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Sample records for irradiated silicon carbide

  1. Neutron irradiation induced amorphization of silicon carbide

    SciTech Connect

    Snead, L.L.; Hay, J.C.

    1998-09-01

    This paper provides the first known observation of silicon carbide fully amorphized under neutron irradiation. Both high purity single crystal hcp and high purity, highly faulted (cubic) chemically vapor deposited (CVD) SiC were irradiated at approximately 60 C to a total fast neutron fluence of 2.6 {times} 10{sup 25} n/m{sup 2}. Amorphization was seen in both materials, as evidenced by TEM, electron diffraction, and x-ray diffraction techniques. Physical properties for the amorphized single crystal material are reported including large changes in density ({minus}10.8%), elastic modulus as measured using a nanoindentation technique ({minus}45%), hardness as measured by nanoindentation ({minus}45%), and standard Vickers hardness ({minus}24%). Similar property changes are observed for the critical temperature for amorphization at this neutron dose and flux, above which amorphization is not possible, is estimated to be greater than 130 C.

  2. Stored energy in irradiated silicon carbide

    SciTech Connect

    Snead, L.L.; Burchell, T.D.

    1997-04-01

    This report presents a short review of the phenomenon of Wigner stored energy release from irradiated graphite and discusses it in relation to neutron irradiation of silicon carbide. A single published work in the area of stored energy release in SiC is reviewed and the results are discussed. It appears from this previous work that because the combination of the comparatively high specific heat of SiC and distribution in activation energies for recombining defects, the stored energy release of SiC should only be a problem at temperatures lower than those considered for fusion devices. The conclusion of this preliminary review is that the stored energy release in SiC will not be sufficient to cause catastrophic heating in fusion reactor components, though further study would be desirable.

  3. Irradiation creep of advanced silicon carbide fibers

    NASA Astrophysics Data System (ADS)

    Scholz, R.; Youngblood, G. E.

    2000-12-01

    The bend stress relaxation (BSR) method was applied to study irradiation enhanced creep (IEC) of small diameter silicon carbide (SiC) fibers after 10 MeV proton irradiation. A first series of tests was conducted on Sylramic™ fibers irradiated at 600°C with average bending stresses of 400 and 667 MPa and for irradiation doses smaller than 0.04 dpa. The BSR results are compared to previously obtained torsional creep test results for the Textron SCS-6™ type SiC fibers by calculating the tensile equivalents for both testing methods. For the Sylramic fibers, the creep constant κ=4.7×10-6 Mpa-1 dpa-1, was a factor of 6 smaller than the κ-value determined for SCS-6 fibers at 600°C. In contrast, for T<900°C the κ-value determined by R.J. Price [Nucl. Technol. 35 (1977) 320] for high purity monolithic β-Si after 7.7 dpa neutron irradiation was only 0.4×10-6 MPa-1 dpa-1.

  4. Evaluation of Neutron Irradiated Silicon Carbide and Silicon Carbide Composites

    SciTech Connect

    Newsome G, Snead L, Hinoki T, Katoh Y, Peters D

    2007-03-26

    The effects of fast neutron irradiation on SiC and SiC composites have been studied. The materials used were chemical vapor deposition (CVD) SiC and SiC/SiC composites reinforced with either Hi-Nicalon{trademark} Type-S, Hi-Nicalon{trademark} or Sylramic{trademark} fibers fabricated by chemical vapor infiltration. Statistically significant numbers of flexural samples were irradiated up to 4.6 x 10{sup 25} n/m{sup 2} (E>0.1 MeV) at 300, 500 and 800 C in the High Flux Isotope Reactor at Oak Ridge National Laboratory. Dimensions and weights of the flexural bars were measured before and after the neutron irradiation. Mechanical properties were evaluated by four point flexural testing. Volume increase was seen for all bend bars following neutron irradiation. Magnitude of swelling depended on irradiation temperature and material, while it was nearly independent of irradiation fluence over the fluence range studied. Flexural strength of CVD SiC increased following irradiation depending on irradiation temperature. Over the temperature range studied, no significant degradation in mechanical properties was seen for composites fabricated with Hi-Nicalon{trademark} Type-S, while composites reinforced with Hi-Nicalon{trademark} or Sylramic fibers showed significant degradation. The effects of irradiation on the Weibull failure statistics are also presented suggesting a reduction in the Weibull modulus upon irradiation. The cause of this potential reduction is not known.

  5. Deuteron irradiation creep of chemically vapor deposited silicon carbide fibers

    NASA Astrophysics Data System (ADS)

    Scholz, R.

    1998-03-01

    Irradiation creep tests were conducted on Textron SCS-6 silicon carbide (SiC) fibers during irradiation with 14 MeV deuterons at 450 and 600°C. The fibers are produced by a CVD procedure; their microstructure may therefore be representative for the matrix of a SiC composite. There is a significant radiation induced increase in creep deformation. Both quantities, irradiation creep strain and creep rate, are higher at 450°C than at 600°C for doses <0.07 dpa.

  6. STATUS OF HIGH FLUX ISOTOPE REACTOR IRRADIATION OF SILICON CARBIDE/SILICON CARBIDE JOINTS

    SciTech Connect

    Katoh, Yutai; Koyanagi, Takaaki; Kiggans, Jim; Cetiner, Nesrin; McDuffee, Joel

    2014-09-01

    Development of silicon carbide (SiC) joints that retain adequate structural and functional properties in the anticipated service conditions is a critical milestone toward establishment of advanced SiC composite technology for the accident-tolerant light water reactor (LWR) fuels and core structures. Neutron irradiation is among the most critical factors that define the harsh service condition of LWR fuel during the normal operation. The overarching goal of the present joining and irradiation studies is to establish technologies for joining SiC-based materials for use as the LWR fuel cladding. The purpose of this work is to fabricate SiC joint specimens, characterize those joints in an unirradiated condition, and prepare rabbit capsules for neutron irradiation study on the fabricated specimens in the High Flux Isotope Reactor (HFIR). Torsional shear test specimens of chemically vapor-deposited SiC were prepared by seven different joining methods either at Oak Ridge National Laboratory or by industrial partners. The joint test specimens were characterized for shear strength and microstructures in an unirradiated condition. Rabbit irradiation capsules were designed and fabricated for neutron irradiation of these joint specimens at an LWR-relevant temperature. These rabbit capsules, already started irradiation in HFIR, are scheduled to complete irradiation to an LWR-relevant dose level in early 2015.

  7. Irradiation and annealing of p-type silicon carbide

    SciTech Connect

    Lebedev, Alexander A.; Bogdanova, Elena V.; Grigor'eva, Maria V.; Lebedev, Sergey P.; Kozlovski, Vitaly V.

    2014-02-21

    The development of the technology of semiconductor devices based on silicon carbide and the beginning of their industrial manufacture have made increasingly topical studies of the radiation hardness of this material on the one hand and of the proton irradiation to form high-receptivity regions on the other hand. This paper reports on a study of the carrier removal rate (V{sub d}) in p-6H-SiC under irradiation with 8 MeV protons and of the conductivity restoration in radiation- compensated epitaxial layers of various p-type silicon carbide polytypes. V{sub d} was determined by analysis of capacitance-voltage characteristics and from results of Hall effect measurements. It was found that the complete compensation of samples with the initial value of Na - Nd ≈ 1.5 × 10{sup 18} cm{sup −3} occurs at an irradiation dose of ∼1.1 × 10{sup 16} cm{sup −2}. It is shown that specific features of the sublimation layer SiC (compared to CVD layers) are clearly manifested upon the gamma and electron irradiation and are hardly noticeable under the proton and neutron irradiation. It was also found that the radiation-induced compensation of SiC is retained after its annealing at ≤1000°C. The conductivity is almost completely restored at T ≥ 1200°C. This character of annealing of the radiation compensation is independent of a silicon carbide polytype and the starting doping level of the epitaxial layer. The complete annealing temperatures considerably exceed the working temperatures of SiC-based devices. It is shown that the radiation compensation is a promising method in the technology of high-temperature devices based on SiC.

  8. Displacement damage in silicon carbide irradiated in fission reactors

    NASA Astrophysics Data System (ADS)

    Heinisch, H. L.; Greenwood, L. R.; Weber, W. J.; Williford, R. E.

    2004-05-01

    Calculations are performed for displacement damage in SiC due to irradiation in the neutron environments of various types of nuclear reactors using the best available models and nuclear data. The displacement damage calculations use recently developed damage functions for SiC that are based on extensive molecular dynamics simulations of displacement events. Displacements per atom (DPA) cross sections for SiC have been calculated as a function of neutron energy, and they are presented here in tabular form to facilitate their use as the standard measure of displacement damage for irradiated SiC. DPA cross sections averaged over the neutron energy spectrum are calculated for neutron spectra in the cores of typical commercial reactors and in the test sample irradiation regions of several materials test reactors used in both past and present irradiation testing. Particular attention is focused on a next-generation high-temperature gas-cooled pebble bed reactor, for which the high-temperature properties of silicon carbide fiber-reinforced silicon carbide composites are well suited. Calculated transmutations and activation levels in a pebble bed reactor are compared to those in other reactors.

  9. Threshold irradiation dose for amorphization of silicon carbide

    SciTech Connect

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

    1997-04-01

    The amorphization of silicon carbide due to ion and electron irradiation is reviewed with emphasis on the temperature-dependent critical dose for amorphization. The effect of ion mass and energy on the threshold dose for amorphization is summarized, showing only a weak dependence near room temperature. Results are presented for 0.56 MeV silicon ions implanted into single crystal 6H-SiC as a function of temperature and ion dose. From this, the critical dose for amorphization is found as a function of temperature at depths well separated from the implanted ion region. Results are compared with published data generated using electrons and xenon ions as the irradiating species. High resolution TEM analysis is presented for the Si ion series showing the evolution of elongated amorphous islands oriented such that their major axis is parallel to the free surface. This suggests that surface of strain effects may be influencing the apparent amorphization threshold. Finally, a model for the temperature threshold for amorphization is described using the Si ion irradiation flux and the fitted interstitial migration energy which was found to be {approximately}0.56 eV. This model successfully explains the difference in the temperature-dependent amorphization behavior of SiC irradiated with 0.56 MeV silicon ions at 1 x 10{sup {minus}3} dpa/s and with fission neutrons irradiated at 1 x 10{sup {minus}6} dpa/s irradiated to 15 dpa in the temperature range of {approximately}340 {+-} 10K.

  10. USE OF SILICON CARBIDE MONITORS IN ATR IRRADIATION TESTING

    SciTech Connect

    K. L. Davis; B. Chase; T. Unruh; D. Knudson; J. L. Rempe

    2012-07-01

    In April 2007, the Department of Energy (DOE) designated the Advanced Test Reactor (ATR) a National Scientific User Facility (NSUF) to advance US leadership in nuclear science and technology. By attracting new users from universities, laboratories, and industry, the ATR will support basic and applied nuclear research and development and help address the nation's energy security needs. In support of this new program, the Idaho National Laboratory (INL) has developed in-house capabilities to fabricate, test, and qualify new and enhanced temperature sensors for irradiation testing. Although most efforts emphasize sensors capable of providing real-time data, selected tasks have been completed to enhance sensors provided in irradiation locations where instrumentation leads cannot be included, such as drop-in capsule and Hydraulic Shuttle Irradiation System (HSIS) or 'rabbit' locations. For example, silicon carbide (SiC) monitors are now available to detect peak irradiation temperatures between 200°C and 800°C. Using a resistance measurement approach, specialized equipment installed at INL's High Temperature Test Laboratory (HTTL) and specialized procedures were developed to ensure that accurate peak irradiation temperature measurements are inferred from SiC monitors irradiated at the ATR. Comparison examinations were completed by INL to demonstrate this capability, and several programs currently rely on SiC monitors for peak temperature detection. This paper discusses the use of SiC monitors at the ATR, the process used to evaluate them at the HTTL, and presents representative measurements taken using SiC monitors.

  11. Proton irradiation creep of beta-silicon carbide

    NASA Astrophysics Data System (ADS)

    Shankar, Vani; Was, Gary S.

    2011-11-01

    In situ irradiation creep behavior of chemically vapor-deposited (CVD) polycrystalline beta silicon carbide (β-SiC) has been studied using proton beam of energies 2.8 MeV and 3.2 MeV. Experiments were conducted at 1183 K and at stresses of 18.5 MPa and 97.9 MPa between dose rates of 1.5 and 2.45 × 10 -6 dpa/s. Strain was measured using a laser speckle extensometer (LSE) and a linear variable differential transformer (LVDT), and temperature was measured using a 2-dimensional infrared pyrometer. Results showed that the total strain rate increased with increasing stress and dose rate. Shifts of XRD peaks following proton irradiation of SiC at 1183 K indicated that swelling had occurred and that it increased with dose. A uniform expansion of the lattice with no X-ray line broadening clearly indicated that the swelling at doses up to 0.37 dpa was due to single point defects. The swelling rate was determined and subtracted from the measured total strain rate to obtain the true creep rate. The creep rate was found to exhibit a linear dependence on the applied tensile stress, and on dose rate to the third power.

  12. Silicon threshold displacement energy determined by photoluminescence in electron-irradiated cubic silicon carbide

    SciTech Connect

    Lefevre, Jeremie; Esnouf, Stephane; Petite, Guillaume; Costantini, Jean-Marc

    2009-01-15

    In view of the potential use of silicon carbide (SiC) in the nuclear industry, it is of major interest to understand point defect formation in this material. This work is a contribution to the determination of the silicon threshold displacement energy in the cubic polytype of SiC using electron irradiations with increasing energies from 275 to 680 keV. The photoluminescence signal of the silicon vacancy was related to the number of displacements per atom in the silicon sublattice. This quantity was calculated taking into account the energy loss and angular dispersion of electrons in the target. A best fit of experimental data was obtained for a displacement cross section using a threshold displacement energy of 25 eV along the [100] lattice direction. We checked the relevance of this result by comparing the experimental concentration of silicon single vacancies measured by electron paramagnetic resonance spectroscopy with the theoretical number of displaced silicon atoms.

  13. Irradiation creep of nano-powder sintered silicon carbide at low neutron fluences

    SciTech Connect

    Koyanagi, Takaaki; Shimoda, Kazuya; Kondo, Sosuke; Hinoki, Tatsuya; Ozawa, Kazumi; Katoh, Yutai

    2014-12-01

    The irradiation creep behavior of nano-powder sintered silicon carbide was investigated using the bend stress relaxation method under neutron irradiation up to 1.9 dpa. The creep deformation was observed at all temperatures ranging from 380 to 1180 °C mainly from the irradiation creep but with the increasing contributions from the thermal creep at higher temperatures. Microstructural observation and data analysis were performed.

  14. Microstructures of beta silicon carbide after irradiation creep deformation at elevated temperatures

    SciTech Connect

    Katoh, Yutai; Kondo, Sosuke; Snead, Lance Lewis

    2008-01-01

    Microstructures of silicon carbide were examined by transmission electron microscopy (TEM) after creep deformation under neutron irradiation. Thin strip specimens of polycrystalline and monocrystalline, chemically vapor-deposited, beta-phase silicon carbide were irradiated in the high flux isotope reactor to 0.7-4.2 dpa at nominal temperatures of 640-1080 C in an elastically pre-strained bend stress relaxation configuration with the initial stress of {approx}100 MPa. Irradiation creep caused permanent strains of 0.6 to 2.3 x 10{sup -4}. Tensile-loaded near-surface portions of the crept specimens were examined by TEM. The main microstructural features observed were dislocation loops in all samples, and appeared similar to those observed in samples irradiated in non-stressed conditions. Slight but statistically significant anisotropy in dislocation loop microstructure was observed in one irradiation condition, and accounted for at least a fraction of the creep strain derived from the stress relaxation. The estimated total volume of loops accounted for 10-45% of the estimated total swelling. The results imply that the early irradiation creep deformation of SiC observed in this work was driven by anisotropic evolutions of extrinsic dislocation loops and matrix defects with undetectable sizes.

  15. Plasma deposition of amorphous silicon carbide thin films irradiated with neutrons

    NASA Astrophysics Data System (ADS)

    Huran, J.; Bohacek, P.; Kucera, M.; Kleinova, A.; Sasinkova, V.; IEE SAS, Bratislava, Slovakia Team; Polymer Institute, SAS, Bratislava, Slovakia Team; Institute of Chemistry, SAS, Bratislava, Slovakia Team

    2015-09-01

    Amorphous silicon carbide and N-doped silicon carbide thin films were deposited on P-type Si(100) wafer by plasma enhanced chemical vapor deposition (PECVD) technology using silane, methane, ammonium and argon gases. The concentration of elements in the films was determined by RBS and ERDA method. Chemical compositions were analyzed by FTIR spectroscopy. Photoluminescence properties were studied by photoluminescence spectroscopy (PL). Irradiation of samples with various neutron fluencies was performed at room temperature. The films contain silicon, carbon, hydrogen, nitrogen and small amount of oxygen. From the IR spectra, the films contained Si-C, Si-H, C-H, Si-N, N-H and Si-O bonds. No significance effect on the IR spectra after neutron irradiation was observed. PL spectroscopy results of films showed decreasing PL intensity after neutron irradiation and PL intensity decreased with increased neutron fluencies. The measured current of the prepared structures increased after irradiation with neutrons and rise up with neutron fluencies.

  16. Quantification of irradiation defects in beta-silicon carbide using Raman spectroscopy

    DOE PAGESBeta

    Koyanagi, T.; Lance, M. J.; Katoh, Y.

    2016-08-11

    Raman spectra from polycrystalline beta-silicon carbide (SiC) were collected following neutron irradiation at 380–1180 °C to 0.011–1.87 displacement per atom. The longitudinal optical (LO) peak shifted to a lower frequency and broadened as a result of the irradiation. The changes observed in the LO phonon line shape and position in neutron-irradiated SiC are explained by a combination of changes in the lattice constant and Young's modulus, and the phonon confinement effect. The phonon confinement model reasonably estimates the defect-defect distance in the irradiated SiC, which is consistent with results from previous experimental studies and simulations.

  17. Neutron irradiation effects on high Nicalon silicon carbide fibers

    SciTech Connect

    Osborne, M.C.; Steiner, D.; Snead, L.L.

    1996-10-01

    The effects of neutron irradiation on the mechanical properties and microstructure of SiC and SiC-based fibers is a current focal point for the development of radiation damage resistant SiC/SiC composites. This report discusses the radiation effects on the Nippon Carbon Hi-Nicalon{trademark} fiber system and also discusses an erratum on earlier results published by the authors on this material. The radiation matrix currently under study is also summarized.

  18. The effect of neutron irradiation on silicon carbide fibers

    SciTech Connect

    Newsome, G.A.

    1997-01-01

    Nine types of SiC fiber have been exposed to neutron radiation in the Advanced Test Reactor at 250 C for various lengths of time ranging from 83 to 128 days. The effects of these exposures have been initially determined using scanning electron microscopy. The fibers tested were Nicalon{trademark} CG, Tyranno, Hi-Nicalon{trademark}, Dow Corning SiC, Carborundum SiC, Textron SCS-6, polymethysilane (PMS) derived SiC from the University of Michigan, and two types of MER SiC fiber. This covers a range of fibers from widely used commercial fibers to developmental fibers. Consistent with previous radiation experiments, Nicalon fiber was severely degraded by the neutron irradiation. Similarly, Tyranno suffered severe degradation. The more advanced fibers which approach the composition and properties of SiC performed well under irradiation. Of these, the Carborundum SiC fiber appeared to perform the best. The Hi-Nicalon and Dow Corning Fibers exhibited good general stability, but also appear to have some surface roughening. The MER fibers and the Textron SCS-6 fibers both had carbon cores which adversely influenced the overall stability of the fibers.

  19. Light ion irradiation creep of Textron SCS-6™ silicon carbide fibers

    NASA Astrophysics Data System (ADS)

    Scholz, R.; Mueller, R.; Lesueur, D.

    2002-12-01

    Creep tests were conducted in torsion on Textron SCS-6™ fibers during an irradiation with light ions in the temperature range 500-1000 °C for doses up to 0.16 dpa. The fibers produced by chemical vapor deposition have a similar structure as a silicon carbide composite matrix produced by chemical vapor infiltration. At 600 °C, the irradiation creep curves were characterized by a continuous drop in creep rate with dose. There was approximately a square root relationship between irradiation creep strain and dose. The creep rate was a linear function of stress. On a decrease in temperature the creep rate increased. At 1000 °C, the creep rate dropped only slightly with dose and decreased if the temperature was lowered. The results are discussed in terms of concentration and mobility of point defects and the change of these quantities with temperature.

  20. Effect of electron irradiation on carrier removal rate in silicon and silicon carbide with 4H modification

    SciTech Connect

    Kozlovskii, V. V.; Emtsev, V. V.; Emtsev, K. V.; Strokan, N. B.; Ivanov, A. M.; Lomasov, V. N.; Oganesyan, G. A.; Lebedev, A. A.

    2008-02-15

    Comparative study of the effect of successive (up to fluences of 3 Multiplication-Sign 10{sup 16} cm{sup -2}) irradiation with 900 keV electrons of samples made of FZ-Si and 4H-SiC (CVD) has been performed for the first time. Measurements on initial and irradiated samples were made using the van der Pauw method for silicon and the capacitance-voltage technique at a frequency of 1 kHz for silicon carbide. In addition, the spectrum of the defect levels introduced was monitored by the DLTS method for SiC. The carrier removal and defect introduction rates were determined for the two materials. It was found that the rates of defect introduction into FZ-Si and 4 H-SiC (CVD) are close to eachy other ({approx}0.1 cm{sup -1}), which is largely due to the almost identical threshold energies of defect generation.

  1. Effect of electron irradiation on carrier removal rate in silicon and silicon carbide with 4H modification

    SciTech Connect

    Kozlovskii, V. V.; Emtsev, V. V. Emtsev, K. V.; Strokan, N. B.; Ivanov, A. M.; Lomasov, V. N.; Oganesyan, G. A.; Lebedev, A. A.

    2008-02-15

    Comparative study of the effect of successive (up to fluences of 3 x 10{sup 16} cm{sup -2}) irradiation with 900 keV electrons of samples made of FZ-Si and 4H-SiC (CVD) has been performed for the first time. Measurements on initial and irradiated samples were made using the van der Pauw method for silicon and the capacitance-voltage technique at a frequency of 1 kHz for silicon carbide. In addition, the spectrum of the defect levels introduced was monitored by the DLTS method for SiC. The carrier removal and defect introduction rates were determined for the two materials. It was found that the rates of defect introduction into FZ-Si and 4 H-SiC (CVD) are close to eachy other ({approx}0.1 cm{sup -1}), which is largely due to the almost identical threshold energies of defect generation.

  2. Method for analyzing passive silicon carbide thermometry with a continuous dilatometer to determine irradiation temperature

    NASA Astrophysics Data System (ADS)

    Campbell, Anne A.; Porter, Wallace D.; Katoh, Yutai; Snead, Lance L.

    2016-03-01

    Silicon carbide is used as a passive post-irradiation temperature monitor because the irradiation defects will anneal out above the irradiation temperature. The irradiation temperature is determined by measuring a property change after isochronal annealing, i.e., lattice spacing, dimensions, electrical resistivity, thermal diffusivity, or bulk density. However, such methods are time-consuming since the steps involved must be performed in a serial manner. This work presents the use of thermal expansion from continuous dilatometry to calculate the SiC irradiation temperature, which is an automated process requiring minimal setup time. Analysis software was written that performs the calculations to obtain the irradiation temperature and removes possible user-introduced error while standardizing the analysis. This method has been compared to an electrical resistivity and isochronal annealing investigation, and the results revealed agreement of the calculated temperatures. These results show that dilatometry is a reliable and less time-intensive process for determining irradiation temperature from passive SiC thermometry.

  3. Method for analyzing passive silicon carbide thermometry with a continuous dilatometer to determine irradiation temperature

    DOE PAGESBeta

    Campbell, Anne A.; Porter, Wallace D.; Katoh, Yutai; Snead, Lance Lewis

    2016-01-14

    Silicon carbide is used as a passive post-irradiation temperature monitor because the irradiation defects will anneal out above the irradiation temperature. The irradiation temperature is determined by measuring a property change after isochronal annealing, i.e., lattice spacing, dimensions, electrical resistivity, thermal diffusivity, or bulk density. However, such methods are time-consuming since the steps involved must be performed in a serial manner. This work presents the use of thermal expansion from continuous dilatometry to calculate the SiC irradiation temperature, which is an automated process requiring minimal setup time. Analysis software was written that performs the calculations to obtain the irradiation temperaturemore » and removes possible user-introduced error while standardizing the analysis. In addition, this method has been compared to an electrical resistivity and isochronal annealing investigation, and the results revealed agreement of the calculated temperatures. These results show that dilatometry is a reliable and less time-intensive process for determining irradiation temperature from passive SiC thermometry.« less

  4. Neutron-irradiation creep of silicon carbide materials beyond the initial transient

    NASA Astrophysics Data System (ADS)

    Koyanagi, Takaaki; Katoh, Yutai; Ozawa, Kazumi; Shimoda, Kazuya; Hinoki, Tatsuya; Snead, Lance L.

    2016-09-01

    Irradiation creep beyond the transient regime was investigated for various silicon carbide (SiC) materials. The materials examined included polycrystalline or monocrystalline high-purity SiC, nanopowder sintered SiC, highly crystalline and near-stoichiometric SiC fibers (including Hi-Nicalon Type S, Tyranno SA3, isotopically-controlled Sylramic and Sylramic-iBN fibers), and a Tyranno SA3 fiber-reinforced SiC matrix composite fabricated through a nano-infiltration transient eutectic phase process. Neutron irradiation experiments for bend stress relaxation tests were conducted at irradiation temperatures ranging from 430 to 1180 °C up to 30 dpa with initial bend stresses of up to ∼1 GPa for the fibers and ∼300 MPa for the other materials. Initial bend stress in the specimens continued to decrease from 1 to 30 dpa. Analysis revealed that (1) the stress exponent of irradiation creep above 1 dpa is approximately unity, (2) the stress normalized creep rate is ∼1 × 10-7 [dpa-1 MPa-1] at 430-750 °C for the range of 1-30 dpa for most polycrystalline SiC materials, and (3) the effects on irradiation creep of initial microstructures-such as grain boundary, crystal orientation, and secondary phases-increase with increasing irradiation temperature.

  5. Neutron-irradiation creep of silicon carbide materials beyond the initial transient

    DOE PAGESBeta

    Katoh, Yutai; Ozawa, Kazumi; Shimoda, Kazuya; Hinoki, Tatsuya; Snead, Lance Lewis; Koyanagi, Takaaki

    2016-06-04

    Irradiation creep beyond the transient regime was investigated for various silicon carbide (SiC) materials. Here, the materials examined included polycrystalline or monocrystalline high-purity SiC, nanopowder sintered SiC, highly crystalline and near-stoichiometric SiC fibers (including Hi-Nicalon Type S, Tyranno SA3, isotopically-controlled Sylramic and Sylramic-iBN fibers), and a Tyranno SA3 fiber–reinforced SiC matrix composite fabricated through a nano-infiltration transient eutectic phase process. Neutron irradiation experiments for bend stress relaxation tests were conducted at irradiation temperatures ranging from 430 to 1180 °C up to 30 dpa with initial bend stresses of up to ~1 GPa for the fibers and ~300 MPa for themore » other materials. Initial bend stress in the specimens continued to decrease from 1 to 30 dpa. Analysis revealed that (1) the stress exponent of irradiation creep above 1 dpa is approximately unity, (2) the stress normalized creep rate is ~1 × 10–7 [dpa–1 MPa–1] at 430–750 °C for the range of 1–30 dpa for most polycrystalline SiC materials, and (3) the effects on irradiation creep of initial microstructures—such as grain boundary, crystal orientation, and secondary phases—increase with increasing irradiation temperature.« less

  6. Irradiation creep of nano-powder sintered silicon carbide at low neutron fluences

    NASA Astrophysics Data System (ADS)

    Koyanagi, T.; Shimoda, K.; Kondo, S.; Hinoki, T.; Ozawa, K.; Katoh, Y.

    2014-12-01

    The irradiation creep behavior of nano-powder sintered silicon carbide was investigated using the bend stress relaxation method under neutron irradiation up to 1.9 dpa. The creep deformation was observed at all temperatures ranging from 380 to 1180 °C mainly from the irradiation creep but with the increasing contributions from the thermal creep at higher temperatures. The apparent stress exponent of the irradiation creep slightly exceeded unity, and instantaneous creep coefficient at 380-790 °C was estimated to be ∼1 × 10-5 [MPa-1 dpa-1] at ∼0.1 dpa and 1 × 10-7 to 1 × 10-6 [MPa-1 dpa-1] at ∼1 dpa. The irradiation creep strain appeared greater than that for the high purity SiC. Microstructural observation and data analysis indicated that the grain-boundary sliding associated with the secondary phases contributes to the irradiation creep at 380-790 °C to 0.01-0.11 dpa.

  7. Silicon carbide ceramic production

    NASA Technical Reports Server (NTRS)

    Suzuki, K.; Shinohara, N.

    1984-01-01

    A method to produce sintered silicon carbide ceramics in which powdery carbonaceous components with a dispersant are mixed with silicon carbide powder, shaped as required with or without drying, and fired in nonoxidation atmosphere is described. Carbon black is used as the carbonaceous component.

