Science.gov

Sample records for direct reaction sintering

  1. Sintering of reaction bonded silicon nitride

    NASA Technical Reports Server (NTRS)

    Mangels, J. A.

    1983-01-01

    A process to produce sintered reaction-bonded Si3N4 (SRBSN) articles has been developed. This process consists of the addition of an appropriate sintering aid to reaction-bonded Si3N4 followed by sintering between 1780 and 2000 C, using an over pressure of nitrogen. The principal advantage of this process is the low sintering shrinkages of 5 to 10 percent. The properties and microstructure of two SRBSN systems sintered with MgO and Y2O3 additives are described and were found to be comparable to corresponding hot-pressed Si3N4 systems. Examples of applications of both systems are illustrated, demonstrating near net shape fabrication capability of the process.

  2. Computer Modeling of Direct Metal Laser Sintering

    NASA Technical Reports Server (NTRS)

    Cross, Matthew

    2014-01-01

    A computational approach to modeling direct metal laser sintering (DMLS) additive manufacturing process is presented. The primary application of the model is for determining the temperature history of parts fabricated using DMLS to evaluate residual stresses found in finished pieces and to assess manufacturing process strategies to reduce part slumping. The model utilizes MSC SINDA as a heat transfer solver with imbedded FORTRAN computer code to direct laser motion, apply laser heating as a boundary condition, and simulate the addition of metal powder layers during part fabrication. Model results are compared to available data collected during in situ DMLS part manufacture.

  3. Morphology characterization of periclase-hercynite refractories by reaction sintering

    NASA Astrophysics Data System (ADS)

    Jiang, Peng; Chen, Jun-hong; Yan, Ming-wei; Li, Bin; Su, Jin-dong; Hou, Xin-mei

    2015-11-01

    A periclase-hercynite brick was prepared via reaction sintering at 1600°C for 6 h in air using magnesia and reaction-sintered hercynite as raw materials. The microstructure development of the periclase-hercynite brick during sintering was investigated using X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy in combination with energy-dispersive X-ray spectroscopy. The results show that during sintering, Fe2+, Fe3+ and Al3+ ions in hercynite crystals migrate and react with periclase to form (Mg1- x Fe x )(Fe2- y Al y )O4 spinel with a high Fe/Al ratio. Meanwhile, Mg2+ in periclase crystals migrates into hercynite crystals and occupies the oxygen tetrahedron vacancies. This Mg2+ migration leads to the formation of (Mg1- u Fe u )(Fe2- v Al v )O4 spinel with a lower Fe/Al ratio and results in Al3+ remaining in hercynite crystals. Cation diffusion between periclase and hercynite crystals promotes the sintering process and results in the formation of a microporous structure.

  4. Sintered-reaction Bonded Silicon Nitride Densified by a Gas Pressure Sintering Process Effects of Rare Earth Oxide Sintering Additives

    SciTech Connect

    Lee, S. H.; Ko, J. W.; Park, Y. J.; Kim, H. D.; Lin, Hua-Tay; Becher, Paul F

    2012-01-01

    Reaction-bonded silicon nitrides containing rare-earth oxide sintering additives were densified by gas pressure sintering. The sintering behavior, microstructure and mechanical properties of the resultant specimens were analyzed. For that purpose, Lu2O3-SiO2 (US), La2O3-MgO (AM) and Y2O3-Al2O3 (YA) additive systems were selected. Among the tested compositions, densification of silicon nitride occurred at the lowest temperature when using the La2O3-MgO system. Since the Lu2O3-SiO2 system has the highest melting temperature, full densification could not be achieved after sintering at 1950oC. However, the system had a reasonably high bending strength of 527 MPa at 1200oC in air and a high fracture toughness of 9.2 MPa m1/2. The Y2O3-Al2O3 system had the highest room temperature bending strength of 1.2 GPa

  5. SOFC chromite sintering and electrolyte/air-electrode interface reactions

    SciTech Connect

    Bates, J.L.; Chick, L.A.; Youngblood, G.E.

    1992-04-01

    Air sintering of chromites was investigated in La(Sr)CrO{sub 3}, La(Ca)CrO{sub 3}, and Y(Ca)CrO{sub 3}. Effects of alkaline earth dopant level and chromium enrichment/depletion on chromite sintered densities and microstructures are discussed. Ac impedance spectroscopy and dc polarization coupled with an unbonded interface cell were used to examine SOFC (solid oxide fuel cells) electrochemical reactions at solid-solid-gas interfaces, particularly for La{sub 1-x}Sr{sub x}MnO{sub 3}. 5 refs.

  6. SOFC chromite sintering and electrolyte/air-electrode interface reactions

    SciTech Connect

    Bates, J.L.; Chick, L.A.; Youngblood, G.E.

    1992-04-01

    Air sintering of chromites was investigated in La(Sr)CrO[sub 3], La(Ca)CrO[sub 3], and Y(Ca)CrO[sub 3]. Effects of alkaline earth dopant level and chromium enrichment/depletion on chromite sintered densities and microstructures are discussed. Ac impedance spectroscopy and dc polarization coupled with an unbonded interface cell were used to examine SOFC (solid oxide fuel cells) electrochemical reactions at solid-solid-gas interfaces, particularly for La[sub 1-x]Sr[sub x]MnO[sub 3]. 5 refs.

  7. Pressureless Reaction Sintering of AlON using Aluminum Orthophosphate as a Transient Liquid Phase

    SciTech Connect

    Michael Bakas; Henry Chu

    2009-01-01

    Use of aluminum oxynitride (AlON) in transparent armor systems has been difficult due to the expense and limitations of the processing methods currently necessary to achieve transparency. Development of a pressureless processing method based on direct reaction sintering of alumina and aluminum nitride powders would reduce costs and provide a more flexible and practical manufacturing method. It may be possible to develop such a processing method using liquid phase sintering; as long as the liquid phase does not remain in the final sample. AlPO4 forms a liquid phase with Al2O3 and AlN at the temperatures required to sinter AlON, and slowly decomposes into P2O5 and alumina. Therefore, it was investigated as a possible transient liquid phase for reaction-sintered AlON. Small compacts of alumina and aluminum nitride with up to of 15wt% AlPO4 additive were pressed and sintered. It was found that AlPO4 formed the requisite transient liquid phase, and it was possible to adjust the process to produce AlON samples with good transmission and densities of 3.66-3.67 g/cc. XRD confirmed the samples formed were AlON, with no trace of any remaining phosphate phases or excess alumina or aluminum nitride. Based on the results, it was concluded that AlPO4 could be utilized as a transient liquid phase to improve the density and transmission of AlON produced by pressureless reaction sintering.

  8. Vitrification of radioactive waste by reaction sintering under pressure

    NASA Astrophysics Data System (ADS)

    Gong, W. L.; Lutze, W.; Abdelouas, A.; Ewing, R. C.

    1999-02-01

    Silicate nuclear waste glasses were synthesized by reaction sintering of powdered precursors under pressure. The glass samples contained a glass matrix phase with embedded zirconia (baddeleyite) particles. A waste composition with 38 wt% of ZrO 2 was prepared with a waste loading of 30-50 wt% at 800°C and 28 MPa, by hot isostatic pressing. The glass former was commercial amorphous silica powder to which simulated waste was added as calcined oxides. Phase compositions and microstructure of the sintered glass samples were characterized using scanning and analytical electron microscopy. The results show that extensive sintering took place and that a continuous glass phase was formed, particularly at higher waste loading. Waste components such as Na 2O, CaO, MnO 2, La 2O 3, Fe 2O 3, Cr 2O 3, and P 2O 5 dissolved completely in the glass phase. ZrO 2 was also dissolved but recrystallized from the glass as aggregates of baddeleyite crystallites surrounding the original silica particles. MCC-1 type chemical durability tests showed that the glasses are durable with dissolution rates similar to or lower than that of the highly durable French R7T7 borosilicate glass. This glass contains 13 wt% high-level radioactive waste from light water reactor fuel reprocessing and has a melting temperature of 1150°C. The long-term chemical durability of our sintered glasses is expected to be as high as that of rhyolitic glasses, based on hydration energies of 3.7 and 3.3 kJ/mole, respectively. Rhyolitic glasses show little alteration over geological periods of time with a typical corrosion rate of 1 μm/1000 yr.

  9. Effect of attrition milling on the reaction sintering of silicon nitride

    NASA Technical Reports Server (NTRS)

    Herbell, T. P.; Glasgow, T. K.; Yeh, H. C.

    1978-01-01

    Silicon powder was ground in a steel attrition mill under nitrogen. Air exposed powder was compacted, prefired in helium, and reaction sintered in nitrogen-4 v/o hydrogen. For longer grinding times, oxygen content, surface area and compactability of the powder increased; and both alpha/beta ratio and degreee of nitridation during sintering increased. Iron content remained constant.

  10. Effect of attrition milling on the reaction sintering of silicon nitride

    NASA Technical Reports Server (NTRS)

    Herbell, T. P.; Glasgow, T. K.; Yeh, H. C.

    1978-01-01

    Silicon powder was ground in a steel attrition mill under nitrogen. Air-exposed powder was compacted, prefired in helium, and reaction-sintered in nitrogen-4 v/o hydrogen. For longer grinding times, oxygen content, surface area and compactability of the powder increased; and both alpha/beta ratio and degree of nitridation during sintering increased. Iron content remained constant.

  11. Sintering Behavior of Metal Powders Involving Microwave-Enhanced Chemical Reaction

    NASA Astrophysics Data System (ADS)

    Takayama, Sadatsugu; Saito, Yasushi; Sato, Motoyasu; Nagasaka, Takuya; Muroga, Takeo; Ninomiya, Yoshihiko

    2006-03-01

    Copper powder compacts were sintered by microwave radiation in air. In this procedure, the samples were sintered by microwave in air without using any special atmosphere, only by protecting them in a container filled with ceramic powder. The enhancement of the deoxidation reaction by the microwave was observed. The samples were analyzed by using scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD) analysis. The samples were deoxidized on the surface and were well sintered to the edge from the inside throughout the entire cross section. The tensile strength of the copper samples sintered by the microwave in air was higher than that found in conventional sintering in N2 gas. No other differences were noticed between the samples sintered by the microwave under the air-rich conditions and in the conventional furnace in H2+N2 gas. The microwave-sintered copper samples were of good quality; for example, the tensile strength measured throughout the cross section was the same as that for the samples sintered in H2+N2 gas by the conventional method.

  12. Sintering Reaction of Pseudoleucite Syenite: Thermodynamic Analysis and Process Evaluation

    NASA Astrophysics Data System (ADS)

    TAN, Danjun; MA, Hongwen; LI, Ge; LIU, Hao; ZOU, Dan

    On the basis of comprehensive analysis of the modal composition of a pseudoleucite syenite ore sample, collected from the Zijin Hill of Lin County, Shanxi Province, thermodynamic analysis of the pseudoleucite syenite sintering process with sodium carbonate as the additive was carried out. It indicated that when the pseudoleucite syenite was sintered at 760-880°C for 1.0-1.5 h, with sodium carbonate as the additive. The decomposition rate of minerals in the pseudoleucite syenite could reach 97.1%. The thermodynamic calculation shows that it needs to consume Na 2CO 3, i.e., 0.65 t treating per ton pseudoleucite syenite ore and approximately 95% of Na 2CO 3 could be recycled. This process consumes heat energy (2.29-2.48)×10 -6 kJ, corresponding to standard coal 190.97-206.82 kg as the thermal efficiency was 40% and CO 2 emission was 0.77-0.81 t. Compared with the Russian limestone-sintering technique, the natural mineral resources and energy consumptions and greenhouse gas emissions of the soda-sintering technique were reduced by 65%, 63%, and 65%, respectively. It is, therefore, feasible that the procedure suggested in this article could be industrialized providing both economic benefit and environmental conservation.

  13. Sintered Reaction Bonded Silicon Parts by Microwave Nitridation Combined with Gas-Pressure Sintering

    SciTech Connect

    Kiggans, J.O.; Mikijelj, B.; Tiegs, T.N.

    1999-01-01

    The cooperative project was a joint development program between Ceradyne and Oak Ridge National Laboratory through Lockheed Martin Energy Research (LMER). Cooperative work was of benefit to both parties. ORNL was able to assess the effect of the microwave nitridation process coupled with gas-pressure sintering for fabrication of parts for advanced diesel engines. Ceradyne gained access to gelcasting expertise and microwave facilities and experience for the nitridation of SRBSN materials. The broad objective of the CRADA between Ceradyne and OIWL was to (1) examine the applicability of the gelcasting technology to fabricate parts from SRBSN, and (2) to assess the effect of the microwave nitridation of silicon process coupled with gas-pressure sintering for fabrication of parts for advanced diesel engines. The following conclusions can be made from the work performed under the CRADA: (1) Gelcasting is a viable method to fabricate SRBSN parts using Ceradyne Si mixtures. However, the technique requires further development prior to being put into commercial use. (2) Microwave heating can be utilized to nitride multiple SRBSN parts. Scale-up of the process to fabricate several kilograms of material (up to 6 kg) per furnace run was demonstrated.

  14. Scale-up of microwave nitridation of sintered reaction bonded silicon nitride parts. Final report

    SciTech Connect

    Tiegs, T.N.; Kiggans, J.O.; Garvey, G.A.

    1997-10-01

    Scale-up were performed in which microwave heating was used to fabricate reaction-bonded silicon nitride and sintered reaction-bonded silicon nitride (SRBSN). Tests were performed in both a 2.45 GHz, 500 liter and a 2.45 GHz, 4000 liter multimode cavities. The silicon preforms processed in the studies were clevis pins for diesel engines. Up to 230 samples were processed in a single microwave furnace run. Data were collected which included weight gains for nitridation and sintering studies were performed using a conventional resistance-heated furnace.

  15. Hot isostatic pressing of direct selective laser sintered metal components

    NASA Astrophysics Data System (ADS)

    Wohlert, Martin Steven

    2000-10-01

    A new manufacturing process combining the benefits of Selective Laser Sintering (SLS) and Hot Isostatic Pressing (HIP) has been developed to permit Rapid Prototyping of high performance metal components. The new process uses Direct Metal SLS to produce a gas impermeable HIP container from the same powdered material that will eventually compose the bulk of the part. The SLS generated capsule performs the functions of the sheet metal container in traditional HIP, but unlike a sheet metal container, the SLSed capsule becomes an integral part of the final component. Additionally, SLS can produce a capsule of far greater geometric complexity than can be achieved by sheet metal forming. Two high performance alloys, Ti-6Al-4V and Inconel 625, were selected for use in the development of the new process. HIP maps were constructed to predict the densification rate of the two materials during HIP processing. Comparison to experimentally determined densification behavior indicated that the maps provide a useful qualitative description of densification rates; however, the accuracy of quantitative predictions was greatly enhanced by tuning key material parameters based on a limited number of experimental HIP cycles. Microstructural characterization of SLS + HIP samples revealed two distinct regions within the components. The outer SLS processed capsule material exhibited a relatively coarse microstructure comparable to a cast, or multi-layer welded structure. No layer boundaries were discernible in the SLS material, with grains observed to grow epitaxially from previously deposited material. The microstructure of the HIP consolidated core material was similar to conventionally HIP processed powder materials, featuring a fine grain structure and preserved prior particle boundaries. The large variation in grain size between the capsule and core materials was reflected in hardness measurements conducted on the Alloy 625 material; however, the variation in hardness was less

  16. Reaction sintered glass: A durable matrix for spinel-forming nuclear waste compositions

    NASA Astrophysics Data System (ADS)

    Gong, W. L.; Lutze, W.; Ewing, R. C.

    2000-01-01

    Glass formation by reaction sintering under isostatic pressure is an innovative process to vitrify refractory-rich high-level radioactive waste. We used a typical defense waste composition, containing spinel-forming components such as ˜4 wt% of Cr 2O 3, ˜23 wt% Al 2O 3, ˜13 wt% Fe 2O 3, and ˜9 wt% UO 2, with CeO 2 simulating UO 2. Reaction sintered silicate glasses with waste loading up to 45 wt% were prepared within three hours, by hot pressing at 800°C. The glass former was amorphous silica. Simulated waste was added as calcined oxides. The reaction sintered glass samples were characterized using scanning and analytical electron microscopy. The results show that extensive reaction sintering took place and a continuous glass phase formed. Waste components such as Na 2O, CaO, MnO 2, and Fe 2O 3, dissolved completely in the continuous glass phase. Cr 2O 3, Al 2O 3, and CeO 2 were only partially dissolved due to incomplete dissolution (Al 2O 3) or super-saturation and reprecipitation (Cr 2O 3 and CeO 2). The precipitation mechanism is related to a time dependent alkali content in the developing glass phase. Short-term corrosion tests in water showed that the glasses are chemically more durable than melted nuclear waste glasses. Based on hydration energies calculations, the long-term chemical durability of our reaction sintered glasses is expected to be comparable to that of rhyolitic and tektite glasses.

  17. Reaction-sintered silicon carbide: newly developed material for lightweight mirrors

    NASA Astrophysics Data System (ADS)

    Tsuno, Katsuhiko; Irikado, Hiroshi; Hamada, Kazuo; Kazuhiko, Ohno; Ishida, Juro; Suyama, Shoko; Itoh, Yoshiyasu; Ebizuka, Noboru; Eto, Hiroaki; Dai, Yutang

    2004-06-01

    Newly developed high-strength reaction-sintered silicon carbide is an attractive material for lightweight optical mirror with two times higher bending strength than other SiC materials. The polished surface has no pore and is suited to visible region as well as infrared without CVD SiC coating. The fabrication process, with low temperature and small shrinkage, is also suited to develop large scale objects.

  18. Sintering behavior of ultrafine silicon carbide powders obtained by vapor phase reaction

    NASA Technical Reports Server (NTRS)

    Okabe, Y.; Miyachi, K.; Hojo, J.; Kato, A.

    1984-01-01

    The sintering behavior of ultrafine SiC powder with average particle size of about 0.01-0.06 microns produced by a vapor phase reaction of the Me4Si-H2 system was studied at the temperature range of 1400-2050 deg. It was found that the homogeneous dispersion of C on SiC particles is important to remove the surface oxide layer effectively. B and C and inhibitive effect on SiC grain growth.

  19. The utilization of microwave heating for the fabrication of sintered reaction-bonded silicon nitride

    SciTech Connect

    Kiggans, J.O.; Tiegs, T.N.; Lin, H.T.; Holcombe, C.E.

    1995-12-31

    The results of studies in which microwave heating was used to fabricate sintered reaction-bonded silicon nitride (SRBSN) are reviewed. These results are compared to parallel studies where conventional heating was used for the fabrication of these materials. Microwave fabrication of SRBSN involves a single heating cycle, whereas conventional processing requires two separate furnace runs and sample packaging steps. SRBSN containing high levels of sintering aids which were fabricated by microwave heating showed improved strength and toughness, as compared to those materials fabricated using a conventional resistance-heated furnace. An analysis of the microstructures of the microwave fabricated materials showed enhanced acicular grain growth as compared to conventionally heated material. Results are presented on studies involving the scale-up of the microwave fabrication process.

  20. Gelcasting of silicon preforms for the production of sintered reaction-bonded silicon nitride

    SciTech Connect

    Kiggans, J.O. Jr.; Nunn, S.D.; Tiegs, T.N.; Davisson, C.C.; Coffey, D.W.; Maria, J.P.

    1995-12-31

    Gelcasting of silicon metal for the production of sintered reaction-bonded silicon nitride (SRBSN) was investigated in order to identify associated advantages over conventional forming techniques, i.e., die and isostatic pressing. Compacts were formed from identical powder mixtures by both gelcasting and pressing, and were nitrided and sintered to produce SRBSN ceramics using both conventional and microwave heating. Characterization of the samples included measurement of green density, green and nitrided pore structure, weight gain during nitridation, final density, microstructure, toughness, and flexural strength. It was found that a more uniform pore structure existed in the green gelcast samples. It is believed that this pore configuration aided in nitridation, and manifested itself in a more uniform final microstructure. In addition, improved mechanical properties were achieved in the gelcast samples. This improvement can be attributed to green microstructure homogeneity. An additional finding of this study was that microwave hearing combined with gelcast forming resulted in SRBSN materials with improved mechanical properties.

  1. Effect of composition on the processing and properties of sintered reaction-bonded silicon nitride

    SciTech Connect

    Tiegs, T.N.; Kiggans, J.O.; Montgomery, F.C.; Lin, H.T.; Barker, D.L.; Snodgrass, J.D.; Sabolsky, E.M.; Coffey, D.W.

    1996-04-01

    The type of silicon powder and sintering additive were found to influence the processing and final mechanical properties of sintered reaction bonded silicon nitride. High purity silicon powders produced low {alpha}-Si{sub 3}N{sub 4} content during nitridation. The Si powder type had no apparent effect on densification. More complete nitridation and higher room temperature mechanical properties were observed for the Si powders with higher Fe contents. However, the higher Fe contents resulted in greater high temperature strength degradation and so there was better high temperature strength retention with the higher purity Si. High {alpha}-Si{sub 3}N{sub 4} contents were found after nitridation with {alpha}-Si{sub 3}N{sub 4} seeded materials and with MgO-Y{sub 2}O{sub 3} as the sintering additive. Densification was inhibited by refractory additives, such as Y{sub 2}O{sub 3}-SiO{sub 2}. The highest room temperature strength and fracture toughness values correlated to high nitrided {alpha}-Si{sub 3}N{sub 4} contents. The high temperature strength behavior was similar for all additive types.

  2. Improved reaction sintered silicon nitride. [protective coatings to improve oxidation resistance

    NASA Technical Reports Server (NTRS)

    Baumgartner, H. R.

    1978-01-01

    Processing treatments were applied to as-nitrided reaction sintered silicon nitride (RSSN) with the purposes of improving strength after processing to above 350 MN/m2 and improving strength after oxidation exposure. The experimental approaches are divided into three broad classifications: sintering of surface-applied powders; impregnation of solution followed by further thermal processing; and infiltration of molten silicon and subsequent carburization or nitridation of the silicon. The impregnation of RSSN with solutions of aluminum nitrate and zirconyl chloride, followed by heating at 1400-1500 C in a nitrogen atmosphere containing silicon monoxide, improved RSSN strength and oxidation resistance. The room temperature bend strength of RSSN was increased nearly fifty percent above the untreated strength with mean absolute strengths up to 420 MN/m2. Strengths of treated samples that were measured after a 12 hour oxidation exposure in air were up to 90 percent of the original as-nitrided strength, as compared to retained strengths in the range of 35 to 60 percent for untreated RSSN after the same oxidation exposure.

  3. Improvement of physicomechanical and chemical propeties of reaction-sintered silicon carbide ceramics

    SciTech Connect

    Dzyadykevich, Yu.V.; Bochar, I.I.

    1994-10-01

    Sic-based materials are currently used in a number of industrial applications because of their high-temperature strength, high Young`s modulus and hardness, low specific weight and thermal expansion, and high wear and erosion resistance. The self-bonded silicon carbide obtained by reaction sintering (RSSC) is one of the most generally employed ceramic materials. It is a nearly pore-free two-phase composite containing 80-90% silicon carbide and 5 - 20% free silicon. For more severe operating conditions, improvement of the traditional methods of manufacturing SiC articles and development of new ones are required. To date, several approaches to the problem have been proposed.

  4. Controlled metal-semiconductor sintering/alloying by one-directional reverse illumination

    DOEpatents

    Sopori, Bhushan L.

    1993-01-01

    Metal strips deposited on a top surface of a semiconductor substrate are sintered at one temperature simultaneously with alloying a metal layer on the bottom surface at a second, higher temperature. This simultaneous sintering of metal strips and alloying a metal layer on opposite surfaces of the substrate at different temperatures is accomplished by directing infrared radiation through the top surface to the interface of the bottom surface with the metal layer where the radiation is absorbed to create a primary hot zone with a temperature high enough to melt and alloy the metal layer with the bottom surface of the substrate. Secondary heat effects, including heat conducted through the substrate from the primary hot zone and heat created by infrared radiation reflected from the metal layer to the metal strips, as well as heat created from some primary absorption by the metal strips, combine to create secondary hot zones at the interfaces of the metal strips with the top surface of the substrate. These secondary hot zones are not as hot as the primary hot zone, but they are hot enough to sinter the metal strips to the substrate.

  5. Controlling Directed Self-Assembly and Sintering of Gold Nanorods in Patterned Block Copolymer Thin Films

    NASA Astrophysics Data System (ADS)

    Lai, Fengyuan

    As the miniaturization of electronic devices continues, proper thermal management is crucial to ensure the optimum performance and reliability of such devices within their specification. Of primary interest are the so-called thermal interface materials to minimize the thermal resistance between the heat source and the heat sink. To this end, polymer nanocomposites composed of a polymer matrix and nanoscale fillers with high thermal conductivity have attracted tremendous attention. It has been demonstrated that the formation of a nanoparticle assembly inside the polymer matrix provides a continuous pathway for efficient heat transfer, and thus it is essential for achieving high thermal conductivity. In this work, we explored the ability to direct the self-assembly of gold nanorods (AuNRs) via patterned block copolymer (BCP) thin films. Selective sequestration of AuNRs with various aspect ratios in one block domain was achieved, with over 30% of the surface covered by an ordered AuNR assembly orienting parallel to the geometric confinement. The final nanostructure resulting from the directed self-assembly process is determined by the competition between thermodynamic consideration and kinetic factors. The coalescence and sintering of the AuNR assembly was accomplished by both furnace thermal annealing and rapid thermal annealing at low temperatures. The mechanism through which efficient sintering occurred is investigated with scanning electron microscopy. It is found that the sintering process initially takes place locally, resulting in small AuNR aggregates. Eventually the aggregates grow into a globally continuous, percolating network structure. In addition, the overall heat transfer coefficient was measured in an environmental scanning electron microscope by following droplet growth over time. The present study opens up new opportunities to accomplish controlled assembly of nanoparticles with high concentration for different nanorod-based applications as well as

  6. Enhancement of thermal shock resistance of reaction sintered mullite–zirconia composites in the presence of lanthanum oxide

    SciTech Connect

    Kumar, P.; Nath, M.; Ghosh, A.; Tripathi, H.S.

    2015-03-15

    Mullite–zirconia composites containing 20 wt.% zirconia were prepared by reaction sintering of zircon flour, sillimanite beach sand and calcined alumina. 0 to 8 mol% of La{sub 2}O{sub 3} with respect to zirconia was used as sintering aid. The effect of additive on the various physical, microstructures, mechanical and thermo-mechanical properties was studied. Quantitative phase analysis shows the change in tetragonal zirconia content with incorporation of lanthanum oxide. La{sub 2}O{sub 3} addition has significantly improved the thermal shock resistance of the samples. Samples without additive retained only 20% of initial flexural strength after 5 cycles, whereas samples containing 5 mol% La{sub 2}O{sub 3} retained almost 78% of its initial flexural strength even after 15 thermal shock cycles. - Highlights: • Mullite–zirconia composites were prepared by reaction sintering route utilizing zircon and sillimanite beach sand. • Lanthanum oxide was used as sintering aid. • The presence of lanthanum oxide decreased the densification temperature. • Lanthanum oxide significantly improved the thermal shock resistance of the composites.

  7. Direct Selective Laser Sintering/Melting of High Density Alumina Powder Layers at Elevated Temperatures

    NASA Astrophysics Data System (ADS)

    Deckers, J.; Meyers, S.; Kruth, J. P.; Vleugels, J.

    Direct selective laser sintering (SLS) or selective laser melting (SLM) are additive manufacturing techniques that can be used to produce three-dimensional ceramic parts directly, without the need for a sacrificial binder. In this paper, a low laser energy density is applied to SLS/SLM high density powder layers of sub-micrometer alumina at elevated temperatures (up to 800̊C). In order to achieve this, a furnace was designed and built into a commercial SLS machine. This furnace was able to produce a homogeneously heated cylindrical zone with a height of 60 mm and a diameter of 32 mm. After optimizing the layer deposition and laser scanning parameters, two ceramic parts with a density up to 85% and grain sizes as low as 5 μm were successfully produced.

  8. Direct selective laser sintering of high performance metals: Machine design, process development and process control

    NASA Astrophysics Data System (ADS)

    Das, Suman

    1998-11-01

    This dissertation describes the development of an advanced manufacturing technology known as Direct Selective Laser Sintering (Direct SLS). Direct SLS is a laser based rapid manufacturing technology that enables production of functional, fully dense, metal and cermet components via the direct, layerwise consolidation of constituent powders. Specifically, this dissertation focuses on a new, hybrid net shape manufacturing technique known as Selective Laser Sintering/Hot Isostatic Pressing (SLS/HIP). The objective of research presented in this dissertation was to establish the fundamental machine technology and processing science to enable direct SLS fabrication of metal components composed of high performance, high temperature metals and alloys. Several processing requirements differentiate direct SLS of metals from SLS of polymers or polymer coated powders. Perhaps the most important distinguishing characteristic is the regime of high temperatures involved in direct SLS of metals. Biasing the temperature of the feedstock powder via radiant preheat prior to and during SLS processing was shown to be beneficial. Preheating the powder significantly influenced the flow and wetting characteristics of the melt. During this work, it was conclusively established that powder cleanliness is of paramount importance for successful layerwise consolidation of metal powders by direct SLS. Sequential trials were conducted to establish optimal bake-out and degas cycles under high vacuum. These cycles agreed well with established practices in the powder metallurgy industry. A study of some of the important transport mechanisms in direct SLS of metals was undertaken to obtain a fundamental understanding of the underlying process physics. This study not only provides an explanation of phenomena observed during SLS processing of a variety of metallic materials but also helps in developing selection schemes for those materials that are most amenable to direct SLS processing. The

  9. High temperature characterization of reaction sintered SiC based materials

    NASA Astrophysics Data System (ADS)

    Lee, S. P.; Jin, J. O.; Park, J. S.; Kohyama, A.; Katoh, Y.; Yoon, H. K.; Bae, D. S.; Kim, I. S.

    2004-08-01

    Monolithic SiC and SiC f/SiC composite materials have been fabricated by a reaction sintering process. The mechanical properties of RS-SiC f/SiC composites reinforced with Hi-Nicalon SiC fiber have been investigated at elevated temperatures, in conjunction with a detailed analysis of their microstructures. The effect of heat treatment on the microstructure and strength of RS-SiC material was also examined. The characterization of RS-SiC based materials was evaluated by means of SEM, EDS and three point bend test. The RS-SiC material showed an average density of 3.0 Mg/cm 3 and an average strength of about 550 MPa. However, the strength of RS-SiC material decreased with increasing heat treatment times. The RS-SiC f/SiC composite also experienced a reduction of room temperature strength at a test temperature of 1300 °C, owing to the creation of internal defects such as matrix oxidation, interfacial debonding and fiber degradation.

  10. Efficient processing of reaction-sintered silicon carbide by anodically oxidation-assisted polishing

    NASA Astrophysics Data System (ADS)

    Tu, Qunzhang; Shen, Xinmin; Zhou, Jianzhao; He, Xiaohui; Yamamura, Kazuya

    2015-10-01

    Reaction-sintered silicon carbide (RS-SiC) is a promising optical material for the space telescope systems. Anodically oxidation-assisted polishing is a method to machine RS-SiC. The electrolyte used in this study is a mixture of hydrogen peroxide (H2O2) and hydrochloric acid (HCl), and the oxidation potential has two modes: constant potential and high-frequency-square-wave potential. Oxide morphologies are compared by scanning electron microscope/energy dispersive x-ray spectroscopy and scanning white-light interferometer. The results indicate that anodic oxidation under constant potential can not only obtain a relatively smooth surface but also be propitious to obtain high material removal rate. The oxidation depth in anodic oxidation under constant potential is calculated by comparing surface morphologies before and after hydrofluoric acid etching. The theoretical oxidation rate is 5.3 nm/s based on the linear Deal-Grove model. Polishing of the oxidized RS-SiC is conducted to validate the machinability of the oxide layer. The obtained surface roughness root-mean-square is around 4.5 nm. Thus, anodically oxidation-assisted polishing can be considered as an efficient method, which can fill the performance gap between the rough figuring and fine finishing of RS-SiC. It can improve the machining quality of RS-SiC parts and promote the application of RS-SiC products.

  11. Interface reaction of optical glass fiber sintered with low-temperature sealing glass

    NASA Astrophysics Data System (ADS)

    Xu, Bo; Liu, Guoying; Zu, Chengkui; Gao, Xiping; Han, Bin; Zhu, Baojing; Yin, Xianyin

    2014-12-01

    Low-temperature sealing glass (320-380°C) can be applied to the hermetic package of optical fiber devices, without the need of metallization. This paper introduced a PbO-ZnO-B2O3-F system low-temperature glass composite which has an softening point as low as 246°C and expansion coefficient of 8.0 ppm/°C. The glass composite was sealed with quartz glass fibers at 360-390°C, then the effect of sintering temperature and holding time on the surface reaction were well investigated. Although the mismatch of expansion coefficient exists within glass fiber, negative expansion filler and parent glass, they combined well with each other after a short time heating. The F- in glass network helped to lower the sealing temperature, wet the oxide surface and promote the combination of parent glass and fibers. The sealing temperature and holding time affect the interface layer and the shape of the fiber. The optimum packaging process should be sealing composite glass and fibers beneath 380°C with shortened holding time as possible. Using glazed glass composite preforms, sealing fiber in a ferrule to achieve compressed package will be helpful to realize hermetic package for optical fiber devices.

  12. Nondestructive Evaluation of the J-2X Direct Metal Laser Sintered Gas Generator Discharge Duct

    NASA Technical Reports Server (NTRS)

    Esther, Elizabeth A.; Beshears, Ronald D.; Lash, Rhonda K.

    2012-01-01

    The J-2X program at NASA's Marshall Space Flight Center (MSFC) procured a direct metal laser sintered (DMLS) gas generator discharge duct from Pratt & Whitney Rocketdyne and Morris Technologies for a test program that would evaluate the material properties and durability of the duct in an engine-like environment. DMLS technology was pursued as a manufacturing alternative to traditional techniques, which used off nominal practices to manufacture the gas generator duct's 180 degree turn geometry. MSFC's Nondestructive Evaluation (NDE) Team performed radiographic, ultrasonic, computed tomographic, and fluorescent penetrant examinations of the duct. Results from the NDE examinations reveal some shallow porosity but no major defects in the as-manufactured material. NDE examinations were also performed after hot-fire testing the gas generator duct and yielded similar results pre and post-test and showed no flaw growth or development.

  13. Interfacial reactions and wetting in Al-Mg sintered by powder metallurgy process

    NASA Astrophysics Data System (ADS)

    Faisal, Heny; Darminto, Triwikantoro, Zainuri, M.

    2016-04-01

    Was conducted to analyze the effect of temperature variation on the bonding interface sintered composite Al-Mg and analyze the effect of variations of the density and hardness sinter. Research carried out by the base material powders of Al, Mg powder and solvent n-butanol. The method used in this study is a powder metallurgy, with a composition of 60% volume fraction of Al - 40% Mg. Al-Mg mixing with n-butanol for 1 hour at 500 rpm. Then the emphasis (cold comression) with a size of 1.4 cm in diameter dies and height of 2.8 cm, is pressed with a force of 20 MPa and held for 15 minutes. After the sample into pellets, then sintered at various temperatures 300 °C, 350 °C, 400 °C and 450 °C. Characterization is done by using the testing green density, sintered density, X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), vickers microhardness, and press test. XRD data analysis done by using X'Pert High Score Plus (HSP) to determine whether there is a new phase is formed. Test results show that the sintered density increasing sintering temperature, the resulting density is also increasing (shrinkage). However, at a temperature of 450 °C decreased (swelling). With the increased sinter density, interfacial bonding getting Kuta and more compact so that its hardness is also increased. From the test results of SEM / EDX, there Mg into Al in the border area. At temperatures of 300 °C, 350 °C, 400 °C, the phase formed is Al, Mg and MgO. While phase is formed at a temperature of 450 °C is aluminum magnesium (Al3Mg2), Aluminum Magnesium Zinc (AlMg2Zn).

  14. Reaction engineering in direct coal liquefaction

    NASA Astrophysics Data System (ADS)

    Shah, Y. T.

    Processes for direct coal liquefaction by solvent extraction are considered along with the structure and properties of coal and the mechanism of coal liquefaction, heteroatom removal during liquefaction, kinetic models for donor-solvent coal liquefaction, the design of coal liquefaction reactors, and the refining of coal liquids. Attention is given to the catalytic hydrogenation of coal in the presence of a solvent, the origin and character of coal, laboratory reactors for rate measurements, reaction networks based on lumped fractions, free-radical reaction models, reactor types, the compatibility of coal-derived liquids and petroleum fuels, the stability of coal liquids, thermal cracking, catalytic hydrotreating, catalytic cracking, and catalytic reforming.

  15. Densification of Reaction Bonded Silicon Nitride with the Addition of Fine Si Powder Effects on the Sinterability and Mechanical Properties

    SciTech Connect

    Lee, Sea-Hoon; Cho, Chun-Rae; Park, Young-Jo; Ko, Jae-Woong; Kim, Hai-Doo; Lin, Hua-Tay; Becher, Paul F

    2013-01-01

    The densification behavior and strength of sintered reaction bonded silicon nitrides (SRBSN) that contain Lu2O3-SiO2 additives were improved by the addition of fine Si powder. Dense specimens (relative density: 99.5%) were obtained by gas-pressure sintering (GPS) at 1850oC through the addition of fine Si. In contrast, the densification of conventional specimens did not complete at 1950oC. The fine Si decreased the onset temperature of shrinkage and increased the shrinkage rate because the additive helped the compaction of green bodies and induced the formation of fine Si3N4 particles after nitridation and sintering at and above 1600oC. The amount of residual SiO2 within the specimens was not strongly affected by adding fine Si powder because most of the SiO2 layer that had formed on the fine Si particles decomposed during nitridation. The maximum strength and fracture toughness of the specimens were 991 MPa and 8.0 MPa m1/2, respectively.

  16. Direct Reactions with MoNA-LISA

    NASA Astrophysics Data System (ADS)

    Kuchera, Anthony

    2016-03-01

    Nuclear reactions can be used to probe the structure of nuclei. Direct reactions, which take place on short time scales, are well-suited for experiments with beams of short-lived nuclei. One such reaction is nucleon knockout where a proton or neutron is removed from the incoming beam from the interaction with a target. Single nucleon knockout reactions have been used to study the single-particle nature of nuclear wave functions. A recent experiment at the National Superconducting Cyclotron Laboratory was performed to measure cross sections from single nucleon knockout reactions for several p-shell nuclei. Detection of the residual nucleus in coincidence with any gamma rays emitted from the target allowed cross sections to ground and excited states to be measured. Together with input from reaction theory, ab initio structure theories can be tested. Simultaneously the accuracy of knockout reaction models can be validated by detecting the knocked out neutron with the Modular Neutron Array and Large multi-Institutional Scintillator Array (MoNA-LISA). Preliminary results from this experiment will be shown. Knockout reactions can also be used to populate nuclei which are neutron unbound, thus emit neutrons nearly instantaneously. The structure of these nuclei, therefore, cannot be probed with gamma ray spectroscopy. However, with large neutron detectors like MoNA-LISA the properties of these short-lived nuclei are able to be measured. Recent results using MoNA-LISA to study the structure of neutron-rich nuclei will be presented. The author would like to acknowledge support from the NNSA and NSF.

  17. The effect of preparation conditions on the structure and mechanical properties of reaction-sintered silicon nitride

    NASA Technical Reports Server (NTRS)

    Heinrich, J.

    1980-01-01

    The microstructure of reaction sintered silicon nitride (RSSN) was changed over a wide range by varying the grain density, grain size of the silicon starting powder, nitriding conditions, and by introducing artificial pores. The influence of single microstructural parameters on mechanical properties like room temperature strength, creep behavior, and resistance to thermal shock was investigated. The essential factors influencing these properties were found to be total porosity, pore size distribution, and the fractions of alpha and beta Si3N4. In view of high temperature engineering applications of RSSN, potentials for optimizing the material's properties by controlled processing are discussed.

  18. Direct Metal Laser Sintering Titanium Dental Implants: A Review of the Current Literature

    PubMed Central

    Mangano, F.; Chambrone, L.; van Noort, R.; Miller, C.; Hatton, P.; Mangano, C.

    2014-01-01

    Statement of Problem. Direct metal laser sintering (DMLS) is a technology that allows fabrication of complex-shaped objects from powder-based materials, according to a three-dimensional (3D) computer model. With DMLS, it is possible to fabricate titanium dental implants with an inherently porous surface, a key property required of implantation devices. Objective. The aim of this review was to evaluate the evidence for the reliability of DMLS titanium dental implants and their clinical and histologic/histomorphometric outcomes, as well as their mechanical properties. Materials and Methods. Electronic database searches were performed. Inclusion criteria were clinical and radiographic studies, histologic/histomorphometric studies in humans and animals, mechanical evaluations, and in vitro cell culture studies on DMLS titanium implants. Meta-analysis could be performed only for randomized controlled trials (RCTs); to evaluate the methodological quality of observational human studies, the Newcastle-Ottawa scale (NOS) was used. Results. Twenty-seven studies were included in this review. No RCTs were found, and meta-analysis could not be performed. The outcomes of observational human studies were assessed using the NOS: these studies showed medium methodological quality. Conclusions. Several studies have demonstrated the potential for the use of DMLS titanium implants. However, further studies that demonstrate the benefits of DMLS implants over conventional implants are needed. PMID:25525434

  19. Direct metal laser sintering titanium dental implants: a review of the current literature.

    PubMed

    Mangano, F; Chambrone, L; van Noort, R; Miller, C; Hatton, P; Mangano, C

    2014-01-01

    Statement of Problem. Direct metal laser sintering (DMLS) is a technology that allows fabrication of complex-shaped objects from powder-based materials, according to a three-dimensional (3D) computer model. With DMLS, it is possible to fabricate titanium dental implants with an inherently porous surface, a key property required of implantation devices. Objective. The aim of this review was to evaluate the evidence for the reliability of DMLS titanium dental implants and their clinical and histologic/histomorphometric outcomes, as well as their mechanical properties. Materials and Methods. Electronic database searches were performed. Inclusion criteria were clinical and radiographic studies, histologic/histomorphometric studies in humans and animals, mechanical evaluations, and in vitro cell culture studies on DMLS titanium implants. Meta-analysis could be performed only for randomized controlled trials (RCTs); to evaluate the methodological quality of observational human studies, the Newcastle-Ottawa scale (NOS) was used. Results. Twenty-seven studies were included in this review. No RCTs were found, and meta-analysis could not be performed. The outcomes of observational human studies were assessed using the NOS: these studies showed medium methodological quality. Conclusions. Several studies have demonstrated the potential for the use of DMLS titanium implants. However, further studies that demonstrate the benefits of DMLS implants over conventional implants are needed. PMID:25525434

  20. In-Situ X-Ray Diffraction Observations of Low Temperature Ag-Nanoink Sintering and High Temperature Eutectic Reaction with Copper

    SciTech Connect

    Elmer, J. W.; Specht, Eliot D

    2012-01-01

    Nanoinks, which contain nm sized metallic particles suspended in an organic dispersant fluid, are finding numerous microelectronic applications. Nanoinks sinter at much lower temperatures than bulk metals due to their high surface area to volume ratio and small radius of curvature, which reduces their melting points significantly below their bulk values. The unusually low melting and sintering temperatures have unique potential for materials joining since their melting points increase dramatically after initial sintering. In this paper Ag nanoink is studied using in-situ synchrotron based x-ray diffraction to follow the kinetics of the initial sintering step by analysis of diffraction patterns, and to directly observe the high remelt temperature of sintered nanoinks. Ag nanoink is further explored as a possible eutectic bonding medium with copper by tracking phase transformations to high temperatures where melting occurs at the Ag-Cu eutectic temperature, demonstrating nanoinks as a viable eutectic bonding medium.

  1. Development of a statistically proven injection molding method for reaction bonded silicon nitride, sintering reaction bonded silicon nitride, and sintered silicon nitride

    NASA Astrophysics Data System (ADS)

    Steiner, Matthias

    A statistically proven, series injection molding technique for ceramic components was developed for the construction of engines and gas turbines. The flow behavior of silicon injection-molding materials was characterized and improved. Hot-isostatic-pressing reaction bonded silicon nitride (HIPRBSN) was developed. A nondestructive component evaluation method was developed. An injection molding line for HIPRBSN engine components precombustion chamber, flame spreader, and valve guide was developed. This line allows the production of small series for engine tests.

  2. Comparison of residual stresses in Inconel 718 simple parts made by electron beam melting and direct laser metal sintering

    DOE PAGESBeta

    Kolbus, Lindsay M.; Payzant, E. Andrew; Cornwell, Paris A.; Watkins, Thomas R.; Babu, Sudarsanam Suresh; Dehoff, Ryan R.; Duty, Chad E.; Lorenz, M.; Ovchinnikova, O. S.

    2015-01-10

    Residual stress profiles were mapped using neutron diffraction in two simple prism builds of Inconel 718: one fabricated with electron beam melting and the other with direct laser sintering. Spatially indexed stress-free cubes were obtained by EDM sectioning equivalent prisms of similar shape. The (311) interplanar spacing examined for the EDM sectioned sample was compared to the interplanar spacings calculated to fulfill force and moment balance. We have shown that Applying force and moment balance is a necessary supplement to the measurements for the stress-free cubes with respect to accurate stress calculations in additively manufactured components. Furthermore, our work hasmore » shown that residual stresses in electron beam melting parts are much smaller than that of direct laser metal sintering parts.« less

  3. Comparison of residual stresses in Inconel 718 simple parts made by electron beam melting and direct laser metal sintering

    SciTech Connect

    Kolbus, Lindsay M.; Payzant, E. Andrew; Cornwell, Paris A.; Watkins, Thomas R.; Babu, Sudarsanam Suresh; Dehoff, Ryan R.; Duty, Chad E.; Lorenz, M.; Ovchinnikova, O. S.

    2015-01-10

    Residual stress profiles were mapped using neutron diffraction in two simple prism builds of Inconel 718: one fabricated with electron beam melting and the other with direct laser sintering. Spatially indexed stress-free cubes were obtained by EDM sectioning equivalent prisms of similar shape. The (311) interplanar spacing examined for the EDM sectioned sample was compared to the interplanar spacings calculated to fulfill force and moment balance. We have shown that Applying force and moment balance is a necessary supplement to the measurements for the stress-free cubes with respect to accurate stress calculations in additively manufactured components. Furthermore, our work has shown that residual stresses in electron beam melting parts are much smaller than that of direct laser metal sintering parts.

  4. Comparison of Residual Stresses in Inconel 718 Simple Parts Made by Electron Beam Melting and Direct Laser Metal Sintering

    NASA Astrophysics Data System (ADS)

    Sochalski-Kolbus, L. M.; Payzant, E. A.; Cornwell, P. A.; Watkins, T. R.; Babu, S. S.; Dehoff, R. R.; Lorenz, M.; Ovchinnikova, O.; Duty, C.

    2015-03-01

    Residual stress profiles were mapped using neutron diffraction in two simple prism builds of Inconel 718: one fabricated with electron beam melting (EBM) and the other with direct laser metal sintering. Spatially indexed stress-free cubes were obtained by electrical discharge machining (EDM) equivalent prisms of similar shape. The (311) interplanar spacings from the EDM sectioned sample were compared to the interplanar spacings calculated to fulfill stress and moment balance. We have shown that applying stress and moment balance is a necessary supplement to the measurements for the stress-free cubes with respect to accurate stress calculations in additively manufactured components. In addition, our work has shown that residual stresses in electron beam melted parts are much smaller than that of direct laser metal sintered parts most likely due to the powder preheating step in the EBM process.

  5. Amyloplast Distribution Directs a Root Gravitropic Reaction

    NASA Astrophysics Data System (ADS)

    Kordyum, Elizabeth

    Immobile higher plants are oriented in the gravitational field due to gravitropim that is a physiological growth reaction and consists of three phases: reception of a gravitational signal by statocytes, its transduction to the elongation zone, and finally the organ bending. As it is known, roots are characterized with positive gravitropism, i. e. they grow in the direction of a gravitational vector, stems - with negative gravitropism, i. e. they grow in the direction opposite to a gravitational vector. According to the Nemec’s and Haberlandt’s starch-statolith hypothesis, amyloplasts in diameter of 1.5 - 3 μ in average, which appear to act as gravity sensors and fulfill a statolythic function in the specialized graviperceptive cells - statocytes, sediment in the direction of a gravitational vector in the distal part of a cell, while a nucleus is in the proximal one. There are reasonable data that confirm the amyloplasts-statoliths participation in gravity perception: 1) correlation between the statoliths localization and the site of gravity sensing, 2) significant redistribution (sedimentation) of amyloplasts in statocytes under gravistimulation in comparison with other cell organelles, 3) root decreased ability to react on gravity under starch removal from amyloplasts, 4) starchless Arabidopsis thaliana mutants are agravitropic, 5) amyloplasts-statoliths do not sediment in the absence of the gravitational vector and are in different parts or more concentrated in the center of statocytes. Plant tropisms have been intensively studied for many decades and continue to be investigated. Nevertheless, the mechanisms by which plants do so is still not clearly explained and many questions on gravisensing and graviresponse remain unanswered. Even accepted hypotheses are now being questioned and recent data are critically evaluated. Although the available data show the Ca2+ and cytoskeleton participation in graviperception and signal transduction, the clear evidence

  6. Amyloplast Distribution Directs a Root Gravitropic Reaction

    NASA Astrophysics Data System (ADS)

    Kordyum, Elizabeth

    Immobile higher plants are oriented in the gravitational field due to gravitropim that is a physiological growth reaction and consists of three phases: reception of a gravitational signal by statocytes, its transduction to the elongation zone, and finally the organ bending. As it is known, roots are characterized with positive gravitropism, i. e. they grow in the direction of a gravitational vector, stems - with negative gravitropism, i. e. they grow in the direction opposite to a gravitational vector. According to the Nemec’s and Haberlandt’s starch-statolith hypothesis, amyloplasts in diameter of 1.5 - 3 μ in average, which appear to act as gravity sensors and fulfill a statolythic function in the specialized graviperceptive cells - statocytes, sediment in the direction of a gravitational vector in the distal part of a cell, while a nucleus is in the proximal one. There are reasonable data that confirm the amyloplasts-statoliths participation in gravity perception: 1) correlation between the statoliths localization and the site of gravity sensing, 2) significant redistribution (sedimentation) of amyloplasts in statocytes under gravistimulation in comparison with other cell organelles, 3) root decreased ability to react on gravity under starch removal from amyloplasts, 4) starchless Arabidopsis thaliana mutants are agravitropic, 5) amyloplasts-statoliths do not sediment in the absence of the gravitational vector and are in different parts or more concentrated in the center of statocytes. Plant tropisms have been intensively studied for many decades and continue to be investigated. Nevertheless, the mechanisms by which plants do so is still not clearly explained and many questions on gravisensing and graviresponse remain unanswered. Even accepted hypotheses are now being questioned and recent data are critically evaluated. Although the available data show the Ca2+ and cytoskeleton participation in graviperception and signal transduction, the clear evidence

  7. First direct 3D visualisation of microstructural evolutions during sintering through X-ray computed microtomography

    SciTech Connect

    Bernard, Dominique . E-mail: bernard@icmcb.u-bordeaux.fr; Gendron, Damien; Heintz, Jean-Marc; Bordere, Sylvie; Etourneau, Jean

    2005-01-03

    X-ray computed microtomography (XCMT) has been applied to ceramic samples of different materials to visualise, for the first time at this scale, real 3D microstructural evolutions during sintering. Using this technique, it has been possible to follow the whole sintering process of the same grains set. Two materials have been studied; a glass powder heat treated at 700 deg. C and a crystallised lithium borate (Li{sub 6}Gd(BO{sub 3}){sub 3}) powder heat treated at 720 deg. C. XCMT measurements have been done after different sintering times. For each material, a sub-volume was individualised and localised on the successive recordings and its 3D images numerically reconstructed. Description of the three-dimensional microstructures evolution is proposed. From the 3D experimental data, quantitative evolutions of parameters such as porosity and neck size are presented for the glass sample. Possibilities offered by this technique to study complex sintering processes, as for lithium borate, are illustrated.

  8. Sintering in Laser Sintering

    NASA Astrophysics Data System (ADS)

    Bourell, David L.

    2016-03-01

    Laser sintering is a popular additive manufacturing technology, particularly for service parts. Invented by C. Deckard in the mid-1980s, the approach of using a laser to densify a powder bed selectively has been extensively researched and has been applied to metals, ceramics, polymers and composites. In the traditional powder-metallurgical sense, sintering involves solid-state atomic transport resulting in neck formation and eventual densification in a powder mass. The use of the term "sintering" as a descriptive term for the powder-bed additive manufacturing process has been problematical to the technical community, because the predominant densification mechanism has been shown for most applications to be melting and reflow. The term has perpetuated as a name for the additive manufacturing process, at least for polymers. The technical term "sintering" is accurately associated with laser sintering insofar as powder pre-processing and part post-processing are concerned. It may also be used to describe formation of "part cake". This paper describes the circumstances surrounding the coining of the term, "laser sintering" and provides some examples of how sintering is used in pre- and post-processing.

  9. Sintering of the reaction products of combustion of alloys in nitrogen

    SciTech Connect

    Maksimov, Y.M.; Raskolenko, L.G.; Zepakova, O.K.; Ziatdinov, M.K.

    1986-05-01

    An investigation of the mechanism of compacting of Fe-V alloy with a sigma-phase structure, a low porosity composite material consisting of alpha-iron and a filler of delta-vanadium nitride, is made after the synthesis surge. Alloys containing 50 wt.% Fe were prepared by sintering in a vacuum furnace of powders of type VEL-1 vandium and special purity carbonyl iron. The mechanism of compacting was studied on specimens in hardened water. Metallographic investigations were made on MIM-7 and PMT-3 instruments and the phase analysis on a DRON-2 instrument. Rapid compacting in combustion of sigma-FeV in nitrogen is determined by combining of the solid-liquid drops formed in the combustion front and consisting of molten iron and vanadium nitrides.

  10. Studies on the scale-up of the microwave-assisted nitridation and sintering of reaction-bonded silicon nitride

    SciTech Connect

    Kiggans, J.O.: Tiegs, T.N.; Kimrey, H.D.

    1996-05-01

    Studies using laboratory test samples have shown that microwave heating produces sintered reaction-bonded silicon nitride materials with improved properties. The final challenge for processing this material by microwave heating is the development of a technology for processing larger batch-size quantities of these materials. Initial microwave scale-up experiments were performed using powder compacts of a bucket tappet geometry. In experiments using microwave-transparent boron nitride sample crucibles, temperature gradients within some crucibles led to larger variations in the sample densities than were obtained with the conventionally processed samples. The use of a microwave-suscepter type crucible made of silicon carbide and boron nitride resulted in an improved temperature uniformity and in density variations comparable to those obtained for the control groups.

  11. Development of Continuous, Direct Feedback Control Systems for Sintering of Metallic Components

    SciTech Connect

    Diran Apelian; Marc M. Baum

    2006-09-18

    N,N.-Ethylenebisstearimide (EBS) is one of the most commonlyused lubricants in the powder metallurgy (PM) industry in the sintering process. During sintering, the lubricated powder compacts are heat-treated to temperatures in excess of 1,200 °C thus fusing adjacent particles and yielding a part with improved mechanical strength. Delubrication commonly is achieved in the first zone of a sintering furnace by heating the part to temperatures in the 500-600 °C temperature range at a fixed rate and under controlled atmospheric conditions; this strategy minimizes defects, carbon contamination, and compact deformation. The de-lubricated part then enters the second zone (commonly in the 1200-1300 °C temperature range) for sintering. The third zone cools the sintered part at a desired rate to obtain the requisite micro-structural properties. Controlled delubrication is imperative towards achieving high quality parts for the following reasons: the elevated thermal gradient at the transition between the first and second zones can cause parts to expand rapidly and develop microscopic fissures (.blistering.); improper gas flows and belt speeds can lead to carbon deposition on the part and at the grain boundaries (sooting); delubrication products deposit throughout the furnace, even in the coolers, which are far removed from the preheating chamber, leading to significant maintenance costs; pollutants emitted in the exhaust stream of furnaces operating inefficiently are increasingly of environmental concern. In practice, lubricant removal is difficult to control, which often leads to reduced yields in PM manufacturing processes. Throughput is another important issue: process control ideally should lead to a delubrication cycle that yields defect-free parts in a minimum of furnace time, thereby increasing productivity and reducing the net energy consumption. Efficient process control requires rapid monitoring of suitable indicators, preferably gasphase products of delubrication

  12. Microwave Nitridation of Sintered Reaction Bonded Silicon Parts for Natural Gas Fueled Diesel Engines

    SciTech Connect

    Edler, J.; Kiggans, J.O.; Suman, A.W.; Tiegs, T.N.

    1999-01-01

    This cooperative project was a joint development program between Eaton Corporation and Lockheed Martin Energy Research (LMER). Cooperative work was of benefit to both parties. ORNL was able to assess up-scale of the microwave nitridation process using a more intricate-shaped part designed for application in advanced diesel engines. Eaton Corporation mined access to microwave facilities and expertise for the nitridation of SRBSN materials. The broad objective of the CRADA established with Eaton Corporation and ORNL was to develop cost-effective silicon nitride ceramics compared to the current materials available. The following conclusions can be made from the work performed under the CRADA: (1) Demonstrated that the binder burnout step can be incorporated into the SRBSN processing in the microwave furnace. (2) Scale-up of the microwave nitridation process using Eaton Corporation parts showed that the nitridation weight gains were essentially identical to those obtained by conventional heating. (3) Combined nitridation and sintering processes using silicon nitride beads as packing powders results in degradation of the mechanical properties. (4) Gelcasting of silicon nitride materials using Eaton Si mixtures was demonstrated.

  13. Apparatus and method for direct measurement of coal ash sintering and fusion properties at elevated temperatures and pressures

    DOEpatents

    Khan, M. Rashid

    1990-01-01

    A high-pressure microdilatometer is provided for measuring the sintering and fusion properties of various coal ashes under the influence of elevated pressures and temperatures in various atmospheres. Electrical resistivity measurements across a sample of coal ash provide a measurement of the onset of the sintering and fusion of the ash particulates while the contraction of the sample during sintering is measured with a linear variable displacement transducer for detecting the initiation of sintering. These measurements of sintering in coal ash at different pressures provide a mechanism by which deleterious problems due to the sintering and fusion of ash in various combustion systems can be minimized or obviated.

  14. Microstructural characterization of silicon nitride ceramics processed by pressureless sintering, overpressure sintering, and sinter/HIP

    SciTech Connect

    Selkregg, K.R. ); More, K.L.; Seshadri, S.G.; McMurtry, C.H. )

    1990-01-01

    Silicon nitride ceramics of the same nominal sialon composition have been sintered under different conditions including atmospheric sintering, overpressure sintering, reaction bonded (nitrided pressureless sinter) and sinter/HIP cycles. The sintered ceramics, which exhibited dramatic differences in fracture toughness, have been characterized by x-ray diffraction, scanning electron microscopy, analytical transmission electron microscopy, and image analysis techniques. Fracture toughness data have been correlated to the microstructural and chemical analysis of the grain boundary phases. The microstructure was the strongest influencing factor on the observed fracture toughness difference. 5 refs., 5 tabs.

  15. Droplet heat transfer and chemical reactions during direct containment heating

    SciTech Connect

    Baker, L. Jr.

    1986-01-01

    A simplified model of heat transfer and chemical reaction has been adapted to evaluate the expected behavior of droplets containing unreacted Zircaloy and stainless steel moving through the containment atmosphere during postulated accidents involving direct containment heating. The model includes internal and external diffusive resistances to reaction. The results indicate that reactions will be incomplete for many conditions characteristic of direct containment heating sequences.

  16. Statistical Description of Cluster Emission Including Direct Reactions

    SciTech Connect

    Betak, Emil

    2006-04-26

    The coalescence idea of the Iwamoto-Harada-Bisplinghoff model within the pre-equilibrium (exciton model) approach to nuclear reactions has been generalized and the links to direct reactions have been outlined.

  17. High-strength reaction-sintered SiC: a new candidate material for large spaceborne telescope systems

    NASA Astrophysics Data System (ADS)

    Yui, Yukari Y.; Kimura, Toshiyoshi; Tange, Yoshio

    2004-11-01

    The high-strength reaction-sintered silicon carbide (RS-SiC) developed and manufactured by Toshiba and NEC-Toshiba Space Systems, NT-SiC, is one of the most promising, excellent and feasible candidates for light-weighted large-diameter space-borne optics that are applied to geostationary earth observations and astronomical observations. Small NT-SiC sample mirrors were manufactured to study basic physical parameters and features, and optical performances of the material, such as the surface conditions of polished NT-SiC, the condition of inner crystal grains, the correlation between the surface roughness and polishing, scattering characteristics, absorbance of solar light and infrared emissivity, and adhesiveness of metal coating. The current state of the art of the development of the NT-SiC mirror and the feasibility of light-weighted large-diameter NT-SiC mirrors for space-borne optics are described. Although technical challenges to achieve the surface roughness that is applicable to ultraviolet mirrors still remain, the optical performance and the physical properties of the present NT-SiC show that it is one of the most excellent mirror material in optical-infrared wavelength region.

  18. Development of energy-absorbing reaction-sintered Si3N4 surface layers on hot-pressed Si3N4

    NASA Technical Reports Server (NTRS)

    Brennan, J. J.

    1981-01-01

    Energy-absorbing Si3N4 surface layers on dense Si3N4 substrates were formed by in-place nitridation of fine-grained silicon powder. Ballistic impact tests performed on samples with 1-mm thick layers at room temperature and 1370 C showed up to an eightfold increase in the energy necessary to fracture the substrate. For maximum impact resistance, a small amount (about 20 vol %) of residual Si must be present in the reaction-sintered Si3N4 surface layer. Thermal cycling to 1370 C did not affect impact resistance, even though a considerable amount of SiO2 formed within the reaction-sintered Si3N4 layer during cycling. Erosion testing of samples in a Mach 0.8 burner rig at 1370 C resulted in minimal surface recession of the surface layer. Chemically vapor-deposited SiC-coated material similarly tested exhibited no surface recession.

  19. Effects of Sm2O3 Content on the Microstructure and Mechanical Properties of Post-Sintered Reaction-Bonded β-SiAlON

    NASA Astrophysics Data System (ADS)

    Li, Yanjun; Liu, Donghua; Zeng, Cunfeng; Shi, Zhongqi; Jin, Zhihao

    2016-03-01

    β-SiAlON materials were fabricated by a reaction bonding combining post-sintering route using raw materials of Si, Al2O3, AlN, etc. Sm2O3 was used as sintering additive with the content of 0, 2, 4, and 6 wt.%, respectively. The reaction-bonded β-SiAlON (RB-β-SiAlON) were post sintered at 1750 °C for 6 h. XRD results showed that the phase composition of both RB-β-SiAlON and post-sintered RB-β-SiAlON (PSRB-β-SiAlON) was β-SiAlON. For RB-β-SiAlON, the apparent porosity was decreased with the increase of Sm2O3 content, while the bending strength (σf) and Vicker's hardness (HV10) was increased accordingly. After the post-sintering procedure, nearly full densified PSRB-β-SiAlON was obtained and the mechanical properties were significantly improved with the addition of Sm2O3 additive. The σf and HV10 of the PSRB-β-SiAlON (4 wt.% Sm2O3) achieved 520 MPa and 16.4 GPa, respectively, which were as 3.5 and 6.3 times high as those of the corresponding RB-β-SiAlON. The Young's modulus (E) and the fracture toughness (K IC) of the dense PSRB-β-SiAlON were increased with the increase of the Sm2O3 content.

  20. Chemical Reactions Directed Peptide Self-Assembly

    PubMed Central

    Rasale, Dnyaneshwar B.; Das, Apurba K.

    2015-01-01

    Fabrication of self-assembled nanostructures is one of the important aspects in nanoscience and nanotechnology. The study of self-assembled soft materials remains an area of interest due to their potential applications in biomedicine. The versatile properties of soft materials can be tuned using a bottom up approach of small molecules. Peptide based self-assembly has significant impact in biology because of its unique features such as biocompatibility, straight peptide chain and the presence of different side chain functionality. These unique features explore peptides in various self-assembly process. In this review, we briefly introduce chemical reaction-mediated peptide self-assembly. Herein, we have emphasised enzymes, native chemical ligation and photochemical reactions in the exploration of peptide self-assembly. PMID:25984603

  1. Toward Direct Reaction-in-Flight Measurements

    NASA Astrophysics Data System (ADS)

    Wilhelmy, Jerry; Bredeweg, Todd; Fowler, Malcolm; Gooden, Matthew; Hayes, Anna; Rusev, Gencho; Caggiano, Joseph; Hatarik, Robert; Henry, Eugene; Tonchev, Anton; Yeaman, Charles; Bhike, Megha; Krishichayan, Krishi; Tornow, Werner

    2016-03-01

    At the National Ignition Facility (NIF) neutrons having energies greater than the equilibrium 14.1 MeV value can be produced via Reaction-in-Flight (RIF) interactions between plasma atoms and upscattered D or T ions. The yield and spectrum of these RIF produced neutrons carry information on the plasma properties as well as information on the stopping power of ions under plasma conditions. At NIF the yield of these RIF neutrons is predicted to be 4-7 orders of magnitude below the peak 14 MeV neutron yield. The current generation of neutron time of flight (nTOF) instrumentation has so far been incapable of detecting these low-yield neutrons primarily due to high photon backgrounds. To date, information on RIF neutrons has been obtained in integral activation experiments using reactions with high energy thresholds such as 169Tm(n,3n)167Tm and 209Bi(n,4n) 206Bi. Initial experiments to selectively suppress photon backgrounds have been performed at TUNL using pulsed monoenergetic neutron beams of 14.9, 18.5, 24.2, and 28.5 MeV impinging on a Bibenzyl scintillator. By placing 5 cm of Pb before the scintillator we were able to selectively suppress the photons from the flash occurring at the production target and enhance the n/_signal by ~6 times.

  2. Direct reactions for nuclear structure and nuclear astrophysics

    SciTech Connect

    Jones, Katherine Louise

    2014-12-18

    Direct reactions are powerful probes for studying the atomic nucleus. Modern direct reaction studies are illuminating both the fundamental nature of the nucleus and its role in nucleosynthetic processes occurring in the cosmos. This report covers experiments using knockout reactions on neutron-deficient fragmentation beams, transfer reactions on fission fragment beams, and theoretical sensitivity studies relating to the astrophysical r-process. Results from experiments on 108,106Sn at the NSCL, and on 131Sn at HRIBF are presented as well as the results from the nucleosynthesis study.

  3. Fusion and direct reactions for strongly and weakly bound projectiles

    NASA Astrophysics Data System (ADS)

    Hugi, M.; Lang, J.; Müller, R.; Ungricht, E.; Bodek, K.; Jarczyk, L.; Kamys, B.; Magiera, A.; Strzałkowski, A.; Willim, G.

    1981-09-01

    The interaction of 6Li, 9Be and 12C projectiles with a 28Si target was investigated by measuring the angular distributions of the elastically scattered projectiles and of the emitted protons, deuterons and α-particles. The experiment was performed in order to deduce direct and compound nucleus process contributions to the total reaction cross section and to study the influence of the projectile structure on the relative importance of these two mechanisms. Optical model parameters and therefore the total reaction cross section are strongly influenced by the binding energy of the projectile. The parameters of the Glas-Mosel model describing the fusion reaction vary smoothly with the atomic number. In the system 9Be + 28Si around 50% of all reactions are direct processes even at energies near the Coulomb barrier, whereas in the other systems the direct part amounts to 15 % ( 12C) and 30 % ( 6Li) only.

