Science.gov

Sample records for densification

  1. Pupil densification: a panorama

    NASA Astrophysics Data System (ADS)

    Martinache, F.; Lardière, O.

    The technique of pupil densification bridges the gap existing between conventionnal optical astronomy observing techniques and optical interferometry: it indeed leads to the concept of hypertelescope: an instrument that can provide direct images at the focus of an interferometer. The hypertelescope is the open sesame for high dynamic imaging with an interferometer: indeed, the elementary remapping of the pupil operated by a densifier not only maximizes the dynamic range and the signal to noise ratio of images but also makes the interferometer compatible with most existing coronagraphic devices. Moreover, a careful discussion about field of view show that for a diluted array, the pupil densification preserves all the relevant high angular resolution information collected by the interferometer and therefore induces no field loss.

  2. Lunar regolith densification

    NASA Technical Reports Server (NTRS)

    Ko, Hon-Yim; Sture, Stein

    1991-01-01

    Core tube samples of the lunar regolith obtained during the Apollo missions showed a rapid increase in the density of the regolith with depth. Various hypotheses have been proposed for the possible cause of this phenomenon, including the densification of the loose regolith material by repeated shaking from the seismic tremors which have been found to occur at regular monthly intervals when the moon and earth are closest to one another. A test bed was designed to study regolith densification. This test bed uses Minnesota Lunar Simulant (MLS) to conduct shaking experiments in the geotechnical centrifuge with an inflight shake table system. By reproducing realistic in-situ regolith properties, the experiment also serves to test penetrator concepts. The shake table system was designed and used for simulation experiments to study effects of earthquakes on terrestrial soil structures. It is mounted on a 15 g-ton geotechnical centrifuge in which the self-weight induced stresses are replicated by testing an n-th scale model in a gravity field which is n times larger than Earth's gravity. A similar concept applies when dealing with lunar prototypes, where the gravity ratio required for proper simulation of lunar gravity effects is that between the centrifugal acceleration and the lunar gravity. Records of lunar seismic tremors, or moonquakes, were obtained. While these records are being prepared for use as the input data to drive the shake table system, records from the El Centro earthquake of 1940 are being used to perform preliminary tests, using a soil container which was previously used for earthquake studies. This container has a laminar construction, with the layers free to slide on each other, so that the soil motion during the simulated earthquake will not be constrained by the otherwise rigid boundaries. The soil model is prepared by pluviating the MLS from a hopper into the laminar container to a depth of 6 in. The container is mounted on the shake table and the

  3. Propellant Densification for Shuttle: The SSME Perspective

    NASA Technical Reports Server (NTRS)

    Greene, William D.; Boxx, Dayna L.; Tiller, Bruce K. (Technical Monitor)

    2002-01-01

    The subject of cryogenic propellant densification as a potential upgrade to the Space Shuttle is a subject that has been raised on several occasions over the last decade. Due to advancements in densification technology made as a part of and in parallel to the X-33 project, the subject was raised and studied once again in May 2001. Across the Space Shuttle program people from many disciplines converged to discuss issues and perform trade studies to determine whether densified propellants was worth pursuing. This paper discusses one of these areas, specifically the Space Shuttle Main Engine (SSME). The effects of propellant densification on steady state performance are presented along with discussions of potential transient performance issues. Engine component redesign and retrofit issues are discussed as well the high level requirements to modify the ground test stands to accommodate propellant densification hardware and tanks. And finally, the matter of programmatic concerns enters the subject at hand as part of a discussion of SSME recertification requirements. In the end, potential benefits to SSME performance can be demonstrated and, subject to the densification scheme chosen, there does not appear to insurmountable technical obstacles.

  4. NUMERICAL MODELING OF CATHODE CONTACT MATERIAL DENSIFICATION

    SciTech Connect

    Koeppel, Brian J.; Liu, Wenning N.; Stephens, Elizabeth V.; Khaleel, Mohammad A.

    2011-11-01

    Numerical modeling was used to simulate the constrained sintering process of the cathode contact layer during assembly of solid oxide fuel cells (SOFCs). A finite element model based on the continuum theory for sintering of porous bodies was developed and used to investigate candidate low-temperature cathode contact materials. Constitutive parameters for various contact materials under investigation were estimated from dilatometry screening tests, and the influence of processing time, processing temperature, initial grain size, and applied compressive stress on the free sintering response was predicted for selected candidate materials. The densification behavior and generated stresses within a 5-cell planar SOFC stack during sintering, high temperature operation, and room temperature shutdown were predicted. Insufficient constrained densification was observed in the stack at the proposed heat treatment, but beneficial effects of reduced grain size, compressive stack preload, and reduced thermal expansion coefficient on the contact layer densification and stresses were observed.

  5. Task 4 supporting technology. Densification requirements definition and test objectives. Propellant densification requirements definition

    NASA Technical Reports Server (NTRS)

    Lak, Tibor; Weeks, D. P.

    1995-01-01

    The primary challenge of the X-33 CAN is to build and test a prototype LO2 and LH2 densification ground support equipment (GSE) unit, and perform tank thermodynamic testing within the 15 month phase 1 period. The LO2 and LH2 propellant densification system will be scaled for the IPTD LO2 and LH2 tank configurations. The IPTD tanks were selected for the propellant technology demonstration because of the potential benefits to the phase 1 plan: tanks will be built in time to support thermodynamic testing; minimum cost; minimum schedule risk; future testing at MSFC will build on phase 1 data base; and densification system will be available to support X-33 and RLV engine test at IPTD. The objective of the task 1 effort is to define the preliminary requirements of the propellant densification GSE and tank recirculation system. The key densification system design parameters to be established in Task 1 are: recirculation flow rate; heat exchanger inlet temperature; heat exchanger outlet temperature; maximum heat rejection rate; vent flow rate (GN2 and GH2); densification time; and tank pressure level.

  6. Task 4 supporting technology. Densification requirements definition and test objectives. Propellant densification requirements definition

    NASA Astrophysics Data System (ADS)

    Lak, Tibor; Weeks, D. P.

    1995-05-01

    The primary challenge of the X-33 CAN is to build and test a prototype LO2 and LH2 densification ground support equipment (GSE) unit, and perform tank thermodynamic testing within the 15 month phase 1 period. The LO2 and LH2 propellant densification system will be scaled for the IPTD LO2 and LH2 tank configurations. The IPTD tanks were selected for the propellant technology demonstration because of the potential benefits to the phase 1 plan: tanks will be built in time to support thermodynamic testing; minimum cost; minimum schedule risk; future testing at MSFC will build on phase 1 data base; and densification system will be available to support X-33 and RLV engine test at IPTD. The objective of the task 1 effort is to define the preliminary requirements of the propellant densification GSE and tank recirculation system. The key densification system design parameters to be established in Task 1 are: recirculation flow rate; heat exchanger inlet temperature; heat exchanger outlet temperature; maximum heat rejection rate; vent flow rate (GN2 and GH2); densification time; and tank pressure level.

  7. Painful connections: densification versus fibrosis of fascia.

    PubMed

    Pavan, Piero G; Stecco, Antonio; Stern, Robert; Stecco, Carla

    2014-01-01

    Deep fascia has long been considered a source of pain, secondary to nerve pain receptors becoming enmeshed within the pathological changes to which fascia are subject. Densification and fibrosis are among such changes. They can modify the mechanical properties of deep fasciae and damage the function of underlying muscles or organs. Distinguishing between these two different changes in fascia, and understanding the connective tissue matrix within fascia, together with the mechanical forces involved, will make it possible to assign more specific treatment modalities to relieve chronic pain syndromes. This review provides an overall description of deep fasciae and the mechanical properties in order to identify the various alterations that can lead to pain. Diet, exercise, and overuse syndromes are able to modify the viscosity of loose connective tissue within fascia, causing densification, an alteration that is easily reversible. Trauma, surgery, diabetes, and aging alter the fibrous layers of fasciae, leading to fascial fibrosis.

  8. Densification Dynamics of Gadolinium-Doped Ceria upon Sintering

    NASA Astrophysics Data System (ADS)

    Sato, Kiminori

    2012-07-01

    Densification behavior upon sintering is studied for gadolinium-doped ceria (GDC) by making use of X-ray diffraction, Archimedes method, high-resolution dilatometry (DLT), and element-specific positron annihilation spectroscopy. We found high concentration of vacancy-like nano-defects at GDC-crystallite interfaces participating in densification. Time-resolved length change and positron lifetime measurements enable to discuss the densification dynamics at the particle boundary relevant to a sintering neck and inside the particles. The particle boundary largely contributes to densification at the initial stage of sintering, whereas the crystallite interface gets to be responsible for prolonged densification. The densification inside the particle is developed by the growth of the crystallites followed by the transfer of Gd atoms from the interfaces to the crystallites.

  9. Isothermal densification and metamorphism of new snow

    NASA Astrophysics Data System (ADS)

    Schleef, S.; Loewe, H.; Schneebeli, M.

    2012-12-01

    The interplay between overburden stress and surface energy induced growth and coarsening is relevant for the densification of snow and porous ice at all densities. The densification of new snow is amenable to high precision experiments on short time scales. To this end we investigate the coupling of densification and metamorphism of new snow via time-lapse tomography experiments in the laboratory. We compare the evolution of density, strain, and specific surface area to previous long-time metamorphism experiments of snow and creep of polycrystalline ice. Experimental conditions are tailored to the requirements of time-lapse tomography and the measurements are conducted under nearly isothermal conditions at -20°C with a duration of two days. Images were taken with temporal resolution of a few hours which reveal precise details of the microstructure evolution due to sintering and compaction. We used different crystal shapes of natural new snow and snow samples obtained by sieving crystals grown in a snowmaker in the laboratory. To simulate the effect of overburden stress due to an overlying snowpack additional weights were applied to the sample. As expected we find an influence of the densification rate on initial density and overburden stress. We calculated strain rates and identified a transient creep behavior with a similar power law for all crystal types which substantially differs from the Andrade creep of polycrystalline ice. As a main result we found that the evolution of the specific surface area is independent of the density and follows a unique decay form for all measurements of each crystal type. The accuracy of the measurements allows to obtain a decay exponent for the SSA which is the same as previously obtained from the long-time regime during isothermal metamorphism after several months. Our preliminary results for all available types of new snow suggest a correlation between the initial density and SSA. We also find snow samples which coincide in

  10. Sol-gel synthesis and densification of aluminoborosilicate powders. Part 2: Densification

    NASA Technical Reports Server (NTRS)

    Bull, Jeffrey; Selvaduray, Guna; Leiser, Daniel

    1992-01-01

    Aluminoborosilicate (ABS) powders, high in alumina content, were synthesized by the sol-gel process utilizing four different methods of synthesis. The effect of these methods on the densification behavior of ABS powder compacts was studied. Five regions of shrinkage in the temperature range 25-1184 C were identified. In these regions, the greatest shrinkage occurred between the gel-to-glass transition temperature (T sub g approximately equal to 835 C) and the crystallization transformation temperature (T sub t approximately equal 900 C). The dominant mechanism of densification in this range was found to be viscous sintering. ABS powders were amorphous to x-rays up to T sub t at which a multiphasic structure crystallized. No 2Al2O3.B2O3 was found in these powders as predicted in the phase diagram. Above T sub t, densification was the result of competing mechanisms including grain growth and boria fluxed viscous sintering. Apparent activation energies for densification in each region varied according to the method of synthesis.

  11. Characterization of CVI densification of ceramic composites

    SciTech Connect

    Starr, T.L.; Stock, S.R.; Lee, S.

    1995-05-01

    Ceramic matrix composites promise higher operating temperature and better thermodynamic efficiency in many enregy conversion systems. In particular, composites fabricated by the chemical vapor infiltration (CVI) process have excellent mechanical properties and, using the forced flow-thermal gradient variation, good processing economics in small scale demonstrations. Scale-up to larger, more complex shapes requires understanding of gas flow through the fiber preform and of the relationship between fiber architecture and densification behavior. This understanding is needed for design of preforms for optimum infiltration. The objective of this research is to observe the deposition of matrix material in the pores of a ceramic fiber preform at various stages of the CVI process. These observations allow us to relate local deposition rates in various regions of the composite to the connectivity of the surrounding network of porosity and to better model the relationship between gas transport and fiber architecture in CVI preforms. Our observation of the CVI process utilizes high resolution X-ray tomographic microscopy (XTM) in collaboration with Dr. John Kinney at Lawrence Livermore National Laboratory with repeated imaging of a small preform specimens after various processing times. We use these images to determine geometry and dimensions of channels between and through layers in cloth lay-up preform during CVI densification and relate these to a transport model.

  12. LIBRA: An inexpensive geodetic network densification system

    NASA Technical Reports Server (NTRS)

    Fliegel, H. F.; Gantsweg, M.; Callahan, P. S.

    1975-01-01

    A description is given of the Libra (Locations Interposed by Ranging Aircraft) system, by which geodesy and earth strain measurements can be performed rapidly and inexpensively to several hundred auxiliary points with respect to a few fundamental control points established by any other technique, such as radio interferometry or satellite ranging. This low-cost means of extending the accuracy of space age geodesy to local surveys provides speed and spatial resolution useful, for example, for earthquake hazards estimation. Libra may be combined with an existing system, Aries (Astronomical Radio Interferometric Earth Surveying) to provide a balanced system adequate to meet the geophysical needs, and applicable to conventional surveying. The basic hardware design was outlined and specifications were defined. Then need for network densification was described. The following activities required to implement the proposed Libra system are also described: hardware development, data reduction, tropospheric calibrations, schedule of development and estimated costs.

  13. The effect of Peltier heat during current activated densification

    NASA Astrophysics Data System (ADS)

    Becker, A.; Angst, S.; Schmitz, A.; Engenhorst, M.; Stoetzel, J.; Gautam, D.; Wiggers, H.; Wolf, D. E.; Schierning, G.; Schmechel, R.

    2012-07-01

    It is shown that current-activated pressure-assisted densification (CAPAD) is sensitive to the Peltier effect. Under CAPAD, the Peltier effect leads to a significant redistribution of heat within the sample during the densification. The densification of highly p-doped silicon nanoparticles during CAPAD and the properties of the obtained samples are investigated experimentally and by computer simulation. Both, simulation and experiments, indicate clearly a higher temperature on the cathode side and a decreasing temperature from the center to the outer shell. Furthermore, computer simulations provide additional insights into the temperature profile which explain the anisotropic properties of the measured sample.

  14. Densification and shape distortion in liquid-phase sintering

    SciTech Connect

    Liu, J.; German, R.M.

    1999-12-01

    Densification and dimensional control are important aspects of liquid-phase sintering. The capillary force and the solid bonding affect both densification and shape preservation. Capillarity, which is orientated isotropically, causes uniform shrinkage and holds grains together to preserve the component shape in the early stage of sintering. On the other hand, solid bonding resists viscous flow and inhibits densification and shape distortion. The capillary force decreases with densification and approaches zero as pores are eliminated. Thus, shape retention eventually requires solid-grain bonding. The solid-grain bonding provides compact rigidity, which is represented by compact strength. Shape distortion occurs when the compact loses its strength. For every situation, there is a critical compact strength above which no shape distortion occurs. Distortion in liquid-phase sintering indicates that the compact strength passed below a critical level.

  15. Consolidation and densification methods for fibrous monolith processing

    SciTech Connect

    Sutaria, Manish P.; Rigali, Mark J.; Cipriani, Ronald A.; Artz, Gregory J.; Mulligan, Anthony C.

    2006-06-20

    Methods for consolidation and densification of fibrous monolith composite structures are provided. Consolidation and densification of two- and three-dimensional fibrous monolith components having complex geometries can be achieved by pressureless sintering. The fibrous monolith composites are formed from filaments having at least a first material composition generally surrounded by a second material composition. The composites are sintered at a pressure of no more than about 30 psi to provide consolidated and densified fibrous monolith composites.

  16. Enhanced Densification of SDC Barrier Layers

    SciTech Connect

    Hardy, John S.; Templeton, Jared W.; Lu, Zigui; Stevenson, Jeffry W.

    2011-09-12

    This technical report explores the Enhanced Densification of SCD Barrier Layers A samaria-doped ceria (SDC) barrier layer separates the lanthanum strontium cobalt ferrite (LSCF) cathode from the yttria-stabilized zirconia (YSZ) electrolyte in a solid oxide fuel cell (SOFC) to prevent the formation of electrically resistive interfacial SrZrO{sub 3} layers that arise from the reaction of Sr from the LSCF with Zr from the YSZ. However, the sintering temperature of this SDC layer must be limited to {approx}1200 C to avoid extensive interdiffusion between SDC and YSZ to form a resistive CeO{sub 2}-ZrO{sub 2} solid solution. Therefore, the conventional SDC layer is often porous and therefore not as impervious to Sr-diffusion as would be desired. In the pursuit of improved SOFC performance, efforts have been directed toward increasing the density of the SDC barrier layer without increasing the sintering temperature. The density of the SDC barrier layer can be greatly increased through small amounts of Cu-doping of the SDC powder together with increased solids loading and use of an appropriate binder system in the screen print ink. However, the resulting performance of cells with these barrier layers did not exhibit the expected increase in accordance with that achieved with the prototypical PLD SDC layer. It was determined by XRD that increased sinterability of the SDC also results in increased interdiffusivity between the SDC and YSZ, resulting in formation of a highly resistive solid solution.

  17. STS propellant densification feasibility study data book

    NASA Technical Reports Server (NTRS)

    Fazah, M. M.

    1994-01-01

    The feasibility of using densification or subcooling with respect to standard temperature propellants on the Space Transportation System (STS) in order to achieve a payload gain is discussed in this report. The objective is to determine the magnitude of the payload gain and to identify any system impacts to the space shuttle on either flight systems or ground systems. Results show that a payload benefit can be obtained by subcooling the liquid hydrogen (LH2) from a nominal temperature of 36.4 R to 28.5 R and by subcooling the liquid oxygen (LO2) from a nominal temperature of 164 R to either 132.1 R or 141.4 R. When the propellants are subcooled to 28.5 R and 132.1 R for the LH2 and LO2, respectively, a maximum payload gain of 7,324 lb can be achieved, and when the propellants are subcooled to 28.5 R and 141.5 R for the LH2 and LO2, respectively, a maximum payload gain of 6,841 lb can be achieved. If the LH2 is subcooled to 28.5 R while the LH2 and LO2 remains at the nominal conditions, a maximum payload gain of 1,303 lb can be achieved.

  18. Permeability during densification of viscous droplets

    NASA Astrophysics Data System (ADS)

    Wadsworth, Fabian; Vasseur, Jérémie; Llewellin, Ed; Dobson, Katherine; Schauroth, Jenny; Heap, Michael; Farquharson, Jamie; Scheu, Bettina; Kendrick, Jackie; Lavallée, Yan; von Aulock, Felix; Dingwell, Donald B.

    2016-04-01

    Fragmentation of magma can yield a transiently granular material, which can subsequently weld back to a fluid-continuum. This process results in dramatic changes in the porosity of the material, which impacts its fluid permeability. We collate published data for the porosity and permeability of volcanic and synthetic materials which have undergone this process to different amounts. By discriminating data for which good microstructural information are provided, we use simple scaling arguments to collapse the data in both the still-granular, high porosity region, and the fluid-continuum low porosity region, such that a universal description can be provided. This allows us to describe the microstructural meaning of permeability scaling, and to infer the controls on the position of this transition between dominantly granular (dispersion) and dominantly fluid-continuum materials. Fractures in coherent magmas are thought to be a primary degassing pathway in high viscosity systems. As a specific application, we consider transiently granular magma being transported through and deposited in these fractures. We finally present a physical model for the kinetics of porosity changes in arrays of viscous droplets and compare this with our experimental data. The combination of the physical model for the evolution of porosity with the scaling between porosity and permeability permits us to describe the evolution of permeability during densification. We anticipate that this will be a useful tool for predicting the longevity of degassing pathways in granular filled cracks, both in conduits and shallow lava domes, as well as during the sedimentation of exceptionally hot ignimbrites undergoing compaction and welding.

  19. Effects of torrefaction and densification on switchgrass pyrolysis products

    SciTech Connect

    Yang, Zixu; Sarkar, Madhura; Kumar, Ajay; Tumuluru, Jaya Shankar; Huhnke, Raymond L.

    2014-12-01

    Abstract The pyrolysis behaviors of four types of pretreated switchgrass (torrefied at 230 and 270 °C, densification, and torrefaction at 270 ºC followed by densification) were studied at three temperatures (500, 600, 700 ºC) using a pyroprobe attached to a gas chromatogram mass spectroscopy (Py-GC/MS). The torrefaction of switchgrass improved its oxygen to carbon ratio and energy content. Contents of anhydrous sugars and phenols in pyrolysis products of torrefied switchgrass were higher than those in pyrolysis products of raw switchgrass. As the torrefaction temperature increased from 230 to 270 °C, the contents of anhydrous sugars and phenols in pyrolysis products increased whereas content of guaiacols decreased. High pyrolysis temperature (600 and 700 °C as compared to 500 °C) enhanced decomposition of lignin and anhydrous sugars, leading to increase in phenols, aromatics and furans. Densification enhanced depolymerization of cellulose and hemicellulose during pyrolysis.

  20. Effects of torrefaction and densification on switchgrass pyrolysis products.

    PubMed

    Yang, Zixu; Sarkar, Madhura; Kumar, Ajay; Tumuluru, Jaya Shankar; Huhnke, Raymond L

    2014-12-01

    The pyrolysis behaviors of four types of pretreated switchgrass (torrefied at 230 and 270°C, densification, and torrefaction at 270°C followed by densification) were studied at three temperatures (500, 600, 700°C) using a pyroprobe attached to a gas chromatogram mass spectroscopy (Py-GC/MS). The torrefaction of switchgrass improved its oxygen to carbon ratio and energy content. Contents of anhydrous sugars and phenols in pyrolysis products of torrefied switchgrass were higher than those in pyrolysis products of raw switchgrass. As the torrefaction temperature increased from 230 to 270°C, the contents of anhydrous sugars and phenols in pyrolysis products increased whereas content of guaiacols decreased. High pyrolysis temperature (600 and 700°C as compared to 500°C) enhanced decomposition of lignin and anhydrous sugars, leading to increase in phenols, aromatics and furans. Densification enhanced depolymerization of cellulose and hemicellulose during pyrolysis.

  1. Consolidation and densification methods for fibrous monolith processing

    SciTech Connect

    Sutaria, Manish P.; Rigali, Mark J.; Cipriani, Ronald A.; Artz, Gregory J.; Mulligan, Anthony C.

    2004-05-25

    Methods for consolidation and densification of fibrous monolith composite structures are provided. Consolidation and densification of two- and three-dimensional fibrous monolith components having complex geometries can be achieved by pressureless sintering. The fibrous monolith composites are formed from filaments having at least a first material composition generally surrounded by a second material composition. The composites are sintered in an inert gas or nitrogen gas at a pressure of no more than about 30 psi to provide consolidated and densified fibrous monolith composites.

  2. Evolution of the ITRFyy Regional Densifications between Successive ITRS Realizations

    NASA Astrophysics Data System (ADS)

    Kenyeres, Ambrus; Legrand, Juliette

    2017-04-01

    The successive realizations of the International Terrestrial Reference System are based on the analysis of space geodetic data series stemming from GNSS, SLR, VLBI and DORIS. Beyond the modeling refinements the realizations (called ITRFyy, where yy denotes the end date of data involved in the solution) includes growing data sets, therefore a gradual quality improvement of the solutions is expected. On regional scale the geodetic reference frame is maintained by densification of the global ITRS realizations using continental scale CORS networks. Such networks are operational in Europe (EPN), North-America (NAREF), South-America (SIRGAS), Africa (AFREF), Asia-Pacific (APREF). Between two ITRS realizations, based on the analysis of the regional CORS network's data the regional reference frame solution may regularly updated with the integration of new, extended data series. According to the present practice in Europe the actual ITRS/ETRS89 realization is updated each 15 weeks using the weekly SINEX product of the EUREF Permanent Network (EPN). This densification approach is a kind of extrapolation of the actual ITRFyy, where the agreement may vary in time as a consequence of new data added and due to changes in network geometry or in intermediate changes in modeling parameters. In this paper the regional ITRF densification methodology is described and the European ITRF2008 densification solution series are reviewed with special emphasis on the agreement level of this series with the published ITRF2014 solution.

  3. Densification and Thermal Properties of Zirconium Diboride Based Ceramics

    DTIC Science & Technology

    2012-01-01

    density as a function of time of attrition milled ZrB2 during spark plasma sintering to a final temperature of 1900°C...as a function of temperature during hot pressing (A) and spark plasma sintering (B) of ZrB2...effects of densification method ( sintering , hot pressing, or spark plasma sintering ) on the microstructure, mechanical, and thermal properties were

  4. Densification and state transition across the Missouri Ozarks landscape

    Treesearch

    Brice B. Hanberry; John M. Kabrick; Hong S. He

    2014-01-01

    World-wide, some biomes are densifying, or increasing in dense woody vegetation, and shifting to alternative stable states. We quantified densification and state transition between forests ecosystems in historical (ca. 1815-1850) and current (2004-2008) surveys of the Missouri Ozark Highlands, a 5-million ha landscape in southern Missouri, USA. To estimate density of...

  5. Microstructure evolution and densification of alumina in liquid phase sintering

    NASA Astrophysics Data System (ADS)

    Dong, Weimin

    The microstructure evolution and densification of alumina during liquid phase sintering were quantified. Quantification included the evolution of pore-size distribution, the redistribution of liquid phase, the densification kinetics, and the fraction of closed and open pores. The results revealed that the small and large pores were filled simultaneously. This is inconsistent with Shaw's model in which liquid fills preferentially the smaller low-coordination-number pores in order to reach a low-energy configuration. The results also recommended that the pressure build-up of the trapped gases in pores due to the closure of open pores might have a significantly negative contribution to the driving force, and consequently cause the termination of the densification of alumina. To demonstrate whether the trapped gases played an important role in the microstructure evolution and the densification of alumina during liquid phase sintering, the following two experiments have been conducted. First, alumina preforms containing artificial pores were penetrated by glass. The results indicated that the trapped gases in pores had a considerable influence on the pore filling process, and ultimately caused the termination of the densification of the alumina preforms. Second, alumina compacts containing different amount of glass were sintered in vacuum. The alumina compact containing 20 vol. % reached full density during vacuum sintering, indicating that the pressure build-up of the trapped gases in pores was the main factor causing the termination of the densification of alumina in the final stage of liquid phase sintering. The limiting relative densities of compacts were calculated theoretically on the basis of a comprehensive analysis of the variation of the capillary pressure and gas pressure in pores with pore size and pore number. The capillary pressure and gas pressure in alumina compact during liquid phase sintering were analyzed on the basis of the above theoretical models

  6. Atomistic pathways of the pressure-induced densification of quartz

    NASA Astrophysics Data System (ADS)

    Liang, Yunfeng; Miranda, Caetano R.; Scandolo, Sandro

    2015-10-01

    When quartz is compressed at room temperature it retains its crystal structure at pressures well above its stability domain (0-2 GPa), and collapses into denser structures only when pressure reaches 20 GPa. Depending on the experimental conditions, pressure-induced densification can be accompanied by amorphization; by the formation of crystalline, metastable polymorphs; and can be preceded by the appearance of an intermediate phase, quartz II, with unknown structure. Based on molecular dynamic simulations, we show that this rich phenomenology can be rationalized through a unified theoretical framework of the atomistic pathways leading to densification. The model emphasizes the role played by the oxygen sublattice, which transforms from a bcc-like order in quartz into close-packed arrangements in the denser structures, through a ferroelastic instability of martensitic nature.

  7. Enhanced densification under shock compression in porous silicon

    DOE PAGES

    Lane, J. Matthew; Thompson, Aidan Patrick; Vogler, Tracy

    2014-10-27

    Under shock compression, most porous materials exhibit lower densities for a given pressure than that of a full-dense sample of the same material. However, some porous materials exhibit an anomalous, or enhanced, densification under shock compression. The mechanism driving this behavior was not completely determined. We present evidence from atomistic simulation that pure silicon belongs to this anomalous class of materials and demonstrate the associated mechanisms responsible for the effect in porous silicon. Atomistic response indicates that local shear strain in the neighborhood of collapsing pores catalyzes a local solid-solid phase transformation even when bulk pressures are below the thermodynamicmore » phase transformation pressure. This metastable, local, and partial, solid-solid phase transformation, which accounts for the enhanced densification in silicon, is driven by the local stress state near the void, not equilibrium thermodynamics. This mechanism may also explain the phenomenon in other covalently bonded materials.« less

  8. Enhanced densification under shock compression in porous silicon

    SciTech Connect

    Lane, J. Matthew; Thompson, Aidan Patrick; Vogler, Tracy

    2014-10-27

    Under shock compression, most porous materials exhibit lower densities for a given pressure than that of a full-dense sample of the same material. However, some porous materials exhibit an anomalous, or enhanced, densification under shock compression. The mechanism driving this behavior was not completely determined. We present evidence from atomistic simulation that pure silicon belongs to this anomalous class of materials and demonstrate the associated mechanisms responsible for the effect in porous silicon. Atomistic response indicates that local shear strain in the neighborhood of collapsing pores catalyzes a local solid-solid phase transformation even when bulk pressures are below the thermodynamic phase transformation pressure. This metastable, local, and partial, solid-solid phase transformation, which accounts for the enhanced densification in silicon, is driven by the local stress state near the void, not equilibrium thermodynamics. This mechanism may also explain the phenomenon in other covalently bonded materials.

  9. Simulation of current-activated pressure-assisted densification

    NASA Astrophysics Data System (ADS)

    Wolf, Dietrich; Angst, Sebastian; Schierning, Gabi

    2013-03-01

    Cohesive particles usually form very porous agglomerates. They support loads up to a consolidation pressure, which increases with decreasing particle size. Compaction of nano-powders can therefore be very costly and time consuming. If the particles are electrically conducting, which is the case e.g. for novel nano-structured thermoelectric materials, the technique of current-activated pressure-assisted densification (CAPAD) turns out to have many advantages. Electrical power deposited locally as Joule heat lowers the consolidation pressure such that particles fill nearby pores. This process leads to fast, scalable densification without much coarsening. Simulations are presented which address the influence of correlations on density and conductivity. They also take thermal conductivity and Peltier coefficient into account. Funded by DFG within the Priority Programme SPP 1386 (Nanostructured Thermoelectrics).

  10. Memory versus irreversibility in the thermal densification of amorphous glasses

    NASA Astrophysics Data System (ADS)

    Ovadyahu, Z.

    2017-06-01

    We report on dynamic effects associated with thermally annealing amorphous indium-oxide films. In this process, the resistance of a given sample may decrease by several orders of magnitude at room temperatures, while its amorphous structure is preserved. The main effect of the process is densification, i.e., increased system density. The study includes the evolution of the system resistivity during and after the thermal treatment, the changes in the conductance noise, and the accompanying changes in the optical properties. The sample resistance is used to monitor the system dynamics during the annealing period as well as the relaxation that ensues after its termination. These reveal slow processes that fit well with a stretched-exponential law, a behavior that is commonly observed in structural glasses. There is an intriguing similarity between these effects and those obtained in high-pressure densification experiments. Both protocols exhibit the "slow spring-back" effect, a familiar response of memory foams. A heuristic picture based on a modified Lennard-Jones potential for the effective interparticle interaction is argued to qualitatively account for these densification-rarefaction phenomena in amorphous materials, whether affected by thermal treatment or by application of high pressure.

  11. Frost Growth and Densification in Laminar Flow Over Flat Surfaces

    NASA Technical Reports Server (NTRS)

    Kandula, Max

    2011-01-01

    One-dimensional frost growth and densification in laminar flow over flat surfaces has been theoretically investigated. Improved representations of frost density and effective thermal conductivity applicable to a wide range of frost circumstances have been incorporated. The validity of the proposed model considering heat and mass diffusion in the frost layer is tested by a comparison of the predictions with data from various investigators for frost parameters including frost thickness, frost surface temperature, frost density and heat flux. The test conditions cover a range of wall temperature, air humidity ratio, air velocity, and air temperature, and the effect of these variables on the frost parameters has been exemplified. Satisfactory agreement is achieved between the model predictions and the various test data considered. The prevailing uncertainties concerning the role air velocity and air temperature on frost development have been elucidated. It is concluded that that for flat surfaces increases in air velocity have no appreciable effect on frost thickness but contribute to significant frost densification, while increase in air temperatures results in a slight increase the frost thickness and appreciable frost densification.

  12. Effects of torrefaction and densification on switchgrass pyrolysis products

    DOE PAGES

    Yang, Zixu; Sarkar, Madhura; Kumar, Ajay; ...

    2014-12-01

    Abstract The pyrolysis behaviors of four types of pretreated switchgrass (torrefied at 230 and 270 °C, densification, and torrefaction at 270 ºC followed by densification) were studied at three temperatures (500, 600, 700 ºC) using a pyroprobe attached to a gas chromatogram mass spectroscopy (Py-GC/MS). The torrefaction of switchgrass improved its oxygen to carbon ratio and energy content. Contents of anhydrous sugars and phenols in pyrolysis products of torrefied switchgrass were higher than those in pyrolysis products of raw switchgrass. As the torrefaction temperature increased from 230 to 270 °C, the contents of anhydrous sugars and phenols in pyrolysis productsmore » increased whereas content of guaiacols decreased. High pyrolysis temperature (600 and 700 °C as compared to 500 °C) enhanced decomposition of lignin and anhydrous sugars, leading to increase in phenols, aromatics and furans. Densification enhanced depolymerization of cellulose and hemicellulose during pyrolysis.« less

  13. Meso-scopic Densification in Brittle Granular Materials

    NASA Astrophysics Data System (ADS)

    Neal, William; Appleby-Thomas, Gareth; Collins, Gareth

    2013-06-01

    Particulate materials are ideally suited to shock absorbing applications due to the large amounts of energy required to deform their inherently complex meso-structure. Significant effort is being made to improve macro-scale material models to represent these atypical materials. On the long road towards achieving this capability, an important milestone would be to understand how particle densification mechanisms are affected by loading rate. In brittle particulate materials, the majority of densification is caused by particle fracture. Macro-scale quasi-static and dynamic compaction curves have been measured that show good qualitative agreement. There are, however, some differences that appear to be dependent on the loading rate that require further investigation. This study aims to investigate the difference in grain-fracture behavior between the quasi-static and shock loading response of brittle glass microsphere beds using a combination of quasi-static and dynamic loading techniques. Results from pressure-density measurements, sample recovery, and meso-scale hydrocode models (iSALE, an in-house simulation package) are discussed to explain the differences in particle densification mechanisms between the two loading rate regimes. Gratefully funded by AWE.plc.

  14. Direct measurement of densification rate using a neutron scattering technique

    NASA Astrophysics Data System (ADS)

    Morris, E. M.; Wingham, D.

    2012-12-01

    A non-destructive method for measuring density, based on neutron-scattering, has been used in the dry snow area of the Greenland Ice Sheet to derive profiles of densification rate over periods ranging from a few days to 5 years. From these observations we have derived a constitutive law for the compaction of dry snow relating strainrate to stress, temperature and the "type" of snow, that is, whether the snow is part of a "winter" wind-compacted layer with rounded grains or a "summer" lower-density hoar layer. We suggest that the processes which allow compaction of the snow also promote sintering, by bringing the snow grains into closer proximity. Higher temperatures increase the initial densification rate for a snow element but also, over time, harden it more rapidly. The net result is a much-reduced apparent activation energy for snow densification, similar to that used by Herron and Langway in their empirical equation derived from ice core density profiles.

  15. Gasification performance of switchgrass pretreated with torrefaction and densification

    SciTech Connect

    Jaya Shankar Tumuluru; Various

    2014-08-01

    The purpose of this study was to investigate gasification performance of four switchgrass pretreatments (torrefaction at 230 and 270 °C, densification, and combined torrefaction and densification) and three gasification temperatures (700, 800 and 900 °C). Gasification was performed in a fixed-bed externally heated reactor with air as an oxidizing agent. Switchgrass pretreatment and gasification temperature had significant effects on gasification performance such as gas yields, syngas lower heating value (LHV), and carbon conversion and cold gas efficiencies. With an increase in the gasification temperature, yields of H2 and CO, syngas LHV, and gasifier efficiencies increased whereas CH4, CO2 and N2 yields decreased. Among all switchgrass pretreatments, gasification performance of switchgrass with combined torrefaction and densification was the best followed by that of densified, raw and torrefied switchgrass. Gasification of combined torrefied and densified switchgrass resulted in the highest yields of H2 (0.03 kg/kg biomass) and CO (0.72 kg/kg biomass), highest syngas LHV (5.08 MJ m-3), CCE (92.53%), and CGE (68.40%) at the gasification temperature of 900 °C.

  16. High temperature densification forming of alumina powder -- Constitutive model and experiments

    SciTech Connect

    Kwon, Y.S.; Kim, K.T.

    1996-10-01

    Densification and grain growth of alumina powder compacts were investigated under pressureless sintering, sinter forging, and hot pressing. A set of constitutive equations by Kwon et al. was used to predict densification under diffusional creep. A novel grain growth equation is proposed by generalizing the grain growth model of Wilkinson and Caceres to predict grain growth during densification forming process of ceramic powders under general loading states. Material parameters in the constitutive equations were determined from experimental data under pressureless sintering and sinter forging. Theoretical predictions by using the constitutive equations for creep densification and grain growth were compared with experimental data of alumina powder compacts.

  17. Propellant Densification Ground Testing Conducted for Launch Vehicles

    NASA Technical Reports Server (NTRS)

    Tomsik, Thomas M.

    2000-01-01

    The NASA Glenn Research Center at Lewis Field has taken the lead in the development of practical densified cryogenic propellants for launch vehicle applications. The technology of subcooling cryogenic propellants below their normal boiling point to produce a denser fluid is one of the key process technologies necessary to meet the challenge of single-stage-to-orbit and reusable launch vehicles. Densified propellants are critical to lowering launch costs because they enable more propellant to be packed into a given unit volume, thus improving the performance by reducing the overall size and weight of the launch vehicle. This two-pronged research and test program has evolved into (1) conducting tank loading tests using densified liquid hydrogen and (2) developing two large-scale propellant densification systems that will be performance tested next year at Glenn. The propellant-loading test program was undertaken at Glenn in coordination with Lockheed Martin Michoud Space Systems. In this testing, the liquid hydrogen recirculation and densification process was simulated, and the thermal stratification of the densified propellant was recorded throughout the tank. The test article was a flight-weight tank constructed from composite materials similar to those to be used on the X-33 launch vehicle. The tank geometry as designed by Lockheed Martin had two cylindrical lobes with a center septum. Liquid hydrogen flow rate, pressure data, and temperature data plotted over time were collected while the subscale tank was filled with 27 R (15 K) densified liquid hydrogen propellant. This testing has validated mathematical models and demonstrated the readiness of densified propellant technology for near-term use. It marks the first time that such a process has been carried out with a multiple-lobe, flight-similar tank. Glenn researchers have also been working on providing a process and critical test data for the continuous production of densified liquid hydrogen (LH2) and

  18. Evaluation of Liquefaction Susceptibility of Clean Sands after Blast Densification

    NASA Astrophysics Data System (ADS)

    Vega Posada, Carlos Alberto

    The effect of earthquakes on infrastructure facilities is an important topic of interest in geotechnical research. A key design issue for such facilities is whether or not liquefaction will occur during an earthquake. The consequences of this type of ground failure are usually severe, resulting in severe damage to a facility and in some cases the loss of human life. One approach to minimize the effect of liquefaction is to improve the ground condition by controlled blasting. The main limitations of the blast densification technique are that the design is mostly empirical and verification studies of densification have resulted in contradictory results in some case studies. In such cases, even though the ground surface settles almost immediately after blasting, common verification tests such as the cone penetration test (CPT), standard penetration test (SPT), and shear wave velocity test (Vs) suggest that the soil mass has not been improved at all. This raises concerns regarding the future performance of the soil and casts doubts on whether or not the improved deposit is still susceptible to liquefaction. In this work, a blast densification program was implemented at the Oakridge Landfill located in Dorchester County, SC, to gain information regarding the condition of a loose sand deposit during and after each blast event. In addition, an extensive laboratory testing program was conducted on reconstituted sand specimens to evaluate the mechanical behavior of saturated and gassy, medium dense sands during monotonic and cyclic loading. The results from the field and laboratory program indicate that gas released during blasting can remain trapped in the soil mass for several years, and this gas greatly affects the mechanical behavior of the sand. Gas greatly increases the liquefaction resistance of the soil. If the gas remains in the sand over the life of a project, then it will maintain this increased resistance to liquefaction, whether or not the penetration

  19. Poisson's Ratio and the Densification of Glass under High Pressure

    SciTech Connect

    Rouxel, T.; Ji, H.; Hammouda, T.; Moreac, A.

    2008-06-06

    Because of a relatively low atomic packing density, (C{sub g}) glasses experience significant densification under high hydrostatic pressure. Poisson's ratio ({nu}) is correlated to C{sub g} and typically varies from 0.15 for glasses with low C{sub g} such as amorphous silica to 0.38 for close-packed atomic networks such as in bulk metallic glasses. Pressure experiments were conducted up to 25 GPa at 293 K on silica, soda-lime-silica, chalcogenide, and bulk metallic glasses. We show from these high-pressure data that there is a direct correlation between {nu} and the maximum post-decompression density change.

  20. Recent Advances and Applications in Cryogenic Propellant Densification Technology

    NASA Technical Reports Server (NTRS)

    Tomsik, Thomas M.

    2000-01-01

    This purpose of this paper is to review several historical cryogenic test programs that were conducted at the NASA Glenn Research Center (GRC), Cleveland, Ohio over the past fifty years. More recently these technology programs were intended to study new and improved denser forms of liquid hydrogen (LH2) and liquid oxygen (LO2) cryogenic rocket fuels. Of particular interest are subcooled cryogenic propellants. This is due to the fact that they have a significantly higher density (eg. triple-point hydrogen, slush etc.), a lower vapor pressure and improved cooling capacity over the normal boiling point cryogen. This paper, which is intended to be a historical technology overview, will trace the past and recent development and testing of small and large-scale propellant densification production systems. Densifier units in the current GRC fuels program, were designed and are capable of processing subcooled LH2 and L02 propellant at the X33 Reusable Launch Vehicle (RLV) scale. One final objective of this technical briefing is to discuss some of the potential benefits and application which propellant densification technology may offer the industrial cryogenics production and end-user community. Density enhancements to cryogenic propellants (LH2, LO2, CH4) in rocket propulsion and aerospace application have provided the opportunity to either increase performance of existing launch vehicles or to reduce the overall size, mass and cost of a new vehicle system.

  1. Increased hydrogen uptake of MOF-5 by powder densification

    NASA Astrophysics Data System (ADS)

    Siegel, Donald; Purewal, Justin; Liu, Dong'an; Sudik, Andrea; Yang, Jun; Maurer, Stefan; Muller, Ulrich

    2011-03-01

    The metal-organic framework MOF-5 has attracted significant attention due to its ability to store large quantities of H2 by mass, up to 10 wt.% absolute at 70 bar at 77K. On the other hand, since MOF-5 is typically obtained as a bulk powder, it exhibits a low volumetric density and poor thermal conductivity---both of which are undesirable characteristics for a hydrogen storage material. Here we explore the extent to which powder densification can overcome these deficiencies, as well as to characterize the impact of densification on crystallinity, pore volume, surface area, and crush strength. MOF-5 powder was processed into cylindrical tablets with densities up to 1.6 g/cm3 by mechanical compaction. We find that optimal hydrogen storage properties are achieved for ρ ~ 0.5 g/cm3 , yielding a 350% increase in volumetric H2 density with only a modest 15% reduction in gravimetric H2 excess in comparison to the powder. Higher densities result in larger reductions in gravimetric excess. Total pore volume and surface area decrease commensurately with the gravimetric capacity, and are linked to an incipient amorphization transformation. Nevertheless, a large fraction of MOF-5 crystallinity remains intact in densities up to 0.75 g/cm3 , as confirmed from powder XRD.

  2. Volcanic sintering: Timescales of viscous densification and strength recovery

    PubMed Central

    Vasseur, Jérémie; Wadsworth, Fabian B; Lavallée, Yan; Hess, Kai-Uwe; Dingwell, Donald B

    2013-01-01

    [1] Sintering and densification are ubiquitous processes influencing the emplacement of both effusive and explosive products of volcanic eruptions. Here we sinter ash-size fragments of a synthetic National Institute of Standards and Technology viscosity standard glass at temperatures at which the resultant melt has a viscosity of ∼108–109 Pa.s at 1bar to assess sintering dynamics under near-surface volcanic conditions. We track the strength recovery via uniaxial compressive tests. We observe that volcanic ash sintering is dominantly time dependent, temperature dependent, and grain size dependent and may thus be interpreted to be controlled by melt viscosity and surface tension. Sintering evolves from particle agglutination to viscous pore collapse and is accompanied by a reduction in connected porosity and an increase in isolated pores. Sintering and densification result in a nonlinear increase in strength. Micromechanical modeling shows that the pore-emanated crack model explains the strength of porous lava as a function of pore fraction and size. PMID:25821262

  3. Active optics concept for hypertelescope aberration control and pupil densification

    NASA Astrophysics Data System (ADS)

    Dohlen, Kjetil; Dargent, Pascal; Ferrari, Marc; Lemaitre, Gerard R.

    2003-02-01

    One of the instrumental concepts under study for large baseline interferometers for high resolution astronomical imaging, in particular applied to exoplanet search and characterisation, is the hypertelescope (HT). Mainly considered for space deployment, this sparse array of mirror segments supported either by a struss structure or by free-flying micro satellites form a giant, diluted primary mirror. The focal plane instrumentation, including pupil densification optics, is located in the primary focus instrument space craft (ISC). Baselines considered for first-generation HTs are of the order of 100 m, but one can envisage kilometric arrays capable of unprecedented angular resolution. Pointing with such a telescope poses orbital navigation problems. Letting the entire array perform a slow sky-scanning motion and navigating the ISC within the primary focal plane in order to follow the image of the object may solve these problems. The ISC must therefore be equipped with aberration correction optics capable of covering a sufficiently large primary field of view, of the order of a few degrees. In this paper we present optical and mechanical concepts for combined aberration correction and pupil densification using multimode deformable mirror (MDM) and mechanically amplified piezo actuator technologies. Among the advantages of such a system over large monolithic corrector optics is the relaxation of piston alignment requirements for primary segments.

  4. The prospects for urban densification: a place-based study

    NASA Astrophysics Data System (ADS)

    Schmidt-Thomé, Kaisa; Haybatollahi, Mohammad; Kyttä, Marketta; Korpi, Jari

    2013-06-01

    Study of the environmental outcomes of urban densification is a highly context-dependent task. Our study shows that collecting and processing place-based survey data by means of the softGIS method is clearly helpful here. With the map-based internet questionnaire each response remains connected to both the physical environment and the everyday life of the respondent. In our study of the Kuninkaankolmio area (located in the Helsinki metropolitan region) the survey data were combined with urban density variables calculated from register-based data on the existing built environment. The regression analysis indicated that the participants in the survey preferred the same density factors for their future residence as they enjoyed in their current neighbourhood. In the second analysis we related the densities of planned infill developments with the interest respondents had shown in these projects. The results show that new and even quite dense infill developments have been found to be rather attractive, with them often being viewed as interesting supplements to the current urban texture. These findings contribute to the ongoing scientific discussion on the feasibility of densification measures and encourage the Kuninkaankolmio planners to proceed, albeit carefully, with the planned infill developments.

  5. Volcanic sintering: Timescales of viscous densification and strength recovery.

    PubMed

    Vasseur, Jérémie; Wadsworth, Fabian B; Lavallée, Yan; Hess, Kai-Uwe; Dingwell, Donald B

    2013-11-16

    [1] Sintering and densification are ubiquitous processes influencing the emplacement of both effusive and explosive products of volcanic eruptions. Here we sinter ash-size fragments of a synthetic National Institute of Standards and Technology viscosity standard glass at temperatures at which the resultant melt has a viscosity of ∼10(8)-10(9) Pa.s at 1bar to assess sintering dynamics under near-surface volcanic conditions. We track the strength recovery via uniaxial compressive tests. We observe that volcanic ash sintering is dominantly time dependent, temperature dependent, and grain size dependent and may thus be interpreted to be controlled by melt viscosity and surface tension. Sintering evolves from particle agglutination to viscous pore collapse and is accompanied by a reduction in connected porosity and an increase in isolated pores. Sintering and densification result in a nonlinear increase in strength. Micromechanical modeling shows that the pore-emanated crack model explains the strength of porous lava as a function of pore fraction and size.

  6. Experimental Studies of Liquefaction and Densification of Liquid Oxygen

    NASA Technical Reports Server (NTRS)

    Partridge, Jonathan Koert

    2010-01-01

    The propellant combination that offers optimum performance is very reactive with a low average molecular weight of the resulting combustion products. Propellant combinations such as oxygen and hydrogen meet the above criteria, however, the propellants in gaseous form require large propellant tanks due to the low density of gas. Thus, rocketry employs cryogenic refrigeration to provide a more dense propellant stored as a liquid. In addition to propellant liquefaction, cryogenic refrigeration can also conserve propellant and provide propellant subcooling and propellant densification. Previous studies analyzed vapor conditioning of a cryogenic propellant, with the vapor conditioning by either a heat exchanger position in the vapor or by using the vapor in a refrigeration cycle as the working fluid. This study analyzes the effects of refrigeration heat exchanger located in the liquid of the common propellant oxidizer, liquid oxygen. This study predicted and determined the mass condensation rate and heat transfer coefficient for liquid oxygen.

  7. Selective laser densification of lithium aluminosilicate glass ceramic tapes

    NASA Astrophysics Data System (ADS)

    Zocca, Andrea; Colombo, Paolo; Günster, Jens; Mühler, Thomas; Heinrich, Jürgen G.

    2013-01-01

    Tapes, cast by blade deposition of a lithium aluminosilicate glass slurry, were sintered using a YAG-fiber laser, with the aim of finding suitable parameters for an additive manufacturing process based on layer-wise slurry deposition and selective laser densification. The influence of the laser parameters (output power and scan velocity) on the sintering was evaluated, by scanning electron microscopy and by X-ray diffraction, on the basis of the quality of the processed layer. Well densified samples could be obtained only in a small window of values for the output power and the scan velocity. The measurement of the width of a set of single scanned lines allowed also to estimate the minimum resolution of the system along the layer plane.

  8. Hydrogen Confinement in Carbon Nanopores: Extreme Densification at Ambient Temperature

    SciTech Connect

    Gallego, Nidia C; He, Lilin; Saha, Dipendu; Contescu, Cristian I; Melnichenko, Yuri B

    2011-01-01

    In-situ small angle neutron scattering (SANS) studies of hydrogen confined in small pores of polyfurfuryl alcohol-derived activated carbon (PFAC) at room-temperature provided for the first time its phase behavior in equilibrium with external H2 at pressures up to 200 bar. The data was used to evaluate the density of the adsorbed fluid, which appears to be a function of both pore size and pressure, and approaches the liquid hydrogen density in narrow nanopores at 200 bar. The surface-molecule interactions responsible for densification of hydrogen within the pores create internal pressures which exceed by a factor of up to ~ 60 the external gas pressures, confirming the benefits of adsorptive over compressive storage. These results can be utilized to guide the development of new carbon adsorbents tailored for maximum hydrogen storage capacities at near ambient temperatures.

  9. Densification of polar snow: Measurements, modeling, and implications for altimetry

    NASA Astrophysics Data System (ADS)

    Morris, E. M.; Wingham, D. J.

    2014-02-01

    Density profiles in the upper 10-14 m of snow have been measured along a 500 km traverse across the Greenland ice sheet, using a neutron scattering technique. Repeat measurements, over periods ranging from a few days to 5 years, allow strain rates to be determined as a function of depth. Very large strain rates are observed in the surface layer of snow over summer periods. In the underlying multiyear snow, strain rate decreases with decreasing porosity. However, once this effect has been removed, the effect of increasing overburden pressure is counteracted by increasing strength of the material. There are fluctuations in strain rate associated with the annual layering, which indicate that winter and summer snow have different strengths. Based on these observations, we derive a new densification equation which includes the effect of snow density and snow type, and the effect of temperature, described by an Arrhenius expression with activation energy of the order of 110 kJ mol-1 and an exponential prefactor determined simply by the temperature history of the snow. For multiyear snow and meteorological conditions that do not vary from year to year, our equation reduces to a form similar to the Herron and Langway equation for first-stage densification. Using the new equation, we calculate the sensitivity of compaction rate to short-term fluctuations in temperature and accumulation as 0.11-0.20 m a-1 K-1 and 0.33-0.95 m a-1(meters water equivalent)-1, respectively, and discuss the consequent uncertainty in satellite measurements of the long-term elevation trend in this area of the Greenland ice sheet.

  10. The affect of densification and dehydroxylation on the mechanical properties of stoichiometric hydroxyapatite bioceramics

    SciTech Connect

    Laasri, S.; Taha, M.; Laghzizil, A.; Hlil, E.K.; Chevalier, J.

    2010-10-15

    This paper reports the effects of processing densification on the mechanical properties of hydroxyapatite bioceramics. Densification of synthetic hydroxyapatite is conducted in the range 1000-1300 {sup o}C. X-ray diffraction and SEM microscopy are used to check the microstructure transformations. Vickers hardness, toughness and Young's modulus are analyzed versus the density and grain size. The sintering temperature and the particle size influence strongly the densification and the resulting mechanical properties. In addition, the critical sintering temperature appears around 1200 {sup o}C and the declined strength at the temperature up to 1200 {sup o}C is found sensitive to the dehydroxylation process of hydroxyapatite.

  11. Liquid Film Capillary Mechanism for Densification of Ceramic Powders during Flash Sintering

    PubMed Central

    Chaim, Rachman

    2016-01-01

    Recently, local melting of the particle surfaces confirmed the formation of spark and plasma during spark plasma sintering, which explains the rapid densification mechanism via liquid. A model for rapid densification of flash sintered ceramics by liquid film capillary was presented, where liquid film forms by local melting at the particle contacts, due to Joule heating followed by thermal runaway. Local densification is by particle rearrangement led by spreading of the liquid, due to local attractive capillary forces. Electrowetting may assist this process. The asymmetric nature of the powder compact represents an invasive percolating system. PMID:28773405

  12. Liquid Film Capillary Mechanism for Densification of Ceramic Powders during Flash Sintering.

    PubMed

    Chaim, Rachman

    2016-04-11

    Recently, local melting of the particle surfaces confirmed the formation of spark and plasma during spark plasma sintering, which explains the rapid densification mechanism via liquid. A model for rapid densification of flash sintered ceramics by liquid film capillary was presented, where liquid film forms by local melting at the particle contacts, due to Joule heating followed by thermal runaway. Local densification is by particle rearrangement led by spreading of the liquid, due to local attractive capillary forces. Electrowetting may assist this process. The asymmetric nature of the powder compact represents an invasive percolating system.

  13. SIRGAS: ITRF densification in Latin America and the Caribbean

    NASA Astrophysics Data System (ADS)

    Brunini, C.; Costa, S.; Mackern, V.; Martínez, W.; Sánchez, L.; Seemüller, W.; da Silva, A.

    2009-04-01

    The continental reference frame of SIRGAS (Sistema de Referencia Geocéntrico para las Américas) is at present realized by the SIRGAS Continuously Operating Network (SIRGAS-CON) composed by about 200 stations distributed over all Latin America and the Caribbean. SIRGAS member countries are qualifying their national reference frames by installing continuously operating GNSS stations, which have to be consistently integrated into the continental network. As the number of these stations is rapidly increasing, the processing strategy of the SIRGAS-CON network was redefined during the SIRGAS 2008 General Meeting in May 2008. The new strategy relies upon the definition of two hierarchy levels: a) A core network (SIRGAS-CON-C) with homogeneous continental coverage and stabile site locations ensures the long-term stability of the reference frame and provides the primary link to the ITRS. Stations belonging to this network have been selected so that each country contributes with a number of stations defined according to its surface and guarantying that the selected stations are the best in operability, continuity, reliability, and geographical coverage. b) Several densification sub-networks (SIRGAS-CON-D) improve the accessibility to the reference frame. The SIRGAS-CON-D sub-networks shall correspond to the national reference frames, i.e., as an optimum there shall be as many sub-networks as countries in the region. The goal is that each country processes its own continuously stations following the SIRGAS processing guidelines, which are defined in accordance with the IERS and IGS standards and conventions. Since at present not all of the countries are operating a processing centre, the existing stations are classified in three densification networks (a Northern, a middle, and a Southern one), which are processed by three local processing centres until new ones are installed. As SIRGAS is defined as a densification of the ITRS, stations included in the core network, as

  14. Densification and Sintering of a Microwave-Plasma-Synthesized Iron Nanopowder

    DTIC Science & Technology

    2003-01-01

    R.J., "Nanoparticulate Materials Densification," Nanostr . Mater. 7 [7], 749-768 (1996). 8. Goetzel, C.G., Treatise on Powder Metallurg,, Vol. 1, Interscience Publishers, Inc., New York, NY, 515 (1949). 204

  15. Enhanced densification of white cast iron powders by cyclic phase transformations under stress

    NASA Astrophysics Data System (ADS)

    Ruano, Oscar A.; Wadsworth, Jeffrey; Sherby, Oleg D.

    1982-03-01

    It is shown that densification of white cast iron powders under stress can be enhanced by multiple phase transformations through thermal cycling. This enhancement occurs by accelerated creep flow during phase changes (transformation superplasticity). The approximate stress range where transformation-assisted densification can occur is shown to be between 1.7 MPa (250 psi) and 34.5 MPa (5000 psi). Below 1.7 MPa insufficient strain occurs during phase transformation to cause significant densification even after many transformation cycles. Above 34.5 MPa, densification occurs principally by normal slip creep. Transformation warm pressing of white cast iron powders leads to dense compacts at low pressures and short times. In addition, because the transformation temperature is low, the ultrafine structures existing in the original powders are retained in the densified compacts.

  16. Macroscopic and Microscopic Investigation of Densification Behavior for Gadolinium-doped Ceria upon Sintering

    NASA Astrophysics Data System (ADS)

    Kosaka, T.; Sato, K.

    2011-10-01

    The densification behaviour of Gadolinium-doped ceria (GDC) upon sintering is investigated from macroscopic and microscopic points of view. The time-resolved length-change measurement with high-resolution dilatometry and positron lifetime spectroscopy are conducted. Positron lifetime spectroscopy reveals the presence of nanovoids at grain boundaries in GDC. Time-dependent length-change measurement reveals that particle rearrangement occurs at the initial stage of sintering. Densifications at the sintering neck and inside the particle grain are discussed.

  17. Densification of functional plasma polymers by momentum transfer during film growth

    SciTech Connect

    Hegemann, Dirk; Koerner, Enrico; Blanchard, Noemi; Drabik, Martin; Guimond, Sebastien

    2012-11-19

    Functional plasma polymers were deposited from pure ethylene discharges and with the addition of carbon dioxide or ammonia. The incorporation of oxygen and nitrogen-containing functional groups depends on the fragmentation in the gas phase as well as on the densification during film growth. While a minimum energy per deposited carbon atom is required for cross-linking, the densification and accompanying reduction of functional group incorporation was found to scale linearly with momentum transfer through ion bombardment during film growth.

  18. Insight into the physics of foam densification via numerical simulation

    NASA Astrophysics Data System (ADS)

    Bardenhagen, S. G.; Brydon, A. D.; Guilkey, J. E.

    2005-03-01

    Foamed materials are increasingly finding application in engineering systems on account of their unique properties. The basic mechanics which gives rise to these properties is well established, they are the result of collapsing the foam microstructure. Despite a basic understanding, the relationship between the details of foam microstructure and foam bulk response is generally unknown. With continued advances in computational power, many researchers have turned to numerical simulation to gain insight into the relationship between foam microstructure and bulk properties. However, numerical simulation of foam microscale deformation is a very challenging computational task and, to date, simulations over the full range of bulk deformations in which these materials operate have not been reported. Here a particle technique is demonstrated to be well-suited for this computational challenge, permitting simulation of the compression of foam microstructures to full densification. Computations on idealized foam microstructures are in agreement with engineering guidelines and various experimental results. Dependencies on degree of microstructure regularity and material properties are demonstrated. A surprising amount of porosity is found in fully-densified foams. The presence of residual porosity can strongly influence dynamic material response and hence needs to be accounted for in bulk (average) constitutive models of these materials.

  19. On the self-damping nature of densification in photonic sintering of nanoparticles

    PubMed Central

    MacNeill, William; Choi, Chang-Ho; Chang, Chih-Hung; Malhotra, Rajiv

    2015-01-01

    Sintering of nanoparticle inks over large area-substrates is a key enabler for scalable fabrication of patterned and continuous films, with multiple emerging applications. The high speed and ambient condition operation of photonic sintering has elicited significant interest for this purpose. In this work, we experimentally characterize the temperature evolution and densification in photonic sintering of silver nanoparticle inks, as a function of nanoparticle size. It is shown that smaller nanoparticles result in faster densification, with lower temperatures during sintering, as compared to larger nanoparticles. Further, high densification can be achieved even without nanoparticle melting. Electromagnetic Finite Element Analysis of photonic heating is coupled to an analytical sintering model, to examine the role of interparticle neck growth in photonic sintering. It is shown that photonic sintering is an inherently self-damping process, i.e., the progress of densification reduces the magnitude of subsequent photonic heating even before full density is reached. By accounting for this phenomenon, the developed coupled model better captures the experimentally observed sintering temperature and densification as compared to conventional photonic sintering models. Further, this model is used to uncover the reason behind the experimentally observed increase in densification with increasing weight ratio of smaller to larger nanoparticles. PMID:26443492

  20. Role of cabbeling in water densification in the Greenland Basin

    NASA Astrophysics Data System (ADS)

    Kasajima, Y.; Johannessen, T.

    2009-07-01

    The effects of cabbeling mixing on water mass modification in the Greenland Sea were explored by hydrographic observations across the Greenland Basin in summer 2006. The neutral surface was chosen as a reference frame, and the strength of cabbeling mixing was quantified by the dianeutral velocity magnitude. Active cabbeling spots were detected with the criterion of the velocity magnitude >1 m/day, and four active cabbeling areas were identified; the west of Bear Island (SB), the Arctic Frontal Zone (AFZ), the central Greenland Sea (CG) and the western Greenland Sea (WG). The most vigorous cabbeling mixing was found at SB, where warm North Atlantic Water (NAW) mixed with cold water from the Barents Sea, inducing a maximum velocity of 7.5 m/day and a maximum density gain of 4.7×10-3 kg/m3. At AFZ and CG, the mixing took place between NAW, modified NAW and Arctic Intermediate Water (AIW), and the density gain at these fronts were 1.5×10-3 kg/m3 (AFZ) and 1.3×10-3 kg/m3 (CG). In the western Greenland Sea, the active cabbeling spots were widely separated and mixing appeared to be rather weak, with a maximum velocity of 2.5 m/day. The mixing source waters at WG were modified NAW, AIW and even denser water, and the density gain in this area was 0.4×10-3 kg/m3. The deepest mixing produced water whose density is equivalent to that of the dense water of the basin, indicating that cabbeling in the western Greenland Sea contributed directly to basin-scale water densification. The water mass modification rate was the highest at AFZ (about 8.0 Sv), suggesting that cabbeling may play an important role in water transformation in the Greenland Basin.

  1. Contribution of TIGA reprocessing to the ITRF densification

    NASA Astrophysics Data System (ADS)

    Rudenko, S.; Dähnn, M.; Gendt, G.; Brandt, A.; Nischan, T.