  8. Irradiation Creep of Chemically Vapor Deposited Silicon Carbide as Estimated by Bend Stress Relaxation Method

    SciTech Connect

    Katoh, Yutai; Snead, Lance Lewis; Hinoki, Tatsuya; Kondo, Sosuke; Kohyama, Akira

    2007-01-01

    The bend stress relaxation technique was applied for an irradiation creep study of high purity, chemically vapor-deposited beta-phase silicon carbide (CVD SiC) ceramic. A constant bend strain was applied to thin strip samples during neutron irradiation to fluences 0.2-4.2 dpa at various temperatures in the range {approx}400 to {approx}1080 C. Irradiation creep strain at <0.7 dpa exhibited only a weak dependence on irradiation temperature. However, the creep strain dependence on fluence was non-linear due to the early domination of the initial transient creep, and a transition in creep behavior was found between 950 and 1080 C. Steady-state irradiation creep compliances of polycrystalline CVD SiC at doses >0.7 dpa were estimated to be 2.7({+-}2.6) x 10{sup -7} and 1.5({+-}0.8) x 10{sup -6} (MPa dpa){sup -1} at {approx}600 to {approx}950 C and {approx}1080 C, respectively, whereas linear-averaged creep compliances of 1-2 x 10{sup -6} (MPa dpa){sup -1} were obtained for doses of 0.6-0.7 dpa at all temperatures. Monocrystalline 3C SiC samples exhibited significantly smaller transient creep strain and greater subsequent deformation when loaded along <0 1 1> direction.

  9. Mechanical- and physical-property changes of neutron-irradiated chemical-vapor-deposited silicon carbide

    SciTech Connect

    Osborne, M.C.; Steiner, D.; Hay, J.C.; Snead, L.L.

    1999-09-01

    Indentation and density measurements have revealed important changes in the mechanical and physical properties of silicon carbide (SiC) due to neutron irradiation. Specifically, the changes in the elastic modulus, hardness, fracture toughness, and density with irradiation have provided an understanding of the expected performance of SiC and SiC composites in nuclear applications. After the accumulated damage has saturated, these mechanical properties were affected primarily by the irradiation temperature. Chemical-vapor-deposited (CVD) SiC was irradiated above the saturation fluence and yielded volumetric swelling of 2.6% and 1.3% for irradiation temperatures of 100--150 C and 500--550 C, respectively. At the same respective temperatures, the elastic modulus decreased from an unirradiated value of 503 GPa to {approximately} 420 and 450 GPa. Conversely, the hardness increased from 36 GPa for the unirradiated at 100--150 C and 500--550 C, respectively. Interestingly, these two independent properties approached almost-constant levels after exposure to a fluence of 0.5 {times} 10{sup 25} n/m{sup 2}, E > 0.1 MeV. Indentation fracture toughness measurements, which were within the range of values in the literature for conventional fracture toughness procedures for SiC, increased from {approximately} 2.8 MPa{center_dot}m{sup 1/2} for the unirradiated samples to 3.7 and 4.2 MPa{center_dot}m{sup 1/2} for the samples that were irradiated at 100--150 C and 500--550 C, respectively.

  10. Tritium trapping in silicon carbide in contact with solid breeder under high flux isotope reactor irradiation

    SciTech Connect

    H. Katsui; Y. Katoh; A. Hasegawa; M. Shimada; Y. Hatano; T. Hinoki; S. Nogami; T. Tanaka; S. Nagata; T. Shikama

    2013-11-01

    The trapping of tritium in silicon carbide (SiC) injected from ceramic breeding materials was examined via tritium measurements using imaging plate (IP) techniques. Monolithic SiC in contact with ternary lithium oxide (lithium titanate and lithium aluminate) as a ceramic breeder was irradiated in the High Flux Isotope Reactor (HFIR) in Oak Ridge, Tennessee, USA. The distribution of photo-stimulated luminescence (PSL) of tritium in SiC was successfully obtained, which separated the contribution of 14C ß-rays to the PSL. The tritium incident from ceramic breeders was retained in the vicinity of the SiC surface even after irradiation at 1073 K over the duration of ~3000 h, while trapping of tritium was not observed in the bulk region. The PSL intensity near the SiC surface in contact with lithium titanate was higher than that obtained with lithium aluminate. The amount of the incident tritium and/or the formation of a Li2SiO3 phase on SiC due to the reaction with lithium aluminate under irradiation likely were responsible for this observation.

  11. Experimental and ab initio study of enhanced resistance to amorphization of nanocrystalline silicon carbide under electron irradiation

    NASA Astrophysics Data System (ADS)

    Jamison, Laura; Zheng, Ming-Jie; Shannon, Steve; Allen, Todd; Morgan, Dane; Szlufarska, Izabela

    2014-02-01

    The crystalline-to-amorphous transition in nanocrystalline silicon carbide (ncSiC) has been studied using 1.25 MeV electron irradiation. When compared to literature values for single crystal silicon carbide under electron irradiation, an increase in the dose to amorphization (DTA) was observed, indicative of an increase in radiation resistance. Factors that contribute to this improvement are grain refinement, grain texture, and a high density of stacking faults (SFs) in this sample of ncSiC. To test the effect of SFs on the DTA, density functional theory simulations were conducted. It was found that SFs reduced the energy barriers for both Si interstitial migration and the rate-limiting defect recovery reaction, which may explain the increased DTA.

  12. Improved toughness of silicon carbide

    NASA Technical Reports Server (NTRS)

    Palm, J. A.

    1976-01-01

    Impact energy absorbing layers (EALs) comprised of partially densified silicon carbide were formed in situ on fully sinterable silicon carbide substrates. After final sintering, duplex silicon carbide structures resulted which were comprised of a fully sintered, high density silicon carbide substrate or core, overlayed with an EAL of partially sintered silicon carbide integrally bonded to its core member. Thermal cycling tests proved such structures to be moderately resistant to oxidation and highly resistant to thermal shock stresses. The strength of the developed structures in some cases exceeded but essentially it remained the same as the fully sintered silicon carbide without the EAL. Ballistic impact tests indicated that substantial improvements in the toughness of sintered silicon carbide were achieved by the use of the partially densified silicon carbide EALs.

  13. High-dose neutron irradiation of Hi-Nicalon Type S silicon carbide composites. Part 2: Mechanical and physical properties

    NASA Astrophysics Data System (ADS)

    Katoh, Yutai; Nozawa, Takashi; Shih, Chunghao; Ozawa, Kazumi; Koyanagi, Takaaki; Porter, Wally; Snead, Lance L.

    2015-07-01

    Nuclear-grade silicon carbide (SiC) composite material was examined for mechanical and thermophysical properties following high-dose neutron irradiation in the High Flux Isotope Reactor at a temperature range of 573-1073 K. The material was chemical vapor-infiltrated SiC-matrix composite with a two-dimensional satin weave Hi-Nicalon Type S SiC fiber reinforcement and a multilayered pyrocarbon/SiC interphase. Moderate (1073 K) to very severe (573 K) degradation in mechanical properties was found after irradiation to >70 dpa, whereas no evidence was found for progressive evolution in swelling and thermal conductivity. The swelling was found to recover upon annealing beyond the irradiation temperature, indicating the irradiation temperature, but only to a limited extent. The observed strength degradation is attributed primarily to fiber damage for all irradiation temperatures, particularly a combination of severe fiber degradation and likely interphase damage at relatively low irradiation temperatures.

  14. High Dose Neutron Irradiation of Hi-Nicalon Type S Silicon Carbide Composites, Part 2. Mechanical and Physical Properties

    SciTech Connect

    Katoh, Yutai; Nozawa, Takashi; Shih, Chunghao Phillip; Ozawa, Kazumi; Koyanagi, Takaaki; Porter, Wallace D; Snead, Lance Lewis

    2015-01-07

    Nuclear-grade silicon carbide (SiC) composite material was examined for mechanical and thermophysical properties following high-dose neutron irradiation in the High Flux Isotope Reactor at a temperature range of 573–1073 K. Likewise, the material was chemical vapor-infiltrated SiC-matrix composite with a two-dimensional satin weave Hi-Nicalon Type S SiC fiber reinforcement and a multilayered pyrocarbon/SiC interphase. Moderate (1073 K) to very severe (573 K) degradation in mechanical properties was found after irradiation to >70 dpa, whereas no evidence was found for progressive evolution in swelling and thermal conductivity. The swelling was found to recover upon annealing beyond the irradiation temperature, indicating the irradiation temperature, but only to a limited extent. Moreover, the observed strength degradation is attributed primarily to fiber damage for all irradiation temperatures, particularly a combination of severe fiber degradation and likely interphase damage at relatively low irradiation temperatures.

  15. Silicon carbide thyristor

    NASA Technical Reports Server (NTRS)

    Edmond, John A. (Inventor); Palmour, John W. (Inventor)

    1996-01-01

    The SiC thyristor has a substrate, an anode, a drift region, a gate, and a cathode. The substrate, the anode, the drift region, the gate, and the cathode are each preferably formed of silicon carbide. The substrate is formed of silicon carbide having one conductivity type and the anode or the cathode, depending on the embodiment, is formed adjacent the substrate and has the same conductivity type as the substrate. A drift region of silicon carbide is formed adjacent the anode or cathode and has an opposite conductivity type as the anode or cathode. A gate is formed adjacent the drift region or the cathode, also depending on the embodiment, and has an opposite conductivity type as the drift region or the cathode. An anode or cathode, again depending on the embodiment, is formed adjacent the gate or drift region and has an opposite conductivity type than the gate.

  16. Silicon nitride/silicon carbide composite powders

    DOEpatents

    Dunmead, Stephen D.; Weimer, Alan W.; Carroll, Daniel F.; Eisman, Glenn A.; Cochran, Gene A.; Susnitzky, David W.; Beaman, Donald R.; Nilsen, Kevin J.

    1996-06-11

    Prepare silicon nitride-silicon carbide composite powders by carbothermal reduction of crystalline silica powder, carbon powder and, optionally, crystalline silicon nitride powder. The crystalline silicon carbide portion of the composite powders has a mean number diameter less than about 700 nanometers and contains nitrogen. The composite powders may be used to prepare sintered ceramic bodies and self-reinforced silicon nitride ceramic bodies.

  17. Silicon carbide reinforced silicon carbide composite

    NASA Technical Reports Server (NTRS)

    Lau, Sai-Kwing (Inventor); Calandra, Salvatore J. (Inventor); Ohnsorg, Roger W. (Inventor)

    2001-01-01

    This invention relates to a process comprising the steps of: a) providing a fiber preform comprising a non-oxide ceramic fiber with at least one coating, the coating comprising a coating element selected from the group consisting of carbon, nitrogen, aluminum and titanium, and the fiber having a degradation temperature of between 1400.degree. C. and 1450.degree. C., b) impregnating the preform with a slurry comprising silicon carbide particles and between 0.1 wt % and 3 wt % added carbon c) providing a cover mix comprising: i) an alloy comprising a metallic infiltrant and the coating element, and ii) a resin, d) placing the cover mix on at least a portion of the surface of the porous silicon carbide body, e) heating the cover mix to a temperature between 1410.degree. C. and 1450.degree. C. to melt the alloy, and f) infiltrating the fiber preform with the melted alloy for a time period of between 15 minutes and 240 minutes, to produce a ceramic fiber reinforced ceramic composite.

  18. Composition Comprising Silicon Carbide

    NASA Technical Reports Server (NTRS)

    Mehregany, Mehran (Inventor); Zorman, Christian A. (Inventor); Fu, Xiao-An (Inventor); Dunning, Jeremy L. (Inventor)

    2012-01-01

    A method of depositing a ceramic film, particularly a silicon carbide film, on a substrate is disclosed in which the residual stress, residual stress gradient, and resistivity are controlled. Also disclosed are substrates having a deposited film with these controlled properties and devices, particularly MEMS and NEMS devices, having substrates with films having these properties.

  19. Improved toughness of silicon carbide

    NASA Technical Reports Server (NTRS)

    Palm, J. A.

    1975-01-01

    Several techniques were employed to apply or otherwise form porous layers of various materials on the surface of hot-pressed silicon carbide ceramic. From mechanical properties measurements and studies, it was concluded that although porous layers could be applied to the silicon carbide ceramic, sufficient damage was done to the silicon carbide surface by the processing required so as to drastically reduce its mechanical strength. It was further concluded that there was little promise of success in forming an effective energy absorbing layer on the surface of already densified silicon carbide ceramic that would have the mechanical strength of the untreated or unsurfaced material. Using a process for the pressureless sintering of silicon carbide powders it was discovered that porous layers of silicon carbide could be formed on a dense, strong silicon carbide substrate in a single consolidation process.

  20. Comparative study of changes in electrical properties of silicon and silicon carbide upon proton irradiation

    SciTech Connect

    Emtsev, V. V. Ivanov, A. M.; Kozlovskii, V. V.; Lebedev, A. A.; Oganesyan, G. A.; Strokan, N. B.

    2010-05-15

    Rates of carrier removal from the conduction band in n-type FZ-Si and 4H-SiC irradiated with 8- and 15-MeV protons at room temperature are discussed. Calculated rates of formation of primary radiation defects (Frenkel pairs) in these materials are presented and compared with the corresponding experimental values. Protons create defects in collision cascades involving recoil atoms formed in the crystal lattice itself. The results are compared with similar data previously obtained in irradiation of n-type FZ-Si and 4H-SiC with 900-keV electrons, in which case isolated so-called close Frenkel pairs are absolutely dominant among primary radiation defects. It has been found that the E-center model adequately describing the decrease in the electrical conductivity of n-FZ-Si upon electron irradiation is inapplicable to interpretation of experimental data for proton-irradiated materials. It is suggested that a pronounced annealing of 'simple' radiation defects of the type of close Frenkel pairs occurs during irradiation at room temperature.

  1. Modified silicon carbide whiskers

    DOEpatents

    Tiegs, T.N.; Lindemer, T.B.

    1991-05-21

    Silicon carbide whisker-reinforced ceramic composites are fabricated in a highly reproducible manner by beneficating the surfaces of the silicon carbide whiskers prior to their usage in the ceramic composites. The silicon carbide whiskers which contain considerable concentrations of surface oxides and other impurities which interact with the ceramic composite material to form a chemical bond are significantly reduced so that only a relatively weak chemical bond is formed between the whisker and the ceramic material. Thus, when the whiskers interact with a crack propagating into the composite the crack is diverted or deflected along the whisker-matrix interface due to the weak chemical bonding so as to deter the crack propagation through the composite. The depletion of the oxygen-containing compounds and other impurities on the whisker surfaces and near surface region is effected by heat treating the whiskers in a suitable oxygen sparging atmosphere at elevated temperatures. Additionally, a sedimentation technique may be utilized to remove whiskers which suffer structural and physical anomalies which render them undesirable for use in the composite. Also, a layer of carbon may be provided on the surface of the whiskers to further inhibit chemical bonding of the whiskers to the ceramic composite material.

  2. Modified silicon carbide whiskers

    DOEpatents

    Tiegs, Terry N.; Lindemer, Terrence B.

    1991-01-01

    Silicon carbide whisker-reinforced ceramic composites are fabricated in a highly reproducible manner by beneficating the surfaces of the silicon carbide whiskers prior to their usage in the ceramic composites. The silicon carbide whiskers which contain considerable concentrations of surface oxides and other impurities which interact with the ceramic composite material to form a chemical bond are significantly reduced so that only a relatively weak chemical bond is formed between the whisker and the ceramic material. Thus, when the whiskers interact with a crack propagating into the composite the crack is diverted or deflected along the whisker-matrix interface due to the weak chemical bonding so as to deter the crack propagation through the composite. The depletion of the oxygen-containing compounds and other impurities on the whisker surfaces and near surface region is effected by heat treating the whiskers in a suitable oxygen sparaging atmosphere at elevated temperatures. Additionally, a sedimentation technique may be utilized to remove whiskers which suffer structural and physical anomalies which render them undesirable for use in the composite. Also, a layer of carbon may be provided on the surface of the whiskers to further inhibit chemical bonding of the whiskers to the ceramic composite material.

  3. Periodic nanostructures self-formed on silicon and silicon carbide by femtosecond laser irradiation

    NASA Astrophysics Data System (ADS)

    Gemini, Laura; Hashida, Masaki; Shimizu, Masahiro; Miyasaka, Yasuhiro; Inoue, Shunsuke; Tokita, Shigeki; Limpouch, Jiri; Mocek, Tomas; Sakabe, Shuji

    2014-10-01

    Laser-induced periodic surface structures (LIPSS) were formed on Si and SiC surfaces by irradiations with femtosecond laser pulses in air. Different kinds of self-organized structures appeared on Si and SiC at laser fluences slightly higher than the damage threshold, which was measured by confocal laser scanning microscope. The characteristic spatial periodicity of every observed structure was estimated reading the peak values of the 2D Fourier transform power spectra obtained from SEM images. The evolution of the spatial periodicity was finally studied with respect to both the laser fluence and the number of laser pulses. As already observed for metals, the behavior of the spatial periodicity on laser fluence can be related to the parametric decay of laser light into surface plasma waves. Our results suggest a wide applicability of the parametric decay model on different materials, making the model a useful tool in view of different applications of LIPSS.

  4. High Dose Neutron Irradiation of Hi-Nicalon Type S Silicon Carbide Composites, Part 2. Mechanical and Physical Properties

    DOE PAGESBeta

    Katoh, Yutai; Nozawa, Takashi; Shih, Chunghao Phillip; Ozawa, Kazumi; Koyanagi, Takaaki; Porter, Wallace D; Snead, Lance Lewis

    2015-01-07

    Nuclear-grade silicon carbide (SiC) composite material was examined for mechanical and thermophysical properties following high-dose neutron irradiation in the High Flux Isotope Reactor at a temperature range of 573–1073 K. Likewise, the material was chemical vapor-infiltrated SiC-matrix composite with a two-dimensional satin weave Hi-Nicalon Type S SiC fiber reinforcement and a multilayered pyrocarbon/SiC interphase. Moderate (1073 K) to very severe (573 K) degradation in mechanical properties was found after irradiation to >70 dpa, whereas no evidence was found for progressive evolution in swelling and thermal conductivity. The swelling was found to recover upon annealing beyond the irradiation temperature, indicating themore » irradiation temperature, but only to a limited extent. Moreover, the observed strength degradation is attributed primarily to fiber damage for all irradiation temperatures, particularly a combination of severe fiber degradation and likely interphase damage at relatively low irradiation temperatures.« less

  5. Silicon carbide sewing thread

    NASA Technical Reports Server (NTRS)

    Sawko, Paul M. (Inventor)

    1995-01-01

    Composite flexible multilayer insulation systems (MLI) were evaluated for thermal performance and compared with currently used fibrous silica (baseline) insulation system. The systems described are multilayer insulations consisting of alternating layers of metal foil and scrim ceramic cloth or vacuum metallized polymeric films quilted together using ceramic thread. A silicon carbide thread for use in the quilting and the method of making it are also described. These systems provide lightweight thermal insulation for a variety of uses, particularly on the surface of aerospace vehicles subject to very high temperatures during flight.

  6. Silicon Carbide Electronic Devices

    NASA Technical Reports Server (NTRS)

    Neudeck, P. G.

    2001-01-01

    The status of emerging silicon carbide (SiC) widebandgap semiconductor electronics technology is briefly surveyed. SiC-based electronic devices and circuits are being developed for use in high-temperature, high-power, and/or high-radiation conditions under which conventional semiconductors cannot function. Projected performance benefits of SiC electronics are briefly illustrated for several applications. However, most of these operational benefits of SiC have yet to be realized in actual systems, primarily owing to the fact that the growth techniques of SiC crystals are relatively immature and device fabrication technologies are not yet sufficiently developed to the degree required for widespread, reliable commercial use. Key crystal growth and device fabrication issues that limit the performance and capability of high-temperature and/or high-power SiC electronics are identified. The electrical and material quality differences between emerging SiC and mature silicon electronics technology are highlighted.

  7. Thermal stability of irradiation-induced point defects in cubic silicon carbide

    SciTech Connect

    Lefevre, Jeremie; Esnouf, Stephane; Petite, Guillaume; Costantini, Jean-Marc

    2009-10-15

    This work aims specifically at studying the evolution of point defects induced by electron irradiation in the cubic polytype of SiC (3C-SiC) at temperatures ranging from 10 to 1450 K by means of photoluminescence (PL) spectroscopy. We identified a first annealing stage between 200 and 245 K, which probably results from migration of interstitials in the carbon sublattice. Moreover, we confirmed the high thermal stability of defect-related PL signals up to about 1100 K and calculated the activation energies associated with their annihilation. Finally, we studied the effect of a high temperature treatment at 1400 K on the D{sub I} center PL intensity in a single-crystal sample irradiated by electrons below the threshold displacement energy of the silicon sublattice. This allows checking the relevance of recent defect models based upon the migration of atoms in the carbon sublattice during the irradiation process. We conclude that the D{sub I} center does not involve the silicon vacancy and could be assigned to an isolated silicon antisite Si{sub C}.

  8. High dose neutron irradiations of Hi-Nicalon Type S silicon carbide composites, Part 1: Microstructural evaluations

    DOE PAGESBeta

    Perez-Bergquist, Alex G.; Nozawa, Takashi; Shih, Chunghao Phillip; Leonard, Keith J.; Snead, Lance Lewis; Katoh, Yutai

    2014-07-01

    Over the past decade, significant progress has been made in the development of silicon carbide (SiC) composites, composed of near-stoichiometric SiC fibers embedded in a crystalline SiC matrix, to the point that such materials can now be considered nuclear grade. Recent neutron irradiation studies of Hi-Nicalon Type S SiC composites showed excellent radiation response at damage levels of 30-40 dpa at temperatures of 300-800 °C. However, more recent studies of these same fiber composites irradiated to damage levels of >70 dpa at similar temperatures showed a marked decrease in ultimate flexural strength, particularly at 300 °C. Here, electron microscopy ismore » used to analyze the microstructural evolution of these irradiated composites in order to investigate the cause of the degradation. While minimal changes were observed in Hi-Nicalon Type S SiC composites irradiated at 800 °C, substantial microstructural evolution is observed in those irradiated at 300° C. Furthermore, carbonaceous particles in the fibers grew by 25% compared to the virgin case, and severe cracking occurred at interphase layers.« less

  9. High dose neutron irradiations of Hi-Nicalon Type S silicon carbide composites, Part 1: Microstructural evaluations

    SciTech Connect

    Perez-Bergquist, Alex G.; Nozawa, Takashi; Shih, Chunghao Phillip; Leonard, Keith J.; Snead, Lance Lewis; Katoh, Yutai

    2014-07-01

    Over the past decade, significant progress has been made in the development of silicon carbide (SiC) composites, composed of near-stoichiometric SiC fibers embedded in a crystalline SiC matrix, to the point that such materials can now be considered nuclear grade. Recent neutron irradiation studies of Hi-Nicalon Type S SiC composites showed excellent radiation response at damage levels of 30-40 dpa at temperatures of 300-800 °C. However, more recent studies of these same fiber composites irradiated to damage levels of >70 dpa at similar temperatures showed a marked decrease in ultimate flexural strength, particularly at 300 °C. Here, electron microscopy is used to analyze the microstructural evolution of these irradiated composites in order to investigate the cause of the degradation. While minimal changes were observed in Hi-Nicalon Type S SiC composites irradiated at 800 °C, substantial microstructural evolution is observed in those irradiated at 300° C. Furthermore, carbonaceous particles in the fibers grew by 25% compared to the virgin case, and severe cracking occurred at interphase layers.

  10. High dose neutron irradiation of Hi-Nicalon Type S silicon carbide composites, Part 1: Microstructural evaluations

    NASA Astrophysics Data System (ADS)

    Perez-Bergquist, Alejandro G.; Nozawa, Takashi; Shih, Chunghao; Leonard, Keith J.; Snead, Lance L.; Katoh, Yutai

    2015-07-01

    Over the past decade, significant progress has been made in the development of silicon carbide (SiC) composites, composed of near-stoichiometric SiC fibers embedded in a crystalline SiC matrix, to the point that such materials can now be considered nuclear grade. Recent neutron irradiation studies of Hi-Nicalon Type S SiC composites showed excellent radiation response at damage levels of 30-40 dpa at temperatures of 300-800 °C. However, more recent studies of these same fiber composites irradiated to damage levels of >70 dpa at similar temperatures showed a marked decrease in ultimate flexural strength, particularly at 300 °C. Here, electron microscopy is used to analyze the microstructural evolution of these irradiated composites in order to investigate the cause of the degradation. While minimal changes were observed in Hi-Nicalon Type S SiC composites irradiated at 800 °C, substantial microstructural evolution is observed in those irradiated at 300 °C. Specifically, carbonaceous particles in the fibers grew by 25% compared to the virgin case, and severe cracking occurred at interphase layers.

  11. Hydrogen-silicon carbide interactions

    NASA Technical Reports Server (NTRS)

    Eckel, Andrew J.; Jacobson, Nathan S.; Misra, Ajay K.; Humphrey, Donald L.

    1989-01-01

    A study of the thermochemistry and kinetics of hydrogen environmental attack of silicon carbide was conducted for temperatures in the range from 1100 C to 1400 C. Thermodynamic maps based on the parameters of pressure and oxygen/moisture content were constructed. With increasing moisture levels, four distinct regions of attack were identified. Each region is defined by the thermodynamically stable solid phases. The theoretically stable solid phases of Region 1 are silicon carbide and silicon. Experimental evidence is provided to support this thermodynamic prediction. Silicon carbide is the single stable solid phase in Region 2. Active attack of the silicon carbide in this region occurs by the formation of gases of SiO, CO, CH4, SiH4, and SiH. Analysis of the kinetics of reaction for Region 2 at 1300 C show the attack of the silicon carbide to be controlled by gas phase diffusion of H2O to the sample. Silicon carbide and silica are the stable phases common to Regions 3 and 4. These two regions are characterized by the passive oxidation of silicon carbide and formation of a protective silica layer.

  12. Hydrogen-silicon carbide interactions

    NASA Technical Reports Server (NTRS)

    Eckel, Andrew J.; Misra, Ajay K.; Humphrey, Donald L.; Jacobson, Nathan S.

    1990-01-01

    A study of the thermochemistry and kinetics of hydrogen environmental attack of silicon carbide was conducted for temperatures in the range from 1100 C to 1400 C. Thermodynamics maps based on the parameters of pressure and oxygen/moisture content were constructed. With increasing moisture levels, four distinct regions of attack were identified. Each region is defined by the thermodynamically stable solid phases. The theoretically stable solid phases of region 1 are silicon carbide and silicon. Experimental evidence is provided to support this thermodynamic prediction. Silicone carbide is the single stable solid phase in region 2. Active attack of the silicon carbide in this region occurs by the formation of gases of SiO, CO, CH4, SiH4 and SiH. Analyses of the kinetics of reaction for region 2 at 1300 C show the attack of the silicon carbide to be controlled by gas phase diffusion of H2O to the sample. Silicon carbide and silica are the stable phases common to regions 3 and 4. These two regions are characterized by the passive oxidation of silicon carbide and formation of a protective silica layer.

  13. Neutron irradiation and frequency effects on the electrical conductivity of nanocrystalline silicon carbide (3C-SiC)

    NASA Astrophysics Data System (ADS)

    Huseynov, Elchin

    2016-09-01

    In this present work nanocrystalline silicon carbide (3C-SiC) has been irradiated with neutron flux (∼ 2 ×1013 ncm-2s-1) up to 20 hours at different periods. Electrical conductivity of nanocrystalline 3C-SiC particles (∼18 nm) is comparatively analyzed before and after neutron irradiation. The frequency dependencies of electrical conductivity of 3C-SiC nanoparticles is reviewed at 100 K-400 K temperature range before and after irradiation. The measurements were carried out at 0.1 Hz-2.5 MHz frequency ranges and at different temperatures. Radiation-induced conductivity (RIC) was observed in the nanocrystalline 3C-SiC particles after neutron irradiation and this conductivity study as a function of frequency are presented. The type of conductivity has been defined based on the interdependence between real and imaginary parts of electrical conductivity function. Based on the obtained results the mechanism behind the electrical conductivity of nanocrystalline 3C-SiC particles is explained in detail.

  14. Silicon Carbide Growth

    NASA Technical Reports Server (NTRS)

    2005-01-01

    Andrew Trunek has focused on supporting the Sic team through the growth of Sic crystals, making observations and conducting research that meets the collective needs and requirements of the team while fulfilling program commitments. Cancellation of the Ultra Efficient Engine Technology (UEET) program has had a significant negative impact on resources and research goals. This report highlights advancements and achievements made with this cooperative agreement over the past year. NASA Glenn Research Center (GRC) continues to make advances in silicon carbide (SiC) research during the past year. Step free surfaces were used as substrates for the deposition of GaN epilayers that yielded very low dislocation densities. Defect free 3C- SiC was successfully nucleated on step free mesas and test diodes were fabricated. Web growth techniques were used to increase the usable surface area of dislocation free SiC by approximately equal to 40%. The greatest advancement has been attained on stepped surfaces of SiC. A metrology standard was developed using high temperature etching techniques titled "Nanometer Step Height Standard". This development culminated in being recognized for a 2004 R&D100 award and the process to produce the steps received a NASA Space Act award.

  15. Palladium interaction with silicon carbide

    NASA Astrophysics Data System (ADS)

    Gentile, M.; Xiao, P.; Abram, T.

    2015-07-01

    In this work the palladium interaction with silicon carbide is investigated by means of complementary analytical techniques such as thermogravimetry (TG), differential scanning calorimetry (DSC), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Thermoscans were carried out on pellets of palladium, α-SiC and β-SiC high purity powders in the temperature range comprised between 293 K and 1773 K, in order to study the effect of temperature on the palladium-silicon carbide reaction. Thermoscans of α-SiC pellets containing 5 at.%Pd show that during differential calorimetry scans three exothermic peaks occurred at 773 K, 1144 K and 1615 K, while thermoscans of β-SiC pellets containing 3 at.%Pd and 5 at.%Pd do not show peaks. For the pellet α-SiC-5 at.%Pd XRD spectra reveal that the first peak is associated with the formation of Pd3Si and SiO2 phases, while the second peak and the third peak are correlated with the formation of Pd2Si phase and the active oxidation of silicon carbide respectively. Thermogravimetry scans show weight gain and weight loss peaks due to the SiO2 phase formation and the active oxidation. Additionally XPS fittings reveal the development of SiCxOy phase during the first exothermic peak up to the temperature of 873 K. The experimental data reveals that alpha silicon carbide is attacked by palladium at lower temperatures than beta silicon carbide and the reaction mechanism between silicon carbide and palladium is strongly affected by silicon carbide oxidation.

