preparing anhydrous actinide metal trichlorides of plutonium or neptunium by reacting an aqueous solution of an actinide metal trichloride selected from the group consisting of plutonium trichloride or neptunium trichloride with a reducing agent capable of converting the actinide metal from an oxidation state of +4 to +3 in a resultant solution, evaporating essentially all the solvent from the resultant solution to yield an actinide trichloride hydrate material, dehydrating the actinide trichloride hydrate material by heating the material in admixture with excess thionyl chloride, and recovering anhydrous actinide trichloride is provided.

  17. Dehydration of plutonium or neptunium trichloride hydrate

    DOEpatents

    Foropoulos, J. Jr.; Avens, L.R.; Trujillo, E.A.

    1992-03-24

    A process is described for preparing anhydrous actinide metal trichlorides of plutonium or neptunium by reacting an aqueous solution of an actinide metal trichloride selected from the group consisting of plutonium trichloride or neptunium trichloride with a reducing agent capable of converting the actinide metal from an oxidation state of +4 to +3 in a resultant solution, evaporating essentially all the solvent from the resultant solution to yield an actinide trichloride hydrate material, dehydrating the actinide trichloride hydrate material by heating the material in admixture with excess thionyl chloride, and recovering anhydrous actinide trichloride.

  18. Certain physical properties of cobalt and nickel borides

    NASA Technical Reports Server (NTRS)

    Kostetskiy, I. I.; Lvov, S. N.

    1981-01-01

    The temperature dependence of the electrical resistivity, the thermal conductivity, and the thermal emf of cobalt and nickel borides were studied. In the case of the nickel borides the magnetic susceptibility and the Hall coefficient were determined at room temperature. The results are discussed with allowance for the current carrier concentration, the effect of various mechanisms of current-carrier scattering and the location of the Fermi level in relation to the 3d band.

  19. DEVELOPMENT OF NDA METHODS FOR NEPTUNIUM METAL

    SciTech Connect

    C. MOSS; ET AL

    2000-10-01

    Many techniques have been developed and applied in the US and other countries for the control of the special nuclear materials (SNM) plutonium and uranium, but no standard methods exist for the determination of neptunium in bulk containers. Such methods are needed because the U.S. Department of Energy requires all Government-owned {sup 237}Np be treated as if it were SNM and the International Atomic Energy Agency is considering how to monitor this material. We present the results of the measurements of several samples of neptunium metal with a variety of techniques. Analysis of passive gamma-ray spectra uniquely identifies the material, provides isotopic ratios for contaminants, such as {sup 243}Am, and may provide information about the shielding, mass, and time since processing. Active neutron interrogation, using the delayed neutron technique in a package monitor, provides useful data even if the neptunium is shielded. The tomographic gamma scanner yields a map of the distribution of the neptunium and shielding in a container. Active photon interrogation with pulses from a 10-MeV linac produces delayed neutrons between pulses, even when the container is heavily shielded. Data from one or more of these techniques can be used to identify the material and estimate a mass in a bulk container.

  20. Neptunium_Oxide_Precipitation_Kinetics_AJohnsen

    SciTech Connect

    Johnsen, A M; Roberts, K E; Prussin, S G

    2012-06-08

    We evaluate the proposed NpO{sub 2}{sup +}(aq)-NpO{sub 2}(cr) reduction-precipitation system at elevated temperatures to obtain primary information on the effects of temperature, ionic strength, O{sub 2} and CO{sub 2}. Experiments conducted on unfiltered solutions at 10{sup -4} M NpO{sub 2}{sup +}(aq), neutral pH, and 200 C indicated that solution colloids strongly affect precipitation kinetics. Subsequent experiments on filtered solutions at 200, 212, and 225 C showed consistent and distinctive temperature-dependent behavior at reaction times {le} 800 hours. At longer times, the 200 C experiments showed unexpected dissolution of neptunium solids, but experiments at 212 C and 225 C demonstrated quasi steady-state neptunium concentrations of 3 x 10{sup -6} M and 6 x 10{sup -6} M, respectively. Solids from a representative experiment analyzed by X-ray diffraction were consistent with NpO{sub 2}(cr). A 200 C experiment with a NaCl concentration of 0.05 M showed a dramatic increase in the rate of neptunium loss. A 200 C experiment in an argon atmosphere resulted in nearly complete loss of aqueous neptunium. Previously proposed NpO{sub 2}{sup +}(aq)-NpO{sub 2}(cr) reduction-precipitation mechanisms in the literature specified a 1:1 ratio of neptunium loss and H{sup +} production in solution over time. However, all experiments demonstrated ratios of approximately 0.4 to 0.5. Carbonate equilibria can account for only about 40% of this discrepancy, leaving an unexpected deficit in H+ production that suggests that additional chemical processes are occurring.

  1. DISSOLUTION OF NEPTUNIUM OXIDE RESIDUES

    SciTech Connect

    Kyser, E

    2009-01-12

    This report describes the development of a dissolution flowsheet for neptunium (Np) oxide (NpO{sub 2}) residues (i.e., various NpO{sub 2} sources, HB-Line glovebox sweepings, and Savannah River National Laboratory (SRNL) thermogravimetric analysis samples). Samples of each type of materials proposed for processing were dissolved in a closed laboratory apparatus and the rate and total quantity of off-gas were measured. Samples of the off-gas were also analyzed. The quantity and type of solids remaining (when visible) were determined after post-dissolution filtration of the solution. Recommended conditions for dissolution of the NpO{sub 2} residues are: Solution Matrix and Loading: {approx}50 g Np/L (750 g Np in 15 L of dissolver solution), using 8 M nitric acid (HNO{sub 3}), 0.025 M potassium fluoride (KF) at greater than 100 C for at least 3 hours. Off-gas: Analysis of the off-gas indicated nitric oxide (NO), nitrogen dioxide (NO{sub 2}) and nitrous oxide (N{sub 2}O) as the only identified components. No hydrogen (H{sub 2}) was detected. The molar ratio of off-gas produced per mole of Np dissolved ranged from 0.25 to 0.4 moles of gas per mole of Np dissolved. A peak off-gas rate of {approx}0.1 scfm/kg bulk oxide was observed. Residual Solids: Pure NpO{sub 2} dissolved with little or no residue with the proposed flowsheet but the NpCo and both sweepings samples left visible solid residue after dissolution. For the NpCo and Part II Sweepings samples the residue amounted to {approx}1% of the initial material, but for the Part I Sweepings sample, the residue amounted to {approx}8 % of the initial material. These residues contained primarily aluminum (Al) and silicon (Si) compounds that did not completely dissolve under the flowsheet conditions. The residues from both sweepings samples contained minor amounts of plutonium (Pu) particles. Overall, the undissolved Np and Pu particles in the residues were a very small fraction of the total solids.

  2. New neptunium(V) borates that exhibit the alexandrite effect.

    PubMed

    Wang, Shuao; Alekseev, Evgeny V; Depmeier, Wulf; Albrecht-Schmitt, Thomas E

    2012-01-01

    A new neptunium(V) borate, K[(NpO(2))B(10)O(14)(OH)(4)], was synthesized using boric acid as a reactive flux. The compound possesses a layered structure in which Np(V) resides in triangular holes, creating a hexagonal-bipyramidal environment around neptunium. This compound is unusual in that it exhibits the Alexandrite effect, a property that is typically restricted to neptunium(IV) compounds. PMID:22145669

  3. Ultralow friction behavior of borided steel surfaces after flash annealing

    SciTech Connect

    Bindal, C.; Erdemir, A.

    1996-02-01

    In this letter, we describe the ultralow friction mechanism of borided steel surfaces subjected to a short-duration, or {open_quote}{open_quote}flash,{close_quote}{close_quote} annealing procedure. In this procedure, a borided steel surface is exposed to high temperature (600 to 800{degree}C) for a short time (3 to 5 min) and then cooled to room temperature in open air. During the high-temperature exposure, boron atoms within the borided layer diffuse to the surface and react spontaneously with oxygen in air. The reaction product is a thin boron oxide film. During cooling, the boron oxide reacts spontaneously with moisture in the surrounding air to form a thin boric acid film. The sliding friction coefficient of a Si{sub 3}N{sub 4} ball against this flash-annealed surface is about 0.06, but is 0.5 and higher against the unborided or borided-only surfaces. Mechanistically, we propose that the ultralow friction behavior of the borided and flash-annealed surface is due mainly to the layered-crystal structure of the boric acid film that forms on the sliding surface. {copyright} {ital 1996 American Institute of Physics.}

  4. Investigation of Neptunium Precipitator Cleanout Options

    SciTech Connect

    Hill, B.C.

    2003-09-08

    Oxalate precipitation followed by filtration is used to prepare plutonium oxalate. Historically, plutonium oxalate has tended to accumulate in the precipitation tanks. These solids are periodically removed by flushing with concentrated (64 percent) nitric acid. The same precipitation tanks will now be used in the processing of neptunium. Literature values indicate that neptunium oxalate may not be as soluble as plutonium oxalate in nitric acid. Although a wide variety of options is available to improve neptunium oxalate solubility for precipitator flushing, most of these options are not practical for use. Many of these options require the use of incompatible or difficult to handle chemicals. Other options would require expensive equipment modifications or are likely to lead to product contamination. Based on review of literature and experimental results, the two best options for flushing the precipitator are (1) 64 percent nitric acid and (2) addition of sodium permanganate follow ed by sodium nitrite. Nitric acid is the easiest option to implement. It is already used in the facility and will not lead to product contamination. Experimental results indicate that neptunium oxalate can be dissolved in concentrated nitric acid (64 percent) at 60 degree C to a concentration of 2.6 to 5.6 grams of Np/liter after at least three hours of heating. A lower concentration (1.1 grams of Np/liter) was measured at 60 degree C after less than two hours of heating. These concentrations are acceptable for flushing if precipitator holdup is low (approximately 100-250 grams), but a second method is required for effective flushing if precipitator holdup is high (approximately 2 kilograms). The most effective method for obtaining higher neptunium concentrations is the use of sodium permanganate followed by the addition of sodium nitrite. There is concern that residual manganese from these flushes could impact product purity. Gas generation during permanganate addition is also a concern

  5. Incorporation of neptunium(VI) into a uranyl selenite.

    PubMed

    Meredith, Nathan A; Polinski, Matthew J; Lin, Jian; Simonetti, Antonio; Albrecht-Schmitt, Thomas E

    2012-10-15

    The incorporation of neptunium(VI) into the layered uranyl selenite Cs[(UO(2))(HSeO(3))(SeO(3))] has yielded the highest level of neptunium uptake in a uranyl compound to date with an average of 12(±3)% substitution of Np(VI) for U(VI). Furthermore, this is the first case in nearly 2 decades of dedicated incorporation studies in which the oxidation state of neptunium has been determined spectroscopically in a doped uranyl compound and also the first time in which neptunium incorporation has resulted in a structural transformation. PMID:23030830

  6. Neptunium flow-sheet verification at reprocessing plants

    SciTech Connect

    Rance, P.; Chesnay, B.; Killeen, T.; Murray, M.; Nikkinen, M.; Petoe, A.; Plumb, J.; Saukkonen, H.

    2007-07-01

    Due to their fissile nature, neptunium and americium have at least a theoretical potential application as nuclear explosives and their proliferation potential was considered by the IAEA in studies in the late 1990's. This work was motivated by an increased awareness of the proliferation potential of americium and neptunium and a number of emerging projects in peaceful nuclear programmes which could result in an increase in the available quantities of these minor actinides. The studies culminated in proposals for various voluntary measures including the reporting of international transfers of separated americium and neptunium, declarations concerning the amount of separated neptunium and americium held by states and the application of flow-sheet verification to ensure that facilities capable of separating americium or neptunium are operated in a manner consistent with that declared. This paper discusses the issue of neptunium flowsheet verification in reprocessing plants. The proliferation potential of neptunium is first briefly discussed and then the chemistry of neptunium relevant to reprocessing plants described with a view to indicating a number of issues relevant to the verification of neptunium flow-sheets. Finally, the scope of verification activities is discussed including analysis of process and engineering design information, plant monitoring and sampling and the potential application of containment and surveillance measures. (authors)

  7. High temperature adsorption process for solidification of plutonium and neptunium

    SciTech Connect

    Korchenkin, K.; Mashkin, A.; Nardova, A.

    1995-12-31

    The problem of plutonium and neptunium converting into solid form has been considered. It was recently been discovered that plutonium and neptunium absorbed well on inorganic porous matrices (silica gel) under definite conditions. In the work presented in this paper plutonium and neptunium sorption on silica gel followed by calcining saturated granules was experimentally investigated. Calcination may proceed at the different temperatures to give the solid dustless plutonium and neptunium compounds suitable both for controlled temporary storage (with possible return radionuclides in nuclear fuel cycle) and for long life disposal.

  8. The characterization of boride layer on the St37 iron

    NASA Astrophysics Data System (ADS)

    Sutrisno, Soegijono, Bambang

    2012-06-01

    The property such as microhardness of boride layer formed on St37 iron was investigated. Boronizing was carried out in a solid medium consisting of nano size powders of 50% B4C as a donor, 45% SiC as a diluent, and 5% KBF4 as an activator treated at the temperature of 1000°C for 8 hours. The phases that were formed on the substrate was found as Fe2B and FeB layer that had smooth and flate shape morphology. The hardness of boride layer on St37 was over 2000 HV, while the hardness of untreated St37 iron was about 123,82 HV. Depending on process time and temperature, the depth of boride layer ranges from 20 to 60 μm, leading to a diffusion controlled process.

  9. Superconductivity and magnetism of complex rhodium borides

    NASA Astrophysics Data System (ADS)

    Burkhanov, G. S.; Lachenkov, S. A.; Khlybov, E. P.; Dankin, D. G.; Kulikova, L. F.

    2013-05-01

    A number of complex rhodium borides with an LuRu4B4-type structure is synthesized; these are DyRh4B4 (samples HP) with T c ≈ 4.5 K, DyRh3.8Ru0.2B4 (samples AM) with T c ≈ 4.5 K, Dy0.8Er0.2Rh3.8Ru0.2B4 (samples AM) with T c ≈ 6.3 K, and HoRh3.8Ru0.2B4 (samples AM) with T c ≈ 6.0 K. The temperature dependence of upper critical field B c2( T) for all the samples under study exhibits an anomalous behavior. In all cases, the curve B c2( T) demonstrates a point of inflection, after which the curve deviates from the classical parabolic law abruptly upward for DyRh4B4 and DyRh3.8Ru0.2B4 (the 1st group of compounds) and downward for the Dy0.8Er0.2Rh3.8Ru0.2B4 and HoRh3.8Ru0.2B4 compounds (the 2nd group). These compounds are found to be characterized by of the following phase transitions: paramagnet → ferrimagnet → superconductor (retained ferrimagnetism) → antiferromagnet (retained superconductivity). The latter transition to the antiferromagnetic state occurs only in the compounds of the 1st group. It is found that, for the DyRh3.8Ru0.2B4 compound, no traditional Meissner effect is observed but the so-called Volleben effect (paramagnetic Meissner effect) takes place.

  10. Dissolution of Neptunium Oxide in Unirradiated Mark 53 Targets

    SciTech Connect

    Rudisill, T.S.

    2002-12-06

    Nine unirradiated Mark 53 targets currently stored at the K-Reactor must be dissolved to allow recovery of the neptunium content. The Mark 53 targets are an aluminum clad, neptunium oxide (NpO2)/aluminum metal cermet used for the production of plutonium-238. The targets will be dissolved in H-Canyon and blended with solutions generated from routine fuel dissolutions for purification by solvent extraction. The increased neptunium concentration should not have a significant effect on the neptunium decontamination factor achieved by the 1st cycle of solvent extraction; however, the neptunium content of the uranium product (1CU) will likely increase in proportion to the increase in the neptunium feed concentration. The recovered neptunium will be combined with the existing inventory of neptunium solution currently stored in H-Canyon. The combined inventory will undergo subsequent purification and conversion to an oxide for shipment to the Oak Ridge National Laboratory where plutonium- 238 will be manufactured using the High Flux Isotope Reactor.

  11. Comparison of neptunium sorption results using batch and column techniques

    SciTech Connect

    Triay, I.R.; Furlano, A.C.; Weaver, S.C.; Chipera, S.J.; Bish, D.L.

    1996-08-01

    We used crushed-rock columns to study the sorption retardation of neptunium by zeolitic, devitrified, and vitric tuffs typical of those at the site of the potential high-level nuclear waste repository at Yucca Mountain, Nevada. We used two sodium bicarbonate waters (groundwater from Well J-13 at the site and water prepared to simulate groundwater from Well UE-25p No. 1) under oxidizing conditions. It was found that values of the sorption distribution coefficient, Kd, obtained from these column experiments under flowing conditions, regardless of the water or the water velocity used, agreed well with those obtained earlier from batch sorption experiments under static conditions. The batch sorption distribution coefficient can be used to predict the arrival time for neptunium eluted through the columns. On the other hand, the elution curves showed dispersivity, which implies that neptunium sorption in these tuffs may be nonlinear, irreversible, or noninstantaneous. As a result, use of a batch sorption distribution coefficient to calculate neptunium transport through Yucca Mountain tuffs would yield conservative values for neptunium release from the site. We also noted that neptunium (present as the anionic neptunyl carbonate complex) never eluted prior to tritiated water, which implies that charge exclusion does not appear to exclude neptunium from the tuff pores. The column experiments corroborated the trends observed in batch sorption experiments: neptunium sorption onto devitrified and vitric tuffs is minimal and sorption onto zeolitic tuffs decreases as the amount of sodium and bicarbonate/carbonate in the water increases.

  12. PERFORMANCE OF THE SAVANNAH RIVER SITE COULOMETER FOR NEPTUNIUM PROCESSACCOUNTABILITY AND NEPTUNIUM OXIDE PRODUCT CHARACTERIZATION

    SciTech Connect

    Holland, M; Patterson Nuessle, P; Sheldon Nichols, S; Joe Cordaro, J; George Reeves, G

    2008-06-04

    The Savannah River Site's (SRS) H-Area B-Line (HB-Line) nuclear facility is processing neptunium solutions for stabilization as an oxide. The oxide will eventually be reprocessed and fabricated into target material and the 237Np irradiated to produce {sup 238}Pu in support of National Aeronautics and Space Administration space program missions. As part of nuclear materials accountability, solution concentrations were measured using a high-precision controlled-potential coulometer developed and manufactured at the SRS for plutonium accountability measurements. The Savannah River Site Coulometer system and measurement methodology for plutonium meets performance standards in ISO 12183-2005, 'Controlled-Potential Coulometric Assay of Plutonium'. The Department of Energy (DOE) does not produce or supply a neptunium metal certified reference material, which makes qualifying a measurement method and determining accuracy and precision difficult. Testing and performance of the Savannah River Site Coulometer indicates that it can be used to measure neptunium process solutions and dissolved neptunium oxide without purification for material control and accountability purposes. Savannah River Site's Material Control and Accountability organization has accepted the method uncertainty for accountability and product characterization measurements.

  13. Subminiature eddy current transducers for studying boride coatings

    NASA Astrophysics Data System (ADS)

    Dmitriev, S. F.; Ishkov, A. V.; Malikov, V. N.; Sagalakov, A. M.

    2016-07-01

    Strengthening of parts and units of machines, increased reliability and longer service life is an important task of modern mechanical engineering. The main objects of study in the work were selected steel 65G and 50HGA, wear-resistant boride coatings ternary system Fe-B-Fe n B which were investigated by scanning electron microscopy and eddy-current nondestructive methods.

  14. Development and application of high strength ternary boride base cermets

    SciTech Connect

    Takagi, Ken-ichi . E-mail: u4381@toyokohan.co.jp

    2006-09-15

    Reaction boronizing sintering is a novel strategy to form a ternary boride coexisting with a metal matrix in a cermet during liquid phase sintering. This new sintering technique has successfully developed world first ternary boride base cermets with excellent mechanical properties such as Mo{sub 2}FeB{sub 2}, Mo{sub 2}NiB{sub 2} and WCoB base ones. In these cermets Mo{sub 2}FeB{sub 2} and Mo{sub 2}NiB{sub 2} base ones consist of a tetragonal M {sub 3}B{sub 2} (M: metal)-type complex boride as a hard phase and a transition metal base matrix. The cermets have already been applied to wear resistant applications such as injection molding machine parts, can making tools, and hot copper extruding dies, etc. This paper focuses on the characteristics, effects of the additional elements on the mechanical properties and structure, and practical applications of the ternary boride base cermets. - Graphical abstract: TRS and hardness of Ni-5B-51Mo-17.5Cr and Ni-5B-51Mo-12.5Cr-5V-xMn mass% cermets as functions of Mn content (Fig. 17)

  15. Transport of neptunium through Yucca Mountain tuffs

    SciTech Connect

    Triay, I.R.; Robinson, B.A.; Mitchell, A.J.; Overly, C.M.; Lopez, R.M.

    1993-12-31

    Neptunium has a high solubility in groundwaters from Yucca Mountain. Uranium in nuclear reactors produces {sup 237}Np which has a half-life of 2.14 {times} 10{sup 6} years. Consequently, the transport of {sup 237}Np through tuffs is of major importance in assessing the performance of a high-level nuclear waste repository at Yucca Mountain. The objective of this work is to determine the amount of Np retardation that is provided by the materials in Yucca Mountain tuffs as a function of groundwater chemistry.

  16. The production of Neptunium-236g.

    PubMed

    Jerome, S M; Ivanov, P; Larijani, C; Parker, D J; Regan, P H

    2014-12-01

    Radiochemical analysis of (237)Np is important in a number of fields, such as nuclear forensics, environmental analysis and measurements throughout the nuclear fuel cycle. However analysis is complicated by the lack of a stable isotope of neptunium. Although various tracers have been used, including (235)Np, (239)Np and even (236)Pu, none are entirely satisfactory. However, (236g)Np would be a better candidate for a neptunium yield tracer, as its long half-life means that it is useable as both a radiometric and mass spectrometric measurements. This radionuclide is notoriously difficult to prepare, and limited in scope. In this paper, we examine the options for the production of (236g)Np, based on work carried out at NPL since 2011. However, this work was primarily aimed at the production of (236)Pu, and not (236g)Np and therefore the rate of production are based on the levels of (236)Pu generated in the irradiation of (i) (238)U with protons, (ii) (235)U with deuterons, (iii) (236)U with protons and (iv) (236)U with deuterons. The derivation of a well-defined cross section is complicated by the relevant paucity of information on the variation of the (236m)Np:(236g)Np production ratio with incident particle energy. Furthermore, information on the purity of (236g)Np so produced is similarly sparse. Accordingly, the existing data is assessed and a plan for future work is presented. PMID:24731718

  17. Neptunium(III) application in extraction chromatography.

    PubMed

    Guérin, Nicolas; Nadeau, Kenny; Larivière, Dominic

    2011-12-15

    This paper describes a novel strategy for actinide separation by extraction chromatography with Np(III) valence adjustment. Neptunium(IV) was reduced to Np(III) using Cr(II) and then selectively separated from uranium (IV) on a TEVA resin. After elution, Np(III) was retained on a DGA resin in order to remove any detrimental chromium impurities. Neptunium(III) formation was demonstrated by the complete and selective elution of Np from TEVA resin (99 ± 7%) in less than 12 mL of 9M HCl from U(IV) (0.7 ± 0.7%). It was determined by UV-visible and kinetic studies that Cr(II) was the only species responsible for the elution of Np(IV) as Np(III) and that the Cr(II) solution could be prepared from 2 to 30 min before its use without the need of complex degassing systems to prevent the oxidation of Np(III) by oxygen. The methodology proposed here with TEVA/DGA resins provides removal of Cr(III) impurities produced at high decontamination factors (2.8 × 10(3) and 7.3 × 10(4) respectively). PMID:22099641

  18. Neptunium Binding Kinetics with Arsenazo(III)

    SciTech Connect

    Leigh R. Martin; Aaron T. Johnson; Stephen P. Mezyk

    2014-08-01

    This document has been prepared to meet FCR&D level 2 milestone M2FT-14IN0304021, “Report on the results of actinide binding kinetics with aqueous phase complexants” This work was carried out under the auspices of the Thermodynamics and Kinetics of Advanced Separations Systems FCR&D work package. The report details kinetics experiments that were performed to measure rates of aqueous phase complexation for pentavalent neptunium with the chromotropic dye Arsenazo III (AAIII). The studies performed were designed to determine how pH, ionic strength and AAIII concentration may affect the rate of the reaction. A brief comparison with hexavalent neptunium is also made. It was identified that as pH was increased the rate of reaction also increased, however increasing the ionic strength and concentration of AAIII had the opposite effect. Interestingly, the rate of reaction of Np(VI) with AAIII was found to be slower than that of the Np(V) reaction.

  19. Nanosize cobalt boride particles: Control of the size and properties

    NASA Astrophysics Data System (ADS)

    Petit, C.; Pileni, M. P.

    1997-02-01

    Cobalt boride is obtained by the reduction of cobalt (2-ethyl hexyl) sulfosuccinate, Co(AOT) 2, by sodium borohydride either in reverse micelles or in a diphasic system. In Co(AOT) 2/Na(AOT)/H 2O reverse micellar solution, the size and polydispersity of the Co 2B particles is controlled by the size of the water droplets, which increases from 4 to 7.5 nm by increasing the water content. In a diphasic system of Co(AOT) 2/isooctane and sodium borohydride in aqueous solution, large and polydisperse particles of cobalt boride are formed (˜ 10 nm), and their magnetization properties are presented. The smallest particles are in a superparamagnetic regime at room temperature, whereas the largest particles show ferromagnetic behavior.

  20. Surface Complexation of Neptunium(V) with Goethite

    SciTech Connect

    Jerden, James L.; Kropf, A. Jeremy

    2007-07-01

    Batch adsorption experiments in which neptunium-bearing solutions were reacted with goethite (alpha-FeOOH) have been performed to study uptake mechanisms in sodium chloride and calcium-bearing sodium silicate solutions. This paper presents results identifying and quantifying the mechanisms by which neptunium is adsorbed as a function of pH and reaction time (aging). Also presented are results from tests in which neptunium is reacted with goethite in the presence of other cations (uranyl and calcium) that may compete with neptunium for sorption sites. The desorption of neptunium from goethite has been studied by re-suspending the neptunium-loaded goethite samples in solutions containing no neptunium. Selected reacted sorbent samples were analyzed by x-ray absorption spectroscopy (XAS) to determine the oxidation state and molecular speciation of the adsorbed neptunium. Results have been used to establish the pH adsorption edge of neptunium on goethite in sodium chloride and calcium-bearing sodium silicate solutions. The results indicate that neptunium uptake on goethite reaches 95% at a pH of approximately 7 and begins to decrease at pH values greater than 8.5. Distribution coefficients for neptunium sorption range from less than 1000 (moles/kg){sub sorbed} / (moles/kg){sub solution} at pH less than 5.0 to greater than 10,000 (moles/kg){sub sorbed} / (moles/kg){sub solution} at pH greater than 7.0. Distribution coefficients as high as 100,000 (moles/kg){sub sorbed} / (moles/kg){sub solution} were recorded for the tests done in calcite equilibrated sodium silicate solutions. XAS results show that neptunium complexes with the goethite surface mainly as Np(V) (although Np(IV) is prevalent in some of the longer-duration sorption tests). The neptunium adsorbed to goethite shows Np-O bond length of approximately 1.8 angstroms which is representative of the Np-O axial bond in the neptunyl(V) complex. This neptunyl(V) ion is coordinated to 5 or 6 equatorial oxygens with Np

  1. Dissolution of Neptunium Oxide in Unirradiated Mark 53 Targets

    SciTech Connect

    Rudisill, T.S.

    2002-06-07

    Nine unirradiated Mark 53 targets currently stored at the K-Reactor must be dissolved to allow recovery of the neptunium content. The Mark 53 targets are an aluminum clad neptunium oxide (NpO2)/aluminum metal cermet used for the production of plutonium-238. The targets will be dissolved in H-Canyon and blended with solutions generated from routine fuel dissolutions for purification by solvent extraction

  2. Neptunium Disposal to the Savannah River Site Tank Farm

    SciTech Connect

    Walker, D.D.

    2004-02-26

    Researchers investigated the neutralization of an acidic neptunium solution from a Savannah River Site (SRS) processing canyon and the properties of the resulting slurry to determine the feasibility of disposal in the SRS tank farm. The acidic solution displayed no properties that precluded the proposed disposal route. Neutralization of the acidic neptunium forms a 4 wt per cent slurry of precipitated metal hydroxides. The insoluble solids consist largely of iron (92 per cent) and neptunium hydroxides (2 per cent). The concentration of soluble neptunium remaining after neutralization equaled much less than previous solubility measurements predicted. Researchers used an apparatus similar to an Ostwald-type viscometer to estimate the consistency of the neptunium slurry with the solids present. The yield stress and consistency of the 4 wt per cent slurry will allow transfer through the tank farm, although concentration of the insoluble solids above 4 wt per cent may cause significant problems due to increased consistency and yield stress. The consistency of the 4 wt per cent slurry is 7.6 centipoise (cP) with a yield stress less than 1 Pascal (Pa). The neptunium slurry, when combined with actual washed radioactive sludge, slightly reduces the yield stress and consistency of the sludge and produces a combined slurry with acceptable rheological properties for vitrification.

  3. Neptunium(III) copper(I) diselenide

    PubMed Central

    Wells, Daniel M.; Skanthakumar, S.; Soderholm, L.; Ibers, James A.

    2009-01-01

    The title compound, NpCuSe2, is the first ternary neptunium transition-metal chalcogenide. It was synthesized from the elements at 873 K in an evacuated fused-silica tube. Single crystals were grown by vapor transport with I2. NpCuSe2 crystallizes in the LaCuS2 structure type and can be viewed as a stacking of layers of CuSe4 tetra­hedra and of double layers of NpSe7 monocapped trigonal prisms along [100]. Because there are no Se—Se bonds in the structure, the formal oxidation states of Np/Cu/Se may be assigned as +III/+I/−II, respectively. PMID:21582032

  4. Gas Generation Testing of Neptunium Oxide at Elevated Temperature

    SciTech Connect

    Duffey, JM

    2004-01-30

    Elevated temperature gas generation tests have been conducted using neptunium dioxide produced on a laboratory scale using the HB-Line Phase II flowsheet. These tests were performed to determine what effect elevated temperatures would have on the neptunium dioxide in comparison to neptunium dioxide tested at ambient temperature. The headspace gas compositions following storage at elevated temperatures associated with normal conditions of transport (NCT) have been measured. These test results show an increase in hydrogen generation rate at elevated temperature and significant removal of oxygen from the headspace gas. The elevated temperature gas generation tests described in this report involved heating small test vessels containing neptunium dioxide and measuring the headspace gas pressure and composition at the end of the test period. Four samples were used in these tests to evaluate the impact of process variables on the gas generation rate. Two samples were calcined to 600 degrees Celsius and two were calcined to 650 degrees Celsius. Each test vessel contained approximately 9.5 g of neptunium dioxide. Following exposure to 75 per cent relative humidity (RH) for five days, these samples were loaded in air and then heated to between 105 and 115 degrees Celsius for about one month. At the conclusion of the test period, the headspace gas of each container was analyzed using a micro-gas chromatograph installed in the glovebox where the experiments were conducted. The pressure, volume, and composition data for the headspace gas samples were used to calculate average H2 generation rates.

  5. Modified Purex first-cycle extraction for neptunium recovery

    SciTech Connect

    Dinh, Binh; Moisy, Philippe; Baron, Pascal; Calor, Jean-Noel; Espinoux, Denis; Lorrain, Brigitte; Benchikouhne-Ranchoux, Magali

    2008-07-01

    A new PUREX first-cycle flowsheet was devised to enhance the extraction yield of neptunium at the extraction step of this cycle. Simulation results (using a qualified process-simulation tool), le d to raising the nitric acid concentration of the feed from 3 M to 4.5 M to allow extraction of more than 99% of the neptunium. This flowsheet was operated in the shielded process cell of ATALANTE facility using pulsed columns and mixer-settlers banks. A 15 kg quantity of genuine oxide fuel of average burn up of 52 GWd/t with cooling time of nearly five years was treated, and the neptunium extraction yield obtained was greater than 99.6%. (authors)

  6. Neptunium(V) Incorporation/Sorption with Uranium(VI) Alteration Products

    SciTech Connect

    Friese, Judah I.; Douglas, Matthew; Buck, Edgar C.; Clark, Susan B.; Hanson, Brady D.

    2004-04-01

    An initial uranium phase that has been observed to form during the corrosion of spent nuclear fuel is the uranium oxy-hydroxide metaschoepite. It has been proposed that neptunium(V) solubility can be limited by its association with this uranium phase. Metaschoepite has been synthesized in the presence of neptunium(V) over the pH range modeled in the proposed Yucca Mountain geologic repository. Uranium (VI) phaseswere synthesized by varying pH and neptunium concentrations. Results of neptunium association with the uranium alteration phases are presented and the relationship to dissolved neptunium concentrations discussed.

  7. Microstructural characterization and some mechanical properties of gas-borided Inconel 600-alloy

    NASA Astrophysics Data System (ADS)

    Makuch, N.; Kulka, M.

    2014-09-01

    The excellent resistance of Ni-based alloys to corrosion and oxidation is well-known. Boriding can be applied to these alloys in order to obtain suitable wear protection. In this paper, two-stage gas boronizing in N2-H2-BCl3 atmosphere is proposed for the producing the boride layer on Inconel®600-alloy. This process consists in two stages alternately repeated: saturation by boron and diffusion annealing. Such a gas boriding is applied in order to accelerate the saturation by boron and its diffusion. It turns out to be more effective because of eliminating the excess of boron, diffusing into the substrate, during the second stage. Microstructure and some mechanical properties of the produced layer are presented. Microstructural characterization is studied with using an optical microscope, scanning electron microscope, energy-dispersive x-ray microanalysis and x-ray diffraction. The diffusion zone consists of the mixture of nickel and chromium borides, occurring in the compact boride zone and in the area located beneath, at grain boundaries. The improved hardness and wear resistance characterize the layer. The formed boride layer is significantly thicker than those-obtained by the pack-boronizing or paste process at comparable temperature and time. Simultaneously, the measured depth of layer is slightly smaller than that-reported for electrolytic boriding.

  8. Characterisation of titanium-titanium boride composites processed by powder metallurgy techniques

    SciTech Connect

    Selva Kumar, M.; Chandrasekar, P.; Chandramohan, P.; Mohanraj, M.

    2012-11-15

    In this work, a detailed characterisation of titanium-titanium boride composites processed by three powder metallurgy techniques, namely, hot isostatic pressing, spark plasma sintering and vacuum sintering, was conducted. Two composites with different volume percents of titanium boride reinforcement were used for the investigation. One was titanium with 20% titanium boride, and the other was titanium with 40% titanium boride (by volume). Characterisation was performed using X-ray diffraction, electron probe micro analysis - energy dispersive spectroscopy and wavelength dispersive spectroscopy, image analysis and scanning electron microscopy. The characterisation results confirm the completion of the titanium boride reaction. The results reveal the presence of titanium boride reinforcement in different morphologies such as needle-shaped whiskers, short agglomerated whiskers and fine plates. The paper also discusses how mechanical properties such as microhardness, elastic modulus and Poisson's ratio are influenced by the processing techniques as well as the volume fraction of the titanium boride reinforcement. - Highlights: Black-Right-Pointing-Pointer Ti-TiB composites were processed by HIP, SPS and vacuum sintering. Black-Right-Pointing-Pointer The completion of Ti-TiB{sub 2} reaction was confirmed by XRD, SEM and EPMA studies. Black-Right-Pointing-Pointer Hardness and elastic properties of Ti-TiB composites were discussed. Black-Right-Pointing-Pointer Processing techniques were compared with respect to their microstructure.

  9. Processing and properties of some alumina-boride composites

    SciTech Connect

    Edirisinghe, M.J.

    1995-10-01

    Alumina (Al{sub 2}O{sub 3}) test bars containing a small (5--10%) volume of titanium diboride (TiB{sub 2}) or zirconium diboride (ZrB{sub 2}) particles have been pressed and sintered (pressureless) in an argon atmosphere. The microstructure of the sintered bodies was characterized by X-ray diffraction and a range of microscopical techniques and shows that 3 ppm (by volume) of oxygen present in the argon caused the boride particles in the surface regions of the test bars to oxidize during sintering, to a greater extent in the Al{sub 2}O{sub 3}-TiB{sub 2} composites. Mechanisms of oxidation are discussed. The boride particles retarded the densification of the composites, to a greater extent in the Al{sub 2}O{sub 3}-ZrB{sub 2} bodies. However, densification in the Al{sub 2}O{sub 3}-ZrB{sub 2} system was enhanced by sintering in an Ar-4% H{sub 2} atmosphere. The decrease in flexural strength due to the retardation of sintering has been overcome in both types of composites.

  10. Reactive Boride Brazing on Low-Alloy Automotive Grade Steel

    NASA Astrophysics Data System (ADS)

    Palanisamy, B.; Upadhyaya, A.

    2011-11-01

    Brazing is a widely used process to improve the performance of steels used in automotive applications. The substrate material is often exposed to harsh conditions in these applications and may affect the service life of the component. Reactive boride brazing aims to improve the mechanical properties of the substrate material by forming a ceramic-metal composite coating in a single-step process in situ. In this study, sintered Ancor 4300 low-alloy steel is used as the substrate with chromium-rich braze and chromium-lean braze materials. The mechanical properties of the brazed samples were studied in detail using microindentation hardness measurements and the transverse rupture test. The results indicate that the brazed superlayer has a 10 times higher hardness. There was a significant improvement in the transverse rupture strength of the steel brazed with the chromium-rich boride as compared to the pure substrate material. In an effort to reduce processing time, green compacts of the substrate were also directly brazed and yielded favorable results.

  11. Discovery of elusive structures of multifunctional transition-metal borides.

    PubMed

    Liang, Yongcheng; Wu, Zhaobing; Yuan, Xun; Zhang, Wenqing; Zhang, Peihong

    2016-01-14

    A definitive determination of crystal structures is an important prerequisite for designing and exploiting new functional materials. Even though tungsten and molybdenum borides (TMBx) are the prototype for transition-metal light-element compounds with multiple functionalities, their elusive crystal structures have puzzled scientists for decades. Here, we discover that the long-assumed TMB2 phases with the simple hP3 structure (hP3-TMB2) are in fact a family of complex TMB3 polytypes with a nanoscale ordering along the axial direction. Compared with the energetically unfavorable and dynamically unstable hP3-TMB2 phase, the energetically more favorable and dynamically stable TMB3 polytypes explain the experimental structural parameters, mechanical properties, and X-ray diffraction (XRD) patterns better. We demonstrate that such a structural and compositional modification from the hP3-TMB2 phases to the TMB3 polytypes originates from the relief of the strong antibonding interaction between d electrons by removing one third of metal atoms systematically. These results resolve the longstanding structural mystery of this class of metal borides and uncover a hidden family of polytypic structures. Moreover, these polytypic structures provide an additional hardening mechanism by forming nanoscale interlocks that may strongly hinder the interlayer sliding movements, which promises to open a new avenue towards designing novel superhard nanocomposite materials by exploiting the coexistence of various polytypes. PMID:26660270

  12. Effect of natural organic materials on cadmium and neptunium sorption

    SciTech Connect

    Kung, K.S.; Triay, I.R.

    1994-10-01

    In a batch sorption study of the effect of naturally occurring organic materials on the sorption of cadmium and neptunium on oxides and tuff surfaces, the model sorbents were synthetic goethite, boehmite, amorphous silicon oxides, and a crushed tuff material from Yucca Mountain, Nevada. An amino acid, 3-(3,4-dihydroxypheny)-DL-alanine (DOPA), and an aquatic-originated fulvic material, Nordic aquatic fulvic acid (NAFA), were used as model organic chemicals. Sorption isotherm results showed that DOPA sorption followed the order aluminum oxide > iron oxide > silicon oxide and that the amount of DOAP sorption for a given sorbent increased as the solution pH was raised. The sorption of cadmium and neptunium on the iron oxide was about ten times higher than that on the aluminum oxide. The sorption of cadmium and neptunium on natural tuff material was much lower than that on aluminum and iron oxides. The sorption of cadmium on iron and aluminum oxides was found to be influenced by the presence of DOPA, and increasing the amount of DOPA coating resulted in higher cadmium sorption on aluminum oxide. However, for iron oxide, cadmium sorption decreased with increasing DOPA concentration. The presence of the model organic materials DOPA and NAFA did not affect the sorption of neptunium on tuff material or on the iron and aluminum oxides. Spectroscopic results indicate that cadmium complexes strongly with DOPA. Therefore, the effect of the organic material, DOPA, on the cadmium sorption is readily observed. However, neptunium is possibly complexed weakly with organic material. Thus, DOPA and NAFA have little effect on neptunium sorption on all sorbents selected for study.

  13. Neptunium redox speciation at the illite surface

    NASA Astrophysics Data System (ADS)

    Marsac, Rémi; Banik, Nidhu lal; Lützenkirchen, Johannes; Marquardt, Christian Michael; Dardenne, Kathy; Schild, Dieter; Rothe, Joerg; Diascorn, Alexandre; Kupcik, Tomas; Schäfer, Thorsten; Geckeis, Horst

    2015-03-01

    Neptunium (Np(V)) sorption onto a purified illite is investigated as a function of pH (3-10) and [NpVO2+]tot(3 × 10-8-3 × 10-4 M) in 0.1 M NaCl under Ar atmosphere. After about one week reaction time, only insignificant variation of Np sorption is observed and the establishment of reaction equilibrium can be assumed. Surprisingly, solid-liquid distribution ratios (Rd) are clearly higher than those measured for Np(V) sorption onto illite under aerobic conditions. The observation that Rd increases with decreasing pe (pe = -log ae-) suggests partial reduction to Np(IV), although measured redox potentials (pe values) at a first glance suggest the predominance of Np(V). Reduction to Np(IV) at the illite surface could indeed be confirmed by X-ray absorption near-edge spectroscopy (XANES). Np speciation in presence of the purified Na-illite under given conditions is consistently described by applying the 2 sites protolysis non-electrostatic surface complexation and cation exchange model. Measured pe data are taken to calculate Np redox state and surface complexation constants for Np(IV) are derived by applying a data fitting procedure. Constants are very consistent with results obtained by applying an existing linear free energy relationship (LFER). Taking Np(IV) surface complexation constants into account shifts the calculated Np(V)/Np(IV) redox borderline in presence of illite surfaces by 3-5 pe units (0.2-0.3 V) towards redox neutral conditions. Our study suggests that Np(V) reduction in presence of a sorbing mineral phase is thermodynamically favored.

  14. The Electronic Properties of Metal Borides and Borocarbides: Differences and Similarities

    NASA Astrophysics Data System (ADS)

    Lassoued, Souheila; Gautier, Régis; Halet, Jean-François

    The bonding and structural arrangement in a few representative ring- or chain-containing solid-state metal borides and boride carbides are analyzed with respect to the electron count of the non-metal entities. Similarities and differences between them are emphasized. More specifically, the bonding in some layered ternary borides of RETB4 formula (RE = rare-earth metal and T = transition metal) is first analyzed and compared to that of the metal boride carbide ScB2C2, which contains a similar non-metal arrangement. Oxidation states are proposed for the boron or boron-carbon networks encountered in these compounds. It seems that they are electron-richer than graphite-like boron networks. In a second part, the bonding in linear boron and boron-carbon chains encapsulated in channels of LiB or RE xByCz is discussed and compared. Cumulenic bond character is favored in these chains.

  15. Sasse Modeling of First Cycle Neptunium (VI) Recovery Flowsheet

    SciTech Connect

    Laurinat, J. E.

    2006-04-01

    A flowsheet has been proposed to separate neptunium from solutions in H-Canyon Tanks 16.4, 12.5, and 11.7 in the First Cycle solvent extraction banks, in which cerium(IV) (Ce(IV)) serves as an agent to oxidize neptunium to neptunium(VI) (Np(VI)). A SASSE (Spreadsheet Algorithm for Stagewise Solvent Extraction) spreadsheet model indicates that the proposed flowsheet is a feasible method for separating neptunium and uranium from sulfates, thorium, and other metal impurities. The proposed flowsheet calls for stripping the sulfates, thorium, and other metal impurities into the 1AW stream and extracting and then stripping the neptunium and uranium into the 1BP stream. SASSE predicts that separation of thorium from the other actinides can be accomplished with actinide losses of 0.01% or less. It is assumed that other metal impurities such as iron, aluminum, and fission products will follow the thorium into 1AW. Due to an organic/aqueous distribution coefficient that is close to one, SASSE predicts that plutonium(VI) (Pu(VI)) is split between the A Bank and B Bank aqueous output streams, with 27% going to 1AW and 73% going to 1BP. An extrapolated distribution coefficient based on unvalidated Ce(IV) distribution measurements at a single nitrate concentration and a comparison with thorium(IV) (Th(IV)) distributions indicates that Ce(IV) could reflux in 1B Bank. If the Ce(IV) distribution coefficient is lower than would be predicted by this single point extrapolation, but still higher than the distribution coefficient for Th(IV), then Ce(IV) would follow Np(VI) and uranium(VI) (U(VI)) into 1BP. The SASSE model was validated using data from a 1964 oxidizing flowsheet for the recovery of Np(VI) in Second Cycle. For the proposed flowsheet to be effective in recovering neptunium, the addition of approximately 0.025 M ceric ammonium nitrate (Ce(NH4)2(NO3)6) to both the 1AF and 1AS streams is required to stabilize the neptunium in the +6

  16. An alternative method of gas boriding applied to the formation of borocarburized layer

    SciTech Connect

    Kulka, M. Makuch, N.; Pertek, A.; Piasecki, A.

    2012-10-15

    The borocarburized layers were produced by tandem diffusion processes: carburizing followed by boriding. An alternative method of gas boriding was proposed. Two-stage gas boronizing in N{sub 2}-H{sub 2}-BCl{sub 3} atmosphere was applied to the formation of iron borides on a carburized substrate. This process consisted in two stages, which were alternately repeated: saturation by boron and diffusion annealing. The microstructure and microhardness of produced layer were compared to those-obtained in case of continuous gas boriding in H{sub 2}-BCl{sub 3} atmosphere, earlier used. The first objective of two-stage boronizing, consisting in acceleration of boron diffusion, has been efficiently implemented. Despite the lower temperature and shorter duration of boronizing, about 1.5 times larger iron borides' zone has been formed on carburized steel. Second objective, the absolute elimination of brittle FeB phase, has failed. However, the amount of FeB phase has been considerably limited. Longer diffusion annealing should provide the boride layer with single-phase microstructure, without FeB phase. - Highlights: Black-Right-Pointing-Pointer Alternative method of gas boriding in H{sub 2}-N{sub 2}-BCl{sub 3} atmosphere was proposed. Black-Right-Pointing-Pointer The process consisted in two stages: saturation by boron and diffusion annealing. Black-Right-Pointing-Pointer These stages of short duration were alternately repeated. Black-Right-Pointing-Pointer The acceleration of boron diffusion was efficiently implemented. Black-Right-Pointing-Pointer The amount of FeB phase in the boride zone was limited.

  17. Nanosized Borides and Carbides for Electroplating. Metal-Matrix Coatings: Specifications, Performance Evaluation

    NASA Astrophysics Data System (ADS)

    Galevskiy, G. V.; Rudneva, V. V.; Galevskiy, S. G.; Il’yashchenko, D. P.; Kartsev, D. S.

    2016-04-01

    This paper summarizes experience of application of nano-sized carbides and borides of titanium and chromium, silicon carbide as components of electro-depositable coating compositions based on nickel, zinc, and chromium. Basic physical and mechanical properties of the coatings are determined. Technological and economic evaluation is completed; practicability of high-cost nano-diamonds substitution for nano-sized borides and carbides is justified.

  18. Plasma boriding of a cobalt-chromium alloy as an interlayer for nanostructured diamond growth

    NASA Astrophysics Data System (ADS)

    Johnston, Jamin M.; Jubinsky, Matthew; Catledge, Shane A.

    2015-02-01

    Chemical vapor deposited (CVD) diamond coatings can potentially improve the wear resistance of cobalt-chromium medical implant surfaces, but the high cobalt content in these alloys acts as a catalyst to form graphitic carbon. Boriding by high temperature liquid baths and powder packing has been shown to improve CVD diamond compatibility with cobalt alloys. We use the microwave plasma-enhanced (PE) CVD process to deposit interlayers composed primarily of the borides of cobalt and chromium. The use of diborane (B2H6) in the plasma feedgas allows for the formation of a robust boride interlayer for suppressing graphitic carbon during subsequent CVD of nano-structured diamond (NSD). This metal-boride interlayer is shown to be an effective diffusion barrier against elemental cobalt for improving nucleation and adhesion of NSD coatings on a CoCrMo alloy. Migration of elemental cobalt to the surface of the interlayer is significantly reduced and undetectable on the surface of the subsequently-grown NSD coating. The effects of PECVD boriding are compared for a range of substrate temperatures and deposition times and are evaluated using glancing-angle X-ray diffraction (XRD), cross-sectional scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and micro-Raman spectroscopy. Boriding of CoCrMo results in adhered nanostructured diamond coatings with low surface roughness.

  19. Precipitation of neptunium dioxide from aqueous solution

    SciTech Connect

    Roberts, K E

    1999-12-01

    Tens of thousands of metric tons of highly radioactive, nuclear waste have been generated in the US. Currently, there is no treatment or disposal facility for these wastes. Of the radioactive elements in high-level nuclear waste, neptunium (Np) is of particular concern because it has a long half-life and may potentially be very mobile in groundwaters associated with a proposed underground disposal site at Yucca Mountain, Nevada. Aqueous Np concentrations observed in previous, short-term solubility experiments led to calculated potential doses exceeding proposed long-term regulatory limits. However, thermodynamic data for Np at 25 C showed that these observed aqueous Np concentrations were supersaturated with respect to crystalline NpO{sub 2}. It was hypothesized that NpO{sub 2} is the thermodynamically stable solid phase in aqueous solution, but it is slow to form in an aqueous solution of NpO{sub 2}{sup +} on the time scale of previous experiments. The precipitation of NpO{sub 2} would provide significantly lower aqueous Np concentrations leading to calculated doses below proposed regulatory limits. To test this hypothesis, solubility experiments were performed at elevated temperature to accelerate any slow precipitation kinetics. Ionic NpO{sub 2}{sup +} (aq) was introduced into very dilute aqueous solutions of NaCl with initial pH values ranging from 6 to 10. The reaction vessels were placed in an oven and allowed to react at 200 C until steady-state aqueous Np concentrations were observed. In all cases, aqueous Np concentrations decreased significantly from the initial value of 10{sup {minus}4} M. The solids that formed were analyzed by x-ray powder diffraction, x-ray absorption spectroscopy, and scanning electron microscopy. The solids were determined to be high-purity crystals of NpO{sub 2}. This is the first time that crystalline NpO{sub 2} has been observed to precipitate from NpO{sub 2}{sup +}(aq) in near-neutral aqueous solutions. The results obtained

  20. Neptunium (VI) and neptunium (VI/V) mixed valence cluster compounds

    SciTech Connect

    May, Iain

    2008-01-01

    Neptunium has three readily accessible oxidation states, IV, V and VI, which can coexist under certain conditions, with the aqueous soluble neptunyl(V) moiety, {l_brace}NpO{sub 2}{r_brace}{sup +}, of most environmental relevance. Careful control of Np chemistry is required during actinide separation processes. In addition, the long half life of the major alpha emitting isotope ({sup 237}Np, t{sub 1/2} = 2.144 x 10{sup 6} years) renders Np a major contributor to the radiotoxicity of nuclear waste as a function of time. Significant quantities of neptunium are generated in nuclear reactors and the current surge in interest in nuclear power will lead to an increase in our need to further understand the chemistry of this element. It is clearly of importance that Np chemistry is well understood and there have been several recent investigations into the structural, spectroscopic and magnetic properties of Np compounds. However, the vast majority of this chemistry has been performed in aqueous solution, prohibiting the use of air and moisture sensitive ligands. This is in stark contrast to uranium and thorium where inert atmosphere chemistry with moisture sensitive donor ligands has flourished, yielding greater insight into the structural and electronic properties of these early actinides. For the uranyl(VI) moiety, {l_brace}UO{sub 2}{r_brace}{sup 2+}, UO{sub 2}Cl{sub 2}(thf){sub 3} (and the desolvated dimer [UO{sub 2}Cl{sub 2}(thf)]{sub 2}) have proven to be excellent moisture-free reagents for inert atmosphere uranyl chemistry. These starting reagents have been used extensively within our group to study soft donor ligand coordination in the uranyl equatorial plane and oxo-activation to Lewis acid coordination. However, until now the absence of such a starting reagent for Np has limited our ability to extend this chemistry any further across the actinide series, which is required if we are to gain a more complete understanding of 5f element chemistry. The synthesis of [Np

  1. Neptunium and plutonium complexes with a sterically encumbered triamidoamine (TREN) scaffold

    DOE PAGESBeta

    Brown, Jessie L.; Gaunt, Andrew J.; King, David M.; Liddle, Stephen T.; Reilly, Sean D.; Scott, Brian L.; Wooles, Ashley J.

    2016-03-11

    Here, the syntheses and characterization of isostructural neptunium(IV) and plutonium(IV) complexes [MIV(TRENTIPS)(Cl)] [An = Np, Pu; TRENTIPS = {N(CH2CH2NSiPri3)3}3] are reported, along with the demonstration that they are likely reduced to the corresponding neptunium(III) and plutonium(III) products [MIII(TRENTIPS)]; this chemistry provides new platforms from which to target a plethora of unprecedented molecular functionalities in transuranic chemistry and the neptunium(IV) molecule is the first structurally characterized neptunium(IV)–amide complex.

  2. Neptunium and plutonium complexes with a sterically encumbered triamidoamine (TREN) scaffold.

    PubMed

    Brown, Jessie L; Gaunt, Andrew J; King, David M; Liddle, Stephen T; Reilly, Sean D; Scott, Brian L; Wooles, Ashley J

    2016-04-01

    The syntheses and characterisation of isostructural neptunium(iv) and plutonium(iv) complexes [An(IV)(TREN(TIPS))(Cl)] [An = Np, Pu; TREN(TIPS) = {N(CH2CH2NSiPr(i)3)3}(3-)] are reported, along with the demonstration that they are likely reduced to the corresponding neptunium(iii) and plutonium(iii) products [An(III)(TREN(TIPS))]; this chemistry provides new platforms from which to target a plethora of unprecedented molecular functionalities in transuranic chemistry and the neptunium(iv) molecule is the first structurally characterised neptunium(iv)-amide complex. PMID:27009799

  3. Speciation-dependent toxicity of neptunium(V) toward chelatobacter heintzii.

    SciTech Connect

    Banaszak, J. E.; Reed, D. T.; Rittmann, B. E.; Chemical Engineering; Northwestern Univ.

    1998-04-15

    This work investigates how chemical speciation controls the toxicity of neptunium and the neptunium-NTA complex toward Chelatobacter heintzii. We studied the effect of aquo and complexed/precipitated neptunium on the growth of C. heintzii in noncomplexing glucose and phosphate-buffered nitrilotriacetic acid (NTA) growth media. Equilibrium chemical speciation modeling and absorption spectroscopy were used to link neptunium speciation to biological growth inhibition. Our results show that metal toxicity of aquo NpO{sub 2}{sup +} significantly limits the growth of C. heintzii at free metal ion concentrations greater than {approx}10{sup -5} M. However, neptunium concentrations {ge}10{sup -4} M do not cause measurable radiotoxicity effects in C. heintzii when present in the form of a neptunium-NTA complex or colloidal/precipitated neptunium phosphate. The neptunium-NTA complex, which is stable under aerobic conditions, is destabilized by microbial degradation of NTA. When phosphate was present, degradation of NTA led to the precipitation of a neptunium-phosphate phase.

  4. Possible Incorporation of Neptunium in Uranyl (VI) Alteration Phases

    SciTech Connect

    Buck, Edgar C.; McNamara, Bruce K.; Douglas, Matthew; Hanson, Brady D.

    2003-11-25

    This study examines existing data on Np behavior from both spent fuel and borosilicate glass tests in effort to resolve issues concerning the selection of possible solubility limiting phases for neptunium and the methods for detecting neptunium at low levels in spent fuel. These issues were raised in a recent report by Finch and Fortner (2002) that argues that the Np analysis with Electron Energy-Loss Spectroscopy (EELS) reported by Buck et al., (1998) is incorrect and that based on a series of experiments with Np-doped U3O8, NpO2 should be adopted as the solubility controlling phase for Np, in the Yucca Mountain performance assessment model. In this report, we will refute the claim that EELS is unable to detect Np and will suggest that the use of NpO2 as the Np solubility controlling phase is not supported by available scientific data from both spent fuel and borosilicate glass.

  5. Extraction of Uranium, Neptunium and Plutonium from Caustic Media

    SciTech Connect

    Delmau, Laetitia H.; Bonnesen, Peter V.; Engle, Nancy L.; Raymond, Kenneth N.; Xu, Jade

    2004-03-28

    5 Fundamental research on uranium, neptunium and plutonium separation from alkaline media using solvent extraction is being conducted. Specific extractants for these actinides from alkaline media have been synthesized to investigate the feasibility of selective removal of these elements. Two families of extractants have been studied: terephthalamide and tetra(hydroxybenzyl)ethylene diamine derivatives. Fundamental studies were conducted to characterize their extraction behavior from a wide variety of aqueous conditions. The terephthalamide derivatives exhibit a significant extraction strength along with a discriminatory behavior among the actinides, plutonium being extracted the most strongly. Quantitative extraction of plutonium and moderate extraction of neptunium and uranium was achieved from a simple caustic solution. Interestingly, strontium is also quantitatively extracted by these derivatives. However, their stability to highly caustic solutions still needs to be imp roved. Tetra(hydroxybenzyl)ethylene diamine derivatives exhibit a very good stability to caustic conditions and are currently being studied.

  6. Plutonium, americium, and neptunium speciation in selected groundwaters

    USGS Publications Warehouse

    Cleveland, J.M.; Rees, T.F.; Nash, K.L.

    1985-01-01

    Speciation was determined at 25 and 90 degree C in four groundwaters from diverse sources: the Sparta aquifer in Louisiana, near the Vacherie salt dome; Mansfield No. 2 well in the Palo Duro Basin, Texas; the Stripa mine in Sweden; and the Waste Isolation Pilot Plant in New Mexico. Neptunium generally was soluble in all waters and was present exclusively as Np(V) and Np(VI), regardless of initial oxidation state. The results indicated that plutonium and neptunium solubilities were determined by the oxidation-reduction properties of the waters, i. e. , their abilities to convert these elements to soluble oxidation states. This was not the case for americium, however; Am(IV) was not detected, and the solubility of this element was determined entirely by the chemical properties of Am(III).

  7. Syntheses of neptunium trichloride and measurements of its melting temperature

    NASA Astrophysics Data System (ADS)

    Hayashi, Hirokazu; Takano, Masahide; Kurata, Masaki; Minato, Kazuo

    2013-09-01

    Neptunium trichloride (NpCl3) of high purity was synthesized by the solid state reaction of neptunium nitride with cadmium chloride. Lattice parameters of hexagonal NpCl3 were determined from the powder X-ray diffraction pattern to be a = 0.7428 ± 0.0001 nm and c = 0.4262 ± 0.0003 nm, which fairly agree with the reported values. The melting temperature of NpCl3 was measured on a sample of about 1 mg, hermetically encapsulated in a gold crucible with a differential thermal analyzer. The value determined was 1070 ± 3 K which is close to the recommended value (1075 ± 30 K) derived from the mean value of the melting temperature of UCl3 and of PuCl3.

  8. RAPID MEASUREMENTS OF NEPTUNIUM OXIDATION STATES USING CHROMATOGRAPHIC RESINS

    SciTech Connect

    Diprete, D; C Diprete, C; Mira Malek, M; Eddie Kyser, E

    2009-03-24

    The Savannah River Site's (SRS) H-Canyon facility uses ceric ammonium nitrate (CAN) to separate impure neptunium (Np) from a high sulfate feed stream. The material is processed using a two-pass solvent extraction purification which relies on CAN to oxidize neptunium to Np(VI) during the first pass prior to extraction. Spectrophotometric oxidation-state analyses normally used to validate successful oxidation to Np(VI) prior to extraction were compromised by this feed stream matrix. Therefore, a rapid chromatographic method to validate successful Np oxidation was developed using Eichrom Industries TRU and TEVA{reg_sign} resins. The method was validated and subsequently transferred to existing operations in the process analytical laboratories.

  9. SEPARATION OF NEPTUNIUM FROM PLUTONIUM BY CHLORINATION AND SUBLIMATION

    DOEpatents

    Fried, S.M.

    1958-11-18

    A process is described for separating neptunium from plutonium. The method consists in chlorinating a mixture of the oxides of Np and Pu by contacting the mixture with carbon tetrachloride at about 500 icient laborato C. ln this manner the Np is converted to the tetrachlorlde and the Pu converted to the trichloride. Since NpCl/sub 4/ is more latile than PuCl/sub 3/, the separation ls effected by vaporing sad subsequently condenslng the NpCl/sub 4/.

  10. Uranium and Neptunium Desorption from Yucca Mountain Alluvium

    SciTech Connect

    C.D. Scism; P.W. Reimus; M. Ding; S.J. Chipera

    2006-03-16

    Uranium and neptunium were used as reactive tracers in long-term laboratory desorption studies using saturated alluvium collected from south of Yucca Mountain, Nevada. The objective of these long-term experiments is to make detailed observations of the desorption behavior of uranium and neptunium to provide Yucca Mountain with technical bases for a more realistic and potentially less conservative approach to predicting the transport of adsorbing radionuclides in the saturated alluvium. This paper describes several long-term desorption experiments using a flow-through experimental method and groundwater and alluvium obtained from boreholes along a potential groundwater flow path from the proposed repository site. In the long term desorption experiments, the percentages of uranium and neptunium sorbed as a function of time after different durations of sorption was determined. In addition, the desorbed activity as a function of time was fit using a multi-site, multi-rate model to demonstrate that different desorption rate constants ranging over several orders of magnitude exist for the desorption of uranium from Yucca Mountain saturated alluvium. This information will be used to support the development of a conceptual model that ultimately results in effective K{sub d} values much larger than those currently in use for predicting radionuclide transport at Yucca Mountain.

  11. XAS and TRLIF spectroscopy of uranium and neptunium in seawater.

    PubMed

    Maloubier, Melody; Solari, Pier Lorenzo; Moisy, Philippe; Monfort, Marguerite; Den Auwer, Christophe; Moulin, Christophe

    2015-03-28

    Seawater contains radionuclides at environmental levels; some are naturally present and others come from anthropogenic nuclear activity. In this report, the molecular speciation in seawater of uranium(VI) and neptunium(V) at a concentration of 5 × 10(-5) M has been investigated for the first time using a combination of two spectroscopic techniques: Time-resolved laser-induced fluorescence (TRLIF) for U and extended X-ray absorption fine structure (EXAFS) for U and Np at the LIII edge. In parallel, the theoretical speciation of uranium and neptunium in seawater at the same concentration is also discussed and compared to spectroscopic data. The uranium complex was identified as the neutral carbonato calcic complex UO2(CO3)3Ca2, which has been previously described in other natural systems. In the case of neptunium, the complex identified is mainly a carbonato complex whose exact stoichiometry is more difficult to assess. The knowledge of the actinide molecular speciation and reactivity in seawater is of fundamental interest in the particular case of uranium recovery and more generally regarding the actinide life cycle within the biosphere in the case of accidental release. This is the first report of actinide direct speciation in seawater medium that can complement inventory data. PMID:25689216

  12. The Growth Behavior of Titanium Boride Layers in α and β Phase Fields of Titanium

    NASA Astrophysics Data System (ADS)

    Lv, Xiaojun; Hu, Lingyun; Shuang, Yajing; Liu, Jianhua; Lai, Yanqing; Jiang, Liangxing; Li, Jie

    2016-07-01

    In this study, the commercially pure titanium was successfully electrochemical borided in a borax-based electrolyte. The process was carried out at a constant cathodic current density of 300 mA cm-2 and at temperatures of 1123 K and 1223 K (850 °C and 950 °C) for 0.5, 1, 2, 3, and 5 hours. The growth behavior of titanium boride layers in the α phase field of titanium was compared with that in the β phase field. After boriding, the presence of both the TiB2 top layer and TiB whisker sub-layer was confirmed by the X-ray diffraction (XRD) and scanning electron microscope. The relationship between the thickness of boride layers and boriding time was found to have a parabolic character in both α and β phase fields of titanium. The TiB whiskers showed ultra-fast growth rate in the β phase field. Its growth rate constant was found to be as high as 3.2002 × 10-13 m2 s-1. Besides, the chemical resistance of the TiB2 layer on the surface of titanium substrate was characterized by immersion tests in molten aluminum.

  13. Metal boride catalysts for indirect liquefaction. Quarterly technical progress report, December 1, 1983-February 29, 1984

    SciTech Connect

    Bartholomew, C.H.

    1984-04-12

    During the sixth quarter four boron-promoted cobalt catalysts were prepared by a new boriding process using diborane gas as the boriding agent. These catalysts were characterized by chemical analysis, BET, H/sub 2/ chemisorption, and x-ray diffraction. Temperature-programmed desorption spectra of H/sub 2/ were obtained for a sodium-promoted cobalt boride and a sodium-promoted Co/SiO/sub 2/. Four cobalt catalysts (unsupported, boron-promoted, sodium-promoted, and doubly-promoted) were tested for CO hydrogenation activity and selectivity at 1 atm and 3 to 4 temperatures in the range of 190 to 240/sup 0/C. About 10% of the surface of cobalt boride consists of reduced metallic cobalt. The addition of sodium to cobalt increases its binding energy with H/sub 2/ and its activation energy for H/sub 2/ adsorption. Boron does not affect the activity of cobalt; sodium decreases it by a factor of 10. Cobalt boride produces lighter hydrocarbon products relative to cobalt; sodium-promoted cobalt produces heavier products, more alcohols, and more CO/sub 2/. 29 references, 10 figures, 4 tables.

  14. The Growth Behavior of Titanium Boride Layers in α and β Phase Fields of Titanium

    NASA Astrophysics Data System (ADS)

    Lv, Xiaojun; Hu, Lingyun; Shuang, Yajing; Liu, Jianhua; Lai, Yanqing; Jiang, Liangxing; Li, Jie

    2016-04-01

    In this study, the commercially pure titanium was successfully electrochemical borided in a borax-based electrolyte. The process was carried out at a constant cathodic current density of 300 mA cm-2 and at temperatures of 1123 K and 1223 K (850 °C and 950 °C) for 0.5, 1, 2, 3, and 5 hours. The growth behavior of titanium boride layers in the α phase field of titanium was compared with that in the β phase field. After boriding, the presence of both the TiB2 top layer and TiB whisker sub-layer was confirmed by the X-ray diffraction (XRD) and scanning electron microscope. The relationship between the thickness of boride layers and boriding time was found to have a parabolic character in both α and β phase fields of titanium. The TiB whiskers showed ultra-fast growth rate in the β phase field. Its growth rate constant was found to be as high as 3.2002 × 10-13 m2 s-1. Besides, the chemical resistance of the TiB2 layer on the surface of titanium substrate was characterized by immersion tests in molten aluminum.

  15. Kinetics of borided 31CrMoV9 and 34CrAlNi7 steels

    SciTech Connect

    Efe, Goezde Celebi; Ipek, Mediha; Ozbek, Ibrahim; Bindal, Cuma

    2008-01-15

    In this study, kinetics of borides formed on the surface of 31CrMoV9 and 34CrAlNi7 steels borided in solid medium consisting of Ekabor II at 850-900-950 deg. C for 2, 4, 6 and 8 h were investigated. Scanning electron microscopy and optical microscopy examinations showed that borides formed on the surface of borided steels have columnar morphology. The borides formed in the coating layer confirmed by X-ray diffraction analysis are FeB, Fe{sub 2}B, CrB, and Cr{sub 2}B. The hardnesses of boride layers are much higher than that of matrix. It was found that depending on process temperature and time the fracture toughness of boride layers ranged from 3.93 to 4.48 MPa m{sup 1/2} for 31CrMoV9 and from 3.87 to 4.40 MPa m{sup 1/2} for 34CrAlNi7 steel. Activation energy, growth rate and growth acceleration of boride layer calculated according to these kinetic studies revealed that lower activation energy results in the fast growth rate and high growth acceleration.

  16. Neptunium multipoles and resonant x-ray Bragg diffraction by neptunium dioxide (NpO2)

    NASA Astrophysics Data System (ADS)

    Lovesey, S. W.; Detlefs, C.; Rodríguez-Fernández, A.

    2012-06-01

    The low-temperature ordered state of neptunium dioxide (NpO2) remains enigmatic. After decades of experimental and theoretical efforts, long-range order of a time-odd (magnetic) high-order atomic multipole moment is now generally considered to be the fundamental order parameter, the most likely candidate being a magnetic triakontadipole (rank 5). To date, however, direct experimental observation of the primary order parameter remains outstanding. In the light of new experimental findings, we re-examine the effect of crystal symmetry on the atomic multipoles and the resulting x-ray resonant scattering signature. Our simulations use the crystallographic point group \\bar {3}m (D3d), because corresponding magnetic groups \\bar {3}{m}^{\\prime}, {\\bar {3}}^{\\prime}{m}^{\\prime} and {\\bar {3}}^{\\prime}m are shown by us to be at odds with a wealth of experimental results. In addition to the previously observed (secondary) quadrupole order, we derive expressions for higher-order multipoles that might be observed in future experiments. In particular, magnetic octupole moments are predicted to contribute to Np M2,3 and L2,3 resonant scattering via E2-E2 events. The Lorentzian-squared lineshape observed at the M4 resonance is shown to be the result of the anisotropy of the 3p3/2 core levels. Quantitative comparison of our calculations to the measured data yields a core-hole width Γ = 2.60(7) eV and a core-state exchange energy \\vert \\varepsilon (\\frac{1}{2})\\vert =0.7 6(2) eV.

