WorldWideScience

Sample records for sic whisker reinforced

  1. Zirconia toughened SiC whisker reinforced alumina composites small business innovation research

    Science.gov (United States)

    Loutfy, R. O.; Stuffle, K. L.; Withers, J. C.; Lee, C. T.

    1987-01-01

    The objective of this phase 1 project was to develop a ceramic composite with superior fracture toughness and high strength, based on combining two toughness inducing materials: zirconia for transformation toughening and SiC whiskers for reinforcement, in a controlled microstructure alumina matrix. The controlled matrix microstructure is obtained by controlling the nucleation frequency of the alumina gel with seeds (submicron alpha-alumina). The results demonstrate the technical feasibility of producing superior binary composites (Al2O3-ZrO2) and tertiary composites (Al2O3-ZrO2-SiC). Thirty-two composites were prepared, consolidated, and fracture toughness tested. Statistical analysis of the results showed that: (1) the SiC type is the key statistically significant factor for increased toughness; (2) sol-gel processing with a-alumina seed had a statistically significant effect on increasing toughness of the binary and tertiary composites compared to the corresponding mixed powder processing; and (3) ZrO2 content within the range investigated had a minor effect. Binary composites with an average critical fracture toughness of 6.6MPam sup 1/2, were obtained. Tertiary composites with critical fracture toughness in the range of 9.3 to 10.1 MPam sup 1/2 were obtained. Results indicate that these composites are superior to zirconia toughened alumina and SiC whisker reinforced alumina ceramic composites produced by conventional techniques with similar composition from published data.

  2. MICROSCOPIC ASPECT AND MECHANICS OF CREEP-FATIGUE FAILURE IN SiC WHISKER REINFORCED ALUMINUM BASE COMPOSITE AT HIGH TEMPERATURE

    National Research Council Canada - National Science Library

    OKAZAKI, Masakazu; TASHIRO, Hiromichi; MIZUTANI, Junnosuke

    1997-01-01

    The microscopic aspect of creep-fatigue failure process in a 6061 aluminum alloy composite reinforced with SiC whiskers, SiCw/6061, was studied at high temperature, with specific attention being paid...

  3. Crucial effect of SiC particles on in situ synthesized mullite whisker reinforced Al2O3-SiC composite during microwave sintering

    Directory of Open Access Journals (Sweden)

    Meng Wei

    2017-06-01

    Full Text Available Mullite whisker reinforced Al2O3-SiC composites were in situ synthesized by microwave sintering at 1500°C for 30min. The influence of SiC particle size on heating process and properties of Al2O3-SiC composite were investigated. The XRD and SEM techniques were carried out to characterize the samples. The thermal shock resistance and flexural strength of the samples were examined through water quenching and three-point bending methods, respectively. It was found that the bridging of mullite whisker appeared between Al2O3 and SiC particles which enhanced the thermal shock resistance. A so-called local hot spot effect was proposed dependent on the coupling of SiC particles with microwave, which was the unique feature of microwave sintering. The maximal thermal shock resistance and flexural strength were obtained for the samples with SiC particle size of ~5μm.

  4. Ceramic Technology Project database: September 1990 summary report. [SiC, SiN, whisker-reinforced SiN, ZrO-toughened aluminas, zirconias, joints

    Energy Technology Data Exchange (ETDEWEB)

    Keyes, B.L.P.

    1992-06-01

    Data generated within the Ceramic Technology Project (CTP) represent a valuable resource for both research and industry. The CTP database was created to provide easy access to this information in electronic and hardcopy forms by using a computerized database and by issuing periodic hardcopy reports on the database contents. This report is the sixth in a series of semiannual database summaries and covers recent additions to the database, including joined brazed specimen test data. It covers 1 SiC, 34 SiN, 10 whisker-reinforced SiN, 2 zirconia-toughened aluminas, 8 zirconias, and 34 joints.

  5. Sliding wear of self-mated Al2O3-SiC whisker-reinforced composites at 23-1200 C

    Science.gov (United States)

    Farmer, S. C.; Dellacorte, C.; Book, P. O.

    1993-01-01

    Microstructural changes occurring during sliding wear of self-mated Al2O3 SiC whisker-reinforced composites were studied using optical, scanning electron microscopy and transmission electron microscopy. Pin-on-disc specimens were slid in air at 2.7 m/s sliding velocity under a 26.5 N load for 1 h. Wear tests were conducted at 23, 600, 800 and 1200 C. Mild wear with a wear factor of 2.4 x 10 exp -7 - 1.5 x 10 exp -6 cu mm /N per m was experienced at all test temperatures. The composite showed evidence of wear by fatigue mechanisms at 800 C and below. Tribochemical reaction (SiC oxidation and reaction of SiO2 and Al2O3) leads to intergranular failure at 1200 C. Distinct microstructural differences existing at each test temperature are reported.

  6. Sliding wear of self-mated Al2O3-SiC whisker reinforced composites at 23-1200 C

    Science.gov (United States)

    Farmer, Serene C.; Book, Patricia O.; Dellacorte, Christopher

    1991-01-01

    Microstructural changes occurring during sliding wear of self-mated Al2O3-SiC whisker reinforced composites were studied using optical, scanning electron microscopy, and transmission electron microscopy. Pin-on-disk specimens were slid in air at 2.7 m/sec sliding velocity under a 26.5 N load for 1 hr. Wear tests were conducted at 23, 600, 800, and 1200 C. Mild wear with a wear factor of 2.4 times 10(exp -7) to 1.5 times 10(exp -6) cu mm/Nm was experienced at all test temperatures. The composite shows evidence of wear by fatigue mechanisms at 800 C and below. Tribochemical reaction (SiC oxidation and reaction of SiO2 and Al2O3) leads to intergranular failure at 1200 C. Distinct microstructural differences existing at each test temperature are reported.

  7. Whisker-reinforced ceramic composites for heat engine components

    Science.gov (United States)

    Duffy, Stephen F.

    1988-01-01

    Much work was undertaken to develop techniques of incorporating SiC whiskers into either a Si3N4 or SiC matrix. The result was the fabrication of ceramic composites with ever-increasing fracture toughness and strength. To complement this research effort, the fracture behavior of whisker-reinforced ceramics is studied so as to develop methodologies for the analysis of structural components fabricated from this toughened material. The results, outlined herein, focus on the following areas: the use of micromechanics to predict thermoelastic properties, theoretical aspects of fracture behavior, and reliability analysis.

  8. 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.

  9. 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.

  10. Biopolymer nanocomposite films reinforced with nanocellulose whiskers

    Science.gov (United States)

    Amit Saxena; Marcus Foston; Mohamad Kassaee; Thomas J. Elder; Arthur J. Ragauskas

    2011-01-01

    A xylan nanocomposite film with improved strength and barrier properties was prepared by a solution casting using nanocellulose whiskers as a reinforcing agent. The 13C cross-polarization magic angle spinning (CP/MAS) nuclear magnetic resonance (NMR) analysis of the spectral data obtained for the NCW/xylan nanocomposite films indicated the signal intensity originating...

  11. Preparation of mullite whiskers reinforced SiC/Al2O3 composites by microwave sintering

    Directory of Open Access Journals (Sweden)

    Wei Li

    2016-12-01

    Full Text Available Mullite whiskers reinforced SiC/Al2O3 composites were prepared by microwave sintering in a microwave chamber with TE666 resonant mode. Original SiC particles were coated with SiO2 using sol-gel processing and mixed with Al2O3 particles. Mullite was formed in the reaction between SiO2 and Al2O3. The isostatically pressed cylindrical pellets were sintered from 1350 °C to 1600 °C for 30 min. Physical and chemical responses were investigated by detecting changes in reflected power during the microwave sintering process. XRD was carried out to characterize the samples and showed that mullite could be formed at 1200 °C. Bridging of mullite whiskers between Al2O3 and SiC particles was observed by SEM and is due to a so-called local hot spot effect, which was the unique feature for microwave sintering. The optimized microwave sintering temperature was 1500 °C corresponding to the maximum amount of mullite whiskers within SiC/Al2O3 composites. The high electro-magnetic field enhanced the decomposition of mullite at higher temperatures above 1550 °C. The mechanical properties of mullite whiskers reinforced SiC/Al2O3 composites are much better than the SiC/Al2O3 composites without mullite whiskers.

  12. A model of toughening effects in whisker-reinforced composites

    Energy Technology Data Exchange (ETDEWEB)

    Hoagland, R.G. (Washington State Univ., Pullman, WA (United States). Dept. of Mechanical and Materials Engineering); Henager, C.H. Jr. (Pacific Northwest Lab., Richland, WA (United States))

    1991-01-01

    A numerical approach is presented that lends itself to modeling the screening or antiscreening effects due solely to modulus differences of a discrete array of whiskers in an elastic matrix. The method is applied to single whiskers, and to examining the issue of whisker orientation of the toughness of ceramic composites. The model results indicate that crack-tip shielding due to modulus defect interactions occurs when the reinforcement has a higher modulus than the matrix material, and that anti-shielding occurs for the opposite case. Results for a single whisker located at the crack-tip (maximum effect) indicate that the crack-tip stress intensity is reduced by about 10% when a modulus ratio of four is assumed. Calculations performed with whisker arrays demonstrate pronounced effects of whisker orientation on the crack-tip screening, being larger for whiskers oriented perpendicular to the crack plane, as expected. Ordered whisker arrays produce larger and more uniform screening than do random whisker arrays. 16 refs., 10 figs.

  13. Method of making in-situ whisker reinforced glass ceramic

    Science.gov (United States)

    Brown, Jesse J.; Hirschfeld, Deidre A.; Lee, K. H.

    1993-02-16

    A heat processing procedure is used to create reinforcing whiskers of TiO.sub.2 in glass-ceramic materials in the LAS and MAS family. The heat processing procedure has particular application in creating TiO.sub.2 in-situ in a modified .beta.-eucryptite system.

  14. Investigation into ramie whisker reinforced arylated soy protein composites

    CSIR Research Space (South Africa)

    Kumar, R

    2010-03-01

    Full Text Available bonding, and dispersion of the whiskers in the matrix [11-14]. Ramie is a plant fiber that has been used since ancient times and is commonly known as China grass. Ramie fibers are widely cultivated plant of industrial importance. We have shown... Reinforced Arylated Soy Protein Composites Rakesh Kumar1,2*, Lina Zhang2 1CSIR MSM, Port Elizabeth 6000, South Africa 2Department of Chemistry, Wuhan University, Wuhan 430072, China Abstract Whiskers were prepared from ramie fibers and were...

  15. Síntesis de whiskers de SiC asistida por microondas

    Directory of Open Access Journals (Sweden)

    Garza-Méndez, F. J.

    2013-06-01

    Full Text Available 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/H2O and ethanol. Throughanalysis of the BET is determined the value of averageporesize (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 β-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.Se desarrolló un nuevo proceso para la síntesis de whiskers de SiC asistida por microondas, basada en la mezcla de xerogeles de sílice y grafito en polvo. Como fuente de energía se emplearon microondas de 2.45 GHz y 1.5 kW de potencia. La sílice mesoporosa se sintetizó vía sol-gel, los precursores usados para esta síntesis fueron TEOS/H2O y etanol. A través del análisis BET se determinó el valor de tamaño de poro promedio (3.0 nm y el área superficial (1090 m2/g. Mediante difracción de rayos-x método de polvos se demostró que la sílice sintetizada es amorfa y que los polvos obtenidos en el microondas corresponden a β-SiC. Para determinar la morfología de los whiskers de SiC se analizó por MEB en el modo de electrones secundarios. El efecto de las microondas en la síntesis de whiskers de SiC se discute en el presente trabajo.

  16. Strain gradient plasticity effects in whisker-reinforced metals

    DEFF Research Database (Denmark)

    Niordson, Christian Frithiof

    2002-01-01

    A metal reinforced by fibers in the micron range is studied using the strain gradient plasticity theory of Fleck and Hutchinson (2001). Cell-model analyzes are used to study the influence of the material length parameters numerically. Different higher order boundary conditions are considered...... at the fiber-matrix interface. The results are presented as overall stress-strain curves for the whisker-reinforced metal, and also contour plots of effective plastic strain are shown. The strain gradient plasticity theory predicts a significant stiffening effect when compared to conventional models...

  17. Synergistically toughening effect of SiC whiskers and nanoparticles in Al2O3-based composite ceramic cutting tool material

    Science.gov (United States)

    Liu, Xuefei; Liu, Hanlian; Huang, Chuanzhen; Wang, Limei; Zou, Bin; Zhao, Bin

    2016-09-01

    In recent decades, many additives with different characteristics have been applied to strengthen and toughen Al2O3-based ceramic cutting tool materials. Among them, SiC whiskers and SiC nanoparticles showed excellent performance in improving the material properties. While no attempts have been made to add SiC whiskers and SiC nanoparticles together into the ceramic matrix and the synergistically toughening effects of them have not been studied. An Al2O3-SiCw-SiCnp advanced ceramic cutting tool material is fabricated by adding both one-dimensional SiC whiskers and zero-dimensional SiC nanoparticles into the Al2O3 matrix with an effective dispersing and mixing process. The composites with 25 vol% SiC whiskers and 25 vol% SiC nanoparticles alone are also investegated for comparison purposes. Results show that the Al2O3-SiCw-SiCnp composite with both 20 vol% SiC whiskers and 5 vol% SiC nanoparticles additives have much improved mechanical properties. The flexural strength of Al2O3-SiCw-SiCnp is 730±95 MPa and fracture toughness is 5.6±0.6 MPa·m1/2. The toughening and strengthening mechanisms of SiC whiskers and nanoparticles are studied when they are added either individually or in combination. It is indicated that when SiC whiskers and nanoparticles are added together, the grains are further refined and homogenized, so that the microstructure and fracture mode ratio is modified. The SiC nanoparticles are found helpful to enhance the toughening effects of the SiC whiskers. The proposed research helps to enrich the types of ceramic cutting tool and is benefit to expand the application range of ceramic cutting tool.

  18. High temperature flow behaviour of SiC reinforced lithium ...

    Indian Academy of Sciences (India)

    Unknown

    Abstract. The compressive flow behaviour of lithium aluminosilicate (LAS) glass, with and without SiC particulate reinforcements, was studied. The LAS glass crystallized to β spodumene during high-temperature testing. The flow behaviour of LAS glass changed from Newtonian to non-Newtonian due to the presence of.

  19. Hydroxyapatite Whisker Reinforced 63s Glass Scaffolds for Bone Tissue Engineering

    Directory of Open Access Journals (Sweden)

    Cijun Shuai

    2015-01-01

    Full Text Available Bioactive glass (BG is widely used for bone tissue engineering. However, poor mechanical properties are the major shortcomings. In the study, hydroxyapatite nanowhisker (HANw was used as a reinforcement to improve the mechanical properties. 63s glass/HANw scaffolds were successfully fabricated by selective laser sintering (SLS. It was found that the optimal compressive strength and fracture toughness were achieved when 10 wt.% HANw was added. This led to 36% increase in compressive strength and 83% increase in fracture toughness, respectively, compared with pure 63s glass scaffolds. Different reinforcement mechanisms were analyzed based on the microstructure investigation. Whisker bridging and whisker pulling-out were efficient in absorbing crack propagating energy, resulting in the improvement of the mechanical properties. Moreover, bioactivity and biocompatibility of the scaffolds were evaluated in vitro. The results showed that composite scaffolds with 10 wt.% HANw exhibited good apatite-forming ability and cellular affinity.

  20. Strain gradient plasticity effects in whisker-reinforced metals

    DEFF Research Database (Denmark)

    Niordson, Christian Frithiof

    2003-01-01

    A metal reinforced by fibers in the micron range is studied using the strain gradient plasticity theory of Fleck and Hutchinson (J. Mech. Phys. Solids 49 (2001) 2245). Cell-model analyses are used to study the influence of the material length parameters numerically, for both a single parameter...

  1. Synthesis of CaSiO{sub 3} Whiskers by alkaline salt flux for biomaterials reinforcement; Sintese de 'Whiskers' de CaSiO{sub 3} em fluxo salino para o reforco de biomateriais

    Energy Technology Data Exchange (ETDEWEB)

    Motisuke, M., E-mail: motisuke@unifesp.br [Universidade Federal de Sao Paulo (UNIFESP), Sao Jose dos Campos, SP (Brazil). Instituto de Ciencia e Tecnologia; Bertran, C.A. [Universidade Estadual de Campinas (UNICAMP), SP (Brazil). Instituto de Quimica

    2011-07-01

    Ceramic materials reinforcement by whiskers has been employed for a long time in a variety of industrial applications. Nevertheless, the materials by which these whiskers are commonly made of (carbide and silicon nitride) do not allow their use in the biomaterials field due to the high toxicity related to these materials. Then, it is of interest to synthesize ceramic whiskers which could reinforce biocompatible ceramic and polymeric biomaterials without harming the patients' health. In this manner, the aim of this work is to propose a synthetic route to produce whiskers of CaSiO{sub 3} (wollastonite): a biocompatible, bioactive and resorbable biomaterial. It was employed the molten salt synthesis at 900°C to grow wollastonite crystals which were characterized by X ray diffraction and scanning electron microscopy. The proposed method was efficient for growing whiskers with aspect ratio ranging 10. (author)

  2. Toward "strong" green nanocomposites: polyvinyl alcohol reinforced with extremely oriented cellulose whiskers.

    Science.gov (United States)

    Jalal Uddin, Ahmed; Araki, Jun; Gotoh, Yasuo

    2011-03-14

    To exploit the maximum potential of cellulose whiskers (CWs), we report here for the first time the successful fabrication of nanocomposites reinforced with highly oriented CWs in a polymer matrix. The nanocomposites were prepared using polyvinyl alcohol (PVA) and a colloidal suspension of cotton-derived CWs. The macroscopically homogeneous PVA-CW suspensions were extruded into cold methanol to form gel fibers followed by a hot drawing. Compared to the neat PVA fiber, the as-spun fiber containing a small amount of CWs (5 wt % of solid PVA) showed higher drawability, leading to an extremely high orientation of CWs with the matrix PVA. The stress-transfer mechanism, a prime determining factor for high mechanical properties of nanocomposites, was studied by X-ray diffraction. The stress on the incorporated CWs was monitored by applying an in situ nondestructive load to the composite fibers. The applied stress to the whole sample was found to be effectively transferred to the CWs inside the composites, suggesting strong interfacial bonding between the filler and the matrix. Effective stress transfer to the oriented whiskers resulted in outstanding enhancement in mechanical properties of the nanocomposites.

  3. Carbon Nanotube (CNT) and Carbon Fiber Reinforced SiC Optical Components Project

    Data.gov (United States)

    National Aeronautics and Space Administration — M Cubed has developed and patented technology to make carbon fiber reinforced SiC composites and components. In addition, the feasibility of doubling the toughness...

  4. Síntese de "whiskers" de CaSiO3 em fluxo salino para elaboração de biomateriais Synthesis of CaSiO3 "whiskers" in alkaline salt flux for biomaterials reinforcement

    Directory of Open Access Journals (Sweden)

    M. Motisuke

    2012-12-01

    Full Text Available Há tempos empregam-se "whiskers" cerâmicos como reforço de materiais nas mais diversas aplicações, porém os materiais com os quais estes são comumente fabricados (carbeto e nitreto de silício não permitem a sua utilização no campo dos biomateriais devido sua elevada toxicidade. Assim, torna-se interessante sintetizar "whiskers" biocompatíveis capazes de reforçar biomateriais cerâmicos e poliméricos sem prejudicar a saúde dos pacientes. Dessa forma, este trabalho tem como objetivo desenvolver e determinar os parâmetros limitantes de uma nova rota de síntese por fusão de sais de "whiskers" de CaSiO3, uma biocerâmica biocompatível, bioativa e reabsorvível. Este método é simples, barato e permite a produção em larga escala. Utilizou-se um fluxo de NaCl/KCl a 900 ºC para sintetizar "whiskers" de wollastonita, que foram caracterizados por difração de raios X e microscopia eletrônica de varredura. O método proposto mostrou-se eficiente, entretanto os tempos de patamar empregados não foram suficientes para garantir 100% de rendimento da reação de formação de CaSiO3, ocorrendo a formação de cristobalita.Materials reinforcement by ceramic whiskers has been employed for a long time in a variety of industrial applications. Nevertheless, the materials by which these whiskers are commonly made of (carbide and silicon nitride do not allow their use in biomaterials field due to their high toxicity. Then, it is of interest to synthesize ceramic whiskers which could reinforce biocompatible ceramic and polymeric biomaterials without harming the patients' health. In this manner, the aim of this work is to propose and analyze the limiting process variables of a new synthetic route to produce whiskers of CaSiO3 (wollastonite: a biocompatible, bioactive and readsorbable biomaterial. It was employed the molten salt synthesis at 900 ºC to grow wollastonite crystals which were characterized by X-ray diffraction and scanning electron

  5. [Effect of amount of silane coupling agent on flexural strength of dental composite resins reinforced with aluminium borate whisker].

    Science.gov (United States)

    Zhu, Ming-yi; Zhang, Xiu-yin

    2015-06-01

    To evaluate the effect of amount of silane coupling agent on flexural strength of dental composite resins reinforced with aluminium borate whisker (ABW). ABW was surface-treated with 0%, 1%, 2%, 3% and 4% silan coupling agent (γ-MPS), and mixed with resin matrix to synthesize 5 groups of composite resins. After heat-cured at 120 degrees centigrade for 1 h, specimens were tested in three-point flexure to measure strength according to ISO-4049. One specimen was selected randomly from each group and observed under scanning electron microscope (SEM). The data was analyzed with SAS 9.2 software package. The flexural strength (117.93±11.9 Mpa) of the group treated with 2% silane coupling agent was the highest, and significantly different from that of the other 4 groups (α=0.01). The amount of silane coupling agent has impact on the flexural strength of dental composite resins reinforced with whiskers; The flexual strength will be reduced whenever the amount is higher or lower than the threshold. Supported by Research Fund of Science and Technology Committee of Shanghai Municipality (08DZ2271100).

  6. The Effect of Mechanical Working on SiC Whisker-Reinforced Aluminum Alloys.

    Science.gov (United States)

    1980-04-01

    FORM .. .RPO T NM ., . GOVT ACCESSION NO. 3- RECIPIENT’S CATALOG NUMBER AMMRC-TPR-80-l1 / 4. ’TI.TC; fd Bob .. - S TYPE OF REPORT & PEmOO COVERED...E., Charlottesville, Virginia 22901 1 ATTN: Military Tech, Mr. Marley Director, Eustis Directorate, U. S. Army Air Mobility Research and Development

  7. Residual stress measurements in an SiC continuous fiber reinforced Ti matrix composite

    NARCIS (Netherlands)

    Willemse, P.F.; Mulder, F.M.; Wei, W.; Rekveldt, M.Th.; Knight, K.S.

    2000-01-01

    During the fabrication of ceramic fiber reinforced metal matrix composites mismatch stresses will be introduced due to differences in thermal expansion coefficients between the matrix and the fibers. Calculations, based on a coaxial cylinder model, [1 and 2] predict that, for a Ti matrix SiC

  8. 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.

  9. High temperature flow behaviour of SiC reinforced lithium ...

    Indian Academy of Sciences (India)

    The flow behaviour of LAS glass changed from Newtonian to non-Newtonian due to the presence of crystalline phase. Further, with the addition of 40 vol.% SiC additions, the strain rate sensitivity of flow stress decreased. While the activation energy for flow in LAS was 300 kJ/mole, it increased to 995 kJ/mole with the ...

  10. SYLRAMIC™ SiC fibers for CMC reinforcement

    Science.gov (United States)

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

    2000-12-01

    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.

  11. Characteristics of Al-Si-Mg Reinforced SiC Composites Produced by Stir Casting Route

    Science.gov (United States)

    Zulfia, A.; Zhakiah, T.; Dhaneswara, D.; Sutopo

    2017-05-01

    Al-Si-Mg alloy that is strengthened by silicon carbide particles has the potential to have excellent mechanical properties with light weight. In this study, metal matrix composites reinforced silicon carbide from 2 vf-% to 15 vf-% and magnesium amounted to 10 wt-% as an external dopant were fabricated by stir casting route. The magnesium was added to promote the wetting between Al matrix and reinforced SiC. The process involved SiC blended inside the molten Al by a stirrer with a rotational speed of 500 rpm at 800 °C for 2 minutes and degassed with Ar gas for 4 minutes to remove all of the gas content in the molten Al. The molten composite was then cast into the plate and tensile test sample molds. The effect of SiC addition on the mechanical properties and microstructure of the composites was investigated. The result showed that the optimum tensile strength was reached at 8 vf-% SiC with the value of 175 MPa, while the elongation was 9.1%. The maximum hardness and wear rate were achieved at 10 vf-% SiC with the values of 57 HRB and 0.0022 mm3/m, respectively. Such increase was related to the microstructures dominated by the presence of Chinese script, primary and eutectic Mg2Si which were contributed to the mechanical properties of the composites.

  12. Effect of SiC Nano powder on Multiaxial Woven and Chopped Randomly Oriented Flax/Sisal Fiber Reinforced composites

    Directory of Open Access Journals (Sweden)

    Kalagi Ganesh R.

    2018-01-01

    Full Text Available A study has been carried out to investigate effect of SiC Nano powder on tensile and impact properties of Multiaxial layers of Flax and Sisal fiber reinforced composites and randomly oriented chopped Flax and Sisal fiber reinforced composites. It has been observed that tensile strength and impact strength were improved using 6% of SiC Nanopowder into Multiaxial layer (+45º/-45º, 0º/90º of Flax and Sisal where as randomly oriented chopped Flax and Sisal fiber reinforced composites are improved in its stiffnes for the same composition of fiber, epoxy and SiC Nano powder. SEM Analysis are done to analyse the distribution of SiC in both Multiaxial layers of Flax and Sisal fiber reinforced composites and randomly oriented chopped Flax and Sisal fiber reinforced composites.

  13. Fabrication of SiC Reinforced Zr0{sub 2} Composites via Polymeric Precursor Route

    Energy Technology Data Exchange (ETDEWEB)

    Mistarihi, Qusai M.; Hong, Soon Hyung; Ryu, Ho Jin [KAIST, Daejeon (Korea, Republic of)

    2015-10-15

    This indicates that as a result of the decomposition of the SMP-730 at temperatures less than or equal to 1500 .deg. C, amorphous SiC was formed. This study suggests that a higher compaction pressure followed by an intermediate decomposition temperature of the polymeric precursor and a higher sintering temperature are needed in order to fabricate interconnected SiC-ZrO{sub 2} composites. A. Ortona et al. fabricated ZrB2-SiC composites with SiC phase surrounding the grains of ZrB2 matrix through a polymeric precursor route by using Si and phenol. S. Li et al. measured the thermal conductivity of Al composites reinforced with a continuous phase SiC and SiC particles and found that the difference in the thermal conductivity measured at room temperature was about 70.2 W/m.K. To the best of authors' knowledge, no study has been performed about the fabrication of the connected SiC microstructure to improve the thermophysical properties of oxides. Zirconium dioxide (ZrO{sub 2}) is one of the potential candidates for use as a matrix for inert matrix fuels (IMF) due to its low neutron absorption cross section, chemical stability, and the compatibility with water. Irradiation and chemical stability testes performed on yttria stabilized zirconia (YSZ) and calcium stabilized zirconia (CSZ) have shown that they have a good irradiation and chemical stability. Despite the good irradiation and chemical stability, its low thermal conductivity is considered the main disadvantage of YSZ. Core loading with the YSZ IMF pellets experienced about a 100 K higher center line temperature than the limit specified for UO{sub 2}.

  14. Experimental Studies on SiC and Rice Husk Ash Reinforced Al Alloy Composite

    Directory of Open Access Journals (Sweden)

    Shivaprakash Y. M.

    2018-01-01

    Full Text Available In this research work Aluminium alloy with Cu (4.5% as the major alloying element is used as the matrix in which SiC and Rice Husk Ash (RHA are dispersed to develop a hybrid composite. The dispersion is done by the motorized stir casting arrangement. The composite is fabricated by varying the proportions of the reinforcements in the base alloy. The composite specimens were tested for density changes, hardness and the wear. The microstructure images showed a uniform dispersion of the reinforcements in the matrix and this resulted in higher strength to weight ratio. The increase in strength of the composite is probably attributed to the increase in the dislocation density. Also, the abrasive wear resistance of the produced composite is found to be superior as compared to the matrix alloy because of the hard-ceramic particles in the reinforcements.

  15. Examining of abrasion resistance of hybrid composites reinforced with SiC and Cgr particles

    Directory of Open Access Journals (Sweden)

    M. Łągiewka

    2008-08-01

    Full Text Available The presented work discusses the influence of the type and volume percentage of particulate reinforcement consisting of mixed silicon carbide and graphite on the abrasion wear of hybrid composites with AlMg10 matrix. Also the macro photos of frictional surfaces have been shown and the results of hardness measurements have been presented. The performed examinations have allowed for stating that the mixture of SiC and Cgr particles changes in favour the tribological properties of the matrix alloy. It has been also proved that introducing hard reinforcing particles along with soft lubricating ones allows for achieving the material exhibiting high abrasion resistance, and moreover, the graphite particles protect the abraded surface from the destructive action of silicon carbide particles. Also hardness measurements have been performed and the resulting conclusion is that the composite hardness increases with an increase in volume fraction of the reinforcing particles.

  16. Thermal Sensitive Shape Memory Behavior of Epoxy Composites Reinforced with Silicon Carbide Whiskers

    Directory of Open Access Journals (Sweden)

    Yongkun Wang

    2017-01-01

    Full Text Available A novel shape memory polymer composite was fabricated by introducing various amounts of silicon carbide whiskers (SiCws into a shape memory epoxy. The relationship between the thermomechanical properties of the system and structural changes were investigated via dynamic mechanical analysis, scanning electron microscopy, and bending tests. The results show that the bend strength of composites can improve by 64.1% when SiCw content reaches 12 wt %. The shape transition temperatures of SiCw/epoxy composites decreased slightly with the increase in SiCw content, but it was noted that all of the composites showed excellent shape memory properties. The shape fixity ratio increased as SiCw content increased (>99%, and the shape recovery ratio slightly decreased as SiCw content increased (>95%. All of the composites nearly recovered to their original shape within 2 min (not 100%, and the shape recovery speed significantly improved at a higher temperature. It is anticipated that tagging products will be used in the aerospace industry.

  17. Product technology and market assessment for silicon carbide whisker reinforced alumina heat-exchanger tubes. Final report

    Energy Technology Data Exchange (ETDEWEB)

    Loutfy, R.O.; Withers, J.C. [Materials and Electrochemical Research Corp., Tucson, AZ (United States); Chakravarti, D. [Arizona Univ., Tucson, AZ (United States)

    1993-10-01

    This report describes a study designed to develop an assessment of key performance features, desirable technical specifications and market potential for silicon carbide whisker-reinforced alumina (henceforth SCWRA) tubes for heat exchanger applications in a number of industries. The results of the first stage of a Delphi study conducted in the US market are presented. The second phase of the study is in progress. The first stage results suggest that there is a small market for SCWRA tubes in heat exchanger applications. The market is expected to grow steadily during the 1990`s. With appropriate performance specifications and competitive pricing, growth should come from (a) new applications that permit recovery in cases that were previously infeasible and (b) selective, partial substitution and replacement of current ceramics and metal/ceramic composites in existing applications. We identify key performance factors and detailed specifications needed in six designated industries (primary metals, fabricated metals, chemicals, glass, utility and incinerators). Reliability, durability and low maintenance costs emerge as critical performance factors across these industries. The data show that although ceramics are recognized as having better properties, enhancing reliability and durability and thus improving maintenance cost performance is a key priority. Such improvements, reflected in the objectives for SCWRA tubes, should facilitate adoption in both new and existing applications. At this time, we are unable to assess market size directly. However, expert judgment provided indices tracking the projected market for heat exchanger tubes from 1990 to 2005.

  18. Effect of reinforcement of AL-6063 with SiC on mechanical behavior and microstructure of metal matrix composites

    Directory of Open Access Journals (Sweden)

    M. K. Aravindan

    2014-03-01

    Full Text Available A phrase heard often in recent years, advanced composite materials like Al/SiC metal matrix composite is gradually becoming very important materials in auto and aerospace industries due to their superior properties. The present study examines the mechanical properties of aluminum (Al-6063/SiC Silicon carbide reinforced particles metal-matrix composites (MMCs by varying weight fractions of SiC. For this (Al-6063/SiC reinforced particles MMCs are fabricated by stir casting method at air atmosphere . The MMCs are prepared in the form of bars with varying the reinforced particles by weight fraction ranging from 2 %, 4 %, 6 %, 8 % and 10 %. The reinforced particles size of SiC is varying between 25-40 microns. The microstructure study shows that the distribution of particles becomes better with increasing weight fraction of SiC. The Mechanical properties like, Ultimate tensile strength (MPa, % Elongation, Hardness (HRB, Yield Strength (N.m are investigated on prepared specimens of MMCs. It was observed that the hardness of the composite is increased gradually from 2-6 % and drastically from 8-10%. The tensile strength and ultimate break load are increased with rising of reinforced weight fraction and the improvement varies between 15.8- 27 % and 2-15 % respectively.

  19. Nonlocal plasticity effects on fibre debonding in a whisker-reinforced metal

    DEFF Research Database (Denmark)

    Niordson, Christian Frithiof; Tvergaard, Viggo

    2002-01-01

    Numerical cell-model analyses for the matrix-fibre debonding in a metal matrix composite are used to study the effect of a characteristic material length in the plasticity description of the matrix material deformations. Characteristic material lengths are already present in the model problem......, in the form of fibre sizes and the length associated with the debonding process, so the nonlocal plasticity model brings in an additional material length. The analyses for metal reinforced by aligned short fibres are used to obtain an understanding of the interaction of the different length scales...

  20. 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).

  1. Wear behaviour of A356 aluminium alloy reinforced with micron and nano size SiC particles

    CSIR Research Space (South Africa)

    Camagu, ST

    2013-07-01

    Full Text Available A method for producing metal matrix composites MMC was successfully implemented for mixing nano and low micron (“Hybrid”) sized SiC reinforcing particles in an aluminium alloy matrix. Due to the improved specific modulus and strength, MMC...

  2. Au ion irradiation of various silicon carbide fiber-reinforced SiC matrix composites

    Energy Technology Data Exchange (ETDEWEB)

    Chaâbane, Nihed, E-mail: nihed.chaabane@cea.fr [CEA, INSTN/UEPTN, F-91191 Gif-sur-Yvette (France); Flem, Marion Le [CEA, DEN/DMN/SRMA, F-91191 Gif-sur-Yvette (France); Tanguy, Morgane [CEA, INSTN/UEPTN, F-91191 Gif-sur-Yvette (France); Urvoy, Stéphane [CEA, DEN/DMN/SRMA, F-91191 Gif-sur-Yvette (France); Sandt, Christophe; Dumas, Paul [Synchrotron SOLEIL, L’Orme des Merisiers, Saint-Aubin, BP 48, 91192 Gif-sur-Yvette Cedex (France); Serruys, Yves [CEA, DEN/DMN/SRMP, Laboratoire JANNUS, F-91191 Gif-sur-Yvette (France)

    2013-08-15

    Silicon carbide fiber-reinforced SiC matrix composites are promising candidates as fuel cladding for several concepts of Generation IV reactors and as structural materials for fusion reactors. The composites used in this study were composed of a SiC matrix obtained by chemical vapor infiltration associated with various fiber types (Tyranno Type-S, Tyranno SA Grade-3 and Hi-Nicalon Type-S) and with a PyC layer as the interphase. 12 MeV Au ions were used for irradiation up to 0.05 and 1 displacement per atom (dpa) fluences at room temperature and 800 °C. Analysis of both microstructure and composition of composites were performed by scanning electron microscopy (SEM), electron probe microanalysis and Raman spectroscopy. At room temperature and low fluence, Raman spectroscopy results showed that irradiation induces a disordered/distorted state into fibers and matrix. With increasing fluence, a total amorphization of these constituents occurs. The increase in the irradiation temperature leads to a damage recovery and partial recrystallization of samples. Image analysis performed from SEM micrographs highlights no significant change in fiber diameter and shape. However, SEM analysis suggests a longitudinal shrinkage of Tyranno Type-S fibers for the composite irradiated at 1 dpa at room temperature and 800 °C. These results are in complete agreement with conclusions from neutron irradiations suggesting an appropriate relevance of irradiations with 12 MeV Au.

  3. Preparation, in vitro degradability, cytotoxicity, and in vivo biocompatibility of porous hydroxyapatite whisker-reinforced poly(L-lactide) biocomposite scaffolds.

    Science.gov (United States)

    Xie, Lu; Yu, Haiyang; Yang, Weizhong; Zhu, Zhuoli; Yue, Li

    2016-01-01

    Biodegradable and bioactive scaffolds with interconnected macroporous structures, suitable biodegradability, adequate mechanical property, and excellent biocompatibility have drawn increasing attention in bone tissue engineering. Hence, in this work, porous hydroxyapatite whisker-reinforced poly(L-lactide) (HA-w/PLLA) composite scaffolds with different ratios of HA and PLLA were successfully developed through compression molding and particle leaching. The microstructure, in vitro mineralization, cytocompatibility, hemocompatibility, and in vivo biocompatibility of the porous HA-w/PLLA were investigated for the first time. The SEM results revealed that these HA-w/PLLA scaffolds possessed interconnected pore structures. Compared with porous HA powder-reinforced PLLA (HA-p/PLLA) scaffolds, HA-w/PLLA scaffolds exhibited better mechanical property and in vitro bioactivity, as more formation of bone-like apatite layers were induced on these scaffolds after mineralization in SBF. Importantly, in vitro cytotoxicity displayed that porous HA-w/PLLA scaffold with HA/PLLA ratio of 1:1 (HA-w1/PLLA1) produced no deleterious effect on human mesenchymal stem cells (hMSCs), and cells performed elevated cell proliferation, indicating a good cytocompatibility. Simultaneously, well-behaved hemocompatibility and favorable in vivo biocompatibility determined from acute toxicity test and histological evaluation were also found in the porous HA-w1/PLLA1 scaffold. These findings may provide new prospects for utilizing the porous HA whisker-based biodegradable scaffolds in bone repair, replacement, and augmentation applications.

  4. Design, preparation and microwave absorbing properties of resin matrix composites reinforced by SiC fibers with different electrical properties

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Haitao, E-mail: xzddlht@163.com [Science and Technology on Advanced Ceramic Fibers and Composites Laboratory, College of Aerospace Science and Engineering, National University of Defense Technology, Changsha 410073 (China); Science and Technology on Scramjet Laboratory, College of Aerospace Science and Engineering, National University of Defense Technology, Changsha 410073 (China); Cheng, Haifeng; Tian, Hao [Science and Technology on Advanced Ceramic Fibers and Composites Laboratory, College of Aerospace Science and Engineering, National University of Defense Technology, Changsha 410073 (China)

    2014-01-15

    Highlights: • SSMASs have better microwave absorbing properties in smaller thickness. • SSMASs can be realized by SiC fibers with different electrical resistivity. • Resistivity of SiC fibers can be regulated by adjusting surface characteristics. • The bandwidth of SSMASs at reflectivity below −10 dB can reach 11.6 GHz. -- Abstract: One kind of sandwich structure microwave absorbing structures (SSMASs) derived from Salisbury absorbers is reported. The impedance characteristics of SSMASs are analyzed, and the mechanisms of broadening microwave absorbing bandwidth are interpreted by Smith chart. In order to realize SSMASs, high electrical resistivity SiC fibers with Si–C–O surface layers and low electrical resistivity SiC fibers with pyrocarbon surface layers are employed and analyzed by SEM, XPS, AES and HRTEM. The conductive model of SiC fibers with pyrocarbon layers is built and electrical resistivity simulation is done. The SSMASs are fabricated by employing plain woven SiC fiber fabrics with high and low electrical resistivity as reinforcements of dielectric layers and lossy layer, respectively. The microwave absorbing properties of SSMASs are measured and compared with simulated results. The results show that the experimental and simulated results are in good agreement, the SSMASs have better wideband microwave absorbing properties, and the microwave absorbing bandwidth at reflectivity below −10 dB can reach 11.6 GHz.

  5. Tribological Potential of Hybrid Composites Based on Zinc and Aluminium Alloys Reinforced with SiC and Graphite Particles

    Directory of Open Access Journals (Sweden)

    D. Džunić

    2012-12-01

    Full Text Available The paper reviews contemporary research in the area of hybrid composites based on zinc and aluminium alloys reinforced with SiC and graphite particles. Metal matrix composites (MMCs based on ZA matrix are being increasingly applied as light-weight and wear resistant materials. Aluminium matrix composites with multiple reinforcements (hybrid AMCsare finding increased applications because of improved mechanical and tribological properties and hence are better substitutes for single reinforced composites. The results of research show that the hybrid composites possess higher hardness, higher tensile strength, better wear resistance and lower coefficient of friction when compared to pure alloys.

  6. Tribological Wear Behaviour and Hardness Measurement of SiC, Al2O3 Reinforced Al. Matrix Hybrid Composite

    Science.gov (United States)

    Subramanian, Senthil Murugan; Vijayan, Jegan; Muthaiah, Velmurugan

    2017-10-01

    In the present study, Aluminium Matrix Hybrid Composite (AMHC) of 6061-T6 alloy reinforced with silicon carbide (SiC) particulate and further addition of aluminium oxide (Al2O3) particulate was fabricated by stir casting process. The wear resistance and frictional properties of that AMHC were studied by performing dry sliding wear test using a pin on disk wear tester. The experiments were conducted at a constant sliding velocity of 1.57 m/s and sliding distance of 1800 m under loading conditions of 10 and 20 N. Further tests were also carried out by keeping Al2O3 percentage (7%) constant and increasing the SiC percentage (10, 15, and 20%). The results show that the reinforcement of the metal matrix with SiC and Al2O3 reduces the wear rate range and also indicate that the wear of the test specimen increases with the increasing load and sliding distance. The coefficient of friction increases with load and increasing volume content of reinforcement. The worn surfaces were examined by scanning electron microscope to study the wear mechanism. By using wear mechanism analysis, the wear surfaces and wear properties of AMHC were determined.

  7. Method for manufacturing whisker preforms and composites

    Science.gov (United States)

    Lessing, P.A.

    1995-11-07

    A process is disclosed for manufacturing Si{sub 3}N{sub 4}/SiAlON whiskers by mixing silicon carbide powder with aluminum nitride powder, adding impurities such as calcium oxide or potassium chloride to control whisker characteristics, forming the mixture in a boron nitrogen mold of desired shaped and hot isostatically pressing the formed mixture in a nitrogen environment to produce whiskers comprised substantially of SiAlON at the nucleating end of the whisker and Si{sub 3}N{sub 4} at the other end of the whisker. In one embodiment, reinforced composites are formed by impregnating the Si{sub 3}N{sub 4}/SiAlON whisker preform with a matrix material such as resin binders, liquid metals, intermetallics or ceramic materials.

  8. An Experimental Study Of Aluminum Alloy Matrix Composite Reinforced SiC Made By Hot Pressing Method

    Directory of Open Access Journals (Sweden)

    Suśniak M.

    2015-06-01

    Full Text Available The present work investigates the possibility of using powder metallurgy processing for producing a metal matrix composite. Materials were prepared from AlSi5Cu2 chips with reinforcement of 10, 15, 20 wt. % silicon carbide. Aluminum alloy chips were milled with SiC powder in a high-energy ball mill by 40 hours. Mechanical alloying process lead to obtain an uniform distribution of hard SiC particles in the metallic matrix and refine the grain size. The consolidation of composite powders was performed by vacuum hot pressing at 450°C, under pressure of 600 MPa by 10 min. The results shows that the addition of SiC particles has a substantial influence on the microstructure and mechanical properties of composite powder as well as consolidated material. Hot pressing is an effective consolidation method which leads to obtain dense AlSi5Cu2/SiC composite with homogeneous structure and advanced mechanical properties.

  9. Fabrication and characterization of laminated SiC composites reinforced with graphene nanoplatelets

    Energy Technology Data Exchange (ETDEWEB)

    Pereira dos Santos Tonello, Karolina, E-mail: karolina.pereira@polito.it; Padovano, Elisa; Badini, Claudio; Biamino, Sara; Pavese, Matteo; Fino, Paolo

    2016-04-06

    Nanosized allotropes of carbon have been attracting a lot of attention recently, but despite the steady growth of the number of scientific works on materials based on graphene family, there is still much to be explored. These two-dimensional carbon materials, such as graphene nanoplatelets, multilayer graphene or few layer graphene have emerged as a possible second phase for reinforcing ceramics, resulting in remarkable properties of these composites. Typically, graphene ceramic matrix composites are prepared by a colloidal or a powder route followed by pressure assisted sintering. Recently other traditional ceramic processes, such as tape casting, were also successfully studied. The aim of this research is to fabricate α-SiC multi-layer composites containing 2, 4 and 8 vol% of graphene nanoplatelets (GNP) by tape casting and study the effect of these additions on the mechanical behavior of the composites. In order to achieve this purpose, samples were pressureless sintered and tested for density and mechanical properties. The elastic modulus was measured by the impulse excitation of vibration method, the hardness by Vickers indentation and fracture toughness using micro Vickers indentation and by three-point bending applying the pre-cracked beam approach. Results showed that up to 4 vol%, the density and mechanical properties were directly proportional to the amount of GNP added but showed a dramatic decrease for 8 vol% of GNP. Composites with 4 vol% of GNP had a 23% increment elastic modulus, while the fracture toughness had a 34% increment compared to SiC tapes fabricated under the same conditions. Higher amounts of GNP induces porosity in the samples, thus decreasing the mechanical properties. This study, therefore, indicates that 4% is an optimal amount of GNP and suggests that excessive amounts of GNP are rather detrimental to the mechanical properties of silicon carbide ceramic materials prepared by tape casting.

  10. Whiskers and fibers of hydroxyapatite; Whiskers e fibras de hidroxiapatita

    Energy Technology Data Exchange (ETDEWEB)

    Cardoso, G.B.C.; Motisuke, M.; Zavaglia, C.A.C., E-mail: guicardoso@fem.unicamp.b [Universidade Estadual de Campinas (UNICAMP), SP (Brazil). Fac. de Engenharia Mecanica. Dept. de Engenharia de Materiais; Arruda, A.C.F. [Universidade Estadual de Campinas (UNICAMP), SP (Brazil). Fac. de Engenharia Mecanica. Dept. de Engenharia de Petroleo

    2009-07-01

    Hydroxyapatite is a bioactive ceramic, which acts in tissue engineering by attracting bone cells. Occasionally it can be used as a biocompatible reinforcement. The mechanical role of this biomaterial can be defined depending of some characteristics analyzed by scanning electron microscope and X ray power diffraction. It can be classified in whiskers and fibers; each one has their own properties, which were discussed in this work. For its use as reinforcement it is necessary matrix with specific characteristics. (author)

  11. Enhanced Compressive Strength of Nanostructured Aluminum Reinforced with SiC Nanoparticles and Investigation of Strengthening Mechanisms and Fracture Behavior

    Science.gov (United States)

    Akbarpour, M. R.; Torknik, F. S.; Manafi, S. A.

    2017-10-01

    In this study, microstructure and mechanical properties of nanostructured Al and Al reinforced with different volume fractions of SiC nanoparticles fabricated through a powder metallurgy route, including high-energy mechanical milling and hot pressing method, were examined. Nanostructured Al and the Al-8 vol.%SiC nanocomposite showed superior compressive strength of ≈300 and ≈412 MPa, respectively, with reasonable ductility. The high strength of the nanocomposite was attributed to the reduced grain size of the Al matrix and homogeneous dispersion of the nanoparticles in the matrix. The effects of nanoparticles on strengthening of Al and fracture mechanisms are presented and discussed.

  12. Creep and Stress-strain Behavior After Creep from Sic Fiber Reinforced, Melt-infiltrated Sic Matrix Composites

    Science.gov (United States)

    Morscher, Gregory N.; Pujar, Vijay

    2004-01-01

    Silicon carbide fiber (Hi-Nicalon Type S, Nippon Carbon) reinforced silicon carbide matrix composites containing melt-infiltrated Si were subjected to creep at 1315 C for a number of different stress conditions, This study is aimed at understanding the time-dependent creep behavior of CMCs for desired use-conditions, and also more importantly, how the stress-strain response changes as a result of the time-temperature-stress history of the crept material. For the specimens that did not rupture, fast fracture experiments were performed at 1315 C or at room temperature immediately following tensile creep. In many cases, the stress-strain response and the resulting matrix cracking stress of the composite change due to stress-redistribution between composite constituents during tensile creep. The paper will discuss these results and its implications on applications of these materials for turbine engine components.

  13. 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.

  14. 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.

  15. Interfacial characterisation in transparent spinel matrix reinforced by SiC fibre

    Czech Academy of Sciences Publication Activity Database

    Chlup, Zdeněk; Dlouhý, Ivo; Gürbüz, S.; Dericioglu, A. F.; Kozák, Vladislav

    2009-01-01

    Roč. 409, - (2009), s. 252-259 ISSN 1013-9826. [Fractography of Advanced Ceramics III. Stará Lesná, 07.09.20058-10.09.2008] R&D Projects: GA ČR(CZ) GA106/06/0724; GA AV ČR IAA200410502 Institutional research plan: CEZ:AV0Z20410507 Keywords : interface * composite * transparent spinel * SiC fibre * fracture characteristics Subject RIV: JI - Composite Materials

  16. Enhanced performance of nano-sized SiC reinforced Al metal matrix nanocomposites synthesized through microwave sintering and hot extrusion techniques

    Directory of Open Access Journals (Sweden)

    M. Penchal Reddy

    2017-10-01

    Full Text Available In the present study, nano-sized SiC (0, 0.3, 0.5, 1.0 and 1.5 vol% reinforced aluminum (Al metal matrix composites were fabricated by microwave sintering and hot extrusion techniques. The structural (XRD, SEM, mechanical (nanoindentation, compression, tensile and thermal properties (co-efficient of thermal expansion-CTE of the developed Al-SiC nanocomposites were studied. The SEM/EDS mapping images show a homogeneous distribution of SiC nanoparticles into the Al matrix. A significant increase in the strength (compressive and tensile of the Al-SiC nanocomposites with the addition of SiC content is observed. However, it is noticed that the ductility of Al-SiC nanocomposites decreases with increasing volume fraction of SiC. The thermal analysis indicates that CTE of Al-SiC nanocomposites decreases with the progressive addition of hard SiC nanoparticles. Overall, hot extruded Al 1.5 vol% SiC nanocomposites exhibited the best mechanical and thermal performance as compared to the other developed Al-SiC nanocomposites. Keywords: Al-SiC nanocomposites, Microwave sintering, Hot extrusion, Mechanical properties, Thermal expansion

  17. Fabrication of SiC particulate reinforced polyester matrix composite and investigation

    Science.gov (United States)

    Selvam, R.; Ravi, S.; Raja, R.

    2017-05-01

    Polymer composite provokes a new alternative material to engineering and domestic application. Polymeric nano composite have been intensively investigated due to the performance improvement when a small amount of nano sized particulates are added to matrix. The distinguished properties of SiC particulates influence to make a polymeric composite. This composite material has many application such as mechanical, automobile, marine, appliances and packaging. The composite material is fabricated in deferent weight ratio and it is characterized to understand the mechanical behavior, which was studied by various testing method under external load.

  18. Fabrication and Mechanical Behavior of Ex Situ Mg-Based Bulk Metallic Glass Matrix Composite Reinforced with Electroless Cu-Coated SiC Particles

    Directory of Open Access Journals (Sweden)

    Xin Wang

    2017-11-01

    Full Text Available Magnesium-based bulk metallic glass matrix composites (BMGMCs have better plasticity than the corresponding bulk metallic glasses (BMGs; however, their strength and density are often compromised due to the fact that the effective reinforcement phase is mostly plastic heavy metal. For lightweight SiC-particle reinforced BMGMCs, interface wettability and the sharpness of the particles often reduce the strengthening effect. In this work, SiC particles were coated with a thin Cu coating by electroless plating, and added to Mg54Cu26.5Ag8.5Gd11 melt in an amount of 5 wt % to prepare a BMGMC. The microstructure of the interface, mechanical behavior and fracture morphology of the BMGMC were studied by scanning electron microscopy and quasi-static compression testing. The results showed that the Cu coating improved the wettability between SiC and the matrix alloy without obvious interfacial reactions, leading to the dispersion of SiC particles in the matrix. The addition of Cu-coated SiC particles improved the plastic deformation ability of Mg54Cu26.5Ag8.5Gd11 BMG, proving that electroless plating was an effective method for controlling the interface microstructure and mechanical behavior of BMGMCs.

  19. Effect of ageing on the mechanical behaviour of aluminium alloy AA2009 reinforced with SIC particles; Influencia del estado de envejecimiento en el comportamiento mecanico de una aleacion de aluminio AA2009 reforzada con particulas de SiC

    Energy Technology Data Exchange (ETDEWEB)

    Rodrigo, P.; Poza, P.; Utrilla, M. v.; Urena, A.

    2005-07-01

    A study of the mechanical behaviour of an aluminium matrix composite (AA2009) reinforced with 15 volume percent of SiC particles has been carried out. The ageing kinetic for this material has been evaluated at two different ageing temperatures (170 and 190 degree centigree). The hardness peaks for the two different precipitation sequences existing in the matrix alloy have been identified. The mechanical behaviour of the composite was also evaluated for the different thermal conditions (as-received and aged). This research has been completed with the identification of the fracture mechanisms by means of observation with scanning electron microscopy (SEM) both of the fracture surface and transversal sections of them. In addition, transmission electron microscopy (TEM) of the treated composites has been used to determine the influence of the SiC particles on the distribution of strengthening phases precipitated in the matrix. (Author) 14 refs.

  20. Identification of sigma and OMEGA phases in AA2009/SiC composites

    Energy Technology Data Exchange (ETDEWEB)

    Rodrigo, P., E-mail: pilar.rodrigo@urjc.e [Departamento de Ciencia e Ingenieria de Materiales, Escuela Superior de Ciencias Experimentales y Tecnologia, Universidad Rey Juan Carlos, c/Tulipan s/n, 28933 Mostoles, Madrid (Spain); Poza, P.; Utrilla, M.V.; Urena, A. [Departamento de Ciencia e Ingenieria de Materiales, Escuela Superior de Ciencias Experimentales y Tecnologia, Universidad Rey Juan Carlos, c/Tulipan s/n, 28933 Mostoles, Madrid (Spain)

    2009-08-12

    The microstructure evolution during ageing treatment at 170 and 190 deg. C of AA2009/SiC composites, reinforced with 15 vol.% particulates and whiskers, was studied by transmission electron microscopy. Besides theta' and S' phases, the typical hardening precipitates on Al-Cu-Mg alloys, it was found the presence of OMEGA and sigma (Al{sub 5}Cu{sub 6}Mg{sub 2}) phases in the matrix. sigma phase was only found in the matrix of particulate composite, while OMEGA phase appeared in both. This phase has not been previously observed in Al matrix composites based on conventional Al-Cu-Mg alloys.

  1. Early stages of sliding wear behaviour of Al[sub 2]O[sub 3] and SiC reinforced aluminium

    Energy Technology Data Exchange (ETDEWEB)

    Bonollo, F. (Dept. for Mechanics and Management Innovation, Univ. of Padova (Italy)); Ceschini, L. (Dept. for Mechanics and Management Innovation, Univ. of Padova (Italy) Inst. of Metallurgy, Univ. of Bologna (Italy)); Garagnani, G.L. (Dept. for Mechanics and Management Innovation, Univ. of Padova (Italy) Inst. of Metallurgy, Univ. of Bologna (Italy)); Palombarini, G. (Dept. for Mechanics and Management Innovation, Univ. of Padova (Italy) Inst. of Metallurgy, Univ. of Bologna (Italy)); Tangerini, I. (Dept. for Mechanics and Management Innovation, Univ. of Padova (Italy) TEMAV, Venezia (Italy)); Zambon, A. (Dept. for Mechanics and Management Innovation, Univ. of Padova (Italy))

    1993-11-01

    Al matrix composites reinforced by 10 vol.% Al[sub 2]O[sub 3] and SiC particles were subjected to dry sliding tests against steel using a slider-on-cylinder tribometer. Damage mechanisms were 'micro-machining' of the steel carried out by ceramic particles, plastic deformation and oxidation of the metal matrix, as well as abrasion. The results were discussed on the basis of the third-body wear model. (orig.).

  2. In-situ Formation of Reinforcement Phases in Ultra High Temperature Ceramic Composites

    Science.gov (United States)

    Stackpoole, Margaret M (Inventor); Gasch, Matthew J (Inventor); Olson, Michael W (Inventor); Hamby, Ian W. (Inventor); Johnson, Sylvia M (Inventor)

    2013-01-01

    A tough ultra-high temperature ceramic (UHTC) composite comprises grains of UHTC matrix material, such as HfB.sub.2, ZrB.sub.2 or other metal boride, carbide, nitride, etc., surrounded by a uniform distribution of acicular high aspect ratio reinforcement ceramic rods or whiskers, such as of SiC, is formed from uniformly mixing a powder of the UHTC material and a pre-ceramic polymer selected to form the desired reinforcement species, then thermally consolidating the mixture by hot pressing. The acicular reinforcement rods may make up from 5 to 30 vol % of the resulting microstructure.

  3. Fatigue Life and Microstructure after Multiple Remelting of A359 Matrix Composites Reinforced with SiC Particles

    Directory of Open Access Journals (Sweden)

    Klasik A.

    2016-12-01

    Full Text Available The article presents the results of fatigue life tests and microstructure examinations of A359 alloy matrix composites (F3S.10S and F3S.30S containing 10 and 30wt% of SiC particles, subjected to multiple remelting by conventional gravity casting. Mechanical characteristics were determined in a modified low cycle fatigue (MLCF test, enabling rapid estimation of fatigue life and other mechanical parameters in practice of any material. Qualitative and quantitative metallographic examinations were also carried out. The quantitative evaluation of microstructure was performed by computer image analysis. A set of geometrical parameters of the reinforcing particles, pores and eutectic precipitates present in the metal matrix was determined. The relationships between the mechanical parameters, structural characteristics and the number of remelting operations were presented. It was found that up to the fourth remelting, the mechanical characteristics, including fatigue life, are slightly deteriorated but decrease gradually in the subsequent operations of remelting. The observed effect is mainly due to the shrinkage porosity occurring as a result of gravity casting. To eliminate this defect, the use of squeeze casting process was recommended. It has also been shown that multiple remelting can be an easy and economically well-founded alternative to other more expensive recycling methods.

  4. Anodization Mechanism on SiC Nanoparticle Reinforced Al Matrix Composites Produced by Power Metallurgy.

    Science.gov (United States)

    Ferreira, Sonia C; Conde, Ana; Arenas, María A; Rocha, Luis A; Velhinho, Alexandre

    2014-12-19

    Specimens of aluminum-based composites reinforced by silicon carbide nanoparticles (Al/SiCnp) produced by powder metallurgy (PM) were anodized under voltage control in tartaric-sulfuric acid (TSA). In this work, the influence of the amount of SiCnp on the film growth during anodizing was investigated. The current density versus time response and the morphology of the porous alumina film formed at the composite surface are compared to those concerning a commercial aluminum alloy (AA1050) anodized under the same conditions. The processing method of the aluminum alloys influences the efficiency of the anodizing process, leading to a lower thicknesses for the unreinforced Al-PM alloy regarding the AA1050. The current density versus time response is strongly dependent on the amount of SiCnp. The current peaks and the steady-state current density recorded at each voltage step increases with the SiCnp volume fraction due to the oxidation of the SiCnp. The formation mechanism of the anodic film on Al/SiCnp composites is different from that occurring in AA1050, partly due the heterogeneous distribution of the reinforcement particles in the metallic matrix, but also to the entrapment of SiCnp in the anodic film.