  4. Maxillary Overdentures Supported by Four Splinted Direct Metal Laser Sintering Implants: A 3-Year Prospective Clinical Study

    PubMed Central

    Mangano, Francesco; Shibli, Jamil Awad; Anil, Sukumaran

    2014-01-01

    Purpose. Nowadays, the advancements in direct metal laser sintering (DMLS) technology allow the fabrication of titanium dental implants. The aim of this study was to evaluate implant survival, complications, and peri-implant marginal bone loss of DMLS implants used to support bar-retained maxillary overdentures. Materials and Methods. Over a 2-year period, 120 implants were placed in the maxilla of 30 patients (18 males, 12 females) to support bar-retained maxillary overdentures (ODs). Each OD was supported by 4 implants splinted by a rigid cobalt-chrome bar. At each annual follow-up session, clinical and radiographic parameters were assessed. The outcome measures were implant failure, biological and prosthetic complications, and peri-implant marginal bone loss (distance between the implant shoulder and the first visible bone-to-implant contact, DIB). Results. The 3-year implant survival rate was 97.4% (implant-based) and 92.9% (patient-based). Three implants failed. The incidence of biological complication was 3.5% (implant-based) and 7.1% (patient-based). The incidence of prosthetic complication was 17.8% (patient-based). No detrimental effects on marginal bone level were evidenced. Conclusions. The use of 4 DMLS titanium implants to support bar-retained maxillary ODs seems to represent a safe and successful procedure. Long-term clinical studies on a larger sample of patients are needed to confirm these results. PMID:25580124

  5. Accuracy evaluation of metal copings fabricated by computer-aided milling and direct metal laser sintering systems

    PubMed Central

    Lee, Wan-Sun; Kim, Woong-Chul

    2015-01-01

    PURPOSE To assess the marginal and internal gaps of the copings fabricated by computer-aided milling and direct metal laser sintering (DMLS) systems in comparison to casting method. MATERIALS AND METHODS Ten metal copings were fabricated by casting, computer-aided milling, and DMLS. Seven mesiodistal and labiolingual positions were then measured, and each of these were divided into the categories; marginal gap (MG), cervical gap (CG), axial wall at internal gap (AG), and incisal edge at internal gap (IG). Evaluation was performed by a silicone replica technique. A digital microscope was used for measurement of silicone layer. Statistical analyses included one-way and repeated measure ANOVA to test the difference between the fabrication methods and categories of measured points (α=.05), respectively. RESULTS The mean gap differed significantly with fabrication methods (P<.001). Casting produced the narrowest gap in each of the four measured positions, whereas CG, AG, and IG proved narrower in computer-aided milling than in DMLS. Thus, with the exception of MG, all positions exhibited a significant difference between computer-aided milling and DMLS (P<.05). CONCLUSION Although the gap was found to vary with fabrication methods, the marginal and internal gaps of the copings fabricated by computer-aided milling and DMLS fell within the range of clinical acceptance (<120 µm). However, the statistically significant difference to conventional casting indicates that the gaps in computer-aided milling and DMLS fabricated restorations still need to be further reduced. PMID:25932310

  6. Fundamental studies of retrograde reactions in direct liquefaction

    SciTech Connect

    Serio, M.A.; Solomon, P.R.; Bassilakis, R.; Kroo, E.

    1989-01-01

    Most of the proposed processing schemes for improving liquefaction yields involve favoring bond-breaking and radical stabilization reactions over the retrograde reactions. The retrograde reactions are often encountered before liquefaction temperatures are reached. The objective of this program is to elucidate and model the retrograde reaction chemistry in direct coal liquefaction through the application of experimental techniques and theoretical models which have been successfully employed at Advanced Fuel Research (AFR) and SRI International (a subcontractor) to understand and predict coal reaction behavior. The study of retrograde reactions is being done using an integrated approach using extensive characterization of the liquefaction chemistry of three kinds of systems: (1) model polymers; (2) coal; and (3) modified coals.

  7. Recent Direct Reaction Experimental Studies with Radioactive Tin Beams

    SciTech Connect

    Jones, K. L.; Ahn, S.; Allmond, J. M.; Ayres, A.; Bardayan, D. W.; Baugher, T.; Bazin, D.; Berryman, J. S.; Bey, A.; Bingham, C.; Cartegni, L.; Cerizza, G.; Chae, K. Y.; Cizewski, J. A.; Gade, A.; Galindo-Uribarri, A.; Garcia-Ruiz, R. F.; Grzywacz, R.; Howard, M. E.; Kozub, R. L.; Liang, J. F.; Manning, B.; Matoš, M.; McDaniel, S.; Miller, D.; Nesaraja, C. D.; O'Malley, P. D.; Padgett, S.; Padilla-Rodal, E.; Pain, S. D.; Pittman, S. T.; Radford, D. C.; Ratkiewicz, A.; Schmitt, K. T.; Shore, A.; Smith, M. S.; Stracener, D. W.; Stroberg, S. R.; Tostevin, J.; Varner, R. L.; Weisshaar, D.; Wimmer, K.; Winkler, R.

    2015-01-01

    Direct reaction techniques are powerful tools to study the single-particle nature of nuclei. Performing direct reactions on short-lived nuclei requires radioactive ion beams produced either via fragmentation or the Isotope Separation OnLine (ISOL) method. Some of the most interesting regions to study with direct reactions are close to the magic numbers where changes in shell structure can be tracked. These changes can impact the final abundances of explosive nucleosynthesis. The structure of the chain of tin isotopes is strongly influenced by the Z = 50 proton shell closure, as well as the neutron shell closures lying in the neutron-rich, N = 82, and neutron-deficient, N = 50, regions. Here, we present two examples of direct reactions on exotic tin isotopes. The first uses a one-neutron transfer reaction and a low-energy reaccelerated ISOL beam to study states in Sn-131 from across the N = 82 shell closure. The second example utilizes a one-neutron knockout reaction on fragmentation beams of neutron-deficient Sn-106,108Sn. In conclusion, In both cases, measurements of γ rays in coincidence with charged particles proved to be invaluable.

  8. Recent Direct Reaction Experimental Studies with Radioactive Tin Beams

    DOE PAGESBeta

    Jones, K. L.; Ahn, S.; Allmond, J. M.; Ayres, A.; Bardayan, D. W.; Baugher, T.; Bazin, D.; Berryman, J. S.; Bey, A.; Bingham, C.; et al

    2015-01-01

    Direct reaction techniques are powerful tools to study the single-particle nature of nuclei. Performing direct reactions on short-lived nuclei requires radioactive ion beams produced either via fragmentation or the Isotope Separation OnLine (ISOL) method. Some of the most interesting regions to study with direct reactions are close to the magic numbers where changes in shell structure can be tracked. These changes can impact the final abundances of explosive nucleosynthesis. The structure of the chain of tin isotopes is strongly influenced by the Z = 50 proton shell closure, as well as the neutron shell closures lying in the neutron-rich, Nmore » = 82, and neutron-deficient, N = 50, regions. Here, we present two examples of direct reactions on exotic tin isotopes. The first uses a one-neutron transfer reaction and a low-energy reaccelerated ISOL beam to study states in Sn-131 from across the N = 82 shell closure. The second example utilizes a one-neutron knockout reaction on fragmentation beams of neutron-deficient Sn-106,108Sn. In conclusion, In both cases, measurements of γ rays in coincidence with charged particles proved to be invaluable.« less

  9. Summary of Liquid Oxygen/Hydrogen, Direct Metal Laser Sintering Injector Testing and Evaluation Effort at Marshall Space Flight Center

    NASA Technical Reports Server (NTRS)

    Barnett, Gregory; Bullard, David B.

    2015-01-01

    The last several years have witnessed a significant advancement in the area of additive manufacturing technology. One area that has seen substantial expansion in application has been laser sintering (or melting) in a powder bed. This technology is often termed 3D printing or various acronyms that may be industry, process, or company specific. Components manufactured via 3D printing have the potential to significantly reduce development and fabrication time and cost. The usefulness of 3D printed components is influenced by several factors such as material properties and surface roughness. This paper details three injectors that were designed, fabricated, and tested in order to evaluate the utility of 3D printed components for rocket engine applications. The three injectors were tested in a hot-fire environment with chamber pressures of approximately 1400 psia. One injector was a 28 element design printed by Directed Manufacturing. The other two injectors were identical 40 element designs printed by Directed Manufacturing and Solid Concepts. All the injectors were swirl-coaxial designs and were subscale versions of a full-scale injector currently in fabrication. The test and evaluation programs for the 28 element and 40 element injectors provided a substantial amount of data that confirms the feasibility of 3D printed parts for future applications. The operating conditions of previously tested, conventionally manufactured injectors were reproduced in the 28 and 40 element programs in order to contrast the performance of each. Overall, the 3D printed injectors demonstrated comparable performance to the conventionally manufactured units. The design features of the aforementioned injectors can readily be implemented in future applications with a high degree of confidence.

  10. Protease-catalysed Direct Asymmetric Mannich Reaction in Organic Solvent

    NASA Astrophysics Data System (ADS)

    Xue, Yang; Li, Ling-Po; He, Yan-Hong; Guan, Zhi

    2012-10-01

    We reported the first enzyme-catalysed, direct, three-component asymmetric Mannich reaction using protease type XIV from Streptomyces griseus (SGP) in acetonitrile. Yields of up to 92% with enantioselectivities of up to 88% e.e. and diastereoselectivities of up to 92:8 (syn:anti) were achieved under the optimised conditions. This enzyme's catalytic promiscuity expands the application of this biocatalyst and provides a potential alternative method for asymmetric Mannich reactions.

  11. Protease-catalysed direct asymmetric Mannich reaction in organic solvent.

    PubMed

    Xue, Yang; Li, Ling-Po; He, Yan-Hong; Guan, Zhi

    2012-01-01

    We reported the first enzyme-catalysed, direct, three-component asymmetric Mannich reaction using protease type XIV from Streptomyces griseus (SGP) in acetonitrile. Yields of up to 92% with enantioselectivities of up to 88% e.e. and diastereoselectivities of up to 92:8 (syn:anti) were achieved under the optimised conditions. This enzyme's catalytic promiscuity expands the application of this biocatalyst and provides a potential alternative method for asymmetric Mannich reactions. PMID:23094136

  12. Protease-catalysed Direct Asymmetric Mannich Reaction in Organic Solvent

    PubMed Central

    Xue, Yang; Li, Ling-Po; He, Yan-Hong; Guan, Zhi

    2012-01-01

    We reported the first enzyme-catalysed, direct, three-component asymmetric Mannich reaction using protease type XIV from Streptomyces griseus (SGP) in acetonitrile. Yields of up to 92% with enantioselectivities of up to 88% e.e. and diastereoselectivities of up to 92:8 (syn:anti) were achieved under the optimised conditions. This enzyme's catalytic promiscuity expands the application of this biocatalyst and provides a potential alternative method for asymmetric Mannich reactions. PMID:23094136

  13. Phase Evolution, Microstructure, and Microwave Dielectric Properties of Reaction-Sintered Li2ZnTi3O8 Ceramic Obtained Using Nanosized TiO2 Reagent

    NASA Astrophysics Data System (ADS)

    Bari, M.; Taheri-Nassaj, E.; Taghipour-Armaki, H.

    2015-10-01

    Dielectric ceramics in the Li2ZnTi3O8 system were synthesized using TiO2 nanoparticle reagent by the reaction-sintering process. The special effects of the TiO2 nanoparticle reagent on the densification, phase distribution, microstructure, and dielectric properties were characterized using powder x-ray diffraction (XRD) analysis and scanning electron microscopy (SEM). A single phase of Li2ZnTi3O8 ceramic was confirmed by the XRD pattern at all temperatures except 1075°C. The reaction between the starting materials was accelerated using TiO2 nanoparticles, with pure Li2ZnTi3O8 phase being created even at low sintering temperature of 900°C, along with increasing green specimen density at the compaction stage. The presence of TiO2 phase in the Li2ZnTi3O8 ceramic improved the value and shifted it to near zero at 1075°C, and the ceramic exhibited excellent microwave dielectric properties of = 23.5, = 71,000 GHz, and = -3.5 ppm/°C.

  14. Direct measurements of radiative capture reactions with DRAGON

    NASA Astrophysics Data System (ADS)

    Christian, Gregory

    2015-10-01

    Direct measurements of radiative proton and alpha capture reactions are crucial for understanding nucleosynthesis in a variety of astrophysical environments, including classical novae, supernovae, X-Ray bursts, and quiescent stellar burning. Often the most important reactions have very low cross sections or involve unstable targets, making laboratory measurements extremely challenging. The detector of recoils and gammas of nuclear reactions (DRAGON) at TRIUMF is a recoil mass separator designed to measure radiative capture reactions in inverse kinematics, with beam suppression factors as high as 1016. When combined with the intense radioactive beams available at the ISAC-I facility, DRAGON's capabilities are unique and world-leading. In this talk, I will give a brief technical overview of DRAGON before presenting results from recent experiments. Some highlights include the first-ever direct measurement of 38K(p , γ) 39Ca, a crucial reaction for determining the endpoint of nova nucleosynthesis, and measurements of 76Se(α , γ) 80Kr. The latter measurements determine the rate of the reverse reaction, 80Kr(γ , α) 76Se, an important waiting point in the synthesis of the p-nuclei. I will also discuss future (and ongoing) developments at DRAGON, including the commissioning of a new chamber for high-precision elastic scattering measurements and plans to determine the 330 keV resonance strength in 18F(p , γ) 19Ne via measurements of 15O(α , γ) 19Ne and 15O + α elastic scattering.

  15. Microwave sintering process model.

    PubMed

    Peng, Hu; Tinga, W R; Sundararaj, U; Eadie, R L

    2003-01-01

    In order to simulate and optimize the microwave sintering of a silicon nitride and tungsten carbide/cobalt toolbits process, a microwave sintering process model has been built. A cylindrical sintering furnace was used containing a heat insulating layer, a susceptor layer, and an alumina tube containing the green toolbit parts between parallel, electrically conductive, graphite plates. Dielectric and absorption properties of the silicon nitride green parts, the tungsten carbide/cobalt green parts, and an oxidizable susceptor material were measured using perturbation and waveguide transmission methods. Microwave absorption data were measured over a temperature range from 20 degrees C to 800 degrees C. These data were then used in the microwave process model which assumed plane wave propagation along the radial direction and included the microwave reflection at each interface between the materials and the microwave absorption in the bulk materials. Heat transfer between the components inside the cylindrical sintering furnace was also included in the model. The simulated heating process data for both silicon nitride and tungsten carbide/cobalt samples closely follow the experimental data. By varying the physical parameters of the sintering furnace model, such as the thickness of the susceptor layer, the thickness of the allumina tube wall, the sample load volume and the graphite plate mass, the model data predicts their effects which are helpful in optimizing those parameters in the industrial sintering process. PMID:15323110

  16. SINTERING METHOD

    DOEpatents

    Googin, J.M.

    1963-11-01

    Methods of making articles by powder metallurgy techniques are presented. An article is made by packing a metal powder into a desired shape, raising the temperature of the powder compact to a sintering temperature in the presence of a reducing gas, and alternately increasing and decreasing the pressure of the gas while the temperatume is being raised. The product has a greater density than can be achieved by sintering for the same length of time at a constant gas pressure. (AEC)

  17. Microstructure and DC electrical conductivity of spinel nickel ferrite sintered in air and nitrogen atmospheres

    SciTech Connect

    Liu, Baogang; Zhou, Kechao; Li, Zhiyou; Zhang, Dou; Zhang, Lei

    2010-11-15

    In recent years, the development of inert anode materials has gained considerable attention because such materials are capable of producing only environment-friendly O{sub 2} and saving energy during aluminum electrolysis. Nickel ferrite was prepared by a solid-state reaction as the inert anode in this study and its microstructures and direct current conductivities were analyzed in detail regarding the effects of different sintering atmospheres. A single-phase spinel structure was confirmed for all samples by X-ray powder diffraction. The grain sizes and the relative densities of the samples sintered in nitrogen increased by over 7 {mu}m and 10.8%, respectively, compared to those sintered in air. The direct current conductivities of the samples sintered in nitrogen showed a drastic increase compared to those sintered in air, believed to be due to the effects of increased Fe{sup 2+} ion concentration at octahedral sites and the increase of the relative density.

  18. Direct measurements of astrophysically important α-induced reactions

    NASA Astrophysics Data System (ADS)

    Avila, Melina

    2016-03-01

    Understanding stellar evolution is one of the primary objectives of nuclear astrophysics. Reaction rates involving α-particles are often key nuclear physics inputs in stellar models. For instance, there are numerous (α , p) reactions fundamental for the understanding of X-ray bursts and the production of 44Ti in core-collapse supernovae. Furthermore, some (α , n) reactions are considered as one of the main neutron sources in the s-process. However, direct measurements of these reactions at relevant astrophysical energies are experimentally challenging because of their small cross section and intensity limitation of radioactive beams. The active target system MUSIC offers a unique opportunity to study (α , p) and (α , n) reactions because its segmented anode allows the investigation of a large energy range in the excitation function with a single measurement. Recent results on the direct measurement of (α , n) and (α , p) measurements in the MUSIC detector will be discussed. This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics, under Contract Number DE-AC02-06CH11357. This research used resources of ANL's ATLAS facility, which is a DOE Office of Science User.

  19. Degradation of artificial sweeteners via direct and indirect photochemical reactions.

    PubMed

    Perkola, Noora; Vaalgamaa, Sanna; Jernberg, Joonas; Vähätalo, Anssi V

    2016-07-01

    We studied the direct and indirect photochemical reactivity of artificial sweeteners acesulfame, saccharin, cyclamic acid and sucralose in environm entally relevant dilute aqueous solutions. Aqueous solutions of sweeteners were irradiated with simulated solar radiation (>290 nm; 96 and 168 h) or ultraviolet radiation (UVR; up to 24 h) for assessing photochemical reactions in surface waters or in water treatment, respectively. The sweeteners were dissolved in deionised water for examination of direct photochemical reactions. Direct photochemical reactions degraded all sweeteners under UVR but only acesulfame under simulated solar radiation. Acesulfame was degraded over three orders of magnitude faster than the other sweeteners. For examining indirect photochemical reactions, the sweeteners were dissolved in surface waters with indigenous dissolved organic matter or irradiated with aqueous solutions of nitrate (1 mg N/L) and ferric iron (2.8 mg Fe/L) introduced as sensitizers. Iron enhanced the photodegradation rates but nitrate and dissolved organic matter did not. UVR transformed acesulfame into at least three products: iso-acesulfame, hydroxylated acesulfame and hydroxypropanyl sulfate. Photolytic half-life was one year for acesulfame and more than several years for the other sweeteners in surface waters under solar radiation. Our study shows that the photochemical reactivity of commonly used artificial sweeteners is variable: acesulfame may be sensitive to photodegradation in surface waters, while saccharin, cyclamic acid and sucralose degrade very slowly even under the energetic UVR commonly used in water treatment. PMID:27023816

  20. Structural performance of cylindrical pressure housings of different ceramic compositions under external pressure loading. Part 3. Sintered reaction bonded silicon nitride ceramic. Final report

    SciTech Connect

    Kurkchubasche, R.R.; Johnson, R.P.; Stachiw, J.D.

    1994-06-01

    Ten 12-inch-OD by 18-inch-long reaction-bonded sintered silicon-nitride cylinders were fabricated, assembled, and pressure tested to determine their suitability for use as external pressure-resistant housings for underwater applications. The material, designated PSX Si3N4, is made by CERCOM, Inc. (Vista, CA) by a proprietary process. The primary advantages of this material are high compressive strength, high elastic modulus, high fracture toughness, and low specific gravity. Pressure test results are presented along with strain gage data and cyclic fatigue life data. Conclusions regarding the suitability of the material for application to pressure housings for underwater applications are presented along with a comparison to WESGO's AL-600 96-percent alumina ceramic, which was chosen as the base of comparison for various advanced materials being evaluated under the same program. Recommendations for design implementation, nondestructive inspection, and further research are made. Ceramics, External pressure housing, Ocean engineering.

  1. Direct Reaction Experimental Studies with Beams of Radioactive Tin Ions

    SciTech Connect

    Jones, K. L.; Ahn, S.H.; Allmond, James M; Ayres, A.; Bardayan, Daniel W; Baugher, T.; Bazin, D.; Beene, James R; Berryman, J. S.; Bey, A.; Bingham, C. R.; Cartegni, L.; Chae, K. Y.; Gade, A.; Galindo-Uribarri, Alfredo {nmn}; Garcia-Ruiz, R.F.; Grzywacz, Robert Kazimierz; Howard, Meredith E; Kozub, R. L.; Liang, J Felix; Manning, Brett M; Matos, M.; McDaniel, S.; Miller, D.; Nesaraja, Caroline D; O'Malley, Patrick; Padgett, S; Padilla-Rodal, Elizabeth; Pain, Steven D; Pittman, S. T.; Radford, David C; Ratkiewicz, Andrew J; Schmitt, Kyle; Smith, Michael Scott; Stracener, Daniel W; Stroberg, S.; Tostevin, Jeffrey A; Varner Jr, Robert L; Weisshaar, D.; Wimmer, K.

    2015-01-01

    The tin chain of isotopes provides a unique region in which to investigate the evolution of single-particle structure, spreading from N = 50 at Sn-100, through 10 stable isotopes and the N = 82 shell closure at Sn-132 out into the r-process path. Direct reactions performed on radioactive ion beams are sensitive spectroscopic tools for studying exotic nuclei. Here we present one experiment knocking out neutrons from tin isotopes that are already neutron deficient and two reactions that add a neutron to neutron-rich Sn-130. Both techniques rely on selective particle identification and the measurement of gamma rays in coincidence with charged ions. We present the goals of the two experiments and the particle identification for the channels of interest. The final results will be presented in future publications.

  2. Direct reaction experimental studies with beams of radioactive tin ions

    SciTech Connect

    Jones, K. L. Ayres, A.; Bey, A.; Burcher, S.; Cartegni, L.; Cerizza, G.; Ahn, S.; Allmond, J. M.; Beene, J. R.; Galindo-Uribarri, A.; Liang, J. F.; Nesaraja, C. D.; Pain, S. D.; Radford, D. C.; Schmitt, K. T.; Smith, M. S.; Stracener, D. W.; Varner, R. L.; Bardayan, D. W.; Baugher, T.; and others

    2015-10-15

    The tin chain of isotopes provides a unique region in which to investigate the evolution of single-particle structure, spreading from N = 50 at {sup 100}Sn, through 10 stable isotopes and the N = 82 shell closure at {sup 132}Sn out into the r-process path. Direct reactions performed on radioactive ion beams are sensitive spectroscopic tools for studying exotic nuclei. Here we present one experiment knocking out neutrons from tin isotopes that are already neutron deficient and two reactions that add a neutron to neutron-rich {sup 130}Sn. Both techniques rely on selective particle identification and the measurement of γ rays in coincidence with charged ions. We present the goals of the two experiments and the particle identification for the channels of interest. The final results will be presented in future publications.

  3. Template directed reactions of 2-aminoadenylic acid derivatives

    NASA Technical Reports Server (NTRS)

    Webb, T. R.; Orgel, L. E.

    1982-01-01

    The template-directed oligomerization of activated derivatives of 2-aminoadenylic acid (paA) on polyuridylic acid (poly(U)) in aqueous buffers was studied. The reaction differs from that of adenylic acid (pA) under identical conditions, in that only di- and tri-nucleotides are observed as substantial products rather than a longer sequence of oligomers. The reaction of paA also differs from that of pA in that it does not require Mg (2+), and is less susceptible to increased temperature. The relevance of these observations to the chemical evolution of polynucleotide replication is discussed. Improved syntheses of paA and its diphosphate are reported.

  4. Direct Reaction of Amides with Nitric Oxide To Form Diazeniumdiolates

    PubMed Central

    2015-01-01

    We report the apparently unprecedented direct reaction of nitric oxide (NO) with amides to generate ions of structure R(C=O)NH–N(O)=NO–, with examples including R = Me (1a) or 3-pyridyl (1b). The sodium salts of both released NO in pH 7.4 buffer, with 37 °C half-lives of 1–3 min. As NO-releasing drug candidates, diazeniumdiolated amides would have the advantage of generating only 1 equiv of base on hydrolyzing exhaustively to NO, in contrast to their amine counterparts, which generate 2 equiv of base. PMID:25210948

  5. Stripping lead from D2EHPA by direct displacement reactions

    SciTech Connect

    Chia, L.M.; O`Keefe, T.J.

    1995-07-01

    The direct removal of lead ions from D2EHPA-kerosene using metallic zinc as the reducing agent was evaluated. The electrochemical process, called galvanic stripping, is a potential alternative stripping technique when standard chemical methods are not adequate. Four parameters found to be important in the rate of lead removal were studied in a factorially designed experiment. The variable evaluated included D2EHPA concentration, temperature, zinc surface area and solution agitation. Temperature and surface area were found to be the most significant, while agitation and D2EHPA concentration had less influence on the reaction. An activation energy of 22.5 Kcal/mole was calculated indicating a chemically-controlled process. The reaction was also sensitive to the concentration of oxygen in the system. The zinc required was considerably in excess of stoichiometry, possibly due to the dissolution and redeposition of lead. In general, the results were encouraging and demonstrated that lead impurities could be removed from D2EHPA using cementation type reactions.

  6. SinterHab

    NASA Astrophysics Data System (ADS)

    Rousek, Tomáš; Eriksson, Katarina; Doule, Ondřej

    2012-05-01

    This project describes a design study for a core module on a Lunar South Pole outpost, constructed by 3D printing technology with the use of in-situ resources and equipped with a bio-regenerative life support system. The module would be a hybrid of deployable (CLASS II) and in-situ built (CLASS III) structures. It would combine deployable membrane structures and pre-integrated rigid elements with a sintered regolith shell for enhanced radiation and micrometeorite shielding. The closed loop ecological system would support a sustainable presence on the Moon with particular focus on research activities. The core module accommodates from four to eight people, and provides laboratories as a test bed for development of new lunar technologies directly in the environment where they will be used. SinterHab also includes an experimental garden for development of new bio-regenerative life support system elements. The project explores these various concepts from an architectural point-of-view particularly, as they constitute the building, construction and interior elements. The construction method for SinterHab is based on 3D printing by sintering of the lunar regolith. Sinterator robotics 3D printing technology proposed by NASA JPL enables construction of future generations of large lunar settlements with little imported material and the use of solar energy. The regolith is processed, placed and sintered by the Sinterator robotics system which combines the NASA ATHLETE and the Chariot remotely controlled rovers. Microwave sintering creates a rigid structure in the form of walls, vaults and other architectural elements. The interior is coated with a layer of inflatable membranes inspired by the TransHab project. The life-support system is mainly bio-regenerative and several parts of the system are intrinsically multifunctional and serve more than one purpose. The plants for food production are also an efficient part of atmosphere revitalization and water treatment. Moreover

  7. MgAl2O4(001) based magnetic tunnel junctions made by direct sputtering of a sintered spinel target

    NASA Astrophysics Data System (ADS)

    Belmoubarik, Mohamed; Sukegawa, Hiroaki; Ohkubo, Tadakatsu; Mitani, Seiji; Hono, Kazuhiro

    2016-03-01

    We developed a fabrication process of an epitaxial MgAl2O4 barrier for magnetic tunnel junctions (MTJs) using a direct sputtering method from an MgAl2O4 spinel sintered target. Annealing the sputter-deposited MgAl2O4 layer sandwiched between Fe electrodes led to the formation of a (001)-oriented cation-disorder spinel with atomically sharp interfaces and lattice-matching with the Fe electrodes. A large tunnel magnetoresistance ratio up to 245% at 297 K (436% at 3 K) was achieved in the Fe/MgAl2O4/Fe(001) MTJ as well as an excellent bias voltage dependence. These results indicate that the direct sputtering is an alternative method for the realization of high performance MTJs with a spinel-based tunnel barrier.

  8. Direct Measurement of Mercury Reactions In Coal Power Plant Plumes

    SciTech Connect

    Leonard Levin

    2005-12-31

    Recent field and pilot-scale results indicate that divalent mercury emitted from power plants may rapidly transform to elemental mercury within the power plant plumes. Simulations of mercury chemistry in plumes based on measured rates to date have improved regional model fits to Mercury Deposition Network wet deposition data for particular years, while not degrading model verification fits for remaining years of the ensemble. The years with improved fit are those with simulated deposition in grid cells in the State of Pennsylvania that have matching MDN station data significantly less than the model values. This project seeks to establish a full-scale data basis for whether or not significant reduction or oxidation reactions occur to mercury emitted from coal-fired power plants, and what numerical redox rate should apply for extension to other sources and for modeling of power plant mercury plumes locally, regionally, and nationally. Although in-stack mercury (Hg) speciation measurements are essential to the development of control technologies and to provide data for input into atmospheric fate and transport models, the determination of speciation in a cooling coal combustion plume is more relevant for use in estimating Hg fate and effects through the atmosphere. It is mercury transformations that may occur in the plume that determine the eventual rate and patterns of mercury deposited to the earth's surface. A necessary first step in developing a supportable approach to modeling any such transformations is to directly measure the forms and concentrations of mercury from the stack exit downwind to full dispersion in the atmosphere. As a result, a study was sponsored by EPRI and jointly funded by EPRI, the U.S Department of Energy (DOE), and the Wisconsin Department of Administration. The study was designed to further our understanding of plume chemistry. The study was carried out at the We Energies Pleasant Prairie Power Plant, Pleasant Prairie, Wisconsin, just

  9. Mechanical properties of (Bi,Sb)2Te3 solid solutions obtained by directional crystallization and spark plasma sintering

    NASA Astrophysics Data System (ADS)

    Lavrent'ev, M. G.; Osvenskii, V. B.; Pivovarov, G. I.; Sorokin, A. I.; Bulat, L. P.; Bublik, V. T.; Tabachkova, N. Yu.

    2016-01-01

    We have studied the temperature dependence of the mechanical strength at uniaxial compression for solid solutions based on bismuth and antimony chalcogenides, which were prepared by three methods: (i) vertical zone melting (VZM), (ii) hot extrusion, and (iii) spark plasma sintering (SPS). In the samples of solid solutions obtained by VZM and extrusion, a brittle-ductile transition was observed in a wised temperature interval of 200-350°C. In nanostructured SPS samples, transition from brittle to plastic fracture was observed within 170-200°C. The room-temperature strength of nanostructured samples was eight to nine times as large as that of VZM samples, and the stress-strain curves of these materials were significantly different. At a temperature of about 300°C, the strength of nanostructured solid solutions decreases to nearly zero.

  10. Effect of process parameters on hardness, temperature profile and solidification of different layers processed by direct metal laser sintering (DMLS)

    NASA Astrophysics Data System (ADS)

    Ahmed, Sazzad Hossain; Mian, Ahsan; Srinivasan, Raghavan

    2016-07-01

    In DMLS process objects are fabricated layer by layer from powdered material by melting induced by a controlled laser beam. Metallic powder melts and solidifies to form a single layer. Solidification map during layer formation is an important route to characterize micro-structure and grain morphology of sintered layer. Generally, solidification leads to columnar, equiaxed or mixture of these two types grain morphology depending on solidification rate and thermal gradient. Eutectic or dendritic structure can be formed in fully equiaxed zone. This dendritic growth has a large effect on material properties. Smaller dendrites generally increase ductility of the layer. Thus, materials can be designed by creating desired grain morphology in certain regions using DMLS process. To accomplish this, hardness, temperature distribution, thermal gradient and solidification cooling rate in processed layers will be studied under change of process variables by using finite element analysis, with specific application to Ti-6Al-4V.

  11. Correlations probed in direct two-nucleon removal reactions

    SciTech Connect

    Simpson, E. C.; Tostevin, J. A.

    2010-10-15

    Final-state-exclusive momentum distributions of fast, forward-traveling residual nuclei, following two-nucleon removal from fast secondary radioactive beams of projectile nuclei, can and have now been measured. Assuming that the most important reaction mechanism is the sudden direct removal of a pair of nucleons from a set of relatively simple, active shell-model orbital configurations, such distributions were predicted to depend strongly on the total angular momentum I carried by the two nucleons--the final-state spin for spin 0{sup +} projectiles. The sensitivity of these now-accessible observables to specific details of the (correlated) two-nucleon wave functions is of importance. We clarify that it is the total orbital angular momentum L of the two nucleons that is the primary factor in determining the shapes and widths of the calculated momentum distributions. It follows that, with accurate measurements, this dependence upon the L makeup of the two-nucleon wave functions could be used to assess the accuracy of (shell- or many-body-) model predictions of these two-nucleon configurations. By using several tailored examples, with specific combinations of active two-nucleon orbitals, we demonstrate that more-subtle structure aspects may be observed, allowing such reactions to probe and/or confirm the details of theoretical model wave functions.

  12. The charge transfer transition phenomenon and microstructure of Eu{sup 3+}-doped NaCaPO{sub 4} phosphors sintered with NH{sub 4}Cl flux via solid-state reaction

    SciTech Connect

    Peng, Yu-Ming; Su, Yan-Kuin; Yang, Ru-Yuan

    2013-05-15

    Graphical abstract: This paper describes: The charge transfer transition phenomenon and microstructure of Eu{sup 3+}-doped NaCaPO{sub 4} phosphors sintered with NH{sub 4}Cl flux via solid-state reaction. The emission intensity of NaCa{sub 0.95}PO{sub 4}:0.05Eu{sup 3+} phosphors with 2 wt.% NH{sub 4}Cl flux is enhanced as the sintering temperature was increased from 800 °C to 1000 °C and reveals the maximum value at 1000 °C. Photoluminescence emission spectra of NaCa{sub 0.95}PO{sub 4}:0.05Eu{sup 3+} phosphors with 2 wt.% NH{sub 4}Cl flux sintered at various sintering temperature for 3 h via solid state reaction method (λ{sub ex} = 270 nm). Highlights: ► NH{sub 4}Cl flux is helpful for enhancing the crystallization degree and decreasing surface defects. ► A single phase of NaCaPO{sub 4}:Eu{sup 3+} phosphor was observed as the sintering temperature was increased from 800 °C to 1000 °C. ► The intensity of the excitation peaks displays a maximum value at 1000 °C. ► The NaCaPO{sub 4} host added with NH{sub 4}Cl flux and sintered at the different temperature can affect the morphology. ► The NaCaPO{sub 4} host added with NH{sub 4}Cl flux and sintered at the different temperature can affect fluorescent properties. - Abstract: NaCa{sub 0.95}PO{sub 4}:0.05Eu{sup 3+} phosphors with 2 wt.% NH{sub 4}Cl flux sintered at various sintering temperature (800, 900, 1000, 1100 °C) for 3 h under air atmosphere were synthesized successfully via solid state reaction method. It is found that the addition of NH{sub 4}Cl flux and different sintering temperatures can affect the morphology and fluorescent properties of NaCa{sub 0.95}PO{sub 4}:0.05Eu{sup 3+} phosphor. The X-ray diffractions show a single phase and the microstructure observations show uniform morphologies for NaCa{sub 0.95}PO{sub 4}:0.05Eu{sup 3+} phosphors sintered at the range from 900 °C to 1000 °C, indicating that addition of 2 wt.% NH{sub 4}Cl flux is helpful for enhancing the crystallization, thus

  13. Enabling direct nanoscale observations of biological reactions with dynamic TEM

    PubMed Central

    Evans, James E.; Browning, Nigel D.

    2013-01-01

    Biological processes occur on a wide range of spatial and temporal scales: from femtoseconds to hours and from angstroms to meters. Many new biological insights can be expected from a better understanding of the processes that occur on these very fast and very small scales. In this regard, new instruments that use fast X-ray or electron pulses are expected to reveal novel mechanistic details for macromolecular protein dynamics. To ensure that any observed conformational change is physiologically relevant and not constrained by 3D crystal packing, it would be preferable for experiments to utilize small protein samples such as single particles or 2D crystals that mimic the target protein's native environment. These samples are not typically amenable to X-ray analysis, but transmission electron microscopy has imaged such sample geometries for over 40 years using both direct imaging and diffraction modes. While conventional transmission electron microscopes (TEM) have visualized biological samples with atomic resolution in an arrested or frozen state, the recent development of the dynamic TEM (DTEM) extends electron microscopy into a dynamic regime using pump-probe imaging. A new second-generation DTEM, which is currently being constructed, has the potential to observe live biological processes with unprecedented spatiotemporal resolution by using pulsed electron packets to probe the sample on micro- and nanosecond timescales. This article reviews the experimental parameters necessary for coupling DTEM with in situ liquid microscopy to enable direct imaging of protein conformational dynamics in a fully hydrated environment and visualize reactions propagating in real time. PMID:23315566

  14. Development of an in-situ multi-component reinforced Al-based metal matrix composite by direct metal laser sintering technique — Optimization of process parameters

    SciTech Connect

    Ghosh, Subrata Kumar; Bandyopadhyay, Kaushik; Saha, Partha

    2014-07-01

    In the present investigation, an in-situ multi-component reinforced aluminum based metal matrix composite was fabricated by the combination of self-propagating high-temperature synthesis and direct metal laser sintering process. The different mixtures of Al, TiO{sub 2} and B{sub 4}C powders were used to initiate and maintain the self-propagating high-temperature synthesis by laser during the sintering process. It was found from the X-ray diffraction analysis and scanning electron microscopy that the reinforcements like Al{sub 2}O{sub 3}, TiC, and TiB{sub 2} were formed in the composite. The scanning electron microscopy revealed the distribution of the reinforcement phases in the composite and phase identities. The variable parameters such as powder layer thickness, laser power, scanning speed, hatching distance and composition of the powder mixture were optimized for higher density, lower porosity and higher microhardness using Taguchi method. Experimental investigation shows that the density of the specimen mainly depends upon the hatching distance, composition and layer thickness. On the other hand, hatching distance, layer thickness and laser power are the significant parameters which influence the porosity. The composition, laser power and layer thickness are the key influencing parameters for microhardness. - Highlights: • The reinforcements such as Al{sub 2}O{sub 3}, TiC, and TiB{sub 2} were produced in Al-MMC through SHS. • The density is mainly influenced by the material composition and hatching distance. • Hatching distance is the major influencing parameter on porosity. • The material composition is the significant parameter to enhance the microhardness. • The SEM micrographs reveal the distribution of TiC, TiB{sub 2} and Al{sub 2}O{sub 3} in the composite.

  15. Comparative analysis on surface property in anodic oxidation polishing of reaction-sintered silicon carbide and single-crystal 4H silicon carbide

    NASA Astrophysics Data System (ADS)

    Shen, Xinmin; Tu, Qunzhang; Deng, Hui; Jiang, Guoliang; He, Xiaohui; Liu, Bin; Yamamura, Kazuya

    2016-04-01

    For effective machining of difficult-to-machine materials, such as reaction-sintered silicon carbide (RS-SiC) and single-crystal 4H silicon carbide (4H-SiC), a novel polishing technique named anodic oxidation polishing was proposed, which combined with the anodic oxidation of substrate and slurry polishing of oxide. By scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM-EDX) observation and atomic force microscopy analysis, both the anodic oxidation behaviors of RS-SiC and 4H-SiC were investigated. Through comparison of the surfaces before and after hydrofluoric acid etching of the oxidized samples by the scanning white light interferometry (SWLI) measurement, the relationships between oxidation depth and oxidation time were obtained, and the calculated oxidation rate for RS-SiC was 5.3 nm/s and that for 4H-SiC was 5.8 nm/s based on the linear Deal-Grove model. Through anodic oxidation polishing of RS-SiC substrate and 4H-SiC substrate, respectively, the surface roughness rms obtained by SWLI was improved to 2.103 nm for RS-SiC and to 0.892 nm for 4H-SiC. Experimental results indicate that anodic oxidation polishing is an effective method for the machining of RS-SiC and 4H-SiC samples, which would improve the process level of SiC substrates and promote the application of SiC products in the fields of optics, ceramics, semiconductors, electronics, and so on.

  16. Optical and biological properties of transparent nanocrystalline hydroxyapatite obtained through spark plasma sintering.

    PubMed

    Li, Zhong; Thompson, Brianna C; Dong, Zhili; Khor, Khiam Aik

    2016-12-01

    Transparent bioceramics have attracted a large amount of research interest as they facilitate direct observation of biointerfacial reactions. Thus far, attempts to achieve transparent hydroxyapatite have been focused on augmenting the sintering pressure and/or extending the sintering duration. This study aims at fabricating transparent HA using a direct and fast spark plasma sintering process with appropriate starting powder and moderate sintering pressure. Three types of raw powder, namely micro-spheres, nano-rods and nano-spheres, were sintered to investigate the optical and biological properties of the compacted pellets. It was found that in terms of transparency, the micro-sphere pellet sintered at 1000°C stood out with an in-line transmittance as high as 84% achieved at 1300nm for a 2mm thick sample. In addition, pellets fabricated from micro-spheres demonstrated the highest cell viability in in vitro biological tests with L929 cells. Living cells cultured on a transparent micro-sphere pellet could be directly and clearly observed by light microscopy. It is thus concluded that the micro-sphere powder is the most desirable raw material to manufacture transparent hydroxyapatite because it could enable dense pellets with notably high transparency and outstanding in vitro biocompatibility to be readily obtained. PMID:27612791

  17. Fundamental studies of retrograde reactions in direct liquefaction

    SciTech Connect

    Serio, M.A.; Solomon, P.R.; Kroo, E.; Charpenay, S.; Bassilakis, R.

    1991-12-17

    The overall objective of the program was to improve the understanding of retrograde reactions and their dependencies on coal rank and structure, and/or coal modifications and reaction conditions. Because retrograde reactions are competitive with bond breaking reactions, an understanding of both is required to shift the competition in favor of the latter. Related objectives were to clarify the conflicting observations reported in literature on such major topics as the role of oxygen groups in retrograde reactions and to provide a bridge from very fundamental studies on pure compounds to phenomenological studies on actual coal. This information was integrated into the FG-DVC model, which was improved and extended to the liquefaction context.

  18. Direct microwave joining of reaction bonded silicon carbide

    SciTech Connect

    Ahmad, I.; Black, W.M.; Silberglitt, R.

    1992-08-01

    A single-mode rectangular resonant cavity operating at 2.45 GHz was used to join, without any interlayer or applied pressure, specimens of reaction bonded silicon carbide. Specimens of 0.95 cm diameter and 0.5 cm height were joined at temperatures 1400-1450 C in 10 to 15 minutes. Specimens of arbitrary shapes and practical sizes were joined in a commercially available 900 watt multi-mode oven with hybrid heating. The joined specimens were sectioned and examined. The joint was not detectable even by scanning electron microscope observation. On heating silicon bleeds out of reaction bonded silicon carbide. The apparent density of the heated reaction bonded silicon carbide was 3.01 gm/cc as compared to 3.05 gm/cc for the as received material. However, the only difference in microstructure was some grain growth of the microwave heated reaction bonded silicon carbide, compared to the as received material. 10 refs.

  19. Chemical reactions occurring during direct solar reduction of CO2.

    PubMed

    Lyma, J L; Jensen, R J

    2001-09-28

    At high temperatures carbon dioxide may absorb solar radiation and react to form carbon monoxide and molecular oxygen. The CO, so produced, may be converted by well-established means to a combustible fuel, such as methanol. We intend to make a future demonstration of the solar reduction of CO2 based on these processes. This paper, however, addresses only the problem of preserving, or even enhancing, the initial photolytic CO by quenching the hot gas with colder H2O or CO2. We present model calculations with a reaction mechanism used extensively in other calculations. If a CO2 gas stream is heated and photolyzed by intense solar radiation and then allowed to cool slowly, it will react back to the initial CO2 by a series of elementary chemical reactions. The back reaction to CO2 can be terminated with the rapid addition of CO2, water, or a mixture. Calculations show that a three-fold quench with pure CO2 will stop the reactions and preserve over 90% of the initial photolytic CO. We find that water has one of two effects. It can either increase the CO level, or it can catalyze the recombination of O and CO to CO2. The gas temperature is the determining factor. If the quench gas is not sufficient to keep the temperature below approximately 1100 K, a chain-branching reaction dominates and the reaction to CO2 occurs. If the temperature stays below that level a chain terminating reaction dominates and the CO is increased. The former case occurs below approximately a fourfold quench with a water/CO2 mixture. The later case occurs when the quench is greater than fourfold. We conclude that CO2, H2O, or a mixture may quench the hot gas stream photolyzed by solar radiation and preserve the photolytic CO. PMID:11589409

  20. Tribological Behavior of Aluminum Alloy AlSi10Mg-TiB2 Composites Produced by Direct Metal Laser Sintering (DMLS)

    NASA Astrophysics Data System (ADS)

    Lorusso, Massimo; Aversa, Alberta; Manfredi, Diego; Calignano, Flaviana; Ambrosio, Elisa Paola; Ugues, Daniele; Pavese, Matteo

    2016-06-01

    Direct metal laser sintering (DMLS) is an additive manufacturing technique for the production of parts with complex geometry and it is especially appropriate for structural applications in aircraft and automotive industries. Aluminum-based metal matrix composites (MMCs) are promising materials for these applications because they are lightweight, ductile, and have a good strength-to-weight ratio This paper presents an investigation of microstructure, hardness, and tribological properties of AlSi10Mg alloy and AlSi10Mg alloy/TiB2 composites prepared by DMLS. MMCs were realized with two different compositions: 10% wt. of microsize TiB2, 1% wt. of nanosize TiB2. Wear tests were performed using a pin-on-disk apparatus on the prepared samples. Performances of AlSi10Mg samples manufactured by DMLS were also compared with the results obtained on AlSi10Mg alloy samples made by casting. It was found that the composites displayed a lower coefficient of friction (COF), but in the case of microsize TiB2 reinforcement the wear rate was higher than with nanosize reinforcements and aluminum alloy without reinforcement. AlSi10Mg obtained by DMLS showed a higher COF than AlSi10Mg obtained by casting, but the wear rate was higher in the latter case.

  1. Chemical Reaction Engineering: Current Status and Future Directions.

    ERIC Educational Resources Information Center

    Dudukovic, M. P.

    1987-01-01

    Describes Chemical Reaction Engineering (CRE) as the discipline that quantifies the interplay of transport phenomena and kinetics in relating reactor performance to operating conditions and input variables. Addresses the current status of CRE in both academic and industrial settings and outlines future trends. (TW)

  2. Novel template-directed anodic phenol-coupling reaction.

    PubMed

    Malkowsky, Itamar M; Rommel, Christina E; Fröhlich, Roland; Griesbach, Ulrich; Pütter, Hermann; Waldvogel, Siegfried R

    2006-09-25

    Substituted phenols were anodically coupled to the corresponding 2,2'-biphenols via tetraphenoxy borate derivatives. This electrochemical method is particularly useful for methyl-substituted substrates, such as 2,4-dimethyl phenol. The selective ortho-coupling reaction can be easily performed on a multikilogram scale. PMID:16874823

  3. Direct Measurement of {sup 21}Na+{alpha} Stellar Reaction

    SciTech Connect

    Binh, D. N.; Kubono, S.; Yamaguchi, H.; Hayakawa, S.; Hashimoto, T.; Kahl, D.; Teranishi, T.; Iwasa, N.; Kume, N.; Kato, S.; Khiem, L. H.; Tho, N. T.; Wakabayashi, Y.

    2010-08-12

    The measurement of the resonant alpha scattering and the {sup 21}Na({alpha}, p) reaction were performed for the first time in inverse kinematics with the thick target method using a {sup 21}Na radioisotope (RI) beam. This paper reports the current result of alpha scattering measurement and its astrophysics implication.

  4. Direct Measurement of 21Na+α Stellar Reaction

    NASA Astrophysics Data System (ADS)

    Binh, D. N.; Kubono, S.; Yamaguchi, H.; Hayakawa, S.; Hashimoto, T.; Kahl, D.; Teranishi, T.; Iwasa, N.; Kume, N.; Kato, S.; Khiem, L. H.; Tho, N. T.; Wakabayashi, Y.

    2010-08-01

    The measurement of the resonant alpha scattering and the 21Na(α, p) reaction were performed for the first time in inverse kinematics with the thick target method using a 21Na radioisotope (RI) beam. This paper reports the current result of alpha scattering measurement and its astrophysics implication.

  5. Direct Measurement of ^21Na+α Stellar Reaction

    NASA Astrophysics Data System (ADS)

    Binh Dam, Nguyen; Yamaguchi, H.; Wakabayashi, Y.; Hayakawa, S.; Hashimoto, T.; Kahl, D.; Kubono, S.; Le, H. K.; Nguyen, T. T.; Iwasa, N.; Kume, N.; Kato, S.; Teranishi, T.

    2009-10-01

    Nucleosynthesis of ^22Na is an interesting subject because of possible γ-ray observation and isotopic anomalies in presolar grain. ^22Na would have been mainly produced in the NeNa cycle. At high temperature conditions, ^21Na(α,p)^24Mg reaction could play a significant role to make flow from the NeNa cycle to the next MgAl cycle and beyond. Clearly, the ^21Na(α,p)^24Mg stellar reaction would bypass ^22Na, resulting in reduction of ^22Na production, therefore, it is strongly coupled to the Ne-E problem. It could be also important to understand the early stage of the rp-process. Experiment was performed using a 39 MeV ^21Na radioactive beam obtained by the CNS Radio Isotope Beam separator CRIB of the University of Tokyo. Both protons and alphas were measured from α+^21Na scattering with a thick ^4He gas target.

  6. Direct reaction measurements with a 132Sn radioactive ion beam

    SciTech Connect

    Jones, Katherine L.; Nunes, Filomena M.; Adekola, Aderemi S.; Bardayan, Dan W.; Blackmon, Jeff; Chae, K. Y.; Chipps, Kelly A.; Cizewski, Jolie A.; Erikson, Luke E.; Harlin, C.; Hatarik, R.; Kapler, R.; Kozub, Raymond L.; Liang, J. F.; Livesay, Ronald J.; Ma, Zhongguo J.; Moazen, B. H.; Nesaraja, Caroline D.; Pain, Steven D.; Patterson, N. P.; Shapira, Dan; Shriner, Jr., John F.; Smith, Michael S.; Swan, Thomas P.; Thomas, Jeff S.

    2011-09-01

    The (d,p) neutron transfer and (d,d) elastic scattering reactions were measured in inverse kinematics using a radioactive ion beam of 132Sn at 630 MeV. The elastic scattering data were taken in a region where Rutherford scattering dominated the reaction, and nuclear effects account for less than 8% of the elastic scattering cross section. The magnitude of the nuclear effects, in the angular range studied, was found to be independent of the optical potential used, allowing the transfer data to be normalized in a reliable manner. The neutron-transfer reaction populated a previously unmeasured state at 1363 keV, which is most likely the single-particle 3p1/2 state expected above the N = 82 shell closure. The data were analyzed using finite-range adiabatic-wave calculations and the results compared with the previous analysis using the distorted-wave Born approximation. Angular distributions for the ground and first-excited states are consistent with the previous tentative spin and parity assignments. Spectroscopic factors extracted from the differential cross sections are similar to those found for the one-neutron states beyond the benchmark doubly magic nucleus 208Pb.

  7. Direct reaction measurements with a (132)Sn radioactive ion beam

    SciTech Connect

    Jones, K. L.; Chae, K. Y.; Kapler, R.; Ma, Zhanwen; Moazen, Brian; Cizewski, J. A.; Hatarik, Robert; Pain, S. D.; Swan, T. P.; Nunes, F. M.; Adekola, Aderemi S; Bardayan, Daniel W; Blackmon, Jeff C; Chae, Kyung Yuk; Liang, J Felix; Nesaraja, Caroline D; Pain, Steven D; Shapira, Dan; Smith, Michael Scott; Chipps, Kelly A; Erikson, Luke; Livesay, R. J.; Harlin, Christopher W; Patterson, N. P.; Thomas, J. S.; Kozub, R. L.; Shriner, Jr., John F

    2011-01-01

    The (d,p) neutron transfer and (d,d) elastic scattering reactions were measured in inverse kinematics using a radioactive ion beam of {sup 132}Sn at 630 MeV. The elastic scattering data were taken in a region where Rutherford scattering dominated the reaction, and nuclear effects account for less than 8% of the elastic scattering cross section. The magnitude of the nuclear effects, in the angular range studied, was found to be independent of the optical potential used, allowing the transfer data to be normalized in a reliable manner. The neutron-transfer reaction populated a previously unmeasured state at 1363 keV, which is most likely the single-particle 3p{sub 1/2} state expected above the N=82 shell closure. The data were analyzed using finite-range adiabatic-wave calculations and the results compared with the previous analysis using the distorted-wave Born approximation. Angular distributions for the ground and first-excited states are consistent with the previous tentative spin and parity assignments. Spectroscopic factors extracted from the differential cross sections are similar to those found for the one-neutron states beyond the benchmark doubly magic nucleus {sup 208}Pb.

  8. Direct reaction measurements with a 132Sn radioactive ion beam

    NASA Astrophysics Data System (ADS)

    Jones, K. L.; Nunes, F. M.; Adekola, A. S.; Bardayan, D. W.; Blackmon, J. C.; Chae, K. Y.; Chipps, K. A.; Cizewski, J. A.; Erikson, L.; Harlin, C.; Hatarik, R.; Kapler, R.; Kozub, R. L.; Liang, J. F.; Livesay, R.; Ma, Z.; Moazen, B.; Nesaraja, C. D.; Pain, S. D.; Patterson, N. P.; Shapira, D.; Shriner, J. F., Jr.; Smith, M. S.; Swan, T. P.; Thomas, J. S.

    2011-09-01

    The (d,p) neutron transfer and (d,d) elastic scattering reactions were measured in inverse kinematics using a radioactive ion beam of 132Sn at 630 MeV. The elastic scattering data were taken in a region where Rutherford scattering dominated the reaction, and nuclear effects account for less than 8% of the elastic scattering cross section. The magnitude of the nuclear effects, in the angular range studied, was found to be independent of the optical potential used, allowing the transfer data to be normalized in a reliable manner. The neutron-transfer reaction populated a previously unmeasured state at 1363 keV, which is most likely the single-particle 3p1/2 state expected above the N=82 shell closure. The data were analyzed using finite-range adiabatic-wave calculations and the results compared with the previous analysis using the distorted-wave Born approximation. Angular distributions for the ground and first-excited states are consistent with the previous tentative spin and parity assignments. Spectroscopic factors extracted from the differential cross sections are similar to those found for the one-neutron states beyond the benchmark doubly magic nucleus 208Pb.

  9. Compaction and Sintering of Mo Powders

    SciTech Connect

    Nunn, Stephen D; Kiggans, Jim; Bryan, Chris

    2013-01-01

    To support the development of Mo-99 production by NorthStar Medical Technologies, LLC, Mo metal powders were evaluated for compaction and sintering characteristics as they relate to Mo-100 accelerator target disk fabrication. Powders having a natural isotope distribution and enriched Mo-100 powder were examined. Various powder characteristics are shown to have an effect on both the compaction and sintering behavior. Natural Mo powders could be cold pressed directly to >90% density. All of the powders, including the Mo-100 samples, could be sintered after cold pressing to >90% density. As an example, a compacted Mo-100 disk reached 89.7% density (9.52 g/cm3) after sintering at 1000 C for 1 hr. in flowing Ar/4%H2. Higher sintering temperatures were required for other powder samples. The relationships between processing conditions and the resulting densities of consolidated Mo disks will be presented.

  10. DIRECT MEASUREMENT OF MERCURY REACTIONS IN COAL POWER PLANT PLUMES

    SciTech Connect

    Leonard Levin

    2004-01-01

    This project was awarded under U.S. Department of Energy (DOE) National Energy Technology Laboratory (NETL) Program Solicitation DE-PS26-02NT41422 and specifically addresses Program Area of Interest: No.5--Environmental and Water Resources. The project team includes the Electric Power Research Institute (EPRI) as the contractor and the University of North Dakota Energy & Environmental Research Center (EERC) and Frontier Geosciences as subcontractors. Wisconsin Energies and its Pleasant Prairie Power Plant acted as host for the field-testing portion of the research. The project is aimed at clarifying the role, rates, and end results of chemical transformations that may occur to mercury that has been emitted from elevated stacks of coal-fired electric power plants. Mercury emitted from power plants emerges in either its elemental, divalent, or particulate-bound form. Deposition of the divalent form is more likely to occur closer to the source than that of the other two forms, due to its solubility in water. Thus, if chemical transformations occur in the stack emissions plume, measurements in the stack may mischaracterize the fate of the material. Initial field and pilot plant measurements have shown significant and rapid chemical reduction of divalent to elemental mercury may occur in these plumes. Mercury models currently assume that the chemical form of mercury occurring in stacks is the same as that which enters the free atmosphere, with no alteration occurring in the emissions plume. Recent data indicate otherwise, but need to be evaluated at full operating scale under field conditions. Prestbo and others have demonstrated the likelihood of significant mercury chemical reactions occurring in power plant plumes (Prestbo et al., 1999; MDNR-PPRP, 2000; EERC, 2001). This experiment will thus increase our understanding of mercury atmospheric chemistry, allowing informed decisions regarding source attribution. The experiment was carried out during the period August 22

  11. DIRECT MEASUREMENT OF MERCURY REACTIONS IN COAL POWER PLANT PLUMES

    SciTech Connect

    Leonard Levin

    2006-06-01

    This project was awarded under U.S. Department of Energy (DOE) National Energy Technology Laboratory (NETL) Program Solicitation DE-PS26-02NT41422 and specifically addresses Program Area of Interest: No.5--Environmental and Water Resources. The project team includes the Electric Power Research Institute (EPRI) as the contractor and the University of North Dakota Energy & Environmental Research Center (EERC) and Frontier Geosciences as subcontractors. Wisconsin Energies and its Pleasant Prairie Power Plant acted as host for the field-testing portion of the research. The project is aimed at clarifying the role, rates, and end results of chemical transformations that may occur to mercury that has been emitted from elevated stacks of coal-fired electric power plants. Mercury emitted from power plants emerges in either its elemental, divalent, or particulate-bound form. Deposition of the divalent form is more likely to occur closer to the source than that of the other two forms, due to its solubility in water. Thus, if chemical transformations occur in the stack emissions plume, measurements in the stack may mischaracterize the fate of the material. Initial field and pilot plant measurements have shown significant and rapid chemical reduction of divalent to elemental mercury may occur in these plumes. Mercury models currently assume that the chemical form of mercury occurring in stacks is the same as that which enters the free atmosphere, with no alteration occurring in the emissions plume. Recent data indicate otherwise, but need to be evaluated at full operating scale under field conditions. Prestbo and others have demonstrated the likelihood of significant mercury chemical reactions occurring in power plant plumes (Prestbo et al., 1999; MDNR-PPRP, 2000; EERC, 2001). This experiment will thus increase our understanding of mercury atmospheric chemistry, allowing informed decisions regarding source attribution. The experiment was carried out during the period August 22

  12. Direct synthesis of thermochromic VO2 through hydrothermal reaction

    NASA Astrophysics Data System (ADS)

    Alie, David; Gedvilas, Lynn; Wang, Zhiwei; Tenent, Robert; Engtrakul, Chaiwat; Yan, Yanfa; Shaheen, Sean E.; Dillon, Anne C.; Ban, Chunmei

    2014-04-01

    Thermochromic VO2 was directly synthesized using hydrothermal techniques. The effects of formation conditions on the structure and morphology of the final product were studied through X-ray diffraction (XRD), and scanning electron microscopy (SEM). Unique hollow sphere morphology was observed for the synthesized VO2 powders. Ex-situ XRD studies after heat treatment confirmed the thermal stability of the VO2 structure. Thermochromic properties, as a consequence of the reversible structural transformation between monoclinic VO2 and tetragonal phases, were observed by Fourier transform infrared spectroscopy (FTIR).

  13. Experimental Guidance of ISB Corrections via Direct Nuclear Reactions

    NASA Astrophysics Data System (ADS)

    Leach, K. G.; Garrett, P. E.; Ball, G. C.; Bangay, J. C.; Bianco, L.; Demand, G. A.; Faestermann, T.; Finlay, P.; Green, K. L.; Hertenberger, R.; Kriicken, R.; Phillips, A. A.; Rand, E. T.; Sumithrarachchi, C. S.; Svensson, C. E.; Towner, I. S.; Triambak, S.; Wirth, H.-F.; Wong, J.

    2011-09-01

    The most recent isospin-symmetry-breaking corrections, δc, of Towner and Hardy for superallowed Fermi β-decay transitions, have included the opening of specific core orbitals. This change has resulted in significant deviations in some of the δc factors from their previous calculations, and an improved agreement of the individual corrected Script Ft values with the overall world average of the 13 most precise cases. While this is consistent with the conserved-vector-current (CVC) hypothesis of the Standard Model, these new calculations must be thoroughly tested, and guidance must be given for the improvement of calculations for the upper-pf shell nuclei. Using the (d,t) reaction mechanism to probe the single neutron wavefunction overlap, information regarding the relevant shell-model configurations needed in the calculation can be determined. An experiment was therefore performed with a 22 MeV polarized deuterium beam from the MP tandem Van de Graaff accelerator in Munich, Germany. Using the Q3D magnetic spectrograph, and a cathode-strip focal-plane detector, outgoing tritons were analyzed at 9 angles between 10° and 60°, up to an excitation energy of 4.8 MeV. This proceeding reports the motivational and experimental details for the 64Zn(d,t)63Zn transfer work presented.

  14. Direct reaction of oximes with sarin, soman, or tabun in vitro.

    PubMed

    Becker, G; Kawan, A; Szinicz, L

    1997-01-01

    The direct reaction of seven pyridinium oximes with the nerve agents sarin, soman, and tabun was followed by a spectrophotometric method. The half-lives (t1/2) of the oximes, the first- and second-order rate constants (k1, k2), and the maximal reaction velocity (vmax) were calculated according to changes in the absorbance of the zwitterion (betaine) peak. In all cases the reaction velocity of the nerve agents with any of the oximes was highest with tabun, followed by sarin and then soman. Comparing the reaction rates of three therapeutically used oximes with the same nerve agent, the highest rate was obtained for soman with obidoxime, for sarin with 2-PAM, and for tabun with HI 6. The maximal reaction velocities reveal that the detoxification of the nerve agents by direct reaction with oximes and the subsequent decomposition of the phosphonyl oxime in vivo do not substantially contribute to the therapeutic effect of these antidotes. PMID:9363846

  15. Direct picosecond time resolution of unimolecular reactions initiated by local mode excitation

    NASA Technical Reports Server (NTRS)

    Scherer, N. F.; Doany, F. E.; Zewail, A. H.; Perry, J. W.

    1986-01-01

    Attention is given to the first results of direct, picosec measurements of the Delta-nu(OH) 5 local mode transition of H2O2. These time-resolved studies yield a direct measure of the unimolecular dissociation rate, and furnish a lower limit for the rate of energy redistribution from the OH stretch to the O-O reaction coordinate. The data thus determined may be used to ascertain the domain of validity for statistical unimolecular reaction rate theories.

  16. Behavior of New Zealand Ironsand During Iron Ore Sintering

    NASA Astrophysics Data System (ADS)

    Wang, Zhe; Pinson, David; Chew, Sheng; Rogers, Harold; Monaghan, Brian J.; Pownceby, Mark I.; Webster, Nathan A. S.; Zhang, Guangqing

    2016-02-01

    A New Zealand ironsand sample was characterized by scanning electron microscopy (SEM), X-ray fluorescence spectroscopy, qualitative and quantitative X-ray diffraction, and electron probe microanalysis. The titanomagnetite-rich ironsand was added into an industrial sinter blend in the proportion of 5 wt pct, and the mixture was uniaxially pressed into cylindrical tablets and sintered in a tube furnace under flowing gas with various oxygen potentials and temperatures to develop knowledge and understanding of the behavior of titanium during sintering. An industrial sinter with the addition of 3 wt pct ironsand was also examined. Both the laboratory and industrial sinters were characterized by optical and SEM. Various morphologies of relict ironsand particles were present in the industrial sinter due to the heterogeneity of sintering conditions, which could be well simulated by the bench-scale sintering experiments. The assimilation of ironsand during sintering in a reducing atmosphere started with the diffusion of calcium into the lattice of the ironsand matrix, and a reaction zone was formed near the boundary within individual ironsand particles where a perovskite phase was generated. With increasing sintering temperature, in a reducing atmosphere, ironsand particles underwent further assimilation and most of the titanium moved from the ironsand particles into a glass phase. In comparison, more titanium remained in the original ironsand particles when sintered in air. Ironsand particles are more resistant to assimilation in an oxidizing atmosphere.

  17. Highly active copper-network catalyst for the direct aldol reaction.

    PubMed

    Ohta, Hidetoshi; Uozumi, Yasuhiro; Yamada, Yoichi M A

    2011-09-01

    The development of a highly active solid-phase catechol-copper network catalyst for direct aldol reaction is described. The catalyst was prepared from an alkyl-chain-linked bis(catechol) and a copper(II) complex. The direct aldol reaction between carbonyl compounds (aldehydes and ketones) and methyl isocyanoacetate was carried out using 0.1-1 mol% [Cu] catalyst to give the corresponding oxazolines at yields of up to 99% and a trans/cis ratio of >99:1. The catalyst was reused with no loss of catalytic activity. A plausible reaction pathway is also described. PMID:21751405

  18. Methods of flash sintering

    DOEpatents

    Raj, Rishi; Cologna, Marco; Francis, John S.

    2016-05-10

    This disclosure provides methods of flash sintering and compositions created by these methods. Methods for sintering multilayered bodies are provided in which a sintered body is produced in less than one minute. In one aspect, each layer is of a different composition, and may be constituted wholly from a ceramic or from a combination of ceramic and metallic particles. When the body includes a layer of an anode composition, a layer of an electrolyte composition and a layer of a cathode composition, the sintered body can be used to produce a solid oxide fuel cell.

  19. Quantitative assignment of reaction directionality in constraint-based models of metabolism: Application to Escherichia coli

    PubMed Central

    Fleming, R.M.T.; Thiele, I.; Nasheuer, H.P.

    2009-01-01

    Constraint based modeling is an approach for quantitative prediction of net reaction flux in genome scale biochemical networks. In vivo, the second law of thermodynamics requires that net macroscopic flux be forward, when the transformed reaction Gibbs energy is negative. We calculate the latter by using (i) group contribution estimates of metabolite species Gibbs energy, combined with (ii) experimentally measured equilibrium constants. In an application to a genome scale stoichiometric model of E. coli metabolism, iAF1260, we demonstrate that quantitative prediction of reaction directionality is increased in scope and accuracy by integration of both data sources, transformed appropriately to in vivo pH, temperature and ionic strength. Comparison of quantitative versus qualitative assignment of reaction directionality in iAF1260, assuming an accommodating reactant concentration range of 0.02 – 20 mM, revealed that quantitative assignment leads to a low false positive, but high false negative, prediction of effectively irreversible reactions. The latter is partly due to the uncertainty associated with group contribution estimates. We also uncovered evidence that the high intracellular concentration of glutamate in E. coli may be essential to direct otherwise thermodynamically unfavorable essential reactions, such as the leucine transaminase reaction, in an anabolic direction. PMID:19783351

  20. Evaluation of fit of cement-retained implant-supported 3-unit structures fabricated with direct metal laser sintering and vacuum casting techniques.

    PubMed

    Oyagüe, Raquel Castillo; Sánchez-Turrión, Andrés; López-Lozano, José Francisco; Montero, Javier; Albaladejo, Alberto; Suárez-García, María Jesús

    2012-07-01

    This study evaluated the vertical discrepancy of implant-fixed 3-unit structures. Frameworks were constructed with laser-sintered Co-Cr, and vacuum-cast Co-Cr, Ni-Cr-Ti, and Pd-Au. Samples of each alloy group were randomly luted in standard fashion using resin-modified glass-ionomer, self-adhesive, and acrylic/urethane-based cements (n = 12 each). Discrepancies were SEM analyzed. Three-way ANOVA and Student-Newman-Keuls tests were run (P < 0.05). Laser-sintered structures achieved the best fit per cement tested. Within each alloy group, resin-modified glass-ionomer and acrylic/urethane-based cements produced comparably lower discrepancies than the self-adhesive agent. The abutment position did not yield significant differences. All misfit values could be considered clinically acceptable. PMID:22075754

  1. Direct elementary reactions of boron and nitrogen at high pressures and temperatures

    SciTech Connect

    Yoo, C.S.; Akella, J.; Cynn, H.; Nicol, M.

    1997-07-01

    Highly exothermic direct reactions between elements boron and nitrogen at high pressures and temperatures yield technologically important forms of hexagonal and cubic boron nitride (BN). The crystal structures of the reaction products vary with pressure. Below 10 GPa, hexagonal BN is the product; cubic or wurzite BN form at higher pressures. Under nitrogen-rich conditions, another hexagonal allotrope occurs; this seems to be a highly transparent, low density h{sup {prime}}-BN. No direct reactions occur at ambient temperature even at pressures as high as 50 GPa, implying that a large activation barrier limits the kinetics of these exothermic processes. Direct reactions between boron and oxygen are also discussed. {copyright} {ital 1997} {ital The American Physical Society}

  2. Fundamental studies of retrograde reactions in direct liquefaction. Topical report, September 30, 1988--September 30, 1989

    SciTech Connect

    Serio, M.A.; Solomon, P.R.; Bassilakis, R.; Kroo, E.

    1989-12-31

    Most of the proposed processing schemes for improving liquefaction yields involve favoring bond-breaking and radical stabilization reactions over the retrograde reactions. The retrograde reactions are often encountered before liquefaction temperatures are reached. The objective of this program is to elucidate and model the retrograde reaction chemistry in direct coal liquefaction through the application of experimental techniques and theoretical models which have been successfully employed at Advanced Fuel Research (AFR) and SRI International (a subcontractor) to understand and predict coal reaction behavior. The study of retrograde reactions is being done using an integrated approach using extensive characterization of the liquefaction chemistry of three kinds of systems: (1) model polymers; (2) coal; and (3) modified coals.

  3. Evaluation of sintering effects on SiC-incorporated UO2 kernels under Ar and Ar-4%H2 environments

    NASA Astrophysics Data System (ADS)

    Silva, Chinthaka M.; Lindemer, Terrence B.; Hunt, Rodney D.; Collins, Jack L.; Terrani, Kurt A.; Snead, Lance L.