    2009-04-01

    Analysis of tide gauge measurements with the purpose of sea level change investigations requires a well defined reference frame. Such reference frame can be realized through precise positions of GPS stations located at or near tide gauges (TIGA stations) and analyzed within the IGS GPS Tide Gauge Benchmark Monitoring Pilot Project (TIGA). To tie this reference frame to the International Terrestrial Reference Frame (ITRF), one should process simultaneously GPS data from TIGA and IGS stations included in the ITRF. A time series of GPS station positions has been recently derived by reprocessing GPS data from about 400 GPS stations globally distributed covering totally time span from 1998 till 2008 using EPOS-Potsdam software developed at GFZ and improved in the recent years. The analysis is based on the use of IERS Conventions 2003, ITRF2005 as a priori reference frame, FES2004 ocean tide loading model, absolute phase centre variations for GPS satellite transmit and ground receive antennae and other models. About 220 stations of the solution are IGS ones and about 180 are TIGA GPS stations that are not IGS ones. The solution includes weekly coordinates of GPS stations, daily values of the Earth rotation parameters and their rates, as well as satellite antenna offsets. On the other hand, our new solution can contribute to the ITRF densification by providing positions of about 200 stations being not present in ITRF2005. The solution can be also used for the integration of regional frames. The paper presents the results of the analysis and the comparison of our solution with ITRF2005 and the solutions of other TIGA and IGS Analysis Centres.

  2. The competition of densification and structure ordering during crystallization of HCP-Mg in the framework of layering

    NASA Astrophysics Data System (ADS)

    Luo, Jie; Jiang, Yewei; Yu, Ronggang; Wu, Yongquan

    2017-06-01

    In this paper, we performed an NPT molecular dynamics simulation of crystallization process of HCP-Mg to probe the competition between densification and structural ordering. Two opposite layering patterns, i.e. outward and inward, were designed for analysis. From the perspective of solid-like cluster (SLC) itself, structural ordering always precedes densification; but from the perspective of SLC's precursor, structural ordering always lags behind densification; the reversion occurs at the closest two liquid layers around SLC. We call it dip-rebound phenomenon. This phenomenon is a completely new finding. It resolves, to some extent, recent debate about whether densification or structural ordering triggers crystallization.

  3. A Technical Review on Biomass Processing: Densification, Preprocessing, Modeling and Optimization

    SciTech Connect

    Jaya Shankar Tumuluru; Christopher T. Wright

    2010-06-01

    It is now a well-acclaimed fact that burning fossil fuels and deforestation are major contributors to climate change. Biomass from plants can serve as an alternative renewable and carbon-neutral raw material for the production of bioenergy. Low densities of 40–60 kg/m3 for lignocellulosic and 200–400 kg/m3 for woody biomass limits their application for energy purposes. Prior to use in energy applications these materials need to be densified. The densified biomass can have bulk densities over 10 times the raw material helping to significantly reduce technical limitations associated with storage, loading and transportation. Pelleting, briquetting, or extrusion processing are commonly used methods for densification. The aim of the present research is to develop a comprehensive review of biomass processing that includes densification, preprocessing, modeling and optimization. The specific objective include carrying out a technical review on (a) mechanisms of particle bonding during densification; (b) methods of densification including extrusion, briquetting, pelleting, and agglomeration; (c) effects of process and feedstock variables and biomass biochemical composition on the densification (d) effects of preprocessing such as grinding, preheating, steam explosion, and torrefaction on biomass quality and binding characteristics; (e) models for understanding the compression characteristics; and (f) procedures for response surface modeling and optimization.

  4. Effects of enzyme loading, densification, and storage on AFEX-pretreated biomass for ethanol production.

    PubMed

    Biersbach, Gwen; Rijal, Binod; Pryor, Scott W; Gibbons, William R

    2015-12-01

    Corn stover, switchgrass, and prairie cordgrass were treated with an ammonia fiber expansion (AFEX) process and a novel densification method (ComPAKco). Separate hydrolysis and fermentation (SHF) and simultaneous saccharification and fermentation (SSF) were used to evaluate impacts of densification. ComPAKco densification is characterized by low-temperature and low-energy requirements, resulting in compacted biomass briquettes (CBB) 1-2 cm square, with a bulk density of 380-460 kg/m(3). Feedstocks were evaluated before and following AFEX pretreatment, after densification, and after storage. Two enzyme doses were tested. The low rate used 5 filter paper units (FPU) of Spezyme CP (cellulase) and 21.3 cellobiase units (CBU) of Novozyme 188 (aka NS50010 [β-glucosidase]) per gram of glucan. The high dosage rate was three times higher and resulted in 40-56 % and 33-82 % higher ethanol yields with SHF and SSF, respectively. Trials revealed no adverse effect on ethanol yield following densification or 6-month storage of densified, AFEX-pretreated feedstocks.

  5. Densification and crystallization of zirconia thin films prepared by sol-gel processing

    SciTech Connect

    Schwartz, R.W.; Voigt, J.A.; Buchheit, C.D.; Boyle, T.J.

    1993-12-31

    We have investigated the effects of precursor nature and heat treatment schedule on the densification and crystallization behavior of sol-gel derived zirconia thin films. Precursor solutions were prepared from n-propanol, zirconium (IV) n-propoxide, and either acetic acid, or 2,4-pentanedione (acac) and water additions. By controlling the ligand type and ligand-to-metal ratio, we were able to prepare films which displayed significant differences in densification behavior. We attribute the dissimilarity in densification to variations in the nature of the as-deposited films, as influenced by ligand type and concentration. While the acac- derived film was a physical gel, (i.e., a physical aggregation of the oligomeric species), the acetic acid-derived film, which exhibited less consolidation, was a chemical gel that could not be redissolved in the parent solvent. Films prepared with large acac/metal ratios and small water additions exhibited minimal crosslinking at 25{degree}C, displayed the greatest consolidation ({approximately}86% shrinkage) and the highest refractive index (n = 2.071) when heat treated. These results indicate the importance that M-O-M bonds (crosslinks) formed at low temperature can have on densification behavior. We also report on the effects of heat-treatment schedules and ramp rates on densification behavior. All of the films of the present study crystallized into the cubic phase, at temperatures ranging from {approximately}400{degree}C to greater than 700{degree}C, depending on the heating rate.

  6. Modeling morphology evolution and densification during solid-state sintering via kinetic Monte Carlo simulation

    NASA Astrophysics Data System (ADS)

    Chen, Shaohua; Xu, Yaopengxiao; Jiao, Yang

    2016-12-01

    Microstructure control is an important subject in solid-state sintering and plays a crucial role in determining post-sintering material properties, such as strength, toughness and density, to name but a few. The preponderance of existing numerical sintering simulations model the morphology evolution and densification process driven by surface energy minimization by either dilating the particles to be sintered or using the vacancy annihilation model. Here, we develop a novel kinetic Monte Carlo model to model morphology evolution and densification during free sintering. Specifically, we derive analytically a heterogeneous densification rate of the sintering system by considering sintering stress induced mass transport. The densification of the system is achieved by modeling the sintering stress induced mass transfer via applying effective particle displacement and grain boundary migration with an efficient two-step iterative interfacial energy minimization procedure. Coarsening is also considered in the later stages of the simulations. We show that our model can accurately capture the diffusion-induced evolution of particle morphology, including neck formation and growth, as well as realistically reproduce the overall densification of the sintered material. The computationally obtained dynamic density evolution curves for both two-particle sintering and many-particle material sintering are found to be in excellent agreement with the corresponding experimental master sintering curves. Our model can be utilized to control a variety of structural and physical properties of the sintered materials, such as the pore size and final material density.

  7. Technoeconomic analysis of wheat straw densification in the Canadian Prairie Province of Manitoba.

    PubMed

    Mupondwa, Edmund; Li, Xue; Tabil, Lope; Phani, Adapa; Sokhansanj, Shahab; Stumborg, Mark; Gruber, Margie; Laberge, Serge

    2012-04-01

    This study presents a technoeconomic analysis of wheat straw densification in Canada's prairie province of Manitoba as an integral part of biomass-to-cellulosic-ethanol infrastructure. Costs of wheat straw bale and pellet transportation and densification are analysed, including densification plant profitability. Wheat straw collection radius increases nonlinearly with pellet plant capacity, from 9.2 to 37km for a 2-35tonnesh(-1) plant. Bales are cheaper under 250km, beyond which the cheapest feedstocks are pellets from the largest pellet plant that can be built to exploit economies of scale. Feedstocks account for the largest percentage of variable costs. Marginal and average cost curves suggest Manitoba could support a pellet plant up to 35tonnesh(-1). Operating below capacity (75-50%) significantly erodes a plant's net present value (NPV). Smaller plants require higher NPV break-even prices. Very large plants have considerable risk under low pellet prices and increased processing costs.

  8. The effects of powder compressibility, speed of capsule filling and pre-compression on plug densification.

    PubMed

    Llusa, Marcos; Faulhammer, Eva; Biserni, Stefano; Calzolari, Vittorio; Lawrence, Simon; Bresciani, Massimo; Khinast, Johannes

    2014-08-25

    This paper describes the effect of powder compressibility and two process parameters of a dosator nozzle capsule filling machine on powder densification during plug formation. One process parameter was the ratio between the powder bed's depth and the length of the nozzle dosing chamber, hereinafter referred to as F. The other one was the speed of capsule filling. This paper demonstrates that powder densification during the capsule filling process is a function of the powder compressibility and the above process parameters (increasing them leads to higher plug density). The Walker model was used to characterize the compressibility of powders at low compression forces and the obtained compressibility coefficient W proved to be a good predictor of powder densification during the capsule filling process. Copyright © 2014 Elsevier B.V. All rights reserved.

  9. Packing densification of binary mixtures of spheres and cubes subjected to 3D mechanical vibrations

    NASA Astrophysics Data System (ADS)

    An, X. Z.; He, S. S.; Feng, H. D.; Qian, Q.

    2015-01-01

    Packing densification of binary mixtures of spheres and cubes, which are large cubes/small spheres and large spheres/small cubes packing systems, under 3D vibrations was studied physically. The influences of vibration conditions such as vibration time, frequency, amplitude, vibration intensity, volume fraction of large particles, and container size on the packing densification were systematically analyzed, and the optimal processing parameters were identified. And the proposed analytical model was validated as well. The results show that the influences of each operating parameter on the packing densification of different binary mixtures have similar trends; however, the maximum packing densities and corresponding optimal parameters are different. The good agreement between physical and analytical results proves the effectiveness of the proposed analytical model. The results provide meaningful information and references for the random dense packings of binary mixtures of cubes and spheres both in industry and in scientific research.

  10. Review: Pressure-Induced Densification of Oxide Glasses at the Glass Transition

    NASA Astrophysics Data System (ADS)

    Kapoor, Saurabh; Wondraczek, Lothar; Smedskjaer, Morten M.

    2017-02-01

    Densification of oxide glasses at the glass transition offers a novel route to develop bulk glasses with tailored properties for emerging applications. Such densification can be achieved in the technologically relevant pressure regime of up to 1GPa. However, the present understanding of the composition-structure-property relationships governing these glasses is limited, with key questions, e.g., related to densification mechanism, remaining largely unanswered. Recent advances in structural characterization tools and high-pressure apparatuses have prompted new research efforts. Here, we review this recent progress and the insights gained in the understanding of the influence of isostatic compression at elevated temperature (so-called hot compression) on the composition-structure-property relationships of oxide glasses. We focus on compression at temperatures at or around the glass transition temperature (Tg), with relevant comparisons made to glasses prepared by pressure quenching and cold compression. We show that permanent densification at 1 GPa sets-in at temperatures above 0.7Tg and the degree of densification increases with increasing compression temperature and time, until attaining an approximately constant value for temperatures above Tg. For glasses compressed at the same temperature/pressure conditions, we demonstrate direct relations between the degree of volume densification and the pressure-induced change in micro-mechanical properties such as hardness, elastic moduli, and extent of the indentation size effect across a variety of glass families. Furthermore, we summarize the results on relaxation behavior of hot compressed glasses. All the pressure-induced changes in the structure and properties exhibit strong composition dependence. The experimental results highlight new opportunities for future investigation and identify research challenges that need to be overcome to advance the field.

  11. Densification characteristics of chromia/alumina castables by particle size distribution

    PubMed Central

    2012-01-01

    The quality of the refractories applied on integrated gasification combined cycle should be a key factor that affects both the reliability and the economics of gasifier operation. To enhance the workability of chromia/alumina castables, three types of ultrafine alumina powder were added to improve the workability. Densification behavior of such castables in the presence of ultrafine alumina was assessed through the measurement of parameters like flow value, viscosity, bulk density, apparent porosity, and microstructure evaluation by an SEM study. It's proved that the specific surface area and particle size distribution of ultrafine powders in matrix parts greatly influence the densification behavior of these castables. PMID:22221548

  12. Densification characteristics of chromia/alumina castables by particle size distribution

    NASA Astrophysics Data System (ADS)

    Zhao, Jingming; Kim, Taesuk; Kim, Gichul; Hwang, Kyuhong; Bae, Dongsik

    2012-01-01

    The quality of the refractories applied on integrated gasification combined cycle should be a key factor that affects both the reliability and the economics of gasifier operation. To enhance the workability of chromia/alumina castables, three types of ultrafine alumina powder were added to improve the workability. Densification behavior of such castables in the presence of ultrafine alumina was assessed through the measurement of parameters like flow value, viscosity, bulk density, apparent porosity, and microstructure evaluation by an SEM study. It's proved that the specific surface area and particle size distribution of ultrafine powders in matrix parts greatly influence the densification behavior of these castables.

  13. Nanostructure formation by dynamic densification and recrystallization of amorphous Ti-Si alloy

    NASA Astrophysics Data System (ADS)

    Counihan, P. J.; Crawford, A.; Thadhani, N. N.

    1998-07-01

    Dynamic densification was used to consolidate mechanically amorphized Ti-Si alloy powders, using a 3-capsule, plate-impact, gas-gun loading system at velocities of 300 and 500 m/s. The recovered amorphous compacts were subsequently annealed above the crystallization temperature. A single-phase nano-structured (50-90 nm) Ti5Si3 compound was produced, as revealed by TEM and XRD analysis. In this paper, the influence of dynamic densification on the crystallization behavior of amorphous Ti-Si, and the formation of nano-crystals will be discussed.

  14. Densification forming of alumina powder -- Effects of power law creep and friction

    SciTech Connect

    Kwon, Y.S.; Kim, K.T.

    1996-10-01

    High temperature forming processes of alumina powder compacts were analyzed by using constitutive equations which are capable of predicting densification and grain growth under diffusional creep and power law creep. Experimental results for alumina powder compacts were compared with finite element calculations by using the constitutive equations. The effects of friction between alumina powder compact and punches during sinter forging of alumina powder compacts were also investigated. Densification mechanism maps of alumina powder, which can be used for the optimization of various process variables, were constructed under hot pressing and general states of stresses.

  15. Effects of thermo-hygro-mechanical densification on the surface characteristics of trembling aspen and hybrid poplar wood veneers

    NASA Astrophysics Data System (ADS)

    Diouf, Papa Niokhor; Stevanovic, Tatjana; Cloutier, Alain; Fang, Chang-Hua; Blanchet, Pierre; Koubaa, Ahmed; Mariotti, Nicolas

    2011-02-01

    The effect of thermo-hygro-mechanical (THM) densification temperature on the surface color, roughness, wettability, and chemical composition of trembling aspen (Populus tremuloides) and hybrid poplar (Populus maximowiczii × P. balsamifera) veneers was investigated. Veneers were subjected to four THM densification temperatures (160 °C, 180 °C, 200 °C, and 220 °C). Veneer color darkened with increasing THM densification temperature. Surface roughness decreased between 160 °C and 200 °C. Wettability decreased after THM densification, but no significant difference was found between treated specimens. ATR-FTIR and XPS results confirmed that THM densification caused major chemical changes in veneer surfaces, and more pronounced at temperatures higher than 160 °C.

  16. Development of Macroscale Models of UO2 Fuel Sintering and Densification using Multiscale Modeling and Simulation

    SciTech Connect

    Ian Greenquist; Michael Tonks

    2016-10-01

    Light water reactor fuel pellets are fabricated using sintering to final densities of 95% or greater. During reactor operation, the porosity remaining in the fuel after fabrication decreases further due to irradiation-assisted densification. While empirical models have been developed to describe this densification process, a mechanistic model is needed as part of the ongoing work by the NEAMS program to develop a more predictive fuel performance code. In this work we will develop a phase field model of sintering of UO2 in the MARMOT code, and validate it by comparing to published sintering data. We will then add the capability to capture irradiation effects into the model, and use it to develop a mechanistic model of densification that will go into the BISON code and add another essential piece to the microstructure-based materials models. The final step will be to add the effects of applied fields, to model field-assisted sintering of UO2. The results of the phase field model will be validated by comparing to data from field-assisted sintering. Tasks over three years: 1. Develop a sintering model for UO2 in MARMOT 2. Expand model to account for irradiation effects 3. Develop a mechanistic macroscale model of densification for BISON

  17. The Influence of Simulated Home and Neighbourhood Densification on Perceived Liveability

    ERIC Educational Resources Information Center

    Thomas, J. A.; Walton, D.; Lamb, S.

    2011-01-01

    This study experimentally manipulated neighbourhood density and home location to reveal the effect of these changes on perceived liveability. Two hypothetical scenarios were provided to 106 households using a Computer-Aided Personal Interview (CAPI). The first scenario examined a densification of the participant's current property, and the second…

  18. The Densification of Molybdenum and Molybdenum Alloy Powders Using Hot Isostatic Pressing.

    DTIC Science & Technology

    1985-08-01

    TECHNICAL REPORT ARLCB-TR-85025 00 THE DENSIFICATION OF MOLYBDENUM (n AND MOLYBDENUM ALLOY POWDERS USING HOT ISOSTATIC PRESSING J. BARRANCO I. AHMAD S...ISOSTATIC PRESSING Final 6. PERFORMING ORG. REPORT NUMBER 7. AUTHOR(o) . CONTRACT OR GRANT NUMBER(e) J. Barranco , I. Ahmad, S. Isserow, and R. Warenchak

  19. Performance Tests of a Liquid Hydrogen Propellant Densification Ground System for the X33/RLV

    NASA Technical Reports Server (NTRS)

    Tomsik, Thomas M.

    1997-01-01

    A concept for improving the performance of propulsion systems in expendable and single-stage-to-orbit (SSTO) launch vehicles much like the X33/RLV has been identified. The approach is to utilize densified cryogenic liquid hydrogen (LH2) and liquid oxygen (LOX) propellants to fuel the propulsion stage. The primary benefit for using this relatively high specific impulse densified propellant mixture is the subsequent reduction of the launch vehicle gross lift-off weight. Production of densified propellants however requires specialized equipment to actively subcool both the liquid oxygen and liquid hydrogen to temperatures below their normal boiling point. A propellant densification unit based on an external thermodynamic vent principle which operates at subatmospheric pressure and supercold temperatures provides a means for the LH2 and LOX densification process to occur. To demonstrate the production concept for the densification of the liquid hydrogen propellant, a system comprised of a multistage gaseous hydrogen compressor, LH2 recirculation pumps and a cryogenic LH2 heat exchanger was designed, built and tested at the NASA Lewis Research Center (LeRC). This paper presents the design configuration of the LH2 propellant densification production hardware, analytical details and results of performance testing conducted with the hydrogen densifier Ground Support Equipment (GSE).

  20. The Influence of Simulated Home and Neighbourhood Densification on Perceived Liveability

    ERIC Educational Resources Information Center

    Thomas, J. A.; Walton, D.; Lamb, S.

    2011-01-01

    This study experimentally manipulated neighbourhood density and home location to reveal the effect of these changes on perceived liveability. Two hypothetical scenarios were provided to 106 households using a Computer-Aided Personal Interview (CAPI). The first scenario examined a densification of the participant's current property, and the second…

  1. 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.

  2. A Review on Biomass Densification Systems to Develop Uniform Feedstock Commodities for Bioenergy Application

    SciTech Connect

    Jaya Shankar Tumuluru; Christopher T. Wright; J. Richard Hess; Kevin L. Kenney

    2011-11-01

    Developing uniformly formatted, densified feedstock from lignocellulosic biomass is of interest to achieve consistent physical properties like size and shape, bulk and unit density, and durability, which significantly influence storage, transportation and handling characteristics, and, by extension, feedstock cost and quality. A variety of densification systems are considered for producing a uniform format feedstock commodity for bioenergy applications, including (a) baler, (b) pellet mill, (c) cuber, (d) screw extruder, (e) briquette press, (f) roller press, (g) tablet press, and (g) agglomerator. Each of these systems has varying impacts on feedstock chemical and physical properties, and energy consumption. This review discusses the suitability of these densification systems for biomass feedstocks and the impact these systems have on specific energy consumption and end product quality. For example, a briquette press is more flexible in terms of feedstock variables where higher moisture content and larger particles are acceptable for making good quality briquettes; or among different densification systems, a screw press consumes the most energy because it not only compresses but also shears and mixes the material. Pretreatment options like preheating, grinding, steam explosion, torrefaction, and ammonia fiber explosion (AFEX) can also help to reduce specific energy consumption during densification and improve binding characteristics. Binding behavior can also be improved by adding natural binders, such as proteins, or commercial binders, such as lignosulphonates. The quality of the densified biomass for both domestic and international markets is evaluated using PFI (United States Standard) or CEN (European Standard).

  3. Densification and grain growth of stainless steel microsize structures fabricated by μMIM

    NASA Astrophysics Data System (ADS)

    Liu, L.; Loh, N. H.; Tay, B. Y.; Tor, S. B.; Murakoshi, Y.; Maeda, R.

    2006-04-01

    Micro metal injection molding (μMIM) is being developed by some researchers for possible mass production of metallic microcomponents. Knowledge of densification and grain growth of structures in the micrometer regime is important for the design of microcomponents due to their impacts on dimensional tolerance and mechanical properties. In this paper, the effects of sintering temperature and time on densification and grain growth of stainless steel microsize structures fabricated by μMIM were investigated. In particular, the density of the microsize structures was compared with that of the components, dimensions in the millimeter range, on which the microsize structures reside. Models proposed by Kang, Brook, and Zhao and Harmer were used to study the densification and grain growth kinetics of microsize structures of ∅100μmat the final stage of sintering. Dense layers were formed on the microsize structures. Thus, the density of the microsize structures is higher than that of the microstructured components. The thickness of the dense layers increased with either increasing temperature or time. Zhao and Harmer’s model for lattice diffusion controlled densification and Brook’s grain growth model for lattice diffusion controlled pore drag exhibited good fits for the experimental results of microsize structures.

  4. Bond-breaking mechanism of vitreous silica densification by IR femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Shcheblanov, Nikita S.; Povarnitsyn, Mikhail E.

    2016-04-01

    The densification of the vitreous silica (v-SiO2) due to laser irradiation appears reasonable to cause the change in refractive index. In this letter, the v-SiO2 densification under IR femtosecond laser irradiation is studied within molecular-dynamics simulation. The single- and multi-pulse interactions are explored numerically with an account of the bond-breaking mechanism. By analyzing the network at nanoscale, the nature of v-SiO2 densification is assigned to the reduction of major ring fractions of six- and seven-membered rings to minor fractions of three- and four-membered rings (related to D 2 and D 1 Raman signatures, respectively). The athermal behavior of v-SiO2 densification is disclosed at different degrees of ionization for both the single- and multi-pulse cases at sub-threshold regimes. The good agreement between calculated and measured D2 defect line and Si-O-Si angle changes argues in favor of the found mechanism.

  5. Saos-2 cell-mediated mineralization on collagen gels: Effect of densification and bioglass incorporation.

    PubMed

    Liu, Gengbo; Pastakia, Meet; Fenn, Michael B; Kishore, Vipuil

    2016-05-01

    Plastic compression is a collagen densification process that has been widely used for the development of mechanically robust collagen-based materials. Incorporation of bioglass within plastically compressed collagen gels has been shown to mimic the microstructural properties of native bone and enhance in vitro cell-mediated mineralization. The current study seeks to decouple the effects of collagen densification and bioglass incorporation to understand the interplay between collagen packing density and presence of bioglass on cell-mediated mineralization. Saos-2 cell-mediated mineralization was assessed as a measure of the osteoconductivity of four different collagen gels: (1) uncompressed collagen gel (UC), (2) bioglass incorporated uncompressed collagen gel (UC + BG), (3) plastically compressed collagen gel (PC), and (4) bioglass incorporated plastically compressed collagen gel (PC + BG). The results indicated that collagen densification enhanced mineralization as shown by SEM, increased alkaline phosphatase activity and produced significantly higher amounts of mineralized nodules on PC gels compared to UC gels. Further, the amount of nodule formation on PC gels was significantly higher compared to UC + BG gels indicating that increase in matrix stiffness due to collagen densification had a greater effect on cell-mediated mineralization compared to bioglass incorporation into loosely packed UC gels. Incorporation of bioglass into PC gels further enhanced mineralization as evidenced by significantly larger nodule size and higher amount of mineralization on PC + BG gels compared to PC gels. In conclusion, collagen densification via plastic compression improves the osteoconductivity of collagen gels. Further, incorporation of bioglass within PC gels has an additive effect and further enhances the osteoconductivity of collagen gels. © 2016 Wiley Periodicals, Inc.

  6. Densification behavior of ceramic and crystallizable glass materials constrained on a rigid substrate

    NASA Astrophysics Data System (ADS)

    Calata, Jesus N.

    2005-11-01

    Constrained sintering is an important process for many applications. The sintering process almost always involves some form of constraint, both internal and external, such as rigid particles, reinforcing fibers and substrates to which the porous body adheres. The densification behavior of zinc oxide and cordierite-base crystallizable glass constrained on a rigid substrate was studied to add to the understanding of the behavior of various materials undergoing sintering when subjected to external substrate constraint. Porous ZnO films were isothermally sintered at temperatures between 900°C and 1050°C. The results showed that the densification of films constrained on substrates is severely reduced. This was evident in the sintered microstructures where the particles are joined together by narrower necks forming a more open structure, instead of the equiaxed grains with wide grain boundaries observed in the freestanding films. The calculated activation energies of densification were also different. For the density range of 60 to 64%, the constrained film had an activation energy of 391 +/- 34 kJ/mole compared to 242 +/- 21 kJ/mole for the freestanding film, indicating a change in the densification mechanism. In-plane stresses were observed during the sintering of the constrained films. Yielding of the films, in which the stresses dropped slight or remained unchanged, occurred at relative densities below 60% before the stresses climbed linearly with increasing density followed by a gradual relaxation. A substantial amount of the stresses remained after cooling. Free and constrained films of the cordierite-base crystallizable glass (glass-ceramic) were sintered between 900°C and 1000°C. The substrate constraint did not have a significant effect on the densification rate but the constrained films eventually underwent expansion. Calculations of the densification activation energy showed that, on average, it was close to 1077 kJ/mole, the activation energy of the glass

  7. Grain growth, densification and mechanical properties of nanocrystalline tungsten carbide-cobalt

    NASA Astrophysics Data System (ADS)

    Wang, Xu

    Over two decades, attempts to produce cemented tungsten carbide with nanocrystalline grain structure have been made to obtain dramatically improved mechanical properties to extend the lifetime and robustness of tungsten carbide tools. The attempts have shown that the conventional methods by liquid phase sintering cannot retain nanoscale grain sizes while achieving full densification because significant grain growth of WC occurs during sintering. There have been many works that focused on developing alternative techniques to liquid phase sintering, such as Microwave Sintering (MS), Spark Plasma Sintering (SPS), High Frequency Induction Heated Sintering (HFIHS), and so on. In all of these investigations, densification is accompanied by significant grain growth. The finest average grain size that is achievable until now is still approximately 100-300 nm. In this research, the challenges of sintering nanocrystalline WC-Co powders were further examined. The key challenge to the production of bulk nanocrystalline cemented tungsten carbide materials is to control the rapid grain growth during the early stage of sintering, especially during heat up stage. In order to understand the mechanisms of grain growth and densification during the early stage of sintering of nanocrystalline WC-Co powders, the sintering behaviors of nanosized WC during the early stages of sintering were studied as a function of temperature and time. The effects of other influencing factors, such as initial grain size, cobalt content, and grain growth inhibitor, were investigated. As a way to make nanocrystalline WC-Co materials, an ultrahigh pressure rapid hot consolidation process (UPRC) was developed. The effects of the UPRC process variables (including heating rate, temperature, holding time, and pressure) on grain growth and densification of the nano powders were studied. Based on the analysis of kinetics of the grain growth and densification and the microstructure evolution during sintering, the

  8. The effect of powder sintering method on the densification and microstructure of pewter alloys

    NASA Astrophysics Data System (ADS)

    Firdaus Ariff, Tasnim; Gabbitas, Brian; Zhang, Deliang

    2009-08-01

    Pewter alloys made from tin, copper and antimony powders were sintered using microwave and conventional vacuum sintering. Three different compositions of the pewter alloy were used; 91Sn6Cu3Sb, 94Sn4Cu2Sb and 97Sn2Cu1Sb. The effect of densification and microstructure of the pewter alloys from varying sintering time and sintering mode were examined and compared. Samples were compacted at 40kN and sintered at 220°C. Samples in the conventional furnace were sintered 60 minutes and 120 minutes, while samples in the microwave furnace were sintered for 15 and 30 minutes. Samples sintered at longer sintering times resulted in higher density for both sintering methods. Microwave sintering produced samples with slightly smaller grain size than the conventionally sintered samples resulting in a better densification. There were no new phases formed from the sintering of pewter alloy.

  9. Silicon nitride-aluminum oxide solid solution (SiAION) formation and densification by pressure sintering

    NASA Technical Reports Server (NTRS)

    Yeh, H. C.; Sanders, W. A.; Fiyalko, J. L.

    1975-01-01

    Stirred-ball-mill-blended Si3N4 and Al2O3 powders were pressure sintered in order to investigate the mechanism of solid solution formation and densification in the Si3N4-Al2O3 system. Powder blends with Si3N4:Al2O3 mole ratios of 4:1, 3:2, and 2:3 were pressure sintered at 27.6-MN/sq m pressure at temperatures to 17000 C (3090 F). The compaction behavior of the powder blends during pressure sintering was determined by observing the density of the powder compact as a function of temperature and time starting from room temperature. This information, combined with the results of X-ray diffraction and metallographic analyses regarding solutioning and phase transformation phenomena in the Si3N4-Al2O3 system, was used to describe the densification behavior.

  10. Nanostructure Formation by Dynamic Densification and Recrystallization of Amorphous Ti-Si Alloy

    NASA Astrophysics Data System (ADS)

    Counihan, P. J.; Thadhani, N. N.

    1997-07-01

    Dynamic densification was used to consolidate mechanically amorphized Ti-Si alloy powders. A 3-capsule, plate-impact, gas-gun loading system was used to densify the powders at impact velocities of 300 and 500 m/s. The recovered compacts were observed to retain the amorphous structure as evidenced by x-ray diffraction (XRD) and transmission microscopy (TEM) analysis. The densified material was subsequently annealed at various temperatures (above the crystallization temperature) to produce a nanocrystalline Ti_5Si3 microstructure. TEM and XRD analysis revealed retention of a nano-grain microstructure (< 100 nm) in the crystallized compacts. In this presentation the influence of dynamic densification on the crystallization of the amorphous compound and retention of the nano-scale grain size in the crystallized compacts will be discussed.

  11. Initial Test Results of Laboratory Scale Hydrogen Liquefaction and Densification System

    NASA Astrophysics Data System (ADS)

    Baik, J. H.; Notardonato, W. U.

    2006-04-01

    Using densified liquid hydrogen as a cryogenic propellant for launch vehicle applications can reduce fuel tank volumes, decrease vapor pressures, and improve cooling capacity over the normal boiling point propellant. A densified liquid hydrogen test bed has been developed using Gifford-McMahon cryocooler to refrigerate hydrogen inside the 150L storage tank at the Florida Solar Energy Center (FSEC). This work is a collaborative effort amongst researchers at FSEC and NASA Kennedy Space Center. The test bed has an integrated refrigeration and storage system with multiple capabilities including hydrogen liquefaction, densification, and zero-boil-off (ZBO) storage test. This paper focuses on the design considerations, the detailed system descriptions, and the results obtained during initial hydrogen liquefaction and densification tests.

  12. Densification and strain hardening of a metallic glass under tension at room temperature.

    PubMed

    Wang, Z T; Pan, J; Li, Y; Schuh, C A

    2013-09-27

    The deformation of metallic glasses involves two competing processes: a disordering process involving dilatation, free volume accumulation, and softening, and a relaxation process involving diffusional ordering and densification. For metallic glasses at room temperature and under uniaxial loading, disordering usually dominates, and the glass can fail catastrophically as the softening process runs away in a localized mode. Here we demonstrate conditions where the opposite, unexpected, situation occurs: the densifying process dominates, resulting in stable plastic deformation and work hardening at room temperature. We report densification and hardening during deformation in a Zr-based glass under multiaxial loading, in a notched tensile geometry. The effect is driven by stress-enhanced diffusional relaxation, and is attended by a reduction in exothermic heat and hardening signatures similar to those observed in the classical thermal relaxation of glasses. The result is significant, stable, plastic, extensional flow in metallic glasses, which suggest a possibility of designing tough glasses based on their flow properties.

  13. Densification of uranium dioxide fuel pellets prepared by spark plasma sintering (SPS)

    NASA Astrophysics Data System (ADS)

    Ge, Lihao; Subhash, Ghatu; Baney, Ronald H.; Tulenko, James S.; McKenna, Edward

    2013-04-01

    An investigation into the influence of processing parameters on densification of UO2 powder during spark plasma sintering (SPS) is presented. A broad range of sintering temperatures, hold time and heating rates have been systematically varied to investigate their influence on the sintered pellet densification process, grain growth, hardness, and Young's modulus. The results revealed that up to 96% theoretical density (TD) pellets can be obtained at a sintering temperature of 1050 °C for 30 s hold time and a total run time of only 10 min. The resulting UO2 pellets had an average Vickers hardness of 6.4 ± 0.4 GPa and Young's modulus of 204 ± 18 GPa, which are in excellent agreement with values reported in literature for UO2 processed by other methods.

  14. Densification kinetics of nanocrystalline zirconia powder using microwave and spark plasma sintering--a comparative study.

    PubMed

    Vasylkiv, Oleg; Demirskyi, Dmytro; Sakka, Yoshio; Ragulya, Andrey; Borodianska, Hanna

    2012-06-01

    Two-stage densification process of nanosized 3 mol% yttria-stabilized zirconia (3Y-SZ) polycrystalline compacts during consolidation via microwave and spark-plasma sintering have been observed. The values of activation energies obtained for microwave and spark-plasma sintering 260-275 kJ x mol(-1) are quite similar to that of conventional sintering of zirconia, suggesting that densification during initial stage is controlled by the grain-boundary diffusion mechanism. The sintering behavior during microwave sintering was significantly affected by preliminary pressing conditions, as the surface diffusion mechanism (230 kJ x mol(-1)) is active in case of cold-isostatic pressing procedure was applied.

  15. The densification of bio-char: Effect of pyrolysis temperature on the qualities of pellets.

    PubMed

    Hu, Qiang; Yang, Haiping; Yao, Dingding; Zhu, Danchen; Wang, Xianhua; Shao, Jingai; Chen, Hanping

    2016-01-01

    The densification of bio-chars pyrolyzed at different temperatures were investigated to elucidate the effect of temperature on the properties of bio-char pellets and determine the bonding mechanism of pellets. Optimized process conditions were obtained with 128MPa compressive pressure and 35% water addition content. Results showed that both the volume density and compressive strength of bio-char pellets initially decreased and subsequently increased, while the energy consumption increased first and then decreased, with the increase of pyrolysis temperature. The moisture adsorption of bio-char pellets was noticeably lower than raw woody shavings but had elevated than the corresponding char particles. Hydrophilic functional groups, particle size and binder were the main factors that contributed to the cementation of bio-char particles at different temperatures. The result indicated that pyrolysis of woody shavings at 550-650°C and followed by densification was suitable to form bio-char pellets for application as renewable biofuels.

  16. Influence of Chemical Composition Variations on Densification During the Sintering of MOX Materials

    NASA Astrophysics Data System (ADS)

    Vaudez, S.; Marlot, C.; Lechelle, J.

    2016-06-01

    The mixed uranium-plutonium oxide (MOX) fabrication process is based on the preparation of UO2 and PuO2 powders. The mixture is pelletized before being sintered at 1973 K (1700 °C) in a reducing atmosphere of Ar/4pctH2/H2O. This paper shows how the densification of MOX fuel is affected during sintering by the moisture content of the gas, the plutonium content of the fuel, and the carbon impurity content in the raw materials. MOX densification can be monitored through dilatometric measurements and gas releases can be continuously analyzed during sintering in terms of their quantity and quality. Variations in the oxygen content in the fuel can be continuously recorded by coupling the dilatometer furnace with an oxygen measurement at the gas outlet. Any carbon-bearing species released, such as CO, can be also linked to densification phenomena when a gas chromatograph is installed at the outlet of the dilatometer. Recommendations on the choice of sintering atmosphere that best optimizes the fuel characteristics have been given on the basis of the results reported in this paper.

  17. Hot isostatic pressing (HIP) of powder mixtures and composites: Packing, densification, and microstructural effects

    SciTech Connect

    Li, E.K.H.; Funkenbusch, P.D. . Department of Mechanical Engineering)

    1993-06-01

    Hot isostatic pressing (HIP) of powder mixtures (containing differently sized components) and of composite powders is analyzed. Recent progress, including development of a simple scheme for estimating radial distribution functions, has made modeling of these systems practical. Experimentally, powders containing bimodal or continuous size distributions are observed to hot isostatically press to a higher density tinder identical processing conditions and to show large differences in the densification rate as a function of density when compared with the monosize powders usually assumed for modeling purposes. Modeling correctly predicts these trends and suggests that they can be partially, but not entirely, attributed to initial packing density differences. Modeling also predicts increased deformation in the smaller particles within a mixture. This effect has also been observed experimentally and is associated with microstructural changes, such as preferential recrystallization of small particles. Finally, consolidation of a composite mixture containing hard, but deformable, inclusions has been modeled for comparison with existing experimental data. Modeling results match both the densification and microstructural observations reported experimentally. Densification is retarded due to contacts between the reinforcing particles which support a significant portion of the applied pressure. In addition, partitioning of deformation between soft matrix and hard inclusion powders results in increased deformation of the softer material.

  18. Spark Plasma Sintering of Commercial Zirconium Carbide Powders: Densification Behavior and Mechanical Properties

    PubMed Central

    Wei, Xialu; Back, Christina; Izhvanov, Oleg; Khasanov, Oleg L.; Haines, Christopher D.; Olevsky, Eugene A.

    2015-01-01

    Commercial zirconium carbide (ZrC) powder is consolidated by Spark Plasma Sintering (SPS). Processing temperatures range from 1650 to 2100 °C. Specimens with various density levels are obtained when performing single-die SPS at different temperatures. Besides the single-die tooling setup, a double-die tooling setup is employed to largely increase the actual applied pressure to achieve higher densification in a shorter processing time. In order to describe the densification mechanism of ZrC powder under SPS conditions, a power-law creep constitutive equation is utilized, whose coefficients are determined by the inverse regression of the obtained experimental data. The densification of the selected ZrC powder is shown to be likely associated with grain boundary sliding and dislocation glide controlled creep. Transverse rupture strength and microhardness of sintered specimens are measured to be up to 380 MPa and 24 GPa, respectively. Mechanical properties are correlated with specimens’ average grain size and relative density to elucidate the co-factor dependencies. PMID:28793550

  19. Densification Process of OH Controlled Hydroxyapatite Ceramics by Spark Plasma Sintering

    SciTech Connect

    Kawagoe, D.; Koga, Y.; Ishida, E. H.; Ioku, K.

    2006-05-15

    Calcium hydroxyapatite, Ca10(PO4)6(OH)2:HA, is the inorganic principle component of natural bones and teeth. It has been already suggested that the amount of OH ion in the crystal structure of HA is closely related to the biocompatibility. The amount of OH ion in current HA, however, has not been controlled. In order to prepare more functional HA ceramics, the amount of OH ion must be controlled. In this study, HA ceramics with different OH amount were prepared from fine HA crystals by spark plasma sintering (SPS). In order to reveal the ideal sintering conditions for preparation of transparent ceramics, densification process on SPS was investigated. The samples were pressed uniaxialy under 60 MPa, and then they were heated by SPS at 800 deg. C, 900 deg. C and 1000 deg. C for 10 min with the heating rate of 25 deg. C{center_dot}min-1. The quantity of OH ion in HA ceramics sintered by SPS was decreased with increasing temperature of sintering. Transparent HA ceramics were prepared by SPS at 900 deg. C and 1000 deg. C. In analysis of the densification behavior during sintering of HA by SPS, dominant sintering mechanism was plastic flow of densification. Transparent ceramics should be the most suitable materials to investigate the interface between human cells and ceramics.

  20. Densification Kinetics and Structural Evolution During Microwave and Pressureless Sintering of 15 nm Titanium Nitride Powder

    NASA Astrophysics Data System (ADS)

    Zgalat-Lozynskyy, Ostap; Ragulya, Andrey

    2016-02-01

    Microwave sintering (MWS) of commercially available 15-nm-size nanocrystalline TiN powder was studied. Densification kinetics and grain growth mechanisms of nano-TiN were evaluated using non-isothermal heating up to 1500 °C with variable heating rates. A true nanocrystalline ceramic with ~80-nm-size grains and 94.5 % theoretical density was obtained via MWS consolidation at 1400 °C. At higher temperatures, however, an uncontrolled grain growth and a formation of bimodal microstructure were noticed. A temperature dependence of grain growth suggested grain boundary sliding as a primary mechanism of densification below 1100-1200 °C. An activation energy of nano-TiN densification under MWS varied from 26 ± 3 kJ/mol at the initial stage of sintering (900-1200 °C) to 162 ± 22 kJ/mol at higher temperatures. In addition, a relationship coupling microstructural characteristics (grain size, grain boundary) with mechanical properties of titanium nitride ceramics obtained via both microwave and pressureless sintering techniques was discussed.

  1. Observation of Porosity Reduction in a Densification-Prone Test Fuel Rod: Data and Analysis

    SciTech Connect

    Cunningham, M. E.; Daniel, J. L.; Lanning, D. D.

    1981-10-01

    Instrumented fuel assembly (IFA)-431 was irradiated in the Halden Boiling Water Reactor (HBWR) for the purpose of extending the steady-state data base. Rod 6 of this assembly began irradiation with UO{sub 2} fuel of 92% theoretical density (TD) that was unstable with respect to in-reactor densification. Thermal resintering tests resulted in a final density of 95.3% TD while post-irradiation examination (PIE) indicated a final density of 96.5% TD. Observed microstructural changes were consistent with published densification studies; there was a marked depletion of submicrometer diameter pores and total pore volume. However, grain size increased only slightly, indicating that internal pellet temperatures did not reach the 1875K applied in resintering tests. Oensification was observed to increase the temperatures in rod 6, but temperatures did not become as high as for a sibling rod that simulated instantaneous densification. Temperatures calculated with U.S. Nuclear Regulatory Commission (NRC) fuel performance computer codes were generally higher than observed temperatures.

  2. Effect of ZnO addition on the purity and densification of forsterite ceramic

    NASA Astrophysics Data System (ADS)

    Tan, C. Y.; Tan, Y. M.; Ramesh, S.; Yap, B. K.

    2017-06-01

    Forsterite was found to the next potential candidate for bone implant application due to its superior mechanical properties as compared to the commonly used hydroxyapatite (HA). Various methods including two-step sintering and improvise synthesis method were introduced in hope to further improve the mechanical properties of forsterite. In this work, sintering additives, particularly zinc oxide (ZnO), was introduced into forsterite to provide enhancement on the densification of forsterite at lower sintering temperature. Forsterite powder was synthesized via solid-state reaction method with heat treatment at 1000°C for 2 hours with 10°C/min ramping rate. Addition of ZnO was conducted using milling process with composition of 0.5 wt% and 1.0 wt% ZnO. Green bulk samples were prepared prior to sintering process at 1200°C to 1500°C for 2 hours with 10°C/min ramping rate. Characterization was conducted in terms of phase stability and densification of forsterite with morphology examination to observe the grain surface of all samples. It was revealed that the addition of ZnO showed a more superior densification as compared to the undoped samples at all sintering regime studied with a maximum relative density obtained at 97.7% by 0.5 wt% ZnO doped sample sintered at 1500°C.

  3. Nanoscale-shape-mediated coupling between temperature and densification in intense pulsed light sintering

    NASA Astrophysics Data System (ADS)

    Bansal, S.; Malhotra, R.

    2016-12-01

    In intense pulsed light sintering (IPL), pulsed large-area visible light from a xenon lamp is absorbed by nanoparticle films or patterns and converted to heat, resulting in rapid sintering of the nanoparticles. This work experimentally characterizes IPL of silver nanoparticle films. A newly observed turning point in the evolution of film temperature during IPL is correlated to the observation, in literature and in this work, that film densification levels off beyond a critical pulse fluence and number of pulses. A computational model is developed that couples electromagnetic finite element analysis, heat transfer models and densification models to predict the evolution of film temperature and density during IPL. This model is able to capture the experimentally observed turning point in temperature during IPL, whereas current models of IPL are unable to do so. It is shown that the temperature turning point occurs due to a coupling between optical absorption and densification in the nanoparticle film, mediated by a change in nanoscale shape of the deposited nanoparticles due to interparticle neck growth. Further, it is found that the optical fluence per pulse has a greater effect on the achievable film density in IPL, as compared to the number of pulses.

  4. Powder densification. 1. Particle-particle basis for incorporation of viscoelastic material properties.

    PubMed

    Lum, S K; Duncan-Hewitt, W C

    1999-02-01

    The present investigation was undertaken to examine the basic unit of densification: the particle-particle indentation. The true interparticle contact area that is established during densification ultimately determines the quality of the tablet compact. By examining the interfacial contact between mutually indenting viscoelastic particles, the process of contact evolution may be represented in mathematical form through extension of the classical Hertzian elastic contact description to encompass material viscoelastic terms. In this way, the time-dependent response of materials to applied loads may be addressed explicitly. The effects of rates of applied loading and maximum load levels were also considered. This analysis was based on viscoelastic stress data collected using an instrumented Instron analyzer during the densification of PMMA/coMMA, a pharmaceutical polymeric coating material. A crossed cylinder matrix compaction geometry was used to simulate the geometry of two mutually indenting spherical particles. Numerical and graphical solutions delineating the relationship between contact area evolution and the prescribed loading force are presented. This particle-particle description of the contacting interface serves as a unit basis for describing the entire powder bed. The powder bed may ultimately be modeled as a collection of these particles in contact.

  5. Influence of autogenous seeding on densification and microstructure in processing of γ-alumina nanopowders

    NASA Astrophysics Data System (ADS)

    Khodabakhshi, F.; Maleksaeedi, S.; Paydar, M. H.; Saadat, S.

    2011-01-01

    The effect of α-Al2O3 seeds and MgO on the densification behavior and microstructure of the nanocrystalline γ-Al2O3 powder was investigated. The required α-Al2O3 seeds were produced by 'autogenous seeding' where the seeds were obtained by calcination of the initial nanosized γ-Al2O3 powders above its transformation temperature and incorporated into γ-Al2O3 matrix. The seeds were characterized by means of laser particle size analyzer, X-ray diffraction, and Brunauer-Emmett-Teller surface analyzer. The simultaneous influence of α-Al2O3 seeds and MgO on γ-Al2O3 behavior was evaluated by differential thermal analysis, densitometry, and electron microscopy. The results showed that simultaneous presence of MgO and seeds in γ-Al2O3 matrix has a great impact on densification and microstructural evolution. The main role of MgO and the seeds are densification enhancement and grain refinement, respectively. The grain morphology is more equiaxed and desirably finer by using smaller seeds prepared using shorter calcination times.

  6. Phase-field simulations of the impact of bimodal pore size distributions on solid-state densification

    NASA Astrophysics Data System (ADS)

    Berry, Bruce E.; Millett, Paul C.

    2017-08-01

    The densification behavior of a porous body subjected to elevated temperature is relevant to many nuclear fuel performance metrics. The diffusional processes that govern such densification occur on microscopic length scales, and depend on the type of material and the nature of the porosity. In this study, we explore how bimodal pore size distributions impact diffusion-based densification relative to monomodal pore sizes for a given overall value of porosity. We utilize a Cahn-Hilliard phase-field model implemented with the MOOSE framework to simulate densification evolution with a range of overall porosities and a variety of porosity distributions between small and large pores. The results demonstrate that bimodal porosity can resist densification to a much greater extent than monomodal porosity. These findings have implications for the microstructural design of metallic nuclear fuels, in which an initial, bimodal porosity may resist early-stage densification and therefore provide collection sites for fission gases, thus reducing in-pile fission gas swelling.

  7. Experimental investigation of uranium dicarbide densification and the influence of free carbon diffusion

    SciTech Connect

    Chidester, K.M.

    1991-04-01

    Because UC{sub 2} fuel is being considered for space reactor applications, an investigation of process parameters and densification mechanisms for this fuel was conducted for the DOE. Uranium dicarbide feed powder was prepared by carbothermic reduction of uranium dicarbide and graphite at 2050 K in vacuum. Uranium dicarbide pellets were prepared by cold pressing at 110 MPa and sintering at 2370 K in contact with niobium, tantalum, or tungsten substrates in argon, argon-hydrogen, and vacuum atmospheres. Argon proved to be the most effective for sintering. A high density front was observed to move through the pellets, starting from the pellet-metal substrate interface. The primary factor controlling this phenomenon is the diffusion of carbon from the uranium dicarbide pellet into the metal substrate. When the carbon level reduces so that no free carbon is present, rapid densification of the uranium dicarbide occurs. The movement of the high density front can be predicted with carbon diffusion equations using the error function. The activation energy for the high density front movement was determined to be {minus}130 to {minus}180 Kcal/mole. An effective diffusion coefficient for carbon diffusion in UC{sub 2} and the movement of the densified region was measured at 8 {times} 10{sup {minus}7} cm{sup 2}/s. This technique can be used to control densification of uranium dicarbide and to control carbon level and grain size in sintered compacts. More information on the fundamental carbon transport mechanism is necessary for complete understanding of the phenomenon. 54 refs., 67 figs.

  8. Spark Plasma Sintering of Cryomilled Nanocrystalline Al Alloy - Part II: Influence of Processing Conditions on Densification and Properties

    NASA Astrophysics Data System (ADS)

    Liu, Dongming; Xiong, Yuhong; Topping, Troy D.; Zhou, Yizhang; Haines, Chris; Paras, Joseph; Martin, Darold; Kapoor, Deepak; Schoenung, Julie M.; Lavernia, Enrique J.

    2012-01-01

    In this study, nanostructured Al 5083 powders, which were prepared via cryomilling, were consolidated using spark plasma sintering (SPS). The influence of processing conditions, e.g., the loading mode, starting microstructure ( i.e., atomized vs cryomilled powders), sintering pressure, sintering temperature, and powder particle size on the consolidation response and associated mechanical properties were studied. Additionally, the mechanisms that govern densification during SPS were discussed also. The results reported herein suggest that the morphology and microstructure of the cryomilled powder resulted in an enhanced densification rate compared with that of atomized powder. The pressure-loading mode had a significant effect on the mechanical properties of the samples consolidated by SPS. The consolidated compact revealed differences in mechanical response when tested along the SPS loading axis and radial directions. Higher sintering pressures improved both the strength and ductility of the samples. The influence of grain size on diffusion was considered on the basis of available diffusion equations, and the results show that densification was attributed primarily to a plastic flow mechanism during the loading pressure period. Once the final pressure was applied, power law creep became the dominant densification mechanism. Higher sintering temperature improved the ductility of the consolidated compact at the expense of strength, whereas samples sintered at lower temperature exhibited brittle behavior. Finally, densification rate was found to be inversely proportional to the particle size.

  9. Initial stage densification during spark plasma sintering of Fe-based amorphous alloy powder: Analysis of viscous flow

    NASA Astrophysics Data System (ADS)

    Paul, Tanaji; Harimkar, Sandip P.

    2016-10-01

    Understanding the mechanism of densification of amorphous alloy powders is important for determining the parameters during sintering of these materials. In this paper, we report on the analysis of densification of Fe48Cr15Mo14Y2C15B6 amorphous alloy powder during spark plasma sintering. Sintering up to 1000 °C resulted in two clearly distinguishable stages of densification: stage I from 320 °C to 740 °C and stage II from 830 °C to 1000 °C. The maximum densification rate during stage I was attained at 585 °C up to which the sample remained fully amorphous. During the entire stage II, the sample was fully crystalline, and the maximum densification rate attained at 935 °C was much lower than that observed during stage I. Viscous flow during stage I was analyzed, yielding an estimate of the activation energy to be 94.0 ± 0.2 kJ mol-1 in the temperature range from 525 °C to 580 °C.

  10. Densification-induced conductivity percolation in high-porosity pharmaceutical microcrystalline cellulose compacts

    NASA Astrophysics Data System (ADS)

    Strømme, M.; Niklasson, G. A.; Ek, R.

    2003-01-01

    The percolation theory is established as a useful tool in the field of pharmaceutical materials science. It is shown that percolation theory, developed for analyzing insulator-conductor transitions, can be applied to describe imperfect dc conduction in pharmaceutical microcrystalline cellulose during densification. The system, in fact, exactly reproduces the values of the percolation threshold and exponent estimated for a three-dimensional random continuum. Our data clearly show a crossover from a power-law percolation theory region to a linear effective medium theory region at a cellulose porosity of ˜0.7.

  11. Impact of densification on microstructure and transport properties of CaFe5O7

    NASA Astrophysics Data System (ADS)

    Delacotte, C.; Hébert, S.; Hardy, V.; Bréard, Y.; Maki, R.; Mori, T.; Pelloquin, D.

    2016-04-01

    Monophasic CaFe5O7 ceramic has been synthesized by solid state route. Its microstructural features have been studied by diffraction techniques and electron microscopy images before and after Spark Plasma Sintering (SPS) annealings. This work is completed by measurements of electrical and thermal properties. Especially, attention is focused around the structural and electronic transition at 360 K for which specific heat measurements have revealed a sharp peak. Densification by SPS techniques led to a significant improvement of electrical conductivity above 360 K.

  12. High conductivity carbon nanotube wires from radial densification and ionic doping

    NASA Astrophysics Data System (ADS)

    Alvarenga, Jack; Jarosz, Paul R.; Schauerman, Chris M.; Moses, Brian T.; Landi, Brian J.; Cress, Cory D.; Raffaelle, Ryne P.

    2010-11-01

    Application of drawing dies to radially densify sheets of carbon nanotubes (CNTs) into bulk wires has shown the ability to control electrical conductivity and wire density. Simultaneous use of KAuBr4 doping solution, during wire drawing, has led to an electrical conductivity in the CNT wire of 1.3×106 S/m. Temperature-dependent electrical measurements show that conduction is dominated by fluctuation-assisted tunneling, and introduction of KAuBr4 significantly reduces the tunneling barrier between individual nanotubes. Ultimately, the concomitant doping and densification process leads to closer packed CNTs and a reduced charge transfer barrier, resulting in enhanced bulk electrical conductivity.

  13. Multi-material laser densification (MMLD) of dental restorations: Process optimization and properties evaluation

    NASA Astrophysics Data System (ADS)

    Li, Xiaoxuan

    This Ph.D. thesis proposes to investigate the feasibility of laser-assisted dental restoration and to develop a fundamental understanding of the interaction between laser beam and dental materials. Traditional dental restorations are produced by the porcelain-fused-to-metal (PFM) process, in which a dental restoration is cast from a metallic alloy and then coated with dental porcelains by multiple furnace-firing processes. PFM method is labor-intensive and hence very expensive. In order to fabricate dental restoration units faster and more cost-effectively, the Solid Freeform Fabrication (SFF) technique has been employed in this study. In particular, a Multi-Material Laser Densification (MMLD) process has been investigated for its potential to fabricate artificial teeth automatically from 3-D computer dental tooth files. Based on the principle of SFF, the MMLD process utilizes a micro-extruder system to deliver commercial dental alloy and porcelain slurry in a computer-controlled pattern line by line and layer by layer. Instead of firing the artificial tooth/teeth in a furnace, the extruded dental materials are laser scanned to convert the loose powder to a fully dense body. Different laser densification parameters including the densification temperature, laser output power, laser beam size, line dimension, ratio of the beam size to line width, beam scanning rate, processing atmosphere and pressure, dental powder state (powder bed or slurry), powder particle size, etc. have been used to evaluate their effects on the microstructures and properties of the laser densified dental body, and hence to optimize MMLD conditions. Furthermore, laser-scanning induced phase transformations in dental porcelains have been studied because the transformations have great impact on coefficient of thermal expansion (CTE) of dental porcelains, which should match that of dental alloy substrate. Since a single dental material line delivered by the MMLD system functions as a "construction

  14. Densification and Electrical Properties of Zinc Oxide Varistors Microwave-Sintered Under Different Oxygen Partial Pressures

    NASA Astrophysics Data System (ADS)

    Lin, Cong; Wang, Bo; Xu, Zheng; Peng, Hu

    2012-11-01

    ZnO varistors were prepared by microwave sintering under different oxygen partial pressures. The temperature profile and the densification behavior in different atmospheres were investigated. It was found that the density of ZnO varistors during sintering was the key factor affecting the absorption of microwave energy. The electrical properties, including the nonlinear properties and capacitance-voltage ( C- V) characteristics, were also carefully studied. The results showed that the oxygen partial pressure has significant effects on the electrical properties of ZnO varistors by changing the concentration of defects through a series of reactions involving oxygen during sintering.

  15. Ion-beam-induced planarization, densification, and exfoliation of low-density nanoporous silica

    NASA Astrophysics Data System (ADS)

    Kucheyev, S. O.; Shin, S. J.

    2017-09-01

    Planarization of low-density nanoporous solids is challenging. Here, we demonstrate that ion bombardment to doses of ˜1015 cm-2 results in significant smoothing of silica aerogels, yielding mirror-like surfaces after metallization. The surface smoothing efficiency scales with the ion energy loss component leading to local lattice heating. Planarization is accompanied by sub-surface monolith densification, resulting in surface exfoliation with increasing ion dose. These findings have implications for the fabrication of graded-density nanofoams, aerogel-based lightweight optical components, and meso-origami.

  16. Densification of Precipitated Yttria Stabilized Zirconia (YSZ) to Achieve Translucent Properties.

    DTIC Science & Technology

    1982-11-30

    CHART NATIONAL BUREAU OF STANDARDS- I963-A S AM-v 0. 17 .00 Technical Report No. 7 Contract No.: US NAVY -N-00014-80-K-0969 DENSIFICATION OF...Department of the Navy Contract No. US NAVY -NO0014-80-K-0969 Reproduction in whole or in part is permited for any purpose of the United States...GRANT NUMBER(#) - :IL, C.,Buchanan- and, D. M. Wilson .US NAVY -N-00014-80-K-0969 . s. PERFORMING ORGANIZATION NAME AND ADDRESS 10. PROGRAM ELEMENT

  17. Firn thickness variations across the Northeast Greenland Ice Stream margins indicating nonlinear densification rates

    NASA Astrophysics Data System (ADS)

    Riverman, K. L.; Anandakrishnan, S.; Alley, R. B.; Peters, L. E.; Christianson, K. A.; Muto, A.

    2013-12-01

    Northeast Greenland Ice Stream (NEGIS) is the largest ice stream in Greenland, draining approximately 8.4% of the ice sheet's area. The flow pattern and stability mechanism of this ice stream are unique to others in Greenland and Antarctica, and merit further study to ascertain the sensitivity of this ice stream to future climate change. Geophysical methods are valuable tools for this application, but their results are sensitive to the structure of the firn and any spatial variations in firn properties across a given study region. Here we present firn data from a 40-km-long seismic profile across the upper reaches of NEGIS, collected in the summer of 2012 as part of an integrated ground-based geophysical survey. We find considerable variations in firn thickness that are coincident with the ice stream shear margins, where a thinner firn layer is present within the margins, and a thicker, more uniform firn layer is present elsewhere in our study region. Higher accumulation rates in the marginal surface troughs due to drift-snow trapping can account for some of this increased densification; however, our seismic results also highlight enhanced anisotropy within the firn and upper ice column that is confined to narrow bands within the shear margins. We thus interpret these large firn thickness variations and abrupt changes in anisotropy as indicators of firn densification dependent on the effective stress state as well as the overburden pressure, suggesting that the strain rate increases nonlinearly with stress across the shear margins. A GPS strain grid maintained for three weeks across both margins observed strong side shearing, with rapid stretching and then compression along particle paths, indicating large deviatoric stresses in the margins. This work demonstrates the importance of developing a high-resolution firn densification model when conducting geophysical field work in regions possessing a complex ice flow history; it also motivates the need for a more

  18. THE EFFECT OF TEMPERATURE AND UNIAXIAL PRESSURE ON THE DENSIFICATION BEHAVIOR OF SILICA AEROGEL GRANULES

    SciTech Connect

    Matyas, Josef; Robinson, Matthew J.; Fryxell, Glen E.

    2012-10-01

    Materials are being developed in U.S. for the removal and immobilization of iodine from gaseous products of nuclear fuel reprocessing in support of the Fuel Cycle Technology Separations and Waste Forms Campaign. The silver-functionalized silica aerogel proved to be an excellent candidate for this treatment because of its high selectivity and sorption capacity for radioiodine and its possible conversion to a durable silica-based waste form. The present study investigated with nitrogen sorption and helium pycnometry the effect of pressureless isothermal sintering at temperatures of 900-1400°C for 2.5-90 min or isothermal hot-pressing at 1200°C for 2.5 min on densification of raw and silver-functionalized silica aerogel granules. Rapid sintering was observed at 1050 and 1200°C. Only 15 min of pressureless sintering at 1200°C resulted in almost complete densification. The macropores disappeared, surface area decreased from 1114 m2/g to 25 m2/g, pore volume from 7.41 cm3/g to 0.09 cm3/g, and adsorption pore size from 18.7 to 7 nm. The skeletal density of sintered granules was similar to the bulk density of amorphous silica (2.2 g/cm3). The hot-pressing accelerated the sintering process, decreasing significantly the pore size and volume.

  19. Differences between eccentric and rotary tablet machines in the evaluation of powder densification behaviour.

    PubMed

    Palmieri, Giovanni F; Joiris, Etienne; Bonacucina, Giulia; Cespi, Marco; Mercuri, Annalisa

    2005-07-14

    Differences in the dynamics of powder densification between eccentric and rotary machine were pointed out by compressing at different compression pressures microcrystalline cellulose, lactose monohydrate and dicalcium phosphate dihydrate and recovering the corresponding stress/strain data in both machines equipped to monitor punches displacement and compression forces. Heckel plots were then obtained from these stress/strain data. Curves obtained in the rotary machine possess a narrower zone of linearity for the calculation of P(Y) and D(A). The effect of the different compression mechanism of the rotary machine on the shape of the Heckel plot is more noticeable in a non-deforming material such as dicalcium phosphate. The effect of the longer dwell time of the rotary machine on the porosity reduction occurring after the maximum pressure has been reached, is more noticeable in a ductile material such as microcrystalline cellulose. Heckel parameters obtained in the rotary press are in some cases different from those recovered in the eccentric machine because of the longer dwell time, machine deflection and punch tilting occurring in the rotary machine, although theoretically they could better describe the material densification in a high speed production rotary machine.