  5. Anodization Mechanism on SiC Nanoparticle Reinforced Al Matrix Composites Produced by Power Metallurgy

    Directory of Open Access Journals (Sweden)

    Sonia C. Ferreira

    2014-12-01

    Full Text Available Specimens of aluminum-based composites reinforced by silicon carbide nanoparticles (Al/SiCnp produced by powder metallurgy (PM were anodized under voltage control in tartaric-sulfuric acid (TSA. In this work, the influence of the amount of SiCnp on the film growth during anodizing was investigated. The current density versus time response and the morphology of the porous alumina film formed at the composite surface are compared to those concerning a commercial aluminum alloy (AA1050 anodized under the same conditions. The processing method of the aluminum alloys influences the efficiency of the anodizing process, leading to a lower thicknesses for the unreinforced Al-PM alloy regarding the AA1050. The current density versus time response is strongly dependent on the amount of SiCnp. The current peaks and the steady-state current density recorded at each voltage step increases with the SiCnp volume fraction due to the oxidation of the SiCnp. The formation mechanism of the anodic film on Al/SiCnp composites is different from that occurring in AA1050, partly due the heterogeneous distribution of the reinforcement particles in the metallic matrix, but also to the entrapment of SiCnp in the anodic film.

  6. Modeling tin whisker growth.

    Energy Technology Data Exchange (ETDEWEB)

    Weinberger, Christopher Robert

    2013-08-01

    Tin, lead, and lead-tin solders are the most commonly used solders due to their low melting temperatures. However, due to the toxicity problems, lead must now be removed from solder materials. This has lead to the re-emergence of the issue of tin whisker growth. Tin whiskers are a microelectronic packaging issue because they can lead to shorts if they grow to sufficient length. However, the cause of tin whisker growth is still not well understood and there is lack of robust methods to determine when and if whiskering will be a problem. This report summarizes some of the leading theories on whisker growth and attempts to provide some ideas towards establishing the role microstructure plays in whisker growth.

  7. Evolution of the internal friction in SIC particle reinforced 8090 Al-Li metal matrix composite; Evolucion de la friccion interna del material compuesto de matriz Al-Li 8090 reforzado con particulas de SiC

    Energy Technology Data Exchange (ETDEWEB)

    Gutierrez-Urrutia, I.; Gallego, I.; No, M. L.; San Juan, J. M.

    2001-07-01

    The present study has been undertaken to investigate the mechanisms of thermal stress relief at the range of temperatures below room temperature for the metal matrix composite Al-Li 8090/SiC. For this aim the experimental technique of internal friction has been used which has been showed up very effective. Several thermal cycles from 453 K to 100 K were used in order to measures the internal friction as well as the elastic modules of the material concluding that thermal stresses are relaxed by microplastic deformation around the reinforcements. It has been also related the variation in the elastic modules with the different levels of precipitation. (Author) 18 refs.

  8. Effects of ultrasonic vibration on microstructure and mechanical properties of nano-sized SiC particles reinforced Al-5Cu composites.

    Science.gov (United States)

    Li, Jianyu; Lü, Shulin; Wu, Shusen; Gao, Qi

    2018-04-01

    Ultrasonic vibration (UV) treatment has been successfully applied to improve the particles distribution of nano-sized SiC particles (SiC p ) reinforced Al-5Cu alloy matrix composites which were prepared by combined processes of dry high energy ball milling and squeeze casting. When UV treatment is applied, the distribution of nano-sized SiC p has been greatly improved. After UV for 1 min, large particles aggregates are broken up into small aggregates due to effects of cavitation and the acoustic streaming. After UV for 5 min, all the particles aggregates are dispersed and the particles are uniformly distributed in the composites. Compared with the Al-5Cu matrix alloy, the ultimate tensile strength, yield strength and elongation of the 1 wt% nano-sized SiC p /Al-5Cu composites treated by UV for 5 min are 270 MPa, 173 MPa and 13.3%, which are increased by 7.6%, 6.8% and 29%, respectively. The improvements of mechanical properties after UV are attributed to the uniform distribution of nano particles, grain refinement of aluminum matrix alloy and reduction of porosity in the composites. Copyright © 2017 Elsevier B.V. All rights reserved.

  9. Synthesis and growth mechanisms of ZrC whiskers fabricated by a VLS process

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Dongju [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of). Nuclear Materials Development Division; Song, Sung Ho [Kongju National Univ., Chungnam (Korea, Republic of). Division of Advanced Materials Engineering

    2017-08-15

    The mechanisms of nano-sized ZrC whisker formation by a vapor-liquid-solid process (VLS) are investigated, which produces a very high purity, single crystal whisker. Rectangular ZrC whiskers with a cross-sectional diameter of 100-200 nm and lengths up to tens of microns are formed under the catalytic effect of nickel. The ZrC whiskers are characterized using scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. ZrC whiskers can be used as a potential reinforcing and strengthening phase for ceramic composites.

  10. Abnormal Transient Liquid Phase Bondability of High-Volume Fraction SiC Particle-Reinforced A356 Composite for Cu Interlayer and the Interlayer Improvement Routes

    Science.gov (United States)

    Zhang, Guifeng; Wei, Zhongxin; Chen, Biqiang; Chen, Bo

    2017-12-01

    Features of transient liquid phase (TLP) bondability of high-volume fraction (70 vol.%) SiC particle-reinforced A356 composite for popular Cu interlayer were investigated. Although Cu foil was melted, molten Cu was completely expulsed, indicating that the numerous SiC particles significantly deteriorated wettability not only at particle/braze metal (P/M) interface, but also at the matrix/braze metal (M/M) interface. For the reason of poor wettability at P/M interface, a model showing there is a "window period" for actual wetting reaction (allowing liquid phase to be in contact with surficial SiC particles) much shorter than nominal isothermal solidification time during TLP bonding of the composite containing sintered ceramic preform was proposed. For the poor wettability at M/M interface, both size effect of too small matrix unit (2 20 μm) and restraint effect of the rigid porous ceramic preform on suppressing oxide film crack on the small matrix unit surface were proposed. Thus, chemical route to disrupt oxide film on the small matrix unit surface should be preferred in braze composition design. For example, Al-27Cu-5Si-2Mg-1Ti braze was developed by co-addition of Mg and Ti to improve wettability and to in situ reinforce bond seam, respectively; Ti also could remedy Mg loss for improving wettability.

  11. Residual stress analysis in carbon fiber-reinforced SiC ceramics; Eigenspannungsanalyse in kohlenstoffaserverstaerkten SiC-Keramiken

    Energy Technology Data Exchange (ETDEWEB)

    Broda, M.

    1998-12-31

    Systematic residual stress analyses are reported, carried out in long-fiber reinforced SiC ceramics. The laminated C{sub fiber}/SiC{sub 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 ({mu}m) have been measured using characteristic X-radiation and applying the sin {sup 2}{psi} 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. 250{mu}m) 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) [Deutsch] Im Rahmen der Arbeit werden systematische Eigenspannungsanalysen an langfaserverstaerkten SiC-Keramiken durchgefuehrt. Hierbei werden polymerpyrolytisch abgeleitete, laminierte C{sub Faser}/SiC{sub Matrix} Proben und Bauteile untersucht, welche industriell gefertigt wurden. Fuer die zerstoerungsfreie Eigenspannungsermittlung kommen verschiedene Beugungsverfahren zum Einsatz. Dadurch kann die Eigenspannungsverteilung in diesen Proben vollstaendig erfasst werden, d.h. der Eigenspannungszustand im Oberflaechenbereich ({mu}m) wird mit Hilfe charakteristischer Roentgenstrahlung unter Nutzung der sin{sup 2}{psi}-Methode als auch der Streuvektor-Methode beschrieben. Fuer die Analyse der Eigenspannungen im Volumen (cm) wird die Neutronenbeugung herangezogen. Um den Spannungszustand in den einzelnen Fasermatten (ca. 250 {mu}m) in Abhaengigkeit ihrer Lage

  12. Analysis of stress-strain, fracture and ductility behavior of aluminum matrix composites containing discontinuous silicon carbide reinforcement

    Science.gov (United States)

    Mcdanels, D. L.

    1984-01-01

    Mechanical properties and stress-strain behavior for several types of commercially fabricated aluminum matrix composites, containing up to 40 vol % discontinuous SiC whisker, nodule, or particulate reinforcement were evaluated. It was found that the elastic modulus of the composites was isotropic, to be independent of type of reinforcement, and to be controlled solely by the volume percentage of SiC reinforcement present. The yield/tensile strengths and ductility were controlled primarily by the matrix alloy and temper condition. Ductility decreased with increasing reinforcement content, however, the fracture strains observed were higher than those reported in the literature for this type of composite. This increase in fracture strain is attributed to cleaner matrix powder and increased mechanical working during fabrication. Conventional aluminum and titanium structural alloys were compared and have shown that the properties of these low cost, lightweight composites have good potential for application to aerospace structures.

  13. Strengthening and toughening of poly(L-lactide) composites by surface modified MgO whiskers

    Energy Technology Data Exchange (ETDEWEB)

    Wen, Wei [Biomaterial Research Laboratory, Department of Material Science and Engineering, College of Science and Engineering, Jinan University, Guangzhou 510632 (China); Luo, Binghong, E-mail: tluobh@jnu.edu.cn [Biomaterial Research Laboratory, Department of Material Science and Engineering, College of Science and Engineering, Jinan University, Guangzhou 510632 (China); Engineering Research Center of Artificial Organs and Materials, Ministry of Education, Guangzhou 510632 (China); Qin, Xiaopeng; Li, Cairong [Biomaterial Research Laboratory, Department of Material Science and Engineering, College of Science and Engineering, Jinan University, Guangzhou 510632 (China); Liu, Mingxian; Ding, Shan [Biomaterial Research Laboratory, Department of Material Science and Engineering, College of Science and Engineering, Jinan University, Guangzhou 510632 (China); Engineering Research Center of Artificial Organs and Materials, Ministry of Education, Guangzhou 510632 (China); Zhou, Changren, E-mail: tcrz9@jnu.edu.cn [Biomaterial Research Laboratory, Department of Material Science and Engineering, College of Science and Engineering, Jinan University, Guangzhou 510632 (China); Engineering Research Center of Artificial Organs and Materials, Ministry of Education, Guangzhou 510632 (China)

    2015-03-30

    Highlights: • The grafted PLLA chain on the surface of g-MgO whisker was ruled out by FTIR spectroscopy and TG/DTG analyses. • The excellent dispersion of g-MgO whiskers and the strong interfacial adhesion of g-MgO whiskers/PLLA composite were proved by FSEM. • Comparing to MgO particles and MgO whiskers, fibrous-like g-MgO whiskers are the most effective reinforcing and toughening fillers for PLLA. - Abstract: To improve both the strength and toughness of poly(L-lactide) (PLLA), fibrous-like MgO whiskers with diameters of 0.15–1 μm and lengths of 15–110 μm were prepared, and subsequently surface modified with L-lactide to obtain grafted MgO whiskers (g-MgO whiskers). The structures and properties of MgO whiskers and g-MgO whiskers were studied. Then, a series of MgO whiskers/PLLA and g-MgO whiskers/PLLA composites were prepared by solution casting method, for comparison, MgO particles/PLLA composite was prepared too. The resulting composites were evaluated in terms of hydrophilicity, crystallinity, dispersion of whiskers, interfacial adhesion and mechanical performance by means of polarized optical microscopy (POM), contact angle measurement, field emission scanning electron microscope (FSEM), transmission electron microscopy (TEM) and tensile testing. The results revealed that the crystallization rate and hydrophilicity of PLLA were improved by the introduction of MgO whiskers and g-MgO whiskers. The g-MgO whiskers can disperse more uniformly in and show stronger interfacial adhesion with the matrix than MgO whiskers as a result of the surface modification. Due to the bridge effect of the whiskers and the excellent interfacial adhesion between g-MgO whiskers and PLLA, g-MgO whiskers/PLLA composites exhibited remarkably higher strength, modulus and toughness compared to the pristine PLLA, MgO particles/PLLA and MgO whiskers/PLLA composites.

  14. Synthetische diamant-whisker

    Science.gov (United States)

    Derjaguin, B. V.; Fedoseev, D. V.

    1994-04-01

    РефератUnter speziellen Bedingungen wachsen auf Metallen und auch Nichtmetallen sehr dünne einkristalline Fäden auf, die man als Whisker bezeichnet. Diese Einkristalle zeigen höchst bemerkenswerte Eigenschaften. Uns ist es gelungen, Diamant-Whisker aufwachsen zu lassen unter Bedingungen, bei denen der Diamant eine metastabile Form von Kohlenstoff darstellt (1, 2). Möglicherweise läβt sich daraus ein Verfahren der epitaktischen Diamantsynthese entwickeln.

  15. On the Mechanical Properties of Hybrid Aluminium 7075 Matrix Composite Material Reinforced with SiC and TiC Produced by Powder Metallurgy Method

    Directory of Open Access Journals (Sweden)

    S. Pradeep Devaneyan

    2017-01-01

    Full Text Available Metal matrix composites are widely used in components of various components of industrial equipment because of their superior material properties like high stiffness to weight ratio and high impact strength and fracture toughness while compared to the conventional material. Due to the concepts of high strength to low weight ratio, Al 7075 was extensively applied in aircraft engine and wings. Even if Al 7075 has higher hardness, higher strength, excellent wear resistance, and high-temperature corrosion protection, it is in need of further enhancement of properties for increasing its applicability. This paper presents the mechanical behavior of aluminium 7075 reinforced with Silicon Carbide (SiC and Titanium Carbide (TiC through powder metallurgy route. These specimens were produced by powder metallurgy method. The hybrid composite was made by Al 7075 alloy as the matrix with Silicon Carbide and Titanium Carbide as reinforcement. Silicon Carbide and Titanium Carbide are mixed in different weight ratio based on the design matrix formulated through a statistical tool, namely, Response Surface Methodology (RSM. Enhanced mechanical properties have been obtained with 90% of Al 7075, 4% of TiC, and 8% of SiC composition in the composite. Coefficient of friction appears to be more which has been determined by ring compression test.

  16. Internal friction and microplasticity of carbon-fiber-reinforced SiC ceramics; Tanso sen`i kyoka SiC ceramics no hakai zenku katei ni okeru naibu masatsu

    Energy Technology Data Exchange (ETDEWEB)

    Ogawa, H.; Nishino, Y.; Asano, S. [Nagoya Institute of Technology, Nagoya (Japan)

    1995-08-20

    Mechanical responses of carbon-fiber-reinforced SiC ceramics before fracture were measured in the strain range below 2 {times} 10{sup {minus}3} by two experimental methods: mechanical hysteresis and internal friction. Load-deflection curves were obtained by the three-point bending deformation in loading-unloading cycles. A little permanent strain was found after the first cycle even in the range where fracture never occurred. A closed hysteresis loop was observed after several cycles and stabilized with a symmetrical shape after more than twenty cycles. Such a stabilized hysteresis loop is attributed to the steady-state microplastic deformation and may cause the amplitude-dependent internal friction. Internal friction was measured in the fundamental mode of free-free resonant vibration as a function of strain amplitude. With increasing the amount of prestrain in the bending deformation, internal friction increased and became sensitive to the strain amplitude. The amplitude-dependent internal friction in the composites is considered to originate from fiber pull-out or microcrack propagation. The internal friction data were analyzed on the basis of the microplasticity theory and converted into the plastic strain expressed as a function of stress. Therefore, it becomes possible to non-destructively study the forerunning process of fracture of the fiber-reinforced ceramics. 23 refs., 6 figs.

  17. Preparation and characterization of keratin-K2Ti6O13 whisker ...

    African Journals Online (AJOL)

    USER

    2010-05-10

    May 10, 2010 ... application of the keratin material as a biomaterial. In this article, it was firstly proposed that potassium hexatitanate (K2Ti6O13) whiskers be used to reinforce keratin film. The effects of coupling agent, whisker content, distribution and orientation on properties of composite were investigated by microscope ...

  18. Design Guidelines for In-Plane Mechanical Properties of SiC Fiber-Reinforced Melt-Infiltrated SiC Composites

    Science.gov (United States)

    Morscher, Gregory N.; Pujar, Vijay V.

    2008-01-01

    In-plane tensile stress-strain, tensile creep, and after-creep retained tensile properties of melt-infiltrated SiC-SiC composites reinforced with different fiber types were evaluated with an emphasis on obtaining simple or first-order microstructural design guidelines for these in-plane mechanical properties. Using the mini-matrix approach to model stress-strain behavior and the results of this study, three basic general design criteria for stress and strain limits are formulated, namely a design stress limit, a design total strain limit, and an after-creep design retained strength limit. It is shown that these criteria can be useful for designing components for high temperature applications.

  19. Analysis of stress-strain, fracture, and ductility behavior of aluminum maxtrix composites containing discontinuous silicon carbide reinforcement

    Science.gov (United States)

    Mcdanels, D. L.

    1985-01-01

    Mechanical properties and stress-strain behavior were evaluated for several types of commercially fabricated aluminum matrix composites, containing up to 40 vol pct discontinuous SiC whisker, nodule, or particulate reinforcement. The elastic modulus of the composites was found to be isotropic, to be independent of type of reinforcement, and to be controlled solely by the volume percentage of SiC reinforcement present. The yield/tensile strengths and ductility were controlled primarily by the matrix alloy and temper condition. Type and orientation of reinforcement had some effect on the strengths of composites, but only for those in which the whisker reinforcement was highly oriented. Ductility decreased with increasing reinforcement content; however, the fracture strains observed were higher than those reported in the literature for this type of composite. This increase in fracture strain was probably attributable to cleaner matrix powder, better mixing, and increased mechanical working during fabrication. Comparison of properties with conventional aluminum and titanium structural alloys showed that the properties of the low-cost, lightweight composites demonstrated very good potential for application to aerospace structures.

  20. High-Temperature Active Soldering of SiC Particle-Reinforced Al-MMC Using a Novel ZnAlGaMgTi Filler Metal

    Science.gov (United States)

    Chen, Biqiang; Zhang, Guifeng; Zhang, Linjie; Xu, Tingting

    2017-10-01

    In order to broaden the application of SiC particle-reinforced aluminum matrix composite in electronics packaging, newly developed ZnAlGaMgTi filler with a low melting point of 418-441 °C was utilized as filler metal for active soldering of aluminum matrix composites (70 vol.%, SiCp/Al-MMCs) for the first time. The effect of loading pressure on joint properties of ZnAlGaMgTi active filler was investigated. The experimental results indicated that novel filler could successfully solder Al-MMCs, and the presence of Mg in the filler enhanced the penetration of Zn, while the forming of Zn-rich barrier layer influenced the active element MPD (melting point depressant) diffusion into parent composite, and the bulk-like (Mg-Si)-rich phase and Ti-containing phase were readily observed at the interface and bond seam. With the increase in loading pressure, the runout phenomenon appeared more significant, and the filler foil thickness and the Zn penetration depth varied pronouncedly. Sound joints with maximum shear strength of 29.6 MPa were produced at 480 °C at 1 MPa, and the crack occurred adjacent to the boundary of SiC particle and then propagated along the interface. A novel model describing the significant mutual diffusion of Al and Zn atoms between the parent material and solder was proposed.

  1. Wear Behavior of Aluminum Alloy 6061-Based Composites Reinforced with SiC, Al2O3, and Red Mud: A Comparative Study

    Science.gov (United States)

    Singla, Yogesh Kumar; Chhibber, Rahul; Bansal, Hitesh; Kalra, Anil

    2015-09-01

    Metal-matrix composites are widely used in shipping, aerospace, automotive, and nuclear applications. Research attempts have been made in the past to reduce the cost of processing of composites, decrease the weight of the composites, and increase the desired performance characteristics. In this research article, an attempt has been made in using red mud obtained as an industrial waste during the production of aluminum from bauxite ore. This article discusses the novel findings of the experimental study on the dry sliding wear behavior of aluminum alloy 6061-based composites reinforced individually with red mud, SiC, and Al2O3. The microstructural characterization of the composites provides the further insight into the structure—wear behavior of the processed composites.

  2. Room-Temperature and High-Temperature Tensile Mechanical Properties of TA15 Titanium Alloy and TiB Whisker-Reinforced TA15 Matrix Composites Fabricated by Vacuum Hot-Pressing Sintering.

    Science.gov (United States)

    Feng, Yangju; Zhang, Wencong; Zeng, Li; Cui, Guorong; Chen, Wenzhen

    2017-04-18

    In this paper, the microstructure, the room-temperature and high-temperature tensile mechanical properties of monolithic TA15 alloy and TiB whisker-reinforced TA15 titanium matrix composites (TiBw/TA15) fabricated by vacuum hot-pressing sintering were investigated. The microstructure results showed that there were no obvious differences in the microstructure between monolithic TA15 alloy and TiBw/TA15 composites, except whether or not the grain boundaries contained TiBw. After sintering, the matrix microstructure presented a typical Widmanstätten structure and the size of primary β grain was consistent with the size of spherical TA15 titanium metallic powders. This result demonstrated that TiBw was not the only factor limiting grain coarsening of the primary β grain. Moreover, the grain coarsening of α colonies was obvious, and high-angle grain boundaries (HAGBs) were distributed within the primary β grain. In addition, TiBw played an important role in the microstructure evolution. In the composites, TiBw were randomly distributed in the matrix and surrounded by a large number of low-angle grain boundaries (LAGBs). Globularization of α phase occurred prior, near the TiBw region, because TiBw provided the nucleation site for the equiaxed α phase. The room-temperature and high-temperature tensile results showed that TiBw distributed at the primary β grain boundaries can strengthen the grain boundary, but reduce the connectivity of the matrix. Therefore, compared to the monolithic TA15 alloy fabricated by the same process, the tensile strength of the composites increased, and the tensile elongation decreased. Moreover, with the addition of TiBw, the fracture mechanism was changed to a mixture of brittle fracture and ductile failure (composites) from ductile failure (monolithic TA15 alloy). The fracture surfaces of TiBw/TA15 composites were the grain boundaries of the primary β grain where the majority of TiB whiskers distributed, i.e., the surfaces of the

  3. Graphene encapsulated and SiC reinforced silicon nanowires as an anode material for lithium ion batteries.

    Science.gov (United States)

    Yang, Yang; Ren, Jian-Guo; Wang, Xin; Chui, Ying-San; Wu, Qi-Hui; Chen, Xianfeng; Zhang, Wenjun

    2013-09-21

    Anode materials play a key role in the performance, in particular the capacity and lifetime, of lithium ion batteries (LIBs). Silicon has been demonstrated to be a promising anode material due to its high specific capacity, but pulverization during cycling and formation of an unstable solid-electrolyte interphase limit its cycle life. Herein, we show that anodes consisting of an active silicon nanowire (Si NW), which is surrounded by a uniform graphene shell and comprises silicon carbide nanocrystals, are capable of serving over 500 cycles in half cells at a high lithium storage capacity of 1650 mA h g(-1). In the anodes, the graphene shell provides a highly-conductive path and prevents direct exposure of Si NWs to electrolytes while the SiC nanocrystals may act as a rigid backbone to retain the integrity of the Si NW in its great deformation process caused by repetitive charging-discharging reactions, resulting in a stable cyclability.

  4. Box-and-Whisker Plots.

    Science.gov (United States)

    Larsen, Russell D.

    1985-01-01

    Box-and-whisker plots (which give rapid visualization of batches of data) can be effectively used to present diverse collections of data used in traditional first-year chemistry courses. Construction of box-and-whisker plots and their use with bond energy data and data on heats of formation and solution are discussed. (JN)

  5. Impact of long-term thermal exposure on a SiC fiber-reinforced copper matrix composite

    Science.gov (United States)

    Kimmig, S.; Elgeti, S.; You, Jeong-Ha

    2013-11-01

    Silicon carbide long fiber-reinforced copper matrix composites offer huge potential as a heat sink material of divertor for applications at temperatures above 300 °C thanks to the beneficial combination of strong ceramic fibers and highly conductive copper. For applications at higher operation temperatures, long term thermal stability is an issue, as thermal exposure may cause a detrimental change in microstructure in terms of chemistry and integrity of the constituents leading to overall deterioration of composite strength. The aim of this study is to investigate the impact of long term thermal exposure at an elevated temperature on a Cu/SiCf composite material. To this end, composite samples were fabricated and subjected to a heat treatment at 550 °C for 400 h. Extensive tensile tests were conducted for a wide range of fibers volume fractions to evaluate the strength before and after the heat treatment. Acoustic emission was detected in situ during tensile tests for tracking the failure events. Microscopic analysis was carried out to capture the chemical change and damage. It turned out that the applied heat treatment caused significant reduction of strength. Microanalysis revealed that infiltration and diffusion of copper into the fibers via the cracks of the damaged fibers are the direct cause of the embrittlement.

  6. The advantages of a tapered whisker.

    Directory of Open Access Journals (Sweden)

    Christopher M Williams

    Full Text Available The role of facial vibrissae (whiskers in the behavior of terrestrial mammals is principally as a supplement or substitute for short-distance vision. Each whisker in the array functions as a mechanical transducer, conveying forces applied along the shaft to mechanoreceptors in the follicle at the whisker base. Subsequent processing of mechanoreceptor output in the trigeminal nucleus and somatosensory cortex allows high accuracy discriminations of object distance, direction, and surface texture. The whiskers of terrestrial mammals are tapered and approximately circular in cross section. We characterize the taper of whiskers in nine mammal species, measure the mechanical deflection of isolated felid whiskers, and discuss the mechanics of a single whisker under static and oscillatory deflections. We argue that a tapered whisker provides some advantages for tactile perception (as compared to a hypothetical untapered whisker, and that this may explain why the taper has been preserved during the evolution of terrestrial mammals.

  7. Mitigating tin whisker risks theory and practice

    CERN Document Server

    Handwerker, Carol A; Bath, Jasbir

    2016-01-01

    Discusses the growth mechanisms of tin whiskers and the effective mitigation strategies necessary to reduce whisker growth risks. This book covers key tin whisker topics, ranging from fundamental science to practical mitigation strategies. The text begins with a review of the characteristic properties of local microstructures around whisker and hillock grains to identify why these particular grains and locations become predisposed to forming whiskers and hillocks. The book discusses the basic properties of tin-based alloy finishes and the effects of various alloying elements on whisker formation, with a focus on potential mechanisms for whisker suppression or enhancement for each element. Tin whisker risk mitigation strategies for each tier of the supply chain for high reliability electronic systems are also described.

  8. Material factors influencing metallic whisker growth

    Science.gov (United States)

    Rodekohr, Chad L.

    Whiskering refers to the formation of slender, long, metallic filaments, much thinner than a human hair, that grow on a metallic thin film surface. They are readily observed for pure and alloyed zinc (Zn), silver (Ag), cadmium (Cd), indium (In), and tin (Sn) surfaces. The longest reported whisker length is 4.5 mm long but most high-aspect ratio whiskers range from 1-500 mum. The focus of this research is upon Sn whiskers. Sn whiskers pose serious reliability problems for the electronics industry and are known to be the source of failure in a wide range of electronic devices, such as nuclear power facilities, heart pacemakers, commercial satellites, aviation radar, telecommunication equipment, and desktop computers. The problem with whiskering has been recently exacerbated by the worldwide shift to lead (Pb) free electronics and the continuing reduction in electrical contact pitches. A thorough understanding of the growth mechanism of Sn whiskers is urgently needed. Currently, there is no universally accepted model that explains the broad range of observations on whiskering. The goals of this research are: (1) to develop a more detailed understanding of the physical mechanisms leading to the initiation and growth of Sn whiskers and (2) to outline reasonable mitigation strategies that could be followed to reduce or eliminate the problem of Sn whiskers. The major contributions of this work are: (1) A reliable method for growing Sn whiskers with predictable incubation times has been developed and tested. (2) A surface oxide is not necessary for whisker growth. (3) Intermetallic compounds (IMC) are not necessary for whisker growth. (4) Smoother, not rougher, substrate surfaces promote whisker growth. (5) Whiskers grow under both compressive and tensile thin film stress states. (6) Whisker growth increases with externally applied compression and tension forces. (7) Sn whiskers are composed of pure Sn except for the expected thin, native Sn oxide on their surface. (8) For

  9. Aluminum matrix composite solidification in microgravity: Effect of the reinforcing phase on nucleation

    Science.gov (United States)

    Barbieri, F.; Patuelli, C.; Giunchi, G.; Grenni, A.

    Among all the solidification processings available for metal matrix composite (MMC) fabrication, the gas pressure liquid infiltration method, recently developed, is very simple and fast. The molten aluminum can be infiltrated either in a preform made up of a three-dimensional array of fibers (SiC whiskers), or in a porous ceramic network. The resulting microstructures present rather low dislocation densities and, short solidification times can avoid interface phase formation. A series of samples with different orientations and volume fractions of the reinforcement, i.e. with different porosity, were examined in order to investigate the reinforcing phase and convection effects on the nucleation and growth of the solid nuclei in the constrained environment existing between the preform fibers.

  10. The compression strength investigations of AW-AlCu4Mg2Mn alloy based composites reinforced with SiC particles

    Directory of Open Access Journals (Sweden)

    A. Kurzawa

    2011-04-01

    Full Text Available In this paper strength tests of composite materials based on AW-AlCu4Mg2Mn obtained in uniaxial compression test was studied.Materials used for examination were made from AW-AlCu4Mg2Mn alloy and porous preforms of SiC particles (grain size 6÷10μm bypressure infiltration (squeeze casting. The stress-strain curves of the materials with 10% vol., 20% vol., 30% vol. particles of SiC, as well unreinforcement alloy and microstructure of scrap surface samples in a plane parallel to the compressive force were analyzed. The investigated metal matrix composites are characterized by marked reduced the plastic strain values with increasing particle strengthening while the unreinforcement materials throughout the range of deformation show considerable plasticity. In the case of the material containing 10% vol of SiC the plastic strain is a slight strengthening of the material. With increasing of the particle content the plasticity decreases. Materials with 20%vol and 30%vol of SiC particles were brittle cracked at much higher values of stress σ.

  11. Silicon Whisker and Carbon Nanofiber Composite Anode

    Science.gov (United States)

    Ma, Junqing (Inventor); Newman, Aron (Inventor); Lennhoff, John (Inventor)

    2015-01-01

    A carbon nanofiber can have a surface and include at least one crystalline whisker extending from the surface of the carbon nanofiber. A battery anode composition can be formed from a plurality of carbon nanofibers each including a plurality of crystalline whiskers.

  12. Investigation into nanocellulosics versus acacia reinforced acrylic films

    Science.gov (United States)

    Yunqiao Pu; Jianguo Zhang; Thomas Elder; Yulin Deng; Paul Gatenholm; Arthur J. Ragauskas

    2007-01-01

    Three closely related cellulosic acrylic latex films were prepared employing acacia pulp fibers, cellulose whiskers and nonocellulose balls and their respective strength properties were determined. Cellulose whisker reinforced composites had enhanced strength properties compared to the acacia pulp and nanoball composites. AFM analysis indicated that the cellulose...

  13. Whisker Formation On Galvanic Tin Surface Layer

    Directory of Open Access Journals (Sweden)

    Radanyi A.L.

    2015-06-01

    Full Text Available The present work reports the effect of substrate composition, thickness of the tin electroplate and its morphology on pressure-induced tin whisker formation. Pure tin deposits of different thickness were obtained on a copper and brass substrates using methane sulfonic industrial bath. The deposits were compressed by a steel bearing ball forming imprint on the surface. The microstructure of tin whiskers obtained at the boundary of each imprint, their length and number were studied using both light and scanning electron microscopy. It was shown that the most intensive formation and growth of whiskers was observed in the first two hours. In general, brass substrate was shown to be more prone to whisker formation than copper independently of the tin coating thickness. The results have been compared with industrial bright tin finish on control unit socket leads and proposals have been made as to modification of the production process in order to minimize the risk of whiskering.

  14. The probabilistic distribution of metal whisker lengths

    Energy Technology Data Exchange (ETDEWEB)

    Niraula, D., E-mail: Dipesh.Niraula@rockets.utoledo.edu; Karpov, V. G., E-mail: victor.karpov@utoledo.edu [Department of Physics and Astronomy, University of Toledo, Toledo, Ohio 43606 (United States)

    2015-11-28

    Significant reliability concerns in multiple industries are related to metal whiskers, which are random high aspect ratio filaments growing on metal surfaces and causing shorts in electronic packages. We derive a closed form expression for the probabilistic distribution of metal whisker lengths. Our consideration is based on the electrostatic theory of metal whiskers, according to which whisker growth is interrupted when its tip enters a random local “dead region” of a weak electric field. Here, we use the approximation neglecting the possibility of thermally activated escapes from the “dead regions,” which is later justified. We predict a one-parameter distribution with a peak at a length that depends on the metal surface charge density and surface tension. In the intermediate range, it fits well the log-normal distribution used in the experimental studies, although it decays more rapidly in the range of very long whiskers. In addition, our theory quantitatively explains how the typical whisker concentration is much lower than that of surface grains. Finally, it predicts the stop-and-go phenomenon for some of the whiskers growth.

  15. Texture coding in the rat whisker system: slip-stick versus differential resonance

    National Research Council Canada - National Science Library

    Wolfe, Jason; Hill, Dan N; Pahlavan, Sohrab; Drew, Patrick J; Kleinfeld, David; Feldman, Daniel E

    2008-01-01

    .... In the resonance model, whisker motion across different textures excites mechanical resonance in distinct subsets of whiskers, due to variation across whiskers in resonance frequency, which varies with whisker length...

  16. Experience-based learning on determining the frictional coefficients of thermoset polymers incorporated with silicon carbide whiskers and chopped carbon fibers at different temperatures

    Science.gov (United States)

    Harrison, Edward; Alamir, Mohammed; Alzahrani, Naif; Asmatulu, Ramazan

    2017-04-01

    High temperature applications of materials have been increasing for various industrial applications, such as automobile brakes, clutches and thrust pads. The big portion of these materials are made out of the polymeric materials with various reinforcements. In the present study, high temperature polymeric materials were incorporated with SiC whiskers and chopped carbon fibers at 0, 5, 10 and 20wt.% and molded into desired size and shape prior to the curing process. These inclusions were selected because of their high mechanical strengths and thermal conductivity values to easily dissipate the frictional heat energy and sustain more external loads. The method of testing involves a metal ramp with an adjustable incline to find the coefficients of static and kinetic frictions by recording time and the angle of movement at various temperatures (e.g., -10°C and 50°C). The test results indicated that increasing the inclusions made drastic improvements on the coefficients of static and kinetic frictions. The undergraduate students were involved in the project and observed all the details of the process during the laboratory studies, as well as data collection, analysis and presentation. This study will be useful for the future trainings of the undergraduate engineering students on the composite, automobile and other manufacturing industries.

  17. Contact Whiskers for Millimeter Wave Diodes

    Science.gov (United States)

    Kerr, A. R.; Grange, J. A.; Lichtenberger, J. A.

    1978-01-01

    Several techniques are investigated for making short conical tips on wires (whiskers) used for contacting millimeter-wave Schottky diodes. One procedure, using a phosphoric and chromic acid etching solution (PCE), is found to give good results on 12 microns phosphor-bronze wires. Full cone angles of 60 degrees-80 degrees are consistently obtained, compared with the 15 degrees-20 degrees angles obtained with the widely used sodium hydroxide etch. Methods are also described for cleaning, increasing the tip diameter (i.e. blunting), gold plating, and testing the contact resistance of the whiskers. The effects of the whisker tip shape on the electrical resistance, inductance, and capacitance of the whiskers are studied, and examples given for typical sets of parameters.

  18. Effect of surface treatment of hydroxyapatite whiskers on the mechanical properties of bis-GMA-based composites

    Energy Technology Data Exchange (ETDEWEB)

    Zhang Hongquan; Zhang Ming, E-mail: htmzhang@polyu.edu.h [Department of Health Technology and Informatics, Hong Kong Polytechnic University (Hong Kong)

    2010-10-01

    The mechanical properties of bis-GMA-based composites filled with hydroxyapatite (HA) particles or whiskers are characterized in this paper. The inherent properties of reinforcements, the bonding strength of the filler-matrix interface and their dispersibility in a polymer matrix were intimately associated with the mechanical performance of the composites. Silanization of both particles and whiskers effectively improved the bonding of the filler-matrix interface, their dispersibility in matrix monomers and filler loading. The particle- and whisker-filled composites showed highly significant differences in both flexural strength and fracture toughness. HA whiskers prepared by hydrothermal homogeneous precipitation had superior dispersibility and wettability in the polymer matrix; no aggregation and entanglement were found in both the products before and after silanization and the resin composites. These features conferred the whiskers having good interface bonding with the polymer matrix and superior reinforcing and toughening effects. For the particulate filler, the addition of HA led to a decrease in the flexural strength for both silane-treated and untreated fillers. Cracks propagated easily through the micropores and voids in the HA aggregates, leading to lower flexural strength and low toughness. However, silanization of HA did not show obvious effects on the elastic modulus of the composites.

  19. Mecanismos de corrosión en materiales compuestos de matriz de aluminio con refuerzo de SiC

    Directory of Open Access Journals (Sweden)

    Ureña, A.

    2004-04-01

    Full Text Available Tested composites were constituted by an AA2009 (Al-Cu-Mg aluminium alloy reinforced with 15 % of SiC, studding two different of morphologies: particles and whiskers. Cyclic polarisation measurements were done in a deaerated aqueous solution of NaCl (3,5 weight % on both kind of composites, for comparative purposes. The following properties were determined from these corrosion tests: pitting potential (Epit, corrosion potential (Ecorr and corrosion density (icorr. Epit is similar for both materials. Electrochemical tests were performed to evaluate Ecorr and icorr versus time. The corrosion potential is more noble for the aluminium alloy without reinforcement. Finally, materials were observed by SEM to characterize the corrosion mechanisms.

    Los materiales compuestos estudiados están constituidos por una aleación AA2009 reforzada con un 15% en volumen de SiC en forma de whiskers y de partículas. Mediante técnicas de polarización cíclica se compara el comportamiento de ambos materiales, en estado de recepción y sometidos a tratamientos térmicos, frente a la corrosión por picadura en disolución acuosa desaireada de NaCl al 3,5% en peso; determinándose el potencial de picadura (Epic, el potencial de corrosión (Ecorr y la densidad de corriente (icorr. Ambos materiales presentaron un potencial de picadura muy similar. También se han llevado a cabo medidas electroquímicas para evaluar el Ecorr y la icorr en función de tiempo de exposición. Los valores de Ecorr obtenidos son más nobles en el caso de la aleación sin reforzar que para el material compuesto, lo que indica un mejor comportamiento en este medio. La caracterización de los materiales y de los mecanismos que rigen la corrosión se ha realizado mediante microscopía de barrido (SEM.

  20. Microwave joining of SiC

    Energy Technology Data Exchange (ETDEWEB)

    Silberglitt, R.; Ahmad, I.; Tian, Y.L. [FM Technologies, Inc., Fairfax, VA (United States)] [and others

    1997-04-01

    The purpose of this work is to optimize the properties of SiC-SiC joints made using microwave energy. The current focus is on identification of the most effective joining methods for scale-up to large tube assemblies, including joining using SiC produced in situ from chemical precursors. During FY 1996, a new microwave applicator was designed, fabricated and tested that provides the capability for vacuum baking of the specimens and insulation and for processing under inert environment. This applicator was used to join continuous fiber-reinforced (CFCC) SiC/SiC composites using a polymer precursor to form a SiC interlayer in situ.

  1. Whisker Formation on SAC305 Soldered Assemblies

    Science.gov (United States)

    Meschter, S.; Snugovsky, P.; Bagheri, Z.; Kosiba, E.; Romansky, M.; Kennedy, J.; Snugovsky, L.; Perovic, D.

    2014-11-01

    This article describes the results of a whisker formation study on SAC305 assemblies, evaluating the effects of lead-frame materials and cleanliness in different environments: low-stress simulated power cycling (50-85°C thermal cycling), thermal shock (-55°C to 85°C), and high temperature/high humidity (85°C/85% RH). Cleaned and contaminated small outline transistors, large leaded quad flat packs (QFP), plastic leaded chip carrier packages, and solder balls with and without rare earth elements (REE) were soldered to custom designed test boards with Sn3Ag0.5Cu (SAC305) solder. After assembly, all the boards were cleaned, and half of them were recontaminated (1.56 µg/cm2 Cl-). Whisker length, diameter, and density were measured. Detailed metallurgical analysis on components before assembly and on solder joints before and after testing was performed. It was found that whiskers grow from solder joint fillets, where the thickness is less than 25 µm, unless REE was present. The influence of lead-frame and solder ball material, microstructure, cleanliness, and environment on whisker characteristics is discussed. This article provides detailed metallurgical observations and select whisker length data obtained during this multiyear testing program.

  2. Room temperature properties of electrical contacts to alumina composites containing silicon carbide whiskers

    Science.gov (United States)

    Bertram, Brian D.; Gerhardt, Rosario A.

    2009-04-01

    The electrical properties of contacts to hot-pressed alumina composites having variable volume fractions of SiC whiskers (Vw) were investigated with impedance spectroscopy and current-mode atomic force microscopy at room temperature. Three different contact materials were studied: sputtered Pt, sputtered Ag, and conductive Ag paint. Electrode properties were characterized while fresh due to instability over long times (˜100 h). For percolated samples with Vw≥0.10, the electrical response of the electrodes is manifested in the complex impedance plane by a semicircle whose properties are rooted in Schottky barrier blocking at metal contacts to surface whiskers participating in percolated linkages. This process was modeled with a parallel resistor-capacitor (RcCc) equivalent circuit having a relaxation frequency ωc. The dependences of the specific contact resistance (ρs) and specific capacitance (Cs) on Vw were in agreement with the microlevel interpretation above. The three contact materials exhibited significantly different properties, indicating sensitivities to metal work function and metal-whisker interfacing. Both Rc and ωc have exponential dependences on dc bias (Vdc) which are related through the equivalent circuit model. The strengths of these exponentials and the degree of nonlinearity in I-Vdc curves increase with the fraction of Vdc dropping at the electrodes. The dependence of Cs on Vdc also indicated symmetrical Schottky blocking and was used to estimate charge carrier concentration in the whiskers as 1017-1019 cm-3 and a barrier height of 0.2-1.6 eV for sputtered Ag.

  3. Whisker encoding of mechanical events during active tactile exploration

    Directory of Open Access Journals (Sweden)

    Yves eBoubenec

    2012-11-01

    Full Text Available Rats use their whiskers to extract a wealth of information about their immediate environment, such as the shape, position or texture of an object. The information is conveyed to mechanoreceptors located within the whisker follicle in the form of a sequence of whisker deflections induced by the whisker/object contact interaction. How the whiskers filter and shape the mechanical information and effectively participate in the coding of tactile features remains an open question to date. In the present article, a biomechanical model was developed that provides predictions of the whisker dynamics during active tactile exploration, amenable to quantitative experimental comparison. This model is based on a decomposition of the whisker profile into a slow, quasi-static sequence and rapid resonant small-scale vibrations. It was applied to the typical situation of a rat whisking across an object. Having derived the quasi-static sequence of whisker deformation, the resonant properties of the whisker were analyzed, taking into account the boundary conditions imposed by the whisker/surface contact. We then focused on two elementary mechanical events that are expected to trigger neural responses, namely (i the whisker/object first contact and (ii the whisker detachment from the object. Both events were found to trigger a deflection wave propagating upward to the mystacial pad at constant velocity of 3-5m/s. This yielded a characteristic mechanical signature at the whisker base, in the form of a large peak of negative curvature occurring 4ms after the event was triggered. The dependence in amplitude and lag of this mechanical signal with the main contextual parameters (such as radial or angular distance was investigated. The model was validated experimentally by comparing its predictions to high-speed video recordings of shock-induced whisker deflections performed on anesthetized rats. The consequences of these results on possible tactile encoding schemes are

  4. Functionalization of Calcium Sulfate/Bioglass Scaffolds with Zinc Oxide Whisker.

    Science.gov (United States)

    Shuai, Cijun; Zhou, Jianhua; Gao, Dan; Gao, Chengde; Feng, Pei; Peng, Shuping

    2016-03-18

    There are urgent demands for satisfactory antibacterial activity and mechanical properties of bone scaffolds. In this study, zinc oxide whisker (ZnOw) was introduced into calcium sulfate/bioglass scaffolds. Antimicrobial behavior was analyzed using Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). The results showed that the scaffolds presented a strong antibacterial activity after introducing ZnOw, due to the antibacterial factors released from the degradation of ZnO. Moreover, ZnOw was also found to have a distinct reinforcing effect on mechanical properties. This was ascribed to whisker pull-out, crack bridging, crack deflection, crack branching and other toughening mechanisms. In addition, the cell culture experiments showed that the scaffolds with ZnOw had a good biocompatibility.

  5. Functionalization of Calcium Sulfate/Bioglass Scaffolds with Zinc Oxide Whisker

    Directory of Open Access Journals (Sweden)

    Cijun Shuai

    2016-03-01

    Full Text Available There are urgent demands for satisfactory antibacterial activity and mechanical properties of bone scaffolds. In this study, zinc oxide whisker (ZnOw was introduced into calcium sulfate/bioglass scaffolds. Antimicrobial behavior was analyzed using Escherichia coli (E. coli and Staphylococcus aureus (S. aureus. The results showed that the scaffolds presented a strong antibacterial activity after introducing ZnOw, due to the antibacterial factors released from the degradation of ZnO. Moreover, ZnOw was also found to have a distinct reinforcing effect on mechanical properties. This was ascribed to whisker pull-out, crack bridging, crack deflection, crack branching and other toughening mechanisms. In addition, the cell culture experiments showed that the scaffolds with ZnOw had a good biocompatibility.

  6. In situ growth of SiC nanowires on RS-SiC substrate(s)

    Science.gov (United States)

    Yang, Wen; Araki, Hiroshi; Hu, Quanli; Ishikawa, Nobuhiro; Suzuki, Hiroshi; Noda, Tetsuji

    2004-03-01

    SiC nanowires over 10 μm in length and 20-100 nm in diameter have been synthesized by a novel in situ chemical vapor growth process on RS-SiC plates. The SiC nanowires were identified as single crystal β-SiC with Si-C chemistry. The growth direction of the nanowires is . The growth mechanism is discussed and a kinetic vapor-solid growth mechanism is proposed. The process demonstrates the possibility to fabricate SiC nanowires in ceramic matrix composites, such as continuous SiC fibers reinforced SiC matrix composites, with the SiC nanowires uniformly dispersed in the matrix.

  7. MICROSTRUCTURAL ANALYSIS OF HOT ISOSTATICALLY PRESSED AL-SIC

    OpenAIRE

    Bronsveld, P.M.; Hosson, J.Th. De; Sargent, M.A.; Alsem, W.H.M.

    1991-01-01

    The difference between extruded and hot isostatically pressed (HIP) Al6061 both with a T6 final heat treatment and with a 30 wt.% SiC particulate reinforcement is one of densification. The higher density of the HIP material is not translated into a stronger material. The Mg2Si precipitation is favoured by the presence of the SiC reinforcement in both samples. HIP powder metallurgy material reveals clearly the original powder particle boundaries, in contrast to the more smeared-out stringers i...

  8. Properties of Doped GaSb Whiskers at Low Temperatures

    Science.gov (United States)

    Khytruk, Igor; Druzhinin, Anatoly; Ostrovskii, Igor; Khoverko, Yuriy; Liakh-Kaguy, Natalia; Rogacki, Krzysztof

    2017-02-01

    Temperature dependencies of GaSb whiskers' resistance doped with Te to concentration of 1.7 × 1018 cm-3 were measured in temperature range 1.5-300 K. At 4.2 K temperature, a sharp drop in the whisker resistance was found. The observed effect is likely connected with the contribution of two processes such as the electron localization in the whiskers and transition in superconducting state at temperature below 4.2 K. The whisker magnetoconductance is considered in the framework of weak antilocalization (WAL) model and connected with subsurface layers of the whiskers. The Shubnikov-de Haas (SdH) oscillatory effect is observed in high-quality n-type GaSb whiskers with tellurium doping concentration near the metal-insulator transition (MIT) for both longitudinal and transverse magnetoresistance.

  9. Innovation Incubator: Whisker Labs Technical Evaluation

    Energy Technology Data Exchange (ETDEWEB)

    Sparn, Bethany F. [National Renewable Energy Lab. (NREL), Golden, CO (United States); Frank, Stephen M. [National Renewable Energy Lab. (NREL), Golden, CO (United States); Earle, Lieko [National Renewable Energy Lab. (NREL), Golden, CO (United States); Scheib, Jennifer G. [National Renewable Energy Lab. (NREL), Golden, CO (United States)

    2017-08-01

    The Wells Fargo Innovation Incubator (IN2) is a program to foster and accelerate startup companies with commercial building energy-efficiency and demand management technologies. The program is funded by the Wells Fargo Foundation and co-administered by the National Renewable Energy Laboratory (NREL). Whisker Labs, an Oakland, California-based company, was one of four awardees in the first IN2 cohort and was invited to participate in the program because of its novel electrical power sensing technology for circuit breakers. The stick-on Whisker meters install directly on the front face of the circuit breakers in an electrical panel using adhesive, eliminating the need to open the panel and install current transducers (CTs) on the circuit wiring.

  10. The Effect of Fiber Architecture on Matrix Cracking in Sic/sic Cmc's

    Science.gov (United States)

    Morscher, Gregory N.

    2005-01-01

    Applications incorporating silicon carbide fiber reinforced silicon carbide matrix composites (CMC's) will require a wide range of fiber architectures in order to fabricate complex shape. The stress-strain response of a given SiC/SiC system for different architectures and orientations will be required in order to design and effectively life-model future components. The mechanism for non-linear stress-strain behavior in CMC's is the formation and propagation of bridged-matrix cracks throughout the composite. A considerable amount of understanding has been achieved for the stress-dependent matrix cracking behavior of SiC fiber reinforced SiC matrix systems containing melt-infiltrated Si. This presentation will outline the effect of 2D and 3D architectures and orientation on stress-dependent matrix-cracking and how this information can be used to model material behavior and serve as the starting point foe mechanistic-based life-models.

  11. 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.

  12. Nanoreinforced biocompatible hydrogels from wood hemicelluloses and cellulose whiskers

    Science.gov (United States)

    Muzaffer Ahmet Karaaslan; Mandla A. Tshabalala; Daniel J. Yelle; Gisela Buschle-Diller

    2011-01-01

    Nanoreinforced hydrogels with a unique network structure were prepared from wood cellulose whiskers coated with chemically modified wood hemicelluloses. The hemicelluloses were modified with 2-hydroxyethylmethacrylate prior to adsorption onto the cellulose whiskers in aqueous medium. Synthesis of the hydrogels was accomplished by in situ radical polymerization of the...

  13. MICROSTRUCTURAL ANALYSIS OF HOT ISOSTATICALLY PRESSED AL-SIC

    NARCIS (Netherlands)

    Bronsveld, P.M.; Hosson, J.Th. De; Sargent, M.A.; Alsem, W.H.M.

    1991-01-01

    The difference between extruded and hot isostatically pressed (HIP) Al6061 both with a T6 final heat treatment and with a 30 wt.% SiC particulate reinforcement is one of densification. The higher density of the HIP material is not translated into a stronger material. The Mg2Si precipitation is

  14. Quantifying the Effect of Stress on Sn Whisker Nucleation Kinetics

    Science.gov (United States)

    Chason, Eric; Vasquez, Justin; Pei, Fei; Jain, Nupur; Hitt, Andrew

    2018-01-01

    Although Sn whiskers have been studied extensively, there is still a need to understand the driving forces behind whisker nucleation and growth. Many studies point to the role of stress, but confirming this requires a quantitative comparison between controlled stress and the resulting whisker evolution. Recent experimental studies applied stress to a Sn layer via thermal cycling and simultaneously monitored the evolution of the temperature, stress and number of nuclei. In this work, we analyze these nucleation kinetics in terms of classical nucleation theory to relate the observed behavior to underlying mechanisms including a stress dependent activation energy and a temperature and stress-dependent whisker growth rate. Non-linear least squares fitting of the data taken at different temperatures and strain rates to the model shows that the results can be understood in terms of stress decreasing the barrier for whisker nucleation.

  15. Organization of sensory feature selectivity in the whisker system.

    Science.gov (United States)

    Bale, Michael R; Maravall, Miguel

    2017-09-14

    Our sensory receptors are faced with an onslaught of different environmental inputs. Each sensory event or encounter with an object involves a distinct combination of physical energy sources impinging upon receptors. In the rodent whisker system, each primary afferent neuron located in the trigeminal ganglion innervates and responds to a single whisker and encodes a distinct set of physical stimulus properties - features - corresponding to changes in whisker angle and shape and the consequent forces acting on the whisker follicle. Here we review the nature of the features encoded by successive stages of processing along the whisker pathway. At each stage different neurons respond to distinct features, such that the population as a whole represents diverse properties. Different neuronal types also have distinct feature selectivity. Thus, neurons at the same stage of processing and responding to the same whisker nevertheless play different roles in representing objects contacted by the whisker. This diversity, combined with the precise timing and high reliability of responses, enables populations at each stage to represent a wide range of stimuli. Cortical neurons respond to more complex stimulus properties - such as correlated motion across whiskers - than those at early subcortical stages. Temporal integration along the pathway is comparatively weak: neurons up to barrel cortex (BC) are sensitive mainly to fast (tens of milliseconds) fluctuations in whisker motion. The topographic organization of whisker sensitivity is paralleled by systematic organization of neuronal selectivity to certain other physical features, but selectivity to touch and to dynamic stimulus properties is distributed in "salt-and-pepper" fashion. Copyright © 2017 The Author(s). Published by Elsevier Ltd.. All rights reserved.

  16. Preparation of Aragonite Whiskers by Dolomite

    Directory of Open Access Journals (Sweden)

    Xu W.R

    2017-01-01

    Full Text Available Aragonite CaCO3 with complicated morphologies needle-like structrues have been successfully synthesized through dolomite as raw materials by the decomposition of urea. The phase of the aragonite whiskers were characterized by X-ray diffraction and Fourier transform infrared, the structrue of the samples was characterized by scanning electron microscope and the effects of different ratio of materials were studied. The result show that the concentration of urea was found to have an effect on the morphology of aragonite crystals. All the prepared crystals were almost aragonite and there was no phase under varied experiment conditions.

  17. Fabrication of SiC mat by radiation processing

    Science.gov (United States)

    Kang, Phil-Hyun; Jeun, Joon-Pyo; Seo, Dong-Kwon; Nho, Young-Chang

    2009-07-01

    Silicon carbide (SiC) exhibits many important properties, such as high intrinsic strength, stiffness, and high temperature stability. Therein, it is considered to be one of the most promising candidates for reinforcement of advanced ceramic matrix composites. The use of preceramic polymers presents the possibility of solving the intricacies involved in obtaining a new generation of ceramic materials. In this study, a radiation processing method was used to fabricate a cured polycarbosilane mat as a preceramic polymer. The polycarbosilane mat was cured by electron beam (e-beam) irradiation up to 10 MGy in an inert gas atmosphere. Next, the e-beam-cured PCS mat, as green fiber, was carbonized to produce the SiC mat. The conversion process of the PCS mat into the SiC mat was investigated by SEM, FT-IR, XRD, and TGA. According to FT-IR analysis, the Si-H peak intensity was observed to decrease as the polymer structure changed from polycarbosilane to SiC. The XRD patterns of SiC showed the diffraction peaks at (1 1 1), (2 2 0), and (3 1 1) which indicated the emergence of β-SiC. TGA curve shows that weight percent of residue of electrospun PCS mat, e-beam-cured PCS mat and pyrolyzed SiC mat up to 1000 °C were 72.5%, 88.3%, and 99.2%, respectively.

  18. Anatomical pathways involved in generating and sensing rhythmic whisker movements.

    Science.gov (United States)

    Bosman, Laurens W J; Houweling, Arthur R; Owens, Cullen B; Tanke, Nouk; Shevchouk, Olesya T; Rahmati, Negah; Teunissen, Wouter H T; Ju, Chiheng; Gong, Wei; Koekkoek, Sebastiaan K E; De Zeeuw, Chris I

    2011-01-01

    The rodent whisker system is widely used as a model system for investigating sensorimotor integration, neural mechanisms of complex cognitive tasks, neural development, and robotics. The whisker pathways to the barrel cortex have received considerable attention. However, many subcortical structures are paramount to the whisker system. They contribute to important processes, like filtering out salient features, integration with other senses, and adaptation of the whisker system to the general behavioral state of the animal. We present here an overview of the brain regions and their connections involved in the whisker system. We do not only describe the anatomy and functional roles of the cerebral cortex, but also those of subcortical structures like the striatum, superior colliculus, cerebellum, pontomedullary reticular formation, zona incerta, and anterior pretectal nucleus as well as those of level setting systems like the cholinergic, histaminergic, serotonergic, and noradrenergic pathways. We conclude by discussing how these brain regions may affect each other and how they together may control the precise timing of whisker movements and coordinate whisker perception.

  19. Automated Tracking of Whiskers in Videos of Head Fixed Rodents

    Science.gov (United States)

    Clack, Nathan G.; O'Connor, Daniel H.; Huber, Daniel; Petreanu, Leopoldo; Hires, Andrew; Peron, Simon; Svoboda, Karel; Myers, Eugene W.

    2012-01-01

    We have developed software for fully automated tracking of vibrissae (whiskers) in high-speed videos (>500 Hz) of head-fixed, behaving rodents trimmed to a single row of whiskers. Performance was assessed against a manually curated dataset consisting of 1.32 million video frames comprising 4.5 million whisker traces. The current implementation detects whiskers with a recall of 99.998% and identifies individual whiskers with 99.997% accuracy. The average processing rate for these images was 8 Mpx/s/cpu (2.6 GHz Intel Core2, 2 GB RAM). This translates to 35 processed frames per second for a 640 px×352 px video of 4 whiskers. The speed and accuracy achieved enables quantitative behavioral studies where the analysis of millions of video frames is required. We used the software to analyze the evolving whisking strategies as mice learned a whisker-based detection task over the course of 6 days (8148 trials, 25 million frames) and measure the forces at the sensory follicle that most underlie haptic perception. PMID:22792058

  20. Automated tracking of whiskers in videos of head fixed rodents.

    Science.gov (United States)

    Clack, Nathan G; O'Connor, Daniel H; Huber, Daniel; Petreanu, Leopoldo; Hires, Andrew; Peron, Simon; Svoboda, Karel; Myers, Eugene W

    2012-01-01

    We have developed software for fully automated tracking of vibrissae (whiskers) in high-speed videos (>500 Hz) of head-fixed, behaving rodents trimmed to a single row of whiskers. Performance was assessed against a manually curated dataset consisting of 1.32 million video frames comprising 4.5 million whisker traces. The current implementation detects whiskers with a recall of 99.998% and identifies individual whiskers with 99.997% accuracy. The average processing rate for these images was 8 Mpx/s/cpu (2.6 GHz Intel Core2, 2 GB RAM). This translates to 35 processed frames per second for a 640 px×352 px video of 4 whiskers. The speed and accuracy achieved enables quantitative behavioral studies where the analysis of millions of video frames is required. We used the software to analyze the evolving whisking strategies as mice learned a whisker-based detection task over the course of 6 days (8148 trials, 25 million frames) and measure the forces at the sensory follicle that most underlie haptic perception.

  1. Texture coding in the rat whisker system: slip-stick versus differential resonance.

    Directory of Open Access Journals (Sweden)

    Jason Wolfe

    2008-08-01

    Full Text Available Rats discriminate surface textures using their whiskers (vibrissae, but how whiskers extract texture information, and how this information is encoded by the brain, are not known. In the resonance model, whisker motion across different textures excites mechanical resonance in distinct subsets of whiskers, due to variation across whiskers in resonance frequency, which varies with whisker length. Texture information is therefore encoded by the spatial pattern of activated whiskers. In the competing kinetic signature model, different textures excite resonance equally across whiskers, and instead, texture is encoded by characteristic, nonuniform temporal patterns of whisker motion. We tested these models by measuring whisker motion in awake, behaving rats whisking in air and onto sandpaper surfaces. Resonant motion was prominent during whisking in air, with fundamental frequencies ranging from approximately 35 Hz for the long Delta whisker to approximately 110 Hz for the shorter D3 whisker. Resonant vibrations also occurred while whisking against textures, but the amplitude of resonance within single whiskers was independent of texture, contradicting the resonance model. Rather, whiskers resonated transiently during discrete, high-velocity, and high-acceleration slip-stick events, which occurred prominently during whisking on surfaces. The rate and magnitude of slip-stick events varied systematically with texture. These results suggest that texture is encoded not by differential resonant motion across whiskers, but by the magnitude and temporal pattern of slip-stick motion. These findings predict a temporal code for texture in neural spike trains.