  16. The Effect of Grain Size on the Radiation Response of Silicon Carbide and its Dependence on Irradiation Species and Temperature

    NASA Astrophysics Data System (ADS)

    Jamison, Laura

    In recent years the push for green energy sources has intensified, and as part of that effort accident tolerant and more efficient nuclear reactors have been designed. These reactors demand exceptional material performance, as they call for higher temperatures and doses. Silicon carbide (SiC) is a strong candidate material for many of these designs due to its low neutron cross-section, chemical stability, and high temperature resistance. The possibility of improving the radiation resistance of SiC by reducing the grain size (thus increasing the sink density) is explored in this work. In-situ electron irradiation and Kr ion irradiation was utilized to explore the radiation resistance of nanocrystalline SiC (nc-SiC), SiC nanopowders, and microcrystalline SiC. Electron irradiation simplifies the experimental results, as only isolated Frenkel pairs are produced so any observed differences are simply due to point defect interactions with the original microstructure. Kr ion irradiation simulates neutron damage, as large radiation cascades with a high concentration of point defects are produced. Kr irradiation studies found that radiation resistance decreased with particle size reduction and grain refinement (comparing nc-SiC and microcrystalline SiC). This suggests that an interface-dependent amorphization mechanism is active in SiC, suggested to be interstitial starvation. However, under electron irradiation it was found that nc-SiC had improved radiation resistance compared to single crystal SiC. This was found to be due to several factors including increased sink density and strength and the presence of stacking faults. The stacking faults were found to improve radiation response by lowering critical energy barriers. The change in radiation response between the electron and Kr ion irradiations is hypothesized to be due to either the change in ion type (potential change in amorphization mechanism) or a change in temperature (at the higher temperatures of the Kr ion

  17. Diamond-silicon carbide composite

    DOEpatents

    Qian, Jiang; Zhao, Yusheng

    2006-06-13

    Fully dense, diamond-silicon carbide composites are prepared from ball-milled microcrystalline diamond/amorphous silicon powder mixture. The ball-milled powder is sintered (P=5–8 GPa, T=1400K–2300K) to form composites having high fracture toughness. A composite made at 5 GPa/1673K had a measured fracture toughness of 12 MPa.dot.m1/2. By contrast, liquid infiltration of silicon into diamond powder at 5 GPa/1673K produces a composite with higher hardness but lower fracture toughness. X-ray diffraction patterns and Raman spectra indicate that amorphous silicon is partially transformed into nanocrystalline silicon at 5 GPa/873K, and nanocrystalline silicon carbide forms at higher temperatures.

  18. Porous silicon carbide (SIC) semiconductor device

    NASA Technical Reports Server (NTRS)

    Shor, Joseph S. (Inventor); Kurtz, Anthony D. (Inventor)

    1996-01-01

    Porous silicon carbide is fabricated according to techniques which result in a significant portion of nanocrystallites within the material in a sub 10 nanometer regime. There is described techniques for passivating porous silicon carbide which result in the fabrication of optoelectronic devices which exhibit brighter blue luminescence and exhibit improved qualities. Based on certain of the techniques described porous silicon carbide is used as a sacrificial layer for the patterning of silicon carbide. Porous silicon carbide is then removed from the bulk substrate by oxidation and other methods. The techniques described employ a two-step process which is used to pattern bulk silicon carbide where selected areas of the wafer are then made porous and then the porous layer is subsequently removed. The process to form porous silicon carbide exhibits dopant selectivity and a two-step etching procedure is implemented for silicon carbide multilayers.

  19. Anisotropic Tribological Properties of Silicon Carbide

    NASA Technical Reports Server (NTRS)

    Miyoshi, K.; Buckley, D. H.

    1980-01-01

    The anisotropic friction, deformation and fracture behavior of single crystal silicon carbide surfaces were investigated in two categories. The categories were called adhesive and abrasive wear processes, respectively. In the adhesive wear process, the adhesion, friction and wear of silicon carbide were markedly dependent on crystallographic orientation. The force to reestablish the shearing fracture of adhesive bond at the interface between silicon carbide and metal was the lowest in the preferred orientation of silicon carbide slip system. The fracturing of silicon carbide occurred near the adhesive bond to metal and it was due to primary cleavages of both prismatic (10(-1)0) and basal (0001) planes.

  20. Infrared Kerr measurements on ferromagnetic silicon and silicon carbide

    NASA Astrophysics Data System (ADS)

    Seo, Jungryeol; Mukherjee, Alok; Arik, Mumtaz Murat; Cerne, John; Liu, Yu; Zhou, Shengqiang; Böttger, Roman; Song, Bo; Wang, Gang

    We measure the infrared (100-1000 meV) Kerr angle in ferromagnetic silicon and silicon carbide. The samples were either neutron irradiated or aluminum doped to induce ferromagnetic behavior. The samples are studied in the 10-300K temperature range at magnetic fields up to 7T. We also explore the dependence of the magneto-optical signal on samples with different irradiation exposure levels. This study provides new information on the optical, magnetic, and electronic properties of these materials. Work supported by NSF-DMR1410599 and the Helmholtz Postdoctoral Program PD-146.

  1. Mechanical Properties of Nanoceramic Silicon Carbide

    NASA Astrophysics Data System (ADS)

    Ojo, Ipidapo; Abunaemeh, Malek; Smith, Cydale; Muntele, Claudiu; Ila, Daryush

    2009-03-01

    Generation IV nuclear reactors will use the TRISO fuels, a type of micro fuel particle. It consists of a fuel kernel coated with four layers of isotropic material. One of the materials considered for these layers is silicon carbide ceramic. This lightweight material can maintain chemical and dimensional stability in adverse environments at very high temperatures up to 3000 C, and it is chemically inert. It is widely used as a semiconductor material in electronics because of its high thermo conductivity, high electric field break down strength, and high maximum current density, which makes it more desirable than silicon. Silicon carbide has a very low coefficient of thermal expansion and has no phase transition that would discontinue its thermal expansion. At the Center for Irradiation of Materials (C.I.M.) we are developing a new fabrication process for nanopowdered silicon carbide for TRISO fuel coating purposes. We also study the mechanical properties of the material produced. Among the different test being performed are particle induced X-ray emission (PIXE) an Rutherford backscattering spectroscopy (RBS). The mechanical properties of interest are hardness (measured by Vickers Hardness machine), toughness (measured by the Anstis equation, KIC= 1.6 x 10-2(E/H)^1/2(P/C0^3/2, where P=load, C0=crack length, E=Young's modulus and H=Vickers Hardness), tensile strength and flexural strength (measured by a three point bend test). Results will be presented during the meeting.

  2. Ultrasonic characterization of microwave joined silicon carbide/silicon carbide

    SciTech Connect

    House, M.B.; Day, P.S.

    1997-05-01

    High frequency (50--150 MHz), ultrasonic immersion testing has been used to characterize the surface and interfacial joint conditions of microwave bonded, monolithic silicon carbide (SiC) materials. The high resolution ultrasonic C-scan images point to damage accumulation after thermal cycling. Image processing was used to study the effects of the thermal cycling on waveform shape, amplitude and distribution. Such information is useful for concurrently engineering material fabrication processes and suitable nondestructive test procedures.

  3. Silicon carbide semiconductor technology for high temperature and radiation environments

    NASA Technical Reports Server (NTRS)

    Matus, Lawrence G.

    1993-01-01

    Viewgraphs on silicon carbide semiconductor technology and its potential for enabling electronic devices to function in high temperature and high radiation environments are presented. Topics covered include silicon carbide; sublimation growth of 6H-SiC boules; SiC chemical vapor deposition reaction system; 6H silicon carbide p-n junction diode; silicon carbide MOSFET; and silicon carbide JFET radiation response.

  4. Methods for producing silicon carbide fibers

    DOEpatents

    Garnier, John E.; Griffith, George W.

    2016-03-01

    Methods of producing silicon carbide fibers. The method comprises reacting a continuous carbon fiber material and a silicon-containing gas in a reaction chamber at a temperature ranging from approximately 1500.degree. C. to approximately 2000.degree. C. A partial pressure of oxygen in the reaction chamber is maintained at less than approximately 1.01.times.10.sup.2 Pascal to produce continuous alpha silicon carbide fibers. Continuous alpha silicon carbide fibers and articles formed from the continuous alpha silicon carbide fibers are also disclosed.

  5. Silicon carbide fibers and articles including same

    DOEpatents

    Garnier, John E; Griffith, George W

    2015-01-27

    Methods of producing silicon carbide fibers. The method comprises reacting a continuous carbon fiber material and a silicon-containing gas in a reaction chamber at a temperature ranging from approximately 1500.degree. C. to approximately 2000.degree. C. A partial pressure of oxygen in the reaction chamber is maintained at less than approximately 1.01.times.10.sup.2 Pascal to produce continuous alpha silicon carbide fibers. Continuous alpha silicon carbide fibers and articles formed from the continuous alpha silicon carbide fibers are also disclosed.

  6. Effects of neutron irradiation on mechanical properties of silicon carbide composites fabricated by nano-infiltration and transient eutectic-phase process

    NASA Astrophysics Data System (ADS)

    Koyanagi, Takaaki; Ozawa, Kazumi; Hinoki, Tatsuya; Shimoda, Kazuya; Katoh, Yutai

    2014-05-01

    Unidirectional silicon carbide (SiC)-fiber-reinforced SiC matrix (SiC/SiC) composites fabricated by a nano-infiltration and transient eutectic-phase (NITE) process were irradiated with neutrons at 600 °C to 0.52 dpa, at 830 °C to 5.9 dpa, and at 1270 °C to 5.8 dpa. The in-plane and trans-thickness tensile and the inter-laminar shear properties were evaluated at ambient temperature. The mechanical characteristics, including the quasi-ductile behavior, the proportional limit stress, and the ultimate tensile strength, were retained subsequent to irradiation. Analysis of the stress-strain hysteresis loop indicated the increased fiber/matrix interface friction and the decreased residual stresses. The inter-laminar shear strength exhibited a significant decrease following irradiation.

  7. Comparison Measurements of Silicon Carbide Temperature Monitors

    SciTech Connect

    J. L. Rempe; K. G. Condie; D. L. Knudson; L. L. Snead

    2010-06-01

    As part of the efforts initiated through the Advanced Test Reactor (ATR) National Scientific User Facility (NSUF) program to make Silicon Carbide (SiC) temperature monitors available, a capability was developed at the Idaho National Laboratory (INL) to complete post-irradiation evaluations of these monitors. INL selected the resistance measurement approach for detecting peak irradiation temperature from SiC temperature monitors. To demonstrate this new capability, comparison measurements were completed by INL and Oak Ridge National Laboratory (ORNL) on identical samples subjected to identical irradiation conditions. Results reported in this paper indicate that the resistance measurement approach can yield similar peak irradiation temperatures if appropriate equipment is used and appropriate procedures are followed.

  8. Method for producing silicon nitride/silicon carbide composite

    DOEpatents

    Dunmead, Stephen D.; Weimer, Alan W.; Carroll, Daniel F.; Eisman, Glenn A.; Cochran, Gene A.; Susnitzky, David W.; Beaman, Donald R.; Nilsen, Kevin J.

    1996-07-23

    Silicon carbide/silicon nitride composites are prepared by carbothermal reduction of crystalline silica powder, carbon powder and optionally crsytalline silicon nitride powder. The crystalline silicon carbide portion of the composite has a mean number diameter less than about 700 nanometers and contains nitrogen.

  9. Polytype distribution in circumstellar silicon carbide.

    SciTech Connect

    Daulton, T. L.; Bernatowicz, T. J.; Lewis, R. S.; Messenger, S.; Stadermann, F. J.; Amari, S.; Materials Science Division; Naval Research Lab.; Washington Univ.; Univ. of Chicago

    2002-06-07

    The inferred crystallographic class of circumstellar silicon carbide based on astronomical infrared spectra is controversial. We have directly determined the polytype distribution of circumstellar SiC from transmission electron microscopy of presolar silicon carbide from the Murchison carbonaceous meteorite. Only two polytypes (of a possible several hundred) were observed: cubic 3C and hexagonal 2H silicon carbide and their intergrowths. We conclude that this structural simplicity is a direct consequence of the low pressures in circumstellar outflows and the corresponding low silicon carbide condensation temperatures.

  10. Polytype distribution in circumstellar silicon carbide.

    PubMed

    Daulton, T L; Bernatowicz, T J; Lewis, R S; Messenger, S; Stadermann, F J; Amari, S

    2002-06-01

    The inferred crystallographic class of circumstellar silicon carbide based on astronomical infrared spectra is controversial. We have directly determined the polytype distribution of circumstellar SiC from transmission electron microscopy of presolar silicon carbide from the Murchison carbonaceous meteorite. Only two polytypes (of a possible several hundred) were observed: cubic 3C and hexagonal 2H silicon carbide and their intergrowths. We conclude that this structural simplicity is a direct consequence of the low pressures in circumstellar outflows and the corresponding low silicon carbide condensation temperatures. PMID:12052956

  11. Pulsed energy synthesis and doping of silicon carbide

    DOEpatents

    Truher, J.B.; Kaschmitter, J.L.; Thompson, J.B.; Sigmon, T.W.

    1995-06-20

    A method for producing beta silicon carbide thin films by co-depositing thin films of amorphous silicon and carbon onto a substrate is disclosed, whereafter the films are irradiated by exposure to a pulsed energy source (e.g. excimer laser) to cause formation of the beta-SiC compound. Doped beta-SiC may be produced by introducing dopant gases during irradiation. Single layers up to a thickness of 0.5-1 micron have been produced, with thicker layers being produced by multiple processing steps. Since the electron transport properties of beta silicon carbide over a wide temperature range of 27--730 C is better than these properties of alpha silicon carbide, they have wide application, such as in high temperature semiconductors, including HETEROJUNCTION-junction bipolar transistors and power devices, as well as in high bandgap solar arrays, ultra-hard coatings, light emitting diodes, sensors, etc.

  12. Pulsed energy synthesis and doping of silicon carbide

    DOEpatents

    Truher, Joel B.; Kaschmitter, James L.; Thompson, Jesse B.; Sigmon, Thomas W.

    1995-01-01

    A method for producing beta silicon carbide thin films by co-depositing thin films of amorphous silicon and carbon onto a substrate, whereafter the films are irradiated by exposure to a pulsed energy source (e.g. excimer laser) to cause formation of the beta-SiC compound. Doped beta-SiC may be produced by introducing dopant gases during irradiation. Single layers up to a thickness of 0.5-1 micron have been produced, with thicker layers being produced by multiple processing steps. Since the electron transport properties of beta silicon carbide over a wide temperature range of 27.degree.-730.degree. C. is better than these properties of alpha silicon carbide, they have wide application, such as in high temperature semiconductors, including hetero-junction bipolar transistors and power devices, as well as in high bandgap solar arrays, ultra-hard coatings, light emitting diodes, sensors, etc.

  13. Silicon Carbide Nanotube Synthesized

    NASA Technical Reports Server (NTRS)

    Lienhard, Michael A.; Larkin, David J.

    2003-01-01

    Carbon nanotubes (CNTs) have generated a great deal of scientific and commercial interest because of the countless envisioned applications that stem from their extraordinary materials properties. Included among these properties are high mechanical strength (tensile and modulus), high thermal conductivity, and electrical properties that make different forms of single-walled CNTs either conducting or semiconducting, and therefore, suitable for making ultraminiature, high-performance CNT-based electronics, sensors, and actuators. Among the limitations for CNTs is their inability to survive in high-temperature, harsh-environment applications. Silicon carbon nanotubes (SiCNTs) are being developed for their superior material properties under such conditions. For example, SiC is stable in regards to oxidation in air to temperatures exceeding 1000 C, whereas carbon-based materials are limited to 600 C. The high-temperature stability of SiCNTs is envisioned to enable high-temperature, harsh-environment nanofiber- and nanotube-reinforced ceramics. In addition, single-crystal SiC-based semiconductors are being developed for hightemperature, high-power electronics, and by analogy to CNTs with silicon semiconductors, SiCNTs with single-crystal SiC-based semiconductors may allow high-temperature harsh-environment nanoelectronics, nanosensors, and nanoactuators to be realized. Another challenge in CNT development is the difficulty of chemically modifying the tube walls, which are composed of chemically stable graphene sheets. The chemical substitution of the CNTs walls will be necessary for nanotube self-assembly and biological- and chemical-sensing applications. SiCNTs are expected to have a different multiple-bilayer wall structure, allowing the surface Si atoms to be functionalized readily with molecules that will allow SiCNTs to undergo self-assembly and be compatible with a variety of materials (for biotechnology applications and high-performance fiber-reinforced ceramics).

  14. Process for making silicon carbide reinforced silicon carbide composite

    NASA Technical Reports Server (NTRS)

    Lau, Sai-Kwing (Inventor); Calandra, Salavatore J. (Inventor); Ohnsorg, Roger W. (Inventor)

    1998-01-01

    A process comprising the steps of: a) providing a fiber preform comprising a non-oxide ceramic fiber with at least one coating, the coating comprising a coating element selected from the group consisting of carbon, nitrogen, aluminum and titanium, and the fiber having a degradation temperature of between 1400.degree. C. and 1450.degree. C., b) impregnating the preform with a slurry comprising silicon carbide particles and between 0.1 wt % and 3 wt % added carbon c) providing a cover mix comprising: i) an alloy comprising a metallic infiltrant and the coating element, and ii) a resin, d) placing the cover mix on at least a portion of the surface of the porous silicon carbide body, e) heating the cover mix to a temperature between 1410.degree. C. and 1450.degree. C. to melt the alloy, and f) infiltrating the fiber preform with the melted alloy for a time period of between 15 minutes and 240 minutes, to produce a ceramic fiber reinforced ceramic composite.

  15. Damage kinetics in silicon carbide

    NASA Astrophysics Data System (ADS)

    Pickup, I. M.; Barker, A. K.

    1998-07-01

    Three silicon carbides of similar density and grain size but manufactured via different routes (reaction bonded, pressureless sintered and pressure assisted densification) have been investigated. High speed photography in conjunction with Hopkinson pressure bar compression tests has revealed that not only does the manufacturing route confer a significant difference in failure kinetics but also modifies the phenomenology of failure. Plate impact experiments using lateral and longitudinal manganin stress gauges have been used to study shear strength behaviour of damaged material. Failure waves have been observed in all three materials and characteristically different damaged material shear strength relationships with pressure have been observed.

  16. Preparation of silicon carbide fibers

    DOEpatents

    Wei, G.C.

    1983-10-12

    Silicon carbide fibers suitable for use in the fabrication of dense, high-strength, high-toughness SiC composites or as thermal insulating materials in oxidizing environments are fabricated by a new, simplified method wherein a mixture of short-length rayon fibers and colloidal silica is homogenized in a water slurry. Water is removed from the mixture by drying in air at 120/sup 0/C and the fibers are carbonized by (pyrolysis) heating the mixture to 800 to 1000/sup 0/C in argon. The mixture is subsequently reacted at 1550 to 1900/sup 0/C in argon to yield pure ..beta..-SiC fibers.

  17. Nitride-bonded silicon carbide composite filter

    SciTech Connect

    Thomson, B.N.; DiPietro, S.G.

    1995-12-01

    The objective of this program is to develop and demonstrate an advanced hot gas filter, using ceramic component technology, with enhanced durability to provide increased resistance to thermal fatigue and crack propagation. The material is silicon carbide fiber reinforced nitride bonded silicon carbide.

  18. Material properties of silicon and silicon carbide foams

    NASA Astrophysics Data System (ADS)

    Jacoby, Marc T.; Goodman, William A.

    2005-08-01

    Silicon and silicon carbide foams provide the lightweighting element for Schafer Corporation's silicon and silicon carbide lightweight mirror systems (SLMSTM and SiC-SLMSTM). SLMSTM and SiC-SLMSTM provide the enabling technology for manufacturing lightweight, athermal optical sub-assemblies and instruments. Silicon and silicon carbide foam samples were manufactured and tested under a Schafer-funded Internal Research and Development program in various configurations to obtain mechanical and thermal property data. The results of the mechanical tests that are reported in this paper include Young's modulus, compression strength, tensile strength, Poisson's ratio and vibrational damping. The results of the thermal tests include thermal conductivity and coefficient of thermal expansion.

  19. Colloidal characterization of ultrafine silicon carbide and silicon nitride powders

    NASA Technical Reports Server (NTRS)

    Whitman, Pamela K.; Feke, Donald L.

    1986-01-01

    The effects of various powder treatment strategies on the colloid chemistry of aqueous dispersions of silicon carbide and silicon nitride are examined using a surface titration methodology. Pretreatments are used to differentiate between the true surface chemistry of the powders and artifacts resulting from exposure history. Silicon nitride powders require more extensive pretreatment to reveal consistent surface chemistry than do silicon carbide powders. As measured by titration, the degree of proton adsorption from the suspending fluid by pretreated silicon nitride and silicon carbide powders can both be made similar to that of silica.

  20. Anisotropic tribological properties of silicon carbide

    NASA Technical Reports Server (NTRS)

    Miyoshi, K.; Buckley, D. H.

    1981-01-01

    The effects of crystallographic orientation on the tribological properties of single-crystal silicon carbide surfaces in contact with various solids are investigated for adhesive and abrasive wear processes. In the adhesive wear process, the adhesion and wear of silicon carbide is found to be markedly dependent on crystallographic orientation. The force resisting shearing fracture of the adhesive bonds at the interface is lower in preferred crystallographic direction of slip. In the abrasive wear process, the 1 0 -1 0 direction on the basal plane of silicon carbide exhibits the lowest coefficient of friction and the greatest resistance to abrasion.

  1. Converted silicon carbide technology developments for optics

    NASA Astrophysics Data System (ADS)

    Duston, Christopher; Woestman, Ken; Vargas, Hugo; deBlonk, Brett

    2007-09-01

    Silicon carbide structures fabricated by converting near-net-shape graphite preforms via Chemical Vapor Conversion (CVC) phase reaction have long provided improved performance components for electronics processing. In recent years, this same technology has been applied to the fabrication of simple and lightweighted mirrors and is moving into optical bench applications. To support the expanded applications, Poco has further evaluated the material properties of SUPERSiC® silicon carbide, developed technologies to mount silicon carbide mirrors on benches of similar and dissimilar materials, and fabricated complex monolithic geometries using in situ conversion bonding of mating graphite components. Overviews of each of these areas will be presented.

  2. Manufacture of silicon carbide using solar energy

    DOEpatents

    Glatzmaier, Gregory C.

    1992-01-01

    A method is described for producing silicon carbide particles using solar energy. The method is efficient and avoids the need for use of electrical energy to heat the reactants. Finely divided silica and carbon are admixed and placed in a solar-heated reaction chamber for a time sufficient to cause a reaction between the ingredients to form silicon carbide of very small particle size. No grinding of silicon carbide is required to obtain small particles. The method may be carried out as a batch process or as a continuous process.

  3. Improved consolidation of silicon carbide

    NASA Technical Reports Server (NTRS)

    Freedman, M. R.; Millard, M. L.

    1986-01-01

    Alpha silicon carbide powder was consolidated by both dry and wet methods. Dry pressing in a double acting steel die yielded sintered test bars with an average flexural strength of 235.6 MPa with a critical flaw size of approximately 100 micro m. An aqueous slurry pressing technique produced sintered test bars with an average flexural strength of 440.8 MPa with a critical flaw size of approximately 25 micro m. Image analysis revealed a reduction in both pore area and pore size distribution in the slurry pressed sintered test bars. The improvements in the slurry pressed material properties are discussed in terms of reduced agglomeration and improved particle packing during consolidation.

  4. Silicon carbide material sintered bodies manufacturing

    NASA Technical Reports Server (NTRS)

    Suzuki, K.; Shinohara, N.

    1984-01-01

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

  5. Silicon Carbide Transistor For Detecting Hydrocarbon Gases

    NASA Technical Reports Server (NTRS)

    Shields, Virgil B.; Ryan, Margaret A.; Williams, Roger M.

    1996-01-01

    Proposed silicon carbide variable-potential insulated-gate field-effect transistor specially designed for use in measuring concentrations of hydrocarbon gases. Devices like this prove useful numerous automotive, industrial, aeronautical, and environmental monitoring applications.

  6. Whatever happened to silicon carbide. [semiconductor devices

    NASA Technical Reports Server (NTRS)

    Campbell, R. B.

    1981-01-01

    The progress made in silicon carbide semiconductor devices in the 1955 to 1975 time frame is examined and reasons are given for the present lack of interest in the material. Its physical and chemical properties and methods of preparation are discussed. Fabrication techniques and the characteristics of silicon carbide devices are reviewed. It is concluded that a combination of economic factors and the lack of progress in fabrication techniques leaves no viable market for SiC devices in the near future.

  7. Silicon carbide mirrors for high power applications

    SciTech Connect

    Takacs, P. Z.

    1981-11-01

    The advent of synchrotron radiation (SR) sources and high energy lasers (HEL) in recent years has brought about the need for optical materials that can withstand the harsh operating conditions in such devices. SR mirrors must be ultra-high vacuum compatible, must withstand intense x-ray irradiation without surface damage, must maintain surface figure under thermal loading and must be capable of being polished to an extremely smooth surface finish. Chemical vapor deposited (CVD) silicon carbide in combination with sintered substrate material meets these requirements and offers additional benefits as well. It is an extremely hard material and offers the possibility of being cleaned and recoated many times without degradation of the surface finish, thereby prolonging the lifetime of expensive optical components. It is an extremely strong material and offers the possibility of weight reduction over conventional mirror materials.

  8. Stabilization of boron carbide via silicon doping

    NASA Astrophysics Data System (ADS)

    Proctor, J. E.; Bhakhri, V.; Hao, R.; Prior, T. J.; Scheler, T.; Gregoryanz, E.; Chhowalla, M.; Giulani, F.

    2015-01-01

    Boron carbide is one of the lightest and hardest ceramics, but its applications are limited by its poor stability against a partial phase separation into separate boron and carbon. Phase separation is observed under high non-hydrostatic stress (both static and dynamic), resulting in amorphization. The phase separation is thought to occur in just one of the many naturally occurring polytypes in the material, and this raises the possibility of doping the boron carbide to eliminate this polytype. In this work, we have synthesized boron carbide doped with silicon. We have conducted a series of characterizations (transmission electron microscopy, scanning electron microscopy, Raman spectroscopy and x-ray diffraction) on pure and silicon-doped boron carbide following static compression to 50 GPa non-hydrostatic pressure. We find that the level of amorphization under static non-hydrostatic pressure is drastically reduced by the silicon doping.

  9. Silicon Carbide Solar Cells Investigated

    NASA Technical Reports Server (NTRS)

    Bailey, Sheila G.; Raffaelle, Ryne P.

    2001-01-01

    The semiconductor silicon carbide (SiC) has long been known for its outstanding resistance to harsh environments (e.g., thermal stability, radiation resistance, and dielectric strength). However, the ability to produce device-quality material is severely limited by the inherent crystalline defects associated with this material and their associated electronic effects. Much progress has been made recently in the understanding and control of these defects and in the improved processing of this material. Because of this work, it may be possible to produce SiC-based solar cells for environments with high temperatures, light intensities, and radiation, such as those experienced by solar probes. Electronics and sensors based on SiC can operate in hostile environments where conventional silicon-based electronics (limited to 350 C) cannot function. Development of this material will enable large performance enhancements and size reductions for a wide variety of systems--such as high-frequency devices, high-power devices, microwave switching devices, and high-temperature electronics. These applications would supply more energy-efficient public electric power distribution and electric vehicles, more powerful microwave electronics for radar and communications, and better sensors and controls for cleaner-burning, more fuel-efficient jet aircraft and automobile engines. The 6H-SiC polytype is a promising wide-bandgap (Eg = 3.0 eV) semiconductor for photovoltaic applications in harsh solar environments that involve high-temperature and high-radiation conditions. The advantages of this material for this application lie in its extremely large breakdown field strength, high thermal conductivity, good electron saturation drift velocity, and stable electrical performance at temperatures as high as 600 C. This behavior makes it an attractive photovoltaic solar cell material for devices that can operate within three solar radii of the Sun.

  10. Direct plasmadynamic synthesis of ultradisperse silicon carbide

    NASA Astrophysics Data System (ADS)

    Sivkov, A. A.; Nikitin, D. S.; Pak, A. Ya.; Rakhmatullin, I. A.

    2013-01-01

    Ultradisperse cubic silicon carbide (β-SiC) has been obtained by direct plasmadynamic synthesis in pulsed supersonic carbon-silicon plasma jet incident on a copper obstacle in argon atmosphere. The powdered product has a high content of β-SiC in the form of single crystals with average size of about 100 nm and nearly perfect crystallographic habit.

  11. Diamond-silicon carbide composite and method

    DOEpatents

    Zhao, Yusheng

    2011-06-14

    Uniformly dense, diamond-silicon carbide composites having high hardness, high fracture toughness, and high thermal stability are prepared by consolidating a powder mixture of diamond and amorphous silicon. A composite made at 5 GPa/1673K had a measured fracture toughness of 12 MPam.sup.1/2. By contrast, liquid infiltration of silicon into diamond powder at 5 GPa/1673K produces a composite with higher hardness but lower fracture toughness.

  12. Silicon carbide sintered body manufactured from silicon carbide powder containing boron, silicon and carbonaceous additive

    NASA Technical Reports Server (NTRS)

    Tanaka, Hidehiko

    1987-01-01

    A silicon carbide powder of a 5-micron grain size is mixed with 0.15 to 0.60 wt% mixture of a boron compound, i.e., boric acid, boron carbide (B4C), silicon boride (SiB4 or SiB6), aluminum boride, etc., and an aluminum compound, i.e., aluminum, aluminum oxide, aluminum hydroxide, aluminum carbide, etc., or aluminum boride (AlB2) alone, in such a proportion that the boron/aluminum atomic ratio in the sintered body becomes 0.05 to 0.25 wt% and 0.05 to 0.40 wt%, respectively, together with a carbonaceous additive to supply enough carbon to convert oxygen accompanying raw materials and additives into carbon monoxide.

