synthesis and characterization of al/sic composite made by stir casting method

International Nuclear Information System (INIS)

Ghauri, K.M.; Ahmad, A.; Ahmad, R.; Din, K.M.; Chaudhry, J.A.

2013-01-01

Ceramics contain a distinctive property of completely absence of slip planes and have least probability of deforming by the application of force. Among these ceramics, the silicon carbide occupies a competent place to be used as a reinforcing agent for aluminum or its alloys. It has the density close to aluminum and is best for making composite having good strength and good heat conductivity. Stir casting has been used to synthesize Al/SiC MMCs by reinforcing silicon carbide particles into aluminum matrix. The reason for using stir casting is to develop technology for the development of MMCs at affordable cost. The selection of SiC as reinforcement and Al as matrix is because of their easy availability. The practical data acquired, analyzed and optimized will be interpreted in the light of information available in the literature and be shared with the relevant industries. The present work was mainly carried out to characterize the SiC/Al composite which was produced by reinforcing the various proportions of SiC (5, 10, 15, 25 and 30%) in aluminum matrix using stir casting technique. Mechanical properties of test specimens made from stir-casted Aluminum-Silicon Carbide composites have been studied using metallographic and mechanical testing techniques. It was observed that as the volume fraction of SiC in the composite is gradually increased, the hardness and toughness increase. However, beyond a level of 25-30 percent SiC, the results are not very consistent, and depend largely on the uniformity of distribution of SiC in the aluminum matrix. (author)

Exploring the effects of SiC reinforcement incorporation on mechanical properties of friction stir welded 7075 aluminum alloy: Fatigue life, impact energy, tensile strength

International Nuclear Information System (INIS)

Bahrami, Mohsen; Helmi, Nader; Dehghani, Kamran; Givi, Mohammad Kazem Besharati

2014-01-01

In the current research, the role of SiC nano-particles in improving the mechanical properties of friction stir welded (FSWed) 7075 aluminum alloy is investigated. To this end, friction stir welding (FSW) was conducted at 1250 rpm and 40 mm/min. The experiment carried out with and without incorporating SiC nano-particles along the joint line. Cross-sectional microstructures of the joints were characterized employing optical and scanning electron microscopy (SEM). Results achieved through X-ray diffraction (XRD) confirmed the presence of SiC powders. Moreover, it was discovered that the volume fraction of the reinforcement particles was 20%. Along with an excellent bonding between SiC nano-particles and aluminum matrix, SEM photograph demonstrated a good dispersion of SiC reinforcements. Atomic force microscopy (AFM) results were also in tight agreement with the recent SEM microstructure. Thanks to the presence of SiC nano-particles, tensile strength, percent elongation, fatigue life, and toughness of the joint improved tremendously. The fracture morphologies were in good agreement with corresponding ductility results

Exploring the effects of SiC reinforcement incorporation on mechanical properties of friction stir welded 7075 aluminum alloy: Fatigue life, impact energy, tensile strength

Energy Technology Data Exchange (ETDEWEB)

Bahrami, Mohsen, E-mail: Mohsen.bahrami@aut.ac.ir [Faculty of Mining and Metallurgical Engineering, Amirkabir University of Technology (AUT), Hafez Avenue, Tehran (Iran, Islamic Republic of); Helmi, Nader [Faculty of Mining and Metallurgical Engineering, Amirkabir University of Technology (AUT), Hafez Avenue, Tehran (Iran, Islamic Republic of); Dehghani, Kamran [Faculty of Mining and Metallurgical Engineering, Amirkabir University of Technology (AUT), Hafez Avenue, Tehran (Iran, Islamic Republic of); Centre of Excellence in Smart Structures and Dynamical Systems (Iran, Islamic Republic of); Givi, Mohammad Kazem Besharati [Department of Mechanical Engineering, University of Tehran, Tehran (Iran, Islamic Republic of)

2014-02-10

In the current research, the role of SiC nano-particles in improving the mechanical properties of friction stir welded (FSWed) 7075 aluminum alloy is investigated. To this end, friction stir welding (FSW) was conducted at 1250 rpm and 40 mm/min. The experiment carried out with and without incorporating SiC nano-particles along the joint line. Cross-sectional microstructures of the joints were characterized employing optical and scanning electron microscopy (SEM). Results achieved through X-ray diffraction (XRD) confirmed the presence of SiC powders. Moreover, it was discovered that the volume fraction of the reinforcement particles was 20%. Along with an excellent bonding between SiC nano-particles and aluminum matrix, SEM photograph demonstrated a good dispersion of SiC reinforcements. Atomic force microscopy (AFM) results were also in tight agreement with the recent SEM microstructure. Thanks to the presence of SiC nano-particles, tensile strength, percent elongation, fatigue life, and toughness of the joint improved tremendously. The fracture morphologies were in good agreement with corresponding ductility results.

Effective moduli of high volume fraction particulate composites

International Nuclear Information System (INIS)

Kwon, P.; Dharan, C.K.H.

1995-01-01

Predictions using current micromechanics theories for the effective moduli of particulate-reinforced composites tend to break down at high volume fractions of the reinforcing phase. The predictions are usually well below experimentally measured values of the Young's modulus for volume fractions exceeding about 0.6. In this paper, the concept of contiguity, which is a measure of phase continuity, is applied to Mori-Tanaka micromechanics theory. It is shown that contiguity of the second phase increases with volume fraction, leading eventually to a reversal in the roles of the inclusion and matrix. In powder metallurgy practice, it is well known that at high volume fractions, sintering and consolidation of the reinforcement make it increasingly continuous and more like the matrix phase, while the former matrix tends to become more like the inclusion phase. The concept of contiguity applied to micromechanics theory results in very good agreement between the predicted Young's modulus and experimental data on tungsten carbide particulate-reinforced cobalt

Effect of SiC Nanowhisker on the Microstructure and Mechanical Properties of WC-Ni Cemented Carbide Prepared by Spark Plasma Sintering

Directory of Open Access Journals (Sweden)

Xiaoyong Ren

2014-01-01

Full Text Available Ultrafine tungsten carbide-nickel (WC-Ni cemented carbides with varied fractions of silicon carbide (SiC nanowhisker (0–3.75 wt.% were fabricated by spark plasma sintering at 1350°C under a uniaxial pressure of 50 MPa with the assistance of vanadium carbide (VC and tantalum carbide (TaC as WC grain growth inhibitors. The effects of SiC nanowhisker on the microstructure and mechanical properties of the as-prepared WC-Ni cemented carbides were investigated. X-ray diffraction analysis revealed that during spark plasma sintering (SPS Ni may react with the applied SiC nanowhisker, forming Ni2Si and graphite. Scanning electron microscopy examination indicated that, with the addition of SiC nanowhisker, the average WC grain size decreased from 400 to 350 nm. However, with the additional fractions of SiC nanowhisker, more and more Si-rich aggregates appeared. With the increase in the added fraction of SiC nanowhisker, the Vickers hardness of the samples initially increased and then decreased, reaching its maximum of about 24.9 GPa when 0.75 wt.% SiC nanowhisker was added. However, the flexural strength of the sample gradually decreased with increasing addition fraction of SiC nanowhisker.

Residual stresses and mechanical properties of Si3N4/SiC multilayered composites with different SiC layers; Las tensiones residuales y las propiedades mecánicas de compuestos multicapa de Si3N4/SiC con diferentes capas de SiC

Energy Technology Data Exchange (ETDEWEB)

Liua, S.; Lia, Y.; Chena, P.; Lia, W.; Gaoa, S.; Zhang, B.; Yeb, F.

2017-11-01

The effect of residual stresses on the strength, toughness and work of fracture of Si3N4/SiC multilayered composites with different SiC layers has been investigated. It may be an effective way to design and optimize the mechanical properties of Si3N4/SiC multilayered composites by controlling the properties of SiC layers. Si3N4/SiC multilayered composites with different SiC layers were fabricated by aqueous tape casting and pressureless sintering. Residual stresses were calculated by using ANSYS simulation, the maximum values of tensile and compressive stresses were 553.2MPa and −552.1MPa, respectively. Step-like fracture was observed from the fracture surfaces. Fraction of delamination layers increased with the residual stress, which can improve the reliability of the materials. Tensile residual stress was benefit to improving toughness and work of fracture, but the strength of the composites decreased. [Spanish] Se ha investigado el efecto de las tensiones residuales en la resistencia, dureza y trabajo de fractura de los compuestos multicapa de Si3N4/SiC con diferentes capas de SiC. Puede ser una manera eficaz de diseñar y optimizar las propiedades mecánicas de los compuestos multicapa de Si3N4/SiC mediante el control de las propiedades de las capas de SiC. Los compuestos multicapa de Si3N4/SiC con diferentes capas de SiC se fabricaron por medio de colado en cinta en medio acuoso y sinterización sin presión. Las tensiones residuales se calcularon mediante el uso de la simulación ANSYS, los valores máximos de las fuerzas de tracción y compresión fueron 553,2 MPa y −552,1 MPa, respectivamente. Se observó una fractura escalonada a partir de las superficies de fractura. La fracción de capas de deslaminación aumenta con la tensión residual, lo que puede mejorar la fiabilidad de los materiales. La fuerza de tracción residual era beneficiosa para la mejora de la dureza y el trabajo de fractura, pero la resistencia de los compuestos disminuyó.

Precession electron diffraction for SiC grain boundary characterization in unirradiated TRISO fuel

International Nuclear Information System (INIS)

Lillo, T.M.; Rooyen, I.J. van; Wu, Y.Q.

2016-01-01

Highlights: • SiC grain orientation determined by TEM-based precession electron diffraction. • Orientation data improved with increasing TEM sample thickness. • Fraction of low angle grain boundaries lower from PED data than EBSD data. • Fractions of high angle and CSL-related boundaries similar to EBSD data. - Abstract: Precession electron diffraction (PED), a transmission electron microscopy-based technique, has been evaluated for the suitability for evaluating grain boundary character in the SiC layer of tristructural isotropic (TRISO) fuel. This work reports the effect of transmission electron microscope (TEM) lamella thickness on the quality of data and establishes a baseline comparison to SiC grain boundary characteristics, in an unirradiated TRISO particle, determined previously using a conventional electron backscatter diffraction (EBSD) scanning electron microscope (SEM)-based technique. In general, it was determined that the lamella thickness produced using the standard focused ion beam (FIB) fabrication process (∼80 nm), is sufficient to provide reliable PED measurements, although thicker lamellae (∼120 nm) were found to produce higher quality orientation data. Also, analysis of SiC grain boundary character from the TEM-based PED data showed a much lower fraction of low-angle grain boundaries compared to SEM-based EBSD data from the SiC layer of a TRISO-coated particle made using the same fabrication parameters and a SiC layer deposited at a slightly lower temperature from a surrogate TRISO particle. However, the fractions of high-angle and coincident site lattice (CSL)-related grain boundaries determined by PED are similar to those found using SEM-based EBSD. Since the grain size of the SiC layer of TRSIO fuel can be as small as 250 nm (Kirchhofer et al., 2013), depending on the fabrication parameters, and since grain boundary fission product precipitates in irradiated TRISO fuel can be nano-sized, the TEM-based PED orientation data

Lamb Wave Assessment of Fiber Volume Fraction in Composites

Science.gov (United States)

Seale, Michael D.; Smith, Barry T.; Prosser, W. H.; Zalameda, Joseph N.

1998-01-01

Among the various techniques available, ultrasonic Lamb waves offer a convenient method of examining composite materials. Since the Lamb wave velocity depends on the elastic properties of a material, an effective tool exists to evaluate composites by measuring the velocity of these waves. Lamb waves can propagate over long distances and are sensitive to the desired in-plane elastic properties of the material. This paper discusses a study in which Lamb waves were used to examine fiber volume fraction variations of approximately 0.40-0.70 in composites. The Lamb wave measurements were compared to fiber volume fractions obtained from acid digestion tests. Additionally, a model to predict the fiber volume fraction from Lamb wave velocity values was evaluated.

Synthesis, microstructure and mechanical properties of Ti3SiC2-TiC composites pulse discharge sintered from Ti/Si/TiC powder mixture

International Nuclear Information System (INIS)

Tian Wubian; Sun Zhengming; Hashimoto, Hitoshi; Du Yulei

2009-01-01

Ti 3 SiC 2 -TiC composites with the volume fractions of TiC from 0 to 90% were fabricated by pulse discharge sintering (PDS) technique using Ti-Si-TiC as starting powders in the sintering temperature range of 1250-1400 deg. C. Phase content and microstructure of the synthesized samples were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The samples sintered at 1400 deg. C are almost fully dense for all compositions with relative density higher than 98%. The phase distribution in the synthesized samples is non-uniform. The Vickers hardness increases almost linearly with the volume fraction of TiC up to a value of 20.1 ± 1.4 GPa at 90 vol.% TiC. The flexural strength increases with the volume fraction of TiC to a maximum value of 655 ± 10 MPa at 50 vol.% TiC. The relationship between microstructure and mechanical properties is discussed.

Comparative study of SiC- and Si-based photovoltaic inverters

Science.gov (United States)

Ando, Yuji; Oku, Takeo; Yasuda, Masashi; Shirahata, Yasuhiro; Ushijima, Kazufumi; Murozono, Mikio

2017-01-01

This article reports comparative study of 150-300 W class photovoltaic inverters (Si inverter, SiC inverter 1, and SiC inverter 2). In these sub-kW class inverters, the ON-resistance was considered to have little influence on the efficiency. The developed SiC inverters, however, have exhibited an approximately 3% higher direct current (DC)-alternating current (AC) conversion efficiency as compared to the Si inverter. Power loss analysis indicated a reduction in the switching and reverse recovery losses of SiC metal-oxide-semiconductor field-effect transistors used for the DC-AC converter is responsible for this improvement. In the SiC inverter 2, an increase of the switching frequency up to 100 kHz achieved a state-of-the-art combination of the weight (1.25 kg) and the volume (1260 cm3) as a 150-250 W class inverter. Even though the increased switching frequency should cause the increase of the switching losses, the SiC inverter 2 exhibited an efficiency comparable to the SiC inverter 1 with a switching frequency of 20 kHz. The power loss analysis also indicated a decreased loss of the DC-DC converter built with SiC Schottky barrier diodes led to the high efficiency for its increased switching frequency. These results clearly indicated feasibility of SiC devices even for sub-kW photovoltaic inverters, which will be available for the applications where compactness and efficiency are of tremendous importance.

Accuracy of cancellous bone volume fraction measured by micro-CT scanning

DEFF Research Database (Denmark)

Ding, Ming; Odgaard, A; Hvid, I

1999-01-01

Volume fraction, the single most important parameter in describing trabecular microstructure, can easily be calculated from three-dimensional reconstructions of micro-CT images. This study sought to quantify the accuracy of this measurement. One hundred and sixty human cancellous bone specimens...... which covered a large range of volume fraction (9.8-39.8%) were produced. The specimens were micro-CT scanned, and the volume fraction based on Archimedes' principle was determined as a reference. After scanning, all micro-CT data were segmented using individual thresholds determined by the scanner...

SiC Seeded Crystal Growth

Science.gov (United States)

Glass, R. C.; Henshall, D.; Tsvetkov, V. F.; Carter, C. H., Jr.

1997-07-01

The availability of relatively large (30 mm) SiC wafers has been a primary reason for the renewed high level of interest in SiC semiconductor technology. Projections that 75 mm SiC wafers will be available in 2 to 3 years have further peaked this interest. Now both 4H and 6H polytypes are available, however, the micropipe defects that occur to a varying extent in all wafers produced to date are seen by many as preventing the commercialization of many types of SiC devices, especially high current power devices. Most views on micropipe formation are based around Frank's theory of a micropipe being the hollow core of a screw dislocation with a huge Burgers vector (several times the unit cell) and with the diameter of the core having a direct relationship with the magnitude of the Burgers vector. Our results show that there are several mechanisms or combinations of these mechanisms which cause micropipes in SiC boules grown by the seeded sublimation method. Additional considerations such as polytype variations, dislocations and both impurity and diameter control add to the complexity of producing high quality wafers. Recent results at Cree Research, Inc., including wafers with micropipe densities of less than 1 cm - 2 (with 1 cm2 areas void of micropipes), indicate that micropipes will be reduced to a level that makes high current devices viable and that they may be totally eliminated in the next few years. Additionally, efforts towards larger diameter high quality substrates have led to production of 50 mm diameter 4H and 6H wafers for fabrication of LEDs and the demonstration of 75 mm wafers. Low resistivity and semi-insulating electrical properties have also been attained through improved process and impurity control. Although challenges remain, the industry continues to make significant progress towards large volume SiC-based semiconductor fabrication.

Determination of bone mineral volume fraction using impedance analysis and Bruggeman model

Energy Technology Data Exchange (ETDEWEB)

Ciuchi, Ioana Veronica; Olariu, Cristina Stefania, E-mail: oocristina@yahoo.com; Mitoseriu, Liliana, E-mail: lmtsr@uaic.ro

2013-11-20

Highlights: • Mineral volume fraction of a bone sample was determined. • Dielectric properties for bone sample and for the collagen type I were determined by impedance spectroscopy. • Bruggeman effective medium approximation was applied in order to evaluate mineral volume fraction of the sample. • The computed values were compared with ones derived from a histogram test performed on SEM micrographs. -- Abstract: Measurements by impedance spectroscopy and Bruggeman effective medium approximation model were employed in order to determine the mineral volume fraction of dry bone. This approach assumes that two or more phases are present into the composite: the matrix (environment) and the other ones are inclusion phases. A fragment of femur diaphysis dense bone from a young pig was investigated in its dehydrated state. Measuring the dielectric properties of bone and its main components (hydroxyapatite and collagen) and using the Bruggeman approach, the mineral volume filling factor was determined. The computed volume fraction of the mineral volume fraction was confirmed by a histogram test analysis based on the SEM microstructures. In spite of its simplicity, the method provides a good approximation for the bone mineral volume fraction. The method which uses impedance spectroscopy and EMA modeling can be further developed by considering the conductive components of the bone tissue as a non-invasive in situ impedance technique for bone composition evaluation and monitoring.

Determination of bone mineral volume fraction using impedance analysis and Bruggeman model

International Nuclear Information System (INIS)

Ciuchi, Ioana Veronica; Olariu, Cristina Stefania; Mitoseriu, Liliana

2013-01-01

Highlights: • Mineral volume fraction of a bone sample was determined. • Dielectric properties for bone sample and for the collagen type I were determined by impedance spectroscopy. • Bruggeman effective medium approximation was applied in order to evaluate mineral volume fraction of the sample. • The computed values were compared with ones derived from a histogram test performed on SEM micrographs. -- Abstract: Measurements by impedance spectroscopy and Bruggeman effective medium approximation model were employed in order to determine the mineral volume fraction of dry bone. This approach assumes that two or more phases are present into the composite: the matrix (environment) and the other ones are inclusion phases. A fragment of femur diaphysis dense bone from a young pig was investigated in its dehydrated state. Measuring the dielectric properties of bone and its main components (hydroxyapatite and collagen) and using the Bruggeman approach, the mineral volume filling factor was determined. The computed volume fraction of the mineral volume fraction was confirmed by a histogram test analysis based on the SEM microstructures. In spite of its simplicity, the method provides a good approximation for the bone mineral volume fraction. The method which uses impedance spectroscopy and EMA modeling can be further developed by considering the conductive components of the bone tissue as a non-invasive in situ impedance technique for bone composition evaluation and monitoring

Switching Performance Evaluation of Commercial SiC Power Devices (SiC JFET and SiC MOSFET) in Relation to the Gate Driver Complexity

DEFF Research Database (Denmark)

Pittini, Riccardo; Zhang, Zhe; Andersen, Michael A. E.

2013-01-01

and JFETs. The recent introduction of SiC MOSFET has proved that it is possible to have highly performing SiC devices with a minimum gate driver complexity; this made SiC power devices even more attractive despite their device cost. This paper presents an analysis based on experimental results...... of the switching losses of various commercially available Si and SiC power devices rated at 1200 V (Si IGBTs, SiC JFETs and SiC MOSFETs). The comparison evaluates the reduction of the switching losses which is achievable with the introduction of SiC power devices; this includes analysis and considerations...

Real-time particle volume fraction measurement in centrifuges by wireless electrical resistance detector

International Nuclear Information System (INIS)

Nagae, Fumiya; Okawa, Kazuya; Matsuno, Shinsuke; Takei, Masahiro; Zhao Tong; Ichijo, Noriaki

2015-01-01

In this study, wireless electrical resistance detector is developed as first step in order to develop electrical resistance tomography (ERT) that are attached wireless communication, and miniaturized. And the particle volume fraction measurement results appropriateness is qualitatively examined. The real-time particle volume fraction measurement is essential for centrifuges, because rotational velocity and supply should be controlled based on the results in order to obtain the effective separation, shorten process time and save energy. However, a technique for the particle volume fraction measurement in centrifuges has not existed yet. In other words, the real-time particle volume fraction measurement in centrifuges becomes innovative technologies. The experiment device reproduces centrifugation in two-phase using particle and salt solution as measuring object. The particle concentration is measured changing rotational velocity, supply and measurement section position. The measured concentration changes coincide with anticipated tendency of concentration changes. Therefore the particle volume fraction measurement results appropriateness are qualitatively indicated. (author)

Crystallization of sheared hard spheres at 64.5% volume fraction

Science.gov (United States)

Swinney, H. L.; Rietz, F.; Schroeter, M.; Radin, C.

2017-11-01

A classic experiment by G.D. Scott Nature 188, 908, 1960) showed that pouring balls into a rigid container filled the volume to an upper limit of 64% of the container volume, which is well below the 74% volume fraction filled by spheres in a hexagonal close packed (HCP) or face center cubic (FCC) lattice. Subsequent experiments have confirmed a ``random closed packed'' (RCP) fraction of about 64%. However, the physics of the RCP limit has remained a mystery. Our experiment on a cubical box filled with 49400 weakly sheared glass spheres reveals a first order phase transition from a disordered to an ordered state at a volume fraction of 64.5%. The ordered state consists of crystallites of mixed FCC and HCP symmetry that coexist with the amorphous bulk. The transition is initiated by homogeneous nucleation: in the shearing process small crystallites with about ten or fewer spheres dissolve, while larger crystallites grow. A movie illustrates the crystallization process. German Academic Exchange Service (DAAD), German Research Foundation (DFG), NSF DMS, and R.A. Welch Foundation.

Palladium transport in SiC

International Nuclear Information System (INIS)

Olivier, E.J.; Neethling, J.H.

2012-01-01

Highlights: ► We investigate the reaction of Pd with SiC at typical HTGR operating temperatures. ► The high temperature mobility of palladium silicides within polycrystalline SiC was studied. ► Corrosion of SiC by Pd was seen in all cases. ► The preferential corrosion and penetration of Pd along grain boundaries in SiC was found. ► The penetration and transport of palladium silicides in SiC along grain boundaries was found. - Abstract: This paper reports on a transmission electron microscopy (TEM) and scanning electron microscopy (SEM) study of Pd corroded SiC. The reaction of Pd with different types of SiC at typical HTGR operating temperatures was examined. In addition the high temperature mobility of palladium silicides within polycrystalline SiC was investigated. The results indicated corrosion of the SiC by Pd in all cases studied. The corrosion leads to the formation of palladium silicides within the SiC, with the predominant phase found being Pd 2 Si. Evidence for the preferential corrosion and penetration of Pd along grain boundaries in polycrystalline SiC was found. The penetration and transport, without significant corrosion, of palladium silicides into polycrystalline SiC along grain boundaries was also observed. Implications of the findings with reference to the use of Tri Isotropic particles in HTGRs will be discussed.

Effect of SiC Content on Microstructure and Wear Resistance of Laser Cladding SiC/Ni60A Composite Coating

Directory of Open Access Journals (Sweden)

ZHAO Long-zhi

2017-03-01

Full Text Available The SiC reinforced Ni60A alloy laser cladding coating on the 45 steel substrate was fabricated with the LDM2500-60 semiconductor laser equipment. The effect of SiC content on microstructure, dilution rate, wear resistance, friction coefficient and microhardness was investigated systematically.The results show that with the increase of SiC content, the microstructure of upper coating is refined obviously, the dilution rate, wear resistance, friction coefficient and microhardness increase firstly and then decrease;when the mass fraction of SiC is 20%, the wear resistance of the cladding coating is the best one, in which the wear loss of coating is only 0.0012g and is 1/36.3 of the matrix;the minimum friction coefficient is 0.464, the friction process is the most stable;the highest microhardness of the cladding coating is 1039.9HV0.2, which is 3.5 times of the substrate;but when the mass fraction of SiC is 25%, the microhardness and wear resistance of coating decrease.

Absorbed fractions for alpha particles in ellipsoidal volumes

International Nuclear Information System (INIS)

Amato, Ernesto; Baldari, Sergio; Italiano, Antonio

2013-01-01

Internal dosimetry of alpha particles is gaining attention due to the increasing applications in cancer treatment and also for the assessment of environmental contamination from radionuclides. We developed a Monte Carlo simulation in GEANT4 in order to calculate the absorbed fractions for monoenergetic alpha particles in the energy interval between 0.1 and 10 MeV, uniformly distributed in ellipsoids made of soft tissue. For each volume, we simulated a spherical shape, three oblate and three prolate ellipsoids, and one scalene shape. For each energy and for every geometrical configuration, an analytical relationship between the absorbed fraction and a ‘generalized radius’ was found; and the dependence of the fit parameters on the alpha energy is discussed and fitted by parametric functions. With the proposed formulation, the absorbed fraction for alpha particles in the energy range explored can be calculated for volumes and for ellipsoidal shapes of practical interest. This method can be applied to the evaluation of absorbed fraction from alpha-emitting radionuclides. The contribution to the deposited energy coming from electron and photon emissions can be accounted for exploiting the specific formulations previously introduced. As an example of application, the dosimetry of 213 Bi and its decay chain in ellipsoids is reported. (paper)

Palladium transport in SiC

Energy Technology Data Exchange (ETDEWEB)

Olivier, E.J., E-mail: jolivier@nmmu.ac.za [Centre for High Resolution Transmission Electron Microscopy, Nelson Mandela Metropolitan University, Port Elizabeth (South Africa); Neethling, J.H. [Centre for High Resolution Transmission Electron Microscopy, Nelson Mandela Metropolitan University, Port Elizabeth (South Africa)

2012-03-15

Highlights: Black-Right-Pointing-Pointer We investigate the reaction of Pd with SiC at typical HTGR operating temperatures. Black-Right-Pointing-Pointer The high temperature mobility of palladium silicides within polycrystalline SiC was studied. Black-Right-Pointing-Pointer Corrosion of SiC by Pd was seen in all cases. Black-Right-Pointing-Pointer The preferential corrosion and penetration of Pd along grain boundaries in SiC was found. Black-Right-Pointing-Pointer The penetration and transport of palladium silicides in SiC along grain boundaries was found. - Abstract: This paper reports on a transmission electron microscopy (TEM) and scanning electron microscopy (SEM) study of Pd corroded SiC. The reaction of Pd with different types of SiC at typical HTGR operating temperatures was examined. In addition the high temperature mobility of palladium silicides within polycrystalline SiC was investigated. The results indicated corrosion of the SiC by Pd in all cases studied. The corrosion leads to the formation of palladium silicides within the SiC, with the predominant phase found being Pd{sub 2}Si. Evidence for the preferential corrosion and penetration of Pd along grain boundaries in polycrystalline SiC was found. The penetration and transport, without significant corrosion, of palladium silicides into polycrystalline SiC along grain boundaries was also observed. Implications of the findings with reference to the use of Tri Isotropic particles in HTGRs will be discussed.

Effect of oxygen on the processes of ion beam synthesis of buried SiC layers in silicon

International Nuclear Information System (INIS)

Artamonov, V.V.; Valakh, M.Ya.; Klyuj, N.I.; Mel'nik, V.P.; Romanyuk, A.B.; Romanyuk, B.N.; Yukhimchuk, V.A.

1998-01-01

The properties of Si-structures with buried silicon carbide (SiC) layers created by high dose carbon implantation into Cz-Si or Fz-Si wafers followed by high-temperature annealing were studied by Raman and infrared spectroscopy. Effect of additional oxygen implantation on the peculiarities of SiC layer formation was also studied. It was shown that under the same implantation and post-implantation annealing conditions the buried SiC layers are more effectively formed in Cz-Si or in Si subjected to additional oxygen implantation. Thus, oxygen in silicon promotes the SiC layer formation due to SiO x precipitate creation and accommodation of the crystal volume in the region where SiC phase is formed

Effect of re-melting on particle distribution and interface formation in SiC reinforced 2124Al matrix composite

Energy Technology Data Exchange (ETDEWEB)

Mandal, Durbadal, E-mail: durbadal73@yahoo.co.in [MEF Division, CSIR-National Metallurgical Laboratory, Jamshedpur 831007 (India); Viswanathan, Srinath [Dept of Metallurgical and Materials Engineering, University of Alabama, Tuscaloosa, AL (United States)

2013-12-15

The interface between metal matrix and ceramic reinforcement particles plays an important role in improving properties of the metal matrix composites. Hence, it is important to find out the interface structure of composite after re-melting. In the present investigation, the 2124Al matrix with 10 wt.% SiC particle reinforced composite was re-melted at 800 °C and 900 °C for 10 min followed by pouring into a permanent mould. The microstructures reveal that the SiC particles are distributed throughout the Al-matrix. The volume fraction of SiC particles varies from top to bottom of the composite plate and the difference increases with the decrease of re-melting temperature. The interfacial structure of re-melted 2124Al–10 wt.%SiC composite was investigated using scanning electron microscopy, an electron probe micro-analyzer, a scanning transmission electron detector fitted with scanning electron microscopy and an X-ray energy dispersive spectrometer. It is found that a thick layer of reaction product is formed at the interface of composite after re-melting. The experimental results show that the reaction products at the interface are associated with high concentration of Cu, Mg, Si and C. At re-melting temperature, liquid Al reacts with SiC to form Al{sub 4}C{sub 3} and Al–Si eutectic phase or elemental Si at the interface. High concentration of Si at the interface indicates that SiC is dissociated during re-melting. The X-ray energy dispersive spectrometer analyses confirm that Mg- and Cu-enrich phases are formed at the interface region. The Mg is segregated at the interface region and formed MgAl{sub 2}O{sub 4} in the presence of oxygen. The several elements identified at the interface region indicate that different types of interfaces are formed in between Al matrix and SiC particles. The Al–Si eutectic phase is formed around SiC particles during re-melting which restricts the SiC dissolution. - Highlights: • Re-melted composite shows homogeneous particle

Pancreas volume and fat fraction in children with Type 1 diabetes.

Science.gov (United States)

Regnell, S E; Peterson, P; Trinh, L; Broberg, P; Leander, P; Lernmark, Å; Månsson, S; Elding Larsson, H

2016-10-01

People with Type 1 diabetes have smaller pancreases than healthy individuals. Several diseases causing pancreatic atrophy are associated with pancreatic steatosis, but pancreatic fat in Type 1 diabetes has not been measured. This cross-sectional study aimed to compare pancreas size and fat fraction in children with Type 1 diabetes and controls. The volume and fat fraction of the pancreases of 22 children with Type 1 diabetes and 29 controls were determined using magnetic resonance imaging. Pancreas volume was 27% smaller in children with diabetes (median 34.9 cm(3) ) than in controls (47.8 cm(3) ; P Pancreas volume correlated positively with age in controls (P = 0.033), but not in children with diabetes (P = 0.649). Pancreas volume did not correlate with diabetes duration, but it did correlate positively with units of insulin/kg body weight/day (P = 0.048). A linear model of pancreas volume as influenced by age, body surface area and insulin units/kg body weight/day found that insulin dosage correlated with pancreas volume after controlling for both age and body surface area (P = 0.009). Pancreatic fat fraction was not significantly different between the two groups (1.34% vs. 1.57%; P = 0.891). Our findings do not indicate that pancreatic atrophy in Type 1 diabetes is associated with an increased pancreatic fat fraction, unlike some other diseases featuring reduced pancreatic volume. We speculate that our results may support the hypotheses that much of pancreatic atrophy in Type 1 diabetes occurs before the clinical onset of the disease and that exogenous insulin administration decelerates pancreatic atrophy after diabetes onset. © 2016 Diabetes UK.

Laser-induced incandescence: Towards quantitative soot volume fraction measurements

Energy Technology Data Exchange (ETDEWEB)

Tzannis, A P; Wienbeucker, F; Beaud, P; Frey, H -M; Gerber, T; Mischler, B; Radi, P P [Paul Scherrer Inst. (PSI), Villigen (Switzerland)

1999-08-01

Laser-Induced Incandescence has recently emerged as a versatile tool for measuring soot volume fraction in a wide range of combustion systems. In this work we investigate the essential features of the method. LII is based on the acquisition of the incandescence of soot when heated through a high power laser pulse. Initial experiments have been performed on a model laboratory flame. The behaviour of the LII signal is studied experimentally. By applying numerical calculations we investigate the possibility to obtain two-dimensional soot volume fraction distributions. For this purpose a combination of LII with other techniques is required. This part is discussed in some extent and the future work is outlined. (author) 4 figs., 3 refs.

Gamma ray densitometry techniques for measuring of volume fractions

International Nuclear Information System (INIS)

Affonso, Renato Raoni Werneck; Silva, Ademir Xavier da; Salgado, Cesar Marques

2015-01-01

Knowledge of the volume fraction in a multiphase flow is of key importance in predicting the performance of many systems and processes. It is therefore an important parameter to characterize such flows. In the context of nuclear techniques, the gamma ray densitometry is promising and this is due to its non-invasive characteristics and very reliable results. It is used in several applications for multiphase flows (water-oil-air), which are employed tools such as: computational fluid dynamics, artificial neural networks and statistical methods of radiation transport, such as the Monte Carlo method. Based on the gamma radiation techniques for measurements of volume fractions, the aim of this paper is to present several techniques developed for this purpose. (author)

Gamma ray densitometry techniques for measuring of volume fractions

Energy Technology Data Exchange (ETDEWEB)

Affonso, Renato Raoni Werneck; Silva, Ademir Xavier da; Salgado, Cesar Marques, E-mail: raoniwa@yahoo.com.br, E-mail: ademir@nuclear.ufrj.br, E-mail: otero@ien.gov.br [Instituto de Engenharia Nuclear (IEN/CNEN-RJ), Rio de Janeiro, RJ (Brazil)

2015-07-01

Knowledge of the volume fraction in a multiphase flow is of key importance in predicting the performance of many systems and processes. It is therefore an important parameter to characterize such flows. In the context of nuclear techniques, the gamma ray densitometry is promising and this is due to its non-invasive characteristics and very reliable results. It is used in several applications for multiphase flows (water-oil-air), which are employed tools such as: computational fluid dynamics, artificial neural networks and statistical methods of radiation transport, such as the Monte Carlo method. Based on the gamma radiation techniques for measurements of volume fractions, the aim of this paper is to present several techniques developed for this purpose. (author)

Dosimetric impact of prostate volume change between CT-based HDR brachytherapy fractions

International Nuclear Information System (INIS)

Kim, Yongbok; Hsu, I-C.; Lessard, Etienne; Vujic, Jasmina; Pouliot, Jean

2004-01-01

Purpose: The objective is to evaluate the prostate volume change and its dosimetric consequences after the insertion of catheters for high-dose-rate brachytherapy. Methods and Materials: For 13 consecutive patients, a spiral CT scan was acquired before each of the 2 fractions, separated on average by 20 hours. The coordinates of the catheters were obtained on 3 axial CT slices corresponding to apex, mid portion, and base portion of the prostate. A mathematical expansion model was used to evaluate the change of prostate volumes between the 2 fractions. It is based on the difference in the cube of the average distance between the centroid and catheter positions. The variation of implant dose-volume histograms between fractions was computed for plans produced by either inverse planning based on simulated annealing or geometric optimization. Results: The average magnitude of either increase or reduction in prostate volume was 7.8% (range, 2-17%). This volume change corresponds to an average prostate radius change of only 2.5% (range, 0.7-5.4%). For 5 patients, the prostate volume increased on average by 9% (range, 2-17%), whereas a reduction was observed for 8 patients by an average of 7% (range, 2-13%). More variation was observed at the prostate base than at mid or apex gland. The comparison of implant dose-volume histograms showed a small reduction of V100 receiving the prescription dose, with an average of 3.5% (range, 0.5-12%) and 2.2% (range, 1-6%) for inverse planning based on our simulated annealing and geometric optimization plans, respectively. Conclusion: Small volume change was observed between treatment fractions. This translates into small changes in dose delivered to the prostate volume

TiC/Ti3SiC2复合材料的制备及其性能研究%Preparation and properties of TiC/Ti3SiC2 composites

Institute of Scientific and Technical Information of China (English)

贾换; 尹洪峰; 袁蝴蝶; 杨祎诺

2012-01-01

以粉末Ti,Si,TiC和炭黑为原料,采用反应热压烧结法制备TiC/Ti3SiC2复合材料.借助XRD和SEM研究TiC含量对TiC/Ti3SiC2复合材料相组成、显微结构及力学特性的影响.结果表明:通过热压烧结可以得到致密度较高的TiC/Ti3SiC2复合材料；引入TiC可以促进Ti3SiC2的生成,当引入TiC的质量分数达30％,TiC/Ti3SiC2复合材料的弯曲强度和断裂韧性分别为406.9 MPa,3.7 MPa·m1/2；复合材料中Ti3SiC2相以穿晶断裂为主,TiC晶粒易产生拔出.%TiC/Ti3SiC2 composites were fabricated by reactive hot pressing sintering method using the mixture powder of Ti, Si, C and TiC as raw material. The effect of TiC content on phase composition, microstructure and mechanical properties of TiC/Ti3SiC2 composites was investigated by X-ray diffraction and scanning electron microscopy. The results demonstrate that dense TiC/ Ti3SiC2 composites can be obtained by hot pressing. The addition of TiC into composites can enhance the formation of TisSiC2. When the additional content of TiC reaches 30% (mass fraction) , the flexural strength and fracture toughness of TiC/Ti3SiC2 composite are 406.9 MPa and 3.7 MPa·m-2, respectively. Ti3SiC2 phase displays intergranular fracture and TiC grain pulls out from Ti3SiC2 matrix when TiC/Ti3SiC2 composite fractures.

Comparative study to use nano-(Al2O3, CuO, and SiC) with water to enhance photovoltaic thermal PV/T collectors

International Nuclear Information System (INIS)

Al-Waeli, Ali H.A.; Chaichan, Miqdam T.; Kazem, Hussein A.; Sopian, K.

2017-01-01

Highlights: • Three types of nanoparticles (Al 2 O 3 , CuO and SiC) were added to water which was used as a base fluid. • The resulted nanofluid was used for cooling an indoor PV/T system. • The used nanofluids improved the thermal and electrical efficiencies of the PV/T system. • The stability of nanofluids was examined for an extended period and found to be stable. • SiC nanofluid showed better thermal conductivity and stability compared with Al 2 O 3 and CuO nanofluids. - Abstract: The reduction in efficiency of photovoltaic (PV) units due to increases in cell temperature occurs when a small part of the absorbed solar radiation is converted into electricity and the remaining part is lost as heat. Recently, the addition of a range of nanomaterials with high thermal conductivity to the cooling fluid in PV/T systems has been the subject of much research. In this study, three nanomaterials were added to water as a base fluid with several volume fractions to determine the best concentration and nanoparticle for this application. The PV/T system was setup in an indoor laboratory. Knowing which material has a better effect on the PV unit in particular, and the PV/T unit in general, is important for deciding which nanomaterial is more suitable for the system. The results reveal that nanofluid gives higher thermal conductivity with very little increase in the fluid density and viscosity compared with the base fluid. The studied volume fractions were 0.5, 1, 2, 3, and 4% and the selected nanoparticles were Al 2 O 3 , CuO, and SiC. It was found that silicon carbide nanoparticles have the best stability and the highest thermal conductivity compared to the other two nano-substances. Copper oxide nanofluid has higher thermal conductivity than aluminium oxide but lower stability, although it was found here that this material reliably stable compared to in other studies. The nanofluid reduced the indoor PV/T system temperature and enhanced its generated power.

Method and apparatus for probing relative volume fractions

Science.gov (United States)

Jandrasits, Walter G.; Kikta, Thomas J.

1998-01-01

A relative volume fraction probe particularly for use in a multiphase fluid system includes two parallel conductive paths defining therebetween a sample zone within the system. A generating unit generates time varying electrical signals which are inserted into one of the two parallel conductive paths. A time domain reflectometer receives the time varying electrical signals returned by the second of the two parallel conductive paths and, responsive thereto, outputs a curve of impedance versus distance. An analysis unit then calculates the area under the curve, subtracts the calculated area from an area produced when the sample zone consists entirely of material of a first fluid phase, and divides this calculated difference by the difference between an area produced when the sample zone consists entirely of material of the first fluid phase and an area produced when the sample zone consists entirely of material of a second fluid phase. The result is the volume fraction.

Scanning Electron Microscopic Studies of Microwave Sintered Al-SiC Nanocomposites and Their Properties

Directory of Open Access Journals (Sweden)

M. A. Himyan

2018-01-01

Full Text Available Al-metal matrix composites (AMMCs reinforced with diverse volume fraction of SiC nanoparticles were synthesized using microwave sintering process. The effects of the reinforcing SiC particles on physical, microstructure, mechanical, and electrical properties were studied. The phase, microstructural, and surface analyses of the composites were systematically conducted using X-ray diffraction (XRD, scanning electron microscope (SEM, and surface profilometer techniques, respectively. The microstructural examination revealed the homogeneous distribution of SiC particles in the Al matrix. Microhardness and compressive strength of nanocomposites were found to be increasing with the increasing volume fraction of SiC particles. Electrical conductivity of the nanocomposites decreases with increasing the SiC content.

Volume fraction calculation in multiphase system such as oil-water-gas using neutron

Energy Technology Data Exchange (ETDEWEB)

Ramos, Robson; Brandao, Luis E.B.; Salgado, Cesar Marques; Pereira, Claudio M.N.A. [Instituto de Engenharia Nuclear (IEN/CNEN-RJ), Rio de Janeiro, RJ (Brazil)]. E-mails: robson@ien.gov.br; brandao@ien.gov.br; otero@ien.gov.br; cmnap@ien.gov.br; Schirru, Roberto; Silva, Ademir Xavier da [Universidade Federal, Rio de Janeiro, RJ (Brazil). Coordenacao dos Programas de Pos-graduacao de Engenharia. Programa de Engenharia Nuclear]. E-mails: schirru@lmp.ufrj.br; ademir@con.ufrj.br

2007-07-01

Multi-phase flows are common in diverse industrial sectors and the attainment of the volume fraction of each element that composes the flow system presents difficulties for the engineering process, therefore, to determine them is very important. In this work is presented methodology for determination of volume fractions in annular three-phase flow systems, such as oil-water-gas, based on the use of nuclear techniques and artificial intelligence. Using the principle of the fast-neutron transmission/scattering, come from an isotopic {sup 241}Am-Be source, and two point detectors, is gotten measured that they are influenced by the variations of the volume fractions of each phase present in the flow. An artificial neural network is trained to correlate such measures with the respective volume fractions. In order to get the data for training of the artificial neural network without necessity to carry through experiments, MCNP-X code is used, that simulates computational of the neutrons transport. The methodology is sufficiently advantageous, therefore, allows to develop a measurement system capable to determine the fractions of the phases (oil-water-gas), with proper requirements of each petroliferous installation and with national technology contributing, possibly, with reduction of costs and increase of productivity. (author)

Volume fraction calculation in multiphase system such as oil-water-gas using neutron

International Nuclear Information System (INIS)

Ramos, Robson; Brandao, Luis E.B.; Salgado, Cesar Marques; Pereira, Claudio M.N.A.; Schirru, Roberto; Silva, Ademir Xavier da

2007-01-01

Multi-phase flows are common in diverse industrial sectors and the attainment of the volume fraction of each element that composes the flow system presents difficulties for the engineering process, therefore, to determine them is very important. In this work is presented methodology for determination of volume fractions in annular three-phase flow systems, such as oil-water-gas, based on the use of nuclear techniques and artificial intelligence. Using the principle of the fast-neutron transmission/scattering, come from an isotopic 241 Am-Be source, and two point detectors, is gotten measured that they are influenced by the variations of the volume fractions of each phase present in the flow. An artificial neural network is trained to correlate such measures with the respective volume fractions. In order to get the data for training of the artificial neural network without necessity to carry through experiments, MCNP-X code is used, that simulates computational of the neutrons transport. The methodology is sufficiently advantageous, therefore, allows to develop a measurement system capable to determine the fractions of the phases (oil-water-gas), with proper requirements of each petroliferous installation and with national technology contributing, possibly, with reduction of costs and increase of productivity. (author)

Influence of titanium volume fraction on the mechanical properties of Mg-Ti composites

Energy Technology Data Exchange (ETDEWEB)

Perez, Pablo; Garces, Gerardo; Adeva, Paloma [Centro Nacional de Investigaciones Metalurgicas (CENIM, CSIC), Madrid (Spain). Dept. de Metalurgia Fisica

2009-03-15

The influence of titanium volume fraction on the mechanical properties of Mg-Ti composites prepared through a powder metallurgy route has been evaluated. Titanium was added as particles smaller than 25 {mu}m and volume fractions ranging from 5 to 15%. The increase in the volume fraction of titanium particles results in a slight decrease in the maximum strength. In contrast to this, the ductility of all composites was significantly enhanced by titanium additions. The mechanical properties can be explained on the basis of texture changes induced by the presence of titanium particles. The decrease in the basal texture along the extrusion direction as the amount of titanium is progressively increased accounts for the decrease in the maximum strength. (orig.)

Characterization of SiC based composite materials by the infiltration of ultra-fine SiC particles

International Nuclear Information System (INIS)

Lee, J.K.; Lee, S.P.; Byun, J.H.

2010-01-01

The fabrication route of SiC materials by the complex compound of ultra-fine SiC particles and oxide additive materials has been investigated. Especially, the effect of additive composition ratio on the characterization of SiC materials has been examined. The characterization of C/SiC composites reinforced with plain woven carbon fabrics was also investigated. The fiber preform for C/SiC composites was prepared by the infiltration of complex mixture into the carbon fabric structure. SiC based composite materials were fabricated by a pressure assisted liquid phase sintering process. SiC materials possessed a good density higher than about 3.0 Mg/m 3 , accompanying the creation of secondary phase by the chemical reaction of additive materials. C/SiC composites also represented a dense morphology in the intra-fiber bundle region, even if this material had a sintered density lower than that of monolithic SiC materials. The flexural strength of SiC materials was greatly affected by the composition ratio of additive materials.

Phenomenological inelastic constitutive equations for SiC and SiC fibers under irradiation

International Nuclear Information System (INIS)

El-Azab, A.; Ghoniem, N.M.

1994-01-01

Experimental data on irradiation-induced dimensional changes and creep in β-SiC and SiC fibers is analyzed, with the objective of studying the constitutive behavior of these materials under high-temperature irradiation. The data analysis includes empirical representation of irradiation-induced dimensional changes in SiC matrix and SiC fibers as function of time and irradiation temperature. The analysis also includes formulation of simple scaling laws to extrapolate the existing data to fusion conditions on the basis of the physical mechanisms of radiation effects on crystalline solids. Inelastic constitutive equations are then developed for SCS-6 SiC fibers, Nicalon fibers and CVD SiC. The effects of applied stress, temperature, and irradiation fields on the deformation behavior of this class of materials are simultaneously represented. Numerical results are presented for the relevant creep functions under the conditions of the fusion reactor (ARIES IV) first wall. The developed equations can be used in estimating the macro mechanical properties of SiC-SiC composite systems as well as in performing time-dependent micro mechanical analysis that is relevant to slow crack growth and fiber pull-out under fusion conditions

Study of volume fractions on biphasic stratified regime using gamma ray

Energy Technology Data Exchange (ETDEWEB)

Salgado, William L.; Brandão, Luis E.B., E-mail: william.otero@hotmail.com, E-mail: brandao@ien.gov.br [Instituto de Engenharia Nuclear (IEN/CNEN-RJ), Rio de Janeiro, RJ (Brazil)

2017-07-01

In the oil industries, interconnected pipelines are used to carry large quantities of petroleum and its byproducts. This modal has an advantage because they are more economical, eliminate a need for stocks and, in addition, great safety in operation minimizing a possibility of loss or theft when transported another way. In many cases, especially in the petrochemical industry, the same pipeline is used to carry more than one type of product. They are called poliduct. In the operation of a poliduct there is a sequence of products to be transported and during the exchange of the product, there are still fractions of the previous product and this generates contamination. It is therefore important to identify precisely this region in order to reduce the costs of reprocessing and treatment of discarded products. In this way, this work presents a methodology to evaluate the sensitivity of the gamma densitometry technique in a study of the calculation of volume fractions in biphasic systems, submitted to the stratified flow regime. Using computational simulations using the Monte Carlo Method with the MCNPX code measurement geometry was proposed that presented a higher sensitivity for the calculation of volume fractions. The relevant technical data to perform a simulation of the scintillator detectors were based on information obtained from the gammagraphy technique. The study had a theoretical validation through analytical equations, and the results show that it is possible to identify volume fractions equivalent to 3%. (author)

Study of volume fractions on biphasic stratified regime using gamma ray

International Nuclear Information System (INIS)

Salgado, William L.; Brandão, Luis E.B.

2017-01-01

In the oil industries, interconnected pipelines are used to carry large quantities of petroleum and its byproducts. This modal has an advantage because they are more economical, eliminate a need for stocks and, in addition, great safety in operation minimizing a possibility of loss or theft when transported another way. In many cases, especially in the petrochemical industry, the same pipeline is used to carry more than one type of product. They are called poliduct. In the operation of a poliduct there is a sequence of products to be transported and during the exchange of the product, there are still fractions of the previous product and this generates contamination. It is therefore important to identify precisely this region in order to reduce the costs of reprocessing and treatment of discarded products. In this way, this work presents a methodology to evaluate the sensitivity of the gamma densitometry technique in a study of the calculation of volume fractions in biphasic systems, submitted to the stratified flow regime. Using computational simulations using the Monte Carlo Method with the MCNPX code measurement geometry was proposed that presented a higher sensitivity for the calculation of volume fractions. The relevant technical data to perform a simulation of the scintillator detectors were based on information obtained from the gammagraphy technique. The study had a theoretical validation through analytical equations, and the results show that it is possible to identify volume fractions equivalent to 3%. (author)

Effect of Reactant Concentration on the Microstructure of SiC Nano wires Grown In Situ within SiC Fiber Preforms

International Nuclear Information System (INIS)

Kim, Weon Ju; Kang, Seok Min; Park, Ji Yeon; Ryu, Woo Seog

2006-01-01

Silicon carbide fiber-reinforced silicon carbide matrix (SiC f /SiC) composites are considered as advanced materials for control rods and other in-core components of high-temperature gas cooled reactors. Although the carbon fiber-reinforced carbon matrix (C f /C) composites are more mature and have advantages in cost, manufacturability and some thermomechanical properties, the SiC f /SiC composites have a clear advantage in irradiation stability, specifically a lower level of swelling and retention of mechanical properties. This offers a lifetime component for control rod application to HTGRs while the Cf/C composites would require 2-3 replacements over the reactor lifetime. In general, the chemical vapor infiltration (CVI) technique has been used most widely to produce SiC f /SiC composites. Although the technique produces a highly pure SiC matrix, it requires a long processing time and inevitably contains large interbundle pores. The present authors have recently developed 'whisker growing-assisted process,' in which one-dimensional SiC nano structures with high aspect ratios such as whiskers, nano wires and nano rods are introduced into the fiber preform before the matrix infiltration step. This novel method can produce SiC f /SiC composites with a lower porosity and an uniform distribution of pores when compared with the conventional CVI. This would be expected to increase mechanical and thermal properties of the SiC f /SiC composites. In order to take full advantage of the whisker growing strategy, however, a homogeneous growth of long whiskers is required. In this study, we applied the atmospheric pressure CVI process without metallic catalysts for the growth of SiC nano wires within stacked SiC fiber fabrics. We focused on the effect of the concentration of a reactant gas on the growth behavior and microstructures of the SiC nano wires and discussed a controlling condition for the homogenous growth of long SiC nano wires

Effect of reinforcement volume fraction on the density & elastic ...

African Journals Online (AJOL)

Effect of reinforcement volume fraction on the density & elastic parameters of BMG's matrix composites. Wahiba Metiri 1, Fatiha Hadjoub1, 2 and Leila Touati Tliba 1. 1 Laboratoire des Semi-Conducteurs, Département de Physique, Faculté des Sciences, Université Badji-. Mokhtar, BP 12, Annaba -23000, Algeria.

SIC Industriemonitor najaar 2003

NARCIS (Netherlands)

Brouwer, N.; de Nooij, M.; Pomp, M.

2003-01-01

In juni 2000 publiceerde de Stichting voor Economisch Onderzoek (SEO) van de Universiteit van Amsterdam in opdracht van Stichting voor Industriebeleid en Communicatie (SIC) een ontwerp voor een SIC industriemonitor met een voorstel voor de inhoud en de structuur van een dergelijke monitor. Op dat

Planar measurements of soot volume fraction and OH in a JP-8 pool fire

Energy Technology Data Exchange (ETDEWEB)

Henriksen, Tara L.; Ring, Terry A.; Eddings, Eric G. [Department of Chemical Engineering, University of Utah, Salt Lake City, UT 84112 (United States); Nathan, Graham J. [School of Mechanical Engineering, University of Adelaide, SA 5005 (Australia); Alwahabi, Zeyad T.; Qamar, Nader [School of Chemical Engineering, University of Adelaide, SA 5005 (Australia)

2009-07-15

The simultaneous measurement of soot volume fraction by laser induced incandescence (LII) and qualitative imaging of OH by laser induced fluorescence (LIF) was performed in a JP-8 pool fire contained in a 152 mm diameter pan. Line of sight extinction was used to calibrate the LII system in a laminar flame, and to provide an independent method of measuring average soot volume fraction in the turbulent flame. The presence of soot in the turbulent flame was found to be approximately 50% probable, resulting in high levels of optical extinction, which increased slightly through the flame from approximately 30% near the base, to approximately 50% at the tip. This high soot loading pushes both techniques toward their detection limit. Nevertheless, useful accuracy was obtained, with the LII measurement of apparent extinction in the turbulent flame being approximately 21% lower than a direct measurement, consistent with the influence of signal trapping. The axial and radial distributions of soot volume fraction are presented, along with PDFs of volume fraction, and new insight into the behavior of soot sheets in pool fires are sought from the simultaneous measurements of OH and LII. (author)

Volume Fraction Dependent Thermal Performance of UAlx-Al Dispersion Target

Energy Technology Data Exchange (ETDEWEB)

Kong, Eui Hyun; Tahk, Young Wook; Kim, Hyun Jung; Oh, Jae Yong; Yim, Jeong Sik [KAERI, Daejeon (Korea, Republic of)

2016-05-15

Unlike U-Al alloys, properties of UAl{sub x}-Al dispersion target can be highly sensitive to volume fraction of UAlx in a target meat due to the interface resistance between target particles and matrix. The interface resistance effects on properties of the target meat including thermal conductivity, thermal expansion coefficient, specific heat, elastic modulus and so on. Thermal performances of a dispersion target meat were theoretically evaluated under normal operation condition of KJRR (Kijang Research Reactor) during short effective full power days (EFPD) of 7 days, based on reported measured thermal conductivities of UAl{sub x}-Al dispersion fuels. Effective thermal conductivity determines maximum temperature of dispersion target plate. And for that volume fraction of UAlx in target meat has to be determined considering manufacturing of target plate without degradation of physical and mechanical characteristics.

Effect of TiC content on the microstructure and properties of Ti3SiC2-TiC composites in situ fabricated by spark plasma sintering

International Nuclear Information System (INIS)

Zhang Jianfeng; Wang Lianjun; Jiang Wan; Chen Lidong

2008-01-01

Spark plasma sintering technique was used to in situ fabricate high dense Ti 3 SiC 2 -TiC composites. The calculated TiC volume content from X-ray diffraction (XRD) is close to the theoretical one. It is found from fracture surface observation that TiC is about 1 μm, and Ti 3 SiC 2 is about 2-10 μm in grain size. The fracture modes consist of intergranular mainly for Ti 3 SiC 2 and transgranular fracture mainly for TiC. With the increasing of TiC volume content, Vickers hardness increases to the maximum value of 13 GPa for Ti 3 SiC 2 -40 vol.%TiC. Fracture toughness and flexural strength of the composites are also improved compared with those of monolithic Ti 3 SiC 2 except for Ti 3 SiC 2 -40 vol.%TiC composite. The main reasons for the sudden decrease of fracture toughness and flexural strength of Ti 3 SiC 2 -40 vol.%TiC composite can be attributed to the relatively lower density, some clusters of TiC in the composite and the transition of fracture mode from intergranular to transgranular. The thermal conductivities decreased with the addition of TiC. The minimum thermal conductivity is 22 W m deg. C -1 for Ti 3 SiC 2 -40 vol.%TiC composite

Trace element determination in presolar SiC grains by synchrotron x-ray fluorescence: Commencement of a coordinated multimethod study

International Nuclear Information System (INIS)

Knight, K.B.; Sutton, S.R.; Newville, M.; Davis, A.M.; Dauphas, N.; Lewis, R.S.; Amari, S.; Steele, I.M.; Savina, M.R.; Pellin, M.J.

2008-01-01

We determined trace element compositions of individual ∼1-3 ?m presolar SiC grains from 6 KJG grains and 26 additionally cleaned KJG grains from the Murchison CM chondrite using nondestructive synchrotron X-ray fluorescence (SXRF). Presolar SiC grains are robust remnants of stellar matter ejected from stars. They survived processing in the early solar system and retain the nucleosynthetic fingerprints of their stellar progenitors. As such, they represent unique physical probes of the interiors of stars. Presolar SiC grains are commonly analyzed by mass spectrometric techniques that determine isotopic compositions and, to some degree, elemental concentrations. These techniques, however, are destructive, and can be subject to matrix effects. Elemental composition data on presolar grains remain scarce and affected by contamination and analytical artifacts. In addition, contamination has plagued isotopic characterization of some elements such as Mo and Ba. We determined trace element compositions of individual ∼1-3 (micro)m presolar SiC grains from the Murchison CM chondrite using nondestructive synchrotron X-ray fluorescence (SXRF). Samples included the KJG fraction, and a second KJG fraction that underwent additional cleaning. As every cleaning step results in some grain loss, one goal of this study was to justify additional cleaning of grains. Six KJG grains and 26 additionally cleaned KJG grains were analyzed, with location and identities of individual grains noted for future correlated isotopic study.

Net-shape forming and properties of high volume fraction SiCp/Al composites

International Nuclear Information System (INIS)

Ren Shubin; Qu Xuanhui; Guo Jia; He Xinbo; Qin Mingli; Shen Xiaoyu

2009-01-01

High performance SiCp/Al composites have been realized their net-shape forming by use of a novel process-ceramic injection molding (CIM) for the preparation of SiC preform and pressureless infiltration of aluminum alloys. The dimension precision of prepared SiCp/Al parts could reach about ±0.3%, and their properties could also better meet the requirement of electronic packaging on the materials. In this paper, the CIM process to fabricate SiC preform and the infiltration of SiC preform by Al alloys have been discussed in detail. Additionally, the properties of prepared SiCp/Al composites have also been given research and evaluation.

Grinding Characteristics Of Directionally Aligned SiC Whisker Wheel-Comparison With Al2O3 Fiber Wheel

Institute of Scientific and Technical Information of China (English)

魏源迁; 山口胜美; 菊泽贤二; 洞口严; 中根正喜

2003-01-01

A unique SiC whisker wheel was invented,in which the whiskers were aligned normally to the grinding wheel surface.In this paper,grindabilities of the SiC whisker wheel are investigated and compared with those of other wheels of SiC grains,Al2O3 grains,as well as Al2O3 long and short fibres which were also aligned normally to the grinding wheel surface,respectively.The main research contents concern grinding characteristics of a directionally aligned SiC whisker wheel such as material-removal volume,wheel-wear rates,integrity of the ground surfaces,grinding ratios and grinding efficiency.Furthermore,grinding wheels of whiskers and fibres have a common disadvantage:they tend to load easily.The authors have proposed a simple method of loading-free grinding to overcome this propensity and investigate some related grinding characteristics under loading-free grinding conditions.

SIC POVMs and Clifford groups in prime dimensions

International Nuclear Information System (INIS)

Zhu Huangjun

2010-01-01

We show that in prime dimensions not equal to 3, each group covariant symmetric informationally complete positive operator valued measure (SIC POVM) is covariant with respect to a unique Heisenberg-Weyl (HW) group. Moreover, the symmetry group of the SIC POVM is a subgroup of the Clifford group. Hence, two SIC POVMs covariant with respect to the HW group are unitarily or antiunitarily equivalent if and only if they are on the same orbit of the extended Clifford group. In dimension 3, each group covariant SIC POVM may be covariant with respect to three or nine HW groups, and the symmetry group of the SIC POVM is a subgroup of at least one of the Clifford groups of these HW groups, respectively. There may exist two or three orbits of equivalent SIC POVMs for each group covariant SIC POVM, depending on the order of its symmetry group. We then establish a complete equivalence relation among group covariant SIC POVMs in dimension 3, and classify inequivalent ones according to the geometric phases associated with fiducial vectors. Finally, we uncover additional SIC POVMs by regrouping of the fiducial vectors from different SIC POVMs which may or may not be on the same orbit of the extended Clifford group.