  17. Neptunium multipoles and resonant x-ray Bragg diffraction by neptunium dioxide (NpO2).

    PubMed

    Lovesey, S W; Detlefs, C; Rodríguez-Fernández, A

    2012-06-27

    The low-temperature ordered state of neptunium dioxide (NpO(2)) remains enigmatic. After decades of experimental and theoretical efforts, long-range order of a time-odd (magnetic) high-order atomic multipole moment is now generally considered to be the fundamental order parameter, the most likely candidate being a magnetic triakontadipole (rank 5). To date, however, direct experimental observation of the primary order parameter remains outstanding. In the light of new experimental findings, we re-examine the effect of crystal symmetry on the atomic multipoles and the resulting x-ray resonant scattering signature. Our simulations use the crystallographic point group ̅3m (D(3d)), because corresponding magnetic groups ̅3m', ̅3'm', and ̅3'm are shown by us to be at odds with a wealth of experimental results. In addition to the previously observed (secondary) quadrupole order, we derive expressions for higher-order multipoles that might be observed in future experiments. In particular, magnetic octupole moments are predicted to contribute to Np M(2,3) and L(2,3) resonant scattering via E2–E2 events. The Lorentzian-squared lineshape observed at the M(4) resonance is shown to be the result of the anisotropy of the 3p(3/2) core levels. Quantitative comparison of our calculations to the measured data yields a core–hole width Γ = 2.60(7) eV and a core-state exchange energy [absolute value]ε(1/2)[absolute value] = 0.76(2) eV. PMID:22652978

  18. Re-evaluating neptunium in uranyl phases derived from corroded spent fuel.

    SciTech Connect

    Fortner, J. A.; Finch, R. J.; Kropf, A. J.; Cunnane, J. C.; Chemical Engineering

    2004-11-01

    Interest in mechanisms that may control radioelement release from corroded commercial spent nuclear fuel (CSNF) has been heightened by the selection of the Yucca Mountain site in Nevada as the repository for high-level nuclear waste in the United States. Neptunium is an important radionuclide in repository models owing to its relatively long half-life and its high aqueous mobility as neptunyl [Np(V)O+2]. The possibility of neptunium sequestration into uranyl alteration phases produced by corroding CSNF would suggest-a process for lowering neptunium concentration and subsequent migration from a geologic repository. However, there remains little experimental evidence that uranyl compounds will, in fact, serve as long-term host phases for the retention of neptunium under conditions expected in a deep geologic repository. To directly explore this possibility, we examined specimens of uranyl alteration phases derived from humid-air-corroded CSNF by X-ray absorption spectroscopy to better determine neptunium uptake in these phases. Although neptunium fluorescence was readily observed from as-received CSNF, it was not observed from the uranyl alteration rind. We establish upper limits for neptunium incorporation into CSNF alteration phases that are significantly below previously reported concentrations obtained by using electron energy loss spectroscopy (EELS). We attribute the discrepancy to a plural-scattering event that creates a spurious EELS peak at the neptunium-MV energy.

  19. Re-Evaluating Neptunium in Uranyl Phases Derived from Corroded Spent Fuel

    SciTech Connect

    Fortner, Jeffrey A.; Finch, Robert J.; Kropf, A. Jeremy; Cunnane, James C.

    2004-11-15

    Interest in mechanisms that may control radioelement release from corroded commercial spent nuclear fuel (CSNF) has been heightened by the selection of the Yucca Mountain site in Nevada as the repository for high-level nuclear waste in the United States. Neptunium is an important radionuclide in repository models owing to its relatively long half-life and its high aqueous mobility as neptunyl [Np(V)O{sub 2}{sup +}]. The possibility of neptunium sequestration into uranyl alteration phases produced by corroding CSNF would suggest a process for lowering neptunium concentration and subsequent migration from a geologic repository. However, there remains little experimental evidence that uranyl compounds will, in fact, serve as long-term host phases for the retention of neptunium under conditions expected in a deep geologic repository. To directly explore this possibility, we examined specimens of uranyl alteration phases derived from humid-air-corroded CSNF by X-ray absorption spectroscopy to better determine neptunium uptake in these phases. Although neptunium fluorescence was readily observed from as-received CSNF, it was not observed from the uranyl alteration rind. We establish upper limits for neptunium incorporation into CSNF alteration phases that are significantly below previously reported concentrations obtained by using electron energy loss spectroscopy (EELS). We attribute the discrepancy to a plural-scattering event that creates a spurious EELS peak at the neptunium-M{sub V} energy.

  20. Evaluation of the Effects of Tank 50H Solids on Dissolved Uranium, Plutonium and Neptunium

    SciTech Connect

    Oji, L.N.

    2003-12-02

    The study of the effects of contacting a simulated salt solution spiked with uranium, plutonium, and neptunium with Tank 50H solids. General findings include: There is no evidence for interaction between Tank 50H solids and uranium from the spiked salt solution. Lack of uranium removal may reflect prior removal of uranium. There is evidence for interaction between Tank 50H solids with plutonium and neptunium as evidenced by loss of these two actinides from the salt solution. The amount of plutonium and neptunium lost from solution increased with an increase in the quantity of Tank 50H solids for a fixed simulant volume. The removal of plutonium and neptunium fit typical sorption isotherms allowing development of loading curves for estimating maximum solids loading. The maximum loading capacities for plutonium and neptunium in the simulants are, respectively, 2.01 and 4.48 micrograms per gram of Tank 50H solids. The oxalate in the Tank 50H solids is not directly responsible for the loss of plutonium and neptunium from the salt solution. The removal of plutonium and neptunium may be attributed to other minor components of the Tank 50H solids. We recommend additional testing to identify the component responsible for the plutonium and neptunium removal.

  1. Neptunium and americium speciation in selected basalt, granite, shale, and tuff ground waters

    USGS Publications Warehouse

    Cleveland, J.M.; Rees, T.F.; Nash, K.L.

    1983-01-01

    Neptunium and americium are relatively insoluble in ground waters containing high sulfate concentrations, particularly at 90??C. The insoluble neptunium species is Np(IV); hence reducing waters should enhance its formation. Americium can exist only in the trivalent state under these conditions, and its solubility also should be representative of that of curium.

  2. Nano-Disperse Borides and Carbides: Plasma Technology Production, Specific Properties, Economic Evaluation

    NASA Astrophysics Data System (ADS)

    Galevskii, G. V.; Rudneva, V. V.; Galevskii, S. G.; Tomas, K. I.; Zubkov, M. S.

    2016-04-01

    The experience of production and study on properties of nano-disperse chromium and titanium borides and carbides, and silicon carbide has been generalized. The structure and special service aspects of utilized plasma-metallurgical complex equipped with a three-jet direct-flow reactor with a capacity of 150 kW have been outlined. Processing, heat engineering and service life characteristics of the reactor are specified. The synthesis parameters of borides and carbides, as well as their basic characteristics in nano-disperse condition and their production flow diagram are outlined. Engineering and economic performance of synthesizing borides in laboratory and industrial conditions is assessed, and the respective segment of the international market as well. The work is performed at State Siberian Industrial University as a project part of the State Order of Ministry of Science and Education of the Russian Federation No. 11.1531/2014/K.

  3. Boride-based nano-laminates with MAX-phase-like behaviour

    SciTech Connect

    Telle, Rainer . E-mail: telle@ghi.rwth-aachen.de; Momozawa, Ai; Music, Denis; Schneider, Jochen M.

    2006-09-15

    MAX-phases being usually composed of transition metals, group A elements and carbon/nitrogen are considered interesting materials for many applications because of their tremendous bulk modulus, 'reversible' plasticity, and machinability. This is mainly due to their unique kind of bonding comprising covalent, ionic as well as metallic bonds providing 'easy' planes of rupture and deformability due to the layered crystal structures. In transition metal boride systems, similar types of bonding are available. In particular the W{sub 2}B{sub 5}-structure type and its stacking variations allow the synthesis of strongly layered crystal structures exhibiting unique delamination phenomena. The paper presents ab initio calculations showing the similarities of bonding between the ternary carbides and the corresponding ternary or quaternary borides. Formation of boride-based nano-laminates from auxiliary liquid phases, from the melt as well as during sintering and precipitation from supersaturated solid solutions will be discussed by means of SEM and TEM studies. The role of impurities weakening the interlayer bonding will be addressed in particular. The pronounced cleavage parallel to the basal plane gives rise for crack deflection and pull-out mechanisms if the laminates are dispersed in brittle matrices such as boron carbide, silicon carbide or other transition metal borides. - Graphical abstract: Some transition metal borides crystallise in a layered structure of alternating stacks of metal and boron atoms giving rise for strongly anisotropic properties. Their preferred cleavage parallel and the deformability perpendicular to the basal plan are similar to the peculiar mechanical behaviour recently described for MAX-phases. Ab initio calculations of the crystal structure prove the weak bonds between the layers for a variety of borides which can be used to reinforce ceramic materials on a nano-scale level.

  4. Surface hardening of steel by boriding in a cold rf plasma

    NASA Technical Reports Server (NTRS)

    Finberg, I.; Avni, R.; Grill, A.; Spalvins, T.; Buckley, D. H.

    1985-01-01

    Scanning electron spectroscopy, X-ray diffractometry, Auger electron spectroscopy, and microhardness measurements, are used to study the surfaces of 4340-steel samples that have been borided in a cold RF plasma which had been initiated in a gas mixture of 2.7 percent diborane in Ar. As a result of the dislocation of the diborane in the plasma, boron is deposited on the surface of the steel substrate and two crystalline phases, tetragonal Fe2B and orthorhombic FeB, are formed. The formation of boride phases then increases the surface microhardness from 2650 MPa to a maximum value of 7740 MPa.

  5. Chemical Speciation of Neptunium in Spent Fuel. 1st Progress Report

    SciTech Connect

    Czerwinski, Ken; Sherman, Christi; Reed, Don

    2000-03-02

    This project will examine the chemical speciation of neptunium in spent nuclear fuel. The R&D fields covered by the project include waste host materials and actinide chemistry. Examination of neptunium is chosen since it was identified as a radionuclide of concern by the NERI workshop. Additionally, information on the chemical form of neptunium in spent fuel is lacking. The identification of the neptunium species in spent fuel would allow a greater scientific based understanding of its long-term fate and behavior in waste forms. Research to establish the application and development of X-ray synchrotrons radiation (XSR) techniques to determine the structure of aqueous, adsorbed, and solid actinide species of importance to nuclear considerations is being conducted at Argonne. These studies extend current efforts within the Chemical Technology Division at Argonne National Laboratory to investigate actinide speciation with more conventional spectroscopic and solids characterization (e.g. SEM, TEM, and XRD) methods. Our project will utilize all these techniques for determining neptunium speciation in spent fuel. We intend to determine the chemical species and oxidation state of neptunium in spent fuel and alteration phases. Different types of spent fuel will be examined. Once characterized, the chemical behavior of the identified neptunium species will be evaluated if it is not present in the literature. Special attention will be given to the behavior of the neptunium species under typical repository near-field conditions (elevated temperature, high pH, varying Eh). This will permit a timely inclusion of project results into near-field geochemical models. Additionally, project results and methodologies have applications to neptunium in the environment, or treatment of neptunium containing waste.

  6. Radiochemistry of uranium, neptunium and plutonium: an updating

    SciTech Connect

    Roberts, R.A.; Choppin, G.R.; Wild, J.F.

    1986-02-01

    This report presents some procedures used in the radiochemical isolation, purification and/or analysis of uranium, neptunium, and plutonium. In this update of the procedures, we have not attempted to discuss the developments in the chemistry of U, Np, and Pu but have restricted the report to the newer procedures, most of which have resulted from the increased emphasis in environmental concern which requires analysis of extremely small amounts of the actinide element in quite complex matrices. The final section of this report describes several schemes for isolation of actinides by oxidation state.

  7. Metal-boride phase formation on tungsten carbide (WC-Co) during microwave plasma chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Johnston, Jamin M.; Catledge, Shane A.

    2016-02-01

    Strengthening of cemented tungsten carbide by boriding is used to improve the wear resistance and lifetime of carbide tools; however, many conventional boriding techniques render the bulk carbide too brittle for extreme conditions, such as hard rock drilling. This research explored the variation in metal-boride phase formation during the microwave plasma enhanced chemical vapor deposition process at surface temperatures from 700 to 1100 °C. We showed several well-adhered metal-boride surface layers consisting of WCoB, CoB and/or W2CoB2 with average hardness from 23 to 27 GPa and average elastic modulus of 600-730 GPa. The metal-boride interlayer was shown to be an effective diffusion barrier against elemental cobalt; migration of elemental cobalt to the surface of the interlayer was significantly reduced. A combination of glancing angle X-ray diffraction, electron dispersive spectroscopy, nanoindentation and scratch testing was used to evaluate the surface composition and material properties. An evaluation of the material properties shows that plasma enhanced chemical vapor deposited borides formed at substrate temperatures of 800 °C, 850 °C, 900 °C and 1000 °C strengthen the material by increasing the hardness and elastic modulus of cemented tungsten carbide. Additionally, these boride surface layers may offer potential for adhesion of ultra-hard carbon coatings.

  8. Surface hardening of St41 low carbon steel by using the hot-pressing powder-pack boriding method

    NASA Astrophysics Data System (ADS)

    Sutrisno, Soegijono, Bambang

    2014-03-01

    This research describes a powder-pack boriding process by using hot-pressing technic for St41 low carbon steel which will improve the hardness on the substrate by forming boride layer solid solution. Those method can reduce the operational cost of the research if it is compared by the conventional method with the asmospheric condition both vacuum system and gas inert condition. The concept of boriding by hot-pressing technic was verified in a laboratory scale. Welldefined and reusedable technic was achieved by using the stainless steel 304 as the container and sealed with a 5 ton pressure. This container was filled boronizing powder consisting of 5%B4C, 90%SiC, and 5%KBF4 to close the St41 low carbon steel specimen inside the container. The St41 boriding specimen was treated at the temperature of 900°C for 8 hours. The boride layer on the substrate was found as FeB and Fe2B phase with the hardness about 1800 HV. This value was more than ten times if compared with the untreated specimen that only had the hardness of 123 HV. Depend on heat treatment temperature, heat treatment time, and powder-pack boriding pressure, the depth of boride layer range from 127 to 165 μm, leading to a diffusion controlled process.

  9. Superabrasive boride and a method of preparing the same by mechanical alloying and hot pressing

    DOEpatents

    Cook, Bruce A.; Harringa, Joel L.; Russell, Alan M.

    2002-08-13

    A ceramic material which is an orthorhombic boride of the general formula: AlMgB.sub.14 :X, with X being a doping agent. The ceramic is a superabrasive, and in most instances provides a hardness of 40 GPa or greater.

  10. Ultra-Fast Boriding in High-Temperature Materials Processing Industries

    SciTech Connect

    2008-12-01

    This factsheet describes a research project whose main objective is to further develop, optimize, scale-up, and commercialize an ultra-fast boriding (also referred to as “boronizing”) process that can provide much higher energy efficiency, productivity, and near-zero emissions in many of the high-temperature materials processing industries.

  11. Structures and stability of novel transition-metal (M =Co ,Rh ,Co and Ir ) borides

    NASA Astrophysics Data System (ADS)

    Wang, Yachun; Wu, Lailei; Lin, Yangzheng; Hu, Qingyang; Li, Zhiping; Liu, Hanyu; Zhang, Yunkun; Gou, Huiyang; Yao, Yansun; Zhang, Jingwu; Gao, Faming; Mao, Ho-kwang

    2015-11-01

    Recent progress of high-pressure technology enables the synthesis of novel metal borides with diverse compositions and interesting properties. A precise characterization of these borides, however, is sometimes hindered by multiphase intergrowth and grain-size limitation in the synthesis process. Here, we theoretically explored new transition-metal borides (M =Co , Rh, and Ir) using a global structure searching method and discovered a series of stable compounds in this family. The predicted phases display a rich variety of stoichiometries and distinct boron networks resulting from the electron-deficient environments. Significantly, we identified a new Ir B1.25 structure as the long-sought structure of the first synthesized Ir-B compound. The simulated x-ray diffraction pattern of the proposed Ir B1.25 structure matches well with the experiment, and the convex hull calculation establishes its thermodynamic stability. Results of the present paper should advance the understanding of transition-metal borides and stimulate experimental explorations of these new and promising materials.

  12. Niobium boride layers deposition on the surface AISI D2 steel by a duplex treatment

    NASA Astrophysics Data System (ADS)

    Kon, O.; Pazarlioglu, S.; Sen, S.; Sen, U.

    2015-03-01

    In this paper, we investigated the possibility of deposition of niobium boride layers on the surface of AISI D2 steel by a duplex treatment. At the first step of duplex treatment, boronizing was performed on AISI D2 steel samples at 1000oC for 2h and then pre-boronized samples niobized at 850°C, 900°C and 950°C using thermo-reactive deposition method for 1-4 h. The presence of the niobium boride layers such as NbB, NbB2 and Nb3B4 and also iron boride phases such as FeB, Fe2B were examined by X-ray diffraction analysis. Scanning electron microscope (SEM) and micro-hardness measurements were realized. Experimental studies showed that the depth of the coating layers increased with increasing temperature and times and also ranged from 0.42 µm to 2.43 µm, depending on treatment time and temperature. The hardness of the niobium boride layer was 2620±180 HV0.005.

  13. Niobium boride layers deposition on the surface AISI D2 steel by a duplex treatment

    SciTech Connect

    Kon, O.; Pazarlioglu, S.

    2015-03-30

    In this paper, we investigated the possibility of deposition of niobium boride layers on the surface of AISI D2 steel by a duplex treatment. At the first step of duplex treatment, boronizing was performed on AISI D2 steel samples at 1000{sup o}C for 2h and then pre-boronized samples niobized at 850°C, 900°C and 950°C using thermo-reactive deposition method for 1–4 h. The presence of the niobium boride layers such as NbB, NbB{sub 2} and Nb{sub 3}B{sub 4} and also iron boride phases such as FeB, Fe{sub 2}B were examined by X-ray diffraction analysis. Scanning electron microscope (SEM) and micro-hardness measurements were realized. Experimental studies showed that the depth of the coating layers increased with increasing temperature and times and also ranged from 0.42 µm to 2.43 µm, depending on treatment time and temperature. The hardness of the niobium boride layer was 2620±180 HV{sub 0.005}.

  14. Potential and limitations of microanalysis SEM techniques to characterize borides in brazed Ni-based superalloys

    SciTech Connect

    Ruiz-Vargas, J.; Siredey-Schwaller, N.; Noyrez, P.; Mathieu, S.; Bocher, P.; and others

    2014-08-15

    Brazed Ni-based superalloys containing complex phases of different Boron contents remain difficult to characterize at the micrometer scale. Indeed Boron is a light element difficult to measure precisely. The state-of-the-art microanalysis systems have been tested on a single crystal MC2 based metal brazed with BNi-2 alloy to identify boride precipitates. Effort has been made to evaluate the accuracy in Boron quantitation. Energy-dispersive and wavelength-dispersive X-ray spectroscopy attached to a Scanning Electron Microscope have first been used to determine the elemental composition of Boron-free phases, and then applied to various types of borides. Results have been compared to the ones obtained using a dedicated electron probe microanalysis, considered here as the reference technique. The most accurate method to quantify Boron using EDS is definitely by composition difference. A precision of 5 at.% could be achieved with optimized data acquisition and post-processing schemes. Attempts that aimed at directly quantifying Boron with various standards using EDS or coupled EDS/WDS gave less accurate results. Ultimately, Electron Backscatter Diffraction combined with localized EDS analysis has proved invaluable in conclusively identifying micrometer sized boride precipitates; thus further improving the characterization of brazed Ni-based superalloys. - Highlights: • We attempt to accurately identify Boron-rich phases in Ni-based superalloys. • EDS, WDS, EBSD systems are tested for accurate identification of these borides. • Results are compared with those obtained by electron probe microanalysis. • Boron was measured with EDS by composition difference with a precision of 5 at. %. • Additional EBSD in phase identification mode conclusively identifies the borides.

  15. Additive-assisted synthesis of boride, carbide, and nitride micro/nanocrystals

    SciTech Connect

    Chen, Bo; Yang, Lishan; Heng, Hua; Chen, Jingzhong; Zhang, Linfei; Xu, Liqiang; Qian, Yitai; Yang, Jian

    2012-10-15

    General and simple methods for the syntheses of borides, carbides and nitrides are highly desirable, since those materials have unique physical properties and promising applications. Here, a series of boride (TiB{sub 2}, ZrB{sub 2}, NbB{sub 2}, CeB{sub 6}, PrB{sub 6}, SmB{sub 6}, EuB{sub 6}, LaB{sub 6}), carbide (SiC, TiC, NbC, WC) and nitride (TiN, BN, AlN, MgSiN{sub 2}, VN) micro/nanocrystals were prepared from related oxides and amorphous boron/active carbon/NaN{sub 3} with the assistance of metallic Na and elemental S. In-situ temperature monitoring showed that the reaction temperature could increase quickly to {approx}850 Degree-Sign C, once the autoclave was heated to 100 Degree-Sign C. Such a rapid temperature increase was attributed to the intense exothermic reaction between Na and S, which assisted the formation of borides, carbides and nitrides. The as-obtained products were characterized by XRD, SEM, TEM, and HRTEM techniques. Results in this report will greatly benefit the future extension of this approach to other compounds. - Graphical abstract: An additive-assisted approach is successfully developed for the syntheses of borides, carbides and nitrides micro/nanocrystals with the assistance of the exothermic reaction between Na and S. Highlights: Black-Right-Pointing-Pointer An additive-assisted synthesis strategy is developed for a number of borides, carbides and nitrides. Black-Right-Pointing-Pointer The reaction mechanism is demonstrated by the case of SiC nanowires. Black-Right-Pointing-Pointer The formation of SiC nanowires is initiated by the exothermic reaction of Na and S.

  16. Dose rate dependence of the speciation of neptunium in irradiated solutions of nitric acid

    SciTech Connect

    Precek, M.; Paulenova, A.; Mincher, B.J.; Mezyk, S.P.

    2013-07-01

    The effects of radiation on the redox speciation of neptunium are of interest due to their impact on the performance of separation of neptunium from highly radioactive solutions of dissolved used nuclear fuel. In this study, the influence of dose rate change from 0.4 kGy/h to 6 kGy/h was examined during irradiation of solutions of initially hexavalent 2.0-2.5 mM neptunium in nitric acid of two different concentrations (0.5 and 1 M). Results indicate that the immediate radiolytic steady-state concentration of neptunium(V) were depressed and its initial radiolytic yield was up to 2-times lower (in 1 M HNO{sub 3} solutions)during irradiations with the higher dose rate. The finding is explained on the basis of the enhancement of the role of oxidizing radicals during the radiolytic process. (authors)

  17. Improving the Adhesion Resistance of the Boride Coatings to AISI 316L Steel Substrate by Diffusion Annealing

    NASA Astrophysics Data System (ADS)

    Campos-Silva, I.; Bernabé-Molina, S.; Bravo-Bárcenas, D.; Martínez-Trinidad, J.; Rodríguez-Castro, G.; Meneses-Amador, A.

    2016-07-01

    In this study, new results about the practical adhesion resistance of boride coating/substrate system formed at the surface of AISI 316 L steel and improved by means of a diffusion annealing process are presented. First, the boriding of AISI 316 L steel was performed by the powder-pack method at 1173 K with different exposure times (4-8 h). The diffusion annealing process was conducted on the borided steels at 1273 K with 2 h of exposure using a diluent atmosphere of boron powder mixture. The mechanical behavior of the boride coating/substrate system developed by both treatments was established using Vickers and Berkovich tests along the depth of the boride coatings, respectively. Finally, for the entire set of experimental conditions, the scratch tests were performed with a continuously increasing normal force, in which the practical adhesion resistance of the boride coating/substrate system was represented by the critical load. The failure mechanisms developed over the surface of the scratch tracks were analyzed; the FeB-Fe2B/substrate system exhibited an adhesive mode, while the Fe2B/substrate system obtained by the diffusion annealing process showed predominantly a cohesive failure mode.

  18. The coexistence of silicon borides with boron-saturated silicon: Metastability of SiB{sub 3}

    SciTech Connect

    Aselage, T.L.

    1998-07-01

    The silicon-rich end of the Si-B phase diagram, defining the silicon boride(s) that coexist in equilibrium with boron-saturated silicon, is poorly known. Understanding this equilibrium has implications for the processing of p{sup +} silicon wafers, whose boron concentrations are near the solubility limit. Additionally, silicon boride precipitates produced by boron-ion-implantation and annealing of crystalline silicon have recently been shown to be efficient internal getters of transition metal ions. The experiments described in this paper probe the stability of these silicon borides. A phase with a boron-carbide-like structure, SiB{sub 3}, grows from boron-saturated silicon in both the solid and the liquid state. However, SiB{sub 3} is not found to be stable in either circumstance. Rather, SiB{sub 3} is a metastable phase whose formation is driven by the relative ease of its nucleation and growth. The silicon boride that exists in stable equilibrium with boron-saturated silicon is SiB{sub 6}. A qualitative understanding of the metastability of SiB{sub 3} comes from recognizing the conflict between the bonding requirements of icosahedral borides such as SiB{sub 3} and the size mismatch between silicon and boron atoms. {copyright} {ital 1998 Materials Research Society.}

  19. Existing Evidence for the Fate of Neptunium in the Yucca Mountain Repository

    SciTech Connect

    Friese, Judah I. ); Buck, Edgar C. ); McNamara, Bruce K. ); Hanson, Brady D. ); Marschman, Steven C. )

    2003-06-18

    Neptunium, because of its long half life, is an element of long-term interest to the Yucca Mountain repository. The fate of neptunium under repository settings is unknown. This report provides a review and new interpretation of past tests on commercial spent nuclear fuel and experimental evidence on the fate of neptunium. Tests on commercial spent nuclear fuel preformed previously at Pacific Northwest National Laboratory (PNNL) used a bathtub setup by immersing spent fuel in either deionized water or a groundwater typical of those at Yucca Mountain. The main goal of the tests was to determine the different concentrations of radionuclides in solution with different types of cladding defects. Neptunium was not the focus of these tests, nor were the tests designed to study neptunium. Drip tests performed at Argonne National Laboratory (ANL) are unsaturated tests that drip water at different rates on spent fuel. Relatively new tests at ANL examine the corrosion of Np-doped U3O8 in humid air at various temperatures. This review concludes that all tests reported here have analytical problems (i.e., relatively high detection limits for Np) and have been configured such that they limit the ability to interpret the available neptunium data. Past tests on spent nuclear fuel do not unambiguously describe neptunium chemistry as there are multiple mechanisms that may explain the observed behavior in each test. One apparently major shortcoming of most tests is that the extent of fuel reaction was limited by the amount of oxygen present in the system. Further detailed studies under repository-relevant conditions, which include the assumption of a constant 20 percent oxygen atmosphere, are needed to provide the data necessary for the development and validation of models used to predict the long-term fate of neptunium and other radionuclides at Yucca Mountain.

  20. Selection of peptides binding to metallic borides by screening M13 phage display libraries

    PubMed Central

    2014-01-01

    Background Metal borides are a class of inorganic solids that is much less known and investigated than for example metal oxides or intermetallics. At the same time it is a highly versatile and interesting class of compounds in terms of physical and chemical properties, like semiconductivity, ferromagnetism, or catalytic activity. This makes these substances attractive for the generation of new materials. Very little is known about the interaction between organic materials and borides. To generate nanostructured and composite materials which consist of metal borides and organic modifiers it is necessary to develop new synthetic strategies. Phage peptide display libraries are commonly used to select peptides that bind specifically to metals, metal oxides, and semiconductors. Further, these binding peptides can serve as templates to control the nucleation and growth of inorganic nanoparticles. Additionally, the combination of two different binding motifs into a single bifunctional phage could be useful for the generation of new composite materials. Results In this study, we have identified a unique set of sequences that bind to amorphous and crystalline nickel boride (Ni3B) nanoparticles, from a random peptide library using the phage display technique. Using this technique, strong binders were identified that are selective for nickel boride. Sequence analysis of the peptides revealed that the sequences exhibit similar, yet subtle different patterns of amino acid usage. Although a predominant binding motif was not observed, certain charged amino acids emerged as essential in specific binding to both substrates. The 7-mer peptide sequence LGFREKE, isolated on amorphous Ni3B emerged as the best binder for both substrates. Fluorescence microscopy and atomic force microscopy confirmed the specific binding affinity of LGFREKE expressing phage to amorphous and crystalline Ni3B nanoparticles. Conclusions This study is, to our knowledge, the first to identify peptides that

  1. Reduction and precipitation of neptunium(V) by sulfate-reducing bacteria.

    SciTech Connect

    Banaszak, J. E.; Rittmann, B. E.; Reed, D. T.

    1999-10-21

    Migration of neptunium, as NpO{sub 2}{sup +}, has been identified as a potentially important pathway for actinide release at nuclear waste repositories and existing sites of subsurface contamination. Reduction of Np(V) to Np(IV) will likely reduce its volubility, resulting in lowered subsurface migration. The ability of sulfate-reducing bacteria (SRB) to utilize Np(V) as an electron acceptor was investigated, because these bacteria are active in many anaerobic aquifers and are known to facilitate the reduction of metals and radionuclides. Pure and mixed cultures of SRB were able to precipitate neptunium during utilization of pyruvate, lactate, and hydrogen as electron donors in the presence and absence of sulfate. The neptunium in the precipitate was identified as Np(IV) using X-ray absorption near edge spectroscopy (XANES) analysis. In mixed-culture studies, the addition of hydrogen to consortia grown by pyruvate fermentation stimulated neptunium reduction and precipitation. Experiments with pure cultures of Desulfovibrio vulgaris, growing by lactate fermentation in the absence of sulfate or by sulfate reduction, confirm that the organism is active in neptunium reduction and precipitation. Based on our results, the activity of SRB in the subsurface may have a significant, and potentially beneficial, impact on actinide mobility by reducing neptunium volubility.

  2. SORPTION OF URANIUM, PLUTONIUM AND NEPTUNIUM ONTO SOLIDS PRESENT IN HIGH CAUSTIC NUCLEAR WASTE STORAGE TANKS

    SciTech Connect

    Oji, L; Bill Wilmarth, B; David Hobbs, D

    2008-05-30

    Solids such as granular activated carbon, hematite and sodium phosphates, if present as sludge components in nuclear waste storage tanks, have been found to be capable of precipitating/sorbing actinides like plutonium, neptunium and uranium from nuclear waste storage tank supernatant liqueur. Thus, the potential may exists for the accumulation of fissile materials in such nuclear waste storage tanks during lengthy nuclear waste storage and processing. To evaluate the nuclear criticality safety in a typical nuclear waste storage tank, a study was initiated to measure the affinity of granular activated carbon, hematite and anhydrous sodium phosphate to sorb plutonium, neptunium and uranium from alkaline salt solutions. Tests with simulated and actual nuclear waste solutions established the affinity of the solids for plutonium, neptunium and uranium upon contact of the solutions with each of the solids. The removal of plutonium and neptunium from the synthetic salt solution by nuclear waste storage tank solids may be due largely to the presence of the granular activated carbon and transition metal oxides in these storage tank solids or sludge. Granular activated carbon and hematite also showed measurable affinity for both plutonium and neptunium. Sodium phosphate, used here as a reference sorbent for uranium, as expected, exhibited high affinity for uranium and neptunium, but did not show any measurable affinity for plutonium.

  3. Thermodynamics of neptunium(V) fluoride and sulfate at elevatedtemperatures

    SciTech Connect

    Rao, Linfeng; Tian, Guoxin; Xia, Yuanxian; Friese, Judah I.

    2006-10-31

    Complexation of neptunium(V) with fluoride and sulfate at elevated temperatures was studied by microcalorimetry. Thermodynamic parameters, including the equilibrium constants and enthalpy of protonation of fluoride and sulfate, and the enthalpy of complexation between Np(V) and fluoride and sulfate at 25 - 70 C were determined. Results show that the complexation of Np(V) with fluoride and sulfate is endothermic and that the complexation is enhanced by the increase in temperature - a three-fold increase in the stability constants of NpO{sub 2}F(aq) and NpO{sub 2}SO{sub 4}{sup -} as the temperature is increased from 25 to 70 C.

  4. Complexation of Neptunium(V) with Fluoride at Elevated Temperatures

    SciTech Connect

    Rao, Linfeng; Tian, Guoxin; Xia, Yuanxian; Friese, Judah I.

    2008-06-16

    Complexation of neptunium(V) with fluoride at elevated temperatures was studied by spectrophotometry and microcalorimetry. Two successive complexes, NpO{sub 2}F(aq) and NpO{sub 2}F{sub 2}{sup -}, were identified by spectrophotometry in the temperature range of 10-70 C. Thermodynamic parameters, including the equilibrium constants and enthalpy of complexation between Np(V) and fluoride at 10-70 C were determined. Results show that the complexation of Np(V) with fluoride is endothermic and that the complexation is enhanced by the increase in temperature - a two-fold increase in the stability constants of NpO{sub 2}F(aq) and more than five-fold increase in the stability constants of NpO{sub 2}F{sub 2}{sup -} as the temperature is increased from 10 to 70 C.

  5. Geomicrobiological redox cycling of the transuranic element neptunium.

    PubMed

    Law, Gareth T W; Geissler, Andrea; Lloyd, Jonathan R; Livens, Francis R; Boothman, Christopher; Begg, James D C; Denecke, Melissa A; Rothe, Jörg; Dardenne, Kathy; Burke, Ian T; Charnock, John M; Morris, Katherine

    2010-12-01

    Microbial processes can affect the environmental behavior of redox sensitive radionuclides, and understanding these reactions is essential for the safe management of radioactive wastes. Neptunium, an alpha-emitting transuranic element, is of particular importance because of its long half-life, high radiotoxicity, and relatively high solubility as Np(V)O(2)(+) under oxic conditions. Here, we describe experiments to explore the biogeochemistry of Np where Np(V) was added to oxic sediment microcosms with indigenous microorganisms and anaerobically incubated. Enhanced Np removal to sediments occurred during microbially mediated metal reduction, and X-ray absorption spectroscopy showed this was due to reduction to poorly soluble Np(IV) on solids. In subsequent reoxidation experiments, sediment-associated Np(IV) was somewhat resistant to oxidative remobilization. These results demonstrate the influence of microbial processes on Np solubility and highlight the critical importance of radionuclide biogeochemistry in nuclear legacy management. PMID:21047117

  6. Application of the underscreened Kondo lattice model to neptunium compounds

    NASA Astrophysics Data System (ADS)

    Thomas, Christopher; da Rosa Simoes, Acirete S.; Iglesias, J. R.; Lacroix, C.; Coqublin, B.

    2012-12-01

    The coexistence of Kondo effect and ferromagnetic order has been observed in many uranium and neptunium compounds such as UTe or Np2PdGa3. This coexistence can be described within the underscreened Anderson lattice model with two f-electrons and S = 1 spins on each site. After performing the Schrieffer-Wolff transformation on this model, we have obtained an effective Hamiltonian with a f-band term in addition to the Kondo interaction for S = 1 spins. The results indicate a coexistence of Kondo effect and ferromagnetic order, with different relative values of the Kondo TK and Curie TC temperatures. We emphasize here especially the case TK < TC where there is a Kondo behavior below TC and a clear decrease of the magnetization below TK. Such a behavior has been observed in the magnetization curves of NpNiSi2 at low temperatures.

  7. Gamma-ray measurements of a 6-kilogram neptunium sphere

    SciTech Connect

    Moss, C. E.; Frankle, C. M.

    2002-01-01

    In order to better determine the properties of {sup 237}Np for criticality safety and nuclear nonproliferation, especially its critical mass, 6070-gram solid sphere was cast on 15 May 2001 in a hot cell. The casting sprue was cut off on a lathe and the casting ground to a final diameter of 8.29 cm. The sphere was enclosed in a spherical tungsten shell 0.523-cm thick to reduce the gamma-ray dose. The neptunium and the tungsten were doubly encapsulated in welded, spherical nickel shells, each 0.381-cm thick. The sprue material was analyzed by mass spectrometry. Here we report the results of the first gamma-ray measurements of this unique item.

  8. Nuclear forensics of a non-traditional sample: Neptunium

    DOE PAGESBeta

    Doyle, Jamie L.; Schwartz, Daniel; Tandon, Lav

    2016-05-16

    Recent nuclear forensics cases have focused primarily on plutonium (Pu) and uranium (U) materials. By definition however, nuclear forensics can apply to any diverted nuclear material. This includes neptunium (Np), an internationally safeguarded material like Pu and U, that could offer a nuclear security concern if significant quantities were found outside of regulatory control. This case study couples scanning electron microscopy (SEM) with quantitative analysis using newly developed specialized software, to evaluate a non-traditional nuclear forensic sample of Np. Here, the results of the morphological analyses were compared with another Np sample of known pedigree, as well as other traditionalmore » actinide materials in order to determine potential processing and point-of-origin.« less

  9. Friction and wear of radiofrequency-sputtered borides, silicides, and carbides

    NASA Technical Reports Server (NTRS)

    Brainard, W. A.; Wheeler, D. R.

    1978-01-01

    The friction and wear properties of several refractory compound coatings were examined. These compounds were applied to 440 C bearing steel surfaces by radiofrequency (RF) sputtering. The refractory compounds were the titanium and molybdenum borides, the titanium and molybdenum silicides, and the titanium, molybdenum, and boron carbides. Friction testing was done with a pin-on-disk wear apparatus at loads from 0.1 to 5.0 newtons. Generally, the best wear properties were obtained when the coatings were bias sputtered onto 440 C disks that had been preoxidized. Adherence was improved because of the better bonding of the coatings to the iron oxide formed during preoxidation. As a class the carbides provided wear protection to the highest loads. Titanium boride coatings provided low friction and good wear properties to moderate loads.

  10. Heat capacity and thermal expansion of icosahedral lutetium boride LuB66

    SciTech Connect

    Novikov, V V; Avdashchenko, D V; Matovnikov, A V; Mitroshenkov, N V; Bud’ko, S L

    2014-01-07

    The experimental values of heat capacity and thermal expansion for lutetium boride LuB66 in the temperature range of 2-300 K were analysed in the Debye-Einstein approximation. It was found that the vibration of the boron sub-lattice can be considered within the Debye model with high characteristic temperatures; low-frequency vibration of weakly connected metal atoms is described by the Einstein model.

  11. Synthesis and Characterization of an Alumina Forming Nanolaminated Boride: MoAlB

    NASA Astrophysics Data System (ADS)

    Kota, Sankalp; Zapata-Solvas, Eugenio; Ly, Alexander; Lu, Jun; Elkassabany, Omar; Huon, Amanda; Lee, William E.; Hultman, Lars; May, Steve J.; Barsoum, Michel W.

    2016-05-01

    The ‘MAlB’ phases are nanolaminated, ternary transition metal borides that consist of a transition metal boride sublattice interleaved by monolayers or bilayers of pure aluminum. However, their synthesis and properties remain largely unexplored. Herein, we synthesized dense, predominantly single-phase samples of one such compound, MoAlB, using a reactive hot pressing method. High-resolution scanning transmission electron microscopy confirmed the presence of two Al layers in between a Mo-B sublattice. Unique among the transition metal borides, MoAlB forms a dense, mostly amorphous, alumina scale when heated in air. Like other alumina formers, the oxidation kinetics follow a cubic time-dependence. At room temperature, its resistivity is low (0.36–0.49 μΩm) and – like a metal – drops linearly with decreasing temperatures. It is also a good thermal conductor (35 Wm‑1K‑1 at 26 °C). In the 25–1300 °C temperature range, its thermal expansion coefficient is 9.5 × 10‑6 K‑1. Preliminary results suggest the compound is stable to at least 1400 °C in inert atmospheres. Moderately low Vickers hardness values of 10.6 ± 0.3 GPa, compared to other transition metal borides, and ultimate compressive strengths up to 1940 ± 103 MPa were measured at room temperature. These results are encouraging and warrant further study of this compound for potential use at high temperatures.

  12. Synthesis and Characterization of an Alumina Forming Nanolaminated Boride: MoAlB.

    PubMed

    Kota, Sankalp; Zapata-Solvas, Eugenio; Ly, Alexander; Lu, Jun; Elkassabany, Omar; Huon, Amanda; Lee, William E; Hultman, Lars; May, Steve J; Barsoum, Michel W

    2016-01-01

    The 'MAlB' phases are nanolaminated, ternary transition metal borides that consist of a transition metal boride sublattice interleaved by monolayers or bilayers of pure aluminum. However, their synthesis and properties remain largely unexplored. Herein, we synthesized dense, predominantly single-phase samples of one such compound, MoAlB, using a reactive hot pressing method. High-resolution scanning transmission electron microscopy confirmed the presence of two Al layers in between a Mo-B sublattice. Unique among the transition metal borides, MoAlB forms a dense, mostly amorphous, alumina scale when heated in air. Like other alumina formers, the oxidation kinetics follow a cubic time-dependence. At room temperature, its resistivity is low (0.36-0.49 μΩm) and - like a metal - drops linearly with decreasing temperatures. It is also a good thermal conductor (35 Wm(-1)K(-1) at 26 °C). In the 25-1300 °C temperature range, its thermal expansion coefficient is 9.5 × 10(-6 )K(-1). Preliminary results suggest the compound is stable to at least 1400 °C in inert atmospheres. Moderately low Vickers hardness values of 10.6 ± 0.3 GPa, compared to other transition metal borides, and ultimate compressive strengths up to 1940 ± 103 MPa were measured at room temperature. These results are encouraging and warrant further study of this compound for potential use at high temperatures. PMID:27220751

  13. Synthesis and Characterization of an Alumina Forming Nanolaminated Boride: MoAlB

    PubMed Central

    Kota, Sankalp; Zapata-Solvas, Eugenio; Ly, Alexander; Lu, Jun; Elkassabany, Omar; Huon, Amanda; Lee, William E.; Hultman, Lars; May, Steve J.; Barsoum, Michel W.

    2016-01-01

    The ‘MAlB’ phases are nanolaminated, ternary transition metal borides that consist of a transition metal boride sublattice interleaved by monolayers or bilayers of pure aluminum. However, their synthesis and properties remain largely unexplored. Herein, we synthesized dense, predominantly single-phase samples of one such compound, MoAlB, using a reactive hot pressing method. High-resolution scanning transmission electron microscopy confirmed the presence of two Al layers in between a Mo-B sublattice. Unique among the transition metal borides, MoAlB forms a dense, mostly amorphous, alumina scale when heated in air. Like other alumina formers, the oxidation kinetics follow a cubic time-dependence. At room temperature, its resistivity is low (0.36–0.49 μΩm) and – like a metal – drops linearly with decreasing temperatures. It is also a good thermal conductor (35 Wm−1K−1 at 26 °C). In the 25–1300 °C temperature range, its thermal expansion coefficient is 9.5 × 10−6 K−1. Preliminary results suggest the compound is stable to at least 1400 °C in inert atmospheres. Moderately low Vickers hardness values of 10.6 ± 0.3 GPa, compared to other transition metal borides, and ultimate compressive strengths up to 1940 ± 103 MPa were measured at room temperature. These results are encouraging and warrant further study of this compound for potential use at high temperatures. PMID:27220751

  14. Direct Hydrogenation Magnesium Boride to Magnesium Borohydride: Demonstration of >11 Weight Percent Reversible Hydrogen Storage

    SciTech Connect

    Severa, Godwin; Ronnebro, Ewa; Jensen, Craig M.

    2010-11-16

    We here for the first time demonstrate direct hydrogenation of magnesium boride, MgB2, to magnesium borohydride, Mg(BH4)2 at 900 bar H2-pressures and 400°C. Upon 14.8wt% hydrogen release, the end-decomposition product of Mg(BH4)2 is MgB2, thus, this is a unique reversible path here obtaining >11wt% H2 which implies promise for a fully reversible hydrogen storage material.

  15. Distinct surface hydration behaviors of boron-rich boride thin film coatings

    NASA Astrophysics Data System (ADS)

    Lu, Xinhong; Liu, Wei; Ouyang, Jun; Tian, Yun

    2014-08-01

    In this work, the surface boron chemical states and surface hydration behaviors of the as-deposited and annealed boron-rich boride thin film coatings, including AlMgB14, TiB2 and AlMgB14-TiB2, were systematically studied by use of X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The XPS results indicate that boron at annealed AlMgB14 film surface can be oxidized; surprisingly, such oxidation does not lead to the formation of boric acid in ambient air. Instead, boric acid can be produced at the surface of annealed TiB2 film and AlMgB14-TiB2 film. It is shown, via the water contact angle measurements, that these boride films exhibit distinct surface wettability characteristics, which are believed to result in the observed surface hydration processes. Furthermore, we found anatase TiO2 formation plays a major role in the surface wetting behaviors for these boride films.

  16. Structure of superhard tungsten tetraboride: a missing link between MB2 and MB12 higher borides.

    PubMed

    Lech, Andrew T; Turner, Christopher L; Mohammadi, Reza; Tolbert, Sarah H; Kaner, Richard B

    2015-03-17

    Superhard metals are of interest as possible replacements with enhanced properties over the metal carbides commonly used in cutting, drilling, and wear-resistant tooling. Of the superhard metals, the highest boride of tungsten--often referred to as WB4 and sometimes as W(1-x)B3--is one of the most promising candidates. The structure of this boride, however, has never been fully resolved, despite the fact that it was discovered in 1961--a fact that severely limits our understanding of its structure-property relationships and has generated increasing controversy in the literature. Here, we present a new crystallographic model of this compound based on refinement against time-of-flight neutron diffraction data. Contrary to previous X-ray-only structural refinements, there is strong evidence for the presence of interstitial arrangements of boron atoms and polyhedral bonding. The formation of these polyhedral--slightly distorted boron cuboctahedra--appears to be dependent upon the defective nature of the tungsten-deficient metal sublattice. This previously unidentified structure type has an intermediary relationship between MB2 and MB12 type boride polymorphs. Manipulation of the fractionally occupied metal and boron sites may provide insight for the rational design of new superhard metals. PMID:25733870

  17. Structure of superhard tungsten tetraboride: A missing link between MB2 and MB12 higher borides

    PubMed Central

    Lech, Andrew T.; Turner, Christopher L.; Mohammadi, Reza; Tolbert, Sarah H.; Kaner, Richard B.

    2015-01-01

    Superhard metals are of interest as possible replacements with enhanced properties over the metal carbides commonly used in cutting, drilling, and wear-resistant tooling. Of the superhard metals, the highest boride of tungsten—often referred to as WB4 and sometimes as W1–xB3—is one of the most promising candidates. The structure of this boride, however, has never been fully resolved, despite the fact that it was discovered in 1961—a fact that severely limits our understanding of its structure–property relationships and has generated increasing controversy in the literature. Here, we present a new crystallographic model of this compound based on refinement against time-of-flight neutron diffraction data. Contrary to previous X-ray–only structural refinements, there is strong evidence for the presence of interstitial arrangements of boron atoms and polyhedral bonding. The formation of these polyhedra—slightly distorted boron cuboctahedra—appears to be dependent upon the defective nature of the tungsten-deficient metal sublattice. This previously unidentified structure type has an intermediary relationship between MB2 and MB12 type boride polymorphs. Manipulation of the fractionally occupied metal and boron sites may provide insight for the rational design of new superhard metals. PMID:25733870

  18. Corrosion behavior of titanium boride composite coating fabricated on commercially pure titanium in Ringer's solution for bioimplant applications.

    PubMed

    Sivakumar, Bose; Singh, Raghuvir; Pathak, Lokesh Chandra

    2015-03-01

    The boriding of commercially pure titanium was performed at 850°C, 910°C, and 1050°C for varied soaking periods (1, 3 and 5h) to enhance the surface properties desirable for bioimplant applications. The coating developed was characterized for the evolution of phases, microstructure and morphology, microhardness, and consequent corrosion behavior in the Ringer's solution. Formation of the TiB2 layer at the outermost surface followed by the TiB whiskers across the borided CpTi is unveiled. Total thickness of the composite layer on the substrates borided at 850, 910, and 1050°C for 5h was found to be 19.1, 26.4, and 18.2μm respectively which includes <3μm thick TiB2 layer. The presence of TiB2 phase was attributed to the high hardness ~2968Hv15gf of the composite coating. The anodic polarization studies in the simulated body fluid unveiled a reduction in the pitting corrosion resistance after boriding the CpTi specimens. However, this value is >0.55VSCE (electrochemical potential in in-vivo physiological environment) and hence remains within the safe region. Both the untreated and borided CpTi specimens show two passive zones associated with different passivation current densities. Among the CpTi borided at various times and temperatures, a 3h treated shows better corrosion resistance. The corrosion of borided CpTi occurred through the dissolution of TiB2. PMID:25579920

  19. Metabolism and gastrointestinal absorption of neptunium and protactinium in adult baboons

    SciTech Connect

    Ralston, L.G.; Cohen, N.; Bhattacharyya, M.H.; Larsen, R.P.; Ayres, L.; Oldham, R.D.; Moretti, E.S.

    1985-01-01

    The metabolism of neptunium and protactinium was studied in adult female baboons following intravenous injection and intragastric intubation. Immediately following intravenous injection (10/sup -1/ to 10/sup -10/ mg Np per kg body wt), neptunium cleared rapidly from blood, deposited primarily in the skeleton (54 +- 5%) and liver (3 +- 0.2%), and was excreted predominantly via urine (40 +- 3%). For the first year post injection, neptunium was retained with a biological half-time of approx.100 days in liver and 1.5 +- 0.2 yr in bone. In comparison, injected protactinium (10/sup -9/ mg/kg) was retained in blood in higher concentrations and was initially eliminated in urine to a lesser extent (6 +- 3%). In vivo measurements indicated that protactinium was retained in bone (65 +- 0.3%) with a half-time of 3.5 +- 0.6 yr. Differences in the physicochemical states of the neptunium or protactinium solutions injected did not alter the metabolic behavior of these nuclides. The gastrointestinal absorption value for neptunium in two fasted baboons, sacrificed at 1 day post administration, was determined to be 0.92 +- 0.04%. Of the total amount of neptunium absorbed, 52 +- 3% was retained in bone, 6 +- 2% was in liver, and 42 +- 0.1% was excreted in urine. A method was developed to estimate GI absorption values for both nuclides in baboons which were not sacrificed. Absorption values calculated by this method for neptunium and protactinium in fasted baboons were 1.8 +- 0.8% and 0.65 +- 0.01%, respectively. Values for fed animals were 1 to 2 orders of magnitude less than those for fasted animals. 14 refs., 3 figs., 4 tabs. (DT)

  20. Neptunium Solubility in the Near-Field Environment of A Proposed Yucca Mountain Repository

    SciTech Connect

    D.C. Sassani

    2004-05-14

    For representing the source-term of a proposed repository at Yucca Mountain, NV, total system performance assessment models evaluate the disequilibrium degradation of the waste forms to capture a bounding rate for radionuclide source-term availability and use solubility constraints that are more representative of longer-term, equilibrium processes to limit radionuclide mass transport from the source-term. These solubility limits capture precipitation processes occurring either as the waste forms alter, or in the near-field environment as chemical conditions evolve. A number of alternative models for solubility controls on dissolved neptunium concentrations have been evaluated. These include idealized models based on precipitation of neptunium as separate oxide minerals and more complex considerations of trace amounts of neptunium being incorporated into the secondary uranyl phases from waste form alteration. Thermodynamic models for neptunium under oxidizing conditions indicate that tetravalent neptunium (NpO{sub 2}) solids are more stable relative to pentavalent (Np{sub 2}O{sub 5}) phases, and thereby set lower dissolved concentrations of neptunyl species. Data on solids and solutions from slow flow through (dripping) tests on spent fuel grains indicate that neptunium is tetravalent in the spent fuel and that over {approx}9 years the neptunium concentrations are near to or below calculated NpO{sub 2} solubility. The possibility of kinetic rate limitations to NpO{sub 2} precipitation has led to temperature-dependent studies of NpO{sub 2} precipitation kinetics and solubility to reduce uncertainties and confirm application of the model.

  1. The effect of high ionic strength on neptunium (V) adsorption to a halophilic bacterium

    NASA Astrophysics Data System (ADS)

    Ams, David A.; Swanson, Juliet S.; Szymanowski, Jennifer E. S.; Fein, Jeremy B.; Richmann, Michael; Reed, Donald T.

    2013-06-01

    The mobility of neptunium (V) in subsurface high ionic strength aqueous systems may be strongly influenced by adsorption to the cell wall of the halophilic bacteria Chromohalobacter sp. This study is the first to evaluate the adsorption of neptunium (V) to the surface of a halophilic bacterium as a function of pH from approximately 2 to 10 and at ionic strengths of 2 and 4 M. This is also the first study to evaluate the effects of carbonate complexation with neptunium (V) on adsorption to whole bacterial cells under high pH conditions. A thermodynamically-based surface complexation model was adapted to describe experimental adsorption data under high ionic strength conditions where traditional corrections for aqueous ion activity are invalid. Adsorption of neptunium (V) was rapid and reversible under the conditions of the study. Adsorption was significant over the entire pH range evaluated for both ionic strength conditions and was shown to be dependent on the speciation of the sites on the bacterial surface and neptunium (V) in solution. Adsorption behavior was controlled by the relatively strong electrostatic attraction of the positively charged neptunyl ion to the negatively charged bacterial surface at pH below circum-neutral. At pH above circum-neutral, the adsorption behavior was controlled by the presence of negatively charged neptunium (V) carbonate complexes resulting in decreased adsorption, although adsorption was still significant due to the adsorption of negatively charged neptunyl-carbonate species. Adsorption in 4 M NaClO4 was enhanced relative to adsorption in 2 M NaClO4 over the majority of the pH range evaluated, likely due to the effect of increasing aqueous ion activity at high ionic strength. The protonation/deprotonation characteristics of the cell wall of Chromohalobacter sp. were evaluated by potentiometric titrations in 2 and 4 M NaClO4. Bacterial titration results indicated that Chromohalobacter sp. exhibits similar proton buffering

  2. Effect of Precipitation Conditions on the Specific Surface Area of Neptunium Oxide

    SciTech Connect

    HILL, BENJAMINC.

    2004-06-01

    Neptunium oxalate was precipitated under nominal and bounding HB-Line flowsheet conditions. The nominal case represents expected normal HB-Line operation. The bounding case represents process flowsheet extremes that could occur which are anticipated to decrease particle size and increase surface area. The neptunium oxalate produced under bounding conditions was used to validate the effectiveness of HB-Line calcination conditions. The maximum specific surface area of the neptunium oxide (NpO2) used in gas generation testing was 5.34 m2/g. Experiments were conducted to verify that even under bounding precipitation conditions the SSA of NpO2 produced would remain within the range evaluated during gas generation testing. The neptunium oxalate from nominal and bounding precipitation conditions was calcined at 600 degrees Celsius and 625 degrees Celsius, respectively, to form NpO2. Samples from each batch of neptunium oxalate were calcined for one, two, or four hours. Results indicate that the SSA of NpO2 continues to decrease between one and four hours. After two hours of calcination at 625 degrees Celsius, the SSA of NpO2 from the bounding case meets the surface area requirements for limiting moisture uptake.

  3. Neptunium as a Tool for Reducing Proliferation Risks with Plutonium: A Technical Analysis of its Efficiency and its Drawbacks

    SciTech Connect

    Greneche, Dominique; Ng, Selena; Guesdon, Bernard; Vinoche, Richard; Delpech, Marc; Golfier, Herve; Dolci, Florence; Poinot-Salanon, Christine

    2006-07-01

    Introducing neptunium into the nuclear fuel cycle has been proposed in the past as a way to impede the diversion or the direct use of plutonium to fabricate a nuclear explosive device. This paper aims to technically analyze the industrial consequences should this proposal be implemented. Two scenarios are considered: 1) adding neptunium to fresh uranium oxide (UOX) fuel before irradiation in a light water reactor; 2) separating neptunium together with plutonium from used UOX fuel and using this combined oxide to fabricate mixed oxide (MOX) fuel before subsequent irradiation in a light water reactor. In both cases, assembly calculations for a pressurized water reactor using fresh fuel doped with neptunium are presented for a wide range of neptunium proportions. Consequences on core and fuel performances and the fuel cycle are analyzed. These are weighed against the potential proliferation resistance benefits of adding neptunium due to the increased quantity of the plutonium isotope {sup 238}Pu in the discharged fuel, or due to the potentially increased detectability through gamma ray emissions of a plutonium-neptunium oxide mixture. Finally, the proliferation risk presented by neptunium itself is discussed. (authors)

  4. Batch sorption results for neptunium transport through Yucca Mountain tuffs. Yucca Mountain Site Characterization Program milestone 3349

    SciTech Connect

    Triay, I.R.; Cotter, C.R.; Huddleston, M.H.; Leonard, D.E.

    1996-09-01

    We studied the sorption of neptunium onto tuffs characteristic of the proposed nuclear waste repository at Yucca Mountain, Nevada. The neptunium was in the Np(V) oxidation state under oxidizing conditions in groundwaters from two wells located close to the repository site (J-13 and UE-25 p No.1). We used devitrified, vitric, zeolitic (with emphasis on clinoptilolite-rich samples), and calcite-rich tuffs characteristic of the geology of the site. Neptunium sorbed well onto calcite and calcite-rich tuffs, indicating that a significant amount of neptunium retardation can be expected under fractured-flow scenarios because of calcite coating of the fractures. Neptunium sorption onto clinoptilolite-rich zeolitic tuffs in J-13 well water (pH from 7 to 8.5) was moderate, increased with decreasing pH, and correlated to surface area and amount of clinoptilolite. Neptunium sorbed poorly onto zeolitic tuffs from UE-25 p No.1 groundwater (pH from 7 to 9) and onto devitrified and vitric tuffs from J-13 and UE-25 p No.1 waters (pH from 7 to 9). Iron oxides appeared to be passivated in tuffs, not seeming to contribute to the observed neptunium sorption, even though neptunium sorption onto synthetic iron oxide is significant.

  5. Speciation of neptunium during sorption and diffusion in natural clay

    NASA Astrophysics Data System (ADS)

    Reich, T.; Amayri, S.; Bӧrner, P. J. B.; Drebert, J.; Frӧhlich, D. R.; Grolimund, D.; Kaplan, U.

    2016-05-01

    In argillaceous rocks, which are considered as a potential host rock for nuclear waste repositories, sorption and diffusion processes govern the migration behaviour of actinides like neptunium. For the safety analysis of such a repository, a molecular-level understanding of the transport and retardation phenomena of radioactive contaminants in the host rock is mandatory. The speciation of Np during sorption and diffusion in Opalinus Clay was studied at near neutral pH using a combination of spatially resolved synchrotron radiation techniques. During the sorption and diffusion experiments, the interaction of 8 μM Np(V) solutions with the clay lead to the formation of spots at the clay-water interface with increased Np concentrations as determined by μ-XRF. Several of these spots are correlated with areas of increased Fe concentration. Np L3-edge μ-XANES spectra revealed that up to 85% of the initial Np(V) was reduced to Np(IV). Pyrite could be identified by μ-XRD as a redox-active mineral phase responsible for the formation of Np(IV). The analysis of the diffusion profile within the clay matrix after an in-diffusion experiment for two months showed that Np(V) is progressively reduced with diffusion distance, i.e. Np(IV) amounted to ≈12% and ≈26% at 30 μm and 525 μm, respectively.

  6. Gastrointestinal absorption of protactinium, uranium, and neptunium in the hamster

    SciTech Connect

    Harrison, J.D.; Stather, J.W.

    1981-10-01

    The gastrointestinal absorption of protactinium, uranium, and neptunium in adult hamsters was measured. The actinide preparations were administered intragastrically and animals were kept 2 to 4 weeks prior to the radiochemical analysis of selected tissue samples. Total absorption was estimated using data for the distribution of the actinides after intravenous injection in soluble form. The values obtained were 3.9 and 0.22% for /sup 231/Pa citrate and /sup 231/Pa fluoride, respectively; 0.77 and 0.11% for /sup 233/U (uranyl) nitrate and /sup 233/U dioxide, respectively; and 0.06 and 0.05% for /sup 237/Np citrate and /sup 237/Np nitrate, respectively. The absorption factors recommended by the International Commission on Radiological Protection for use in calculating annual limits on intake for occupationally exposed workers are: 0.1% for all compounds of Pa; 5 and 0.2% for soluble hexavalent and relatively insoluble tetravalent forms of U, respectively; and 1.0% for all chemical forms of Np. The experimental basis for these values is discussed.

  7. Fate of neptunium in an anaerobic, methanogenic microcosm.

    SciTech Connect

    Banaszak, J. E.

    1998-12-21

    Neptunium is found predominantly as Np(IV) in reducing environments, but Np(V) in aerobic environments. However, currently it is not known how the interplay between biotic and abiotic processes affects Np redox speciation in the environment. In order to evaluate the effect of anaerobic microbial activity on the fate of Np in natural systems, Np(V) was added to a microcosminoculated with anaerobic sediments from a metal-contaminated fresh water lake. The consortium included metal-reducing, sulfate-reducing, and methanogenic microorganisms, and acetate was supplied as the only exogenous substrate. Addition of more than 10{sup {minus}5} M Np did not inhibit methane production. Total Np volubility in the active microcosm, as well as in sterilized control samples, decreased by nearly two orders of magnitude. A combination of analytical techniques, including VIS-NIR absorption spectroscopy and XANES, identified Np(IV) as the oxidation state associated with the sediments. The similar results from the active microcosm and the abiotic controls suggest that microbian y produced Mn(II/HI) and Fe(II) may serve as electron donors for Np reduction.

  8. Report on neptunium speciation by NMR and optical spectroscopies

    SciTech Connect

    Tait, C.D.; Palmer, P.D.; Ekberg, S.A.; Clark, D.L.

    1995-11-01

    Hydrolysis and carbonate complexation reactions were examined for NpO{sub 2}{sup 2+} and NpO{sub 2}{sup +} ions by a variety of techniques including potentiometric titration, UV-Vis-NIR and NMR spectroscopy. The equilibrium constant for the reaction 3NpO{sub 2}(CO{sub 3}){sub 3}{sup 4{minus}} + 3H{sup +} {rightleftharpoons} (NpO{sub 2}){sub 3}(CO{sub 3}){sub 6}{sup 6{minus}} + 3HCO{sub 3}{sup {minus}} was determined to be logK = 19.7 ({plus_minus} 0.8) (I = 2.5 m). {sup 17}O NMR spectroscopy of NpO{sub 2}{sup n+} ions (n = 1,2) reveals a readily observable {sup 17}O resonance for n = 2, but not for n = 1. The first hydrolysis constant for NpO{sub 2}{sup +} was studied as a function of temperature, and the functional form for the temperature-dependent equilibrium constant for the reaction written as NpO{sub 2}{sup +} + H{sub 2}O {rightleftharpoons} NpO{sub 2}OH + H{sup +} was found to be logK = 2.28 {minus} 3780/T, where T is in {degree}K. Finally, the temperature dependence of neptunium(V) carbonate complexation constants was studied. For the first carbonate complexation constant, the appropriate functional form was found to be log{beta}{sub 01} = 1.47 + 786/T.

  9. PREFACE: The 16th International Symposium on Boron, Borides and Related Materials (ISBB 2008)

    NASA Astrophysics Data System (ADS)

    Tanaka, Takaho

    2009-07-01

    This volume of Journal of Physics: Conference Series contains invited and contributed peer-reviewed papers that were presented at the 16th International Symposium on Boron, Borides and Related Materials (ISBB 2008), which was held on 7-12 September 2008, at Kunibiki Messe, Matsue, Japan. This triennial symposium has a half-century long history starting from the 1st meeting in 1959 at Asbury Park, New Jersey. We were very pleased to organize ISBB 2008, which gathered chemists, physicists, materials scientists as well as diamond and high-pressure researchers. This meeting had a strong background in the boron-related Japanese research history, which includes the discovery of superconductivity in MgB2 and development of Nd-Fe-B hard magnets and of YB66 soft X-ray monochromator. The scope of ISBB 2008 spans both basic and applied interdisciplinary research that is centered on boron, borides and related materials, and the collection of articles defines the state of the art in research on these materials. The topics are centered on: 1. Preparation of new materials (single crystals, thin films, nanostructures, ceramics, etc) under normal or extreme conditions. 2. Crystal structure and chemical bonding (new crystal structures, nonstoichiometry, defects, clusters, quantum-chemical calculations). 3. Physical and chemical properties (band structure, phonon spectra, superconductivity; optical, electrical, magnetic, emissive, mechanical properties; phase diagrams, thermodynamics, catalytic activity, etc) in a wide range of temperatures and pressures. 4. Applications and prospects (thermoelectric converters, composites, ceramics, coatings, etc) There were a few discoveries of new materials, such as nanomaterials, and developments in applications. Many contributions were related to 4f heavy Fermion systems of rare-earth borides. Exotic mechanisms of magnetism and Kondo effects have been discussed, which may indicate another direction of development of boride. Two special sessions

  10. Synthesis and Characterization of Low-Cost Superhard Transition-Metal Borides

    NASA Astrophysics Data System (ADS)

    Kaner, Richard

    2013-06-01

    The increasing demand for high-performance cutting and forming tools, along with the shortcomings of traditional tool materials such as diamond (unable to cut ferrous materials), cubic boron nitride (expensive) and tungsten carbide (relatively-low hardness), has motivated the search for new superhard materials for these applications. This has led us to a new class of superhard materials, dense refractory transition-metal borides, which promise to address some of the existing problems of conventional superhard materials. For example, we have synthesized rhenium diboride (ReB2) using arc melting at ambient pressure. This superhard material has demonstrated an excellent electrical conductivity and superior mechanical properties, including a Vickers hardness of 48.0 GPa (under an applied load of 0.49 N). To further increase the hardness and lower the materials costs, we have begun exploring high boron content metal borides including tungsten tetraboride (WB4) . We have synthesized WB4 by arc melting and studied its hardness and high-pressure behavior. With a similar Vickers hardness (43.3 GPa under a load of 0.49 N) and bulk modulus (326-339 GPa) to ReB2, WB4 offers a lower cost alternative and has the potential to be used in cutting tools. To further enhance the hardness of this superhard metal, we have created the binary and ternary solid solutions of WB4 with Cr, Mn and Ta, the results of which show a hardness increase of up to 20 percent. As with other metals, these metallic borides can be readily cut and shaped using electric discharge machining (EDM).

  11. Physical, chemical, and catalytic properties of borided cobalt Fischer-Tropsch catalysts

    SciTech Connect

    Wang, J.

    1987-01-01

    Unsupported and alumina-supported borided cobalt catalysts were prepared by chemical reduction of anhydrous cobalt acetate at 25/sup 0/C using B/sub 2/H/sub 6//THF or NaBH/sub 4//diglyme solution as the reducing agent. These catalysts were further activated in H/sub 2/ at 250/sup 0/C prior to use. The physical and chemical properties of these catalysts were characterized by chemical analysis, BET surface area measurements, H/sub 2/ and CO adsorption measurements, X-ray Diffraction, and Temperature Programmed Desorption of CO. The catalytic properties of these catalysts for hydrogenation of CO to hydrocarbons were investigated at 160 - 300/sup 0/C, 1 and 10 atm, and H/sub 2//CO ratio of 2 in a differential conversion range of less than 8%. The data show that unsupported, Na-free, borided cobalt is much more active than Na-containing borided cobalt and pure cobalt on a site basis. Similarly, CoB/Al/sub 2/O/sub 3/ is more than an order of magnitude more active than Co/Al/sub 2/O/sub 3/ is more than an order of magnitude more active than Co/Al/sub 2/O/sub 3/ but has similar selectivity; its selectivity for C/sub 5//sup +/ hydrocarbons, however, is very high (> 75 wt%) at low reaction temperatures (e.g. 170/sup 0/C) or at low H/sub 2//CO ratios (e.g. less than or equal to 1). The observed changes in catalytic and adsorption behavior are consistent with an electron-donor model in which boron atoms donate electrons to cobalt. Na was found to lower catalytic activity of cobalt while increasing selectivity for light hydrocarbons, olefins, and CO/sub 2/ products.

  12. Indentation strength of ultraincompressible rhenium boride, carbide, and nitride from first-principles calculations

    NASA Astrophysics Data System (ADS)

    Zang, Chenpeng; Sun, Hong; Tse, John S.; Chen, Changfeng

    2012-07-01

    Using a recently developed first-principles approach for determining indentation strength [Z. Pan, H. Sun, and C. Chen, Phys. Rev. Lett.0031-9007 PRLTAO10.1103/PhysRevLett.98.135505 98, 135505 (2007); Z. Pan, H. Sun, and C. Chen, Phys. Rev. Lett.0031-9007 PRLTAO10.1103/PhysRevLett.102.055503 102, 055503 (2009)], we performed calculations of the ideal strength of hexagonal Re, Re3N, Re2N, Re2C, Re2B, and ReB2 in various shear deformation directions beneath the Vickers indentor. Our results show that the normal compressive pressure beneath the indentor weakens the strength of these electron-rich rhenium boride, carbide, and nitride compounds that belong to a distinct class of ultraincompressible and ultrahard materials. The reduction of indentation strength in these materials stems from lateral bond and volume expansions driven by the normal compressive pressure mediated by the high-density valence electrons in these structures. We compare the calculated indentation strength to the Poisson's ratio, which measures the lateral structural expansion, for the rhenium boride, carbide, and nitride compounds as well as diamond and cubic boron nitride. Our analysis indicates that although the normal pressure beneath the indentor generally leads to more significant reduction of indentation strength in materials with larger Poisson's ratios, crystal and electronic structures also play important roles in determining the structural response under indentation. The present study reveals structural deformation modes and the underlying atomistic mechanisms in transition-metal boride, carbide, and nitride compounds under the Vickers indentation. The results are distinctive from those of the traditional covalent superhard materials. The insights obtained from this work have important implications for further exploration and design of ultrahard materials.

  13. Metal-boride catalysts for indirect liquefaction. Quarterly technical progress report, December 1, 1982-February 28, 1983

    SciTech Connect

    Bartholomew, C.H.

    1983-03-15

    Four iron-boride catalysts were prepared. Washing with methanol did not change the iron phase composition as did water. Potassium borohydride reduction produces essentially the same iron phases as sodium borohydride reduction. Solution phase reductions with NH/sub 3/BH/sub 3/ were not productive. Reduction of ferric citrate with sodium borohydride produced a highly magnetic Fe/sub 2/B which was easily washed. Reduction of cobalt boride catalysts at a low temperature resulted in a catalyst with unusual selectivities in CO hydrogenation, i.e. the product contained more than 95% C/sub 5/-C/sub 16/ hydrocarbons. However, this catalyst deactivated rapidly.

  14. Factors Controlling Redox Speciation of Plutonium and Neptunium in Extraction Separation Processes

    SciTech Connect

    Paulenova, Alena; Vandegrift, III, George F.

    2013-09-24

    The objective of the project was to examine the factors controlling redox speciation of plutonium and neptunium in UREX+ extraction in terms of redox potentials, redox mechanism, kinetics and thermodynamics. Researchers employed redox-speciation extractions schemes in parallel to the spectroscopic experiments. The resulting distribution of redox species w studied uring spectroscopic, electrochemical, and spectro-electrochemical methods. This work reulted in collection of data on redox stability and distribution of redox couples in the nitric acid/nitrate electrolyte and the development of redox buffers to stabilize the desired oxidation state of separated radionuclides. The effects of temperature and concentrations on the redox behavior of neptunium were evaluated.

  15. Characterization of Neptunium Oxide Generated Using the HB-Line Phase II Flowsheet

    SciTech Connect

    Duffey, J

    2003-08-29

    Approximately 98 grams of neptunium(IV) oxide (NpO{sub 2}) were produced at the Savannah River Technology Center (SRTC) for use in gas generation tests to support the neptunium stabilization program at the Savannah River Site (SRS). The NpO{sub 2} was produced according to the anticipated HB-Line flowsheet consisting of anion exchange, oxalate precipitation, filtration, and calcination. Characterization of the NpO{sub 2} product to be used in gas generation tests included bulk and tap density measurements, X-ray diffraction, particle size distribution, specific surface area measurements, and moisture analysis.

  16. Intrinsic formation of nanocrystalline neptunium dioxide under neutral aqueous conditions relevant to deep geological repositories.