  2. Bio-Inspired PVDF-Based, Mouse Whisker Mimicking, Tactile Sensor

    Directory of Open Access Journals (Sweden)

    Mohsin Islam Tiwana

    2016-10-01

    Full Text Available The design and fabrication of a Polyvinylidene fluoride (PVDF based, mouse (or rodent whisker mimicking, tactile sensor is presented. Unlike previous designs reported in the literature, this sensor mimics the mouse whisker not only mechanically, but it also makes macro movements just like a real mouse whisker in a natural environment. We have developed a mathematical model and performed finite element analysis using COMSOL, in order to optimise the whisker to have the same natural frequency as that of a biological whisker. Similarly, we have developed a control system that enables the whisker mimicking sensor to vibrate at variable frequencies and conducted practical experiments to validate the response of the sensor. The natural frequency of the whisker can be designed anywhere between 35 and 110 Hz, the same as a biological whisker, by choosing different materials and physical dimensions. The control system of this sensor enables the whisker to vibrate between 5 and 236 Hz.

  3. Silicon Whisker and Carbon Nanofiber Composite Anode Project

    Data.gov (United States)

    National Aeronautics and Space Administration — Physical Sciences Inc. (PSI) has successfully developed a silicon whisker and carbon nanofiber composite anode for lithium ion batteries on a Phase I program. PSI...

  4. Whisker Formation Induced by Component and Assembly Ionic Contamination

    Science.gov (United States)

    Snugovsky, Polina; Meschter, Stephan; Bagheri, Zohreh; Kosiba, Eva; Romansky, Marianne; Kennedy, Jeffrey

    2012-02-01

    This paper describes the results of an intensive whisker formation study on Pb-free assemblies with different levels of cleanliness. Thirteen types of as-received surface-mount and pin-through-hole components were cleaned and intentionally contaminated with solutions containing chloride, sulfate, bromide, and nitrate. Then the parts were assembled on double-sided boards that were also cleaned or intentionally contaminated with three fluxes having different halide contents. The assemblies were subjected to high-temperature/high-humidity testing (85°C/85% RH). Periodic examination found that contamination triggered whisker formation on both exposed tin and solder fillets. Whisker occurrence and parameters depending on the type and level of contamination are discussed. Cross-sections were used to assess the metallurgical aspects of whisker formation and the microstructural changes occurring during corrosion.

  5. Silicon Whisker and Carbon Nanofiber Composite Anode Project

    Data.gov (United States)

    National Aeronautics and Space Administration — Physical Sciences Inc. (PSI) proposes to develop a silicon whisker and carbon nanofiber composite anode for lithium ion batteries on a Phase I program. This anode...

  6. Low-temperature strain gauges based on silicon whiskers

    Directory of Open Access Journals (Sweden)

    Druzhinin A. A.

    2008-08-01

    Full Text Available To create low-temperature strain gauges based on p-type silicon whiskers tensoresistive characteristics of these crystals in 4,2—300 K temperature range were studied. On the basis of p-type Si whiskers with different resistivity the strain gauges for different materials operating at cryogenic temperatures with extremely high gauge factor at 4,2 K were developed, as well as strain gauges operating at liquid helium temperatures in high magnetic fields.

  7. Experimentally determined wear behavior of an Al2O3-SiC composite from 25 to 1200 C

    Science.gov (United States)

    Dellacorte, Christopher; Farmer, Serene C.; Book, Patricia O.

    1990-01-01

    The sliding wear behavior of a self-mated alumina-silicon carbide whisker toughened composite was studied using optical, scanning electron (SEM) and transmission electron (TEM) microscopy. Because of its excellent strength and toughness properties this composite material is under consideration for use in heat engine applications for sliding contacts which operate at elevated temperatures. The composite's wear behavior and especially its wear mechanisms are not well understood. Pin-on-disk specimens were slid in air at 2.7 m/s sliding velocity, under a 26.5-N load, at temperatures 25 to 1200 C. Pin wear increased with increasing temperature. Based upon the microscopic analyses, the wear mechanism seems to be loosening of the reinforcing whiskers due to frictional and bulk heating. This leads to whisker pullout and increased wear.

  8. Low dose irradiation performance of SiC interphase SiC/SiC composites

    Science.gov (United States)

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

    1998-03-01

    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 1.1×10 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.

  9. A novel biomimetic whisker technology based on fiber Bragg grating and its application

    Science.gov (United States)

    Zhao, Chenlu; Jiang, Qi; Li, Yibin

    2017-09-01

    The paper describes a novel, biomimetic whisker-based sensing technology following the basic design of the facial whiskers of animals such as rats and mice. The sensor consists of a 3× 2 whisker array on each side of a robot. In experiments with the artificial whiskers, the motor drives rotating whiskers, and the center wavelength of a fiber Bragg grating pasted on the whisker will shift when the whisker touches an obstacle. The distance will be obtained by processing the wavelength shift data with algorithms. Then the shape recognition can be realized by postprocessing the distance data. The experimental results prove that the whisker array is capable of accurately gathering the distance and shape information of an object.

  10. Preparation of Polyaniline-Doped Fullerene Whiskers

    Directory of Open Access Journals (Sweden)

    Bingzhe Wang

    2013-01-01

    Full Text Available Fullerene C60 whiskers (FWs doped with polyaniline emeraldine base (PANI-EB were synthesized by mixing PANI-EB/N-methyl pyrrolidone (NMP colloid and FWs suspension based on the nature of the electron acceptor of C60 and electron donor of PANI-EB. Scanning electron microscopy (SEM, Fourier transform infrared (FT-IR, and ultraviolet-visible (UV-Vis spectra characterized the morphology and molecular structure of the FWs doped with PANI-EB. SEM observation showed that the smooth surface of FWs was changed to worm-like surface morphology after being doped with PANI-EB. The UV-Vis spectra suggested that charge-transfer (CT complex of C60 and PANI-EB was formed as PANI-EBδ+-C60δ-. PANI-EB-doped FWs might be useful as a new type of antibacterial and self-cleaning agent as well as multifunctional material to improve the human health and living environment.

  11. Interlayer tunneling spectroscopy of mixed-phase BSCCO superconducting whiskers

    Science.gov (United States)

    Kizilaslan, O.; Truccato, M.; Simsek, Y.; Aksan, M. A.; Koval, Y.; Müller, P.

    2016-06-01

    In this work, we present a study on the interlayer tunneling spectroscopy (ITS) of mixed-phase BiSrCaCuO (BSCCO) superconducting whiskers. The tunneling experiments were carried out on the artificial cross-whisker (twist angle of 90°) junctions. A multiple superconducting energy gap in the cross-whisker junctions was observed, which is attributed to the presence of different doping levels of two Bi2Sr2CaCu2O8+δ phases (Bi-2212), rather than two different phases, in the BSCCO whiskers, namely Bi2Sr2CaCu2O8+δ and Bi2Sr2Ca2Cu3O8+δ (Bi-2212 and Bi-2223). The temperature dependence of the energy gaps was discussed in the framework of the BCS T-dependence. On the other hand, the carrier concentration of the cross-whisker junction was changed by the carrier injection process. The effects of the carrier injection on the critical current, I c, and the ITS of intrinsic Josephson junctions were investigated in details.

  12. Whisker movements evoked by stimulation of single motor neurons in the facial nucleus of the rat

    NARCIS (Netherlands)

    L.J. Herfst (Lucas); M. Brecht (Michael)

    2008-01-01

    textabstractThe lateral facial nucleus is the sole output structure whose neuronal activity leads to whisker movements. To understand how single facial nucleus neurons contribute to whisker movement we combined single-cell stimulation and high-precision whisker tracking. Half of the 44 stimulated

  13. Modeling the Elastic Modulus of 2D Woven CVI SiC Composites

    Science.gov (United States)

    Morscher, Gregory N.

    2006-01-01

    The use of fiber, interphase, CVI SiC minicomposites as structural elements for 2D-woven SiC fiber reinforced chemically vapor infiltrated (CVI) SiC matrix composites is demonstrated to be a viable approach to model the elastic modulus of these composite systems when tensile loaded in an orthogonal direction. The 0deg (loading direction) and 90deg (perpendicular to loading direction) oriented minicomposites as well as the open porosity and excess SiC associated with CVI SiC composites were all modeled as parallel elements using simple Rule of Mixtures techniques. Excellent agreement for a variety of 2D woven Hi-Nicalon(TradeMark) fiber-reinforced and Sylramic-iBN reinforced CVI SiC matrix composites that differed in numbers of plies, constituent content, thickness, density, and number of woven tows in either direction (i.e, balanced weaves versus unbalanced weaves) was achieved. It was found that elastic modulus was not only dependent on constituent content, but also the degree to which 90deg minicomposites carried load. This depended on the degree of interaction between 90deg and 0deg minicomposites which was quantified to some extent by composite density. The relationships developed here for elastic modulus only necessitated the knowledge of the fractional contents of fiber, interphase and CVI SiC as well as the tow size and shape. It was concluded that such relationships are fairly robust for orthogonally loaded 2D woven CVI SiC composite system and can be implemented by ceramic matrix composite component modelers and designers for modeling the local stiffness in simple or complex parts fabricated with variable constituent contents.

  14. DC Characterisation of C60 Whiskers and Nanowhiskers

    DEFF Research Database (Denmark)

    Larsson, Michael; Kjelstrup-Hansen, Jakob; Lucyszyn, Stepan

    2007-01-01

    on C60 whiskers and nanowhiskers with diameters in the range 650 nm to 1.3 mm are reported for the first time. Samples are attached to pre-patterned planar and raised electrodes using FIB-deposited tungsten. A low resistivity of 3 Wcm is measured in air, on a C60 whisker having a diameter of 650 nm......-invasive electrical connections with samples. Preliminary results of such trials are presented, indicating it to be a feasible alternative to the use of deposited electrodes....

  15. Fabrication of fiber-reinforced composites by chemical vapor infiltration

    Energy Technology Data Exchange (ETDEWEB)

    Besmann, T.M.; McLaughlin, J.C. [Oak Ridge National Lab., TN (United States). Metals and Ceramics Div.; Probst, K.J.; Anderson, T.J. [Univ. of Florida, Gainesville, FL (United States). Dept. of Chemical Engineering; Starr, T.L. [Georgia Inst. of Tech., Atlanta, GA (United States). Dept. of Materials Science and Engineering

    1997-12-01

    Silicon carbide-based heat exchanger tubes are of interest to energy production and conversion systems due to their excellent high temperature properties. Fiber-reinforced SiC is of particular importance for these applications since it is substantially tougher than monolithic SiC, and therefore more damage and thermal shock tolerant. This paper reviews a program to develop a scaled-up system for the chemical vapor infiltration of tubular shapes of fiber-reinforced SiC. The efforts include producing a unique furnace design, extensive process and system modeling, and experimental efforts to demonstrate tube fabrication.

  16. The effect of whisker movement on radial distance estimation: a case study in comparative robotics

    Directory of Open Access Journals (Sweden)

    Mathew H Evans

    2013-01-01

    Full Text Available Whisker movement has been shown to be under active control in certain specialist animals such as rats and mice. Though this whisker movement is well characterised, the role and effect of this movement on subsequent sensing is poorly understood. One method for investigating this phenomena is to generate artificial whisker deflections with robotic hardware under different movement conditions. A limitation of this approach is that assumptions must be made in the design of any artificial whisker actuators, which will impose certain restrictions on the whisker-object interaction. In this paper we present three robotic whisker platforms, each with different mechanical whisker properties and actuation mechanisms. A feature-based classifier is used to simultaneously discriminate radial distance to contact and contact speed for the first time. We show that whisker-object contact speed predictably affects deflection magnitudes, invariant of whisker material or whisker movement trajectory. We propose that rodent whisker control allows the animal to improve sensing accuracy by regulating contact speed induced touch-to-touch variability.

  17. The effect of whisker movement on radial distance estimation: a case study in comparative robotics.

    Science.gov (United States)

    Evans, Mathew H; Fox, Charles W; Lepora, Nathan F; Pearson, Martin J; Sullivan, J Charles; Prescott, Tony J

    2012-01-01

    Whisker movement has been shown to be under active control in certain specialist animals such as rats and mice. Though this whisker movement is well characterized, the role and effect of this movement on subsequent sensing is poorly understood. One method for investigating this phenomena is to generate artificial whisker deflections with robotic hardware under different movement conditions. A limitation of this approach is that assumptions must be made in the design of any artificial whisker actuators, which will impose certain restrictions on the whisker-object interaction. In this paper we present three robotic whisker platforms, each with different mechanical whisker properties and actuation mechanisms. A feature-based classifier is used to simultaneously discriminate radial distance to contact and contact speed for the first time. We show that whisker-object contact speed predictably affects deflection magnitudes, invariant of whisker material or whisker movement trajectory. We propose that rodent whisker control allows the animal to improve sensing accuracy by regulating contact speed induced touch-to-touch variability.

  18. Vortex Shedding in the Wake Induced by a Real Elephant Seal Whisker

    Science.gov (United States)

    Turk, Jodi; Omilion, Alexis; Zhang, Wei; Kim, Jeong-Jae; Kim, Jeong-Ju; Choi, Woo-Rak; Lee, Sang-Joon

    2017-11-01

    Biomimicry has been adopted to create innovative solutions in a vast range of applications. One such application is the design of seal-whisker-inspired flow sensors for autonomous underwater vehicles (AUVs). In dark, cramped, and unstable terrain AUVs are not able to maneuver using visual and sonar-based navigation. Hence, it is critical to use underwater flow sensors to accurately detect minute disturbances in the surroundings. Certain seal whiskers exhibit a unique undulating three-dimensional morphology that can reduce vortex induced vibrations (VIVs) if the major axis of the whisker cross-section is aligned to the inflow. This allows the seal to precisely track prey fish upstream using solely their whiskers. The current study aims to understand the effect of a real seal whisker's morphology on the vortex shedding behavior. Despite extensive studies of wake induced by scaled whisker-like models, the vortex shedding in the wake of a real seal whisker is not well understood. A series of experiments are conducted with a high-speed Particle Imaging Velocimetry (PIV) system in a water channel to examine the vortex shedding downstream from a smooth whisker and an undulating whisker at a Reynolds number of a few hundred. Results of the vortex shedding induced by real seal whiskers can provide insights on developing high-sensitivity underwater flow sensors for AUVs and other whisker-inspired structures.

  19. Facile Synthesis of Electroconductive AZO@TiO2 Whiskers and Their Application in Textiles

    Directory of Open Access Journals (Sweden)

    Hui Ma

    2016-01-01

    Full Text Available The electroconductive AZO@TiO2 whiskers have been successfully prepared via coating Al doped ZnO onto TiO2 whisker. The orthogonal tests were employed to optimize the synthetic conditions. The crystallographic structure and the morphology of the AZO@TiO2 whiskers and the polypropylene nonwoven fabrics modified with AZO@TiO2 whiskers were characterized by X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscope, four-probe meter, and electrometer. The results showed the AZO@TiO2 whiskers exhibited good electroconductive performance. Moreover, the polypropylene nonwoven fabrics modified with AZO@TiO2 whiskers revealed excellent antistatic performance indicating wide application of AZO@TiO2 whiskers in the antistatic textiles.

  20. Effect of SiC particle addition on microstructure of Mg2Si/Al composite

    Directory of Open Access Journals (Sweden)

    Zhao Yuguang

    2014-03-01

    Full Text Available In the present study, by adding SiC particles into Al-Si-Mg melt, Mg2Si and SiC particles hybrid reinforced Al matrix composites were fabricated through the Mg2Si in situ synthesis in melt combined with the SiC ex situ stir casting. The as-cast microstructure containing primary Mg2Si and SiC particles that distribute homogenously in Al matrix was successfully achieved. The effects of SiC particle addition on the microstructure of Mg2Si/Al composites were investigated by using scanning electron microscopy (SEM and XRD. The results show that, with increasing the fraction of the SiC particles from 5wt.% to 10wt.%, the morphologies of the primary Mg2Si particulates in the prepared samples remain polygonal, but the size of the primary phase decreases slightly. However, when the SiC particle addition reaches 15wt.%, the morphologies of the primary Mg2Si particulates change partially from polygonal to quadrangular with a decrease in size from 50 μm to 30 μm. The size of primary Al dendrites decreases with increasing fraction of the SiC particles from 0wt.% to 15wt.%. The morphology of the eutectic Mg2Si phase changes from a fiber-form to a short fiber-form and/or a dot-like shape with increasing fraction of the SiC particles. Furthermore, no significant change in dendrite arm spacing (DAS was observed in the presence of SiC particles.

  1. Understanding and predicting metallic whisker growth and its effects on reliability : LDRD final report.

    Energy Technology Data Exchange (ETDEWEB)

    Michael, Joseph Richard; Grant, Richard P.; Rodriguez, Mark Andrew; Pillars, Jamin; Susan, Donald Francis; McKenzie, Bonnie Beth; Yelton, William Graham

    2012-01-01

    Tin (Sn) whiskers are conductive Sn filaments that grow from Sn-plated surfaces, such as surface finishes on electronic packages. The phenomenon of Sn whiskering has become a concern in recent years due to requirements for lead (Pb)-free soldering and surface finishes in commercial electronics. Pure Sn finishes are more prone to whisker growth than their Sn-Pb counterparts and high profile failures due to whisker formation (causing short circuits) in space applications have been documented. At Sandia, Sn whiskers are of interest due to increased use of Pb-free commercial off-the-shelf (COTS) parts and possible future requirements for Pb-free solders and surface finishes in high-reliability microelectronics. Lead-free solders and surface finishes are currently being used or considered for several Sandia applications. Despite the long history of Sn whisker research and the recently renewed interest in this topic, a comprehensive understanding of whisker growth remains elusive. This report describes recent research on characterization of Sn whiskers with the aim of understanding the underlying whisker growth mechanism(s). The report is divided into four sections and an Appendix. In Section 1, the Sn plating process is summarized. Specifically, the Sn plating parameters that were successful in producing samples with whiskers will be reviewed. In Section 2, the scanning electron microscopy (SEM) of Sn whiskers and time-lapse SEM studies of whisker growth will be discussed. This discussion includes the characterization of straight as well as kinked whiskers. In Section 3, a detailed discussion is given of SEM/EBSD (electron backscatter diffraction) techniques developed to determine the crystallography of Sn whiskers. In Section 4, these SEM/EBSD methods are employed to determine the crystallography of Sn whiskers, with a statistically significant number of whiskers analyzed. This is the largest study of Sn whisker crystallography ever reported. This section includes a

  2. Chemical precursors to zinc sulfide: ZnS whisker synthesis

    Science.gov (United States)

    Guiton, T. A.; Czekaj, C. L.; Rau, M. S.; Geoffroy, G. L.; Pantano, C. G.

    1988-07-01

    Currently, Chemical Vapor Deposition (CVD) derived zinc sulfide is one of the most widely used infrared optical window materials. Unfortunately, for numerous applications it does not possess optimum mechanical properties. To fabricate infrared transmitting ZnS/ZnS composites requires the development of high aspect ratio, micron sized ZnS whiskers. Although larger ZnS single crystals and whiskers have been made by a variety of high temperature routes, alternative routes have been sought for greater ZnS whisker morphology control. Low temperature organometallic routes are attractive for this purpose. The precursor compound used in this study is the known pentameric species (EtZn(SBut))5. One of the most successful routes involves the reaction of (EtZn(SBU sup t))5 with hydrogen sulfide at ambient or sub-ambient temperature to yield a precipitate which is subsequently heated under flowing H2S at 500 C to yield a mixture of sub-micron particles and single-crystal ZnS whiskers. Transmission electron micrographs of the (EtZn(SBU sup t))5 products indicate that the ZnS morphology is critically dependent on the rate of H2S reaction. Corresponding X-ray/electron diffraction, electron microscopy, elemental analysis, NMR and infrared spectroscopies have been conducted. A summary of the chemical methods, product characterization results, and proposed synthesis mechanisms are presented.

  3. Isoniazid loaded gelatin-cellulose whiskers nanoparticles for ...

    Indian Academy of Sciences (India)

    Natural polymers like gelatin have been used as a potential drug carrier for controlled delivery applications due to their various advantages over synthetic polymers. Cellulose Whiskers (CWs) have the capacity to form strong hydrogen bonds which help in controlling the release of drug and also provide goodstrength to the ...

  4. Isoniazid loaded gelatin-cellulose whiskers nanoparticles for ...

    Indian Academy of Sciences (India)

    Abstract. Natural polymers like gelatin have been used as a potential drug carrier for controlled delivery applications due to their various advantages over synthetic polymers. Cellulose Whiskers (CWs) have the capacity to form strong hydrogen bonds which help in controlling the release of drug and also provide good.

  5. Manual Whisker Annotator (MWA: A Modular Open-Source Tool

    Directory of Open Access Journals (Sweden)

    Brett M. Hewitt

    2016-04-01

    Full Text Available Rodents are key to generating translational data for healthcare research. Behavioural analyses, in particular, are integral to the non-invasive monitoring of rodent health and welfare. Finding quantitative behavioural measures mitigates stress, allowing for the animal behave freely while also enabling the same animal to be studied over the time-course of its life. Locomotion and whisking are both such quantitative behavioural measures, and have been found to be significantly impacted in rodent models of neurodegenerative disease. While automatic trackers of whiskers and locomotion exist, a manual tracker is required to validate these approaches, and also to annotate complex videos where these automatic versions fail. Manually annotating whiskers for research purposes is a long and tedious task and current software does little to provide an intuitive and simple interface to carry out this task. This led to the creation of the Manual Whisker Annotator (MWA. MWA is an open source, portable whisker annotation tool developed for the Windows platform. Not only does MWA make the process much quicker, it also provides added statistical tools to analyse the data. MWA was developed in C# and WPF using the .NET framework, and could be used in any situation where annotating or tracking multiple targets is desired.

  6. Box-and-Whisker Plots Applied to Food Chemistry

    Science.gov (United States)

    Ferreira, Joao E. V.; Miranda, Ricardo M.; Figueiredo, Antonio F.; Barbosa, Jardel P.; Brasil, Edykarlos M.

    2016-01-01

    Box-and-whisker plots or simply boxplots are powerful graphical representations that give an overview of a data set. In this work five different examples illustrate the applications of boxplots in food chemistry. The examples involve relative sweetness of sugars and sugar alcohols with respect to sucrose, the potassium content of fruits and…

  7. 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.

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

    Directory of Open Access Journals (Sweden)

    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.

  9. Wear Behaviour of Al-6061/SiC Metal Matrix Composites

    Science.gov (United States)

    Mishra, Ashok Kumar; Srivastava, Rajesh Kumar

    2017-04-01

    Aluminium Al-6061 base composites, reinforced with SiC particles having mesh size of 150 and 600, which is fabricated by stir casting method and their wear resistance and coefficient of friction has been investigated in the present study as a function of applied load and weight fraction of SiC varying from 5, 10, 15, 20, 25, 30, 35 and 40 %. The dry sliding wear properties of composites were investigated by using Pin-on-disk testing machine at sliding velocity of 2 m/s and sliding distance of 2000 m over a various loads of 10, 20 and 30 N. The result shows that the reinforcement of the metal matrix with SiC particulates up to weight percentage of 35 % reduces the wear rate. The result also show that the wear of the test specimens increases with the increasing load and sliding distance. The coefficient of friction slightly decreases with increasing weight percentage of reinforcements. The wear surfaces are examined by optical microscopy which shows that the large grooved regions and cavities with ceramic particles are found on the worn surface of the composite alloy. This indicates an abrasive wear mechanism, which is essentially a result of hard ceramic particles exposed on the worn surfaces. Further, it was found from the experimentation that the wear rate decreases linearly with increasing weight fraction of SiC and average coefficient of friction decreases linearly with increasing applied load, weight fraction of SiC and mesh size of SiC. The best result has been obtained at 35 % weight fraction and 600 mesh size of SiC.

  10. Magnetic susceptibility and magnetoresistance of neutron-irradiated doped SI whiskers

    Energy Technology Data Exchange (ETDEWEB)

    Druzhinin, A.A., E-mail: druzh@polynet.lviv.ua [Lviv Polytechnic National University, S. Bandera Str., 12, Lviv 79013 (Ukraine); International Laboratory of High Magnetic Fields and Low Temperatures, Wroclaw (Poland); Ostrovskii, I.P.; Khoverko, Yu.M. [Lviv Polytechnic National University, S. Bandera Str., 12, Lviv 79013 (Ukraine); International Laboratory of High Magnetic Fields and Low Temperatures, Wroclaw (Poland); Rogacki, K. [International Laboratory of High Magnetic Fields and Low Temperatures, Wroclaw (Poland); Litovchenko, P.G.; Pavlovska, N.T. [Institute of Nuclear Researches, NAS of Ukraine, 47, Prospect Nauky, 03028 Kyiv (Ukraine); Pavlovskyy, Yu.V.; Ugrin, Yu.O. [Ivan Franko Drohobych State Pedagogical University, 24, Franko str., 82100 Drohobych (Ukraine)

    2015-11-01

    The effect of 8.6·10{sup 17} n/cm{sup 2} fast neutron irradiation on the magnetic susceptibility and magnetoresistance of Si whiskers with impurity concentration near metal–insulator transition (MIT) has been studied. Neutron irradiated specimens with boron concentration away of MIT are mainly diamagnetic with a small amount of paramagnetic centers originated from dangling bonds on the whisker surface. It has been established that at temperatures near 4.2 K, a significant contribution to the conductivity is made by light charge carriers of low concentration but with high mobility. The as grown whiskers with impurity concentration correspondent to MIT showed hysteresis loops in magnetization at temperature of liquid helium. Besides hysteresis loops in magnetoresistance was observed for whiskers under compression stress at low temperature up to 7 K. The possible reason of the effect can be magnetic interaction between impurities centers in subsurface region of the whisker with the orbital moment of dangle bounds in the whisker core–shell interstices. - Highlights: • Neutron irradiation influence on magnetic susceptibility of Si whiskers is studied. • Neutron irradiated Si whiskers with boron concentration away of MIT are diamagnetic. • Whiskers in the vicinity to MIT showed hysteresis loops in magnetoresistance. • Whiskers in the vicinity to MIT showed hysteresis loops in magnetic susceptibility.

  11. In situ toughened SiC ceramics with Al-B-C additions and oxide-coated SiC platelet/SiC composites

    Energy Technology Data Exchange (ETDEWEB)

    Cao, J. [Univ. of California, Berkeley, CA (United States). Dept. of Materials Science and Mineral Engineering]|[Lawrence Berkeley National Lab., CA (United States). Materials Sciences Div.

    1996-12-01

    This work aimed at fabrication and characterization of high toughness SiC ceramics through the applications of in situ toughening and SiC platelet reinforcement. The processing-microstructure-property relations of hot pressed SiC with Al, B, and C additions (designated as ABC-SiC) were investigated. Through a liquid phase sintering mechanism, dense SiC was obtained by hot pressing at a temperature as low as 1,700 C with 3 wt% Al, 0.6 wt% B, and 2 wt% C additions. These sintering aids also enhanced the {beta}-to-{alpha} (3C-to-4H) phase transformation, which promoted SiC grains to grow into plate-like shapes. Under optimal processing conditions, the microstructure exhibited high-aspect-ratio plate-shaped grains with a thin (< 1 nm) Al-containing amorphous grain boundary film. The mechanical properties of the toughened SiC and the composites were evaluated in comparison with a commercial Hexoloy SiC under identical test conditions. The C-curve behavior was examined using the strength-indentation load relationship and compared with that directly measured using precracked compact tension specimens. The in situ toughened ABC-SiC exhibited much improved flaw tolerance and a significantly rising R-curve behavior. A steady-state toughness in excess of 9 MPam{sup 1/2} was recorded for the ABC-SiC in comparison to a single valued toughness below 3 MPam{sup 1/2} for the Hexoloy. Toughening in the ABC-SiC was mainly attributed to grain bridging and subsequent pullout of the plate-shaped grains. The high toughness ABC-SiC exhibited a bend strength of 650 MPa with a Weibull modulus of 19; in comparison, the commercial SiC showed a bend strength of 400 MPa with a Weibull modulus of 6. Higher fracture toughness was also achieved by the reinforcement of SiC platelets, encapsulated with alumina, yttria, or silica, in a SiC matrix.

  12. A radial map of multi-whisker correlation selectivity in the rat barrel cortex.

    Science.gov (United States)

    Estebanez, Luc; Bertherat, Julien; Shulz, Daniel E; Bourdieu, Laurent; Léger, Jean-François

    2016-11-21

    In the barrel cortex, several features of single-whisker stimuli are organized in functional maps. The barrel cortex also encodes spatio-temporal correlation patterns of multi-whisker inputs, but so far the cortical mapping of neurons tuned to such input statistics is unknown. Here we report that layer 2/3 of the rat barrel cortex contains an additional functional map based on neuronal tuning to correlated versus uncorrelated multi-whisker stimuli: neuron responses to uncorrelated multi-whisker stimulation are strongest above barrel centres, whereas neuron responses to correlated and anti-correlated multi-whisker stimulation peak above the barrel-septal borders, forming rings of multi-whisker synchrony-preferring cells.

  13. Whisker-Like Formations in Sn-3.0Ag-Pb Alloys

    Directory of Open Access Journals (Sweden)

    Koncz-Horváth D.

    2017-06-01

    Full Text Available In this study, different types of whisker-like formations of Sn-3.0Ag based alloy were presented. In the experimental process the amount of Pb element was changed between 1000 and 2000 ppm, and the furnace atmosphere and cooling rate were also modified. The novelty of this work was that whisker-like formations in macro scale size were experienced after an exothermic reaction. The whiskers of larger sizes than general provided opportunities to investigate the microstructure and the concentration nearby the whiskers. In addition, the whisker-like formations from Sn-Ag based bulk material did not only consist of pure tin but tin and silver phases. The whisker-like growth appeared in several forms including hillock, spire and nodule shaped formations in accordance with parameters. It was observed that the compound phases were clustered in many cases mainly at hillocks.

  14. Mystacial Whisker Layout and Musculature in the Guinea Pig (Cavia porcellus): A Social, Diurnal Mammal.

    Science.gov (United States)

    Grant, Robyn A; Delaunay, Mariane G; Haidarliu, Sebastian

    2017-03-01

    All mammals (apart from apes and humans) have whiskers that make use of a similar muscle arrangement. Whisker specialists, such as rats and mice, tend to be nocturnal and arboreal, relying on their whisker sense of touch to guide exploration around tree canopies at night. As such, nocturnal arboreal rodents have many whiskers that are organised into a grid-like pattern, and moved using a complex array of muscles. Indeed, most arboreal, nocturnal mammals tend to have specialised whiskers that are longer and arranged in a dense, regular grid, compared with terrestrial, diurnal mammals. The guinea pig diverged early from murid rodents (around 75 million years ago), and are ground-dwelling, diurnal animals. It would be predicted that, as a terrestrial mammal, they may have less whiskers and a reduced muscle architecture compared to arboreal, nocturnal rodents. We examined the mystacial whisker layout, musculature and movement capacity of Guinea pig (Cavia porcellus) whiskers and found that they did indeed have a disorganized whisker layout, with a fortification around the eye area. In addition, there was a reduction in musculature, especially in the intrinsic muscles. Despite guinea pigs not cyclically moving their whiskers, the mystacial musculature was still very similar to that of murid rodents. We suggest that the conserved presence of whisker layout and musculature, even in visual mammals such as primates and guinea pigs, may indicate that whiskers still play an important role in these animals, including protecting the eyes and being involved in tactile social behaviors. Anat Rec, 300:527-536, 2017. © 2016 Wiley Periodicals, Inc. © 2016 Wiley Periodicals, Inc.

  15. Surface modification of magnesium hydroxide sulfate hydrate whiskers using a silane coupling agent by dry process

    Energy Technology Data Exchange (ETDEWEB)

    Zhu, Donghai, E-mail: zhudonghai-2001@163.com [Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, Xining, 810008 (China); Key Laboratory of Comprehensive and Highly Efficient Utilization of Salt Lake Resources, Chinese Academy of Sciences, Xining, 810008 (China); Nai, Xueying [Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, Xining, 810008 (China); Key Laboratory of Comprehensive and Highly Efficient Utilization of Salt Lake Resources, Chinese Academy of Sciences, Xining, 810008 (China); Lan, Shengjie; Bian, Shaoju [Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, Xining, 810008 (China); Key Laboratory of Comprehensive and Highly Efficient Utilization of Salt Lake Resources, Chinese Academy of Sciences, Xining, 810008 (China); University of Chinese Academy of Sciences, Beijing, 100049 (China); Liu, Xin [Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, Xining, 810008 (China); Key Laboratory of Comprehensive and Highly Efficient Utilization of Salt Lake Resources, Chinese Academy of Sciences, Xining, 810008 (China); Li, Wu, E-mail: driverlaoli@163.com [Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, Xining, 810008 (China); Key Laboratory of Comprehensive and Highly Efficient Utilization of Salt Lake Resources, Chinese Academy of Sciences, Xining, 810008 (China)

    2016-12-30

    Highlights: • Dry process was adopted to modify the surface of MHSH whiskers using silane. • Si−O−Mg bonds were formed directly by the reaction between Si−OC{sub 2}H{sub 5} and −OH of MHSH. • Dispersibility and compatibility of modified whiskers greatly improved in organic phase. • Thermal stability of whiskers was enhanced after modified. - Abstract: In order to improve the compatibility of magnesium hydroxide sulfate hydrate (MHSH) whiskers with polymers, the surface of MHSH whiskers was modified using vinyltriethoxysilane (VTES) by dry process. The possible mechanism of the surface modification and the interfacial interactions between MHSH whiskers and VTES, as well as the effect of surface modification, were studied. Scanning electronic microscopy (SEM), transmission electron microscopy (TEM) and X-ray powder diffraction (XRD) analyses showed that the agglomerations were effectively separated and a thin layer was formed on the surface of the whiskers after modification. Fourier transform infrared (FT-IR) spectroscopy and X-ray photoelectron spectroscopy (XPS) analyses showed that the VTES molecules were bound to the surface of MHSH whiskers after modification. Chemical bonds (Si−O−Mg) were formed by the reaction between Si−OC{sub 2}H{sub 5} or Si−OH and the hydroxyl group of MHSH whiskers. The effect of surface modification was evaluated by sedimentation tests, contact angle measurements and thermogravimetric analysis (TGA). The results showed that the surface of MHSH whiskers was transformed from hydrophilic to hydrophobic, and the dispersibility and the compatibility of MHSH whiskers were significantly improved in the organic phase. Additionally, the thermal stability of the VTES-modified MHSH whiskers was improved significantly.

  16. An Empirical Model for Estimating the Probability of Electrical Short Circuits from Tin Whiskers. Part 2

    Science.gov (United States)

    Courey, Karim; Wright, Clara; Asfour, Shihab; Onar, Arzu; Bayliss, Jon; Ludwig, Larry

    2009-01-01

    In this experiment, an empirical model to quantify the probability of occurrence of an electrical short circuit from tin whiskers as a function of voltage was developed. This empirical model can be used to improve existing risk simulation models. FIB and TEM images of a tin whisker confirm the rare polycrystalline structure on one of the three whiskers studied. FIB cross-section of the card guides verified that the tin finish was bright tin.

  17. The vortex glass to liquid transition in Bi2212 whisker

    Science.gov (United States)

    Zheng, P.; Zhou, Y. Q.; Chen, Z. J.; Luo, S.; Wang, W. H.; He, Y. S.; Duo, J.

    1999-05-01

    Through scaling the dc I- V isotherms of Bi2212 whisker in magnetic field H‖ c, the vortex glass-liquid transition is found in Bi2212 whisker whereas it does not appear in Bi2212 crystal slab [R. Behr, J. Kotzler, G. Nakielski, M. Baumann, M. Kaufmann, J. Kowalewski, Physica C 235 (1994) 2669]. The critical exponents are ν=0.5, z=4.0. We found that the critical exponents are influenced by the planar defects of the sample. The result was compared to those of single crystals and films [Behr et al., 1994; H. Yamasaki, K. Endo, S. Kosaka, M. Umeda, S. Yoshida, K. Kajimura, Phys. Rev. B 50 (17) (1994) 12959].

  18. Whisker growth on Sn thin film accelerated under gamma-ray induced electric field

    Science.gov (United States)

    Killefer, Morgan; Borra, Vamsi; Al-Bayati, Ahmed; Georgiev, Daniel G.; Karpov, Victor G.; Ishmael Parsai, E.; Shvydka, Diana

    2017-10-01

    We report on the growth of tin metal whiskers significantly accelerated under non-destructive gamma-ray irradiation. Sn thin film, evaporated on glass substrate, was subjected to a total of 60 h of irradiation. The irradiated samples demonstrated enhanced whisker development, in both densities and lengths, resulting in an acceleration factor of  ∼50. We attribute the observed enhancement to gamma-ray induced electrostatic fields, affecting whisker kinetics. These fields are due to the substrate charging under gamma-rays. We propose that gamma-ray irradiation can be a much needed tool for accelerated testing of whisker propensity.

  19. Surface modification of magnesium hydroxide sulfate hydrate whiskers using a silane coupling agent by dry process

    Science.gov (United States)

    Zhu, Donghai; Nai, Xueying; Lan, Shengjie; Bian, Shaoju; Liu, Xin; Li, Wu

    2016-12-01

    In order to improve the compatibility of magnesium hydroxide sulfate hydrate (MHSH) whiskers with polymers, the surface of MHSH whiskers was modified using vinyltriethoxysilane (VTES) by dry process. The possible mechanism of the surface modification and the interfacial interactions between MHSH whiskers and VTES, as well as the effect of surface modification, were studied. Scanning electronic microscopy (SEM), transmission electron microscopy (TEM) and X-ray powder diffraction (XRD) analyses showed that the agglomerations were effectively separated and a thin layer was formed on the surface of the whiskers after modification. Fourier transform infrared (FT-IR) spectroscopy and X-ray photoelectron spectroscopy (XPS) analyses showed that the VTES molecules were bound to the surface of MHSH whiskers after modification. Chemical bonds (Sisbnd Osbnd Mg) were formed by the reaction between Sisbnd OC2H5 or Sisbnd OH and the hydroxyl group of MHSH whiskers. The effect of surface modification was evaluated by sedimentation tests, contact angle measurements and thermogravimetric analysis (TGA). The results showed that the surface of MHSH whiskers was transformed from hydrophilic to hydrophobic, and the dispersibility and the compatibility of MHSH whiskers were significantly improved in the organic phase. Additionally, the thermal stability of the VTES-modified MHSH whiskers was improved significantly.

  20. The application and research status of tin whisker formation in electric usage

    Science.gov (United States)

    Zhao, Heng; Liu, Qing-bin; Lan, Yuan-pei; Wang, Hua; Yao, Da-wei

    2017-05-01

    `Hair Like' crystalline structure grows from most pure tin or zinc finishes. Usually, the diameter of tin whisker is up to 10 mm and the length of tin whisker is typically 1 µm. In detail, the questions for tin whisker formation are classified into 6 categories: 1. Residual stress with in the tin plating; 2. Intermetallic Formation; 3. Externally Applied Compressive Stress; 4. Bending and Stretching; 5. Scratches and Nicks; 6. Coefficient of Thermal Expansion Mismatches. The result shows that, whisker formation could causes electrical short circuit (High current of whisker melting), debris contamination (Sensitive Optical and Micro Electrical Mechanical System) and metal vapor (Vaporize Damage). Thus, it is suggested that environmental tests and standards (Whisker Shape, Temperature, Pressure, Moisture, Thermal Cycling, and Electrical Field) are required for suppressing whisker formation. Nowadays, the new standards committee of Europe Union acts RoHS (Restriction of certain Hazardous Substances) and WEEE (Waste Electrical and Electronic Equipment) to restrict Pb usage. Thus, new compounds adding to alloys to suppress whiskers are required in electronic application area. In summary, the tin whisker formation is largely influenced by compositions and precipitations.

  1. Bioinspired active whisker sensor for robotic vibrissal tactile sensing

    Science.gov (United States)

    Ju, Feng; Ling, Shih-Fu

    2014-12-01

    A whisker transducer (WT) inspired by rat’s vibrissal tactile perception is proposed based on a transduction matrix model characterizing the electro-mechanical transduction process in both forward and backward directions. It is capable of acting as an actuator to sweep the whisker and simultaneously as a sensor to sense the force, motion, and mechanical impedance at whisker tip. Its validity is confirmed by numerical simulation using a finite element model. A prototype is then fabricated and its transduction matrix is determined by parameter identification. The calibrated WT can accurately sense mechanical impedance which is directly related to stiffness, mass and damping. Subsequent vibrissal tactile sensing of sandpaper texture reveals that the real part of mechanical impedance sensed by WT is correlated with sandpaper roughness. Texture discrimination is successfully achieved by inputting the real part to a k-means clustering algorithm. The mechanical impedance sensing ability as well as other features of the WT such as simultaneous-actuation-and-sensing makes it a good solution to robotic tactile sensing.

  2. The Formation of Graphite Whiskers in the Primitive Solar Nebula

    Science.gov (United States)

    Nuth, Joseph A., III; Kimura, Yuki; Lucas, Christopher; Ferguson, Frank; Johnson, Natasha M.

    2010-02-01

    It has been suggested that carbonaceous grains are efficiently destroyed in the interstellar medium and must either reform in situ at very low pressures and temperatures or in an alternative environment more conducive to grain growth. Graphite whiskers have been discovered associated with high-temperature phases in meteorites such as calcium aluminum inclusions and chondrules, and it has been suggested that the expulsion of such material from protostellar nebulae could significantly affect the optical properties of the average interstellar grain population. We have experimentally studied the potential for Fischer-Tropsch and Haber-Bosch type reactions to produce organic materials in protostellar systems from the abundant H2, CO, and N2 reacting on the surfaces of available silicate grains. When graphite grains are repeatedly exposed to H2, CO, and N2 at 875 K abundant graphite whiskers are observed to form on or from the surfaces of the graphite grains. In a dense, turbulent nebula, such extended whiskers are very likely to be broken off, and fragments could be ejected either in polar jets or by photon pressure after transport to the outer reaches of the nebula.

  3. The Formation of Graphite Whiskers in the Primitive Solar Nebula

    Science.gov (United States)

    Nuth, Joseph A., III; Kimura, Yuki; Lucas, Christopher; Ferguson, Frank; Johnson, Natasha M.

    2010-01-01

    It has been suggested that carbonaceous grains are efficiently destroyed in the interstellar medium and must either reform in situ at very low pressures and temperatures or in an alternative environment more conducive to grain growth. Graphite whiskers have been discovered associated with high-temperature phases in meteorites such as calcium aluminum inclusions and chondrules, and it has been suggested that the expulsion of such material from proto stellar nebulae could significantly affect the optical properties of the average interstellar grain population. We have experimentally studied the potential for Fischer-Tropsch and Haber-Bosch type reactions to produce organic materials in protostellar systems from the abundant H2, CO, and N2 reacting on the surfaces of available silicate grains. When graphite grains are repeatedly exposed to H2, CO, and N2 at 875 K abundant graphite whiskers are observed to form on or from the surfaces of the graphite grains. In a dense, turbulent nebula, such extended whiskers are very likely to be broken off, and fragments could be ejected either in polar jets or by photon pressure after transport to the outer reaches of the nebula.

  4. Preparation technique of SiCp reinforced Al matrix composite

    Directory of Open Access Journals (Sweden)

    HAO Bin

    2006-05-01

    Full Text Available A new preparation technique—"block dispersal and cast" method is introduced, and three kinds of powder mixing methods, vertical, horizontal and inclining styles, are compared. The results demonstrate that the inclining style is the best way to mix powders. The Al and nano SiC powders are pressed into blocks, dipped into molten Al, stirred into mold so that SiC/Al matrix composites can be obtained at last. The microstructure of SiC particle reinforced Al matrix composite prepared by "block dispersal and cast" method have been studied using scanning electron microscopy (SEM. Phase analysis has also been conducted by means of X-ray diffraction (XRD. The results show that nano SiC particles can be dispersed uniformly in Al matrix. Thus, it is feasible to prepare SiC particle reinforced Al matrix composites by this method.

  5. Modeling the emergence of whisker direction maps in rat barrel cortex.

    Directory of Open Access Journals (Sweden)

    Stuart P Wilson

    Full Text Available Based on measuring responses to rat whiskers as they are mechanically stimulated, one recent study suggests that barrel-related areas in layer 2/3 rat primary somatosensory cortex (S1 contain a pinwheel map of whisker motion directions. Because this map is reminiscent of topographic organization for visual direction in primary visual cortex (V1 of higher mammals, we asked whether the S1 pinwheels could be explained by an input-driven developmental process as is often suggested for V1. We developed a computational model to capture how whisker stimuli are conveyed to supragranular S1, and simulate lateral cortical interactions using an established self-organizing algorithm. Inputs to the model each represent the deflection of a subset of 25 whiskers as they are contacted by a moving stimulus object. The subset of deflected whiskers corresponds with the shape of the stimulus, and the deflection direction corresponds with the movement direction of the stimulus. If these two features of the inputs are correlated during the training of the model, a somatotopically aligned map of direction emerges for each whisker in S1. Predictions of the model that are immediately testable include (1 that somatotopic pinwheel maps of whisker direction exist in adult layer 2/3 barrel cortex for every large whisker on the rat's face, even peripheral whiskers; and (2 in the adult, neurons with similar directional tuning are interconnected by a network of horizontal connections, spanning distances of many whisker representations. We also propose specific experiments for testing the predictions of the model by manipulating patterns of whisker inputs experienced during early development. The results suggest that similar intracortical mechanisms guide the development of primate V1 and rat S1.

  6. Mechanical properties study of particles reinforced aluminum matrix composites by micro-indentation experiments

    National Research Council Canada - National Science Library

    Yuan Zhanwei Li Fuguo Zhang Peng Chen Bo Xue Fengmei

    2014-01-01

    By using instrumental micro-indentation technique, the microhardness and Young's modulus of SiC particles reinforced aluminum matrix composites were investigated with micro- compression-tester (MCT...

  7. Significantly Enhanced Dielectric Performances and High Thermal Conductivity in Poly(vinylidene fluoride)-Based Composites Enabled by SiC@SiO2 Core-Shell Whiskers Alignment.

    Science.gov (United States)

    He, Dalong; Wang, Yao; Song, Silong; Liu, Song; Deng, Yuan

    2017-12-27

    Design of composites with ordered fillers arrangement results in anisotropic performances with greatly enhanced properties along a specific direction, which is a powerful tool to optimize physical properties of composites. Well-aligned core-shell SiC@SiO2 whiskers in poly(vinylidene fluoride) (PVDF) matrix has been achieved via a modified spinning approach. Because of the high aspect ratio of SiC whiskers, strong anisotropy and significant enhancement in dielectric constant were observed with permittivity 854 along the parallel direction versus 71 along the perpendicular direction at 20 vol % SiC@SiO2 loading, while little increase in dielectric loss was found due to the highly insulating SiO2 shell. The anisotropic dielectric behavior of the composite is perfectly understood macroscopically to have originated from anisotropic intensity of interfacial polarization based on an equivalent circuit model of two parallel RC circuits connected in series. Furthermore, finite element simulations on the three-dimensional distribution of local electric field, polarization, and leakage current density in oriented SiC@SiO2/PVDF composites under different applied electrical field directions unambiguously revealed that aligned core-shell SiC@SiO2 whiskers with a high aspect ratio significantly improved dielectric performances. Importantly, the thermal conductivity of the composite was synchronously enhanced over 7 times as compared to that of PVDF matrix along the parallel direction at 20 vol % SiC@SiO2 whiskers loading. This study highlights an effective strategy to achieve excellent comprehensive properties for high-k dielectrics.

  8. Contributions of Stress and Oxidation on the Formation of Whiskers in Pb-free Solders

    Science.gov (United States)

    2016-01-29

    environmental legislation continues to increase the life-cycle cost of lead in electronics, the instances of whisker driven failures in these devices...Department of Defense Strategic Environmental Research and Development Program (SERDP). The publication of this report does not indicate... environmental factors influencing formation of tin whiskers on electrodeposited lead free, tin coatings over copper (or copper containing) substrates is the

  9. Eliminating Whisker Growth by Indium Addition in Electroplated Sn on Copper Substrate

    Science.gov (United States)

    Das Mahapatra, S.; Majumdar, B. S.; Dutta, I.; Bhassyvasantha, S.

    2017-07-01

    Whisker growth from Sn coatings is a reliability concern in electronic packages, until recently mitigated by Pb addition. Recently, it was demonstrated that doping with In dramatically reduces whisker growth in 1 μm thick Sn. Here, we present the results of In-doping on whisker growth from 3 μm and 6 μm thick Sn-films and explore the reasons behind this mitigation, and compare the results with a baseline sample of pure Sn and a control sample of tri-layer Sn-In-Sn, all subjected to identical thermal treatments. It is shown that In addition completely stops whisker growth from electroplated Sn. The impact of In addition on the film microstructure and the role of the surface oxide coating are investigated. Previous work had shown that while In addition reduces grain boundary diffusivity, it does not fully account for the observed dramatic reduction of whisker growth. In this work, it is shown by Auger electron spectroscopy and x-ray photoelectron spectroscopy that In is incorporated in the surface-oxide. Since whisker-growth is contingent on the presence of a tenacious surface-oxide, this suggests that the alteration of the oxide properties may be responsible for the observed reduction in whisker growth. Finite element modeling is utilized to demonstrate that a reduction of the elastic modulus of the surface oxide would reduce the driving force of Sn whisker growth, thus proffering a rationale for the effect of In incorporation.

  10. Mechanical Behaviour of Alumina Silicon Carbide Reinforced Particulate Reinforced Metal Matrix Composite

    Science.gov (United States)

    Raghu Ram, K. S.; Sweanney Bandi, Sharon Rose; Sivarama Krishna, Ch.

    2017-08-01

    The present study was aimed at evaluating the effect of hardness and impact strength of Aluminum Al2O3SiC particulate reinforced Composites. These AMCs with multiple reinforcement (hybrid MMCs) are finding increased applications in aerospace, automobile, space, underwater and transportation applications. An effort is made to enhance the Hardness, flexural strength and Impact properties of AMCs by reinforcing Aluminum matrix with Varying Proportion of small particles of Al2O3SiC by stir casting method. Aluminum alloy matrix varying proportions of Al2O3SiC particulates were fabricated. The microstructure, hardness and impact strength properties of the fabricated AMCs were analyzed. The optical microstructure study revealed the homogeneous dispersion of Al2O3SiC particles in the matrix. Based on the results obtained from the Hardness and Impact of the metal matrix composites it is observed that, the hardness and impact strength increases with increase in the amount of reinforcement content.

  11. Contributions of stress and oxidation on the formation of whiskers in Pb-free solders

    Energy Technology Data Exchange (ETDEWEB)

    Duncan, A. J. [Savannah River Site (SRS), Aiken, SC (United States). Savannah River National Lab. (SRNL); Hoffman, E. N. [Savannah River Site (SRS), Aiken, SC (United States). Savannah River National Lab. (SRNL)

    2016-01-01

    Understanding the environmental factors influencing formation of tin whiskers on electrodeposited lead free, tin coatings over copper (or copper containing) substrates is the topic of this study . An interim report* summarized initial observations as to the role of stress and oxide formation on whisker growth. From the initial results, two main areas were chosen to be the focus of additional research: the demonstration of effects of elastic stress state in the nucleation of whiskers and the confirmation of the effect of oxygen content in the formation of whiskers. Different levels of elastic stress were induced with the incorporation of a custom designed fixture that loaded the sample in a four-point bending configuration and were maintained in an environmental chamber under conditions deemed favorable for whisker growth. The effects of oxygen content were studied by aging substrates in gas vials of varying absolute pressure and different oxygen partial pressure.

  12. Rat whisker motor cortex is subdivided into sensory-input and motor-output areas

    Directory of Open Access Journals (Sweden)

    Jared B Smith

    2013-01-01

    Full Text Available Rodent whisking is an exploratory behavior that can be modified by sensory feedback. Consistent with this, many whisker-sensitive cortical regions project to agranular motor (MI cortex, but the relative topography of these afferent projections has not been established. Intracranial microstimulation (ICMS evokes whisker movements that are used to map the functional organization of MI, but no study has compared the whisker-related inputs to MI with the ICMS sites that evoke whisker movements. To elucidate this relationship, anterograde tracers were placed in posterior parietal cortex (PPC and in the primary (SI and secondary (SII somatosensory cortical areas so that their labeled projections to MI could be analyzed with respect to ICMS sites that evoke whisker movements. Projections from SI and SII terminate in a narrow zone that marks the transition between the medial (AGm and lateral agranular (AGl cortical areas, but PPC projects more medially and terminates in AGm proper. Paired recordings of MI neurons indicate that the region between AGm and AGl is highly responsive to whisker deflections, but neurons in AGm display negligible responses to whisker stimulation. By contrast, AGm microstimulation is more effective in evoking whisker movements than microstimulation of the transitional region between AGm and AGl. The AGm region was also found to contain a larger concentration of corticotectal neurons, which could convey whisker-related information to the facial nucleus. These results indicate that rat whisker motor cortex is comprised of at least two functionally distinct subregions: a sensory processing zone in the transitional region between AGm and AGl, and a motor output region located more medially in AGm proper.

  13. Polycrystalline SiC as source material for the growth of fluorescent SiC layers

    DEFF Research Database (Denmark)

    Kaiser, M.; Hupfer, T.; Jokubavicus, V.

    2013-01-01

    Polycrystalline doped SiC act as source for fluorescent SiC. We have studied the growth of individual grains with different polytypes in the source material. We show an evolution and orientation of grains of different polytypes in polycrystalline SiC ingots grown by the Physical Vapor Transport m...

  14. The effects of temperature and humidity on the growth of tin whisker and hillock from Sn5Nd alloy

    Energy Technology Data Exchange (ETDEWEB)

    Li, Cai-Fu [Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016 (China); Liu, Zhi-Quan, E-mail: zqliu@imr.ac.cn [Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016 (China); Shang, Jian-Ku [Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016 (China)

    2013-02-15

    Highlights: Black-Right-Pointing-Pointer Tin whiskers and hillocks grow from Sn5Nd alloy due to oxidation. Black-Right-Pointing-Pointer Temperature and humidity can affect the oxidation and the growth diversities. Black-Right-Pointing-Pointer Growth models of whiskers and hillocks were proposed upon microstructural study. Black-Right-Pointing-Pointer The proposed models can explain the characteristics of whiskers and hillocks. - Abstract: The effects of exposure time, temperature and humidity on the growth of tin whisker and hillock from Sn5Nd alloy were investigated via scanning electron microscopy. It was found that tin whiskers grew from NdSn{sub 3} compound, while hillocks grew from the tin matrix around the NdSn{sub 3} compound, which was induced by the oxidation of NdSn{sub 3} compound by oxygen and water vapor in the ambient. More tin whiskers and/or hillocks were extruded from the substrate with longer exposure time, higher temperature and higher humidity. This resulted in the formation of various morphologies of tin extrusions at different storage conditions, including thread-like, spiral, flute-like, claw-like, sprout-like, chrysanthemum-like and rod-like whiskers, as well as hillocks. Tin whisker was extruded from the crack of the surface Nd(OH){sub 3} layer which serves as the mold of tin whisker growth. And the proposed growth models of tin whisker and hillock on Sn-Nd alloy can explain the diversity of the whisker morphology.

  15. Influence of Ni-P Coated SiC and Laser Scan Speed on the Microstructure and Mechanical Properties of IN625 Metal Matrix Composites

    Science.gov (United States)

    Sateesh, N. H.; Kumar, G. C. Mohan; Krishna, Prasad

    2015-12-01

    Nickel based Inconel-625 (IN625) metal matrix composites (MMCs) were prepared using pre-heated nickel phosphide (Ni-P) coated silicon carbide (SiC) reinforcement particles by Direct Metal Laser Sintering (DMLS) additive manufacturing process under inert nitrogen atmosphere to obtain interface influences on MMCs. The distribution of SiC particles and microstructures were characterized using optical and scanning electron micrographs, and the mechanical behaviours were thoroughly examined. The results clearly reveal that the interface integrity between the SiC particles and the IN625 matrix, the mixed powders flowability, the SiC ceramic particles and laser beam interaction, and the hardness, and tensile characteristics of the DMLS processed MMCs were improved effectively by the use of Ni-P coated SiC particles.

  16. 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...

  17. Tin Whisker Electrical Short Circuit Characteristics. Part 2

    Science.gov (United States)

    Courey, Karim J.; Asfour, Shihab S.; Onar, Arzu; Bayliss, Jon A.; Ludwig, Lawrence L.; Wright, Maria C.

    2009-01-01

    Existing risk simulations make the assumption that when a free tin whisker has bridged two adjacent exposed electrical conductors, the result is an electrical short circuit. This conservative assumption is made because shorting is a random event that has an unknown probability associated with it. Note however that due to contact resistance electrical shorts may not occur at lower voltage levels. In our first article we developed an empirical probability model for tin whisker shorting. In this paper, we develop a more comprehensive empirical model using a refined experiment with a larger sample size, in which we studied the effect of varying voltage on the breakdown of the contact resistance which leads to a short circuit. From the resulting data we estimated the probability distribution of an electrical short, as a function of voltage. In addition, the unexpected polycrystalline structure seen in the focused ion beam (FIB) cross section in the first experiment was confirmed in this experiment using transmission electron microscopy (TEM). The FIB was also used to cross section two card guides to facilitate the measurement of the grain size of each card guide's tin plating to determine its finish.

  18. Crystalline instability of Bi-2212 superconducting whiskers near room temperature

    Energy Technology Data Exchange (ETDEWEB)

    Cagliero, Stefano; Khan, Mohammad Mizanur Rahman [Torino Universita, ' NIS' Centre of Excellence, Dip. Chimica Generale e Chimica Organica, and CNISM UdR, Turin (Italy); Torino Universita, ' NIS' Centre of Excellence, Dip. Fisica Sperimentale, and CNISM UdR, Turin (Italy); Agostino, Angelo [Torino Universita, ' NIS' Centre of Excellence, Dip. Chimica Generale e Chimica Organica, and CNISM UdR, Turin (Italy); Truccato, Marco [Torino Universita, ' NIS' Centre of Excellence, Dip. Fisica Sperimentale, and CNISM UdR, Turin (Italy); Orsini, Francesco; Marinone, Massimo; Poletti, Giulio [Universita degli Studi di Milano, Istituto di Fisiologia Generale e Chimica Biologica, Milan (Italy); CNR-INFM-S3 NRC, Modena (Italy); Lascialfari, Alessandro [Universita degli Studi di Milano, Istituto di Fisiologia Generale e Chimica Biologica, Milan (Italy); CNR-INFM-S3 NRC, Modena (Italy); Universita degli Studi di Pavia, INFM-CNR c/o Dipartimento di Fisica A. Volta, Pavia (Italy)

    2009-05-15

    We report new evidences for the thermodynamic instability of whisker crystals in the Bi-Sr-Ca-Cu-O (BSCCO) system. Annealing treatments at 90 C have been performed on two sets of samples, which were monitored by means of X-rays diffraction (XRD) and atomic force microscopy (AFM) measurements, respectively. Two main crystalline domains of Bi{sub 2}Sr{sub 2}CuCa{sub 2}O{sub 8+x} (Bi-2212) were identified in the samples by the XRD data, which underwent an evident crystalline segregation after about 60 hours. Very fast dynamics of the surface modifications was also described by the AFM monitoring. Two typologies of surface structures formed after about 3 annealing hours: continuous arrays of dome shaped bodies were observed along the edges of the whiskers, while in the central regions a dense texture of flat bodies was found. These modifications are described in terms of the formation of simple oxide clusters involving a degradation of the internal layers. (orig.)