  20. GNSS-based densification of the ITRF velocity field through a collaborative approach

    NASA Astrophysics Data System (ADS)

    Legrand, Juliette; Bruyninx, Carine; Craymer, Michael; Dawson, John; Griffiths, Jake; Kenyeres, Ambrus; Rebischung, Paul; Sánchez, Laura; Santamaría-Gómez, Alvaro; Saria, Elifuraha; Altamimi, Zuheir

    2015-04-01

    The objective of the IAG Working Group "Integration of Dense Velocity Fields in the ITRF" is to provide a GNSS-based dense, unified and reliable velocity field globally referenced in the ITRF (International Terrestrial Reference Frame) and useful for geodynamical and geophysical interpretations. The WG is embedded in IAG Sub-Commission 1.3 "Regional Reference Frames" where it coexists with the Regional Reference Frame Sub-Commissions AFREF (Africa), APREF (Asia & Pacific), EUREF (Europe), NAREF (North America), SCAR (Antarctica), SIRGAS (Latin America & Caribbean). These IAG Regional Reference Frame sub-commissions are responsible for providing GNSS-based densified weekly solutions for their region. To obtain such a densified velocity field, the WG combined the individual weekly solutions from 7 individual contributors (AFREF, APREF, EUREF, NAREF (NGS, GSB), SIRGAS, IGS) and then stacked these weekly combined solutions in order to derive a ITRF2008 densification as well as the associated residual position time series for more than 2800 sites. Here we present the latest densification results.

  1. Temperature and speed of testing influence on the densification and recovery of polyurethane foams

    NASA Astrophysics Data System (ADS)

    Apostol, Dragoş Alexandru; Constantinescu, Dan Mihai

    2013-02-01

    Polyurethane foams with densities of 35, 93, and 200 kg/m3 were tested in compression at three levels of temperatures as: -60 °C, 23 °C, and 80 °C. The influence of speed of testing from 2 mm/min up to 6 m/s (0.0014 to 545 s-1) on the response of the foams is analyzed. Testing is done separately on the rise direction and on the in-plane direction of the foams, and differences in their behavior are commented. With interpolation functions which approximate the plateau and densification region, the specific strain energy is calculated together with the energy efficiency and onset strain of densification. A Nagy-type phenomenological strain-rate-dependent model is proposed to generate engineering stress-strain curves and is validated through comparison with experimental stress-strain curves obtained at different speeds of testing. Starting from a reference experimental curve, two material parameters which are density and temperature dependent are established. Foam recovery for each density of the polyurethane foams is analyzed as a function of direction of testing, temperature, and speed of testing.

  2. Ferret-mouse differences in interkinetic nuclear migration and cellular densification in the neocortical ventricular zone.

    PubMed

    Okamoto, Mayumi; Shinoda, Tomoyasu; Kawaue, Takumi; Nagasaka, Arata; Miyata, Takaki

    2014-09-01

    The thick outer subventricular zone (OSVZ) is characteristic of the development of human neocortex. How this region originates from the ventricular zone (VZ) is largely unknown. Recently, we showed that over-proliferation-induced acute nuclear densification and thickening of the VZ in neocortical walls of mice, which lack an OSVZ, causes reactive delamination of undifferentiated progenitors and invasion by these cells of basal areas outside the VZ. In this study, we sought to determine how VZ cells behave in non-rodent animals that have an OSVZ. A comparison of mid-embryonic mice and ferrets revealed: (1) the VZ is thicker and more pseudostratified in ferrets. (2) The soma and nuclei of VZ cells were horizontally and apicobasally denser in ferrets. (3) Individual endfeet were also denser on the apical (ventricular) surface in ferrets. (4) In ferrets, apicalward nucleokinesis was less directional, whereas basalward nucleokinesis was more directional; consequently, the nuclear density in the periventricular space (within 16 μm of the apical surface) was smaller in ferrets than in mice, despite the nuclear densification seen basally in ferrets. These results suggest that species-specific differences in nucleokinesis strategies may have evolved in close association with the magnitudes and patterns of nuclear stratification in the VZ. Copyright © 2014 The Authors. Published by Elsevier Ireland Ltd.. All rights reserved.

  3. Simulation of the densification of real open-celled foam microstructures

    NASA Astrophysics Data System (ADS)

    Brydon, A. D.; Bardenhagen, S. G.; Miller, E. A.; Seidler, G. T.

    2005-12-01

    Ubiquitous in nature and finding applications in engineering systems, cellular solids are an increasingly important class of materials. Foams are an important subclass of cellular solids with applications as packing materials and energy absorbers due to their unique properties. A better understanding of foam mechanical properties and their dependence on microstructural details would facilitate manufacture of tailored materials and development of constitutive models for their bulk response. Numerical simulation of these materials, while offering great promise toward furthering understanding, has also served to convincingly demonstrate the inherent complexity and associated modeling challenges. The large range of deformations which foams are subjected to in routine engineering applications is a fundamental source of complication in modeling the details of foam deformation on the scale of foam struts. It requires accurate handling of large material deformations and complex contact mechanics, both well established numerical challenges. A further complication is the replication of complex foam microstructure geometry in numerical simulations. Here various advantages of certain particle methods, in particular their compatibility with the determination of three-dimensional geometry via X-ray microtomography, are exploited to simulate the compression of "real" foam microstructures into densification. With attention paid to representative volume element size, predictions are made regarding bulk response, dynamic effects, and deformed microstructural character, for real polymeric, open-cell foams. These predictions include a negative Poisson's ratio in the stress plateau, and increased difficulty in removing residual porosity during densification.

  4. Regional Densification of a Global VTEC Model Based on B-Spline Representations

    NASA Astrophysics Data System (ADS)

    Erdogan, Eren; Schmidt, Michael; Dettmering, Denise; Goss, Andreas; Seitz, Florian; Börger, Klaus; Brandert, Sylvia; Görres, Barbara; Kersten, Wilhelm F.; Bothmer, Volker; Hinrichs, Johannes; Mrotzek, Niclas

    2017-04-01

    The project OPTIMAP is a joint initiative of the Bundeswehr GeoInformation Centre (BGIC), the German Space Situational Awareness Centre (GSSAC), the German Geodetic Research Institute of the Technical University Munich (DGFI-TUM) and the Institute for Astrophysics at the University of Göttingen (IAG). The main goal of the project is the development of an operational tool for ionospheric mapping and prediction (OPTIMAP). Two key features of the project are the combination of different satellite observation techniques (GNSS, satellite altimetry, radio occultations and DORIS) and the regional densification as a remedy against problems encountered with the inhomogeneous data distribution. Since the data from space-geoscientific mission which can be used for modeling ionospheric parameters, such as the Vertical Total Electron Content (VTEC) or the electron density, are distributed rather unevenly over the globe at different altitudes, appropriate modeling approaches have to be developed to handle this inhomogeneity. Our approach is based on a two-level strategy. To be more specific, in the first level we compute a global VTEC model with a moderate regional and spectral resolution which will be complemented in the second level by a regional model in a densification area. The latter is a region characterized by a dense data distribution to obtain a high spatial and spectral resolution VTEC product. Additionally, the global representation means a background model for the regional one to avoid edge effects at the boundaries of the densification area. The presented approach based on a global and a regional model part, i.e. the consideration of a regional densification is called the Two-Level VTEC Model (TLVM). The global VTEC model part is based on a series expansion in terms of polynomial B-Splines in latitude direction and trigonometric B-Splines in longitude direction. The additional regional model part is set up by a series expansion in terms of polynomial B-splines for

  5. Effect of PF impregnation and surface densification on the mechanical properties of small-scale wood laminated poles

    Treesearch

    Huaqiang Yu; Chung Y. Hse; Zehui Jiang

    2009-01-01

    The wood poles in the United States are from high-valued trees that are becoming more expensive and less available. Wood laminated composite poles (LCP) are a kind of alternative to solid poles. Considerable interest has developed in last century in the resin impregnation and wood surface densification to improve its physical and mechanical properties. In this...

  6. Measurement of kernel swelling and buffer densification in irradiated UCO-TRISO particles

    NASA Astrophysics Data System (ADS)

    Bower, Gordon R.; Ploger, Scott A.; Demkowicz, Paul A.; Hunn, John D.

    2017-04-01

    Radiation-induced volume changes in the fuel kernels and buffer layers of UCO-TRISO particles irradiated to an average burnup of 16.1% FIMA have been determined. Measurements of particle dimensions were made on polished cross-sections of 56 irradiated particles at several different polish planes. The data were then analyzed to compute the equivalent spherical diameters of the kernels and the various coating layers, and these were compared to the average as-fabricated values to determine changes due to irradiation. The kernel volume was found to have increased by an average of 26 ± 6%. Buffer volume decreased by an average of 39 ± 2% due to densification.

  7. Measurement of kernel swelling and buffer densification in irradiated UCO-TRISO particles

    DOE PAGES

    Bower, Gordon R.; Ploger, Scott A.; Demkowicz, Paul A.; ...

    2017-01-06

    We determined from radiation-induced volume changes in the fuel kernels and buffer layers of UCO-TRISO particles an average burnup of 16.1% FIMA. Measurements of particle dimensions were made on polished cross-sections of 56 irradiated particles at several different polish planes. Furthermore, the data were then analyzed to compute the equivalent spherical diameters of the kernels and the various coating layers, and these were compared to the average as-fabricated values to determine changes due to irradiation. The kernel volume was found to have increased by an average of 26 ± 6%. Buffer volume decreased by an average of 39 ± 2%more » due to densification.« less

  8. Densification of silicon carbide using oxy-nitride additives for space-based telescope mirror applications

    NASA Astrophysics Data System (ADS)

    Kumar, R. Suresh; Shukla, Anoop K.; Babu, Sankaranarayanan; Sivakumar, Dhenuvakonda; Gandhi, Ashutosh S.

    2011-07-01

    Densification behavior of alpha silicon carbide (SiC) during vacuum hot pressing was studied up to 1900ºC with sintering additives based on AlN and Y2O3 in different proportions. Near theoretical density was obtained with a total sintering additive content of < 4 vol.%. The microstructure of SiC sintered with AlN+Y2O3 revealed fine equiaxed grains against the additional elongated grains exhibited by SiC sintered with AlN alone. The SiC having high density exhibited very good strength, elastic modulus, high thermal conductivity, low coefficient of thermal expansion and excellent polishability for telescope mirror applications.

  9. Densification effects of the carbon nanotube pillar array on field-emission properties

    NASA Astrophysics Data System (ADS)

    Wang, Kuang-Yu; Chou, Chia-Hsin; Liao, Chan-Yu; Li, Yu-Ren; Cheng, Huang-Chung

    2016-06-01

    In this study, a simple densification method for carbon nanotube (CNT) pillars is proposed to achieve high-performance field emission characteristics and stable emission. Through capillary force during solution evaporation, the CNT density in each pillar can be increased by about six times without causing damage to the crystallinity of CNTs. The densified CNT pillars exhibit lower series resistance, sharper pillars, better contacts, higher thermal conductivity, and better mechanical stiffness than as-grown ones. Therefore, the threshold field of the field emitter with such CNT pillars of 50 µm height can be reduced to 1.98 V/µm, as compared with 2.2 V/µm for the undensified ones. Moreover, the fluctuation of field-emission current decreases from 15.5 to 9.4% after the stress tests at a field of 2 V/µm for 1800 s. These findings imply that the densified CNT pillars are promising for the field-emission applications.

  10. Effect of sintering temperature on densification and mechanical properties of pressureless sintered CNT-alumina nanocomposites

    NASA Astrophysics Data System (ADS)

    Bakhsh, N.; Khalid, F. A.; Hakeem, Abbas S.

    2014-06-01

    Carbon nanotubes (CNTs) exhibit excellent mechanical, electrical and thermal properties thus have been considered for applications in the production of nanocomposite materials. This work presents results of sintered CNTs-reinforced alumina nanocomposites that can be used for many structural and engineering applications. Gas purging sonication (GPS) was used to achieve homogeneous dispersion of CNTs in alumina powder. Nanocomposites were synthesized by conventional pressureless sintering technique using varying amounts of CNTs in alumina matrix. Densification, hardness and fracture toughness of the resulted nanocomposites were examined. It is found that considerable improvement in fracture toughness at 1 wt% CNT-alumina nanocomposite has occurred. Role of CNTs in improving the fracture toughness of nanocomposites is explained which is attributed to well known bridging and pullout mechanism of CNTs in the matrix.

  11. Contribution of GPS techniques to the densification and to quasi-real Universal Time estimation.

    NASA Astrophysics Data System (ADS)

    Gambis, D.; Eisop, E.

    The determination of Universal Time is mainly based on the inertial VLBI technique. Due to the difficulty of determining the long-term behaviour of the non rotating system realized through the orbit orientation, Universal Time cannot be accurately derived from GPS technique; still GPS technique gives information on the high-frequency UT1 behaviour on time scales limited to a couple of months. This signal can be used for densification of the UT1 series as well as for UT1 extensions on a quasi-real-time basis from the current VLBI available value. In that case, errors are about 60 microseconds for a 5-day interval. This represents an improvement of an order of magnitude with respect to the current prediction of UT1 based on auto-regressive processes.

  12. Influence of oxide-based sintering additives on densification and mechanical behavior of tricalcium phosphate (TCP).

    PubMed

    Bhatt, Himesh A; Kalita, Samar J

    2007-05-01

    In this research, we studied and analyzed the effects of four different oxide-based sintering additives on densification, mechanical behavior, biodegradation and biocompatibility of tricalcium phosphate (TCP) bioceramics. Selective sintering additives were introduced into pure TCP ceramics, in small quantities, through homogeneous mixing, using a mortar and pestle. The consequent powders of different compositions were pressed into cylindrical compacts, uniaxially and sintered at elevated temperatures, 1150 degrees C and 1250 degrees C, separately in a muffle furnace. X-ray powder diffraction technique was used to analyze the phase-purity of TCP after sintering. Hardness of these sintered specimens was evaluated using a Vickers hardness tester. Sintered cylindrical samples were tested under uniaxial compressive loading, as a function of composition to determine their failure strength. Biodegradation studies conducted using simulated body fluid under dynamic environment, revealed that these additives could control the rate of resorption and hardness degradation of TCP ceramics.

  13. Regional Densification of the ITRF through the Integration of National Active GNSS Network Products

    NASA Astrophysics Data System (ADS)

    Kenyeres, Ambrus; Horvath, Tivadar; Stangl, Gunter; Garayt, Bruno; Hansen, Dionne; Valdes, Marcellino; Caporali, Alessandro; Figurski, Mariusz; Georgiev, Ivan; Droscak, Branislav; Franke, Peter; Jumare, Izolde; Nagl, Jaroslav; Pihlak, Priit; Huisman, Lennard

    2015-04-01

    The actual realization of the ITRS represents the most precise station positions and velocities at selected set of sites. The scientific and practical applications may require the access to the global 3D reference frame in a dense network without loss of consistency and reliability. Relying on the long term homogeneously analyzed data the dense national permanent GNSS networks shall be the ideal tool for such reference frame densification. In the frame of the ongoing EPN densification the national active networks are integrated and a homogeneous, dense position and velocity product is being derived based on the actual ITRS realization and using the EPN as backbone infrastructure. In order to minimize inconsistencies (e.g. site naming, discontinuities, constraint handling) the only way to get a uniform, homogeneous cumulative solution from national to global scales is the integration done relying on the weekly SINEX product level. The integration is being performed using the CATREF software (Altamimi et al, IGN) and based on the Minimum Constraint approach. The derived position and velocity product will be an essential material for various geokinematic studies (PGR, intraplate and plate boundary zone investigations), and also for the better definition and realization of ETRS89. This work is very well inline with the goals of relevant European initiatives in the frame of EPOS, EUREF (WG on Deformation Models), CEGRN, EUPOS, IAG (WG on Unified Dense Velocity Fields). The work is well in progress, up to 15 years of weekly SINEX files are already available and analyzed from 17 countries, and considering the countries in negotiation phase the full continental coverage will be reached within few years. The actual database contains more close to 3000 sites. In this presentation a status report is shown and the first version of the position/velocity product with related interpretation options are introduced as well.

  14. Hot forging of melt quenched powder: Microstructure development and kinetics of densification

    NASA Astrophysics Data System (ADS)

    Keshavan, Hrishikesh

    Hot powder forging is a new process for making scalable and cost-effective nanocrystalline ceramics. It utilizes powder typically between 5 mum to 25 mum to nucleate very stable crystallite sizes well below 100 nm. These particles superplastically deform at relatively moderate temperature and stress. Hence, rapid densification at high creep rates is achieved with limited grain growth. A novel way to achieve high creep rate is to take advantage of partially amorphous powders that are obtained by one of the many available rapid quenching processes. Our study uses a plasma flame to melt the spray-dried aggregates of a particular composition and rapidly quench into water that results in metastable, optically transparent powder. The plasma sprayed powder is first hot pressed to obtain cylindrical pellets and then hot-forged at various stresses and temperatures to obtain optimum creep rates. Eutectic oxide compositions were studied due to their low melting point and better glass forming ability in an effort to optimize both the composition and processing parameters. Five binary compositions of alumina, zirconia and magnesium aluminate spinel and the effect of adding borosilicate glass on creep rates and microstructure were investigated. Their phase evolution and crystallite growth were examined in a detailed annealing study. The final densities after hot forging were composition dependent and ranged from 86% to 100% at 1350°C. Creep rates of the binary eutectic increased by an order of magnitude when alumina was substituted with spinel or when borosilicate glass was added. The highest creep rate obtained would correspond to 10-4 1/s for 40 MPa at 1350°C. SEM studies confirm that the densification is by plastic deformation of particles. TEM studies reveal nano-sized zirconia either in an alumina or spinel matrix. The grain morphology was cellular in compositions without glass and acicular in compositions with glass.

  15. Long-term impact of ankle sprains on postural control and fascial densification.

    PubMed

    Kalichman, Leonid; Lachman, Hila; Freilich, Naama

    2016-10-01

    To evaluate the effect of a past ankle sprain (AS) on postural control and fascial changes in the adjacent body segment. 20 young, healthy subjects with a history (≥6 months) of significant (Grades 2, 3) lateral ASs and 20 controls with no history of AS were recruited to cross-sectional case-control study. All subjects performed the Star Excursion Balance Test (SEBT). The Stecco method was used to evaluate fascial densification in the calf and upper foot areas. The leg with the AS in the study group vs. the right leg in the control group exhibited significant differences (lower scores of SEBT test in the AS group) for the following directions: anterior (p < 0.001), antero-lateral (p < 0.001), posterior (P = 0.028), postero-medial (P = 0.001), medial (P = 0.001), antero-medial (p < 0.001). A comparison between the leg with an AS in the study group and the right leg in the control group showed a significantly high prevalence of fascial densification for the talus internal rotation (p = 0.014), talus retromotion (p = 0.001), talus lateral (p = 0.040) and pes external rotation (p = 0.060) points. There are long term effects of an AS on postural control and on the sensitivity and movability of the fascia in the calf and foot. Copyright © 2016 Elsevier Ltd. All rights reserved.

  16. Densification behavior, doping profile and planar waveguide laser performance of the tape casting YAG/Nd:YAG/YAG ceramics

    NASA Astrophysics Data System (ADS)

    Ge, Lin; Li, Jiang; Qu, Haiyun; Wang, Juntao; Liu, Jiao; Dai, Jiawei; Zhou, Zhiwei; Liu, Binglong; Kou, Huamin; Shi, Yun; Wang, Zheng; Pan, Yubai; Gao, Qingsong; Guo, Jingkun

    2016-10-01

    The sintering behavior and doping concentration profile of the planar waveguide YAG/Nd:YAG/YAG ceramics by the tape casting and solid-state reaction method were investigated on the basis of densification trajectory, microstructure evolution, and Nd3+ ions diffusion. The porosity of the green body by tape casting and cold isostatic pressing is about 38.6%. And the green bodies were consolidated from 1100 °C to 1800 °C for 0.5-20 h to study the densification and the doping diffusion behaviors. At the temperature higher than 1500 °C, pure YAG phase is formed, followed by the densification and grain growth process. With the increase of temperature, two sintering stages occur, corresponding to remarkable densification and significant grain growth, respectively. The mechanism controlling densification at 1550 °C is grain boundary diffusion. The diffusion of Nd3+ ions is more sensitive to temperature than the sintering time, and the minimum temperature required for the obvious diffusion of Nd3+ ions is higher than 1700 °C. Finally, planar waveguide YAG/1.5 at.%Nd:YAG/YAG transparent ceramics with in-line transmittance of 84.8% at 1064 nm were obtained by vacuum-sintering at 1780 °C for 30 h. The fluorescence lifetime of 4F3/2 state of Nd3+ in the specimen is about 259 μs. The prepared ceramic waveguide was tested in a laser amplifier and the laser pulse was amplificated from 87 mJ to 238 mJ, with the pump energy of 680 mJ.

  17. Densification behavior, nanocrystallization, and mechanical properties of spark plasma sintered Fe-based bulk amorphous alloys

    NASA Astrophysics Data System (ADS)

    Singh, Ashish Kumar

    Fe-based amorphous alloys are gaining increasing attention due to their exceptional wear and corrosion resistance for potential structural applications. Two major challenges that are hindering the commercialization of these amorphous alloys are difficulty in processing of bulk shapes (diameter > 10 mm) and lack of ductility. Spark plasma sintering (SPS) is evolving as a promising technique for processing bulk shapes of amorphous and nanocrystalline materials. The objective of this work is to investigate densification behavior, nanocrystallization, and mechanical properties of SPS sintered Fe-based amorphous alloys of composition Fe48Cr15Mo14Y2C15B6. SPS processing was performed in three distinct temperature ranges of amorphous alloys: (a) below glass transition temperature (Tg), (b) between Tg and crystallization temperature (Tx), and (c) above Tx. Punch displacement data obtained during SPS sintering was correlated with the SPS processing parameters such as temperature, pressure, and sintering time. Powder rearrangement, plastic deformation below T g, and viscous flow of the material between Tg and Tx were observed as the main densification stages during SPS sintering. Micro-scale temperature distributions at the point of contact and macro-scale temperature distribution throughout the sample during SPS of amorphous alloys were modeled. The bulk amorphous alloys are expected to undergo structural relaxation and nanocrystallization during SPS sintering. X-ray diffraction (XRD), small angle neutron scattering (SANS), and transmission electron microscopy (TEM) was performed to investigate the evolution of nanocrystallites in SPS sintered Fe-based bulk amorphous alloys. The SANS analysis showed significant scattering for the samples sintered in the supercooled region indicating local structural and compositional changes with the profuse nucleation of nano-clusters (~4 nm). Compression tests and microhardness were performed on the samples sintered at different

  18. Mathematical Model and Experimental Results for Cryogenic Densification and Sub-Cooling Using a Submerged Cooling Source

    NASA Technical Reports Server (NTRS)

    Partridge, J. K.; Notardonato, W. U.; Johnson, W. L.; Tuttle, J. W.

    2011-01-01

    Among the many factors that determine overall rocket performance, propellant density is important because it affects the size of the rocket. Thus, in order to decrease the size of a rocket, it may be desirable to increase the density of propellants. This study analyzes the concept of increasing the propellant density by employing a cooling source submerged in the liquid propellant. A simple, mathematical model was developed to predict the rate of densification and the propellant temperature profile. The mathematical model is generic and applicable to multiple propellants. The densification rate was determined experimentally by submerging a cooling source in liquid oxygen at constant, positive pressure, and measuring the time rate of change in temperature with respect to vertical position. The results from the mathematical model provided a reasonable fit when compared to experimental results.

  19. The Effect of High-pressure Densification on Ballistic-penetration Resistance of a Soda-lime Glass

    DTIC Science & Technology

    2011-01-01

    available in the ANSYS/ Autodyn materials library [26]. Further details of the JH2 model for brittle mate- rials are provided in the remainder of this...Applications 4.2.1 Modifications to the EOS An examination of the polynomial EOS for glass as implemented in the ANSYS/ Autodyn material library...ANSYS/ Autodyn object code to form a new executable. 4.2.2 Modifications of the strength model Irreversible densification of glass is assumed to increase

  20. Key parameters governing the densification of cubic-Li7La3Zr2O12 Li+ conductors

    NASA Astrophysics Data System (ADS)

    Yi, Eongyu; Wang, Weimin; Kieffer, John; Laine, Richard M.

    2017-06-01

    Cubic-Li7La3Zr2O12 (LLZO) is regarded as one of the most promising solid electrolytes for the construction of inherently safe, next generation all-solid-state Li batteries. Unfortunately, sintering these materials to full density with controlled grain sizes, mechanical and electrochemical properties relies on energy and equipment intensive processes. In this work, we elucidate key parameters dictating LLZO densification by tracing the compositional and structural changes during processing calcined and ball-milled Al3+ doped LLZO powders. We find that the powders undergo ion (Li+/H+) exchange during room temperature processing, such that on heating, the protonated LLZO lattice collapses and crystallizes to its constituent oxides, leading to reaction driven densification at < 1000 °C, prior to sintering of LLZO grains at higher temperatures. It is shown that small particle sizes and protonation cannot be decoupled, and actually aid densification. We conclude that using fully decomposed nanoparticle mixtures, as obtained by liquid-feed flame spray pyrolysis, provides an ideal approach to use high surface and reaction energy to drive densification, resulting in pressureless sintering of Ga3+ doped LLZO thin films (25 μm) at 1130 °C/0.3 h to ideal microstructures (95 ± 1% density, 1.2 ± 0.2 μm average grain size) normally accessible only by pressure-assisted sintering. Such films offer both high ionic conductivity (1.3 ± 0.1 mS cm-1) and record low ionic area specific resistance (2 Ω cm2).

  1. Densification and residual stress induced by CO2 laser-based mitigation of SiO2 surfaces

    SciTech Connect

    Feit, M D; Matthews, M J; Soules, T F; Stolken, J S

    2010-10-21

    Knowing the ultimate surface morphology resulting from CO{sub 2} laser mitigation of induced laser damage is important both for determining adequate treatment protocols, and for preventing deleterious intensification upon subsequent illumination of downstream optics. Physical effects such as evaporation, viscous flow and densification can strongly affect the final morphology of the treated site. Evaporation is a strong function of temperature and will play a leading role in determining pit shapes when the evaporation rate is large, both because of material loss and redeposition. Viscous motion of the hot molten material during heating and cooling can redistribute material due to surface tension gradients (Marangoni effect) and vapor recoil pressure effects. Less well known, perhaps, is that silica can densify as a result of structural relaxation, to a degree depending on the local thermal history. The specific volume shrinkage due to structural relaxation can be mistaken for material loss due to evaporation. Unlike evaporation, however, local density change can be reversed by post annealing. All of these effects must be taken into account to adequately describe the final morphology and optical properties of single and multiple-pass mitigation protocols. We have investigated, experimentally and theoretically, the significance of such densification on residual stress and under what circumstances it can compete with evaporation in determining the ultimate post treatment surface shape. In general, understanding final surface configurations requires taking all these factors including local structural relaxation densification, and therefore the thermal history, into account. We find that surface depressions due to densification can dominate surface morphology in the non-evaporative regime when peak temperatures are below 2100K.

  2. Densification Behavior and Performances of C/C Composites Derived from Various Carbon Matrix Precursors

    NASA Astrophysics Data System (ADS)

    Shao, H. C.; Xia, H. Y.; Liu, G. W.; Qiao, G. J.; Xiao, Z. C.; Su, J. M.; Zhang, X. H.; Li, Y. J.

    2014-01-01

    Three types of carbon/carbon (C/C) composites were manufactured by densifying the needled carbon fiber preform through resin and pitch impregnation/carbonization repeatedly, as well as propylene pyrolysis by chemical vapor infiltration plus carbonization after the resin impregnation/carbonization. The densification behavior and performances (involving electric, thermal, and mechanical properties, as well as impurity) of the C/C composites were investigated systematically. The results show that besides the processing and testing conditions, the electric resistivity, thermal conductivity (TC), coefficient of thermal expansion (CTE), strength, and fracture, as well as impurity content and composition of the C/C composites were closely related to the fiber orientation, interfacial bonding between carbon fiber and carbon matrix, material characteristics of the three precursors and the resulting matrix carbons. In particular, the resin-carbon matrix C/C (RC/C) composites had the highest electric resistivity, tensile, and flexural strength, as well as impurity content. Meanwhile, the pitch-carbon matrix C/C (PC/C) composites possessed the highest TC and CTE in the parallel and vertical direction. And most of the performances of pyro-carbon/resin carbon matrix C/C composites were between those of the RC/C and PC/C composites except the impurity content.

  3. Effect of the compaction platform on the densification parameters of tableting excipients with different deformation mechanisms.

    PubMed

    Rojas, John; Hernandez, Santiago

    2014-01-01

    Several compaction models have been attempted to explain the compression and compaction phenomena of excipients. However, the resulting parameters could be influenced by the compaction platform such as dwell time, compact mass, geometry and type of material. The goal of this study is to assess the effect of these variables on the densification parameters obtained from key models such as Heckel, non-linear Heckel, Kawakita, Carstensen, and Leuenberger. The relationship among the parameters derived was determined by employing a Principal Component Analysis. Results indicated that factors such as compact geometry, consolidation time and compact mass had a negligible impact on parameters such as tensile strength, yield pressure and compressibility. On the contrary, the excipient type had the largest influence on these parameters. Further, the Leuenberger (γ) and Carstensen (f) parameters were highly correlated and related to the excipient deformation mechanism. Sorbitol and PVP-k30 were the most highly compactable excipients and were characterized for having a low yield pressure (P(y)), compressibility (a), and critical porosity (ε(c)). The magnitude of these parameters was highly dependent on the consolidation behavior of each material.

  4. Laser induced densification of cerium gadolinium oxide: Application to single-chamber solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Mariño, Mariana; Rieu, Mathilde; Viricelle, Jean-Paul; Garrelie, Florence

    2016-06-01

    In single-chamber solid oxide fuel cells (SC-SOFC), anode and cathode are placed in a gas chamber where they are exposed to a fuel/air mixture. Similarly to conventional dual-chamber SOFC, the anode and the cathode are separated by an electrolyte. However, as in the SC-SOFC configuration the electrolyte does not play tightness role between compartments, this one can be a porous layer. Nevertheless, it is necessary to have a diffusion barrier to prevent the transportation of hydrogen produced locally at the anode to the cathode that reduces fuel cell performances. This study aims to obtain directly a diffusion barrier through the surface densification of the electrolyte Ce0.9Gd0.1O1.95 (CGO) by a laser treatment. KrF excimer laser and Yb fiber laser irradiations were used at different fluences and number of pulses to modify the density of the electrolyte coating. Microstructural characterizations confirmed the modifications on the surface of the electrolyte for appropriate experimental conditions showing either grain growth or densified but cracked surfaces. Gas permeation and electrical conductivities of the modified electrolyte were evaluated. Finally SC-SOFC performances were improved for the cells presenting grain growth at the electrolyte surface.

  5. Improved progressive TIN densification filtering algorithm for airborne LiDAR data in forested areas

    NASA Astrophysics Data System (ADS)

    Zhao, Xiaoqian; Guo, Qinghua; Su, Yanjun; Xue, Baolin

    2016-07-01

    Filtering of light detection and ranging (LiDAR) data into the ground and non-ground points is a fundamental step in processing raw airborne LiDAR data. This paper proposes an improved progressive triangulated irregular network (TIN) densification (IPTD) filtering algorithm that can cope with a variety of forested landscapes, particularly both topographically and environmentally complex regions. The IPTD filtering algorithm consists of three steps: (1) acquiring potential ground seed points using the morphological method; (2) obtaining accurate ground seed points; and (3) building a TIN-based model and iteratively densifying TIN. The IPTD filtering algorithm was tested in 15 forested sites with various terrains (i.e., elevation and slope) and vegetation conditions (i.e., canopy cover and tree height), and was compared with seven other commonly used filtering algorithms (including morphology-based, slope-based, and interpolation-based filtering algorithms). Results show that the IPTD achieves the highest filtering accuracy for nine of the 15 sites. In general, it outperforms the other filtering algorithms, yielding the lowest average total error of 3.15% and the highest average kappa coefficient of 89.53%.

  6. Hierarchical densification and negative thermal expansion in Ce-based metallic glass under high pressure.

    PubMed

    Luo, Qiang; Garbarino, Gaston; Sun, Baoan; Fan, Dawei; Zhang, Yue; Wang, Zhi; Sun, Yajuan; Jiao, Jin; Li, Xiaodong; Li, Pengshan; Mattern, Norbert; Eckert, Jürgen; Shen, Jun

    2015-02-02

    The polyamorphsim in amorphous materials is one of the most fascinating topics in condensed matter physics. In amorphous metals, the nature of polyamorphic transformation is poorly understood. Here we investigate the structural evolution of a Ce-based metallic glass (MG) with pressure at room temperature (RT) and near the glass transition temperature by synchrotron X-ray diffraction, uncovering novel behaviours. The MG shows hierarchical densification processes at both temperatures, arising from the hierarchy of interatomic interactions. In contrast with a continuous and smooth process for the low- to medium-density amorphous state transformation at RT, a relatively abrupt and discontinuous transformation around 5.5 GPa is observed at 390 K, suggesting a possible weak first-order nature. Furthermore, both positive and abnormal-negative thermal expansion behaviours on medium-range order are observed in different pressure windows, which could be related to the low-energy vibrational motions and relaxation of the weakly linked solute-centred clusters.

  7. Growth and densification of frost around a circular cylinder under humid air on cross flow

    NASA Astrophysics Data System (ADS)

    Madrid, Victor; Sanchez, Fausto; Martinez, Simon; Morales, Arturo

    2015-03-01

    Formation, growth and densification of frost around a circular cylinder under humid air on cross flow at different Reynolds numbers has been numerically studied using the finite volume method. The frost formation phenomenon takes place when humidity goes through a desublimation phase change at a temperature lower than its solidification point. Continuity, momentum, energy and mass transport equations have been solved for a whole domain including both phases, gas and solid, and the two components in the gas phase, i.e. dry air and humidity. The mass of water that goes from the gas to the solid phase is used as a source term in the mass conservation equation for solid phase and as a sink for the gas phase, affecting source terms in all the other conservation equations (energy and momentum) also. A volume of fraction conservation equation for solid phase is used to obtain local fractions of ice droplets, considering formally as frost those fraction values greater than a critical value. Once those local fractions are known, local frost properties such as density and thermal conductivity can be calculated as functions of the phase fraction allowing to compute the evolution of growth and local properties of frost. Authors aknowledge financial support from CONACYT through Project 221993.

  8. Powder bed binder jet 3D printing of Inconel 718: Densification, microstructural evolution and challenges

    DOE PAGES

    Nandwana, Peeyush; Elliott, Amy M.; Siddel, Derek; ...

    2017-01-03

    Traditional manufacturing of Inconel 718 components from castings and thermomechanical processing routes involve extensive post processing and machining to attain the desired geometry. Additive manufacturing (AM) technologies including direct energy deposition (DED), selective laser melting (SLM), electron beam melting (EBM) and binder jet 3D printing (BJ3DP) can minimize scrap generation and reduce lead times. While there is extensive literature on the use of melting and solidification based AM technologies, there has been limited research on the use of binder jet 3D printing. In this paper, a brief review on binder jet additive manufacturing of Inconel 718 is presented. In addition,more » existing knowledge on sintering of Inconel 718 has been extended to binder jet 3D printing. We found that supersolidus liquid phase sintering (SLPS) is necessary to achieve full densification of Inconel 718. SLPS is sensitive to the feedstock chemistry that has a strong influence on the liquid volume fraction at the processing temperature. Based on these results, we discuss an empirical framework to determine the role of powder particle size and liquid volume fraction on sintering kinetics. In conclusion, the role of powder packing factor and binder saturation on microstructural evolution is discussed. The current challenges in the use of BJ3DP for fabrication of Inconel 718, as well as, extension to other metal systems, are presented.« less

  9. Effect of nanoscale powders and microwave sintering on densification of alumina ceramics

    NASA Astrophysics Data System (ADS)

    Yun, Han-Sol; Kim, Jong-Chan; Jeong, Dae-Yong; Cho, Nam-Hee

    2016-11-01

    Nanoscale alumina (Al2O3) powders with an average size of 100, 200, or 300 nm were sintered to investigate the effects of the initial powder size on the densification behavior under the application of microwaves (2.45 GHz, 2 kW). The sintering was performed using microwave-assisted sintering (MWS) and conventional sintering (CS) methods in the temperature range of 1100-1600 °C for 0-180 min. The Al2O3 samples prepared with the 100-nm-sized powders using MWS exhibited a relative density (RD) of over 90% when sintered at 1200 °C for 10 min; the same RD was achieved at 1500 °C when the sintering was performed for the same time using CS. However, a sintering temperature difference of 100 °C for a RD of 90% was observed between the MWS and CS methods for the 300-nm-sized powders. Nano-grained ( 290 nm) Al2O3 ceramics with a high density of ≥90% were obtained from nanoscale powders ( 100 nm) using MWS methods. The response of the nanoscale powders to microwaves was more significant as the initial powder size decreased from 300 to 100 nm.

  10. Effect of Heating Rate on the Pressureless Sintering Densification of a Nickel-Based Superalloy

    NASA Astrophysics Data System (ADS)

    Levasseur, David; Brochu, Mathieu

    2016-05-01

    Pressureless sintering of Inconel 718 has important technological applications for the densification of metal injection molding or additive manufacturing of parts with powder/binder systems. The effect of heating rates ranging from 15 to 200 K/minute on the sintering behavior of fine (-325 mesh) Inconel 718 powders was studied using the master sintering curve (MSC) concept. A pressureless pulsed electric current sintering setup was used to heat samples. The temperature at the onset of sintering increased as the heating rate increased. The formation of a supersolidus liquid fraction was shifted toward higher temperatures for increased heating rates. The apparent activation energy of sintering was obtained by least squares fitting of the sintering data to the MSC and was in good agreement with the lattice diffusion activation energy of the alloying elements present in Inconel 718. The MSC followed different kinetics for low heating rates (≤50 K/minute) and high heating rates (≥75 K/minute), and these differences were related to liquation kinetics.

  11. Frost Growth and Densification on a Flat Surface in Laminar Flow with Variable Humidity

    NASA Technical Reports Server (NTRS)

    Kandula, M.

    2012-01-01

    Experiments are performed concerning frost growth and densification in laminar flow over a flat surface under conditions of constant and variable humidity. The flat plate test specimen is made of aluminum-6031, and has dimensions of 0.3 mx0.3 mx6.35 mm. Results for the first variable humidity case are obtained for a plate temperature of 255.4 K, air velocity of 1.77 m/s, air temperature of 295.1 K, and a relative humidity continuously ranging from 81 to 54%. The second variable humidity test case corresponds to plate temperature of 255.4 K, air velocity of 2.44 m/s, air temperature of 291.8 K, and a relative humidity ranging from 66 to 59%. Results for the constant humidity case are obtained for a plate temperature of 263.7 K, air velocity of 1.7 m/s, air temperature of 295 K, and a relative humidity of 71.6 %. Comparisons of the data with the author's frost model extended to accommodate variable humidity suggest satisfactory agreement between the theory and the data for both constant and variable humidity.

  12. Densification of a continuous random network model of amorphous SiO2 glass.

    PubMed

    Li, Neng; Sakidja, Ridwan; Aryal, Sitaram; Ching, Wai-Yim

    2014-01-28

    We have investigated the mechanism of densification of a nearly perfect continuous random network (CRN) model of amorphous SiO2 (a-SiO2) glass with 1296 atoms and periodic boundary conditions. The model has no under- or over-coordinated atoms and small bond length and bond angle distributions. This near-perfect model is systematically densified up to a pressure of 80 GPa using ab initio constant-pressure technique. By assessing a full spectrum of properties including atomic structure, bonding characteristics, effective charges, bond order values, electron density of states, localization of wave functions, elastic and mechanical properties, and interband optical absorption at each pressure, we reveal the pertinent details on the structural, mechanical and optical characteristics of the glass model under pressure. They all confirm the central theme that amorphous to amorphous phase transformation (AAPT) from a low-density state to a high-density state is at a pressure between 20 and 35 GPa in this nearly ideal a-SiO2 network. This pressure range represents an upper limit for such a transition in vitreous silica. The phase transformation roots from the change of Si-O bonding from a mixture of ionic and covalent nature at low pressure to a highly covalent bonding under high pressure. In addition, the calculated theoretical refractive index of the glass model as a function of the pressure is reported for the first time and in good agreement with the available experimental data.

  13. Pretreatment of Hardwood and Miscanthus with Trametes versicolor for Bioenergy Conversion and Densification Strategies.

    PubMed

    Kalinoski, Ryan M; Flores, Hector D; Thapa, Sunil; Tuegel, Erin R; Bilek, Michael A; Reyes-Mendez, Evelin Y; West, Michael J; Dumonceaux, Tim J; Canam, Thomas

    2017-05-20

    The pretreatment of plant biomass negatively impacts the economics of many bioenergy and bioproduct processes due to the thermochemical requirements for deconstruction of lignocelluluose. An effective strategy to reduce these severity requirements is to pretreat the biomass with white-rot fungi, such as Trametes versicolor, which have the innate ability to deconstruct lignocellulose with a suite of specialized enzymes. In the present study, the effects of 12 weeks of pretreatment with a wild-type strain (52J) and a cellobiose dehydrogenase-deficient strain (m4D) of T. versicolor on hardwood and Miscanthus were explored. Both strains of T. versicolor led to significant decreases of insoluble lignin and significant increases of soluble lignin after acid hydrolysis, which suggests improved lignin extractability. The glucose yields after saccharification using an enzyme cocktail containing chitinase were similar or significantly higher with 52J-treated biomass compared to untreated hardwood and Miscanthus, respectively. The fungal treated biomass, regardless of the strain used, also showed significant increases in energy content and compressive strength of pellets. Overall, the use of T. versicolor as a pretreatment agent for hardwood and Miscanthus could be an environmentally friendly strategy for conversion technologies that require delignification and saccharification, and/or processes that require densification and transport.

  14. Densification of sol-gel silica thin films induced by hard X-rays generated by synchrotron radiation.

    PubMed

    Innocenzi, Plinio; Malfatti, Luca; Kidchob, Tongjit; Costacurta, Stefano; Falcaro, Paolo; Marmiroli, Benedetta; Cacho-Nerin, Fernando; Amenitsch, Heinz

    2011-03-01

    In this article the effects induced by exposure of sol-gel thin films to hard X-rays have been studied. Thin films of silica and hybrid organic-inorganic silica have been prepared via dip-coating and the materials were exposed immediately after preparation to an intense source of light of several keV generated by a synchrotron source. The samples were exposed to increasing doses and the effects of the radiation have been evaluated by Fourier transform infrared spectroscopy, spectroscopic ellipsometry and atomic force microscopy. The X-ray beam induces a significant densification on the silica films without producing any degradation such as cracks, flaws or delamination at the interface. The densification is accompanied by a decrease in thickness and an increase in refractive index both in the pure silica and in the hybrid films. The effect on the hybrid material is to induce densification through reaction of silanol groups but also removal of the organic groups, which are covalently bonded to silicon via Si-C bonds. At the highest exposure dose the removal of the organic groups is complete and the film becomes pure silica. Hard X-rays can be used as an efficient and direct writing tool to pattern coating layers of different types of compositions.

  15. Vibrational dynamics of permanently densified GeO{sub 2} glasses: Densification-induced changes in the boson peak

    SciTech Connect

    Orsingher, L.; Fontana, A.; Gilioli, E.; Carini, G. Jr.; Carini, G.; Tripodo, G.; Unruh, T.; Buchenau, U.

    2010-03-28

    Vitreous GeO{sub 2}, one of the main prototypes of strong glasses, was densified at several pressures up to 6 GPa, achieving more than 20% of densification. The density dependence of the vibrational density of states and of the low temperature properties of these glasses was investigated by means of inelastic neutron scattering and calorimetric measurements. With increasing density, both the boson peak and the bump in c{sub p}/T{sup 3} versus T plot exhibit variations which are stronger than the elastic medium expectation. If one reduces the measured spectra to a common master curve, one finds that this is only possible for the densified samples; the first densification step has an additional effect, similar to other cases in the literature. Nevertheless, the existence of a master curve for the three densified samples proves that the total number of excess modes remains constant on further densification. The experimental data are discussed in the framework of different theoretical models.

  16. Densification of molybdenum and molybdenum alloy powders using hot isostatic pressing. Final technical report

    SciTech Connect

    Barranco, J.; Ahmad, I.; Isserow, S.; Warenchak, R.

    1985-08-01

    This study was conducted to determine a superior erosion-resistant gun-barrel liner material with improved properties at higher temperatures. Four categories of powders were examined: 1. TZM spherical containing 0.5 titanium, 0.08 zirconium, and 0.02 carbon (wt. % nominally), balance molybdenum (Mo), produced by REP (Rotating Electrode Process), PREP (Plasma Rotating Electrode Process), and PMRS (Plasma Melted and Rapidly Solidified); 2. Mo reduced 2 and 5 microns; 3. Mo-0.1% cobalt, co-reduced; 4. Mo-5 wt. % alumina (A12O3), dispersion strengthened. Hot Isostatic Pressing (HIP) densification occurred at 15-30 Ksi, 1300-1600 C, for 1.5 to 3.0 hours. The TZM REP/PREP powders (220/74 microns) were not fully densified even at 1600 C, 30 Ksi, 3 hours. Point-particle contact prevented complete void elimination. TZM PMRS powder (24.7 microns) achieved 99% of theoretical density while maintaining a small grain size (10.4 ASTM eq.) Bend deflection and fracture energies were approximately three times those for PREP powder at a bend rupture strength of about 120 Ksi. Mo reduced and Mo-0.1% Co powders showed less (or the same) ductility with increasing HIP temperatures. Fractures were intergranular with decreased bend rupture and compression strength. The Mo-5A1/sub 2/O/sub 3/ powder maintained a fine grain size (13 ASTM eq.), but with fracture energies usually less than 0.6 in.-lbs. Included are results from bending and compression testing with metallographic and fracture mode interpretation.

  17. Densification and permeability reduction in hot-pressed calcite: A kinetic model

    NASA Astrophysics Data System (ADS)

    Zhu, Wenlu; Evans, Brian; Bernabé, Yves

    1999-11-01

    Laboratory studies on hot isostatically pressed (HIP) calcite reveal that the evolution of porosity and permeability during mechanical compaction can be divided into two distinct regimes. At high porosities, permeability is related approximately to porosity raised to the third power. However, below a porosity called the crossover porosity, the power law relationship no longer applies, and permeability reduction is accelerated. At a porosity of ˜4%, permeability becomes too low to be measured, indicating that a percolation threshold has been reached. In previous studies the time evolutions of porosity and permeability were not predicted, and further, the crossover porosity was introduced as an empirical input parameter. In this study we developed a unified model combining crack healing with densification by power law creep to reproduce porosity evolution as a function of time. Both the healing and the creep are deterministically controlled by the pressure and temperature. Permeability can then be calculated by incorporating quantitative microstructural data (i.e., pore size distribution) into a three-dimensional cubic network model. We were able to reproduce the permeability-porosity relationship in hot-pressed calcite aggregates in both high- and low-porosity regimes. In particular, our model predicted a crossover porosity of ˜7% and a percolation threshold of ˜4%, both in a good agreement with the experimental data. However, we generally overestimated the absolute values of permeability. Because the model yielded correct absolute permeability values in the case when the pore size distribution was known, we suppose that at least part of the error arises from inadequate data for microstructure.

  18. The effect of punch tilting in evaluating powder densification in a rotary tablet machine.

    PubMed

    Cespi, Marco; Misici-Falzi, Monica; Bonacucina, Giulia; Ronchi, Sara; Palmieri, Giovanni F

    2008-03-01

    The effect of punch tilting on the mechanism of punch penetration in the die of a rotary tablet machine during the compression cycle was evaluated by installing four displacement transducers on one station of a rotary machine. Two transducers were symmetrically positioned beside the upper punch in the upper turret, and the other two transducers were similarly placed beside the lower punch in the lower turret. Microcrystalline cellulose and dicalcium phosphate dihydrate were compressed at 5, 10, 15 and 20 kN using two different machine speeds, in order to quantify the effect of punch tilting in the evaluation of punch penetration. These compression data served to construct the powder bed reduction curves, from which it was possible to establish that punch tilting is directly proportional to the compression force used. Tilting is maximal at the beginning of the dwell time, disappears at half dwell time, and reaches a new maximum at the end of the dwell time. In latter case, tilting occurred in the direction opposite that of the first maximum. The impact of tilting in powder densification behaviour, evaluated through the construction of Heckel plots, depends on the compression force used in the analysis. Heckel plots are as distorted as the compression force is elevated. Consequently, the calculated Heckel parameters differ from the real values. Unless a very low compression force is used, a proper Heckel analysis can be performed in a rotary machine only if it is fitted with a device that includes the effect of punch tilting in the evaluation of punch penetration. (Copyright) 2008 Wiley-Liss, Inc.

  19. Seasonal Variations In Density Profiles And Densification Process At Mts. Logan And Wrangell

    NASA Astrophysics Data System (ADS)

    Kanamori, S.; Shiraiwa, T.; Goto-Azuma, K.; Benson, C. S.; Naruse, R.

    2004-12-01

    Detailed density measurements were carried out for ice cores which were drilled at Mt. Logan (60° 35'20"N, 140° 36'15"W; 4135m a.s.l.; Shiraiwa et al., 2003) and Mt. Wrangell (62° 00'N, 140° 03'W; 4100m a.s.l.; Shiraiwa et al., 2004). The detailed density profiles show periodic fluctuations which seem to indicate seasonal cycles. In Mt. Logan, the number of annual layers which are estimated from the density profile agrees well with that estimated from the oxygen isotope data (Goto-Azuma et al., 2003) and the age of the ice core estimated from tritium peaks. On the other hand, in Mt. Wrangell, the number of annual layers from the density profile is quite different from that of the hydrogen isotope profile. The accumulation time series reconstructed from the density profile in Mt. Wrangell shows significant correlations with precipitation data of weather stations that locate near Mt. Wrangell. Accumulation rate and mean annual temperature at both sites are estimated to be almost the same (Benson & Motyka, 1978; Shiraiwa et al., 2003; Goto-Azuma et al., 2003; Shiraiwa et al., 2004). However, their firn/ice transition depths (Mt. Logan: 50m, Mt. Wrangell: 90m) are considerably different. This difference cannot be explained only from the difference in initial densities. Densification rate in Mt. Logan is higher than in Mt. Wrangell, i.e. compactive viscosity coefficient calculated from depth-density profile in Mt. Wrangell is more than double of the value in Mt. Logan.

  20. Densification of ∼5 nm-thick SiO2 layers by nitric acid oxidation

    NASA Astrophysics Data System (ADS)

    Choi, Jaeyoung; Joo, Soyeong; Park, Tae Joo; Kim, Woo-Byoung

    2017-08-01

    Low-temperature nitric acid (HNO3) oxidation of Si (NAOS) has been used to improve the interface and electrical properties of ∼5 nm-thick SiO2/Si layers produced by plasma-enhanced chemical vapor deposition (PECVD). Investigations of the physical properties and electrical characteristics of these thin films revealed that although their thickness is not changed by NAOS, the leakage current density at a gate bias voltage of -1 V decreases by about two orders of magnitude from 1.868 × 10-5 A/cm2. This leakage current density was further reduced by post-metallization annealing (PMA) at 250 °C for 10 min in a 5 vol.% hydrogen atmosphere, eventually reaching a level (5.2 × 10-8 A/cm2) approximately three orders of magnitude less than the as-grown SiO2 layer. This improvement is attributed to a decrease in the concentration of suboxide species (Si1+, Si2+ and Si3+) in the SiO2/Si interface, as well as a decrease in the equilibrium density of defect sites (Nd) and fixed charge density (Nf). The barrier height (Vt) generated by a Poole-Frenkel mechanism also increased from 0.205 to 0.371 eV after NAOS and PMA. The decrease in leakage current density is therefore attributed to a densification of the SiO2 layer in combination with the removal of OH species and increase in interfacial properties at the SiO2/Si interface.

  1. Densification, phase stability and in vitro biocompatibility property of hydroxyapatite-10 wt% silver composites.

    PubMed

    Nath, Shekhar; Kalmodia, Sushma; Basu, Bikramjit

    2010-04-01

    In this paper, we demonstrate how a simple fabrication route, i.e., pressureless sintering of mechanically mixed powders can be employed to develop hydroxyapatite (HAp, Ca(10)(PO(4))(6)(OH)(2))-silver (Ag) bioceramic composites with superior combination of physical (hardness, toughness), non-cytotoxicity, cytocompatiblity and anti-microbial property. The densification results show that such composites can be sintered at 1200 degrees C for 2 h near to theoretical density (>98% rho(th).) An important observation is that the dissociation of HAp phase can be prevented during sintering up to 1300 degrees C for 2 h in HAp-10 wt% Ag composites. The stability of HAp in presence of silver is discussed in reference to the results obtained using XRD, FTIR and Raman spectroscopy. The hardness values of the composites are comparable (approximately 6.5 GPa) to that of pure HAp, despite of the presence of softer Ag particles. The sintered composites exhibit modest crack growth resistance property and their toughness varies in the range of 0.9-1.2 MPa m(0.5), depending on sintering temperature. For selected samples, the in vitro characterization was performed using mouse fibroblast (L929) and human osteosarcoma (MG63) cell lines. The combination of biochemical assays (MTT, ALP and osteocalcin) confirm that HAp-10 wt% Ag biocomposites have comparable or even better cellular viability, osteogenic differentiation and bone mineralization as well as osteoinduction property. Antibacterial experiments involving gram-negative bacteria, Escherichia coli confirm excellent bactericidal property of HAp-10 wt% Ag composites, sintered using mechanically mixed powders.

  2. The Effect of High-Pressure Devitrification and Densification on Ballistic-Penetration Resistance of Fused Silica

    NASA Astrophysics Data System (ADS)

    Grujicic, M.; Avuthu, V.; Snipes, J. S.; Ramaswami, S.; Galgalikar, R.

    2015-12-01

    Recent experimental and molecular-level computational analyses have indicated that fused silica, when subjected to pressures of several tens of GPa, can experience irreversible devitrification and densification. Such changes in the fused-silica molecular-level structure are associated with absorption and/or dissipation of the strain energy acquired by fused silica during high-pressure compression. This finding may have important practical consequences in applications for fused silica such as windshields and windows of military vehicles, portholes in ships, ground vehicles, spacecraft, etc. In the present work, our prior molecular-level computational results pertaining to the response of fused silica to high pressures (and shear stresses) are used to enrich a continuum-type constitutive model (that is, the so-called Johnson-Holmquist-2, JH2, model) for this material. Since the aforementioned devitrification and permanent densification processes modify the response of fused silica to the pressure as well as to the deviatoric part of the stress, changes had to be made in both the JH2 equation of state and the strength model. To assess the potential improvements in respect to the ballistic-penetration resistance of this material brought about by the fused-silica devitrification and permanent densification processes, a series of transient non-linear dynamics finite-element analyses of the transverse impact of a fused-silica test plate with a solid right-circular cylindrical steel projectile were conducted. The results obtained revealed that, provided the projectile incident velocity and, hence, the attendant pressure, is sufficiently high, fused silica can undergo impact-induced devitrification, which improves its ballistic-penetration resistance.

  3. Remote sensing of impervious surface growth: A framework for quantifying urban expansion and re-densification mechanisms

    NASA Astrophysics Data System (ADS)

    Shahtahmassebi, Amir Reza; Song, Jie; Zheng, Qing; Blackburn, George Alan; Wang, Ke; Huang, Ling Yan; Pan, Yi; Moore, Nathan; Shahtahmassebi, Golnaz; Sadrabadi Haghighi, Reza; Deng, Jing Song

    2016-04-01

    A substantial body of literature has accumulated on the topic of using remotely sensed data to map impervious surfaces which are widely recognized as an important indicator of urbanization. However, the remote sensing of impervious surface growth has not been successfully addressed. This study proposes a new framework for deriving and summarizing urban expansion and re-densification using time series of impervious surface fractions (ISFs) derived from remotely sensed imagery. This approach integrates multiple endmember spectral mixture analysis (MESMA), analysis of regression residuals, spatial statistics (Getis_Ord) and urban growth theories; hence, the framework is abbreviated as MRGU. The performance of MRGU was compared with commonly used change detection techniques in order to evaluate the effectiveness of the approach. The results suggested that the ISF regression residuals were optimal for detecting impervious surface changes while Getis_Ord was effective for mapping hotspot regions in the regression residuals image. Moreover, the MRGU outputs agreed with the mechanisms proposed in several existing urban growth theories, but importantly the outputs enable the refinement of such models by explicitly accounting for the spatial distribution of both expansion and re-densification mechanisms. Based on Landsat data, the MRGU is somewhat restricted in its ability to measure re-densification in the urban core but this may be improved through the use of higher spatial resolution satellite imagery. The paper ends with an assessment of the present gaps in remote sensing of impervious surface growth and suggests some solutions. The application of impervious surface fractions in urban change detection is a stimulating new research idea which is driving future research with new models and algorithms.

  4. Effect of Heating Rate on Densification and Grain Growth During Spark Plasma Sintering of 93W-5.6Ni-1.4Fe Heavy Alloys

    NASA Astrophysics Data System (ADS)

    Hu, Ke; Li, Xiaoqiang; Qu, Shengguan; Li, Yuanyuan

    2013-09-01

    Blended 93W-5.6Ni-1.4Fe powders were sintered via the spark plasma sintering (SPS) technique using heating rates from 10 K min-1 to 380 K min-1 (10 °C min-1 to 380 °C min-1). The kinetics of densification and grain growth were analyzed to identify heating rate effects during the SPS of 93W-5.6Ni-1.4Fe powders. The activation energies for densification were calculated and compared with the experimental values for diffusion and other mass transport phenomena. The results show that for the slowly heated specimens [heating rate <100 K min-1 (100 °C min-1)], densification occurs mainly through dissolution-precipitation of W through the matrix phase and W grain boundary diffusion. The concurrent grain growth is dominated by surface diffusion at a low sintering temperature and by solution-reprecipitation and Ni-enhanced W grain boundary diffusion at a higher temperature. For the specimens sintered with heating rates higher than 100 K min-1 (100 °C min-1), the apparent activation energy value for the mechanism controlling densification is a strong function of the relative density, and fast densification controlled by multiple diffusion mechanisms and intensive viscous flow dominates over the grain growth. High SPS heating rate is favorable to obtain high density and fine-grained tungsten heavy alloys.

  5. Synthesis of nanoparticles of Cu, Sb, Sn, SnSb and Cu2Sb by densification and atomization process.

    PubMed

    Lafont, Ugo; Simonin, Loïc; Tabrizi, Nooshin S; Schmidt-Ott, Andreas; Kelder, Erik M

    2009-04-01

    Here we present a technique based on an initial densification of solid precursor materials using magnetic pulses followed by an atomization process via spark discharging. These two processes allow changing bulky micron sized materials into nanoparticles (5-60 nm). The resulting intermediates and nanomaterials have been characterized using electron microscopy (TEM, SEM) and X-ray diffraction to show the texture and structure evolution between the initial bulk phase and the final nanoparticles. In this paper we present the nanoparticle formation of certain metals (Cu, Sn, Sb), alloys and intermetallics (SnSb, Cu2Sb) starting with pure elemental powders.

  6. Effects of densification of precursor pellets on microstructures and critical current properties of YBCO melt-textured bulks

    NASA Astrophysics Data System (ADS)

    Setoyama, Yui; Shimoyama, Jun-ichi; Motoki, Takanori; Kishio, Kohji; Awaji, Satoshi; Kon, Koichi; Ichikawa, Naoki; Inamori, Satoshi; Naito, Kyogo

    2016-12-01

    Effects of densification of precursor disks on the density of residual voids and critical current properties for YBCO melt-textured bulk superconductors were systematically investigated. Six YBCO bulks were prepared from precursor pellets with different initial particle sizes of YBa2Cu3Oy (Y123) powder and applied pressures for pelletization. It was revealed that use of finer Y123 powder and consolidation using cold-isostatic-pressing (CIP) with higher pressures result in reduction of residual voids at inner regions of bulks and enhance Jc especially under low fields below the second peak.

  7. Targeted linkage map densification to improve cell wall related QTL detection and interpretation in maize.

    PubMed

    Courtial, Audrey; Thomas, Justine; Reymond, Matthieu; Méchin, Valérie; Grima-Pettenati, Jacqueline; Barrière, Yves

    2013-05-01

    Several QTLs for cell wall degradability and lignin content were previously detected in the F288 × F271 maize RIL progeny, including a set of major QTLs located in bin 6.06. Unexpectedly, allelic sequencing of genes located around the bin 6.06 QTL positions revealed a monomorphous region, suggesting that these QTLs were likely "ghost" QTLs. Refining the positions of all QTLs detected in this population was thus considered, based on a linkage map densification in most important QTL regions, and in several large still unmarked regions. Re-analysis of data with an improved genetic map (173 markers instead of 108) showed that ghost QTLs located in bin 6.06 were then fractionated over two QTL positions located upstream and downstream of the monomorphic region. The area located upstream of bin 6.06 position carried the major QTLs, which explained from 37 to 59 % of the phenotypic variation for per se values and extended on only 6 cM, corresponding to a physical distance of 2.2 Mbp. Among the 92 genes present in the corresponding area of the B73 maize reference genome, nine could putatively be considered as involved in the formation of the secondary cell wall [bHLH, FKBP, laccase, fasciclin, zinc finger C2H2-type and C3HC4-type (two genes), NF-YB, and WRKY]. In addition, based on the currently improved genetic map, eight QTLs were detected in bin 4.09, while only one QTL was highlighted in the initial investigation. Moreover, significant epistatic interaction effects were shown for all traits between these QTLs located in bin 4.09 and the major QTLs located in bin 6.05. Three genes related to secondary cell wall assembly (ZmMYB42, COV1-like, PAL-like) underlay QTL support intervals in this newly identified bin 4.09 region. The current investigations, even if they were based only on one RIL progeny, illustrated the interest of a targeted marker mapping on a genetic map to improve QTL position.

  8. Controlling the oxygen potential to improve the densification and the solid solution formation of uranium-plutonium mixed oxides

    NASA Astrophysics Data System (ADS)

    Berzati, Ségolène; Vaudez, Stéphane; Belin, Renaud C.; Léchelle, Jacques; Marc, Yves; Richaud, Jean-Christophe; Heintz, Jean-Marc

    2014-04-01

    Diffusion mechanisms occurring during the sintering of oxide ceramics are affected by the oxygen content of the atmosphere, as it imposes the nature and the concentration of structural defects in the material. Thus, the oxygen partial pressure, p(O2), of the sintering gas has to be precisely controlled, otherwise a large dispersion in various parameters, critical for the manufacturing of ceramics such as nuclear oxides fuels, is likely to occur. In the present work, the densification behaviour and the solid solution formation of a mixed uranium-plutonium oxide (MOX) were investigated. The initial mixture, composed of 70% UO2 + 30% PuO2, was studied at p(O2) ranging from 10-15 to 10-4 atm up to 1873 K both with dilatometry and in situ high temperature X-ray diffraction. This study has shown that the initial oxides UO2+x and PuO2-x first densify during heating and then the solid solution formation starts at about 200 K higher. The densification and the formation of the solid solution both occur at a lower temperature when p(O2) increases. Based on this result, it is possible to better define the sintering atmosphere, eventually leading to optimized parameters such as density, oxygen stoichiometry and cations homogenization of nuclear ceramics and of a wide range of industrial ceramic materials.