    PubMed

    Husar, Richard; Hübner, René; Hennig, Christoph; Martin, Philippe M; Chollet, Mélanie; Weiss, Stephan; Stumpf, Thorsten; Zänker, Harald; Ikeda-Ohno, Atsushi

    2015-01-25

    The dilution of aqueous neptunium carbonate complexes induces the intrinsic formation of nanocrystalline neptunium dioxide (NpO2) particles, which are characterised by UV/Vis and X-ray absorption spectroscopies and transmission electron microscopy. This new route of nanocrystalline NpO2 formation could be a potential scenario for the environmental transport of radionuclides from the waste repository (i.e. under near-field alkaline conditions) to the geological environment (i.e. under far-field neutral conditions). PMID:25479067

  17. Electroplating of the superconductive boride MgB2 from molten salts

    NASA Astrophysics Data System (ADS)

    Abe, Hideki; Yoshii, Kenji; Nishida, Kenji; Imai, Motoharu; Kitazawa, Hideaki

    2005-02-01

    An electroplating technique of the superconductive boride MgB2 onto graphite substrates is reported. Films of MgB2 with a thickness of tens micrometer were fabricated on the planar and curved surfaces of graphite substrates by means of electrolysis on a mixture of magnesium chloride, potassium chloride, sodium chloride, and magnesium borate fused at 600 °C under an Ar atmosphere. The electrical resistivity and magnetization measurements revealed that the electroplated MgB2 films undergo a superconducting transition with the critical temperature (Tc) of 36 K.

  18. Improved carbides and new borides for HVOF and their coating properties

    SciTech Connect

    Froning, M.J.; Keller, H.

    1995-12-31

    In the presented paper, investigations on HVOF coatings produced from a new family of powders will be discussed. The influence of microstructure, composition and production methods will be discussed in view of powder properties and resulting coating properties. New boride powders and coatings will be compared with regard to their properties deposition, efficiency, hardness, surface roughness, bond strength, and wear against commercial WC-Co and cr3C2-NiCr coatings. Additionally, improved WC- and CrC-based powders and coatings will be compared with regard to oxidation and erosion resistance.

  19. Infiltration processing of boron carbide-, boron-, and boride-reactive metal cermets

    DOEpatents

    Halverson, Danny C.; Landingham, Richard L.

    1988-01-01

    A chemical pretreatment method is used to produce boron carbide-, boron-, and boride-reactive metal composites by an infiltration process. The boron carbide or other starting constituents, in powder form, are immersed in various alcohols, or other chemical agents, to change the surface chemistry of the starting constituents. The chemically treated starting constituents are consolidated into a porous ceramic precursor which is then infiltrated by molten aluminum or other metal by heating to wetting conditions. Chemical treatment of the starting constituents allows infiltration to full density. The infiltrated precursor is further heat treated to produce a tailorable microstructure. The process at low cost produces composites with improved characteristics, including increased toughness, strength.

  20. Sensitive redox speciation of neptunium by CE-ICP-MS.

    PubMed

    Stöbener, Nils; Amayri, Samer; Gehl, Aaron; Kaplan, Ugras; Malecha, Kurtis; Reich, Tobias

    2012-11-01

    Capillary electrophoresis (CE) was used to separate the neptunium oxidation states Np(IV) and Np(V), which are the only oxidation states of Np that are stable under environmental conditions. The CE setup was coupled to an inductively coupled plasma mass spectrometer (Agilent 7500ce) using a Mira Mist CE nebulizer and a Scott-type spray chamber. The combination of the separation capacity of CE with the detection sensitivity of inductively coupled plasma mass spectrometry (ICP-MS) allows identification and quantification of Np(IV) and Np(V) at the trace levels expected in the far field of a nuclear waste repository. Limits of detection of 1 × 10(-9) and 5 × 10(-10) mol L(-1) for Np(IV) and Np(V), respectively, were achieved, with a linear range from 10(-9) to 10(-6) mol L(-1). The method was applied to study the redox speciation of the Np remaining in solution after interaction of 5 × 10(-7) mol L(-1) Np(V) with Opalinus Clay. Under mildly oxidizing conditions, a Np sorption of 31% was found, with all the Np remaining in solution being Np(V). A second sorption experiment performed in the presence of Fe(2+) led to complete sorption of the Np onto the clay. After desorption with HClO(4), a mixture of Np(IV) and Np(V) was found in solution by CE-ICP-MS, indicating that some of the sorbed Np had been reduced to Np(IV) by Fe(2+). PMID:23052867

  1. Experimental study on neptunium migration under in situ geochemical conditions

    NASA Astrophysics Data System (ADS)

    Kumata, M.; Vandergraaf, T. T.

    1998-12-01

    Results are reported for migration experiments performed with Np under in situ geochemical conditions over a range of groundwater flow rates in columns of crushed rock in a specially designed facility at the 240-level of the Underground Research Laboratory (URL) near Pinawa, Manitoba, Canada. This laboratory is situated in an intrusive granitic rock formation, the Lac du Bonnet batholith. Highly altered granitic rock and groundwater were obtained from a major subhorizontal fracture zone at a depth of 250 m in the URL. The granite was wet-crushed and wet-sieved with groundwater from this fracture zone. The 180-850-μm size fraction was selected and packed in 20-cm long, 2.54-cm in diameter Teflon™-lined stainless steel columns. Approximately 30-ml vols of groundwater containing 3HHO and 237Np were injected into the columns at flow rates of 0.3, 1, and 3 ml/h, followed by elution with groundwater, obtained from the subhorizontal fracture, at the same flow rates, for a period of 95 days. Elution profiles for 3HHO were obtained, but no 237Np was detected in the eluted groundwater. After terminating the migration experiments, the columns were frozen, the column material was removed and cut into twenty 1-cm thick sections and each section was analyzed by gamma spectrometry. Profiles of 237Np were obtained for the three columns. A one-dimensional transport model was fitted to the 3HHO breakthrough curves to obtain flow parameters for this experiment. These flow parameters were in turn applied to the 237Np concentration profiles in the columns to produce sorption and dispersion coefficients for Np. The results show a strong dependence of retardation factors ( Rf) on flow rate. The decrease in the retarded velocity of the neptunium ( Vn) varied over one order of magnitude under the geochemical conditions for these experiments.

  2. Spectroscopic investigations of neptunium`s and plutonium`s oxidation states in sol-gel glasses as a function of initial valance and thermal history

    SciTech Connect

    Stump, N.A.; Haire, R.G.; Dai, S.

    1996-12-01

    Several oxidation states of neptunium and plutonium, Pu(III),Pu (IV), PU(VI), Np(IV), Np(V) and Np (VI), were studied in glasses prepared by a sol-gel technology. The oxidation state of these actinides was determined primarily by absorption spectrometry and followed as a function of the solidification process, subsequent aging and thermal treatments. It was determined that the initial oxidation state of the actinides in the starting solutions was essentially maintained through the solidification process to form the glasses. However, during densification and removal of residual solvents at elevated temperatures, both actinides in the different sol-gel products converted completely to their tetravalent states. These results are discussed in terms of our findings in comparable studies that only the tetravalent states of plutonium and neptunium are formed in glasses prepared by dissolving their dioxides in different molten- glass formulations.

  3. Neptunium - Uranium - Plutonium Co-Extraction in TBP-based Solvent Extraction Processes for Spent Nuclear Fuel Recycling

    SciTech Connect

    Arm, S.T.; Abrefah, J.; Lumetta, G.J.; Sinkov, S.I.

    2007-07-01

    The US, through the Global Nuclear Energy Partnership, is currently engaged in efforts aimed at closing the nuclear fuel cycle. Neptunium behavior is important to understand for transuranic recycling because of its complex oxidation chemistry. The Pacific Northwest National Laboratory is investigating neptunium oxidation chemistry in the context of the PUREX process. Neptunium extraction in the PUREX process relies on maintaining either IV or V oxidation states. Qualitative conversion of neptunium(V) to neptunium(VI) was achieved within 5 hours in 6 M nitric acid at 95 deg. C. However, the VI state was not maintained during a batch contact test simulating the PUREX process and neptunium reduced to the V state, rendering it inextractable. Vanadium(V) was found to be effective in maintaining neptunium(VI) by adding it to a simulated irradiated nuclear fuel feed in 6 M nitric acid and to the scrub acid in the batch contact simulation of the PUREX process. Computer simulations of the PUREX process with a typical irradiated nuclear fuel in 6 M nitric acid as feed indicated little impact of the higher acid concentration on the behavior of fission products of moderate extractability. We plan to perform countercurrent tests of this modified PUREX process in the near future. (authors)

  4. Boronic acid flux synthesis and crystal growth of uranium and neptunium boronates and borates: a low-temperature route to the first neptunium(V) borate.

    PubMed

    Wang, Shuao; Alekseev, Evgeny V; Miller, Hannah M; Depmeier, Wulf; Albrecht-Schmitt, Thomas E

    2010-11-01

    Molten methylboronic acid has been used as a reactive flux to prepare the first neptunium(V) borate, NpO(2)[B(3)O(4)(OH)(2)] (NpBO-1), and the first actinide boronate, UO(2)(CH(3)BO(2))(H(2)O) (UCBO-1). NpBO-1 contains cation-cation interactions between the neptunyl units. In contrast, the presence of the methyl groups in the uranyl boronate leads to a one-dimensional structure. PMID:20919728

  5. Amorphous nickel boride membrane on a platinum–nickel alloy surface for enhanced oxygen reduction reaction

    PubMed Central

    He, Daping; Zhang, Libo; He, Dongsheng; Zhou, Gang; Lin, Yue; Deng, Zhaoxiang; Hong, Xun; Wu, Yuen; Chen, Chen; Li, Yadong

    2016-01-01

    The low activity of the oxygen reduction reaction in polymer electrolyte membrane fuel cells is a major barrier for electrocatalysis, and hence needs to be optimized. Tuning the surface electronic structure of platinum-based bimetallic alloys, a promising oxygen reduction reaction catalyst, plays a key role in controlling its interaction with reactants, and thus affects the efficiency. Here we report that a dealloying process can be utilized to experimentally fabricate the interface between dealloyed platinum–nickel alloy and amorphous nickel boride membrane. The coating membrane works as an electron acceptor to tune the surface electronic structure of the platinum–nickel catalyst, and this composite catalyst composed of crystalline platinum–nickel covered by amorphous nickel boride achieves a 27-times enhancement in mass activity relative to commercial platinum/carbon at 0.9 V for the oxygen reduction reaction performance. Moreover, this interactional effect between a crystalline surface and amorphous membrane can be readily generalized to facilitate the 3-times higher catalytic activity of commercial platinum/carbon. PMID:27503412

  6. Amorphous nickel boride membrane on a platinum-nickel alloy surface for enhanced oxygen reduction reaction

    NASA Astrophysics Data System (ADS)

    He, Daping; Zhang, Libo; He, Dongsheng; Zhou, Gang; Lin, Yue; Deng, Zhaoxiang; Hong, Xun; Wu, Yuen; Chen, Chen; Li, Yadong

    2016-08-01

    The low activity of the oxygen reduction reaction in polymer electrolyte membrane fuel cells is a major barrier for electrocatalysis, and hence needs to be optimized. Tuning the surface electronic structure of platinum-based bimetallic alloys, a promising oxygen reduction reaction catalyst, plays a key role in controlling its interaction with reactants, and thus affects the efficiency. Here we report that a dealloying process can be utilized to experimentally fabricate the interface between dealloyed platinum-nickel alloy and amorphous nickel boride membrane. The coating membrane works as an electron acceptor to tune the surface electronic structure of the platinum-nickel catalyst, and this composite catalyst composed of crystalline platinum-nickel covered by amorphous nickel boride achieves a 27-times enhancement in mass activity relative to commercial platinum/carbon at 0.9 V for the oxygen reduction reaction performance. Moreover, this interactional effect between a crystalline surface and amorphous membrane can be readily generalized to facilitate the 3-times higher catalytic activity of commercial platinum/carbon.

  7. Amorphous nickel boride membrane on a platinum-nickel alloy surface for enhanced oxygen reduction reaction.

    PubMed

    He, Daping; Zhang, Libo; He, Dongsheng; Zhou, Gang; Lin, Yue; Deng, Zhaoxiang; Hong, Xun; Wu, Yuen; Chen, Chen; Li, Yadong

    2016-01-01

    The low activity of the oxygen reduction reaction in polymer electrolyte membrane fuel cells is a major barrier for electrocatalysis, and hence needs to be optimized. Tuning the surface electronic structure of platinum-based bimetallic alloys, a promising oxygen reduction reaction catalyst, plays a key role in controlling its interaction with reactants, and thus affects the efficiency. Here we report that a dealloying process can be utilized to experimentally fabricate the interface between dealloyed platinum-nickel alloy and amorphous nickel boride membrane. The coating membrane works as an electron acceptor to tune the surface electronic structure of the platinum-nickel catalyst, and this composite catalyst composed of crystalline platinum-nickel covered by amorphous nickel boride achieves a 27-times enhancement in mass activity relative to commercial platinum/carbon at 0.9 V for the oxygen reduction reaction performance. Moreover, this interactional effect between a crystalline surface and amorphous membrane can be readily generalized to facilitate the 3-times higher catalytic activity of commercial platinum/carbon. PMID:27503412

  8. Mixed-valent neptunium(IV/V) compound with cation-cation-bound six-membered neptunyl rings.

    PubMed

    Jin, Geng Bang

    2013-11-01

    A new mixed-valent neptunium(IV/V) compound has been synthesized by evaporation of a neptunium(V) acidic solution. The structure of the compound features cation-cation-bound six-membered neptunyl(V) rings. These rings are further connected by Np(IV) ions through cation-cation interactions (CCIs) into a three-dimensional neptunium cationic open framework. This example illustrates the possibility of isolating neptunyl(V) CCI oligomers in inorganic systems using other cations to compete with Np(V) in bonding with the neptunyl oxygen. PMID:24187926

  9. Photoelectron, nuclear gamma-ray and infrared absorption spectroscopic studies of neptunium in sodium silicate glass

    SciTech Connect

    Veal, B.W.; Carnall, W.T.; Dunlap, B.D.; Mitchell, A.W.; Lam, D.J.

    1986-04-01

    The valence state of neptunium ions in sodium silicate glasses prepared under reducing and oxidizing conditions has been investigated by the x-ray photoelectron, Moessbauer and optical absorption spectroscopic techniques. Results indicate that the Np ions are tetravalent in glasses prepared under reducing conditions and pentavalent in glasses prepared under oxidizing conditions.

  10. Gastrointestinal absorption of neptunium in primates: effect of ingested mass, diet, and fasting

    SciTech Connect

    Metivier, H.; Bourges, J.; Fritsch, P.; Nolibe, D.; Masse, R.

    1986-05-01

    Absorption and retention of neptunium were determined in baboons after intragastric administration of neptunium nitrate solutions at pH 1. The effects of mass, diet, and fasting on absorption were studied. At higher mass levels (400-800 micrograms Np/kg), absorption was about 1%; at lower mass intakes (0.0009-0.005 micrograms Np/kg), absorption was reduced by 10- to 20-fold. The addition of an oxidizing agent (Fe3+) increased gastrointestinal absorption and supported the hypothesis of a reduction of Np (V) when loss masses were ingested. Diets depleted of or enriched with hydroxy acids did not modify retention of neptunium but increased urinary excretion with increasing hydroxy acid content. The diet enriched with milk components reduced absorption by a factor of 5. Potatoes increased absorption and retention by a factor 5, not necessarily due to the effect of phytate. Fasting for 12 or 24 h increased retention and absorption by factors of about 3 and 10, respectively. Data obtained in baboons when low masses of neptunium were administered suggest that the f1 factor used by ICRP should be decreased. However, fasting as encountered in certain nutritional habits is a factor to be taken into consideration.

  11. Criticality of a Neptunium-237 sphere surrounded with highly enriched uranium shells and an iron reflector

    SciTech Connect

    Sanchez, R. G.; Loaiza, D. J.; Hayes, D. K.; Kimpland, R. H.

    2004-01-01

    An additional experiment has been performed using the recently cast 6-kg {sup 237}Np sphere. The experiment consisted of surrounding the neptunium sphere with highly enriched uranium and an iron reflector. The purpose of the critical experiment is to provide additional criticality data that can be used to validate criticality safety evaluations involving the deposition of neptunium. It is well known that {sup 237}Np is primarily produced by successive neutron capture events in {sup 235}U or through the (n, 2n) reaction in {sup 238}U. These nuclear reactions lead to the production of {sup 237}U, which decays by beta emission into {sup 237}Np. In addition, in the spent fuel, {sup 241}Am decays by alpha emission into {sup 237}Np. Because {sup 237}Np is a threshold fissioner, the best reflectors for critical systems containing neptunium are those materials that exhibit good neutron scattering properties such as low carbon steel (99 wt % Fe). In this experiment, the iron reflector reduced the amount of uranium used in the critical experiment and increased the importance of the neptunium sphere.

  12. High-temperature X-ray diffraction study of uranium-neptunium mixed oxides.

    PubMed

    Chollet, Mélanie; Belin, Renaud C; Richaud, Jean-Christophe; Reynaud, Muriel; Adenot, Frédéric

    2013-03-01

    Incorporating minor actinides (MAs = Am, Np, Cm) in UO2 fertile blankets is a viable option to recycle them. Despite this applied interest, phase equilibria between uranium and MAs still need to be thoroughly investigated, especially at elevated temperatures. In particular, few reports on the U-Np-O system are available. In the present work, we provide for the first time in situ high-temperature X-ray diffraction results obtained during the oxidation of (U1-yNpy)O2 uranium-neptunium mixed oxides up to 1373 K and discuss subsequent phase transformations. We show that (i) neptunium stabilizes the UO2-type fluorite structure at high temperature and that (ii) the U3O8-type orthorhombic structure is observed in a wide range of compositions. We clearly demonstrate the incorporation of neptunium in this phase, which was a controversial question in previous studies up to now. We believe it is the particular stability of the tetravalent state of neptunium that is responsible for the observed phase relationships. PMID:23409700

  13. The influence of phonon anharmonicity on thermal and elastic properties of neptunium

    NASA Astrophysics Data System (ADS)

    Filanovich, A.; Povzner, A.

    2013-06-01

    A self-consistent thermodynamic model describing the thermal and elastic properties of α- and β-phases of neptunium was developed. The presence of strong phonon anharmonicity of Np is established. The obtained results are in good agreement with the experimental data and enable to predict the Np properties in wide temperature range.

  14. Investigation of composition and chemical state of elements in iron boride by the method of X-ray photoelectron spectroscopy

    NASA Astrophysics Data System (ADS)

    Alyoshin, V. G.; Kharlamov, A. I.; Prokopenko, V. M.

    1981-06-01

    The composition and chemical state of iron and boron in the surface layer of iron boride under different kinds of pretreatment of samples have been investigated by the method of X-ray photo-electron spectroscopy. It has been found that in the initial sample there is oxygen chemically combined with iron and boron atoms. Upon heating (450°C) in hydrogen, in argon, and in vacuo there occurs removal of oxygen only from iron atoms (no pure iron was found to be formed). Boron oxidizes and there probably appears a new surface combination of boron with oxygen in which the bonding energy of 1 s electrons is higher than that in B 2O 3. Treatment of the iron boride surface with argon ions and with protons ensures uniform removal of oxygen from iron and boron atoms. It has been found that thermal treatment of iron boride leads to depletion of iron atoms from the sample surface layer, and pickling with argon ions and with protons leads to strong enrichment. Iron boride samples subjected to Ar + and H + bombardment tend to undergo significant oxidation when subsequently exposed to air at room temperature.

  15. Synthesis of transition metal borides layers under pulsed electron-beams treatment in a vacuum for surface hardening of instrumental steels

    NASA Astrophysics Data System (ADS)

    Milonov, A. S.; Danzheev, B. A.; Smirnyagina, N. N.; Dasheev, D. E.; Kim, T. B.; Semenov, A. P.

    2015-11-01

    The saturation of the surface layers of metals and alloys with boron is conducted for increasing their surface hardness, wear resistance, etc. Multicomponent layers containing in its composition borides of refractory metals, as a rule, are formed by the methods of chemical- thermal processing in the interaction of boriding component with refractory one or by the method of saturation of refractory metal impurities or alloy with boron. In this work, we studied the features of vanadium and iron borides formation on the surface of instrumental steels U8A and R18 under the influence of intense electron beams in continuous and pulse modes.

  16. PLUTONIUM-238 RECOVERY FROM IRRADIATED NEPTUNIUM TARGETS USING SOLVENT EXTRACTION

    SciTech Connect

    Scott Herbst; Terry Todd; Jack Law; Bruce Mincher; Steve Frank; John Swanson

    2006-10-01

    The United States Department of Energy proposes to re-establish a domestic capability for producing plutonium-238 (238Pu) to fuel radioisotope power systems primarily in support of future space missions. A conceptual design report is currently being prepared for a new 238Pu, and neptunium-237 (237Np) target fabrication and processing facility tentatively to be built at the Idaho National Laboratory (INL) in the USA. The facility would be capable of producing at least 5 kg of 238Pu-oxide powder per year. Production of 238Pu requires fabrication of 237Np targets with subsequent irradiation in the existing Advanced Test Reactor (ATR) located at the INL. The targets are 237Np oxide dispersed in a compact of powdered aluminum and clad with aluminum metal. The 238Pu product is separated and purified from the residual 237Np, aluminum matrix, and fission products. The unconverted 237Np is also a valuable starting material and is separated, purified and recycled to the target fabrication process. The proposed baseline method for separating and purifying 238Pu and unconverted 237Np post irradiation is by anion exchange (IX). Separation of Pu from Np by IX was chosen as the baseline method because of the method’s proven ability to produce a quality Pu product and because it is amenable to the relatively small scale, batch type production methods used (small batches of ~200g 238Pu are processed at a time). Multiple IX cycles are required involving substantial volumes of nitric acid and other process solutions which must be cleaned and recycled or disposed of as waste. Acid recycle requires rather large evaporator systems, including one contained in a hot cell for remote operation. Finally, the organic based anion exchange resins are rapidly degraded due to the high a-dose and associated heat production from 238Pu decay, and must be regularly replaced (and disposed of as waste). In summary, IX is time consuming, cumbersome, and requires substantial tankage to accommodate the

  17. Preparation and sintering of refractory metal borides, carbides and nitrides of high purity

    SciTech Connect

    Sane, A.Y.

    1987-09-15

    The method of preparing a consolidated and purified Group IVb, Vb, or VIb refractory metal boride, carbide, nitride, or mixture, combination or cermet thereof by means of aided, reduced pressure and elevated temperature conditions is described. It consists of: (a) establishing a composition for a second stage reaction step of reaction sintering and adapted for enhanced production of desired product; (b) providing sintering aid at least in part together with the composition and resting the composition upon the sintering aid, which aid is solid at normal pressure and temperatures and aids via the vapor phase at the pressure and temperature conditions of the second stage reaction step; (c) reducing the pressure around the composition; (d) heating the composition at a temperature for sintering; while (e) establishing sintering aid atmosphere in contact with the composition; and (f) maintaining the heating for a time sufficient to consolidate the composition, and thereby prepare a consolidate and purified product.

  18. Valence fluctuations of europium in the boride Eu4Pd29+x B8

    NASA Astrophysics Data System (ADS)

    Gumeniuk, Roman; Schnelle, Walter; Ahmida, Mahmoud A.; Abd-Elmeguid, Mohsen M.; Kvashnina, Kristina O.; Tsirlin, Alexander A.; Leithe-Jasper, Andreas; Geibel, Christoph

    2016-03-01

    We synthesized a high-quality sample of the boride Eu4Pd29+x B8 (x  =  0.76) and studied its structural and physical properties. Its tetragonal structure was solved by direct methods and confirmed to belong to the Eu4Pd29B8 type. All studied physical properties indicate a valence fluctuating Eu state, with a valence decreasing continuously from about 2.9 at 5 K to 2.7 at 300 K. Maxima in the T dependence of the susceptibility and thermopower at around 135 K and 120 K, respectively, indicate a valence fluctuation energy scale on the order of 300 K. Analysis of the magnetic susceptibility evidences some inconsistencies when using the ionic interconfigurational fluctuation (ICF) model, thus suggesting a stronger relevance of hybridization between 4f and valence electrons compared to standard valence-fluctuating Eu systems.

  19. Identification of delamination failure of boride layer on common Cr-based steels

    NASA Astrophysics Data System (ADS)

    Taktak, Sukru; Tasgetiren, Suleyman

    2006-10-01

    Adhesion is an important aspect in the reliability of coated components. With low-adhesion of interfaces, different crack paths may develop depending on the local stress field at the interface and the fracture toughness of the coating, substrate, and interface. In the current study, an attempt has been made to identify the delamination failure of coated Cr-based steels by boronizing. For this reason, two commonly used steels (AISI H13, AISI 304) are considered. The steels contain 5.3 and 18.3 wt.% Cr, respectively. Boriding treatment is carried out in a slurry salt bath consisting of borax, boric acid, and ferrosilicon at a temperature range of 800 950 °C for 3, 5, and 7 h. The general properties of the boron coating are obtained by mechanical and metallographic characterization tests. For identification of coating layer failure, some fracture toughness tests and the Daimler-Benz Rockwell-C adhesion test are used.

  20. A new tetragonal boride phase in FeAl+B type alloys

    SciTech Connect

    Pierron, X.; Baker, I.

    1997-12-31

    The structure and composition of a previously unreported second phase were investigated in both Fe-43Al-0.12B and Fe-48Al-0.12B alloys. Energy dispersive x-ray and electron energy loss spectroscopy showed that the precipitates contained boron and were enriched in iron. This new boride phase had a tetragonal symmetry, with a{sub t} = 4a{sub B2} and c{sub t} = a{sub B2}, where a{sub B2} is the matrix lattice parameter. The effect of iron content and heat treatments on the microstructure of those two boron-doped FeAl alloys are discussed.

  1. Valence fluctuations of europium in the boride Eu4Pd(29+x)B8.

    PubMed

    Gumeniuk, Roman; Schnelle, Walter; Ahmida, Mahmoud A; Abd-Elmeguid, Mohsen M; Kvashnina, Kristina O; Tsirlin, Alexander A; Leithe-Jasper, Andreas; Geibel, Christoph

    2016-03-23

    We synthesized a high-quality sample of the boride Eu4Pd(29+x)B8 (x  =  0.76) and studied its structural and physical properties. Its tetragonal structure was solved by direct methods and confirmed to belong to the Eu4Pd29B8 type. All studied physical properties indicate a valence fluctuating Eu state, with a valence decreasing continuously from about 2.9 at 5 K to 2.7 at 300 K. Maxima in the T dependence of the susceptibility and thermopower at around 135 K and 120 K, respectively, indicate a valence fluctuation energy scale on the order of 300 K. Analysis of the magnetic susceptibility evidences some inconsistencies when using the ionic interconfigurational fluctuation (ICF) model, thus suggesting a stronger relevance of hybridization between 4f and valence electrons compared to standard valence-fluctuating Eu systems. PMID:26895077

  2. Cobalt-Boride: An efficient and robust electrocatalyst for Hydrogen Evolution Reaction

    NASA Astrophysics Data System (ADS)

    Gupta, Suraj; Patel, Nainesh; Miotello, Antonio; Kothari, D. C.

    2015-04-01

    This work presents Cobalt-Boride (Co-B) as a non-noble, efficient and robust electrocatalyst for Hydrogen Evolution Reaction (HER) active in aqueous solution of wide pH values. In neutral solution, amorphous Co-B nanoparticles (30-50 nm size) generate high current density (10 mA/cm2) at low overpotential (250 mV) with Tafel slope of 75 mV/dec following Volmer-Heyrovsky reaction mechanism. Highly active Co surface sites created by electronic transfer from B to Co (as inferred from XPS analysis and supported by theoretical calculations) are responsible for this significant HER activity in wide range of pH (4-9) values. Stability and reusability tests also demonstrate the robust nature of the catalyst.

  3. Refractory Boride Formation and Microstructure Evolution during Solidification of Titanium-Boron and Titanium Aluminum-Boron Alloys

    NASA Astrophysics Data System (ADS)

    Hyman, Mark Edward

    1990-01-01

    gamma-TiAl alloys targeted for use as a structural material in advanced aerospace applications lack adequate creep strength at high temperatures. Incorporation of hard refractory second phase particles (e.g. TiB _2) exhibiting large aspect ratios (i.e. needles) can increase creep strength by constraining the plastic flow of the matrix during high temperature service. Matrix microstructure evolution and refractory boride formation in binary Ti-B and Ti-(25-52) at% Al and <= ~ 6 at% B alloys during conventional solidification is examined. The effects of rapid solidification processing (RSP) on microstructure evolution and boride morphology in ternary alloys is examined in electromagnetically levitated droplets processed via gas and splat quenching. A liquidus projection near the Ti-Al edge binary is deduced from a combination of computer modelling efforts and experimental evidence. The primary fields of crystallization sequentially traversed with increasing Al content starting from the Ti-B edge binary are: TiB to Ti_3B_4 to TiB_2 and beta to alpha to gamma for B-rich (i.e. ~5 at% B) and dilute alloys, respectively. A monovariant line of the type, L to M + TiB_2 (where M = beta, alpha , and gamma) was found to run slightly below the ~1 at% B isoconcentration line near the equiatomic TiAl composition. Matrix microstructure evolution and boride formation in these ternary alloys can be explained using the proposed liquidus projection for the Ti-Al-B system. TiB_2 forms in Ti-Al-B alloys (i.e. >= 35 at% Al) with various morphologies--blocky, plate/needle and flakes--and are extensively characterized by TEM and SEM. Their growth mechanisms leading to their various morphologies is discussed. Aside from the boride phases formed, the solidification microstructures of the Ti-Al -B alloys of interest showed essentially the same constituent phases as those of binary Ti-Al alloys of similar composition. Characterization of supercooled ternary droplets dilute in B (i.e. <=1 at% B

  4. PREFACE: The 16th International Symposium on Boron, Borides and Related Materials (ISBB 2008)

    NASA Astrophysics Data System (ADS)

    Tanaka, Takaho

    2009-07-01

    This volume of Journal of Physics: Conference Series contains invited and contributed peer-reviewed papers that were presented at the 16th International Symposium on Boron, Borides and Related Materials (ISBB 2008), which was held on 7-12 September 2008, at Kunibiki Messe, Matsue, Japan. This triennial symposium has a half-century long history starting from the 1st meeting in 1959 at Asbury Park, New Jersey. We were very pleased to organize ISBB 2008, which gathered chemists, physicists, materials scientists as well as diamond and high-pressure researchers. This meeting had a strong background in the boron-related Japanese research history, which includes the discovery of superconductivity in MgB2 and development of Nd-Fe-B hard magnets and of YB66 soft X-ray monochromator. The scope of ISBB 2008 spans both basic and applied interdisciplinary research that is centered on boron, borides and related materials, and the collection of articles defines the state of the art in research on these materials. The topics are centered on: 1. Preparation of new materials (single crystals, thin films, nanostructures, ceramics, etc) under normal or extreme conditions. 2. Crystal structure and chemical bonding (new crystal structures, nonstoichiometry, defects, clusters, quantum-chemical calculations). 3. Physical and chemical properties (band structure, phonon spectra, superconductivity; optical, electrical, magnetic, emissive, mechanical properties; phase diagrams, thermodynamics, catalytic activity, etc) in a wide range of temperatures and pressures. 4. Applications and prospects (thermoelectric converters, composites, ceramics, coatings, etc) There were a few discoveries of new materials, such as nanomaterials, and developments in applications. Many contributions were related to 4f heavy Fermion systems of rare-earth borides. Exotic mechanisms of magnetism and Kondo effects have been discussed, which may indicate another direction of development of boride. Two special sessions

  5. A Structural Study of Neptunium-Bearing Uranium Oxides

    NASA Astrophysics Data System (ADS)

    Finch, R. J.

    2002-05-01

    Neptunium is an element of significant concern at several contaminated DOE sites, as well as being potentially the largest long-term contributor of radiation dose to people living near the high-level nuclear-waste repository recently recommended by the President for construction at Yucca Mountain, Nevada. In order to understand potential structural effects of Np substitution into uranium minerals, we have synthesized a series of Np-doped U oxides and present here results of a structural study of Np-doped U3O8 (NpxU3-xO8). Although not a mineral, U3O8 bears significant structural similarities to numerous uranyl minerals with both known and potential importance as radionuclide hosts in the environment (Burns et al., Can. Mineral. 34, 845, 1997). Qualitative chemical analyses of U3O8 powders by energy-dispersive x-ray emission spectroscopy (EDS) in a scanning electron microscope indicate that sample powders are homogeneous at the micrometer scale. Further examinations by electron energy-loss spectroscopy (EELS) and EDS in a transmission electron microscope do not reveal compositional inhomogeneities or discernable variability in the Np:U ratios within samples having Np:U ratios of 1:80 and 1:8. Bulk samples of Np-doped U3O8 powders having Np:U ratios of 1:160, 1:80, 1:25, and 1:8, were also analyzed by X-ray absorption near-edge spectroscopy (XANES), which indicates that Np occupies distorted U sites and is predominantly tetravalent. X-ray powder diffraction (XRD) analyses of pure U3O8 and Np-doped U3O8 show that incorporation of Np into U3O8 affects positions and intensities of diffraction peaks, but that all samples are isostructural with alpha-U3O8. No spurious diffraction peaks are observed in any powder patterns of U3O8 with Np:U from 1:160 to 1:8. Lattice parameters vary smoothly as a function of Np concentration. The c cell parameter (perpendicular to the plane of the structural sheets in U3O8) shows little or no dependence on Np concentration, whereas the a

  6. Boronic Acid Flux Synthesis and Crystal Growth of Uranium and Neptunium Boronates and Borates: A Low Temperature Route to the First Neptunium(V) Borate

    SciTech Connect

    Wang, Shuao; Alekseev, Evgeny V.; Miller, Hannah M.; Depmeier, Wulf; Albrecht-Schmitt, Thomas E.

    2010-10-04

    Molten methylboronic acid has been used as a reactive flux to prepare the first neptunium(V) borate, NpO2[B3O4(OH)2] (NpBO-1), and the first actinide boronate, UO2(CH3BO2)(H2O) (UCBO-1). NpBO-1 contains cation-cation interactions between the neptunyl units. In contrast, the presence of the methyl groups in the uranyl boronate leads to a one-dimensional structure.

  7. Interlayer utilization (including metal borides) for subsequent deposition of NSD films via microwave plasma CVD on 316 and 440C stainless steels

    NASA Astrophysics Data System (ADS)

    Ballinger, Jared

    Diamond thin films have promising applications in numerous fields due to the extreme properties of diamonds in conjunction with the surface enhancement of thin films. Biomedical applications are numerous including temporary implants and various dental and surgical instruments. The unique combination of properties offered by nanostructured diamond films that make it such an attractive surface coating include extreme hardness, low obtainable surface roughness, excellent thermal conductivity, and chemical inertness. Regrettably, numerous problems exist when attempting to coat stainless steel with diamond generating a readily delaminated film: outward diffusion of iron to the surface, inward diffusion of carbon limiting necessary surface carbon precursor, and the mismatch between the coefficients of thermal expansion yielding substantial residual stress. While some exotic methods have been attempted to overcome these hindrances, the most common approach is the use of an intermediate layer between the stainless steel substrate and the diamond thin film. In this research, both 316 stainless steel disks and 440C stainless steel ball bearings were tested with interlayers including discrete coatings and graded, diffusion-based surface enhancements. Titanium nitride and thermochemical diffusion boride interlayers were both examined for their effectiveness at allowing for the growth of continuous and adherent diamond films. Titanium nitride interlayers were deposited by cathodic arc vacuum deposition on 440C bearings. Lower temperature diamond processing resulted in improved surface coverage after cooling, but ultimately, both continuity and adhesion of the nanostructured diamond films were unacceptable. The ability to grow quality diamond films on TiN interlayers is in agreement with previous work on iron and low alloy steel substrates, and the similarly seen inadequate adhesion strength is partially a consequence of the lacking establishment of an interfacial carbide phase

  8. Chemical speciation of neptunium in spent fuel. Annual report for period 15 August 1999 to 15 August 2000

    SciTech Connect

    Ken Czerwinski; Don Reed

    2000-09-01

    (B204) This project will examine the chemical speciation of neptunium in spent nuclear fuel. The R&D fields covered by the project include waste host materials and actinide chemistry. Examination of neptunium is chosen since it was identified as a radionuclide of concern by the NERI workshop. Additionally, information on the chemical form of neptunium in spent fuel is lacking. The identification of the neptunium species in spent fuel would allow a greater scientific based understanding of its long-term fate and behavior in waste forms. Research to establish the application and development of X-ray synchrotrons radiation (XSR) techniques to determine the structure of aqueous, adsorbed, and solid actinide species of importance to nuclear considerations is being conducted at Argonne. These studies extend current efforts within the Chemical Technology Division at Argonne National Laboratory to investigate actinide speciation with more conventional spectroscopic and solids characterization (e.g. SEM, TEM, and XRD) methods. Our project will utilize all these techniques for determining neptunium speciation in spent fuel. We intend to determine the chemical species and oxidation state of neptunium in spent fuel and alteration phases. Different types of spent fuel will be examined. Once characterized, the chemical behavior of the identified neptunium species will be evaluated if it is not present in the literature. Special attention will be given to the behavior of the neptunium species under typical repository near-field conditions (elevated temperature, high pH, varying Eh). This will permit a timely inclusion of project results into near-field geochemical models. Additionally, project results and methodologies have applications to neptunium in the environment, or treatment of neptunium containing waste. Another important aspect of this project is the close cooperation between a university and a national laboratory. The PI has a transuranic laboratory at MIT where

  9. Pt-B System Revisited: Pt2B, a New Structure Type of Binary Borides. Ternary WAl12-Type Derivative Borides.

    PubMed

    Sologub, Oksana; Salamakha, Leonid; Rogl, Peter; Stöger, Berthold; Bauer, Ernst; Bernardi, Johannes; Giester, Gerald; Waas, Monika; Svagera, Robert

    2015-11-16

    On the basis of a detailed study applying X-ray single-crystal and powder diffraction, differential scanning calorimetry, and scanning electron microscopy analysis, it was possible to resolve existing uncertainties in the Pt-rich section (≥65 atom % Pt) of the binary Pt-B phase diagram above 600 °C. The formation of a unique structure has been observed for Pt2B [X-ray single-crystal data: space group C2/m, a = 1.62717(11) nm, b = 0.32788(2) nm, c = 0.44200(3) nm, β = 104.401(4)°, RF2 = 0.030]. Within the homogeneity range of "Pt3B", X-ray powder diffraction phase analysis prompted two structural modifications as a function of temperature. The crystal structure of "hT-Pt3B" complies with the hitherto reported structure of anti-MoS2 [space group P63/mmc, a = 0.279377(2) nm, c = 1.04895(1) nm, RF = 0.075, RI = 0.090]. The structure of the new "[Formula: see text]T-Pt3B" is still unknown. The formation of previously reported Pt∼4B has not been confirmed from binary samples. Exploration of the Pt-rich section of the Pt-Cu-B system at 600 °C revealed a new ternary compound, Pt12CuB6-y [X-ray single-crystal data: space group Im3̅, a = 0.75790(2) nm, y = 3, RF2 = 0.0129], which exhibits the filled WAl12-type structure accommodating boron in the interstitial trigonal-prismatic site 12e. The isotypic platinum-aluminum-boride was synthesized and studied. The solubility of copper in binary platinum borides has been found to attain ∼7 atom % Cu for Pt2B but to be insignificant for "[Formula: see text]T-Pt3B". The architecture of the new Pt2B structure combines puckered layers of boron-filled and empty [Pt6] octahedra (anti-CaCl2-type fragment) alternating along the x axis with a double layer of boron-semifilled [Pt6] trigonal prisms interbedded with a layer of empty tetrahedra and tetragonal pyramids (B-deficient α-T[Formula: see text]I fragment). Assuming boron vacancies ordering (space group R3), the Pt12CuB6-y structure exhibits serpentine-like columns of edge

  10. Long-term desorption behavior of uranium and neptunium in heterogeneous volcanic tuff materials /

    SciTech Connect

    Dean, Cynthia A.

    2010-05-01

    Uranium and neptunium desorption were studied in long-term laboratory experiments using four well-characterized volcanic tuff cores collected from southeast of Yucca Mountain, Nevada. The objectives of the experiments were to 1. Demonstrate a methodology aimed at characterizing distributions of sorption parameters (attributes of multiple sorption sites) that can be applied to moderately-sorbing species in heterogeneous systems to provide more realistic reactive transport parameters and a more realistic approach to modeling transport in heterogeneous systems. 2. Focus on uranium and neptunium because of their high solubility, relatively weak sorption, and high contributions to predicted dose in Yucca Mountain performance assessments. Also, uranium is a contaminant of concern at many DOE legacy sites and uranium mining sites.

  11. Development of Defined, Minimal, and Complete Media for the Growth of Hyphomicrobium neptunium

    PubMed Central

    Havenner, Jeffrey A.; McCardell, Barbara A.; Weiner, Ronald M.

    1979-01-01

    A complete synthetic medium containing 15 amino acids, a minimal synthetic medium (GAMS) containing 4 amino acids, and a supplemented minimal medium (GAMS + calcium pantothenate) have been developed for the cultivation of Hyphomicrobium neptunium ATCC 15444. Depending on the complexity of the synthetic media, generation times were approximately 2 to 3 times longer, and maximum cell densities were 0.3 to 0.9 log10 lower than in ZoBell marine broth 2216. The fates of 14C-labeled amino acids in GAMS were monitored. Results suggested that H. neptunium was auxotrophic for methionine, utilized glutamic acid as a primary energy source, and readily anabolized and catabolized serine and aspartic acid. Individual amino acid concentrations above 125 mM induced prolonged lag periods, whereas only methionine was not growth limiting at a concentration as low as 2 mM. PMID:16345413

  12. Kinetics of oxidation of pentavalent neptunium by pentavalent vanadium in solutions of nitric acid

    NASA Astrophysics Data System (ADS)

    Precek, Martin; Paulenova, Alena

    2010-03-01

    Management of the oxidation state of neptunium in the reprocessing of spent nuclear fuel by solvent extraction is very important. The kinetics of the oxidation of neptunium(V) by vanadium(V) in solutions of nitrate acid was investigated at constant ionic strength 4M. The reaction rate is first order with respect to Np(V) and V(V). The effects of proton concentration on the apparent second order rate constant k1" was determined for temperature 25°C as k1" = (0.99±0.03)·[H+]1.21M-1s-1. Activation parameters associated with the overall reaction have been calculated; the standard reaction enthalpy and entropy were 52.6±0.9 kJ/mol and -55.8±0.9 J/K/mol respectively.

  13. Theoretical studies on level structures and transition properties of neptunium ions

    NASA Astrophysics Data System (ADS)

    Zhou, W. D.; Dong, C. Z.; Wang, Q. M.; Wang, X. L.; Saber, I. A.

    2012-10-01

    Multiconfiguration Dirac-Fock (MCDF) method was employed to calculate the ionization potentials, ionic radii, excitation energies and oscillator strengths for neptunium ions. In the calculations, main valence correlation effects, Breit interaction and QED effects were taken into account. The good consistency with other available theoretical values demonstrates the validity of the present calculations. These theoretical results therefore can be used to predict some physicochemical properties of Np and its oxides.

  14. Comparison of sample preparation methods for reliable plutonium and neptunium urinalysis using automatic extraction chromatography.

    PubMed

    Qiao, Jixin; Xu, Yihong; Hou, Xiaolin; Miró, Manuel

    2014-10-01

    This paper describes improvement and comparison of analytical methods for simultaneous determination of trace-level plutonium and neptunium in urine samples by inductively coupled plasma mass spectrometry (ICP-MS). Four sample pre-concentration techniques, including calcium phosphate, iron hydroxide and manganese dioxide co-precipitation and evaporation were compared and the applicability of different techniques was discussed in order to evaluate and establish the optimal method for in vivo radioassay program. The analytical results indicate that the various sample pre-concentration approaches afford dissimilar method performances and care should be taken for specific experimental parameters for improving chemical yields. The best analytical performances in terms of turnaround time (6h) and chemical yields for plutonium (88.7 ± 11.6%) and neptunium (94.2 ± 2.0%) were achieved by manganese dioxide co-precipitation. The need of drying ashing (≥ 7h) for calcium phosphate co-precipitation and long-term aging (5d) for iron hydroxide co-precipitation, respectively, rendered time-consuming analytical protocols. Despite the fact that evaporation is also somewhat time-consuming (1.5d), it endows urinalysis methods with better reliability and repeatability compared with co-precipitation techniques. In view of the applicability of different pre-concentration techniques proposed previously in the literature, the main challenge behind relevant method development is pointed to be the release of plutonium and neptunium associated with organic compounds in real urine assays. In this work, different protocols for decomposing organic matter in urine were investigated, of which potassium persulfate (K2S2O8) treatment provided the highest chemical yield of neptunium in the iron hydroxide co-precipitation step, yet, the occurrence of sulfur compounds in the processed sample deteriorated the analytical performance of the ensuing extraction chromatographic separation with chemical

  15. Pre-irradiation spatial distribution and stability of boride particles in rapidly solidified boron-doped stainless steels

    SciTech Connect

    Kanani, N.; Arnberg, L.; Harling, O.K.

    1981-01-01

    The time temperature behavior of boride particles has been studied in rapidly solidified ultra low carbon and nitrogen modified 316 stainless steel with 0.088% boron and 0.45% zirconium. The results show that the as-splat-cooled specimens exhibit precipitates at the grain boundaries and triple junctions. For temperatures up to about 750/sup 0/C no significant microstructural changes occur for short heat treatment times. In the temperature range of 750 to 950/sup 0/C, however, particles typically 100 to 500 A in diameter containing Zr and B are formed within the grains. Higher temperatures enhance the formation of such particles and give rise to particle networks. The results show that a fine and uniform distribution of the boride particles almost exclusively within the grains can be achieved if proper annealing conditions are chosen. This type of distribution is an important requirement for the homogeneous production of helium during neutron irradiation in fast reactors.

  16. Synthesis and characterization of nitrogen-phosphorus-based fire retardants modified by boride/propanetriol flyeidyl ether complex

    NASA Astrophysics Data System (ADS)

    Kang, Haijiao; Ma, Linrong; Zhang, Shifeng; Li, Jianzhang

    2015-07-01

    A Boride/propanetriol glyeidyl ether (B/PTGE) complex was employed to intensify the fire resistance capabilities of nitrogen-phosphorus (NP) fire retardants by reacting with phosphoric acid and urea to yield nitrogen-phosphorus-boron-PTGE fire retardants. The effects of NPB-PTGE fire retardants on wooden properties were characterized by limit oxygen index (LOI), cone calorimetry, X-ray Diffraction (XRD) and scanning electron microscopy (SEM). The results depict that the fire resistance of the B/PTGE complex modified by NP-based fire retardants was improved significantly. The PTGE was at 10% boride at 2%, and the treated wood has the LOI of 52%, which is 11.46% higher compared with woods treated with NP fire retardant.

  17. Influence of dissolved organic substances in groundwater on sorption behavior of americium and neptunium

    SciTech Connect

    Boggs, S. Jr.; Seitz, M.G.

    1984-01-01

    Groundwaters typically contain dissolved organic carbon consisting largely of high molecular weight compounds of humic and fulvic acids. To evaluate whether these dissolved organic substances can enhance the tranport of radionuclides through the groundwater system, experiments were conducted to examine the sorption of americium and neptunium onto crushed basalt in the presence of dissolved humic- and fulvic-acid organic carbon introduced into synthetic groundwater. The partitioning experiments with synthetic groundwater show that increasing the concentration of either humic or fulvic acid in the water has a significant inhibiting effect on sorption of both americium and neptunium. At 22/sup 0/C, adsorption of these radionuclides, as measured by distribution ratios (the ratio of nuclide sorbed onto the solid to nuclide in solution at the end of the experiment), decreased by 25% to 50% by addition of as little as 1 mg/L dissolved organic carbon and by one to two orders of magnitude by addition of 100 to 200 mg/L dissolved organic carbon. Distribution ratios measured in solutions reacted at 90/sup 0/C similarly decreased with the addition of dissolved organic carbon but generally ranged from one to two orders of magnitude higher than those determined in the 22/sup 0/C experiment. These results suggest that organic carbon dissolved in deep groundwaters may significantly enhance the mobility of radionuclides of americium and neptunium. 23 references, 5 figures, 11 tables.

  18. Molecular toolbox for genetic manipulation of the stalked budding bacterium Hyphomonas neptunium.

    PubMed

    Jung, Alexandra; Eisheuer, Sabrina; Cserti, Emöke; Leicht, Oliver; Strobel, Wolfgang; Möll, Andrea; Schlimpert, Susan; Kühn, Juliane; Thanbichler, Martin

    2015-01-01

    The alphaproteobacterium Hyphomonas neptunium proliferates by a unique budding mechanism in which daughter cells emerge from the end of a stalk-like extension emanating from the mother cell body. Studies of this species so far have been hampered by the lack of a genetic system and of molecular tools allowing the regulated expression of target genes. Based on microarray analyses, this work identifies two H. neptunium promoters that are activated specifically by copper and zinc. Functional analyses show that they have low basal activity and a high dynamic range, meeting the requirements for use as a multipurpose expression system. To facilitate their application, the two promoters were incorporated into a set of integrative plasmids, featuring a choice of two different selection markers and various fluorescent protein genes. These constructs enable the straightforward generation and heavy metal-inducible synthesis of fluorescent protein fusions in H. neptunium, thereby opening the door to an in-depth analysis of polar growth and development in this species. PMID:25398860

  19. Effects of Titanium Doping in Titanomagnetite on Neptunium Sorption and Speciation.

    PubMed

    Wylie, E Miller; Olive, Daniel T; Powell, Brian A

    2016-02-16

    Neptunium-237 is a radionuclide of great interest owing to its long half-life (2.14 × 10(6) years) and relative mobility as the neptunyl ion (NpO2(+)) under many surface and groundwater conditions. Reduction to tetravalent neptunium (Np(IV)) effectively immobilizes the actinide in many instances due to its low solubility and strong interactions with natural minerals. One such mineral that may facilitate the reduction of neptunium is magnetite (Fe(2+)Fe(3+)2O4). Natural magnetites often contain titanium impurities which have been shown to enhance radionuclide sorption via titanium's influence on the Fe(2+)/Fe(3+) ratio (R) in the absence of oxidation. Here, we provide evidence that Ti-substituted magnetite reduces neptunyl species to Np(IV). Titanium-substituted magnetite nanoparticles were synthesized and reacted with NpO2(+) under reducing conditions. Batch sorption experiments indicate that increasing Ti concentration results in higher Np sorption/reduction values at low pH. High-resolution transmission electron microscopy of the Ti-magnetite particles provides no evidence of NpO2 nanoparticle precipitation. Additionally, X-ray absorption spectroscopy confirms the nearly exclusive presence of Np(IV) on the titanomagnetite surface and provides supporting data indicating preferential binding of Np to terminal Ti-O sites as opposed to Fe-O sites. PMID:26756748

  20. Molecular Toolbox for Genetic Manipulation of the Stalked Budding Bacterium Hyphomonas neptunium

    PubMed Central

    Jung, Alexandra; Eisheuer, Sabrina; Cserti, Emöke; Leicht, Oliver; Strobel, Wolfgang; Möll, Andrea; Schlimpert, Susan; Kühn, Juliane

    2014-01-01

    The alphaproteobacterium Hyphomonas neptunium proliferates by a unique budding mechanism in which daughter cells emerge from the end of a stalk-like extension emanating from the mother cell body. Studies of this species so far have been hampered by the lack of a genetic system and of molecular tools allowing the regulated expression of target genes. Based on microarray analyses, this work identifies two H. neptunium promoters that are activated specifically by copper and zinc. Functional analyses show that they have low basal activity and a high dynamic range, meeting the requirements for use as a multipurpose expression system. To facilitate their application, the two promoters were incorporated into a set of integrative plasmids, featuring a choice of two different selection markers and various fluorescent protein genes. These constructs enable the straightforward generation and heavy metal-inducible synthesis of fluorescent protein fusions in H. neptunium, thereby opening the door to an in-depth analysis of polar growth and development in this species. PMID:25398860

  1. Complexation of neptunium(V) with fluoride in aqueous solutions at elevated temperatures

    SciTech Connect

    Tian, Guoxin; Rao, Linfeng; Xia, Yuanxian; Friese, Judah I.

    2009-02-01

    Over the past several decades, the production and testing of nuclear weapons in the U.S. have created significant amounts of high-level nuclear wastes (HLW) that are currently stored in underground tanks across the U.S. DOE (Department of Energy) sites. Eventually, the HLW will be made into the waste form and disposed of in geological repositories for HLW. Among the radioactive materials, neptunium is of great concern in the post-closure chemical environment in the repository because of the long half-life of 237Np (2.14•106 years) and the high mobility of Np(V), the most stable oxidation state of neptunium. It is estimated that 237Np, together with 129I and 99Tc, will be the major contributors to the potential total annual dose from the repository beyond 10000 years [1]. Due to the high radiation energy released from the HLW, the postclosure repository is expected to remain at elevated temperatures for thousands of years [1]. If the waste package is breached and becomes in contact with groundwater, neptunium, as well as other radioactive materials will be in aqueous solutions at elevated temperatures. Interactions of radioactive materials with the chemical components in groundwater play an important role in determining their migration in the repository. To predict the migration behavior of neptunium, it is necessary to have sufficient and reliable thermodynamic data on its complexation with the ligands that are present in the groundwater of the repository (e.g., OH–, F–, SO42– ,PO43– and CO32) at elevated temperatures. However, such data are scarce and scattered for 25°C, and nearly nonexistent for elevated temperatures [2]. To provide reliable thermodynamic data, we have conducted investigations of the complexation of actinides, including thorium, uranium, neptunium and plutonium, at elevated temperatures. Thermodynamic parameters, including formation constants, enthalpy and heat capacity of complexation are experimentally determined. This paper

  2. Mineralogic controls on aqueous neptunium(V) concentrations in silicate systems

    NASA Astrophysics Data System (ADS)

    Alessi, Daniel S.; Szymanowski, Jennifer E. S.; Forbes, Tori Z.; Quicksall, Andrew N.; Sigmon, Ginger E.; Burns, Peter C.; Fein, Jeremy B.

    2013-02-01

    The presence of radioactive neptunium in commercially spent nuclear fuel is problematic due to its mobility in environmental systems upon oxidation to the pentavalent state. As uranium is the major component of spent fuel, incorporation of neptunium into resulting U(VI) mineral phases would potentially influence its release into environmental systems. Alternatively, aqueous neptunium concentrations may be buffered by solid phase Np2O5. In this study, we investigate both of these controls on aqueous neptunium(V) concentrations. We synthesize two uranyl silicates, soddyite, (UO2)2SiO4·2H2O, and boltwoodite, (K, Na)(UO2)(SiO3OH)·1.5H2O, each in the presence of two concentrations of aqueous Np(V). Electron microscopy and electron diffraction analyses of the synthesized phases show that while significant neptunyl incorporation occurred into soddyite, the Np(V) in the boltwoodite systems largely precipitated as a secondary phase, Np2O5(s). The release of Np(V) from each system into aqueous solution was measured for several days, until steady-state concentrations were achieved. Using existing solubility constants (Ksp) for pure soddyite and boltwoodite, we compared predicted equilibrium aqueous U(VI) concentrations with the U(VI) concentrations released in the solubility experiments. Our experiments reveal that Np(V) incorporation into soddyite increases the concentration of aqueous U in equilibrium with the solid phase, perhaps via the formation of a metastable phase. In the mixed boltwoodite - Np2O5(s) system, the measured aqueous U(VI) activities are consistent with those predicted to be in equilibrium with boltwoodite under the experimental conditions, a result that is consistent with our conclusion that little Np(V) incorporation occurred into the boltwoodite. In the boltwoodite systems, the measured Np concentrations are likely controlled by the presence of Np2O5 nanoparticles, suggesting an additional potential mobility vector for Np in geologic systems. Our

  3. EVALUATING EFFECTS OF NEPTUNIUM ON THE SRS METHOD FOR CONTROLLED POTENTIAL COULOMETRIC ASSAY OF PLUTONIUM IN SULFURIC ACID SUPPORTING ELECTROLYTE

    SciTech Connect

    Holland, M; Sheldon Nichols, S

    2008-05-09

    A study of the impact of neptunium on the coulometric assay of plutonium in dilute sulfuric acid was performed. Weight aliquots of plutonium standard solutions were spiked with purified neptunium solution to evaluate plutonium measurement performance for aliquots with Pu:Np ratios of 50:1, 30:1, 20:1, 15:1, and 10:1. Weight aliquots of the pure plutonium standard solution were measured as controls. Routine plutonium instrument control standards were also measured. The presence of neptunium in plutonium aliquots significantly increases the random uncertainty associated with the plutonium coulometric measurement performed in accordance with ISO12183:2005.7 However, the presence of neptunium does not appear to degrade electrode performance and conditioning as aliquots of pure plutonium that were interspersed during the measurement of the mixed Pu:Np aliquots continued to achieve the historical short-term random uncertainty for the method. Lack of adequate control of the neptunium oxidation state is suspected to be the primary cause of the elevated measurement uncertainty and will be pursued in a future study.

  4. Suppression of Boride Formation in Transient Liquid Phase Bonding of Pairings of Parent Superalloy Materials with Different Compositions and Grain Structures and Resulting Mechanical Properties

    NASA Astrophysics Data System (ADS)

    Steuer, Susanne; Singer, Robert F.

    2014-07-01

    Two Ni-based superalloys, columnar grained Alloy 247 and single-crystal PWA1483, are joined by transient liquid phase bonding using an amorphous brazing foil containing boron as a melting point depressant. At lower brazing temperatures, two different morphologies of borides develop in both base materials: plate-like and globular ones. Their ratio to each other is temperature dependent. With very high brazing temperatures, the deleterious boride formation in Alloy 247 can be totally avoided, probably because the three-phase-field moves to higher alloying element contents. For the superalloy PWA1483, the formation of borides cannot be completely avoided at high brazing temperatures as incipient melting occurs. During subsequent solidification of these areas, Chinese-script-like borides precipitate. The mechanical properties (tensile tests at room and elevated temperatures and short-term creep rupture tests at elevated temperatures) for brazed samples without boride precipitation are very promising. Tensile strengths and creep times to 1 pct strain are comparable, respectively, higher than the ones of the weaker parent material for all tested temperatures and creep conditions (from 90 to 100 pct rsp. 175 to 250 pct).

  5. Preliminary investigation of zirconium boride ceramals for gas-turbine blade applications

    NASA Technical Reports Server (NTRS)

    Hoffman, Charles A

    1953-01-01

    Zirconium boride ZrB2 ceramals were investigated for possible gas-turbine-blade application. Included in the study were thermal shock evaluations of disks, preliminary turbine-blade operation, and observations of oxidation resistance. Thermal shock disks of the following three compositions were studied: (a) 97.5 percent ZrB2 plus 2.5 percent B by weight; (b) 92.5 percent ZrB2 plus 7.5 percent B by weight; and (c) 100 percent ZrB2. Thermal shock disks were quenched from temperatures of 1800 degrees, 2000 degrees, 2200 degrees, and 2400 degrees F. The life of turbine blades containing 93 percent ZrB2 plus 7 percent B by weight was determined in gas-turbine tests. The blades were run at approximately 1600 degrees F and 15,000 to 26,000 rpm. The thermal shock resistance of the 97.5 percent ZrB2 plus 2.5 percent boron ceramals compares favorably with that of TiC plus Co and TiC plus Ni ceramals. Oxidation of the disks during the thermal shock evaluation was slight for the comparatively short time (8.3 hr) up through 2000 degrees F. Oxidation of a specimen was severe, however, after 100 hours at 2000 degrees F. The turbine blade performance evaluation of the 93 percent ZrB2 plus 7 percent B composition was preliminary in scope ; no conclusions can be drawn.

  6. Mechanical properties of laser-deposited composite boride coating using nanoindentation

    SciTech Connect

    Agarwal, A.; Dahotre, N.B.

    2000-02-01

    Nanoindentation proves to be an effective technique to measure mechanical properties of composite materials, as it has high spatial resolution that enables estimation of properties even from fine grains, particles, and precipitates. The elastic modulus, E, of the composite boride coating deposited on AISI 1010 steel using the laser surface engineering (LSE) process has been computed using the nanoindentation technique. The highest E value of 477.3 GPa was achieved for coating in a sample that contained 0.69 volume fraction of TiB{sub 2} particles in the coating after processing with the highest laser traverse speed of 33 mm/s. A comparison between the theoretical and experimental computation of the elastic modulus suggests that theoretical elastic modulus values are lower than computed elastic modulus, as the latter includes the effect of dissolution of fine TiB{sub 2} particles in Fe matrix and metastable phase formation such as Fe{sub a}B{sub b} and Ti{sub m}B{sub n}. Dissolution of fine TiB{sub 2} particles in the Fe matrix in the coating region has been corroborated by transmission electron microscope (TEM) micrographs and corresponding energy-dispersive spectroscope (EDS) analysis and selected area diffraction (SAD) pattern.

  7. High borides: determining the features and details of lattice dynamics from neutron spectroscopy

    NASA Astrophysics Data System (ADS)

    Alekseev, P. A.

    2015-04-01

    We review wide-ranging research that combines inelastic neutron scattering spectroscopy with phenomenological and ab initio calculations to study the lattice dynamics and specifics of the electron-phonon interaction in three-dimensional boron cluster network systems M B_6 and M B12 ( M= {La}, {Sm}, and {Yb}, {Lu}, {Zr}). A close similarity is found between the atomic vibration spectra of these systems, which is fundamentally due to a strong hierarchy of interatomic interaction in these systems and which manifests itself both in the shape of the low-energy phonon dispersion and in the position of the high-energy edge of the spectrum. Manifestations of strong electron-phonon interactions in the lattice vibration spectra of borides are studied in detail and their relation to the nature and features of the valence-unstable state of rare-earth ions is examined. Resonance nonadiabaticity and magnetovibration interaction effects in spin- and valence-fluctuating systems are given special attention.

  8. Electronic spectra and magnetic properties of RB6, RB12 and RB2C2 borides

    NASA Astrophysics Data System (ADS)

    Baranovskiy, A. E.; Grechnev, G. E.; Logosha, A. V.; Svechkarev, I. V.; Filippov, V. B.; Shitsevalova, N. Yu.; Oga, O. J.; Eriksson, O.

    2006-01-01

    The electronic structures of R B6, R B12 and R B2C2 borides are studied ab initio by using the full-potential linear muffin-tin orbital method. This study includes the promising materials for spin electronics with reported high temperature ferromagnetism, namely, doped divalent hexaborides CaB6, SrB6, BaB6, and the CaB2C2 compound, as well as Kondo semiconductors, SmB6 and YbB12. For CaB6 and SrB6 a semiconducting band structure has been obtained, whereas a semimetallic ground state is revealed for CaB2C2 and doped hexaborides. For YB6, LaB6, CaB2C2 and the semimetallic Ba1-x Lax B6 alloys we have performed spin-polarized band structure calculations in an external field to evaluate the induced spin and orbital magnetic moments. These calculations indicate a feasibility of the field-induced weak ferromagnetic phase in CaB2C2 and the La doped hexaborides. The LSDA and GGA calculations for different spin configurations of YbB12 point to a possibility of antiferromagnetic coupling between Yb3+ ions. For SmB6 and YbB12 our LSDA, GGA, and LSDA+U calculations have not revealed the hybridization gap for configurations with trivalent Sm3+ and Yb3+.

  9. Charge-Driven Structural Transformation and Valence Versatility of Boron Sheets in Magnesium Borides

    NASA Astrophysics Data System (ADS)

    Zhao, Yufeng; Ban, Chunmei; Xu, Qiang; Wei, Suhuai; Dillon, Anne C.; National Renewable Energy Laboratory Team

    2011-03-01

    We show here that boron sheets exhibit highly versatile valence and the layered boron materials may hold the promise for a high energy-density magnesium-ion battery. Practically, boron is superior to previously known multi-valence materials, especially transition metal compounds, which are heavy, expensive, and often not benign. Based on Density Functional Theory simulations, we have predicted a series of stable magnesium borides MgBx with a broad range of stoichiometries, 2 x <= 16, by removing magnesium atoms from MgB2. The layered boron structures are preserved through an in-plane topological transformation between the hexagonal lattice domains and triangular domains. The process can be reversibly switched as the charge transfer changes with Mg insertion/extraction. The mechanism of such a charge-driven transformation originates from the versatile valence state of boron in its planar form. The discovery of these new physical phenomena suggests the design of a high-capacity magnesium-boron battery. Funded by the U.S. Department of Energy under subcontract number DE-AC36-08GO28308 through: DOE Office of Energy Efficiency and Renewable Energy Office of the Vehicle Technologies Program.

  10. EFFECT OF COMPOSITION OF SELECTED GROUNDWATERS FROM THE BASIN AND RANGE PROVINCE ON PLUTONIUM, NEPTUNIUM, AND AMERICIUM SPECIATION.

    USGS Publications Warehouse

    Rees, Terry F.; Cleveland, Jess M.; Nash, Kenneth L.

    1984-01-01

    The speciation of plutonium, neptunium, and americium was determined in groundwaters from four sources in the Basin and Range Province: the lower carbonate aquifer, Nevada Test Site (NTS) (Crystal Pool); alluvial fill, Frenchman Flat, NTS (well 5C); Hualapai Valley, Arizona (Red Lake south well); and Tularosa Basin, New Mexico (Rentfrow well). The results were interpreted to indicate that plutonium and, to a lesser extent, neptunium are least soluble in reducing groundwaters containing a large concentration of sulfate ion and a small concentration of strongly complexing anions. The results further emphasize the desirability of including studies such as this among the other site-selection criteria for nuclear waste repositories.

  11. Crystal and Electronic Structures of Neptunium Nitrides Synthesized Using a Fluoride Route

    SciTech Connect

    Silva, G W Chinthaka M; Weck, Dr. Phil F.; Eunja, Dr. Kim; Yeamans, Dr. Charles B.; Cerefice, Gary S.; Sattelberger, Alfred P; Czerwinski, Ken R.

    2012-01-01

    A low-temperature fluoride route was utilized to synthesize neptunium mononitride, NpN. Through the development of this process, two new neptunium nitride species, NpN{sub 2} and Np{sub 2}N{sub 3}, were identified. The NpN{sub 2} and Np{sub 2}N{sub 3} have crystal structures isomorphous to those of UN{sub 2} and U{sub 2}N{sub 3}, respectively. NpN{sub 2} crystallizes in a face-centered cubic CaF{sub 2}-type structure with a space group of Fm3m and a refined lattice parameter of 5.3236(1) {angstrom}. The Np{sub 2}N{sub 3} adopts the body-centered cubic Mn{sub 2}O{sub 3}-type structure with a space group of Ia{bar 3}. Its refined lattice parameter is 10.6513(4) {angstrom}. The NpN synthesis at temperatures {le} 900 C using the fluoride route discussed here was also demonstrated. Previous computational studies of the neptunium nitride system have focused exclusively on the NpN phase because no evidence was reported experimentally on the presence of NpN{sub x} systems. Here, the crystal structures of NpN{sub 2} and Np{sub 2}N{sub 3} are discussed for the first time, confirming the experimental results by density functional calculations (DFT). These DFT calculations were performed within the local-density approximation (LDA+U) and the generalized-gradient approximation (GGA+U) corrected with an effective Hubbard parameter to account for the strong on-site Coulomb repulsion between Np 5f electrons. The effects of the spin-orbit coupling in the GGA+U calculations have also been investigated for NpN{sub 2} and NpN.

  12. Crystal and electronic structures of neptunium nitrides synthesized using a fluoride route.

    PubMed

    Silva, G W Chinthaka; Weck, Philippe F; Kim, Eunja; Yeamans, Charles B; Cerefice, Gary S; Sattelberger, Alfred P; Czerwinski, Kenneth R

    2012-02-15

    A low-temperature fluoride route was utilized to synthesize neptunium mononitride, NpN. Through the development of this process, two new neptunium nitride species, NpN(2) and Np(2)N(3), were identified. The NpN(2) and Np(2)N(3) have crystal structures isomorphous to those of UN(2) and U(2)N(3), respectively. NpN(2) crystallizes in a face-centered cubic CaF(2)-type structure with a space group of Fm3m and a refined lattice parameter of 5.3236(1) Å. The Np(2)N(3) adopts the body-centered cubic Mn(2)O(3)-type structure with a space group of Ia3. Its refined lattice parameter is 10.6513(4) Å. The NpN synthesis at temperatures ≤900 °C using the fluoride route discussed here was also demonstrated. Previous computational studies of the neptunium nitride system have focused exclusively on the NpN phase because no evidence was reported experimentally on the presence of NpN(x) systems. Here, the crystal structures of NpN(2) and Np(2)N(3) are discussed for the first time, confirming the experimental results by density functional calculations (DFT). These DFT calculations were performed within the local-density approximation (LDA+U) and the generalized-gradient approximation (GGA+U) corrected with an effective Hubbard parameter to account for the strong on-site Coulomb repulsion between Np 5f electrons. The effects of the spin-orbit coupling in the GGA+U calculations have also been investigated for NpN(2) and NpN. PMID:22280303

  13. The synthesis and characterization of neptunium hydroxysulfate, Np(OH)/sub 2/SO/sub 4/

    SciTech Connect

    Wester, D.W.; Mulak, J.; Banks, R.; Carnall, W.T.

    1982-11-15

    Neptunium (IV) hydroxysulfate, Np(OH)/sub 2/SO/sub 4/, was synthesized using hydrothermal techniques. The X-ray powder diffraction pattern indicates that the compound is isomorphous with the Th(IV) and U(IV) analogs. Cell constants for the three compounds clearly show the effects of the actinide contraction. Visible and near-ir spectra are consistent with the presence of Np(IV) and are compared to spectra of Np(IV) in acidic solution. The ir spectrum contains bands which are assigned to the hydroxy and sulfate groups.

  14. Gastrointestinal absorption of plutonium, uranium and neptunium in fed and fasted adult baboons: Application to humans

    SciTech Connect

    Bhattacharyya, M.H.; Larsen, R.P.; Oldham, R.D.; Moretti, E.S. ); Cohen, N.; Ralston, L.G.; Ayres, L. )

    1992-03-01

    Gastrointestinal (GI) absorption values of plutonium, uranium, and neptunium were determined in fed and fasted adult baboons. A dual isotope method of determining GI absorption, which does not require animal sacrifice, was validated and shown to compare well with the sacrifice method (summation of oral isotope in urine with that in tissues at sacrifice). For all three elements, mean GI absorption values were significantly high (5- to 50-fold) in 24-hour (h)-fasted animals than in fed animals, and GI absorption values for baboons agreed well with those for humans.