  19. Reinforcement active learning in the vibrissae system: optimal object localization.

    Science.gov (United States)

    Gordon, Goren; Dorfman, Nimrod; Ahissar, Ehud

    2013-01-01

    Rats move their whiskers to acquire information about their environment. It has been observed that they palpate novel objects and objects they are required to localize in space. We analyze whisker-based object localization using two complementary paradigms, namely, active learning and intrinsic-reward reinforcement learning. Active learning algorithms select the next training samples according to the hypothesized solution in order to better discriminate between correct and incorrect labels. Intrinsic-reward reinforcement learning uses prediction errors as the reward to an actor-critic design, such that behavior converges to the one that optimizes the learning process. We show that in the context of object localization, the two paradigms result in palpation whisking as their respective optimal solution. These results suggest that rats may employ principles of active learning and/or intrinsic reward in tactile exploration and can guide future research to seek the underlying neuronal mechanisms that implement them. Furthermore, these paradigms are easily transferable to biomimetic whisker-based artificial sensors and can improve the active exploration of their environment. Copyright © 2012 Elsevier Ltd. All rights reserved.

  20. Methods of radiation effects evaluation of SiC/SiC composite and SiC fibers

    Energy Technology Data Exchange (ETDEWEB)

    Youngblood, G.E.; Jones, R.H. [Pacific Northwest National Lab., Richland, WA (United States)

    1998-03-01

    This report covers material presented at the IEA/Jupiter Joint International Workshop on SiC/SiC Composites for Fusion structural Applications held in conjunction with ICFRM-8, Sendai, Japan, Oct. 23--24, 1997. Several methods for radiation effects evaluation of SiC fibers and fiber-reinforced SiC/SiC composite are presented.

  1. Growth of whiskers from Sn surfaces: Driving forces and growth mechanisms

    Science.gov (United States)

    Chason, Eric; Jadhav, Nitin; Pei, Fei; Buchovecky, Eric; Bower, Allan

    2013-05-01

    Sn whiskers are thin filaments that grow spontaneously out of the surface of coatings on Cu and have become a critical reliability problem in Pb-free electronics. In this review, we focus on what creates the driving force for whiskers (or more rounded “hillocks”), and what determines where on the surface they will form. Experimental studies are reviewed that quantify the relationship between the Cu-Sn intermetallic (IMC) formation, stress in the layer and whisker/hillock density. Measurements of the mechanical properties show how stress relaxation in the Sn layer is intimately related to how much stress develops due to the IMC formation. Real-time scanning electron microscope (SEM)/focused ion beam (FIB) studies are described that illustrate the whisker/hillock growth process in detail. Whiskers are found to grow out of a single grain on the surface with little lateral growth while hillock growth is accompanied by extensive grain growth and crystallite rotation. Electron-backscattering detection (EBSD) shows the grain structure around where the whiskers/hillocks form, indicating that whiskers can grow out of pre-existing grains and do not require the nucleation of new grains. This has led to a picture in which stress builds up due to IMC growth and causes whiskers/hillocks to form at “weak grains”, i.e., grains that have a stress relaxation mechanism that becomes active at a lower stress than its neighbors. FEA (finite element analysis) calculations are used to simulate the evolving stress and whisker growth for several different mechanisms that may lead to “weak” grains.

  2. Toxicity in vitro of some silicon carbides and silicon nitrides: whiskers and powders.

    Science.gov (United States)

    Svensson, I; Artursson, E; Leanderson, P; Berglind, R; Lindgren, F

    1997-03-01

    The objectives of this work were to investigate the toxicity of silicon carbide whiskers and powders and silicon nitride whiskers and powders and to compare their toxicity with the toxicity of crocidolite. The effects studied were inhibition of the cloning efficiency of V79 cells, formation of DNA strand breaks by means of a nick translation assay, formation of oxygen radicals in three different assays, and the ability to stimulate neutrophils to produce hydroxyl radicals. All materials showed concentration-dependent inhibition of the cloning efficiency of V79 cells. The inhibition by the most toxic whiskers was in the same order of magnitude as that of crocidolite. Milled whiskers and powders were less toxic than the whiskers. There was a high DNA breaking potential for crocidolite and four of the silicon carbide whiskers and a rather low one for the other materials. Formation of hydroxyl radicals was found for crocidolite and one of the silicon carbide whiskers. In the neutrophil activation test, there was a great variation in the different materials' abilities to activate neutrophils. There was also a good correlation between chemiluminescence and H2O2 formation. The highest activation was found in neutrophils exposed to two of the silicon carbide whiskers and one milled whisker. The conclusion of the investigation is that some of the ceramic materials studied had damaging biological effects comparable to or greater than those of crocidolite. The results from the investigation clearly imply that caution is needed in the introduction of new ceramic fiber materials, so that the correct precautions and protective devices are used in order to avoid harm to the personnel handling the material.

  3. Reactividad entre whiskers de α-SiC y aluminio durante el procesado por vía líquida de materiales compuestos de matriz metálica

    Directory of Open Access Journals (Sweden)

    Ureña, A.

    1999-06-01

    Full Text Available The reactivity between α-SiC whiskers and an aluminium alloy (Al-Cu-Mg, both present in a metal matrix composite, has been studied when such matrix is in molten state. Using mainly transmission electron microscopy (TEM and electron microdiffraction (ED, the nature and morphology of the reaction products generated at the α-SiC/aluminium interface, when this last melts under different condition which simulate casting and welding procedures for metal matrix composites, have been characterised. Both the formation of Al4C3 aggregates with platelet morphology generated by dissolution-reaction mechanisms, and aciculate crystals of the same carbide form by complete dissolution of the α-SiC whiskers and later Al4C3 precipitation into the molten aluminium. Ternary Al-Si carbides with high chemical stability have been also identified by TEMED (β-Al4SiC4, being its formation related with higher energetic conditions than for the Al4C3.

    Se realiza un estudio de la reactividad entre whiskers de α-SiC y una aleación de aluminio en estado líquido (Al-Cu-Mg, que forman parte de un material compuesto de matriz metálica. Empleando fundamentalmente técnicas de microscopía electrónica de barrido (MEB y de transmisión (MET, junto con difracción de electrones (DE, se ha caracterizado la naturaleza y morfología de los productos de reacción que se generan en la intercara α-SiC/aluminio, cuando éste funde en diferentes condiciones que simulan procesos de fabricación y soldadura del material compuesto. Se ha observado tanto la formación de agregados de Al4C3 con morfología tabular producidos por mecanismos de disolución-reacción de los whiskers, como de cristales aciculares del mismo tipo de carburo formados por disolución total de α-SiC y precipitación en el aluminio fundido. Se ha determinado también que, en condiciones suficientemente energéticas, pueden llegar a formarse carburos ternarios de aluminio y silicio (β-Al4SiC4 que

  4. Alumina reinforced tetragonal zirconia (TZP) composites. Final technical report, July 1, 1993--December 31, 1996

    Energy Technology Data Exchange (ETDEWEB)

    Shetty, D.K.

    1997-06-01

    This final technical report summarizes the significant research results obtained during the period July 1, 1993 through December 31, 1996 in the DOE-supported research project entitled, {open_quotes}Alumina Reinforced Tetragonal Zirconia (TZP) Composites{close_quotes}. The objective of the research was to develop high-strength and high-toughness ceramic composites by combining mechanisms of platelet, whisker or fiber reinforcement with transformation toughening. The approach used included reinforcement of Celia- or yttria-partially-stabilized zirconia (Ce-TZP or Y-TZP) with particulates, platelets, or continuous filaments of alumina.

  5. Lateral boron distribution in polycrystalline SiC source materials

    DEFF Research Database (Denmark)

    Linnarsson, M. K.; Kaiser, M.; Liljedahl, R.

    2013-01-01

    Polycrystalline SiC containing boron and nitrogen are used in growth of fluorescent SiC for white LEDs. Two types of doped polycrystalline SiC have been studied in detail with secondary ion mass spectrometry: sintered SiC and poly-SiC prepared by sublimation in a physical vapor transport setup. T...

  6. The control of interface and microstructure of SiC/Al composites by sol-gel techniques

    DEFF Research Database (Denmark)

    Kindl, B.; Liu, Y.L.; Nyberg, E.

    1992-01-01

    A process and additives have been developed to coat SiC whiskers and particulate reinforcements. The treated whiskers are shown to have low reactivity toward the aluminium matrix and to be well dispersed. The process is simple and inexpensive, and it is shown that the mechanical properties...

  7. SYNTHESIS AND STRUCTURAL CHARACTERISTICS OF MAGNESIUM AND ZINC DOPED HYDROXYAPATITE WHISKERS

    Directory of Open Access Journals (Sweden)

    Hongquan Zhang

    2017-07-01

    Full Text Available Mg and Zn doped hydroxyapatite whiskers were successfully prepared by hydrothermal homogeneous precipitation using amide additives. The morphology and structure of the products were characterized using SEM, XRD, and FTIR. It was shown that all samples prepared using ˂ 10 % mol L-1 Mg or Zn ions were identified as HA. Further increasing their concentration gave rise to the appearance of the second phase. The Mg or Zn doped HA whiskers had a length of 60 - 110 mm and aspect ratio of 30 - 50, when the concentration of Mg or Zn ions were ˂ 5mol%. Substitution of Mg or Zn impaired the crystallization of HA whiskers and led to changes in the morphology, lattice parameters and XRD peaks diffraction position, which demonstrated that Mg or/and Zn ions were incorporated into the unit cell of HA, rather than just absorption on the surface of the whiskers.

  8. Encoding of Whisker Vibration by Rat Barrel Cortex Neurons: Implications for Texture Discrimination

    National Research Council Canada - National Science Library

    Arabzadeh, Ehsan; Petersen, Rasmus S; Diamond, Mathew E

    2003-01-01

    .... What is the representation of texture in rat somatosensory cortex? We hypothesize that as rats "whisk" over a surface, the spatial frequency of a grooved or pebbled texture is converted to a temporal frequency of whisker vibration...

  9. Biology of nesting crested, least, and whiskered auklets at Buldir Island, Alaska

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — During avifaunal investigations at Buldir Island 1974-1976, some aspects of the biology of Crested, Least, and Whiskered Auklets were investigated in a colony where...

  10. Study of ferromagnetism in Mn-doped ZnO whisker arrays

    Indian Academy of Sciences (India)

    WINTEC

    -doped ZnO whiskers. magnetizations exist up to 300 K. This magnetization difference can be attributed to the following: For FC sample at room temperature, the ferromagnetic ordering appears obviously under the magnetic field of 1T. When.

  11. Fused traditional and geometric morphometrics demonstrate pinniped whisker diversity.

    Directory of Open Access Journals (Sweden)

    Carly C Ginter

    Full Text Available Vibrissae (whiskers are important components of the mammalian tactile sensory system, and primarily function as detectors of vibrotactile information from the environment. Pinnipeds possess the largest vibrissae among mammals and their vibrissal hair shafts demonstrate a diversity of shapes. The vibrissae of most phocid seals exhibit a beaded morphology with repeating sequences of crests and troughs along their length. However, there are few detailed analyses of pinniped vibrissal morphology, and these are limited to a few species. Therefore, we comparatively characterized differences in vibrissal hair shaft morphologies among phocid species with a beaded profile, phocid species with a smooth profile, and otariids with a smooth profile using traditional and geometric morphometric methods. Traditional morphometric measurements (peak-to-peak distance, crest width, trough width and total length were collected using digital photographs. Elliptic Fourier analysis (geometric morphometrics was used to quantify the outlines of whole vibrissae. The traditional and geometric morphometric datasets were subsequently combined by mathematically scaling each to true rank, followed by a single eigendecomposition. Quadratic discriminant function analysis demonstrated that 79.3, 97.8 and 100% of individuals could be correctly classified to their species based on vibrissal shape variables in the traditional, geometric and combined morphometric analyses, respectively. Phocids with beaded vibrissae, phocids with smooth vibrissae, and otariids each occupied distinct morphospace in the geometric morphometric and combined data analyses. Otariids split into two groups in the geometric morphometric analysis and gray seals appeared intermediate between beaded- and smooth-whiskered species in the traditional and combined analyses. Vibrissal hair shafts modulate the transduction of environmental stimuli to the mechanoreceptors in the follicle-sinus complex (F-SC, which

  12. Neonatal whisker trimming causes long-lasting changes in structure and function of the somatosensory system.

    Science.gov (United States)

    Lee, Li-Jen; Chen, Wan-Jung; Chuang, Ya-Wen; Wang, Yu-Chun

    2009-10-01

    The significance of very early experience in the maturation of whisker-to-barrel system comes primarily from neonatal whisker or infraorbital nerve lesion studies conducted prior to the formation of cortical barrels. However, the surgical procedures damage the sensory pathway; it is difficult to examine the consequence after the recovery of sensory deprivation. To address this issue, we performed a neonatal whisker-cut (WC) paradigm and examined their behavioral performance during P30 to P35. With fully regrown whiskers, the rats that had whisker cut from the date of birth (P0) to postnatal day (P) 3 (WC 0-3) exhibited shorter crossable distance in the gap-crossing test. However, the rats had whisker cut at P3 only (WC 3) behaved normally in this test, suggesting the critical period for the development of whisker-specific tactile function is P0-P3, agreed with previous findings demonstrated by lesion methods. In the WC 0-3 rats, the cortical areas in the layer IV somatosensory region in relation to the trimmed whiskers were enlarged and the spiny stellate neurons within had larger dendritic span and greater spine density. Furthermore, more long and multiple-head spines were found in these rats. With abnormal structure and function in the somatosensory system, the WC 0-3 rats showed higher explorative activity and more frequent social interactions. Our results have demonstrated that the early tactile deprivation, similar to early visual deprivation, perturbed the developmental program of the brain and affected later behaviors in various aspects.

  13. Joining technology—A challenge for the use of SiC components in HTRs

    Energy Technology Data Exchange (ETDEWEB)

    Herrmann, M., E-mail: marion.herrmann@tu-dresden.de; Meisel, P.; Lippmann, W.; Hurtado, A.

    2016-09-15

    The availability of suitable joining technologies is paramount to the further advancement of ceramic components and their use in HTRs. Among other joining technologies, a modified brazing technology using a laser beam for heating the components to be joined has been developed at TU Dresden. The laser-induced heating behavior of the ceramic material is determined by the interactions between the material and the laser beam. This was shown in two different silicon carbide materials (SSiC and SiC{sub f}-reinforced ceramic material) using a diode laser with wavelengths 808 nm and 940 nm. The laser-based technique was illustrated by three different examples: sealing of monolithic SiC with a pin configuration for fuel claddings, sealing of SiC heat pipes with a length of 1 m, and demonstration of the transferability of the laser technique to fiber-reinforced components by means of a SiC{sub f}/SiCN material. Because the covalent bonding of SiC does not allow conventional welding, much research has been devoted to developing alternative filler systems. Glass or glass–ceramic fillers enable the tailoring of properties such as CTE and viscosity. Glasses are thermally stable up to their glass transition temperatures. It was shown that the crystallization of the yttrium aluminosilicate glass composition of the present work allows it to be used at 1050 °C without any significant changes occurring in braze tightness. For the SiC heat pipes with sodium as the working fluid, a sodium-resistant metal braze consisting of Ni–Ti–Si was formed. The long-term resistance of this filler to sodium at 800 °C was proven. The results demonstrate the possibility of using the laser-based joining technique for the joining of different SiC materials as well as for different brazing materials.

  14. Method of producing novel silicon carbide articles. [Patent application

    Science.gov (United States)

    Milewski, J.V.

    1982-06-18

    A method of producing articles comprising reaction-bonded silicon carbide (SiC) and graphite (and/or carbon) is given. The process converts the graphite (and/or carbon) in situ to SiC, thus providing the capability of economically obtaining articles made up wholly or partially of SiC having any size and shape in which graphite (and/or carbon) can be found or made. When the produced articles are made of an inner graphite (and/or carbon) substrate to which SiC is reaction bonded, these articles distinguish SiC-coated graphite articles found in the prior art by the feature of a strong bond having a gradual (as opposed to a sharply defined) interface which extends over a distance of mils. A method for forming SiC whisker-reinforced ceramic matrices is also given. The whisker-reinforced articles comprise SiC whiskers which substantially retain their structural integrity.

  15. Bibliography on Ceramic Matrix Composites and Reinforcing Whiskers, Platelets, and Fibers, 1970-1990

    Science.gov (United States)

    1993-08-01

    I P (AD D142 252) Struk, L I. Yuga , A 1. Presented at the 90th Annual Meeting of Fushchich, 0. 1. Lugovskaya. E. S the American Ceramic Society...Nitride-Base Georgia Technical Research ,,titute, Composite Materials Atlanta Panasyuk, A. D. Struk, L. I. Annual Report, January-December Yuga , A.I...2.1.2.86 Xue, Liang A. 8.3.0.3, 9.3.0.5 Yuga , A. 1. 4.1.3.10, 4.1.3.12 Yust, C. S. 2.1.2.60, 2.1.2.103, 2.1.2.111 Yakushkina, V. S. 2.1.4.71 Yamada, Osamu

  16. Effects of Chitin Whiskers on Physical Properties and Osteoblast Culture of Alginate Based Nanocomposite Hydrogels.

    Science.gov (United States)

    Huang, Yao; Yao, Mengyu; Zheng, Xing; Liang, Xichao; Su, Xiaojuan; Zhang, Yu; Lu, Ang; Zhang, Lina

    2015-11-09

    Novel nanocomposite hydrogels composed of polyelectrolytes alginate and chitin whiskers with biocompatibility were successfully fabricated based on the pH-induced charge shifting behavior of chitin whiskers. The chitin whiskers with mean length and width of 300 and 20 nm were uniformly dispersed in negatively charged sodium alginate aqueous solution, leading to the formation of the homogeneous nanocomposite hydrogels. The experimental results indicated that their mechanical properties were significantly improved compared to alginate hydrogel and the swelling trends were inhibited as a result of the strong electrostatic interactions between the chitin whiskers and alginate. The nanocomposite hydrogels exhibited certain crystallinity and hierarchical structure with nanoscale chitin whiskers, similar to the structure of the native extracellular matrix. Moreover, the nanocomposite hydrogels were successfully applied as bone scaffolds for MC3T3-E1 osteoblast cells, showing their excellent biocompatibility and low cytotoxicity. The results of fluorescent micrographs and scanning electronic microscope (SEM) images revealed that the addition of chitin whiskers into the nanocomposite hydrogels markedly promoted the cell adhesion and proliferation of the osteoblast cells. The biocompatible nanocomposite hydrogels have potential application in bone tissue engineering.

  17. Contributions of Stress And Oxidation on the Formation of Whiskers in Pb-Free Solders

    Energy Technology Data Exchange (ETDEWEB)

    Duncan, Andrew J. [Savannah River Site (SRS), Aiken, SC (United States). Savannah River National Lab. (SRNL). Materials Science & Technology; Hoffman, Elizabeth N. [Savannah River Site (SRS), Aiken, SC (United States). Savannah River National Lab. (SRNL)

    2014-03-25

    This report summarizes the research activities of WP-1754. The study focusses on the environmental factors influencing formation of lead free whiskers on electrodeposited tin coatings over copper (or copper containing) substrates. Much of the initial results are summarized in an interim report. From the initial results, two main areas were chosen to be the focus of additional research: the demonstration of effects of elastic stress state in the nucleation of whiskers and the confirmation of the effect of oxygen/nitrogen ratio in the formation of whiskers. Different levels of elastic stress were induced with the incorporation of a custom designed fixture that loaded the substrates in a four-point bending configuration and were maintained in an environmental chamber under conditions deemed favorable for whisker growth. The results show that induced elastic stress slightly increased the concentration of nucleation sites of whiskers. The effects of oxygen content were studied by aging substrates in gas vials of varying absolute pressure and different oxygen/nitrogen ratios. The concentration of whiskers were measured and appear to be sensitive to absolute pressure but are not sensitive to oxygen content (as previously observed).

  18. Growth of cadmium oxide whiskers on cadmium sulphide single crystals with copper as growth activator

    Energy Technology Data Exchange (ETDEWEB)

    Koparanova, N.; Simov, S. (Bylgarska Akademiya na Naukite, Sofia. Inst. po Fizika na Tvyrdoto Tyalo); Genchev, D. (Bylgarska Akademiya na Naukite, Sofia. Inst. za Yadrena Izsledvaniya i Yadrena Energetika); Metchenov, G. (Research Inst. of Criminalistics and Criminology, Sofia (Bulgaria))

    1985-02-01

    Some results on the growth and morphology of cadmium oxide whiskers, obtained on cadmium sulphide single crystals with copper as a growth activator, are presented in this work. Cadmium oxide whiskers have been obtained on brace 112-bar0 brace faces of cadmium sulphide plates with a copper layer deposited in advance. The whiskers grew during the annealing of the plates in a weak stream of technically pure argon at temperatures 670 to 730 deg C for 15 min to 3.5 h. Details about the procedure have been given elsewhere. The composition and morphology of the whiskers have been studied by an X-ray microanalyser JEOL 35 DDS and a scanning electron microscope JEOL, JSM 35. The optical microscopic observations have shown that after annealing, a gray-black granular layer is formed on the cadmium sulphide single crystals and this layer can easily be separated from the crystal substrate. Under the granular layer the crystal is heavily damaged. The whiskers grow on the granular layer and they are coloured yellow-brown or red-brown. The maximum whisker length attains several hundreds of micrometres and in some cases up to 1 mm or more.

  19. Prenatal Ethanol Exposure and Whisker Clipping Disrupt Ultrasonic Vocalizations and Play Behavior in Adolescent Rats

    Science.gov (United States)

    Waddell, Jaylyn; Yang, Tianqi; Ho, Eric; Wellmann, Kristen A.; Mooney, Sandra M.

    2016-01-01

    Prenatal ethanol exposure can result in social deficits in humans and animals, including altered social interaction and poor communication. Rats exposed to ethanol prenatally show reduced play fighting, and a combination of prenatal ethanol exposure and neonatal whisker clipping further reduces play fighting compared with ethanol exposure alone. In this study, we explored whether expression of hedonic ultrasonic vocalizations (USVs) correlated with the number of playful attacks by ethanol-exposed rats, rats subjected to postnatal sensory deprivation by whisker clipping or both compared to control animals. In normally developing rats, hedonic USVs precede such interactions and correlate with the number of play interactions exhibited in dyads. Pregnant Long-Evans rats were fed an ethanol-containing liquid diet or a control diet. After birth, male and female pups from each litter were randomly assigned to the whisker-clipped or non-whisker-clipped condition. Animals underwent a social interaction test with a normally developing play partner during early or late-adolescence. USVs were recorded during play. Prenatal ethanol exposure reduced both play and hedonic USVs in early adolescence compared to control rats and persistently reduced social play. Interestingly, ethanol exposure, whisker clipping and the combination abolished the significant correlation between hedonic USVs and social play detected in control rats in early adolescence. This relationship remained disrupted in late adolescence only in rats subjected to both prenatal ethanol and whisker clipping. Thus, both insults more persistently disrupted the relationship between social communication and social play. PMID:27690116

  20. Prenatal Ethanol Exposure and Whisker Clipping Disrupt Ultrasonic Vocalizations and Play Behavior in Adolescent Rats

    Directory of Open Access Journals (Sweden)

    Jaylyn Waddell

    2016-09-01

    Full Text Available Prenatal ethanol exposure can result in social deficits in humans and animals, including altered social interaction and poor communication. Rats exposed to ethanol prenatally show reduced play fighting, and a combination of prenatal ethanol exposure and neonatal whisker clipping further reduces play fighting compared with ethanol exposure alone. In this study, we explored whether expression of hedonic ultrasonic vocalizations (USVs correlated with the number of playful attacks by ethanol-exposed rats, rats subjected to postnatal sensory deprivation by whisker clipping or both compared to control animals. In normally developing rats, hedonic USVs precede such interactions and correlate with the number of play interactions exhibited in dyads. Pregnant Long-Evans rats were fed an ethanol-containing liquid diet or a control diet. After birth, male and female pups from each litter were randomly assigned to the whisker-clipped or non-whisker-clipped condition. Animals underwent a social interaction test with a normally developing play partner during early or late-adolescence. USVs were recorded during play. Prenatal ethanol exposure reduced both play and hedonic USVs in early adolescence compared to control rats and persistently reduced social play. Interestingly, ethanol exposure, whisker clipping and the combination abolished the significant correlation between hedonic USVs and social play detected in control rats in early adolescence. This relationship remained disrupted in late adolescence only in rats subjected to both prenatal ethanol and whisker clipping. Thus, both insults more persistently disrupted the relationship between social communication and social play.

  1. Investigation of Whisker Growth from Alkaline Non-cyanide Zinc Electrodeposits

    Science.gov (United States)

    Wu, L.; Ashworth, M. A.; Wilcox, G. D.

    2017-02-01

    Electroplated zinc finishes have been widely used in the packaging of electronic products for many years as a result of their excellent corrosion resistance and relatively low cost. However, the spontaneous formation of whiskers on zinc electroplated components, which are capable of resulting in electrical shorting or other damaging effects, can be highly problematic for the reliability of long-life electrical and electronic equipment. This work investigated the mechanism for whisker growth from zinc electrodeposited mild steel substrates. The incubation time for whisker growth from the surface of nodules on the surface of the electrodeposit was considerably reduced compared with that from the planar deposit surface. Recrystallisation of the as-deposited columnar structure was observed at the whisker root. This result is consistent with some recent whisker growth models based on recrystallisation. There was no evidence of iron-zinc (Fe-Zn) intermetallic formation at the iron/zinc (Fe/Zn) interface or within the zinc coating beneath the whiskers.

  2. A new strategy for TiO2 whiskers mediated multi-mode cancer treatment

    Science.gov (United States)

    Xu, Peipei; Wang, Ruju; Ouyang, Jian; Chen, Bing

    2015-02-01

    Traditional Chinese medicine (TCM) which functions as chemotherapeutic or adjuvantly chemotherapeutic agents has been drawing a great many eyeballs for its easy obtain and significant antitumor effects accompanied with less toxic and side effects. PDT (photodynamic therapy) utilizes the fact that certain compounds coined as photosensitizers, when exposed to light of a specific wavelength, are capable of generating cytotoxic reactive oxygen species (ROS) such as hydroxyl radical, hydrogen peroxide, and superoxide to kill cancer cells. Combinations of cancer therapeutic modalities are studied to improve the efficacy of treatment. This study aimed to explore a new strategy of coupling of titanium dioxide whiskers (TiO2 Ws) with the anticancer drug gambogic acid (GA) in photodynamic therapy. The nanocomposites were coined as GA-TiO2. The combination of TiO2 Ws with GA induced a remarkable enhancement in antitumor activity estimated by MTT assay, nuclear DAPI staining, and flow cytometry. Furthermore, the possible signaling pathway was explored by reverse transcription polymerase chain reaction (RT-PCR) and Western blot assay. These results identify TiO2 Ws of good biocompatibility and photocatalytic activity. In human leukemia cells (K562 cells), TiO2 Ws could obviously increase the intracellular concentration of GA and enhance its potential antitumor efficiency, suggesting that TiO2 Ws could act as an efficient drug delivery carrier targeting GA to carcinoma cells. Moreover, photodynamic GA-TiO2 nanocomposites could induce an evident reinforcement in antitumor activity with UV illumination. These results reveal that such modality combinations put forward a promising proposal in cancer therapy.

  3. Preparation of biomorphic SiC ceramics

    Directory of Open Access Journals (Sweden)

    Egelja A.

    2008-01-01

    Full Text Available This paper deals with a new method for producing non-oxide ceramic using wood as a template. SiC with a woodlike microstructure has been prepared by carbothermal reduction reactions of Tilia wood/TEOS composite at 1873K. The porous carbon preform was infiltrated with TEOS (Si(OC2H54, as a source of silica, without pressure at 298K. The morphology of resulting porous SiC ceramics, as well as the conversion mechanism of wood to SiC ceramics, have been investigated by scanning electron microscopy (SEM/EDS and X-ray diffraction analysis (XRD. Obtained SiC ceramics consists of β-SiC with traces of α-SiC.

  4. Ultra High Temperature (UHT) SiC Fiber (Phase 2)

    Science.gov (United States)

    Dicarlo, James A.; Jacobson, Nathan S.; Lizcano, Maricela; Bhatt, Ramakrishna T.

    2015-01-01

    Silicon-carbide fiber-reinforced silicon-carbide ceramic matrix composites (SiCSiC CMC) are emerginglightweight re-usable structural materials not only for hot section components in gas turbine engines, but also for controlsurfaces and leading edges of reusable hypersonic vehicles as well as for nuclear propulsion and reactor components. Ithas been shown that when these CMC are employed in engine hot-section components, the higher the upper usetemperature (UUT) of the SiC fiber, the more performance benefits are accrued, such as higher operating temperatures,reduced component cooling air, reduced fuel consumption, and reduced emissions. The first generation of SiCSiC CMC with a temperature capability of 2200-2400F are on the verge of being introduced into the hot-section components ofcommercial and military gas turbine engines.Today the SiC fiber type currently recognized as the worlds best in terms ofthermo-mechanical performance is the Sylramic-iBN fiber. This fiber was previously developed by the PI at NASA GRC using patented processes to improve the high-cost commercial Sylramic fiber, which in turn was derived from anotherlow-cost low-performance commercial fiber. Although the Sylramic-iBN fiber shows state-of-the art creep and rupture resistance for use temperatures above 2550oF, NASA has shown by fundamental creep studies and model developmentthat its microstructure and creep resistance could theoretically be significantly improved to produce an Ultra HighTemperature (UHT) SiC fiber.This Phase II Seedling Fund effort has been focused on the key objective of effectively repeating the similar processes used for producing the Sylramic-iBN fiber using a design of experiments approach to first understand the cause of the less than optimum Sylramic-iBN microstructure and then attempting to develop processconditions that eliminate or minimize these key microstructural issues. In so doing, it is predicted that that theseadvanced process could result in an UHT SiC

  5. Development of Sic Gas Sensor Systems

    Science.gov (United States)

    Hunter, G. W.; Neudeck, P. G.; Okojie, R. S.; Beheim, G. M.; Thomas, V.; Chen, L.; Lukco, D.; Liu, C. C.; Ward, B.; Makel, D.

    2002-01-01

    Silicon carbide (SiC) based gas sensors have significant potential to address the gas sensing needs of aerospace applications such as emission monitoring, fuel leak detection, and fire detection. However, in order to reach that potential, a range of technical challenges must be overcome. These challenges go beyond the development of the basic sensor itself and include the need for viable enabling technologies to make a complete gas sensor system: electrical contacts, packaging, and transfer of information from the sensor to the outside world. This paper reviews the status at NASA Glenn Research Center of SiC Schottky diode gas sensor development as well as that of enabling technologies supporting SiC gas sensor system implementation. A vision of a complete high temperature microfabricated SiC gas sensor system is proposed. In the long-term, it is believed that improvements in the SiC semiconductor material itself could have a dramatic effect on the performance of SiC gas sensor systems.

  6. Selection of head and whisker coordination strategies during goal-oriented active touch.

    Science.gov (United States)

    Schroeder, Joseph B; Ritt, Jason T

    2016-04-01

    In the rodent whisker system, a key model for neural processing and behavioral choices during active sensing, whisker motion is increasingly recognized as only part of a broader motor repertoire employed by rodents during active touch. In particular, recent studies suggest whisker and head motions are tightly coordinated. However, conditions governing the selection and temporal organization of such coordinated sensing strategies remain poorly understood. We videographically reconstructed head and whisker motions of freely moving mice searching for a randomly located rewarded aperture, focusing on trials in which animals appeared to rapidly "correct" their trajectory under tactile guidance. Mice orienting after unilateral contact repositioned their whiskers similarly to previously reported head-turning asymmetry. However, whisker repositioning preceded head turn onsets and was not bilaterally symmetric. Moreover, mice selectively employed a strategy we term contact maintenance, with whisking modulated to counteract head motion and facilitate repeated contacts on subsequent whisks. Significantly, contact maintenance was not observed following initial contact with an aperture boundary, when the mouse needed to make a large corrective head motion to the front of the aperture, but only following contact by the same whisker field with the opposite aperture boundary, when the mouse needed to precisely align its head with the reward spout. Together these results suggest that mice can select from a diverse range of sensing strategies incorporating both knowledge of the task and whisk-by-whisk sensory information and, moreover, suggest the existence of high level control (not solely reflexive) of sensing motions coordinated between multiple body parts. Copyright © 2016 the American Physiological Society.

  7. The Influence of Coating Oxide Metal on Surface of SiC Particles to Elastic Modulus of Al/SiC Composites

    Directory of Open Access Journals (Sweden)

    Dedi Priadi

    2008-11-01

    Full Text Available The isotropic composites of Al/SiC is made by powder metallurgy method, the quality of mechanical materials depend on interfacial bonding between matrix (Al and reinforcement (SiC. The quality of interfacial bonding can influence to elastic modulus of composites which is made by solid process. SiC particles were coated by metal oxide aim to enhance quality interfacial bonding between matrix and reinforcement. These research using three kinds of coating materials, which are Mg oxide, Cu oxide and Al oxide, and these materials were deposited on surface of SiC particles. From three kinds of materials coating Al2O3 is the best to enhance quality interfacial bonding between matrix and reinforce than the others as CuO or MgO. There is Intermetalic phase formatted on CuO coating, and MgO coating have many porous where they can make decrease quality of Al-SiC composites. All of volume fraction of SiC on the Al/SiC composites, which oxide aluminum coating on SiC surface have highest value of elastic modulus than the others metal oxides.

  8. A kind of carbon whiskers in new structure and morphology

    Institute of Scientific and Technical Information of China (English)

    DONG; Jian

    2001-01-01

    [1]Endo, M., Saito, R., Dresselhaus, M. S. et al. From carbon fibers to nanotubes, in Carbon Nanotubes Preparations and Properties (ed. Ebbesen, T. W.), New York: CRC Press Inc., 1997, 54-66.[2]Baker, R. T. K., Baker, M. A., Harris, P. S. et al., Nucleation and growth of carbon deposits from the nickel catalyzed de-composition of acetylene, J.Catal., 1972, 26(7): 51.[3]Audier, M., Coulon, M., Kinetic and microscopic aspects of catalytic carbon growth, Carbon, 1985, 23(3): 317.[4]Oberlin, A., Endo, M., Koyama, T., High resolution microscope observations of graphitized carbon fibers, Carbon, 1976, 14(1): 133.[5]Bacon, R., Growth, structure, and properties of graphite whiskers, Journal of Applied Physics, 1960, 31(2): 283.[6]Murayama, H., Maeda, M., A novel form of filamentous graphite, Nature, 1990, 345(28): 791.[7]Pimpinelli, A., Villain, J., Physics of Crystal Growth, New York: Cambridge University Press, 1998, 62-64.[8]Minkoff, I., Solidification and Cast Structure, Chichester: Wiley, 1986, 42-47.[9]Pierson, H. O., Handbook of Carbon, Graphite, Diamond, and Fullerenes: Properties, Processing, and Applications, Park Ridge: Noyes Publications, 1993, 151.[10]Bennema, P., Spiral growth and surface roughing: Developments since Burton, Cabrera and Frank, Journal of Crystal Growth, 1984, 69(2): 182.

  9. Isolation of whiskers from natural sources and their dispersed in a non-aqueous medium

    Directory of Open Access Journals (Sweden)

    Mauro Vestena

    Full Text Available Abstract Whiskers have been used as a nanomaterial dispersed in polymer matrices to modify the microscopic and macroscopic properties of the polymer. These nanomaterials can be isolated from cellulose, one of the most abundant natural renewable sources of biodegradable polymer. In this study, whiskers were isolated from sugarcane bagasse and corn cob straw fibers. Initially, the cellulose fiber was treated through an alkaline/oxidative process followed by acid hydrolysis. Dimethylformamide and dimethyl sulfoxide were used to replace the aqueous medium for the dispersion of the whiskers. For the solvent exchange, dimethylformamide or dimethyl sulfoxide was added to the aqueous dispersion and the water was then removed by fractional distillation. FTIR, TGA, XRD, TEM, Zeta and DLS techniques were used to evaluate the efficiency of the isolation process as well as the morphology and dimensions of the whiskers. The dimensions of the whiskers are comparable with values reported in the literature, maintaining the uniformity and homogeneity in both aqueous and non-aqueous solvents.

  10. Terrestrial whisker growth experiments which anticipate some special effects of a space station environment

    Science.gov (United States)

    Hobbs, H. H.

    1983-01-01

    The effects of the absence of gravitationally driven thermal convection on the growth of whiskers by chemical reduction of metal salts was studied. It was possible to accomplish nearly complete suppression of such convection. Suppression of the convection does indeed effect the growth but in subtle, not necessarily detrimental ways: none of the changes observed were such as to hamper efforts to produce whiskers in space. Copper whiskers grown from cuprous iodide respond most positively to the suppression of convection; therefore, they are strongly recommended for tests in the space environment. Cobalt whiskers grown from cobaltous bromide show the greatest independence from conditions of convection and applied electric fields of any material studied; therefore, this medium is highly recommended. A strong pulse of electric field forces the whiskers to stick to the growth vessel top plate, this facilitates study or "harvesting'. On the space station it is recommended that the growth vessels be mounted outside the laboratory and joined with the station by means of double vacuum valves and gas service lines.

  11. Peculiarities of magnetoresistance in InSb whiskers at cryogenic temperatures

    Energy Technology Data Exchange (ETDEWEB)

    Druzhinin, A., E-mail: druzh@polynet.lviv.ua [Lviv Polytechnic National University, Bandera Str., 12, 79013 Lviv (Ukraine); International Laboratory of High Magnetic Fields and Low Temperatures, Gajowicka 95, Wroclaw (Poland); Ostrovskii, I.; Khoverko, Yu. [Lviv Polytechnic National University, Bandera Str., 12, 79013 Lviv (Ukraine); International Laboratory of High Magnetic Fields and Low Temperatures, Gajowicka 95, Wroclaw (Poland); Liakh-Kaguy, N.; Khytruk, I. [Lviv Polytechnic National University, Bandera Str., 12, 79013 Lviv (Ukraine); Rogacki, K. [International Laboratory of High Magnetic Fields and Low Temperatures, Gajowicka 95, Wroclaw (Poland)

    2015-12-15

    Highlights: • Magnetoresistance in InSb whiskers with impurity concentration near MIT is studied. • SdH oscillations of transverse and longitudinal magnetoresistance are examined. • Mechanisms of electron scattering are determined • Main crystal parameters of InSb whiskers are determined. - Abstract: The study of the magnetoresistance in InSb whiskers with an impurity concentration in the vicinity to the metal-insulator phase transition, at low temperature range 4.2–77 K, and in fields, with induction up to 14 T, was conducted. The presence of Shubnikov-de Haas oscillations in both transverse and longitudinal magnetoresistance was observed. The following parameters of InSb whiskers were defined: period of oscillations 0.1 T{sup −1}, cyclotron effective mass of electrons m{sub c} ≈ 0.14m{sub o,} concentration of charge carriers 2.3 × 10{sup 17} cm{sup −3}, g-factor g{sup *} ≈ 30 and Dingle temperature T{sub D} = 14.5 K. To determine the nature of crystal defects, the electron scattering processes on the short-range potential, caused by interaction with polar and nonpolar optical phonons, piezoelectric and acoustic phonons, static strain centers and ionized impurities in n-InSb whiskers, with defect concentration 2.9 × 10{sup 17} cm{sup −3}, are considered. The temperature dependences of electron mobility in the range 4.2–500 K were calculated.

  12. Isolation of whiskers from natural sources and their dispersed in a non-aqueous medium

    Energy Technology Data Exchange (ETDEWEB)

    Vestena, Mauro; Gross, Idejan Padilha; Pires, Alfredo Tiburcio Nunes; Muller, Carmen Maria Olivera, E-mail: mauro@utfpr.edu.br [Universidade Federal Santa Catarina (UFSC), Florianopolis, SC (Brazil)

    2016-10-15

    Whiskers have been used as a nano material dispersed in polymer matrices to modify the microscopic and macroscopic properties of the polymer. These nanomaterials can be isolated from cellulose, one of the most abundant natural renewable sources of biodegradable polymer. In this study, whiskers were isolated from sugarcane bagasse and corn cob straw fibers. Initially, the cellulose fiber was treated through an alkaline/oxidative process followed by acid hydrolysis. Dimethylformamide and dimethyl sulfoxide were used to replace the aqueous medium for the dispersion of the whiskers. For the solvent exchange, dimethylformamide or dimethyl sulfoxide was added to the aqueous dispersion and the water was then removed by fractional distillation. FTIR, TGA, XRD, TEM, Zeta and DLS techniques were used to evaluate the efficiency of the isolation process as well as the morphology and dimensions of the whiskers. The dimensions of the whiskers are comparable with values reported in the literature, maintaining the uniformity and homogeneity in both aqueous and non-aqueous solvents. (author)

  13. Tactile soft-sparse mean fluid-flow imaging with a robotic whisker array.

    Science.gov (United States)

    Tuna, Cagdas; Jones, Douglas L; Kamalabadi, Farzad

    2015-08-04

    An array of whiskers is critical to many mammals to survive in their environment. However, current engineered systems generally employ vision, radar or sonar to explore the surroundings, not having sufficiently benefited from tactile perception. Inspired by the whisking animals, we present here a novel tomography-based tactile fluid-flow imaging technique for the reconstruction of surroundings with an artificial whisker array. The moment sensed at the whisker base is the weighted integral of the drag force per length, which is proportional to the relative velocity squared on a whisker segment. We demonstrate that the 2D cross-sectional mean fluid-flow velocity-field can be successfully mapped out by collecting moment measurements at different angular positions with the whisker array. We use a regularized version of the FOCal underdetermined system solver algorithm with a smoothness constraint to obtain soft-sparse static estimates of the 2D cross-sectional velocity-squared distribution. This new proposed approach has the strong potential to be an alternative environmental sensing technology, particularly in dark or murky environments.

  14. Comparison of Microstructure and Mechanical Properties of A356/SiC Metal Matrix Composites Produced by Two Different Melting Routes

    Directory of Open Access Journals (Sweden)

    Shashi Prakash Dwivedi

    2014-01-01

    Full Text Available A356/SiC metal matrix composites with different weight percent of SiC particles were fabricated by two different techniques such as mechanical stir casting and electromagnetic stir casting. The results of macrostructure, microstructure, and XRD study revealed uniform distribution, grain refinement, and low porosity in electromagnetic stir casing samples. The mechanical results showed that the addition of SiC particles led to the improvement in tensile strength, hardness, toughness, and fatigue life. It indicates that type of fabrication process and percentage of reinforcement are the effective factors influencing the mechanical properties. It is observed that when percentage of reinforcement increases in electromagnetic stir casting, best mechanical properties are obtained.

  15. Joining of SiC ceramics and SiC/SiC composites

    Energy Technology Data Exchange (ETDEWEB)

    Rabin, B.H. [Idaho National Engineering Lab., Idaho Falls, ID (United States)

    1995-08-01

    This project has successfully developed a practical and reliable method for fabricating SiC ceramic-ceramic joints. This joining method has the potential to facilitate the use of SiC-based ceramics in a variety of elevated temperature fossil energy applications. The technique is based on a reaction bonding approach that provides joint interlayers compatible with SiC, and excellent joint mechanical properties at temperatures exceeding 1000{degrees}C. Recent efforts have focused on transferring the joining technology to industry. Several industrial partners have been identified and collaborative research projects are in progress. Investigations are focusing on applying the joining method to sintered a-SiC and fiber-reinforced SiC/SiC composites for use in applications such as heat exchangers, radiant burners and gas turbine components.

  16. Joining of SiC ceramics and SiC/SiC composites

    Energy Technology Data Exchange (ETDEWEB)

    Rabin, B.H. [Idaho National Engineering Lab., Idaho Falls, ID (United States)

    1996-08-01

    This project has successfully developed a practical and reliable method for fabricating SiC ceramic-ceramic joints. This joining method will permit the use of SiC-based ceramics in a variety of elevated temperature fossil energy applications. The technique is based on a reaction bonding approach that provides joint interlayers compatible with SiC, and excellent joint mechanical properties at temperatures exceeding 1000{degrees}C. Recent emphasis has been given to technology transfer activities, and several collaborative research efforts are in progress. Investigations are focusing on applying the joining method to sintered {alpha}-SiC and fiber-reinforced SiC/SiC composites for use in applications such as heat exchangers, radiant burners and gas turbine components.

  17. Box, Line, and Midgap Plots: Effects of Display Characteristics on the Accuracy and Bias of Estimates of Whisker Length.

    Science.gov (United States)

    Stock, William A.; Behrens, John T.

    1991-01-01

    The accuracy and bias of estimates of whisker length based on box, line, and midgap plots were examined. For each type of graph, 20 different undergraduates (n=60) viewed 48 single-plot graphs. Whisker-length estimates for box and line plots were more accurate and less biased than those for midgap plots. (TJH)

  18. Magnetism in nanocrystalline SiC films

    Science.gov (United States)

    Semenov, A. V.; Pashchenko, V. O.; Khirnyi, V. F.; Kozlovskyi, A. A.; Mateichenko, P. V.

    2015-11-01

    Magnetism been studied in two series of nanocrystalline SiC films obtained by the method of direct deposition of ions with an energy of ~100 eV at temperatures 1150 °C and 1200 C. There were separated the contributions of diamagnetism, paramagnetism and superparamagnetism+ferromagnetism. Magnetization value of the films correlates with the deposition temperature. In the films deposited at higher temperatures the value of magnetization was by 1.5 times lower. It was concluded that induced magnetism in nanocrystalline SiC films is caused by interaction of magnetic moments of neutral VSiVC divacancies in separate nanocrystals. The estimated concentration of neutral VSiVC divacancies in nanocrystalline SiC films is ~1020 cm-3.

  19. High yield polycarbosilane precursors to stoichiometric SiC. Synthesis, pyrolysis and application

    Energy Technology Data Exchange (ETDEWEB)

    Interrante, L.V.; Wu, H.J. [Rensselaer Polytechnic Inst., Troy, NY (United States). Dept. of Chemistry; Whitmarsh, C.W.; Sherwood, W. [Starfire Systems, Inc., Glenville, NY (United States); Lewis, R.; Maciel, G. [Colorado State Univ., Fort Collins, CO (United States). Dept. of Chemistry

    1994-12-31

    The synthesis and properties of two polycarbosilanes that have essentially a ``SiH{sub 2}CH{sub 2}`` composition is described. One of these polymers is a highly branched hydridopolycarbosilane (HPCS) derived from Grignard coupling of Cl{sub 3}SiCH{sub 2}Cl followed by LiAlH{sub 4} reduction. This synthesis is amenable to large scale production and the authors are exploring applications of HPCS as a source of SiC coatings and its allyl-derivative, AHPCS, as a matrix source for SiC and C-fiber reinforced composites. These polymers thermoset on heating at 200--400 C (or at 100 C with a catalyst) and give near stoichiometric SiC with low O content in ca. 80% yield on pyrolysis to 1,000 C. The second method involves ring-opening polymerization of 1,1,3,3-tetrachlorodisilacyclobutane and yields a high molecular weight, linear polymer that can be reduced to [SiH{sub 2}CH{sub 2}]{sub n} (PSE), the monosilicon analog of polyethylene. In contrast to high density polyethylene which melts at 135 C, PSE is a liquid at room temperature which crystallizes at ca. 5 C. On pyrolysis to 1,000 C, PSE gives stoichiometric, nanocrystalline, SiC in virtually quantitative yield. The polymer-to-ceramic conversion was examined for PSE by using TGA, mass spec., solid state NMR, and IR methods yielding information regarding the cross-linking and structural evolution processes. The results of these studies of the polymer-to-ceramic conversion process and their efforts to employ the AHPCS polymer as a source of SiC matrices are described.

  20. Tapered ZnO Whiskers: {hkil}-Specific Mosaic Twinning VLS Growth from a Partially Molten Bottom Source

    Directory of Open Access Journals (Sweden)

    Chen Shuei-Yuan

    2009-01-01

    Full Text Available Abstract Zn particulates overlaid with wurtzite (W-type ZnO condensates having nearly orthogonal and facets were found to self-catalyze unusual tapered W-ZnO whiskers upon isothermal atmospheric annealing, i.e., thermal oxidation, at 600 °C. Analytical electron microscopic observations indicated that such whiskers formed tapered slabs having mosaic and twinned domains. The tapered whiskers can be rationalized by an alternative vapor–liquid–solid growth, i.e., {hkil}-specific coalescence twinning growth from the ZnO condensates taking advantage of a partially molten bottom source of Zn and the adsorption of atoms at the whisker tips and ledges under the influence of capillarity effect. The tapered whiskers having strong photoluminescence at 391 nm and with a considerable flexibility could have potential applications.

  1. Visual Map Shifts based on Whisker-Guided Cues in the Young Mouse Visual Cortex

    Directory of Open Access Journals (Sweden)

    Kohei Yoshitake

    2013-12-01

    Full Text Available Mice navigate nearby space using their vision and whiskers, and young mice learn to integrate these heterogeneous inputs in perceptual space. We found that cortical responses were depressed in the primary visual cortex of young mice after wearing a monocular prism. This depression was uniformly observed in the primary visual cortex and was eliminated by whisker trimming or lesions in the posterior parietal cortex. Compensatory visual map shifts of responses elicited via the eye that had worn the prism were also observed. As a result, cortical responses elicited via each eye were clearly separated when a visual stimulus was placed in front of the mice. A comparison of response areas before and after prism wearing indicated that the map shifts were produced by depression with spatial eccentricity. Visual map shifts based on whisker-guided cues may serve as a model for investigating the cellular and molecular mechanisms underlying higher sensory integration in the mammalian brain.

  2. Whisker-mediated transformation of peanut with chitinase gene enhances resistance to leaf spot disease

    Directory of Open Access Journals (Sweden)

    Mahmood ul Hassan

    2016-07-01

    Full Text Available Peanut (Arachis hypogaea is an important legume and oilseed crop, native to South America and grown in all tropical and temperate regions of the world. A simplified and rapid direct gene delivery system in peanut was developed by vortexing silicon carbide whiskers with callus and with plasmid harboring chitinase and hygromcin genes. The effects of callus age and whisker quantity on transformation efficiency were evaluated. Transformation efficiency (6.88% was highest when 200 mg of whiskers were used with 5 µg plasmid for 2 g of 20-day-old callus. Hygromcin-resistant calli were regenerated to complete plants which produced seeds normally. Transgene insertion and number of transgene copieswere confirmed by PCR and southern blot analyses, respectively. Transgene expression was evaluated by a pathogenecity test and RT-PCR analysis. In transgenic events, the resistance level to leaf spot disease was far higher than in control plants.

  3. Variation in plumage, molt, and morphology of the Whiskered Auklet (Aethia pygmaea) in Alaska

    Science.gov (United States)

    Pitocchelli, Jay; Piatt, John F.; Carter, Harry R.

    2003-01-01

    We studied molt and size variation in Whiskered Auklets collected at sea in August from the Aleutian Islands in 1992 and 1993. We evaluated size differences from external and skeletal measurements. Adults were molting extensively in August, indicating that molt began in July. Primaries 1-5 had been completely replaced, while primaries 6-8 were in various stages of replacement, and primaries 9 and 10 were old in most birds. We also found that juveniles were not molting. This pattern is similar to other species of small auklets where breeding and molt in adults overlap, but juveniles do not molt until the following summer. This suggests that Whiskered Auklets are subjected to similar ecological constraints as other auklets. We provide the first skeletal measurements of Whiskered Auklets and some new external measurements. Results of statistical analyses indicate that there is no sexual dimorphism in adults. A small sample of juveniles suggests that they are similar in size to adults.

  4. Stability to irradiation of SiGe whisker crystals used for sensors of physical values

    Directory of Open Access Journals (Sweden)

    Druzhinin A. A.

    2011-04-01

    Full Text Available An influence of g-irradiation (Co60 with doze up to 1—1018 сm–2 and magnetic field with induction up to 14 T on conduction of 1–xGex (х = 0,03 whisker crystals with resistivity of 0,08—0,025 Оhm·сm in temperature range 4,2—300 K have been studied. It is shown that whisker crystals resistance faintly varies under irradiation with doze 2·1017 сm–2, while their magnetoresistance substantially changes. The strain sensors stable to irradiation action operating in high magnetic fields on the base of the whiskers have been designed.

  5. Estudio de la reactividad entre aleaciones de aluminio y partículas de SiC

    Directory of Open Access Journals (Sweden)

    Ureña, A.

    2000-04-01

    Full Text Available The SiC reinforcement particles react with the molten aluminium to form Al4C3 that is brittle and sensitive to the the humidity. This reaction degrades the properties of the SiC reinforced aluminium matrix composites. The extend of the reaction in the Al/SiC interface depends on the fabrication parameters such as the temperature, residence time, atmosphere and chemical composition of the aluminium matrix and the reinforcement. Systematic studies on the reactivity between the SiC particles and molten aluminium alloys have been performed, analysing the effect of the presence of a SiO2 layer, which was formed by oxidation on the ceramic particles before their incorporation into the melt, as a protective barrier for preventing the attack of the SiC. As well, the effect of the metal matrix composition on the interfacial reactivity has been studied employing different aluminium alloys: AA1070 (99,7% Al, A-319.0 (Al-6Si-3Cu and A-332.0 (Al-11Si-1,5Cu. The composites were prepared by mixture of SiC particles (30 % vol. %, cold pressure and fusion at 900 ºC, varying the residence time in the furnace, which simulated a cast fabrication process. The results are compared with those obtained for a metal matrix composite (AA2014/SiC/13p.

    Las partículas de refuerzo de SiC reaccionan con el aluminio fundido y forman Al4C3 que es frágil y sensible al contacto con la humedad, lo que degrada las propiedades de los materiales compuestos constituidos por ambos componentes. La reacción en la intercara Al/SiC depende de varios parámetros de fabricación como temperatura, tiempo de residencia, atmósfera y composición química, tanto de la matriz de aluminio como del refuerzo de SiC. Se han realizado estudios sistemáticos de reactividad entre partículas de SiC y aluminio fundido, analizando el efecto que tiene la formación de una capa de SiO2 por oxidación de las partículas cerámicas, antes de su incorporación en el fundido, como barrera protectora

  6. Prospects for SiC electronics and sensors

    OpenAIRE

    Nick G. Wright; Alton B. Horsfall; Vassilevski, Konstantin

    2008-01-01

    There has been substantial international research effort in the development of SiC electronics over the last ten years. With promising applications in power electronics, hostile-environment electronics, and sensors, there is considerable industrial interest in SiC as a material for electronics. However, issues relating to crystal growth and the difficulties of material processing have restricted SiC devices to relatively limited use to date. The eventual success of SiC as an electronic techno...

  7. The 'whisker sign' as an indicator of ochronosis in skeletal scintigraphy

    Energy Technology Data Exchange (ETDEWEB)

    Paul, R.; Ylinen, S.L. (Turku Univ. (Finland). Dept. of Nuclear Medicine)

    1991-03-01

    A patient with alkaptonuria and ochronotic arthrosis was imaged twice with ({sup 99m}Tc-DPD) - once during a bout of arthritic knee pain and once when symptom-free. There was a marked accumulation of radioactivity in the large joints. During the episode of arthritis the knee joints had a higher uptake than when the patient was without symptoms. The intervertebral discs showed a high uptake which extended laterally from the axial vertebral column; the finding gave an impression of whiskers, and this 'whisker sign' may be characteristic of ochronosis. (orig.).

  8. Universal Converter Using SiC

    Energy Technology Data Exchange (ETDEWEB)

    Dallas Marckx; Brian Ratliff; Amit Jain; Matthew Jones

    2007-01-01

    The grantee designed a high power (over 1MW) inverter for use in renewable and distributed energy systems, such as PV cells, fuel cells, variable speed wind turbines, micro turbines, variable speed gensets and various energy storage methods. The inverter uses 10,000V SiC power devices which enable the use of a straight-forward topology for medium voltage (4,160VAC) without the need to cascade devices or topologies as is done in all commercial, 4,160VAC inverters today. The use of medium voltage reduces the current by nearly an order of magnitude in all current carrying components of the energy system, thus reducing size and cost. The use of SiC not only enables medium voltage, but also the use of higher temperatures and switching frequencies, further reducing size and cost. In this project, the grantee addressed several technical issues that stand in the way of success. The two primary issues addressed are the determination of real heat losses in candidate SiC devices at elevated temperature and the development of high temperature packaging for SiC devices.

  9. 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

  10. Reaction-bonded Si3N4 and SiC matrix composites

    Science.gov (United States)

    Bhatt, Ramakrishna T.; Behrendt, Donald R.

    1992-01-01

    A development status evaluation is presented for the reaction-bonded SiC- and Si3N4-matrix types of fiber-reinforced ceramic-matrix composite (FRCMC). A variety of reaction-bonding methods are being pursued for FRCMC fabrication: CVI, CVD, directed metal oxidation, and self-propagating high-temperature synthesis. Due to their high specific modulus and strength, toughness, and fabricability, reaction-bonded FRCMC are important candidate materials for such heat-engine components as combustor liners, nozzles, and turbine and stator blading. The improvement of long-term oxidative stability in these composites is a major goal of current research.

  11. Technique for measuring irradiation creep in polycrystalline SiC fibers

    Energy Technology Data Exchange (ETDEWEB)

    Youngblood, G.E.; Hamilton, M.L.; Jones, R.H. [Pacific Northwest National Lab., Richland, WA (United States)

    1996-10-01

    A bend stress relaxation (BSR) test has been designed to examine irradiation enhanced creep in polycrystalline SiC fibers being considered for fiber reinforcement in SiC/SiC composite. Thermal creep results on Nicalon-CG and Hi-Nicalon were shown to be consistent with previously published data with Hi-Nicalon showing about a 100{degrees}C improvement in creep resistance. Preliminary data was also obtained on Nicalon-S that demonstrated that its creep resistance is greater than that of Hi-Nicalon.

  12. Structure of MMCs with SiC Particles after Gas-tungsten Arc Welding

    Directory of Open Access Journals (Sweden)

    Przełożyńska E.

    2015-12-01

    Full Text Available The gas-tungsten arc (GTA welding behaviors of a magnesium matrix composite reinforced with SiC particles were examined in terms of microstructure characteristics and process efficiencies. This study focused on the effects of the GTAW process parameters (like welding current in the range of 100/200 A on the size of the fusion zone (FZ. The analyses revealed the strong influence of the GTA welding process on the width and depth of the fusion zone and also on the refinement of the microstructure in the fusion zone. Additionally, the results of dendrite arm size (DAS measurements were presented.

  13. Enhanced tensile, hardness and wear behaviors of pure aluminum matrix reinforced with steel chips via powder metallurgy technique

    Science.gov (United States)

    Mahmoud Emara, Mohamed

    2017-04-01

    The mechanical properties and wear behavior of aluminum matrix reinforced with steel machining chips was investigated. Pure aluminum was reinforced with 5, 7.5, and 10 wt% steel chips with an average size of 100 μm using powder metallurgy technique. Aluminum reinforced with 5 and 10 Wt.% SiC particles were manufactured for comparison. The investigation showed clear evidence that the addition of steel machining chips resulted in significantly low porosity levels in the aluminum matrix composites compared with the use of SiC as reinforcement. The mechanical properties (tensile and hardness) as well as the wear resistance were also observed to improve with the use of the steel machining chips as reinforcement. The results demonstrate the capability of steel machining chips to act as efficient reinforcing material and a reliable cost effective candidate in the development of aluminum matrix composites.

