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Sample records for al2o3 single crystals

  1. Photochromism of vacancy-related defects in thermochemically reduced α-Al2O3:Mg single crystals

    NASA Astrophysics Data System (ADS)

    Ramírez, R.; Tardío, M.; González, R.; Chen, Y.; Kokta, M. R.

    2005-02-01

    Oxygen vacancies and their aggregates are produced much more readily in Mg-doped α-Al2O3 than in undoped α-Al2O3 single crystals during thermochemical reduction at high temperatures. A reversible photochromic effect was discovered in Mg-doped Al2O3 crystals containing large concentrations of oxygen divacancies. Alternate excitation with 5.0 and 3.69 eV light results in brown or yellowish-green coloration, respectively. The yellowish-green coloration can also be restored by thermal anneals at temperatures of about 750 K.

  2. Thermal expansion and elastic anisotropy in single crystal Al2O3 and SiC reinforcements

    NASA Technical Reports Server (NTRS)

    Salem, Jonathan A.; Li, Zhuang; Bradt, Richard C.

    1994-01-01

    In single crystal form, SiC and Al2O3 are attractive reinforcing components for high temperature composites. In this study, the axial coefficients of thermal expansion and single crystal elastic constants of SiC and Al2O3 were used to determine their coefficients of thermal expansion and Young's moduli as a function of crystallographic orientation and temperature. SiC and Al2O3 exhibit a strong variation of Young's modulus with orientation; however, their moduli and anisotropies are weak functions of temperature below 1000 C. The coefficients of thermal expansion exhibit significant temperature dependence, and that of the non-cubic Al2O3 is also a function of crystallographic orientation.

  3. Molten Al and (0001) α-Al2O3 Single Crystal: Interface Stability

    NASA Astrophysics Data System (ADS)

    Aguilar-santillan, Joaquin

    2016-10-01

    The roughness on the " c"-plane (0001) sapphire single crystal reduces wetting of molten aluminum under Ar gas (99.999 pct) and PO2 10-15 Pa from 1073 K to 1473 K (800 °C to 1200 °C). The contact angle effect was partially understood by the roughness factor, R; however, the interfacial phenomenon involving this effect is yet a topic to study as it also depends, between other things, on the shape of droplet and the relationship to its substrate. The theory explains that the surface tension of liquid aluminum obtained by the sessile drop test can be determined just when a substrate is polished or free of any surface imperfection. However, roughness of sapphire (0001) surface promotes an apparent surface tension that exhibits different trends of wetting to that proposed in previous studies. This property adds to the interfacial wetting phenomena obtained from the Al-Al2O3 couple system and provides answers for contact angle trends toward a much more stable interface, which when coupled with thermodynamic conditions may help in the manufacturing, deterioration, and reliability of the system.

  4. Optical properties and tunable laser action of Verneuil-grown single crystals of Al2O3:Ti3+

    NASA Astrophysics Data System (ADS)

    Moncorge, R.; Boulon, G.; Vivien, D.; Lejus, A. M.; Collongues, R.

    1988-06-01

    Using the Verneuil technique, the authors have grown large single crystals of Al2O3:Ti3+ having concentrations up to 0.15 percent. Laser action was observed in this material, tunable over the range 700-810 nm. Losses in the 800-nm region are less than 0.03/cm (below the detection limit in the measurements).

  5. Hydrogen-deuterium exchange induced by an electric field in α-Al2O3 single crystals

    NASA Astrophysics Data System (ADS)

    Ramírez, R.; Colera, I.; Gonz&Ález, R.; Savoini, B.; Chen, Y.

    Hydrogen and deuterium are observed in α-Al2O3 crystals in the form of OH- and OD- radicals, respectively, which absorb in the infrared region. Infrared-absorption measurements were used to monitor diffusion of deuterons and protons in α-Al2O3 single crystals under the application of a moderate electric field parallel to the crystallographic c-axis, in the temperature range of 973-1333K. A linear dependence of the percent of exchange with both annealing time and applied voltage is observed, indicating that ionic conduction was taking place. The activation energy for the H+ ↔; D+ exchange was determined to be 2.4 eV, less than half the value obtained by pure thermal means, suggesting that under the application of an electric field the deuteron (proton) diffusion mechanism is different.

  6. Preparation and characterization of Co epitaxial thin films on Al2O3(0001) single-crystal substrates

    NASA Astrophysics Data System (ADS)

    Yabuhara, Osamu; Ohtake, Mitsuru; Nukaga, Yuri; Futamoto, Masaaki

    2011-01-01

    Co epitaxial thin films were prepared on Al2O3(0001) single-crystal substrates in a substrate temperature range between 50 and 500 °C by ultra high vacuum molecular beam epitaxy. Effects of substrate temperature on the structure and the magnetic properties of the films were investigated. The films grown at temperatures lower than 150 °C consist of fcc- Co(111) crystal. With increasing the substrate temperature, hcp-Co(0001) crystal coexists with the fcc crystal and the volume ratio of hcp to fcc crystal increases. The films prepared at temperatures higher than 250 °C consist primarily of hcp crystal. The film growth seems to follow island-growth mode. The films consisting primarily of hcp crystal show perpendicular magnetic anisotropy. The domain structure and the magnetization properties are influenced by the magnetocrystalline anisotropy and the shape anisotropy caused by the film surface roughness.

  7. Study of Blue Photoluminescence in Titanium Doped Al2O3 Single-Crystals

    NASA Astrophysics Data System (ADS)

    Daimon, T.; Naruse, H.; Watanabe, H.; Oda, H.; Yamanaka, A.

    2011-05-01

    Optical properties have been investigated in titanium doped sapphire, prepared under oxidized condition. Charge-transfer transitions to 3d states of tetravalent Ti4+ from 2p ones of O2- are found to be located below the fundamental absorption edge of Al2O3. The photo-excitation for this band leads to the intense blue emission, the spectrum of which is quite different from the luminescence of the d-d transitions in trivalent Ti3+. The UV-irradiation also leads to an absorption peak below the charge-transfer band, resulted from that the photo-excited electrons in part form color centers. The post-annealing at higher temperatures above 300°C completely destroys the color centers. The blue photoluminescence is found to be greatly suppressed by the UV-irradiation and is recovered by the post-annealing. This fact indicates that the color centers prevent the blue emission.

  8. Effect of Composite Fabrication on the Strength of Single Crystal Al2O3 Fibers in Two Fe-Base Alloy Composites

    NASA Technical Reports Server (NTRS)

    Draper, Susan L.; Aiken, Beverly J. M.

    1998-01-01

    Continuous single-crystal Al2O3 fibers have been incorporated into a variety of metal and intermetallic matrices and the results have consistently indicated that the fiber strength had been reduced by 32 to 50% during processing. Two iron-based alloys, FeNiCoCrAl and FeAlVCMn, were chosen as matrices for Al2O3 fiber reinforced metal matrix composites (MMC) with the goal of maintaining Al2O3 fiber strength after composite processing. The feasibility of Al2O3/FeNiCoCrAl and Al2O3/FeAlVCMn composite systems for high temperature applications were assessed in terms of fiber-matrix chemical compatibility, interfacial bond strength, and composite tensile properties. The strength of etched-out fibers was significantly improved by choosing matrices containing less reactive elements. The ultimate tensile strength (UTS) values of the composites could generally be predicted with existing models using the strength of etched-out fibers. However, the UTS of the composites were less than desired due to a low fiber Weibull modulus. Acoustic emission analysis during tensile testing was a useful tool for determining the efficiency of the fibers in the composite and for determining the failure mechanism of the composites.

  9. Structural and Magnetic Properties of Fe and Au Ion-Implanted Al2O3 Single Crystals

    NASA Astrophysics Data System (ADS)

    Kinoshita, Ryosuke; Sakamoto, Isao; Hayashi, Nobuyuki; Nomura, Kiyoshi; Honda, Shigeo; Ishida, Tomoya; Iio, Satoshi; Tashiro, Hiroyuki; Toriyama, Tamotsu

    2011-01-01

    Au ion implantation in Fe ion-implanted Al2O3 (Fe/Al2O3) has been performed in order to tailor the structural, magnetic and optical properties of Fe granules in Al2O3 matrix. After Au ion implantation, Rutherford backscattering (RBS) measurements indicate the decrease and the redistribution of retained Fe atoms with the inclusion of Au atoms, and the patterns of X-ray diffraction (XRD) show the formation of Au granules in the Fe/Al2O3. Besides, the magnetization curves of the Fe/Al2O3 after Au ion implantation show still the superparamagnetic characteristics and the decrease of saturation magnetization, and the optical absorption measurements indicate the formation of Au granules in the Fe/Al2O3 in accordance with the XRD result. In addition, we investigated a behavior of Fe granules in Al2O3 matrix by conversion electron Mössbauer spectroscopy (CEMS), which indicates the decrease of superparamagnetic state as a function of Au ion dose. As a result, it is suggested that Au ion implantation has potentialities to tailor the physical properties of Fe granules in Al2O3 matrix.

  10. Hydrogen-isotope transport induced by an electric field in α-Al2O3 single crystals

    NASA Astrophysics Data System (ADS)

    Ramírez, R.; Colera, I.; González, R.; Chen, Y.; Kokta, M. R.

    2004-01-01

    Infrared-absorption measurements were used to characterize OH- and OD- stretching frequencies in Al2O3 crystals both nominally pure and doped with either Ti, V, or Mg impurities. Impurities, cooling rates, and ultraviolet irradiation affect the distribution of various OH- (OD-) band intensities. Polarization experiments determined the precise angle of OH- (OD-) ions protruding from the basal plane for several OH- (OD-) bands. Most were <15°, with one at 21°. Diffusion of isotopic species was performed with and without an electric field. Without an electric field, indiffusion is possible only by exchanging with an existing species. With an electric field, indiffusion occurs by exchange as well as occupying new sites. Incorporation of hydrogen (deuterium) was investigated by subjecting the crystals to a moderate electric field both parallel and perpendicular to the crystallographic c axis, in the temperature range 973 1300 K in H2O (or D2O) vapor. An initial linear dependence of the percent of exchange with annealing time and applied voltage was observed, indicating that ionic conduction is the dominant mechanism. The activation energy for the H+iff D+ exchange was determined to be ≈2.4 eV with an electric field of 3000 V/cm applied either parallel or perpendicular to the c axis. The estimated proton (deuteron) mobility is μ=(6±1)×10-8 cm2/(V s).

  11. Anisotropy of electrical conductivity in dc due to intrinsic defect formation in α-Al2O3 single crystal implanted with Mg ions

    NASA Astrophysics Data System (ADS)

    Tardío, M.; Egaña, A.; Ramírez, R.; Muñoz-Santiuste, J. E.; Alves, E.

    2016-07-01

    The electrical conductivity in α-Al2O3 single crystals implanted with Mg ions in two different crystalline orientations, parallel and perpendicular to c axis, was investigated. The samples were implanted at room temperature with energies of 50 and 100 keV and fluences of 1 × 1015, 5 × 1015 and 5 × 1016 ions/cm2. Optical characterization reveals slight differences in the absorption bands at 6.0 and 4.2 eV, attributed to F type centers and Mie scattering from Mg precipitates, respectively. DC electrical measurements using the four and two-point probe methods, between 295 and 490 K, were used to characterize the electrical conductivity of the implanted area (Meshakim and Tanabe, 2001). Measurements in this temperature range indicate that: (1) the electrical conductivity is thermally activated independently of crystallographic orientation, (2) resistance values in the implanted region decrease with fluence levels, and (3) the I-V characteristic of electrical contacts in samples with perpendicular c axis orientation is clearly ohmic, whereas contacts are blocking in samples with parallel c axis. When thin layers are sequentially removed from the implanted region by immersing the sample in a hot solution of nitric and fluorhydric acids the electrical resistance increases until reaching the values of non-implanted crystal (Jheeta et al., 2006). We conclude that the enhancement in conductivity observed in the implanted regions is related to the intrinsic defects created by the implantation rather than to the implanted Mg ions (da Silva et al., 2002; Tardío et al., 2001; Tardío et al., 2008).

  12. High Temperature Elastic Properties of Single Crystal Mullite (Approximately 2.5Al2O3.SiO2) by Brillouin Spectroscopy

    NASA Technical Reports Server (NTRS)

    Palko, James W.; Sayir, Ali; Sinogeikin, Stanislav V.; Kriven, Waltraud M.; Bass, Jay D.; Farmer, Serene C. (Technical Monitor)

    2001-01-01

    The complete elastic tensor of mullite has been determined by brillouin spectroscopy at room temperature and elevated temperatures up to 1200C. Equivalent, isotropic moduli (bulk, shear, and Young's) have been calculated. The room temperature values obtained using Voigt-Reuss-Hill averaging are: K(sub VRH) = 173.5 + 6.9 GPa, G(sub VRH) = 88.0 + 3.5 GPa, E(sub VRH) = 225.9 + 9.0 GPa. All moduli show relatively gradual decreases with temperature. The temperature derivatives obtained for the equivalent, isotropic moduli are: dK(sub VRH)/dT = - 17.5 + 2.5 MPa/deg. C, dG(sub VRH)/dT = -8.8 + 1.4 MPa/deg. C, dE(sub VRH)/dT = -22.6 + 2.8 MPa/deg C. Substantial differences between bulk properties calculated from the single crystal measurements in this study and the properties reported in the literature for polycrystalline sintered mullite are identified, indicating the importance of factors such as microstructure, intergranular phases, and composition to the elasticity of mullite ceramics.

  13. Luminescent properties of Al2O3:Ce single crystalline films under synchrotron radiation excitation

    NASA Astrophysics Data System (ADS)

    Zorenko, Yu.; Zorenko, T.; Gorbenko, V.; Savchyn, V.; Voznyak, T.; Fabisiak, K.; Zhusupkalieva, G.; Fedorov, A.

    2016-09-01

    The paper is dedicated to study the luminescent and scintillation properties of the Al2O3:Ce single crystalline films (SCF) grown by LPE method onto saphire substrates from PbO based flux. The structural quality of SCF samples was investigated by XRD method. For characterization of luminescent properties of Al2O3:Ce SCFs the cathodoluminescence spectra, scintillation light yield (LY) and decay kinetics under excitation by α-particles of Pu239 source were used. We have found that the scintillation LY of Al2O3:Ce SCF samples is relatively large and can reach up to 50% of the value realized in the reference YAG:Ce SCF. Using the synchrotron radiation excitation in the 3.7-25 eV range at 10 K we have also determined the basic parameters of the Ce3+ luminescence in Al2O3 host.

  14. Influence of the Al2O3 partial-monolayer number on the crystallization mechanism of TiO2 in ALD TiO2/Al2O3 nanolaminates and its impact on the material properties

    NASA Astrophysics Data System (ADS)

    Testoni, G. E.; Chiappim, W.; Pessoa, R. S.; Fraga, M. A.; Miyakawa, W.; Sakane, K. K.; Galvão, N. K. A. M.; Vieira, L.; Maciel, H. S.

    2016-09-01

    TiO2/Al2O3 nanolaminates are being investigated to obtain unique materials with chemical, physical, optical, electrical and mechanical properties for a broad range of applications that include electronic and energy storage devices. Here, we discuss the properties of TiO2/Al2O3 nanolaminate structures constructed on silicon (1 0 0) and glass substrates using atomic layer deposition (ALD) by alternatively depositing a TiO2 sublayer and Al2O3 partial-monolayer using TTIP-H2O and TMA-H2O precursors, respectively. The Al2O3 is formed by a single TMA-H2O cycle, so it is a partial-monolayer because of steric hindrance of the precursors, while the TiO2 sublayer is formed by several TTIP-H2O cycles. Overall, each nanolaminate incorporates a certain number of Al2O3 partial-monolayers with this number varying from 10-90 in the TiO2/Al2O3 nanolaminate grown during 2700 total reaction cycles of TiO2 at a temperature of 250 °C. The fundamental properties of the TiO2/Al2O3 nanolaminates, namely film thickness, chemical composition, microstructure and morphology were examined in order to better understand the influence of the number of Al2O3 partial-monolayers on the crystallization mechanism of TiO2. In addition, some optical, electrical and mechanical properties were determined and correlated with fundamental characteristics. The results show clearly the effect of Al2O3 partial-monolayers as an internal barrier, which promotes structural inhomogeneity in the film and influences the fundamental properties of the nanolaminate. These properties are correlated with gas phase analysis that evidenced the poisoning effect of trimethylaluminum (TMA) pulse during the TiO2 layer growth, perturbing the growth per cycle and consequently the overall film thickness. It was shown that the changes in the fundamental properties of TiO2/Al2O3 nanolaminates had little influence on optical properties such as band gap and transmittance. However, in contrast, electrical properties as resistivity

  15. Crystallization kinetics of BaO-Al2O3-SiO2 glasses

    NASA Technical Reports Server (NTRS)

    Bansal, Narottam P.; Hyatt, Mark J.

    1988-01-01

    Barium aluminosilicate glasses are being investigated as matrix materials in high-temperature ceramic composites for structural applications. Kinetics of crystallization of two refractory glass compositions in the barium aluminosilicate system were studied by differential thermal analysis (DTA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). From variable heating rate DTA, the crystallization activation energies for glass compositions (wt percent) 10BaO-38Al2O3-51SiO2-1MoO3 (glass A) and 39BaO-25Al2O3-35SiO2-1MoO3 (glass B) were determined to be 553 and 558 kJ/mol, respectively. On thermal treatment, the crystalline phases in glasses A and B were identified as mullite (3Al2O3-2SiO2) and hexacelsian (BaO-Al2O3-2SiO2), respectively. Hexacelsian is a high-temperature polymorph which is metastable below 1590 C. It undergoes structural transformation into the orthorhombic form at approximately 300 C accompanied by a large volume change which is undesirable for structural applications. A process needs to be developed where stable monoclinic celsian, rather than hexacelsian, precipitates out as the crystal phase in glass B.