    2013-11-01

    Silicon carbide (SiC) is suggested as an oxygen getter in UO2 kernels used for tristructural isotropic (TRISO) particle fuels and to prevent kernel migration during irradiation. Scanning electron microscopy and X-ray diffractometry analyses performed on sintered kernels verified that an internal gelation process can be used to incorporate SiC in UO2 fuel kernels. Even though the presence of UC in either argon (Ar) or Ar-4%H2 sintered samples suggested a lowering of the SiC up to 3.5-1.4 mol%, respectively, the presence of other silicon-related chemical phases indicates the preservation of silicon in the kernels during sintering process. UC formation was presumed to occur by two reactions. The first was by the reaction of SiC with its protective SiO2 oxide layer on SiC grains to produce volatile SiO and free carbon that subsequently reacted with UO2 to form UC. The second process was direct UO2 reaction with SiC grains to form SiO, CO, and UC. A slightly higher density and UC content were observed in the sample sintered in Ar-4%H2, but both atmospheres produced kernels with ˜95% of theoretical density. It is suggested that incorporating CO in the sintering gas could prevent UC formation and preserve the initial SiC content.

  4. Silicon nitride sintered body

    NASA Technical Reports Server (NTRS)

    Suzuki, K.; Shinohara, N.

    1984-01-01

    The sintering of silicon carbide and it production are described. The method of production is by calcination in which molding is followed by sintering without compression. The invention improves the composition of the silicon carbide ceramic. Six examples of the invention are illustrated and discussed.

  5. Enantiomerically pure bithiophene diphosphine oxides as catalysts for direct double aldol reactions.

    PubMed

    Genoni, Andrea; Benaglia, Maurizio; Rossi, Sergio; Celentano, Giuseppe

    2013-10-01

    The direct aldol reaction between aryl methyl ketones with aromatic aldehydes in the presence of tetrachlorosilane and a catalytic amount of a chiral bithiophene diphosphine oxide was studied; the product of double aldol addition was isolated as diacetate in good diastereoselectivity (up to 95:5) and enantioselectivities up to 91%. The reaction with heteroaromatic aldehydes was also investigated leading to the corresponding 1,3 diols, in some cases with excellent stereoselectivities. PMID:23744602

  6. Novel hydrophilic nanostructured microtexture on direct metal laser sintered Ti-6Al-4V surfaces enhances osteoblast response in vitro and osseointegration in a rabbit model.

    PubMed

    Hyzy, Sharon L; Cheng, Alice; Cohen, David J; Yatzkaier, Gustavo; Whitehead, Alexander J; Clohessy, Ryan M; Gittens, Rolando A; Boyan, Barbara D; Schwartz, Zvi

    2016-08-01

    The purpose of this study was to compare the biological effects in vivo of hierarchical surface roughness on laser sintered titanium-aluminum-vanadium (Ti-6Al-4V) implants to those of conventionally machined implants on osteoblast response in vitro and osseointegration. Laser sintered disks were fabricated to have micro-/nano-roughness and wettability. Control disks were computer numerical control (CNC) milled and then polished to be smooth (CNC-M). Laser sintered disks were polished smooth (LST-M), grit blasted (LST-B), or blasted and acid etched (LST-BE). LST-BE implants or implants manufactured by CNC milling and grit blasted (CNC-B) were implanted in the femurs of male New Zealand white rabbits. Most osteoblast differentiation markers and local factors were enhanced on rough LST-B and LST-BE surfaces in comparison to smooth CNC-M or LST-M surfaces for MG63 and normal human osteoblast cells. To determine if LST-BE implants were osteogenic in vivo, we compared them to implant surfaces used clinically. LST-BE implants had a unique surface with combined micro-/nano-roughness and higher wettability than conventional CNC-B implants. Histomorphometric analysis demonstrated a significant improvement in cortical bone-implant contact of LST-BE implants compared to CNC-B implants after 3 and 6 weeks. However, mechanical testing revealed no differences between implant pullout forces at those time points. LST surfaces enhanced osteoblast differentiation and production of local factors in vitro and improved the osseointegration process in vivo. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 2086-2098, 2016. PMID:27086616

  7. Analysis of weblike network structures of directed graphs for chemical reactions in methane plasmas

    NASA Astrophysics Data System (ADS)

    Sakai, Osamu; Nobuto, Kyosuke; Miyagi, Shigeyuki; Tachibana, Kunihide

    2015-10-01

    Chemical reactions of molecular gases like methane are so complicated that a chart of decomposed and/or synthesized species originating from molecules in plasma resembles a weblike network in which we write down species and reactions among them. Here we consider properties of the network structures of chemical reactions in methane plasmas. In the network, atoms/molecules/radical species are assumed to form nodes and chemical reactions correspond to directed edges in the terminology of graph theory. Investigation of the centrality index reveals importance of CH3 in the global chemical reaction, and difference of an index for each radical species between cases with and without electrons clarifies that the electrons are at an influential position to tighten the network structure.

  8. Analysis of weblike network structures of directed graphs for chemical reactions in methane plasmas

    SciTech Connect

    Sakai, Osamu Nobuto, Kyosuke; Miyagi, Shigeyuki; Tachibana, Kunihide

    2015-10-15

    Chemical reactions of molecular gases like methane are so complicated that a chart of decomposed and/or synthesized species originating from molecules in plasma resembles a weblike network in which we write down species and reactions among them. Here we consider properties of the network structures of chemical reactions in methane plasmas. In the network, atoms/molecules/radical species are assumed to form nodes and chemical reactions correspond to directed edges in the terminology of graph theory. Investigation of the centrality index reveals importance of CH{sub 3} in the global chemical reaction, and difference of an index for each radical species between cases with and without electrons clarifies that the electrons are at an influential position to tighten the network structure.

  9. The Trojan Horse method for nuclear astrophysics: Recent results for direct reactions

    SciTech Connect

    Tumino, A.; Gulino, M.; Spitaleri, C.; Cherubini, S.; Romano, S.; Cognata, M. La; Pizzone, R. G.; Rapisarda, G. G.; Lamia, L.

    2014-05-09

    The Trojan Horse method is a powerful indirect technique to determine the astrophysical factor for binary rearrangement processes A+x→b+B at astrophysical energies by measuring the cross section for the Trojan Horse (TH) reaction A+a→B+b+s in quasi free kinematics. The Trojan Horse Method has been successfully applied to many reactions of astrophysical interest, both direct and resonant. In this paper, we will focus on direct sub-processes. The theory of the THM for direct binary reactions will be shortly presented based on a few-body approach that takes into account the off-energy-shell effects and initial and final state interactions. Examples of recent results will be presented to demonstrate how THM works experimentally.

  10. PRECO-D2: program for calculating preequilibrium and direct reaction double differential cross sections

    SciTech Connect

    Kalbach, C.

    1985-02-01

    The code PRECO-D2 uses the exciton model for preequilibrium nuclear reactions to describe the emission of particles with mass numbers of 1 to 4 from an equilibrating composite nucleus. A distinction is made between open and closed configurations in this system and between the multi-step direct (MSD) and multi-step compound (MSC) components of the preequilibrium cross section. Additional MSD components are calculated semi-empirically to account for direct nucleon transfer reactions and direct knockout processes involving cluster degrees of freedom. Evaporation from the equilibrated composite nucleus is included in the full MSC cross section. Output of energy differential and double differential cross sections is provided for the first particle emitted from the composite system. Multiple particle emission is not considered. This report describes the reaction models used in writing PRECO-D2 and explains the organization and utilization of the code. 21 refs.

  11. The Trojan Horse method for nuclear astrophysics: Recent results for direct reactions

    NASA Astrophysics Data System (ADS)

    Tumino, A.; Spitaleri, C.; Cherubini, S.; Gulino, M.; La Cognata, M.; Lamia, L.; Pizzone, R. G.; Rapisarda, G. G.; Romano, S.

    2014-05-01

    The Trojan Horse method is a powerful indirect technique to determine the astrophysical factor for binary rearrangement processes A+x→b+B at astrophysical energies by measuring the cross section for the Trojan Horse (TH) reaction A+a→B+b+s in quasi free kinematics. The Trojan Horse Method has been successfully applied to many reactions of astrophysical interest, both direct and resonant. In this paper, we will focus on direct sub-processes. The theory of the THM for direct binary reactions will be shortly presented based on a few-body approach that takes into account the off-energy-shell effects and initial and final state interactions. Examples of recent results will be presented to demonstrate how THM works experimentally.

  12. Sintered wire cesium dispenser photocathode

    DOEpatents

    Montgomery, Eric J; Ives, R. Lawrence; Falce, Louis R

    2014-03-04

    A photoelectric cathode has a work function lowering material such as cesium placed into an enclosure which couples a thermal energy from a heater to the work function lowering material. The enclosure directs the work function lowering material in vapor form through a low diffusion layer, through a free space layer, and through a uniform porosity layer, one side of which also forms a photoelectric cathode surface. The low diffusion layer may be formed from sintered powdered metal, such as tungsten, and the uniform porosity layer may be formed from wires which are sintered together to form pores between the wires which are continuous from the a back surface to a front surface which is also the photoelectric surface.

  13. Direct and compound reactions induced by unstable helium beams near the Coulomb barrier

    NASA Astrophysics Data System (ADS)

    Navin, A.; Tripathi, V.; Blumenfeld, Y.; Nanal, V.; Simenel, C.; Casandjian, J. M.; de France, G.; Raabe, R.; Bazin, D.; Chatterjee, A.; Dasgupta, M.; Kailas, S.; Lemmon, R. C.; Mahata, K.; Pillay, R. G.; Pollacco, E. C.; Ramachandran, K.; Rejmund, M.; Shrivastava, A.; Sida, J. L.; Tryggestad, E.

    2004-10-01

    Reactions induced by radioactive 6,8 He beams from the SPIRAL facility were studied on 63,65 Cu and 188,190,192 Os targets and compared to reactions with the stable 4He projectiles from the Mumbai Pelletron. Partial residue cross sections for fusion and neutron transfer obtained from the measured intensities of characteristic in-beam γ rays for the 6He + 63,65 Cu systems are presented. Coincidence measurements of heavy reaction products, identified by their characteristic γ rays, with projectilelike charged particles, provide direct evidence for a large transfer cross section with Borromean nuclei 6He at 19.5 and 30 MeV and 8He at 27 MeV. Reaction cross sections were also obtained from measured elastic angular distributions for 6,8 He +Cu systems. Cross sections for fusion and direct reactions with 4,6 He beams on heavier targets of 188,192 Os at 30 MeV are also presented. The present work underlines the need to distinguish between various reaction mechanisms leading to the same products before drawing conclusions about the effect of weak binding on the fusion process. The feasibility of extracting small cross sections from inclusive in-beam γ -ray measurements for reaction studies near the Coulomb barrier with low intensity isotope separation on-line beams is highlighted.

  14. Direct and compound reactions induced by unstable helium beams near the Coulomb barrier

    SciTech Connect

    Navin, A.; Tripathi, V.; Chatterjee, A.; Kailas, S.; Mahata, K.; Ramachandran, K.; Shrivastava, A.; Blumenfeld, Y.; Tryggestad, E.; Nanal, V.; Pillay, R.G.; Simenel, C.; Casandjian, J.M.; France, G. de; Rejmund, M.; Raabe, R.; Pollacco, E.C.; Sida, J.L.; Dasgupta, M.

    2004-10-01

    Reactions induced by radioactive {sup 6,8}He beams from the SPIRAL facility were studied on {sup 63,65}Cu and {sup 188,190,192}Os targets and compared to reactions with the stable {sup 4}He projectiles from the Mumbai Pelletron. Partial residue cross sections for fusion and neutron transfer obtained from the measured intensities of characteristic in-beam {gamma} rays for the {sup 6}He+{sup 63,65}Cu systems are presented. Coincidence measurements of heavy reaction products, identified by their characteristic {gamma} rays, with projectilelike charged particles, provide direct evidence for a large transfer cross section with Borromean nuclei {sup 6}He at 19.5 and 30 MeV and {sup 8}He at 27 MeV. Reaction cross sections were also obtained from measured elastic angular distributions for {sup 6,8}He+Cu systems. Cross sections for fusion and direct reactions with {sup 4,6}He beams on heavier targets of {sup 188,192}Os at 30 MeV are also presented. The present work underlines the need to distinguish between various reaction mechanisms leading to the same products before drawing conclusions about the effect of weak binding on the fusion process. The feasibility of extracting small cross sections from inclusive in-beam {gamma}-ray measurements for reaction studies near the Coulomb barrier with low intensity isotope separation on-line beams is highlighted.

  15. Noncovalent Substrate-Directed Enantioselective Heck Reactions: Synthesis of S- and P-Stereogenic Heterocycles.

    PubMed

    de Azambuja, Francisco; Carmona, Rafaela C; Chorro, Tomaz H D; Heerdt, Gabriel; Correia, Carlos Roque D

    2016-08-01

    S- and P-Stereogenic heterocycles were synthesized by a remarkably simple enantioselective Heck desymmetrization reaction based on the unprecedented noncovalent directing effect of S=O and P=O functionalities. Selected prochiral symmetric substrates were efficiently arylated using the recently disclosed chiral PyraBOx ligand under mild and open-flask reaction conditions. Several five-membered aryl- sulfones, sulfoxides, and phosphine oxides were synthesized in good to excellent yields, in good to high diastereoselectivity, and enantiomeric ratios up to 98:2. Theoretical calculations also support the noncovalent directing effect of the S=O and P=O functionalities during the arylation process. PMID:27273079

  16. Branched Arylalkenes from Cinnamates: Selectivity Inversion in Heck Reactions by Carboxylates as Deciduous Directing Groups.

    PubMed

    Tang, Jie; Hackenberger, Dagmar; Goossen, Lukas J

    2016-09-01

    A decarboxylative Mizoroki-Heck coupling of aryl halides with cinnamic acids has been developed in which the carboxylate group directs the arylation into its β-position before being tracelessly removed through protodecarboxylation. In the presence of a copper/palladium catalyst, both electron-rich and electron-deficient aryl bromides and chlorides bearing numerous functionalities were successfully coupled with broadly available cinnamates, with selective formation of 1,1-disubstituted alkenes. This reaction concept, in which the carboxylate acts as a deciduous directing group, ideally complements traditional 1,2-selective Heck reactions of styrenes. PMID:27485163

  17. Microstructural and continuum evolution modeling of sintering.

    SciTech Connect

    Braginsky, Michael V.; Olevsky, Eugene A.; Johnson, D. Lynn; Tikare, Veena; Garino, Terry J.; Arguello, Jose Guadalupe, Jr.

    2003-12-01

    deformation during. The continuum portion is based on a finite element formulation that allows 3D components to be modeled using SNL's nonlinear large-deformation finite element code, JAS3D. This tool provides a capability to model sintering of complex three-dimensional components. The model was verified by comparing to simulations results published in the literature. The model was validated using experimental results from various laboratory experiments performed by Garino. In addition, the mesoscale simulations were used to study anisotropic shrinkage in aligned, elongated powder compacts. Anisotropic shrinkage occurred in all compacts with aligned, elongated particles. However, the direction of higher shrinkage was in some cases along the direction of elongation and in other cases in the perpendicular direction depending on the details of the powder compact. In compacts of simple-packed, mono-sized, elongated particles, shrinkage was higher in the direction of elongation. In compacts of close-packed, mono-sized, elongated particles and of elongated particles with a size and shape distribution, the shrinkage was lower in the direction of elongation. We also explored the concept of a sintering stress tensor rather than the traditional sintering stress scalar concept for the case of anisotropic shrinkage. A thermodynamic treatment of this is presented. A method to calculate the sintering stress tensor is also presented. A user-friendly code that can simulate microstructural evolution during sintering in 2D and in 3D was developed. This code can run on most UNIX platforms and has a motif-based GUI. The microstructural evolution is shown as the code is running and many of the microstructural features, such as grain size, pore size, the average grain boundary length (in 2D) and area (in 3D), etc. are measured and recorded as a function of time. The overall density as the function of time is also recorded.

  18. Sintering titanium powders

    SciTech Connect

    Gerdemann, Stephen J.; Alman, David E.

    2005-09-01

    Recently, there has been renewed interest in low-cost titanium. Near-net-shape powder metallurgy offers the potential of manufacturing titanium articles without costly and difficult forming and machining operations; hence, processing methods such as conventional press-and-sinter, powder forging and powder injection molding are of interest. The sintering behavior of a variety of commercial and experimental titanium powders was studied. Commercial powders were acquired that were produced different routes: (i) sponge fines from the primary titanium processing; (ii) via the hydride-dehydride process; and (iii) gas atomization. The influence of vacuum sintering time (0.5 to 32 hrs) and temperature (1200, 1275 or 1350°C) on the microstructure (porosity present) of cold pressed powders was studied. The results are discussed in terms of the difference in powder characteristics, with the aim of identify the characteristics required for full density via press-and-sinter processing. Near-net-shape tensile bars were consolidated via cold pressed and sintered. After sintering, a sub-set of the tensile bars was hot-isostatic pressed (HIPed). The microstructure and properties of the bars were compared in the sintered and HIPed conditions.

  19. Reaction ensemble molecular dynamics: Direct simulation of the dynamic equilibrium properties of chemically reacting mixtures

    NASA Astrophysics Data System (ADS)

    Brennan, John K.; Lísal, Martin; Gubbins, Keith E.; Rice, Betsy M.

    2004-12-01

    A molecular simulation method to study the dynamics of chemically reacting mixtures is presented. The method uses a combination of stochastic and dynamic simulation steps, allowing for the simulation of both thermodynamic and transport properties. The method couples a molecular dynamics simulation cell (termed dynamic cell) to a reaction mixture simulation cell (termed control cell) that is formulated upon the reaction ensemble Monte Carlo (RxMC) method, hence the term reaction ensemble molecular dynamics. Thermodynamic and transport properties are calculated in the dynamic cell by using a constant-temperature molecular dynamics simulation method. RxMC forward and reverse reaction steps are performed in the control cell only, while molecular dynamics steps are performed in both the dynamic cell and the control cell. The control cell, which acts as a sink and source reservoir, is maintained at reaction equilibrium conditions via the RxMC algorithm. The reaction ensemble molecular dynamics method is analogous to the grand canonical ensemble molecular dynamics technique, while using some elements of the osmotic molecular dynamics method, and so simulates conditions that directly relate to real, open systems. The accuracy and stability of the method is assessed by considering the ammonia synthesis reaction N2+3H2⇔2NH3 . It is shown to be a viable method for predicting the effects of nonideal environments on the dynamic properties (particularly diffusion) as well as reaction equilibria for chemically reacting mixtures.

  20. SINTERED REFRACTORY MASS

    DOEpatents

    Williams, A.E.

    1955-09-01

    A method is given for joining sintered masses of refractory compounds. It consists in maintaining the masses in contact with each other by application of a moderate pressure, while they are at sintering temperature. The sintered masses are subjected to am applied pressure of about 1/2 to 1 ton per square inch of the surface in contact for about 10 minutes, and the temperature employed may be fropn about 1400 deg C to 2000 deg C. Refractory oxides to which the invention may be applied are beryllia, alumina, thoria, and magnesia.

  1. Microwave sintering of ceramics

    SciTech Connect

    Snyder, W.B.

    1989-01-01

    Successful adaptation of microwave heating to the densification of ceramic materials require a marriage of microwave and materials technologies. Using an interdisciplinary team of microwave and materials engineers, we have successfully demonstrated the ability to density ceramic materials over a wide range of temperatures. Microstructural evolution during microwave sintering has been found to be significantly different from that observed in conventional sintering. Our results and those of others indicate that microwave sintering has the potential to fabricate components to near net shape with mechanical properties equivalent to hot pressed or hot isostatically pressed material. 6 refs., 11 figs.

  2. Investigation of photochemical reaction products of glucose formed during direct UV detection in CE.

    PubMed

    Schmid, Thomas; Himmelsbach, Markus; Buchberger, Wolfgang W

    2016-04-01

    In CE, saccharides are accessible to direct UV detection due to a photochemical reaction in the detection window of the separation capillary resulting in the formation of UV absorbing substances. Employing a CE method that allows long in-capillary irradiation with subsequent UV and MS detection, the present study could identify several reaction products of glucose. Among these were UV absorbing substances so far unknown to be formed during direct UV detection with the chemical formulas C4 H6 O2 , C5 H6 O4 , C5 H8 O3, and C6 H8 O5 . Investigations of the impact of the irradiation time revealed differences between these reaction products suggesting differing reaction mechanisms especially for the smallest products. More detailed information could be obtained by experiments with isotope-labeled substrates performed to determine the parts of glucose that are converted to the particular reaction products. In addition, structural formulas for the reaction products were suggested based on HPLC-MS/MS measurements of off-line irradiated glucose solutions which revealed the existence of functional groups such as carboxylic acid or aldehyde groups. PMID:26257208

  3. Direct dynamics simulations of the hydrogen abstraction reaction Cl + CF₃CF₂CH₂OH.

    PubMed

    Yu, Ang-Yang; Zhang, Hong-Xing

    2013-10-01

    The mechanism and kinetics of 2,2,3,3,3-pentafluoropropanol (CF₃CF₂CH₂OH) reaction with Chlorine atom (Cl) is investigated in this work. Two hydrogen abstraction channels of the title reaction are identified. The geometries of all the stationary points in the potential energy surface are obtained at the BHandHLYP/6-311G level, and the energies of the selected points along the minimum energy path (MEP) are improved by the CCSD(T) method. A dual-level direct dynamics method is employed to study the kinetic nature of the hydrogen-abstraction reaction channels. The calculated rate coefficients show that the hydrogen abstraction from the CH2 group is the primary channel. The calculated total rate coefficients are in best agreement with the experimental values. The four-parameter rate coefficients expression of the title reaction between the temperatures 200 K and 1000 K is provided. PMID:23942600

  4. Expanding the Enzyme Universe: Accessing Non-Natural Reactions by Mechanism-Guided Directed Evolution

    PubMed Central

    Renata, Hans; Wang, Z. Jane

    2015-01-01

    High selectivities and exquisite control over reaction outcomes entice chemists to use biocatalysts in organic synthesis. However, many useful reactions are not accessible because they are not in nature’s known repertoire. We will use this review to outline an evolutionary approach to engineering enzymes to catalyze reactions not found in nature. We begin with examples of how nature has discovered new catalytic functions and how such evolutionary progressions have been recapitulated in the laboratory starting from extant enzymes. We then examine non-native enzyme activities that have been discovered and exploited for chemical synthesis, emphasizing reactions that do not have natural counterparts. The new functions have mechanistic parallels to the native reaction mechanisms that often manifest as catalytic promiscuity and the ability to convert from one function to the other with minimal mutation. We present examples of how non-natural activities have been improved by directed evolution, mimicking the process used by nature to create new catalysts. Examples of new enzyme functions include epoxide opening reactions with non-natural nucleophiles catalyzed by a laboratory-evolved halohydrin dehalogenase, cyclopropanation and other carbene transfer reactions catalyzed by cytochrome P450 variants, and non-natural modes of cyclization by a modified terpene synthase. Lastly, we describe discoveries of non-native catalytic functions that may provide future opportunities for expanding the enzyme universe. PMID:25649694

  5. Directed electrostatic activation in enantioselective organocatalytic cyclopropanation reactions: a computational study.

    PubMed

    Georgieva, Miglena K; Duarte, Filipe J S; Santos, A Gil

    2016-07-01

    Cyclopropane rings are versatile building blocks in organic chemistry. Their synthesis, by the reaction of sulfur ylides with α,β-unsaturated carbonyl compounds, has recently aroused renewed interest after the discovery of efficient catalysis by using (S)-indoline-2-carboxylic acid. In order to rationalize the behavior of this catalyst, MacMillan proposed a directed electrostatic activation (DEA) mechanism, in which the negative carboxylate group interacts with the positive thionium moiety, thus reducing the activation energy and increasing the reaction rate. More recently, Mayr refuted some of MacMillan conclusions, but accepted the DEA mechanism as a justification for the experimental high reaction rates. In contrast, our results indicate that the selectivity obtained in the process seems to result from several strong hydrogen bond interactions between the two reacting species, while no strong evidence for a DEA mechanism was found. We also concluded that the hydrogen bonds don't improve the reaction rate by lowering the activation energy of the rate-determining step, but can do it by promoting efficient reaction trajectories due to long-range complexation of the reagents. Finally, our results confirm that the cyclopropanation reaction occurs by a two-step mechanism, and that the overall enantioselectivity depends on the relative energies of the two steps, averaged by the relative populations of the iminium intermediates that are initially formed in the reaction. PMID:27223461

  6. Sintered wire annode

    DOEpatents

    Falce, Louis R.; Ives, R. Lawrence

    2007-12-25

    A plurality of high atomic number wires are sintered together to form a porous rod that is parted into porous disks which will be used as x-ray targets. A thermally conductive material is introduced into the pores of the rod, and when a stream of electrons impinges on the sintered wire target and generates x-rays, the heat generated by the impinging x-rays is removed by the thermally conductive material interspersed in the pores of the wires.

  7. Direct Catalytic Asymmetric Mannich-Type Reaction of α- and β-Fluorinated Amides.

    PubMed

    Brewitz, Lennart; Arteaga, Fernando Arteaga; Yin, Liang; Alagiri, Kaliyamoorthy; Kumagai, Naoya; Shibasaki, Masakatsu

    2015-12-23

    The last two decades have witnessed the emergence of direct enolization protocols providing atom-economical and operationally simple methods to use enolates for stereoselective C-C bond-forming reactions, eliminating the inherent drawback of the preformation of enolates using stoichiometric amounts of reagents. In its infancy, direct enolization relied heavily on the intrinsic acidity of the latent enolates, and the reaction scope was limited to readily enolizable ketones and aldehydes. Recent advances in this field enabled the exploitation of carboxylic acid derivatives for direct enolization, offering expeditious access to synthetically versatile chiral building blocks. Despite the growing demand for enantioenriched fluorine-containing small molecules, α- and β-fluorinated carbonyl compounds have been neglected in direct enolization chemistry because of the competing and dominating defluorination pathway. Herein we present a comprehensive study on direct and highly stereoselective Mannich-type reactions of α- and β-fluorine-functionalized 7-azaindoline amides that rely on a soft Lewis acid/hard Brønsted base cooperative catalytic system to guarantee an efficient enolization while suppressing undesired defluorination. This protocol contributes to provide a series of fluorinated analogs of enantioenriched β-amino acids for medicinal chemistry. PMID:26652911

  8. Direct measurement of the 22Ne(p,γ)23Na reaction cross section at LUNA

    NASA Astrophysics Data System (ADS)

    Ferraro, Federico; LUNA Collaboration

    2016-06-01

    The 22Ne(p, γ)23Na reaction takes part in the NeNa cycle of hydrogen burning, influencing the production of the elements between 20Ne and 27Al in red giant stars, asymptotic giant stars and classical novae. The 22Ne(p,γ)27Na reaction rate is very uncertain because of a large number of tentative resonances in the Gamow window, where only upper limits were quoted in literature. A direct measurement of the 22Ne(p, γ)23Na reaction cross section has been carried out at LUNA using a windowless differential-pumping gas target with two high- purity germanium (HPGe) detectors. A new measurement with a 4π bismuth germanate (BGO) summing detector is ongoing. During the HPGe phase of the experiment the strengths of the resonances at 156.2 keV, 189.5 keV and 259.7 keV have been directly measured for the first time and their contribution to the reaction rate has been calculated. The decay scheme of the newly discovered resonances has been established as well and some improved upper limits on the unobserved resonances have been put. The BGO detector with its 70% γ-detection efficiency allows to measure the cross section at lower energy. In order to further investigate the resonances at 71 keV and 105 keV and the direct-capture component, the data taking is ongoing.

  9. Direct detection of pyridine formation by the reaction of CH (CD) with pyrrole: a ring expansion reaction

    SciTech Connect

    Soorkia, Satchin; Taatjes, Craig A.; Osborn, David L.; Selby, Talitha M.; Trevitt, Adam J.; Wilson, Kevin R.; Leone, Stephen R.

    2010-03-16

    The reaction of the ground state methylidyne radical CH (X2Pi) with pyrrole (C4H5N) has been studied in a slow flow tube reactor using Multiplexed Photoionization Mass Spectrometry coupled to quasi-continuous tunable VUV synchrotron radiation at room temperature (295 K) and 90 oC (363 K), at 4 Torr (533 Pa). Laser photolysis of bromoform (CHBr3) at 248 nm (KrF excimer laser) is used to produce CH radicals that are free to react with pyrrole molecules in the gaseous mixture. A signal at m/z = 79 (C5H5N) is identified as the product of the reaction and resolved from 79Br atoms, and the result is consistent with CH addition to pyrrole followed by Helimination. The Photoionization Efficiency curve unambiguously identifies m/z = 79 as pyridine. With deuterated methylidyne radicals (CD), the product mass peak is shifted by +1 mass unit, consistent with the formation of C5H4DN and identified as deuterated pyridine (dpyridine). Within detection limits, there is no evidence that the addition intermediate complex undergoes hydrogen scrambling. The results are consistent with a reaction mechanism that proceeds via the direct CH (CD) cycloaddition or insertion into the five-member pyrrole ring, giving rise to ring expansion, followed by H atom elimination from the nitrogen atom in the intermediate to form the resonance stabilized pyridine (d-pyridine) molecule. Implications to interstellar chemistry and planetary atmospheres, in particular Titan, as well as in gas-phase combustion processes, are discussed.

  10. Direct simulation of proton-coupled electron transfer reaction dynamics and mechanisms

    NASA Astrophysics Data System (ADS)

    Kretchmer, Joshua S.; Miller, Thomas F., III

    2014-03-01

    Proton-coupled electron transfer (PCET) reactions, in which both an electron and an associated proton undergo reactive transfer, play an important role in many chemical and biological systems. Due to the complexity of this class of reactions, a variety of different mechanisms fall under the umbrella of PCET. However, the physical driving forces that determine the preferred mechanism in a given system still remain poorly understood. Towards this end, we extend ring polymer molecular dynamics (RPMD), a path-integral quantum dynamics method, to enable the direct simulation and characterization of PCET reaction dynamics in both fully atomistic and system-bath models of organometallic catalysts. In addition to providing validation for the simulation method via extensive comparison with existing PCET rate theories, we analyze the RPMD trajectories to investigate the competition between the concerted and sequential reaction mechanisms for PCET, elucidating the large role of the solvent in controlling the preferred mechanism. We further employ RPMD to determine the kinetics and mechanistic features of concerted PCET reactions across different regimes of electronic and vibrational coupling, providing evidence for a new and distinct PCET reaction mechanism.

  11. Direct use of the mass output of a thermobalance for controlling the reaction rate of solid-state reactions

    NASA Astrophysics Data System (ADS)

    Diánez, M. J.; Pérez Maqueda, L. A.; Criado, J. M.

    2004-08-01

    Sample controlled thermal analysis equipment has been developed constituted by an electrobalance in which the mass output (TG signal) is directly used for monitoring the temperature of thermal decomposition reactions under constant rate thermal analysis (CRTA) or stepwise isothermal analysis (SIA) control. The sample weight is programmed to follow a preset linear decrease as a function of the time by means of a conventional controller, that at the time control a second conventional temperature programmer. The CRTA control is achieved by controlling the temperature is such a way that if the mass input is higher than the setpoint, the temperature increases at a predefined heating rate; while if the mass input is lower than the setpoint, the temperature decreases at a predefined cooling rate. The SIA control is achieved by selecting the run-hold command from the menu of the digital input of the temperature programmer. In such a case, the programmed linear heating schedule is in progress while the sample weight is higher than the setpoint and an isothermal dwell is maintained as soon as the weight becomes lower than the setpoint. The direct use of the mass output for the control provides a higher sensitivity for selecting very low values of constant reaction rates than the more conventional methods using the DTG output as control parameter. The thermal degradation of polyvinye chloride (PVC) has been used for checking the behavior of the equipment here developed, showing that the dehydrochlorination of PVC is controlled either by a nucleation and growth of nuclei or by a random scission of the main chain of the polymer.

  12. Sintering Theory and Practice

    NASA Astrophysics Data System (ADS)

    German, Randall M.

    1996-01-01

    Although sintering is an essential process in the manufacture of ceramics and certain metals, as well as several other industrial operations, until now, no single book has treated both the background theory and the practical application of this complex and often delicate procedure. In Sintering Theory and Practice, leading researcher and materials engineer Randall M. German presents a comprehensive treatment of this subject that will be of great use to manufacturers and scientists alike. This practical guide to sintering considers the fact that while the bonding process improves strength and other engineering properties of the compacted material, inappropriate methods of control may lead to cracking, distortion, and other defects. It provides a working knowledge of sintering, and shows how to avoid problems while accounting for variables such as particle size, maximum temperature, time at that temperature, and other problems that may cause changes in processing. The book describes the fundamental atomic events that govern the transformation from particles to solid, covers all forms of the sintering process, and provides a summary of many actual production cycles. Building from the ground up, it begins with definitions and progresses to measurement techniques, easing the transition, especially for students, into advanced topics such as single-phase solid-state sintering, microstructure changes, the complications of mixed particles, and pressure-assisted sintering. German draws on some six thousand references to provide a coherent and lucid treatment of the subject, making scientific principles and practical applications accessible to both students and professionals. In the process, he also points out and avoids the pitfalls found in various competing theories, concepts, and mathematical disputes within the field. A unique opportunity to discover what sintering is all about--both in theory and in practice What is sintering? We see the end product of this thermal

  13. Synthetic Studies on Tricyclic Diterpenoids: Direct Allylic Amination Reaction of Isopimaric Acid Derivatives.

    PubMed

    Timoshenko, Mariya A; Kharitonov, Yurii V; Shakirov, Makhmut M; Bagryanskaya, Irina Yu; Shults, Elvira E

    2016-02-01

    A selective synthesis of 7- or 14-nitrogen containing tricyclic diterpenoids was completed according to a strategy in which the key step was the catalyzed direct allylic amination of methyl 14α-hydroxy-15,16-dihydroisopimarate with a wide variety of nitrogenated nucleophiles. It was revealed that the selectivity of the reaction depends on the nature of nucleophile. The catalyzed reaction of the mentioned diterpenoid allylic alcohol with 3-nitroaniline, 3-(trifluoromethyl)aniline, and 4-(trifluoromethyl)aniline yield the subsequent 7α-, 7β- and 14αnitrogen-containing diterpenoids. The reaction with 2-nitroaniline, 4-nitro-2-chloroaniline, 4-methoxy-2-nitroaniline, phenylsulfamide, or tert-butyl carbamate proceeds with the formation of 7α-nitrogen-substituted diterpenoids as the main products. PMID:27308214

  14. DIRECT COMPARISON OF KINETIC AND LOCAL EQUILIBRIUM FORMULATIONS FOR SOLUTE TRANSPORT AFFECTED BY SURFACE REACTIONS.

    USGS Publications Warehouse

    Bahr, Jean M.; Rubin, Jacob

    1987-01-01

    Modeling transport of reacting solutes in porous media often requires a choice between models based on the local equilibrium assumption (LEA) and models involving reaction kinetics. Direct comparison of the mathematical formulations for these two types of transport models can aid in this choice. For cases of transport affected by surface reaction, such a comparison is made possible by a new derivation procedure. This procedure yields a kinetics-based formulation that is the sum of the LEA formulation and one or more kinetically influenced terms. The dimensionless form of the new kinetics-based formulation facilitates identification of critical parameter groupings which control the approach to transport behavior consistent with LEA model predictions. Results of numerical experiments demonstrate that criteria for LEA applicability can be expressed conveniently in terms of these parameter groupings. The derivation procedure is demonstrated for examples of surface reactions including first-order reversible sorption, Langmuir-type kinetics and binary, homovalent ion exchange.

  15. Synthetic Studies on Tricyclic Diterpenoids: Direct Allylic Amination Reaction of Isopimaric Acid Derivatives†

    PubMed Central

    Timoshenko, Mariya A.; Kharitonov, Yurii V.; Shakirov, Makhmut M.; Bagryanskaya, Irina Yu.

    2015-01-01

    Abstract A selective synthesis of 7‐ or 14‐nitrogen containing tricyclic diterpenoids was completed according to a strategy in which the key step was the catalyzed direct allylic amination of methyl 14α‐hydroxy‐15,16‐dihydroisopimarate with a wide variety of nitrogenated nucleophiles. It was revealed that the selectivity of the reaction depends on the nature of nucleophile. The catalyzed reaction of the mentioned diterpenoid allylic alcohol with 3‐nitroaniline, 3‐(trifluoromethyl)aniline, and 4‐(trifluoromethyl)aniline yield the subsequent 7α‐, 7β‐ and 14αnitrogen‐containing diterpenoids. The reaction with 2‐nitroaniline, 4‐nitro‐2‐chloroaniline, 4‐methoxy‐2‐nitroaniline, phenylsulfamide, or tert‐butyl carbamate proceeds with the formation of 7α‐nitrogen‐substituted diterpenoids as the main products. PMID:27308214

  16. Atmospheric chemistry. Direct kinetic measurement of the reaction of the simplest Criegee intermediate with water vapor.

    PubMed

    Chao, Wen; Hsieh, Jun-Ting; Chang, Chun-Hung; Lin, Jim Jr-Min

    2015-02-13

    Carbonyl oxides, or Criegee intermediates, are important transient species formed in the reactions of unsaturated hydrocarbons with ozone. Although direct detection of Criegee intermediates has recently been realized, the main atmospheric sink of Criegee intermediates remains unclear. We report ultraviolet absorption spectroscopic measurements of the lifetime of the simplest Criegee intermediate, CH2OO, at various relative humidity levels up to 85% at 298 kelvin. An extremely fast decay rate of CH2OO was observed at high humidity. The observed quadratic dependence of the decay rate on water concentration implied a predominant reaction with water dimer. On the basis of the water dimer equilibrium constant, the effective rate coefficient of the CH2OO + (H2O)2 reaction was determined to be 6.5 (±0.8) × 10(-12) cubic centimeters per second. This work would help modelers to better constrain the atmospheric concentrations of CH2OO. PMID:25569112

  17. Sintering studies project

    NASA Astrophysics Data System (ADS)

    Lange, F. F.; Knapp, W. J.

    1985-05-01

    A new concept explains the factors which influence the sinterability of ceramic (and metal) powders. This theory, based on the thermodynamics consideration of pore disappearance, is centered on the coordination number of distribution of pores within the initial powder compact and on the changes in the pore coordination number during sintering. Thermodynamic arguments show that only pores with a coordination number less than a critical value (R > R sub c) can disappear by diffusion. The coordination number of a pore is the number of touching particles that surround and the pore size. This concept suggested the following phenomena: (1) consolidation forces that increase bulk density will eliminate pores with high coordination numbers and thus increase the sinterability of the powder compact, (2) multiple-particle packing units containing pores with low coordination (R < R sub c) will first densify during sintering to increase the size and coordination number of pores between the densifying packing units, (3)grain growth, supported by dense packing units, will decrease the coordination number of pores enlarged by local densification. i.e., normal grain growth is advantageous to sinterability, and (4) compressive stress produced by either surface tension effects or hot pressing cause the dense regions to deform, thus closing pores between the dense regions and reducing their coordination number.

  18. The direct application of the polymerase chain reaction to DNA extracted from foods.

    PubMed

    Dickinson, J H; Kroll, R G; Grant, K A

    1995-04-01

    Two methods for the successful extraction of DNA from foods are described. The rapid lysis method uses a proteinase K buffer system to lyse cells and solubilize food samples. DNA is then precipitated using isopropanol. The second method achieves cell lysis using toluene and mutanolysin, and solubilization using guanidium thiocyanate. Following protein removal with organic solvents DNA is precipitated with isopropanol. Both methods enabled the polymerase chain reaction to be applied directly to DNA extracted from samples of cheese, coleslaw and raw chicken and allowed the direct rapid, sensitive and specific detection of Yersinia enterocolitica, Aerococcus viridans and Listeria monocytogenes in these foods. PMID:7766115

  19. Reactions on interfaces in heterophase TiN-Mo, TiN-W, ZrN-Mo, and ZrN-W materials during sintering

    SciTech Connect

    Pshenichnaya, O.V.; Verkhovodov, P.A.

    1985-08-01

    This paper reports on a study of the reactions on contact surfaces of solid titanium nitride and zirconium nitride specimens with molybdenum and tungsten in a vacuum corresponding to 0.01 Pa at temperatures in the range, 1900-2150/sup 0/C. The starting materials were titanium nitride containing 21.3% N and 0.3% O/sub 2/ dissolved in the TIN lattice; zirconium nitride containing 0.6-0.8% O/sub 2/; molybdenum with the impurities 0.02% C, 0.05% Ti, and 0.08% Zr; and tungsten with the impurities of 0.01% Si and 0.02% Hf. Polished end faces of specimens were pressed against each other with a small force, and in that position the specimens were annealed for an hour, after which microsections prepared in planes perpendicular to the control surfaces were investigated metallographically and by electron probe microanalysis. It is concluded that the development of bonds at interfaces between titanium nitride and zirconium nitride on the one hand, and molybdenum and tungsten on the other, is a consequence of diffusional reactions between the elements of the nitride phases and the metals which are accompanied by the formation of metal-base solid solutions localized within narrow contact zones.

  20. Electrical Property of Conventionally Sintered ZnO

    NASA Astrophysics Data System (ADS)

    Tak, S. K.; Shekhwat, M. S.; Mangal, R.

    ZnO powder was synthesized by solid state reaction method. The synthesized powder was granulated and pressed using uni-axial press for preparing the pallets. The prepared pellets were sintered in conventional furnace at different temperatures (900-1300° C). The phase study was done by powder X-ray diffraction and it was found that the there is no other phase present in the synthesized material but the peak intensity is increasing with temperature. The crystallite size of the synthesized ZnO powder was found to be increase with temperature. The effect of sintering on grain growth is investigated by scanning electron microscopy (SEM). SEM revels that the average grain size is increases with increase in sintering temperature. AC impedance of these samples was decreased markedly with increased sintering temperature. In present work the effect of sintering temperatures and hold time on micro structural and electrical properties of ZnO ceramics is carried out.

  1. Evaluation of sintering effects on SiC incorporated UO2 kernels under Ar and Ar-4%H2 environments

    SciTech Connect

    Silva, Chinthaka M; Lindemer, Terrence; Hunt, Rodney Dale; Collins, Jack Lee; Terrani, Kurt A; Snead, Lance Lewis

    2013-01-01

    Silicon carbide (SiC) is suggested as an oxygen getter in UO2 kernels used for TRISO particle fuels to lower oxygen potential and prevent kernel migration during irradiation. Scanning electron microscopy and X-ray diffractometry analyses performed on sintered kernels verified that internal gelation process can be used to incorporate SiC in urania fuel kernels. Sintering in either Ar or Ar-4%H2 at 1500 C lowered the SiC content in the UO2 kernels to some extent. Formation of UC was observed as the major chemical phase in the process, while other minor phases such as U3Si2C2, USi2, U3Si2, and UC2 were also identified. UC formation was presumed to be occurred by two reactions. The first was the SiC reaction with its protective SiO2 oxide layer on SiC grains to produce volatile SiO and free carbon that subsequently reacted with UO2 to form UC. The second process was direct UO2 reaction with SiC grains to form SiO, CO, and UC, especially in Ar-4%H2. A slightly higher density and UC content was observed in the sample sintered in Ar-4%H2, but the use of both atmospheres produced kernels with ~95% of theoretical density. It is suggested that incorporating CO in the sintering gas would prevent UC formation and preserve the initial SiC content.

  2. Direct determination of the activation energy for the reaction of nitric oxide with ozone

    SciTech Connect

    Borders, R.A.

    1981-01-01

    The activation energy for the reaction of nitric oxide with ozone has been directly measured as a function of temperature. The instrument constructed for this study consisted of two flow tubes that are connected together at each end, where the reaction zone temperature of each flow tube was controlled independently. The reaction of nitric oxide and ozone was pseudo-first order ((NO)/(O/sub 3/) greater than or equal to 250) and studied by following the reduction of the chemiluminescence of one of the products (NO/sup *//sub 2/(/sup 2/B/sub 1,2/)) of the reaction. The chemiluminescence was measured using a microcomputer-controlled photon counter designed for these studies. The activation energy has been found to vary with temperature. The activation energy varies from 2390 +/- 10 calories at 216 K to 2970 +/- 60 calories at 333 K. The variation over the complete temperature range studied (204-353 K) is large enough (650 calories) that the errors associated with the method cannot account for all of the variation. There are other pathways for this reaction other than ground state reactants going to ground state products, and their contribution to the activation energy (approx.500 calories) has been found to be sufficient to account for the observed variation with temperature when added to the variation predicted by either transition state (180 calories) or collision (150 calories) theory.

  3. Particle beams in ultrastrong laser fields: direct laser acceleration and radiation reaction effects

    NASA Astrophysics Data System (ADS)

    Salamin, Yousef I.; Li, Jian-Xing; Hatsagortsyan, Karen Z.; Tamburini, Matteo; Di Piazza, Antonino; Keitel, Christoph H.

    2015-03-01

    Several aspects of the interaction of particle beams with ultrastrong laser fields are discussed. Firstly, we consider regimes when radiation reaction is not essential and it is demonstrated that employing chirped laser pulses, significant improvement of the direct acceleration of particles can be achieved. Results from single- and many-particle calculations of the particle acceleration, in vacuum, by plane-wave fields, as well as in tightly-focused laser beams, show that the mean energies and their spreads qualify them for important applications. Secondly, we investigate the effect of radiation reaction in electron-laser-beam interactions. Signatures of the quantum radiation reaction during the interaction of an electron bunch with a focused superstrong ultrashort laser pulse can be observed in a characteristic behavior of the spectral bandwidth, and the angular spread of the nonlinear Compton radiation on the laser pulse duration. Furthermore, it is shown that the radiation reaction effects can be employed to control the electron dynamics via the nonlinear interplay between the Lorentz and radiation reaction forces. In particular, it is shown that an ultrarelativistic electron bunch colliding head- on with a strong bichromatic laser pulse can be deflected in a controllable way, by changing either the relative phase or the relative amplitude between the two frequency components of the bichromatic field.

  4. Studies of the initial reactions that occur during direct coal liquefaction

    SciTech Connect

    Stohl, F.V.

    1989-01-01

    Reactions that occur during preconversion processing of coal in direct liquefaction can be either beneficial or harmful. The objectives of this work are to identify the types of compounds and process conditions that give rise to retrogressive reactions during preconversion processing. Experiments have been performed to evaluate the impacts of temperature, catalysts, mineral matter, and hydrogen donors on these reactions. Initial studies have been carried out using dibenzyl ether (DBE) because ether linkages represent one type of bonding believed to be present in coal (1). Previous studies have analyzed the kinetics and mechanisms of thermolysis of DBE (2,3) and have also used DBE to study effects of process variables in coal liquefaction (4). Results of thermal reactions with DBE have shown that the main reaction products are toluene, benzaldehyde, benzyl alcohol and benzene (2). In the presence of catalysts such as ZnCl/sub 2/, the product distributions are more complicated and can obtain significant amounts of material with higher molecular weights than DBE (5,6). 8 refs., 2 tabs.

  5. Sintering of Synroc D

    SciTech Connect

    Robinson, G.

    1982-06-01

    Sintering has been investigated as a method for the mineralization and densification of high-level nuclear defense waste powder. Studies have been conducted on Synroc D composite powder LS04. Optimal densification has been found to be highly dependent on the characteristics of the starting material. Powder subjected to milling, which was believed to reduce the level of agglomeration and possibly particle size, was found to densify better than powder not subjected to this milling. Densities of greater than 95% of theoretical could be achieved for samples sintered at 1150 to 1200/sup 0/C. Mineralogy was found to be as expected for Synroc D for samples sintered in a CO/sub 2//CO atmosphere where the Fe/sup +2//Fe/sup +3/ ratio was maintained at 1.0 to 5.75. In a more oxidizing, pure CO/sub 2/ atmosphere a new phase, not previously identified in Synroc D, was found.

  6. Ab initio study of the H + HONO reaction: Direct abstraction versus indirect exchange processes

    SciTech Connect

    Hsu, C.C.; Lin, M.C.; Mebel, A.M.; Melius, C.F.

    1997-01-02

    The mechanism of the H + HONO reaction (for which no experimental data are available) has been elucidated by ab initio molecular orbital calculations using modified G2 and BAC-MP4 methods. These results indicate that the reaction occurs predominantly by two indirect metathetical processes. One produces OH + HNO and H{sub 2}O + NO from the decomposition of vibrationally excited hydroxyl nitroxide, HN(O)OH, formed by H atom addition to the N atom of HONO. The other produces H{sub 2}O + NO from the decomposition of vibrationally excited dihydroxylamino radical, N(OH){sub 2}, formed by H atom addition to the terminal O atom. These indirect displacement processes are much more efficient than the commonly assumed, direct H-abstraction reaction producing H{sub 2} + NO{sub 2}. A transition-state theory calculation for the direct abstraction reaction and RRKM calculations for the two indirect displacement processes give rise to the following rate constants, in units of cm{sup 3} molecule{sup -1} s{sup -1} for the 300-3500 K temperature range under atmospheric conditions: k{sub H(2)} = 3.33 x 10{sup -16}T{sup 1.55} exp(-3328.5/T), k{sub OH} = 9.36 x 10{sup -14}T{sup 0.86} exp(-2500.8/T), k{sub H(2)O} = 1.35 x 10{sup -17}T{sup 1.89} exp-(-1935.7/T), where the rate constant for H{sub 2}O production represents the sum from both indirect displacement reactions. 32 refs., 3 figs., 7 tabs.

  7. Direct measurement of Criegee intermediate (CH2OO) reactions with acetone, acetaldehyde, and hexafluoroacetone.

    PubMed

    Taatjes, Craig A; Welz, Oliver; Eskola, Arkke J; Savee, John D; Osborn, David L; Lee, Edmond P F; Dyke, John M; Mok, Daniel W K; Shallcross, Dudley E; Percival, Carl J

    2012-08-14

    Criegee biradicals, i.e., carbonyl oxides, are critical intermediates in ozonolysis and have been implicated in autoignition chemistry and other hydrocarbon oxidation systems, but until recently the direct measurement of their gas-phase kinetics has not been feasible. Indirect determinations of Criegee intermediate kinetics often rely on the introduction of a scavenger molecule into an ozonolysis system and analysis of the effects of the scavenger on yields of products associated with Criegee intermediate reactions. Carbonyl species, in particular hexafluoroacetone (CF(3)COCF(3)), have often been used as scavengers. In this work, the reactions of the simplest Criegee intermediate, CH(2)OO (formaldehyde oxide), with three carbonyl species have been measured by laser photolysis/tunable synchrotron photoionization mass spectrometry. Diiodomethane photolysis produces CH(2)I radicals, which react with O(2) to yield CH(2)OO + I. The formaldehyde oxide is reacted with a large excess of a carbonyl reactant and both the disappearance of CH(2)OO and the formation of reaction products are monitored. The rate coefficient for CH(2)OO + hexafluoroacetone is k(1) = (3.0 ± 0.3) × 10(-11) cm(3) molecule(-1) s(-1), supporting the use of hexafluoroacetone as a Criegee-intermediate scavenger. The reactions with acetaldehyde, k(2) = (9.5 ± 0.7) × 10(-13) cm(3) molecule(-1) s(-1), and with acetone, k(3) = (2.3 ± 0.3) × 10(-13) cm(3) molecule(-1) s(-1), are substantially slower. Secondary ozonides and products of ozonide isomerization are observed from the reactions of CH(2)OO with acetone and hexafluoroacetone. Their photoionization spectra are interpreted with the aid of quantum-chemical and Franck-Condon-factor calculations. No secondary ozonide was observable in the reaction of CH(2)OO with acetaldehyde, but acetic acid was identified as a product under the conditions used (4 Torr and 293 K). PMID:22481381

  8. Li Intercalation into Graphite: Direct Optical Imaging and Cahn-Hilliard Reaction Dynamics.

    PubMed

    Guo, Yinsheng; Smith, Raymond B; Yu, Zhonghua; Efetov, Dmitri K; Wang, Junpu; Kim, Philip; Bazant, Martin Z; Brus, Louis E

    2016-06-01

    Lithium intercalation into graphite is a critical process in energy storage technology. Studies of Li intercalation kinetics have proved challenging due to structural and phase complexity, and sample heterogeneity. Here we report direct time- and space-resolved, all-optical measurement of Li intercalation. We use a single crystal graphite electrode with lithographically defined disc geometry. All-optical, Raman and reflectance measurements distinguish the intrinsic intercalation process from side reactions, and provide new insight into the microscopic intercalation process. The recently proposed Cahn-Hilliard reaction (CHR) theory quantitatively captures the observed phase front spatial patterns and dynamics, using a two-layer free-energy model with novel, generalized Butler-Volmer kinetics. This approach unites Cahn-Hilliard and electrochemical kinetics, using a thermodynamically consistent description of the Li injection reaction at the crystal edge that involves a cooperative opening of graphene planes. The excellent agreement between experiment and theory presented here, with single-crystal resolution, provides strong support for the CHR theory of solid-state reactions. PMID:27203128

  9. Direct numerical simulation of shear localization and decomposition reactions in shock-loaded HMX crystal

    SciTech Connect

    Austin, Ryan A.; Barton, Nathan R.; Reaugh, John E.; Fried, Laurence E.

    2015-05-14

    A numerical model is developed to study the shock wave ignition of HMX crystal. The model accounts for the coupling between crystal thermal/mechanical responses and chemical reactions that are driven by the temperature field. This allows for the direct numerical simulation of decomposition reactions in the hot spots formed by shock/impact loading. The model is used to simulate intragranular pore collapse under shock wave loading. In a reference case: (i) shear-enabled micro-jetting is responsible for a modest extent of reaction in the pore collapse region, and (ii) shear banding is found to be an important mode of localization. The shear bands, which are filled with molten HMX, grow out of the pore collapse region and serve as potential ignition sites. The model predictions of shear banding and reactivity are found to be quite sensitive to the respective flow strengths of the solid and liquid phases. In this regard, it is shown that reasonable assumptions of liquid-HMX viscosity can lead to chemical reactions within the shear bands on a nanosecond time scale.

  10. Direct numerical simulation of shear localization and decomposition reactions in shock-loaded HMX crystal

    DOE PAGESBeta

    Austin, Ryan A.; Barton, Nathan R.; Reaugh, John E.; Fried, Laurence E.

    2015-05-14

    A numerical model is developed to study the shock wave ignition of HMX crystal. The model accounts for the coupling between crystal thermal/mechanical responses and chemical reactions that are driven by the temperature field. This allows for the direct numerical simulation of decomposition reactions in the hot spots formed by shock/impact loading. The model is used to simulate intragranular pore collapse under shock wave loading. In a reference case: (i) shear-enabled micro-jetting is responsible for a modest extent of reaction in the pore collapse region, and (ii) shear banding is found to be an important mode of localization. The shearmore » bands, which are filled with molten HMX, grow out of the pore collapse region and serve as potential ignition sites. The model predictions of shear banding and reactivity are found to be quite sensitive to the respective flow strengths of the solid and liquid phases. In this regard, it is shown that reasonable assumptions of liquid-HMX viscosity can lead to chemical reactions within the shear bands on a nanosecond time scale.« less

  11. Sintering silicon nitride

    NASA Technical Reports Server (NTRS)

    Bansal, Narottam P. (Inventor); Levine, Stanley R. (Inventor); Sanders, William A. (Inventor)

    1993-01-01

    Oxides having a composition of (Ba(1-x)Sr(x))O-Al2O3-2SiO2 are used as sintering aids for producing an improved silicon nitride ceramic material. The x must be greater than 0 to insure the formation of the stable monoclinic celsian glass phase.

  12. app_sintering.cpp

    Energy Science and Technology Software Center (ESTSC)

    2012-09-12

    This application simulates simple solid state sintering by incorporating all the active mechanisms, namely, curvature-driven gain growth, pore shaping and migration by surface diffusion, and creation, diffusion and annihilation of vacancies. It is an application developed for SPPARKS and has to be run within this framework.

  13. Direct Observation of Sulfur Radicals as Reaction Media in lithium Sulfur Batteries

    SciTech Connect

    Wang, Qiang; Zheng, Jianming; Walter, Eric D.; Pan, Huilin; Lu, Dongping; Zuo, Pengjian; Chen, Honghao; Deng, Zhiqun; Liaw, Bor Yann; Yu, Xiqian; Yang, Xiaoning; Zhang, Jiguang; Liu, Jun; Xiao, Jie

    2014-12-09

    Lithium sulfur (Li-S) battery has been regaining tremendous interest in recent years because of its attractive attributes such as high gravimetric energy, low cost and environmental benignity. However, it is still not conclusively known how polysulfide ring/chain participates in the whole cycling and whether the discharge and charge process follow the same pathway. Herein, we demonstrate the direct observation of sulfur radicals by using in situ electron paramagnetic resonance (EPR) technique. Based on the concentration changes of sulfur radicals at different potentials, it is revealed that the chemical and electrochemical reactions in Li-S cell are driven each other to proceed through sulfur radicals, leading to two completely different reaction pathways during discharge and charge. The proposed radical mechanism may provide new insights to investigate the interactions between sulfur species and the electrolyte, inspiring novel strategies to develop Li-S battery technology.

  14. Direct Observation of Sulfur Radicals as Reaction Media in Lithium Sulfur Batteries

    DOE PAGESBeta

    Wang, Qiang; Zheng, Jianming; Walter, Eric; Pan, Huilin; Lv, Dongping; Zuo, Pengjian; Chen, Honghao; Deng, Z. D.; Liaw, Bor Y.; Yu, Xiqian; et al

    2015-01-09

    Lithium sulfur (Li-S) battery has been regaining tremendous interest in recent years because of its attractive attributes such as high gravimetric energy, low cost and environmental benignity. However, it is still not conclusively known how polysulfide ring/chain participates in the whole cycling and whether the discharge and charge processes follow the same pathway. Herein, we demonstrate the direct observation of sulfur radicals by using in situ electron paramagnetic resonance (EPR) technique. Based on the concentration changes of sulfur radicals at different potentials and the electrochemical characteristics of the cell, it is revealed that the chemical and electrochemical reactions in Li-Smore » cell are driving each other to proceed through sulfur radicals, leading to two completely different reaction pathways during discharge and charge. The proposed radical mechanism may provide new perspectives to investigate the interactions between sulfur species and the electrolyte, inspiring novel strategies to develop Li-S battery technology.« less

  15. Direct Observation of Sulfur Radicals as Reaction Media in Lithium Sulfur Batteries

    SciTech Connect

    Wang, Qiang; Zheng, Jianming; Walter, Eric; Pan, Huilin; Lv, Dongping; Zuo, Pengjian; Chen, Honghao; Deng, Z. D.; Liaw, Bor Y.; Yu, Xiqian; Yang, Xiao-Qing; Zhang, Ji-Guang; Liu, Jun; Xiao, Jie

    2015-01-09

    Lithium sulfur (Li-S) battery has been regaining tremendous interest in recent years because of its attractive attributes such as high gravimetric energy, low cost and environmental benignity. However, it is still not conclusively known how polysulfide ring/chain participates in the whole cycling and whether the discharge and charge processes follow the same pathway. Herein, we demonstrate the direct observation of sulfur radicals by using in situ electron paramagnetic resonance (EPR) technique. Based on the concentration changes of sulfur radicals at different potentials and the electrochemical characteristics of the cell, it is revealed that the chemical and electrochemical reactions in Li-S cell are driving each other to proceed through sulfur radicals, leading to two completely different reaction pathways during discharge and charge. The proposed radical mechanism may provide new perspectives to investigate the interactions between sulfur species and the electrolyte, inspiring novel strategies to develop Li-S battery technology.

  16. Graphene-Catalyzed Direct Friedel-Crafts Alkylation Reactions: Mechanism, Selectivity, and Synthetic Utility.

    PubMed

    Hu, Feng; Patel, Mehulkumar; Luo, Feixiang; Flach, Carol; Mendelsohn, Richard; Garfunkel, Eric; He, Huixin; Szostak, Michal

    2015-11-18

    Transition-metal-catalyzed alkylation reactions of arenes have become a central transformation in organic synthesis. Herein, we report the first general strategy for alkylation of arenes with styrenes and alcohols catalyzed by carbon-based materials, exploiting the unique property of graphenes to produce valuable diarylalkane products in high yields and excellent regioselectivity. The protocol is characterized by a wide substrate scope and excellent functional group tolerance. Notably, this process constitutes the first general application of graphenes to promote direct C-C bond formation utilizing polar functional groups anchored on the GO surface, thus opening the door for an array of functional group alkylations using benign and readily available graphene materials. Mechanistic studies suggest that the reaction proceeds via a tandem catalysis mechanism in which both of the coupling partners are activated by interaction with the GO surface. PMID:26496423

  17. Transient Thermal Impedance Measurements on Low-Temperature-Sintered Nanoscale Silver Joints

    NASA Astrophysics Data System (ADS)

    Mei, Yunhui; Wang, Tao; Cao, Xiao; Chen, Gang; Lu, Guo-Quan; Chen, Xu

    2012-11-01

    A measurement system for thermal impedance ( Z th) was developed to evaluate the transient thermal performance of sintered nanoscale silver joints. Five different temperature profiles for low-temperature sintering were evaluated by Z th measurements of the joints. The thermal impedance of the sintered samples was altered by the different sintering conditions. Samples that underwent heating profiles with a separate drying stage offered lower thermal impedance than those sintered directly. Exerting pressure of more than 1 MPa during sintering insignificantly improved the thermal impedance. Besides, the impedance could be lowered by extending the holding time of the drying stage and applying pressure as low as 1 MPa during sintering. Characterization of microstructures of the sintered layers was performed by scanning electron microscopy (SEM). With more cracks present, the thermal impedance of the chip joints increased. The presence of cracks was possibly attributed to fast drying or the lack of a drying step.

  18. Chimerogenesis in estimation of specificity and pathway directions for cytochrome p45017alpha catalyzed reactions.

    PubMed

    Gilep, A A; Estabrook, R W; Usanov, S A

    2004-04-01

    Cytochrome P45017alpha is a key enzyme in steroid hormone biosynthesis. It catalyzes the reaction of 17alpha-hydroxylation of progesterone (P4) and pregnenolone (P5) and the 17,20-lyase reaction resulting in side chain cleavage of C21 steroids to form C19 steroids. Depending on the activity of cytochrome P45017alpha, steroid hormone biosynthesis pathways are directed either for biosynthesis of mineralocorticoids and glucocorticoids or sex hormones. The formation of sex hormones starts from biosynthesis of androstenedione. Androstenedione formation is a result of two reactions: 17,20-lyase reaction of 17alpha-hydroxyprogesterone (Delta4-pathway) and 3beta-hydroxysteroid dehydrogenase/Delta4,Delta5-isomerase reaction using dehydroepiandrosterone as substrate (Delta5-pathway). In case of exclusive direction of the 17,20-lyase reaction either through the Delta4- or the Delta5-pathway, the formation of sex hormones depends more on specificity and activity of 3beta-hydroxysteroid-dehydrogenase/Delta4,Delta5-isomerase. Depending on species, the cytochromes P45017alpha can utilize as a substrate for 17,20-lyase activity Delta4-steroids, Delta5-steroids, or both types of steroids. To identify the structural elements of cytochrome P45017alpha responsible for substrate recognition, in the present work we used exchange of homologous fragments of cytochrome P45017alpha having different types of activities. We engineered more than 10 different types of chimeric cytochrome P45017alpha. Chimeric cytochromes P45017alpha have been expressed in E. coli and purified. The expression of chimeric cytochrome P45017alpha with the point of exchange between exons III and IV results in inability of the recombinant hemeprotein to properly bind heme. The determination of activity of chimeric cytochromes P45017alpha shows that the structural element responsible for switching activity between Delta4- or Delta5-pathway is located in the region of polypeptide chain coded by exons II-V of CYP17 gene

  19. Bifunctional Brønsted Base Catalyzes Direct Asymmetric Aldol Reaction of α-Keto Amides.

    PubMed

    Echave, Haizea; López, Rosa; Palomo, Claudio

    2016-03-01

    The first enantioselective direct cross-aldol reaction of α-keto amides with aldehydes, mediated by a bifunctional ureidopeptide-based Brønsted base catalyst, is described. The appropriate combination of a tertiary amine base and an aminal, and urea hydrogen-bond donor groups in the catalyst structure promoted the exclusive generation of the α-keto amide enolate which reacted with either non-enolizable or enolizable aldehydes to produce highly enantioenriched polyoxygenated aldol adducts without side-products resulting from dehydration, α-keto amide self-condensation, aldehyde enolization, and isotetronic acid formation. PMID:26835655

  20. Reaction Mechanism of Siderite Lump in Coal-Based Direct Reduction

    NASA Astrophysics Data System (ADS)

    Zhu, Deqing; Luo, Yanhong; Pan, Jian; Zhou, Xianlin

    2016-02-01

    Siderite is one of the significant iron ore resources in China and yet is difficult to upgrade by traditional beneficiation processes. A process of coal-based direct reduction-magnetic separation was successfully developed for the beneficiation of siderite. However, few studies have thoroughly investigated the mechanism of the direct reduction of siderite. In order to reveal the reaction mechanism of coal-based direct reduction of siderite lump, thermodynamics of direct reduction was investigated with coal as the reductant. The thermodynamics results indicate that coal-based direct reduction process of siderite lump at 1,050°C follows the steps as FeCO3→ Fe3O4→ FeO → Fe, which is verified by chemical titration analysis, X-ray diffraction and scanning electron microscope. The microstructure of siderite sample varies with different reduction stages and some 45% porosity induced by thermal decomposition of siderite is conductive to subsequent reduction. The conversion of FeO to Fe is the main reduction rate-controlling step. The reduced product with the metallic iron size over 30 μm can be effectively beneficiated by wet magnetic separation after grinding. The obvious layered structure of reduced product is due to different heat transfer resistance, CO and CO2 concentration.

  1. Extrusion of spark plasma sintered aluminum-carbon nanotube composites at various sintering temperatures.

    PubMed

    Kwon, Hansang; Kawasaki, Akira

    2009-11-01

    The combined processes of spark plasma sintering and hot extrusion were used to fabricate a multi-walled carbon nanotube (MWCNT) reinforced aluminum (Al) matrix composite. The structural defects of carbon nanotubes (CNT) at various sintering temperatures were investigated by Raman spectroscopy. A small amount of Al liquid phase was generated and it reacted with disordered CNTs, even during the solid-state spark plasma sintering process. The influence of Al carbides generated by the reaction between Al and disordered CNTs is discussed from a microstructural viewpoint and in relation to tensile strength. We conclude that structurally controlled CNTs could potentially be attractive for metal matrix applications, and could significantly improve the mechanical properties of AI-CNT composites. PMID:19908562

  2. Microwave versus conventional sintering of silicon carbide tiles

    SciTech Connect

    Kass, M.D.; Caughman, J.B.O.; Forrester, S.C.; Akerman, A.

    1997-05-07

    Silicon carbide is being evaluated as an armor material because of its lightweight, high-hardness, and excellent armor efficiency. However, one of the problems associated with silicon carbide is the high cost associated with achieving fully dense tiles. Full density requires either hot pressing and sintering or reaction bonding. Past efforts have shown that hot pressed tiles have a higher armor efficiency than those produced by reaction bonded sintering. An earlier stuy showed that the acoustic properties of fully-dense silicon carbide tiles were enhanced through the use of post-sintered microwave heat treatments. One of the least expensive forming techniques is to isostatically press-and-sinter. In this study, the authors have used microwave energy to densify silicon carbide green bodies. Microwave sintering has been demonstrated to be a very quick way to sinter ceramics such as alumina to exceptionally high densities. Previous work has shown that microwave post treatment of fully-dense reaction bonded silicon carbide tiles significantly improves the acoustic properties of the tiles. These properties include Poisson`s ratio, Young`s modulus, shear modulus, and bulk modulus.

  3. Direct nuclear-pumped lasers using the He-3/n,p/H-3 reaction

    NASA Technical Reports Server (NTRS)

    Deyoung, R. J.; Jalufka, N. W.; Hohl, F.

    1978-01-01

    A description is presented of experimental results concerning a specific class of direct nuclear-pumped lasers classified as 'volumetric nuclear lasers'. In the considered laser system a fissioning gas, He-3, is mixed with the lasing gas to form a homogeneous mixture, resulting in uniform volume excitation. In typical volumetric nuclear lasers a fast-burst reactor is used as a source of neutrons which penetrate a polyethylene moderator. Here the fast neutrons are thermalized. After thermalization, neutrons scatter into the laser cell. Nuclear reactions produce a proton of 0.56 MeV and a tritium ion of 0.19. These ions produce secondary electrons which pump the laser medium creating a population inversion. The results reported demonstrate direct nuclear pumping of He-3-Ar, Xe, Kr, and Cl with the considered system.