  14. An organometallic route to micron-sized whiskers of zinc sulfide

    Science.gov (United States)

    Czekaj, C. L.; Rau, M. S.; Geoffroy, G. L.; Guiton, T. A.; Pantano, C. G.

    1988-06-01

    A number of technologies require the development of high performance optical materials that also meet stringent specifications of optical transparency and thermal, chemical, and mechanical properties. For example, an infrared transmitting window material should have low thermal expansion, high melting and decomposition temperatures, chemical inertness to hydrolysis and oxidation, and high fracture toughness. One of the most attractive materials for many infrared optical applications is Zinc sulfide, but this material, as presently fabricated, does not process the required mechanical properties. One approach to improving the mechanical properties of a material is to form a self-similar composite, in this case, ZnS whiskers in polycrystalline ZnS matrix. To fabricate IR transmitting ZnS/ZnS composites, it would be necessary to use micron-sized whiskers of ZnS that have length to width ratios (aspect ratios) greater than 10. No present methodology exists for the convenient, large-scale preparation of such whiskers, although larger single crystals and whiskers of ZnS have been made by a variety of high temperature (less than 900 C), generally vapor-phase, routes.

  15. Adjustable tunneling barrier in bi-based high-Tc cross-whisker junctions

    Science.gov (United States)

    Kizilaslan, O.; Simsek, Y.; Aksan, M. A.; Koval, Y.; Yakinci, M. E.; Müller, P.

    2015-02-01

    We present a study of cross-whisker junctions with electronically modified tunneling barriers. Cross-whisker junctions were successfully prepared by annealing two crossed Bi-based whisker bars at temperatures of around 840 °C. In addition to the artificially produced junction at the interface, intrinsic Josephson junctions in the respective bars of the cross were observed. The artificial junction exhibited reproducible and almost ideal junction characteristics. The tunneling barrier/interface properties were controlled by carrier injection in c-axis direction. Using this process, we were able to reduce the tunneling resistance from 408 Ω to 30 Ω. At the same time, the critical current did rise by a factor of 4. Subsequently, the critical current was doubled while the tunneling resistance stayed constant. We interpret this observation in terms of the counter-play between transparency of the barrier and the carrier concentration of the electrodes. In this sense, we can consider the current injection procedure as an electronic gluing process of the two cross-junction whisker bars.

  16. Parallel pathways from whisker and visual sensory cortices to distinct frontal regions of mouse neocortex.

    Science.gov (United States)

    Sreenivasan, Varun; Kyriakatos, Alexandros; Mateo, Celine; Jaeger, Dieter; Petersen, Carl C H

    2017-07-01

    The spatial organization of mouse frontal cortex is poorly understood. Here, we used voltage-sensitive dye to image electrical activity in the dorsal cortex of awake head-restrained mice. Whisker-deflection evoked the earliest sensory response in a localized region of primary somatosensory cortex and visual stimulation evoked the earliest responses in a localized region of primary visual cortex. Over the next milliseconds, the initial sensory response spread within the respective primary sensory cortex and into the surrounding higher order sensory cortices. In addition, secondary hotspots in the frontal cortex were evoked by whisker and visual stimulation, with the frontal hotspot for whisker deflection being more anterior and lateral compared to the frontal hotspot evoked by visual stimulation. Investigating axonal projections, we found that the somatosensory whisker cortex and the visual cortex directly innervated frontal cortex, with visual cortex axons innervating a region medial and posterior to the innervation from somatosensory cortex, consistent with the location of sensory responses in frontal cortex. In turn, the axonal outputs of these two frontal cortical areas innervate distinct regions of striatum, superior colliculus, and brainstem. Sensory input, therefore, appears to map onto modality-specific regions of frontal cortex, perhaps participating in distinct sensorimotor transformations, and directing distinct motor outputs.

  17. Estimating the Probability of Electrical Short Circuits from Tin Whiskers. Part 2

    Science.gov (United States)

    Courey, Karim J.; Asfour, Shihab S.; Onar, Arzu; Bayliss, Jon A.; Ludwig, Larry L.; Wright, Maria C.

    2009-01-01

    To comply with lead-free legislation, many manufacturers have converted from tin-lead to pure tin finishes of electronic components. However, pure tin finishes have a greater propensity to grow tin whiskers than tin-lead finishes. Since tin whiskers present an electrical short circuit hazard in electronic components, simulations have been developed to quantify the risk of said short circuits occurring. Existing risk simulations make the assumption that when a free tin whisker has bridged two adjacent exposed electrical conductors, the result is an electrical short circuit. This conservative assumption is made because shorting is a random event that had an unknown probability associated with it. Note however that due to contact resistance electrical shorts may not occur at lower voltage levels. In our first article we developed an empirical probability model for tin whisker shorting. In this paper, we develop a more comprehensive empirical model using a refined experiment with a larger sample size, in which we studied the effect of varying voltage on the breakdown of the contact resistance which leads to a short circuit. From the resulting data we estimated the probability distribution of an electrical short, as a function of voltage.

  18. 3D printed biomimetic whisker-based sensor with co-planar capacitive sensing

    NARCIS (Netherlands)

    Delamare, John; Sanders, Remco G.P.; Krijnen, Gijsbertus J.M.

    2016-01-01

    This paper describes the development of a whisker sensor for tactile purposes and which is fabricated by 3D printing. Read-out consists of a capacitive measurement of a co-planar capacitance which is affected by a dielectric that is driven into the electric field of the capacitance. The current

  19. Estimating the Probability of Electrical Short Circuits from Tin Whiskers. Part 2

    Science.gov (United States)

    Courey, Karim J.; Asfour, Shihab S.; Onar, Arzu; Bayliss, Jon A.; Ludwig, Larry L.; Wright, Maria C.

    2010-01-01

    To comply with lead-free legislation, many manufacturers have converted from tin-lead to pure tin finishes of electronic components. However, pure tin finishes have a greater propensity to grow tin whiskers than tin-lead finishes. Since tin whiskers present an electrical short circuit hazard in electronic components, simulations have been developed to quantify the risk of said short circuits occurring. Existing risk simulations make the assumption that when a free tin whisker has bridged two adjacent exposed electrical conductors, the result is an electrical short circuit. This conservative assumption is made because shorting is a random event that had an unknown probability associated with it. Note however that due to contact resistance electrical shorts may not occur at lower voltage levels. In our first article we developed an empirical probability model for tin whisker shorting. In this paper, we develop a more comprehensive empirical model using a refined experiment with a larger sample size, in which we studied the effect of varying voltage on the breakdown of the contact resistance which leads to a short circuit. From the resulting data we estimated the probability distribution of an electrical short, as a function of voltage. In addition, the unexpected polycrystalline structure seen in the focused ion beam (FIB) cross section in the first experiment was confirmed in this experiment using transmission electron microscopy (TEM). The FIB was also used to cross section two card guides to facilitate the measurement of the grain size of each card guide's tin plating to determine its finish .

  20. Rat whisker movement after facial nerve lesion: Evidence for autonomic contraction of skeletal muscle.

    NARCIS (Netherlands)

    Heaton, J.T.; Sheu, S.H.; Hohman, M.H.; Knox, C.J.; Weinberg, J.S.; Kleiss, I.J.; Hadlock, T.A.

    2014-01-01

    Vibrissal whisking is often employed to track facial nerve regeneration in rats; however, we have observed similar degrees of whisking recovery after facial nerve transection with or without repair. We hypothesized that the source of non-facial nerve-mediated whisker movement after chronic

  1. Validation of the Dynamic Recrystallization (DRX) Mechanism for Whisker and Hillock Growth on Sn Thin Films

    Science.gov (United States)

    Vianco, P. T.; Neilsen, M. K.; Rejent, J. A.; Grant, R. P.

    2015-10-01

    A study was performed to validate a first-principles model for whisker and hillock formation based on the cyclic dynamic recrystallization (DRX) mechanism in conjunction with long-range diffusion. The test specimens were evaporated Sn films on Si having thicknesses of 0.25 μm, 0.50 μm, 1.0 μm, 2.0 μm, and 4.9 μm. Air annealing was performed at 35°C, 60°C, 100°C, 120°C, or 150°C over a time duration of 9 days. The stresses, anelastic strains, and strain rates in the Sn films were predicted by a computational model based upon the constitutive properties of 95.5Sn-3.9Ag-0.6Cu (wt.%) as a surrogate for pure Sn. The cyclic DRX mechanism and, in particular, whether long whiskers or hillocks were formed, was validated by comparing the empirical data against the three hierarchal requirements: (1) DRX to occur at all: ɛc = A D o m Z n , (2) DRX to be cyclic: D o tensile stress-driven diffusion mechanism, confirmed the pervasiveness of long-range diffusion so that it did not control whisker or hillock formation other than a small loss of activity by reduced thermal activation at lower temperatures. A first-principles DRX model paves the way to develop like mitigation strategies against long whisker growth.

  2. High-temperature pressure sensors with strain gauges based on silicon whiskers

    OpenAIRE

    Druzhinin A. A.; Kutrakov A. P.; Maryamova I. I.

    2012-01-01

    Studies aimed at the creating of piezoresistive pressure sensors based on silicon whiskers, operating at high temperatures were carried out. Using the glass adhesive for strain gauges mounting on spring elements of covar alloy gave the possibility to elevate the sensor’s operating temperature range. Several modifications of pressure sensors based on the proposed strain-unit design were developed.

  3. High-temperature pressure sensors with strain gauges based on silicon whiskers

    Directory of Open Access Journals (Sweden)

    Druzhinin A. A.

    2012-12-01

    Full Text Available Studies aimed at the creating of piezoresistive pressure sensors based on silicon whiskers, operating at high temperatures were carried out. Using the glass adhesive for strain gauges mounting on spring elements of covar alloy gave the possibility to elevate the sensor’s operating temperature range. Several modifications of pressure sensors based on the proposed strain-unit design were developed.

  4. Effect Of SiC Particles On Sinterability Of Al-Zn-Mg-Cu P/M Alloy

    Directory of Open Access Journals (Sweden)

    Rudianto H.

    2015-06-01

    Full Text Available Premix Al-5.5Zn-2.5Mg-0.5Cu alloy powder was analyzed as matrix in this research. Gas atomized powder Al-9Si with 20% volume fraction of SiC particles was used as reinforcement and added into the alloy with varied concentration. Mix powders were compacted by dual action press with compaction pressure of 700 MPa. High volume fraction of SiC particles gave lower green density due to resistance of SiC particles to plastic deformation during compaction process and resulted voids between particles and this might reduce sinterability of this mix powder. Sintering was carried out under ultra high purity nitrogen gas from 565°-580°C for 1 hour. High content of premix Al-5.5Zn-2.5Mg-0.5Cu alloy powder gave better sintering density and reached up to 98% relative. Void between particles, oxide layer on aluminum powder and lower wettability between matrix and reinforcement particles lead to uncompleted liquid phase sintering, and resulted on lower sintering density and mechanical properties on powder with high content of SiC particles. Mix powder with wt90% of Alumix 431D and wt10% of Al-9Si-vf20SiC powder gave higher tensile strength compare to another mix powder for 270 MPa. From chemical compositions, sintering precipitates might form after sintering such as MgZn2, CuAl2 and Mg2Si. X-ray diffraction, DSC-TGA, and SEM were used to characterize these materials.

  5. Fiber/matrix interfaces for SiC/SiC composites: Multilayer SiC coatings

    Energy Technology Data Exchange (ETDEWEB)

    Halverson, H.; Curtin, W.A. [Virginia Polytechnic Institute and State Univ., Blacksburg, VA (United States)

    1996-08-01

    Tensile tests have been performed on composites of CVI SiC matrix reinforced with 2-d Nicalon fiber cloth, with either pyrolitic carbon or multilayer CVD SiC coatings [Hypertherm High-Temperature Composites Inc., Huntington Beach, CA.] on the fibers. To investigate the role played by the different interfaces, several types of measurements are made on each sample: (i) unload-reload hysteresis loops, and (ii) acoustic emission. The pyrolitic carbon and multilayer SiC coated materials are remarkably similar in overall mechanical responses. These results demonstrate that low-modulus, or compliant, interface coatings are not necessary for good composite performance, and that complex, hierarchical coating structures may possibly yield enhanced high-temperature performance. Analysis of the unload/reload hysteresis loops also indicates that the usual {open_quotes}proportional limit{close_quotes} stress is actually slightly below the stress at which the 0{degrees} load-bearing fibers/matrix interfaces slide and are exposed to atmosphere.

  6. Vacancies in SiC nanopowders

    Energy Technology Data Exchange (ETDEWEB)

    Kityk, I.V.; Makowska-Janusik, M. [Technical Univ. of Czestochowa (Poland). Inst. of Phys.; Kassiba, A.; Charpentier, C. [Laboratoire de Physique de l' Etat Condense, UPRES-A6087, Universite du Maine, Avenue Olivier Messiaen, 72085 Cedex 9, LeMans (France); Tuesu, K. [Research Informatic Science Department, Tohoku University, 2-1-4 Katahira, Aoba-ku, 982-12, Sendai (Japan); Ling, Y. [Michigan Molecular Institute, 48640, Midland, MI (United States)

    2000-08-31

    Origin of vacancies in the large-sized SiC nanocrystals (higher than 10 nm) has been investigated using theoretical band structure calculations and experimental electronic paramagnetic resonance (EPR) measurements. Influence of geometry sizes on appearance of concrete vacancy has been studied. The theoretical approach includes self-consistent norm-conserving pseudopotential band energy calculations and geometry structure optimisation. The performed calculations show that the presence of the vacancies is a necessary attribute of the SiC nanocrystallites. Moreover, the type and concentration of the vacancies are dependent on the nanoparticle geometry. We have revealed that spin-polarised states of intracrystallite vacancies differ essentially from vacancies in the bulk crystals. A comparison between the performed theoretical simulations and obtained EPR experimental data shows the possibility of using the proposed methods for prediction of vacancy appearance in the binary nanocrystallites and possibility for their operation. (orig.)

  7. ZnO whiskers and belts in chestnut husk-like structures: synthesis and proof of chemomechanical transduction.

    Science.gov (United States)

    Alessandri, Ivano; Bergese, Paolo; Depero, Laura E

    2009-02-01

    The preparation of chestnut husk-like ZnO starting from Zn powders is described, pointing out the role of ZnO(1-x) seeds in the self-catalytic liquid-solid growth process. The final architecture is made up of ZnO whiskers stemming from ZnO platelets which are self-assembled into spheroidal agglomerates. Whiskers can be converted into belts by using polyvinylpyrrolidone and configurations exhibiting whiskers and belts on the same husk are obtained through a sequential growth procedure. Polystyrene microspheres are employed in Raman microscopy proof of concept experiments to demonstrate the potential of ZnO whiskers in transduction of chemomechanical interactions, which opens promising perspectives for in-vivo bioapplications.

  8. Fabrication and properties of aluminum silicate fibrous materials with in situ synthesized K2Ti6O13 whiskers

    Science.gov (United States)

    Liu, Hao; Wei, Nan; Wang, Zhou-fu; Wang, Xi-tang; Ma, Yan

    2017-11-01

    To improve their mechanical and thermal insulation properties, aluminum silicate fibrous materials with in situ synthesized K2Ti6O13 whiskers were prepared by firing a mixture of short aluminum silicate fibers and gel powders obtained from a sol-gel process. During the preparation process, the fiber surface was coated with K2Ti6O13 whiskers after the fibers were subjected to a heat treatment carried out at various temperatures. The effects of process parameters on the microstructure, compressive strength, and thermal conductivity were analyzed systematically. The results show that higher treatment temperatures and longer treatment durations promoted the development of K2Ti6O13 whiskers on the surface of aluminum silicate fibers; in addition, the intersection structure between whiskers modulated the morphology and volume of the multi-aperture structure among fibers, substantially increasing the fibers' compressive strength and reducing their heat conduction and convective heat transfer at high temperatures.

  9. Pós de Al2O3/SiC obtidos a partir de reação de redução carbotérmica Al2O3/SiC powders from carbothermal reduction reaction

    Directory of Open Access Journals (Sweden)

    F. M. Spiandorello

    1999-12-01

    Full Text Available Neste trabalho foram utilizadas matérias-primas naturais para a obtenção de pós Al2O3/SiC através da redução carbotérmica das mesmas por um agente rico em carbono. Os aluminossilicatos estudados foram caulim, cianita e ilita-moscovita, sendo que os mesmos foram reduzidos ou por negro de fumo ou por grafite. Os pós resultantes da reação foram caracterizados por microscopia eletrônica de varredura e transmissão, difração de raios X e picnometria de hélio. Durante a reação, as diferenças existentes tanto na estrutura das matérias-primas quanto na composição química produziram pós com morfologia diversa. Foram encontradas estruturas como grandes aglomerados esféricos, whiskers, partículas e aglomerados fibrosos.In this work natural raw materials were used to obtain Al2O3/SiC powders by carbothermal reduction. The aluminosilicates studied were kaolin, kyanite and illite-muscovite and the reductor agents were carbon black or graphite. The reaction powders were characterized by transmission and scanning electron microscopy, X-ray diffraction and helium picnometry. During the reaction, the differences among the raw materials structures as well as into the chemical composition produced powders with several morphologies. Big spherical agglomerates, whiskers, particles and fibrous clusters were found.

  10. Neural Computation via Neural Geometry: A Place Code for Inter-whisker Timing in the Barrel Cortex?

    Science.gov (United States)

    Wilson, Stuart P.; Bednar, James A.; Prescott, Tony J.; Mitchinson, Ben

    2011-01-01

    The place theory proposed by Jeffress (1948) is still the dominant model of how the brain represents the movement of sensory stimuli between sensory receptors. According to the place theory, delays in signalling between neurons, dependent on the distances between them, compensate for time differences in the stimulation of sensory receptors. Hence the location of neurons, activated by the coincident arrival of multiple signals, reports the stimulus movement velocity. Despite its generality, most evidence for the place theory has been provided by studies of the auditory system of auditory specialists like the barn owl, but in the study of mammalian auditory systems the evidence is inconclusive. We ask to what extent the somatosensory systems of tactile specialists like rats and mice use distance dependent delays between neurons to compute the motion of tactile stimuli between the facial whiskers (or ‘vibrissae’). We present a model in which synaptic inputs evoked by whisker deflections arrive at neurons in layer 2/3 (L2/3) somatosensory ‘barrel’ cortex at different times. The timing of synaptic inputs to each neuron depends on its location relative to sources of input in layer 4 (L4) that represent stimulation of each whisker. Constrained by the geometry and timing of projections from L4 to L2/3, the model can account for a range of experimentally measured responses to two-whisker stimuli. Consistent with that data, responses of model neurons located between the barrels to paired stimulation of two whiskers are greater than the sum of the responses to either whisker input alone. The model predicts that for neurons located closer to either barrel these supralinear responses are tuned for longer inter-whisker stimulation intervals, yielding a topographic map for the inter-whisker deflection interval across the surface of L2/3. This map constitutes a neural place code for the relative timing of sensory stimuli. PMID:22022245

  11. Neural computation via neural geometry: a place code for inter-whisker timing in the barrel cortex?

    Directory of Open Access Journals (Sweden)

    Stuart P Wilson

    2011-10-01

    Full Text Available The place theory proposed by Jeffress (1948 is still the dominant model of how the brain represents the movement of sensory stimuli between sensory receptors. According to the place theory, delays in signalling between neurons, dependent on the distances between them, compensate for time differences in the stimulation of sensory receptors. Hence the location of neurons, activated by the coincident arrival of multiple signals, reports the stimulus movement velocity. Despite its generality, most evidence for the place theory has been provided by studies of the auditory system of auditory specialists like the barn owl, but in the study of mammalian auditory systems the evidence is inconclusive. We ask to what extent the somatosensory systems of tactile specialists like rats and mice use distance dependent delays between neurons to compute the motion of tactile stimuli between the facial whiskers (or 'vibrissae'. We present a model in which synaptic inputs evoked by whisker deflections arrive at neurons in layer 2/3 (L2/3 somatosensory 'barrel' cortex at different times. The timing of synaptic inputs to each neuron depends on its location relative to sources of input in layer 4 (L4 that represent stimulation of each whisker. Constrained by the geometry and timing of projections from L4 to L2/3, the model can account for a range of experimentally measured responses to two-whisker stimuli. Consistent with that data, responses of model neurons located between the barrels to paired stimulation of two whiskers are greater than the sum of the responses to either whisker input alone. The model predicts that for neurons located closer to either barrel these supralinear responses are tuned for longer inter-whisker stimulation intervals, yielding a topographic map for the inter-whisker deflection interval across the surface of L2/3. This map constitutes a neural place code for the relative timing of sensory stimuli.

  12. Response properties of whisker-associated primary afferent neurons following infraorbital nerve transection with microsurgical repair in adult rats

    OpenAIRE

    Xiao, Bo; Zanoun, Rami R.; Carvell, George E.; Simons, Daniel J.; Washington, Kia M.

    2016-01-01

    The rodent whisker/trigeminal system, characterized by high spatial and temporal resolution, provides an experimental model for developing new therapies for improving sensory functions of damaged peripheral nerves. Here, we use controlled whisker stimulation and single-unit recordings of trigeminal ganglion cells to examine in detail the nature and time course of functional recovery of mechanoreceptive afferents following nerve transection with microsurgical repair of the infraorbital nerve (...

  13. Neonatal Whisker Trimming Impairs Fear/Anxiety-Related Emotional Systems of the Amygdala and Social Behaviors in Adult Mice.

    Directory of Open Access Journals (Sweden)

    Hitomi Soumiya

    Full Text Available Abnormalities in tactile perception, such as sensory defensiveness, are common features in autism spectrum disorder (ASD. While not a diagnostic criterion for ASD, deficits in tactile perception contribute to the observed lack of social communication skills. However, the influence of tactile perception deficits on the development of social behaviors remains uncertain, as do the effects on neuronal circuits related to the emotional regulation of social interactions. In neonatal rodents, whiskers are the most important tactile apparatus, so bilateral whisker trimming is used as a model of early tactile deprivation. To address the influence of tactile deprivation on adult behavior, we performed bilateral whisker trimming in mice for 10 days after birth (BWT10 mice and examined social behaviors, tactile discrimination, and c-Fos expression, a marker of neural activation, in adults after full whisker regrowth. Adult BWT10 mice exhibited significantly shorter crossable distances in the gap-crossing test than age-matched controls, indicating persistent deficits in whisker-dependent tactile perception. In contrast to controls, BWT10 mice exhibited no preference for the social compartment containing a conspecific in the three-chamber test. Furthermore, the development of amygdala circuitry was severely affected in BWT10 mice. Based on the c-Fos expression pattern, hyperactivity was found in BWT10 amygdala circuits for processing fear/anxiety-related responses to height stress but not in circuits for processing reward stimuli during whisker-dependent cued learning. These results demonstrate that neonatal whisker trimming and concomitant whisker-dependent tactile discrimination impairment severely disturbs the development of amygdala-dependent emotional regulation.

  14. Long-Term Extensive Ectopic Hair Growth on the Spinal Cord of Mice from Transplanted Whisker Follicles.

    Directory of Open Access Journals (Sweden)

    Wenluo Cao

    Full Text Available We have previously demonstrated that hair follicles contain nestin-expressing pluripotent stem cells that can effect nerve and spinal cord repair upon transplantation. In the present study, isolated whisker follicles from nestin-driven green fluorescent protein (ND-GFP mice were histocultured on Gelfoam for 3 weeks for the purpose of transplantation to the spinal cord to heal an induced injury. The hair shaft was cut off from Gelfoam-histocultured whisker follicles, and the remaining part of the whisker follicles containing GFP-nestin expressing pluripotent stem cells were transplanted into the injured spinal cord of nude mice, along with the Gelfoam. After 90 days, the mice were sacrificed and the spinal cord lesion was observed to have healed. ND-GFP expression was intense at the healed area of the spinal cord, as observed by fluorescence microscopy, demonstrating that the hair follicle stem cells were involved in healing the spinal cord. Unexpectedly, the transplanted whisker follicles sprouted out remarkably long hair shafts in the spinal cord during the 90 days after transplantation of Gelfoam whisker histocultures to the injured spine. The pigmented hair fibers, grown from the transplanted whisker histocultures, curved and enclosed the spinal cord. The unanticipated results demonstrate the great potential of hair growth after transplantation of Gelfoam hair follicle histocultures, even at an ectopic site.

  15. SiC Power MOSFET with Improved Gate Dielectric

    Energy Technology Data Exchange (ETDEWEB)

    Sbrockey, Nick M; Tompa, Gary S; Spencer, Michael G; Chandrashekhar, Chandra MVS

    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.

  16. 500?C SiC JFET Driver Circuits and Packaging Project

    Data.gov (United States)

    National Aeronautics and Space Administration — In the proposed development, SiC JFET control circuitry and normally-off SiC JFET power switch will be integrated in a single SiC chip that will provide digital...

  17. Cryptic mammalian species: a new species of whiskered bat (Myotis alcathoe n. sp.) in Europe

    Science.gov (United States)

    von Helversen, O.; Heller, K.-G.; Mayer, F.; Nemeth, A.; Volleth, M.; Gombkötö, P.

    2001-05-01

    The analysis of morphological, behavioural and genetic characters of whiskered bats revealed a new European bat species within the family Vespertilionidae. We describe the morphology, karyology, genetic similarity, ecology and distribution of Myotis alcathoe n. sp. It closely resembles Myotis mystacinus, Myotis brandtii and Myotis ikonnikovi in morphology, but all four species show clear genetic differences in two mitochondrial genes (ND1 and 12S rRNA). Myotis alcathoe n. sp. is the smallest species among the European whiskered bats and uses the highest-frequency echolocation calls of all the European Myotis species. It prefers to hunt in small valleys with deciduous trees and flowing water, which is an endangered habitat. Records from Greece and Hungary indicate a distribution range in south-eastern Europe.

  18. Rat Whisker Movement after Facial Nerve Lesion: Evidence for Autonomic Contraction of Skeletal Muscle

    OpenAIRE

    Heaton, James T.; Sheu, Shu-Hsien; Hohman, Marc H.; Knox, Christopher J.; Weinberg, Julie S.; Kleiss, Ingrid J.; Hadlock, Tessa A.

    2014-01-01

    Vibrissal whisking is often employed to track facial nerve regeneration in rats; however, we have observed similar degrees of whisking recovery after facial nerve transection with or without repair. We hypothesized that the source of non-facial nerve-mediated whisker movement after chronic denervation was from autonomic, cholinergic axons traveling within the infraorbital branch of the trigeminal nerve (ION). Rats underwent unilateral facial nerve transection with repair (N=7) or resection wi...

  19. The peripheral and central changes resulting from cutting or crushing the afferent nerve supply to the whiskers.

    Science.gov (United States)

    Waite, P M; Cragg, B G

    1982-01-22

    In neonatal rats, crushing or cutting the infraorbital nerve, the sensory nerve supply to the whiskers, has been found to prevent cortical barrel formation. However, both procedures are followed by regeneration of one-third to one-half of the nerve fibres and reinnervation of the whiskers. By counting fibres in individual whisker follicle nerves, it has been shown that 29-67% (mean 45%) of the myelinated fibres regenerate to the whiskers after a crush compared to 24-56% (mean 39%) after a cut. Further differences between the crush and cut lesions were indicated by studies on the time course of regeneration. Counts of the regenerating fibres at various ages as well as recordings of cortical evoked potentials in normal, nerve-crushed and nerve-cut animals showed that recovery was 3-4 days earlier in the nerve-crushed, compared with the nerve-cut animals. In normal and nerve-crushed animals the evoked potential was first detectable 2-3 days after birth while the response after nerve cut could not be recorded until day 7. Even after 60 days the amplitude of responses on both crushed and cut pathways was only about one-third of normal, while the latency was prolonged (normal 5.8 +/- 0.25 ms, crush 6.5 +/- 0.26 ms, cut 7.7 +/- 0.67 ms). Central changes occurring as a result of nerve cut or crush have been studied by microelectrode recordings from the trigeminal nucleus (the first synaptic level) and the somatosensory cortex. These also indicate clearly the greater severity of the cut lesion. Thus, in crushed animals, all levels of the trigeminal nucleus as well as the cortex show only minor modifications. The whiskers occupy the same total area and responses from all whiskers are present at their normal sites. However, after nerve cut, the responses from both the trigeminal nucleus and cortex show clear abnormalities. The total whisker area is reduced with a concomitant expansion of responses from the nose, check, lower jaw, and whiskers by the eye and ear. In addition

  20. REINFORCED COMPOSITE PANEL

    DEFF Research Database (Denmark)

    2003-01-01

    A composite panel having front and back faces, the panel comprising facing reinforcement, backing reinforcement and matrix material binding to the facing and backing reinforcements, the facing and backing reinforcements each independently comprising one or more reinforcing sheets, the facing...... by matrix material, the facing and backing reinforcements being interconnected to resist out-of-plane relative movement. The reinforced composite panel is useful as a barrier element for shielding structures, equipment and personnel from blast and/or ballistic impact damage....

  1. Zinc oxide crystal whiskers as a novel sorbent for solid-phase extraction of flavonoids.

    Science.gov (United States)

    Wang, Licheng; Shangguan, Yangnan; Hou, Xiudan; Jia, Yong; Liu, Shujuan; Sun, Yingxin; Guo, Yong

    2017-08-15

    As a novel solid-phase extraction material, zinc oxide crystal whiskers were used to extract flavonoid compounds and showed good extraction abilities. X-ray diffraction, scanning electron microscopy with energy dispersive X-ray spectroscopy and surface area/pore volume characterized the sorbent. The zinc oxide was packed into a solid-phase extraction micro-column and its extraction ability was evaluated by four model flavonoid compounds. The sample loading and elution parameters were optimized and the zinc oxide based analytical method for flavonoids was established. It showed that the method has wide linearities from 1 to 150μg/L and low limits of detection at 0.25μg/L. The relative standard deviations of a single column repeatability and column to column reproducibility were less than 6.8% and 10.6%. Several real samples were analyzed by the established method and satisfactory results were obtained. The interactions between flavonoids and zinc oxide were calculated and proved to be from the Van der Waals' forces between the 4p and 5d orbitals from zinc atom and the neighboring π orbitals from flavonoid phenyl groups. Moreover, the zinc oxide crystal whiskers showed good stability and could be reused more than 50 times under the operation conditions. This work proves that the zinc oxide crystal whiskers are a good candidate for flavonoids enrichment. Copyright © 2017. Published by Elsevier B.V.

  2. Electron Spectroscopy Study of SiC,

    Science.gov (United States)

    1983-09-01

    Liquid nitrogen cooling is supplied to the central copper block of the sample holder by flexible spiral stainless steel capillary. This cooling facility...sapphire disks from thinner copper blocks at both sides. The outer copper blocks hold 1.5 mm diameter W rods to which are welded a pair of 0.375 mm...sputtering was sufficient to implant F+ and Ar+ ions deep enough in the SiC surface layer, so that the implanted F and Ar could not be removed-by thermal

  3. Mechanical properties of SiC composites neutron irradiated under light water reactor relevant temperature and dose conditions

    Science.gov (United States)

    Koyanagi, Takaaki; Katoh, Yutai

    2017-10-01

    Silicon carbide (SiC) fiber-reinforced SiC matrix (SiC/SiC) composites are being actively investigated for use in accident-tolerant core structures of light water reactors (LWRs). Owing to the limited number of irradiation studies previously conducted at LWR-coolant temperature, this study examined SiC/SiC composites following neutron irradiation at 230-340 °C to 2.0 and 11.8 dpa in the High Flux Isotope Reactor. The investigated materials were chemical vapor infiltrated (CVI) SiC/SiC composites with three different reinforcement fibers. The fiber materials were monolayer pyrolytic carbon (PyC) -coated Hi-Nicalon™ Type-S (HNS), Tyranno™ SA3 (SA3), and SCS-Ultra™ (SCS) SiC fibers. The irradiation resistance of these composites was investigated based on flexural behavior, dynamic Young's modulus, swelling, and microstructures. There was no notable mechanical properties degradation of the irradiated HNS and SA3 SiC/SiC composites except for reduction of the Young's moduli by up to 18%. The microstructural stability of these composites supported the absence of degradation. In addition, no progressive swelling from 2.0 to 11.8 dpa was confirmed for these composites. On the other hand, the SCS composite showed significant mechanical degradation associated with cracking within the fiber. This study determined that SiC/SiC composites with HNS or SA3 SiC/SiC fibers, a PyC interphase, and a CVI SiC matrix retain their properties beyond the lifetime dose for LWR fuel cladding at the relevant temperature.

  4. 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...

  5. Support for the slip hypothesis from whisker-related tactile perception of rats in a noisy environment

    Science.gov (United States)

    Waiblinger, Christian; Brugger, Dominik; Whitmire, Clarissa J.; Stanley, Garrett B.; Schwarz, Cornelius

    2015-01-01

    Rodents use active whisker movements to explore their environment. The “slip hypothesis” of whisker-related tactile perception entails that short-lived kinematic events (abrupt whisker movements, called “slips”, due to bioelastic whisker properties that occur during active touch of textures) carry the decisive texture information. Supporting this hypothesis, previous studies have shown that slip amplitude and frequency occur in a texture-dependent way. Further, experiments employing passive pulsatile whisker deflections revealed that perceptual performance based on pulse kinematics (i.e., signatures that resemble slips) is far superior to the one based on time-integrated variables like frequency and intensity. So far, pulsatile stimuli were employed in a noise free environment. However, the realistic scenario involves background noise (e.g., evoked by rubbing across the texture). Therefore, if slips are used for tactile perception, the tactile neuronal system would need to differentiate slip-evoked spikes from those evoked by noise. To test the animals under these more realistic conditions, we presented passive whisker-deflections to head-fixed trained rats, consisting of “slip-like” events (waveforms mimicking slips occurring with touch of real textures) embedded into background noise. Varying the (i) shapes (ramp or pulse); (ii) kinematics (amplitude, velocity, etc.); and (iii) the probabilities of occurrence of slip-like events, we observed that rats could readily detect slip-like events of different shapes against noisy background. Psychophysical curves revealed that the difference of slip event and noise amplitude determined perception, while increased probability of occurrence (frequency) had barely any effect. These results strongly support the notion that encoding of kinematics dominantly determines whisker-related tactile perception while the computation of frequency or intensity plays a minor role. PMID:26528148

  6. Support for the slip hypothesis from whisker-related tactile perception of rats in a noisy environment

    Directory of Open Access Journals (Sweden)

    Christian eWaiblinger

    2015-10-01

    Full Text Available Rodents use active whisker movements to explore their environment. The ‘slip hypothesis’ of whisker-related tactile perception entails that short-lived kinematic events (abrupt whisker movements, called ‘slips’, due to bioelastic whisker properties that occur during active touch of textures carry the decisive texture information. Supporting this hypothesis, previous studies have shown that slip amplitude and frequency occur in a texture dependent way. Further, experiments employing passive pulsatile whisker deflections revealed that perceptual performance based on pulse kinematics (i.e. signatures that resemble slips is far superior to the one based on time-integrated variables like frequency and intensity. So far, pulsatile stimuli were employed in a noise free environment. However, the realistic scenario involves background noise (e.g. evoked by rubbing across the texture. Therefore, if slips are used for tactile perception, the tactile neuronal system would need to differentiate slip-evoked spikes from those evoked by noise. To test the animals under these more realistic conditions, we presented passive whisker-deflections to head-fixed trained rats, consisting of 'slip-like' events (waveforms mimicking slips occurring with touch of real textures embedded into background noise. Varying the i shapes (ramp or pulse, ii kinematics (amplitude, velocity, etc., and iii the probabilities of occurrence of slip-like events, we observed that rats could readily detect slip-like events of different shapes against noisy background. Psychophysical curves revealed that the difference of slip event and noise amplitude determined perception, while increased probability of occurrence (frequency had barely any effect. These results strongly support the notion that encoding of kinematics dominantly determines whisker-related tactile perception while the computation of frequency or intensity plays a minor role.

  7. Synthesis of biomorphic SiC ceramic from bamboo charcoal.

    Science.gov (United States)

    Zhu, Jiangtao; Kwong, Fung Luen; Ng, Dickon Hang Leung

    2009-02-01

    Biomorphic SiC ceramic was successfully synthesized by reaction sintering between bamboo charcoal and a Si/SiO2 powder mixture. The charcoal was converted into an entirely SiC ceramic inherited with the original bamboo structure. Samples were characterized according to their crystallinity, morphology, microstructures and pore structures. We found that various morphological SiC structures were formed in different parts of the charcoal which depended on the morphology of the textures. The length of SiC nanowires were up to micron size. They were grown in the direction. The number of micropores in the converted biomorphic SiC was less than the original bamboo charcoal, but the pore diameter was larger.

  8. Structural characterization of SiC nanoparticles

    Science.gov (United States)

    Sun, Baoxing; Xie, Ruobing; Yu, Cun; Li, Cheng; Xu, Hongjie

    2017-10-01

    The structure and size of SiC nanoparticles were studied by different characterization methods including small angle X-ray scattering (SAXS), transmission electron microscope (TEM), and X-ray diffraction (XRD). The results showed that particle size distributions determined respectively from SAXS and TEM are comparable and follow the log-normal function. The size distribution of the particles is between 10 to 100 nm with most of them being in the range of 20–50 nm. The average particle size is around 42 nm. XRD identifies the phase of the SiC nanoparticles and suggests the average size of the single crystalline domain to be around 21 nm. The combined results from XRD and SAXS suggest the existence of many polycrystals, which is confirmed by the HRTEM observation of particles with twins and stacking faults. The material synthesis methods leading to various particle sizes are also discussed. Project supported by the National Natural Science Foundation of China (No. 11505273) and the Strategic Priority Research Program of the Chinese Academy of Sciences (No. XDA02000000).

  9. Epitaxial sic devices for radiation dosimetry

    Energy Technology Data Exchange (ETDEWEB)

    Bruzzi, M; Menichelli, D.; Pini, S.; Sciortino, S. [INFN, Firenze (Italy); Firenze Univ., Firenze (Italy). Dipartimento di Energetica; Bucciolini, M. [INFN, Firenze (Italy); Firenze Univ., Firenze (Italy). Dipartimento di Fisiopatologia Clinica; Nava, F. [Modena Univ., Modena (Italy). Dipartimento di Fisica; INFN, Bologna (Italy)

    2002-07-01

    The current response of SiC on-line dosimeters to {gamma}-radiation from{sup 60}Co and {sup 167}Cs {gamma}-sources, X-photons and 22MeV electrons from linear accelerator has been investigated. The devices used are 4H-SiC epitaxial n-type layer deposited onto a 4H-SiC n{sup +} type substrate wafer doped with nitrogen. Single-pad Schottky contacts have been produced by deposition of a 1000A gold film on the epitaxial layer and ohmic contacts have been deposited on the rear substrate side. The detector has been then embedded in epoxy resin and studied in the dose and dose-rate ranges 0.1-1 Gy 0.1-10Gy/min. A signal response comparable to that of silicon standard dosimeters has been measured with the unbiased SiC device. The released charge and induced current have been observed to increase linearly respectively with the dose and dose-rate. A preliminary study on the changes in the sensibility of the device after a {gamma}-rays accumulated dose up to 10kGy is also presented.

  10. Processing of sintered alpha SiC

    Science.gov (United States)

    Storm, R. S.

    1984-01-01

    Processing methods of sintered alpha SiC for engine applications are developed in a cost effective manner, using a submicron sized powder blended with sintering aids (boron and carbon). The processes for forming a green powder compact, such as dry pressing, cold isostatic pressing and green machining, slip casting, aqueous extrusion, plastic extrusion, and injection molding, are described. Dry pressing is the simplest route to component fabrication, and is carried out at approximately 10,000 psi pressure, while in the cold isostatic method the pressure could go as high as 20,000 psi. Surfactants are added to control settling rates and casting characteristics in the slip casting. The aqueous extrusion process is accomplished by a hydraulic ram forcing the aqueous mixture through a die. The plastic forming processes of extrusion and injection molding offer the potential of greater diversity in shape capacity. The physical properties of sintered alpha SiC (hardness, Young's modulus, shear modulus, and thermal diffusivity) are extensively tested. Corrosion resistance test results of silicon carbide are included.

  11. Tensile Mechanical Properties and Strengthening Mechanism of Hybrid Carbon Nanotube and Silicon Carbide Nanoparticle-Reinforced Magnesium Alloy Composites

    Directory of Open Access Journals (Sweden)

    Xia Zhou

    2012-01-01

    Full Text Available AZ91 magnesium alloy hybrid composites reinforced with different hybrid ratios of carbon nanotubes (CNTs and silicon carbide (SiC nanoparticulates were fabricated by semisolid stirring assisted ultrasonic cavitation. The results showed that grains of the matrix in the AZ91/(CNT + SiC composites were obviously refined after adding hybrid CNTs and SiC nanoparticles to the AZ91 alloy, and the room-temperature mechanical properties of AZ91/(CNT + SiC hybrid composites were improved comparing with the unreinforced AZ91 matrix. In addition, the tensile mechanical properties of the AZ91 alloy-based hybrid composites were considerably improved at the mass hybrid ratio of 7 : 3 for CNTs and SiC nanoparticles; in particular, the tensile and yield strength were increased, respectively, by about 45 and 55% after gravity permanent mould casting. The reason for an increase in the room-temperature strength of the hybrid composites should be mainly attributable to the larger hybrid ratio of CNTs and SiC nanoparticles, the coefficient of thermal expansion (CTE mismatch between matrix and hybrid reinforcements, the dispersive strengthening effects (Orowan strengthening, and the grain refining (Hall-Petch effect.

  12. Synergetic Effect of Graphene and MWCNTs on Microstructure and Mechanical Properties of Cu/Ti3SiC2/C Nanocomposites

    Science.gov (United States)

    Jiang, Xiaosong; Song, Tingfeng; Shao, Zhenyi; Liu, Wanxia; Zhu, Degui; Zhu, Minhao

    2017-11-01

    Multi-walled carbon nanotubes (MWCNTs) and graphenes have been taken for novel reinforcements due to their unique structure and performance. However, MWCNTs or graphenes reinforced copper matrix composites could not catch up with ideal value due to reinforcement dispersion in metal matrix, wettability to metal matrix, and composite material interface. Taking advantage of the superior properties of one-dimensional MWCNTs and two-dimensional graphenes, complementary performance and structure are constructed to create a high contact area between MWCNTs and graphenes to the Cu matrix. Mechanical alloying, hot pressing, and hot isostatic pressing techniques are used to fabricate Cu matrix self-lubricating nanocomposites. Effects of MWCNTs and graphenes on mechanical properties and microstructures of Cu/Ti3SiC2/C nanocomposites are studied. The fracture and strengthening mechanisms of Cu/Ti3SiC2/C nanocomposites are explored on the basis of structure and composition of Cu/Ti3SiC2/C nanocomposites with formation and function of interface.

  13. Synergetic Effect of Graphene and MWCNTs on Microstructure and Mechanical Properties of Cu/Ti3SiC2/C Nanocomposites.

    Science.gov (United States)

    Jiang, Xiaosong; Song, Tingfeng; Shao, Zhenyi; Liu, Wanxia; Zhu, Degui; Zhu, Minhao

    2017-11-28

    Multi-walled carbon nanotubes (MWCNTs) and graphenes have been taken for novel reinforcements due to their unique structure and performance. However, MWCNTs or graphenes reinforced copper matrix composites could not catch up with ideal value due to reinforcement dispersion in metal matrix, wettability to metal matrix, and composite material interface. Taking advantage of the superior properties of one-dimensional MWCNTs and two-dimensional graphenes, complementary performance and structure are constructed to create a high contact area between MWCNTs and graphenes to the Cu matrix. Mechanical alloying, hot pressing, and hot isostatic pressing techniques are used to fabricate Cu matrix self-lubricating nanocomposites. Effects of MWCNTs and graphenes on mechanical properties and microstructures of Cu/Ti3SiC2/C nanocomposites are studied. The fracture and strengthening mechanisms of Cu/Ti3SiC2/C nanocomposites are explored on the basis of structure and composition of Cu/Ti3SiC2/C nanocomposites with formation and function of interface.

  14. 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.

  15. Influence of Reinforcement Size on Microplastic Deformation Behavior of SiCP/Al Composites

    Science.gov (United States)

    Yan, Yiwu; Geng, Lin; Liu, Dayong

    The microplastic deformation behavior of 20 vol.% SiCp/Al composites with various SiC particle sizes were investigated. The SiC particles are in four nominal sizes of 1, 5, 20 and 56 µm. The experimental results showed that the micro-yield strength is very sensitive to composite microstructure features. As the particle size increases, the micro-yield strength of composites decrease firstly, and then increase. The observed results were attributed to thermal residual stress and dislocation density due to the large difference in coefficient of thermal expansion between the matrix and reinforcement.

  16. Effect of holding time on microstructure and mechanical properties of SiC/SiC joints brazed by Ag-Cu-Ti + B4C composite filler

    OpenAIRE

    Dai, Xiangyu; Cao, Jian; Tian, Yingtao; Chen, Zhe; Song, Xiaoguo; Feng, Jicai

    2016-01-01

    The composite fillers have a number of advantages comparing with the traditional filler metals, and have been widely used for brazing ceramics. However, previous researches mainly focus on the strengthening mechanism of either whiskers or particles. It is still of great interest to investigate the reinforcement effect with the presence of both whiskers and particles. In this study, Ag-Cu-Ti + B4C composite filler was developed to braze SiC ceramics, and effects of holding time on the microstr...

  17. Compatibility of SiC and SiC Composites with Molten Lead

    Energy Technology Data Exchange (ETDEWEB)

    H Tunison

    2006-03-07

    The choice of structural material candidates to contain Lead at 1000 C are limited in number. Silicon carbide composites comprise one choice of possible containment materials. Short term screening studies (120 hours) were undertaken to study the behavior of Silicon Carbide, Silicon Nitride, elemental Silicon and various Silicon Carbide fiber composites focusing mainly on melt infiltrated composites. Isothermal experiments at 1000 C utilized graphite fixtures to contain the Lead and material specimens under a low oxygen partial pressure environment. The corrosion weight loss values (grams/cm{sup 2} Hr) obtained for each of the pure materials showed SiC (monolithic CVD or Hexoloy) to have the best materials compatibility with Lead at this temperature. Increased weight loss values were observed for pure Silicon Nitride and elemental Silicon. For the SiC fiber composite samples those prepared using a SiC matrix material performed better than Si{sub 3}N{sub 4} as a matrix material. Composites prepared using a silicon melt infiltration process showed larger corrosion weight loss values due to the solubility of silicon in lead at these temperatures. When excess silicon was removed from these composite samples the corrosion performance for these material improved. These screening studies were used to guide future long term exposure (both isothermal and non-isothermal) experiments and Silicon Carbide composite fabrication work.

  18. Large-Scale Growth of Tubular Aragonite Whiskers through a MgCl2-Assisted Hydrothermal Process

    Directory of Open Access Journals (Sweden)

    Changyin Dong

    2011-08-01

    Full Text Available In this paper, we have developed a facile MgCl2-assissted hydrothermal synthesis route to grow tubular aragonite whiskers on a large scale. The products have been characterized by powder X-ray diffraction (XRD, optical microscopy, and scanning electronic microscopy (SEM. The results show the as-grown product is pure tubular aragonite crystalline whiskers with a diameter of 5–10 mm and a length of 100–200 mm, respectively. The concentration of Mg2+ plays an important role in determining the quality and purity of the products. Furthermore, the method can be extended to fabricate CaSO4 fibers. The high quality of the product and the mild conditions used mean that the present route has good prospects for the growth of inorganic crystalline whiskers.

  19. An Empirical Model for Estimating the Probability of Electrical Short Circuits from Tin Whiskers-Part I

    Science.gov (United States)

    Courey, Karim; Wright, Clara; Asfour, Shihab; Bayliss, Jon; Ludwig, Larry

    2008-01-01

    Existing risk simulations make the assumption that when a free tin whisker has bridged two adjacent exposed electrical conductors, the result is an electrical short circuit. This conservative assumption is made because shorting is a random event that has a currently unknown probability associated with it. Due to contact resistance, electrical shorts may not occur at lower voltage levels. In this experiment, we study the effect of varying voltage on the breakdown of the contact resistance which leads to a short circuit. From this data, we can estimate the probability of an electrical short, as a function of voltage, given that a free tin whisker has bridged two adjacent exposed electrical conductors. In addition, three tin whiskers grown from the same Space Shuttle Orbiter card guide used in the aforementioned experiment were cross sectioned and studied using a focused ion beam (FIB).

  20. Polymer precursors for SiC ceramic materials

    Science.gov (United States)

    Litt, Morton H.

    1986-01-01

    Work on precursor polymers to SiC was performed, concentrating on polymers made from decamethyl cyclohexasilyene units. The initial approach was to synthesize mixed diphenyl decamethyl cyclohexasilane, dephenylate, and polymerize. This produced polymers which had yields of up to 50 percent SiC. (Theoretical yield is 75 percent). The present approach is to make the polymer through the intermediate trans-1,4-diphenyl decamethyl cyclohexasilane. This should produce a crystalline polymer and high strength fibers. These will be thermally decomposed to SiC fibers. This requires new chemistry which is currently being studied.

  1. 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...... and current are presented. Switching losses analysis is made according to the experiment results. The switching characteristics study and switching losses analysis could give some guidelines of gate driver IC and gate resistance selection, switching losses estimation and circuit design of SiC MOSFETs....

  2. 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 mechanism...... is analysed in detail. According to the analysis, the optimal circuit design to minimize the parasitic parametric is introduced for a clean switching waveform. Experiment results show the clean switching waveform of SiC MOSFET. Guidelines are established for circuit design....

  3. Microstructure and mechanical behavior of stir-cast Zn–27Al based composites reinforced with rice husk ash, silicon carbide, and graphite

    Directory of Open Access Journals (Sweden)

    Kenneth Kanayo Alaneme

    2017-04-01

    Full Text Available The microstructure and mechanical properties of Zn–27Al based composites reinforced with rice husk ash (RHA, silicon carbide (SiC, and graphite (Cg particles have been investigated. The Zn–27Al composites consisting of varied weight ratios of the reinforcing materials were produced using the stir casting process. Hardness test, tensile properties evaluation, fracture toughness determination, and microstructural examination, were used to characterize the composites produced. Results show that the microstructures of the composites are similar, consisting of the dendritic structure of the Zn–27Al alloy matrix with fine dispersion of the reinforcing particles. The hardness of the composites decreased with increase in the weight percent of RHA (and corresponding decrease in SiC weight percent in the reinforcement. The tensile strength and yield strength decreased slightly with increase in the weight ratio of RHA in the composites with a maximum of 8.5% and 9.6% reductions respectively observed for as much as 40% RHA (corresponding to 40% reduction in SiC in the hybrid reinforcement. Although some of the composite compositions containing RHA had slightly higher % elongation values compared with those without RHA, it was generally observed that the % elongation was invariant to the composite RHA content. The fracture toughness of the composites increases with increase in the weight percent of RHA with as much as a 20% increase obtained for as much as 40% RHA (corresponding to 40% reduction in SiC in the hybrid reinforcement.

  4. PROPERTIES OF CHITIN REINFORCES COMPOSITES: A REVIEW ...

    African Journals Online (AJOL)

    Despite the denaturing of chitin, the most widely used method of extractiong chitin from seashells is the chemical method. Chitin whiskers known by different name in literature can only be prepared by using hydrochloric acid. The rod-like particles of chitin whiskers have an average lengths and widths of 200 ± 20 nm and 8 ...

  5. Characteristics of Commercial SiC and Synthetic SiC as an Aggregate in Geopolymer Composites

    Science.gov (United States)

    Irfanita, R.; Afifah, K. N.; Asrianti; Subaer

    2017-03-01

    This main objective of this study is to investigate the effect silicon carbide (SiC) as an aggregate on the mechanical strength and microstructure of the geopolymer composites. The geopolymers binder were produced by using alkaline activation method of metakaolin and cured at 70oC for 2 hours. In this study commercial and synthetic SiC were used as aggregate to produce composite structure. Synthetic SiC was produced from rice husk ash and coconut shell carbon calcined at 750oC for 2 hours. The addition of SiC in geopolymers paste was varied from 0.25g, 0.50g to 0.75g to form geopolymers composites. The chemical compositions and crystallinity level of SiC and the resulting composites were measured by means of Rigaku MiniFlexII X-Ray Diffraction (XRD). The microstructure of SiC and the composites were examined by using Tescan Vega3SB Scanning Electron Microscopy (SEM). The physical and mechanical properties of the samples were determined based on apparent porosity, bulk density, and three bending flexural strength measurements. The results showed that the commercial and synthetic SiC were effectively produced geopolymers composites with different microstructure, physical and mechanical strength.

  6. Multidimensional characterisation of biomechanical structures by combining Atomic Force Microscopy and Focused Ion Beam: A study of the rat whisker.

    Science.gov (United States)

    Adineh, Vahid Reza; Liu, Boyin; Rajan, Ramesh; Yan, Wenyi; Fu, Jing

    2015-07-01

    Understanding the heterogeneity of biological structures, particularly at the micro/nano scale can offer insights valuable for multidisciplinary research in tissue engineering and biomimicry designs. Here we propose to combine nanocharacterisation tools, particularly Focused Ion Beam (FIB) and Atomic Force Microscopy (AFM) for three dimensional mapping of mechanical modulus and chemical signatures. The prototype platform is applied to image and investigate the fundamental mechanics of the rat face whiskers, a high-acuity sensor used to gain detailed information about the world. Grazing angle FIB milling was first applied to expose the interior cross section of the rat whisker sample, followed by a "lift-out" method to retrieve and position the target sample for further analyses. AFM force spectroscopy measurements revealed a non-uniform pattern of elastic modulus across the cross section, with a range from 0.8GPa to 13.5GPa. The highest elastic modulus was found at the outer cuticle region of the whisker, and values gradually decreased towards the interior cortex and medulla regions. Elemental mapping with EDS confirmed that the interior of the rat whisker is dominated by C, O, N, S, Cl and K, with a significant change of elemental distribution close to the exterior cuticle region. Based on these data, a novel comprehensive three dimensional (3D) elastic modulus model was constructed, and stress distributions under realistic conditions were investigated with Finite Element Analysis (FEA). The simulations could well account for the passive whisker deflections, with calculated resonant frequency as well as force-deflection for the whiskers being in good agreement with reported experimental data. Limitations and further applications are discussed for the proposed FIB/AFM approach, which holds good promise as a unique platform to gain insights on various heterogeneous biomaterials and biomechanical systems. Copyright © 2015 Acta Materialia Inc. Published by Elsevier

  7. Probability distributions of whisker-surface contact: quantifying elements of the rat vibrissotactile natural scene.

    Science.gov (United States)

    Hobbs, Jennifer A; Towal, R Blythe; Hartmann, Mitra J Z

    2015-08-01

    Analysis of natural scene statistics has been a powerful approach for understanding neural coding in the auditory and visual systems. In the field of somatosensation, it has been more challenging to quantify the natural tactile scene, in part because somatosensory signals are so tightly linked to the animal's movements. The present work takes a step towards quantifying the natural tactile scene for the rat vibrissal system by simulating rat whisking motions to systematically investigate the probabilities of whisker-object contact in naturalistic environments. The simulations permit an exhaustive search through the complete space of possible contact patterns, thereby allowing for the characterization of the patterns that would most likely occur during long sequences of natural exploratory behavior. We specifically quantified the probabilities of 'concomitant contact', that is, given that a particular whisker makes contact with a surface during a whisk, what is the probability that each of the other whiskers will also make contact with the surface during that whisk? Probabilities of concomitant contact were quantified in simulations that assumed increasingly naturalistic conditions: first, the space of all possible head poses; second, the space of behaviorally preferred head poses as measured experimentally; and third, common head poses in environments such as cages and burrows. As environments became more naturalistic, the probability distributions shifted from exhibiting a 'row-wise' structure to a more diagonal structure. Results also reveal that the rat appears to use motor strategies (e.g. head pitches) that generate contact patterns that are particularly well suited to extract information in the presence of uncertainty. © 2015. Published by The Company of Biologists Ltd.

  8. Rat whisker movement after facial nerve lesion: evidence for autonomic contraction of skeletal muscle.

    Science.gov (United States)

    Heaton, James T; Sheu, Shu Hsien; Hohman, Marc H; Knox, Christopher J; Weinberg, Julie S; Kleiss, Ingrid J; Hadlock, Tessa A

    2014-04-18

    Vibrissal whisking is often employed to track facial nerve regeneration in rats; however, we have observed similar degrees of whisking recovery after facial nerve transection with or without repair. We hypothesized that the source of non-facial nerve-mediated whisker movement after chronic denervation was from autonomic, cholinergic axons traveling within the infraorbital branch of the trigeminal nerve (ION). Rats underwent unilateral facial nerve transection with repair (N=7) or resection without repair (N=11). Post-operative whisking amplitude was measured weekly across 10weeks, and during intraoperative stimulation of the ION and facial nerves at ⩾18weeks. Whisking was also measured after subsequent ION transection (N=6) or pharmacologic blocking of the autonomic ganglia using hexamethonium (N=3), and after snout cooling intended to elicit a vasodilation reflex (N=3). Whisking recovered more quickly and with greater amplitude in rats that underwent facial nerve repair compared to resection (Pnerve-mediated whisking was elicited by electrical stimulation of the ION, temporarily diminished following hexamethonium injection, abolished by transection of the ION, and rapidly and significantly (Precovery period (indicative of reinnervation), but re-appeared in the resected rats after undergoing ION transection (indicative of motor denervation). Cholinergic, parasympathetic axons traveling within the ION innervate whisker pad vasculature, and immunohistochemistry for vasoactive intestinal peptide revealed these axons branching extensively over whisker pad muscles and contacting neuromuscular junctions after facial nerve resection. This study provides the first behavioral and anatomical evidence of spontaneous autonomic innervation of skeletal muscle after motor nerve lesion, which not only has implications for interpreting facial nerve reinnervation results, but also calls into question whether autonomic-mediated innervation of striated muscle occurs naturally in

  9. Solidification characteristics of atomized AlCu4Mg1-SiC composite powders

    Directory of Open Access Journals (Sweden)

    Yamanoglu R.

    2012-01-01

    Full Text Available In this study, rapidly solidified metal matrix composite powders have been produced by PREP (Plasma rotating electrode process atomization. AlCu4Mg1 alloy is used as the matrix material while SiC particles, with about 650 nm average particle size, are used as the reinforcement phase. The microstructural and solidification characteristics of composite particles are studied using optical and scanning electron microscope (SEM. The relationship between secondary dendrite arm spacing (SDAS and particle diameter was examined, and these composite powders were found to have dendritic and equiaxed solidification with a fine eutectic phase. SDAS measurements using various sized particles show that secondary dendrite arm spacing slightly decreases with the decrease in particle size.

  10. A Calculation of Elastic Flexural Vibrations of Whisker Crystals Irradiated with Nanosecond Electron Beams

    Science.gov (United States)

    Chebodayev, M. I.

    2017-10-01

    Within the framework of the linear thermal elasticity theory a dynamic thermoelastic bending of a whisker crystal is considered under conditions of its irradiation with a high-current electron beam of nanosecond duration. It is shown that the characteristic time of leveling the temperature of superthin pin-type rod nonuniformely heated over its thickness is comparable with the period of the fundamental wave of flexural vibrations. This gives rise to a considerable decrease in the bending amplitude, which is concurrent with the heat conduction processes.

  11. Influence of Milling Time on the Crystallite Size of AlSi5Cu2/SiC Composite Powder

    Directory of Open Access Journals (Sweden)

    Suśniak M.

    2016-06-01

    Full Text Available AlSi5Cu2/SiC nanocrystalline composite powder was successfully obtained by mechanical alloying of AlSi5Cu2 chips with reinforcement of 0, 10, 15, 20 wt. % of silicon carbide. X-ray powder diffraction was used to characterize obtained material. Detailed analyses using transmission and scanning electron microscopy have been conducted in order to collaborate the grain size measurement determined from the XRD analyses. Powders produced in a planetary ball mill with milling time: 1, 5, 10, 15, 20 and 40 hours, have shown shape and size evaluation during mechanical alloying process. It can be seen tendency to decrease the size of the grain as the milling time is increased. It is also noted that the grains of composites (AlSi5Cu2/SiC are smaller than samples prepares without SiC addition. 40 hours of milling lead to formed very small grains of Al phase (20 nm in average in composite powder.