  9. Sub-micron fracture mechanism in silica-based glass activated by permanent densification from high-strain loading

    SciTech Connect

    Wereszczak, Andrew A.; Waters, Shirley B.; Parten, Randy J.; Pye, L. David

    2016-04-26

    Several silica-based glasses were fractured at high strain energy via drop-weight testing on small specimens. A cylindrical specimen geometry was chosen to promote initially simple, axisymmetric, and uniform compressive loading. The imposed uniaxial compressive strain at impact was sufficiently high to qualitatively cause permanent densification. Produced fragments were collected for postmortem and a fraction of them, for all the silica-based glasses, consistently had distinct sub-micron-sized fractures (~ 300–1000 nm), designated here as “microkernels”, on their surfaces. They would most often appear as a sub-micron pore on the fragment - apparently if the microkernel had popped out as a consequence of the local crack plane running through it, tensile-strain release, and the associated formation of the fragment it was on. No fractographic evidence was found to show the microkernels were associated with local failure initiation. However, their positioning and habit sometimes suggested they were associated with localized crack branching and that they could have influenced secondary fracturing that occurred during overall crushing and comminution and associated fragment size and shape creation. Furthermore, the size range of these microkernels is much too small to affect structural flexure strength of these glasses for most applications but are of a size and concentration that may affect their ballistic, shock, crush, and comminution responses when permanent densification is concomitantly occurring.

  10. Sub-micron fracture mechanism in silica-based glass activated by permanent densification from high-strain loading

    DOE PAGES

    Wereszczak, Andrew A.; Waters, Shirley B.; Parten, Randy J.; ...

    2016-04-26

    Several silica-based glasses were fractured at high strain energy via drop-weight testing on small specimens. A cylindrical specimen geometry was chosen to promote initially simple, axisymmetric, and uniform compressive loading. The imposed uniaxial compressive strain at impact was sufficiently high to qualitatively cause permanent densification. Produced fragments were collected for postmortem and a fraction of them, for all the silica-based glasses, consistently had distinct sub-micron-sized fractures (~ 300–1000 nm), designated here as “microkernels”, on their surfaces. They would most often appear as a sub-micron pore on the fragment - apparently if the microkernel had popped out as a consequence ofmore » the local crack plane running through it, tensile-strain release, and the associated formation of the fragment it was on. No fractographic evidence was found to show the microkernels were associated with local failure initiation. However, their positioning and habit sometimes suggested they were associated with localized crack branching and that they could have influenced secondary fracturing that occurred during overall crushing and comminution and associated fragment size and shape creation. Furthermore, the size range of these microkernels is much too small to affect structural flexure strength of these glasses for most applications but are of a size and concentration that may affect their ballistic, shock, crush, and comminution responses when permanent densification is concomitantly occurring.« less

  11. The AlSi10Mg samples produced by selective laser melting: single track, densification, microstructure and mechanical behavior

    NASA Astrophysics Data System (ADS)

    Wei, Pei; Wei, Zhengying; Chen, Zhen; Du, Jun; He, Yuyang; Li, Junfeng; Zhou, Yatong

    2017-06-01

    This densification behavior and attendant microstructural characteristics of the selective laser melting (SLM) processed AlSi10Mg alloy affected by the processing parameters were systematically investigated. The samples with a single track were produced by SLM to study the influences of laser power and scanning speed on the surface morphologies of scan tracks. Additionally, the bulk samples were produced to investigate the influence of the laser power, scanning speed, and hatch spacing on the densification level and the resultant microstructure. The experimental results showed that the level of porosity of the SLM-processed samples was significantly governed by energy density of laser beam and the hatch spacing. The tensile properties of SLM-processed samples and the attendant fracture surface can be enhanced by decreasing the level of porosity. The microstructure of SLM-processed samples consists of supersaturated Al-rich cellular structure along with eutectic Al/Si situated at the cellular boundaries. The Si content in the cellular boundaries increases with increasing the laser power and decreasing the scanning speed. The hardness of SLM-processed samples was significantly improved by this fine microstructure compared with the cast samples. Moreover, the hardness of SLM-processed samples at overlaps was lower than the hardness observed at track cores.

  12. Sub-micron fracture mechanism in silica-based glass activated by permanent densification from high-strain loading

    SciTech Connect

    Wereszczak, Andrew A.; Waters, Shirley B.; Parten, Randy J.; Pye, L. David

    2016-04-26

    Several silica-based glasses were fractured at high strain energy via drop-weight testing on small specimens. A cylindrical specimen geometry was chosen to promote initially simple, axisymmetric, and uniform compressive loading. The imposed uniaxial compressive strain at impact was sufficiently high to qualitatively cause permanent densification. Produced fragments were collected for postmortem and a fraction of them, for all the silica-based glasses, consistently had distinct sub-micron-sized fractures (~ 300–1000 nm), designated here as “microkernels”, on their surfaces. They would most often appear as a sub-micron pore on the fragment - apparently if the microkernel had popped out as a consequence of the local crack plane running through it, tensile-strain release, and the associated formation of the fragment it was on. No fractographic evidence was found to show the microkernels were associated with local failure initiation. However, their positioning and habit sometimes suggested they were associated with localized crack branching and that they could have influenced secondary fracturing that occurred during overall crushing and comminution and associated fragment size and shape creation. Furthermore, the size range of these microkernels is much too small to affect structural flexure strength of these glasses for most applications but are of a size and concentration that may affect their ballistic, shock, crush, and comminution responses when permanent densification is concomitantly occurring.

  13. Boost in room temperature thermoelectric performance of PbSe:Alx through band modification and low densification

    NASA Astrophysics Data System (ADS)

    Gayner, Chhatrasal; Sharma, Raghunandan; Das, Malay K.; Kar, Kamal K.

    2016-10-01

    Optimization of the transport properties of PbSe to maximize its thermoelectric performance at room temperature has been achieved through a combination of elemental doping and low densification. Al doped PbSe (PbSe:Alx; 0 ≤ x ≤ 0.06) with both lattice substitutional (Pb site) and interstitial occupation has been synthesized through solid state reaction. High Seebeck coefficient of ˜300 to 400 μV/K is noticed at 300 to 500 K. This, combined with the lower thermal conductivity of ˜1.20 W/m K, provides an improved ZT value as high as ˜0.67 at 300 K to the PbSe:Alx Also, by substituting Al in PbSe, maximum power factors of ˜20 to 26.6 μW/cm K2 at 310 K are produced. The high room temperature thermoelectric performance of PbSe:Alx has been attributed to the mix contribution of the Al impurity states and the low densification. The strategy may be utilized to cost effective development of the low working temperature thermoelectric devices.

  14. 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.

  15. Taguchi Analysis on the Effect of Process Parameters on Densification During Spark Plasma Sintering of HfB2-20SiC (Preprint)

    DTIC Science & Technology

    2011-11-01

    AFRL-RX-WP-TP-2011-4397 TAGUCHI ANALYSIS ON THE EFFECT OF PROCESS PARAMATERS ON DENSIFICATION DURING SPARK PLASMA SINTERING OF HfB2-20SiC...of various process variables on the densification during spark plasma sintering of HfB2-20SiC was studied using Taguchi analysis. The statistical...achieved on sintering at 2100°C for 8 minutes at 30 kN pressure and heating rate of 100 K/min. 15. SUBJECT TERMS taguchi analysis; spark plasma

  16. Liquid Oxygen Propellant Densification Unit Ground Tested With a Large-Scale Flight-Weight Tank for the X-33 Reusable Launch Vehicle

    NASA Technical Reports Server (NTRS)

    Tomsik, Thomas M.

    2002-01-01

    Propellant densification has been identified as a critical technology in the development of single-stage-to-orbit reusable launch vehicles. Technology to create supercooled high-density liquid oxygen (LO2) and liquid hydrogen (LH2) is a key means to lowering launch vehicle costs. The densification of cryogenic propellants through subcooling allows 8 to 10 percent more propellant mass to be stored in a given unit volume, thereby improving the launch vehicle's overall performance. This allows for higher propellant mass fractions than would be possible with conventional normal boiling point cryogenic propellants, considering the normal boiling point of LO2 and LH2.

  17. Volcanic sintering and densification of glassy and crystalline ash: Kinetics, strength recovery and seismogenicity

    NASA Astrophysics Data System (ADS)

    Vasseur, J.; Wadsworth, F. B.; Lavallee, Y.; Hess, K.; Dingwell, D. B.

    2013-12-01

    consideration permitted us to explore the effect of sintering on the stress required for dynamic macroscopic failure of synthesized samples at conditions relevant to volcanic conduits. Sintering and densification results in a non linear increase in strength and micromechanical modelling shows that the pore-emanated crack model explains this trend as a function of pore fraction and size. We also assessed the ability of precursory microseismic signals to be used as a failure forecast proxy according to drastic changes in porosity (˜40 to 0%) and material strength (>100 MPa). Homogeneous single-phase liquids to heterogeneous multi-phase (pores in glasses, pores and crystals in other volcanic rocks) liquids display different microseismic patterns preceding bulk sample failure, somewhat mimicking the range of seismic precursory signals observed at volcanoes with magma of similar viscosity and mechanical characteristics. Defect-free glass for example will rapidly accumulate a huge amount of strain energy as it requires to exceed an elevated strength for failure (˜500-700 MPa) and suddenly release it via pervasing microfracturing. Associated microseismic acceleration will display almost no or very late forewarning and seismic-based failure prediction will be hard to make.

  18. Densification kinetics of glassy and crystalline volcanic ash and subsequent predictability associated with its fragmentation

    NASA Astrophysics Data System (ADS)

    Vasseur, Jeremie; Wadsworth, Fabian; Lavallée, Yan; Hess, Kai-Uwe; Dingwell, Donald

    2014-05-01

    consideration permitted us to explore the effect of sintering on the stress required for dynamic macroscopic failure of synthesized samples at conditions relevant to volcanic conduits. Sintering and densification results in a non linear increase in strength and micromechanical modelling shows that the pore-emanated crack model explains this trend as a function of pore fraction and size. We also assessed the ability of precursory microseismic signals to be used as a failure forecast proxy according to drastic changes in porosity (˜40 to 0%) and material strength (>102 MPa). Homogeneous single-phase liquids to heterogeneous multi-phase (pores in glasses, pores and crystals in other volcanic rocks) liquids display different microseismic patterns preceding bulk sample failure, somewhat mimicking the range of seismic precursory signals observed at volcanoes with magma of similar viscosity and mechanical characteristics. Defect-free glass for example will rapidly accumulate a huge amount of strain energy as it requires to exceed an elevated strength for failure (˜500-700 MPa) and suddenly release it via localised microfracturing. Microseismic acceleration associated with defect-poor rocks/magmas display trial or occasionally little forewarning with the implication that seismic-based failure prediction may be difficult to make in real-time monitoring.

  19. The effects of sintering aids on defects, densification, and single crystal conversion of transparent neodymium:YAG ceramics

    NASA Astrophysics Data System (ADS)

    Stevenson, Adam J.

    Nd:YAG transparent ceramics have the potential to replace Czochralski grown single crystals in high power laser applications. However, after more than 20 years of development, there has been only limited application of these potentially revolutionary materials. In order to improve the processing and properties of Nd:YAG transparent ceramics and facilitate increased adoption, this dissertation explores the effects of sintering aids on defects, densification and single crystal conversion (SCC) of Nd:YAG ceramics. To explore the role of SiO2 doping in densification and microstructure development of Nd:YAG transparent ceramics, 1 at% Nd:YAG powders were doped with 0.035--0.28 wt% SiO2 and vacuum sintered between 1484°C and 1750°C. 29Si magic-angle spinning nuclear magnetic resonance showed that Si4+ substitutes onto tetrahedrally coordinated Al 3+ sites at sintering temperatures ≥1600°C. High resolution transmission electron microscopy showed no grain boundary second phases for all silica levels in samples sintered at 1600--1750°C. Coarsening was limited by a solute drag mechanism as suggested by cubic grain growth kinetics and TEM energy dispersive x-ray spectroscopy observations of increased Nd3+ concentration near grain boundaries. Increasing SiO 2 content increased both densification and grain growth rate and led to increasingly coarsening-dominated sintering trajectories. The average grain size could be controlled (2.8 microm--18 microm) in highly transparent ceramics using a combination of SiO2 content, sintering temperature, and sintering time. B2O3-SiO2 was shown to act as a transient liquid phase sintering aid that reduces the sintering temperature of Nd:YAG ceramics to 1600°C. 1 at% Nd:YAG ceramics were doped with 0.34--1.35 mol% B2O3-SiO2 and sintered between 1100°C and 1700°C. Dilatometric measurements showed that B2O 3-SiO2 additions increase the densification rate during intermediate stage sintering relative to SiO2 doped samples. B3+ content is

  20. Garnet-Forming Reactions in Felsic Orthogneiss: Implications for Progressive Strengthening and Densification of the Lower Continental Crust

    NASA Astrophysics Data System (ADS)

    Williams, M. L.; Jercinovic, M. J.; Mahan, K. H.; Dumond, G.; Regan, S.; Holland, M.

    2012-12-01

    Growth of garnet and pyroxene in orthogneiss from the Athabasca Granulite terrane (AGT), northern Saskatchewan, provides a model for progressive densification and strengthening of the lower continental crust. Two distinct assemblages and textures are preserved in granitic and granodioritic gneiss. Low-strain orthogneiss displays igneous textures and assemblages with Qtz, Kfs, Pl, Opx, and Mag (+/- Bt and Hbl). High-strain, dynamically recrystallized, tectonites contain Grt, Cpx, Qtz, Kfs, Na-rich Pl, and relict Opx. The reaction (Opx + Ca-richer Pl = Grt + Cpx + Na-richer Pl) is informally called the "Mary reaction" after documented occurrences in the Mary Granite. It represents the transition from medium-pressure to high-pressure granulite (Green and Ringwood, 1967), but reaction progress was achieved in these deep crustal rocks along an isobaric cooling path at ca. 1 GPa (40 km) pressures. Ambient P-T conditions are well within the product stability field. Abundance of the product assemblage (Grt + Pyx) increases with deformation. Metastable igneous assemblages are widely preserved in low-strain samples. With increasing strain, Grt occurs within recrystallized mantles of feldspar porphyroclasts; Cpx occurs in the deformed tails of Opx crystals. Deformation is interpreted to aid in the breakdown of plagioclase and/or the nucleation of garnet and pyroxene. Garnet and pyroxene modes have been observed to reach nearly 10% in the AGT, but larger amounts are possible because Ca-rich Pl and Opx remnants are widely preserved. Densities increase from ca. 2.6 to ca. 3.0 g/cm, and modeled P-wave velocities approach 7.0 km/s. The reaction occurred at least twice in the AGT, (2.6 and 1.9 Ga), and may have occurred at other times during the long deep crustal residence. Thus, densification can occur incrementally and corresponds with the time and intensity of later tectonism. The Mary reaction provides a mechanism for significant densification and strengthening of lower

  1. Garnet-forming reactions in felsic orthogneiss: Implications for densification and strengthening of the lower continental crust

    NASA Astrophysics Data System (ADS)

    Williams, M. L.; Dumond, G.; Mahan, K.; Regan, S.; Holland, M.

    2014-11-01

    Growth of garnet and pyroxene in orthogneiss from the Athabasca granulite terrane (AGT), northern Saskatchewan, provides a model for progressive densification and strengthening of the lower continental crust with implications for the recycling and long-term evolution of continental crust. Two distinct assemblages and textures are preserved in granitic and granodioritic gneiss. Low-strain orthogneiss displays igneous textures and assemblages of Opx+Kfs+Pl+Mag+Qz (± Bt, Hbl, Ilm). High-strain, dynamically recrystallized tectonites have additional garnet, clinopyroxene, and a more Na-rich plagioclase, along with relict orthopyroxene. The reaction (Opx+Ca-rich Pl=Grt+Cpx+Na-rich Pl+Qz) is informally called the ;Mary reaction; after documented occurrences in the Mary granitoid batholith. The reaction represents the transition from medium-pressure to high-pressure granulite (Green and Ringwood, 1967), but reaction progress was achieved in these deep crustal rocks along an isobaric cooling path at ca. 1 GPa (35-40 km-depth). Ambient P-T conditions were well within the product (low-T-side) stability field. The abundance of the product assemblage (Grt+Cpx+Na-rich Pl) increases with deformation. Metastable igneous assemblages are widely preserved in low-strain samples. With increasing strain, garnet occurs within recrystallized mantles of plagioclase porphyroclasts, and clinopyroxene occurs in the deformed tails of orthopyroxene crystals. Deformation is interpreted to aid in the breakdown of plagioclase and/or the nucleation of garnet and clinopyroxene. Garnet and pyroxene modes have been observed to exceed 10 vol% in the AGT, but larger amounts are possible because Ca-rich plagioclase and orthopyroxene remnants are widely preserved. Densities increase from ca. 2.6 to ca. 3.0 g /cm3 and modeled P-wave velocities approach 7.0 km/s in felsic rocks. Densities in mafic rocks approach 3.4cm3. The reaction occurred at least twice in the AGT, 2.6 and 1.9 Ga, and may have occurred

  2. Assessment of densification and mechanical property of AISI 8630 steel composition on different heat treatments produced through hot upsetting powder preform forging

    NASA Astrophysics Data System (ADS)

    Bala, Y. G.; Sankaranarayanan, S. Raman; Pandey, K. S.

    2015-11-01

    The present investigation was carried out to evaluate the densification, mechanical properties, microstructural and fractrography effects of AISI 8630 steel composition developed through powder preform forging under different heat treated conditions. Sintered preforms of different aspect ratios such as 0.6, 0.9, and 1.2 were hot upset forged to disc shape to different height strain to analysis the densification mechanism. Certain relationships relating strains, Poisson's ratio relating densification have revealed the effect of preform geometry on densification kinetics and resulted in the polynomial expression with justified regression coefficient greater the 0.9 or unity. The preforms of aspect ratio of 1.1 were hot upset forged to square cross section bars and transferred to different quenching medium like oil, water, furnace and air to assess its mechanical properties. Comparing the temperament of the heat treatments, sintered forged homogenised water quenched sample upshot in the maximum Tensile strength with least per centage elongation andthe furnace cooled sample shows the maximum toughness with desirable per centage elongation and least tensile strength. Microstructure stated the presence of varying ferrite and pearlite distribution and fractograph studies has disclosed the mixed mode of failure on the effect of varying heat treatments progression has affected the properties significantly.

  3. Understanding the densification process of Bi2Sr2CaCu2Ox round wires with overpressure processing and its effect on critical current density.

    PubMed

    Matras, M R; Jiang, J; Larbalestier, D C; Hellstrom, E E

    2016-10-01

    Overpressure (OP) processing increases the critical current density (JC ) of Bi2Sr2CaCu2Ox (2212) round wires by shrinking the surrounding Ag matrix around the 2212 filaments, driving them close to full density and greatly increasing the 2212 grain connectivity. Indeed densification is vital for attaining the highest JC . Here, we investigate the time and temperature dependence of the wire densification. We find that the wire diameter decreases by 3.8 ± 0.3 % after full heat treatment at 50 atm and 100 atm OP. At 50 atm OP pressure, the filaments start densifying above 700 °C and reach a 3.30 ± 0.07 % smaller diameter after 2 h at 820 °C, which is below the melting point of 2212 powder. The densification is homogeneous and does not change the filament shape before melting. The growth of non-superconducting phases is observed at 820 °C, suggesting that time should be minimized at high temperature prior to melting the 2212 powder. Study of an open-ended 2.2 m long wire sample shows that full densification and the high OP JC (JC varies by about 3.1 times over the 2.2 m long wire) is reached about 1 m from the open ends, thus showing that coil-length wires can be protected from leaky seals by adding at least 1 m of sacrificial wire at each end.

  4. Identifying viscosities implicit in current firn-densification models: a step toward a physical-process-based constitutive relation for firn

    NASA Astrophysics Data System (ADS)

    Horlings, Brita I.; Waddington, Edwin D.; Stevens, C. Max

    2017-04-01

    Firn densification rate determines the age of air in bubbles in ice cores, and is a primary uncertainty in conversion of volume changes to mass changes for altimetry surveys of the polar ice sheets. However, most current firn models are empirically tuned to local temperature and accumulation rate because not all physical processes that affect firn densification at the grain scale are adequately understood or measured. With generally fewer tunable parameters than active physical processes, impacts of such missing processes have instead typically been lumped together. As the next step toward developing a microphysical-process-based constitutive relation for firn, effective viscosity is used as the constitutive parameter in eight firn-densification models. Effective viscosity is implicitly identified in each model, and is dependent on factors such as stress, strain rate, temperature, and grain-growth processes. The models are forced with temperature and accumulation rate to find the effective viscosities. Preliminary results indicate that there are major qualitative differences in some of the models' viscosity definitions, which indicate discrepancies in implicit descriptions of physical processes. Such differences include discontinuous viscosity at the zone 1-2 boundary (at density of 550 kg m-3), and discrepant viscosity trends that potentially indicate lumping of multiple processes. Each firn model describes densification uniquely, and these results confirm that processes are either oversimplified in different ways or are missing in the definitions. Future work will involve developing a viscosity function based explicitly on multiple processes which will help to prioritize future field measurements and lab studies.

  5. Controllable film densification and interface flatness for high-performance amorphous indium oxide based thin film transistors

    SciTech Connect

    Ou-Yang, Wei E-mail: TSUKAGOSHI.Kazuhito@nims.go.jp; Mitoma, Nobuhiko; Kizu, Takio; Gao, Xu; Lin, Meng-Fang; Tsukagoshi, Kazuhito E-mail: TSUKAGOSHI.Kazuhito@nims.go.jp; Nabatame, Toshihide

    2014-10-20

    To avoid the problem of air sensitive and wet-etched Zn and/or Ga contained amorphous oxide transistors, we propose an alternative amorphous semiconductor of indium silicon tungsten oxide as the channel material for thin film transistors. In this study, we employ the material to reveal the relation between the active thin film and the transistor performance with aid of x-ray reflectivity study. By adjusting the pre-annealing temperature, we find that the film densification and interface flatness between the film and gate insulator are crucial for achieving controllable high-performance transistors. The material and findings in the study are believed helpful for realizing controllable high-performance stable transistors.

  6. Influence of ECAP on Densification Behaviour in the PM Aluminium Al-Mg-Si-Cu-Fe Alloy

    NASA Astrophysics Data System (ADS)

    Bidulská, Jana; Kvačkaj, Tibor; Kočiško, Róbert; Bidulský, Róbert; Grande, Marco Actis

    2010-09-01

    The main aim of this paper is to show how ECAP influences the densification behaviour of PM aluminium alloys. An aluminium based powder (Al-Mg-Si-Cu-Fe) was used as material to be investigated. After applying different compacting pressures, specimens were dewaxed in a ventilated furnace at 400 °C for 60 min. Sintering was carried out in a vacuum furnace at 610 °C for 30 min. The specimens were ECAPed for 1 pass. Optical characterization was carried out on the minimum of 10 different image fields. The results were measured for each pore individually in order to describe the dimensional and morphological porosity characteristics. ECAP influences the porosity distribution in terms of the severe shear deformation involved.

  7. Simulation of the Densification of Semicrystalline Polymer Powders during the Selective Laser Sintering Process: Application to Nylon-12,

    SciTech Connect

    Dong, L.; Makradi, A.; Ahzi, Said; Remond, Y.; Sun, Xin

    2008-06-01

    The heating and densification processes of semi-crystalline polymer powders, during the selective laser sintering process, are simulated using the finite element method. Based on previously developed three-dimensional approach for the sintering of amorphous polymer powders, the modeling methodology is extended to semi-crystalline polymers by taking into account the effects of latent heat during melting. In these simulations, the temperature dependent thermal conductivity, specific heat, density and the effect of latent heat are computed then used as material constants for the integration of the heat equation. Results for temperature and density distribution using Nylon-12 powder are presented and discussed. The effects of processing parameters on the density distribution are also presented.

  8. Pressure-induced densification in GeO2 glass: A transmission x-ray microscopy study

    NASA Astrophysics Data System (ADS)

    Lin, Yu; Zeng, Qiaoshi; Yang, Wenge; Mao, Wendy L.

    2013-12-01

    Nanoscale transmission x-ray microscopy measurements have been performed to determine the effect of pressure (P) on the volume (V) change in GeO2 glass up to 38.5 GPa. The P-V data show a continuous increase upon compression, indicating that the density-driven structural transformation is a gradual process. Over the pressure range studied, a transition is observed at approximately 10-13 GPa, where the material displays distinct compression behaviors. The pressure-induced densification that involves the coordination number change has been discussed. Using this newly developed high-pressure imaging technique with tens of nanometer resolution, we have provided a direct and unequivocal way for measuring density of amorphous materials to much higher pressures with accuracy rivaling x-ray diffraction of crystalline solids.

  9. Full densification of inkjet-printed copper conductive tracks on a flexible substrate utilizing a hydrogen plasma sintering

    NASA Astrophysics Data System (ADS)

    Kwon, Young-Tae; Lee, Young-In; Kim, Seil; Lee, Kun-Jae; Choa, Yong-Ho

    2017-02-01

    Low temperature sintering techniques are crucial in developing flexible printed electronics. In this work, we demonstrate a novel hydrogen plasma sintering method that achieves a full reduction and densification of inkjet-printed patterns using a copper complex ion ink. After inkjet printing on polyethylene terephthalate (PET) substrates, both hydrogen plasma and conventional hydrogen thermal treatment were employed to compare the resulting microstructures, electrical properties and anti-oxidation behavior. The plasma treated pattern shows a fully densified microstructure with a resistivity of 3.23 μΩ cm, while the thermally treated pattern shows a relatively poor microstructure and high resistivity. In addition, the hydrogen plasma-treated copper pattern retains its electrical resistivity for one month without any significant decrease. This novel hydrogen plasma sintering technique could be used to produce conductive patterns with excellent electrical properties, allowing for highly reliable flexible printed electronics.

  10. The effect of volume phase changes, mass transport, sunlight penetration, and densification on the thermal regime of icy regoliths

    NASA Technical Reports Server (NTRS)

    Fanale, Fraser P.; Salvail, James R.; Matson, Dennis L.; Brown, Robert H.

    1990-01-01

    The present quantitative modeling of convective, condensational, and sublimational effects on porous ice crust volumes subjected to solar radiation encompasses the effect of such insolation's penetration of visible bandpass-translucent light, but opaque to the IR bandpass. Quasi-steady-state temperatures, H2O mass fluxes, and ice mass-density change rates are computed as functions of time of day and ice depth. When the effects of latent heat and mass transport are included in the model, the enhancement of near-surface temperature due to the 'solid-state greenhouse effect' is substantially diminished. When latent heat, mass transport, and densification effects are considered, however, a significant solid-state greenhouse effect is shown to be compatible with both morphological evidence for high crust strengths and icy shell decoupling from the lithosphere.

  11. The effect of volume phase changes, mass transport, sunlight penetration, and densification on the thermal regime of icy regoliths

    NASA Technical Reports Server (NTRS)

    Fanale, Fraser P.; Salvail, James R.; Matson, Dennis L.; Brown, Robert H.

    1990-01-01

    The present quantitative modeling of convective, condensational, and sublimational effects on porous ice crust volumes subjected to solar radiation encompasses the effect of such insolation's penetration of visible bandpass-translucent light, but opaque to the IR bandpass. Quasi-steady-state temperatures, H2O mass fluxes, and ice mass-density change rates are computed as functions of time of day and ice depth. When the effects of latent heat and mass transport are included in the model, the enhancement of near-surface temperature due to the 'solid-state greenhouse effect' is substantially diminished. When latent heat, mass transport, and densification effects are considered, however, a significant solid-state greenhouse effect is shown to be compatible with both morphological evidence for high crust strengths and icy shell decoupling from the lithosphere.

  12. Formulation, Pretreatment, and Densification Options to Improve Biomass Specifications for Co-Firing High Percentages with Coal

    SciTech Connect

    Jaya Shankar Tumuluru; J Richard Hess; Richard D. Boardman; Shahab Sokhansanj; Christopher T. Wright; Tyler L. Westover

    2012-06-01

    There is a growing interest internationally to use more biomass for power generation, given the potential for significant environmental benefits and long-term fuel sustainability. However, the use of biomass alone for power generation is subject to serious challenges, such as feedstock supply reliability, quality, and stability, as well as comparative cost, except in situations in which biomass is locally sourced. In most countries, only a limited biomass supply infrastructure exists. Alternatively, co-firing biomass alongwith coal offers several advantages; these include reducing challenges related to biomass quality, buffering the system against insufficient feedstock quantity, and mitigating the costs of adapting existing coal power plants to feed biomass exclusively. There are some technical constraints, such as low heating values, low bulk density, and grindability or size-reduction challenges, as well as higher moisture, volatiles, and ash content, which limit the co-firing ratios in direct and indirect co-firing. To achieve successful co-firing of biomass with coal, biomass feedstock specifications must be established to direct pretreatment options in order to modify biomass materials into a format that is more compatible with coal co-firing. The impacts on particle transport systems, flame stability, pollutant formation, and boiler-tube fouling/corrosion must also be minimized by setting feedstock specifications, which may include developing new feedstock composition by formulation or blending. Some of the issues, like feeding, co-milling, and fouling, can be overcome by pretreatment methods including washing/leaching, steam explosion, hydrothermal carbonization, and torrefaction, and densification methods such as pelletizing and briquetting. Integrating formulation, pretreatment, and densification will help to overcome issues related to physical and chemical composition, storage, and logistics to successfully co-fire higher percentages of biomass ( > 40

  13. Understanding the Impacts of AFEX™ Pretreatment and Densification on the Fast Pyrolysis of Corn Stover, Prairie Cord Grass, and Switchgrass.

    PubMed

    Sundaram, Vijay; Muthukumarappan, Kasiviswanathan; Gent, Stephen

    2017-03-01

    Lignocellulosic feedstocks corn stover, prairie cord grass, and switchgrass were subjected to ammonia fiber expansion (AFEX™) pretreatment and densified using extrusion pelleting and ComPAKco densification technique. The effects of AFEX™ pretreatment and densification were studied on the fast pyrolysis product yields. Feedstocks were milled in a hammer mill using three different screen sizes (2, 4, and 8 mm) and were subjected to AFEX™ pretreatment. The untreated and AFEX™-pretreated feedstocks were moisture adjusted at three levels (5, 10, and 15 % wb) and were extruded using a lab-scale single screw extruder. The barrel temperature of the extruder was maintained at 75, 100, and 125 °C. Durability of the extruded pellets made from AFEX™-pretreated corn stover, prairie cord grass, and switchgrass varied from 94.5 to 99.2, 94.3 to 98.7, and 90.1 to 97.5 %, respectively. Results of the thermogravimetric analysis showed the decrease in the decomposition temperature of the all the feedstocks after AFEX™ pretreatment indicating the increase in thermal stability. Loose and densified feedstocks were subjected to fast pyrolysis in a lab-scale reactor, and the yields (bio-oil and bio-char) were measured. Bio-char obtained from the AFEX™-pretreated feedstocks exhibited increased bulk and particle density compared to the untreated feedstocks. The properties of the bio-oil were statistically similar for the untreated, AFEX™-pretreated, and AFEX™-pretreated densified feedstocks. Based on the bio-char and bio-oil yields, the AFEX™-pretreated feedstocks and the densified AFEX™-pretreated feedstocks (pellets and PAKs) exhibited similar behavior. Hence, it can be concluded that densifying the AFEX™-pretreated feedstocks could be a viable option in the biomass-processing depots to reduce the transportation costs and the logistical impediments without affecting the product yields.

  14. Gravity induced densification of floating crude oil by granular materials: Effect of particle size and surface morphology.

    PubMed

    Boglaienko, Daria; Tansel, Berrin

    2016-06-15

    Densification and sedimentation of floating crude oil to the bottom of water column reduces the radius of a spill and its mobility, preventing direct contamination of beaches, coastal flora and fauna. Performances of different natural granular materials were evaluated for capturing efficiency of floating fresh South Louisiana crude oil. The granular materials studied were quartz sand with medium (20-30mesh) and fine (40-100mesh) particle size, limestone with coarse (4-10mesh) and medium (16-40mesh) particle size, beach sand (20-80mesh), and clay (kaolin with ferric oxide; passing 200mesh). Beach sand (mixture of quartz and limestone 20-80mesh) and limestone (16-40mesh) demonstrated better performance for capture, densification and submergence of the crude oil among the materials evaluated. The behavior of granular particles with the hydrophobic phase can be classified as (1) immersion entrapment inside the hydrophobic phase (slurry), and (2) partial encapsulation of the hydrophobic phase by a single layer of particles (raft). With crude oil, the particles were primarily entrapped within the hydrophobic phase. Study of the effect of particle size and morphology (i.e., porosity) of the granular materials on capture performance showed that average surface pore size did not have a significant effect on aggregation with oil, however, higher capture efficiency was observed with materials of higher surface porosity (beach sand and limestone). The experiments revealed that there is a critical particle size range (passing 10mesh) which resulted in more effective aggregation of the granular materials with crude oil.

  15. Firn density profile at Megadunes, East Antarctica, calls for an improved densification model for low accumulation sites.

    NASA Astrophysics Data System (ADS)

    Suwa, M.; Severinghaus, J. P.

    2004-12-01

    We report a density profile of the firn at Megadunes, East Antarctica (80o78'S; 124o50'E). The Megadunes site is characterized by a low mass accumulation rate (2.9 g/cm2/yr) and cold temperature (mean annual = -49.5oC). Validating existing firn densification models using a density profile of such a site is important because such models, either purely empirical or mechanistic, have been calibrated with few sites that are analogous to a glacial condition (ultralow accumulation and temperature). We make use of CO2 concentrations in the lock-in (or non-diffusive) zone to obtain the accumulation rate, assuming that the gas in the lock-in zone ages at the same rate as the surrounding ice [Battle et al., 1996], and assuming that the gas enclosure rate must equal the long-term mean accumulation rate. This estimate is preliminary and may change when results from beta analysis of cores become available. Our density profile shows that the widely used pure empirical model by Herron and Langway [1980] overestimates the close-off depth by 16 %, and the semi-mechanistic model by Pimienta and Barnola [Barnola et al., 1991] also overestimates the close-off depth by 26 %. Our study at the Megadunes site indicates that the δ 15N of N2 paradox for glacial ice from East Antarctica would have partly resulted from a poorly calibrated densification model for a `glacial-like' condition and a thick convective zone as we observed at the Megadunes site [Severinghaus et al., in prep].

  16. The effect of high-pressure devitrification and densification on ballistic-penetration resistance of fused silica

    NASA Astrophysics Data System (ADS)

    Avuthu, Vasudeva Reddy

    Despite the clear benefits offered by more advanced transparent materials, (e.g. transparent ceramics offer a very attractive combination of high stiffness and high hardness levels, highly-ductile transparent polymers provide superior fragment-containing capabilities, etc.), ballistic ceramic-glass like fused-silica remains an important constituent material in a majority of transparent impact-resistant structures (e.g. windshields and windows of military vehicles, portholes in ships, ground vehicles and spacecraft) used today. Among the main reasons for the wide-scale use of glass, the following three are most frequently cited: (i) glass-structure fabrication technologies enable the production of curved, large surface-area, transparent structures with thickness approaching several inches; (ii) relatively low material and manufacturing costs; and (iii) compositional modifications, chemical strengthening, and controlled crystallization have been demonstrated to be capable of significantly improving the ballistic properties of glass. In the present work, the potential of high-pressure devitrification and densification of fused-silica as a ballistic-resistance-enhancement mechanism is investigated computationally. In the first part of the present work, all-atom molecular-level computations are carried out to infer the dynamic response and material microstructure/topology changes of fused silica subjected to ballistic impact by a nanometer-sized hard projectile. The analysis was focused on the investigation of specific aspects of the dynamic response and of the microstructural changes such as the deformation of highly sheared and densified regions, and the conversion of amorphous fused silica to SiO2 crystalline allotropic modifications (in particular, alpha-quartz and stishovite). The microstructural changes in question were determined by carrying out a post-processing atom-coordination procedure. This procedure suggested the formation of high-density stishovite (and

  17. Drastically Enhancing Moduli of Graphene-Coated Carbon Nanotube Aerogels via Densification While Retaining Temperature Invariant Superelasticity and Ultrahigh Efficiency.

    PubMed

    Tsui, Michelle N; Kim, Kyu Hun; Islam, Mohammad F

    2017-10-09

    Lightweight open-cell foams that are simultaneously superelastic, possess exceptionally high Young's moduli (Y), exhibit ultrahigh efficiency, and resist fatigue as well as creep are particularly desirable as structural frameworks. Unfortunately, many of these features are orthogonal in foams of metals, ceramics, and polymers, particularly under large temperature variations. In contrast, foams of carbon allotropes including carbon nanotubes and graphene developed over the last few years exhibit these desired properties but have low Y due to low density,  = 0.5-10 mg/mL. Densification of these foams enhances Y although below expectation and also dramatically degrades other properties because of drastic changes in microstructure. We have recently developed size and shape tunable graphene-coated single-walled carbon nanotube (SWCNT) aerogels that display superelasticity at least up to a compressive strain () = 80%, fatigue and creep resistance, and ultrahigh efficiency over -100-500 °C. Unfortunately, Y of these aerogels is only ≈ 0.75 MPa due to low  ≈ 14 mg/mL, limiting their competitiveness as structural foams. We report fabrication of similar aerogels but with  spanning more than an order of magnitude from 16-400 mg/mL through controlled isostatic compression in the presence of a polymer coating circumventing any microstructural changes in stark contrast to other foams of carbon allotropes. The compressive stress () versus  measurements show that the densification of aerogels from  ≈ 16 mg/mL to  ≈ 400 mg/mL dramatically enhances Y from 0.9 MPa to 400 MPa while maintaining superelasticity at least up to  = 10% even at the highest . The storage (E') and loss (E″) moduli measured in the linear regime show ultralow loss coefficient, tan  = E″/E' ≈ 0.02, that remains constant over three decades of frequencies (0.628-628 rad/s), suggesting unusually high frequency-invariant efficiency. Furthermore, these aerogels retain

  18. On the Densification Behavior of (0.2, 0.5, and 1 Wt Pct) CNT-YSZ Ceramic Composites Processed via Spark Plasma Sintering

    NASA Astrophysics Data System (ADS)

    Karanam, Abhinav; Bichler, Lukas; Fong, Randy

    2015-08-01

    Yttria-Stabilized Zirconia (YSZ) is a promising thermal insulating ceramic for high temperature applications due to its stability and chemical inertness. As was demonstrated with other technical ceramics ( e.g., Alumina), addition of Single-Wall Carbon Nanotubes (CNTs) to a ceramic matrix may significantly enhance its mechanical properties. In this work, 8 mol pct YSZ with 0.2, 0.5, and 1 wt pct CNT composites were fabricated via the spark plasma sintering process. The densification, Vicker's microhardness, specific gravity, and microstructure evolution of the composites were investigated. The results suggest that the addition of CNTs to YSZ hindered densification and grain growth during SPS processing leading to inhomogeneous grain size distribution. However, the CNTs had a profound impact on the hardness of the composite ceramics, with an increase from 697 HV (YSZ) to 1195 HV (1 wt pctCNT-YSZ).

  19. Understanding the densification process of Bi2Sr2CaCu2O x round wires with overpressure processing and its effect on critical current density

    NASA Astrophysics Data System (ADS)

    Matras, M. R.; Jiang, J.; Larbalestier, D. C.; Hellstrom, E. E.

    2016-10-01

    Overpressure (OP) processing increases the critical current density ({{\\boldsymbol{J}}}{{C}}) of Bi2Sr2CaCu2O x (2212) round wires by shrinking the surrounding Ag matrix around the 2212 filaments, driving them close to full density and greatly increasing the 2212 grain connectivity. Indeed densification is vital for attaining the highest {{\\boldsymbol{J}}}{{C}}. Here, we investigate the time and temperature dependence of the wire densification. We find that the wire diameter decreases by 3.8 ± 0.3% after full heat treatment at 50 atm and 100 atm OP. At 50 atm OP pressure, the filaments start densifying above 700 °C and reach a 3.30 ± 0.07% smaller diameter after 2 h at 820 °C, which is below the melting point of 2212 powder. The densification is homogeneous and does not change the filament shape before melting. The growth of non-superconducting phases is observed at 820 °C, suggesting that time should be minimized at high temperature prior to melting the 2212 powder. Study of an open-ended 2.2 m long wire sample shows that full densification and the high OP {{\\boldsymbol{J}}}{{C}} ({{\\boldsymbol{J}}}{{C}} varies by about 3.1 times over the 2.2 m long wire) is reached about 1 m from the open ends, thus showing that coil-length wires can be protected from leaky seals by adding at least 1 m of sacrificial wire at each end.

  20. Influence of processing parameters on laser penetration depth and melting/re-melting densification during selective laser melting of aluminum alloy

    NASA Astrophysics Data System (ADS)

    Yu, Guanqun; Gu, Dongdong; Dai, Donghua; Xia, Mujian; Ma, Chenglong; Chang, Kun

    2016-10-01

    A three-dimensional mesoscopic model, considering the powder-to-solid transition, motion of gas bubbles within molten pool and the effect of surface tension, has been established in order to investigate the evolution rule of pores and re-melting densification mechanism during selective laser melting of AlSi10Mg. The results indicated that re-melting phenomenon of previous fabricated layer induced by laser melting of current powder layer played a crucial role on the increase in densification rate. During the re-melting process, the trapped gas pores in previous layer rose up swiftly and came to the surface consequently, resulting in remarkably elevated densification in previous layer. The influences of laser scan speed on the single-track morphology, types of pores and laser penetration depth have also been studied. It showed that the maximum re-melting depth (31 µm) was attained, and meanwhile, pores left in preceding layer got eliminated completely due to the mass transfer within molten pool, when an appropriate laser scan speed (150 mm/s) was applied. In this case, reasonable laser energy per unit length and irradiation time tended to enhance the laser penetration depth for powder bed and decrease the porosity in as-fabricated layer. A series of experimental study were performed to verify the reliability of the above mesoscopic simulation, including the surface topography of single track and the types of pores. The redistribution of bubbles between the adjacent layers as well as the localized re-melting densification, which were observed from the longitudinal section of samples, was in good agreement with simulation results.

  1. Engineering strain, densification, order parameter and magnetic properties of FePt thin films by dense electronic excitations

    NASA Astrophysics Data System (ADS)

    Gupta, Rekha; Sehdev, Neeru; Asokan, K.; Kanjilal, D.; Annapoorni, S.

    2014-08-01

    FePt films prepared by DC sputtering on Si ⟨100⟩ substrates when annealed at 600 °C for 1 h exhibited a structurally ordered and magnetically hard L10 phase. These FePt films were exposed to dense electronic excitations by using 100 MeV oxygen ions as a function of increasing fluences. Such excitations induce pressure and result in the enhancement of order parameter by increasing strain on the FePt films. Apart from this, the surface morphological images from field emission scanning electron microscopy reveal a densification of the films consequent to irradiation and are correlated with the details obtained from Rutherford back scattering analysis. The variation in the values of coercivity correlates well with the change in volume percentage of face centered tetragonal and face centered cubic phase. A coercivity of 14.7 kOe with order parameter 0.92 is achieved at a fluence of 5 × 1012 ions/cm2. The theoretical simulation of the demagnetization curve shows a strong correlation of coercivity and order parameter between the experimentally obtained values with that of simulation. The effect of irradiation induced strain, the structural ordering and coercivity of FePt films as a function of fluences have been discussed.

  2. Kinetic Stability of MOF-5 in Humid Environments: Impact of Powder Densification, Humidity Level, and Exposure Time.

    PubMed

    Ming, Yang; Purewal, Justin; Yang, Jun; Xu, Chunchuan; Soltis, Rick; Warner, James; Veenstra, Mike; Gaab, Manuela; Müller, Ulrich; Siegel, Donald J

    2015-05-05

    Metal-organic frameworks (MOFs) are an emerging class of microporous, crystalline materials with potential applications in the capture, storage, and separation of gases. Of the many known MOFs, MOF-5 has attracted considerable attention because of its ability to store gaseous fuels at low pressure with high densities. Nevertheless, MOF-5 and several other MOFs exhibit limited stability upon exposure to reactive species such as water. The present study quantifies the impact of humid air exposure on the properties of MOF-5 as a function of exposure time, humidity level, and morphology (i.e., powders vs pellets). Properties examined include hydrogen storage capacity, surface area, and crystallinity. Water adsorption/desorption isotherms are measured using a gravimetric technique; the first uptake exhibits a type V isotherm with a sudden increase in uptake at ∼50% relative humidity. For humidity levels below this threshold only minor degradation is observed for exposure times up to several hours, suggesting that MOF-5 is more stable than generally assumed under moderately humid conditions. In contrast, irreversible degradation occurs in a matter of minutes for exposures above the 50% threshold. Fourier transform infrared spectroscopy indicates that molecular and/or dissociated water is inserted into the skeletal framework after long exposure times. Densification into pellets can slow the degradation of MOF-5 significantly, and may present a pathway to enhance the stability of some MOFs.

  3. Zirconium Carbide Produced by Spark Plasma Sintering and Hot Pressing: Densification Kinetics, Grain Growth, and Thermal Properties

    DOE PAGES

    Wei, Xialu; Back, Christina; Izhvanov, Oleg; ...

    2016-07-14

    Spark plasma sintering (SPS) has been employed to consolidate a micron-sized zirconium carbide (ZrC) powder. ZrC pellets with a variety of relative densities are obtained under different processing parameters. The densification kinetics of ZrC powders subjected to conventional hot pressing and SPS are comparatively studied by applying similar heating and loading profiles. Due to the lack of electric current assistance, the conventional hot pressing appears to impose lower strain rate sensitivity and higher activation energy values than those which correspond to the SPS processing. A finite element simulation is used to analyze the temperature evolution within the volume of ZrCmore » specimens subjected to SPS. The control mechanism for grain growth during the final SPS stage is studied via a recently modified model, in which the grain growth rate dependence on porosity is incorporated. Finally, the constant pressure specific heat and thermal conductivity of the SPS-processed ZrC are determined to be higher than those reported for the hot-pressed ZrC and the benefits of applying SPS are indicated accordingly.« less

  4. Zirconium Carbide Produced by Spark Plasma Sintering and Hot Pressing: Densification Kinetics, Grain Growth, and Thermal Properties

    PubMed Central

    Wei, Xialu; Back, Christina; Izhvanov, Oleg; Haines, Christopher D.; Olevsky, Eugene A.

    2016-01-01

    Spark plasma sintering (SPS) has been employed to consolidate a micron-sized zirconium carbide (ZrC) powder. ZrC pellets with a variety of relative densities are obtained under different processing parameters. The densification kinetics of ZrC powders subjected to conventional hot pressing and SPS are comparatively studied by applying similar heating and loading profiles. Due to the lack of electric current assistance, the conventional hot pressing appears to impose lower strain rate sensitivity and higher activation energy values than those which correspond to the SPS processing. A finite element simulation is used to analyze the temperature evolution within the volume of ZrC specimens subjected to SPS. The control mechanism for grain growth during the final SPS stage is studied via a recently modified model, in which the grain growth rate dependence on porosity is incorporated. The constant pressure specific heat and thermal conductivity of the SPS-processed ZrC are determined to be higher than those reported for the hot-pressed ZrC and the benefits of applying SPS are indicated accordingly. PMID:28773697

  5. Zirconium Carbide Produced by Spark Plasma Sintering and Hot Pressing: Densification Kinetics, Grain Growth, and Thermal Properties

    SciTech Connect

    Wei, Xialu; Back, Christina; Izhvanov, Oleg; Haines, Christopher; Olevsky, Eugene

    2016-07-14

    Spark plasma sintering (SPS) has been employed to consolidate a micron-sized zirconium carbide (ZrC) powder. ZrC pellets with a variety of relative densities are obtained under different processing parameters. The densification kinetics of ZrC powders subjected to conventional hot pressing and SPS are comparatively studied by applying similar heating and loading profiles. Due to the lack of electric current assistance, the conventional hot pressing appears to impose lower strain rate sensitivity and higher activation energy values than those which correspond to the SPS processing. A finite element simulation is used to analyze the temperature evolution within the volume of ZrC specimens subjected to SPS. The control mechanism for grain growth during the final SPS stage is studied via a recently modified model, in which the grain growth rate dependence on porosity is incorporated. Finally, the constant pressure specific heat and thermal conductivity of the SPS-processed ZrC are determined to be higher than those reported for the hot-pressed ZrC and the benefits of applying SPS are indicated accordingly.

  6. Densification of tube-shaped transparent conducting oxide target at reduced temperature via initial heat treatment under pressure

    NASA Astrophysics Data System (ADS)

    Lee, Sung-Pyo; Lee, Jong-Rak; Chung, Tai-Joo; Paek, Yeong-Kyeun; Yang, Seung-Ho; Hong, Gil-Su; Oh, Kyung-Sik

    2015-11-01

    Transparent conducting oxide such as aluminum doped ZnO (Al-ZnO) needs to be prepared in a tube-shaped target for prolonged life time during sputtering. To prevent warping and coarsening during preparation, the densification of tube-shaped target need to be achieved at reduced temperature. In this study, tube-shaped 2 wt% Al-ZnO was prepared via two-step sintering route, consisted with initial heat treatment (IHT) at 700 °C or 800 °C under mild external pressure (1 MPa) and subsequent pressureless sintering at 1300 °C or 1350 °C. By applying pressure during the IHT, the density obtained by sintering at 1300 °C increased by 2.38% and reached the same level of density as material sintered at 1350 °C. The reduced sintering temperature rendered a fine grained tube, suitable for prevention of nodules during sputtering. The IHT under external pressure had limited effects for tall tubes, where loss of pressure was anticipated due to the difficulty in fine filling the pressing medium within the mold.

  7. Improved transport properties and connectivity of in situ MgB 2 wires obtained by Cold High Pressure Densification (CHPD)

    NASA Astrophysics Data System (ADS)

    Flükiger, R.; Hossain, M. S. A.; Senatore, C.; Rindfleisch, M.

    2011-11-01

    The critical current density, Jc, of in situ MgB2 wires with C4H6O5 (malic acid) has been strongly enhanced by means of Cold High Pressure Densification (CHPD) at pressures up to 2.5 GPa prior to reaction. An increase in Jc by factors 2 and 8 was observed at 4.2 and 20 K, regardless of the applied field. Densified wires were found to exhibit a higher homogeneity due to enhanced connectivity. In addition, a higher C content was found, as shown by the lattice parameter change, the decrease of Tc, the shift of the calorimetric Tc distribution and a reduced anisotropy in tapes obtained from the same wires. The higher C content in densified wires is responsible for the observed enhancement of Birr by more than 1 T, up to 11 T at 20 K. Almost isotropic Jc values were obtained for C4H6O5 added square wires of 1 × 0.6 mm2 cross section, the values of Jc(4.2 K) = 1 × 104 A/cm2 for fields // and ⊥ to the wider surface being obtained at 13.8 and 13.1 T (1 μV/cm criterion), the values for 20 K being 6.4 and 6.2 T, respectively. The method was successfully applied to mono- and multifilamentary wires with lengths up to several meters, suggesting applicability for industrial lengths.

  8. Densification mechanisms of haplogranite glasses as a function of water content and pressure based on density and Raman data

    NASA Astrophysics Data System (ADS)

    Ardia, P.; Di Muro, A.; Giordano, D.; Massare, D.; Sanchez-Valle, C.; Schmidt, M. W.

    2014-08-01

    This study investigates the effect of pressure (1 atm-2.5 GPa) and water (0.15, 2.7, 3.6 and 5.2 wt% H2O) on the network structure of alkali-rich alumino-silicate glasses synthesized at 1000 °C. Density increases linearly with pressure in the water-poor composition, while in the water-rich glasses and above 1.5 GPa densification decreases with pressure. Raman data suggest that several structural changes follow one upon another with increasing pressure and water content. The almost dry glasses undergo large modifications of the network ring structure with pressure, namely a decrease in average T-O-T angle, change in ring size statistics and possibly an increasingly homogeneous distribution of Al- and Si-rich domains at high pressure. Water dissolution favors a homogenization of ring sizes at low pressures. Pressure essentially induces a decrease in the average intertetrahedral angle and, above 1.5 GPa, a possible redistribution of Al/Si-rich regions. Pressure induces an increase in O-H bonding but decreases the O-H bond strength. The observed structural modifications are consistent with the decreasing net effect of pressure on viscosity as temperature and water increase through variation of the activation volume of viscosity.

  9. Mass densification and defect restoration in chemical vapor deposition silicon dioxide film using Ar plasma excited by microwave

    SciTech Connect

    Kawase, Kazumasa Motoya, Tsukasa; Uehara, Yasushi; Teramoto, Akinobu; Suwa, Tomoyuki; Ohmi, Tadahiro

    2014-09-01

    Silicon dioxide (SiO{sub 2}) films formed by chemical vapor deposition (CVD) have been treated with Ar plasma excited by microwave. The changes of the mass densities, carrier trap densities, and thicknesses of the CVD-SiO{sub 2} films with the Ar plasma treatments were investigated. The mass density depth profiles were estimated with X-Ray Reflectivity (XRR) analysis using synchrotron radiation. The densities of carrier trap centers due to defects of Si-O bond network were estimated with X-ray Photoelectron Spectroscopy (XPS) time-dependent measurement. The changes of the thicknesses due to the oxidation of Si substrates were estimated with the XRR and XPS. The mass densities of the CVD-SiO{sub 2} films are increased by the Ar plasma treatments. The carrier trap densities of the films are decreased by the treatments. The thicknesses of the films are not changed by the treatments. It has been clarified that the mass densification and defect restoration in the CVD-SiO{sub 2} films are caused by the Ar plasma treatments without the oxidation of the Si substrates.

  10. A new constitutive model for simulation of softening, plateau, and densification phenomena for trabecular bone under compression.

    PubMed

    Lee, Chi-Seung; Lee, Jae-Myung; Youn, BuHyun; Kim, Hyung-Sik; Shin, Jong Ki; Goh, Tae Sik; Lee, Jung Sub

    2017-01-01

    A new type of constitutive model and its computational implementation procedure for the simulation of a trabecular bone are proposed in the present study. A yield surface-independent Frank-Brockman elasto-viscoplastic model is introduced to express the nonlinear material behavior such as softening beyond yield point, plateau, and densification under compressive loads. In particular, the hardening- and softening-dominant material functions are introduced and adopted in the plastic multiplier to describe each nonlinear material behavior separately. In addition, the elasto-viscoplastic model is transformed into an implicit type discrete model, and is programmed as a user-defined material subroutine in commercial finite element analysis code. In particular, the consistent tangent modulus method is proposed to improve the computational convergence and to save computational time during finite element analysis. Through the developed material library, the nonlinear stress-strain relationship is analyzed qualitatively and quantitatively, and the simulation results are compared with the results of compression test on the trabecular bone to validate the proposed constitutive model, computational method, and material library.

  11. Correlation between triple phase boundary and the microstructure of Solid Oxide Fuel Cell anodes: The role of composition, porosity and Ni densification

    NASA Astrophysics Data System (ADS)

    Lu, Xuekun; Heenan, Thomas M. M.; Bailey, Josh J.; Li, Tao; Li, Kang; Brett, Daniel J. L.; Shearing, Paul R.

    2017-10-01

    This study aims to correlate the active triple phase boundaries (TPBs) to the variation of as-prepared anode microstructures and Ni densifications based on the reconstructed 3D volume of an SOFC anode, providing a point of comparison with theoretical studies that reveal the relationship of TPBs and the material microstructure using randomly packed spheres models. The TPB degradation mechanisms are explained using a particle network model. The results indicate that in low porosity regime, the TPBs sharply increase with the porosity until the percolation threshold (10%); at intermediate porosity (10%-25%), a balance of surface area between three phases is more critical than that of volume fraction to reach the optimal TPB density; in the high porosity regime (>25%), the TPBs start to drop due to the shrinkage and detachment of Ni/YSZ interfaces. The TPB density is inversely proportional to the degree of Ni densification as long as the Ni content is above the percolation threshold (35%) and can be improved by 70% within 7% change of porosity provided that the over-densification is mitigated. This has implications for the design of SOFC microstructures as well for electrode durability, where Ni agglomeration is known to deleteriously impact long-term operation.

  12. Liquid Oxygen Propellant Densification Production and Performance Test Results With a Large-Scale Flight-Weight Propellant Tank for the X33 RLV

    NASA Technical Reports Server (NTRS)

    Tomsik, Thomas M.; Meyer, Michael L.

    2010-01-01

    This paper describes in-detail a test program that was initiated at the Glenn Research Center (GRC) involving the cryogenic densification of liquid oxygen (LO2). A large scale LO2 propellant densification system rated for 200 gpm and sized for the X-33 LO2 propellant tank, was designed, fabricated and tested at the GRC. Multiple objectives of the test program included validation of LO2 production unit hardware and characterization of densifier performance at design and transient conditions. First, performance data is presented for an initial series of LO2 densifier screening and check-out tests using densified liquid nitrogen. The second series of tests show performance data collected during LO2 densifier test operations with liquid oxygen as the densified product fluid. An overview of LO2 X-33 tanking operations and load tests with the 20,000 gallon Structural Test Article (STA) are described. Tank loading testing and the thermal stratification that occurs inside of a flight-weight launch vehicle propellant tank were investigated. These operations involved a closed-loop recirculation process of LO2 flow through the densifier and then back into the STA. Finally, in excess of 200,000 gallons of densified LO2 at 120 oR was produced with the propellant densification unit during the demonstration program, an achievement that s never been done before in the realm of large-scale cryogenic tests.

  13. Intrawire resistance, AC loss and strain dependence of critical current in MgB2 wires with and without cold high-pressure densification

    NASA Astrophysics Data System (ADS)

    Zhou, C.; Gao, P.; Krooshoop, H. J. G.; Dhallé, M.; Sumption, M. D.; Rindfleisch, M.; Tomsic, M.; Kulich, M.; Senatore, C.; Nijhuis, A.

    2014-07-01

    The intrawire resistance and alternating current (AC) loss of two MgB2 wires with filaments surrounded by Nb barriers have been measured and analyzed. Relatively high values of filament-to-matrix contact resistivity are found in the MgB2 wires; the values are two or three orders higher than those commonly found in NbTi or Nb3Sn wires. Considering the high porosity of the MgB2 filaments, cold high-pressure densification has been applied on the two MgB2 wires to investigate its impact on intrawire resistance and AC loss. The intrawire resistance is measured with a direct four-probe voltage-current method at various temperatures. The AC loss is measured by vibrating sample magnetometer measurements at 4.2 K. In addition to the intrawire resistance measurements, the critical current of MgB2 wires before and after densification is measured with a U-shaped bending spring at 4.2 K as function of axial strain. The critical current in densified MgB2 wires is found to be higher than that in the same wire without densification; it is also less sensitive to the applied axial strain.

  14. Real-time assessment of granule densification in high shear wet granulation and application to scale-up of a placebo and a brivanib alaninate formulation.

    PubMed

    Narang, Ajit S; Sheverev, Valery A; Stepaniuk, Vadim; Badawy, Sherif; Stevens, Tim; Macias, Kevin; Wolf, Avi; Pandey, Preetanshu; Bindra, Dilbir; Varia, Sailesh

    2015-03-01

    Real-time monitoring and control of high shear wet granulation (HSWG) using process analytical technologies is crucial to process design, scale-up, and reproducible manufacture. Although significant progress has been made in real-time measurement of granule size distribution using focused beam reflectance measurement (FBRM), real-time in-line assessment of granule densification remains challenging. In this study, a drag force flow (DFF) sensor was developed and used to probe wet mass consistency in real-time. In addition, responses from FBRM and DFF sensors were compared to assess complementarity of information on granulation progress from the two probes. A placebo and a brivanib alaninate formulation were granulated with different concentrations of binder or water, respectively, while measuring granule size growth, densification, and DFF sensor response. The DFF sensor was able to quantitatively characterize with high resolution a response of wet mass consistency distinct from granule size distribution. The wet mass consistency parameter correlated well with granule densification, which was shown as a critical material attribute that correlated with tablet dissolution. In addition, application of DFF sensor to scale-up of granulation was demonstrated. These results showed the value of wet mass consistency measurement using DFF for WG monitoring and control.

  15. The effect of biomass densification on structural sugar release and yield in biofuel feedstock and feedstock blends

    DOE PAGES

    Wolfrum, Edward J.; Nagle, Nicholas J.; Ness, Ryan M.; ...

    2017-01-13

    In this work, we examined the behavior of feedstock blends and the effect of a specific feedstock densification strategy (pelleting) on the release and yield of structural carbohydrates in a laboratory-scale dilute acid pretreatment (PT) and enzymatic hydrolysis (EH) assay. We report overall carbohydrate release and yield from the two-stage PT-EH assay for five single feedstocks (two corn stovers, miscanthus, switchgrass, and hybrid poplar) and three feedstock blends (corn stover-switchgrass, corn stover-switchgrass-miscanthus, and corn stover-switchgrass-hybrid poplar). We first examined the experimental results over time to establish the robustness of the PT-EH assay, which limits the precision of the experimental results.more » The use of two different control samples in the assay enabled us to identify (and correct for) a small bias in the EH portion of the combined assay for some runs. We then examined the effect of variable pretreatment reaction conditions (residence time, acid loading, and reactor temperature) on the conversion of a single feedstock (single-pass corn stover, CS-SP) in order to establish the range of pretreatment reaction conditions likely to provide optimal conversion data. Finally, we applied the assay to the 16 materials (8 feedstocks in 2 formats, loose and pelleted) over a more limited range of pretreatment experimental conditions. The four herbaceous feedstocks behaved similarly, while the hybrid poplar feedstock required higher pretreatment temperatures for optimal results. As expected, the yield data for three blended feedstocks were the average of the yield data for the individual feedstocks. As a result, the pelleting process appears to provide a slightly positive effect on overall total sugar yield.« less

  16. Defect models for sintering and densification of Al/sub 2/O/sub 3/:Ti and Al/sub 2/O/sub 3/:Zr

    SciTech Connect

    Kroger, F.A.

    1984-06-01

    A defect model proposed to explain the effect of titanium doping on the rate of sintering of Al/sub 2/O/sub 3/ is revised to fit the oxidizing conditions of the experiments. The model accounts for the observed change in sintering rate by a change from rate limitation by ions to rate limitation by electrons, but requires the presence of an unusually large concentration of acceptor impurities in the material. Models similar to the ones originally proposed account for the rate of densification of Al/sub 2/O/sub 3/:Zr by hot-pressing in vacuo, provided it is extended by including electronics defects.

  17. Liquid propellant densification

    NASA Technical Reports Server (NTRS)

    Lak, Tibor I. (Inventor); Petrilla, Steve P. (Inventor); Lozano, Martin E. (Inventor)

    1997-01-01

    Super cooling the cryogenic liquid propellant in a vehicle propellant tank densities the propellant allowing the vehicle propellant tank to carry more fuel in the same volume tank while lowering the vapor pressure and thus the tank operating pressure. Lowering the tank operating pressure reduces the stress and therefore allows the walls of the tank to be thinner. Both the smaller tank volume and thinner tank wall results in an overall smaller and lighter vehicle with increased payload capability. The cryogenic propellant can be supercooled well below the normal boiling point temperature level by transporting the liquid propellant from the vehicle tanks to a ground based cooling unit which utilizes a combination of heat exchanger and compressor. The compressor lowers the coolant fluid bath pressure resulting in a low temperature boiling liquid which is subsequently used to cool the recirculating liquid. The cooled propellant is then returned to the vehicle propellant tank. In addition to reducing the vehicle size and weight the invention also allows location of the vent valve on the ground, elimination of on-board recirculation pumps or bleed systems, smaller and lighter engine pumps and valves, lighter and more stable ullage gas, and significant reduction in tank fill operation. All of these mentioned attributes provide lower vehicle weight and cost.

  18. Cryogenic Propellant Densification Study

    NASA Technical Reports Server (NTRS)

    Ewart, R. O.; Dergance, R. H.