  13. Method of fabricating porous silicon carbide (SiC)

    NASA Technical Reports Server (NTRS)

    Shor, Joseph S. (Inventor); Kurtz, Anthony D. (Inventor)

    1995-01-01

    Porous silicon carbide is fabricated according to techniques which result in a significant portion of nanocrystallites within the material in a sub 10 nanometer regime. There is described techniques for passivating porous silicon carbide which result in the fabrication of optoelectronic devices which exhibit brighter blue luminescence and exhibit improved qualities. Based on certain of the techniques described porous silicon carbide is used as a sacrificial layer for the patterning of silicon carbide. Porous silicon carbide is then removed from the bulk substrate by oxidation and other methods. The techniques described employ a two-step process which is used to pattern bulk silicon carbide where selected areas of the wafer are then made porous and then the porous layer is subsequently removed. The process to form porous silicon carbide exhibits dopant selectivity and a two-step etching procedure is implemented for silicon carbide multilayers.

  14. Joining of silicon carbide composites for fusion energy applications

    NASA Astrophysics Data System (ADS)

    Lewinsohn, C. A.; Singh, M.; Shibayama, T.; Hinoki, T.; Ando, M.; Katoh, Y.; Kohyama, A.

    2000-12-01

    Joining of silicon carbide based materials has been recognized as one of the enabling technologies for the successful utilization of ceramic components in fusion energy systems. Sintered silicon carbide (Hexoloy SA) and silicon carbide (Hi-Nicalon™) fiber reinforced silicon carbide matrix composites have been joined using reaction forming/bonding based joining technologies. The room- and high-temperature mechanical properties and fractography of ceramic joints have been reported.

  15. Deposition method for producing silicon carbide high-temperature semiconductors

    DOEpatents

    Hsu, George C.; Rohatgi, Naresh K.

    1987-01-01

    An improved deposition method for producing silicon carbide high-temperature semiconductor material comprising placing a semiconductor substrate composed of silicon carbide in a fluidized bed silicon carbide deposition reactor, fluidizing the bed particles by hydrogen gas in a mildly bubbling mode through a gas distributor and heating the substrate at temperatures around 1200.degree.-1500.degree. C. thereby depositing a layer of silicon carbide on the semiconductor substrate.

  16. Silicon carbide, an emerging high temperature semiconductor

    NASA Technical Reports Server (NTRS)

    Matus, Lawrence G.; Powell, J. Anthony

    1991-01-01

    In recent years, the aerospace propulsion and space power communities have expressed a growing need for electronic devices that are capable of sustained high temperature operation. Applications for high temperature electronic devices include development instrumentation within engines, engine control, and condition monitoring systems, and power conditioning and control systems for space platforms and satellites. Other earth-based applications include deep-well drilling instrumentation, nuclear reactor instrumentation and control, and automotive sensors. To meet the needs of these applications, the High Temperature Electronics Program at the Lewis Research Center is developing silicon carbide (SiC) as a high temperature semiconductor material. Research is focussed on developing the crystal growth, characterization, and device fabrication technologies necessary to produce a family of silicon carbide electronic devices and integrated sensors. The progress made in developing silicon carbide is presented, and the challenges that lie ahead are discussed.

  17. Joining of porous silicon carbide bodies

    DOEpatents

    Bates, Carl H.; Couhig, John T.; Pelletier, Paul J.

    1990-05-01

    A method of joining two porous bodies of silicon carbide is disclosed. It entails utilizing an aqueous slip of a similar silicon carbide as was used to form the porous bodies, including the sintering aids, and a binder to initially join the porous bodies together. Then the composite structure is subjected to cold isostatic pressing to form a joint having good handling strength. Then the composite structure is subjected to pressureless sintering to form the final strong bond. Optionally, after the sintering the structure is subjected to hot isostatic pressing to further improve the joint and densify the structure. The result is a composite structure in which the joint is almost indistinguishable from the silicon carbide pieces which it joins.

  18. Varying potential silicon carbide gas sensor

    NASA Technical Reports Server (NTRS)

    Shields, Virgil B. (Inventor); Ryan, Margaret A. (Inventor); Williams, Roger M. (Inventor)

    1997-01-01

    A hydrocarbon gas detection device operates by dissociating or electro-chemically oxidizing hydrocarbons adsorbed to a silicon carbide detection layer. Dissociation or oxidation are driven by a varying potential applied to the detection layer. Different hydrocarbon species undergo reaction at different applied potentials so that the device is able to discriminate among various hydrocarbon species. The device can operate at temperatures between 100.degree. C. and at least 650.degree. C., allowing hydrocarbon detection in hot exhaust gases. The dissociation reaction is detected either as a change in a capacitor or, preferably, as a change of current flow through an FET which incorporates the silicon carbide detection layers. The silicon carbide detection layer can be augmented with a pad of catalytic material which provides a signal without an applied potential. Comparisons between the catalytically produced signal and the varying potential produced signal may further help identify the hydrocarbon present.

  19. Silicon carbide, an emerging high temperature semiconductor

    NASA Astrophysics Data System (ADS)

    Matus, Lawrence G.; Powell, J. Anthony

    In recent years, the aerospace propulsion and space power communities have expressed a growing need for electronic devices that are capable of sustained high temperature operation. Applications for high temperature electronic devices include development instrumentation within engines, engine control, and condition monitoring systems, and power conditioning and control systems for space platforms and satellites. Other earth-based applications include deep-well drilling instrumentation, nuclear reactor instrumentation and control, and automotive sensors. To meet the needs of these applications, the High Temperature Electronics Program at the Lewis Research Center is developing silicon carbide (SiC) as a high temperature semiconductor material. Research is focussed on developing the crystal growth, characterization, and device fabrication technologies necessary to produce a family of silicon carbide electronic devices and integrated sensors. The progress made in developing silicon carbide is presented, and the challenges that lie ahead are discussed.

  20. Liquid phase sintering of silicon carbide

    DOEpatents

    Cutler, R.A.; Virkar, A.V.; Hurford, A.C.

    1989-05-09

    Liquid phase sintering is used to densify silicon carbide based ceramics using a compound comprising a rare earth oxide and aluminum oxide to form liquids at temperatures in excess of 1,600 C. The resulting sintered ceramic body has a density greater than 95% of its theoretical density and hardness in excess of 23 GPa. Boron and carbon are not needed to promote densification and silicon carbide powder with an average particle size of greater than one micron can be densified via the liquid phase process. The sintered ceramic bodies made by the present invention are fine grained and have secondary phases resulting from the liquid phase. 4 figs.

  1. On the sintering of silicon carbide

    NASA Technical Reports Server (NTRS)

    Gugel, E.

    1986-01-01

    This document deals with the sintering of silicon carbide using pressureless sintering. This technique makes it possible to sinter a primarily covalent material to usable densities up to over 98% thD without having to use a high amount of sinter additives as is the case with other non-oxide ceramic materials. The process takes place rapidly, and it is also possible to produce relatively thick-walled structural parts without major problems. This sheds more light on the true characteristics of silicon carbide in one structural part, since there is no second or nearly no second phase. Heat pressing has improved stability.

  2. Liquid phase sintering of silicon carbide

    DOEpatents

    Cutler, Raymond A.; Virkar, Anil V.; Hurford, Andrew C.

    1989-01-01

    Liquid phase sintering is used to densify silicon carbide based ceramics using a compound comprising a rare earth oxide and aluminum oxide to form liquids at temperatures in excess of 1600.degree. C. The resulting sintered ceramic body has a density greater than 95% of its theoretical density and hardness in excess of 23 GPa. Boron and carbon are not needed to promote densification and silicon carbide powder with an average particle size of greater than one micron can be densified via the liquid phase process. The sintered ceramic bodies made by the present invention are fine grained and have secondary phases resulting from the liquid phase.

  3. Tough silicon nitride matrix composites using Textron silicon carbide monofilaments

    SciTech Connect

    Foulds, W.; Lecostaouec, J.F.; Landry, C.; Dipietro, S.; Vasilos, T.

    1989-10-01

    The use of Textron SCS silicon carbide monofilament fibers as a reinforcement for silicon nitride is described. Samples were processed by both chemical vapor infiltration and hot pressing. Mechanical tests were performed in flexure, tension, and in shear. A ballistic test demonstrated high velocity impact toughness. 5 refs.

  4. Design considerations and experimental analysis for silicon carbide power rectifiers

    NASA Astrophysics Data System (ADS)

    Khemka, V.; Patel, R.; Chow, T. P.; Gutmann, R. J.

    1999-10-01

    In this paper we present the investigation of properties of silicon carbide power rectifiers, in particular Schottky, PiN and advanced hybrid power rectifiers such as the trench MOS barrier Schottky rectifier. Analysis of the forward, reverse and switching experimental characteristics are presented and these silicon carbide rectifiers are compared to silicon devices. Silicon carbide Schottky rectifiers are attractive for applications requiring blocking voltage in excess of 100 V as the use of Si is precluded by its large specific on-resistance. Analysis of power dissipation indicates that silicon carbide Schottky rectifiers offer significant improvement over silicon counterparts. Silicon carbide junction rectifiers, on the other hand, are superior to silicon counterparts only for blocking voltage greater than 2000 V. Performance of acceptor (boron) and donor (phosphorus) implanted experimental silicon carbide junction rectifiers are presented and compared. Some of the recent developments in silicon carbide rectifiers have been described and compared with theory and our experimental results. The well established silicon rectifiers theory are often inadequate to describe the characteristics of the experimental silicon carbide junction rectifiers and appropriate generalization of these theories are presented. Experimental trench MOS barrier Schottky rectifiers (TMBS) have demonstrated significant improvement in leakage current compared to planar Schottky devices. Performance of current state-of-the-art silicon carbide rectifiers are far from theoretical predictions. Availability of high-quality silicon carbide crystals is crucial to successful realization of these performance projections.

  5. Tribological properties of sintered polycrystalline and single crystal silicon carbide

    NASA Technical Reports Server (NTRS)

    Miyoshi, K.; Buckley, D. H.; Srinivasan, M.

    1982-01-01

    Tribological studies and X-ray photoelectron spectroscopy analyses were conducted with sintered polycrystalline and single crystal silicon carbide surfaces in sliding contact with iron at various temperatures to 1500 C in a vacuum of 30 nPa. The results indicate that there is a significant temperature influence on both the friction properties and the surface chemistry of silicon carbide. The main contaminants on the as received sintered polycrystalline silicon carbide surfaces are adsorbed carbon, oxygen, graphite, and silicon dioxide. The surface revealed a low coefficient of friction. This is due to the presence of the graphite on the surface. At temperatures of 400 to 600 C graphite and copious amount of silicon dioxide were observed on the polycrystalline silicon carbide surface in addition to silicon carbide. At 800 C, the amount of the silicon dioxide decreased rapidly and the silicon carbide type silicon and carbon peaks were at a maximum intensity in the XPS spectra. The coefficients of friction were high in the temperature range 400 to 800 C. Small amounts of carbon and oxygen contaminants were observed on the as received single crystal silicon carbide surface below 250 C. Silicon carbide type silicon and carbon peaks were seen on the silicon carbide in addition to very small amount of graphite and silicon dioxide at temperatures of 450 to 800 C.

  6. Ceramic Fabric Coated With Silicon Carbide

    NASA Technical Reports Server (NTRS)

    Riccitiello, S. R.; Smith, M.; Goldstein, H.; Zimmerman, N.

    1988-01-01

    Material used as high-temperature shell. Ceramic fabric coated with silicon carbide (SiC) serves as tough, heat-resistant covering for other refractory materials. Developed to protect reusable insulating tiles on advanced space transportation systems. New covering makes protective glaze unnecessary. Used on furnace bricks or on insulation for engines.

  7. PWR cores with silicon carbide cladding

    SciTech Connect

    Dobisesky, J. P.; Carpenter, D.; Pilat, E.; Kazimi, M. S.

    2012-07-01

    The feasibility of using silicon carbide rather than Zircaloy cladding, to reach higher power levels and higher discharge burnups in PWRs has been evaluated. A preliminary fuel design using fuel rods with the same dimensions as in the Westinghouse Robust Fuel Assembly but with fuel pellets having 10 vol% central void has been adopted to mitigate the higher fuel temperatures that occur due to the lower thermal conductivity of the silicon carbide and to the persistence of the open clad-pellet gap over most of the fuel life. With this modified fuel design, it is possible to achieve 18 month cycles that meet present-day operating constraints on peaking factor, boron concentration, reactivity coefficients and shutdown margin, while allowing batch average discharge burnups up to 80 MWD/kgU and peak rod burnups up to 100 MWD/kgU. Power uprates of 10% and possibly 20% also appear feasible. For non-uprated cores, the silicon carbide-clad fuel has a clear advantage that increases with increasing discharge burnup. Even for comparable discharge burnups, there is a savings in enriched uranium. Control rod configuration modifications may be required to meet the shutdown margin criterion for the 20% up-rate. Silicon carbide's ability to sustain higher burnups than Zircaloy also allows the design of a licensable two year cycle with only 96 fresh assemblies, avoiding the enriched uranium penalty incurred with use of larger batch sizes due to their excessive leakage. (authors)

  8. High Q silicon carbide microdisk resonator

    SciTech Connect

    Lu, Xiyuan; Lee, Jonathan Y.; Feng, Philip X.-L.; Lin, Qiang

    2014-05-05

    We demonstrate a silicon carbide (SiC) microdisk resonator with optical Q up to 5.12 × 10{sup 4}. The high optical quality, together with the diversity of whispering-gallery modes and the tunability of external coupling, renders SiC microdisk a promising platform for integrated quantum photonics applications.

  9. Reliable Breakdown Obtained in Silicon Carbide Rectifiers

    NASA Technical Reports Server (NTRS)

    Neudeck, Philip G.

    1997-01-01

    The High Temperature Integrated Electronics and Sensor (HTIES) Program at the NASA Lewis Research Center is currently developing silicon carbide (SiC) for use in harsh conditions where silicon, the semiconductor used in nearly all of today's electronics, cannot function. Silicon carbide's demonstrated ability to function under extreme high-temperature, high-power, and/or high-radiation conditions will enable significant improvements to a far-ranging variety of applications and systems. These range from improved high-voltage switching for energy savings in public electric power distribution and electric vehicles, to more powerful microwave electronics for radar and cellular communications, to sensor and controls for cleaner-burning, more fuel-efficient jet aircraft and automobile engines.

  10. Defect Structure and Evolution in Silicon Carbide Irradiated to 1 dpa-SiC at 1100 C

    SciTech Connect

    D.J. Senor; G.E. Youngblood; L.R. Greenwood; D.V. Archer; D.L. Alexander; M.C. Chen; G.A. Newsome

    2002-05-13

    Transmission electron microscopy (TEM), swelling measurements, isochronal annealing, and thermal diffusivity testing were used to characterize the effects of radiation damage in SiC. Together, these techniques provided a comprehensive set of tools for observing and characterizing the structure and evolution of radiation-induced defects in SiC as a function of irradiation temperature and dose. In this study, two types of dense, crystalline, monolithic SiC were subjected to irradiation doses up to 1 dpa-SiC at a temperature of 1100 C, as well as post-irradiation annealing up to 1500 C. The microscopic defect structures observed by TEM were correlated to changes in the macroscopic dimensions, thermal diffusivity and thermal conductivity. The results demonstrated the value of using ultrapure {beta}SiC as an effective reference material to characterize the nature of expected radiation damage in other, more complex, SiC-based materials such as SiC/SiC composites.

  11. Defect Structure and Evolution in Silicon Carbide Irradiated to 1 dpa-SiC at 1100 degrees C

    SciTech Connect

    Senor, David J.; Youngblood, Gerald E.; Greenwood, Lawrence R.; Archer, Dale V.; Alexander, David L.; Chen, Mon-Chao; Newsome, George A.

    2003-05-01

    Transmission electron microscopy, swelling measurements, isochronal annealing, and thermal diffusivity testing were used to characterize the effects of radiation damage in SiC. Together, these techniques provided a comprehensive set of tools for observing and characterizing the structure and evolution of radiation-induced defects in SiC as a function of irradiation temperature and dose. In this study, two types of dense, crystalline, monolithic SiC were subjected to irradiation doses up to 1 dpa-SiC at a temperature of 1100?C, as well as post-irradiation annealing up to 1500?C. The microscopic defect structures observed by TEM were correlated to changes in the macroscopic dimensions, thermal diffusivity and thermal conductivity. The results demonstrated the value of using ultrapure beta-SiC as an effective reference material to characterize the nature of expected radiation damage in other, more complex, SiC-based materials such as SiC/SiC composites.

  12. Making a Silicon-Nitride/Silicon-Carbide Composite

    NASA Technical Reports Server (NTRS)

    Bhatt, R. T.

    1987-01-01

    Hot pressing and nitriding produce strong fiber/matrix material. Fabrication method developed for processing strong and tough silicon-based ceramic composite material, SiC/RBSN, which consists of reaction-bonded Si3N4 (RBSN) reinforced by continuous-length, high-modulus, high strength silicon carbide (SiC) fibers prepared by chemical-vapor deposition method. Increased toughness and ultimate strength of SiC/RBSN composite makes it potential structural material for advanced heat engines.

  13. Silicon Carbide and Silicon Carbide Composites for Fusion Reactor Applications

    SciTech Connect

    Hinoki, Tatsuya; Hasegawa, Akira; Katoh, Yutai; Snead, Lance Lewis; Jung, H.C.; Katsui, Hirokazu; Kondo, Sosuke; Zhong, Z. H.; Park, Y. H.; Shih, Chunghao; Ozawa, Kazumi; Parish, Chad M; Meisner, Roberta Ann

    2013-01-01

    This paper reviews recent achievements as to "nuclear-grade" SiC composites in particular for materials-system integration. SiC composite component development are reviewed including VHTR control rod scale model and compact intermediate heat exchanger scale mode by current joining and assembly techniques. Joining methods for SiC to metal and results of characterization of joint shear strength by the torsion tests using small specimens were also reviewed. The recent results of neutron irradiation experiments were also reviewed including detailed analysis of mechanical properties, irradiation creep and preliminary results on tritium behavior in SiC.

  14. Producing Silicon Carbide for Semiconductor Devices

    NASA Technical Reports Server (NTRS)

    Hsu, G. C.; Rohatgi, N. K.

    1986-01-01

    Processes proposed for production of SiC crystals for use in semiconductors operating at temperatures as high as 900 degrees C. Combination of new processes produce silicon carbide chips containing epitaxial layers. Chips of SiC first grown on porous carbon matrices, then placed in fluidized bed, where additional layer of SiC grows. Processes combined to yield complete process. Liquid crystallization process used to make SiC particles or chips for fluidized-bed process.

  15. Acoustic microscopy of silicon carbide materials

    NASA Technical Reports Server (NTRS)

    Khandelwal, P. K.; Heitman, P. W.; Yuhas, D.; Vorres, C. L.

    1982-01-01

    It is shown that scanning laser acoustic microscopy (SLAM) is able to detect such fracture-controlling flaws in dense silicon carbide materials as surface voids, whose diameter-by-depth size is a minimum of 75 by 17 microns in reaction-bonded SiC and 68 by 25 microns in alpha-SiC. Surface conditions such as pitting, which have been found to limit the discernibility of drilled holes, become important when pit and drilled hole sizes become comparable.

  16. Low blow Charpy impact of silicon carbides

    NASA Technical Reports Server (NTRS)

    Abe, H.; Chandan, H. C.; Bradt, R. C.

    1978-01-01

    The room-temperature impact resistance of several commercial silicon carbides was examined using an instrumented pendulum-type machine and Charpy-type specimens. Energy balance compliance methods and fracture toughness approaches, both applicable to other ceramics, were used for analysis. The results illustrate the importance of separating the machine and the specimen energy contributions and confirm the equivalence of KIc and KId. The material's impact energy was simply the specimen's stored elastic strain energy at fracture.

  17. Mechanical properties of Silicon Carbide Nanowires

    NASA Astrophysics Data System (ADS)

    Alkhateeb, Abdullah; Zhang, Daqing; McIlroy, David; Aston, David Eric

    2004-05-01

    Silicon carbide nanowires could be potentially useful for high strength materials which lead to the interest in understanding their mechanical properties. In this report we use the digital pulse force microscopy to analyze the mechanical properties of SiC nanowires .Stiffness and adhesion images of SiC nanowires on silicon grating were obtained and calibrated force-distance curves were plotted along the wire which spans on a 1.5 micron trench. Moreover, spring constant and Young's modules have been calculated from the linear part of the force-distance curves.

  18. Microwave joining of silicon carbide using several different approaches

    SciTech Connect

    Ahmad, I.; Silberglitt, R. ); Black, W.M.; Sa'adaldin, H.S. . Dept. of Electrical and Computer Engineering); Katz, J.D. )

    1992-01-01

    Microwave joining of sintered silicon carbide, both to itself and reaction bonded silicon carbide, has been accomplished in a single-mode rectangular resonant cavity. Several approaches using different interlayer materials were employed to join sintered silicon carbide. Effective joining of reaction bonded silicon carbide to itself and sintered silicon carbide was accomplished without the use of any interlayer material in the single-mode resonant cavity as well as in a multi-mode oven. Specimens cut from 3/8'' diameter-rods were joined in the single-mode cavity, whereas a variety of arbitrary shapes and larger specimens (of reaction bonded silicon carbide) were joined in the multi-mode oven.

  19. Microwave joining of silicon carbide using several different approaches

    SciTech Connect

    Ahmad, I.; Silberglitt, R.; Black, W.M.; Sa`adaldin, H.S.; Katz, J.D.

    1992-07-01

    Microwave joining of sintered silicon carbide, both to itself and reaction bonded silicon carbide, has been accomplished in a single-mode rectangular resonant cavity. Several approaches using different interlayer materials were employed to join sintered silicon carbide. Effective joining of reaction bonded silicon carbide to itself and sintered silicon carbide was accomplished without the use of any interlayer material in the single-mode resonant cavity as well as in a multi-mode oven. Specimens cut from 3/8`` diameter-rods were joined in the single-mode cavity, whereas a variety of arbitrary shapes and larger specimens (of reaction bonded silicon carbide) were joined in the multi-mode oven.

  20. Friction and deformation behavior of single-crystal silicon carbide

    NASA Technical Reports Server (NTRS)

    Miyoshi, K.; Buckley, D. H.

    1977-01-01

    Friction and deformation studies were conducted with single-crystal silicon carbide in sliding contact with diamond. When the radius of curvature of the spherical diamond rider was large (0.3), deformation of silicon carbide was primarily elastic. Under these conditions the friction coefficient was low and did not show a dependence on the silicon carbide orientation. Further, there was no detectable cracking of the silicon carbide surfaces. When smaller radii of curvature of the spherical diamond riders (0.15 and 0.02 mm) or a conical diamond rider was used, plastic grooving occured and the silicon carbide exhibited anisotropic friction and deformation behavior. Under these conditions the friction coefficient depended on load. Anisotropic friction and deformation of the basal plane of silicon carbide was controlled by the slip system. 10101120and cleavage of1010.

  1. Silicon carbide-silicon composite having improved oxidation resistance and method of making

    NASA Technical Reports Server (NTRS)

    Luthra, Krishan Lal (Inventor); Wang, Hongyu (Inventor)

    1999-01-01

    A Silicon carbide-silicon matrix composite having improved oxidation resistance at high temperatures in dry or water-containing environments is provided. A method is given for sealing matrix cracks in situ in melt infiltrated silicon carbide-silicon matrix composites. The composite cracks are sealed by the addition of various additives, such as boron compounds, into the melt infiltrated silicon carbide-silicon matrix.

  2. Method of making silicon carbide-silicon composite having improved oxidation resistance

    NASA Technical Reports Server (NTRS)

    Luthra, Krishan Lal (Inventor); Wang, Hongyu (Inventor)

    2002-01-01

    A Silicon carbide-silicon matrix composite having improved oxidation resistance at high temperatures in dry or water-containing environments is provided. A method is given for sealing matrix cracks in situ in melt infiltrated silicon carbide-silicon matrix composites. The composite cracks are sealed by the addition of various additives, such as boron compounds, into the melt infiltrated silicon carbide-silicon matrix.

  3. Optical waveguide formed by cubic silicon carbide on sapphire substrates

    NASA Technical Reports Server (NTRS)

    Tang, Xiao; Wongchotigul, Kobchat; Spencer, Michael G.

    1991-01-01

    Optical confinement in beta silicon carbide (beta-SiC) thin films on sapphire substrate is demonstrated. Measurements are performed on waveguides formed by the mechanical transfer of thin beta-SiC films to sapphire. Recent results of epitaxial films of SiC on sapphire substrates attest to the technological viability of optoelectronic devices made from silicon carbide. Far-field mode patterns are shown. It is believed that this is the first step in validating a silicon carbide optoelectronic technology.

  4. Colloidal characterization of silicon nitride and silicon carbide

    NASA Technical Reports Server (NTRS)

    Feke, Donald L.

    1986-01-01

    The colloidal behavior of aqueous ceramic slips strongly affects the forming and sintering behavior and the ultimate mechanical strength of the final ceramic product. The colloidal behavior of these materials, which is dominated by electrical interactions between the particles, is complex due to the strong interaction of the solids with the processing fluids. A surface titration methodology, modified to account for this interaction, was developed and used to provide fundamental insights into the interfacial chemistry of these systems. Various powder pretreatment strategies were explored to differentiate between true surface chemistry and artifacts due to exposure history. The colloidal behavior of both silicon nitride and carbide is dominated by silanol groups on the powder surfaces. However, the colloid chemistry of silicon nitride is apparently influenced by an additional amine group. With the proper powder treatments, silicon nitride and carbide powder can be made to appear colloidally equivalent. The impact of these results on processing control will be discussed.

  5. Uniform nano-ripples on the sidewall of silicon carbide micro-hole fabricated by femtosecond laser irradiation and acid etching

    SciTech Connect

    Khuat, Vanthanh; Chen, Tao; Gao, Bo; Si, Jinhai Ma, Yuncan; Hou, Xun

    2014-06-16

    Uniform nano-ripples were observed on the sidewall of micro-holes in silicon carbide fabricated by 800-nm femtosecond laser and chemical selective etching. The morphology of the ripple was analyzed using scanning electronic microscopy. The formation mechanism of the micro-holes was attributed to the chemical reaction of the laser affected zone with mixed solution of hydrofluoric acid and nitric acid. The formation of nano-ripples on the sidewall of the holes could be attributed to the standing wave generated in z direction due to the interference between the incident wave and the reflected wave.

  6. Silicon nitride/silicon carbide composite densified materials prepared using composite powders

    DOEpatents

    Dunmead, S.D.; Weimer, A.W.; Carroll, D.F.; Eisman, G.A.; Cochran, G.A.; Susnitzky, D.W.; Beaman, D.R.; Nilsen, K.J.

    1997-07-01

    Prepare silicon nitride-silicon carbide composite powders by carbothermal reduction of crystalline silica powder, carbon powder and, optionally, crystalline silicon nitride powder. The crystalline silicon carbide portion of the composite powders has a mean number diameter less than about 700 nanometers and contains nitrogen. The composite powders may be used to prepare sintered ceramic bodies and self-reinforced silicon nitride ceramic bodies.

  7. PROPERTIES OF DEFECTS AND IMPLANTS IN Mg+ IMPLANTED SILICON CARBIDE

    SciTech Connect

    Jiang, Weilin; Zhu, Zihua; Varga, Tamas; Bowden, Mark E.; Manandhar, Sandeep; Roosendaal, Timothy J.; Hu, Shenyang Y.; Henager, Charles H.; Kurtz, Richard J.; Wang, Yongqiang

    2013-09-25

    As a candidate material for fusion reactor designs, silicon carbide (SiC) under high-energy neutron irradiation undergoes atomic displacement damage and transmutation reactions that create magnesium as one of the major metallic products. The presence of Mg and lattice disorder in SiC is expected to affect structural stability and degrade thermo-mechanical properties that could limit SiC lifetime for service. We have initiated a combined experimental and computational study that uses Mg+ ion implantation and multiscale modeling to investigate the structural and chemical effects in Mg implanted SiC and explore possible property degradation mechanisms.

  8. Silicon carbide/SRBSN composites

    SciTech Connect

    Razzell, A.G.; Lewis, M.H.

    1991-08-01

    Ceramic matrix composites have been produced using unidirectionally aligned Textron SCS-6 fibers in a sintered reaction bonded silicon nitride (SRBSN) matrix. A tape casting technique was used to produce a prepreg sheet that could be cut and stacked to form a layup. Sintering aids were MgO, Al2O3, and Y2O3 either singly or in combination, final sintering being carried out under pressure at temperatures up to 1750 C. The three-point bend strength of the material varied between 448 and 513 MPa and showed no variation with oxidation time at 1000 C up to 25 hours. Interfacial shear strength measured by indentation was 4 MPa; some samples had a reaction layer at the interface and a shear strength of greater than MPa. Within sections 6 mm from exposed fiber ends, the interfacial carbon layers were partially removed, and the interfacial shear strength was reduced with increasing oxidation time. 4 refs.

  9. Ultrafine alumina coated silicon carbide particles for alumina-silicon carbide nanocomposites

    SciTech Connect

    Warrier, K.G.K.; Hareesh, U.S.; Damodaran, A.D.