SU-E-T-429: Uncertainties of Cell Surviving Fractions Derived From Tumor-Volume Variation Curves

International Nuclear Information System (INIS)

Chvetsov, A

2014-01-01

Purpose: To evaluate uncertainties of cell surviving fraction reconstructed from tumor-volume variation curves during radiation therapy using sensitivity analysis based on linear perturbation theory. Methods: The time dependent tumor-volume functions V(t) have been calculated using a twolevel cell population model which is based on the separation of entire tumor cell population in two subpopulations: oxygenated viable and lethally damaged cells. The sensitivity function is defined as S(t)=[δV(t)/V(t)]/[δx/x] where δV(t)/V(t) is the time dependent relative variation of the volume V(t) and δx/x is the relative variation of the radiobiological parameter x. The sensitivity analysis was performed using direct perturbation method where the radiobiological parameter x was changed by a certain error and the tumor-volume was recalculated to evaluate the corresponding tumor-volume variation. Tumor volume variation curves and sensitivity functions have been computed for different values of cell surviving fractions from the practically important interval S 2 =0.1-0.7 using the two-level cell population model. Results: The sensitivity functions of tumor-volume to cell surviving fractions achieved a relatively large value of 2.7 for S 2 =0.7 and then approached zero as S 2 is approaching zero Assuming a systematic error of 3-4% we obtain that the relative error in S 2 is less that 20% in the range S2=0.4-0.7. This Resultis important because the large values of S 2 are associated with poor treatment outcome should be measured with relatively small uncertainties. For the very small values of S2<0.3, the relative error can be larger than 20%; however, the absolute error does not increase significantly. Conclusion: Tumor-volume curves measured during radiotherapy can be used for evaluation of cell surviving fractions usually observed in radiation therapy with conventional fractionation

Influence of bress laminate volume fraction on electromechanical properties of externally laminated coated conductor tapes

Energy Technology Data Exchange (ETDEWEB)

Bautista, Zhierwinjay M.; Shin, Hyung Seop [Dept. of Mechanical Design Engineering, Andong National University, Andong (Korea, Republic of); Lee, Jae Hun; Lee, Hun Ju; Moon, Seung Hyun [SuNAM Co Ltd., Anseong (Korea, Republic of)

2016-09-15

The enhancement of mechanical properties of coated conductor (CC) tapes in practical application are usually achieved by reinforcing through lamination or electroplating metal layers on either sides of the CC tape. Mechanical or electromechanical properties of the CC tapes have been largely affected by the lamination structure under various loading modes such as tension, bending or even cyclic. In this study, the influence of brass laminate volume fraction on electromechanical properties of RCE-DR processed Gadolinium-barium-copper-oxide (GdBCO) CC tapes was investigated. The samples used were composed of single-side and both-side laminate of brass layer to the Cu-stabilized CC tape and their Ic behaviors were compared to those of the Cu-stabilized CC tape without external lamination. The stress/strain dependences of Ic in laminated CC tapes under uniaxial tension were analyzed and the irreversible stress/strain limits were determined. As a result, the increase of brass laminate volume fraction initially increased the irreversible strain limit and became gradual. The corresponding irreversible stress limit, however, showed no difference even though the brass laminate volume fraction increased to 3.4. But the irreversible load limit linearly increased with the brass laminate volume fraction.

Crack and wear behavior of SiC particulate reinforced aluminium based metal matrix composite fabricated by direct metal laser sintering process

International Nuclear Information System (INIS)

Ghosh, Subrata Kumar; Saha, Partha

2011-01-01

In this investigation, crack density and wear performance of SiC particulate (SiCp) reinforced Al-based metal matrix composite (Al-MMC) fabricated by direct metal laser sintering (DMLS) process have been studied. Mainly, size and volume fraction of SiCp have been varied to analyze the crack and wear behavior of the composite. The study has suggested that crack density increases significantly after 15 volume percentage (vol.%) of SiCp. The paper has also suggested that when size (mesh) of reinforcement increases, wear resistance of the composite drops. Three hundred mesh of SiCp offers better wear resistance; above 300 mesh the specific wear rate increases significantly. Similarly, there has been no improvement of wear resistance after 20 vol.% of reinforcement. The scanning electron micrographs of the worn surfaces have revealed that during the wear test SiCp fragments into small pieces which act as abrasives to result in abrasive wear in the specimen.

The coupled effect of fiber volume fraction and void fraction on hydraulic fluid absorption of quartz/BMI laminates

Science.gov (United States)

Hurdelbrink, Keith R.; Anderson, Jacob P.; Siddique, Zahed; Altan, M. Cengiz

2016-03-01

Bismaleimide (BMI) resin with quartz (AQ581) fiber reinforcement is a composite material frequently used in aerospace applications, such as engine cowlings and radomes. Various composite components used in aircrafts are exposed to different types of hydraulic fluids, which may lead to anomalous absorption behavior over the service life of the composite. Accurate predictive models for absorption of liquid penetrants are particularly important as the composite components are often exposed to long-term degradation due to absorbed moisture, hydraulic fluids, or similar liquid penetrants. Microstructural features such as fiber volume fraction and void fraction can have a significant effect on the absorption behavior of fiber-reinforced composites. In this paper, hydraulic fluid absorption characteristics of quartz/BMI laminates fabricated from prepregs preconditioned at different relative humidity and subsequently cured at different pressures are presented. The composite samples are immersed into hydraulic fluid at room temperature, and were not subjected to any prior degradation. To generate process-induced microvoids, prepregs were conditioned in an environmental chamber at 2% or 99% relative humidity at room temperature for a period of 24 hours prior to laminate fabrication. To alter the fiber volume fraction, the laminates were fabricated at cure pressures of 68.9 kPa (10 psi) or 482.6 kPa (70 psi) via a hot-press. The laminates are shown to have different levels of microvoids and fiber volume fractions, which were observed to affect the absorption dynamics considerably and exhibited clear non-Fickian behavior. A one-dimensional hindered diffusion model (HDM) was shown to be successful in predicting the hydraulic fluid absorption. Model prediction indicates that as the fabrication pressure increased from 68.9 kPa to 482.6 kPa, the maximum fluid content (M∞) decreased from 8.0% wt. to 1.0% wt. The degree of non-Fickian behavior, measured by hindrance coefficient (�

Volume fraction prediction in biphasic flow using nuclear technique and artificial neural network

International Nuclear Information System (INIS)

Salgado, Cesar M.; Brandao, Luis E.B.

2015-01-01

The volume fraction is one of the most important parameters used to characterize air-liquid two-phase flows. It is a physical value to determine other parameters, such as the phase's densities and to determine the flow rate of each phase. These parameters are important to predict the flow pattern and to determine a mathematical model for the system. To study, for example, heat transfer and pressure drop. This work presents a methodology for volume fractions prediction in water-gas stratified flow regime using the nuclear technique and artificial intelligence. The volume fractions calculate in biphasic flow systems is complex and the analysis by means of analytical equations becomes very difficult. The approach is based on gamma-ray pulse height distributions pattern recognition by means of the artificial neural network. The detection system uses appropriate broad beam geometry, comprised of a ( 137 Cs) energy gamma-ray source and a NaI(Tl) scintillation detector in order measure transmitted beam whose the counts rates are influenced by the phases composition. These distributions are directly used by the network without any parameterization of the measured signal. The ideal and static theoretical models for stratified regime have been developed using MCNP-X code, which was used to provide training, test and validation data for the network. The detector also was modeled with this code and the results were compared to experimental photopeak efficiency measurements of radiation sources. The proposed network could obtain with satisfactory prediction of the volume fraction in water-gas system, demonstrating to be a promising approach for this purpose. (author)

Volume fraction prediction in biphasic flow using nuclear technique and artificial neural network

Energy Technology Data Exchange (ETDEWEB)

Salgado, Cesar M.; Brandao, Luis E.B., E-mail: otero@ien.gov.br, E-mail: brandao@ien.gov.br [Instituto de Engenharia Nuclear (IEN/CNEN-RJ), Rio de Janeiro, RJ (Brazil)

2015-07-01

The volume fraction is one of the most important parameters used to characterize air-liquid two-phase flows. It is a physical value to determine other parameters, such as the phase's densities and to determine the flow rate of each phase. These parameters are important to predict the flow pattern and to determine a mathematical model for the system. To study, for example, heat transfer and pressure drop. This work presents a methodology for volume fractions prediction in water-gas stratified flow regime using the nuclear technique and artificial intelligence. The volume fractions calculate in biphasic flow systems is complex and the analysis by means of analytical equations becomes very difficult. The approach is based on gamma-ray pulse height distributions pattern recognition by means of the artificial neural network. The detection system uses appropriate broad beam geometry, comprised of a ({sup 137}Cs) energy gamma-ray source and a NaI(Tl) scintillation detector in order measure transmitted beam whose the counts rates are influenced by the phases composition. These distributions are directly used by the network without any parameterization of the measured signal. The ideal and static theoretical models for stratified regime have been developed using MCNP-X code, which was used to provide training, test and validation data for the network. The detector also was modeled with this code and the results were compared to experimental photopeak efficiency measurements of radiation sources. The proposed network could obtain with satisfactory prediction of the volume fraction in water-gas system, demonstrating to be a promising approach for this purpose. (author)

Research on SiC Whisker Prepared by H-PSO

Directory of Open Access Journals (Sweden)

WANG Yao

2017-10-01

Full Text Available SiC whiskers were prepared on the matrix of graphite by using high hydrogenous silicone oil(PSO as raw material. The effect of surface conditions of graphite and heating temperature on the growth of SiC whisker was mainly studied in this paper. The main factor which affects the nucleation and growth of SiC whisker is the heating temperature, with the heating temperature rising, the production of SiC whisker increases. The surface condition of graphite matrix also influences the growth of SiC whisker. With the nucleation points provided by graphite matrix defects increasing, the production of SiC whisker incleases and SiC whisker starts to overlap with each other. The formation process of SiC whisker includes two steps:nucleation and growth. SiC whisker nucleates at low temperature and grows at high temperature, which follows the VLS (vapor-liquid-solid growth mechanism.

Volume fraction dependence of transient absorption signal and nonlinearities in metal nanocolloids

International Nuclear Information System (INIS)

Jayabalan, J; Singh, Asha; Khan, Salahuddin; Chari, Rama

2013-01-01

Electron–lattice thermalization dynamics in metal nanoparticles or in bulk metal is usually estimated by measuring the decay time of the change in transmission following an optical excitation. Such measurements can be performed in transient absorption geometry using a femtosecond laser. We find that for silver nanoplatelet/water colloids, the decay time of the transient absorption depends on the volume fraction of silver in water. By estimating the volume fraction dependence of nonlinearities in the same samples, we show that the variation in the measured decay time is due to pump-depletion effects present in the sample. The correct correction factor for taking into account pump-depletion effects in fifth- and higher-order nonlinearities is also presented. (paper)

Volume fraction dependence and reorganization in cluster-cluster aggregation processes

NARCIS (Netherlands)

Garderen, van H.F.; Dokter, W.H.; Beelen, T.P.M.; Santen, van R.A.; Pantos, E.; Michels, M.A.J.; Hilbers, P.A.J.

1995-01-01

Off-lattice diffusion limited cluster aggregation simulations in two dimensions have been performed in a wide volume fraction range between 0.001 and 0.60. Starting from a system of 10 000 monomers with radius 0.5, that follow Brownian trajectories, larger aggregates are generated by bond formation

Effect of Fiber Volume Fraction and Water Absorption toward Bending Strength of Coconut Filters/ Polyester Composite

Directory of Open Access Journals (Sweden)

I Putu Lokantara

2012-11-01

Full Text Available The variation of fibre volume and the duration of water soaking take influence on the mechanical properties of composite. This research aim is to know the influence of fraction volume fibre and soaking duration on the mineral watertoward the tensile strength and flexural of polyester-coconut-tapis composite. This research used coconut-tapis fibre which is cut 1 cm in length with 0%, 5%, 7,5%, and 10% fiber volume fraction, unsaturated-polyester (UPRs matrix resin type Yucalac 157 BQTN-EX, and MEKPO hardener. The flexure specimen are made by press hand lay-up method and cut according ASTM D790-03 for the flexure test. The result of flexure test shows that the duration of soaking and the fiber volume fraction give a significant effect on the flexural strength of composite. The highest strength are reached by composite with 10% fibre volume on 48 hour soaking time equal to 41.994 MPa. The flexure modulus happenend shows increasing until 24 hour soaking time. The highest modulus are reached by composite with 10% fibre volume equal to 7.114 GPa while the lowest are reached by composite with 0% fibre volume equal to 3,023 GPa.

Soot volume fraction fields in unsteady axis-symmetric flames by continuous laser extinction technique.

Science.gov (United States)

Kashif, Muhammad; Bonnety, Jérôme; Guibert, Philippe; Morin, Céline; Legros, Guillaume

2012-12-17

A Laser Extinction Method has been set up to provide two-dimensional soot volume fraction field time history at a tunable frequency up to 70 Hz inside an axis-symmetric diffusion flame experiencing slow unsteady phenomena preserving the symmetry. The use of a continuous wave laser as the light source enables this repetition rate, which is an incremental advance in the laser extinction technique. The technique is shown to allow a fine description of the soot volume fraction field in a flickering flame exhibiting a 12.6 Hz flickering phenomenon. Within this range of repetition rate, the technique and its subsequent post-processing require neither any method for time-domain reconstruction nor any correction for energy intrusion. Possibly complemented by such a reconstruction method, the technique should support further soot volume fraction database in oscillating flames that exhibit characteristic times relevant to the current efforts in the validation of soot processes modeling.

The capability of radial basis function to forecast the volume fractions of the annular three-phase flow of gas-oil-water.

Science.gov (United States)

Roshani, G H; Karami, A; Salehizadeh, A; Nazemi, E

2017-11-01

The problem of how to precisely measure the volume fractions of oil-gas-water mixtures in a pipeline remains as one of the main challenges in the petroleum industry. This paper reports the capability of Radial Basis Function (RBF) in forecasting the volume fractions in a gas-oil-water multiphase system. Indeed, in the present research, the volume fractions in the annular three-phase flow are measured based on a dual energy metering system including the 152 Eu and 137 Cs and one NaI detector, and then modeled by a RBF model. Since the summation of volume fractions are constant (equal to 100%), therefore it is enough for the RBF model to forecast only two volume fractions. In this investigation, three RBF models are employed. The first model is used to forecast the oil and water volume fractions. The next one is utilized to forecast the water and gas volume fractions, and the last one to forecast the gas and oil volume fractions. In the next stage, the numerical data obtained from MCNP-X code must be introduced to the RBF models. Then, the average errors of these three models are calculated and compared. The model which has the least error is picked up as the best predictive model. Based on the results, the best RBF model, forecasts the oil and water volume fractions with the mean relative error of less than 0.5%, which indicates that the RBF model introduced in this study ensures an effective enough mechanism to forecast the results. Copyright © 2017 Elsevier Ltd. All rights reserved.

Wear of semi-solid rheocast SiCp/Al metal matrix composites

CSIR Research Space (South Africa)

Curle, UA

2010-09-01

Full Text Available ). Hardness increases as the volume fractions of SiC increases. Wear rates of the MMCs in the F and T6 heat treatment conditions were assessed with a metallographic preparation machine. It is found that the 11% SiC MMC wear rate is higher on SiC abrasives...

Irradiation damage of SiC semiconductor device (I)

International Nuclear Information System (INIS)

Park, Ji Yeon; Kim, Weon Ju

2000-09-01

This report reviewed the irradiation damage of SiC semiconductor devices and examined a irradiation behavior of SiC single crystal as a pre-examination for evaluation of irradiation behavior of SiC semiconductor devices. The SiC single was crystal irradiated by gamma-beam, N+ ion and electron beam. Annealing examinations of the irradiated specimens also were performed at 500 deg C. N-type 6H-SiC dopped with N+ ion was used and irradiation doses of gamma-beam, N+ion and electron beam were up to 200 Mrad, 1x10 16 N + ions/cm 2 and 3.6 x 10 17 e/cm 2 and 1.08 x 10 18 e/cm 2 , respectively. Irradiation damages were analyzed by the EPR method. Additionally, properties of SiC, information about commercial SiC single crystals and the list of web sites with related to the SiC device were described in the appendix

Irradiation damage of SiC semiconductor device (I)

Energy Technology Data Exchange (ETDEWEB)

Park, Ji Yeon; Kim, Weon Ju

2000-09-01

This report reviewed the irradiation damage of SiC semiconductor devices and examined a irradiation behavior of SiC single crystal as a pre-examination for evaluation of irradiation behavior of SiC semiconductor devices. The SiC single was crystal irradiated by gamma-beam, N+ ion and electron beam. Annealing examinations of the irradiated specimens also were performed at 500 deg C. N-type 6H-SiC dopped with N+ ion was used and irradiation doses of gamma-beam, N+ion and electron beam were up to 200 Mrad, 1x10{sup 16} N{sup +} ions/cm{sup 2} and 3.6 x 10{sup 17} e/cm{sup 2} and 1.08 x 10{sup 18} e/cm{sup 2} , respectively. Irradiation damages were analyzed by the EPR method. Additionally, properties of SiC, information about commercial SiC single crystals and the list of web sites with related to the SiC device were described in the appendix.

Matrix densification of SiC composites by sintering process

International Nuclear Information System (INIS)

Kim, Young-Wook; Jang, Doo-Hee; Eom, Jung-Hye; Chun, Yong-Seong

2007-02-01

The objectives of this research are to develop a process for dense SiC fiber-SiC composites with a porosity of 5% or less and to develop high-strength SiC fiber-SiC composites with a strength of 500 MPa or higher. To meet the above objectives, the following research topics were investigated ; new process development for the densification of SiC fiber-SiC composites, effect of processing parameters on densification of SiC fiber-SiC composites, effect of additive composition on matrix microstructure, effects of additive composition and content on densification of SiC fiber-SiC composites, mechanical properties of SiC fiber-SiC composites, effect of fiber coating on densification and strength of SiC fiber-SiC composites, development of new additive composition. There has been a great deal of progress in the development of technologies for the processing and densification of SiC fiber-SiC composites and in better understanding of additive-densification-mechanical property relations as results of this project. Based on the progress, dense SiC fiber-SiC composites (≥97%) and high strength SiC fiber-SiC composites (≥600 MPa) have been developed. Development of 2D SiC fiber-SiC composites with a relative density of ≥97% and a strength of ≥600 MPa can be counted as a notable achievement

Improved thermoelectric performance of CdO by adding SiC fibers versus by adding SiC nanoparticles inclusions

Science.gov (United States)

Liang, S.; Li, Longjiang

2018-03-01

We report the improved thermoelectric (TE) performance of CdO by alloying with SiC fibers. In contrast to the lowered thermoelectric figure of merit (ZT) in a CdO matrix with SiC nanoparticle composites, an appreciable ZT value increment of about 36% (from 0.32 to 0.435) at 1000 K was obtained in the CdO matrix with SiC fiber composites. Both kinds of composites show substantially decreased thermal conductivity due to additional phonon scattering by the nano-inclusions. Compared to the very high electrical resistivity (ρ ˜ 140 μΩ m) for 5 at. % SiC nanoparticle composites, SiC fiber composites favorably maintained a very low ρ (˜30 μΩ m) even with 5 at. % SiC at 1000 K. We think the substantial difference of specific surface areas of these two nano-inclusions (30 m2/g for fibers vs 300 m2/g for nanoparticles) might play a crucial role to fine tune the TE performance. Larger interface could be inductive to diffusion and electron acceptor activation, which affect carrier mobility considerably. This work might hint at an alternative approach to improve TE materials' performance.

Neutron displacement damage cross sections for SiC

International Nuclear Information System (INIS)

Huang Hanchen; Ghoniem, N.

1993-01-01

Calculations of neutron displacement damage cross sections for SiC are presented. We use Biersack and Haggmark's empirical formula in constructing the electronic stopping power, which combines Lindhard's model at low PKA energies and Bethe-Bloch's model at high PKA energies. The electronic stopping power for polyatomic materials is computed on the basis of Bragg's Additivity Rule. A continuous form of the inverse power law potential is used for nuclear scattering. Coupled integro-differential equations for the number of displaced atoms j, caused by PKA i, are then derived. The procedure outlined above gives partial displacement cross sections, displacement cross sections for each specie of the lattice, and for each PKA type. The corresponding damage rates for several fusion and fission neutron spectra are calculated. The stoichiometry of the irradiated material is investigated by finding the ratio of displacements among various atomic species. The role of each specie in displacing atoms is also investigated by calculating the fraction of displacements caused by each PKA type. The study shows that neutron displacement damage rates of SiC in typical magnetic fusion reactor first walls will be ∝10-15 dpa MW -1 m 2 ; in typical lead-protected inertial confinement fusion reactor first walls they will be ∝15-20 dpa MW -1 m 2 . For fission spectra, we find that the neutron displacement damage rate of SiC is ∝74 dpa per 10 27 n/m 2 in FFTF, ∝39 dpa per 10 27 n/m 2 in HFIR, and 25 dpa per 10 27 n/m 2 in NRU. Approximately 80% of displacement atoms are shown to be of the carbon-type. (orig.)

Role of Defects in Swelling and Creep of Irradiated SiC

Energy Technology Data Exchange (ETDEWEB)

Szlufarska, Izabela [Univ. of Wisconsin, Madison, WI (United States); Voyles, Paul [Univ. of Wisconsin, Madison, WI (United States); Sridharan, Kumar [Univ. of Wisconsin, Madison, WI (United States); Katoh, Yutai [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

2016-01-16

Silicon carbide is a promising cladding material because of its high strength and relatively good corrosion resistance. However, SiC is brittle and therefore SiC-based components need to be carefully designed to avoid cracking and failure by fracture. In design of SiC-based composites for nuclear reactor applications it is essential to take into account how mechanical properties are affected by radiation and temperature, or in other words, what strains and stresses develop in this material due to environmental conditions. While thermal strains in SiC can be predicted using classical theories, radiation-induced strains are much less understood. In particular, it is critical to correctly account for radiation swelling and radiation creep, which contribute significantly to dimensional instability of SiC under radiation. Swelling typically increases logarithmically with radiation dose and saturates at relatively low doses (damage levels of a few dpa). Consequently, swelling-induced stresses are likely to develop within a few months of operation of a reactor. Radiation-induced volume swelling in SiC can be as high as 2%, which is significantly higher than the cracking strain of 0.1% in SiC. Swelling-induced strains will lead to enormous stresses and fracture, unless these stresses can be relaxed via some other mechanism. An effective way to achieve stress relaxation is via radiation creep. Although it has been hypothesized that both radiation swelling and radiation creep are driven by formation of defect clusters, existing models for swelling and creep in SiC are limited by the lack of understanding of specific defects that form due to radiation in the range of temperatures relevant to fuel cladding in light water reactors (LWRs) (<1000°C). For example, defects that can be detected with traditional transmission electron microscopy (TEM) techniques account only for 10-45% of the swelling measured in irradiated SiC. Here, we have undertaken an integrated experimental and

Role of Defects in Swelling and Creep of Irradiated SiC

International Nuclear Information System (INIS)

Szlufarska, Izabela; Voyles, Paul; Sridharan, Kumar; Katoh, Yutai

2016-01-01

Silicon carbide is a promising cladding material because of its high strength and relatively good corrosion resistance. However, SiC is brittle and therefore SiC-based components need to be carefully designed to avoid cracking and failure by fracture. In design of SiC-based composites for nuclear reactor applications it is essential to take into account how mechanical properties are affected by radiation and temperature, or in other words, what strains and stresses develop in this material due to environmental conditions. While thermal strains in SiC can be predicted using classical theories, radiation-induced strains are much less understood. In particular, it is critical to correctly account for radiation swelling and radiation creep, which contribute significantly to dimensional instability of SiC under radiation. Swelling typically increases logarithmically with radiation dose and saturates at relatively low doses (damage levels of a few dpa). Consequently, swelling-induced stresses are likely to develop within a few months of operation of a reactor. Radiation-induced volume swelling in SiC can be as high as 2%, which is significantly higher than the cracking strain of 0.1% in SiC. Swelling-induced strains will lead to enormous stresses and fracture, unless these stresses can be relaxed via some other mechanism. An effective way to achieve stress relaxation is via radiation creep. Although it has been hypothesized that both radiation swelling and radiation creep are driven by formation of defect clusters, existing models for swelling and creep in SiC are limited by the lack of understanding of specific defects that form due to radiation in the range of temperatures relevant to fuel cladding in light water reactors (LWRs) (<1000°C). For example, defects that can be detected with traditional transmission electron microscopy (TEM) techniques account only for 10-45% of the swelling measured in irradiated SiC. Here, we have undertaken an integrated experimental and

Controlling thermal deformation by using composite materials having variable fiber volume fraction

International Nuclear Information System (INIS)

Bouremana, M.; Tounsi, A.; Kaci, A.; Mechab, I.

2009-01-01

In application, many thin structural components such as beams, plates and shells experience a through-thickness temperature variation. This temperature variation can produce both an in-plane expansion and an out-of-plane (bending) curvature. Given that these thin components interact with or connect to other components, we often wish to minimize the thermal deformation or match the thermal deformation of another component. This is accomplished by using a composite whose fibers have a negative axial thermal expansion coefficient. By varying the fiber volume fraction within a symmetric laminated beam to create a functionally graded material (FGM), certain thermal deformations can be controlled or tailored. Specifically, a beam can be designed which does not curve under a steady-state through-thickness temperature variation. Continuous gradation of the fiber volume fraction in the FGM layer is modelled in the form of a mth power polynomial of the coordinate axis in thickness direction of the beam. The beam results are independent of the actual temperature values, within the limitations of steady-state heat transfer and constant material properties. The influence of volume fiber fraction distributions are studied to match or eliminate an in-plane expansion coefficient, or to match a desired axial stiffness. Combining two fiber types to create a hybrid FGM can offer desirable increase in axial and bending stiffness while still retaining the useful thermal deformation behavior.

Soot volume fraction in a piloted turbulent jet non-premixed flame of natural gas

Energy Technology Data Exchange (ETDEWEB)

Qamar, N.H.; Alwahabi, Z.T.; King, K.D. [Fluid Mechanics, Energy and Combustion Group, University of Adelaide, Adelaide, SA 5005 (Australia); School of Chemical Engineering, University of Adelaide, Adelaide, SA 5005 (Australia); Chan, Q.N. [Fluid Mechanics, Energy and Combustion Group, University of Adelaide, Adelaide, SA 5005 (Australia); School of Chemical Engineering, University of Adelaide, Adelaide, SA 5005 (Australia); School of Mechanical Engineering, University of Adelaide, Adelaide, SA 5005 (Australia); Nathan, G.J. [Fluid Mechanics, Energy and Combustion Group, University of Adelaide, Adelaide, SA 5005 (Australia); School of Mechanical Engineering, University of Adelaide, Adelaide, SA 5005 (Australia); Roekaerts, D. [Department of Multi-Scale Physics, Faculty of Applied Sciences, Delft University of Technology, Lorentzweg, 1, NL-2628 CJ Delft (Netherlands)

2009-07-15

Planar laser-induced incandescence (LII) has been used to measure soot volume fraction in a well-characterised, piloted, turbulent non-premixed flame known as the ''Delft Flame III''. Simulated Dutch natural gas was used as the fuel to produce a flame closely matching those in which a wide range of previous investigations, both experimental and modelling, have been performed. The LII method was calibrated using a Santoro-style burner with ethylene as the fuel. Instantaneous and time-averaged data of the axial and radial soot volume fraction distributions of the flame are presented here along with the Probability Density Functions (PDFs) and intermittency. The PDFs were found to be well-characterised by a single exponential distribution function. The distribution of soot was found to be highly intermittent, with intermittency typically exceeding 97%, which increases measurement uncertainty. The instantaneous values of volume fraction are everywhere less than the values in strained laminar flames. This is consistent with the soot being found locally in strained flame sheets that are convected and distorted by the flow. (author)

An investigation of the relation between the 30 meter running time and the femoral volume fraction in the thigh

Directory of Open Access Journals (Sweden)

MY Tasmektepligil

2009-12-01

Full Text Available Leg components are thought to be a related to speed. Only a limited number of studies have, however, examined the interaction between speed and bone size. In this study, we examined the relationship between the time taken by football players to run thirty meters and the fraction which the femur forms compared to the entire thigh region. Data collected from thirty male football players of average age 17.3 (between 16-19 years old were analyzed. First we detected the thirty meter running times and then we estimated the volume fraction of the femur to the entire thigh region using stereological methods on magnetic resonance images. Our data showed that there was a highly negative relationship between the 30 meter running times and the volume fraction of the bone to the thigh region. Thus, 30 meter running time decreases as the fraction of the bone to the thigh region increases. In other words, speed increases as the fraction of bone volume increases. Our data indicate that selecting sportsman whose femoral volume fractions are high will provide a significant benefit to enhancing performance in those branches of sports which require speed. Moreover, we concluded that training which can increase the bone volume fraction should be practiced when an increase in speed is desired and that the changes in the fraction of thigh region components should be monitored during these trainings.

Effect of inclusion of SiC particulates on the mechanical resistance behaviour of stir-cast AA6063/SiC composites

International Nuclear Information System (INIS)

Balasubramanian, I.; Maheswaran, R.

2015-01-01

Highlights: • AA6063/SiC composites with different weight percent are stir cast. • Resistance properties against indentation, stretching force and sliding force are studied. • Increase in initiation of cleavage facets and reduces the tensile strength for 15% SiC. • Transition from micro ploughing to micro cutting wear mechanism is less due to SiC inclusion. - Abstract: This study investigates the mechanical resistance behaviour of AA6063 particulate composites with the inclusion of micron-sized silicon carbide (SiC) particles with different weight percentages in an AA6063 aluminium matrix. AA6063/SiC particulate composites containing 0, 5, 10, and 15 weight percent of SiC particles were produced by stir casting. Standard mechanical tests were conducted on the composite plates, and the mechanical resistance to indentation, tensile force and sliding force are evaluated. It has been observed that upon addition of SiC particles, the resistance against indentation is increased and the resistance against tensile force is initially increased and then decreased. Furthermore, using scanning electron microscopy (SEM), the fracture appearance of the broken specimen subjected to tensile force and morphological changes in the surface subjected to sliding force are analysed. The SEM images reveal that the addition of SiC particles in the AA6063 aluminium matrix initiates more cleavage facets. This leads to brittle fracture in the specimen subjected to tensile forces and less transition from material displacement to material removal in the specimen subjected to sliding forces

SU-E-T-480: Radiobiological Dose Comparison of Single Fraction SRS, Multi-Fraction SRT and Multi-Stage SRS of Large Target Volumes Using the Linear-Quadratic Formula

International Nuclear Information System (INIS)

Ding, C; Hrycushko, B; Jiang, S; Meyer, J; Timmerman, R

2014-01-01

Purpose: To compare the radiobiological effect on large tumors and surrounding normal tissues from single fraction SRS, multi-fractionated SRT, and multi-staged SRS treatment. Methods: An anthropomorphic head phantom with a centrally located large volume target (18.2 cm 3 ) was scanned using a 16 slice large bore CT simulator. Scans were imported to the Multiplan treatment planning system where a total prescription dose of 20Gy was used for a single, three staged and three fractionated treatment. Cyber Knife treatment plans were inversely optimized for the target volume to achieve at least 95% coverage of the prescription dose. For the multistage plan, the target was segmented into three subtargets having similar volume and shape. Staged plans for individual subtargets were generated based on a planning technique where the beam MUs of the original plan on the total target volume are changed by weighting the MUs based on projected beam lengths within each subtarget. Dose matrices for each plan were export in DICOM format and used to calculate equivalent dose distributions in 2Gy fractions using an alpha beta ratio of 10 for the target and 3 for normal tissue. Results: Singe fraction SRS, multi-stage plan and multi-fractionated SRT plans had an average 2Gy dose equivalent to the target of 62.89Gy, 37.91Gy and 33.68Gy, respectively. The normal tissue within 12Gy physical dose region had an average 2Gy dose equivalent of 29.55Gy, 16.08Gy and 13.93Gy, respectively. Conclusion: The single fraction SRS plan had the largest predicted biological effect for the target and the surrounding normal tissue. The multi-stage treatment provided for a more potent biologically effect on target compared to the multi-fraction SRT treatments with less biological normal tissue than single-fraction SRS treatment

Palladium assisted silver transport in polycrystalline SiC

Energy Technology Data Exchange (ETDEWEB)

Neethling, J.H., E-mail: Jan.Neethling@nmmu.ac.za [Physics Department, Nelson Mandela Metropolitan University, PO Box 77000, Port Elizabeth 6031 (South Africa); O' Connell, J.H.; Olivier, E.J. [Physics Department, Nelson Mandela Metropolitan University, PO Box 77000, Port Elizabeth 6031 (South Africa)

2012-10-15

The transport of silver in polycrystalline 3C-SiC and hexagonal 6H-SiC has been investigated by annealing the SiC samples in contact with a Pd-Ag compound at temperatures of 800 and 1000 Degree-Sign C and times of 24 and 67 h. The Pd was added in an attempt to improve the low wetting of SiC by Ag and further because Pd is produced in measurable concentrations in coated particles during reactor operation. Pd is also known to coalesce at the IPyC-SiC interface and to chemically attack the SiC layer. SEM, TEM and EDS were used to show that the Ag penetrates polycrystalline SiC along grain boundaries together with Pd. It is suggested that Ag transport in SiC takes place along grain boundaries in the form of moving nodules consisting of a Ag-Pd mixture. It is assumed that the nodules move along grain boundaries by dissolving the SiC at the leading edge followed by the reprecipitation of SiC at the trailing edge. Since the solubility of Cs in Ag and Pd is extremely low, it is unlikely that Cs will penetrate the SiC together with the Ag-Pd compound if present at the IPyC-SiC interface. If it is assumed that the dominant transport mechanism of Ag in intact polycrystalline SiC is indeed the Pd assisted mechanism, then the stabilization of Pd (and other metallic fission products) in the kernel could be a way of mitigating Ag release from TRISO-coated particles.

Palladium assisted silver transport in polycrystalline SiC

International Nuclear Information System (INIS)

Neethling, J.H.; O’Connell, J.H.; Olivier, E.J.

2012-01-01

The transport of silver in polycrystalline 3C-SiC and hexagonal 6H-SiC has been investigated by annealing the SiC samples in contact with a Pd–Ag compound at temperatures of 800 and 1000 °C and times of 24 and 67 h. The Pd was added in an attempt to improve the low wetting of SiC by Ag and further because Pd is produced in measurable concentrations in coated particles during reactor operation. Pd is also known to coalesce at the IPyC–SiC interface and to chemically attack the SiC layer. SEM, TEM and EDS were used to show that the Ag penetrates polycrystalline SiC along grain boundaries together with Pd. It is suggested that Ag transport in SiC takes place along grain boundaries in the form of moving nodules consisting of a Ag–Pd mixture. It is assumed that the nodules move along grain boundaries by dissolving the SiC at the leading edge followed by the reprecipitation of SiC at the trailing edge. Since the solubility of Cs in Ag and Pd is extremely low, it is unlikely that Cs will penetrate the SiC together with the Ag–Pd compound if present at the IPyC–SiC interface. If it is assumed that the dominant transport mechanism of Ag in intact polycrystalline SiC is indeed the Pd assisted mechanism, then the stabilization of Pd (and other metallic fission products) in the kernel could be a way of mitigating Ag release from TRISO-coated particles.

Performance enhancement of direct ethanol fuel cell using Nafion composites with high volume fraction of titania

Science.gov (United States)

Matos, B. R.; Isidoro, R. A.; Santiago, E. I.; Fonseca, F. C.

2014-12-01

The present study reports on the performance enhancement of direct ethanol fuel cell (DEFC) at 130 °C with Nafion-titania composite electrolytes prepared by sol-gel technique and containing high volume fractions of the ceramic phase. It is found that for high volume fractions of titania (>10 vol%) the ethanol uptake of composites is largely reduced while the proton conductivity at high-temperatures is weakly dependent on the titania content. Such tradeoff between alcohol uptake and conductivity resulted in a boost of DEFC performance at high temperatures using Nafion-titania composites with high fraction of the inorganic phase.

FE simulation of the indentation deformation of SiC modified vinylester composites in respect to their abrasive wear performance

Directory of Open Access Journals (Sweden)

2008-10-01

Full Text Available The abrasive sliding friction and wear behaviours of silicon carbide (SiC filled vinylester (VE composites were investigated. The average grain size of the incorporated SiC particles was varied, holding the volume content of them in every case at 16 vol%. Mechanical properties (hardness, compression modulus, yield stress of the filled and neat VE were determined. The tribological properties were investigated in block (composite – on – ring (steel test configuration. The steel counter bodies were covered with abrasive papers of different graining. Coefficient of friction (COF and specific wear rate of the VE + SiC composites were determined. It was observed that the wear resistance increases with increasing average filler grain size and with decreasing abrasiveness of the counter surface. The COF of the VE + SiC composites is independent of the size of the incorporated particles, but it is strongly influenced by the abrasiveness of the counter body. The worn surfaces of the VE + SiC systems were analysed in scanning electron microscope (SEM to deduce the typical wear mechanisms. The size effect of the SiC filler particles onto the abrasive wear characteristics was investigated by assuming that the roughness peaks of the abrasive paper and the indenter of the microhardness test cause similar micro scaled contact deformations in the composites. Therefore FE method was used to simulate the micro scaled deformation process in the VE + SiC systems during microindentation tests. The FE results provided valuable information on how to explain the size effect of the incorporated SiC filler.

Distribution of the grain limit character in SiC and its effect on the diffusion of fission products in the TRISO fuel particles; Distribucion del caracter de limite de grano en SiC y su efecto sobre la difusion de los productos de fision en las particulas de combustible TRISO

Energy Technology Data Exchange (ETDEWEB)

Cancino T, F.; Lopez H, E., E-mail: Eddie.lopez@cinvestav.edu.mx [IPN, Centro de Investigacion y de Estudios Avanzados, Unidad Saltillo, Av. Industria Metalurgica 1062, Zona Industrial, 25900 Ramos Arizpe, Coahuila (Mexico)

2017-09-15

At present is accepted that silver diffuses through silicium carbide (SiC) by diffusion in grain boundaries, although little is known about the characteristics of grain boundaries in SiC, and how these change depending on the type of sample. In this work, was observed that there are small but important differences between the SiC in the tri-structural isotropic (TRISO) particles and that of the monoliths, which could explain some of the differences observed in experiments on diffusion in the literature. Five different types (coatings and monoliths) of SiC produced by chemical vapor deposition (CVD) were characterized by electron backscatter diffraction (EBSD). In all the samples the SiC was mainly composed of high-angle grain boundaries (∼ 65%), with a small fraction of grain boundaries of low-angle (about 15%) and 20% of the coincidence site lattice (CSL). The morphology of the monoliths is constituted by large grains, surrounded by smaller grains; in the particles of the TRISO fuel, both columnar and equi axial grains were observed, with a more uniform distribution over the surface of the coating. (Author)

Artificial neural network and neutron application in a volume fraction calculation in annular and stratified multiphase system

International Nuclear Information System (INIS)

Ramos, Robson; Brandao, Luis E.B.; Pereira, Claudio M.N.A.; Schirru, Roberto; Silva, Ademir Xavier da

2009-01-01

Multiphase flows, type oil-water-gas are very common among different industrial activities, such as chemical industries and petroleum extraction, and its measurements show some difficulties to be taken. Precisely determining the volume fraction of each one of the elements that composes a multiphase flow is very important in chemical plants and petroleum industries. This work presents a methodology able to determine volume fraction on Annular and Stratified multiphase flow system with the use of neutrons and artificial intelligence, using the principles of transmission/scattering of fast neutrons from a 241 Am-Be source and measurements of point flow that are influenced by variations of volume fractions. The proposed geometries used on the mathematical model was used to obtain a data set where the thicknesses referred of each material had been changed in order to obtain volume fraction of each phase providing 119 compositions that were used in the simulation with MCNP-X -computer code based on Monte Carlo Method that simulates the radiation transport. An artificial neural network (ANN) was trained with data obtained using the MCNP-X, and used to correlate such measurements with the respective real fractions. The ANN was able to correlate the data obtained on the simulation with MCNP-X with the volume fractions of the multiphase flows (oil-water-gas), both in the pattern of annular flow as stratified, resulting in a average relative error (%) for each production set of: annular (air = 3.85; water = 4.31; oil=1.08); stratified (air = 3.10, water 2.01, oil = 1.45). The method demonstrated good efficiency in the determination of each material that composes the phases, thus demonstrating the feasibility of the technique. (author)

Taking SiC Power Devices to the Final Frontier: Addressing Challenges of the Space Radiation Environment

Science.gov (United States)

Lauenstein, Jean-Marie; Casey, Megan

2017-01-01

Silicon carbide power device technology has the potential to enable a new generation of aerospace power systems that demand high efficiency, rapid switching, and reduced mass and volume in order to expand space-based capabilities. For this potential to be realized, SiC devices must be capable of withstanding the harsh space radiation environment. Commercial SiC components exhibit high tolerance to total ionizing dose but to date, have not performed well under exposure to heavy ion radiation representative of the on-orbit galactic cosmic rays. Insertion of SiC power device technology into space applications to achieve breakthrough performance gains will require intentional development of components hardened to the effects of these highly-energetic heavy ions. This work presents heavy-ion test data obtained by the authors over the past several years for discrete SiC power MOSFETs, JFETs, and diodes in order to increase the body of knowledge and understanding that will facilitate hardening of this technology to space radiation effects. Specifically, heavy-ion irradiation data taken under different bias, temperature, and ion beam conditions is presented for devices from different manufacturers, and the emerging patterns discussed.

Preparation of SiC and Ag/SiC coatings on TRISO surrogate particles by Pulsed Laser Deposition

International Nuclear Information System (INIS)

Lustfeld, Martin; Reinecke, Anne-Maria; Lippman, Wolfgang; Hurtado, Antonio; Ruiz-Moreno, Ana

2014-01-01

Recently published research results suggest significant advantages of using nanocrystalline instead of coarse grained SiC for nuclear applications. In this work it was attempted to prepare nanocrystalline SiC coatings on TRISO surrogate kernels using the pulsed laser deposition (PLD) process. As a plasma-based physical vapor deposition process, PLD allows the synthesis of dense and stoichiometric coatings in the amorphous or nanocrystalline phase. Two different types of TRISO surrogate kernels were used with outer diameters of 500 pm and 800 μm, respectively: plain Al_2O_3 kernels and ZrO_2 kernels coated with TRISO-like buffer and pyrolytic carbon (PyC) layers. In a second step, the PLD process was used for the preparation of multilayer coatings consisting of a Ag layer buried with a SiC layer. The samples were analyzed regarding their morphology, microstructure, crystalline phase and chemical composition using scanning electron microscopy (SEM), laser scanning microscopy (LSM), x-ray diffraction (XRD) and energy- dispersive x-ray spectroscopy (EDX). The samples will be used in future work for out-of-pile investigations of both thermal stability and Ag retention capability of nanocrystalline SiC layers. X-ray diflraction measurements did not confirm nano crystallinity of the SiC coatings, but rather indicated that the coatings were mainly amorphous possibly with a little fraction of the nanocrystalline phase. Further analyses showed that some of the SiC coatings had an adequate stoichiometric composition and that Ag/SiC multilayer coatings were successfully produced by PLD. Coatings on TRISO- like buffer and PyC layers exhibited good adhesion to the substrate while coatings on Al_2O_3 kernels were susceptible to delamination. The results suggest that PLD is generally suitable for SiC coating of TRISO particles. However, further optimization of the process parameters such as the coating temperature is needed to obtain fine- grained non-columnar SiC layers that are

Distribution of the grain limit character in SiC and its effect on the diffusion of fission products in the TRISO fuel particles

International Nuclear Information System (INIS)

Cancino T, F.; Lopez H, E.

2017-09-01

At present is accepted that silver diffuses through silicium carbide (SiC) by diffusion in grain boundaries, although little is known about the characteristics of grain boundaries in SiC, and how these change depending on the type of sample. In this work, was observed that there are small but important differences between the SiC in the tri-structural isotropic (TRISO) particles and that of the monoliths, which could explain some of the differences observed in experiments on diffusion in the literature. Five different types (coatings and monoliths) of SiC produced by chemical vapor deposition (CVD) were characterized by electron backscatter diffraction (EBSD). In all the samples the SiC was mainly composed of high-angle grain boundaries (∼ 65%), with a small fraction of grain boundaries of low-angle (about 15%) and 20% of the coincidence site lattice (CSL). The morphology of the monoliths is constituted by large grains, surrounded by smaller grains; in the particles of the TRISO fuel, both columnar and equi axial grains were observed, with a more uniform distribution over the surface of the coating. (Author)

Orthorhombic Intermediate State in the Zinc Blende to Rocksalt Transformation Path of SiC at High Pressure

International Nuclear Information System (INIS)

Catti, Michele

2001-01-01

The mechanism of the B3/B1 phase transition of SiC has been investigated by periodic LCAO-DFT least-enthalpy calculations. A new transformation pathway, based on a Pmm2 orthorhombic intermediate state with two SiC units per cell, is found to be energetically favored over the traditional R3m mechanism. The computed activation enthalpy is 0.75eV/SiC unit at the predicted transition pressure of 92GPa (B3LYP functional). Activation enthalpy and activation volume vs pressure are analyzed to characterize the kinetic aspects of the transformation

Simulations of Proton Implantation in Silicon Carbide (SiC)

Science.gov (United States)

2016-03-31

Simulations of Proton Implantation in Silicon Carbide (SiC) Jonathan P. McCandless, Hailong Chen, Philip X.-L. Feng Electrical Engineering, Case...of implanting protons (hydrogen ions, H+) into SiC thin layers on silicon (Si) substrate, and explore the ion implantation conditions that are...relevant to experimental radiation of SiC layers. Keywords: silicon carbide (SiC); radiation effects; ion implantation ; proton; stopping and range of

Bulk Thermoelectric Materials Reinforced with SiC Whiskers

Science.gov (United States)

Akao, Takahiro; Fujiwara, Yuya; Tarui, Yuki; Onda, Tetsuhiko; Chen, Zhong-Chun

2014-06-01

SiC whiskers have been incorporated into Zn4Sb3 compound as reinforcements to overcome its extremely brittle nature. The bulk samples were prepared by either hot-extrusion or hot-pressing techniques. The obtained products containing 1 vol.% to 5 vol.% SiC whiskers were confirmed to exhibit sound appearance, high density, and fine-grained microstructure. Mechanical properties such as the hardness and fracture resistance were improved by the addition of SiC whiskers, as a result of dispersion strengthening and microstructural refinement induced by a pinning effect. Furthermore, crack deflection and/or bridging/pullout mechanisms are invoked by the whiskers. Regarding the thermoelectric properties, the Seebeck coefficient and electrical resistivity values comparable to those of the pure compound are retained over the entire range of added whisker amount. However, the thermal conductivity becomes large with increasing amount of SiC whiskers because of the much higher conductivity of SiC relative to the Zn4Sb3 matrix. This results in a remarkable degradation of the dimensionless figure of merit in the samples with addition of SiC whiskers. Therefore, the optimum amount of SiC whiskers in the Zn4Sb3 matrix should be determined by balancing the mechanical properties and thermoelectric performance.

Models for high cell density bioreactors must consider biomass volume fraction: Cell recycle example.

Science.gov (United States)

Monbouquette, H G

1987-06-01

Intrinsic models, which take into account biomass volume fraction, must be formulated for adequate simulation of high-biomass-density fermentations with cell recycle. Through comparison of corresponding intrinsic and non-intrinsic models in dimensionless form, constraints for non-intrinsic model usage in terms of biokinetic and fermenter operating parameters can be identified a priori. Analysis of a simple product-inhibition model indicates that the non-intrinsic approach is suitable only when the attainable biomass volume fraction in the fermentation broth is less than about 0.10. Inappropriate application of a non-intrinsic model can lead to gross errors in calculated substrate and product concentrations, substrate conversion, and volumetric productivity.

Models for high cell density bioreactors must consider biomass volume fraction: cell recycle example

Energy Technology Data Exchange (ETDEWEB)

Monbouquette, H.G.

1987-06-01

Intrinsic models, which take into account biomass volume fraction, must be formulated for adequate simulation of high-biomass-density fermentations with cell recycle. Through comparison of corresponding intrinsic and non-intrinsic models in dimensionless form, constraints for non-intrinsic model usage in terms of biokinetic and fermenter operating parameters can be identified a priori. Analysis of a simple product-inhibition model indicates that the non-intrinsic approach is suitable only when the attainable biomass volume fraction in the fermentation broth is less than about 0.10. Inappropriate application of a non-intrinsic model can lead to gross errors in calculated substrate and product concentrations, substrate conversion, and volumetric productivity. (Refs. 14).

Effects of diluents on soot surface temperature and volume fraction in diluted ethylene diffusion flames at pressure

KAUST Repository

Kailasanathan, Ranjith Kumar Abhinavam

2014-05-20

Soot surface temperature and volume fraction are measured in ethylene/air coflowing laminar diffusion flames at high pressures, diluted with one of four diluents (argon, helium, nitrogen, and carbon dioxide) using a two-color technique. Both temperature and soot measurements presented are line-of-sight averages. The results aid in understanding the kinetic and thermodynamic behavior of the soot formation and oxidation chemistry with changes in diluents, ultimately leading to possible methods of reducing soot emission from practical combustion hardware. The diluted fuel and coflow exit velocities (top-hat profiles) were matched at all pressures to minimize shear effects. In addition to the velocity-matched flow rates, the mass fluxes were held constant for all pressures. Addition of a diluent has a pronounced effect on both the soot surface temperature and volume fraction, with the helium diluted flame yielding the maximum and carbon dioxide diluted flame yielding minimum soot surface temperature and volume fraction. At low pressures, peak soot volume fraction exists at the tip of the flame, and with an increase in pressure, the location shifts lower to the wings of the flame. Due to the very high diffusivity of helium, significantly higher temperature and volume fraction are measured and explained. Carbon dioxide has the most dramatic soot suppression effect. By comparing the soot yield with previously measured soot precursor concentrations in the same flame, it is clear that the lower soot yield is a result of enhanced oxidation rates rather than a reduction in precursor formation. Copyright © 2014 Taylor & Francis Group, LLC.

Calculation of Steam Volume Fraction in Subcooled Boiling

Energy Technology Data Exchange (ETDEWEB)

Rouhani, S Z

1967-06-15

An analysis of subcooled boiling is presented. It is assumed that heat is removed by vapor generation, heating of the liquid that replaces the detached bubbles, and to some extent by single phase heat transfer. Two regions of subcooled boiling are considered and a criterion is provided for obtaining the limiting value of subcooling between the two regions. Condensation of vapor in the subcooled liquid is analysed and the relative velocity of vapor with respect to the liquid is neglected in these regions. The theoretical arguments result in some equations for the calculation of steam volume fraction and true liquid subcooling.

Artificial neural network and neutron application in a volume fraction calculation in annular and stratified multiphase system

Energy Technology Data Exchange (ETDEWEB)

Ramos, Robson; Brandao, Luis E.B.; Pereira, Claudio M.N.A., E-mail: robson@ien.gov.b, E-mail: brandao@ien.gov.b, E-mail: cmnap@ien.gov.b [Instituto de Engenharia Nuclear (IEN/CNEN-RJ), Rio de Janeiro, RJ (Brazil). Div. de Radiofarmacos; Schirru, Roberto; Silva, Ademir Xavier da, E-mail: schirru@lmp.ufrj.b, E-mail: ademir@con.ufrj.b [Coordenacao dos Programas de Pos-Graduacao de Engenharia (COPPE/UFRJ), RJ (Brazil). Nuclear Engineering Dept.

2009-07-01

Multiphase flows, type oil-water-gas are very common among different industrial activities, such as chemical industries and petroleum extraction, and its measurements show some difficulties to be taken. Precisely determining the volume fraction of each one of the elements that composes a multiphase flow is very important in chemical plants and petroleum industries. This work presents a methodology able to determine volume fraction on Annular and Stratified multiphase flow system with the use of neutrons and artificial intelligence, using the principles of transmission/scattering of fast neutrons from a {sup 241}Am-Be source and measurements of point flow that are influenced by variations of volume fractions. The proposed geometries used on the mathematical model was used to obtain a data set where the thicknesses referred of each material had been changed in order to obtain volume fraction of each phase providing 119 compositions that were used in the simulation with MCNP-X -computer code based on Monte Carlo Method that simulates the radiation transport. An artificial neural network (ANN) was trained with data obtained using the MCNP-X, and used to correlate such measurements with the respective real fractions. The ANN was able to correlate the data obtained on the simulation with MCNP-X with the volume fractions of the multiphase flows (oil-water-gas), both in the pattern of annular flow as stratified, resulting in a average relative error (%) for each production set of: annular (air = 3.85; water = 4.31; oil=1.08); stratified (air = 3.10, water 2.01, oil = 1.45). The method demonstrated good efficiency in the determination of each material that composes the phases, thus demonstrating the feasibility of the technique. (author)

Characterization of SiCf/SiC and CNT/SiC composite materials produced by liquid phase sintering

International Nuclear Information System (INIS)

Lee, J.K.; Lee, S.P.; Cho, K.S.; Byun, J.H.; Bae, D.S.

2011-01-01

This paper dealt with the microstructure and mechanical properties of SiC based composites reinforced with different reinforcing materials. The composites were fabricated using reinforcing materials of carbon nanotubes (CNT) and Tyranno Lox-M SiC chopped fibers. The volume fraction of carbon nanotubes was also varied in this composite system. An Al 2 O 3 -Y 2 O 3 powder mixture was used as a sintering additive in the consolidation of the SiC matrix. The characterization of the composites was investigated by means of SEM and three point bending tests. These composites showed a dense morphology of the matrix region, by the creation of a secondary phase. The composites reinforced with SiC chopped fibers possessed a flexural strength of about 400 MPa at room temperature. The flexural strength of the carbon nanotubes composites had a tendency to decrease with increased volume fraction of the reinforcing material.

Grafted SiC nanocrystals

DEFF Research Database (Denmark)

Saini, Isha; Sharma, Annu; Dhiman, Rajnish

2017-01-01

), raman spectroscopy and X-ray diffraction (XRD) measurements. UV–Visible absorption spectroscopy was used to study optical properties such as optical energy gap (Eg), Urbach's energy (Eu), refractive index (n), real (ε1) and imaginary (ε2) parts of dielectric constant of PVA as well as PVA......Polyvinyl alcohol (PVA) grafted SiC (PVA-g-SiC)/PVA nanocomposite was synthesized by incorporating PVA grafted silicon carbide (SiC) nanocrystals inside PVA matrix. In-depth structural characterization of resulting nanocomposite was carried out using fourier transform infrared spectroscopy (FTIR...

SiC Power MOSFET with Improved Gate Dielectric

Energy Technology Data Exchange (ETDEWEB)

Sbrockey, Nick M. [Structured Materials Industries, Inc., Piscataway, NJ (United States); Tompa, Gary S. [Structured Materials Industries, Inc., Piscataway, NJ (United States); Spencer, Michael G. [Structured Materials Industries, Inc., Piscataway, NJ (United States); Chandrashekhar, Chandra M.V. S. [Structured Materials Industries, Inc., Piscataway, NJ (United States)

2010-08-23

In this STTR program, Structured Materials Industries (SMI), and Cornell University are developing novel gate oxide technology, as a critical enabler for silicon carbide (SiC) devices. SiC is a wide bandgap semiconductor material, with many unique properties. SiC devices are ideally suited for high-power, highvoltage, high-frequency, high-temperature and radiation resistant applications. The DOE has expressed interest in developing SiC devices for use in extreme environments, in high energy physics applications and in power generation. The development of transistors based on the Metal Oxide Semiconductor Field Effect Transistor (MOSFET) structure will be critical to these applications.

Synthesis of whiskers of SiC microwave assisted; Sintesis de whiskers de SiC asistida por microondas

Energy Technology Data Exchange (ETDEWEB)

Garza-Mendez, F. J.; Vanegas, A. J.; Vazquez, B. A.; Garza-Paz, J.

2013-06-01

We developed a new process for the synthesis of SiC whiskers assisted by microwaves; this is based on the mixture of silica xerogels and graphite powder. As energy source were used microwaves of 2.45 GHz and 1.0 kW of power RMS. On the other hand, mesoporous silica was synthesized via sol-gel, the precursors used were TEOS/H{sub 2}O and ethanol. Through analysis of the BET is determined the value of average pore size (3.0 nm) and the surface area (1090 m2/g).By mean of X-Ray diffraction it was demonstrated that the silica obtained is an amorphous solid and, the powders obtained in the microwave synthesis are {beta}-SiC. Synthesized SiC powders were observed using a SEM in secondary electron mode, it was observed that this powders consists of SiC whiskers. The effect of microwaves on the synthesis of whiskers of SiC is discussed in the present work. (Author) 19 refs.

D-region ion-neutral coupled chemistry (Sodankylä Ion Chemistry, SIC) within the Whole Atmosphere Community Climate Model (WACCM 4) - WACCM-SIC and WACCM-rSIC

Science.gov (United States)

Kovács, Tamás; Plane, John M. C.; Feng, Wuhu; Nagy, Tibor; Chipperfield, Martyn P.; Verronen, Pekka T.; Andersson, Monika E.; Newnham, David A.; Clilverd, Mark A.; Marsh, Daniel R.

2016-09-01

This study presents a new ion-neutral chemical model coupled into the Whole Atmosphere Community Climate Model (WACCM). The ionospheric D-region (altitudes ˜ 50-90 km) chemistry is based on the Sodankylä Ion Chemistry (SIC) model, a one-dimensional model containing 307 ion-neutral and ion recombination, 16 photodissociation and 7 photoionization reactions of neutral species, positive and negative ions, and electrons. The SIC mechanism was reduced using the simulation error minimization connectivity method (SEM-CM) to produce a reaction scheme of 181 ion-molecule reactions of 181 ion-molecule reactions of 27 positive and 18 negative ions. This scheme describes the concentration profiles at altitudes between 20 km and 120 km of a set of major neutral species (HNO3, O3, H2O2, NO, NO2, HO2, OH, N2O5) and ions (O2+, O4+, NO+, NO+(H2O), O2+(H2O), H+(H2O), H+(H2O)2, H+(H2O)3, H+(H2O)4, O3-, NO2-, O-, O2, OH-, O2-(H2O), O2-(H2O)2, O4-, CO3-, CO3-(H2O), CO4-, HCO3-, NO2-, NO3-, NO3-(H2O), NO3-(H2O)2, NO3-(HNO3), NO3-(HNO3)2, Cl-, ClO-), which agree with the full SIC mechanism within a 5 % tolerance. Four 3-D model simulations were then performed, using the impact of the January 2005 solar proton event (SPE) on D-region HOx and NOx chemistry as a test case of four different model versions: the standard WACCM (no negative ions and a very limited set of positive ions); WACCM-SIC (standard WACCM with the full SIC chemistry of positive and negative ions); WACCM-D (standard WACCM with a heuristic reduction of the SIC chemistry, recently used to examine HNO3 formation following an SPE); and WACCM-rSIC (standard WACCM with a reduction of SIC chemistry using the SEM-CM method). The standard WACCM misses the HNO3 enhancement during the SPE, while the full and reduced model versions predict significant NOx, HOx and HNO3 enhancements in the mesosphere during solar proton events. The SEM-CM reduction also identifies the important ion-molecule reactions that affect the partitioning of

Quantitative grain-scale ferroic domain volume fractions and domain switching strains from three-dimensional X-ray diffraction data

DEFF Research Database (Denmark)

Oddershede, Jette; Majkut, Marta; Caosyd, Qinghua

2015-01-01

A method for the extension of the three-dimensional X-ray diffraction technique to allow the extraction of domain volume fractions in polycrystalline ferroic materials is presented. This method gives access to quantitative domain volume fractions of hundreds of independent embedded grains within...... are applied to tetragonal coarse-grained Ba0.88Ca0.12Zr0.06Ti0.94O3 and rhombohedral fine-grained (0.82)Bi0.5Na0.5TiO3–(0.18)Bi0.5K0.5TiO3 electroceramic materials. The fitted volume fraction information is used to calculate grain-scale non-180° ferroelectric domain switching strains. The absolute errors...