    1978-01-01

    Ground and vehicle system requirements are evaluated for the use of densified cryogenic propellants in advanced space transportation systems. Propellants studied were slush and triple point liquid hydrogen, triple point liquid oxygen, and slush and triple point liquid methane. Areas of study included propellant production, storage, transfer, vehicle loading and system requirements definition. A savings of approximately 8.2 x 100,000 Kg can be achieved in single stage to orbit gross liftoff weight for a payload of 29,484 Kg by utilizing densified cryogens in place of normal boiling point propellants.

  19. Effects of Powder Attributes and Laser Powder Bed Fusion (L-PBF) Process Conditions on the Densification and Mechanical Properties of 17-4 PH Stainless Steel

    NASA Astrophysics Data System (ADS)

    Irrinki, Harish; Dexter, Michael; Barmore, Brenton; Enneti, Ravi; Pasebani, Somayeh; Badwe, Sunil; Stitzel, Jason; Malhotra, Rajiv; Atre, Sundar V.

    2016-03-01

    The effects of powders attributes (shape and size distribution) and critical processing conditions (energy density) on the densification and mechanical properties of laser powder bed fusion (L-PBF) 17-4 PH stainless steel were studied using four types of powders. The % theoretical density, ultimate tensile strength and hardness of both water- and gas-atomized powders increased with increased energy density. Gas-atomized powders showed superior densification and mechanical properties when processed at low energy densities. However, the % theoretical density and mechanical properties of water-atomized powders were comparable to gas-atomized powders when sintered at a high energy density of 104 J/mm3. An important result of this study was that, even at high % theoretical density (97% ± 1%), the properties of as-printed parts could vary over a relatively large range (UTS: 500-1100 MPa; hardness: 25-39 HRC; elongation: 10-25%) depending on powder characteristics and process conditions. The results also demonstrate the feasibility of using relatively inexpensive water-atomized powders as starting raw material instead of the typically used gas-atomized powders to fabricate parts using L-PBF techniques by sintering at high energy densities.

  20. The Impact of Densification by Means of Informal Shacks in the Backyards of Low-Cost Houses on the Environment and Service Delivery in Cape Town, South Africa

    PubMed Central

    Govender, Thashlin; Barnes, Jo M.; Pieper, Clarissa H.

    2011-01-01

    This paper investigates the state-sponsored low cost housing provided to previously disadvantaged communities in the City of Cape Town. The strain imposed on municipal services by informal densification of unofficial backyard shacks was found to create unintended public health risks. Four subsidized low-cost housing communities were selected within the City of Cape Town in this cross-sectional survey. Data was obtained from 1080 persons with a response rate of 100%. Illegal electrical connections to backyard shacks that are made of flimsy materials posed increased fire risks. A high proportion of main house owners did not pay for water but sold water to backyard dwellers. The design of state-subsidised houses and the unplanned housing in the backyard added enormous pressure on the existing municipal infrastructure and the environment. Municipal water and sewerage systems and solid waste disposal cannot cope with the increased population density and poor sanitation behaviour of the inhabitants of these settlements. The low-cost housing program in South Africa requires improved management and prudent policies to cope with the densification of state-funded low-cost housing settlements. PMID:21695092

  1. A comparison study on the densification behavior and mechanical properties of gelcast vs conventionally formed B{sub 4}C sintered conventionally and by microwaves

    SciTech Connect

    Menchhofer, P.A.; Kiggans, J.O.; Morrow, M.S.; Schechter, D.E.

    1996-06-01

    The utilization of microwave energy for reaching high temperatures necessary to densify B{sub 4}C powder is compared with conventional means of sintering by evaluating the mechanical properties after densification. Microwave energy has been shown to be an effective means for achieving high sintered densities, even though temperatures of {approximately} 2,250 C are required. In this study, green preforms of B{sub 4}C specimens were sintered by both conventional and microwave heating. This study also utilized an advanced forming method called ``Gelcasting`` developed at ORNL. Gelcasting is a fluid forming process whereby high solids suspensions of powders containing dissolved monomers are cast into a mold, then polymerized or ``gelled`` in situ. This investigation compares microstructures and mechanical properties of both Gelcast B{sub 4}C and ``conventionally`` die-pressed B{sub 4}C. The microstructures and final mechanical properties of B{sub 4}C specimens are discussed.

  2. Hot-pressed Sm2Fe17Nx/Fe-Co composites: Factors controlling densification and in situ nitrogenization of Sm2Fe17 phase

    NASA Astrophysics Data System (ADS)

    Gabay, A. M.; Akdogan, N. G.; Hadjipanayis, G. C.; Marinescu, M.; Liu, J. F.; Ali, A.

    2008-04-01

    The effects of powder preparation and conditions of hot pressing on the structure and density of consolidated Sm2Fe17Nx and Sm2Fe17Nx/Fe-Co magnets have been studied. Densities achieved in the case of Sm2Fe17Nx powders prepared through a low-energy milling were higher than after a high-energy milling. The difference is mostly caused by the different particle size, and it can be eliminated by an additional low-energy milling of the coarse high-energy milled powder. The presence of a ductile soft magnetic phase greatly facilitates densification, leading to considerably higher absolute and relative densities in hot-pressed Sm2Fe17Nx/Fe0.65Co0.35 composites. We have found that during hot pressing, nitrogenization of the Sm2Fe17 phase may occur in situ if pressed together with Fe-Co-N powders. Because Fe-Co-N releases nitrogen below the decomposition temperature of Sm2Fe17Nx, we were able to fabricate the Sm2Fe17Nx/Fe0.65Co0.35 composite with the density up to 7.6g/cm3 by hot-pressing mixtures of Sm2Fe17 and (Fe0.65Co0.35)89N11 powders.

  3. Preparation of spherical ultrafine copper powder via hydrogen reduction-densification of Mg(OH)2-coated Cu2O powder

    NASA Astrophysics Data System (ADS)

    Wang, Yue-jun; Zhou, Kang-gen

    2012-11-01

    A novel process was developed to produce spherical copper powder for multilayer ceramic capacitors (MLCC). Spherical ultrafine cuprous oxide (Cu2O) powder was prepared by glucose reduction of Cu(OH)2. The Cu2O particles were coated by Mg(OH)2 and reduced to metallic copper particles. At last, the copper particles were densified by high-temperature heat treatment. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), tap density, and thermogravimetry (TG). It is found that the shape and size distribution of the copper powder are determined by the Cu2O powder and the copper particles do not agglomerate during high-temperature heat treatment because of the existence of Mg(OH)2 coating. After densification at high temperature, the particle tap density increases from 3.30 to 4.18 g/cm3 and the initial oxidation temperature rises from 125 to 150°C.

  4. Data on the densification during sintering of binder jet printed samples made from water- and gas-atomized alloy 625 powders.

    PubMed

    Mostafaei, Amir; Hughes, Eamonn T; Hilla, Colleen; Stevens, Erica L; Chmielus, Markus

    2017-02-01

    Binder jet printing (BJP) is a metal additive manufacturing method that manufactures parts with complex geometry by depositing powder layer-by-layer, selectively joining particles in each layer with a polymeric binder and finally curing the binder. After the printing process, the parts still in the powder bed must be sintered to achieve full densification (A. Mostafaei, Y. Behnamian, Y.L. Krimer, E.L. Stevens, J.L. Luo, M. Chmielus, 2016; A. Mostafaei, E. Stevens, E. Hughes, S. Biery, C. Hilla, M. Chmielus, 2016; A. Mostafaei, Y. Behnamian, Y.L. Krimer, E.L. Stevens, J.L. Luo, M. Chmielus, 2016) [1-3]. The collected data presents the characterization of the as-received gas- and water-atomized alloy 625 powders, BJP processing parameters and density of the sintered samples. The effect of sintering temperatures on the microstructure and the relative density of binder jet printed parts made from differently atomized nickel-based superalloy 625 powders are briefly compared in this paper. Detailed data can be found in the original published papers by authors in (A. Mostafaei, J. Toman, E.L. Stevens, E.T. Hughes, Y.L. Krimer, M. Chmielus, 2017) [4].

  5. Use of in-die powder densification parameters in the implementation of process analytical technologies for tablet production on industrial scale.

    PubMed

    Cespi, Marco; Perinelli, Diego R; Casettari, Luca; Bonacucina, Giulia; Caporicci, Giuseppe; Rendina, Filippo; Palmieri, Giovanni F

    2014-12-30

    The use of process analytical technologies (PAT) to ensure final product quality is by now a well established practice in pharmaceutical industry. To date, most of the efforts in this field have focused on development of analytical methods using spectroscopic techniques (i.e., NIR, Raman, etc.). This work evaluated the possibility of using the parameters derived from the processing of in-line raw compaction data (the forces and displacement of the punches) as a PAT tool for controlling the tableting process. To reach this goal, two commercially available formulations were used, changing the quantitative composition and compressing them on a fully instrumented rotary pressing machine. The Heckel yield pressure and the compaction energies, together with the tablets hardness and compaction pressure, were selected and evaluated as discriminating parameters in all the prepared formulations. The apparent yield pressure, as shown in the obtained results, has the necessary sensitivity to be effectively included in a PAT strategy to monitor the tableting process. Additional investigations were performed to understand the criticalities and the mechanisms beyond this performing parameter and the associated implications. Specifically, it was discovered that the efficiency of the apparent yield pressure depends on the nominal drug title, the drug densification mechanism and the error in pycnometric density. In this study, the potential of using some parameters derived from the compaction raw data has been demonstrated to be an attractive alternative and complementary method to the well established spectroscopic techniques to monitor and control the tableting process. The compaction data monitoring method is also easy to set up and very cost effective.

  6. The enhanced Jc and Birr of in situ MgB2 wires and tapes alloyed with C4H6O5 (malic acid) after cold high pressure densification

    NASA Astrophysics Data System (ADS)

    Hossain, M. S. A.; Senatore, C.; Flükiger, R.; Rindfleisch, M. A.; Tomsic, M. J.; Kim, J. H.; Dou, S. X.

    2009-09-01

    Cold high pressure densification, a method recently introduced at GAP in Geneva, was applied for improving the transport critical current density, Jc, and the irreversibility field, Birr, of monofilamentary in situ MgB2 wires and tapes alloyed with 10 wt% C4H6O5 (malic acid). Tapes densified at 1.48 GPa exhibited after reaction an enhancement of Jc from 2 to 4 × 104 A cm-2 at 4.2 K/10 T and from 0.5 to 4 × 104 A cm-2 at 20 K/5 T, while the Birr was enhanced from 19.3 to 22 T at 4.2 K and from 7.5 to 10.0 T at 20 K. Cold densification also caused a strong enhancement of B(104), the field at which Jc takes the value 1 × 104 A cm-2. For tapes subjected to 1.48 GPa, B(10^{4})^{\\parallel } and B(10^{4})^{ \\perp } at 4.2 K were found to increase from 11.8 and 10.5 T to 13.2 and 12.2 T, respectively. Almost isotropic conditions were obtained for rectangular wires with aspect ratios a/b<2 subjected to 2.0 GPa, where B(10^{4})^{\\parallel }=12.7 and B(10^{4})^{ \\perp }=12.5 T were obtained. At 20 K, the wires exhibited an almost isotropic behavior, with B(10^{4})^{\\parallel }=5.9 T and B(10^{4})^{ \\perp }=5.75 T, Birr(20 K) being ~10 T. These values are equal to or higher than the highest values reported so far for isotropic in situ wires with SiC or other carbon based additives. Further improvements are expected on optimizing the cold high pressure densification process, which has the potential for fabrication of MgB2 wires of industrial lengths.

  7. Ultrasonic sensing of powder densification

    NASA Technical Reports Server (NTRS)

    Lu, Yichi; Wadley, Haydn N. G.; Parthasarathi, Sanjai

    1992-01-01

    An independent scattering theory has been applied to the interpretation of ultrasonic velocity measurements made on porous metal samples produced either by a cold or a high-temperature compaction process. The results suggest that the pores in both processes are not spherical, an aspect ration of 1:3 fitting best with the data for low (less than 4 percent) pore volume fractions. For the hot compacted powders, the pores are smooth due to active diffusional processes during processing. For these types of voids, the results can be extended to a pore fraction of 10 percent, at which point voids form an interconnected network that violates the model assumptions. The cold pressed samples are not as well predicted by the theory because of poor particle bonding.

  8. Influences of Gd2Ti2O7 sintering aid on the densification, ionic conductivity and thermal expansion of Gd0.1Ce0.9O1.95 electrolyte for solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Guo, Ting; Zhang, Lei; Song, Xiao; Dong, Xiaolei; Shirolkar, Mandar M.; Wang, Meng; Li, Ming; Wang, Haiqian

    2014-09-01

    The effects of Gd2Ti2O7 (GT) as sintering aid on the densification, electrical properties and thermal expansion of Gd0.1Ce0.9O1.95 (GDC) are examined. Samples added with TiO2 sintering aid are also tested for comparison. It is found that by sintering at a moderate temperature of 1400 °C for 5 h, the relative density of the GT-added GDC can reach over 97% as the molar ratio of GT/GDC reaches 0.02 or higher. XRD analysis indicates that GT does not react with GDC, while TiO2 reacts with Gd in GDC to form GT. The ionic conductivities of the GT-added and the TiO2-added GDC are analyzed by AC impedance spectroscopy at 500-700 °C. The result shows that although the ionic conductivity of the GT-added GDC decreases as the GT/GDC molar ratio increases up to 0.05, it is still higher than that of 8YSZ and much higher than that of the GDC added with an equivalent amount of TiO2. It is also found that the thermal expansion coefficient of GDC decreases as the amount of GT increases. These results show that GT is an excellent sintering aid for GDC, and the optimal molar ratio of GT/GDC is 0.02 in terms of densification and ionic conductivity.

  9. Gas-Solid Interactions During Nonisothermal Heat Treatment of a High-Strength CrMnCN Austenitic Steel Powder: Influence of Atmospheric Conditions and Heating Rate on the Densification Behavior

    NASA Astrophysics Data System (ADS)

    Krasokha, Nikolaj; Weber, Sebastian; Huth, Stephan; Zumsande, Kathrin; Theisen, Werner

    2012-11-01

    This work deals with gas-solid interactions between a high-alloyed steel powder and the surrounding atmosphere during continuous heating. It is motivated by the recently developed corrosion-resistant CrMnCN austenitic cast steels. Here, powder metallurgical processing would be desirable to manufacture highly homogeneous parts and/or novel corrosion-resistant metal-matrix composites. However, the successful use of this new production route calls for a comprehensive investigation of interactions between the sintering atmosphere and the metallic powder to prevent undesirable changes to the chemical composition, e.g., degassing of nitrogen or evaporation of manganese. In this study, dilatometric measurements combined with residual gas analysis, high-temperature X-ray diffraction (XRD) measurements, and thermodynamic equilibrium calculations provided detailed information about the influence of different atmospheric conditions on the microstructure, constitution, and densification behavior of a gas-atomized CrMnCN steel powder during continuous heating. Intensive desorption of nitrogen led to the conclusion that a vacuum atmosphere is not suitable for powder metallurgical (PM) processing. Exposure to an N2-containing atmosphere resulted in the formation of nitrides and lattice expansion. Experimental findings have shown that the N content can be controlled by the nitrogen partial pressure. Furthermore, the reduction of surface oxides because of a carbothermal reaction at elevated temperatures and the resulting enhancement of the powder's densification behavior are discussed in this work.

  10. Matlab based automatization of an inverse surface temperature modelling procedure for Greenland ice cores using an existing firn densification and heat diffusion model

    NASA Astrophysics Data System (ADS)

    Döring, Michael; Kobashi, Takuro; Kindler, Philippe; Guillevic, Myriam; Leuenberger, Markus

    2016-04-01

    In order to study Northern Hemisphere (NH) climate interactions and variability, getting access to high resolution surface temperature records of the Greenland ice sheet is an integral condition. For example, understanding the causes for changes in the strength of the Atlantic meridional overturning circulation (AMOC) and related effects for the NH [Broecker et al. (1985); Rahmstorf (2002)] or the origin and processes leading the so called Dansgaard-Oeschger events in glacial conditions [Johnsen et al. (1992); Dansgaard et al., 1982] demand accurate and reproducible temperature data. To reveal the surface temperature history, it is suitable to use the isotopic composition of nitrogen (δ15N) from ancient air extracted from ice cores drilled at the Greenland ice sheet. The measured δ15N record of an ice core can be used as a paleothermometer due to the nearly constant isotopic composition of nitrogen in the atmosphere at orbital timescales changes only through firn processes [Severinghaus et. al. (1998); Mariotti (1983)]. To reconstruct the surface temperature for a special drilling site the use of firn models describing gas and temperature diffusion throughout the ice sheet is necessary. For this an existing firn densification and heat diffusion model [Schwander et. al. (1997)] is used. Thereby, a theoretical δ15N record is generated for different temperature and accumulation rate scenarios and compared with measurement data in terms of mean square error (MSE), which leads finally to an optimization problem, namely the finding of a minimal MSE. The goal of the presented study is a Matlab based automatization of this inverse modelling procedure. The crucial point hereby is to find the temperature and accumulation rate input time series which minimizes the MSE. For that, we follow two approaches. The first one is a Monte Carlo type input generator which varies each point in the input time series and calculates the MSE. Then the solutions that fulfil a given limit

  11. Effect of LiF as Sintering Agent on the Densification and Phase Formation in Al2O3-4 Wt Pct Nb2O5 Ceramic Compound

    NASA Astrophysics Data System (ADS)

    Santos, J. L.; Marçal, R. L. S. B.; Jesus, P. R. R.; Gomes, A. V.; Lima, E. P.; Monteiro, S. N.; de Campos, J. B.; Louro, L. H. L.

    2017-10-01

    Different amounts of LiF were added to an Al2O3-4 pct Nb2O5 basic ceramic, as sintering agent. Improved new ceramics were obtained with LiF concentrations varying from 0.25 to 1.50 wt pct and three sintering temperatures of 1573 K, 1623 K, and 1673 K (1300 °C, 1350 °C, and 1400 °C). The addition of 0.5 wt pct LiF yielded the highest densification, 94 pct of the theoretical density, in association with a sintering temperature of 1673 K (1400 °C). Based on X-ray diffraction (XRD), this improvement was due not only to the presence of transformed phases, more precisely Nb3O7F, but also to the absence of LiAl5O8. The preferential interaction of LiF with Nb2O5, instead of Al2O3, contributed to increase the alumina sintering ability by liquid phase formation. Scanning electron microscopy (SEM) results revealed well-connected grains and isolated pores, whereas the chemical composition analysis by energy dispersive energy (EDX) indicated a preferential interaction of fluorine with niobium, in agreement with the results of XRD. It was also observed from thermal analysis that the polyethylene glycol binder burnout temperature increased for all LiF concentrations. This may be related to the formation of hydrogen bridge bonds.

  12. Evaluation des apports solaires a l'echelle d'un quartier urbain en periode de chauffe selon sa typologie, son orientation et sa latitude dans un contexte de densification de la ville

    NASA Astrophysics Data System (ADS)

    Chenard, Laurent

    Mass urbanization is a major issue for town administrators. Population increase will have an impact on the quality of the environment for citizens. Government will have to take decisions to limit those effects. Green energies are part of the solution to reach fixed goals by the public administration for sustainable development. Passive solar energy is studied in this work in an urban canopy located in five different towns: San Francisco, Montreal, Bordeaux, Lyon and Stockholm. Passive solar energy is calculated in the heating season. Direct and diffuse solar radiation is considered by using the Perez model. Radiosity is not taken into account. Heating demand is calculated by the heating degree day method. Seven urban forms have been created to determine the amount of solar energy entering in every window of the urban canopy while taking into account urban context and forms. Optimal orientation of the canopy shows an increase of 5% of the passive solar radiation from original orientation, 180 degrees rotation from first orientation straight south. This value goes lower when stories are added to the urban context. A rotation of 90 degrees from the first orientation shows a decrease of 6 to 15% in solar passive gain. Densification of the urban canopy by adding stories to the buildings results in a loss up to 65% of the solar gain for the first story. It is showed that solar passive energy has a low ratio of 5% for space heating for old buildings, 1960 constructions. Today's buildings have a difference between passive solar energy and heating demand of 10 to 75% depending on the model and location.

  13. HIP densification project. Final CRADA report

    SciTech Connect

    Franco-Ferreira, E.A.; Finkelstein, W.

    1997-08-29

    An investigation was conducted to evaluate the use of HIPed aluminum castings as near-net-shape blanks for large electrostatic focusing electrodes in ion lithography machines. The electrodes must have very smooth finishes which are free of pores and other defects. This has heretofore been achieved by rough-machining the blanks out of large forged aluminum billets and final diamond-turning. The use of a near-net-shape casting for the blank was expected to save a significant amount of money and time. The test was conducted on a single cast blank which was supplied by the Partner in the HIPed and stress relieved condition. Rough machining and diamond turning operations conducted by LMES/ER revealed that the casting contained unacceptably large defects. The conclusion was reached that HIPed aluminum castings in the large sizes and of the quality levels required would probably be unobtainable in a cost-effective manner. An alternative approach, using ring forgings assembled by electron beam welding was proposed and investigated by LMES/ER. Although an electrode blank was not obtained, the study indicated that this approach would be successful and cost-effective.

  14. ELECTROKINETIC DENSIFICATION OF COAL FINES IN WASTE PONDS

    SciTech Connect

    E. James Davis

    1999-12-18

    The objective of this research was to demonstrate that electrokinetics can be used to remove colloidal coal and mineral particles from coal-washing ponds and lakes without the addition of chemical additives such as salts and polymeric flocculants. The specific objectives were: Design and develop a scaleable electrophoresis apparatus to clarify suspensions of colloidal coal and clay particles; Demonstrate the separation process using polluted waste water from the coal-washing facilities at the coal-fired power plants in Centralia, WA; Develop a mathematical model of the process to predict the rate of clarification and the suspension electrical properties needed for scale up.

  15. APPARATUS FOR THE DENSIFICATION AND ENERGIZATION OF CHARGED PARTICLES

    DOEpatents

    Post, R.F.; Coensgen, F.H.

    1962-12-18

    This patent relates to a device for materially increasing the energy and density of a plasma to produce conditions commensurate with the establishment and promotion of controlled thermonuclear reactions. To this end the device employs three successive stages of magnetic compression, each stage having magnetic mirrors to compress a plasma, the mirrors being moveable to transfer the plasma to successive stages for further compression. Accordingly, a plasma introduced to the first stage is increased in density and energy in stepwide fashion by virtue of the magnetic compression in the successive stages such that the plasma upon reaching the last stage is of extremely high energy and density commensurate the plasma particles undergoing thermonuclear reactions. The principal novelty of the device resides in the provision of a unidirectional magnetic field which increases in stepwise fashion in coaxially communicating compression chambers of progressively decreasing lengths and diameters. Pulsed magnetic fields are superimposed upon the undirectional field and are manipulated to establish resultant magnetic compression fields which increase in intensity and progressively move, with respect to time, through the compression chambers in the direction of the smallest one thereof. The resultant field in the last compression chamber is hence of relatively high intensity, and the density and energy of the plasma confined therein are correspondingly high. (AEC)

  16. Laser Densification and Doping of Sol-Gel Glasses

    DTIC Science & Technology

    1992-02-29

    meeting, Keswick, Aug. 1990. 4. A. Charlton, M. A. Meneses -Nava, D. J. Shaw and T. A. King "Gel-silica lasers and optics", Proc. 4th OGAMM meeting, 105...I. T. McKinnie, M. A. Meneses -Nava and T. A. King "A tunable visible solid state laser" J. Mod. Opt. 39, 1992.

  17. Densification of powder metallurgy billets by a roll consolidation technique

    NASA Technical Reports Server (NTRS)

    Sellman, W. H.; Weinberger, W. R.

    1973-01-01

    Container design is used to convert partially densified powder metallurgy compacts into fully densified slabs in one processing step. Technique improves product yield, lowers costs and yields great flexibility in process scale-up. Technique is applicable to all types of fabricable metallic materials that are produced from powder metallurgy process.

  18. ELECTROKINETIC DENSIFICATION OF COAL FINES IN WASTE PONDS

    SciTech Connect

    E. James Davis

    1998-05-01

    The objective of this research is to demonstrate that electrokinetics can be used to remove colloidal coal and mineral particles from coal-washing ponds and lakes without the addition of chemical additives such as salts and polymeric flocculants. In this experimental and analytical study the authors elucidate the transport processes that control the rate of concentrated colloidal particle removal, demonstrate the process on a laboratory scale, and develop the scale-up laws needed to design commercial-scale processes. The authors are also addressing the fundamental problems associated with particle-particle interactions (electrical and hydrodynamic), the effects of particle concentration on the applied electric field, the electrochemical reactions that occur at the electrodes, and the prediction of power requirements.

  19. ELECTROKINETIC DENSIFICATION OF COAL FINES IN WASTE PONDS

    SciTech Connect

    E. James Davis

    1996-04-01

    The objective of this research is to apply electrokinetics to remove colloidal coal and mineral particles from coal washing ponds without the addition of chemical additives. Colloidal particles do not settle gravitationally, but because their surfaces are charged one can produce settling by applying an external electric field. Of specific interest is a lake near Centralia, Washington used to wash coal prior to combustion in an electrical power generation facility. Laboratory experiments have demonstrated that electrokinetic treatment is feasible, so this project is examining how to scale up laboratory results to an industrial level. Electrode configurations, power requirements, and system properties are being studied.

  20. ELECTROKINETIC DENSIFICATION OF COAL FINES IN WASTE PONDS

    SciTech Connect

    E. James Davis

    1997-04-30

    The objective of this research is to demonstrate that electrokinetics can be used to remove colloidal coal and mineral particles from coal-washing ponds and lakes without the addition of chemical additives such as salts and polymeric flocculants. In this experimental and analytical study the authors elucidate the transport processes that control the rate of concentrated colloidal particle removal, demonstrate the process on a laboratory scale, and develop the scale-up laws needed to design commercial-scale processes. They then address the fundamental problems associated with particle-particle interactions (electrical and hydrodynamic), the effects of particle concentration on the applied electric field, the electrochemical reactions that occur at the electrodes, and the prediction of power requirements.

  1. Energy densification of biomass-derived organic acids

    DOEpatents

    Wheeler, M. Clayton; van Walsum, G. Peter; Schwartz, Thomas J.; van Heiningen, Adriaan

    2013-01-29

    A process for upgrading an organic acid includes neutralizing the organic acid to form a salt and thermally decomposing the resulting salt to form an energy densified product. In certain embodiments, the organic acid is levulinic acid. The process may further include upgrading the energy densified product by conversion to alcohol and subsequent dehydration.

  2. Ab initio simulation of permanent densification in silica glass

    NASA Astrophysics Data System (ADS)

    Ryuo, Emina; Wakabayashi, Daisuke; Koura, Akihide; Shimojo, Fuyuki

    2017-08-01

    To clarify the microscopic structure of densified Si O2 glass, we have conducted ab initio molecular-dynamics simulations on the decompression process of Si O2 glass in its relaxed state from high pressures up to 40 GPa. When decompressed from high pressures above at least 15 GPa, the density and structure always converge to those of densified glass, while the coordination number of silicon decreases to four rapidly. This is in good agreement with previous experimental studies and strongly suggests that densified glass behaves as a high-pressure polymorph of Si O2 glass. In comparison to ordinary glass, although the coordination number of densified glass is almost the same, the size of an intermediate-range network consisting of Si O4 tetrahedra is smaller. Detailed analyses clarify that Si O4 tetrahedra in densified glass are deformed and the Si-O bonds are less covalent.

  3. Hydrocycloning thickening: dewatering and densification of fine particulates

    SciTech Connect

    Lin, I.J.

    1987-01-01

    The paper reviews integrated ore-dressing machines with particular reference to hydrocyclones and describes a new concept, the cyclo-thick apparatus, which combines features of the hydrocyclone and the thickener in a single machine. Field tests conducted with the cyclo-thick demonstrated that the unit is remarkably simple and clean in design, and can effectively separate, dewater, and densify fine particulates. This unit should be considered as a viable alternative when evaluating potential solutions to a given separation, thickening, or filtration problem. Various practical applications are proposed.

  4. Modeling the densification of metal matrix composite monotape

    NASA Technical Reports Server (NTRS)

    Elzey, D. M.; Wadley, H. N. G.

    1993-01-01

    We present a first model that enables prediction of the density (and its time evolution) of a monotape lay-up subjected to a hot isostatic or vacuum hot pressing consolidation cycle. Our approach is to break down the complicated (and probabilistic) consolidation problem into simple, analyzable parts and to combine them in a way that correctly represents the statistical aspects of the problem, the change in the problem's interior geometry, and the evolving contributions of the different deformation mechanisms. The model gives two types of output. One is in the form of maps showing the relative density dependence upon pressure, temperature, and time for step function temperature and pressure cycles. They are useful for quickly determining the best place to begin developing an optimized process. The second gives the evolution of density over time for any (arbitrary) applied temperature and pressure cycle. This has promise for refining process cycles and possibly for process control. Examples of the models application are given for Ti3Al + Nb, gamma TiAl, Ti6Al4V, and pure aluminum.

  5. Densification of nano-yttria powders for IR window applications

    NASA Astrophysics Data System (ADS)

    Willingham, Charles B.; Wahl, Joseph M.; Hogan, Patrick K.; Kupferberg, Lenn C.; Wong, Thomas Y.; De, Alok M.

    2003-09-01

    Commerically available yttrium oxide nanopowders were evaluated as starting materials for preparation of transparent materials. The objective is an yttria optical ceramic exhibiting approximately one micrometer grain size to provide increased strength and thermal shock resistance. Three vendors were selected to provide nanoscale powders for testing and evaluation. They were compared to a conventional (5 μm) powder previously used to prepare optical quality ceramic yttria. While all of the selected nanopowders had impurity levels that were too high to allow processing to full transparency, two of the samples were processed to full density and moderate transparency was produced in one. In preparation for processing via Hot Isostatic Press (HIP) samples were sintered to a closed pore state at temperatures as low as 1400 °C, and with soak times as short as 12 minutes at 1550 °C. The use of ultrasonic attenuation as a technique for measuring particle size distributions in slurries was explored and found to be an invaluable tool when colloidally processing nanopowders. Finally, the areas most important for continued improvements were identified.

  6. Role of cabbeling in water densification in the Greenland Basin

    NASA Astrophysics Data System (ADS)

    Kasajima, Y.; Johannessen, T.

    2008-09-01

    The contribution of cabbeling mixing to water mass modification in the Greenland Sea was explored from hydrographic observation across the Greenland Basin in summer 2006. Neutral surface was chosen as a reference frame, and the strength of cabbeling mixing was determined by the dianeutral velocity magnitude. Water types in the area were classified into North Atlantic Water (NAW), modified North Atlantic Water (mNAW), water from Barents Sea near Bear Island (BIW), Arctic Intermediate Water (AIW) and Deep Water (DW), and significant cabbeling-induced velocity (>1 m/day) appeared at the interfaces of these water types below the seasonal pycnocline. The mixing between BIW and NAW in the eastern periphery was the most vigorous, where mixing-induced velocity reached 7.5 m/day which accompanied NAW production of 123 m3/day through transformation of BIW. Cabbeling in the Arctic Frontal Zone was found of two types; mixing within NAW in the upper layer and mixing within mNAW in the lower layer with a maximum velocity of 3 m/day. Source waters in the central Greenland Basin were AIW and mNAW and produced a vertical velocity of 4 m/day. In the western part of the Greenland Basin, the areas of active cabbeling were widely separated and each mixing point appeared rather weak, with a maximum velocity of 2.5 m/day. The average density gain in the eastern periphery was 0.003 kg/m3 while it was 0.001 kg/m3 in the other areas, though the impact of cabbeling on the bulk buoyancy change was highest in the western Greenland Sea. The frontal areas occupied approximately 50% of the whole analysis area and the total density gain due to cabbeling mixing in the Greenland Basin as a whole was estimated as 6.7×10-4 kg/m3.

  7. Preparation, Purification and Densification of Zinc Sulfide Powder from Organometallics

    DTIC Science & Technology

    1989-01-01

    oxidized samples contained about 2 mol % ZnSO4 and EPR spectra provided evidence for S02- radicals. The ZnSO 4 impurity was converted to ZnO by heating at...1.0 g of KI in 40 mL of water . Tl- !Iquid was transferred to a beaker, treated with 0.3 g of N-2-hydroxyethylpiperazine-N’-2-ethanesulfonic acid...detection of organic 6 molecules such as tetrahydrofuran and ethanol is 10-4 mol per mol of Zn. The estimated accuracy is ± 30%. Ozone Treatment of

  8. Synthesis and densification of lutetium pyrosilicate from lutetia and silica

    SciTech Connect

    Tripathi, Himansu S.; Sarin, Vinod K. . E-mail: sarin@bu.edu

    2007-02-15

    Cerium-doped lutetium pyrosilicate (Lu{sub 2}Si{sub 2}O{sub 7}:Ce) powder was synthesized by solid state reaction of Lu{sub 2}O{sub 3} and SiO{sub 2}. Stoichiometric mixtures of the starting materials were heat treated at various different temperatures and their phase contents were measured by XRD technique. It was found that the first step in the formation of Lu{sub 2}Si{sub 2}O{sub 7} (LPS) is the appearance of Lu{sub 2}SiO{sub 5} (LSO). This takes place at 1100 deg. C, fully 300 deg. C below the first appearance of LPS. Between 1400 and 1500 deg. C both LSO and LPS coexist in the calcined batch, but by 1550 deg. C all LSO is completely converted to LPS. LPS formation temperature does not have appreciable effect on the density of the hot pressed samples. Hot pressed samples obtained from powder synthesized at 1650 deg. C are nearly transparent, although the particle size of the starting powder is higher than that of the powder formed at lower temperatures.

  9. Geospatial Modelling Approach for 3d Urban Densification Developments

    NASA Astrophysics Data System (ADS)

    Koziatek, O.; Dragićević, S.; Li, S.

    2016-06-01

    With growing populations, economic pressures, and the need for sustainable practices, many urban regions are rapidly densifying developments in the vertical built dimension with mid- and high-rise buildings. The location of these buildings can be projected based on key factors that are attractive to urban planners, developers, and potential buyers. Current research in this area includes various modelling approaches, such as cellular automata and agent-based modelling, but the results are mostly linked to raster grids as the smallest spatial units that operate in two spatial dimensions. Therefore, the objective of this research is to develop a geospatial model that operates on irregular spatial tessellations to model mid- and high-rise buildings in three spatial dimensions (3D). The proposed model is based on the integration of GIS, fuzzy multi-criteria evaluation (MCE), and 3D GIS-based procedural modelling. Part of the City of Surrey, within the Metro Vancouver Region, Canada, has been used to present the simulations of the generated 3D building objects. The proposed 3D modelling approach was developed using ESRI's CityEngine software and the Computer Generated Architecture (CGA) language.

  10. A New Process for Final Densification of Ceramics

    DTIC Science & Technology

    1988-05-14

    fluid solution is calculated from the integrated gas volume measured by a dry test meter. A Newport Scientific supercritical fluid extraction system... Dry Test MeterSample gg. CollectorJ Pressure Reduction Valve Extraction Vessel Compressor CO2 Supply FIGURE 8 EXPERIMENTAL APPARATUS FOR

  11. Buried Oxide Densification for Low Power, Low Voltage CMOS Applications

    NASA Technical Reports Server (NTRS)

    Allen, L. P.; Anc, M. J.; Dolan, B.; Jiao, J.; Guss, B.; Seraphin, S.; Liu, S. T.; Jenkins, W.

    1998-01-01

    Special technology and circuit architecture are of growing interest for implementation of circuits which operate at low supply voltages and consume low power levels without sacrificing performance[1]. Use of thin buried oxide SOI substrates is a primary approach to simultaneously achieve these goals. A significant aspect regarding SIMOX SOI for low voltage, low power applications is the reliability and performance of the thin buried oxide. In addition, when subjected to high total dose irradiation, the silicon islands within the BOX layer of SIMOX can store charges and significantly effect the back channel threshold voltages of devices. Thus, elimination of the islands within the buried oxide (BOX) layer is preferred in order to prevent leakage through these conductive islands and charge build-up within the buried oxide layer. A differential (2-step) ramp rate as applied to full and 100 nm BOX SIMOX was previously reported to play a significant role in the stoichiometry and island formation within the buried layer[2]. This paper focus is on the properties of a thin (120nm) buried oxide as a function of the anneal ramp rate and the temperature of anneal. In this research, we have found an improvement in the buried oxide stoichiometry with the use of a slower, singular ramp rate for specified thin buried oxides, with slower ramp rates and higher temperatures of anneal suggested for reducing the presence of Si islands within the BOX layer.

  12. The Role of Additives in the Densification of Nitrogen Ceramics.

    DTIC Science & Technology

    1979-10-01

    28 56 l6e/o -20 05 15 25 Cc Si Al Oe/oN 28 56 16elo -80 𔃻 e/o N 7 60 2 -40 V, 0 -20 250 300 350 nrn Figure 28. 1F and UV transmission spectra for...200 02 102 12 202 M i( i..... rh rr,- t (ii) o~ I qt IPb 1 , (iii) o ’o ’_ Fp (iv) O(fCi (v) Ca ! r n i 005 010 05 0M 0 225 sin22 Figure 53. Observed...Trent: B. Ceram. R.A., (1972). 66. I. Colquhoun, S. Wild, P. Grieveson and K.H. Jack, Proc. B. Ceram. Soc. 22, 207, (1973). 67. K. Blegen , "Special

  13. Densification of Herbaceous Bioenergy Feedstocks for Transportation and Handling

    USDA-ARS?s Scientific Manuscript database

    A vital component of a sustainable bioconversion industry that continues to be conceptualized and addressed by many is the supply, collection, and delivery of lignocellulosic feedstocks --- the feedstock supply system --- to bioconversion facilities. Lindley and Backer (1994) identified that low bul...

  14. A REVIEW ON BIOMASS DENSIFICATION TECHNOLOGIE FOR ENERGY APPLICATION

    SciTech Connect

    JAYA SHANKAR TUMULURU; CHRISTOPHER T. WRIGHT

    2010-08-01

    The world is currently facing challenges to reduce the dependence on fossil fuels and to achieve a sustainable renewable supply. Renewable energies represent a diversity of energy sources that can help to maintain the equilibrium of different ecosystems. Among the various sources of renewable energy, biomass is finding more uses as it is considered carbon neutral since the carbondioxide released during its use is already part of the carbon cycle (Arias et al., 2008). Increasing the utilization of biomass for energy can help to reduce the negative CO2 impact on the environment and help to meet the targets established in the Kyoto Protocol (UN, 1998). Energy from biomass can be produced from different processes like thermochemical (combustion, gasification, and pyrolysis), biological (anaerobic digestion, fermentation) or chemical (esterification) where direct combustion can provide a direct near-term energy solution (Arias et al., 2008). Some of the inherent problems with raw biomass materials, like low bulk density, high moisture content, hydrophilic nature and low calorific value, limit the ease of use of biomass for energy purposes (Arias et al., 2008). In fact, due to its low energy density compared to fossil fuels, high volumes of biomass will be needed; adding to problems associated with storage, transportation and feed handling at a cogeneration plant. Furthermore, grinding biomass pulverizes, can be very costly and in some cases impractical. All of these drawbacks have given rise to the development of new technologies in order to increase the quality of biomass fuels. The purpose of the work is mainly in four areas 1) Overview of the torrefaction process and to do a literature review on i) Physical properties of torrefied raw material and torrefaction gas composition. 2) Basic principles in design of packed bed i) Equations governing the flow of material in packed bed ii) Equations governing the flow of the gases in packed bed iii) Effect of physical properties of the raw materials on the packed bed design 3) Design of packed bed torrefier of different capacities. 4) Development of an excel sheet for calculation of length and diameter of the packed bed column based on the design considerations.

  15. Densification of salt-occluded zeolite a powders to a leach-resistant monolith

    SciTech Connect

    Lewis, M.A.; Fischer, D.F.; Murhpy, C.D.

    1993-10-01

    Pyrochemical processing of spent fuel from the Integral Fast Reactor (IFR) yields a salt waste of LiCl-KCl that contains approximately 6 wt% fission products, primarily as CsCl and SrCl{sub 2}. Past work has shown that zeolite A will preferentially sorb cesium and strontium and will encapsulate the salt waste in a leach-resistant, radiation-resistant aluminosilicate matrix. However, a method is sill needed to convert the salt-occluded zeolite powders into a form suitable for geologic disposal. We are thus investigating a method that forms bonded zeolite by hot pressing a mixture of glass frit and salt-occluded zeolite powders at 990 K (717{degree}C) and 28 MPa. The leach resistance of the bonded zeolite was measured in static leach tests run for 28 days in 363 K (90{degree}C) deionized water. Normalized release rates of all elements in the bonded zeolite were low, <1 g/m{sup 2} d. Thus, the bonded zeolite may be a suitable waste form for IFR salt waste.

  16. Impact of Mixed Feedstocks and Feedstock Densification on Ionic Liquid Pretreatment Efficiency

    SciTech Connect

    Jian Shi; Vicki S. Thompson; Neal A. Yancey; Vitalie Stavila; Blake A. Simmons; Seema Singh

    2013-01-01

    Background: Lignocellulosic biorefineries must be able to efficiently process the regional feedstocks that are available at cost-competitive prices year round. These feedstocks typically have low energy densities and vary significantly in composition. One potential solution to these issues is blending and/or densifying the feedstocks in order to create a uniform feedstock. Results/discussion: We have mixed four feedstocks - switchgrass, lodgepole pine, corn stover, and eucalyptus - in flour and pellet form and processed them using the ionic liquid 1-ethyl-3-methylimidazolium acetate. Sugar yields from both the mixed flour and pelletized feedstocks reach 90% within 24 hours of saccharification. Conclusions: Mixed feedstocks, in either flour or pellet form, are efficiently processed using this pretreatment process, and demonstrate that this approach has significant potential.

  17. Densification and structural transitions in networks that grow by node copying

    NASA Astrophysics Data System (ADS)

    Bhat, U.; Krapivsky, P. L.; Lambiotte, R.; Redner, S.

    2016-12-01

    We introduce a growing network model, the copying model, in which a new node attaches to a randomly selected target node and, in addition, independently to each of the neighbors of the target with copying probability p . When p <1/2 , this algorithm generates sparse networks, in which the average node degree is finite. A power-law degree distribution also arises, with a nonuniversal exponent whose value is determined by a transcendental equation in p . In the sparse regime, the network is "normal," e.g., the relative fluctuations in the number of links are asymptotically negligible. For p ≥1/2 , the emergent networks are dense (the average degree increases with the number of nodes N ), and they exhibit intriguing structural behaviors. In particular, the N dependence of the number of m cliques (complete subgraphs of m nodes) undergoes m -1 transitions from normal to progressively more anomalous behavior at an m -dependent critical values of p . Different realizations of the network, which start from the same initial state, exhibit macroscopic fluctuations in the thermodynamic limit: absence of self-averaging. When linking to second neighbors of the target node can occur, the number of links asymptotically grows as N2 as N →∞ , so that the network is effectively complete as N →∞ .

  18. Oxidative torrefaction of biomass residues and densification of torrefied sawdust to pellets.

    PubMed

    Wang, Congwei; Peng, Jianghong; Li, Hui; Bi, Xiaotao T; Legros, Robert; Lim, C J; Sokhansanj, Shahab

    2013-01-01

    Oxidative torrefaction of sawdust with a carrier gas containing 3-6% O(2) was investigated in a TG and a fluidized bed reactor, with the properties of the torrefied sawdust and pellets compared with traditional torrefaction without any O(2), as well as the dry raw material. It is found that the oxidative torrefaction process produced torrefied sawdust and pellets of similar properties as normally torrefied sawdust and corresponding pellets, especially on the density, energy consumption for pelletization, higher heating value and energy yield. For moisture absorption and hardness of the torrefied pellets, the oxidative torrefaction process showed slightly poor but negligible performance. Therefore, it is feasible to use oxygen laden combustion flue gases as the carrier gas for torrefaction of biomass. Besides, torrefied sawdust can be made into dense and strong pellets of high hydrophobicity at a higher die temperature than normally used in the production of traditional control pellets.

  19. Does densification influence the steam pretreatment and enzymatic hydrolysis of softwoods to sugars?

    PubMed

    Kumar, Linoj; Tooyserkani, Zahra; Sokhansanj, Shahab; Saddler, Jack N

    2012-10-01

    The global trade in wood pellets continues to grow. However, their potential as a feedstock for large scale cellulosic ethanol production has not been evaluated. We anticipated that the reduced moisture content and pressure exerted on the wood biomass during the pelletisation process would result in some carbohydrate loss as well as making the biomass more recalcitrant to pretreatment and subsequent hydrolysis. However, when softwood chips and pellets were steam pretreated at medium severity, little hemicellulose loss occurred while more than two-thirds of the cellulose present in the cellulose rich water insoluble fractions were hydrolysed (at 20 FPU cellulase/g cellulose). In addition, prior steaming substantially reduced the particle size of the wood chips enabling direct pelletisation without the need for grinding. Surprisingly, it was also possible to apply a single steam pretreatment to facilitate both pelletisation and subsequent enzymatic hydrolysis without the need for a further pretreatment step.

  20. Sol-gel synthesis and densification of aluminoborosilicate powders. Part 1: Synthesis

    NASA Technical Reports Server (NTRS)

    Bull, Jeffrey; Selvaduray, Guna; Leiser, Daniel

    1992-01-01

    Aluminoborosilicate powders high in alumina content were synthesized by the sol-gel process utilizing various methods of preparation. Properties and microstructural effects related to these syntheses were examined. After heating to 600 C for 2 h in flowing air, the powders were amorphous with the metal oxides comprising 87 percent of the weight and uncombusted organics the remainder. DTA of dried powders revealed a T(sub g) at approximately 835 C and an exotherm near 900 C due to crystallization. Powders derived from aluminum secbutoxide consisted of particles with a mean diameter 5 microns less than those from aluminum isopropoxide. Powders synthesized with aluminum isopropoxide produced agglomerates comprised of rod shaped particulates while powders made with the secbutoxide precursor produced irregular glassy shards. Compacts formed from these powders required different loadings for equivalent densities according to the method of synthesis.

  1. Sintering boron carbide ceramics without grain growth by plastic deformation as the dominant densification mechanism

    NASA Astrophysics Data System (ADS)

    Ji, Wei; Rehman, Sahibzada Shakir; Wang, Weimin; Wang, Hao; Wang, Yucheng; Zhang, Jinyong; Zhang, Fan; Fu, Zhengyi

    2015-10-01

    A new ceramic sintering approach employing plastic deformation as the dominant mechanism is proposed, at low temperature close to the onset point of grain growth and under high pressure. Based on this route, fully dense boron carbide without grain growth can be prepared at 1,675-1,700 °C and under pressure of (≥) 80 MPa in 5 minutes. The dense boron carbide shows excellent mechanical properties, including Vickers hardness of 37.8 GPa, flexural strength of 445.3 MPa and fracture toughness of 4.7 MPa•m0.5. Such a process should also facilitate the cost-effective preparation of other advanced ceramics for practical applications.

  2. 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.

  3. Densification of chemical vapor deposition silicon dioxide film using oxygen radical oxidation

    NASA Astrophysics Data System (ADS)

    Kawase, Kazumasa; Teramoto, Akinobu; Umeda, Hiroshi; Suwa, Tomoyuki; Uehara, Yasushi; Hattori, Takeo; Ohmi, Tadahiro

    2012-02-01

    Silicon dioxide (SiO2) films formed by chemical vapor deposition (CVD) were treated with oxygen radical oxidation using Ar/O2 plasma excited by microwave. The mass density depth profiles, carrier trap densities, and current-voltage characteristics of the radical-oxidized CVD-SiO2 films were investigated. The mass density depth profiles were estimated with x ray reflectivity measurement using synchrotron radiation of SPring-8. The carrier trap densities were estimated with x ray photoelectron spectroscopy time-dependent measurement. The mass densities of the radical-oxidized CVD-SiO2 films were increased near the SiO2 surface. The densities of the carrier trap centers in these films were decreased. The leakage currents of the metal-oxide-semiconductor capacitors fabricated by using these films were reduced. It is probable that the insulation properties of the CVD-SiO2 film are improved by the increase in the mass density and the decrease in the carrier trap density caused by the restoration of the Si-O network with the radical oxidation.

  4. Correction and Densification of Uas-Based Photogrammetric Thermal Point Cloud

    NASA Astrophysics Data System (ADS)

    Akcay, O.; Erenoglu, R. C.; Erenoglu, O.

    2016-06-01

    Photogrammetric processing algorithms can suffer problems due to either the initial image quality (noise, low radiometric quality, shadows and so on) or to certain surface materials (shiny or textureless objects). This can result in noisy point clouds and/or difficulties in feature extraction. Specifically, dense point clouds which are generated with photogrammetric method using a lightweight thermal camera, are more noisy and sparse than the point clouds of high-resolution digital camera images. In this paper, new method which produces more reliable and dense thermal point cloud using the sparse thermal point cloud and high resolution digital point cloud was considered. Both thermal and digital images were obtained with UAS (Unmanned Aerial System) based lightweight Optris PI 450 and Canon EOS 605D camera images. Thermal and digital point clouds, and orthophotos were produced using photogrammetric methods. Problematic thermal point cloud was transformed to a high density thermal point cloud using image processing methods such as rasterizing, registering, interpolation and filling. The results showed that the obtained thermal point cloud - up to chosen processing parameters - was 87% more densify than the original point cloud. The second improvement was gained at the height accuracy of the thermal point cloud. New densified point cloud has more consistent elevation model while the original thermal point cloud shows serious deviations from the expected surface model.

  5. Sintering boron carbide ceramics without grain growth by plastic deformation as the dominant densification mechanism

    PubMed Central

    Ji, Wei; Rehman, Sahibzada Shakir; Wang, Weimin; Wang, Hao; Wang, Yucheng; Zhang, Jinyong; Zhang, Fan; Fu, Zhengyi

    2015-01-01

    A new ceramic sintering approach employing plastic deformation as the dominant mechanism is proposed, at low temperature close to the onset point of grain growth and under high pressure. Based on this route, fully dense boron carbide without grain growth can be prepared at 1,675–1,700 °C and under pressure of (≥) 80 MPa in 5 minutes. The dense boron carbide shows excellent mechanical properties, including Vickers hardness of 37.8 GPa, flexural strength of 445.3 MPa and fracture toughness of 4.7 MPa•m0.5. Such a process should also facilitate the cost-effective preparation of other advanced ceramics for practical applications. PMID:26503706

  6. Dynamic densification of metal matrix-coated fibre composites: modelling and processing

    SciTech Connect

    Peng, H.X.; Dunne, F.P.E. . E-mail: fionn.dunne@eng.ox.ac.uk; Grant, P.S.; Cantor, B.

    2005-02-01

    The consolidation processing of Ti-6Al-4V matrix-coated fibre (MCF) composite under vacuum hot pressing (VHP) has been investigated. A new test methodology has been developed for the determination of in situ matrix coating creep properties. In using the methodology, only a single, simple test is required, together with finite element modelling of the single fibre compression test. The creep coefficient and stress index have been determined for electron beam evaporated physical vapour deposited Ti-6Al-4V at 900 deg. C to be 1.23 x 10{sup -5} and 1.3, respectively. Consolidation experiments have been carried out on multi-ply MCF arrays under vacuum hot pressing. Finite element models have been developed for the dynamic consolidation of both square and hexagonal fibre packings. The creep constants for the Ti-6Al-4V, determined using the single fibre test, were assigned to the coating in the finite element models. Excellent agreement between predicted and experimental results was achieved, providing verification of the single fibre test methodology for the determination of creep constants.

  7. Densification and Devitrification of Fused Silica Induced by Ballistic Impact: A Computational Investigation

    DTIC Science & Technology

    2015-03-25

    and P. G. Dehmer, “Effect of the tin- vs. air-side plate-glass orientation on the impact response and penetration resistance of a laminated ...Computational investigation of impact energy absorption capability of polyurea coatings via deformation-induced glass transition,” Materials Science and...the multi-hit ballistic-protection performance of laminated transparent-armor systems,” Journal of Materials Engineering and Performance, vol. 21, no

  8. State-of-the-Art Applicability of Conventional Densification Techniques to Increase Disposal Area Storage Capacity

    DTIC Science & Technology

    1977-04-01

    flocculants are polyacrylamides that have different molecular weights and ionic conditions. Based on experience with phos- phatic slimes, it appears that...slurry, starch is added, thereby flocculating ¼ the solids to an average size of about 10 P. The resultant slurry at 15 to 20 percent solids by weight...flocculated and dewatered to a condition of 28 to 30 percent solids by weight by the use of starch alo~ie and that by the addition of under- drains and

  9. The early crystal nucleation process in hard spheres shows synchronised ordering and densification

    NASA Astrophysics Data System (ADS)

    Berryman, Joshua T.; Anwar, Muhammad; Dorosz, Sven; Schilling, Tanja

    2016-12-01

    We investigate the early part of the crystal nucleation process in the hard sphere fluid using data produced by computer simulation. We find that hexagonal order manifests continuously in the overcompressed liquid, beginning approximately one diffusion time before the appearance of the first "solid-like" particle of the nucleating cluster, and that a collective influx of particles towards the nucleation site occurs simultaneously to the ordering process: the density increases leading to nucleation are generated by the same individual particle displacements as the increases in order. We rule out the presence of qualitative differences in the early nucleation process between medium and low overcompressions and also provide evidence against any separation of translational and orientational order on the relevant lengthscales.

  10. Evaluation of Underdrainage Techniques for the Densification of Fine-Grained Dredged Material.

    DTIC Science & Technology

    1981-03-01

    i.e., collector pipe size and spacing and drain thickness) can be made without difficulty ( Cedergren 1977, and Department of the Army, Office, Chief...accomplished. 93 REFERENCES Cedergren , H. R. 1977. Seepage, Drainaj, and Flow Nets, 2nd Edit ion, Wiley, New York, N. Y. Department of the Army, Office

  11. Method and apparatus for in-situ densification of geomaterials for sealing applications

    DOEpatents

    Finley, R.E.; Zeuch, D.H.

    1997-04-22

    A method and apparatus is described for forming improved seals in boreholes formed in host rock by using the apparatus to introduce a feedstock into the borehole and simultaneously subjecting the introduced feedstock to both compressive and shear stresses until the borehole becomes filled and sealed. 3 figs.

  12. Method and apparatus for in-densification of geomaterials for sealing applications

    DOEpatents

    Finley, Ray E.; Zeuch, David H.

    1997-01-01

    A method and apparatus (10) for forming improved seals in boreholes (101) formed in host rock (100) by using the apparatus (10) to introduce a feedstock (60) into the borehole (101) and simultaneously subject the introduced feedstock to both compressive and shear stresses until the borehole becomes filled and sealed.

  13. Conductivity percolation in loosely compacted microcrystalline cellulose: An in situ study by dielectric spectroscopy during densification.

    PubMed

    Nilsson, Martin; Frenning, Göran; Gråsjö, Johan; Alderborn, Göran; Strømme, Maria

    2006-10-19

    The present study aims at contributing to a complete understanding of the water-induced ionic charge transport in cellulose. The behavior of this transport in loosely compacted microcrystalline cellulose (MCC) powder was investigated as a function of density utilizing a new type of measurement setup, allowing for dielectric spectroscopy measurement in situ during compaction. The ionic conductivity in MCC was found to increase with increasing density until a leveling-out was observed for densities above approximately 0.7 g/cm3. Further, it was shown that the ionic conductivity vs density followed a percolation type behavior signifying the percolation of conductive paths in a 3D conducting network. The density percolation threshold was found to be between approximately 0.2 and 0.4 g/cm3, depending strongly on the cellulose moisture content. The observed percolation behavior was attributed to the forming of interparticulate bonds in the MCC and the percolation threshold dependence on moisture was linked to the moisture dependence of particle rearrangement and plastic deformation in MCC during compaction. The obtained results add to the understanding of the density-dependent water-induced ionic transport in cellulose showing that, at given moisture content, the two major parameters determining the magnitude of the conductivity are the connectedness of the interparticluate bonds and the connectedness of pores with a diameter in the 5-20 nm size range. At densities between approximately 0.7 and 1.2 g/cm3 both the bond and the pore networks have percolated, facilitating charge transport through the MCC compact.

  14. Densification of the ITRF through the weekly combination of regional and global GNSS solutions

    NASA Astrophysics Data System (ADS)

    Legrand, J.; Bruyninx, C.; Saria, E.; Griffiths, J.; Craymer, M. R.; Dawson, J. H.; Kenyeres, A.; Santamaría-Gómez, A.; Sanchez, L.; Altamimi, Z.

    2012-12-01

    The IAG Working Group (WG) "Integration of Dense Velocity Fields in the ITRF" was created in 2011 as a follow-up of the WG "Regional Dense Velocity Fields" (2007-2011). The goal of the WG is to densify the International Terrestrial Reference Frame (ITRF) using regional GNSS solutions as well as global solutions. This was originally done by combining several cumulative position/velocity solutions submitted to the WG by the global analysis center (ULR) and the IAG regional reference frame sub-commissions (APREF, EUREF, SIRGAS, NAREF) analysis centers. However, several test combinations together with the comparison of the residual position time series demonstrated the limitations of this approach. In June 2012, the WG decided to adopt a new approach based on a weekly combination of the GNSS solutions. This new approach will enable us to mitigate network effects, have full control over the discontinuities and the velocity constraints, manage the different data spans and derive residual position time series in addition to a velocity field. All initial contributors have agreed to submit weekly solutions and in addition initial contacts have been made with other sub-commissions, particularly Africa, in order to extent the densified velocity field to all continents. Preliminary results of the analysis of weekly solutions will be presented. More details on the WG are available from http://epncb.oma.be/IAG/.

  15. Spatiotemporal densification of river water level time series by multimission satellite altimetry

    NASA Astrophysics Data System (ADS)

    Tourian, M. J.; Tarpanelli, A.; Elmi, O.; Qin, T.; Brocca, L.; Moramarco, T.; Sneeuw, N.

    2016-02-01

    Limitations of satellite radar altimetry for operational hydrology include its spatial and temporal sampling as well as measurement problems caused by local topography and heterogeneity of the reflecting surface. In this study, we develop an approach that eliminates most of these limitations to produce an approximately 3 day temporal resolution water level time series from the original typically (sub)monthly data sets for the Po River in detail, and for Congo, Mississippi, and Danube Rivers. We follow a geodetic approach by which, after estimating and removing intersatellite biases, all virtual stations of several satellite altimeters are connected hydraulically and statistically to produce water level time series at any location along the river. We test different data-selection strategies and validate our method against the extensive available in situ data over the Po River, resulting in an average correlation of 0.7, Root-Mean-Square Error of 0.8 m, bias of -0.4 m, and Nash-Sutcliffe Efficiency coefficient of 0.5. We validate the transferability of our method by applying it to the Congo, Mississippi, and Danube Rivers, which have very different geomorphological and climatic conditions. The methodology yields correlations above 0.75 and Nash-Sutcliffe coefficients of 0.84 (Congo), 0.34 (Mississippi), and 0.35 (Danube).

  16. 3-D multilateration for measurement of earth crustal deformation and network densification

    NASA Technical Reports Server (NTRS)

    Ong, K. M.

    1973-01-01

    Discussion of how range and range-difference data types can make possible precise three-dimensional measurement of ground station positions and the position of an artificial signal source, without explicit dependence upon the signal source trajectory. An effective strategy for such measurement is to combine the multilateration approach with a VLBI system using natural radio sources. The VLBI methods would provide a coarse grid of three-dimensional benchmark locations on a regional and global scale. Multilateration stations would then occupy these coarse grid locations and provide a means for highly portable, relatively low-cost units to then densify networks on a regional and local scale. Because a multilateration approach can make use of strong artificial radio sources, it makes possible the use of relatively low-cost, highly mobile stations. Such mobile stations are virtually essential for three dimensional surveying in heavily urbanized areas or in rugged terrain.

  17. Environmental Education Excursions and Proximity to Urban Green Space--Densification in a "Compact City"

    ERIC Educational Resources Information Center

    Wolsink, Maarten

    2016-01-01

    The value of urban green space for environmental education fieldwork is empirically investigated in a study among all secondary schools in Amsterdam. The article describes how the proximity of schools to green spaces emerges as a new factor in the "sustainable city" and the "compact city" debate. For fieldwork excursions…

  18. CHALLENGES AND STRATEGIES ON FIBROUS FEEDSTUFFS DENSIFICATION AND ITS INTERACTION WITH LIQUID INGREDIENTS

    SciTech Connect

    Pordesimo, Lester O.; Tumuluru, Jaya Shankar

    2015-10-01

    There has been continuing interest and support in using herbaceous biomass, mostly agricultural crop residues, in the U.S. as feedstocks for producing bioenergy, liquid transportation fuels, and industrial chemicals/materials. With the potential of greater collection of agricultural crop residues for the foregoing industrial applications there will be a commensurate greater availability of crop residues for utilization in agricultural production. Agricultural crop residues are typically used in agricultural production as roughage or bedding for cattle. Use of herbaceous biomass, corn stover of greatest interest at the present time, and processing coproducts thereof, as a feed ingredient presents an opportunity to reduce ration costs and improve livestock enterprise profitability by replacing an amount of corn and other feed grains in livestock diets with proper formulation. The obvious advantage of utilizing corn stover is its wide availability and low cost.

  19. Densification of a thick disk preform with silicon carbide matrix by CVI process

    SciTech Connect

    Huynh, T.; Burkland, C.V.; Bustamante, B.

    1991-10-01

    A chemical vapor infiltration (CVI) process was used to fabricate a ceramic matrix composite (CMC) bladed rotor. The demonstration article was based on an uncooled design for an expendable turbine engine. A thick-disk preform of 2-D polar woven Nicalon fiber was densified with silicon carbide matrix by CVI process. The composite disk was densified to 90 +/- 2 percent of the theoretical density (about 2.94 g/cu cm). The densified composite disk was ultrasonically machined into net shape per design configuration. The machining operation included conventional surface grinding and computerized ultrasonic machining of the blades. The evaluation of the CMC rotor included NDE, microstructural analysis, micromechanical material modeling, finite element disk analysis, and a cold spin test. 2 refs.

  20. In-situ emplacement and densification of geomaterials for sealing applications

    SciTech Connect

    Finley, R.E.; Zeuch, D.H.

    1995-12-31

    A method and apparatus are described for forming improved seals in boreholes formed in host rock by using the apparatus to introduce a feedstock into the borehole and simultaneously subject the introduced feedstock to both compressive and shear stresses until the borehole becomes filled and sealed. These seals are primarily intended to restrict the movement of radioactive or hazardous materials into the accessible environment.

  1. Effect of Oxidation on the Densification of Sinterable RBSN (Reaction-Bonded Silicon Nitride).

    DTIC Science & Technology

    1986-01-01

    pressure/temperature cycle. Some bars were preoxidized at 10000C prior to sintering to increase the oxygen content (SiO2 ) of the speci- - mens and...tering process. Those kinetics are influenced by the amount and stability of each component or compound formed and the reaction path. Additionally...yttrium-nitrogen apatite (Y5Si301 2N) with a small amount of free silicon also detected. The densities of the specimens were between 2.4 and 2.5 g/cc

  2. Effect of Coprecipitation Parameters on Powder Characteristics and on Densification of PZT Ceramics.

    DTIC Science & Technology

    1982-09-01

    34* diffraction using a Phillips Norelco Diffractometer with filtered Ni K radiati-n. The powders were also subjected to DTA and TGA analysis using... TGA analysis showed the first two peaks to be associated with weight loss, the maximum loss occurring near 300oC. From Fig. 4a it is evident that I0

  3. Glass-reinforced hydroxyapatite composites: secondary phase proportions and densification effects on biaxial bending strength.