  15. Determination of neptunium in environmental samples by extraction chromatography after valence adjustment.

    PubMed

    Guérin, Nicolas; Langevin, Marc-Antoine; Nadeau, Kenny; Labrecque, Charles; Gagné, Alexandre; Larivière, Dominic

    2010-12-01

    Neptunium(V) ions are unstable in acid media, which limits their extraction on chromatographic resins. We developed a novel analytical method to measure Np by either α-spectrometry or inductively coupled plasma mass spectrometry (ICP-MS) after extraction chromatography as Np(VI). We investigated the reactivity of various oxidizing reagents, and determined the retention capacity of Np(IV, V, and VI) on various extraction chromatographic supports. A simple method using two UTEVA resins was used to rapidly detect Np in soil and sediment samples. PMID:20630769

  16. Unusual redox stability of neptunium in the ionic liquid [Hbet][Tf(2)N].

    PubMed

    Long, Kristy; Goff, George; Runde, Wolfgang

    2014-07-25

    The behavior of neptunium in the ionic liquid betaine bistriflimide, [Hbet][Tf2N], has been studied spectroscopically at room temperature and 60 °C for the first time. An unprecedented complex redox chemistry is observed, with up to three oxidation states (iv, v and vi) and up to six Np species existing simultaneously. Both redox reactions and coordination of betaine are observed for Np(iv), (v) and (vi). Elevating the temperature accelerates the coordination of Np(v) with betaine and reduction reactions slow down. PMID:24752760

  17. Peak Stripping Methodology for Plutonium Analysis in the Presence of Neptunium

    SciTech Connect

    Hodge, Christ

    2005-05-17

    Quantitative Plutonium analysis depends upon the accurate identification of the assay peak. The Np[Pa] equilibrium pair introduces interfering peaks in {sup 239}Pu, {sup 238}Pu, and {sup 235}U assay peak region. When an interfering peak is present, it negates the assay unless an appropriate technique can be developed to deal with the interference. Peak Stripping is one such technique. Peak stripping involves an algorithm to strip an entire peak from another, resulting in a spectrum that can then be analyzed for the isotope of interest. A simpler method is a ''pseudo-peak-stripping'' whereby the effects of the interfering peak are quantified and those effects are stripped from the assay data. In this case the integrated peak areas are analyzed and corrected. There are two methods presented in this paper. Both assimilate the integrated data for the assay peak regions (in this case {sup 238}Pu, {sup 239}Pu, and {sup 235}U) and for the Neptunium/Protactinium secular equilibrium pair (Np[Pa]). Using Np[Pa] assumes that the Protactinium has come to equilibrium with Neptunium. This requires only {approx}6 months from the time chemical purification. Therefore it is a valid assumption in most cases. A correction is then applied to the assay peak areas to ''strip'' the underlying effects of Np[Pa].

  18. Electronic structure of the Np MT 5 ( M = Fe, Co, Ni; T = Ga, In) series of neptunium compounds

    NASA Astrophysics Data System (ADS)

    Lukoyanov, A. V.; Shorikov, A. O.; Anisimov, V. I.

    2016-03-01

    Evolution of the electronic structure of the Np MGa5 ( M = Fe, Co, Ni) series of neptunium compounds, whose crystal structure is similar to that of the known family of Pu115 superconductors, was studied by the LDA + U + SO method. The calculations took into account both the strong electron correlations and the spin‒orbit coupling in the 5 f shell of neptunium. For the first time, the electronic structure was calculated for a hypothetical series of compounds in which gallium is replaced with indium. Parameters of the crystal structure of the given series were obtained using the relationship between the parameters of the crystal structure of the earlier-studied compounds PuCoGa5 and PuCoIn5. The analysis of the electronic structure and characteristics of neptunium ions calculated in the framework of the LDA + U + SO method showed that the neptunium ions in Np MIn5 with M = Fe, Co, and Ni should have an electron configuration closer to f 4, but a spin and magnetic characteristics close to those in Np MGa5.

  19. PROCESS FOR EXTRACTING NEPTUNIUM AND PLUTONIUM FROM NITRIC ACID SOLUTIONS OF SAME CONTAINING URANYL NITRATE WITH A TERTIARY AMINE

    DOEpatents

    Sheppard, J.C.

    1962-07-31

    A process of selectively extracting plutonium nitrate and neptunium nitrate with an organic solution of a tertiary amine, away from uranyl nitrate present in an aqueous solution in a maximum concentration of 1M is described. The nitric acid concentration is adjusted to about 4M and nitrous acid is added prior to extraction. (AEC)

  20. Nano-Borides and Silicide Dispersed Composite Coating on AISI 304 Stainless Steel by Laser-Assisted HVOF Spray Deposition

    NASA Astrophysics Data System (ADS)

    Sharma, Prashant; Majumdar, Jyotsna Dutta

    2014-10-01

    The study concerned a detailed microstructural investigation of nano-borides (Cr2B and Ni3B) and nano-silicide (Ni2Si) dispersed γ-nickel composite coating on AISI 304 stainless steel by HVOF spray deposition of the NiCrBSi precursor powder and subsequent laser surface melting. A continuous wave diode laser with an applied power of 3 kW and scan speed of 20 mm/s in argon shroud was employed. The characterization of the surface in terms of microstructure, microtexture, phases, and composition were carried out and compared with the as-coated (high-velocity oxy-fuel sprayed) surface. Laser surface melting led to homogenization and refinement of microstructures with the formation of few nano-silicides of nickel along with nano-borides of nickel and chromium (Ni3B, Cr2B, and Cr2B3). A detailed microtexture analysis showed the presence of no specific texture in the as-sprayed and laser-melted surface of Cr2B and Ni3B phases. The average microhardness was improved to 750-900 VHN as compared to 250 VHN of the as-received substrate. Laser surface melting improved the microhardness further to as high as 1400 VHN due to refinement of microstructure and the presence of silicides.

  1. Loading Capacities for Uranium, Plutonium and Neptunium in High Caustic Nuclear Waste Storage Tanks Containing Selected Sorbents

    SciTech Connect

    OJI, LAWRENCE

    2004-11-16

    In this study the loading capacities of selected actinides onto some of the most common sorbent materials which are present in caustic nuclear waste storage tanks have been determined. Some of these transition metal oxides and activated carbons easily absorb or precipitate plutonium, neptunium and even uranium, which if care is not taken may lead to unwanted accumulation of some of these fissile materials in nuclear waste tanks during waste processing. Based on a caustic synthetic salt solution simulant bearing plutonium, uranium and neptunium and ''real'' nuclear waste supernate solution, the loading capacities of these actinides onto iron oxide (hematite), activated carbon and anhydrous sodium phosphate have been determined. The loading capacities for plutonium onto granular activated carbon and iron oxide (hematite) in a caustic synthetic salt solution were, respectively, 3.4 0.22 plus or minus and 5.5 plus or minus 0.38 microgram per gram of sorbent. The loading capacity for plutonium onto a typical nuclear waste storage tank sludge solids was 2.01 microgram per gram of sludge solids. The loading capacities for neptunium onto granular activated carbon and iron oxide (hematite) in a caustic synthetic salt solution were, respectively, 7.9 plus or minus 0.52 and greater than 10 microgram per gram of sorbent. The loading capacity for neptunium onto a typical nuclear waste storage tank sludge solids was 4.48 microgram per gram of sludge solids. A typical nuclear waste storage tank solid material did not show any significant affinity for uranium. Sodium phosphate showed significant affinity for both neptunium and uranium, with loading capacities of 6.8 and 184.6 plus or minus 18.5 microgram per gram of sorbent, respectively.

  2. The Wyckoff positional order and polyhedral intergrowth in the M3B2- and M5B3-type boride precipitated in the Ni-based superalloys.

    PubMed

    Hu, X B; Zhu, Y L; Sheng, N C; Ma, X L

    2014-01-01

    Ni-based single superalloys play a crucial role in the hottest parts of jet engines. However, due to the complex geometry and macro-segregation during the solidification process, the cast defect such as stray grains is inevitable. Therefore, the transient liquid phase (TLP) bonding which can join several small single crystalline castings together is gradually believed to be an effective method for improving the yields of production of the complex components. The melting point depressant element B is always added into the interlayer filler material. Consequently, borides including the M3B2 and M5B3 phase usually precipitate during the TLP bonding process. So a comprehensive knowledge of the fine structural characteristics of the borides is very critical for an accurate evaluation of the TLP bonding process. In this work, by means of the aberration-corrected transmission electron microscopy, we show, at an atomic scale, the Wyckoff positional order phenomenon of the metal atoms in the unit cell of M3B2- and M5B3-type boride. Meanwhile, the defect along the (001) plane of the above two types of boride are determined to be the polyhedral intergrowth with complex configurations. PMID:25482386

  3. Surface decoration through electrostatic interaction leading to enhanced reactivity: Low temperature synthesis of nanostructured chromium borides (CrB and CrB{sub 2})

    SciTech Connect

    Menaka,; Kumar, Bharat; Kumar, Sandeep; Ganguli, A.K.

    2013-04-15

    The present study describes a novel low temperature route at ambient pressure for the synthesis of nanocrystalline chromium borides (CrB and CrB{sub 2}) without using any flux or additives. The favorable and intimate mixing of nanoparticles of chromium acetate (Cr source) and boron forms an active chromium–boron precursor which decomposes at much lower temperature (400 °C) to form CrB (which is ∼1000 °C less than the known ambient pressure synthesis). The chromium acetate nanoparticles (∼5 nm) decorate the larger boron particles (150–200 nm) due to electrostatic interactions resulting from opposing surface charges of boron (zeta potential:+48.101 mV) and chromium acetate (zeta potential:−4.021 mV) in ethanolic medium and is evident in the TEM micrographs. The above method leads to the formation of pure CrB film like structure at 400 °C and nanospheres (40–60 nm) at 600 °C. Also, chromium diboride (CrB{sub 2}) nanoparticles (25 nm) could be obtained at 1000 °C. - Graphical abstract: Variation of surface charge of reactants, precursor and the products, chromium borides (CrB and CrB{sub 2}). Highlights: ► Novel borothermal reduction process for synthesis of chromium boride. ► Significant lowering of reaction temperature to obtain nanocrystalline chromium boride. ► Enhanced reactivity due to appropriate surface interactions.

  4. The Wyckoff positional order and polyhedral intergrowth in the M3B2- and M5B3-type boride precipitated in the Ni-based superalloys

    PubMed Central

    Hu, X. B.; Zhu, Y. L.; Sheng, N. C.; Ma, X. L.

    2014-01-01

    Ni-based single superalloys play a crucial role in the hottest parts of jet engines. However, due to the complex geometry and macro-segregation during the solidification process, the cast defect such as stray grains is inevitable. Therefore, the transient liquid phase (TLP) bonding which can join several small single crystalline castings together is gradually believed to be an effective method for improving the yields of production of the complex components. The melting point depressant element B is always added into the interlayer filler material. Consequently, borides including the M3B2 and M5B3 phase usually precipitate during the TLP bonding process. So a comprehensive knowledge of the fine structural characteristics of the borides is very critical for an accurate evaluation of the TLP bonding process. In this work, by means of the aberration-corrected transmission electron microscopy, we show, at an atomic scale, the Wyckoff positional order phenomenon of the metal atoms in the unit cell of M3B2- and M5B3-type boride. Meanwhile, the defect along the (001) plane of the above two types of boride are determined to be the polyhedral intergrowth with complex configurations. PMID:25482386

  5. The Wyckoff positional order and polyhedral intergrowth in the M3B2- and M5B3-type boride precipitated in the Ni-based superalloys

    NASA Astrophysics Data System (ADS)

    Hu, X. B.; Zhu, Y. L.; Sheng, N. C.; Ma, X. L.

    2014-12-01

    Ni-based single superalloys play a crucial role in the hottest parts of jet engines. However, due to the complex geometry and macro-segregation during the solidification process, the cast defect such as stray grains is inevitable. Therefore, the transient liquid phase (TLP) bonding which can join several small single crystalline castings together is gradually believed to be an effective method for improving the yields of production of the complex components. The melting point depressant element B is always added into the interlayer filler material. Consequently, borides including the M3B2 and M5B3 phase usually precipitate during the TLP bonding process. So a comprehensive knowledge of the fine structural characteristics of the borides is very critical for an accurate evaluation of the TLP bonding process. In this work, by means of the aberration-corrected transmission electron microscopy, we show, at an atomic scale, the Wyckoff positional order phenomenon of the metal atoms in the unit cell of M3B2- and M5B3-type boride. Meanwhile, the defect along the (001) plane of the above two types of boride are determined to be the polyhedral intergrowth with complex configurations.

  6. LIBS Spectral Data for a Mixed Actinide Fuel Pellet Containing Uranium, Plutonium, Neptunium and Americium

    SciTech Connect

    Judge, Elizabeth J.; Berg, John M.; Le, Loan A.; Lopez, Leon N.; Barefield, James E.

    2012-06-18

    Laser-induced breakdown spectroscopy (LIBS) was used to analyze a mixed actinide fuel pellet containing 75% UO{sub 2}/20% PuO{sub 2}/3% AmO{sub 2}/2% NpO{sub 2}. The preliminary data shown here is the first report of LIBS analysis of a mixed actinide fuel pellet, to the authors knowledge. The LIBS spectral data was acquired in a plutonium facility at Los Alamos National Laboratory where the sample was contained within a glove box. The initial installation of the glove box was not intended for complete ultraviolet (UV), visible (VIS) and near infrared (NIR) transmission, therefore the LIBS spectrum is truncated in the UV and NIR regions due to the optical transmission of the window port and filters that were installed. The optical collection of the emission from the LIBS plasma will be optimized in the future. However, the preliminary LIBS data acquired is worth reporting due to the uniqueness of the sample and spectral data. The analysis of several actinides in the presence of each other is an important feature of this analysis since traditional methods must chemically separate uranium, plutonium, neptunium, and americium prior to analysis. Due to the historic nature of the sample fuel pellet analyzed, the provided sample composition of 75% UO{sub 2}/20% PuO{sub 2}/3% AmO{sub 2}/2% NpO{sub 2} cannot be confirm without further analytical processing. Uranium, plutonium, and americium emission lines were abundant and easily assigned while neptunium was more difficult to identify. There may be several reasons for this observation, other than knowing the exact sample composition of the fuel pellet. First, the atomic emission wavelength resources for neptunium are limited and such techniques as hollow cathode discharge lamp have different dynamics than the plasma used in LIBS which results in different emission spectra. Secondly, due to the complex sample of four actinide elements, which all have very dense electronic energy levels, there may be reactions and

  7. Structural and Physical Properties Diversity of New CaCu5-Type Related Europium Platinum Borides

    PubMed Central

    2013-01-01

    Three novel europium platinum borides have been synthesized by arc melting of constituent elements and subsequent annealing. They were characterized by X-ray powder and single-crystal diffraction: EuPt4B, CeCo4B type, P6/mmm, a = 0.56167(2) nm, c = 0.74399(3) nm; Eu3Pt7B2, Ca3Al7Cu2 type as an ordered variant of PuNi3, R3̅m, a = 0.55477(2) nm, c = 2.2896(1) nm; and Eu5Pt18B6–x, a new unique structure type, Fmmm, a = 0.55813(3) nm, b = 0.95476(5) nm, c = 3.51578(2) nm. These compounds belong to the CaCu5 family of structures, revealing a stacking sequence of CaCu5-type slabs with different structural units: CaCu5 and CeCo3B2 type in EuPt4B; CeCo3B2 and Laves MgCu2 type in Eu3Pt7B2; and CaCu5-, CeCo3B2-, and site-exchange ThCr2Si2-type slabs in Eu5Pt18B6–x. The striking motif in the Eu5Pt18B6–x structure is the boron-centered Pt tetrahedron [BPt4], which build chains running along the a axis and plays a decisive role in the structure arrangement by linking the terminal fragments of repeating blocks of fused Eu polyhedra. Physical properties of two compounds, EuPt4B and Eu3Pt7B2, were studied. Both compounds were found to order magnetically at 36 and 57 K, respectively. For EuPt4B a mixed-valence state of the Eu atom was confirmed via magnetic and specific heat measurements. Moreover, the Sommerfeld value of the specific heat of Eu3Pt7B2 was found to be extraordinarily large, on the order of 0.2 J/mol K2. PMID:23540751

  8. Neptunium(V) adsorption to bacteria at low and high ionic strength

    SciTech Connect

    Ams, David A; Swanson, Juliet S; Reed, Donald T; Fein, Jeremy B

    2010-12-08

    Np(V) is expected to be the predominant oxidation state of neptunium in aerobic natural waters. Np(V), as the NpO{sub 2}{sup +} aquo and associated complexed species, is readily soluble, weakly interacting with geologic media, and has a high redox stability under a relatively wide range of subsurface conditions. These chemical properties, along with a long half-life make it a primary element of concern regarding long-term nuclear waste storage and subsurface contaminant. The fate and transport of neptunium in the environment may be influenced by adsorption onto bacterial surfaces. The adsorption of neptunium to bacterial surfaces ties the mobility of the contaminant to the mobility of the bacterium. In this study, the adsorption of the neptunyl (NpO{sub 2}{sup +}) ion was evaluated at low ionic strength on a common soil bacterium and at high ionic strength on a halophilic bacterium isolated from a briny groundwater near the Waste Isolation Pilot Plant (WIPP) in southeast New Mexico. Adsorption experiments were performed in batch reactors as a function of pH, ionic strength, and bacterialNp mass ratio. Np(V) adsorption was modeled using a surface complexation approach with the mathematical program FITEQL to determine functional group specific binding constants. The data from acid and base titrations of the bacteria were also modeled to estimate the concentrations and deprotonation constants of discrete bacterial surface functional groups. Bacterial functional group characteristics and Np(V) adsorption behavior between the soil bacterium and the halophilic bacterium were compared. These results highlight the key similarities and differences in actinide adsorption behavior in environments of significantly different ionic strength. Similarities in adsorption behavior may be linked to similarities in the characteristics of the moieties between all bacterial cell walls. Differences in adsorption behavior may reflect differences in ionic strength effects, rather than

  9. Neptunium(V) Adsorption to Bacteria at Low and High Ionic Strength

    NASA Astrophysics Data System (ADS)

    Ams, D.; Swanson, J. S.; Reed, D. T.

    2010-12-01

    Np(V) is expected to be the predominant oxidation state of neptunium in aerobic natural waters. Np(V), as the NpO2+ aquo and associated complexed species, is readily soluble, interacts weakly with geologic media, and has a high redox stability under a relatively wide range of subsurface conditions. These chemical properties, along with a long half-life make it a primary element of concern regarding long-term nuclear waste storage and subsurface containment. The fate and transport of neptunium in the environment may be influenced by adsorption onto bacterial surfaces. The adsorption of neptunium to bacterial surfaces ties the mobility of the contaminant to the mobility of the bacterium. In this study, the adsorption of the neptunyl (NpO2+) ion was evaluated at low ionic strength on a common soil bacterium and at high ionic strength on a halophilic bacterium isolated from a briny groundwater near the Waste Isolation Pilot Plant (WIPP) in southeast New Mexico. Adsorption experiments were performed in batch reactors as a function of pH, ionic strength, and bacteria/Np mass ratio. Np(V) adsorption was modeled using a surface complexation approach with the mathematical program FITEQL to determine functional group specific binding constants. The data from acid and base titrations of the bacteria used were also modeled to estimate the concentrations and deprotonation constants of discrete bacterial surface functional groups. Bacterial functional group characteristics and Np(V) adsorption behavior between the soil bacterium and the halophilic bacterium were compared. These results highlight key similarities and differences in actinide adsorption behavior in environments of significantly different ionic strength. The observed adsorption behavior may be linked to similarities and differences in the characteristics of the moieties between the cell walls of common gram-negative soil and halophilic bacteria. Moreover, differences in adsorption behavior may also reflect ionic

  10. Straightforward reductive routes to air-stable uranium(III) and neptunium(III) materials.

    PubMed

    Cross, Justin N; Villa, Eric M; Darling, Victoria R; Polinski, Matthew J; Lin, Jian; Tan, Xiaoyan; Kikugawa, Naoki; Shatruk, Michael; Baumbach, Ryan; Albrecht-Schmitt, Thomas E

    2014-07-21

    Studies of trivalent uranium (U(3+)) and neptunium (Np(3+)) are restricted by the tendency of these ions to oxidize in the presence of air and water, requiring manipulations to be carried out in inert conditions to produce trivalent products. While the organometallic and high-temperature reduction chemistry of U(3+) and, to a much smaller extent, Np(3+) has been explored, the study of the oxoanion chemistry of these species has been limited despite their interesting optical and magnetic properties. We report the synthesis of U(3+) and Np(3+) sulfates by utilizing zinc amalgam as an in situ reductant with absolutely no regard to the exclusion of O2 or water. By employing this method we have developed a family of alkali metal U(3+) and Np(3+) sulfates that are air and water stable. The structures, electronic spectra, and magnetic behavior are reported. PMID:24964279

  11. Young geologist trades neptunium for newspapers as 2012 AGU Mass Media Fellow

    NASA Astrophysics Data System (ADS)

    Adams, Mary Catherine

    2012-05-01

    Though the lure of rocks, minerals, and radioactive elements took her away from her original studies, one geology Ph.D. candidate is returning to her journalism roots this summer as AGU's 2012 Mass Media Science and Engineering Fellow. Jessica Morrison is one of 12 young scientists nationwide who are trading in their lab coats for reporters' notebooks in mid-June as part of the program coordinated by the American Association for the Advancement of Science, which helps young scientists cultivate communication skills to help disseminate scientific information to general audiences. Morrison is a Ph.D. student in the Department of Civil Engineering and Geological Sciences at the University of Notre Dame. She spends her days in a laboratory investigating the geochemistry of actinides, the radioactive elements in the "no man's land" of the periodic table—the section that often gets left off or moved to the bottom. These are elements like uranium, neptunium, and plutonium.

  12. Mineralogical Charecteristics of Yucca Mountain Alluvium and Effects on Neptunium (V) Sorption

    SciTech Connect

    M. Ding; S.J. Chipera; P.W. Reimus

    2006-09-05

    Saturated alluvium is expected to serve as an important natural barrier to radionuclide transport at Yucca Mountain, the proposed geological repository for disposal of high-level nuclear wastes. {sup 237}Np(V) (half-life = 2.4 x 10{sup 5} years) has been identified as one of the radionuclides that could potentially contribute the greatest dose to humans because of its relatively high solubility and weak adsorption to volcanic tuffs under oxidizing conditions. The previous studies suggested that the mineralogical characteristics of the alluvium play an important role in the interaction between Np(V) and the alluvium. The purpose of this study is to further evaluate the mineralogical basis for Neptunium (V) sorption by saturated alluvium located down-gradient of Yucca Mountain.

  13. THERMODYNAMICS OF NEPTUNIUM(V) FLOURIDE AND SULFATE AT ELEVATED TEMPERATURES

    SciTech Connect

    L. Rao; G. Tian; Y. Xia; J.I. Friese

    2006-03-06

    Complexation of neptunium(V) with fluoride and sulfate at elevated, temperatures was studied by microcalorimetry. Thermodynamic parameters, including the equilibrium constants and enthalpy of protonation of fluoride and sulfate, and the enthalpy of complexation between Np(V) and fluoride and sulfate at 25-70 C were determined. Results show that the complexation of Np(V) with fluoride and sulfate is endothermic and that the complexation is enhanced by the increase in temperature--a threefold increase in the stability constants of NpO{sub 2}F(aq) and NpO{sub 2}SO{sub 4}{sup -} as the temperature is increased from 25 to 70 C.

  14. Experimental Measurements of Short-Lived Fission Products from Uranium, Neptunium, Plutonium and Americium

    SciTech Connect

    Metz, Lori A.; Payne, Rosara F.; Friese, Judah I.; Greenwood, Lawrence R.; Kephart, Jeremy D.; Pierson, Bruce D.

    2009-11-01

    Fission yields are especially well characterized for long-lived fission products. Modeling techniques incorporate numerous assumptions and can be used to deduce information about the distribution of short-lived fission products. This work is an attempt to gather experimental (model-independent) data on the short-lived fission products. Fissile isotopes of uranium, neptunium, plutonium and americium were irradiated under pulse conditions at the Washington State University 1 MW TRIGA reactor to achieve ~108 fissions. The samples were placed on a HPGe (high purity germanium) detector to begin counting in less than 3 minutes post irradiation. The samples were counted for various time intervals ranging from 5 minutes to 1 hour. The data was then analyzed to determine which radionuclides could be quantified and compared to the published fission yield data.

  15. Neptunium(V) sorption on quartz and albite in aqueous suspension; Annual progress report

    SciTech Connect

    Kohler, M.; Leckie, J.O.

    1991-10-01

    The behavior of neptunium in the subsurface environment is of interest since neptunium isotopes are included in nuclear waste. Previous work investigated the sorption behavior of Np onto {alpha}-Fe{sub 2}O{sub 3} (hematite), an accessory mineral of the Yucca Mountain repository. The work reported herein involves the much more abundant silicate minerals quartz and albite, and is a logical continuation of the ongoing task. In previous work increased sorption was observed in systems containing hematite and EDTA, a ligand which acts as a surrogate for organic complexing agents. In addition, increased partial pressures of CO{sub 2} are common in many ground waters and the effects of carbonate on sorption of radionuclides have to be studied as well. At concentration levels of 10{sup {minus}7} M, Np(V) does not adsorb strongly on quartz and albite up to pH values of approximately 9 at solid/solution ratios of 30 to 40 g/l. Significant adsorption (> 20%) occurs on both minerals only at pH > 9. Pretreatment of albite affects the sorption behavior of this mineral at pH > 9, possibly due to the formation of secondary mineral phases at the albite surface. EDTA does not adsorb on quartz at concentrations of 10{sup {minus}6} M. In the presence of 50 {mu}M EDTA, Np(V) sorption seems to be restricted. EDTA at the 10{sup {minus}6} M level adsorbs onto albite to an appreciable degree at pH values < 7.5. One {mu}M EDTA has no effect on Np(V) adsorption onto albite. Carbonate species adsorb on quartz and albite, both cases showing a maximum in sorption at pH 6.5 to 7 where HCO{sub 3}{sup {minus}} is the predominant solution species.

  16. Radioactive waste forms stabilized by ChemChar gasification: characterization and leaching behavior of cerium, thorium, protactinium, uranium, and neptunium.

    PubMed

    Marrero, T W; Morris, J S; Manahan, S E

    2004-02-01

    The uses of a thermally reductive gasification process in conjunction with vitrification and cementation for the long-term disposal of low level radioactive materials have been investigated. gamma-ray spectroscopy was used for analysis of carrier-free protactinium-233 and neptunium-239 and a stoichiometric amount of cerium (observed cerium-141) subsequent to gasification and leaching, up to 48 days. High resolution ICP-MS was used to analyze the cerium, thorium, and uranium from 46 to 438 days of leaching. Leaching procedures followed the guidance of ASTM Procedure C 1220-92, Standard Test Method for Static Leaching of Monolithic Waste Forms for Disposal of Radioactive Waste. The combination of the thermally reductive pretreatment, vitrification and cementation produced a highly non-leachable form suitable for long-term disposal of cerium, thorium, protactinium, uranium, and neptunium. PMID:14637345

  17. 2-Page Summary for Neptunium solubility in the Near-field Environment of A Proposed Yucca Mountain Repository

    SciTech Connect

    D. Sassani; A. Van Luik; J. Summerson

    2005-03-29

    The total system performance assessment (TSPA) for the proposed repository at Yucca Mountain, NV, includes a wide variety of processes to evaluate the potential release of radionuclides from the Engineered Barrier System into the unsaturated zone of the geosphere. The principal processes controlling radionuclide release and mobilization from the waste forms are captured in the model to assess the dissolved concentrations of radionuclides in the source-term. The TSPA model of the source-term incorporates the far-from-equilibrium dissolution of, for example, spent nuclear fuel (SNF) to capture bounding rates of radionuclide availability as the SNF degrades. In addition, for individual radionuclides, the source-term model evaluates solubility constraints that are more indicative of longer-term, equilibrium processes that can limit the potential mass transport from the source term in those cases. These solubility limits represent phase saturation and precipitation processes that can occur either at the waste form as it alters, or at other locations in the near-field environment (e.g., within the invert) if chemical conditions are different. Identification and selection of applicable constraints for solubility-limited radionuclide concentrations is a primary focus in formulating the source-term model for the TSPA. Neptunium is a long-lived radionuclide that becomes a larger fraction of the potential dose as radioactive decay of other radionuclides proceeds. To delineate appropriate long-term source-term controls on dissolved neptunium concentrations, a number of alternative models have been defined. The models are based on data both collected within the Yucca Mountain Project and taken from published literature, and have been evaluated against independent data sets to assess their applicability. The alternative models encompass ones based on precipitation of neptunium within its own separate oxide phases (i.e., ''pure'' Np-phases), and those where neptunium is

  18. Separation of plutonium and neptunium species by capillary electrophoresis-inductively coupled plasma-mass spectrometry and application to natural groundwater samples.

    PubMed

    Kuczewski, Bernhard; Marquardt, Christian M; Seibert, Alice; Geckeis, Horst; Kratz, Jens Volker; Trautmann, Norbert

    2003-12-15

    Capillary electrophoresis (CE) was coupled to ICPMS in order to combine the good performance of this separation technique with the high sensitivity of the ICPMS for the analysis of plutonium and neptunium oxidation states. The combination of a fused-silica capillary with a MicroMist AR 30-I-FM02 nebulizer and a Cinnabar small-volume cyclonic spray chamber yielded the best separation results. With this setup, it was possible to separate a model element mixture containing neptunium (NpO2(+)), uranium (UO2(2+)), lanthanum (La3+), and thorium (Th4+) in 1 M acetic acid. The same conditions were also suitable for the separation of various oxidation states of plutonium and neptunium in different aqueous samples. All separations were obtained within less than 15 min. A detection limit of 50 ppb identical with 2 x 10(-7) M (3-fold standard deviation of a blank) was achieved. To prove the negligible disturbance of the plutonium and neptunium redox equilibria during the CE separations, plutonium and neptunium speciation by CE-ICPMS in acidic solutions was compared with the results of UV/visible absorption spectroscopy and was found to be in good agreement. The CE-ICPMS system was also applied to study the reduction of Pu(VI) in a humic acid-containing groundwater at different pH values. PMID:14670034

  19. Processing development of 4 tantalum carbide-hafnium carbide and related carbides and borides for extreme environments

    NASA Astrophysics Data System (ADS)

    Gaballa, Osama Gaballa Bahig

    Carbides, nitrides, and borides ceramics are of interest for many applications because of their high melting temperatures and good mechanical properties. Wear-resistant coatings are among the most important applications for these materials. Materials with high wear resistance and high melting temperatures have the potential to produce coatings that resist degradation when subjected to high temperatures and high contact stresses. Among the carbides, Al4SiC4 is a low density (3.03 g/cm3), high melting temperature (>2000°C) compound, characterized by superior oxidation resistance, and high compressive strength. These desirable properties motivated this investigation to (1) obtain high-density Al4SiC4 at lower sintering temperatures by hot pressing, and (2) to enhance its mechanical properties by adding WC and TiC to the Al4SiC4. Also among the carbides, tantalum carbide and hafnium carbide have outstanding hardness; high melting points (3880°C and 3890°C respectively); good resistance to chemical attack, thermal shock, and oxidation; and excellent electronic conductivity. Tantalum hafnium carbide (Ta4HfC 5) is a 4-to-1 ratio of TaC to HfC with an extremely high melting point of 4215 K (3942°C), which is the highest melting point of all currently known compounds. Due to the properties of these carbides, they are considered candidates for extremely high-temperature applications such as rocket nozzles and scramjet components, where the operating temperatures can exceed 3000°C. Sintering bulk components comprised of these carbides is difficult, since sintering typically occurs above 50% of the melting point. Thus, Ta4 HfC5 is difficult to sinter in conventional furnaces or hot presses; furnaces designed for very high temperatures are expensive to purchase and operate. Our research attempted to sinter Ta4HfC5 in a hot press at relatively low temperature by reducing powder particle size and optimizing the powder-handling atmosphere, milling conditions, sintering

  20. Quantitative NDA measurements of advanced reprocessing product materials containing uranium, neptunium, plutonium, and americium

    NASA Astrophysics Data System (ADS)

    Goddard, Braden

    The ability of inspection agencies and facility operators to measure powders containing several actinides is increasingly necessary as new reprocessing techniques and fuel forms are being developed. These powders are difficult to measure with nondestructive assay (NDA) techniques because neutrons emitted from induced and spontaneous fission of different nuclides are very similar. A neutron multiplicity technique based on first principle methods was developed to measure these powders by exploiting isotope-specific nuclear properties, such as the energy-dependent fission cross sections and the neutron induced fission neutron multiplicity. This technique was tested through extensive simulations using the Monte Carlo N-Particle eXtended (MCNPX) code and by one measurement campaign using the Active Well Coincidence Counter (AWCC) and two measurement campaigns using the Epithermal Neutron Multiplicity Counter (ENMC) with various (alpha,n) sources and actinide materials. Four potential applications of this first principle technique have been identified: (1) quantitative measurement of uranium, neptunium, plutonium, and americium materials; (2) quantitative measurement of mixed oxide (MOX) materials; (3) quantitative measurement of uranium materials; and (4) weapons verification in arms control agreements. This technique still has several challenges which need to be overcome, the largest of these being the challenge of having high-precision active and passive measurements to produce results with acceptably small uncertainties.

  1. Dissolution of Neptunium and Plutonium Oxides Using a Catalyzed Electrolytic Process

    SciTech Connect

    Hylton, TD

    2004-10-25

    This report discusses the scoping study performed to evaluate the use of a catalyzed electrolytic process for dissolving {sup 237}Np oxide targets that had been irradiated to produce {sup 238}Pu oxide. Historically, these compounds have been difficult to dissolve, and complete dissolution was obtained only by adding hydrofluoric acid to the nitric acid solvent. The presence of fluoride in the mixture is undesired because the fluoride ions are corrosive to tank and piping systems and the fluoride ions cause interferences in the spectrophotometric analyses. The goal is to find a dissolution method that will eliminate these issues and that can be incorporated into a processing system to support the domestic production and purification of {sup 238}Pu. This study evaluated the potential of cerium(IV) ions, a strong oxidant, to attack and dissolve the oxide compounds. In the dissolution process, the cerium(IV) ions are reduced to cerium(III) ions, which are not oxidants. Therefore, an electrolytic process was incorporated to continuously convert cerium(III) ions back to cerium(IV) ions so that they can dissolve more of the oxide compounds. This study showed that the neptunium and plutonium oxides were successfully dissolved and that more development work should be performed to optimize the procedure.

  2. Thermodynamic modeling of neptunium(V)-acetate complexation in concentrated NaCl media

    SciTech Connect

    Novak, C.F.; Borkowski, M.; Choppin, G.R.

    1995-09-01

    The complexation of neptunium(V), Np(V), with the acetate anion, Ac{sup -}, was measured in sodium chloride media to high concentration using an extraction technique. The data were interpreted using the thermodynamic formalism of Pitzer, which is valid to high electrolyte concentrations. A consistent model for the deprotonation constants of acetic acid in NaCl and NaClO{sub 4} media was developed. For the concentrations of acetate expected in a waste repository, only the neutral complex NpO{sub 2}Ac(aq) was important in describing the interactions between the neptunyl ion and acetate. The thermodynamic stability constant log {beta}{sup 0}{sub 101} for the reaction NpO{sub 2}{sup +} + Ac{sup -} {leftrightarrow} NpO{sub 2}Ac was calculated to be 1.46{plus_minus}0.11. This weak complexing behavior between the neptunyl ion and acetate indicates that acetate will not significantly enhance dissolved Np(V) concentrations in ground waters associated with nuclear waste repositories that may contain acetate.

  3. Application of the S=1 underscreened Anderson lattice model to Kondo uranium and neptunium compounds

    NASA Astrophysics Data System (ADS)

    Thomas, Christopher; da Rosa Simões, Acirete S.; Iglesias, J. R.; Lacroix, C.; Perkins, N. B.; Coqblin, B.

    2011-01-01

    Magnetic properties of uranium and neptunium compounds showing the coexistence of the Kondo screening effect and ferromagnetic order are investigated within the Anderson lattice Hamiltonian with a two-fold degenerate f level in each site, corresponding to 5f2 electronic configuration with S=1 spins. A derivation of the Schrieffer-Wolff transformation is presented and the resulting Hamiltonian has an effective f-band term, in addition to the regular exchange Kondo interaction between the S=1 f spins and the s=1/2 spins of the conduction electrons. The resulting effective Kondo lattice model can describe both the Kondo regime and a weak delocalization of the 5f electrons. Within this model we compute the Kondo and Curie temperatures as a function of model parameters, namely the Kondo exchange interaction constant JK, the magnetic intersite exchange interaction JH, and the effective f bandwidth. We deduce, therefore, a phase diagram of the model which yields the coexistence of the Kondo effect and ferromagnetic ordering and also accounts for the pressure dependence of the Curie temperature of uranium compounds such as UTe.

  4. Gas Generation Testing of Neptunium Oxide Generated Using the HB-Line Phase IIFlowsheet

    SciTech Connect

    Duffey, J

    2003-08-29

    The hydrogen (H{sub 2}) gas generation rate for neptunium dioxide (NpO{sub 2}) samples produced on a laboratory scale using the HB-Line Phase II flowsheet has been measured following exposure to 75% relative humidity (RH). As expected, the observed H{sub 2} generation rates for these samples increase with increasing moisture content. A maximum H{sub 2} generation rate of 1.8 x 10{sup -6} moles per day per kilogram (mol {center_dot} day{sup -1} kg{sup -1}) was observed for NpO{sub 2} samples with approximately one and one-half times (1 1/2 X) the expected specific surface area (SSA) for the HB-Line Phase II product. The SSA of NpO{sub 2} samples calcined at 650 C is similar to plutonium dioxide (PuO{sub 2}) calcined at 950 C according to the Department of Energy (DOE) standard for packaging and storage of PuO{sub 2}. This low SSA of the HB-Line Phase II product limits moisture uptake to less than 0.2 weight percent (wt %) even with extended exposure to 75% RH.

  5. On the transferability of electron density in binary vanadium borides VB, V3B4 and VB2.

    PubMed

    Terlan, Bürgehan; Akselrud, Lev; Baranov, Alexey I; Borrmann, Horst; Grin, Yuri

    2015-12-01

    Binary vanadium borides are suitable model systems for a systematic analysis of the transferability concept in intermetallic compounds due to chemical intergrowth in their crystal structures. In order to underline this structural relationship, topological properties of the electron density in VB, V3B4 and VB2 reconstructed from high-resolution single-crystal X-ray diffraction data as well as derived from quantum chemical calculations, are analysed in terms of Bader's Quantum Theory of Atoms in Molecules [Bader (1990). Atoms in Molecules: A Quantum Theory, 1st ed. Oxford: Clarendon Press]. The compounds VB, V3B4 and VB2 are characterized by a charge transfer from the metal to boron together with two predominant atomic interactions, the shared covalent B-B interactions and the polar covalent B-M interactions. The resembling features of the crystal structures are well reflected by the respective B-B interatomic distances as well as by ρ(r) values at the B-B bond critical points. The latter decrease with an increase in the corresponding interatomic distances. The B-B bonds show transferable electron density properties at bond critical points depending on the respective bond distances. PMID:26634735

  6. Mechanism and kinetics of sodium borohydride hydrolysis over crystalline nickel and nickel boride and amorphous nickel-boron nanoparticles

    NASA Astrophysics Data System (ADS)

    Wu, Zhijie; Mao, Xikang; Zi, Qin; Zhang, Rongrong; Dou, Tao; Yip, Alex C. K.

    2014-12-01

    The initial hydrogen generation turnover rates during the hydrolysis of sodium borohydride over nickel catalysts (crystalline nickel (Ni), crystalline nickel boride (Ni3B), and amorphous nickel-boron (Ni-B) nanoparticles) were measured to investigate the reaction kinetics and mechanisms by varying the reactant concentrations and reaction temperatures. Nickel catalysts with and without boron follow different hydrolysis pathways; hydroxide ions are involved in the activation of reactant molecules over Ni3B and Ni-B catalysts. This study explicitly reports the zero-order and first-order reaction kinetics with respect to the reactant concentration over Ni, Ni3B and Ni-B catalysts. The initial hydrogen generation turnover rates and activation energies determined from the experimental data indicate that the amorphous Ni-B nanoparticles exhibit the highest turnover rate and lowest activation energy for the hydrolysis of borohydride among the investigated catalysts. This study provides a general strategy for the development of borohydride hydrolysis catalysts via the modification of a metal catalyst using boron, which causes the crystalline structure to become amorphous and leads to electron-rich, highly undercoordinated metal atoms at the surface.

  7. Transition metal carbides, nitrides and borides, and their oxygen containing analogs useful as water gas shift catalysts

    DOEpatents

    Thompson, Levi T.; Patt, Jeremy; Moon, Dong Ju; Phillips, Cory

    2003-09-23

    Mono- and bimetallic transition metal carbides, nitrides and borides, and their oxygen containing analogs (e.g. oxycarbides) for use as water gas shift catalysts are described. In a preferred embodiment, the catalysts have the general formula of M1.sub.A M2.sub.B Z.sub.C O.sub.D, wherein M1 is selected from the group consisting of Mo, W, and combinations thereof; M2 is selected from the group consisting of Fe, Ni, Cu, Co, and combinations thereof; Z is selected from the group consisting of carbon, nitrogen, boron, and combinations thereof; A is an integer; B is 0 or an integer greater than 0; C is an integer; O is oxygen; and D is 0 or an integer greater than 0. The catalysts exhibit good reactivity, stability, and sulfur tolerance, as compared to conventional water shift gas catalysts. These catalysts hold promise for use in conjunction with proton exchange membrane fuel cell powered systems.

  8. Precipitation of Niobium Boride Phases at the Base Metal/Weld Metal Interface in Dissimilar Weld Joints

    NASA Astrophysics Data System (ADS)

    Výrostková, Anna; Kepič, Ján; Homolová, Viera; Falat, Ladislav

    2015-07-01

    In this work, the analysis of failure mechanism in the heat affected zone is described in dissimilar weld joints between advanced martensitic steel T92 and Ni-base weld metal. The joints were treated with two different post-weld heat treatments and tested. For the creep, tensile, and Charpy impact tests, the samples with interfacially located notch were used. Moreover long term aging at 625 °C was applied before the tensile and notch toughness tests. Decohesion fractures ran along carbides at the T92 BM/WM interfaces in case of the modified PWHT, whereas type IV cracking was the prevailing failure mechanism after the classical PWHT in the creep test. In the notch tensile and Charpy impact tests, with the notch at T92 base metal/weld metal interface, fractures ran along the interface with a hard phase on the fracture surface along with the ductile dimple and brittle quasi-cleavage fracture. The phase identified as niobium boride (either NbB and/or Nb3B2) was produced during welding at the end of the solidification process. It was found in the welds regardless of the post-weld heat treatment and long-term aging.

  9. The effect of temperature on the sorption of technetium, uranium, neptunium and curium on bentonite, tuff and granodiorite

    SciTech Connect

    Baston, G.M.N.; Berry, J.A.; Brownsword, M.; Heath, T.G.; Ilett, D.J.; Tweed, C.J.; Yui, M.

    1997-12-31

    A study of the sorption of the radioelements technetium; uranium; neptunium; and curium onto geological materials has been carried out as part of the PNC program to increase confidence in the performance assessment for a high-level radioactive waste repository in Japan. Batch sorption experiments have been performed in order to study the sorption of the radioelements onto bentonite, tuff and granodiorite from equilibrated de-ionized water under strongly-reducing conditions at both room temperature and at 60 C. Mathematical modelling using the geochemical speciation program HARPHRQ in conjunction with the HATCHES database has been undertaken in order to interpret the experimental results.

  10. ELECTRONICS UPGRADE TO THE SAVANNAH RIVER NATIONAL LABORATORY COULOMETER FOR PLUTONIUM AND NEPTUNIUM ASSAY

    SciTech Connect

    Cordaro, J.; Holland, M.; Reeves, G.; Nichols, S.; Kruzner, A.

    2011-07-08

    The Savannah River Site (SRS) has the analytical measurement capability to perform high-precision plutonium concentration measurements by controlled-potential coulometry. State-of-the-art controlled-potential coulometers were designed and fabricated by the Savannah River National Laboratory and installed in the Analytical Laboratories process control laboratory. The Analytical Laboratories uses coulometry for routine accountability measurements of and for verification of standard preparations used to calibrate other plutonium measurement systems routinely applied to process control, nuclear safety, and other accountability applications. The SRNL Coulometer has a demonstrated measurement reliability of {approx}0.05% for 10 mg samples. The system has also been applied to the characterization of neptunium standard solutions with a comparable reliability. The SRNL coulometer features: a patented current integration system; continuous electrical calibration versus Faraday's Constants and Ohm's Law; the control-potential adjustment technique for enhanced application of the Nernst Equation; a wide operating room temperature range; and a fully automated instrument control and data acquisition capability. Systems have been supplied to the International Atomic Energy Agency (IAEA), Russia, Japanese Atomic Energy Agency (JAEA) and the New Brunswick Laboratory (NBL). The most recent vintage of electronics was based on early 1990's integrated circuits. Many of the components are no longer available. At the request of the IAEA and the Department of State, SRNL has completed an electronics upgrade of their controlled-potential coulometer design. Three systems have built with the new design, one for the IAEA which was installed at SAL in May 2011, one system for Los Alamos National Laboratory, (LANL) and one for the SRS Analytical Laboratory. The LANL and SRS systems are undergoing startup testing with installation scheduled for this summer.

  11. Kinetics of neptunium(V) sorption and desorption on goethite: An experimental and modeling study

    NASA Astrophysics Data System (ADS)

    Tinnacher, Ruth M.; Zavarin, Mavrik; Powell, Brian A.; Kersting, Annie B.

    2011-11-01

    Various sorption phenomena, such as aging, hysteresis and irreversible sorption, can cause differences between contaminant (ad)sorption and desorption behavior and lead to apparent sorption 'asymmetry'. We evaluate the relevance of these characteristics for neptunium(V) (Np(V)) sorption/desorption on goethite using a 34-day flow-cell experiment and kinetic modeling. Based on experimental results, the Np(V) desorption rate is much slower than the (ad)sorption rate, and appears to decrease over the course of the experiment. The best model fit with a minimum number of fitting parameters was achieved with a multi-reaction model including (1) an equilibrium Freundlich site (site 1), (2) a kinetically-controlled, consecutive, first-order site (site 2), and (3) a parameter ψ, which characterizes the desorption rate on site 2 based on a concept related to transition state theory (TST). This approach allows us to link differences in adsorption and desorption kinetics to changes in overall reaction pathways, without assuming different adsorption and desorption affinities (hysteresis) or irreversible sorption behavior a priori. Using modeling as a heuristic tool, we determined that aging processes are relevant. However, hysteresis and irreversible sorption behavior can be neglected within the time-frame (desorption over 32 days) and chemical solution conditions evaluated in the flow-cell experiment. In this system, desorption reactions are very slow, but they are not irreversible. Hence, our data do not justify an assumption of irreversible Np(V) sorption to goethite in transport models, which effectively limits the relevance of colloid-facilitated Np(V) transport to near-field environments. However, slow Np(V) desorption behavior may also lead to a continuous contaminant source term when metals are sorbed to bulk mineral phases. Additional long-term experiments are recommended to definitely rule out irreversible Np(V) sorption behavior at very low surface loadings and

  12. Complex formation between neptunium(V) and various thiosemicarbazide derivatives in aqueous solution

    SciTech Connect

    Chuguryan, D.G.; Dzyubenko, V.I.; Gerbeleu, N.V.

    1987-01-01

    Complex formation between neptunium(V) and various thiosemicarbazide derivatives in solution has been studied spectrophotometrically in the pH range 4-10. Stepwise formation of three types of complexes, with composition NpO/sub 2/HA, NpO/sub 2/A/sup -/, and NpOHA/sup 2 -/, has been demonstrated with salicylaldehyde thiosemicarbazone (H/sub 2/L) and salicylaldehyde S-methyl-isothiosemicarbazone (H/sub 2/Q) at t = 25 +/- 1/sup 0/C and ..mu.. = 0.05. The logarithmic stability constants of the first two complexes are 5.14 +/- 0.06, 11.85 +/- 0.04 and 8.42 +/- 0.09, 13.33 +/- 0.015 for H/sub 2/L and H/sub 2/Q, respectively; equilibrium constants for the formation of hydroxo complexes of the form NpO/sub 2/OHL/sup 2 -/ and NpO/sub 2/OHQ/sup 2 -/ were also determined, and found to be equal to (2.23 +/-0.37) x 10/sup -5/ and (5.02 +/- 0.9) x 10/sup -5/, respectively. In the case of S-methyl-N/sub 1/,N/sub 4/-bis(salicylidene)isothiosemicarbazide (H/sub 2/Z), only one type of complex is formed under these experimental conditions, namely, NpO/sub 2/Z/sup -/, with a logarithmic stability constant of 4.78 +/- 0.03. Dissociation constants for H/sub 2/Q and H/sub 2/Z were also determined.

  13. Immobilization and recovery of thorium, a neptunium surrogate, using phase-separated glasses

    SciTech Connect

    Meaker, T.F.; Karraker, D.; Tosten, M.; Pareizs, J.M.; Ramsey, W.G.

    1997-12-31

    The Savannah River Site has the majority of the United States` supply of neptunium currently stored in an acid solution in one of their canyon facilities. A program is being developed that could be utilized to ship this material, as glass, to Oak Ridge National Laboratory where the Np could be leached from the glass, purified by ion exchange and made into target material for the production of Pu-238. Ion exchange purification dictates no material be in the leachate making the isolation of the Np difficult. The authors have developed a process using thorium as a surrogate for Np that could immobilize the Np into a soda borosilicate glass for shipment. To achieve recovery of the Np, the glass can be phase separated prior to leaching with nitric acid. Phase separation would produce a Np-rich sodium-borate phase and a Si-rich phase similar to a Vycor{reg_sign} glass. The nitric acid selectively attacks the sodium-borate phase allowing high Np recovery in a solution that contains only sodium and boron. These can be easily separated from Np by ion exchange. Essentially all of the silicon which would interfere with ion exchange by precipitation is retained in the Vycor{reg_sign}-type phase. This technology may also be applied to other actinides stored in relatively pure solutions. This paper will report the optimization of variables for maximizing Th (a Np surrogate) recovery while minimizing Si release. Th solubility in glass, heat treatment conditions and leaching parameters will be discussed. Transmission Electron Microscopy (TEM) with energy dispersive spectroscopy (EDS) data will be included to show phase separation after heat treatment.

  14. Neptunium(V) sorption to goethite at attomolar to micromolar concentrations.

    PubMed

    Snow, Mathew S; Zhao, Pihong; Dai, Zurong; Kersting, Annie B; Zavarin, Mavrik

    2013-01-15

    Sorption of 10(-18)-10(-5)M neptunium (Np) to goethite was examined using liquid scintillation counting and gamma spectroscopy. A combination approach using (239)Np and long lived (237)Np was employed to span this wide concentration range. (239)Np detection limits were determined to be 2×10(-18)M and 3×10(-17)M for liquid scintillation counting and gamma spectroscopy, respectively. Sorption was found to be linear below 10(-11)M, in contrast to the non-linear behavior observed at higher concentrations both here and in the literature. 2-site and 3-site Langmuir models were used to simulate sorption behavior over the entire 10(-18)-10(-5)M range. The 3-site model fit yielded Type I and II site densities of 3.56 sites/nm(2) (99.6%) and 0.014±0.007 sites/nm(2) (0.4±0.1%), consistent with typical "high affinity" and "low affinity" sites reported in the literature [21]. Modeling results for both models suggest that sorption below ~10(-11)M is controlled by a third (Type III) site with a density on the order of ~7×10(-5)sites/nm(2) (~0.002%). While the nature of this "site" cannot be determined from isotherm data alone, the sorption data at ultra-low Np concentrations indicate that Np(V) sorption to goethite at environmentally relevant concentrations will be (1) linear and (2) higher than previous (high concentration) laboratory experiments suggest. PMID:23079039

  15. Kinetics of reduction of plutonium(VI) and neptunium(VI) by sulfide in neutral and alkaline solutions

    USGS Publications Warehouse

    Nash, K.L.; Cleveland, J.M.; Sullivan, J.C.; Woods, M.

    1986-01-01

    The rate of reduction of plutonium(VI) and neptunium(VI) by bisulfide ion in neutral and mildly alkaline solutions has been investigated by the stopped-flow technique. The reduction of both of these ions to the pentavalent oxidation state appears to occur in an intramolecular reaction involving an unusual actinide(VI)-hydroxide-bisulfide complex. For plutonium the rate of reduction is 27.4 (??4.1) s-1 at 25??C with ??H* = +33.2 (??1.0) kJ/mol and ??S* = -106 (??4) J/(mol K). The apparent stability constant for the transient complex is 4.66 (??0.94) ?? 103 M-1 at 25??C with associated thermodynamic parameters of ??Hc = +27.7 (??0.4) kJ/mol and ??Sc = +163 (??2) J/(mol K). The corresponding rate and stability constants are determined for the neptunium system at 25??C (k3 = 139 (??30) s-1, Kc. = 1.31 (??0.32) ?? 103 M-1), but equivalent parameters cannot be determined at reduced temperatures. The reaction rate is decreased by bicarbonate ion. At pH > 10.5, a second reaction mechanism, also involving a sulfide complex, is indicated. ?? 1986 American Chemical Society.

  16. Higher borides and oxygen-enriched Mg-B-O inclusions as possible pinning centers in nanostructural magnesium diboride and the influence of additives on their formation

    NASA Astrophysics Data System (ADS)

    Prikhna, Tatiana; Gawalek, Wolfgang; Savchuk, Yaroslav; Tkach, Vasiliy; Danilenko, Nikolay; Wendt, Michael; Dellith, Jan; Weber, Harold; Eisterer, Michael; Moshchil, Viktor; Sergienko, Nina; Kozyrev, Artem; Nagorny, Peter; Shapovalov, Andrey; Melnikov, Vladimir; Dub, Sergey; Litzkendorf, Doris; Habisreuther, Tobias; Schmidt, Christa; Mamalis, Athanasios; Sokolovsky, Vladimir; Sverdun, Vladimir; Karau, Fridrich; Starostina, Alexandra

    2010-10-01

    The study of high pressure (2 GPa) synthesized MgB 2-based materials allows us to conclude that higher borides (with near MgB 12 stoichiometry) and oxygen-enriched Mg-B-O inclusions can be pinning centers in nanostructural magnesium diboride matrix (with average grain sizes of 15-37 nm). It has been established that additions of Ti or SiC as well as manufacturing temperature can affect the size, amount and distribution of these inclusions in the material structure and thus, influence critical current density. The superconducting behavior of materials with near MgB 12 stoichiometry of matrix is discussed.

  17. Site-preferential design of itinerant ferromagnetic borides: experimental and theoretical investigation of MRh6B3 (M = Fe, Co).

    PubMed

    Misse, Patrick R N; Gillessen, Michael; Fokwa, Boniface P T

    2011-10-17

    Single-phase polycrystalline samples of the compounds MRh(6)B(3) (M = Fe, Co) as well as single crystals of CoRh(6)B(3) have been synthesized by arc-melting the elements under a purified argon atmosphere in a water-cooled copper crucible. The characterization of the new phases was achieved by using single-crystal and powder X-ray diffraction as well as EDX measurements. The two phases are isotypic and crystallize in the hexagonal Th(7)Fe(3) structure type (space group P6(3)mc, no. 186, Z = 2). In this structure, the magnetically active atoms (Fe, Co) are preferentially found on only one of the three available rhodium sites, and together with rhodium they build a three-dimensional network of interconnected (Rh/M)(3) triangles. Magnetic properties investigations show that both phases order ferromagnetically below Curie temperatures of 240 K (for FeRh(6)B(3)) and 150 K (for CoRh(6)B(3)). First-principles DFT calculations correctly reproduce not only the lattice parameters but also the ground state magnetic ordering in the two phases. These calculations also show that the long-range magnetic ordering in both phases occurs via indirect ferromagnetic coupling between the iron atoms mediated by rhodium. This magnetic structural model also predicts the saturation magnetizations to be 4.02 μ(B) for FeRh(6)B(3) (3.60 μ(B) found experimentally) and 2.75 μ(B) for CoRh(6)B(3). Furthermore, both phases are predicted to be metallic conductors as expected for these intermetallic borides. PMID:21905755

  18. Effect of higher borides and inhomogeneity of oxygen distribution on critical current density of undoped and doped magnesium diboride

    NASA Astrophysics Data System (ADS)

    Prikhna, T. A.; Gawalek, W.; Tkach, V. M.; Danilenko, N. I.; Savchuk, Ya M.; Dub, S. N.; Moshchil, V. E.; Kozyrev, A. V.; Sergienko, N. V.; Wendt, M.; Melnikov, V. S.; Dellith, J.; Weber, H.; Eisterer, M.; Schmidt, Ch; Habisreuther, T.; Litzkendorf, D.; Vajda, J.; Shapovalov, A. P.; Sokolovsky, V.; Nagorny, P. A.; Sverdun, V. B.; Kosa, J.; Karau, F.; Starostina, A. V.

    2010-06-01

    The effect of doping with Ti, Ta, SiC in complex with synthesis temperature on the amount and distribution of structural inhomogeneities in MgB2 matrix of high-pressure-synthesized-materials (2 GPa) which can influence pinning: higher borides (MgB12) and oxygen-enriched Mg-B-O inclusions, was established and a mechanism of doping effect on jc increase different from the generally accepted was proposed. Near theoretically dense SiC-doped material exhibited jc= 106 A/cm2 in 1T field and Hirr =8.5 T at 20 K. The highest jc in fields above 9, 6, and 4 T at 10, 20, and 25 K, respectively, was demonstrated by materials synthesized at 2 GPa, 600 °C from Mg and B without additions (at 20 K jc= 102 A/cm2 in 10 T field). Materials synthesized from Mg and B taken up to 1:20 ratio were superconductive. The highest jc (6×104 A/cm2 at 20 K in zero field, Hirr= 5 T) and the amount of SC phase (95.3% of shielding fraction), Tc being 37 K were demonstrated by materials having near MgB12 composition of the matrix. The materials with MgB12 matrix had a doubled microhardness of that with MgB2 matrix (25±1.1 GPa and 13.08±1.07 GPa, at a load of 4.9 N, respectively).

  19. Anomalous effect of vanadium boride seeding on thermoelectric properties of YB{sub 22}C{sub 2}N

    SciTech Connect

    Prytuliak, A.; Maruyama, S.; Mori, T.

    2013-05-15

    Highlights: ► We doped YB{sub 22}C{sub 2}N; the long awaited n-type counterpart to p-type boron carbide. ► VB{sub 2} seeding of YB{sub 22}C{sub 2}N showed striking results. ► Thermal treatment effects led to VB{sub 2} being intrinsically doped. ► Large increase of both Seebeck coefficient and electrical conductivity was obtained. - Abstract: Vanadium boride seeded YB{sub 22}C{sub 2}N were synthesized and the thermoelectric properties investigated. YB{sub 22}C{sub 2}N is representative of the series of rare earth borocarbonitrides which is the potential long awaited n-type counterpart to p-type boron carbide. VB{sub 2} seeded samples of YB{sub 22}C{sub 2}N were prepared using VB{sub 2} directly as an initial additive and V{sub 2}O{sub 3} which also results in formation of vanadium diboride in the final product. The resistivity and Seebeck coefficient of samples were measured in the temperature range of 323 K to 1073 K. A dramatic effect of thermal treatment on the Seebeck coefficient of VB{sub 2} seeded samples was observed, and it is indicated that there is possible partial intrinsic doping of vanadium into YB{sub 22}C{sub 2}N. VB{sub 2} is revealed to be a promising additive to improve the thermoelectric properties of YB{sub 22}C{sub 2}N. An enhancement of more than 220% of the maximum absolute value of the Seebeck coefficient was obtained while the resistivity was also reduced considerably.

  20. Single crystal studies on Co-containing {tau}-borides Co{sub 23-x}M{sub x}B{sub 6} (M=Al, Ga, Sn, Ti, V, Ir) and the boron-rich {tau}-boride Co{sub 12.3}Ir{sub 8.9}B{sub 10.5}

    SciTech Connect

    Kotzott, Dominik; Ade, Martin; Hillebrecht, Harald

    2009-03-15

    Single crystals of the cubic {tau}-Borides Co{sub 23-x}M{sub x}B{sub 6} (M=Al, Ga, Sn) were synthesised from the elements at temperatures between 1200 and 1500 deg. C. According to the structure refinements one (Ga, Sn: 8c) or two (Al: 4a and 8c) of the four independent metal sites show a mixed occupation Co/M resulting in the compositions Co{sub 20.9}Al{sub 2.1}B{sub 6}, Co{sub 21.9}Ga{sub 1.1}B{sub 6}, and Co{sub 21.4}Sn{sub 1.6}B{sub 6}, respectively. Melts with Indium gave access to Co{sub 23}B{sub 6} as the first binary {tau}-boride (Fm3-barm,a=10.4618(13) A, 104 refl., 14 param., R{sub 1}(F)=0.0132, wR{sub 2}(F{sup 2})=0.0210). With M=Ir mixed occupations occur for all sites and the boron content varies. The composition for the boron-poor single crystal was Co{sub 16.2}Ir{sub 6.8}B{sub 6}. A higher Ir-content enables the uptake of additional boron resulting in a composition Co{sub 12.3}Ir{sub 8.9}B{sub 10.5}. This can be explained be the substitution of metal atoms on the 8c-site by B{sub 4}-tetrahedra. A boron-rich phase was observed for the first time for a {tau}-boride of cobalt. All compositions were confirmed by EDX measurements. - Graphical Abstract: Single crystal investigations on {tau}-borides Co/M/B with M = Al, Ga, In, Sn, V, Ti, Ir explained the substitution processes. Furthermore the yielded the first binary boride, Co{sub 23}B{sub 6}, and a boron-rich Co{sub 12.3}Ir{sub 8.9}B{sub 10.5} containing B{sub 4}-tetrahedra.

  1. Surface complexation of neptunium (V) onto whole cells and cell componets of Shewanella alga

    SciTech Connect

    Reed, Donald Timothy; Deo, Randhir P; Rittmann, Bruce E; Songkasiri, Warinthorn

    2008-01-01

    We systematically quantified surface complexation of neptunium(V) onto whole cells of Shewanella alga strain BrY and onto cell wall and extracellular polymeric substances (EPS) of S. alga. We first performed acid and base titrations and used the mathematical model FITEQL with constant-capacitance surface-complexation to determine the concentrations and deprotonation constants of specific surface functional groups. Deprotonation constants most likely corresponded to a carboxyl site associated with amino acids (pK{sub a} {approx} 2.4), a carboxyl group not associated with amino acids (pK{sub a} {approx} 5), a phosphoryl site (pK{sub a} {approx} 7.2), and an amine site (pK{sub a} > 10). We then carried out batch sorption experiments with Np(V) and each of the S. alga components at different pHs. Results show that solution pH influenced the speciation of Np(V) and each of the surface functional groups. We used the speciation sub-model of the biogeochemical model CCBATCH to compute the stability constants for Np(V) complexation to each surface functional group. The stability constants were similar for each functional group on S. alga bacterial whole cells, cell walls, and EPS, and they explain the complicated sorption patterns when they are combined with the aqueous-phase speciation of Np(V). For pH < 8, NpO{sub 2}{sup +} was the dominant form of Np(V), and its log K values for the low-pK{sub a} carboxyl, other carboxyl, and phosphoryl groups were 1.75, 1.75, and 2.5 to 3.1, respectively. For pH greater than 8, the key surface ligand was amine >XNH3+, which complexed with NpO{sub 2}(CO{sub 3}){sub 3}{sup 5-}. The log K for NpO{sub 2}(CO{sub 3}){sub 3}{sup 5-} complexed onto the amine groups was 3.1 to 3.6. All of the log K values are similar to those of Np(V) complexes with aqueous carboxyl and N-containing carboxyl ligands. These results point towards the important role of surface complexation in defining key actinide-microbiological interactions in the subsurface.

  2. Chemical speciation of neptunium(VI) under strongly alkaline conditions. Structure, composition, and oxo ligand exchange.

    PubMed

    Clark, David L; Conradson, Steven D; Donohoe, Robert J; Gordon, Pamela L; Keogh, D Webster; Palmer, Phillip D; Scott, Brian L; Tait, C Drew

    2013-04-01

    Hexavalent neptunium can be solubilized in 0.5-3.5 M aqueous MOH (M = Li(+), Na(+), NMe4(+) = TMA(+)) solutions. Single crystals were obtained from cooling of a dilute solution of Co(NH3)6Cl3 and NpO2(2+) in 3.5 M [N(Me)4]OH to 5 °C. A single-crystal X-ray diffraction study revealed the molecular formula of [Co(NH3)6]2[NpO2(OH)4]3·H2O, isostructural with the uranium analogue. The asymmetric unit contains three distinct NpO2(OH)4(2-) ions, each with pseudooctahedral coordination geometry with trans-oxo ligands. The average Np═O and Np-OH distances were determined to be 1.80(1) and 2.24(1) Å, respectively. EXAFS data and fits at the Np L(III)-edge on solid [Co(NH3)6]2[NpO2(OH)4]3·H2O and aqueous solutions of NpO2(2+) in 2.5 and 3.5 M (TMA)OH revealed bond lengths nearly identical with those determined by X-ray diffraction but with an increase in the number of equatorial ligands with increasing (TMA)OH concentration. Raman spectra of single crystals of [Co(NH3)6]2[NpO2(OH)4]3·H2O reveal a ν1(O═Np═O) symmetric stretch at 741 cm(-1). Raman spectra of NpO2(2+) recorded in a 0.6-2.2 M LiOH solution reveal a single ν1 frequency of 769 cm(-1). Facile exchange of the neptunyl oxo ligands with the water solvent was also observed with Raman spectroscopy performed with (16)O- and (18)O-enriched water solvent. The combination of EXAFS and Raman data suggests that NpO2(OH)4(2-) is the dominant solution species under the conditions of study and that a small amount of a second species, NpO2(OH)5(3-), may also be present at higher alkalinity. Crystal data for [Co(NH3)6]2[NpO2(OH)4]3·H2O: monoclinic, space group C2/c, a = 17.344(4) Å, b = 12.177(3) Å, c = 15.273 Å, β = 120.17(2)°, Z = 4, R1 = 0.0359, wR2 = 0.0729. PMID:23485079

  3. Effect of Oxalate on the Recycle of Neptunium Filtrate Solution by Anion Exchange

    SciTech Connect

    Kyser, E

    2004-11-18

    A series of laboratory column runs has been performed that demonstrates the recovery of neptunium (Np) containing up to 0.05 M oxalate. Np losses were generally less than one percent to the raffinate for feed solutions that contained 2 to 10 g Np/L. Up to 16 percent Np losses were observed with lower Np feed concentrations, but those losses were attributed to the shortened residence times rather than the higher oxalate to Np ratios. Losses in the plant are expected to be significantly less due to the lower cross-section flowrate possible with existing plant pumps. Elimination of the permanganate treatment of filtrates appears to be reasonable since the amount of Np in those filtrates does not appear to be practical to recover. Combination of untreated filtrates with other actinide rich solutions is not advisable as precipitation problems are likely. If untreated filtrates are kept segregated from other actinide rich streams, the recovery of the remaining Np is probably still possible, but could be limited due to the excessively high oxalate to Np ratio. The persistence of hydrazine/hydrazoic acid in filtrate solutions dictates that the nitrite treatment be retained to eliminate those species from the filtrates prior to transfer to the canyon. Elimination of the permanganate treatment of precipitator flushes and recovery by anion exchange does not appear to be limited by the oxalate effect on anion exchange. Np from solutions with higher oxalate to Np molar ratios than expected in precipitator flushes was recovered with low to modest losses. Solubility problems appear to be unlikely when the moles of oxalate involved are less than the total number of moles of Np due to complexation effects. The presence of significant concentrations of iron (Fe) in the solutions will further decrease the probability of Np oxalate precipitation due the formation of Fe oxalate complexes. Np oxalate solubility data in 8 M HNO{sub 3} with from one to six times as much oxalate as Np have

  4. New Synthetic Methods and Structure-Property Relationships in Neptunium, Plutonium, and Americium Borates. Final report

    SciTech Connect

    Albrecht-Schmitt, Thomas Edward

    2013-09-14

    The past three years of support by the Heavy Elements Chemistry Program have been highly productive in terms of advanced degrees awarded, currently supported graduate students, peer-reviewed publications, and presentations made at universities, national laboratories, and at international conferences. Ph.D. degrees were granted to Shuao Wang and Juan Diwu, who both went on to post-doctoral appointments at the Glenn T. Seaborg Center at Lawrence Berkeley National Laboratory with Jeff Long and Ken Raymond, respectively. Pius Adelani completed his Ph.D. with me and is now a post-doc with Peter C. Burns. Andrea Alsobrook finished her Ph.D. and is now a post-doc at Savannah River with Dave Hobbs. Anna Nelson completed her Ph.D. and is now a post-doc with Rod Ewing at the University of Michigan. As can be gleaned from this list, students supported by the Heavy Elements Chemistry grant have remained interested in actinide science after leaving my program. This follows in line with previous graduates in this program such as Richard E. Sykora, who did his post-doctoral work at Oak Ridge National Laboratory with R. G. Haire, and Amanda C. Bean, who is a staff scientist at Los Alamos National Laboratory, and Philip M. Almond and Thomas C. Shehee, who are both staff scientists at Savannah River National Laboratory, Gengbang Jin who is a staff scientist at Argonne National Lab, and Travis Bray who has been a post-doc at both LBNL and ANL. Clearly this program is serving as a pipe-line for students to enter into careers in the national laboratories. About half of my students depart the DOE complex for academia or industry. My undergraduate researchers also remain active in actinide chemistry after leaving my group. Dan Wells was a productive undergraduate of mine, and went on to pursue a Ph.D. on uranium and neptunium chalcogenides with Jim Ibers at Northwestern. After earning his Ph.D., he went directly into the nuclear industry.

  5. A Simple Kinetic Model for the Growth of Fe2B Layers on AISI 1026 Steel During the Powder-pack Boriding

    NASA Astrophysics Data System (ADS)

    Flores-Rentería, M. A.; Ortiz-Domínguez, M.; Keddam, M.; Damián-Mejía, O.; Elias-Espinosa, M.; Flores-González, M. A.; Medina-Moreno, S. A.; Cruz-Avilés, A.; Villanueva-Ibañez, M.

    2015-02-01

    This work focused on the determination of boron diffusion coefficient through the Fe2B layers on AISI 1026 steel using a mathematical model. The suggested model solves the mass balance equation at the (Fe2B/substrate) interface. This thermochemical treatment was carried out in the temperature range of 1123-1273 K for a treatment time ranging from 2 to 8 h. The generated boride layers were characterized by different experimental techniques such as light optical microscopy, scanning electron microscopy, XRD analysis and the Daimler-Benz Rockwell-C indentation technique. As a result, the boron activation energy for AISI 1026 steel was estimated as 178.4 kJ/mol. Furthermore, this kinetic model was validated by comparing the experimental Fe2B layer thickness with the predicted one at a temperature of 1253 K for 5 h of treatment. A contour diagram relating the layer thickness to the boriding parameters was proposed to be used in practical applications.