Salinity independent volume fraction prediction in water-gas-oil multiphase flows using artificial neural networks

Energy Technology Data Exchange (ETDEWEB)

Salgado, C.M.; Pereira, Claudio M.N.A.; Brandao, Luis E.B., E-mail: otero@ien.gov.b, E-mail: cmnap@ien.gov.b, E-mail: brandao@ien.gov.b [Instituto de Engenharia Nuclear (DIRA/IEN/CNEN-RJ), Rio de Janeiro, RJ (Brazil). Div. de Radiofarmacos

2011-07-01

This work investigates the response of a volume fraction prediction system for water-gas-oil multiphase flows considering variations on water salinity. The approach is based on gamma-ray pulse height distributions pattern recognition by means the artificial neural networks (ANNs). The detection system uses appropriate fan beam geometry, comprised of a dual-energy gamma-ray source and two NaI(Tl) detectors adequately positioned outside the pipe in order measure transmitted and scattered beams. An ideal and static theoretical model for annular flow regime have been developed using MCNP-X code, which was used to provide training, test and validation data for the ANN. More than 500 simulations have been done, in which water salinity have been ranged from 0 to 16% in order to cover a most practical situations. Validation tests have included values of volume fractions and water salinity different from those used in ANN training phase. The results presented here show that the proposed approach may be successfully applied to material volume fraction prediction on watergas- oil multiphase flows considering practical (real) levels of variations in water salinity. (author)

Salinity independent volume fraction prediction in water-gas-oil multiphase flows using artificial neural networks

International Nuclear Information System (INIS)

Salgado, C.M.; Pereira, Claudio M.N.A.; Brandao, Luis E.B.

2011-01-01

This work investigates the response of a volume fraction prediction system for water-gas-oil multiphase flows considering variations on water salinity. The approach is based on gamma-ray pulse height distributions pattern recognition by means the artificial neural networks (ANNs). The detection system uses appropriate fan beam geometry, comprised of a dual-energy gamma-ray source and two NaI(Tl) detectors adequately positioned outside the pipe in order measure transmitted and scattered beams. An ideal and static theoretical model for annular flow regime have been developed using MCNP-X code, which was used to provide training, test and validation data for the ANN. More than 500 simulations have been done, in which water salinity have been ranged from 0 to 16% in order to cover a most practical situations. Validation tests have included values of volume fractions and water salinity different from those used in ANN training phase. The results presented here show that the proposed approach may be successfully applied to material volume fraction prediction on watergas- oil multiphase flows considering practical (real) levels of variations in water salinity. (author)

Influence of defects in SiC (0001) on epitaxial graphene

International Nuclear Information System (INIS)

Guo Yu; Guo Li-Wei; Lu Wei; Huang Jiao; Jia Yu-Ping; Sun Wei; Li Zhi-Lin; Wang Yi-Fei

2014-01-01

Defects in silicon carbide (SiC) substrate are crucial to the properties of the epitaxial graphene (EG) grown on it. Here we report the effect of defects in SiC on the crystalline quality of EGs through comparative studies of the characteristics of the EGs grown on SiC (0001) substrates with different defect densities. It is found that EGs on high quality SiC possess regular steps on the surface of the SiC and there is no discernible D peak in its Raman spectrum. Conversely, the EG on the SiC with a high density of defects has a strong D peak, irregular stepped morphology and poor uniformity in graphene layer numbers. It is the defects in the SiC that are responsible for the irregular stepped morphology and lead to the small domain size in the EG. (rapid communication)

Optimization of the fractionated irradiation scheme considering physical doses to tumor and organ at risk based on dose–volume histograms

Energy Technology Data Exchange (ETDEWEB)

Sugano, Yasutaka [Graduate School of Health Sciences, Hokkaido University, Kita-12, Nishi-5, Kita-ku, Sapporo, Hokkaido 060-0812 (Japan); Mizuta, Masahiro [Laboratory of Advanced Data Science, Information Initiative Center, Hokkaido University, Kita-11, Nishi-5, Kita-ku, Sapporo, Hokkaido 060-0811 (Japan); Takao, Seishin; Shirato, Hiroki; Sutherland, Kenneth L. [Department of Radiation Medicine, Graduate School of Medicine, Hokkaido University, Kita-15, Nishi-5, Kita-ku, Sapporo, Hokkaido 060-8638 (Japan); Date, Hiroyuki, E-mail: date@hs.hokudai.ac.jp [Faculty of Health Sciences, Hokkaido University, Kita-12, Nishi-5, Kita-ku, Sapporo, Hokkaido 060-0812 (Japan)

2015-11-15

Purpose: Radiotherapy of solid tumors has been performed with various fractionation regimens such as multi- and hypofractionations. However, the ability to optimize the fractionation regimen considering the physical dose distribution remains insufficient. This study aims to optimize the fractionation regimen, in which the authors propose a graphical method for selecting the optimal number of fractions (n) and dose per fraction (d) based on dose–volume histograms for tumor and normal tissues of organs around the tumor. Methods: Modified linear-quadratic models were employed to estimate the radiation effects on the tumor and an organ at risk (OAR), where the repopulation of the tumor cells and the linearity of the dose-response curve in the high dose range of the surviving fraction were considered. The minimization problem for the damage effect on the OAR was solved under the constraint that the radiation effect on the tumor is fixed by a graphical method. Here, the damage effect on the OAR was estimated based on the dose–volume histogram. Results: It was found that the optimization of fractionation scheme incorporating the dose–volume histogram is possible by employing appropriate cell surviving models. The graphical method considering the repopulation of tumor cells and a rectilinear response in the high dose range enables them to derive the optimal number of fractions and dose per fraction. For example, in the treatment of prostate cancer, the optimal fractionation was suggested to lie in the range of 8–32 fractions with a daily dose of 2.2–6.3 Gy. Conclusions: It is possible to optimize the number of fractions and dose per fraction based on the physical dose distribution (i.e., dose–volume histogram) by the graphical method considering the effects on tumor and OARs around the tumor. This method may stipulate a new guideline to optimize the fractionation regimen for physics-guided fractionation.

Cerebral blood volume alterations during fractional pneumoencephalography

International Nuclear Information System (INIS)

Voigt, K.; Greitz, T.

1976-01-01

Simultaneous and continuous measurements of the cerebral blood volume (CBV), cerebrospinal fluid (CSF) and blood pressure were carried out in six patients during fractional pneumoencephalography in order to examine intracranial volumetric interactions. Three patients (Group A) showed normal encephalographic findings, and in three patients (Group B) communicating hydrocephalus with convexity block was found encephalographically. In all patients the injection of air was followed by an immediate increase of CSF pressure and blood pressure and a concomitant decrease of CBV. The initial CSF pressure was invariably re-established within 3 to 3.5 min. During this time interval the CBV of the patients of Group B decreased significantly and 30 percent more than that of Group A. Furthermore, after restoration of the original CSF pressure, CBV returned to its initial level in all patients of Group A, whereas it remained unchanged or showed a further decrease in the patients of Group B. Removal of an amount of CSF corresponding to half of the amount of injected air was followed by a significant reactive hyperemic response in two normal patients. The intracranial volumetric alterations during fractional pneumoencephalography are discussed in detail with respect to the underlying physiologic mechanisms and are suggested as a model for acute and low pressure hydrocephalus

[Application of Raman spectroscopy to investigation of CVD-SIC fiber].

Science.gov (United States)

Liu, Bin; Yang, Yan-Qing; Luo, Xian; Huang, Bin

2011-11-01

The CVD-SiC fiber was studied by using laser Raman spectra. It was found that the sharp TO peak exists in the first SiC deposit layer, indicating the larger SiC grains. But the second SiC deposit layer is with small grains. Raman peak of carbon and silicon was detected respectively in the first and second layer. Compared with that of the single SiC fiber, the TO peaks move to the high wave number for the SiC fiber in SiC(f)/Ti-6Al-4V composite. It indicates that the compressive thermal residual stress is present in the SiC fiber during the fabrication of the composite because of the mismatched coefficient of thermal expansion between Ti-6Al-4V matrix and SiC fiber. The average thermal residual stress of the SiC fiber in SiC(f)/Ti-6Al-4V composite was calculated to be 318 MPa and the residual stress in first deposit layer is 436 MPa which is much higher than that in the second layer.

The equivalent electrical permittivity of gas-solid mixtures at intermediate solid volume fractions.

Energy Technology Data Exchange (ETDEWEB)

Torczynski, John Robert; Ceccio, Steven Louis; Tortora, Paul Richard

2005-07-01

Several mixture models are evaluated for their suitability in predicting the equivalent permittivity of dielectric particles in a dielectric medium for intermediate solid volume fractions (0.4 to 0.6). Predictions of the Maxwell, Rayleigh, Bottcher and Bruggeman models are compared to computational simulations of several arrangements of solid particles in a gas and to the experimentally determined permittivity of a static particle bed. The experiment uses spherical glass beads in air, so air and glass permittivity values (1 and 7, respectively) are used with all of the models and simulations. The experimental system used to measure the permittivity of the static particle bed and its calibration are described. The Rayleigh model is found to be suitable for predicting permittivity over the entire range of solid volume fractions (0-0.6).

Amorphization and the effect of implanted ions in SiC

International Nuclear Information System (INIS)

Snead, L.L.; Zinkle, S.J.

1994-01-01

The effects of implanted ion chemistry and displacement damage on the amorphization threshold dose of SiC were studied using cross-section transmission electron microscopy. Room temperature as well as 200 and 400 C irradiations were carried out with 3.6 MeV Fe, 1.8 MeV Cl, 1 MeV He or 0.56 MeV Si ions. The room temperature amorphization threshold dose in irradiated regions well separated from the implanted ions was found to range from 0.3 to 0.5 dpa for the four different ion species. The threshold dose for amorphization in the He, Si and Fe ion-implanted regions was also ∼0.3 to 0.5 dpa. On the other hand, the amorphization threshold in the Cl-implanted region was only about 0.1 dpa. The volume change associated with amorphization was ∼17%. No evidence for amorphization was obtained in specimens irradiated at 200 or 400 C. An understanding of the microstructural evolution of SiC under irradiation is critical to the application of these materials in fusion energy systems

Residual stress analysis in carbon fiber-reinforced SiC ceramics

International Nuclear Information System (INIS)

Broda, M.

1998-01-01

Systematic residual stress analyses are reported, carried out in long-fiber reinforced SiC ceramics. The laminated C fiber /SiC matrix specimens used were prepared by polymer pyrolysis, and the structural component specimens used are industrial products. Various diffraction methods have been applied for non-destructive evaluation of residual stress fields, so as to completely detect the residual stresses and their distribution in the specimens. The residual stress fields at the surface (μm) have been measured using characteristic X-radiation and applying the sin 2 ψ method as well as the scatter vector method. For residual stress field analysis in the mass volume (cm), neutron diffraction has been applied. The stress fields in the fiber layers (approx. 250μm) have been measured as a function of their location within the laminated composite by using an energy-dispersive method and synchrotron radiation. By means of the systematic, process-accompanying residual stress and phase analyses, conclusions can be drawn as to possible approaches for optimization of fabrication parameters. (orig./CB) [de

Study of volume fractions for stratified and annular regime in multiphase flows using gamma-rays and artificial neural network

International Nuclear Information System (INIS)

Salgado, Cesar M.; Brandao, Luis Eduardo; Pereira, Claudio M.N.A.; Ramos, Robson; Schirru, Roberto; Silva, Ademir X.

2007-01-01

This work presents methodology based on the use of nuclear technique and artificial intelligence for attainment of volume fractions in stratified and annular multiphase flow regime, oil-water-gas, very frequent in the offshore industry petroliferous. Using the principles of absorption and scattering of gamma-rays and an adequate geometry scheme of detection with two detectors and two energies measurement are gotten and they vary as changes in the volume fractions of flow regime occur. The MCNP-X code was used in order to provide the data training for artificial neural network that matched such information with the respective actual volume fractions of each material. (author)

Study of volume fractions for stratified and annular regime in multiphase flows using gamma-rays and artificial neural network

Energy Technology Data Exchange (ETDEWEB)

Salgado, Cesar M.; Brandao, Luis Eduardo; Pereira, Claudio M.N.A.; Ramos, Robson [Instituto de Engenharia Nuclear (IEN/CNEN-RJ), Rio de Janeiro, RJ (Brazil)]. E-mail: otero@ien.gov.br; brandao@ien.gov.br; cmnap@ien.gov.br; robson@ien.gov.br; Schirru, Roberto; Silva, Ademir X. [Universidade Federal do Rio de Janeiro (UFRJ), RJ (Brazil). Coordenacao dos Programas de Pos-Graduacao de Engenharia (COPPE). Programa de Energia Nuclear (PEN)]. E-mails: ademir@con.ufrj.br; schirru@lmp.ufrj.br

2007-07-01

This work presents methodology based on the use of nuclear technique and artificial intelligence for attainment of volume fractions in stratified and annular multiphase flow regime, oil-water-gas, very frequent in the offshore industry petroliferous. Using the principles of absorption and scattering of gamma-rays and an adequate geometry scheme of detection with two detectors and two energies measurement are gotten and they vary as changes in the volume fractions of flow regime occur. The MCNP-X code was used in order to provide the data training for artificial neural network that matched such information with the respective actual volume fractions of each material. (author)

SiC as an oxidation-resistant refractory material. Pt. 1

International Nuclear Information System (INIS)

Schlichting, J.

1979-01-01

Uses his own investigations and gives a literature survey on the oxidation and corrosion behaviour of SiC (in the form of a pure SiC powder, hot-pressed and reaction-sintered materials). The excellent stability of SiC in oxidizing atmosphere is due to the development of protective SiO 2 coatings. Any changes in these protective coatings (e.g. due to impurities with corrosive media, high porosity of SiC, etc.) lead in most cases to increased rates of oxidation and thus restrict the field of application of SiC. (orig.) [de

Non-equilibrium Inertial Separation Array for High-throughput, Large-volume Blood Fractionation.

Science.gov (United States)

Mutlu, Baris R; Smith, Kyle C; Edd, Jon F; Nadar, Priyanka; Dlamini, Mcolisi; Kapur, Ravi; Toner, Mehmet

2017-08-30

Microfluidic blood processing is used in a range of applications from cancer therapeutics to infectious disease diagnostics. As these applications are being translated to clinical use, processing larger volumes of blood in shorter timescales with high-reliability and robustness is becoming a pressing need. In this work, we report a scaled, label-free cell separation mechanism called non-equilibrium inertial separation array (NISA). The NISA mechanism consists of an array of islands that exert a passive inertial lift force on proximate cells, thus enabling gentler manipulation of the cells without the need of physical contact. As the cells follow their size-based, deterministic path to their equilibrium positions, a preset fraction of the flow is siphoned to separate the smaller cells from the main flow. The NISA device was used to fractionate 400 mL of whole blood in less than 3 hours, and produce an ultrapure buffy coat (96.6% white blood cell yield, 0.0059% red blood cell carryover) by processing whole blood at 3 mL/min, or ∼300 million cells/second. This device presents a feasible alternative for fractionating blood for transfusion, cellular therapy and blood-based diagnostics, and could significantly improve the sensitivity of rare cell isolation devices by increasing the processed whole blood volume.

Structural and thermal characterization of polyvinylalcohol grafted SiC nanocrystals

DEFF Research Database (Denmark)

Saini, Isha; Sharma, Annu; Dhiman, Rajnish

2017-01-01

introduced in the characteristic TO and LO mode of vibration of SiC nanocrystals after grafting procedure.XRD analysis confirmed that the grafting procedure did not alter the crystalline geometry of SiC nanocrystals. TEM and SEM images further support the FTIR and Raman spectroscopic results and confirm...... of semiconducting SiC nanocrystals using a novel method. FTIR spectroscopy reveals the introduction of new peaks corresponding to various functional groups of PVA alongwith the presence of characteristic Si-C vibrational peak in the spectra of grafted SiC nanocrystals. Raman spectra depict the presence of changes...... the presence of PVA layer around SiC nanocrystals. Thermal degradation behavior of PVA-g-SiC nanocrystals has been studied using TGA analysis....

SiC Nanoparticles Toughened-SiC/MoSi2-SiC Multilayer Functionally Graded Oxidation Protective Coating for Carbon Materials at High Temperatures

Science.gov (United States)

Abdollahi, Alireza; Ehsani, Naser; Valefi, Zia; Khalifesoltani, Ali

2017-05-01

A SiC nanoparticle toughened-SiC/MoSi2-SiC functionally graded oxidation protective coating on graphite was prepared by reactive melt infiltration (RMI) at 1773 and 1873 K under argon atmosphere. The phase composition and anti-oxidation behavior of the coatings were investigated. The results show that the coating was composed of MoSi2, α-SiC and β-SiC. By the variations of Gibbs free energy (calculated by HSC Chemistry 6.0 software), it could be suggested that the SiC coating formed at low temperatures by solution-reprecipitation mechanism and at high temperatures by gas-phase reactions and solution-reprecipitation mechanisms simultaneously. SiC nanoparticles could improve the oxidation resistance of SiC/MoSi2-SiC multiphase coating. Addition of SiC nanoparticles increases toughness of the coating and prevents spreading of the oxygen diffusion channels in the coating during the oxidation test. The mass loss and oxidation rate of the SiC nanoparticle toughened-SiC/MoSi2-SiC-coated sample after 10-h oxidation at 1773 K were only 1.76% and 0.32 × 10-2 g/cm3/h, respectively.

Determination of volume fraction in biphasic flows oil-gas and water-gas using artificial neural network and gamma densitometry

International Nuclear Information System (INIS)

Peixoto, Philippe Netto Belache

2016-01-01

This study presents a methodology based on the principles of gamma ray attenuation to identify volume fractions in biphasic systems composed of oil-gas-water and gas which are found in the offshore oil industry. This methodology is based on the acknowledgment counts per second on the photopeak energy using a detection system composed of a NaI (Tl) detector, a source of 137 Cs without collimation positioned at 180 ° relative to the detector on a smooth stratified flow regime. The mathematical modeling for computational simulation using the code MCNP-X was performed using the experimental measurements of the detector characteristics (energy resolution and efficiency), characteristics of the material water and oil (density and coefficient attenuation) and measurement of the volume fractions. To predict these fractions were used artificial neural networks (ANNs), and to obtain an adequate training the ANNs for the prediction of volume fractions were simulated a larger number of volume fractions in MCNP-X. The experimental data were used in the set data necessary for validation of ANNs and the data generated using the computer code MCNP-X were used in training and test sets of the ANNs. Were used ANNs of type feed-forward Multilayer Perceptron (MLP) and analyzed two functions of training, Levenberg-Marquardt (LM) and gradient descent with momentum (GDM), both using the Backpropagation training algorithm. The ANNs identified correctly the volume fractions of the multiphase system with mean relative errors lower than 1.21 %, enabling the application of this methodology for this purpose. (author)

Stability analysis of SiO2/SiC multilayer coatings

International Nuclear Information System (INIS)

Fu Zhiqiang; Jean-Charles, R.

2006-01-01

The stability behaviours of SiC coatings and SiO 2 /SiC coatings in helium with little impurities are studied by HSC Chemistry 4.1, the software for analysis of Chemical reaction and equilibrium in multi-component complex system. It is found that in helium with a low partial pressure of oxidative impurities under different total pressure, the key influence factor controlling T cp of SiC depends is the partial pressure of oxidative impurities; T cp of SiC increases with the partial pressure of oxidative impurities. In helium with a low partial pressure of different impurities, the key influence factor of T cs of SiO 2 are both the partial pressure of impurities and the amount of impurities for l mol SiO 2 ; T cs of SiO 2 increases with the partial pressure of oxidative impurities at the same amount of the impurities for 1 mol SiO 2 while it decreases with the amount of the impurities for 1 mm SiO 2 at the same partial pressure of the impurities. The influence of other impurities on T cp of SiC in He-O 2 is studied and it is found that CO 2 , H 2 O and N-2 increase T cp of SiC in He-O 2 while H 2 , CO and CH 4 decrease T cp of SiC He-O 2 . When there exist both oxidative impurities and reductive impurities, their effect on T cs of SiO 2 can be suppressed by the other. In HTR-10 operation atmosphere, SiO 2 /SiC coatings can keep stable status at higher temperature than SiC coatings, so SiO 2 /SiC coatings is more suitable to improve the oxidation resistance of graphite in HTR-10 operation atmosphere compared with SiC coatings. (authors)

Physical aging and structural recovery in a colloidal glass subjected to volume-fraction jump conditions

Science.gov (United States)

Peng, Xiaoguang; McKenna, Gregory B.

2016-04-01

Three important kinetic phenomena have been cataloged by Kovacs in the investigation of molecular glasses during structural recovery or physical aging. These are responses to temperature-jump histories referred to as intrinsic isotherms, asymmetry of approach, and memory effect. Here we use a thermosensitive polystyrene-poly (N -isopropylacrylamide)-poly (acrylic acid) core-shell particle-based dispersion as a colloidal model and by working at a constant number concentration of particles we use temperature changes to create volume-fraction changes. This imposes conditions similar to those defined by Kovacs on the colloidal system. We use creep experiments to probe the physical aging and structural recovery behavior of colloidal glasses in the Kovacs-type histories and compare the results with those seen in molecular glasses. We find that there are similarities in aging dynamics between molecular glasses and colloidal glasses, but differences also persist. For the intrinsic isotherms, the times teq needed for relaxing or evolving into the equilibrium (or stationary) state are relatively insensitive to the volume fraction and the values of teq are longer than the α -relaxation time τα at the same volume fraction. On the other hand, both of these times grow at least exponentially with decreasing temperature in molecular glasses. For the asymmetry of approach, similar nonlinear behavior is observed for both colloidal and molecular glasses. However, the equilibration time teq is the same for both volume-fraction up-jump and down-jump experiments, different from the finding in molecular glasses that it takes longer for the structure to evolve into equilibrium for the temperature up-jump condition than for the temperature down-jump condition. For the two-step volume-fraction jumps, a memory response is observed that is different from observations of structural recovery in two-step temperature histories in molecular glasses. The concentration dependence of the dynamics

SOLA-VOF, 2-D Transient Hydrodynamic Using Fractional Volume of Fluid Method

International Nuclear Information System (INIS)

Nichols, B.D.; Hirt, C.W.; Hotchkiss, R.S.

1991-01-01

1 - Description of problem or function: SOLA-VOF is a program for the solution of two-dimensional transient fluid flow with free boundaries, based on the concept of a fractional volume of fluid (VOF). Its basic mode of operation is for single fluid calculations having multiple free surfaces. However, SOLA-VOF can also be used for calculations involving two fluids separated by a sharp interface. In either case, the fluids may be treated as incompressible or as having limited compressibility. Surface tension forces with wall adhesion are permitted in both cases. Internal obstacles may be defined by blocking out any desired combination of cells in the mesh, which is composed of rectangular cells of variable size. 2 - Method of solution: The basis of the SOLA-VOF method is the fractional volume of fluid scheme for tracking free boundaries. In this technique, a function F(x,y,t) is defined whose value is unity at any point occupied by fluid and zero elsewhere. When averaged over the cells of a computational mesh, the average value of F in a cell is equal to the fractional volume of the cell occupied by fluid. In particular, a unit value of F corresponds to a cell full of fluid, whereas a zero value indicates that the cell contains no fluid. Cells with F values between zero and one contain a free surface. SOLA-VOF uses an Eulerian mesh of rectangular cells having variable sizes. The fluid equations solved are the finite difference approximations of the Navier-Stokes equations. 3 - Restrictions on the complexity of the problem: The setting of array dimensions is controlled through PARAMETER statements

Modeling the Effect of Glass Microballoon (GMB) Volume Fraction on Behavior of Sylgard/GMB Composites.

Energy Technology Data Exchange (ETDEWEB)

Brown, Judith Alice [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Long, Kevin Nicholas [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

2017-05-01

This work was done to support customer questions about whether a Sylgard/Glass Microballoon (GMB) potting material in current use could be replaced with pure Sylgard and if this would significantly change stresses imparted to internal components under thermal cycling conditions. To address these questions, we provide micromechanics analysis of Sylgard/GMB materials using both analytic composite theory and finite element simulations to better understand the role of the GMB volume fraction in determining thermal expansion coefficient, elastic constants, and behavior in both confined and unconfined compression boundary value problems. A key finding is that damage accumulation in the material from breakage of GMBs significantly limits the global stress magnitude and results in a plateau stress behavior over large ranges of compressive strain. The magnitude of this plateau stress is reduced with higher volume fractions of GMBs. This effect is particularly pronounced in confined compression, which we estimate bears the most similarity to the application of interest. This stress-limiting damage mechanism is not present in pure Sylgard, however, and the result is much higher stresses under confined compression. Thus, we recommend that some volume fraction greater than 10% GMBs be used for confined deformation applications.

Damping behavior of polymer composites with high volume fraction of NiMnGa powders

Science.gov (United States)

Sun, Xiaogang; Song, Jie; Jiang, Hong; Zhang, Xiaoning; Xie, Chaoying

2011-03-01

Polymer composites inserted with high volume fraction (up to 70 Vol%) of NiMnGa powders were fabricated and their damping behavior was investigated by dynamic mechanical analysis. It is found that the polymer matrix has little influence on the transformation temperatures of NiMnGa powders. A damping peak appears for NiMnGa/epoxy resin (EP) composites accompanying with the martensitic transformation or reverse martensitic transformation of NiMnGa powders during cooling or heating. The damping capacity for NiMnGa/EP composites increases linearly with the increase of volume fraction of NiMnGa powders and, decreases dramatically as the test frequency increases. The fracture strain of NiMnGa/EP composites decrease with the increase of NiMnGa powders.

Computational Modeling of Radiation Phenomenon in SiC for Nuclear Applications

Science.gov (United States)

Ko, Hyunseok

Silicon carbide (SiC) material has been investigated for promising nuclear materials owing to its superior thermo-mechanical properties, and low neutron cross-section. While the interest in SiC has been increasing, the lack of fundamental understanding in many radiation phenomena is an important issue. More specifically, these phenomena in SiC include the fission gas transport, radiation induced defects and its evolution, radiation effects on the mechanical stability, matrix brittleness of SiC composites, and low thermal conductivities of SiC composites. To better design SiC and SiC composite materials for various nuclear applications, understanding each phenomenon and its significance under specific reactor conditions is important. In this thesis, we used various modeling approaches to understand the fundamental radiation phenomena in SiC for nuclear applications in three aspects: (a) fission product diffusion through SiC, (b) optimization of thermodynamic stable self-interstitial atom clusters, (c) interface effect in SiC composite and their change upon radiation. In (a) fission product transport work, we proposed that Ag/Cs diffusion in high energy grain boundaries may be the upper boundary in unirradiated SiC at relevant temperature, and radiation enhanced diffusion is responsible for fast diffusion measured in post-irradiated fuel particles. For (b) the self-interstitial cluster work, thermodynamically stable clusters are identified as a function of cluster size, shape, and compositions using a genetic algorithm. We found that there are compositional and configurational transitions for stable clusters as the cluster size increases. For (c) the interface effect in SiC composite, we investigated recently proposed interface, which is CNT reinforced SiC composite. The analytical model suggests that CNT/SiC composites have attractive mechanical and thermal properties, and these fortify the argument that SiC composites are good candidate materials for the cladding

High density plasma via hole etching in SiC

International Nuclear Information System (INIS)

Cho, H.; Lee, K.P.; Leerungnawarat, P.; Chu, S.N.G.; Ren, F.; Pearton, S.J.; Zetterling, C.-M.

2001-01-01

Throughwafer vias up to 100 μm deep were formed in 4H-SiC substrates by inductively coupled plasma etching with SF 6 /O 2 at a controlled rate of ∼0.6 μm min-1 and use of Al masks. Selectivities of >50 for SiC over Al were achieved. Electrical (capacitance-voltage: current-voltage) and chemical (Auger electron spectroscopy) analysis techniques showed that the etching produced only minor changes in reverse breakdown voltage, Schottky barrier height, and near surface stoichiometry of the SiC and had high selectivity over common frontside metallization. The SiC etch rate was a strong function of the incident ion energy during plasma exposure. This process is attractive for power SiC transistors intended for high current, high temperature applications and also for SiC micromachining

40 CFR 63.2854 - How do I determine the weighted average volume fraction of HAP in the actual solvent loss?

Science.gov (United States)

2010-07-01

... volume fraction of HAP in the actual solvent loss? 63.2854 Section 63.2854 Protection of Environment... AIR POLLUTANTS FOR SOURCE CATEGORIES National Emission Standards for Hazardous Air Pollutants: Solvent... average volume fraction of HAP in the actual solvent loss? (a) This section describes the information and...

Electronic states density and solution volume of hydrogen solution in SiC alloys

International Nuclear Information System (INIS)

Gervasoni, J.L.; Furnari, J.C.

2012-01-01

The new reactor concepts are characterized by higher efficiency, better utilization of nuclear fuel and nuclear waste minimization. This approach means that this will be to enter a new and deep structural analysis of materials with a tensile strength significantly higher than those currently used radiation. To achieve high performance parameters, continuous research and testing of new materials will be needed. In this paper we concentrate on the analysis of SiC alloys, because due to their unique properties, this alloy can be used in high temperature conditions, where the silicon, semiconductor material of choice does not work (author)

New constructions of approximately SIC-POVMs via difference sets

Science.gov (United States)

Luo, Gaojun; Cao, Xiwang

2018-04-01

In quantum information theory, symmetric informationally complete positive operator-valued measures (SIC-POVMs) are related to quantum state tomography (Caves et al., 2004), quantum cryptography (Fuchs and Sasaki, 2003) [1], and foundational studies (Fuchs, 2002) [2]. However, constructing SIC-POVMs is notoriously hard. Although some SIC-POVMs have been constructed numerically, there does not exist an infinite class of them. In this paper, we propose two constructions of approximately SIC-POVMs, where a small deviation from uniformity of the inner products is allowed. We employ difference sets to present the first construction and the dimension of the approximately SIC-POVMs is q + 1, where q is a prime power. Notably, the dimension of this framework is new. The second construction is based on partial geometric difference sets and works whenever the dimension of the framework is a prime power.

SU-E-T-427: Cell Surviving Fractions Derived From Tumor-Volume Variation During Radiotherapy for Non-Small Cell Lung Cancer: Comparison with Predictive Assays

Energy Technology Data Exchange (ETDEWEB)

Chvetsov, A; Schwartz, J; Mayr, N [University of Washington, Seattle, WA (United States); Yartsev, S [London Health Sciences Centre, London, Ontario (Canada)

2014-06-01

Purpose: To show that a distribution of cell surviving fractions S{sub 2} in a heterogeneous group of patients can be derived from tumor-volume variation curves during radiotherapy for non-small cell lung cancer. Methods: Our analysis was based on two data sets of tumor-volume variation curves for heterogeneous groups of 17 patients treated for nonsmall cell lung cancer with conventional dose fractionation. The data sets were obtained previously at two independent institutions by using megavoltage (MV) computed tomography (CT). Statistical distributions of cell surviving fractions S{sup 2} and cell clearance half-lives of lethally damaged cells T1/2 have been reconstructed in each patient group by using a version of the two-level cell population tumor response model and a simulated annealing algorithm. The reconstructed statistical distributions of the cell surviving fractions have been compared to the distributions measured using predictive assays in vitro. Results: Non-small cell lung cancer presents certain difficulties for modeling surviving fractions using tumor-volume variation curves because of relatively large fractional hypoxic volume, low gradient of tumor-volume response, and possible uncertainties due to breathing motion. Despite these difficulties, cell surviving fractions S{sub 2} for non-small cell lung cancer derived from tumor-volume variation measured at different institutions have similar probability density functions (PDFs) with mean values of 0.30 and 0.43 and standard deviations of 0.13 and 0.18, respectively. The PDFs for cell surviving fractions S{sup 2} reconstructed from tumor volume variation agree with the PDF measured in vitro. Comparison of the reconstructed cell surviving fractions with patient survival data shows that the patient survival time decreases as the cell surviving fraction increases. Conclusion: The data obtained in this work suggests that the cell surviving fractions S{sub 2} can be reconstructed from the tumor volume

SU-E-T-427: Cell Surviving Fractions Derived From Tumor-Volume Variation During Radiotherapy for Non-Small Cell Lung Cancer: Comparison with Predictive Assays

International Nuclear Information System (INIS)

Chvetsov, A; Schwartz, J; Mayr, N; Yartsev, S

2014-01-01

Purpose: To show that a distribution of cell surviving fractions S 2 in a heterogeneous group of patients can be derived from tumor-volume variation curves during radiotherapy for non-small cell lung cancer. Methods: Our analysis was based on two data sets of tumor-volume variation curves for heterogeneous groups of 17 patients treated for nonsmall cell lung cancer with conventional dose fractionation. The data sets were obtained previously at two independent institutions by using megavoltage (MV) computed tomography (CT). Statistical distributions of cell surviving fractions S 2 and cell clearance half-lives of lethally damaged cells T1/2 have been reconstructed in each patient group by using a version of the two-level cell population tumor response model and a simulated annealing algorithm. The reconstructed statistical distributions of the cell surviving fractions have been compared to the distributions measured using predictive assays in vitro. Results: Non-small cell lung cancer presents certain difficulties for modeling surviving fractions using tumor-volume variation curves because of relatively large fractional hypoxic volume, low gradient of tumor-volume response, and possible uncertainties due to breathing motion. Despite these difficulties, cell surviving fractions S 2 for non-small cell lung cancer derived from tumor-volume variation measured at different institutions have similar probability density functions (PDFs) with mean values of 0.30 and 0.43 and standard deviations of 0.13 and 0.18, respectively. The PDFs for cell surviving fractions S 2 reconstructed from tumor volume variation agree with the PDF measured in vitro. Comparison of the reconstructed cell surviving fractions with patient survival data shows that the patient survival time decreases as the cell surviving fraction increases. Conclusion: The data obtained in this work suggests that the cell surviving fractions S 2 can be reconstructed from the tumor volume variation curves measured

Atomic force microscopy imaging to measure precipitate volume fraction in nickel-based superalloys

International Nuclear Information System (INIS)

Bourhettar, A.; Troyon, M.; Hazotte, A.

1995-01-01

In nickel-based superalloys, quantitative analysis of scanning electron microscopy images fails in providing accurate microstructural data, whereas more efficient techniques are very time-consuming. As an alternative approach, the authors propose to perform quantitative analysis of atomic force microscopy images of polished/etched surfaces (quantitative microprofilometry). This permits the measurement of microstructural parameters and the depth of etching, which is the main source of measurement bias. Thus, nonbiased estimations can be obtained by extrapolation of the measurements up to zero etching depth. In this article, the authors used this approach to estimate the volume fraction of γ' precipitates in a nickel-based superalloy single crystal. Atomic force microscopy images of samples etched for different times show definition, homogeneity, and contrast high enough to perform image analysis. The result after extrapolation is in very good agreement with volume fraction values available from published reports

Development of the fabrication process of SiC composite by polycarbosilane

International Nuclear Information System (INIS)

Park, Ji Yeon; Kim, Weon Ju; Kim, Jung Il; Ryu, Woo Seog

2004-11-01

This technical report reviewed the fabrication process of fiber reinforced ceramic composites, characteristics of the PIP process, and applications of SiC f /SiC composite to develop a silicon carbide composite by PIP method. Additionally, characteristics and thermal behaviors of a PCS+SiC powder slurry and infiltration behaviors of slurry into the SiC fabric was evaluated. The stacking behaviors of SiC fabrics infiltrated a PCS+SiC powder slurry was also investigated. Using this stacked preforms, SiC f /SiC composites were fabricated by the electron beam curing and pyrolysis process and the thermal oxidation curing and pyrolysis process, respectively. And the characteristics of both composites were compared

Near-surface and bulk behavior of Ag in SiC

International Nuclear Information System (INIS)

Xiao, H.Y.; Zhang, Y.; Snead, L.L.; Shutthanandan, V.; Xue, H.Z.; Weber, W.J.

2012-01-01

Highlights: ► Ag release from SiC poses problems in safe operation of nuclear reactors. ► Near-surface and bulk behavior of Ag are studied by ab initio and ion beam methods. ► Ag prefers to adsorb on the surface rather than in the bulk SiC. ► At high temperature Ag desorbs from the surface instead of diffusion into bulk SiC. ► Surface diffusion may be a dominating mechanism accounting for Ag release from SiC. - Abstract: The diffusive release of fission products, such as Ag, from TRISO particles at high temperatures has raised concerns regarding safe and economic operation of advanced nuclear reactors. Understanding the mechanisms of Ag diffusion is thus of crucial importance for effective retention of fission products. Two mechanisms, i.e., grain boundary diffusion and vapor or surface diffusion through macroscopic structures such as nano-pores or nano-cracks, remain in debate. In the present work, an integrated computational and experimental study of the near-surface and bulk behavior of Ag in silicon carbide (SiC) has been carried out. The ab initio calculations show that Ag prefers to adsorb on the SiC surface rather than in the bulk, and the mobility of Ag on the surface is high. The energy barrier for Ag desorption from the surface is calculated to be 0.85–1.68 eV, and Ag migration into bulk SiC through equilibrium diffusion process is not favorable. Experimentally, Ag ions are implanted into SiC to produce Ag profiles buried in the bulk and peaked at the surface. High-temperature annealing leads to Ag release from the surface region instead of diffusion into the interior of SiC. It is suggested that surface diffusion through mechanical structural imperfection, such as vapor transport through cracks in SiC coatings, may be a dominating mechanism accounting for Ag release from the SiC in the nuclear reactor.

A comparative study on the property determination of metal matrix composites using ultrasonic and eddy current techniques

International Nuclear Information System (INIS)

Jeong, Hyun Jo

1997-01-01

Ultrasonic and eddy current methods were developed for the quantitative determination of material properties in particulate reinforced metal matrix composites. The proposed techniques employed measurements of ultrasonic velocity and eddy current conductivity, together with theoretical models which relate the effective anisotropic properties of the composites to their microstructures. The approach was used for a wide range of SiC particulate reinforced Al matrix(SiC p /Al) composites to estimate the particulate volume fractions of the composites. The SiC p volume fraction was calculated by coupling the measured velocity and conductivity with their corresponding model predictions. Both methods were shown to be reliable in determining the reinforcement volume fractions. However, the ultrasonic method was found to be better than the eddy current method, since the electrical conductivity was sensitive to the presence of intermetallic compounds formed during processing stage.

Conversion of wood flour/SiO2/phenolic composite to porous SiC ceramic containing SiC whiskers

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Li Zhong

2013-01-01

Full Text Available A novel wood flour/SiO2/phenolic composite was chosen to be converted into porous SiC ceramic containing SiC whiskers via carbothermal reduction. At 1550°C the composite is converted into porous SiC ceramic with pore diameters of 10~40μm, and consisting of β-SiC located at the position of former wood cell walls. β-SiC wire-like whiskers of less than 50 nm in diameter and several tens to over 100 μm in length form within the pores. The surface of the resulting ceramic is coated with β-SiC necklace-like whiskers with diameters of 1~2μm.

Microwave joining of SiC ceramics and composites

Energy Technology Data Exchange (ETDEWEB)

Ahmad, I.; Silberglitt, R.; Tian, Y.L. [FM Technologies, Inc., Fairfax, VA (United States); Katz, J.D. [Los Alamos National Lab., NM (United States)

1997-04-01

Potential applications of SiC include components for advanced turbine engines, tube assemblies for radiant burners and petrochemical processing and heat exchangers for high efficiency electric power generation systems. Reliable methods for joining SiC are required in order to cost-effectively fabricate components for these applications from commercially available shapes and sizes. This manuscript reports the results of microwave joining experiments performed using two different types of SiC materials. The first were on reaction bonded SiC, and produced joints with fracture toughness equal to or greater than that of the base material over an extended range of joining temperatures. The second were on continuous fiber-reinforced SiC/SiC composite materials, which were successfully joined with a commercial active brazing alloy, as well as by using a polymer precursor.

Volume fractions of DCE-MRI parameter as early predictor of histologic response in soft tissue sarcoma: A feasibility study.

Science.gov (United States)

Xia, Wei; Yan, Zhuangzhi; Gao, Xin

2017-10-01

To find early predictors of histologic response in soft tissue sarcoma through volume transfer constant (K trans ) analysis based on dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI). 11 Patients with soft tissue sarcoma of the lower extremity that underwent preoperative chemoradiotherapy followed by limb salvage surgery were included in this retrospective study. For each patient, DCE-MRI data sets were collected before and two weeks after therapy initiation, and histologic tumor cell necrosis rate (TCNR) was reported at surgery. The DCE-MRI volumes were aligned by registration. Then, the aligned volumes were used to obtain the K trans variation map. Accordingly, three sub-volumes (with increased, decreased or unchanged K trans ) were defined and identified, and fractions of the sub-volumes, denoted as F + , F - and F 0 , respectively, were calculated. The predictive ability of volume fractions was determined by using area under a receiver operating characteristic curve (AUC). Linear regression analysis was performed to investigate the relationship between TCNR and volume fractions. In addition, the K trans values of the sub-volumes were compared. The AUC for F - (0.896) and F 0 (0.833) were larger than that for change of tumor longest diameter ΔD (0.625) and the change of mean K trans ΔK trans ¯ (0.792). Moreover, the regression results indicated that TCNR was directly proportional to F 0 (R 2 =0.75, P=0.0003), while it was inversely proportional to F - (R 2 =0.77, P=0.0002). However, TCNR had relatively weak linear relationship with ΔK trans ¯ (R 2 =0.64, P=0.0018). Additionally, TCNR did not have linear relationship with DD (R 2 =0.16, P=0.1246). The volume fraction F - and F 0 have potential as early predictors of soft tissue sarcoma histologic response. Copyright © 2017 Elsevier B.V. All rights reserved.

Introduction of nano-laminate Ti3SiC2 and SiC phases into Cf-C composite by liquid silicon infiltration method

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Omid Yaghobizadeh

2017-03-01

Full Text Available The material Cf-C-SiC-Ti3SiC2 is promising for high temperature application. Due to the laminated structure and special properties, the Ti3SiC2 is one of the best reinforcements for Cf-C-SiC composites. In this paper, Cf-C-SiC-Ti3SiC2 composites were fabricated by liquid silicon infiltration (LSI method; the effect of the TiC amount on the various composites properties were studied. For samples with 0, 50 and 90 vol.% of TiC, the results show that bending strength are 168, 190, and 181 MPa; porosities are 3.2, 4.7, and 9%; the fracture toughness are 6.1, 8.9, and 7.8 MPa∙m1/2; interlaminar shear strength are 27, 36, and 30 MPa; the amount of the MAX phase are 0, 8.5, and 5.6 vol.%, respectively. These results show that amount of TiC is not the main effective parameter in synthesis of Ti3SiC2. The existence of carbon promotes the synthesis of Ti3SiC2 indicating that only sufficient carbon content can lead to the appearance of Ti3SiC2 in the LSI process.

Homoepitaxial VPE growth of SiC active layers

Energy Technology Data Exchange (ETDEWEB)

Burk, A.A. Jr. [Northrop Grumman Electron. Sensors and Syst. Div., Baltimore, MD (United States); Rowland, L.B. [Northrop Grumman Sci. and Technol. Center, Pittsburgh, PA (United States)

1997-07-01

SiC active layers of tailored thickness and doping form the heart of all SiC electronic devices. These layers are most conveniently formed by vapor phase epitaxy (VPE). Exacting requirements are placed upon the SiC-VPE layers` material properties by both semiconductor device physics and available methods of device processing. In this paper, the current ability of the SiC-VPE process to meet these requirements is described along with continuing improvements in SiC epitaxial reactors, processes and materials. (orig.) 48 refs.

Interfacial effect on physical properties of composite media: Interfacial volume fraction with non-spherical hard-core-soft-shell-structured particles.

Science.gov (United States)

Xu, Wenxiang; Duan, Qinglin; Ma, Huaifa; Chen, Wen; Chen, Huisu

2015-11-02

Interfaces are known to be crucial in a variety of fields and the interfacial volume fraction dramatically affects physical properties of composite media. However, it is an open problem with great significance how to determine the interfacial property in composite media with inclusions of complex geometry. By the stereological theory and the nearest-surface distribution functions, we first propose a theoretical framework to symmetrically present the interfacial volume fraction. In order to verify the interesting generalization, we simulate three-phase composite media by employing hard-core-soft-shell structures composed of hard mono-/polydisperse non-spherical particles, soft interfaces, and matrix. We numerically derive the interfacial volume fraction by a Monte Carlo integration scheme. With the theoretical and numerical results, we find that the interfacial volume fraction is strongly dependent on the so-called geometric size factor and sphericity characterizing the geometric shape in spite of anisotropic particle types. As a significant interfacial property, the present theoretical contribution can be further drawn into predicting the effective transport properties of composite materials.

Rare earth element abundances in presolar SiC

Science.gov (United States)

Ireland, T. R.; Ávila, J. N.; Lugaro, M.; Cristallo, S.; Holden, P.; Lanc, P.; Nittler, L.; Alexander, C. M. O'D.; Gyngard, F.; Amari, S.

2018-01-01

Individual isotope abundances of Ba, lanthanides of the rare earth element (REE) group, and Hf have been determined in bulk samples of fine-grained silicon carbide (SiC) from the Murchison CM2 chondrite. The analytical protocol involved secondary ion mass spectrometry with combined high mass resolution and energy filtering to exclude REE oxide isobars and Si-C-O clusters from the peaks of interest. Relative sensitivity factors were determined through analysis of NIST SRM reference glasses (610 and 612) as well as a trace-element enriched SiC ceramic. When normalised to chondrite abundances, the presolar SiC REE pattern shows significant deficits at Eu and Yb, which are the most volatile of the REE. The pattern is very similar to that observed for Group III refractory inclusions. The SiC abundances were also normalised to s-process model predictions for the envelope compositions of low-mass (1.5-3 M⊙) AGB stars with close-to-solar metallicities (Z = 0.014 and 0.02). The overall trace element abundances (excluding Eu and Yb) appear consistent with the predicted s-process patterns. The depletions of Eu and Yb suggest that these elements remained in the gas phase during the condensation of SiC. The lack of depletion in some other moderately refractory elements (like Ba), and the presence of volatile elements (e.g. Xe) indicates that these elements were incorporated into SiC by other mechanisms, most likely ion implantation.

Prediction of gas volume fraction in fully-developed gas-liquid flow in a vertical pipe

International Nuclear Information System (INIS)

Islam, A.S.M.A.; Adoo, N.A.; Bergstrom, D.J.; Wang, D.F.

2015-01-01

An Eulerian-Eulerian two-fluid model has been implemented for the prediction of the gas volume fraction profile in turbulent upward gas-liquid flow in a vertical pipe. The two-fluid transport equations are discretized using the finite volume method and a low Reynolds number κ-ε turbulence model is used to predict the turbulence field for the liquid phase. The contribution to the effective turbulence by the gas phase is modeled by a bubble induced turbulent viscosity. For the fully-developed flow being considered, the gas volume fraction profile is calculated using the radial momentum balance for the bubble phase. The model potentially includes the effect of bubble size on the interphase forces and turbulence model. The results obtained are in good agreement with experimental data from the literature. The one-dimensional formulation being developed allows for the efficient assessment and further development of both turbulence and two-fluid models for multiphase flow applications in the nuclear industry. (author)

Prediction of gas volume fraction in fully-developed gas-liquid flow in a vertical pipe

Energy Technology Data Exchange (ETDEWEB)

Islam, A.S.M.A.; Adoo, N.A.; Bergstrom, D.J., E-mail: nana.adoo@usask.ca [University of Saskatchewan, Department of Mechanical Engineering, Saskatoon, SK (Canada); Wang, D.F. [Canadian Nuclear Laboratories, Chalk River, ON (Canada)

2015-07-01

An Eulerian-Eulerian two-fluid model has been implemented for the prediction of the gas volume fraction profile in turbulent upward gas-liquid flow in a vertical pipe. The two-fluid transport equations are discretized using the finite volume method and a low Reynolds number κ-ε turbulence model is used to predict the turbulence field for the liquid phase. The contribution to the effective turbulence by the gas phase is modeled by a bubble induced turbulent viscosity. For the fully-developed flow being considered, the gas volume fraction profile is calculated using the radial momentum balance for the bubble phase. The model potentially includes the effect of bubble size on the interphase forces and turbulence model. The results obtained are in good agreement with experimental data from the literature. The one-dimensional formulation being developed allows for the efficient assessment and further development of both turbulence and two-fluid models for multiphase flow applications in the nuclear industry. (author)

SiC Conversion Coating Prepared from Silica-Graphite Reaction

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Back-Sub Sung

2017-01-01

Full Text Available The β-SiC conversion coatings were successfully synthesized by the SiO(v-graphite(s reaction between silica powder and graphite specimen. This paper is to describe the effects on the characteristics of the SiC conversion coatings, fabricated according to two different reaction conditions. FE-SEM, FE-TEM microstructural morphologies, XRD patterns, pore size distribution, and oxidation behavior of the SiC-coated graphite were investigated. In the XRD pattern and SAD pattern, the coating layers showed cubic SiC peak as well as hexagonal SiC peak. The SiC coatings showed somewhat different characteristics with the reaction conditions according to the position arrangement of the graphite samples. The SiC coating on graphite, prepared in reaction zone (2, shows higher intensity of beta-SiC main peak (111 in XRD pattern as well as rather lower porosity and smaller main pore size peak under 1 μm.

About SIC POVMs and discrete Wigner distributions

International Nuclear Information System (INIS)

Colin, Samuel; Corbett, John; Durt, Thomas; Gross, David

2005-01-01

A set of d 2 vectors in a Hilbert space of dimension d is called equiangular if each pair of vectors encloses the same angle. The projection operators onto these vectors define a POVM which is distinguished by its high degree of symmetry. Measures of this kind are called symmetric informationally complete, or SIC POVMs for short, and could be applied for quantum state tomography. Despite its simple geometrical description, the problem of constructing SIC POVMs or even proving their existence seems to be very hard. It is our purpose to introduce two applications of discrete Wigner functions to the analysis of the problem at hand. First, we will present a method for identifying symmetries of SIC POVMs under Clifford operations. This constitutes an alternative approach to a structure described before by Zauner and Appleby. Further, a simple and geometrically motivated construction for an SIC POVM in dimensions two and three is given (which, unfortunately, allows no generalization). Even though no new structures are found, we hope that the re-formulation of the problem may prove useful for future inquiries

Fabrication of mullite-bonded porous SiC ceramics from multilayer-coated SiC particles through sol-gel and in-situ polymerization techniques

Science.gov (United States)

Ebrahimpour, Omid

In this work, mullite-bonded porous silicon carbide (SiC) ceramics were prepared via a reaction bonding technique with the assistance of a sol-gel technique or in-situ polymerization as well as a combination of these techniques. In a typical procedure, SiC particles were first coated by alumina using calcined powder and alumina sol via a sol-gel technique followed by drying and passing through a screen. Subsequently, they were coated with the desired amount of polyethylene via an in-situ polymerization technique in a slurry phase reactor using a Ziegler-Natta catalyst. Afterward, the coated powders were dried again and passed through a screen before being pressed into a rectangular mold to make a green body. During the heating process, the polyethylene was burnt out to form pores at a temperature of about 500°C. Increasing the temperature above 800°C led to the partial oxidation of SiC particles to silica. At higher temperatures (above 1400°C) derived silica reacted with alumina to form mullite, which bonds SiC particles together. The porous SiC specimens were characterized with various techniques. The first part of the project was devoted to investigating the oxidation of SiC particles using a Thermogravimetric analysis (TGA) apparatus. The effects of particle size (micro and nano) and oxidation temperature (910°C--1010°C) as well as the initial mass of SiC particles in TGA on the oxidation behaviour of SiC powders were evaluated. To illustrate the oxidation rate of SiC in the packed bed state, a new kinetic model, which takes into account all of the diffusion steps (bulk, inter and intra particle diffusion) and surface oxidation rate, was proposed. Furthermore, the oxidation of SiC particles was analyzed by the X-ray Diffraction (XRD) technique. The effect of different alumina sources (calcined Al2O 3, alumina sol or a combination of the two) on the mechanical, physical, and crystalline structure of mullite-bonded porous SiC ceramics was studied in the

Research Progress of Optical Fabrication and Surface-Microstructure Modification of SiC

Directory of Open Access Journals (Sweden)

Fang Jiang

2012-01-01

Full Text Available SiC has become the best candidate material for space mirror and optical devices due to a series of favorable physical and chemical properties. Fine surface optical quality with the surface roughness (RMS less than 1 nm is necessary for fine optical application. However, various defects are present in SiC ceramics, and it is very difficult to polish SiC ceramic matrix with the 1 nm RMS. Surface modification of SiC ceramics must be done on the SiC substrate. Four kinds of surface-modification routes including the hot pressed glass, the C/SiC clapping, SiC clapping, and Si clapping on SiC surface have been reported and reviewed here. The methods of surface modification, the mechanism of preparation, and the disadvantages and advantages are focused on in this paper. In our view, PVD Si is the best choice for surface modification of SiC mirror.

New Possibilities of Power Electronic Structures Using SiC Technology

Directory of Open Access Journals (Sweden)

Robert Sul

2006-01-01

Full Text Available This paper is dedicated to the recent unprecedented boom of SiC electronic technology. The contribution deals with brief survey of those properties. In particular, the differences (both good and bad between SiC electronics technology and well-known silicon VLSI technology are highlighted. Projected performance benefits of SiC electronics are given for several large-scale applications on the end of the contribution. The basic properties of SiC material have been discussed already on the beginning of 80’s, also at our university.

SiC nanoparticles as potential carriers for biologically active substances

Science.gov (United States)

Guevara-Lora, Ibeth; Czosnek, Cezary; Smycz, Aleksandra; Janik, Jerzy F.; Kozik, Andrzej

2009-01-01

Silicon carbide SiC thanks to its many advantageous properties has found numerous applications in diverse areas of technology. In this regard, its nanosized forms often with novel properties have been the subject of intense research in recent years. The aim of this study was to investigate the binding of biologically active substances onto SiC nanopowders as a new approach to biomolecule immobilization in terms of their prospective applications in medicine or for biochemical detection. The SiC nanoparticles were prepared by a two-stage aerosol-assisted synthesis from neat hexamethyldisiloxane. The binding of several proteins (bovine serum albumin, high molecular weight kininogen, immunoglobulin G) on SiC particle surfaces was demonstrated at the levels of 1-2 nanograms per mg of SiC. These values were found to significantly increase after suitable chemical modifications of nanoparticle surfaces (by carbodiimide or 3-aminopropyltrietoxysilane treatment). The study of SiC biocompatibility showed a lack of cytotoxicity against macrophages-like cells below the concentration of 1 mg nanoparticles per mL. In summary, we demonstrated the successful immobilization of the selected substances on the SiC nanoparticles. These results including the cytotoxicity study make nano-SiC highly attractive for potential applications in medicine, biotechnology or molecular detection.

Influence of microstructure on hydrothermal corrosion of chemically vapor processed SiC composite tubes

Science.gov (United States)

Kim, Daejong; Lee, Ho Jung; Jang, Changheui; Lee, Hyeon-Geun; Park, Ji Yeon; Kim, Weon-Ju

2017-08-01

Multi-layered SiC composites consisting of monolithic SiC and a SiCf/SiC composite are one of the accident tolerant fuel cladding concepts in pressurized light water reactors. To evaluate the integrity of the SiC fuel cladding under normal operating conditions of a pressurized light water reactor, the hydrothermal corrosion behavior of multi-layered SiC composite tubes was investigated in the simulated primary water environment of a pressurized water reactor without neutron fluence. The results showed that SiC phases with good crystallinity such as Tyranno SA3 SiC fiber and monolithic SiC deposited at 1200 °C had good corrosion resistance. However, the SiC phase deposited at 1000 °C had less crystallinity and severely dissolved in water, particularly the amorphous SiC phase formed along grain boundaries. Dissolved hydrogen did not play a significant role in improving the hydrothermal corrosion resistance of the CVI-processed SiC phases containing amorphous SiC, resulting in a significant weight loss and reduction of hoop strength of the multi-layered SiC composite tubes after corrosion.

Measurement of Soot Volume Fraction and Temperature for Oxygen-Enriched Ethylene Combustion Based on Flame Image Processing

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Weijie Yan

2017-05-01

Full Text Available A method for simultaneously visualizing the two-dimensional distributions of temperature and soot volume fraction in an ethylene flame was presented. A single-color charge-coupled device (CCD camera was used to capture the flame image in the visible spectrum considering the broad-response spectrum of the R and G bands of the camera. The directional emissive power of the R and G bands were calibrated and used for measurement. Slightly increased temperatures and reduced soot concentration were predicted in the central flame without self-absorption effects considered, an iterative algorithm was used for eliminating the effect of self-absorption. Nine different cases were presented in the experiment to demonstrate the effects of fuel mass flow rate and oxygen concentration on temperature and soot concentration in three different atmospheres. For ethylene combustion in pure-air atmosphere, as the fuel mass flow rate increased, the maximum temperature slightly decreased, and the maximum soot volume fraction slightly increased. For oxygen fractions of 30%, 40%, and 50% combustion in O2/N2 oxygen-enhanced atmospheres, the maximum flame temperatures were 2276, 2451, and 2678 K, whereas combustion in O2/CO2 atmospheres were 1916, 2322, and 2535 K. The maximum soot volume fractions were 4.5, 7.0, and 9.5 ppm in oxygen-enriched O2/N2 atmosphere and 13.6, 15.3, and 14.8 ppm in oxygen-enriched O2/CO2 atmosphere. Compared with the O2/CO2 atmosphere, combustion in the oxygen-enriched O2/N2 atmosphere produced higher flame temperature and larger soot volume fraction. Preliminary results indicated that this technique is reliable and can be used for combustion diagnosis.

Effects of local single and fractionated X-ray doses on rat bone marrow blood flow and red blood cell volume

International Nuclear Information System (INIS)

Pitkaenen, M.A.; Hopewell, J.W.

1985-01-01

Time and dose dependent changes in blood flow and red blood cell volume were studied in the locally irradiated bone marrow of the rat femur after single and fractionated doses of X-rays. With the single dose of 10 Gy the bone marrow blood flow although initially reduced returned to the control levels by seven months after irradiation. With doses >=15 Gy the blood flow was still significantly reduced at seven months. The total dose levels predicted by the nominal standard dose equation for treatments in three, six or nine fractions produced approximately the same degree of reduction in the bone marrow blood flow seven months after the irradiation. However, the fall in the red blood cell volume was from 23 to 37% greater in the three fractions groups compared with that in the nine fractions groups. Using the red blood cell volume as a parameter the nominal standard dose formula underestimated the severity of radiation damage in rat bone marrow at seven months for irradiation with small numbers of large dose fractions. (orig.) [de

Challenges in Switching SiC MOSFET without Ringing

DEFF Research Database (Denmark)

Li, Helong; Munk-Nielsen, Stig

2014-01-01

Switching SiC MOSFET without ringing in high frequency applications is important for meeting the EMI (ElectroMagnetic Interference) standard. Achieving a clean switching waveform of SiC MOSFET without additional components is becoming a challenge. In this paper, the switching oscillation mechanis...

MAX Phase Modified SiC Composites for Ceramic-Metal Hybrid Cladding Tubes

International Nuclear Information System (INIS)

Jung, Yang-Il; Kim, Sun-Han; Park, Dong-Jun; Park, Jeong-Hwan; Park, Jeong-Yong; Kim, Hyun-Gil; Koo, Yang-Hyun

2015-01-01

A metal-ceramic hybrid cladding consists of an inner zirconium tube, and an outer SiC fiber-matrix SiC ceramic composite with surface coating as shown in Fig. 1 (left-hand side). The inner zirconium allows the matrix to remain fully sealed even if the ceramic matrix cracks through. The outer SiC composite can increase the safety margin by taking the merits of the SiC itself. In addition, the outermost layer prevents the dissolution of SiC during normal operation. On the other hand, a ceramic-metal hybrid cladding consists of an outer zirconium tube, and an inner SiC ceramic composite as shown in Fig. 1 (right-hand side). The outer zirconium protects the fuel rod from a corrosion during reactor operation, as in the present fuel claddings. The inner SiC composite, additionally, is designed to resist the severe oxidation under a postulated accident condition of a high-temperature steam environment. Reaction-bonded SiC was fabricated by modifying the matrix as the MAX phase. The formation of Ti 3 SiC 2 was investigated depending on the compositions of the preform and melt. In most cases, TiSi 2 was the preferential phase because of its lowest melting point in the Ti-Si-C system. The evidence of Ti 3 SiC 2 was the connection with the pressurizing

Packaging Technologies for 500C SiC Electronics and Sensors

Science.gov (United States)

Chen, Liang-Yu

2013-01-01

Various SiC electronics and sensors are currently under development for applications in 500C high temperature environments such as hot sections of aerospace engines and the surface of Venus. In order to conduct long-term test and eventually commercialize these SiC devices, compatible packaging technologies for the SiC electronics and sensors are required. This presentation reviews packaging technologies developed for 500C SiC electronics and sensors to address both component and subsystem level packaging needs for high temperature environments. The packaging system for high temperature SiC electronics includes ceramic chip-level packages, ceramic printed circuit boards (PCBs), and edge-connectors. High temperature durable die-attach and precious metal wire-bonding are used in the chip-level packaging process. A high temperature sensor package is specifically designed to address high temperature micro-fabricated capacitive pressure sensors for high differential pressure environments. This presentation describes development of these electronics and sensor packaging technologies, including some testing results of SiC electronics and capacitive pressure sensors using these packaging technologies.