    1996-12-31

    Aluminum oxide, toughened by fine and uniform dispersion of silicon carbide particles has been found to possess interesting high temperature properties of high toughness and strength. Recent reports suggest that the finer the silicon carbide size, the better would be the fracture toughness. By addition of as few as 5 vol% submicron SiC particles strengthened Al{sub 2}O{sub 3} from 350 MPa to 1 GPa, with toughness as high as 4.7 Mpa m{sup {1/2}}. The mechanism of such high extent of fracture toughness has been investigated to be due to crack deflection and microcracking introduced by thermal expansion mismatch between particles and matrix grains, although the real contributions from the silicon carbide nanoparticles are still under investigation. In all these cases the primary requirement for most effective composite is the fine, uniform size of the particles and their homogeneous dispersion in the alumina matrix. Usual methods adopted for the preparation of composites such as physical mixing of alumina and silicon carbide particles often result in localized agglomerations and inhomogeneity making the composite inferior in properties.

  10. Excess carbon in silicon carbide

    SciTech Connect

    Shen, X; Oxley, Mark P.; Puzyrev, Y; Tuttle, B R; Duscher, Gerd; Pantelides, Sokrates T.

    2010-01-01

    The application of SiC in electronic devices is currently hindered by low carrier mobility at the SiC/SiO{sub 2} interfaces. Recently, it was reported that 4H-SiC/SiO{sub 2} interfaces might have a transition layer on the SiC substrate side with C/Si ratio as high as 1.2, suggesting that carbon is injected into the SiC substrate during oxidation or other processing steps. We report finite-temperature quantum molecular dynamics simulations that explore the behavior of excess carbon in SiC. For SiC with 20% excess carbon, we find that, over short time ({approx} 24 ps), carbon atoms bond to each other and form various complexes, while the silicon lattice is largely unperturbed. These results, however, suggest that at macroscopic times scale, C segregation is likely to occur; therefore a transition layer with 20% extra carbon would not be stable. For a dilute distribution of excess carbon, we explore the pairing of carbon interstitials and show that the formation of dicarbon interstitial cluster is kinetically very favorable, which suggests that isolated carbon clusters may exist inside SiC substrate.

  11. Improved silicon carbide for advanced heat engines

    NASA Technical Reports Server (NTRS)

    Whalen, T. J.; Winterbottom, W. L.

    1986-01-01

    Work performed to develop silicon carbide materials of high strength and to form components of complex shape and high reliability is described. A beta-SiC powder and binder system was adapted to the injection molding process and procedures and process parameters developed capable of providing a sintered silicon carbide material with improved properties. The initial effort has been to characterize the baseline precursor materials (beta silicon carbide powder and boron and carbon sintering aids), develop mixing and injection molding procedures for fabricating test bars, and characterize the properties of the sintered materials. Parallel studies of various mixing, dewaxing, and sintering procedures have been carried out in order to distinguish process routes for improving material properties. A total of 276 MOR bars of the baseline material have been molded, and 122 bars have been fully processed to a sinter density of approximately 95 percent. The material has a mean MOR room temperature strength of 43.31 ksi (299 MPa), a Weibull characteristic strength of 45.8 ksi (315 MPa), and a Weibull modulus of 8.0. Mean values of the MOR strengths at 1000, 1200, and 14000 C are 41.4, 43.2, and 47.2 ksi, respectively. Strength controlling flaws in this material were found to consist of regions of high porosity and were attributed to agglomerates originating in the initial mixing procedures. The mean stress rupture lift at 1400 C of five samples tested at 172 MPa (25 ksi) stress was 62 hours and at 207 MPa (30 ksi) stress was 14 hours. New fluid mixing techniques have been developed which significantly reduce flaw size and improve the strength of the material. Initial MOR tests indicate the strength of the fluid-mixed material exceeds the baseline property by more than 33 percent.

  12. Similarities and distinctions of defect production by fast electron and proton irradiation: Moderately doped silicon and silicon carbide of n-type

    SciTech Connect

    Emtsev, V. V. Ivanov, A. M.; Kozlovski, V. V.; Lebedev, A. A.; Oganesyan, G. A.; Strokan, N. B.; Wagner, G.

    2012-04-15

    Effects of irradiation with 0.9 MeV electrons as well as 8 and 15 MeV protons on moderately doped n-Si grown by the floating zone (FZ) technique and n-SiC (4H) grown by chemical vapor deposition are studied in a comparative way. It has been established that the dominant radiation-produced defects with involvement of V group impurities differ dramatically in electron- and proton-irradiated n-Si (FZ), in spite of the opinion on their similarity widespread in literature. This dissimilarity in defect structures is attributed to a marked difference in distributions of primary radiation defects for the both kinds of irradiation. In contrast, DLTS spectra taken on electron- and proton-irradiated n-SiC (4H) appear to be similar. However, there are very much pronounced differences in the formation rates of radiation-produced defects. Despite a larger production rate of Frenkel pairs in SiC as compared to that in Si, the removal rates of charge carriers in n-SiC (4H) were found to be considerably smaller than those in n-Si (FZ) for the both electron and proton irradiation. Comparison between defect production rates in the both materials under electron and proton irradiation is drawn.

  13. Process for forming silicon carbide films and microcomponents

    DOEpatents

    Hamza, A.V.; Balooch, M.; Moalem, M.

    1999-01-19

    Silicon carbide films and microcomponents are grown on silicon substrates at surface temperatures between 900 K and 1700 K via C{sub 60} precursors in a hydrogen-free environment. Selective crystalline silicon carbide growth can be achieved on patterned silicon-silicon oxide samples. Patterned SiC films are produced by making use of the high reaction probability of C{sub 60} with silicon at surface temperatures greater than 900 K and the negligible reaction probability for C{sub 60} on silicon dioxide at surface temperatures less than 1250 K. 5 figs.

  14. Process for forming silicon carbide films and microcomponents

    DOEpatents

    Hamza, Alex V.; Balooch, Mehdi; Moalem, Mehran

    1999-01-01

    Silicon carbide films and microcomponents are grown on silicon substrates at surface temperatures between 900 K and 1700 K via C.sub.60 precursors in a hydrogen-free environment. Selective crystalline silicon carbide growth can be achieved on patterned silicon-silicon oxide samples. Patterned SiC films are produced by making use of the high reaction probability of C.sub.60 with silicon at surface temperatures greater than 900 K and the negligible reaction probability for C.sub.60 on silicon dioxide at surface temperatures less than 1250 K.

  15. Revised activation estimates for silicon carbide

    SciTech Connect

    Heinisch, H.L.; Cheng, E.T.; Mann, F.M.

    1996-10-01

    Recent progress in nuclear data development for fusion energy systems includes a reevaluation of neutron activation cross sections for silicon and aluminum. Activation calculations using the newly compiled Fusion Evaluated Nuclear Data Library result in calculated levels of {sup 26}Al in irradiated silicon that are about an order of magnitude lower than the earlier calculated values. Thus, according to the latest internationally accepted nuclear data, SiC is much more attractive as a low activation material, even in first wall applications.

  16. Structural relaxation of amorphous silicon carbide.

    PubMed

    Ishimaru, Manabu; Bae, In-Tae; Hirotsu, Yoshihiko; Matsumura, Syo; Sickafus, Kurt E

    2002-07-29

    We have examined amorphous structures of silicon carbide (SiC) using both transmission electron microscopy and a molecular-dynamics approach. Radial distribution functions revealed that amorphous SiC contains not only heteronuclear (Si-C) bonds but also homonuclear (Si-Si and C-C) bonds. The ratio of heteronuclear to homonuclear bonds was found to change upon annealing, suggesting that structural relaxation of the amorphous SiC occurred. Good agreement was obtained between the simulated and experimentally measured radial distribution functions. PMID:12144449

  17. Molybdenum disilicide composites reinforced with zirconia and silicon carbide

    SciTech Connect

    Petrovic, J.J.

    1992-12-31

    This patent pertains to compositions consisting essentially of molybdenum disilicide, silicon carbide, and a zirconium oxide component. The silicon carbide used in the compositions is in whisker or powder form. The zirconium oxide component is pure zirconia or partially stabilized zirconia or fully stabilized zirconia. Fabrication, fracture toughness, and bend strength are covered.

  18. Critically coupled surface phonon-polariton excitation in silicon carbide.

    PubMed

    Neuner, Burton; Korobkin, Dmitriy; Fietz, Chris; Carole, Davy; Ferro, Gabriel; Shvets, Gennady

    2009-09-01

    We observe critical coupling to surface phonon-polaritons in silicon carbide by attenuated total reflection of mid-IR radiation. Reflectance measurements demonstrate critical coupling by a double scan of wavelength and incidence angle. Critical coupling occurs when prism coupling loss is equal to losses in silicon carbide and the substrate, resulting in maximal electric field enhancement. PMID:19724526

  19. Molybdenum disilicide composites reinforced with zirconia and silicon carbide

    DOEpatents

    Petrovic, J.J.

    1995-01-17

    Compositions are disclosed consisting essentially of molybdenum disilicide, silicon carbide, and a zirconium oxide component. The silicon carbide used in the compositions is in whisker or powder form. The zirconium oxide component is pure zirconia or partially stabilized zirconia or fully stabilized zirconia.

  20. Molybdenum disilicide composites reinforced with zirconia and silicon carbide

    DOEpatents

    Petrovic, John J.

    1995-01-01

    Compositions consisting essentially of molybdenum disilicide, silicon carbide, and a zirconium oxide component. The silicon carbide used in the compositions is in whisker or powder form. The zirconium oxide component is pure zirconia or partially stabilized zirconia or fully stabilized zirconia.

  1. An investigation on gamma attenuation behaviour of titanium diboride reinforced boron carbide-silicon carbide composites

    NASA Astrophysics Data System (ADS)

    Buyuk, Bulent; Beril Tugrul, A.

    2014-04-01

    In this study, titanium diboride (TiB2) reinforced boron carbide-silicon carbide composites were investigated against Cs-137 and Co-60 gamma radioisotope sources. The composite materials include 70% boron carbide (B4C) and 30% silicon carbide (SiC) by volume. Titanium diboride was reinforced to boron carbide-silicon carbide composites as additive 2% and 4% by volume. Average particle sizes were 3.851 µm and 170 nm for titanium diboride which were reinforced to the boron carbide silicon carbide composites. In the experiments the gamma transmission technique was used to investigate the gamma attenuation properties of the composite materials. Linear and mass attenuation coefficients of the samples were determined. Theoretical mass attenuation coefficients were calculated from XCOM computer code. The experimental results and theoretical results were compared and evaluated with each other. It could be said that increasing the titanium diboride ratio causes higher linear attenuation values against Cs-137 and Co-60 gamma radioisotope sources. In addition decreasing the titanium diboride particle size also increases the linear and mass attenuation properties of the titanium diboride reinforced boron carbide-silicon carbide composites.

  2. The growth of cubic silicon carbide on a compliant substrate

    NASA Technical Reports Server (NTRS)

    Mitchell, Sharanda; Soward, Ida

    1995-01-01

    Research has shown that silicon carbide grown on silicon and 6H silicon carbide has problems associated with these substrates. This is because silicon and silicon carbide has a 20% lattice mismatch and cubic silicon carbide has not been successfully achieved on 6H silicon carbide. We are investigating the growth of silicon carbide on a compliant substrate in order to grow defect free silicon carbide. This compliant substrate consists of silicon/silicon dioxide with 1200 A of single crystal silicon on the top layer. We are using this compliant substrate because there is a possibility that the silicon dioxide layer and the carbonized layer will allow the silicon lattice to shrink or expand to match the lattice of the silicon carbide. This would improve the electrical properties of the film for the use of device fabrication. When trying to grow silicon carbide, we observed amorphous film. To investigate, we examined the process step by step using RHEED. RHEED data showed that each step was amorphous. We found that just by heating the substrate in the presence of hydrogen it changed the crystal structure. When heated to 1000 C for 2 minutes, RHEED showed that there was an amorphous layer on the surface. We also heated the substrate to 900 C for 2 minutes and RHEED data showed that there was a deterioration of the single crystalline structure. We assumed that the presence of oxygen was coming from the sides of the silicon dioxide layer. Therefore, we evaporated 2500 A of silicon to all four edges of the wafer to try to enclose the oxygen. When heating the evaporated wafer to 900 C the RHEED data showed single crystalline structure however at 1000 C the RHEED data showed deterioration of the single crystalline structure. We conclude that the substrate itself is temperature dependent and that the oxygen was coming from the sides of the silicon dioxide layer. We propose to evaporate more silicon on the edges of the wafer to eliminate the escape of oxygen. this will allow

  3. Reaction bonded silicon carbide gimbaled pointing mirror

    NASA Astrophysics Data System (ADS)

    Robichaud, J.; Akerstrom, A.; Frey, S.; Crompton, D.; Cucchiaro, P.; Deveau, G.; Peters, M.; Mason, S.; Ullathorne, C.

    2007-09-01

    A Silicon Carbide (SiC) based wide field of view Pointing Mirror Assembly (PMA) has been developed to provide two axis line-of-sight control for a fixed, space based imaging sensor. Thermal modeling has been completed in order to project the excellent thermal stability anticipated from the SiC PMA, and closed loop servo testing of the hardware has been conducted in order to quantify the bandwidth associated with line-of-sight control. In addition to the system level testing the SiC mirror substrate itself has been tested for thermal stability. We also report on results obtained with a novel polishing technique which has been applied in order to allow optical finishing of the two-phased Reaction Bonded (RB) SiC mirror substrate without the need for Silicon or SiC claddings.

  4. Silicon carbide - Progress in crystal growth

    NASA Technical Reports Server (NTRS)

    Powell, J. Anthony

    1987-01-01

    Recent progress in the development of two processes for producing large-area high-quality single crystals of SiC is described: (1) a modified Lely process for the growth of the alpha polytypes (e.g., 6H SiC) initially developed by Tairov and Tsvetkov (1978, 1981) and Ziegler et al. (1983), and (2) a process for the epitaxial growth of the beta polytype on single-crystal silicon or other substrates. Growth of large-area cubic SiC on Si is described together with growth of defect-free beta-SiC films on alpha-6H SiC crystals and TiC lattice. Semiconducting qualities of silicon carbide crystals grown by various techniques are discussed.

  5. Silicon Carbide Nanotube Oxidation at High Temperatures

    NASA Technical Reports Server (NTRS)

    Ahlborg, Nadia; Zhu, Dongming

    2012-01-01

    Silicon Carbide Nanotubes (SiCNTs) have high mechanical strength and also have many potential functional applications. In this study, SiCNTs were investigated for use in strengthening high temperature silicate and oxide materials for high performance ceramic nanocomposites and environmental barrier coating bond coats. The high · temperature oxidation behavior of the nanotubes was of particular interest. The SiCNTs were synthesized by a direct reactive conversion process of multiwall carbon nanotubes and silicon at high temperature. Thermogravimetric analysis (TGA) was used to study the oxidation kinetics of SiCNTs at temperatures ranging from 800degC to1300degC. The specific oxidation mechanisms were also investigated.

  6. An overview of silicon carbide device technology

    NASA Technical Reports Server (NTRS)

    Neudeck, Philip G.; Matus, Lawrence G.

    1992-01-01

    Recent progress in the development of silicon carbide (SiC) as a semiconductor is briefly reviewed. This material shows great promise towards providing electronic devices that can operate under the high-temperature, high-radiation, and/or high-power conditions where current semiconductor technologies fail. High quality single crystal wafers have become available, and techniques for growing high quality epilayers have been refined to the point where experimental SiC devices and circuits can be developed. The prototype diodes and transistors that have been produced to date show encouraging characteristics, but by the same token they also exhibit some device-related problems that are not unlike those faced in the early days of silicon technology development. Although these problems will not prevent the implementation of some useful circuits, the performance and operating regime of SiC electronics will be limited until these device-related issues are solved.

  7. Converting a carbon preform object to a silicon carbide object

    NASA Technical Reports Server (NTRS)

    Levin, Harry (Inventor)

    1990-01-01

    A process for converting in depth a carbon or graphite preform object to a silicon carbide object, silicon carbide/silicon object, silicon carbide/carbon-core object, or a silicon carbide/silicon/carbon-core object, by contacting it with silicon liquid and vapor over various lengths of contact time in a reaction chamber. In the process, a stream comprised of a silicon-containing precursor material in gaseous phase below the decomposition temperature of said gas and a coreactant, carrier or diluent gas such as hydrogen is passed through a hole within a high emissivity, thin, insulating septum into the reaction chamber above the melting point of silicon. The thin septum has one face below the decomposition temperature of the gas and an opposite face exposed to the reaction chamber. Thus, the precursor gas is decomposed directly to silicon in the reaction chamber. Any stream of decomposition gas and any unreacted precursor gas from the reaction chamber is removed. A carbon or graphite preform object placed in the reaction chamber is contacted with the silicon. The carbon or graphite preform object is recovered from the reactor chamber after it has been converted to a desired silicon carbide, silicon and carbon composition.

  8. Silicon Carbide: The Problem with Laboratory Spectra

    NASA Astrophysics Data System (ADS)

    Speck, A. K.; Hofmeister, A. M.; Barlow, M. J.

    2000-03-01

    The interpretation of astronomical observations of infrared (IR) silicon carbide (SiC) features in the spectra of carbon stars have revealed discrepancies between the work of astronomers and that of meteoriticists. The silicon carbide observed around carbon stars has been attributed to one type of SiC (α) while meteoritic samples believed to have formed around such stars are of another type of SiC (β). The key to solving this problem has been to understand the sources of laboratory data used by astronomers in order to interpret the IR spectra. Through comparison of thin film IR absorption spectra and spectra taken using finely ground samples dispersed in potassium bromide (KBr) pellets we show that the previously invoked ``KBr matrix-correction'' is unnecessary for powder dispersions obtained from very fine grain sizes of SiC. Comparison of our data and previous measurements show that dust around carbon stars is β-SiC, consistent with laboratory studies of presolar grains in meteorites. The implications of these findings affect twenty years of work. The IR spectroscopic laboratory data used by astronomers to identify dust species in space must be carefully scrutinized to ensure that the KBr correction is not responsible for further misattributions of minerals in astronomical dust features.

  9. Improved silicon carbide for advanced heat engines

    NASA Technical Reports Server (NTRS)

    Whalen, Thomas J.

    1988-01-01

    This is the third annual technical report for the program entitled, Improved Silicon Carbide for Advanced Heat Engines, for the period February 16, 1987 to February 15, 1988. The objective of the original program was the development of high strength, high reliability silicon carbide parts with complex shapes suitable for use in advanced heat engines. Injection molding is the forming method selected for the program because it is capable of forming complex parts adaptable for mass production on an economically sound basis. The goals of the revised program are to reach a Weibull characteristic strength of 550 MPa (80 ksi) and a Weibull modulus of 16 for bars tested in 4-point loading. Two tasks are discussed: Task 1 which involves materials and process improvements, and Task 2 which is a MOR bar matrix to improve strength and reliability. Many statistically designed experiments were completed under task 1 which improved the composition of the batches, the mixing of the powders, the sinter and anneal cycles. The best results were obtained by an attritor mixing process which yielded strengths in excess of 550 MPa (80 ksi) and an individual Weibull modulus of 16.8 for a 9-sample group. Strengths measured at 1200 and 1400 C were equal to the room temperature strength. Annealing of machined test bars significantly improved the strength. Molding yields were measured and flaw distributions were observed to follow a Poisson process. The second iteration of the Task 2 matrix experiment is described.

  10. Improved silicon carbide for advanced heat engines

    NASA Technical Reports Server (NTRS)

    Whalen, Thomas J.

    1987-01-01

    This is the second annual technical report entitled, Improved Silicon Carbide for Advanced Heat Engines, and includes work performed during the period February 16, 1986 to February 15, 1987. The program is conducted for NASA under contract NAS3-24384. The objective is the development of high strength, high reliability silicon carbide parts with complex shapes suitable for use in advanced heat engines. The fabrication methods used are to be adaptable for mass production of such parts on an economically sound basis. Injection molding is the forming method selected. This objective is to be accomplished in a two-phase program: (1) to achieve a 20 percent improvement in strength and a 100 percent increase in Weibull modulus of the baseline material; and (2) to produce a complex shaped part, a gas turbine rotor, for example, with the improved mechanical properties attained in the first phase. Eight tasks are included in the first phase covering the characterization of the properties of a baseline material, the improvement of those properties and the fabrication of complex shaped parts. Activities during the first contract year concentrated on two of these areas: fabrication and characterization of the baseline material (Task 1) and improvement of material and processes (Task 7). Activities during the second contract year included an MOR bar matrix study to improve mechanical properties (Task 2), materials and process improvements (Task 7), and a Ford-funded task to mold a turbocharger rotor with an improved material (Task 8).

  11. Improved silicon carbide for advanced heat engines

    NASA Technical Reports Server (NTRS)

    Whalen, Thomas J.; Mangels, J. A.

    1986-01-01

    The development of silicon carbide materials of high strength was initiated and components of complex shape and high reliability were formed. The approach was to adapt a beta-SiC powder and binder system to the injection molding process and to develop procedures and process parameters capable of providing a sintered silicon carbide material with improved properties. The initial effort was to characterize the baseline precursor materials, develop mixing and injection molding procedures for fabricating test bars, and characterize the properties of the sintered materials. Parallel studies of various mixing, dewaxing, and sintering procedures were performed in order to distinguish process routes for improving material properties. A total of 276 modulus-of-rupture (MOR) bars of the baseline material was molded, and 122 bars were fully processed to a sinter density of approximately 95 percent. Fluid mixing techniques were developed which significantly reduced flaw size and improved the strength of the material. Initial MOR tests indicated that strength of the fluid-mixed material exceeds the baseline property by more than 33 percent. the baseline property by more than 33 percent.

  12. Dispersion aspects of silicon carbide gelcasting

    SciTech Connect

    Bleier, A.

    1991-09-01

    The principal objective of this research was to increase the solid loading of silicon carbide (SiC) powder, in an appropriate liquid medium, to a level that is useful for gelcasting technology. A number of factors that determine the maximum concentration of silicon carbide that can be incorporated into a pourable ceramic suspension have been identified. The pH of the system is the most critical processing parameter. Its proper adjustment (pH 11 to 13) allows SiC concentrations exceeding 50%, based on volume, to be routinely achieved without the use of additional dispersing agents. The particle size of SiC was also found to affect the maximum, attainable concentration. The surface area of the powder and the presence of free carbon in the powder, though not significantly influencing the suspension properties, determine the concentration of initiator required to induce polymerization and gelation. SiC specimens have been gelcast for powders in the size range of 0.8 to 8.5 {mu}m; the powders employed contain either {approximately} 0 or 19% carbon by weight. Finally, the generation of bubbles, typically encountered by the use of ammonia to adjust pH has been circumvented by the use of tetramethylammonium hydroxide.

  13. Development of silicon carbide composites for fusion

    SciTech Connect

    Snead, L.L. )

    1993-08-01

    The use of silicon carbide composites for structural materials is of growing interest in the fusion community. However, radiation effects in these materials are virtually unexplored, and the general state of ceramic matrix composites for nonnuclear applications is still in its infancy. Research into the radiation response of the most popular silicon carbide composite, namely, the chemically vapor-deposited (CVD) SiC-carbon-Nicalon fiber system is discussed. Three areas of interest are the stability of the fiber and matrix materials, the stability of the fiber-matrix interface, and the true activation of these [open quotes]reduced activity[close quotes] materials. Two methods are presented that quantitatively measure the effect of radiation on fiber and matrix elastic modulus as well as the fiber-matrix interfacial strength. The results of these studies show that the factor limiting the radiation performance of the CVD SiC-carbon-Nicalon system is degradation of the Nicalon fiber, which leads to a weakened carbon interface. The activity of these composites is significantly higher than expected and is dominated by impurity isotopes. 52 refs., 12 figs., 3 tabs.

  14. Oxidation kinetics of coated silicon carbide fiber-reinforced silicon carbide (SiC/SiC)

    SciTech Connect

    Fox, D.S.

    1994-12-31

    Silicon carbide fiber-reinforced silicon carbide (SiC/SiC) was exposed for 100 hours to dry, flowing oxygen. Oxidation kinetics were determined via thermogravimetric analysis at 981{degrees}, 1204{degrees} and 1316{degrees}C (1800{degrees}, 2200{degrees} and 2400{degrees}F). The effectiveness of three external coating systems applied for oxidation protection is discussed. In all cases, weight gains were observed, and the pyrolytic carbon interface layer remained intact. A CVD SiC external coating is the most promising due to low oxidation kinetics resulting from solid silica formation. A borosilicate glass was observed on the surface of two of the materials that have boron-containing coatings.

  15. Production and characterization of nanostructured silicon carbide

    NASA Astrophysics Data System (ADS)

    Wallis, Kendra Lee

    Nanostructured materials continue to attract attention because of their new and interesting properties, which are very different from their macrostructured equivalents. Since the size of grain and surface differs, a better understanding of the microstructure, the mechanism of formation, and methods of controlling surface properties is necessary. In this study, nanostructured silicon carbide has been produced from the solid-solid reaction of a mixture of silicon nanopowder and carbon multiwalled nanotubes (MWNT) sintered by induction. A study of the reaction rate at different temperatures has yielded a value for the activation energy of 254 +/- 36 kJ/mol, and has led to the conclusion that the reaction is diffusion-controlled. A second method produced pure silicon carbide nanowires using a procedure which kept the solid reactants, silicon powder and MWNT, separated while sintering at a constant temperature of 1200°C. Silicon in the vapor-phase reacted at the surface of the MWNTs followed by diffusion of both precursors through the product phase boundary. The reaction time was varied, and a morphological study has been done describing changes in shape and size as a function of time. The initial reaction produced a layer of SiC providing the outer shell of coaxial structures with carbon nanotubes inside. As Si and C diffused through the product phase to react at the interface, the tube became filled with SiC to form solid SiC nanowires, and the outer diameter of the nanowires grew continuously as reaction time increased. After long sintering times, growth continued in two dimensions, fusing nanowires together into planar structures. In addition, the precursor form of carbon was varied, and nanowires produced by two different types of nanotubes have been studied. The produced SiC nanowires show cubic crystal structure. After a few hours of sintering, stacking faults began to occur inside the wires, and the frequency of occurrence of the stacking faults increased as

  16. Direct microwave joining of reaction bonded silicon carbide

    SciTech Connect

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

    1992-08-01

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

  17. Predicting Two-Dimensional Silicon Carbide Monolayers.

    PubMed

    Shi, Zhiming; Zhang, Zhuhua; Kutana, Alex; Yakobson, Boris I

    2015-10-27

    Intrinsic semimetallicity of graphene and silicene largely limits their applications in functional devices. Mixing carbon and silicon atoms to form two-dimensional (2D) silicon carbide (SixC1-x) sheets is promising to overcome this issue. Using first-principles calculations combined with the cluster expansion method, we perform a comprehensive study on the thermodynamic stability and electronic properties of 2D SixC1-x monolayers with 0 ≤ x ≤ 1. Upon varying the silicon concentration, the 2D SixC1-x presents two distinct structural phases, a homogeneous phase with well dispersed Si (or C) atoms and an in-plane hybrid phase rich in SiC domains. While the in-plane hybrid structure shows uniform semiconducting properties with widely tunable band gap from 0 to 2.87 eV due to quantum confinement effect imposed by the SiC domains, the homogeneous structures can be semiconducting or remain semimetallic depending on a superlattice vector which dictates whether the sublattice symmetry is topologically broken. Moreover, we reveal a universal rule for describing the electronic properties of the homogeneous SixC1-x structures. These findings suggest that the 2D SixC1-x monolayers may present a new "family" of 2D materials, with a rich variety of properties for applications in electronics and optoelectronics. PMID:26394207

  18. Separation of Nuclear Fuel Surrogates from Silicon Carbide Inert Matrix

    SciTech Connect

    Dr. Ronald Baney

    2008-12-15

    The objective of this project has been to identify a process for separating transuranic species from silicon carbide (SiC). Silicon carbide has become one of the prime candidates for the matrix in inert matrix fuels, (IMF) being designed to reduce plutonium inventories and the long half-lives actinides through transmutation since complete reaction is not practical it become necessary to separate the non-transmuted materials from the silicon carbide matrix for ultimate reprocessing. This work reports a method for that required process.l

  19. In situ ion irradiation of zirconium carbide

    NASA Astrophysics Data System (ADS)

    Ulmer, Christopher J.; Motta, Arthur T.; Kirk, Mark A.

    2015-11-01

    Zirconium carbide (ZrC) is a candidate material for use in one of the layers of TRISO coated fuel particles to be used in the Generation IV high-temperature, gas-cooled reactor, and thus it is necessary to study the effects of radiation damage on its structure. The microstructural evolution of ZrCx under irradiation was studied in situ using the Intermediate Voltage Electron Microscope (IVEM) at Argonne National Laboratory. Samples of nominal stoichiometries ZrC0.8 and ZrC0.9 were irradiated in situ using 1 MeV Kr2+ ions at various irradiation temperatures (T = 20 K-1073 K). In situ experiments made it possible to continuously follow the evolution of the microstructure during irradiation using diffraction contrast imaging. Images and diffraction patterns were systematically recorded at selected dose points. After a threshold dose during irradiations conducted at room temperature and below, black-dot defects were observed which accumulated until saturation. Once created, the defect clusters did not move or get destroyed during irradiation so that at the final dose the low temperature microstructure consisted only of a saturation density of small defect clusters. No long-range migration of the visible defects or dynamic defect creation and elimination were observed during irradiation, but some coarsening of the microstructure with the formation of dislocation loops was observed at higher temperatures. The irradiated microstructure was found to be only weakly dependent on the stoichiometry.

  20. Method of preparing silicon carbide particles dispersed in an electrolytic bath for composite electroplating of metals

    DOEpatents

    Peng, Yu-Min; Wang, Jih-Wen; Liue, Chun-Ying; Yeh, Shinn-Horng

    1994-01-01

    A method for preparing silicon carbide particles dispersed in an electrolytic bath for composite electroplating of metals includes the steps of washing the silicon carbide particles with an organic solvent; washing the silicon carbide particles with an inorganic acid; grinding the silicon carbide particles; and heating the silicon carbide particles in a nickel-containing solution at a boiling temperature for a predetermined period of time.