    PubMed

    Lopes, M A; Monteiro, F J; Santos, J D

    1999-01-01

    CaO-P(2)O(5) glasses with additions of MgO and CaF(2) were used as a sintering aid of hydroxyapatite, and glass-reinforced hydroxyapatite composites obtained. Glasses promoted significant changes in the microstructure of the composites, namely with the formation of tricalcium phosphate secondary phases, beta and alpha-TCP. Quantitative phase analysis was performed by the Rietveld method using General Structure Analysis Software. Grain size measurements were carried out on SEM photomicrographs, using a planimetric procedure according to ASTM E 112-88. Flexural bending strength was determined from concentric ring-on-ring testing. Flexural bending strength (FBS) of glass-reinforced hydroxyapatite composites was found to be about twice or three times higher than that of unreinforced hydroxyapatite and tended to depend more on porosity and beta and alpha-TCP secondary phases, rather than on grain size. Traces of alpha-tricalcium phosphate significantly enhanced the strength of the composites. Using the rule of mixtures to estimate the zero porosity bending strength, the Duckworth-Knudsen model applied to the composites gave a porosity correction factor, b, with a value of 4.02. Weibull statistics were also used to analyze biaxial strength data and the level of reinforcement obtained by comparing failure probability for the composites and for the unreinforced hydroxyapatite. Lower activation energies for grain growth were observed for the composites compared to unreinforced hydroxyapatite, which should be attributed to the presence of a liquid glassy phase that promotes atomic diffusion during the sintering process.

  4. NaF-assisted combustion synthesis of MoSi2 nanoparticles and their densification behavior

    NASA Astrophysics Data System (ADS)

    Nersisyan, Hayk H.; Lee, Tae Hyuk; Ri, Vladislav; Lee, Jong Hyeon; Suh, Hoyoung; Kim, Jin-Gyu; Son, Hyeon Taek; Kim, Yong-Ho

    2017-03-01

    The exothermic reduction of oxides mixture (MoO3+2SiO2) by magnesium in NaF melt enables the synthesis of nanocrystalline MoSi2 powders in near-quantitative yields. The combustion wave with temperature of about 1000-1200 °C was recorded in highly diluted by NaF starting mixtures. The by-products of combustion reaction (NaF and MgO) were subsequently removed by leaching with acid and washing with water. The as-prepared MoSi2 nanopowder composed of spherical and dendritic shape particles was consolidated using the spark plasma sintering method at 1200-1500 °C and 50 MPa for 10 min. The result was dense compacts (98.6% theoretical density) possessing submicron grains and exhibiting hardness of 8.74-12.92 GPa.

  5. Rotation-based technique for the rapid densification of tubular collagen gel scaffolds.

    PubMed

    Loy, Caroline; Lainé, Audrey; Mantovani, Diego

    2016-12-01

    Type I collagen gel is often used as a tubular scaffold because of its easy molding properties as well as its biocompatibility, low immunogenicity and ability to be remodelled by cells. However, its highly hydrated structure contributes to its weak mechanical properties and reduces its ability to be handled, which is important in tubular tissue engineering. Although cell-driven remodelling of collagen matrices is known to reinforce their mechanical properties, this process can take weeks. This study introduces a novel, simple, and rapid technique using a rotational bioreactor to expel water and densify collagen under sterile conditions to generate denser and stronger collagen gel scaffolds. This process produces a dense tubular-shaped collagen gel which, compared to standard collagen gel scaffolds, shows a decreased wall thickness and a four-fold increase in collagen concentration. A denser collagen fiber network observed by immunofluorescence staining and mechanical characterisation shows a twenty-fold increase in the elastic modulus of the dense constructs which maintain cell viability inside the scaffold. Moreover, by simply modifying the scaffold mold, customised shapes and sizes can be obtained to provide a wide range of applications, including complex tubular geometries and multi-layered scaffolds for the culture of various cell types and tissues. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  6. Environmental Education Excursions and Proximity to Urban Green Space--Densification in a "Compact City"

    ERIC Educational Resources Information Center

    Wolsink, Maarten

    2016-01-01

    The value of urban green space for environmental education fieldwork is empirically investigated in a study among all secondary schools in Amsterdam. The article describes how the proximity of schools to green spaces emerges as a new factor in the "sustainable city" and the "compact city" debate. For fieldwork excursions…

  7. Optimization of Preprocessing and Densification of Sorghum Stover at Full-scale Operation

    SciTech Connect

    Neal A. Yancey; Jaya Shankar Tumuluru; Craig C. Conner; Christopher T. Wright

    2011-08-01

    Transportation costs can be a prohibitive step in bringing biomass to a preprocessing location or biofuel refinery. One alternative to transporting biomass in baled or loose format to a preprocessing location, is to utilize a mobile preprocessing system that can be relocated to various locations where biomass is stored, preprocess and densify the biomass, then ship it to the refinery as needed. The Idaho National Laboratory has a full scale 'Process Demonstration Unit' PDU which includes a stage 1 grinder, hammer mill, drier, pellet mill, and cooler with the associated conveyance system components. Testing at bench and pilot scale has been conducted to determine effects of moisture on preprocessing, crop varieties on preprocessing efficiency and product quality. The INLs PDU provides an opportunity to test the conclusions made at the bench and pilot scale on full industrial scale systems. Each component of the PDU is operated from a central operating station where data is collected to determine power consumption rates for each step in the process. The power for each electrical motor in the system is monitored from the control station to monitor for problems and determine optimal conditions for the system performance. The data can then be viewed to observe how changes in biomass input parameters (moisture and crop type for example), mechanical changes (screen size, biomass drying, pellet size, grinding speed, etc.,), or other variations effect the power consumption of the system. Sorgum in four foot round bales was tested in the system using a series of 6 different screen sizes including: 3/16 in., 1 in., 2 in., 3 in., 4 in., and 6 in. The effect on power consumption, product quality, and production rate were measured to determine optimal conditions.

  8. Cladding hull decontamination and densification process. Part 1. The prototype cladding hull decontamination system

    SciTech Connect

    Lambright, T.M.; Montgomery, D.R.

    1980-04-01

    A prototype system for decontaminating Zircaloy-4 cladding hulls has been assembled and tested at Pacific Northwest Laboratory. The decontamination process consists of treatment with a gaseous mixture of hydrogen fluoride (HF) and argon (Ar) followed by a dilute aqueous etch of ammonium oxalate, ammonium citrate, ammonium fluoride, and hydrogen peroxide. The continuous cleaning process described in this report successfully descaled small portions of most charges, but was unable to handle the original design capacity of 4 kg/hr because of problems in the following areas: control of HF reactor temperatures, regulation of HF and argon mixtures and flows, isolation of the HF reactor atmosphere from the aqueous washer/rinser atmosphere, regulation of undesirable side reactions, and control over hull transport through the system. Due to the limited time available to solve these problems, the system did not attain fully operational status. The work was performed with unirradiated hulls that simulated irradiated hulls. The system was not built to be remotely operable. The process chemistry and system equipment are described in this report with particular emphasis on critical operating areas. Recommendations for improved system operation are included.

  9. Sintering boron carbide ceramics without grain growth by plastic deformation as the dominant densification mechanism.

    PubMed

    Ji, Wei; Rehman, Sahibzada Shakir; Wang, Weimin; Wang, Hao; Wang, Yucheng; Zhang, Jinyong; Zhang, Fan; Fu, Zhengyi

    2015-10-27

    A new ceramic sintering approach employing plastic deformation as the dominant mechanism is proposed, at low temperature close to the onset point of grain growth and under high pressure. Based on this route, fully dense boron carbide without grain growth can be prepared at 1,675-1,700 °C and under pressure of (≥) 80 MPa in 5 minutes. The dense boron carbide shows excellent mechanical properties, including Vickers hardness of 37.8 GPa, flexural strength of 445.3 MPa and fracture toughness of 4.7 MPa•m(0.5). Such a process should also facilitate the cost-effective preparation of other advanced ceramics for practical applications.

  10. Ensuring near-optimum homogeneity and densification levels in nano-reinforced ceramics

    NASA Astrophysics Data System (ADS)

    Dassios, Konstantinos G.; Barkoula, Nektaria-Marianthi; Alafogianni, Panagiota; Bonnefont, Guillaume; Fantozzi, Gilbert; Matikas, Theodore E.

    2016-04-01

    The development of a new generation of high temperature ceramic materials for aerospace applications, reinforced at a scale closer to the molecular level and three orders of magnitude less than conventional fibrous reinforcements, by embedded carbon nanotubes, has recently emerged as a uniquely challenging scientific effort. The properties of such materials depend strongly on two main factors: i) the homogeneity of the dispersion of the hydrophobic medium throughout the ceramic volume and ii) the ultimate density of the resultant product after sintering of the green body at the high-temperatures and pressures required for ceramic consolidation. The present works reports the establishment of two independent experimental strategies which ensure achievement of near perfect levels of tube dispersion homogeneity and fully dense final products. The proposed methodologies are validated across non-destructive evaluation data of materials performance.

  11. Study of Material Densification of In718 in the Higher Throughput Parameter Regime

    NASA Technical Reports Server (NTRS)

    Cordner, Samuel

    2016-01-01

    Selective Laser Melting (SLM) is a powder bed fusion additive manufacturing process used increasingly in the aerospace industry to reduce the cost, weight, and fabrication time for complex propulsion components. Previous optimization studies for SLM using the Concept Laser M1 and M2 machines at NASA Marshall Space Flight Center have centered on machine default parameters. The objective of this project is to characterize how heat treatment affects density and porosity from a microscopic point of view. This is performs using higher throughput parameters (a previously unexplored region of the manufacturing operating envelope for this application) on material consolidation. Density blocks were analyzed to explore the relationship between build parameters (laser power, scan speed, and hatch spacing) and material consolidation (assessed in terms of density and porosity). The study also considers the impact of post-processing, specifically hot isostatic pressing and heat treatment, as well as deposition pattern on material consolidation in the higher energy parameter regime. Metallurgical evaluation of specimens will also be presented. This work will contribute to creating a knowledge base (understanding material behavior in all ranges of the AM equipment operating envelope) that is critical to transitioning AM from the custom low rate production sphere it currently occupies to the world of mass high rate production, where parts are fabricated at a rapid rate with confidence that they will meet or exceed all stringent functional requirements for spaceflight hardware. These studies will also provide important data on the sensitivity of material consolidation to process parameters that will inform the design and development of future flight articles using SLM.

  12. Synthesis and densification of MoSi{sub 2} by self-propagating high-temperature synthesis

    SciTech Connect

    Gi-Wook Lee, Hyun-Woo Lee, Yong-Seog Kim

    1995-12-31

    The possibility of producing dense MoSi{sub 2} by the thermal explosion mode of Self-propagating High-temperature Synthesis(SHS) was demonstrated. It was shown that the density of MoSi{sub 2} produced by SHS process without applied pressure can be increased by a proper combination of processing parameters such as heating rate, addition of alloying elements, processing atmosphere, and Mo and Si powder sizes used. The heating rate and alloying elements were found to influence the density Of MoSi{sub 2} formed the most. Proper combinations of the processing is parameter yielded MoSi{sub 2} with density close to 90% theoretical density which comparable to pressurelessly sintered MoSi{sub 2}.

  13. Low-cost densification of permanent GPS networks for natural hazard mitigation: First tests on GSI's GEONET network

    NASA Astrophysics Data System (ADS)

    Rizos, Chris; Han, Shaowei; Ge, Linlin; Chen, Horng-Yue; Hatanaka, Yuki; Abe, Kaoru

    2000-10-01

    Researchers from The University of New South Wales (UNSW), Australia, and from the Geographical Survey Institute (GSI), Japan, have commenced a joint project to develop, deploy and test an innovative hardware/software system design for an automatic, continuously-operated ground deformation monitoring system based on low-cost GPS receiver technology. Conventional continuously-operated GPS (CGPS) networks, such as the one established in Japan by GSI to precisely measure earth surface movement, are very expensive. The high cost being primarily due to the fact that dual-frequency receivers are used. Japan's nationwide GEONET network is the world's largest, numbering nearly 1000 receiver stations, with an average station spacing of the order of 30 km. In order to densify such CGPS networks (important when high spatial resolution for the monitoring of the deformation phenomenon is required), and to promote the use of the CGPS technique in lesser developed countries, a significantly cheaper system architecture is needed. The proposed design is an integrated, dual-mode network consisting of low-cost, single-frequency GPS receivers across the area of interest, surrounded by a sparser network of dual-frequency GPS receivers. Initial tests of data collected at selected stations in the GEONET network have already shown that through enhanced data processing algorithms a CGPS network containing both single-frequency and dual-frequency receivers would be able to deliver better than centimetre level accuracies, at considerably lower cost than present systems based exclusively on dual-frequency instrumentation. This paper reports the results of the first field test of this new CGPS system design, in the Tsukuba area of Japan, in August 1999. The test network consisted of: (a) several stations of the GEONET network surrounding (b) an inner network of four single-frequency Canadian Marconi GPS receivers installed by UNSW researchers. The data from both the GEONET and the UNSW receivers were processed using a specially modified version of the Bernese GPS Software Package. The software first processes the GEONET GPS station data in order to generate empirical corrections which are then applied to the double-differenced data of the GPS baselines located within the test area enclosed by the dual-frequency CGPS stations. These corrections have the effect of improving baseline solution accuracy by up to an order of magnitude, even for baselines ranging up to 100 km in length. The baselines connecting the inner network to the surrounding GEONET stations are processed in a number of modes, including 24 hr files (as is the standard practice for geodynamic applications) and hourly data files (as in volcano deformation monitoring applications). The results indicate that single-frequency-with-correction processing can achieve accuracies of better than 5 mm in the horizontal components and 3 cm in height, while the dual-frequency results can achieve accuracies better than 2 mm in the horizontal components and 6 mm in height. In the authors' opinion, for certain geodynamic applications there are no significant differences between the single-frequency-with-correction results and the dual-frequency results, especially for the horizontal components.

  14. From simulation to implementation: low-cost densification of permanent GPS networks in support of geodetic applications

    NASA Astrophysics Data System (ADS)

    Chen, H.-Y.; Rizos, C.; Han, S.

    2001-10-01

    Permanent GPS networks have been established since the 1980s to support a variety of geodetic applications, ranging from local deformation monitoring to large-scale crustal motion measurement. Continuously operating GPS (CGPS) networks, consisting of geodetic-grade, dual-frequency receiver systems, generally support relative positioning to sub-centimetre accuracy, even for baselines up to several thousand kilometres in length. However, due to their comparatively high cost, the density of such GPS stations is rarely high enough to support all geodetic applications. For example, although the Geographical Survey Institute has established nearly 1000 permanent GPS stations across Japan, the average inter-station spacing is of the order of 30 km. This paper describes a method by which a sub-network of comparatively low-cost, single-frequency GPS receivers can be deployed to increase the density of typical CGPS networks. In this way it is possible to increase the spatial resolution of the measured ground deformation, while still maintaining the same level of precision as a CGPS network comprised entirely of dual-frequency GPS receivers. In order to reduce the system biases associated with single-frequency data processing, an innovative medium-range GPS positioning technique that combines the processing of single-frequency and dual-frequency data is proposed. Several data sets are analysed in order to address critical issues such as: 'Can the technique work equally well for different geographic locations across Asia, traversing large elevation changes, in various seasons?', 'Can the sub-network incorporate single-frequency receivers of different brands while maintaining similar levels of precision?', and 'Can the sub-network yield generally uniform high precision results for different baseline lengths?' The analyses undertaken by the authors confirm that the proposed technique can achieve relative accuracies similar to those obtained from dual-frequency, static positioning, over inter-station distances up to a few tens of kilometres, under a variety of operational environments. These investigations are a necessary first step in making this technique an operational reality.

  15. All-Atom Molecular-Level Analysis of the Ballistic-Impact-Induced Densification and Devitrification of Fused Silica

    NASA Astrophysics Data System (ADS)

    Grujicic, M.; Snipes, J. S.; Ramaswami, S.; Yavari, R.; Barsoum, R. S.

    2015-08-01

    All-atom molecular-level computations are carried out to infer the dynamic response and material microstructure/topology changes of fused silica subjected to ballistic impact by a hard projectile. The analysis was focused on the investigation of specific aspects of the dynamic response and of the microstructural changes such as the deformation of highly sheared and densified regions and the conversion of amorphous fused silica to SiO2 crystalline allotropic modifications (in particular, α-quartz and stishovite). The microstructural changes in question were determined by carrying out a post-processing atom-coordination procedure. This procedure suggested the formation of stishovite (and perhaps α-quartz) within fused silica during ballistic impact. To rationalize the findings obtained, the all-atom molecular-level computational analysis is complemented by a series of quantum-mechanics density functional theory (DFT) computations. The latter computations enable determination of the relative potential energies of the fused silica, α-quartz, and stishovite under ambient pressure (i.e., under their natural densities) as well as under imposed (as high as 50 GPa) pressures (i.e., under higher densities) and shear strains. In addition, the transition states associated with various fused-silica devitrification processes were identified. The results obtained are found to be in good agreement with their respective experimental counterparts.

  16. Simplicity in melt densification in multicomponent magmatic reservoirs in Earth’s interior revealed by multinuclear magnetic resonance

    PubMed Central

    Lee, Sung Keun

    2011-01-01

    Pressure-induced changes in properties of multicomponent silicate melts in magma oceans controlled chemical differentiation of the silicate earth and the composition of partial melts that might have formed hidden reservoirs. Although melt properties show complex pressure dependences, the melt structures at high pressure and the atomistic origins of these changes are largely unknown because of their complex pressure–composition dependence, intrinsic to multicomponent magmatic melts. Chemical constraints such as the nonbridging oxygen (NBO) content at 1 atm, rather than the structural parameters for melt polymerization, are commonly used to account for pressure-induced changes in the melt properties. Here, we show that the pressure-induced NBO fraction in diverse silicate melts show a simple and general trend where all the reported experimental NBO fractions at high pressure converge into a single decaying function. The pressure-induced changes in the NBO fraction account for and predict the silica content, nonlinear variations in entropy, and the transport properties of silicate melts in Earth’s mantle. The melt properties at high pressure are largely different from what can be predicted for silicate melts with a fixed NBO fraction at 1 atm. The current results with simplicity in melt polymerization at high pressure provide a molecular link to the chemical differentiation, possibly missing Si content in primary mantle through formation of hidden Si-rich mantle reservoirs.

  17. Effect of Surface Densification on the Microstructure and Mechanical Properties of Powder Metallurgical Gears by Using a Surface Rolling Process

    PubMed Central

    Peng, Jingguang; Zhao, Yan; Chen, Di; Li, Kiade; Lu, Wei; Yan, Biao

    2016-01-01

    Powder metallurgy (PM) components are widely used in the auto industry due to the advantage of net-shape forming, low cost, and high efficiency. Still, usage of PM components is limited in the auto industry when encountering rigorous situations, like heavy load, due to lower strength, hardness, wear resistance, and other properties compared to wrought components due to the existence of massive pores in the PM components. In this study, through combining the powder metallurgy process and rolling process, the pores in the PM components were decreased and a homogenous densified layer was formed on the surface, which resulted in the enhancement of the strength, hardness, wear resistance, and other properties, which can expand its range of application. In this paper, we study the impact of different rolling feeds on the performance of the components’ surfaces. We found that with the increase of the rolling feed, the depth of the densified layer increased. PMID:28773970

  18. Influence of Boehmite Precursor on Aluminosilicate Aerogel Pore Structure, Phase Stability and Resistance to Densification at High Temperatures

    NASA Technical Reports Server (NTRS)

    Hurwitz, Frances I.; Guo, Haiquan; Newlin, Katy N.

    2011-01-01

    Aluminosilicate aerogels are of interest as constituents of thermal insulation systems for use at temperatures higher than those attainable with silica aerogels. It is anticipated that their effectiveness as thermal insulators will be influenced by their morphology, pore size distribution, physical and skeletal densities. The present study focuses on the synthesis of aluminosilicate aerogel from a variety of Boehmite (precursors as the Al source, and tetraethylorthosilicate (TEOS) as the Si source, and the influence of starting powder on pore structure and thermal stability.

  19. Granular encapsulation of light hydrophobic liquids (LHL) in LHL-salt water systems: Particle induced densification with quartz sand.

    PubMed

    Boglaienko, Daria; Tansel, Berrin; Sukop, Michael C

    2016-02-01

    Addition of granular materials to floating crude oil slicks can be effective in capturing and densifying the floating hydrophobic phase, which settles by gravity. Interaction of light hydrophobic liquids (LHL) with quartz sand was investigated in LHL-salt water systems. The LHLs studied were decane, tetradecane, hexadecane, benzene, toluene, ethylbenzene, m-xylene, and 2-cholorotoluene. Experiments were conducted with fine quartz sand (passing sieve No. 40 with openings 0.425 mm). Each LHL was dyed with few crystals of Sudan IV dye for ease of visual observation. A volume of 0.5 mL of each LHL was added to 100 mL salt water (34 g/L). Addition of one gram of quartz sand to the floating hydrophobic liquid layer resulted in formation of sand-encapsulated globules, which settled due to increased density. All LHLs (except for a few globules of decane) formed globules covered with fine sand particles that were heavy enough to settle by gravity. The encapsulated globules were stable and retained their shape upon settling. Polarity of hydrophobic liquids as the main factor of aggregation with minerals was found to be insufficient to explain LHL aggregation with sand. Contact angle measurements were made by submerging a large quartz crystal with the LHL drop on its surface into salt water. A positive correlation was observed between the wetting angle of LHL and the LHL volume captured (r = 0.75). The dependence of the globule density on globule radius was analyzed in relation to the coverage (%) of globule surface (LHL-salt water interface) by fine quartz particles.

  20. Microstructural study and densification analysis of hot work tool steel matrix composites reinforced with TiB{sub 2} particles

    SciTech Connect

    Fedrizzi, A.; Pellizzari, M.; Zadra, M.; Marin, E.

    2013-12-15

    Hot work tool steels are characterized by good toughness and high hot hardness but are less wear resistant than other tooling materials, such as high speed steel. Metal matrix composites show improved tribological behavior, but not much work has been done in the field of hot work tool steels. In this paper TiB{sub 2}-reinforced hot work tool steel matrix composites were produced by spark plasma sintering (SPS). Mechanical alloying (MA) was proposed as a suited process to improve the composite microstructure. Density measurements and microstructure confirmed that MA promotes sintering and produces a fine and homogeneous dispersion of reinforcing particles. X-ray diffraction patterns of the sintered composites highlighted the formation of equilibrium Fe{sub 2}B and TiC, as predicted by thermodynamic calculations using Thermo-Calc® software. Scanning electron microscopy as well as scanning Kelvin probe force microscopy highlighted the reaction of the steel matrix with TiB{sub 2} particles, showing the formation of a reaction layer at the TiB{sub 2}-steel interface. Phase investigations pointed out that TiB{sub 2} is not chemically stable in steel matrix because of the presence of carbon even during short time SPS. - Highlights: • TiB{sub 2} reinforced steel matrix composites were produced by spark plasma sintering. • TiB{sub 2} was successfully dispersed in the steel matrix by mechanical alloying. • Steel and TiB{sub 2} react during sintering forming equilibrium Fe{sub 2}B and TiC. • The new phases were investigated by means of AFM, Volta potential and XRD analyses.

  1. Urban Change: Understanding how expansion and densification relate to demographic change and their implications for climate change.

    NASA Astrophysics Data System (ADS)

    Balk, D.; Jones, B.; Liu, Z.; Nghiem, S. V.; Pesaresi, M.

    2015-12-01

    Urbanization is the most demographic significant trend of the 21st century particularly in Asia. Characterizing it in a spatial context is difficult given the moderate resolution data provided by traditional sources of demographic data. Previous work on Saigon has shown by using these data together that much more about the correlates and potential consequences of change in the form and expansion of urban change can be learned than with a single data source alone. In this paper, we expand our analysis to two other much different urban and socioeconomic settings: Dhaka and Beijing. Particularly, where the demographic and socioeconomic indicators of change are too infrequent to capture annual change, use of satellites in combination with demographic data may be especially useful for capturing change in exurban and periurban areas, or in smaller cities within larger urban agglomerations. Using spatial regression techniques, we estimate statistical relationships between remotely sensed data sets to assess the ability demographic changes to predict urban changes as detected by two different satellite measures of change 2000-2010 in Dhaka, Saigon, and Beijing. We then predict socioeconomic outcomes associated with emissions and vulnerability proxies. We use two much different types of satellite data -- the Dense Sample Method (DSM) analysis of the NASA scatterometer data and new built-up area data from the Global Human Settlement Layer of the JRC - which respectively proxy for increases in building heights (vertical expansion) and impervious surface-type changes (horizontal expansion). These different data products help us to better understand the evolution of the built environment and urban form, while the underlying demographic data provide information regarding composition of urban population change, at different levels of economic development, built-upness, and population density. Combining these types of data yields important, high resolution spatial information that provides a more accurate understanding of urban processes, particularly in the context of climate change (as shown in Figure 1). Together these will help understand the form of urban change as well as the relationship between urban change, vulnerability and population distribution within and on the periphery of growing cities.

  2. Characterization of pore evolution in ceramics during creep failure and densification. Final report, April 15, 1984--April 14, 1995

    SciTech Connect

    Page, R.A.; Chan, K.S.

    1995-04-01

    This research program was divided into two phases, one involving creep cavitation, the other cavity evolution during sintering. In the former, work was aimed at determining the effect of microstructure and stress state upon creep cavitation, while in the latter, the principal objective was the characterization of pore evolution during sintering. In order to meet these objectives, the creep cavitation portion of the program was centered around small-angle neutron scattering, supplemented by electron microscopy and precision density measurements. The neutron scattering measurements yielded cavity nucleation and growth rates, and average pore, size, distribution, and morphology. These data were used to evaluate current cavitation models, and to implement improved modelling efforts. Additionally, stereoimaging analysis was used to determine grain boundary sliding displacements, which appear to be the critical driving force responsible for cavity nucleation and early growth. Effort in the pore sintering phase focussed on characterization of pore evolution during intermediate and final stage sintering of alumina using both single and multiple scattering techniques. Electron microscopy, density measurements, and mercury intrusion porosimetry measurements complemented the scattering results. The effects of sintering trajectory, green state, powder morphology, and additives were evaluated. These results were compared to current sintering models.

  3. Microwave-Assisted Alkali Pre-Treatment, Densification and Enzymatic Saccharification of Canola Straw and Oat Hull

    PubMed Central

    Agu, Obiora S.; Tabil, Lope G.; Dumonceaux, Tim

    2017-01-01

    The effects of microwave-assisted alkali pre-treatment on pellets’ characteristics and enzymatic saccharification for bioethanol production using lignocellulosic biomass of canola straw and oat hull were investigated. The ground canola straw and oat hull were immersed in distilled water, sodium hydroxide and potassium hydroxide solutions at two concentrations (0.75% and 1.5% w/v) and exposed to microwave radiation at power level 713 W and three residence times (6, 12 and 18 min). Bulk and particle densities of ground biomass samples were determined. Alkaline-microwave pre-treated and untreated samples were subjected to single pelleting test in an Instron universal machine, pre-set to a load of 4000 N. The measured parameters, pellet density, tensile strength and dimensional stability were evaluated and the results showed that the microwave-assisted alkali pre-treated pellets had a significantly higher density and tensile strength compared to samples that were untreated or pre-treated by microwave alone. The chemical composition analysis showed that microwave-assisted alkali pre-treatment was able to disrupt and break down the lignocellulosic structure of the samples, creating an area of cellulose accessible to cellulase reactivity. The best enzymatic saccharification results gave a high glucose yield of 110.05 mg/g dry sample for canola straw ground in a 1.6 mm screen hammer mill and pre-treated with 1.5% NaOH for 18 min, and a 99.10 mg/g dry sample for oat hull ground in a 1.6 mm screen hammer mill and pre-treated with 0.75% NaOH for 18 min microwave-assisted alkali pre-treatments. The effects of pre-treatment results were supported by SEM analysis. Overall, it was found that microwave-assisted alkali pre-treatment of canola straw and oat hull at a short residence time enhanced glucose yield. PMID:28952504

  4. Effect of the Amine Concentration on Phase Evolution and Densification in Printed Films Using Cu(II) Complex Ink.

    PubMed

    Choi, Yun-Hyuk; Hong, Seong-Hyeon

    2015-07-28

    The nucleation and growth behavior of Cu nanoparticles during thermal heating of Cu(II) complex inks for printed Cu metallization were investigated, particularly focusing on the effects of the amine concentration on the microstructure evolution and electrical conductivity. Herein, the dual effects of hexylamine as a reducing agent dissociating the carboxyl group from the precursor and a capping agent hindering the subsequent growth of Cu nuclei were confirmed. On the basis of such dual effects of amine, the sufficient complexation of the Cu(II) precursor with a high amine concentration in the ink led to the single-route growth of Cu nanoparticles during thermal heating, which resulted in the dense film with a narrow particle size distribution exhibiting a high electrical conductivity. The electrical conductivity of the film could be further enhanced by a reducing atmosphere with formic acid. Significantly, the understanding of the ink chemistry and the nucleation and growth kinetics in the metal ion complex or metal-organic decomposition (MOD) ink can provide the design rules for the formulation of the solution-type inks to control the microstructure of printed metallization.

  5. Microwave-Assisted Alkali Pre-Treatment, Densification and Enzymatic Saccharification of Canola Straw and Oat Hull.

    PubMed

    Agu, Obiora S; Tabil, Lope G; Dumonceaux, Tim

    2017-03-26

    The effects of microwave-assisted alkali pre-treatment on pellets' characteristics and enzymatic saccharification for bioethanol production using lignocellulosic biomass of canola straw and oat hull were investigated. The ground canola straw and oat hull were immersed in distilled water, sodium hydroxide and potassium hydroxide solutions at two concentrations (0.75% and 1.5% w/v) and exposed to microwave radiation at power level 713 W and three residence times (6, 12 and 18 min). Bulk and particle densities of ground biomass samples were determined. Alkaline-microwave pre-treated and untreated samples were subjected to single pelleting test in an Instron universal machine, pre-set to a load of 4000 N. The measured parameters, pellet density, tensile strength and dimensional stability were evaluated and the results showed that the microwave-assisted alkali pre-treated pellets had a significantly higher density and tensile strength compared to samples that were untreated or pre-treated by microwave alone. The chemical composition analysis showed that microwave-assisted alkali pre-treatment was able to disrupt and break down the lignocellulosic structure of the samples, creating an area of cellulose accessible to cellulase reactivity. The best enzymatic saccharification results gave a high glucose yield of 110.05 mg/g dry sample for canola straw ground in a 1.6 mm screen hammer mill and pre-treated with 1.5% NaOH for 18 min, and a 99.10 mg/g dry sample for oat hull ground in a 1.6 mm screen hammer mill and pre-treated with 0.75% NaOH for 18 min microwave-assisted alkali pre-treatments. The effects of pre-treatment results were supported by SEM analysis. Overall, it was found that microwave-assisted alkali pre-treatment of canola straw and oat hull at a short residence time enhanced glucose yield.

  6. Effect of Surface Densification on the Microstructure and Mechanical Properties of Powder Metallurgical Gears by Using a Surface Rolling Process.

    PubMed

    Peng, Jingguang; Zhao, Yan; Chen, Di; Li, Kiade; Lu, Wei; Yan, Biao

    2016-10-19

    Powder metallurgy (PM) components are widely used in the auto industry due to the advantage of net-shape forming, low cost, and high efficiency. Still, usage of PM components is limited in the auto industry when encountering rigorous situations, like heavy load, due to lower strength, hardness, wear resistance, and other properties compared to wrought components due to the existence of massive pores in the PM components. In this study, through combining the powder metallurgy process and rolling process, the pores in the PM components were decreased and a homogenous densified layer was formed on the surface, which resulted in the enhancement of the strength, hardness, wear resistance, and other properties, which can expand its range of application. In this paper, we study the impact of different rolling feeds on the performance of the components' surfaces. We found that with the increase of the rolling feed, the depth of the densified layer increased.

  7. Snow accumulation, surface height change, and firn densification at Summit, Greenland: Insights from 2 years of in situ observation

    NASA Astrophysics Data System (ADS)

    Dibb, Jack E.; Fahnestock, Mark

    2004-12-01

    Weekly measurements of surface height change were made at an accumulation forest of 100 stakes at Summit, Greenland, over a 2-year period (17 August 2000 to 8 August 2002). On average, the surface height relative to the stakes increased 64 (±4.8) cm in the first year and 65 (±5.3) cm in the second, identical to the average (65 ± 4.5 cm yr-1) previously reported for the period 1991-1995 in a similar forest 28 km to the southwest. The continuous 2-year data set indicates that the rate of surface rise was not constant, with the summers of 2001 and 2002 both showing markedly slower increases. On-site weather observations suggest that more new snow fell during the summer months than in any other season, consistent with results from previous snow pit and modeling studies yet apparently at odds with the slow rate of height increase. Density profiles from a series of 1-m-deep snow pits sampled monthly reveal that the thickness of the most recent year of accumulated snow (25 cm water equivalent) decreased rapidly between late May and early July, and the layers remained thin through early September. The thinning of the top year is clearly due to compaction in the snowpack. Combining the observed variations in annual layer thickness with a linear height increase based on assumed constant accumulation at 0.18 cm d-1 explains much of the variation in surface height found in the stake measurements. Estimated surface height changes can be forced to exactly match the stake measurements by combining changes in annual layer thickness with a variable accumulation rate over the intervals between pits. This exercise suggests that during the 2 years of this study a consistent seasonal pattern in accumulation was not apparent, rather the intervals indicated to have had enhanced accumulation in the first year (August-October and March-April) apparently had reduced accumulation in the second year.

  8. On the densification of cubic ZrO{sub 2} nanocondensates by capillarity force and turbostratic C–Si–H multiple shell

    SciTech Connect

    Wu, Chao-Hsien; Chen, Shuei-Yuan; Shen, Pouyan

    2013-04-15

    A turbostratic C–Si–H lamellar phase with 0.35–0.39 nm interspacing and ZrO{sub 2} condensates having cubic (c), tetragonal and monoclinic structures stabilized by increasing particle size were synthesized by pulsed laser ablation on Zr plate in TEOS and characterized by X-ray/electron diffraction and optical spectroscopy. The c-ZrO{sub 2} phase ca. 10% denser than the ambient lattice was stabilized as 3–10 nm sized cubo-octahedral nanoparticles but as abnormal large-sized (up to 30 nm) ones when encapsulated by the C{sub 1−x}Si{sub x}:H multiple shell with defective graphite-like structure units to exert an effective compressive stress. The potential application of such core–shell nanostructure with enhanced binding of Zr and O ions and implication for natural dynamic occurrence of the C{sub 1−x}Si{sub x}:H phase are addressed. - Graphical abstract: Lattice image of a typical cubic-ZrO{sub 2} particle densified by the turbostratic Si{sub x}C{sub 1−x}:H shell. Highlights: ► Turbostratic C–Si–H lamellar phase and ZrO{sub 2} condensates were synthesized by PLA. ► The c-ZrO{sub 2} phase ca. 10% denser than the ambient lattice was stabilized as 3–10 nm. ► The c-ZrO{sub 2} particles up to 30 nm were densified when encapsulated by the C{sub 1−x}Si{sub x}:H multiple shell. ► Tight ion binding of the c-ZrO{sub 2} due to capillarity force and turbostratic shell.

  9. How well is firn densification represented by a physically-based multilayer model? Model evaluation for the Devon Ice Cap, Nunavut, Canada

    NASA Astrophysics Data System (ADS)

    Gascon, G.; Sharp, M. J.; Burgess, D. O.; Bezeau, P. L.; Bush, A. B.; Morin, S.; Lafaysse, M.

    2013-12-01

    Mass loss from polar ice sheets and ice caps contributes significantly to eustatic sea level rise and has been increasing since the beginning of the 21st century. Refreezing and retention of meltwater in firn currently limit the amount of surface runoff from polar ice sheets and ice caps that reaches the oceans. Evaluation of how accurately snowpack models can capture the hydrological processes that govern refreezing and retention is critical to determining how well they are likely to simulate future glacier mass balance changes and their implications for global sea level. Here, we compare simulations with the Crocus snowpack model with the evolving firn stratigraphy recorded in 14 firn cores drilled at 4 elevations in the accumulation zone of the Devon Ice Cap, Canada during a period of rapid summer warming between 2004 and 2012. Simulations were forced with a combination of surface meteorological observations and NCEP's NARR reanalysis data. Crocus performs relatively well at all sites, with modeled mass bias in the upper 15 m of the firn ranging between -2 and +16% relative to observations. Model over-estimation of mass retention is caused by a combination of excess refreezing of meltwater in the upper 4 m of the firn, and underestimation of the preservation of residual firn beneath thick ice layers due to overestimation of vertical flow of meltwater through such layers.

  10. Influence of La2Zr2O7 Additive on Densification and Li+ Conductivity for Ta-Doped Li7La3Zr2O12 Garnet

    NASA Astrophysics Data System (ADS)

    Huang, Xiao; Shen, Chen; Rui, Kun; Jin, Jun; Wu, Meifen; Wu, Xiangwei; Wen, Zhaoyin

    2016-10-01

    A high-conductivity solid electrolyte, La2Zr2O7 (LZO) added to Li6.4La3Zr1.4Ta0.6O12 (LLZTO), was prepared via conventional solid-state reactions and sintered at 1100°C for 10 h, which is tens of Celsius degrees lower than the typical sintering temperature for LLZTO. The addition of LZO did not bring in any impurities. LZO acted as a sintering aid to densify the LLZTO from a relative density of 77% up to 90%, which was comparable to that of pure LLZTO sintered at 1200°C. The 6 wt.% LZO-LLZTO samples sintered at 1100°C and 1200°C exhibited a room-temperature conductivity of 1.92 × 10-4 S/cm and 5.84 × 10-4 S/cm, respectively, which were higher than that of pure LLZTO samples. Glass-like phases observed at grain boundaries in LZO-LLZTO ceramics indicated that LZO promoted the formation of the glass-like phases binding together LLZTO grains and thus leading to enhanced density and conductivity of LLZTO.

  11. The Impact of Pore Structure on Densification Efficiency of 2-D Carbon-Carbon Composites and Its Relationship to Mechanical Properties

    DTIC Science & Technology

    2011-03-01

    protecting them from brittle fracture. Carbon-carbon composites also have a very high fracture toughness which causes them to be very resistant to...crack propagation while their high fatigue tolerance and resistance to creep give these composites an almost infinite service life [18]. However...Carbon-carbon composites have two main weaknesses. The first is their poor oxidation resistance [7]. They are not able to maintain strength or

  12. Direct observation of large shock impedance jump upon shock-induced densification of powdered materials confirmed by in situ shock pressure and particle velocity measurements

    NASA Astrophysics Data System (ADS)

    Kobayashi, Takamichi

    2014-07-01

    Shock pressure and particle velocity measurements have been performed separately on a powdered material under a similar shock loading condition by employing time-resolved luminescence spectroscopy and velocity interferometry (VISAR). Shock pressure measurement adopts the pressure-shift characteristic of ruby crystal that is used as a window material. Exactly the same shock condition could be realized for the particle velocity measurement by using a sapphire crystal as a window. A good agreement between the results of two different measurements has been obtained and they indicate a 7 times or more increase in shock impedance of the powdered material.

  13. Investigation of the Deposition and Densification Parameters on the Mechanical Properties of Pressurized Spray Deposited (PSD) 3-D Printed Ceramic Components

    SciTech Connect

    Menchhofer, Paul A.; Becker, Benjamin

    2016-07-28

    Oak Ridge National Laboratory (ORNL) and HotEnd Works teamed to investigate the use of pressurized spray deposition (PSD) technology for the production of ceramic parts via additive manufacturing. Scanning electron microscopy of sintered parts provided by HotEnd Works revealed voids large enough to compromise the mechanical properties of PSD manufactured parts. Scanning electron microscopy and particle size analysis of the alumina oxide powder feedstocks indicated that the powders contained some large particles and some agglomerations in the powder. Further classification of the powder feedstocks and removal of the agglomerates by sonication in the liquid used for the PSD process are recommended. Analysis of sintered parts indicated that the sonic modulus for the alumina part is consistent with other known values for alumina. The density for this part was determined by standard Archimedes immersion density methods and was found to be > 99.7 % of the theoretical density for pure alumina.

  14. Studies on densification, mechanical, micro-structural and structure–properties relationship of magnesium aluminate spinel refractory aggregates prepared from Indian magnesite

    SciTech Connect

    Ghosh, Chandrima; Ghosh, Arup; Haldar, Manas Kamal

    2015-01-15

    The present work intends to study the development of magnesium aluminate spinel aggregates from Indian magnesite in a single firing stage. The raw magnesite has been evaluated in terms of chemical analysis, differential thermal analysis, thermogravimetric analysis, infrared spectroscopy, and X-ray diffraction. The experimental batch containing Indian magnesite and calcined alumina has been sintered in the temperature range of 1550 °C–1700 °C. The sintered material has been characterized in terms of physico-chemical properties like bulk density, apparent porosity, true density, relative density and thermo-mechanical/mechanical properties like hot modulus of rupture, thermal shock resistance, cold modulus of rupture and structural properties by X-ray diffraction in terms of phase identification and evaluation of crystal structure parameters of corresponding phases by Rietveld analysis. The microstructures developed at different temperatures have been analyzed by field emission scanning electron microscope study and compositional analysis of the developed phase has been carried out by energy dispersive X-ray study. - Highlights: • The studies have been done to characterize the developed magnesium aluminate spinel. • The studies reveal correlation between refractory behavior of spinel and developed microstructures. • The studies show the values of lattice parameters of developed phases.

  15. A newly-developed effective direct current assisted sintering technique for electrolyte film densification of anode-supported solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Liu, Yajie; Hao, Xiaoming; Wang, Zhenhua; Wang, Jiawei; Qiao, Jinshuo; Yan, Yiming; Sun, Kening

    2012-10-01

    In order to lower the sintering temperature and shorten firing time, a novel, effective and facile technique has been developed for sintering Yttria-stabilized zirconia (YSZ) electrolyte thin film. Herein this technique, which employs a weak direct current (DC), is used for the first time in the manufacture of the anode-supported solid oxide fuel cell (SOFC). A single cell is directly assembled using a pre-sintered anode/electrolyte and screen printed cathode and subsequently sintered under electric assistance from room temperature to 800 °C at a heating rate of 5 °C min-1. A fully dense YSZ electrolyte film can be observed by scanning electron microscopy (SEM) and the open circuit voltages (OCVs) are in accordance with theoretical values, confirming that the cell possesses a dense YSZ film. Using hydrogen fuel, the maximum power density of this cell was 0.8, 1.1 and 1.4 W cm-2 at 650, 700 and 750 °C, respectively. We believe this DC assisted sintering technique (DC-AST) may not only reduce the cost, but also maintain the anode nanostructure, thus offering a potentially useful manufacturing technique for SOFCs.

  16. A molecular dynamics study of densification mechanisms in calcium silicate glasses CaSi2O5 and CaSiO3 at pressures of 5 and 10 GPa.

    PubMed

    Mead, R N; Mountjoy, G

    2006-10-21

    Molecular dynamics is used to obtain models of (CaO)(x)(SiO(2))(1-x) glasses, with compositions CaSi(2)O(5) (x=0.33) and CaSiO(3) (x=0.50), at pressures of 5 and 10 GPa. At 5 GPa there are increases in Ca and Si coordinations for x=0.33, whereas for x=0.50 there is distortion of CaO(N) polyhedra but no substantial change in coordination. At 10 GPa the Ca coordination increases by approximately 20% for x=0.33 and by approximately 10% for x=0.50. This increase is due to increased Ca bonds to bridging oxygens (O(b)), since nonbridging oxygens (O(nb)) are already highly bonded to Ca, and the proportion of O(nb) is decreasing due to changes in the silica network. At 10 GPa there are approximately 20% of fivefold and a few percent of sixfold coordinated Si. Since the new Si-O bonds involve the conversion of O(nb) to O(b), there is a corresponding increase in the network connectivity. The x=0.50 glass is more resistant to deformation because there is less possibility to convert O(nb) to O(b) due to lower Si content. The changes in Ca-O, Si-Ca, and Ca-Ca correlations are predicted to produce changes in the x-ray diffraction structure factor S(Q), including a shift of the first sharp diffraction peak to higher Q values.

  17. Crystallization, densification and dielectric properties of CaO–MgO–Al{sub 2}O{sub 3}–SiO{sub 2} glass with ZrO{sub 2} as nucleating agent

    SciTech Connect

    Hsiang, Hsing-I; Yung, Shi-Wen; Wang, Chung-Ching

    2014-12-15

    SEM micrographs for the pure CaO–MgO–Al{sub 2}O{sub 3}–SiO{sub 2} glass sintered at 850–1000 °C (a) 850 °C, (b) 900 °C, (c) 950 °C, (d) 1000 °C. - Highlights: • ZrO{sub 2} effects on the crystallization of LTCC glass system were investigated. • ZrO{sub 2} effects on the dielectric properties of LTCC glass system were investigated. • LTCC with a dielectric constant of 6.65 and a low dielectric loss can be obtained. - Abstract: The zirconium oxide effects on the crystallization and dielectric properties of CaO–MgO–Al{sub 2}O{sub 3}–SiO{sub 2} (CMAS) glass were investigated. The results showed that phyllosiloxide and anorthite crystallites were observed in sequence during sintering. For glass added with 8 wt% ZrO{sub 2}, homogeneously dispersed tetragonal ZrO{sub 2} crystallites were observed at 850 °C. The as-prepared CMAS glass–ceramics exhibited a dielectric constant of about 6–7 and a dielectric loss below 0.005 at 100 MHz. The dielectric properties of CMAS glass with 8 wt% ZrO{sub 2} sintered at 850 °C show a low dielectric constant of 6.65 and a dielectric loss tangent of about 2.5 × 10{sup −3}, which provides a promising candidate for LTCC applications.

  18. Microstructural Modeling and Toughening of Si3N4 Ceramics for High Temperature Engine Applications

    DTIC Science & Technology

    1993-08-01

    content The error * was used as one densification bars are a 95 % confidence interval. additive . An equimolar mixture of ytterbia and samaria was the...low additive levels Two HIP densification processes which produced R-curve in HIP silicon nitride were demonstrated. The first densification process...eutectic within a matrix that had a single rare earth as the densification additive . The agglomerates were formed by spray drying the powders. Before

  19. Forced chemical vapor infiltration of tubular geometries: Modeling, design, and scale-up

    SciTech Connect

    Stinton, D.P.; Besmann, T.M.; Matlin, W.M.; Starr, T.L.; Curtain, W.A.

    1995-10-01

    The development of thick-walled, tubular ceramic composites has involved investigations of different fiber architectures and fixturing to obtain optimal densification and mechanical properties. The current efforts entail modeling of the densification process in order to increase densification uniformity and decrease processing time. In addition, the process is being scaled to produce components with a 10 cm outer diameter.

  20. Smooth-Surfaced Carbon/Carbon Reflector Panels

    NASA Technical Reports Server (NTRS)

    Schmitigal, Wesley P.; Jacoy, Paul J.; Porter, Christopher C.; Hickey, Gregory S.

    1992-01-01

    Surface-densification technique integral to fabrication of reflective, lightweight, low-outgassing radio-antenna-reflector panels including carbon/carbon surface laminates supported by carbon/carbon core structures. Densification prevents "print-through" of carbon fibers on surface. When properly densified, surface polished to smooth finish.

  1. Minuteman 3/Mark 12A reentry carbon-carbon nosetip production

    NASA Astrophysics Data System (ADS)

    1980-06-01

    One densified billet out of each 36 processed is randomly selected and subjected to the Production Lot Sampling Tests specified in paragraph 5.2.3 of the Equipment Test Plan, AVSD-0325-78-CR dated 14 March 1979. During this report several PLS billets were tested. These are as follows: PLS-5 from densification Lot 6, PLS-6 from densification Lot 8, PLS-7 from densification Lot 9, PLS-8 from densification Lot 10 and PLS-9 from densification Lot 11. All data has been compiled on previously presented Figures 7, 8, and 9 from the Equipment Test Plan, and included herein as the General Test Report, Production Lot Sampling, in accordance with CDRL Sequence Number 081A2.

  2. Computerized Powder Metallurgy (P/M) Forging Techniques

    DTIC Science & Technology

    1980-09-01

    these rules to complex components requires an understanding of the behavior of porous materials with respect to densification, flow and fracture and...shape for densification and non-aggravating metal flow . This was accomplished by recognizing characteristic deformation modes in the input shape for...FORCINGS 27 3.1 Introduction 27 iv ’ 3.2 Basic Equations 28 3.2.1 Yield Behavior 28 3.2.2 Flow Rule 29 3.2.3 Densification 31 3.3 Application

  3. Hardness of dense beta-Si3N4

    NASA Technical Reports Server (NTRS)

    Greskovich, C.; Yeh, H. C.

    1983-01-01

    The effects of small changes in the concentration of an oxygen content densification aid on the room temperature microhardness of hot isostatically pressed and sintered beta-Si3N4 ceramics are studied. The compositions studied were Si3N4 containing 7 wt. pct BeSiN2, a fixed nonoxide densification aid, and 1.9-3.7 wt. pct oxygen as a second, variable densification aid. A proportional relationship between high density and high oxygen content, regardless of heat treatment type, is noted.

  4. Manufacturing and mechanical properties of calcium phosphate biomaterials

    NASA Astrophysics Data System (ADS)

    Laasri, S.; Taha, M.; Hlil, E. K.; Laghzizil, A.; Hajjaji, A.

    2012-10-01

    In this study, the influence of powder manufacturing and sintering temperature on densification, microstructure and mechanical properties of dense β-tricalcium phosphate (β-TCP) bioceramic has been studied. Densification results show that the β-TCP can be sintered at 1160 °C for 3 hours to have good density and high performance mechanic properties (Vickers hardness, toughness and Young's modulus). X-ray diffraction and SEM microscopy are used to check the microstructure changes during the sintering temperature. The used processing of β-TCP ceramic improved its densification, microstructure homogeneity and mechanical properties.

  5. Hardness of dense beta-Si3N4

    NASA Technical Reports Server (NTRS)

    Greskovich, C.; Yeh, H. C.

    1983-01-01

    The effects of small changes in the concentration of an oxygen content densification aid on the room temperature microhardness of hot isostatically pressed and sintered beta-Si3N4 ceramics are studied. The compositions studied were Si3N4 containing 7 wt. pct BeSiN2, a fixed nonoxide densification aid, and 1.9-3.7 wt. pct oxygen as a second, variable densification aid. A proportional relationship between high density and high oxygen content, regardless of heat treatment type, is noted.

  6. Systematics of compaction for porous metal and metal-oxide systems

    NASA Astrophysics Data System (ADS)

    Fredenburg, D. A.; Lang, J. M.; Coe, J. D.; Scharff, R. J.; Dattelbaum, D. M.; Chisolm, E. D.

    2017-01-01

    The effects of particle morphology and initial density is examined with respect to the shock densification response of initially porous metal (Cu) and metal-oxide (CeO2) materials. Specifically, the ability of a continuum-level compaction model to capture the measured densification trends as a function of initial density and particle morphology are investigated. Particle morphology is observed to have little effect on the densification response of both Cu and CeO2, while initial density appears to have a stronger effect. In terms of continuum-level compaction strength, Cu and CeO2 exhibit dissimilar trends.

  7. Determination of densified biomass mass properties using 3D laser scanning and image analysis

    USDA-ARS?s Scientific Manuscript database

    Biomass densification is viewed as the indispensable feedstock preprocessing operation for efficient transport, storage, material flow through machines, and handling activities. Accurate mass properties of densified biomass such as surface area, volume, and envelope density form fundamental data for...

  8. Application of 3D Scanned Imaging Methodology for Volume, Surface Area, and Envelope Density Evaluation of Densified Biomass

    USDA-ARS?s Scientific Manuscript database

    Measurement of surface area, volume, and density is an essential for quantifying, evaluating, and designing the biomass densification, storage, and transport operations. Acquiring accurate and repeated measurements of these parameters for hygroscopic densified biomass are not straightforward and on...

  9. Modeling powder encapsulation in dosator-based machines: I. Theory.

    PubMed

    Khawam, Ammar

    2011-12-15

    Automatic encapsulation machines have two dosing principles: dosing disc and dosator. Dosator-based machines compress the powder to plugs that are transferred into capsules. The encapsulation process in dosator-based capsule machines was modeled in this work. A model was proposed to predict the weight and length of produced plugs. According to the model, the plug weight is a function of piston dimensions, powder-bed height, bulk powder density and precompression densification inside dosator while plug length is a function of piston height, set piston displacement, spring stiffness and powder compressibility. Powder densification within the dosator can be achieved by precompression, compression or both. Precompression densification depends on the powder to piston height ratio while compression densification depends on piston displacement against powder. This article provides the theoretical basis of the encapsulation model, including applications and limitations. The model will be applied to experimental data separately.

  10. Comparison of the halving of tablets prepared with eccentric and rotary tablet presses.

    PubMed

    Sovány, T; Kása, P; Pintye-Hódi, K

    2009-01-01

    The aim of this study was to compare the densification of powder mixtures on eccentric and rotary tablet presses and to establish relationships with the halving properties of the resulting scored tablets. This is an important problem because the recent guidelines of EU require verification of the equal masses of tablet halves. The models of Walker, Heckel, and Kawakita were used to describe the powder densification on the two machines. The calculated parameters revealed that the shorter compression cycle of rotary machines results in poorer densification and lower tablet hardness at a given compression force. This is manifested in poorer halving properties, which are influenced mainly by the hardness. Better densification improves the halving even at lower tablet hardness. This demonstrates that these parameters can be good predictors of tablet halving properties.

  11. Preparation of transparent oxyapatite ceramics by combined use of freeze-drying and spark-plasma sintering.

    PubMed

    Chesnaud, A; Bogicevic, C; Karolak, F; Estournès, C; Dezanneau, G

    2007-04-21

    Lanthanum silicate oxyapatites, ion-conducting materials presenting a strong aversion against densification, have been obtained in the form of dense transparent ceramics, by combining the beneficial use of freeze-drying and spark plasma sintering methods.

  12. Fuel cell system with interconnect

    DOEpatents

    Liu, Zhien; Goettler, Richard; Delaforce, Philip Mark

    2016-03-08

    The present invention includes a fuel cell system having an interconnect that reduces or eliminates diffusion (leakage) of fuel and oxidant by providing an increased densification, by forming the interconnect as a ceramic/metal composite.

  13. Lunar regolith and structure mechanics

    NASA Technical Reports Server (NTRS)

    Barnes, Frank; Ko, Hon-Yim; Sture, Stein; Carter, Tyrone R.; Evenson, Kraig A.; Nathan, Mark P.; Perkins, Steve W.

    1991-01-01

    The topics are presented in viewgraph form and include the following: modeling of regolith-structure interaction in extraterrestrial constructed facilities; densification of lunar soil simulant; and vibration assisted penetration of lunar soil simulant.

  14. Mechanical Properties of Cellular Materials

    SciTech Connect

    Solem, J.C.; Dienes, J.K.

    1999-07-09

    The authors calculated the stress-strain relation for elastomeric foam from an ab initio theory, which shows that the plateau and densification regions should be described by a hyperbola. The theory seems to agree reasonably well with experiment.

  15. Creep of metal-type organic compounds. 4: Application to hot isostatic pressing

    SciTech Connect

    Davies, G.C.; Jones, D.R.H.

    1997-02-01

    Hot isostatic pressing (HIP) experiments using the metal analogue materials camphene and succinonitrile are described. Data obtained previously from uniaxial creep experiments are used in densification rate equations for HIP taken from the literature, and the predicted densification behavior is compared with experimental data. The HIP equations are then modified to include two different representations of the friction stress arising from a dispersed phase of fine, hard particles. In each case the modified theory adequately describes the experimental data.

  16. In situ ion-beam analysis and modification of sol-gel zirconia thin films

    SciTech Connect

    Levine, T.E.; Yu, Ning; Kodali, P.; Walter, K.C.; Nastasi, M.; Tesmer, J.R.; Maggiore, C.J.; Mayer, J.W.

    1995-05-01

    We report the investigation of ion-beam-induced densification of sol-gel zirconia thin films via in situ ion backscattering spectrometry. We have irradiated three regions of a sample with neon, argon, and krypton ions. For each ion species, a series of irradiation and analysis steps were performed using an interconnected 3 MV tandem accelerator. The technique offers the advantages of minimizing the variation of experimental parameters and sequentially monitoring the densification phenomenon with increasing ion dose.

  17. Use of silicon in liquid sintered silicon nitrides and sialons

    DOEpatents

    Raj, R.; Baik, S.

    1984-12-11

    This invention relates to the production of improved high density nitrogen based ceramics by liquid-phase densification of silicon nitride or a compound of silicon-nitrogen-oxygen-metal, e.g. a sialon. In the process and compositions of the invention minor amounts of finely divided silicon are employed together with the conventional liquid phase producing additives to enhance the densification of the resultant ceramic. 4 figs.

  18. Use of free silicon in liquid phase sintering of silicon nitrides and sialons

    DOEpatents

    Raj, R.; Baik, S.

    1985-11-12

    This invention relates to the production of improved high density nitrogen based ceramics by liquid-phase densification of silicon nitride or a compound of silicon-nitrogen-oxygen-metal, e.g. a sialon. In the process and compositions of the invention minor amounts of finely divided silicon are employed together with the conventional liquid phase producing additives to enhance the densification of the resultant ceramic. 4 figs.

  19. Use of silicon in liquid sintered silicon nitrides and sialons

    DOEpatents

    Raj, Rishi; Baik, Sunggi

    1984-12-11

    This invention relates to the production of improved high density nitrogen based ceramics by liquid-phase densification of silicon nitride or a compound of silicon-nitrogen-oxygen-metal, e.g. a sialon. In the process and compositions of the invention minor amounts of finely divided silicon are employed together with the conventional liquid phase producing additives to enhance the densification of the resultant ceramic.

  20. Use of free silicon in liquid phase sintering of silicon nitrides and sialons

    DOEpatents

    Raj, Rishi; Baik, Sunggi

    1985-11-12

    This invention relates to the production of improved high density nitrogen based ceramics by liquid-phase densification of silicon nitride or a compound of silicon-nitrogen-oxygen-metal, e.g. a sialon. In the process and compositions of the invention minor amounts of finely divided silicon are employed together with the conventional liquid phase producing additives to enhance the densification of the resultant ceramic.

  1. Composite Ceramic Superconducting Wires for Electric Motor Applications

    DTIC Science & Technology

    1990-01-31

    densification , as Y-123 filaments can reach densities estimated around 95 % in only two seconds. Densification is accompanied by dramatic...rings, but to find a system that will work. Additional brush testing that still needs to be done is to look at the effects of speed and brush pressure on...D~T IC ,LL COPY cvm i CJ SIXTH QUARTERLY REPORT II • ’ FOR THE PROJECT I "COMPOSITE CERAMIC SUPERCONDUCTINGiWIRES FOR ELECTRIC MOTOR APPLICATIONS" 2

  2. Damages to optical silica glass: processes and mechanisms

    NASA Astrophysics Data System (ADS)

    Luo, Sheng-Nian; Zheng, Lianqing; An, Qi; Wu, Heng-An; Xia, Kaiwen; Ni, Sidao

    2007-01-01

    We present recent results of molecular dynamics simulations to illustrate the processes and mechanisms in damages to silica glass, including densification, cavitation, fragmentation and agglomeration via photon, electron, ion and neutron radiations and stresses. Radiation of glass creates point defects (vacancies and interstitials), and subsequent structure relaxation induces densification. Nanovoid below a certain size and rapid-quenching of silica liquid can also densify a glass. Hot spots due to photon-absorbing impurities in glass may cause local densification and cavitation as well. Densification can also be induced by compressional stress, and spall, by tensile stress. The densified glasses, regardless of the exact processes, share similar structural and vibrational properties, for example, the five-fold coordinated Si atoms. Densification is essentially a kinetic frustration during structure relaxation driven by excessive free energy, e.g., due to defects or stresses. The point-defect mechanism is dominant for densification without compression and complemented by thermal spike mechanism in thermal processes. Defects, thermal effects and stresses may interplay in a general damage process in silica glass.

  3. Fabrication of Mechanically Tunable and Bioactive Metal Scaffolds for Biomedical Applications.

    PubMed

    Jung, Hyun-Do; Lee, Hyun; Kim, Hyoun-Ee; Koh, Young-Hag; Song, Juha

    2015-12-08

    Biometal systems have been widely used for biomedical applications, in particular, as load-bearing materials. However, major challenges are high stiffness and low bioactivity of metals. In this study, we have developed a new method towards fabricating a new type of bioactive and mechanically reliable porous metal scaffolds-densified porous Ti scaffolds. The method consists of two fabrication processes, 1) the fabrication of porous Ti scaffolds by dynamic freeze casting, and 2) coating and densification of the porous scaffolds. The dynamic freeze casting method to fabricate porous Ti scaffolds allowed the densification of porous scaffolds by minimizing the chemical contamination and structural defects. The densification process is distinctive for three reasons. First, the densification process is simple, because it requires a control of only one parameter (degree of densification). Second, it is effective, as it achieves mechanical enhancement and sustainable release of biomolecules from porous scaffolds. Third, it has broad applications, as it is also applicable to the fabrication of functionally graded porous scaffolds by spatially varied strain during densification.

  4. The processing and potential applications of porous silicon

    SciTech Connect

    Syyuan Shieh.

    1992-07-01

    Stability of a cylindrical pore under the influence of surface energy is important for porous silicon (PS) processing in the integrated circuit industry. Once the zig-zag cylindrical pores of porous silicon or oxidized porous silicon (OPS) are unstable and breakup into rows of isolated spherical pores, oxidation of PS and densification/nitridation of OPS become difficult. Swing to difficulty transport of reactant gas (O{sub 2}, NH{sub 3}) or the trapped gas (for densification of OPS). A first order analysis of the stability of a cylindrical pore or cylinder is considered first. Growth of small sinusoidal perturbations by viscous flow or evaporation/condensation result in dependence of perturbation growth rate on perturbation wavelength. Rapid thermal oxidation (RTO) of porous silicon is proposed as an alternative for the tedious two-step 300 and 800C oxidation process. Transmission electron microscopy, energy dispersive spectroscopy ESCA are used for quality control. Also, rapid thermal nitridation of oxidized porous silicon in ammonia is proposed to enhance OPS resistance to HF solution. Pores breakup of OPS results in a trapped gas problem during densification. Wet helium is proposed as OPS densification ambient gas to shorten densification time. Finally, PS is proposed to be an extrinsic gettering center in silicon wafers. The suppression of oxidation-induced stacking faults is used to demonstrate the gettering ability. Possible mechanism is discussed.

  5. The processing and potential applications of porous silicon

    SciTech Connect

    Shieh, Syyuan

    1992-07-01

    Stability of a cylindrical pore under the influence of surface energy is important for porous silicon (PS) processing in the integrated circuit industry. Once the zig-zag cylindrical pores of porous silicon or oxidized porous silicon (OPS) are unstable and breakup into rows of isolated spherical pores, oxidation of PS and densification/nitridation of OPS become difficult. Swing to difficulty transport of reactant gas (O2, NH3) or the trapped gas (for densification of OPS). A first order analysis of the stability of a cylindrical pore or cylinder is considered first. Growth of small sinusoidal perturbations by viscous flow or evaporation/condensation result in dependence of perturbation growth rate on perturbation wavelength. Rapid thermal oxidation (RTO) of porous silicon is proposed as an alternative for the tedious two-step 300 and 800C oxidation process. Transmission electron microscopy, energy dispersive spectroscopy ESCA are used for quality control. Also, rapid thermal nitridation of oxidized porous silicon in ammonia is proposed to enhance OPS resistance to HF solution. Pores breakup of OPS results in a trapped gas problem during densification. Wet helium is proposed as OPS densification ambient gas to shorten densification time. Finally, PS is proposed to be an extrinsic gettering center in silicon wafers. The suppression of oxidation-induced stacking faults is used to demonstrate the gettering ability. Possible mechanism is discussed.