  16. Preparation and catalytic behavior of CeO2 nanoparticles on Al2O3 crystal

    NASA Astrophysics Data System (ADS)

    Hattori, Takashi; Kobayashi, Katsutoshi; Ozawa, Masakuni

    2017-01-01

    In this work, we examined the preparation, morphology, and catalytic behavior of CeO2 nanoparticles (NPs) on Al2O3(0001) crystal substrates. A CeO2 NP layer was prepared by the dipping method using a CeO2 nanocrystal colloid solution. Even after heat treatment at 1000 °C, the CeO2 NP layer maintained the granular morphology of CeO2 with a grain diameter of less than 40 nm. CeO2 NPs on an Al2O3 crystal showed higher oxidation activity for gaseous hydrogen at moderate temperatures and enhanced oxygen release properties of CeO2, compared with CeO2 powder. This was due to the highly dispersed CeO2 NPs and the interaction between CeO2 NPs and Al2O3; this clarified the importance of the Al2O3 support for the CeO2 catalyst.

  17. Effect of Al2O3 on the Crystallization of Mold Flux for Casting High Al Steel

    NASA Astrophysics Data System (ADS)

    Zhou, Lejun; Wang, Wanlin; Zhou, Kechao

    2015-06-01

    In order to lower the weight of automotive bodies for better fuel-efficiency and occupant safety, the demand for high Al-containing advanced high strength steel, such as transformation-induced plasticity and twinning-induced plasticity steel, is increasing. However, high aluminum content in steels would tend to significantly affect the properties of mold flux during the continuous casting process. In this paper, a kinetic study of the effect of Al2O3 content on the crystallization behavior of mold flux was conducted by using the single hot thermocouple technique and the Johnson-Mehl-Avrami model combined with the Arrhenius Equation. The results suggested that Al2O3 behaves as an amphoteric oxide in the crystallization process of mold flux. The precipitated phases of mold flux change from cuspidine (Ca4Si2O7F2) into nepheline (NaAlSiO4) and CaF2, and then into gehlenite (Ca2Al2SiO7) with the increase of Al2O3 content. The kinetics study of the isothermal crystallization process indicated that the effective crystallization rate ( k) and Avrami exponent ( n) also first increased and then decreased with the increase of Al2O3 content. The values for the crystallization activation energy of mold flux with different Al2O3 contents were E R0.8A7 = 150.76 ± 17.89 kJ/mol, E R0.8A20 = 136.43 ± 6.48 kJ/mol, E R0.8A30 = 108.63 ± 12.25 kJ/mol and E R0.8A40 = 116.15 ± 8.17 kJ/mol.

  18. Surface Formation of Single Silicon Wafer Polished with Nano-sized Al2O3 Powders

    NASA Astrophysics Data System (ADS)

    Sun, Yu-li; Zuo, Dun-wen; Zhu, Yong-wei; Wang, Min

    2007-12-01

    Ice polishing single silicon wafers with nano-sized Al2O3 abrasives can be known as ice fixed abrasives chemical mechanical polishing (IFA-CMP). TAn abrasive slurry was made of nano-sized Al2O3 particles dispersed in de-ionized water with a surfactant and the slurry was frozen to form an ice polishing pad. Then polishing tests of blanket silicon wafers with the above ice polishing pad were carried out. The morphologies and surface roughness of the polished silicon wafers were observed and examined on an atomic force microscope. The subsurface damage was assessed by means of cross-section transmission electron microscopy. The surface chemical constituents of the polished silicon wafers were characterized using X-ray photoelectron spectroscopy in order to gain insight into the chemical mechanisms in the process. Scratch resistance of the single silicon wafer was measured by nanoscratching using a nanoindenter to explore the mechanical removal mechanism. The results show that a super smooth surface with an average roughness of 0.367 nm is obtained within 1000 nm × 1000 nm and there is a perfect silicon diamond structure without any microcracks in the subsurface. The removal of material is dominated by the coactions of ductile regime machining and chemical corrosion. In the end, a model of material removal of IFA-CMP is built.

  19. Quartz crystal microbalance studies of Al2O3 atomic layer deposition using trimethylaluminum and water at 125 degrees C.

    PubMed

    Wind, R A; George, S M

    2010-01-28

    Al(2)O(3) atomic layer deposition (ALD) growth with Al(CH(3))(3) (trimethylaluminum (TMA)) and H(2)O as the reactants was examined at the relatively low temperature of 125 degrees C using quartz crystal microbalance (QCM) measurements. The total Al(2)O(3) ALD mass gain per cycle (MGPC) and MGPCs during the individual TMA and H(2)O reactions were measured versus TMA and H(2)O exposures. The Al(2)O(3) MGPC increased with increasing H(2)O and TMA exposures at fixed TMA and H(2)O exposures, respectively. However, the TMA and H(2)O reactions were not completely self-limiting. The slower surface reaction kinetics at lower temperature may require very long exposures for the reactions to reach completion. The Al(2)O(3) MGPCs increased quickly versus H(2)O exposure and slowly reached limiting values that were only weakly dependent on the TMA doses. Small TMA exposures were also sufficient for the Al(2)O(3) MGPCs to reach different limiting values for different H(2)O doses. The TMA MGPCs increased for higher TMA exposures at all H(2)O exposures. In contrast, the H(2)O MGPCs decreased for higher TMA exposures at all H(2)O exposures. This decrease may occur from more dehydroxylation at larger hydroxyl coverages after the H(2)O exposures. The hydroxyl coverage after the H(2)O exposure was dependent only on the H(2)O exposure. The Al(2)O(3) MGPC was also linearly dependent on the hydroxyl coverage after the H(2)O dose. Both the observed hydroxyl coverage versus H(2)O exposure and the Al(2)O(3) ALD growth versus H(2)O and TMA exposures were fit using modified Langmuir adsorption isotherm expressions where the pressures are replaced with exposures. These results should be useful for understanding low-temperature Al(2)O(3) ALD, which is important for coating organic, polymeric, and biological substrates.

  20. The crystallization kinetics and thermal conductivity of alumina/fluorescein sodium salt (Al2O3/FSS) composites

    NASA Astrophysics Data System (ADS)

    Yakuphanoglu, Fahrettin; Sekerci, M.

    2005-01-01

    The thermal conductivity and crystallization mechanism of alumina (Al2O3)/fluorescein sodium salt (FSS) composites prepared by the powder metallurgy method have been investigated by means of differential thermal analysis. The Kissinger method is applied to determine the crystallization kinetics from the endotherm peaks. The activation energy E and Avrami parameter n were calculated. The kinetic parameters (E and n) have made it possible to postulate the type of crystal growth exhibited in the crystallization process. The crystallization growth is found to be one-dimensional for the composite system. The thermal conductivity of the composite system was also determined by differential scanning calorimetry.

  1. Preparation of crystal-controlled Y-TZP/Al2O3 nanocomposites

    NASA Astrophysics Data System (ADS)

    Fang, Y.; Zhang, Y.; Hu, L.

    2012-12-01

    ZrO2-Y2O3-Al2O3 nanocrystalline powders with different grain sizes have been synthesized using a chemical coprecipitation method. Nano-powders were compacted uniaxially and densified in a vacuum hot-pressing furnace. Density, pore size distribution, grain size and composition of the composites were determined by various techniques, including BET gas absorption, field-emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD). It has been shown that the porosity, grain and pore size of the ceramics can be controlled by the initial powder size and sintering temperature. Fully densified ceramics with narrow grain size distribution in the range of 100 ˜ 500 nm could be obtained.

  2. CO oxidation mechanism on the γ-Al2O3 supported single Pt atom: First principle study

    NASA Astrophysics Data System (ADS)

    Gao, Hongwei

    2016-08-01

    Understanding the role of metal-support interaction for the supported single-atom catalysts is very important in heterogeneous catalysis. Here, Three different CO oxidation mechanisms on Pt/γ-Al2O3 catalyst were probed by periodic density functional theory (DFT) calculations in detail, namely the reactive O*sbnd Osbnd C*dbnd O intermediate mechanism, the reactive CO3 intermediate mechanism and the Pt-Al3+ double sites mechanism. According to the calculated results analysis, we concluded that the dominant reaction pathway at the low temperatures is the reactive O*sbnd Osbnd C*dbnd O intermediate mechanism. Our results are in very good agreement with the experimental evidence for O*sbnd Osbnd C*dbnd O coverage on Pt/γ-Al2O3 at room temperature by an in situ diffuse reflectance infrared detector.

  3. Nonlinear optical response of nanocomposites based on KDP single crystal with incorporated Al2O3*nH2O nanofibriles under CW and pulsed laser irradiation at 532 nm

    NASA Astrophysics Data System (ADS)

    Popov, A. S.; Uklein, A. V.; Multian, V. V.; Dantec, R. Le; Kostenyukova, E. I.; Bezkrovnaya, O. N.; Pritula, I. M.; Gayvoronsky, V. Ya.

    2016-11-01

    Optical properties and nonlinear optical response due to the CW and pulsed laser radiation self-action at 532 nm were studied in composites based on KDP single crystals with incorporated nanofibriles of nanostructured oxyhydroxide of aluminum (NOA). It was shown a high optical quality and structural homogeneity of nanocomposites KDP:NOA by the transmittance spectra, elastic optical scattering and XRD analysis. It was observed manifestation of the second harmonic generation efficiency enhancement in the KDP:NOA versus the nominally pure KDP (λ=1064 nm, τ=1 ns) that is correlated with efficient refractive index self-modulation Δn ∼10-4 (λ=532 nm, τ=30 ps). In the pyramidal and prismatic growth sectors of the nominally pure KDP crystal it was shown opposite signs of the photoinduced variations both of the refractive index and of the optical absorption/bleaching due to resonant excitation of the native defects at 532 nm. It should be considered for the wide-aperture laser frequency KDP family based convertors fabrication.

  4. Low-temperature growth of single-walled carbon nanotube using Al2O3/Pd/Al2O3 multilayer catalyst by alcohol gas source method at high vacuum

    NASA Astrophysics Data System (ADS)

    Kiribayashi, Hoshimitsu; Ogawa, Seigo; Kozawa, Akinari; Saida, Takahiro; Naritsuka, Shigeya; Maruyama, Takahiro

    2016-06-01

    We carried out single-walled carbon nanotube (SWCNT) growth at 500 and 600 °C using Al2O3/Pd/Al2O3 multilayer catalysts on SiO2/Si substrates by the alcohol gas source method. When the ethanol pressures were 1 × 10-4 and 1 × 10-3 Pa, radial-breathing-mode (RBM) peaks and sharp G band peaks appeared in Raman spectra, indicating the growth of SWCNTs even at 500 °C. When the growth temperature and ethanol pressure were 500 °C and 1 × 10-4 Pa, respectively, the growth rate decreased gradually with the growth time, but the SWCNT growth continued for more than 4 h and the diameter distribution changed as the growth proceeded. X-ray photoelectron spectroscopy measurements showed that oxidized Pd catalyst particles were reduced to metallic states after the SWCNT growth started.

  5. Single grain analysis on a nanoscale in ZrO2:Al2O3 nano-composites by means of high-resolution scanning transmission electron Microscopy

    NASA Astrophysics Data System (ADS)

    Brossmann, Ulrich; Albu, Mihaela; Hofer, Ferdinand; Würschum, Roland

    2016-12-01

    Nano-particulate powders of Al2O3:ZrO2 composites and the pure constituents were prepared by microwave plasma process synthesis and studied by high resolution scanning transmission electron microscopy. The ZrO2:Al2O3 nanocomposite samples showed a structure of randomly arranged, crystalline grains of both ZrO2 and Al2O3 with a size in the range of 3-5 nm. For each constituent, both cubic and monoclinic grains were observed. Similarly prepared, single phase Al2O3 nanoparticles were found to be completely amorphous. In the case of ZrO2, the crystallite size and the fraction of the monoclinic ZrO2 phase is noticeably reduced in the ZrO2:Al2O3 nanocomposite in comparison to single phase samples. The observation of ultra-small crystalline Al2O3 in the composite samples, is tentatively ascribed to a modification of the interface energy by the contact of Al2O3 and ZrO2 as well as a possible uptake of ZrO2 into the Al2O3 grains from the gas phase during synthesis.

  6. Influence of Al 2O 3 additions on the crystallization mechanism and properties of diopside/anorthite hybrid glass-ceramics for LED packaging materials

    NASA Astrophysics Data System (ADS)

    Kang, Mina; Kang, Seunggu

    2011-07-01

    The crystallization mechanism and properties of diopside (CaMgSi 2O 6)/anorthite (CaAl 2Si 2O 8) hybrid glass-ceramics fabricated from a CMSA (CaO-MgO-SiO 2-Al 2O 3) glass system were studied as a function of Al 2O 3 additions. The parent glass prepared was pressed to pellets isostatically and was sintered to produce glass-ceramics. A non-isothermal analysis was performed to study the crystallization behavior of diopside/anorthite hybrid glass-ceramics using differential thermal analysis (DTA) with various heating rates (5-20 K min -1) and John-Mehl-Avrami and Kissinger equations. The occupying ratio of diopside and anorthite phases, crystal identification and microstructure in the glass-ceramics containing various Al 2O 3 contents were analyzed. Also the thermal conductivity and density of diopside/anorthite composites were measured to apply to LED packaging materials. The main crystalline phases for CaO-MgO-SiO 2-Al 2O 3 glass-ceramics system containing 8.6 wt% or less Al 2O 3, and 15.9 wt% or more Al 2O 3 were the diopside and anorthite, respectively. The difference (Δ T) of initiation temperature for crystallized ( Tx) and glass transition temperature ( Tg), calculated from the DTA curve for a glass is inversely proportional to the density of glass-ceramics fabricated from the glass. The highest crystallization temperature was 946 °C for the glass-ceramics containing 27.4 wt% Al 2O 3, which is low enough to apply the LTCC process. The glass-ceramics of diopside base with no Al 2O 3 added had the highest thermal conductivity of 2.372 W/m °C among all specimens fabricated in this study.

  7. Interface Properties of Atomic-Layer-Deposited Al2O3 Thin Films on Ultraviolet/Ozone-Treated Multilayer MoS2 Crystals.

    PubMed

    Park, Seonyoung; Kim, Seong Yeoul; Choi, Yura; Kim, Myungjun; Shin, Hyunjung; Kim, Jiyoung; Choi, Woong

    2016-05-11

    We report the interface properties of atomic-layer-deposited Al2O3 thin films on ultraviolet/ozone (UV/O3)-treated multilayer MoS2 crystals. The formation of S-O bonds on MoS2 after low-power UV/O3 treatment increased the surface energy, allowing the subsequent deposition of uniform Al2O3 thin films. The capacitance-voltage measurement of Au-Al2O3-MoS2 metal oxide semiconductor capacitors indicated n-type MoS2 with an electron density of ∼10(17) cm(-3) and a minimum interface trap density of ∼10(11) cm(-2) eV(-1). These results demonstrate the possibility of forming a high-quality Al2O3-MoS2 interface by proper UV/O3 treatment, providing important implications for their integration into field-effect transistors.

  8. Linear and nonlinear optical properties of KDP crystals with incorporated Al2O3ṡnH2O nanoparticles

    NASA Astrophysics Data System (ADS)

    Pritula, I. M.; Kosinova, A. V.; Bezkrovnaya, O. N.; Kolybaeva, M. I.; Puzikov, V. M.; Lopin, A. V.; Tkachenko, V. F.; Kopylovsky, M. A.; Yatsyna, V. O.; Gayvoronsky, V. Ya.

    2013-10-01

    Optical and nonlinear optical properties of a novel composite system based on KDP single crystals with embedded nanoparticles of nanostructured oxyhydroxide of aluminum (Al2O3·nH2O, NOA), were studied. KDP crystals with NOA nanoparticles (KDP:NOA) possess high optical quality and homogeneity. Optical spectroscopy showed the presence of an absorption band at 270 nm caused by NOA nanoparticles incorporated in the KDP matrix. There was observed an enhancement of nonlinear refractive index and inversion of its sign in KDP:NOA crystals in comparison with nominally pure KDP crystals under excitation of picosecond laser pulses. The obtained results demonstrate that KDP:NOA is a promising composite material for optoelectronics and nonlinear optics.

  9. Crystallization behavior and properties of BaO-Al2O3-2SiO2 glass matrices

    NASA Technical Reports Server (NTRS)

    Drummond, Charles H., III; Bansal, Narottam P.

    1990-01-01

    Glass of stoichiometric celsian composition, BaO-Al2O3-SiO2, has a density of 3.39 g/cu cm, a thermal expansion coefficient of 6.6 x 10 to the -6th/C, a glass-transition temperature of 910 C, and a dilatometric softening point of 925 C. On heat treatment, only hexacelsian crystallized out on the surface, but both celsian and hexacelsian were present in the bulk. Effects of cold isostatic pressing (CIP), sintering, and hot-pressing, in the presence and absence of an additive, on the formation of the celsian phase in the glass have been studied. CIP'd samples, after appropriate heat treatments, always crystallized out as celsian, whereas presence of 5-10 wt pct of an additive was necessary for formation of celsian in sintered as well as hot-pressed specimens. Green density increased with CIP'ing pressure but had no effect on sintered density. Hot-pressing resulted in fully dense samples.