  6. ELECTRONIC SOLUTION SPECTRA FOR URANIUM AND NEPTUNIUM IN OXIDATION STATES (III) TO (VI) IN ANHYDROUS HYDROGEN FLUORIDE

    SciTech Connect

    Baluka, M.; Edelstein, N.; O'Donnell, T. A.

    1980-10-01

    Spectra have been recorded for solutions in anhydrous hydrogen fluoride (AHF) of uranium and neptunium in oxidation states (III) to (VI). The spectra for U(III), Np(III) and Np(IV) in AHF are very similar to those in acidified aqueous solution, but that for U(IV) suggests that the cationic species is UF{sub 2}{sup 2+}. The AHF spectra for the elements in oxidation states (V) and (VI) are not comparable with those of the formally analogous aqueous solutions, where the elements exist as well-defined dioxo-cations. However, the AHF spectra can be related to spectra in the gas phase, in the solid state or in non-aqueous solvents for each element in its appropriate oxidation state.

  7. A theoretical study of the structures and chemical bonds of neptunium (III) molecules by a density functional method

    NASA Astrophysics Data System (ADS)

    Yin, Yao-Peng; Dong, Chen-Zhong; Du, Lei-Qiang; Wu, Fang-Xian; Ding, Xiao-Bin

    2014-10-01

    In this paper, equilibrium structures and chemical bond characteristics of neptunium trihalide molecules NpX3 (X = F, Cl, Br and I) have been investigated by using density functional theory (DFT). The influences of the size of the relativistic effective core potential (RECP) have been examined on the molecular structures. The chemical bond characteristics have also been systematically studied by calculating the density of states (DOS), bond length differences and electronic charge distributions. We have determined that the chemical bonds are mainly ionic in those molecules, and the covalency is enhancing while ionicity decreases from NpF3 to NpI3. The calculated bond energies show that the interaction strength in NpX3 molecules becomes weaker as the halogen atoms becoming heavier.

  8. ESTIMATED NEPTUNIUM SEDIMENT SORPTION VALUES AS A FUNCTION OF PH AND MEASURED BARIUM AND RADIUM KD VALUES

    SciTech Connect

    Kaplan, D.

    2011-01-13

    The objective of this document is to provide traceability and justification for a select few new geochemical data used in the Special Analysis entitled 'Special Analysis for the Dose Assessment of the Final Inventories in Center Slit Trenches One through Five'. Most values used in the Special Analysis came from the traditional geochemical data package, however, some recent laboratory measurements have made it possible to estimate barium K{sub d} values. Additionally, some recent calculations were made to estimate neptunium K{sub d} values as a function of pH. The assumptions, justifications, and calculations needed to generate these new values are presented in this document, and the values are summarized.

  9. Determination of technetium-99, neptunium-237 and isotopes of thorium in uranyl nitrate solutions from a reprocessing plant, using double-focusing ICP-MS

    SciTech Connect

    Mitterrand, B.; Leprovost, P.; Delaunay, J.; Vian, A.M.

    1998-12-31

    The determination of some radionuclides in uranyl nitrate solutions from a reprocessing plant through chemical or radiochemical methods may be tedious, with poor precision. Quadrupole ICP-MS and, more recently, double-focusing ICP-MS, with high resolution capabilities, have proved to be very efficient tools for such determinations. These improvements will be illustrated by the examples of Technetium-99, Neptunium-237 and Thorium.

  10. High-throughput sequential injection method for simultaneous determination of plutonium and neptunium in environmental solids using macroporous anion-exchange chromatography, followed by inductively coupled plasma mass spectrometric detection.

    PubMed

    Qiao, Jixin; Hou, Xiaolin; Roos, Per; Miró, Manuel

    2011-01-01

    This paper reports an automated analytical method for rapid and simultaneous determination of plutonium and neptunium in soil, sediment, and seaweed, with detection via inductively coupled plasma mass spectrometry (ICP-MS). A chromatographic column packed with a macroporous anion exchanger (AG MP-1 M) was incorporated in a sequential injection (SI) system for the efficient retrieval of plutonium, along with neptunium, from matrix elements and potential interfering nuclides. The sorption and elution behavior of plutonium and neptunium onto AG MP-1 M resin was compared with a commonly utilized AG 1-gel-type anion exchanger. Experimental results reveal that the pore structure of the anion exchanger plays a pivotal role in ensuring similar separation behavior of plutonium and neptunium along the separation protocol. It is proven that plutonium-242 ((242)Pu) performs well as a tracer for monitoring the chemical yield of neptunium when using AG MP-1 M resin, whereby the difficulties in obtaining a reliable and practicable isotopic neptunium tracer are overcome. An important asset of the SI setup is the feasibility of processing up to 100 g of solid substrates using a small-sized (ca. 2 mL) column with chemical yields of neptunium and plutonium being ≥79%. Analytical results of three certified/standard reference materials and two solid samples from intercomparison exercises are in good agreement with the reference values at the 0.05 significance level. The overall on-column separation can be completed within 3.5 h for 10 g of soil samples. Most importantly, the anion-exchange mini-column suffices to be reused up to 10-fold with satisfactory chemical yields (>70%), as demanded in environmental monitoring and emergency scenarios, making the proposed automated assembly well-suited for unattended and high-throughput analysis. PMID:21121695

  11. X-Ray photoelectron spectroscopy study of radiofrequency-sputtered titanium, carbide, molybdenum carbide, and titanium boride coatings and their friction properties

    NASA Technical Reports Server (NTRS)

    Brainard, W. A.; Wheeler, D. R.

    1977-01-01

    Radiofrequency sputtered coatings of titanium carbide, molybdenum carbide and titanium boride were tested as wear resistant coatings on stainless steel in a pin on disk apparatus. X-ray photoelectron spectroscopy (XPS) was used to analyze the sputtered films with regard to both bulk and interface composition in order to obtain maximum film performance. Significant improvements in friction behavior were obtained when properly biased films were deposited on deliberately preoxidized substrates. XPS depth profile data showed thick graded interfaces for bias deposited films even when adherence was poor. The addition of 10 percent hydrogen to the sputtering gas produced coatings with thin poorly adherent interfaces. Results suggest that some of the common practices in the field of sputtering may be detrimental to achieving maximum adherence and optimum composition for these refractory compounds.

  12. Metallic Borides, La2Re3B7 and La3Re2B5, Featuring Extensive Boron-Boron Bonding.

    PubMed

    Bugaris, Daniel E; Malliakas, Christos D; Chung, Duck Young; Kanatzidis, Mercouri G

    2016-02-15

    La2Re3B7 and La3Re2B5 have been synthesized in single-crystalline form from a molten La/Ni eutectic at 1000 °C in the first example of the flux crystal growth of ternary rare-earth rhenium borides. Both compounds crystallize in their own orthorhombic structure types, with La2Re3B7 (space group Pcca) having lattice parameters a = 7.657(2) Å, b = 6.755(1) Å, and c = 11.617(2) Å, and La3Re2B5 (space group Pmma) having lattice parameters a = 10.809(2) Å, b = 5.287(1) Å, and c = 5.747(1) Å. The compounds possess three-dimensional framework structures that are built up from rhenium boride polyhedra and boron-boron bonding. La3Re2B5 features fairly common B2 dumbbells, whereas La2Re3B7 has unique one-dimensional subunits composed of alternating triangular B3 and trans-B4 zigzag chain fragments. Also observed in La3Re2B5 is an unusual coordination of B by an octahedron of La atoms. Electronic band structure calculations predict that La2Re3B7 is a semimetal, which is observed in the electrical resistivity data as measured on single crystals, with behavior obeying the Bloch-Grüneisen model and a room-temperature resistivity ρ300 K of ∼375 μΩ cm. The electronic band structure calculations also suggest that La3Re2B5 is a regular metal. PMID:26812202

  13. Pressed boride cathodes

    NASA Technical Reports Server (NTRS)

    Wolski, W.

    1985-01-01

    Results of experimental studies of emission cathodes made from lanthanum, yttrium, and gadolinium hexaborides are presented. Maximum thermal emission was obtained from lanthanum hexaboride electrodes. The hexaboride cathodes operated stably under conditions of large current density power draw, at high voltages and poor vacuum. A microtron electron gun with a lanthanum hexaboride cathode is described.

  14. Laboratory And Lysimeter Experimentation And Transport Modeling Of Neptunium And Strontium In Savannah River Site Sediments

    SciTech Connect

    Kaplan, Daniel I.; Powell, B. A.; Miller, Todd J.

    2012-09-24

    The Savannah River Site (SRS) conducts performance assessment (PA) calculations to determine the appropriate amount of low-level radiological waste that can be safely disposed on site. Parameters are included in these calculations that account for the interaction between the immobile solid phase and the mobile aqueous phase. These parameters are either the distribution coefficient (K{sub d} value) or the apparent solubility value (K{sub sp}). These parameters are readily found in the literature and are used throughout the DOE complex. One shortcoming of K{sub d} values is that they are only applicable to a given set of solid and aqueous phase conditions. Therefore, a given radionuclide may have several K{sub d} values as it moves between formations and comes into contact with different solids and different aqueous phases. It is expected that the K{sub d} construct will be appropriate to use for a majority of the PA and for a majority of the radionuclides. However, semi-mechanistic models would be more representative in isolated cases where the chemistry is especially transitory or the radionuclide chemistry is especially complex, bringing to bear multiple species of varying sorption tendencies to the sediment. Semi-mechanistic models explicitly accommodate the dependency of K{sub d} values, or other sorption parameters, on contaminant concentration, competing ion concentrations, pH-dependent surface charge on the adsorbent, and solute species distribution. Incorporating semi-mechanistic concepts into geochemical models is desirable to make the models more robust and technically defensible. Furthermore, these alternative models could be used to augment or validate a Kd?based DOE Order 435.1 Performance Assessment. The objectives of this study were to: 1) develop a quantitative thermodynamically-based model for neptunium sorption to SRS sediments, and 2) determine a sorption constant from an SRS 11-year lysimeter study. The modeling studies were conducted with

  15. The electronic structure, mechanical and thermodynamic properties of Mo{sub 2}XB{sub 2} and MoX{sub 2}B{sub 4} (X = Fe, Co, Ni) ternary borides

    SciTech Connect

    He, TianWei; Jiang, YeHua E-mail: jfeng@seas.harvard.edu; Zhou, Rong; Feng, Jing E-mail: jfeng@seas.harvard.edu

    2015-08-21

    The mechanical properties, electronic structure and thermodynamic properties of the Mo{sub 2}XB{sub 2} and MoX{sub 2}B{sub 4} (X = Fe, Co, Ni) ternary borides were calculated by first-principles methods. The elastic constants show that these ternary borides are mechanically stable. Formation enthalpy of Mo{sub 2}XB{sub 2} and MoX{sub 2}B{sub 4} (X = Fe, Co, Ni) ternary borides are at the range of −118.09 kJ/mol to −40.14 kJ/mol. The electronic structures and chemical bonding characteristics are analyzed by the density of states. Mo{sub 2}FeB{sub 2} has the largest shear and Young's modulus because of its strong chemical bonding, and the values are 204.3 GPa and 500.3 GPa, respectively. MoCo{sub 2}B{sub 4} shows the lowest degree of anisotropy due to the lack of strong direction in the bonding. The Debye temperature of MoFe{sub 2}B{sub 4} is the largest among the six phases, which means that MoFe{sub 2}B{sub 4} possesses the best thermal conductivity. Enthalpy shows an approximately linear function of the temperature above 300 K. The entropy of these compounds increase rapidly when the temperature is below 450 K. The Gibbs free energy decreases with the increase in temperature. MoCo{sub 2}B{sub 4} has the lowest Gibbs free energy, which indicates the strongest formation ability in Mo{sub 2}XB{sub 2} and MoX{sub 2}B{sub 4} (X = Fe, Co, Ni) ternary borides.

  16. Verifying the Presence of Low Levels of Neptunium in a Uranium Matrix with Electron Energy-Loss Spectroscopy

    SciTech Connect

    Buck, Edgar C.; Douglas, Matthew; Wittman, Richard S.

    2010-01-01

    This paper examines the problems associated with the analysis of low levels of neptunium (Np) in a uranium (U) matrix with electron energy-loss spectroscopy (EELS) on the transmission electron microscope (TEM). The detection of Np in a matrix of uranium (U) can be impeded by the occurrence of a plural scattering event from U (U-M5 + U-O4,5) that results in severe overlap on the Np-M5 edge at 3665 eV. Low levels (1600 - 6300 ppm) of Np can be detected in U solids by confirming the energy gap between the Np-M5 and Np-M4 edges is at 184 eV and showing that the M4/M5 ratio for the Np is smaller than that for U. The Richardson-Lucy deconvolution method was applied to energy-loss spectral images and was shown to increase the signal to noise. This method also improves the limits of detection for Np in a U matrix.

  17. Formation of neptunium(IV)-silica colloids at near-neutral and slightly alkaline pH.

    PubMed

    Husar, Richard; Weiss, Stephan; Hennig, Christoph; Hübner, René; Ikeda-Ohno, Atsushi; Zänker, Harald

    2015-01-01

    The reducing conditions in a nuclear waste repository render neptunium tetravalent. Thus, Np is often assumed to be immobile in the subsurface. However, tetravalent actinides can also become mobile if they occur as colloids. We show that Np(IV) is able to form silica-rich colloids in solutions containing silicic acid at concentrations of both the regions above and below the "mononuclear wall" of silicic acid at 2 × 10(-3) M (where silicic acid is expected to start polymerization). These Np(IV)-silica colloids have a size of only very few nanometers and can reach significantly higher concentrations than Np(IV) oxyhydroxide colloids. They can be stable in the waterborne form over longer spans of time. In the Np(IV)-silica colloids, the actinide--oxygen--actinide bonds are increasingly replaced by actinide--oxygen--silicon bonds due to structural incorporation of Si. Possible implications of the formation of such colloids for environmental scenarios are discussed. PMID:25401282

  18. Potential for radionuclide immobilization in the EBS/NFE: solubility limiting phases for neptunium, plutonium, and uranium

    SciTech Connect

    Rard, J. A., LLNL

    1997-10-01

    Retardation and dispersion in the far field of radionuclides released from the engineered barrier system/near field environment (EBS/NFE) may not be sufficient to prevent regulatory limits being exceeded at the accessible environment. Hence, a greater emphasis must be placed on retardation and/or immobilization of radionuclides in the EBS/NFE. The present document represents a survey of radionuclide-bearing solid phases that could potentially form in the EBS/NFE and immobilize radionuclides released from the waste package and significantly reduce the source term. A detailed literature search was undertaken for experimental solubilities of the oxides, hydroxides, and various salts of neptunium, plutonium, and uranium in aqueous solutions as functions of pH, temperature, and the concentrations of added electrolytes. Numerous solubility studies and reviews were identified and copies of most of the articles were acquired. However, this project was only two months in duration, and copies of some the identified solubility studies could not be obtained at short notice. The results of this survey are intended to be used to assess whether a more detailed study of identified low- solubility phase(s) is warranted, and not as a data base suitable for predicting radionuclide solubility. The results of this survey may also prove useful in a preliminary evaluation of the efficacy of incorporating chemical additives to the EBS/NFE that will enhance radionuclide immobilization.

  19. Ternary Borides Cr2AlB2, Cr3AlB4, and Cr4AlB6: The First Members of the Series (CrB2)nCrAl with n = 1, 2, 3 and a Unifying Concept for Ternary Borides as MAB-Phases.

    PubMed

    Ade, Martin; Hillebrecht, Harald

    2015-07-01

    Single crystals of the ternary borides Cr2AlB2, Cr3AlB4, Cr4AlB6, MoAlB, WAlB, Mn2AlB2, and Fe2AlB2 were grown from the elements with an excess of Al. Structures were refined by X-ray methods on the basis of single crystal data. All compounds crystallize in orthorhombic space groups. In each case boron atoms show the typical trigonal prisms BM6. The BM6-units are linked by common rectangular faces forming B-B-bonds. Thus, zigzag chains of boron atoms are obtained for MoAlB, WAlB, and M2AlB2 (M = Cr, Mn, Fe); chains of hexagons for Cr3AlB4; and double chains of hexagons for Cr4AlB6. The same subunits are known for the binary borides CrB, Cr3B4, Cr2B3, and β-WB, too. The boride partial structures are separated by single layers of Al-atoms in the case of the chromium compounds and double layers for WAlB, i.e., W2Al2B2. All crystal structures can be described using a unified building set principle with quadratic 4(4)-nets of metal atoms. The different compositions and crystal structures are obtained by different numbers of metal layers in the corresponding parts according to the formula (MB)2Aly(MB2)x. This principle is an extension of a scheme which was developed for the boridecarbides of niobium. Furthermore, there is a close similarity to the group of ternary carbides MAl(MC)n, so-called MAX-phases. Therefore, they might be named as "MAB-phases". The pronounced two-dimensionality and the mixture of strong covalent and metallic interactions make MAB-phases to promising candidates for interesting material properties. All compositions were confirmed by EDX measurements. Additionally, microhardness measurements were performed. PMID:26069993

  20. Radionuclide sorption in Yucca Mountain tuffs with J-13 well water: Neptunium, uranium, and plutonium. Yucca Mountain site characterization program milestone 3338

    SciTech Connect

    Triay, I.R.; Cotter, C.R.; Kraus, S.M.; Huddleston, M.H.

    1996-08-01

    We studied the retardation of actinides (neptunium, uranium, and plutonium) by sorption as a function of radionuclide concentration in water from Well J-13 and of tuffs from Yucca Mountain. Three major tuff types were examined: devitrified, vitric, and zeolitic. To identify the sorbing minerals in the tuffs, we conducted batch sorption experiments with pure mineral separates. These experiments were performed with water from Well J-13 (a sodium bicarbonate groundwater) under oxidizing conditions in the pH range from 7 to 8.5. The results indicate that all actinides studied sorb strongly to synthetic hematite and also that Np(V) and U(VI) do not sorb appreciably to devitrified or vitric tuffs, albite, or quartz. The sorption of neptunium onto clinoptilolite-rich tuffs and pure clinoptilolite can be fitted with a sorption distribution coefficient in the concentration range from 1 X 10{sup -7} to 3 X 10{sup -5} M. The sorption of uranium onto clinoptilolite-rich tuffs and pure clinoptilolite is not linear in the concentration range from 8 X 10{sup -8} to 1 X 10{sup -4} M, and it can be fitted with nonlinear isotherm models (such as the Langmuir or the Freundlich Isotherms). The sorption of neptunium and uranium onto clinoptilolite in J-13 well water increases with decreasing pH in the range from 7 to 8.5. The sorption of plutonium (initially in the Pu(V) oxidation state) onto tuffs and pure mineral separates in J-13 well water at pH 7 is significant. Plutonium sorption decreases as a function of tuff type in the order: zeolitic > vitric > devitrified; and as a function of mineralogy in the order: hematite > clinoptilolite > albite > quartz.

  1. Critical Role of Water Content in the Formation and Reactivity of Uraniu, Neptunium, and Plutonium Iodates Under Hydrothermal Conditions: Implications for the Oxidative Dissolution of Spent Nuclear Fuel

    SciTech Connect

    Bray, T. H.; Ling, Jie; Choi, E- Sang; Brooks, James S.; Beitz, James V.; Sykora, Richard E.; Haire, Richard {Dick} G; Stanbury, David M.; Albrecht-Schmitt, Thomas E.

    2007-01-01

    The reactions of {sup 237}NpO{sub 2} with excess iodate under acidic hydrothermal conditions result in the isolation of the neptunium(IV), neptunium(V), and neptunium(VI) iodates, Np(IO{sub 3}){sub 4}, Np(IO{sub 3}){sub 4}{center_dot}nH{sub 2}O{center_dot}nHIO{sub 3}, NpO2(IO3), NpO2(IO3)2(H2O), and NpO{sub 2}(IO{sub 3}){sub 2}{center_dot}H{sub 2}O, depending on both the pH and the amount of water present in the reactions. Reactions with less water and lower pH favor reduced products. Although the initial redox processes involved in the reactions between {sup 237}NpO{sub 2} or {sup 242}PuO{sub 2} and iodate are similar, the low solubility of Pu(IO{sub 3}){sub 4} dominates product formation in plutonium iodate reactions to a much greater extent than does Np(IO{sub 3}){sub 4} in the neptunium iodate system. UO{sub 2} reacts with iodate under these conditions to yield uranium(VI) iodates solely. The isotypic structures of the actinide(IV) iodates, An(IO{sub 3}){sub 4} (An = Np, Pu), are reported and consist of one-dimensional chains of dodecahedral An(IV) cations bridged by iodate anions. The structure of Np(IO3)4{center_dot}nH2O{center_dot}nHIO3 is constructed from NpO9 tricapped-trigonal prisms that are bridged by iodate into a polar three-dimensional framework structure. Second-harmonic-generation measurements on a polycrystalline sample of the Th analogue of Np(IO{sub 3}){sub 4}{center_dot}nH{sub 2}O{center_dot}nHIO{sub 3} reveal a response of approximately 12x that of {alpha}-SiO{sub 2}. Single-crystal magnetic susceptibility measurements of Np(IO{sub 3}){sub 4} show magnetically isolated Np(IV) ions.

  2. Measurement of total alpha activity of neptunium, plutonium, and americium in highly radioactive Hanford waste by iron hydroxide precipitation and 2-heptanone solvent extraction

    SciTech Connect

    Maiti, T.C.; Kaye, J.H.

    1992-06-01

    An improved method has been developed to concentrate the major alpha-emitting actinide elements neptunium, plutonium, and americium from samples with high salt content such as those resulting from efforts to characterize Hanford storage tank waste. Actinide elements are concentrated by coprecipitation of their hydroxides using iron carrier. The iron is removed by extraction from 8M HCI with 2-heptanone. The actinide elements remain in the aqueous phase free from salts, iron, and long-lived fission products. Recoveries averaged 98 percent.

  3. Sequential injection approach for simultaneous determination of ultratrace plutonium and neptunium in urine with accelerator mass spectrometry.

    PubMed

    Qiao, Jixin; Hou, Xiaolin; Roos, Per; Lachner, Johannes; Christl, Marcus; Xu, Yihong

    2013-09-17

    An analytical method was developed for simultaneous determination of ultratrace level plutonium (Pu) and neptunium (Np) using iron hydroxide coprecipitation in combination with automated sequential injection extraction chromatography separation and accelerator mass spectrometry (AMS) measurement. Several experimental parameters affecting the analytical performance were investigated and compared including sample preboiling operation, aging time, amount of coprecipitating reagent, reagent for pH adjustment, sedimentation time, and organic matter decomposition approach. The overall analytical results show that preboiling and aging are important for obtaining high chemical yields for both Pu and Np, which is possibly related to the aggregation and adsorption behavior of organic substances contained in urine. Although the optimal condition for Np and Pu simultaneous determination requires 5-day aging time, an immediate coprecipitation without preboiling and aging could also provide fairly satisfactory chemical yields for both Np and Pu (50-60%) with high sample throughput (4 h/sample). Within the developed method, (242)Pu was exploited as chemical yield tracer for both Pu and Np isotopes. (242)Pu was also used as a spike in the AMS measurement for quantification of (239)Pu and (237)Np concentrations. The results show that, under the optimal experimental condition, the chemical yields of (237)Np and (242)Pu are nearly identical, indicating the high feasibility of (242)Pu as a nonisotopic tracer for (237)Np determination in real urine samples. The analytical method was validated by analysis of a number of urine samples spiked with different levels of (237)Np and (239)Pu. The measured values of (237)Np and (239)Pu by AMS exhibit good agreement (R(2) ≥ 0.955) with the spiked ones confirming the reliability of the proposed method. PMID:23952680

  4. INCORPORATION OF PENTAVALENT NEPTUNIUM INTO URANYL PHASES THAT MAY FORM AS ALTERATION PRODUCTS OF SPENT NUCLEAR FUEL

    SciTech Connect

    NA

    2005-06-21

    Laboratory-scale simulations and studies of natural analogues have shown that alteration of spent nuclear fuel in a moist, oxidizing environment results in the formation of a variety of uranyl phases. Neptunium-237 has a half-life of 2.14 million years, and the pentavalent oxidation state is soluble in groundwater. Release of Np-237 from spent nuclear fuel in a geological repository may significantly impact the long-term performance of such a repository. Incorporation of Np, in the pentavalent oxidation state, into uranyl phases by substitution for hexavalent U is likely because of the similarity of the coordination environments of these two cations, but a charge-balance mechanism is required for substitution. A preliminary study has shown incorporation of pentavalent Np into powders of the uranyl silicate uranophane, and Na-compreignacite, a uranyl oxyhydrate [1]. Using synthesis experiments under mild hydrothermal conditions, we are examining the incorporation of pentavalent Np into selected uranyl oxyhydrates and silicates as a function of temperature and the pH of the mother solution. Analyses of powders of these uranyl phases has demonstrated both temperature and pH dependences for incorporation. Experiments are underway directed at the synthesis of single crystals of uranyl phases in the presence of 500-750 ppm pentavalent Np. The intent is to develop a basic understanding of the crystallographic and crystal chemical factors that impact incorporation of pentavalent Np into uranyl phases. Following synthesis, crystals are analyzed for Np using laser ablation ICP-MS. Preliminary results for Na-substituted metaschoepite indicate significant Np has been incorporated into the crystals. Additional phases under study include compreignacite, becquerelite, soddyite, zippeite, and (UO{sub 2}){sub 3}(PO{sub 4}){sub 2}(H{sub 2}O){sub 4}.

  5. Stability and crystal chemistry of the ternary borides M2(Ni21-xMx)B6 (M tbnd Ti, Zr, Hf)

    NASA Astrophysics Data System (ADS)

    Artini, C.; Provino, A.; Valenza, F.; Pani, M.; Cacciamani, G.

    2016-01-01

    A crystallochemical study was undertaken to investigate the structural stability and the compositional extent of the ternary borides M2(Ni21-xMx)B6 (M tbnd Ti, Zr, Hf). This phase often occurs during the production of MB2 joints by means of Ni-B brazing alloys. Samples with the nominal compositions M2Ni21B6 and M3Ni20B6 were synthesized by arc melting and characterized by optical and electron microscopy, and X-ray diffraction. Crystal structure refinements were performed by the Rietveld method. The compositional boundaries of the ternary phases were experimentally determined and found strictly related to the M/Ni size ratio. The stability of this structure is mainly determined by the capability of the structure to expand under the effect of the Ni substitution by the M atom. The CALPHAD modeling of the three M-Ni-B ternary systems in the Ni-rich corner of the phase diagram, performed on the basis of the obtained structural data, shows a good agreement with experimental results.

  6. An XPS study of the adherence of refractory carbide, silicide, and boride RF-sputtered wear-resistant coatings. [X-ray Photoelectron Spectroscopy of steel surfaces

    NASA Technical Reports Server (NTRS)

    Brainard, W. A.; Wheeler, D. R.

    1978-01-01

    Radio frequency sputtering was used to deposit refractory carbide, silicide, and boride coatings on 440-C steel substrates. Both sputter etched and pre-oxidized substrates were used and the films were deposited with and without a substrate bias. The composition of the coatings was determined as a function of depth by X-ray photoelectron spectroscopy combined with argon ion etching. Friction and wear tests were conducted to evaluate coating adherence. In the interfacial region there was evidence that bias may produce a graded interface for some compounds. Biasing, while generally improving bulk film stoichiometry, can adversely affect adherence by removing interfacial oxide layers. Oxides of all film constituents except carbon and iron were present in all cases but the iron oxide coverage was only complete on the preoxidized substrates. The film and iron oxides were mixed in the MoSi2 and Mo2C films but layered in the Mo2B5 films. In the case of mixed oxides, preoxidation enhanced film adherence. In the layered case it did not.

  7. Microstructural Characterization and Wear Behavior of Nano-Boride Dispersed Coating on AISI 304 Stainless Steel by Hybrid High Velocity Oxy-Fuel Spraying Laser Surface Melting

    NASA Astrophysics Data System (ADS)

    Sharma, Prashant; Majumdar, Jyotsna Dutta

    2015-07-01

    The current study concerns the detailed microstructural characterization and investigation of wear behavior of nano-boride dispersed coating developed on AISI 304 stainless steel by high velocity oxy-fuel spray deposition of nickel-based alloy and subsequent laser melting. There is a significant refinement and homogenization of microstructure with improvement in microhardness due to laser surface melting (1200 VHN as compared to 945 VHN of as-sprayed and 250 VHN of as-received substrate). The high temperature phase stability of the as-coated and laser melted surface has been studied by differential scanning calorimeter followed by detailed phase analysis at room and elevated temperature. There is a significant improvement in wear resistance of laser melted surface as compared to as-sprayed and the as-received one due to increased hardness and reduced coefficient of friction. The mechanism of wear has been investigated in details. Corrosion resistance of the coating in a 3.56 wt pct NaCl solution is significantly improved (4.43 E-2 mm/year as compared to 5 E-1 mm/year of as-sprayed and 1.66 mm/year of as-received substrate) due to laser surface melting as compared to as-sprayed surface.

  8. Synthesis, crystal structure, and physical properties of a new boride Ga2Ni21B20 with a modified Zn2Ni21B20-type structure

    NASA Astrophysics Data System (ADS)

    Zheng, Qiang; Gumeniuk, Roman; Schnelle, Walter; Prots, Yurii; Burkhardt, Ulrich; Leithe-Jasper, Andreas

    2016-05-01

    A ternary boride Ga2Ni21B20, with modified Zn2Ni21B20-type structure (space group I4/mmm, and lattice parameters a = 7.2164(1) Å, c = 14.2715(4) Å), was synthesized from the constituent elements. Single crystal diffraction data reveal Ni at 8f site splitting into 16m position with nearly half occupancy. In this structure, [Ni6B20] cages share ligand boron atoms with [Ga2B4Ni9] hexa-capped square prisms, forming two dimensional layers. Layers are interconnected via Ga-Ni interactions and build up a three-dimensional framework. Quasi-two-dimensional infinite planar nets formed by intercrossed Ni atoms are embedded. Ga2Ni21B20 is a metallic Pauli paramagnet, in agreement with electronic structure calculations, resulting in 8.2 states eV-1 f.u-1 at the Fermi level.

  9. Sensitive redox speciation of iron, neptunium, and plutonium by capillary electrophoresis hyphenated to inductively coupled plasma sector field mass spectrometry.

    PubMed

    Graser, Carl-Heinrich; Banik, Nidhu Lal; Bender, Kerstin Anne; Lagos, Markus; Marquardt, Christian Michael; Marsac, Rémi; Montoya, Vanessa; Geckeis, Horst

    2015-10-01

    The long-term safety assessment for nuclear waste repositories requires a detailed understanding of actinide (geo)chemistry. Advanced analytical tools are required to gain insight into actinide speciation in a given system. The geochemical conditions in the vicinity of a nuclear repository control the redox state of radionuclides, which in turn has a strong impact on their mobility. Besides the long-lived radionuclides plutonium (Pu) and neptunium (Np), which are key elements in high level nuclear waste, iron (Fe) represents a main component in natural systems controlling redox-related geochemical processes. Measuring the oxidation state distribution for redox sensitive radionuclides and other metal ions is challenging at trace concentrations below the detection limit of most available spectroscopic methods (≥10(-6) M). Consequently, ultrasensitive new analytical techniques are required. Capillary electrophoresis (CE) is a suitable separation method for metal cations. CE hyphenated to inductively coupled plasma sector field mass spectrometry (CE-ICP-SF-MS) was used to measure the redox speciation of Pu (III, IV, V, VI), Np (IV, V, VI), and Fe (II, III) at concentrations lower than 10(-7) M. CE coupling and separation parameters such as sample gas pressure, make up flow rate, capillary position, auxiliary gas flow, as well as the electrolyte system were optimized to obtain the maximum sensitivity. We obtain detection limits of 10(-12) M for Np and Pu. The various oxidation state species of Pu and Np in different samples were separated by application of an acetate-based electrolyte system. The separation of Fe (II) and Fe (III) was investigated using different organic complexing ligands, EDTA, and o-phenanthroline. For the Fe redox system, a limit of detection of 10(-8) M was calculated. By applying this analytical system to sorption studies, we were able to underline previously published results for the sorption behavior of Np in highly diluted concentrations, and

  10. History of ``NANO''-Scale VERY EARLY Solid-State (and Liquid-State) Physics/Chemistry/Metallurgy/ Ceramics; Interstitial-Alloys Carbides/Nitrides/Borides/...Powders and Cermets, Rock Shocks, ...

    NASA Astrophysics Data System (ADS)

    Maiden, Colin; Siegel, Edward

    History of ``NANO'': Siegel-Matsubara-Vest-Gregson[Mtls. Sci. and Eng. 8, 6, 323(`71); Physica Status Solidi (a)11,45(`72)] VERY EARLY carbides/nitrides/borides powders/cermets solid-state physics/chemistry/metallurgy/ ceramics FIRST-EVER EXPERIMENTAL NANO-physics/chemistry[1968 ->Physica Status Solidi (a)11,45(`72); and EARLY NANO-``physics''/NANO-``chemistry'' THEORY(after: Kubo(`62)-Matsubara(`60s-`70s)-Fulde (`65) [ref.: Sugano[Microcluster-Physics, Springer('82 `98)

  11. Crystal structures and compressibility of novel iron borides Fe{sub 2}B{sub 7} and Fe{sub x}B{sub 50} synthesized at high pressure and high temperature

    SciTech Connect

    Bykova, E.; Gou, H.; Bykov, M.; Hanfland, M.; Dubrovinsky, L.; Dubrovinskaia, N.

    2015-10-15

    We present here a detailed description of the crystal structures of novel iron borides, Fe{sub 2}B{sub 7} and Fe{sub x}B{sub 50} with various iron content (x=1.01(1), 1.04(1), 1.32(1)), synthesized at high pressures and high temperatures. As revealed by high-pressure single-crystal X-ray diffraction, the structure of Fe{sub 2}B{sub 7} possesses short incompressible B–B bonds, which make it as stiff as diamond in one crystallographic direction. The volume compressibility of Fe{sub 2}B{sub 7} (the bulk modulus K{sub 0}= 259(1.8) GPa, K{sub 0}′= 4 (fixed)) is even lower than that of FeB{sub 4} and comparable with that of MnB{sub 4}, known for high bulk moduli among 3d metal borides. Fe{sub x}B{sub 50} adopts the structure of the tetragonal δ-B, in which Fe atoms occupy an interstitial position. Fe{sub x}B{sub 50} does not show considerable anisotropy in the elastic behavior. - Graphical abstract: Crystal structures of novel iron borides, Fe{sub 2}B{sub 7} and Fe{sub x}B{sub 50} (x=1.01(1), 1.04(1), 1.32(1)). - Highlights: • Novel iron borides, Fe{sub 2}B{sub 7} and Fe{sub x}B{sub 50}, were synthesized under HPHT conditions. • Fe{sub 2}B{sub 7} has a unique orthorhombic structure (space group Pbam). • Fe{sub 2}B{sub 7} possesses short incompressible B–B bonds that results in high bulk modulus. • Fe{sub x}B{sub 50} adopts the structure of the tetragonal δ-B composed of B{sub 12} icosahedra. • In Fe{sub x}B{sub 50} intraicosahedral bonds are stiffer than intericosahedral ones.

  12. Ternary borides Nb7Fe3B8 and Ta7Fe3B8 with Kagome-type iron framework.

    PubMed

    Zheng, Qiang; Gumeniuk, Roman; Borrmann, Horst; Schnelle, Walter; Tsirlin, Alexander A; Rosner, Helge; Burkhardt, Ulrich; Reissner, Michael; Grin, Yuri; Leithe-Jasper, Andreas

    2016-06-21

    Two new ternary borides TM7Fe3B8 (TM = Nb, Ta) were synthesized by high-temperature thermal treatment of samples obtained by arc-melting. This new type of structure with space group P6/mmm, comprises TM slabs containing isolated planar hexagonal [B6] rings and iron centered TM columns in a Kagome type of arrangement. Chemical bonding analysis in Nb7Fe3B8 by means of the electron localizability approach reveals two-center interactions forming the Kagome net of Fe and embedded B, while weaker multicenter bonding present between this net and Nb atoms. Magnetic susceptibility measurements reveal antiferromagnetic order below TN = 240 K for Nb7Fe3B8 and TN = 265 K for Ta7Fe3B8. Small remnant magnetization below 0.01μB per f.u. is observed in the antiferromagnetic state. The bulk nature of the magnetic transistions was confirmed by the hyperfine splitting of the Mössbauer spectra, the sizable anomalies in the specific heat capacity, and the kinks in the resistivity curves. The high-field paramagnetic susceptibilities fitted by the Curie-Weiss law show effective paramagnetic moments μeff≈ 3.1μB/Fe in both compounds. The temperature dependence of the electrical resistivity also reveals metallic character of both compounds. Density functional calculations corroborate the metallic behaviour of both compounds and demonstrate the formation of a sizable local magnetic moment on the Fe-sites. They indicate the presence of both antiferro- and ferrromagnetic interactions. PMID:27216270

  13. Expansion of the rich structures and magnetic properties of neptunium selenites: soft ferromagnetism in Np(SeO3)2.

    PubMed

    Diefenbach, Kariem; Lin, Jian; Cross, Justin N; Dalal, Naresh S; Shatruk, Michael; Albrecht-Schmitt, Thomas E

    2014-07-21

    Two new neptunium selenites with different oxidation states of the metal centers, Np(IV)(SeO3)2 and Np(VI)O2(SeO3), have been synthesized under mild hydrothermal conditions at 200 °C from the reactions of NpO2 and SeO2. Np(SeO3)2 crystallizes as brown prisms (space group P21/n, a = 7.0089(5) Å, b = 10.5827(8) Å, c = 7.3316(5) Å, β = 106.953(1)°); whereas NpO2(SeO3) crystals are garnet-colored with an acicular habit (space group P21/m, a = 4.2501(3) Å, b = 9.2223(7) Å, c = 5.3840(4) Å, β = 90.043(2)°). Single-crystal X-ray diffraction studies reveal that the structure of Np(SeO3)2 features a three-dimensional (3D) framework consisting of edge-sharing NpO8 units that form chains that are linked via SeO3 units to create a 3D framework. NpO2(SeO3) possesses a lamellar structure in which each layer is composed of NpO8 hexagonal bipyramids bridged via SeO3(2-) anions. Bond-valence sum calculations and UV-vis-NIR absorption spectra support the assignment of tetravalent and hexavalent states of neptunium in Np(SeO3)2 and NpO2(SeO3), respectively. Magnetic susceptibility data for Np(SeO3)2 deviates substantially from typical Curie-Weiss behavior, which can be explained by large temperature-independent paramagnetic (TIP) effects. The Np(IV) selenite shows weak ferromagnetic ordering at 3.1(1) K with no detectable hysteresis, suggesting soft ferromagnetic behavior. PMID:24964359

  14. Identifying Sources of Non-fallout Nuclear Contamination in Hudson River Sediments by Plutonium and Neptunium isotope ratios.

    NASA Astrophysics Data System (ADS)

    Kenna, T. C.; Chillrud, S. N.

    2002-12-01

    In an effort to identify and characterize nuclear contaminants released from sources contained within the Hudson River drainage basin, Pu isotopes and 237Np have been measured in a series of sediment cores collected from various locations within the region. During the last several decades, the Hudson River has received input of radioactive contamination from several sources. The first and most significant, has been global fallout, which was a result of atmospheric testing of nuclear weapons primarily by governments of the United States and Former Soviet Union in the 1950s and 1960s. The second, is contamination resulting from reactor releases at the Indian Point Nuclear Power Plant (IPNPP) located on the Hudson River about 35 miles north of New York City. This facility began operation in 1962. A third source of radioactive contamination to the region is contamination resulting from activities at the Knolls Atomic Power Laboratory (KAPL) located on the Mohawk River, which began operation in 1946. Our research entails identifying different sources of nuclear contamination by measurement of plutonium and neptunium isotopic ratios by inductively coupled plasma mass spectrometry (ICP-MS). The isotopic composition of a nuclear contaminant is a sensitive indicator of its origin. By comparing the isotopic composition measured in fluvial sediments to mean values reported for global fallout (i.e. 240Pu/239Pu = 0.18 ñ 0.014, 237Np/239Pu = 0.48 ñ 0.07, and 241Pu/239Pu = .00194 ñ 00028) it is possible to identify contaminants as non-fallout in origin. To date, we have analyzed selected samples from 3 sediment cores collected from the following locations: 1) the Mohawk River downstream of KAPL, 2) the Hudson River above its confluence with the Mohawk River, and 3) the lower Hudson River at a location in close proximity to IPNPP. Isotopic analysis of sediments from the Mohawk River indicates contamination that is clearly non-fallout in origin (240Pu/239Pu ranges between 0

  15. Cd - Np (Cadmium - Neptunium)

    NASA Astrophysics Data System (ADS)

    Predel, B.

    This document is part of Volume 12 Phase Equilibria, Crystallographic and Thermodynamic Data of Binary Alloys', Subvolume B 'B - Ba … Cu - Zr, Supplement to Subvolumes IV/5B, IV/5C and IV/5D', of Landolt-Börnstein - Group IV 'Physical Chemistry'.

  16. B - Np (Boron - Neptunium)

    NASA Astrophysics Data System (ADS)

    Predel, B.

    This document is part of Volume 12 Phase Equilibria, Crystallographic and Thermodynamic Data of Binary Alloys', Subvolume B 'B - Ba … Cu - Zr, Supplement to Subvolumes IV/5B, IV/5C and IV/5D', of Landolt-Börnstein - Group IV 'Physical Chemistry'.

  17. Ternary rare earth metal boride carbides containing two-dimensional boron carbon network: The crystal and electronic structure of R2B4C (R=Tb, Dy, Ho, Er)

    NASA Astrophysics Data System (ADS)

    Babizhetskyy, Volodymyr; Zheng, Chong; Mattausch, Hansjürgen; Simon, Arndt

    2007-12-01

    The ternary rare earth boride carbides R2B4C (R=Tb, Dy, Ho, Er) have been synthesized by reacting the elements at temperatures between 1800 and 2000K. The crystal structure of Dy2B4C has been determined from single-crystal X-ray diffraction data. It crystallizes in a new structure type in the orthorhombic space group Immm (a=3.2772(6) Å, b=6.567(2) Å, c=7.542(1) Å, Z=2, R1=0.035 (wR2=0.10) for 224 reflections with Io>2σ(Io)). Boron atoms form infinite chains of fused B6 rings in [100] joined with carbon atoms into planar, two-dimensional networks which alternate with planar sheets of rare earth metal atoms. The electronic structure of Dy2B4C was also analyzed using the tight-binding extended Hückel method.

  18. Ternary boride product and process

    NASA Technical Reports Server (NTRS)

    Clougherty, Edward V. (Inventor)

    1976-01-01

    A hard, tough, strong ceramic body is formed by hot pressing a mixture of a powdered metal and a powdered metal diboride. The metal employed is zirconium, titanium or hafnium and the diboride is the diboride of a different member of the same group of zirconium, titanium or hafnium to form a ternary composition. During hot pressing at temperatures above about 2,000.degree.F., a substantial proportion of acicular ternary monoboride is formed.

  19. Method for determination of neptunium in large-sized urine samples using manganese dioxide coprecipitation and 242Pu as yield tracer.

    PubMed

    Qiao, Jixin; Hou, Xiaolin; Roos, Per

    2013-02-01

    A novel method for bioassay of large volumes of human urine samples using manganese dioxide coprecipitation for preconcentration was developed for rapid determination of (237)Np. (242)Pu was utilized as a nonisotopic tracer to monitor the chemical yield of (237)Np. A sequential injection extraction chromatographic (SI-EC) system coupled with inductively coupled plasma mass spectrometry (ICPMS) was exploited to facilitate the rapid column separation and quantification. The analytical results demonstrated satisfactory performance of the MnO(2) coprecipitation as indicated by the high chemical yields close to 100% and high separation capacity of processing up to 5 L of human urine samples. The MnO(2) coprecipitation process is simple and straightforward in which a batch (8-12) of samples can be pretreated within 4 h (i.e., <0.5 h/sample). In connection with the automated column separation and ICPMS quantification, which takes less than 1.5 h in total, the overall analytical time was on average less than 2 h for each sample. The high effectiveness and sample throughput make the developed method well suited for urine bioassay of (237)Np in routine monitoring of occupationally internal radiation exposure and rapid analysis of neptunium contamination level for emergency preparedness. PMID:23252688

  20. Synthesis, phase structure and microstructure of monazite-type Ce1-xPrxPO4 solid solutions for immobilization of minor actinide neptunium

    NASA Astrophysics Data System (ADS)

    Zeng, Pan; Teng, Yuancheng; Huang, Yi; Wu, Lang; Wang, Xiaohuan

    2014-09-01

    Praseodymium was used as the surrogate for trivalent minor actinide neptunium, and a complete series of pure monazite-type Ce1-xPrxPO4 (x = 0-1) solid solutions were successfully prepared by the solid state reaction. The effects of calcining temperature, holding time and Pr content on the structure of Ce1-xPrxPO4 solid solutions were investigated. The results show that although Pr6O11 (Pr23+Pr44+O11) exists two stabilized oxidation states, there has been no tetravalent praseodymium phosphate during the synthesis process. The optimized temperature for the synthesis of Ce0.8Pr0.2PO4 solid solution is more than 1100 °C, and a hypothetical reaction mechanism is also proposed. Besides, the crystalline grains coarsen as the increasing of holding time. The linear variation of unit cell parameters and a gradual hypsochromic shift in the Raman spectra are observed with the increase of Pr content, indicating that cerium is progressively replaced by praseodymium and Ce1-xPrxPO4 solid solutions were prepared.

  1. Structural Properties and Charge Distribution of the Sodium Uranium, Neptunium, and Plutonium Ternary Oxides: A Combined X-ray Diffraction and XANES Study.

    PubMed

    Smith, Anna L; Martin, Philippe; Prieur, Damien; Scheinost, Andreas C; Raison, Philippe E; Cheetham, Anthony K; Konings, Rudy J M

    2016-02-15

    The charge distributions in α-Na2UO4, Na3NpO4, α-Na2NpO4, Na4NpO5, Na5NpO6, Na2PuO3, Na4PuO5, and Na5PuO6 are investigated in this work using X-ray absorption near-edge structure (XANES) spectroscopy at the U-L3, Np-L3, and Pu-L3 edges. In addition, a Rietveld refinement of monoclinic Na2PuO3, in space group C2/c, is reported for the first time, and the existence of the isostructural Na2NpO3 phase is revealed. In contrast to measurements in solution, the number of published XANES data for neptunium and plutonium solid phases with a valence state higher than IV is very limited. The present results cover a wide range of oxidation states, namely, IV to VII, and can serve as reference for future investigations. The sodium actinide series show a variety of local coordination geometries, and correlations between the shape of the XANES spectra and the local structural environments are discussed herein. PMID:26835549

  2. Atomic site preferences and its effect on magnetic structure in the intermetallic borides M{sub 2}Fe(Ru{sub 0.8}T{sub 0.2}){sub 5}B{sub 2} (M=Sc, Ti, Zr; T=Ru, Rh, Ir)

    SciTech Connect

    Brgoch, Jakoah; Mahmoud, Yassir A.; Miller, Gordon J.

    2012-12-15

    The site preference for a class of intermetallic borides following the general formula M{sub 2}Fe(Ru{sub 0.8}T{sub 0.2}){sub 5}B{sub 2} (M=Sc, Ti, Zr; T=Ru, Rh, Ir), has been explored using ab initio and semi-empirical electronic structure calculations. This intermetallic boride series contains two potential sites, the Wyckoff 2c and 8j sites, for Rh or Ir to replace Ru atoms. Since the 8j site is a nearest neighbor to the magnetically active Fe atom, whereas the 2c site is a next nearest neighbor, the substitution pattern should play an important role in the magnetic structure of these compounds. The substitution preference is analyzed based on the site energy and bond energy terms, both of which arise from a tight-binding evaluation of the electronic band energy, and are known to influence the locations of atoms in extended solids. According to these calculations, the valence electron-rich Rh and Ir atoms prefer to occupy the 8j site, a result also corroborated by experimental evidence. Additionally, substitution of Rh or Ir at the 8j site results in a modification of the magnetic structure that ultimately results in larger local magnetic moment on the Fe atoms. - Graphical abstract: The site preference for electron rich atoms to occupy the 8j (gray) site is identified in these intermetallic borides, while the magnetic structure is modified as a function of the substituted atoms band center. Highlights: Black-Right-Pointing-Pointer We identify the energetics dictating the site preference in a series of intermetallic borides. Black-Right-Pointing-Pointer Establish substitution rules for use in future directed synthetic preparations. Black-Right-Pointing-Pointer Identified changes in magnetic structure that accompany the site preference.

  3. Synthesis and crystal structures of the new metal-rich ternary borides Ni{sub 12}AlB{sub 8}, Ni{sub 12}GaB{sub 8} and Ni{sub 10.6}Ga{sub 0.4}B{sub 6}-examples for the first B{sub 5} zig-zag chain fragment

    SciTech Connect

    Ade, Martin; Kotzott, Dominik; Hillebrecht, Harald

    2010-08-15

    Single crystals of the new borides Ni{sub 12}AlB{sub 8}, and Ni{sub 10.6}Ga{sub 0.4}B{sub 6} were synthesized from the elements and characterized by XRD and EDXS measurements. The crystal structures were refined on the basis of single crystal data. Ni{sub 12}AlB{sub 8} (oC252, Cmce, a=10.527(2), b=14.527(2), c=14.554(2) A, Z=12, 1350 reflections, 127 parameters, R{sub 1}(F)=0.0284, wR{sub 2}(F{sup 2})=0.0590) represents a new structure type with isolated B atoms and B{sub 5} fragments of a B-B zig-zag chain. Because the pseudotetragonal metric crystals are usually twinned. Ni{sub 10.6}Ga{sub 0.4}B{sub 6} (oP68, Pnma, a=12.305(2), b=2.9488(6), c=16.914(3) A, Z=4, 1386 reflections, 86 parameters, R{sub 1}(F)=0.0394, wR{sub 2}(F{sup 2})=0.104) is closely related to binary Ni borides. The structure contains B-B zig-zag chains and isolated B atoms. Ni{sub 12}GaB{sub 8} is isotypical to the Al-compound (a=10.569(4), b=14.527(4) and c=14.557(5) A). - Graphical abstract: Pentameric B{sub 5}-units are longest fragments of a B-B zig-zag chain ever characterized in a boride. They are found in the structures of Ni{sub 12}AlB{sub 8} and Ni{sub 12}GaB{sub 8}. The compounds are formed on annealing boron-rich {tau}-borides like Ni{sub 20}AlB{sub 14}.

  4. First-principles study of structural stability, elastic and electronic properties of ternary rare earth-transition metal—Borides and carbides (RTxZ, R=Sc, Y, and La, T=Pt and Pd, Z=B and C, and x=2, 3, and 4)

    NASA Astrophysics Data System (ADS)

    Yao, Tiankai; Wang, Yachun; Li, Hui; Lian, Jie; Zhang, Jingwu; Gou, Huiyang

    2013-12-01

    Using first-principles total energy calculations (CASTEP code), the structural stability, elastic, and electronic properties of ternary rare earth-transition metal borides and carbides (RTxZ, R=Sc, Y, and La, T=Pt and Pd, Z=B and C, and x=2, 3, and 4) compounds were studied. Results show that RT3Z compounds with tetragonal P4mm structure are energetically more favorable than usually cubic perovskite-type structure. Furthermore, RT3Z with perovskite structure is found to be mechanically unstable with the negative C44. Formation enthalpy calculations indicate that Pt-based borides are easier to be synthesized compared with Pd-based ones and counterpart carbides, respectively. Elastic constants, bulk moduli, shear moduli, Young's moduli, and Poisson's ratio of studied compounds have been calculated. Also, all the studied compounds show ductile behavior. Moreover, total and partial density of states (DOSs) and bonding charge density were employed to elucidate the bonding features of these compounds. The results reveal that the covalency between Pt-5d and Z-2p as well as T-nd (n=4 for Pd and 5 for Pt) and B-2p states, are the cause of the relatively higher elastic moduli of Pt-based compounds and R-T-borides, respectively.

  5. Quantum chemistry study of uranium(VI), neptunium(V), and plutonium(IV,VI) complexes with preorganized tetradentate phenanthrolineamide ligands.

    PubMed

    Xiao, Cheng-Liang; Wu, Qun-Yan; Wang, Cong-Zhi; Zhao, Yu-Liang; Chai, Zhi-Fang; Shi, Wei-Qun

    2014-10-20

    The preorganized tetradentate 2,9-diamido-1,10-phenanthroline ligand with hard-soft donors combined in the same molecule has been found to possess high selectivity toward actinides in an acidic aqueous solution. In this work, density functional theory (DFT) coupled with the quasi-relativistic small-core pseudopotential method was used to investigate the structures, bonding nature, and thermodynamic behavior of uranium(VI), neptunium(V), and plutonium(IV,VI) with phenanthrolineamides. Theoretical optimization shows that Et-Tol-DAPhen and Et-Et-DAPhen ligands are both coordinated with actinides in a tetradentate chelating mode through two N donors of the phenanthroline moiety and two O donors of the amide moieties. It is found that [AnO2L(NO3)](n+) (An = U(VI), Np(V), Pu(VI); n = 0, 1) and PuL(NO3)4 are the main 1:1 complexes. With respect to 1:2 complexes, the reaction [Pu(H2O)9](4+)(aq) + 2L(org) + 2NO3(-)(aq) → [PuL2(NO3)2](2+)(org) + 9H2O(aq) might be another probable extraction mechanism for Pu(IV). From the viewpoint of energy, the phenanthrolineamides extract actinides in the order of Pu(IV) > U(VI) > Pu(VI) > Np(V), which agrees well with the experimental results. Additionally, all of the thermodynamic reactions are more energetically favorable for the Et-Tol-DAPhen ligand than the Et-Et-DAPhen ligand, indicating that substitution of one ethyl group with one tolyl group can enhance the complexation abilities toward actinide cations (anomalous aryl strengthening). PMID:25268674

  6. Electronic structure and bonding of the 3d transition metal borides, MB, M =Sc, Ti, V, Cr, Mn, Fe, Co, Ni, and Cu through all electron ab initio calculations

    NASA Astrophysics Data System (ADS)

    Tzeli, Demeter; Mavridis, Aristides

    2008-01-01

    The electronic structure and bonding of the ground and some low-lying states of all first row transition metal borides (MB), ScB, TiB, VB, CrB, MnB, FeB, CoB, NiB, and CuB have been studied by multireference configuration interaction (MRCI) methods employing a correlation consistent basis set of quintuple cardinality (5Z). It should be stressed that for all the above nine molecules, experimental results are essentially absent, whereas with the exception of ScB and CuB the remaining seven species are studied theoretically for the first time. We have constructed full potential energy curves at the MRCI/5Z level for a total of 27 low-lying states, subsequently used to extract binding energies, spectroscopic parameters, and bonding schemes. In addition, some 20 or more states for every MB species have been examined at the MRCI/4Z level of theory. The ground state symmetries and corresponding binding energies (in kcal/mol) are Σ-5(ScB), 76; Δ6(TiB), 65; Σ+7(VB), 55; Σ+6(CrB), 31; Π5(MnB), 20; Σ-4(FeB), 54; Δ3(CoB), 66; Σ+2(NiB), 79; and Σ+1(CuB), 49.

  7. New ternary rare-earth metal boride carbides R{sub 15}B{sub 4}C{sub 14} (R=Y, Gd-Lu) containing BC{sub 2} units: Crystal and electronic structures, magnetic properties

    SciTech Connect

    Babizhetskyy, Volodymyr; Simon, Arndt; Mattausch, Hansjuergen; Hiebl, Kurt; Zheng Chong

    2010-10-15

    The ternary rare-earth boride carbides R{sub 15}B{sub 4}C{sub 14} (R=Y, Gd-Lu) were prepared from the elements by arc-melting followed by annealing in silica tubes at 1270 K for 1 month. The crystal structures of Tb{sub 15}B{sub 4}C{sub 14} and Er{sub 15}B{sub 4}C{sub 14} were determined from single crystal X-ray diffraction data. They crystallize in a new structure type in space group P4/mnc (Tb{sub 15}B{sub 4}C{sub 14}: a=8.1251(5) A, c=15.861(1) A, Z=2, R{sub 1}=0.041 (wR{sub 2}=0.088) for 1023 reflections with I{sub o}>2{sigma}(I{sub o}); Er{sub 15}B{sub 4}C{sub 14}: a=7.932(1) A, c=15.685(2) A, Z=2, R{sub 1}=0.037 (wR{sub 2}=0.094) for 1022 reflections with I{sub o}>2{sigma}(I{sub o})). The crystal structure contains discrete carbon atoms and bent CBC units in octahedra and distorted bicapped square antiprisms, respectively. In both structures the same type of disorder exists. One R atom position needs to be refined as split atom position with a ratio 9:1 indicative of a 10% substitution of the neighboring C{sup 4-} by C{sub 2}{sup 4-}. The actual composition has then to be described as R{sub 15}B{sub 4}C{sub 14.2}. The isoelectronic substitution does not change the electron partition of R{sub 15}B{sub 4}C{sub 14} which can be written as (R{sup 3+}){sub 15}(C{sup 4-}){sub 6}(CBC{sup 5-}){sub 4{center_dot}}e{sup -}. The electronic structure was studied with the extended Hueckel method. The investigated compounds Tb{sub 15}B{sub 4}C{sub 14}, Dy{sub 15}B{sub 4}C{sub 14} and Er{sub 15}B{sub 4}C{sub 14} are hard ferromagnets with Curie temperatures T{sub C}=145, 120 and 50 K, respectively. The coercive field B{sub C}=3.15 T for Dy{sub 15}B{sub 4}C{sub 14} is quite remarkable. - Graphical abstract: The ternary rare earth boride carbides R{sub 15}B{sub 4}C{sub 14} (R=Y, Gd-Lu) were prepared from the elements by arc-melting followed by annealing in silica tubes at 1270 K for 1 month. Tb{sub 15}B{sub 4}C{sub 14} is a new member of the rare-earth metal boride carbide

  8. Ternary rare earth metal boride carbides containing two-dimensional boron-carbon network: The crystal and electronic structure of R{sub 2}B{sub 4}C (R=Tb, Dy, Ho, Er)

    SciTech Connect

    Babizhetskyy, Volodymyr Zheng Chong; Mattausch, Hansjuergen; Simon, Arndt

    2007-12-15

    The ternary rare earth boride carbides R{sub 2}B{sub 4}C (R=Tb, Dy, Ho, Er) have been synthesized by reacting the elements at temperatures between 1800 and 2000K. The crystal structure of Dy{sub 2}B{sub 4}C has been determined from single-crystal X-ray diffraction data. It crystallizes in a new structure type in the orthorhombic space group Immm (a=3.2772(6) A, b=6.567(2) A, c=7.542(1) A, Z=2, R1=0.035 (wR{sub 2}=0.10) for 224 reflections with I{sub o}>2{sigma}(I{sub o})). Boron atoms form infinite chains of fused B{sub 6} rings in [100] joined with carbon atoms into planar, two-dimensional networks which alternate with planar sheets of rare earth metal atoms. The electronic structure of Dy{sub 2}B{sub 4}C was also analyzed using the tight-binding extended Hueckel method. - Graphical abstract: Dy{sub 2}B{sub 4}C crystallizes a new structure type where planar 6{sup 3}-Dy metal atom layers alternate with planar non-metal layers consisting of ribbons of fused B{sub 6} hexagons bridged by carbon atoms. Isostructural analogues with Tb, Ho and Er have also been characterized.

  9. In{sub 3}Ir{sub 3}B, In{sub 3}Rh{sub 3}B and In{sub 5}Ir{sub 9}B{sub 4}, the first indium platinum metal borides

    SciTech Connect

    Kluenter, Wilhelm; Jung, Walter . E-mail: walter.jung@uni-koeln.de

    2006-09-15

    The first indium platinum metal borides have been synthesized and structurally characterized by single crystal X-ray diffraction data. In{sub 3}Ir{sub 3}B and In{sub 3}Rh{sub 3}B are isotypic. They crystallize with the hexagonal space group P6-bar 2m and Z=1. The lattice constants are a=685.78(1)pm, c=287.30(1)pm for In{sub 3}Ir{sub 3}B and a=678.47(3)pm, c=288.61(6)pm for In{sub 3}Rh{sub 3}B. The structure which is derived from the Fe{sub 2}P type is characterized by columns of boron centered triangular platinum metal prisms inserted in a three-dimensional indium matrix. The indium atoms are on split positions. In{sub 5}Ir{sub 9}B{sub 4} (hexagonal, space group P6-bar 2m, a=559.0(2)pm, c=1032.6(3)pm, Z=1) crystallizes with a structure derived from the CeCo{sub 3}B{sub 2} type. The structure can be interpreted as a layer as well as a channel structure. In part the indium atoms are arranged at the vertices of a honeycomb net (Schlaefli symbol 6{sup 3}) separating slabs consisting of double layers of triangular Ir{sub 6}B prisms, and in part they form a linear chain in a hexagonal channel formed by iridium prisms and indium atoms of the honeycomb lattice.

  10. New ternary rare-earth metal boride carbides R15B 4C 14 ( R=Y, Gd-Lu) containing BC 2 units: Crystal and electronic structures, magnetic properties

    NASA Astrophysics Data System (ADS)

    Babizhetskyy, Volodymyr; Simon, Arndt; Mattausch, Hansjürgen; Hiebl, Kurt; Zheng, Chong

    2010-10-01

    The ternary rare-earth boride carbides R15B 4C 14 ( R=Y, Gd-Lu) were prepared from the elements by arc-melting followed by annealing in silica tubes at 1270 K for 1 month. The crystal structures of Tb 15B 4C 14 and Er 15B 4C 14 were determined from single crystal X-ray diffraction data. They crystallize in a new structure type in space group P4/ mnc (Tb 15B 4C 14: a=8.1251(5) Å, c=15.861(1) Å, Z=2, R1=0.041 (w R2=0.088) for 1023 reflections with Io>2 σ( Io); Er 15B 4C 14: a=7.932(1) Å, c=15.685(2) Å, Z=2, R1=0.037 (w R2=0.094) for 1022 reflections with Io>2 σ( Io)). The crystal structure contains discrete carbon atoms and bent CBC units in octahedra and distorted bicapped square antiprisms, respectively. In both structures the same type of disorder exists. One R atom position needs to be refined as split atom position with a ratio 9:1 indicative of a 10% substitution of the neighboring C 4- by C 24-. The actual composition has then to be described as R15B 4C 14.2. The isoelectronic substitution does not change the electron partition of R15B 4C 14 which can be written as ( R3+) 15(C 4-) 6(CBC 5-) 4•e -. The electronic structure was studied with the extended Hückel method. The investigated compounds Tb 15B 4C 14, Dy 15B 4C 14 and Er 15B 4C 14 are hard ferromagnets with Curie temperatures TC=145, 120 and 50 K, respectively. The coercive field BC=3.15 T for Dy 15B 4C 14 is quite remarkable.

  11. Single crystal studies on boron-rich {tau}-borides Ni{sub 23-x}M{sub x}B{sub 6} (M=Zn, Ga, In, Sn, Ir)-The surprising occurrence of B{sub 4}-tetraheda as a normal case?

    SciTech Connect

    Kotzott, Dominik; Ade, Martin; Hillebrecht, Harald

    2010-10-15

    Single crystals of the cubic {tau}-borides Ni{sub 23-x}M{sub x}B{sub 6} (M=Zn, Ga, In, Sn, Ir) were synthesised from the elements at temperatures between 1200 and 1500 {sup o}C. The structure refinements show that the existence of boron-rich phases is quite common. Starting from the idealised composition Ni{sub 20}M'{sub 3}B{sub 6} a part of the metal atoms on site 8c is substituted by B{sub 4} tetrahedra. For M'=Ga a complete exchange seems to be possible leading to the composition Ni{sub 20}GaB{sub 14}. For M'=Zn and Sn the formation of solid solutions is less extended. For M'=In no exchange is observed but an unusual pattern of Ni/In distribution is observed. With M=Ir mixed occupations occur for all sites and the boron content varies, too. All compositions were confirmed by EDX measurements. - Graphical abstract: Crystal structure of {tau}-Borides M{sub 23}B{sub 6}; M1: M{sub 8}-cubes, M2: M{sub 12}-cuboctahedra centred by M3, isolated M-atoms: M4; grey circles: boron, black circles: metal atoms.

  12. Boron induced structure modifications in Pd-Cu-B system: new Ti2Ni-type derivative borides Pd3Cu3B and Pd5Cu5B2.

    PubMed

    Sologub, Oksana; Salamakha, Leonid P; Eguchi, Gaku; Stöger, Berthold; Rogl, Peter F; Bauer, Ernst

    2016-03-21

    The formation of two distinct derivative structures of Ti2Ni-type, interstitial Pd3Cu3B and substitutive Pd5Cu5B2, has been elucidated in Pd-Cu-B alloys from analysis of X-ray single crystal and powder diffraction data and supported by SEM. The metal atom arrangement in the new boride Pd3Cu3B (space group Fd3m, W3Fe3C-type structure, a = 1.1136(3) nm) follows the pattern of atom distribution in the CdNi-type structure. Pd5Cu5B2 (space group F(4)3m, a = 1.05273(5) nm) exhibits a non-centrosymmetric substitutive derivative of the Ti2Ni-type structure. The reduction of symmetry on passing from Ti2Ni-type structure to Pd5Cu5B2 corresponds to the loss of an inversion centre delivered by an ordered occupation of the Ni position (32e) by dissimilar atoms, Cu and B. In both structures, the boron atom centers Pd forming [BPd6] octahedra in Pd3Cu3B and [BPd6] trigonal prisms in Pd5Cu5B2. Neither a perceptible homogeneity range nor mutual solid solubility was observed for two compounds at 600 °C, while in as cast conditions Pd5Cu5B2 exhibits an extended homogeneity range formed by a partial substitution of Cu atoms (in 24f) by Pd (Pd5+xCu5-xB2, 0 ≤x≤ 1). Electrical resistivity measurements performed on Pd3Cu3B as well as on Pd-poor and Pd-rich termini of Pd5+xCu5-xB2 annealed at 600 °C and in as cast conditions respectively demonstrated the absence of any phase transitions for this compounds in the temperature region from 0.3 K to 300 K. PMID:26875687

  13. New examples of ternary rare-earth metal boride carbides containing finite boron carbon chains: The crystal and electronic structure of RE15B6C20 (RE=Pr, Nd)

    NASA Astrophysics Data System (ADS)

    Babizhetskyy, Volodymyr; Mattausch, Hansjürgen; Simon, Arndt; Hiebl, Kurt; Ben Yahia, Mouna; Gautier, Régis; Halet, Jean-François

    2008-08-01

    The ternary rare-earth metal boride carbides RE15B6C20 (RE=Pr, Nd) were synthesized by co-melting the elements. They exist above 1270 K. Their crystal structures were determined from single-crystal X-ray diffraction data. Both crystallize in the space group P1¯, Z=1, a=8.3431(8) Å, b=9.2492(9) Å, c=8.3581(8) Å, α=84.72(1)°, β=89.68(1)°, γ =84.23(1)° (R1=0.041 (wR2=0.10) for 3291 reflections with Io>2σ(Io)) for Pr15B6C20, and a=8.284(1) Å, b=9.228(1) Å, c=8.309(1) Å, α=84.74(1)°, β=89.68(1)°, γ=84.17(2)° (R1=0.033 (wR2=0.049) for 2970 reflections with Io>2σ(Io)) for Nd15B6C20. Their structure consists of a three-dimensional framework of rare-earth metal atoms resulting from the stacking of slightly corrugated and distorted square nets, leading to cavities filled with unprecedented B2C4 finite chains, disordered C3 entities and isolated carbon atoms, respectively. Structural and theoretical analyses suggest the ionic formulation (RE3+)15([B2C4]6-)3([C3]4-)2(C4-)2·11ē. Accordingly, density functional theory calculations indicate that the compounds are metallic. Both structural arguments as well as energy calculations on different boron vs. carbon distributions in the B2C4 chains support the presence of a CBCCBC unit. Pr15B6C18 exhibits antiferromagnetic order at TN=7.9 K, followed by a meta-magnetic transition above a critical external field B>0.03 T. On the other hand, Nd15B6C18 is a ferromagnet below TC≈40 K.

  14. (Pt1-xCux)3Cu2B and Pt9Cu3B5, the first examples of copper platinum borides. Observation of superconductivity in a novel boron filled β-Mn-type compound

    NASA Astrophysics Data System (ADS)

    Salamakha, Leonid P.; Sologub, Oksana; Stöger, Berthold; Michor, Herwig; Bauer, Ernst; Rogl, Peter F.

    2015-09-01

    New ternary copper platinum borides have been synthesized by arc melting of pure elements followed by annealing at 600 °C. The structures have been studied by X-ray single crystal and powder diffraction. (Pt1-xCux)3Cu2B (x=0.33) forms a B-filled β-Mn-type structure (space group P4132; a=0.6671(1) nm). Cu atoms are distributed preferentially on the 8c atom sites, whereas the 12d site is randomly occupied by Pt and Cu atoms (0.670(4) Pt±0.330(4) Cu). Boron is located in octahedral voids of the parent β-Mn-type structure. Pt9Cu3B5 (space group P-62m; a=0.9048(3) nm, c=0.2908(1) nm) adopts the Pt9Zn3B5-δ-type structure. It has a columnar architecture along the short translation vector exhibiting three kinds of [Pt6] trigonal prism columns (boron filled, boron semi-filled and empty) and Pt channels with a pentagonal cross section filled with Cu atoms. The striking structural feature is a [Pt6] cluster in form of an empty trigonal prism at the origin of the unit cell, which is surrounded by coupled [BPt6] and [Pt6] trigonal prisms, rotated perpendicularly to the central one. There is no B-B contact as well as Cu-B contact in the structure. The relationships of Pt9Cu3B5 structure with the structure of Ti1+xOs2-xRuB2 as well as with the structure families of metal sulfides and aluminides have been elucidated. (Pt1-xCux)3Cu2B (x=0.3) (B-filled β-Mn-type structure) is a bulk superconductor with a transition temperature of about 2.06 K and an upper critical field μ0HC2(0)WHH of 1.2 T, whereas no superconducting transition has been observed up to 0.3 K in Pt9Cu3B5 (Pt9Zn3B5-δ-type structure) from electrical resistivity measurements.

  15. Synthesis, crystal structure investigation and magnetism of the complex metal-rich boride series Cr{sub x}(Rh{sub 1-y}Ru{sub y}){sub 7-x}B{sub 3} (x=0.88-1; y=0-1) with Th{sub 7}Fe{sub 3}-type structure

    SciTech Connect

    Misse, Patrick R.N.; Mbarki, Mohammed; Fokwa, Boniface P.T.