  12. Reinforcements for high temperature ceramics. Final report

    Energy Technology Data Exchange (ETDEWEB)

    Kyriacou, C.I.; Sepulveda, J.L.; Watson, M.A. [Keramont Corp., Tucson, AZ (United States)

    1992-04-01

    A method has been investigated and developed to grow TiB{sub 2} whiskers by the VLS mechanism. The reaction was carried out in a quartz tube 3 in. in diameter, 30 in. long at about 1150{degrees}C in the presence of a catalyst. The basic experimental parameters, a substrate, and a catalyst, for the growth of the whiskers have been defined. The whiskers produced have shown variable size and morphology depending on the experimental conditions, and location of the whiskers from the input port. The corrosion of the catalyst by the gas environment, and the gas distribution profile in the furnace had a serious effect on the reproducibility of the experimental results, and the overall yield of whiskers.

  13. Structure-property relations for silicon nitride matrix composites reinforced with pyrolytic carbon pre-coated Hi-Nicalon fibers

    NARCIS (Netherlands)

    Kooi, B.J.; Hosson, J.Th.M. De; Olivier, C.; Veyret, J.B.

    1999-01-01

    Si3N4 matrix composites reinforced with pyrolytic carbon pre-coated Hi-Nicalon (SiC) fibers, were studied using tensile testing and transmission electron microscopy. Three types of samples were evaluated all with a nominal coating thickness of 200 nm. The composites were densified by hot pressing at

  14. Microplastic flow in SIC/AL composites

    Energy Technology Data Exchange (ETDEWEB)

    Shi, N. [Los Alamos National Lab., NM (United States); Arsenault, R.J. [Univ. of Maryland, College Park, MD (United States)

    1995-12-31

    Experimentally it has been determined that if a composite containing a reinforcement which has a different (in general lower) thermal coefficient of expansion as compared to the matrix, then upon cooling from the processing or annealing temperature, plastic relaxation of the misfit strain will occur. Also, experimentally it has been shown that as the size of the reinforcement is increased, i.e., from small spheres to large spheres, there is a decrease in the summation of the effective plastic strain in the matrix. In other words there is a decrease in the average dislocation density in the matrix. However, if the shape of the reinforcement is changed from spherical to short fiber to continuous filament, then the dislocation density increases. This experimental data is obtained at a constant volume fraction. A very simple model of plastic relaxation based on prismatic punching of dislocations from the interface can account for the decrease in the dislocation density with an increase reinforcement size, and the increase in dislocation density when changing the shape from a sphere to a continuous filament. A FEM analysis of the shape factor is also capable of predicting the correct trend. However, at present the continuum mechanics methods that have been investigated can not predict the size dependence. A simple model to explain the size effect in Al{sub 2}O{sub 3}/NiAl composites based on the deformation characteristics of NiAl will be discussed.

  15. SiC MOSFETs based split output half bridge inverter

    DEFF Research Database (Denmark)

    Li, Helong; Munk-Nielsen, Stig; Beczkowski, Szymon

    2014-01-01

    . This paper makes the current commutation mechanism and efficiency analysis of half bridge with split output based on SiC MOSFETs. Current commutation process analysis is illustrated together with LTspice simulation and afterwards, verified by the experimental results of a double pulse test circuit with split......Body diode of SiC MOSFETs has a relatively high forward voltage drop and still experiences reverse recovery phenomenon. Half bridge with split output aims to decouple both the body diode and junction capacitance of SiC MOSFETs, therefore achieving a reduced switching loss in a bridge configuration...... output. The double pulse test shows the devices' current during commutation process and the reduced switching losses of SiC MOSFETs compared to that of the traditional half bridge. The efficiency comparison is presented with experimental results of half bridge power inverter with split output...

  16. Development of SiC Large Tapered Crystal Growth

    Science.gov (United States)

    Neudeck, Phil

    2011-01-01

    Research Focus Area: Power Electronics, Temperature Tolerant Devices. Demonstrate initial feasibility of totally new "Large Tapered Crystal" (LTC) process for growing vastly improved large-diameter wide-band gap wafers. Addresses Targets: The goal of this research is to experimentally investigate and demonstrate feasibility of the key unproven LTC growth processes in SiC. Laser-assisted growth of long SiC fiber seeds. Radial epitaxial growth enlargement of seeds into large SiC boules. Uniqueness and Impacts open a new technology path to large-diameter SiC and GaN wafers with 1000-fold defect density improvement at 2-4 fold lower cost. Leapfrog improvement in wide band gap power device capability and cost.

  17. SiC Avalanche Photodiodes and Arrays Project

    Data.gov (United States)

    National Aeronautics and Space Administration — Aymont Technology, Inc. (Aymont) will demonstrate the feasibility of SiC p-i-n avalanche photodiodes (APD) arrays. Aymont will demonstrate 4 x 4 arrays of 2 mm2 APDs...

  18. SiC power MOSFETs performance, robustness and technology maturity

    OpenAIRE

    Castellazzi, Alberto; Fayyaz, Asad; Romano, G; Yang, Li; Riccio, M.; Irace, A.

    2016-01-01

    Relatively recently, SiC power MOSFETs have transitioned from being a research exercise to becoming an industrial reality. The potential benefits that can be drawn from this technology in the electrical energy conversion domain have been amply discussed and partly demonstrated. Before their widespread use in the field, the transistors need to be thoroughly investigated and later validated for robustness and longer term stability and reliability. This paper proposes a review of commercial SiC ...

  19. 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

  20. Excimer laser assisted chemical machining of SiC ceramic

    Science.gov (United States)

    Hibi, Yuko; Enomoto, Yuji; Kikuchi, Kaoru; Shikata, Nobuo; Ogiso, Hisato

    1995-02-01

    A highly effective method of machining ceramic has been newly developed using a krypton fluoride (KrF) excimer laser with a 248 nm wavelength. The laser was irradiated on SiC in water to form a soft hydrous oxide layer by photochemical reaction. The softened layer was then cut with a diamond tool to form a mirror surface finish. The optimum conditions were found for both high machining rate and better surface integrity of SiC.

  1. Effects of waste eggshells and SiC addition on specific strength and thermal expansion of hybrid green metal matrix composite.

    Science.gov (United States)

    Sharma, Satpal; Dwivedi, Shashi Prakash

    2017-07-05

    Chicken eggshell waste is an industrial byproduct, and its disposal constitutes a serious environmental hazard. Chicken eggshell can be used in commercial products to produce new materials with low cost and density. Low density material which can sustain at higher temperature is a remarkable area of research. Keeping these facts in the mind, the present investigation aims to study the physical behaviour, specific strength and thermal expansion of AA2014/SiC/carbonized eggshell hybrid green metal matrix composites. Microstructure of hybrid green metal matrix shows that the reinforcement particles (SiC particulates and carbonized eggshells particles) are uniformly distributed in the matrix AA2014 alloy. Specific strength for the composites containing 2.5wt.% SiC and up to 7.5wt.% carbonized eggshell was observed to be higher than that of the other selected composites. While for the same composition (AA2014/2.5% SiC/7.5% carbonized eggshell composites), porosity was observed lower than other selected composites. The results revealed that sample of AA2014/2.5% SiC/7.5% carbonized eggshell showed minimum cross sectional area reduction after the thermal expansion at 450°C among all the selected samples. Overall costs of hybrid metal matrix composites were also calculated. Copyright © 2017 Elsevier B.V. All rights reserved.

  2. SPHERICAL INDENTATION OF SiC

    Energy Technology Data Exchange (ETDEWEB)

    Wereszczak, Andrew A [ORNL; Johanns, Kurt E [ORNL

    2007-01-01

    Instrumented Hertzian indentation testing was performed on several grades of SiCs and the results and preliminary interpretations are presented. The grades included hot-pressed and sintered compositions. One of the hot-pressed grades was additionally subjected to high temperature heat treatment to produce a coarsened grain microstructure to enable the examination of exaggerated grain size on indentation response. Diamond spherical indenters were used in the testing. Indentation load, indentation depth of penetration, and acoustic activity were continually measured during each indentation test. Indentation response and postmortem analysis of induced damage (e.g., ring/cone, radial and median cracking, quasi-plasticity) are compared and qualitatively as a function of grain size. For the case of SiC-N, the instrumented spherical indentation showed that yielding initiated at an average contact stress 12-13 GPa and that there was another event (i.e., a noticeable rate increase in compliance probably associated with extensive ring and radial crack formations) occurring around an estimated average contact stress of 19 GPa.

  3. Prussian Blue Modified Solid Carbon Nanorod Whisker Paste Composite Electrodes: Evaluation towards the Electroanalytical Sensing of H2O2

    Directory of Open Access Journals (Sweden)

    Carolin Siimenson

    2012-01-01

    Full Text Available Metallic impurity free solid carbon nanorod “Whiskers” (SCNR Whiskers, a derivative of carbon nanotubes, are explored in the fabrication of a Prussian Blue composite electrode and critically evaluated towards the mediated electroanalytical sensing of H2O2. The sensitivity and detection limits for H2O2 on the paste electrodes containing 20% (w/w Prussian Blue, mineral oil, and carbon nanorod whiskers were explored and found to be 120 mA/(M cm2 and 4.1 μM, respectively, over the concentration range 0.01 to 0.10 mM. Charge transfer constant for the 20% Prussian Blue containing SCNR Whiskers paste electrode was calculated, for the reduction of Prussian Blue to Prussian White, to reveal a value of 1.8±0.2 1/s (α=0.43, N=3. Surprisingly, our studies indicate that these metallic impurity-free SCNR Whiskers, in this configuration, behave electrochemically similar to that of an electrode constructed from graphite.

  4. Developing an Empirical Model for Estimating the Probability of Electrical Short Circuits from Tin Whiskers. Part 2

    Science.gov (United States)

    Courey, Karim J.; Asfour, Shihab S.; Onar, Arzu; Bayliss, Jon A.; Ludwig, Larry L.; Wright, Maria C.

    2009-01-01

    To comply with lead-free legislation, many manufacturers have converted from tin-lead to pure tin finishes of electronic components. However, pure tin finishes have a greater propensity to grow tin whiskers than tin-lead finishes. Since tin whiskers present an electrical short circuit hazard in electronic components, simulations have been developed to quantify the risk of said short circuits occurring. Existing risk simulations make the assumption that when a free tin whisker has bridged two adjacent exposed electrical conductors, the result is an electrical short circuit. This conservative assumption is made because shorting is a random event that had an unknown probability associated with it. Note however that due to contact resistance electrical shorts may not occur at lower voltage levels. In our first article we developed an empirical probability model for tin whisker shorting. In this paper, we develop a more comprehensive empirical model using a refined experiment with a larger sample size, in which we studied the effect of varying voltage on the breakdown of the contact resistance which leads to a short circuit. From the resulting data we estimated the probability distribution of an electrical short, as a function of voltage. In addition, the unexpected polycrystalline structure seen in the focused ion beam (FIB) cross section in the first experiment was confirmed in this experiment using transmission electron microscopy (TEM). The FIB was also used to cross section two card guides to facilitate the measurement of the grain size of each card guide's tin plating to determine its finish.

  5. Effect of SiC weight percentage on tribological properties of Al-SiC metal matrix composites under acid environment

    Directory of Open Access Journals (Sweden)

    Smrutiranjan Pradhan

    2017-06-01

    Full Text Available In this paper, Al-SiC MMCs reinforced with different weight percentages of SiC content (5 wt.%, 7.5 wt.% and 10 wt.% are fabricated through the liquid stir casting method. The effect of weight percentage of SiC on friction and wear properties of Al-SiC MMC is investigated. Tribological tests are conducted under acid environment in a pin-on-disk tribotester by varying the design parameters (applied normal load and sliding speed while the duration of each experiment is kept constant for 30 minutes. It is seen from the result that wear increases with increase in applied load and sliding speed but friction coefficient shows a decreasing trend with increase in load. The addition of SiC reinforcement increases the wear resistance of the metal matrix composite. The scanning electron microscope (SEM and energy dispersive X-Ray (EDX technique are used to analyse the wear mechanism of worn surface. From the microstructure study, it is seen that adhesive, abrasive and corrosive wear mechanisms are present for removal of material from the Al-SiC MMCs.

  6. Synthesis, Electromagnetic and Wave-Absorbing Properties of a FeNi Alloy Nano-Whisker/Particle Mixture

    Science.gov (United States)

    Zhou, Jia; Zhu, Zheng-Hou; Xiong, Chao

    2017-11-01

    A Fe20Ni80 alloy nano-whisker/particle mixture was synthesized by a hydrazine hydrate reduction method at 60°C. Electromagnetic parameters of the alloy nano-whisker/particle mixture after a 0.3-T magnetic treatment were measured in the 1.0-8.0 GHz range using an E5063A vector network analyzer. The results showed that the real part (ɛ') of the complex permittivity of the Fe20Ni80 alloy nano-whisker/particle mixture in the 1.0-8.0 GHz range was between 23 and 18, and the imaginary part (ɛ″) was approximately 4. The real part (μ') of the complex permeability in 1.0-5.0 GHz range decreased greatly with increasing frequency, from a maximum of 2.5 to a minimum of 1. The imaginary part (μ″) presented a parabolic shape change; when the frequency was 4.0 GHz, there was a maximum of 1.5. After the 0.3-T magnetic treatment, both the real part (ɛ') and the imaginary part (ɛ″) of the complex permittivity decreased: the real part (μ') of the complex permeability increased sharply, and the imaginary part (μ″) decreased slightly. The dissipation factor (tgδ) of the Fe20Ni80 alloy nano-whisker/particle mixture in the 4.0-7.0 GHz range was approximately 1.0, which shows it has excellent wave-absorbing properties. The thickness of interference-absorbing was approximately 11 mm at 1.0 GHz; it decreased with increasing frequency. The thickness of interference-absorbing was 2.5-2 mm in the 4.0-8.0 GHz range, which shows that the Fe20Ni80 alloy nano-whisker/particle mixture has good interference-absorbing properties when the thickness is 2 mm.

  7. Synthesis, Electromagnetic and Wave-Absorbing Properties of a FeNi Alloy Nano-Whisker/Particle Mixture

    Science.gov (United States)

    Zhou, Jia; Zhu, Zheng-Hou; Xiong, Chao

    2018-02-01

    A Fe20Ni80 alloy nano-whisker/particle mixture was synthesized by a hydrazine hydrate reduction method at 60°C. Electromagnetic parameters of the alloy nano-whisker/particle mixture after a 0.3-T magnetic treatment were measured in the 1.0-8.0 GHz range using an E5063A vector network analyzer. The results showed that the real part ( ɛ') of the complex permittivity of the Fe20Ni80 alloy nano-whisker/particle mixture in the 1.0-8.0 GHz range was between 23 and 18, and the imaginary part ( ɛ″) was approximately 4. The real part ( μ') of the complex permeability in 1.0-5.0 GHz range decreased greatly with increasing frequency, from a maximum of 2.5 to a minimum of 1. The imaginary part ( μ″) presented a parabolic shape change; when the frequency was 4.0 GHz, there was a maximum of 1.5. After the 0.3-T magnetic treatment, both the real part ( ɛ') and the imaginary part ( ɛ″) of the complex permittivity decreased: the real part ( μ') of the complex permeability increased sharply, and the imaginary part ( μ″) decreased slightly. The dissipation factor ( tgδ) of the Fe20Ni80 alloy nano-whisker/particle mixture in the 4.0-7.0 GHz range was approximately 1.0, which shows it has excellent wave-absorbing properties. The thickness of interference-absorbing was approximately 11 mm at 1.0 GHz; it decreased with increasing frequency. The thickness of interference-absorbing was 2.5-2 mm in the 4.0-8.0 GHz range, which shows that the Fe20Ni80 alloy nano-whisker/particle mixture has good interference-absorbing properties when the thickness is 2 mm.

  8. Response properties of whisker-associated primary afferent neurons following infraorbital nerve transection with microsurgical repair in adult rats.

    Science.gov (United States)

    Xiao, Bo; Zanoun, Rami R; Carvell, George E; Simons, Daniel J; Washington, Kia M

    2016-03-01

    The rodent whisker/trigeminal system, characterized by high spatial and temporal resolution, provides an experimental model for developing new therapies for improving sensory functions of damaged peripheral nerves. Here, we use controlled whisker stimulation and single-unit recordings of trigeminal ganglion cells to examine in detail the nature and time course of functional recovery of mechanoreceptive afferents following nerve transection with microsurgical repair of the infraorbital nerve (ION) branch of the trigeminal nerve in adult rats. Response measures include rapid vs. slow adaptation, firing rate, interspike intervals, latency, and angular (directional) tuning. Whisker-evoked responses, readily observable by 3 wk post-transection, recover progressively for at least the next 5 wk. All cells in transected animals, as in control cases, responded to deflections of single whiskers only, but topography within the ganglion was clearly disrupted. The time course and extent of recovery of quantitative response measures were receptor dependent. Cells displaying slowly adapting (SA) properties recovered more quickly than rapidly adapting (RA) populations, and for some response measures-notably evoked firing rates-closely approached or attained control levels by 8 wk post-transection. Angular tuning of RA cells was slightly better than control units, whereas SA tuning did not differ from control values. Nerve conduction times and refractory periods, examined separately using electrical stimulation of the ION, were slower than normal in all transected animals and poorly reflected recovery of whisker-evoked response latencies and interspike intervals. Results underscore the need for multiple therapeutic strategies that target different aspects of functional restitution following peripheral nerve injury. Copyright © 2016 the American Physiological Society.

  9. Food reinforcement during infancy.

    Science.gov (United States)

    Kong, Kai Ling; Epstein, Leonard H

    2016-11-01

    The motivation to eat, as operationalized by measuring how hard someone will work for food, is cross-sectionally and prospectively related to obesity. Persons high in food reinforcement consume more calories, and energy intake mediates the relationship between food reinforcement and obesity. Research has shown avid sucking for milk in early infancy predicts later adiposity, and the relationship between food reinforcement and excess body weight has been observed in infants as young as 9months of age. New methodological developments in studying food reinforcement in infants and young children provide the first opportunity to study the origin of food reinforcement. This review seeks to provide background on the measurement of food reinforcement, and to present, for the first time, prenatal and postnatal predictors of infant food reinforcement. Lastly, potential mechanisms for an increasing trajectory of food reinforcement throughout development are proposed. Copyright © 2016 Elsevier Inc. All rights reserved.

  10. Effect of preceramic and Zr coating on impregnation behaviors of SiC ceramic composite

    Science.gov (United States)

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

    2015-01-01

    SiC fiber-reinforced ceramic composites were fabricated using a polymer impregnation and pyrolysis process. To develop the low temperature process, the pyrolysis was conducted at 600 °C in air. Both a microstructural observation and a mechanical test were utilized for the evaluation of the impregnation. For the impregnation, two kinds of polycarbosilane having a different degree of cross-linking were used. The level of cross-linking affected the ceramic yield of the composites. The cross-linking under oxygen containing atmosphere resulted in a dense matrix and high density of filling. However, tight bonding between the matrix and fibers in the fully dense composite samples, which was obtained using a cross-linking agent of divinylbenzene, turned out to be deteriorative on the mechanical properties. The physical isolation of fibers from matrix phase in the composites was very important to attain a mechanical ductility. The brittle fracture was alleviated by introducing an interphase coating with metallic Zr. The combination of forming the dense matrix and interphase coating should be a necessary condition for the SiCf/SiC fiber-reinforce composite, and it is practicable by controlling the process parameters.

  11. Amorphization of SiC under ion and neutron irradiation

    Science.gov (United States)

    Snead, L. L.; Zinkle, S. J.; Hay, J. C.; Osborne, M. C.

    1998-05-01

    This paper presents results on the microstructure and physical properties of SiC amorphized by both ion and neutron irradiation. Specifically, 0.56 MeV Si ions have been implanted in single crystal 6H-SiC from ambient through >200°C and the critical threshold for amorphization was measured as a function of the irradiation temperature. From a high resolution transmission electron microscopy (HRTEM) study of the crystalline to amorphous transition region in these materials, elongated pockets of amorphous material oriented parallel to the free surface are observed. Single crystal 6H-SiC and hot pressed and sintered 6H and 3C SiC were neutron irradiated at approximately 70°C to a dose of ˜2.56 dpa causing complete amorphization. Property changes resulting from the crystal to amorphous transition in SiC include a density decrease of 10.8%, a hardness decrease from 38.7 to 21.0 GPa, and a decrease in elastic modulus from 528 to 292 GPa. Recrystallization of the amorphized, single crystal 6H-SiC appears to occur in two stages. In the temperature range of ˜800-1000°C, crystallites nucleate and slowly grow. In the temperature range of 1125-1150°C spontaneous nucleation and rapid growth of crystallites occur. It is further noted that amorphized 6H (alpha) SiC recrystallizes to highly faulted fcc (beta) SiC.

  12. ELID grinding of SiC ultra lightweight mirror

    Science.gov (United States)

    Eto, Hiroaki; Dai, Yutang; Ebizuka, Noboru; Saito, Yasutaka; Suzuki, Toru; Lin, Weimin; Ohmori, Hitoshi; Ebisuzaki, Toshikazu; Takami, Hideki

    2017-11-01

    Silicon carbide (SiC) is the most advantageous as the material of various telescope mirrors, because SiC has high stiffness, high thermal conductivity, low thermal expansion and low density and so on [1] [2]. However, since SiC is very hard, it is difficult to obtain the surfaces efficiently by using ordinary grinding method. Therefore, we developed the ultra lightweight mirror by ELID (ELectrolytic In-process Dressing) grinding method and ultra-precision grinding machine. ELID grinding method is the new grinding technology which one of authors invented, produces the quality of the high surface efficiently, and is effective in processing of a very hard material, such as crystalline silicon and sapphire, ceramics, glasses, hard metals and so on. SiC mirror for space telescope is designed as regular polygon rib structures in the rear face for reducing weight, and both the optical face and the backside ribs are so thin that deformation of the mirror cannot disregard. Therefore, in order to feed back deformation of the mirror to the orbit of grinding wheel, it is necessary to analyze deformation. In this research, we present the results which fabricated mirrors of sintered SiC by the ELID grinding method, the numerical calculation results of the profile deformations analyzed by FEM, and new jig for Φ360mm a mirror.

  13. Management of Reinforcement Corrosion

    DEFF Research Database (Denmark)

    Küter, André; Geiker, Mette Rica; Møller, Per

    Reinforcement corrosion is the most important cause for deterioration of reinforced concrete structures, both with regard to costs and consequences. Thermodynamically consistent descriptions of corrosion mechanisms are expected to allow the development of innovative concepts for the management...... of reinforcement corrosion....

  14. Fiber reinforced engineering plastics

    Science.gov (United States)

    Daniel F. Caulfield; Rodney E. Jacobson; Karl D. Sears; John H. Underwood

    2001-01-01

    Although natural fiber reinforced commodity thermoplastics have a wide range of nonstructural applications in the automotive and decking industries, there have been few reports of cellulosic fiber-reinforced engineering thermoplastics. The commonly held belief has been that the only thermoplastics amenable to natural-fibre reinforcement are limited to low-melting (...

  15. Warm temperature (170-280°C) uniaxial compresion of SiC reinforced MMCs

    CSIR Research Space (South Africa)

    Gxowa, Zizo

    2017-10-01

    Full Text Available and constant strain of 0.3. Engineering stress-strain curves showed that the best deformation was achieved when sintered MMC compacts were uniaxially compressed at 280°C and strain rate of 5s-1 using a soaking time of 20min.The best deformation was achieved...

  16. Macroscopic quantum coherence in charge density wave whisker NbSe{sub 3} under strain

    Energy Technology Data Exchange (ETDEWEB)

    Zheng, P.; Chen, Z.J.; Jiang, Q.; Jin, D. [Physics Institute, Laboratory of Ultra-Low Temperature Physics, Chinese Academy of Sciences, Beijing (China)

    2000-07-03

    The magnetoresistance oscillation of the charge density wave (CDW) material NbSe{sub 3} whisker has been studied under strain at different temperatures (4.2 K, 30 K, 40 K). With a constant measuring current, the magnetoresistance (MR) curves oscillate at 30 K while they are smooth at 4.2 K and become a series of zigzag curves at 40 K. These oscillation periods are {delta}H, rather than {delta}(1/H ). It is found that either increasing the temperature to 40 K, or straining the sample to a displacement as large as {epsilon}=3.1%, makes the regular oscillations disappear. By analysing the data, we found our results can be interpreted as the quantum coherence effect of a moving CDW. (author)

  17. The posterior parietal cortex as integrative hub for whisker sensorimotor information.

    Science.gov (United States)

    Mohan, Hemanth; de Haan, Roel; Mansvelder, Huibert D; de Kock, Christiaan P J

    2018-01-01

    Our daily life consists of a continuous interplay between incoming sensory information and outgoing motor plans. Particularly during goal-directed behavior and active exploration of the sensory environment, brain circuits are merging sensory and motor signals. This is referred to as sensorimotor integration and is relevant for locomotion, vision or tactile exploration. The somatosensory (tactile) system is an attractive modality to study sensorimotor integration in health and disease, motivated by the need for revolutionary technology that builds upon conceptual understanding of sensorimotor integration, such as brain-machine-interfaces and neuro-prosthetics. In this perspective, we focus on the rat whisker system and put forward the posterior parietal cortex as a potential circuit where sensorimotor integration could occur during active somatosensation. Copyright © 2017 The Author(s). Published by Elsevier Ltd.. All rights reserved.

  18. Whisker: a client-server high-performance multimedia research control system.

    Science.gov (United States)

    Cardinal, Rudolf N; Aitken, Michael R F

    2010-11-01

    We describe an original client-server approach to behavioral research control and the Whisker system, a specific implementation of this design. The server process controls several types of hardware, including digital input/output devices, multiple graphical monitors and touchscreens, keyboards, mice, and sound cards. It provides a way to access this hardware for client programs, communicating with them via a simple text-based network protocol based on the standard Internet protocol. Clients to implement behavioral tasks may be written in any network-capable programming language. Applications to date have been in experimental psychology and behavioral and cognitive neuroscience, using rodents, humans, nonhuman primates, dogs, pigs, and birds. This system is flexible and reliable, although there are potential disadvantages in terms of complexity. Its design, features, and performance are described.

  19. Thermochemistry and growth mechanism of SiC nanowires

    Science.gov (United States)

    Chen, Jianjun; Ding, Lijuan; Xin, Lipeng; Zeng, Fan; Chen, Jun

    2017-09-01

    The chemical reaction thermodynamics and a novel two-stage growth mechanism of SiC nanowires synthesized by carbothermal reduction reactions were investigated based on the Si-C-O systems over a wide temperature range (1050 ≤ T ≤ 2000 K). The carbothermal reduction reaction process involves the fast formation of gaseous SiO and CO crucial intermediates, and the further carbon reduction of SiO to SiC. The relationship between the free energy changes and temperature at different pressures was also discussed. Some fundamental data in the work can help to analyze the thermochemistry of the carbothermal reduction reaction in the Si-C-O system, which is beneficial to optimize the temperature, pressure and the input precursors for controlling the SiC nanowire growth.

  20. Active coatings for SiC particles to reduce the degradation by liquid aluminium during processing of aluminium matrix composites: study of interfacial reactions.

    Science.gov (United States)

    Ureña, A.; Rodrigo, P.; Baldonedo, J. L.; Gil, L.

    2001-02-01

    The application of a surface coating on SiC particles is studied as an alternative means of solving problems of reactivity between SiC reinforcements and molten aluminium and problems of low wetting which limit the application of casting routes for fabrication of Al-SiCp composites. The selected active barrier was a ceramic composed of SiO2, which was generated by controlled oxidation of the SiC particles. The coating behaves as an active barrier, preventing a direct reaction between molten aluminium and SiC to form Al4C3 as the main degradation product. At the same time, the SiO2 provokes other interfacial reactions, which are responsible for an improvement in wetting behaviour. Composites were prepared by mixing and compacting SiC particles with Al powders followed by melting in a vacuum furnace, and varying the residence time. Transmission electron microscopy (TEM), high resolution electron microscopy (HREM) and field emission TEM were employed as the main characterization techniques to study the interfacial reactions occurring between the barrier and the molten aluminium. These studies showed that the SiO2 coating behaves as an active barrier which reacts with the molten Al to form a glassy phase Al-Si-O. This compound underwent partial crystallization during the composite manufacture to form mullite. The formation of an outer crystalline layer, composed mainly of Al2O3, was also detected. Participation of other secondary interface reactions inside the active barrier was also identified by HREM techniques.

  1. Study on the mechanism of surface modification of magnesium oxysulfate whisker

    Energy Technology Data Exchange (ETDEWEB)

    Dang, Li [Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, Xining 810008 (China); University of Chinese Academy of Sciences, Beijing 100049 (China); Nai, Xueying; Zhu, Donghai [Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, Xining 810008 (China); Jing, Yanwei [Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, Xining 810008 (China); University of Chinese Academy of Sciences, Beijing 100049 (China); Liu, Xin; Dong, Yaping [Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, Xining 810008 (China); Li, Wu, E-mail: driverlaoli@163.com [Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, Xining 810008 (China)

    2014-10-30

    Graphical abstract: - Highlights: • Physisorbed lauric acid was ruled out by FT-IR spectroscopy. • The inexistence of physisorbed magnesium laurate was proved by DSC analyses. • {sup 13}C NMR further verified the formation of COO–Mg< bonds on the surface of MOSw. • “Acid-base neutralization” was proved by the pH meter monitoring synchronously. • The type of surface modification of MOSw was proved to be chemical adsorption only. - Abstract: Hydrophobic-lipophilic magnesium oxysulfate whisker (MOSw) was prepared by surface modification with lauric acid and the surface morphology of MOSw was examined with field emission scanning electron microscope (FESEM). X-ray powder diffraction (XRD) was used to characterize the crystalline degree of MOSw and modified MOSw (MOSw-LA). Both FESEM and XRD suggested that modification occurred on the surface of MOSw exclusively. The inexistence of physisorbed lauric acid was proved by Fouier transform infrared (FT-IR) spectroscopy. Thermogravimetric analyses ruled out the possibility that magnesium laurate (LA-Mg) physisorbed on the surface of MOSw-LA. Solid state {sup 13}C nuclear magnetic resonance ({sup 13}C NMR) further verified the formation of COO–Mg< bonds based on the significant changes of chemical shift and decrease in intensity. Hence, we confirmed that the type of surface modification of MOSw with lauric acid was chemical adsorption taken place between lauric acid and Mg<. In order to study the dynamic state approach of this reaction, a pH meter was employed to monitor the reaction process synchronously, and then we proposed a reaction mechanism which was similar to the “acid-base neutralization”. This research provides a detailed explanation for a kind of surface modification, which may be further used in the performance of whisker/polymer matrix composites.

  2. Formation of SiC thin films by chemical vapor deposition with vinylsilane precursor

    Science.gov (United States)

    Doi, Takuma; Takeuchi, Wakana; Jin, Yong; Kokubun, Hiroshi; Yasuhara, Shigeo; Nakatsuka, Osamu; Zaima, Shigeaki

    2018-01-01

    We have examined the formation of SiC thin films by chemical vapor deposition (CVD) using vinylsilane and investigated the chemical bonding state and crystallinity of the prepared SiC thin films. We achieved the formation of a Si–H–less SiC film at growth temperatures as low as 600 °C. Also, we investigated the in situ doping effect of N by the incorporation of NH3 gas in the SiC growth and demonstrated that the chemical composition of N in SiC thin films was controlled by adjusting the NH3 flow rate. In addition, we examined the growth of SiC thin films on a Cu substrate and achieved the formation of a SiC thin film while avoiding any significant reaction between SiC and Cu at a growth temperature of 700 °C.

  3. 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.

  4. Status and Prospects of SiC Power Devices

    Science.gov (United States)

    Bakowski, Mietek

    Silicon Carbide (SiC) power devices offer significant benefits of improved efficiency, dynamic performance and reliability of electronic and electric systems. The challenges and prospects of SiC power device development are reviewed considering different device types. A close correlation between an exponential increase of current handling capability during the last ten years and improvement in substrate quality is demonstrated. The voltage range of silicon and SiC unipolar and bipolar power devices with respect to the on-state voltage is determined based on device simulations. 4H-SiC unipolar devices are potentially superior to all silicon devices up to 5kV design voltage and to all SiC bipolar devices up to 5-6kV design voltage for temperatures up to 150°C. The low end of SiC unipolar devices is determined to be around 200V design voltage provided substrate resistance is reduced by reducing the thickness of the substrate down to 100μm. The influence of reduced channel mobility on the specific on-resistance of 4H-SiC and 3C-SiC DMOSFETs is shown. It has been demonstrated that 3C-SiC DMOSFETs could be a better choice compared to 4H-SiC DMOSFETs in the voltage range below 1.2kV utilising better channel mobility and larger substrate size obtainable in the near future in 3C-SiC polytype. An impact of the super junction (SJ) concept on silicon and SiC MOSFET specific on-resistance limits is demonstrated.

  5. Recent developments in SiC single-crystal electronics

    Science.gov (United States)

    Ivanov, P. A.; Chelnokov, V. E.

    1992-07-01

    The present paper is an analytical review of the last five or six years of research and development in SiC. It outlines the major achievements in single crystal growth and device technology. Electrical performance of SiC devices designed during these years and some new trends in SiC electronics are also discussed. During the 1980s the studies on sublimation and liquid-phase epitaxial growth of SiC single crystal were continued successfully. At that time, such methods as chemical vapour deposition, thermal oxidation, 'dry' plasma etching and ion implantation which yielded good results with silicon, came into use. As a result of the technological progress, discrete devices appeared, which incorporated the potential advantages of SiC as a wide bandgap material. Among these were high temperature (500-600 degrees C) rectifier diodes and field-effect transistors, high efficiency light-emitting diodes for the short-wave region of the visible spectrum, and detectors of ultraviolet radiation. It should be stressed that the devices were of commercial quality and could be applied in various fields (control systems of automobile engines, aerospace apparatus, geophysical equipment, colour displays in information systems, etc.). The developments in technology and the promising results of research on electrical performance of the devices already available give hope that in the near future SiC may become the basic material for power microwave devices, and for thermo- and radiation-resistant integrated circuits. This process can be stimulated by further perfection of single-crystal substrates of large area, by development of stable high temperature ohmic contacts, micro- and heterostructures.

  6. Detection Simulation of SiC Semiconductor Detector

    Energy Technology Data Exchange (ETDEWEB)

    Choi, Hong Yeop; Kim, Jeong Dong; Lee, Yong Deok; Kim, Ho Dong [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

    2013-10-15

    In a high radiation environment, it has received attention as a material for detecting radiation (neutron). As the field of application of a SIC neutron detector, the semiconductor detector used in cosmic rays was proposed by Ruddy. Recently, X-ray and low-energy gamma ray spectrometry with SiC detectors has been reported. Its usability has recently been being proved in neutron dose surveillance in BNCT (Boron-Capture Neutron Therapy), thermal neutron detection in a waste drum, nuclear material surveillance, and fast neutron detection. In addition, in 2006, an experiment was actually performed by Natsume on spent nuclear fuel. SIC is suitable for radiation surveillance in a complex radiation field emitted from spent nuclear fuel and the pyropocess process. In the radiation field of spent nuclear fuel, neutrons and gamma rays are generated. In this research, the performance of a SiC detector made at KAERI was evaluated to obtain a discriminated neutron signal. First, using neutron ({sup 252}Cf), alpha ({sup 241}Am), and gamma ({sup 60}Co) sources, a SiC semi- conductor detector was tested. The energy spectrum in a complex radiation field was simulated using the MCNPX 2.5. Finally, the experimental results by Ruddy were compared with the simulation results. Research result, whether the SiC semiconductor detector operating or not was confirmed through the simulation according to the neutron, gamma. The simulation results were similar to those of Ruddy. A further study is underway to investigate the discriminated neutron signal of a complex radiation field.

  7. High temperature deformation behaviour of particulate reinforced aluminium composites

    Energy Technology Data Exchange (ETDEWEB)

    Kwon, Hyuk Chon; Yoon, Eui Pak [Hanyang Univ., Seoul (Korea, Republic of)

    1995-10-01

    The hot deformation behaviour of particulate reinforced aluminium 6061 Al composite were investigated by hot compression tests in the temperature range from 623 K to 823 K with strain rate of 10{sup -3} {approx} 5.0 S{sup -1}. The effect of reinforced particulate volume fraction, mean diameter on the high temperature flow stress has also been studied. Experimental results showed that the increase in the volume fraction of reinforcement contributed to the rising of yield stress, but the stress above the yield point appeared to be steady at all volume fractions. The apparent activation energy for deformation was 290 kJ/mol for un reinforced 6061 Al, 327 kJ/mol for 6061 Al-20 vol.% SiC composite and 531 kJ/mol for 6061 Al-20 vol.% Al{sub 2}0{sub 3} composite. It appeared that Al{sub 2}0{sub 3} reinforced composites was more difficult to hot deform. (author). 21 refs., 9 figs., 3 tab.

  8. Packaging Technology for SiC High Temperature Electronics

    Science.gov (United States)

    Chen, Liang-Yu; Neudeck, Philip G.; Spry, David J.; Meredith, Roger D.; Nakley, Leah M.; Beheim, Glenn M.; Hunter, Gary W.

    2017-01-01

    High-temperature environment operable sensors and electronics are required for long-term exploration of Venus and distributed control of next generation aeronautical engines. Various silicon carbide (SiC) high temperature sensors, actuators, and electronics have been demonstrated at and above 500 C. A compatible packaging system is essential for long-term testing and application of high temperature electronics and sensors in relevant environments. This talk will discuss a ceramic packaging system developed for high temperature electronics, and related testing results of SiC integrated circuits at 500 C facilitated by this high temperature packaging system, including the most recent progress.

  9. Supernova Reverse Shocks and SiC Growth

    OpenAIRE

    Deneault, E. A. -N.; Clayton, D. D.; Heger, A.

    2003-01-01

    We present new mechanisms by which the isotopic compositions of X-type grains of presolar SiC are altered by reverse shocks in Type II supernovae. We address three epochs of reverse shocks: pressure wave from the H envelope near t = 10$^6$s; reverse shock from the presupernova wind near 10$^8-10^9$s; reverse shock from the ISM near 10$^{10}$s. Using 1-D hydrodynamics we show that the first creates a dense shell of Si and C atoms near 10$^6$s in which the SiC surely condenses. The second rever...

  10. Habituation of reinforcer effectiveness

    Directory of Open Access Journals (Sweden)

    David R Lloyd

    2014-01-01

    Full Text Available In this paper we propose an integrative model of habituation of reinforcer effectiveness (HRE that links behavioral and neural based explanations of reinforcement. We argue that habituation of reinforcer effectiveness (HRE is a fundamental property of reinforcing stimuli. Most reinforcement models implicitly suggest that the effectiveness of a reinforcer is stable across repeated presentations. In contrast, an HRE approach predicts decreased effectiveness due to repeated presentation. We argue that repeated presentation of reinforcing stimuli decreases their effectiveness and that these decreases are described by the behavioral characteristics of habituation (McSweeney and Murphy, 2009;Rankin et al., 2009. We describe a neural model that postulates a positive association between dopamine neurotransmission and HRE. We present evidence that stimulant drugs, which artificially increase dopamine neurotransmission, disrupt (slow normally occurring HRE and also provide evidence that stimulant drugs have differential effects on operant responding maintained by reinforcers with rapid vs. slow HRE rates. We hypothesize that abnormal HRE due to genetic and/or environmental factors may underlie some behavioral disorders. For example, recent research indicates that slow-HRE is predictive of obesity. In contrast ADHD may reflect ‘accelerated-HRE’. Consideration of HRE is important for the development of effective reinforcement based treatments. Finally, we point out that most of the reinforcing stimuli that regulate daily behavior are non-consumable environmental/social reinforcers which have rapid-HRE. The almost exclusive use of consumable reinforcers with slow-HRE in pre-clinical studies with animals may have caused the importance of HRE to be overlooked. Further study of reinforcing stimuli with rapid-HRE is needed in order to understand how habituation and reinforcement interact and regulate behavior.

  11. 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.

  12. Epitaxial grapheme on SiC(0001) and SiC(000-1): a photoelectron diffraction (XPD) study

    Energy Technology Data Exchange (ETDEWEB)

    Lima, L.H.; Siervo, A.; Landers, R. [Universidade Estadual de Campinas (IFGW/UNICAMP), SP (Brazil). Inst. de Fisica Gleb Wataghin; Goncalves, A.B.; Lacerda, R.G. [Universidade Federal de Minas Gerais (UFMG), Belo Horizonte, MG (Brazil). Dept. de Fisica; Tapia, P.H. [Universidad Tecnica Federico Santa Maria, Valparaiso (Chile)

    2011-07-01

    Full text. A flat, single layer of graphite known as grapheme has become the focus of studies due to its exceptional properties and fascinating applications. Large scale grapheme layers for a possible application can be grown epitaxially on SiC by Si sublimation. Even before the interest in grapheme, the surface of SiC was already extensively studied. It exhibits a large variety of surface reconstructions and these reconstructions are very dependent of sample preparation and orientation (0001) or (000-1). In this study, we show a preliminary investigation of the structural properties of grapheme layers on SiC (0001) e SiC (000-1) by photoelectron diffraction (XPD). The surfaces were prepared by heating the 1x1 surface to temperatures of about 1150 deg C in high ultra vacuum and the various reconstructions were monitored by Low Energy Electron Diffraction (LEED) and X-Ray Photoelectron Spectroscopy (XPS). In particular for the Si-terminated surface, that is SiC(0001), the interface between grapheme and SiC is characterized by the so-called (6{radical}3 x 6{radical}3) R30 deg reconstruction (buffer layer). The interpretation of this reconstruction, which is the initial stage of graphitization, has lead to controversy in the literature. We will further discuss the buffer layer structure in terms of the XPD results. The XPD experiments were performed at SGM beam line at LNLS using photons with 400/450 eV probing the Si2p and C1s core level. The C1s signal was separate in to contributions from volume and surface and compares the experimental results with photoelectron multiple scattering calculations performed with the MSCD package

  13. Bi-2212 and Y123 highly curved single-crystal-like objects: whiskers, bows and ring-like structures

    Science.gov (United States)

    Badica, Petre; Agostino, Angelo; Mizanur Rahman Khan, Mohammad; Cagliero, Stefano; Plapcianu, Carmen; Pastero, Linda; Truccato, Marco; Hayasaka, Yuichiro; Jakob, Gerhard

    2012-10-01

    High-temperature superconducting objects of Bi2Sr2CaCu2O8 and Y Ba2Cu3O7 highly curved in the ab-plane, such as curved/kinked whiskers, bows and ring-like structures, were obtained within a solid-liquid-solid (SLS) grass-like growth mechanism. As-grown objects are crystals with three-dimensional epitaxy similar to conventional single crystals: they can be viewed as crystal parts ‘cut’ from a conventional rectangular crystal. Between our curved objects and conventional crystals, whiskers or thin films there are some differences in the superconducting properties induced only by the shape factors and no new physics is observed. Some details of the growth mechanism are discussed, emphasizing curved-line formation.

  14. 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

  15. Stress Analysis of SiC MEMS Using Raman Spectroscopy

    Science.gov (United States)

    Ness, Stanley J.; Marciniak, M. A.; Lott, J. A.; Starman, L. A.; Busbee, J. D.; Melzak, J. M.

    2003-03-01

    During the fabrication of Micro-Electro-Mechanical Systems (MEMS), residual stress is often induced in the thin films that are deposited to create these systems. These stresses can cause the device to fail due to buckling, curling, or fracture. Industry is looking for ways to characterize the stress during the deposition of thin films in order to reduce or eliminate device failure. Micro-Raman spectroscopy has been successfully used to characterize poly-Si MEMS devices made with the MUMPS® process. Raman spectroscopy was selected because it is nondestructive, fast and has the potential for in situ stress monitoring. This research attempts to use Raman spectroscopy to analyze the stress in SiC MEMS made with the MUSiC® process. Raman spectroscopy is performed on 1-2-micron-thick SiC thin films deposited on silicon, silicon nitride, and silicon oxide substrates. The most common poly-type of SiC found in thin film MEMS made with the MUSiC® process is 3C-SiC. Research also includes baseline spectra of 6H, 4H, and 15R poly-types of bulk SiC.

  16. Passivation of SiC device surfaces by aluminum oxide

    Science.gov (United States)

    Hallén, A.; Usman, M.; Suvanam, S.; Henkel, C.; Martin, D.; Linnarsson, M. K.

    2014-03-01

    A steady improvement in material quality and process technology has made electronic silicon carbide devices commercially available. Both rectifying and switched devices can today be purchased from several vendors. This successful SiC development over the last 25 years can also be utilized for other types of devices, such as light emitting and photovoltaic devices, however, there are still critical problems related to material properties and reliability that need to be addressed. This contribution will focus on surface passivation of SiC devices. This issue is of utmost importance for further development of SiC MOSFETs, which so far has been limited by reliability and low charge carrier surface mobilities. Also bipolar devices, such as BJTs, LEDs, or PV devices will benefit from more efficient and reliable surface passivation techniques in order to maintain long charge carrier lifetimes. Silicon carbide material enables the devices to operate at higher electric fields, higher temperatures and in more radiation dense applications than silicon devices. To be able to utilize the full potential of the SiC material, it is therefore necessary to develop passivation layers that can sustain these more demanding operation conditions. In this presentation it will also be shown that passivation layers of Al2O3 deposited by atomic layer deposition have shown superior radiation hardness properties compared to traditional SiO2-based passivation layers.

  17. Conducted EMI in Inverters with SiC Transistors

    NARCIS (Netherlands)

    Gong, X.

    2013-01-01

    Conducted EMI in Inverters with SiC Transistors Electromagnetic Interference (EMI) is the main side effect accompanied with the fast voltage and current switching transients in power electronics applications. Compliance of the Electromagnetic Compatibility (EMC) standard is prescribed for any power

  18. 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 ...

  19. Crystal growth and characterization of fluorescent SiC

    DEFF Research Database (Denmark)

    Wellmann, P.; Kaiser, M.; Hupfer, T.

    Silicon carbide (SiC) is widely used as substrate for nitride based light emitting diodes (LEDs). For today’s white LEDs mainly a sandwich structure of a blue or ultra violet LED and a yellowish phosphorus is used. In the frame of European project we study a concept to implement the functionality...

  20. Performance of bulk SiC radiation detectors

    CERN Document Server

    Cunningham, W; Lamb, G; Scott, J; Mathieson, K; Roy, P; Bates, R; Thornton, P; Smith, K M; Cusco, R; Glaser, M; Rahman, M

    2002-01-01

    SiC is a wide-gap material with excellent electrical and physical properties that may make it an important material for some future electronic devices. The most important possible applications of SiC are in hostile environments, such as in car/jet engines, within nuclear reactors, or in outer space. Another area where the material properties, most notably radiation hardness, would be valuable is in the inner tracking detectors of particle physics experiments. Here, we describe the performance of SiC diodes irradiated in the 24 GeV proton beam at CERN. Schottky measurements have been used to probe the irradiated material for changes in I-V characteristics. Other methods, borrowed from III-V research, used to study the irradiated surface include atomic force microscope scans and Raman spectroscopy. These have been used to observe the damage to the materials surface and internal lattice structure. We have also characterised the detection capabilities of bulk semi-insulating SiC for alpha radiation. By measuring ...

  1. Porous Alumina Ceramics Modified with SiC Nanopowder

    OpenAIRE

    Zaķe-Tiļuga, I; Švinka, R; Švinka, V

    2011-01-01

    The aim of this study was to clarify how addition of plasma synthesized SiC nanopowder (up to 5 wt%) affect some properties (e.g., shrinkage, bending strength and thermal shock resistance) of porous alumina ceramics produced by slip casting method.

  2. Low Temperature Photoluminescence of 6H fluorescent SiC

    DEFF Research Database (Denmark)

    Wei, Yi; Künecke, Ulrike; Jokubavicius, Valdas

    We have presented the low temperature photoluminescence (PL) measurements of three 6H fluorescent Silicon Carbide (f-SiC) samples. The epilayers of the f-SiC samples were nitrogenboron co-doped and grown by fast sublimation growth process (FSGP) method on the bulk 6H SiC substrates. The doping...

  3. Microstructural and mechanical behaviors of nano-SiC-reinforced AA7075-O FSW joints prepared through two passes

    Energy Technology Data Exchange (ETDEWEB)

    Bahrami, Mohsen, E-mail: Mohsen.bahrami@aut.ac.ir [Faculty of Mining and Materials Engineering, Amirkabir University of Technology (AUT), Hafez Aveenue, Tehran (Iran, Islamic Republic of); Farahmand Nikoo, Mohsen [Faculty of Mining and Materials Engineering, Amirkabir University of Technology (AUT), Hafez Aveenue, Tehran (Iran, Islamic Republic of); Besharati Givi, Mohammad Kazem [Department of Mechanical Engineering, University of Tehran, Tehran (Iran, Islamic Republic of)

    2015-02-25

    In this paper, a threaded tapered pin tool was employed to fabricate a 2-pass friction stir welded (FSWed) joint. To investigate the benefits of nano-sized SiC particles on microstructural and mechanical properties of the joint, the experiment was repeated while SiC particles had been inserted along the joint line. In another joint, a square pin tool was applied in the second pass to evaluate the effectiveness of switching pin geometry between passes on the aforementioned properties. Microstructural features including grain size, second phase particles and reinforcement distribution were examined via optical and scanning electron microscopy (SEM) techniques. In addition to satisfactory connections between SiC particles and the matrix, the most homogenous particles distribution was observed in the specimen FSWed with both pin tools. This observation was further supported by atomic force microscopy (AFM) examination. Additionally, the foregoing joint demonstrated the maximum tensile strength which was synonymous with its smallest grain size. During tensile testing, SiC-free joint and SiC-reinforced ones fractured from stir zone (SZ) and base metal, respectively. Moreover, SiC-free joint showed necking phenomenon. SEM results showed that the SiC-reinforced specimens possessed ductile fracture morphologies. On the other hand, SiC-free specimen showed a quasi-cleavage fracture mode confirming its moderate percent elongation. In the meantime, SiC-reinforced specimens exhibited superior hardness level to SiC-free specimen.

  4. First principle identification of SiC monolayer as an efficient catalyst for CO oxidation

    Energy Technology Data Exchange (ETDEWEB)

    Sinthika, S., E-mail: ranjit.t@res.srmuniv.ac.in, E-mail: sinthika90@gmail.com; Thapa, Ranjit, E-mail: ranjit.t@res.srmuniv.ac.in, E-mail: sinthika90@gmail.com [SRM Research Institute, SRM University, Kattankulathur 603203, Tamil Nadu (India); Reddy, C. Prakash [Department of Physics and Nanotechnology, SRM University, Kattankulathur 603203, Tamil Nadu (India)

    2015-06-24

    Using density functional theory, we investigated the electronic properties of SiC monolayer and tested its catalytic activity toward CO oxidation. The planar nature of a SiC monolayer is found to stable and is a high band gap semiconductor. CO interacts physically with SiC surface, whereas O{sub 2} is adsorbed with moderate binding. CO oxidation on SiC monolayer prefers the Eley Rideal mechanism over the Langmuir Hinshelwood mechanism, with an easily surmountable activation barrier during CO{sub 2} formation. Overall metal free SiC monolayer can be used as efficient catalyst for CO oxidation.

  5. Whiskers amiss, a new vibrissae and hair mutation near the Krt1 cluster on mouse chromosome 11.

    Science.gov (United States)

    Taylor, L A; Harris, M J; Juriloff, D M

    2000-04-01

    Whiskers amiss (wam) is a new spontaneous recessive mutation in the SELH/Bc strain of mice that causes a phenotype of askew, sometimes kinked or curled, breakable whiskers and disheveled-appearing body hair, apparently owing to disoriented guard hairs. Heterozygotes on three genetic backgrounds are indistinguishable from normal. Using informative SSLPs in the F2 generation after crosses to two normal strains, we have mapped wam to the region of the type I keratin cluster on Chromosome (Chr) 11, within an approximately 6-cM segment according to the current Mouse Genome Database (MGD) map position of flanking SSLPs. Although several other hair mutations also map to the Krt1 region (Re, Rim3, Bdai, Bsk), none has a hair and whisker phenotype similar to that of wam, and, because all are transmitted as dominants, interpretable complementation tests could not be done. Scabbing and tissue loss occur on the rims of the pinnae and tail tip in some aging wam homozygotes, suggesting that wam may be an animal model of a genetic ectodermal disorder. The SELH/Bc strain background appears to have an unusually high rate of spontaneous mutation; wam is the sixth mutation to be described.

  6. Experimental study of thermo-mechanical behavior of SiC composite tubing under high temperature gradient using solid surrogate

    Energy Technology Data Exchange (ETDEWEB)

    Alva, Luis; Shapovalov, Kirill [University of South Carolina, Mechanical Engineering Department (United States); Jacobsen, George M.; Back, Christina A. [General Atomics (United States); Huang, Xinyu, E-mail: huangxin@mailbox.sc.edu [University of South Carolina, Mechanical Engineering Department (United States)

    2015-11-15

    Nuclear grade silicon carbide fiber (SiC{sub f}) reinforced silicon carbide matrix (SiC{sub m}) composite is a promising candidate material for accident tolerance fuel (ATF) cladding. A major challenge is ensuring the mechanical robustness of the ceramic cladding under accident conditions. In this work the high temperature mechanical response of a SiC{sub f}–SiC{sub m} composite tubing is studied using a novel thermo-mechanical test method. A solid surrogate tube is placed within and bonded to the SiC{sub f}–SiC{sub m} sample tube using a ceramic adhesive. The bonded tube pair is heated from the center using a ceramic glower. During testing, the outer surface temperature of the SiC sample tube rises up to 1274 K, and a steep temperature gradient develops through the thickness of the tube pair. Due to CTE mismatch and the temperature gradient, the solid surrogate tube induces high tensile stress in the SiC sample. During testing, 3D digital image correlation (DIC) method is used to map the strains on the outer surface of the SiC-composite, and acoustic emissions (AE) are monitored to detect the onset and progress of material damage. The thermo-mechanical behavior of SiC-composite sample is compared with that of monolithic SiC samples. Finite element models are developed to estimate stress–strain distribution within the tube assembly. Model predicted surface strain matches the measured surface strain using the DIC method. AE activities indicated a progressive damage process for SiC{sub f}–SiC{sub m} composite samples. For the composites tested in this study, the threshold mechanical hoop strain for matrix micro-cracking to initiate in SiC{sub f}–SiC{sub m} sample is found to be ∼300 microstrain.

  7. Carbon Nanotubes Reinforced Composites for Biomedical Applications

    National Research Council Canada - National Science Library

    Wang, Wei; Zhu, Yuhe; Liao, Susan; Li, Jiajia

    2014-01-01

    .... The review introduced fabrication of CNTs reinforced composites (CNTs reinforced metal matrix composites, CNTs reinforced polymer matrix composites, and CNTs reinforced ceramic matrix composites...

  8. Mechanical Properties and Corrosion Behaviour of Aluminium Hybrid Composites Reinforced with Silicon Carbide and Bamboo Leaf Ash

    Directory of Open Access Journals (Sweden)

    K.K. Alaneme

    2013-03-01

    Full Text Available The viability of developing low cost – high performance Al matrix hybrid composites with the use of bamboo leaf ash (an agro waste ash and silicon carbide as complementing reinforcements was investigated. Silicon carbide (SiCparticulates added with 0, 2, 3, and 4 wt% bamboo leaf ash (BLA were utilized to prepare 10 wt% of the reinforcing phase with Al-Mg-Si alloy as matrix using two-step stir casting method. Microstructural characterization, mechanical properties evaluation and corrosion behaviour were used to assess the performance of the composites. The results show that the hardness, ultimate tensile strength, and percent elongation of the hybrid composites decrease with increase in BLA content. The fracture toughness of the hybrid composites were however superior to that of the single reinforced Al - 10 wt% SiC composite. Only the 2 wt % BLA containing hybrid composite had specific strength value comparable to that of the single reinforced composite. In 5wt% NaCl solution, it was observed that the 2 and 3 wt % BLA containing hybrid composites had higher corrosion resistance in comparison to the single reinforced Al - 10 wt% SiC composite but the reverse trend was observed in 0.3M H2SO4 solution where the single reinforced had superior corrosion resistance.

  9. The Reinforcement Learning Competitions

    NARCIS (Netherlands)

    Whiteson, S.; Tanner, B.; White, A.

    2010-01-01

    This article reports on the reinforcement learning competitions, which have been held annually since 2006. In these events, researchers from around the world developed reinforcement learning agents to compete in domains of various complexity and difficulty. We focus on the 2008 competition, which

  10. Continuous Reinforced Concrete Beams

    DEFF Research Database (Denmark)

    Hoang, Cao Linh; Nielsen, Mogens Peter

    1996-01-01

    This report deals with stress and stiffness estimates of continuous reinforced concrete beams with different stiffnesses for negative and positive moments e.g. corresponding to different reinforcement areas in top and bottom. Such conditions are often met in practice.The moment distribution...

  11. Effects of Surface Treatment Processes of SiC Ceramic on Interfacial Bonding Property of SiC-AFRP

    Directory of Open Access Journals (Sweden)

    WEI Ru-bin

    2016-12-01

    Full Text Available To improve the interfacial bonding properties of SiC-aramid fiber reinforced polymer matrix composites (SiC-AFRP, the influences of etching process of SiC ceramic, coupling treatment process, and the adhesives types on the interfacial peel strength of SiC-AFRP were studied. The results show that the surface etching process and coupling treatment process of silicon carbide ceramic can effectively enhance interfacial bonding property of the SiC-AFRP. After soaked the ceramic in K3Fe(CN6 and KOH mixed etching solution for 2 hours, and coupled with vinyl triethoxy silane coupling agent, the interfacial peel strength of the SiC-AFRP significantly increases from 0.45kN/m to 2.20kN/m. EVA hot melt film with mass fraction of 15%VA is ideal for interface adhesive.

  12. Composite Intersection Reinforcement

    Science.gov (United States)

    Misciagna, David T. (Inventor); Fuhrer, Jessica J. (Inventor); Funk, Robert S. (Inventor); Tolotta, William S. (Inventor)

    2013-01-01

    An assembly and method for manufacturing a composite reinforcement for unitizing a structure are provided. According to one embodiment, the assembly includes a base having a plurality of pins extending outwardly therefrom to define a structure about which a composite fiber is wound to define a composite reinforcement preform. The assembly also includes a plurality of mandrels positioned adjacent to the base and at least a portion of the composite reinforcement preform, and a cap that is positioned over at least a portion of the plurality of mandrels. The cap is configured to engage each of the mandrels to support the mandrels and the composite reinforcement preform during a curing process to form the composite reinforcement.

  13. Phase-slip centers in superconducting whiskers of Pb with small concentrations of In and Bi

    Science.gov (United States)

    Damaschke, B.; Tidecks, R.

    1990-05-01

    The current-induced transition from the superconducting to the normal state in whiskers from Pb, Pb-In and Pb-Bi has been investigated. Very close to the critical temperature T c0 the voltage-current (V-I) characteristics show linear portions that are not separated by voltage jumps. For lower temperatures a voltage-step structure occurs. The temperature region over which the step structure extends is shifted towards T c0 for decreasing mean free path l of the conduction electrons. The differential resistance of the first linear part of the characteristics in most cases does not depend on temperature like the related normal-like length that is proportional to l1/2 in agreement with the phase-slip model of Skocpol, Beasley, and Tinkham. Very close to T c0 the time-averaged supercurrent still flowing above the critical current is about the critical current itself. The shape and the characteristic properties of the V I characteristics are compared with theoretical predictions.