  10. Crystallization behavior and properties of BaO-Al2O3-2SiO2 glass matrices

    NASA Technical Reports Server (NTRS)

    Drummond, Charles H., III; Bansal, Narottam P.

    1990-01-01

    Glass of stoichiometric celsian composition, BaO-Al2O3-2SiO2, is a potential glass-ceramic matrix for high-temperature composites. The glass has a density of 3.39 g/cu cm, thermal expansion coefficient of 6.6 x 10(exp -6)/deg C glass transition temperature of 910 C, and dilatometric softening point of 925 C. On heat treatment, only hexacelsian crystallized out on the surface, but both celsian and hexacelsian were present in the bulk. Effects of cold isostatic pressing (CIP), sintering, and hot pressing, in the presence and absence of an additive, on the formation of the celsian phase in the glass were studied. CIP'ed samples, after appropriate heat treatments, always crystallized out as celsian whereas the presence of 5 to 10 weight percent of an additive was necessary for formation of celsian in sintered as well as hot pressed specimens. Green density increased with CIP'ing pressure but had no effect on sintered density. Hot pressing resulted in fully dense samples.

  11. Crystallization paths in SiO2-Al2O3-CaO system as a genotype of silicate materials

    NASA Astrophysics Data System (ADS)

    Lutsyk, V. I.; Zelenaya, A. E.

    2013-12-01

    The phases trajectories in the fields of primary crystallization of cristobalite (SiO2cr), tridymite (SiO2tr), mullite (3Al2O3-2SiO2) and in a field of liquid immiscibility are analyzed on a basis of computer model for T-x-y diagram of SiO2-Al2O3-CaO system. The concentration fields with unique set of microconstituents and the fields without individual crystallization schemes and microconstituents are revealed.

  12. Single and combined effects of aluminum (Al2O3) and zinc (ZnO) oxide nanoparticles in a freshwater fish, Carassius auratus.

    PubMed

    Benavides, María; Fernández-Lodeiro, Javier; Coelho, Pedro; Lodeiro, Carlos; Diniz, Mário S

    2016-12-01

    The increasing use of nanoparticles (NPs) worldwide has raised some concerns about their impact on the environment. The aim of the study was to assess the toxicity of metal oxide nanoparticles, singly or combined, in a freshwater fish (Carassius auratus). The fish were exposed for 7, 14, and 21 days to different concentrations of NPs (10 μg Al2O3.L(-1), 10 μg ZnO.L(-1), 10 μg Al2O3.L(-1) plus 10 μg ZnO.L(-1), 100 μg Al2O3.L(-1), 100 μg ZnO.L(-1), and 100 μg Al2O3.L(-1) plus 100 μg ZnO.L(-1)). At the end of each exposure period, antioxidant enzyme activity (catalase, glutathione-S-transferase, and superoxide dismutase), lipid peroxidation, and histopathology were assessed in the gills and livers of C. auratus. The results show an increase in catalase (CAT) and superoxide dismutase (SOD) activity in the gills and livers of fish, especially after 14 days of exposure to single and combined NPs, followed by a reduction at 21 days. An increase in glutathione S-transferase (GST) was observed in gills after 7 days for all tested NP concentrations (single and combined); while in livers, a significant increase was determined after 14 days of exposure to 100 μg.L(-1) of both single ZnO and Al2O3 NPs. Lipid peroxidation (LPO) significantly increased in gills after 7 days of exposure to 100 μg.L(-1) Al2O3 NPs (single or combined). In livers, LPO increased significantly after 7 days of exposure to all tested concentrations of both single ZnO and Al2O3 (except for 10 μg Al2O3.L(-1)), and after 14 days of exposure to ZnO (10 and 100 μg.L(-1)) and Al2O3 (100 μg.L(-1)). The results from histological observations suggest that exposure to metal oxide NPs affected both livers and gills, presenting alterations such as gill hyperplasia and liver degeneration. However, the most pronounced effects were found in gills. In general, this study shows that the tested NPs, single or combined, are capable of causing sub-lethal effects on C. auratus, but when

  13. High Temperature Mechanical Characterization and Analysis of Al2O3 /Al2O3 Composition

    NASA Technical Reports Server (NTRS)

    Gyekenyesi, John Z.; Jaskowiak, Martha H.

    1999-01-01

    Sixteen ply unidirectional zirconia coated single crystal Al2O3 fiber reinforced polycrystalline Al2O3 was tested in uniaxial tension at temperatures to 1400 C in air. Fiber volume fractions ranged from 26 to 31%. The matrix has primarily open porosity of approximately 40%. Theories for predicting the Young's modulus, first matrix cracking stress, and ultimate strength were applied and evaluated for suitability in predicting the mechanical behavior of Al2O3/Al2O3 composites. The composite exhibited pseudo tough behavior (increased area under the stress/strain curve relative to monolithic alumina) from 22 to 1400 C. The rule-of-mixtures provides a good estimate of the Young's modulus of the composite using the constituent properties from room temperature to approximately 1200 C for short term static tensile tests in air. The ACK theory provides the best approximation of the first matrix cracking stress while accounting for residual stresses at room temperature. Difficulties in determining the fiber/matrix interfacial shear stress at high temperatures prevented the accurate prediction of the first matrix cracking stress above room temperature. The theory of Cao and Thouless, based on Weibull statistics, gave the best prediction for the composite ultimate tensile strength.

  14. Crystallographic Texture and Orientation Variants in Al2O3-Y3Al5O12 Directionally Solidified Eutectic Crystals

    NASA Technical Reports Server (NTRS)

    Frazer, Colleen S.; Dickey, Elizabeth C.; Sayir, Ali; Farmer, Serene (Technical Monitor)

    2001-01-01

    Eutectic rods of Al2O3 and Y3Al5O12 were grown by a laser-heated float zone method, and their microstructure and crystallographic texture were studied by scanning electron microscopy, electron backscattered diffraction and x-ray diffraction. The composites were found to be highly textured with two twin-related crystallographic orientation relationships between the phases. Electron backscattered diffraction was employed to determine the spatial distribution of the orientational variants within the samples and to define the crystallographic orientation of various microstructural features.

  15. Effect of zinc-borate glass addition on the thermal properties of the cordierite/Al2O3 composites containing nano-sized spinel crystal.

    PubMed

    Jo, Sinae; Kang, Seunggu

    2013-11-01

    Low-melting zinc-borate glass was added to the cordierite/Al2O3 composite in order to improve the sintering facility of Al2O3 and formation of nano-sized spinel crystal of high thermal conductivity. Increasing the ZnO/B2O3 ratio in the zinc-borate glass increased the ZnAl2O4 spinel and decreased the Al4B2O9 crystal peak intensities in X-ray diffraction pattern. The XRD peak intensities of the ZnAl2O4 spinel and Al4B2O9 crystals in the specimen containing 10 wt% zinc-borate glass (10G series) are higher than that of the specimen containing 5 wt% zinc-borate glass (5G series). The microstructures of most 10G series specimens had the flower-shaped crystal which was composed of 50 nm wide and 250 nm long needle-like crystals and identified as ZnAl2O4 spinel phase. The thermal conductivity of the 10G series specimen was higher than that of the 5G series in any ZnO/B2O3 ratio due to the formation of plenty of nano-sized ZnAl2O4 spinel of high thermal conductivity. Particularly, the thermal conductivity of the cordierite/Al2O3 composite containing 10 wt% zinc-borate glass of ZnO/B2O3 weight ratio = 1.5 was 3.8 W/Km which is much higher than that of the published value (3.0 W/Km).

  16. Dipolar interactions and their influence on the critical single domain grain size of Ni in layered Ni/Al(2)O(3) composites.

    PubMed

    Das, R; Gupta, A; Kumar, D; Oh, S H; Pennycook, S J; Hebard, A F

    2008-09-24

    Pulsed laser deposition has been used to fabricate Ni/Al(2)O(3) multilayer composites in which Ni nanoparticles with diameters in the range of 3-60 nm are embedded as layers in an insulating Al(2)O(3) host. At fixed temperatures, the coercive fields plotted as a function of particle size show well-defined peaks, which define a critical size that delineates a crossover from coherently rotating single domain to multiple domain behavior. We observe a shift in peak position to higher grain size as temperature increases and describe this shift with theory that takes into account the decreasing influence of dipolar magnetic interactions from thermally induced random orientations of neighboring grains.

  17. Dipolar interactions and their influence on the critical single domain grain size of Ni in layered Ni/Al(2)O(3) composites

    SciTech Connect

    Das, R; Gupta, A.; Ho, S; Pennycook, Stephen J; Hebard, A.

    2008-01-01

    Pulsed laser deposition has been used to fabricate Ni/Al2O3 multilayer composites in which Ni nanoparticles with diameters in the range of 3 60 nm are embedded as layers in an insulating Al2O3 host. At fixed temperatures, the coercive fields plotted as a function of particle size show well-defined peaks, which define a critical size that delineates a crossover from coherently rotating single domain to multiple domain behavior. We observe a shift in peak position to higher grain size as temperature increases and describe this shift with theory that takes into account the decreasing influence of dipolar magnetic interactions from thermally induced random orientations of neighboring grains.

  18. Modelling Equilibrium and Fractional Crystallization in the System MgO-FeO-CaO-Al2O3-SiO2

    NASA Technical Reports Server (NTRS)

    Herbert, F.

    1985-01-01

    A mathematical modelling technique for use in petrogenesis calculations in the system MgO-FeO-CaO-Al2O3-SiO2 is reported. Semiempirical phase boundary and elemental distribution information was combined with mass balance to compute approximate equilibrium crystallization paths for arbitrary system compositions. The calculation is applicable to a range of system compositions and fractionation calculations are possible. The goal of the calculation is the computation of the composition and quantity of each phase present as a function of the degree of solidification. The degree of solidification is parameterized by the heat released by the solidifying phases. The mathematical requirement for the solution of this problem is: (1) An equation constraining the composition of the magma for each solid phase in equilibrium with the liquidus phase, and (2) an equation for each solid phase and each component giving the distribution of that element between that phase and the magma.

  19. Quantum chemical simulation of the self-trapped hole in α-Al2O3 crystals

    NASA Astrophysics Data System (ADS)

    Jacobs, P. W. M.; Kotomin, E. A.

    1992-08-01

    Atomistic simulations of hole self-trapping in a pure corundum crystal have been undertaken using three different approaches. The inward Jahn-Teller displacement of two O atoms (on which 80% of the hole density is concentrated), accompanied by the outward displacement of the two nearest Al atoms, gives the energetically most favorable configuration, thus suggesting a self-trapped-hole (STH) model analogous to that in alkali halides (VK center). The optical absorption of STH and three possible kinds of thermally activated hops are discussed in relation to experimental data.

  20. Raman study of TiO2 role in SiO2-Al2O3-MgO-TiO2-ZnO glass crystallization.

    PubMed

    Furić, Kresimir; Stoch, Leszek; Dutkiewicz, Jan

    2005-05-01

    Tough glass-ceramic material of special mechanical properties with nanosize crystal phases formed by appropriately controlled crystallization was studied by Raman spectroscopy. It was obtained by TiO2 activated crystallization of Mg-aluminosilicate glass of SiO2-Al2O3-MgO-TiO2-ZnO composition. Crystallization was preceded by a change in the TiO2 structural position and state, which is manifested by a changed color of glass from yellow into blue shortly before the glass transformation (Tg) temperature. Raman spectroscopy was applied to explain the mechanism of this process and to establish the role of TiO2 in the early stage of glass crystallization that precedes a complete crystal phase formation. The starting glasses were found in almost complete disorder, since all bands were weak, broad and dominated by a Bose band at about 90 cm-1. After the sample annealing all bands turned out better resolved and the Bose band practically disappeared, both confirming the amorphous structure reorganization process. A multiplet observed in the vicinity of 150 cm-1 we assigned to the anatase and other titania structures that can be considered prime centers of crystallization. Finally, in the closest neighborhood of the Rayleigh line the low frequency mode characterizing nanoparticles was observed. According to this band theory, the mean size of initial titania crystallites is about 10nm for all samples, but the size distribution varies within factor two among them.

  1. Single Pd Atoms on θ-Al2O3 (010) Surface do not Catalyze NO Oxidation.

    PubMed

    Narula, Chaitanya K; Allard, Lawrence F; Moses-DeBusk, Melanie; Stocks, G Malcom; Wu, Zili

    2017-04-03

    New convenient wet-chemistry synthetic routes have made it possible to explore catalytic activities of a variety of single supported atoms, however, the single supported atoms on inert substrates (e.g. alumina) are limited to adatoms and cations of Pt, Pd, and Ru. Previously, we have found that single supported Pt atoms are remarkable NO oxidation catalysts. In contrast, we report that Pd single atoms are completely inactive for NO oxidation. The diffuse reflectance infra-red spectroscopy (DRIFTS) results show the absence of nitrate formation on catalyst. To explain these results, we explored modified Langmuir-Hinshelwood type pathways that have been proposed for oxidation reactions on single supported atom. In the first pathway, we find that there is energy barrier for the release of NO2 which prevent NO oxidation. In the second pathway, our results show that there is no driving force for the formation of O=N-O-O intermediate or nitrate on single supported Pd atoms. The decomposition of nitrate, if formed, is an endothermic event.

  2. Characterization of SDC-Al2O3 solid electrolyte

    NASA Astrophysics Data System (ADS)

    Ramesh, S.; Raju, K. C. James; Reddy, C. Vishnuvardhan

    2012-06-01

    SDC20-Al2O3 materials were synthesized through the sol-gel method. Dense SDC20-Al2O3 ceramics were obtained through sintering the pellets at 1300°C. SDC20-Al2O3 materials were characterized by XRD, SEM and impedance spectroscopy. XRD measurements indicate that synthesized materials crystallized in cubic structure. Average crystallite size of the samples was in the range 11-12 nm. The relative density of SDC20-Al2O3 samples was over 95% of the theoretical density. Addition of Al2O3 promotes densification. Surface morphology was analyzed using SEM. The two-probe a.c. impedance spectroscopy was used to study the total ionic conductivity of doped and co-doped ceria in the temperature range 350-700°C. The SDC20-Al2O3 composition showed improved total ionic conductivity and minimum activation energy.

  3. Single Pd Atoms on θ-Al2O3 (010) Surface do not Catalyze NO Oxidation

    DOE PAGES

    Narula, Chaitanya K.; Allard, Lawrence F.; Moses-DeBusk, Melanie; ...

    2017-04-03

    New convenient wet chemistry synthetic routes have made it possible to explore catalytic activities of a variety of single supported atoms. The majority of single supported atoms have been synthesized on active supports which participate in oxidation reactions. The single supported atoms on inert substrates (e.g. alumina) are limited to Pt adatoms and Pd cations, and are generally active toward CO oxidation. In this manuscript, we show that single Pd atoms on -alumina show high CO oxidation activity; however, they exhibit no detectable NO oxidation under our experimental conditions. This led us to employ first principles modeling to explore multiplemore » Langmuir-Hinshelwood-type pathways to explain high CO oxidation activity but lack of NO oxidation activity. For completeness, we have also examined Eley-Riedel pathways. We find that a pathway that involves carbonate or nitrate as an intermediate can explain the experimental results of CO and NO oxidation on single alumina supported Pd cations.« less

  4. Effect of SiO2 on the Crystallization Behaviors and In-Mold Performance of CaF2-CaO-Al2O3 Slags for Drawing-Ingot-Type Electroslag Remelting

    NASA Astrophysics Data System (ADS)

    Shi, Cheng-Bin; Li, Jing; Cho, Jung-Wook; Jiang, Fang; Jung, In-Ho

    2015-10-01

    The crystallization characteristics of CaF2-CaO-Al2O3 slags with varying amounts of SiO2 were experimentally studied. The effects of slag crystallization behaviors on the horizontal heat transfer and lubrication performance in drawing-ingot-type electroslag remelting (ESR) were also evaluated in terms of as-cast ingots surface quality and drawing-ingot operation. The results show that increasing SiO2 addition from 0 to 6.8 mass pct strongly suppresses the crystallization of ESR type CaF2-CaO-Al2O3 slags. The crystallization temperature of the studied slags decreases with the increase in SiO2 addition. The liquidus temperatures of the slags also show a decreasing trend with increasing SiO2 content. In CaF2-CaO-Al2O3-(SiO2) slags, faceted 11CaO·7Al2O3·CaF2 crystals precipitate first during continuous cooling of the slag melts, followed by the formation of CaF2 at lower temperatures. 11CaO·7Al2O3·CaF2 was confirmed to be the dominant crystalline phase in the studied slags. CaF2-CaO-Al2O3 slags with a small amount of SiO2 addition are favorable for providing sound lubrication and horizontal heat transfer in mold for drawing-ingot-type ESR, which consequently bring the improvement in the surface quality of ESR ingot and drawing-ingot operating practice as demonstrated by plant trials.