    2012-08-15

    Powder samples and single crystals of the new complex boride series Cr{sub x}(Rh{sub 1-y}Ru{sub y}){sub 7-x}B{sub 3} (x=0.88-1; y=0-1) have been synthesized by arc-melting the elements under purified argon atmosphere on a water-cooled copper crucible. The products, which have metallic luster, were structurally characterized by single-crystal and powder X-ray diffraction as well as EDX measurements. Within the whole solid solution range the hexagonal Th{sub 7}Fe{sub 3} structure type (space group P6{sub 3}mc, no. 186, Z=2) was identified. Single-crystal structure refinement results indicate the presence of chromium at two sites (6c and 2b) of the available three metal Wyckoff sites, with a pronounced preference for the 6c site. An unexpected Rh/Ru site preference was found in the Ru-rich region only, leading to two different magnetic behaviors in the solid solution: The Rh-rich region shows a temperature-independent (Pauli) paramagnetism whereas an additional temperature-dependent paramagnetic component is found in the Ru-rich region. - Graphical abstract: The new complex boride series Cr{sub x}(Rh{sub 1-y}Ru{sub y}){sub 7-x}B{sub 3} (x=0.88-1; y=0-1) has been synthesized by arc melting the elements under purified argon atmosphere. Beside the 3d/4d site preference within the whole solid solution, an unexpected Rh/Ru site preference was found in the Ru-rich region only, leading to two different magnetic behaviors: The Rh-rich region shows a temperature-independent (Pauli) paramagnetism whereas an additional temperature-dependent paramagnetic component is found in the Ru-rich region. Highlights: Black-Right-Pointing-Pointer Synthesis of a new boride series fulfilling Vegard Acute-Accent s rule. Black-Right-Pointing-Pointer 3d/4d site preference. Black-Right-Pointing-Pointer Unexpected Ru/Rh site preference. Black-Right-Pointing-Pointer Rh-rich region is Pauli paramagnetic. Black-Right-Pointing-Pointer Ru-rich region is Pauli and temperature-dependent paramagnetic.

  16. The complex metal-rich boride Ti{sub 1+x}Rh{sub 2-x+y}Ir{sub 3-y}B{sub 3} (x=0.68, y=1.06) with a new structure type containing B{sub 4} zigzag fragments: Synthesis, crystal chemistry and theoretical calculations

    SciTech Connect

    Goerens, Christian; Fokwa, Boniface P.T.

    2012-08-15

    Polycrystalline samples and single crystals of the new complex boride Ti{sub 1+x}Rh{sub 2-x+y}Ir{sub 3-y}B{sub 3} (x=0.68; y=1.06) were synthesized by arc-melting the elements in a water-cooled copper crucible under an argon atmosphere and characterized by X-Ray diffraction as well as EDX measurements. The crystal structure was refined on the basis of single crystal data. The new phase, which represents a new structure type containing trans zigzag B{sub 4} fragments as well as isolated boron atoms crystallizes in the orthorhombic space group Pbam (Nr. 55) with the lattice parameters a=8.620(1) A, b=14.995(2) A and c=3.234(1) A. First-principles density functional theory calculations using the Vienna ab-initio simulation package (VASP) were performed on an appropriate structural model (using a supercell approach) and the experimental crystallographic data could be reproduced accurately. Based on this model, the density of states and crystal orbital Hamilton population (for bonding analysis) were calculated, using the linear muffin-tin orbital atomic sphere approximation (LMTO-ASA) method. According to these calculations, this metal-rich compound should be metallic, as expected. Furthermore, very strong boron-boron interactions are observed in the trans zigzag B{sub 4} fragment, which induce a clear differentiation of two types of metal-boron contacts with different strength. The observed three-dimensional metal-metal interaction is in good agreement with the predicted metallic behavior. - graphical abstract: The structure of Ti{sub 1.68(2)}Rh{sub 2.38(6)}Ir{sub 1.94(4)} B{sub 3}, a new structure type containing planar trans zigzag B{sub 4} units, is another example which illustrates the tendency of metal-rich borides to form B-B bonds with increasing boron content. Beside the B{sub 4} fragment it exhibits one-dimensional chains of titanium atoms and hold one-dimensional strings of face-sharing empty tetrahedral and square pyramidal clusters (see figure). Highlights

  17. Measured solubilities and speciations from oversaturation experiments of neptunium, plutonium, and americium in UE-25p No. 1 well water from the Yucca Mountain region: Milestone report 3329-WBS1.2.3.4.1.3.1

    SciTech Connect

    Nitsche, H.; Roberts, K.; Prussin, T.; Mueller, A.; Becraft, K.; Keeney, D.; Carpenter, S.A.; Gatti, R.C.

    1994-04-01

    Solubility and speciation are important in understanding aqueous radionuclide transport through the geosphere. They define the source term for transport retardation processes such as sorption and colloid formation. Solubility and speciation data are useful in verifying the validity of geochemical codes that are a part of predictive transport models. Results are presented from solubility and speciation experiments of {sup 237}NpO{sub 2}{sup +}, {sup 239}Pu{sup 4+}, and {sup 241}Am{sup 3+}/Nd{sup 3+} in a modified UE-25p No. 1 groundwater (from the Yucca Mountain region, Nevada, which is being investigated as a potential high-level nuclear waste disposal site) at two different temperatures (25{degree} and 60{degree}C) and three pH values (6.0, 7.0, 8.5). The solubility-controlling steady-state solids were identified and the speciation and/or oxidation states present in the supernatant solutions were determined. The neptunium solubility decreased with increasing temperature and pH. Plutonium concentrations significantly decreased with increasing temperature at pH 6 and 7. The concentration at pH 8.5 hardly decreased at all with increasing temperature. At both temperatures the concentrations were highest at pH 8.5, lowest at pH 7, and in between at pH 6. For the americium/neodymium solutions, the solubility decreased significantly with increasing temperature and increased somewhat with increasing pH.

  18. Measured solubilities and speciations of neptunium, plutonium, and americium in a typical groundwater (J-13) from the Yucca Mountain region; Milestone report 3010-WBS 1.2.3.4.1.3.1

    SciTech Connect

    Nitsche, H.; Gatti, R.C.; Standifer, E.M.

    1993-07-01

    Solubility and speciation data are important in understanding aqueous radionuclide transport through the geosphere. They define the source term for transport retardation processes such as sorption and colloid formation. Solubility and speciation data are useful in verifying the validity of geochemical codes that are part of predictive transport models. Results are presented from solubility and speciation experiments of {sup 237}NpO{sub 2}{sup +}, {sup 239}Pu{sup 4+}, {sup 241}Am{sup 3+}/Nd{sup 3+}, and {sup 243}Am{sup 3+} in J-13 groundwater (from the Yucca Mountain region, Nevada, which is being investigated as a potential high-level nuclear waste disposal site) at three different temperatures (25{degree}, 60{degree}, and 90{degree}C) and pH values (5.9, 7.0, and 8.5). The solubility-controlling steady-state solids were identified and the speciation and/or oxidation states present in the supernatant solutions were determined. The neptunium solubility decreased with increasing temperature and pH. Plutonium concentrations decreased with increasing temperature and showed no trend with pH. The americium solutions showed no clear solubility trend with increasing temperature and increasing pH.

  19. Combustion synthesis of boride and other composites

    DOEpatents

    Halverson, Danny C.; Lum, Beverly Y.; Munir, Zuhair A.

    1989-01-01

    A self-sustaining combustion synthesis process for producing hard, tough, lightweight B.sub.4 C/TiB.sub.2 composites is based on the thermodynamic dependence of adiabatic temperature and product composition on the stoichiometry of the B.sub.4 C and TiB.sub.2 reactants. For lightweight products the composition must be relatively rich in the B.sub.4 C component. B.sub.4 C-rich composites are obtained by varying the initial temperature of the reactants. The product is hard, porous material whose toughness can be enhanced by filling the pores with aluminum or other metal phases using a liquid metal infiltration process. The process can be extended to the formation of other composites having a low exothermic component.

  20. Combustion synthesis of boride and other composites

    DOEpatents

    Halverson, D.C.; Lum, B.Y.; Munir, Z.A.

    1988-07-28

    A self-sustaining combustion synthesis process for producing hard, tough, lightweight B/sub 4/C/TiB/sub 2/ composites is described. It is based on the thermodynamic dependence of adiabatic temperature and product composition on the stoichiometry of the B/sub 4/C and TiB/sub 2/ reactants. For lightweight products the composition must be relatively rich in the B/sub 4/C component. B/sub 4/C-rich composites are obtained by varying the initial temperature of the reactants. The product is hard, porous material whose toughness can be enhanced by filling the pores with aluminum or other metal phases using a liquid metal infiltration process. The process can be extended to the formation of other composites having a low exothermic component. 9 figs., 4 tabs.

  1. Thermal analysis, phase equilibria, and superconducting properties in magnesium boride and carbon doped magnesium boride

    NASA Astrophysics Data System (ADS)

    Bohnenstiehl, Scot David

    In this work, the low temperature synthesis of MgB2 from Mg/B and MgH2/B powder mixtures was studied using Differential Scanning Calorimetry (DSC). For the Mg/B powder mixture, two exothermic reaction events were observed and the first reaction event was initiated by the decomposition of Mg(OH)2 on the surface of the magnesium powder. For the MgH 2/B powder mixture, there was an endothermic event at ˜375 °C (the decomposition of MgH2 into H2 and Mg) and an exothermic event ˜600 °C (the reaction of Mg and B). The Kissinger analysis method was used to estimate the apparent activation energy of the Mg and B reaction using DSC data with different furnace ramp rates. The limitations of MgB2 low temperature synthesis led to the development of a high pressure induction furnace that was constructed using a pressure vessel and an induction heating power supply. The purpose was to not only synthesize more homogeneous MgB2 samples, but also to determine whether MgB2 melts congruently or incongruently. A custom implementation of the Smith Thermal Analysis method was developed and tested on aluminum and AlB2, the closest analogue to MgB2. Measurements on MgB2 powder and a high purity Mg/B elemental mixture confirmed that MgB2 melts incongruently and decomposes into a liquid and MgB4 at ˜1445 °C at 10 MPa via peritectic decomposition. Another measurement using a Mg/B elemental mixture with impure boron suggested that ˜0.7 wt% carbon impurity in the boron raised the incongruent melting temperature to ˜1490-1500 °C. Lastly, the solubility limit for carbon in MgB2 was studied by making samples from B4C and Mg at 1530 °C, 1600 °C and 1700 °C in the high pressure furnace. All three samples had three phases: Mg, MgB2C2, and carbon doped MgB2. The MgB 2C2 and carbon doped MgB2 grain size increased with temperature and the 1700 °C sample had needle-like grains for both phases. The presence of the ternary phase, MgB2C2, suggested that the maximum doping limit for carbon in MgB2 had been reached. The 1530 °C sample was characterized by Electron Probe Microanalysis at the University of Oregon and the average carbon concentration was estimated to be ˜5.9 at%. Further investigation using TEM found MgO inclusions in the 1530 °C sample which were not detected with X-ray diffraction.

  2. Synthesis, crystal structure investigation and magnetism of the complex metal-rich boride series Crx(Rh1-yRuy)7-xB3 (x=0.88-1; y=0-1) with Th7Fe3-type structure

    NASA Astrophysics Data System (ADS)

    Misse, Patrick R. N.; Mbarki, Mohammed; Fokwa, Boniface P. T.

    2012-08-01

    Powder samples and single crystals of the new complex boride series Crx(Rh1-yRuy)7-xB3 (x=0.88-1; y=0-1) have been synthesized by arc-melting the elements under purified argon atmosphere on a water-cooled copper crucible. The products, which have metallic luster, were structurally characterized by single-crystal and powder X-ray diffraction as well as EDX measurements. Within the whole solid solution range the hexagonal Th7Fe3 structure type (space group P63mc, no. 186, Z=2) was identified. Single-crystal structure refinement results indicate the presence of chromium at two sites (6c and 2b) of the available three metal Wyckoff sites, with a pronounced preference for the 6c site. An unexpected Rh/Ru site preference was found in the Ru-rich region only, leading to two different magnetic behaviors in the solid solution: The Rh-rich region shows a temperature-independent (Pauli) paramagnetism whereas an additional temperature-dependent paramagnetic component is found in the Ru-rich region.

  3. (Pt{sub 1–x}Cu{sub x}){sub 3}Cu{sub 2}B and Pt{sub 9}Cu{sub 3}B{sub 5}, the first examples of copper platinum borides. Observation of superconductivity in a novel boron filled β-Mn-type compound

    SciTech Connect

    Salamakha, Leonid P.; Sologub, Oksana; Stöger, Berthold; Michor, Herwig; Bauer, Ernst; Rogl, Peter F.

    2015-09-15

    New ternary copper platinum borides have been synthesized by arc melting of pure elements followed by annealing at 600 °C. The structures have been studied by X-ray single crystal and powder diffraction. (Pt{sub 1−x}Cu{sub x}){sub 3}Cu{sub 2}B (x=0.33) forms a B-filled β-Mn-type structure (space group P4{sub 1}32; a=0.6671(1) nm). Cu atoms are distributed preferentially on the 8c atom sites, whereas the 12d site is randomly occupied by Pt and Cu atoms (0.670(4) Pt±0.330(4) Cu). Boron is located in octahedral voids of the parent β-Mn-type structure. Pt{sub 9}Cu{sub 3}B{sub 5} (space group P-62m; a=0.9048(3) nm, c=0.2908(1) nm) adopts the Pt{sub 9}Zn{sub 3}B{sub 5–δ}-type structure. It has a columnar architecture along the short translation vector exhibiting three kinds of [Pt{sub 6}] trigonal prism columns (boron filled, boron semi-filled and empty) and Pt channels with a pentagonal cross section filled with Cu atoms. The striking structural feature is a [Pt{sub 6}] cluster in form of an empty trigonal prism at the origin of the unit cell, which is surrounded by coupled [BPt{sub 6}] and [Pt{sub 6}] trigonal prisms, rotated perpendicularly to the central one. There is no B–B contact as well as Cu–B contact in the structure. The relationships of Pt{sub 9}Cu{sub 3}B{sub 5} structure with the structure of Ti{sub 1+x}Os{sub 2−x}RuB{sub 2} as well as with the structure families of metal sulfides and aluminides have been elucidated. (Pt{sub 1–x}Cu{sub x}){sub 3}Cu{sub 2}B (x=0.3) (B-filled β-Mn-type structure) is a bulk superconductor with a transition temperature of about 2.06 K and an upper critical field μ{sub 0}H{sub C2}(0){sup WHH} of 1.2 T, whereas no superconducting transition has been observed up to 0.3 K in Pt{sub 9}Cu{sub 3}B{sub 5} (Pt{sub 9}Zn{sub 3}B{sub 5–δ}-type structure) from electrical resistivity measurements. - Highlights: • First two copper platinum borides, (Pt{sub 0.67}Cu{sub 0.33}){sub 3}Cu{sub 2}B and Pt{sub 9}Cu{sub 3}B

  4. The neptunium-iron phase diagram

    NASA Astrophysics Data System (ADS)

    Gibson, J. K.; Haire, R. G.; Beahm, E. C.; Gensini, M. M.; Maeda, A.; Ogawa, T.

    1994-08-01

    The phase relations in the Np-Fe alloy system have been elucidated using differential thermal analysis. A phase diagram for this system is postulated based upon the experimental results, regular-solution model calculations, and an expected correspondence to the U-Fe and Pu-Fe diagrams. The postulated Np-Fe diagram is characterized by limited terminal solid solubilities, two intermetallic solid phases, NpFe 2 and Np 6Fe, and two eutectics.

  5. Neptunium Valence Chemistry in Anion Exchange Processing

    SciTech Connect

    KYSER, EDWARD

    2003-02-01

    The current anion resin in use in HB-Line Phase II, Reillex{trademark} HPQ, was tested in the laboratory under expected plant conditions for Np processing and was found to load between 50 and 70 g Np per liter of resin. Losses varied from 0.2 to 15 percent depending on a number of parameters. Hydrazine in the feed at 0.02 to 0.05 M appeared to keep the Np from oxidizing and increasing the losses within four to seven days after the FS addition. Losses of up to three percent were observed five days after FS addition when hydrazine was not used in the feed, compared with 0.3 percent when the feed was loaded immediately after FS addition. Based on these test results the following processing conditions are recommended: (1) Feed conditions: 8 M HNO{sub 3}, 0.02 M hydrazine, 0.05 M excess FS, less than 5 days storage of solution after FS addition. (2) Wash conditions: 100 liters of 8 M HNO{sub 3}, no FS, no hydrazine. (3) Elution conditions: 0.17 M HNO{sub 3}, 0.05 M hydrazine, no FS. (4) Precipitation feed conditions: 0.03 M excess ascorbic acid, no additional hydrazine, no FS, precipitation within three days.

  6. Solvent-extraction purification of neptunium

    SciTech Connect

    Kyser, E.A.; Hudlow, S.L.

    2008-07-01

    The Savannah River Site (SRS) has recovered {sup 237}Np from reactor fuel that is currently being processed into NpO{sub 2} for future production of {sup 238}Pu. Several purification flowsheets have been utilized. An oxidizing solvent-extraction (SX) flowsheet was used to remove Fe, sulfate ion, and Th while simultaneously {sup 237}Np, {sup 238}Pu, u, and nonradioactive Ce(IV) was extracted into the tributyl phosphate (TBP) based organic solvent. A reducing SX flowsheet (second pass) removed the Ce and Pu and recovered both Np and U. The oxidizing flowsheet was necessary for solutions that contained excessive amounts of sulfate ion. Anion exchange was used to perform final purification of Np from Pu, U, and various non-actinide impurities. The Np(IV) in the purified solution was then oxalate-precipitated and calcined to an oxide for shipment to other facilities for storage and future target fabrication. Performance details of the SX purification and process difficulties are discussed. (authors)

  7. Neptunium(V) adsorption to calcite.

    PubMed

    Heberling, Frank; Brendebach, Boris; Bosbach, Dirk

    2008-12-12

    The migration behavior of the actinyl ions U(VI)O2(2+), Np(V)O2+ and Pu(V,VI)O2(+,2+) in the geosphere is to a large extend controlled by sorption reactions (inner- or outer-sphere adsorption, ion-exchange, coprecipitation/structural incorporation) with minerals. Here NpO2+ adsorption onto calcite is studied in batch type experiments over a wide range of pH (6.0-9.4) and concentration (0.4 microM-40 microM) conditions. pH is adjusted by variation of CO2 partial pressure. Adsorption is found to be pH dependent with maximal adsorption at pH 8.3 decreasing with increasing and decreasing pH. pH dependence of adsorption decreases with increasing Np(V) concentration. EXAFS data of neptunyl adsorbed to calcite and neptunyl in the supernatant shows differences in the Np(V)-O-yl distance, 1.85+/-0.01 angstroms for the adsorbed and 1.82+/-0.01 angstroms for the solution species. The equatorial environment of the neptunyl in solution shows about 5 oxygen neighbours at 2.45+/-0.02 angstroms. For adsorbed neptunyl there are also about 5 oxygen neighbours at 2.46+/-0.01 angstroms. An additional feature in the adsorbed species' R-space spectrum can be related to carbonate neighbours, 3 to 6 carbon backscatterers (C-eq) at 3.05+/-0.03 angstroms and 3 to 6 oxygen backscatterers (O-eq2) at 3.31+/-0.02 angstroms. The differences in the Np(V)-O-yl distance and the C-eq and O-eq2 backscatterers which are only present for the adsorbed species indicate inner-sphere bonding of the adsorbed neptunyl species to the calcite surface. Experiments on adsorption kinetics indicate that after a fast surface adsorption process a continuous slow uptake occurs which may be explained by incorporation via surface dissolution and reprecipitation processes. This is also indicated by the part irreversibility of the adsorption as shown by increased KD values after desorption compared to adsorption. PMID:18973965

  8. Investigation of magnetic properties and electronic structure of layered-structure borides AlT{sub 2}B{sub 2} (T=Fe, Mn, Cr) and AlFe{sub 2–x}Mn{sub x}B{sub 2}

    SciTech Connect

    Chai, Ping; Stoian, Sebastian A.; Tan, Xiaoyan; Dube, Paul A.; Shatruk, Michael

    2015-04-15

    magnetic properties of these materials. - Graphical abstract: We follow a gradual evolution of magnetic properties in a series of ternary borides AlT{sub 2}B{sub 2}, from non-magnetic AlCr{sub 2}B{sub 2} and AlMn{sub 2}B{sub 2} to ferromagnetic AlFe{sub 2}B{sub 2}. - Highlights: • AlT{sub 2}B{sub 2} (T=Fe, Mn, Cr) and AlFe{sub 2−x}Mn{sub x}B{sub 2} were prepared by arc‐melting. • Bulk ferromagnetism of AlFe{sub 2}B{sub 2} is gradually suppressed by the introduction of Mn. • AlMn{sub 2}B{sub 2} and AlCr{sub 2}B{sub 2} do not exhibit magnetic ordering. • Nonmagnetic (Mn‐rich) and ferromagnetic (Fe‐rich) clustering in AlFe{sub 2–x}Mn{sub x}B{sub 2}. • Ferromagnetism is suppressed due to weakening of antibonding T–T interactions.

  9. Investigation of the fracture mechanics of boride composites

    NASA Technical Reports Server (NTRS)

    Clougherty, E. V.; Pober, R. L.; Kaufman, L.

    1972-01-01

    Significant results were obtained in fabrication studies of the role of metallic additives of Zr, Ti, Ni, Fe and Cr on the densification of ZrB2. All elemental additions lower the processing temperatures required to effect full densification of ZrB2. Each addition effects enhanced densification by a clearly distinguishable and different mechanism and the resulting fabricated materials are different. A significant improvement in strength and fracture toughness was obtained for the ZrB2/Ti composition. Mechanical characterization studies for the ZrB2/SiC/C composites and the new ZrB2/Metal materials produced data relevant to the effect of impacting load on measured impact energies, a specimen configuration for which controlled fracture could occur in a suitably hard testing apparatus, and fracture strength data. Controlled fracture--indicative of measurable fracture toughness--was obtained for the ZrB2-SiC-C composite, and a ZrB2/Ti composite fabricated from ZrB2 with an addition of 30 weight per cent Ti. The increased strength and toughness of the ZrB2/Ti composite is consistent with the presence of a significantly large amount of a fine grained acicular phase formed by reaction of Ti with ZrB2 during processing.

  10. Magnesium boride superconductors: Processing, characterization and enhancement of critical fields

    NASA Astrophysics Data System (ADS)

    Bhatia, Mohit

    In this work, the basic formation of in-situ MgB2, and how variations in the formation process influence the electrical and magnetic properties of this material was studied. Bulk MgB2 samples were prepared by stoichiometric, elemental powder mixing and compaction followed by heat-treatment. Strand samples were prepared by a modified powder-in-tube technique with subsequent heat-treatment. The influence of various heat-treatment schedules on the formation reaction was studied. Two different optimum heat-treatment windows were indentified, namely, low-temperature heat-treatment (below the melting point of Mg i.e. between 620--650°C) and high-temperature heat-treatment (>650°C) for the preparation of MgB2 with good transport properties. XRD was used to confirm phase formation and microstructural variations were studied with the help of SEM. Following a study of the reaction temperature regimes, the focus turned to critical field enhancement via doping with various compounds targeting either the Mg or the B sites. The effects of these dopants on the superconducting properties, in particular the critical fields, were studied. Large increases in irreversibility field, muoH irr, and upper critical field, Bc2, of bulk and strand superconducting MgB2 were achieved by separately adding SiC, amorphous C, and selected metal diborides (NaB2, ZrB 2, TiB2) in bulk samples and three different sizes of SiC (˜200 nm, 30 nm and 15 nm) in strand samples. Lattice spacing shifts and resistivity measurements (on some samples) were consistent with dopant introduction to the lattice. It was also found that both muoH irr and Bc2 depend on the sensing current level which may be an indication of current path percolations. These increases in the Bc2 were also complimented by an increase in the transport Jcs, especially for the SiC doped samples. It was important to differentiate between the effects on the transport properties arising from possible particulate enhanced flux pinning from that due to Bc2 enhancements, associated with smaller length scale disorder. Flux pinning analysis performed on SiC doped samples showed that while some small level of particulate-enhanced pinning was present, the majority of the pinning was associated with a grain boundary mechanism, suggesting that transport Jc increases were predominantly Bc2 related. Lastly, since the residual resistivity of a material is directly related to the electron scattering and hence Bc2, it can therefore be used as a measure to confirm the dopant introduction into the lattice. Normal-state resistivities were measured for various binary and doped MgB2 samples as a function of temperature. These resistivities were modeled based on the Bloch-Gruneissen equations. This allowed extraction of the residual resistivities, Debye temperatures and current carrying volume fractions for these samples, as well as providing information on the electron-phonon coupling constant. The residual resistivity was found to increase by a factor of three, Debye temperature decreased and the electron-phonon coupling constant increased marginally for the SiC doped samples as compared to the binary sample. This change in rho0 and theta D confirmed the XRD evidence that the dopants were increasing mu oHirr and Bc2 by substituting on the B and Mg sites of the crystalline lattice.

  11. Charge transfer and negative curvature energy in magnesium boride nanotubes

    NASA Astrophysics Data System (ADS)

    Tang, Hui; Ismail-Beigi, Sohrab

    2016-07-01

    Using first-principles calculations based on density functional theory, we study the energetics and charge transfer effects in MgBx nanotubes and two-dimensional (2D) sheets. The behavior of adsorbed Mg on 2D boron sheets is found to depend on the amount of electron transfer between the two subsystems. The amount is determined by both the density of adsorbed Mg as well as the atomic-scale structure of the boron subsystem. The degree of transfer can lead to repulsive or attractive Mg-Mg interactions. In both cases, model MgBx nanotubes built from 2D MgBx sheets can display negative curvature energy: a relatively unusual situation in nanosystems where the energy cost to curve the parent 2D sheet into a small-diameter nanotube is negative. Namely, the small-diameter nanotube is energetically preferred over the corresponding flat sheet. We also discuss how these findings may manifest themselves in experimentally synthesized MgBx nanotubes.

  12. Designing thin film materials — Ternary borides from first principles

    PubMed Central

    Euchner, H.; Mayrhofer, P.H.

    2015-01-01

    Exploiting the mechanisms responsible for the exceptional properties of aluminum based nitride coatings, we apply ab initio calculations to develop a recipe for designing functional thin film materials based on ternary diborides. The combination of binary diborides, preferring different structure types, results in supersaturated metastable ternary systems with potential for phase transformation induced effects. For the exemplary cases of MxW1 − xB2 (with M = Al, Ti, V) we show by detailed ab initio calculations that the respective ternary solid solutions are likely to be experimentally accessible by modern depositions techniques. PMID:26082562

  13. Neptunium Thiophosphate Chemistry: Intermediate Behavior between Uranium and Plutonium

    SciTech Connect

    Jin, Geng Bang; Skanthakumar, S; Haire, Richard G.; Soderholm, L; Ibers, James A.

    2011-01-01

    Black crystals of Np(PS4), Np(P2S6)2, K11Np7(PS4)13, and Rb11Np7(PS4)13 have been synthesized by the reactions of Np, P2S5, and S at 1173 and 973 K; Np, K2S, P, and S at 773 K; and Np, Rb2S3, P, and S at 823 K, respectively. The structures of these compounds have been characterized by single-crystal X-ray diffraction methods. Np(PS4) adopts a three-dimensional structure with Np atoms coordinated to eight S atoms from four bidentate PS4 3 ligands in a distorted square antiprismatic arrangement. Np(PS4) is isostructural to Ln(PS4) (Ln = LaNd, Sm, GdEr). The structure of Np(P2S6)2 is constructed from three interpenetrating diamondtype frameworks with Np atoms coordinated to eight S atoms from four bidentate P2S6 2 ligands in a distorted square antiprismatic geometry. The centrosymmetric P2S6 2 anion comprises two PS2 groups connected by two bridging S centers. Np(P2S6)2 is isostructural to U(P2S6)2. A11Np7(PS4)13 (A = K, Rb) adopts a threedimensional channel structure built from interlocking [Np7(PS4)13]11-screw helices with A cations residing in the channels. The structure of A11Np7(PS4)13 includes four crystallographically independent Np atoms. Three are connected to eight S atoms in bicapped trigonal prisms. The other Np atom is connected to nine S atoms in a tricapped trigonal prism. A11Np7(PS4)13 is isostructural to A11U7(PS4)13. From NpS bond distances and charge-balance, we infer that Np is trivalent in Np(PS4) and tetravalent in Np(P2S6)2 and A11Np7(PS4)13.Np exhibits a behavior intermediate betweenUand Pu in its thiophosphate chemistry.

  14. Fluorescence studies of neptunium and plutonium hexafluoride vapors

    SciTech Connect

    Beitz, J.V.; Williams, C.W.; Carnall, W.T.

    1982-03-01

    The first observation of fluorescence from gas phase, electronically excited, transuranic hexafluorides is reported. Fluorescence peaking at 1360 nm was observed from /sup 237/NpF/sub 6/ gas excited at 1064 nm. The measured fluroescence lifetime was 3.53 +- 0.01 ms, independent of NpF/sub 6/ pressure. Fluourescence peaking at 2300 nm has been observed from /sup 242/PuF/sub 6/ gas excited at 1064 nm. The measured fluorescence lifetime was 204 +- 12 ..mu..s, independent of PuF/sub 6/ pressure. In both cases the emitting state is assigned as a vibronic component of the first excited electronic state of the hexafluoride based on previously reported absorption spectra and energy level calculations. Fluorescence in the 1900 and 4800 nm region was observed from PuF/sub 6/ gas excited at 532 nm. The lifetime of this fluorescence was 86 +- 4. The emitting state giving rise to this shorter-lived fluorescence was not identified. Estimated fluorescence quantum yields are reported.

  15. Removal of Pu238 from Neptunium Solution by Anion Exchange

    SciTech Connect

    KYSER, EDWARD

    2003-12-01

    A new anion flowsheet for use in HB-Line was tested in the lab with Reillex{trademark} HPQ for removal of Pu{sup 238} contamination from Np. Significant rejection of Pu{sup 238} was observed by washing with 6 to 12 bed volumes (BV) of reductive wash containing reduced nitric acid concentration along with both ferrous sulfamate (FS) and hydrazine. A shortened-height column was utilized in these tests to match changes in the plant equipment. Lab experiments scaled to plant batch sizes of 1500 to 2200 g Np were observed with modest losses for up-flow washing. Down-flow washing was observed to have high losses. The following are recommended conditions for removing Pu{sup 238} from Np solutions by anion exchange in HB-Line: (1) Feed conditions: Up-flow 6.4-8 M HNO{sub 3}, 0.02 M hydrazine, 0.05 M excess FS, less than 5 days storage of solution after FS addition. (2) Reductive Wash conditions: Up-flow 6-12 BV of 6.4 M HNO{sub 3}, 0.05 M FS, 0.05 M hydrazine. 1.8 mL/min/cm{sup 2} flowrate. (3) Decontamination Wash conditions: Up-flow 1-2 BV of 6.4-8 M HNO{sub 3}, no FS, no hydrazine. (4) Elution conditions: Down-flow 0.17 M HNO{sub 3}, 0.05 M hydrazine, no FS.

  16. The transuranium elements: From neptunium and plutonium to element 112

    SciTech Connect

    Hoffman, D.C. |

    1996-07-26

    Beginning in the 1930`s, both chemists and physicists became interested in synthesizing new artificial elements. The first transuranium element, Np, was synthesized in 1940. Over the past six decades, 20 transuranium elements have been produced. A review of the synthesis is given. The procedure of naming the heavy elements is also discussed. It appears feasible to produce elements 113 and 114. With the Berkeley Gas-filled Separator, it should be possible to reach the superheavy elements in the region of the spherical Z=114 shell, but with fewer neutrons than the N=184 spherical shell. 57 refs, 6 figs.

  17. The influence of desulfovibrio desulfuricans on neptunium chemistry.

    SciTech Connect

    Soderholm, L.; Williams, C.; Antonio, M. R.; Tischler, M. L.; Markos, M.

    1999-12-20

    The role of biotic Np(V) reduction is studied in light of its potential role in the environmental immobilization of this hazardous radionuclide. The speciation of Np in Desulfovibrio desulfuricans cultures is compared with Np speciation in the spent medium and in the uninoculated medium. Precipitates formed in all three samples. Optical spectroscopy and X-ray absorption near edge structure (XANES) were used to determine that Np(V) is almost quantitatively reduced in all three samples and that the precipitate is an amorphous Np(IV) species. These results demonstrate that the reduction of Np is independent of Desulfovibrio desulfuricans. The underlying chemistry associated with these results is discussed.

  18. Thermodynamics of Neptunium (V) Complexes with Phosphate at Elevated Temperatures

    SciTech Connect

    Xia, Y.; Friese, Judah I.; Bachelor, Paula P.; Moore, Dean A.; Rao, Linfeng

    2009-06-01

    Abstract – The complexation of Np(V) with phosphate at elevated temperatures was studied by a synergistic extraction method. A mixed buffer solution of TRIS and MES was used to maintain an appropriate pH value during the distribution experiments. The distribution ratio of Np(V) between the organic and aqueous phases was found to decrease as the concentrations of phosphate were increased. Stability constants of the 1:1 and 1:2 Np(V)-HPO42- complexes, dominant in the aqueous phase under the experimental conditions, were calculated from the effect of [HPO42-] on the distribution ratio. The thermodynamic parameters including enthalpy and entropy of complexation between Np(V) and HPO42- at 25o C – 55o C were calculated by the temperature coefficient method.

  19. Symmetry, Optical Properties and Thermodynamics of Neptunium(V) Complexes

    SciTech Connect

    Rao, Linfeng; Tian, Guoxin

    2009-12-21

    Recent results on the optical absorption and symmetry of the Np(V) complexes with dicarboxylate and diamide ligands are reviewed. The importance of recognizing the 'silent' feature of centrosymmetric Np(V) species in analyzing the absorption spectra and calculating the thermodynamic constants of Np(V) complexes is emphasized.

  20. First-principles theory of multipolar order in neptunium dioxide

    NASA Astrophysics Data System (ADS)

    Suzuki, M.-T.; Magnani, N.; Oppeneer, P. M.

    2010-12-01

    We provide a first-principles, materials-specific theory of multipolar order and superexchange in NpO2 by means of a noncollinear local-density approximation +U (LDA+U) method. Our calculations offer a precise microscopic description of the triple- q antiferro ordered phase in the absence of any dipolar moment. We find that, while the most common nondipolar degrees of freedom (e.g., electric quadrupoles and magnetic octupoles) are active in the ordered phase, both the usually neglected higher-order multipoles (electric hexadecapoles and magnetic triakontadipoles) have at least an equally significant effect.

  1. Crystal dynamics and thermal properties of neptunium dioxide

    NASA Astrophysics Data System (ADS)

    Maldonado, P.; Paolasini, L.; Oppeneer, P. M.; Forrest, T. R.; Prodi, A.; Magnani, N.; Bosak, A.; Lander, G. H.; Caciuffo, R.

    2016-04-01

    We report an experimental and theoretical investigation of the lattice dynamics and thermal properties of the actinide dioxide NpO2. The energy-wave-vector dispersion relation for normal modes of vibration propagating along the [001 ] , [110 ] , and [111 ] high-symmetry lines in NpO2 at room temperature has been determined by measuring the coherent one-phonon scattering of x rays from an ˜1.2 -mg single-crystal specimen, the largest available single crystal for this compound. The results are compared against ab initio phonon dispersions computed within the first-principles density functional theory in the generalized gradient approximation plus Hubbard U correlation (GGA+U ) approach, taking into account third-order anharmonicity effects in the quasiharmonic approximation. Good agreement with the experiment is obtained for calculations with an on-site Coulomb parameter U =4 eV and Hund's exchange J =0.6 eV in line with previous electronic structure calculations. We further compute the thermal expansion, heat capacity, thermal conductivity, phonon linewidth, and thermal phonon softening, and compare with available experiments. The theoretical and measured heat capacities are in close agreement with another. About 27% of the calculated thermal conductivity is due to phonons with energy higher than 25 meV (˜6 THz ), suggesting an important role of high-energy optical phonons in the heat transport. The simulated thermal expansion reproduces well the experimental data up to about 1000 K, indicating a failure of the quasiharmonic approximation above this limit.

  2. Neptunium estimation in dissolver and high-level-waste solutions

    SciTech Connect

    Pathak, P.N.; Prabhu, D.R.; Kanekar, A.S.; Manchanda, V.K.

    2008-07-01

    This papers deals with the optimization of the experimental conditions for the estimation of {sup 237}Np in spent-fuel dissolver/high-level waste solutions using thenoyltrifluoroacetone as the extractant. (authors)

  3. Neptunium thiophosphate chemistry: intermediate behavior between uranium and plutonium.

    PubMed

    Jin, Geng Bang; Skanthakumar, S; Haire, Richard G; Soderholm, L; Ibers, James A

    2011-10-01

    Black crystals of Np(PS(4)), Np(P(2)S(6))(2), K(11)Np(7)(PS(4))(13), and Rb(11)Np(7)(PS(4))(13) have been synthesized by the reactions of Np, P(2)S(5), and S at 1173 and 973 K; Np, K(2)S, P, and S at 773 K; and Np, Rb(2)S(3), P, and S at 823 K, respectively. The structures of these compounds have been characterized by single-crystal X-ray diffraction methods. Np(PS(4)) adopts a three-dimensional structure with Np atoms coordinated to eight S atoms from four bidentate PS(4)(3-) ligands in a distorted square antiprismatic arrangement. Np(PS(4)) is isostructural to Ln(PS(4)) (Ln = La-Nd, Sm, Gd-Er). The structure of Np(P(2)S(6))(2) is constructed from three interpenetrating diamond-type frameworks with Np atoms coordinated to eight S atoms from four bidentate P(2)S(6)(2-) ligands in a distorted square antiprismatic geometry. The centrosymmetric P(2)S(6)(2-) anion comprises two PS(2) groups connected by two bridging S centers. Np(P(2)S(6))(2) is isostructural to U(P(2)S(6))(2). A(11)Np(7)(PS(4))(13) (A = K, Rb) adopts a three-dimensional channel structure built from interlocking [Np(7)(PS(4))(13)](11-)-screw helices with A cations residing in the channels. The structure of A(11)Np(7)(PS(4))(13) includes four crystallographically independent Np atoms. Three are connected to eight S atoms in bicapped trigonal prisms. The other Np atom is connected to nine S atoms in a tricapped trigonal prism. A(11)Np(7)(PS(4))(13) is isostructural to A(11)U(7)(PS(4))(13). From Np-S bond distances and charge-balance, we infer that Np is trivalent in Np(PS(4)) and tetravalent in Np(P(2)S(6))(2) and A(11)Np(7)(PS(4))(13). Np exhibits a behavior intermediate between U and Pu in its thiophosphate chemistry. PMID:21882821

  4. Fluorescence studies of neptunium and plutonium hexafluoride vapors

    NASA Astrophysics Data System (ADS)

    Beitz, James V.; Williams, Clayton W.; Carnall, W. T.

    1982-03-01

    The first observation of fluorescence from gas phase, electronically excited, transuranic hexafluorides is reported. Fluorescence peaking at 1360 nm was observed from 237NpF6 gas excited at 1064 nm. The measured fluroescence lifetime was 3.53±0.01 ms, independent of NpF6 pressure. Fluourescence peaking at 2300 nm has been observed from 242PuF6 gas excited at 1064 nm. The measured fluorescence lifetime was 204±12 μs, independent of PuF6 pressure. In both cases the emitting state is assigned as a vibronic component of the first excited electronic state of the hexafluoride based on previously reported absorption spectra and energy level calculations. Fluorescence in the 1900 and 4800 nm region was observed from PuF6 gas excited at 532 nm. The lifetime of this fluorescence was 86±4. The emitting state giving rise to this shorter-lived fluorescence was not identified. Estimated fluorescence quantum yields are reported.

  5. Hydrothermal Synthesis and Structure of Neptunium(V) Oxide

    SciTech Connect

    Forbes, Tori Z.; Burns, Peter C.; Soderholm, L. |; Skanthakumar, S.

    2007-07-01

    Single crystals of Np{sub 2}O{sub 5} have been synthesized by low-temperature hydrothermal reaction of a (NpO{sub 2}){sup +} stock solution with natural calcite crystals. The structure of Np{sub 2}O{sub 5} was solved by direct methods and refined on the basis of F{sup 2} for all unique data collected on a Bruker X-ray diffractometer equipped with an APEX II CCD detector. Np{sub 2}O{sub 5} is monoclinic, space group P2/c, with a = 8.168(2) A, b = 6.584(1) A, c = 9.3130(2) A, {beta} = 116.01(1) deg., V = 449.8(2) A{sup 3}, and Z = 1. The structure contains chains of edge-sharing neptunyl pentagonal bi-pyramids linked into sheets through cation-cation interactions with distorted neptunyl square bi-pyramids. Additional cation-cation interactions connect the sheets into a three-dimensional framework. The formation of Np{sub 2}O{sub 5} on the surface of calcite crystals has important implications for the precipitation of isolated neptunyl phases in natural aqueous systems. (authors)

  6. Neptunium(V) sorption behavior on clinoptilolite, quartz and montmorillonite

    SciTech Connect

    Bertetti, F.P.; Pabalan, R.T.; Turner, D.R.; Almendarez, M.G.

    1996-08-01

    Performance assessment models have identified {sup 237}Np as a radionuclide of concern in meeting release limits established for the geologic disposal of high-level nuclear waste at the proposed repository at Yucca Mountain, Nevada. In this study, quartz, clinoptilolite, and montmorillonite, which are minerals representative of phases that occur both in the rock matrix and as fracture coatings at Yucca Mountain, were reacted with {sup 237}Np-bearing solutions to characterize the sorption behavior of Np(V) on these minerals. Batch experiments were conducted over a wide range of conditions in which pH of solution, surface loading, sorbent surface area, initial concentration of Np(V), and partial pressure of CO{sub 2} were varied. Initial Np(V) concentrations were between 1 {times} 10{sup {minus}7} and 1 {times} 10{sup {minus}6} M in electrolyte solutions of 0.1 or 0.01 M NaNO{sub 3}. The oxidation state of Np in solution was verified with NIR spectroscopy and by solvent extraction. Prior to the start of experiments, minerals were pretreated to eliminate impurities, and the clinoptilolite and montmorillonite were converted to Na-form by ion exchange with NaCl solutions. Results indicate that, for all three minerals, Np(V) sorption begins at pH values coincident with the start of hydrolysis in solution ({approximately}7). For solutions undersaturated with respect to atmospheric CO{sub 2}, sorption increases continuously with increasing pH. Under equilibrium with atmospheric CO{sub 2}, Np(V) sorption is important in the pH range (7--9.5) where NpO{sub 2}(OH){sup 0}(aq) is significant, whereas sorption is inhibited at higher pH where neptunyl carbonate complexes are the predominant species.

  7. The complexation behavior of neptunium and plutonium with nitrilotriacetic acid

    SciTech Connect

    Nitsche, H.; Becraft, K.

    1990-08-01

    The first stability constant of NpO{sub 2}{sup +} with nitrilotriacetic acid (NTA) was determined at four ionic strengths (0.5, 1.0, 2.0, 3.0 M) using spectrophotometry. Nonlinear least-squares data fitting identified the complex as NpO{sub 2}NTA{sup 2-}. The Specific Ion Interaction Theory (S.I.T) approximation method was used to determine the stability constants at infinite dilution. First results on Pu{sup 4+} and PuO{sub 2}{sup 2+} complexation with NTA are reported. The stability constant for the Pu(NTA){sup +} complex at I = 0.1 M strength is given. From results for PuO{sub 2}{sup 2+} complexation with NTA (I = 1 M) at pH < 3, the stability constant was derived for PuO{sub 2} NTA{sup {minus}}. At pH > 3, NTA partially reduced PuO{sub 2}{sup 2+} to PuO{sub 2}{sup +}. 3 refs., 5 figs., 4 tabs.

  8. The partitioning of uranium and neptunium onto hydrothermally altered concrete

    SciTech Connect

    Zhao, P.; Allen, P.G.; Sylwester, E.R.; Viani, B.E.

    1999-10-14

    Cementitious materials that are used to construct the ground support for high-level repositories have a high probability of interacting with radionuclide-bearing fluids derived from failed waste packages. Cementitious materials provide a highly alkaline environment; pore fluids in concrete can have pH {gt} 10 for thousands to hundreds of thousands of years. Studies have shown that fresh concrete and cement phases strongly retard or immobilize certain actinides. Consequently, cementitious materials may serve as a barrier to the release of the radionuclides to the far field. However, the effect of thermal alteration of these materials, which may occur in high-level repositories, on their interaction with radionuclides has not been addressed. In contrast to retardation, colloidal silica-enriched particles that are abundant in the pore fluids of cementitious materials may facilitate radionuclide migration through the near-field into the adjacent geological environment. Due to the uncertainties of these two opposite effects, it is important to investigate the interaction of actinides with cementitious materials under varying conditions. It is expected that cementitious materials in high-level waste repositories will be subjected to and altered by hot dry and/or humid conditions forhundreds to thousands of years by the time they interact with radionuclide-bearing fluids. After alteration, the chemical and mineralogical properties of these materials will be significantly different from that of the as-placed or fresh concrete. To assess the effect that this alteration would have on radionuclide interactions, samples of hardened concrete (untreated concrete) were hydrothermally heated at 200 C for 8 months (treated concrete). The concrete used in the experiments consisted of portland cement with an aggregate of dolomitic limestone. X-ray diffraction analysis has shown that portlandite and amorphous calcium silicate hydrate gels were converted to the crystalline calcium silicate hydrate minerals tobermorite, xonotlite, and scawtite, and clay minerals by the hydrothermal treatment. Calcite, dolomite, and quartz in the aggregate were unchanged by the treatment. This paper presents the results of batch experiments to obtain partition coefficients for U(VI) and Np(V) on untreated and treated concrete in 0.01 M NaCl and 0.01 M NaHCO{sub 3} solutions as functions of the concentration of the radionuclides, pH and time.

  9. Neptunium redox behavior and solubility in J-13 conditions

    SciTech Connect

    Efurd, D.W.; Runde, W.; Tait, C.D.

    1997-08-01

    In order to confirm that the redox reaction Np(V) to Np(IV) may occur, studies are being conducted including exposure of Np(V) to solutions of known E{sub h} vs pH, temperature. Analytic results from ongoing solubility experiments from undersaturation, using Np solids formed in previous oversaturation experiments, are reported.

  10. Formation of molybdenum boride cermet coating by the detonation spray process

    NASA Astrophysics Data System (ADS)

    Yang, Gao; Zu-Kun, Hei; Xiaolei, Xu; Gang, Xin

    2001-09-01

    The effects of the powder particle size and the acetylene/oxygen gas flow ratio during the detonation spray process on the amount of molybdenum phase, porosity, and hardness of the coatings using MoB powder were investigated by x-ray diffraction (XRD), scanning electron microscopy (SEM), etc. The results show that the presence of metallic molybdenum in the coating results from decomposition of MoB powder during thermal spray. The compositions of the coatings are metallic Mo, MoB, and Mo2B, which are different from the phases of the original powder. The amount of molybdenum phase increases monotonously with the oxygen/acetylene ratio, but the increasing rate for the fine powder is faster than that for the coarse powder. The porosity and hardness of the coating are related to the amount of molybdenum phase. The phase constitution of the coating is discussed.

  11. Superconductivity and spin fluctuations in the actinoid-platinum metal borides {Th ,U } Pt3B

    NASA Astrophysics Data System (ADS)

    Bauer, E.; Royanian, E.; Michor, H.; Sologub, O.; Scheidt, E.-W.; Gonçalves, A. P.; Bursik, J.; Wolf, W.; Reith, D.; Blaas-Schenner, C.; Moser, R.; Podloucky, R.; Rogl, P.

    2015-07-01

    Investigating the phase relations of the system {Th ,U } -Pt-B at 900 °C the formation of two compounds has been observed: cubic ThPt3B with P m 3 ¯m structure as a representative of the perovskites, and tetragonal UPt3B with P 4 m m structure being isotypic to the noncentrosymmetric structure of CePt3B . The crystal structures of the two compounds are defined by combined x-ray diffraction and transmission electron microscopy. Characterization of physical properties for ThPt3B reveals a superconducting transition at 0.75 K and an upper critical field at T =0 exceeding 0.4 T. For nonsuperconducting UPt3B a metallic resistivity behavior was found in the entire temperature range; at very low temperatures spin fluctuations become evident and the resistivity ρ (T ) follows non-Fermi liquid characteristics, ρ =ρ0+A T n with n =1.6 . Density functional theory (DFT) calculations were performed for both compounds for both types of structures. They predict that the experimentally claimed cubic structure of ThPt3B is thermodynamically not stable in comparison to a tetragonal phase, with a very large enthalpy difference of 25 kJ/mol, which cannot be explained by the formation energy of B vacancies. However, the presence of random boron vacancies possibly stabilizes the cubic structure via a local strain compensation mechanism during the growth of the crystal. For UPt3B the DFT results agree well with the experimental findings.

  12. Improving Hardness and Toughness of Boride Composites Based on AIMgB14

    SciTech Connect

    Justin Steven Peters

    2007-12-01

    The search for new super-hard materials has usually focused on strongly bonded, highly symmetric crystal structures similar to diamond. The two hardest single-phase materials, diamond and cubic boron nitride (cBN), are metastable, and both must be produced at high temperatures and pressures, which makes their production costly. In 2000, a superhard composite based on a low-symmetry, boron-rich compound was reported. Since then, many advances have been made in the study of this AlMgB{sub 14}-TiB{sub 2} composite. The composite has been shown to exhibit hardness greater than either of its constituent phases, relying on its sub-micron microstructure to provide hardening and strengthening mechanisms. With possible hardness around 40 GPa, an AlMgB{sub 14} - 60 vol% TiB{sub 2} approaches the hardness of cBN, yet is amenable to processing under ambient pressure conditions. There are interesting aspects of both the AlMgB{sub 14} and TiB{sub 2} phases. AlMgB{sub 14} is comprised of a framework of boron, mostly in icosahedral arrangements. It is part of a family of 12 known compounds with the same boron lattice, with the metal atoms replaced by Li, Na, Y or a number of Lanthanides. Another peculiar trait of this family of compounds is that every one contains a certain amount of intrinsic vacancies on one or both of the metal sites. These vacancies are significant, ranging from 3 to 43% of sites depending on the composition. TiB{sub 2} is a popular specialty ceramic material due to its high hardness, moderate toughness, good corrosion resistance, and high thermal and electrical conductivity. The major drawback is the difficulty of densification of pure TiB2 ceramics. A combination of sintering aids, pressure, and temperatures of 1800 C are often required to achieve near full density articles. The AlMgB{sub 14} - TiB{sub 2} composites can achieve 99% density from hot-pressing at 1400 C. This is mostly due to the preparation of powders by a high-energy milling technique known as mechanical alloying. The resulting fine powders have high activity, and Fe from wear debris acts as a sintering aid. Mechanical alloying improves the sinterability of the composite material, it has the same effect on pure TiB{sub 2}. TiB{sub 2} processed by high-energy milling has been found to achieve 99% theoretical density at 1400 C with the addition of {approx}1 wt% Fe. Both the AlMgB{sub 14} - TiB{sub 2} composites and pure TiB{sub 2} produced from these methods have enhanced mechanical properties due to their fine microstructures. These materials show exceptional promise in the field of wear resistance. This includes cutting tools, erosion resistant coatings, and low-friction sliding contacts to name a few. Under certain wear conditions, the composite material can show performance on par with that of current high-end cBN and WC materials tailored for wear resistance. The composite material also exhibits low reactivity with Ti alloys, a pre-requisite for effective machining of these alloys, a trait that few hard materials possess.

  13. Iron cobalt boride and iron zirconium silicide-based nanocomposite soft magnetic alloys and application

    NASA Astrophysics Data System (ADS)

    Long, Jianguo

    Nanocrystalline composite soft magnetic materials, which consist of nanoscale crystalline ferromagnetic phases (typical 10 nm) homogeneously dispersed in an amorphous matrix are derived from crystallizing amorphous ribbons. The excellent soft magnetic properties, such as extremely low coercivities, high permeabilities, low energy losses, etc, have attracted the major interest and research activity in both academic community and industrial community in the past two decades. In this thesis, two classes of nanocrystalline composite soft magnetic alloys are developed from their amorphous precursors, accompanying the analysis on their sturctural evolution, thermal kinetics and variou magnetic properties. FeCoB based nanocrystalline composite soft magnetic alloy is developed, in collaboration with Magnetics Division at Spang & Company, for application in high frequency and high temperature. This class of nanocrystalline composite alloy has the nominal composition (FeCo)80Nb4[BGe(Si)] 15Cu1. The crystallization products are bcc FeCo for primary crystallization at 410°C and (FeCoNb)23B 6 for second crystallization. The average grain size is below 10 nm after annealed at 500°C for 1 hour. After transverse field annealing at its primary crystallization temperature, the core loss significantly decreased to the value which can comparable with other commercial soft magnetic alloy. Another class of nanocrystalline composite soft magnetic alloy is Fe based and Boron free alloy. This class of soft magnetic alloy with the nominal composition Fe79ZrxSi20- xCu1 was developed for low cost on raw materials. The nanocrystalline phase alpha-Fe(Si) with average grain size 10 nm was observed in this kind alloy annealed at 460°C for 1 hour. Cu acts as the nucleation agent for making the precipitated nanocrystals uniform and very fine. The measurement of core loss shows the alloy annealed at 460°C for 2 hour has the relatively core loss which can be comparable that of other commericial nanocrystalline soft magnetic alloy. Moreover, the analysis on hysteresis behavior and magnetic domain under different annealing conditions are discussed. The Preisach Distribution evaluated by first order reverse curves (FORCs) indicates the reversible process is dominant when the grain size at the sample is close to 10 nm. The irreversible part should be ascribed to the pinning sites by the grain boundaries which is significant when the large grains exist in the sample.

  14. Elastic stability and electronic structure of tantalum boride investigated via first-principles density functional calculations

    NASA Astrophysics Data System (ADS)

    Chen, Hai-Hua; Bi, Yan; Cheng, Yan; Ji, Guangfu; Cai, Lingcang

    2012-10-01

    The elastic properties, electronic structure and thermodynamic behavior of the TaB have been investigated for the first time in this work. Using first-principles plane-wave ultrasoft-pseudopotential density functional theory (DFT), the ground state properties and equation of state of TaB have been obtained. The average zero-pressure bulk modulus of TaB is 302 GPa. By analyzing the elastically anisotropic behavior and the relative structure parameters of TaB, we found that the crystal cell along the b-axis was more compressible than along the a and c axes. The calculated ratio of bulk modulus and shear modulus (B/G) for TaB is 1.58, demonstrating that TaB is rather brittle. From the elastic stiffness constants, we found that TaB in the Cmcm phase is mechanically stable. The calculated hardness of TaB is 28.6 GPa which is close to the previous data. Moreover, using the Gibbs 2 model, the thermodynamic properties such as the thermal expansion and Debye temperature of TaB have been obtained firstly. At the ambient temperature, the Debye temperatures of TaB are 792 K and 845 K from GGA calculation and LDA calculation, respectively.

  15. Microstructure and mechanical properties of titanium alloys reinforced with titanium boride

    NASA Astrophysics Data System (ADS)

    Hill, Davion M.

    Microstructure features in TiB-reinforced titanium alloys are correlated with mechanical properties. Both laser deposition and arc melting are used to fabricate test alloys where microstructure evolution with heat treatment is examined. SEM and TEM investigations of microstructure are coupled with 3D reconstruction to provide an adequate picture of phases in these alloys. Mechanical properties are then studied. Wear testing of several test alloys is presented, followed by hardness and modulus measurements of individual phases via micro- and nano-indentation as well as a novel micro-compression technique. Bulk mechanical properties are then tested in Ti-6Al-4V and Ti-555 (Ti-5Al-5V-5Mo-3Cr-1Fe) with varying amounts of boron. Image processing methods are then applied to high resolution back-scattered scanning electron microscope images to quantify microstructure features in the tensile test specimens, and these values are then correlated with mechanical properties.

  16. Wetting of boride cathode coatings by low-melting-point cryolite and liquid aluminum

    NASA Astrophysics Data System (ADS)

    Kataev, A. A.; Karimov, K. R.; Chernov, Ya. B.; Kulik, N. P.; Malkov, V. B.; Antonov, B. D.; Vovkotrub, E. G.; Zaikov, Yu. P.

    2010-08-01

    The liquid meniscus that forms on a solid sample in contact with a melt is weighed to determine the angles of wetting of the following three types of cathode coatings by aluminum and low-melting-point cryolite with a high potassium fluoride content: a hot-pressed titanium diboride sample, borated steel, and borated-aluminized steel. Information on the corrosion resistance of these materials in liquid electrolysis bath media is obtained.

  17. Microcalorimetric measurement of reaction enthalpies in solutions of uranium and neptunium compounds

    SciTech Connect

    Schreiner, F.; Friedman, A.M.; Richards, R.R.; Sullivan, J.C.

    1984-01-01

    The formation of complexes of uranyl and neptunyl(VI) ions with carbonate and hydrogen carbonate has been studied by titration microcalorimetry. The measurements were carried out with a computer-controlled microcalorimeter which is described in detail. Sample volumes are typically in the range of 1.5 to 2.5 ccm, containing about 0.05 millimole of the ionic species to be studied. The small volume renders the calorimeter useful for the measurement of uncommon and strongly radioactive substances. Enthalpies of reaction were obtained for the formation of the dicarbonato and the tricarbonato uranyl ions in a sulfate medium of ionic strength 1.6. The enthalpies are ..delta..H/sub 2/ = -39.6 +- 1 kJ/mol and -57.5 +- 1.5 kJ/mol, respectively. The titration data for the neptunyl(VI) - carbonate system yield a value of -50 +- 2 kJ/mol for the tricarbonato-neptunyl ion when interpreted in analogy to the uranyl system.

  18. Plutonium and Neptunium Speciation and Mobility in Soils and the Subsurface

    SciTech Connect

    Stout, Stephen A.; Reilly, Sean D.; Neu, Mary P.

    2006-06-01

    The DOE is conducting cleanup and stabilization activities at its nuclear weapons development sites, many of which have accumulated plutonium in soils for 60 years. To properly control Pu migration in soils and groundwaters within Federal sites and onto public lands, better evaluate the public risk, and design effective remediation strategies, a fundamental understanding of Pu speciation and environmental transport is needed. The DOE is increasingly relying on monitored natural attenuation (MNA) for site stewardship. While this is practical, and defensible based on fundamental actinide chemistry and most environmental data, there are significant gaps in the foundation of the approach. Key among them is the inability to project migration rates and redistribution of actinide contaminants, particularly given the diversity and heterogeneity of sites. Matrix sorption/desorption processes are the main factors that determine contaminant transport, but little data of this type are available for Pu or Np with minerals and sediments. To support MNA and predictive geochemical models we conducted the following research: (1) Studied environmentally relevant Pu and Np species. (2) Determined the mechanisms and thermodynamics of interactions of Pu and Np species with Mn and Fe (oxy)hydroxides and with sediments, including actinide sorption/desorption during mineral formation and redox cycling.

  19. Absence of superconductivity in fluorine-doped neptunium pnictide NpFeAsO

    NASA Astrophysics Data System (ADS)

    Walters, A. C.; Walker, H. C.; Springell, R.; Krisch, M.; Bosak, A.; Hill, A. H.; Zvorişte-Walters, C. E.; Colineau, E.; Griveau, J.-C.; Bouëxière, D.; Eloirdi, R.; Caciuffo, R.; Klimczuk, T.

    2015-08-01

    X-ray diffraction, specific heat, magnetic susceptibility and inelastic x-ray scattering measurements on the transurarium oxypnictides NpFeAsO and NpFeAsO0.85F0.15 are presented. No superconductivity down to 2 K was observed upon fluorine doping, contrary to the structurally analogous rare-earth pnictides. No modification of the phonon density of states was observed upon doping with fluorine. We discuss our results in light of the latest experimental and theoretical studies on the role of phonons in the superconducting pnictide compounds.

  20. Identification of hexanuclear Actinide(IV) carboxylates with Thorium, Uranium and Neptunium by EXAFS spectroscopy

    NASA Astrophysics Data System (ADS)

    Hennig, Christoph; Takao, Shinobu; Takao, Koichiro; Weiss, Stephan; Kraus, Werner; Emmerling, Franziska; Meyer, Michel; Scheinost, Andreas C.

    2013-04-01

    Hydrated actinide(IV) ions undergo hydrolysis and further polymerization and precipitation with increasing pH. The resulting amorphous and partly crystalline oxydydroxides AnOn(OH)4-2n·xH2O can usually be observed as colloids above the An(IV) solubility limit. The aging process of such colloids results in crystalline AnO2. The presence of carboxylates in the solution prevents the occurrence of such colloids by formation of polynuclear complexes through a competing reaction between hydrolysis and ligation. The majority of recently described carboxylates reveals a hexanuclear core of [An6(μ3-O)4(μ3-OH)4]12+ terminated by 12 carboxylate ligands. We found that the An(IV) carboxylate solution species remain often preserved in crystalline state. The An(IV) carboxylates show An-An distances which are ~ 0.03 Å shorter than the An-An distances in AnO2 like colloids. The difference in the distances could be used to identify such species in solution.

  1. Kinetics and Equilibrium Sorption Models: Fitting Plutonium, Strontium, Uranium and Neptunium Loading on Monosodium Titanate (MST)

    SciTech Connect

    Fondeur, F

    2006-03-08

    The Dubinin-Astashov (DA) isotherm parameters for U, Pu, Sr and Np have been updated to include additional data obtained since the original derivation. The DA isotherms were modified to include a kinetic function derived by Rahn to describe sorbate loading from the beginning of sorption up to steady state. The final functions describe both kinetic and thermodynamic sorption.

  2. Fabrication and characterization of americium, neptunium and curium bearing MOX fuels obtained by powder metallurgy process

    NASA Astrophysics Data System (ADS)

    Lebreton, Florent; Prieur, Damien; Jankowiak, Aurélien; Tribet, Magaly; Leorier, Caroline; Delahaye, Thibaud; Donnet, Louis; Dehaudt, Philippe

    2012-01-01

    MOX fuel pellets containing up to 1.4 wt% of Minor Actinides (MA), i.e. Am, Np and Cm, were fabricated to demonstrate the technical feasibility of powder metallurgy process involving, pelletizing and sintering in controlled atmosphere. The compounds were then characterized using XRD, SEM and EDX/EPMA. Dense pellets were obtained which closed porosity mean size is equal to 7 μm. The results indicate the formation of (U, Pu)O 2 solid solution. However, microstructure contains some isolated UO 2 grains. The distribution of Am and Cm appears to be homogeneous whereas Np was found to be clustered at some locations.

  3. Site-selective magnetic order of neptunium in Np2Ni17

    NASA Astrophysics Data System (ADS)

    Hen, A.; Magnani, N.; Griveau, J.-C.; Eloirdi, R.; Colineau, E.; Sanchez, J.-P.; Halevy, I.; Kozub, A. L.; Shick, A. B.; Orion, I.; Caciuffo, R.

    2015-07-01

    We present the results obtained by superconducting quantum interference device (SQUID) magnetometry, specific heat, and Mössbauer spectroscopy measurements carried out on Np2Ni17 polycrystalline samples. We show that long-range magnetic order, with a moment μ(2 b )˜2.25 μB, occurs below TN=17.5 K on the Np (2 b ) sites. A nontrivial situation is observed in that the other Np sites (2 d ) do not take part to the order transition and carry only an induced moment of about 0.2 μB below TN. A combined analysis of the different experimental data sets allowed us to determine key parameters associated with the electronic structure of the system. The experimental results are discussed against first-principles electronic structure calculations based on the spin-polarized local spin density approximation plus Hubbard interaction.

  4. Absence of superconductivity in fluorine-doped neptunium pnictide NpFeAsO.

    PubMed

    Walters, A C; Walker, H C; Springell, R; Krisch, M; Bosak, A; Hill, A H; Zvorişte-Walters, C E; Colineau, E; Griveau, J-C; Bouëxière, D; Eloirdi, R; Caciuffo, R; Klimczuk, T

    2015-08-19

    X-ray diffraction, specific heat, magnetic susceptibility and inelastic x-ray scattering measurements on the transurarium oxypnictides NpFeAsO and NpFeAsO0.85F0.15 are presented. No superconductivity down to 2 K was observed upon fluorine doping, contrary to the structurally analogous rare-earth pnictides. No modification of the phonon density of states was observed upon doping with fluorine. We discuss our results in light of the latest experimental and theoretical studies on the role of phonons in the superconducting pnictide compounds. PMID:26214712

  5. Understanding the interactions of neptunium and plutonium ions with graphene oxide: scalar-relativistic DFT investigations.

    PubMed

    Wu, Qun-Yan; Lan, Jian-Hui; Wang, Cong-Zhi; Zhao, Yu-Liang; Chai, Zhi-Fang; Shi, Wei-Qun

    2014-11-01

    Due to the vast application potential of graphene oxide (GO)-based materials in nuclear waste processing, it is of pivotal importance to investigate the interaction mechanisms between actinide cations such as Np(V) and Pu(IV, VI) ions and GO. In this work, we have considered four types of GOs modified by hydroxyl, carboxyl, and carbonyl groups at the edge and epoxy group on the surface, respectively. The structures, bonding nature, and binding energies of Np(V) and Pu(IV, VI) complexes with GOs have been investigated systematically using scalar-relativistic density functional theory (DFT). Geometries and harmonic frequencies suggest that Pu(IV) ions coordinate more easily with GOs compared to Np(V) and Pu(VI) ions. NBO and electron density analyses reveal that the coordination bond between Pu(IV) ions and GO possesses more covalency, whereas for Np(V) and Pu(VI) ions electrostatic interaction dominates the An-OG bond. The binding energies in aqueous solution reveal that the adsorption abilities of all GOs for actinide ions follow the order of Pu(IV) > Pu(VI) > Np(V), which is in excellent agreement with experimental observations. It is expected that this study can provide useful information for developing more efficient GO-based materials for radioactive wastewater treatment. PMID:25302669

  6. Criticality experiments and benchmarks for cross section evaluation: the neptunium case

    NASA Astrophysics Data System (ADS)

    Leong, L. S.; Tassan-Got, L.; Audouin, L.; Paradela, C.; Wilson, J. N.; Tarrio, D.; Berthier, B.; Duran, I.; Le Naour, C.; Stéphan, C.

    2013-03-01

    The 237Np neutron-induced fission cross section has been recently measured in a large energy range (from eV to GeV) at the n_TOF facility at CERN. When compared to previous measurement the n_TOF fission cross section appears to be higher by 5-7% beyond the fission threshold. To check the relevance of n_TOF data, we apply a criticality experiment performed at Los Alamos with a 6 kg sphere of 237Np, surrounded by enriched uranium 235U so as to approach criticality with fast neutrons. The multiplication factor ke f f of the calculation is in better agreement with the experiment (the deviation of 750 pcm is reduced to 250 pcm) when we replace the ENDF/B-VII.0 evaluation of the 237Np fission cross section by the n_TOF data. We also explore the hypothesis of deficiencies of the inelastic cross section in 235U which has been invoked by some authors to explain the deviation of 750 pcm. With compare to inelastic large distortion calculation, it is incompatible with existing measurements. Also we show that the v of 237Np can hardly be incriminated because of the high accuracy of the existing data. Fission rate ratios or averaged fission cross sections measured in several fast neutron fields seem to give contradictory results on the validation of the 237Np cross section but at least one of the benchmark experiments, where the active deposits have been well calibrated for the number of atoms, favors the n_TOF data set. These outcomes support the hypothesis of a higher fission cross section of 237Np.

  7. Spectrophotometric and electrochemical study of neptunium ions in molten NaCl-CsCl eutectic

    NASA Astrophysics Data System (ADS)

    Uehara, Akihiro; Nagai, Takayuki; Fujii, Toshiyuki; Shirai, Osamu; Yamana, Hajimu

    2013-06-01

    The chemical oxidation states of NpO2+, Np4+ and Np3+ in NaCl-CsCl eutectic were controlled by using Cl2, O2, H2 and Ar gas mixtures, the redox behavior and electronic absorption properties of their Np ions were studied. The Np4+ was prepared from NpO2Cl by bubbling Cl2 gas into the melt in the presence of carbon rod. Np3+ was quantitatively prepared by bubbling H2-Ar gas mixture. The molar absorptivities of NpO2+, Np4+ and Np3+ were determined in molten NaCl-CsCl eutectic at 923 K and hypersensitive transitions of Np4+ and Np3+ ions were assigned. Since the polarizing ability of the cations in the NaCl-CsCl eutectic is lower than that in some other melts, it has been shown that the coordination symmetry of the Np-Cl complex is higher. In the electrochemical measurement of Np4+, the cathodic current for the reduction of Np4+ was found to be controlled by the diffusion of Np4+. The temperature dependence of the diffusion coefficient between 823 and 923 K was formulated to be lnD=-4304/T-6.172. The formal redox potential of the Np4+|Np3+ couple depended on the temperature, this dependence was formulated as ENp|Np∘'=-1.313+6.210×10-4T V (vs. Cl2|Cl-).

  8. Validation of Cross Sections with Criticality Experiment and Reaction Rates: the Neptunium Case

    NASA Astrophysics Data System (ADS)

    Leong, L. S.; Tassan-Got, L.; Audouin, L.; Berthier, B.; Le Naour, C.; Stéphan, C.; Paradela, C.; Tarrío, D.; Duran, I.

    2014-04-01

    The 237Np neutron-induced fission cross section has been recently measured in a large energy range (from eV to GeV) at the n_TOF facility at CERN. When compared to previous measurements the n_TOF fission cross section appears to be higher by 5-7% beyond the fission threshold. To check the relevance of the n_TOF data, we considered a criticality experiment performed at Los Alamos with a 6 kg sphere of 237Np, surrounded by uranium highly enriched in 235U so as to approach criticality with fast neutrons. The multiplication factor keff of the calculation is in better agreement with the experiment when we replace the ENDF/B-VII.0 evaluation of the 237Np fission cross section by the n_TOF data. We also explored the hypothesis of deficiencies of the inelastic cross section in 235U which has been invoked by some authors to explain the deviation of 750 pcm. The large modification needed to reduce the deviation seems to be incompatible with existing inelastic cross section measurements. Also we show that the νbar of 237Np can hardly be incriminated because of the high accuracy of the existing data. Fission rate ratios or averaged fission cross sections measured in several fast neutron fields seem to give contradictory results on the validation of the 237Np cross section but at least one of the benchmark experiments, where the active deposits have been well calibrated for the number of atoms, favors the n_TOF data set. These outcomes support the hypothesis of a higher fission cross section of 237Np.

  9. TOWARD AN IMPROVED UNDERSTANDING OF STRUCTURE AND MAGNETISM IN NEPTUNIUM AND PLUTONIUM PHOSPHONATES AND SULFONATES

    SciTech Connect

    Albrecht-Schmitt, Thomas

    2012-03-01

    This grant supported the exploratory synthesis of new actinide materials with all of the actinides from thorium to californium with the exceptions of protactinium and berkelium. We developed detailed structure-property relationships that allowed for the identification of novel materials with selective ion-exchange, selective oxidation, and long-range magnetic ordering. We found novel bonding motifs and identified periodic trends across the actinide series. We identified structural building units that would lead to desired structural features and novel topologies. We also characterized many different spectroscopic trends across the actinide series. The grant support the preparation of approximately 1200 new compounds all of which were structurally characterized.