  4. Microwave sintering versus conventional sintering of NiCuZn ferrites. Part I: Densification evolution

    NASA Astrophysics Data System (ADS)

    Zhu, Jianhua; Ouyang, Chenxin; Xiao, Shumin; Gao, Yongyi

    2016-06-01

    This work reports the recent study on the microwave sintering (MS) versus conventional sintering (CS) of NiCuZn ferrites, with particular interests in the densification evolution. NiCuZn ferrite powders were synthesized through the solid state reaction route. Densification behaviors of ferrite samples under the two types of thermal sources were monitored in real-time. Meanwhile, the influences of additives (1 wt% BSZ glass or 1 wt% Bi2O3) on the densifications were also investigated. Both constant heating rate (CHR) and master sintering curve (MSC) models were used to evaluate the sintering activation energy (Q). Results demonstrated that the microwave-enhanced diffusion mainly occurs at the intermediate sintering stage. The Q-value estimated by MSC method agreed well with that from CHR method. With the influence of microwave electromagnetic field, the activation energy of NiCuZn ferrites was decreased by roughly 100-150 kJ/mol. In addition, doping a small amount of additives could improve densification degree and reduce the minimal energy to activate diffusion mechanisms.

  5. Collision simulation of sintered dust aggregates

    NASA Astrophysics Data System (ADS)

    Sirono, Sin-iti; Ueno, Haruta

    Collisional evolution of dust aggregates is the initial process of the planet formation. Sticking velocity, below which collisional sticking of an aggregate happens, is a crucial quantity in the collisional evolution. In the standard model of protoplanetary nebula, the maximum collisional velocity is around 50m/s. Therefore, if a planetesimal is formed through direct collisional sticking, the sticking velocity should be higher than 50m/s. Even if a planetesimal is formed by other mechanism such as anticyclonic vortices, substantial growth of an aggregate is required because the motion of an aggregate should be decoupled from that of gas. Collisional simulation of icy dust aggregates (Wada et al. 2009, ApJ 702, 1490) showed that the sticking velocity was larger than 50m/s and planetesimal formation by collisional sticking was possible. However, sintering of ice proceeds in a wide area of a protoplanetary nebula (Sirono 2011, ApJ 765, 50). Sintering enlarges a neck, connection between adjacent dust grains, and changes the mechanical properties of a dust aggregate. Here we performed collisional simulations between sintered dust aggregates taking account of sintering. We found that the sticking velocity was decreased substantially down to 20m/s. This result suggests that a planetesimal is not formed by direct collisional sticking and that the planetesimal formation proceeded in particular regions in a protoplanetary nebula.

  6. Direct visualization of a cycloaddition reaction on frozen asymmetric Si dimers at room temperature

    NASA Astrophysics Data System (ADS)

    Baik, Jaeyoon; Ihm, Kyuwook; Ha, Taekyun; An, Ki-Seok; Ahn, Joung Real; Park, Chong-Yun

    2016-07-01

    We firstly report an experimental visualization of a cycloaddition reaction on RT frozen asymmetric Si dimers. The frozen Si dimers with a local c(4 × 2) order were prepared by pinning flip-flopping Si dimers by using molecules. This RT pristine c(4 × 2) structure was used to determine what Si atom of an asymmetric Si dimer bonds to a molecule at the initial stage of the RT cycloaddition reaction, which has been a long-standing puzzling issue. This made it possible to compare directly experimental cycloaddition reactions with theoretical ones. As a prototype for the experiment, a 1,3-butadiene molecule adsorbed between Si dimer rows was used. The 1,3-butadiene molecule was found to prefer a symmetric Si pair on the frozen Si dimers, i.e., two electrophilic lower atoms of asymmetric Si dimers. This result is consistent with the theoretical prediction that a 1,3-diene molecule prefers a symmetric Si pair on the Si(001)c(4 × 2) surface. This experimental approach can also be applied to other studies for the adsorption of a molecule on a Si(001) surface at room temperature.

  7. Probable new type of reaction mechanism: Double. cap alpha. direct transfer process

    SciTech Connect

    Xu Shu-wei; Wu Guo-hua; Miao Rong-zhi; Han Fei

    1983-10-01

    It is assumed that /sup 8/Be consists of two ..cap alpha.. particles which are close to each other in configuration space. A spectroscopic density of /sup 8/Be cluster in the residue nuclei is then obtained, which is proportional to the square of the preformation probability of ..cap alpha.. particle at nuclear surface. Using the improved method of parametrization of EFR-DWBA overlap integral,/sup 1//sup en-dash//sup 2/ we calculate the double differential energy spectra and angular distributions of ..cap alpha.. particles for the reactions /sup 209/Bi (/sup 12/C, ..cap alpha..) /sup 217/Fr and extract the preformation probability of ..cap alpha.. particle at the surface of /sup 217/Fr nuclei from fitting the experimental data. The agreement within the range of calculation error between the preformation probabilities extracted from transfer reactions and ..cap alpha.. decay suggests that the reaction /sup 209/Bi(/sup 12/C, ..cap alpha..) /sup 217/Fr may be explained as a double ..cap alpha.. direct transfer process.

  8. Electrified emotions: Modulatory effects of transcranial direct stimulation on negative emotional reactions to social exclusion.

    PubMed

    Riva, Paolo; Romero Lauro, Leonor J; Vergallito, Alessandra; DeWall, C Nathan; Bushman, Brad J

    2015-01-01

    Social exclusion, ostracism, and rejection can be emotionally painful because they thwart the need to belong. Building on studies suggesting that the right ventrolateral prefrontal cortex (rVLPFC) is associated with regulation of negative emotions, the present experiment tests the hypothesis that decreasing the cortical excitability of the rVLPFC may increase negative emotional reactions to social exclusion. Specifically, we applied cathodal transcranial direct current stimulation (tDCS) over the rVLPFC and predicted an increment of negative emotional reactions to social exclusion. In Study 1, participants were either socially excluded or included, while cathodal tDCS or sham stimulation was applied over the rVLPFC. Cathodal stimulation of rVLPFC boosted the typical negative emotional reaction caused by social exclusion. No effects emerged from participants in the inclusion condition. To test the specificity of tDCS effects over rVLPFC, in Study 2, participants were socially excluded and received cathodal tDCS or sham stimulation over a control region (i.e., the right posterior parietal cortex). No effects of tDCS stimulation were found. Our results showed that the rVLPFC is specifically involved in emotion regulation and suggest that cathodal stimulation can increase negative emotional responses to social exclusion. PMID:25139575

  9. Reactions to threat and personality: psychometric differentiation of intensity and direction dimensions of human defensive behaviour.

    PubMed

    Perkins, Adam M; Corr, Philip J

    2006-04-25

    Gray and McNaughton [Gray JA, McNaughton N. The neuropsychology of anxiety. Oxford: Oxford University Press; 2000] predict that fear is associated with orientation away from threat whereas anxiety is associated with orientation towards threat; this first dimension of 'defensive direction' is independent of a second dimension of 'defensive intensity'. Defensive reactions were measured using a threat scenario questionnaire developed by Blanchard et al. [Blanchard DC, Hynd AL, Minke KA, Minemoto T, Blanchard RJ. Human defensive behaviours to threat scenarios show parallels to fear- and anxiety-related defence patterns of non-human mammals. Neurosci Biobehav Rev 2001;25:761-70] who found that responses paralleled the defensive reactions of rodents faced with real threats. In a sample of 141 participants we replicated Blanchard et al.'s findings as well as confirming the Gray and McNaughton hypotheses. As predicted, trait anxiety was associated with a tendency to orientate towards threat. In addition, the personality trait of psychoticism (tough-mindedness) was related to defensive intensity with low scorers on psychoticism being more sensitive to threat in general and high scorers being more threat insensitive. A well-established personality measure of general punishment sensitivity, namely the Carver and White [Carver CS, White TL. Behavioural inhibition, behavioural activation, and affective responses to impending reward and punishment: the BIS/BAS scales. J Pers Soc Psychol 1994;67:319-33] BIS scale, was positively correlated with both defensive intensity and direction. These data indicate that the threat scenario questionnaire has some validity as a measure of human reactions to threat. PMID:16406105

  10. Sintered composite filter

    DOEpatents

    Bergman, W.

    1986-05-02

    A particulate filter medium formed of a sintered composite of 0.5 micron diameter quartz fibers and 2 micron diameter stainless steel fibers is described. Preferred composition is about 40 vol.% quartz and about 60 vol.% stainless steel fibers. The media is sintered at about 1100/sup 0/C to bond the stainless steel fibers into a cage network which holds the quartz fibers. High filter efficiency and low flow resistance are provided by the smaller quartz fibers. High strength is provided by the stainless steel fibers. The resulting media has a high efficiency and low pressure drop similar to the standard HEPA media, with tensile strength at least four times greater, and a maximum operating temperature of about 550/sup 0/C. The invention also includes methods to form the composite media and a HEPA filter utilizing the composite media. The filter media can be used to filter particles in both liquids and gases.

  11. Sintered wire cathode

    DOEpatents

    Falce, Louis R.; Ives, R. Lawrence

    2009-06-09

    A porous cathode structure is fabricated from a plurality of wires which are placed in proximity to each other in elevated temperature and pressure for a sintering time. The sintering process produces the porous cathode structure which may be divided into a plurality of individual porous cathodes, one of which may be placed into a dispenser cathode support which includes a cavity for containing a work function reduction material such as BaO, CaO, and Al.sub.2O.sub.3. The work function reduction material migrates through the pores of the porous cathode from a work replenishment surface adjacent to the cavity of the dispenser cathode support to an emitting cathode surface, thereby providing a dispenser cathode which has a uniform work function and therefore a uniform electron emission.

  12. SINTERING METAL OXIDES

    DOEpatents

    Roake, W.E.

    1960-09-13

    A process is given for producing uranium dioxide material of great density by preparing a compacted mixture of uranium dioxide and from 1 to 3 wt.% of calcium hydride, heating the mixture to at least 675 deg C for decomposition of the hydride and then for sintering, preferably in a vacuum, at from 1550 to 2000 deg C. Calcium metal is formed, some uranium is reduced by the calcium to the metal and a product of high density is obtained.

  13. A Macroscopic Reaction: Direct Covalent Bond Formation between Materials Using a Suzuki-Miyaura Cross-Coupling Reaction

    NASA Astrophysics Data System (ADS)

    Sekine, Tomoko; Kakuta, Takahiro; Nakamura, Takashi; Kobayashi, Yuichiro; Takashima, Yoshinori; Harada, Akira

    2014-09-01

    Cross-coupling reactions are important to form C-C covalent bonds using metal catalysts. Although many different cross-coupling reactions have been developed and applied to synthesize complex molecules or polymers (macromolecules), if cross-coupling reactions are realized in the macroscopic real world, the scope of materials should be dramatically broadened. Here, Suzuki-Miyaura coupling reactions are realized between macroscopic objects. When acrylamide gel modified with an iodophenyl group (I-gel) reacts with a gel possessing a phenylboronic group (PB-gel) using a palladium catalyst, the gels bond to form a single object. This concept can also be adapted for bonding between soft and hard materials. I-gel or PB-gel selectively bonds to the glass substrates whose surfaces are modified with an electrophile or nucleophile, respectively.

  14. A Macroscopic Reaction: Direct Covalent Bond Formation between Materials Using a Suzuki-Miyaura Cross-Coupling Reaction

    PubMed Central

    Sekine, Tomoko; Kakuta, Takahiro; Nakamura, Takashi; Kobayashi, Yuichiro; Takashima, Yoshinori; Harada, Akira

    2014-01-01

    Cross-coupling reactions are important to form C–C covalent bonds using metal catalysts. Although many different cross-coupling reactions have been developed and applied to synthesize complex molecules or polymers (macromolecules), if cross-coupling reactions are realized in the macroscopic real world, the scope of materials should be dramatically broadened. Here, Suzuki-Miyaura coupling reactions are realized between macroscopic objects. When acrylamide gel modified with an iodophenyl group (I-gel) reacts with a gel possessing a phenylboronic group (PB-gel) using a palladium catalyst, the gels bond to form a single object. This concept can also be adapted for bonding between soft and hard materials. I-gel or PB-gel selectively bonds to the glass substrates whose surfaces are modified with an electrophile or nucleophile, respectively. PMID:25231557

  15. Incidence of enteroviruses in Mamala Bay, Hawaii using cell culture and direct polymerase chain reaction methodologies.

    PubMed

    Reynolds, K A; Roll, K; Fujioka, R S; Gerba, C P; Pepper, I L

    1998-06-01

    The consequence of point and nonpoint pollution sources, discharged into marine waters, on public recreational beaches in Mamala Bay, Hawaii was evaluated using virus cell culture and direct reverse transcriptase-polymerase chain reaction (RT-PCR). Twelve sites, nine marine, two freshwater (one stream and one canal), and one sewage, were assessed either quarterly or monthly for 1 year to detect the presence of human enteric viruses. Water samples were concentrated from initial volumes of 400 L to final volumes of 30 mL using Filterite electronegative cartridge filters and a modified beef extract elution procedure. Cell culture was applied using the Buffalo Green Monkey kidney cell line to analyze samples for enteroviruses. Positive samples were also evaluated by RT-PCR, using enterovirus-specific primers. Levels of RT-PCR inhibition varied with each concentrated sample. Resin column purification increased PCR detection sensitivity by at least one order of magnitude in a variety of sewage outfall and recreational marine water samples but not in the freshwater canal samples. Using cell culture, viable enteroviruses were found in 50 and 17% of all outfall and canal samples, respectively. Samples were positive at beaches 8% of the time. These data illustrate the potential public health hazard associated with recreational waters. Using direct PCR, viruses were detected at the outfall but were not found in any beach or canal samples, in part, owing to substances that inhibit PCR. Therefore, conventional cell culture is the most effective means of detecting low levels of infectious enteroviruses in environmental waters, whereas direct RT-PCR is rendered less effective by inhibitory compounds and low equivalent reaction volumes. PMID:9734309

  16. Anisotropic constitutive model and FE simulation of the sintering process of slip cast traditional porcelain

    NASA Astrophysics Data System (ADS)

    Sarbandi, B.; Besson, J.; Boussuge, M.; Ryckelynck, D.

    2010-06-01

    Slip cast ceramic components undergo both sintering shrinkage and creep deformation caused by gravity during the firing cycle. In addition sintering may be anisotropic due to the development of preferential directions during slip casting. Both phenomena induce complex deformations of parts which make the design of casting molds difficult. To help solving this problem, anisotropic constitutive equations are proposed to represent the behavior of the ceramic compacts during sintering. The model parameters are identified using tests allowing to characterize both sintering and creep. The model was implemented in a finite element software and used to simulate the deformation of a traditional ceramic object during sintering.

  17. Anisotropic constitutive model and FE simulation of the sintering process of slip cast traditional porcelain

    SciTech Connect

    Sarbandi, B.; Besson, J.; Boussuge, M.; Ryckelynck, D.

    2010-06-15

    Slip cast ceramic components undergo both sintering shrinkage and creep deformation caused by gravity during the firing cycle. In addition sintering may be anisotropic due to the development of preferential directions during slip casting. Both phenomena induce complex deformations of parts which make the design of casting molds difficult. To help solving this problem, anisotropic constitutive equations are proposed to represent the behavior of the ceramic compacts during sintering. The model parameters are identified using tests allowing to characterize both sintering and creep. The model was implemented in a finite element software and used to simulate the deformation of a traditional ceramic object during sintering.

  18. Direct growth of flower-like manganese oxide on reduced graphene oxide towards efficient oxygen reduction reaction.

    PubMed

    Zhang, Jintao; Guo, Chunxian; Zhang, Lianying; Li, Chang Ming

    2013-07-18

    Three-dimensional manganese oxide is directly grown on reduced graphene oxide (RGO) sheets, exhibiting comparable catalytic activity, higher selectivity and better stability towards oxygen reduction reaction than those of the commercial Pt/XC-72 catalyst. PMID:23745182

  19. Direct Enantioselective Vinylogous Mannich Reaction of Ketimines with γ-Butenolide by Using Cinchona Alkaloid Amide/Zinc(II) Catalysts.

    PubMed

    Nakamura, Shuichi; Yamaji, Ryota; Hayashi, Masashi

    2015-06-26

    A direct enantioselective vinylogous Mannich reaction of ketimines with γ-butenolide has been developed. Good yields and enantioselectivities were observed for the reaction of various ketimines by using a cinchona alkaloid amide/Zn(OTf)2 catalyst and Et3N. Both enantiomers of the products could be obtained by using pseudoenantiomeric chiral catalysts. PMID:25944609

  20. Pressureless sintering of plasma-reacted nanosemicrystalline silicon nitride ceramics with doped sintering additives

    NASA Astrophysics Data System (ADS)

    Ryu, Kevin Hojun

    For the past few years, synthesis and consolidation of ceramics using nanoparticles have been a focus of much research. The obvious advantage is their low process temperatures (<200°C). In addition, the process results in super-plastic deformation, and drastically enhances the mechanical properties of the ceramics. Recently, a plasma-assisted chemical reaction was adopted to produce nanosize Si3N4 powders that have the characteristics of sintering additive elements on individual particles. Homogeneous size distribution of the additives can eliminate inhomogeneous shrinkage of the sintered body during the mixing process. In this work, the behavior of plasma-reacted nano-size Si3N 4 powders intrinsically doped with sintering additives was explored. These particles were doped with Y2O3 and Al2O 3, and processed under a low process temperature in the absence of pressurizing equipment. Several experiments were performed to address the effects of the powders on the phase transformation rate from a to b phase, and on the mechanical properties due to the microstructure evolution under different sintering conditions. The existence of sintering additive elements in each individual powder was verified by electron microscope and energy dispersive spectroscopy. The doped powders were 60% crystalline and had a specific surface area of ˜24 m2/g. The powders showed excellent sinterability at low temperature, compared to the other powders used in commercial processes. In spite of the low process temperature, the a→ b phase transformation occurred rapidly. The homogeneous distribution of Si3N4 powders was speculated as the reason for fast phase transformation. In addition, evolution of the microstructures in different sintering conditions produced materials with vastly different mechanical properties. Thus, one may obtain ceramics with desired mechanical properties by carefully controlling the sintering additives. Finally, a mathematical model, based on the previous work done by

  1. Comparison of conventional and microwave sintering on Y-ferrite

    NASA Astrophysics Data System (ADS)

    Obulesu, K. Rama; James Raju, K. C.

    2013-06-01

    In this paper we are comparing the results of the conventional and microwave sintered samples of Zn2-Y(Ba2Zn2Fe12O22) ferrite. Y ferrite sample was synthesized using the commercial solid-state reaction method. In CS process, the sample was sintered in muffle furnace at 1200°C for 6 h. In MS process, the sample was sintered at 1120 °C for 30 min in air at the rate of 10°C per min. X-ray powder diffraction revealed that a single phase rhombohedral structure with space group R3m (166) for both samples. The average grain size of CS sample is 1.5-2μm which is greater than MS sample. Magnetic properties also changed with the microwave sintering. These results demonstrate that the strong microwave method is an alternative way to synthesize high performance Y ferrite.

  2. Reduction of nitroaromatics sorbed to black carbon by direct reaction with sorbed sulfides.

    PubMed

    Xu, Wenqing; Pignatello, Joseph J; Mitch, William A

    2015-03-17

    Sorption to black carbons is an important sink for organic contaminants in sediments. Previous research has suggested that black carbons (graphite, activated carbon, and biochar) mediate the degradation of nitrated compounds by sulfides by at least two different pathways: reduction involving electron transfer from sulfides through conductive carbon regions to the target contaminant (nitroglycerin) and degradation by sulfur-based intermediates formed by sulfide oxidation (RDX). In this study, we evaluated the applicability of black carbon-mediated reactions to a wider variety of contaminant structures, including nitrated and halogenated aromatic compounds, halogenated heterocyclic aromatic compounds, and halogenated alkanes. Among these compounds, black carbon-mediated transformation by sulfides over a 3-day time scale was limited to nitroaromatic compounds. The reaction for a series of substituted nitroaromatics proceeded by reduction, as indicated by formation of 3-bromoaniline from 3-bromonitrobenzene, and inverse correlation of log kobs with energy of the lowest unoccupied molecular orbital (ELUMO). The log kobs was correlated with sorbed sulfide concentration, but no reduction of 3-bromonitrobenzene was observed in the presence of graphite and sulfite, thiosulfate, or polysulfides. Whereas nitroglycerin reduction occurred in an electrochemical cell containing sheet graphite electrodes in which the reagents were placed in separate compartments, nitroaromatic reduction only occurred when sulfides were present in the same compartment. The results suggest that black carbon-mediated reduction of sorbed nitroaromatics by sulfides involves electron transfer directly from sorbed sulfides rather than transfer of electrons through conductive carbon regions. The existence of three different reaction pathways suggests a complexity to the sulfide-carbon system compared to the iron-carbon system, where contaminants are reduced by electron transfer through conductive carbon

  3. Reactive sintering of SiC

    NASA Technical Reports Server (NTRS)

    Kim, Y. W.; Lee, J. G.

    1984-01-01

    Investigation of the sintering processes involved in the sintering of SiC revealed a connection between the types and quantities of sintering additives or catalysts and densification, initial shrinkage, and weight loss of the sintered SiC material. By sintering processes, is meant the methods of mass transport, namely solid vapor transport and grain boundary diffusion.

  4. Zone sintering of ceramic fuels

    DOEpatents

    Matthews, R. Bruce; Chidester, Kenneth M.; Moore, H. Gene

    1994-01-01

    Cold pressed UC.sub.2 fuel compacts are sintered at temperatures greater than about 1850.degree. C. while in contact with a sintering facilitator material, e.g., tantalum, niobium, tungsten or a metal carbide such as uranium carbide, thereby allowing for a reduction in the overall porosity and leaving the desired product, i.e., a highly dense, large-grained uranium dicarbide. The process of using the sintering facilitator materials can be applied in the preparation of other carbide materials.

  5. Reaction injection molding and direct covalent bonding of OSTE+ polymer microfluidic devices

    NASA Astrophysics Data System (ADS)

    Sandström, N.; Shafagh, R. Z.; Vastesson, A.; Carlborg, C. F.; van der Wijngaart, W.; Haraldsson, T.

    2015-07-01

    In this article, we present OSTE+RIM, a novel reaction injection molding (RIM) process that combines the merits of off-stoichiometric thiol-ene epoxy (OSTE+) thermosetting polymers with the fabrication of high quality microstructured parts. The process relies on the dual polymerization reactions of OSTE+ polymers, where the first curing step is used in OSTE+RIM for molding intermediately polymerized parts with well-defined shapes and reactive surface chemistries. In the facile back-end processing, the replicated parts are directly and covalently bonded and become fully polymerized using the second curing step, generating complete microfluidic devices. To achieve unprecedented rapid processing, high replication fidelity and low residual stress, OSTE+RIM uniquely incorporates temperature stabilization and shrinkage compensation of the OSTE+ polymerization during molding. Two different OSTE+ formulations were characterized and used for the OSTE+RIM fabrication of optically transparent, warp-free and natively hydrophilic microscopy glass slide format microfluidic demonstrator devices, featuring a storage modulus of 2.3 GPa and tolerating pressures of at least 4 bars.

  6. Direct and Absolute Quantification of over 1800 Yeast Proteins via Selected Reaction Monitoring.

    PubMed

    Lawless, Craig; Holman, Stephen W; Brownridge, Philip; Lanthaler, Karin; Harman, Victoria M; Watkins, Rachel; Hammond, Dean E; Miller, Rebecca L; Sims, Paul F G; Grant, Christopher M; Eyers, Claire E; Beynon, Robert J; Hubbard, Simon J

    2016-04-01

    Defining intracellular protein concentration is critical in molecular systems biology. Although strategies for determining relative protein changes are available, defining robust absolute values in copies per cell has proven significantly more challenging. Here we present a reference data set quantifying over 1800Saccharomyces cerevisiaeproteins by direct means using protein-specific stable-isotope labeled internal standards and selected reaction monitoring (SRM) mass spectrometry, far exceeding any previous study. This was achieved by careful design of over 100 QconCAT recombinant proteins as standards, defining 1167 proteins in terms of copies per cell and upper limits on a further 668, with robust CVs routinely less than 20%. The selected reaction monitoring-derived proteome is compared with existing quantitative data sets, highlighting the disparities between methodologies. Coupled with a quantification of the transcriptome by RNA-seq taken from the same cells, these data support revised estimates of several fundamental molecular parameters: a total protein count of ∼100 million molecules-per-cell, a median of ∼1000 proteins-per-transcript, and a linear model of protein translation explaining 70% of the variance in translation rate. This work contributes a "gold-standard" reference yeast proteome (including 532 values based on high quality, dual peptide quantification) that can be widely used in systems models and for other comparative studies. PMID:26750110

  7. Direct and sensitive detection of a pathogenic protozoan, Toxoplasma gondii, by polymerase chain reaction.

    PubMed Central

    Burg, J L; Grover, C M; Pouletty, P; Boothroyd, J C

    1989-01-01

    We applied the polymerase chain reaction to detection of the pathogenic protozoan Toxoplasma gondii based on our identification of a 35-fold-repetitive gene (the B1 gene) as a target. Using this procedure, we were able to amplify and detect the DNA of a single organism directly from a crude cell lysate. This level of sensitivity also allowed us to detect the B1 gene from purified DNA samples containing as few as 10 parasites in the presence of 100,000 human leukocytes. This is representative of the maximal cellular infiltration (10(5)/ml) in 1 ml of cerebrospinal fluid obtained from patients with toxoplasmic encephalitis. The B1 gene is present and conserved in all six T. gondii strains tested to date, including two isolates from patients with acquired immunodeficiency syndrome. No signal was detected by using this assay and DNAs from a variety of other organisms, including several which might be found in the central nervous system of an immunocompromised host. This combination of sensitivity and specificity should make detection of the B1 gene based on polymerase chain reaction amplification a very useful method for diagnosis of toxoplasmosis both in immunocompromised hosts and in congenitally infected fetuses. Images PMID:2768467

  8. Direct and Absolute Quantification of over 1800 Yeast Proteins via Selected Reaction Monitoring*

    PubMed Central

    Lawless, Craig; Holman, Stephen W.; Brownridge, Philip; Lanthaler, Karin; Harman, Victoria M.; Watkins, Rachel; Hammond, Dean E.; Miller, Rebecca L.; Sims, Paul F. G.; Grant, Christopher M.; Eyers, Claire E.; Beynon, Robert J.

    2016-01-01

    Defining intracellular protein concentration is critical in molecular systems biology. Although strategies for determining relative protein changes are available, defining robust absolute values in copies per cell has proven significantly more challenging. Here we present a reference data set quantifying over 1800 Saccharomyces cerevisiae proteins by direct means using protein-specific stable-isotope labeled internal standards and selected reaction monitoring (SRM) mass spectrometry, far exceeding any previous study. This was achieved by careful design of over 100 QconCAT recombinant proteins as standards, defining 1167 proteins in terms of copies per cell and upper limits on a further 668, with robust CVs routinely less than 20%. The selected reaction monitoring-derived proteome is compared with existing quantitative data sets, highlighting the disparities between methodologies. Coupled with a quantification of the transcriptome by RNA-seq taken from the same cells, these data support revised estimates of several fundamental molecular parameters: a total protein count of ∼100 million molecules-per-cell, a median of ∼1000 proteins-per-transcript, and a linear model of protein translation explaining 70% of the variance in translation rate. This work contributes a “gold-standard” reference yeast proteome (including 532 values based on high quality, dual peptide quantification) that can be widely used in systems models and for other comparative studies. PMID:26750110

  9. Monitoring transcranial direct current stimulation induced changes in cortical excitability during the serial reaction time task.

    PubMed

    Ambrus, Géza Gergely; Chaieb, Leila; Stilling, Roman; Rothkegel, Holger; Antal, Andrea; Paulus, Walter

    2016-03-11

    The measurement of the motor evoked potential (MEP) amplitudes using single pulse transcranial magnetic stimulation (TMS) is a common method to observe changes in motor cortical excitability. The level of cortical excitability has been shown to change during motor learning. Conversely, motor learning can be improved by using anodal transcranial direct current stimulation (tDCS). In the present study, we aimed to monitor cortical excitability changes during an implicit motor learning paradigm, a version of the serial reaction time task (SRTT). Responses from the first dorsal interosseous (FDI) and forearm flexor (FLEX) muscles were recorded before, during and after the performance of the SRTT. Online measurements were combined with anodal, cathodal or sham tDCS for the duration of the SRTT. Negative correlations between the amplitude of online FDI MEPs and SRTT reaction times (RTs) were observed across the learning blocks in the cathodal condition (higher average MEP amplitudes associated with lower RTs) but no significant differences in the anodal and sham conditions. tDCS did not have an impact on SRTT performance, as would be predicted based on previous studies. The offline before-after SRTT MEP amplitudes showed an increase after anodal and a tendency to decrease after cathodal stimulation, but these changes were not significant. The combination of different interventions during tDCS might result in reduced efficacy of the stimulation that in future studies need further attention. PMID:26826607

  10. Measurement of Neutron-Induced, Angular-Momentum-Dependent Fission Probabilities Direct Reactions

    NASA Astrophysics Data System (ADS)

    Koglin, Johnathon; Jovanovic, Igor; Burke, Jason; Casperson, Robert

    2015-04-01

    The surrogate method has previously been used to successfully measure (n , f) cross sections of a variety of difficult to produce actinide isotopes. These measurements are inaccurate at excitation energies below 1.5 MeV where the distribution of angular momentum states populated in the compound nucleus created by neutron absorption significantly differs from that arising from direct reactions. A method to measure the fission probability of individual angular momentum states arising from 239 Pu(d , pf) and 239 Pu(α ,α' f) reactions has been developed. This method consists on charged particle detectors with 40 keV FWHM resolution at 13 angles up and downstream of the beam. An array of photovoltaic (solar) cells is used to measure the angular distribution of fission fragments with high angular resolution. This distribution uniquely identifies the populated angular momentum states. These are fit to expected distributions to determine the contribution of each state. The charged particle and fission matrix obtained from these measurements determines fission probabilities of specific angular momentum states in the transition nucleus. Development of this scheme and first results will be discussed. This material is based upon work supported by the U.S. Department of Homeland Security under Grant Award Number 2012-DN-130-NF0001.

  11. Production of sintered porous metal fluoride pellets

    DOEpatents

    Anderson, L.W.; Stephenson, M.J.

    1973-12-25

    Porous pellets characterized by a moderately reactive crust and a softer core of higher reactivity are produced by forming agglomerates containing a metal fluoride powder and a selected amount ofwater. The metal fluoride is selected to be sinterable and essentially non-reactive with gaseous fluorinating agents. The agglomerates are contacted with a gaseous fluorinating agent under controlled conditions whereby the heat generated by localized reaction of the agent and water is limited to values effccting bonding by localized sintering. Porous pellets composed of cryolite (Na/sub 3/AlF/sub 6/) can be used to selectively remove trace quantities of niobium pentafluoride from a feed gas consisting predominantly of uranium hexafluoride. (Official Gazette)

  12. Report on the sintering and properties of MgO and MgO-5% TiC

    SciTech Connect

    Bengisu, M.; Inal, O.T.

    1992-07-01

    Sintering of technical grade MgO yields higher fractional densities compared to pure MgO. TiC reacts with MgO under sintering of MgO-TiC composites in air, yielding Mg{sub 2}TiO{sub 4} and CO or CO{sub 2}. This can be suppressed in vacuum by plasma sintering. Plasma sintering of MgO at 1300 C and short times does not produce satisfactory results. 5 vol% TiC increases the sinterability of MgO during conventional air sintering; larger additions (50 vol%) decrease sinterability due to macropores formed by gaseous reaction product. Microwave sintering of MgO is possible. Mechanical properties of MgO are improved by additions of small amounts of TiC to starting powders.

  13. pH-dependent electron transfer reaction and direct bioelectrocatalysis of the quinohemoprotein pyranose dehydrogenase.

    PubMed

    Takeda, Kouta; Matsumura, Hirotoshi; Ishida, Takuya; Yoshida, Makoto; Igarashi, Kiyohiko; Samejima, Masahiro; Ohno, Hiroyuki; Nakamura, Nobuhumi

    2016-08-26

    A pyranose dehydrogenase from Coprinopsis cinerea (CcPDH) is an extracellular quinohemoeprotein, which consists a b-type cytochrome domain, a pyrroloquinoline-quinone (PQQ) domain, and a family 1-type carbohydrate-binding module. The electron transfer reaction of CcPDH was studied using some electron acceptors and a carbon electrode at various pH levels. Phenazine methosulfate (PMS) reacted directly at the PQQ domain, whereas cytochrome c (cyt c) reacted via the cytochrome domain of intact CcPDH. Thus, electrons are transferred from reduced PQQ in the catalytic domain of CcPDH to heme b in the N-terminal cytochrome domain, which acts as a built-in mediator and transfers electron to a heterogenous electron transfer protein. The optimal pH values of the PMS reduction (pH 6.5) and the cyt c reduction (pH 8.5) differ. The catalytic currents for the oxidation of l-fucose were observed within a range of pH 4.5 to 11. Bioelectrocatalysis of CcPDH based on direct electron transfer demonstrated that the pH profile of the biocatalytic current was similar to the reduction activity of cyt c characters. PMID:27338639

  14. Spark plasma sintering of titanium aluminide intermetallics and its composites

    NASA Astrophysics Data System (ADS)

    Aldoshan, Abdelhakim Ahmed

    Titanium aluminide intermetallics are a distinct class of engineering materials having unique properties over conventional titanium alloys. gamma-TiAl compound possesses competitive physical and mechanical properties at elevated temperature applications compared to Ni-based superalloys. gamma-TiAl composite materials exhibit high melting point, low density, high strength and excellent corrosion resistance. Spark plasma sintering (SPS) is one of the powder metallurgy techniques where powder mixture undergoes simultaneous application of uniaxial pressure and pulsed direct current. Unlike other sintering techniques such as hot iso-static pressing and hot pressing, SPS compacts the materials in shorter time (< 10 min) with a lower temperature and leads to highly dense products. Reactive synthesis of titanium aluminide intermetallics is carried out using SPS. Reactive sintering takes place between liquid aluminum and solid titanium. In this work, reactive sintering through SPS was used to fabricate fully densified gamma-TiAl and titanium aluminide composites starting from elemental powders at different sintering temperatures. It was observed that sintering temperature played significant role in the densification of titanium aluminide composites. gamma-TiAl was the predominate phase at different temperatures. The effect of increasing sintering temperature on microhardness, microstructure, yield strength and wear behavior of titanium aluminide was studied. Addition of graphene nanoplatelets to titanium aluminide matrix resulted in change in microhardness. In Ti-Al-graphene composites, a noticeable decrease in coefficient of friction was observed due to the influence of self-lubrication caused by graphene.

  15. Direct coupling between stress, strain and adsorption reactions - A study on coal-CO2 systems

    NASA Astrophysics Data System (ADS)

    Hol, S.; Peach, C. J.; Spiers, C. J.

    2012-12-01

    Though it is well-known that adsorption reactions frequently assist deformation of porous rocks, very little understanding exists on the direct coupling with stress state and strain. One of the materials in which adsorption plays a large role is coal, as is observed in the particular case of Enhanced Coalbed Methane Production (ECBM), which involves the geological storage of CO2 and the recovery of CH4. In this case, adsorption and the associated swelling cause significant injectivity problems, which is experienced in almost all pilot field projects to date. This suggests that indeed a strong fundamental coupling exists between CO2 sorption, changes in the mechanical state of the coal matrix and changes in the transport properties of the system, and illustrates the need to understand coupled stress-strain-sorption behaviour. In this contribution, we describe several important observations made on coal-CO2 systems that can learn us about many other natural, stressed adsorbate-adsorbent systems. In our experiments, first of all, the adsorption of CO2 in the coal matrix gave rise to swelling. Although this is well-known, we found that the total volumetric strain occurring under unconfined conditions can be realistically modelled (up to at least 100 MPa) as the sum of an adsorption-related expansion term and an elastic compression term. Second, effective in situ stresses will directly reduce the sorption capacity, and associated swelling of the coal matrix significantly. Our general thermodynamic model for the effect of a 3D stress state on adsorbed CO2 concentration supports this observation, and also shows that "self-stressing", as a result of CO2 adsorption occurring under conditions of restricted or zero strain (i.e. fully constrained conditions), will more than double the expected in situ stresses. A constitutive equation was developed to describe the full coupling between stress state, total strain (i.e. combined strain of adsorption processes and poroelasticity

  16. 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.

  17. QM/QM' Direct Molecular Dynamics of Water-Accelerated Diels-Alder Reaction.

    PubMed

    Liu, Fengjiao; Yang, Zhongyue; Mei, Ye; Houk, K N

    2016-07-01

    A QM/QM' direct molecular dynamics study of a water-accelerated Diels-Alder reaction in aqueous solution is reported. Cyclopentadiene and methyl vinyl ketone are known to react faster in water than in nonpolar solvents. We have explored how polarization of water molecules afforded by PM3 influences the nature of the transition state, and the reaction dynamics. We compare the results with previous studies on QM/MM and QM/MM+3QM water simulations from our laboratory. Transition state sampling in vacuum PM3 water boxes indicates that the asynchronicity is 0.54 Å in QM/QM', as compared to 0.48 Å in QM/MM, and 0.54 Å in QM/MM+3QM water. The mean time gap between the formation of two C-C bonds is 19 fs for QM/QM', compared to 20 fs for QM/MM, and 25 fs for QM/MM+3QM water. The samplings and time gaps are qualitatively consistent, indicating that water polarization is not significant in sampling and dynamics of bonding changes. The dynamics of hydrogen bonding between reacting molecules and water molecules was also analyzed. From reactants to transition states, H-bond shortening is 0.4 Å by QM/QM', while only 0.15 Å for QM/MM and QM/MM+3QM water. From reactants to transition states, the mean value of the H-bond angle increases by 19° in QM/QM', but only 4° in QM/MM, and 10° in QM/MM+3QM water. These suggest that water polarization is essential for the correct representation of dynamical formation of hydrogen bonds in the transition state by water reorientation. QM/QM' overestimates the hydrogen bonding enhancement because of its underestimation of neutral hydrogen bonding within the reactants, a general deficiency of PM3. PMID:27092967

  18. Microwave sintering of multiple aritcles

    SciTech Connect

    Blake, R.D.; Katz, J.D.

    1992-12-31

    Disclosed are apparatus and method for producing articles of alumina and of alumina and silicon carbide in which the articles are sintered at high temperatures using microwave radiation. The articles are placed in a sintering container which is placed in a microwave cavity for heating. The rates at which heating and cooling take place is controlled.

  19. Microwave sintering of multiple articles

    DOEpatents

    Blake, Rodger D.; Katz, Joel D.

    1993-01-01

    Apparatus and method for producing articles of alumina and of alumina and silicon carbide in which the articles are sintered at high temperatures using microwave radiation. The articles are placed in a sintering container which is placed in a microwave cavity for heating. The rates at which heating and cooling take place is controlled.

  20. Refolding of lysozyme by quasistatic and direct dilution reaction paths: A first-order-like state transition

    NASA Astrophysics Data System (ADS)

    Chang, Chia-Ching; Yeh, Xu-Cheng; Lee, Hui-Ting; Lin, Po-Yen; Kan, Lou-Sing

    2004-07-01

    A first-order-like state transition model is considered to be a global reaction mechanism to directly folded proteins from an unfolded state to its native form. In order to verify the general applicability of this mechanism, we used lysozyme as a model protein. It was fully unfolded by 4.5M urea, 0.1M dithiothreitol (DTT) in pH3 and refolded to its native form by way of an overcritical reaction path (a quasistatic process) or directly crossing transition boundary path (a directly dilution process). In addition to the two states coexisting in the direct folding path, lyzosyme might be trapped in a glassy state. However, it can escape from the glassy state by concentration twice. This indicates the existence of a state transition line or boundary in the direct folding reaction. However, lysozyme can continuously fold from unfolded to native by an overcritical reaction path. During the overcritical path, four stable folding intermediates and native lysozyme were obtained. The secondary structures, particle size distributions, thermal stabilities, and oxidation state of disulfide bonds of folding intermediates were analyzed by circular dichroism spectra, dynamic light scattering, differential scanning calorimetry, and Raman spectra, respectively. According to the data, the intermediates of both the overcritical reaction and the direct crossing transition boundary paths can be described by a common concept pertaining to a model that undergoes collapse, sequential, and first-order-like state transition. This indicated that protein folding by way of different reaction paths might follow a similar folding mechanism—i.e., a mechanism of overcritical folding of intermediates. A protein folding reaction diagram is postulated and discussed. In spite of a global interaction mechanism the α -helix is formed prior to the β -sheet, which may indicate that protein folding is initiated by local interactions.

  1. Effect of milling and leaching on the structure of sintered silicon

    NASA Technical Reports Server (NTRS)

    Yeh, H. C.; Glasgow, T. K.; Herbell, T. P.

    1980-01-01

    The effects of attrition milling and acid leaching on the sintering behavior and the resultant structures of two commercial silicon powders were investigated. Sintering was performed in He for 16 hours at 1200, 1250, and 1300 C. Compacts of as-received Si did not densify during sintering. Milling reduced the average particle size to below 0.5 microns and enhanced densification (1.75 g/cc). Leaching milled Si further enhanced densification (1.90 g/cc max.) and decreased structural coarsening. After sintering, the structure of the milled and leached powder compacts appears favorable for the production of reaction bonded silicon nitride.

  2. Laser sintering of copper nanoparticles

    NASA Astrophysics Data System (ADS)

    Zenou, Michael; Ermak, Oleg; Saar, Amir; Kotler, Zvi

    2014-01-01

    Copper nanoparticle (NP) inks serve as an attractive potential replacement to silver NP inks in functional printing applications. However their tendency to rapidly oxidize has so far limited their wider use. In this work we have studied the conditions for laser sintering of Cu-NP inks in ambient conditions while avoiding oxidation. We have determined the regime for stable, low-resistivity copper (< ×3 bulk resistivity value) generation in terms of laser irradiance and exposure duration and have indicated the limits on fast processing. The role of pre-drying conditions on sintering outcome has also been studied. A method, based on spectral reflectivity measurements, was used for non-contact monitoring of the sintering process evolution. It also indicates preferred spectral regions for sintering. Finally, we illustrated how selective laser sintering can generate high-quality, fine line (<5 µm wide) and dense copper circuits.

  3. Manufacture of sintered silicon nitrides

    NASA Technical Reports Server (NTRS)

    Iwai, T.

    1985-01-01

    Sintered silicon nitrides are manufactured by sintering Si3N powder containing 2 to 15% in wt of a powder mixture composed of nitride powder of lanthanide or Y 100 parts and AIN powder less than 100 parts at 1500 to 1900 deg. temperature under a pressure of less than 200 Kg/sq. cm. The sintered Si3N has high mechanical strength in high temperature. Thus, Si3N4 93.0, Y 5.0 and AlN 2.0% in weight were wet mixed in acetone in N atom, molded and sintered at 1750 deg. and 1000 Kg/sq. cm. to give a sintered body having high hardness.

  4. Numerical simulation of electric field assisted sintering

    NASA Astrophysics Data System (ADS)

    McWilliams, Brandon A.

    A fully coupled thermal-electric-sintering finite element model was developed and implemented to explore electric field assisted sintering techniques (FAST). FAST is a single step processing operation for producing bulk materials from powders, in which the powder is heated by the application of electric current under pressure. This process differs from other powder processing techniques such as hot isostatic pressing (HIP) and traditional press and sinter operations where the powder or compact is heated externally, in that the powder is heated directly as a result of internal Joule heating (for conductive powders) and/or by direct conduction from the die and punches. The overall result is much more efficient heating which allows heating rates of >1000°C/min to be achieved which is desirable for sintering bulk nanocrystalline and other novel high performance materials. Previous modeling efforts on FAST have only considered the thermal-electric aspect of the problem and have neglected densification. In addition to the introduction of a sintering model, a detailed thermal-electric study of process parameters was carried out in order to identify key system variables and quantify their effect on the overall system response and subsequent thermal history of a consolidated sample. This analysis was compared to empirical data from a parallel experimental study and shown to satisfactorily predict the observed trends. This model was then integrated with a phenomenologically based sintering model to capture the densification of the sample. This fully coupled model was used to predict densification kinetics under FAST like conditions and examine the evolution of material properties as the sample transitions from a loose powder to a fully dense compact and the resulting effect on the electrical and thermal fields within the compact. This model was also used to explore the effect of non-uniform thermal, electrical, stress and density fields on the final geometry and local

  5. Sintered silicon nitrode recuperator fabrication

    NASA Technical Reports Server (NTRS)

    Gatti, A.; Chiu, W. S.; Mccreight, L. R.

    1980-01-01

    The preliminary design and a demonstration of the feasibility of fabricating submodules of an automotive Stirling engine recuperator for waste heat recovery at 370 C are described. Sinterable silicon nitride (Sialon) tubing and plates were fabricated by extrusion and hydrostatic pressing, respectively, suitable for demonstrating a potential method of constructing ceramic recuperator-type heat exchangers. These components were fired in nitrogen atmosphere to 1800 C without significant scale formation so that they can be used in the as-fired condition. A refractory glass composition (Al2O3 x 4.5 CaO.MgO x 11SiO2) was used to join and seal component parts by a brazing technique which formed strong recuperator submodules capable of withstanding repeated thermal cycling to 1370 C. The corrosion resistance of these materials to Na2SO4 + NaCl carbon mixtures was also assessed in atmospheres of air, hydrogen and CO2-N2-H2O mixtures at both 870 C and 1370 C for times to 1000 hours. No significant reaction was observed under any of these test conditions.

  6. Advanced unidirectional photocurrent generation via cytochrome c as reaction partner for directed assembly of photosystem I.

    PubMed

    Stieger, Kai R; Feifel, Sven C; Lokstein, Heiko; Lisdat, Fred

    2014-08-01

    Conversion of light into an electrical current based on biohybrid systems mimicking natural photosynthesis is becoming increasingly popular. Photosystem I (PSI) is particularly useful in such photo-bioelectrochemical devices. Herein, we report on a novel biomimetic approach for an effective assembly of photosystem I with the electron transfer carrier cytochrome c (cyt c), deposited on a thiol-modified gold-surface. Atomic force microscopy and surface plasmon resonance measurements have been used for characterization of the assembly process. Photoelectrochemical experiments demonstrate a cyt c mediated generation of an enhanced unidirectional cathodic photocurrent. Here, cyt c can act as a template for the assembly of an oriented and dense layer of PSI and as wiring agent to direct the electrons from the electrode towards the photosynthetic reaction center of PSI. Furthermore, three-dimensional protein architectures have been formed via the layer-by-layer deposition technique resulting in a successive increase in photocurrent densities. An intermittent cyt c layer is essential for an efficient connection of PSI layers with the electrode and for an improvement of photocurrent densities. PMID:24957935

  7. Directly Grafting Alkanethiol on Bare Si (111) by UV-assisted Photochemical Reaction

    NASA Astrophysics Data System (ADS)

    Chang, Lo-Yueh; Shiu, Hung-Wei; Gwo, Shangjr; Chen, Chia-Hao

    2014-03-01

    Self-assembled monolayers (SAMs) are organic molecules that self-assembled and closely packed on substrate surface. The surface physic and chemical properties are dependent on the controllable tail of SAMs. Therefore, SAMs is attracting a lot of attention in bio-sensing, nano-manipulating, and microfluidic field. The alkanethiol on noble metal surface, such as gold and silver, is a well-known SAM system to understand the fundamental properties. However, alkanethiols grown on semiconductor surfaces was less systematically studied, especially on bare silicon surface, despite their prospective applications. To have in-depth understanding of such system, we tried to grow alkanethiol SAMs on hydrogen-terminated Si surface by UV-assisted photochemical reaction. The resulting monolayer was studied by means of water contact angle measurement, synchrotron radiation based X-ray photoemission spectroscopy, and polarization dependent near-edge X-ray absorption fine structure. The combined characterization probes revealed a hydrophobic ambient surface, and the n-alkanethiols were directly attached on Si through Si-S bond that formed a highly order monolayer to prevent the air oxidation and contamination.

  8. Carborane Substituents Promote Direct Electrophilic Insertion over Reduction-Metalation Reactions.

    PubMed

    Man, Wing Y; Ellis, David; Rosair, Georgina M; Welch, Alan J

    2016-03-24

    Two-electron reduction of 1,1'-bis(o-carborane) followed by reaction with [Ru(η-mes)Cl2 ]2 affords [8-(1'-1',2'-closo-C2 B10 H11 )-4-(η-mes)-4,1,8-closo-RuC2 B10 H11 ]. Subsequent two-electron reduction of this species and treatment with [Ru(η-arene)Cl2 ]2 results in the 14-vertex/12-vertex species [1-(η-mes)-9-(1'-1',2'-closo-C2 B10 H11 )-13-(η-arene)-1,13,2,9-closo-Ru2 C2 B10 H11 ] by direct electrophilic insertion, promoted by the carborane substituent in the 13-vertex/12-vertex precursor. When arene=mesitylene (mes), the diruthenium species is fluxional in solution at room temperature in a process that makes the metal-ligand fragments equivalent. A unique mechanism for this fluxionality is proposed and is shown to be fully consistent with the observed fluxionality or nonfluxionality of a series of previously reported 14-vertex dicobaltacarboranes. PMID:26934539

  9. Direct Observation of Intermediates Involved in the Interruption of the Bischler-Napieralski Reaction.

    PubMed

    White, Kolby L; Mewald, Marius; Movassaghi, Mohammad

    2015-08-01

    The first mechanistic investigation of electrophilic amide activation of α,α-disubstituted tertiary lactams and the direct observation of key intermediates by in situ FTIR, (1)H, (13)C, and (19)F NMR in our interrupted Bischler-Napieralski-based synthetic strategy to the aspidosperma alkaloids, including a complex tetracyclic diiminium ion, is discussed. The reactivity of a wide range of pyridines with trifluoromethanesulfonic anhydride was systematically examined, and characteristic IR absorption bands for the corresponding N-trifluoromethanesulfonylated pyridinium trifluoromethanesulfonates were assigned. The reversible formation of diiminium ether intermediates was studied, providing insight into divergent mechanistic pathways as a function of the steric environment of the amide substrate and stoichiometry of reagents. Importantly, when considering base additives during electrophilic amide activation, more hindered α-quaternary tertiary lactams require the use of non-nucleophilic pyridine additives in order to avoid deactivation via a competing desulfonylation reaction. The isolation and full characterization of a tetracyclic iminium trifluoromethanesulfonate provided additional correlation between in situ characterization of sensitive intermediates and isolable compounds involved in this synthetic transformation. PMID:26166404

  10. Direct Observation of Intermediates Involved in the Interruption of the Bischler–Napieralski Reaction

    PubMed Central

    White, Kolby L.; Mewald, Marius; Movassaghi, Mohammad

    2015-01-01

    The first mechanistic investigation of electrophilic amide activation of α,α-disubstituted tertiary lactams and the direct observation of key intermediates by in situ FTIR, 1H, 13C, and 19F NMR in our interrupted Bischler–Napieralski based synthetic strategy to the aspidosperma alkaloids, including a complex tetracyclic diiminium ion, is discussed. The reactivity of a wide range of pyridines with trifluoromethanesulfonic anhydride was systematically examined, and characteristic IR absorption bands for the corresponding N-trifluoromethanesulfonylated pyridinium trifluoromethanesulfonates were assigned. The reversible formation of diiminium ether intermediates was studied, providing insight into divergent mechanistic pathways as a function of the steric environment of the amide substrate and stoichiometry of reagents. Importantly, when considering base additives during electrophilic amide activation, more hindered α-quaternary tertiary lactams require the use of non-nucleophilic pyridine additives in order to avoid deactivation via a competing desulfonylation reaction. The isolation and full characterization of a tetracyclic iminium trifluoromethanesulfonate provided additional correlation between in situ characterization of sensitive intermediates and isolable compounds involved in this synthetic transformation. PMID:26166404

  11. Direct Excitation of the Reaction Coordinate: Overtone-Induced Predissociation of the Hydroxymethyl Radical

    NASA Astrophysics Data System (ADS)

    Reisler, Hanna; Ryazanov, Mikhail; Rodrigo, Chirantha P.

    2011-06-01

    The overtone-induced vibrational predissociation of the hydroxymethyl radical is achieved following excitation of the radical to the third O-H stretch overtone. The excited O-H stretch is also the bond that breaks; i.e. overtone excitation is in the reaction coordinate. The production of H atoms takes place via tunneling through the barrier to the H + formaldehyde channel. H-atom photofragment yield spectra in the region of the third overtone reveal two mixed bands with contributions from the third OH overtone and a combination band comprised of two quanta of OH stretch and one quantum of CH asymmetric stretch. Using velocity map imaging, sliced images of H-atom products are obtained with kinetic energy resolution sufficient to reveal the vibrational structure in the formaldehyde co-fragment. As expected, most of the formaldehyde molecules are born without vibrational excitation but some exhibit excitation in other modes, such as wagging and CO stretch. The rotational contours of the vibrational bands are well described by temperatures in the range 100-150 K. Slice imaging allows scanning the pump laser while monitoring H fragments in selected kinetic energy ranges, and in this way it is demonstrated that all the observed vibrational levels of formaldehyde have their parentage in the hydroxymethyl radical. The barrier to isomerization to methoxy is comparable to the barrier to direct dissociation and the role of isomerization is investigated by using partially deuterated radicals.

  12. An overview of the 19F(p,α0)16 O reaction with direct methods

    NASA Astrophysics Data System (ADS)

    Dell’Aquila, D.; Lombardo, I.

    2016-04-01

    The study of the 19F(p,α)16O reaction at low energy is important both for Nuclear Structure and Astrophysics. Despite of its importance, the S-factor of this reaction is poorly known, especially at astrophysical energies. We present an overview of the 19F(p,α0)16O reaction cross section, as obtained from recent direct measurements and from published works in the literature. We include in the systematic also data from an unpublished work, where several excitation functions and angular distributions for α0 and απ channels are reported.

  13. Low-Energy resonances in the 22Ne(p,γ)23Na reaction directly observed at LUNA

    NASA Astrophysics Data System (ADS)

    Depalo, Rosanna; LUNA Collaboration

    2016-04-01

    The neon-sodium cycle of hydrogen burning influences the synthesis of the elements between 20Ne and 27Al in AGB stars and classical novae explosions. The 22Ne(p,γ)23Na reaction rate is very uncertain because of a large number of unobserved resonances lying in the Gamow window. A new direct study of the 22Ne(p,γ)23Na reaction has been performed at the Laboratory for Underground Nuclear Astrophysics (LUNA) using a windowless gas target and two HPGe detectors. Several resonances have been observed for the first time in a direct experiment.

  14. Following the steps of a reaction by direct imaging of many individual molecules.

    PubMed

    van Vörden, Dennis; Wortmann, Ben; Schmidt, Nico; Lange, Manfred; Robles, Roberto; Brendel, Lothar; Bobisch, Christian A; Möller, Rolf

    2016-06-01

    The dehydrogenation and dechlorination of FeOEP-Cl on Cu(111) has been studied in detail by scanning tunneling microscopy. Although, it is not possible to follow the reaction of an individual molecule, the complete pathway of the reaction with 22 inequivalent intermediate states and the rates of the involved processes are revealed. This is achieved by combining the analysis of a large data set showing thousands of molecules in the different stages of the reaction with numerical simulations. PMID:27230941

  15. New Direction in Hydrogeochemical Transport Modeling: Incorporating Multiple Kinetic and Equilibrium Reaction Pathways

    SciTech Connect

    Steefel, C.I.

    2000-02-02

    At least two distinct kinds of hydrogeochemical models have evolved historically for use in analyzing contaminant transport, but each has important limitations. One kind, focusing on organic contaminants, treats biodegradation reactions as parts of relatively simple kinetic reaction networks with no or limited coupling to aqueous and surface complexation and mineral dissolution/precipitation reactions. A second kind, evolving out of the speciation and reaction path codes, is capable of handling a comprehensive suite of multicomponent complexation (aqueous and surface) and mineral precipitation and dissolution reactions, but has not been able to treat reaction networks characterized by partial redox disequilibrium and multiple kinetic pathways. More recently, various investigators have begun to consider biodegradation reactions in the context of comprehensive equilibrium and kinetic reaction networks (e.g. Hunter et al. 1998, Mayer 1999). Here we explore two examples of multiple equilibrium and kinetic reaction pathways using the reactive transport code GIMRT98 (Steefel, in prep.): (1) a computational example involving the generation of acid mine drainage due to oxidation of pyrite, and (2) a computational/field example where the rates of chlorinated VOC degradation are linked to the rates of major redox processes occurring in organic-rich wetland sediments overlying a contaminated aerobic aquifer.

  16. Computational explorations of mechanisms and ligand-directed selectivities of copper-catalyzed Ullmann-type reactions.

    PubMed

    Jones, Gavin O; Liu, Peng; Houk, K N; Buchwald, Stephen L

    2010-05-01

    Computational investigations of ligand-directed selectivities in Ullmann-type coupling reactions of methanol and methylamine with iodobenzene by beta-diketone- and 1,10-phenanthroline-ligated Cu(I) complexes are reported. Density functional theory calculations using several functionals were performed on both the nucleophile formation and aryl halide activation steps of these reactions. The origin of ligand-directed selectivities in N- versus O-arylation reactions as described in a previous publication (J. Am. Chem. Soc. 2007, 129, 3490-3491) were studied and explained. The selectivities observed experimentally are derived not from initial Cu(I)(nucleophile) complex formation but from the subsequent steps involving aryl halide activation. The arylation may occur via single-electron transfer (SET) or iodine atom transfer (IAT), depending on the electron-donating abilities of the ligand and nucleophile. Mechanisms involving either oxidative addition/reductive elimination or sigma-bond metathesis are disfavored. SET mechanisms are favored in reactions promoted by the beta-diketone ligand; N-arylation is predicted to be favored in these cases, in agreement with experimental results. The phenanthroline ligand promotes O-arylation reactions via IAT mechanisms in preference to N-arylation reactions, which occur via SET mechanisms; this result is also in agreement with experimental results. PMID:20387898

  17. Insight into organic reactions from the direct random phase approximation and its corrections

    SciTech Connect

    Ruzsinszky, Adrienn; Zhang, Igor Ying; Scheffler, Matthias

    2015-10-14

    The performance of the random phase approximation (RPA) and beyond-RPA approximations for the treatment of electron correlation is benchmarked on three different molecular test sets. The test sets are chosen to represent three typical sources of error which can contribute to the failure of most density functional approximations in chemical reactions. The first test set (atomization and n-homodesmotic reactions) offers a gradually increasing balance of error from the chemical environment. The second test set (Diels-Alder reaction cycloaddition = DARC) reflects more the effect of weak dispersion interactions in chemical reactions. Finally, the third test set (self-interaction error 11 = SIE11) represents reactions which are exposed to noticeable self-interaction errors. This work seeks to answer whether any one of the many-body approximations considered here successfully addresses all these challenges.

  18. Fundamental studies of retrograde reactions in direct liquefaction. Final report, September 20, 1988--November 20, 1990

    SciTech Connect

    Serio, M.A.; Solomon, P.R.; Kroo, E.; Charpenay, S.; Bassilakis, R.

    1991-12-17

    The overall objective of the program was to improve the understanding of retrograde reactions and their dependencies on coal rank and structure, and/or coal modifications and reaction conditions. Because retrograde reactions are competitive with bond breaking reactions, an understanding of both is required to shift the competition in favor of the latter. Related objectives were to clarify the conflicting observations reported in literature on such major topics as the role of oxygen groups in retrograde reactions and to provide a bridge from very fundamental studies on pure compounds to phenomenological studies on actual coal. This information was integrated into the FG-DVC model, which was improved and extended to the liquefaction context.

  19. Direct Diazo-Transfer Reaction on β-lactam: Synthesis and Preliminary Biological Activities of 6-Triazolylpenicillanic Acids

    PubMed Central

    Chen, Po C.; Emrich, Rebekah E.; Patel, Pratiq A.

    2009-01-01

    In this study we report the first example of a direct diazo-transfer reaction on readily available 6-aminopenicillanates to give 6-azidopenicillanates in high yield. Subsequent Cu(I)-catalyzed Huisgen cycloaddition between these 6-azidopenicillanates and assorted terminal alkynes facilely furnished 6-triazolylpenicillanic acids was. Preliminary biological screening indicates that these triazolylpenicillanic acids possess low to moderate antibacterial activities. PMID:17855098

  20. Ceramic powder for sintering materials

    NASA Technical Reports Server (NTRS)

    Akiya, H.; Saito, A.

    1984-01-01

    Surface activity of ceramic powders such as MgO and Al2O3, for use in sintering with sp. emphasis on their particle size, shape, particle size distribution, packing, and coexisting additives and impurities are reviewed.

  1. PLANETESIMAL FORMATION INDUCED BY SINTERING

    SciTech Connect

    Sirono, Sin-iti

    2011-06-01

    Sintering of H{sub 2}O ice proceeds in an icy dust aggregate as the temperature increases due to the infall to the central star. By numerical simulations, I show that fragmentation of the aggregate by sintering occurs at a particular region of a protoplanetary nebula. The fragments accumulate at the region because their infalling velocity is low. The dust surface density exceeds the critical surface density required for gravitational instability to form planetesimals.

  2. The sintering of nitrogen ceramics

    SciTech Connect

    Hampshire, S.

    1986-01-01

    The mechanism of densification with oxide additives and the role of the ..cap alpha..-BETA phase transformation is investigated in a detailed kinetic study. Selected compositions in the Si-Al-O-N system are detailed, with and without additives. Although the work is mainly concerned with the identification of the mechanisms of sintering, some property measurements on a sintered BETA-sialon are reported and the feasibility of preparing pure ..cap alpha..-sialon phases is explored.

  3. Method of sintering ceramic materials

    DOEpatents

    Holcombe, Cressie E.; Dykes, Norman L.

    1992-01-01

    A method for sintering ceramic materials is described. A ceramic article is coated with layers of protective coatings such as boron nitride, graphite foil, and niobium. The coated ceramic article is embedded in a container containing refractory metal oxide granules and placed within a microwave oven. The ceramic article is heated by microwave energy to a temperature sufficient to sinter the ceramic article to form a densified ceramic article having a density equal to or greater than 90% of theoretical density.

  4. Method of sintering ceramic materials

    DOEpatents

    Holcombe, C.E.; Dykes, N.L.

    1992-11-17

    A method for sintering ceramic materials is described. A ceramic article is coated with layers of protective coatings such as boron nitride, graphite foil, and niobium. The coated ceramic article is embedded in a container containing refractory metal oxide granules and placed within a microwave oven. The ceramic article is heated by microwave energy to a temperature sufficient to sinter the ceramic article to form a densified ceramic article having a density equal to or greater than 90% of theoretical density. 2 figs.

  5. Degradation of octylphenol and nonylphenol by ozone - part I: direct reaction.

    PubMed

    Ning, Bo; Graham, Nigel J D; Zhang, Yanping

    2007-06-01

    This aqueous reaction between ozone and two alkylphenols (APs), namely octylphenol (OP) and nonylphenol (NP), has been investigated. Both compounds are important endocrine disrupting chemicals, which arise from the biodegradation of alkylphenol ethoxylates and are often found at relatively high concentrations in wastewater effluents. In this paper the results of an experimental study are presented which provide values for the reaction rate constants between molecular ozone and undissociated OP and NP, and overall reaction rate constants for the degradation of the two APs at pH values in the range of 7-9. The kinetic rate constants for OP and NP degradation by molecular ozone were 4.33(+/-0.18) x 10(4) and 3.90(+/-0.10) x 10(4) M(-1) s(-1), and the reaction stoichiometry was similar in both cases and equal to approximately 1.3:1 ([O3]:[AP]). The overall second order reaction rate constants for the two APs increased significantly with increasing pH, which is believed to be mainly due to the increasing influence of indirect radical reaction with increasing pH; this aspect is considered in more detail in a companion paper. A preliminary investigation of the reaction mechanism suggests that an initial product of ozonation is hydroxyl-alkyl phenol. PMID:17349676

  6. Direct conversion from Jerusalem artichoke to hydroxymethylfurfural (HMF) using the Fenton reaction.

    PubMed

    Seo, Yeong Hwan; Han, Jong-In

    2014-05-15

    A simple method for hydroxymethylfurfural (HMF) production from non-crop biomass of the Jerusalem artichoke was developed using the Fenton reaction, in a mixture of 2-butanol and water. Four parameters (temperature, reaction time, Fe(2+) concentration, and H2O2 concentration) were identified as experimental factors, and HMF yield was selected as the response parameter. The experimental factors were optimised by employing Response Surface Methodology (RSM). The maximum HMF yield, of 46%, was obtained with a reaction time of 90 min, Fe(2+) concentration of 1.3 mM, and 0.47 M of H2O2 at 180 °C. PMID:24423522

  7. Electrical Sintering of Silver Nanoparticle Ink Studied by In-Situ TEM Probing

    PubMed Central

    Hummelgård, Magnus; Zhang, Renyun; Nilsson, Hans-Erik; Olin, Håkan

    2011-01-01

    Metallic nanoparticle inks are used for printed electronics, but to reach acceptable conductivity the structures need to be sintered, usually using a furnace. Recently, sintering by direct resistive heating has been demonstrated. For a microscopic understanding of this Joule heating sintering method, we studied the entire process in real time inside a transmission electron microscope equipped with a movable electrical probe. We found an onset of Joule heating induced sintering and coalescence of nanoparticles at power levels of 0.1–10 mW/m3. In addition, a carbonization of the organic shells that stabilize the nanoparticles were found, with a conductivity of 4 105 Sm−1. PMID:21390314

  8. Estimation of Sintering Kinetics of Oxidized Magnetite Pellet Using Optical Dilatometer

    NASA Astrophysics Data System (ADS)

    Sandeep Kumar, T. K.; Viswanathan, Neelakantan Nurni; Ahmed, Hesham M.; Andersson, Charlotte; Björkman, Bo

    2015-04-01

    The quality of magnetite pellet is primarily determined by the physico-chemical changes the pellet undergoes as it makes excursion through the gaseous and thermal environment in the induration furnace. Among these physico-chemical processes, the oxidation of magnetite phase and the sintering of oxidized magnetite (hematite) and magnetite (non-oxidized) phases are vital. Rates of these processes not only depend on the thermal and gaseous environment the pellet gets exposed in the induration reactor but also interdependent on each other. Therefore, a systematic study should involve understanding these processes in isolation to the extent possible and quantify them seeking the physics. With this motivation, the present paper focusses on investigating the sintering kinetics of oxidized magnetite pellet. For the current investigation, sintering experiments were carried out on pellets containing more than 95 pct magnetite concentrate from LKAB's mine, dried and oxidized to completion at sufficiently low temperature to avoid sintering. The sintering behavior of this oxidized pellet is quantified through shrinkage captured by Optical Dilatometer. The extent of sintering characterized by sintering ratio found to follow a power law with time i.e., Kt n . The rate constant K for sintering was determined for different temperatures from isothermal experiments. The rate constant, K, varies with temperature as and the activation energy ( Q) and reaction rate constant ( K') are estimated. Further, the sintering kinetic equation was also extended to a non-isothermal environment and validated using laboratory experiments.

  9. Fabrication of particle dispersed inert matrix fuel based on liquid phase sintered SiC

    NASA Astrophysics Data System (ADS)

    Pavlyuchkov, D.; Baney, R. H.; Tulenko, J. S.; Seifert, H. J.

    2011-08-01

    In the present work, liquid phase sintered SiC (LPS-SiC) was proposed as an inert matrix for the particle dispersed inert matrix fuel (IMF). The fuel particles containing plutonium and minor actinides were substituted with pure yttria stabilized zirconia beads. The LPS-SiC matrix was produced from the initial mixtures prepared using submicron sized α-SiC powder and oxide additives Al 2O 3, Y 2O 3 in the amount of 10 wt.% with the molar ratio 1Y 2O 3/1Al 2O 3. Powder mixtures were sintered using two sintering methods; namely conventional high temperature sintering and novel spark plasma sintering at different temperatures depending on the method applied in order to obtain dense samples. The phase reaction products were identified using X-ray diffraction (XRD) and microstructures were investigated using light microscopy and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDX) techniques. The influence of powder mixing methods, sintering temperatures, pressures applied and holding time on the density of the obtained pellets was investigated. The samples sintered by slow conventional sintering show lower relative density and more pronounced interaction between the fuel particles and matrix in comparison with those obtained with the fast spark plasma sintering method.

  10. Studies of the initial reactions that occur during direct coal liquefaction

    SciTech Connect

    Stohl, F.V.

    1989-01-01

    The objectives of this work are to identify the types of compounds and process conditions that give rise to retrogressive reactions during preconversion processing. Experiments have been performed to evaluate the impacts of temperature, pressure, catalysts, mineral matter, and hydrogen donor on these reactions. Initial studies have been carried out using dibenzyl ether (DBE) because ether linkages represent one type of bonding believed to be present in coal. Previous studies have analyzed the kinetics and mechanism of thermolysis of DBE and have also used DBE to study effects of process variables in coal liquefaction. Results of thermal reactions with DBE have shown that the main reaction products are toluene, benzaldehyde, benzyl alcohol and benzene. In the presence of catalysts such as ZnCl{sub 2}, the product distributions are more complicated and can contain significant amounts of material with higher molecular weights than DBE. 8 refs., 8 figs.