  5. Influence of Content of Al2O3 on Structure and Properties of Nanocomposite Nb-B-Al-O films.

    PubMed

    Liu, Na; Dong, Lei; Dong, Lei; Yu, Jiangang; Pan, Yupeng; Wan, Rongxin; Gu, Hanqing; Li, Dejun

    2015-12-01

    Nb-B-Al-O nanocomposite films with different power of Al2O3 were successfully deposited on the Si substrate via multi-target magnetron co-sputtering method. The influences of Al2O3's content on structure and properties of obtained nanocomposite films through controlling Al2O3's power were investigated. Increasing the power of Al2O3 can influence the bombarding energy and cause the momentum transfer of NbB2. This can lead to the decreasing content of Al2O3. Furthermore, the whole films showed monocrystalline NbB2's (100) phase, and Al2O3 shaded from amorphous to weak cubic-crystalline when decreasing content of Al2O3. This structure and content changes were proof by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). When NbB2 grains were far from each other in lower power of Al2O3, the whole films showed a typical nanocomposite microstructure with crystalline NbB2 grains embedded in a matrix of an amorphous Al2O3 phase. Continuing increasing the power of Al2O3, the less content of Al2O3 tended to cause crystalline of cubic-Al2O3 between the close distances of different crystalline NbB2 grains. The appearance of cubic-crystallization Al2O3 can help to raise the nanocomposite films' mechanical properties to some extent. The maximum hardness and elastic modulus were up to 21.60 and 332.78 GPa, which were higher than the NbB2 and amorphous Al2O3 monolithic films. Furthermore, this structure change made the chemistry bond of O atom change from the existence of O-Nb, O-B, and O-Al bonds to single O-Al bond and increased the specific value of Al and O. It also influenced the hardness in higher temperature, which made the hardness variation of different Al2O3 content reduced. These results revealed that it can enhance the films' oxidation resistance properties and keep the mechanical properties at high temperature. The study highlighted the importance of controlling the Al2O3's content to prepare

  6. Fluoride evaporation and crystallization behavior of CaF2-CaO-Al2O3-(TiO2) slag for electroslag remelting of Ti-containing steels

    NASA Astrophysics Data System (ADS)

    Shi, Cheng-bin; Cho, Jung-wook; Zheng, Ding-li; Li, Jing

    2016-06-01

    To elucidate the behavior of slag films in an electroslag remelting process, the fluoride evaporation and crystallization of CaF2-CaO-Al2O3-(TiO2) slags were studied using the single hot thermocouple technique. The crystallization mechanism of TiO2-bearing slag was identified based on kinetic analysis. The fluoride evaporation and incubation time of crystallization in TiO2-free slag are found to considerably decrease with decreasing isothermal temperature down to 1503 K. Fish-bone and flower-like CaO crystals precipitate in TiO2-free slag melt, which is accompanied by CaF2 evaporation from slag melt above 1503 K. Below 1503 K, only near-spherical CaF2 crystals form with an incubation time of less than 1 s, and the crystallization is completed within 1 s. The addition of 8.1wt% TiO2 largely prevents the fluoride evaporation from slag melt and promotes the slag crystallization. TiO2 addition leads to the precipitation of needle-like perovskite (CaTiO3) crystals instead of CaO crystals in the slag. The crystallization of perovskite (CaTiO3) occurs by bulk nucleation and diffusion-controlled one-dimensional growth.

  7. Characteristics of ethylene glycol-Al2O3 nanofluids prepared by utilizing Al2O3 nanoparticles synthesized from local bauxite

    NASA Astrophysics Data System (ADS)

    Syarif, D. G.

    2016-11-01

    Nanoparticles of Al2O3 have been synthesized from local bauxite mineral, and ethylene glycol (EG)-Al2O3 nanofluids have been prepared. Powder Al(OOH) was extracted from local bauxite using bayer process, and heated at 600°C for 3 hours to get Al2O3 nanoparticles. XRD analyses showed that the Al2O3 nanoparticles crystallizes in γ-Al2O3 with crystallite size of 4.12 nm. The specific surface area of the ACO3 nanoparticles was 296.72 m2/gr. Viscosity of the EG-Al2O3 nanofluids was temperature dependent, and decreased with increasing temperature. The viscosity of the nanofluids increased with the concentration of the Al2O3 nanoparticles. Meanwhile, Critical Heat Flux (CHF) enhancement of the nanofluids increased with the concentration of the Al2O3 nanoparticles. The largest CHF enhancement was 54% at Al2O3 concentration of 0.095 vol %.

  8. Crystallization Kinetics and Mechanism of CaO-Al2O3-Based Mold Flux for Casting High-Aluminum TRIP Steels

    NASA Astrophysics Data System (ADS)

    Shi, Cheng-Bin; Seo, Myung-Duk; Wang, Hui; Cho, Jung-Wook; Kim, Seon-Hyo

    2014-09-01

    Non-isothermal crystallization of the newly developed lime-alumina-based mold fluxes was investigated using differential scanning calorimetry. The crystallization kinetic parameters were determined by Ozawa equation, the combined Avrami-Ozawa equation, and the differential iso-conversional method of Friedman. It was found that Ozawa method failed to describe the non-isothermal crystallization behavior of the mold fluxes. The Avrami exponent determined by the combined Avrami-Ozawa equation indicates that the crystallization of cuspidine occurs through bulk nucleation and reaction-controlled three-dimensional growth, and then transforms to reaction-controlled two-dimensional growth at the crystallization later stage in lime-alumina-based mold fluxes with higher B2O3 content. For the mold fluxes with lower B2O3 content (10.8 mass pct), the crystallization of cuspidine is bulk nucleation and reaction-controlled two-dimensional growth at the crystallization primary stage followed by a diffusion-controlled two-dimensional growth process. The crystallization of CaF2 in mold flux originates from bulk nucleation and diffusion-controlled three-dimensional growth, which then transforms to two-dimensional growth. FE-SEM observations support these kinetic analysis results. The effective activation energy for cuspidine crystallization in the mold flux with higher B2O3 and Na2O contents increases as the crystallization progresses, and then decreases at the relative degree of crystallinity greater than 60 pct. The transition point of this trend approximately corresponds to the relative degree of crystallinity at which the crystallization mode of cuspidine transforms. For the mold fluxes with lower B2O3 and Na2O contents, the effective activation energy for cuspidine formation varies monotonically with the increase in the relative degree of crystallinity.

  9. Crystallization Kinetics and Mechanism of CaO-Al2O3-Based Mold Flux for Casting High-Aluminum TRIP Steels

    NASA Astrophysics Data System (ADS)

    Shi, Cheng-Bin; Seo, Myung-Duk; Wang, Hui; Cho, Jung-Wook; Kim, Seon-Hyo

    2015-02-01

    Non-isothermal crystallization of the newly developed lime-alumina-based mold fluxes was investigated using differential scanning calorimetry. The crystallization kinetic parameters were determined by Ozawa equation, the combined Avrami-Ozawa equation, and the differential iso-conversional method of Friedman. It was found that Ozawa method failed to describe the non-isothermal crystallization behavior of the mold fluxes. The Avrami exponent determined by the combined Avrami-Ozawa equation indicates that the crystallization of cuspidine occurs through bulk nucleation and reaction-controlled three-dimensional growth, and then transforms to reaction-controlled two-dimensional growth at the crystallization later stage in lime-alumina-based mold fluxes with higher B2O3 content. For the mold fluxes with lower B2O3 content (10.8 mass pct), the crystallization of cuspidine is bulk nucleation and reaction-controlled two-dimensional growth at the crystallization primary stage followed by a diffusion-controlled two-dimensional growth process. The crystallization of CaF2 in mold flux originates from bulk nucleation and diffusion-controlled three-dimensional growth, which then transforms to two-dimensional growth. FE-SEM observations support these kinetic analysis results. The effective activation energy for cuspidine crystallization in the mold flux with higher B2O3 and Na2O contents increases as the crystallization progresses, and then decreases at the relative degree of crystallinity greater than 60 pct. The transition point of this trend approximately corresponds to the relative degree of crystallinity at which the crystallization mode of cuspidine transforms. For the mold fluxes with lower B2O3 and Na2O contents, the effective activation energy for cuspidine formation varies monotonically with the increase in the relative degree of crystallinity.

  10. What determines the interfacial configuration of Nb/Al2O3 and Nb/MgO interface

    PubMed Central

    Du, J. L.; Fang, Y.; Fu, E. G.; Ding, X.; Yu, K. Y.; Wang, Y. G.; Wang, Y. Q.; Baldwin, J. K.; Wang, P. P.; Bai, Q.

    2016-01-01

    Nb films are deposited on single crystal Al2O3 (110) and MgO(111) substrates by e-beam evaporation technique. Structure of Nb films and orientation relationships (ORs) of Nb/Al2O3 and Nb/MgO interface are studied and compared by the combination of experiments and simulations. The experiments show that the Nb films obtain strong (110) texture, and the Nb film on Al2O3(110) substrate shows a higher crystalline quality than that on MgO(111) substrate. First principle calculations show that both the lattice mismatch and the strength of interface bonding play major roles in determining the crystalline perfection of Nb films and ORs between Nb films and single crystal ceramic substrates. The fundamental mechanisms for forming the interfacial configuration in terms of the lattice mismatch and the strength of interface bonding are discussed. PMID:27698458

  11. CO oxidation on supported single Pt atoms: experimental and ab initio density functional studies of CO interaction with Pt atom on θ-Al2O3(010) surface.

    PubMed

    Moses-DeBusk, Melanie; Yoon, Mina; Allard, Lawrence F; Mullins, David R; Wu, Zili; Yang, Xiaofan; Veith, Gabriel; Stocks, G Malcolm; Narula, Chaitanya K

    2013-08-28

    Although there are only a few known examples of supported single-atom catalysts, they are unique because they bridge the gap between homogeneous and heterogeneous catalysis. Here, we report the CO oxidation activity of monodisperse single Pt atoms supported on an inert substrate, θ-alumina (Al2O3), in the presence of stoichiometric oxygen. Since CO oxidation on single Pt atoms cannot occur via a conventional Langmuir-Hinshelwood scheme (L-H scheme) which requires at least one Pt-Pt bond, we carried out a first-principles density functional theoretical study of a proposed pathway which is a variation on the conventional L-H scheme and inspired by the organometallic chemistry of platinum. We find that a single supported Pt atom prefers to bond to O2 over CO. CO then bonds with the oxygenated Pt atom and forms a carbonate which dissociates to liberate CO2, leaving an oxygen atom on Pt. Subsequent reaction with another CO molecule regenerates the single-atom catalyst. The energetics of the proposed mechanism suggests that the single Pt atoms will get covered with CO3 unless the temperature is raised to eliminate CO2. We find evidence for CO3 coverage at room temperature supporting the proposed mechanism in an in situ diffuse reflectance infrared study of CO adsorption on the catalyst's supported single atoms. Thus, our results clearly show that supported Pt single atoms are catalytically active and that this catalytic activity can occur without involving the substrate. Characterization by electron microscopy and X-ray absorption studies of the monodisperse Pt/θ-Al2O3 are also presented.

  12. Microstructural development of protective Al2O3 scales

    NASA Technical Reports Server (NTRS)

    Smialek, J. L.

    1984-01-01

    Microstructural characteristics of Al2O3 scales grown as protective coatings on NiCrAl alloys used in jet engines are described. The alloys were pure or doped with 0.3 percent Zr or Y and oxidized in 1 atm air at 1100 C for 0.1, 1 or 20.0 hr. The scales were then examined under a microscope. Transient epitaxial scales, formed during the 0.1 hr treatment and containing Ni, Cr and Al, consisted of a mosaic of subgrains and precipitates of different phases. The Y and Zr dopants had no effect on the nucleation site locations. The appearance of intergranular porosity at 0.1 hr was exacerbated after the 1 hr treatment. A bimodal void distribution appeared after 20 hr, when no porosity was evident. The detection of local areas of preferred orientation is taken as a spur to further studies of scale growth to gain control of the grain size or even to produce single crystal scales.

  13. Comparison of ALD and IBS Al2O3 films for high power lasers

    NASA Astrophysics Data System (ADS)

    Liu, Hao; Jensen, Lars; Becker, Jürgen; Wurz, Marc Christopher; Ma, Ping; Ristau, Detlev

    2016-12-01

    Atomic layer deposition (ALD) has been widely studied in Micro-electronics due to its self-terminating property. ALD also grows film coatings with precise thickness and nodular-free structure, which are desirable properties for high power coatings. The depositing process was studied to produce uniform, stable and economic Al2O3 single layers. The layer properties relevant to high power laser industry were studied and compared with IBS Al2O3 single layers. ALD Al2O3 showed a stable growth of 0.104 nm/cycle, band gap energy of 6.5 eV and tensile stress of about 480 MPa. It also showed a low absorption at wavelength 1064 nm within several ppm, and LIDT above 30 J/cm2. These properties are superior to the reference IBS Al2O3 single layers and indicate a high versatility of ALD Al2O3 for high power coatings.

  14. Metastability in the MgAl2O4-Al2O3 System

    DOE PAGES

    Wilkerson, Kelley R.; Smith, Jeffrey D.; Hemrick, James G.

    2014-07-22

    Aluminum oxide must take a spinel form ( γ-Al2O3) at elevated temperatures in order for extensive solid solution to form between MgAl2O4 and α-Al2O3. The solvus line between MgAl2O4 and Al2O3 has been defined at 79.6 wt% Al2O3 at 1500°C, 83.0 wt% Al2O3 at 1600°C, and 86.5 wt% Al2O3 at 1700°C. A metastable region has been defined at temperatures up to 1700°C which could have significant implications for material processing and properties. Additionally, initial processing could have major implications on final chemistry. The spinel solid solution region has been extended to form an infinite solid solution with Al2O3 at elevatedmore » temperatures. A minimum in melting at 1975°C and a chemistry of 96 wt% Al2O3 rather than a eutectic is present, resulting in no eutectic crystal formation during solidification.« less

  15. TiO2 effect on crystallization mechanism and physical properties of nano glass-ceramics of MgO-Al2O3-SiO2 glass system.

    PubMed

    Jo, Sinae; Kang, Seunggu

    2013-05-01

    The effect of TiO2 on the degree of crystallization, thermal properties and microstructure for MgO-Al2O3-SiO2 glass-ceramics system containing 0-13 wt% TiO2 and 0-1.5 wt% B2O3 in which the cordierite is the main phase was studied. Using Kissinger and Augis-Bennett equations, the activation energy, 510 kJ/mol and Avrami constant, 1.8 were calculated showing the surface-oriented crystallization would be preferred. The alpha-cordierite phase was generated in the glass-ceramics of containing TiO2 of 0-5.6 wt%. However, for the glass-ceramics of TiO2 content above 7 wt%, an alpha-cordierite disappeared and micro-cordierite phase was formed. The glass-ceramics of no TiO2 added had spherical crystals of few tens nanometer size spread in the matrix. As TiO2 content increased up to 5.6 wt%, a lump of dendrite was formed. In the glass-ceramics containing TiO2 7-13 wt%, in which the main phase is micro-cordierite, the dendrite crystal disappeared and a few hundred nanometer sized crystal particles hold tightly each other were generated. The thermal conductivity of glass-ceramics of both a-cordierite and micro-cordierite base decreased with TiO2 contend added. The thermal conductivity of glass-ceramics of 1.5 wt% TiO2 added was 3.4 W/mK which is 36% higher than that of glass-ceramics of no TiO2 added. The sintering temperature for 1.5 wt% TiO2 glass-ceramics was 965 degrees C which could be concluded as to apply to LTCC process for LED packaging.

  16. Influences of CaO on Crystallization, Microstructures, and Properties of BaO-Al2O3-B2O3-SiO2 Glass-Ceramics

    NASA Astrophysics Data System (ADS)

    Li, Bo; Tang, Bo; Xu, Mingjiang

    2015-10-01

    We have developed BaO-CaO-Al2O3-B2O3-SiO2 glass-ceramics with high thermal coefficient of expansion (TCE) to overcome thermal mismatch at board level. The crystalline phases include quartz (major), cristobalite (minor), and bazirite BaZrSi3O9 (minor). Calculations from whole-pattern fitting show that the crystallinity varies slightly within the range of 33.48% to 34.89%, while the mass fraction of the phases changes remarkably with the CaO content. This indicates that CaO cannot promote crystallization of Ba-Al-B-Si glass, but effectively suppresses the phase transformation from quartz to cristobalite, making the thermal expansion curves linear. An empirical equation for the TCE versus the temperature and the amount of CaO is established. Furthermore, the densification mechanism of Ca modifiers is revealed. Due to its higher field strength than Ba, substitution of Ca increases the glass viscosity and inhibits ion diffusion. Excessive CaO is thus harmful to the density, bending strength, and electrical properties. The sample with 10 wt.% CaO sintered at 950°C exhibited high bending strength (154.1 MPa) and high TCE (12.38 ppm/°C) as well as good electrical properties ( ɛ = 6.2, tan δ = 5 × 10-4, ρ = 3.8 × 1012 Ω cm).

  17. A comparison of the doppler-broadened positron annihilation spectra of neutron irradiated Al 2O 3 and MgAl 2O 3

    NASA Astrophysics Data System (ADS)

    Jones, P. L.; Schaffer, J. P.; Cocks, F. H.; Clinard, F. W.; Hurley, G. F.

    1985-01-01

    Radiation damage studies of oxides and ceramics have become of increasing importance due to the projected use of these materials in thermonuclear fusion reactors as electronic insulators and first wall materials. In addition these materials are important in RAD waste disposal. As part of a study of the defect structure in radiation damaged ceramics Doppler-broadened positron annihilation spectra have been obtained for a series of single crystal sapphire (α-Al 2O 3) and polycrystal (1:1) and (1:2) magnesium aluminate spinel (MgO·Al 2O 3 and MgO-2Al 2O 3) samples. These samples were irradiated in EBR-II to a fluence of 3 × 10 25 n/m 2 (E > 0.1 MeV) at 740°C, and 2 × 10 26 n/m 2 (E > 0.1 MeV) at ~ 550°C respectively. Positron annihilation spectra lineshapes for the irradiated, annealed, and as-received samples of both materials were compared using S parameter analysis. These calculations were made on deconvoluted gamma ray spectra that were free of any instrumental broadening effects. In this way, absolute S parameter changes could be calculated. The observed changes in the S parameter are consistent with independent volume swelling measurements for both the α-A1 2O 3 and the (1:2) MgAl 2O 4 samples. However, the change in S parameter measured for the (1:1) spinel is contrary to the measured volume change. This apparent anomaly indicates a predominence of interstitial as opposed to vacancy type defects in this material.