  10. Prediction Models for Plutonium, Strontium, Uranium and Neptunium Loading onto Monosodium Titanate (MST)

    SciTech Connect

    Fondeur, F. F.; Hobbs, D. T.; Barnes, M. J.; Peters, T. B.; Fink, S. D.

    2005-07-11

    The DA isotherm parameters for U, Pu, Sr and Np have been updated to include additional data obtained since the original derivation. The DA isotherms were modified to include a kinetic function derived by Rahn to describe sorbate loading from the beginning of sorption up to equilibrium. The final functions describe both kinetic and thermodynamic sorption. We selected the Rahn function to describe radionuclide sorption because it originates from diffusion and absorption controlled sorption. An investigation of the thermal behavior of radionuclide sorption on MST as shown by this data revealed the sorption process is diffusion (or transport) controlled (in solution). Transport in solution can in theory be accelerated by vigorous mixing but the range of available mixing speed in the facility design will probably not be sufficient to markedly increase radionuclide sorption rate on MST from diffusion-controlled sorption. The laboratory studies included mixing energies hydraulically-scaled to match those of the Actinide Removal Process and these likely approximate the range of energies available in the Salt Waste Processing Facility.

  11. Redox and complexation interactions of neptunium(V) with quinonoid-enriched humic derivatives

    SciTech Connect

    Shcherbina, Natalia S.; Perminova, Irina V.; Kalmykov, Stephan N.; Kovalenko, Anton N.; Novikov, Alexander P.; Haire, Richard {Dick} G

    2007-01-01

    Actinides in their higher valence states (e.g., MO{sub 2}{sup +} and MO{sub 2}{sup 2+}, where M can be Np, Pu, etc) possess a higher potential for migration and in turn pose a substantial environmental threat. To minimize this potential for migration, reducing them to lower oxidation states (e.g., their tetravalent state) can be an attractive and efficient remedial process. These lower oxidation states are often much less soluble in natural aqueous media and are, therefore, less mobile in the environment. The research presented here focuses on assessing the performance of quinonoid-enriched humic derivatives with regards to complexing and/or reducing Np(V) present in solution. These 'designer' humics are essentially derived reducing agents that can serve as reactive components of a novel humic-based remediation technology. The derivatives are obtained by incorporating different quinonoid-moieties into leonardite humic acids. Five quinonoid-derivatives are tested in this work and all five prove more effective as reducing agents for selected actinides than the parent leonardite humic acid, and the hydroquinone derivatives are better than the catechol derivatives. The reduction kinetics and the Np(V) species formed with the different derivatives are studied via a batch mode using near-infrared (NIR)-spectroscopy. Np(V) reduction by the humic derivatives under anoxic conditions at 293 K and at pH 4.7 obeys first-order kinetics. Rate constants range from 1.70 x 10{sup -6} (parent humic acid) to 1.06 x 10{sup -5} sec{sup -1} (derivative with maximum hydroquinone content). Stability constants for Np(V)-humic complexes calculated from spectroscopic data produce corresponding Log{beta} values of 2.3 for parent humic acid and values ranging from 2.5 to 3.2 at pH 4.7 and from 3.3 to 3.7 at pH 7.4 for humic derivatives. Maximum constants are observed for hydroquinone-enriched derivatives. It is concluded that among the humic derivatives tested, the hydroquinone-enriched ones are the most useful for addressing remedial needs of actinide-contaminated aquifers.

  12. Neptunium(V) partitioning to uranium(VI) oxide and peroxide solids.

    PubMed

    Douglas, Matthew; Clark, Sue B; Friese, Judah I; Arey, Bruce W; Buck, Edgar C; Hanson, Brady D

    2005-06-01

    Metaschoepite, [(UO2)8O2(OH)12] x 10H2O, and metastudtite, UO4 x 4H2O, are alteration phases anticipated in a spent nuclear fuel repository following the moist oxidation of UO2 on a geologic time scale. Dissolved concentrations and hence potential mobility of other radionuclides in the fuel, such as the neptunyl cation (NpO2+), will likely be determined by the extent of their partitioning into these U(VI) solids. 237Np is of particular interest due to its potential high mobility and long half-life (2.1 x 10(6) years.) In this study, metaschoepite has been precipitated and subsequently transformed to studtite in the presence of dissolved Np. The metaschoepite and studtite solids that formed initially contained <10 and 6500 ppm Np, respectively. Batch dissolution studies of these solids at pH 6 demonstrate release of Np that exceeds congruent dissolution of U from metastudtite; furthermore, the released Np cation remains in solution. Thus, although the Np partitions into the metastudtite solid initially, it is released to solution over time, indicating that metastudtite is not likely to serve as a host solid for Np incorporation or sorption of the neptunyl cation on long time scales. PMID:15984790

  13. Redox and complexation interactions of neptunium(V) with quinonoid-enriched humic derivatives.

    PubMed

    Shcherbina, Natalia S; Perminova, Irina V; Kalmykov, Stepan N; Kovalenko, Anton N; Haire, Richard G; Novikov, Alexander P

    2007-10-15

    Actinides in their higher valence states (e.g., MO2+ and MO2(2+), where M can be Np, Pu, etc) possess a higher potential for migration and in turn pose a substantial environmental threat. To minimize this potential for migration, reducing them to lower oxidation states (e.g., their tetravalent state) can be an attractive and efficient remedial process. These lower oxidation states are often much less soluble in natural aqueous media and are, therefore, less mobile in the environment. The research presented here focuses on assessing the performance of quinonoid-enriched humic derivatives with regardsto complexing and/ or reducing Np(V) present in solution. These "designer" humics are essentially derived reducing agents that can serve as reactive components of a novel humic-based remediation technology. The derivatives are obtained by incorporating different quinonoid-moieties into leonardite humic acids. Five quinonoid-derivatives are tested in this work and all five prove more effective as reducing agents for selected actinides than the parent leonardite humic acid, and the hydroquinone derivatives are better than the catechol derivatives. The reduction kinetics and the Np(V) species formed with the different derivatives are studied via a batch mode using near-infrared (NIR)-spectroscopy. Np(V) reduction by the humic derivatives under anoxic conditions at 293 K and at pH 4.7 obeys first-order kinetics. Rate constants range from 1.70 x 10(-6) (parent humic acid) to 1.06 x 10(-5) sec(-1) (derivative with maximum hydroquinone content). Stability constants for Np(V)-humic complexes calculated from spectroscopic data produce corresponding Logbeta values of 2.3 for parent humic acid and values ranging from 2.5 to 3.2 at pH 4.7 and from 3.3 to 3.7 at pH 7.4 for humic derivatives. Maximum constants are observed for hydroquinone-enriched derivatives. It is concluded that among the humic derivatives tested, the hydroquinone-enriched ones are the most useful for addressing remedial needs of actinide-contaminated aquifers. PMID:17993141

  14. Sorption of uranium(6+) and neptunium(5+) by surfactant-modified natural zeolites

    SciTech Connect

    Prikryl, J.D.; Pabalan, R.T.

    1999-07-01

    Experiments were conducted to determine the ability of surfactant-modification to enhance the ability of natural zeolites to sorb U(6+) and Np(5+). Natural zeolite material, comprised mainly of clinoptilolite and treated with the cationic surfactant hexadecyltrimethylammonium-bromide (HDTMA), was reacted with U(6+) and Np(5+) solutions open to the atmosphere and having a range of radionuclide concentration, pH, and NaCl concentration. The results indicate surfactant-modification of the zeolite enhances its ability to sorb U(6+), particularly at pHs greater than six where U(6+) sorption on unmodified zeolite is typically low due to formation of anionic U(6+) aqueous carbonate complexes. In contrast, there is little enhancement of Np(5+) sorption onto surfactant-modified zeolite. The presence of chloride anions in solution makes surfactant-modification less effective. The enhanced sorption of U(6+) is interpreted to be due to anion exchange with counterions on the external portion of a surfactant bilayer or admicelles.

  15. Stuies of neptunium(V) sorption on montmorillonite, clinoptilolite, quartz and {alpha}-alumina

    SciTech Connect

    Bertetti, F.P.; Pabalan, R.T.; Turner, D.R.; Almendarez, M.G.

    1996-10-01

    {sup 237}Np is a particular concern to the safety suitability of Yucca Mountain, Nevada, as a geologic repository for high-level nuclear wastes. In this study, montmorillonite, clinoptilolite, quartz, and {alpha}-alumina were reacted with {sup 237}Np-bearing solutions to characterize the sorption behavior of Np(V) on these minerals. Batch experiments were conducted at room temperature (20{plus_minus}2{degrees}C) over a range of conditions in which solution pH, sorbent surface area, initial concentration of N(V), ionic strength, and partial pressure of CO{sub 2} were varied. For all the minerals studied, Np(V) sorption begins at pH values coincident with the start of Np hydrolysis in solution ({approximately}6.5-7). For solutions undersaturated with respect to atmospheric CO{sub 2}, sorption increases continuously with increasing pH. For solutions at equilibrium with atmospheric CO{sub 2}, the {open_quotes}sorption envelope{close_quotes} is coincident with the calculated predominance field (pH {approximately}7-9.5) of the NpO{sub 2}(OH){sup 0}(aq) species, and sorption is inhibited at higher pH where neptunyl carbonate complexes predominate. Modeling of the sorption behavior of Np(V) was performed using a surface complexation-approach (Diffuse-Layer Model).

  16. Distribution of neptunium and plutonium in New Mexico lichen samples (Usnea arizonica) contaminated by atmospheric fallout

    DOE PAGESBeta

    Oldham, Jr., Warren J.; Hanson, Susan K.; Lavelle, Kevin B.; Miller, Jeffrey L.

    2015-08-30

    In this study, the concentrations of 237Np, 239Pu and 240Pu were determined in lichen samples (Usnea arizonica) that were collected from ten locations in New Mexico between 2011 and 2013 using isotope dilution inductively-coupled plasma mass spectrometry (ID-ICP-MS). The observed isotopic ratios for 237Np/239Pu and 240Pu/239Pu indicate trace contamination from global and regional fallout (e.g. Trinity test and atmospheric testing at the Nevada Test Site). The fact that actinide contamination is detected in recent lichen collections suggests continuous re-suspension of fallout radionuclides even 50 years after ratification of the Limited Test Ban Treaty.

  17. Fission cross sections of some thorium, uranium, neptunium and plutonium isotopes relative to /sup 235/U

    SciTech Connect

    Meadows, J W

    1983-10-01

    Earlier results from the measurements, at this Laboratory, of the fission cross sections of /sup 230/Th, /sup 232/Th, /sup 233/U, /sup 234/U, /sup 236/U, /sup 238/U, /sup 237/Np, /sup 239/Pu, /sup 240/Pu, and /sup 242/Pu relative to /sup 235/U are reviewed with revisions to include changes in data processing procedures, alpha half lives and thermal fission cross sections. Some new data have also been included. The current experimental methods and procedures and the sample assay methods are described in detail and the sources of error are presented in a systematic manner. 38 references.

  18. Neptunium Transport Behavior in the Vicinity of Underground Nuclear Tests at the Nevada Test Site

    SciTech Connect

    Zhao, P; Tinnacher, R M; Zavarin, M; Williams, R W; Kersting, A B

    2010-12-03

    We used short lived {sup 239}Np as a yield tracer and state of the art magnetic sector ICP-MS to measure ultra low levels of {sup 237}Np in a number of 'hot wells' at the Nevada National Security Site (NNSS), formerly known as the Nevada Test Site (NTS). The results indicate that {sup 237}Np concentrations at the Almendro, Cambric, Dalhart, Cheshire and Chancellor sites, are in the range of 3 x 10{sup -5} to 7 x 10{sup -2} pCi/L and well below the MCL for alpha emitting radionuclides (15 pCi/L) (EPA, 2009). Thus, while Np transport is believed to occur at the NNSS, activities are expected to be well below the regulatory limits for alpha-emitting radionuclides. We also compared {sup 237}Np concentration data to other radionuclides, including tritium, {sup 14}C, {sup 36}Cl, {sup 99}Tc, {sup 129}I, and plutonium, to evaluate the relative {sup 237}Np transport behavior. Based on isotope ratios relative to published unclassified Radiologic Source Terms (Bowen et al., 1999) and taking into consideration radionuclide distribution between melt glass, rubble and groundwater (IAEA, 1998), {sup 237}Np appears to be substantially less mobile than tritium and other non-sorbing radionuclides, as expected. However, this analysis also suggests that {sup 237}Np mobility is surprisingly similar to that of plutonium. The similar transport behavior of Np and Pu can be explained by one of two possibilities: (1) Np(IV) and Pu(IV) oxidation states dominate under mildly reducing NNSS groundwater conditions resulting in similar transport behavior or (2) apparent Np transport is the result of transport of its parent {sup 241}Pu and {sup 241}Am isotopes and subsequent decay to {sup 237}Np. Finally, measured {sup 237}Np concentrations were compared to recent Hydrologic Source Term (HST) models. The 237Np data collected from three wells in Frenchman Flat (RNM-1, RNM-2S, and UE-5n) are in good agreement with recent HST transport model predictions (Carle et al., 2005). The agreement provides confidence in the results of the predictive model. The comparison to Cheshire HST model predictions (Pawloski et al, 2001) is somewhat ambiguous due to the low concentration resolution of the particle transport model.

  19. NEPTUNIUM IV AND V SORPTIN TO END-MEMBER SUBSURFACE SEDIMENTS TO THE SAVANNAH RIVER SITE

    SciTech Connect

    Kaplan, D.

    2009-11-13

    Migration of Np through the subsurface is expected to be primarily controlled by sorption to sediments. Therefore, understanding and quantifying Np sorption to sediments and sediments from the Savannah River Site (SRS) is vital to ensure safe disposal of Np bearing wastes. In this work, Np sorption to two sediments representing the geological extremes with respect to sorption properties expected in the SRS subsurface environment (named 'subsurface sandy sediment' and 'subsurface clayey sediment') was examined under a variety of conditions. First a series of baseline sorption tests at pH 5.5 under an oxic atmosphere was performed to understand Np sorption under typical subsurface conditions. These experiments indicated that the baseline K{sub d} values for the subsurface sandy and subsurface clayey sediments are 4.26 {+-} 0.24 L kg{sup -1} and 9.05 {+-} 0.61 L kg{sup -1}, respectively. These Np K{sub d} values of SRS sediments are the first to be reported since Sheppard et al. (1979). The previous values were 0.25 and 0.16 L kg{sup -1} for a low pH sandy sediment. To examine a possible range of K{sub d} values under various environmental scenarios, the effects of natural organic matter (NOM, also a surrogate for cellulose degradation products), the presence of various chemical reductants, and an anaerobic atmosphere on Np sorption were examined. The presence of NOM resulted in an increase in the Np K{sub d} values for both sediments. This behavior is hypothesized to be the result of formation of a ternary Np-NOM-sediment complex. Slight increases in the Np sorption (K{sub d} 13-24 L kg{sup -1}) were observed when performing experiments in the presence of chemical reductants (dithionite, ascorbic acid, zero-valent iron) or under anaerobic conditions. Presumably, the increased sorption can be attributed to a slight reduction of Np(V) to Np(IV), the stronger sorbing form of Np. The most significant result of this study is the finding that Np weakly sorbs to both end member sediments and that Np only has a slight tendency to reduce to its stronger sorbing form, even under the most strongly reducing conditions expected under natural SRS conditions. Also, it appears that pH has a profound effect on Np sorption. Based on the these new measurements and the revelations about Np redox chemistry, the following changes to 'Best K{sub d}' values, as defined in Kaplan (2006), for SRS performance assessment calculations are recommended.

  20. Assessment of Neptunium, Americium, and Curium in the Savannah River Site Environment

    SciTech Connect

    Carlton, W.H.

    1997-12-17

    A series of documents has been published in which the impact of various radionuclides released to the environment by Savannah River Site (SRS) operations has been assessed. The quantity released, the disposition of the radionuclides in the environment, and the dose to offsite individuals has been presented for activation products, carbon cesium, iodine, plutonium, selected fission products, strontium, technetium, tritium, uranium, and the noble gases. An assessment of the impact of nonradioactive mercury also has been published.This document assesses the impact of radioactive transuranics released from SRS facilities since the first reactor became operational late in 1953. The isotopes reported here are 239Np, 241Am, and 244Cm.

  1. LITERATURE REVIEW ON THE SORPTION OF PLUTONIUM, URANIUM, NEPTUNIUM, AMERICIUM AND TECHNETIUM TO CORROSION PRODUCTS ON WASTE TANK LINERS

    SciTech Connect

    Li, D.; Kaplan, D.

    2012-02-29

    The Savannah River Site (SRS) has conducted performance assessment (PA) calculations to determine the risk associated with closing liquid waste tanks. The PA estimates the risk associated with a number of scenarios, making various assumptions. Throughout all of these scenarios, it is assumed that the carbon-steel tank liners holding the liquid waste do not sorb the radionuclides. Tank liners have been shown to form corrosion products, such as Fe-oxyhydroxides (Wiersma and Subramanian 2002). Many corrosion products, including Fe-oxyhydroxides, at the high pH values of tank effluent, take on a very strong negative charge. Given that many radionuclides may have net positive charges, either as free ions or complexed species, it is expected that many radionuclides will sorb to corrosion products associated with tank liners. The objective of this report was to conduct a literature review to investigate whether Pu, U, Np, Am and Tc would sorb to corrosion products on tank liners after they were filled with reducing grout (cementitious material containing slag to promote reducing conditions). The approach was to evaluate radionuclides sorption literature with iron oxyhydroxide phases, such as hematite ({alpha}-Fe{sub 2}O{sub 3}), magnetite (Fe{sub 3}O{sub 4}), goethite ({alpha}-FeOOH) and ferrihydrite (Fe{sub 2}O{sub 3} {center_dot} 0.5H{sub 2}O). The primary interest was the sorption behavior under tank closure conditions where the tanks will be filled with reducing cementitious materials. Because there were no laboratory studies conducted using site specific experimental conditions, (e.g., high pH and HLW tank aqueous and solid phase chemical conditions), it was necessary to extend the literature review to lower pH studies and noncementitious conditions. Consequently, this report relied on existing lower pH trends, existing geochemical modeling, and experimental spectroscopic evidence conducted at lower pH levels. The scope did not include evaluating the appropriateness of K{sub d} values for the Fe-oxyhydroxides, but instead to evaluate whether it is a conservative assumption to exclude this sorption process of radionuclides onto tank liner corrosion products in the PA model. This may identify another source for PA conservatism since the modeling did not consider any sorption by the tank liner.

  2. Tetrapositive plutonium, neptunium, uranium, and thorium coordination complexes: chemistry revealed by electron transfer and collision induced dissociation.

    PubMed

    Gong, Yu; Tian, Guoxin; Rao, Linfeng; Gibson, John K

    2014-04-17

    The Pu(4+), Np(4+), and U(4+) ions, which have large electron affinities of ∼34.6, ∼33.6, and ∼32.6 eV, respectively, were stabilized from solution to the gas phase upon coordination by three neutral tetramethyl-3-oxa-glutaramide ligands (TMOGA). Both collision induced dissociation (CID) and electron transfer dissociation (ETD) of Pu(TMOGA)3(4+) reveal the propensity for reduction of Pu(IV) to Pu(III), by loss of TMOGA(+) in CID and by simple electron transfer in ETD. The reduction of Pu(IV) is in distinct contrast to retention of Th(IV) in both CID and ETD of Th(TMOGA)3(4+), where only the C-Oether bond cleavage product was observed. U(TMOGA)3(4+) behaves similarly to Th(TMOGA)3(4+) upon CID and ETD, while the fragmentation patterns of Np(TMOGA)3(4+) lie between those of Pu(TMOGA)3(4+) and U(TMOGA)3(4+). It is notable that the gas-phase fragmentation behaviors of these exceptional tetrapositive complexes parallel fundamental differences in condensed phase chemistry within the actinide series, specifically the tendency for reduction from the IV to III oxidation states. PMID:24660979

  3. Neptunium (V) Adsorption to a Halophilic Bacterium Under High Ionic Strength Conditions: A Surface Complexation Modeling Approach

    SciTech Connect

    Ams, David A

    2012-06-11

    Rationale for experimental design: Np(V) -- important as analog for Pu(V) and for HLW scenarios; High ionic strength -- relevant to salt-based repositories such as the WIPP; Halophilic microorganisms -- representative of high ionic strength environments. For the first time showed: Significant adsorbant to halophilic microorganisms over entire pH range under high ionic strength conditions; Strong influence of ionic strength with increasing adsorption with increasing ionic strength (in contrast to trends of previous low ionic strength studies); Effect of aqueous Np(V) and bacterial surface site speciation on adsorption; and Developed thermodynamic models that can be incorporated into geochemical speciation models to aid in the prediction of the fate and transport of Np(V) in more complex systems.

  4. Analysis of trace neptunium in the vicinity of underground nuclear tests at the Nevada National Security Site.

    PubMed

    Zhao, P; Tinnacher, R M; Zavarin, M; Kersting, A B

    2014-11-01

    A high sensitivity analytical method for (237)Np analysis was developed and applied to groundwater samples from the Nevada National Security Site (NNSS) using short-lived (239)Np as a yield tracer and HR magnetic sector ICP-MS. The (237)Np concentrations in the vicinity of the Almendro, Cambric, Dalhart, Cheshire, and Chancellor underground nuclear test locations range from <4 × 10(-4) to 2.6 mBq/L (6 × 10(-17)-4.2 × 10(-13) mol/L). All measured (237)Np concentrations are well below the drinking water maximum contaminant level for alpha emitters identified by the U.S. EPA (560 mBq/L). Nevertheless, (237)Np remains an important indicator for radionuclide transport rates at the NNSS. Retardation factor ratios were used to compare the mobility of (237)Np to that of other radionuclides. The results suggest that (237)Np is less mobile than tritium and other non-sorbing radionuclides ((14)C, (36)Cl, (99)Tc and (129)I) as expected. Surprisingly, (237)Np and plutonium ((239,240)Pu) retardation factors are very similar. It is possible that Np(IV) exists under mildly reducing groundwater conditions and exhibits a retardation behavior that is comparable to Pu(IV). Independent of the underlying process, (237)Np is migrating downgradient from NNSS underground nuclear tests at very low but measureable concentrations. PMID:25078472

  5. First-principles investigation of higher oxides of uranium and neptunium: U3O8 and Np2O5

    NASA Astrophysics Data System (ADS)

    Yun, Y.; Rusz, J.; Suzuki, M.-T.; Oppeneer, P. M.

    2011-02-01

    A computational study is presented of the structural, electronic, and magnetic properties of U3O8 and Np2O5, which are actinide oxides in a higher oxidation state than the tetravalent state of the common dioxide phases, UO2 and NpO2. The calculations are based on the density functional theory+U approach, in which additional Coulomb correlations on the actinide atom are taken into account. The calculated properties of these two higher oxidized actinide oxides are analyzed and compared to those of their tetravalent analogs. The optimized structural parameters of these noncubic oxides are found to be in reasonable agreement with available experimental data. U3O8 is predicted to be a magnetic insulator, having one U atom in a hexavalent oxidation state and two U atoms in a pentavalent oxidation state. For Np2O5, which is also predicted to be an insulator, a complicated noncollinear magnetic structure is computed, leading to a nonzero overall magnetization with a slight antiferromagnetic canting. The calculated electronic structures are presented and the variation of the U 5f or Np 5f-O 2p hybridization with the oxidation state is analyzed. With increasing oxygen content, the nearly localized 5f electrons of the actinide elements are more positioned near the Fermi level and the hybridization between 5f and 2p states is markedly increased.

  6. Surface Complexation of Neptunium(V) onto Whole Cells and Cell Components of Shewanella alga: Modeling and Experimental Study

    SciTech Connect

    Deo, Randhir P.; Songkasiri, Warinthorn; Rittmann, Bruce E.; Reed, Donald T.

    2012-04-30

    We systematically quantified surface complexation of Np(V) onto whole cells, cell wall, and extracellular polymeric substances (EPS) of Shewanella alga strain BrY. We first performed acid and base titrations and used the mathematical model FITEQL to estimate the concentrations and deprotonation constants of specific surface functional groups. Deprotonation constants most likely corresponded to a carboxyl group not associated with amino acids (pK{sub a} {approx} 5), a phosphoryl site (pK{sub a} {approx} 7.2), and an amine site (pK{sub a} > 10). We then carried out batch sorption experiments with Np(V) and each of the S. alga components as a function of pH. Since significant Np(V) sorption was observed on S. alga whole cells and its components in the pH range 2-5, we assumed the existence of a fourth site: a low-pK{sub a} carboxyl site (pK{sub a} {approx} 2.4) that is associated with amino acids. We used the SPECIATE submodel of the biogeochemical model CCBATCH to compute the stability constants for Np(V) complexation to each surface functional group. The stability constants were similar for each functional group on S. alga bacterial whole cells, cell walls, and EPS, and they explain the complicated sorption patterns when they are combined with the aqueous-phase speciation of Np(V). For pH < 8, the aquo NpO{sub 2}{sup +} species was the dominant form of Np(V), and its log K values for the low-pK{sub a} carboxyl, mid-pK{sub a} carboxyl, and phosphoryl groups were 1.8, 1.8, and 2.5-3.1, respectively. For pH greater than 8, the key surface ligand was amine > XNH{sub 3}{sup +}, which complexed with NpO{sub 2}(CO{sub 3}){sub 3}{sup 5-}. The log K for NpO{sub 2}(CO{sub 3}){sub 3}{sup 5-} complexed onto the amine groups was 3.1-3.9. All of the log K values are similar to those of Np(V) complexes with aqueous carboxyl and N-containing carboxyl ligands. These results help quantify the role of surface complexation in defining actinide-microbiological interactions in the subsurface.

  7. In situ spectroscopic identification of neptunium(V) inner-sphere complexes on the hematite-water interface.

    PubMed

    Müller, Katharina; Gröschel, Annett; Rossberg, André; Bok, Frank; Franzen, Carola; Brendler, Vinzenz; Foerstendorf, Harald

    2015-02-17

    Hematite plays a decisive role in regulating the mobility of contaminants in rocks and soils. The Np(V) reactions at the hematite-water interface were comprehensively investigated by a combined approach of in situ vibrational spectroscopy, X-ray absorption spectroscopy and surface complexation modeling. A variety of sorption parameters such as Np(V) concentration, pH, ionic strength, and the presence of bicarbonate was considered. Time-resolved IR spectroscopic sorption experiments at the iron oxide-water interface evidenced the formation of a single monomer Np(V) inner-sphere sorption complex. EXAFS provided complementary information on bidentate edge-sharing coordination. In the presence of atmospherically derived bicarbonate the formation of the bis-carbonato inner-sphere complex was confirmed supporting previous EXAFS findings.1 The obtained molecular structure allows more reliable surface complexation modeling of recent and future macroscopic data. Such confident modeling is mandatory for evaluating water contamination and for predicting the fate and migration of radioactive contaminants in the subsurface environment as it might occur in the vicinity of a radioactive waste repository or a reprocessing plant. PMID:25597326

  8. Theoretical study on K, L, and M X-ray transition energies and rates of neptunium and its ions

    NASA Astrophysics Data System (ADS)

    Ismail Abdalla, Saber; Dong, Chen-Zhong; Wang, Xiang-Li; Zhou, Wei-Dong; Wu, Zhong-Wen

    2014-02-01

    The transition energies and electric dipole (E1) transition rates of the K, L, and M lines in neutral Np have been theoretically determined from the MultiConfiguration Dirac—Fock (MCDF) method. In the calculations, the contributions from Breit interaction and quantum electrodynamics (QED) effects (vacuum polarization and self-energy), as well as nuclear finite mass and volume effects, are taken into account. The calculated transition energies and rates are found to be in good agreement with other experimental and theoretical results. The accuracy of the results is estimated and discussed. Furthermore, we calculated the transition energies of the same lines radiating from the decaying transitions of the K-, L-, and M-shell hole states of Np ions with the charge states Np1+ to Np6+ for the first time. We found that for a specific line, the corresponding transition energies relating to all the Np ions are almost the same; it means the outermost electrons have a very small influence on the inner-shell transition processes.

  9. Complexation of Neptunium(V) with Glutaroimide Dioxime: A Study by Absorption Spectroscopy, Microcalorimetry, and Density Functional Theory Calculations.

    PubMed

    Ansari, Seraj A; Bhattacharyya, Arunasis; Zhang, Zhicheng; Rao, Linfeng

    2015-09-01

    Complexation of NpO2(+) ions with glutaroimide dioxime (H2L), a cyclic imide dioxime ligand that has been shown to form strong complexes with UO2(2+) in aqueous solutions, was studied by absorption spectroscopy and microcalorimetry in 1.0 M NaClO4 aqueous solutions. NpO2(+) forms two successive complexes, NpO2(HL)(aq) and NpO2(HL)2(-) (where HL(-) stands for the partially deprotonated glutaroimide dioxime ligand), with stability constants of log β111 = 17.8 ± 0.1 and log β122 = 33.0 ± 0.2, respectively. The complexation is both enthalpy- and entropy-driven, with negative enthalpies (ΔH111 = -52.3 ± 1.0 kJ/mol and ΔH122 = -96.1 ± 1.4 kJ/mol) and positive entropies (ΔS111 = 164 ± 3 J/mol/K and ΔS122 = 310 ± 4 J/mol/K). The thermodynamic parameters suggest that, similar to complexation of UO2(2+), the ligand coordinates with NpO2(+) in a tridentate mode, via the two oxygen atoms of the oxime groups and the nitrogen atom of the imide group. Density functional theory calculations have helped to interpret the optical absorption properties of the NpO2(HL)2(-) complex, by showing that the cis and trans configurations of the complex have very similar energies so that both configurations could be present in the aqueous solutions. It is the noncentrosymmetric cis configuration that makes the 5f → 5f transition allowable so that the NpO2(HL)2(-) complex absorbs in the near-IR region. PMID:26263050

  10. Electron paramagnetic resonance and electron nuclear double resonance of 237-neptunium hexafluoride in uranium hexafluoride single crystals

    NASA Astrophysics Data System (ADS)

    Butler, James E.; Hutchison, Clyde A., Jr.

    1981-03-01

    The EPR and ENDOR spectra of 237NpF6 molecules dilutely substituted for host molecules in single crystals of UF6 at temperatures between 1.2 and 2.1 °K have been obtained at microwave frequencies, ˜9.4 and ˜9.7 GHz. Approximate values are given for the parameters in a spin Hamiltonian formalism that describes the measurements. The results are discussed.

  11. Distribution of neptunium and plutonium in New Mexico lichen samples (Usnea arizonica) contaminated by atmospheric fallout

    SciTech Connect

    Oldham, Jr., Warren J.; Hanson, Susan K.; Lavelle, Kevin B.; Miller, Jeffrey L.

    2015-08-30

    In this study, the concentrations of 237Np, 239Pu and 240Pu were determined in lichen samples (Usnea arizonica) that were collected from ten locations in New Mexico between 2011 and 2013 using isotope dilution inductively-coupled plasma mass spectrometry (ID-ICP-MS). The observed isotopic ratios for 237Np/239Pu and 240Pu/239Pu indicate trace contamination from global and regional fallout (e.g. Trinity test and atmospheric testing at the Nevada Test Site). The fact that actinide contamination is detected in recent lichen collections suggests continuous re-suspension of fallout radionuclides even 50 years after ratification of the Limited Test Ban Treaty.

  12. Determining Sources and Transport of Nuclear Contamination in Hudson River Sediments with Plutonium, Neptunium, and Cesium isotope ratios

    NASA Astrophysics Data System (ADS)

    Kenna, T. C.; Chillrud, S. N.; Chaky, D. A.; Simpson, H. J.; McHugh, C. M.; Shuster, E. L.; Bopp, R. F.

    2004-12-01

    Different sources of radioactive contamination contain characteristic and identifiable isotopic signatures, which can be used to study sediment transport. We focus on Pu-239, Pu-240, Np-237 and Cs-137, which are strongly bound to fine grained sediments. The Hudson River drainage basin has received contamination from at least three separate sources: 1) global fallout from atmospheric testing of nuclear weapons, which contributed Pu, Np and Cs; 2) contamination resulting from reactor releases at the Indian Point Nuclear Power Plant (IPNPP) located on the Hudson River Estuary ˜70km north of New York Harbor, where records document releases of Cs-137; 3) contamination resulting from activities at the Knolls Atomic Power Laboratory (KAPL) located on the Mohawk River, where incomplete records document releases of Cs-137 but no mention is made of Pu or Np. Here we report measurements of Pu isotopes, Np-237 and Cs-137 for a series of sediment cores collected from various locations within the drainage basin: 1) Mohawk River downstream of KAPL, 2) Hudson River upstream of its confluence with the Mohawk River, and 3) lower Hudson River at a location in close proximity to IPNPP. In addition, we present data from selected samples from two other lower Hudson River locations: One site located ˜30km downstream of IPNPP and another ˜30km upstream of IPNPP. By comparing the isotopic ratios Pu-240/Pu-239, Np-237/Pu-239, and Cs-137/Pu-239, measured in fluvial sediments to mean global fallout values, it is possible to identify and resolve different sources of non-fallout contamination. To date, isotopic data for sediments indicate non-fallout sources of Pu-239, Pu-240, and Cs-137; Np-237, however, appears to originate from global fallout only. Mohawk River sediments downstream of KAPL exhibit enrichments in Pu-239, Pu-240, and Cs-137 that are 7 to 20 times higher than levels expected from global fallout as indicated from Np-237. The elevated levels, non-fallout isotopic signatures, and core location are all consistent with KAPL being a source of Pu and Cs isotopes. Sediments from upper Hudson River and a section of the lower Hudson Estuary both contain Cs-137 levels that are more than twice that expected from global fallout. While elevated Cs-137 in selected lower Hudson samples is consistent with reported reactor releases from IPNPP, there is no known source of non-fallout Cs in the upper Hudson. We have been able to estimate end-member isotopic compositions of radionuclides originating from KAPL as well as detect its presence and estimate its contribution to contaminant inventories far downstream in tidal Hudson sediments. By comparing KAPL-derived Pu-239 inventories measured in the Mohawk and Lower Hudson Rivers, we estimate a dilution factor of ˜140. While there is isotopic evidence of KAPL derived radionuclides in all the lower Hudson sediments that we have analyzed, elevated levels of Cs-137 (not attributable to KAPL)were only observed in sediments collected in the vicinity of IPNPP and those collected 30km downstream of the plant's location. We attribute the elevated Cs-137 levels in these Lower Hudson sediments to contamination originating from IPNPP. The lack of elevated levels of Cs-137 in sediments collected 30km upstream of the plant's location plus a dilution factor for Upper Hudson sediments that is larger than that estimated for Mohawk River sediments alone, allows us to conclude that Cs-137 enrichment observed in the Upper Hudson is not likely to be a significant source of Cs-137 contamination to lower Hudson River sediments.

  13. DEMONSTRATION OF THE DWPF FLOWSHEET IN THE SRNL SHIELDED CELLS WITH TANK 40 AND H CANYON NEPTUNIUM

    SciTech Connect

    Pareizs, J; Bradley Pickenheim, B; Cj Bannochie, C; Michael Stone, M

    2009-04-28

    The Defense Waste Processing Facility (DWPF) is currently processing Sludge Batch 5 (SB5) from Tank 40. SB5 contains the contents of Tank 51 from November 2008, qualified by the Savannah River National Laboratory (SRNL) and the heel in Tank 40 remaining from Sludge Batch 4. Current Liquid Waste Operations (LWO) plans are to (1) decant supernatant from Tank 40 to remove excess liquid caused by a leaking slurry pump and (2) receive a Np stream from H Canyon It should be noted that the Np stream contains significant nitrate requiring addition of nitrite to Tank 40 to maintain a high nitrite to nitrate ratio for corrosion control. SRNL has been requested to qualify the proposed changes; determine the impact on DWPF processability in terms of hydrogen generation, rheology, etc.; evaluate antifoam addition strategy; and evaluate mercury stripping. Therefore, SRNL received a 3 L sample of Tank 40 following the transfer of Tank 51 to Tank 40 (Tank Farm Sample HTF-40-08-157 to be used in testing and to perform the required Waste Acceptance Product Specifications radionuclide analyses). Based on Tank Farm projections, SRNL decanted a portion* of the sample, added sodium nitrite, and added a Np solution from H Canyon representative of the Np to be dispositioned to Tank 40 (neutralized to 0.6 M excess hydroxide). The resulting material was used in a DWPF Chemical Process Cell (CPC) demonstration -- a Sludge Receipt and Adjustment Tank (SRAT) cycle and a Slurry Mix Evaporator (SME) cycle. Preliminary data from the demonstration has been reported previously. This report includes discussion of these results and additional results, including comparisons to Tank Farm projections and the SB5 demonstration.

  14. UNDERSTANDING VARIATION IN PARTITION COEFFICIENT KD, VALUES, VOLUME III: AMERICIUM, ARSENIC, CURIUM, IODINE, NEPTUNIUM, RADIUM, AND TECHNETIUM

    EPA Science Inventory

    This report describes the conceptualization, measurement, and use of the partition (or distribution) coefficient, Kd, parameter, and the geochemical aqueous solution and sorbent properties that are most important in controlling adsorption/retardation behavior of selected contamin...

  15. Revision and meta-analysis of selected biosphere parameter values for chlorine, iodine, neptunium, radium, radon and uranium.

    PubMed

    Sheppard, S C; Sheppard, M I; Tait, J C; Sanipelli, B L

    2006-01-01

    There is a continual supply of new experimental data that are relevant to the assessment of the potential impacts of nuclear fuel waste disposal. In the biosphere, the traditional assessment models are data intensive, and values are needed for several thousand parameters. This is augmented further when measures of central tendency, statistical dispersion, correlations and truncations are required for each parameter to allow probabilistic risk assessment. Recent reviews proposed values for 10-15 key element-specific parameters relevant to (36)Cl, (129)I, (222)Rn, (226)Ra, (237)Np and (238)U, and some highlights from this data update are summarized here. Several parameters for Np are revised downward by more than 10-fold, as is the fish/water concentration ratio for U. Soil solid/liquid partition coefficients, Kd, are revised downward by 10-770-fold for Ra. Specific parameters are discussed in detail, including degassing of I from soil; sorption of Cl in soil; categorization of plant/soil concentration ratios for U, Ra and Np; Rn transfer from soil to indoor air; Rn degassing from surface water; and the Ca dependence of Ra transfers. PMID:16759770

  16. Effect of Fe2+ Oxidation on the Removal of 238Pu from Neptunium Solution by Anion Exchange

    SciTech Connect

    KYSER, EDWARD

    2004-06-01

    The effect of ferrous sulfamate (FS) oxidation and variation in nitric acid concentration on the removal of {sup 238}Pu contamination from Np by the HB-Line anion exchange flowsheet has been tested. Significant rejection of {sup 238}Pu was observed by washing with a reductive wash solution containing 6.0 to 6.8 M nitric acid (HNO{sub 3}) with as little as 30% of the Fe{sup 2+} from the FS remaining in its reduced form. To achieve the desired 30% removal of {sup 238}Pu from the process, conditions should be controlled to maintain the Fe{sup 2+}/Fe{sup 3+} ratio in the reductive wash to be greater than 60%/40% (or 1.5). Since Fe{sup 2+} oxidation is strongly affected by temperature and nitric acid concentration, these parameters (as well as time after FS addition) need to be controlled to ensure predictable results. A shortened-height column was utilized in these tests to match changes in the plant equipment. Lab experiments scaled to plant batch sizes of 2000 g Np were observed with modest losses for ''up-flow'' washing. The following are recommended conditions for removing {sup 238}Pu from Np solutions by anion exchange in HB-Line: (1) Feed conditions: ''Up-flow'' 6.4-8.0 M HNO{sub 3}, 0.02 M hydrazine (N{sub 2}H{sub 4}), 0.05 M excess FS. (2) Reductive Wash conditions: ''Up-flow'' 6 Bed volumes (BV) of 6.4 M HNO{sub 3}, 0.05 M FS (minimum 0.03M Fe{sup 2+} during wash cycle), 0.05 M hydrazine, less than 1.8 mL/min/cm{sup 2} flowrate. (3) Decontamination Wash conditions: ''Up-flow'' 1-2 BV of 6.4-8.0 M HNO{sub 3}, no FS, no hydrazine, less than 1.8 mL/min/cm{sup 2} flowrate. (4) Elution conditions: ''Down-flow'' 0.17 M HNO{sub 3}, 0.05 M hydrazine, no FS.

  17. Synthesis of ferromagnetic nanoparticles, formic acid oxidation catalyst nanocomposites, and late-transition metal-boride intermetallics by unique synthetic methods and single-source precursors

    NASA Astrophysics Data System (ADS)

    Wellons, Matthew S.

    The design, synthesis, and characterization of magnetic alloy nanoparticles, supported formic acid oxidation catalysts, and superhard intermetallic composites are presented. Ferromagnetic equatomic alloy nanoparticles of FePt, FePd, and CoPt were synthesized utilizing single-source heteronuclear organometallic precursors supported on an inert water-soluble matrix. Direct conversion of the precursor-support composite to supported ferromagnetic nanoparticles occurs under elevated temperatures and reducing conditions with metal-ion reduction and minimal nanoparticle coalescence. Nanoparticles were easily extracted from the support by addition of water and characterized in structure and magnetic properties. Palladium and platinum based nanoparticles were synthesized with microwave-based and chemical metal-ion reduction strategies, respectively, and tested for catalytic performance in a direct formic acid fuel cell (DFAFC). A study of palladium carbide nanocomposites with various carbonaceous supports was conducted and demonstrated strong activity comparable to commercially available palladium black, but poor catalytic longevity. Platinum-lead alloy nanocomposites synthesized with chemical reduction and supported on Vulcan carbon demonstrated strong activity, excellent catalytic longevity, and were subsequently incorporated into a prototype DFAFC. A new method for the synthesis of superhard ceramics on polymer substrates called Confined Plasma Chemical Deposition (CPCD) was developed. The CPCD method utilizes a tuned Free Electron Laser to selectively decompose the single-source precursor, Re(CO)4(B3H8), in a plasma-like state resulting in the superhard intermetallic ReB2 deposited on polymer substrates. Extension of this method to the synthesis of other hard of superhard ceramics; WB4, RuB2, and B4C was demonstrated. These three areas of research show new synthetic methods and novel materials of technological importance, resulting in a substantial advance in their respective fields.

  18. CaNi/sub 12/B/sub 6/: a new boride of the SrNi/sub 12/B/sub 6/ structure type

    SciTech Connect

    Leshko, L.V.; Kuz'ma, Yu.B.

    1987-11-01

    The structure of CaNi/sub 12/B/sub 6/ has been examined from the diffraction pattern (DRON-3.0, Cu K/sub ..cap alpha../ radiation). When the pattern had been indexed to the hexagonal system, the cell parameters were found as ..cap alpha.. = 9.542 (3); c = 7.420 (3) A. The coordinates of the Ca and Ni atoms were refined via the PMNK program with an SM-4 computer, with the initial coordinates those for the metal atoms in SrNi/sub 12/B/sub 6/. The coordinates of the boron atoms were not refined, being taken the same as in SrNi/sub 12/B/sub 6/. The final values for the coordinates (space group R3m) are Ca at 3 (..cap alpha..) 000, B = 3.3 (5) A/sup 2/; 18 Nil at 18 (g) (x = 0.369(2)), B = 0.7(1) A/sup 2/; 18Ni2 at 18 (h) (x = 0.426(1), z = 0.031(2)), B = 0.5(1) A/sup 2/; 18B at 18 (h) (x = 0.191, z = 0.042), B = 3.3(5) A/sup 2/. The intensities were calculated for these coordinates, reliability factor R = 0.108

  19. Superconductivity in a New Pseudo-Binary Li2B(Pd1-xPtx)3 (x=0--1) Boride System

    NASA Astrophysics Data System (ADS)

    Badica, Petre; Kondo, Takaaki; Togano, Kazumasa

    2005-03-01

    Recently we have found superconductivity in a cubic antiperovskite-like compound Li2BPd3. A new pseudo-binary complete solid solution Li2B(Pd1-xPtx)3, x=0--1 with similar structure has been synthesized and observation of superconductivity in the entire x-range is reported. Our results strongly suggest that superconductivity is of bulk type. Critical temperature Tc is decreasing approximately linearly with amount (x) of Pt from 7.2-8 K for Li2BPd3 to 2.2-2.8 K for Li2BPt3. From isothermal magnetization (M-H) measurements, lower critical fields Hc1 (138 Oe/x=0, 38 Oe/x=1), upper critical fields Hc2WHH (3.4 T/x=0, 1 T/x=1), coherence length ξ(0) (9.8 nm/x=0, 17.9 nm/x=1) and penetration depth λ(0) (190 nm/x=0, 364 nmx=1) were estimated and shown to follow approximately linear dependencies with x, either. Structure and superconducting similarities with MgCNi3, viewed as a bridge between low and high Tc superconductors are increasing the expectations that Li2B(Pd1-xPtx)3, x=0--1 superconductor can be included in the same class of ‘intermediate’ superconductors. For x=0--1 a weak fish-tail effect was observed at low and intermediate fields. Apart from this effect, some samples for x=1 have shown magnetization jumps at fields close to Hc2.

  20. Synthesis and crystal structure of Mg{sub 2}B{sub 24}C, a new boron-rich boride related to 'tetragonal boron I'

    SciTech Connect

    Adasch, Volker; Hess, Kai-Uwe; Vojteer, Natascha; Hillebrecht, Harald . E-mail: harald.hillebrecht@ac.uni-freiburg.de

    2006-07-15

    Single crystals of Mg{sub 2}B{sub 24}C, a new boron-rich boridecarbide of magnesium, were synthesized as black needles and columns by reaction of the elements in Ta ampoules and BN crucibles at 1300 deg. C. The crystal structure was determined by X-ray diffraction (P-4n2, a=8.9391(13)A, c=5.0745(10)A, Z=2, 713 reflections, 64 variables, R{sub 1}(F)=0.0235, wR{sub 2}(I)=0.0591). It is closely related to 'tetragonal boron I' and can be described as a tetragonal rod packing of corner-linked B{sub 12} icosahedra with C and Mg atoms in the voids. Each B{sub 12} icosahedron has 2 B-C bonds and 10 exohedral bonds to other icosahedra, 2 within the rod and 4x2 to neighbouring rods. The isolated C atoms are 4-fold coordinated forming distorted tetrahedra. Mg is placed on two crystallographically independent positions within the three-dimensional B{sub 12}C network. Mg{sub 2}B{sub 24}C is the first example for a compound related to 'tetragonal boron I' with a stoichiometric composition.

  1. Identification of specific phonon contributions in BCS-type superconductivity of boride-carbide crystals with a layer-like structure

    NASA Astrophysics Data System (ADS)

    Uzunok, H. Y.; Tütüncü, H. M.; Özer, S.; Ugˇur, Ş.; Srivastava, G. P.

    2015-03-01

    We report on an ab initio study of the BCS-type superconductivity in the intermetallic borocarbides YPd2B2C, YPt2B2C and LaPt2B2C with a layer-like structure. The largest contribution to the electron-phonon coupling constant λ is identified to come from transverse acoustic phonons at a zone-edge, arising from the atomic vibrations in the boron-transition metal layer. A detailed examination of the atomic geometry in the boron-transition metal layer, the electron-phonon coupling constant λ, and the logarithmically averaged phonon frequency ωln helps explain the relatively higher superconducting temperature Tc of YPd2B2C (20.6 K) compared to that of YPt2B2C (11.3 K) and LaPt2B2C (10.40 K).

  2. Structural arrangements of the ternary metal boride carbide compounds MB 2C 4 ( M=Mg, Ca, La and Ce) from first-principles theory

    NASA Astrophysics Data System (ADS)

    Fang, Chang-Ming; Bauer, Joseph; Saillard, Jean-Yves; Halet, Jean-François

    2007-09-01

    The structural arrangements of the ternary metal borocarbides MB 2C 4 ( M=Mg, Ca; La and Ce) are investigated using density-functional theory (DFT) calculations within the generalized gradient approximation (GGA). Results indicate that these compounds adopt a layered structure consisting of graphite-like B 2C 4 layers alternating with metal sheets. Within the hexagonal layers, the coloring with the -C-C-C-B-C-B- sequence is energetically more stable than that with the -C-C-C-C-B-B- one. The electronic structures of these compounds, mainly determined by the B 2C 4 sheets, can be rationalized with the simple valence electron distribution M2+[B 2C 4] 2-xe -, with the metals essentially acting as two-electron donors with respect to the boron-carbon network, the other x electrons remaining in the relatively narrow d and/or f bands of the metals. Accordingly, MB 2C 4 are narrow band-gap semiconductors (Δ E≈0.2-0.4 eV) with M=Mg and Ca. On the other hand, with M=La and Ce, the compounds are conducting with a relatively high density of states at the Fermi level predominantly metal in character with substantial B/C π* antibonding state admixture.

  3. Effect of double addition of V and Cr on the properties of Mo2NiB2 ternary boride-based cermets

    NASA Astrophysics Data System (ADS)

    Shiota, Yuusuke; Miyajima, Yuuta; Fujima, Takuya; Takagi, Ken-ichi

    2009-06-01

    The effect of double addition of V and Cr on the mechanical properties and microstructure of Mo2NiB2 base cermet was investigated. Total additional amount of V and Cr was fixed to 12.5 mass% and the fraction between the two additives was varied. Transverse rupture strength (TRS) and Rockwell A-scale hardness (HRA) were measured on the cermets and discussed together with their microstructure obtained by X-ray diffraction (XRD) and backscattered electron images (COMP). Addition of 2.5-mass% Cr and 10-mass% V showed the highest mechanical properties. Microstructural analysis revealed that brittle orthoronbic-M5B3 phase was formed in high V fraction. The corrosion resistance of the cermets against hydrochloric acid was superior to that of JIS SUS 304. The resistance against nitric acid decreased with decreasing Cr content and was lower than that of SUS 304.

  4. Plutonium-238 processing at Savannah River Plant

    SciTech Connect

    Burney, G.A.

    1983-01-01

    Plutonium-238 is produced by irradiating NpO/sub 2/-Al cermet slugs or tubes with neutrons. The neptunium-237 is produced as a by-product when natural or enriched uranium is irradiated with neutrons. The neptunium is separated by solvent extraction and ion exchange and precipitated as neptunium oxalate. Neptunium oxalate is calcined to neptunium oxide and fabricated into targets for irradiation. The irradiation conditions are controlled to produce plutonium with 80 to 90 wt % /sup 238/Pu.

  5. Role of Anions and Reaction Conditions in the Preparation of Uranium(VI), Neptunium(VI), and Plutonium(VI) Borates

    SciTech Connect

    none,

    2011-02-03

    U(VI), Np(VI), and Pu(VI) borates with the formula AnO2[B8O11(OH)4] (An = U, Np, Pu) have been prepared via the reactions of U(VI) nitrate, Np(VI) perchlorate, or Pu(IV) or Pu(VI) nitrate with molten boric acid. These compounds are all isotypic and consist of a linear actinyl(VI) cation, AnO22+, surrounded by BO3 triangles and BO4 tetrahedra to create an AnO8 hexagonal bipyramidal environment. The actinyl bond lengths are consistent with actinide contraction across this series. The borate anions bridge between actinyl units to create sheets. Additional BO3 triangles and BO4 tetrahedra extend from the polyborate layers and connect these sheets together to form a three-dimensional chiral framework structure. UV-vis-NIR absorption and fluorescence spectroscopy confirms the hexavalent oxidation state in all three compounds. Bond-valence parameters are developed for Np(VI).

  6. Solubility and speciation results from over- and undersaturation experiments on neptunium, plutonium, and americium in water from Yucca Mountain region well UE-25p {number_sign}1

    SciTech Connect

    Nitsche, H.; Roberts, K.; Becraft, K.; Prussin, T.; Keeney, D.; Carpenter, S.A.; Hobart, D.E.

    1995-11-01

    Solubility and speciation are important in understanding aqueous radionuclide transport through the geosphere. Results are compared from solubility and speciation experiments from oversaturation and undersaturation of {sup 237}NpO{sub 2{sup +}}, {sup 239}Pu{sup 4+}, and {sup 241}Am{sup 3+}/Nd{sup 3+} in a modified UE-25p-1 groundwater (from the Yucca Mountain region, Nevada, which is being investigated as a potential high-level nuclear waste disposal site) at 60 C and three pH values (6.0, 7.0, 8.5). In the oversaturation experiments, the solubility-controlling steady-state solids were identified and the speciation and/or oxidation states present in the supernatant solutions were determined. The characterized solids were then reintroduced into fresh solutions of the modified UE-25p-1 groundwater to approach the steady state from undersaturation. For the undersaturation experiments, the solubility-controlling steady-state solids were also identified and the speciation and/or oxidation states present in the supernatant solutions were determined. The Np solubility decreased with increasing pH in both the over- and undersaturation experiments. The steady-state concentrations from the two experiments agreed to within an order of magnitude. Pu concentrations from over- and undersaturation agree very well in the pH 6 and 7 experiments. The pH 8.5 oversaturation experiment resulted in a steady-state concentration one order of magnitude above its undersaturation counterpart. For the Am/Nd solutions, the pH 6 and pH 7 experiments resulted in equivalent steady-state concentrations from both over and undersaturation. The pH 8.5 oversaturation experiment was 100 times more soluble than its undersaturation counterpart. 48 refs.

  7. Metabolic studies of neptunium in the adult baboon: retention, distribution, kinetics, and enhanced excretion by chelation therapy. Technical progress report summary

    SciTech Connect

    Not Available

    1984-01-01

    These investigations provided additional data on the uptake, distribution, retention and excretion of Np-237, Np-239 and Pa-233 in baboons following single intravenous or gavage administration. The influence of oxidation state, chemical medium, pH, mass, etc. on the metabolism of these radionuclides is related.

  8. Ab-Initio Study on Plutonium Compounds Pu3M (M=Al, Ga, In), PuNp and Elemental Neptunium

    SciTech Connect

    Kutepov, A L

    2005-09-07

    Using spin-polarized relativistic density functional theory the electronic and magnetic structures for the plutonium compounds Pu{sub 3}M(M = Al; Ga; In) and PuNp have been investigated. For the first group of compounds the enhanced hybridization between Pu 5f and p-states of alloying element, as it has been found in spin-polarized calculations, is believed to be the main reason for the higher formation energies obtained in such kind of studies in comparison with the non-spin-polarized case. Also, comparative analysis of the actinides U, Np, Pu, Am, and Cm has been performed based on their electronic and magnetic structure. Some noticeable difference in the calculated magnetic structure was discovered between the actinide with local magnetic moments (Cm) and the actinides (Pu, Am) in which magnetic moments were found only in the calculations.

  9. Cerium(IV), neptunium(IV), and plutonium(IV) 1,2-phenylenediphosphonates: correlations and differences between early transuranium elements and their proposed surrogates.

    PubMed

    Diwu, Juan; Wang, Shuao; Liao, Zuolei; Burns, Peter C; Albrecht-Schmitt, Thomas E

    2010-11-01

    The in situ hydrothermal reduction of Np(VI) to Np(IV) and Pu(VI) to Pu(IV) in the presence of 1,2-phenylenediphosphonic acid (PhP2) results in the crystallization of Np[C(6)H(4)(PO(3)H)(2)](2)·2H(2)O (NpPhP2) and Pu[C(6)H(4)(PO(3)H)(PO(3)H(2))][C(6)H(4)(PO(3)H)(PO(3))]·2H(2)O (PuPhP2), respectively. Similar reactions have been explored with Ce(IV) resulting in the isolation of the Ce(IV) phenylenediphosphonate Ce[C(6)H(4)(PO(3)H)(PO(3)H(2))][C(6)H(4)(PO(3)H)(PO(3))]·2H(2)O (CePhP2). Single crystal diffraction studies reveal that although all these three compounds all crystallize in the triclinic space group P1̅, only PuPhP2 and CePhP2 are isotypic, whereas NpPhP2 adopts a distinct structure. In the cerium and plutonium compounds edge-sharing dimers of MO(8) polyhedra are bridged by the diphosphonate ligand to create one-dimensional chains. NpPhP2 also forms chains. However, the NpO(8) units are monomeric. The protonation of the ligands is also different in the two structure types. Furthermore, the NpO(8) polyhedra are best described as square antiprisms (D(4d)), whereas the CeO(8) and PuO(8) units are trigonal dodecahedra (D(2d)). Bond-valence parameters of R(o) = 1.972 and b = 0.538 have been derived for Np(4+) using a combination of the data reported in this work with that available in crystallographic databases. The UV-vis-NIR absorption spectra of NpPhP2 and PuPhP2 are also reported and used to confirm the tetravalent oxidation states. PMID:20919712

  10. Further examples of the failure of surrogates to properly model the structural and hydrothermal chemistry of transuranium elements: Insights provided by uranium and neptunium diphosphonates

    SciTech Connect

    Nelson, Anna-Gay D; Bray, Travis H; Zhang, Wei; Haire, Richard G.; Sayler, Todd S.; Albrecht-Schmitt, Thomas E

    2008-01-01

    In situ hydrothermal reduction of Np(VI) to Np(IV) in the presence of methylenediphosphonic acid (C1P2) results in the crystallization of Np[CH2(PO3)2](H2O)2 (NpC1P2-1). Similar reactions have been explored with U(VI) resulting in the isolation of the U(IV) diphosphonate U[CH2(PO3)2](H2O) (UC1P2-1), and the two U(VI) diphosphonates (UO2)2[CH2(PO3)2](H2O)3 H2O (UC1P2-2) and UO2[CH2(PO3H)2](H2O) (UC1P2-3). Single crystal diffraction studies of NpC1P2-1 reveal that it consists of eight-coordinate Np(IV) bound by diphosphonate anions and two coordinating water molecules to create a polar three-dimensional framework structure wherein the water molecules reside in channels. The structure of UC1P2-1 is similar to that of NpC1P2-1 in that it also adopts a three-dimensional structure. However, the U(IV) centers are seven-coordinate with only a single bound water molecule. UC1P2-2 and UC1P2-3 both contain U(VI). Nevertheless, their structures are quite distinct with UC1P2-2 being composed of corrugated layers containing UO6 and UO7 units bridged by C1P2; whereas, UC1P2-3 is found as a polar three-dimensional network structure containing only pentagonal bipyramidal U(VI). Fluorescence measurements on UC1P2-2 and UC1P2-3 exhibit emission from the uranyl moieties with classical vibronic fine-structure.

  11. Aqueous complexation of thorium(IV), uranium(IV), neptunium(IV), plutonium(III/IV), and cerium(III/IV) with DTPA.

    PubMed

    Brown, M Alex; Paulenova, Alena; Gelis, Artem V

    2012-07-16

    Aqueous complexation of Th(IV), U(IV), Np(IV), Pu(III/IV), and Ce(III/IV) with DTPA was studied by potentiometry, absorption spectrophotometry, and cyclic voltammetry at 1 M ionic strength and 25 °C. The stability constants for the 1:1 complex of each trivalent and tetravalent metal were calculated. From the potentiometric data, we report stability constant values for Ce(III)DTPA, Ce(III)HDTPA, and Th(IV)DTPA of log β(101) = 20.01 ± 0.02, log β(111) = 22.0 ± 0.2, and log β(101) = 29.6 ± 1, respectively. From the absorption spectrophotometry data, we report stability constant values for U(IV)DTPA, Np(IV)DTPA, and Pu(IV)DTPA of log β(101) = 31.8 ± 0.1, 32.3 ± 0.1, and 33.67 ± 0.02, respectively. From the cyclic voltammetry data, we report stability constant values for Ce(IV) and Pu(III) of log β(101) = 34.04 ± 0.04 and 20.58 ± 0.04, respectively. The values obtained in this work are compared and discussed with respect to the ionic radius of each cationic metal. PMID:22738207

  12. Role of anions and reaction conditions in the preparation of uranium(VI), neptunium(VI), and plutonium(VI) borates.

    PubMed

    Wang, Shuao; Villa, Eric M; Diwu, Juan; Alekseev, Evgeny V; Depmeier, Wulf; Albrecht-Schmitt, Thomas E

    2011-03-21

    U(VI), Np(VI), and Pu(VI) borates with the formula AnO(2)[B(8)O(11)(OH)(4)] (An = U, Np, Pu) have been prepared via the reactions of U(VI) nitrate, Np(VI) perchlorate, or Pu(IV) or Pu(VI) nitrate with molten boric acid. These compounds are all isotypic and consist of a linear actinyl(VI) cation, AnO(2)(2+), surrounded by BO(3) triangles and BO(4) tetrahedra to create an AnO(8) hexagonal bipyramidal environment. The actinyl bond lengths are consistent with actinide contraction across this series. The borate anions bridge between actinyl units to create sheets. Additional BO(3) triangles and BO(4) tetrahedra extend from the polyborate layers and connect these sheets together to form a three-dimensional chiral framework structure. UV-vis-NIR absorption and fluorescence spectroscopy confirms the hexavalent oxidation state in all three compounds. Bond-valence parameters are developed for Np(VI). PMID:21291194

  13. Formation of soluble hexanuclear neptunium(IV) nanoclusters in aqueous solution: growth termination of actinide(IV) hydrous oxides by carboxylates.

    PubMed

    Takao, Koichiro; Takao, Shinobu; Scheinost, Andreas C; Bernhard, Gert; Hennig, Christoph

    2012-02-01

    Complexation of Np(IV) with several carboxylates (RCOO(-); R = H, CH(3), or CHR'NH(2); R' = H, CH(3), or CH(2)SH) in moderately acidic aqueous solutions was studied by using UV-vis-NIR and X-ray absorption spectroscopy. As the pH increased, all investigated carboxylates initiated formation of water-soluble hexanuclear complexes, Np(6)(μ-RCOO)(12)(μ(3)-O)(4)(μ(3)-OH)(4), in which the neighboring Np atoms are connected by RCOO(-)syn-syn bridges and the triangular faces of the Np(6) octahedron are capped with μ(3)-O(2-)/μ(3)-OH(-). The structure information of Np(6)(μ-RCOO)(12)(μ(3)-O)(4)(μ(3)-OH)(4) in aqueous solution was extracted from the extended X-ray absorption fine structure data: Np-O(2-) = 2.22-2.23 Å (coordination number N = 1.9-2.2), Np-O(RCOO(-)) and Np-OH(-) = 2.42-2.43 Å (N = 5.6-6.7 in total), Np···C(RCOO(-)) = 3.43 Å (N = 3.3-3.9), Np···Np(neighbor) = 3.80-3.82 Å (N = 3.6-4.0), and Np···Np(terminal) = 5.39-5.41 Å (N = 1.0-1.2). For the simpler carboxylates, the gross stability constants of Np(6)(μ-RCOO)(12)(μ(3)-O)(4)(μ(3)-OH)(4) and related monomers, Np(RCOO)(OH)(2)(+), were determined from the UV-vis-NIR titration data: when R = H, log β(6,12,-12) = 42.7 ± 1.2 and log β(1,1,-2) = 2.51 ± 0.05 at I = 0.62 M and 295 K; when R = CH(3), log β(6,12,-12) = 52.0 ± 0.7 and log β(1,1,-2) = 3.86 ± 0.03 at I = 0.66 M and 295 K. PMID:22220853

  14. Quantitative Electron-Excited X-Ray Microanalysis of Borides, Carbides, Nitrides, Oxides, and Fluorides with Scanning Electron Microscopy/Silicon Drift Detector Energy-Dispersive Spectrometry (SEM/SDD-EDS) and NIST DTSA-II.

    PubMed

    Newbury, Dale E; Ritchie, Nicholas W M

    2015-10-01

    A scanning electron microscope with a silicon drift detector energy-dispersive X-ray spectrometer (SEM/SDD-EDS) was used to analyze materials containing the low atomic number elements B, C, N, O, and F achieving a high degree of accuracy. Nearly all results fell well within an uncertainty envelope of ±5% relative (where relative uncertainty (%)=[(measured-ideal)/ideal]×100%). Quantification was performed with the standards-based "k-ratio" method with matrix corrections calculated based on the Pouchou and Pichoir expression for the ionization depth distribution function, as implemented in the NIST DTSA-II EDS software platform. The analytical strategy that was followed involved collection of high count (>2.5 million counts from 100 eV to the incident beam energy) spectra measured with a conservative input count rate that restricted the deadtime to ~10% to minimize coincidence effects. Standards employed included pure elements and simple compounds. A 10 keV beam was employed to excite the K- and L-shell X-rays of intermediate and high atomic number elements with excitation energies above 3 keV, e.g., the Fe K-family, while a 5 keV beam was used for analyses of elements with excitation energies below 3 keV, e.g., the Mo L-family. PMID:26365439

  15. Synthesis and characterization of titanium carbide, titanium boron carbonitride, titanium boride/titanium carbide and titanium carbide/chromium carbide multilayer coatings by reactive and ion beam assisted, electron beam-physical vapor deposition (EB-PVD)

    NASA Astrophysics Data System (ADS)

    Wolfe, Douglas Edward

    The purpose of the present work was to investigate the synthesis of titanium carbide, TiBCN, TiB2/TiC and TiC/Cr23C6 multilayer coatings by several methods of electron beam-physical vapor deposition (EB-PVD) and examine the affects of various processing parameters on the properties and microstructures of the coatings. TiC was successfully deposited by reactive ion beam assisted (RIBA), EB-PVD and the results were compared to various titanium carbide coatings deposited by a variety of techniques. The affects of substrate temperature and ion beam current density were correlated with composition, hardness, changes in the lattice parameter, degree of crystallographic texture, residual stress, surface morphology, and microstructure. The average Vicker's hardness number was found to increase with increasing ion beam current density and increase over the substrate temperature range of 250°C to 650°C. The average Vicker's hardness number decreased at a substrate temperature of 750°C as a result of texturing and microstructure. The present investigation shows that the average Vicker's hardness number is not only a function of the composition, but also the microstructure including the degree of crystallographic texture. TiB2/TiC multilayer coatings were deposited by argon ion beam assisted, EB-PVD with varying number of total layers to two different film thicknesses under slightly different deposition conditions. In both cases, the hardness of the coatings increased with increasing number of total layers. The adhesion of the coatings ranged from 30 N to 50 N, with the better adhesion values obtained with the thinner coatings. The crystallographic texture coefficients of both the TiC and TiB2 layers were found to change with increasing number of total layers. The multilayer design was found to significantly affect the microstructure and grain size of the deposited coatings. The fracture toughness was found to decrease with increasing number of total layers and was attributed to the increase in hardness and reduction in the total amount of compressive stress. TiBCN coatings were synthesized by the co-evaporation of titanium, titanium diboride, and carbon (through tungsten) while simultaneously bombarding the substrate surface with a mixture of argon and nitrogen ionized gas which has not been performed to the author's knowledge. The bulk composition was determined by EPMA and suggests that TiBCN has a wide compositional range similar to TiN and TiC. The TiBCN coatings were determined to be nano-crystalline with a cubic crystallographic structure. The average Vicker's hardness number of the TiBCN coatings ranged from 2777 VHN0.050 to 3343 VHN0.050 with the highest value reported for the higher concentrations of boron. The adhesion of the coatings to WC-6wt.Co-0.3wt.%TaC was found to increase from 20 N to 52 N with decreasing compressive stress. Lastly, multilayer titanium carbide and chromium carbide coatings with varying individual layer thickness were synthesized by the co-evaporation of Ti, Cr and C through tungsten at elevated temperatures. The average Vicker's hardness number was found to increase from 1302 VHN0.050 to 2052 VHN0.050 by changing the individual layer thickness of the multilayers. In addition, the grain size, measured compressive stress, and fracture toughness values all decreased with decreasing individual layer thickness.

  16. Structural arrangements of the ternary metal boride carbide compounds MB{sub 2}C{sub 4} (M=Mg, Ca, La and Ce) from first-principles theory

    SciTech Connect

    Fang Changming Bauer, Joseph; Saillard, Jean-Yves; Halet, Jean-Francois

    2007-09-15

    The structural arrangements of the ternary metal borocarbides MB{sub 2}C{sub 4} (M=Mg, Ca; La and Ce) are investigated using density-functional theory (DFT) calculations within the generalized gradient approximation (GGA). Results indicate that these compounds adopt a layered structure consisting of graphite-like B{sub 2}C{sub 4} layers alternating with metal sheets. Within the hexagonal layers, the coloring with the -C-C-C-B-C-B- sequence is energetically more stable than that with the -C-C-C-C-B-B- one. The electronic structures of these compounds, mainly determined by the B{sub 2}C{sub 4} sheets, can be rationalized with the simple valence electron distribution M{sup 2+}[B{sub 2}C{sub 4}]{sup 2-}xe{sup -}, with the metals essentially acting as two-electron donors with respect to the boron-carbon network, the other x electrons remaining in the relatively narrow d and/or f bands of the metals. Accordingly, MB{sub 2}C{sub 4} are narrow band-gap semiconductors ({delta}E{approx}0.2-0.4 eV) with M=Mg and Ca. On the other hand, with M=La and Ce, the compounds are conducting with a relatively high density of states at the Fermi level predominantly metal in character with substantial B/C{pi}* antibonding state admixture. - Graphical abstract: Density-functional theory calculations on the structural arrangements of the ternary metal borocarbides MB{sub 2}C{sub 4} (M=Mg, Ca; La and Ce) indicate that these compounds adopt a layered structure consisting of graphite-like B{sub 2}C{sub 4} layers alternating with metal sheets. Within the hexagonal layers, the coloring with the -C-C-C-B-C-B- sequence is energetically more stable than that with the -C-C-C-C-B-B- one.

  17. Zr{sub 2}Ir{sub 6}B with an eightfold superstructure of the cubic perovskite-like boride ZrIr{sub 3}B{sub 0.5}: Synthesis, crystal structure and bonding analysis

    SciTech Connect

    Hermus, Martin; Fokwa, Boniface P.T.

    2010-04-15

    Single phase powder samples and single crystals of Zr{sub 2}Ir{sub 6}B were successfully synthesized by arc-melting the elements in a water-cooled copper crucible under an argon atmosphere. Superstructure reflections were observed both on powder and on single crystal diffraction data, leading to an eightfold superstructure of ZrIr{sub 3}B{sub x} phase. The new phase, which has a metallic luster, crystallizes in space group Fm3-barm (no. 225) with the lattice parameters a=7.9903(4) A, V=510.14(4) A{sup 3}. Its crystal structure was refined on the basis of powder as well as single crystal data. The single crystal refinement converged to R{sub 1}=0.0239 and wR{sub 2}=0.0624 for all 88 unique reflections and 6 parameters. Zr{sub 2}Ir{sub 6}B is isotypic to Ti{sub 2}Rh{sub 6}B and its structure can be described as a defect double perovskite, A{sub 2}BB'O{sub 6}, where the A site is occupied by zirconium, the B site by boron, the O site by iridium but the B' site is vacant, leading to the formation of empty and boron-filled octahedral Ir{sub 6} clusters. According to the result of tight-binding electronic structure calculations, Ir-B and Ir-Zr interactions are mainly responsible for the structural stability of the phase. According to COHP bonding analysis, the strongest bonding occurs for the Ir-B contacts, and the Ir-Ir bonding within the empty clusters is two times stronger than that in the BIr{sub 6} octahedra. - Graphical abstract: Zr{sub 2}Ir{sub 6}B crystallizes with an eightfold superstructure of the already reported simple cubic perovskite ZrIr{sub 3}B{sub x}. According to the result of tight-binding electronic structure calculations, Ir-B and Ir-Zr interactions are mainly responsible for its structural stability, and the Ir-Ir bonding within the empty Ir{sub 6} clusters is two times stronger than that in the BIr{sub 6} octahedra.