  14. Magnetoresistance of proton irradiated Si0.97Ge0.03 whiskers

    Directory of Open Access Journals (Sweden)

    Nadezhda T. Pavlovskaya

    2016-09-01

    The effects of proton irradiation and high magnetic fields on the magnetoresistance of Si1-xGex (x = 0,03 whiskers in the 4.2–300 K temperature range has been studied. A slight decrease in the electrical resistance of the crystals in the 4.2–40 K temperature range during irradiation with small proton doses and a significant increase in their resistance in the entire investigated temperature range for a dose of 1×1017 p+/cm2 have been found. The ionization energy of the impurity atoms in different magnetic fields has been calculated. It has been revealed that the energy level of the impurity depends on the magnetic field but slightly which in turn indicates a independence of the concentration of holes on the magnetic field. It has been shown that a significant magnetoresistance at all studied temperatures was due to the magnetic field-caused decrease in the mobility of free carriers (holes. It has been found that the concentration of holes depends on magnetic field but a little. Conclusion has been made about a negligible expansion of the band gap in magnetic fields of up to 8 T.

  15. Stability of Neural Firing in the Trigeminal Nuclei under Mechanical Whisker Stimulation

    Directory of Open Access Journals (Sweden)

    Valeri A. Makarov

    2010-01-01

    Full Text Available Sensory information handling is an essentially nonstationary process even under a periodic stimulation. We show how the time evolution of ridges in the wavelet spectrum of spike trains can be used for quantification of the dynamical stability of the neuronal responses to a stimulus. We employ this method to study neuronal responses in trigeminal nuclei of the rat provoked by tactile whisker stimulation. Neurons from principalis (Pr5 and interpolaris (Sp5i show the maximal stability at the intermediate (50 ms stimulus duration, whereas Sp5o cells “prefer” shorter (10 ms stimulation. We also show that neurons in all three nuclei can perform as stimulus frequency filters. The response stability of about 33% of cells exhibits low-pass frequency dynamics. About 57% of cells have band-pass dynamics with the optimal frequency at 5 Hz for Pr5 and Sp5i, and 4 Hz for Sp5o, and the remaining 10% show no prominent dependence on the stimulus frequency. This suggests that the neural coding scheme in trigeminal nuclei is not fixed, but instead it adapts to the stimulus characteristics.

  16. Elements of solid state electronics based on soi-structures and si whiskers for cryogenic temperatures

    Directory of Open Access Journals (Sweden)

    Druzhinin A. A.

    2014-12-01

    Full Text Available The paper presents the study results of electrical properties of polycrystalline silicon films in silicon-on-insulator structures and Si whiskers in the temperature range of 4,2—70 K obtained by impedance measurements in the frequency range from 10 Hz to 250 kHz and the possibility of their use in solid-state electronics, functioning at cryogenic temperatures. Characteristics of samples obtained with impedance measurements allow to predict certain specifications of reactive elements of solid state electronics based on polycrystalline and single crystalline silicon, operable at low temperatures. Using the established dependencies, separate elements in the form of solid-state electronics capacitive and inductive elements as well as a combined system in an oscillatory circuit, operable at cryogenic temperatures, have been suggested. The features of developed system depend on the structure of samples and their doping level, which allows to change the required parameters of the elements of solid state electronics in a wide range.

  17. Whisker Deprivation Drives Two Phases of Inhibitory Synapse Weakening in Layer 4 of Rat Somatosensory Cortex.

    Directory of Open Access Journals (Sweden)

    Melanie A Gainey

    Full Text Available Inhibitory synapse development in sensory neocortex is experience-dependent, with sustained sensory deprivation yielding fewer and weaker inhibitory synapses. Whether this represents arrest of synapse maturation, or a more complex set of processes, is unclear. To test this, we measured the dynamics of inhibitory synapse development in layer 4 of rat somatosensory cortex (S1 during continuous whisker deprivation from postnatal day 7, and in age-matched controls. In deprived columns, spontaneous miniature inhibitory postsynaptic currents (mIPSCs and evoked IPSCs developed normally until P15, when IPSC amplitude transiently decreased, recovering by P16 despite ongoing deprivation. IPSCs remained normal until P22, when a second, sustained phase of weakening began. Delaying deprivation onset by 5 days prevented the P15 weakening. Both early and late phase weakening involved measurable reduction in IPSC amplitude relative to prior time points. Thus, deprivation appears to drive two distinct phases of active IPSC weakening, rather than simple arrest of synapse maturation.

  18. Facile synthesis of Cu/tetrapod-like ZnO whisker compounds with enhanced photocatalytic properties

    Science.gov (United States)

    Liu, Hong; Liu, Huarong; Fan, Ximei

    2017-09-01

    Cu/tetrapod-like ZnO whisker (T-ZnOw) compounds were successfully synthesized using N2H4 \\cdot H2O as a reducing agent by a simple reduction method without any insert gas at room temperature. The crystal phase composition and morphology of the as-prepared samples were investigated by XRD, SEM and FESEM tests. The photocatalytic property of the as-prepared samples was detected by the degradation of methyl orange (MO) aqueous solution under UV irradiation. It can be found that Cu nanoparticles (CuNPs) dispersed on the surface of T-ZnOw increased with the increasing of Cu/Zn molar ratios (Cu/Zn MRs), and an octahedral structure of CuNPs was obtained when the sample was prepared with less than and equal to 7.30% Cu/Zn MR, but tended to a spherical or nanorod structure of CuNPs densely arranged on the surface of T-ZnOw, which is prepared by Cu/Zn MRs up to 22.00%. All the compounds exhibited excellent photocatalytic activity in decomposing of MO than T-ZnOw, the photocatalytic property of the samples increased with the increasing of Cu/Zn MRs up to 7.30%, while it decreases when further increasing the Cu/Zn MRs. The Schottky barrier of the Cu/T-ZnOw compound can effectively capture photoinduced electrons from the interface and enhanced the photocatalytic property of T-ZnOw.

  19. Microstructure and Mechanical Behaviour of Stir-Cast Al-Mg-Sl Alloy Matrix Hybrid Composite Reinforced with Corn Cob Ash and Silicon Carbide

    Directory of Open Access Journals (Sweden)

    Oluwagbenga Babajide Fatile

    2014-10-01

    Full Text Available In this present study, the microstructural and mechanical behaviour of Al-Mg-Si alloy matrix composites reinforced with silicon carbide (SiC and Corn cob ash (An agro‑waste was investigated. This research work was aimed at assessing the suitability of developing low cost- high performance Al-Mg-Si hybrid composite. Silicon carbide (SiC particulates added with 0,1,2,3 and 4 wt% Corn cob ash (CCA were utilized to prepare 10 wt% of the reinforcing phase with Al-Mg-Si alloy as matrix using two-step stir casting method. Microstructural characterization, density measurement, estimated percent porosity, tensile testing, and micro‑hardness measurement were used to characterize the composites produced. From the results obtained, CCA has great potential to serve as a complementing reinforcement for the development of low cost‑high performance aluminum hybrid composites.

  20. Neurons in the barrel cortex turn into processing whisker and odor signals: a cellular mechanism for the storage and retrieval of associative signals

    Directory of Open Access Journals (Sweden)

    Dangui eWang

    2015-08-01

    Full Text Available Associative learning and memory are essential to logical thinking and cognition. How the neurons are recruited as associative memory cells to encode multiple input signals for their associated storage and distinguishable retrieval remains unclear. We studied this issue in the barrel cortex by in vivo two-photon calcium imaging, electrophysiology and neural tracing in our mouse model that the simultaneous whisker and olfaction stimulations led to odorant-induced whisker motion. After this cross-modal reflex arose, the barrel and piriform cortices connected. More than 40% of barrel cortical neurons became to encode odor signal alongside whisker signal. Some of these neurons expressed distinct activity patterns in response to acquired odor signal and innate whisker signal, and others encoded similar pattern in response to these signals. In the meantime, certain barrel cortical astrocytes encoded odorant and whisker signals. After associative learning, the neurons and astrocytes in the sensory cortices are able to store the newly learnt signal (cross-modal memory besides the innate signal (native-modal memory. Such associative memory cells distinguish the differences of these signals by programming different codes and signify the historical associations of these signals by similar codes in information retrievals.

  1. Ethanolic extract of Astragali radix and Salviae radix prohibits oxidative brain injury by psycho-emotional stress in whisker removal rat model.

    Directory of Open Access Journals (Sweden)

    Hyeong-Geug Kim

    Full Text Available Myelophil, an ethanolic extract of Astragali Radix and Salviae Radix, has been clinically used to treat chronic fatigue and stress related disorders in South Korea. In this study, we investigated the protective effects of Myelophil on a whisker removal-induced psycho-emotional stress model. SD rats were subjected to whisker removal after oral administration of Myelophil or ascorbic acid for consecutive 4 days. Whisker removal considerably increased total reactive oxygen species in serum levels as well as cerebral cortex and hippocampal regions in brain tissues. Lipidperoxidation levels were also increased in the cerebral cortex, hippocampus regions, and brain tissue injuries as shown in histopathology and immunohistochemistry. However, Myelophil significantly ameliorated these alterations, and depletion of glutathione contents in both cerebral cortex and hippocampus regions respectively. Serum levels of corticosterone and adrenaline were notably altered after whisker removal stress, whereas these abnormalities were significantly normalized by pre-treatment with Myelophil. The NF-κB was notably activated in both cerebral cortex and hippocampus after whisker removal stress, while it was efficiently blocked by pre-treatment with Myelophil. Myelophil also significantly normalizes alterations of tumor necrosis factor-α, interleukin (IL-1β, IL-6 and interferon-γ in both gene expressions and protein levels. These results suggest that Myelophil has protective effects on brain damages in psycho-emotional stress, and the underlying mechanisms involve regulation of inflammatory proteins, especially NF-κB modulation.

  2. Mechanical and Tribological Characteristics of TIG Hardfaced Dispersive Layer by Reinforced with Particles Extruded Aluminium

    Directory of Open Access Journals (Sweden)

    R. Dimitrova

    2017-05-01

    Full Text Available The article presents the results of the implemented technology for generation of hardfaced dispersive layers obtained by additive material containing reinforcing phase of non-metal particles. The wear resistant coatings are deposited on pure aluminium metal matrix by shielded gas metal-arc welding applying tungsten inert gas (TIG with extruded aluminium wire reinforced by particles as additive material. Wire filler is produced by extrusion of a pack containing metalized and plated by flux micro/nano SiC particles. The metalized particles implanting in the metal matrix and its dispersive hardfacing are realized by solid-state welding under conditions of hot plastic deformation. Tribological characteristics are studied of the hardfaced layers of dispersive reinforced material on pure aluminium metal matrix with and without flux. Hardness profiles of the hardfaced layers are determined by nanoindentation. The surface layers are studied by means of Scanning Electron Microscopy (SEM and Energy Dispersive X-ray (EDX analysis. Increase by 15-31 % of the wear resistance of the hardfaced layers and 30-40 % of their hardness was found, which is due to the implanted in the layer reinforcing phase of metalized micro/nano SiC particles.

  3. Comportamiento frente a la corrosión del material compuesto 2124/SiC

    Directory of Open Access Journals (Sweden)

    López-Caballero, J. A.

    2005-12-01

    Full Text Available A comparative study was performed on the corrosion behaviour of an aluminium matrix composite reinforced with silicon carbide particles, obtained by powder metallurgic. The 2124/SiC material was heat treated using T4 and T6 procedures. The T6 heat treatment induced the formation of several intermetallics and reducing the corrosion resistance. The silicon carbide particles did not have a cathodic behaviour as compared with the aluminium matrix. However, these particles produced a diminution in the corrosion resistance due to the formation of more active zones in the matrix/reinforced interface. These ceramic particles caused intermetallic precipitation and deformation originating in the surrounding zones localized corrosion.

    Se realiza un estudio comparativo del comportamiento frente a la corrosión de la aleación de aluminio 2124 reforzada con partículas de carburo de silicio, obtenida por pulvimetalurgia y con tratamientos térmicos T4 y T6. Los resultados experimentales muestran que el tratamiento térmico T6 induce la formación de numerosos intermetálicos que reducen la resistencia a la corrosión. Las partículas de carburo de silicio no tienen un comportamiento catódico con respecto a la matriz de aluminio, sin embargo, disminuyen la resistencia a la corrosión, ya que generan zonas más activas en la interfase matriz/ refuerzo, debido a la acumulación de dislocaciones, tensiones residuales y a la precipitación de intermetálicos.

  4. Intercalated europium metal in epitaxial graphene on SiC

    Science.gov (United States)

    Anderson, Nathaniel A.; Hupalo, Myron; Keavney, David; Tringides, Michael C.; Vaknin, David

    2017-10-01

    X-ray magnetic circular dichroism (XMCD) reveals the magnetic properties of intercalated europium metal under graphene on SiC(0001). The intercalation of Eu nanoclusters (average size 2.5 nm) between graphene and SiC substate are formed by deposition of Eu on epitaxially grown graphene that is subsequently annealed at various temperatures while keeping the integrity of the graphene layer. Using sum-rules analysis of the XMCD of Eu M4 ,5 edges at T =15 K, our samples show paramagnetic-like behavior with distinct anomaly at T ≈90 K, which may be related to the Nèel transition, TN=91 K, of bulk metal Eu. We find no evidence of ferromagnetism due to EuO or antiferromagnetism due to Eu2O3 , indicating that the graphene layer protects the intercalated metallic Eu against oxidation over months of exposure to atmospheric environment.

  5. 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.

  6. POWDER INJECTION MOLDING OF SIC FOR THERMAL MANAGEMENT V

    Directory of Open Access Journals (Sweden)

    Valmikanathan Onbattuvelli

    2012-06-01

    Full Text Available Silicon carbide (SiC exhibits many functional properties that are relevant to applications in electronics, aerospace, defense and automotive industries. However, the successful translation of these properties into final applications lies in the net-shaping of ceramics into fully dense microstructures. Increasing the packing density of the starting powders is one effective route to achieve high sintered density and dimensional precision. The present paper presents an in-depth study on the effects of nanoparticle addition on the powder injection molding process (PIM of SiC powder-polymer mixtures. In particular, bimodal mixtures of nanoscale and sub-micrometer particles are found to have significantly increased powder packing characteristics (solids loading in the powder-polymer mixtures. The influence of nanoparticle addition on the multi-step PIM process is examined. The above results provide new perspectives which could impact a wide range of materials, powder processing techniques and applications.

  7. Surface functionalization and biomedical applications based on SiC

    Energy Technology Data Exchange (ETDEWEB)

    Yakimova, R; Petoral, R M Jr; Yazdi, G R; Vahlberg, C; Spetz, A Lloyd; Uvdal, K [Department of Physics, Chemistry and Biology, Linkoeping University, SE-58183 Linkoeping (Sweden)

    2007-10-21

    The search for materials and systems, capable of operating long term under physiological conditions, has been a strategy for many research groups during the past years. Silicon carbide (SiC) is a material, which can meet the demands due to its high biocompatibility, high inertness to biological tissues and to aggressive environment, and the possibility to make all types of electronic devices. This paper reviews progress in biomedical and biosensor related research on SiC. For example, less biofouling and platelet aggregation when exposed to blood is taken advantage of in a variety of medical implantable materials while the robust semiconducting properties can be explored in surface functionalized bioelectronic devices. (review article)

  8. 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.

  9. Progress of d0 magnetism in SiC

    Science.gov (United States)

    Wang, Yutian; Liu, Chenguang; Zhang, Yuming

    2017-03-01

    The properties of defect-induced ferromagnetism ({{{d}}}0 magnetism) in SiC belong to carbon-based material which has been systematically investigated after graphite. In this paper, we reviewed our research progress about {{{d}}}0 magnetism in two aspects, i.e., magnetic source and magnetic coupling mechanism. The {{{V}}}{{Si}} {{{V}}}{{C}} divacancies have been evidenced as the probable source of {{{d}}}0 magnetism in SiC. To trace the ferromagnetic source in microscopic and electronic view, the p electrons of the nearest-neighbor carbon atoms, which are around the {{{V}}}{{Si}} {{{V}}}{{C}} divacancies, are sourced. For magnetic coupling mechanism, a higher divacancy concentration leads to stronger paramagnetic interaction but not stronger ferromagnetic coupling. So the {{{d}}}0 magnetism can probably be explained as a local effect which is incapable of scaling up with the volume.

  10. Effect of Porosity on Particle Erosion Wear Behavior of Lab. Scale SICF/SIC Composites

    Science.gov (United States)

    Suh, Min-Soo; Kohyama, Akira

    The use of silicon-based ceramics and composites as combustor liners and turbine vanes provides the potential of improving next-generation turbine engine performance, through lower emissions and higher cycle efficiency, relative to today's use of super alloy hot-section components. As a series of research for FOD resistant, a particle erosion wear test was carried out for continuous Pre-SiC fiber-reinforced SiC matrix composites with a new concept of lab. scale fabrication by LPS process. The result shows that aperture (some form of porosity) between fiber and interface has a deleterious effect on erosion resistance. Aperture along the fiber interfaces consequently causes a severe wear in the form of fiber detachment. Wear rate increase proportional as contents of open porosity increases. For nearly full dense composite materials of about 0.5 % porosity, are about 200 % more wear-resistant than about 5 % porous composites. Grain growth and consolidate condition of matrix which directly affects to FOD resistant are also discussed.

  11. Oxidation Behavior and Mechanism of Al4SiC4 in MgO-C-Al4SiC4 System

    Directory of Open Access Journals (Sweden)

    Huabai Yao

    2017-06-01

    Full Text Available Al4SiC4 powder with high purity was synthesized using the powder mixture of aluminum (Al, silicon (Si, and carbon (C at 1800 °C in argon. Their oxidation behavior and mechanism in a MgO-C-Al4SiC4 system was investigated at 1400–1600 °C. XRD, SEM, and energy dispersive spectrometry (EDS were adopted to analyze the microstructure and phase evolution. The results showed that the composition of oxidation products was closely related to the atom diffusion velocity and the compound oxide layer was generated on Al4SiC4 surface. In addition, the effect of different CO partial pressure on the oxidation of Al4SiC4 crystals was also studied by thermodynamic calculation. This work proves the great potential of Al4SiC4 in improving the MgO-C materials.

  12. Simulations of Proton Implantation in Silicon Carbide (SiC)

    Science.gov (United States)

    2016-03-31

    philip.feng@case.edu Abstract: We report on exploratory research effort with preliminary results on investigating fundamental radiation effects in...of implanting protons (hydrogen ions, H+) into SiC thin layers on silicon (Si) substrate, and explore the ion implantation conditions that are...create SiC-on-insulator (SiC-on-SiO2) films and structures [4,5]. It is important to understand and control the implantation depth. Presented here

  13. SiC Microsensor with Piezoresistive Diamond Sensing Elements

    Science.gov (United States)

    1992-12-31

    AD-A.61 346 SiC MICROSENSOR WITH PIEZORESISTIVE DIAMOND SENSING ELEMENTS Kuli/e Semiconductor Products, Inc Principal Investigator: Dr. A.D. Kurtz...Davidson and A.D. Kurtz 7. PERORMING ORGANIZATION NAM.(S) ANO AD-SS-ES) PIRJQAMr( OAGANLM Kulite Semiconductor Products, Inc. REPORT NUMBER One Willow...techniques have been developed for Si, which allow the fabrication of integral force collector- piezoresistor networks [2]. However, there are fundamental

  14. SiC device development for high temperature sensor applications

    Science.gov (United States)

    Shor, J. S.; Goldstein, David; Kurtz, A. D.; Osgood, R. M.

    1992-01-01

    Progress made in the processing and characterization of 3C-SiC for high temperature sensor applications is reviewed. Piezoresistance properties of silicon carbide and the temperature coefficient of resistivity of n-type beta-SiC are presented. In addition, photoelectrical etching and dopant selective etch-stops in SiC and high temperature Ohmic contacts for n-type beta-SiC sensors are discussed.

  15. 1 GHz, 200 C, SiC MESFET Clapp Oscillator

    Science.gov (United States)

    Ponchak, George E.; Schwartz, Zachary D.

    2005-01-01

    A SiC Clapp oscillator frabricated on an alumina substrate with chip capacitors and spiral inductors is designed for high temperature operation at 1 gigahertz. The oscillator operated from 30 to 200 C with an output power of 21.8 dBm at 1 gigahertz and 200 C. The efficiency at 200 C is 15 percent. The frequency variation over the temperature range is less than 0.5 percent.

  16. Modelling of ion implantation in SiC crystals

    Energy Technology Data Exchange (ETDEWEB)

    Chakarov, Ivan [SILVACO International, 4701 Patrick Henry Drive, Building 2, Santa Clara, CA 95054 (United States)]. E-mail: ivan.chakarov@silvaco.com; Temkin, Misha [SILVACO International, 4701 Patrick Henry Drive, Building 2, Santa Clara, CA 95054 (United States)

    2006-01-15

    An advanced electronic stopping model for ion implantation in SiC has been implemented within the binary collision approximation. The model has been thoroughly tested and validated for Al implantation into 4H-, 6H-SiC under different initial implant conditions. A very good agreement between calculated and experimental profiles has been achieved. The model has been integrated in an industrial technology CAD process simulator.

  17. Algorithms for Reinforcement Learning

    CERN Document Server

    Szepesvari, Csaba

    2010-01-01

    Reinforcement learning is a learning paradigm concerned with learning to control a system so as to maximize a numerical performance measure that expresses a long-term objective. What distinguishes reinforcement learning from supervised learning is that only partial feedback is given to the learner about the learner's predictions. Further, the predictions may have long term effects through influencing the future state of the controlled system. Thus, time plays a special role. The goal in reinforcement learning is to develop efficient learning algorithms, as well as to understand the algorithms'

  18. Surface engineering of SiC via sublimation etching

    Energy Technology Data Exchange (ETDEWEB)

    Jokubavicius, Valdas, E-mail: valjo@ifm.liu.se [Department of Physics, Chemistry and Biology, Linköping University, 581 83 Linköping (Sweden); Yazdi, Gholam R.; Ivanov, Ivan G. [Department of Physics, Chemistry and Biology, Linköping University, 581 83 Linköping (Sweden); Niu, Yuran; Zakharov, Alexei [Max Lab, Lund University, S-22100 Lund (Sweden); Iakimov, Tihomir; Syväjärvi, Mikael; Yakimova, Rositsa [Department of Physics, Chemistry and Biology, Linköping University, 581 83 Linköping (Sweden)

    2016-12-30

    Highlights: • Comparison of 6H-, 4H- and 3C-SiC sublimation etching. • Effects of Si-C and Si-C-Ta chemical systems on etching mechanisms. • Effect of etching ambient on surface reconstruction. • Application of etched 4H-SiC surface for the growth of graphene nanoribbons is illustrated. - Abstract: We present a technique for etching of SiC which is based on sublimation and can be used to modify the morphology and reconstruction of silicon carbide surface for subsequent epitaxial growth of various materials, for example graphene. The sublimation etching of 6H-, 4H- and 3C-SiC was explored in vacuum (10{sup −5} mbar) and Ar (700 mbar) ambient using two different etching arrangements which can be considered as Si-C and Si-C-Ta chemical systems exhibiting different vapor phase stoichiometry at a given temperature. The surfaces of different polytypes etched under similar conditions are compared and the etching mechanism is discussed with an emphasis on the role of tantalum as a carbon getter. To demonstrate applicability of such etching process graphene nanoribbons were grown on a 4H-SiC surface that was pre-patterned using the thermal etching technique presented in this study.

  19. Estudio de la protección del refuerzo de partículas de SiC mediante barreras activas por sol-gel en materiales compuestos de matriz de aluminio

    Directory of Open Access Journals (Sweden)

    Ureña, A.

    2004-04-01

    Full Text Available A microcrystalline, homogeneous and transparent sol – gel silica coating has been developed to avoid the degradation and improve the wettability of aluminium matrix composites reinforced with SiC particles. Composite aluminium matrix samples have been made by cold powder compaction, and the coating efficiency has been checked by melting the samples several temperature and times. The coating reduces the appearance of Al4C3, showing that the degradation resistance of the new material is much higher than that of the uncovered SiC particles composite one.

    Con objeto de prevenir la degradación y mejorar la mojabilidad de los materiales compuestos de matriz de aluminio reforzados con partículas de SiC se ha desarrollado un recubrimiento microcristalino, homogéneo y transparente de SiO2 obtenido por el método sol-gel. La eficacia del recubrimiento como barrera se ha comprobado realizando ensayos de fusión a diferentes tiempos y temperaturas sobre pastillas de material compuesto de matriz de aluminio obtenidas por compactación en frío de polvos. El recubrimiento limita la formación de Al4C3, lo que indica que la resistencia a la degradación del nuevo material es muy superior a la del fabricado con partículas de SiC sin recubrir.

  20. Modeling reinforced concrete durability.

    Science.gov (United States)

    2014-06-01

    This project developed a next-generation modeling approach for projecting the extent of : reinforced concrete corrosion-related damage, customized for new and existing Florida Department of : Transportation bridges and suitable for adapting to broade...

  1. Alternate approach slab reinforcement.

    Science.gov (United States)

    2010-06-01

    The upper mat of reinforcing steel, in exposed concrete bridge approach slabs, is prone to corrosion damage. Chlorides applied to the highways : for winter maintenance can penetrate this concrete layer. Eventually chlorides reach the steel and begin ...

  2. 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

  3. Reinforcement Learning: A Survey

    OpenAIRE

    Kaelbling, L. P.; Littman, M. L.; Moore, A. W.

    1996-01-01

    This paper surveys the field of reinforcement learning from a computer-science perspective. It is written to be accessible to researchers familiar with machine learning. Both the historical basis of the field and a broad selection of current work are summarized. Reinforcement learning is the problem faced by an agent that learns behavior through trial-and-error interactions with a dynamic environment. The work described here has a resemblance to work in psychology, but differs considerably in...

  4. Atomic probe microscopy of 3C SiC films grown on 6H SiC substrates

    Science.gov (United States)

    Steckl, A. J.; Roth, M. D.; Powell, J. A.; Larkin, D. J.

    1993-01-01

    The surface of 3C SiC films grown on 6H SiC substrates has been studied by atomic probe microscopy in air. Atomic-scale images of the 3C SiC surface have been obtained by STM which confirm the 111 line type orientation of the cubic 3C layer grown on the 0001 plane type surface of the hexagonal 6H substrate. The nearest-neighbor atomic spacing for the 3C layer has been measured to be 3.29 +/- 0.2 A, which is within 7 percent of the bulk value. Shallow terraces in the 3C layer have been observed by STM to separate regions of very smooth growth in the vicinity of the 3C nucleation point from considerably rougher 3C surface regions. These terraces are oriented at right angles to the growth direction. Atomic force microscopy has been used to study etch pits present on the 6H substrate due to high temperature HCl cleaning prior to CVD growth of the 3C layer. The etch pits have hexagonal symmetry and vary in depth from 50 nm to 1 micron.

  5. Mechanical and tribological studies on nano particles reinforced hybrid aluminum based composite

    Directory of Open Access Journals (Sweden)

    Muley Aniruddha V.

    2015-01-01

    Full Text Available Hybrid metal matrix composites are new class of materials due to their better mechanical properties which can be achieved through proper selection and combination of materials. The work reported in this paper is based on fabrication of hybrid composites by using nano particles as reinforcements. The hybrid composites were fabricated by reinforcing them with nano sized SiC and Al2O3 particles in order to study mechanical and tribological properties of these enhanced materials. A stir casting method was used to obtain hybrid composites. LM 6 aluminum alloy was used as a matrix material. The results shown increase in hardness as well as in ultimate tensile strength of the composites with small wt.% of nano-sized hybrid reinforcements. The composites produced also exhibit better tribological properties.

  6. Synthesis and Characterization of Multi Wall Carbon Nanotubes (MWCNT) Reinforced Sintered Magnesium Matrix Composites

    Science.gov (United States)

    Vijaya Bhaskar, S.; Rajmohan, T.; Palanikumar, K.; Bharath Ganesh Kumar, B.

    2016-04-01

    Metal matrix composites (MMCs) reinforced with ceramic nano particles (less than 100 nm), termed as metal matrix nano composites (MMNCs), can overcome those disadvantages associated with the conventional MMCs. MMCs containing carbon nanotubes are being developed and projected for diverse applications in various fields of engineering like automotive, avionic, electronic and bio-medical sectors. The present investigation deals with the synthesis and characterization of hybrid magnesium matrix reinforced with various different wt% (0-0.45) of multi wall carbon nano tubes (MWCNT) and micro SiC particles prepared through powder metallurgy route. Microstructure and mechanical properties such as micro hardness and density of the composites were examined. Microstructure of MMNCs have been investigated by scanning electron microscope, X-ray diffraction and energy dispersive X-ray spectroscopy (EDS) for better observation of dispersion of reinforcement. The results indicated that the increase in wt% of MWCNT improves the mechanical properties of the composite.

  7. Whiskers de fibra de sisal obtidos sob diferentes condições de hidrólise ácida: efeito do tempo e da temperatura de extração Whiskers from sisal fibers obtained under different acid hydrolysis conditions: effect of time and temperature of extraction

    Directory of Open Access Journals (Sweden)

    Kelcilene B. R. Teodoro

    2011-01-01

    Full Text Available Neste trabalho, os efeitos de diferentes condições de tempo e temperatura usados para a preparação de whiskers de sisal foram investigados com o objetivo de se determinar a influência destes parâmetros experimentais na morfologia, cristalinidade e estabilidade térmica dos materiais preparados. A obtenção dos whiskers deu-se após o pré-branqueamento da fibra de sisal com solução alcalina de peróxido de hidrogênio. A fibra branqueada foi submetida ao processo de hidrólise com solução de ácido sulfúrico 60% (m/m sob três diferentes condições de temperatura e tempos de extração: 45 °C e 60 minutos (WS45_60; 45 °C e 75 minutos (WS45_75 e 60 °C e 30 minutos (WS60_30. Os whiskers foram caracterizados quanto à morfologia por microscopia eletrônica de transmissão (MET, quanto à cristalinidade (DRX, carga superficial (potencial zeta , teor de enxofre (análise elementar e quanto à estabilidade térmica por termogravimetria (TGA. Os resultados mostraram que os whiskers de sisal apresentaram comprimento e diâmetro médios e 210 nm e 5 nm respectivamente. Devido à alta aglomeração dos whiskers, diferenças relativas às características dimensionais não puderam ser determinadas. Os resultados obtidos revelaram uma forte dependência da cristalinidade final dos whiskers com a temperatura e tempo de extração. O uso de temperatura mais alta (60 °C associado a um menor tempo de extração (30 minutos resulta em whiskers com boa estabilidade térmica (235 °C, maior cristalinidade e sem o comprometimento da estrutura cristalina da celulose.In this work, the effects of different conditions of time and temperature, used for the preparation of whiskers from sisal, were investigated to determine the influence of experimental parameters on morphology, crystallinity and thermal stability of materials prepared. The whiskers were obtained after the bleaching of sisal raw fiber with a solution of hydrogen peroxide alkaline. The

  8. In Vitro Corrosion and Cytocompatibility Properties of Nano-Whisker Hydroxyapatite Coating on Magnesium Alloy for Bone Tissue Engineering Applications

    Directory of Open Access Journals (Sweden)

    Huawei Yang

    2015-03-01

    Full Text Available We report here the successful fabrication of nano-whisker hydroxyapatite (nHA coatings on Mg alloy by using a simple one-step hydrothermal process in aqueous solution. The nHA coating shows uniform structure and high crystallinity. Results indicate that nHA coating is promising for improving the in vitro corrosion and cytocompatibility properties of Mg-based implants and devices for bone tissue engineering. In addition, the simple hydrothermal deposition method used in the current study is also applicable to substrates with complex shapes or surface geometries.

  9. Corrosion behaviour of groundnut shell ash and silicon carbide hybrid reinforced Al-Mg-Si alloy matrix composites in 3.5% NaCl and 0.3M H2SO4 solutions

    Directory of Open Access Journals (Sweden)

    Kenneth Kanayo ALANEME

    2015-05-01

    Full Text Available The corrosion behaviour of Al-Mg-Si alloy based composites reinforced with groundnut shell ash (GSA and silicon carbide (SiC was investigated. The aim is to assess the corrosion properties of Al-Mg-Si alloy based hybrid reinforced composites developed using different mix ratios of GSA (a cheaply processed agro waste derivative which served as partial replacement for SiC and SiC as reinforcing materials. GSA and SiC mixed in weight ratios 0:1, 1:3, 1:1, 3:1, and 1:0 were utilized to prepare 6 and 10 wt% of the reinforcing phase with Al‐Mg‐Si alloy as matrix using two‐step stir casting method. Mass loss and corrosion rate measurement was used to study the corrosion behaviour of the produced composites in 3.5% NaCl and 0.3M H2SO4 solutions. The results show that the Al-Mg-Si alloy based composites containing 6 and 10 wt% GSA and SiC in varied weight ratios were resistant to corrosion in 3.5% NaCl solution. The composites were however more susceptible to corrosion in 0.3M H2SO4 solution (in comparison with the 3.5% NaCl solution. It was noted that the Al-Mg-Si/6 wt% GSA-SiC hybrid composite grades containing GSA and SiC in weight ratio 1:3 and 3:1 respectively exhibited superior corrosion resistance in the 0.3M H2SO4 solution compared to other composites produced for this series. In the case of the Al-Mg-Si/10 wt% GSA-SiC hybrid composite grades, the corrosion resistance was relatively superior for the composites containing a greater weight ratio of GSA (75% and 100% in 0.3M H2SO4 solution.

  10. Characterization of femtosecond-laser-induced periodic structures on SiC substrates

    Science.gov (United States)

    Miyagawa, Reina; Ohno, Yutaka; Deura, Momoko; Yonenaga, Ichiro; Eryu, Osamu

    2018-02-01

    We investigated the crystalline state of femtosecond-laser-induced periodic structures using a transmission electron microscope (TEM). The core of the 200-nm-pitch periodic nanostructures on SiC retained a high crystalline quality continued from the SiC substrate, where the crystal orientation was aligned with that of the SiC substrate. These results suggest that the periodic nanostructures were formed by periodic etching and not by rearrangement. At high laser power, microstructures with sizes larger than 2 µm were formed on the periodic nanostructures. The microstructures were amorphous and extended from the amorphous SiC layer that covered the periodic nanostructures.

  11. Review of data on irradiation creep of monolithic SiC

    Energy Technology Data Exchange (ETDEWEB)

    Garner, F.A.; Youngblood, G.E.; Hamilton, M.L. [Pacific Northwest National Laboratory, Richland, WA (United States)

    1996-04-01

    An effort is now underway to design an irradiation creep experiment involving SiC composites to SiC fibers. In order to successfully design such an experiment, it is necessary to review and assess the available data for monolithic SiC to establish the possible bounds of creep behavior for the composite. The data available show that monolithic SiC will indeed creep at a higher rate under irradiation compared to that of thermal creep, and surprisingly, it will do so in a temperature-dependant manner that is typical of metals.

  12. Formation and characterization of porous SiC by anodic oxidation using potassium persulfate solution

    Science.gov (United States)

    Iwasa, Y.; Kamiyama, S.; Iwaya, M.; Takeuchi, T.; Akasaki, I.

    2018-01-01

    The formation process of porous SiC by anodic oxidation was investigated, aiming at the generation of pure white light with a high color rendering index (CRI) and high luminous efficiency. The efficiency of white light emission from porous SiC and its wavelength are strongly dependent on the porous structure such as the average pore size and porosity. In this study, we examined the structure and optical properties of porous SiC by adding potassium persulfate (K2S2O8) as an oxidant in HF solution to control the porosity of porous SiC formed by anodic oxidation. By increasing the amount of the oxidant, we enhanced the integrated light emission intensity of porous SiC to 81 times that of bulk SiC. Through the study of porous SiC we demonstrated that the peak wavelength of the porous SiC could be controlled from 370 to 500 nm. Porous SiC created by anodic oxidation was thus proven to have great potential for realizing high-CRI white light generation using LEDs.

  13. 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.

  14. 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

  15. Microstructural, phase evolution and corrosion properties of silicon carbide reinforced pulse electrodeposited nickel–tungsten composite coatings

    Energy Technology Data Exchange (ETDEWEB)

    Singh, Swarnima; Sribalaji, M. [Materials Science and Engineering, Indian Institute of Technology Patna, Navin Government Polytechnic Campus, Patliputra Colony, Patna, Bihar 800013 (India); Wasekar, Nitin P.; Joshi, Srikant; Sundararajan, G. [International Advanced Research Centre for Powder Metallurgy & New Materials (ARCI) Hyderabad, Balapur P.O., Hyderabad, Andhra Pradesh 500005 (India); Singh, Raghuvir [CSIR-National Metallurgical Laboratory, Jamshedpur, Jharkhand 831007 (India); Keshri, Anup Kumar, E-mail: anup@iitp.ac.in [Materials Science and Engineering, Indian Institute of Technology Patna, Navin Government Polytechnic Campus, Patliputra Colony, Patna, Bihar 800013 (India)

    2016-02-28

    Graphical abstract: - Highlights: • Pulse electrodeposited Ni–W–SiC coating has been synthesized successfully. • Dome to turtle like structure has been observed on addition of SiC in Ni–W coating. • Formation of W(Ni) solid solution was observed on adding 5 g/l SiC in Ni–W coating. • Corrosion resistance improved for Ni–W–5 g/l SiC coating. • Texture formation and continuous barrier layer enhanced the corrosion resistance. - Abstract: Silicon carbide (SiC) reinforced nickel–tungsten (Ni–W) coatings were successfully fabricated on steel substrate by pulse electrodeposition method (PED) and the amount of SiC was varied as 0 g/l, 2 g/l, and 5 g/l in Ni–W coating. Effect of subsequent addition of SiC on microstructures, phases and on corrosion property of the coating was investigated. Field emission scanning electron microscopy (FE-SEM) image of the surface morphology of the coating showed the transformation from the dome like structure to turtle shell like structure. X-ray diffraction (XRD) of Ni–W–5 g/l SiC showed the disappearance of (220) plane of Ni(W), peak splitting in major peak of Ni(W) and formation of distinct peak of W(Ni) solid solution. Absence of (220) plane, peak splitting and presence of W(Ni) solid solution was explained by the high resolution transmission electron microscopy (HR-TEM) images. Tafel polarization plot was used to study the corrosion property of the coatings in 0.5 M NaCl solution. Ni–W–5 g/l SiC coating was showed higher corrosion resistance (i.e. ∼21% increase in corrosion potential, E{sub corr}) compared to Ni–W coating. Two simultaneous phenomena have been identified for the enhanced corrosion resistance of Ni–W–5 g/l SiC coating. (a) Presence of crystallographic texture (b) formation of continuous double barrier layer of NiWO{sub 4} and SiO{sub 2}.

  16. Studies on Mechanical Behaviour of Aluminium/Nickel Coated Silicon Carbide Reinforced Functionally Graded Composite

    Directory of Open Access Journals (Sweden)

    A. Mohandas

    2017-06-01

    Full Text Available The aim of the work is to fabricate functionally graded aluminium (Al-Si6Cu/ nickel coated SiC metal matrix composite using centrifugal casting route. SiC particles (53-80 µm were coated with nickel using electroless coating technique to enhance the wettability with aluminium matrix. Several attempts were made to coat nickel on SiC by varying the process temperature (65 °C, 75 °C, and 85 °C to obtain a uniform coating. Silicon particles coated with nickel were characterised using EDS enabled Field Emission Scanning Electron Microscope and it was found that the maximum nickel coating on SiC occurred at a process temperature of 75°C. This nickel coated SiC particles were used as the reinforcement for the manufacture of functionally graded metal matrix composite and a cast specimen of dimensions 150×90×15 mm was obtained. To ensure the graded properties in the fabricated composites, microstructure (at a distance of 1, 7 and 14 mm and hardness (at a distance of 1, 3, 7, 10 and 14 mm from outer periphery taken in the radial direction was analysed using Zeiss Axiovert metallurgical microscope and Vickers micro hardness tester respectively. The microstructure reveals presence of more SiC particles at the outer periphery compared to inner periphery and the hardness test shows that the hardness also decreased from outer periphery (90 HV to inner periphery (78 HV.Tensile strength of specimen from outer zone (1-7mm and inner zone (8-14 mm of casting was also tested and found out a value of 153.3 Mpa and 123.3 Mpa for the outer zone and inner zone respectively. An important observation made was that the outer periphery of casting was particle rich and the inner periphery was particle deficient because of centrifugal force and variation in density between aluminium matrix and reinforcement. Functionally graded Al/SiC metal matrix composite could be extensively used in automotive industry especially in the manufacture of liners and brake drums.

  17. Low Cost Fabrication of Silicon Carbide Based Ceramics and Fiber Reinforced Composites

    Science.gov (United States)

    Singh, M.; Levine, S. R.

    1995-01-01

    A low cost processing technique called reaction forming for the fabrication of near-net and complex shaped components of silicon carbide based ceramics and composites is presented. This process consists of the production of a microporous carbon preform and subsequent infiltration with liquid silicon or silicon-refractory metal alloys. The microporous preforms are made by the pyrolysis of a polymerized resin mixture with very good control of pore volume and pore size thereby yielding materials with tailorable microstructure and composition. Mechanical properties (elastic modulus, flexural strength, and fracture toughness) of reaction-formed silicon carbide ceramics are presented. This processing approach is suitable for various kinds of reinforcements such as whiskers, particulates, fibers (tows, weaves, and filaments), and 3-D architectures. This approach has also been used to fabricate continuous silicon carbide fiber reinforced ceramic composites (CFCC's) with silicon carbide based matrices. Strong and tough composites with tailorable matrix microstructure and composition have been obtained. Microstructure and thermomechanical properties of a silicon carbide (SCS-6) fiber reinforced reaction-formed silicon carbide matrix composites are discussed.

  18. Behavior of reinforced concrete beams reinforced with GFRP bars

    Directory of Open Access Journals (Sweden)

    D. H. Tavares

    Full Text Available The use of fiber reinforced polymer (FRP bars is one of the alternatives presented in recent studies to prevent the drawbacks related to the steel reinforcement in specific reinforced concrete members. In this work, six reinforced concrete beams were submitted to four point bending tests. One beam was reinforced with CA-50 steel bars and five with glass fiber reinforced polymer (GFRP bars. The tests were carried out in the Department of Structural Engineering in São Carlos Engineering School, São Paulo University. The objective of the test program was to compare strength, reinforcement deformation, displacement, and some anchorage aspects between the GFRP-reinforced concrete beams and the steel-reinforced concrete beam. The results show that, even though four GFRP-reinforced concrete beams were designed with the same internal tension force as that with steel reinforcement, their capacity was lower than that of the steel-reinforced beam. The results also show that similar flexural capacity can be achieved for the steel- and for the GFRP-reinforced concrete beams by controlling the stiffness (reinforcement modulus of elasticity multiplied by the bar cross-sectional area - EA and the tension force of the GFRP bars.

  19. Low Activation Joining of SiC/SiC Composites for Fusion Applications: Modeling Thermal and Irradiation-induced Swelling Effects on Integrity of Ti3SiC2/SiC Joint

    Energy Technology Data Exchange (ETDEWEB)

    Nguyen, Ba Nghiep; Henager, Charles H.; Kurtz, Richard J.; Ferraris, M.; Katoh, Yutai

    2017-03-31

    This work developed a continuum damage mechanics model that incorporates thermal expansion combined with irradiation-induced swelling effects to study the origin of cracking observed in recent irradiation experiments. Micromechanical modeling using an Eshelby-Mori-Tanaka approach was used to compute the thermoelastic properties of the Ti3SiC2/SiC joint needed for the model. In addition, a microstructural dual-phase Ti3SiC2/SiC model was developed to determine irradiation-induced swelling of the composite joint at a given temperature resulting from differential swelling of SiC and the Ti3SiC2 MAX phase. Three cases for the miniature torsion hourglass (THG) specimens containing a Ti3SiC2/SiC joint were analyzed corresponding to three irradiation temperatures: 800oC, 500oC, and 400oC.

  20. A system for delivering mechanical stimulation and robot-assisted therapy to the rat whisker pad during facial nerve regeneration.

    Science.gov (United States)

    Heaton, James T; Knox, Christopher J; Malo, Juan S; Kobler, James B; Hadlock, Tessa A

    2013-11-01

    Functional recovery is typically poor after facial nerve transection and surgical repair. In rats, whisking amplitude remains greatly diminished after facial nerve regeneration, but can recover more completely if the whiskers are periodically mechanically stimulated during recovery. Here we present a robotic "whisk assist" system for mechanically driving whisker movement after facial nerve injury. Movement patterns were either preprogrammed to reflect natural amplitudes and frequencies, or movements of the contralateral (healthy) side of the face were detected and used to control real-time mirror-like motion on the denervated side. In a pilot study, 20 rats were divided into nine groups and administered one of eight different whisk assist driving patterns (or control) for 5-20 minutes, five days per week, across eight weeks of recovery after unilateral facial nerve cut and suture repair. All rats tolerated the mechanical stimulation well. Seven of the eight treatment groups recovered average whisking amplitudes that exceeded controls, although small group sizes precluded statistical confirmation of group differences. The potential to substantially improve facial nerve recovery through mechanical stimulation has important clinical implications, and we have developed a system to control the pattern and dose of stimulation in the rat facial nerve model.

  1. A Preliminary Evaluation of Lyophilized Gelatin Sponges, Enhanced with Platelet-Rich Plasma, Hydroxyapatite and Chitin Whiskers for Bone Regeneration

    Directory of Open Access Journals (Sweden)

    Andrew J. Spence

    2013-04-01

    Full Text Available The purpose of this study was to perform a number of preliminary in vitro evaluations on an array of modified gelatin gel sponge scaffolds for use in a bone graft application. The gelatin gels were modified through the addition of a number of components which each possess unique properties conducive to the creation and regeneration of bone: a preparation rich in growth factors (PRGF, a bioactive, lyophilized form of platelet-rich plasma, hydroxyapatite, and chitin whiskers. Platelet-rich plasma therapy is an emerging practice that has proven effective in a number of clinical applications, including enhancing bone repair through improved deposition of new bony matrix and angiogenesis. As such, the inclusion of PRGF in our gelatin scaffolds was intended to significantly enhance scaffold bioactivity, while the addition of hydroxyapatite and chitin whiskers were anticipated to increase scaffold strength. Additionally, the gelatin sponges, which readily dissolve in aqueous solutions, were subjected to 1-Ethyl-3-[3-dimethylaminopropyl]carbodiimide hydrochloride (EDC cross-linking, either during or post-gelation, to control their rate of degradation. Scaffolds were evaluated in vitro with respect to compressive strength, mass loss/degradation, protein release, and cellular interaction, with results demonstrating the potential of the gelatin gel sponge scaffold for use in the regeneration of bone.

  2. A system for studying facial nerve function in rats through simultaneous bilateral monitoring of eyelid and whisker movements.

    Science.gov (United States)

    Heaton, James T; Kowaleski, Jeffrey M; Bermejo, Roberto; Zeigler, H Philip; Ahlgren, David J; Hadlock, Tessa A

    2008-06-30

    The occurrence of inappropriate co-contraction (synkinesis) of facially innervated muscles in humans is a common sequela of facial nerve injury and recovery. We have developed a system for studying facial nerve function and synkinesis in restrained rats using non-contact opto-electronic techniques that enable simultaneous bilateral monitoring of eyelid and whisker movements. Whisking is monitored in high spatio-temporal resolution using laser micrometers, and eyelid movements are detected using infrared diode and phototransistor pairs that respond to the increased reflection when the eyelids cover the cornea. To validate the system, 8 rats were tested with multiple 5-min sessions that included corneal air puffs to elicit blink and scented air flows to elicit robust whisking. Four rats then received unilateral facial nerve section and were tested at weeks 3-6. Whisking and eye blink behavior occurred both spontaneously and under stimulus control, with no detectable difference from published whisking data. Proximal facial nerve section caused an immediate ipsilateral loss of whisking and eye blink response, but some ocular closures emerged due to retractor bulbi muscle function. The independence observed between whisker and eyelid control indicates that this system may provide a powerful tool for identifying abnormal co-activation of facial zones resulting from aberrant axonal regeneration.

  3. The functional upregulation of piriform cortex is associated with cross-modal plasticity in loss of whisker tactile inputs.

    Directory of Open Access Journals (Sweden)

    Bing Ye

    Full Text Available Cross-modal plasticity is characterized as the hypersensitivity of remaining modalities after a sensory function is lost in rodents, which ensures their awareness to environmental changes. Cellular and molecular mechanisms underlying cross-modal sensory plasticity remain unclear. We aim to study the role of different types of neurons in cross-modal plasticity.In addition to behavioral tasks in mice, whole-cell recordings at the excitatory and inhibitory neurons, and their two-photon imaging, were conducted in piriform cortex. We produced a mouse model of cross-modal sensory plasticity that olfactory function was upregulated by trimming whiskers to deprive their sensory inputs. In the meantime of olfactory hypersensitivity, pyramidal neurons and excitatory synapses were functionally upregulated, as well as GABAergic cells and inhibitory synapses were downregulated in piriform cortex from the mice of cross-modal sensory plasticity, compared with controls. A crosswire connection between barrel cortex and piriform cortex was established in cross-modal plasticity.An upregulation of pyramidal neurons and a downregulation of GABAergic neurons strengthen the activities of neuronal networks in piriform cortex, which may be responsible for olfactory hypersensitivity after a loss of whisker tactile input. This finding provides the clues for developing therapeutic strategies to promote sensory recovery and substitution.

  4. Determination of He and D permeability of neutron-irradiated SiC tubes to examine the potential for release due to micro-cracking

    Energy Technology Data Exchange (ETDEWEB)

    Katoh, Yutai [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Hu, Xunxiang [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Koyanagi, Takaaki [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Singh, Gyanender P. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

    2017-07-01

    Driven by the need to enlarge the safety margins of light water reactors in both design-basis and beyond-design-basis accident scenarios, the research and development of accident-tolerant fuel (ATF) has become an importance topic in the nuclear engineering and materials community. Continuous SiC fiber-reinforced SiC matrix ceramic composites are under consideration as a replacement for traditional zirconium alloy cladding owing to their high-temperature stability, chemical inertness, and exceptional irradiation resistance. Among the key technical feasibility issues, potential failure of the fission product containment due to probabilistic penetrating cracking has been identified as one of the two most critical feasibility issues, together with the radiolysisassisted hydrothermal corrosion of SiC. The experimental capability to evaluate the hermeticity of SiC-based claddings is an urgent need. In this report, we present the development of a comprehensive permeation testing station established in the Low Activation Materials Development and Analysis laboratory at Oak Ridge National Laboratory. Preliminary results for the hermeticity evaluation of un-irradiated monolithic SiC tubes, uncoated and coated SiC/SiC composite tubes, and neutron-irradiated monolithic SiC tubes at room temperature are exhibited. The results indicate that this new permeation testing station is capable of evaluating the hermeticity of SiC-based tubes by determining the helium and deuterium permeation flux as a function of gas pressure at a high resolution of 8.07 x 10-12 atm-cc/s for helium and 2.83 x 10-12 atm-cc/s for deuterium, respectively. The detection limit of this system is sufficient to evaluate the maximum allowable helium leakage rate of lab-scale tubular samples, which is linearly extrapolated from the evaluation standard used for a commercial as-manufactured light water reactor fuel rod at room temperature. The un-irradiated monolithic SiC tube is hermetic, as

  5. Effect of reinforcement on the cutting forces while machining metal matrix composites–An experimental approach

    Directory of Open Access Journals (Sweden)

    Ch. Shoba

    2015-12-01

    Full Text Available Hybrid metal matrix composites are of great interest for researchers in recent years, because of their attractive superior properties over traditional materials and single reinforced composites. The machinabilty of hybrid composites becomes vital for manufacturing industries. The need to study the influence of process parameters on the cutting forces in turning such hybrid composite under dry environment is essentially required. In the present study, the influence of machining parameters, e.g. cutting speed, feed and depth of cut on the cutting force components, namely feed force (Ff, cutting force (Fc, and radial force (Fd has been investigated. Investigations were performed on 0, 2, 4, 6 and 8 wt% Silicon carbide (SiC and rice husk ash (RHA reinforced composite specimens. A comparison was made between the reinforced and unreinforced composites. The results proved that all the cutting force components decrease with the increase in the weight percentage of the reinforcement: this was probably due to the dislocation densities generated from the thermal mismatch between the reinforcement and the matrix. Experimental evidence also showed that built-up edge (BUE is formed during machining of low percentage reinforced composites at high speed and high depth of cut. The formation of BUE was captured by SEM, therefore confirming the result. The decrease of cutting force components with lower cutting speed and higher feed and depth of cut was also highlighted. The related mechanisms are explained and presented.

  6. Spontaneous growth of whiskers from an interlayer of Mo sub 2 C beneath a diamond particle deposited in a combustion-flame

    Energy Technology Data Exchange (ETDEWEB)

    Okada, Katsuyuki; Komatsu, Shojiro; Ishigaki, Takamasa; Matsumoto, Seiichiro; Moriyoshi, Yusuke (National Inst. for Research in Inorganic Materials, Tsukuba, Ibaraki (Japan))

    1992-02-01

    When diamond particles deposited on a molybdenum substrate in a C{sub 2}H{sub -}O{sub 2} combustion-flame were kept for one year in the ambient atmosphere at room temperature, spontaneous whisker growth from an interlayer of Mo{sub 2}C beneath the diamond particles took place. The whiskers were clarified by electron probe micro-analysis (EPMA) and transmission electron microscopy (TEM) in a polycrystal composed of MoO{sub 2}, MoOC, and Mo{sub 2}C. The growth mechanism of them is discussed from two different points of view as follows: One is that the oxidation of an interlayer of Mo{sub 2}C beneath a diamond particle effectively reduces the surface free energy between the interlayer and diamond particle; consequently, the whisker can grow by using a screw dislocation. The other is that the internal stress existing between a diamond particle and an Mo{sub 2}C interlayer provides a very reactive zone where the growth of whisker takes place through the oxidation of Mo{sub 2}C. (orig.).

  7. Effect of hydroxyapatite spheres, whiskers, and nanoparticles on mechanical properties of a model BisGMA/TEGDMA composite initially and after storage.

    Science.gov (United States)

    Lezaja, Maja; Veljovic, Djordje N; Jokic, Bojan M; Cvijovic-Alagic, Ivana; Zrilic, Milorad M; Miletic, Vesna

    2013-11-01

    This study investigated the effect of shape, size, and surface modification of hydroxyapatite (HAP) fillers on the degree of conversion (DC) and mechanical properties of a model BisGMA/TEGDMA composite initially and after 4 weeks of storage. Ten percent of conventional glass fillers were replaced by HAP spheres (Sph), silicon-doped spheres (SphSi), whiskers (Wh), silicon-doped whiskers (WhSi), and nanosized HAP particles (Nano). Spheres were specifically structured agglomerates consisting of a central void and radially orientated primary particles, whereas whiskers were compact monocrystals. DC, Vickers hardness (HV), flexural strength (Fs), flexural modulus (Ef), compressive strength (Cs), and compressive modulus (Ec) were tested. There were no significant differences in the DC between all tested groups. HV decreased by 5.4-17% with the addition of HAP, while Fs increased by 13.9-29% except in Nano group (decrease by 13%). After storage, Sph and SphSi groups showed similar HV, Ef, Cs and Ec and higher Fs than the control. The fracture mode of HAP spheres was through the central void whereas whiskers showed longitudinal delamination, transverse, and mixed fractures. HAP spheres with or without silicon- doping have a potential to be part of the filler content of dental composites. Copyright © 2013 Wiley Periodicals, Inc.

  8. The influence of silicon substitution on the properties of spherical- and whisker-like biphasic α-calcium-phosphate/hydroxyapatite particles.

    Science.gov (United States)

    Jokic, B; Mitric, M; Popovic, M; Sima, L; Petrescu, S M; Petrovic, R; Janackovic, Dj

    2011-10-01

    In this work, the influence of the morphology of hydroxyapatite particles on silicon substitution through hydrothermal synthesis performed under the same conditions was investigated. Spherical- and whisker-like hydroxyapatite particles were obtained starting from calcium-nitrate, sodium dihydrogen phosphate, disodium-ethylenediaminetetraacetic acid and urea (used only for the synthesis of whisker-like particles) dissolved in aqueous solutions. Silicon was introduced into the solution using tetraethylorthosilicate. X-ray diffraction, infrared spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy and transmission electron microscopy indicate that silicon doping induce different phase compositions and bioactivity of spherical- and whisker-like hydroxyapatite particles obtained under the same hydrothermal conditions. Silicon-substituted, spherical hydroxyapatites particles showed greater phase transformation to silicon-substituted α- calcium-phosphate compared with whiskers-like hydroxyapatite particles synthesized with the same amount of added silicon. Metabolic activity assay performed with SaOs2 osteosarcoma cells showed better biocompatibility of annealed biphasic spherical-like particles compared with annealed whiskerlike particles while dried spherical-like particles induce high cytotoxicity effect.

  9. Modelling reinforcement corrosion in concrete

    DEFF Research Database (Denmark)

    Michel, Alexander; Geiker, Mette Rica; Stang, Henrik

    2012-01-01

    A physio-chemical model for the simulation of reinforcement corrosion in concrete struc-tures was developed. The model allows for simulation of initiation and subsequent propaga-tion of reinforcement corrosion. Corrosion is assumed to be initiated once a defined critical chloride threshold...... is reached causing the formation of anodic and cathodic regions along the reinforcement. Critical chloride thresholds, randomly distributed along the reinforcement sur-face, link the initiation and propagation phase of reinforcement corrosion. To demonstrate the potential use of the developed model......, a numerical example is pre-sented, that illustrates the formation of corrosion cells as well as propagation of corrosion in a reinforced concrete structure....

  10. Synthesis of SiC from rice husk in a plasma reactor

    Indian Academy of Sciences (India)

    Abstract. A new route for production of SiC from rice husk is reported by employing thermal plasma technique. The formation of -SiC is observed in a short time of 5 min. The samples are characterized by XRD and SEM.

  11. Study of indentation induced cracks in MoSi2-reaction bonded SiC ...

    Indian Academy of Sciences (India)

    Unknown

    SiC ceramics. O P CHAKRABARTI*, P K DAS and S MONDAL. Central Glass and Ceramic Research Institute, Kolkata 700 032, India. Abstract. MoSi2–RBSC composite samples were prepared by infiltration of Si–2 at.% Mo melt into a preform of commercial SiC and petroleum coke powder. The infiltrated sample had a ...

  12. Broadband Antireflection and Light Extraction Enhancement in Fluorescent SiC with Nanodome Structures

    DEFF Research Database (Denmark)

    Ou, Yiyu; Zhu, Xiaolong; Jokubavicius, Valdas

    2014-01-01

    We demonstrate a time-efficient and low-cost approach to fabricate Si3N4 coated nanodome structures in fluorescent SiC. Nanosphere lithography is used as the nanopatterning method and SiC nanodome structures with Si3N4 coating are formed via dry etching and thin film deposition process. By using...

  13. 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 beh...

  14. 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...

  15. 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.

  16. Development of Simulink-Based SiC MOSFET Modeling Platform for Series Connected Devices

    DEFF Research Database (Denmark)

    Tsolaridis, Georgios; Ilves, Kalle; Reigosa, Paula Diaz

    2016-01-01

    A new MATLAB/Simulink-based modeling platform has been developed for SiC MOSFET power modules. The modeling platform describes the electrical behavior f a single 1.2 kV/ 350 A SiC MOSFET power module, as well as the series connection of two of them. A fast parameter initialization is followed...