  11. Processing optimization and sintering time dependent magnetic and optical behaviors of Aurivillius Bi{sub 5}Ti{sub 3}FeO{sub 15} ceramics

    SciTech Connect

    Chen Guang; Sun Lin; Ren Qing; Xu Wenfei; Yang Jing; Tang Xiaodong; Bai Wei; Duan Chungang; Chu Junhao; Wu Jing; Meng Xiangjian

    2013-01-21

    Aurivillius Bi{sub 5}Ti{sub 3}FeO{sub 15} (BTF) ceramics were synthesized using the conventional solid state reaction method by optimizing excess of Bi{sub 2}O{sub 3} and sintering time. Their structures, magnetic, and optical properties were investigated in detail. The optimum process to sinter pure Aurivillius BTF ceramics was confirmed to be 3 wt. % excess Bi{sub 2}O{sub 3} to compensate the Bi volatilization at 1050 Degree-Sign C for 240 min (BTF-240M). The microstructure and crystalline structure of the BTF ceramics had little dependence on the sintering time from the x-ray diffraction (XRD) and scanning electron microscopic data. Nevertheless, the magnetic and optical properties were closely related with the sintering time. The overall magnetic behavior of these BTF ceramics was superparamagnetic (SPM), whereas there were unambiguous clues for the existence of antiferromagnetic (AFM) interactions. However, whether the SPM behavior was intrinsic or arised from a tiny amount of spinel Fe{sub 3}O{sub 4} impurity phase cannot be thoroughly ruled out in the XRD detection limit in the present stage. The AFM interactions were weakened upon extending the sintering time. The effective magnetic moment ({mu}{sub eff}), however, demonstrated different dependency on the sintering time. It increased with the sintering time from 80 min to 240 min, and then dropped with further extending the sintering time. Compared with other BTF ceramics, the BTF-240M ceramic showed the highest values of the refractive index n and real part {epsilon}{sub 1}, as well as the lowest ones of the extinction coefficient k and imagine part {epsilon}{sub 2} in whole photon energy range. Finally, a direct inter-band transition was confirmed for these BTF ceramics and optical energy band gaps were determined to be about 3.08, 3.18, and 3.39 eV for 80 min, 150 min, and 240 min sintered BTF ceramics, respectively, yet abnormal optical behavior was observed in BTF-360M ceramic.

  12. Metal-Catalyzed Chemical Reaction of Single Molecules Directly Probed by Vibrational Spectroscopy.

    PubMed

    Choi, Han-Kyu; Park, Won-Hwa; Park, Chan-Gyu; Shin, Hyun-Hang; Lee, Kang Sup; Kim, Zee Hwan

    2016-04-01

    The study of heterogeneous catalytic reactions remains a major challenge because it involves a complex network of reaction steps with various intermediates. If the vibrational spectra of individual molecules could be monitored in real time, one could characterize the structures of the intermediates and the time scales of reaction steps without ensemble averaging. Surface-enhanced Raman scattering (SERS) spectroscopy does provide vibrational spectra with single-molecule sensitivity, but typical single-molecule SERS signals exhibit spatial heterogeneities and temporal fluctuations, making them difficult to be used in single-molecule kinetics studies. Here we show that SERS can monitor the single-molecule catalytic reactions in real time. The surface-immobilized reactants placed at the junctions of well-defined nanoparticle-thin film structures produce time-resolved SERS spectra with discrete, step-transitions of photoproducts. We interpret that such SERS-steps correspond to the reaction events of individual molecules occurring at the SERS hotspot. The analyses of the yield, dynamics, and the magnitude of such SERS steps, along with the associated spectral characteristics, fully support our claim. In addition, a model that is based on plasmonic field enhancement and surface photochemistry reproduces the key features of experimental observation. Overall, the result demonstrates that it is possible, under well-controlled conditions, to differentiate the chemical and physical processes contributing to the single-molecule SERS signals, and thus shows the use of single-molecule SERS as a tool for studying the metal-catalyzed organic reactions. PMID:26964567

  13. Comparison of demographic and direct methods to calculate probabilistic maturation reaction norms for Flemish Cap cod (Gadus morhua)

    PubMed Central

    Pérez-Rodríguez, Alfonso; Morgan, Marie Joanne; Saborido-Rey, Fran

    2009-01-01

    Age and length at maturation have declined in many fish populations and this has been hypothesized to be a genetic change caused by high fishing mortality. Probabilistic Maturation Reaction Norms (PMRNs) have been used as a tool to gain a better understanding of the possible genetic nature of these changes. The demographic and direct methods are two ways to calculate PMRNs. The data requirements are more often met for the demographic method than for the direct method which requires the identification of recruit spawners. However, the demographic method relies on more assumptions than the direct method, typically assuming equality of growth and mortality rates for immature and mature individuals within an age class. This study provides the first direct comparison of demographic and direct methods and shows that both methods produce comparable results. Differences between methods are hypothesized to be owed to possible differences in growth rate between mature and immature individuals in Flemish Cap cod. PMID:25567881

  14. A selection rule for the directions of electronic fluxes during unimolecular pericyclic reactions in the electronic ground state

    NASA Astrophysics Data System (ADS)

    Manz, Jörn; Yamamoto, Kentaro

    2012-05-01

    Unimolecular pericyclic reactions in a non-degenerate electronic ground state proceed under the constraint of zero electronic angular momentum. This restriction engenders a selection rule on the directions of electronic fluxes. Accordingly, clockwise or counter-clockwise fluxes are 'forbidden', whereas pincer-like fluxes (which consist of concerted clockwise and counter-clockwise fluxes) are 'allowed'. The selection rule is illustrated for three reactions: the degenerate Cope rearrangement of hexadiene, hydrogen transfer in malonaldehyde, and double proton transfer in the formic acid dimer.

  15. Dynamic Reaction Mechanisms of ClO¯ with CH3Cl: Comparison Between Direct Dynamics Trajectory Simulations and Experiment.

    PubMed

    Yu, Feng

    2016-03-24

    We have investigated the dynamic reaction mechanisms of *ClO¯ with CH3Cl (the asterisk is utilized to label a different Cl atom). Ab initio molecular dynamics simulations at the MP2/6-31+G(d,p) level of theory have been employed to compute the dynamic trajectories. On the basis of our simulations, the dynamic reaction pathways for the bimolecular nucleophilic substitution (SN2) reaction channel and SN2-induced elimination reaction channel are clearly illustrated. For the SN2 reaction channel, some trajectories directly dissociate to the final products of CH3O*Cl and Cl¯, whereas the others involve the dynamic Cl¯···CH3O*Cl intermediate complex. As to the SN2-induced elimination reaction channel, the trajectories lead to the final products of CH2O, HCl, and *Cl¯ through the dynamic Cl¯···CH3O*Cl intermediate complex. More significantly, the product branching ratios of Cl¯ and *Cl¯ predicted by our simulations are basically consistent with previous experimental results (Villano et al. J. Am. Chem. Soc. 2009, 131, 8227-8233). PMID:26928354

  16. Sintering of lunar glass and basalt

    NASA Technical Reports Server (NTRS)

    Allen, Carlton C.; Hines, Joy A.; Mckay, David S.; Morris, Richard V.

    1992-01-01

    Experiments were conducted to study the sintering behavior of glass and basalt lunar soil simulants. The degree of sintering was assessed by compressive strength testing and microanalysis. Both crushed glass and basalt sinter significantly at 1000 C, with the basalt attaining its maximum strength at 1100 C. Initial sintering occurs in less than 15 min, and the degree of sintering does not increase significantly with time after about 30 min. Glass sinters more readily than crystalline material. Sintering and devitrification both occur on a time scale of minutes in the heated glass, but sintering is apparently more rapid. The processes of sintering and oxygen release by hydrogen reduction of lunar soil are synergistic, and could be combined to produce two extremely useful products at a lunar base.

  17. Production of reactive sintered nickel aluminide

    SciTech Connect

    Cooper, R.M.

    1993-01-01

    Effort over the past 3 months was directed at increasing manufacturing capacity (ball milling) and improving product quality. Orders for the powder have increased, mainly for plasma spray powders. NiAl is an excellent coat between a metal and a ceramic, and its use instead of cobalt should extending operating range for carbide tools. The feather phase in the sintered Ni[sub 3]Al was identified to be a Ni-rich phase nucleated on the grain boundaries with 10 wt % Al composition. The ductile to brittle temperature of powder extruded NiAl was found to be between 500 and 600 C, and shows a 50% elongation at 600 C.

  18. Directing reaction pathways by catalyst active-site selection using self-assembled monolayers.

    PubMed

    Pang, Simon H; Schoenbaum, Carolyn A; Schwartz, Daniel K; Medlin, J Will

    2013-01-01

    One key route for controlling reaction selectivity in heterogeneous catalysis is to prepare catalysts that exhibit only specific types of sites required for desired product formation. Here we show that alkanethiolate self-assembled monolayers with varying surface densities can be used to tune selectivity to desired hydrogenation and hydrodeoxygenation products during the reaction of furfural on supported palladium catalysts. Vibrational spectroscopic studies demonstrate that the selectivity improvement is achieved by controlling the availability of specific sites for the hydrogenation of furfural on supported palladium catalysts through the selection of an appropriate alkanethiolate. Increasing self-assembled monolayer density by controlling the steric bulk of the organic tail ligand restricts adsorption on terrace sites and dramatically increases selectivity to desired products furfuryl alcohol and methylfuran. This technique of active-site selection simultaneously serves both to enhance selectivity and provide insight into the reaction mechanism. PMID:24025780

  19. Catalytic Asymmetric Reactions of 4-Substituted Indoles with Nitroethene: A Direct Entry to Ergot Alkaloid Structures.

    PubMed

    Romanini, Simone; Galletti, Emilio; Caruana, Lorenzo; Mazzanti, Andrea; Himo, Fahmi; Santoro, Stefano; Fochi, Mariafrancesca; Bernardi, Luca

    2015-12-01

    A domino Friedel-Crafts/nitro-Michael reaction between 4-substituted indoles and nitroethene is presented. The reaction is catalyzed by BINOL-derived phosphoric acid catalysts, and delivers the corresponding 3,4-ring-fused indoles with very good results in terms of yields and diastereo- and enantioselectivities. The tricyclic benzo[cd]indole products bear a nitro group at the right position to serve as precursors of ergot alkaloids, as demonstrated by the formal synthesis of 6,7-secoagroclavine from one of the adducts. DFT calculations suggest that the outcome of the reaction stems from the preferential evolution of a key nitronic acid intermediate through a nucleophilic addition pathway, rather than to the expected "quenching" through protonation. PMID:26486074

  20. Optimization of the sintering atmosphere for high-density hydroxyapatite–carbon nanotube composites

    PubMed Central

    White, Ashley A.; Kinloch, Ian A.; Windle, Alan H.; Best, Serena M.

    2010-01-01

    Hydroxyapatite–carbon nanotube (HA–CNT) composites have the potential for improved mechanical properties over HA for use in bone graft applications. Finding an appropriate sintering atmosphere for this composite presents a dilemma, as HA requires water in the sintering atmosphere to remain phase pure and well hydroxylated, yet CNTs oxidize at the high temperatures required for sintering. The purpose of this study was to optimize the atmosphere for sintering these composites. While the reaction between carbon and water to form carbon monoxide and hydrogen at high temperatures (known as the ‘water–gas reaction’) would seem to present a problem for sintering these composites, Le Chatelier's principle suggests this reaction can be suppressed by increasing the concentration of carbon monoxide and hydrogen relative to the concentration of carbon and water, so as to retain the CNTs and keep the HA's structure intact. Eight sintering atmospheres were investigated, including standard atmospheres (such as air and wet Ar), as well as atmospheres based on the water–gas reaction. It was found that sintering in an atmosphere of carbon monoxide and hydrogen, with a small amount of water added, resulted in an optimal combination of phase purity, hydroxylation, CNT retention and density. PMID:20573629

  1. Changes in diffusivity due to sintering in metallized iron oxide pellets

    NASA Astrophysics Data System (ADS)

    Wright, J. K.; Morrison, A. L.

    1982-09-01

    The work discussed in this communication forms part of a much larger study aimed at the mathematical and experimental simulation of direct reduction processes occurring in shaft furnaces of the Midrex, HyL III, Purofer, and Nippon Steel Corporation types. In these processes, iron oxide burdens are subjected to environments in which both the temperature and gas compositions change continuously. Previous work1 showed that reduction under such non-isothermal conditions caused iron oxide pellets initially to swell by up to 10 pct and then shrink to give overall pellet contractions of up to 15 pct by the latter stages of reduction. Microstructural examination indicated that the pellet contractions were due to sintering of the porous, high surface-area iron formed in the initial stages of reduction. The sintering reaction is advantageous in that it tends to increase the strength of the metallized pellets;2 however, the accompanying structural changes can also impede the diffusion of reacting gases into and out of the pellets and thus retard the reaction rates.

  2. Folylpolyglutamate synthetase: direct evidence for an acyl phosphate intermediate in the enzyme-catalyzed reaction

    SciTech Connect

    Banerjee, R.; McGuire, J.J.; Shane, B.; Coward, J.K.

    1986-05-01

    The nature of the intermediate in the reaction catalyzed by folylpoly-..gamma..-glutamate synthetase (FPGS) has been investigated. Incubation of ..cap alpha..,..gamma..-(/sup 18/O)methotrexate with ATP, glutamate, and FPGS resulted in the formation of (/sup 18/O)phosphate, thus providing strong evidence for the formation of a ..gamma..-glutamyl phosphate during catalysis. The inorganic phosphate formed in the enzyme-catalyzed reaction was separated from other products and substrates by chromatography on DEAE-cellulose, then converted to the trimethyl ester, and analyzed by mass spectroscopy. Stoichiometric formation of (/sup 18/O)phosphate was observed in the case of the E. coli enzyme, isolated from a transformant containing the cloned FPGS-dihydrofolate synthetase (folC) gene. In addition, /sup 31/P-NMR analysis of the phosphate isolated from the reaction using E. coli FPGS showed the expected /sup 18/O-isotopic perturbations due to both singly bonded and doubly bonded P-/sup 18/O species. Similar experiments were carried out with FPGS isolated from hog liver. In this case, the small amounts of pure enzyme available precluded use of the NMR technique. However, mass spectral analysis of the derivatized phosphate product revealed the presence of (/sup 18/O)-trimethyl phosphate, thus indicating that the reaction catalyzed by the mammalian enzyme also proceeds via an acyl phosphate intermediate.

  3. A modified reaction cartridge for direct protein sequencing on polymeric membranes.

    PubMed

    Sheer, D G; Yuen, S; Wong, J; Wasson, J; Yuan, P M

    1991-10-01

    A newly designed reaction vessel implements a vertical cross-flow type reactor with the Applied Biosystems multi-mode reaction cartridge design. This cartridge is designed for sequencing samples on polyvinylidine difluoride-type membranes. The benefits of this design include a reduced reaction chamber volume that results in lower rates of chemical consumption and less risk of sample loss or contamination during sequencing. Visualization of the membrane in the reaction chamber during sequencing facilitates optimization of drying, washing, extraction and transfer times. The cycle modifications described in this report are designed to optimize post-coupling extraction, cleavage and post-cleavage extraction steps during "flow across" conditions for polymeric membranes. Also, efficient washing and drying of membranes allows for a fast cycle time of 30 minutes when using Pulsed Liquid chemistry. Examples of Blott cartridge utility for sequencing polyvinylidine difluoride-bound proteins in the low picomole range are shown by analyzing samples prepared by a two-dimensional purification scheme using the 230A HPEC and sodium dodecyl sulfate polyacrylamide gel electrophoresis. PMID:1793588

  4. Theoretical investigations of reactions of some radicals with HO sub 2. 1. Hydrogen abstractions by direct mechanisms

    SciTech Connect

    Toohey, D.W.; Anderson, J.G. )

    1989-02-09

    Ab initio quantum mechanical methods are used to calculate saddle-point geometries and energies for hydrogen abstractions from HO{sub 2} by N, ClO, O, Cl, H, OH, and F assuming direct attack at the hydrogen atom. Results are consistent with bond energy-bond order principles and indicate that activation energies for these reactions should decrease with increasing exothermicity of reaction. In addition, the large rate constant for OH + HO{sub 2} {yields} H{sub 2}O + O{sub 2} is interpreted to be due to long-range dipole-dipole attraction, leading ultimately to formation of a hydrogen bond and to stabilization of an early transition state. Results for the ClO + HO{sub 2} {yields} HOCl + O{sub 2} reaction suggest a dual mechanism dominated by direct abstraction at high temperatures and by elimination from a stable intermediate at lower temperatures, perhaps the only reaction in this series which does so. These results are in good agreement with current experimental rate data.

  5. Studies on the synthesis of (-)-spinosyn a: application of the steric directing group strategy to transannular Diels-Alder reactions.

    PubMed

    Frank, Scott A; Roush, William R

    2002-06-14

    A highly diastereoselective and enantioselective synthesis of the decahydro-as-indacene nucleus 12 of (-)-spinosyn A (1) is reported. By implementing the steric directing group strategy, tricyclic lactone 37 was produced from a remarkably diastereoselective transannular Diels-Alder reaction of lactone 9. The tricyclic core of the natural product was then obtained by using an Ireland-Claisen ring contraction of 37. Reversal of the order of these two steps resulted in an almost complete loss of diastereoselectivity. PMID:12054969

  6. Mechanical properties of β-SiC fabricated by spark plasma sintering

    NASA Astrophysics Data System (ADS)

    Yamamoto, Takeshi A.; Kondou, Takayuki; Kodera, Yasuhiro; Ishii, Takashi; Ohyanagi, Manshi; Munir, Zuhair A.

    2005-08-01

    The consolidation of SiC nanopowder synthesized by the mechanical alloying method was subsequently accomplished by spark plasma sintering of 1700 °C for 10 min under an applied pressure of 40 MPa. The SiC sintered compact with relative density of 98% consisted of nano-sized particles smaller than 100 nm. This phenomenon resulted in the ordering process of stacking disordered structure formed by mechanical alloying. In this work, the effect of grain size and relative density on the mechanical properties were studied. The mechanical properties of sintered compacts were evaluated and compared with the reference samples fabricated from the commercial SiC powder (β-SiC, 0.3 µm, IBIDEN Co., Gifu, Japan) with sintering additive (B-C mixture). The Vickers hardness and bending strength of those sintered compacts increased with the increment of the density. However, the mechanical properties were lower than those of reference samples in case of lower density, even though the mechanical property was close to that of reference sample in case of higher density. This phenomenon was considered for the difference of bond strength between grains because those sintered compacts were fabricated without any sintering additives, while those reference samples were fabricated by accelerating the grain bonding with a sintering additive of B-C mixture. In other words, those results indicated that the effect of sintering additive affected on mechanical properties directly.

  7. First direct measurement of the 11C (α ,p )14N stellar reaction by an extended thick-target method

    NASA Astrophysics Data System (ADS)

    Hayakawa, S.; Kubono, S.; Kahl, D.; Yamaguchi, H.; Binh, D. N.; Hashimoto, T.; Wakabayashi, Y.; He, J. J.; Iwasa, N.; Kato, S.; Komatsubara, T.; Kwon, Y. K.; Teranishi, T.

    2016-06-01

    The 11C(α,p ) 14N reaction is an important α -induced reaction competing with β -limited hydrogen-burning processes in high-temperature explosive stars. We directly measured its reaction cross sections both for the ground-state transition (α ,p0) and the excited-state transitions (α ,p1) and (α ,p2) at relevant stellar energies 1.3-4.5 MeV by an extended thick-target method featuring time of flight for the first time. We revised the reaction rate by numerical integration including the (α ,p1) and (α ,p2) contributions and also low-lying resonances of (α ,p0) using both the present and the previous experimental data which were totally neglected in the previous compilation works. The present total reaction rate lies between the previous (α ,p0) rate and the total rate of the Hauser-Feshbach statistical model calculation, which is consistent with the relevant explosive hydrogen-burning scenarios such as the ν p process.

  8. Acid-Base Pairs in Lewis Acidic Zeolites Promote Direct Aldol Reactions by Soft Enolization.

    PubMed

    Lewis, Jennifer D; Van de Vyver, Stijn; Román-Leshkov, Yuriy

    2015-08-17

    Hf-, Sn-, and Zr-Beta zeolites catalyze the cross-aldol condensation of aromatic aldehydes with acetone under mild reaction conditions with near quantitative yields. NMR studies with isotopically labeled molecules confirm that acid-base pairs in the Si-O-M framework ensemble promote soft enolization through α-proton abstraction. The Lewis acidic zeolites maintain activity in the presence of water and, unlike traditional base catalysts, in acidic solutions. PMID:26138135

  9. Direct observation of ultrafast-electron-transfer reactions unravels high effectiveness of reductive DNA damage.

    PubMed

    Nguyen, Jenny; Ma, Yuhan; Luo, Ting; Bristow, Robert G; Jaffray, David A; Lu, Qing-Bin

    2011-07-19

    Both water and electron-transfer reactions play important roles in chemistry, physics, biology, and the environment. Oxidative DNA damage is a well-known mechanism, whereas the relative role of reductive DNA damage is unknown. The prehydrated electron (e(pre)-), a novel species of electrons in water, is a fascinating species due to its fundamental importance in chemistry, biology, and the environment. e(pre)- is an ideal agent to observe reductive DNA damage. Here, we report both the first in situ femtosecond time-resolved laser spectroscopy measurements of ultrafast-electron-transfer (UET) reactions of e(pre)- with various scavengers (KNO(3), isopropanol, and dimethyl sulfoxide) and the first gel electrophoresis measurements of DNA strand breaks induced by e(pre)- and OH(•) radicals co-produced by two-UV-photon photolysis of water. We strikingly found that the yield of reductive DNA strand breaks induced by each e(pre)- is twice the yield of oxidative DNA strand breaks induced by each OH(•) radical. Our results not only unravel the long-standing mystery about the relative role of radicals in inducing DNA damage under ionizing radiation, but also challenge the conventional notion that oxidative damage is the main pathway for DNA damage. The results also show the potential of femtomedicine as a new transdisciplinary frontier and the broad significance of UET reactions of e(pre)- in many processes in chemistry, physics, biology, and the environment. PMID:21730183

  10. Genetically encoded norbornene directs site-specific cellular protein labelling via a rapid bioorthogonal reaction

    NASA Astrophysics Data System (ADS)

    Lang, Kathrin; Davis, Lloyd; Torres-Kolbus, Jessica; Chou, Chungjung; Deiters, Alexander; Chin, Jason W.

    2012-04-01

    The site-specific incorporation of bioorthogonal groups via genetic code expansion provides a powerful general strategy for site-specifically labelling proteins with any probe. However, the slow reactivity of the bioorthogonal functional groups that can be encoded genetically limits the utility of this strategy. We demonstrate the genetic encoding of a norbornene amino acid using the pyrrolysyl tRNA synthetase/tRNACUA pair in Escherichia coli and mammalian cells. We developed a series of tetrazine-based probes that exhibit ‘turn-on’ fluorescence on their rapid reaction with norbornenes. We demonstrate that the labelling of an encoded norbornene is specific with respect to the entire soluble E. coli proteome and thousands of times faster than established encodable bioorthogonal reactions. We show explicitly the advantages of this approach over state-of-the-art bioorthogonal reactions for protein labelling in vitro and on mammalian cells, and demonstrate the rapid bioorthogonal site-specific labelling of a protein on the mammalian cell surface.

  11. REUSABLE REACTION VESSEL

    DOEpatents

    Soine, T.S.

    1963-02-26

    This patent shows a reusable reaction vessel for such high temperature reactions as the reduction of actinide metal chlorides by calcium metal. The vessel consists of an outer metal shell, an inner container of refractory material such as sintered magnesia, and between these, a bed of loose refractory material impregnated with thermally conductive inorganic salts. (AEC)

  12. Silicon carbide material sintered bodies manufacturing

    NASA Technical Reports Server (NTRS)

    Suzuki, K.; Shinohara, N.

    1984-01-01

    A method is described for producing a high density silicon carbide sintering substance which contains aluminum oxide. The sintering is done in CO gas atmosphere, which is kept at 2 to 20 atmospheric pressures.

  13. Direct detection of Mycobacterium tuberculosis in respiratory specimens in a clinical laboratory by polymerase chain reaction.

    PubMed Central

    Forbes, B A; Hicks, K E

    1993-01-01

    The emergence of epidemic multiple-drug-resistant (MDR) strains of Mycobacterium tuberculosis in conjunction with an increase in the number of reported cases of tuberculosis (TB) represents a major public health problem. In light of a recent outbreak of MDR M. tuberculosis at our center, we began the development of a polymerase chain reaction (PCR) assay for the rapid diagnosis of pulmonary TB using two sets of primers, one based on the IS6110 repeated sequence of M. tuberculosis and the other based on the protein antigen b (PAB). Reaction conditions were first optimized as to the appropriate extraction protocol and the concentrations of primer pairs, nucleotides, and MgCl2. Following a preliminary evaluation of the assay with clinical specimens, extraction and amplification procedures were further modified. PAB and IS6110 primers detected between 2 and 23 and 0.023 and 0.23 CFU of M. tuberculosis, respectively, in pooled, M. tuberculosis-negative sputa by our optimized PCR assay. After routine processing for mycobacteria, 734 specimens were subsequently amplified. DNA for amplification was obtained by boiling and beating the sediments with Tween 20. For each reaction, DNA (10 microliters) was added to an amplification mixture containing 12 pmol of IS6110 primers, 20 pmol of PAB primers, 2 mM MgCl2, 200 microM nucleotides, and 2.5 U of Taq polymerase and the mixture was then amplified for 40 cycles. The sensitivity and specificity of our PCR assay were 87.2 and 97.7%, respectively. We were unable to interpret the results for seven specimens (1%). In our experience, PCR proved to be a useful rapid diagnostic test for TB in a clinical setting and a valuable epidemiological tool for determining exposure groups in the hospital setting. Our findings also underscore the need for the systematic optimization of PCR assay conditions. Images PMID:8349744

  14. Direct conversion of cellulose and hemicellulose to fermentable sugars by a microbially-driven Fenton reaction.

    PubMed

    Sekar, Ramanan; Shin, Hyun Dong; DiChristina, Thomas J

    2016-10-01

    The aim of this work was to develop a microbially-driven Fenton reaction that fragments cellulose and hemicellulose, degrades cellodextrins and xylodextrins, and produces short-chain oligosaccharides and monomeric sugars in a single bioreactor. The lignocellulose degradation system operates at neutral pH and does not require addition of conventional lignocellulose-degrading enzymes, thus avoiding problems associated with enzyme accessibility and specificity. The ability to produce useful bioproducts was demonstrated by production of the bioplastic polyhydroxybutyrate with the xylan degradation products as starting substrate. PMID:27469094

  15. Shrinkage and Sintering Behavior of a Low-Temperature Sinterable Nanosilver Die-Attach Paste

    NASA Astrophysics Data System (ADS)

    Wang, Tao; Zhao, Meihua; Chen, Xu; Lu, Guo-Quan; Ngo, Khai; Luo, Shufang

    2012-09-01

    The drying and densification behavior of a nanosilver paste was studied by shrinkage and weight-loss measurements to provide fundamental understanding on the sintering behavior of the nanomaterial for packaging power devices and modules. The measured shrinkage behavior was found to be in good agreement with the weight-loss behavior of the paste as measured by thermogravitational analysis, and the comparison offered direct evidence of ~10% shrinkage contributed by late-stage densification of silver nanoparticles (NPs). It was found that sintered silver joints could be achieved without cracks or delamination under a ramp-soak temperature profile for bonding small-area chips, e.g., 3 mm × 3 mm or smaller. However, for bonding large-area chips, e.g., 5 mm × 5 mm or larger, rapid evaporation of the entrapped organic species caused the chips to delaminate, leading to large longitudinal cracks at the joint interface. Finally, examination of the microstructure evolution of the silver die-attach material revealed that binder molecules inhibited necking of the silver NPs and delayed densification during the sintering process of the nanosilver paste.

  16. Statistical Hauser-Feshbach theory with width-fluctuation correction including direct reaction channels for neutron-induced reactions at low energies

    NASA Astrophysics Data System (ADS)

    Kawano, T.; Capote, R.; Hilaire, S.; Chau Huu-Tai, P.

    2016-07-01

    A model to calculate particle-induced reaction cross sections with statistical Hauser-Feshbach theory including direct reactions is given. The energy average of the scattering matrix from the coupled-channels optical model is diagonalized by the transformation proposed by Engelbrecht and Weidenmüller [C. A. Engelbrecht and H. A. Weidenmüller, Phys. Rev. C 8, 859 (1973), 10.1103/PhysRevC.8.859]. The ensemble average of S -matrix elements in the diagonalized channel space is approximated by a model of Moldauer [P. A. Moldauer, Phys. Rev. C 12, 744 (1975), 10.1103/PhysRevC.12.744] using the newly parametrized channel degree-of-freedom νa to better describe the Gaussian orthogonal ensemble (GOE) reference calculations. The Moldauer approximation is confirmed by a Monte Carlo study using a randomly generated S matrix, as well as the GOE threefold integration formula. The method proposed is applied to the 238U(n ,n' ) cross-section calculation in the fast-energy range, showing an enhancement in the inelastic scattering cross sections.

  17. Dislocation generation during early stage sintering.

    NASA Technical Reports Server (NTRS)

    Sheehan, J. E.; Lenel, F. V.; Ansell, G. S.

    1973-01-01

    Discussion of the effects of capillarity-induced stresses on dislocations during early stage sintering. A special version of Hirth's (1963) theoretical calculation procedures modified to describe dislocation nucleation on planes meeting the sintering body's neck surface obliquely is shown to predict plastic flow at stress levels know to exist between micron size metal particles in the early stages of sintering.

  18. Kinetics and toxicity of direct reaction between ozone and 1,2-dihydrobenzene in dilute aqueous solution.

    PubMed

    Zaror, C; Carrasco, V; Perez, L; Soto, G; Mondaca, M A; Mansilla, H

    2001-01-01

    The presence of toxic aromatic organic compounds in industrial wastewater affects the efficiency of conventional biological treatment. The oxidizing power of ozone represents an interesting pretreatment to reduce toxicity and increase biodegradability. At low pH, ozone is known to attack electron-rich structures by direct electrophilic reactions which open aromatic rings, and generate smaller oxidized compounds. This paper reports experimental results on kinetic and toxicity aspects of ozone direct reactions with 1,2-dihydrobenzene. This toxic compound is frequently found in cellulose bleaching effluents. Although the reaction pathway is rather complex, 4-carbon compounds, such as maleic acid, are readily formed during the first stage of ozonation. These 4-carbon compounds are further oxidized to form smaller molecules (mostly 2-carbon, such as oxalic acid). The apparent kinetics of 1,2-dihydrobenzene follows a second order law, with a rate constant around 0.36 (dm3 mmol-1s-1), at pH 2 and 20 degrees C. Results show that the BOD:COD ratio increase five-fold as ozonation progresses. Furthermore, the mutagenicity of 1,2-dihydrobenzene totally disappears as the aromatic compound is destroyed by ozonation. PMID:11380197

  19. Local mode excitation and direct unimolecular reaction rate measurements in tetramethyldioxetane

    SciTech Connect

    Cannon, B.D.; Crim, F.F.

    1981-08-15

    Direct excitation of overtone vibrations combined with time-resolved detection of product chemiluminescence produces both overtone vibration excitation spectra and directly measured unimolecular decay rates of tetramethyldioxetane. The spectra show increasingly pure local mode character in higher vibrational levels and exhibit splittings which arise from nonequivalent sites occupied by methyl hydrogens. The temporal evolution of the signal reflects the unimolecular decomposition rate of the highly vibrationally excited molecule, and comparing the observed behavior to Rice--Ramsperger--Kassel--Marcus theory calculations shows that they adequately describe the decomposition if properly averaged over the thermal vibrational energy content of the molecule.

  20. Exact model reduction with delays: closed-form distributions and extensions to fully bi-directional monomolecular reactions

    PubMed Central

    Leier, Andre; Barrio, Manuel; Marquez-Lago, Tatiana T.

    2014-01-01

    In order to systematically understand the qualitative and quantitative behaviour of chemical reaction networks, scientists must derive and analyse associated mathematical models. However, biochemical systems are often very large, with reactions occurring at multiple time scales, as evidenced by signalling pathways and gene expression kinetics. Owing to the associated computational costs, it is then many times impractical, if not impossible, to solve or simulate these systems with an appropriate level of detail. By consequence, there is a growing interest in developing techniques for the simplification or reduction of complex biochemical systems. Here, we extend our recently presented methodology on exact reduction of linear chains of reactions with delay distributions in two ways. First, we report that it is now possible to deal with fully bi-directional monomolecular systems, including degradations, synthesis and generalized bypass reactions. Second, we provide all derivations of associated delays in analytical, closed form. Both advances have a major impact on further reducing computational costs, while still retaining full accuracy. Thus, we expect our new methodology to respond to current simulation needs in pharmaceutical, chemical and biological research. PMID:24694895

  1. Direct observation of the transition state of ultrafast electron transfer reaction of a radiosensitizing drug bromodeoxyuridine

    SciTech Connect

    Wang, C.-R.; Hu, A.; Lu, Q.-B.

    2006-06-28

    Replacement of thymidine in DNA by bromodeoxyuridine (BrdU) has long been known to enhance DNA damage and cell death induced by ionizing/UV radiation, but the mechanism of action of BrdU at the molecular level is poor understood. Using time-resolved femtosecond laser spectroscopy, we obtain the real-time observation of the transition state of the ultrafast electron transfer (ET) reaction of BrdU with the precursor to the hydrated electron, which is a general product in ionizing/UV radiation. The results show that the ET reaction is completed within 0.2 picosecond (ps) after the electronic excitation, leading to the formation of a transition state BrdU*{sup -} with a lifetime of {approx}1.5 ps that then dissociates into Br{sup -} and a high reactive radical dU{sup *}. The present results can greatly enhance our understanding not only of the mechanism of BrdU as a radio-/photosensitizer but of the role of prehydrated electrons in electron-initiated processes in biological and environmental systems.

  2. Direct observation of the transition state of ultrafast electron transfer reaction of a radiosensitizing drug bromodeoxyuridine

    NASA Astrophysics Data System (ADS)

    Wang, C.-R.; Hu, A.; Lu, Q.-B.

    2006-06-01

    Replacement of thymidine in DNA by bromodeoxyuridine (BrdU) has long been known to enhance DNA damage and cell death induced by ionizing/UV radiation, but the mechanism of action of BrdU at the molecular level is poor understood. Using time-resolved femtosecond laser spectroscopy, we obtain the real-time observation of the transition state of the ultrafast electron transfer (ET) reaction of BrdU with the precursor to the hydrated electron, which is a general product in ionizing/UV radiation. The results show that the ET reaction is completed within 0.2picosecond (ps) after the electronic excitation, leading to the formation of a transition state BrdU*- with a lifetime of ˜1.5ps that then dissociates into Br- and a high reactive radical dU*. The present results can greatly enhance our understanding not only of the mechanism of BrdU as a radio-/photosensitizer but of the role of prehydrated electrons in electron-initiated processes in biological and environmental systems.

  3. SINTERING OF NASCENT CALCIUM OXIDE

    EPA Science Inventory

    The paper discusses the measurement of the sintering rate of CaO in a nitrogen atmosphere at temperatures of 700-1100 C. CaO prepared from ultrapure CaCO3 was compared with an impure CaO derived from limestone. Both materials yielded an initial surface area of 104 sq m/g. The rat...

  4. Microwave sintering of boron carbide

    DOEpatents

    Blake, R.D.; Katz, J.D.; Petrovic, J.J.; Sheinberg, H.

    1988-06-10

    A method for forming boron carbide into a particular shape and densifying the green boron carbide shape. Boron carbide in powder form is pressed into a green shape and then sintered, using a microwave oven, to obtain a dense boron carbide body. Densities of greater than 95% of theoretical density have been obtained. 1 tab.

  5. Sintering additives for zirconia ceramics

    SciTech Connect

    Wu, S.

    1986-01-01

    This book is an overview of sintering science and its application to zirconia materials including CaO, MgO, and Y/sub 2/O/sub 3/-CeO/sub 2/ doped materials. This book is a reference for first-time exposure to zirconia materials technology, particularly densification.

  6. Direct functionalization processes: a journey from palladium to copper to iron to nickel to metal-free coupling reactions.

    PubMed

    Mousseau, James J; Charette, André B

    2013-02-19

    The possibility of finding novel disconnections for the efficient synthesis of organic molecules has driven the interest in developing technologies to directly functionalize C-H bonds. The ubiquity of these bonds makes such transformations attractive, while also posing several challenges. The first, and perhaps most important, is the selective functionalization of one C-H bond over another. Another key problem is inducing reactivity at sites that have been historically unreactive and difficult to access without prior inefficient prefunctionalization. Although remarkable advances have been made over the past decade toward solving these and other problems, several difficult tasks remain as researchers attempt to bring C-H functionalization reactions into common use. The functionalization of sp(3) centers continues to be challenging relative to their sp and sp(2) counterparts. Directing groups are often needed to increase the effective concentration of the catalyst at the targeted reaction site, forming thermodynamically stable coordination complexes. As such, the development of removable or convertible directing groups is desirable. Finally, the replacement of expensive rare earth reagents with less expensive and more sustainable catalysts or abandoning the use of catalysts entirely is essential for future practicality. This Account describes our efforts toward solving some of these quandaries. We began our work in this area with the direct arylation of N-iminopyridinium ylides as a universal means to derivatize the germane six-membered heterocycle. We found that the Lewis basic benzoyl group of the pyridinium ylide could direct a palladium catalyst toward insertion at the 2-position of the pyridinium ring, forming a thermodynamically stable six-membered metallocycle. Subsequently we discovered the arylation of the benzylic site of 2-picolonium ylides. The same N-benzoyl group could direct a number of inexpensive copper salts to the 2-position of the pyridinium ylide

  7. Effect of milling and leaching on the structure of sintered silicon

    NASA Technical Reports Server (NTRS)

    Yeh, H. C.; Glascow, T. K.; Herbell, T. P.

    1980-01-01

    Sintering was performed in He for 16 hours at 1200, 1250, and 1300 C. Compacts of as-received Si did not densify during sintering. Milling reduced the average particle size to below 0.5 micrometer and enhanced densification (1.75 g/cc). Leaching milled Si further enhanced densification (1.90 g/cc max.) and decreased structural coarsening. After sintering, the structure of the milled and leached powder compacts appears favorable for the production of reaction bonded silicon nitride.

  8. Direct observation of enhanced plasmon-driven catalytic reaction activity of Au nanoparticles supported on reduced graphene oxides by SERS.

    PubMed

    Liang, Xiu; You, Tingting; Liu, Dapeng; Lang, Xiufeng; Tan, Enzhong; Shi, Jihua; Yin, Penggang; Guo, Lin

    2015-04-21

    Graphene-based nanocomposites have recently attracted tremendous research interest in the field of catalysis due to their unique optical and electronic properties. However, direct observation of enhanced plasmon-driven catalytic activity of Au nanoparticles (NPs) supported on reduced graphene oxides (Au/rGO) has rarely been reported. Herein, based on the reduction from 4-nitrobenzenethiol (4-NBT) to p,p'-dimercaptoazobenzene (DMAB), the catalytic property of Au/rGO nanocomposites was investigated and compared with corresponding Au NP samples with similar size distribution. Our results show that Au/rGO nanocomposites could serve as a good catalytic and analytic platform for plasmon-driven chemical reactions. In addition, systematic comparisons were conducted during power- and time-dependent surface-enhanced Raman scattering (SERS) experiments, which exhibited a lower power threshold and higher catalytic efficiency for Au/rGO as compared to Au NPs toward the reaction. PMID:25793752

  9. Dynamic simulation of impurity transport and chemical reactions in a Bridgman furnace for directional solidification of multi-crystalline silicon

    NASA Astrophysics Data System (ADS)

    Bellmann, M. P.; Panjwani, B.; Syvertsen, M.; Meese, E. A.

    2013-04-01

    Numerical results from a dynamic simulation of impurity transport and reactions in a Bridgman furnace for directional solidification of multi-crystalline silicon are presented and compared to experimental results. The simulation includes the calculation of the thermal field, melt and gas flow velocity field, transport and chemical reactions of oxygen and carbon impurities for the entire process based on heating, melting and solidification phases. Carbon and oxygen distribution in the ingot is analyzed experimentally by means of FT-IR spectroscopy and LECO combustion method, the CO development by means of an μ-GC gas analyzer. The simulated impurity distribution in the ingot and the CO development above the free melt surface are in good agreement with the experimental results. Furthermore the results indicate that the carbon solubility limit is already reached at the stage of melting and SiC precipitates are likely to form at the early stage of growth.

  10. Direct measurement of the {sup 18}F(p,{alpha}){sup 15}O reaction at nova temperatures

    SciTech Connect

    Beer, C. E.; Laird, A. M.; Bentley, M. A.; Diget, C. A.; Fox, S. P.; Fulton, B. R.; Murphy, A. St. J.; Davinson, T.; Salter, P.; Buchman, L.; Davids, B.; Hager, U.; Howell, D.; Martin, L.; Ruiz, C.; Ruprecht, G.; Vockenhuber, C.; Walden, P.

    2011-04-15

    The {sup 18}F(p,{alpha}){sup 15}O reaction rate is crucial for understanding the final abundance of {sup 18}F predicted by nova models. The {gamma}-ray emission in the first few hours after a nova outburst is expected to be dominated by 511 keV annihilation photons from the decay of {sup 18}F, and so understanding its production can provide important constraints on the conditions during the outburst when compared with observations. Results are presented from the lowest-energy direct measurement to date, performed at the Isotope Separator and Accelerator radioactive beam facility at the TRIUMF laboratory, Canada. Cross section measurements at center-of-mass energies of 250, 330, 453, and 673 keV are obtained and the results compared to previous data and R-matrix calculations. The implications for the overall reaction rate in the context of nova explosions have been discussed.

  11. Direct Measurement of the Effective Rate Constant for Primary Charge Separation in Isolated Photosystem II Reaction Centers

    SciTech Connect

    Greenfield, S. R.; Seibert, M.; Govindjee; Wasielewski, M. R.

    1997-03-27

    Transient absorption measurements of the pheophytin a anion band and Qx band bleach region using preferential excitation of P680 are performed on isolated photosystem II reaction centers to determine the effective rate constant for charge separtion. A novel analysis of the Qx band bleach region explicity takes the changing background into account in order to directly measure the rate of growth of the bleach. Both spectral regions reveal biphasic kinetics, with a ca. (8 ps)-1 rate constant for the faster component, and a ca. (50 ps)-1 rate constant for the slower component. We propose that the fster component corresponds to the effective rate constant for charge separation from within the equilibrated reaction center core and provides a lower limit for the intrinsic rate constant for charge separation. The slower component corresponds to charge separation that is limited by slow energy transfer from a long-wavelength accessory chlorophyll a.

  12. Investigation of chemical and electrochemical reactions mechanisms in a direct carbon fuel cell using olive wood charcoal as sustainable fuel

    NASA Astrophysics Data System (ADS)

    Elleuch, Amal; Halouani, Kamel; Li, Yongdan

    2015-05-01

    Direct carbon fuel cell (DCFC) is a high temperature fuel cell using solid carbon as fuel. The use of environmentally friendly carbon material constitutes a promising option for the DCFC future. In this context, this paper focuses on the use of biomass-derived charcoal renewable fuel. A practical investigation of Tunisian olive wood charcoal (OW-C) in planar DCFCs is conducted and good power density (105 mW cm-2) and higher current density (550 mA cm-2) are obtained at 700 °C. Analytical and predictive techniques are performed to explore the relationships between fuel properties and DCFC chemical and electrochemical mechanisms. High carbon content, carbon-oxygen groups and disordered structure, are the key parameters allowing the achieved good performance. Relatively complex chain reactions are predicted to explain the gas evolution within the anode. CO, H2 and CH4 participation in the anodic reaction is proved.

  13. Direct Synthesis of Highly Substituted Pyrroles and Dihydropyrroles Using Linear Selective Hydroacylation Reactions.

    PubMed

    Majhail, Manjeet K; Ylioja, Paul M; Willis, Michael C

    2016-06-01

    Rhodium(I) catalysts incorporating small bite-angle diphosphine ligands, such as (Cy2 P)2 NMe or bis(diphenylphosphino)methane (dppm), are effective at catalysing the union of aldehydes and propargylic amines to deliver the linear hydroacylation adducts in good yields and with high selectivities. In situ treatment of the hydroacylation adducts with p-TSA triggers a dehydrative cyclisation to provide the corresponding pyrroles. The use of allylic amines, in place of the propargylic substrates, delivers functionalised dihydropyrroles. The hydroacylation reactions can also be combined in a cascade process with a Rh(I) -catalysed Suzuki-type coupling employing aryl boronic acids, providing a three-component assembly of highly substituted pyrroles. PMID:27106284

  14. A novel mechanism for direct real-time polymerase chain reaction that does not require DNA isolation from prokaryotic cells

    PubMed Central

    Soejima, Takashi; Xiao, Jin-zhong; Abe, Fumiaki

    2016-01-01

    Typically, polymerase chain reaction (PCR) is performed after DNA isolation. Real-time PCR (qPCR), also known as direct qPCR in mammalian cells with weak membranes, is a common technique using crude samples subjected to preliminary boiling to elute DNA. However, applying this methodology to prokaryotic cells, which have solid cell walls, in contrast to mammalian cells which immediately burst in water, can result in poor detection. We successfully achieved PCR elongation with the addition of 1.3 cfu of Cronobacter muytjensii to a newly developed direct qPCR master mix without performing any crude DNA extraction (detection limit of 1.6 × 100 cfu/ml for the test sample compared with a detection limit of 1.6 × 103 cfu/ml primarily for crude (boiling) or classical DNA isolation). We revealed that the chromosomal DNA retained in prokaryotic cells can function as a PCR template, similarly to the mechanism in in situ PCR. Elucidating this reaction mechanism may contribute to the development of an innovative master mix for direct qPCR to detect genes in a single bacterium with solid cell walls and might lead to numerous novel findings in prokaryotic genomics research. PMID:27334801

  15. A novel mechanism for direct real-time polymerase chain reaction that does not require DNA isolation from prokaryotic cells.

    PubMed

    Soejima, Takashi; Xiao, Jin-Zhong; Abe, Fumiaki

    2016-01-01

    Typically, polymerase chain reaction (PCR) is performed after DNA isolation. Real-time PCR (qPCR), also known as direct qPCR in mammalian cells with weak membranes, is a common technique using crude samples subjected to preliminary boiling to elute DNA. However, applying this methodology to prokaryotic cells, which have solid cell walls, in contrast to mammalian cells which immediately burst in water, can result in poor detection. We successfully achieved PCR elongation with the addition of 1.3 cfu of Cronobacter muytjensii to a newly developed direct qPCR master mix without performing any crude DNA extraction (detection limit of 1.6 × 10(0) cfu/ml for the test sample compared with a detection limit of 1.6 × 10(3) cfu/ml primarily for crude (boiling) or classical DNA isolation). We revealed that the chromosomal DNA retained in prokaryotic cells can function as a PCR template, similarly to the mechanism in in situ PCR. Elucidating this reaction mechanism may contribute to the development of an innovative master mix for direct qPCR to detect genes in a single bacterium with solid cell walls and might lead to numerous novel findings in prokaryotic genomics research. PMID:27334801

  16. C-H Coupling Reactions Directed by Sulfoxides: Teaching an Old Functional Group New Tricks.

    PubMed

    Pulis, Alexander P; Procter, David J

    2016-08-16

    Sulfoxides are classical functional groups for directing the stoichiometric metalation and functionalization of C-H bonds. In recent times, sulfoxides have been given a new lease on life owing to the development of modern synthetic methods that have arisen because of their unique reactivity. They have recently been used in catalytic C-H activation proceeding via coordination of an internal sulfoxide to a metal or through the action of an external sulfoxide ligand. Furthermore, sulfoxides are able to capture nucleophiles and electrophiles to give sulfonium salts, which subsequently enable the formation of C-C bonds at the expense of C-H bonds. This Review summarizes a renaissance period in the application of sulfoxides arising from their versatility in directing C-H functionalization. PMID:27409984

  17. Feasibility of Traveling Wave Direct Energy Conversion of Fission Reaction Fragments

    NASA Technical Reports Server (NTRS)

    Tarditi, A. G.; George, J. A.; Miley, G. H.; Scott, J. H.

    2013-01-01

    Fission fragment direct energy conversion has been considered in the past for the purpose of increasing nuclear power plant efficiency and for advanced space propulsion. Since the fragments carry electric charge (typically in the order of 20 e) and have 100 MeV-range kinetic energy, techniques utilizing very high-voltage DC electrodes have been considered. This study is focused on a different approach: the kinetic energy of the charged fission fragments is converted into alternating current by means of a traveling wave coupling scheme (Traveling Wave Direct Energy Converter, TWDEC), thereby not requiring the utilization of high voltage technology. A preliminary feasibility analysis of the concept is introduced based on a conceptual level study and on a particle simulation model of the beam dynamics.

  18. Nonenzymatic template-directed reactions on altritol oligomers, preorganized analogues of oligonucleotides

    NASA Technical Reports Server (NTRS)

    Kozlov, I. A.; Zielinski, M.; Allart, B.; Kerremans, L.; Van Aerschot, A.; Busson, R.; Herdewijn, P.; Orgel, L. E.; Bada, J. L. (Principal Investigator)

    2000-01-01

    Altritol nucleic acids (ANAs) are RNA analogues with a phosphorylated D-altritol backbone. The nucleobase is attached at the 2-(S)-position of the carbohydrate moiety. We report that ANA oligomers are superior to the corresponding DNA, RNA, and HNA (hexitol nucleic acid) in supporting efficient nonenzymatic template-directed synthesis of complementary RNAs from nucleoside-5'-phosphoro-2-methyl imidazolides. Activated ANA and HNA monomers do not oligomerize efficiently on DNA, RNA, HNA, or ANA templates.

  19. Replication Experiments in Microgravity Liquid Phase Sintering

    NASA Astrophysics Data System (ADS)

    German, Randall M.; Johnson, John L.

    2016-05-01

    Although considerable experience exists with sintering on Earth, the behavior under reduced gravity conditions is poorly understood. This study analyzes replica microgravity liquid phase sintering data for seven tungsten alloys (35 to 88 wt pct tungsten) sintered for three hold times (1, 180, or 600 minutes) at 1773 K (1500 °C) using 0.002 pct of standard gravity. Equivalent sintering is performed on Earth using the same heating cycles. Microgravity sintering results in a lower density and more shape distortion. For Earth-based sintering, minimized distortion is associated with low liquid contents to avoid solid settling and slumping. Distortion in microgravity sintering involves viscous spreading of the component at points of contact with the containment crucible. Distortion in microgravity is minimized by short hold times; long hold times allow progressive component reshaping toward a spherical shape. Microgravity sintering also exhibits pore coalescence into large, stable voids that cause component swelling. The microgravity sintering results show good replication in terms of mass change and sintered density. Distortion is scattered but statistically similar between the replica microgravity runs. However, subtle factors, not typically of concern on Earth, emerge to influence microgravity sintering, such that ground experiments do not provide a basis to predict microgravity behavior.

  20. Direct measurements of OH and other product yields from the HO2 + CH3C(O)O2 reaction

    NASA Astrophysics Data System (ADS)

    Winiberg, F. A. F.; Dillon, T. J.; Orr, S. C.; Groß, C. B. M.; Bejan, I.; Brumby, C. A.; Evans, M. J.; Smith, S. C.; Heard, D. E.; Seakins, P. W.

    2015-10-01

    The reaction CH3C(O)O2 + HO2 → CH3C(O)OOH + O2 (Reaction R5a), CH3C(O)OH + O3 (Reaction R5b), CH3 + CO2 + OH + O2 (Reaction R5c) was studied in a series of experiments conducted at 1000 mbar and (293 ± 2) K in the HIRAC simulation chamber. For the first time, products, (CH3C(O)OOH, CH3C(O)OH, O3 and OH) from all three branching pathways of the reaction have been detected directly and simultaneously. Measurements of radical precursors (CH3OH, CH3CHO), HO2 and some secondary products HCHO and HCOOH further constrained the system. Fitting a comprehensive model to the experimental data, obtained over a range of conditions, determined the branching ratios α(R5a) = 0.37 ± 0.10, α(R5b) = 0.12 ± 0.04 and α(R5c) = 0.51 ± 0.12 (errors at 2σ level). Improved measurement/model agreement was achieved using k(R5) = (2.4 ± 0.4) × 10-11 cm3 molecule-1 s-1, which is within the large uncertainty of the current IUPAC and JPL recommended rate coefficients for the title reaction. The rate coefficient and branching ratios are in good agreement with a recent study performed by Groß et al. (2014b); taken together, these two studies show that the rate of OH regeneration through Reaction (R5) is more rapid than previously thought. GEOS-Chem has been used to assess the implications of the revised rate coefficients and branching ratios; the modelling shows an enhancement of up to 5 % in OH concentrations in tropical rainforest areas and increases of up to 10 % at altitudes of 6-8 km above the equator, compared to calculations based on the IUPAC recommended rate coefficient and yield. The enhanced rate of acetylperoxy consumption significantly reduces PAN in remote regions (up to 30 %) with commensurate reductions in background NOx.

  1. Direct measurements of OH and other product yields from the HO2 + CH3C(O)O2 reaction

    NASA Astrophysics Data System (ADS)

    Winiberg, Frank A. F.; Dillon, Terry J.; Orr, Stephanie C.; Groß, Christoph B. M.; Bejan, Iustinian; Brumby, Charlotte A.; Evans, Matthew J.; Smith, Shona C.; Heard, Dwayne E.; Seakins, Paul W.

    2016-03-01

    The reaction CH3C(O)O2 + HO2 → CH3C(O)OOH + O2 (Reaction R5a), CH3C(O)OH + O3 (Reaction R5b), CH3 + CO2 + OH + O2 (Reaction R5c) was studied in a series of experiments conducted at 1000 mbar and (293 ± 2) K in the HIRAC simulation chamber. For the first time, products, (CH3C(O)OOH, CH3C(O)OH, O3 and OH) from all three branching pathways of the reaction have been detected directly and simultaneously. Measurements of radical precursors (CH3OH, CH3CHO), HO2 and some secondary products HCHO and HCOOH further constrained the system. Fitting a comprehensive model to the experimental data, obtained over a range of conditions, determined the branching ratios α(R5a) = 0.37 ± 0.10, α(R5b) = 0.12 ± 0.04 and α(R5c) = 0.51 ± 0.12 (errors at 2σ level). Improved measurement/model agreement was achieved using k(R5) = (2.4 ± 0.4) × 10-11 cm3 molecule-1 s-1, which is within the large uncertainty of the current IUPAC and JPL recommended rate coefficients for the title reaction. The rate coefficient and branching ratios are in good agreement with a recent study performed by Groß et al. (2014b); taken together, these two studies show that the rate of OH regeneration through Reaction (R5) is more rapid than previously thought. GEOS-Chem has been used to assess the implications of the revised rate coefficients and branching ratios; the modelling shows an enhancement of up to 5 % in OH concentrations in tropical rainforest areas and increases of up to 10 % at altitudes of 6-8 km above the equator, compared to calculations based on the IUPAC recommended rate coefficient and yield. The enhanced rate of acetylperoxy consumption significantly reduces PAN in remote regions (up to 30 %) with commensurate reductions in background NOx.

  2. Cold press sintering of simulated lunar basalt

    NASA Technical Reports Server (NTRS)

    Altemir, D. A.

    1993-01-01

    In order to predict the conditions for which the lunar regolith may be adequately sintered, experiments were conducted in which samples of simulated lunar basalt (MLS-1) were pressed at high pressures and then heated in an electric furnace. This sintering process may be referred to as cold press sintering since the material is pressed at room temperature. Although test articles were produced which possessed compressive strengths comparable to that of terrestrial concrete, the cold press sintering process requires very high press pressures and sintering temperatures in order to achieve that strength. Additionally, the prospect of poor internal heat transfer adversely affecting the quality of sintered lunar material is a major concern. Therefore, it is concluded that cold press sintering will most likely be undesirable for the production of lunar construction materials.

  3. Gravitational Role in Liquid Phase Sintering

    NASA Technical Reports Server (NTRS)

    Upadhyaya, Anish; Iacocca, Ronald G.; German, Randall M.

    1998-01-01

    To comprehensively understand the gravitational effects on the evolution of both the microstructure and the macrostructure during liquid phase sintering, W-Ni-Fe alloys with W content varying from 35 to 98 wt.% were sintered in microgravity. Compositions that slump during ground-based sintering also distort when sintered under microgravity. In ground-based sintering, low solid content alloys distort with a typical elephant-foot profile, while in microgravity, the compacts tend to spheroidize. This study shows that microstructural segregation occurs in both ground-based as well as microgravity sintering. In ground-based experiments, because of the density difference between the solid and the liquid phase, the solid content increases from top to the bottom of the sample. In microgravity, the solid content increases from periphery to the center of the samples. This study also shows that the pores during microgravity sintering act as a stable phase and attain anomalous shapes.

  4. Multiple Reaction Monitoring for Direct Quantitation of Intact Proteins Using a Triple Quadrupole Mass Spectrometer.

    PubMed

    Wang, Evelyn H; Combe, Peter C; Schug, Kevin A

    2016-05-01

    Methods that can efficiently and effectively quantify proteins are needed to support increasing demand in many bioanalytical fields. Triple quadrupole mass spectrometry (QQQ-MS) is sensitive and specific, and it is routinely used to quantify small molecules. However, low resolution fragmentation-dependent MS detection can pose inherent difficulties for intact proteins. In this research, we investigated variables that affect protein and fragment ion signals to enable protein quantitation using QQQ-MS. Collision induced dissociation gas pressure and collision energy were found to be the most crucial variables for optimization. Multiple reaction monitoring (MRM) transitions for seven standard proteins, including lysozyme, ubiquitin, cytochrome c from both equine and bovine, lactalbumin, myoglobin, and prostate-specific antigen (PSA) were determined. Assuming the eventual goal of applying such methodology is to analyze protein in biological fluids, a liquid chromatography method was developed. Calibration curves of six standard proteins (excluding PSA) were obtained to show the feasibility of intact protein quantification using QQQ-MS. Linearity (2-3 orders), limits of detection (0.5-50 μg/mL), accuracy (<5% error), and precision (1%-12% CV) were determined for each model protein. Sensitivities for different proteins varied considerably. Biological fluids, including human urine, equine plasma, and bovine plasma were used to demonstrate the specificity of the approach. The purpose of this model study was to identify, study, and demonstrate the advantages and challenges for QQQ-MS-based intact protein quantitation, a largely underutilized approach to date.Graphical Abstract. PMID:26956437

  5. Multiple Reaction Monitoring for Direct Quantitation of Intact Proteins Using a Triple Quadrupole Mass Spectrometer

    NASA Astrophysics Data System (ADS)

    Wang, Evelyn H.; Combe, Peter C.; Schug, Kevin A.

    2016-03-01

    Methods that can efficiently and effectively quantify proteins are needed to support increasing demand in many bioanalytical fields. Triple quadrupole mass spectrometry (QQQ-MS) is sensitive and specific, and it is routinely used to quantify small molecules. However, low resolution fragmentation-dependent MS detection can pose inherent difficulties for intact proteins. In this research, we investigated variables that affect protein and fragment ion signals to enable protein quantitation using QQQ-MS. Collision induced dissociation gas pressure and collision energy were found to be the most crucial variables for optimization. Multiple reaction monitoring (MRM) transitions for seven standard proteins, including lysozyme, ubiquitin, cytochrome c from both equine and bovine, lactalbumin, myoglobin, and prostate-specific antigen (PSA) were determined. Assuming the eventual goal of applying such methodology is to analyze protein in biological fluids, a liquid chromatography method was developed. Calibration curves of six standard proteins (excluding PSA) were obtained to show the feasibility of intact protein quantification using QQQ-MS. Linearity (2-3 orders), limits of detection (0.5-50 μg/mL), accuracy (<5% error), and precision (1%-12% CV) were determined for each model protein. Sensitivities for different proteins varied considerably. Biological fluids, including human urine, equine plasma, and bovine plasma were used to demonstrate the specificity of the approach. The purpose of this model study was to identify, study, and demonstrate the advantages and challenges for QQQ-MS-based intact protein quantitation, a largely underutilized approach to date.

  6. Multiple Reaction Monitoring for Direct Quantitation of Intact Proteins Using a Triple Quadrupole Mass Spectrometer

    NASA Astrophysics Data System (ADS)

    Wang, Evelyn H.; Combe, Peter C.; Schug, Kevin A.

    2016-05-01

    Methods that can efficiently and effectively quantify proteins are needed to support increasing demand in many bioanalytical fields. Triple quadrupole mass spectrometry (QQQ-MS) is sensitive and specific, and it is routinely used to quantify small molecules. However, low resolution fragmentation-dependent MS detection can pose inherent difficulties for intact proteins. In this research, we investigated variables that affect protein and fragment ion signals to enable protein quantitation using QQQ-MS. Collision induced dissociation gas pressure and collision energy were found to be the most crucial variables for optimization. Multiple reaction monitoring (MRM) transitions for seven standard proteins, including lysozyme, ubiquitin, cytochrome c from both equine and bovine, lactalbumin, myoglobin, and prostate-specific antigen (PSA) were determined. Assuming the eventual goal of applying such methodology is to analyze protein in biological fluids, a liquid chromatography method was developed. Calibration curves of six standard proteins (excluding PSA) were obtained to show the feasibility of intact protein quantification using QQQ-MS. Linearity (2-3 orders), limits of detection (0.5-50 μg/mL), accuracy (<5% error), and precision (1%-12% CV) were determined for each model protein. Sensitivities for different proteins varied considerably. Biological fluids, including human urine, equine plasma, and bovine plasma were used to demonstrate the specificity of the approach. The purpose of this model study was to identify, study, and demonstrate the advantages and challenges for QQQ-MS-based intact protein quantitation, a largely underutilized approach to date.

  7. Direct observation of vibrational coherence in bacterial reaction centers using femtosecond absorption spectroscopy.

    PubMed

    Vos, M H; Lambry, J C; Robles, S J; Youvan, D C; Breton, J; Martin, J L

    1991-10-15

    It is shown that vibrational coherence modulates the femtosecond kinetics of stimulated emission and absorption of reaction centers of purple bacteria. In the DLL mutant of Rhodobacter capsulatus, which lacks the bacteriopheophytin electron acceptor, oscillations with periods of approximately 500 fs and possibly also of approximately 2 ps were observed, which are associated with formation of the excited state. The kinetics, which reflect primary processes in Rhodobacter sphaeroides R-26, were modulated by oscillations with a period of approximately 700 fs at 796 nm and approximately 2 ps at 930 nm. In the latter case, at 930 nm, where the stimulated emission of the excited state, P*, is probed, oscillations could only be resolved when a sufficiently narrow (10 nm) and concomitantly long pump pulse was used. This may indicate that the potential energy surface of the excited state is anharmonic or that low-frequency oscillations are masked when higher frequency modes are also coherently excited, or both. The possibility is discussed that the primary charge separation may be a coherent and adiabatic process coupled to low-frequency vibrational modes. PMID:1924348

  8. Direct Coombs antiglobulin reactions in Gambian children with Plasmodium falciparum malaria. I. Incidence and class specificity.

    PubMed Central

    Facer, C A; Bray, R S; Brown, J

    1979-01-01

    Gambian children with past or present Plasmodium falciparum malaria were investigated for the incidence of Coombs positivity using monospecific antisera. Approximately 50% were positive and the most frequent form of erythrocyte sensitization was with C3d. Other specificities, EIgG, EIgGC3d and EIgGC4bC3d were less common. Erthyrocytes were never found sensitized with IgA or IgM. There was no correlation between a positive test and age, tribal status or level of parasitaemia at presentation, although a positive test was often found in association with anaemia. Sensitized erythrocytes were present in the circulation for a period of up to 6 weeks following initial observation. The mechanism of erythrocyte sensitization is not known, but the results suggest a Type III complex-mediated hypersensitivity involving parasite antigen-antibody complexes. It is likely that these reactions contribute to the pathogenesis of the anaemia in falciparum malaria. Images FIG. 3 PMID:371880

  9. Hot-spring sinter deposits in the Alvord-Pueblo Valley, Harney County, Oregon

    SciTech Connect

    Cummings, M.L.; St. John, A.M. . Dept. of Geology)

    1993-04-01

    Silica sinter deposits occur at Borax Lake, Alvord Hot Springs, and Mickey Springs in the Alvord-Pueblo Valley. Although the sinter deposits occur in areas of active hot springs, sinter is not being deposited. Hot springs are localized along faults that have been active since the Pleistocene. The sinter deposits formed after the drying of glacial Lake Alvord, but before and during extensive wind deflation of glacial-lacustrine sediments. At Mickey Springs, sinter rests directly on unaltered, unconsolidated lithic-rich sand. At Borax Lake, sinter overlies unaltered diatomite, but some armoring, presumably by silica, of the 30 m vent has developed. Field relations suggest rapid dumping of silica from solution without alteration of the country rock at the vent. Discharge of thermal fluids and cold groundwater along the same structure may have produced colloidal silica carried in a solution stripped of dissolved silica. Sinter is composed of opal-a, traces of detrital feldspar and quartz, and evaporation-related boracite. The concentration of Sb is similar among the three sinter deposits (20 to 70 ppm); however, As, Cs, and Br are highest at Borax Lake (5 to 560 ppm; 26 to 118 ppm; 5 to 1,040 ppm) while Hg is highest at Mickey Springs (1.0 to 5.2 ppm).

  10. Preliminary characterization of plasma-sintered beryllides as advanced neutron multipliers

    NASA Astrophysics Data System (ADS)

    Nakamichi, M.; Kim, J. H.; Munakata, K.; Shibayama, T.; Miyamoto, M.

    2013-11-01

    Advanced neutron multipliers with low swelling and high stability at high temperatures are desired for pebble bed blankets of demonstration fusion power (DEMO) reactors. Beryllium intermetallic compounds (beryllides) are the most promising advanced neutron multipliers. The plasma sintering method has been selected as a new synthesis method for beryllides because this method is very simple and easy to control. Plasma sintering is a non-conventional consolidation process. The plasma sintering results in starting-powder particle surface activation that enhances sinterability and reduces high temperature exposure. The sintering properties of beryllides were evaluated. Results show that intermetallic beryllide compounds such as Be12Ti, Be17Ti2 and Be2Ti can be directly synthesized by the plasma sintering method from mixed elemental powders of Be and Ti at a temperature below the melting point. The preliminary characterization of plasma-sintered Be-Ti beryllide was carried out including examination of oxidation with water vapor, microstructure analysis, irradiation effects, and deuterium retention compared with beryllium (Be) metal. The preliminary characterization revealed that the plasma-sintered Be-Ti beryllide sample performs well as a neutron multiplier. This beryllide sample has better oxidation resistance, higher radiation resistance and lower deuterium retention than Be metal.

  11. Flash (Ultra-Rapid) Spark-Plasma Sintering of Silicon Carbide.

    PubMed

    Olevsky, Eugene A; Rolfing, Stephen M; Maximenko, Andrey L

    2016-01-01

    A new ultra-rapid process of flash spark plasma sintering is developed. The idea of flash spark plasma sintering (or flash hot pressing - FHP) stems from the conducted theoretical analysis of the role of thermal runaway phenomena for material processing by flash sintering. The major purpose of the present study is to theoretically analyze the thermal runaway nature of flash sintering and to experimentally address the challenge of uncontrollable thermal conditions by the stabilization of the flash sintering process through the application of the external pressure. The effectiveness of the developed FHP technique is demonstrated by the few seconds-long consolidation of SiC powder in an industrial spark plasma sintering device. Specially designed sacrificial dies heat the pre-compacted SiC powder specimens to a critical temperature before applying any voltage to the powder volume and allowing the electrode-punches of the SPS device setup to contact the specimens and pass electric current through them under elevated temperatures. The experimental results demonstrate that flash sintering phenomena can be realized using conventional SPS devices. The usage of hybrid heating SPS devices is pointed out as the mainstream direction for the future studies and utilization of the new flash hot pressing (ultra-rapid spark plasma sintering) technique. PMID:27624641

  12. Ortho-Functionalized Aryltetrazines by Direct Palladium-Catalyzed C-H Halogenation: Application to Fast Electrophilic Fluorination Reactions.