  18. CeO2 nanocrystals and solid-phase heteroepitaxy of CeAlO3 interlayer on Al2O3(0 0 0 1) substrate

    NASA Astrophysics Data System (ADS)

    Hattori, Takashi; Ozawa, Masakuni

    2017-04-01

    Grain growth and interfacial solid state of CeO2 nanocrystals (NCs) layer on Al2O3(0 0 0 1) substrate were examined. CeO2 NCs layer on Al2O3(0 0 0 1) was prepared by dipping method using CeO2 nanocrystals colloid solution. After heat treatment at 1000 °C in air, CeO2 NCs layer was formed on Al2O3(0 0 0 1). The CeO2 NCs sintered to form a surface layer with an interlayer of CeAlO3 after heat treatment at 950 °C in H2/Ar, leading to dense and smooth CeO2 NCs layer on Al2O3(0 0 0 1) substrate. CeAlO3 was grown via diffusion of CeO2-x (non-stoichiometric CeO2) and Al2O3, suggesting solid-phase reaction heteroepitaxy mechanism on Al2O3(0 0 0 1) single crystal substrate.

  19. Towards advanced structural analysis of iron oxide clusters on the surface of γ-Al2O3 using EXAFS

    NASA Astrophysics Data System (ADS)

    Boubnov, Alexey; Roppertz, Andreas; Kundrat, Matthew D.; Mangold, Stefan; Reznik, Boris; Jacob, Christoph R.; Kureti, Sven; Grunwaldt, Jan-Dierk

    2016-11-01

    Iron oxide centres are structurally investigated in 0.1% Fe/γ-Al2O3, which is known as highly active catalyst, for instance in the oxidation of CO. The sample was characterised by using X-ray absorption spectroscopy (XAS) in terms of X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS), Mössbauer spectroscopy, X-ray diffraction (XRD) and transmission electron microscopy (TEM). These analyses evidenced high dispersion of the iron oxide entities without significant presence of bulk-like aggregates associated with the low Fe content of the catalyst. A library of structural models of Al2O3-supported surface Fe was created as input for EXAFS fitting. Additionally, several model structures of Fe substituting Al ions in bulk γ-Al2O3 were created with optimised geometry based on density-functional theory (DFT) calculations. From EXAFS refinement of the best 8 out of 24 models, it was found that the trivalent Fe ions are coordinated by 4-5 oxygen atoms and are located on octahedral lattice sites of the exposed surfaces of γ-Al2O3. These iron oxide species exist mainly as a mixture of monomeric and binuclear species and due to the low concentration represent suitable model systems as alternative to single crystal systems for structure-function relationships.

  20. Al2O3 fiber strength degradation in metal and intermetallic matrix composites

    NASA Technical Reports Server (NTRS)

    Draper, S. L.; Locci, I. E.

    1994-01-01

    The mechanisms for fiber damage in single crystal Al2O3 fiber-reinforced composites were investigated. Both fiber fragmentation and fiber strength degradation were observed in composites with a variety of matrix compositions. Four mechanisms that may be contributing to the fiber strength loss have been proposed and include matrix reaction, reaction with binders, residual stress-induced damage, and pressure from hot pressing. The effect of matrix reaction was separated from the other three effects by sputter-coating the matrices on cleaned fibers and annealing with a temperature profile that simulates processing conditions. These experiments revealed that Y and Cr in FeCrAlY base alloys and Zr in NiAl alloys reacted with the fiber, and grooves and adherent particles were formed on the fiber surface which were responsible for the strength loss. The effects of the matrix reaction appeared to dominate over the other possible mechanisms, although evidence for reaction with binders was also found. Ridges on the fiber surface, which reflected the grain boundaries of the matrix, were also observed. In order for single-crystal Al2O3 to be used as a fiber in MMC's and IMC's, a matrix or protective coating which minimizes matrix reaction during processing will be necessary. Of the matrices investigated, the Thermo-span(sup TM) alloy was the least damaging to fiber properties.

  1. Proactive control of the metal-ceramic interface behavior of thermal barrier coatings using an artificial alpha-Al2O 3 layer

    NASA Astrophysics Data System (ADS)

    Su, Yi-Feng

    The reliability and life of thermal barrier coatings (TBCs) used in the hottest sections of advanced aircraft engines and power generation systems are largely dictated by: (1) the ability of a metallic bond coating to form an adherent thermally grown oxide (TGO) at the metal-ceramic interface and (2) the rate at which the TGO grows upon oxidation. It is postulated that a thin alpha-Al2O3 layer, if it could be directly deposited on a Ni-based alloy, will guide the alloy surface to form a TGO that is more tenacious and slower growing than what is attainable with state-of-the-art bond coatings. A chemical vapor deposition (CVD) process was used to directly deposit an alpha-Al2O3 layer on the surface of a single crystal Ni-bases superalloy. The layer was 150 nm thick, and consisted of small columnar grains (˜100 to 200 nm) with alpha-Al2O 3 as the major phase with a minute amount of theta-Al2O 3. Within 0.5 h of oxidation at 1150°C, the resulting TGO formed on the alloy surface underwent significant lateral grain growth. Consequently, within this time scale, the columnar nature of the TGO became well established. After 50 h, a network of ridges was clearly observed on the TGO surface instead of equiaxed grains typically observed on uncoated alloy surface. Comparison of the TGO morphologies observed with and without the CVD-Al2O 3 layer suggested that the transient oxidation of the alloy surface was considerably reduced. The alloy coated with the CVD-Al2O 3 layer also produced a much more adherent and slow growing TGO in comparison to that formed on the uncoated alloy surface. The CVD-Al2O 3 layer also improved its spallation resistance. Without the CVD-Al 2O3 layer, more than 50% of the TGO spalled off the alloy surface after 500 h in oxidation with significant wrinkling of the TGO that remained on the alloy surface. In contrast, the TGO remained intact with the CVD-Al2O3 layer after the 500 h exposure. Furthermore, the CVD layer significantly reduced the degree of

  2. Effect of Al2O3 Addition on the Precipitated Phase Transformation in Ti-Bearing Blast Furnace Slags

    NASA Astrophysics Data System (ADS)

    Li, Zhongmin; Li, Jinfu; Sun, Yongqi; Seetharaman, Seshadri; Liu, Lili; Wang, Xidong; Zhang, Zuotai

    2016-04-01

    The present paper aims to provide a fundamental understanding on phase change of Ti-enriched crystalline phase induced by Al2O3 addition in Ti-bearing blast furnace slags with different basicities using Single Hot Thermocouple Technique and X-ray Diffraction. The results showed that an increase in the Al2O3 content led to phase change from rutile or perovskite to Mg3Al4Ti8O25 and prompted crystallization of the slags with basicity of 0.60 and 0.75, whereas only CaTiO3 was precipitated at a basicity of 0.95. Both thermodynamic and kinetic analyses were conducted to study the slag crystallization, which would throw light on phase change and enhanced crystallization. To further reveal the relationship with Al2O3 addition on slag structure and crystallization, Fourier transform infrared spectroscopy and magic angle spinning-nuclear magnetic resonance were adopted, with AlO4 tetrahedra and AlO6 octahedra observed in the slag. For slags with the basicity of 0.60 and 0.75, AlO6 octahedron, which was suggested to induce the phase change from TiO2 or CaTiO3 to Mg3Al4Ti8O25, was detected at high Al2O3 content. On the other hand, in slags with the basicity of 0.95, abundant Ca2+ may be connected to TiO6 octahedra, resulting in CaTiO3 formation.

  3. Wetting of the (0001) α-Al2O3 Sapphire Surface by Molten Aluminum: Effect of Surface Roughness

    NASA Astrophysics Data System (ADS)

    Aguilar-Santillan, Joaquin

    2010-03-01

    The wetting of molten aluminum on the “ c”-plane (0001) of single-crystal α-Al2O3 (sapphire) was studied by the sessile drop technique from 800 °C (1073 K) to 1200 °C (1473 K). Systematically increasing the (0001) surface roughness by SiC abrasion increased the wetting contact angle, resulting in reduced wetting. The surface roughness factor R originally defined by Wenzel, was determined as a function of the abrasion, temperature, and time. The wetting decreases as the surface roughness increases. Rough surfaces also create time and temperature effects on wetting, changing those for a smoothly polished surface. The existence of a high-temperature surface structural transition for (0001) of α-Al2O3, which has been previously suggested, was confirmed. Increased roughness R accents the effect of the surface structural transition, increasing the wetting contact angle changes during the transition.

  4. Directionally solidified Al2O3/GAP eutectic ceramics by micro-pulling-down method

    NASA Astrophysics Data System (ADS)

    Cao, Xue; Su, Haijun; Guo, Fengwei; Tan, Xi; Cao, Lamei

    2016-11-01

    We reported a novel route to prepare directionally solidified (DS) Al2O3/GAP eutectic ceramics by micro-pulling-down (μ-PD) method. The eutectic crystallizations, microstructure characters and evolutions, and their mechanical properties were investigated in detail. The results showed that the Al2O3/GAP eutectic composites can be successfully fabricated through μ-PD method, possessed smooth surface, full density and large crystal size (the maximal size: φ90 mm × 20 mm). At the process of Diameter, the as-solidified Al2O3/GAP eutectic presented a combination of "Chinese script" and elongated colony microstructure with complex regular structure. Inside the colonies, the rod-type or lamellar-type eutectic microstructures with ultra-fine GAP surrounded by the Al2O3 matrix were observed. At an appropriate solidificational rate, the binary eutectic exhibited a typical DS irregular eutectic structure of "chinese script" consisting of interpenetrating network of α-Al2O3 and GAP phases without any other phases. Therefore, the interphase spacing was refined to 1-2 µm and the irregular microstructure led to an outstanding vickers hardness of 17.04 GPa and fracture toughness of 6.3 MPa × m1/2 at room temperature.

  5. Silicon solar cells with Al2O3 antireflection coating

    NASA Astrophysics Data System (ADS)

    Dobrzański, Leszek; Szindler, Marek; Drygała, Aleksandra; Szindler, Magdalena

    2014-09-01

    The paper presents the possibility of using Al2O3 antireflection coatings deposited by atomic layer deposition ALD. The ALD method is based on alternate pulsing of the precursor gases and vapors onto the substrate surface and then chemisorption or surface reaction of the precursors. The reactor is purged with an inert gas between the precursor pulses. The Al2O3 thin film in structure of the finished solar cells can play the role of both antireflection and passivation layer which will simplify the process. For this research 50×50 mm monocrystalline silicon solar cells with one bus bar have been used. The metallic contacts were prepared by screen printing method and Al2O3 antireflection coating by ALD method. Results and their analysis allow to conclude that the Al2O3 antireflection coating deposited by ALD has a significant impact on the optoelectronic properties of the silicon solar cell. For about 80 nm of Al2O3 the best results were obtained in the wavelength range of 400 to 800 nm reducing the reflection to less than 1%. The difference in the solar cells efficiency between with and without antireflection coating was 5.28%. The LBIC scan measurements may indicate a positive influence of the thin film Al2O3 on the bulk passivation of the silicon.

  6. Radiation endurance in Al2O3 nanoceramics

    NASA Astrophysics Data System (ADS)

    García Ferré, F.; Mairov, A.; Ceseracciu, L.; Serruys, Y.; Trocellier, P.; Baumier, C.; Kaïtasov, O.; Brescia, R.; Gastaldi, D.; Vena, P.; Beghi, M. G.; Beck, L.; Sridharan, K.; di Fonzo, F.

    2016-09-01

    The lack of suitable materials solutions stands as a major challenge for the development of advanced nuclear systems. Most issues are related to the simultaneous action of high temperatures, corrosive environments and radiation damage. Oxide nanoceramics are a promising class of materials which may benefit from the radiation tolerance of nanomaterials and the chemical compatibility of ceramics with many highly corrosive environments. Here, using thin films as a model system, we provide new insights into the radiation tolerance of oxide nanoceramics exposed to increasing damage levels at 600 °C –namely 20, 40 and 150 displacements per atom. Specifically, we investigate the evolution of the structural features, the mechanical properties, and the response to impact loading of Al2O3 thin films. Initially, the thin films contain a homogeneous dispersion of nanocrystals in an amorphous matrix. Irradiation induces crystallization of the amorphous phase, followed by grain growth. Crystallization brings along an enhancement of hardness, while grain growth induces softening according to the Hall-Petch effect. During grain growth, the excess mechanical energy is dissipated by twinning. The main energy dissipation mechanisms available upon impact loading are lattice plasticity and localized amorphization. These mechanisms are available in the irradiated material, but not in the as-deposited films.

  7. Radiation endurance in Al2O3 nanoceramics

    PubMed Central

    García Ferré, F.; Mairov, A.; Ceseracciu, L.; Serruys, Y.; Trocellier, P.; Baumier, C.; Kaïtasov, O.; Brescia, R.; Gastaldi, D.; Vena, P.; Beghi, M. G.; Beck, L.; Sridharan, K.; Di Fonzo, F.

    2016-01-01

    The lack of suitable materials solutions stands as a major challenge for the development of advanced nuclear systems. Most issues are related to the simultaneous action of high temperatures, corrosive environments and radiation damage. Oxide nanoceramics are a promising class of materials which may benefit from the radiation tolerance of nanomaterials and the chemical compatibility of ceramics with many highly corrosive environments. Here, using thin films as a model system, we provide new insights into the radiation tolerance of oxide nanoceramics exposed to increasing damage levels at 600 °C –namely 20, 40 and 150 displacements per atom. Specifically, we investigate the evolution of the structural features, the mechanical properties, and the response to impact loading of Al2O3 thin films. Initially, the thin films contain a homogeneous dispersion of nanocrystals in an amorphous matrix. Irradiation induces crystallization of the amorphous phase, followed by grain growth. Crystallization brings along an enhancement of hardness, while grain growth induces softening according to the Hall-Petch effect. During grain growth, the excess mechanical energy is dissipated by twinning. The main energy dissipation mechanisms available upon impact loading are lattice plasticity and localized amorphization. These mechanisms are available in the irradiated material, but not in the as-deposited films. PMID:27653832

  8. Oxygen diffusion in alpha-Al2O3. Ph.D. Thesis

    NASA Technical Reports Server (NTRS)

    Cawley, J. D.; Halloran, J. W.; Cooper, A. R.

    1984-01-01

    Oxygen self diffusion coefficients were determined in single crystal alpha-Al2O3 using the gas exchange technique. The samples were semi-infinite slabs cut from five different boules with varying background impurities. The diffusion direction was parallel to the c-axis. The tracer profiles were determined by two techniques, single spectrum proton activation and secondary ion mass spectrometry. The SIMS proved to be a more useful tool. The determined diffusion coefficients, which were insensitive to impurity levels and oxygen partial pressure, could be described by D = .00151 exp (-572kJ/RT) sq m/s. The insensitivities are discussed in terms of point defect clustering. Two independent models are consistent with the findings, the first considers the clusters as immobile point defect traps which buffer changes in the defect chemistry. The second considers clusters to be mobile and oxygen diffusion to be intrinsic behavior, the mechanism for oxygen transport involving neutral clusters of Schottky quintuplets.

  9. Raman spectroscopic study of Ni/Al 2O 3 catalyst

    NASA Astrophysics Data System (ADS)

    Aminzadeh, A.; Sarikhani-fard, H.

    1999-07-01

    In this article a preliminary Raman spectroscopic study of Ni/Al 2O 3 catalyst of the type used for the steam reformation of methane is reported. With several prepared samples of this catalyst and using FT-Raman and conventional dispersive Raman technique, it is shown how Raman spectroscopy can be used to monitor the exact conditions during the preparation of the catalyst. Raman data shows that despite a strong fluorescence background, some useful information can be obtained. According to these data, when the calcination temperature is raised above 1000°C, the gamma alumina ( γ-Al 2O 3) is converted to alpha alumina ( α-Al 2O 3) as it is expected. It further shows that Ni is not present as NiO: it is probably embedded in the crystal structure of γ-Al 2O 3 as NiAl 2O 4 (the spinel structure) or constituted as a solid solution with Al 2O 3.

  10. Research on microcracks avoidance in processing of α-Al2O3 by ultrashort laser pulses

    NASA Astrophysics Data System (ADS)

    Wang, Cheng-Wei; Zhao, Quan-Zhong

    2013-07-01

    The optical crystal α-Al2O3 has been widely used as the matrix of ruby and blue sapphire for its wide transparency, high thermal conductivity, big scale and low cost. α-Al2O3 is so hard that cutter is easily abraded. Micromachining of α-Al2O3 by ultrashort pulsed laser is superior to the traditional mechanical approach as its non-contact and cold machining features. However, unexpected cracks on the surface of α-Al2O3 are observed after femtosecond laser machining. In order to hinder the crack source from stretching, we optimize the laser parameters accompanied with annealing. The crack-free machining can be achieved. Three-dimensional α-Al2O3 microstructures free from fracture, such as cylinder, barrel and sphere are demonstrated.