SiC for microwave power transistors

Energy Technology Data Exchange (ETDEWEB)

Sriram, S.; Siergiej, R.R.; Clarke, R.C.; Agarwal, A.K.; Brandt, C.D. [Northrop Grumman Sci. and Technol. Center, Pittsburgh, PA (United States)

1997-07-16

The advantages of SiC for high power, microwave devices are discussed. The design considerations, fabrication, and experimental results are described for SiC MESFETs and SITs. The highest reported f{sub max} for a 0.5 {mu}m MESFET using semi-insulating 4H-SiC is 42 GHz. These devices also showed a small signal gain of 5.1 dB at 20 GHz. Other 4H-SiC MESFETs have shown a power density of 3.3 W/mm at 850 MHz. The largest SiC power transistor reported is a 450 W SIT measured at 600 MHz. The power output density of this SIT is 2.5 times higher than that of comparable silicon devices. SITs have been designed to operate as high as 3.0 GHz, with a 3 cm periphery part delivering 38 W of output power. (orig.) 28 refs.

Formation mechanism of SiC in C-Si system by ion irradiation

International Nuclear Information System (INIS)

Hishita, Shunichi; Aizawa, Takashi; Suehara, Shigeru; Haneda, Hajime

2003-01-01

The irradiation effects of 2 MeV He + , Ne + , and Ar + ions on the film structure of the C-Si system were investigated with RHEED and XPS. The ion dose dependence of the SiC formation was kinetically analyzed. The SiC formation at moderate temperature was achieved by 2 MeV ion irradiation when the thickness of the initial carbon films was appropriate. The evolution process of the SiC film thickness consisted of the 3 stages. The first stage was the steep increase of the SiC, and was governed by the inelastic collision. The second was the gentle increase of the SiC, and was governed by the diffusion. The last was the decrease of the SiC, and was caused by the sputtering. The formation mechanism of the SiC was discussed. (author)

Residual stress and mechanical properties of SiC ceramic by heat treatment

International Nuclear Information System (INIS)

Yoon, H.K.; Kim, D.H.; Shin, B.C.

2007-01-01

Full text of publication follows: Silicon carbide is a compound of relatively low density, high hardness, elevated thermal stability and good thermal conductivity, resulting in good thermal shock resistance. Because of these properties, SiC materials are widely used as abrasives and refractories. In this study, SiC single and poly crystals was grown by the sublimation method using the SiC seed crystal and SiC powder as the source material. Mechanical properties of SiC single and poly crystals are carried out by using the nano-indentation method and small punch test after the heat treatment. As a result, mechanical properties of SiC poly crystal had over double than single. And SiC single and poly crystals were occurred residual stress, but residual stress was shown relaxant properties by the effect of heat treatment. (authors)

Efficacy and safety of 10,600-nm carbon dioxide fractional laser on facial skin with previous volume injections

Directory of Open Access Journals (Sweden)

Josiane Hélou

2013-01-01

Full Text Available Background: Fractionated carbon dioxide (CO 2 lasers are a new treatment modality for skin resurfacing. The cosmetic rejuvenation market abounds with various injectable devices (poly-L-lactic acid, polymethyl-methacrylate, collagens, hyaluronic acids, silicone. The objective of this study is to examine the efficacy and safety of 10,600-nm CO 2 fractional laser on facial skin with previous volume injections. Materials and Methods: This is a retrospective study including 14 patients treated with fractional CO 2 laser and who have had previous facial volume restoration. The indication for the laser therapy, the age of the patients, previous facial volume restoration, and side effects were all recorded from their medical files. Objective assessments were made through clinical physician global assessment records and improvement scores records. Patients′ satisfaction rates were also recorded. Results: Review of medical records of the 14 patients show that five patients had polylactic acid injection prior to the laser session. Eight patients had hyaluronic acid injection prior to the laser session. Two patients had fat injection, two had silicone injection and one patient had facial thread lift. Side effects included pain during the laser treatment, post-treatment scaling, post-treatment erythema, hyperpigmentation which spontaneously resolved within a month. Concerning the previous facial volume restoration, no granulomatous reactions were noted, no facial shape deformation and no asymmetry were encountered whatever the facial volume product was. Conclusion: CO 2 fractional laser treatments do not seem to affect facial skin which had previous facial volume restoration with polylactic acid for more than 6 years, hyaluronic acid for more than 0.5 year, silicone for more than 6 years, or fat for more than 1.4 year. Prospective larger studies focusing on many other variables (skin phototype, injected device type are required to achieve better

Irradiation damages in Ti3SiC2

International Nuclear Information System (INIS)

Nappe, J.C.; Grosseau, Ph.; Guilhot, B.; Audubert, F.; Beauvy, M.

2007-01-01

Carbides, by their remarkable properties, are considered as possible materials (fuel cans) in reactor of generation IV. Among those studied, Ti 3 SiC 2 is particularly considered because it joins both the ceramics and metals properties. Nevertheless, its behaviour under irradiation is not known. Characterizations have been carried out on samples irradiated at 75 MeV krypton ions. They have revealed that TiO 2 (formed at the surface of Ti 3 SiC 2 ) is pulverized by the irradiation and that the crystal lattice of Ti 3 SiC 2 dilates with c. (O.M.)

A framework to measure myocardial extracellular volume fraction using dual-phase low dose CT images

International Nuclear Information System (INIS)

Liu, Yixun; Summers, Ronald M.; Yao, Jianhua; Liu, Songtao; Sibley, Christopher T.; Bluemke, David A.; Nacif, Marcelo S.

2013-01-01

Purpose: Myocardial extracellular volume fraction (ECVF) is a surrogate imaging biomarker of diffuse myocardial fibrosis, a hallmark of pathologic ventricular remodeling. Low dose cardiac CT is emerging as a promising modality to detect diffuse interstitial myocardial fibrosis due to its fast acquisition and low radiation; however, the insufficient contrast in the low dose CT images poses great challenge to measure ECVF from the image. Methods: To deal with this difficulty, the authors present a complete ECVF measurement framework including a point-guided myocardial modeling, a deformable model-based myocardium segmentation, nonrigid registration of pre- and post-CT, and ECVF calculation. Results: The proposed method was evaluated on 20 patients by two observers. Compared to the manually delineated reference segmentations, the accuracy of our segmentation in terms of true positive volume fraction (TPVF), false positive volume fraction (FPVF), and average surface distance (ASD), were 92.18% ± 3.52%, 0.31% ± 0.10%, 0.69 ± 0.14 mm, respectively. The interobserver variability measured by concordance correlation coefficient regarding TPVF, FPVF, and ASD were 0.95, 0.90, 0.94, respectively, demonstrating excellent agreement. Bland-Altman method showed 95% limits of agreement between ECVF at CT and ECVF at MR. Conclusions: The proposed framework demonstrates its efficiency, accuracy, and noninvasiveness in ECVF measurement and dramatically advances the ECVF at cardiac CT toward its clinical use

A framework to measure myocardial extracellular volume fraction using dual-phase low dose CT images

Energy Technology Data Exchange (ETDEWEB)

Liu, Yixun; Summers, Ronald M.; Yao, Jianhua, E-mail: JYao@cc.nih.gov [Clinical Image Processing Service, Radiology and Imaging Sciences, NIH Clinical Center, Bethesda, Maryland 20892 (United States); Liu, Songtao; Sibley, Christopher T.; Bluemke, David A. [Radiology and Imaging Sciences, NIH Clinical Center, Bethesda, Maryland 20892-1182 and Molecular Biomedical Imaging Laboratory, National Institute of Biomedical Imaging and Bioengineering, NIH Clinical Center, Bethesda, Maryland 20892 (United States); Nacif, Marcelo S. [Radiology and Imaging Sciences, NIH Clinical Center, Bethesda, Maryland 20892-1182 (United States)

2013-10-15

Purpose: Myocardial extracellular volume fraction (ECVF) is a surrogate imaging biomarker of diffuse myocardial fibrosis, a hallmark of pathologic ventricular remodeling. Low dose cardiac CT is emerging as a promising modality to detect diffuse interstitial myocardial fibrosis due to its fast acquisition and low radiation; however, the insufficient contrast in the low dose CT images poses great challenge to measure ECVF from the image. Methods: To deal with this difficulty, the authors present a complete ECVF measurement framework including a point-guided myocardial modeling, a deformable model-based myocardium segmentation, nonrigid registration of pre- and post-CT, and ECVF calculation. Results: The proposed method was evaluated on 20 patients by two observers. Compared to the manually delineated reference segmentations, the accuracy of our segmentation in terms of true positive volume fraction (TPVF), false positive volume fraction (FPVF), and average surface distance (ASD), were 92.18% ± 3.52%, 0.31% ± 0.10%, 0.69 ± 0.14 mm, respectively. The interobserver variability measured by concordance correlation coefficient regarding TPVF, FPVF, and ASD were 0.95, 0.90, 0.94, respectively, demonstrating excellent agreement. Bland-Altman method showed 95% limits of agreement between ECVF at CT and ECVF at MR. Conclusions: The proposed framework demonstrates its efficiency, accuracy, and noninvasiveness in ECVF measurement and dramatically advances the ECVF at cardiac CT toward its clinical use.

ECG-gated blood pool tomography in the determination of left ventricular volume, ejection fraction, and wall motion

International Nuclear Information System (INIS)

Underwood, S.R.; Ell, P.J.; Jarritt, P.H.; Emanuel, R.W.; Swanton, R.H.

1984-01-01

ECG-gated blood pool tomography promises to provide a ''gold standard'' for noninvasive measurement of left ventricular volume, ejection fraction, and wall motion. This study compares these measurements with those from planar radionuclide imaging and contrast ventriculography. End diastolic and end systolic blood pool images were acquired tomographically using an IGE400A rotating gamma camera and Star computer, and slices were reconstructed orthogonal to the long axis of the heart. Left ventricular volume was determined by summing the areas of the slices, and wall motion was determined by comparison of end diastolic and end systolic contours. In phantom experiments this provided an accurate measurement of volume (r=0.98). In 32 subjects who were either normal or who had coronary artery disease left ventricular volume (r=0.83) and ejection fraction (r=0.89) correlated well with those using a counts based planar technique. In 16 of 18 subjects who underwent right anterior oblique X-ray contrast ventriculography, tomographic wall motion agreed for anterior, apical, and inferior walls, but abnormal septal motion which was not apparent by contrast ventriculography, was seen in 12 subjects tomographically. All 12 had disease of the left anterior descending coronary artery and might have been expected to have abnormal septal motion. ECG-gated blood pool tomography can thus determine left ventricular volume and ejection fraction accurately, and provides a global description of wall motion in a way that is not possible from any single planar image

TRISO coated fuel particles with enhanced SiC properties

International Nuclear Information System (INIS)

Lopez-Honorato, E.; Tan, J.; Meadows, P.J.; Marsh, G.; Xiao, P.

2009-01-01

The silicon carbide (SiC) layer used for the formation of TRISO coated fuel particles is normally produced at 1500-1650 deg. C via fluidized bed chemical vapor deposition from methyltrichlorosilane in a hydrogen environment. In this work, we show the deposition of SiC coatings with uniform grain size throughout the coating thickness, as opposed to standard coatings which have larger grain sizes in the outer sections of the coating. Furthermore, the use of argon as the fluidizing gas and propylene as a carbon precursor, in addition to hydrogen and methyltrichlorosilane, allowed the deposition of stoichiometric SiC coatings with refined microstructure at 1400 and 1300 deg. C. The deposition of SiC at lower deposition temperatures was also advantageous since the reduced heat treatment was not detrimental to the properties of the inner pyrolytic carbon which generally occurs when SiC is deposited at 1500 deg. C. The use of a chemical vapor deposition coater with four spouts allowed the deposition of uniform and spherical coatings.

Evaluation of gamma prime volume fractions and lattice misfits in a nickel base superalloy using the external standard X-ray diffraction method

Energy Technology Data Exchange (ETDEWEB)

Tiley, J., E-mail: jaimie.tiley@wpafb.af.mil [Air Force Research Laboratory, Materials and Manufacturing Directorate, WPAFB, OH (United States); Viswanathan, G.B. [Air Force Research Laboratory, Materials and Manufacturing Directorate, WPAFB, OH (United States); Hwang, J.Y. [Materials Engineering Department, University of North Texas, Denton, TX (United States); Shiveley, A. [Air Force Research Laboratory, Materials and Manufacturing Directorate, WPAFB, OH (United States); Banerjee, R. [Materials Engineering Department, University of North Texas, Denton, TX (United States)

2010-11-25

The unconstrained lattice parameters and volume fractions of {gamma}' for a low misfit nickel based superalloy were evaluated using X-ray diffraction techniques. Extraction techniques were used to provide unconstrained {gamma}' powders for both water quenched and slow cooled samples that were aged at 760 deg. C for 0, 25, 50, 100, and 200 h. The external standard method was used to determine the volume fraction for the unaged water quenched sample and the slow cooled sample aged for 200 h. These two extremes in processing conditions provided an increase in the total volume fraction of {gamma}'.

Detail study of SiC MOSFET switching characteristics

DEFF Research Database (Denmark)

Li, Helong; Munk-Nielsen, Stig

2014-01-01

This paper makes detail study of the latest SiC MOSFETs switching characteristics in relation to gate driver maximum current, gate resistance, common source inductance and parasitic switching loop inductance. The switching performance of SiC MOSFETs in terms of turn on and turn off voltage...

Use of fractional dose–volume histograms to model risk of acute rectal toxicity among patients treated on RTOG 94-06

International Nuclear Information System (INIS)

Tucker, Susan L.; Michalski, Jeff M.; Bosch, Walter R.; Mohan, Radhe; Dong, Lei; Winter, Kathryn; Purdy, James A.; Cox, James D.

2012-01-01

Background and purpose: For toxicities occurring during the course of radiotherapy, it is conceptually inaccurate to perform normal-tissue complication probability analyses using the complete dose–volume histogram. The goal of this study was to analyze acute rectal toxicity using a novel approach in which the fit of the Lyman–Kutcher–Burman (LKB) model is based on the fractional rectal dose–volume histogram (DVH). Materials and methods: Grade ⩾2 acute rectal toxicity was analyzed in 509 patients treated on Radiation Therapy Oncology Group (RTOG) protocol 94-06. These patients had no field reductions or treatment-plan revisions during therapy, allowing the fractional rectal DVH to be estimated from the complete rectal DVH based on the total number of dose fractions delivered. Results: The majority of patients experiencing Grade ⩾2 acute rectal toxicity did so before completion of radiotherapy (70/80 = 88%). Acute rectal toxicity depends on fractional mean rectal dose, with no significant improvement in the LKB model fit when the volume parameter differs from n = 1. The incidence of toxicity was significantly lower for patients who received hormone therapy (P = 0.024). Conclusions: Variations in fractional mean dose explain the differences in incidence of acute rectal toxicity, with no detectable effect seen here for differences in numbers of dose fractions delivered.

Advances in wide bandgap SiC for optoelectronics

DEFF Research Database (Denmark)

Ou, Haiyan; Ou, Yiyu; Argyraki, Aikaterini

2014-01-01

Silicon carbide (SiC) has played a key role in power electronics thanks to its unique physical properties like wide bandgap, high breakdown field, etc. During the past decade, SiC is also becoming more and more active in optoelectronics thanks to the progress in materials growth and nanofabrication...

Fractionation in normal tissues: the (α/β)eff concept can account for dose heterogeneity and volume effects.

Science.gov (United States)

Hoffmann, Aswin L; Nahum, Alan E

2013-10-07

The simple Linear-Quadratic (LQ)-based Withers iso-effect formula (WIF) is widely used in external-beam radiotherapy to derive a new tumour dose prescription such that there is normal-tissue (NT) iso-effect when changing the fraction size and/or number. However, as conventionally applied, the WIF is invalid unless the normal-tissue response is solely determined by the tumour dose. We propose a generalized WIF (gWIF) which retains the tumour prescription dose, but replaces the intrinsic fractionation sensitivity measure (α/β) by a new concept, the normal-tissue effective fractionation sensitivity, [Formula: see text], which takes into account both the dose heterogeneity in, and the volume effect of, the late-responding normal-tissue in question. Closed-form analytical expressions for [Formula: see text] ensuring exact normal-tissue iso-effect are derived for: (i) uniform dose, and (ii) arbitrary dose distributions with volume-effect parameter n = 1 from the normal-tissue dose-volume histogram. For arbitrary dose distributions and arbitrary n, a numerical solution for [Formula: see text] exhibits a weak dependence on the number of fractions. As n is increased, [Formula: see text] increases from its intrinsic value at n = 0 (100% serial normal-tissue) to values close to or even exceeding the tumour (α/β) at n = 1 (100% parallel normal-tissue), with the highest values of [Formula: see text] corresponding to the most conformal dose distributions. Applications of this new concept to inverse planning and to highly conformal modalities are discussed, as is the effect of possible deviations from LQ behaviour at large fraction sizes.

Research Progress on Preparation for Biomass-based SiC Ceramic

Directory of Open Access Journals (Sweden)

CUI He-shuai

2017-08-01

Full Text Available Silicon carbide (SiC ceramics prepared by the conventional process has excellent properties and wide application prospects, but the increased cost of high-temperature preparation process restricts its further development. In contrast, the abundant porous structure of biomass makes itself to be ideal replacement of SiC ceramic prepared at low temperature. This paper reviewed the structure characteristics, preparation methods, pyrolysis mechanism and influence parameters of biomass-based SiC ceramic, and eventually explored the current problems and development trends of the pretreatment of carbon source and silicon source, the pyrolysis process and the application research on the preparation for biomass-based SiC ceramic.

An unstructured finite volume solver for two phase water/vapour flows based on an elliptic oriented fractional step method

International Nuclear Information System (INIS)

Mechitoua, N.; Boucker, M.; Lavieville, J.; Pigny, S.; Serre, G.

2003-01-01

Based on experience gained at EDF and Cea, a more general and robust 3-dimensional (3D) multiphase flow solver has been being currently developed for over three years. This solver, based on an elliptic oriented fractional step approach, is able to simulate multicomponent/multiphase flows. Discretization follows a 3D full unstructured finite volume approach, with a collocated arrangement of all variables. The non linear behaviour between pressure and volume fractions and a symmetric treatment of all fields are taken into account in the iterative procedure, within the time step. It greatly enforces the realizability of volume fractions (i.e 0 < α < 1), without artificial numerical needs. Applications to widespread test cases as static sedimentation, water hammer and phase separation are shown to assess the accuracy and the robustness of the flow solver in different flow conditions, encountered in nuclear reactors pipes. (authors)

Fabrication of Multi-Layerd SiC Composite Tube for LWR Applications

Energy Technology Data Exchange (ETDEWEB)

Kim, Daejong; Jung, Choonghwan; Kim, Weonju; Park, Jiyeon [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of); Lee, Jongmin [Chungnam National Univ., Daejeon (Korea, Republic of)

2013-05-15

In this study, the chemical vapor deposition (CVD) and chemical vapor infiltration (CVI) methods were employed for the fabrication of the composite tubes. SiC ceramics and SiC-based composites have recently been studied for LWR fuel cladding applications because of good mechanical/physical properties, neutron irradiation resistance and excellent compatibility with coolant under severe accident. A multi-layered SiC composite tube as the nuclear fuel cladding is composed of the monolith SiC inner layer, SiC/SiC composite intermediate layer, and monolith SiC outer layer. Since all constituents should be highly pure, stoichiometric to achieve the good properties, it has been considered that the chemical process is a well-suited technique for the fabrication of the SiC phases.

Determining the fracture resistance of advanced SiC fiber reinforced SiC matrix composites

International Nuclear Information System (INIS)

Nozawa, T.; Katoh, Y.; Kishimoto, H.

2007-01-01

Full text of publication follows: One of the perceived advantages for highly-crystalline and stoichiometric silicon carbide (SiC) and SiC composites, e.g., advanced SiC fiber reinforced chemically-vapor-infiltrated (CVI) SiC matrix composites, is the retention of fast fracture properties after neutron irradiation at high-temperatures (∼1000 deg. C) to intermediate-doses (∼15 dpa). Accordingly, it has been clarified that the maximum allowable stress (or strain) limit seems unaffected in certain irradiation conditions. Meanwhile, understanding the mechanism of crack propagation from flaws, as potential weakest link to cause composite failure, is somehow lacking, despite that determining the strength criterion based on the fracture mechanics will eventually become important considering the nature of composites' fracture. This study aims to evaluate crack propagation behaviors of advanced SiC/SiC and to provide fundamentals on fracture resistance of the composites to define the strength limit for the practical component design. For those purposes, the effects of irreversible energies related to interfacial de-bonding, fiber bridging, and microcrack forming on the fracture resistance were evaluated. Two-dimensional SiC/SiC composites were fabricated by CVI or nano-infiltration and transient-eutectic-phase (NITE ) methods. Hi-Nicalon TM Type-S or Tyranno TM -SA fibers were used as reinforcements. In-plane mode-I fracture resistance was evaluated by the single edge notched bend technique. The key finding is the continuous Load increase with the crack growth for any types of advanced composites, while many studies specified the gradual load decrease for the conventional composites once the crack initiates. This high quasi-ductility appeared due primarily to high friction (>100 MPa) at the fiber/matrix interface using rough SiC fibers. The preliminary analysis based on the linear elastic fracture mechanics, which does not consider the effects of irreversible energy

Thermosetting resins with high fractions of free volume and inherently low dielectric constants.

Science.gov (United States)

Lin, Liang-Kai; Hu, Chien-Chieh; Su, Wen-Chiung; Liu, Ying-Ling

2015-08-18

This work demonstrates a new class of thermosetting resins, based on Meldrum's acid (MA) derivatives, which have high fractions of free volume and inherently low k values of about 2.0 at 1 MHz. Thermal decomposition of the MA groups evolves CO2 and acetone to create air-trapped cavities so as to reduce the dielectric constants.

Ag Transport Through Non-Irradiated and Irradiated SiC

Energy Technology Data Exchange (ETDEWEB)

Szlufarska, Izabela [Univ. of Wisconsin, Madison, WI (United States); Morgan, Dane [Univ. of Wisconsin, Madison, WI (United States); Blanchard, James [Univ. of Wisconsin, Madison, WI (United States)

2016-01-11

Silicon carbide is the main barrier to diffusion of fission products in the current design of TRistuctural ISOtropic (TRISO) coated fuel particles, and Ag is one of the few fission products that have been shown to escape through this barrier. Because the SiC coating in TRISO is exposed to radiation throughout the lifetime of the fuel, understanding of how radiation changes the transport of the fission products is essential for the safety of the reactor. The goals of this project are: (i) to determine whether observed variation in integral release measurements of Ag through SiC can be explained by differences in grain size and grain boundary (GB) types among the samples; (2) to identify the effects of irradiation on diffusion of Ag through SiC; (3) to discover phenomena responsible for significant solubility of Ag in polycrystalline SiC. To address these goals, we combined experimental analysis of SiC diffusion couples with modeling studies of diffusion mechanisms through bulk and GBs of this material. Comparison between results obtained for pristine and irradiated samples brings in insights into the effects of radiation on Ag transport.

Ag Transport Through Non-Irradiated and Irradiated SiC

International Nuclear Information System (INIS)

Szlufarska, Izabela; Morgan, Dane; Blanchard, James

2016-01-01

Silicon carbide is the main barrier to diffusion of fission products in the current design of TRistuctural ISOtropic (TRISO) coated fuel particles, and Ag is one of the few fission products that have been shown to escape through this barrier. Because the SiC coating in TRISO is exposed to radiation throughout the lifetime of the fuel, understanding of how radiation changes the transport of the fission products is essential for the safety of the reactor. The goals of this project are: (i) to determine whether observed variation in integral release measurements of Ag through SiC can be explained by differences in grain size and grain boundary (GB) types among the samples; (2) to identify the effects of irradiation on diffusion of Ag through SiC; (3) to discover phenomena responsible for significant solubility of Ag in polycrystalline SiC. To address these goals, we combined experimental analysis of SiC diffusion couples with modeling studies of diffusion mechanisms through bulk and GBs of this material. Comparison between results obtained for pristine and irradiated samples brings in insights into the effects of radiation on Ag transport.

Preparation and infrared absorption properties of buried SiC layers

International Nuclear Information System (INIS)

Yan Hui; Chen Guanghua; Wong, S.P.; Kwok, R.W.M.

1997-01-01

Buried SiC layers were formed by using a metal vapor vacuum arc (MEVVA) ion source, with C + ions implanted into Si substrates under different doses. In the present study, the extracted voltage was 50 kV and the ion dose was varied from 3.0 x 10 17 to 1.6 x 10 18 cm -2 . According to infrared absorption measurements, it was fount that the structure of the buried SiC layers depended on the ion dose. Moreover, the results also demonstrated that the buried SiC layers including cubic crystalline SiC could be synthesized at an averaged substrate temperature of lower than 400 degree C with the MEVVA ion source

Quantitative gated SPECT: the effect of reconstruction filter on calculated left ventricular ejection fractions and volumes

International Nuclear Information System (INIS)

Wright, Graham A.; McDade, Mark; Martin, William; Hutton, William

2002-01-01

Gated SPECT (GSPECT) offers the possibility of obtaining additional functional information from perfusion studies, including calculation of left ventricular ejection fraction (LVEF). The calculation of LVEF relies upon the identification of the endocardial surface, which will be affected by the spatial resolution and statistical noise in the reconstructed images. The aim of this study was to compare LVEFs and ventricular volumes calculated from GSPECT using six reconstruction filters. GSPECT and radionuclide ventriculography (RNVG) were performed on 40 patients; filtered back projection was used to reconstruct the datasets with each filter. LVEFs and volumes were calculated using the Cedars-Sinai QGS package. The correlation coefficient between RNVG and GSPECT ranged from 0.81 to 0.86 with higher correlations for smoother filters. The narrowest prediction interval was 11±2%. There was a trend towards higher LVEF values with smoother filters, the ramp filter yielding LVEFs 2.55±3.10% (p<0.001) lower than the Hann filter. There was an overall fall in ventricular volumes with smoother filters with a mean difference of 13.98±10.15 ml (p<0.001) in EDV between the Butterworth-0.5 and Butterworth-0.3 filters. In conclusion, smoother reconstruction filters lead to lower volumes and higher ejection fractions with the QGS algorithm, with the Butterworth-0.4 filter giving the highest correlation with LVEFs from RNVG. Even if the optimal filter is chosen the uncertainty in the measured ejection fractions is still too great to be clinically acceptable. (author)

Temperature Dependence of Mechanical Properties of TRISO SiC Coatings

International Nuclear Information System (INIS)

Kim, Do Kyung; Park, Kwi Il; Lee, Hyeon Keun; Seong, Young Hoon; Lee, Seung Jun

2009-04-01

SiC coating layer has been introduced as protective layer in TRISO nuclear fuel particle of high temperature gas cooled reactor (HTGR) due to excellent mechanical stability at high temperature. It is important to study for high temperature stability in SiC coating layers, because TRISO fuel particles were operating at high temperature around 1000 .deg. C. In this study, the nanoindentation test and micro tensile test were conducted in order to measure the mechanical properties of SiC coating layers at elevated temperature. SiC coating film was fabricated on the carbon substrate using chemical vapor deposition process with different microstructures and thicknesses. Nanoindentation test was performed for the analysis of the hardness, modulus and creep properties up to 500 .deg. C. Impression creep method applied to nanoindentation and creep properties of SiC coating layers were characterized by nanoindentation creep test. The fracture strength of SiC coating layers was measured by the micro tensile method at room temperature and 500 .deg. C. From the results, we can conclude that the hardness and fracture strength are decreased with temperature and no significant change in the modulus is observed with increase in temperature. The deformation mechanism for indentation creep and creep rate changes as the testing temperature increased

Tema 8. Principis físics dels semiconductors (Resum)

OpenAIRE

Beléndez Vázquez, Augusto

2011-01-01

Resum del "Tema 8. Principis físics dels semiconductors" de l'assignatura "Fonaments Físics de l'Enginyeria I" de "Grau en Enginyeria en So i Imatge" impartit a l'Escola Politècnica Superior de la Universitat d'Alacant.

Entropy of level-cut random Gaussian structures at different volume fractions.

Science.gov (United States)

Marčelja, Stjepan

2017-10-01

Cutting random Gaussian fields at a given level can create a variety of morphologically different two- or several-phase structures that have often been used to describe physical systems. The entropy of such structures depends on the covariance function of the generating Gaussian random field, which in turn depends on its spectral density. But the entropy of level-cut structures also depends on the volume fractions of different phases, which is determined by the selection of the cutting level. This dependence has been neglected in earlier work. We evaluate the entropy of several lattice models to show that, even in the cases of strongly coupled systems, the dependence of the entropy of level-cut structures on molar fractions of the constituents scales with the simple ideal noninteracting system formula. In the last section, we discuss the application of the results to binary or ternary fluids and microemulsions.

Entropy of level-cut random Gaussian structures at different volume fractions

Science.gov (United States)

Marčelja, Stjepan

2017-10-01

Cutting random Gaussian fields at a given level can create a variety of morphologically different two- or several-phase structures that have often been used to describe physical systems. The entropy of such structures depends on the covariance function of the generating Gaussian random field, which in turn depends on its spectral density. But the entropy of level-cut structures also depends on the volume fractions of different phases, which is determined by the selection of the cutting level. This dependence has been neglected in earlier work. We evaluate the entropy of several lattice models to show that, even in the cases of strongly coupled systems, the dependence of the entropy of level-cut structures on molar fractions of the constituents scales with the simple ideal noninteracting system formula. In the last section, we discuss the application of the results to binary or ternary fluids and microemulsions.

Usefulness of acoustic quantification method in left ventricular volume and ejection fraction. Compared with ventriculography and scintigraphy

International Nuclear Information System (INIS)

Shibata, Takahiro; Honda, Youichi; Kashiwagi, Hidehiko

1996-01-01

Acoustic quantification method (AQ: on-line automated boundary detection system) has proved to have a good correlation with left ventriculography (LVG) and scintigraphy (SG) in patients with normal left ventricular (LV) function. The aim of this study is to determine whether AQ is also useful in patients with abnormal LV function. We examined 54 patients with LV asynergy. End-diastolic volumes with AQ, LVG and SG were 77, 135, 118 ml. A good correlation was found between AQ and LVG and SG (LVG; r=0.81, SG; r=0.68). End-systolic volumes with AQ, LVG and SG were 38, 64 and 57 ml. Left ventricular volumes obtained from AQ had a good correlation with LVG and SG, but were underestimated. LV ejection fraction obtained from AQ had good correlation with those with LVG and SG (LVG; r=0.84. SG; r=0.77). On-line AQ appears to be a useful noninvasive method for evaluation of the left ventricular ejection fraction, but care must be exercised when estimations of left ventricular volumes are made. (author)

Dose fractionated gamma knife radiosurgery for large arteriovenous malformations on daily or alternate day schedule outside the linear quadratic model: Proof of concept and early results. A substitute to volume fractionation.

Science.gov (United States)

Mukherjee, Kanchan Kumar; Kumar, Narendra; Tripathi, Manjul; Oinam, Arun S; Ahuja, Chirag K; Dhandapani, Sivashanmugam; Kapoor, Rakesh; Ghoshal, Sushmita; Kaur, Rupinder; Bhatt, Sandeep

2017-01-01

To evaluate the feasibility, safety and efficacy of dose fractionated gamma knife radiosurgery (DFGKRS) on a daily schedule beyond the linear quadratic (LQ) model, for large volume arteriovenous malformations (AVMs). Between 2012-16, 14 patients of large AVMs (median volume 26.5 cc) unsuitable for surgery or embolization were treated in 2-3 of DFGKRS sessions. The Leksell G frame was kept in situ during the whole procedure. 86% (n = 12) patients had radiologic evidence of bleed, and 43% (n = 6) had presented with a history of seizures. 57% (n = 8) patients received a daily treatment for 3 days and 43% (n = 6) were on an alternate day (2 fractions) regimen. The marginal dose was split into 2 or 3 fractions of the ideal prescription dose of a single fraction of 23-25 Gy. The median follow up period was 35.6 months (8-57 months). In the three-fraction scheme, the marginal dose ranged from 8.9-11.5 Gy, while in the two-fraction scheme, the marginal dose ranged from 11.3-15 Gy at 50% per fraction. Headache (43%, n = 6) was the most common early postoperative complication, which was controlled with short course steroids. Follow up evaluation of at least three years was achieved in seven patients, who have shown complete nidus obliteration in 43% patients while the obliteration has been in the range of 50-99% in rest of the patients. Overall, there was a 67.8% reduction in the AVM volume at 3 years. Nidus obliteration at 3 years showed a significant rank order correlation with the cumulative prescription dose (p 0.95, P value 0.01), with attainment of near-total (more than 95%) obliteration rates beyond 29 Gy of the cumulative prescription dose. No patient receiving a cumulative prescription dose of less than 31 Gy had any severe adverse reaction. In co-variate adjusted ordinal regression, only the cumulative prescription dose had a significant correlation with common terminology criteria for adverse events (CTCAE) severity (P value 0.04), independent of age, AVM volume

Additive Manufacturing of SiC Based Ceramics and Ceramic Matrix Composites

Science.gov (United States)

Halbig, Michael Charles; Singh, Mrityunjay

2015-01-01

Silicon carbide (SiC) ceramics and SiC fiber reinforcedSiC ceramic matrix composites (SiCSiC CMCs) offer high payoff as replacements for metals in turbine engine applications due to their lighter weight, higher temperature capability, and lower cooling requirements. Additive manufacturing approaches can offer game changing technologies for the quick and low cost fabrication of parts with much greater design freedom and geometric complexity. Four approaches for developing these materials are presented. The first two utilize low cost 3D printers. The first uses pre-ceramic pastes developed as feed materials which are converted to SiC after firing. The second uses wood containing filament to print a carbonaceous preform which is infiltrated with a pre-ceramic polymer and converted to SiC. The other two approaches pursue the AM of CMCs. The first is binder jet SiC powder processing in collaboration with rp+m (Rapid Prototyping+Manufacturing). Processing optimization was pursued through SiC powder blending, infiltration with and without SiC nano powder loading, and integration of nanofibers into the powder bed. The second approach was laminated object manufacturing (LOM) in which fiber prepregs and laminates are cut to shape by a laser and stacked to form the desired part. Scanning electron microscopy was conducted on materials from all approaches with select approaches also characterized with XRD, TGA, and bend testing.

Birth weight and neonatal adiposity prediction using fractional limb volume obtained with 3D ultrasound.

Science.gov (United States)

O'Connor, Clare; O'Higgins, Amy; Doolan, Anne; Segurado, Ricardo; Stuart, Bernard; Turner, Michael J; Kennelly, Máireád M

2014-01-01

The objective of this investigation was to study fetal thigh volume throughout gestation and explore its correlation with birth weight and neonatal body composition. This novel technique may improve birth weight prediction and lead to improved detection rates for fetal growth restriction. Fractional thigh volume (TVol) using 3D ultrasound, fetal biometry and soft tissue thickness were studied longitudinally in 42 mother-infant pairs. The percentages of neonatal body fat, fat mass and fat-free mass were determined using air displacement plethysmography. Correlation and linear regression analyses were performed. Linear regression analysis showed an association between TVol and birth weight. TVol at 33 weeks was also associated with neonatal fat-free mass. There was no correlation between TVol and neonatal fat mass. Abdominal circumference, estimated fetal weight (EFW) and EFW centile showed consistent correlations with birth weight. Thigh volume demonstrated an additional independent contribution to birth weight prediction when added to the EFW centile from the 38-week scan (p = 0.03). Fractional TVol performed at 33 weeks gestation is correlated with birth weight and neonatal lean body mass. This screening test may highlight those at risk of fetal growth restriction or macrosomia.

Low dose irradiation performance of SiC interphase SiC/SiC composites

International Nuclear Information System (INIS)

Snead, L.L.; Lowden, R.A.; Strizak, J.; More, K.L.; Eatherly, W.S.; Bailey, J.; Williams, A.M.; Osborne, M.C.; Shinavski, R.J.

1998-01-01

Reduced oxygen Hi-Nicalon fiber reinforced composite SiC materials were densified with a chemically vapor infiltrated (CVI) silicon carbide (SiC) matrix and interphases of either 'porous' SiC or multilayer SiC and irradiated to a neutron fluence of 1.1 x 10 25 n m -2 (E>0.1 MeV) in the temperature range of 260 to 1060 C. The unirradiated properties of these composites are superior to previously studied ceramic grade Nicalon fiber reinforced/carbon interphase materials. Negligible reduction in the macroscopic matrix microcracking stress was observed after irradiation for the multilayer SiC interphase material and a slight reduction in matrix microcracking stress was observed for the composite with porous SiC interphase. The reduction in strength for the porous SiC interfacial material is greatest for the highest irradiation temperature. The ultimate fracture stress (in four point bending) following irradiation for the multilayer SiC and porous SiC interphase materials was reduced by 15% and 30%, respectively, which is an improvement over the 40% reduction suffered by irradiated ceramic grade Nicalon fiber materials fabricated in a similar fashion, though with a carbon interphase. The degradation of the mechanical properties of these composites is analyzed by comparison with the irradiation behavior of bare Hi-Nicalon fiber and Morton chemically vapor deposited (CVD) SiC. It is concluded that the degradation of these composites, as with the previous generation ceramic grade Nicalon fiber materials, is dominated by interfacial effects, though the overall degradation of fiber and hence composite is reduced for the newer low-oxygen fiber. (orig.)

An Extension of SIC Predictions to the Wiener Coactive Model.

Science.gov (United States)

Houpt, Joseph W; Townsend, James T

2011-06-01

The survivor interaction contrasts (SIC) is a powerful measure for distinguishing among candidate models of human information processing. One class of models to which SIC analysis can apply are the coactive, or channel summation, models of human information processing. In general, parametric forms of coactive models assume that responses are made based on the first passage time across a fixed threshold of a sum of stochastic processes. Previous work has shown that that the SIC for a coactive model based on the sum of Poisson processes has a distinctive down-up-down form, with an early negative region that is smaller than the later positive region. In this note, we demonstrate that a coactive process based on the sum of two Wiener processes has the same SIC form.

Influence of primary α-phase volume fraction on the mechanical properties of Ti-6Al-4V alloy at different strain rates and temperatures

Science.gov (United States)

Ren, Yu; Zhou, Shimeng; Luo, Wenbo; Xue, Zhiyong; Zhang, Yajing

2018-03-01

Bimodal microstructures with primary α-phase volume fractions ranging from 14.3% to 57.1% were gained in Ti-6Al-4V (Ti-64) alloy through annealed in two-phase region at various temperatures below the β-transus point. Then the influence of the primary α-phase volume fraction on the mechanical properties of Ti-64 were studied. The results show that, at room temperature and a strain rate of 10‑3 s‑1, the yield stress decreases but the fracture strain augments with added primary α-phase volume fraction. The equiaxed primary α-phase possesses stronger ability to coordinate plastic deformation, leading to the improvement of the ductile as well as degradation of the strength of Ti-64 with higher primary α-phase volume fraction. As the temperature goes up to 473 K, the quasi-static yield stress and ultimate strength decrease first and then increase with the incremental primary α-phase volume fraction, due to the interaction between the work hardening and the softening caused by the DRX and the growth of the primary α-phase. At room temperature and a strain rate of 3×103 s‑1, the varying pattern of strength with the primary α-phase volume fraction resembles that at a quasi-static strain rate. However, the flow stress significantly increases but the strain-hardening rate decreases compared to those at quasi-static strain rate due to the competition between the strain rate hardening and the thermal softening during dynamic compression process.

SiO 2/SiC interface proved by positron annihilation

Science.gov (United States)

Maekawa, M.; Kawasuso, A.; Yoshikawa, M.; Itoh, H.

2003-06-01

We have studied positron annihilation in a Silicon carbide (SiC)-metal/oxide/semiconductor (MOS) structure using a monoenergetic positron beam. The Doppler broadening of annihilation quanta were measured as functions of the incident positron energy and the gate bias. Applying negative gate bias, significant increases in S-parameters were observed. This indicates the migration of implanted positrons towards SiO 2/SiC interface and annihilation at open-volume type defects. The behavior of S-parameters depending on the bias voltage was well correlated with the capacitance-voltage ( C- V) characteristics. We observed higher S-parameters and the interfacial trap density in MOS structures fabricated using the dry oxidation method as compared to those by pyrogenic oxidation method.

SiO2/SiC interface proved by positron annihilation

International Nuclear Information System (INIS)

Maekawa, M.; Kawasuso, A.; Yoshikawa, M.; Itoh, H.

2003-01-01

We have studied positron annihilation in a Silicon carbide (SiC)-metal/oxide/semiconductor (MOS) structure using a monoenergetic positron beam. The Doppler broadening of annihilation quanta were measured as functions of the incident positron energy and the gate bias. Applying negative gate bias, significant increases in S-parameters were observed. This indicates the migration of implanted positrons towards SiO 2 /SiC interface and annihilation at open-volume type defects. The behavior of S-parameters depending on the bias voltage was well correlated with the capacitance-voltage (C-V) characteristics. We observed higher S-parameters and the interfacial trap density in MOS structures fabricated using the dry oxidation method as compared to those by pyrogenic oxidation method

Self Absorbed Fraction for Electrons and Beta Particles in Small Spherical Volumes

International Nuclear Information System (INIS)

Grosev, D.

2003-01-01

Absorbed fraction and target organ mass are important parameters of internal dosimetry calculations that define the geometry of the system. Standard MIRD (Medical Internal Radiation Dosimetry) formalism assumes that the absorbed fraction for non-penetrating radiations (e.g., electrons, beta particles) is 1. This may not be correct in cases where dimensions of organs/tissues are comparable with the ranges of electrons/beta particles. Such is the case for example in radiodine ablation of thyroid remnant tissue. In this work the self-absorbed fraction (source and target volumes are the same) for monoenergetic electrons and beta particles is calculated for small spherical volumes of various sizes and unit density. Absorbed fraction can be expressed as an integral of the product of two quantities: (a) Scaled beta dose point kernel (mean absorbed dose rate per activity of the point source in infinite homogenous medium), F β ; (b) special geometrical reduction factor (GRF). F β is calculated using EGS4 Monte Carlo (MC) code for transport of electrons and photons. MC source code calculates the deposition of energy inside concentric spherical shells around the isotropic point source of electrons/beta particles in infinite medium (water). Shell thickness was δr=0.02·X 90 , where X 90 represents the radius of the sphere inside which 90% of the source energy is absorbed. Number of concentric spherical shells was 100, 10000 electron histories were started in each program run, and 10 runs were repeated for statistical reason. Numerical integration of the product of F β , calculated by MC program, and GRF for sphere was done using Simpson method. Absorbed fractions were calculated for spheres with mass from 0.01-20 g (r = 0.13 - 1.68 cm). Results are given for monoenergetic electrons with kinetic energy T=0.2, 0.4, 1.0 MeV, and for three beta emitters 1 31I , 3 2P , 9 0Y . For quantitative dosimetric protocols in radioiodine ablation therapy, results for 1 31I are of

Application of artificial neural networks for the prediction of volume fraction using spectra of gamma rays backscattered by three-phase flows

Science.gov (United States)

Gholipour Peyvandi, R.; Islami Rad, S. Z.

2017-12-01

The determination of the volume fraction percentage of the different phases flowing in vessels using transmission gamma rays is a conventional method in petroleum and oil industries. In some cases, with access only to the one side of the vessels, attention was drawn toward backscattered gamma rays as a desirable choice. In this research, the volume fraction percentage was measured precisely in water-gasoil-air three-phase flows by using the backscatter gamma ray technique andthe multilayer perceptron (MLP) neural network. The volume fraction determination in three-phase flows requires two gamma radioactive sources or a dual-energy source (with different energies) while in this study, we used just a 137Cs source (with the single energy) and a NaI detector to analyze backscattered gamma rays. The experimental set-up provides the required data for training and testing the network. Using the presented method, the volume fraction was predicted with a mean relative error percentage less than 6.47%. Also, the root mean square error was calculated as 1.60. The presented set-up is applicable in some industries with limited access. Also, using this technique, the cost, radiation safety and shielding requirements are minimized toward the other proposed methods.

Synthesis of micro-sized interconnected Si-C composites

Science.gov (United States)

Wang, Donghai; Yi, Ran; Dai, Fang

2016-02-23

Embodiments provide a method of producing micro-sized Si--C composites or doped Si--C and Si alloy-C with interconnected nanoscle Si and C building blocks through converting commercially available SiO.sub.x (0

The effect of SiC particle size on the properties of Cu–SiC composites

International Nuclear Information System (INIS)

Celebi Efe, G.; Zeytin, S.; Bindal, C.

2012-01-01

Graphical abstract: The relative densities of Cu–SiC composites sintered at 700 °C for 2 h are ranged from 97.3% to 91.8% for SiC with 1 μm particle size and 97.5% to 95.2% for SiC with 5 μm particle size, microhardness of composites ranged from 143 to 167 HV for SiC having 1 μm particle size and 156–182 HVN for SiC having 5 μm particle size and the electrical conductivity of composites changed between 85.9% IACS and 55.7% IACS for SiC with 1 μm particle size, 87.9% IACS and 65.2%IACS for SiC with 5 μm particle size. It was found that electrical conductivity of composites containing SiC with 5 μm particle size is better than that of Cu–SiC composites containing SiC with particle size of 1 μm. Highlights: ► In this research, the effect of SiC particle size on some properties of Cu–SiC composites were investigated. ► The mechanical properties were improved. ► The electrical properties were obtained at desirable level. -- Abstract: SiC particulate-reinforced copper composites were prepared by powder metallurgy (PM) method and conventional atmospheric sintering. Scanning electron microscope (SEM), X-ray diffraction (XRD) techniques were used to characterize the sintered composites. The effect of SiC content and particle size on the relative density, hardness and electrical conductivity of composites were investigated. The relative densities of Cu–SiC composites sintered at 700 °C for 2 h are ranged from 97.3% to 91.8% for SiC with 1 μm particle size and from 97.5% to 95.2% for SiC with 5 μm particle size. Microhardness of composites ranged from 143 to 167 HV for SiC having 1 μm particle size and from 156 to 182 HV for SiC having 5 μm particle size. The electrical conductivity of composites changed between 85.9% IACS and 55.7% IACS for SiC with 1 μm particle size, between 87.9% IACS and 65.2% IACS for SiC with 5 μm particle size.

Near-field radiative heat transfer between graphene-covered hyperbolic metamaterials

Science.gov (United States)

Hong, Xiao-Juan; Li, Jian-Wen; Wang, Tong-Biao; Zhang, De-Jian; Liu, Wen-Xing; Liao, Qing-Hua; Yu, Tian-Bao; Liu, Nian-Hua

2018-04-01

We propose the use of graphene-covered silicon carbide (SiC) nanowire arrays (NWAs) for theoretical studies of near-field radiative heat transfer. The SiC NWAs exhibit a hyperbolic characteristic at an appropriately selected filling-volume fraction. The surface plasmon supported by graphene and the hyperbolic modes supported by SiC NWAs significantly affect radiative heat transfer. The heat-transfer coefficient (HTC) between the proposed structures is larger than that between SiC NWAs. We also find that the chemical potential of graphene plays an important role in modulating the HTC. The tunability of chemical potential through gate voltage enables flexible control of heat transfer using the graphene-covered SiC NWAs.

InP-based photonic integrated circuit platform on SiC wafer.

Science.gov (United States)

Takenaka, Mitsuru; Takagi, Shinichi

2017-11-27

We have numerically investigated the properties of an InP-on-SiC wafer as a photonic integrated circuit (PIC) platform. By bonding a thin InP-based semiconductor on a SiC wafer, SiC can be used as waveguide cladding, a heat sink, and a support substrate simultaneously. Since the refractive index of SiC is sufficiently low, PICs can be fabricated using InP-based strip and rib waveguides with a minimum bend radius of approximately 7 μm. High-thermal-conductivity SiC underneath an InP-based waveguide core markedly improves heat dissipation, resulting in superior thermal properties of active devices such as laser diodes. The InP-on-SiC wafer has significantly smaller thermal stress than InP-on-SiO 2 /Si wafer, which prevents the thermal degradation of InP-based devices during high-temperature processes. Thus, InP on SiC provides an ideal platform for high-performance PICs.

Factors affecting the corrosion of SiC layer by fission product palladium

International Nuclear Information System (INIS)

Dewita, E.

2000-01-01

HTR is one of the advanced nuclear reactors which has inherent safety system, graphite moderated and helium gas cooled. In general, these reactors are designed with the TRISO coated particle consist of four coating layers that are porous pyrolytic carbon (PyC). inner dense PyC (IPyC), silicon carbide (SiC), and outer dense PyC (OPyC). Among the four coating layers, the SiC plays an important role beside in retaining metallic fission products, it also provides mechanical strength to fuel particle. However, results of post irradiation examination indicate that fission product palladium can react with and corrode SiC layer, This assessment is conducted to get the comprehension about resistance of SiC layer on irradiation effects, especially in order to increase the fuel bum-up. The result of this shows that the corrosion of SiC layer by fission product palladium is beside depend on the material characteristics of SiC, and also there are other factors that affect on the SiC layer corrosion. Fuel enrichment, bum-up, and irradiation time effect on the palladium flux in fuel kernel. While, the fuel density, vapour pressure of palladium (the degree depend on the irradiation temperature and kernel composition) effect on palladium migration in fuel particle. (author)

SiC fibre by chemical vapour deposition on tungsten filament

Indian Academy of Sciences (India)

Unknown

SiC fibre by chemical vapour deposition on tungsten filament ... CMCs), in defence and industrial applications. SiC has attractive ... porosity along with chemical purity. This is lacking .... reactor. Since mercury is very toxic it should be removed.

The annealing effects on irradiated SiC piezo resistive pressure sensor

International Nuclear Information System (INIS)

Almaz, E.; Blue, T. E.; Zhang, P.

2009-01-01

The effects of temperature on annealing of Silicon Carbide (SiC) piezo resistive pressure sensor which was broken after high fluence neutron irradiation, were investigated. Previously, SiC piezo resistive sensor irradiated with gamma ray and fast neutron in the Co-60 gamma-ray irradiator and Beam Port 1 (BP1) and Auxiliary Irradiation Facility (AIF) at the Ohio State University Nuclear Reactor Laboratory (OSUNRL) respectively. The Annealing temperatures were tested up to 400 C. The Pressure-Output voltage results showed recovery after annealing process on SiC piezo resistive pressure sensor. The bridge resistances of the SiC pressure sensor stayed at the same level up to 300 C. After 400 C annealing, the resistance values changed dramatically.

Recent progress of ultrahigh voltage SiC devices for particle accelerator

International Nuclear Information System (INIS)

Fukuda, Kenji; Tsuji, Takashi; Shiomi, Hiromu; Mizushima, Tomonori; Yonezawa, Yoshiyuki; Kondo, Chikara; Otake, Yuji

2016-01-01

Silicon carbide (SiC) is the promising material for next power electronics technology used in the field such as HEV, EV, and railway, electric power infrastructure. SiC enables power devices with low loss to easily operate in an ultrahigh-voltage region because of the high breakdown electric field of SiC. In this paper, we report static and dynamic electric performances of 3300 V class SiC SBDs, IE-MOSFETs, >10 kV PiN diodes and IE-IGBTs. Especially, the electrical characteristics of IE-IGBT with the blocking voltage of 16.5 kV indicate the sufficient ability to convert the thyratron in high power RF system of an accelerator. (author)

Elaboration of silicon carbides nano particles (SiC): from the powder synthesis to the sintered ceramic

International Nuclear Information System (INIS)

Reau, A.

2008-01-01

Materials for the reactor cores of the fourth generation will need materials supporting high temperatures with fast neutrons flux. SiC f /SiC ceramics are proposed. One of the possible elaboration process is to fill SiC fiber piece with nano particles SiC powder and to strengthen by sintering. The aim of this thesis is to obtain a nano structured SiC ceramic as a reference for the SiC f /SiC composite development and to study the influence of the fabrication parameters. (A.L.B.)

Detection and analysis of particles with failed SiC in AGR-1 fuel compacts

Energy Technology Data Exchange (ETDEWEB)

Hunn, John D., E-mail: hunnjd@ornl.gov [Oak Ridge National Laboratory (ORNL), P.O. Box 2008, Oak Ridge, TN 37831-6093 (United States); Baldwin, Charles A.; Gerczak, Tyler J.; Montgomery, Fred C.; Morris, Robert N.; Silva, Chinthaka M. [Oak Ridge National Laboratory (ORNL), P.O. Box 2008, Oak Ridge, TN 37831-6093 (United States); Demkowicz, Paul A.; Harp, Jason M.; Ploger, Scott A. [Idaho National Laboratory (INL), P.O. Box 1625, Idaho Falls, ID 83415-6188 (United States)

2016-09-15

Highlights: • Cesium release was used to detect SiC failure in HTGR fuel. • Tristructural-isotropic particles with SiC failure were isolated by gamma screening. • SiC failure was studied by X-ray tomography and SEM. • SiC degradation was observed after irradiation and subsequent safety testing. - Abstract: As the primary barrier to release of radioactive isotopes emitted from the fuel kernel, retention performance of the SiC layer in tristructural isotropic (TRISO) coated particles is critical to the overall safety of reactors that utilize this fuel design. Most isotopes are well-retained by intact SiC coatings, so pathways through this layer due to cracking, structural defects, or chemical attack can significantly contribute to radioisotope release. In the US TRISO fuel development effort, release of {sup 134}Cs and {sup 137}Cs are used to detect SiC failure during fuel compact irradiation and safety testing because the amount of cesium released by a compact containing one particle with failed SiC is typically ten or more times higher than that released by compacts without failed SiC. Compacts with particles that released cesium during irradiation testing or post-irradiation safety testing at 1600–1800 °C were identified, and individual particles with abnormally low cesium retention were sorted out with the Oak Ridge National Laboratory (ORNL) Irradiated Microsphere Gamma Analyzer (IMGA). X-ray tomography was used for three-dimensional imaging of the internal coating structure to locate low-density pathways through the SiC layer and guide subsequent materialography by optical and scanning electron microscopy. All three cesium-releasing particles recovered from as-irradiated compacts showed a region where the inner pyrocarbon (IPyC) had cracked due to radiation-induced dimensional changes in the shrinking buffer and the exposed SiC had experienced concentrated attack by palladium; SiC failures observed in particles subjected to safety testing were

The effect of different fibre volume fraction on mechanical properties of banana/pineapple leaf (PaLF)/glass hybrid composite

Science.gov (United States)

Hanafee, Z. M.; Khalina, A.; Norkhairunnisa, M.; Syams, Z. Edi; Liew, K. E.

2017-09-01

This paper investigates the effect of fibre volume fraction on mechanical properties of banana-pineapple leaf (PaLF)-glass reinforced epoxy resin under tensile loading. Uniaxial tensile tests were carried out on specimens with different fibre contents (30%, 40%, 50% in weight). The composite specimens consists of 13 different combinations. The effect of hybridisation between synthetic and natural fibre onto tensile properties was determined and the optimum fibre volume fraction was obtained at 50% for both banana and PaLF composites. Additional 1 layer of woven glass fibre increased the tensile strength of banana-PaLF composite up to 85%.

Fractional filling with the microdepot technique as an alternative to bolus hyaluronic acid injections in facial volume restoration.

Science.gov (United States)

Lim, Adrian C; Lowe, Patricia M

2011-05-01

For volume restoration of the face, hyaluronic acid is conventionally injected through long, large-bore, 18-gauge needles because of the higher viscosity subtypes required. These hyaluronic acids are either more highly cross-linked or larger in particle size than the less-viscous subtypes. The microdepot injection technique involves using the 31-gauge BD insulin syringe (Becton-Dickinson, North Ryde, NSW Australia) to deposit small amounts of filler (0.05-0.1 mL) throughout the area of volume loss. The procedure is extremely well tolerated, requiring only topical and ice anaesthesia. Using this method, volume restoration can be achieved naturally and progressively over a period of time. Fractional filling every 3-4 months is continued until the desired level of volume correction is attained. Patients undergoing fractional filling followed over a 12-month period did not indicate any observable compromise in filler longevity, even when highly viscous hyaluronic acid fillers were injected through small-bore, 31-gauge insulin syringes. © 2011 The Authors. Australasian Journal of Dermatology © 2011 The Australasian College of Dermatologists.

Transformation from amorphous to nano-crystalline SiC thin films ...

Indian Academy of Sciences (India)

Administrator

phous SiC to cubic nano-crystalline SiC films with the increase in the gas flow ratio. Raman scattering ... Auger electron spectroscopy showed that the carbon incorporation in the .... with a 514 nm Ar+ laser excitation source and the laser.

Evaluation of liquid-phase sintering SiC using as additive the system Al2O3/DyO3

International Nuclear Information System (INIS)

Oliveira, M.R.; Atilio, I.; Garcia, G.C.R.; Ribeiro, S.

2012-01-01

The objective of this work was to study the liquid-phase sintering SiC with additives that has not been studied yet, Al 2 O 3 /Dy 2 O 3 , with 10% in volume. The powders were mixed, dried, and pressed in uniaxial and isostatic pressing. It was studied the melting temperature of the additives and bars were sintered at temperatures of 1900, 1950 e 2000 deg C, with averaged linear shrinkage of 17%, phase transformations of β-SiC into α-SiC and formation of Dy 3 Al 5 O 12 at all temperatures. The results showed that for further densification, the temperature of 1950 deg C is enough for a higher densification, with a low wetting angle, transformations of SiC and formation of Dy 3 Al 5 O 12 . (author)

Critical Void Volume Fraction fc at Void Coalescence for S235JR Steel at Low Initial Stress Triaxiality

Science.gov (United States)

Grzegorz Kossakowski, Paweł; Wciślik, Wiktor

2017-10-01

The paper is concerned with the nucleation, growth and coalescence of microdefects in the form of voids in S235JR steel. The material is known to be one of the basic steel grades commonly used in the construction industry. The theory and methods of damage mechanics were applied to determine and describe the failure mechanisms that occur when the material undergoes deformation. Until now, engineers have generally employed the Gurson-Tvergaard- Needleman model. This material model based on damage mechanics is well suited to define and analyze failure processes taking place in the microstructure of S235JR steel. It is particularly important to determine the critical void volume fraction fc , which is one of the basic parameters of the Gurson-Tvergaard-Needleman material model. As the critical void volume fraction fc refers to the failure stage, it is determined from the data collected for the void coalescence phase. A case of multi-axial stresses is considered taking into account the effects of spatial stress state. In this study, the parameter of stress triaxiality η was used to describe the failure phenomena. Cylindrical tensile specimens with a circumferential notch were analysed to obtain low values of initial stress triaxiality (η = 0.556 of the range) in order to determine the critical void volume fraction fc . It is essential to emphasize how unique the method applied is and how different it is from the other more common methods involving parameter calibration, i.e. curve-fitting methods. The critical void volume fraction fc at void coalescence was established through digital image analysis of surfaces of S235JR steel, which involved studying real, physical results obtained directly from the material tested.

The Effect of Fiber Strength Stochastics and Local Fiber Volume Fraction on Multiscale Progressive Failure of Composites

Science.gov (United States)

Ricks, Trenton M.; Lacy, Jr., Thomas E.; Bednarcyk, Brett A.; Arnold, Steven M.

2013-01-01

Continuous fiber unidirectional polymer matrix composites (PMCs) can exhibit significant local variations in fiber volume fraction as a result of processing conditions that can lead to further local differences in material properties and failure behavior. In this work, the coupled effects of both local variations in fiber volume fraction and the empirically-based statistical distribution of fiber strengths on the predicted longitudinal modulus and local tensile strength of a unidirectional AS4 carbon fiber/ Hercules 3502 epoxy composite were investigated using the special purpose NASA Micromechanics Analysis Code with Generalized Method of Cells (MAC/GMC); local effective composite properties were obtained by homogenizing the material behavior over repeating units cells (RUCs). The predicted effective longitudinal modulus was relatively insensitive to small (8%) variations in local fiber volume fraction. The composite tensile strength, however, was highly dependent on the local distribution in fiber strengths. The RUC-averaged constitutive response can be used to characterize lower length scale material behavior within a multiscale analysis framework that couples the NASA code FEAMAC and the ABAQUS finite element solver. Such an approach can be effectively used to analyze the progressive failure of PMC structures whose failure initiates at the RUC level. Consideration of the effect of local variations in constituent properties and morphologies on progressive failure of PMCs is a central aspect of the application of Integrated Computational Materials Engineering (ICME) principles for composite materials.

Fission-product SiC reaction in HTGR fuel

International Nuclear Information System (INIS)

Montgomery, F.