    PubMed

    Testa, Christelle; Gigot, Élodie; Genc, Semra; Decréau, Richard; Roger, Julien; Hierso, Jean-Cyrille

    2016-04-25

    A general catalyzed direct C-H functionalization of s-tetrazines is reported. Under mild reaction conditions, N-directed ortho-C-H activation of tetrazines allows the introduction of various functional groups, thus forming carbon-heteroatom bonds: C-X (X=I, Br, Cl) and C-O. Based on this methodology, we developed electrophilic mono- and poly-ortho-fluorination of tetrazines. Microwave irradiation was optimized to afford fluorinated s-aryltetrazines, with satisfactory selectivity, within only ten minutes. This work provides an efficient and practical entry for further accessing highly substituted tetrazine derivatives (iodo, bromo, chloro, fluoro, and acetate precursors). It gives access to ortho-functionalized aryltetrazines which are difficult to obtain by classical Pinner-like syntheses. PMID:27010438

  13. Detection of short tandem repeat polymorphisms from human nails using direct polymerase chain reaction method.

    PubMed

    Tie, Jian; Uchigasaki, Seisaku

    2014-11-01

    Human nail is an important forensic material for parental testing and individual identification in large-scale disasters. Detection of STR polymorphism from hard tissues generally requires DNA purification, which is technically complicated and time consuming. In the present study, we attempted to detect STR polymorphisms from untreated human nail samples by direct PCR amplification method using the primer mixture supplied with the GenePrint® SilverSTR® III System or the AmpFℓSTR® Identifiler® PCR Amplification Kit, and Tks Gflex DNA polymerase known to be effective for amplification from crude samples. A nail fragment measuring approximately 1.5 mm in breadth and 0.5 mm in length was placed directly into a PCR tube, and various PCR conditions were tested. The PCR products were analyzed by denaturing acrylamide gel electrophoresis or CE. Multiple STR polymorphisms were detected successfully. This method that detects STR polymorphisms not only from fresh human fingernails, but also from old nail fragments stored at room temperature for up to 10 years is expected to become a novel DNA analytical method in forensic medicine and genetic studies. PMID:24934775

  14. Direct synthesis of thermochromic VO{sub 2} through hydrothermal reaction

    SciTech Connect

    Alie, David; Gedvilas, Lynn; Wang, Zhiwei; Tenent, Robert; Engtrakul, Chaiwat; Yan, Yanfa; Shaheen, Sean E.; Dillon, Anne C.; Ban, Chunmei

    2014-04-01

    Thermochromic VO{sub 2} was directly synthesized using hydrothermal techniques. The effects of formation conditions on the structure and morphology of the final product were studied through X-ray diffraction (XRD), and scanning electron microscopy (SEM). Unique hollow sphere morphology was observed for the synthesized VO{sub 2} powders. Ex-situ XRD studies after heat treatment confirmed the thermal stability of the VO{sub 2} structure. Thermochromic properties, as a consequence of the reversible structural transformation between monoclinic VO{sub 2} and tetragonal phases, were observed by Fourier transform infrared spectroscopy (FTIR). - Graphical abstract: Thermochromic VO{sub 2} crystals with hollow spherical and asterisk shape were directly synthesized using hydrothermal techniques. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) studies confirmed the thermal stability and the reversible thermochromic properties of the VO{sub 2} structure. - Highlights: • One-step synthesis of thermochromic VO{sub 2} monoclinic phase, and VO{sub 2} (A and B phases) using hydrothermal technique. VO{sub 2} (A), VO{sub 2} (B). • Identification of the relationship between synthesis conditions and the morphology/structure of the final products. • Formation of VO{sub 2} monoclinic phase with an interesting hollow sphere shape. • Demonstration of superior thermal stability of the VO{sub 2} monoclinic phase. • Characterizing the thermochromic properties of VO{sub 2} monoclinic phase.

  15. Metal-porphyrin: a potential catalyst for direct decomposition of N(2)O by theoretical reaction mechanism investigation.

    PubMed

    Maitarad, Phornphimon; Namuangruk, Supawadee; Zhang, Dengsong; Shi, Liyi; Li, Hongrui; Huang, Lei; Boekfa, Bundet; Ehara, Masahiro

    2014-06-17

    The adsorption of nitrous oxide (N2O) on metal-porphyrins (metal: Ti, Cr, Fe, Co, Ni, Cu, or Zn) has been theoretically investigated using density functional theory with the M06L functional to explore their use as potential catalysts for the direct decomposition of N2O. Among these metal-porphyrins, Ti-porphyrin is the most active for N2O adsorption in the triplet ground state with the strongest adsorption energy (-13.32 kcal/mol). Ti-porphyrin was then assessed for the direct decomposition of N2O. For the overall reaction mechanism of three N2O molecules on Ti-porphyrin, two plausible catalytic cycles are proposed. Cycle 1 involves the consecutive decomposition of the first two N2O molecules, while cycle 2 is the decomposition of the third N2O molecule. For cycle 1, the activation energies of the first and second N2O decompositions are computed to be 3.77 and 49.99 kcal/mol, respectively. The activation energy for the third N2O decomposition in cycle 2 is 47.79 kcal/mol, which is slightly lower than that of the second activation energy of the first cycle. O2 molecules are released in cycles 1 and 2 as the products of the reaction, which requires endothermic energies of 102.96 and 3.63 kcal/mol, respectively. Therefore, the O2 desorption is mainly released in catalytic cycle 2 of a TiO3-porphyrin intermediate catalyst. In conclusion, regarding the O2 desorption step for the direct decomposition of N2O, the findings would be very useful to guide the search for potential N2O decomposition catalysts in new directions. PMID:24856812

  16. Enhancing the methanol tolerance of platinum nanoparticles for the cathode reaction of direct methanol fuel cells through a geometric design

    PubMed Central

    Feng, Yan; Ye, Feng; Liu, Hui; Yang, Jun

    2015-01-01

    Mastery over the structure of nanoparticles might be an effective way to enhance their performance for a given application. Herein we demonstrate the design of cage-bell nanostructures to enhance the methanol tolerance of platinum (Pt) nanoparticles while remaining their catalytic activity for oxygen reduction reaction. This strategy starts with the synthesis of core-shell-shell nanoparticles with Pt and silver (Ag) residing respectively in the core and inner shell regions, which are then agitated with saturated sodium chloride (NaCl) solution to eliminate the Ag component from the inner shell region, leading to the formation of bimetallic nanoparticles with a cage-bell structure, defined as a movable Pt core enclosed by a metal shell with nano-channels, which exhibit superior methanol-tolerant property in catalyzing oxygen reduction reaction due to the different diffusion behaviour of methanol and oxygen in the porous metal shell of cage-bell structured nanoparticles. In particular, the use of remarkably inexpensive chemical agent (NaCl) to promote the formation of cage-bell structured particles containing a wide spectrum of metal shells highlights its engineering merit to produce highly selective electrocatalysts on a large scale for the cathode reaction of direct methanol fuel cells. PMID:26578100

  17. Atomic scale dynamics of a solid state chemical reaction directly determined by annular dark-field electron microscopy

    PubMed Central

    Pennycook, Timothy J.; Jones, Lewys; Pettersson, Henrik; Coelho, João; Canavan, Megan; Mendoza-Sanchez, Beatriz; Nicolosi, Valeria; Nellist, Peter D.

    2014-01-01

    Dynamic processes, such as solid-state chemical reactions and phase changes, are ubiquitous in materials science, and developing a capability to observe the mechanisms of such processes on the atomic scale can offer new insights across a wide range of materials systems. Aberration correction in scanning transmission electron microscopy (STEM) has enabled atomic resolution imaging at significantly reduced beam energies and electron doses. It has also made possible the quantitative determination of the composition and occupancy of atomic columns using the atomic number (Z)-contrast annular dark-field (ADF) imaging available in STEM. Here we combine these benefits to record the motions and quantitative changes in the occupancy of individual atomic columns during a solid-state chemical reaction in manganese oxides. These oxides are of great interest for energy-storage applications such as for electrode materials in pseudocapacitors. We employ rapid scanning in STEM to both drive and directly observe the atomic scale dynamics behind the transformation of Mn3O4 into MnO. The results demonstrate we now have the experimental capability to understand the complex atomic mechanisms involved in phase changes and solid state chemical reactions. PMID:25532123

  18. Enhancing the methanol tolerance of platinum nanoparticles for the cathode reaction of direct methanol fuel cells through a geometric design

    NASA Astrophysics Data System (ADS)

    Feng, Yan; Ye, Feng; Liu, Hui; Yang, Jun

    2015-11-01

    Mastery over the structure of nanoparticles might be an effective way to enhance their performance for a given application. Herein we demonstrate the design of cage-bell nanostructures to enhance the methanol tolerance of platinum (Pt) nanoparticles while remaining their catalytic activity for oxygen reduction reaction. This strategy starts with the synthesis of core-shell-shell nanoparticles with Pt and silver (Ag) residing respectively in the core and inner shell regions, which are then agitated with saturated sodium chloride (NaCl) solution to eliminate the Ag component from the inner shell region, leading to the formation of bimetallic nanoparticles with a cage-bell structure, defined as a movable Pt core enclosed by a metal shell with nano-channels, which exhibit superior methanol-tolerant property in catalyzing oxygen reduction reaction due to the different diffusion behaviour of methanol and oxygen in the porous metal shell of cage-bell structured nanoparticles. In particular, the use of remarkably inexpensive chemical agent (NaCl) to promote the formation of cage-bell structured particles containing a wide spectrum of metal shells highlights its engineering merit to produce highly selective electrocatalysts on a large scale for the cathode reaction of direct methanol fuel cells.

  19. Enhancing the methanol tolerance of platinum nanoparticles for the cathode reaction of direct methanol fuel cells through a geometric design.

    PubMed

    Feng, Yan; Ye, Feng; Liu, Hui; Yang, Jun

    2015-01-01

    Mastery over the structure of nanoparticles might be an effective way to enhance their performance for a given application. Herein we demonstrate the design of cage-bell nanostructures to enhance the methanol tolerance of platinum (Pt) nanoparticles while remaining their catalytic activity for oxygen reduction reaction. This strategy starts with the synthesis of core-shell-shell nanoparticles with Pt and silver (Ag) residing respectively in the core and inner shell regions, which are then agitated with saturated sodium chloride (NaCl) solution to eliminate the Ag component from the inner shell region, leading to the formation of bimetallic nanoparticles with a cage-bell structure, defined as a movable Pt core enclosed by a metal shell with nano-channels, which exhibit superior methanol-tolerant property in catalyzing oxygen reduction reaction due to the different diffusion behaviour of methanol and oxygen in the porous metal shell of cage-bell structured nanoparticles. In particular, the use of remarkably inexpensive chemical agent (NaCl) to promote the formation of cage-bell structured particles containing a wide spectrum of metal shells highlights its engineering merit to produce highly selective electrocatalysts on a large scale for the cathode reaction of direct methanol fuel cells. PMID:26578100

  20. Reaction behavior of Ni-Re alloys during direct current polarization in sulfuric acid solutions

    NASA Astrophysics Data System (ADS)

    Bryukvin, V. A.; Elemesov, T. B.; Levchuk, O. M.; Bol'shikh, A. O.

    2016-01-01

    The macrokinetic regularities of the reactivity of synthesized Ni-Re (20 and 60 wt %) alloys in a sulfuric acid solution (100 g/L, 25-40°C) during direct current polarization are studied using physicochemical methods. The phase composition of the synthesized alloys is determined by the formation of solid solutions as a function of the initial Ni/Re weight ratio. These are two types of nickel solid solutions (Ni16Re0.2 and Ni14Re0.9) and one rhenium solution (Ni1.1Re). These solid solutions are anodically oxidized in the sequence of their structural rearrangement Ni16Re0.2 → Ni14Re0.9 → Ni1.1Re with a combined transition of the metals into an electrolyte solution. These solid solutions provide the reduction of Ni3+ to Ni2+ due to the depolarization ability of rhenium, being their component.

  1. Knockout confirmation for Hurries: rapid genotype identification of Trypanosoma cruzi transfectants by polymerase chain reaction directly from liquid culture.

    PubMed

    Alcantara, Monica Visnieski; Fragoso, Stenio Perdigão; Picchi, Gisele Fernanda Assine

    2014-07-01

    Gene knockout is a widely used approach to evaluate loss-of-function phenotypes and it can be facilitated by the incorporation of a DNA cassette having a drug-selectable marker. Confirmation of the correct knockout cassette insertion is an important step in gene removal validation and has generally been performed by polymerase chain reaction (PCR) assays following a time-consuming DNA extraction step. Here, we show a rapid procedure for the identification of Trypanosoma cruzi transfectants by PCR directly from liquid culture - without prior DNA extraction. This simple approach enabled us to generate PCR amplifications from different cultures varying from 106-108 cells/mL. We also show that it is possible to combine different primer pairs in a multiplex detection reaction and even to achieve knockout confirmation with an extremely simple interpretation of a real-time PCR result. Using the "culture PCR" approach, we show for the first time that we can assess different DNA sequence combinations by PCR directly from liquid culture, saving time in several tasks for T. cruzi genotype interrogation. PMID:24936912

  2. Virus-based Photo-Responsive Nanowires Formed By Linking Site-Directed Mutagenesis and Chemical Reaction

    PubMed Central

    Murugesan, Murali; Abbineni, Gopal; Nimmo, Susan L.; Cao, Binrui; Mao, Chuanbin

    2013-01-01

    Owing to the genetic flexibility and error-free bulk production, bio-nanostructures such as filamentous phage showed great potential in materials synthesis, however, their photo-responsive behaviour is neither explored nor unveiled. Here we show M13 phage genetically engineered with tyrosine residues precisely fused to the major coat protein is converted into a photo-responsive organic nanowire by a site-specific chemical reaction with an aromatic amine to form an azo dye structure on the surface. The resulting azo-M13-phage nanowire exhibits reversible photo-responsive properties due to the photo-switchable cis-trans isomerisation of the azo unit formed on the phage. This result shows that site-specific display of a peptide on bio-nanostructures through site-directed genetic mutagenesis can be translated into site-directed chemical reaction for developing advanced materials. The photo-responsive properties of the azo-M13-phage nanowires may open the door for the development of light controllable smart devices for use in non-linear optics, holography data storage, molecular antenna, and actuators. PMID:23673356

  3. Virus-based photo-responsive nanowires formed by linking site-directed mutagenesis and chemical reaction.

    PubMed

    Murugesan, Murali; Abbineni, Gopal; Nimmo, Susan L; Cao, Binrui; Mao, Chuanbin

    2013-01-01

    Owing to the genetic flexibility and error-free bulk production, bio-nanostructures such as filamentous phage showed great potential in materials synthesis, however, their photo-responsive behaviour is neither explored nor unveiled. Here we show M13 phage genetically engineered with tyrosine residues precisely fused to the major coat protein is converted into a photo-responsive organic nanowire by a site-specific chemical reaction with an aromatic amine to form an azo dye structure on the surface. The resulting azo-M13-phage nanowire exhibits reversible photo-responsive properties due to the photo-switchable cis-trans isomerisation of the azo unit formed on the phage. This result shows that site-specific display of a peptide on bio-nanostructures through site-directed genetic mutagenesis can be translated into site-directed chemical reaction for developing advanced materials. The photo-responsive properties of the azo-M13-phage nanowires may open the door for the development of light controllable smart devices for use in non-linear optics, holography data storage, molecular antenna, and actuators. PMID:23673356

  4. Virus-based Photo-Responsive Nanowires Formed By Linking Site-Directed Mutagenesis and Chemical Reaction

    NASA Astrophysics Data System (ADS)

    Murugesan, Murali; Abbineni, Gopal; Nimmo, Susan L.; Cao, Binrui; Mao, Chuanbin

    2013-05-01

    Owing to the genetic flexibility and error-free bulk production, bio-nanostructures such as filamentous phage showed great potential in materials synthesis, however, their photo-responsive behaviour is neither explored nor unveiled. Here we show M13 phage genetically engineered with tyrosine residues precisely fused to the major coat protein is converted into a photo-responsive organic nanowire by a site-specific chemical reaction with an aromatic amine to form an azo dye structure on the surface. The resulting azo-M13-phage nanowire exhibits reversible photo-responsive properties due to the photo-switchable cis-trans isomerisation of the azo unit formed on the phage. This result shows that site-specific display of a peptide on bio-nanostructures through site-directed genetic mutagenesis can be translated into site-directed chemical reaction for developing advanced materials. The photo-responsive properties of the azo-M13-phage nanowires may open the door for the development of light controllable smart devices for use in non-linear optics, holography data storage, molecular antenna, and actuators.

  5. Electron flow to oxygen in higher plants and algae: rates and control of direct photoreduction (Mehler reaction) and rubisco oxygenase.

    PubMed

    Badger, M R; von Caemmerer, S; Ruuska, S; Nakano, H

    2000-10-29

    Linear electron transport in chloroplasts produces a number of reduced components associated with photosystem I (PS I) that may subsequently participate in reactions that reduce O2. The two primary reactions that have been extensively studied are: first, the direct reduction of O2 to superoxide by reduced donors associated with PS I (the Mehler reaction), and second, the rubisco oxygenase (ribulose 1,5-bisphosphate carboxylase oxygenase EC 4.1.1.39) reaction and associated peroxisomal and mitochondrial reactions of the photorespiratory pathway. This paper reviews a number of recent and past studies with higher plants, algae and cyanobacteria that have attempted to quantify O2 fluxes under various conditions and their contributions to a number of roles, including photon energy dissipation. In C3 and Crassulacean acid metabolism (CAM) plants, a Mehler O2 uptake reaction is unlikely to support a significant flow of electron transport (probably less than 10%). In addition, if it were present it would appear to scale with photosynthetic carbon oxidation cycle (PCO) and photosynthetic carbon reduction cycle (PCR) activity This is supported by studies with antisense tobacco plants with reduced rubisco at low and high temperatures and high light, as well as studies with potatoes, grapes and madrone during water stress. The lack of significant Mehler in these plants directly argues for a strong control of Mehler reaction in the absence of ATP consumption by the PCR and PCO cycles. The difference between C3 and C4 plants is primarily that the level of light-dependent O2 uptake is generally much lower in C4 plants and is relatively insensitive to the external CO2 concentration. Such a major difference is readily attributed to the operation of the C4 CO2 concentrating mechanism. Algae show a range of light-dependent O2 uptake rates, similar to C4 plants. As in C4 plants, the O2 uptake appears to be largely insensitive to CO2, even in species that lack a CO2 concentrating

  6. Sintered composite medium and filter

    DOEpatents

    Bergman, Werner

    1987-01-01

    A particulate filter medium is formed of a sintered composite of 0.5 micron diameter quartz fibers and 2 micron diameter stainless steel fibers. A preferred composition is about 40 vol. % quartz and about 60 vol. % stainless steel fibers. The media is sintered at about 1100.degree. C. to bond the stainless steel fibers into a cage network which holds the quartz fibers. High filter efficiency and low flow resistance are provided by the smaller quartz fibers. High strength is provided by the stainless steel fibers. The resulting media has a high efficiency and low pressure drop similar to the standard HEPA media, with tensile strength at least four times greater, and a maximum operating temperature of about 550.degree. C. The invention also includes methods to form the composite media and a HEPA filter utilizing the composite media. The filter media can be used to filter particles in both liquids and gases.

  7. Microwave enhanced sintering of ceramics

    SciTech Connect

    Wroe, F.C.R.; Rowley, A.T.

    1995-12-31

    It is now well known that microwave dielectric heating can be used to increase the Wintering rates and to reduce the sintering times of ceramic materials. However, the nature of the mechanism causing this enhanced sintering is still far from understood, with many workers attributing the effect to a reduction in the activation energy even though there is no real physical basis for this assumption. Although the mechanism is not understood, many results have indicated that the effect is non thermal in nature, i.e. the enhancement would not be reproduced if conventional heat could be applied in exactly the same way (volumetrically) as microwave heat. By careful control of the relative proportions of microwave and conventional heating, it has been possible to separate the thermal (heating) effects from the non-thermal effects. This paper discusses the results obtained, and show that they are consistent with recent theories of enhanced diffusion.

  8. Non-Sintered Nickel Electrode

    DOEpatents

    Bernard, Patrick; Dennig, Corinne; Cocciantelli, Jean-Michel; Alcorta, Jose; Coco, Isabelle

    2002-01-01

    A non-sintered nickel electrode contains a conductive support and a paste comprising an electrochemically active material containing nickel hydroxide and a binder which is a mixture of an elastomer and a crystalline polymer. The proportion of the elastomer is in the range 25% to 60% by weight of the binder and the proportion of the crystalline polymer is in the range 40% to 75% by weight of the binder.

  9. Characterization of Mycobacterium tuberculosis complex direct repeat sequence for use in cycling probe reaction.

    PubMed Central

    Beggs, M L; Cave, M D; Marlowe, C; Cloney, L; Duck, P; Eisenach, K D

    1996-01-01

    Cycling probe technology (CPT) is a unique and simple method for the detection of specific target sequences. CPT utilizes a chimeric DNA-RNA-DNA probe providing an RNase H-sensitive scissile linkage when bound to a complementary target sequence. For this study a diagnostic assay based on CPT was developed for the detection of the 36-bp direct repeat (DR) region in Mycobacterium tuberculosis. To determine the feasibility of using the DR for detecting M. tuberculosis by CPT, a wide variety of mycobacteria were tested by Southern blot hybridization with three DR probes to verify their specificity. The entire DR region of Mycobacterium bovis 401 was sequenced, and the data were used to design a PCR assay that would allow us to estimate the number of DRs present in a variety of strains. A CPT assay which uses a probe complementary to the DR region was developed and evaluated with synthetic targets and genomic DNA from mycobacteria. In summary, the 36-bp DR provides an attractive target for detecting M. tuberculosis because the sequence is present in high copy numbers in the genome, is specific for the M. tuberculosis complex, and is found in strains that lack IS6110. PMID:8940435

  10. New Directions: Ozone-initiated reaction products indoors may be more harmful than ozone itself

    NASA Astrophysics Data System (ADS)

    Weschler, Charles J.

    2004-10-01

    Epidemiological studies have found associations between ozone concentrations measured at outdoor monitoring stations and certain adverse health outcomes. As a recent example, Gent et al. (2003, Journal of the American Medical Association 290, 1859-1867) have observed an association between ozone levels and respiratory symptoms as well as the use of maintenance medication by 271 asthmatic children living in Connecticut and the Springfield area of Massachusetts. In another example, Gilliland et al. (2001, Epidemiology 12, 43-54) detected an association between short-term increases in ozone levels and increased absences among 4th grade students from 12 southern California communities during the period from January to June 1996. Although children may spend a significant amount of time outdoors, especially during periods when ozone levels are elevated, they spend a much larger fraction of their time indoors. I hypothesize that exposure to the products of ozone-initiated indoor chemistry is more directly responsible for the health effects observed in the cited epidemiological studies than is exposure to outdoor ozone itself.

  11. Low Temperature Sintering of PZT

    NASA Astrophysics Data System (ADS)

    Medesi, A.; Greiner, T.; Benkler, M.; Megnin, C.; Hanemann, T.

    2014-11-01

    This paper describes the fabrication and characterization of lead zirconate titanate (PZT) films fired in a liquid-phase sintering process at 900 °C in air. In detail the manufacturing of piezoelectric multilayers with internal pure silver (Tm = 961 °C) electrodes are reported. The feasibility of ten sintering aids in two different volume fractions was investigated for a commercial hard PZT powder (PIC 181, PI Ceramics) with respect to density, microstructure, mechanical behaviour, and piezoelectric properties. Li2O, Li2CO3, PbO, MnO2, V2O5, CuO, Bi2O3, the eutectic mixtures Cu2O·PbO and PbO·WO3 and the ternary system Li2CO3·Bi2O3·CuO (LBCu) have been tested as liquid phase sintering aids. The combination of PZT with LBCu showed the best results. With 5 vol.% LBCu an average relative density of 97% and a characteristic breaking strength of 77 MPa was achieved. Composition of PZT with 2 vol.% LBCu exhibits the highest averaged piezoelectrical charge constant (d33) of 181 pC/N.

  12. Effect of sintering temperature on the electrolysis of TiO2

    NASA Astrophysics Data System (ADS)

    Li, Ze-quan; Ru, Li-yue; Bai, Cheng-guang; Zhang, Na; Wang, Hai-hua

    2012-07-01

    The effects of sintering temperature on the microstructure and the conductivity of TiO2 cathodes were studied by examining the phase composition, microstructure, and element contents of the sintered cathodes and the cathodic products using X-ray diffraction and scanning electronic microscopy-energy dispersive spectrometry. The oxygen vacancy, conductivity, average pore diameter, and specific surface area of the sintered cathodes were detected by X-ray photoelectron spectroscopy, four-point probe, and ASPA 2010. The results showed that TiO2 phase transformations occurred, and oxygen vacancies formed with the increase of sintering temperature. The cathodic conductivity improved, but the average pore diameter and the effective response area of the TiO2 cathode were reduced when the sintering temperature increased. These phenomena could weaken the contact between reaction ions and electrons and also had the same effect on the cathodes and the molten salt. Moreover, they were disadvantageous to ion migration, so a lower sintering temperature was favorable for the microstructure of electrolysis. Consequently, the cathodic conductivity may be improved, but the microstructure became compact with the increase of sintering temperature. The cathodic products at different temperatures indicated that the cathodic conductivity was more important for electrolysis.

  13. Ultra-fast and energy-efficient sintering of ceramics by electric current concentration

    NASA Astrophysics Data System (ADS)

    Zapata-Solvas, E.; Gómez-García, D.; Domínguez-Rodríguez, A.; Todd, R. I.

    2015-02-01

    Electric current activated/assisted sintering (ECAS) techniques, such as electrical discharge sintering (EDS) or resistive sintering (RS), have been intensively investigated for longer than 50 years. In this work, a novel system including an electrically insulated graphite die for Spark Plasma Sintering (SPS) is described, which allows the sintering of any refractory ceramic material in less than 1 minute starting from room temperature with heating rates higher than 2000°C/min and an energy consumption up to 100 times lower than with SPS. The system alternates or combines direct resistive sintering (DRS) and indirect resistive sintering (IRS). Electrical insulation of the die has been achieved through the insertion of a film made of alumina fibers between the graphite die and the graphite punches, which are protected from the alumina fiber film by a graphite foil. This system localized the electric current directly through the sample (conductive materials) as in DRS and EDS, or through the thin graphite foil (non-conductive materials) as in IRS, and is the first system capable of being used under EDS or RS conditions independently combining current concentration/localization phenomena.

  14. Ultra-fast and energy-efficient sintering of ceramics by electric current concentration

    PubMed Central

    Zapata-Solvas, E.; Gómez-García, D.; Domínguez-Rodríguez, A.; Todd, R. I.

    2015-01-01

    Electric current activated/assisted sintering (ECAS) techniques, such as electrical discharge sintering (EDS) or resistive sintering (RS), have been intensively investigated for longer than 50 years. In this work, a novel system including an electrically insulated graphite die for Spark Plasma Sintering (SPS) is described, which allows the sintering of any refractory ceramic material in less than 1 minute starting from room temperature with heating rates higher than 2000°C/min and an energy consumption up to 100 times lower than with SPS. The system alternates or combines direct resistive sintering (DRS) and indirect resistive sintering (IRS). Electrical insulation of the die has been achieved through the insertion of a film made of alumina fibers between the graphite die and the graphite punches, which are protected from the alumina fiber film by a graphite foil. This system localized the electric current directly through the sample (conductive materials) as in DRS and EDS, or through the thin graphite foil (non-conductive materials) as in IRS, and is the first system capable of being used under EDS or RS conditions independently combining current concentration/localization phenomena. PMID:25686537

  15. Nuclear Ordered Phases of Solid 3He in Silver Sinters

    NASA Astrophysics Data System (ADS)

    Schuberth, Erwin A.; Kath, Matthias; Bago, Simone

    2006-09-01

    To determine the exact spin structure of the nuclear magnetic ordered phases of solid 3He, the U2D2 low field and the high field phases above 0.4 T, a European Research and Training Network for neutron scattering from the ordered solid was established which consisted of a collaboration with the Hahn Meitner Institute, Berlin, and other European and US groups. For this experiment it is crucial to grow a single crystal within the sinter needed for cooling the solid to temperatures of the order of 500 μK and to keep it cold long enough to measure a magnetic neutron diffraction. The sinter is also necessary to absorb the major part (> 90%) of the heat generated by the neutron capture and decay reaction of the 3He nucleus. In this work we studied the growth of crystals in Ag sinters of different pore sizes and with different growth speeds to find an optimal way to obtain single crystalline samples, or at least samples with only a few grains. We used SQUID magnetometry and NMR to measure the magnetization in the ordered phases. They were indicated by the known drop of the intensity, both in the NMR signal and in the dc magnetization, for the U2D2 phase, and by an increase of about 30% for the high field phase. The best results for cooling were obtained with sinters made from 700 Å "Japanese powder" with a packing fraction of 50% which were annealed at 130 °C after sintering and then had a calculated particle size of about 4200 Å. In the dc magnetization we found a paramagnetic surface contribution from a few monolayers of 3He down to 500 μK in addition to the bulk magnetization.

  16. Post-Stroke Walking Behaviors Consistent with Altered Ground Reaction Force Direction Control Advise New Approaches to Research and Therapy.

    PubMed

    Boehm, Wendy L; Gruben, Kreg G

    2016-02-01

    Recovery of walking after stroke requires an understanding of how motor control deficits lead to gait impairment. Traditional therapy focuses on removing specific observable gait behaviors that deviate from unimpaired walking; however, those behaviors may be effective compensations for underlying problematic motor control deficits rather than direct effects of the stroke. Neurological deficits caused by stroke are not well understood, and thus, efficient interventions for gait rehabilitation likely remain unrealized. Our laboratory has previously characterized a post-stroke control deficit that yields a specific difference in direction of the ground reaction force (F, limb endpoint force) exerted with the hemiplegic limb of study participants pushing on both stationary and moving pedals while seated. That task was not dependent on F to retain upright posture, and thus, the task did not constrain F direction. Rather, the F direction was the product of neural preference. It is not known if this specific muscle coordination deficit causes the observed walking deviations, but if present during walking, the deficit would prevent upright posture unless counteracted by compensatory behaviors. Compensations are presented that mechanically counteract the F misdirection to allow upright posture. Those compensations are similar to behaviors observed in stroke patients. Based on that alignment between predictions of this theory and clinical observations, we theorize that post-stroke gait results from the attempt to compensate for the underlying F misdirection deficit. Limb endpoint force direction has been shown to be trainable in the paretic upper limb, making it a feasible goal in the lower limb. If this F misdirection theory is valid, these ideas have tremendous promise for advancing the field of post-stroke gait rehabilitation. PMID:26639659

  17. Simulation and Experimental Study on the Efficiency of Traveling Wave Direct Energy Conversion for Application to Aneutronic Fusion Reactions

    NASA Astrophysics Data System (ADS)

    Tarditi, Alfonso; Chap, Andrew; Miley, George; Scott, John

    2013-10-01

    A study based on both Particle-in-cell (PIC) simulation and experiments is being developed to study the physics of the Traveling Wave Direct Energy Converter (TWDEC,) with the perspective of application to aneutronic fusion reaction products and space propulsion. The PIC model is investigating in detail the key TWDEC physics process by simulating the time-dependent transfer of energy from the ion beam to an electric load connected to ring-type electrodes in cylindrical symmetry. An experimental effort is in progress on a TWDEC test article at NASA, Johnson Space Center with the purpose of studying the conditions for improving the efficiency of the direct energy conversion process. Using a scaled-down ion energy source, the experiment is primarily focused on the effect of the (bunched) beam density on the efficiency and on the optimization of the electrode design. The simulation model is guiding the development of the experimental configuration and will provide details of the beam dynamics for direct comparison with experimental diagnostics. Work supported by NASA, Johnson Space Center.

  18. The influence of sintering on the dispersion of carbon nanotubes in ceramic matrix composites

    NASA Astrophysics Data System (ADS)

    Tapasztó, Orsolya; Lemmel, Hartmut; Markó, Márton; Balázsi, Katalin; Balázsi, Csaba; Tapasztó, Levente

    2014-10-01

    Optimizing the dispersion of carbon nanostructures in ceramic matrix composites is a fundamental technological challenge. So far most efforts have been focused on improving the dispersion of nanostructures during the powder phase processing, due to the limited information and control on their possible redistribution during the sintering. Here, we address this issue by comparing multi-walled carbon nanotubes reinforced Si3N4 composites prepared from the same starting powder dispersion but sintered using two different techniques. We employ ultra-small angle neutron scattering measurements to gain reliable information on the dispersion of nanostructures allowing a direct comparison of their redistribution during the sintering.

  19. Dye-sensitized solar cells based on nanocrystalline titania electrodes made at various sintering temperatures.

    PubMed

    Stathatos, Elias; Lianos, Panagiotis

    2007-02-01

    Dye-sensitized solar cells were made by using nanocrystalline titania deposited on Fluorine-doped SnO2 (FTO) electrodes. Nanocrystalline titania deposition was made by the sol-gel method using reverse micelles of bis(2-ethylhexyl) sulfosuccinate sodium salt (AOT) in cyclohexane as reaction medium. This surfactant could be easily removed from the deposited nanocomposite organic-inorganic film by simple rinsing with distilled water, without affecting titania adherence on FTO electrode. These nanocrystalline titania electrodes were used to make solar cells either without sintering or after sintering at various temperatures. Sintering extensively affected short circuit current but had small effect on device open-circuit voltage. Thus satisfactory photovoltaic response could be obtained even with devices made of non-sintered (room-temperature) titania. PMID:17450794

  20. An investigation of the effect of pore scale flow on average geochemical reaction rates using direct numerical simulation

    SciTech Connect

    Rafa, S. Molins; Trebotich, D.; Steefel, C. I.; Shen, C.

    2012-02-01

    The scale-dependence of geochemical reaction rates hinders their use in continuum scale models intended for the interpretation and prediction of chemical fate and transport in subsurface environments such as those considered for geologic sequestration of CO{sub 2}. Processes that take place at the pore scale, especially those involving mass transport limitations to reactive surfaces, may contribute to the discrepancy commonly observed between laboratory-determined and continuum-scale or field rates. Here, the dependence of mineral dissolution rates on the pore structure of the porous media is investigated by means of pore scale modeling of flow and multicomponent reactive transport. The pore scale model is comprised of high performance simulation tools and algorithms for incompressible flow and conservative transport combined with a general-purpose multicomponent geochemical reaction code. The model performs direct numerical simulation of reactive transport based on an operator-splitting approach to coupling transport and reactions. The approach is validated with a Poiseuille flow single-pore experiment and verified with an equivalent 1D continuum-scale model of a capillary tube packed with calcite spheres. Using the case of calcite dissolution as an example, the high resolution model is used to demonstrate that non-uniformity in the flow field at the pore scale has the effect of decreasing the overall reactivity of the system, even when systems with identical reactive surface area are considered. The effect becomes more pronounced as the heterogeneity of the reactive grain packing increases, particularly where the flow slows sufficiently such that the solution approaches equilibrium locally and the average rate becomes transport-limited.

  1. Towards reducing DBP formation potential of drinking water by favouring direct ozone over hydroxyl radical reactions during ozonation.

    PubMed

    De Vera, Glen Andrew; Stalter, Daniel; Gernjak, Wolfgang; Weinberg, Howard S; Keller, Jurg; Farré, Maria José

    2015-12-15

    When ozonation is employed in advanced water treatment plants to produce drinking water, dissolved organic matter reacts with ozone (O3) and/or hydroxyl radicals (OH) affecting disinfection byproduct (DBP) formation with subsequently used chlorine-based disinfectants. This study presents the effects of varying exposures of O3 and •OH on DBP concentrations and their associated toxicity generated after subsequent chlorination. DBP formation potential tests and in vitro bioassays were conducted after batch ozonation experiments of coagulated surface water with and without addition of tertiary butanol (t-BuOH, 10 mM) and hydrogen peroxide (H2O2, 1 mg/mg O3), and at different pH (6-8) and transferred ozone doses (0-1 mg/mg TOC). Although ozonation led to a 24-37% decrease in formation of total trihalomethanes, haloacetic acids, haloacetonitriles, and trihaloacetamides, an increase in formation of total trihalonitromethanes, chloral hydrate, and haloketones was observed. This effect however was less pronounced for samples ozonated at conditions favoring molecular ozone (e.g., pH 6 and in the presence of t-BuOH) over •OH reactions (e.g., pH 8 and in the presence of H2O2). Compared to ozonation only, addition of H2O2 consistently enhanced formation of all DBP groups (20-61%) except trihalonitromethanes. This proves that •OH-transformed organic matter is more susceptible to halogen incorporation. Analogously, adsorbable organic halogen (AOX) concentrations increased under conditions that favor •OH reactions. The ratio of unknown to known AOX, however, was greater at conditions that promote direct O3 reactions. Although significant correlation was found between AOX and genotoxicity with the p53 bioassay, toxicity tests using 4 in vitro bioassays showed relatively low absolute differences between various ozonation conditions. PMID:26378731

  2. Direct measurement of {sup 4}He({sup 12}C, {sup 16}O){gamma} reaction near stellar energy

    SciTech Connect

    Fujita, K.; Sagara, K.; Teranishi, T.; Goto, T.; Iwabuchi, R.; Matsuda, S.; Oba, N.; Taniguchi, M.; Yamaguchi, H.

    2010-08-12

    A cross section measurement with a direct {sup 16}O detection method for the reaction energy from E{sub cm} = 2.4 down to 0.7 MeV is planned at Kyushu University Tandem Laboratory (KUTL). To perform the experiment successfully and to get the quantitative information of the cross section within the 10% error, we have newly developed several instruments in 2009, such as a blow-in type windowless gas target and movable slit system placed in the recoil mass separator. By using the windowless blow-in gas target, a pressure of 24 Torr was achieved. The effective thickness along the beam axis was measured by p+{sup 4}He scattering. Thanks to the movable slits installed in a recoil mass separator and the trajectory analysis, we found effective reduction of background conditions from the {sup 12}C beam.

  3. Continuum quasiparticle random-phase approximation for astrophysical direct neutron capture reactions on neutron-rich nuclei

    NASA Astrophysics Data System (ADS)

    Matsuo, Masayuki

    2015-03-01

    I formulate a many-body theory to calculate the cross section of direct radiative neutron capture reaction by means of the Hartree-Fock-Bogoliubov mean-field model and the continuum quasiparticle random-phase approximation (QRPA). A focus is put on very-neutron-rich nuclei and low-energy neutron kinetic energy in the range from 1 keV to several MeV, which is relevant to the rapid neutron capture process of nucleosynthesis. I begin with the photoabsorption cross section and the E 1 strength function. Next, in order to apply the reciprocity theorem, I decompose the cross section into partial cross sections corresponding to different channels of one- and two-neutron emission decays of photo-excited states. A numerical example is shown for the photo-absorption of 142Sn and the neutron capture of 141Sn .

  4. The chemical mechanism of the limonene ozonolysis reaction in the SOA formation: A quantum chemistry and direct dynamic study

    NASA Astrophysics Data System (ADS)

    Sun, Tingli; Wang, Yudong; Zhang, Chenxi; Sun, Xiaomin; Wang, Wenxing

    2011-03-01

    The ozonolysis of limonene is one of the most important processes for secondary organic aerosol formation and a detailed understanding of the atmospheric chemistry of d-limonene is highly urgent. In this paper, the reaction of d-limonene with O 3 has been studied using high level molecular orbital theory. A detailed description of the possible ozonolysis mechanism in the presence of H 2O or NO is provided. The main products obtained are keto-limonene, limononic acid and 7OH-lim, which are low vapor pressure compounds. On the basis of the quantum chemical information, the direct dynamic calculation is performed and the rate constants are calculated over a temperature range of 200˜800 K using the transition state theory and canonical varitional transition state theory with small-curvature tunneling effect. The four-parameter formula of rate constants with the temperature is fitted and the lifetimes of the reaction species in the troposphere are estimated according to the rate constants, which can provide helpful information to the model simulation study.

  5. Detection of Mycobacterium tuberculosis in clinical specimens by polymerase chain reaction and Gen-Probe Amplified Mycobacterium Tuberculosis Direct Test.

    PubMed Central

    Abe, C; Hirano, K; Wada, M; Kazumi, Y; Takahashi, M; Fukasawa, Y; Yoshimura, T; Miyagi, C; Goto, S

    1993-01-01

    The polymerase chain reaction (PCR) using oligonucleotides based on the repetitive sequence (IS986) of Mycobacterium tuberculosis as a primer and the Gen-Probe Amplified Mycobacterium Tuberculosis Direct Test (MTD), which combines an M. tuberculosis rRNA amplification method with the hybridization protection assay format, were evaluated for detection of M. tuberculosis in clinical samples. The detection limits of these two assay systems based on nucleic acid amplification for cultured M. tuberculosis were less than 10 cells per reaction. A total of 135 sputum specimens were examined by the two assay systems. The PCR and the MTD systems for detection of M. tuberculosis gave overall positivity rates of 84.2% (32 of 38) and 91.9% (34 of 37), respectively, as compared with 71.9% (23 of 32) by smear and 96.9% (31 of 32) by culture in the liquid medium MB-Check. Procedures for sample preparation used in the two methods were different. Although the sensitivities of the PCR and MTD appeared to be similar to that of culture with the MB-Check system, the two methods based on nucleic acid amplification should be very useful for rapid detection of M. tuberculosis infections without the long time required for culture of M. tuberculosis. Images PMID:8308121

  6. On the sintering of silicon carbide

    NASA Technical Reports Server (NTRS)

    Gugel, E.

    1986-01-01

    This document deals with the sintering of silicon carbide using pressureless sintering. This technique makes it possible to sinter a primarily covalent material to usable densities up to over 98% thD without having to use a high amount of sinter additives as is the case with other non-oxide ceramic materials. The process takes place rapidly, and it is also possible to produce relatively thick-walled structural parts without major problems. This sheds more light on the true characteristics of silicon carbide in one structural part, since there is no second or nearly no second phase. Heat pressing has improved stability.

  7. Sintering aids for yttria partially stabilized zirconia

    SciTech Connect

    Montross, C.S.

    1987-01-01

    High-purity yttria partially stabilized zirconia does not sinter readily. Commercial production of the powder and finished parts has allowed contamination by silica and aluminosilicates to enhance the sintering via a liquid-phase mechanism at 1400/sup 0/C. This research analyzed several simple metal oxides as possible nonglassy sintering aids to enhance the sintering of high-purity yttria partially stabilized zirconia, Y-PSZ, without the deleterious effects of the glass contamination. Of the metal oxides analyzed: iron oxide, bismuth oxide, chromia, niobia, tantala, tungsten oxide and mullite, only one metal oxide, iron oxide resulted in enhanced sintering. The iron oxide doped Y-PSZ exhibited better sinterability than high purity Y-PSZ and equivalent/better sinterability than glass doped Y-PSZ. The iron oxide doped Y-PSZ had a higher tetragonal content at lower sintering temperatures and at lower densities than glass doped Y-PSZ. This resulted in higher fracture toughness at lower temperatures than the glass doped Y-PSZ. Additionally, the iron oxide doped Y-PSZ showed a better resistance to low temperature high humidity degradation than glass doped Y-PSZ under identical conditions. Problems of bloating common to high surface area ultra fine powders and exhibited by the glass doped Y-PSZ were not alleviated by the use of the nonglassy metal oxide sintering aids.

  8. Iodine(III)-Catalyzed Cascade Reactions Enabling a Direct Access to β-Lactams and α-Hydroxy-β-amino Acids.

    PubMed

    Patzelt, Christoph; Pöthig, Alexander; Gulder, Tanja

    2016-07-15

    In the presented method, a one-pot metal-free access to β-lactams is provided. The developed strategy employs a hypervalent iodine(III)-triggered bromination/rearrangement/cyclization cascade reaction that allows the straightforward synthesis of a broad range of structurally different lactams from cheap and easily available imides. This triple cascade reaction is furthermore extendable by an in situ ring-opening reaction, giving direct access to isoserine derivatives from simple imines in a four-step, one-pot reaction. PMID:27380445

  9. Permeability, drying, and sintering of pressure filtered ceramic nanopowders

    NASA Astrophysics Data System (ADS)

    Sweeney, Sean M.

    2002-01-01

    point of drying (when fracture is most likely during drying). Agreement between maximum safe drying stresses and measured sample strengths is found to be good (to within better than a factor of 2) for boehmite samples, but not very good (off by a factor of ˜7) for nanocrystalline 3Y-TZP samples. Sub-critical crack growth is indicated as the source of this deviation in nanocrystalline 3Y-TZP samples. Literature studies of the sintering of chloride-derived 3Y-TZP nanopowders have documented numerous sintering problems including inability to reach full density, desintering, cracking, and the formation of a dense shell with less dense interior. To explain the poor sintering behavior of samples of one nanocrystalline 3Y-TZP powder, the origin of such a dense shell microstructure is determined. Three possible reasons for a dense shell microstructure are examined and rejected: exothermic reactions with the sintering atmosphere, pre-existing density gradients in the green compact, and thermal gradients occurring during sintering. A combination of gas flow/diffusion, thermodynamic, and sintering calculations are used to show that the evolution of a structure-coarsening gas (hydrogen chloride) during sintering causes the formation of a dense shell microstructure, and explains the poor densification behavior of this system. Two solutions to the problem are compared: (1) a thermal treatment composed of an extended hold at 1000°C to allow HCl gas removal before the onset of closed porosity (at about 90-93% of theoretical density), and (2) a chemical treatment performed by washing pre-sintered (500°C/30 min) samples at room temperature using a concentrated ammonium hydroxide solution to remove chlorides. The thermal treatment is found to be superior for removing residual chlorine and allowing full density to be achieved during sintering.

  10. Influencing factor of sinter body strength and its effects on iron ore sintering indexes

    NASA Astrophysics Data System (ADS)

    Zhang, Guo-liang; Wu, Sheng-li; Su, Bo; Que, Zhi-gang; Hou, Chao-gang; Jiang, Yao

    2015-06-01

    Sinter body strength, which reflects the strength of sinter, plays an important role in the improvement of sinter. In this study, the sinter body strengths of iron ores were measured using a microsintering method. The relationship between the chemical composition and sinter body strength was discussed. Moreover, sinter-pot tests were performed. The effects of sinter body strength on the sintering indexes were then elucidated, and the bottom limit of sinter body strength of blending ores was confirmed. In the results, the compressive strengths (CSs) of iron ores are observed to decrease with the increasing of the contents of loss on ignition (LOI), SiO2, and Al2O3; however, LOI of less than 3wt% does not substantially influence the CSs of fine ores. In the case of similar mineral composition, the porosity, in particular, the ratio between the number of large pores and the total number of pores, strongly influences the sinter body strength. With an increase of the blending-ore CSs used in sinter-pot tests, the yield, productivity, and tumbler strength increase, and the solid fuel consumption decreases. The CSs of the blending ores only slightly affect the sintering time. The CS bottom limit of the blending ores is 310 N. When the CSs of the blending ores increase by 10%, the yield, productivity, and tumbler index increase by 1.9%, 2.8%, and 2.0%, respectively, and the solid fuel consumption decreases by 1.9%.

  11. SELF SINTERING OF RADIOACTIVE WASTES

    DOEpatents

    McVay, T.N.; Johnson, J.R.; Struxness, E.G.; Morgan, K.Z.

    1959-12-29

    A method is described for disposal of radioactive liquid waste materials. The wastes are mixed with clays and fluxes to form a ceramic slip and disposed in a thermally insulated container in a layer. The temperature of the layer rises due to conversion of the energy of radioactivity to heat boillng off the liquid to fomn a dry mass. The dry mass is then covered with thermal insulation, and the mass is self-sintered into a leach-resistant ceramic cake by further conversion of the energy of radioactivity to heat.

  12. Field assisted sintering of dense Al-substituted cubic phase Li7La3Zr2O12 solid electrolytes

    NASA Astrophysics Data System (ADS)

    Zhang, Yanhua; Chen, Fei; Tu, Rong; Shen, Qiang; Zhang, Lianmeng

    2014-12-01

    High performance lithium ion conducting Li7La3Zr2O12 solid electrolytes are prepared for the first time by field assisted sintering technology (FAST). The effect of sintering temperature on the phase compositions, microstructure and Li ionic conductivity is systematically investigated. The results show that pure cubic phase LLZO can be obtained at a range of temperatures from 1100 to 1180 °C for no more than 10 min. For the sample sintered at 1150 °C, a maximum relative density of 99.8% with a total ionic conductivity as high as 5.7 × 10-4 S cm-1 are obtained at room temperature. This value is the highest among the present research. Compared with the traditional preparation methods, the current FAST is very promising to obtain high performance LLZO for its advantages of very short sintering time, a single preparation step of reaction-densification processing, and relatively lower sintering temperature.

  13. Capillary-based fully integrated and automated system for nanoliter polymerase chain reaction analysis directly from cheek cells.

    PubMed

    He, Y; Zhang, Y H; Yeung, E S

    2001-07-27

    A miniaturized, integrated and automated system based on capillary fluidics has been developed for nanoliter DNA analysis directly from cheek cells. All steps for DNA analysis, including injecting aqueous reagents and DNA samples, mixing the solutions together, thermal cell lysis, polymerase chain reaction (PCR), transfer and injection of PCR product, separation, sizing and detection of those products are performed in a capillary-based integrated system. A small amount of cheek cells collected by a plastic toothpick is directly dissolved in the PCR cocktail in a plastic vial or mixed on-line with a small volume of PCR cocktail (125 nl) in the capillary. After thermal cell lysis and PCR in a microthermal cycler, the DNA fragments are mixed with DNA size standards and transferred to a micro-cross for injection and separation by capillary gel electrophoresis. Programmable syringe pumps, switching valves, multiposition and freeze-thaw valves are used for microfluidic control in the entire system. This work establishes the feasibility of performing all the steps of DNA analysis from real samples in a capillary-based nanoliter integrated system. PMID:11521874

  14. Detection of glucose based on direct electron transfer reaction of glucose oxidase immobilized on highly ordered polyaniline nanotubes.

    PubMed

    Wang, Ziyi; Liu, Shuna; Wu, Ping; Cai, Chenxin

    2009-02-15

    An amperometric glucose biosensor based on the direct electron transfer of glucose oxidase (GOx) was developed by electrochemically entrapping GOx onto the inner wall of highly ordered polyaniline nanotubes (nanoPANi), which was synthesized using anodic aluminum oxide (AAO) membrane as a template. The cyclic voltammetric results indicated that GOx immobilized on the nanoPANi underwent direct electron transfer reaction, and the cyclic voltammogram displayed a pair of well-defined and nearly symmetric redox peaks with a formal potential of -405 +/- 5 mV and an apparent electron transfer rate constant of 5.8 +/- 1.6 s(-1). The biosensor had good electrocatalytic activity toward oxidation of glucose and exhibited a rapid response (approximately 3 s), a low detection limit (0.3 +/- 0.1 microM), a useful linear range (0.01-5.5 mM), high sensitivity (97.18 +/- 4.62 microA mM(-1) cm(-2)), higher biological affinity (the apparent Michaelis-Mentan constant was estimated to be 2.37 +/- 0.5 mM) as well as good stability and repeatability. In addition, the common interfering species, such as ascorbic acid, uric acid, and 4-acetamidophenol, did not cause any interference due to the use of a low detection potential (-0.3 V vs SCE). The biosensor can also be used for quantification of the concentration of glucose in real clinical samples. PMID:19170516

  15. Numerical study of the process parameters in spark plasma sintering (sps)

    NASA Astrophysics Data System (ADS)

    Chowdhury, Redwan Jahid

    Spark plasma sintering (SPS) is one of the most widely used sintering techniques that utilizes pulsed direct current together with uniaxial pressure to consolidate a wide variety of materials. The unique mechanisms of SPS enable it to sinter powder compacts at a lower temperature and in a shorter time than the conventional hot pressing, hot isostatic pressing and vacuum sintering process. One of the limitations of SPS is the presence of temperature gradients inside the sample, which could result in non-uniform physical and microstructural properties. Detailed study of the temperature and current distributions inside the sintered sample is necessary to minimize the temperature gradients and achieve desired properties. In the present study, a coupled thermal-electric model was developed using finite element codes in ABAQUS software to investigate the temperature and current distributions inside the conductive and non-conductive samples. An integrated experimental-numerical methodology was implemented to determine the system contact resistances accurately. The developed sintering model was validated by a series of experiments, which showed good agreements with simulation results. The temperature distribution inside the sample depends on some process parameters such as sample and tool geometry, punch and die position, applied current and thermal insulation around the die. The role of these parameters on sample temperature distribution was systematically analyzed. The findings of this research could prove very useful for the reliable production of large size sintered samples with controlled and tailored properties.

  16. Direct sGC Activation Bypasses NO Scavenging Reactions of Intravascular Free Oxy-Hemoglobin and Limits Vasoconstriction

    PubMed Central

    Tabima, D. Marcela; Specht, Patricia A.C.; Tejero, Jesús; Champion, Hunter C.; Kim-Shapiro, Daniel B.; Baust, Jeff; Mik, Egbert G.; Hildesheim, Mariana; Stasch, Johannes-Peter; Becker, Eva-Maria; Truebel, Hubert

    2013-01-01

    Abstract Aims: Hemoglobin-based oxygen carriers (HBOC) provide a potential alternative to red blood cell (RBC) transfusion. Their clinical application has been limited by adverse effects, in large part thought to be mediated by the intravascular scavenging of the vasodilator nitric oxide (NO) by cell-free plasma oxy-hemoglobin. Free hemoglobin may also cause endothelial dysfunction and platelet activation in hemolytic diseases and after transfusion of aged stored RBCs. The new soluble guanylate cyclase (sGC) stimulator Bay 41-8543 and sGC activator Bay 60-2770 directly modulate sGC, independent of NO bioavailability, providing a potential therapeutic mechanism to bypass hemoglobin-mediated NO inactivation. Results: Infusions of human hemoglobin solutions and the HBOC Oxyglobin into rats produced a severe hypertensive response, even at low plasma heme concentrations approaching 10 μM. These reactions were only observed for ferrous oxy-hemoglobin and not analogs that do not rapidly scavenge NO. Infusions of L-NG-Nitroarginine methyl ester (L-NAME), a competitive NO synthase inhibitor, after hemoglobin infusion did not produce additive vasoconstriction, suggesting that vasoconstriction is related to scavenging of vascular NO. Open-chest hemodynamic studies confirmed that hypertension occurred secondary to direct effects on increasing vascular resistance, with limited negative cardiac inotropic effects. Intravascular hemoglobin reduced the vasodilatory potency of sodium nitroprusside (SNP) and sildenafil, but had no effect on vasodilatation by direct NO-independent activation of sGC by BAY 41-8543 and BAY 60-2770. Innovation and Conclusion: These data suggest that both sGC stimulators and sGC activators could be used to restore cyclic guanosine monophosphate-dependent vasodilation in conditions where cell-free plasma hemoglobin is sufficient to inhibit endogenous NO signaling. Antioxid. Redox Signal. 19, 2232–2243. PMID:23697678

  17. Hematobiochemical alterations and direct blood polymerase chain reaction detection of Theileria annulata in naturally infected crossbred cows

    PubMed Central

    Ganguly, Anita; Bhanot, Vandna; Bisla, R. S.; Ganguly, Indrajit; Singh, Harpreet; Chaudhri, S. S.

    2015-01-01

    Aim: The aim was to determine hemato-biochemical changes and rapid diagnosis of Theileria annulata in naturally infected crossbred cows. Materials and Methods: Blood samples from lactating crossbred cows (n=40) between 3 and 7 years of age and showing clinical signs of tropical theileriosis were collected, with or without anticoagulant, and analyzed for tropical theileriosis by direct smear, direct blood polymerase chain reaction (PCR) detection of merozoite-piroplasm surface antigen (Tams1) gene specific amplicon, estimation of hematological and biochemical parameters. Healthy crossbred cows (n=6), examined free from hemoprotozoan infections were included as control. Results: The infected crossbred cows revealed significantly (p<0.001) lower values of total erythrocytic counts (4.46±0.2 × 106/µL), hemoglobin (Hb 6.025±0.39 g%), packed cell volume (17.05±1.1%), mean corpuscular volume (37.94±1.70 fL) and mean corpuscular Hb (13.5±0.48 pg; p<0.002) compared with healthy control. The serum samples of infected cows revealed profound (p<0.05) hyponatremia (Na 133.21±2.36 mEq/l) and hypocalcemia (Ca 8.39±0.34 mg%). Infected crossbred cows showed a significant increase (p<0.05) of mean serum activity of alanine aminotransferase (61.45±13.36 U/L), aspartate aminotransferase (146.1±20.97 U/L), blood urea nitrogen (28.26±3.90 mg%), creatinine (1.55±0.13 mg%), direct bilirubin (0.33±0.04 mg%; p<0.001) and lactate dehydrogenase (3001.32±167.0 U/L; p<001). Blood direct PCR revealed a 721-bp fragment amplified from the target gene encoding 30-kDa major merozoite surface antigen of T. annulata using specific primer pairs. This assay was positive for all the infected animals. Conclusion: The assessments of hemato-biochemical parameters in T. annulata infected crossbred cows may be useful in understanding disease pathogenesis, prognosis and corrective measures for supportive therapy. Moreover, blood direct PCR can reliably be used for rapid detection of T. annulata

  18. DESULFURIZATION OF STEEL MILL SINTER PLANT GASES

    EPA Science Inventory

    The report gives results of an evaluation of the technical and economic feasibility of using limestone scrubbing technology to control sinter plant emissions. Data from Soviet and Japanese sinter plants employing limestone scrubbing technology were used to develop a realistic des...

  19. Superplastic Titanium Tube Applies Pressure For Sintering

    NASA Technical Reports Server (NTRS)

    Mueller, Allen H.; Pleimann, Thomas R.

    1992-01-01

    In newly developed technique, titanium vessel filled with gas to exert pressure necessary for sintering. Used in brazing, sintering, and hot forming. Simplifies fabrication of parts having complicated shapes and has potential for variety of applications, including fabrication of heat pipes for high-performance vehicles.

  20. Method of sintering materials with microwave radiation

    DOEpatents

    Kimrey, Jr., Harold D.; Holcombe, Jr., Cressie E.; Dykes, Norman L.

    1994-01-01

    A method of sintering ceramic materials following: A compacted article comprising inorganic particles coated with carbon is provided, the carbon providing improved microwave coupling. The compacted article is then heated by microwave radiation to a temperature and for a period of time sufficient to sinter the compacted article.

  1. Rate control sintering of the uranium dioxide

    NASA Astrophysics Data System (ADS)

    Kuzmin, R. S.; Baranov, V. G.; Burlakova, M. A.; Mikhalchik, V. V.; Tenishev, A. V.

    2016-04-01

    The application of rate controlled sintering (RCS) technique for fabricating oxide fuel pellets in industrial conditions is investigated. Green pellets of UO2 (with no additives) which underwent industrial-type compacting were sintered in reducing Ar - 8% H2 medium using dynamic and isothermal RCS modes with exposure at 1600 °C during 8 hours. Decreasing shrinkage rate resulted in growth of sintered density for the dynamic RCS mode. Opposite to the results of earlier works [1,2], decreasing heating rate did not result in reducing sintering rate. Isothermal mode allowed sintering rate to be maintained between 0.1- 0.15%/min. Temperature-time modes obtained using RCS are close to the operation mode of through-type furnace used for mass production.

  2. Simulation of Sintering of Layered Structures

    SciTech Connect

    OLEVSKY,EUGENE; TIKARE,VEENA; GARINO,TERRY J.; BRAGINSKY,MICHAEL V.

    2000-11-22

    An integrated approach, combining the continuum theory of sintering and Potts model based mesostructure evolution analysis, is used to solve the problem of bi-layered structure sintering. Two types of bi-layered structures are considered: layers of the same material with different initial porosity, and layers of two different materials. The effective sintering stress for the bi-layer powder sintering is derived, both at the meso- and the macroscopic levels. Macroscopic shape distortions and spatial distributions of porosity are determined as functions of the dimensionless specific time of sintering. The effect of the thickness of the layers on shrinkage, warpage, and pore-grain structure is studied. Ceramic ZnO powders are employed as a model experimental system to assess the model predictions.

  3. Manufacture of high-density ceramic sinters

    NASA Technical Reports Server (NTRS)

    Hibata, Y.

    1986-01-01

    High density ceramic sinters are manufactured by coating premolded or presintered porous ceramics with a sealing material of high SiO2 porous glass or nitride glass and then sintering by hot isostatic pressing. The ceramics have excellent abrasion and corrosion resistances. Thus LC-10 (Si3N2 powder) and Y2O3-Al2O3 type sintering were mixed and molded to give a premolded porous ceramic (porosity 37%, relative bulk density 63%). The ceramic was dipped in a slurry containing high SiO2 porous glass and an alcohol solution of cellulose acetate and dried. The coated ceramic was treated in a nitrogen atmosphere and then sintered by hot isostatic pressing to give a dense ceramic sinter.

  4. Pressureless sintered Sialons with low amounts of sintering aid

    NASA Technical Reports Server (NTRS)

    Arias, A.

    1978-01-01

    Two Beta prime - Sialons of composition Si2.6Al0.393y0.007O0.4N3.6 and Si2.6Al0.384Y0.014O0.4N3.6 were pressureless sintered from mixtures of Y2O3 and separately milled Beta -Si3N4, AlN, and SiO2. These Sialons had densities of over 98% of theoretical, four-point bend strengths of 460 and 155 MPa at room temperature and 1400 C, respectively, and 1400 C oxidation rates lower than those reported for hot pressed Si3N4 and for a stronger Sialon with 2.5 weight percentage Y2O3.

  5. No direct by maternal effects interaction detected for pre-weaning growth in Romane sheep using a reaction norm model

    PubMed Central

    2013-01-01

    Background The pre-weaning growth of lambs, an important component of meat production, depends on maternal and direct effects. These effects cannot be observed directly and models used to study pre-weaning growth assume that they are additive. However, it is reasonable to suggest that the influence of direct effects on growth may differ depending on the value of maternal effects i.e. an interaction may exist between the two components. Methods To test this hypothesis, an experiment was carried out in Romane sheep in order to obtain observations of maternal phenotypic effects (milk yield and milk quality) and pre-weaning growth of the lambs. The experiment consisted of mating ewes that had markedly different maternal genetic effects with rams that contributed very different genetic effects in four replicates of a 3 × 2 factorial plan. Milk yield was measured using the lamb suckling weight differential technique and milk composition (fat and protein contents) was determined by infrared spectroscopy at 15, 21 and 35 days after lambing. Lambs were weighed at birth and then at 15, 21 and 35 days. An interaction between genotype (of the lamb) and environment (milk yield and quality) for average daily gain was tested using a restricted likelihood ratio test, comparing a linear reaction norm model (interaction model) to a classical additive model (no interaction model). Results A total of 1284 weights of 442 lambs born from 166 different ewes were analysed. On average, the ewes produced 2.3 ± 0.8 L milk per day. The average protein and fat contents were 50 ± 4 g/L and 60 ± 18 g/L, respectively. The mean 0–35 day average daily gain was 207 ± 46 g/d. Results of the restricted likelihood ratio tests did not highlight any significant interactions between the genotype of the lambs and milk production of the ewe. Conclusions Our results support the hypothesis of additivity of maternal and direct effects on growth that is currently applied in genetic

  6. Pressureless sintered beta prime-Si3N4 solid solution: Fabrication, microstructure, and strength

    NASA Technical Reports Server (NTRS)

    Dutta, S.

    1977-01-01

    Si3N4, AlN, and Al2O3 were used as basic constituents in a study of the pressureless sintering of beta prime-Si3N4 solid solution as a function of temperature. Y2O3-SiO2 additions were used to promote liquid-phase sintering. The sintered specimens were characterized with respect to density, microstructure, strength, oxidation, and thermal shock resistance. Density greater than 98 percent of theoretical was achieved by pressureless sintering at 1750 C. The microstructure consisted essentially of fine-grained beta prime-Si3N4 solid solution as the major phase. Modulus of rupture strengths up to 483 MPa were achieved at moderate temperature (1000 C), but decreased to 228 MPa at 1380 C. This substantial strength loss was attributed to a glassy grain boundary phase formed during cooling from the sintering temperature. The best oxidation resistance was exhibited by a composition containing 3 mol % Y2O3-SiO2 additives. Water quench thermal shock resistance was equivalent to that of reaction sintered silicon nitride but lower than hot-pressed silicon nitride.

  7. Pressureless sintered beta-prime-Si3N4 solid solution - Fabrication, microstructure, and strength

    NASA Technical Reports Server (NTRS)

    Dutta, S.

    1977-01-01

    Pressureless sintering of beta-prime-Si3N4 solid solution was studied as a function of temperature using Si3N4, A1N, and Al2O3 as basic constituents. Y2O3-SiO2 additions were used to promote liquid-phase sintering. The sintered specimens were characterized with respect to density, microstructure, strength, oxidation, and thermal shock resistance. Density greater than 98 percent of theoretical was achieved by pressureless sintering at 1750 C. The microstructure consisted essentially of fine-grained beta-prime-Si3N4 solid solution as the major phase. Modulus of rupture strengths up to 483 M Pa were achieved at moderate temperature (1000 C), but decreased to 228 M Pa at 1380 C. This substantial strength loss was attributed to a 'glassy' grain boundary phase formed during cooling from the sintering temperature. The best oxidation resistance was exhibited by a composition containing 3 mol % Y2O3-SiO2 additives. Water quench thermal shock resistance was equivalent to that of reaction sintered silicon nitride but lower than hot-pressed silicon nitride.

  8. Scale-up of the nitridation and sintering of silicon preforms using microwave heating

    SciTech Connect

    Kiggans, J.O. Jr.; Tiegs, T.N.; Davisson, C.C.; Morrow, M.S.; Garvey, G.J.

    1996-05-01

    Scale-up studies were performed in which microwave heating was used to fabricate reaction-bonded silicon nitride and sintered reaction-bonded silicon nitride (SRBSN). Tests were performed in both a 2.45 GHz, 500 liter and a 2.45 GHz, 4,000 liter multimode cavities. A variety of sizes, shapes, and compositions of silicon preforms were processed in the studies, including bucket tappets and clevis pins for diesel engines. Up to 230 samples were processed in a single microwave furnace run. Data were collected which included weight gains for nitridation experiments, and final densities for nitridation and sintering experiments. For comparison, nitridation and sintering studies were performed using a conventional resistance-heated furnace.

  9. Graphite immobilisation in iron phosphate glass composite materials produced by microwave and conventional sintering routes

    NASA Astrophysics Data System (ADS)

    Mayzan, M. Z. H.; Stennett, M. C.; Hyatt, N. C.; Hand, R. J.

    2014-11-01

    An investigation of microwave and conventional processing of iron phosphate based graphite glass composite materials as potential wasteforms for the immobilisation of irradiated graphite is reported. For the base iron phosphate glass, full reaction of the raw materials and formation of a glass melt occurs with consequent removal of porosity at 8 min microwave processing. When graphite is present, iron phosphate crystalline phases are formed with higher levels of residual porosity than in the sample prepared using conventional sintering under argon. It is found that graphite reacts with the microwave field when in powder form but this reaction is minimised when the graphite is incorporated into a pellet, and that the graphite also impedes sintering of the glass. Mössbauer spectroscopy indicates that reduction of iron also occurs with concomitant graphite oxidation. Conventionally sintered samples had lower porosities than the equivalent microwaved ones.

  10. Effect of glow discharge sintering in the properties of a composite material fabricated by powder metallurgy

    NASA Astrophysics Data System (ADS)

    Cardenas, A.; Pineda, Y.; Sarmiento Santos, A.; Vera, E.

    2016-02-01

    Composite samples of 316 stainless steel and SiC were produced by powder metallurgy. Starting materials were mixed in different proportions and compacted to 700MPa. Sintering stage was performed by abnormal glow discharge plasma with direct current in an inert atmosphere of argon. The process was conducted at a temperature of 1200°C±5°C with a heating rate of 100°C/min. This work shows, the effectiveness of plasma sintering process to generate the first contacts between particles and to reduce vacancies. This fact is confirmed by comparing green and sintered density of the material. The results of porosity show a decrease after plasma sintering. Wear tests showed the wear mechanisms, noting that at higher SiC contents, the wear resistance decreases due to poor matrix-reinforcement interaction and by the porosity presence which causes matrix-reinforcement sliding.

  11. Effect of cobalt addition on the liquid-phase sintering of W-Cu prepared by the fluidized bed reduction method

    SciTech Connect

    Joo, S.K.; Lee, S.W.; Ihn, T.H. . Dept. of Metallurgy)

    1994-08-01

    A new process, fluidized bed reduction (FBR) method, was applied for fabrication of uniform W-Cu sintered material. Liquid-phase sintering was carried out to obtain fully densified W-Cu composite, and the effect of cobalt addition on the sintering behavior was investigated. It was found that fully densified material could not be obtained even after sintering at 1,200 C for 4 hours in the case of 75W-25Cu, while more than 96 pct density could be obtained as soon as the sintering temperature reached 1,200 C when 0.5 wt pct cobalt was added prior to the sintering. It has been found that the wetting angle of the liquid copper is reduced significantly by the addition of cobalt, and the formation reaction of Co[sub 7]W[sub 6] intermetallic compound at the surface of the tungsten powder is mainly responsible for the enhancement of the densification process.