  6. Sintering kinetic studies in nonstoichiometric strontium titanate ceramics

    SciTech Connect

    Amaral, Luis; Senos, Ana M.R. Vilarinho, Paula M.

    2009-02-04

    The effect of nonstoichiometry on the densification of SrTiO{sub 3} ceramics with Sr/Ti ratios from 0.997 to 1.02 was systematically addressed. The kinetics of densification was studied by dilatometric analysis. X-ray diffraction, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used for crystallographic and microstructure characterization. Ti excess enhanced matter transport during sintering whereas Sr excess decreased it. The shrinkage rate and average grain size increased with the decrease of Sr/Ti ratio. Close values of the activation energy for the initial densification and the near constant onset temperature for densification suggest that identical transport mechanisms control the densification of all the compositions. Small excesses of TiO{sub 2} and SrO were mostly incorporated into the perovskite lattice inducing alterations in the defect chemistry of the material and the mass transport during sintering is controlled by Sr vacancies. Very small stoichiometric variations have a strong influence on the sintering kinetics and resulting microstructure of ST ceramics.

  7. Sintering behavior of doped ZnO powders for high field varistors

    SciTech Connect

    Ghirlanda, M.

    1990-08-01

    The sintering of ZnO varistor precursor powders, doped with Co, Mn and different concentrations of Bi and Al, is investigated and discussed in relation with sintering models. One purpose of the present study is to provide information valuable for the fabrication of high field varistors. As the fundamental parameter of these electronic components is the breakdown voltage per unit of thickness, which is determined by the number of grain boundaries per linear dimension, the grain size and the sintered density are crucial variables, and the sintering is a central step in the manufacturing of such varistors. Sintering experiments performed at constant heating rate in a loading dilatometer provide data on the densification and creep of the compacted powders. Another goal of the present study is to provide an experimental basis for the interpretation of the evolution of the ratio between densification rate and creep rate in terms of competition between densification and microstructure coarsening. This is accomplished by taking advantage of the variety of sintering behaviors that takes place in the system ZnO-Bi-Al: the comparison of these behaviors allows us to correlate the macroscopic sintering parameters to the evolution of the microstructure. It results that, while in non-doped powders densification and coarsening develop in a balanced way, resulting in the constancy of the ratio between densification rate and creep rate, the effect of the dopants on the sintering kinetics alters such a balance, leading this ratio to vary. 17 figs.

  8. One step sintering of homogenized bauxite raw material and kinetic study

    NASA Astrophysics Data System (ADS)

    Gao, Chang-he; Jiang, Peng; Li, Yong; Sun, Jia-lin; Zhang, Jun-jie; Yang, Huan-ying

    2016-10-01

    A one-step sintering process of bauxite raw material from direct mining was completed, and the kinetics of this process was analyzed thoroughly. The results show that the sintering kinetics of bauxite raw material exhibits the liquid-phase sintering behavior. A small portion of impurities existed in the raw material act as a liquid phase. After X-ray diffraction analyses, scanning electron microscopy observations, and kinetics calculations, sintering temperature and heating duration were determined as the two major factors contributing to the sintering process and densification of bauxite ore. An elevated heating temperature and longer duration favor the densification process. The major obstacle for the densification of bauxite material is attributed to the formation of the enclosed blowhole during liquid-phase sintering.

  9. Fabrication and characterization of Si3N4 ceramics without additives by high pressure hot pressing

    NASA Technical Reports Server (NTRS)

    Shimada, M.; Tanaka, A.; Yamada, T.; Koizumi, M.

    1984-01-01

    High pressure hot-pressing of Si3N4 without additives was performed using various kinds of Si3N4 powder as starting materials, and the relation between densification and alpha-beta phase transformation was studied. The temperature dependences of Vickers microhardness and fracture toughness were also examined. Densification of Si3N4 was divided into three stages, and it was found that densification and phase transformation of Si3N4 under pressure were closely associated. The results of the temperature dependence of Vickers microhardness indicated that the high-temperature hardness was strongly influenced not only by the density and microstructure of sintered body but also by the purity of starting powder. The fracture toughness values of Si3N4 bodies without additives were 3.29-4.39 MN/m to the 3/2 power and independent of temperature up to 1400 C.

  10. Optimal Base Station Density of Dense Network: From the Viewpoint of Interference and Load

    PubMed Central

    Feng, Zhiyong

    2017-01-01

    Network densification is attracting increasing attention recently due to its ability to improve network capacity by spatial reuse and relieve congestion by offloading. However, excessive densification and aggressive offloading can also cause the degradation of network performance due to problems of interference and load. In this paper, with consideration of load issues, we study the optimal base station density that maximizes the throughput of the network. The expected link rate and the utilization ratio of the contention-based channel are derived as the functions of base station density using the Poisson Point Process (PPP) and Markov Chain. They reveal the rules of deployment. Based on these results, we obtain the throughput of the network and indicate the optimal deployment density under different network conditions. Extensive simulations are conducted to validate our analysis and show the substantial performance gain obtained by the proposed deployment scheme. These results can provide guidance for the network densification. PMID:28891997

  11. Seeded optically driven avalanche ionization in molecular and noble gases

    NASA Astrophysics Data System (ADS)

    Polynkin, Pavel; Pasenhow, Bernard; Driscoll, Nicholas; Scheller, Maik; Wright, Ewan M.; Moloney, Jerome V.

    2012-10-01

    We report experimental and numerical results on the dual laser-pulse plasma excitation in molecular and noble gases at atmospheric pressure. Dilute plasma channels generated through filamentation of ultraintense femtosecond laser pulses in air, argon, and helium are densified through the application of multijoule nanosecond heater pulses. Plasma densification in molecular gases is always accompanied by the fragmentation of the plasma channels into discrete bubbles, while in atomic gases, under certain conditions, the densified channels remain smooth and continuous. The densification effect in atomic gases persists through considerably longer delays between the femtosecond and nanosecond pulses compared to that in molecular gases. Using rate equations we trace this difference in the temporal dynamics of densification to the different cooling mechanisms operative in atomic and molecular cases.

  12. Rapid fabrication of ceramic composite tubes using chemical vapor infiltration

    SciTech Connect

    Starr, T.L.; Chiang, D.; Besmann, T.M.; Stinton, D.P.; McLaughlin, J.C.; Matlin, W.M.

    1996-06-01

    Ceramic composite tubes can be fabricated with silicon carbide matrix and Nicalon fiber reinforcement using forced flow-thermal gradient chemical vapor infiltration (FCVI). The process model GTCVI is used to design the equipment configuration and to identify conditions for rapid, uniform densification. The initial injector and mandrel design produced radial and longitudinal temperature gradients too large for uniform densification. Improved designs have been evaluated with the model. The most favorable approach utilizes a free-standing preform and an insulated water-cooled gas injector. Selected process conditions are based on the temperature limit of the fiber, matrix stoichiometry and reagent utilization efficiency. Model runs for a tube 12 inches long, 4 inches OD and 1/4 inch wall thickness show uniform densification in approximately 15 hours.

  13. Dynamic patterns of compaction in brittle porous media

    NASA Astrophysics Data System (ADS)

    Guillard, François; Golshan, Pouya; Shen, Luming; Valdes, Julio R.; Einav, Itai

    2015-10-01

    Brittle porous media exhibit a variety of irreversible patterns during densification, including stationary and moving compaction bands in rocks, foams, cereal packs and snow. We have recently found moving compaction bands in cereal packs; similar bands have been detected in snow. However, the question of generality remains: under what conditions can brittle porous media disclose other densification patterns? Here, using a new heuristic lattice spring model undergoing repeated crushing events, we first predict the possible emergence of new types of dynamic compaction; we then discover and confirm these new patterns experimentally in compressed cereal packs. In total, we distinguish three observed compaction patterns: short-lived erratic compaction bands, multiple oscillatory propagating compaction bands reminiscent of critical phenomena near phase transitions, and diffused irreversible densification. The manifestation of these three different patterns is mapped in a phase diagram using two dimensionless groups that represent fabric collapse and external dissipation.

  14. Mechanical and Electrochemical Characterization of Super-Solidus Sintered Austenitic Stainless Steel (316L)

    NASA Astrophysics Data System (ADS)

    Muthuchamy, A.; Raja Annamalai, A.; Ranka, Rishabh

    2016-08-01

    The present study compares the mechanical and electrochemical behaviour of austenitic (AISI 316L) stainless steel compacted at various pressures (200, 400 and 600 MPa) and conventionally sintered at super-solidus temperature of 1,400°C. The electrochemical behaviour was investigated in 0.1 N H2SO4 solution by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The shrinkage decreased and densification has been increased with increasing pressure. The mechanical and electrochemical behaviour with pressure has been correlated with densification response and microstructure (pore type, volume and morphology). Highest densification ( 92% theoretical) achieved at 600 MPa (compaction pressure) and 1,400°C (sintering temperature) resulted in excellent combination of tensile strength and ductility (456 ± 40 MPa, 25 ± 1.1%), while showing excellent corrosion resistance (0.1 mmpy or 4.7 mpy).

  15. Sintering of Mullite-Containing Materials: I, Effect of Composition

    SciTech Connect

    Sacks, Michael D.; Pask, Joseph A.

    1982-02-01

    Sintering behavior of mullite-containing powders was studied over a range of chemical compositions (Al203/Si02 ratio). Densification measurements were made for both liquid phase-containing and solid state systems. Small amounts of liquid phase were observed to have a significant effect on densification rate. A linear relationship was obtained between the percent of theoretical density and the logarithm of time for compositions in the range 73-75 wt% Al2O3. Currently available models for intermediate stage sintering kinetics were considered to be inadequate for these systems. Lastly, grain boundary transport or diffusion appeared to be the primary mechanism of densification.

  16. Sintering aid for lanthanum chromite refractories

    DOEpatents

    Flandermeyer, Brian K.; Poeppel, Roger B.; Dusek, Joseph T.; Anderson, Harlan U.

    1988-01-01

    An electronically conductive interconnect layer for use in a fuel cell or other electrolytic device is formed with sintering additives to permit densification in a monolithic structure with the electrode materials. Additions including an oxide of boron and a eutectic forming composition of Group 2A metal fluorides with Group 3B metal fluorides and Group 2A metal oxides with Group 6B metal oxides lower the required firing temperature of lanthanum chromite to permit densification to in excess of 94% of theoretical density without degradation of electrode material lamina. The monolithic structure is formed by tape casting thin layers of electrode, interconnect and electrolyte materials and sintering the green lamina together under common densification conditions.

  17. Synthesis and Characterization of Microwave Sintered Silica Xerogel Produced from Rice Husk Ash

    NASA Astrophysics Data System (ADS)

    Sudiana, I. N.; Mitsudo, S.; Nishiwaki, T.; Susilowati, P. E.; Lestari, L.; Firihu, M. Z.; Aripin, H.

    2016-08-01

    Silica xerogel ceramic produced from rice husk ash (RHA) taken from South East Sulawesi Indonesia has been successfully sintered by using a millimeter waves (MMW) heating system with a 28 GHz gyrotron as radiation source. The ceramic was also sintered by using an electric furnace where served as a comparison. Densification, microstructural, and morphological characterization of the silica were then investigated by using an Archimedes densification measurement method device, a X-ray diffraction (XRD) and a Scanning Electron Microscopy (SEM), respectively. Effect of microwave energy on the properties of silica xerogel ceramic were evaluated and discussed and compared to conventionally sintered results. The notably different densification and microstructure of sintered samples after sintering were found. The results suggest that microwave radiation provides a microwave effect during sintering.

  18. Synthesis of MgO-CaO-Al2O3-SiO2 nanocomposite powder by polymeric complex method as a novel sintering additive of AlN ceramics

    NASA Astrophysics Data System (ADS)

    Lee, Hwa-Jun; Cho, Woo-Seok; Kim, Hyeong Jun; Pan, Wei; Shahid, Mohammad; Ryu, Sung-Soo

    2016-09-01

    A MgO-CaO-Al2O3-SiO2 (MCAS) nanocomposite powder with a particle size of 50 nm and a specific surface area of 40.6 m2/g was successfully synthesized via heat-treatment of polymeric precursors containing Mg, Ca, Al and Si in air at 700 °C for 5 h. It was characterized as a novel sintering additive for the densification AlN ceramics at a low temperature below 1600 °C. It was found that the nanosized MCAS powder was suitable for the densification of AlN ceramics. In particular, full densification could be achieved when only 1.0 wt% MCAS additive-doped AlN powder compact was sintered for 1 h at 1600 °C, and a thermal conductivity of 84 W/m·K was attained.

  19. Strategies for the deconvolution of hypertelescope images

    NASA Astrophysics Data System (ADS)

    Aime, C.; Lantéri, H.; Diet, M.; Carlotti, A.

    2012-07-01

    Aims: We study the possibility of deconvolving hypertelescope images and propose a procedure that can be used provided that the densification factor is small enough to make the process reversible. Methods: We present the simulation of hypertelescope images for an array of cophased densified apertures. We distinguish between two types of aperture densification, one called FAD (full aperture densification) corresponding to Labeyrie's original technique, and the other FSD (full spectrum densification) corresponding to a densification factor twice as low. Images are compared to the Fizeau mode. A single image of the observed object is obtained in the hypertelescope modes, while in the Fizeau mode the response produces an ensemble of replicas of the object. Simulations are performed for noiseless images and in a photodetection regime. Assuming first that the point spread function (PSF) does not change much over the object extent, we use two classical techniques to deconvolve the images, namely the Richardson-Lucy and image space reconstruction algorithms. Results: Both algorithms fail to achieve satisfying results. We interpret this as meaning that it is inappropriate to deconvolve a relation that is not a convolution, even if the variation in the PSF is very small across the object extent. We propose instead the application of a redilution to the densified image prior to its deconvolution, i.e. to recover an image similar to the Fizeau observation. This inverse operation is possible only when the rate of densification is no more than in the FSD case. This being done, the deconvolution algorithms become efficient. The deconvolution brings together the replicas into a single high-quality image of the object. This is heuristically explained as an inpainting of the Fourier plane. This procedure makes it possible to obtain improved images while retaining the benefits of hypertelescopes for image acquisition consisting of detectors with a small number of pixels.

  20. Dilatometric study of U1-xAmxO2±δ and U1-xCexO2±δ reactive sintering

    NASA Astrophysics Data System (ADS)

    Horlait, Denis; Feledziak, Alex; Lebreton, Florent; Clavier, Nicolas; Prieur, Damien; Dacheux, Nicolas; Delahaye, Thibaud

    2013-10-01

    In order to reduce the radiotoxicity of nuclear fuel waste, the transmutation of americium in U1-xAmxO2±δ dedicated fuels is considered. A convenient route to produce such fuels is reactive sintering from a UO2+δ/AmO2-δ green pellet, i.e., a single heat treatment during which both the densification and the formation of the U1-xAmxO2±δ solid solution occur. The mechanisms of such sintering are however barely known and require experimental data. In this aim, the densification through reactive sintering of a UO2+δ/AmO2-δ sample was monitored by dilatometry. The obtained results were compared to those reported for the formation of the U1-xAmxO2±δ solid solution monitored by in situ high-temperature X-ray diffraction. To assess the use of Ce as a substitute of Am, similar dilatometric studies were also carried out on UO2+δ/CeO2 pellets. Obtained results show that the use of a reactive sintering causes a delay in the densification process associated to the competition between solid solution formation and densification, which yields limitations in pellet final densities. The importance of redox behavior of Am (or Ce) on the achievement of solid solution formation and densification are also discussed, especially based on discrepancies in densification behavior between UO2+δ/AmO2-δ and UO2+δ/CeO2.

  1. Cast iron freezing mechanisms

    NASA Technical Reports Server (NTRS)

    Lillybeck, N. P.; Smith, James E., Jr.

    1987-01-01

    This task focused on liquid phase sintering and infiltration studies of refractory metals and metal composites. Particular emphases was placed on those powered metal compacts which produce liquid alloys in sintering. For this class of materials, heating to a two phase region causes the constituent components to react, forming an alloy liquid which must wet the solid phase. Densification is initially driven by the free energy effects which cause rapid rearrangement. Further densification occurs by evaporation and condensation, surface diffusion, bulk flow, and volume diffusion.

  2. Modeling of chemical vapor infiltration for composite fabrication

    SciTech Connect

    Starr, T.L.; Besmann, T.M.

    1993-12-31

    We describe our ongoing efforts to develop a general, validated, 3-D, finite-volume model for the chemical vapor infiltration (CVI) process. The model simulates preform densification for both isothermal (ICVI) and forced flow-thermal gradient (FCVI) variations of the process, but is most useful for FCVI where specification and control of flow rates and temperature profiles are critical to rapid, uniform densification. The model has been validated experimentally for both ICVI and FCVI fabrication of SiC/SiC composites.

  3. Temperature dependence of inductively coupled plasma assisted growth of TiN thin films.

    SciTech Connect

    Meng, W. J.; Curtis, T. J.; Rehn, L. E.; Baldo, P. M.; Materials Science Division; Louisiana State Univ.

    1999-11-01

    The use of low pressure high density plasmas to assist the synthesis of ceramic thin film materials is in its infancy. Using an inductively coupled plasma assisted magnetron sputtering system, we examine the dependence of plasma-assisted growth of TiN thin films on growth temperature at different ratios of ion flux to neutral atom flux. Our results indicate that a temperature independent densification of TiN films occurs above a certain ion to neutral atom flux ratio. As an example of this temperature independent densification, we demonstrate the formation of dense B1 TiN crystalline thin films at growth temperatures down to {approx}100 K.

  4. Hot-pressing of shock-activated aluminum nitride

    SciTech Connect

    Beauchamp, E.K.; Carr, M.J.; Graham, R.A. )

    1987-01-01

    Aluminum nitride powders were subjected to explosive shock treatment at 17 and 22 GPa and then hot-pressed. The ram pressure required to obtain equivalent densification behavior in hot-pressing was 16 MPa lower in shocked powders than in unshocked powders in the pressure regime in which deformation is attributed to dislocation motion. Transmission electron microscopy on hot-pressed samples confirmed that dislocation processes were active in both shocked and unshocked powders. The higher densification rates in shocked material are related to dynamic recrystallization which is promoted by the high dislocation densities and results in enhanced dislocation motion.

  5. Unusual energy state evolution in Ce-based metallic glass under high pressure

    NASA Astrophysics Data System (ADS)

    Ge, T. P.; Wang, C.; Tan, J.; Ma, T.; Yu, X. H.; Jin, C. Q.; Wang, W. H.; Bai, H. Y.

    2017-05-01

    Metallic Glasses (MGs) are always aging toward the lower energy state, which leads to higher density, modulus, and hardness. We find that high pressure (HP) could lead to similar densification and hardening while the energy is increased. The comparison between two processes under HP and ambient pressure shows that densification happens in denser regions in MGs under HP, while it happens in looser regions under ambient pressure, which leads to the opposite energy changes in the two conditions. This result breaks the common wisdom about the relationship between the free volume and enthalpy and displays different structural and energy evolutions in MGs.

  6. Ground demonstration of hypertelescopes

    NASA Astrophysics Data System (ADS)

    Gillet, S.; Riaud, P.; Lardière, O.; Dejonghe, J.; Labeyrie, A.; Borkowski, V.; Arnold, L.

    2002-10-01

    We have built a 10 cm diameter interferometer having 78 apertures of 1 mm diameter and using a direct snapshot imaging mode: the pupil densification also called hypertelescope. We have tested the direct snapshot performance of this hypertelescope with laboratory simulated multiple stars and on the sky. Characterizations of our hypertelescope limited science results but this test offers interesting perspectives for the future on the ground and in space. Densification may have applications in various fields such as providing a similar limiting magnitude but with a significantly increased angular resolution compared to a monolithic telescope with a same collecting surface.

  7. IRAN: laboratory test bench for hypertelescope pupil-plane recombination

    NASA Astrophysics Data System (ADS)

    Allouche, F.; Vakili, F.; Glindemann, A.; Aristidi, E.; Abe, L.; Fossat, E.; Douet, R.

    2008-07-01

    In 2004, our group proposed IRAN, an alternative beam-combination technique to the so-called hypertelescope imaging method introduced by Labeyrie in the 1990s. We have recently set up a laboratory experiment aiming at validating our image densification approach instead of the pupil densification scheme of Labeyrie. In our experiment, seven sub-apertures illuminated by laser sources are recombined using the IRAN scheme. The validation of the IRAN recombination consists basically in retrieving the point-spread intensity distribution (PSID), demonstrating the conservation of the object-image convolution relation. We will introduce IRAN, compare it to the hyper-telescope, and present the experimental results that we obtained.

  8. Bio-Inspired Ceramic/Carbon Composites

    DTIC Science & Technology

    2013-05-01

    sintering   temperatures   resulted   in   fine   grains   but   poor...densification   while   high-­‐ sintering   temperatures   promoted   densification   but   also   grain   growth   with   formation   of... Alumina  and  yittria  were  added  as  additives  to  trigger  liquid  state   sintering .  The   total  amount

  9. Basic science of new aerogels. Final report

    SciTech Connect

    1996-08-01

    Feasibility of making monolithic composite aerogels containing silica and natural clay minerals, synthetic clay minerals or zeolites has been demonstrated, using two different processes; up to 30 wt% of the mineral phase has been successfully added. Addition of natural and synthetic clay minerals or zeolites to silica aerosols was shown to retard densification. Composite silica aerogels showed significant surface area still present after sintering at 800 or 1000 C. For most samples, 1 wt% of the second phase is equally effective in retarding densification as 10 wt%. Composite aerogels, in general, had lower hardness values than pure silica. Hardness values were inversely proportional to aerogel pore radius.

  10. 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.

  11. Microalloying of transition metal silicides by mechanical activation and field-activated reaction

    DOEpatents

    Munir, Zuhair A.; Woolman, Joseph N.; Petrovic, John J.

    2003-09-02

    Alloys of transition metal suicides that contain one or more alloying elements are fabricated by a two-stage process involving mechanical activation as the first stage and densification and field-activated reaction as the second stage. Mechanical activation, preferably performed by high-energy planetary milling, results in the incorporation of atoms of the alloying element(s) into the crystal lattice of the transition metal, while the densification and field-activated reaction, preferably performed by spark plasma sintering, result in the formation of the alloyed transition metal silicide. Among the many advantages of the process are its ability to accommodate materials that are incompatible in other alloying methods.

  12. 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.

  13. Reaction synthesis of heat-resistant materials

    SciTech Connect

    Deevi, S.C.; Sikka, V.K.

    1995-12-31

    Exothermicity associated with the synthesis of aluminides can be utilized to obtain aluminides of transition metals. Combustion synthesis, extrusion, and hot pressing were utilized to obtain dense intermetallics and their composites. Composites were analyzed by X- ray diffraction and microscopy techniques, and tensile properties were measured on button-head and sheet specimens of intermetallics and their composites. Mechanical properties of intermetallics obtained by reaction synthesis and densification compare well with conventionally processed materials. Reaction-synthesis principles were also extended to weld overlays. Possible approaches to obtaining dense products by reaction synthesis and densification are summarized in a schematic illustration. 19 refs., 14 figs., 3 tabs.

  14. Modeling the interaction of ultrasound with pores

    NASA Technical Reports Server (NTRS)

    Lu, Yichi; Wadley, Haydn N. G.; Parthasarathi, Sanjai

    1991-01-01

    Factors that affect ultrasonic velocity sensing of density during consolidation of metal powders are examined. A comparison is made between experimental results obtained during the final stage of densification and the predictions of models that assume either a spherical or a spheroidal pore shape. It is found that for measurements made at low frequencies during the final stage of densification, relative density (pore fraction) and pore shape are the two most important factors determining the ultrasonic velocity, the effect of pore size is negligible.

  15. Anomalous lattice expansion in yttria stabilized zirconia under simultaneous applied electric and thermal fields: A time-resolved in situ energy dispersive x-ray diffractometry study with an ultrahigh energy synchrotron probe

    NASA Astrophysics Data System (ADS)

    Akdoğan, E. K.; Şavklıyıldız, İ.; Biçer, H.; Paxton, W.; Toksoy, F.; Zhong, Z.; Tsakalakos, T.

    2013-06-01

    Nonisothermal densification in 8% yttria doped zirconia (8YSZ) particulate matter of 250 nm median particle size was studied under 215 V/cm dc electric field and 9 °C/min heating rate, using time-resolved in-situ high temperature energy dispersive x-ray diffractometry with a polychromatic 200 keV synchrotron probe. Densification occurred in the 876-905 °C range, which resulted in 97% of the theoretical density. No local melting at particle-particle contacts was observed in scanning electron micrographs, implying densification was due to solid state mass transport processes. The maximum current draw at 905 °C was 3 A, corresponding to instantaneous absorbed power density of 570 W/cm3. Densification of 8YSZ was accompanied by anomalous elastic volume expansions of the unit cell by 0.45% and 2.80% at 847 °C and 905 °C, respectively. The anomalous expansion at 905 °C at which maximum densification was observed is characterized by three stages: (I) linear stage, (II) anomalous stage, and (III) anelastic recovery stage. The densification in stage I (184 s) and II (15 s) was completed in 199 s, while anelastic relaxation in stage III lasted 130 s. The residual strains (ɛ) at room temperature, as computed from tetragonal (112) and (211) reflections, are ɛ(112) = 0.05% and ɛ(211) = 0.13%, respectively. Time dependence of (211) and (112) peak widths (β) show a decrease with both exhibiting a singularity at 905 °C. An anisotropy in (112) and (211) peak widths of {β(112)/β(211)} = (3:1) magnitude was observed. No phase transformation occurred at 905 °C as verified from diffraction spectra on both sides of the singularity, i.e., the unit cell symmetry remains tetragonal. We attribute the reduction in densification temperature and time to ultrafast ambipolar diffusion of species arising from the superposition of mass fluxes due to Fickian diffusion, thermodiffusion (Soret effect), and electromigration, which in turn are a consequence of a superposition of chemical

  16. Anomalous lattice expansion in yttria stabilized zirconia under simultaneous applied electric and thermal fields: A time-resolved in situ energy dispersive x-ray diffractometry study with an ultrahigh energy synchrotron probe

    SciTech Connect

    Akdogan, E. K.; Savkl Latin-Small-Letter-Dotless-I y Latin-Small-Letter-Dotless-I ld Latin-Small-Letter-Dotless-I z, I.; Bicer, H.; Paxton, W.; Toksoy, F.; Tsakalakos, T.; Zhong, Z.

    2013-06-21

    Nonisothermal densification in 8% yttria doped zirconia (8YSZ) particulate matter of 250 nm median particle size was studied under 215 V/cm dc electric field and 9 Degree-Sign C/min heating rate, using time-resolved in-situ high temperature energy dispersive x-ray diffractometry with a polychromatic 200 keV synchrotron probe. Densification occurred in the 876-905 Degree-Sign C range, which resulted in 97% of the theoretical density. No local melting at particle-particle contacts was observed in scanning electron micrographs, implying densification was due to solid state mass transport processes. The maximum current draw at 905 Degree-Sign C was 3 A, corresponding to instantaneous absorbed power density of 570 W/cm{sup 3}. Densification of 8YSZ was accompanied by anomalous elastic volume expansions of the unit cell by 0.45% and 2.80% at 847 Degree-Sign C and 905 Degree-Sign C, respectively. The anomalous expansion at 905 Degree-Sign C at which maximum densification was observed is characterized by three stages: (I) linear stage, (II) anomalous stage, and (III) anelastic recovery stage. The densification in stage I (184 s) and II (15 s) was completed in 199 s, while anelastic relaxation in stage III lasted 130 s. The residual strains ({epsilon}) at room temperature, as computed from tetragonal (112) and (211) reflections, are {epsilon}{sub (112)} = 0.05% and {epsilon}{sub (211)} = 0.13%, respectively. Time dependence of (211) and (112) peak widths ({beta}) show a decrease with both exhibiting a singularity at 905 Degree-Sign C. An anisotropy in (112) and (211) peak widths of {l_brace} {beta}{sub (112)}/{beta}{sub (211)}{r_brace} = (3:1) magnitude was observed. No phase transformation occurred at 905 Degree-Sign C as verified from diffraction spectra on both sides of the singularity, i.e., the unit cell symmetry remains tetragonal. We attribute the reduction in densification temperature and time to ultrafast ambipolar diffusion of species arising from the

  17. Preparation of YSZ-TZP solid electrolytes by gel-casting technology.

    PubMed

    Li, Guojun; Ren, Ruiming

    2011-06-01

    8 mol% yttria stabilized zirconia, TZP: 3 mol% yttria stabilized tetragonal zirconia polycrystal) solid electrolytes were prepared by gel-casting technology. The densification, microstructure, mechanical and electrical properties were characterized and discussed. The densification of YSZ-TZP solid electrolytes increased with increasing TZP content. The strength and fracture toughness showed a maximum value when TZP was 20 vol.%. However, addition of TZP decreased the conductivities of solid electrolyte. Copyright © 2011 The Research Centre for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.

  18. Effects of various additives on sintering of aluminum nitride

    NASA Technical Reports Server (NTRS)

    Komeya, K.; Inoue, H.; Tsuge, A.

    1982-01-01

    Effects of thirty additives on sintering A/N were investigated. The addition of alkali earth oxides and rare earth oxides gave fully densified aluminum nitride. This is due to the formation of nitrogen-containing aluminate liquid in the system aluminum nitride-alkali earth oxides or rare earth oxides. Microstructural studies of the sintered specimens with the above two types of additives suggested that the densification was due to the liquid phase sintering. Additions of silicon compounds resulted in poor densification by the formation of highly refractory compounds such as A/N polytypes.

  19. 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

  20. Interaction of oil sands tailings particles with polymers and microbial cells: First steps toward reclamation to soil.

    PubMed

    Voordouw, Gerrit

    2013-04-01

    Production of bitumen by surface mining of Alberta's oil sands has given rise to tailings ponds, containing large volumes of finely dispersed clays (10(8) m(3)), which settle only slowly. The mature fine tailings (MFT) in these ponds are operationally defined as consisting of particles smaller than 44 μm with a solids content in excess of 30% (w/w). Increasing the rate of densification of MFT is a rate-limiting step in tailings pond reclamation. Accelerated densification has been achieved through mixing of MFT with sand in the presence of calcium sulfate as a binding agent to generate consolidated tailings. Addition of negatively charged polymer, together with either calcium or magnesium ions, is similarly effective. Although toxic to higher aquatic life, tailings ponds harbour a wide variety of mainly anaerobic microbes. These convert residual hydrocarbon, causing methane emissions of up to 10(4) m(3) day(-1). Interestingly, anaerobic microbial activity also accelerates tailings pond densification. Hence, many technologies designed to accelerate densification move tailings, at least conceptually, towards soil in which sand and clay particles are linked by large amounts of humic and fulvic acid polymers supporting large numbers of microbes in a mechanically stable structure.

  1. Gas pressure sintering of silicon nitride to optimize fracture toughness

    SciTech Connect

    Tiegs, T.N.; Nunn, S.D.; Beavers, T.M.; Menchhofer, P.A.; Barker, D.L.; Coffey, D.W.

    1995-06-01

    Gas-pressure sintering (GPS) can be used to densify silicon nitride containing a wide variety of sintering additives. Parameters affecting the sintering behavior include densification temperature, densification time, grain growth temperature, grain growth time and heating rates. The Si{sub 3}N{sub 4}-6% Y{sub 2}O{sub 3}-2% A1{sub 2}O{sub 3} samples sintered to high densities at all conditions used in the present study, whereas the Si{sub 3}N{sub 4}-Sr{sub 2}La{sub 4}Yb{sub 4}(SiO{sub 4}){sub 6}O{sub 2} samples required the highest temperatures and longest times to achieve densities {ge}98 % T. D. The main effect on the fracture toughness for Si{sub 3}N{sub 4}-6% Y{sub 2}O{sub 3}-2% A1{sub 2}O{sub 3} samples was the use of a lower densification temperature, which was 1900C in the present study. For the Si{sub 3}N{sub 4}-Sr{sub 2}La{sub 4}Yb{sub 4}SiO4{sub 4}){sub 6}O{sub 2} composition, fracture toughness was sensitive to and improved by a slower heating rate (10c/min), a lower densification temperature (1900`), a higher grain growth temperature (2000C), and a longer grain growth time (2 h).

  2. The Synthesis of Cadmium Doped Mesoporous TiO2

    SciTech Connect

    Li, Xiaohong S.; Fryxell, Glen E.; Engelhard, Mark H.; Wang, Chong M.

    2007-06-01

    Cd doped mesoporous titanium oxide was prepared using non-ionic surfactants and easily handled titanium precursors. The Cd doping was found to be able to significantly inhibit the growth of anatase crystal size, stabilize the mesoporous structure, and retard the densification of nanoporous TiO2 at elevated temperatures.

  3. 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.

  4. Attachment system for silica tiles. [thermal protection for space shuttle orbiter

    NASA Technical Reports Server (NTRS)

    Dotts, R. L.; Holt, J. W. (Inventor)

    1982-01-01

    An improved method for markedly increasing the bond strength between a rigid, porous refractory material and non-rigid substrate by densifying the face of the rigid material opposing the substrate is discussed. Densification is accomplished by wetting the refractory material and then impregnating it with a composite slurry having a particle size to fill voids of the porous material.

  5. Preliminary investigation of biological resistance, water absorption and swelling of thermally compressed pine wood panels

    Treesearch

    Oner Unsal; S. Nami Kartal; Zeki Candan; Rachel Arango; Carol A. Clausen; Frederick Green

    2008-01-01

    Wood can be modified by compressive, thermal and chemical treatments. Compression of wood under thermal conditions is resulted in densification of wood. This study evaluated decay and termite resistance of thermally compressed pine wood panels at either 5 or 7 MPa and at either 120 or 150°C for one hour. The process caused increases in density and decreases in...

  6. High-Energy-Density LCA-Coupled Structural Energetic Materials for Counter WMD Applications

    DTIC Science & Technology

    2014-04-01

    morphology , etc.) of reactants. In the case of the equivolumetric Ta+Fe2O3 powder mixtures, pre-densification results in generating Fe2O3 as the more...published in the following papers. • N.N. Thadhani and J.K. Cochran, "Energetic Materials", DTRA Basic and Applied Research Program Newsletter , V2, N3, p

  7. Novel Processing of Infrared Transmitting ZrO2-ZrW2O8 Nanocomposites

    DTIC Science & Technology

    2013-09-01

    processing approaches such as melt spinning and flash sintering . The latter seemed to produce nanostructured nearly fully dense nanocomposites. Zr02...The nanostructured powder compacts are densified employing recently developed " flash sintering " technique. Accomplishments In our research we were...process or low temperature densification needs to be employed. Flash sintering Flash sintering is a novel sintering route recently developed by Raj

  8. Potential use of only Yb2O3 in producing dense Si3N4 ceramics with high thermal conductivity by gas pressure sintering

    PubMed Central

    Zhu, Xinwen; Zhou, You; Hirao, Kiyoshi; Ishigaki, Takamasa; Sakka, Yoshio

    2010-01-01

    Yb2O3 is an efficient sintering additive for enhancing not only thermal conductivity but also the high-temperature mechanical properties of Si3N4 ceramics. Here we report the fabrication of dense Si3N4 ceramics with high thermal conductivity by the gas pressure sintering of α-Si3N4 powder compacts, using only Yb2O3 as an additive, at 1900 °C under a nitrogen pressure of 1 MPa. The effects of Yb2O3 content, sample packing condition and sintering time on the densification, microstructure and thermal conductivity were investigated. Curves of the density plotted against the Yb2O3 content exhibited a characteristic ‘N’ shape with a local minimum at 3 mol% Yb2O3 and nearly complete densification below and above this concentration. The effects of the sample packing condition on the densification, microstructure and thermal conductivity strongly depended on the Yb2O3 content. The embedded condition led to more complete densification but also to a decrease in thermal conductivity from 119 to 94 W m-1 K−1 upon 1 mol% Yb2O3 addition. The sample packing condition had little effect on the density and thermal conductivity (102–106 W m−1 K−1) at 7 mol% Yb2O3. The thermal conductivity value was strongly related to the microstructure. PMID:27877368

  9. Physical and chemical evaluation of furniture waste briquettes.

    PubMed

    Moreno, Ana Isabel; Font, Rafael; Conesa, Juan A

    2016-03-01

    Furniture waste is mainly composed of wood and upholstery foam (mostly polyurethane foam). Both of these have a high calorific value, therefore, energy recovery would be an appropriate process to manage these wastes. Nevertheless, the drawback is that the energy content of these wastes is limited due to their low density mainly that of upholstery foam. Densification of separate foam presents difficulties due to its elastic character. The significance of this work lies in obtaining densified material by co-densification of furniture wood waste and polyurethane foam waste. Densification of furniture wood and the co-densification of furniture wood waste with polyurethane foam have been studied. On the one hand, the parameters that have an effect on the quality of the furniture waste briquettes have been analysed, i.e., moisture content, compaction pressure, presence of lignin, etc. The maximum weight percentage of polyurethane foam that can be added with furniture wood waste to obtain durable briquettes and the optimal moisture were determined. On the other hand, some parameters were analysed in order to evaluate the possible effect on the combustion. The chemical composition of waste wood was compared with untreated wood biomass; the higher nitrogen content and the concentration of some metals were the most important differences, with a significant difference of Ti content.

  10. Landscape heterogeneity compensates for fuel reduction treatment effects on Northern flying squirrel populations

    Treesearch

    R. Sollmann; Angela White; Gina Tarbill; Patricia Manley; Eric E. Knapp

    2016-01-01

    In the dry forests of the western United States frequent fires historically maintained a diversity of habitats in multiple seral stages. Over the past century, fire suppression and preferential harvest of large trees has led to a densification and homogenization of forests, making them more prone to larger and more severe wildfires. In response, fuel reduction...

  11. Thermal Stability of Milled Nanocrystalline Tungsten Powders

    DTIC Science & Technology

    2011-05-01

    energy for sintering and develop master sintering curves. The final density of the sintered samples was tested using the Archimedes method. Grain size...Curve Calculations Classical sintering theory distinguishes three different stages in the sintering process based upon the dominant sintering...the third stage of sintering where volume diffusion tends to dominate. Many sintering theories have been developed to describe the densification

  12. Microstructure and mechanical properties of pressureless sintered B4C- C composite using phenolic resin

    NASA Astrophysics Data System (ADS)

    Nikravan, A.; Baharvandi, H. R.; Jebelli, F. B.; Abdizadeh, H.; Ehsani, N.

    2007-10-01

    Boron carbide is an extremely promising material for a variety of applications that require high hardness and good wear resistance. However, due to the very high sintering temperatures which are required for B4C densification, wide spread use of that is limited. Various solutions have been studied to modifying densification behavior of B4C. Pressureless sintering in the presence of different additives has been tried by researchers. The effect of additives such as TiB2, SiC, Al, B, ZrO2, talc and Si have been evaluated. It was shown that the densification and mechanical properties may be improved with sintering aids. The Effects of phenolic resin additive on the microstructure and mechanical properties of B4C were explained in this study. Experimental composition was batched corresponding from 0 to 10 wt% of the additive. All samples were sintered for 60 minutes at 2150°C. The heating and cooling rates were 10°C/min for all samples. It was found that below 7.5 wt% of phenolic resin additive, the density increased with additive increasing and above that, decreased by phenolic resin addition. Mechanical properties such as fracture toughness, strength and hardness increased as a result of densification enhancement.

  13. Microstructure and mechanical properties of pressureless sintered B 4C-C composite using phenolic resin

    NASA Astrophysics Data System (ADS)

    Nikravan, A.; Baharvandi, H. R.; Jebelli, F. B.; Abdizadeh, H.; Ehsani, N.

    2007-07-01

    Boron carbide is an extremely promising material for a variety of applications that require high hardness and good wear resistance. However, due to the very high sintering temperatures which are required for B 4C densification, wide spread use of that is limited. Various solutions have been studied to modifying densification behavior of B 4C. Pressureless sintering in the presence of different additives has been tried by researchers. The effect of additives such as TiB II, SiC, Al, B, ZrO II, talc and Si have been evaluated. It was shown that the densification and mechanical properties may be improved with sintering aids. The Effects of phenolic resin additive on the microstructure and mechanical properties of B 4C were explained in this study. Experimental composition was batched corresponding from 0 to 10 wt% of the additive. All samples were sintered for 60 minutes at 2150°C. The heating and cooling rates were 10°C/min for all samples. It was found that below 7.5 wt% of phenolic resin additive, the density increased with additive increasing and above that, decreased by phenolic resin addition. Mechanical properties such as fracture toughness, strength and hardness increased as a result of densification enhancement.

  14. Magnetic pinch compression of silica glass

    NASA Technical Reports Server (NTRS)

    Bless, S. J.

    1974-01-01

    SiO2 glass has been irreversibly densified by pressures up to 250 kbar produced in a magnetic pinch apparatus. The threshold for significant densification was about 60 kbar. The recovered densities agree better with published shock wave results than with static results.

  15. Laser peening for reducing hydrogen embrittlement

    SciTech Connect

    Hackel, Lloyd A.; Zaleski, Tania M.; Chen, Hao-Lin; Hill, Michael R.; Liu, Kevin K.

    2010-05-25

    A laser peening process for the densification of metal surfaces and sub-layers and for changing surface chemical activities provides retardation of the up-take and penetration of atoms and molecules, particularly Hydrogen, which improves the lifetime of such laser peened metals. Penetration of hydrogen into metals initiates an embrittlement that leaves the material susceptible to cracking.

  16. Preparation of cermets

    DOEpatents

    Morgan, Chester S.

    1978-01-01

    Cermets are produced by the process of forming a physical mixture of a ceramic powder material with an elemental metal precursor compound and by decomposing the elemental metal precursor compound within the mixture. The decomposition step may be carried out either prior to or during a forming and densification step.

  17. Bonding Heat-Resistant Fabric to Tile

    NASA Technical Reports Server (NTRS)

    Holt, J. W.; Smiser, L. W.

    1985-01-01

    Acid etching, densification, and silica cement ensure strong bond. Key step in preparation for bonding to glazed tile is etching quartz fabric and tile with acid. This increases adhesion of silica cement used to form bond. Procedures use high-temperature materials exclusively and therefore suitable for securing flexible seals and heat barriers around doors and viewing ports in furnaces and kilns.

  18. Vehicle-Snow Interaction: Modeling, Testing and Validation

    DTIC Science & Technology

    2009-10-12

    Pressure *J.H. Lee, J. of Terramechanics (2009) Three zones: I: Elastic II: Hardening (via cavity expansion theory and Drucker - Prager criterion) III...Densification (via upper bound theory and Drucker - Prager criterion) UNCLAS: Dist A. Approved for public release Potential Deformation Mechanisms A

  19. Synthesis of increased-density bismuth-based superconductors with cold isostatic pressing and heat treating

    DOEpatents

    Lanagan, Michael T.; Picciolo, John J.; Dorris, Stephen E.

    1997-01-01

    The present invention is directed to a process for producing high temperature superconducting ceramic materials. More particularly, the present invention is directed to a process that enhances the densification of Bi.sub.1.8 Pb.sub.0.4 Sr.sub.2 Ca.sub.2 Cu.sub.3 O.sub.10 "BSCCO" ceramics.

  20. Effect of temperature during wood torrefaction on the formation of lignin liquid intermediates

    Treesearch

    Manuel Raul Pelaez-Samaniego; Vikram Yadama; Manuel Garcia-Perez; Eini Lowell; Armando G. McDonald

    2014-01-01

    Torrefaction enhances physical properties of lignocellulosic biomass and improves its grindability. Energy densification, via fuel pellets production, is one of the most promising uses of torrefaction. Lignin contributes to self-bonding of wood particles during pelletization. In biomass thermal pretreatment, part oflignin (in the form of lignin liquid intermediates –...

  1. Integrated Visible Photonics for Trapped-Ion Quantum Computing

    DTIC Science & Technology

    2017-06-10

    PECVD oxide that is annealed in nitrogen for densification and hydrogen desorption. We then deposit a100-nm LPCVD Si3N4 waveguide layer. Waveguide...layers are very similar to one another with the loss in Layer 1 being slightly lower, perhaps due to the increased thermal cycling . We also note

  2. Progress on the development of seismic resilient Tall CLT Buildings in the Pacific Northwest

    Treesearch

    Shiling Pei; Jeffrey Berman; Daniel Dolan; John van de Lindt; James Ricles; Richard Sause; Hans-Erik Blomgren; Marjan Popovski; Douglas Rammer

    2014-01-01

    As urban densification occurs in U.S. regions of high seismicity, there is a natural demand for seismically resilient tall buildings that are reliable, economically viable, and can be rapidly constructed. In urban regions on the west coast of the U.S., specifically the Pacific Northwest, there is significant interest in utilizing CLT in 8-20 story residential and...

  3. Contrasting impacts of climate and competition on large sugar pine growth and defense in a fire-excluded forest of the Central Sierra Nevada

    Treesearch

    Andrew Slack; Jeffrey Kane; Eric Knapp; Rosemary Sherriff

    2017-01-01

    Many forest ecosystems with a large pine component in the western United States have experienced environmental stress associated with climate change and increased competition with forest densification in the absence of fire. Information on how changes in climate and competition affect carbon allocation to tree growth and defense is needed to anticipate changes to tree...

  4. Potential use of only Yb2O3 in producing dense Si3N4 ceramics with high thermal conductivity by gas pressure sintering.

    PubMed

    Zhu, Xinwen; Zhou, You; Hirao, Kiyoshi; Ishigaki, Takamasa; Sakka, Yoshio

    2010-12-01

    Yb2O3 is an efficient sintering additive for enhancing not only thermal conductivity but also the high-temperature mechanical properties of Si3N4 ceramics. Here we report the fabrication of dense Si3N4 ceramics with high thermal conductivity by the gas pressure sintering of α-Si3N4 powder compacts, using only Yb2O3 as an additive, at 1900 °C under a nitrogen pressure of 1 MPa. The effects of Yb2O3 content, sample packing condition and sintering time on the densification, microstructure and thermal conductivity were investigated. Curves of the density plotted against the Yb2O3 content exhibited a characteristic 'N' shape with a local minimum at 3 mol% Yb2O3 and nearly complete densification below and above this concentration. The effects of the sample packing condition on the densification, microstructure and thermal conductivity strongly depended on the Yb2O3 content. The embedded condition led to more complete densification but also to a decrease in thermal conductivity from 119 to 94 W m(-1) K(-1) upon 1 mol% Yb2O3 addition. The sample packing condition had little effect on the density and thermal conductivity (102-106 W m(-1) K(-1)) at 7 mol% Yb2O3. The thermal conductivity value was strongly related to the microstructure.

  5. Relationships between wildland fires and watershed hydrology across the contiguous U.S

    Treesearch

    Dennis W. Hallema; Ge Sun; Peter V. Caldwell; Steve Norman; Erika C. Cohen; Yongqiang Liu; Steve McNulty

    2016-01-01

    Wildland fires contribute to the natural succession in forested watersheds by stimulating growth and biodiversity. Notwithstanding, these fires present an increasing hazard at the wildland-urban interface, and cover large areas as a result of the high fire severity associated with forest densification.

  6. Impact of reductive N2/H2 plasma on porous low-dielectric constant SiCOH thin films

    NASA Astrophysics Data System (ADS)

    Cui, Hao; Carter, Richard J.; Moore, Darren L.; Peng, Hua-Gen; Gidley, David W.; Burke, Peter A.

    2005-06-01

    Porous low-dielectric constant (low-κ) SiCOH thin films deposited using a plasma-enhanced chemical-vapor deposition have been comprehensively characterized before and after exposure to a reactive-ion-etch-type plasma of N2 and H2 chemistry. The low-κ film studied in this work is a carbon-doped silicon oxide film with a dielectric constant (κ) of 2.5. Studies show that a top dense layer is formed as a result of significant surface film densification after exposure to N2/H2 plasma while the underlying bulk layer remains largely unchanged. The top dense layer is found to seal the porous bulk SiCOH film. SiCOH films experienced significant thickness reduction, κ increase, and leakage current degradation after plasma exposure, accompanied by density increase, pore collapse, carbon depletion, and moisture content increase in the top dense layer. Both film densification and removal processes during N2/H2 plasma treatment were found to play important roles in the thickness reduction and κ increase of this porous low-κ SiCOH film. A model based upon mutually limiting film densification and removal processes is proposed for the continuous thickness reduction during plasma exposure. A combination of surface film densification, thickness ratio increase of top dense layer to bulk layer, and moisture content increase results in the increase in κ value of this SiCOH film.

  7. THE IMPACT OF FIRN COMPACTION ON ESTIMATES OF ICE SHEET MASS BALANCE

    NASA Astrophysics Data System (ADS)

    Li, J.; Zwally, H. J.

    2009-12-01

    Deriving the mass change dM/dt from the altimetry surface elevation change dH/dt requires information of changes in both present accumulation rate and the surface temperature together with the knowledge of bedrock rebound. The conventional theory that multiplying an effective density ranging from 0.3-0.9 to the altimeter derived surface elevation change dH/dt to obtain the mass change is fundamentally limited. A method of estimating the mass change of the ice sheet using altimetry data combined with firn densification model is presented. By using the unified firn densification model, the altimetry derived surface elevation change dH/dt is due to the following components: the present accumulation rate driven dHA/dt; the surface air temperature and accumulation rate driven compaction rates dCT/dt and dCA/dt; the long-term ice dynamic imbalance dHL/dt, together with the bedrock rebound dB/dt that may be obtained from the numerical models. The firn densification model also allows the calculation of the firn density ρA that is associated with the impact of the changes in accumulation rate. We use the ICESat derived surface elevation change dH/dt (2003-2007) data and the firn densification model forced by the changes in monthly surface air temperature from AVHRR (1982-2007), and the accumulation rate due to the temperature change to estimate the mass balances of Greenland and Antarctic ice sheets.

  8. Predicting bending stiffness of randomly oriented hybrid panels

    Treesearch

    Laura Moya; William T.Y. Tze; Jerrold E. Winandy

    2010-01-01

    This study was conducted to develop a simple model to predict the bending modulus of elasticity (MOE) of randomly oriented hybrid panels. The modeling process involved three modules: the behavior of a single layer was computed by applying micromechanics equations, layer properties were adjusted for densification effects, and the entire panel was modeled as a three-...

  9. Shrub removal in reforested post-fire areas increases native plant species richness

    Treesearch

    Gabrielle N. Bohlman; Malcolm North; Hugh D. Safford

    2016-01-01

    Large, high severity fires are becoming more prevalent in Sierra Nevada mixed-conifer forests, largely due to heavy fuel loading and forest densification caused by past and current management practices. In post-fire areas distant from seed trees, conifers are often planted to re-establish a forest and to prevent a potential type-conversion to shrub fields. Typical...

  10. Tailored Net-Shape Powder Composites by Spark Plasma Sintering

    NASA Astrophysics Data System (ADS)

    Khaleghi, Evan Aryan

    This dissertation investigates the ability to produce net-shape and tailored composites in spark plasma sintering (SPS), with an analysis of how grain growth, densification, and mechanical properties are affected. Using alumina and four progressively anisotropic dies, we studied the impact of specimen shape on densification. We found specimen shape had an impact on overall densification, but no impact on localized properties. We expected areas of the specimen to densify differently, or have higher grain growth, based on current anisotropy in the specimen during sintering, and preliminary results indicated this, but further investigation showed this did not occur. Overall average grain size and porosity decreased as shape complexity increased. In Fe-V-C steel, we mechanical alloyed two rapidly solidified powders, and used spark sintering to retain the properties imparted during the rapid solidification. We noticed VC grains being produced during densification, which improved the final properties. We conducted spark plasma extrusion (SPE) of aluminum to understand the effect on microstructure. We found, through an analysis of the grain structure, that SPE did have a grain deformation potential, and grain size was severely decreased compared to conventional sintering. Dynamic recrystallization did not occur, due to the reduced temperatures we were able to extrude with SPS. Finally, we examined whether there were particular sintering conditions for SPS that reduced the complexity of the grain growth and porosity relationship to one similar to conventional sintering, of the form G = k G0 ε -1/. We found that although a reasonable case could be made for free sintering, as found in the literature, for hot-pressing and SPS the conditions required go against the common knowledge in grain growth and densification kinetics. We were able to fit our data very well to the model, but the correlated results do not make physical sense.

  11. Effect of low temperature anneals and nonthermal treatments on the properties of gap fill oxides used in SiGe and III-V devices

    NASA Astrophysics Data System (ADS)

    Ryan, E. Todd; Morin, Pierre; Madan, Anita; Mehta, Sanjay

    2016-07-01

    Silicon dioxide is used to electrically isolate CMOS devices such as fin field effect transistors by filling gaps between the devices (also known as shallow trench isolation). The gap fill oxide typically requires a high temperature anneal in excess of 1000 °C to achieve adequate electrical properties and oxide densification to make the oxide compatible with subsequent fabrication steps such as fin reveal etch. However, the transition from Si-based devices to high mobility channel materials such as SiGe and III-V semiconductors imposes more severe thermal limitations on the processes used for device fabrication, including gap fill oxide annealing. This study provides a framework to quantify and model the effect of anneal temperature and time on the densification of a flowable silicon dioxide as measured by wet etch rate. The experimental wet etch rates allowed the determination of the activation energy and anneal time dependence for oxide densification. Dopant and self-diffusion can degrade the channel material above a critical temperature. We present a model of self-diffusion of Ge and Si in SiGe materials. Together these data allowed us to map the thermal process space for acceptable oxide wet etch rate and self-diffusion. The methodology is also applicable to III-V devices, which require even lower thermal budget. The results highlight the need for nonthermal oxide densification methods such as ultraviolet (UV) and plasma treatments. We demonstrate that several plasma treatments, in place of high temperature annealing, improved the properties of flowable oxide. In addition, UV curing prior to thermal annealing enables acceptable densification with dramatically reduced anneal temperature.

  12. Seasonal and Interannual Variations of Ice Sheet Surface Elevation at the Summit of Greenland: Observed and Modeled

    NASA Technical Reports Server (NTRS)

    Zwally, H. Jay; Jun, Li; Koblinsky, Chester J. (Technical Monitor)

    2001-01-01

    Observed seasonal and interannual variations in the surface elevation over the summit of the Greenland ice sheet are modeled using a new temperature-dependent formulation of firn-densification and observed accumulation variations. The observed elevation variations are derived from ERS (European Remote Sensing)-1 and ERS-2 radar altimeter data for the period between April 1992 and April 1999. A multivariate linear/sine function is fitted to an elevation time series constructed from elevation differences measured by radar altimetry at orbital crossovers. The amplitude of the seasonal elevation cycle is 0.25 m peak-to-peak, with a maximum in winter and a minimum in summer. Inter-annually, the elevation decreases to a minimum in 1995, followed by an increase to 1999, with an overall average increase of 4.2 cm a(exp -1) for 1992 to 1999. Our densification formulation uses an initial field-density profile, the AWS (automatic weather station) surface temperature record, and a temperature-dependent constitutive relation for the densification that is based on laboratory measurements of crystal growth rates. The rate constant and the activation energy commonly used in the Arrhenius-type constitutive relation for firn densification are also temperature dependent, giving a stronger temperature and seasonal amplitudes about 10 times greater than previous densification formulations. Summer temperatures are most important, because of the strong non-linear dependence on temperature. Much of firn densification and consequent surface lowering occurs within about three months of the summer season, followed by a surface build-up from snow accumulation until spring. Modeled interannual changes of the surface elevation, using the AWS measurements of surface temperature and accumulation and results of atmospheric modeling of precipitation variations, are in good agreement with the altimeter observations. In the model, the surface elevation decreases about 20 cm over the seven years due

  13. Dehydrogenation and Sintering of TiH2: An In Situ Study

    NASA Astrophysics Data System (ADS)

    Chen, Gang; Liss, Klaus D.; Auchterlonie, Graeme; Tang, Huiping; Cao, Peng

    2017-06-01

    This first-ever study investigated dehydrogenation and microstructural evolution of TiH2 during sintering under vacuum using in situ neutron diffraction, in situ transmission electron microscopy, and ex situ neutron tomography. The densification behavior, microstructure, hydrogen concentration, and in situ phase transformation were reported. The shrinkage, weight loss percentage, and densification of the TiH2 powder compact monotonically increase with sintering temperature, while the open porosity behaves differently; porosity first increases at the initial sintering stage and then decreases during further sintering. The in situ phase transformation observations reveal that dehydrogenation starts from the outer area of either a particle or a powder compact and progressively carries forward into the interior of the particle or the compact. A shrinking core model was proposed to elucidate the dehydrogenation process for a single particle and a powder compact.

  14. Investigation of TiC/Si{sub 3}N{sub 4} and TiN-coated TiC/Si{sub 3}N{sub 4} composites

    SciTech Connect

    Jow-Lay Huang; Boy-Yuan Shew; Ding-Fwu Lii

    1996-12-31

    Silicon nitride containing various compositions of as received TiC and TiN-coated TiC were hot pressed at 1800{degrees}C for 1 h in a nitrogen atmosphere. In TiN-coated TiC/Si{sub 3}N{sub 4} composites, TiC reacted firstly with the TiN coating to form a titanium carbonitride interlayer at 1450{degrees}C, which essentially reduced further reactions between TiC and Si{sub 3}N{sub 4} and enhanced densification. TiN-coated TiC/Si{sub 3}N{sub 4} composites exhibited better densification, flexural strength and fracture toughness than those of as received TiC/Si{sub 3}N{sub 4}.

  15. Indentation size effect and the plastic compressibility of glass

    SciTech Connect

    Smedskjaer, Morten M.

    2014-06-23

    Oxide glasses exhibit significant densification under an applied isostatic pressure at the glass transition temperature. The glass compressibility is correlated with the chemical composition and atomic packing density, e.g., borate glasses with planar triangular BO{sub 3} units are more disposed for densification than silicate glasses with tetrahedral units. We here show that there is a direct relation between the plastic compressibility following hot isostatic compression and the extent of the indentation size effect (ISE), which is the decrease of hardness with indentation load exhibited by most materials. This could suggest that the ISE is correlated with indentation-induced shear bands, which should form in greater density when the glass network is more adaptable to volume changes through structural and topological rearrangements under an applied pressure.

  16. Novel preparation techniques for thin metal-ceramic composite membranes

    SciTech Connect

    Yeung, K.L.; Varma, A.

    1995-09-01

    Composite metal membranes obtained by supporting thin metallic films on ceramic substrates have good thermal and mechanical stability. The use of a thin metal film increases transmembrane flux, while retaining high permselectivity that is characteristic of metallic membranes. Novel techniques have been developed for preparing metal-ceramic composite membranes. By the appropriate use of osmotic pressure, the microstructure, porosity, and thickness of the deposited metal can be systematically manipulated. Three new procedures are described for film densification and fabrication: (1) the osmotic pressure is used to densify an existing supported metal membrane; (2) densification and growth of the film is managed under the influence of osmotic pressure by using a dilute plating solution; and (3) films of varying porosity are deposited on the ceramic membrane by combining electroless deposition and osmotic pressure. Silver, palladium, and palladium-silver films prepared by these techniques on a commercial alumina membrane (Membralox) are thermally more stable than similar films deposited by conventional electroless plating.

  17. Challenges in scaling up biofuels infrastructure.

    PubMed

    Richard, Tom L

    2010-08-13

    Rapid growth in demand for lignocellulosic bioenergy will require major changes in supply chain infrastructure. Even with densification and preprocessing, transport volumes by mid-century are likely to exceed the combined capacity of current agricultural and energy supply chains, including grain, petroleum, and coal. Efficient supply chains can be achieved through decentralized conversion processes that facilitate local sourcing, satellite preprocessing and densification for long-distance transport, and business models that reward biomass growers both nearby and afar. Integrated systems that are cost-effective and energy-efficient will require new ways of thinking about agriculture, energy infrastructure, and rural economic development. Implementing these integrated systems will require innovation and investment in novel technologies, efficient value chains, and socioeconomic and policy frameworks; all are needed to support an expanded biofuels infrastructure that can meet the challenges of scale.

  18. Hot isostatic pressing of intermetallic powders

    NASA Astrophysics Data System (ADS)

    Schaefer, R. J.; Kushner, B. G.

    The application of the intelligent processing of materials (IPM) approach to powder densification by hot isostatic pressing (HIP) is made possible by the development of in situ sensors, process models and adaptive control strategies. The challenge is to optimize the process schedule for new materials to achieve densification, shape and microstructural goals. The development of an IPM system for HIP of intermetallic powders is described. The primary sensor used in this system employs eddy currents to measure changes of sample dimensions, while the process model is that of Ashby et al., reformulated to more closely describe real materials in real HIP process cycles. Process cycles are developed by combining a knowledge base derived from experts with the process model refined by sensor measurements.

  19. Effect of powder characteristics on gas-pressure sintering of Si{sub 3}N{sub 4} with rare earth additives

    SciTech Connect

    Tiegs, T.N.; Nunn, S.D.; Walls, C.A.; Barker, D.; Davisson, C.; Jones, P.J.

    1993-09-01

    Several Si{sub 3}N{sub 4} powders, synthesized by various methods and having different surface areas, oxygen contents and impurity levels, were examined. During early stage densification, all powders showed similar shrinkage with the diimide ederived powder exhibiting delayed {alpha}/{beta} transformation compared to the other powders. The diimide and gas-phase derived powders achieved the highest final densities. Improved densification was observed by increasing the oxygen content and this also resulted in high toughness for some materials with rare earth apatite additives. However, the increased oxygen resulted in reduced high temperature strength. Fracture toughnesses (K{sub Ic}) up to 10 MPa{radical}m were obtained for some compositions.

  20. Effects of pressure and temperature on hot pressing a sialon. [Si-Al-O-N ceramics

    NASA Technical Reports Server (NTRS)

    Yeh, H. C.; Waters, W. J.

    1977-01-01

    The combined effects of temperature and pressure on the resulting density of a sialon (i.e., a ceramic composed of Si, Al, O, and N) are evaluated. Pressures in the 3.5-27.5 MPa range and temperatures in the 1550-1750 C range are considered. It is found that: (1) fully dense sialon bodies may be produced at lower temperatures than those usually used in the field, (2) the phase equilibrium reaction is increased by increased pressure, (3) the iso-density contour may be used to help design the desired microstructure, (4) phase changes occurring in the sample during hot pressing influenced sialon densification to a large extent, and (5) microstructures exceeding 98% theoretical density suggest that plastic deformation has contributed to densification.

  1. Processing of crack-free high density polycrystalline LiTaO3 ceramics

    SciTech Connect

    Chen, Ching-Fong; Brennecka, Geoff L.; King, Graham; Tegtmeier, Eric L.; Holesinger, Terry; Ivy, Jacob; Yang, Pin

    2016-11-04

    Our work achieved high density (99.9%) polycrystalline LiTaO3. The keys to the high density without cracking were the use of LiF-assisted densification to maintain fine grain size as well as the presence of secondary lithium aluminate phases as grain growth inhibitors. The average grain size of the hot pressed polycrystalline LiTaO3 is less than 5 μm, limiting residual stresses caused by the anisotropic thermal expansion. Dilatometry results clearly indicate liquid phase sintering via the added LiF sintering aid. Efficient liquid phase sintering allows densification during low temperature hot pressing. Electron microscopy confirmed the high-density microstructure. Furthermore, Rietveld analysis of neutron diffraction data revealed the presence of LiAlO2 and LiAl5O8 minority phases and negligible substitutional defect incorporation in LiTaO3.