  11. Coherent 3D nanostructure of γ-Al2O3: Simulation of whole X-ray powder diffraction pattern

    NASA Astrophysics Data System (ADS)

    Pakharukova, V. P.; Yatsenko, D. A.; Gerasimov, E. Yu.; Shalygin, A. S.; Martyanov, O. N.; Tsybulya, S. V.

    2017-02-01

    The structure and nanostructure features of nanocrystalline γ-Al2O3 obtained by dehydration of boehmite with anisotropic platelet-shaped particles were investigated. The original models of 3D coherent nanostructure of γ-Al2O3 were constructed. The models of nanostructured γ-Al2O3 particles were first confirmed by a direct simulation of powder X-Ray diffraction (XRD) patterns using the Debye Scattering Equation (DSE) with assistance of high-resolution transmission electron microscopy (HRTEM) study. The average crystal structure of γ-Al2O3 was shown to be tetragonally distorted. The experimental results revealed that thin γ-Al2O3 platelets were heterogeneous on a nanometer scale and nanometer-sized building blocks were separated by partially coherent interfaces. The XRD simulation results showed that a specific packing of the primary crystalline blocks in the nanostructured γ-Al2O3 particles with formation of planar defects on {001}, {100}, and {101} planes nicely accounted for pronounced diffuse scattering, anisotropic peak broadening and peak shifts in the experimental XRD pattern. The identified planar defects in cation sublattice seem to be described as filling cation non-spinel sites in existing crystallographic models of γ-Al2O3 structure. The overall findings provided an insight into the complex nanostructure, which is intrinsic to the metastable γ-Al2O3 oxide.

  12. High Temperature Aerogels in the Al2O3-SiO2 System

    NASA Technical Reports Server (NTRS)

    Hurwitz, Frances I.; Aranda, Denisse V.; Gallagher, Meghan E.

    2008-01-01

    Al2O3-SiO2 aerogels are of interest as constituents of thermal insulation systems for use at high temperatures. Al2O3 and mullite aerogels are expected to crystallize at higher temperatures than their SiO2 counterparts, hence avoiding the shrinkages that accompany the formation of lower temperature SiO2 phases and preserving pore structures into higher temperature regimes. The objective of this work is to determine the influence of processing parameters on shrinkage, gel structure (including surface area, pore size and distribution) and pyrolysis behavior.

  13. Role of oxygen pressure on the structural, morphological and optical properties of c-Al2O3 films deposited by thermal evaporator

    NASA Astrophysics Data System (ADS)

    Khan, Ijaz Ahmad; Amna, Noureen; Kanwal, Nosheen; Razzaq, Maleeha; Farid, Amjad; Amin, Nasir; Ikhlaq, Uzma; Saleem, Murtaza; Ahmad, Riaz

    2017-03-01

    Aluminum oxide (c-Al2O3) films are deposited for various (0.5, 1, 1.5 and 2 mbar) oxygen pressures on glass substrates by thermal evaporator. The x-ray diffraction patterns exhibit the development of single diffraction peak related to c-Al2O3 phase which grows along (2 2 0) orientation up to 1.5 mbar pressure. For 2 mbar pressure, the deposited film becomes amorphous because no diffraction peak is observed. A minimum FWHM and maximum crystallite size of c-Al2O3 (2 2 0) plane is observed for 1 mbar pressure. The enhanced crystallite size of c-Al2O3 (2 2 0) plane is responsible to decrease the dislocation density and residual stresses developed during the deposition process. The field emission scanning electron microscopic analysis reveals the formation of smooth, uniform and compact films showing uniform distribution of nano-particles of different shapes and sizes. The energy dispersive x-ray spectroscopic analysis confirms the presence of Al whose content is decreased with the increase of oxygen pressures. The ellipsometric analysis confirms that the refractive index and the thickness of c-Al2O3 film deposited for 0.5 mbar pressure are found to 1.685 and 124.43 nm respectively. In short, the crystal structure, surface morphology, film thickness and refractive index of c-Al2O3 films are associated with the increase of oxygen pressures.

  14. (100) facets of γ-Al2O3: the active surfaces for alcohol dehydration reactions

    SciTech Connect

    Kwak, Ja Hun; Mei, Donghai; Peden, Charles HF; Rousseau, Roger J.; Szanyi, Janos

    2011-05-01

    Temperature programmed desorption (TPD) of ethanol, and methanol dehydration reaction were studied on γ-Al2O3 in order to identify the catalytic active sites for alcohol dehydration reactions. Two high temperature (> 473 K) desorption features were observed following ethanol adsorption. Samples calcined at T≤473 K displayed a desorption feature in the 523-533 K temperature range, while those calcined at T ≥ 673 K showed a single desorption feature at 498 K. The switch from the high to low temperature ethanol desorption correlated well with the dehydroxylation of the (100) facets of γ-Al2O3 that was predicted at 550 K DFT calculations. Theoretical DFT simulations of the mechanism of dehydration. on clean and hydroxylated γ-Al2O3(100) surfaces, find that a concerted elimination of ethylene from an ethanol molecule chemisorbed at an Al3+ pentacoordinated site is the rate limiting step for catalytic cycle on both surfaces. Furthermore, titration of the pentacoordinate Al3+ sites on the (100) facets of γ-Al2O3 by BaO completely turned off the methanol dehydration reaction activity. These results unambiguously demonstrate that only the (100) facets on γ-Al2O3 are the catalytic active surfaces for alcohol dehydration.

  15. Synthesis and thermal characterization of Al2O3 nanoparticles

    NASA Astrophysics Data System (ADS)

    Ismardi, A.; Rosadi, O. M.; Kirom, M. R.; Syarif, D. G.

    2016-11-01

    Al2O3 nanoparticle has been successfully synthesized using sol gel method from AlCl3. The obtained nanoparticles was then characterized for grain size measurement, the size of nanoparticles was 6 nm by using surface area meter (SAM) and Transmission Electron Microscopy (TEM). The crystallinity property of the product was then checked with XRD spectroscopy, the result shows that the diffraction peaks were match with the 10-0425 JCPDS database. Thermal property of the Al2O3 nanoparticles was then studied by mixing it with engine base fluid as nanofluid. The usage of nanofluid was expected to be heat absorber and woulo increase cooling process in cooling machine. The results showed that cooling time increases when the concentration of nanofluid was increased. Finally, it is concluded that thermal property of Al2O3 was studied and applicable to be mixed with engine coolant of cooler machine to reduce cooling time process.

  16. Growth, Quantitative Growth Analysis, and Applications of Graphene on γ-Al2O3 catalysts

    PubMed Central

    Park, Jaehyun; Lee, Joohwi; Choi, Jung-Hae; Hwang, Do Kyung; Song, Yong-Won

    2015-01-01

    The possibilities offered by catalytic γ-Al2O3 substrates are explored, and the mechanism governing graphene formation thereon is elucidated using both numerical simulations and experiments. The growth scheme offers metal-free synthesis at low temperature, grain-size customization, large-area uniformity of electrical properties, single-step preparation of graphene/dielectric structures, and readily detachable graphene. We quantify based on thermodynamic principles the activation energies associated with graphene nucleation/growth on γ-Al2O3, verifying the low physical and chemical barriers. Importantly, we derive a universal equation governing the adsorption-based synthesis of graphene over a wide range of temperatures in both catalytic and spontaneous growth regimes. Experimental results support the equation, highlighting the catalytic function of γ-Al2O3 at low temperatures. The synthesized graphene is manually incorporated as a ‘graphene sticker’ into an ultrafast mode-locked laser. PMID:26137994

  17. Latent tracks and associated strain in Al2O3 irradiated with swift heavy ions

    NASA Astrophysics Data System (ADS)

    O'Connell, J. H.; Rymzhanov, R. A.; Skuratov, V. A.; Volkov, A. E.; Kirilkin, N. S.

    2016-05-01

    The morphology of latent ion tracks induced by high energy heavy ions in Al2O3 was investigated using a combination of high resolution transmission electron microscopy (HRTEM), exit wave reconstruction, geometric phase analysis and numerical simulations. Single crystal α-Al2O3 crystals were irradiated with 167 MeV Xe ions along the c-axis to fluences between 1 × 1010 and 1 × 1013 cm-2. Planar TEM lamella were prepared by focused ion beam (FIB) and geometrical phase analysis was performed on the phase image of the reconstructed complex electron wave at the specimen exit surface in order to estimate the latent strain around individual track cores. In addition to the experimental data, the material excitation in a SHI track was numerically simulated by combining Monte-Carlo code, describing the excitation of the electronic subsystem, with classical molecular dynamics of the lattice atoms. Experimental and simulation data both showed that the relaxation of the excess lattice energy results in the formation of a cylinder-like disordered region of about 4 nm in diameter consisting of an underdense core surrounded by an overdense shell. Modeling of the passage of a second ion in the vicinity of this disordered region revealed that this damaged area can be restored to a near damage free state. The estimation of a maximal effective distance of recrystallization between the ion trajectories yields values of about 6-6.5 nm which are of the same order of magnitude as those estimated from the saturation density of latent ion tracks detected by TEM.

  18. Structural study of radiolytic catalysts Ni-Ce/Al2O3 and Ni-Pt/Al2O3

    NASA Astrophysics Data System (ADS)

    Seridi, F.; Chettibi, S.; Keghouche, N.; Beaunier, P.; Belloni, J.

    2017-01-01

    Ni-Ce and Ni-Pt bimetallic catalysts supported over α-Al2O3 are synthesized by using co-impregnation method, and then reduced, each via radiolytic process or thermal H2-treatment. For Ni-Ce/Al2O3, the structural study reveals that Ce is alloyed with Ni as Ce2Ni7 nanoparticles in the radiation-reduced catalysts, while it segregates to the surface in the form of CeO2 in the H2-reduced catalysts. For Ni-Pt/Al2O3 radiolytic catalysts, Ni, Pt, NiPt and Ni3Pt nanoparticles, which size is 3.5 nm, are observed. When the radiation-reduced samples are tested in the benzene hydrogenation, they both display high conversion rate. However, the Ni-Pt/Al2O3 is more efficient than Ni-Ce/Al2O3. The performance of the catalysts is correlated with the high dispersion of the metal and the presence of intermetallic Ni-Pt and Ni-Ce phases. It is compared to that of other radiolytic monometallic/oxide catalysts of the literature.

  19. Removal of nitrate and phosphate using chitosan/Al2O3/Fe3O4 composite nanofibrous adsorbent: Comparison with chitosan/Al2O3/Fe3O4 beads.

    PubMed

    Bozorgpour, Farahnaz; Ramandi, Hossein Fasih; Jafari, Pooya; Samadi, Saman; Yazd, Shabnam Sharif; Aliabadi, Majid

    2016-12-01

    In the present study the chitosan/Al2O3/Fe3O4 composite nanofibrous adsorbent was prepared by electrospinning process and its application for the removal of nitrate and phosphate were compared with chitosan/Al2O3/Fe3O4 composite bead adsorbent. The influence of Al2O3/Fe3O4 composite content, pH, contact time, nitrate and phosphate initial concentrations and temperature on the nitrate and phosphate sorption using synthesized bead and nanofibrous adsorbents was investigated in a single system. The reusability of chitosan/Al2O3/Fe3O4 composite beads and nanofibers after five sorption-desorption cycles were carried out. The Box-Behnken design was used to investigate the interaction effects of adsorbent dosage, nitrate and phosphate initial concentrations on the nitrate and phosphate removal efficiency. The pseudo-second-order kinetic model and known Freundlich and Langmuir isotherm models were used to describe the kinetic and equilibrium data of nitrate and phosphate sorption using chitosan/Al2O3/Fe3O4 composite beads and nanofibers. The influence of other anions including chloride, fluoride and sulphate on the sorption efficiency of nitrate and phosphate was examined. The obtained results revealed the higher potential of chitosan/Al2O3/Fe3O4 composite nanofibers for nitrate and phosphate compared with chitosan/Al2O3/Fe3O4 composite beads.

  20. Band offsets and trap-related electron transitions at interfaces of (100)InAs with atomic-layer deposited Al2O3

    NASA Astrophysics Data System (ADS)

    Chou, H.-Y.; O'Connor, E.; O'Mahony, A.; Povey, I. M.; Hurley, P. K.; Dong, Lin; Ye, P. D.; Afanas'ev, V. V.; Houssa, M.; Stesmans, A.

    2016-12-01

    Spectral analysis of optically excited currents in single-crystal (100)InAs/amorphous (a-)Al2O3/metal structures allows one to separate contributions stemming from the internal photoemission (IPE) of electrons into alumina and from the trapping-related displacement currents. IPE spectra suggest that the out-diffusion of In and, possibly, its incorporation in a-Al2O3 lead to the development of ≈0.4 eV wide conduction band (CB) tail states. The top of the InAs valence band is found at 3.45 ± 0.10 eV below the alumina CB bottom, i.e., at the same energy as at the GaAs/a-Al2O3 interface. This corresponds to the CB and the valence band offsets at the InAs/a-Al2O3 interface of 3.1 ± 0.1 eV and 2.5 ± 0.1 eV, respectively. However, atomic-layer deposition of alumina on InAs results in additional low-energy electron transitions with spectral thresholds in the range of 2.0-2.2 eV, which is close to the bandgap of AlAs. The latter suggests the interaction of As with Al, leading to an interlayer containing Al-As bonds providing a lower barrier for electron injection.

  1. The FTIR studies of gels and thin films of Al2O3-TiO2 and Al2O3-TiO2-SiO2 systems.

    PubMed

    Adamczyk, Anna; Długoń, Elżbieta

    2012-04-01

    In this work, samples in form of bulk ones and thin films were obtained using the sol-gel method. The bulk samples were heated at different temperatures (500 °C, 850 °C and 1100 °C) corresponding to the annealing process of coatings, deposited on different substrates by dipping and pulling out samples from the proper sol with the stable speed. Thin films of both Al2O3-TiO2 and Al2O3-TiO2-SiO2 systems were deposited on carbon, steel and titanium substrates in two different ways: as single layers obtained from Al2O3 sol, TiO2 sol and Al2O3 sol or deposited as mixed coatings from Al2O3-TiO2 sol as well as Al2O3-TiO2-SiO2 one. All bulk samples were studied by the FTIR spectroscopy and the X-ray diffractometry while thin films were also investigated by the electron microscopy. In the IR spectra of Al2O3-TiO2 samples, as well as gels and coatings, bands due to the vibrations of AlO bonds of the octahedrally and tetrahedrally coordinated aluminum were observed. The IR spectra of samples of Al2O3-TiO2-SiO2 system differ from that of Al2O3-TiO2 ones in presence of bands assigned to the SiO bond vibrations and in positions of bands due to AlO bond vibrations. In all spectra of bulk samples and coatings, the positions of TiO bond vibrations were ascribed basing on the IR spectra of the pure anatase and rutile.

  2. Distinctive electrical properties in sandwich-structured Al2O3/low density polyethylene nanocomposites

    NASA Astrophysics Data System (ADS)

    Wang, Si-Jiao; Zha, Jun-Wei; Li, Wei-Kang; Dang, Zhi-Min

    2016-02-01

    The sandwich-structured Al2O3/low density polyethylene (Al2O3/LDPE) nanocomposite dielectrics consisting of layer-by-layer with different concentration Al2O3 loading were prepared by melt-blending and following hot pressing method. The space charge distribution from pulsed electro-acoustic method and breakdown strength of the nanocomposites were investigated. Compared with the single-layer Al2O3/LDPE nanocomposites, the sandwich-structured nanocomposites remarkably suppressed the space charge accumulation and presented higher breakdown strength. The charges in the sandwich-structured nanocomposites decayed much faster than that in the single-layer nanocomposites, which was attributed to an effective electric field caused by the formation of the interfacial space charges. The energy depth of shallow and deep traps was estimated as 0.73 eV and 1.17 eV in the sandwich-structured nanocomposites, respectively, according to the thermal excitation theoretical model we proposed. This work provides an attractive strategy of design and fabrication of polymer nanocomposites with excellent space charge suppression.

  3. Consolidation of Al2O3 Nano-Ceramic Powders for High Power Micro-Wave Window

    DTIC Science & Technology

    2007-09-19

    Development, Korea Atomic Energy Research Institute, 150 Dukjin-dong Yuseong-gu Daejeon, 305-353, Korea 1. INTRODUCTION In material aspect, the sapphire...Al2O3) is very attractive material for window in the high power application. However, the fabrication and following process is very difficult and...much expansive. In addition, the intrinsic defects like F, F+ center in single crystalline Al2O3 act as heat generation sites during passing the high

  4. Transparent and flexible capacitors based on nanolaminate Al2O3/TiO2/Al2O3.

    PubMed

    Zhang, Guozhen; Wu, Hao; Chen, Chao; Wang, Ti; Yue, Jin; Liu, Chang

    2015-01-01

    Transparent and flexible capacitors based on nanolaminate Al2O3/TiO2/Al2O3 dielectrics have been fabricated on indium tin oxide-coated polyethylene naphthalate substrates by atomic layer deposition. A capacitance density of 7.8 fF/μm(2) at 10 KHz was obtained, corresponding to a dielectric constant of 26.3. Moreover, a low leakage current density of 3.9 × 10(-8) A/cm(2) at 1 V has been realized. Bending test shows that the capacitors have better performances in concave conditions than in convex conditions. The capacitors exhibit an average optical transmittance of about 70% in visible range and thus open the door for applications in transparent and flexible integrated circuits.