1981-01-01

The primary barrier to release of fission product from any of the fuel types into the primary circuit of the HTGR are the coatings on the fuel particles. Both pyrolytic carbon and silicon carbide coatings are very effective in retaining fission gases under normal operating conditions. One of the possible performance limitations which has been observed in irradiation tests of TRISO fuel is chemical interaction of the SiC layer with fission products. This reaction reduces the thickness of the SiC layer in TRISO particles and can lead to release of fission products from the particles if the SiC layer is completely penetrated. The experimental section of this report describes the results of work at General Atomic concerning the reaction of fission products with silicon carbide. The discussion section describes data obtained by various laboratories and includes (1) a description of the fission products which have been found to react with SiC; (2) a description of the kinetics of silicon carbide thinning caused by fission product reaction during out-of-pile thermal gradient heating and the application of these kinetics to in-pile irradiation; and (3) a comparison of silicon carbide thinning in LEU and HEU fuels

SiC substrate defects and III-N heteroepitaxy

Energy Technology Data Exchange (ETDEWEB)

Poust, B D [Department of Materials Science and Engineering, University of California, Los Angeles, CA 90095 (United States); Koga, T S [Department of Materials Science and Engineering, University of California, Los Angeles, CA 90095 (United States); Sandhu, R [Department of Materials Science and Engineering, University of California, Los Angeles, CA 90095 (United States); Heying, B [Northrop Grumman Space Technology, Space and Electronics Group, Redondo Beach, CA 90278 (United States); Hsing, R [Northrop Grumman Space Technology, Space and Electronics Group, Redondo Beach, CA 90278 (United States); Wojtowicz, M [Northrop Grumman Space Technology, Space and Electronics Group, Redondo Beach, CA 90278 (United States); Khan, A [Department of Electrical Engineering, University of South Carolina, Columbia, SC (United States); Goorsky, M S [Department of Materials Science and Engineering, University of California, Los Angeles, CA 90095 (United States)

2003-05-21

This study addressed how defects in SiC substrates influence the crystallographic properties of AlGaN/GaN layers deposited by metallorganic vapour phase epitaxy and by molecular beam epitaxy. We employed double crystal reflection x-ray topography using symmetric (0008) and (00012) reflections with CuK{alpha} radiation ({lambda} = 1.54 A) to image dislocations, micropipes, and low angle boundaries in SiC substrates. Lattice strain near the core of a micropipe defect was estimated to be of the order of 10{sup -7}. The substrates investigated exhibited radial patterns of strain and, primarily, of tilt of the order of tens of arcsec. After deposition of the AlGaN and GaN layers, DCXRT images were generated from the substrate (0008) or (00012) and GaN epitaxial layer (0004) reflections. Full-width at half-maximum values ranging from {approx}100 to 300 arcsec were typical of the GaN reflections, while those of the 4H-SiC reflections were {approx}20-70 arcsec. Micropipes, tilt boundaries, and inclusions in the SiC were shown to produce structural defects in the GaN layers. A clear correlation between SiC substrate defects and GaN defects has been established.

SiC substrate defects and III-N heteroepitaxy

International Nuclear Information System (INIS)

Poust, B D; Koga, T S; Sandhu, R; Heying, B; Hsing, R; Wojtowicz, M; Khan, A; Goorsky, M S

2003-01-01

This study addressed how defects in SiC substrates influence the crystallographic properties of AlGaN/GaN layers deposited by metallorganic vapour phase epitaxy and by molecular beam epitaxy. We employed double crystal reflection x-ray topography using symmetric (0008) and (00012) reflections with CuKα radiation (λ = 1.54 A) to image dislocations, micropipes, and low angle boundaries in SiC substrates. Lattice strain near the core of a micropipe defect was estimated to be of the order of 10 -7 . The substrates investigated exhibited radial patterns of strain and, primarily, of tilt of the order of tens of arcsec. After deposition of the AlGaN and GaN layers, DCXRT images were generated from the substrate (0008) or (00012) and GaN epitaxial layer (0004) reflections. Full-width at half-maximum values ranging from ∼100 to 300 arcsec were typical of the GaN reflections, while those of the 4H-SiC reflections were ∼20-70 arcsec. Micropipes, tilt boundaries, and inclusions in the SiC were shown to produce structural defects in the GaN layers. A clear correlation between SiC substrate defects and GaN defects has been established

A Grande Reportagem no contexto informativo SIC

OpenAIRE

Colaço, Vanessa Alexandra Francisco

2014-01-01

Os telespectadores querem ver grandes reportagens? Como evoluíram as audiências da Grande Reportagem SIC? É este o produto premium da estação? Terá este formato um investimento e continuidade garantidas? Estas são algumas das questões formuladas e às quais se procurou dar resposta neste Relatório de Estágio. Neste trabalho traça-se o perfil do programa Grande Reportagem SIC, clarificando a linha editorial que lhe serviu de base, procurando perceber as suas dinâmicas e passando em revista mome...

High Temperature Memories in SiC Technology

OpenAIRE

Ekström, Mattias

2014-01-01

This thesis is part of the Working On Venus (WOV) project. The aim of the project is to design electronics in silicon carbide (SiC) that can withstand the extreme surface environmen  of Venus. This thesis investigates some possible computer memory technologies that could survive on the surface of Venus. A memory must be able to function at 460 °C and after a total radiation dose of at least 200 Gy (SiC). This thesis is a literature survey. The thesis covers several Random-Access Memory (RAM) ...

Defects induced by helium implantation in SiC

International Nuclear Information System (INIS)

Oliviero, E.; Barbot, J.F.; Declemy, A.; Beaufort, M.F.; Oliviero, E.

2008-01-01

SiC is one of the considered materials for nuclear fuel conditioning and for the fabrication of some core structures in future nuclear generation reactors. For the development of this advance technology, a fundamental research on this material is of prime importance. In particular, the implantation/irradiation effects have to be understood and controlled. It is with this aim that the structural alterations induced by implantation/irradiation in SiC are studied by different experimental techniques as transmission electron microscopy, helium desorption, X-ray diffraction and Rutherford backscattering spectrometry. In this work, the different types of defects induced by helium implantation in SiC, point or primary defects (obtained at low energy (∼100 eV) until spread defects (obtained at higher energy (until ∼2 MeV)) are exposed. The amorphization/recrystallization and swelling phenomena are presented too. (O.M.)

SiC nanocrystals as Pt catalyst supports for fuel cell applications

DEFF Research Database (Denmark)

Dhiman, Rajnish; Morgen, Per; Skou, E.M.

2013-01-01

A robust catalyst support is pivotal to Proton Exchange Membrane Fuel Cells (PEMFCs) to overcome challenges such as catalyst support corrosion, low catalyst utilization and overall capital cost. SiC is a promising candidate material which could be applied as a catalyst support in PEMFCs. Si...... on the nanocrystals of SiC-SPR and SiC-NS by the polyol method. The SiC substrates are subjected to an acid treatment to introduce the surface groups, which help to anchor the Pt nano-catalysts. These SiC based catalysts have been found to have a higher electrochemical activity than commercially available Vulcan...... based catalysts (BASF & HISPEC). These promising results signal a new era of SiC based catalysts for fuel cell applications....

Stress Wave attenuation in SiC3D/Al Composite

International Nuclear Information System (INIS)

Yuan Chunyuan; Wang Yangwei; Li Guoju; Zhang Xu; Gao Jubin

2013-01-01

SiC 3D /Al composite is a kind of special composite with interpenetrating network microstructure. The attenuation properties of stress wave propagation along the SiC 3D /Al composite are studied by a Split Hopkinson Pressure Bar system and FEM simulations, and the attenuation mechanism is discussed in this paper. Results show that the attenuation rate of the stress wave in the composite is up to 1.73MPa·mm −1 . The reduction of the amplitude of waves is caused by that plenty of interfaces between SiC and Al within the composite acting with stress waves. When the incident plane wave reaches the SiC 3D /Al interface, reflection wave and transmission wave propagates in different directions along the irregular interface between SiC phase and aluminium phase due to the impedance mismatch of them, which leads to the divergence of stress wave. At the same time, some stress micro-focuses occurs in the aluminium phase for the complex wave superimposition, and some plastic deformation may take place within such micro-regions, which results in the consumption of stress wave energy. In conclusion, the stress wave attenuation is derived from divergence and consumption of stress wave.

Thermal Diffusivity and Thermal Conductivity of Dispersed Glass Sphere Composites Over a Range of Volume Fractions

Science.gov (United States)

Carson, James K.

2018-06-01

Glass spheres are often used as filler materials for composites. Comparatively few articles in the literature have been devoted to the measurement or modelling of thermal properties of composites containing glass spheres, and there does not appear to be any reported data on the measurement of thermal diffusivities over a range of filler volume fractions. In this study, the thermal diffusivities of guar-gel/glass sphere composites were measured using a transient comparative method. The addition of the glass beads to the gel increased the thermal diffusivity of the composite, more than doubling the thermal diffusivity of the composite relative to the diffusivity of the gel at the maximum glass volume fraction of approximately 0.57. Thermal conductivities of the composites were derived from the thermal diffusivity measurements, measured densities and estimated specific heat capacities of the composites. Two approaches to modelling the effective thermal diffusivity were considered.

Biomimetic synthesis of cellular SiC based ceramics from plant ...

Indian Academy of Sciences (India)

Unknown

SiC based materials so derived can be used in structural applications and in designing high temperature filters and catalyst supports. Keywords. Biomimetic synthesis; carbonaceous biopreform; biomorphic Si–SiC ceramic composites; porous cellular SiC ceramics. 1. Introduction. In recent years, there has been tremendous ...

Reliability Concerns for Flying SiC Power MOSFETs in Space

Science.gov (United States)

Galloway, K. F.; Witulski, A. F.; Schrimpf, R. D.; Sternberg, A. L.; Ball, D. R.; Javanainen, A.; Reed, R. A.; Sierawski, B. D.; Lauenstein, J-M

2018-01-01

SiC power MOSFETs are space-ready in terms of typical reliability measures. However, single event burnout (SEB) often occurs at voltages 50% or lower than specified breakdown. Data illustrating burnout for 1200 V devices is reviewed and the space reliability of SiC MOSFETs is discussed.

Pd/CeO2/SiC Chemical Sensors

Science.gov (United States)

Lu, Weijie; Collins, W. Eugene

2005-01-01

The incorporation of nanostructured interfacial layers of CeO2 has been proposed to enhance the performances of Pd/SiC Schottky diodes used to sense hydrogen and hydrocarbons at high temperatures. If successful, this development could prove beneficial in numerous applications in which there are requirements to sense hydrogen and hydrocarbons at high temperatures: examples include monitoring of exhaust gases from engines and detecting fires. Sensitivity and thermal stability are major considerations affecting the development of high-temperature chemical sensors. In the case of a metal/SiC Schottky diode for a number of metals, the SiC becomes more chemically active in the presence of the thin metal film on the SiC surface at high temperature. This increase in chemical reactivity causes changes in chemical composition and structure of the metal/SiC interface. The practical effect of the changes is to alter the electronic and other properties of the device in such a manner as to degrade its performance as a chemical sensor. To delay or prevent these changes, it is necessary to limit operation to a temperature sensor structures. The present proposal to incorporate interfacial CeO2 films is based partly on the observation that nanostructured materials in general have potentially useful electrical properties, including an ability to enhance the transfer of electrons. In particular, nanostructured CeO2, that is CeO2 with nanosized grains, has shown promise for incorporation into hightemperature electronic devices. Nanostructured CeO2 films can be formed on SiC and have been shown to exhibit high thermal stability on SiC, characterized by the ability to withstand temperatures somewhat greater than 700 C for limited times. The exchanges of oxygen between CeO2 and SiC prevent the formation of carbon and other chemical species that are unfavorable for operation of a SiC-based Schottky diode as a chemical sensor. Consequently, it is anticipated that in a Pd/CeO2/SiC Schottky

Synthesis of boron nitride nanotubes with SiC nanowire as template

International Nuclear Information System (INIS)

Zhong, B.; Song, L.; Huang, X.X.; Wen, G.W.; Xia, L.

2011-01-01

Highlights: → Boron nitride nanotubes (BNNTs) have been fabricated using SiC nanowires as template. → SiC nanowires could be effectively etched out by the vapors decomposed from ammonia borane, leading to the formation of BNNTs. → A template self-sacrificing mechanism is responsible for the formation of BNNTs. -- Abstract: A novel template method for the preparation of boron nitride nanotubes (BNNTs) using SiC nanowire as template and ammonia borane as precursor is reported. We find out that the SiC nanowires could be effectively etched out by the vapors decomposed from ammonia borane, leading to the formation of BNNTs. The as-prepared products are well characterized by means of complementary analytical techniques. A possible formation mechanism is disclosed. The method developed here paves the way for large scale production of BNNTs.

Nanocrystalline SiC film thermistors for cryogenic applications

Science.gov (United States)

Mitin, V. F.; Kholevchuk, V. V.; Semenov, A. V.; Kozlovskii, A. A.; Boltovets, N. S.; Krivutsa, V. A.; Slepova, A. S.; Novitskii, S. V.

2018-02-01

We developed a heat-sensitive material based on nanocrystalline SiC films obtained by direct deposition of carbon and silicon ions onto sapphire substrates. These SiC films can be used for resistance thermometers operating in the 2 K-300 K temperature range. Having high heat sensitivity, they are relatively low sensitive to the magnetic field. The designs of the sensors are presented together with a discussion of their thermometric characteristics and sensitivity to magnetic fields.

Effects of diluents on soot surface temperature and volume fraction in diluted ethylene diffusion flames at pressure

KAUST Repository

Kailasanathan, Ranjith Kumar Abhinavam; Zhang, Ji; Fang, Tiegang; Roberts, William L.

2014-01-01

Soot surface temperature and volume fraction are measured in ethylene/air coflowing laminar diffusion flames at high pressures, diluted with one of four diluents (argon, helium, nitrogen, and carbon dioxide) using a two-color technique. Both

Plasmon-assisted photoluminescence enhancement of SiC nanocrystals by proximal silver nanoparticles

International Nuclear Information System (INIS)

Zhang, N.; Dai, D.J.; Fan, J.Y.

2012-01-01

Highlights: ► We studied metal surface plasmon-enhanced photoluminescence in SiC nanocrystals. ► The integrated emission intensity can be enhanced by 17 times. ► The coupling between SiC emission and Ag plasmon oscillation induces the enhancement. ► The enhancement is tunable with varied spacing thickness of electrolytes. - Abstract: Plasmon-enhanced photoluminescence has wide application potential in many areas, whereas the underlying mechanism is still in debate. We report the photoluminescence enhancement in SiC nanocrystal–Ag nanoparticle coupled system spaced by the poly(styrene sulfonic acid) sodium salt/poly(allylamine hydrochloride) polyelectrolyte bilayers. The integrated luminescence intensity can be improved by up to 17 times. Our analysis indicates that the strong coupling between the SiC nanocrystals and the surface plasmon oscillation of the silver nanoparticles is the major cause of the luminescence enhancement. These findings will help to understand the photoluminescence enhancement mechanism as well as widen the applications of the SiC nanocrystals in photonics and life sciences.

The role of Pd in the transport of Ag in SiC

International Nuclear Information System (INIS)

Olivier, E.J.; Neethling, J.H.

2013-01-01

This paper presents results in support of a newly proposed transport mechanism to account for the release of Ag from intact TRISO particles during HTR reactor operation. The study reveals that the migration of Ag in polycrystalline SiC can occur in association with Pd, a relatively high yield metallic fission product. The migration takes place primarily along grain boundary routes, seen in the form of distinct Pd, Ag and Si containing nodules. Pd is known to rapidly migrate to the SiC and iPyC interface within TRISO particles during operation. It has been shown to chemically corrode the SiC to form palladium silicides. These palladium silicides are found present along SiC grain boundaries in nodule like form. It is suggested that Ag penetrates these nodules together with the palladium silicide, to form a Pd, Ag and Si solution capable of migrating along SiC grain boundaries over time.

The role of Pd in the transport of Ag in SiC

Energy Technology Data Exchange (ETDEWEB)

Olivier, E.J., E-mail: jolivier@nmmu.ac.za [Centre for High Resolution Transmission Electron Microscopy, Nelson Mandela Metropolitan University, Port Elizabeth (South Africa); Neethling, J.H. [Centre for High Resolution Transmission Electron Microscopy, Nelson Mandela Metropolitan University, Port Elizabeth (South Africa)

2013-01-15

This paper presents results in support of a newly proposed transport mechanism to account for the release of Ag from intact TRISO particles during HTR reactor operation. The study reveals that the migration of Ag in polycrystalline SiC can occur in association with Pd, a relatively high yield metallic fission product. The migration takes place primarily along grain boundary routes, seen in the form of distinct Pd, Ag and Si containing nodules. Pd is known to rapidly migrate to the SiC and iPyC interface within TRISO particles during operation. It has been shown to chemically corrode the SiC to form palladium silicides. These palladium silicides are found present along SiC grain boundaries in nodule like form. It is suggested that Ag penetrates these nodules together with the palladium silicide, to form a Pd, Ag and Si solution capable of migrating along SiC grain boundaries over time.

Nucleation and growth of polycrystalline SiC

DEFF Research Database (Denmark)

Kaiser, M.; Schimmel, S.; Jokubavicius, V.

2014-01-01

The nucleation and bulk growth of polycrystalline SiC in a 2 inch PVT setup using isostatic and pyrolytic graphite as substrates was studied. Textured nucleation occurs under near-thermal equilibrium conditions at the initial growth stage with hexagonal platelet shaped crystallites of 4H, 6H and 15......R polytypes. It is found that pyrolytic graphite results in enhanced texturing of the nucleating gas species. Reducing the pressure leads to growth of the crystallites until a closed polycrystalline SiC layer containing voids with a rough surface is developed. Bulk growth was conducted at 35 mbar Ar...

A Comparative Study of Clear Corneal Phacoemulsification with Rigid IOL Versus SICS; the Preferred Surgical Technique in Low Socio-economic group Patients of Rural Areas.

Science.gov (United States)

Devendra, Jaya; Agarwal, Smita; Singh, Pankaj Kumar

2014-11-01

Low socio-economic group patients from rural areas often opt for free cataract surgeries offered by charitable organisations. SICS continues to be a time tested technique for cataract removal in such patients. In recent times, camp patients are sometimes treated by clear corneal phacoemulsification with implantation of a rigid IOL, which being more cost effective is often provided for camp patients. This study was undertaken to find out which surgical technique yielded better outcomes and was more suited for high volume camp surgery. To find the better surgical option- phacoemulsification with rigid IOL or SICS, in poor patients from rural areas. A prospective randomised controlled trial of cataract patients operated by two different techniques. One hundred and twelve eyes were selected and were randomly allocated into two groups of 56 eyes each. At completion of the study, data was analysed for 52 eyes operated by clear corneal phacoemulsification and implantation of a rigid IOL, and 56 eyes operated by SICS. Unpaired t-test was used to calculate the p- value. The results were evaluated on the following criteria. The mean post-operative astigmatism at the end of four weeks - was significantly higher in phacoemulsification group as compared to SICS group The BCVA (best corrected visual acuity) at the end of four weeks - was comparable in both groups. Subjective complaints and/ or complications: In phaco group two patients required sutures and seven had striate keratitis , while none in SICS group. Complaint of irritation was similar in both groups. Surgical time- was less for SICS group as compared to phaco group. SICS by virtue of being a faster surgery with more secure wound and significantly less astigmatism is a better option in camp patients from rural areas as compared to phacoemulsification with rigid IOL.

A randomized trial comparing bladder volume consistency during fractionated prostate radiation therapy

LENUS (Irish Health Repository)

Mullaney, L.

2014-01-10

Organ motion is a contributory factor to the variation in location of the prostate and organs at risk during a course of fractionated prostate radiation therapy (RT). A prospective randomized controlled trial was designed with the primary endpoint to provide evidence-based bladder-filling instructions to achieve a consistent bladder volume (BV) and thus reduce the bladder-related organ motion. The secondary endpoints were to assess the incidence of acute and late genitourinary (GU) and gastrointestinal (GI) toxicity for patients and patients’ satisfaction with the bladder-filling instructions.

PhySIC: a veto supertree method with desirable properties.

Science.gov (United States)

Ranwez, Vincent; Berry, Vincent; Criscuolo, Alexis; Fabre, Pierre-Henri; Guillemot, Sylvain; Scornavacca, Celine; Douzery, Emmanuel J P

2007-10-01

This paper focuses on veto supertree methods; i.e., methods that aim at producing a conservative synthesis of the relationships agreed upon by all source trees. We propose desirable properties that a supertree should satisfy in this framework, namely the non-contradiction property (PC) and the induction property (PI). The former requires that the supertree does not contain relationships that contradict one or a combination of the source topologies, whereas the latter requires that all topological information contained in the supertree is present in a source tree or collectively induced by several source trees. We provide simple examples to illustrate their relevance and that allow a comparison with previously advocated properties. We show that these properties can be checked in polynomial time for any given rooted supertree. Moreover, we introduce the PhySIC method (PHYlogenetic Signal with Induction and non-Contradiction). For k input trees spanning a set of n taxa, this method produces a supertree that satisfies the above-mentioned properties in O(kn(3) + n(4)) computing time. The polytomies of the produced supertree are also tagged by labels indicating areas of conflict as well as those with insufficient overlap. As a whole, PhySIC enables the user to quickly summarize consensual information of a set of trees and localize groups of taxa for which the data require consolidation. Lastly, we illustrate the behaviour of PhySIC on primate data sets of various sizes, and propose a supertree covering 95% of all primate extant genera. The PhySIC algorithm is available at http://atgc.lirmm.fr/cgi-bin/PhySIC.

Passivation of hexagonal SiC surfaces by hydrogen termination

International Nuclear Information System (INIS)

Seyller, Thomas

2004-01-01

Surface hydrogenation is a well established technique in silicon technology. It is easily accomplished by wet-chemical procedures and results in clean and unreconstructed surfaces, which are extremely low in charged surface states and stable against oxidation in air, thus constituting an ideal surface preparation. As a consequence, methods for hydrogenation have been sought for preparing silicon carbide (SiC) surfaces with similar well defined properties. It was soon recognized, however, that due to different surface chemistry new ground had to be broken in order to find a method leading to the desired monatomic hydrogen saturation. In this paper the results of H passivation of SiC surfaces by high-temperature hydrogen annealing will be discussed, thereby placing emphasis on chemical, structural and electronic properties of the resulting surfaces. In addition to their unique properties, hydrogenated hexagonal SiC {0001} surfaces offer the interesting possibility of gaining insight into the formation of silicon- and carbon-rich reconstructions as well. This is due to the fact that to date hydrogenation is the only method providing oxygen-free surfaces with a C to Si ratio of 1:1. Last but not least, the electronic properties of hydrogen-free SiC {0001} surfaces will be alluded to. SiC {0001} surfaces are the only known semiconductor surfaces that can be prepared in their unreconstructed (1 x 1) state with one dangling bond per unit cell by photon induced hydrogen desorption. These surfaces give indications of a Mott-Hubbard surface band structure

Large area SiC coating technology of RBSC for semiconductor processing component

International Nuclear Information System (INIS)

Park, Ji Yeon; Kim, Weon Ju

2001-06-01

As the semiconductor process is developed for the larger area wafer and the larger-scale integration, the processing fixtures are required to have excellent mechanical and high temperature properties. This highlights the importance of silicon carbide-based materials as a substitute for quartz-based susceptors. In this study, SiC coating technology on reaction sintered (RS) SiC with thickness variation of +/- 10% within a diameter of 8 inch by low pressure chemical vapor deposition has been developed for making a plate type SiC fixture such as heater, baffle, etc., with a diameter of 12 inch. Additionally, a state of art on fabrication technology and products of the current commercial SiC fixtures has been described

Large area SiC coating technology of RBSC for semiconductor processing component

Energy Technology Data Exchange (ETDEWEB)

Park, Ji Yeon; Kim, Weon Ju

2001-06-01

As the semiconductor process is developed for the larger area wafer and the larger-scale integration, the processing fixtures are required to have excellent mechanical and high temperature properties. This highlights the importance of silicon carbide-based materials as a substitute for quartz-based susceptors. In this study, SiC coating technology on reaction sintered (RS) SiC with thickness variation of +/- 10% within a diameter of 8 inch by low pressure chemical vapor deposition has been developed for making a plate type SiC fixture such as heater, baffle, etc., with a diameter of 12 inch. Additionally, a state of art on fabrication technology and products of the current commercial SiC fixtures has been described.

Characterisation of 10 kV 10 A SiC MOSFET

DEFF Research Database (Denmark)

Eni, Emanuel-Petre; Incau, Bogdan Ioan; Munk-Nielsen, Stig

2015-01-01

The objective of this paper is to characterize and evaluate the static and dynamic performances of 10 kV 10 A 4H-SIC MOSFETs at high temperatures. The results show good electrical performances of the SiC MOSFETs for high temperature operations. The double-pulse test results showed interesting...

CVD of SiC and AlN using cyclic organometallic precursors

Science.gov (United States)

Interrante, L. V.; Larkin, D. J.; Amato, C.

1992-01-01

The use of cyclic organometallic molecules as single-source MOCVD precursors is illustrated by means of examples taken from our recent work on AlN and SiC deposition, with particular focus on SiC. Molecules containing (AlN)3 and (SiC)2 rings as the 'core structure' were employed as the source materials for these studies. The organoaluminum amide, (Me2AlNH2)3, was used as the AlN source and has been studied in a molecular beam sampling apparatus in order to determine the gas phase species present in a hot-wall CVD reactor environment. In the case of SiC CVD, a series of disilacyclobutanes (Si(XX')CH2)2 (with X and X' = H, CH3, and CH2SiH2CH3), were examined in a cold-wall, hot-stage CVD reactor in order to compare their relative reactivities and prospective utility as single-source CVD precursors. The parent compound, disilacyclobutane, (SiH2CH2)2, was found to exhibit the lowest deposition temperature (ca. 670 C) and to yield the highest purity SiC films. This precursor gave a highly textured, polycrystalline film on the Si(100) substrates.

Effects of morphology and wavelength on the measurement accuracy of soot volume fraction by laser extinction

Science.gov (United States)

Wang, Ya-fei; Huang, Qun-xing; Wang, Fei; Chi, Yong; Yan, Jian-hua

2018-01-01

A novel method to evaluate the quantitative effects of soot morphology and incident wavelength on the measurement accuracy of soot volume fraction, by the laser extinction (LE) technique is proposed in this paper. The results indicate that the traditional LE technique would overestimate soot volume fraction if the effects of morphology and wavelength are not considered. Before the agglomeration of isolated soot primary particles, the overestimation of the LE technique is in the range of 2-20%, and rises with increasing primary particle diameter and with decreasing incident wavelength. When isolated primary particles are agglomerated into fractal soot aggregates, the overestimation would exceed 30%, and rise with increasing primary particle number per soot aggregate, fractal dimension and fractal prefactor and with decreasing incident wavelength to a maximum value of 55%. Finally, based on these results above, the existing formula of the LE technique gets modified, and the modification factor is 0.65-0.77.

Deposition of thin ultrafiltration membranes on commercial SiC microfiltration tubes

DEFF Research Database (Denmark)

Facciotti, Marco; Boffa, Vittorio; Magnacca, Giuliana

2014-01-01

Porous SiC based materials present high mechanical, chemical and thermal robustness, and thus have been largely applied to water-filtration technologies. In this study, commercial SiC microfiltration tubes with nominal pore size of 0.04 m were used as carrier for depositing thin aluminium oxide....... After 5 times coating, a 5.6 µm thick γ-Al2O3 layer was obtained. This membrane shows retention of ~75% for polyethylene glycol molecules with Mn of 8 and 35 kDa, indicating that, despite their intrinsic surface roughness, commercial SiC microfiltration tubes can be applied as carrier for thin...... ultrafiltration membranes. This work also indicates that an improvement of the commercial SiC support surface smoothness may greatly enhance permeance and selectivity of Υ-Al2O3 ultrafiltration membranes by allowing the deposition of thinner defect-free layers....

White light emission from fluorescent SiC with porous surface

DEFF Research Database (Denmark)

Lu, Weifang; Ou, Yiyu; Fiordaliso, Elisabetta Maria

2017-01-01

We report for the frst time a NUV light to white light conversion in a N-B co-doped 6H-SiC (fuorescent SiC) layer containing a hybrid structure. The surface of fuorescent SiC sample contains porous structures fabricated by anodic oxidation method. After passivation by 20nm thick Al2O3, the photol......We report for the frst time a NUV light to white light conversion in a N-B co-doped 6H-SiC (fuorescent SiC) layer containing a hybrid structure. The surface of fuorescent SiC sample contains porous structures fabricated by anodic oxidation method. After passivation by 20nm thick Al2O3...... the bulk fuorescent SiC layer. A high color rendering index of 81.1 has been achieved. Photoluminescence spectra in porous layers fabricated in both commercial n-type and lab grown N-B co-doped 6H-SiC show two emission peaks centered approximately at 460nm and 530nm. Such bluegreen emission phenomenon can......, the photoluminescence intensity from the porous layer was signifcant enhanced by a factor of more than 12. Using a porous layer of moderate thickness (~10µm), high-quality white light emission was realized by combining the independent emissions of blue-green emission from the porous layer and yellow emission from...

Assessment of vasodilator therapy in patients with severe congestive heart failure: limitations of measurements of left ventricular ejection fraction and volumes

International Nuclear Information System (INIS)

Firth, B.G.; Dehmer, G.J.; Markham, R.V. Jr.; Willerson, J.T.; Hillis, L.D.

1982-01-01

Although noninvasive techniques are often used to assess the effect of vasodilator therapy in patients with congestive heart failure, it is unknown whether changes in noninvasively determined left ventricular ejection fraction, volume, or dimension reliably reflect alterations in intracardiac pressure and flow. Accordingly, we compared the acute effect of sodium nitroprusside on left ventricular volume and ejection fraction (determined scintigraphically) with its effect on intracardiac pressure and forward cardiac index (determined by thermodilution) in 12 patients with severe, chronic congestive heart failure and a markedly dilated left ventricle. Nitroprusside (infused at 1.3 +/- 1.1 [mean +/- standard deviation] microgram/kg/min) caused a decrease in mean systemic arterial, mean pulmonary arterial, and mean pulmonary capillary wedge pressure as well as a concomitant increase in forward cardiac index. Simultaneously, left ventricular end-diastolic and end-systolic volume indexes decreased, but the scintigraphically determined cardiac index did not change significantly. Left ventricular ejection fraction averaged 0.19 +/- 0.05 before nitroprusside administration and increased by less than 0.05 units in response to nitroprusside in 11 of 12 patients. The only significant correlation between scintigraphically and invasively determined variables was that between the percent change in end-diastolic volume index and the percent change in pulmonary capillary wedge pressure (r . 0.68, p . 0.01). Although nitroprusside produced changes in scintigraphically determined left ventricular ejection fraction, end-systolic volume index, and cardiac index, these alterations bore no predictable relation to changes in intracardiac pressure, forward cardiac index, or vascular resistance. Furthermore, nitroprusside produced a considerably greater percent change in the invasively measured variables than in the scintigraphically determined ones

Influence of load and reinforcement content on selected tribological properties of Al/SiC/Gr hybrid composites

Directory of Open Access Journals (Sweden)

Sandra Veličković

2018-04-01

Full Text Available Hybrid materials with the metal matrix are important engineering materials due to their outstanding mechanical and tribological properties. Here are presented selected tribological properties of the hybrid composites with the matrix made of aluminum alloy and reinforced by the silicon carbide and graphite particles. The tribological characteristics of such materials are superior to characteristics of the matrix – the aluminum alloy, as well as to characteristics of the classical metal-matrix composites with a single reinforcing material. Those characteristics depend on the volume fractions of the reinforcing components, sizes of the reinforcing particles, as well as on the fabrication process of the hybrid composites. The considered tribological characteristics are the friction coefficient and the wear rate as functions of the load levels and the volume fractions of the graphite and the SiC particles. The wear rate increases with increase of the load and the Gr particles content and with reduction of the SiC particles content. The friction coefficient increases with the load, as well as with the SiC particles content increase.

Strength and conductivity of unidirectional copper composites reinforced by continuous SiC fibers

International Nuclear Information System (INIS)

Kimmig, S.; Allen, I.; You, J.H.

2013-01-01

A SiC long fiber-reinforced copper composite offers a beneficial combination of high strength and high thermal conductivity at elevated temperatures. Both properties make the composite a promising material for the heat sink of high-heat-flux components. In this work, we developed a novel Cu/SiC f composite using the Sigma fiber. Based on HIP technique, a metallurgical process was established for fabricating high quality specimens using a TiC interface coating. Extensive tensile tests were conducted on the unidirectionally reinforced composite at 20 °C and 300 °C for a wide range of fiber volume fraction (V f ). In this paper, a large amount of test data is presented. The transversal thermal conductivity varies from 260 to 130 W/mK at 500 °C as V f is increased from 13% to 37%. The tensile strength reached up to 1246 MPa at 20 °C for V f = 37.6%, where the fracture strain was limited to 0.8%. The data of both elastic modulus and ultimate strength exhibited a good agreement with the rule-of-mixture predictions indicating a high quality of the materials. The strength of the composite with the Sigma fibers turned out to be superior to those of the SCS6 fibers at 300 °C, although the SCS6 fiber actually has a higher strength than the Sigma fiber. The fractographic pictures of tension test and fiber push-out test manifested a sufficient interfacial bonding

System modeling and identification in indicator dilution method for assessment of ejection fraction and pulmonary blood volume

NARCIS (Netherlands)

Bharath, H.N.; Prabhu, K.M.M.; Korsten, H.H.M.; Mischi, M.

2012-01-01

Clinically relevant cardiovascular parameters, such as pulmonary blood volume (PBV) and ejection fraction (EF), can be assessed through indicator dilution techniques. Among these techniques, which are typically invasive due to the need for central catheterization, contrast ultrasonography provides a

Qualification of SiC materials for fusion and fission reactors

International Nuclear Information System (INIS)

Ryazanov, Alexander

2009-01-01

Ceramic materials such as silicon carbide (SiC) and SiC/SiC composites are both considered, due to their high-temperature strength, pseudo-ductile fracture behavior and low-induced radioactivity, as candidate materials for fusion reactor (test blanket module for ITER) and high temperature gas-cooled reactors (HTGR). The radiation swelling and creep of SiC are very important physical phenomena that determine the radiation resistance of them in these reactors. Other important problem which exists especially in fusion reactor is an effect of accumulation of high concentrations of helium atoms in SiC (up to 15000-20000 at.ppm) due to (n,α) nuclear reaction on physical mechanical properties. An understanding of the physical mechanism of this phenomenon is very important for the investigations of helium atom effect on radiation swelling in SiC. In this report a compilation of non-irradiated and irradiated properties of SiC are provided and analyzed in terms of their application to fusion and high temperature gas cooled reactors. Special topic of this report is oriented on the micro structural changes in chemically vapor-deposited (CVD) high-purity beta-SiC during neutron and ion irradiations at elevated temperatures. The evolutions of various radiation induced defects including dislocation loops, network dislocations and cavities are presented here as a function of irradiation temperature and fluencies. These observations are discussed in relation with such irradiation phenomena in SiC as low temperature swelling and cavity swelling. One of the main difficulties in the radiation damage studies of SiC materials lies in the absence of theoretical models and interpretation of many physical mechanisms of radiation phenomena including the radiation swelling and creep. The point defects in ceramic materials are characterized by the charge states and they can have an effective charge. The internal effective electrical field is formed due to the accumulation of charged point

10kV SiC MOSFET split output power module

DEFF Research Database (Denmark)

Beczkowski, Szymon; Li, Helong; Uhrenfeldt, Christian

2015-01-01

The poor body diode performance of the first generation of 10kV SiC MOSFETs and the parasitic turn-on phenomenon limit the performance of SiC based converters. Both these problems can potentially be mitigated using a split output topology. In this paper we present a comparison between a classical...

Energy efficiency improvement target for SIC 34 - fabricated metal products

Energy Technology Data Exchange (ETDEWEB)

Byrer, T. G.; Billhardt, C. F.; Farkas, M. S.

1977-03-15

A March 15, 1977 revision of a February 15, 1977 document on the energy improvement target for the Fabricated Metal Products industry (SIC 34) is presented. A net energy savings in 1980 of 24% as compared with 1972 energy consumption in SIC 34 is considered a realistic goal. (ERA citation 04:045008)

SiC Coating Process Development Using H-PCS in Supercritical CO2

International Nuclear Information System (INIS)

Park, Kwangheon; Jung, Wonyoung

2013-01-01

We tried SiC coating using supercritical fluids. Supercritical fluids are the substance exists over critical temperature and critical pressure. It is hard to expect that there would be a big change as single-solvent as the fluid is incompressible and the space between the molecules is almost steady. But the fluid which is being supercritical can bring a great change when it is changed its pressure near its critical point, showing its successive change in the density, viscosity, diffusion coefficient and the polarity. We have tested the 'H-PCS into SiC' coating experiment with supercritical CO 2 which has the high penetration, low viscosity as well as the high density and the high solubility that shows the property of the fluid. This experiment is for SiC coating using H-PCS in supercritical CO 2 . It shows the clear difference that the penetration of H-PCS into the SiC between dip coating method and using the supercritical CO 2 If we can make a metal cladding with SiC composites as a protective layer, the use of the cladding will be very broad and diverse. Inherent safe nuclear fuels can be possible that can stand under severe accident conditions. SiC is known to be one of a few materials that maintain very corrosion-resistant properties under tough corrosive environments. The metal cladding with SiC composites as a protective layer will be a high-tech product that can be used in many applications including chemical, material, and nuclear engineering and etc

Tema 8. Principis físics dels semiconductors (Guia del tema)

OpenAIRE

Beléndez Vázquez, Augusto

2011-01-01

Guia del "Tema 8. Principis físics dels semiconductors" de l'assignatura "Fonaments Físics de l'Enginyeria I" de "Grau en Enginyeria en So i Imatge" impartit a l'Escola Politècnica Superior de la Universitat d'Alacant.

Diodes of nanocrystalline SiC on n-/n+-type epitaxial crystalline 6H-SiC

Science.gov (United States)

Zheng, Junding; Wei, Wensheng; Zhang, Chunxi; He, Mingchang; Li, Chang

2018-03-01

The diodes of nanocrystalline SiC on epitaxial crystalline (n-/n+)6H-SiC wafers were investigated, where the (n+)6H-SiC layer was treated as cathode. For the first unit, a heavily boron doped SiC film as anode was directly deposited by plasma enhanced chemical vapor deposition method on the wafer. As to the second one, an intrinsic SiC film was fabricated to insert between the wafer and the SiC anode. The third one included the SiC anode, an intrinsic SiC layer and a lightly phosphorus doped SiC film besides the wafer. Nanocrystallization in the yielded films was illustrated by means of X-ray diffraction, transmission electronic microscope and Raman spectrum respectively. Current vs. voltage traces of the obtained devices were checked to show as rectifying behaviors of semiconductor diodes, the conduction mechanisms were studied. Reverse recovery current waveforms were detected to analyze the recovery performance. The nanocrystalline SiC films in base region of the fabricated diodes are demonstrated as local regions for lifetime control of minority carriers to improve the reverse recovery properties.

Effect of Ti and Si interlayer materials on the joining of SiC ceramics

Energy Technology Data Exchange (ETDEWEB)

Jung, Yang Il; Park, Jung Hwan; Kim, Hyun Gil; Park, Dong Jun; Park, Jeong Yong; Kim, Weon Ju [LWR Fuel Technology Division, Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

2016-08-15

SiC-based ceramic composites are currently being considered for use in fuel cladding tubes in light-water reactors. The joining of SiC ceramics in a hermetic seal is required for the development of ceramic-based fuel cladding tubes. In this study, SiC monoliths were diffusion bonded using a Ti foil interlayer and additional Si powder. In the joining process, a very low uniaxial pressure of ∼0.1 MPa was applied, so the process is applicable for joining thin-walled long tubes. The joining strength depended strongly on the type of SiC material. Reaction-bonded SiC (RB-SiC) showed a higher joining strength than sintered SiC because the diffusion reaction of Si was promoted in the former. The joining strength of sintered SiC was increased by the addition of Si at the Ti interlayer to play the role of the free Si in RB-SiC. The maximum joint strength obtained under torsional stress was ∼100 MPa. The joint interface consisted of TiSi{sub 2}, Ti{sub 3}SiC{sub 2}, and SiC phases formed by a diffusion reaction of Ti and Si.

Micromechanics of fiber pull-out and crack bridging in SCS-6 SiC- CVD SiC composite system at high-temperature

International Nuclear Information System (INIS)

El-Azab, A.; Ghoniem, N.M.

1993-01-01

A micro mechanical model is developed to study fiber pull-out and crack bridging in fiber reinforced SiC-SiC composites with time dependent thermal creep. By analyzing the creep data for monolithic CVD SiC (matrix) and the SCS-6 SiC fibers in the temperature range 900-1250 degrees C, it is found that the matrix creep rates can be ignored in comparison to those of fibers. Two important relationships are obtained: (1) a time dependent relation between the pull-out stress and the relative sliding distance between the fiber and matrix for the purpose of analyzing pull-out experiments, and (2) the relation between the bridging stress and the crack opening displacement to be used in studying the mechanics and stability of matrix crack bridged by fibers at high temperatures. The present analysis can also be applied to Nicalon-reinforced CVD SiC matrix system since the Nicalon fibers exhibit creep characteristics similar to those of the SCS-6 fibers

SiC Optically Modulated Field-Effect Transistor

Science.gov (United States)

Tabib-Azar, Massood

2009-01-01

An optically modulated field-effect transistor (OFET) based on a silicon carbide junction field-effect transistor (JFET) is under study as, potentially, a prototype of devices that could be useful for detecting ultraviolet light. The SiC OFET is an experimental device that is one of several devices, including commercial and experimental photodiodes, that were initially evaluated as detectors of ultraviolet light from combustion and that could be incorporated into SiC integrated circuits to be designed to function as combustion sensors. The ultraviolet-detection sensitivity of the photodiodes was found to be less than desired, such that it would be necessary to process their outputs using high-gain amplification circuitry. On the other hand, in principle, the function of the OFET could be characterized as a combination of detection and amplification. In effect, its sensitivity could be considerably greater than that of a photodiode, such that the need for amplification external to the photodetector could be reduced or eliminated. The experimental SiC OFET was made by processes similar to JFET-fabrication processes developed at Glenn Research Center. The gate of the OFET is very long, wide, and thin, relative to the gates of typical prior SiC JFETs. Unlike in prior SiC FETs, the gate is almost completely transparent to near-ultraviolet and visible light. More specifically: The OFET includes a p+ gate layer less than 1/4 m thick, through which photons can be transported efficiently to the p+/p body interface. The gate is relatively long and wide (about 0.5 by 0.5 mm), such that holes generated at the body interface form a depletion layer that modulates the conductivity of the channel between the drain and the source. The exact physical mechanism of modulation of conductivity is a subject of continuing research. It is known that injection of minority charge carriers (in this case, holes) at the interface exerts a strong effect on the channel, resulting in amplification

SYLRAMICTM SiC fibers for CMC reinforcement

International Nuclear Information System (INIS)

Jones, Richard E.; Petrak, Dan; Rabe, Jim; Szweda, Andy

2000-01-01

Dow Corning researchers developed SYLRAMIC SiC fiber specifically for use in ceramic-matrix composite (CMC) components for use in turbine engine hot sections where excellent thermal stability, high strength and high thermal conductivity are required. This is a stoichiometric SiC fiber with a high degree of crystallinity, high tensile strength, high tensile modulus and good thermal conductivity. Owing to the small diameter, this textile-grade fiber can be woven into 2-D and 3-D structures for CMC fabrication. These properties are also of high interest to the nuclear community. Some initial studies have shown that SYLRAMIC fiber shows very good dimensional stability in a neutron flux environment, which offers further encouragement. This paper will review the properties of SYLRAMIC SiC fiber and then present the properties of polymer impregnation and pyrolysis (PIP) processed CMC made with this fiber at Dow Corning. While these composites may not be directly applicable to applications of interest to this audience, we believe that the properties shown will give good evidence that the fiber should be suitable for high temperature structural applications in the nuclear arena

ToF-MEIS stopping measurements in thin SiC films

International Nuclear Information System (INIS)

Linnarsson, M.K.; Khartsev, S.; Primetzhofer, D.; Possnert, G.; Hallén, A.

2014-01-01

Electronic stopping in thin, amorphous, SiC films has been studied by time-of-flight medium energy ion scattering and conventional Rutherford backscattering spectrometry. Amorphous SiC films (8, 21 and 36 nm) were prepared by laser ablation using a single crystalline silicon carbide target. Two kinds of substrate films, one with a lower atomic mass (carbon) and one with higher atomic mass (iridium) compared to silicon has been used. Monte Carlo simulations have been used to evaluate electronic stopping from the shift in energy for the signal scattered from Ir with and without SiC. The two kinds of samples are used to illustrate the strength and challenges for ToF-MEIS compared to conventional RBS

Preparation of biomorphic SiC ceramic by carbothermal reduction of oak wood charcoal

International Nuclear Information System (INIS)

Qian Junmin; Wang Jiping; Jin Zhihao

2004-01-01

Highly porous silicon carbide (SiC) ceramic with woodlike microstructure has been prepared at 1400-1600 deg. C by carbothermal reduction reaction of charcoal/silica composites in static argon atmosphere. These composites were fabricated by infiltrating silica sol into a porous biocarbon template from oak wood using a vacuum/pressure infiltration process. The morphology of resulting porous SiC ceramic, as well as the conversion mechanism of wood to porous SiC ceramic, have been investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) techniques. Experimental results show that the biomorphic cellular morphology of oak wood charcoal is remained in the porous SiC ceramic with high precision that consists of β-SiC with traces of α-SiC. Silica in the charcoal/silica composites exists in the cellular pores in form of fibers and rods. The SiC strut material is formed by gas-solid reaction between SiO (g) and C (s) during the charcoal-to-ceramic conversion. The densification of SiC strut material may occur at moderate temperatures and holding time

Preparation of biomorphic SiC ceramic by carbothermal reduction of oak wood charcoal

Energy Technology Data Exchange (ETDEWEB)

Qian Junmin; Wang Jiping; Jin Zhihao

2004-04-25

Highly porous silicon carbide (SiC) ceramic with woodlike microstructure has been prepared at 1400-1600 deg. C by carbothermal reduction reaction of charcoal/silica composites in static argon atmosphere. These composites were fabricated by infiltrating silica sol into a porous biocarbon template from oak wood using a vacuum/pressure infiltration process. The morphology of resulting porous SiC ceramic, as well as the conversion mechanism of wood to porous SiC ceramic, have been investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) techniques. Experimental results show that the biomorphic cellular morphology of oak wood charcoal is remained in the porous SiC ceramic with high precision that consists of {beta}-SiC with traces of {alpha}-SiC. Silica in the charcoal/silica composites exists in the cellular pores in form of fibers and rods. The SiC strut material is formed by gas-solid reaction between SiO (g) and C (s) during the charcoal-to-ceramic conversion. The densification of SiC strut material may occur at moderate temperatures and holding time.

Feasibility study on the application of carbide (ZrC, SiC) for VHTR

Energy Technology Data Exchange (ETDEWEB)

Park, Ji Yeon; Kim, Weon Ju; Jung, Choong Hwan; Ryu, Woo Seog; Kim, Si Hyeong; Jang, Moon Hee; Lee, Young Woo

2006-08-15

A feasibility study on the coating process of ZrC for the TRISO nuclear fuel and applications of SiC as high temperature materials for the core components has performed to develop the fabrication process for the advanced ZrC TRISO fuels and the high temperature structural components for VHTR, respectively. In the case of ZrC coating, studies were focused on the comparisons of the developed coating processes for screening of our technology, the evaluations of the reactions parameters for a ZrC deposition by the thermodynamic calculations and the preliminary coating experiments by the chloride process. With relate to SiC ceramics, our interesting items are as followings; an analysis of applications and specifications of the SiC components and collections of the SiC properties and establishments of data base. For these purposes, applications of SiC ceramics for the GEN-IV related components as well as the fusion reactor related ones were reviewed. Additionally, the on-going activities with related to the ZrC clad and the SiC composites discussed in the VHTR GIF-PMB, were reviewed to make the further research plans at the section 1 in chapter 3.

Microwave joining of SiC

Energy Technology Data Exchange (ETDEWEB)

Silberglitt, R.; Ahmad, I. [FM Technologies, Inc., Fairfax, VA (United States); Black, W.M. [George Mason Univ., Fairfax, VA (United States)] [and others

1995-05-01

The purpose of this work is to optimize the properties of SiC-SiC joints made using microwave energy. The current focus is on optimization of time-temperature profiles, production of SiC from chemical precursors, and design of new applicators for joining of long tubes.

The effect of the volume fraction and viscosity on the compression and tension behavior of the cobalt-ferrite magneto-rheological fluids

Directory of Open Access Journals (Sweden)

H. Shokrollahi

2016-03-01

Full Text Available The purpose of this work is to investigate the effects of the volume fraction and bimodal distribution of solid particles on the compression and tension behavior of the Co-ferrite-based magneto-rheological fluids (MRFs containing silicon oil as a carrier. Hence, Co-ferrite particles (CoFe2O4 with two various sizes were synthesized by the chemical co-precipitation method and mixed so as to prepare the bimodal MRF. The X-Ray Diffraction (XRD analysis, Fourier Transform Infrared Spectroscopy (FTIR, Laser Particle Size Analysis (LPSA and Vibrating Sample Magnetometer (VSM were conducted to examine the structural and magnetic properties, respectively. The results indicated that the increase of the volume fraction has a direct increasing influence on the values of the compression and tension strengths of fluids. In addition, the compression and tension strengths of the mixed MRF sample (1.274 and 0.647 MPa containing 60 and 550 nm samples were higher than those of the MRF sample with the same volume fraction and uniform particle size of 550 nm.

Properties of SiC semiconductor detector of fast neutrons investigated using MCNPX code

International Nuclear Information System (INIS)

Sedlakova, K.; Sagatova, A.; Necas, V.; Zatko, B.

2013-01-01

The potential of silicon carbide (SiC) for use in semiconductor nuclear radiation detectors has been long recognized. The wide bandgap of SiC (3.25 eV for 4H-SiC polytype) compared to that for more conventionally used semiconductors, such as silicon (1.12 eV) and germanium (0.67 eV), makes SiC an attractive semiconductor for use in high dose rate and high ionization nuclear environments. The present work focused on the simulation of particle transport in SiC detectors of fast neutrons using statistical analysis of Monte Carlo radiation transport code MCNPX. Its possibilities in detector design and optimization are presented.(authors)

Determination of irradiation temperature using SiC temperature monitors

International Nuclear Information System (INIS)

Maruyama, Tadashi; Onose, Shoji

1999-01-01

This paper describes a method for detecting the change in length of SiC temperature monitors and a discussion is made on the relationship between irradiation temperature and the recovery in length of SiC temperature monitors. The SiC specimens were irradiated in the experimental fast reactor JOYO' at the irradiation temperatures around 417 to 645degC (design temperature). The change in length of irradiated specimens was detected using a dilatometer with SiO 2 glass push rod in an infrared image furnace. The temperature at which recovery in macroscopic length begins was obtained from the annealing intersection temperature. The results of measurements indicated that a difference between annealing intersection temperature and the design temperature sometimes reached well over ±100degC. A calibration method to obtain accurate irradiation temperature was presented and compared with the design temperature. (author)

Systematic Investigation of Magnetostriction in Composite Magnetorheological Elastomers: the Effect of Particle Shape, Alignment, and Volume Fraction

Science.gov (United States)

Kassner, Christopher; Rieger, William; von Lockette, Paris; Lofland, Samuel

2013-03-01

We have completed a study of the magnetoelastic properties of several types of magnetorheological elastomers (MREs), composites consisting of magnetic particles cured in an elastic matrix. We have made a number of samples with different particle arrangements (pseudo-random and aligned), volume fraction, and particle shape (rods, spheres, and disks) and measured the field dependent strain in order to determine the magnetostriction. We found that the magnetostriction in these samples is highly dependent on the sample particle shape (aspect ratio) and volume fraction and ordering to a lesser extent. While much of the past work has focused on spherical particles, our results indicate that both rods and disks can yield enhanced results. We discuss our findings in terms of magnetic energy of the particles and elastic energy of the matrix. We then consider the issue of optimization. This work was supported in part by NSF Grant CMMI - 0927326.

Synthesis of nanostructured SiC using the pulsed laser deposition technique

International Nuclear Information System (INIS)

Zhang, H.X.; Feng, P.X.; Makarov, V.; Weiner, B.R.; Morell, G.

2009-01-01

We report the new results on the direct synthesis of nanostructured silicon carbide (SiC) materials using the pulsed laser deposition technique. Scanning electron microscopy images revealed that SiC nanoholes, nanosprouts, nanowires, and nanoneedles were obtained. The crystallographic structure, chemical composition, and bond structure of the nanoscale SiC materials were investigated using X-ray diffraction, energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and Raman scattering spectroscopy. The transverse optical mode and longitudinal optical mode in Raman spectra were found to become sharper as the substrate temperature was increased, while the material structure evolved from amorphous to crystalline

Fabrication of SiC nanopillars by inductively coupled SF6/O2 plasma etching

International Nuclear Information System (INIS)

Choi, J H; Bano, E; Latu-Romain, L; Dhalluin, F; Chevolleau, T; Baron, T

2012-01-01

In this paper, we demonstrate a top-down fabrication technique for nanometre scale silicon carbide (SiC) pillars using inductively coupled plasma etching. A set of experiments in SF 6 -based plasma was carried out in order to realize high aspect ratio SiC nanopillars. The etched SiC nanopillars using a small circular mask pattern (115 nm diameter) show high aspect ratio (7.4) with a height of 2.2 µm at an optimum bias voltage (300 V) and pressure (6 mTorr). Under the optimal etching conditions using a large circular mask pattern with 370 nm diameter, the obtained SiC nanopillars exhibit high anisotropy features (6.4) with a large etch depth (>7 µm). The etch characteristic of the SiC nanopillars under these conditions shows a high etch rate (550 nm min -1 ) and a high selectivity (over 60 for Ni). We also studied the etch profile of the SiC nanopillars and mask evolution over the etching time. As the mask pattern size shrinks in nanoscale, vertical and lateral mask erosion plays a crucial role in the etch profile of the SiC nanopillars. Long etching process makes the pillars appear with a hexagonal shape, coming from the crystallographic structure of α-SiC. It is found that the feature of pillars depends not only on the etching process parameters, but also on the crystallographic structure of the SiC phase. (paper)

Highly flexible and robust N-doped SiC nanoneedle field emitters

KAUST Repository

Chen, Shanliang

2015-01-23

Flexible field emission (FE) emitters, whose unique advantages are lightweight and conformable, promise to enable a wide range of technologies, such as roll-up flexible FE displays, e-papers and flexible light-emitting diodes. In this work, we demonstrate for the first time highly flexible SiC field emitters with low turn-on fields and excellent emission stabilities. n-Type SiC nanoneedles with ultra-sharp tips and tailored N-doping levels were synthesized via a catalyst-assisted pyrolysis process on carbon fabrics by controlling the gas mixture and cooling rate. The turn-on field, threshold field and current emission fluctuation of SiC nanoneedle emitters with an N-doping level of 7.58 at.% are 1.11 V μm-1, 1.55 V μm-1 and 8.1%, respectively, suggesting the best overall performance for such flexible field emitters. Furthermore, characterization of the FE properties under repeated bending cycles and different bending states reveal that the SiC field emitters are mechanically and electrically robust with unprecedentedly high flexibility and stabilities. These findings underscore the importance of concurrent morphology and composition controls in nanomaterial synthesis and establish SiC nanoneedles as the most promising candidate for flexible FE applications. © 2015 Nature Publishing Group All rights reserved.

Highly flexible and robust N-doped SiC nanoneedle field emitters

KAUST Repository

Chen, Shanliang; Ying, Pengzhan; Wang, Lin; Wei, Guodong; Gao, Fengmei; Zheng, Jinju; Shang, Minhui; Yang, Zuobao; Yang, Weiyou; Wu, Tao

2015-01-01

Flexible field emission (FE) emitters, whose unique advantages are lightweight and conformable, promise to enable a wide range of technologies, such as roll-up flexible FE displays, e-papers and flexible light-emitting diodes. In this work, we demonstrate for the first time highly flexible SiC field emitters with low turn-on fields and excellent emission stabilities. n-Type SiC nanoneedles with ultra-sharp tips and tailored N-doping levels were synthesized via a catalyst-assisted pyrolysis process on carbon fabrics by controlling the gas mixture and cooling rate. The turn-on field, threshold field and current emission fluctuation of SiC nanoneedle emitters with an N-doping level of 7.58 at.% are 1.11 V μm-1, 1.55 V μm-1 and 8.1%, respectively, suggesting the best overall performance for such flexible field emitters. Furthermore, characterization of the FE properties under repeated bending cycles and different bending states reveal that the SiC field emitters are mechanically and electrically robust with unprecedentedly high flexibility and stabilities. These findings underscore the importance of concurrent morphology and composition controls in nanomaterial synthesis and establish SiC nanoneedles as the most promising candidate for flexible FE applications. © 2015 Nature Publishing Group All rights reserved.

Effect of Carbon Concentration on the Sputtering of Carbon-Rich SiC Bombarded by Helium Ions

Directory of Open Access Journals (Sweden)

Xinghao Liang

2018-02-01

Full Text Available Silicon carbide (SiC is considered as an important material for nuclear engineering due to its excellent properties. Changing the carbon content in SiC can regulate and control its elastic and thermodynamic properties, but a simulation study of the effect of carbon content on the sputtering (caused by the helium ions of SiC is still lacking. In this work, we used the Monte-Carlo and molecular dynamics simulation methods to study the effects of carbon concentration, incidence energy, incident angle, and target temperature on the sputtering yield of SiC. The results show that the incident ions’ energy and angle have a significant effect on sputtering yield of SiC when the carbon concentration in SiC is around 62 at %, while the target temperature has a little effect on the sputtering yield of SiC. Our work might provide theoretical support for the experimental research and engineering application of carbon fiber-reinforced SiC that be used as the plasma-facing material in tokamak fusion reactors.

Effects of SiC and MgO on aluminabased ceramic foams filters

OpenAIRE

CAO Da-li; ZHOU Jing-yi; JIN Yong-ming

2007-01-01

Alumina-based foam ceramic filters were fabricated by using alumina, SiC, magnesia powder as major materials. It has been found that this ceramic filter has a uniform macrostructure for filtering molten metals. The influences of SiC and magnesia content, the sintering temperatures on ceramic properties were discussed. Aluminabased foam ceramic filters containing 2.2 mass% magnesia and 7.6 mass% SiC has a compressive strength of 1.36 MPa and a thermal shock resistance of 5 times. Its main phas...

Heteroepitaxy of zinc-blende SiC nano-dots on Si substrate by organometallic ion beam

International Nuclear Information System (INIS)

Matsumoto, T.; Kiuchi, M.; Sugimoto, S.; Goto, S.

2006-01-01

The self-assembled SiC nano-dots were fabricated on Si(111) substrate at low-temperatures using the organometallic ion beam deposition technique. The single precursor of methylsilicenium ions (SiCH 3 + ) with the energy of 100 eV was deposited on Si(111) substrate at 500, 550 and 600 deg. C. The characteristics of the self-assembled SiC nano-dots were analyzed by reflection high-energy electron diffraction (RHEED), Raman spectroscopy and atomic force microscope (AFM). The RHEED patterns showed that the crystal structure of the SiC nano-dots formed on Si(111) substrate was zinc-blende SiC (3C-SiC) and it was heteroepitaxy. The self-assembled SiC nano-dots were like a dome in shape, and their sizes were the length of 200-300 nm and the height of 10-15 nm. Despite the low-temperature of 500 deg. C as SiC crystallization the heteroepitaxial SiC nano-dots were fabricated on Si(111) substrate using the organometallic ion beam

Microstructure of SiC ceramics fabricated by pyrolysis of electron beam irradiated polycarbomethylsilane containing precursors

International Nuclear Information System (INIS)

Xu Yunshu; Tanaka, Shigeru

2003-01-01

A modified gel-casting method was developed to form the ceramics precursor matrix by using polycarbomehylsilane (PCMS) and SiC powder. The polymer precursor was mixed with SiC powder in toluene, and then the slurry samples were cast into designed shapes. The pre-ceramic samples were then irradiated by 2.0 MeV electron beam generated by a Cockcroft-Walton type accelerator in He gas flow to about 15 MGy. The cured samples were pyrolyzed and sintered into SiC ceramics at 1300degC in Ar gas. The modified gel-casting method leaves almost no internal stress in the pre-ceramic samples, and the electron beam curing not only diminished the amount of pyrolysis gaseous products but also enhanced the interface binding of the polymer converted SiC and the grains of SiC powder. Optical microscope, AFM and SEM detected no visible internal or surface cracks in the final SiC ceramics matrix. A maximum value of 122 MPa of flexural strength of the final SiC ceramics was achieved. (author)

Spherical nanostructured Si/C composite prepared by spray drying technique for lithium ion batteries anode

Energy Technology Data Exchange (ETDEWEB)

Chen Libao [Energy Science and Technology Laboratory, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050 (China); Graduate School of Chinese Academy of Sciences, Beijing 100049 (China); Xie Xiaohua [Energy Science and Technology Laboratory, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050 (China); Graduate School of Chinese Academy of Sciences, Beijing 100049 (China); Wang Baofeng [Department of Chemical Engineering, Shanghai Jiao Tong University, Shanghai 200240 (China); Wang Ke [Energy Science and Technology Laboratory, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050 (China); Xie Jingying [Energy Science and Technology Laboratory, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050 (China) and Graduate School of Chinese Academy of Sciences, Beijing 100049 (China)]. E-mail: jyxie@mail.sim.ac.cn

2006-07-15

Spherical nanostructured Si/C composite was prepared by spray drying technique, followed by heat treatment, in which nanosized silicon and fine graphite particles were homogeneously embedded in carbon matrix pyrolyzed by phenol formaldehyde resin. Cyclic voltammetry tests showed two pairs of redox peaks corresponding to lithiation and delithiation of Si/C composite. The Si/C composite exhibited a reversible capacity of 635 mAh g{sup -1} and good cycle performance used in lithium ion batteries. To improve cycle performance of this Si/C composite further, the carbon-coated Si/C composite was synthesized by the second spray drying and heat treatment processing. The cycle performance of carbon-coated Si/C composite was improved significantly, which was attributed to the formation of stable SEI passivation layers on the outer surface of carbon shell which protected the bared silicon from exposing to electrolyte directly.