  12. Effect of cobalt addition on the liquid-phase sintering of W-Cu prepared by the fluidized bed reduction method

    NASA Astrophysics Data System (ADS)

    Joo, Seung-Ki; Lee, Seok-Woon; Ihn, Tae-Hyoung

    1994-08-01

    A new process, fluidized bed reduction (FBR) method, was applied for fabrication of uniform W-Cu sintered material. Liquid-phase sintering was carried out to obtain fully densified W-Cu composite, and the effect of cobalt addition on the sintering behavior was investigated. It was found that fully densified material could not be obtained even after sintering at 1200 °C for 4 hours in the case of 75W-25Cu, while more than 96 pct density could be obtained as soon as the sintering temperature reached 1200 °C when 0.5 wt pct cobalt was added prior to the sintering. It has been found that the wetting angle of the liquid copper is reduced significantly by the addition of cobalt, and the formation reaction of Co7W6 intermetallic compound at the surface of the tungsten powder is mainly responsible for the enhancement of the densification process.

  13. Effects of adding alumina to the nickel-zirconia anode materials for solid oxide fuel cells and a two-step sintering method for half-cells

    NASA Astrophysics Data System (ADS)

    Song, Xiao; Dong, Xiaolei; Li, Ming; Wang, Haiqian

    2016-03-01

    The co-sintering process of half-cells has an important effect on the flatness and performance of solid oxide fuel cells. In this study, we report a two-step sintering method to fabricate flat three-layer half-cells. The first sintering step is a freestanding sintering process at a low temperature (1280 °C). The second sintering step is a constrained sintering process at 1400 °C. The shrinkage of the anode support layer (ASL) and the curvature of the half-cell can be adjusted by adding Al2O3 into the ASL in the first sintering step. Effects of Al2O3 addition on the NiO-YSZ anode material are also studied. We find that NiO reacts with Al2O3 to form NiAl2O4 spinel at the early sintering stage. This reaction transiently promotes the grain growth of NiO. Once the reaction terminates and the NiAl2O4 spinel is formed, the grain growth of NiO will be suppressed, even at higher sintering temperatures. Our results indicate that by a proper amount (approximately 0.2 wt%) of Al2O3 addition, smaller NiO grains can be obtained while the side effects of NiAl2O4 are negligible, which is favorable to increase the conductivity and stability of the ASL, and can enhance the performance of SOFC.

  14. The Absence of Plasma in"Spark Plasma Sintering"

    SciTech Connect

    Hulbert, Dustin M.; Anders, Andre; Dudina, Dina V.; Andersson, Joakim; Jiang, Dongtao; Unuvar, Cosan; Anselmi-Tamburini, Umberto; Lavernia, Enrique J.; Mukherjee, Amiya K.

    2008-04-10

    Spark plasma sintering (SPS) is a remarkable method for synthesizing and consolidating a large variety of both novel and traditional materials. The process typically uses moderate uni-axial pressures (<100 MPa) in conjunction with a pulsing on-off DC current during operation. There are a number of mechanisms proposed to account for the enhanced sintering abilities of the SPS process. Of these mechanisms, the one most commonly put forth and the one that draws the most controversy involves the presence of momentary plasma generated between particles. This study employees three separate experimental methods in an attempt to determine the presence or absence of plasma during SPS. The methods employed include: in-situ atomic emission spectroscopy, direct visual observation and ultra-fast in-situ voltage measurements. It was found using these experimental techniques that no plasma is present during the SPS process. This result was confirmed using several different powders across a wide spectrum of SPS conditions.

  15. Real-time monitoring of the progress of polymerization reactions directly on surfaces at open atmosphere by ambient mass spectrometry.

    PubMed

    Nørgaard, Asger W; Vaz, Boniek G; Lauritsen, Frants R; Eberlin, Marcos N

    2010-12-15

    The progress of an on-surface polymerization process involving alkyl and perfluoroalkyl silanes and siloxanes was monitored in real-time via easy ambient sonic spray ionization mass spectrometry (EASI-MS). When sprayed on surfaces, the organosilicon compounds present in commercially available nanofilm products (NFPs) react by condensation to form a polymeric coating. A NFP for coating of floor materials (NFP-1) and a second NFP for coating tiles and ceramics (NFP-2) were applied to glass, filter paper or cotton surfaces and the progress of the polymerization was monitored by slowly scanning the surface. Via EASI(+)-MS monitoring, significant changes in the composition of hydrolysates and condensates of 1H,1H,2H,2H-perfluorooctyl triisopropoxysilane (NFP-1) and hexadecyl triethoxysilane (NFP-2) were observed over time. The abundances of the hydrolyzed species decreased compared with those of the non-hydrolysed species for both NFP-1 and NFP-2 and the heavier oligomers became relatively more abundant over a period of 15-20 min. A similar tendency favouring the heavier oligomers was observed via EASI(-)-MS. This work illustrates the potential of ambient mass spectrometry for the direct monitoring of polymerization reactions on surfaces. PMID:21072800

  16. Oxygen reduction reaction in a droplet on graphite: direct evidence that the edge is more active than the basal plane.

    PubMed

    Shen, Anli; Zou, Yuqin; Wang, Qiang; Dryfe, Robert A W; Huang, Xiaobing; Dou, Shuo; Dai, Liming; Wang, Shuangyin

    2014-09-26

    Carbon-based metal-free electrocatalysts for the oxygen reduction reaction (ORR) in alkaline medium have been extensively investigated with the aim of replacing the commercially available, but precious platinum-based catalysts. For the proper design of carbon-based metal-free electrocatalysts for the ORR, it would be interesting to identify the active sites of the electrocatalyst. The ORR was now studied with an air-saturated electrolyte solution droplet (diameter ca. 15 μm), which was deposited at a specified position either on the edge or on the basal plane of highly oriented pyrolytic graphite. Electrochemical measurements suggest that the edge carbon atoms are more active than the basal-plane ones for the ORR. This provides a direct way to identify the active sites of carbon materials for the ORR. Ball-milled graphite and carbon nanotubes with more exposed edges were also prepared and showed significantly enhanced ORR activity. DFT calculations elucidated the mechanism by which the charged edge carbon atoms result in the higher ORR activity. PMID:25124986

  17. Investigation on natural diets of larval marine animals using peptide nucleic acid-directed polymerase chain reaction clamping.

    PubMed

    Chow, Seinen; Suzuki, Sayaka; Matsunaga, Tadashi; Lavery, Shane; Jeffs, Andrew; Takeyama, Haruko

    2011-04-01

    The stomach contents of the larvae of marine animals are usually very small in quantity and amorphous, especially in invertebrates, making morphological methods of identification very difficult. Nucleotide sequence analysis using polymerase chain reaction (PCR) is a likely approach, but the large quantity of larval (host) DNA present may mask subtle signals from the prey genome. We have adopted peptide nucleic acid (PNA)-directed PCR clamping to selectively inhibit amplification of host DNA for this purpose. The Japanese spiny lobster (Panulirus japonicus) and eel (Anguilla japonica) were used as model host and prey organisms, respectively. A lobster-specific PNA oligomer (20 bases) was designed to anneal to the sequence at the junction of the 18 S rDNA gene and the internal transcribed spacer 1 (ITS1) of the lobster. PCR using eukaryote universal primers for amplifying the ITS1 region used in conjunction with the lobster-specific PNA on a mixed DNA template of lobster and eel demonstrated successful inhibition of lobster ITS1 amplification while allowing efficient amplification of eel ITS1. This method was then applied to wild-caught lobster larvae of P. japonicus and P. longipes bispinosus collected around Ryukyu Archipelago, Japan. ITS1 sequences of a wide variety of animals (Ctenophora, Cnidaria, Crustacea, Teleostei, Mollusca, and Chaetognatha) were detected. PMID:20535520

  18. Direct measurement of {sup 4}He({sup 12}C, {sup 16}O)gamma reaction at KUTL

    SciTech Connect

    Fujita, K.; Sagara, K.; Teranishi, T.; Goto, T.; Iwabuchi, R.; Matsuda, S.; Nakano, K.; Oba, N.; Taniguchi, M.; Yamaguchi, H.

    2010-06-01

    A {sup 12}C+{sup 4}He->{sup 16}O+gamma is regarded as the very important reaction to know the evolution of heavy stars. The cross section is, however, still unknown in spite of more than 40 years experiment in the world because of an existence of a resonance state of {sup 16}O at sub-threshold region. A cross section measurement with the direct detection of the produced {sup 16}O from E{sub cm} = 2.4 downto 0.7 MeV have been planned at Kyushu University Tandem Laboratory(KUTL). Detection of the {sup 16}O is the most possible method at low energy, since a detection efficiency of the {sup 16}O is very high.The new windowless blow-in gas target was developed to achieve the pressure of 24 Torr. Many movable slit were installed in a recoil mass separator, so that the backgrounds generated by the {sup 12}C beam was eliminated effectively. The results of recent experiments at E{sub cm} = 2.4 and 1.5 MeV are reported.

  19. Nondestructive evaluation of sintered ceramics

    NASA Technical Reports Server (NTRS)

    Baaklini, George Y.; Klima, Stanley J.; Sanders, William A.

    1988-01-01

    Radiography and several acoustic and thermoacoustic microscopy techniques are investigated for application to structural ceramics for advanced heat engines. A comparison is made of the results obtained from the use of scanning acoustic microscopy (SAM), scanning laser acoustic microscopy (SLAM), and thermoacoustic microscopy (TAM). These techniques are evaluated on research samples of green and sintered monolithic silicon nitrides and silicon carbides in the form of modulus-of-rupture (MOR) bars containing deliberately introduced flaws. Strengths and limitations of the techniques are described, with the emphasis being on statistics of detectability of flaws that constitute potential fracture origins. Further, it is shown that radiographic evaluation and guidance helped develop uniform high-density Si3N4 MOR bars with improved four-point flexural strength (875, 544, and 462 MPa at room temperature, 1200 C, 1370 C, respectively) and reduced scatter in bend strength.

  20. Direct measurement of the (23)Na(α,p)(26)Mg reaction cross section at energies relevant for the production of galactic (26)Al.

    PubMed

    Almaraz-Calderon, S; Bertone, P F; Alcorta, M; Albers, M; Deibel, C M; Hoffman, C R; Jiang, C L; Marley, S T; Rehm, K E; Ugalde, C

    2014-04-18

    The 1809-keV γ ray from the decay of (26)Al(g) is an important target for γ-ray astronomy. In the convective C/Ne burning shell of massive presupernova stars, the (23)Na(α,p)(26)Mg reaction directly influences the production of (26)Al. We have performed a direct measurement of the (23)Na(α,p)(26)Mg reaction cross section at the appropriate astrophysically important energies. The stellar rate calculated in the present work is larger than the recommended rate by nearly a factor of 40 and could strongly affect the production of (26)Al in massive stars. PMID:24785033

  1. Thermoelectric transport properties of polycrystalline titanium diselenide co-intercalated with nickel and titanium using spark plasma sintering

    SciTech Connect

    Holgate, T.C.; Zhu, S.; Zhou, M.; Bangarigadu-Sanasy, S.; Kleinke, H.; He, J.; Tritt, T.M.

    2013-01-15

    Polycrystalline samples of nickel intercalated (0-5%) TiSe{sub 2} were attempted via solid-state reaction in evacuated quartz tubes followed by densification using a spark plasma sintering process. X-ray diffraction data indicated that mixed NiSe{sub 2} and TiSe{sub 2} phases were present after initial synthesis by solid-state reaction, but a pure TiSe{sub 2} phase was present after the spark plasma sintering. While EPMA data reveals the stoichiometry to be near 1:1.8 (Ti:Se) for all samples, comparisons of the measured bulk densities to the theoretical densities suggest that the off stoichiometry is a result of the co-intercalation of both Ni and Ti rather than Se vacancies. Due to the presence of excess Ti (0.085-0.130 per formula) in the van der Waals gap of all the samples, the sensitive electron-hole balance is offset by the additional Ti-3d electrons, leading to an increase in the thermopower (n-type) over pristine, stoichiometric TiSe{sub 2}. The effects of the co-intercalation of both Ni and Ti in TiSe{sub 2} on the structural, thermal, and electrical properties are discussed herein. - Graphical abstract: Co-intercalation of nickel and excess titanium into the van der Waals gap of TiSe{sub 2} via solid state synthesis followed by spark plasma sintering results in a systematic shift in the ratio of hole and electron carrier concentration, which is close to unity for pristine TiSe{sub 2}. This directly affects the electrical transport properties, and as the structural disorder induced by intercalation suppresses the lattice thermal conductivity, co-intercalation is an effective route to enhance the thermoelectric properties of transition metal diselenides. Highlights: Black-Right-Pointing-Pointer Single phase bulk Ni and Ti co-intercalated TiSe{sub 2} samples prepared by spark plasma sintering. Black-Right-Pointing-Pointer Density and X-ray diffraction suggest that the Ni and excess Ti are ordered in the Van der Waals gap. Black-Right-Pointing-Pointer Co

  2. Sorption enhanced reaction process for direct production of fuel-cell grade hydrogen by low temperature catalytic steam-methane reforming

    NASA Astrophysics Data System (ADS)

    Beaver, Michael G.; Caram, Hugo S.; Sircar, Shivaji

    New experimental data are reported to demonstrate that a sorption enhanced reaction (SER) concept can be used to directly produce fuel-cell grade H 2 (<20 ppm CO) by carrying out the catalytic, endothermic, steam-methane reforming (SMR) reaction (CH 4 + 2H 2O ↔ CO 2 + 4H 2) in presence of a CO 2 selective chemisorbent such as K 2CO 3 promoted hydrotalcite at reaction temperatures of 520 and 550 °C, which are substantially lower than the conventional SMR reaction temperatures of 700-800 °C. The H 2 productivity of the sorption enhanced reactor can be large, and the conversion of CH 4 to H 2 can be very high circumventing the thermodynamic limitations of the SMR reaction due to the application of the Le Chetalier's principle in the SER concept. Mathematical simulations of a cyclic two-step SER concept showed that the H 2 productivity of the process (moles of essentially pure H 2 produced per kg of catalyst-chemisorbent admixture in the reactor per cycle) is much higher at a reaction temperature of 590 °C than that at 550 or 520 °C. On the other hand, the conversion of feed CH 4 to high purity H 2 product is relatively high (>99+%) at all three temperatures. The conversion is much higher than that in a conventional catalyst-alone reactor at these temperatures, and it increases only moderately (<1%) as the reaction temperature is increased from 520 to 590 °C. These results are caused by complex interactions of four phenomena. They are (a) favorable thermodynamic equilibrium of the highly endothermic SMR reaction at the higher reaction temperature, (b) faster kinetics of SMR reaction at higher temperatures, (c) favorable removal of CO 2 from the reaction zone at lower temperatures, and (d) higher cyclic working capacity for CO 2 chemisorption at higher temperature.

  3. Liquid phase sintering of silicon carbide

    DOEpatents

    Cutler, R.A.; Virkar, A.V.; Hurford, A.C.

    1989-05-09

    Liquid phase sintering is used to densify silicon carbide based ceramics using a compound comprising a rare earth oxide and aluminum oxide to form liquids at temperatures in excess of 1,600 C. The resulting sintered ceramic body has a density greater than 95% of its theoretical density and hardness in excess of 23 GPa. Boron and carbon are not needed to promote densification and silicon carbide powder with an average particle size of greater than one micron can be densified via the liquid phase process. The sintered ceramic bodies made by the present invention are fine grained and have secondary phases resulting from the liquid phase. 4 figs.

  4. Thermal barrier coating resistant to sintering

    DOEpatents

    Subramanian, Ramesh; Sabol, Stephen M.

    2001-01-01

    A device (10) having a ceramic thermal barrier coating layer (16) characterized by a microstructure having gaps (18) with a sintering inhibiting material (22) disposed on the columns (20) within the gaps (18). The sintering resistant material (22) is stable over the range of operating temperatures of the device (10) and is not soluble with the underlying ceramic layer (16). For a YSZ ceramic layer (16) the sintering resistant layer (22) may preferably be aluminum oxide or yttrium aluminum oxide, deposited as a continuous layer or as nodules.

  5. Liquid phase sintering of silicon carbide

    DOEpatents

    Cutler, Raymond A.; Virkar, Anil V.; Hurford, Andrew C.

    1989-01-01

    Liquid phase sintering is used to densify silicon carbide based ceramics using a compound comprising a rare earth oxide and aluminum oxide to form liquids at temperatures in excess of 1600.degree. C. The resulting sintered ceramic body has a density greater than 95% of its theoretical density and hardness in excess of 23 GPa. Boron and carbon are not needed to promote densification and silicon carbide powder with an average particle size of greater than one micron can be densified via the liquid phase process. The sintered ceramic bodies made by the present invention are fine grained and have secondary phases resulting from the liquid phase.

  6. A multi-component domino reaction for the direct access to polyfunctionalized indoles via intermolecular allylic esterification and indolation†

    PubMed Central

    Jiang, Bo; Yi, Mian-Shuai; Shi, Feng; Pindi, Suresh; McDowell, Patrick

    2013-01-01

    A novel multi-component reaction for the synthesis of polyfunctionalized indoles and bis-indoles has been established. The reaction pathways were controlled by varying enamines with different substitution patterns to give polyfunctionalized indoles and bis-indoles selectively. The reaction proceeds at a fast speed within 15–30 min with water as the major byproduct, which makes work-up convenient. PMID:22038299

  7. A comparative study of conventionally sintered and microwave sintered nickel zinc ferrite

    SciTech Connect

    Rani, Rekha; Juneja, J. K.; Raina, K. K.; Kotnala, R. K.; Prakash, Chandra

    2014-04-24

    For the present work, nickel zinc ferrite having compositional formula Ni{sub 0.8}Zn{sub 0.2}Fe{sub 2}O{sub 4} was synthesized by conventional solid state method and sintered in conventional and microwave furnaces. Pellets were sintered with very short soaking time of 10 min at 1150 °C in microwave furnace whereas 4 hrs of soaking time was selected for conventional sintering at 1200 °C. Phase formation was confirmed by X-ray diffraction analysis technique. Scanning electron micrographs were taken for microstructural study. Dielectric properties were studied as a function of temperature. To study magnetic behavior, M-H hysteresis loops were recorded for both samples. It is observed that microwave sintered sample could obtain comparable properties to the conventionally sintered one in lesser soaking time at lower sintering temperature.

  8. Direct polymerase chain reaction from blood and tissue samples for rapid diagnosis of bovine leukemia virus infection

    PubMed Central

    NISHIMORI, Asami; KONNAI, Satoru; IKEBUCHI, Ryoyo; OKAGAWA, Tomohiro; NAKAHARA, Ayako; MURATA, Shiro; OHASHI, Kazuhiko

    2016-01-01

    Bovine leukemia virus (BLV) infection induces bovine leukemia in cattle and causes significant financial harm to farmers and farm management. There is no effective therapy or vaccine; thus, the diagnosis and elimination of BLV-infected cattle are the most effective method to eradicate the infection. Clinical veterinarians need a simpler and more rapid method of diagnosing infection, because both nested polymerase chain reaction (PCR) and real-time PCR are labor intensive, time-consuming, and require specialized molecular biology techniques and expensive equipment. In this study, we describe a novel PCR method for amplifying the BLV provirus from whole blood, thus eliminating the need for DNA extraction. Although the sensitivity of PCR directly from whole blood (PCR-DB) samples as measured in bovine blood containing BLV-infected cell lines was lower than that of nested PCR, the PCR-DB technique showed high specificity and reproducibility. Among 225 clinical samples, 49 samples were positive by nested PCR, and 37 samples were positive by PCR-DB. There were no false positive samples; thus, PCR-DB sensitivity and specificity were 75.51% and 100%, respectively. However, the provirus loads of the samples detected by nested PCR and not PCR-DB were quite low. Moreover, PCR-DB also stably amplified the BLV provirus from tumor tissue samples. PCR-DB method exhibited good reproducibility and excellent specificity and is suitable for screening of thousands of cattle, thus serving as a viable alternative to nested PCR and real-time PCR. PMID:26911373

  9. Direct polymerase chain reaction from blood and tissue samples for rapid diagnosis of bovine leukemia virus infection.

    PubMed

    Nishimori, Asami; Konnai, Satoru; Ikebuchi, Ryoyo; Okagawa, Tomohiro; Nakahara, Ayako; Murata, Shiro; Ohashi, Kazuhiko

    2016-06-01

    Bovine leukemia virus (BLV) infection induces bovine leukemia in cattle and causes significant financial harm to farmers and farm management. There is no effective therapy or vaccine; thus, the diagnosis and elimination of BLV-infected cattle are the most effective method to eradicate the infection. Clinical veterinarians need a simpler and more rapid method of diagnosing infection, because both nested polymerase chain reaction (PCR) and real-time PCR are labor intensive, time-consuming, and require specialized molecular biology techniques and expensive equipment. In this study, we describe a novel PCR method for amplifying the BLV provirus from whole blood, thus eliminating the need for DNA extraction. Although the sensitivity of PCR directly from whole blood (PCR-DB) samples as measured in bovine blood containing BLV-infected cell lines was lower than that of nested PCR, the PCR-DB technique showed high specificity and reproducibility. Among 225 clinical samples, 49 samples were positive by nested PCR, and 37 samples were positive by PCR-DB. There were no false positive samples; thus, PCR-DB sensitivity and specificity were 75.51% and 100%, respectively. However, the provirus loads of the samples detected by nested PCR and not PCR-DB were quite low. Moreover, PCR-DB also stably amplified the BLV provirus from tumor tissue samples. PCR-DB method exhibited good reproducibility and excellent specificity and is suitable for screening of thousands of cattle, thus serving as a viable alternative to nested PCR and real-time PCR. PMID:26911373

  10. Direct total cross section measurement of the 16O(α,γ)20Ne reaction at Ec.m.=2.26 MeV

    NASA Astrophysics Data System (ADS)

    Hager, U.; Brown, J. R.; Buchmann, L.; Carmona-Gallardo, M.; Erikson, L.; Fallis, J.; Greife, U.; Hutcheon, D.; Ottewell, D.; Ruiz, C.; Sjue, S.; Vockenhuber, C.

    2011-08-01

    In stellar helium burning, 16O represents the endpoint of the helium-burning sequence due to the low rate of 16O(α,γ)20Ne. We present a new direct measurement of the total capture reaction rate of 16O(α,γ)20Ne at Ec.m.=2.26MeV employing the DRAGON recoil separator. For the first time, the total S factor and its contributing direct capture transitions could be determined in one experiment.

  11. Sintering of sponge and hydride-dehydride titanium powders

    SciTech Connect

    Alman, David E.; Gerdemann, Stephen J.

    2004-04-01

    The sintering behavior of compacts produced from sponge and hydride-dehydride (HDH) Ti powders was examined. Compacts were vacuum sintered at 1200 or 1300 deg C for 30, 60, 120, 240, 480 or 960 minutes. The porosity decreased with sintering time and/or temperature in compacts produced from the HDH powders. Compacts produced from these powders could be sintered to essentially full density. However, the sintering condition did not influence the amount of porosity present in compacts produced from the sponge powders. These samples could only be sintered to a density of 97% theoretical. The sintering behavior was attributed to the chemical impurities in the powders.

  12. Reactive atomization of silicon to form in situ oxide sintering aids

    NASA Astrophysics Data System (ADS)

    Wu, Y.; Zeng, X.; Lavernia, E. J.; Schoenung, J. M.

    1996-08-01

    The present investigation demonstrated the feasibility of using reactive atomization to produce Si powder with in situ oxide sintering aids. With further process optimization, this powder may be an alternative starting material to the conventional, mechanically blended, Si-plus-oxide powder used to produce commercial sintered reaction bonded silicon nitride (SRBSN). In the reactive atomization approach, yttrium and aluminum additives were introduced into silicon metal during induction melting. Reactive atomization was accomplished using a N2-5 pct O2 mixture as the atomization gas. During atomization, oxygen in the atomization gas reacted with Y and Al in the Si melt to produce Y2O3 and Al2O3, which act as in situ sintering aids. The reactive atomized powder demonstrated a Gaussian distribution with a mean diameter of 36 μm. The powder fines (<38 μm) were used to produce cold isostatically pressed compacts that were subsequently reaction bonded and sintered. The results demonstrate that β-Si3N4 formed during reaction bonding and sintering. The density of the SRBSN was 77 pct of theoretical. Transmission electron microscopy (TEM) studies indicated the presence of a glassy phase on the grain boundaries, which is typical in SRBSN and indicative of the presence of the in situ sintering aids. A kinetic model was used to study the influence of processing parameters, such as droplet temperature and oxygen partial pressure, on the kinetics of oxide formation during reactive atomization. The results suggest that the volume fraction of oxides increases with increasing droplet temperature and oxygen partial pressure in the atomization gas mixture.

  13. Nanostructured CoSi Obtained by Spark Plasma Sintering

    NASA Astrophysics Data System (ADS)

    Longhin, Marco; Viennois, Romain; Ravot, Didier; Robin, Jean-Jacques; Villeroy, Benjamin; Vaney, Jean-Baptiste; Candolfi, Christophe; Lenoir, Bertrand; Papet, Philippe

    2015-06-01

    Cobalt monosilicide is a cheap, environmentally friendly thermoelectric material for medium temperatures (200-700°C). While its power factor is similar to the state-of-the-art thermoelectric materials, its thermal conductivity is too large to reach high ZT values. Nanostructuring might be an interesting strategy to reduce the phonon mean free path thereby improving the thermoelectric performance. In this paper, we report on a 35% reduction of the thermal conductivity of n-type CoSi by a nanostructuring approach. CoSi nanostructured powders were synthesized by arc melting, followed by 4° h mechanical milling. By optimizing the spark plasma sintering thermal and pressure cycle, pellets with 5â€"10% porosity were obtained. During sintering, a small amount of Co2Si extra phase appeared and grains coarsened. After sintering, the pellets remained nanostructured, with an averaged grain size of 70 nm. The reduction of thermal conductivity is ascribed to a decrease in both the electronic and lattice contributions. The former is directly related to a decrease in the electrical conductivity, which appears to be the limiting factor preventing nanostructured CoSi from reaching enhanced thermoelectric performances.

  14. Direct study of the α -nucleus optical potential at astrophysical energies using the 64Zn(p ,α )61Cu reaction

    NASA Astrophysics Data System (ADS)

    Gyürky, Gy.; Fülöp, Zs.; Halász, Z.; Kiss, G. G.; Szücs, T.

    2014-11-01

    In the model calculations of heavy element nucleosynthesis processes the nuclear reaction rates are taken from statistical model calculations which utilize various nuclear input parameters. It is found that in the case of reactions involving α particles the calculations bear a high uncertainty owing to the largely unknown low-energy α -nucleus optical potential. Experiments are typically restricted to higher energies and therefore no direct astrophysical consequences can be drawn. In the present work a (p ,α ) reaction is used for the first time to study the α -nucleus optical potential. The measured 64Zn (p ,α )61Cu cross section is uniquely sensitive to the α -nucleus potential and the measurement covers the whole astrophysically relevant energy range. By the comparison to model calculations, direct evidence is provided for the incorrectness of global optical potentials used in astrophysical models.

  15. Thermal barrier coating resistant to sintering

    DOEpatents

    Subramanian, Ramesh; Seth, Brig B.

    2005-08-23

    A device (10) is made, having a ceramic thermal barrier coating layer (16) characterized by a microstructure having gaps (18) with a sintering inhibiting material (22) disposed on the columns (20) within the gaps (18). The sintering resistant material (22) is stable over the range of operating temperatures of the device (10), is not soluble with the underlying ceramic layer (16) and is applied by a process that is not an electron beam physical vapor deposition process. The sintering inhibiting material (22) has a morphology adapted to improve the functionality of the sintering inhibiting material (22), characterized as continuous, nodule, rivulet, grain, crack, flake and combinations thereof and being disposed within at least some of the vertical and horizontal gaps.

  16. Sintered electrode for solid oxide fuel cells

    DOEpatents

    Ruka, Roswell J.; Warner, Kathryn A.

    1999-01-01

    A solid oxide fuel cell fuel electrode is produced by a sintering process. An underlayer is applied to the electrolyte of a solid oxide fuel cell in the form of a slurry, which is then dried. An overlayer is applied to the underlayer and then dried. The dried underlayer and overlayer are then sintered to form a fuel electrode. Both the underlayer and the overlayer comprise a combination of electrode metal such as nickel, and stabilized zirconia such as yttria-stabilized zirconia, with the overlayer comprising a greater percentage of electrode metal. The use of more stabilized zirconia in the underlayer provides good adhesion to the electrolyte of the fuel cell, while the use of more electrode metal in the overlayer provides good electrical conductivity. The sintered fuel electrode is less expensive to produce compared with conventional electrodes made by electrochemical vapor deposition processes. The sintered electrodes exhibit favorable performance characteristics, including good porosity, adhesion, electrical conductivity and freedom from degradation.

  17. Spark plasma sintering of aluminum matrix composites

    NASA Astrophysics Data System (ADS)

    Yadav, Vineet

    2011-12-01

    Aluminum matrix composites make a distinct category of advanced engineering materials having superior properties over conventional aluminum alloys. Aluminum matrix composites exhibit high hardness, yield strength, and excellent wear and corrosion resistance. Due to these attractive properties, aluminum matrix composites materials have many structural applications in the automotive and the aerospace industries. In this thesis, efforts are made to process high strength aluminum matrix composites which can be useful in the applications of light weight and strong materials. Spark Plasma Sintering (SPS) is a relatively novel process where powder mixture is consolidated under the simultaneous influence of uniaxial pressure and pulsed direct current. In this work, SPS was used to process aluminum matrix composites having three different reinforcements: multi-wall carbon nanotubes (MWCNTs), silicon carbide (SiC), and iron-based metallic glass (MG). In Al-CNT composites, significant improvement in micro-hardness, nano-hardness, and compressive yield strength was observed. The Al-CNT composites further exhibited improved wear resistance and lower friction coefficient due to strengthening and self-lubricating effects of CNTs. In Al-SiC and Al-MG composites, microstructure, densification, and tribological behaviors were also studied. Reinforcing MG and SiC also resulted in increase in micro-hardness and wear resistance.

  18. Reaction Mechanism for Direct Proton Transfer from Carbonic Acid to a Strong Base in Aqueous Solution II: Solvent Coordinate-Dependent Reaction Path.

    PubMed

    Daschakraborty, Snehasis; Kiefer, Philip M; Miller, Yifat; Motro, Yair; Pines, Dina; Pines, Ehud; Hynes, James T

    2016-03-10

    The protonation of methylamine base CH3NH2 by carbonic acid H2CO3 within a hydrogen (H)-bonded complex in aqueous solution was studied via Car-Parrinello dynamics in the preceding paper (Daschakraborty, S.; Kiefer, P. M.; Miller, Y.; Motro, Y.; Pines, D.; Pines, E.; Hynes, J. T. J. Phys. Chem. B 2016, DOI: 10.1021/acs.jpcb.5b12742). Here some important further details of the reaction path are presented, with specific emphasis on the water solvent's role. The overall reaction is barrierless and very rapid, on an ∼100 fs time scale, with the proton transfer (PT) event itself being very sudden (<10 fs). This transfer is preceded by the acid-base H-bond's compression, while the water solvent changes little until the actual PT occurrence; this results from the very strong driving force for the reaction, as indicated by the very favorable acid-protonated base ΔpKa difference. Further solvent rearrangement follows immediately the sudden PT's production of an incipient contact ion pair, stabilizing it by establishment of equilibrium solvation. The solvent water's short time scale ∼120 fs response to the incipient ion pair formation is primarily associated with librational modes and H-bond compression of water molecules around the carboxylate anion and the protonated base. This is consistent with this stabilization involving significant increase in H-bonding of hydration shell waters to the negatively charged carboxylate group oxygens' (especially the former H2CO3 donor oxygen) and the nitrogen of the positively charged protonated base's NH3(+). PMID:26876428

  19. Reactive sintering of TiAl–Ti5Si3 in situ composites

    SciTech Connect

    Alman, David E.

    2005-06-01

    TiAl with between 0 and 20 vol%Ti5Si3 was produced by reactive sintering (700 °C for 15 min in vacuum) of cold pressed compacts of elemental Ti, Al and Si powder. The results show that adding Si to Ti and Al reduces the swelling associated with reactive sintering of TiAl, as composites containing more than 5 vol%Ti5Si3 densified during reactive sintering. However, composites containing more than 10 vol%Ti5Si3 did not retain their shape and the TiAl+20 vol%Ti5Si3 composite completely melted during the sintering process. A thermodynamic analysis indicated that the simultaneous formation of TiAl and Ti5Si3 increases the adiabatic flame temperature during the reaction between the powders. In fact, the analysis predicted that the maximum temperature of the reaction associated with the formation TiAl+20 vol%Ti5Si3 should exceed the melting point of TiAl, and this was observed experimentally. Differential thermal analysis (DTA) revealed that an Al–Si eutectic reaction occurred in mixtures of Ti, Al and Si powders prior to the formation of the TiAl and Ti5Si3 phases. There was no such pre-reaction formation of a eutectic liquid in Ti and Al powder mixtures. The formation of the pre-reaction liquid and the increase in adiabatic flame temperature resulted in the melting that occurred and the enhanced densification (minimization of swelling) during reactive sintering of the in situ composites.

  20. Pressureless sintering of whisker-toughened ceramic composites

    DOEpatents

    Tiegs, T.N.

    1993-05-04

    A pressureless sintering method is disclosed for use in the production of whisker-toughened ceramic composites wherein the sintered density of composites containing up to about 20 vol. % SiC whiskers is improved by reducing the average aspect ratio of the whiskers to from about 10 to about 20. Sintering aids further improve the density, permitting the production of composites containing 20 vol. % SiC with sintered densities of 94% or better of theoretical density by a pressureless sintering method.

  1. Pressureless sintering of whisker-toughened ceramic composites

    DOEpatents

    Tiegs, Terry N.

    1993-01-01

    A pressureless sintering method is disclosed for use in the production of whisker-toughened ceramic composites wherein the sintered density of composites containing up to about 20 vol. % SiC whiskers is improved by reducing the average aspect ratio of the whiskers to from about 10 to about 20. Sintering aids further improve the density, permitting the production of composites containing 20 vol. % SiC with sintered densities of 94% or better of theoretical density by a pressureless sintering method.

  2. Pressureless sintering of whiskered-toughened ceramic composites

    DOEpatents

    Tiegs, Terry N.

    1994-01-01

    A pressureless sintering method is disclosed for use in the production of whisker-toughened ceramic composites wherein the sintered density of composites containing up to about 20 vol. % SiC whiskers is improved by reducing the average aspect ratio of the whiskers to from about 10 to about 20. Sintering aids further improve the density, permitting the production of composites containing 20 vol. % SiC with sintered densities of 94% or better of theoretical density by a pressureless sintering method.

  3. Thermal barrier coating resistant to sintering

    DOEpatents

    Subramanian, Ramesh; Seth, Brij B.

    2004-06-29

    A device (10) is made, having a ceramic thermal barrier coating layer (16) characterized by a microstructure having gaps (18) with a sintering inhibiting material (22) disposed on the columns (20) within the gaps (18). The sintering resistant material (22) is stable over the range of operating temperatures of the device (10), is not soluble with the underlying ceramic layer (16) and is applied by a process that is not an electron beam physical vapor deposition process.

  4. Spark plasma sintering of TiNi nano-powders for biological application

    NASA Astrophysics Data System (ADS)

    Fu, Y. Q.; Gu, Y. W.; Shearwood, C.; Luo, J. K.; Flewitt, A. J.; Milne, W. I.

    2006-11-01

    Nano-sized TiNi powder with an average size of 50 nm was consolidated using spark plasma sintering (SPS) at 800 °C for 5 min. A layer of anatase TiO2 coating was formed on the sintered TiNi by chemical reaction with a hydrogen peroxide (H2O2) solution at 60 °C followed by heat treatment at 400 °C to enhance the bioactivity of the metal surface. Cell culture using osteoblast cells and a biomimetic test in simulated body fluid proved the biocompatibility of the chemically treated SPS TiNi.

  5. Silver Ink Formulations for Sinter-free Printing of Conductive Films.

    PubMed

    Black, Kate; Singh, Jetinder; Mehta, Danielle; Sung, Sarah; Sutcliffe, Christopher J; Chalker, Paul R

    2016-01-01

    Inkjet printing offers an attractive method for the deposition of metal interconnects in electronic systems and enables a low-cost, environmentally friendly route to manufacture. However, virtually all current metal inkjet processes require post-deposition sintering treatments to achieve the optimum electrical conductivity, because the growth mechanism involves coalescence of discrete nanoparticles. A manufacturing process that reduces the number of steps by directly printing silver, removing the need to sinter the printed metal, would be highly advantageous. Here we describe a, sinter-free process that results in the direct printing of crystalline silver. This process exploits the chemistries developed for Atomic Layer Deposition (ALD), to form the basis of a new ink formulation, which we term; Reactive Organometallic inks (ROM). These ROM ink formulations are capable of depositing low temperature, high conductivity metal films, without the need for subsequent sintering treatments. To reduce the temperature for direct formation of metallic Ag, we have added an alcohol as a catalytic reducing agent to dissociate the organometallic component. Silver films printed from our novel ROM ink, on a glass substrate at 120 °C, are electrically conductive with a typical resistivity as low as 39.2% that of bulk silver, without the need for sintering. PMID:26857286

  6. Silver Ink Formulations for Sinter-free Printing of Conductive Films

    NASA Astrophysics Data System (ADS)

    Black, Kate; Singh, Jetinder; Mehta, Danielle; Sung, Sarah; Sutcliffe, Christopher. J.; Chalker, Paul. R.

    2016-02-01

    Inkjet printing offers an attractive method for the deposition of metal interconnects in electronic systems and enables a low-cost, environmentally friendly route to manufacture. However, virtually all current metal inkjet processes require post-deposition sintering treatments to achieve the optimum electrical conductivity, because the growth mechanism involves coalescence of discrete nanoparticles. A manufacturing process that reduces the number of steps by directly printing silver, removing the need to sinter the printed metal, would be highly advantageous. Here we describe a, sinter-free process that results in the direct printing of crystalline silver. This process exploits the chemistries developed for Atomic Layer Deposition (ALD), to form the basis of a new ink formulation, which we term; Reactive Organometallic inks (ROM). These ROM ink formulations are capable of depositing low temperature, high conductivity metal films, without the need for subsequent sintering treatments. To reduce the temperature for direct formation of metallic Ag, we have added an alcohol as a catalytic reducing agent to dissociate the organometallic component. Silver films printed from our novel ROM ink, on a glass substrate at 120 °C, are electrically conductive with a typical resistivity as low as 39.2% that of bulk silver, without the need for sintering.

  7. Silver Ink Formulations for Sinter-free Printing of Conductive Films

    PubMed Central

    Black, Kate; Singh, Jetinder; Mehta, Danielle; Sung, Sarah; Sutcliffe, Christopher. J.; Chalker, Paul. R.

    2016-01-01

    Inkjet printing offers an attractive method for the deposition of metal interconnects in electronic systems and enables a low-cost, environmentally friendly route to manufacture. However, virtually all current metal inkjet processes require post-deposition sintering treatments to achieve the optimum electrical conductivity, because the growth mechanism involves coalescence of discrete nanoparticles. A manufacturing process that reduces the number of steps by directly printing silver, removing the need to sinter the printed metal, would be highly advantageous. Here we describe a, sinter-free process that results in the direct printing of crystalline silver. This process exploits the chemistries developed for Atomic Layer Deposition (ALD), to form the basis of a new ink formulation, which we term; Reactive Organometallic inks (ROM). These ROM ink formulations are capable of depositing low temperature, high conductivity metal films, without the need for subsequent sintering treatments. To reduce the temperature for direct formation of metallic Ag, we have added an alcohol as a catalytic reducing agent to dissociate the organometallic component. Silver films printed from our novel ROM ink, on a glass substrate at 120 °C, are electrically conductive with a typical resistivity as low as 39.2% that of bulk silver, without the need for sintering. PMID:26857286

  8. A study on flash sintering and related phenomena in titania and its composite with alumina

    NASA Astrophysics Data System (ADS)

    Shikhar

    In 2010, Cologna et. al. [1] reported that with a help of small electric field 120 Vcm-1, the sintering temperature of 3 mol % yittria stabilized zirconia could be brought down to 850°C from 1450°C. On top of reducing the temperature requirements, the green sample could be sintered from starting density of 50% to near full density in mere 5 seconds, a sintering rate three orders of magnitude higher than conventional methods. This discovery led to the emergence of a new field of enhanced sintering with electric field, named "Flash Sintering". The objective of this thesis is to understand the phenomenological behavior of flash-sintering and related phenomena on titania and its composites with alumina at elevated temperature. The possible mechanisms to explain flash sintering are discussed: Joule heating and the avalanche of defect generation [2], both induced by the rapid rise in conductivity just before the onset of the flash. Apparently, both mechanisms play a role. The thesis covers the response of pure titania and composites of titania-alumina under flash and compared with conventional sintering. We start with the sintering behavior of pure titania and observe lowering of sintering temperature requirements with higher applied electric field. The conductivity of titania during flash is also measured, and compared with the nominal conductivity of titania at equivalent temperatures. The conductivity during flash is determined to be have a different activation energy. For the composites of titania-alumina, effect of flash on the constrained sintering was studied. It is a known fact that sintering of one component of composite slows down when the other component of a different densification rate is added to it, called constrained sintering. In our case, large inclusions of alumina particles were added to nano-grained titania green compact that hindered its densification. Flash sintering was found to be overcoming this problem and near full densification was achieved

  9. Spark Plasma Sintering of Ultracapacitors

    SciTech Connect

    Hill, Curtis W.; Boatner, Lynn A.; Tucker, Dennis; Kolopus, James A.; Cheng, Zhongyang

    2016-01-01

    A solid-state ultracapacitor module to replace standard electrochemical batteries would achieve major performance gains and mass/volume reduction. This report summarizes a project to evaluate an alternative sintering process to produce a solid-state ultracapacitor to overcome the limitations of both the electrochemical batteries presently in use on spacecraft and of currently available electrochemical ultracapacitors. It will provide a robust energy storage device with higher reliability, wider working temperature range, longer lifetime, and less weight and volume than electrochemical batteries. As modern electronics decrease in size, more efficient and robust remote power is needed. Current state-of-the-art rechargeable batteries cannot be rapidly charged, contain harmful chemicals, and suffer from early wear-out mechanisms. Solid-state ultracapacitors are recyclable energy storage devices that offer the promise of higher power and a greater number of charge/discharge cycles than current rechargeable batteries. In addition, the theoretical energy density when compared to current electrochemical batteries indicates that a significant weight savings is possible. This is a project to develop a very high density solid-state ultracapacitor with giant permittivity and acceptable dielectric loss to overcome the energy-density barrier such that it will be a suitable replacement for batteries.

  10. Zn migration during spark plasma sintering of thermoelectric Zn4Sb3

    NASA Astrophysics Data System (ADS)

    Yin, Hao; Christensen, Mogens; Lock, Nina; Iversen, Bo B.

    2012-07-01

    The phase homogeneity of spark plasma sintered thermoelectric Zn4Sb3 pellets along the pressing direction has been studied by potential Seebeck microprobe scanning and spatially resolved x-ray diffraction. Significant variations in the Seebeck coefficient reflect presence of different crystalline phases. The emergence of the ZnSb phase at the bottom of the pellet and metallic Zn impurity at the top explains the variation in the Seebeck coefficients. Quantitative phase distributions along the pressing axis were determined from the Rietveld refinements of spatially resolved x-ray diffraction patterns. These reveal a migration of highly mobilized Zn atoms under the direct current applied during spark plasma sintering.

  11. Effect of Addition of Mill Scale on Sintering of Iron Ores

    NASA Astrophysics Data System (ADS)

    Wang, Zhe; Pinson, David; Chew, Sheng; Monaghan, Brian J.; Pownceby, Mark I.; Webster, Nathan A. S.; Rogers, Harold; Zhang, Guangqing

    2016-06-01

    Iron-rich (65 to 70 pct total Fe) mill scale generated during processing by steel mills can be recycled by using it as a ferrous raw material in the sintering process. The effect of mill scale addition on the phase formation of sintered specimens from an industrial sinter blend containing 0 to 15 wt pct mill scale was examined, and the mineral phases formed during sintering under various conditions (T = 1523 K to 1598 K [1250 °C to 1325 °C] and gas compositions of pO2 = 0.5, 5 and 21 kPa) were quantitatively measured. For samples sintered in air (pO2 = 21 kPa), there was negligible effect of mill scale addition on the phases formed. The oxidation of the mill scale was complete, and phases such as Silico-Ferrite of Calcium and Aluminum (SFCA), SFCA-I, and hematite dominated. Under lower oxygen partial pressures (pO2 = 0.5 or 5 kPa), and throughout the temperature range examined, the mill scale was converted to magnetite, with the extent of reaction controlled by the hematite-magnetite conversion kinetics. When sintered in the gas mixture with pO2 = 5 kPa, an increase in the mill scale content from 0 to 15 wt pct resulted in a decrease of hematite and total SFCA phases and a corresponding increase in the amount of magnetite which formed. The oxidation of wustite in mill scale to magnetite decreased the local partial pressure of O2 and increased sintering temperature, which promoted the decomposition of hematite.

  12. Novel rearrangements in the reactions directed toward preparation of spiro-N,N-ketals: reactions of naphthalene-1,8-diamine with ninhydrin and isatin.

    PubMed

    Akita, Motoko; Seto, Hideyuki; Aoyama, Reiko; Kimura, Junko; Kobayashi, Keiji

    2012-01-01

    Spiro-N,N-ketal 5, consisting of a phthaloperine heterocyclic ring and a naphtha[1,8-ef][1,4]diazepine ring, was obtained along with spiro-N,N-ketal 2 via 2,2-condensation in the reaction of ninhydrin with naphthalene-1,8-diamine. Their molecular structures were elucidated by X-ray crystal structural analysis. Aside from these spiro compounds, the diazapleiadiene compound 3 formed by 1,2-condensation and the 1,4-isoquinolinedione compound 4 arising from ring expansion were isolated. When isatin was reacted with naphthalene-1,8-diamine, spiro-N,N-ketal 6 and the two 1H-perimidine-based compounds 7 and 8 were isolated. Compound 8 was revealed to undergo a fast dynamic prototropic tautomerization in solution. Plausible mechanisms of the formation of the products are proposed. PMID:23174903

  13. Simultaneous Light-Directed Synthesis of Mirror-Image Microarrays in a Photochemical Reaction Cell with Flare Suppression

    PubMed Central

    2013-01-01

    The use of photolabile protecting groups is a versatile and well-established means of synthesizing high complexity microarrays of biopolymers, such as nucleic acids and peptides, for high-throughput analysis. The synthesis takes place in a photochemical reaction cell which positions the microarray substrate at the focus of the optical system delivering the light and which can be connected to a fluidics system which delivers appropriate reagents to the surface in synchrony with the light exposure. Here we describe a novel photochemical reaction cell which allows for the simultaneous synthesis of microarrays on two substrates. The reaction cell positions both substrates within the limited depth-of-focus of the optical system while maintaining the necessary reagent flow conditions. The resulting microarrays are mirror images of each other but otherwise essentially identical. The new reaction cell doubles the throughput of microarray synthesis without increasing the consumption of reagents. In addition, a secondary flow chamber behind the reaction cell can be filled with an absorbent and index-matching fluid to eliminate reflections from light exiting the reaction cell assembly, greatly reducing unintended light exposure that reduces the sequence fidelity of the microarray probes. PMID:23968455

  14. Effect of autoclaving and sintering on the formation of β-wollastonite.

    PubMed

    Ismail, Hamisah; Shamsudin, Roslinda; Abdul Hamid, Muhammad Azmi

    2016-01-01

    β-wollastonite (β-CaSiO3) was synthesized from rice husk ash and calcium carbonate, and a study of the effects of the autoclaving and sintering steps is presented here. Autoclaving and sintering at 8h and 2h yielded the β-wollastonite phase in full, with improved crystallinity. Nucleation between rice husk ash and calcium oxide occurred around 135 °C, pressure 0.24 MPa, and growth proved to be more crystalline after the ripening period. For shorter processing times, and for both unsintered and unautoclaved samples, cristobalite and unstable tricalcium silicate phases were present. Crystallite size was increased by longer sintering times but reduced by longer autoclaving times. The β-wollastonite obtained had a random branch-like structure. In conclusion, the introduction of the autoclaving step successfully obtained β-wollastonite from a reaction between rice husk ash and calcium oxide. PMID:26478406

  15. A Simple and Facile Iodination Method for Improving Sinterability and Electrical Conductivity of Silver Thick Films

    NASA Astrophysics Data System (ADS)

    Zhou, Jian; Gan, Weiping; Li, Yingfen; Luo, Lin; Pan, Qiaoyun; Xiong, Zhijun

    2014-09-01

    Micro-sized silver powders were decorated with nano-scaled Ag/AgI clusters on the surface via a simple reaction with iodine and subsequent exposure to sunshine. Surface morphologies, crystal structures, and thermal properties of the powders were characterized. The powders with different mole ratios of I:Ag (0:100, 2:100, 10:100) were employed in silver pastes to evaluate sinterability and electrical conductivity of thick films. Microstructures and sheet resistance of the films were investigated by scanning electron microscopy and the four-point probe method. The particles coated with and without nano-sized Ag/AgI clusters showed different sintering behaviors. Moreover, clear necks were formed between the Ag particles with the ratio of 2:100 even at 570°C, whereas those untreated remained discrete. However, over-decoration lowered sinterability and electrical conductivity.

  16. Synthesis, characterization and sintering behaviour of indialite ceramic from fly ash.

    PubMed

    Yao, Zhitong; Tan, Shengheng; Xia, Meisheng; Ye, Ying; Li, Jinhui

    2011-10-01

    Indialite ceramic was prepared using fly ash and magnesium carbonate powder as precursors. The effects of sintering aids LiOH · H2O and TiO2 on its crystallization and morphology evolution were studied as well. X-ray diffraction results indicated that the formation of indialite was achieved by solid-state sintering reactions at 1200 °C for 4 h. With increasing amounts of LiOH · H2O, the viscosity decreased and β-spodumene, spinel phases started to develop at the expense of indialite. Scanning electron microscopy observations revealed that the surface of the sintered samples became smoother with higher porosity losses and grain size reduction. As the TiO2 contents increased from 4 to 10%, dauphine-twinned quartz and rutile were formed by simultaneously consuming indialite. In this process, the viscosity showed no significant changes. PMID:20671003

  17. Effect of sintering on electrical properties of yttrium doped Li-based NASICON compounds

    SciTech Connect

    Kothari, Dharmesh H.; Kanchan, D. K. Dave, Gargi

    2015-08-28

    Electrical properties of Lithium based Li{sub 1.3}Al{sub 0.3-x}Y{sub x}Ti{sub 1.7}(PO{sub 4}){sub 3} (LAYTP) system was prepared using solid state reaction route. The samples were subjected to differing duration of sintering. X-ray diffraction was used to investigate the microstructure while density measurement was performed to determine the effect of sintering on the density of the prepared samples. Electrical properties of the material were studied using impedance spectroscopy, in frequency range 20 MHz to 1 Hz and in temperature range 303 K to 423 K. It was found that sample with least amount of yttrium and which was sintered for least duration had superior conductivity over other samples. It was also found that grain boundary conductivity improved marginally for sample with higher proportion of yttrium heat treated for longer duration.

  18. Microwave Sintered 3D Printed Tricalcium Phosphate Scaffolds for Bone Tissue Engineering

    PubMed Central

    Tarafder, Solaiman; Balla, Vamsi Krishna; Davies, Neal M.; Bandyopadhyay, Amit; Bose, Susmita

    2014-01-01

    We report here the fabrication of three dimensional (3D) interconnected macro porous tricalcium phosphate (TCP) scaffolds with controlled internal architecture by direct 3D printing (3DP), and high mechanical strength by microwave sintering. TCP scaffolds with 27%, 35% and 41% designed macro porosity having pore sizes of 500 μm, 750 μm, and 1000 μm, respectively, have been fabricated via direct 3DP. These scaffolds are then sintered at 1150 °C and 1250 °C in conventional electric muffle furnace as well as microwave furnace. Total open porosity between 42% and 63% is obtained in the sintered scaffolds due to the presence of intrinsic micro pores along with the designed pores. A significant increase in compressive strength, between 46% and 69%, is achieved by microwave sintering as compared to conventional sintering as a result of efficient densification. A maximum compressive strength of 10.95 ± 1.28 MPa and 6.62 ± 0.67 MPa is achieved for scaffolds with 500 μm designed pores (~400 μm after sintering) sintered in microwave and conventional furnaces, respectively. An increase in cell density with a decrease in macro pore size is observed during in vitro cell-material interactions using human osteoblast cells. Histomorphological analysis reveals that the presence of both micro and macro pores facilitated osteoid like new bone formation when tested in the femoral defect on Sprague-Dawley rats. Our results show that bioresorbable 3D printed TCP scaffolds have great potential in tissue engineering applications for bone tissue repair and regeneration. PMID:22396130

  19. Direct RNA detection without nucleic acid purification and PCR: Combining sandwich hybridization with signal amplification based on branched hybridization chain reaction.

    PubMed

    Xu, Yao; Zheng, Zhi

    2016-05-15

    We have developed a convenient, robust and low-cost RNA detection system suitable for high-throughput applications. This system uses a highly specific sandwich hybridization to capture target RNA directly onto solid support, followed by on-site signal amplification via 2-dimensional, branched hybridizing chain polymerization through toehold-mediated strand displacement reaction. The assay uses SYBR Green to detect targets at concentrations as low as 1pM, without involving nucleic acid purification or any enzymatic reaction, using ordinary oligonucleotides without modification or labeling. The system was demonstrated in the detection of malaria RNA in blood and GAPDH gene expression in cell lysate. PMID:26761615

  20. Improvement in the Performance of Bulk MgB2 Material through Optimization of Sintering Process

    NASA Astrophysics Data System (ADS)

    Kobayashi, H.; Muralidhar, M.; Koblischka, M. R.; Inoue, K.; Murakami, M.

    Enhancement of the critical current density (Jc) in MgB2 bulk material is very important for engineering applications. It has been found that the optimization of the sintering temperature leads to high Jc values in bulk MgB2 material. In our recent work, the highest trapped field value was recorded in the sample sintered at 775oC. The present investigation has focused on methods to improve further Jc values of the disk-shape bulk MgB2 superconductors by optimizing sintering conditions. MgB2 samples were subjected to a solid state reaction at 775, 780, 785, 795, 800 and 805oC for 3 h in pure Ar atmosphere. XRD analysis showed that all the samples were single phase MgB2. The magnetization measurements confirmed a sharp superconducting transition with onset Tc at around 38.7 K. Atomic force microscopy observation indicated that the number of nano meter size grains is more in samples processed 3 h at 805oC has compared to the samples sintered at 775oC. As a result, the highest Jc value of 245 kA/cm2 at 20 K was obtained for the sample sintered at 805oC for 3 h.

  1. Microwave sintering of nanopowder ZnNb2O6: Densification, microstructure and microwave dielectric properties

    NASA Astrophysics Data System (ADS)

    Bafrooei, H. Barzegar; Nassaj, E. Taheri; Hu, C. F.; Huang, Q.; Ebadzadeh, T.

    2014-12-01

    High density ZnNb2O6 ceramics were successfully fabricated by microwave sintering of ZnO-Nb2O5 and ZnNb2O6 nanopowders. Phase formation, microstructure and microwave electrical properties of the microwave sintered (MS) and microwave reaction sintered (MRS) specimens were examined using X-ray diffraction, field emission scanning electron microscopy and microwave dielectric properties measurement. Specimens were sintered in a temperature range from 950 to 1075 °C for 30 min at an interval of 25 °C using a microwave furnace operated at 2.45 GHz frequency, 3 kW power. XRD pattern revealed the formation of pure columbite phase of ZnNb2O6. The SEM micrographs show grain growth and reduction in porosity of specimens with the increase in sintering temperature. Good combination of microwave dielectric properties (εr~23.6, Qf~64,300 GHz and τf~-66 ppm/°C and εr~24, Qf~75,800 GHz and τf~-64 ppm/°C) was obtained for MS- and MRS-prepared samples at 1000 °C and 1050 °C for 30 min, respectively.

  2. Comparison of effect of induction and classical sintering to mechanical properties of powder metal components

    NASA Astrophysics Data System (ADS)

    Çivi, Can; Atik, Enver

    2012-09-01

    Because of solidifying to component, sintering is the most important step of the production of powder metal parts. Generally it is made classical furnace. Alternatively sintering furnace, it is done that induction sintering studies. Induction sintering provide a grand time and energy savings since components hot up rapidly and sintering time is lower than classical sintering in furnace. Because of that induction sintering is an important alternative at sintering process. In this study, mechanical properties of induction sintered Fe based components included Cu and Graphite were compared with classical sintered components. Parameters of same mechanical properties of induction sintered and classical sintered components were identified.

  3. Solid-state sintering of tungsten heavy alloys

    SciTech Connect

    Gurwell, W.E.

    1994-10-01

    Solid-state sintering is a technologically important step in the fabrication of tungsten heavy alloys. This work addresses practical variables affecting the sinterability: powder particle size, powder mixing, and sintering temperature and time. Compositions containing 1 to 10 micrometer ({mu}M) tungsten (W) powders can be fully densified at temperatures near the matrix solidus. Blending with an intensifier bar provided good dispersion of elemental powders and good as-sintered mechanical properties under adequate sintering conditions. Additional ball milling increases powder bulk density which primarily benefits mold and die filling. Although fine, 1 {mu}m W powder blends have high sinterability, higher as-sintered ductilities are reached in shorter sintering times with coarser, 5 {mu}m W powder blends; 10{mu}m W powder blends promise the highest as-sintered ductilities due to their coarse microstructural W.

  4. Direct evidence for an acyl phosphate intermediate in the folylpoly-. gamma. -glutamate synthetase and dihydrofolate synthetase-catalyzed reactions

    SciTech Connect

    Banerjee, R.

    1987-01-01

    The mechanism of the reactions catalyzed by two enzymes, namely dihydrofolate synthetase (DHFS) and folylpoly-..gamma..-glutamate synthetase (FPGS), has been investigated. The nature of the intermediate in each of the two reactions was monitored simultaneously in the multifunctional enzyme, FPGS/DHFS from E. coli. The latter was isolated from a transformant containing the cloned FPGS/DHFS gene. Incubation of (/sup 18/O)-H/sub 2/Pte and (/sup 17/O)-glutamate with ATP and the enzyme, resulted in the formation of (/sup 18/O)- and (/sup 17/O)-P/sub i/, thus providing strong evidence for the formation of an acyl phosphate species during catalysis of each reaction. The inorganic phosphate formed in the enzyme-catalyzed reaction was purified by chromatography on DEAE-cellulose, then converted to the trimethyl ester and analyzed by mass spectroscopy /sup 17/O NMR and /sup 31/P NMR. Stoichiometric formation of (/sup 17/O)- and (/sup 18/O)-Pi was observed. /sup 31/P NMR analysis showed the expected /sup 18/O-induced isotopic perturbations. The presence of (/sup 17/O)-trimethyl phosphate was revealed by /sup 17/O NMR. The mechanism of the FPGS-catalyzed reaction was also investigated with the antifolate (/sup 18/O)-methotrexate.

  5. Direct ab initio dynamics studies on the hydrogen-abstraction reactions of OH radicals with HOX (X = F, Cl, and Br).

    PubMed

    Wang, Li; Liu, Jing-Yao; Li, Ze-Sheng; Sun, Chia-Chung

    2004-03-01

    The hydrogen abstract reactions of OH radicals with HOF (R1), HOCl (R2), and HOBr (R3) have been studied systematically by a dual-level direct-dynamics method. The geometries and frequencies of all the stationary points are optimized at the MP2/6-311+G(2d, 2p) level of theory. A hydrogen-bonded complex is located at the product channel for the OH + HOBr reaction. To improve the energetics information along the minimum energy path (MEP), single-point energy calculations are carried out at the CCSD(T)/6-311++G(3df, 3pd) level of theory. Interpolated single-point energy (ISPE) method is employed to correct the energy profiles for the three reactions. It is found that neither the barrier heights (DeltaE) nor the H-O bond dissociation energies [D(H-O)] exhibit any clear-cut linear correlations with the halogen electronegative. The decrease of DeltaE and D(H-O) for the three reactions are in order of HOF > HOBr > HOCl. Rate constants for each reaction are calculated by canonical variational transition-state theory (CVT) with a small-curvature tunneling correction (SCT) within 200-2000 K. The agreement of the rate constants with available experimental values for reactions R2 and R3 at 298 K is good. Our results show that the variational effect is small while the tunneling correction has an important contribution in the calculation of rate constants in the low-temperature range. Due to the lack of the kinetic data of these reactions, the present theoretical results are expected to be useful and reasonable to estimate the dynamical properties of these reactions over a wide temperature range where no experimental value is available. PMID:14735573

  6. Histological Comparison in Rats between Carbonate Apatite Fabricated from Gypsum and Sintered Hydroxyapatite on Bone Remodeling.

    PubMed

    Ayukawa, Yasunori; Suzuki, Yumiko; Tsuru, Kanji; Koyano, Kiyoshi; Ishikawa, Kunio

    2015-01-01

    Carbonate apatite (CO3Ap), the form of apatite found in bone, has recently attracted attention. The purpose of the present study was to histologically evaluate the tissue/cellular response toward the low-crystalline CO3Ap fabricated using a dissolution-precipitation reaction with set gypsum as a precursor. When set gypsum was immersed in a 100°C 1 mol/L Na3PO4 aqueous solution for 24 h, the set gypsum transformed into CO3Ap. Both CO3Ap and sintered hydroxyapatite (s-HAp), which was used as a control, were implanted into surgically created tibial bone defects of rats for histological evaluation. Two and 4 weeks after the implantation, histological sections were created and observed using light microscopy. The CO3Ap granules revealed both direct apposition of the bone matrix by osteoblasts and osteoclastic resorption. In contrast, the s-HAp granules maintained their contour even after 4 weeks following implantation which implied that there was a lack of replacement into the bone. The s-HAp granules were sometimes encapsulated with fibrous tissue, and macrophage polykaryon was occasionally observed directly apposed to the implanted granules. From the viewpoint of bone remodeling, the CO3Ap granules mimicked the bone matrix, suggesting that CO3Ap may be an appropriate bone substitute. PMID:26504813

  7. Catalytic Asymmetric Reactions of 4‐Substituted Indoles with Nitroethene: A Direct Entry to Ergot Alkaloid Structures

    PubMed Central

    Romanini, Simone; Galletti, Emilio; Caruana, Lorenzo; Mazzanti, Andrea; Himo, Fahmi

    2015-01-01

    Abstract A domino Friedel–Crafts/nitro‐Michael reaction between 4‐substituted indoles and nitroethene is presented. The reaction is catalyzed by BINOL‐derived phosphoric acid catalysts, and delivers the corresponding 3,4‐ring‐fused indoles with very good results in terms of yields and diastereo‐ and enantioselectivities. The tricyclic benzo[cd]indole products bear a nitro group at the right position to serve as precursors of ergot alkaloids, as demonstrated by the formal synthesis of 6,7‐secoagroclavine from one of the adducts. DFT calculations suggest that the outcome of the reaction stems from the preferential evolution of a key nitronic acid intermediate through a nucleophilic addition pathway, rather than to the expected “quenching” through protonation. PMID:26486074

  8. The ultraviolet photochemistry of diacetylene - Direct detection of primary products of the metastable C4H2* + C4H2 reaction

    NASA Technical Reports Server (NTRS)

    Bandy, Ralph E.; Lakshminarayan, Chitra; Frost, Rex K.; Zwier, Timothy S.

    1993-01-01

    The products of diacetylene's ultraviolet photochemistry over the 245-220 nm region were directly determined in experiments where C4H2 was excited within a small reaction tube attached to a pulsed nozzle. The products formed in the collisions of C4H2* with C4H2 were subsequently ionized by vacuum UV radiation (at 118 nm) in the ion source of a time-of-flight mass spectrometer. It was found that the reaction of C4H2* with C4H2 produces C6H2 (+C2H2), C8H2 (+2H,H2), and C8H3 (+H), confirming the results of Glicker and Okabe (1987). Under certain conditions, secondary products were observed. Mechanisms for the observed reactions are proposed.

  9. Gravitational Effects on Distortion in Sintering

    NASA Technical Reports Server (NTRS)

    German, Randall M.

    2003-01-01

    During sintering a powder compact gains strength through low-temperature interparticle bonding, usually induced by solid-state surface diffusion, followed by further strength contributions from high-temperature densification. In cases where a liquid phase forms, sintering densification is accelerated and shape retention is sustained while open pores remain and contribute capillary forces. Unfortunately, sintering densification requires the compact become thermally softened to a point where creep strain rates reach levels near 10(exp -2)/s when the liquid forms. On the other hand, thermal softening of the powder compact substantially reduces the strength at high temperatures. Therefore, the in situ strength evolution during sintering is a primary focus to separate compact densification (as required for high performance) with minimized distortion (as required for net-shaping). With respect to gravitation effects on distortion during sintering there are two points of substantial weakness - prior to significant interparticle bonding and during final pore closure. This research is focused on understanding the competition among interparticle neck growth, densification, thermal softening, grain boundary wetting, capillary effects associated with liquid wetting and residual porosity, and gravity. Most surprising is the apparent role of gravity, where the deviatoric stress acting on the powder structure induces skeletal formation that reduces distortion. In contrast with theory, microgravity samples exhibit more distortion yet fail to fully densify. Results are presented on the experimental concepts supporting an emerging model of sintering strength evolution that enables understanding of both distortion and densification. The experiments have relied on tungsten heavy alloys, various combinations of dihedral angle, pore size, initial porosity, liquid:solid ratio, and heating rates. On Earth, the dominant factor with respect to distortion is the starting body heterogeneity

  10. Vacuum-sintered body of a novel apatite for artificial bone

    NASA Astrophysics Data System (ADS)

    Tamura, Kenichi; Fujita, Tatsushi; Morisaki, Yuriko

    2013-12-01

    We produced regenerative artificial bone material and bone parts using vacuum-sintered bodies of a novel apatite called "Titanium medical apatite (TMA®)" for biomedical applications. TMA was formed by chemically connecting a Ti oxide molecule with the reactive [Ca10(PO4)6] group of Hydroxyapatite (HAp). The TMA powders were kneaded with distilled water, and solid cylinders of compacted TMA were made by compression molding at 10 MPa using a stainless-steel vessel. The TMA compacts were dried and then sintered in vacuum (about 10-3 Pa) or in air using a resistance heating furnace in the temperature range 1073-1773 K. TMA compacts were sintered at temperatures greater than 1073 K, thus resulting in recrystallization. The TMA compact bodies sintered in the range 1273-1773 K were converted into mixtures composed of three crystalline materials: α-TCP (tricalcium phosphate), β-TCP, and Perovskite-CaTiO3. The Perovskite crystals were stable and hard. In vacuum-sintering, the Perovskite crystals were transformed into fibers (approximately 1 µm in diameter × 8 µm in length), and the fiber distribution was uniform in various directions. We refer to the TMA vacuum-sintered bodies as a "reinforced composite material with Perovskite crystal fibers." However, in atmospheric sintering, the Perovskite crystals were of various sizes and were irregularly distributed as a result of the effect of oxygen. After sintering temperature at 1573 K, the following results were obtained: the obtained TMA vacuum-sintered bodies (1) were white, (2) had a density of approximately 2300 kg/m3 (corresponding to that of a compact bone or a tooth), and had a thermal conductivity of approximately 31.3 W/(m·K) (corresponding to those of metal or ceramic implants). Further, it was possible to cut the TMA bodies into various forms with a cutting machine. An implant made of TMA and inserted into a rabbit jaw bone was covered by new bone tissues after just one month because of the high

  11. Generation of single-stranded DNA by the polymerase chain reaction and its application to direct sequencing of the HLA-DQA locus.

    PubMed Central

    Gyllensten, U B; Erlich, H A

    1988-01-01

    Single-copy sequences can be enzymatically amplified from genomic DNA by the polymerase chain reaction. By using unequal molar amounts of the two amplification primers, it is possible in a single step to amplify a single-copy gene and produce an excess of single-stranded DNA of a chosen strand for direct sequencing or for use as a hybridization probe. Further, individual alleles in a heterozygote can be sequenced directly by using allele-specific oligonucleotides either in the amplification reaction or as sequencing primers. By using these methods, we have studied the allelic diversity at the HLA-DQA locus and its association with the serologically defined HLA-DR and -DQ types. This analysis has revealed a total of eight alleles and three additional haplotypes. This procedure has wide applications in screening for mutations in human genes and facilitates the linking of enzymatic amplification of genes to automated sequencing. Images PMID:3174659

  12. Optimisation of the derivatisation reaction and subsequent headspace solid-phase microextraction method for the direct determination of chlorophenols in red wine.