  17. The first muon beam from a new highly-intense DC muon source, MuSIC

    Science.gov (United States)

    Tran, Nam Hoai; MuSIC Collaboration

    2012-09-01

    A new DC muon source, MuSIC, is now under construction at Research Center for Nuclear Physics (RCNP), Osaka University, Japan. The MuSIC adopts a new pion/muon collection system and a curved transport solenoid. These techniques are important in realization of future muon programs such as the muon to electron conversion experiments (COMET/Mu2e), neutrino factories, and muon colliders. The pion capture magnet and a part of the transport solenoid have been built and beam tests were carried out to assess the MuSIC's performance. Muon lifetime measurements and muonic X-ray measurements have been used for estimation of muon yield of the MuSIC. The result indicates that the MuSIC would be one of the most intense DC muon beams in the world.

  18. Interaction between magnetic moments and itinerant carriers in d0 ferromagnetic SiC

    Science.gov (United States)

    Liu, Yu; Yuan, Ye; Liu, Fang; Böttger, Roman; Anwand, Wolfgang; Wang, Yutian; Semisalova, Anna; Ponomaryov, Alexey N.; Lu, Xia; N'Diaye, Alpha T.; Arenholz, Elke; Heera, Viton; Skorupa, Wolfgang; Helm, Manfred; Zhou, Shengqiang

    2017-05-01

    Elucidating the interaction between magnetic moments and itinerant carriers is an important step to spintronic applications. Here, we investigate magnetic and transport properties in d0 ferromagnetic SiC single crystals prepared by postimplantation pulsed laser annealing. Magnetic moments are contributed by the p states of carbon atoms, but their magnetic circular dichroism is different from that in semi-insulating SiC samples. The anomalous Hall effect and negative magnetoresistance indicate the influence of d0 spin order on free carriers. The ferromagnetism is relatively weak in N-implanted SiC compared with that in Al-implanted SiC after annealing. The results suggest that d0 magnetic moments and itinerant carriers can interact with each other, which will facilitate the development of SiC spintronic devices with d0 ferromagnetism.

  19. The influence of carbon on the structure of preceramic polymer derived SiC

    Energy Technology Data Exchange (ETDEWEB)

    Kolaya, L.E.; Lewis, N. [Lockheed Martin Corp., Schenectady, NY (United States)

    1997-01-01

    The microstructure of SiC produced from allyl-hydridopolycarbosilane (AHPCS) was studied after thermal treatments at temperatures up to 1600 C. SiC samples were prepared in contact with pyrocarbon, carbon fiber, carbon felt, carbon powder, and graphite. Each of these configurations was examined using optical, scanning electron, and transmission electron microscopy. The resultant microstructure of the SiC in the vicinity of the carbon/graphite source was different for each sample. In some cases the grains were uniform, equiaxed and about the same size as SiC grains derived from neat AHPCS. Other samples exhibited accelerated grain growth in the vicinity of the carbon, and occasionally appeared to mimic the original carbon structure. Understanding and controlling such behavior will facilitate the fabrication of polymer derived stoichiometric SiC, and also has significant implications for the fabrication of SiC/SiC composites with a pyrocarbon interface and polymer derived matrix.

  20. 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......-circuit-current-based criterion; and 2) the gate-voltage-based criterion. The applicability of these two criteria makes possible the SCSOA evaluation of SiC MOSFETs with some safety margins in order to avoid unnecessary failures during their SCSOA characterization. SiC MOSFET power modules from two different manufacturers...... are experimentally tested in order to demonstrate the procedure of the method. The obtained results can be used to have a better insight of the SCSOA of SiC MOSFETs and their physical limits....

  1. Cohort profile: the Social Inequality in Cancer (SIC) cohort study.

    Science.gov (United States)

    Nordahl, Helene; Hvidtfeldt, Ulla Arthur; Diderichsen, Finn; Rod, Naja Hulvej; Osler, Merete; Frederiksen, Birgitte Lidegaard; Prescott, Eva; Tjønneland, Anne; Lange, Theis; Keiding, Niels; Andersen, Per Kragh; Andersen, Ingelise

    2014-12-01

    The Social Inequality in Cancer (SIC) cohort study was established to determine pathways through which socioeconomic position affects morbidity and mortality, in particular common subtypes of cancer. Data from seven well-established cohort studies from Denmark were pooled. Combining these cohorts provided a unique opportunity to generate a large study population with long follow-up and sufficient statistical power to develop and apply new methods for quantification of the two basic mechanisms underlying social inequalities in cancer-mediation and interaction. The SIC cohort included 83 006 participants aged 20-98 years at baseline. A wide range of behavioural and biological risk factors such as smoking, physical inactivity, alcohol intake, hormone replacement therapy, body mass index, blood pressure and serum cholesterol were assessed by self-administered questionnaires, physical examinations and blood samples. All participants were followed up in nationwide demographic and healthcare registries. For those interested in collaboration, further details can be obtained by contacting the Steering Committee at the Department of Public Health, University of Copenhagen, at inan@sund.ku.dk. © The Author 2014; all rights reserved. Published by Oxford University Press on behalf of the International Epidemiological Association.

  2. Integrated photonic filters based on SiC multilayer structures

    Energy Technology Data Exchange (ETDEWEB)

    Vieira, M.A., E-mail: mv@isel.ipl.pt [Electronics Telecommunication and Computer Dept. ISEL, R. Conselheiro Emídio Navarro, 1949-014, Lisboa (Portugal); CTS-UNINOVA, Quinta da Torre, Monte da Caparica, 2829-516, Caparica (Portugal); Vieira, M. [Electronics Telecommunication and Computer Dept. ISEL, R. Conselheiro Emídio Navarro, 1949-014, Lisboa (Portugal); CTS-UNINOVA, Quinta da Torre, Monte da Caparica, 2829-516, Caparica (Portugal); DEE-FCT-UNL, Quinta da Torre, Monte da Caparica, 2829-516, Caparica (Portugal); Louro, P.; Silva, V.; Fantoni, A. [Electronics Telecommunication and Computer Dept. ISEL, R. Conselheiro Emídio Navarro, 1949-014, Lisboa (Portugal); CTS-UNINOVA, Quinta da Torre, Monte da Caparica, 2829-516, Caparica (Portugal)

    2013-06-15

    Combined tunable WDM converters based on SiC multilayer photonic active filters are analyzed. The operation combines the properties of active long-pass and short-pass wavelength filter sections into a capacitive active band-pass filter. The sensor element is a multilayered heterostructure produced by PE-CVD. The configuration includes two stacked SiC p–i–n structures sandwiched between two transparent contacts. Transfer function characteristics are studied both theoretically and experimentally. Results show that optical bias activated photonic device combines the demultiplexing operation with the simultaneous photodetection and self amplification of an optical signal acting the device as an integrated photonic filter in the visible range. Depending on the wavelength of the external background and irradiation side, the device acts either as a short- or a long-pass band filter or as a band-stop filter. The output waveform presents a nonlinear amplitude-dependent response to the wavelengths of the input channels. A numerical simulation and a two building-blocks active circuit are presented and give insight into the physics of the device.

  3. Residual stresses and mechanical properties of Si3N4/SiC multilayered composites with different SiC layers

    Directory of Open Access Journals (Sweden)

    Shichao Liu

    2017-07-01

    Full Text Available 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 553.2 MPa and −552.1 MPa, 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.

  4. Model for the Effect of Fiber Bridging on the Fracture Resistance of Reinforced-Carbon-Carbon

    Science.gov (United States)

    Chan, Kwai S.; Lee, Yi-Der; Hudak, Stephen J., Jr.

    2009-01-01

    A micromechanical methodology has been developed for analyzing fiber bridging and resistance-curve behavior in reinforced-carbon-carbon (RCC) panels with a three-dimensional (3D) composite architecture and a silicon carbide (SiC) surface coating. The methodology involves treating fiber bridging traction on the crack surfaces in terms of a weight function approach and a bridging law that relates the bridging stress to the crack opening displacement. A procedure has been developed to deduce material constants in the bridging law from the linear portion of the K-resistance curve. This report contains information on the application of procedures and outcomes.

  5. Developmental Reinforcement and Education.

    Science.gov (United States)

    Garris, Raymond P.

    Using a developmental model, the author explains a hierarchy which describes how a young child learns to respond to various types of environmental stimuli and discusses some educational consequences of a reinforcement stimuli deficit. Development is seen to take place in succession beginning with the primary level, proceeding to the social,…

  6. Glass Fibre Reinforced Polymers

    NARCIS (Netherlands)

    Nikolaou, N.; Karagianni, L.; Sarakiniatti, M.V.

    2014-01-01

    This "designers' manual" is made during the TIDO-course AR0533 Innovation & Sustainability. Fibre reinforced polymers (FRPs) have been used in many applications over the years, from new construction to retrofitting. They are lightweight, no-corrosive, exhibit high specific strength and specific

  7. Turbomachine blade reinforcement

    Science.gov (United States)

    Garcia Crespo, Andres Jose

    2016-09-06

    Embodiments of the present disclosure include a system having a turbomachine blade segment including a blade and a mounting segment coupled to the blade, wherein the mounting segment has a plurality of reinforcement pins laterally extending at least partially through a neck of the mounting segment.

  8. Reinforcement and learning

    NARCIS (Netherlands)

    Servedio, M.R.; Sæther, S.A.; Sætre, G.-P.

    2009-01-01

    Evidence has been accumulating to support the process of reinforcement as a potential mechanism in speciation. In many species, mate choice decisions are influenced by cultural factors, including learned mating preferences (sexual imprinting) or learned mate attraction signals (e.g., bird song). It

  9. Reinforced aerodynamic profile

    DEFF Research Database (Denmark)

    2010-01-01

    The present invention relates to the prevention of deformations in an aerodynamic profile caused by lack of resistance to the bending moment forces that are created when such a profile is loaded in operation. More specifically, the invention relates to a reinforcing element inside an aerodynamic...

  10. Short fiber reinforced thermoplastic blends

    NARCIS (Netherlands)

    Malchev, P.G.

    2008-01-01

    The present thesis investigates the potential of short fiber reinforced thermoplastic blends, a combination of an immiscible polymer blend and a short fiber reinforced composite, to integrate the easy processing solutions available for short fiber reinforced composites with the high mechanical

  11. 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

  12. Microstructure and Mechanical Properties of Cr-SiC Particles-Reinforced Fe-Based Alloy Coating

    Science.gov (United States)

    Wang, Fu-cheng; Du, Xiao-dong; Zhan, Ma-ji; Lang, Jing-wei; Zhou, Dan; Liu, Guang-fu; Shen, Jian

    2015-12-01

    In this study, SiC particles were first coated with Cr to form a layer that can protect the SiC particles from dissolution in the molten pool. Then, the Cr-SiC powder was injected into the tail of molten pool during plasma-transferred arc welding process (PTAW), where the temperature was relatively low, to prepare Cr-SiC particles reinforced Fe-based alloy coating. The microstructure and phase composition of the powder and surface coatings were analyzed, and the element distribution and hardness at the interfacial region were also evaluated. The protective layer consists of Cr3Si, Cr7C3, and Cr23C6, which play an important role in the microstructure and mechanical properties. The protective layer is dissolved in the molten pool forming a flocculent region and a transition region between the SiC particles and the matrix. The tribological performance of the coating was also assessed using a ring-block sliding wear tester with GGr15 grinding ring under 490 and 980 N load. Cr-SiC particles-reinforced coating has a lower wear rate than the unreinforced coating.

  13. Ultimate Load Behaviour of Reinforced Concrete Beam with Corroded Reinforcement

    Science.gov (United States)

    Kanchana Devi, A.; Ramajaneyulu, K.; Sundarkumar, S.; Ramesh, G.; Bharat Kumar, B. H.; Krishna Moorthy, T. S.

    2017-12-01

    Corrosion of reinforcement reduces the load carrying capacity, energy dissipation and ductility of Reinforced Concrete (RC) members. In the present study, reinforcements of RC beam are subjected to 10, 25, and 30% corrosion and the respective RC beams are tested to evaluate their ultimate load behaviour. A huge drop in energy dissipation capacity of the RC beam is observed beyond the corrosion level of 10%. Further, nonlinear finite element analysis is employed to assess the load-displacement behaviour and ultimate load of RC beam. The corrosion induced damage to the reinforcement is represented in the finite element model by modifying its mechanical properties based on the results reported in the literature. The resultant load versus displacement curves of reinforced concrete beams are obtained. Good correlation is observed between the finite element analysis results and that obtained from experimental investigation on the control beam. The experimental results are also compared with the finite element analysis results for RC beams with corroded reinforcement. In order to understand the effect of corrosion on the mechanical properties of reinforcement, the corroded reinforcements are modelled in nonlinear finite element analysis by (i) reducing the area of reinforcement alone (ii) by reducing both area and mechanical properties and (iii) reducing the mechanical properties without reducing the area of steel as reported in literature. The results obtained for the beam with corroded reinforcement confirms reduction in yield stress and ultimate stress of the reinforcement steel.

  14. Research on Hot Compressive Deformation of TiBw/TA15 Composite Cylindrical Billet with Network-Distributed Reinforcements

    Science.gov (United States)

    Zhang, Rui; Wang, DongJun; Yuan, ShiJian

    2017-10-01

    A TA15 matrix composite reinforced by 3.5 vol.% TiB whiskers with a network microstructure was fabricated by the reaction hot pressing method. After sintering, the composite developed a net-like microstructure. To improve the mechanical properties, a cylindrical billet of the as-sintered TiBw/TA15 composite was subjected to upsetting and swaging operations with intermediate heating at 1000°C. The original equiaxed network units were stretched slightly, and the matrix had a microstructure evolution from a basket structure to a bi-modal structure after hot forging. The results of tensile tests at room temperature showed that the ultimate tensile strength and elongation of the composite increased by 8.2% and 130%, respectively, while the yield strength appeared to remain constant. Furthermore, the mechanical properties of the as-forged composite also improved at an elevated temperature.

  15. Thermochemical Degradation Mechanisms for the Reinforced Carbon/Carbon Panels on the Space Shuttle

    Science.gov (United States)

    Jacobson, Nathan S.; Rapp, Robert A.

    1995-01-01

    The wing leading edge and nose cone of the Space Shuttle are fabricated from a reinforced carbon/carbon material (RCC). The material attains its oxidation resistance from a diffusion coating of SiC and a glass sealant. During re-entry, the RCC material is subjected to an oxidizing high temperature environment, which leads to degradation via several mechanisms. These mechanisms include oxidation to form a silica scale, reaction of the SiO2 with the SiC to evolve gaseous products, viscous flow of the glass, and vaporization of the glass. Each of these is discussed in detail. Following extended service and many missions, the leading-edge wing surfaces have exhibited small pinholes. A chloridation/oxidation mechanism is proposed to arise from the NaCl deposited on the wings from the sea-salt laden air in Florida. This involves a local chloridation reaction of the SiC and subsequent re-oxidation at the external surface. Thermodynamic calculations indicate the feasibility of these reactions at active pits. Kinetic calculations predict pore depths close to those observed.

  16. SnO2-core/SiOx-shell coaxial whiskers with a needle-like morphology

    Science.gov (United States)

    Kim, Hyoun Woo; Kim, Hyo Sung; Kebede, Mesfin Abayneh; Na, Han Gil; Yang, Ju Chan

    2010-02-01

    Needle-shaped structures of tin oxide (SnO2) were coated with a shell layer of SiOx via a sputtering method. The diameters of the SiOx-coated structures gradually became thinner, leading to the formation of sharp tips. The whiskers consisted of a crystalline SnO2 core surrounded by an amorphous SiOx shell. The photoluminescence (PL) spectrum with a Gaussian fitting exhibited yellow-green and orange light emission bands, and the overall shape and intensity of the PL spectrum were not changed by the SiOxcoating. The results of this study suggest that sputtering can be employed to achieve the layered growth of shell layers on a variety of nanostructures.

  17. Fabrication of SiC hardened bodies with geopolymer binders using a warm press method

    Science.gov (United States)

    Hashimoto, Shinobu; Kubota, Kosuke; Ando, Kotaro; Tsutani, Masaki; Diko, Yusuke; Honda, Sawao; Iwamoto, Yuji

    2017-09-01

    Novel SiC hardened bodies with geopolymer binders using a warm press method were fabricated. In this study, two methods were tried. The first method used a conventional powder mixture consisted of SiC and geopolymer particles as starting materials. In the second method, SiC particles was first immersed in hydrochloric acid solution with 2.5 mol/L and then heated at 1200 °C for 6 h to form a reactive aluminosilicate layer at the surface of SiC particles. Subsequently, the resultant SiC particles mixed with a fixed amount of sodium hydroxide solution with various concentrations were put into a steel mold which was set in the warm press device. This second method was defined as a chemical assist processing. As this warm press condition, heating temperature was 130 °C and pressed at 240 MPa for 30 min simultaneously. When a powder mixture consisted of geopolymer and SiC particles was used, the compressive strength of the hardened bodies decreased with the amount of SiC particles. On the contrary, when the chemical assist processing method was selected, the compressive strength of the hardened bodies increased with the concentration of the sodium hydroxide solution. When the sodium hydroxide solution was 4 mol/L was used, the compressive strength of the hardened body reached to 170 MPa which was the maximum value in this study.

  18. Nanostructured composite reinforced material

    Science.gov (United States)

    Seals, Roland D [Oak Ridge, TN; Ripley, Edward B [Knoxville, TN; Ludtka, Gerard M [Oak Ridge, TN

    2012-07-31

    A family of materials wherein nanostructures and/or nanotubes are incorporated into a multi-component material arrangement, such as a metallic or ceramic alloy or composite/aggregate, producing a new material or metallic/ceramic alloy. The new material has significantly increased strength, up to several thousands of times normal and perhaps substantially more, as well as significantly decreased weight. The new materials may be manufactured into a component where the nanostructure or nanostructure reinforcement is incorporated into the bulk and/or matrix material, or as a coating where the nanostructure or nanostructure reinforcement is incorporated into the coating or surface of a "normal" substrate material. The nanostructures are incorporated into the material structure either randomly or aligned, within grains, or along or across grain boundaries.

  19. Reinforced Airfoil Shaped Body

    DEFF Research Database (Denmark)

    2011-01-01

    The present invention relates to an airfoil shaped body with a leading edge and a trailing edge extending along the longitudinal extension of the body and defining a profile chord, the airfoil shaped body comprising an airfoil shaped facing that forms the outer surface of the airfoil shaped body...... and surrounds an internal volume of the body, a distance member that is connected to the facing inside the body and extends from the facing and into the internal volume of the body, and at least one reinforcing member that operates in tension for reinforcing the facing against inward deflections...... and that is connected to the facing inside the internal volume of the body at the same side of the profile chord as the connection of the distance member to the facing and to the distance member at a distance from the facing....

  20. Mechanically reinforced glass beams

    DEFF Research Database (Denmark)

    Nielsen, Jens Henrik; Olesen, John Forbes

    2007-01-01

    The use of glass as a load carrying material in structural elements is rarely seen even though glass is a popular material for many architects. This is owed to the unreliable and low tensile strength, which is due to surface flaws and high brittleness of the material. These properties lead...... to breakage without any warning or ductility, which can be catastrophic if no precautions are taken. One aspect of this issue is treated here by looking at the possibility of mechanically reinforcing glass beams in order to obtain ductile failure for such a structural component. A mechanically reinforced...... laminated float glass beam is constructed and tested in four-point bending. The beam consist of 4 layers of glass laminated together with a slack steel band glued onto the bottom face of the beam. The glass parts of the tested beams are \\SI{1700}{mm} long and \\SI{100}{mm} high, and the total width of one...

  1. South Oregon Coast Reinforcement.

    Energy Technology Data Exchange (ETDEWEB)

    United States. Bonneville Power Administration.

    1998-05-01

    The Bonneville Power Administration is proposing to build a transmission line to reinforce electrical service to the southern coast of Oregon. This FYI outlines the proposal, tells how one can learn more, and how one can share ideas and opinions. The project will reinforce Oregon`s south coast area and provide the necessary transmission for Nucor Corporation to build a new steel mill in the Coos Bay/North Bend area. The proposed plant, which would use mostly recycled scrap metal, would produce rolled steel products. The plant would require a large amount of electrical power to run the furnace used in its steel-making process. In addition to the potential steel mill, electrical loads in the south Oregon coast area are expected to continue to grow.

  2. Fracture strength estimation of SiC block for IS process

    Energy Technology Data Exchange (ETDEWEB)

    Takegami, Hiroaki, E-mail: takegami.hiroaki@jaea.go.jp [Japan Atomic Energy Agency, 4002, Narita-cho, Oarai-machi, Higashiibaraki-gun, Ibaraki 311-1393 (Japan); Terada, Atsuhiko; Onuki, Kaoru; Hino, Ryutaro [Japan Atomic Energy Agency, 4002, Narita-cho, Oarai-machi, Higashiibaraki-gun, Ibaraki 311-1393 (Japan)

    2011-12-15

    Highlights: Black-Right-Pointing-Pointer We proposed a strength estimation method for large-scale SiC structure. Black-Right-Pointing-Pointer The strength estimation was carried out by using the effective volume and the optimized Weibull modulus of SiC. Black-Right-Pointing-Pointer The fracture strength of small-scale SiC obtained from fracture test was well within the estimation of the proposed method. - Abstract: The Japan Atomic Energy Agency has been conducting R and D on thermochemical water-splitting Iodine-Sulfur (IS) process for hydrogen production to meet massive demand in the future hydrogen economy. A concept of sulfuric acid decomposer was developed featuring a heat exchanger block made of SiC. Recent activity has focused on the reliability assessment of SiC block. Although knowing the strength of SiC block is important for the reliability assessment, it is difficult to evaluate a large-scale ceramics structure without destructive test. In this study, a novel approach for strength estimation of SiC structure was proposed. Since accurate strength estimation of individual ceramics structure is difficult, a prediction method of minimum strength in the structure of the same design was proposed based on effective volume theory and optimized Weibull modulus. Optimum value of the Weibull modulus was determined for estimating the lowest strength. The strength estimation line was developed by using the determined modulus. The validity of the line was verified by destructive test of SiC block model, which is small-scale model of the SiC block. The fracture strength of small-scale model satisfied the predicted strength.

  3. Polycrystalline SiC fibers from organosilicon polymers

    Science.gov (United States)

    Lipowitz, Jonathan; Rabe, James A.; Zank, Gregg A.

    1991-01-01

    Various organosilicon polymers have been converted into small diameter, fine-grained silicon carbide fibers by melt spinning, crosslinking, and pyrolyzing to greater than 1600 C. The high pyrolysis temperature densifies the fiber and causes CO evolution which removes nearly all oxygen. An additive prevents the loss of strength normally associated with such treatments. Silicon carbide fibres with up to 2.6 GPa (380 ksi) tensile strength, greater than 420 GPa (greater than 60 Msi) elastic modulus, and 3.1-3.2 mg/cu m density have been prepared via this process. Their microstructure consists of greater than 95 wt pct B-SiC crystallites averaging 30-40 nm diameter, with varying amounts of graphitic carbon between the SiC grains. Under inert conditions, the fibers can be thermally aged at least 12 h/1800 C with minimal change in properties.

  4. Creep of chemically vapour deposited SiC fibres

    Science.gov (United States)

    Dicarlo, J. A.

    1986-01-01

    The creep, thermal expansion, and elastic modulus properties for chemically vapor deposited SiC fibers were measured between 1000 and 1500 C. Creep strain was observed to increase logarithmically with time, monotonically with temperature, and linearly with tensile stress up to 600 MPa. The controlling activation energy was 480 + or - 20 kJ/mole. Thermal pretreatments near 1200 and 1450 C were found to significantly reduce fiber creep. These results coupled with creep recovery observations indicate that below 1400 C fiber creep is anelastic with negligible plastic component. This allowed a simple predictive method to be developed for describing fiber total deformation as a function of time, temperature, and stress. Mechanistic analysis of the property data suggests that fiber creep is the result of beta-SiC grain boundary sliding controlled by a small percent of free silicon in the grain boundaries.

  5. Relativistic energies for the SiC radical

    Energy Technology Data Exchange (ETDEWEB)

    Jia, Chun-Sheng [Southwest Petroleum University, State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Chengdu (China); Shui, Zheng-Wei [Southwest Petroleum University, School of Vocational and Technical Education, Nanchong (China)

    2015-11-15

    The analytical solutions of the Dirac equation with the modified Rosen-Morse potential energy model have been explored. Under the condition of the spin symmetry, we present the bound state energy equation. In the nonrelativistic limit, the relativistic energy equation becomes the nonrelativistic energy form deduced within the framework of the Schroedinger equation. We find that the relativistic effect of the relative motion of the ions leads to a little decrease in the vibrational energies when the vector potential is equal to the scalar potential for the electronic ground state of the SiC radical, while to an increase in those if the vector potential is greater than the scalar potential. (orig.)

  6. SiC MOSFET Switching Power Amplifier Project Summary

    Science.gov (United States)

    Miller, Kenneth E.; Ziemba, Timothy; Prager, James; Slobodov, Ilia; Henson, Alex

    2017-10-01

    Eagle Harbor Technologies has completed a Phase I/II program to develop SiC MOSFET based Switching Power Amplifiers (SPA) for precision magnet control in fusion science applications. During this program, EHT developed several units have been delivered to the Helicity Injected Torus (HIT) experiment at the University of Washington to drive both the voltage and flux circuits of the helicity injectors. These units are capable of switching 700 V at 100 kHz with an adjustable duty cycle from 10 - 90% and a combined total output current of 96 kA for 4 ms (at max current). The SPAs switching is controlled by the microcontroller at HIT, which adjusts the duty cycle to maintain a specific waveform in the injector. The SPAs include overcurrent and shoot-through protection circuity. EHT will present an overview of the program including final results for the SPA waveforms. With support of DOE SBIR.

  7. Effect of SiC volume fraction and particle size on the fatigue resistance of a 2080 Al/SiC{sub p} composite

    Energy Technology Data Exchange (ETDEWEB)

    Chawla, N.; Andres, C.; Jones, J.W. [Univ. of Michigan, Ann Arbor, MI (United States); Allison, J.E. [Ford Motor Co., Dearborn, MI (United States)

    1998-11-01

    The effect of SiC volume fraction and particle size on the fatigue behavior of 2080 Al was investigated. Matrix microstructure in the composite and the unreinforced alloy was held relatively constant by the introduction of a deformation stage prior to aging. It was found that increasing volume fraction and decreasing particle size resulted in an increase in fatigue resistance. Mechanisms responsible for this behavior are described in terms of load transfer from the matrix to the high stiffness reinforcement, increasing obstacles for dislocation motion in the form of S{prime} precipitates, and the decrease in strain localization with decreasing reinforcement interparticle spacing as a result of reduced particle size. Microplasticity was also observed in the composite, in the form of stress-strain hysteresis loops, and is related to stress concentrations at the poles of the reinforcement. Finally, intermetallic inclusions in the matrix acted as fatigue crack initiation sites. The effect of inclusion size and location on fatigue life of the composites is discussed.

  8. 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.

  9. 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.

  10. Electrical Impact of SiC Structural Crystal Defects on High Electric Field Devices (Invited)

    Science.gov (United States)

    Neudeck, Philip G.

    1999-01-01

    As illustrated by the invited paper at this conference and other works, SiC wafers and epilayers contain a variety of crystallographic imperfections, including micropipes, closed-core screw dislocations, grain boundaries, basal plane dislocations, heteropolytypic inclusions, and surfaces that are often damaged and contain atomically rough features like step bunching and growth pits or hillocks. Present understanding of the operational impact of various crystal imperfections on SiC electrical devices is reviewed, with an emphasis placed on high-field SiC power devices and circuits.

  11. 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.

  12. 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.

  13. Effect of SiC particle size on the microstructure and properties of cold-sprayed Al/SiCp composite coating

    Science.gov (United States)

    Yu, Min; Hua, Junwei

    2017-07-01

    The Al5056/SiC composite coatings were prepared by cold spraying. Experimental results show that the SiC content in the composite coating deposited with the SiC powder having an average size of 67 μm (Al5056/SiC-67) is similar to that deposited with the SiC powder having an average size of 27 μm (Al5056/SiC-27). The microhardness and cohesion strength of Al5056/SiC-67 coating are higher than those of the Al5056/SiC-27 coating. In addition, the Al5056/SiC-67 coating having a superior wear resistance because of the coarse SiC powder with a superior kinetic energy contributes to the deformation resistance of the matrix Al5056 particles.

  14. Fiber reinforced silicon-containing arylacetylene resin composites

    Directory of Open Access Journals (Sweden)

    2007-12-01

    Full Text Available A silicon-containing arylacetylene resin (SAR, a poly(dimethylsilyleneethynylene phenyleneethynylene (PMSEPE, was synthesized. The PMSEPE is a solid resin at ambient temperature with a softening temperature about 60°C and soluble in some solvents like tetrahydrofuran. The melt viscosity of the PMSEPE resin is less than 1 Pa•s. The resin could cure at the temperature of lower than 200°C. Fiber reinforced PMSEPE composites were prepared from prepregs which were made by the impregnation of fibers in PMSEPE resin solution. The composites exhibit good mechanical properties at room temperature and 250°C. The observation on fracture surfaces of the composites reinforced by glass fibers and carbon fibers demonstrates that the adhesion between the fibers and resin is good. The results from an oxyacetylene flame test show that the composites have good ablation performance and XRD analyses indicate that SiC forms in the residues during the ablation of the composites.

  15. Mechanical Spectroscopy of MgB2 Containing Sic / Spektroskopia Mechaniczna MgB2 Zawierającego Sic

    Directory of Open Access Journals (Sweden)

    Silva M.R.

    2015-12-01

    Full Text Available The compound magnesium diboride (MgB2 has been well-known since the 1950s; however, its superconducting properties were unknown. Intrinsic characteristics of MgB2 make this material a promising candidate for technological applications, although the low value of the irreversibility field and the decrease in critical current density with the increase in the magnetic field considerably reduce its utility. The present work aimed to study the effect of carbon-based doping on anelastic properties of MgB2 as measured by mechanical spectroscopy. The samples were prepared by using the powder-intube method. The samples were made with 5, 7.5, and 10 wt.% of silicon carbide (SiC. The results reveal complex mechanical loss spectra caused by the interaction between point defects and surface defects in the crystalline lattice of MgB2.

  16. Electrical Discharge Machining of Al (6351-5% SiC-10% B4C Hybrid Composite: A Grey Relational Approach

    Directory of Open Access Journals (Sweden)

    S. Suresh Kumar

    2014-01-01

    Full Text Available The goal of the present experimental work is to optimize the electrical discharge machining (EDM parameters of aluminum alloy (Al 6351 matrix reinforced with 5 wt.% silicon carbide (SiC and 10 wt.% boron carbide (B4C particles fabricated through the stir casting route. Multiresponse optimization was carried out through grey relational analysis (GRA with an objective to minimize the machining characteristics, namely electrode wear ratio (EWR, surface roughness (SR and power consumption (PC. The optimal combination of input parameters is identified, which shows the significant enhancement in process characteristics. Contributions of each machining parameter to the responses are calculated using analysis of variance (ANOVA. The result shows that the pulse current contributes more (83.94% to affecting the combined output responses.

  17. Wetting and reaction characteristics of crystalline and amorphous SiO2 derived rice-husk ash and SiO2/SiC substrates with Al-Si-Mg alloys

    Science.gov (United States)

    Bahrami, A.; Pech-Canul, M. I.; Gutiérrez, C. A.; Soltani, N.

    2015-12-01

    A study of the wetting behavior of three substrate types (SiC, SiO2-derived RHA and SiC/SiO2-derived RHA) by two Al-Si-Mg alloys using the sessile drop method has been conducted, using amorphous and crystalline SiO2 in the experiment. Mostly, there is a transition from non-wetting to wetting contact angles, being the lowest θ values achieved with the alloy of high Mg content in contact with amorphous SiO2. The observed wetting behavior is attributed to the deposited Mg on the substrates. A strong diffusion of Si from the SiC/Amorphous RHA substrate into the metal drop explains the free Si segregated at the drop/substrate interface and drop surface. Although incorporation of both SiO2-derived RHA structures into the SiC powder compact substrates increases the contact angles in comparison with the SiC substrate alone, the still observed acute contact angles in RHA/SiC substrates make them promising for fabrication of composites with high volume fraction of reinforcement by the pressureless infiltration technique. The observed wetting characteristics, with decrease in surface tension and contact angles is explained by surface related phenomena. Based on contact angle changes, drop dimensions and surface tension values, as well as on the interfacial elemental mapping, and XRD analysis of substrates, some wetting and reaction pathways are proposed and discussed.

  18. 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

  19. Silicon Carbide (SiC) Power Processing Unit (PPU) for Hall Effect Thrusters Project

    Data.gov (United States)

    National Aeronautics and Space Administration — In this SBIR project, APEI, Inc. is proposing to develop a high efficiency, rad-hard 3.8 kW silicon carbide (SiC) Power Processing Unit (PPU) for Hall Effect...

  20. Light extraction efficiency enhancement for fluorescent SiC based white light-emitting diodes

    DEFF Research Database (Denmark)

    Ou, Haiyan; Ou, Yiyu; Argyraki, Aikaterini

    Fluorescent SiC based white light-emitting diodes(LEDs) light source, as an innovative energy-efficient light source, would even have longer lifetime, better light quality and eliminated blue-tone effect, compared to the current phosphor based white LED light source. In this paper, the yellow....... At a device level, the focus is on improving the light extraction efficiency due to the rather high refractive index of SiC by nanostructuring the surface of SiC. Both periodic nanostructures made by e-beam lithography and nanosphere lithography and random nanostructures made by self-assembled Au nanosphere...... fluorescent Boron-Nitrogen co-doped 6H SiC is optimized in terms of source material, growth condition, dopant concentration, and carrier lifetime by using photoluminescence, pump-probe spectroscopy etc. The internal quantum efficiency is measured and the methods to increase the efficiency have been explored...

  1. 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.

  2. Breakthrough in Power Electronics from SiC: May 25, 2004 - May 31, 2005

    Energy Technology Data Exchange (ETDEWEB)

    Marckx, D. A.

    2006-03-01

    This report explores the premise that silicon carbide (SiC) devices would reduce substantially the cost of energy of large wind turbines that need power electronics for variable speed generation systems.

  3. Synthesis of One-Dimensional SiC Nanostructures from a Glassy Buckypaper

    Energy Technology Data Exchange (ETDEWEB)

    Ding, Mengning; Star, Alexander

    2013-02-21

    A simple and scalable synthetic strategy was developed for the fabrication of one-dimensional SiC nanostructures - nanorods and nanowires. Thin sheets of single-walled carbon nanotubes (SWNTs) were prepared by vacuum filtration and were washed repeatedly with sodium silicate (Na₂SiO₃) solution. The resulting “glassy buckypaper” was heated at 1300 - 1500 °C under Ar/H₂ to allow a solid state reaction between C and Si precursors to form a variety of SiC nanostructures. The morphology and crystal structures of SiC nanorods and nanowires were characterized using scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), energy dispersive xray spectroscopy (EDX), electron diffraction (ED) and x-ray diffraction (XRD) techniques. Furthermore, electrical conductance measurements were performed on SiC nanorods, demonstrating their potential applications in high-temperature sensors and control systems.

  4. Ultra-Lightweight, High Efficiency Silicon-Carbide (SIC) Based Power Electronic Converters Project

    Data.gov (United States)

    National Aeronautics and Space Administration — In Phase I of this project, APEI, Inc. proved the feasibility of creating ultra-lightweight power converters (utilizing now emerging silicon carbide [SiC] power...

  5. Promise and Challenges of High-Voltage SiC Bipolar Power Devices

    Directory of Open Access Journals (Sweden)

    Tsunenobu Kimoto

    2016-11-01

    Full Text Available Although various silicon carbide (SiC power devices with very high blocking voltages over 10 kV have been demonstrated, basic issues associated with the device operation are still not well understood. In this paper, the promise and limitations of high-voltage SiC bipolar devices are presented, taking account of the injection-level dependence of carrier lifetimes. It is shown that the major limitation of SiC bipolar devices originates from band-to-band recombination, which becomes significant at a high-injection level. A trial of unipolar/bipolar hybrid operation to reduce power loss is introduced, and an 11 kV SiC hybrid (merged pin-Schottky diodes is experimentally demonstrated. The fabricated diodes with an epitaxial anode exhibit much better forward characteristics than diodes with an implanted anode. The temperature dependence of forward characteristics is discussed.

  6. FABRICATION AND MATERIAL ISSUES FOR THE APPLICATION OF SiC COMPOSITES TO LWR FUEL CLADDING

    Directory of Open Access Journals (Sweden)

    WEON-JU KIM

    2013-08-01

    Full Text Available The fabrication methods and requirements of the fiber, interphase, and matrix of nuclear grade SiCf/SiC composites are briefly reviewed. A CVI-processed SiCf/SiC composite with a PyC or (PyC-SiCn interphase utilizing Hi-Nicalon Type S or Tyranno SA3 fiber is currently the best combination in terms of the irradiation performance. We also describe important material issues for the application of SiC composites to LWR fuel cladding. The kinetics of the SiC corrosion under LWR conditions needs to be clarified to confirm the possibility of a burn-up extension and the cost-benefit effect of the SiC composite cladding. In addition, the development of end-plug joining technology and fission products retention capability of the ceramic composite tube would be key challenges for the successful application of SiC composite cladding.

  7. Ultra-Lightweight, High Efficiency Silicon-Carbide (SIC) Based Power Electronic Converters Project

    Data.gov (United States)

    National Aeronautics and Space Administration — This Small Business of Innovation Research Phase I proposal seeks to investigate and prove the feasibility of developing highly efficient, ultra-lightweight SiC...

  8. Decentralized Nonlinear Controller Based SiC Parallel DC-DC Converter Project

    Data.gov (United States)

    National Aeronautics and Space Administration — This proposal is aimed at demonstrating the feasibility of a Decentralized Control based SiC Parallel DC-DC Converter Unit (DDCU) with targeted application for...

  9. SiC nanocrystals as Pt catalyst supports for fuel cell applications

    DEFF Research Database (Denmark)

    Dhiman, Rajnish; Johnson, Erik; Skou, Eivind Morten

    2013-01-01

    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......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...... based catalysts (BASF & HISPEC). These promising results signal a new era of SiC based catalysts for fuel cell...

  10. Synthesis of boron nitride nanotubes with SiC nanowire as template

    Energy Technology Data Exchange (ETDEWEB)

    Zhong, B.; Song, L. [School of Materials Science and Engineering, Harbin Institute of Technology at Weihai, Weihai 264209 (China); Huang, X.X. [School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001 (China); Wen, G.W., E-mail: g.wen@hit.edu.cn [School of Materials Science and Engineering, Harbin Institute of Technology at Weihai, Weihai 264209 (China); School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001 (China); Xia, L. [School of Materials Science and Engineering, Harbin Institute of Technology at Weihai, Weihai 264209 (China)

    2011-09-15

    Highlights: {yields} Boron nitride nanotubes (BNNTs) have been fabricated using SiC nanowires as template. {yields} SiC nanowires could be effectively etched out by the vapors decomposed from ammonia borane, leading to the formation of BNNTs. {yields} 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.

  11. 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.

  12. Detection of effective recombination centers in fluorescent SiC using thermally stimulated luminescence

    DEFF Research Database (Denmark)

    Wei, Yi; Künecke, Ulrike; Wellmann, Peter

    Two n-type 6H fluorescent SiC (f-SiC) samples have been characterized using thermally stimulated luminescence (TSL) spectroscopy, where the dominant carriers recombination regime has been found via the numerical simulations....

  13. 40 CFR 372.23 - SIC and NAICS codes to which this Part applies.

    Science.gov (United States)

    2010-07-01

    ..., and Confectionery Stores); Except 311340—Exception is limited to facilities primarily engaged in the... premises (previously classified under SIC 5441, Candy, Nut, and Confectionery Stores); Except 311811—Retail...

  14. SUPERPOLISHED SI COATED SIC OPTICS FOR RAPID MANUFACTURE OF LARGE APERTURE UV AND EUV TELESCOPES Project

    Data.gov (United States)

    National Aeronautics and Space Administration — SSG/Tinsley proposes an innovative optical manufacturing process that will allow the advancement of state-of-the-art Silicon Carbide (SiC) mirrors for large aperture...

  15. Visible Blind SiC Array with Low Noise Readout Project

    Data.gov (United States)

    National Aeronautics and Space Administration — To date, we have (i) designed and fabricated both common cathode and common anode SiC detector arrays; (ii) designed and fabricated the detector packaging (FPA), and...

  16. Brazing of SiC using Cu-Si non reactive alloys

    Energy Technology Data Exchange (ETDEWEB)

    Gasse, A. [C.E.A., CEREM-DEM, Grenoble (France); Chaumat, G. [C.E.A., CEREM-DEM, Grenoble (France); Rado, C. [INPG/LTCM-ENSEEG, Saint Martin d`Heres (France); Eustathopoulos, N. [INPG/LTCM-ENSEEG, Saint Martin d`Heres (France)

    1995-12-31

    SiC was brazed with a Cu 24 at% Si alloy under high vacuum at 1473 K. This alloy well wets SiC without any measurable reactivity and after cooling, leads to an interface which appears to be strong. It was found that the degree of filling of the joint by the alloy depends mainly on the geometry of the ceramic-metal-vapour system. It is shown that geometrical factors influence the kinetics of deoxidation of both alloys and SiC surfaces and, as a consequence, considerably modify the wetting kinetics and filling of the joint. Successful helium-tight tube/plate brazed joints have been obtained. Nevertheless, thermal expansion mismatch remains considerable between the SiC and the Cu-Si alloy. Further work is needed to improve the mechanical behaviour of such junctions to avoid crack formation. (orig./MM)

  17. 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...

  18. In-situ synchrotron micro-diffraction study of surface, interface, grain structure, and strain/stress evolution during Sn whisker/hillock formation

    Energy Technology Data Exchange (ETDEWEB)

    Pei, Fei; Bower, Allan F.; Chason, Eric [School of Engineering, Brown University, Providence, Rhode Island 02912 (United States); Jadhav, Nitin [IBM, Hopewell Junction, New York 12533 (United States); Buchovecky, Eric [Saint-Gobain, Northboro R& D Center, Northborough, Massachusetts 01532 (United States); Liu, Wenjun; Tischler, Jonathan Z.; Xu, Ruqing [Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439 (United States); Ice, Gene E. [Oak Ridge National Lab, Oak Ridge, Tennessee 37831 (United States)

    2016-03-14

    We have performed X-ray synchrotron micro-diffraction measurements to study the processes controlling the formation of hillocks and whiskers in Sn layers on Cu. The studies were done in real-time on Sn layers that were electro-deposited immediately before the X-ray measurements were started. This enabled a region of the sample to be monitored from the as-deposited state until after a hillock feature formed. In addition to measuring the grain orientation and deviatoric strain (via Laue diffraction), the X-ray fluorescence was monitored to quantify the evolution of the Sn surface morphology and the formation of intermetallic compound (IMC) at the Sn-Cu interface. The results capture the simultaneous growth of the feature and the corresponding film stress, grain orientation, and IMC formation. The observations are compared with proposed mechanisms for whisker/hillock growth and nucleation.

  19. Extraction and characterization of cellulose nano whiskers from balsa wood; Extracao e caracterizacao de nanocristais de celulose obtidos da madeira balsa

    Energy Technology Data Exchange (ETDEWEB)

    Morelli, Carolina L.; Bretas, Rosario E.S., E-mail: bretas@ufscar.br [Universidade Federal de Sao Carlos - UFSCar, Sao Carlos, SP (Brazil); Marconcini, Jose M. [Embrapa Instrumentacao, Sao Carlos, SP (Brazil); Pereira, Fabiano V. [Universidade Federal de Minas Gerais - UFMG, Belo Horizonte, MG (Brazil); Branciforti, Marcia C. [Universidade de Sao Paulo - USP, Sao Carlos, SP (Brazil)

    2011-07-01

    In this study cellulose nano whiskers were obtained from balsa wood. For this purpose, fibers of balsa wood were subjected to hydrolysis reactions for lignin and hemi cellulose digestion and acquisition of nano-scale cellulose. Cellulose nano crystals obtained had medium length and thickness of 176 nm and 7 nm respectively. Infrared spectroscopy and x-ray diffraction showed that the process used for extracting nano whiskers could digest nearly all the lignin and hemi cellulose from the balsa fiber and still preserve the aspect ratio and crystallinity, satisfactory enough for future application in polymer nano composites. Thermogravimetry showed that the onset temperature of thermal degradation of cellulose nano crystals (226 degree C) was higher than the temperature of the balsa fiber (215 degree C), allowing its use in molding processes with many polymers from the molten state.(author)

  20. Growth of single phase Bi sub 2 Sr sub 2 CaCu sub 2 O sub x whiskers using optimized starting compositions for glassy precursors

    CERN Document Server

    Sugimata, E; Kume, E; Sakai, S

    2003-01-01

    Single phase Bi sub 2 Sr sub 2 CaCu sub 2 O sub x whiskers were grown by optimized starting compositions for glassy precursors. The most optimal starting composition ratio and the composition after the whisker growth were found to be Bi : Sr : Ca : Al = 0.96 : 1.10 : 0.37 : 1.21 : 0.61 and Bi sub 2 sub . sub 2 sub 5 Sr sub 2 sub . sub 0 sub 9 Ca sub 0 sub . sub 8 sub 7 Cu sub 2 sub . sub 0 sub 0 O sub x , respectively. From the results of R-T characteristics, it was determined that there was no intergrowth of the Bi sub 2 Sr sub 2 Ca sub 2 Cu sub 3 O sub x phase. (author)

  1. [Reinforcement learning by striatum].

    Science.gov (United States)

    Kunisato, Yoshihiko; Okada, Go; Okamoto, Yasumasa

    2009-04-01

    Recently, computational models of reinforcement learning have been applied for the analysis of neuroimaging data. It has been clarified that the striatum plays a key role in decision making. We review the reinforcement learning theory and the biological structures such as the brain and signals such as neuromodulators associated with reinforcement learning. We also investigated the function of the striatum and the neurotransmitter serotonin in reward prediction. We first studied the brain mechanisms for reward prediction at different time scales. Our experiment on the striatum showed that the ventroanterior regions are involved in predicting immediate rewards and the dorsoposterior regions are involved in predicting future rewards. Further, we investigated whether serotonin regulates both the reward selection and the striatum function are specialized reward prediction at different time scales. To this end, we regulated the dietary intake of tryptophan, a precursor of serotonin. Our experiment showed that the activity of the ventral part of the striatum was correlated with reward prediction at shorter time scales, and this activity was stronger at low serotonin levels. By contrast, the activity of the dorsal part of the striatum was correlated with reward prediction at longer time scales, and this activity was stronger at high serotonin levels. Further, a higher proportion of small reward choices, together with a higher rate of discounting of delayed rewards is observed in the low-serotonin condition than in the control and high-serotonin conditions. Further examinations are required in future to assess the relation between the disturbance of reward prediction caused by low serotonin and mental disorders related to serotonin such as depression.

  2. Effect of dopants on the morphology of porous SiC

    DEFF Research Database (Denmark)

    Lu, Weifang; Iwasa, Yoshimi; Ou, Yiyu

    Porous SiC samples with different doping level were fabricated and investigated by using anodic oxidation method. The morphology of the porous structures was explained by space charge layer width, which was affected by the free carrier-dopants concentration.......Porous SiC samples with different doping level were fabricated and investigated by using anodic oxidation method. The morphology of the porous structures was explained by space charge layer width, which was affected by the free carrier-dopants concentration....

  3. Josephson coupling in junctions made of monolayer graphene on SiC

    OpenAIRE

    Jouault, B.; Charpentier, S.; Massarotti, D.; Michon, A.; Paillet, M.; Huntzinger, J. -R.; Tiberj, A.; Zahab, A.; Bauch, T.; Lucignano, P.; Tagliacozzo, A.; Lombardi, F.; Tafuri, F.

    2016-01-01

    Graphene on silicon carbide (SiC) has proved to be highly successful in Hall conductance quantization for its homogeneity at the centimetre scale. Robust Josephson coupling has been measured in co-planar diffusive Al/monololayer graphene/Al junctions. Graphene on SiC substrates is a concrete candidate to provide scalability of hybrid Josephson graphene/superconductor devices, giving also promise of ballistic propagation.

  4. 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.

  5. SiC fibre by chemical vapour deposition on tungsten filament

    Indian Academy of Sciences (India)

    A CVD system for the production of continuous SiC fibre was set up. The process of SiC coating on 19 m diameter tungsten substrate was studied. Methyl trichloro silane (CH3SiCl3) and hydrogen reactants were used. Effect of substrate temperature (1300–1500°C) and concentration of reactants on the formation of SiC ...

  6. The development of chemically vapor deposited mullite coatings for the corrosion protection of SiC

    Energy Technology Data Exchange (ETDEWEB)

    Auger, M.; Hou, P.; Sengupta, A.; Basu, S.; Sarin, V. [Boston Univ., MA (United States)

    1998-05-01

    Crystalline mullite coatings have been chemically vapor deposited onto SiC substrates to enhance the corrosion and oxidation resistance of the substrate. Current research has been divided into three distinct areas: (1) Development of the deposition processing conditions for increased control over coating`s growth rate, microstructure, and morphology; (2) Analysis of the coating`s crystal structure and stability; (3) The corrosion resistance of the CVD mullite coating on SiC.

  7. 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 the studied SiC MOSFET power modules is formulated based on the two proposed criteria....

  8. 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....

  9. Wear Resistance Analysis of A359/SiC/20p Advanced Composite Joints Welded by Friction Stir Welding

    Directory of Open Access Journals (Sweden)

    O. Cuevas Mata

    Full Text Available Abstract Advancement in automotive part development demands new cost-effective materials with higher mechanical properties and improved wear resistance as compared to existing materials. For instance, Aluminum Matrix Composites (AMC shows improved mechanical properties as wear and abrasion resistance, high strength, chemical and dimensional stability. Automotive industry has focused in AMC for a variety of applications in automotive parts in order to improve the fuel economy, minimize vehicle emissions, improve design options, and increase the performance. Wear resistance is one of the most important factors in useful life of the automotive components, overall in those components submitted to mechanical systems like automotive brakes and suspensions. Friction Stir Welding (FSW rises as the most capable process to joining AMC, principally for the capacity to weld without compromising their ceramic reinforcement. The aim of this study is focused on the analysis of wear characteristics of the friction-stir welded joint of aluminum matrix reinforced with 20 percent in weight silicon carbide composite (A359/SiC/20p. The experimental procedure consisted in cut samples into small plates and perform three welds on these with a FSW machine using a tool with 20 mm shoulder diameter and 8 mm pin diameter. The wear features of the three welded joints and parent metal were analyzed at constant load applying 5 N and a rotational speed of 100 rpm employing a Pin-on - Disk wear testing apparatus, using a sapphire steel ball with 6 mm diameter. The experimental results indicate that the three welded joints had low friction coefficient compared with the parent metal. The results determine that the FSW process parameters affect the wear resistance of the welded joints owing to different microstructural modifications during welding that causes a low wear resistance on the welded zone.

  10. Social Influence as Reinforcement Learning

    Science.gov (United States)

    2016-01-13

    SECURITY CLASSIFICATION OF: This project examined a reinforcement learning model of conformity and social influence. Under this model, individuals...Oct-2015 Approved for Public Release; Distribution Unlimited Final Report: Social Influence as Reinforcement Learning The views, opinions and/or...Research Triangle Park, NC 27709-2211 W911NF-14-1-0001 - Final Report - Social Influence as Reinforcement Learning REPORT DOCUMENTATION PAGE 11. SPONSOR

  11. High Temperature Interactions of Metallic Matrices with Ceramic Reinforcements

    Science.gov (United States)

    1990-12-31

    temperatura range were extensive; various metal silicides, metalIcarbides, ternary metal-slilcon-carbides, and unreacted carbon were formed as layered...Couples 3.2.1 Preparation of SiC Ceramic: The polycrystalline SiC substrates, designated as Hexoloy, were obtained from the Carborundum Corporation ...and was received from Engelhard Corporation . The metal pieces were cut into a similar size to that of the SiC, mechanically ground with #600 SiC papers

  12. Effects of Ni catalyzer on growth velocity and morphology of vapor growth SiC nano-fibers

    Energy Technology Data Exchange (ETDEWEB)

    Xu Xianfeng; Xiao Peng; Xiong Xiang; Huang Boyun [State Key Lab. for Powder Metallurgy, Central South University, Changsha, 410083 (China)], E-mail: xu-xianfeng@163.com

    2009-03-01

    Using Ni granules as a catalyzer, composite felts reinforced by both SiC nano-fibers (SiC-NFs) and carbon fibers were prepared at 1273K. SiC-NFs were deposited on the surface of the carbon fibers in-situ by chemical vapor growth. The microstructure and morphology of the fibers after being electroplated and deposited were characterized by scanning electron microscopy and transmission electron microscopy. The phase of the fibers after being deposited was characterized by X-ray diffractometry. The results show that the SiC-NFs produced by chemical vapor growth are single crystals of {beta}-SiC. It was found that Ni catalyzer had important effects on the growth of SiC-NFs. Smaller nano-granules were more active as catalyzers, resulting SiC-NFs appeared more spindle-like and had a more homogeneous dispersion. The weight change of the samples before and after deposition shows that a longer electroplating times results in SiC-NFs having a faster growth velocity.

  13. Elevated temperature strength, aging response and creep of aluminum matrix composites

    Energy Technology Data Exchange (ETDEWEB)

    Bhagat, R.B.; Amateau, M.F.; House, M.B.; Meinert, K.C.; Nisson, P. (Pennsylvania State University, State College (United States))

    1992-01-01

    The effect of reinforcement on the high-temperature performance of aluminum matrix composites was investigated using samples of 6061 aluminum alloy reinforced with planar-random graphite fibers, SiC whiskers, or alumina particles, which were aged at 150 and 200 C for up to 500 hrs. As indicated by the results of microhardness tests, all specimens exhibited accelerated aging response, with the response depending on the characteristics of the reinforcement. Both the graphite-fiber- and SiC-whisker-reinforced composites showed a substantially increased strengths over that of the wrought 6061 Al at all temperatures. The graphite-fiber- and the SiC-whisker-reinforced composites were found to retain their tensile strength and stiffness in the overaged condition of the matrix. The whisker-reinforced composite showed significant resistance to creep at temperatures between 232 and 350 C under stresses of up to 100 MPa, while the particulate composite had a moderate increase in creep resistance. 51 refs.

  14. Structural and thermal characterization of polyvinylalcohol grafted SiC nanocrystals

    Science.gov (United States)

    Saini, Isha; Sharma, Annu; Dhiman, Rajnish; Ram, Sita; Sharma, Pawan K.

    2017-07-01

    In the present work, Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, x-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were employed to ascertain the grafting of an organic layer of polyvinyl alcohol (PVA) onto the surface 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 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 the presence of PVA layer around SiC nanocrystals. Thermal degradation behavior of PVA-g-SiC nanocrystals has been studied using TGA analysis.

  15. 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.

  16. 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.

  17. Velcro-Inspired SiC Fuzzy Fibers for Aerospace Applications.

    Science.gov (United States)

    Hart, Amelia H C; Koizumi, Ryota; Hamel, John; Owuor, Peter Samora; Ito, Yusuke; Ozden, Sehmus; Bhowmick, Sanjit; Syed Amanulla, Syed Asif; Tsafack, Thierry; Keyshar, Kunttal; Mital, Rahul; Hurst, Janet; Vajtai, Robert; Tiwary, Chandra Sekhar; Ajayan, Pulickel M

    2017-04-19

    The most recent and innovative silicon carbide (SiC) fiber ceramic matrix composites, used for lightweight high-heat engine parts in aerospace applications, are woven, layered, and then surrounded by a SiC ceramic matrix composite (CMC). To further improve both the mechanical properties and thermal and oxidative resistance abilities of this material, SiC nanotubes and nanowires (SiCNT/NWs) are grown on the surface of the SiC fiber via carbon nanotube conversion. This conversion utilizes the shape memory synthesis (SMS) method, starting with carbon nanotube (CNT) growth on the SiC fiber surface, to capitalize on the ease of dense surface morphology optimization and the ability to effectively engineer the CNT-SiC fiber interface to create a secure nanotube-fiber attachment. Then, by converting the CNTs to SiCNT/NWs, the relative morphology, advantageous mechanical properties, and secure connection of the initial CNT-SiC fiber architecture are retained, with the addition of high temperature and oxidation resistance. The resultant SiCNT/NW-SiC fiber can be used inside the SiC ceramic matrix composite for a high-heat turbo engine part with longer fatigue life and higher temperature resistance. The differing sides of the woven SiCNT/NWs act as the "hook and loop" mechanism of Velcro but in much smaller scale.

  18. Associations of unilateral whisker and olfactory signals induce synapse formation and memory cell recruitment in bilateral barrel cortices: cellular mechanism for unilateral training toward bilateral memory

    Directory of Open Access Journals (Sweden)

    Zilong Gao

    2016-12-01

    Full Text Available Somatosensory signals and operative skills learned by unilateral limbs can be retrieved bilaterally. In terms of cellular mechanism underlying this unilateral learning toward bilateral memory, we hypothesized that associative memory cells in bilateral cortices and synapse innervations between them were produced. In the examination of this hypothesis, we have observed that paired unilateral whisker and odor stimulations led to odorant-induced whisker motions in bilateral sides, which were attenuated by inhibiting the activity of barrel cortices. In the mice that showed bilateral cross-modal responses, the neurons in both sides of barrel cortices became to encode this new odor signal alongside the innate whisker signal. Axon projections and synapse formations from the barrel cortex, which was co-activated with the piriform cortex, toward its contralateral barrel cortex were upregulated. Glutamatergic synaptic transmission in bilateral barrel cortices was upregulated and GABAergic synaptic transmission was downregulated. The associative activations of the sensory cortices facilitate new axon projection, glutamatergic synapse formation and GABAergic synapse downregulation, which drive the neurons to be recruited as associative memory cells in the bilateral cortices. Our data reveals the productions of associative memory cells and synapse innervations in bilateral sensory cortices for unilateral training toward bilateral memory.

  19. Reconstruction of intracortical whisker-evoked local field potential from electrocorticogram using a model trained for spontaneous activity in the rat barrel cortex.

    Science.gov (United States)

    Watanabe, Hidenori; Sakatani, Tomoya; Suzuki, Takafumi; Sato, Masa-Aki; Nishimura, Yukio; Nambu, Atsushi; Kawato, Mitsuo; Isa, Tadashi

    2014-10-01

    Electrocorticogram (ECoG) has provided neural information from the cortical surfaces, is widely used in clinical applications, and expected to be useful for brain-machine interfaces. Recent studies have defined the relationship between neural activity in deep layers of the cerebral cortex and ECoG. However, it is still unclear whether this relationship is shared across different brain states. In this study, spontaneous activity and whisker-evoked responses in the barrel cortex of anesthetized rats were recorded with a 32-channel ECoG electrode array and 32-channel linear silicon probe electrodes, respectively. Spontaneous local field potentials (LFPs) at various depths could be reconstructed with high accuracy (R>0.9) by a linear weighted summation of spontaneous ECoG. Current source density analysis revealed that the reconstructed LFPs correctly represented laminar profiles of current sinks and sources as well as the raw LFP. Moreover, when we applied the spontaneous activity model to reconstruction of LFP from the whisker-related ECoG, high accuracy of reconstruction could be obtained (R>0.9). Our results suggest that the ECoG carried rich information about synaptic currents in the deep layers of the cortex, and the same reconstruction model can be applied to estimate both spontaneous activity and whisker-evoked responses. Copyright © 2014 Elsevier Ireland Ltd and the Japan Neuroscience Society. All rights reserved.

  20. Wear-dependent specific coefficients in a mechanistic model for turning of nickel-based superalloy with ceramic tools

    Directory of Open Access Journals (Sweden)

    López de Lacalle Luis Norberto

    2017-09-01

    Full Text Available Difficult to cut materials such as nickel and titanium alloys are used in the aeronautical industry, the former alloys due to its heat-resistant behavior and the latter for the low weight - high strength ratio. Ceramic tools made out alumina with reinforce SiC whiskers are a choice in turning for roughing and semifinishing workpiece stages. Wear rate is high in the machining of these alloys, and consequently cutting forces tends to increase along one operation.