Spherical nanostructured Si/C composite prepared by spray drying technique for lithium ion batteries anode

International Nuclear Information System (INIS)

Chen Libao; Xie Xiaohua; Wang Baofeng; Wang Ke; Xie Jingying

2006-01-01

Spherical nanostructured Si/C composite was prepared by spray drying technique, followed by heat treatment, in which nanosized silicon and fine graphite particles were homogeneously embedded in carbon matrix pyrolyzed by phenol formaldehyde resin. Cyclic voltammetry tests showed two pairs of redox peaks corresponding to lithiation and delithiation of Si/C composite. The Si/C composite exhibited a reversible capacity of 635 mAh g -1 and good cycle performance used in lithium ion batteries. To improve cycle performance of this Si/C composite further, the carbon-coated Si/C composite was synthesized by the second spray drying and heat treatment processing. The cycle performance of carbon-coated Si/C composite was improved significantly, which was attributed to the formation of stable SEI passivation layers on the outer surface of carbon shell which protected the bared silicon from exposing to electrolyte directly

Structural and electrical characterization of ion beam synthesized and n-doped SiC layers

Energy Technology Data Exchange (ETDEWEB)

Serre, C.; Perez-Rodriguez, A.; Romano-Rodriguez, A.; Morante, J.R. [Barcelona Univ. (Spain). Dept. Electronica; Panknin, D.; Koegler, R.; Skorupa, W. [Forschungszentrum Rossendorf, Dresden (Germany); Esteve, J.; Acero, M.C. [CSIC, Bellaterra (Spain). Centre Nacional de Microelectronica

2001-07-01

This work reports preliminary data on the ion beam synthesis of n-doped SiC layers. For this, two approaches have been studied: (i) doping by ion implantation (with N{sup +}) of ion beam synthesized SiC layers and (ii) ion beam synthesis of SiC in previously doped (with P) Si wafers. In the first case, the electrical data show a p-type overcompensation of the SiC layer in the range of temperatures between -50 C and 125 C. The structural (XRD) and in-depth (SIMS, Spreading Resistance) analysis of the samples suggest this overcompensation to be induced by p-type active defects related to the N{sup +} ion implantation damage, and therefore the need for further optimization their thermal processing. In contrast, the P-doped SiC layers always show n-type doping. This is also accompanied by a higher structural quality, being the spectral features of the layers similar to those from the not doped material. Electrical activation of P in the SiC lattice is about one order of magnitude lower than in Si. These data constitute, to our knowledge, the first results reported on the doping of ion beam synthesized SiC layers. (orig.)

A comparative study on electrical characteristics of 1-kV pnp and npn SiC bipolar junction transistors

Science.gov (United States)

Okuda, Takafumi; Kimoto, Tsunenobu; Suda, Jun

2018-04-01

We investigate the electrical characteristics of 1-kV pnp SiC bipolar junction transistors (BJTs) and compare them with those of npn SiC BJTs. The base resistance, current gain, and blocking capability are characterized. It is found that the base resistance of pnp SiC BJTs is two orders of magnitude lower than that of npn SiC BJTs. However, the obtained current gains are low below unity in pnp SiC BJTs, whereas npn SiC BJTs exhibit a current gain of 14 without surface passivation. The reason for the poor current gain of pnp SiC BJTs is discussed.

Detection and Analysis of Particles with Failed SiC in AGR-1 Fuel Compacts

International Nuclear Information System (INIS)

Hunn, John D.; Baldwin, Charles A.; Gerczak, Tyler J.; Montgomery, Fred C.; Morris, Robert N.; Silva, Chinthaka M.; Demkowicz, Paul A.; Harp, Jason M.; Ploger, Scott A.

2014-01-01

As the primary barrier to release of radioactive isotopes emitted from the fuel kernel, retention performance of the SiC layer in tristructural isotropic (TRISO) coated particles is critical to the overall safety of reactors that utilize this fuel design. Most isotopes are well-retained by intact SiC coatings, so pathways through this layer due to cracking, structural defects, or chemical attack can significantly contribute to radioisotope release. In the US TRISO fuel development effort, release of "1"3"4Cs and "1"3"7Cs are used to detect SiC failure during fuel compact irradiation and safety testing because the amount of cesium released by a compact containing one particle with failed SiC is typically ten or more times higher than that released by compacts without failed SiC. Compacts with particles that released cesium during the AGR-1 irradiation test or post-irradiation safety testing at 1600– 1800°C were identified, and individual particles with abnormally low cesium retention were sorted out with the ORNL Irradiated Microsphere Gamma Analyzer (IMGA). X-ray tomography was used for three-dimensional imaging of the internal coating structure to locate low-density pathways through the SiC layer and guide subsequent materialography by optical and scanning electron microscopy. All three cesium-releasing particles recovered from as-irradiated compacts showed a region where the inner pyrocarbon (IPyC) had cracked due to radiation-induced dimensional changes in the shrinking buffer and the exposed SiC had experienced concentrated attack by palladium; SiC failures observed in particles subjected to safety testing were related to either fabrication defects or showed extensive Pd corrosion through the SiC where it had been exposed by similar IPyC cracking. (author)

Pseudo Dirac dispersion in Mn-intercalated graphene on SiC

KAUST Repository

Kahaly, M. Upadhyay

2013-07-01

The atomic and electronic structures of bulk C6Mn, bulk C 8Mn, and Mn-intercalated graphene on SiC(0 0 0 1) and SiC(0001̄) are investigated by density functional theory. We find for both configurations of Mn-intercalated graphene a nonmagnetic state, in agreement with the experimental situation for SiC(0 0 0 1), and explain this property. The electronic structures around the Fermi energy are dominated by Dirac-like cones at energies consistent with data from angular resolved photoelectron spectroscopy [Gao et al., ACS Nano. 6 (2012) 6562]. However, our results demonstrate that the corresponding states trace back to hybridized Mn d orbitals, and not to the graphene. © 2013 Elsevier B.V. All rights reserved.

Pseudo Dirac dispersion in Mn-intercalated graphene on SiC

KAUST Repository

Kahaly, M. Upadhyay; Kaloni, Thaneshwor P.; Schwingenschlö gl, Udo

2013-01-01

The atomic and electronic structures of bulk C6Mn, bulk C 8Mn, and Mn-intercalated graphene on SiC(0 0 0 1) and SiC(0001̄) are investigated by density functional theory. We find for both configurations of Mn-intercalated graphene a nonmagnetic state, in agreement with the experimental situation for SiC(0 0 0 1), and explain this property. The electronic structures around the Fermi energy are dominated by Dirac-like cones at energies consistent with data from angular resolved photoelectron spectroscopy [Gao et al., ACS Nano. 6 (2012) 6562]. However, our results demonstrate that the corresponding states trace back to hybridized Mn d orbitals, and not to the graphene. © 2013 Elsevier B.V. All rights reserved.

A route to strong p-doping of epitaxial graphene on SiC

KAUST Repository

Cheng, Yingchun; Schwingenschlö gl, Udo

2010-01-01

The effects of Au intercalation on the electronic properties of epitaxialgraphenegrown on SiC{0001} substrates are studied using first principles calculations. A graphenemonolayer on SiC{0001} restores the shape of the pristine graphene dispersion

SiC Composite for Fuel Structure Applications

Energy Technology Data Exchange (ETDEWEB)

Yueh, Ken [Electric Power Research Inst. (EPRI), Charlotte, NC (United States)

2017-12-22

Extensive evaluation was performed to determine the suitability of using SiC composite as a boiling water reactor (BWR) fuel channel material. A thin walled SiC composite box, 10 cm in dimension by approximately 1.5 mm wall thickness was fabricated using chemical vapor deposition (CVD) for testing. Mechanical test results and performance evaluations indicate the material could meet BWR channel mechanical design requirement. However, large mass loss of up to 21% was measured in in-pile corrosion test under BWR-like conditions in under 3 months of irradiation. A fresh sister sample irradiated in a follow-up cycle under PWR conditions showed no measureable weight loss and thus supports the hypothesis that the oxidizing condition of the BWR-like coolant chemistry was responsible for the high corrosion rate. A thermodynamic evaluation showed SiC is not stable and the material may oxidize to form SiO₂ and CO₂. Silica has demonstrated stability in high temperature steam environment and form a protective oxide layer under severe accident conditions. However, it does not form a protective layer in water under normal BWR operational conditions due to its high solubility. Corrosion product stabilization by modifying the SiC CVD surface is an approach evaluated in this study to mitigate the high corrosion rate. Titanium and zirconium have been selected as stabilizing elements since both TiSiO₄ and ZrSiO₄ are insoluble in water. Corrosion test results in oxygenated water autoclave indicate TiSiO4 does not form a protective layer. However, zirconium doped test samples appear to form a stable continuous layer of ZrSiO₄ during the corrosion process. Additional process development is needed to produce a good ZrSiC coating to verify functionality of the mitigation concept.

SiC nanofibers grown by high power microwave plasma chemical vapor deposition

International Nuclear Information System (INIS)

Honda, Shin-ichi; Baek, Yang-Gyu; Ikuno, Takashi; Kohara, Hidekazu; Katayama, Mitsuhiro; Oura, Kenjiro; Hirao, Takashi

2003-01-01

Silicon carbide (SiC) nanofibers have been synthesized on Si substrates covered by Ni thin films using high power microwave chemical vapor deposition (CVD). Characterization using transmission electron microscopy (TEM) combined with electron energy-dispersive X-ray spectroscopy (EDX) revealed that the resultant fibrous nanostructures were assigned to β-SiC with high crystallinity. The formation of SiC nanofibers can be explained by the vapor liquid solid (VLS) mechanism in which precipitation of SiC occurs from the supersaturated Ni nanoparticle containing Si and C

The physics of epitaxial graphene on SiC(0001)

International Nuclear Information System (INIS)

Kageshima, H; Hibino, H; Tanabe, S

2012-01-01

Various physical properties of epitaxial graphene grown on SiC(0001) are studied. First, the electronic transport in epitaxial bilayer graphene on SiC(0001) and quasi-free-standing bilayer graphene on SiC(0001) is investigated. The dependences of the resistance and the polarity of the Hall resistance at zero gate voltage on the top-gate voltage show that the carrier types are electron and hole, respectively. The mobility evaluated at various carrier densities indicates that the quasi-free-standing bilayer graphene shows higher mobility than the epitaxial bilayer graphene when they are compared at the same carrier density. The difference in mobility is thought to come from the domain size of the graphene sheet formed. To clarify a guiding principle for controlling graphene quality, the mechanism of epitaxial graphene growth is also studied theoretically. It is found that a new graphene sheet grows from the interface between the old graphene sheets and the SiC substrate. Further studies on the energetics reveal the importance of the role of the step on the SiC surface. A first-principles calculation unequivocally shows that the C prefers to release from the step edge and to aggregate as graphene nuclei along the step edge rather than be left on the terrace. It is also shown that the edges of the existing graphene more preferentially absorb the isolated C atoms. For some annealing conditions, experiments can also provide graphene islands on SiC(0001) surfaces. The atomic structures are studied theoretically together with their growth mechanism. The proposed embedded island structures actually act as a graphene island electronically, and those with zigzag edges have a magnetoelectric effect. Finally, the thermoelectric properties of graphene are theoretically examined. The results indicate that reducing the carrier scattering suppresses the thermoelectric power and enhances the thermoelectric figure of merit. The fine control of the Fermi energy position is thought to

Fluorescent SiC with pseudo-periodic moth-eye structures

DEFF Research Database (Denmark)

Ou, Yiyu; Aijaz, Imran; Ou, Haiyan

2012-01-01

White light-emitting diodes (LEDs) consisting of a nitride-based blue LED chip and phosphor are very promising candidates for the general lighting applications as energy-saving sources. Recently, donor-acceptor doped fluorescent SiC has been proven as a highly efficient wavelength converter...... to enhance the extraction efficiency, we present a simple method to fabricate the pseudo-periodic moth-eye structures on the surface of the fluorescent SiC. A thin gold layer is deposited on the fluorescent SiC first. Then the thin gold layer is treated by rapid thermal processing. After annealing, the thin...... gold layer turns into discontinuous nano-islands. The average size of the islands is dependent on the annealing condition which could be well controlled. By using the reactive-ion etching, pseudo-periodic moth-eye structures would be obtained using the gold nano-islands as a mask layer. Reactive...

Structural Analysis of Polyhedral Oligomeric Silsesquioxane Coated SiC Nanoparticles and Their Applications in Thermoset Polymers

International Nuclear Information System (INIS)

Reza-E-Rabby, M.; Jeelani, Sh.; Rangari, V. K.

2015-01-01

The SiC nanoparticles (NPs) were sonochemically coated with Octa Isobutyl (OI) polyhedral oligomeric silsesquioxane (POSS) to create a compatible interface between particle and thermoset polymer. X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) techniques were used to analyze the structure of OI-POSS coated SiC nanoparticles. These results revealed the formation of a covalent bonding between SiC and OI-POSS. The transmission electron microscopy (TEM) analysis of OI-POSS coated SiC nanoparticles has also shown the indication of attachment between these two nanoparticles. The OI-POSS coated SiC nanoparticles were further reinforced into a thermoset resin system in order to evaluate mechanical and thermal properties of nano composites. The flexural strength, modulus, and glass transition temperature were found to be enhanced while SiC and OI-POSS coated SiC were infused into epoxy system compared to those properties of neat epoxy resin

Structural Analysis of Polyhedral Oligomeric Silsesquioxane Coated SiC Nanoparticles and Their Applications in Thermoset Polymers

Directory of Open Access Journals (Sweden)

Md. Reza-E-Rabby

2015-01-01

Full Text Available The SiC nanoparticles (NPs were sonochemically coated with OctaIsobutyl (OI polyhedral oligomeric silsesquioxane (POSS to create a compatible interface between particle and thermoset polymer. X-ray photoelectron spectroscopy (XPS, Fourier transform infrared spectroscopy (FTIR, and X-ray diffraction (XRD techniques were used to analyze the structure of OI-POSS coated SiC nanoparticles. These results revealed the formation of a covalent bonding between SiC and OI-POSS. The transmission electron microscopy (TEM analysis of OI-POSS coated SiC nanoparticles has also shown the indication of attachment between these two nanoparticles. The OI-POSS coated SiC nanoparticles were further reinforced into a thermoset resin system in order to evaluate mechanical and thermal properties of nanocomposites. The flexural strength, modulus, and glass transition temperature were found to be enhanced while SiC and OI-POSS coated SiC were infused into epoxy system compared to those properties of neat epoxy resin.

Applications, Prospects and Challenges of Silicon Carbide Junction Field Effect Transistor (SIC JFET

Directory of Open Access Journals (Sweden)

Frederick Ojiemhende Ehiagwina

2016-09-01

Full Text Available Properties of Silicon Carbide Junction Field Effect Transistor (SiC JFET such as high switching speed, low forward voltage drop and high temperature operation have attracted the interest of power electronic researchers and technologists, who for many years developed devices based on Silicon (Si.  A number of power system Engineers have made efforts to develop more robust equipment including circuits or modules with higher power density. However, it was realized that several available power semiconductor devices were approaching theoretical limits offered by Si material with respect to capability to block high voltage, provide low on-state voltage drop and switch at high frequencies. This paper presents an overview of the current applications of SiC JFET in circuits such as inverters, rectifiers and amplifiers. Other areas of application reviewed include; usage of the SiC JFET in pulse signal circuits and boost converters. Efforts directed toward mitigating the observed increase in electromagnetic interference were also discussed. It also presented some areas for further research, such as having more applications of SiC JFET in harsh, high temperature environment. More work is needed with regards to SiC JFET drivers so as to ensure stable and reliable operation, and reduction in the prices of SiC JFETs through mass production by industries.

High temperature oxidation behavior of SiC coating in TRISO coated particles

International Nuclear Information System (INIS)

Liu, Rongzheng; Liu, Bing; Zhang, Kaihong; Liu, Malin; Shao, Youlin; Tang, Chunhe

2014-01-01

Highlights: • High temperature oxidation tests of SiC coating in TRISO particles were carried out. • The dynamic oxidation process was established. • Oxidation mechanisms were proposed. • The existence of silicon oxycarbides at the SiO 2 /SiC interface was demonstrated. • Carbon was detected at the interface at high temperatures and long oxidation time. - Abstract: High temperature oxidation behavior of SiC coatings in tristructural-isotropic (TRISO) coated particles is crucial to the in-pile safety of fuel particles for a high temperature gas cooled reactor (HTGR). The postulated accident condition of air ingress was taken into account in evaluating the reliability of the SiC layer. Oxidation tests of SiC coatings were carried out in the ranges of temperature between 800 and 1600 °C and time between 1 and 48 h in air atmosphere. Based on the microstructure evolution of the oxide layer, the mechanisms and kinetics of the oxidation process were proposed. The existence of silicon oxycarbides (SiO x C y ) at the SiO 2 /SiC interface was demonstrated by X-ray photospectroscopy (XPS) analysis. Carbon was detected by Raman spectroscopy at the interface under conditions of very high temperatures and long oxidation time. From oxidation kinetics calculation, activation energies were 145 kJ/mol and 352 kJ/mol for the temperature ranges of 1200–1500 °C and 1550–1600 °C, respectively

Growth of graphene from SiC{0001} surfaces and its mechanisms

International Nuclear Information System (INIS)

Norimatsu, Wataru; Kusunoki, Michiko

2014-01-01

Graphene, a one-atom-layer carbon material, can be grown by thermal decomposition of SiC. On Si-terminated SiC(0001), graphene nucleates at steps and grows layer-by-layer, and as a result a homogeneous monolayer or bilayer can be obtained. We demonstrate this mechanism both experimentally and theoretically. On the C-face (000 1-bar ), multilayer graphene nucleates not only at steps, but also on the terraces. These differences reflect the distinct differences in the reactivity of these faces. Due to its high quality and structural controllability, graphene on SiC{0001} surfaces will be a platform for high-speed graphene device applications. (paper)

PhySIC_IST: cleaning source trees to infer more informative supertrees.

Science.gov (United States)

Scornavacca, Celine; Berry, Vincent; Lefort, Vincent; Douzery, Emmanuel J P; Ranwez, Vincent

2008-10-04

Supertree methods combine phylogenies with overlapping sets of taxa into a larger one. Topological conflicts frequently arise among source trees for methodological or biological reasons, such as long branch attraction, lateral gene transfers, gene duplication/loss or deep gene coalescence. When topological conflicts occur among source trees, liberal methods infer supertrees containing the most frequent alternative, while veto methods infer supertrees not contradicting any source tree, i.e. discard all conflicting resolutions. When the source trees host a significant number of topological conflicts or have a small taxon overlap, supertree methods of both kinds can propose poorly resolved, hence uninformative, supertrees. To overcome this problem, we propose to infer non-plenary supertrees, i.e. supertrees that do not necessarily contain all the taxa present in the source trees, discarding those whose position greatly differs among source trees or for which insufficient information is provided. We detail a variant of the PhySIC veto method called PhySIC_IST that can infer non-plenary supertrees. PhySIC_IST aims at inferring supertrees that satisfy the same appealing theoretical properties as with PhySIC, while being as informative as possible under this constraint. The informativeness of a supertree is estimated using a variation of the CIC (Cladistic Information Content) criterion, that takes into account both the presence of multifurcations and the absence of some taxa. Additionally, we propose a statistical preprocessing step called STC (Source Trees Correction) to correct the source trees prior to the supertree inference. STC is a liberal step that removes the parts of each source tree that significantly conflict with other source trees. Combining STC with a veto method allows an explicit trade-off between veto and liberal approaches, tuned by a single parameter.Performing large-scale simulations, we observe that STC+PhySIC_IST infers much more informative

A Short-Circuit Safe Operation Area Identification Criterion for SiC MOSFET Power Modules

DEFF Research Database (Denmark)

Reigosa, Paula Diaz; Iannuzzo, Francesco; Luo, Haoze

2017-01-01

This paper proposes a new method for the investigation of the short-circuit safe operation area (SCSOA) of state-of-the-art SiC MOSFET power modules rated at 1.2 kV based on the variations in SiC MOSFET electrical parameters (e.g., short-circuit current and gate–source voltage). According...... to the experimental results, two different failure mechanisms have been identified, both reducing the short-circuit capability of SiC power modules with respect to discrete SiC devices. Based on such failure mechanisms, two short-circuit safety criteria have been formulated: 1) the short-circuit...

Using of the Modern Semiconductor Devices Based on the SiC

Directory of Open Access Journals (Sweden)

Pavel Drabek

2008-01-01

Full Text Available This paper deals with possibility of application of the semiconductor devices based on the SiC (Silicon Carbide inthe power electronics. Basic synopsis of SiC based materials problems are presented, appreciation of their properties incomparison with current using power semiconductor devices ((IGBT, MOSFET, CoolFET transistors.

Oxidation of SiC cladding under Loss of Coolant Accident (LOCA) conditions in LWRs

International Nuclear Information System (INIS)

Lee, Y.; Yue, C.; Arnold, R. P.; McKrell, T. J.; Kazimi, M. S.

2012-01-01

An experimental assessment of Silicon Carbide (SiC) cladding oxidation rate in steam under conditions representative of Loss of Coolant Accidents (LOCA) in light water reactors (LWRs) was conducted. SiC oxidation tests were performed with monolithic alpha phase tubular samples in a vertical quartz tube at a steam temperature of 1140 deg. C and steam velocity range of 1 to 10 m/sec, at atmospheric pressure. Linear weight loss of SiC samples due to boundary layer controlled reaction of silica scale (SiO 2 volatilization) was experimentally observed. The weight loss rate increased with increasing steam flow rate. Over the range of test conditions, SiC oxidation rates were shown to be about 3 orders of magnitude lower than the oxidation rates of zircaloy 4. A SiC volatilization correlation for developing laminar flow in a vertical channel is formulated. (authors)

Al-oxynitride interfacial layer investigations for Pr{sub X}O{sub Y} on SiC and Si

Energy Technology Data Exchange (ETDEWEB)

Henkel, K; Karavaev, K; Torche, M; Schwiertz, C; Burkov, Y; Schmeisser, D [Brandenburgische Technische Universitaet Cottbus, Angewandte Physik-Sensorik, K-Wachsmann-Allee 17, 03046 Cottbus (Germany)], E-mail: henkel@tu-cottbus.de

2008-01-15

We investigate the dielectric properties of Praseodymium based oxides Pr{sub X}O{sub Y} by preparing MIS (metal insulator semiconductor) structures consisting of Pr{sub X}O{sub Y} as a high-k insulating layer and silicon (Si) or silicon carbide (SiC) as semiconductor substrates. The use of a buffer layer between Pr{sub X}O{sub Y} and the semiconductor is necessary as we found deleterious reactions between these materials such as silicate and graphite formation. Possessing a higher permittivity value ({epsilon}{sub r}) than silicon dioxide (SiO{sub 2}) and good lattice matching in conjunction with similar thermal expansion coefficient to SiC, we focus on aluminum oxynitride (AlON) as a suitable buffer layer for this high-k/wide-bandgap system. In our spectroscopic investigations we found a decrease or indeed prevention of silicon diffusion into the oxide and an increased Pr{sub 2}O{sub 3} fraction after deposition. In electrical characterizations of Pr{sub X}O{sub Y}/AlON stacks we found considerable improvements in the leakage current by several orders on both substrates, especially on silicon where we obtain values down to 10{sup -7}A/cm{sup 2} at a CET (capacitance equivalent thickness) of 4nm. We observed interface state densities in the range of 5 x 10{sup 11}-1 x 10{sup 12}/eVcm{sup 2} and 1-5 x 10{sup 12}/eVcm{sup 2} on Si and SiC, respectively.

Failure probabilities of SiC clad fuel during a LOCA in public acceptable simple SMR (PASS)

Energy Technology Data Exchange (ETDEWEB)

Lee, Youho, E-mail: euo@kaist.ac.kr; Kim, Ho Sik, E-mail: hskim25@kaist.ac.kr; NO, Hee Cheon, E-mail: hcno@kaist.ac.kr

2015-10-15

Highlights: • Graceful operating conditions of SMRs markedly lower SiC cladding stress. • Steady-state fracture probabilities of SiC cladding is below 10{sup −7} in SMRs. • PASS demonstrates fuel coolability (T < 1300 °C) with sole radiation in LOCA. • SiC cladding failure probabilities of PASS are ∼10{sup −2} in LOCA. • Cold gas gap pressure controls SiC cladding tensile stress level in LOCA. - Abstract: Structural integrity of SiC clad fuels in reference Small Modular Reactors (SMRs) (NuScale, SMART, IRIS) and a commercial pressurized water reactor (PWR) are assessed with a multi-layered SiC cladding structural analysis code. Featured with low fuel pin power and temperature, SMRs demonstrate markedly reduced incore-residence fracture probabilities below ∼10{sup −7}, compared to those of commercial PWRs ∼10{sup −6}–10{sup −1}. This demonstrates that SMRs can serve as a near-term deployment fit to SiC cladding with a sound management of its statistical brittle fracture. We proposed a novel SMR named Public Acceptable Simple SMR (PASS), which is featured with 14 × 14 assemblies of SiC clad fuels arranged in a square ring layout. PASS aims to rely on radiative cooling of fuel rods during a loss of coolant accident (LOCA) by fully leveraging high temperature tolerance of SiC cladding. An overarching assessment of SiC clad fuel performance in PASS was conducted with a combined methodology—(1) FRAPCON-SiC for steady-state performance analysis of PASS fuel rods, (2) computational fluid dynamics code FLUENT for radiative cooling rate of fuel rods during a LOCA, and (3) multi-layered SiC cladding structural analysis code with previously developed SiC recession correlations under steam environments for both steady-state and LOCA. The results show that PASS simultaneously maintains desirable fuel cooling rate with the sole radiation and sound structural integrity of fuel rods for over 36 days of a LOCA without water supply. The stress level of

Determination of volume fraction in biphasic flows oil-gas and water-gas using artificial neural network and gamma densitometry; Determinacao de fracoes de volume em fluxos bifasicos oleo-gas e agua-gas utilizando redes neurais artificiais e densitometria gama

Energy Technology Data Exchange (ETDEWEB)

Peixoto, Philippe Netto Belache

2016-07-01

This study presents a methodology based on the principles of gamma ray attenuation to identify volume fractions in biphasic systems composed of oil-gas-water and gas which are found in the offshore oil industry. This methodology is based on the acknowledgment counts per second on the photopeak energy using a detection system composed of a NaI (Tl) detector, a source of {sup 137}Cs without collimation positioned at 180 ° relative to the detector on a smooth stratified flow regime. The mathematical modeling for computational simulation using the code MCNP-X was performed using the experimental measurements of the detector characteristics (energy resolution and efficiency), characteristics of the material water and oil (density and coefficient attenuation) and measurement of the volume fractions. To predict these fractions were used artificial neural networks (ANNs), and to obtain an adequate training the ANNs for the prediction of volume fractions were simulated a larger number of volume fractions in MCNP-X. The experimental data were used in the set data necessary for validation of ANNs and the data generated using the computer code MCNP-X were used in training and test sets of the ANNs. Were used ANNs of type feed-forward Multilayer Perceptron (MLP) and analyzed two functions of training, Levenberg-Marquardt (LM) and gradient descent with momentum (GDM), both using the Backpropagation training algorithm. The ANNs identified correctly the volume fractions of the multiphase system with mean relative errors lower than 1.21 %, enabling the application of this methodology for this purpose. (author)

Investigation of the Fission Products Silver, Palladium and Cadmium in Neutron Irradiated SiC using a Cs-Corrected HRTEM

International Nuclear Information System (INIS)

Rooyen, I.J. van; Olivier, E.J.; Neethling, J.H

2014-01-01

Electron microscopy investigations of selected coated particles from the first advanced gas reactor experiment (AGR-1) at Idaho National Laboratory (INL) provided important information on fission product distribution and chemical composition in the SiC layer. Furthermore, recent STEM analyses led to the discovery of Ag at SiC grain boundaries and triple junctions. As these Ag precipitates were nano-sized, high resolution transmission electron microscopy (HRTEM) was used to provide more information at the atomic level. This paper describes some of the first HRTEM results obtained from the examination of a particle from Compact 4-1-1, which was irradiated to an average burnup of 19.38% fissions per initial metal atom (FIMA), a time-average, volume-averaged temperature of 1072°C; a time-average, peak temperature of 1182°C and an average fast fluence of 4.13x10 21 n/cm 2 . Based on gamma-ray analysis, it is estimated that this particle may have released as much as 10% of its available Ag-110m inventory during irradiation. The HRTEM investigation focused on Ag, Pd, and Cd due to the interest in Ag transport mechanisms and possible correlation with Pd and Ag previously found. Additionally, Compact 4-1-1 contains fuel particles fabricated with a different fuel carrier gas composition and lower deposition temperatures for the SiC layer relative to the Baseline fabrication conditions, which are expected to reduce the concentration of SiC defects resulting from uranium dispersion. Small Ag precipitates were observed at a distance of about 6.5 micron from the inner PyC-SiC interface. Pd, Ag, and Cd were found to co-exist in some of the SiC grain boundaries and triple junctions. This study confirmed the presence of Pd both at inter- and intragranular sites; in the latter case specifically at stacking faults. Small Ag precipitates were observed at a distance of about 6.5 microns from the inner PyC/SiC interface. (author)

Features of film growth during plasma anodizing of Al 2024/SiC metal matrix composite

Energy Technology Data Exchange (ETDEWEB)

Xue Wenbin [Key Laboratory for Radiation Beam Technology and Materials Modification, Institute of Low Energy Nuclear Physics, Beijing Normal University, Beijing 100875 (China)]. E-mail: xuewb@bnu.edu.cn

2006-07-15

Plasma anodizing is a novel promising process to fabricate corrosion-resistant protective films on metal matrix composites. The corrosion-resistant films were prepared by plasma anodizing on SiC reinforced aluminum matrix composite. The morphology and microstructure of films were analyzed by scanning electron microscopy. Specifically, the morphology of residual SiC reinforcement particles in the film was observed. It is found that the most SiC reinforcement particles have been molten to become silicon oxide, but a few tiny SiC particles still remain in the film close to the composite/film interface. This interface is irregular due to the hindering effect of SiC particles on the film growth. Morphology and distribution of residual SiC particles in film provide direct evidence to identify the local melt occurs in the interior of plasma anodizing film even near the composite/film interface. A model of film growth by plasma anodizing on metal matrix composites was proposed.

Features of film growth during plasma anodizing of Al 2024/SiC metal matrix composite

International Nuclear Information System (INIS)

Xue Wenbin

2006-01-01

Plasma anodizing is a novel promising process to fabricate corrosion-resistant protective films on metal matrix composites. The corrosion-resistant films were prepared by plasma anodizing on SiC reinforced aluminum matrix composite. The morphology and microstructure of films were analyzed by scanning electron microscopy. Specifically, the morphology of residual SiC reinforcement particles in the film was observed. It is found that the most SiC reinforcement particles have been molten to become silicon oxide, but a few tiny SiC particles still remain in the film close to the composite/film interface. This interface is irregular due to the hindering effect of SiC particles on the film growth. Morphology and distribution of residual SiC particles in film provide direct evidence to identify the local melt occurs in the interior of plasma anodizing film even near the composite/film interface. A model of film growth by plasma anodizing on metal matrix composites was proposed

The effect of strain path change on subgrain volume fraction determined from in situ X-ray measurements

DEFF Research Database (Denmark)

Wejdemann, Christian; Poulsen, Henning Friis; Lienert, U.

2009-01-01

to additional 5% strain is performed in situ while mapping a selected X-ray reflection from one particular bulk grain with high angular resolution. The reciprocal space maps are analyzed with a recently developed fitting method, and a correlation is found between the evolution of the subgrain volume fraction...

Thermal Conductivity Measurement and Analysis of Fully Ceramic Microencapsulated fuel

International Nuclear Information System (INIS)

Lee, H. G.; Kim, D. J.; Park, J. Y.; Kim, W. J.; Lee, S. J.

2015-01-01

FCM nuclear fuel is composed of tristructural isotropic(TRISO) fuel particle and SiC ceramic matrix. SiC ceramic matrix play an essential part in protecting fission product. In the FCM fuel concept, fission product is doubly protected by TRISO coating layer and SiC ceramic matrix in comparison with the current commercial UO2 fuel system of LWR. In addition to a safety enhancement of FCM fuel, thermal conductivity of SiC ceramic matrix is better than that of UO2 fuel. Because the centerline temperature of FCM fuel is lower than that of the current UO2 fuel due to the difference of thermal conductivity of fuel, an operational release of fission products from the fuel can be reduced. SiC ceramic has attracted for nuclear fuel application due to its high thermal conductivity properties with good radiation tolerant properties, a low neutron absorption cross-section and a high corrosion resistance. Thermal conductivity of ceramic matrix composite depends on the thermal conductivity of each component and the morphology of reinforcement materials such as fibers and particles. There are many results about thermal conductivity of fiber-reinforced composite like as SiCf/SiC composite. Thermal conductivity of SiC ceramics and FCM pellets with the volume fraction of TRISO particles were measured and analyzed by analytical models. Polycrystalline SiC ceramics and FCM pellets with TRISO particles were fabricated by hot press sintering with sintering additives. Thermal conductivity of the FCM pellets with TRISO particles of 0 vol.%, 10 vol.%, 20 vol.%, 30 vol.% and 40 vol.% show 68.4, 52.3, 46.8, 43.0 and 34.5 W/mK, respectively. As the volume fraction of TRISO particles increased, the measured thermal conductivity values closely followed the prediction of Maxwell's equation

De interactie van SiC met Fe, Ni en hun legeringen

NARCIS (Netherlands)

Schiepers, R.C.J.

1991-01-01

De interactie tussen SiC en metalen gebaseerd op Fe en Ni is bestudeerd in het temperatuurtraject 700-1035°C door middel van vaste-stof-diffusiekoppels. In de koppels van SiC met Fe, Ni en hun legeringen treden hevige reakties op, die de vorming van een goede verbinding verhinderen. Door het grate

Manufacturing and characterization of porous SiC for flow channel inserts in dual-coolant blanket designs

International Nuclear Information System (INIS)

Bereciartu, Ainhoa; Ordas, Nerea; Garcia-Rosales, Carmen; Morono, Alejandro; Malo, Marta; Hodgson, Eric R.; Abella, Jordi; Sedano, Luis

2011-01-01

SiC is the primary candidate for the flow channel inserts in dual-coolant blanket concepts. Porous SiC ceramics are attractive candidates for this non-structural application, since they can satisfy the required properties through a low cost manufacturing route, compared to SiC f /SiC. This work shows first results of the manufacturing of porous SiC ceramics prepared with different amounts of Y 2 O 3 and Al 2 O 3 as sintering additives. C powders were used as pore-formers by their burnout during oxidation after sintering. Comparison of microstructure, porosity, flexural strength, thermal and electrical conductivity and corrosion under Pb-15.7Li of porous SiC without and with sintering additives is presented. The addition of 2.5 wt.% of Y 2 O 3 and Al 2 O 3 improves the mechanical properties, and reduces the thermal and electrical conductivity down to reasonable values. Preliminary corrosion tests under Pb-15.7 Li at 500 deg. C show that the absence of a dense coating on porous SiC leads to poor corrosion behavior.

Fabrication of SiCp/Al Alloy Composites by In-situ Vacuum Hot Press Process

Energy Technology Data Exchange (ETDEWEB)

Choi, S. W.; Hong, S. K.; Kim, Y. M.; Kang, C. S. [Chonnam National University, Kwangju (Korea); Chang, S. Y. [Hanyang University, Seoul (Korea)

2001-07-01

SiCp/pure Al and SiCp/2024Al MMCs were fabricated by in-situ VHP process designed specially just in this study which is composed of the vacuum hot press at range from R.T. to 500 deg.C and the continuous extrusion without canning process at 520 deg.C. It was investigated the effect of SiC particle size, volume fraction and extrusion ratio on the tensile properties and micro structure in all composites. In case of the 10:1 extrusion ratio, but SiCp/pure Al and SiCp/2024Al composites were shown a sound appearance and a good micro structure without crack of SiCp as well as uniform distribution of SiCp. However, in case of the 16:1 extrusion ratio, the number of cracked SiC particles more than increased in a higher volume fraction composite and 2024Al matrix composite compared with pure Al matrix one. The tensile strength of the composites reinforced smaller SiCp was higher than that of the bigger SiCp reinforced in same volume fraction and extrusion ratio. (author) 14 refs., 14 figs.

Inter fraction variations in rectum and bladder volumes and dose distributions during high dose rate brachytherapy treatment of the uterine cervix investigated by repetitive CT-examinations

International Nuclear Information System (INIS)

Hellebust, Taran Paulsen; Dale, Einar; Skjoensberg, Ane; Olsen, Dag Rune

2001-01-01

Purpose: To evaluate variation of dose to organs at risk for patients receiving fractionated high dose rate gynaecological brachytherapy by using CT-based 3D treatment planning and dose-volume histograms (DVH). Materials and methods: Fourteen patients with cancer of the uterine cervix underwent three to six CT examinations (mean 4.9) during their course of high-dose-rate brachytherapy using radiographically compatible applicators. The rectal and bladder walls were delineated and DVHs were calculated. Results: Inter fraction variation of the bladder volume (CV mean =44.1%) was significantly larger than the inter fraction variation of the mean dose (CV mean =19.9%, P=0.005) and the maximum dose (CV mean =17.5%, P=0.003) of the bladder wall. The same trend was seen for rectum, although the figures were not significantly different. Performing CT examinations at four of seven brachytherapy fractions reduced the uncertainty to 4 and 7% for the bladder and rectal doses, respectively. A linear regression analysis showed a significant, negative relationship between time after treatment start and the whole bladder volume (P=0.018), whereas no correlation was found for the rectum. For both rectum and bladder a linear regression analysis revealed a significant, negative relationship between the whole volume and median dose (P<0.05). Conclusion: Preferably a CT examination should be provided at every fraction. However, this is logistically unfeasible in most institutions. To obtain reliable DVHs the patients will in the future undergo 3-4 CT examinations during the course of brachytherapy at our institution. Since this study showed an association between large bladder volumes and dose reductions, the patients will be treated with a standardized bladder volume

The development of SiC whisker fabrication technology for nuclear applications

International Nuclear Information System (INIS)

Kang, Thae Khapp; Kuk, Il Hiun; Kim, Chang Kyu; Lee, Jae Chun; Lee, Ho Jin; Park, Soon Dong; Im, Gyeong Soo

1991-02-01

Some important experiments for whisker growth reactions, fabrication processes, and experiments for fabricarion of whisker reinforced composites have been performed. In order to investigate growth reaction of SiC whiskers, a conventional carbothermic reaction was tested. Based on the results of carbothermic process, a new process called silicothermic reaction was planned and some basic experiments were performed. Reaction characteristics of silicon monoxide, core material for SiC whisker growth in both of the reactions were investigated for basic data. Additionally, a hydrofluoric acid leaching process was tested for developing SiC whisker recovery process, and powder metallurgy process and melt sqeeze process were tried to develop aluminum-SiC whisker composites. (Author)

Small Incision Cataract Surgery (SICS with Clear Corneal Incision and SICS with Scleral Incision – A Comparative Study

Directory of Open Access Journals (Sweden)

Md Shafiqul Alam

2014-01-01

Full Text Available Background: Age related cataract is the leading cause of blindness and visual impairment throughout the world. With the advent of microsurgical facilities simple cataract extraction surgery has been replaced by small incision cataract surgery (SICS with posterior chamber intra ocular lens implant, which can be done either with clear corneal incision or scleral incision. Objective: To compare the post operative visual outcome in these two procedures of cataract surgery. Materials and method: This comparative study was carried out in the department of Ophthalmology, Delta Medical College & Hospital, Dhaka, Bangladesh, during the period of January 2010 to December 2012. Total 60 subjects indicated for age related cataract surgery irrespective of sex with the age range of 40-80 years with predefined inclusion and exclusion criteria were enrolled in the study. Subjects were randomly and equally distributed in 2 groups; Group A for SICS with clear corneal incision and group B for SICS with scleral incision. Post operative visual out come was evaluated by determining visual acuity and astigmatism in different occasions and was compared between groups. Statistical analysis was done by SPSS for windows version12. Results: The highest age incidence (43.3% was found between 61 to 70 years of age group. Among study subjects 40 were male and 20 were female. Preoperative visual acuity and astigmatism were evenly distributed between groups. Regarding postoperative unaided visual outcome, 6/12 or better visual acuity was found in 19.98% cases in group A and 39.6% cases in group B at 1st week. At 6th week 6/6 vision was found in 36.3% in Group A and 56.1% in Group B and 46.2% in group A and 66% in group B without and with correction respectively. With refractive correction, 6/6 vision was attained in 60% subjects of group A and 86.67% of group B at 8th week. Post operative visual acuity was statistically significant in all occasions. Postoperative astigmatism of

Left ventricular ejection fraction and volumes as measured by 3D echocardiography and ultrafast computed tomography

International Nuclear Information System (INIS)

Vieira, Marcelo Luiz Campos; Nomura, Cesar H.; Tranchesi Junior, Bernardino; Oliveira, Wercules A. de; Naccarato, Gustavo; Serpa, Bruna S.; Passos, Rodrigo B.D.; Funari, Marcelo B. G.; Fischer, Claudio H.; Morhy, Samira S.

2009-01-01

Background: Real-time three-dimensional echocardiography (RT-3D-Echo) and ultrafast computed tomography (CT) are two novel methods for the analysis of LV ejection fraction and volumes. Objective: To compare LVEF and volume measurements as obtained using RT-3D-Echo and ultrafast CT. Methods: Thirty nine consecutive patients (27 men, mean age of 57+- 12 years) were studied using RT-3D-Echo and 64-slice ultrafast CT. LVEF and LV volumes were analyzed. Statistical analysis: coefficient of correlation (r: Pearson), Bland-Altman analysis, linear regression analysis, 95% CI, p 5 .58)%; end-diastolic volume ranged from 49.6 to 178.2 (87+-27.8) ml; end-systolic volume ranged from 11.4 to 78 (33.1+-13.6) ml. CT scan measurements: LVEF ranged from 53 to 86% (67.8+-7.78); end-diastolic volume ranged from 51 to 186 (106.5+-30.3) ml; end-systolic volume ranged from 7 to 72 (35.5+-13.4)ml. Correlations between RT-3D-Echo and CT were: LVEF (r: 0.7888, p<0.0001, 95% CI 0.6301 to 0.8843); end-diastolic volume (r: 0.7695, p<0.0001, 95% CI 0.5995 to 0.8730); end-systolic volume (r: 0.8119, p<0.0001, 95% CI 0.6673 to 0.8975). Conclusion: Good correlation between LVEF and ventricular volume parameters as measured by RT-3D-Echo and 64-slice ultrafast CT was found in the present case series. (author)

Fabrication and characterization of SiC and ZrC composite coating on TRISO coated particle

Energy Technology Data Exchange (ETDEWEB)

Lee, H. G.; Lee, S. H.; Kim, D. J.; Park, J. Y.; Kim, W. J. [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

2016-10-15

SiC coating is widely suggested as structural materials for nuclear application due to its excellent high irradiation resistance properties and high temperature mechanical properties. SiC coating on TRistructural-ISOtropic (TRISO) coated fuel particles plays an important role as a protective layer from radioactive fission gas and a mechanical structural layer. TRISO coating layer was deposited on a spherical particle by a FBCVD method. The ZrO{sub 2} spherical particles were used as a simulant kernel. TRISO coating layers consisting of a porous buffer layer, an inner PyC layer were sequentially deposited before depositing SiC or ZrC coating layer. In order investigate the phase of each composite coating layer, Raman analysis was conducted. SiC, ZrC coating and SiC/ZrC composite coating on spherical particle were successfully deposited via FBCVD method by adjusting source gas flow rate. In the SiC and ZrC composite coating, SiC phase and ZrC phase were observed by XRD and SEM analysis. In the condition of 100 sccm of ZrCl{sub 4}, 25 sccm of CH{sub 4}, and 30 sccm of MTS, only two phases of SiC and ZrC were observed and two phases are located with clean grain boundary.

A route to strong p-doping of epitaxial graphene on SiC

KAUST Repository

Cheng, Yingchun

2010-11-09

The effects of Au intercalation on the electronic properties of epitaxialgraphenegrown on SiC{0001} substrates are studied using first principles calculations. A graphenemonolayer on SiC{0001} restores the shape of the pristine graphene dispersion, where doping levels between strongly n-doped and weakly p-doped can be achieved by altering the Au coverage. We predict that Au intercalation between the two C layers of bilayer graphenegrown on SiC{0001} makes it possible to achieve a strongly p-doped graphene state, where the p-doping level can be controlled by means of the Au coverage.

Effects of SiC and MgO on aluminabased ceramic foams filters

Directory of Open Access Journals (Sweden)

CAO Da-li

2007-11-01

Full Text Available Alumina-based foam ceramic filters were fabricated by using alumina, SiC, magnesia powder as major materials. It has been found that this ceramic filter has a uniform macrostructure for filtering molten metals. The influences of SiC and magnesia content, the sintering temperatures on ceramic properties were discussed. Aluminabased foam ceramic filters containing 2.2 mass% magnesia and 7.6 mass% SiC has a compressive strength of 1.36 MPa and a thermal shock resistance of 5 times. Its main phases after 1 hour sintering at 1 500 consist of alumina, silicon carbide, spinel and mullite.

Pulsed laser deposition of SiC thin films at medium substrate temperatures

International Nuclear Information System (INIS)

Katharria, Y.S.; Kumar, Sandeep; Choudhary, R.J.; Prakash, Ram; Singh, F.; Lalla, N.P.; Phase, D.M.; Kanjilal, D.

2008-01-01

Systematic studies of thin silicon carbide (SiC) films deposited on Si (100) substrates using pulsed laser deposition technique at room temperature, 370 deg. C and 480 deg. C are carried out. X-ray photoelectron spectroscopy showed the formation of SiC bonds in the films at these temperatures along with some graphitic carbon clusters. Fourier transform infrared analysis also confirmed the formation of SiC nanocrystallites in the films. Transmission electron microscopy and electron diffraction were used to study the structural properties of nanocrystallites formed in the films. Surface morphological analysis using atomic force microscopy revealed the growth of smooth films

Electrical measurement of radiation effect in SiC

Energy Technology Data Exchange (ETDEWEB)

Kanazawa, Satoshi; Kamiya, Koji; Kanno, Ikuo [Kyoto Univ. (Japan). Faculty of Engineering] [and others

1996-04-01

For aiming to limited resources and environmental conservations on the Earth, development of controlling element workable under high temperature environment was investigated so as to establish a high grade and optimum controlling system. In order to observe changes of electrical properties before and after irradiation and after annealing, and to investigate changes of carrier concentration and movability after irradiating neutron from reactor and accelerator for the SiC single crystal wafer, elucidation on neutron irradiation effect of SiC as well as finding an optimum method on nuclear conversion injection were investigated. For this reason, SiC surface was purified by its etching and was treated thermally at 1000degC for about 30 min. under argon gas atmosphere after vacuum depositing nickel on it. And then, it was irradiated neutron using Kyoto University reactor (LTL), Linac and University of Tokyo reactor (YAYOI) to measure changes of resistivity using van der Pauw. As a result, it was found that LTL irradiation data was under investigation of measuring method, that in Linac no meaning change was observed because of low irradiation, and that only YAYOI data showed increase of resistivity. (G.K.)

Influence of extrusion parameters on sic distribution and properties of AA6061/SiC composites produced by kobo method

Energy Technology Data Exchange (ETDEWEB)

WoĨniak, Jarosáaw; Kostecki, Marek; Broniszewski, Kamil; Olszyna, Andrzej [Faculty of Material Science and Engineering, Warsaw University of Technology, Warsaw (Poland); Bochniak, Wáodzimierz [Faculty of Non-Ferrous Metals, AGH University of Science and Technology, Cracow (Poland)

2013-07-01

The influence of extrusion parameters on reinforcements distribution and properties of AA6061+x% vol. SiC p (x=0; 2.5; 5; 7.5; 10) composites was discussed in this paper The averages size of AA6061 and SiC particles were 10.6 μ m and 0.42 μ m, respectively. The composites were consolidated via powder metallurgy processing (without the sintering) and extruded by KoBo method. The microstructure was examined on each steps of production. High values of density for all produced composites were achieved. Additionally, hardness and Young’s modulus were investigated. The best reinforcement distribution and mechanical properties were obtained for composites extruded with the highest extrusion ratio. Key words: aluminum alloy, extrusion, aged hardening, metal matrix composites, microstructure.

Control of the graphene growth rate on capped SiC surface under strong Si confinement

International Nuclear Information System (INIS)

Çelebi, C.; Yanık, C.; Demirkol, A.G.; Kaya, İsmet İ.

2013-01-01

Highlights: ► Graphene is grown on capped SiC surface with well defined cavity size. ► Graphene growth rate linearly increases with the cavity height. ► Graphene uniformity is reduced with thickness. - Abstract: The effect of the degree of Si confinement on the thickness and morphology of UHV grown epitaxial graphene on (0 0 0 −1) SiC is investigated by using atomic force microscopy and Raman spectroscopy measurements. Prior to the graphene growth process, the C-face surface of a SiC substrate is capped by another SiC comprising three cavities on its Si-rich surface with depths varying from 0.5 to 2 microns. The Si atoms, thermally decomposed from the sample surface during high temperature annealing of the SiC cap /SiC sample stack, are separately trapped inside these individual cavities at the sample/cap interface. Our analyses show that the growth rate linearly increases with the cavity height. It was also found that stronger Si confinement yields more uniform graphene layers.

High efficiency three-phase power factor correction rectifier using SiC switches

DEFF Research Database (Denmark)

Kouchaki, Alireza; Nymand, Morten

2017-01-01

This paper presents designing procedure of a high efficiency 5 kW silicon-carbide (SiC) based threephase power factor correction (PFC). SiC switches present low capacitive switching loss compared to the alternative Si switches. Therefore, the switching frequency can be increased and hence the siz...

Kronig-Penney-like description for band gap variation in SiC polytypes

NARCIS (Netherlands)

Backes, W.H.; Nooij, de F.C.; Bobbert, P.A.; van Haeringen, W.

1996-01-01

A one-dimensional Kronig-Penney-like model for envelope wave functions is presented to explain the band gap variation of SiC polytypes. In this model the envelope functions obey discontinuous boundary conditions. The electronic band gaps of cubic and several hexagonal and rhombohedral SiC polytypes

Testing of porous SiC with dense coating under relevant conditions for Flow Channel Insert application

Energy Technology Data Exchange (ETDEWEB)

Ordás, N., E-mail: nordas@ceit.es [CEIT and Tecnun (University of Navarra), Manuel de Lardizábal 15, 20018 San Sebastián (Spain); Bereciartu, A.; García-Rosales, C. [CEIT and Tecnun (University of Navarra), Manuel de Lardizábal 15, 20018 San Sebastián (Spain); Moroño, A.; Malo, M.; Hodgson, E.R. [CIEMAT, Avenida Complutense 22, 28040 Madrid (Spain); Abellà, J.; Colominas, S. [Institut Químic de Sarrià, University Ramon Llull, Via Augusta 390, 08017 Barcelona (Spain); Sedano, L. [CIEMAT, Avenida Complutense 22, 28040 Madrid (Spain)

2014-10-15

Highlights: • Porous SiC coated by CVD with a dense coating was developed for Flow Channel Inserts (FCI) in dual-coolant blanket concept. • Porous SiC was obtained following the sacrificial template technique, using Al{sub 2}O{sub 3} and Y{sub 2}O{sub 3} as sintering additives. • Flexural strength, thermal and electrical conductivity, and microstructure of uncoated and coated porous SiC are presented. • Adhesion of coating to porous SiC and its corrosion behavior under Pb-17.5Li at 700 °C are shown. - Abstract: Thermally and electrically insulating porous SiC ceramics are attractive candidates for Flow Channel Inserts (FCI) in dual-coolant blanket concepts thanks to its relatively inexpensive manufacturing route. To prevent tritium permeation and corrosion by Pb-15.7 a dense coating has to be applied on the porous SiC. Despite not having structural function, FCI must exhibit sufficient mechanical strength to withstand strong thermal gradients and thermo-electrical stresses during operation. This work summarizes the results on the development of coated porous SiC for FCI. Porous SiC was obtained following the sacrificial template technique, using Al{sub 2}O{sub 3} and Y{sub 2}O{sub 3} as sintering additives and a carbonaceous phase as pore former. Sintering was performed in inert gas at 1850–1950 °C during 15 min to 3 h, followed by oxidation at 650 °C to eliminate the carbonaceous phase. The most promising bulk materials were coated with a ∼30 μm thick dense SiC by CVD. Results on porosity, bending tests, thermal and electrical conductivity are presented. The microstructure of the coating, its adhesion to the porous SiC and its corrosion behavior under Pb-17.5Li are also shown.

Deposition of SiC thin films by PECVD

CERN Document Server

Cho, N I; Kim, C K

1999-01-01

The SiC films were deposited on Si substrate by the decomposition of CH sub 3 SiCl sub 3 (methylthrichlorosilane) molecules in a high frequency discharge field. From the Raman spectra, it is conjectured that the deposited film are formed into the polycrystalline structure. The photon absorption measurement reveal that the band gap of the electron energy state are to be 2.4 eV for SiC, and 2.6 eV for Si sub 0 sub . sub 4 C sub 0 sub . sub 6 , respectively. In the high power density regime, methyl-radicals decompose easily and increases the carbon concentration in plasma and result in the growing films.

Switching Investigations on a SiC MOSFET in a TO-247 Package

DEFF Research Database (Denmark)

Anthon, Alexander; Hernandez Botella, Juan Carlos; Zhang, Zhe

2014-01-01

This paper deals with the switching behavior of a SiC MOSFET in a TO-247 package. Based on simulations, critical parasitic inductances in the circuit layout are analyzed and their effect on the switching losses highlighted. Especially the common source inductance, a critical parameter in a TO-247...... package, has a major influence on the switching energy. Crucial design guidelines for an improved double pulse test circuit are introduced which are used for practical investigations on the switching behavior. Switching energies of a SiC MOSFET in a TO-247 package is measured depending on varying gate...... resistance and loop inductances. With total switching energy of 340.24 μJ, the SiC MOSFET has more than six times lower switching losses than a regular Si IGBT. Implementing the SiC switches in a 3 kW T-Type inverter topology, efficiency improvements of 0.8 % are achieved and maximum efficiency of 97...

Effects of retained austenite volume fraction, morphology, and carbon content on strength and ductility of nanostructured TRIP-assisted steels

Energy Technology Data Exchange (ETDEWEB)

Shen, Y.F., E-mail: shenyf@smm.neu.edu.cn [Key Laboratory for Anisotropy and Texture of Materials (MOE), Northeastern University, 3 Wenhua Road, Shenyang 110004 (China); Qiu, L.N. [Key Laboratory for Anisotropy and Texture of Materials (MOE), Northeastern University, 3 Wenhua Road, Shenyang 110004 (China); Sun, X. [Pacific Northwest National Laboratory, PO Box 999, Richland, WA 99352 (United States); Zuo, L. [Key Laboratory for Anisotropy and Texture of Materials (MOE), Northeastern University, 3 Wenhua Road, Shenyang 110004 (China); Liaw, P.K. [Department of Materials Science and Engineering, The University of Tennessee, Knoxville, TN 37996 (United States); Raabe, D. [Max-Planck-Institut fuer Eisenforschung, Max-Planck-Str. 1, 8, 40237 Düsseldorf (Germany)

2015-06-11

With a suite of multi-modal and multi-scale characterization techniques, the present study unambiguously proves that a substantially-improved combination of ultrahigh strength and good ductility can be achieved by tailoring the volume fraction, morphology, and carbon content of the retained austenite (RA) in a transformation-induced-plasticity (TRIP) steel with the nominal chemical composition of 0.19C–0.30Si–1.76Mn–1.52Al (weight percent, wt%). After intercritical annealing and bainitic holding, a combination of ultimate tensile strength (UTS) of 1100 MPa and true strain of 50% has been obtained, as a result of the ultrafine RA lamellae, which are alternately arranged in the bainitic ferrite around junction regions of ferrite grains. For reference, specimens with a blocky RA, prepared without the bainitic holding, yield a low ductility (35%) and a low UTS (800 MPa). The volume fraction, morphology, and carbon content of RA have been characterized using various techniques, including the magnetic probing, scanning electron microscopy (SEM), electron-backscatter-diffraction (EBSD), and transmission electron microscopy (TEM). Interrupted tensile tests, mapped using EBSD in conjunction with the kernel average misorientation (KAM) analysis, reveal that the lamellar RA is the governing microstructure component responsible for the higher mechanical stability, compared to the blocky one. By coupling these various techniques, we quantitatively demonstrate that in addition to the RA volume fraction, its morphology and carbon content are equally important in optimizing the strength and ductility of TRIP-assisted steels.

Mechanical Properties and Elastic Constants Due to Damage Accumulation and Amorphization in SiC

International Nuclear Information System (INIS)

Gao, Fei; Weber, William J.

2004-01-01

Damage accumulation due to cascade overlap, which was simulated previously, has been used to study the changes of elastic constants, bulk and elastic moduli as a function of dose. These mechanical properties generally decrease with increasing dose, and the rapid decrease at low-dose level indicates that point defects and small clusters play an important role in the changes of elastic constants rather than topological disorder. The internal strain relaxation has no effect on the elastic constants, C11 and C12, in perfect SiC, but it has a significant influence on all elastic constants calculated in damaged SiC. The elastic constants in the cascade-amorphized (CA) SiC decrease about 19%, 29% and 46% for C11, C12 and C44, respectively. The bulk modulus decrease 23% and the elastic modulus decreases 29%, which is consistent with experimental measurements. The stability of both the perfect SiC and CA-SiC under hydrostatic tension has been also investigated. All mechanical properties in the CA-SiC exhibit behavior similar to that in perfect SiC, but the critical stress at which the CA-SiC becomes structurally unstable is one order of magnitude smaller than that for perfect SiC

Structural, thermal, dielectric spectroscopic and AC impedance properties of SiC nanoparticles doped PVK/PVC blend

Science.gov (United States)

Alghunaim, Naziha Suliman

2018-06-01

Nanocomposite films based on poly (N-vinylcarbazole)/polyvinylchloride (PVK/PVC) blend doped with different concentrations of Silicon Carbide (SiC) nanoparticles have been prepared. The X-ray diffraction, Ultra violet-visible spectroscopy, thermogravimetric analysis and electrical spectroscopic has been used to characterize these nanocomposites. The X-ray analysis confirms the semi-crystalline nature of the films. The intensity of the main X-ray peak is decreased due to the interaction between the PVK/PVC and SiC. The main SiC peaks are absent due to complete dissolution of SiC in polymeric matrices. The UV-Vis spectra indicated that the band gap optical energy is affected by adding SiC nanoparticles because the charges transfer complexes between PVK/PVC with amount of SiC. The thermal stability is improved and the estimated values of ε‧ and ε″ are increased with increasing for SiC content due to the free charge carriers which in turn increase the ionic conductivity of the doped samples. The plots of tan δ with frequency are studied. A single peak from the plot between tan δ and Log (f) is appeared and shifted towards the higher frequency confirmed the presence of relaxing dipoles moment.

Characteristics of electrocodeposited Ni–Co–SiC composite coating

Indian Academy of Sciences (India)

Unknown

improve the properties of coating further, Cr plating was also performed. Since the ... rectifier was used for d.c. current of 2 amp. After code- .... Table 2. Variation in hardness with volume fraction of SiC particles on the deposits as functions of.