  5. On the Structural and Chemical Characteristics of Co/Al2O3/graphene Interfaces for Graphene Spintronic Devices.

    PubMed

    Canto, Bárbara; Gouvea, Cristol P; Archanjo, Bráulio S; Schmidt, João E; Baptista, Daniel L

    2015-09-23

    We report a detailed investigation of the structural and chemical characteristics of thin evaporated Al2O3 tunnel barriers of variable thickness grown onto single-layer graphene sheets. Advanced electron microscopy and spectrum-imaging techniques were used to investigate the Co/Al2O3/graphene/SiO2 interfaces. Direct observation of pinhole contacts was achieved using FIB cross-sectional lamellas. Spatially resolved EDX spectrum profiles confirmed the presence of direct point contacts between the Co layer and the graphene. The high surface diffusion properties of graphene led to cluster-like Al2O3 film growth, limiting the minimal possible thickness for complete barrier coverage onto graphene surfaces using standard Al evaporation methods. The results indicate a minimum thickness of nominally 3 nm Al2O3, resulting in a 0.6 nm rms rough film with a maximum thickness reaching 5 nm.

  6. On the Structural and Chemical Characteristics of Co/Al2O3/graphene Interfaces for Graphene Spintronic Devices

    PubMed Central

    Canto, Bárbara; Gouvea, Cristol P.; Archanjo, Bráulio S.; Schmidt, João E.; Baptista, Daniel L.

    2015-01-01

    We report a detailed investigation of the structural and chemical characteristics of thin evaporated Al2O3 tunnel barriers of variable thickness grown onto single-layer graphene sheets. Advanced electron microscopy and spectrum-imaging techniques were used to investigate the Co/Al2O3/graphene/SiO2 interfaces. Direct observation of pinhole contacts was achieved using FIB cross-sectional lamellas. Spatially resolved EDX spectrum profiles confirmed the presence of direct point contacts between the Co layer and the graphene. The high surface diffusion properties of graphene led to cluster-like Al2O3 film growth, limiting the minimal possible thickness for complete barrier coverage onto graphene surfaces using standard Al evaporation methods. The results indicate a minimum thickness of nominally 3 nm Al2O3, resulting in a 0.6 nm rms rough film with a maximum thickness reaching 5 nm. PMID:26395513

  7. Structural and phase transition of α-Al2O3 powders obtained by co-precipitation method

    NASA Astrophysics Data System (ADS)

    Bharthasaradhi, R.; Nehru, L. C.

    2016-01-01

    Aluminium oxide has been synthesized by co-precipitation technique at different annealing temperature. Powder XRD confirms the formation of α-Al2O3 with rhombohedral crystal structure having lattice constant a = 4.76 Å and b = 12.99 Å by the Scherer formula, the average crystallite size is estimated to be 66 nm. The scanning electron microscope results expose the fact that the α-Al2O3 nanomaterials are seemingly porous in nature and highly agglomerated. Chemical composition of aluminium oxide is confirmed by energy dispersive spectroscopy. The molecular functional group is confirmed by FTIR. Optical absorption of α-Al2O3 has been studied in the UV-vis region and its direct band gap is estimated to be 5.97 eV. This study involves the structural and phase transition of Al2O3 and also indicates that α-Al2O3 has considerable properties, deserving further investigation for the energetic materials with excellent properties for the possibility of using thin-layer α-Al2O3 as a thermo luminescence material.

  8. Electron paramagnetic resonance of Er3+ ions in a polycrystalline α-Al2O3

    NASA Astrophysics Data System (ADS)

    Asatryan, H. R.; Zakharchenya, R. I.; Kutsenko, A. B.; Babunts, R. A.; Baranov, P. G.

    2007-06-01

    The EPR spectra of rare-earth Er3+ ions in a polycrystalline corundum α-Al2O3 synthesized by the sol-gel technology were revealed. It is shown that the EPR spectra belong to the Er3+ ions in the ground state corresponding to the lower Stark sublevel of the 4 I 15/2 term and can be described by the spin Hamiltonian of axial symmetry with an effective spin S = 1/2 and the g tensor with components g ‖ = 12.176 and g ⊥ = 4.14. The average value of the g tensor ( = 6.82) corresponds to the Γ7 state in a cubic field. Erbium is assumed to substitute for aluminum in the Al2O3 corundum crystal. The local symmetry C 3 of the Al3+ ion remains despite the pronounced expansion of the lattice around the Er3+ ion.

  9. Development of lasers optimized for pumping Ti:Al2O3 lasers

    NASA Technical Reports Server (NTRS)

    Rines, Glen A.; Schwarz, Richard A.

    1994-01-01

    Laboratory demonstrations that were completed included: (1) an all-solid-state, broadly tunable, single-frequency, Ti:Al2O3 master oscillator, and (2) a technique for obtaining 'long' (nominally 100- to 200-ns FWHM) laser pulses from a Q-switched, Nd oscillator at energy levels commensurate with straightforward amplification to the joule level. A diode-laser-pumped, Nd:YLF laser with intracavity SHG was designed, constructed, and evaluated. With this laser greater than 0.9 W of CW, output power at 523.5 nm with 10 W of diode-laser pump power delivered to the Nd:YLF crystal was obtained. With this laser as a pump source, for the first time, to our knowledge, an all solid-state, single frequency, Ti:Al203 laser with sufficient output power to injection seed a high-energy oscillator over a 20-nm bandwidth was demonstrated. The pulsed laser work succeeded in demonstrating pulse-stretching in a Q-switched Nd:YAG oscillator. Pulse energies greater than 50-mJ were obtained in pulses with 100- to 200-ns pulsewidths (FWHM).

  10. Al2O3-based nanofluids: a review

    PubMed Central

    2011-01-01

    Ultrahigh performance cooling is one of the important needs of many industries. However, low thermal conductivity is a primary limitation in developing energy-efficient heat transfer fluids that are required for cooling purposes. Nanofluids are engineered by suspending nanoparticles with average sizes below 100 nm in heat transfer fluids such as water, oil, diesel, ethylene glycol, etc. Innovative heat transfer fluids are produced by suspending metallic or nonmetallic nanometer-sized solid particles. Experiments have shown that nanofluids have substantial higher thermal conductivities compared to the base fluids. These suspended nanoparticles can change the transport and thermal properties of the base fluid. As can be seen from the literature, extensive research has been carried out in alumina-water and CuO-water systems besides few reports in Cu-water-, TiO2-, zirconia-, diamond-, SiC-, Fe3O4-, Ag-, Au-, and CNT-based systems. The aim of this review is to summarize recent developments in research on the stability of nanofluids, enhancement of thermal conductivities, viscosity, and heat transfer characteristics of alumina (Al2O3)-based nanofluids. The Al2O3 nanoparticles varied in the range of 13 to 302 nm to prepare nanofluids, and the observed enhancement in the thermal conductivity is 2% to 36%. PMID:21762528

  11. Al2O3-based nanofluids: a review.

    PubMed

    Sridhara, Veeranna; Satapathy, Lakshmi Narayan

    2011-07-16

    Ultrahigh performance cooling is one of the important needs of many industries. However, low thermal conductivity is a primary limitation in developing energy-efficient heat transfer fluids that are required for cooling purposes. Nanofluids are engineered by suspending nanoparticles with average sizes below 100 nm in heat transfer fluids such as water, oil, diesel, ethylene glycol, etc. Innovative heat transfer fluids are produced by suspending metallic or nonmetallic nanometer-sized solid particles. Experiments have shown that nanofluids have substantial higher thermal conductivities compared to the base fluids. These suspended nanoparticles can change the transport and thermal properties of the base fluid. As can be seen from the literature, extensive research has been carried out in alumina-water and CuO-water systems besides few reports in Cu-water-, TiO2-, zirconia-, diamond-, SiC-, Fe3O4-, Ag-, Au-, and CNT-based systems. The aim of this review is to summarize recent developments in research on the stability of nanofluids, enhancement of thermal conductivities, viscosity, and heat transfer characteristics of alumina (Al2O3)-based nanofluids. The Al2O3 nanoparticles varied in the range of 13 to 302 nm to prepare nanofluids, and the observed enhancement in the thermal conductivity is 2% to 36%.

  12. Atomistic simulation of the pressure-temperature-volume diagram in α-Al 2O 3

    NASA Astrophysics Data System (ADS)

    Franco, R.; Blanco, M. A.; Martín Pendás, A.; Francisco, E.; Recio, J. M.

    1996-04-01

    We report the results of a theoretical investigation that explores for the first time temperature effects on the pressure-volume relationship in corundum. The ionic interactions within the α-Al 2O 3 crystal are modelized using the electron gas formalism along with electronic wavefunctions that are allowed to relax with crystal strains. A non-empirical Debye model is applied to account for the thermal contributions. Our study reveals that the crystal responds isotropically under both high-temperature and high-pressure conditions. Good agreement with hydrostatic and quasi-hydrostatic experimental data is achieved.

  13. The electrical conductivity of Al2O3 under shock-compression

    PubMed Central

    Liu, Hanyu; Tse, John S.; Nellis, W. J.

    2015-01-01

    Sapphire (Al2O3) crystals are used below 100 GPa as anvils and windows in dynamic-compression experiments because of their transparency and high density. Above 100 GPa shock pressures, sapphire becomes opaque and electrically conducting because of shock-induced defects. Such effects prevent temperature and dc conductivity measurements of materials compressed quasi-isentropically. Opacities and electrical conductivities at ~100 GPa are non-equilibrium, rather than thermodynamic parameters. We have performed electronic structure calculations as a guide in predicting and interpreting shock experiments and possibly to discover a window up to ~200 GPa. Our calculations indicate shocked sapphire does not metallize by band overlap at ~300 GPa, as suggested previously by measured non-equilibrium data. Shock-compressed Al2O3 melts to a metallic liquid at ~500 GPa and 10,000 K and its conductivity increases rapidly to ~2000 Ω−1cm−1 at ~900 GPa. At these high shock temperatures and pressures sapphire is in thermal equilibrium. Calculated conductivity of Al2O3 is similar to those measured for metallic fluid H, N, O, Rb, and Cs. Despite different materials, pressures and temperatures, and compression techniques, both experimental and theoretical, conductivities of all these poor metals reach a common end state typical of strong-scattering disordered materials. PMID:26239369

  14. The response of thermally and optically stimulated luminescence from Al2O3:C to high-energy heavy charged particles

    NASA Technical Reports Server (NTRS)

    Gaza, R.; Yukihara, E. G.; McKeever, S. W. S.

    2004-01-01

    The thermoluminescence (TL) and optically stimulated luminescence (OSL) response of Al2O3 dosimeters to high-energy heavy charged particles (HCP) has been studied using the heavy ion medical accelerator at Chiba, Japan. The samples were Al2O3 single-crystal chips, of the type usually known as TLD-500, and Luxel(TM) dosimeters (Al2O3:C powder in plastic) from Landauer Inc. The samples were exposed to 4He (150 MeV/u), 12C (400 MeV/u), 28Si (490 MeV/us) and 56Fe (500 MeV/u) ions, with linear energy transfer values covering the range from 2.26 to 189 keV/micrometers in water and doses from 1 to 100 mGy (to water). A 90Sr/90Y beta source, calibrated against a 60Co secondary standard, was used for calibration purposes. For OSL, we used both continuous-wave OSL measurements (CW-OSL, using green light stimulation at 525 nm) and pulsed OSL measurements (POSL, using 532 nm stimulation from a Nd:YAG Q-switched laser). The efficiencies (eta HCP, gamma) of the different HCPs at producing OSL or TL were observed to depend not only upon the linear energy transfer (LET) of the HCP, but also upon the sample type (single crystal chip or Luxel(TM)) and the luminescence method used to define the signal--i.e. TL, CW-OSL initial intensity, CW-OSL total area, or POSL. Observed changes in shape of the decay curve lead to potential methods for extracting LET information of unknown radiation fields. A discussion of the results is given, including the potential use of OSL from Al2O3 in the areas of space radiation dosimetry and radiation oncology. c2004 Elsevier Ltd. All rights reserved.

  15. The response of thermally and optically stimulated luminescence from Al2O3:C to high-energy heavy charged particles.

    PubMed

    Gaza, R; Yukihara, E G; McKeever, S W S

    2004-01-01

    The thermoluminescence (TL) and optically stimulated luminescence (OSL) response of Al2O3 dosimeters to high-energy heavy charged particles (HCP) has been studied using the heavy ion medical accelerator at Chiba, Japan. The samples were Al2O3 single-crystal chips, of the type usually known as TLD-500, and Luxel(TM) dosimeters (Al2O3:C powder in plastic) from Landauer Inc. The samples were exposed to 4He (150 MeV/u), 12C (400 MeV/u), 28Si (490 MeV/us) and 56Fe (500 MeV/u) ions, with linear energy transfer values covering the range from 2.26 to 189 keV/micrometers in water and doses from 1 to 100 mGy (to water). A 90Sr/90Y beta source, calibrated against a 60Co secondary standard, was used for calibration purposes. For OSL, we used both continuous-wave OSL measurements (CW-OSL, using green light stimulation at 525 nm) and pulsed OSL measurements (POSL, using 532 nm stimulation from a Nd:YAG Q-switched laser). The efficiencies (eta HCP, gamma) of the different HCPs at producing OSL or TL were observed to depend not only upon the linear energy transfer (LET) of the HCP, but also upon the sample type (single crystal chip or Luxel(TM)) and the luminescence method used to define the signal--i.e. TL, CW-OSL initial intensity, CW-OSL total area, or POSL. Observed changes in shape of the decay curve lead to potential methods for extracting LET information of unknown radiation fields. A discussion of the results is given, including the potential use of OSL from Al2O3 in the areas of space radiation dosimetry and radiation oncology.

  16. Athermal fading of luminescence in Al2 O3 ceramic substrates

    NASA Astrophysics Data System (ADS)

    Terry, Ian; Kouroukla, Eftychia; Bailiff, Ian K.

    2015-03-01

    Retrospective dosimetry aims to reconstruct ionising radiation dose to populations following a radiological incident using materials not designed for that purpose. Sintered alumina ceramic can function as a dosimeter with its luminescence properties and related trapped charge storage mechanism. Its widespread use as a substrate in surface mount devices and incorporation in devices such as mobile phones make it a ubiquitous potential dosimeter. We investigated the optically (OSL) and thermally (TL) stimulated luminescence properties of sintered alumina substrates. In contrast to their single crystal analogue developed for personal dosimetry, Al2O3:C, the substrates exhibit a significant loss of trapped charge (fading) within hours following irradiation at RT that seriously limits their utility for dosimetry over an extended timescale. The fading rates of OSL and TL signals of 0402 resistors were analysed under various storage conditions (time and temperature), complemented by a study of their microstructure. The results support a model of athermal loss of trapped charge due to electron tunnelling from trapping states; this contrasting behaviour is attributed to a physical modification of the trap environment arising from the manufacturing process.

  17. Surface Crystallization of a MgO/Y2O3/SiO2/Al2O3/ZrO2 Glass: Growth of an Oriented β-Y2Si2O7 Layer and Epitaxial ZrO2

    NASA Astrophysics Data System (ADS)

    Wisniewski, Wolfgang; Seidel, Sabrina; Patzig, Christian; Rüssel, Christian

    2017-03-01

    The crystallization behavior of a glass with the composition 54.7 SiO2·10.9 Al2O3·15.0 MgO·3.4 ZrO2·16.0 Y2O3 is studied using X-ray diffraction (XRD), scanning electron microscopy (SEM) including electron backscatter diffraction (EBSD) and (scanning) transmission electron microscopy [(S)TEM] including energy-dispersive X-ray spectrometry (EDXS). This glass shows the sole surface crystallization of four different yttrium silicates of the composition Y2Si2O7 (YS). The almost simultaneous but independent nucleation of α-, β-, δ-, and ε-YS at the surface is followed by growth into the bulk, where ε-YS quickly dominates a first crystallized layer. An accumulation of Mg at the growth front probably triggers a secondary nucleation of β-YS, which forms a thin compact layer before fragmenting into a highly oriented layer of fine grained crystals occupying the remaining bulk. The residual glass between the YS growth structures allows the crystallization of indialite, yttrium stabilized ZrO2 (Y-ZrO2) and very probably μ-cordierite during cooling. Hence, this glass basically shows the inverted order of crystallization observed in other magnesium yttrium alumosilicate glasses containing less Y2O3. An epitaxial relationship between Y-ZrO2 and ε-YS is proven and multiple twinning relationships occur in the YS phases.

  18. Surface Crystallization of a MgO/Y2O3/SiO2/Al2O3/ZrO2 Glass: Growth of an Oriented β-Y2Si2O7 Layer and Epitaxial ZrO2

    PubMed Central

    Wisniewski, Wolfgang; Seidel, Sabrina; Patzig, Christian; Rüssel, Christian

    2017-01-01

    The crystallization behavior of a glass with the composition 54.7 SiO2·10.9 Al2O3·15.0 MgO·3.4 ZrO2·16.0 Y2O3 is studied using X-ray diffraction (XRD), scanning electron microscopy (SEM) including electron backscatter diffraction (EBSD) and (scanning) transmission electron microscopy [(S)TEM] including energy-dispersive X-ray spectrometry (EDXS). This glass shows the sole surface crystallization of four different yttrium silicates of the composition Y2Si2O7 (YS). The almost simultaneous but independent nucleation of α-, β-, δ-, and ε-YS at the surface is followed by growth into the bulk, where ε-YS quickly dominates a first crystallized layer. An accumulation of Mg at the growth front probably triggers a secondary nucleation of β-YS, which forms a thin compact layer before fragmenting into a highly oriented layer of fine grained crystals occupying the remaining bulk. The residual glass between the YS growth structures allows the crystallization of indialite, yttrium stabilized ZrO2 (Y-ZrO2) and very probably μ-cordierite during cooling. Hence, this glass basically shows the inverted order of crystallization observed in other magnesium yttrium alumosilicate glasses containing less Y2O3. An epitaxial relationship between Y-ZrO2 and ε-YS is proven and multiple twinning relationships occur in the YS phases. PMID:28281661

  19. Influence of calcination temperature on the surface area of submicron-sized Al2O3 electrospun fibers

    NASA Astrophysics Data System (ADS)

    Shin, Hyeon Ung; Ramsier, Rex D.; Chase, George G.