    PubMed

    Martínez-Uruñuela, Almudena; González-Sáiz, José María; Pizarro, Consuelo

    2004-09-10

    An acetylation reaction for the derivatisation of the three chlorophenols involved in cork taint was optimised using a Doehlert design for direct application in wine samples. In this first step, the optimum reaction pH, by adding different amounts of KHCO3, and the required quantity of derivatisation reagent were fixed. Then a series of parameters relevant for the headspace solid-phase microextraction process, such as desorption conditions, salt addition and agitation sample were evaluated. A simultaneous study of the type of fibre and extraction temperature was performed at five levels and based on the results obtained the rest of factors (sample volume and exposition time) that could potentially affect the extraction yields were optimised by a central composite design. According to the validation of the method, we propose here, to our knowledge, the first application of solid-phase microextraction for the direct analysis of chlorophenols in red wine samples. PMID:15481251

  13. Direct Total Cross Section Measurement of the 16O(α,γ)20Ne Reaction at Ec.m. = 2.26 MeV

    SciTech Connect

    Hager, Ulrike; Brown, James R.; Buchmann, Lothar R.; Carmona-Gallardo, Mariano; Erikson, Luke E.; Fallis, Jennifer S.; Greife, Uwe; Hutcheon, Dave; Ottewell, Dave; Ruiz, Chris; Sjue, Sky; Vockenhuber, Cristof

    2011-08-23

    In stellar helium burning, (16)O represents the endpoint of the helium-burning sequence due to the low rate of (16)O(alpha,gamma)(20)Ne. We present a new direct measurement of the total capture reaction rate of (16)O(alpha,gamma)(20)Ne at E(c.m.) = 2.26MeV employing the DRAGON recoil separator. For the first time, the total S factor and its contributing direct capture transitions could be determined in one experiment.

  14. A highly efficient solvent-free asymmetric direct aldol reaction organocatalyzed by recoverable (S)-binam-L-prolinamides. ESI-MS evidence of the enamine-iminium formation.

    PubMed

    Guillena, Gabriela; Hita, Maria del Carmen; Nájera, Carmen; Viózquez, Santiago F

    2008-08-01

    Recoverable (S(a))-binam-L-prolinamide in combination with benzoic acid is used as catalysts in the direct aldol reaction between cycloalkyl, alkyl, and alpha-functionalized ketones and aldehydes under solvent-free reaction conditions. Three different methods are assayed: simple conventional magnetic stirring, magnetic stirring after previous dissolution in THF and evaporation, and ball mill technique. These procedures allow one to reduce not only the amount of required ketone to 2 equiv but also the reaction time to give the aldol products with regio-, diastereo-, and enantioselectivities comparable to those in organic or aqueous solvents. Generally anti-isomers are mainly obtained with enantioselectivities up to 97%. The reaction can be carried out under these conditions also using aldehydes as nucleophiles, yielding after in situ reduction of the aldol products the corresponding chiral 1,3-diols with moderate to high enantioselectivities mainly as anti-isomers. The aldol reaction has been studied by the use of positive ESI-MS technique, providing the evidence of the formation of the corresponding enamine-iminium intermediates. PMID:18598088

  15. Plasma-Activated Sintering of Aluminum Nitride

    NASA Astrophysics Data System (ADS)

    Hensley, J. E.; Risbud, S. H.; Groza, J. R.; Yamazaki, K.

    1993-10-01

    The use of a new plasma- activated sintering (PAS) process to densify aluminum nitride (AIN) powders to nearly full theoretical density (97 to >99%) in 5 to 10 min was investigated. The process consists of a pulse activation step, followed by sintering at 1730 to 1800 °C using resistance heating in carbon dies. Submicron size (~0.44 μm) AIN powders of low oxygen content (<1 wt%) were consolidated to near full density in both air and vacuum with no sintering aids or binders. Transmission electron microscopy (TEM) examination revealed an equiaxed, submicron grain structure (~0.77 μm) with no apparent pores or intergranular phases. X- ray powder diffraction revealed no secondary crystalline phases.

  16. Spark Plasma Sintering of Titanium Spherical Particles

    NASA Astrophysics Data System (ADS)

    Abedi, Mohammad; Moskovskikh, Dmitry O.; Rogachev, Alexander S.; Mukasyan, Alexander S.

    2016-07-01

    The densification kinetics for sintering of titanium spherical particles under two different experimental schemes, i.e., current-assisted and current-insulated were investigated. It was shown that measurable densification rate differences between the two schemes are recognized only for the preheating stage. For current-assisted experiments, consolidation starts at lower temperatures than for current-insulated samples. Also at high heating rates, the change of sample porosity all through the preheating stage is higher for current-assisted conditions, while at relatively low heating rates (i.e., less than 100 K/min) they are comparable. All through the isothermal sintering stage, at a temperature of 1073 K (800 °C), the shrinkage rates are comparable for both experimental schemes within the measurement accuracy. The explanation of the observed effects within the framework of conventional sintering theory is also provided.

  17. Direct Catalytic Asymmetric Mannich Reaction with Dithiomalonates as Excellent Mannich Donors: Organocatalytic Synthesis of (R)-Sitagliptin.

    PubMed

    Bae, Han Yong; Kim, Mun Jong; Sim, Jae Hun; Song, Choong Eui

    2016-08-26

    In this study, dithiomalonates (DTMs) were demonstrated to be exceptionally efficient Mannich donors in terms of reactivity and stereoselectivity in cinchona-based-squaramide-catalyzed enantioselective Mannich reactions of diverse imines or α-amidosulfones as imine surrogates. Owing to the superior reactivity of DTMs as compared to conventional malonates, the catalyst loading could be reduced to 0.1 mol % without the erosion of enantioselectivity (up to 99 % ee). Furthermore, by the use of a DTM, even some highly challenging primary alkyl α-amidosulfones were smoothly converted into the desired adducts with excellent enantioselectivity (up to 97 % ee), whereas the use of a malonate or monothiomalonate resulted in no reaction under identical conditions. The synthetic utility of the chiral Mannich adducts obtained from primary alkyl substrates was highlighted by the organocatalytic, coupling-reagent-free synthesis of the antidiabetic drug (-)-(R)-sitagliptin. PMID:27486059

  18. Mechanical properties of hydroxyapatite-zirconia compacts sintered by two different sintering methods.

    PubMed

    Curran, Declan J; Fleming, Thomas J; Towler, Mark R; Hampshire, Stuart

    2010-04-01

    Microwave sintering is traditionally employed to reduce the sintering temperature required to densify powder compacts. The effect of microwave heating on hydroxyapatite (HA)-zirconia (ZrO2) green bodies has been investigated in order to understand how microwave energy may affect the physical and mechanical properties of the resultant densified composites. Laboratory synthesised nano-sized HA and a commercial nano-sized ZrO2 powder have been ball milled to create mixtures containing 0-5 wt% ZrO2 loadings. Compacts were microwave sintered at either 700, 1000 or 1200 degrees C with a 1 h hold time. Comparative firings were also performed in a resistive element furnace using the same heating profile in order to assess the differences between conventional and microwave heating on the physical, mechanical and microstructural properties of the composites. Samples sintered at 700 degrees C show little sign of densification with open porosities of approximately 50%. Composites conventionally sintered at 1000 degrees C were between 65 and 75% dense, whereas the samples microwave sintered at this temperature were between 55 and 65% dense. Samples sintered at 1200 degreesbC showed the greatest degree of densification (>80%) with a corresponding reduction in open porosities. TCP generation occurred as a consequence of sintering at 1200 degrees C, even with 0 wt% ZrO2, and increased degradation of the HA phase to form significant amounts of TCP occurred with increasing additions of ZrO2, along with increasing open porosity. Nanosized ZrO2 prevents the densification of the HA matrix by effectively pinning grain boundaries and this effect is more pronounced in the MS materials. Similar strengths are achieved between the microwave and conventionally sintered samples. Greater amount of open porosity and pore interconnectivity are seen in the MS samples, which are considered to be useful for biomedical applications as they can promote osteo-integration. PMID:20037773

  19. Microwave sintering of large alumina bodies

    SciTech Connect

    Blake, R.D.; Katz, J.D.

    1993-05-01

    The application of microwaves as an energy source for materials processing of large alumina bodies at elevated temperatures has been limited to date. Most work has concerned itself with small laboratory samples. The nonuniformity of the microwave field within a cavity subjects large alumina bodies to areas of concentrated energy, resulting in uneven heating and subsequent cracking. Smaller bodies are not significantly affected by field nonuniformity due to their smaller mass. This work will demonstrate a method for microwave sintering of large alumina bodies while maintaining their structural integrity. Several alumina configurations were successfully sintered using a method which creates an artificial field or environment within the microwave cavity.

  20. Microwave sintering of large alumina bodies

    SciTech Connect

    Blake, R.D.; Katz, J.D.

    1993-01-01

    The application of microwaves as an energy source for materials processing of large alumina bodies at elevated temperatures has been limited to date. Most work has concerned itself with small laboratory samples. The nonuniformity of the microwave field within a cavity subjects large alumina bodies to areas of concentrated energy, resulting in uneven heating and subsequent cracking. Smaller bodies are not significantly affected by field nonuniformity due to their smaller mass. This work will demonstrate a method for microwave sintering of large alumina bodies while maintaining their structural integrity. Several alumina configurations were successfully sintered using a method which creates an artificial field or environment within the microwave cavity.

  1. Process for microwave sintering boron carbide

    DOEpatents

    Holcombe, Cressie E.; Morrow, Marvin S.

    1993-01-01

    A method of microwave sintering boron carbide comprises leaching boron carbide powder with an aqueous solution of nitric acid to form a leached boron carbide powder. The leached boron carbide powder is coated with a glassy carbon precursor to form a coated boron carbide powder. The coated boron carbide powder is consolidated in an enclosure of boron nitride particles coated with a layer of glassy carbon within a container for microwave heating to form an enclosed coated boron carbide powder. The enclosed coated boron carbide powder is sintered within the container for microwave heating with microwave energy.

  2. Process for microwave sintering boron carbide

    DOEpatents

    Holcombe, C.E.; Morrow, M.S.

    1993-10-12

    A method of microwave sintering boron carbide comprises leaching boron carbide powder with an aqueous solution of nitric acid to form a leached boron carbide powder. The leached boron carbide powder is coated with a glassy carbon precursor to form a coated boron carbide powder. The coated boron carbide powder is consolidated in an enclosure of boron nitride particles coated with a layer of glassy carbon within a container for microwave heating to form an enclosed coated boron carbide powder. The enclosed coated boron carbide powder is sintered within the container for microwave heating with microwave energy.

  3. Directional errors of movements and their correction in a discrete tracking task. [pilot reaction time and sensorimotor performance

    NASA Technical Reports Server (NTRS)

    Jaeger, R. J.; Agarwal, G. C.; Gottlieb, G. L.

    1978-01-01

    Subjects can correct their own errors of movement more quickly than they can react to external stimuli by using three general categories of feedback: (1) knowledge of results, primarily visually mediated; (2) proprioceptive or kinaesthetic such as from muscle spindles and joint receptors, and (3) corollary discharge or efference copy within the central nervous system. The effects of these feedbacks on simple reaction time, choice reaction time, and error correction time were studied in four normal human subjects. The movement used was plantarflexion and dorsiflexion of the ankle joint. The feedback loops were modified, by changing the sign of the visual display to alter the subject's perception of results, and by applying vibration at 100 Hz simultaneously to both the agonist and antagonist muscles of the ankle joint. The central processing was interfered with when the subjects were given moderate doses of alcohol (blood alcohol concentration levels of up to 0.07%). Vibration and alcohol increase both the simple and choice reaction times but not the error correction time.

  4. New sintering process adjusts magnetic value of ferrite cores

    NASA Technical Reports Server (NTRS)

    Vinal, A. W.

    1964-01-01

    A two-phase sintering technique based on time and temperature permits reversible control of the coercive threshold of sintered ferrite cores. Threshold coercivity may be controlled over a substantial range of values by selective control of the cooling rate.

  5. Study of Softening and Melting Behaviour of Iron Ore Sinter and Pellets

    NASA Astrophysics Data System (ADS)

    Shatokha, Volodymyr; Velychko, Olexandr

    2012-06-01

    Softening and melting behaviour of the iron ore materials was studied towards understanding the mechanism of formation of liquid slag and metal phases in the pre-reduced sinter and pellets. Wide range of the sinter and pellets samples was investigated revealing the effect of gangue amount and composition on temperature indices corresponding to gas permeability loss in the bed (T1) and to the largest portion of liquid products dripping (T2). For both sinter and pellets, the growth of bacisity is followed by T1 increase which is explained by raised temperature of primary liquid phase appearance during the heating-reduction treatment. Relationship of T2 with the bacisity corresponds to the basicity effect on slag liquidus temperature. Both slag and metal phases were only partially evacuated from the crucible with essential portions of both phases captured in the coke bed. Growing divergence of the basicities of effluent slag and of slag captured in crucible was observed with the increase of sinter basicity. Increased share of the effluent metal with the sinter bacisity growth is explained by the decreased adhesion of slag to iron surface which assists carburization. Growth of melt-down temperature with the increase of gangue amount is explained by less active carburization owing to larger quantity of slag minimising direct contact of sponge with carbonaceous materials.

  6. Synthesis of BaTiO[subscript 3]-20wt%CoFe[subscript 2]O[subscript 4] Nanocomposites via Spark Plasma Sintering

    SciTech Connect

    Ghosh, Dipankar; Han, Hyuksu; Nino, Juan C.; Subhash, Ghatu; Jones, Jacob L.

    2012-10-23

    Barium titanate-20wt% cobalt ferrite (BaTiO{sub 3}-20wt%CoFe{sub 2}O{sub 4}) nanocomposites were sintered from nanocrystalline BaTiO{sub 3} and CoFe{sub 2}O{sub 4} powders using spark plasma sintering (SPS) and pressureless sintering (PS) techniques. Using SPS, dense polycrystalline composites were obtained at a sintering temperature as low as 860 C and a time of 5 min whereas PS required a higher sintering temperature (1150 C) and time (120 min) to obtain similarly dense composites. Microstructural analysis of the composites showed that both the techniques retained nanocrystalline grain sizes after sintering. High resolution X-ray diffraction measurements revealed that the BaTiO{sub 3}-20wt%CoFe{sub 2}O{sub 4} composites sintered by the SPS technique did not exhibit formation of any new phase(s) due to reaction between the BaTiO{sub 3} and CoFe{sub 2}O{sub 4} phases during sintering. However, the PS technique resulted in the formation of additional phases (other than the BaTiO{sub 3} and CoFe{sub 2}O{sub 4} phases) in the composites. While the composites synthesized by SPS were of superior phase-purity, evidence of Fe diffusion from the spinel to the perovskite phase was found from X-ray diffraction and permittivity measurements.

  7. The effect of electric field intensification at interparticle contacts in microwave sintering

    PubMed Central

    Qiao, Xiuchen; Xie, Xiaoying

    2016-01-01

    The nature of microwave sintering cannot be explained in the past and has been generally called microwave effect. Here we show that the E-field intensification is the reason of microwave fast sintering of solid state inorganic compounds. The intensification degree varied with dielectric constant of compound, distance between two particles, angle between the direction of E-field and the normal to the surface at the adjacent point of two spheres. Ultra-high temperature caused by E-field intensification leads to fusing of solid materials at contact zone and enhances the mass transportation. The key to develop a microwave energy-saved sintering method is to control the distance between particles and uniformity of particles instead of the particle size. PMID:27586521

  8. Multi-Scale Modeling of Liquid Phase Sintering Affected by Gravity: Preliminary Analysis

    NASA Technical Reports Server (NTRS)

    Olevsky, Eugene; German, Randall M.

    2012-01-01

    A multi-scale simulation concept taking into account impact of gravity on liquid phase sintering is described. The gravity influence can be included at both the micro- and macro-scales. At the micro-scale, the diffusion mass-transport is directionally modified in the framework of kinetic Monte-Carlo simulations to include the impact of gravity. The micro-scale simulations can provide the values of the constitutive parameters for macroscopic sintering simulations. At the macro-scale, we are attempting to embed a continuum model of sintering into a finite-element framework that includes the gravity forces and substrate friction. If successful, the finite elements analysis will enable predictions relevant to space-based processing, including size and shape and property predictions. Model experiments are underway to support the models via extraction of viscosity moduli versus composition, particle size, heating rate, temperature and time.

  9. The effect of electric field intensification at interparticle contacts in microwave sintering.

    PubMed

    Qiao, Xiuchen; Xie, Xiaoying

    2016-01-01

    The nature of microwave sintering cannot be explained in the past and has been generally called microwave effect. Here we show that the E-field intensification is the reason of microwave fast sintering of solid state inorganic compounds. The intensification degree varied with dielectric constant of compound, distance between two particles, angle between the direction of E-field and the normal to the surface at the adjacent point of two spheres. Ultra-high temperature caused by E-field intensification leads to fusing of solid materials at contact zone and enhances the mass transportation. The key to develop a microwave energy-saved sintering method is to control the distance between particles and uniformity of particles instead of the particle size. PMID:27586521

  10. Mechanism for the Direct Synthesis of H2O2 on Pd Clusters: Heterolytic Reaction Pathways at the Liquid-Solid Interface.

    PubMed

    Wilson, Neil M; Flaherty, David W

    2016-01-20

    Direct synthesis (H2 + O2 → H2O2) is a promising reaction for producing H2O2, which can replace chlorinated oxidants in industrial processes. The mechanism of this reaction and the reasons for the importance of seemingly unrelated factors (e.g., Pd cluster size and solvent pH) remain unclear despite significant research. We propose a mechanism for H2O2 formation on Pd clusters consistent with steady-state H2O2 and H2O formation rates measured as functions of reactant pressures and temperature and the interpretations of proton concentration effects. H2O2 forms by sequential proton-electron transfer to O2 and OOH surface intermediates, whereas H2O forms by O-O bond rupture within OOH surface species. Direct synthesis, therefore, does not proceed by the Langmuir-Hinshelwood mechanism often invoked. Rather, H2O2 forms by heterolytic reaction pathways resembling the two-electron oxygen reduction reaction (ORR); however, the chemical potential of H2 replaces an external electrical potential as the thermodynamic driving force. Activation enthalpies (ΔH(⧧)) for H2O formation increase by 14 kJ mol(-1) when Pd cluster diameters increase from 0.7 to 7 nm because changes in the electronic structure of Pd surface atoms decrease their propensity to cleave O-O bonds. ΔH(⧧) values for H2O2 remain nearly constant because barriers for proton-electron transfer depend weakly on the coordinative saturation of Pd surface atoms. Collectively, these results provide a self-consistent mechanism, which clarifies many studies in which H2O2 rates and selectivities were shown to depend on the concentration of acid/halide additives and Pd cluster size. These findings will guide the rational design of selective catalysts for direct synthesis. PMID:26597848

  11. The kinetics of the O2/CO2 reaction in molten carbonate - Reaction orders for O2 and CO2 on NiO. [in fuel cells

    NASA Technical Reports Server (NTRS)

    Winnick, J.; Ross, P. N.

    1980-01-01

    The kinetics of the O2/CO2 reaction in molten carbonate is investigated using paste electrolytes and nickel sinter electrodes. A two-step approach to the determination of reaction orders is employed. First, exchange currents at various P(CO2) and P(O2) were measured using the low polarization method. Second, alpha(+) and alpha(-) values were obtained from the slope of the Allen-Hickling plot for current densities low enough so that concentration polarization within the electrode can be neglected. The reaction orders are + 1/4 in CO2 and + 5/8 in O2 in the cathodic direction, and - 3/4 in CO2 and + 1/8 in O2 in the anodic direction.

  12. Enhanced Sintering of TiNi Shape Memory Foams under Mg Vapor Atmosphere

    NASA Astrophysics Data System (ADS)

    Aydoğmuş, Tarik; Bor, Şakir

    2012-12-01

    TiNi alloy foams are promising candidates for biomaterials to be used as artificial orthopedic implant materials for bone replacement applications in biomedical sector. However, certain problems exist in their processing routes, such as formation of unwanted secondary intermetallic phases leading to brittleness and deterioration of shape memory and superelasticity characteristics; and the contamination during processing resulting in oxides and carbonitrides which affect mechanical properties negatively. Moreover, the eutectic reaction present in Ti-Ni binary system at 1391 K (1118 °C) prevents employment of higher sintering temperatures (and higher mechanical properties) even when equiatomic prealloyed powders are used because of Ni enrichment of TiNi matrix as a result of oxidation. It is essential to prevent oxidation of TiNi powders during processing for high-temperature (>1391 K i.e., 1118 °C) sintering practices. In the current study, magnesium powders were used as space holder material to produce TiNi foams with the porosities in the range of 40 to 65 pct. It has been found that magnesium prevents secondary phase formation and contamination. It also prevents liquid phase formation while enabling employment of higher sintering temperatures by two-step sintering processing: holding the sample at 1373 K (1100 °C) for 30 minutes, and subsequently sintering at temperatures higher than the eutectic temperature, 1391 K (1118 °C). By this procedure, magnesium may allow sintering up to temperatures close to the melting point of TiNi. TiNi foams produced with porosities in the range of 40 to 55 pct were found to be acceptable as implant materials in the light of their favorable mechanical properties.

  13. Combining direct residence time measurements and biogeochemistry to calculate in-situ reaction rates in the hyporheic zone

    NASA Astrophysics Data System (ADS)

    Pittroff, Marco; Gilfedder, Benjamin

    2015-04-01

    The hyporheic zone is an active interface between groundwater, riparian and surface water systems. Exchange and reaction of water, nutrients, and organic matter occur due to variations in surface and groundwater flow regimes, bed topography and active biogeochemistry fuelled by bioavailable carbon. There has been an increasing focus on coupling the residence time of surface water in the hyporheic zone with biogeochemical reactions. However, there are very few tracers that can be used to measure residence times in-situ, especially in complex groundwater-surface water settings. In this work we have used the natural radioisotope Radon (222Rn) as an in-situ tracer for river water residence time in a riffle-pool sequence (Rote Main River), and combined this information with biogeochemical parameters (DOC and C quality, O3, NO3, CO2). We can clearly observe a dependence of reaction progress on the water residence times, with oxygen and nitrate reduction following inverse logarithmic trends as a function of time. By comparing with initial concentrations (the river end member) with riverbed levels we have estimated first-order in-situ reduction rates for nitrate and oxygen. Nitrate reduction rates are at the higher end of published values, which is likely due to the continual supply of bioavailable carbon from the river system. This work helps to better understand the function and efficiency of the hyporheic zone as a natural filter for redox sensitive species such as nitrate at the groundwater - steam interface. It also provides a useful method for estimating residence times in complex, higher order river systems.

  14. Diagnosis of. alpha. sub 1 -antitrypsin deficiency by enzymatic amplification of human genomic DNA and direct sequencing of polymerase chain reaction products

    SciTech Connect

    Newton, C.R.; Graham, A.; Powell, S.; Gammack, A.; Riley, J.; Markham, A.F. ); Kalsheker, N. )

    1988-09-12

    The authors have compared sequencing of cloned polymerase chain reaction (PCR) products and the direct sequencing of PCR products in the examination of individuals from six families affected with {alpha}{sub 1}-antitrypsin (AAT) deficiency. In families where paternity was in question they confirmed consanguinity by DNA fingerprinting using a panel of locus-specific minisatellite probes. They demonstrate that direct sequencing of PCR amplification products is the method of choice for the absolutely specific diagnosis of AAT deficiency and can distinguish normals, heterozygotes and homozygotes in a single, rapid and facile assay. Furthermore, they demonstrate the reproducibility of the PCR and a rapid DNA isolation procedure. They have also shown that two loci can be simultaneously amplified and that the PCR product from each locus can be independently examined by direct DNA sequencing.

  15. Direct monitoring of photo-induced reactions on well-defined metal oxide surfaces using vibrational spectroscopy

    NASA Astrophysics Data System (ADS)

    Rohmann, Christoph; Wang, Yuemin; Muhler, Martin; Metson, James; Idriss, Hicham; Wöll, Christof

    2008-07-01

    Reflection-absorption infra red spectroscopy (RAIRS) has been successfully used to study a prototype photochemical reaction: the photooxidation of CO over rutile TiO 2(1 1 0) single crystal surfaces. RAIRS-results revealed the presence of irreversibly adsorbed CO on top of the five fold coordinated surface Ti atoms with a vibration frequency of 2190 cm -1 at 110 K. Because fundamental problems have so far prohibited the detection of CO on metal oxide single crystals with IR-spectroscopy (in contrast to the situation for powders), high resolution electron energy loss spectroscopy (HREELS) was also employed for further confirmation.

  16. Importance of elastic scattering to particle direction determination in Monte Carlo calculations of DT reactions in flight

    SciTech Connect

    Devaney, J.J.

    1982-04-01

    The importance of single, large-angle, nuclear-coulombic, nuclear-hadronic, hadronic-coulombic interference, and multiple nuclear-coulombic scattering is investigated for tritons incident on deuterium, iron, and plutonium for very high temperatures and densities and for ordinary liquid and solid densities at low temperature. Depending on the accuracy desired, we conclude that for 10-keV-temperature DT plasmas it is not necessary to include elastic scattering deflection in reaction-in-flight calculations. For higher temperatures or where angular accuracies greater than 10/sup 0/ are significant or for higher Z targets or for other special circumstances, one must include elastic scattering from coulomb forces.

  17. Direct Synthesis of Palladium Catalyst on Supporting WS2 Nanotubes and its Reactivity in Cross-Coupling Reactions.

    PubMed

    Višić, Bojana; Cohen, Hagai; Popovitz-Biro, Ronit; Tenne, Reshef; Sokolov, Viacheslav I; Abramova, Natalya V; Buyanovskaya, Anastasiya G; Dzvonkovskii, Sergei L; Lependina, Olga L

    2015-10-01

    Palladium nanoparticles were deposited on multiwall WS2 nanotubes. The composite nanoparticles were characterized by a variety of techniques. The Pd nanoparticles were deposited uniformly on the surface of WS2 nanotubes. An epitaxial relationship between the (111) plane of Pd and the (013) plane of WS2 was mostly observed. The composite nanoparticles were found to perform efficiently as catalysts for cross-coupling (Heck and Suzuki) reactions. The role of the nanotubes' support in the catalytic process is briefly discussed. PMID:26097214

  18. Sintering analysis of sub-micron-sized nickel powders: Kinetic Monte Carlo simulation verified by FIB-SEM reconstruction

    NASA Astrophysics Data System (ADS)

    Hara, Shotaro; Ohi, Akihiro; Shikazono, Naoki

    2015-02-01

    Since sintering of sub-micron-sized particles is a critical phenomenon affecting the electrochemical performance and reliability of solid oxide fuel cell systems, a better understanding of this microstructure-related process is of great importance. In this study, we show that kinetic Potts Monte Carlo modeling is capable of quantitatively predicting the three-dimensional (3D) microstructure evolution over an entire stage of nickel sintering at the sub-micron scale. This is achieved through direct comparison of simulation results and 3D microstructural analysis using focused ion beam-scanning electron microscopy. We show that grain boundary diffusion is the dominant mechanism on densification, while surface diffusion has an impact on the coarsening during sub-micron scale sintering, only acting as one of the multiple mechanisms of sintering.

  19. Microwave sintering of single plate-shaped articles

    DOEpatents

    Katz, Joel D.; Blake, Rodger D.

    1995-01-01

    Apparatus and method for high temperature sintering of plate-shaped articles of alumina, magnesia, silica, yttria, zirconia, and mixtures thereof using microwave radiation. An article is placed within a sintering structure located within a sintering container which is placed in a microwave cavity for heating. The rates at which heating and cooling take place is controlled.

  20. Microwave sintering of single plate-shaped articles

    DOEpatents

    Katz, J.D.; Blake, R.D.

    1995-07-11

    Apparatus and method are disclosed for high temperature sintering of plate-shaped articles of alumina, magnesia, silica, yttria, zirconia, and mixtures thereof using microwave radiation. An article is placed within a sintering structure located within a sintering container which is placed in a microwave cavity for heating. The rates at which heating and cooling take place is controlled. 2 figs.

  1. Microwave sintering of Yb:YAG transparent laser ceramics

    NASA Astrophysics Data System (ADS)

    Esposito, Laura; Piancastelli, Andreana; Bykov, Yury; Egorov, Sergei; Eremeev, Anatolii

    2013-02-01

    Reactive sintering of YAG based ceramics is generally performed under high vacuum in graphite-free furnaces in order to guarantee the elimination of pores and absence of any contamination. An alternative densification technique is the field assisted process such as spark plasma sintering and microwave sintering. Both of these methods are characterized by very fast heating rates, low sintering temperatures and short sintering times. The microwave sintering process is different from electric resistance heating since heat is generated in the bulk of the powder compact through electromagnetic radiation absorption and creates within its body uniform temperature distribution. Microwave sintering of laser ceramics is advantageously distinguished by the absence of any elements having high temperature such as electric heaters or dies which materials can contaminate the sintered parts. In addition, the inverse temperature distribution that exists within the body under volumetric microwave heating is favorable for elimination of porosity. Microwave sintering of Yb:YAG samples were tested and the obtained results are presented. The samples were sintered on a gyrotron-based system operating at a frequency of 24 GHz with microwave power up to 6 kW. Reactive sintering of YAG doped with 1.0, 5.0, and 9.8 at.% Yb2O3 was performed in different temperature-time regimes. The microstructure and the optical transmittance of the obtained samples were compared to those of samples obtained by conventional high vacuum sintering.

  2. First Direct Measurement of the O17(p,γ)F18 Reaction Cross Section at Gamow Energies for Classical Novae

    NASA Astrophysics Data System (ADS)

    Scott, D. A.; Caciolli, A.; Di Leva, A.; Formicola, A.; Aliotta, M.; Anders, M.; Bemmerer, D.; Broggini, C.; Campeggio, M.; Corvisiero, P.; Elekes, Z.; Fülöp, Zs.; Gervino, G.; Guglielmetti, A.; Gustavino, C.; Gyürky, Gy.; Imbriani, G.; Junker, M.; Laubenstein, M.; Menegazzo, R.; Marta, M.; Napolitani, E.; Prati, P.; Rigato, V.; Roca, V.; Somorjai, E.; Salvo, C.; Straniero, O.; Strieder, F.; Szücs, T.; Terrasi, F.; Trezzi, D.

    2012-11-01

    Classical novae are important contributors to the abundances of key isotopes, such as the radioactive F18, whose observation by satellite missions could provide constraints on nucleosynthesis models in novae. The O17(p,γ)F18 reaction plays a critical role in the synthesis of both oxygen and fluorine isotopes, but its reaction rate is not well determined because of the lack of experimental data at energies relevant to novae explosions. In this study, the reaction cross section has been measured directly for the first time in a wide energy range Ec.m.≃200-370keV appropriate to hydrogen burning in classical novae. In addition, the Ec.m.=183keV resonance strength, ωγ=1.67±0.12μeV, has been measured with the highest precision to date. The uncertainty on the O17(p,γ)F18 reaction rate has been reduced by a factor of 4, thus leading to firmer constraints on accurate models of novae nucleosynthesis.

  3. First direct measurement of the 17O(p,γ)18F reaction cross section at Gamow energies for classical novae.

    PubMed

    Scott, D A; Caciolli, A; Di Leva, A; Formicola, A; Aliotta, M; Anders, M; Bemmerer, D; Broggini, C; Campeggio, M; Corvisiero, P; Elekes, Z; Fülöp, Zs; Gervino, G; Guglielmetti, A; Gustavino, C; Gyürky, Gy; Imbriani, G; Junker, M; Laubenstein, M; Menegazzo, R; Marta, M; Napolitani, E; Prati, P; Rigato, V; Roca, V; Somorjai, E; Salvo, C; Straniero, O; Strieder, F; Szücs, T; Terrasi, F; Trezzi, D

    2012-11-16

    Classical novae are important contributors to the abundances of key isotopes, such as the radioactive (18)F, whose observation by satellite missions could provide constraints on nucleosynthesis models in novae. The (17)O(p,γ)(18)F reaction plays a critical role in the synthesis of both oxygen and fluorine isotopes, but its reaction rate is not well determined because of the lack of experimental data at energies relevant to novae explosions. In this study, the reaction cross section has been measured directly for the first time in a wide energy range E(c.m.)~/= 200-370 keV appropriate to hydrogen burning in classical novae. In addition, the E(c.m.)=183 keV resonance strength, ωγ=1.67±0.12 μeV, has been measured with the highest precision to date. The uncertainty on the (17)O(p,γ)(18)F reaction rate has been reduced by a factor of 4, thus leading to firmer constraints on accurate models of novae nucleosynthesis. PMID:23215474

  4. Ultrasonic and dielectric characterization of microwave-sintered and conventionally sintered zinc oxide

    SciTech Connect

    Martin, L.P.; Dadon, D.; Rosen, M.; Gershon, D.; Birman, A.; Levush, B.; Carmel, Y.

    1996-10-01

    Zinc oxide samples were prepared by microwave- and conventional-sintering processes using identical time-temperature profiles. Comparison of postsintering properties as a function of residual porosity over the range of 0%--35% indicated no significant difference in the ultrasonic velocity-porosity relations or the elastic moduli for the samples prepared by the two techniques. The real and imaginary parts of the permittivity of the samples processed by the two techniques were measured over a wide frequency range. In both cases, there was an increase in the measured permittivity values with decreasing porosity; however, the microwave-sintered samples had considerably higher values. Porosity levels were evaluated using bulk density measurements and scanning electron microscopy analysis. Significantly more densification was observed at intermediate temperatures for microwave sintering than for conventional sintering.

  5. Sintering behavior of Lanthana-bearing nanostructured ferritic steel consolidated via spark plasma sintering

    DOE PAGESBeta

    Pasebani, Somayeh; Charit, Indrajit; Butt, Darryl P.; Cole, James I.; Wu, Yaqiao; Burns, Jatuporn

    2015-08-03

    Elemental powder mixture of Fe–14Cr–1Ti–0.3Mo–0.5La2O3 (wt%) composition is mechanically alloyed for different milling durations (5, 10 and 20 h) and subsequently consolidated via spark plasma sintering under vacuum at 950 °C for 7 min. The effects of milling time on the densification behavior and density/microhardness are studied. The sintering activation energy is found to be close to that of grain boundary diffusion. The bimodal grain structure created in the milled and sintered material is found to be a result of milling and not of sintering alone. The oxide particle diameter varies between 2 and 70 nm. As a result, facetedmore » precipitates smaller than 10 nm in diameter are found to be mostly La–Ti–Cr-enriched complex oxides that restrict further recrystallization and related phenomena.« less

  6. Mechanism of sintering and fracture of superfluxed iron-ore sinters

    NASA Astrophysics Data System (ADS)

    Malysheva, T. Ya.; Gibadulin, M. F.; Mansurova, N. R.; Lekin, V. P.

    2007-06-01

    Mineral formation in the binders of a commercial sinter with a basicity of 1.6 at the Magnitogorsk Metallurgical Integrated Works has been found to be determined by the crystallization of two morphological forms of high-iron aluminosilicoferrite (namely, dendritic and lamellar forms) from the melt. In a sintering zone, an association of dendritic aluminosilicoferrite crystals and dicalcium silicate Ca2SiO4 forms in high-calcium melt regions separated from magnetite grains. This association leads to the fracture of the finished product as a result of the phase transformation of Ca2SiO4 from the β into the γ modification during sinter cooling. Lamellar aluminosilicoferrites forming in high-iron sinter volumes serve as a high-strength binder for ore grains.

  7. Sintering behavior of Lanthana-bearing nanostructured ferritic steel consolidated via spark plasma sintering

    SciTech Connect

    Pasebani, Somayeh; Charit, Indrajit; Butt, Darryl P.; Cole, James I.; Wu, Yaqiao; Burns, Jatuporn

    2015-08-03

    Elemental powder mixture of Fe–14Cr–1Ti–0.3Mo–0.5La2O3 (wt%) composition is mechanically alloyed for different milling durations (5, 10 and 20 h) and subsequently consolidated via spark plasma sintering under vacuum at 950 °C for 7 min. The effects of milling time on the densification behavior and density/microhardness are studied. The sintering activation energy is found to be close to that of grain boundary diffusion. The bimodal grain structure created in the milled and sintered material is found to be a result of milling and not of sintering alone. The oxide particle diameter varies between 2 and 70 nm. As a result, faceted precipitates smaller than 10 nm in diameter are found to be mostly La–Ti–Cr-enriched complex oxides that restrict further recrystallization and related phenomena.

  8. Synthesis of PtRu nanoparticles from the hydrosilylation reaction and application as catalyst for direct methanol fuel cell.

    PubMed

    Huang, Junchao; Liu, Zhaolin; He, Chaobin; Gan, Leong Ming

    2005-09-01

    Nanosized Pt, PtRu, and Ru particles were prepared by a novel process, the hydrosilylation reaction. The hydrosilylation reaction is an effective method of preparation not only for Pt particles but also for other metal colloids, such as Ru. Vulcan XC-72 was selected as catalyst support for Pt, PtRu, and Ru colloids, and TEM investigations showed nanoscale particles and narrow size distribution for both supported and unsupported metals. All Pt and Pt-rich catalysts showed the X-ray diffraction pattern of a face-centered cubic (fcc) crystal structure, whereas the Ru and Ru-rich alloys were more typical of a hexagonal close-packed (hcp) structure. As evidenced by XPS, most Pt and Ru atoms in the nanoparticles were zerovalent, except a trace of oxidation-state metals. The electrooxidation of liquid methanol on these catalysts was investigated at room temperature by cyclic voltammetry and chronoamperometry. The results concluded that some alloy catalysts showed higher catalytic activities and better CO tolerance than the Pt-only catalyst; Pt56Ru44/C have displayed the best electrocatalytic performance among all carbon-supported catalysts. PMID:16853117

  9. Multistep sintering to synthesize fast lithium garnets

    NASA Astrophysics Data System (ADS)

    Xu, Biyi; Duan, Huanan; Xia, Wenhao; Guo, Yiping; Kang, Hongmei; Li, Hua; Liu, Hezhou

    2016-01-01

    A multistep sintering schedule is developed to synthesize Li7La3Zr2O12 (LLZO) doped with 0.2 mol% Al3+. The effect of sintering steps on phase, relative density and ionic conductivity of Al-doped LLZO has been evaluated using powder X-Ray diffraction (XRD), scanning electron microscopy (SEM), 27Al magic spinning nuclear magnetic resonance (NMR) spectroscopy and electrochemical impedance spectroscopy (EIS). The results show that by holding the sample at 900 °C for 6 h, the mixture of tetragonal and cubic garnet phases are obtained; by continuously holding at 1100 °C for 6 h, the tetragonal phase completely transforms into cubic phase; by holding at 1200 °C, the relative density increases without decomposition of the cubic phase. The Al-LLZO pellets after multistep sintering exhibit cubic phase, relative density of 94.25% and ionic conductivity of 4.5 × 10-4 S cm-1 at room temperature. Based on the observation, a sintering model is proposed and discussed.

  10. Contact material for pressure-sintering ferrites

    NASA Technical Reports Server (NTRS)

    Wentworth, C.

    1970-01-01

    Pressure-sintering, in which the unfired laminated ferrite plane is placed between two flat punches and pressed during firing, reduces lateral firing shrinkage to less than one percent. A decrease in thickness of the laminate produces the required volume shrinkage. Phlogopite is the most suitable contact material investigated.

  11. Effect of gravity on liquid phase sintering

    NASA Technical Reports Server (NTRS)

    Mookherji, T.; Mcanelly, W. B.; Mckannan, E. C.

    1974-01-01

    The unique conditions offered by the earth orbital environment in material processing involving both solid and liquid phases, such as liquid phase sintering, were studied. An experimental development program involving both test and theoretical work was initiated. Experimental work using material combinations selected such that maximum information about the effect of gravity can be derived has been conducted. Wetting of the solid phase by the liquid during sintering is an important phenomenon in liquid phase sintering, and gravity has influence on both capillary phenomenon and density segregation; hence, material combinations were selected such that these two effects can be suitably studies. The experimental work is meant to form the basis for similar comparative work done under low-g conditions. The part of the model dealing with the capillary phenomenon, as related to liquid phase sintering and the effect of gravity on it, suggest that gravity will have negligible effect on the Bond number and that the cohesive force is dependent on both the amount of liquid phase and the angle of contact.

  12. METHOD FOR PREPARATION OF SINTERABLE BERYLLIUM OXIDE

    DOEpatents

    Sturm, B.J.

    1963-08-13

    High-purity beryllium oxide for nuclear reactor applications can be prepared by precipitation of beryllium oxalate monohydrate from aqueous solution at a temperature above 50 deg C and subsequent calcination of the precipitate. Improved purification with respect to metallic impurities is obtained, and the product beryllium oxide sinters reproducibly to a high density. (AEC)

  13. Sintered diamond compacts using metallic cobalt binders

    NASA Technical Reports Server (NTRS)

    Libby, W. F.; Katzman, H.

    1972-01-01

    Method is developed for sintering diamond powder which uses metallic cobalt as binder. Present samples show maximum microhardness of over 3000 kg/sq mm on Knoop scale. Material may be used as hard surface coating or may compete with cubic boron nitride as abrasive grain.

  14. Sintered electrode for solid oxide fuel cells

    DOEpatents

    Ruka, R.J.; Warner, K.A.

    1999-06-01

    A solid oxide fuel cell fuel electrode is produced by a sintering process. An underlayer is applied to the electrolyte of a solid oxide fuel cell in the form of a slurry, which is then dried. An overlayer is applied to the underlayer and then dried. The dried underlayer and overlayer are then sintered to form a fuel electrode. Both the underlayer and the overlayer comprise a combination of electrode metal such as nickel, and stabilized zirconia such as yttria-stabilized zirconia, with the overlayer comprising a greater percentage of electrode metal. The use of more stabilized zirconia in the underlayer provides good adhesion to the electrolyte of the fuel cell, while the use of more electrode metal in the overlayer provides good electrical conductivity. The sintered fuel electrode is less expensive to produce compared with conventional electrodes made by electrochemical vapor deposition processes. The sintered electrodes exhibit favorable performance characteristics, including good porosity, adhesion, electrical conductivity and freedom from degradation. 4 figs.

  15. Sintering of BaCe(0.85)Y(0.15)O3-(Beta) With/Without SrTiO Dopant

    NASA Technical Reports Server (NTRS)

    Dynys, Fred; Sayir, Ali; Heimann, Paula J.

    2004-01-01

    The sintering behavior of BaCe(0.85)Y(0.15)O3-(Beta) doped with SrTiO is described. Complete reaction and crystallization of perovskite phase by solid state was achieved by calcining at 1200 degrees C for 24 hours.Smaples were sintered at 1450 degrees C, 1550 degrees C, and 1650 degrees C. SrTiOsub3 enhanced sintering, while optimal dopant level was different for powders synthesized by solid state and co-precipitation. Both powders exhibit similar grain growth behavior.

  16. Sintering behavior of Cr in different atmospheres and its effect on the microstructure and properties of copper-based composite materials

    NASA Astrophysics Data System (ADS)

    Wang, Ye; Yan, Qing-zhi; Zhang, Fei-fei; Ge, Chang-chun; Zhang, Xiao-lu; Zhao, Hai-qin

    2013-12-01

    Copper matrix composites consisting of chromium (Cr) or ferrochrome (Cr-Fe) as strengthening elements and molybdenum disulfide as a lubricant had been sintered in nitrogen and hydrogen atmosphere, respectively. Their morphology and energy-dispersive X-ray spectrometry (EDS) analysis showed that serious interaction occurred between MoS2 and Cr (or Cr-Fe) particles when the samples were sintered in hydrogen atmosphere. Chromium sulfide compound (Cr x S y ) was formed as a reaction product, which decreased the density and strength of the composites remarkably. This interaction was inhibited when the samples were sintered in nitrogen atmosphere; thus, the mechanical properties of the composites were improved.

  17. Direct Synthesis of 5-Aryl Barbituric Acids by Rhodium(II)-Catalyzed Reactions of Arenes with Diazo Compounds**

    PubMed Central

    Best, Daniel; Burns, David J; Lam, Hon Wai

    2015-01-01

    A commercially available rhodium(II) complex catalyzes the direct arylation of 5-diazobarbituric acids with arenes, allowing straightforward access to 5-aryl barbituric acids. Free N—H groups are tolerated on the barbituric acid, with no complications arising from N—H insertion processes. This method was applied to the concise synthesis of a potent matrix metalloproteinase (MMP) inhibitor. PMID:25959544

  18. Learning on Their Own: Vocationally Oriented Self-Directed Learning Projects. [and] Invited Reaction: Learning on Their Own.

    ERIC Educational Resources Information Center

    Clardy, Alan; Willis, Verna J.

    2000-01-01

    In Clardy's study, 56 employees described 109 vocationally oriented self-directed learning projects undertaken. Projects were categorized as induced (spurred by imbalance between job expectations and capability), voluntary (fueled by personal motivation), or synergistic (combined motivation with the spark of workplace circumstances). Willis'…

  19. DNA Concentration-Dependent Dissociation of EcoRI: Direct Transfer or Reaction during Hopping

    PubMed Central

    Sidorova, Nina Y.; Scott, Thomas; Rau, Donald C.

    2013-01-01

    Direct transfer of proteins between DNA helices is a recognized important feature of the recognition site search process. Direct transfer is characterized by a dissociation rate that depends on total DNA concentration. This is taken as evidence for the formation of an intermediate DNA-protein-DNA ternary complex. We find that the dissociation rate of EcoRI-DNA-specific complexes at 80 mM NaCl depends on the concentration of competitor oligonucleotide suggesting that direct transfer contributes to EcoRI dissociation. This dependence on competitor DNA concentration is not seen at 180 mM salt. A careful examination of the salt concentration dependence of the dissociation rate, however, shows that the predictions for the formation of a ternary complex are not observed experimentally. The findings can be rationalized by considering that just after dissociating from a DNA fragment the protein remains in close proximity to that fragment, can reassociate with it, and diffuse back to the recognition site rather than bind to an oligonucleotide in solution, a hopping excursion. The probability that a protein will bind to an oligonucleotide during a hop can be approximately calculated and shown to explain the data. A dependence of the dissociation rate of a DNA-protein complex on competitor DNA concentration does not necessarily mean direct transfer. PMID:23528089

  20. Silanones and silanethiones from the reactions of transient silylenes with oxiranes and thiiranes in solution. The direct detection of diphenylsilanethione.

    PubMed

    Kostina, Svetlana S; Leigh, William J

    2011-03-30

    The transient silylenes SiMe(2) and SiPh(2) react with cyclohexene oxide (CHO), propylene oxide (PrO), and propylene sulfide (PrS) in hydrocarbon solvents to form products consistent with the formation of the corresponding transient silanones and silanethiones, respectively. Laser flash photolysis studies show that these reactions proceed via multistep sequences involving the intermediacy of the corresponding silylene-oxirane or -thiirane complexes, which are formed with rate constants close to the diffusion limit in all cases and exhibit UV absorption spectra similar to those of the corresponding complexes with the nonreactive O- and S-donors, tetrahydrofuran and tetrahydrothiophene. The SiMe(2)-PrO and SiPh(2)-PrO complexes both exhibit lifetimes of ca. 300 ns, and are longer-lived than the corresponding complexes with CHO, which are both in the range of 230-240 ns. On the other hand, the silylene-PrS complexes are considerably shorter-lived and vary with silyl substituent; the SiMe(2)-PrS complex decays with the excitation laser pulse (i.e., τ ≤ 25 ns), while the SiPh(2)-PrS complex exhibits τ = 48 ± 3 ns. The decay of the SiPh(2)-PrS complex affords a long-lived transient product exhibiting λ(max) ≈ 275 nm, which has been assigned to diphenylsilanethione (Ph(2)Si═S) on the basis of its second order decay kinetics and absolute rate constants for reaction with methanol, tert-butanol, acetic acid, and n-butyl amine, for which values in the range of 1.4 × 10(8) to 3.2 × 10(9) M(-1) s(-1) are reported. The experimental rate constants for decay of the SiMe(2)-epoxide and -PrS complexes indicate free energy barriers (ΔG(‡)) of ca. 8.5 and ≤7.1 kcal mol(-1) for the rate-determining steps leading to dimethylsilanone and -silanethione, respectively, which are compared to the results of DFT (B3LYP/6-311+G(d,p)) calculations of the reactions of SiH(2) and SiMe(2) with oxirane and thiirane. The calculations predict a stepwise C-O cleavage mechanism

  1. TiO2 doped UO2 fuels sintered by spark plasma sintering

    NASA Astrophysics Data System (ADS)

    Yao, Tiankai; Scott, Spencer M.; Xin, Guoqing; Lian, Jie

    2016-02-01

    UO2 fuels doped with oxide additives Cr2O3 and TiO2 display larger grain size, improving fission product retention capability and thus accident tolerance. Spark plasma sintering (SPS) was applied to consolidate TiO2-doped UO2 fuel pellets with 0.5 wt % dopant concentration, above its solubility, in order to induce eutectic phase formation and promote sintering kinetics. The grain size can reach 80 μm by sintering at 1700 °C for 20 min, and liquid U-Ti-O eutectic phase occurs at the triple junction of grain boundaries and significantly improves grain growth during sintering. The oxide additive also impedes the reduction of the initial hyperstoichiometric fuel powders to more stoichiometric fuel pellets upon SPS process. Thermal-mechanical properties of the sintered doped fuel pellets including thermal conductivity and hardness are measured and compared with undoped fuel pellets. The enlarged grain size (80 μm) and densification within short sintering duration highlight the immense possibility of SPS in fabricating large grained UO2 fuel pellets to improve fuel performance.

  2. Infiltration behavior of sintering liquid on nuclei ores during low-titanium ore sintering process

    NASA Astrophysics Data System (ADS)

    Liu, Dong-hui; Zhang, Jian-liang; Xue, Xun; Wang, Guang-wei; Li, Ke-jiang; Liu, Zheng-jian

    2016-06-01

    Sinter strength is dependent not only on the self-intensity of the residual rude and bonding phase but also on the bonding degree between them. The infiltration behavior of sintering liquid on nuclei ores influences the bonding degree, which ultimately determines the sinter strength. Infiltration tests were conducted using micro-sinter equipment. The infiltration area index of original liquid (IAO), infiltration volume index of secondary liquid (IVS), and sinter body bonding strength (SBS) were proposed to study the melt infiltration behavior. The results show that the IVS first increases and then decreases with increasing TiO2 content in adhering fines, whereas the IAO exhibits the opposite behavior. Compared with the original liquid, the secondary liquid shows lower porosity, smaller pores, and more uniform distribution. The SBS increases first and then decreases with increasing IAO and TiO2 content, and reaches a maximum when the IAO and TiO2 contents are approximately 0.5 and 2.0wt%, respectively. The SBS first increases and then tends to be stable with increasing IVS. The TiO2 content is suggested to be controlled to approximately 2.0wt% in low-titanium ore sintering.

  3. Sintering of Lunar and Simulant Glass

    NASA Technical Reports Server (NTRS)

    Cooper, Bonnie L.

    2007-01-01

    Most oxygen-extraction techniques are temperature-dependent, with higher temperatures resulting in higher oxygen yield. An example is hydrogen reduction, in which the optimum process temperature is 1050 C. However, glass-rich lunar soil begins to show the effects of sintering at temperatures of 900 C or lower. Sintering welds particles together due to viscous relaxation of the glass in the sample. One approach to avoid problems related to sintering, such as difficulty in removing waste material from the reactor, is to keep the soil in motion. One of several methods being studied to accomplish this is fluidized-bed processing techniques, in which the grains are kept in motion by the action of flowing reductant gas. The spent material can be removed from the chamber while still fluidized, or the fluidizing motion can continue until the material has cooled below approx. 500 C. Until end-to-end prototypes are built that can remove the heated soil, the most practical option is to keep the bed fluidized while cooling the waste material. As ISRU technology advances, another option will become valuable, which is to intentionally sinter the material to a great enough extent that it becomes a brick. The free iron in lunar soil is magnetic, and ferromagnetic bricks can be manipulated by robotic systems using electromagnetic end effectors. Finally, if an electromagnetic field is applied to the soil while the brick is being formed, the brick itself will become a magnet. This property can be used to create self-aligning bricks or other building materials that do not require fasteners. Although sintering creates a challenge for early lunar surface systems, knowledge gained during prototype development will be valuable for the advanced lunar outpost.

  4. [Future direction of pharmacogenomics: identification of genes associated with risk of adverse drug reactions using genome-wide association study].

    PubMed

    Mushiroda, Taisei

    2014-01-01

    Drug-induced skin rash characterized by an acute inflammatory reaction of skin and mucous membranes is dose-independent, unpredictable, and sometimes life-threatening. In recent years, the U.S. Food and Drug Administration (FDA) has recommended genotyping of polymorphisms in the human leukocyte antigen (HLA) prior to drug administration for the avoidance of severe skin rash induced by drugs, such as abacavir and carbamazepine. A genome-wide association study (GWAS) is useful for the identification of genomic biomarkers that can predict the efficacy or risk of toxicity of various drugs. We identified novel susceptibility loci associated with the risk of a skin rash induced by nevirapine and carbamazepine in Thai and Japanese populations, respectively, through case-control GWAS with high-throughput single-nucleotide polymorphism (SNP) genotyping technology. In order to apply the genomic biomarkers to clinical therapeutics, prospective clinical trials will be necessary for the evaluation of an intervention based on genetic tests. PMID:24724431

  5. Molecular simulation of AG nanoparticle nucleation from solution: redox-reactions direct the evolution of shape and structure.

    PubMed

    Milek, Theodor; Zahn, Dirk

    2014-08-13

    The association of Ag(+) ions and the early stage of Ag nanoparticle nucleation are investigated from molecular dynamics simulations. Combining special techniques for tackling crystal nucleation from solution with efficient approaches to model redox-reactions, we unravel the structural evolution of forming silver nanoparticles as a function of the redox-potential in the solution. Within a range of only 1 eV, the redox-potential is demonstrated to have a drastic effect on both the inner structure and the overall shape of the forming particles. On the basis of our simulations we identify surface charge and its distribution as an atomic scale mechanism that accounts for creating/avoiding 5-fold coordination polyhedra and thus the degree of (multiple)-twinning in silver nanoparticles. PMID:25078975

  6. Regulating emotions uniquely modifies reaction time, rate of force production, and accuracy of a goal-directed motor action.

    PubMed

    Beatty, Garrett F; Fawver, Bradley; Hancock, Gabriella M; Janelle, Christopher M

    2014-02-01

    We investigated how emotion regulation (ER) strategies influence the execution of a memory guided, ballistic pinch grip. Participants (N=33) employed ER strategies (expressive suppression, emotional expression, and attentional deployment) while viewing emotional stimuli (IAPS images). Upon stimulus offset, participants produced a targeted pinch force aimed at 10% of their maximum voluntary contraction. Performance measures included reaction time (RT), rate of force production, and performance accuracy. As hypothesized, attentional deployment resulted in the slowest RT, largest rate of force production, and poorest performance accuracy. In contrast, expressive suppression reduced the rate of force production and increased performance accuracy relative to emotional expression and attentional deployment. Findings provide evidence that emotion regulation strategies uniquely influence human movement. Future work should further delineate the interacting role that emotion regulation strategies have in modulating both affective experience and motor performance. PMID:24576703

  7. Pressureless sintering of whiskered-toughened ceramic composites

    DOEpatents

    Tiegs, T.N.

    1994-12-27

    A pressureless sintering method is disclosed for use in the production of whisker-toughened ceramic composites wherein the sintered density of composites containing up to about 20 vol. % SiC whiskers is improved by reducing the average aspect ratio of the whiskers to from about 10 to about 20. Sintering aids further improve the density, permitting the production of composites containing 20 vol. % SiC with sintered densities of 94% or better of theoretical density by a pressureless sintering method. 6 figures.

  8. Comparative sinterability of combustion synthesized and commercial titanium carbides

    SciTech Connect

    Manley, B.W.

    1984-11-01

    The influence of various parameters on the sinterability of combustion synthesized titanium carbide was investigaged. Titanium carbide powders, prepared by the combustion synthesis process, were sintered in the temperature range 1150 to 1600/sup 0/C. Incomplete combustion and high oxygen contents were found to be the cause of reduced shrinkage during sintering of the combustion syntheized powders when compared to the shrinkage of commercial TiC. Free carbon was shown to inhibit shrinkage. The activation energy for sintering was found to depend on stoichiometry (C/Ti). With decreasing C/Ti, the rate of sintering increased. 29 references, 16 figures, 13 tables.

  9. Multiple-functional capsule catalysts: a tailor-made confined reaction environment for the direct synthesis of middle isoparaffins from syngas.

    PubMed

    He, Jingjiang; Liu, Zhenlin; Yoneyama, Yoshiharu; Nishiyama, Norikazu; Tsubaki, Noritatsu

    2006-11-01

    A capsule catalyst for isoparaffin synthesis based on Fischer-Tropsch reaction was designed by coating a H-ZSM-5 membrane onto the surface of the pre-shaped Co/SiO(2) pellet. Morphological and chemical analysis showed that the capsule catalyst had a core-shell structure. A compact, integral shell of H-ZSM-5 crystallized firmly on the Co/SiO(2) substrate without crack. Syngas passed through the zeolite membrane to reach the Co/SiO(2) catalyst to be converted, and all hydrocarbons formed with straight chain structure must enter the zeolite channels to undergo hydrocracking as well as isomerization in this tailor-made confined reaction environment. A narrow, anti-Anderson-Schultz-Flory law product distribution was observed on these capsule catalysts. Contrary to a mechanical mixture of H-ZSM-5 and Co/SiO(2), C(10+) hydrocarbons were suppressed completely on this novel capsule catalyst, and the selectivity of middle isoparaffins was considerably improved. The carbon number distribution of the products depended on the thickness of the zeolite membrane, and it was possible to selectively synthesize specified distillates, such as gasoline-range, or heavier hydrocarbons from syngas directly, by simply adjusting the thickness of the zeolite membrane of the capsule catalyst. This kind of capsule catalysts can be extended to various consecutive reaction systems as the shell and core components are independent catalysts for different reactions. At the same time, shape selectivity and space-confined effects can be expected for the reactant, intermediates and product of the sequential reactions. PMID:16850512

  10. Regioselective and Stepwise Syntheses of Functionalized BODIPY Dyes through Palladium-Catalyzed Cross-Coupling Reactions and Direct C-H Arylations.

    PubMed

    Feng, Zeya; Jiao, Lijuan; Feng, Yuanmei; Yu, Changjiang; Chen, Na; Wei, Yun; Mu, Xiaolong; Hao, Erhong

    2016-08-01

    Regioselective and stepwise syntheses of a series of functionalized BODIPY dyes through palladium-catalyzed cross-coupling reactions and direct C-H arylations have been developed. In particular, this method allows the straightforward synthesis of 2,6-dibromo-3,5-diarylBODIPYs and 2-bromo-3-arylBODIPYs from polybrominated BODIPYs. The X-ray structure of intermediates 5a-c indicated that the palladium was first inserted into the C-Br bonds at 3,5-positions of brominated BODIPYs. The resulting 2,6-dibromo-substituted BODIPYs are potential long wavelength photosensitizers which are not easily accessible using previous methods. PMID:27362954

  11. A direct underground measurement of the {sup 17}O(p,α){sup 14}N reaction cross-section at energies of astrophysical interest

    SciTech Connect

    Bruno, C. G.; Collaboration, LUNA

    2014-05-09

    The {sup 17}O(p,α){sup 14}N reaction plays a key role in many stellar sites, including classical novae and massive stars. Our knowledge of these scenarios might be improved by a precise measurement of the reaction’s cross-section at astrophysical energies. A direct attempt is currently underway in the Gran Sasso Laboratory, Italy, using the underground LUNA 400kV accelerator. The background reduction afforded by the underground environment is essential to the success of this challenging measurement. A purpose-built experimental setup has been simulated and commissioned. Preliminary results are presented.

  12. Chiroptical Probing of Lanthanide-Directed Self-Assembly Formation Using btp Ligands Formed in One-Pot Diazo-Transfer/Deprotection Click Reaction from Chiral Amines.

    PubMed

    Byrne, Joseph P; Martínez-Calvo, Miguel; Peacock, Robert D; Gunnlaugsson, Thorfinnur

    2016-01-11

    A series of enantiomeric 2,6-bis(1,2,3-triazol-4-yl)pyridines (btp)-containing ligands was synthesized by a one-pot two-step copper-catalyzed amine/alkyne click reaction. The Eu(III) - and Tb(III) -directed self-assembly formation of these ligands was studied in CH3 CN by monitoring their various photophysical properties, including their emerging circular dichroism and circularly polarized luminescence. The global analysis of the former enabled the determination of both the stoichiometry and the stability constants of the various chiral supramolecular species in solution. PMID:26555573

  13. Reaction of thermal laminar boundary layer to stepwise change in heat conduction and specific heat of the wall in the direction of flow

    SciTech Connect

    Sapelkin, V.A.; Sergeev, Yu.V.

    1988-03-01

    The conjugate problem of nonsteady heat transfer between a laminar boundary layer with a pressure gradient and a wall with stepwise change in its thermophysical properties (heat conduction and volume specific heat) in the longitudinal direction is solved by the finite-difference method for an incompressible liquid and a wall whose internal surface is heat insulated. The results of the calculations show that the reaction of the thermal boundary layer to discontinuity in the thermophysical properties of the wall is nonunique and multi-parametric. Since these parameters determine the thickness of the thermal boundary layer it may be concluded that thin thermal boundary layers react more strongly than thick layers.

  14. Sintering of zirconia ceramics using microwave and spark heating techniques

    NASA Astrophysics Data System (ADS)

    Ivashutenko, A. S.; Frangulyan, T. S.; Ghyngazov, S. A.; Petrova, A. B.

    2016-02-01

    The paper presents the results of an complex study of structural and mechanical properties of zirconia ceramics sintered using different techniques. The samples were sintered via the conventional method of heating, in the field of microwave radiation and spark plasma. The experimental data indicates that a microwave field and spark plasma have a stimulating effect on zirconia ceramics sintering. In contrast to the microwave sintering, spark plasma sintering provides ceramics with improved properties at similar time-temperature annealing modes. Moreover, the properties of the ceramics under spark plasma sintering at T=1300 °C are similar to the properties of the ceramics sintered in a microwave field at T=1400 °C.

  15. Chemical Sintering Generates Uniform Porous Hyaluronic Acid Hydrogels

    PubMed Central

    Cam, Cynthia; Segura, Tatiana

    2014-01-01

    Implantation of scaffolds for tissue repair has been met with limited success primarily due to the inability to achieve vascularization within the construct. Many strategies have shifted to incorporate pores into these scaffolds to encourage rapid cellular infiltration and subsequent vascular ingrowth. We utilized an efficient chemical sintering technique to create a uniform network of polymethyl methacrylate (PMMA) microspheres for porous hyaluronic acid hydrogel formation. The porous hydrogels generated from chemical sintering possessed comparable pore uniformity and interconnectivity as the commonly used non- and heat sintering techniques. Moreover, similar cell response to the porous hydrogels generated from each sintering approach was observed in cell viability, spreading, proliferation in vitro, as well as, cellular invasion in vivo. We propose chemical sintering of PMMA microspheres using a dilute acetone solution as an alternative method to generating porous hyaluronic acid hydrogels since it requires equal or ten-fold less processing time as the currently used non-sintering or heat sintering technique, respectively. PMID:24120847

  16. Spark plasma sintering of tungsten-yttrium oxide composites from chemically synthesized nanopowders and microstructural characterization

    NASA Astrophysics Data System (ADS)

    Yar, M. A.; Wahlberg, Sverker; Bergqvist, Hans; Salem, H. G.; Johnsson, Mats; Muhammed, Mamoun

    2011-05-01

    Nano-crystalline W-1%Y 2O 3 (wt.%) powder was produced by a modified solution chemical reaction of ammonium paratungstate (APT) and yttrium nitrate. The precursor powder was found to consist of particles of bimodal morphology i.e. large APT-like particles up to 20 μm and rectangular yttrium containing ultrafine plates. After thermal processing tungsten crystals were evolved from W-O-Y plate like particles. spark plasma sintering (SPS) was used to consolidate the powder at 1100 and 1200 °C for different holding times in order to optimize the sintering conditions to yield high density but with reduced grain growth. Dispersion of yttrium oxide enhanced the sinterability of W powder with respect to lanthanum oxide. W-1%Y 2O 3 composites with sub-micron grain size showed improved density and mechanical properties as compared to W-La 2O 3 composites. Sample sintered in two steps showed improved density, due to longer holding time at lower temperature (900 °C) and less grain growth due to shorter holding time at higher temperature i.e. 1 min at 1100 °C.

  17. Effect of sintering on the microstructural and mechanical properties of meleagris gallopova hydroxyapatite.

    PubMed

    Pazarlioglu, S Serdar; Gokce, Hasan; Ozyegin, Sevgi; Salman, Serdar

    2014-01-01

    In this study, we obtained hydroxyapatite powders from the femur bones of meleagris gallopova at three steps and sintered at five different temperatures. The reactions, which occur during sintering of obtained powders, have been characterized by X-ray diffraction (XRD) patterns, scanning electron microscope (SEM), differential thermal analysis (DTA), thermo-gravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR) techniques. The mechanical properties of meleagris gallopova hydroxyapatite powders were determined by the measurements of density, hardness, porosity, activation energy for grain growth, variation of average grain sizes, fracture toughness and compression strength. The Fourier transform infrared spectra and the thermogravimetric analysis/differential thermal analysis thermograms of meleagris gallopova hydroxyapatite powders indicated that the presence of organic compounds were completely removed from the matrice. The X-ray diffraction patterns showed that decomposition of meleagris gallopova hydroxyapatite into tricalcium phosphate and calcium oxide was observed for the sintered samples at 1300°C. At the same temperature, formation of microcracks were also detected by scanning electron microscopy image. Mechanical tests showed that maximum hardness, fracture toughness and compression strength values were measured for the sintered samples at 1200°C. PMID:24948459

  18. Fabrication of solid-phase-sintered SiC-based composites with short carbon fibers

    NASA Astrophysics Data System (ADS)

    Li, Xian-hui; Yan, Qing-zhi; Han, Yong-jun; Cao, Mei-qi; Ge, Chang-chun

    2014-11-01

    Solid-phase-sintered SiC-based composites with short carbon fibers (Csf/SSiC) in concentrations ranging from 0 to 10wt% were prepared by pressureless sintering at 2100°C. The phase composition, microstructure, density, and flexural strength of the composites with different Csf contents were investigated. SEM micrographs showed that the Csf distributed in the SSiC matrix homogeneously with some gaps at the fiber/matrix interfaces. The densities of the composites decreased with increasing Csf content. However, the bending strength first increased and then decreased with increasing Csf content, reaching a maximum value of 390 MPa at a Csf content of 5wt%, which was 60 MPa higher than that of SSiC because of the pull-out strengthening mechanism. Notably, Csf was graphitized and damaged during the sintering process because of the high temperature and reaction with boron derived from the sintering additive B4C; this graphitization degraded the fiber strengthening effect.

  19. Power deposition in He from the volumetric He-3/n,p/H-3 reaction. [for direct nuclear pumped lasers

    NASA Technical Reports Server (NTRS)

    De Young, R. J.; Winters, P. A.

    1977-01-01

    Calculations are presented in this paper which show the amount of power that can be expected to be deposited in He-3 for typical direct nuclear-pumped lasers presently in use. The calculations were performed taking into consideration the cylindrical geometry of the system, the depletion of the thermal flux across the tube cross section, and the energy loss of the protons to the cell walls. If a laser efficiency of 1% is assumed, the results indicate a steady-state laser output of 12.5 kW from a volume of 152.6 cu cm or 82 W/cu cm can be achieved.

  20. Chirality imprinting and direct asymmetric reaction screening using a stereodynamic Brønsted/Lewis acid receptor.

    PubMed

    Bentley, Keith W; Proano, Daysi; Wolf, Christian

    2016-01-01

    Molecular recognition, activation and dynamic self-assembly with Brønsted and Lewis acids play a central role across the chemical sciences including catalysis, crystal engineering, supramolecular architectures and drug design. Despite this general advance, the utilization of the corresponding binding motifs for fast and robust quantitative chemosensing of chiral compounds in a complicate matrix has remained challenging. Here we show that a stereodynamic probe carrying complementary boronic acid and urea units achieves this goal with hydroxy carboxylic acids. Synergistic dual-site binding and instantaneous chirality imprinting result in characteristic ultraviolet and CD readouts that allow instantaneous determination of the absolute configuration, enantiomeric excess and concentration of the target compound even in complex mixtures. The robustness and practicality of this strategy for high-throughput screening purposes is demonstrated. Comprehensive sensing of only 0.5 mg of a crude reaction mixture of an asymmetric reduction eliminates cumbersome work-up protocols and minimizes analysis time, labour and waste production. PMID:27549926