Proposal of a SiC disposal canister for very deep borehole disposal

Energy Technology Data Exchange (ETDEWEB)

Choi, Heui-Joo; Lee, Minsoo; Lee, Jong-Youl; Kim, Kyungsu [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

2016-10-15

In this paper authors proposed a silicon carbide, SiC, disposal canister for the DBD concept in Korea. A. Kerber et al. first proposed the SiC canister for a geological disposal of HLW, CANDU or HTR spent nuclear fuels. SiC has some drawbacks in welding or manufacturing a large canister. Thus, we designed a double layered disposal canister consisting of a stainless steel outer layer and a SiC inner layer. KAERI has been interested in developing a very deep borehole disposal (DBD) of HLW generated from pyroprocessing of PWR spent nuclear fuel and supported the relevant R and D with very limited its own budget. KAERI team reviewed the DBD concept proposed by Sandia National Laboratories (SNL) and developed its own concept. The SNL concept was based on the steel disposal canister. The authors developed a new technology called cold spray coating method to manufacture a copper-cast iron disposal canister for a geological disposal of high level waste in Korea. With this method, 8 mm thin copper canister with 400 mm in diameter and 1200 mm in height was made. In general, they do not give any credit on the lifetime of a disposal canister in DBD concept unlike the geological disposal. In such case, the expensive copper canister should be replaced with another one. We designed a disposal canister using SiC for DBD. According to an experience in manufacturing a small size canister, the fabrication of a large-size one is a challenge. Also, welding of SiC canister is not easy. Several pathways are being paved to overcome it.

In-situ synchrotron x-ray study of MgB2 formation when doped by SiC

Science.gov (United States)

Abrahamsen, A. B.; Grivel, J.-C.; Andersen, N. H.; Herrmann, M.; Häßler, W.; Birajdar, B.; Eibl, O.; Saksl, K.

2008-02-01

We have studied the evolution of the reaction xMg + 2B + ySiC → zMg1-p(B1-qCq)2 + yMg2Si in samples of 1, 2, 5 and 10 wt% SiC doping. We found a coincident formation of MgB2 and Mg2Si, whereas the crystalline part of the SiC nano particles is not reacting at all. Evidence for incorporation of carbon into the MgB2 phase was established from the decrease of the a-axis lattice parameter upon increasing SiC doping. An estimate of the MgB2 lower limit grain size was found to decrease from L100 = 795 Å and L002 = 337 Å at 1 wt% SiC to L100 = 227 Å and L002= 60 Å at 10 wt% SiC. Thus superconductivity might be suppressed at 10 wt% SiC doping due to the grain size approaching the coherence length.

The fractionation of adipose tissue procedure to obtain stromal vascular fractions for regenerative purposes

NARCIS (Netherlands)

van Dongen, Joris A.; Stevens, Hieronymus P.; Parvizi, Mojtaba; van der Lei, Berend; Harmsen, Martin C.

2016-01-01

Autologous adipose tissue transplantation is clinically used to reduce dermal scarring and to restore volume loss. The therapeutic benefit on tissue damage more likely depends on the stromal vascular fraction of adipose tissue than on the adipocyte fraction. This stromal vascular fraction can be

Large volume TENAX {sup registered} extraction of the bioaccessible fraction of sediment-associated organic compounds for a subsequent effect-directed analysis

Energy Technology Data Exchange (ETDEWEB)

Schwab, K.; Brack, W. [UFZ - Helmholtz Centre or Environmental Research, Leipzig (Germany). Dept. of Effect-Directed Analysis

2007-06-15

Background, Aim and Scope: Effect-directed analysis (EDA) is a powerful tool for the identification of key toxicants in complex environmental samples. In most cases, EDA is based on total extraction of organic contaminants leading to an erroneous prioritization with regard to hazard and risk. Bioaccessibility-directed extraction aims to discriminate between contaminants that take part in partitioning between sediment and biota in a relevant time frame and those that are enclosed in structures, that do not allow rapid desorption. Standard protocols of targeted extraction of rapidly desorbing, and thus bioaccessible fraction using TENAX {sup registered} are based only on small amounts of sediment. In order to get sufficient amounts of extracts for subsequent biotesting, fractionation, and structure elucidation a large volume extraction technique needs to be developed applying one selected extraction time and excluding toxic procedural blanks. Materials and Methods: Desorption behaviour of sediment contaminants was determined by a consecutive solid-solid extraction of sediment using TENAX {sup registered} fitting a tri-compartment model on experimental data. Time needed to remove the rapidly desorbing fraction trap was calculated to select a fixed extraction time for single extraction procedures. Up-scaling by about a factor of 100 provided a large volume extraction technique for EDA. Reproducibility and comparability to small volume approach were proved. Blanks of respective TENAX {sup registered} mass were investigated using Scenedesmus vacuolatus and Artemia salina as test organisms. Results: Desorption kinetics showed that 12 to 30 % of sediment associated pollutants are available for rapid desorption. t{sub r}ap is compound dependent and covers a range of 2 to 18 h. On that basis a fixed extraction time of 24 h was selected. Validation of large volume approach was done by the means of comparison to small method and reproducibility. The large volume showed a good

An improved design of TRISO particle with porous SiC inner layer by fluidized bed-chemical vapor deposition

Energy Technology Data Exchange (ETDEWEB)

Liu, Rongzheng; Liu, Malin, E-mail: liumalin@tsinghua.edu.cn; Chang, Jiaxing; Shao, Youlin; Liu, Bing

2015-12-15

Tristructural-isotropic (TRISO) particle has been successful in high temperature gas cooled reactor (HTGR), but an improved design is required for future development. In this paper, the coating layers are reconsidered, and an improved design of TRISO particle with porous SiC inner layer is proposed. Three methods of preparing the porous SiC layer, called high methyltrichlorosilane (MTS) concentration method, high Ar concentration method and hexamethyldisilane (HMDS) method, are experimentally studied. It is indicated that porous SiC layer can be successfully prepared and the density of SiC layer can be adjusted by tuning the preparation parameters. Microstructure and characterization of the improved TRISO coated particle are given based on scanning electron microscope (SEM), X-ray diffraction (XRD), Raman scattering and energy dispersive X-ray (EDX) analysis. It can be found that the improved TRISO coated particle with porous SiC layer can be mass produced successfully. The formation mechanisms of porous SiC layer are also discussed based on the fluidized bed-chemical vapor deposition principle. - Graphical abstract: An improved design of TRISO particle with porous SiC inner layer to replace the inner porous pyrolytic carbon layer was proposed and prepared by FB-CVD method. This new design is aimed to reduce the total internal pressure of the particles by reducing the formation of CO and to reduce the risks of amoeba effect. - Highlights: • An improved design of TRISO particle with porous SiC inner layer was proposed. • Three methods of preparing porous SiC layer are proposed and experimentally studied. • The density of porous SiC layer can be controlled by adjusting experimental parameters. • Formation mechanisms of porous SiC layer were given based on the FB-CVD principle. • TRISO particles with porous SiC inner layer were mass produced successfully.

In-situ synthesis of SiC particles by the structural evolution of TiCx in Al–Si melt

International Nuclear Information System (INIS)

Nie, Jinfeng; Li, Dakui; Wang, Enzhao; Liu, Xiangfa

2014-01-01

Highlights: • A facile method to in-situ synthesize SiC was developed utilizing the structural evolution of TiC x in Al–Si melt. • The SiC particles have the size range from 2.5 to 7.5 μm and a block-like morphology. • The SiC particles and (SiC + TiB 2 ) hybrid-particles reinforced Al–18Si composite were prepared. • The wear resistance effect of SiC on the based alloy was investigated. - Abstract: A facile method has been developed to in-situ synthesize SiC particles utilizing the structural instability and evolution of TiC x in Al–Si melt. It is considered that the synthesis of SiC particles occurs via the gradual reaction between TiC x and Si atoms, whilst Si content plays the crucial role in this approach. If the Si content in the melt is above 30%, TiC x directly reacts with Si and Al to form SiC, but the needle-like TiAl x Si y phase formed simultaneously will do harm to the mechanical properties of the composites. Thus, it is proposed to add B element in the melt to transform the TiAl x Si y into TiB 2 particles. Therefore, the SiC and (SiC + TiB 2 ) hybrid-particles reinforced Al–18Si composites were successfully prepared using the method. In the composites, the SiC particles have the size range from 2.5 to 7.5 μm and a block-like morphology. Furthermore, the mechanical properties of base alloy, including the wear resistance and macro-hardness, have been obviously improved by the in-situ SiC particles. Besides, the relevant underlying mechanisms are also discussed

High efficiency battery converter with SiC devices for residential PV systems

DEFF Research Database (Denmark)

Pham, Cam; Teodorescu, Remus; Kerekes, Tamas

2013-01-01

The demand for high efficiency and higher power density is a challenge for Si-based semiconductors due to the physical characteristics of material. These can be overcome by employing wide-band-gap materials like SiC. This paper compares a second generator SiC MOSFETs against a normally-on Trench...

Manufacturing: SiC Power Electronics for Variable Frequency Motor Drives

Energy Technology Data Exchange (ETDEWEB)

Horowitz, Kelsey A [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Bench Reese, Samantha R [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Remo, Timothy W [National Renewable Energy Laboratory (NREL), Golden, CO (United States)

2017-08-15

This brochure, published as an annual research highlight of the Clean Energy Manufacturing Analysis Center (CEMAC), summarizes CEMAC analysis of silicon carbide (SiC) power electronics for variable frequency motor drives. The key finding presented is that variations in manufacturing expertise, yields, and access to existing facilities impact regional costs and manufacturing location decisions for SiC ingots, wafers, chips, and power modules more than do core country-specific factors such as labor and electricity costs.

Intra-fraction motion of larynx radiotherapy

Science.gov (United States)

Durmus, Ismail Faruk; Tas, Bora

2018-02-01

In early stage laryngeal radiotherapy, movement is an important factor. Thyroid cartilage can move from swallowing, breathing, sound and reflexes. The effects of this motion on the target volume (PTV) during treatment were examined. In our study, the target volume movement during the treatment for this purpose was examined. Thus, setup margins are re-evaluated and patient-based PTV margins are determined. Intrafraction CBCT was scanned in 246 fractions for 14 patients. During the treatment, the amount of deviation which could be lateral, vertical and longitudinal axis was determined. ≤ ± 0.1cm deviation; 237 fractions in the lateral direction, 202 fractions in the longitudinal direction, 185 fractions in the vertical direction. The maximum deviation values were found in the longitudinal direction. Intrafraction guide in laryngeal radiotherapy; we are sure of the correctness of the treatment, the target volume is to adjust the margin and dose more precisely, we control the maximum deviation of the target volume for each fraction. Although the image quality of intrafraction-CBCT scans was lower than the image quality of planning CT, they showed sufficient contrast for this work.

Study on the detection of three-dimensional soot temperature and volume fraction fields of a laminar flame by multispectral imaging system

International Nuclear Information System (INIS)

Ni, Mingjiang; Zhang, Haidan; Wang, Fei; Xie, Zhengchao; Huang, Qunxing; Yan, Jianhua; Cen, Kefa

2016-01-01

Highlights: • Multispectral flame images were used to reconstruct the soot temperature and volume fraction. • The proposed multi-wavelength method and the original two-color method were compared. • The effect of signal to noise ratio (SNR) was discussed. • The best number of selected wavelengths was determined to be 6–11. - Abstract: Charge-coupled device (CCD) cameras with liquid crystal tunable filters (LCTF) were introduced to capture the multispectral flame images for obtaining the line-of-sight radiation intensities. A least square QR decomposition method was applied to solve the reconstruction matrix equation and obtain the multi-wavelength local emission distributions from which temperature and volume fraction profiles can be retrieved. Compared with the original two-color method, the use of a wide range of spectral data was proved to be capable of reducing the reconstruction error. Reconstruction results of the two methods with different signal to noise ratio (SNR) were discussed. The effect of selected wavelength number is analyzed and the best number is determined to be in the range of 6–11. The proposed multispectral imaging system was verified to be feasible for the reconstruction of temperature and soot volume fraction distributions according to the experimental measurement results.

Growth and characterization of high-purity SiC single crystals

Science.gov (United States)

Augustine, G.; Balakrishna, V.; Brandt, C. D.

2000-04-01

High-purity SiC single crystals with diameter up to 50 mm have been grown by the physical vapor transport method. Finite element analysis was used for thermal modeling of the crystal growth cavity in order to reduce stress in the grown crystal. Crystals are grown in high-purity growth ambient using purified graphite furniture and high-purity SiC sublimation sources. Undoped crystals up to 50 mm in diameter with micropipe density less than 100 cm -2 have been grown using this method. These undoped crystals exhibit resistivities in the 10 3 Ω cm range and are p-type due to the presence of residual acceptor impurities, mainly boron. Semi-insulating SiC material is obtained by doping the crystal with vanadium. Vanadium has a deep donor level located near the middle of the band gap, which compensates the residual acceptor resulting in semi-insulating behavior.

Hydrogen activated axial inter-conversion in SiC nanowires

International Nuclear Information System (INIS)

Ruemmeli, Mark H.; Adebimpe, David B.; Borowiak-Palen, Ewa; Gemming, Thomas; Ayala, Paola; Ioannides, Nicholas; Pichler, Thomas; Huczko, Andrzej; Cudzilo, Stanislaw; Knupfer, Martin; Buechner, Bernd

2009-01-01

A facile low pressure annealing route using NH 3 as a hydrogen source for the structural and chemical modification of SiC nanowires (SiCNWs) is presented. The developed route transforms SiCNWs into tubular SiC nanostructures while coaxial SiO 2 /SiCNWs reverse their sheath/core structure. Our findings suggest a decomposition process induced via the preferential substitution of silicon by hydrogen and via the difference in diffusion rates of available atomic species, which leads to axial structural rearrangement. In addition to these effects, the procedure improves the crystallinity of the samples. The process could be exploited as a viable route to manipulate a variety of nanostructures and films for doping and etching and structural manipulation. - Graphical abstract: SiC and SiO 2 /SiCNWs are shown to be structurally modified through a hydrogen activated replacement route which can even lead to the axial inter-conversion of species. The process could be exploited as a viable route to manipulate a variety of nanostructures and films for doping and etching and structural manipulation

Normal Isocurvature Surfaces and Special Isocurvature Circles (SIC)

Science.gov (United States)

Manoussakis, Gerassimos; Delikaraoglou, Demitris

2010-05-01

An isocurvature surface of a gravity field is a surface on which the value of the plumblines' curvature is constant. Here we are going to study the isocurvature surfaces of the Earth's normal gravity field. The normal gravity field is a symmetric gravity field therefore the isocurvature surfaces are surfaces of revolution. But even in this case the necessary relations for their study are not simple at all. Therefore to study an isocurvature surface we make special assumptions to form a vector equation which will hold only for a small coordinate patch of the isocurvature surface. Yet from the definition of the isocurvature surface and the properties of the normal gravity field is possible to express very interesting global geometrical properties of these surfaces without mixing surface differential calculus. The gradient of the plumblines' curvature function is vertical to an isocurvature surface. If P is a point of an isocurvature surface and "Φ" is the angle of the gradient of the plumblines' curvature with the equatorial plane then this direction points to the direction along which the curvature of the plumbline decreases / increases the most, and therefore is related to the strength of the normal gravity field. We will show that this direction is constant along a line of curvature of the isocurvature surface and this line is an isocurvature circle. In addition we will show that at each isocurvature surface there is at least one isocurvature circle along which the direction of the maximum variation of the plumblines' curvature function is parallel to the equatorial plane of the ellipsoid of revolution. This circle is defined as a Special Isocurvature Circle (SIC). Finally we shall prove that all these SIC lye on a special surface of revolution, the so - called SIC surface. That is to say, a SIC is not an isolated curve in the three dimensional space.

Passivation of surface-nanostructured f-SiC and porous SiC

DEFF Research Database (Denmark)

Ou, Haiyan; Lu, Weifang; Ou, Yiyu

The further enhancement of photoluminescence from nanostructured fluorescent silicon carbide (f-SiC) and porous SiC by using atomic layer deposited (ALD) Al2O3 is studied in this paper.......The further enhancement of photoluminescence from nanostructured fluorescent silicon carbide (f-SiC) and porous SiC by using atomic layer deposited (ALD) Al2O3 is studied in this paper....

Ohmic Contacts to P-Type SiC

National Research Council Canada - National Science Library

Crofton, John

2000-01-01

Alloys of aluminum (Al) have previously been used as ohmic contacts to p-type SiC, however the characteristics and performance of these contacts is drastically affected by the type and composition of the Al alloy...

Electronic Structure and Chemical Bond of Ti3SiC2 and Adding Al Element

Institute of Scientific and Technical Information of China (English)

MIN Xinmin; LU Ning; MEI Bingchu

2006-01-01

The relation among electronic structure, chemical bond and property of Ti3SiC2 and Al-doped was studied by density function and discrete variation (DFT-DVM) method. When Al element is added into Ti3SiC2, there is a less difference of ionic bond, which does not play a leading role to influent the properties. After adding Al, the covalent bond of Al and the near Ti becomes somewhat weaker, but the covalent bond of Al and the Si in the same layer is obviously stronger than that of Si and Si before adding. Therefore, in preparation of Ti3SiC2, adding a proper quantity of Al can promote the formation of Ti3SiC2. The density of state shows that there is a mixed conductor character in both of Ti3SiC2 and adding Al element. Ti3SiC2 is with more tendencies to form a semiconductor. The total density of state near Fermi lever after adding Al is larger than that before adding, so the electric conductivity may increase after adding Al.

Characterization of the evolution of the volume fraction of precipitates in aged AlMgSiCu alloys using DSC technique

International Nuclear Information System (INIS)

Esmaeili, Shahrzad; Lloyd, David J.

2005-01-01

Differential scanning calorimetry is used to quantify the evolution of the volume fraction of precipitates during age hardening in AlMgSiCu alloys. The calorimetry tests are run on alloy samples after aging for various times at 180 deg. C and the change in the collective heat effects from the major precipitation and dissolution processes in each run are used to determine the precipitation state of the samples. The method is implemented on alloys with various thermal histories prior to artificial aging, including commercial pre-aging histories. The estimated values for the relative volume fraction of precipitates are compared with the results from a newly developed analytical method using isothermal calorimetry and a related quantitative transmission electron microscopy work. Excellent agreement is obtained between the results from various methods

Tailoring of SiC nanoprecipitates formed in Si

Energy Technology Data Exchange (ETDEWEB)

Velisa, G., E-mail: gihan.velisa@cea.fr [CEA, DEN, Service de Recherches de Métallurgie Physique, Laboratoire JANNUS, F-91191 Gif-sur-Yvette (France); Horia Hulubei National Institute for Physics and Nuclear Engineering, P.O. Box MG-6, 077125 Magurele (Romania); Trocellier, P. [CEA, DEN, Service de Recherches de Métallurgie Physique, Laboratoire JANNUS, F-91191 Gif-sur-Yvette (France); Thomé, L. [Centre de Spectrométrie Nucléaire et de Spectrométrie de Masse, UMR8609, Bât. 108, 91405 Orsay (France); Vaubaillon, S. [CEA, INSTN, UEPTN, Laboratoire JANNUS, F-91191 Gif-sur-Yvette (France); Miro, S.; Serruys, Y.; Bordas, É. [CEA, DEN, Service de Recherches de Métallurgie Physique, Laboratoire JANNUS, F-91191 Gif-sur-Yvette (France); Meslin, E. [CEA, DEN, Service de Recherches de Métallurgie Physique, F-91191 Gif-sur-Yvette (France); Mylonas, S. [Centre de Spectrométrie Nucléaire et de Spectrométrie de Masse, UMR8609, Bât. 108, 91405 Orsay (France); Coulon, P.E. [Ecole Polytechnique, Laboratoire des Solides Irradiés, CEA/DSM/IRAMIS-CNRS, 91128 Palaiseau Cedex (France); Leprêtre, F.; Pilz, A.; Beck, L. [CEA, DEN, Service de Recherches de Métallurgie Physique, Laboratoire JANNUS, F-91191 Gif-sur-Yvette (France)

2013-07-15

The SiC synthesis through single-beam of C{sup +}, and simultaneous-dual-beam of C{sup +} and Si{sup +} ion implantations into a Si substrate heated at 550 °C has been studied by means of three complementary analytical techniques: nuclear reaction analysis (NRA), Raman, and transmission electron microscopy (TEM). It is shown that a broad distribution of SiC nanoprecipitates is directly formed after simultaneous-dual-beam (520-keV C{sup +} and 890-keV Si{sup +}) and single-beam (520-keV C{sup +}) ion implantations. Their shape appear as spherical (average size ∼4–5 nm) and they are in epitaxial relationship with the silicon matrix.

Liquid phase sintered SiC ceramics from starting materials of different grade Cerâmicas à base de SiC sinterizadas via fase líquida a partir de matérias-primas de diferentes purezas

Directory of Open Access Journals (Sweden)

V. A. Izhevskyi

2004-09-01

Full Text Available Possibility of high performance ceramics manufactured from commercial SiC powder of technical grade has been shown. Sintering behavior and microstructure formation under conditions of liquid phase sintering (LPS with oxynitride sintering aids (AlN-Y2O3 of three SiC-based compositions have been investigated. Two of the compositions were based on Alcoa 1000 SiC powder of technical grade, and the third one, which was used as a reference, was based on H.C. Starck UF-15 fine grade commercial powder. Milling process used for Alcoa 1000 SiC powder granulometry improvement has been investigated in detail, while chemical treatment of milled SiC powders has been used for pick-up impurities removal. Dilatometric experiments showed that SiC powder of technical grade after appropriate treatment exhibits sinterability comparable with the fine grade SiC. Microstructural investigations performed on sintered samples showed that the final microstructure of the Alcoa 1000 SiC based materials was practically identical with the H.C. Starck SiC based reference ones. Preliminary investigations of hardness and fracture toughness were carried out revealing excellent results for the materials produced from cheaper, nationally produced starting powder.Neste trabalho é apresentada a possibilidade de obtenção de cerâmicas de SiC de alto desempenho a partir de matéria-prima comercial de grau técnico. Foi realizado o estudo de sinterização via fase líquida e desenvolvimento microestrutural de três composições à base de SiC tendo como aditivos de sinterização AlN e Y2O3 . Duas destas composições são à base de SiC-1000 da Alcoa, grau técnico, e a terceira, utilizada como referência, à base do UF-15 da H.C. Starck - Alemanha, pó comercial de granulometria fina. O processo de moagem do pó SiC-1000 da Alcoa foi acompanhado por medidas de distribuição granulométrica e posterior ataque químico, para remoção de impurezas. Os pós de grau técnico, ap

Immunoglobulin G levels during collection of large volume plasma for fractionation.

Science.gov (United States)

Burkhardt, Thomas; Rothe, Remo; Moog, Rainer

2017-06-01

There is a need of comprehensive work dealing with the quality of plasma for fractionation with respect to the IgG content as today most plasma derivates are used to treat patients with immunodeficiencies and autoimmune disorders. Therefore, a prospective study was carried out to analyse IgG levels before plasmapheresis and every 200ml collected plasma. Fifty-four experienced plasmapheresis donors were recruited for subsequent 850ml plasmapheresis using the Aurora Plasmapheresis System. Donorś peripheral blood counts were analysed before and after plasmapheresis using an electronic counter. Total protein, IgG and citrate were measured turbidometrically before, during and after apheresis as well as in the plasma product. Furthermore, platelets, red and white blood cells were analysed as parameters of product quality. An average of 2751±247ml blood was processed in 47±6min. The collected plasma volume was 850±1mL and citrate consumption was 177±15mL. A continuous drop of donors' IgG level was observed during plasmapheresis. The drop was 13% of the IgG baseline value at 800mL collected plasma. Total protein, IgG and cell counts of the plasma product met current guidelines of plasma for fractionation. Donors' IgG levels during apheresis showed a steady decrease without compromising the quality of plasma product. Copyright © 2017 Elsevier Ltd. All rights reserved.

Effects of AlN on the densification and mechanical properties of pressureless-sintered SiC ceramics

Directory of Open Access Journals (Sweden)

Qisong Li

2016-02-01

Full Text Available In the present work, SiC ceramics was fabricated with AlN using B4C and C as sintering aids by a solid-state pressureless-sintered method. The effects of AlN contents on the densification, mechanical properties, phase compositions, and microstructure evolutions of as-obtained SiC ceramics were thoroughly investigated. AlN was found to promote further densification of the SiC ceramics due to its evaporation over 1800 °C, transportation, and solidification in the pores resulted from SiC grain coarsening. The highest relative density of 99.65% was achieved for SiC sample with 15.0 wt% AlN by the pressureless-sintered method at 2130 °C for 1 h in Ar atmosphere. Furthermore, the fracture mechanism for SiC ceramics containing AlN tended to transfer from single transgranular fracture mode to both transgranular fracture and intergranular fracture modes when the sample with 30.0 wt% AlN sintered at 1900 °C for 1 h in Ar. Also, SiC ceramics with 30.0 wt% AlN exhibited the highest fracture toughness of 5.23 MPa m1/2 when sintered at 1900 °C.

Hydrogen generation due to water splitting on Si - terminated 4H-Sic(0001) surfaces

Science.gov (United States)

Li, Qingfang; Li, Qiqi; Yang, Cuihong; Rao, Weifeng

2018-02-01

The chemical reactions of hydrogen gas generation via water splitting on Si-terminated 4H-SiC surfaces with or without C/Si vacancies were studied by using first-principles. We studied the reaction mechanisms of hydrogen generation on the 4H-SiC(0001) surface. Our calculations demonstrate that there are major rearrangements in surface when H2O approaches the SiC(0001) surface. The first H splitting from water can occur with ground-state electronic structures. The second H splitting involves an energy barrier of 0.65 eV. However, the energy barrier for two H atoms desorbing from the Si-face and forming H2 gas is 3.04 eV. In addition, it is found that C and Si vacancies can form easier in SiC(0001)surfaces than in SiC bulk and nanoribbons. The C/Si vacancies introduced can enhance photocatalytic activities. It is easier to split OH on SiC(0001) surface with vacancies compared to the case of clean SiC surface. H2 can form on the 4H-SiC(0001) surface with C and Si vacancies if the energy barriers of 1.02 and 2.28 eV are surmounted, respectively. Therefore, SiC(0001) surface with C vacancy has potential applications in photocatalytic water-splitting.

Study on porosity of ceramic SiC using small angle neutron scattering

International Nuclear Information System (INIS)

Li Jizhou; Yang Jilian; Kang Jian; Ye Chuntang

1996-01-01

The mechanical properties of functional heat-resistant ceramics SiC are significantly influenced by the concentration and dimensions of pores. Small angle neutron scattering measurements for 3 SiC samples with different densities are performed on C1-2 SANS instrument of the University of Tokyo. Two groups of the neutron data are obtained using 8 and 16 m of secondary flight path, 1 and 0.7 nm of neutron wave lengths, respectively. After deduction of background measurement and transmission correction, both neutron data are linked up with each other. The patterns of neutron data of 3 samples with Q range from 0.028∼0.5 nm -1 are almost with axial symmetry, showing that the shape of pores is almost spherical. Using Mellin transform, size distributions of pores in 3 samples are obtained. The average size (∼19 nm) of pores for hot-pressed SiC sample with higher density is smaller than the others (∼ 21 nm). It seems to be the reason why the density of hot-pressed SiC sample is higher than not hot-pressed sample

The influence of various dielectric parameters on the reststrahlen region of SiC

International Nuclear Information System (INIS)

Engelbrecht, J.A.A.; Rooyen, I.J. van

2011-01-01

The reststrahlen region of SiC is analysed with the goal of establishing the origin of different shapes of this band, by varying the dielectric parameters involved when simulating the reststrahlen region as obtained by infrared reflectance. -- Research highlights: → An anomalous peak observed in the reststrahlen band of SiC was investigated. → The reflection spectrum of SiC in the reststrahlen region was simulated by theoretical calculations. → The influence on the reststrahlen band of the dielectric parameters used in the simulations is discussed. → Dielectric parameters used in the simulations did not yield the anomalous peak that is observed experimentally.

The influence of various dielectric parameters on the reststrahlen region of SiC

Energy Technology Data Exchange (ETDEWEB)

Engelbrecht, J.A.A., E-mail: Japie.Engelbrecht@nmmu.ac.z [Physics Department, Nelson Mandela Metropolitan University, PO Box 77000, Port Elizabeth 6031 (South Africa); Rooyen, I.J. van [Physics Department, Nelson Mandela Metropolitan University, PO Box 77000, Port Elizabeth 6031 (South Africa); National Laser Centre, CSIR, PO Box 395, Pretoria 0001 (South Africa)

2011-02-01

The reststrahlen region of SiC is analysed with the goal of establishing the origin of different shapes of this band, by varying the dielectric parameters involved when simulating the reststrahlen region as obtained by infrared reflectance. -- Research highlights: {yields} An anomalous peak observed in the reststrahlen band of SiC was investigated. {yields} The reflection spectrum of SiC in the reststrahlen region was simulated by theoretical calculations. {yields} The influence on the reststrahlen band of the dielectric parameters used in the simulations is discussed. {yields} Dielectric parameters used in the simulations did not yield the anomalous peak that is observed experimentally.

Defects annihilation behavior of neutron-irradiated SiC ceramics densified by liquid-phase-assisted method after post-irradiation annealing

Directory of Open Access Journals (Sweden)

Mohd Idzat Idris

2016-12-01

Full Text Available Numerous studies on the recovery behavior of neutron-irradiated high-purity SiC have shown that most of the defects present in it are annihilated by post-irradiation annealing, if the neutron fluence is less than 1×1026 n/m2 (>0.1MeV and the irradiation is performed at temperatures lower than 973K. However, the recovery behavior of SiC fabricated by the nanoinfiltrated and transient eutectic phase (NITE process is not well understood. In this study, the effects of secondary phases on the irradiation-related swelling and recovery behavior of monolithic NITE-SiC after post-irradiation annealing were studied. The NITE-SiC specimens were irradiated in the BR2 reactor at fluences of up to 2.0–2.5×1024 n/m2 (E>0.1MeV at 333–363K. This resulted in the specimens swelling up ∼1.3%, which is 0.1% higher than the increase seen in concurrently irradiated high-purity SiC. The recovery behaviors of the specimens after post-irradiation thermal annealing were examined using a precision dilatometer; the specimens were heated at temperatures of up to 1673K using a step-heating method. The recovery curves were analyzed using a first-order model, and the rate constants for each annealing step were obtained to determine the activation energy for volume recovery. The NITE-A specimen (containing 12 wt% sintering additives recovered completely after annealing at ∼1573K; however, it shrank because of the volatilization of the oxide phases at 1673K. The NITE-B specimen (containing 18wt% sintering additives did not recover fully, since the secondary phase (YAG was crystallized during the annealing process. The recovery mechanism of NITE-A SiC was based on the recombination of the C and Si Frenkel pairs, which were very closely sited or only slightly separated at temperatures lower than 1223K, as well as the recombination of the slightly separated C Frenkel pairs and the migration of C and Si interstitials at temperatures of 1223–1573K. That is to say, the

X-ray micro computed tomography characterization of cellular SiC foams for their applications in chemical engineering

Energy Technology Data Exchange (ETDEWEB)

Ou, Xiaoxia [School of Chemical Engineering and Analytical Science, The University of Manchester, M13 9PL (United Kingdom); Zhang, Xun; Lowe, Tristan [Henry Moseley X-ray Imaging Facility, Materials Science Centre, School of Materials, The University of Manchester, M13 9PL (United Kingdom); Blanc, Remi [FEI, 3 Impasse Rudolf Diesel, BP 50227, 33708 Mérignac (France); Rad, Mansoureh Norouzi [School of Chemical Engineering and Analytical Science, The University of Manchester, M13 9PL (United Kingdom); Wang, Ying [Henry Moseley X-ray Imaging Facility, Materials Science Centre, School of Materials, The University of Manchester, M13 9PL (United Kingdom); Batail, Nelly; Pham, Charlotte [SICAT SARL, 20 Place des Halles, 67000 Strasbourg (France); Shokri, Nima; Garforth, Arthur A. [School of Chemical Engineering and Analytical Science, The University of Manchester, M13 9PL (United Kingdom); Withers, Philip J. [Henry Moseley X-ray Imaging Facility, Materials Science Centre, School of Materials, The University of Manchester, M13 9PL (United Kingdom); Fan, Xiaolei, E-mail: xiaolei.fan@manchester.ac.uk [School of Chemical Engineering and Analytical Science, The University of Manchester, M13 9PL (United Kingdom)

2017-01-15

Open-cell SiC foams clearly are promising materials for continuous-flow chemical applications such as heterogeneous catalysis and distillation. X-ray micro computed tomography characterization of cellular β-SiC foams at a spatial voxel size of 13.6{sup 3} μm{sup 3} and the interpretation of morphological properties of SiC open-cell foams with implications to their transport properties are presented. Static liquid hold-up in SiC foams was investigated through in-situ draining experiments for the first time using the μ-CT technique providing thorough 3D information about the amount and distribution of liquid hold-up inside the foam. This will enable better modeling and design of structured reactors based on SiC foams in the future. In order to see more practical uses, μ-CT data of cellular foams must be exploited to optimize the design of the morphology of foams for a specific application. - Highlights: •Characterization of SiC foams using novel X-ray micro computed tomography. •Interpretation of structural properties of SiC foams regarding to their transport properties. •Static liquid hold-up analysis of SiC foams through in-situ draining experiments.

Porous SiC ceramics fabricated by quick freeze casting and solid state sintering

Directory of Open Access Journals (Sweden)

Feng Wang

2017-06-01

Full Text Available Porous SiC ceramics with uniform microstructure were fabricated by quick freezing in liquid nitrogen and solid state sintering. Poly (vinyl alcohol (PVA was added as binder and pore morphology controller in this work. The microstructure and mechanical properties of porous SiC ceramics could be controlled by the composition of the aqueous slurries. Both solid content of the slurries and PVA content impacted on the pore structures and mechanical properties of the porous SiC ceramics. The solid content of slurries and PVA content varied from 60 to 67.5 wt% and 2–6 wt%, respectively. Besides, the grain morphology of ceramics was also tailored by changing the sintering temperature from 2050 to 2150 °C. Porous SiC ceramics with an average porosity of 42.72%, flexural strength of 59.28 MPa were obtained at 2150 °C from 67.5 wt% slurries with 2 wt% PVA.

Preparation of SiC Compacts by the Rapid Proto typing Machine

International Nuclear Information System (INIS)

Abdelrahman, A.A.M.; Ahmed, A.Z.; Elmasry, M.A.A.

2008-01-01

The preparation of ceramic green bodies from powders by the rapid proto typing is a promising technique. In this work SiC green bodies were prepared from black SiC powder mixed with 10 wt % organic binder namely Ave be SP G20 starch. Different liquid binders were investigated and were successful in producing strong green bodies such as NH 4 OH in the ph range 9-10 or 1 % HCl solution in water and or a mixture of 1% NH 4 Cl and NH 4 OH in the ph range of 8.5 to 9. The green bodies were then preheated at 200 degree C to eliminate the starch by thermal decomposition. After that these parts were infiltrated using molten silicon at 1450 degree C in Argon atmosphere. Unfortunately it was impossible to infiltrate the green bodies using liquid silicon. Another technique was followed which is dipping of the green bodies in liquid silicon. This method was successful. The densities of the green and dipped bodies were determined and they were examined under the metallo graph and SEM. It was found that no SiC dissolved in the silicon after dipping. This was concluded from the presence of sharp corners of SiC grains

Nanomechanical properties of SiC films grown from C{sub 60} precursors using atomic force microscopy

Energy Technology Data Exchange (ETDEWEB)

Morse, K. [Colorado School of Mines, Golden, CO (United States); Balooch, M.; Hamza, A.V.; Belak, J. [Lawrence Livermore National Lab., CA (United States)

1994-12-01

The mechanical properties of SiC films grown via C{sub 60} precursors were determined using atomic force microscopy (AFM). Conventional silicon nitride and modified diamond cantilever AFM tips were employed to determine the film hardness, friction coefficient, and elastic modulus. The hardness is found to be between 26 and 40 GPa by nanoindentation of the film with the diamond tip. The friction coefficient for the silicon nitride tip on the SiC film is about one third that for silicon nitride sliding on a silicon substrate. By combining nanoindentation and AFM measurements an elastic modulus of {approximately}300 GPa is estimated for these SiC films. In order to better understand the atomic scale mechanisms that determine the hardness and friction of SiC, we simulated the molecular dynamics of a diamond indenting a crystalline SiC substrate.

Effect of organic additives on mechanical properties of SiC ceramics prepared by a modified gelcasting method

Directory of Open Access Journals (Sweden)

Feng Wang

2016-12-01

Full Text Available A novel and simple gel system of isobutylene and maleic anhydride (PIBM was used to prepare SiC ceramics. The rheological behaviour of the SiC slurries was investigated as function of organic additives. The SiC slurries with 0.2 wt.% PIBM and 0.2 wt.% tetramethylammonium hydroxide (TMAH showed low viscosity, which was favourable for casting SiC green bodies. In order to obtain homogeneous green bodies, polyvinyl alcohol (PVA was used to assist the dispersion of carbon black in the slurries, and polyethylene glycol (PEG was added to inhibit the surface exfoliation of green bodies. The content of PVA was controlled carefully to avoid the warpage of green bodies during the drying process. Finally, homogeneous defect-free SiC green bodies were successfully fabricated via aqueous gelcasting. The SiC ceramics sintered at 2100 °C (prepared from slurries with solid content of 60 wt.% showed an average flexural strength of 305.7 MPa with porosity of 19.92%.

Validity of automated measurement of left ventricular ejection fraction and volume using the Philips EPIQ system.

Science.gov (United States)

Hovnanians, Ninel; Win, Theresa; Makkiya, Mohammed; Zheng, Qi; Taub, Cynthia

2017-11-01

To assess the efficiency and reproducibility of automated measurements of left ventricular (LV) volumes and LV ejection fraction (LVEF) in comparison to manually traced biplane Simpson's method. This is a single-center prospective study. Apical four- and two-chamber views were acquired in patients in sinus rhythm. Two operators independently measured LV volumes and LVEF using biplane Simpson's method. In addition, the image analysis software a2DQ on the Philips EPIQ system was applied to automatically assess the LV volumes and LVEF. Time spent on each analysis, using both methods, was documented. Concordance of echocardiographic measures was evaluated using intraclass correlation (ICC) and Bland-Altman analysis. Manual tracing and automated measurement of LV volumes and LVEF were performed in 184 patients with a mean age of 67.3 ± 17.3 years and BMI 28.0 ± 6.8 kg/m 2 . ICC and Bland-Altman analysis showed good agreements between manual and automated methods measuring LVEF, end-systolic, and end-diastolic volumes. The average analysis time was significantly less using the automated method than manual tracing (116 vs 217 seconds/patient, P Automated measurement using the novel image analysis software a2DQ on the Philips EPIQ system produced accurate, efficient, and reproducible assessment of LV volumes and LVEF compared with manual measurement. © 2017, Wiley Periodicals, Inc.

Creep behavior for advanced polycrystalline SiC fibers

Energy Technology Data Exchange (ETDEWEB)

Youngblood, G.E.; Jones, R.H. [Pacific Northwest National Lab., Richland, WA (United States); Kohyama, Akira [Kyoto Univ. (Japan)] [and others

1997-04-01

A bend stress relaxation (BSR) test has been utilized to examine irradiation enhanced creep in polycrystalline SiC fibers which are under development for use as fiber reinforcement in SiC/SiC composite. Qualitative, S-shaped 1hr BSR curves were compared for three selected advanced SiC fiber types and standard Nicalon CG fiber. The temperature corresponding to the middle of the S-curve (where the BSR parameter m = 0.5) is a measure of a fiber`s thermal stability as well as it creep resistance. In order of decreasing thermal creep resistance, the measured transition temperatures were Nicalon S (1450{degrees}C), Sylramic (1420{degrees}C), Hi-Nicalon (1230{degrees}C) and Nicalon CG (1110{degrees}C).

A probabilistic method for determining the volume fraction of pre-embedded capsules in self-healing materials

International Nuclear Information System (INIS)

Lv, Zhong; Chen, Huisu

2014-01-01

Autonomous healing of cracks using pre-embedded capsules containing healing agent is becoming a promising approach to restore the strength of damaged structures. In addition to the material properties, the size and volume fraction of capsules influence crack healing in the matrix. Understanding the crack and capsule interaction is critical in the development and design of structures made of self-healing materials. Assuming that the pre-embedded capsules are randomly dispersed we theoretically model flat ellipsoidal crack interaction with capsules and determine the probability of a crack intersecting the pre-embedded capsules i.e. the self-healing probability. We also develop a probabilistic model of a crack simultaneously meeting with capsules and catalyst carriers in two-component self-healing system matrix. Using a risk-based healing approach, we determine the volume fraction and size of the pre-embedded capsules that are required to achieve a certain self-healing probability. To understand the effect of the shape of the capsules on self-healing we theoretically modeled crack interaction with spherical and cylindrical capsules. We compared the results of our theoretical model with Monte-Carlo simulations of crack interaction with capsules. The formulae presented in this paper will provide guidelines for engineers working with self-healing structures in material selection and sustenance. (paper)

Preparation and performance of Pt/PTFE/Foam SiC as a hydrophobic catalyst for LPCE

International Nuclear Information System (INIS)

He, Jianchao; Wang, Heyi; Xiao, Chengjian; Li, Jiamao; Chen, Ping; Hou, Jingwei

2016-01-01

Highlights: • A new type of foam material, Foam SiC with three-dimensional network structure, was chosen as the carrier of catalyst. • Foam SiC was hydrophobic treated by PTFE, and achieved a good hydrophobic property. • Pt/PTFE/Foam SiC was prepared by impregnation method with Pt-organic solution and gaseous phase reduction method. • The hydrophobic catalysts were packed with Dixon phosphor bronze gauze rings (about 3 mm × 3 mm) in LPCE system to test the catalytic performance. • The effect of different size of the catalyst on LPCE was been tested. - Abstract: Platinum catalysts supported on a composite of polytetrafluoroethylene (PTFE) and Foam SiC (Pt/PTFE/Foam SiC) have been proposed and prepared by an impregnation method. The as-prepared Pt/PTFE/Foam SiC was characterized by compression load testing, dynamic contact angle measurement, SEM, XRD, and TEM. The results show that the catalyst prepared by triple hydrophobic treatment had an initial contact angle of 134.2°, a good compression performance of 3.2 MPa, and platinum nanoparticles of 12.1 nm (average size). The catalytic activity of the catalyst was tested with different packing methods, reaction temperatures, and gas-liquid ratios. An excellent hydrogen isotope exchange performance was observed using a hydrophilic packing material-to-catalyst ratio of 25% and reaction temperature of 80 °C. Pt/PTFE/Foam SiC may be used as a hydrophobic catalyst for a water detritiation system (WDS) via a liquid-phase catalytic exchange process (LPCE).

Preparation and performance of Pt/PTFE/Foam SiC as a hydrophobic catalyst for LPCE

Energy Technology Data Exchange (ETDEWEB)

He, Jianchao; Wang, Heyi, E-mail: hywang@caep.cn; Xiao, Chengjian; Li, Jiamao; Chen, Ping; Hou, Jingwei

2016-12-15

Highlights: • A new type of foam material, Foam SiC with three-dimensional network structure, was chosen as the carrier of catalyst. • Foam SiC was hydrophobic treated by PTFE, and achieved a good hydrophobic property. • Pt/PTFE/Foam SiC was prepared by impregnation method with Pt-organic solution and gaseous phase reduction method. • The hydrophobic catalysts were packed with Dixon phosphor bronze gauze rings (about 3 mm × 3 mm) in LPCE system to test the catalytic performance. • The effect of different size of the catalyst on LPCE was been tested. - Abstract: Platinum catalysts supported on a composite of polytetrafluoroethylene (PTFE) and Foam SiC (Pt/PTFE/Foam SiC) have been proposed and prepared by an impregnation method. The as-prepared Pt/PTFE/Foam SiC was characterized by compression load testing, dynamic contact angle measurement, SEM, XRD, and TEM. The results show that the catalyst prepared by triple hydrophobic treatment had an initial contact angle of 134.2°, a good compression performance of 3.2 MPa, and platinum nanoparticles of 12.1 nm (average size). The catalytic activity of the catalyst was tested with different packing methods, reaction temperatures, and gas-liquid ratios. An excellent hydrogen isotope exchange performance was observed using a hydrophilic packing material-to-catalyst ratio of 25% and reaction temperature of 80 °C. Pt/PTFE/Foam SiC may be used as a hydrophobic catalyst for a water detritiation system (WDS) via a liquid-phase catalytic exchange process (LPCE).

Diffusion of Ag, Au and Cs implants in MAX phase Ti3SiC2

Energy Technology Data Exchange (ETDEWEB)

Jiang, Weilin; Henager, Charles H.; Varga, Tamas; Jung, Hee Joon; Overman, Nicole R.; Zhang, Chonghong; Gou, Jie

2015-05-16

MAX phases (M: early transition metal; A: elements in group 13 or 14; X: C or N), such as titanium silicon carbide (Ti3SiC2), have a unique combination of both metallic and ceramic properties, which make them attractive for potential nuclear applications. Ti3SiC2 has been considered as a possible fuel cladding material. This study reports on the diffusivities of fission product surrogates (Ag and Cs) and a noble metal Au (with diffusion behavior similar to Ag) in this ternary compound at elevated temperatures, as well as in dual-phase nanocomposite of Ti3SiC2/3C-SiC and polycrystalline CVD 3C-SiC for behavior comparisons. Samples were implanted with Ag, Au or Cs ions and characterized with various methods, including x-ray diffraction, electron backscatter diffraction, energy dispersive x-ray spectroscopy, Rutherford backscattering spectrometry, helium ion microscopy, and transmission electron microscopy. The results show that in contrast to immobile Ag in 3C-SiC, there is a significant outward diffusion of Ag in Ti3SiC2 within the dual-phase nanocomposite during Ag ion implantation at 873 K. Similar behavior of Au in polycrystalline Ti3SiC2 was also observed. Cs out-diffusion and release from Ti3SiC2 occurred during post-implantation thermal annealing at 973 K. This study suggests caution and further studies in consideration of Ti3SiC2 as a fuel cladding material for advanced nuclear reactors operating at very high temperatures.

Loss Model and Efficiency Analysis of Tram Auxiliary Converter Based on a SiC Device

Directory of Open Access Journals (Sweden)

Hao Liu

2017-12-01

Full Text Available Currently, the auxiliary converter in the auxiliary power supply system of a modern tram adopts Si IGBT as its switching device and with the 1700 V/225 A SiC MOSFET module commercially available from Cree, an auxiliary converter using all SiC devices is now possible. A SiC auxiliary converter prototype is developed during this study. The author(s derive the loss calculation formula of the SiC auxiliary converter according to the system topology and principle and each part loss in this system can be calculated based on the device datasheet. Then, the static and dynamic characteristics of the SiC MOSFET module used in the system are tested, which aids in fully understanding the performance of the SiC devices and provides data support for the establishment of the PLECS loss simulation model. Additionally, according to the actual circuit parameters, the PLECS loss simulation model is set up. This simulation model can simulate the actual operating conditions of the auxiliary converter system and calculate the loss of each switching device. Finally, the loss of the SiC auxiliary converter prototype is measured and through comparison it is found that the loss calculation theory and PLECS loss simulation model is valuable. Furthermore, the thermal images of the system can prove the conclusion about loss distribution to some extent. Moreover, these two methods have the advantages of less variables and fast calculation for high power applications. The loss models may aid in optimizing the switching frequency and improving the efficiency of the system.

Intracapillary HbO2 saturations in murine tumours and human tumour xenografts measured by cryospectrophotometry: relationship to tumour volume, tumour pH and fraction of radiobiologically hypoxic cells.

Science.gov (United States)

Rofstad, E K; Fenton, B M; Sutherland, R M

1988-05-01

Frequency distributions for intracapillary HbO2 saturation were determined for two murine tumour lines (KHT, RIF-1) and two human ovarian carcinoma xenograft lines (MLS, OWI) using a cryospectrophotometric method. The aim was to search for possible relationships between HbO2 saturation status and tumour volume, tumour pH and fraction of radiobiologically hypoxic cells. Tumour pH was measured by 31P NMR spectroscopy. Hypoxic fractions were determined from cell survival curves for tumours irradiated in vivo and assayed in vitro. Tumours in the volume range 100-4000 mm3 were studied and the majority of the vessels were found to have HbO2 saturations below 10%. The volume-dependence of the HbO2 frequency distributions differed significantly among the four tumour lines; HbO2 saturation status decreased with increasing tumour volume for the KHT, RIF-1 and MLS lines and was independent of tumour volume for the OWI line. The data indicated that the rate of decrease in HbO2 saturation status during tumour growth was related to the rate of development of necrosis. The volume-dependence of tumour pH was very similar to that of the HbO2 saturation status for all tumour lines. Significant correlations were therefore found between HbO2 saturation status and tumour pH, both within tumour lines and across the four tumour lines, reflecting that the volume-dependence of both parameters probably was a compulsory consequence of reduced oxygen supply conditions during tumour growth. Hypoxic fraction increased during tumour growth for the KHT, RIF-1 and MLS lines and was volume-independent for the OWI line, suggesting a relationship between HbO2 saturation status and hypoxic fraction within tumour lines. However, there was no correlation between these two parameters across the four tumour lines, indicating that the hypoxic fraction of a tumour is not determined only by the oxygen supply conditions; other parameters may also be important, e.g. oxygen diffusivity, rate of oxygen

Pore Formation Process of Porous Ti3SiC2 Fabricated by Reactive Sintering

Directory of Open Access Journals (Sweden)

Huibin Zhang

2017-02-01

Full Text Available Porous Ti3SiC2 was fabricated with high purity, 99.4 vol %, through reactive sintering of titanium hydride (TiH2, silicon (Si and graphite (C elemental powders. The reaction procedures and the pore structure evolution during the sintering process were systematically studied by X-ray diffraction (XRD and scanning electron microscope (SEM. Our results show that the formation of Ti3SiC2 from TiH2/Si/C powders experienced the following steps: firstly, TiH2 decomposed into Ti; secondly, TiC and Ti5Si3 intermediate phases were generated; finally, Ti3SiC2 was produced through the reaction of TiC, Ti5Si3 and Si. The pores formed in the synthesis procedure of porous Ti3SiC2 ceramics are derived from the following aspects: interstitial pores left during the pressing procedure; pores formed because of the TiH2 decomposition; pores formed through the reactions between Ti and Si and Ti and C powders; and the pores produced accompanying the final phase synthesized during the high temperature sintering process.

Corrosion and wear behavior of functionally graded Al2024/SiC composites produced by hot pressing and consolidation

Energy Technology Data Exchange (ETDEWEB)

Erdemir, Fatih; Canakci, Aykut, E-mail: aykut@ktu.edu.tr; Varol, Temel; Ozkaya, Serdar

2015-09-25

Highlights: • Functionally graded Al2024/SiC composites were produced by hot pressing. • Effect of the number of graded layers was investigated on the corrosion behavior. • Functionally graded composites has the most corrosion resistant than composites. • Wear mechanisms of Al2024/SiC composites were explained. - Abstract: Functionally graded Al2024/SiC composites (FGMs) with varying percentage of SiC (30–60%) were produced by hot pressing and consolidation method. The effects of SiC content and number of layers of Al2024/SiC FGMs on the corrosion and wear behaviors were investigated. The microstructures of these composites were characterized by a scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS). The corrosion performances of composites were evaluated by potentiodynamic polarization scans in 3.5% NaCl solution. Corrosion experiments shows that corrosion rate (1109 mpy) of two layered FGMs which containing 50 wt.% SiC were much higher than Al2024 matrix (2569 mpy) and Al2024/50 wt.% SiC composite (2201 mpy). Mechanical properties of these composites were evaluated by microhardness measurements and ball-on-disk wear tests. As the applied load change from 15 to 20 N, the wear rates of the Al2024 increased significantly and wear mechanism transformed from mild to severe wear regime. It has been shown that Al2024/40 wt.% SiC composite has lower wear rate where adhesive and abrasive wear mechanisms play a major role.

Airborne release fractions/rates and respirable fractions for nonreactor nuclear facilities. Volume 2, Appendices

International Nuclear Information System (INIS)

1994-12-01

This document contains compiled data from the DOE Handbook on Airborne Release Fractions/Rates and Respirable Fractions for Nonreactor Nuclear facilities. Source data and example facilities utilized, such as the Plutonium Recovery Facility, are included

Effect of SiC whisker addition on the microstructures and mechanical properties of Ti(C, N)-based cermets

International Nuclear Information System (INIS)

Wu, Peng; Zheng, Yong; Zhao, Yongle; Yu, Haizhou

2011-01-01

Ti(C, N)-based cermets with addition of SiC whisker (SiC w ) were prepared by vacuum sintering. The microstructures of the prepared cermets were investigated by using X-ray diffractometry (XRD) and scanning electron microscopy (SEM). Mechanical properties such as transverse rupture strength (TRS), fracture toughness (K IC ) and hardness (HRA) were also measured. It was found that the grain size of the cermets was affected by the SiC whisker addition. The cermets with 1.0 wt.% SiC whisker addition exhibited the smallest grain size. The porosities of the cermets increased with increasing SiC whisker additions. The addition of the SiC whisker had no influence on the phase constituents of the cermets. Compared with the cermets with no whisker addition, the highest TRS and fracture toughness for cermets with 1.0 wt.% SiC whisker addition increased by about 24% and 29%, respectively. The strengthening mechanisms were attributed to finer grain size, homogeneous microstructure and moderate thickness of rim phase. The toughening mechanisms were characterized by crack deflection, whisker bridging and whisker pulling-out.

CMR reference values for left ventricular volumes, mass, and ejection fraction using computer-aided analysis : The Framingham Heart Study

NARCIS (Netherlands)

Chuang, Michael L.; Gona, Philimon; Hautvast, Gilion L.T.F.; Salton, Carol J.; Breeuwer, Marcel; O'Donnell, Christopher J.; Manning, Warren J.

Purpose To determine sex-specific reference values for left ventricular (LV) volumes, mass, and ejection fraction (EF) in healthy adults using computer-aided analysis and to examine the effect of age on LV parameters. Materials and Methods We examined data from 1494 members of the Framingham Heart

Correlations Between Arrangement of Reinforcing Particles and Mechanical Properties in Pressure Die Cast AlSi11-SiC Composites

Directory of Open Access Journals (Sweden)

Konopka Z.

2014-06-01

Full Text Available The work presents the investigation results concerning the structure of composite pressure die castings with AlSi11 alloy matrix reinforced with SiC particles. Examination has been held for composites containing 10 and 20 volume percent of SiC particles. The arrangement of the reinforcing particles within the matrix has been qualitatively assessed in specimens cut out of the castings. The index of distribution was determined on the basis of particle count in elementary measuring fields. The tensile strength, the yield point and elongation of the obtained composite were measured. Composite castings were produced at various values of the piston velocity in the second stage of injection, diverse intensification pressure values, and various injection gate width values. The regression equation describing the change of the considered arrangement particles index and mechanical properties were found as a function of the pressure die casting parameters. The infuence of particle arrangement in composite matrix on mechanical properties these material was examined and the functions of correlations between values were obtained. The conclusion gives the analysis and the interpretation of the obtained results.

Optical study on neutron irradiation effect on hexagonal SiC single crystal

Energy Technology Data Exchange (ETDEWEB)

Okada, Moritami; Kimura, Itsurou; Kanazawa, Satoshi; Kanno, Ikuo; Kamiya, Koji [Kyoto Univ. (Japan); Nakata, Toshitake; Watanabe, Masanori; Nakagawa, Masuo; Atobe, Kozo

1996-04-01

It is well known that SiC is a higher radiation resistant semiconductor on comparison with Si and Ge. Recently, on accompanying with advancement of developing program on nuclear fission reactor on space, development of electronic element workable effectively under severe radiation environment is desired. SiC is expected as one of such elements. Therefore, because of considering importance of understanding the effect on fundamental properties of SiC electronic element under radiation environment before its development, some studies on it was executed. In this paper, according to find out induction of interesting defect center in hexagonal 4H- and 6H-SiC single crystals irradiated with reactor neutron on light absorption and SER test, outlines of these experimental results were reported. (G.K.)

A porous SiC ammonia sensor

NARCIS (Netherlands)

Connolly, E.J.; Timmer, B.H.; Pham, H.T.M.; Groeneweg, J.; Sarro, P.M.; Olthuis, Wouter; French, P.J.

2005-01-01

When used as the dielectric in a capacitive sensing arrangement, porous SiC has been found to be extremely sensitive to the presence of ammonia (NH3) gas. The exact sensing method is still not clear, but NH3 levels as low as 0.5 ppm could be detected. We report the fabrication and preliminary

Origin of the high p-doping in F intercalated graphene on SiC

KAUST Repository

Cheng, Yingchun

2011-08-04

The atomic and electronic structures of F intercalated epitaxialgraphene on a SiC(0001) substrate are studied by first-principles calculations. A three-step fluorination process is proposed. First, F atoms are intercalated between the graphene and the SiC, which restores the Dirac point in the band structure. Second, saturation of the topmost Si dangling bonds introduces p-doping up to 0.37 eV. Third, F atoms bond covalently to the graphene to enhance the p-doping. Our model explains the highly p-doped state of graphene on SiC after fluorination [A. L. Walter et al., Appl. Phys. Lett. 98, 184102 (2011)].

A Fast Electro-Thermal Co-Simulation Modeling Approach for SiC Power MOSFETs

DEFF Research Database (Denmark)

Ceccarelli, Lorenzo; Bahman, Amir Sajjad; Iannuzzo, Francesco

2017-01-01

The purpose of this work is to propose a novel electro-thermal co-simulation approach for the new generation of SiC MOSFETs, by development of a PSpice-based compact and physical SiC MOSFET model including temperature dependency of several parameters and a Simulink-based thermal network. The PSpice...... the FEM simulation of the DUT’s structure, performed in ANSYS Icepack. A MATLAB script is used to process the simulation data and feed the needed settings and parameters back into the simulation. The parameters for a CREE 1.2 kV/30 A SiC MOSFET have been identified and the electro-thermal model has been...

Development of High-Temperature, High-Power, High-Efficiency, High-Voltage Converters Using Silicon Carbide (SiC) Delivery Order 0003: SiC High Voltage Converters, N-Type Ohmic Contract Development for SiC Power Devices

National Research Council Canada - National Science Library

Cheng, Lin; Mazzola, Michael S

2006-01-01

... ? SiC interfaces and silicide top surfaces is important for producing uniformly low contact resistances to achieve device operation at high-current levels without hot spot formation and contact degradation...

Enhanced thermoelectric properties of nano SiC dispersed Bi2Sr2Co2Oy Ceramics

Science.gov (United States)

Hu, Qiujun; Wang, Kunlun; Zhang, Yingjiu; Li, Xinjian; Song, Hongzhang

2018-04-01

The thermoelectric properties of Bi2Sr2Co2Oy + x wt% nano SiC (x = 0.00, 0.025, 0.05, 0.1, 0.2, and 0.3) prepared by the solid-state reaction method were investigated from 300 K to 923 K. The resistivity can be reduced effectively by adding a small amount of SiC nano particles, which is attributed to the increase of the carrier concentration. At the same time, the Seebeck coefficients can be improved effectively due to the energy filtering effect that low energy carriers are strongly dispersed at the interface between the SiC nano particles and the matrix. The decrease of thermal conductivity is due to the increase of the scattering ability of the phonons by the SiC nanoparticles distributed at the boundary of the matrix. As a result, the Bi2Sr2Co2Oy + x wt% SiC composites exhibit better thermoelectric properties. The maximum ZT value 0.24 is obtained when x = 0.05 at 923 K. Compared with the sample without SiC nano particles, the ZT value is increased by about 59.7%.

Friction Stir Processing of Copper-Coated SiC Particulate-Reinforced Aluminum Matrix Composite

Directory of Open Access Journals (Sweden)

Chih-Wei Huang

2018-04-01

Full Text Available In the present work, we proposed a novel friction stir processing (FSP to produce a locally reinforced aluminum matrix composite (AMC by stirring copper-coated SiC particulate reinforcement into Al6061 alloy matrix. Electroless-plating process was applied to deposit the copper surface coating on the SiC particulate reinforcement for the purpose of improving the interfacial adhesion between SiC particles and Al matrix. The core-shell SiC structure provides a layer for the atomic diffusion between aluminum and copper to enhance the cohesion between reinforcing particles and matrix on one hand, the dispersion of fine copper in the Al matrix during FSP provides further dispersive strengthening and solid solution strengthening, on the other hand. Hardness distribution and tensile results across the stir zone validated the novel concept in improving the mechanical properties of AMC that was realized via FSP. Optical microscope (OM and Transmission Electron Microscopy (TEM investigations were conducted to investigate the microstructure. Energy dispersive spectrometer (EDS, electron probe micro-analyzer (EPMA, and X-ray diffraction (XRD were explored to analyze the atomic inter-diffusion and the formation of intermetallic at interface. The possible strengthening mechanisms of the AMC containing Cu-coated SiC particulate reinforcement were interpreted. The concept of strengthening developed in this work may open a new way of fabricating of particulate reinforced metal matrix composites.