  1. Tunable plasticity in amorphous silicon carbide films.

    PubMed

    Matsuda, Yusuke; Kim, Namjun; King, Sean W; Bielefeld, Jeff; Stebbins, Jonathan F; Dauskardt, Reinhold H

    2013-08-28

    Plasticity plays a crucial role in the mechanical behavior of engineering materials. For instance, energy dissipation during plastic deformation is vital to the sufficient fracture resistance of engineering materials. Thus, the lack of plasticity in brittle hybrid organic-inorganic glasses (hybrid glasses) often results in a low fracture resistance and has been a significant challenge for their integration and applications. Here, we demonstrate that hydrogenated amorphous silicon carbide films, a class of hybrid glasses, can exhibit a plasticity that is even tunable by controlling their molecular structure and thereby leads to an increased and adjustable fracture resistance in the films. We decouple the plasticity contribution from the fracture resistance of the films by estimating the "work-of-fracture" using a mean-field approach, which provides some insight into a potential connection between the onset of plasticity in the films and the well-known rigidity percolation threshold. PMID:23876200

  2. Development of a silicon carbide sewing thread

    NASA Technical Reports Server (NTRS)

    Sawko, Paul M.; Vasudev, Anand

    1989-01-01

    A silicon carbide (SiC) sewing thread has been designed which consists of a two-ply yarn in a 122 turns-per-meter-twist construction. Two processing aids in thread construction were evaluated. Prototype blankets were sewn using an SiC thread prepared either with polytetrafluoroethylene sizing or with an overwrap of rayon/dacron service yarn. The rayon/dacron-wrapped SiC thread was stronger, as shown by higher break-strength retention and less damage to the outer-mold-line fabric. This thread enables thermal protection system articles to be sewn or joined, or have perimeter close-out of assembled parts when using SiC fabric for high-temperature applications.

  3. Quantitative Ultrasound Characterization of Silicon Carbide Mirrors

    NASA Astrophysics Data System (ADS)

    Portune, A. R.; Haber, R. A.

    2010-02-01

    Silicon carbide mirrors were characterized using several qualitative and quantitative nondestructive ultrasound techniques in order to determine the most efficient method for rapid performance evaluations. Ultrasound testing was performed in immersion using both phased array and single transducer systems in pulse-echo configuration. C-scan images of top and bottom surface reflected signal peak amplitudes were used to qualitatively locate and identify homogeneity variations within the mirror materials. Quantitative analysis of normalized amplitude histograms revealed significant differences in homogeneity estimations between phased array and single transducer test methods. Acoustic spectroscopy over the 10-33 MHz regime identified bulk microstructural differences between high and low amplitude regions in the samples. While ultrasound phased array performed well at rapidly locating surface and subsurface heterogeneities, it could not match the resolution and clarity of single transducer C-scan images or the insight of acoustic spectroscopy analyses.

  4. Novel Silicon Carbide Detector for Active Inspections

    SciTech Connect

    F. H. Ruddy; J.G. Seidel; R.W. Flammang

    2007-03-01

    The need to address increasingly challenging inspection requirements (such as large volume objects, very fast inspection throughputs, potentially significant shielding, etc.) for such items as nuclear materials and explosives will require the use of active interrogation technologies. While these active technologies can successfully address these challenges by inducing unique, temporal signatures, the inspection environment will also induce overall “background signals” that can be orders of magnitude larger than the induced signatures. Detectors that can successfully operate in these types of customized, inspection environments (pulsed and continuous) and successfully extract induced signature data are clearly needed and will effectively define the limitations of any active inspection system. A novel silicon carbide detector is now being investigated to successfully address both neutron- and photon/bremsstrahlung-type inspection applications. While this paper describes this detector and highlights efforts related to neutron inspection, it will focus on its neutron and gamma-ray/photon detection performance in neutron- and bremssstrahlung-type inspection applications.

  5. Nanoporous Silicon Carbide for Nanoelectromechanical Systems Applications

    NASA Technical Reports Server (NTRS)

    Hossain, T.; Khan, F.; Adesida, I.; Bohn, P.; Rittenhouse, T.; Lienhard, Michael (Technical Monitor)

    2003-01-01

    A major goal of this project is to produce porous silicon carbide (PSiC) via an electroless process for eventual utilization in nanoscale sensing platforms. Results in the literature have shown a variety of porous morphologies in SiC produced in anodic cells. Therefore, predictability and reproducibility of porous structures are initial concerns. This work has concentrated on producing morphologies of known porosity, with particular attention paid toward producing the extremely high surface areas required for a porous flow sensor. We have conducted a parametric study of electroless etching conditions and characteristics of the resulting physical nanostructure and also investigated the relationship between morphology and materials properties. Further, we have investigated bulk etching of SiC using both photo-electrochemical etching and inductively-coupled-plasma reactive ion etching techniques.

  6. Amorphization of Silicon Carbide by Carbon Displacement

    SciTech Connect

    Devanathan, Ram; Gao, Fei; Weber, William J.

    2004-05-10

    We have used molecular dynamics simulations to examine the possibility of amorphizing silicon carbide (SiC) by exclusively displacing C atoms. At a defect generation corresponding to 0.2 displacements per atom, the enthalpy surpasses the level of melt-quenched SiC, the density decreases by about 15%, and the radial distribution function shows a lack of long-range order. Prior to amorphization, the surviving defects are mainly C Frenkel pairs (67%), but Si Frenkel pairs (18%) and anti-site defects (15%) are also present. The results indicate that SiC can be amorphized by C sublattice displacements. Chemical short-range disorder, arising mainly from interstitial production, plays a significant role in the amorphization.

  7. Chemical Mechanical Polishing of Silicon Carbide

    NASA Technical Reports Server (NTRS)

    Powell, J. Anthony; Pirouz

    1999-01-01

    The High Temperature Integrated Electronics and Sensors (HTIES) team at the NASA Lewis Research Center is developing silicon carbide (SiC) as an enabling electronic technology for many aerospace applications. The Lewis team is focusing on the chemical vapor deposition of the thin, single-crystal SiC films from which devices are fabricated. These films, which are deposited (i.e., epitaxially "grown") on commercial wafers, must consist of a single crystal with very few structural defects so that the derived devices perform satisfactorily and reliably. Working in collaboration (NASA grant) with Professor Pirouz of Case Western Reserve University, we developed a chemical-mechanical polishing (CMP) technique for removing the subsurface polishing damage prior to epitaxial growth of the single-crystal SiC films.

  8. Temperature-dependent reflectivity of silicon carbide

    NASA Technical Reports Server (NTRS)

    Ng, Daniel

    1992-01-01

    The spectral reflectivity of a commercial silicon carbide (SiC) ceramic surface was measured at wavelengths from 2.5 to 14.5 microns and at temperatures ranging from 358 to 520 K using a NASA-developed multiwavelength pyrometer. The SiC surface reflectivity was low at the short wavelengths, decreasing to almost zero at 10 microns, then increasing rapidly to a maximum at approximately 12.5 microns, and decreasing gradually thereafter. The reflectivity maximum increased in magnitude with increasing surface temperature. The wavelength and temperature dependence can be explained in terms of the classical dispersion theory of crystals and the Lorentz electron theory. Electronic transitions between the donor state and the conduction band states were responsible for the dispersion. The concentration of the donor state in SiC was determined to be approximately 4 x 10 exp 18 and its ionization energy was determined to be approximately 71 meV.

  9. Method of producing silicon carbide articles

    DOEpatents

    Milewski, John V.

    1985-01-01

    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.

  10. Comparison of silicon oxide and silicon carbide absorber materials in silicon thin-film solar cells

    NASA Astrophysics Data System (ADS)

    Walder, Cordula; Kellermann, Martin; Wendler, Elke; Rensberg, Jura; von Maydell, Karsten; Agert, Carsten

    2015-02-01

    Since solar energy conversion by photovoltaics is most efficient for photon energies at the bandgap of the absorbing material the idea of combining absorber layers with different bandgaps in a multijunction cell has become popular. In silicon thin-film photovoltaics a multijunction stack with more than two subcells requires a high bandgap amorphous silicon alloy top cell absorber to achieve an optimal bandgap combination. We address the question whether amorphous silicon carbide (a-SiC:H) or amorphous silicon oxide (a-SiO:H) is more suited for this type of top cell absorber. Our single cell results show a better performance of amorphous silicon carbide with respect to fill factor and especially open circuit voltage at equivalent Tauc bandgaps. The microstructure factor of single layers indicates less void structure in amorphous silicon carbide than in amorphous silicon oxide. Yet photoconductivity of silicon oxide films seems to be higher which could be explained by the material being not truly intrinsic. On the other hand better cell performance of amorphous silicon carbide absorber layers might be connected to better hole transport in the cell.

  11. Amorphous silicon carbide films prepared using vaporized silicon ink

    NASA Astrophysics Data System (ADS)

    Masuda, Takashi; Shen, Zhongrong; Takagishi, Hideyuki; Ohdaira, Keisuke; Shimoda, Tatsuya

    2014-03-01

    The deposition of wide-band-gap silicon films using nonvacuum processes rather than conventional vacuum processes is of substantial interest because it may reduce cost. Herein, we present the optical and electrical properties of p-type hydrogenated amorphous silicon carbide (a-SiC:H) films prepared using a nonvacuum process in a simple chamber with a vaporized silicon ink consisting of cyclopentasilane, cyclohexene, and decaborane. The incorporation of carbon into the silicon network induced by the addition of cyclohexene to the silicon ink resulted in an increase in the optical band gap (Eg) of films from 1.56 to 2.11 eV. The conductivity of films with Eg < 1.9 eV is comparable to that of conventional a-SiC:H films prepared using a vacuum process, while the films with Eg > 1.9 eV show lower conductivity than expected because of the incorporation of excess carbon without the formation of Si-C bonds.

  12. A review of oxide, silicon nitride, and silicon carbide brazing

    SciTech Connect

    Santella, M.L.; Moorhead, A.J.

    1987-01-01

    There is growing interest in using ceramics for structural applications, many of which require the fabrication of components with complicated shapes. Normal ceramic processing methods restrict the shapes into which these materials can be produced, but ceramic joining technology can be used to overcome many of these limitations, and also offers the possibility for improving the reliability of ceramic components. One method of joining ceramics is by brazing. The metallic alloys used for bonding must wet and adhere to the ceramic surfaces without excessive reaction. Alumina, partially stabilized zirconia, and silicon nitride have high ionic character to their chemical bonds and are difficult to wet. Alloys for brazing these materials must be formulated to overcome this problem. Silicon carbide, which has some metallic characteristics, reacts excessively with many alloys, and forms joints of low mechanical strength. The brazing characteristics of these three types of ceramics, and residual stresses in ceramic-to-metal joints are briefly discussed.

  13. Silicon carbide nanowires synthesized with phenolic resin and silicon powders

    NASA Astrophysics Data System (ADS)

    Zhao, Hongsheng; Shi, Limin; Li, Ziqiang; Tang, Chunhe

    2009-02-01

    Large-scale silicon carbide nanowires with the lengths up to several millimeters were synthesized by a coat-mix, moulding, carbonization, and high-temperature sintering process, using silicon powder and phenolic resin as the starting materials. Ordinary SiC nanowires, bamboo-like SiC nanowires, and spindle SiC nanochains are found in the fabricated samples. The ordinary SiC nanowire is a single-crystal SiC phase with a fringe spacing of 0.252 nm along the [1 1 1] growth direction. Both of the bamboo-like SiC nanowires and spindle SiC nanochains exhibit uniform periodic structures. The bamboo-like SiC nanowires consist of amorphous stem and single-crystal knots, while the spindle SiC nanochains consist of uniform spindles which grow uniformly on the entire nanowires.

  14. Silicon carbide materials for high duty seal applications

    SciTech Connect

    Berroth, K.E. )

    1990-12-01

    Properties, fabrication, and high-duty applications of silicon carbide grades are discussed. The two types of silicon carbide, i.e., reaction-bonded and sintered, are considered. The potential for adhesion and the lack of dry running abilities lead to a variety of microstructures. For reaction-bonded silicon carbide, the microstructure can be a tool for optimization of the tribological behavior. Besides the high corrosion resistance of the material, its thermal conductivity is excellent. Grain sizes of about 40-50 microns are used in high-duty applications. Reaction-bonded silicon carbide with residual content of carbon graphite has improved tribological/hydrodynamic characteristics and performs well in sealing hard faces.

  15. Conventional and Microwave Joining of Silicon Carbide Using Displacement Reactions

    NASA Technical Reports Server (NTRS)

    Kingsley, J.; Yiin, T.; Barmatz, M.

    1995-01-01

    Microwave heating was used to join Silicon Carbide rods using a thin TiC /Si tape interlayer . Microwaves quickly heated the rods and tape to temperatures where solid-state displacement reactions between TiC and Si occurred.

  16. Tribological properties of silicon carbide in metal removal process

    NASA Technical Reports Server (NTRS)

    Miyoshi, K.; Buckley, D. H.

    1980-01-01

    This paper reviews material properties of adhesion, friction and wear of single-crystal silicon carbide in contact with metals and alloys involved in a metal removal process such as grinding. The tribological properties in the metal removal processes are divided into properties which remove metal by adhesion between sliding surfaces, and metal removal by silicon carbide sliding against a metal, indenting it, and plowing a series of grooves or furrows. The paper also deals with fracture and deformation characteristics of the silicon carbide surface; the adhesion, friction and metal transfer to silicon carbide is related to the relative chemical activity of the metals. Atomic size and content of alloying elements play a dominant role in controlling adhesion and friction properties of alloys. The friction and abrasive wear decrease as the shear strength of the bulk metal increases.

  17. Silicon carbide for high-temperature heat exchangers

    NASA Astrophysics Data System (ADS)

    Penty, R. A.; Bjerklie, J. W.

    1982-02-01

    It is noted that ceramic heat exchangers are now being used industrially in low-pressure applications, such as recuperators and air preheaters, and that serious consideration is being given to using ceramic materials for high-pressure heat exchangers. The principal advantage of using ceramic heat exchangers in the candidate applications is the potential for higher temperature service or increased life over that obtainable with metallic exchangers. Silicon carbide-based materials are now in service in many areas. The use of low-pressure ceramic recuperators constructed of silicon carbide has demonstrated fuel savings exceeding 40% in high-temperature industrial furnaces. At a material temperature of 1375 C, the demonstrated lifetime of some silicon carbide tubes is 12 to 15 months. The availability of silicon carbide materials is discussed, together with properties required for designing reliable heat exchangers. Attention is also given to the usual failure mode encountered in the field.

  18. Process for preparing fine grain silicon carbide powder

    DOEpatents

    Wei, G.C.

    Method of producing fine-grain silicon carbide powder comprises combining methyltrimethoxysilane with a solution of phenolic resin, acetone and water or sugar and water, gelling the resulting mixture, and then drying and heating the obtained gel.

  19. Single-Event Effects in Silicon Carbide Power Devices

    NASA Technical Reports Server (NTRS)

    Lauenstein, Jean-Marie; Casey, Megan C.; LaBel, Kenneth A.; Ikpe, Stanley; Topper, Alyson D.; Wilcox, Edward P.; Kim, Hak; Phan, Anthony M.

    2015-01-01

    This report summarizes the NASA Electronic Parts and Packaging Program Silicon Carbide Power Device Subtask efforts in FY15. Benefits of SiC are described and example NASA Programs and Projects desiring this technology are given. The current status of the radiation tolerance of silicon carbide power devices is given and paths forward in the effort to develop heavy-ion single-event effect hardened devices indicated.

  20. High-Q silicon carbide photonic-crystal cavities

    NASA Astrophysics Data System (ADS)

    Lee, Jonathan Y.; Lu, Xiyuan; Lin, Qiang

    2015-01-01

    We demonstrate one-dimensional photonic-crystal nanobeam cavities in amorphous silicon carbide. The fundamental mode exhibits intrinsic optical quality factor as high as 7.69 × 104 with mode volume ˜ 0.60 ( λ / n ) 3 at wavelength 1.5 μm. A corresponding Purcell factor value of ˜104 is the highest reported to date in silicon carbide optical cavities. The device exhibits great potential for integrated nonlinear photonics and cavity nano-optomechanics.

  1. Silicon carbide tritium permeation barrier for steel structural components.

    SciTech Connect

    Causey, Rion A.; Garde, Joseph Maurico; Buchenauer, Dean A.; Calderoni, Pattrick; Holschuh, Thomas, Jr.; Youchison, Dennis Lee; Wright, Matt; Kolasinski, Robert D.

    2010-09-01

    Chemical vapor deposited (CVD) silicon carbide (SiC) has superior resistance to tritium permeation even after irradiation. Prior work has shown Ultrametfoam to be forgiving when bonded to substrates with large CTE differences. The technical objectives are: (1) Evaluate foams of vanadium, niobium and molybdenum metals and SiC for CTE mitigation between a dense SiC barrier and steel structure; (2) Thermostructural modeling of SiC TPB/Ultramet foam/ferritic steel architecture; (3) Evaluate deuterium permeation of chemical vapor deposited (CVD) SiC; (4) D testing involved construction of a new higher temperature (> 1000 C) permeation testing system and development of improved sealing techniques; (5) Fabricate prototype tube similar to that shown with dimensions of 7cm {theta} and 35cm long; and (6) Tritium and hermeticity testing of prototype tube.

  2. Tribological properties of silicon carbide in metal removal process

    NASA Technical Reports Server (NTRS)

    Miyoshi, K.; Buckley, D. H.

    1980-01-01

    Material properties are considered as they relate to adhesion, friction, and wear of single crystal silicon carbide in contact with metals and alloys that are likely to be involved in a metal removal process such as grinding. Metal removal from adhesion between sliding surfaces in contact and metal removal as a result of the silicon carbide sliding against a metal, indenting into it, and plowing a series of grooves or furrows are discussed. Fracture and deformation characteristics of the silicon carbide surface are also covered. The adhesion, friction, and metal transfer to silicon carbide is related to the relative chemical activity of the metals. The more active the metal, the higher the adhesion and friction, and the greater the metal transfer to silicon carbide. Atomic size and content of alloying elements play a dominant role in controlling adhesion, friction, and abrasive wear properties of alloys. The friction and abrasive wear (metal removal) decrease linearly as the shear strength of the bulk metal increases. They decrease as the solute to solvent atomic radius ratio increases or decreases linearly from unity, and with an increase of solute content. The surface fracture of silicon carbide is due to cleavages of 0001, 10(-1)0, and/or 11(-2)0 planes.

  3. Thermal properties of wood-derived silicon carbide and copper-silicon carbide composites

    NASA Astrophysics Data System (ADS)

    Pappecena, Kristen E.

    Wood-derived ceramics and composites have been of interest in recent years due to their unique microstructures, which lead to tailorable properties. The porosity and pore size distribution of each wood type is different, which yields variations in properties in the resultant materials. The thermal properties of silicon carbide ceramics and copper-silicon carbide composites derived from wood were studied as a function of their pore structures. Wood was pyrolyzed at temperatures ranging from 300-2400°C to yield porous carbon. The progression toward long-range order was studied as a function of pyrolyzation temperature. Biomorphic silicon carbide (bioSiC) is a porous ceramic material resulting from silicon melt infiltration of these porous carbon materials. BioSiC has potential applicability in many high temperature environments, particularly those in which rapid temperature changes occur. To understand the behavior of bioSiC at elevated temperatures, the thermal and thermo-mechanical properties were studied. The thermal conductivity of bioSiC from five precursors was determined using flash diffusivity at temperatures up to 1100°C. Thermal conductivity results varied with porosity, temperature and orientation, and decreased from 42-13 W/mK for porosities of 43-69%, respectively, at room temperature. The results were compared with to object-oriented finite-element analysis (OOF). OOF was also used to model and understand the heat-flow paths through the complex bioSiC microstructures. The thermal shock resistance of bioSiC was also studied, and no bioSiC sample was found to fail catastrophically after up to five thermal shock cycles from 1400°C to room temperature oil. Copper-silicon carbide composites have potential uses in thermal management applications due to the high thermal conductivity of each phase. Cu-bioSiC composites were created by electrodeposition of copper into bioSiC pores. The detrimental Cu-SiC reaction was avoided by using this room temperature

  4. Advanced Measurements of Silicon Carbide Ceramic Matrix Composites

    SciTech Connect

    Farhad Farzbod; Stephen J. Reese; Zilong Hua; Marat Khafizov; David H. Hurley

    2012-08-01

    Silicon carbide (SiC) is being considered as a fuel cladding material for accident tolerant fuel under the Light Water Reactor Sustainability (LWRS) Program sponsored by the Nuclear Energy Division of the Department of Energy. Silicon carbide has many potential advantages over traditional zirconium based cladding systems. These include high melting point, low susceptibility to corrosion, and low degradation of mechanical properties under neutron irradiation. In addition, ceramic matrix composites (CMCs) made from SiC have high mechanical toughness enabling these materials to withstand thermal and mechanical shock loading. However, many of the fundamental mechanical and thermal properties of SiC CMCs depend strongly on the fabrication process. As a result, extrapolating current materials science databases for these materials to nuclear applications is not possible. The “Advanced Measurements” work package under the LWRS fuels pathway is tasked with the development of measurement techniques that can characterize fundamental thermal and mechanical properties of SiC CMCs. An emphasis is being placed on development of characterization tools that can used for examination of fresh as well as irradiated samples. The work discuss in this report can be divided into two broad categories. The first involves the development of laser ultrasonic techniques to measure the elastic and yield properties and the second involves the development of laser-based techniques to measurement thermal transport properties. Emphasis has been placed on understanding the anisotropic and heterogeneous nature of SiC CMCs in regards to thermal and mechanical properties. The material properties characterized within this work package will be used as validation of advanced materials physics models of SiC CMCs developed under the LWRS fuels pathway. In addition, it is envisioned that similar measurement techniques can be used to provide process control and quality assurance as well as measurement of

  5. Friction and wear behavior of single-crystal silicon carbide in contact with titanium

    NASA Technical Reports Server (NTRS)

    Miyoshi, K.; Buckley, D. H.

    1977-01-01

    Sliding friction experiments were conducted with single crystal silicon carbide in sliding contact with titanium. Results indicate that the friction coefficient is greater in vacuum than in argon and that this is due to the greater adhesion or adhesive transfer in vacuum. Thin films of silicon carbide transferred to titanium also adhered to silicon carbide both in argon at atmospheric pressure and in high vacuum. Cohesive bonds fractured on both the silicon carbide and titanium surfaces. The wear debris of silicon carbide created by fracture plowed the silicon carbide surface in a plastic manner. The friction characteristics of titanium in contact with silicon carbide were sensitive to the surface roughness of silicon carbide, and the friction coefficients were higher for a rough surface of silicon carbide than for a smooth one. The difference in friction results was due to plastic deformation (plowing of titanium).

  6. Understanding the Irradiation Behavior of Zirconium Carbide

    SciTech Connect

    Motta, Arthur; Sridharan, Kumar; Morgan, Dane; Szlufarska, Izabela

    2013-10-11

    Zirconium carbide (ZrC) is being considered for utilization in high-temperature gas-cooled reactor fuels in deep-burn TRISO fuel. Zirconium carbide possesses a cubic B1-type crystal structure with a high melting point, exceptional hardness, and good thermal and electrical conductivities. The use of ZrC as part of the TRISO fuel requires a thorough understanding of its irradiation response. However, the radiation effects on ZrC are still poorly understood. The majority of the existing research is focused on the radiation damage phenomena at higher temperatures (>450{degree}C) where many fundamental aspects of defect production and kinetics cannot be easily distinguished. Little is known about basic defect formation, clustering, and evolution of ZrC under irradiation, although some atomistic simulation and phenomenological studies have been performed. Such detailed information is needed to construct a model describing the microstructural evolution in fast-neutron irradiated materials that will be of great technological importance for the development of ZrC-based fuel. The goal of the proposed project is to gain fundamental understanding of the radiation-induced defect formation in zirconium carbide and irradiation response by using a combination of state-of-the-art experimental methods and atomistic modeling. This project will combine (1) in situ ion irradiation at a specialized facility at a national laboratory, (2) controlled temperature proton irradiation on bulk samples, and (3) atomistic modeling to gain a fundamental understanding of defect formation in ZrC. The proposed project will cover the irradiation temperatures from cryogenic temperature to as high as 800{degree}C, and dose ranges from 0.1 to 100 dpa. The examination of this wide range of temperatures and doses allows us to obtain an experimental data set that can be effectively used to exercise and benchmark the computer calculations of defect properties. Combining the examination of radiation

  7. Silicon nano-carbide in strengthening and ceramic technologies

    NASA Astrophysics Data System (ADS)

    Rudneva, V. V.; Galevsky, G. V.; Kozyrev, N. A.

    2015-09-01

    Technological advantages and conditions of new quality assurance of coatings and products, provided by silicon nano-carbide, have been ascertained in the course of composite electrodeposition of coatings, structural ceramics patterning, and surface hardening of steels via electro-explosive alloying. Silicon nano-carbide has been recommended to be used as a component of wear and corrosion resistant chromium carbide electrodeposited coatings, which can be operated at high temperatures and used for strengthening tools and equipment including those with a complex microrelief of functional surfaces. Silicon nano-carbide as a component of composite “silicon carbide - boron - carbon” can be applied to produce ceramic half products via solid phase sintering in argon under pressure of 0.1 MPa and temperature 2273 K. Application of silicon nano-carbide in technology of tool steel surface hardening via electroexplosive alloying ensures obtaining of a high micro-hard, wear and heat resistant shielding layer which is about 20 μm deep.

  8. Metal-like self-organization of periodic nanostructures on silicon and silicon carbide under femtosecond laser pulses

    SciTech Connect

    Gemini, Laura; Hashida, Masaki; Shimizu, Masahiro; Miyasaka, Yasuhiro; Inoue, Shunsuke; Tokita, Shigeki; Sakabe, Shuji; Limpouch, Jiri; Mocek, Tomas

    2013-11-21

    Periodic structures were generated on Si and SiC surfaces by irradiation with femtosecond laser pulses. Self-organized structures with spatial periodicity of approximately 600 nm appear on silicon and silicon carbide in the laser fluence range just above the ablation threshold and upon irradiation with a large number of pulses. As in the case of metals, the dependence of the spatial periodicity on laser fluence can be explained by the parametric decay of laser light into surface plasma waves. The results show that the proposed model might be universally applicable to any solid state material.

  9. Process for coating an object with silicon carbide

    NASA Technical Reports Server (NTRS)

    Levin, Harry (Inventor)

    1989-01-01

    A process for coating a carbon or graphite object with silicon carbide by contacting it with silicon liquid and vapor over various lengths of contact time. In the process, a stream of silicon-containing precursor material in gaseous phase below the decomposition temperature of said gas and a co-reactant, carrier or diluent gas such as hydrogen is passed through a hole within a high emissivity, thin, insulating septum into a reaction chamber above the melting point of silicon. The thin septum has one face below the decomposition temperature of the gas and an opposite face exposed to the reaction chamber. The precursor gas is decomposed directly to silicon in the reaction chamber. A stream of any decomposition gas and any unreacted precursor gas from said reaction chamber is removed. The object within the reaction chamber is then contacted with silicon, and recovered after it has been coated with silicon carbide.

  10. Aluminum-silicon eutectic alloy improves electrical and mechanical contact to silicon carbide

    NASA Technical Reports Server (NTRS)

    Shier, J. S.

    1970-01-01

    Alloy contact layer is made at relatively low temperature and has good wetting characteristics. Contacts adhere well to silicon carbide surface, penetrating about 300 to 500 angstroms into it. Contacts are ohmic on p-type silicon carbide and blocking on n-type.

  11. Bright Single Photon Emitter in Silicon Carbide

    NASA Astrophysics Data System (ADS)

    Lienhard, Benjamin; Schroeder, Tim; Mouradian, Sara; Dolde, Florian; Trong Tran, Toan; Aharonovich, Igor; Englund, Dirk

    Efficient, on-demand, and robust single photon emitters are of central importance to many areas of quantum information processing. Over the past 10 years, color centers in solids have emerged as excellent single photon emitters. Color centers in diamond are among the most intensively studied single photon emitters, but recently silicon carbide (SiC) has also been demonstrated to be an excellent host material. In contrast to diamond, SiC is a technologically important material that is widely used in optoelectronics, high power electronics, and microelectromechanical systems. It is commercially available in sizes up to 6 inches and processes for device engineering are well developed. We report on a visible-spectrum single photon emitter in 4H-SiC. The emitter is photostable at both room and low temperatures, and it enables 2 million photons/second from unpatterned bulk SiC. We observe two classes of orthogonally polarized emitters, each of which has parallel absorption and emission dipole orientations. Low temperature measurements reveal a narrow zero phonon line with linewidth < 0.1 nm that accounts for more than 30% of the total photoluminescence spectrum. To our knowledge, this SiC color emitter is the brightest stable room-temperature single photon emitter ever observed.

  12. Palladium Implanted Silicon Carbide for Hydrogen Sensing

    NASA Technical Reports Server (NTRS)

    Muntele, C. I.; Ila, D.; Zimmerman, R. L.; Muntele, L.; Poker, D. B.; Hensley, D. K.; Larkin, David (Technical Monitor)

    2001-01-01

    Silicon carbide is intended for use in fabrication of high-temperature, efficient hydrogen sensors. Traditionally, when a palladium coating is applied on the exposed surface of SiC, the chemical reaction between palladium and hydrogen produces a detectable change in the surface chemical potential. We have produced both a palladium coated SiC as well as a palladium, ion implanted SiC sensor. The palladium implantation was done at 500 C into the Si face of 6H, N-type SiC at various energies, and at various fluences. Then, we measured the hydrogen sensitivity response of each fabricated sensor by exposing them to hydrogen while monitoring the current flow across the p-n junction(s), with respect to time. The sensitivity of each sensor was measured at temperatures between 27 and 300 C. The response of the SiC sensors produced by Pd implantation has revealed a completely different behaviour than the SiC sensors produced by Pd deposition. In the Pd-deposited SiC sensors as well as in the ones reported in the literature, the current rises in the presence of hydrogen at room temperature as well as at elevated temperatures. In the case of Pd-implanted SiC sensors, the current decreases in the presence of hydrogen whenever the temperature is raised above 100 C. We will present the details and conclusions from the results obtained during this meeting.