  18. Borohydride complexes of europium(ii) and ytterbium(ii) and their conversion to metal borides. Structures of (l)4YbBh42 (L = Ch3Cn, C5H5N). (Reannouncement with new availability information)

    SciTech Connect

    White, J.P.; Deng, H.; Shore, S.G.

    1991-12-31

    Borohydride complexes of numerous metal ions are known. We have found that acetonitrile and pyridine are exceptionally good ligands for lathanide(II) ions. They promote formation of complexes with boron hydride and carborane anions. Use of these amines allows isolation of complexes that would otherwise be insoluble or unstable in other solvents. When these amines are employed as solvents, stable lanthanide(II) borohydride complexes can be isolated.

  19. Nickel and titanium nanoboride composite coating

    NASA Astrophysics Data System (ADS)

    Efimova, K. A.; Galevsky, G. V.; Rudneva, V. V.; Kozyrev, N. A.; Orshanskaya, E. G.

    2015-09-01

    Electrodeposition conditions, structural-physical and mechanical properties (microhardness, cohesion with a base, wear resistance, corrosion currents) of electroplated composite coatings on the base of nickel with nano and micro-powders of titanium boride are investigated. It has been found out that electro-crystallization of nickel with boride nanoparticles is the cause of coating formation with structural fragments of small sizes, low porosity and improved physical and mechanical properties. Titanium nano-boride is a component of composite coating, as well as an effective modifier of nickel matrix. Nano-boride of the electrolyte improves efficiency of the latter due to increased permissible upper limit of the cathodic current density.

  20. A Study on the Microstructures and Toughness of Fe-B Cast Alloy Containing Rare Earth

    NASA Astrophysics Data System (ADS)

    Yi, Dawei; Zhang, Zhiyun; Fu, Hanguang; Yang, Chengyan; Ma, Shengqiang; Li, Yefei

    2015-02-01

    This study investigates the effect of cerium on the microstructures, mechanical properties of medium carbon Fe-B cast alloy. The as-cast microstructure of Fe-B cast alloy consists of the eutectic boride, pearlite, and ferrite. Compared with the coarse eutectic borides in the unmodified alloy, the eutectic boride structures in the modified alloy are greatly refined. Cerium promotes the formation of Ce2O3 phase. Ce2O3 can act as effective heterogeneous nuclei of primary austenite, and refine austenite and boride. After heat treatment, the impact toughness of the modified alloy is higher than that of the unmodified alloy because there are more broken borides in the modified alloy. Meanwhile, the fracture mechanism of medium carbon Fe-B alloy is depicted and analyzed by using fractography.

  1. Methods of repairing a substrate

    NASA Technical Reports Server (NTRS)

    Riedell, James A. (Inventor); Easler, Timothy E. (Inventor)

    2011-01-01

    A precursor of a ceramic adhesive suitable for use in a vacuum, thermal, and microgravity environment. The precursor of the ceramic adhesive includes a silicon-based, preceramic polymer and at least one ceramic powder selected from the group consisting of aluminum oxide, aluminum nitride, boron carbide, boron oxide, boron nitride, hafnium boride, hafnium carbide, hafnium oxide, lithium aluminate, molybdenum silicide, niobium carbide, niobium nitride, silicon boride, silicon carbide, silicon oxide, silicon nitride, tin oxide, tantalum boride, tantalum carbide, tantalum oxide, tantalum nitride, titanium boride, titanium carbide, titanium oxide, titanium nitride, yttrium oxide, zirconium boride, zirconium carbide, zirconium oxide, and zirconium silicate. Methods of forming the ceramic adhesive and of repairing a substrate in a vacuum and microgravity environment are also disclosed, as is a substrate repaired with the ceramic adhesive.

  2. Determination of ²³⁷Np in environmental and nuclear samples: a review of the analytical method.

    PubMed

    Thakur, P; Mulholland, G P

    2012-08-01

    A number of analytical methods has been developed and used for the determination of neptunium in environmental and nuclear fuel samples using alpha, ICP-MS spectrometry, and other analytical techniques. This review summarizes and discusses development of the radiochemical procedures for separation of neptunium (Np), since the beginning of the nuclear industry, followed by a more detailed discussion on recent trends in the separation of neptunium. This article also highlights the progress in analytical methods and issues associated with the determination of neptunium in environmental samples. PMID:22542354

  3. SEPARATION PROCESS FOR TRANSURANIC ELEMENT AND COMPOUNDS THEREOF

    DOEpatents

    Magnusson, L.B.

    1958-04-01

    A process is described for the separation of neptunium, from aqueous solutions of neptunium, plutonium, uraniunn, and fission prcducts. This separation from an acidic aqueous solution of a tetravalent neptuniunn can be made by contacting the solution with a certain type of chelating,; agent, preferably dissolved in an organic solvent, to form a neptunium chelate compound. When the organic solvent is present, the neptunium chelate compound is extracted; otherwise, it precipitates from the aqueous solution and is separated by any suitable means. The chelating agent is a fluorinated BETA -diketone. such as trifluoroacetyl acetone.

  4. Further Insights into Intermediate- and Mixed-Valency in Neptunium Oxoanion Compounds: Structure and Absorption Spectroscopy of K2[(NpO2)3B10O16(OH)2(NO3)2

    SciTech Connect

    Wang, Shuao; Alekseev, Evgeny V.; Depmeier, Wulf; Albrecht-Schmitt, Thomas E.

    2010-01-01

    The reaction of Np(V) chloride with molten boric acid results in the disproportionation of Np(V) into Np(IV) and Np(VI), and the crystallization of K{sub 2}[(NpO{sub 2}){sub 3}B{sub 10}O{sub 16}(OH){sub 2}(NO{sub 3}){sub 2}]. UV-vis-NIR spectroscopy demonstrates that in addition to the Np(VI) and Np(V) found in the crystal structure, Np(IV) is also present.

  5. A Linear trans-Bis(imido) Neptunium(V) Actinyl Analog: Np(V)(NDipp)2((t)Bu2bipy)2Cl (Dipp = 2,6-(i)Pr2C6H3).

    PubMed

    Brown, Jessie L; Batista, Enrique R; Boncella, James M; Gaunt, Andrew J; Reilly, Sean D; Scott, Brian L; Tomson, Neil C

    2015-08-01

    The discovery that imido analogs of actinyl dioxo cations can be extended beyond uranium into the transuranic elements is presented. Synthesis of the Np(V) complex, Np(NDipp)2((t)Bu2bipy)2Cl (1), is achieved through treatment of a Np(IV) precursor with a bipyridine coligand and lithium-amide reagent. Complex 1 has been structurally characterized, analyzed by (1)H NMR and UV-vis-NIR spectroscopies, and the electronic structure evaluated by DFT calculations. PMID:26200434

  6. Calculated Thermodynamic Functions for Gas Phase Uranium, Neptunium, Plutonium, and Americium Oxides (AnO3), Oxyhydroxides (AnO2(OH)2), Oxychlorides (AnO2Cl2), and Oxyfluorides (AnO2F2)

    SciTech Connect

    Ebbinghaus, B B

    2002-10-31

    Based on known and estimated molecular constants, the thermodynamic functions, C{sub p}, S{sup o}, H{sup o}-H{sup o}(298), and -(G{sup o} - H{sup o}(298))/T, have been calculated and tabulated for actinide vapors species of the formulas AnO{sub 3}(g), AnO{sub 2}(OH){sub 2}(g), AnO{sub 2}Cl{sub 2}(g), and AnO{sub 2}F{sub 2}(g) where An = U, Np, Pu, and Am. A method to calculate the thermodynamic functions for the mixed species, AnO{sub 2}ClOH(g), AnO{sub 2}FOH(g), and AnO{sub 2}FCl(g), is also given.

  7. A Linear trans -Bis(imido) Neptunium(V) Actinyl Analog: NpV (NDipp)2 ( tBu2 bipy)2Cl (Dipp = 2,6- i Pr2C6H3)

    DOE PAGESBeta

    Brown, Jessie L.; Batista, Enrique R.; Boncella, James M.; Gaunt, Andrew J.; Reilly, Sean D.; Scott, Brian L.; Tomson, Neil C.

    2015-07-22

    We present the discovery that imido analogs of actinyl dioxo cations can be extended beyond uranium into the transuranic elements. Synthesis of the Np(V) complex, Np(NDipp)2(tBu2bipy)2Cl (1), is achieved through treatment of a Np(IV) precursor with a bipyridine co-ligand and lithium-amide reagent. Complex 1 has been structurally characterized, analyzed by 1H NMR and UV/vis/NIR spectroscopies, and the electronic structure evaluated by DFT calculations.

  8. Solubility and speciation results from oversaturation experiments on neptunium, plutonium and americium in a neutral electrolyte with a total carbonate similar to water from Yucca Mountain Region Well UE- 25p No. 1

    SciTech Connect

    Torretto, P.; Becraft, K.; Prussin, T.; Roberts, K.; Carpenter, S.; Hobart, D.; Nitsche, H.

    1995-12-01

    Solubility and speciation are important in understanding aqueous radionuclide transport through the geosphere. They define the source term for transport retardation processes such as sorption and colloid formation. Solubility and speciation data are useful in verifying the validity of geochemical codes that are a part of predictive transport models. Solubility experiments will approach solution equilibrium from both oversaturation and undersaturation. In these experiments, we have approached the solubility equilibrium from oversaturation, Results are given for solubility and speciation experiments from oversaturation of {sup 237} NpO{sub 2}{sup +} {sup 239}Pu{sup 4+}, and {sup 241}Am{sup 3+}/Nd{sup 3+} in a neutral electrolyte containing a total carbonate concentration similar to groundwater from the Yucca Mountain region, Nevada, which is being investigated as a potential high-level nuclear waste disposal site, at 25{degrees}C and three pH values. In these experiments, the solubilitycontrolling steady-state solids were identified and the speciation and/or oxidation states present in the supernatant solutions were determined.

  9. Microstructure and properties of borocarburized and laser-modified 17CrNi6-6 steel

    NASA Astrophysics Data System (ADS)

    Kulka, M.; Makuch, N.; Pertek, A.; Piasecki, A.

    2012-06-01

    Two-step process: carburizing followed by boriding was applied to the formation of borocarburized layers. The boride layer formed on the substrate of changeable chemical and phase composition (e.g. borocarburized layer) was called "gradient boride layer", in contrast to "typical boride layer", formed on the substrate of constant chemical and phase composition. Until now, the typical heat treatment of borocarburized layer consisted of treatment through hardening: quenching in oil and low-temperature tempering. In this paper, instead of treatment through hardening, laser-heat treatment was employed. The properties of such layer were compared to the properties of typical carburized layer. Three zones characterized the microstructure of laser-modified borocarburized layer: iron borides (FeB+Fe 2B) of modified morphology, hardened carburized zone (heat affected zone) and carburized layer without heat treatment. X-ray microanalysis indicated the increased boron concentration close to the surface due to the occurrence of a mixture of FeB and Fe 2B borides. Near to the hardened carburized zone, Fe 2B phase occurred in the laser-modified boride zone. Laser-heat treated borocarburized layer was characterized by higher microhardness at the surface than that obtained in case of carburized layer. It was caused by the iron borides (FeB+Fe 2B) occurrence at the surface, as a consequence of boriding process. However, the carburized layer was characterized by considerably larger hardened zone. Higher abrasive wear resistance, but lower low-cycle fatigue strength in comparison with the carburized layer, characterized the gradient boride layer formed by borocarburizing and laser surface modification. The indentation craters obtained on the surface of laser-heat treated borocarburized layer revealed sufficient cohesion (HF3 standard). The use of laser-modified borocarburized layers may be advantageous under conditions of high abrasive wear of mating parts. In case of parts, which

  10. Thermal expansion and lattice dynamics of RB66 compounds at low temperatures

    SciTech Connect

    Novikov, V V; Avdashchenko, D V; Mitroshenkov, N V; Matovnikov, A V; Budko, Serguei L

    2014-10-01

    Thermal characteristics of the phonon and magnon subsystems of icosahedral borides RB66 (R = Gd, Tb, Dy, Ho, Eu, or Lu) have been studied based on the obtained experimental data on the thermal expansion of the borides and the earlier results on their heat capacity in the range of 2–300 K. The contribution to the expansion of borides containing paramagnetic R 3+ ions, which is characteristic of transition to the spin-glass state, has been revealed. The phonon spectrum moments of RB66 compounds and the Grüneisen parameters have been calculated.

  11. NEUTRONIC REACTOR FUEL COMPOSITION

    DOEpatents

    Thurber, W.C.

    1961-01-10

    Uranium-aluminum alloys in which boron is homogeneously dispersed by adding it as a nickel boride are described. These compositions have particular utility as fuels for neutronic reactors, boron being present as a burnable poison.

  12. Ceramic material suitable for repair of a space vehicle component in a microgravity and vacuum environment, method of making same, and method of repairing a space vehicle component

    NASA Technical Reports Server (NTRS)

    Riedell, James A. (Inventor); Easler, Timothy E. (Inventor)

    2009-01-01

    A precursor of a ceramic adhesive suitable for use in a vacuum, thermal, and microgravity environment. The precursor of the ceramic adhesive includes a silicon-based, preceramic polymer and at least one ceramic powder selected from the group consisting of aluminum oxide, aluminum nitride, boron carbide, boron oxide, boron nitride, hafnium boride, hafnium carbide, hafnium oxide, lithium aluminate, molybdenum silicide, niobium carbide, niobium nitride, silicon boride, silicon carbide, silicon oxide, silicon nitride, tin oxide, tantalum boride, tantalum carbide, tantalum oxide, tantalum nitride, titanium boride, titanium carbide, titanium oxide, titanium nitride, yttrium oxide, zirconium diboride, zirconium carbide, zirconium oxide, and zirconium silicate. Methods of forming the ceramic adhesive and of repairing a substrate in a vacuum and microgravity environment are also disclosed, as is a substrate repaired with the ceramic adhesive.

  13. Interfacial reactions between titanium and borate glass

    SciTech Connect

    Brow, R.K.; Saha, S.K.; Goldstein, J.I.

    1992-12-31

    Interfacial reactions between melts of several borate glasses and titanium have been investigated by analytical scanning electron microscopy (SEM) and x-ray photoelectron spectroscopy (XPS). A thin titanium boride interfacial layer is detected by XPS after short (30 minutes) thermal treatments. ASEM analyses after longer thermal treatments (8--120 hours) reveal boron-rich interfacial layers and boride precipitates in the Ti side of the interface.

  14. Radioactivity studies: Final report, June 1985-August 1986

    SciTech Connect

    Ralston, L.; Cohen, N.

    1987-11-01

    We instigated studies of neptunium metabolism in two nonhuman primate species to derive dosimetric parameters necessary for accurate human radiation risk assessments. The metabolism of neptunium was studied in adult female baboons and tamarins following intravenous injection and intragastric intubation. Neptunium-237 and /sup 239/Np isotopes were prepared as citrate, nitrate, and bicarbonate complexs with valence states of +4, +5 and +6. Samples of blood, urine, feces and autopsy tissues were measured by both gamma-ray and alpha spectrometry techniques. Retention of injected neptunium was determined in vivo using whole and partial body gamma-scintillation spectroscopy. Immediately following intravenous injection, neptunium (+5 and +6) cleared rapidly from blood, deposited primarily in the skeleton (54 +- 5%) and liver (3 +- 1%), and was excreted predominately via urine (40 +- 3%). For the first year post injection, neptunium was retained with a composite biological half-time of 100 yrs in liver and 1.5 yrs in bone. In comparison, injected Np(+4) was retained in blood in higher concentrations and was eliminated initially via urine to a lesser extent (12%). Np(+4) was deposited primarily in the carcass (38 +- 4%) and liver (43 +- 4%). Differences in the chemical forms and radionuclide concentrations injected did not alter neptunium metabolic patterns. 78 refs., 20 figs., 30 tabs.

  15. Microstructural development in transient liquid-phase bonding

    NASA Astrophysics Data System (ADS)

    Gale, W. F.; Wallach, E. R.

    1991-10-01

    The applicability of conventional models of the transient liquid-phase (TLP) bonding process to the joining of nickel using ternary Ni-Si-B insert metals is considered in this article. It is suggested that diffusion of boron out of the liquid and into the solid substrate before the equilibration of the liquid and solid phases can result in the development of significant boron concentrations in the substrate. This, in turn, leads to the precipitation of boride phases in the substrate during holding at bonding temperatures below the binary nickel-boron eutectic temperature. The formation of boride phases during holding at the bonding temperature is of importance, because first, it is not predicted by the standard models of the TLP process, and second, the borides are not removed by prolonged holding at the bonding temperature and therefore may influence the in-service properties of the joint. In contrast, when bonding above the binary nickel-boron eutectic temperature, localized liquation of the substrate takes place. This liquid region resolidifies following prolonged holding and does not result in the formation of persistent boride phases. Experimental support is presented for the formation of borides during bonding, and characterization of the boride phases formed in the substrate is described.

  16. Alpha self-irradiation effects in ternary oxides of actinides elements: The zircon-like phases Am{sup III}VO{sub 4} and A{sup II}Np{sup IV}(VO{sub 4}){sub 2} (A=Sr, Pb)

    SciTech Connect

    Goubard, F. . E-mail: fabrice.goubard@chim.u-cergy.fr; Griesmar, P.; Tabuteau, A.

    2005-06-15

    We report the experimental studies of irradiation damage from alpha decay in neptunium and americium vanadates versus cumulative dose. The isotopes used were the transuranium {alpha}-emitter {sup 237}Np and the {alpha},{gamma}-emitter {sup 241}Am. Neptunium and americium vanadates self-irradiation was studied by X-ray diffraction method (XRD). The comparison of the powder diffraction patterns reveal that the irradiation has no apparent effect on the neptunium phases while the americium vanadate swells and becomes metamict as a function of cumulative dose.

  17. Influence of laser alloying with boron and niobium on microstructure and properties of Nimonic 80A-alloy

    NASA Astrophysics Data System (ADS)

    Makuch, N.; Piasecki, A.; Dziarski, P.; Kulka, M.

    2015-12-01

    Ni-base superalloys were widely used in aeronautics, chemical and petrochemical industries due to their high corrosion resistance, high creep and rupture strength at high temperature. However, these alloys were not considered for applications in which conditions of appreciable mechanical wear were predominant. The diffusion boriding provided suitable protection against wear. Unfortunately, this process required long duration and high temperature. In this study, instead of the diffusion process, the laser alloying with boron and niobium was used in order to produce the hard and wear resistant layer on Nimonic 80A-alloy. The laser-alloying was carried out as a two-step process. First, the external cylindrical surface of specimens was pre-placed with a paste containing boron and niobium. Then, the pre-placed coating and the thin surface layer of the substrate were re-melted by a laser beam. The high laser beam power (P=1.56 kW) and high averaging irradiance (E=49.66 kW/cm2) provided the thick laser re-melted zone. The laser-borided layers were significantly thicker (470 μm) in comparison with the layers obtained as a consequence of the diffusion boriding. Simultaneously, the high overlapping of multiple laser tracks (86%) caused that the laser-alloyed layer was uniform in respect of the thickness. The produced layer consisted of nickel borides (Ni3B, Ni2B, Ni4B3, NiB), chromium borides (CrB, Cr2B), niobium borides (NbB2, NbB) and Ni-phase. The presence of hard borides caused the increase in microhardness up to 1000 HV in the re-melted zone. However, the measured values were lower than those-characteristic of niobium borides, chromium borides and nickel borides. The presence of the soft Ni-phase in re-melted zone was the reason for such a situation. After laser alloying, the significant increase in abrasive wear resistance was also observed. The mass wear intensity factor, as well as the relative mass loss of the laser-alloyed specimens, was over 10 times smaller in

  18. Np Behavior in Synthesized Uranyl Phases: Results of Initial Tests

    SciTech Connect

    Friese, Judah I.; Douglas, Matthew; McNamara, Bruce K.; Clark, Sue B.; Hanson, Brady D.

    2004-09-28

    Initial tests were completed at Pacific Northwest National Laboratory for developing a potential mechanism to retard the mobility of neptunium at the Yucca Mountain repository. Neptunium is of concern because of its mobility in the environment and long half life, contributing a large percentage of the potential dose over extended times at the perimeter of the site. The mobility of neptunium could be retarded by associating with uranium mineral phases. The following four uranium mineral phases were examined and are potential secondary phases expected to form as a result of interactions of spent nuclear fuel with the local environment: meta-schoepite, studtite, uranophane, and sodium boltwoodite. The fate of the neptunium was examined in these synthetic experiments.

  19. Lab Scale Production of NpO2

    SciTech Connect

    Duffey, J

    2003-08-29

    The Savannah River Site (SRS) plans to disposition its legacy H-Canyon neptunium to Oak Ridge National Laboratory after converting it to oxide in HB-Line. Neptunium oxide, (NpO{sub 2}) was produced at the Savannah River Technology Center using the anticipated HB-Line flowsheet conditions. The oxide was produced from a neptunium nitrate solution via anion exchange, oxalate precipitation, and calcination at either 600 C or 650 C. The 98 grams of NpO{sub 2} produced in the laboratory should be representative of material produced in HB-Line and is to be used for gas generation testing to support radioactive material transportation safety analysis as part of the neptunium stabilization and disposition program at SRS. Results of each step of the oxide production will be presented.

  20. A survey of metallurgical research on several actinides

    SciTech Connect

    Olivas, J.D.; Schonfeld, F.W.

    1993-11-01

    A Los Alamos perspective on metallurgical research on neptunium, plutonium, americium, curium, and californium is presented. Alloying behaviors of these metals are discussed. Metal fabrication technologies, principally for plutonium, are emphasized.

  1. PRODUCING ENERGY AND RADIOACTIVE FISSION PRODUCTS

    DOEpatents

    Segre, E.; Kennedy, J.W.; Seaborg, G.T.

    1959-10-13

    This patent broadly discloses the production of plutonium by the neutron bombardment of uranium to produce neptunium which decays to plutonium, and the fissionability of plutonium by neutrons, both fast and thermal, to produce energy and fission products.

  2. PROGRESS REPORT. TRANSURANIC INTERFACIAL REACTION STUDIES ON MANGANESE OXIDE HYDROXIDE MINERAL SURFACES

    EPA Science Inventory

    Several DOE sites have been contaminated by transuranic radionuclide (TRU) discharges including neptunium and plutonium. Their interaction with the surrounding geological media can affect the transport and remediation of these radionuclides in the environment. Manganese based min...

  3. TRANSURANIC INTERFACIAL REACTION STUDIES ON MANGANESE OXIDE HYDROXIDE MINERAL SURFACES

    EPA Science Inventory

    Several DOE sites have been contaminated by transuranic radionuclide (TRU) discharges. Of these TRU, neptunium and plutonium are highly toxic and potentially mobile in the vadose zone. Modeling predictions of their potential hazard to humans require reliable estimates of migrat...

  4. METHOD OF SEPARATING Pu FROM METATHESIZED BiPO$sub 4$ CARRIER

    DOEpatents

    Knox, W.J.; Thompson, S.G.

    1960-05-31

    A process is given for separating uranium, neptunium, and/or plutonium from a bismuth hydroxide carrier by selective dissolution of these actinides with nitric acid of a concentration of from 0.05 to 0.5N.

  5. Integrated study of the behavior of transuranic elements in the marine environment

    SciTech Connect

    Choppin, G. R.; Morse, J. W.

    1981-01-01

    In order to construct a model of radionuclide kinetics in an aquatic ecosystem, americium ions were chosen for study. Results will be applied to thorium, plutonium, neptunium and uranium for comparison of environmental behavior. (PSB)

  6. Relativistic effects on the thermal expansion of the actinide elements

    SciTech Connect

    Soederlind, P.; Nordstroem, L.; Lou Yongming; Johansson, B. )

    1990-09-01

    The room-temperature linear thermal-expansion coefficient is calculated for the light actinides thorium, protactinium, uranium, neptunium, and plutonium for the fcc crystal structure. The relativistic spin-orbit interaction is included in these calculations. We show that the spin-orbit splitting of the 5{ital f} band gives rise to a considerable increase of the thermal expansion and to a large extent explains the observed anomalously large thermal expansion for the neptunium and plutonium metals.

  7. A study on the formation of solid state nanoscale materials using polyhedral borane compounds

    NASA Astrophysics Data System (ADS)

    Romero, Jennifer V.

    The formation of boron containing materials using a variety of methods was explored. The pyrolysis of a metal boride precursor solution can be accomplished using a one-source method by combining TiCl4, B10H 14 and CH3CN in one reaction vessel and pyrolyzing it at temperatures above 900 °C. Amorphous dark blue colored films were obtained after the pyrolysis reactions. Well-defined spherical shaped grains or particles were observed by SEM. The amorphous films generated contained titanium, however, the determination of the boron content of the films was inconclusive. This one pot method making metal boride thin films has the advantage of being able to dictate the stoichiometry of the reactants. Another part of this work represents the first report of both the use of metal boride materials and the use of a titanium-based compound for the formation of nanotubes. This method provides a facile method for generating well-formed boron-containing carbon nanotubes in a "one-pot" process through an efficient aerosol process. The formation of metal boride corrosion resistant layers was also explored. It was shown that metallic substrates can be effectively boronized using paste mixtures containing boron carbide and borax. The formation of a Fe4B 2 iron boride phase was achieved, however, this iron boride phase does not give enough corrosion protection. The formation of a corrosion resistant metal boride coating with strong adhesion was accomplished by boronization of a thermal sprayed nickel layer on the surface of steel. Surfactants were explored as possible nanoreactors in which metal boride nanoparticles could be formed to use as nanotube growth catalyst via room temperature reaction. Different surfactants were used, but none of them successfully generated very well dispersed metal boride nanoparticles. Nanoparticles with varying shapes and sizes were generated which were highly amorphous. The carboxylic acid derivative of closo-C2B 10 cages was explored as a ligand in the

  8. A novel RE-chrome-boronizing technology assisted by fast multiple rotation rolling treatment at low temperature

    NASA Astrophysics Data System (ADS)

    Yuan, Xing-dong; Xu, Bin; Cai, Yu-cheng

    2015-12-01

    The boride layer was fabricated on the surface of carbon steel by a novel RE-Chrome-Boronizing technology assisted by fast multiple rotation rolling (FMRR) treatment at low temperature. The microstructure of the boride layer was characterized by using scanning electron microscopy (SEM). The microstructure of the top surface layer of substrate was characterized by transmission electron microscopy (TEM) and high resolution rransmission electron microscopy (HRTEM). Experimental results showed that a nanostructured layer with grain size of approximately 30 nm was obtained; the amorphous phase and high-density dislocations were observed in upper-layer of FMRR samples, which led to the reduction of diffusion activation energy of boron atoms. Boride layers fabricated on the FMRR samples are continuous, dense, uniform, and low in brittleness. The penetrating rate was enhanced significantly when the FMRR samples were Cr-Rare earth-boronized at 650 °C for 6 h. The thickness of the boride layer of FMRR samples on carbon steel was approximately 25 μm when the duration was 60 min, which was approximately 1.5 times higher than the original sample. The boride layer consisted of mainly Fe2B, and adheres well to the metallic substrate.

  9. Thermodynamical and thermoelectric properties of boron doped YPd3 and YRh3

    NASA Astrophysics Data System (ADS)

    Dwivedi, Shalini; Sharma, Ramesh; Sharma, Yamini

    2016-05-01

    The structural, electronic, thermal, and optical properties of borides of cubic non-magnetic YX3 (X=Rh, Pd) compounds and their borides which crystallize in the AuCu3 structure have been studied using the density functional theory (DFT). The flat bands in the vicinity of EF which are associated with superconductivity appear in YPd3 and YRh3 band structures. However, the B s-states enhance the flat band only in YRh3B. The optical properties clearly show that boron insertion modifies the absorption and transmittance. The YX3 alloys and their borides exhibit valuable changes in the thermopower and ZT. It is observed that the properties of the Y-X intermetallics change significantly for the Y-Rh and Y-Pd alloys and the presence of single boron atom modifies the properties to a great extent.

  10. Method of boronizing transition-metal surfaces

    SciTech Connect

    Koyama, K.; Shimotake, H.

    1981-08-28

    A method is presented for preparing a boride layer on a transition metal substrate for use in corrosive environments or as a harden surface in machine applications. This method is particularly useful in treating current collectors for use within a high temperature and corrosive electrochemical cell environment. A melt of a alkali metal boride tetrafluoride salt including such as KF to lower its melting point is prepared including a dissolved boron containing material, for instance NiB, MnB/sub 2/, or CrB/sub 2/. A transition metal to be coated is immersed in the melt at a temperature of no more than 700/sup 0/C and a surface boride layer of that transition metal is formed within a period of about 24 hours on the substrate surface.

  11. Silicon carbide sintered body manufactured from silicon carbide powder containing boron, silicon and carbonaceous additive

    NASA Technical Reports Server (NTRS)

    Tanaka, Hidehiko

    1987-01-01

    A silicon carbide powder of a 5-micron grain size is mixed with 0.15 to 0.60 wt% mixture of a boron compound, i.e., boric acid, boron carbide (B4C), silicon boride (SiB4 or SiB6), aluminum boride, etc., and an aluminum compound, i.e., aluminum, aluminum oxide, aluminum hydroxide, aluminum carbide, etc., or aluminum boride (AlB2) alone, in such a proportion that the boron/aluminum atomic ratio in the sintered body becomes 0.05 to 0.25 wt% and 0.05 to 0.40 wt%, respectively, together with a carbonaceous additive to supply enough carbon to convert oxygen accompanying raw materials and additives into carbon monoxide.

  12. Synthesis and Characterization of TiB2 Reinforced Aluminium Matrix Composites: A Review

    NASA Astrophysics Data System (ADS)

    Kumar, Narendra; Gautam, Gaurav; Gautam, Rakesh Kumar; Mohan, Anita; Mohan, Sunil

    2015-09-01

    Aluminium-matrix composites (AMCs) are developed to meet the demands of light weight high performance materials in aerospace, automotive, marine and other applications. The properties of AMCs can be tailored suitably by combinations of matrix, reinforcement and processing route. AMCs are one of the most attractive alternatives for the manufacturing of light weight and high strength parts due to their low density and high specific strength. There are various techniques for preparing the AMCs with different reinforcement particles. In AMCs, the reinforcements are usually in the form of metal oxides, carbides, borides, nitrides and their combination. Among the various reinforcements titanium di-boride (TiB2) is of much interest due to its excellent stiffness, hardness, and wear resistance. This paper attempts to provide an overview to explore the possibilities of synthesizing titanium di-boride reinforced AMCs with different techniques. The mechanical and tribological properties of these composites have been emphasized to project these as tribo-materials.

  13. Investigation of the structure and properties of boron-containing coatings obtained by electron-beam treatment

    SciTech Connect

    Krivezhenko, Dina S. Drobyaz, Ekaterina A. Bataev, Ivan A. Chuchkova, Lyubov V.

    2015-10-27

    An investigation of surface-hardened materials obtained by cladding with an electron beam injected into the air atmosphere was carried out. Structural investigations of coatings revealed that an increase in boron carbide concentration in a saturating mixture contributed to a rise of a volume fraction of iron borides in coatings. The maximum hardened depth reached 2 mm. Hardened layers were characterized by the formation of heterogeneous structure which consisted of iron borides and titanium carbides distributed uniformly in the eutectic matrix. Areas of titanium boride conglomerations were detected. It was found that an increase in the boron carbide content led to an enhancement in hardness of the investigated materials. Friction testing against loosely fixed abrasive particles showed that electron-beam cladding of powder mixtures containing boron carbides, titanium, and iron in air atmosphere allowed enhancing a resistance of materials hardened in two times.

  14. Wear resistance of composite coatings produced by thermal spraying

    SciTech Connect

    Klinskaya, N.A.

    1995-12-31

    Injection of refractory additions (carbides, borides, oxides etc.) into self-fluxing alloys is a well-known technique for their hardening. Nevertheless the matter of influence of refractory components on the structure and characteristics of composite coatings is not studied well enough. This paper presents the results of investigations of gas thermal coatings (plasma and detonation ones) on the base of stellite with refractory components in the form of borides such as CrB{sub 2}, TiB{sub 2}, (TiCr)B{sub 2}. This study is concerned with the influence of refractory additions (carbides, borides, oxides) on the wear resistance sprayed coatings based on self-fluxing alloys NiCrBSi and CoCrBSi.

  15. Influence of heat treatment on microstructure and hot crack susceptibility of laser-drilled turbine blades made from Rene 80

    SciTech Connect

    Osterle, W. Krause, S.; Neidel, A.; Oder, G.; Voelker, J.

    2008-11-15

    Turbine components from conventionally cast nickel-base alloy Rene 80 show different hot cracking susceptibilities depending on their heat treatment conditions leading to slightly different microstructures. Electron probe micro-analysis, focused ion beam technique and analytical transmission electron microscopy were applied to reveal and identify grain boundary precipitates and the {gamma}-{gamma}'-microstructure. The distribution of borides along grain boundaries was evaluated statistically by quantitative metallography. The following features could be correlated with an increase of cracking susceptibility: i) Increasing grain size, ii) increasing fraction of grain boundaries with densely spaced borides, iii) lack of secondary {gamma}'-particles in matrix channels between the coarse cuboidal {gamma}'-precipitates. The latter feature seems to be responsible for linking-up of cracked grain boundary precipitates which occurred as an additional cracking mechanism after one heat treatment, whereas decohesion at the boride-matrix-interface in the heat affected zone of laser-drilled holes was observed for both heat treatments.

  16. Method of boronizing transition metal surfaces

    DOEpatents

    Koyama, Koichiro; Shimotake, Hiroshi

    1983-01-01

    A method is presented for preparing a boride layer on a transition metal substrate for use in corrosive environments or as a harden surface in machine applications. This method is particularly useful in treating current collectors for use within a high temperature and corrosive electrochemical cell environment. A melt of a alkali metal boride tetrafluoride salt including such as KF to lower its melting point is prepared including a dissolved boron containing material, for instance NiB, MnB.sub.2, or CrB.sub.2. A transition metal to be coated is immersed in the melt at a temperature of no more than 700.degree. C. and a surface boride layer of that transition metal is formed within a period of about 24 hours on the substrate surface.

  17. Method of boronizing transition metal surfaces

    DOEpatents

    Koyama, Koichiro; Shimotake, Hiroshi.

    1983-08-16

    A method is presented for preparing a boride layer on a transition metal substrate for use in corrosive environments or as a harden surface in machine applications. This method is particularly useful in treating current collectors for use within a high temperature and corrosive electrochemical cell environment. A melt of a alkali metal boride tetrafluoride salt including such as KF to lower its melting point is prepared including a dissolved boron containing material, for instance NiB, MnB[sub 2], or CrB[sub 2]. A transition metal to be coated is immersed in the melt at a temperature of no more than 700 C and a surface boride layer of that transition metal is formed within a period of about 24 hours on the substrate surface. 4 figs.

  18. Influence of a corrosive-abrasive medium on the wear resistance of 12Kh18N10T steel with surface hardening

    SciTech Connect

    Golubets, V.M.; Kozub, V.V.; Shchuiko, Ya.V.; Pashechko, M.I.

    1987-11-01

    The authors study the wear and corrosion resistance of 12Kh18N10T steel after diffusion boriding, electrospark alloying, and combined hardening in a corrosive abrasive medium consisting of 50 percent sand and 3 percent NaCl with hydrochloric acid added to obtain a pH of 1. Metallographic analysis revealed a 40-micrometer-deep case with a microhardness of 6-8.5 GPa on the surface. X-ray diffraction established that the boride case consists of an FeB phase alloyed with chromium and nickel. Results are graphed.

  19. Electrically conductive containment vessel for molten aluminum

    DOEpatents

    Holcombe, C.E.; Scott, D.G.

    1984-06-25

    The present invention is directed to a containment vessel which is particularly useful in melting aluminum. The vessel of the present invention is a multilayered vessel characterized by being electrically conductive, essentially nonwettable by and nonreactive with molten aluminum. The vessel is formed by coating a tantalum substrate of a suitable configuration with a mixture of yttria and particulate metal 10 borides. The yttria in the coating inhibits the wetting of the coating while the boride particulate material provides the electrical conductivity through the vessel. The vessel of the present invention is particularly suitable for use in melting aluminum by ion bombardment.

  20. Electrically conductive containment vessel for molten aluminum

    DOEpatents

    Holcombe, Cressie E.; Scott, Donald G.

    1985-01-01

    The present invention is directed to a containment vessel which is particularly useful in melting aluminum. The vessel of the present invention is a multilayered vessel characterized by being electrically conductive, essentially nonwettable by and nonreactive with molten aluminum. The vessel is formed by coating a tantalum substrate of a suitable configuration with a mixture of yttria and particulate metal borides. The yttria in the coating inhibits the wetting of the coating while the boride particulate material provides the electrical conductivity through the vessel. The vessel of the present invention is particularly suitable for use in melting aluminum by ion bombardment.

  1. Association of broad icosahedral Raman bands with substitutional disorder in SiB{sub 3} and boron carbide

    SciTech Connect

    Aselage, T.L.; Tallant, D.R.

    1998-02-01

    The structure of silicon boride, SiB{sub 3}, is based on 12-atom, boron-rich icosahedra in which silicon atoms substitute for some boron atoms. Raman bands associated with vibrations of icosahedral atoms in SiB{sub 3} are quite broad, reflecting this substitutional disorder. Comparing the Raman spectra of other icosahedral borides with SiB{sub 3}, only boron carbides have similarly broad icosahedral Raman bands. The direct correlation of broad icosahedral Raman bands with substitutional disorder supports the proposition that carbon atoms replace icosahedral boron atoms in boron carbides of all compositions. {copyright} {ital 1998} {ital The American Physical Society}

  2. Investigations on Microstructures and Toughness of Fe-B Cast Alloy Containing Titanium and Nitrogen

    NASA Astrophysics Data System (ADS)

    Yi, Dawei; Zhang, Zhiyun; Fu, Hanguang; Yang, Chengyan

    2013-11-01

    The effects of titanium and nitrogen elements on the microstructure and impact toughness of the Fe-B alloy have been studied. The results show that the borides are refined after the additions of titanium and nitrogen elements. With the additions of titanium and nitrogen, titanium nitrides are formed in the Fe-B alloy. Titanium nitride can act as effective heterogeneous nuclei of primary austenite, and promote the refinement of austenite and boride. After heat treatment, the impact toughness of Fe-B alloys modified by titanium and nitrogen elements is higher than that of ordinary alloy.

  3. New Process for Grain Refinement of Aluminum. Final Report

    SciTech Connect

    Dr. Joseph A. Megy

    2000-09-22

    A new method of grain refining aluminum involving in-situ formation of boride nuclei in molten aluminum just prior to casting has been developed in the subject DOE program over the last thirty months by a team consisting of JDC, Inc., Alcoa Technical Center, GRAS, Inc., Touchstone Labs, and GKS Engineering Services. The Manufacturing process to make boron trichloride for grain refining is much simpler than preparing conventional grain refiners, with attendant environmental, capital, and energy savings. The manufacture of boride grain refining nuclei using the fy-Gem process avoids clusters, salt and oxide inclusions that cause quality problems in aluminum today.

  4. Brazing Inconel 625 Using Two Ni/(Fe)-Based Amorphous Filler Foils

    NASA Astrophysics Data System (ADS)

    Chen, Wen-Shiang; Shiue, Ren-Kae

    2012-07-01

    For MBF-51 filler, the brazed joint consists of interfacial grain boundary borides, coarse Nb6Ni16Si7, and Ni/Cr-rich matrix. In contrast, the VZ-2106 brazed joint is composed of interfacial Nb6Ni16Si7 precipitates as well as grain boundary borides, coarse Nb6Ni16Si7, and Ni/Cr/Fe-rich matrix. The maximum tensile strength of 443 MPa is obtained from the MBF-51 brazed specimen. The tensile strengths of VZ-2106 brazed joints are approximately 300 MPa. Both amorphous filler foils demonstrate potential in brazing IN-625 substrate.

  5. Removal of dissolved actinides from alkaline solutions by the method of appearing reagents

    DOEpatents

    Krot, Nikolai N.; Charushnikova, Iraida A.

    1997-01-01

    A method of reducing the concentration of neptunium and plutonium from alkaline radwastes containing plutonium and neptunium values along with other transuranic values produced during the course of plutonium production. The OH.sup.- concentration of the alkaline radwaste is adjusted to between about 0.1M and about 4M. [UO.sub.2 (O.sub.2).sub.3 ].sup.4- ion is added to the radwastes in the presence of catalytic amounts of Cu.sup.+2, Co.sup.+2 or Fe.sup.+2 with heating to a temperature in excess of about 60.degree. C. or 85.degree. C., depending on the catalyst, to coprecipitate plutonium and neptunium from the radwaste. Thereafter, the coprecipitate is separated from the alkaline radwaste.

  6. Analysis of boron carbides' electronic structure

    NASA Technical Reports Server (NTRS)

    Howard, Iris A.; Beckel, Charles L.

    1986-01-01

    The electronic properties of boron-rich icosahedral clusters were studied as a means of understanding the electronic structure of the icosahedral borides such as boron carbide. A lower bound was estimated on bipolaron formation energies in B12 and B11C icosahedra, and the associated distortions. While the magnitude of the distortion associated with bipolaron formation is similar in both cases, the calculated formation energies differ greatly, formation being much more favorable on B11C icosahedra. The stable positions of a divalent atom relative to an icosahedral borane was also investigated, with the result that a stable energy minimum was found when the atom is at the center of the borane, internal to the B12 cage. If incorporation of dopant atoms into B12 cages in icosahedral boride solids is feasible, novel materials might result. In addition, the normal modes of a B12H12 cluster, of the C2B10 cage in para-carborane, and of a B12 icosahedron of reduced (D sub 3d) symmetry, such as is found in the icosahedral borides, were calculated. The nature of these vibrational modes will be important in determining, for instance, the character of the electron-lattice coupling in the borides, and in analyzing the lattice contribution to the thermal conductivity.

  7. Vapor pressure and evaporation rate of certain heat-resistant compounds in a vacuum at high temperatures

    NASA Technical Reports Server (NTRS)

    Bolgar, A. S.; Verkhoglyadova, T. S.; Samsonov, G. V.

    1985-01-01

    The vapor pressure and evaporation rate of borides of titanium, zirconium, and chrome; and of strontium and carbides of titanium, zirconium, and chrome, molybdenum silicide; and nitrides of titanium, niobium, and tantalum in a vacuum were studied. It is concluded that all subject compounds evaporate by molecular structures except AlB sub 12' which dissociates, losing the aluminum.

  8. Development of high temperature stable Ohmic and Schottky contacts on n-gallium nitride

    NASA Astrophysics Data System (ADS)

    Khanna, Rohit

    In this work the effort was made to towards develop and investigate high temperature stable Ohmic and Schottky contacts for n type GaN. Various borides and refractory materials were incorporated in metallization scheme to best attain the desired effect of minimal degradation of contacts when placed at high temperatures. This work focuses on achieving a contact scheme using different borides which include two Tungsten Borides (namely W2B, W2B 5), Titanium Boride (TiB2), Chromium Boride (CrB2) and Zirconium Boride (ZrB2). Further a high temperature metal namely Iridium (Ir) was evaluated as a potential contact to n-GaN, as part of continuing improved device technology development. The main goal of this project was to investigate the most promising boride-based contact metallurgies on GaN, and finally to fabricate a High Electron Mobility Transistor (HEMT) and compare its reliability to a HEMT using present technology contact. Ohmic contacts were fabricated on n GaN using borides in the metallization scheme of Ti/Al/boride/Ti/Au. The characterization of the contacts was done using current-voltage measurements, scanning electron microscopy (SEM) and Auger Electron Spectroscopy (AES) measurements. The contacts formed gave specific contact resistance of the order of 10-5 to 10-6 Ohm-cm2. A minimum contact resistance of 1.5x10-6 O.cm 2 was achieved for the TiB2 based scheme at an annealing temperature of 850-900°C, which was comparable to a regular ohmic contact of Ti/Al/Ni/Au on n GaN. When some of borides contacts were placed on a hot plate or in hot oven for temperature ranging from 200°C to 350°C, the regular metallization contacts degraded before than borides ones. Even with a certain amount of intermixing of the metallization scheme the boride contacts showed minimal roughening and smoother morphology, which, in terms of edge acuity, is crucial for very small gate devices. Schottky contacts were also fabricated and characterized using all the five boride

  9. Ultracapacitor current collector

    DOEpatents

    Jerabek, Elihu Calfin; Mikkor, Mati

    2001-10-16

    An ultracapacitor having two solid, nonporous current collectors, two porous electrodes separating the collectors, a porous separator between the electrodes and an electrolyte occupying the pores in the electrodes and separator. At least one of the current collectors comprises a conductive metal substrate coated with a metal nitride, carbide or boride coating.

  10. Magnetic properties and magnetic hardening mechansim of Pt-Co-B alloys

    NASA Technical Reports Server (NTRS)

    Qiu, Ning; Flanagan, F.; Wittig, James E.

    1994-01-01

    The intrinsic coercivity is found to be maximized in the Pt42Co45B13 ternary alloy which is undercooled and rapidly solidified (quenched using a 70 m/s wheel speed after undercooling), and then annealed (800 C for 2400 min). The same alloy, processed at slower cooling rates and annealed in the same way, has a much larger scale microstructure and a much lower resulting magnetic coercivity. The microstructure which would optimize the coercitvity of this coercivity of this ternary alloy is a completely ordered L1(sub zero) Pt-Co matrix with a submicron magnetic single-domion Co-boride precipitate. The L1(sub zero) phase is highly anistropic magnetically while the Co-boride precipate is somewhat less so. Annealing treatments designed to produced single-domain Co-boride precipitates enhance the coercivity. This suggests that the refined microstructures is responsible for the high coercivities found in the rapidly solidified and annealed alloy. The magnetic domain wall thickness for a Co-boride precipitate is determined from both experimental observation and theoretical calculation in order to evaluate its influence on the coercivity of the alloy. The effects of the pinning of domain walls and the barrier to the nucleation of reverse domains on the coercivity are discussed. Both microstrucutral analysis and theoretical calculation indicate that the high coercivities in the Pt42Co45B13 alloy are due to the difficult nucleation of reverse magnetic domains.

  11. Thermal emission property of solid solution Gd{sub 1-x}Nd{sub x}B{sub 6} (x=0, 0.6, 0.8)

    SciTech Connect

    Xing Zhang, Jiu; Hong Bao, Li; Lin Zhou, Shen E-mail: Baolihong_10@yahoo.com.cn

    2011-07-01

    In this paper, to further explore the excellent emission properties of rare earth boride cathode, herein we present the synthesis, characterization and properties of polycrystalline Nd{sub 1-x}Gd{sub x}B{sub 6} (x = 0, 0.6, 0.8) bulk via arc plasma and reactive SPS. (author)

  12. First international conference on surface engineering

    SciTech Connect

    Bucklow, I.A.

    1986-01-01

    This book contains 21 papers. Some of the titles are: The production of MCrAlHf diffusion coating in a single step pack process; Boride surface modifications; Surface boronising of metals and alloys; Hot zirconium cathode sputtered layers for useful surface modification; and Ceramics and cements in surface engineering.

  13. Boron Carbides As Thermo-electric Materials

    NASA Technical Reports Server (NTRS)

    Wood, Charles

    1988-01-01

    Report reviews recent theoretical and experimental research on thermoelectric materials. Recent work with narrow-band semiconductors demonstrated possibility of relatively high thermoelectric energy-conversion efficiencies in materials withstanding high temperatures needed to attain such efficiencies. Among promising semiconductors are boron-rich borides, especially boron carbides.

  14. Laser Boronizing of Stainless Steel with Direct Diode Laser

    NASA Astrophysics Data System (ADS)

    Kusuhara, Takayoshi; Morimoto, Junji; Abe, Nobuyuki; Tsukamoto, Masahiro

    Boronizing is a thermo-chemical surface treatment in which boron atoms are diffused into the surface of a work piece to form borides with the base material. When applied to the metallic materials, boronizing provides wear and abrasion resistance comparable to sintered carbides. However conventional boronizing is carried out at temperatures ranging from 800°C to 1050°C and takes from one to several hours. The structure and properties of the base material is influenced considerably by the high temperature and long treatment time. In order to avoid these drawbacks of conventional boronizing, laser-assisted boronizing is investigated which activates the conventional boronizing material and the work piece with a high density laser power. In this study, effect of laser characteristics was examined on the laser boronizing of stainless steel. After laser boronizing, the microstructure of the boride layer was analyzed with an optical microscope, electron probe micro analyser(EPMA) and X-ray diffractometer (XRD). The mechanical properties of borided layer were evaluated using Vickers hardness tester and sand erosion tester. Results showed that the boride layer was composed of NiB, CrB, FeB and Fe2B, and get wear resistance.

  15. Photovoltaic cell

    DOEpatents

    Gordon, Roy G.; Kurtz, Sarah

    1984-11-27

    In a photovoltaic cell structure containing a visibly transparent, electrically conductive first layer of metal oxide, and a light-absorbing semiconductive photovoltaic second layer, the improvement comprising a thin layer of transition metal nitride, carbide or boride interposed between said first and second layers.

  16. Analysis of boron carbides' electronic structure. Final technical report, 18 July 1984-17 August 1986

    SciTech Connect

    Howard, I.A.; Beckel, C.L.

    1986-08-01

    The electronic properties of boron-rich icosahedral clusters were studied as a means of understanding the electronic structure of the icosahedral borides such as boron carbide. A lower bound was estimated on bipolaron formation energies in B/sub 12/ and B/sub 11/C icosahedra, and the associated distortions. While the magnitude of the distortion associated with bipolaron formation is similar in both cases, the calculated formation energies differ greatly, formation being much more favorable on B11C icosahedra. The stable positions of a divalent atom relative to an icosahedral borane was also investigated, with the result that a stable energy minimum was found when the atom is at the center of the borane, internal to the B/sub 12/ cage. If incorporation of dopant atoms into B/sub 12/ cages in icosahedral boride solids is feasible, novel materials might result. In addition, the normal modes of a B/sub 12/H/sub 12/ cluster, of the C/sub 2/B/sub 10/ cage in para-carborane, and of a B/sub 12/ icosahedron of reduced (D sub 3d) symmetry, such as is found in the icosahedral borides, were calculated. The nature of these vibrational modes will be important in determining, for instance, the character of the electron-lattice coupling in the borides, and in analyzing the lattice contribution to the thermal conductivity.

  17. Characterization of natural zeolite clinoptilolite for sorption of contaminants

    NASA Astrophysics Data System (ADS)

    Xingu-Contreras, E.; García-Rosales, G.; García-Sosa, I.; Cabral-Prieto, A.; Solache-Ríos, M.

    2015-06-01

    The nanoparticles technology has received considerable attention for its potential applications in groundwater treatment for the removal of various pollutants as Cadmium. In this work, iron boride nanoparticles were synthesized in pure form and in presence of homo-ionized zeolite clinoptilolite, as support material. These materials were used for removing Cd (II) from aqueous solutions containing 10, 50, 100, 150, 200, 250, 300 and 400 mg/L. The characterization of these materials was made by using X-ray Diffraction, Scanning Electron Microscopy and Mössbauer Spectroscopy. Pure iron boride particles show a broad X-ray diffraction peak centered at 45∘ (2 𝜃), inferring the presence of nanocrystals of Fe2B as identified from Mössbauer Spectroscopy. The size of these Fe2B particles was within the range of 50 and 120 nm. The maximum sorption capacities for Cd (II) of iron boride particles and supported iron boride particles in homo-ionized zeolitic material were nearly 100 %. For homo-ionized zeolite and homo-ionized zeolite plus sodium borohydride was ≥ 95 %.

  18. Investigation on the coprecipitation of transuranium elements from alkaline solutions by the method of appearing reagents. Study of the effects of waste components on decontamination from Np(IV) and Pu(IV)

    SciTech Connect

    Bessonov, A.A.; Budantseva, N.A.; Gelis, A.V.; Nikonov, M.V.; Shilov, V.P.

    1997-09-01

    The third stage of the study on the homogeneous coprecipitation of neptunium and plutonium from alkaline high-level radioactive waste solutions by the Method of Appearing Reagents has been completed. Alkaline radioactive wastes exist at the U.S. Department of Energy Hanford Site. The recent studies investigated the effects of neptunium chemical reductants, plutonium(IV) concentration, and the presence of bulk tank waste solution components on the decontamination from tetravalent neptunium and plutonium achieved by homogeneous coprecipitation. Data on neptunium reduction to its tetravalent state in alkaline solution of different NaOH concentrations are given. Eleven reductants were tested to find those most suited to remove neptunium, through chemical reduction, from alkaline solution by homogeneous coprecipitation. Hydrazine, VOSO{sub 4}, and Na{sub 2}S{sub 2}O{sub 4} were found to be the most effective reductants. The rates of reduction with these reductants were comparable with the kinetics of carrier formation. Solution decontamination factors of about 400 were attained for 10{sup -6}M neptunium. Coprecipitation of plutonium(IV) with carriers obtained as products of thermal hydrolysis, redox transformations, and catalytic decomposition of [Co(NH{sub 3}){sub 6}]{sup 3+}, [Fe(CN){sub 5}NO]{sup 2-}, Cr(NO{sub 3}){sub 3}, KMnO{sub 4}, and Li{sub 4}UO{sub 2}(O{sub 2}){sub 3} was studied and results are described. Under optimum conditions, a 100-fold decrease of plutonium concentration was possible with each of these reagents.

  19. Laser surface modification of carburized and borocarburized 15CrNi6 steel

    SciTech Connect

    Kulka, M. . E-mail: coolka@sol.put.poznan.pl; Pertek, A.

    2007-05-15

    The paper presents the results of laser heat treatment (LHT) of carburized and borocarburized 15CrNi6 low-carbon steel. Laser tracks were arranged by CO{sub 2} laser beam as multiple tracks formed in the shape of a helical line. The microstructure and properties of these diffusion layers were compared with those obtained after through-hardening. The microstructure after carburizing and LHT consists of adjacent characteristic zones: re-melted zone (coarse-grained martensite), carburized layer with heat affected zone (fine acicular martensite), carburized layer without heat treatment and the substrate (ferrite and pearlite). The highest measured microhardness (about 820 HV) was observed in re-melted and heat affected zones. The increase of distance from the surface was accompanied by a gradual decrease of microhardness up to 400 HV beneath the HAZ and up to 250 HV in the core of steel. The carburized layer after LHT exhibited a higher resistance to frictional wear compared to a carburized layer after through-hardening. The microstructure after borocarburizing and LHT consists of the following characteristic zones: iron borides of laser-modified morphology (FeB and Fe{sub 2}B), carburized layer with heat affected zone (martensite and alloyed cementite), carburized layer without heat treatment and the substrate (ferrite and pearlite). The highest microhardness was obtained in the iron boride zone. The microhardness of FeB boride extended up to 2200 HV and for the Fe{sub 2}B boride up to about 1300-1600 HV. With increased distance from the surface, the microhardness gradually decreases to 800 HV in HAZ, 400-450 HV in the carburized layer without heat treatment and to 250 HV in low-carbon substrate. The iron borides after LHT assume a globular shape, which leads to a lower texture and porosity of the borided layers. The increased resistance to friction wear of the borocarburized layers is certified in comparison with the borided layer after conventional heat treatment

  20. Transuranic interfacial reaction studies on manganese oxidemineral surfaces

    SciTech Connect

    Shaughnessy, Dawn A.; Nitsche, Heino; Serne, R. Jeffrey; Shuh,David K.; Waychunas, Glenn A.; Booth, Corwin H.; Cantrell, Kirk J.

    2002-05-15

    Several DOE sites have been contaminated by transuranicradionuclide (TRU) discharges including neptunium and plutonium. Theirinteraction with the surrounding geological media can affect thetransport and remediation of these radionuclides in the environment.Manganese based minerals, present as minor phases in the vadose zone, canpreferentially sequester TRU over other minerals present in largerquantities. The objective of this project is to understand theinteractions between plutonium and neptunium and manganese oxyhydroxideminerals to predict potential hazards they represent to the environment,as well as to provide important scientific information for the design ofeffective remediation strategies for contaminated DOE sites.

  1. Investigation of sulfur-tolerant catalysts for selective synthesis of hydrocarbon liquids from coal-derived gases. Annual technical progress report, September 19, 1980-September 18, 1981

    SciTech Connect

    Bartholomew, C.H.

    1981-10-31

    During the past contract year, considerable progress was made in characterization and activity/selectivity testing of iron and cobalt catalysts. Preparation of boride promoted cobalt and iron catalysts was refined and nearly completed. H/sub 2/ and CO adsorption and oxygen titration measurements were performed on a number of supported and unsupported catalysts, especially several boride promoted cobalt and iron catalysts. Activity/selectivity tests of 3 and 15% Fe/SiO/sub 2/ and Co/SiO/sub 2/ and of 6 borided cobalt and iron catalysts were completed. The product distributions for iron and cobalt boride catalysts are unusual and interesting. Boron promoted iron is more active and stable than iron/silica; cobalt boride has an unusually high selectivity for alcohols. Tests to determine effects of H/sub 2/S poisoning on activity/selectivity properties of 15% Co/SiO/sub 2/ indicate that a significant loss of activity occurs over a period of 24 to 28 h in the presence of 10 to 20 ppM H/sub 2/S. Product selectivity to liquids increased through a maximum during the gradual addition of sulfur. Reactant CO and H/sub 2/S interact partially to form COS which is less toxic than H/sub 2/S. H/sub 2/ and CO adsorption data were obtained for 3, 6 and 9% Co/ZSM-5 catalysts prepared and reactor tested by PETC. The unusual and interesting results suggest that metal-support interactions may have an important influence on reactant adsorption properties.

  2. Multi-component boron coatings on low carbon steel AISI 1018

    NASA Astrophysics Data System (ADS)

    Suwattananont, Naruemon

    Boronizing and metalizing are thermo-chemical surface hardening treatments in which boron and metal atoms diffuse into the metal substrate forming metallic boride layers, providing complex properties of B-Me-Fe system. To study multi-component boron coatings on low carbon steel AISI 1018, the simultaneous powder pack method of boronizing and metalizing was selected to perform the coatings. One B-Fe system and eight boron-metal (B-Me-Fe) systems from transition metals group IVB (Ti, Zr, HO, group VB (Nb, Ta), and group VIB (Cr, Mo, W) were studied. The system specimens were thereto-chemically treated at 950°C for 4 hours in a crucible containing powder mixture of boron source, transition metal powder, and activator. After the heat treatment process, the multi-component boron coatings were characterized by using optical microscope, microhardness tester, TGA, XRD, and Synchrotron microdiffraction. The coating morphology was observed and the coating thickness was measured as well as the microhardness across the depth of coating. The corrosion resistance of the coatings was evaluated by the continuous weighting method. The high temperature oxidation was also detected by isothermal method at a temperature range of 400-800°C for 24 hours. The Rietveld refinement method was used to examine the quantitative phase analysis, crystalline size, microstrain and lattice parameters of the multi-component boron coatings. The results have shown that adding transition metals into the B-Fe system caused the formation of solid solution of transition-metal borides. The distortion of crystal lattice parameters generated microstrain in the boride phase. The Synchrotron microdiffraction confirmed the presence of about 5-10 microns of transition-metal boride phase at the surface. Moreover, the additional transition metal can provide better corrosion and high temperature oxidation resistance to the B-Fe system, preventing the deboronizing and stabilizing the boride phases.

  3. A Linear trans -Bis(imido) Neptunium(V) Actinyl Analog: NpV (NDipp)2 ( tBu2 bipy)2Cl (Dipp = 2,6- i Pr2C6H3)

    SciTech Connect

    Brown, Jessie L.; Batista, Enrique R.; Boncella, James M.; Gaunt, Andrew J.; Reilly, Sean D.; Scott, Brian L.; Tomson, Neil C.

    2015-07-22

    We present the discovery that imido analogs of actinyl dioxo cations can be extended beyond uranium into the transuranic elements. Synthesis of the Np(V) complex, Np(NDipp)2(tBu2bipy)2Cl (1), is achieved through treatment of a Np(IV) precursor with a bipyridine co-ligand and lithium-amide reagent. Complex 1 has been structurally characterized, analyzed by 1H NMR and UV/vis/NIR spectroscopies, and the electronic structure evaluated by DFT calculations.

  4. 10 CFR Appendix K to Part 50 - ECCS Evaluation Models

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... the radioactive decay of actinides, including neptunium and plutonium generated during operation, as... radioactive properties. The actinide decay heat chosen shall be that appropriate for the time in the fuel... heat generation rates from radioactive decay of fission products shall be assumed to be equal to...

  5. 10 CFR Appendix K to Part 50 - ECCS Evaluation Models

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... the radioactive decay of actinides, including neptunium and plutonium generated during operation, as... radioactive properties. The actinide decay heat chosen shall be that appropriate for the time in the fuel... heat generation rates from radioactive decay of fission products shall be assumed to be equal to...

  6. 10 CFR Appendix K to Part 50 - ECCS Evaluation Models

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... the radioactive decay of actinides, including neptunium and plutonium generated during operation, as... radioactive properties. The actinide decay heat chosen shall be that appropriate for the time in the fuel... heat generation rates from radioactive decay of fission products shall be assumed to be equal to...

  7. 10 CFR Appendix K to Part 50 - ECCS Evaluation Models

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... the radioactive decay of actinides, including neptunium and plutonium generated during operation, as... radioactive properties. The actinide decay heat chosen shall be that appropriate for the time in the fuel... heat generation rates from radioactive decay of fission products shall be assumed to be equal to...

  8. Method for the recovery of actinide elements from nuclear reactor waste

    DOEpatents

    Horwitz, E. Philip; Delphin, Walter H.; Mason, George W.

    1979-01-01

    A process for partitioning and recovering actinide values from acidic waste solutions resulting from reprocessing of irradiated nuclear fuels by adding hydroxylammonium nitrate and hydrazine to the waste solution to adjust the valence of the neptunium and plutonium values in the solution to the +4 oxidation state, thus forming a feed solution and contacting the feed solution with an extractant of dihexoxyethyl phosphoric acid in an organic diluent whereby the actinide values, most of the rare earth values and some fission product values are taken up by the extractant. Separation is achieved by contacting the loaded extractant with two aqueous strip solutions, a nitric acid solution to selectively strip the americium, curium and rare earth values and an oxalate solution of tetramethylammonium hydrogen oxalate and oxalic acid or trimethylammonium hydrogen oxalate to selectively strip the neptunium, plutonium and fission product values. Uranium values remain in the extractant and may be recovered with a phosphoric acid strip. The neptunium and plutonium values are recovered from the oxalate by adding sufficient nitric acid to destroy the complexing ability of the oxalate, forming a second feed, and contacting the second feed with a second extractant of tricaprylmethylammonium nitrate in an inert diluent whereby the neptunium and plutonium values are selectively extracted. The values are recovered from the extractant with formic acid.

  9. Modeling of Diffusion of Plutonium in Other Metals and of Gaseous Species in Plutonium-Based Systems

    SciTech Connect

    Bernard R. Cooper; Gayanath W. Fernando; S. Beiden; A. Setty; E.H. Sevilla

    2004-07-02

    Establish standards for temperature conditions under which plutonium, uranium, or neptunium from nuclear wastes permeates steel, with which it is in contact, by diffusion processes. The primary focus is on plutonium because of the greater difficulties created by the peculiarities of face-centered-cubic-stabilized (delta) plutonium (the form used in the technology generating the waste).

  10. CONTAMINANT-ORGANIC COMPLEXES: THEIR STRUCTURE AND ENERGETICS IN SURFACE DECONTAMINATION PROCESSES

    EPA Science Inventory

    The current debate over possible decontamination processes for U.S. Department of Energy (DOE) facilities is centered on disparate decontamination problems, but the key contaminants (uranium [U], plutonium [Pu], and neptunium [Np]) are universally important. There is no single d...

  11. Rapid determination of (237)Np and plutonium isotopes in urine by inductively-coupled plasma mass spectrometry and alpha spectrometry.

    PubMed

    Maxwell, Sherrod L; Culligan, Brian K; Jones, Vernon D; Nichols, Sheldon T; Noyes, Gary W; Bernard, Maureen A

    2011-08-01

    A new rapid separation method was developed for the measurement of plutonium and neptunium in urine samples by inductively-coupled plasma mass spectrometry (ICP-MS) and/or alpha spectrometry with enhanced uranium removal. This method allows separation and preconcentration of plutonium and neptunium in urine samples using stacked extraction chromatography cartridges and vacuum box flow rates to facilitate rapid separations. There is an increasing need to develop faster analytical methods for emergency response samples. There is also enormous benefit to having rapid bioassay methods in the event that a nuclear worker has an uptake (puncture wound, etc.) to assess the magnitude of the uptake and guide efforts to mitigate dose (e.g., tissue excision and chelation therapy). This new method focuses only on the rapid separation of plutonium and neptunium with enhanced removal of uranium. For ICP-MS, purified solutions must have low salt content and low concentration of uranium due to spectral interference of (238)U(1)H(+) on m/z 239. Uranium removal using this method is enhanced by loading plutonium and neptunium initially onto TEVA resin, then moving plutonium to DGA resin where additional purification from uranium is performed with a decontamination factor of almost 1×10(5). If UTEVA resin is added to the separation scheme, a decontamination factor of ~3 × 10(6) can be achieved. PMID:21709507

  12. Determination of a three-step excitation and ionization scheme for resonance ionization and ultratrace analysis of Np-237

    NASA Astrophysics Data System (ADS)

    Raeder, S.; Stöbener, N.; Gottwald, T.; Passler, G.; Reich, T.; Trautmann, N.; Wendt, K.

    2011-03-01

    The long-lived radio isotope 237Np is generated within the nuclear fuel cycle and represents a major hazard in the final disposal of nuclear waste. Related geochemical research requires sensitive methods for the detection of ultratrace amounts of neptunium in environmental samples. Resonance ionization mass spectrometry (RIMS) has proven to be one of the most sensitive methods for the detection of plutonium. A precondition for the application of RIMS to ultratrace analysis of neptunium is the knowledge of an efficient and selective scheme for optical excitation and ionization. Therefore, a multitude of medium to high-lying atomic levels in neptunium was located by applying in-source resonance ionization spectroscopy. By using excitation via six previously known first excited, intermediate levels of odd parity, a set of twelve so far unknown high-lying levels of even parity were identified and studied further for their suitability in resonant excitation/ionization schemes. Autoionizing resonances for efficient ionization of neptunium atoms were subsequently accessed spectroscopically. Altogether five resonance ionization schemes were investigated and characterized concerning their saturation behavior and relative efficiency. Applying a calibrated sample, an overall efficiency of 0.3 % was determined.

  13. Behavior of Np(VII, VI, V) in Silicate Solutions

    SciTech Connect

    Shilov, V P.; Fedoseev, A M.; Yusov, A B.; Delegard, Calvin H.

    2004-11-30

    Spectrophotometric methods were used to investigate the properties of neptunium(VII), (VI), and (V) in silicate solution. The transition of cationic neptunium(VII) to anionic species in non-complexing environments proceeds in the range of ?? 5.5 to 7.5. In the presence of carbonate, this transition occurs at ?? 10.0 to 11.5 and in silicate solutions at ?? 10.5-12.0. These findings show that cationic neptunium(VII) forms complexes with both carbonate and silicate and that the silicate complex is stronger than that of the carbonate. The competition of complex formation reactions for neptunium(VI) with carbonate and silicate and on the known complex stability constant of NpO2(CO3)34- allowed the NpO2SiO3 complex stability constant, log ? = 16.5, to be estimated. Determination of the formation constant of Np(V) complexes with SiO32- was not possible using similar methods.

  14. Use of glassy carbon as a working electrode in controlled potential coulometry.

    PubMed

    Plock, C E; Vasquez, J

    1969-11-01

    Glassy carbon has been used as the working electrode in controlled potential coulometry. The results of coulometric investigations of chromium, copper, iron, uranium and neptunium are compared with results obtained with platinum or mercury working electrodes. The accuracy of results with the glassy carbon electrode compares favourably with the results obtainable with the other electrodes, but the precision is poorer. PMID:18960665

  15. 15. VIEW OF LABORATORY EQUIPMENT IN THE BUILDING 771 ANALYTICAL ...

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

    15. VIEW OF LABORATORY EQUIPMENT IN THE BUILDING 771 ANALYTICAL LABORATORY. THE LAB ANALYZED SAMPLES FOR PLUTONIUM, AMERICIUM, URANIUM, NEPTUNIUM, AND OTHER RADIOACTIVE ISOTOPES. (9/25/62) - Rocky Flats Plant, Plutonium Recovery & Fabrication Facility, North-central section of plant, Golden, Jefferson County, CO

  16. 10 CFR 110.23 - General license for the export of byproduct material.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ...) Actinium-225 and -227, americium-241 and -242m, californium-248, -249, -250, -251, -252, -253, and -254... this Part. Exports of americium and neptunium are subject to the reporting requirements listed in paragraph (b) of this section. (3) For americium-241, exports must not exceed 0.6 TBq (16 curies) per...

  17. Discovery of isotopes of the transuranium elements with 93≤Z≤98

    SciTech Connect

    Fry, C.; Thoennessen, M.

    2013-01-15

    One hundred and five isotopes of the transuranium elements neptunium, plutonium, americium, curium, berkelium, and californium have been observed so far; the discovery of these isotopes is described. For each isotope a brief summary of the first refereed publication, including the production and identification method, is presented.

  18. Discovery of isotopes of the transuranium elements with 93≤Z≤98

    NASA Astrophysics Data System (ADS)

    Fry, C.; Thoennessen, M.

    2013-01-01

    One hundred and five isotopes of the transuranium elements neptunium, plutonium, americium, curium, berkelium, and californium have been observed so far; the discovery of these isotopes is described. For each isotope a brief summary of the first refereed publication, including the production and identification method, is presented.

  19. Study of actinide chemistry in saturated potassium fluoride solution

    NASA Technical Reports Server (NTRS)

    Cohen, D.; Thalmayer, C. E.

    1969-01-01

    Study concerning the chemistry of actinides in saturated KF solution included work with neptunium, uranium, and americium. Solubilities, absorption spectra, oxidation-reduction reactions, and solid compounds which can be produced in KF solution were examined. The information is used for preparation of various materials from salts of the actinides.

  20. Quantitative Analysis of Radionuclides in Process and Environmental Samples

    SciTech Connect

    Boni, A.L.

    2003-02-21

    An analytical method was developed for the radiochemical separation and quantitative recovery of ruthenium, zirconium, niobium, neptunium, cobalt, iron, zinc, strontium, rare earths, chromium and cesium from a wide variety of natural materials. This paper discusses this analytical method, based on the anion exchange properties of the various radionuclides, although both ion exchange and precipitation techniques are incorporated.