  2. Modeling of fibrous preforms for CVI fabrication

    SciTech Connect

    Starr, T.L.; Chiang, D.Y.

    1995-08-01

    This program involves modeling the chemical vapor infiltration (CVI) of tube shapes in support of experimental process development at Oak Ridge National Laboratory (ORNL). The previously developed tube model, including radiative heat transfer, has been modified to match the new, larger reactor at ORNL. For infiltrating tubes 4{double_prime} OD and 12-18{double_prime} L, higher reactant flow rate is needed for rapid densification. Two new processing schemes are being investigated. In the first, the processing parameters - temperature, flow rate, etc. - are varied through the run in order to maintain optimum densification performance. in the second, processing conditions near the end of the run are adjusted to close residual porosity and to produce a gas-tight tube. For each of these, model runs will identify process schedules prior to experimental runs at ORNL.

  3. Processing of crack-free high density polycrystalline LiTaO3 ceramics

    DOE PAGES

    Chen, Ching-Fong; Brennecka, Geoff L.; King, Graham; ...

    2016-11-04

    Our work achieved high density (99.9%) polycrystalline LiTaO3. The keys to the high density without cracking were the use of LiF-assisted densification to maintain fine grain size as well as the presence of secondary lithium aluminate phases as grain growth inhibitors. The average grain size of the hot pressed polycrystalline LiTaO3 is less than 5 μm, limiting residual stresses caused by the anisotropic thermal expansion. Dilatometry results clearly indicate liquid phase sintering via the added LiF sintering aid. Efficient liquid phase sintering allows densification during low temperature hot pressing. Electron microscopy confirmed the high-density microstructure. Furthermore, Rietveld analysis of neutronmore » diffraction data revealed the presence of LiAlO2 and LiAl5O8 minority phases and negligible substitutional defect incorporation in LiTaO3.« less

  4. Synthesis of high-strength W-Ta ultrafine-grain composites

    SciTech Connect

    Ott, R. T.; Yang, X. Y.; Guyer, D. E.; Chauhan, S.; Sordelet, D. J.

    2015-09-30

    Bulk samples of an ultrafine-grained tungsten–tantalum composite alloy have been synthesized by consolidating mechanically milled composite powders. The grain growth during densification is limited due to the submicron-scale layering of the individual metals in the composite particles and the relatively low sintering temperature (1300 °C). The ultrafine microstructure of the high-density (~99% theoretical density) samples leads to a high yield stress of ~3 GPa under quasi-static uniaxial compression. A tendency for Ta-rich solid-solution formation during densification was observed, and the high-temperature phase equilibria in the composite powders were examined further using high-energy x-ray diffraction at temperatures up to 1300 °C.

  5. Origin of the refractive-index increase in laser-written waveguides in glasses

    SciTech Connect

    Ponader, Carl W.; Schroeder, Joseph F.; Streltsov, Alexander M.

    2008-03-15

    We present firm evidence that the mechanism for the refractive-index increase in fused silica caused by irradiation with ultrafast intense laser pulses is the densification of glass. This conclusion is based on the correlation observed between the refractive-index values in waveguides in silica produced by focused femtosecond laser pulses and the shift of the central frequency of {omega}{sub 4} (TO) band (Si-O stretching mode) in micro-Raman spectra. These data were compared with the relation of the Raman shift to density and to refractive index changes in glasses modified by high pressure or irradiation. We conclude that the measured refractive-index increase in silica waveguides can be explained by densification of glass and exclude other hypothesis such as fictive-temperature effect, color center formation, etc.

  6. Can the use of pulsed direct current induce oscillation in the applied pressure during spark plasma sintering?

    PubMed Central

    Salamon, David; Eriksson, Mirva; Nygren, Mats; Shen, Zhijian

    2012-01-01

    The spark plasma sintering (SPS) process is known for its rapid densification of metals and ceramics. The mechanism behind this rapid densification has been discussed during the last few decades and is yet uncertain. During our SPS experiments we noticed oscillations in the applied pressure, related to a change in electric current. In this study, we investigated the effect of pulsed electrical current on the applied mechanical pressure and related changes in temperature. We eliminated the effect of sample shrinkage in the SPS setup and used a transparent quartz die allowing direct observation of the sample. We found that the use of pulsed direct electric current in our apparatus induces pressure oscillations with the amplitude depending on the current density. While sintering Ti samples we observed temperature oscillations resulting from pressure oscillations, which we attribute to magnetic forces generated within the SPS apparatus. The described current–pressure–temperature relations might increase understanding of the SPS process. PMID:27877472

  7. The crucial effect of early-stage gelation on the mechanical properties of cement hydrates

    NASA Astrophysics Data System (ADS)

    Ioannidou, Katerina; Kanduč, Matej; Li, Lunna; Frenkel, Daan; Dobnikar, Jure; Del Gado, Emanuela

    2016-07-01

    Gelation and densification of calcium-silicate-hydrate take place during cement hydration. Both processes are crucial for the development of cement strength, and for the long-term evolution of concrete structures. However, the physicochemical environment evolves during cement formation, making it difficult to disentangle what factors are crucial for the mechanical properties. Here we use Monte Carlo and Molecular Dynamics simulations to study a coarse-grained model of cement formation, and investigate the equilibrium and arrested states. We can correlate the various structures with the time evolution of the interactions between the nano-hydrates during the preparation of cement. The novel emerging picture is that the changes of the physicochemical environment, which dictate the evolution of the effective interactions, specifically favour the early gel formation and its continuous densification. Our observations help us understand how cement attains its unique strength and may help in the rational design of the properties of cement and related materials.

  8. The microstructure, mechanical and electrical properties of Niobium pentoxide-doped Titanium oxide ceramic targets

    NASA Astrophysics Data System (ADS)

    Ling, Qi; Xu, TingTing; Wu, LianZi; Peng, Wei; Zhu, ZuoXiang; Xie, ShengHui; Yang, HaiPeng; Gao, JiHua; Gao, Ling; Yang, HaiTao

    2017-03-01

    Nb2O5 doped TiO2 (NTO) ceramic targets were prepared by sintering in Ar at l350 °C for 2 hours. The morphologies structures, densification behavior, mechanical and electrical properties of the sintered ceramic targets with different doping concentration were investigated. The results show that the Nb2O5 content of increase from 0 wt% to 10 wt% not only enhance the densification but promote the grain growth. The morphologies, compositions, microstructure, and chemical states were characterized by SEM and XRD. The relative density, grain size and resistivity of 7.5 wt% content sintered at 1350 °C in Ar were 94.5%, 13.76 μm, and 7.8×10‑2 Ω·cm, respectively.

  9. The crucial effect of early-stage gelation on the mechanical properties of cement hydrates

    PubMed Central

    Ioannidou, Katerina; Kanduč, Matej; Li, Lunna; Frenkel, Daan; Dobnikar, Jure; Del Gado, Emanuela

    2016-01-01

    Gelation and densification of calcium–silicate–hydrate take place during cement hydration. Both processes are crucial for the development of cement strength, and for the long-term evolution of concrete structures. However, the physicochemical environment evolves during cement formation, making it difficult to disentangle what factors are crucial for the mechanical properties. Here we use Monte Carlo and Molecular Dynamics simulations to study a coarse-grained model of cement formation, and investigate the equilibrium and arrested states. We can correlate the various structures with the time evolution of the interactions between the nano-hydrates during the preparation of cement. The novel emerging picture is that the changes of the physicochemical environment, which dictate the evolution of the effective interactions, specifically favour the early gel formation and its continuous densification. Our observations help us understand how cement attains its unique strength and may help in the rational design of the properties of cement and related materials. PMID:27417911

  10. Microwave assisted sintering of Al-Cu-Mg-Si-Sn alloy.

    PubMed

    Padmavathi, Chandran; Upadhyaya, Anish; Agrawal, Dinesh

    2012-01-01

    Microwave sintering has been a well-established technique to consolidate metal powders due to its instantaneous volumetric and rapid heating as compared to conventional heating. Al-3.8Cu-1Mg-0.8Si-0.3Sn (2712) alloy powders were compacted (200 and 400 MPa) and microwave sintered at different temperatures (570 to 630 degrees C) under different atmospheres (vacuum, N2, Ar and H2). Increasing sintering temperature enhanced sintered density from 91% to 98%. Sintering under vacuum at 590 degrees C was more efficient with a densification parameter of 0.36 followed by N2, Ar and H2. Regardless of the sintering condition, phase analysis via XRD revealed the presence of only alpha-Al peak attributed to lesser time available for diffusion of alloying elements. In addition, microstructural inhomogeneity leading to more intergranular melt formation was observed for all sintered compacts. Contrasting to densification, sintering in N2 resulted in better corrosion resistance.

  11. Integral throat entrance development, qualification and production for the Antares 3 nozzle

    NASA Technical Reports Server (NTRS)

    Clayton, F. I.; Dirling, R. B.; Eitman, D. A.; Loomis, W. C.

    1982-01-01

    Although design analyses of a G-90 graphite integral throat entrance for the Antares 3 solid rocket motor nozzle indicated acceptable margins of safety, the nozzle throat insert suffered a thermostructural failure during the first development firing. Subsequent re-analysis using properties measured on material from the same billet as the nozzle throat insert showed negative margins. Carbon-carbon was investigated and found to result in large positive margins of safety. The G-90 graphite was replaced by SAI fast processed 4-D material which uses Hercules HM 10000 fiber as the reinforcement. Its construction allows powder filling of the interstices after preform fabrication which accelerates the densification process. Allied 15V coal tar pitch is then used to complete densification. The properties were extensively characterized on this material and six nozzles were subjected to demonstration, development and qualification firings.

  12. Advances in beryllium powder consolidation simulation

    SciTech Connect

    Reardon, B.J.

    1998-12-01

    A fuzzy logic based multiobjective genetic algorithm (GA) is introduced and the algorithm is used to optimize micromechanical densification modeling parameters for warm isopressed beryllium powder, HIPed copper powder and CIPed/sintered and HIPed tantalum powder. In addition to optimizing the main model parameters using the experimental data points as objective functions, the GA provides a quantitative measure of the sensitivity of the model to each parameter, estimates the mean particle size of the powder, and determines the smoothing factors for the transition between stage 1 and stage 2 densification. While the GA does not provide a sensitivity analysis in the strictest sense, and is highly stochastic in nature, this method is reliable and reproducible in optimizing parameters given any size data set and determining the impact on the model of slight variations in each parameter.

  13. Limiting magnitude of hypertelescopes

    NASA Astrophysics Data System (ADS)

    Surya, Arun

    Optical stellar interferometers have demonstrated milli-arcsecond resolution with few apertures spaced hundreds of meters apart. To obtain rich direct images, many apertures will be needed, for a better sampling of the incoming wavefront. The coherent imaging thus achievable improves the sensitivity with respect to the incoherent combination of successive fringed exposures, heretofore achieved in the form of optical aperture synthesis. For efficient use of highly diluted apertures, this can be done with pupil densification, a technique also called ``Hypertelescope Imaging". Using numerical simulations we have found out the limiting magnitude of hypertelescopes over different baselines and pupil densifications. Here we discuss the advantages of using hypertelescope systems over classical pairwise optical interferometry.

  14. Sintering and microstructure of silicon carbide ceramic with Y3Al5O12 added by sol-gel method*

    PubMed Central

    Guo, Xing-zhong; Yang, Hui

    2005-01-01

    Silicon carbide (SiC) ceramic with YAG (Y3Al5O12) additive added by sol-gel method was liquid-phase sintered at different sintering temperatures, and the sintering mechanism and microstructural characteristics of resulting silicon carbide ceramics were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and elemental distribution of surface (EDS). YAG (yttrium aluminum garnet) phase formed before the sintering and its uniform distribution in the SiC/YAG composite powder decreased the sintering temperature and improved the densification of SiC ceramic. The suitable sintering temperature was 1860 °C with the specimen sintered at this temperature having superior sintering and mechanical properties, smaller crystal size and fewer microstructure defects. Three characteristics of improved toughness of SiC ceramic with YAG added by sol-gel method were microstructural densification, main-crack deflection and crystal ‘bridging’. PMID:15682507

  15. High-strength zirconium diboride-based ceramic composites consolidated by low-temperature hot pressing

    NASA Astrophysics Data System (ADS)

    Guo, Shuqi; Kagawa, Yutaka

    2012-08-01

    Two compositions of ZrB2-based ceramic composites containing Si3N4, Al2O3 and Y2O3 have been hot-pressed at different temperatures between 1673 and 1773 K for 60 min in vacuum. The densification behavior of the composites was examined during the sintering process. The microstructures of the composites were characterized by scanning electron microscopy, and the crystalline phases were identified by x-ray diffraction. The effects of Al2O3 and Y2O3 additives on the densification behavior and flexural strength were assessed. A relative density of ˜95% was obtained after sintering at 1723 K or higher temperatures. The microstructures of the composites consisted of (Zr,Y)B2, α-Si3N4 and Y3(Al,Si)5O12 phases. The room-temperature flexural strength increased with the amount of additives and approached 1 GPa.

  16. Microstructures of Nanotubes Reinforced Alumina Fabricated by Two Fast-Sintering Methods

    NASA Astrophysics Data System (ADS)

    Huang, L. W.; Fu, Z. Y.; Wang, H.; Lee, S. W.; Niihara, K.

    2011-03-01

    Spark plasma sintering (SPS) and Self-propagating High-temperature Synthesis/ quick pressing (SHS/QP) methods were used to fabricate nanotubes reinforced alumina. The difference in microstructure was discussed. In the SHS/QP process, the maximum densification temperature is 1660°C and the heating rate is about 1600°C /min. The whole densification process in SHS/QP is very short, which is much beneficial to protect the nanotubes and restrain the growing of grains. The fracture toughness of the sample prepared by SHS/QP is up to 4.9MPam½ for 1mass% CNTs/Al2O3 composites, which shows excellent toughening effects of nanotubes.

  17. Sintering and microstructure of silicon carbide ceramic with Y3Al5O12 added by sol-gel method.

    PubMed

    Guo, Xing-Zhong; Yang, Hui

    2005-03-01

    Silicon carbide (SiC) ceramic with YAG (Y3Al5O12) additive added by sol-gel method was liquid-phase sintered at different sintering temperatures, and the sintering mechanism and microstructural characteristics of resulting silicon carbide ceramics were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and elemental distribution of surface (EDS). YAG (yttrium aluminum garnet) phase formed before the sintering and its uniform distribution in the SiC/YAG composite powder decreased the sintering temperature and improved the densification of SiC ceramic. The suitable sintering temperature was 1860 degrees C with the specimen sintered at this temperature having superior sintering and mechanical properties, smaller crystal size and fewer microstructure defects. Three characteristics of improved toughness of SiC ceramic with YAG added by sol-gel method were microstructural densification, main-crack deflection and crystal 'bridging'.

  18. Compositional effects on Si3N4 fracture surfaces

    NASA Technical Reports Server (NTRS)

    Hench, L. L.; Ohuchi, F.; Vaidyanathan, P. N.; Dutta, S.

    1983-01-01

    Surface analysis techniques (X-ray, infrared reflection spectroscopy, Auger electron spectroscopy) applied to the same samples reveal that fracture surfaces of Si3N4 with Y2O3 densification aids possess a higher concentration of oxygen than the bulk. The oxide densification aids thus concentrate in the grain boundaries, and even low-temperature fracture is seen as occurring preferentially within the oxygen-enriched grain boundaries. It is found that increasing the concentrations of Y2O3 and Al2O3 increases the oxygen content of the fracture surface. A range of 13-15 percent Y2O3 + 6 percent Al2O3 gives an amorphous grain-boundary phase that is resistant to devitrification. Fracture occurs through the amorphous phase, and heat treatment at 1000 C has little effect on the amorphous phase.

  19. In Situ Synthesis Aluminum Borate Whiskers Reinforced TiB2 Matrix Composites for Application in Aluminum Reduction Cells

    NASA Astrophysics Data System (ADS)

    Zhang, Gang; Yang, Jianhong

    2013-11-01

    The TiB2 matrix ceramics reinforced by aluminum borate whiskers (Al18B4O33 w) had been prepared by the pressureless sintering method. The mechanical properties and densification behavior of the TiB2 matrix ceramics were investigated. The results showed that Al18B4O33 w was in situ synthesized by the reaction of boehmite (AlOOH) and TiB2 powders during the sintering process. Increasing the sintering temperature had benefited for densification of the TiB2 matrix ceramics. Al18B4O33 w could increase the flexural strength and Vicker's hardness. It is obtained that the maximum value Vicker's hardness with 1.81 GPa and flexural strength with 82 MPa for samples sintered at 1600°C.

  20. Miniature low-pass filter in low-loss 9k7 LTCC

    SciTech Connect

    Dai, Steve Xunhu; Hsieh, Lung -Hwa

    2015-09-30

    DuPont 9k7 low-temperature cofired ceramic (LTCC) is a low-loss, or high-quality-factor Q, tape system targeting at radio frequency (RF) applications. This paper reports on the effect of a critical process parameter, the heating rate, on the densification and dielectric properties of the 9k7 LTCC. The role of competing densification and crystallization during the sintering of 9k7 is discussed. The high Q of DuPont 9K7 can be used to improve RF system performance, for example a better receiver noise figure, by designing embedded passive RF components such as inductors, capacitors and filters. Furthermore, miniaturized multilayer low-pass filters (LPF) with a wide stopband were fabricated to showcase the technology.

  1. Miniature lowpass filters in low loss 9k7 LTCC

    SciTech Connect

    Dai, Steve; Hsieh, Lung -Hwa

    2015-07-01

    DuPont 9k7 low temperature cofired ceramic (LTCC) is a low loss, or high quality factor Q, tape system targeting at radio frequency (RF) applications. This paper reports the effect of a critical process parameter, heating rate, on the densification and dielectric properties of the 9k7 LTCC. The role of competing densification and crystallization during the sintering of 9k7 is discussed. The high Q of DuPont 9K7 can be used to improve RF system performance, for example a better receiver noise figure, by designing embedded passive RF components such as inductors, capacitors and filters. As a result, miniaturized multilayer low pass filters (LPF) with a wide stopband were fabricated to showcase the technology.

  2. Can the use of pulsed direct current induce oscillation in the applied pressure during spark plasma sintering?

    PubMed

    Salamon, David; Eriksson, Mirva; Nygren, Mats; Shen, Zhijian

    2012-02-01

    The spark plasma sintering (SPS) process is known for its rapid densification of metals and ceramics. The mechanism behind this rapid densification has been discussed during the last few decades and is yet uncertain. During our SPS experiments we noticed oscillations in the applied pressure, related to a change in electric current. In this study, we investigated the effect of pulsed electrical current on the applied mechanical pressure and related changes in temperature. We eliminated the effect of sample shrinkage in the SPS setup and used a transparent quartz die allowing direct observation of the sample. We found that the use of pulsed direct electric current in our apparatus induces pressure oscillations with the amplitude depending on the current density. While sintering Ti samples we observed temperature oscillations resulting from pressure oscillations, which we attribute to magnetic forces generated within the SPS apparatus. The described current-pressure-temperature relations might increase understanding of the SPS process.

  3. Powder processing for fabricating Si{sub 3}N{sub 4} ceramics

    SciTech Connect

    Kamiya, Hidehiro; Naito, Makio; Hotta, Tadashi; Isomura, Kenji; Tsubaki, Junichiro; Uematsu, Keizo

    1997-10-01

    Usually, the densification of silicon nitride ceramics requires a sintering aid, e.g., alumina and yttria fine powders. Many types of dispersants have been used to obtain a uniform mixture of silicon nitride and sintering aid. These dispersants affect the microstructure and strength of the spray-dried granules. However, few studies have been made of the effects of the microstructure and strength of spray-dried granules. However, few studies have been made of the effects of the microstructure and strength of spray-dried granules on the sintered and mechanical properties of non-oxide ceramics. This article shows the effect of such intergranular porosity--controlled by the strength and structure of spray-dried granules--on the densification of green compacts during sintering. Furthermore, relationships between the fracture strength distribution of spray-dried granules and bending strength distributions of sintered bodies are discussed.

  4. Mass transport measurements and modeling for chemical vapor infiltration

    SciTech Connect

    Starr, T.L.; Chiang, D.Y.; Fiadzo, O.G.; Hablutzel, N.

    1997-12-01

    This project involves experimental and modeling investigation of densification behavior and mass transport in fiber preforms and partially densified composites, and application of these results to chemical vapor infiltration (CVI) process modeling. This supports work on-going at ORNL in process development for fabrication of ceramic matrix composite (CMC) tubes. Tube-shaped composite preforms are fabricated at ORNL with Nextel{trademark} 312 fiber (3M Corporation, St. Paul, MN) by placing and compressing several layers of braided sleeve on a tubular mandrel. In terms of fiber architecture these preforms are significantly different than those made previously with Nicalon{trademark} fiber (Nippon Carbon Corp., Tokyo, Japan) square weave cloth. The authors have made microstructure and permeability measurements on several of these preforms and a few partially densified composites so as to better understand their densification behavior during CVI.

  5. Compaction dynamics of crunchy granular material

    NASA Astrophysics Data System (ADS)

    Guillard, François; Golshan, Pouya; Shen, Luming; Valdès, Julio R.; Einav, Itai

    2017-06-01

    Compaction of brittle porous material leads to a wide variety of densification patterns. Static compaction bands occurs naturally in rocks or bones, and have important consequences in industry for the manufacturing of powder tablets or metallic foams for example. Recently, oscillatory compaction bands have been observed in brittle porous media like snow or cereals. We will discuss the great variety of densification patterns arising during the compaction of puffed rice, including erratic compaction at low velocity, one or several travelling compaction bands at medium velocity and homogeneous compaction at larger velocity. The conditions of existence of each pattern are studied thanks to a numerical spring lattice model undergoing breakage and is mapped to the phase diagram of the patterns based on dimensionless characteristic quantities. This also allows to rationalise the evolution of the compaction behaviour during a single test. Finally, the localisation of compaction bands is linked to the strain rate sensitivity of the material.

  6. 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.

  7. Fabrication of 13Cr-2Mo Ferritic/Martensitic Oxide-Dispersion-Strengthened Steel Components by Mechanical Alloying and Spark-Plasma Sintering

    NASA Astrophysics Data System (ADS)

    Bogachev, I.; Grigoryev, E.; Khasanov, O. L.; Olevsky, E.

    2014-06-01

    The outcomes of the mechanical alloying of 13Cr-2Mo ferritic/martensitic steel and yttria (oxide-dispersion-strengthened steel) powders in a ball mill are reported in terms of the powder particle size and morphology evolution. The optimal ball mill rotation speed and the milling time are discussed. The densification kinetics of the mechanically alloyed powder during the process of spark-plasma sintering is analyzed. An optimal set of the compaction processing parameters, including the maximum temperature, the dwell time, and the heating rate, is determined. The specifics of the densification are discussed in terms of the impact of major spark-plasma sintering parameters as well as the possible phase transformations occurring during compaction processing.

  8. High temperature strain gages

    NASA Technical Reports Server (NTRS)

    Gregory, Otto J. (Inventor); You, Tao (Inventor)

    2011-01-01

    A ceramic strain gage based on reactively sputtered indium-tin-oxide (ITO) thin films is used to monitor the structural integrity of components employed in aerospace propulsion systems operating at temperatures in excess of 1500.degree. C. A scanning electron microscopy (SEM) of the thick ITO sensors reveals a partially sintered microstructure comprising a contiguous network of submicron ITO particles with well defined necks and isolated nanoporosity. Densification of the ITO particles was retarded during high temperature exposure with nitrogen thus stabilizing the nanoporosity. ITO strain sensors were prepared by reactive sputtering in various nitrogen/oxygen/argon partial pressures to incorporate more nitrogen into the films. Under these conditions, sintering and densification of the ITO particles containing these nitrogen rich grain boundaries was retarded and a contiguous network of nano-sized ITO particles was established.

  9. Lunar regolith penetrators and cutters

    NASA Technical Reports Server (NTRS)

    Barnes, Frank; Sture, Stein

    1991-01-01

    An apparatus was designed and built for conducting simulation experiments on cutting tool penetration in the centrifuge. This equipment is mounted on the laminar container which is used for the regolith densification study, so that the end product of the latter, i.e., a regolith bed with the proper density profile, can be used directly for the penetration tests. In this apparatus, an etching tool is suspended through a pulley system by the action of a double acting air cylinder. By adjusting the air pressure acting on each side of the cylinder, the net downward force acting on the tool can be controlled. The penetration of the tool is measured by an LVDT. This apparatus was proof-tested in the centrifuge and is ready for use in conjunction with the regolith densification experiments.

  10. Indentation size effect and the plastic compressibility of glass

    NASA Astrophysics Data System (ADS)

    Smedskjaer, Morten M.

    2014-06-01

    Oxide glasses exhibit significant densification under an applied isostatic pressure at the glass transition temperature. The glass compressibility is correlated with the chemical composition and atomic packing density, e.g., borate glasses with planar triangular BO3 units are more disposed for densification than silicate glasses with tetrahedral units. We here show that there is a direct relation between the plastic compressibility following hot isostatic compression and the extent of the indentation size effect (ISE), which is the decrease of hardness with indentation load exhibited by most materials. This could suggest that the ISE is correlated with indentation-induced shear bands, which should form in greater density when the glass network is more adaptable to volume changes through structural and topological rearrangements under an applied pressure.

  11. Direct observation of grain rotations during coarsening of a semisolid Al-Cu alloy

    NASA Astrophysics Data System (ADS)

    Dake, Jules M.; Oddershede, Jette; Sørensen, Henning O.; Werz, Thomas; Cole Shatto, J.; Uesugi, Kentaro; Schmidt, Søren; Krill, Carl E.

    2016-10-01

    Sintering is a key technology for processing ceramic and metallic powders into solid objects of complex geometry, particularly in the burgeoning field of energy storage materials. The modeling of sintering processes, however, has not kept pace with applications. Conventional models, which assume ideal arrangements of constituent powders while ignoring their underlying crystallinity, achieve at best a qualitative description of the rearrangement, densification, and coarsening of powder compacts during thermal processing. Treating a semisolid Al-Cu alloy as a model system for late-stage sintering—during which densification plays a subordinate role to coarsening—we have used 3D X-ray diffraction microscopy to track the changes in sample microstructure induced by annealing. The results establish the occurrence of significant particle rotations, driven in part by the dependence of boundary energy on crystallographic misorientation. Evidently, a comprehensive model for sintering must incorporate crystallographic parameters into the thermodynamic driving forces governing microstructural evolution.

  12. The roles of CHPD: superior critical current density and n-value obtained in binary in situ MgB2 cables

    NASA Astrophysics Data System (ADS)

    Hossain, M. S. A.; Motaman, A.; Barua, S.; Patel, D.; Mustapic, M.; Kim, J. H.; Maeda, M.; Rindfleisch, M.; Tomsic, M.; Cicek, O.; Melisek, T.; Kopera, L.; Kario, A.; Ringsdorf, B.; Runtsch, B.; Jung, A.; Dou, S. X.; Goldacker, W.; Kovac, P.

    2014-09-01

    A binary magnesium diboride (MgB2) cable has been assembled by braiding six Nb/Monel sheathed monofilament strands around a central copper stabilizer for improving the operational environment. The total critical current (Ic) of the braided cable is obtained by multiplying the Ic of six single wires, without any dissipation. In this work, various mechanical deformations, i.e., swaging, two-axial rolling, groove rolling, and cold high-pressure densification (CHPD) at 1.8 GPa have been applied to the 6-stranded cable to obtain additional densification. The highest critical current density at both 4.2 and 20 K has been achieved in this work through the CHPD treated cable due to higher filament mass density. The present results are promising in view of the cable, particularly in power applications at industrial lengths that pave the way to seeking an optimal protocol to meet a practical functionality.

  13. Development of an improved toughness hyperpure silica reflective heat shield

    NASA Technical Reports Server (NTRS)

    Rusert, E. L.; Hackett, T. L.; Drennan, D. N.

    1979-01-01

    High purity three dimensionally woven silica-silica materials were evaluated for use as a tough reflective heat shield for planetary entry probes. A special weave design was selected to minimize light piping effects through the heat shield thickness. Various weave spacings were evaluated for densification efficiency with an 0.7 micron particle size high purity silica. Spectral hemispherical reflectance was measured from 0.2 to 2.5 microns at room temperature. Reflectance increases due to densification and purity of material were measured. Reflectance of 3D hyperpure silica was higher than 3D astroquartz silica for all wavelengths. Mechanical properties were measured in beam flexure and beam shear tests. Results indicated strengths lower than reported for slip cast fused silica. Low strengths were attributed to low densities achieved through vacuum impregnation.

  14. Spark Plasma Sintering of Titanium Spherical Particles

    NASA Astrophysics Data System (ADS)

    Abedi, Mohammad; Moskovskikh, Dmitry O.; Rogachev, Alexander S.; Mukasyan, Alexander S.

    2016-10-01

    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.

  15. Miniature low-pass filter in low-loss 9k7 LTCC

    DOE PAGES

    Dai, Steve Xunhu; Hsieh, Lung -Hwa

    2015-09-30

    DuPont 9k7 low-temperature cofired ceramic (LTCC) is a low-loss, or high-quality-factor Q, tape system targeting at radio frequency (RF) applications. This paper reports on the effect of a critical process parameter, the heating rate, on the densification and dielectric properties of the 9k7 LTCC. The role of competing densification and crystallization during the sintering of 9k7 is discussed. The high Q of DuPont 9K7 can be used to improve RF system performance, for example a better receiver noise figure, by designing embedded passive RF components such as inductors, capacitors and filters. Furthermore, miniaturized multilayer low-pass filters (LPF) with a widemore » stopband were fabricated to showcase the technology.« less

  16. Miniature lowpass filters in low loss 9k7 LTCC

    DOE PAGES

    Dai, Steve; Hsieh, Lung -Hwa

    2015-07-01

    DuPont 9k7 low temperature cofired ceramic (LTCC) is a low loss, or high quality factor Q, tape system targeting at radio frequency (RF) applications. This paper reports the effect of a critical process parameter, heating rate, on the densification and dielectric properties of the 9k7 LTCC. The role of competing densification and crystallization during the sintering of 9k7 is discussed. The high Q of DuPont 9K7 can be used to improve RF system performance, for example a better receiver noise figure, by designing embedded passive RF components such as inductors, capacitors and filters. As a result, miniaturized multilayer low passmore » filters (LPF) with a wide stopband were fabricated to showcase the technology.« less

  17. An Analysis of Shock-Compression in Mo-Si Powder Mixtures Using Recovery and Time-Resolved Measurements

    NASA Astrophysics Data System (ADS)

    Vandersall, Kevin S.; Thadhani, Naresh N.

    1999-06-01

    The densification and reaction characteristics in the Mo-Si system were investigated utilizing recovery experiments as well as time resolved measurements with in-situ stress gages. The starting sample in all cases consisted of statically pressed Mo + 2 Si powder mixtures ( ~55% TMD). The recovery experiments were performed using the Sandia Momma Bear and Momma Bear A fixtures with baratol and composition B explosives respectively. The instrumented experiments were performed in a capsule design similar to that of the Momma Bear, but modified to incorporate poly-vinyl di-flouride (PVDF) stress gages at the front and rear surfaces of the powder. These experiments were performed using a single stage gas gun in the velocity range of 500 m/s to 1 km/s. The instrumented experiments allow the crush strength, densification history, and reaction threshold to be mapped at increasing pressure to correlate with reaction observed in the recovery experiments.

  18. Finite volume model for forced flow/thermal gradient chemical vapor infiltration

    SciTech Connect

    Starr, T.L.; Smith, A.W.

    1991-03-01

    The forced flow/thermal gradient chemical vapor infiltration process (FCVI) has proven to be a successfully technique for fabrication of ceramic matrix composites. It is particularly attractive for thick components which cannot be fabricated using the conventional, isothermal method (ICVI). Although it offers processing times that are at least an order of magnitude shorter than ICVI, FCVI has not been used to fabricate parts of complex geometry and is perceived by many to be unsuitable for such components. The major concern is that selection and control of the flow pattern and thermal profile for optimum infiltration can be a difficult and costly exercise. In order to reduce this effort, we are developing a computer model for FCVI that simulates the densification process for given component geometry, reactor configuration and operating parameters. Used by a process engineer, this model can dramatically reduce the experimental effort needed to obtain uniform densification.

  19. Fabrication and properties of erbium oxide

    SciTech Connect

    Neuman, A.; Platero, M.; Romero, R.; McClellan, K.J.; Petrovic, J.J.

    1997-03-01

    Erbium oxide (Er{sub 2}O{sub 3}) is a rare earth oxide of interest because of its chemical and thermal stability and high melting point, 2,430 C. However, there is relatively little information available regarding the relation between the structure and the mechanical properties of this material. A densification study of polycrystalline erbium oxide powders is reported here. Erbium oxide pellets were uniaxially pressed (40--280 MPa) and sintered (1,500--1,800 C) in order to obtain density data for as-received commercial powders. In addition, the particle size and distribution of as-received powders were varied by milling and the effects on densification were studied. The powders were characterized for particle size, phase and impurity content and surface area. The mechanical properties of high density sintered erbium oxide bodies were characterized using indentation hardness and toughness as a function of temperature and microstructure. Relations between the microstructure and mechanical properties are described.

  20. Sintering characteristics of nanocrystalline TiO sub 2

    SciTech Connect

    Hahn, H.; Logas, J.; Averback, R.S. Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 )

    1990-03-01

    The microstructural development of compacted nanocrystalline TiO{sub 2} powder was studied as a function of sintering temperature up to 1000 {degree}C. Grain growth was monitored using x-ray diffraction and scanning electron microscopy. The specific surface area and total porosity were determined quantitatively using the nitrogen adsorption BET. The density was measured by gravimetry using Archimedes principle. The green body density of compacted {ital n}-TiO{sub 2} with average grain size of 14 nm is as high as 75% of theoretical bulk density. Low temperature surface diffusion leads to the disappearance of small pores, while noticeable densification commences at 600 {degree}C and reaches near theoretical values at 900 {degree}C. Grain growth also begins at 600 {degree}C, accelerating rapidly by 1000 {degree}C. Hot isostatic pressing is observed to enhance densification while suppressing grain growth.

  1. Dehydrogenation and Sintering of TiH2: An In Situ Study

    NASA Astrophysics Data System (ADS)

    Chen, Gang; Liss, Klaus D.; Auchterlonie, Graeme; Tang, Huiping; Cao, Peng

    2017-03-01

    This first-ever study investigated dehydrogenation and microstructural evolution of TiH2 during sintering under vacuum using in situ neutron diffraction, in situ transmission electron microscopy, and ex situ neutron tomography. The densification behavior, microstructure, hydrogen concentration, and in situ phase transformation were reported. The shrinkage, weight loss percentage, and densification of the TiH2 powder compact monotonically increase with sintering temperature, while the open porosity behaves differently; porosity first increases at the initial sintering stage and then decreases during further sintering. The in situ phase transformation observations reveal that dehydrogenation starts from the outer area of either a particle or a powder compact and progressively carries forward into the interior of the particle or the compact. A shrinking core model was proposed to elucidate the dehydrogenation process for a single particle and a powder compact.

  2. Discrete element simulation of powder compaction in cold uniaxial pressing with low pressure

    NASA Astrophysics Data System (ADS)

    Rojek, Jerzy; Nosewicz, Szymon; Jurczak, Kamila; Chmielewski, Marcin; Bochenek, Kamil; Pietrzak, Katarzyna

    2016-11-01

    This paper presents numerical studies of powder compaction in cold uniaxial pressing. The powder compaction in this work is considered as an initial stage of a hot pressing process so it is realized with relatively low pressure (up to 50 MPa). Hence the attention has been focused on the densification mechanisms at this range of pressure and models suitable for these conditions. The discrete element method employing spherical particles has been used in the numerical studies. Numerical simulations have been performed for two different contact models—the elastic Hertz-Mindlin-Deresiewicz model and the plastic Storåkers model. Numerical results have been compared with the results of laboratory tests of the die compaction of the NiAl powder. Comparisons have shown that the discrete element method is capable to represent properly the densification mechanisms by the particle rearrangement and particle deformation.

  3. Large Scale Production of Densified Hydrogen to the Triple Point and Below

    NASA Technical Reports Server (NTRS)

    Swanger, A. M.; Notardonato, W. U.; Fesmire, J. E.; Jumper, K. M.; Johnson, W. L.; Tomsik, T. M.

    2017-01-01

    Recent demonstration of advanced liquid hydrogen storage techniques using Integrated Refrigeration and Storage technology at NASA Kennedy Space Center led to the production of large quantities of densified liquid and slush hydrogen in a 125,000 L tank. Production of densified hydrogen was performed at three different liquid levels and LH2 temperatures were measured by twenty silicon diode temperature sensors. Overall densification performance of the system is explored, and solid mass fractions are calculated. Experimental data reveal hydrogen temperatures dropped well below the triple point during testing, and were continuing to trend downward prior to system shutdown. Sub-triple point temperatures were seen to evolve in a time dependent manner along the length of the horizontal, cylindrical vessel. The phenomenon, observed at two fill levels, is detailed herein. The implications of using IRAS for energy storage, propellant densification, and future cryofuel systems are discussed.

  4. Compressive elasticity of polydisperse biopolymer gels

    NASA Astrophysics Data System (ADS)

    Xu, Xinpeng; Safran, Samuel A.

    2017-05-01

    We theoretically predict the nonlinear elastic responses of polydisperse biopolymer gels to uniaxial compression. We analyze the competition between compressive stiffening due to polymer densification by out-going solvent flow and compressive softening due to continuous polymer buckling. We point out that the polydispersity in polymer lengths can result in an intrinsic, equilibrium mode of nonaffine compression: nonuniform strain but with uniform force distribution, which is found to be more energetically preferable than affine deformation. In this case, the gel softens significantly after the onset of polymer buckling at small compression, but as compression increases, densification-induced stiffening becomes important and a modulus plateau should be observed for a large range of strain. We also relate our results to recent compression experiments on collagen gels and fibrin gels.

  5. Effects of applied pressure on hot-pressing of Beta-SiC

    NASA Technical Reports Server (NTRS)

    Kinoshita, M.; Matsumura, H.; Iwasa, M.; Hayami, R.

    1984-01-01

    The effects of applied pressure on the densification during hot pressing of beta-SiC compacts were investigated. Beta-SiC powder is Starck made and has the average particle size of about 0.7 micrometer. Hot pressing experiments were carried out in graphite dies at temperatures of 1700 deg to 2300 deg C and at the pressures up to 1000 kg/sq cm. The compacts containing 1 weight percent B4C were examined. Sintered compacts were examined for microstructure and the Rockwell A-scale hardness was measured. The B4C addition was very effective to mitigate the hot pressing conditions. It is found that densification goes with the strengthening of the bonding and does not occur in particle deformation due to concentrated stress.

  6. Chemical Preconversion: Application of Low-Severity Pretreatment Chemistries for Commoditization of Lignocellulosic Feedstock

    SciTech Connect

    David N. Thompson; Timothy Campbell; Bryan Bals; Troy Runge; Farzaneh Teymouri

    2013-05-01

    Securing biofuels project financing is challenging, in part because of risks in feedstock supply. Commoditization of the feedstock and decoupling its supply from the biorefinery will promote greater economies of scale, reduce feedstock supply risk and reduce the need for overdesign of biorefinery pretreatment technologies. We present benefits and detractions of applying low-severity chemical treatments or ‘chemical preconversion treatments’ to enable this approach through feedstock modification and densification early in the supply chain. General structural modifications to biomass that support cost-effective densification and transportation are presented, followed by available chemistries to achieve these modifications with minimal yield loss and the potential for harvesting value in local economies. A brief review of existing biomass pretreatment technologies for cellulolytic hydrolysis at biorefineries is presented, followed by a discussion toward economically applying the underlying chemistries at reduced severity in light of capital and operational limitations of small-scale feedstock depots.

  7. Realization of ETRF2000 as a New Terrestrial Reference Frame in Republic of Serbia

    NASA Astrophysics Data System (ADS)

    Blagojevic, D.; Vasilic, V.

    2012-12-01

    The International Earth Rotation and Reference Systems Service (IERS) is a joint service of the International Association of Geodesy (IAG) and the International Astronomical Union (IAU), which provides the scientific community with the means for computing the transformation from the International Celestial Reference System (ICRS) to the International Terrestrial Reference System (ITRS). It further maintains the realizations of these systems by appropriate coordinate sets called "frames". The densification of terrestrial frame usually serves as official frame for positioning and navigation tasks within the territory of particular country. One of these densifications was recently performed in order to establish new reference frame for Republic of Serbia. The paper describes related activities resulting in ETRF2000 as a new Serbian terrestrial reference frame.

  8. Effects of pressure and temperature on hot pressing a sialon. [Si-Al-O-N ceramics

    NASA Technical Reports Server (NTRS)

    Yeh, H. C.; Waters, W. J.

    1977-01-01

    The combined effects of temperature and pressure on the resulting density of a sialon (i.e., a ceramic composed of Si, Al, O, and N) are evaluated. Pressures in the 3.5-27.5 MPa range and temperatures in the 1550-1750 C range are considered. It is found that: (1) fully dense sialon bodies may be produced at lower temperatures than those usually used in the field, (2) the phase equilibrium reaction is increased by increased pressure, (3) the iso-density contour may be used to help design the desired microstructure, (4) phase changes occurring in the sample during hot pressing influenced sialon densification to a large extent, and (5) microstructures exceeding 98% theoretical density suggest that plastic deformation has contributed to densification.

  9. A Fundamental Study of Fatigue in Powder Metallurgy Aluminum Alloys.

    DTIC Science & Technology

    1981-08-01

    Rearick (20) have confirmed the beneficial effect of material flow during densification; endurance limits in rotating bend on P/M processed compositions...INTRODUCTION Recent studies on aluminum alloys have shown that lateral flow during consolidation, aimed at eliminating porosity and the fragmentation of surface...removed from each forging. Slices cut from the forgings were solution treated at a temperature of 488C (910*F) for two hours and water quenched. The

  10. Local Atomic Structure Deviation from Average Structure of Na0.5Bi0.5TiO3: Combined X-ray and Neutron Total Scattering Study

    DTIC Science & Technology

    2013-03-27

    calcination of the particles, and after sintering and densification of polycrystalline materials) to examine the possible influences of strain, grain...and Na2CO3 (99.5% purity, Alfa Aesar) were first calcined at 800 ◦C for 2 h and some powder was retained for structural characterization after this...synthesis step (hereafter referred to as “ calcined ”). Samples were then also sintered and densified into pellets at 1100 ◦C for 1 h. The sintered pellets

  11. Microstructure of hot-pressed Al2O3-Si3N4 mixtures as a function of holding temperature

    NASA Technical Reports Server (NTRS)

    Yeh, H. C.

    1976-01-01

    Powder mixtures of 40 m/o Si3N4-60 m/o Al2O3 were hot-pressed at 4000 psi at various holding temperatures from 1100 C to 1700 C. Scanning Electron Microscopy and Transmission Electro Microscopy results were correlated to X-ray phase analysis and density measurements. The progressively developed microstructure was used to interpret the densification behavior of SiAlON. Photomicrographs of microstructures are shown.

  12. Proton conducting ceramics in membrane separations

    DOEpatents

    Brinkman, Kyle S; Korinko, Paul S; Fox, Elise B; Chen, Frank

    2015-04-14

    Perovskite materials of the general formula SrCeO.sub.3 and BaCeO.sub.3 are provided having improved conductivity while maintaining an original ratio of chemical constituents, by altering the microstructure of the material. A process of making Pervoskite materials is also provided in which wet chemical techniques are used to fabricate nanocrystalline ceramic materials which have improved grain size and allow lower temperature densification than is obtainable with conventional solid-state reaction processing.

  13. Imaging with hypertelescopes: a simple modal approach

    NASA Astrophysics Data System (ADS)

    Aime, C.

    2008-05-01

    Aims: We give a simple analysis of imaging with hypertelescopes, a technique proposed by Labeyrie to produce snapshot images using arrays of telescopes. The approach is modal: we describe the transformations induced by the densification onto a sinusoidal decomposition of the focal image instead of the usual point spread function approach. Methods: We first express the image formed at the focus of a diluted array of apertures as the product R_0(α) X_F(α) of the diffraction pattern of the elementary apertures R_0(α) by the object-dependent interference term X_F(α) between all apertures. The interference term, which can be written in the form of a Fourier Series for an extremely diluted array, produces replications of the object, which makes observing the image difficult. We express the focal image after the densification using the approach of Tallon and Tallon-Bosc. Results: The result is very simple for an extremely diluted array. We show that the focal image in a periscopic densification of the array can be written as R_0(α) X_F(α/γ), where γ is the factor of densification. There is a dilatation of the interference term while the diffraction term is unchanged. After de-zooming, the image can be written as γ2 X_F(α)R_0(γ α), an expression which clearly indicates that the final image corresponds to the center of the Fizeau image intensified by γ2. The imaging limitations of hypertelescopes are therefore those of the original configuration. The effect of the suppression of image replications is illustrated in a numerical simulation for a fully redundant configuration and a non-redundant one.

  14. Ground Operations Demonstration Unit for Liquid Hydrogen (GODU LH2)

    NASA Technical Reports Server (NTRS)

    Notardonato, William U.

    2015-01-01

    When the technology associated with zero loss storage and transfer is implemented, NASA can reduce the LH2 losses and procurement costs by up to 30 compared to historical Shuttle numbers. This return on investment is based on the mission manifest and commodity use. LH2 densification can provide improved launch vehicle ascent performance by minimizing the size of the LH2 tanks or storing more mass of propellant in the given tank volume.

  15. Fabrication and characterization of ultrahigh-volume- fraction aligned carbon nanotube-polymer composites.

    PubMed

    Wardle, Brian L; Saito, Diego S; García, Enrique J; Hart, A John; de Villoria, Roberto Guzmán; Verploegen, Eric A

    2008-07-17

    Aligned CNT nanocomposites with variable volume fraction, up to 20%, are demonstrated. Biaxial mechanical densification of aligned CNT forests, followed by capillarity-driven wetting using unmodified aerospace-grade polymers, creates centimeter-scale specimens. Characterizations confirm CNT alignment and dispersion in the thermosets, providing a useful platform for controlled nanoscale interaction and nanocomposite property studies that emphasize anisotropy. Copyright © 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  16. Microwave sintering of alumina-SiC composites at 2. 45 and 60 GHz

    SciTech Connect

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

    1988-01-01

    Composites of alumina-10 vol % silicon carbide whiskers were sintered to 70% of theoretical density using both 2.45 and 60 GHz microwave radiation. Further densification was inhibited by formation of a constrained network of whiskers. Alumina-10 vol % silicon carbide platelet composites were sintered to 94% of theoretical density with 2.45 GHz microwaves in less than 20 minutes. 4 refs., 11 figs.

  17. Processing of Advanced Ceramics Which Have Potential for Use in Gas Turbine Aero Engines

    DTIC Science & Technology

    1989-02-01

    ramiques de pointe A base de nitrure ou carbure de silicium , Si3N4 et SiC, produites par pressage isostatique b chaud sont des mathriaux qui pourraient...avantages qu’offre cette m~thode de densification. Cependant, il apparaft qu’en soumettant au pressage isostatique A chaud du nitrure de silicium produit...solid product. Several forming methods are shown schematically in Fig. I. Often, organic binders and/or plasticizers are used in the forming stage

  18. 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.

  19. Fabrication and Characterization of Novel Refractory Coatings Using Combinatorial Nanocalorimetry

    DTIC Science & Technology

    2015-07-21

    sintering , reactive densification, and spark plasma sintering . The properties of bulk ceramics fabricated...Goutier, F., Trolliard, G., Valette, S., Maître, A. & Estournès, C. Role of impurities on the spark plasma sintering of ZrC< sub> x</sub>–ZrB< sub> 2</sub...Ceramic Society 29, 995- 1011 (2009). 58 Zamora, V., Ortiz, A. L., Guiberteau, F. & Nygren, M. Spark - plasma sintering of ZrB2

  20. Directly Written DFB Waveguide Lasers Using Femtosecond Laser Pulses

    NASA Astrophysics Data System (ADS)

    Ams, Martin; Dekker, Peter; Marshall, Graham D.; Little, Douglas J.; Withford, Michael J.

    2010-10-01

    There is still significant speculation regarding the nature of femtosecond laser induced index change in bulk glasses with colour centre formation and densification the main candidates. In the work presented here, we fabricated waveguide Bragg gratings in doped and undoped phosphate glasses and use these as a diagnostic for monitoring subtle changes in the induced refractive index during photo- and thermal annealing experiments. Reductions in grating strengths during such experiments were attributed to the annihilation of colour centres.

  1. Annealing dynamics of waveguide Bragg gratings: evidence of femtosecond laser induced colour centres.

    PubMed

    Dekker, P; Ams, M; Marshall, G D; Little, D J; Withford, M J

    2010-02-15

    There is still significant speculation regarding the nature of femtosecond laser induced index change in bulk glasses with colour centre formation and densification the main candidates. In the work presented here, we fabricated waveguide Bragg gratings in doped and undoped phosphate glasses and use these as a diagnostic for monitoring subtle changes in the induced refractive index during photo- and thermal annealing experiments. Reductions in grating strengths during such experiments were attributed to the annihilation of colour centres.

  2. Defect-dependent colossal negative thermal expansion in UiO-66(Hf) metal-organic framework.

    PubMed

    Cliffe, Matthew J; Hill, Joshua A; Murray, Claire A; Coudert, François-Xavier; Goodwin, Andrew L

    2015-05-07

    Thermally-densified hafnium terephthalate UiO-66(Hf) is shown to exhibit the strongest isotropic negative thermal expansion (NTE) effect yet reported for a metal-organic framework (MOF). Incorporation of correlated vacancy defects within the framework affects both the extent of thermal densification and the magnitude of NTE observed in the densified product. We thus demonstrate that defect inclusion can be used to tune systematically the physical behaviour of a MOF.

  3. Characterisation of Mg biodegradable stents produced by magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Elmrabet, N.; Botterill, N.; Grant, D. M.; Brown, P. D.

    2015-10-01

    Novel Mg-minitubes for biodegradable stent applications have been produced using PVD magnetron sputtering. The minitubes were characterised, as a function of annealing temperature, using a combination of SEM/EDS, XRD and hardness testing. The as-deposited minitubes exhibited columnar grain structures with high levels of porosity. Slight alteration to the crystal structure from columnar to equiaxed grain growth was demonstrated at elevated temperature, along with increased material densification, hardness and corrosion resistance.

  4. Materials Research Society, Symposium Proceedings, Volume 521. Porous and Cellular Materials for Structural Applications

    DTIC Science & Technology

    1998-04-15

    local densification. Such behavior is typical of that found in the transverse compression of honeycombs [8], bonded cylinders [18], etc. These...34 thick. Bonding between the core and face is achieved using a standard industrial epoxy adhesive . After imaging the internal cell configuration, the...structural two component epoxy adhesive (Krafft KAIEP A12/B9 [14]). The adhesive was cured at room temperature for 24 h. The surface of the specimens

  5. Pelletization process of postproduction plant waste

    NASA Astrophysics Data System (ADS)

    Obidziński, S.

    2012-07-01

    The results of investigations on the influence of material, process, and construction parameters on the densification process and density of pellets received from different mixtures of tobacco and fine-grained waste of lemon balm are presented. The conducted research makes it possible to conclude that postproduction waste eg tobacco and lemon balm wastes can be successfully pelletized and used as an ecological, solid fuels.

  6. Modelling of Coalescence of PMMA Particles/Farz Factor

    NASA Astrophysics Data System (ADS)

    Farzaneh, S.; Tcharkhtchi, A.

    2011-05-01

    In this study we are interested by sintering phenomenon during rotational molding of PMMA. It is well known that sintering begins by coalescence of grains and follows by powder densification. First we have followed the coalescence of two grains; then the coalescence of several grains is studied in order to see the effect of other grains on this phenomenon. In the basis of the Bellehumeur's model, a new model has been proposed to consider this effect. This model was validated by the experiments.

  7. Lightweight Multifunctional Linear Cellular Alloy Ballistic Structures

    DTIC Science & Technology

    2006-04-26

    for densification. For this program, square cell LCA honeycomb with both maraging steel and super invar compositions were fabricated using SAI’s...provide high levels of energy absorption; 5 to 7 times that of that of conventional materials. Maraging steel honeycomb structure having a density of 2.1 g...cm3 and yield strength ~650 MPa, has been shown to absorb ~180 MJ/m3. Figure 2 shows stress train curves for maraging steel under quasistatic and

  8. Theoretical Studies of Materials for High-Power Infrared Coatings

    DTIC Science & Technology

    1975-12-31

    as low as ^ = 10 cmŕ and A = 10 on a KBr internal reflec- tion plate. Auger -electron- spectroscopy measurements indicated a correlation be...resulting in optical densification or additional absorption in the window region. Photoemission and Auger spectroscopies , which we are now using to...one film was analyzed at Physical Electronics, Inc., by a combination Auger spectroscopy /sputtering operation to obtain the profile of the

  9. Associations of parameters characterizing the time course of the tabletting process on a reciprocating and on a rotary tabletting machine for high-speed production.

    PubMed

    Konkel, P; Mielck, J B

    1998-03-01

    A series of modern direct-compression excipients with differing mechanisms of deformation and densification, Karion Instant Pharma, Vivacel 200, Cellactose, Tablettose, and Parmcompress, after admixing magnesium stearate, have been tabletted (400 mg, 10 mm flat-faced punches) on an eccentric machine, Fette E XI at 43.6 rpm, and on a rotary machine, Fette PT 2090 at 20, 60, and 90 rpm, to graded maximum forces (3, 5, 10, 15 kN, respectively). Force/time (E XI and PT 2090) and displacement/time (E XI) curves were recorded. From the data on the E XI, parameters of a modified Weibull function, slopes of the Heckel function, quotients of partial areas under the curves, and the differences between times of maximum forces and the respective maximum densifications, t(diff), were calculated. From the data on the PT 2090, partial areas under the curves for the upper punch, various quotients of these areas, and the peak-offset times, t(off), the times of maximum force relative to the middle of the dwell time, t(dwell), were calculated. Close associations were found between the area A1 reI during the precompression phase (PT 2090) and the Heckel slope (E XI), between the quotient of partial areas before and after the middle of t(dwell) (PT 2090) and that of partial areas before and after maximum densification (E XI), and between t(off) (PT 2090) and t(diff) (E XI). However, certain materials (e.g. Karion Instant, Vivacel) showed marked deviations in behavior by particular parameters on the two machines. The results from both machines with respect to densification behavior complement one another.

  10. Electro-induced mechanical and thermal responses of carbon nanotube fibers.

    PubMed

    Meng, Fancheng; Zhang, Xiaohua; Li, Ru; Zhao, Jingna; Xuan, Xiaohui; Wang, Xinhao; Zou, Jingyun; Li, Qingwen

    2014-04-23

    The electromechanical and electrothermal responses of carbon nanotube fibers provide new ways to use energy conversion, including the modulation of assembly structures by alternative densification and relaxation. The most efficient way to strengthen the tensile strength up to 2.32-2.50 GPa is shown as well as a microscale, nanotube-based Chinese calligraphy brush. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  11. Monolithic microcircuit techniques and processes

    NASA Technical Reports Server (NTRS)

    Kennedy, B. W.

    1972-01-01

    Brief discussions of the techniques used to make dielectric and metal thin film depositions for monolithic circuits are presented. Silicon nitride deposition and the properties of silicon nitride films are discussed. Deposition of dichlorosilane and thermally grown silicon dioxide are reported. The deposition and thermal densification of borosilicate, aluminosilicate, and phosphosilicate glasses are discussed. Metallization for monolithic circuits and the characteristics of thin films are also included.

  12. Characterization of Pressureless Sintered Boron Carbide

    DTIC Science & Technology

    2013-03-01

    the most common additive, free carbon ( graphite ), increases densification up to 98% of the theoretical density (5) (2.47 g/cm 3 ). However, its...imperfections on the surface were analyzed by EDS to be almost pure carbon . Further EDS analysis showed this graphite to account for a significant...error; variations in carbon could be due to graphite or surface contamination, and the negligible amounts of oxygen detected are most likely due to

  13. Sinterable Ceramic Powders from Laser Heated Gas Phase Reactions and Rapidly Solidified Ceramic Materials.

    DTIC Science & Technology

    1984-07-01

    ceramic materials. Unusual, attractive densification characteristics have already been observedl with the amorphous powders that can be produced by the...increase with oxygen partial pressure. In air, the effect of additives on surface tension parallelled their effect on the melting point. In most cases...the compositional effects were approximately linear; TiO 2 , an exception, caused a sharp decrease in I for small additions that were followed by

  14. Pest resistant MoSi2-based materials containing in-situ grown .beta.-Si3N4whiskers

    NASA Technical Reports Server (NTRS)

    Hebsur, Mohan G. (Inventor)

    2001-01-01

    A MoSi.sub.2 pest resistant material includes in-situ grown .beta.-Si.sub.3 N.sub.4 whiskers. In addition to excellent pest resistance, the material provides a lower coefficient of thermal expansion for better match with continuous reinforcing fibers such as SiC fibers. A two stage heating and pressing production technique enables lower temperature processing with substantially full densification.

  15. Pest resistant MoSi2-based materials containing in-situ grown .beta.-Si3N4 whiskers

    NASA Technical Reports Server (NTRS)

    Hebsur, Mohan G. (Inventor)

    2002-01-01

    A MoSi.sub.2 pest resistant material includes in-situ grown .beta.-Si.sub.3 N.sub.4 whiskers. In addition to excellent pest resistance, the material provides a lower coefficient of thermal expansion for better match with continuous reinforcing fibers such as SiC fibers. A two stage heating and pressing production technique enables lower temperature processing with substantially full densification.

  16. Issues and Potential Program on Denatured Fuel Utilization.

    DTIC Science & Technology

    1978-12-01

    to current U02 fuel performance codes. The parameters of interest include the following: 0 fuel densification; * pellet- clad interaction (ratcheting...Mechanical sorting used. Tube rolling Expands tube and crushes fuel in tube. fuel chrushing Fuel cladding Mechanical screen device separates fuel...separator from cladding pieces. Assumes tube shear and whole bundle shear are comparable in cost. Special dissolvers Constructed of material to contain

  17. Behavior of sodium borosilicate glasses under compression using molecular dynamics

    SciTech Connect

    Kilymis, D. A.; Ispas, S.; Delaye, J.-M.

    2015-09-07

    We have performed classical molecular dynamics simulations in order to study the changes under compression in the local and medium range structural properties of three sodium borosilicate glasses with varying sodium content. These glasses have been isostatically compressed up to 20 GPa and then decompressed in order to analyze the different mechanisms that affect densification, alongside with the permanent modifications of the structure after a full compression/decompression cycle. The results show that the atomic packing is the prominent characteristic that governs the amount of densification in the glass, as well as the setup of the permanent densification. During compression, the bulk modulus increases linearly up to approximately 15 GPa and more rapidly for higher pressures, a behavior which is reflected on the rate of increase of the average coordination for B and Na. Radial distribution functions at different pressures during the cycle help to quantify the amount of distortions in the elementary structural units, with a pronounced shortening of the Na–Na and Na–O bond lengths during compression. A subsequent decomposition of the glassy matrix into elementary Voronoi volumes verifies the high compressibility of Na-rich regions.

  18. Linking high-pressure structure and density of albite liquid near the glass transition

    NASA Astrophysics Data System (ADS)

    Gaudio, Sarah J.; Lesher, Charles E.; Maekawa, Hideki; Sen, Sabyasachi

    2015-05-01

    The pressure-induced densification of NaAlSi3O8 liquid is determined following annealing immediately above the glass transition and upon quenching from superliquidus temperatures. High-field 27Al magic-angle-spinning NMR spectroscopy is used to investigate the corresponding changes in Al coordination environment that accompany the densification. We show that samples synthesized by quenching from superliquidus temperatures record lower fictive pressures (Pf) than annealed samples at the same nominal load and have lower recovered densities and average Al coordination number. Accounting for differences in Pf brings melt-quench and annealed samples into excellent agreement. The proportion of [5]Al increases from ∼3% to 29% and [6]Al from 0% to 8% between 1.8 and 7.2 GPa. The production of high-coordinated Al ([5]Al + [6]Al) with pressure is most dramatic above 3 GPa. Changes in network topology and structural disorder as revealed by the high-field 27Al NMR spectra provide new insights into the structural mechanisms of densification of the albite liquid. We posit that it is an overall weakening of the network structure on compression that is largely responsible for the anomalous pressure dependence of the transport properties observed for this liquid below ∼5 GPa.

  19. Meso-scale Computational Investigation of Shock-Wave Attenuation by Trailing Release Wave in Different Grades of Polyurea

    NASA Astrophysics Data System (ADS)

    Grujicic, Mica; Snipes, J. S.; Ramaswami, S.; Yavari, R.; Ramasubramanian, M. K.

    2014-01-01

    Over the past several years, considerable research efforts have been made toward investigating polyurea, a segmented thermoplastic elastomer, and particularly its shock-mitigation capacity, i.e., an ability to attenuate and disperse shock-waves. These research efforts have clearly established that the shock-mitigation capacity of polyurea is closely related to its chemistry, processing route, and the resulting microstructure. Polyurea typically possesses a nano-segregated microstructure consisting of (high glass transition temperature, T g) hydrogen-bonded discrete hard domains and a (low T g) contiguous soft matrix. While the effect of polyurea microstructure on its shock-mitigation capacity is well-established, it is not presently clear what microstructure-dependent phenomena and processes control its shock-mitigation capacity. To help identify these phenomena and processes, meso-scale simulations of the formation of nano-segregated microstructure and its interaction with a leading shock-wave and a trailing release-wave is analyzed in the present work. The results obtained revealed that shock-induced hard-domain densification makes an important contribution to the superior shock-mitigation capacity of polyurea, and that the extent of densification is a sensitive function of the polyurea soft-segment molecular weight. In particular, the ability of release-waves to capture and neutralize shock-waves has been found to depend strongly on the extent of shock-induced hard-domain densification and, thus, on the polyurea soft-segment molecular weight.

  20. Modeling of forced flow/thermal gradient chemical vapor infiltration

    SciTech Connect

    Starr, T.L.; Smith, A.W. )

    1992-09-01

    The forced flow/thermal gradient chemical vapor infiltration process (FCVI) has proven to be a successful technique for fabrication of ceramic matrix composites. It is particularly attractive for thick components which cannot be fabricated using the conventional, isothermal method (ICVI). Although it offers processing times that are at least an order of magnitude shorter than ICVI, FCVI has not been used to fabricate parts of complex geometry and is perceived by some to be unsuitable for such components. The major concern Is that selection and control of the flow pattern and thermal profile for optimum infiltration can be a difficult and costly exercise. In order to reduce this effort, we are developing a computer model for FCVI that simulates the densification process for given component geometry, reactor configuration and operating parameters. Used by a process engineer, this model can dramatically reduce the experimental effort needed to obtain uniform densification. A one-dimensional process model, described in a previous interim report, has demonstrated good agreement with experimental results in predicting overall densification time and density uniformity during processing and the effect of various fiber architectures and operating parameters on these process issues. This model is fundamentally unsuitable for more complex geometries, however, and extension to two- and three-dimensions is necessary. This interim report summarizes our progress since the previous interim report toward development of a finite volume'' model for FCVI.