Selected mechanical properties of aluminum composite materials reinforced with SiC particles

Directory of Open Access Journals (Sweden)

A. Kurzawa

2008-07-01

Full Text Available This work presents the results of research concerning influence of ceramic particles’ content of silicon carbide on selected mechanical properties of type AW-AlCu4Mg2Mn - SiC composite materials. Composites produced of SiC particles with pressure infiltration method of porous preform and subject to hot plastic forming in the form of open die forging were investigated. The experimental samples contained from 5% up to 45% of reinforcing SiC particles of 8÷10μm diameter. Studies of strength properties demonstrated that the best results, in case of tensile strength as well as offset yield strength, might be obtained while applying reinforcement in the amount of 20-25% vol. of SiC. Application of higher than 25% vol. contents of reinforcing particles leads to gradual strength loss. The investigated composites were characterized by very high functional properties, such as hardness and abrasive wear resistance, whose values increase strongly with the increase of reinforcement amount. The presented results of the experiments shall allow for a more precise component selection of composite materials at the stage of planning and design of their properties.

Preparation and characterization of the electrodeposited Cr-Al{sub 2}O{sub 3}/SiC composite coating

Energy Technology Data Exchange (ETDEWEB)

Gao Jifeng, E-mail: readlot@tom.com [State Key Laboratory of Mould Technology, Institute of Materials Science and Engineering, Huazhong University of Science and Technology, Wuhan 430074 (China); Suo Jinping, E-mail: jpsuo@yahoo.com.cn [State Key Laboratory of Mould Technology, Institute of Materials Science and Engineering, Huazhong University of Science and Technology, Wuhan 430074 (China)

2011-09-01

To increase the SiC content in Cr-based coatings, Cr-Al{sub 2}O{sub 3}/SiC composite coatings were plated in Cr(VI) baths which contained Al{sub 2}O{sub 3}-coated SiC powders. The Al{sub 2}O{sub 3}-coated SiC composite particles were synthesized by calcining the precursor prepared by heterogeneous deposition method. The transmission electron microscopy analysis of the particles showed that the nano-SiC particle was packaged by alumina. The zeta potential of the particles collected from the bath was up to +23 mV, a favorable condition for the co-deposition of the particles and chromium. Pulse current was used during the electrodeposition. Scanning Electron Microscopy (SEM) indicated that the coating was compact and combined well with the substrate. Energy dispersive X-ray analysis of Cr-Al{sub 2}O{sub 3}/SiC coatings demonstrated that the concentration of SiC in the coating reached about 2.5 wt.%. The corrosion behavior of the composite coating was studied by potentiodynamic polarization and electrochemical impedance spectroscopy techniques. The data obtained suggested that the Al{sub 2}O{sub 3}/SiC particles significantly enhanced the corrosion resistance of the composite coating in 0.05 M HCl solution.

Interface and interaction of graphene layers on SiC(0001[combining macron]) covered with TiC(111) intercalation.

Science.gov (United States)

Wang, Lu; Wang, Qiang; Huang, Jianmei; Li, Wei-Qi; Chen, Guang-Hui; Yang, Yanhui

2017-10-11

It is important to understand the interface and interaction between the graphene layer, titanium carbide [TiC(111)] interlayer, and silicon carbide [SiC(0001[combining macron])] substrates in epitaxial growth of graphene on silicon carbide (SiC) substrates. In this study, the fully relaxed interfaces which consist of up to three layers of TiC(111) coatings on the SiC(0001[combining macron]) as well as the graphene layers interactions with these TiC(111)/SiC(0001[combining macron]) were systematically studied using the density functional theory-D2 (DFT-D2) method. The results showed that the two layers of TiC(111) coating with the C/C-terminated interfaces were thermodynamically more favorable than one or three layers of TiC(111) on the SiC(0001[combining macron]). Furthermore, the bonding of the Ti-hollow-site stacked interfaces would be a stronger link than that of the Ti-Fcc-site stacked interfaces. However, the formation of the C/Ti/C and Ti/C interfaces implied that the first upper carbon layer can be formed on TiC(111)/SiC(0001[combining macron]) using the decomposition of the weaker Ti-C and C-Si interfacial bonds. When growing graphene layers on these TiC(111)/SiC(0001[combining macron]) substrates, the results showed that the interaction energy depended not only on the thickness of the TiC(111) interlayer, but also on the number of graphene layers. Bilayer graphene on the two layer thick TiC(111)/SiC(0001[combining macron]) was thermodynamically more favorable than a monolayer or trilayer graphene on these TiC(111)/SiC(0001[combining macron]) substrates. The adsorption energies of the bottom graphene layers with the TiC(111)/SiC(0001[combining macron]) substrates increased with the decrease of the interface vertical distance. The interaction energies between the bottom, second and third layers of graphene on the TiC(111)/SiC(0001[combining macron]) were significantly higher than that of the freestanding graphene layers. All of these findings provided

Myocardial T1 and extracellular volume fraction mapping at 3 tesla

Directory of Open Access Journals (Sweden)

Lee Jason J

2011-11-01

Full Text Available Abstract Background To compare 11 heartbeat (HB and 17 HB modified lock locker inversion recovery (MOLLI pulse sequence at 3T and to establish preliminary reference values for myocardial T1 and the extracellular volume fraction (ECV. Methods Both phantoms and normal volunteers were scanned at 3T using 11 HB and 17 HB MOLLI sequence with the following parameters: spatial resolution = 1.75 × 1.75 × 10 mm on a 256 × 180 matrix, TI initial = 110 ms, TI increment = 80 ms, flip angle = 35°, TR/TE = 1.9/1.0 ms. All volunteers were administered Gadolinium-DTPA (Magnevist, 0.15 mmol/kg, and multiple post-contrast MOLLI scans were performed at the same pre-contrast position from 3.5-23.5 minutes after a bolus contrast injection. Late gadolinium enhancement (LGE images were also acquired 12-30 minutes after the gadolinium bolus. Results T1 values of 11 HB and 17 HB MOLLI displayed good agreement in both phantom and volunteers. The average pre-contrast myocardial and blood T1 was 1315 ± 39 ms and 2020 ± 129 ms, respectively. ECV was stable between 8.5 to 23.5 minutes post contrast with an average of 26.7 ± 1.0%. Conclusion The 11 HB MOLLI is a faster method for high-resolution myocardial T1 mapping at 3T. ECV fractions are stable over a wide time range after contrast administration.

Broadband antireflection nanodome structures on SiC substrate

DEFF Research Database (Denmark)

Ou, Yiyu; Zhu, Xiaolong; Møller, Uffe Visbech

2013-01-01

Nanodome structures are demonstrated on the SiC substrate by using nanosphere lithography and dry etching. Significant surface antireflection has been observed over a broad spectral range from 400 nm to 1600 nm....

A glimpse beneath Antarctic sea ice: observation of platelet-layer thickness and ice-volume fraction with multifrequency EM

Science.gov (United States)

Hoppmann, Mario; Hunkeler, Priska A.; Hendricks, Stefan; Kalscheuer, Thomas; Gerdes, Rüdiger

2016-04-01

In Antarctica, ice crystals (platelets) form and grow in supercooled waters below ice shelves. These platelets rise, accumulate beneath nearby sea ice, and subsequently form a several meter thick, porous sub-ice platelet layer. This special ice type is a unique habitat, influences sea-ice mass and energy balance, and its volume can be interpreted as an indicator of the health of an ice shelf. Although progress has been made in determining and understanding its spatio-temporal variability based on point measurements, an investigation of this phenomenon on a larger scale remains a challenge due to logistical constraints and a lack of suitable methodology. In the present study, we applied a lateral constrained Marquardt-Levenberg inversion to a unique multi-frequency electromagnetic (EM) induction sounding dataset obtained on the ice-shelf influenced fast-ice regime of Atka Bay, eastern Weddell Sea. We adapted the inversion algorithm to incorporate a sensor specific signal bias, and confirmed the reliability of the algorithm by performing a sensitivity study using synthetic data. We inverted the field data for sea-ice and platelet-layer thickness and electrical conductivity, and calculated ice-volume fractions within the platelet layer using Archie's Law. The thickness results agreed well with drillhole validation datasets within the uncertainty range, and the ice-volume fraction yielded results comparable to other studies. Both parameters together enable an estimation of the total ice volume within the platelet layer, which was found to be comparable to the volume of landfast sea ice in this region, and corresponded to more than a quarter of the annual basal melt volume of the nearby Ekström Ice Shelf. Our findings show that multi-frequency EM induction sounding is a suitable approach to efficiently map sea-ice and platelet-layer properties, with important implications for research into ocean/ice-shelf/sea-ice interactions. However, a successful application of this

The origin of a peak in the reststrahlen region of SiC

International Nuclear Information System (INIS)

Engelbrecht, J.A.A.; Rooyen, I.J. van; Henry, A.; Janzén, E.; Olivier, E.J.

2012-01-01

A peak in the reststrahlen region of SiC is analyzed in order to establish the origin of this peak. The peak can be associated with a thin damaged layer on the SiC wafers, and a relation is found between surface roughness and the height of this peak, by modeling the damaged layer as an additional layer when simulating the reflectivity from the wafers.

The origin of a peak in the reststrahlen region of SiC

Energy Technology Data Exchange (ETDEWEB)

Engelbrecht, J.A.A., E-mail: Japie.Engelbrecht@nmmu.ac.za [Physics Department, Nelson Mandela Metropolitan University, PO Box 77000, Port Elizabeth 6031 (South Africa); Rooyen, I.J. van [Physics Department, Nelson Mandela Metropolitan University, PO Box 77000, Port Elizabeth 6031 (South Africa); Henry, A.; Janzen, E. [Department of Physics, Chemistry and Biology, Linkoeping University, SE-581 83 Linkoeping (Sweden); Olivier, E.J. [Physics Department, Nelson Mandela Metropolitan University, PO Box 77000, Port Elizabeth 6031 (South Africa)

2012-05-15

A peak in the reststrahlen region of SiC is analyzed in order to establish the origin of this peak. The peak can be associated with a thin damaged layer on the SiC wafers, and a relation is found between surface roughness and the height of this peak, by modeling the damaged layer as an additional layer when simulating the reflectivity from the wafers.

Scaling relations between trabecular bone volume fraction and microstructure at different skeletal sites.

Science.gov (United States)

Räth, Christoph; Baum, Thomas; Monetti, Roberto; Sidorenko, Irina; Wolf, Petra; Eckstein, Felix; Matsuura, Maiko; Lochmüller, Eva-Maria; Zysset, Philippe K; Rummeny, Ernst J; Link, Thomas M; Bauer, Jan S

2013-12-01

In this study, we investigated the scaling relations between trabecular bone volume fraction (BV/TV) and parameters of the trabecular microstructure at different skeletal sites. Cylindrical bone samples with a diameter of 8mm were harvested from different skeletal sites of 154 human donors in vitro: 87 from the distal radius, 59/69 from the thoracic/lumbar spine, 51 from the femoral neck, and 83 from the greater trochanter. μCT images were obtained with an isotropic spatial resolution of 26μm. BV/TV and trabecular microstructure parameters (TbN, TbTh, TbSp, scaling indices ( and σ of α and αz), and Minkowski Functionals (Surface, Curvature, Euler)) were computed for each sample. The regression coefficient β was determined for each skeletal site as the slope of a linear fit in the double-logarithmic representations of the correlations of BV/TV versus the respective microstructure parameter. Statistically significant correlation coefficients ranging from r=0.36 to r=0.97 were observed for BV/TV versus microstructure parameters, except for Curvature and Euler. The regression coefficients β were 0.19 to 0.23 (TbN), 0.21 to 0.30 (TbTh), -0.28 to -0.24 (TbSp), 0.58 to 0.71 (Surface) and 0.12 to 0.16 (), 0.07 to 0.11 (), -0.44 to -0.30 (σ(α)), and -0.39 to -0.14 (σ(αz)) at the different skeletal sites. The 95% confidence intervals of β overlapped for almost all microstructure parameters at the different skeletal sites. The scaling relations were independent of vertebral fracture status and similar for subjects aged 60-69, 70-79, and >79years. In conclusion, the bone volume fraction-microstructure scaling relations showed a rather universal character. © 2013.

Mechanical performance of SiC three-layer cladding in PWRs

Energy Technology Data Exchange (ETDEWEB)

Angelici Avincola, Valentina, E-mail: valentina.avincola@kit.edu [Karlsruhe Institute of Technology, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen (Germany); Guenoun, Pierre, E-mail: pguenoun@mit.edu [Massachusetts Institute of Technology, 77 Massachusetts Ave, Cambridge, MA 02139 (United States); Shirvan, Koroush, E-mail: kshirvan@mit.edu [Massachusetts Institute of Technology, 77 Massachusetts Ave, Cambridge, MA 02139 (United States)

2016-12-15

Highlights: • FEA calculations of the stress distribution in SiC three-layer cladding. • Simulation of SiC mechanical performance under operation and accident conditions. • Failure probability analysis of SiC in steady-state and accident conditions. - Abstract: The silicon carbide cladding concept is currently under investigation with regard to increasing the accident tolerance and economic performance of light-water reactor fuels. In this work, the stress fields in the multi-layered silicon carbide cladding for LWR fuels are calculated using the commercial finite element analysis software ADINA. The material properties under irradiation are implemented as a function of temperature. The cladding is studied under operating and accident conditions, specifically for the loss-of-coolant accident (LOCA). During the LOCA, the blowdown and the reflood phases are modeled, including the quench waterfront. The calculated stresses along the cladding thickness show a high sensitivity to the assumptions regarding material properties. The resulting stresses are compared with experimental data and the probability of failure is calculated considering a Weibull model.

Pre-chemotherapy values for left and right ventricular volumes and ejection fraction by gated tomographic radionuclide angiography using a cadmium-zinc-telluride detector gamma camera

DEFF Research Database (Denmark)

Haarmark, Christian; Haase, Christine; Jensen, Maria Maj

2016-01-01

age and both left and right ventricular volumes in women (r = -0.4, P right end systolic ventricular volume in men (r = -0.3, P = .001). CONCLUSION: A set of reference values for cardiac evaluation prior to chemotherapy in cancer patients without other known cardiopulmonary......BACKGROUND: Estimation of left ventricular ejection fraction (LVEF) using equilibrium radionuclide angiography is an established method for assessment of left ventricular function. The purpose of this study was to establish normative data on left and right ventricular volumes and ejection fraction......, using cadmium-zinc-telluride SPECT camera. METHODS AND RESULTS: From routine assessments of left ventricular function in 1172 patients, we included 463 subjects (194 men and 269 women) without diabetes, previous potentially cardiotoxic chemotherapy, known cardiovascular or pulmonary disease. The lower...

Advantages and Limits of 4H-SIC Detectors for High- and Low-Flux Radiations

Science.gov (United States)

Sciuto, A.; Torrisi, L.; Cannavò, A.; Mazzillo, M.; Calcagno, L.

2017-11-01

Silicon carbide (SiC) detectors based on Schottky diodes were used to monitor low and high fluxes of photons and ions. An appropriate choice of the epilayer thickness and geometry of the surface Schottky contact allows the tailoring and optimizing the detector efficiency. SiC detectors with a continuous front electrode were employed to monitor alpha particles in a low-flux regime emitted by a radioactive source with high energy (>5.0 MeV) or generated in an ion implanter with sub-MeV energy. An energy resolution value of 0.5% was measured in the high energy range, while, at energy below 1.0 MeV, the resolution becomes 10%; these values are close to those measured with a traditional silicon detector. The same SiC devices were used in a high-flux regime to monitor high-energy ions, x-rays and electrons of the plasma generated by a high-intensity (1016 W/cm2) pulsed laser. Furthermore, SiC devices with an interdigit Schottky front electrode were proposed and studied to overcome the limits of the such SiC detectors in the detection of low-energy (˜1.0 keV) ions and photons of the plasmas generated by a low-intensity (1010 W/cm2) pulsed laser. SiC detectors are expected to be a powerful tool for the monitoring of radioactive sources and ion beams produced by accelerators, for a complete characterization of radiations emitted from laser-generated plasmas at high and low temperatures, and for dosimetry in a radioprotection field.

Effect of Copper Coated SiC Reinforcements on Microstructure, Mechanical Properties and Wear of Aluminium Composites

Science.gov (United States)

Kori, P. S.; Vanarotti, Mohan; Angadi, B. M.; Nagathan, V. V.; Auradi, V.; Sakri, M. I.

2017-08-01

Experimental investigations are carried out to study the influence of copper coated Silicon carbide (SiC) reinforcements in Aluminum (Al) based Al-SiC composites. Wear behavior and mechanical Properties like, ultimate tensile strength (UTS) and hardness are studied in the present work. Experimental results clearly revealed that, an addition of SiC particles (5, 10 and 15 Wt %) has lead in the improvement of hardness and ultimate tensile strength. Al-SiC composites containing the Copper coated SiC reinforcements showed better improvement in mechanical properties compared to uncoated ones. Characterization of Al-SiC composites are carried out using optical photomicrography and SEM analysis. Wear tests are carried out to study the effects of composition and normal pressure using Pin-On Disc wear testing machine. Results suggested that, wear rate decreases with increasing SiC composition, further an improvement in wear resistance is observed with copper coated SiC reinforcements in the Al-SiC metal matrix composites (MMC’s).

The Oxidation Rate of SiC in High Pressure Water Vapor Environments

Science.gov (United States)

Opila, Elizabeth J.; Robinson, R. Craig

1999-01-01

CVD SiC and sintered alpha-SiC samples were exposed at 1316 C in a high pressure burner rig at total pressures of 5.7, 15, and 25 atm for times up to 100h. Variations in sample emittance for the first nine hours of exposure were used to determine the thickness of the silica scale as a function of time. After accounting for volatility of silica in water vapor, the parabolic rate constants for Sic in water vapor pressures of 0.7, 1.8 and 3.1 atm were determined. The dependence of the parabolic rate constant on the water vapor pressure yielded a power law exponent of one. Silica growth on Sic is therefore limited by transport of molecular water vapor through the silica scale.

Methods for growth of relatively large step-free SiC crystal surfaces

Science.gov (United States)

Neudeck, Philip G. (Inventor); Powell, J. Anthony (Inventor)

2002-01-01

A method for growing arrays of large-area device-size films of step-free (i.e., atomically flat) SiC surfaces for semiconductor electronic device applications is disclosed. This method utilizes a lateral growth process that better overcomes the effect of extended defects in the seed crystal substrate that limited the obtainable step-free area achievable by prior art processes. The step-free SiC surface is particularly suited for the heteroepitaxial growth of 3C (cubic) SiC, AlN, and GaN films used for the fabrication of both surface-sensitive devices (i.e., surface channel field effect transistors such as HEMT's and MOSFET's) as well as high-electric field devices (pn diodes and other solid-state power switching devices) that are sensitive to extended crystal defects.

Electric-field-dependent phase volume fractions and enhanced piezoelectricity near the polymorphic phase boundary of (K0.5Na0.5)1-xLixNbO3 textured ceramics

Science.gov (United States)

Ge, Wenwei; Li, Jiefang; Viehland, D.; Chang, Yunfei; Messing, Gary L.

2011-06-01

The structure, ferroelectric and piezoelectric properties of textured (K0.5Na0.5)0.98Li0.02NbO3 ceramics were investigated as a function of temperature and dc bias E. X-ray diffraction revealed an orthorhombic (O) → tetragonal (T) polymorphic phase boundary (PPB). Phase coexistence was found near the PPB over a 30 °C temperature range, where the relative phase volume fractions changed with temperature. Furthermore, increasing E applied along the texture direction resulted in a notable increase in the volume fraction of the T phase at the expense of the O phase, effectively shifting the O → T boundary to lower temperature. An enhancement in the piezoelectric properties was found to accompany this increase in the T volume fraction.

Investigating the evolution of the phase behavior of AOT-based w/o microemulsions in dodecane as a function of droplet volume fraction.

Science.gov (United States)

Ganguly, R; Choudhury, N

2012-04-15

AOT-based water in oil (w/o) microemulsions are one of the most extensively studied reverse micellar systems because of their rich phase behavior and their ability to form in the absence of any co-surfactant. The aggregation characteristics and interaction of the microemulsion droplets in these systems are known to be governed by AOT-oil compatibility and water to AOT molar ratio (w). In this manuscript by using Dynamic Light Scattering (DLS) and viscometry techniques, we show that droplet volume fraction too plays an important role in shaping the phase behavior of these microemulsions in dodecane. The phase separation characteristics and the evolution of the viscosity and the hydrodynamic radius of the microemulsion droplets on approaching the cloud points have thus been found to undergo complete transformation as one goes from low to high droplet volume fraction even at a fixed 'w'. Modeling of the DLS data attributes this to the weakening of inter droplet attractive interaction caused by the growing dominance of the excluded volume effect with increase in droplet volume fraction. In the literature, the inter droplet attractive interaction driven phase separation in these microemulsions is explained based on gas-liquid type phase transition, conceptualized in the framework of Baxter adhesive hard sphere theory. The modeling of our viscosity data, however, does not support such proposition as the characteristic stickiness parameter (τ(-1)) of the microemulsion droplets in this system remains much lower than the critical value (τ(c)(-1)≈10.25) required to enforce such phase transition. Copyright © 2012 Elsevier Inc. All rights reserved.

Development of SiC Neutron Detector Assembly to Measure the Neutron Flux of the Reactor Core

Energy Technology Data Exchange (ETDEWEB)

Park, Se Hwan; Park, June Sic; Shin, Hee Sung; Kim, Ho Dong [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of); Kim, Yong Kyun [Hanyang University, Seoul (Korea, Republic of)

2012-05-15

At present, the conventional detector to measure the neutron at harsh environment is a Self Powered Neutron Detector (SPND). Rhodium(Rh)-103 is in the SPND. When neutron is incident on the Rhodium, the neutron capture reaction occurs, and the Rh-103 is converted to Rh-104. The Rh-104 is decayed to Pd-104 by {beta}-decay, and electrons are generated as the decay products. Because of the half life of Rh-104, approximately 5 minutes are required for the SPND output to reach the equilibrium condition. Therefore the on-line monitoring of the nuclear reactor state is limited if the neutron flux in the reactor core is monitored with the SPND. Silicon carbide (SiC) has the possibility to be developed as neutron detector at harsh environment, because the SiC can be operative at high temperature and high neutron flux conditions. Previously, the basic operation properties of the SiC detector were studied. Also, the radiation response of the SiC detector was studied at high neutron and gamma dose rate. The measurement results for an ex-core neutron flux monitor or a neutron flux monitor of the spent fuel were published. The SiC detector was also developed as neutron detector to measure the fissile material with active interrogation method. However, the studies about the development of SiC detector are still limited. In the present work, the radiation damage effect of the SiC detector was studied. The detector structure was determined based on the study, and a neutron detector assembly was made with the SiC detectors. The neutron and gamma-ray response of the detector assembly is presented in this paper. The detector assembly was positioned in the HANARO research reactor core, the performance test was done. The preliminary results are also included in this paper

Pressureless sintering behavior and mechanical properties of ZrB2–SiC composites: effect of SiC content and particle size

Directory of Open Access Journals (Sweden)

Mehri Mashhadi

2015-10-01

Full Text Available In the present paper, ZrB2–SiC composites were prepared by pressureless sintering at temperatures of 2000–2200 °C for 1 h under argon atmosphere. In order to prepare composite samples, ZrB2 powder was milled for 2 h, then the reinforcing particles including of micron and nano-sized SiC powder were added. The mixtures were formed and, after the pyrolysis, they were sintered. Densification, microstructural and mechanical properties of ZrB2–SiC composites were investigated. The shrinkage of samples was measured both before and after the sintering, and the microstructure of samples was examined using scanning electron microscopy (SEM, equipped with EDS spectroscopy. Both mass fraction and size of SiC powder have a great effect on relative density, porosity, shrinkage, hardness and microstructure of these composites. The highest relative density and hardness were 98.12% and 15.02 GPa, respectively, in ZrB2–10 wt% SiCnano composite sintered at 2200 °C.

Microstrain evolution during creep of a high volume fraction superalloy

Energy Technology Data Exchange (ETDEWEB)

Ma, S. [Materials Department, New Mexico Tech, Socorro, NM 87801 (United States); Brown, D. [Los Alamos National Laboratory, Los Alamos, NM (United States); Bourke, M.A.M. [Los Alamos National Laboratory, Los Alamos, NM (United States); Daymond, M.R. [Rutherford Appleton Laboratory, ISIS Facility, Chilton, Didcot, Oxon OX11 0QX (United Kingdom); Majumdar, B.S. [Materials Department, New Mexico Tech, Socorro, NM 87801 (United States)]. E-mail: majumdar@nmt.edu

2005-06-15

The creep of superalloys containing a high volume fraction of {gamma}' phase is significantly influenced by initial misfit and by the evolution of internal stresses. An in situ neutron diffraction technique was used to monitor elastic microstrains in a polycrystalline superalloy, CM247 LC. The misfit was nearly zero at room temperature and it increased to -0.17% at 900 deg. C. These values are rationalized in terms of thermal mismatch using an eigenstrain formulation and a simple formula is derived to relate the thermal mismatch to the misfit strain. During creep at 425 MPa at 900 deg. C, the material exhibited primarily tertiary behavior. For grains with [0 0 1] axis close to the loading direction, the elastic microstrain in the loading direction increased with creep time for the {gamma}' phase, whereas the opposite occurred for the {gamma} phase. These results are explained in terms of constrained deformation in the narrow {gamma} channels and by an interface dislocation buildup. TEM analysis of the crept microstructure provides evidence of the interface dislocation network.

Mechanical properties of hot-pressed SiC-TiC composites

Directory of Open Access Journals (Sweden)

Kamil Kornaus

2017-12-01

Full Text Available SiC-TiC composites, with 0, 5, 10 and 20 vol.% of TiC, were sintered by the hot-pressing technique at temperature of 2000 °C under argon atmosphere. SiC sintering process was activated by liquid phase created by the reaction between Al2O3 and Y2O3, in which it is possible to dissolve passivating oxide layers (SiO2 and TiO2 and partially SiC and TiC carbides. Microstructure observation and density measurements confirmed that the composites were dense with uniformly distributed components. Differences in thermal expansion coefficients between SiC and TiC led to complex stress state occurrence. These stresses combined with the liquid-derived separate phase between grains boundaries increased fracture toughness of the composites, which ranged from 5.8 to 6.3 MPa·m0.5. Opposite to the bending strength, fracture toughness increased with the TiC volume fraction. By means of simulation of residual thermal stresses in the composites, it was found that with the increasing volume fraction of TiC, tensile stress in TiC grains is reduced simultaneously with strong rise of compressive stresses in the matrix.

Investigation on the Short Circuit Safe Operation Area of SiC MOSFET Power Modules

DEFF Research Database (Denmark)

Reigosa, Paula Diaz; Luo, Haoze; Iannuzzo, Francesco

2016-01-01

This paper gives a better insight of the short circuit capability of state-of-the-art SiC MOSFET power modules rated at 1.2 kV by highlighting the physical limits under different operating conditions. Two different failure mechanisms have been identified, both reducing the short-circuit capability...... of SiC power modules in respect to discrete SiC devices. Based on such failure mechanisms, two short circuit criteria (i.e., short circuit current-based criterion and gate voltage-based criterion) are proposed in order to ensure their robustness under short-circuit conditions. A Safe Operation Area (SOA...

A Kochen–Specker inequality from a SIC

International Nuclear Information System (INIS)

Bengtsson, Ingemar; Blanchfield, Kate; Cabello, Adán

2012-01-01

Yu and Oh (eprint) have given a state-independent proof of the Kochen–Specker theorem in three dimensions using only 13 rays. The proof consists of showing that a non-contextual hidden variable theory necessarily leads to an inequality that is violated by quantum mechanics. We give a similar proof making use of 21 rays that constitute a SIC (symmetric informationally-complete positive operator-valued measure) and a complete set of MUB (mutually unbiased bases). A theory-independent inequality is also presented using the same 21 rays, as required for experimental tests of contextuality. -- Highlights: ► We find a state-independent Kochen–Specker inequality in dimension 3 with 21 rays. ► The rays constitute a SIC (9 rays) and a complete set of MUB (12 rays). ► Orthogonalities among the rays produce the Hesse configuration. ► The rays also give a state-independent non-contextual hidden variable inequality. ► We show that both inequalities are violated by quantum mechanics.

Study on extrusion process of SiC ceramic matrix

Science.gov (United States)

Dai, Xiao-Yuan; Shen, Fan; Ji, Jia-You; Wang, Shu-Ling; Xu, Man

2017-11-01

In this thesis, the extrusion process of SiC ceramic matrix has been systematically studied.The effect of different cellulose content on the flexural strength and pore size distribution of SiC matrix was discussed.Reselts show that with the increase of cellulose content, the flexural strength decreased.The pore size distribution in the sample was 1um-4um, and the 1um-2um concentration was more concentrated. It is found that the cellulose content has little effect on the pore size distribution.When the cellulose content is 7%, the flexural strength of the sample is 40.9Mpa. At this time, the mechanical properties of the sample are the strongest.

Two new constructions of approximately SIC-POVMs from multiplicative characters

Science.gov (United States)

Luo, Gaojun; Cao, Xiwang

2017-12-01

In quantum information theory, symmetric informationally complete positive operator-valued measures (SIC-POVMs) are relevant to quantum state tomography [8], quantum cryptography [15], and foundational studies [16]. In general, it is hard to construct SIC-POVMs and only a few classes of them existed, as we know. Moreover, we do not know whether there exists an infinite class of them. Many researchers tried to construct approximately symmetric informationally complete positive operator-valued measures (ASIC-POVMs). In this paper, we propose two new constructions of ASIC-POVMs for prime power dimensions only by using multiplicative characters over finite fields.

Early implementation of SiC cladding fuel performance models in BISON

Energy Technology Data Exchange (ETDEWEB)

Powers, Jeffrey J. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

2015-09-18

SiC-based ceramic matrix composites (CMCs) [5–8] are being developed and evaluated internationally as potential LWR cladding options. These development activities include interests within both the DOE-NE LWR Sustainability (LWRS) Program and the DOE-NE Advanced Fuels Campaign. The LWRS Program considers SiC ceramic matrix composites (CMCs) as offering potentially revolutionary gains as a cladding material, with possible benefits including more efficient normal operating conditions and higher safety margins under accident conditions [9]. Within the Advanced Fuels Campaign, SiC-based composites are a candidate ATF cladding material that could achieve several goals, such as reducing the rates of heat and hydrogen generation due to lower cladding oxidation rates in HT steam [10]. This work focuses on the application of SiC cladding as an ATF cladding material in PWRs, but these work efforts also support the general development and assessment of SiC as an LWR cladding material in a much broader sense.

Characteristics of hot-pressed fiber-reinforced ceramics with SiC matrix

Science.gov (United States)

Miyoshi, Tadahiko; Kodama, Hironori; Sakamoto, Hiroshi; Goto, Akihiro; Iijima, Shiroo

1989-11-01

Silicon carbide ceramics’ matrix composites with SiC or C filaments were fabricated through hot pressing, and the effects of the filament pullout on their fracture toughness were experimentally investigated. The C-rich coating layers on the SiC filaments were found to have a significant effect on the frictional stress at the filament/matrix interfaces, through assising the filamet pullout from the matrix. Although the coating layers were apt to burn out in the sintering process of SiC matrix compposites, a small addition of carbon to the raw materials was found to be effective for the retention of the layers on the fibers, thus increasing the fracture toughness of the composites. The fracture toughness of the C filament/SiC matrix composite increased with temperature due to the larger interfacial frictional stress at higher temperatures, because of the higher thermal expansion of the filament in the radial direction than that of the matrix.

Oxidation of BN-coated SiC fibers in ceramic matrix composites

International Nuclear Information System (INIS)

Sheldon, B.W.; Sun, E.Y.

1996-01-01

Thermodynamic calculations were performed to analyze the simultaneous oxidation of BN and SiC. The results show that, with limited amounts of oxygen present, the formation of SiO 2 should occur prior to the formation of B 2 O 3 . This agrees with experimental observations of oxidation in glass-ceramic matrix composites with BN-coated SiC fibers, where a solid SiO 2 reaction product containing little or no boron has been observed. The thermodynamic calculations suggest that this will occur when the amount of oxygen available is restricted. One possible explanation for this behavior is that SiO 2 formation near the external surfaces of the composite closes off cracks or pores, such that vapor phase O 2 diffusion into the composite occurs only for a limited time. This indicates that BN-coated SiC fibers will not always oxidize to form significant amounts of a low-melting, borosilicate glass

High power RF performance test of an improved SiC load

Energy Technology Data Exchange (ETDEWEB)

Hwang, W.H.; Kim, S.H.; Park, Y.J. [Pohang Accelerator Lab., Pohang Inst. of Sceince and Technology, Pohang (KR)] [and others

1998-11-01

Two prototypes of SiC loads sustaining a maximum peak power of 50 MW were fabricated by Nihon Koshuha Co. in Japan. The PAL conducted the high power RF performance tests of SiC loads to verify the operation characteristics for the application to the PLS Linac. The in-situ facility for the K 12 module was used for the test, which consists of a modulator and klystron system, waveguide network, vacuum and cooling system, and RF analyzing equipment. As the test results, no breakdown appeared up to 50 MW peak power of 1 {mu}s pulse width at a repetition rate of 50 Hz. However, as the peak power increased above 20 MW at 4 {mu}s with 10 Hz, the breakdown phenomena has been observed. Analysing the test results with the current operation power level of PLS Linac, it is confirmed that the SiC loads well satisfy the criteria of the PLS Linac operation. (author)

Damage profiles and ion distribution in Pt-irradiated SiC

Energy Technology Data Exchange (ETDEWEB)

Xue, H.Z. [Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN 37996 (United States); Zhang, Y., E-mail: Zhangy1@ornl.gov [Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN 37996 (United States); Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831 (United States); Zhu, Z. [Pacific Northwest National Laboratory, P.O. Box 999, Richland, WA 99352 (United States); Zhang, W.M. [Department of Radiation Therapy, Peking University First Hospital, Beijing 100034 (China); Bae, I.-T. [Small Scale Systems Integration and Packaging Center, State University of New York at Binghamton, P.O. Box 6000, Binghamton, NY 13902 (United States); Weber, W.J. [Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN 37996 (United States); Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831 (United States)

2012-09-01

Single crystalline 6H-SiC samples were irradiated at 150 K with 2 MeV Pt ions. The local volume swelling was determined by electron energy loss spectroscopy (EELS), and a nearly sigmoidal dependence on irradiation dose is observed. The disorder profiles and ion distribution were determined by Rutherford backscattering spectrometry (RBS), transmission electron microscopy, and secondary ion mass spectrometry. Since the volume swelling reaches 12% over the damage region at high ion fluence, the effect of lattice expansion is considered and corrected for in the analysis of RBS spectra to obtain depth profiles. Projectile and damage profiles are estimated by SRIM (Stopping and Range of Ions in Matter). When compared with the measured profiles, the SRIM code predictions of ion distribution and the damage profiles are underestimated due to significant overestimation of the electronic stopping power for the slow heavy Pt ions. By utilizing the reciprocity method, which is based on the invariance of the inelastic energy loss in ion-solid collisions against interchange of projectile and target atom, a much lower electronic stopping power is deduced. A simple approach, based on reducing the density of SiC target in SRIM simulation, is proposed to compensate the overestimated SRIM electronic stopping power values, which results in improved agreement between predicted and measured damage profiles and ion ranges.

Conformal Thin Film Packaging for SiC Sensor Circuits in Harsh Environments

Science.gov (United States)

Scardelletti, Maximilian C.; Karnick, David A.; Ponchak, George E.; Zorman, Christian A.

2011-01-01

In this investigation sputtered silicon carbide annealed at 300 C for one hour is used as a conformal thin film package. A RF magnetron sputterer was used to deposit 500 nm silicon carbide films on gold metal structures on alumina wafers. To determine the reliability and resistance to immersion in harsh environments, samples were submerged in gold etchant for 24 hours, in BOE for 24 hours, and in an O2 plasma etch for one hour. The adhesion strength of the thin film was measured by a pull test before and after the chemical immersion, which indicated that the film has an adhesion strength better than 10(exp 8) N/m2; this is similar to the adhesion of the gold layer to the alumina wafer. MIM capacitors are used to determine the dielectric constant, which is dependent on the SiC anneal temperature. Finally, to demonstrate that the SiC, conformal, thin film may be used to package RF circuits and sensors, an LC resonator circuit was fabricated and tested with and without the conformal SiC thin film packaging. The results indicate that the SiC coating adds no appreciable degradation to the circuits RF performance. Index Terms Sputter, silicon carbide, MIM capacitors, LC resonators, gold etchants, BOE, O2 plasma

Cl-intercalated graphene on SiC: Influence of van der Waals forces

KAUST Repository

Cheng, Yingchun; Zhu, Zhiyong; Schwingenschlö gl, Udo

2013-01-01

The atomic and electronic structures of Cl-intercalated epitaxial graphene on SiC are studied by first-principles calculations. By increasing the Cl concentration, doping levels from n-type to slightly p-type are achieved on the SiC(0001) surface, while a wider range of doping levels is possible on the SiC(0001̄) surface. We find that the Cl atoms prefer bonding to the substrate rather than to the graphene. By varying the Cl concentration the doping level can be tailored. Consideration of van der Waals forces improves the distance between the graphene and the substrate as well as the binding energy, but it is not essential for the formation energy. For understanding the doping mechanism the introduction of non-local van der Waals contributions to the exchange correlation functional is shown to be essential. Copyright © EPLA, 2013.

Behaviors of SiC fibers at high temperature

International Nuclear Information System (INIS)

Colin, C.; Falanga, V.; Gelebart, L.

2010-01-01

On the one hand, considering the improvements of mechanical and thermal behaviours of the last generation of SiC fibers (Hi-Nicalon S, Tyranno SA3); on the other hand, regarding physical and chemical properties and stability under irradiation, SiC/SiC composites are potential candidates for nuclear applications in advanced fission and fusion reactors. CEA must characterize and optimize these composites before their uses in reactors. In order to study this material, CEA is developing a multi-scale approach by modelling from fibers to bulk composite specimen: fibres behaviours must be well known in first. Thus, CEA developed a specific tensile test device on single fibers at high temperature, named MecaSiC. Using this device, we have already characterized the thermoelastic and thermoelectric behaviours of SiC fibers. Additional results about the plastic properties at high temperatures were also obtained. Indeed, we performed tensile tests between 1200 degrees C up to 1700 degrees C to characterize this plastic behaviour. Some thermal annealing, up to 3 hours at 1700 degrees C, had been also performed. Furthermore, we compare the mechanical behaviours with the thermal evolution of the electric resistivity of these SiC fibers. Soon, MecaSiC will be coupled to a new charged particle accelerator. Thus, in this configuration, we will be able to study in-situ irradiation effects on fibre behaviours, as swelling or creep for example

Structure of MnSi on SiC(0001)

Science.gov (United States)

Meynell, S. A.; Spitzig, A.; Edwards, B.; Robertson, M. D.; Kalliecharan, D.; Kreplak, L.; Monchesky, T. L.

2016-11-01

We report on the growth and magnetoresistance of MnSi films grown on SiC(0001) by molecular beam epitaxy. The growth resulted in a textured MnSi(111) film with a predominantly [1 1 ¯0 ] MnSi (111 )∥[11 2 ¯0 ] SiC(0001) epitaxial relationship, as demonstrated by transmission electron microscopy, reflection high energy electron diffraction, and atomic force microscopy. The 500 ∘C temperature required to crystallize the film leads to a dewetting of the MnSi layer. Although the sign of the lattice mismatch suggested the films would be under compressive stress, the films acquire an in-plane tensile strain likely driven by the difference in thermal expansion coefficients between the film and substrate during annealing. As a result, the magnetoresistive response demonstrates that the films possess a hard-axis out-of-plane magnetocrystalline anisotropy.

Compósitos SiCf /SiC utilizados em sistemas de proteção térmica SiCf /SiC composites for thermal protection systems

Directory of Open Access Journals (Sweden)

M. Florian

2005-09-01

Full Text Available Compósitos de carbeto de silício (SiC reforçado com fibras de carbeto de silício (SiCf são materiais candidatos em potencial para utilização em sistemas de proteção térmica em altas temperaturas devido principalmente à boa condutividade térmica na direção da fibra e muito baixa condutividade térmica na direção transversal à fibra, alta dureza, estabilidade térmica e à corrosão por oxidação. O compósito SiCf/SiC possui uma matriz de SiC reforçada com fibras contínuas policristalinas de SiC e é obtido por reações de conversão em altas temperaturas e atmosfera controlada, utilizando o compósito carbono/carbono como precursor. O processo de Reação Química em Vapor (CVR foi utilizado para a fabricação de compósitos SiCf/SiC com alta pureza na fase de SiC-beta. O compósito precursor de carbono/carbono foi fabricado com fibra de carbono não estabilizada e matriz carbonosa derivada da resina fenólica na forma de carbono isotrópico. O compósito convertido exibiu uma densidade de 1,75 g/cm³, com 40% de porosidade aberta e resistência à flexão de 80 MPa medida por ensaio flexão em 4 pontos. A área especifica medida pela técnica de BET é dependente da temperatura de conversão e das condições inicias do precursor de carbono, podendo chegar a 18 m²/g.Composites based on silicon carbide are potential candidate materials for thermal protection systems mainly due to its good thermal conductivity in fiber direction and very low transversal thermal conductivity, high hardness, corrosion and thermal resistance. SiCf/SiC composite presents a SiC matrix reinforced with SiC polycrystalline continuous fibers. The composite was obtained by conversion reactions at high temperature and controlled atmosphere from a carbon/carbon composite precursor. The CVR process was used to fabricate SiC /SiC composite with crystalline high-purity beta-SiC from a carbon-carbon precursor fabricated with non-stabilized carbon fiber and

Elaboration of silicon carbides nano particles (SiC): from the powder synthesis to the sintered ceramic; Elaboration de ceramiques nanostructurees en carbure de silicium (SiC): de la synthese de poudre a la ceramique frittee

Energy Technology Data Exchange (ETDEWEB)

Reau, A. [CEA Saclay, Dept. des Materiaux pour le Nucleaire (DEN/DANS/DMN/SRMA), 91 - Gif-sur-Yvette (France)

2008-07-01

Materials for the reactor cores of the fourth generation will need materials supporting high temperatures with fast neutrons flux. SiC{sub f}/SiC ceramics are proposed. One of the possible elaboration process is to fill SiC fiber piece with nano particles SiC powder and to strengthen by sintering. The aim of this thesis is to obtain a nano structured SiC ceramic as a reference for the SiC{sub f}/SiC composite development and to study the influence of the fabrication parameters. (A.L.B.)

Effect of LaB6 on the thermal shock property of MoSi2-SiC coating for carbon/carbon composites

International Nuclear Information System (INIS)

Li Ting; Li Hejun; Shi Xiaohong

2013-01-01

Highlights: ► LaB 6 -MoSi 2 -SiC and MoSi 2 -SiC multi-composition coatings were coated on C/C composites by pack cementation. ► The microstructure and thermal shock resistance of both coatings were investigated. ► The addition of LaB 6 can increase the compactness, flexural strength and fracture toughness of the MoSi 2 -SiC coating simultaneously. ► Both coatings bond well with the substrates before and after thermal cycling oxidation between 1773 K and room temperature. ► The LaB 6 -MoSi 2 -SiC coated C/C shows better thermal shock resistance than the MoSi 2 -SiC coated C/C. - Abstract: LaB 6 -MoSi 2 -SiC and MoSi 2 -SiC coatings were prepared on the surface of carbon/carbon composites by pack cementation method. The crystal structures of the coatings were measured by X-ray diffraction. The morphologies and element distributions were also analyzed by scanning electron microscopy and energy dispersive spectroscopy, respectively. The effect of LaB 6 on the microstructure and thermal shock resistance of MoSi 2 -SiC coating was investigated. The results indicated that the LaB 6 -MoSi 2 -SiC coating possessed a denser structure and superior thermal shock resistance. After 25 times of thermal cycling oxidation between 1773 K and room temperature, the weight losses of the LaB 6 -MoSi 2 -SiC and MoSi 2 -SiC coated samples were 0.627% and 2.019%, respectively.

The development of SiC whisker fabrication technology for nuclear applications

International Nuclear Information System (INIS)

Kang, Thae Khapp; Kuk, Il Hiun; Lee, Jae Chun; Rhee, Chang Kyu; Lee, Ho Jin; Park, Soon Dong

1990-02-01

Important process factors of carbothermic process for the growth of SiC whiskers were investigated. The crystalline form of silicon dioxide, amount of carbon addition, graphite, silicon, catalysts, additive and reaction temperature were chosen as the main factors. Morphology of the resultant products was grouped into 3 different types; whisker,noodle and power types. The addition of catalyst affected in most the formation of SiC whiskers. Effects of catalyst and additive additions and reaction atmospheres on the morphology anf growth of SiC whiskers were investigated, silicon monoxide power and carbon monoxide gas were used as the raw materials. The addition of an iron containing catalyst resulted in a very long thread-like growth of the whiskers, while that of sodium chloride helical curlings. Addition of hydrogen to the non-oxidizing atmosphere enhanced the whisker formations. Crystallization of amorphous silicon monoxide raw powder was investigated at high temperatures up to 1500 deg C in Ar atmosphere using graphite crucible. Up to 900 deg C no crystallization occurred, while at 1100 - 1300 deg C silicon formation, and at 1500 deg C silicon dioxide and silicon carbide formations were detected. A slight weight loss began 1300 deg C, and the weight loss became about 33 % at 1500 deg C. After the formation reaction of SiC whiskers, the reaction products were leached by hydrofluoric acids. The optimum concentration of the hydrofluoric acid was 2 %. (author)

Characteristics of Fabricated SiC Neutron Detectors for Neutron Flux Monitoring

Energy Technology Data Exchange (ETDEWEB)

Kim, Han Soo; Ha, Jang Ho; Park, Se Hwan; Lee, Kyu Hong [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of); Lee, Cheol Ho [Hanyang University, Seoul (Korea, Republic of)

2011-05-15

An SPND (Self-powered Neutron Detector) is commonly used for neutron detection in NPP (Nuclear Power Plant) by virtue of un-reactivity for gamma-rays. But it has a drawback, which is that it cannot detect neutrons in real time due to beta emissions (about > 48 s) after reactions between neutrons and {sup 103}Rh in an SPND. And Generation IV reactors such as MSR (Molten-salt reactor), SFR (Sodium-cooled fast reactor), and GFR (Gas-cooled fast reactor) are designed to compact size and integration type. For GEN IV reactor, neutron monitor also must be compact-sized to apply such reactor easily and much more reliable. The wide band-gap semiconductors such as SiC, AlN, and diamond make them an attractive alternative in applications in harsh environments by virtue of the lower operating voltage, faster charge-collection times compared with gas-filled detectors, and compact size.1) In this study, two PIN-type SiC semiconductor neutron detectors, which are for fast neutron detection by elastic and inelastic scattering SiC atoms and for thermal neutron detection by charged particle emissions of 6LiF reaction, were designed and fabricated for NPP-related applications. Preliminary tests such as I-V and alpha response were performed and neutron responses at ENF in HANARO research reactor were also addressed. The application feasibility of the fabricated SiC neutron detector as an in-core neutron monitor was discussed

A comparative study of low energy radiation responses of SiC, TiC and ZrC

International Nuclear Information System (INIS)

Jiang, M.; Xiao, H.Y.; Zhang, H.B.; Peng, S.M.; Xu, C.H.; Liu, Z.J.; Zu, X.T.

2016-01-01

In this study, an ab initio molecular dynamics method is employed to compare the responses of SiC, TiC and ZrC to low energy irradiation. It reveals that C displacements are dominant in the cascade events of the three carbides. The associated defects in SiC are mainly Frenkel pairs and antisite defects, whereas damage end states in TiC and ZrC generally consist of Frenkel pairs and very few antisite defects are created. It is proposed that the susceptibility to antisite formation in SiC contributes to its crystalline-to-amorphous transformation under irradiation that is observed experimentally. The stronger radiation tolerance of TiC and ZrC than SiC can be originated from their different electronic structures, i.e., the and bonds are a mixture of covalent, metallic, and ionic character, whereas the bond is mainly covalent. The presented results provide underlying mechanisms for defect generation in SiC, TiC and ZrC, and advance the fundamental understanding of the radiation resistances of carbide materials.

Stratification of mixtures in evaporating liquid films occurs only for a range of volume fractions of the smaller component

Science.gov (United States)

Sear, Richard P.

2018-04-01

I model the drying of a liquid film containing small and big colloid particles. Fortini et al. [Phys. Rev. Lett. 116, 118301 (2016)] studied these films with both computer simulation and experiment. They found that at the end of drying, the mixture had stratified with a layer of the smaller particles on top of the big particles. I develop a simple model for this process. The model has two ingredients: arrest of the diffusion of the particles at high density and diffusiophoretic motion of the big particles due to gradients in the volume fraction of the small particles. The model predicts that stratification only occurs over a range of initial volume fractions of the smaller colloidal species. Above and below this range, the downward diffusiophoretic motion of the big particles is too slow to remove the big particles from the top of the film, and so there is no stratification. In agreement with earlier work, the model also predicts that large Péclet numbers for drying are needed to see stratification.

Temperature effect on the inter-micellar collision and maximum packaging volume fraction in water/AOT/isooctane micro-emulsions

International Nuclear Information System (INIS)

Guettari, Moez; Ben Naceur, Imen; Kassab, Ghazi; Tajouri, Tahar

2016-01-01

We have studied the viscosity behaviour of water/AOT/isooctane micro-emulsions as a function of the volume fraction of the dispersed phase over a temperature range from the (298.15 to 328.15) K. For all the studied temperature range, a sharp increase of the viscosities is observed when the droplets concentration was varied. Several equations based on hard sphere model were examined to explain the behaviours of micro-emulsions under temperature and concentration effects. According to these equations, the shape factor and the inter-particle interaction parameters were found to be dependent on temperature which is in contradiction with experimental results reported in the literature. A modified Vand equation, taking into account the inter-particle collision time, is used to interpret the results obtained. This deviation is attributed to the aggregation of the droplets which becomes important by increasing temperature. The maximum packaging volume fraction of particles Φ_d_m and the intrinsic viscosity [η] were determined according to the Krieger and Dougherty equation through the temperature range studied. These two parameters were shown to be dependent on temperature but their product was found to be constant and close to 2 as reported in theory.

Integer, fractional, and anomalous quantum Hall effects explained with Eyring's rate process theory and free volume concept.

Science.gov (United States)

Hao, Tian

2017-02-22

The Hall effects, especially the integer, fractional and anomalous quantum Hall effects, have been addressed using Eyring's rate process theory and free volume concept. The basic assumptions are that the conduction process is a common rate controlled "reaction" process that can be described with Eyring's absolute rate process theory; the mobility of electrons should be dependent on the free volume available for conduction electrons. The obtained Hall conductivity is clearly quantized as with prefactors related to both the magnetic flux quantum number and the magnetic quantum number via the azimuthal quantum number, with and without an externally applied magnetic field. This article focuses on two dimensional (2D) systems, but the approaches developed in this article can be extended to 3D systems.

Residual Stress Measurement of SiC tile/Al7075 Hybrid Composites by Neutron Diffraction

Energy Technology Data Exchange (ETDEWEB)

Park, Jong Bok; Lee, Jun Ho; Hong, Soon Hyung; Ryu, Ho Jin [KAIST, Daejeon (Korea, Republic of); Lee, Sang Bok; Lee, Sang Kwan [Korea Institute of Materials Science, Changwon (Korea, Republic of); Muslihd, M. Rifai [Center for Advanced Materials Science and Technology, Tangerang (India)

2016-05-15

In this research, SiC which has low density, high compressive strength, and high elastic modulus was used to fabricate the armor plate. In addition, Al which has low density and high toughness was used for a metal matrix of the composites. If two materials are combined, the composite can be effective materials for light weight armor applications. However, the existence of a large difference in coefficients of thermal expansion (CTE) between SiC and Al matrix, SiC/Al composites can have residual stresses while cooled in the fabrication process. Previous research reported that residual stresses in the composites or microstructures have an effect on the fatigue life and their mechanical properties. Some researchers reported about the residual stresses in the SiCp/Al metal matrix composites by numerical simulation systems, X-ray diffraction, and destructive methods. In order to analyze the residual stress of SiC/Al composites, the neutron diffraction as the non-destructive method was performed in this research. The 50 vol.% SiC{sub p}/Al7075 composites and SiC tile inserted 50 vol.% SiC{sub p}/Al7075 hybrid composites were measured to analyze the residual stress of Al (111) and SiC (111). Both samples had the tensile residual stresses in the Al (111) and the compressive residual stresses in the SiC (111) due to the difference in CTE.

Methodology Development for SiC Sensor Signal Modelling in the Nuclear Reactor Radiation Environments

International Nuclear Information System (INIS)

Cetnar, J.; Krolikowski, I.P.

2013-06-01

This paper deals with SiC detector simulation methodology for signal formation by neutrons and induced secondary radiation as well as its inverse interpretation. The primary goal is to achieve the SiC capability of simultaneous spectroscopic measurements of neutrons and gamma-rays for which an appropriate methodology of the detector signal modelling and its interpretation must be adopted. The process of detector simulation is divided into two basically separate but actually interconnected sections. The first one is the forward simulation of detector signal formation in the field of the primary neutron and secondary radiations, whereas the second one is the inverse problem of finding a representation of the primary radiation, based on the measured detector signals. The applied methodology under development is based on the Monte Carlo description of radiation transport and analysis of the reactor physics. The methodology of SiC detector signal interpretation will be based on the existing experience in neutron metrology developed in the past for various neutron and gamma-ray detection systems. Since the novel sensors based on SiC are characterised by a new structure, yet to be finally designed, the methodology for particle spectroscopic fluence measurement must be developed while giving a productive feed back to the designing process of SiC sensor, in order to arrive at the best possible design. (authors)

Large-scale synthesis of monodisperse SiC nanoparticles with adjustable size, stoichiometric ratio and properties by fluidized bed chemical vapor deposition

Energy Technology Data Exchange (ETDEWEB)

Liu, Rongzheng; Liu, Malin, E-mail: liumalin@tsinghua.edu.cn; Chang, Jiaxing [Tsinghua University, Institute of Nuclear and New Energy Technology, Collaborative Innovation Center of Advanced Nuclear Energy Technology (China)

2017-02-15

A facile fluidized bed chemical vapor deposition method was proposed for the synthesis of monodisperse SiC nanoparticles by using the single precursor of hexamethyldisilane (HMDS). SiC nanoparticles with average particle size from 10 to 200 nm were obtained by controlling the temperature and the gas ratio. An experimental chemical vapor deposition phase diagram of SiC in the HMDS-Ar-H{sub 2} system was obtained and three regions of SiC-Si, SiC and SiC-C can be distinguished. The BET surface area and the photoluminescence properties of the SiC nanoparticles can be adjusted by changing the nanoparticle size. For the SiC nanospheres with free carbon, a novel hierarchical structure with 5 ~ 8 nm SiC nanoparticles embedded into the graphite matrix was obtained. The advantages of fluidized bed technology for the preparation of SiC nanoparticles were proposed based on the features of homogenous reaction zone, narrow temperature distribution, ultra-short reactant residence time and mass production.

Large-scale synthesis of monodisperse SiC nanoparticles with adjustable size, stoichiometric ratio and properties by fluidized bed chemical vapor deposition

International Nuclear Information System (INIS)

Liu, Rongzheng; Liu, Malin; Chang, Jiaxing

2017-01-01

A facile fluidized bed chemical vapor deposition method was proposed for the synthesis of monodisperse SiC nanoparticles by using the single precursor of hexamethyldisilane (HMDS). SiC nanoparticles with average particle size from 10 to 200 nm were obtained by controlling the temperature and the gas ratio. An experimental chemical vapor deposition phase diagram of SiC in the HMDS-Ar-H_2 system was obtained and three regions of SiC-Si, SiC and SiC-C can be distinguished. The BET surface area and the photoluminescence properties of the SiC nanoparticles can be adjusted by changing the nanoparticle size. For the SiC nanospheres with free carbon, a novel hierarchical structure with 5 ~ 8 nm SiC nanoparticles embedded into the graphite matrix was obtained. The advantages of fluidized bed technology for the preparation of SiC nanoparticles were proposed based on the features of homogenous reaction zone, narrow temperature distribution, ultra-short reactant residence time and mass production.

Influence of Fiber Volume Fraction on the Tensile Properties and Dynamic Characteristics of Coconut Fiber Reinforced Composite

OpenAIRE

Izzuddin Zaman; Al Emran Ismail; Muhamad Khairudin Awang

2011-01-01

The utilization of coconut fibers as reinforcement in polymer composites has been increased significantly due to their low cost and high specific mechanical properties. In this paper, the mechanical properties and dynamic characteristics of a proposed combined polymer composite which consist of a polyester matrix and coconut fibers are determined. The influence of fibers volume fraction (%) is also evaluated and composites with volumetric amounts of coconut fiber up to 15% are fabricated. In ...

Oxygen isotopic exchange occurring during dry thermal oxidation of 6H SiC

Energy Technology Data Exchange (ETDEWEB)

Vickridge, I.C. E-mail: vickridge@gps.jussieu.fr; Tromson, D.; Trimaille, I.; Ganem, J.-J.; Szilagyi, E.; Battistig, G

2002-05-01

SiC is a large band gap semiconductor, promising for high power and high frequency devices. The thermal oxide is SiO{sub 2} however the growth rates of thermal oxide on SiC are substantially slower than on Si, and different along the polar directions (<0 0 0 1-bar> and <0 0 0 1> in the hexagonal polytypes). Thorough understanding of the oxide growth mechanisms may give us new insights into the nature of the SiO{sub 2}/SiC interface, crucial for device applications. We have determined growth kinetics for ultra-dry thermal oxidation of 6H SiC at 1100 deg. C for pressures from 3 to 200 mbar. At 3 mbar, the lowest pressure studied, the oxide growth rates along the two polar directions are virtually the same. At higher pressures growth is faster on the carbon-terminated (0 0 0 1-bar) face. After consecutive oxidations at 1100 deg. C and 100 mbar in {sup 18}O{sub 2} and {sup 16}O{sub 2} gases, {sup 18}O depth profiles show significant isotopic exchange and oxygen movement within the oxide during oxidation.

Swift heavy ion irradiation effects in SiC measured by positrons

Energy Technology Data Exchange (ETDEWEB)

Liszkay, L.; Kajcsos, Zs.; Szilagyi, E. [KFKI Research Inst. for Nuclear and Particle Physics, Budapest (Hungary); Havancsak, K. [Dept. for Solid State Physics, Eoetvoes Univ., Budapest (Hungary); Barthe, M.F.; Desgardin, P.; Henry, L. [CNRS Centre d' Etudes et de Recherches par Irradiation, Orleans (France); Battistig, G. [Research Inst. for Technical Physics and Materials Science, Budapest (Hungary); Skuratov, V.A. [Joint Inst. of Nuclear Research, Moscow (Russian Federation). Bogoliubov Lab. of Theoretical Physics

2001-07-01

N-type 6H SiC single crystals irradiated with swift (246 MeV) Kr ions at room temperature (the implantation depth being 21 {mu}m) were investigated by conventional positron lifetime and Doppler-broadening measurements as well as with the application of a slow positron beam. The fluence dependence of the irradiation-induced defects was studied in the 1 x 10{sup 10} - 1 x 10{sup 14} ion cm{sup -2} range. In the fluence and depth range studied, no sign of amorphization (or creation of large voids) was seen in the Kr irradiated crystals. The positron annihilation results were compared with atomic displacement calculations by TRIM. A simple model was used to describe the trapping effect and determine the relationship between the atomic displacement densities and the positron trapping. The 225 ps lifetime of the open-volume defects created suggests that the V{sub Si}-V{sub C} divacancy is the dominant trapping site in the implanted zone. (orig.)

UV laser drilling of SiC for semiconductor device fabrication

Energy Technology Data Exchange (ETDEWEB)

Krueger, Olaf; Schoene, Gerd; Wernicke, Tim; John, Wilfred; Wuerfl, Joachim; Traenkle, Guenther [Ferdinand-Braun-Institut fuer Hoechstfrequenztechnik, Gustav-Kirchhoff-Str. 4, 12489 Berlin (Germany)

2007-04-15

Pulsed UV laser processing is used to drill micro holes in silicon carbide (SiC) wafers supporting AlGaN/GaN transistor structures. Direct laser ablation using nanosecond pulses has been proven to provide an efficient way to create through and blind holes in 400 {mu}m thick SiC. When drilling through, openings in the front pads are formed, while blind holes stop {approx}40 {mu}m before the backside and were advanced to the electrical contact pad by subsequent plasma etching without an additional mask. Low induction connections (vias) between the transistor's source pads and the ground on the backside were formed by metallization of the holes. Micro vias having aspect ratios of 5-6 have been processed in 400 {mu}m SiC. The process flow from wafer layout to laser drilling is available including an automated beam alignment that allows a positioning accuracy of {+-}1 {mu}m with respect to existing patterns on the wafer. As proven by electrical dc and rf measurements the laser-assisted via technologies have successfully been implemented into fabrication of AlGaN/GaN high-power transistors.