  13. Improved silicon carbide for advanced heat engines

    NASA Technical Reports Server (NTRS)

    Whalen, Thomas J.

    1989-01-01

    The development of high strength, high reliability silicon carbide parts with complex shapes suitable for use in advanced heat engines is studied. Injection molding was the forming method selected for the program because it is capable of forming complex parts adaptable for mass production on an economically sound basis. The goals were to reach a Weibull characteristic strength of 550 MPa (80 ksi) and a Weibull modulus of 16 for bars tested in four-point loading. Statistically designed experiments were performed throughout the program and a fluid mixing process employing an attritor mixer was developed. Compositional improvements in the amounts and sources of boron and carbon used and a pressureless sintering cycle were developed which provided samples of about 99 percent of theoretical density. Strengths were found to improve significantly by annealing in air. Strengths in excess of 550 MPa (80 ksi) with Weibull modulus of about 9 were obtained. Further improvements in Weibull modulus to about 16 were realized by proof testing. This is an increase of 86 percent in strength and 100 percent in Weibull modulus over the baseline data generated at the beginning of the program. Molding yields were improved and flaw distributions were observed to follow a Poisson process. Magic angle spinning nuclear magnetic resonance spectra were found to be useful in characterizing the SiC powder and the sintered samples. Turbocharger rotors were molded and examined as an indication of the moldability of the mixes which were developed in this program.

  14. Material testing of silicon carbide mirrors

    NASA Astrophysics Data System (ADS)

    Witkin, David B.; Palusinski, Iwona A.

    2009-08-01

    The Aerospace Corporation is developing a space qualification method for silicon carbide optical systems that covers material verification through system development. One of the initial efforts has been to establish testing protocols for material properties. Three different tests have been performed to determine mechanical properties of SiC: modulus of rupture, equibiaxial flexural strength and fracture toughness. Testing materials and methods have been in accordance with the respective ASTM standards. Material from four vendors has been tested to date, as part of the MISSE flight program and other programs. Data analysis has focused on the types of issues that are important when building actual components- statistical modeling of test results, understanding batch-to-batch or other source material variations, and relating mechanical properties to microstructures. Mechanical properties are needed as inputs to design trade studies and development and analysis of proof tests, and to confirm or understand the results of non-destructive evaluations of the source materials. Measuring these properties using standardized tests on a statistically valid number of samples is intended to increase confidence for purchasers of SiC spacecraft components that materials and structures will perform as intended at the highest level of reliability.

  15. Casimir forces from conductive silicon carbide surfaces

    NASA Astrophysics Data System (ADS)

    Sedighi, M.; Svetovoy, V. B.; Broer, W. H.; Palasantzas, G.

    2014-05-01

    Samples of conductive silicon carbide (SiC), which is a promising material due to its excellent properties for devices operating in severe environments, were characterized with the atomic force microscope for roughness, and the optical properties were measured with ellipsometry in a wide range of frequencies. The samples show significant far-infrared absorption due to concentration of charge carriers and a sharp surface phonon-polariton peak. The Casimir interaction of SiC with different materials is calculated and discussed. As a result of the infrared structure and beyond to low frequencies, the Casimir force for SiC-SiC and SiC-Au approaches very slowly the limit of ideal metals, while it saturates significantly below this limit if interaction with insulators takes place (SiC-SiO2). At short separations (<10 nm) analysis of the van der Waals force yielded Hamaker constants for SiC-SiC interactions lower but comparable to those of metals, which is of significance to adhesion and surface assembly processes. Finally, bifurcation analysis of microelectromechanical system actuation indicated that SiC can enhance the regime of stable equilibria against stiction.

  16. Thermal equation of state of silicon carbide

    NASA Astrophysics Data System (ADS)

    Wang, Yuejian; Liu, Zhi T. Y.; Khare, Sanjay V.; Collins, Sean Andrew; Zhang, Jianzhong; Wang, Liping; Zhao, Yusheng

    2016-02-01

    A large volume press coupled with in-situ energy-dispersive synchrotron X-ray was used to probe the change of silicon carbide (SiC) under high pressure and temperature (P-T) up to 8.1 GPa and 1100 K. The obtained pressure-volume-temperature data were fitted to a modified high-T Birch-Murnaghan equation of state, yielding values of a series of thermo-elastic parameters, such as the ambient bulk modulus KTo = 237(2) GPa, temperature derivative of the bulk modulus at a constant pressure (∂K/∂T)P = -0.037(4) GPa K-1, volumetric thermal expansivity α(0, T) = a + bT with a = 5.77(1) × 10-6 K-1 and b = 1.36(2) × 10-8 K-2, and pressure derivative of the thermal expansion at a constant temperature (∂α/∂P)T = 6.53 ± 0.64 × 10-7 K-1 GPa-1. Furthermore, we found the temperature derivative of the bulk modulus at a constant volume, (∂KT/∂T)V, equal to -0.028(4) GPa K-1 by using a thermal pressure approach. In addition, the elastic properties of SiC were determined by density functional theory through the calculation of Helmholtz free energy. The computed results generally agree well with the experimentally determined values.

  17. Methods for producing silicon carbide architectural preforms

    NASA Technical Reports Server (NTRS)

    DiCarlo, James A. (Inventor); Yun, Hee (Inventor)

    2010-01-01

    Methods are disclosed for producing architectural preforms and high-temperature composite structures containing high-strength ceramic fibers with reduced preforming stresses within each fiber, with an in-situ grown coating on each fiber surface, with reduced boron within the bulk of each fiber, and with improved tensile creep and rupture resistance properties for each fiber. The methods include the steps of preparing an original sample of a preform formed from a pre-selected high-strength silicon carbide ceramic fiber type, placing the original sample in a processing furnace under a pre-selected preforming stress state and thermally treating the sample in the processing furnace at a pre-selected processing temperature and hold time in a processing gas having a pre-selected composition, pressure, and flow rate. For the high-temperature composite structures, the method includes additional steps of depositing a thin interphase coating on the surface of each fiber and forming a ceramic or carbon-based matrix within the sample.

  18. Silicon Carbide Technologies for Lightweighted Aerospace Mirrors

    NASA Astrophysics Data System (ADS)

    Matson, L.; Chen, M.; Deblonk, B.; Palusinski, I.

    The use of monolithic glass and beryllium to produce lightweighted aerospace mirror systems has reached its limits due to the long lead times, high processing costs, environmental effects and launch load/weight requirements. New material solutions and manufacturing processes are required to meet DoD's directed energy weapons, reconnaissance/surveillance, and secured communications needs. Over the past several years the Air Force, MDA, and NASA has focused their efforts on the fabrication, lightweighting, and scale-up of numerous silicon carbide (SiC) based materials. It is anticipated that SiC can be utilized for most applications from cryogenic to high temperatures. This talk will focus on describing the SOA for these (near term) SiC technology solutions for making mirror structural substrates, figuring and finishing technologies being investigated to reduce cost time and cost, and non-destructive evaluation methods being investigated to help eliminate risk. Mirror structural substrates made out of advanced engineered materials (far term solutions) such as composites, foams, and microsphere arrays for ultra lightweighting will also be briefly discussed.

  19. Casimir force measurements from silicon carbide surfaces

    NASA Astrophysics Data System (ADS)

    Sedighi, M.; Svetovoy, V. B.; Palasantzas, G.

    2016-02-01

    Using an atomic force microscope we performed measurements of the Casimir force between a gold- coated (Au) microsphere and doped silicon carbide (SiC) samples. The last of these is a promising material for devices operating under severe environments. The roughness of the interacting surfaces was measured to obtain information for the minimum separation distance upon contact. Ellipsometry data for both systems were used to extract optical properties needed for the calculation of the Casimir force via the Lifshitz theory and for comparison to the experiment. Special attention is devoted to the separation of the electrostatic contribution to the measured total force. Our measurements demonstrate large contact potential V0(≈0.67 V ) , and a relatively small density of charges trapped in SiC. Knowledge of both Casimir and electrostatic forces between interacting materials is not only important from the fundamental point of view, but also for device applications involving actuating components at separations of less than 200 nm where surface forces play dominant role.

  20. The diffusion bonding of silicon carbide and boron carbide using refractory metals

    SciTech Connect

    Cockeram, B.V.

    1999-10-01

    Joining is an enabling technology for the application of structural ceramics at high temperatures. Metal foil diffusion bonding is a simple process for joining silicon carbide or boron carbide by solid-state, diffusive conversion of the metal foil into carbide and silicide compounds that produce bonding. Metal diffusion bonding trials were performed using thin foils (5 {micro}m to 100 {micro}m) of refractory metals (niobium, titanium, tungsten, and molybdenum) with plates of silicon carbide (both {alpha}-SiC and {beta}-SiC) or boron carbide that were lapped flat prior to bonding. The influence of bonding temperature, bonding pressure, and foil thickness on bond quality was determined from metallographic inspection of the bonds. The microstructure and phases in the joint region of the diffusion bonds were evaluated using SEM, microprobe, and AES analysis. The use of molybdenum foil appeared to result in the highest quality bond of the metal foils evaluated for the diffusion bonding of silicon carbide and boron carbide. Bonding pressure appeared to have little influence on bond quality. The use of a thinner metal foil improved the bond quality. The microstructure of the bond region produced with either the {alpha}-SiC and {beta}-SiC polytypes were similar.

  1. Method for forming fibrous silicon carbide insulating material

    DOEpatents

    Wei, George C.

    1984-01-01

    A method whereby silicon carbide-bonded SiC fiber composites are prepared from carbon-bonded C fiber composites is disclosed. Carbon-bonded C fiber composite material is treated with gaseous silicon monoxide generated from the reaction of a mixture of colloidal silica and carbon black at an elevated temperature in an argon atmosphere. The carbon in the carbon bond and fiber is thus chemically converted to SiC resulting in a silicon carbide-bonded SiC fiber composite that can be used for fabricating dense, high-strength high-toughness SiC composites or as thermal insulating materials in oxidizing environments.

  2. Method for forming fibrous silicon carbide insulating material

    DOEpatents

    Wei, G.C.

    1983-10-12

    A method whereby silicon carbide-bonded SiC fiber composites are prepared from carbon-bonded C fiber composites is disclosed. Carbon-bonded C fiber composite material is treated with gaseous silicon monoxide generated from the reaction of a mixture of colloidal silica and carbon black at an elevated temperature in an argon atmosphere. The carbon in the carbon bond and fiber is thus chemically converted to SiC resulting in a silicon carbide-bonded SiC fiber composite that can be used for fabricating dense, high-strength high-toughness SiC composites or as thermal insulating materials in oxidizing environments.

  3. Surface Figure Measurement of Silicon Carbide Mirrors at Cryogenic Temperatures

    NASA Technical Reports Server (NTRS)

    Blake, Peter; Mink, Ronald G.; Chambers, John; Robinson, F. David; Content, David; Davila, Pamela

    2005-01-01

    The surface figure of a developmental silicon carbide mirror, cooled to 87 K and then 20 K within a cryostat, was measured with unusually high precision at the Goddard Space Flight Center (GSFC). The concave spherical mirror, with a radius of 600 mm and a clear aperture of 150 mm, was fabricated of sintered silicon carbide. The mirror was mounted to an interface plate representative of an optical bench, made of the material Cesic@, a composite of silicon, carbon, and silicon carbide. The change in optical surface figure as the mirror and interface plate cooled from room temperature to 20 K was 3.7 nm rms, with a standard uncertainty of 0.23 nm in the rms statistic. Both the cryo-change figure and the uncertainty are among the lowest such figures yet published. This report describes the facilities, experimental methods, and uncertainty analysis of the measurements.

  4. Occurrence of airborne silicon carbide fibers during industrial production of silicon carbide.

    PubMed

    Bye, E; Eduard, W; Gjønnes, J; Sørbrøden, E

    1985-04-01

    Airborne dust from the production of silicon carbide has been analyzed for particle morphology and composition. Fibers of alpha silicon carbide were identified by scanning electron microscopy (SEM) combined with energy dispersive X-ray spectrometry (EDS) and transmission electron microscopy (TEM) with selected area electron diffraction techniques (SAED). Micrographs taken at high magnification revealed several stacking periods along the fiber axis, and one or more of the polytypes 2H, 4H, or 6H could be distinguished. Preliminary investigations applying SEM showed that 80% of the fibers had diameters of less than 0.5 micron and a length greater than 5 micron. Fiber concentrations were examined by the counting of stationary and personal samples in an optical phase contrast microscope. The fiber levels in the three plants investigated were low and less than 1 fiber/cc of air (10(6) fibers/m3). Dust samples from the handling of raw material, including recycled material, contained up to 5 fibers/cc (5 X 10(6) fibers/m3). PMID:4001899

  5. Interface reactions between silicon carbide and interlayers in silicon carbide copper metal matrix composites

    NASA Astrophysics Data System (ADS)

    Köck, T.; Brendel, A.; Bolt, H.

    2007-05-01

    Novel copper matrix composites reinforced with silicon carbide fibres are considered as a new generation of heat sink materials for the divertor of future fusion reactors. The divertor is exposed to intense particle bombardment and heat loads of up to 15 MW m-2. This component consists of the plasma-facing material which is bonded to the actively cooled heat sink. Due to its high thermal conductivity of about 400 W m-1 K-1 copper is a promising material for the heat sink. To increase the mechanical properties of copper at working temperature (823 K), silicon carbide fibres with a diameter of 140 μm are used to reinforce the interface area between the plasma-facing material and the heat sink. Push-out tests show that the adhesion between SiC fibre and Cu matrix without any interlayer is very low. To increase the fibre-matrix bonding the fibres are coated with Cr and W with a thickness of 300-400 nm before Cu deposition by magnetron sputtering. Push-out tests on these modified fibres show a significant increase in adhesion compared to the fibres without interlayer. XRD investigations after a heat treatment at 923 K show a chromium carbide (Cr23C6, Cr3C2) formation and the absence of chromium silicides. In the case of a W interlayer a W2C formation is detected and also no tungsten silicides. Single-fibre tensile tests were performed to investigate the influence of the reaction zone on the ultimate tensile strength of the fibres. The ultimate tensile strength for fibres without interlayer remains constant at about 2200 MPa after annealing at 923 K. The fibres with chromium and tungsten interlayers, respectively, show a decrease of about 30% of the ultimate tensile strength after the heat treatment at 923 K.

  6. Excitation and recombination dynamics of vacancy-related spin centers in silicon carbide

    SciTech Connect

    Hain, T. C.; Hertel, T.; Fuchs, F.; Astakhov, G. V.; Soltamov, V. A.; Baranov, P. G.; Dyakonov, V.

    2014-04-07

    We generate silicon vacancy related defects in high-quality epitaxial silicon carbide layers by means of electron irradiation. By controlling the irradiation fluence, the defect concentration is varied over several orders of magnitude. We establish the excitation profile for optical pumping of these defects and evaluate the optimum excitation wavelength of 770 nm. We also measure the photoluminescence dynamics at room temperature and find a monoexponential decay with a characteristic lifetime of 6.1 ns. The integrated photoluminescence intensity depends linear on the excitation power density up to 20 kW/cm{sup 2}, indicating a relatively small absorption cross section of these defects.

  7. Diamond-Silicon Carbide Composite And Method For Preparation Thereof

    DOEpatents

    Qian, Jiang; Zhao, Yusheng

    2005-09-06

    Fully dense, diamond-silicon carbide composites are prepared from ball-milled microcrystalline diamond/amorphous silicon powder mixture. The ball-milled powder is sintered (P=5-8 GPa, T=1400K-2300K) to form composites having high fracture toughness. A composite made at 5 GPa/1673K had a measured fracture toughness of 12 MPa.multidot.m.sup.1/2. By contrast, liquid infiltration of silicon into diamond powder at 5 GPa/1673K produces a composite with higher hardness but lower fracture toughness. X-ray diffraction patterns and Raman spectra indicate that amorphous silicon is partially transformed into nanocrystalline silicon at 5 GPa/873K, and nanocrystalline silicon carbide forms at higher temperatures.

  8. Microwave versus conventional sintering of silicon carbide tiles

    SciTech Connect

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

    1997-05-07

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

  9. Silicon Carbide Diodes Performance Characterization and Comparison With Silicon Devices

    NASA Technical Reports Server (NTRS)

    Lebron-Velilla, Ramon C.; Schwarze, Gene E.; Trapp, Scott

    2003-01-01

    Commercially available silicon carbide (SiC) Schottky diodes from different manufacturers were electrically tested and characterized at room temperature. Performed electrical tests include steady state forward and reverse I-V curves, as well as switching transient tests performed with the diodes operating in a hard switch dc-to-dc buck converter. The same tests were performed in current state of the art silicon (Si) and gallium arsenide (GaAs) Schottky and pn junction devices for evaluation and comparison purposes. The SiC devices tested have a voltage rating of 200, 300, and 600 V. The comparison parameters are forward voltage drop at rated current, reverse current at rated voltage and peak reverse recovery currents in the dc to dc converter. Test results show that steady state characteristics of the tested SiC devices are not superior to the best available Si Schottky and ultra fast pn junction devices. Transient tests reveal that the tested SiC Schottky devices exhibit superior transient behavior. This is more evident at the 300 and 600 V rating where SiC Schottky devices showed drastically lower reverse recovery currents than Si ultra fast pn diodes of similar rating.

  10. Palladium-defect complexes in diamond and silicon carbide

    NASA Astrophysics Data System (ADS)

    Abiona, A. A.; Kemp, W.; Timmers, H.; Bharuth-Ram, K.

    2015-04-01

    Time Differential Perturbed Angular Correlations (TDPAC) studies, supported by Density Functional Theory (DFT) modelling, have shown that palladium atoms in silicon and germanium pair with vacancies. Building on these results, here we present DFT predictions and some tentative TDPAC results on palladium-defect complexes and site locations of palladium impurities in diamond and silicon carbide. For both diamond and silicon carbide, the DFT calculations predict that a split-vacancy V-PdBI-V complex is favoured, with the palladium atom on a bond-centred interstitial site having a nearest-neighbour semi-vacancy on either side. Consistent with experimental results, this configuration is also assigned to palladium complexes in silicon and germanium. For silicon carbide, the DFT modelling predicts furthermore that a palladium atom in replacing a carbon atom moves to a bond-centred interstitial site and pairs with a silicon vacancy to form a complex that is more stable than that of a palladium atom which replaces a silicon atom and then moves to a bond-centred interstitial site pairings with a carbon vacancy. These two competing alternatives differ by 8.94 eV. The favourable pairing with a silicon vacancy is also supported independently by TRIM Monte Carlo calculations, which predict that more silicon vacancies than carbon vacancies are created during heavy ion. implantation.

  11. Amorphous silicon carbide passivating layers for crystalline-silicon-based heterojunction solar cells

    NASA Astrophysics Data System (ADS)

    Boccard, Mathieu; Holman, Zachary C.

    2015-08-01

    Amorphous silicon enables the fabrication of very high-efficiency crystalline-silicon-based solar cells due to its combination of excellent passivation of the crystalline silicon surface and permeability to electrical charges. Yet, amongst other limitations, the passivation it provides degrades upon high-temperature processes, limiting possible post-deposition fabrication possibilities (e.g., forcing the use of low-temperature silver pastes). We investigate the potential use of intrinsic amorphous silicon carbide passivating layers to sidestep this issue. The passivation obtained using device-relevant stacks of intrinsic amorphous silicon carbide with various carbon contents and doped amorphous silicon are evaluated, and their stability upon annealing assessed, amorphous silicon carbide being shown to surpass amorphous silicon for temperatures above 300 °C. We demonstrate open-circuit voltage values over 700 mV for complete cells, and an improved temperature stability for the open-circuit voltage. Transport of electrons and holes across the hetero-interface is studied with complete cells having amorphous silicon carbide either on the hole-extracting side or on the electron-extracting side, and a better transport of holes than of electrons is shown. Also, due to slightly improved transparency, complete solar cells using an amorphous silicon carbide passivation layer on the hole-collecting side are demonstrated to show slightly better performances even prior to annealing than obtained with a standard amorphous silicon layer.

  12. Amorphous silicon carbide passivating layers for crystalline-silicon-based heterojunction solar cells

    DOE PAGESBeta

    Boccard, Mathieu; Holman, Zachary C.

    2015-08-14

    With this study, amorphous silicon enables the fabrication of very high-efficiency crystalline-silicon-based solar cells due to its combination of excellent passivation of the crystalline silicon surface and permeability to electrical charges. Yet, amongst other limitations, the passivation it provides degrades upon high-temperature processes, limiting possible post-deposition fabrication possibilities (e.g., forcing the use of low-temperature silver pastes). We investigate the potential use of intrinsic amorphous silicon carbide passivating layers to sidestep this issue. The passivation obtained using device-relevant stacks of intrinsic amorphous silicon carbide with various carbon contents and doped amorphous silicon are evaluated, and their stability upon annealing assessed, amorphousmore » silicon carbide being shown to surpass amorphous silicon for temperatures above 300°C. We demonstrate open-circuit voltage values over 700 mV for complete cells, and an improved temperature stability for the open-circuit voltage. Transport of electrons and holes across the hetero-interface is studied with complete cells having amorphous silicon carbide either on the hole-extracting side or on the electron-extracting side, and a better transport of holes than of electrons is shown. Also, due to slightly improved transparency, complete solar cells using an amorphous silicon carbide passivation layer on the hole-collecting side are demonstrated to show slightly better performances even prior to annealing than obtained with a standard amorphous silicon layer.« less

  13. Amorphous silicon carbide passivating layers for crystalline-silicon-based heterojunction solar cells

    SciTech Connect

    Boccard, Mathieu; Holman, Zachary C.

    2015-08-14

    With this study, amorphous silicon enables the fabrication of very high-efficiency crystalline-silicon-based solar cells due to its combination of excellent passivation of the crystalline silicon surface and permeability to electrical charges. Yet, amongst other limitations, the passivation it provides degrades upon high-temperature processes, limiting possible post-deposition fabrication possibilities (e.g., forcing the use of low-temperature silver pastes). We investigate the potential use of intrinsic amorphous silicon carbide passivating layers to sidestep this issue. The passivation obtained using device-relevant stacks of intrinsic amorphous silicon carbide with various carbon contents and doped amorphous silicon are evaluated, and their stability upon annealing assessed, amorphous silicon carbide being shown to surpass amorphous silicon for temperatures above 300°C. We demonstrate open-circuit voltage values over 700 mV for complete cells, and an improved temperature stability for the open-circuit voltage. Transport of electrons and holes across the hetero-interface is studied with complete cells having amorphous silicon carbide either on the hole-extracting side or on the electron-extracting side, and a better transport of holes than of electrons is shown. Also, due to slightly improved transparency, complete solar cells using an amorphous silicon carbide passivation layer on the hole-collecting side are demonstrated to show slightly better performances even prior to annealing than obtained with a standard amorphous silicon layer.

  14. Amorphous silicon carbide passivating layers for crystalline-silicon-based heterojunction solar cells

    SciTech Connect

    Boccard, Mathieu; Holman, Zachary C.

    2015-08-14

    Amorphous silicon enables the fabrication of very high-efficiency crystalline-silicon-based solar cells due to its combination of excellent passivation of the crystalline silicon surface and permeability to electrical charges. Yet, amongst other limitations, the passivation it provides degrades upon high-temperature processes, limiting possible post-deposition fabrication possibilities (e.g., forcing the use of low-temperature silver pastes). We investigate the potential use of intrinsic amorphous silicon carbide passivating layers to sidestep this issue. The passivation obtained using device-relevant stacks of intrinsic amorphous silicon carbide with various carbon contents and doped amorphous silicon are evaluated, and their stability upon annealing assessed, amorphous silicon carbide being shown to surpass amorphous silicon for temperatures above 300 °C. We demonstrate open-circuit voltage values over 700 mV for complete cells, and an improved temperature stability for the open-circuit voltage. Transport of electrons and holes across the hetero-interface is studied with complete cells having amorphous silicon carbide either on the hole-extracting side or on the electron-extracting side, and a better transport of holes than of electrons is shown. Also, due to slightly improved transparency, complete solar cells using an amorphous silicon carbide passivation layer on the hole-collecting side are demonstrated to show slightly better performances even prior to annealing than obtained with a standard amorphous silicon layer.

  15. A study of silicon carbide synthesis from waste serpentine.

    PubMed

    Cheng, T W; Hsu, C W

    2006-06-01

    There are 60000 tons of serpentine wastes produced in year 2004 in Taiwan. This is due to the well-developed joints in the serpentine ore body as well as the stringent requirements of the particle size and chemical composition of serpentine by iron making company. The waste also creates considerable environmental problems. The purpose of this study is reutilization of waste serpentine to produce a high value silica powder after acid leaching. These siliceous microstructure products obtained from serpentine would be responsible for high reactivity and characteristic molecular sieving effect. In this study, the amorphous silica powder was then synthesized to silicon carbide with the C/SiO(2) molar ratio of 3. The experiment results show that silicon carbide can be synthesized in 1550 degrees C. The formed silicon carbide was whisker beta type SiC which can be used as raw materials for industry. PMID:16405956

  16. Processing, texture and mechanical properties of sintered silicon carbide

    NASA Technical Reports Server (NTRS)

    Landfermann, H.; Hausner, H.

    1988-01-01

    With regard to its favorable properties, in particular those shown at high temperatures, silicon carbide is of great interest for applications related to the construction of engines and turbines. Thus, silicon carbide could replace heat-resisting alloys with the objective to achieve a further increase in operational temperature. The present investigation is concerned with approaches which can provide silicon carbide material with suitable properties for the intended applications, taking into account the relations between characteristics of the raw material, material composition, sinter conditions, and results of the sintering process. The effects of density and texture formation on the mechanical properties are studied. It is found that a dense material with a fine-grained microstructure provides optimal mechanical properties, while any deviation from this ideal condition can lead to a considerable deterioration with respect to the material properties.

  17. Solar silicon from directional solidification of MG silicon produced via the silicon carbide route

    NASA Technical Reports Server (NTRS)

    Rustioni, M.; Margadonna, D.; Pirazzi, R.; Pizzini, S.

    1986-01-01

    A process of metallurgical grade (MG) silicon production is presented which appears particularly suitable for photovoltaic (PV) applications. The MG silicon is prepared in a 240 KVA, three electrode submerged arc furnace, starting from high grade quartz and high purity silicon carbide. The silicon smelted from the arc furnace was shown to be sufficiently pure to be directionally solidified to 10 to 15 kg. After grinding and acid leaching, had a material yield larger than 90%. With a MG silicon feedstock containing 3 ppmw B, 290 ppmw Fe, 190 ppmw Ti, and 170 ppmw Al, blended with 50% of off grade electronic grade (EG) silicon to reconduct the boron content to a concentration acceptable for solar cell fabrication, the 99% of deep level impurities were concentrated in the last 5% of the ingot. Quite remarkably this material has OCV values higher tham 540 mV and no appreciable shorts due to SiC particles.

  18. Liquid-phase reaction-bonding of silicon carbide using alloyed silicon-molybdenum melts

    SciTech Connect

    Messner, R.P.; Chiang, Y.M. . Dept. of Materials Science and Engineering)

    1990-05-01

    The authors have investigated reaction-forming of silicon carbide by the infiltration of carbonaceous preforms using alloyed silicon melts, in order to synthesize composite materials free of the residual silicon phase that has previously limited mechanical properties and upper use temperatures. In this approach, rejection of the alloying component(s) from the primary silicon carbide phase into the remaining melt results in the formation of a secondary refractory phase, such as a silicide, in place of residual free silicon. Experiments conducted in the Si-Mo melt system show that relatively dense ({gt}90%) silicon carbide-molybdenum silicide materials free of residual silicon and residual carbon can be obtained. A model for reactive infiltration based on time-dependent permeabilities is proposed. Processing variables important for control of the reaction rate relative to the infiltration rate, and associated processing flaws, are discussed.

  19. The Active Oxidation of Silicon Carbide

    NASA Technical Reports Server (NTRS)

    Jacobson, Nathan S.; Myers, Dwight L.

    2009-01-01

    The high temperature oxidation of silicon carbide occurs in two very different modes. Passive oxidation forms a protective oxide film which limits further attack of the SiC: SiC(s) + 3/2 O2(g) = SiO2(s) + CO(g) Active oxidation forms a volatile oxide and may lead to extensive attack of the SiC: SiC(s) + O2(g) = SiO(g) + CO(g) Generally passive oxidation occurs at higher oxidant pressures and active oxidation occurs at lower oxidant pressures and elevated temperatures. Active oxidation is a concern for reentry, where the flight trajectory involves the latter conditions. Thus the transition points and rates of active oxidation are a major concern. Passive/active transitions have been studied by a number of investigators. An examination of the literature indicates many questions remain regarding the effect of impurity, the hysteresis of the transition (i.e. the difference between active-to-passive and passive-toactive), and the effect of total pressure. In this study we systematically investigate each of these effects. Experiments were done in both an alumina furnace tube and a quartz furnace tube. It is known that alumina tubes release impurities such as sodium and increase the kinetics in the passive region [1]. We have observed that the active-to-passive transition occurs at a lower oxygen pressure when the experiment is conducted in alumina tubes and the resultant passive silica scale contains sodium. Thus the tests in this study are conducted in quartz tubes. The hysteresis of the transition has been discussed in the detail in the original theoretical treatise of this problem for pure silicon by Wagner [2], yet there is little mention of it in subsequent literature. Essentially Wagner points out that the active-to-passive transition is governed by the criterion for a stable Si/SiO2 equilibria and the passive-to-active transition is governed by the decomposition of the SiO2 film. A series of experiments were conducted for active-to-passive and passive

  20. Role of silicon dangling bonds in the electronic properties of epitaxial graphene on silicon carbide.

    PubMed

    Ridene, Mohamed; Kha, Calvin S; Flipse, Cees F J

    2016-03-29

    In this paper, we study the electronic properties of epitaxial graphene (EG) on silicon carbide by means of ab initio calculations based on the local spin density approximation + U method taking into account the Coulomb interaction between Si localized electrons. We show that this interaction is not completely suppressed but is screened by carbon layers grown on-top of silicon carbide. This finding leads to a good qualitative understanding of the experimental results reported on EG on silicon carbide. Our results highlight the presence of the Si localized states and might explain the anomalous Hanle curve and the high values of spin relaxation time in EG. PMID:26891244

  1. Role of silicon dangling bonds in the electronic properties of epitaxial graphene on silicon carbide

    NASA Astrophysics Data System (ADS)

    Ridene, Mohamed; Kha, Calvin S.; Flipse, Cees F. J.

    2016-03-01

    In this paper, we study the electronic properties of epitaxial graphene (EG) on silicon carbide by means of ab initio calculations based on the local spin density approximation + U method taking into account the Coulomb interaction between Si localized electrons. We show that this interaction is not completely suppressed but is screened by carbon layers grown on-top of silicon carbide. This finding leads to a good qualitative understanding of the experimental results reported on EG on silicon carbide. Our results highlight the presence of the Si localized states and might explain the anomalous Hanle curve and the high values of spin relaxation time in EG.

  2. High-Q silicon carbide photonic-crystal cavities

    SciTech Connect

    Lee, Jonathan Y.; Lu, Xiyuan; Lin, Qiang

    2015-01-26

    We demonstrate one-dimensional photonic-crystal nanobeam cavities in amorphous silicon carbide. The fundamental mode exhibits intrinsic optical quality factor as high as 7.69 × 10{sup 4} with mode volume ∼0.60(λ/n){sup 3} at wavelength 1.5 μm. A corresponding Purcell factor value of ∼10{sup 4} is the highest reported to date in silicon carbide optical cavities. The device exhibits great potential for integrated nonlinear photonics and cavity nano-optomechanics.

  3. Electronic states in epitaxial graphene fabricated on silicon carbide

    SciTech Connect

    Davydov, S. Yu.

    2011-08-15

    An analytical expression for the density of states of a graphene monolayer interacting with a silicon carbide surface (epitaxial graphene) is derived. The density of states of silicon carbide is described within the Haldane-Anderson model. It is shown that the graphene-substrate interaction results in a narrow gap of {approx}0.01-0.06 eV in the density of states of graphene. The graphene atom charge is estimated; it is shown that the charge transfer from the substrate is {approx}10{sup -3}-10{sup -2}e per graphene atom.

  4. Flaw imaging and ultrasonic techniques for characterizing sintered silicon carbide

    NASA Technical Reports Server (NTRS)

    Baaklini, George Y.; Abel, Phillip B.

    1987-01-01

    The capabilities were investigated of projection microfocus x-radiography, ultrasonic velocity and attenuation, and reflection scanning acoustic microscopy for characterizing silicon carbide specimens. Silicon carbide batches covered a range of densities and different microstructural characteristics. Room temperature, four point flexural strength tests were conducted. Fractography was used to identify types, sizes, and locations of fracture origins. Fracture toughness values were calculated from fracture strength and flaw characterization data. Detection capabilities of radiography and acoustic microscopy for fracture-causing flaws were evaluated. Applicability of ultrasonics for verifying material strength and toughness was examined.

  5. Radiographic and ultrasonic characterization of sintered silicon carbide

    NASA Technical Reports Server (NTRS)

    Baaklini, G. Y.; Abel, P. B.

    1988-01-01

    The capabilities were investigated of projection microfocus X-radiography, ultrasonic velocity and attenuation, and reflection scanning acoustic microscopy for characterizing silicon carbide specimens. Silicon carbide batches covered a range of densities and different microstructural characteristics. Room temperature, four point flexural strength tests were conducted. Fractography was used to identify types, sizes, and locations of fracture origins. Fracture toughness values were calculated from fracture strength and flaw characterization data. Detection capabilities of radiography and acoustic microscopy for fracture-causing flaws were evaluated. Applicability of ultrasonics for verifying material strength and toughness was examined.

  6. Silicon carbide alloys: Research reports in materials science

    SciTech Connect

    Dobson, M.M.

    1986-01-01

    The book draws from work done on other silicon materials, silicon nitrides and sialons, to emphasize the importance of the SiC system. A comprehensive treatment of non-oxide silicon ceramics, this work is of special interest to researchers involved in ceramics, materials science, and high-temperature technology. This book covers the alloys of silicon carbide with aluminum nitride. Crystallography and experimental methods including sample preparation, furnace methods, X-ray and electron diffraction, optical and electron microscopy and chemical analysis are covered.

  7. Nuclear breeder reactor fuel element with silicon carbide getter

    DOEpatents

    Christiansen, David W.; Karnesky, Richard A.

    1987-01-01

    An improved cesium getter 28 is provided in a breeder reactor fuel element or pin in the form of an extended surface area, low density element formed in one embodiment as a helically wound foil 30 located with silicon carbide, and located at the upper end of the fertile material upper blanket 20.

  8. Silicon carbide and other films and method of deposition

    NASA Technical Reports Server (NTRS)

    Mehregany, Mehran (Inventor); Zorman, Christian A. (Inventor); Fu, Xiao-An (Inventor); Dunning, Jeremy L. (Inventor)

    2007-01-01

    A method of depositing a ceramic film, particularly a silicon carbide film, on a substrate is disclosed in which the residual stress, residual stress gradient, and resistivity are controlled. Also disclosed are substrates having a deposited film with these controlled properties and devices, particularly MEMS and NEMS devices, having substrates with films having these properties.

  9. Silicon carbide and other films and method of deposition

    NASA Technical Reports Server (NTRS)

    Mehregany, Mehran (Inventor); Zorman, Christian A. (Inventor); Fu, Xiao-An (Inventor); Dunning, Jeremy (Inventor)

    2011-01-01

    A method of depositing a ceramic film, particularly a silicon carbide film, on a substrate is disclosed in which the residual stress, residual stress gradient, and resistivity are controlled. Also disclosed are substrates having a deposited film with these controlled properties and devices, particularly MEMS and NEMS devices, having substrates with films having these properties.

  10. The development of silicon carbide-based power electronics devices

    NASA Astrophysics Data System (ADS)

    Hopkins, Richard H.; Perkins, John F.

    1995-01-01

    In 1989 Westinghouse created an internally funded initiative to develop silicon carbide materials and device technology for a variety of potential commercial and military applications. Westinghouse saw silicon carbide as having the potential for dual use. For space applications, size and weight reductions could be achieved, together with increased reliability. Terrestrially, uses in harsh-temperature environments would be enabled. Theoretically, the physical and electrical properties of silicon carbide were highly promising for high-power, high-temperature, radiation-hardened electronics. However, bulk material with the requisite electronic qualities was not available, and the methods needed to produce a silicon carbide wafer—to fabricate high-quality devices—and to transition these technologies into a commercial product were considered to be a high-risk investment. It was recognized that through a collaborative effort, the CCDS could provide scientific expertise in several areas, thus reducing this risk. These included modeling of structures, electrical contacts, dielectrics, and epitaxial growth. This collaboration has been very successful, with developed technologies being transferred to Westinghouse.

  11. Sintered silicon carbide molded body and method for its production

    NASA Technical Reports Server (NTRS)

    Omori, M.; Sendai, M.; Ohira, K.

    1984-01-01

    Sintered silicon carbide shapes are described. They are produced by using a composition containing an oxide of at least one element chosen from the group: Li, Be, Mg, Si, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Nb, Mo, Ba, Tc, Ta, W and Th as a supplement to known sintering aids.

  12. Improved epitaxial process for fabricating silicon carbide semiconductor devices

    NASA Technical Reports Server (NTRS)

    Will, H. A.; Powell, J. A.

    1974-01-01

    Process of growing expitaxial silicon carbide (SiC) layers on SiC substrates so that epitaxial growth is perpendicular to c-axis by chemical vapor deposition process at temperatures of 1590 to 1660 K minimizes variations in stacking sequence and problems associated with high temperatures.

  13. Mechanical properties of some silicon carbide reinforced aluminum composites

    SciTech Connect

    Tsangarakis, N.; Andrews, B.O.; Cavallaro, C.

    1987-05-01

    The mechanical properties of several particulate and continuous fiber silicon carbide-reinforced aluminum composites were examined. The tensile strength of a 47 percent silicon carbide fiber unidirectionally-reinforced aluminum composite was 1273 and 76 MPa parallel and normal to the fiber direction, respectively. The tensile strength of (0 deg/90 deg) 4s and (0/sub 2/90/0)s composites were 629 and 864 MPa, respectively. The tensile properties of a 30 percent silicon carbide particulate reinforced aluminum were found to depend on the chemistry of the metal matrix. The endurance limits of the fiber and the particulate reinforced aluminum were at the most 55 percent and 33 percent of the respective tensile strengths. The fracture toughness of the fiber reinforced composite varied with specimen width, while that of the particulate reinforced composite was 21-29 MPa sq rt m. The fatigue crack growth rate in the latter composite decreased with material thickness. There were indications that the fatigue crack growth rate in the silicon carbide particulate reinforced aluminum may be independent of variations in the chemistry of the metal matrix. 6 references.

  14. Analytical and experimental evaluation of joining silicon carbide to silicon carbide and silicon nitride to silicon nitride for advanced heat engine applications, phase 2

    NASA Astrophysics Data System (ADS)

    Sundberg, G. J.; Vartabedian, A. M.; Wade, J. A.; White, C. S.

    1994-10-01

    The purpose of joining, Phase 2 was to develop joining technologies for HIP'ed Si3N4 with 4wt% Y2O3 (NCX-5101) and for a siliconized SiC (NT230) for various geometries including: butt joins, curved joins and shaft to disk joins. In addition, more extensive mechanical characterization of silicon nitride joins to enhance the predictive capabilities of the analytical/numerical models for structural components in advanced heat engines was provided. Mechanical evaluation were performed by: flexure strength at 22 C and 1,370 C, stress rupture at 1,370 C, high temperature creep, 22 C tensile testing and spin tests. While the silicon nitride joins were produced with sufficient integrity for many applications, the lower join strength would limit its use in the more severe structural applications. Thus, the silicon carbide join quality was deemed unsatisfactory to advance to more complex, curved geometries. The silicon carbide joining methods covered within this contract, although not entirely successful, have emphasized the need to focus future efforts upon ways to obtain a homogeneous, well sintered parent/join interface prior to siliconization. In conclusion, the improved definition of the silicon carbide joining problem obtained by efforts during this contract have provided avenues for future work that could successfully obtain heat engine quality joins.

  15. Analytical and experimental evaluation of joining silicon carbide to silicon carbide and silicon nitride to silicon nitride for advanced heat engine applications Phase 2. Final report

    SciTech Connect

    Sundberg, G.J.; Vartabedian, A.M.; Wade, J.A.; White, C.S.

    1994-10-01

    The purpose of joining, Phase 2 was to develop joining technologies for HIP`ed Si{sub 3}N{sub 4} with 4wt% Y{sub 2}O{sub 3} (NCX-5101) and for a siliconized SiC (NT230) for various geometries including: butt joins, curved joins and shaft to disk joins. In addition, more extensive mechanical characterization of silicon nitride joins to enhance the predictive capabilities of the analytical/numerical models for structural components in advanced heat engines was provided. Mechanical evaluation were performed by: flexure strength at 22 C and 1,370 C, stress rupture at 1,370 C, high temperature creep, 22 C tensile testing and spin tests. While the silicon nitride joins were produced with sufficient integrity for many applications, the lower join strength would limit its use in the more severe structural applications. Thus, the silicon carbide join quality was deemed unsatisfactory to advance to more complex, curved geometries. The silicon carbide joining methods covered within this contract, although not entirely successful, have emphasized the need to focus future efforts upon ways to obtain a homogeneous, well sintered parent/join interface prior to siliconization. In conclusion, the improved definition of the silicon carbide joining problem obtained by efforts during this contract have provided avenues for future work that could successfully obtain heat engine quality joins.

  16. Evaluation of microstructural damage and alteration of polytypes to determine the aging of silicon carbide

    SciTech Connect

    Koenig, T. W.; Mishra, B.; Olson, D. L.; Meshi, L.; Foxman, Z.; Landau, A.; Riesterer, J. L.; Kennedy, J. R.

    2013-01-25

    Irradiated silicon carbide (SiC) exhibits higher carrier content but a decrease in conductivity with increased irradiation. It was theorized that this conflicting data was due to structural damage due to irradiation. This theory was supported by the fact that non-irradiated 50{mu}m thick SiC is transparent for visible light and the higher the irradiation dose, the material of the same thickness became less transparent. However, changes in microscopy and polyforms observed by transmission electron microscopy in SiC due to irradiation were minor. Although existence of different polymorphs of SiC was documented, direct proof of the proposed theory has not yet been achieved.

  17. MAGNESIUM PRECIPITATION AND DIFUSSION IN Mg+ ION IMPLANTED SILICON CARBIDE

    SciTech Connect

    Jiang, Weilin; Jung, Hee Joon; Kovarik, Libor; Wang, Zhaoying; Roosendaal, Timothy J.; Zhu, Zihua; Edwards, Danny J.; Hu, Shenyang Y.; Henager, Charles H.; Kurtz, Richard J.; Wang, Yongqiang

    2015-03-02

    As a candidate material for fusion reactor applications, silicon carbide (SiC) undergoes transmutation reactions under high-energy neutron irradiation with magnesium as the major metallic transmutant; the others include aluminum, beryllium and phosphorus in addition to helium and hydrogen gaseous species. Calculations by Sawan et al. predict that at a dose of ~100 dpa (displacements per atom), there is ~0.5 at.% Mg generated in SiC. The impact of these transmutants on SiC structural stability is currently unknown. This study uses ion implantation to introduce Mg into SiC. Multiaxial ion-channeling analysis of the as-produced damage state indicates a lower dechanneling yield observed along the <100> axis. The microstructure of the annealed sample was examined using high-resolution scanning transmission electron microscopy. The results show a high concentration of likely non-faulted tetrahedral voids and possible stacking fault tetrahedra near the damage peak. In addition to lattice distortion, dislocations and intrinsic and extrinsic stacking faults are also observed. Magnesium in 3C–SiC prefers to substitute for Si and it forms precipitates of cubic Mg2Si and tetragonal MgC2. The diffusion coefficient of Mg in 3C–SiC single crystal at 1573 K has been determined to be 3.8 ± 0.4E-19 m2/s.

  18. Evaluation of CVD silicon carbide for synchrotron radiation mirrors

    SciTech Connect

    Takacs, P.Z.

    1981-07-01

    Chemical vapor deposited silicon carbide (CVD SiC) is a recent addition to the list of materials suitable for use in the harsh environment of synchrotron radiation (SR) beam lines. SR mirrors for use at normal incidence must be ultrahigh vacuum compatible, must withstand intense x-ray irradiation without surface damage, must be capable of being polished to an extremely smooth surface finish, and must maintain surface figure under thermal loading. CVD SiC exceeds the performance of conventional optical materials in all these areas. It is, however, a relatively new optical material. Few manufacturers have experience in producing optical quality material, and few opticians have experience in figuring and polishing the material. The CVD material occurs in a variety of forms, sensitively dependent upon reaction chamber production conditions. We are evaluating samples of CVD SiC obtained commercially from various manufacturers, representing a range of deposition conditions, to determine which types of CVD material are most suitable for superpolishing. At the time of this writing, samples are being polished by several commercial vendors and surface finish characteristics are being evaluated by various analytical methods.

  19. Radiolytic hydrogen generation at silicon carbide-water interfaces

    NASA Astrophysics Data System (ADS)

    Schofield, Jennifer; Reiff, Sarah C.; Pimblott, Simon M.; LaVerne, Jay A.

    2016-02-01

    While many of the proposed uses of SiC in the nuclear industry involve systems that are assumed to be dry, almost all materials have dissociated chemisorbed water associated with their surface, which can undergo chemistry in radiation fields. Silicon carbide α-phase and β-phase nanoparticles with water were irradiated with γ-rays and 5 MeV 4He ions followed by the determination of the production of molecular hydrogen, H2, and characterization of changes in the particle surface. The yields of H2 from SiC-water slurries were always greater than expected from a simple mixture rule indicating that the presence of SiC was influencing the production of H2 from water, probably through an energy transfer from the solid to liquid phase. Although the increase in H2 yields was modest, a decrease in the water mass percentage led to an increase in H2 yields, especially for very low amounts of water. Surface analysis techniques included diffuse reflectance infrared Fourier transform spectroscopy (DRIFT), nitrogen absorption with the Brunauer - Emmett - Teller (BET) methodology for surface area determination, X-ray diffraction (XRD), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). Little change in the SiC surface was observed following radiolysis except for some conversion of β-phase SiC to the α-phase and the formation of SiO2 with He ion radiolysis.

  20. A silicon carbide room-temperature single-photon source.

    PubMed

    Castelletto, S; Johnson, B C; Ivády, V; Stavrias, N; Umeda, T; Gali, A; Ohshima, T

    2014-02-01

    Over the past few years, single-photon generation has been realized in numerous systems: single molecules, quantum dots, diamond colour centres and others. The generation and detection of single photons play a central role in the experimental foundation of quantum mechanics and measurement theory. An efficient and high-quality single-photon source is needed to implement quantum key distribution, quantum repeaters and photonic quantum information processing. Here we report the identification and formation of ultrabright, room-temperature, photostable single-photon sources in a device-friendly material, silicon carbide (SiC). The source is composed of an intrinsic defect, known as the carbon antisite-vacancy pair, created by carefully optimized electron irradiation and annealing of ultrapure SiC. An extreme brightness (2×10(6) counts s(-1)) resulting from polarization rules and a high quantum efficiency is obtained in the bulk without resorting to the use of a cavity or plasmonic structure. This may benefit future integrated quantum photonic devices. PMID:24240243

  1. Fabrication and properties of silicon carbide nanowires

    NASA Astrophysics Data System (ADS)

    Shim, Hyun Woo

    2008-12-01

    Silicon carbide (SiC), with excellent electrical, thermal, and mechanical properties, is a promising material candidate for future devices such as high-temperature electronics and super-strong lightweight structures. Combined with superior intrinsic properties, the nanomaterials of SiC show further advantages thanks to nanoscale effects. This thesis reports the growth mechanism, the self-integration, and the friction of SiC nanowires. The study involves nanowires fabrication using thermal evaporation, structure characterization using electron microscopy, friction measurement, and theoretical modeling. The study on nanowire growth mechanism requires understanding of the surfaces and interfaces of nanowire crystal. The catalyzed growth of SiC nanowires involves interfaces between source vapor, catalytic liquid, and nanowire solid. Our experimental observation includes the periodical twinning in a faceted SiC nanowire and three stage structure transitions during the growth. The proposed theoretical model shows that such phenomenon is the result of surface energy minimization process during the catalytic growth. Surface interactions also exist between nanowires, leading to their self-integration. Our parametric growth study reveals novel self-integration of SiC-SiO 2 core-shell nanowires as a result of SiO2 joining. Attraction between nanowires through van der Waals force and enhanced SiO2 diffusion at high temperature transform individual nanowires to the integrated nanojunctions, nanocables, and finally nanowebs. We also show that such joining process becomes effective either during growth or by annealing. The solid friction is a result of the interaction between two solid surfaces, and it depends on the adhesion and the deformation of two contacting solids among other factors. Having strong adhesion as shown from gecko foot-hairs, nanostructured materials should also have strong friction; this study is the first to investigate friction of nanostructures under

  2. Silicon carbide high temperature thermoelectric flow sensor

    NASA Astrophysics Data System (ADS)

    Lei, Man I.

    Current high temperature flow measurement devices are bulky, expensive and have slow response time. Therefore, there has been increasing demand for developing a flow sensor that has high temperature capability yet is small in size, fast in response time, and low in cost through mass fabrication. In this thesis, a high temperature flow sensor utilizing micromachining and microfabrication technology has been designed, simulated, fabricated, packaged and tested. This micro flow sensor is developed based on heavily-nitrogen-doped polycrystalline silicon carbide (n-SiC) thin film, a high temperature semiconductor well known for its mechanical robustness and chemical inertness in high temperatures and harsh environments. The small thermal mass and wide operating temperature range provide an excellent platform for a flow sensor operating with the thermal sensing principle. The n-SiC thermoelectric flow sensor prototype developed here is based on the calorimetric sensing mechanism. The sensor has a n-SiC heater for thermal marker creation, an upstream and a downstream n-SiC/p-Si thermopile for flow sensing, and a n-SiC thermistor for ambient temperature monitoring. This device is packaged in a stainless steel enclosure with a bypass channel. The tested flow range is between 0 to 20,000 sccm. The flow sensor has demonstrated high temperature capability and mechanical robustness up to 450 °C on a hotplate at zero flow condition, and up to 300 °C in a heated flow stream. The device has a response time of 8 ms. Maximum power consumption is 96 mW when operated at 8 mA (12 V) and 45 mW when operated at 5 mA (9V), with a sensor warm-up time less than 1 minute. In addition, the thermoelectric properties of n-SiC have been thoroughly studied through the characterization of the electrical resistivity, the Seebeck coefficient and the thermal conductivity of n-SiC thin film. The 0.93 microm-thick, n-SiC thin film utilized in the thermoelectric flow sensor has an electrical

  3. Selective-area laser deposition (SALD) Joining of silicon carbide with silicon carbide filler

    NASA Astrophysics Data System (ADS)

    Harrison, Shay Llewellyn

    Selective Area Laser Deposition (SALD) is a gas-phase, solid freeform fabrication (SFF) process that utilizes a laser-driven, pyrolytic gas reaction to form a desired solid product. This solid product only forms in the heated zone of the laser beam and thus can be selectively deposited by control of the laser position. SALD Joining employs the SALD method to accomplish 'welding' of ceramic structures together. The solid reaction product serves as a filler material to bond the two parts. The challenges involved with ceramic joining center around the lack of a liquid phase, little plastic deformation and diffusivity and poor surface wetting for many ceramic materials. Due to these properties, traditional metal welding procedures cannot be applied to ceramics. Most alternative ceramic welding techniques use some form of a metal addition to overcome these material limitations. However, the metal possesses a lower ultimate use temperature than the ceramic substrate and therefore it decreases the temperature range over which the joined part can be safely used. SALD Joining enjoys several advantages over these ceramic welding procedures. The solid filler material chemistry can be tailored to match the type of ceramic substrate and therefore fabricate monolithic joints. The SALD filler material bonds directly to the substrate and the joined structure is made in a one step process, without any post-processing. The research documented in this dissertation focused on SALD Joining of silicon carbide structures with silicon carbide filler material. A historical progression of gas-phase SFF research and a literature review of the most prominent ceramic joining techniques are provided. A variety of SiC substrates were examined, as were various conditions of gas precursor pressures and mixtures, laser beam scan speed and joint configuration. The SALD material was characterized for composition and structure by x-ray diffraction, transmission electron microscopy and nuclear magnetic

  4. Method of fabricating silicon carbide coatings on graphite surfaces

    DOEpatents

    Varacalle, Jr., Dominic J.; Herman, Herbert; Burchell, Timothy D.

    1994-01-01

    The vacuum plasma spray process produces well-bonded, dense, stress-free coatings for a variety of materials on a wide range of substrates. The process is used in many industries to provide for the excellent wear, corrosion resistance, and high temperature behavior of the fabricated coatings. In this application, silicon metal is deposited on graphite. This invention discloses the optimum processing parameters for as-sprayed coating qualities. The method also discloses the effect of thermal cycling on silicon samples in an inert helium atmosphere at about 1600.degree.C. which transforms the coating to silicon carbide.

  5. Method of fabricating silicon carbide coatings on graphite surfaces

    DOEpatents

    Varacalle, D.J. Jr.; Herman, H.; Burchell, T.D.

    1994-07-26

    The vacuum plasma spray process produces well-bonded, dense, stress-free coatings for a variety of materials on a wide range of substrates. The process is used in many industries to provide for the excellent wear, corrosion resistance, and high temperature behavior of the fabricated coatings. In this application, silicon metal is deposited on graphite. This invention discloses the optimum processing parameters for as-sprayed coating qualities. The method also discloses the effect of thermal cycling on silicon samples in an inert helium atmosphere at about 1,600 C which transforms the coating to silicon carbide. 3 figs.

  6. Protective coating for alumina-silicon carbide whisker composites

    DOEpatents

    Tiegs, Terry N.

    1989-01-01

    Ceramic composites formed of an alumina matrix reinforced with silicon carbide whiskers homogenously dispersed therein are provided with a protective coating for preventing fracture strength degradation of the composite by oxidation during exposure to high temperatures in oxygen-containing atmospheres. The coating prevents oxidation of the silicon carbide whiskers within the matrix by sealing off the exterior of the matrix so as to prevent oxygen transport into the interior of the matrix. The coating is formed of mullite or mullite plus silicon oxide and alumina and is formed in place by heating the composite in air to a temperature greater than 1200.degree. C. This coating is less than about 100 microns thick and adequately protects the underlying composite from fracture strength degradation due to oxidation.

  7. Diffusion Bonding of Silicon Carbide Ceramics using Titanium Interlayers

    NASA Technical Reports Server (NTRS)

    Halbig, Michael C.; Singh, Mrityunjay; Shpargel, Tarah P.; Kiser, James D.

    2006-01-01

    Robust joining approaches for silicon carbide ceramics are critically needed to fabricate leak free joints with high temperature mechanical capability. In this study, titanium foils and physical vapor deposited (PVD) titanium coatings were used to form diffusion bonds between SiC ceramics using hot pressing. Silicon carbide substrate materials used for bonding include sintered SiC and two types of CVD SiC. Microscopy results show the formation of well adhered diffusion bonds. The bond strengths as determined from pull tests are on the order of several ksi, which is much higher than required for a proposed application. Microprobe results show the distribution of silicon, carbon, titanium, and other minor elements across the diffusion bond. Compositions of several phases formed in the joint region were identified. Potential issues of material compatibility and optimal bond formation will also be discussed.

  8. Catastrophic degradation of the interface of epitaxial silicon carbide on silicon at high temperatures

    NASA Astrophysics Data System (ADS)

    Pradeepkumar, Aiswarya; Mishra, Neeraj; Kermany, Atieh Ranjbar; Boeckl, John J.; Hellerstedt, Jack; Fuhrer, Michael S.; Iacopi, Francesca

    2016-07-01

    Epitaxial cubic silicon carbide on silicon is of high potential technological relevance for the integration of a wide range of applications and materials with silicon technologies, such as micro electro mechanical systems, wide-bandgap electronics, and graphene. The hetero-epitaxial system engenders mechanical stresses at least up to a GPa, pressures making it extremely challenging to maintain the integrity of the silicon carbide/silicon interface. In this work, we investigate the stability of said interface and we find that high temperature annealing leads to a loss of integrity. High-resolution transmission electron microscopy analysis shows a morphologically degraded SiC/Si interface, while mechanical stress measurements indicate considerable relaxation of the interfacial stress. From an electrical point of view, the diode behaviour of the initial p-Si/n-SiC junction is catastrophically lost due to considerable inter-diffusion of atoms and charges across the interface upon annealing. Temperature dependent transport measurements confirm a severe electrical shorting of the epitaxial silicon carbide to the underlying substrate, indicating vast predominance of the silicon carriers in lateral transport above 25 K. This finding has crucial consequences on the integration of epitaxial silicon carbide on silicon and its potential applications.

  9. SILICON CARBIDE CERAMICS FOR COMPACT HEAT EXCHANGERS

    SciTech Connect

    DR. DENNIS NAGLE; DR. DAJIE ZHANG

    2009-03-26

    Silicon carbide (SiC) materials are prime candidates for high temperature heat exchangers for next generation nuclear reactors due to their refractory nature and high thermal conductivity at elevated temperatures. This research has focused on demonstrating the potential of liquid silicon infiltration (LSI) for making SiC to achieve this goal. The major advantage of this method over other ceramic processing techniques is the enhanced capability of making high dense, high purity SiC materials in complex net shapes. For successful formation of net shape SiC using LSI techniques, the carbon preform reactivity and pore structure must be controlled to allow the complete infiltration of the porous carbon structure which allows complete conversion of the carbon to SiC. We have established a procedure for achieving desirable carbon properties by using carbon precursors consisting of two readily available high purity organic materials, crystalline cellulose and phenolic resin. Phenolic resin yields a glassy carbon with low chemical reactivity and porosity while the cellulose carbon is highly reactive and porous. By adjusting the ratio of these two materials in the precursor mixtures, the properties of the carbons produced can be controlled. We have identified the most favorable carbon precursor composition to be a cellulose resin mass ratio of 6:4 for LSI formation of SiC. The optimum reaction conditions are a temperature of 1800 C, a pressure of 0.5 Torr of argon, and a time of 120 minutes. The fully dense net shape SiC material produced has a density of 2.96 g cm{sup -3} (about 92% of pure SiC) and a SiC volume fraction of over 0.82. Kinetics of the LSI SiC formation process was studied by optical microscopy and quantitative digital image analysis. This study identified six reaction stages and provided important understanding of the process. Although the thermal conductivity of pure SiC at elevated temperatures is very high, thermal conductivities of most commercial Si

  10. Growth of silicon carbide crystals on a seed while pulling silicon crystals from a melt

    NASA Technical Reports Server (NTRS)

    Ciszek, T. F.; Schwuttke, G. H. (Inventor)

    1979-01-01

    A saturated solution of silicon and an element such as carbon having a segregation coefficient less than unity is formed by placing a solid piece of carbon in a body of molten silicon having a temperature differential decreasing toward the surface. A silicon carbide seed crystal is disposed on a holder beneath the surface of the molten silicon. As a rod or ribbon of silicon is slowly pulled from the melt, a supersaturated solution of carbon in silicon is formed in the vicinity of the seed crystal. Excess carbon is emitted from the solution in the form of silicon carbide which crystallizes on the seed crystal held in the cool region of the melt.