    2016-03-01

    Submicron-sized Al2O3 fibers were formed by calcination of electrospun aluminum acetate/PVP composite fibers. At 650 °C, the fibers were amorphous. As the calcination temperature increased to 750 °C, the fibers transitioned from amorphous to 49 % crystalline gamma phase Al2O3. The crystallinity further increased with calcination temperature to 80 % gamma Al2O3 at 950 °C, but decreased above 950 °C as the crystal structure began to change to alpha phase. The fiber diameters tended to decrease as calcination temperature increased to 950 °C but increased as the alpha phase was formed at temperatures above 950 °C. Surface areas as measured by BET decreased as gamma phase crystallinity increased. Further decrease in surface area as the gamma phase crystal structure transitioned to alpha phase indicated changing internal pore structures of the fibers.

  20. Impurity Enhancement of Al_2O_3/Al Adhesion

    NASA Astrophysics Data System (ADS)

    Wang, Xiao-Gang; Smith, John R.; Zhang, Wenqing; Evans, Anthony

    2003-03-01

    Our first-principles computations indicate that the clean Al_2O_3/Al interface is relatively weak - weaker than bulk Al. Fracture experiments reveal that the interface is relatively strong with observed failure in bulk Al, however. This paradox is resolved via doping effects of the common impurity C. We have found that only 1/3 of a monolayer of carbon segregated to the interface can increase the work of separation by a factor of 3. The resulting strong interface is consistent with fracture experiments. It arises due to void formation in the interface, which provides low-strain sites for the carbon to segregate to. The degree of void formation is consistent with the relatively high heat of oxide formation of Al.

  1. Enhanced thermal stability of carbon nanotubes by plasma surface modification in Al2O3 composites

    NASA Astrophysics Data System (ADS)

    Cho, Hoonsung; Shi, Donglu; Guo, Yan; Lian, Jie; Ren, Zhifeng; Poudel, Bed; Song, Yi; Abot, Jandro L.; Singh, Dileep; Routbort, Jules; Wang, Lumin; Ewing, Rodney C.

    2008-10-01

    A plasma polymerization method was employed to deposit an ultrathin pyrrole film of 3 nm onto the surfaces of single wall carbon nanotubes (SWCNTs) and Al2O3 nanoparticles for developing high-strength nanocomposites. The surfaces of plasma coated SWCNTs and Al2O3 nanoparticles were studied by high resolution transmission electron microscopy (TEM) and time-of-flight secondary ion mass spectroscopy. After sintering the SWCNTs-Al2O3 composites at different temperatures (maximum of 1200 °C), the thermal stability of plasma-coated SWCNTs was significantly increased, compared to their uncoated counterparts. After hot-press sintering, the SWCNTs without plasma coating were essentially decomposed into amorphous clusters in the composites, leading to degraded mechanical properties. However, under the same sintering conditions, the plasma surface modified SWCNTs were well preserved and distributed in the composite matrices. The effects of plasma surface coating on the thermal stability of SWCNTs and mechanical behavior of the nanocomposites are discussed.

  2. High-temperature degradation in plasma-enhanced chemical vapor deposition Al2O3 surface passivation layers on crystalline silicon

    NASA Astrophysics Data System (ADS)

    Kühnhold, Saskia; Saint-Cast, Pierre; Kafle, Bishal; Hofmann, Marc; Colonna, Francesco; Zacharias, Margit

    2014-08-01

    In this publication, the activation and degradation of the passivation quality of plasma-enhanced chemical vapor deposited aluminum oxide (Al2O3) layers with different thicknesses (10 nm, 20 nm, and 110 nm) on crystalline silicon (c-Si) during long and high temperature treatments are investigated. As indicated by Fourier Transform Infrared Spectroscopy, the concentration of tetrahedral and octahedral sites within the Al2O3 layer changes during temperature treatments and correlates with the amount of negative fixed charges at the Si/Al2O3 interface, which was detected by Corona Oxide Characterization of Semiconductors. Furthermore, during a temperature treatment at 820 °C for 30 min, the initial amorphous Al2O3 layer crystallize into the γ-Al2O3 structure and was enhanced by additional oxygen as was proven by x-ray diffraction measurements and underlined by Density Functional Theory simulations. The crystallization correlates with the increase of the optical density up to 20% while the final Al2O3 layer thickness decreases at the same time up to 26%. All observations described above were detected to be Al2O3 layer thickness dependent. These observations reveal novel aspects to explain the temperature induced passivation and degradation mechanisms of Al2O3 layers at a molecular level like the origin of the negative fixe charges at the Si/SiOx/Al2O3 interface or the phenomena of blistering. Moreover, the crystal phase of Al2O3 does not deliver good surface passivation due to a high concentration of octahedral sites leading to a lower concentration of negative fixed charges at the interface.

  3. Study of ZrO2/Al2O3/ZrO2 and Al2O3/ZrO2/Al2O3 stack structures deposited by sol-gel method on Si

    NASA Astrophysics Data System (ADS)

    Vitanov, P.; Harizanova, A.; Ivanova, T.; Dimitrova, T.

    2010-02-01

    Based on our previous experience with pseudobinary alloys of (Al2O3)x(ZrO2)1-x as high-k materials and passivating coatings for solar cells, stack systems of ZrO2/Al2O3/ZrO2and Al2O3/ZrO2/Al2O3, deposited by simple and low cost sol-gel technology have been studied. The thin films of ZrO2 and Al2O3 were sequentially obtained on Si substrates including spin coating deposition from stable solutions. High resolution scanning electron microscopy (HRSEM) was used to compare the morphology of the nanolaminates. The layers were optically characterized by UV-VIS spectrophotometry. The electrical measurements were carried out on metal-insulator-semiconductor (MIS) structures. Their leakage current and relative permittivity were determined.

  4. Antimicrobial effect of Al2O3, Ag and Al2O3/Ag thin films on Escherichia coli and Pseudomonas putida

    NASA Astrophysics Data System (ADS)

    Angelov, O.; Stoyanova, D.; Ivanova, I.; Todorova, S.

    2016-10-01

    The influence of Al2O3, Ag and Al2O3/Ag thin films on bacterial growth of Gramnegative bacteria Pseudomonas putida and Escherichia coli is studied. The nanostructured thin films are deposited on glass substrates without intentional heating through r.f. magnetron sputtering in Ar atmosphere of Al2O3 and Ag targets or through sequential sputtering of Al2O3 and Ag targets, respectively. The individual Ag thin films (thickness 8 nm) have a weak bacteriostatic effect on Escherichia coli expressed as an extended adaptive phase of the bacteria up to 5 hours from the beginning of the experiment, but the final effect is only 10 times lower bacterial density than in the control. The individual Al2O3 film (20 nm) has no antibacterial effect against two strains E. coli - industrial and pathogenic. The Al2O3/Ag bilayer films (Al2O3 20 nm/Ag 8 nm) have strong bactericidal effect on Pseudomonas putida and demonstrate an effective time of disinfection for 2 hours. The individual films Al2O3 and Ag have not pronounced antibacterial effect on Pseudomonas putida. A synergistic effect of Al2O3/Ag bilayer films in formation of oxidative species on the surface in contact with the bacterial suspension could be a reason for their antimicrobial effect on E. coli and P. putida.

  5. The effect of boron oxide on the crystallization behavior of MgAl2O4 spinel phase during the cooling of the CaO-SiO2-10 mass.% MgO-30 mass.%Al2O3 systems

    NASA Astrophysics Data System (ADS)

    Park, Joo Hyun

    2010-12-01

    The microstructural characteristics of the CaO-SiO2-B2O3-10 mass.% MgO-30 mass.% Al2O3 systems solidified during slow cooling from 1600 °C were investigated using SEM-EDS and a thermochemical computation package. The effect of boron oxide on the crystallization behavior of the spinel in the aluminosilicate system was observed because boron oxide is believed to become a potential flux to reduce the melting point of the liquid oxides. The primary crystalline phase was spinel, mainly MgAl2O4, irrespective of the boron content. The liquidus temperature T L continuously decreased as the boron oxide content increased, indicating that the boron oxide decreased the activity of the MgAl2O4 spinel phase in liquid melts at high temperatures. The size of the spinel crystals increased as the temperature range for the solid + liquid coexisting region, viz. the mushy zone, increased. In the present systems, because the T L continuously decreased with the increase in the boron oxide content, the viscosity of the liquid oxide may have affected the crystallization behavior of the spinel during cooling. Based on these results, an injection of a small amount of B2O3 flux into molten steel containing liquid aluminosilicate inclusions is not recommended because large spinel crystals can originate from the changes in the thermophysical properties of the liquid inclusions due to the incorporation of boron oxide into the aluminosilicate networks.

  6. X-ray and optical crystallographic parameters investigations of high frequency induction melted Al-(alpha-Al(2)O(3)) alloys.

    PubMed

    Bourbia, A; Draissia, M; Bedboudi, H; Boulkhessaim, S; Debili, M Y

    2010-01-01

    This article deals with the microstructural strengthening mechanisms of aluminium by means of hard alpha-Al(2)O(3) alumina fine particles. A broad of understanding views covering materials preparations, elaboration process, characterization techniques and associated microstructural characteristic parameters measurements is given. In order to investigate the microstructural characteristic parameters and the mechanical strengthening mechanisms of pure aluminium by hard fine particles, a set of Al-(alpha-Al(2)O(3)) alloys samples were made under vacuum by high fusion temperature melting, the high frequency (HF) process, and rapidly solidified under ambient temperature from a mixture of cold-compacted high-pure fine Al and alpha-Al(2)O(3) powders. The as-solidified Al-(alpha-Al(2)O(3)) alloys were characterized by means of X-ray diffraction (XRD) analyses, optical microscopy observations and Vickers microhardness tests in both brut and heat-treated states. It was found that the as-solidified HF Al-(alpha-Al(2)O(3)) alloys with compositions below 4 wt.% (alpha-Al(2)O(3)) are single-phase microstructures of the solid solution FCC Al phase and over two-phase microstructures of the solid solution FCC Al and the Rhombohedral alpha-Al(2)O(3) phases. The optical micrographs reveal the presence of a grain size refinement in these alloys. Vickers microhardness of the as-solidified Al-(alpha-Al(2)O(3)) is increased by means of pure fine alpha-Al(2)O(3) alumina particles. These combined effects of strengthening and grain size refinement observed in the as-solidified Al-(alpha-Al(2)O(3)) alloys are essentially due to a strengthening of Al by the alpha-Al(2)O(3) alumina particles insertion in the (HF) melted and rapidly solidified alloys.

  7. Al2O3 passivation effect in HfO2·Al2O3 laminate structures grown on InP substrates.

    PubMed

    Kang, Hang-Kyu; Kang, Yu-Seon; Kim, Dae-Kyoung; Baik, Min; Song, Jin Dong; An, Youngseo; Kim, Hyoungsub; Cho, Mann-Ho

    2017-04-07

    The passivation effect of an Al2O3 layer on electrical properties were investigated in HfO2--Al2O3 laminate structures grown on InP substrate by atomic layer deposition (ALD). The chemical state using HR-XPS showed that interfacial reactions were dependent on the presence of the Al2O3 passivation layer and its sequence in the HfO2--Al2O3 laminate structures. The Al2O3/HfO2/Al2O3 structure showed the best electrical characteristics, due to the interfacial reaction, compared with those of different stacking structures. The top Al2O3 layer suppressed the interdiffusion of oxidizing species into the HfO2 films, while the bottom Al2O3 layer blocked the outdiffusion of In and P atoms. As a result, the formation of In-O bonds was effectively suppressed in the Al2O3/HfO2/Al2O3/InP structure than that of HfO2-on-InP system. Moreover, conductance data revealed that the Al2O3/ layer on InP reduces the midgap traps to 2.6 × 10(12) eV(-1)cm(-2) (compared with that of HfO2/InP = 5.4 × 10(12) eV(-1)cm(-2)). The suppression of gap states caused by the outdiffusion of In atoms significantly controls the degradation of capacitors caused by leakage current through the stacked oxide layers.

  8. Orientation relationship between α-Fe precipitate and α-Al2O3 matrix in iron-implanted sapphire.

    PubMed

    Wang, Y; Liu, X P; Qin, G W

    2014-07-01

    Fe ions were implanted into α-Al2O3 single crystals (sapphire) at room temperature and annealed in a reducing atmosphere. The orientation relationships (ORs) between α-Fe particles and sapphire matrix were investigated using transmission electron microscopy (TEM). All the α-Fe particles have the orientation relationship (OR) of (111)α-Fe||(0001)sapphire and [11¯0]α-Fe||[112¯0]sapphire with sapphire. This OR is predicted precisely by the coincidence of reciprocal lattice points (CRLP) method. The other OR of (110)α-Fe||(0001)sapphire and [111]α-Fe||[51¯4¯0]sapphire reported before is confirmed by the same method to be one of the secondary preferred orientation relationships in the α-Fe/sapphire system.

  9. Theoretical study on (Al2O3)n (n = 1-10 and 30) fullerenes and H2 adsorption properties.

    PubMed

    Sun, Jiao; Lu, Wen-Cai; Zhang, Wei; Zhao, Li-Zhen; Li, Ze-Sheng; Sun, Chia-Chung

    2008-04-07

    The structures and stabilities of (Al2O3)n (n = 1-10 and 30) clusters were studied by means of first principles calculations. The calculated results reveal that the global minima of small (Al2O3)n (n = 1-5) clusters are cage structures with high symmetries, in which Al and O atoms are three- and two-coordinated, respectively, and are linked to neighbors via single bonds. Beyond (Al2O3)5, we calculated both cage and cage-dimer structures for (Al2O3)n (n = 6-10), and the results show that, at this size range, cage-dimer structures are more stable than cage structures. Furthermore, an onion-like motif for (Al2O3)10 was studied, and it is interesting to find that, at this size, the onion structure is more favorable than cage and cage-dimer structures. For large clusters, a shell structure of Al60O90 is suggested. Electronic properties and calculations on hydrogen adsorption of these aluminum oxide structures are reported, and we discuss their possible use as hydrogen storage materials.

  10. Diffusion of oxygen in amorphous Al2O3, Ta2O5, and Nb2O5

    NASA Astrophysics Data System (ADS)

    Nakamura, R.; Toda, T.; Tsukui, S.; Tane, M.; Ishimaru, M.; Suzuki, T.; Nakajima, H.

    2014-07-01

    The self-diffusivity of oxygen in amorphous Al2O3 (a-Al2O3), a-Ta2O5, and a-Nb2O5 was investigated along with structural analysis in terms of pair distribution function (PDF). The low activation energy, ˜1.2 eV, for diffusion in the oxides suggests a single atomic jump of oxygen ions mediated via vacancy-like defects. However, the pre-exponential factor for a-Ta2O5 and a-Nb2O5 with lower bond energy was two orders of magnitude larger than that for a-Al2O3 with higher bond energy. PDF analyses revealed that the short-range configuration in a-Ta2O5 and a-Nb2O5 was more broadly distributed than that in a-Al2O3. Due to the larger variety of atomic configurations of a-Ta2O5 and a-Nb2O5, these oxides have a higher activation entropy for diffusion than a-Al2O3. The entropy term for diffusion associated with short-range structures was shown to be a dominant factor for diffusion in amorphous oxides.

  11. Enhanced Sintering of β"-Al2O3/YSZ with the Sintering Aids of TiO2 and MnO2

    SciTech Connect

    Lu, Xiaochuan; Li, Guosheng; Kim, Jin Yong; Meinhardt, Kerry D.; Sprenkle, Vincent L.

    2015-07-11

    β"-Al2O3 has been the dominated choice for the electrolyte materials of sodium batteries because of its high ionic conductivity, excellent stability with the electrode materials, satisfactory mechanical strength, and low material cost. To achieve adequate electrical and mechanical performance, sintering of β"-Al2O3 is typically carried out at temperatures above 1600oC with deliberate efforts on controlling the phase, composition, and microstructure. Here, we reported a simple method to fabricate β"-Al2O3/YSZ electrolyte at relatively lower temperatures. With the starting material of boehmite, single phase of β"-Al2O3 can be achieved at as low as 1200oC. It was found that TiO2 was extremely effective as a sintering aid for the densification of β"-Al2O3 and similar behavior was observed with MnO2 for YSZ. With the addition of 2 mol% TiO2 and 5 mol% MnO2, the β"-Al2O3/YSZ composite was able to be densified at as low as 1400oC with a fine microstructure and good electrical/mechanical performance. This study demonstrated a new approach of synthesis and sintering of β"-Al2O3/YSZ composite, which represented a simple and low-cost method for fabrication of high-performance β"-Al2O3/YSZ electrolyte.

  12. Non-volatile Al2O3 Memory using Nanoscale Al-rich Al2O3 Thin Film as a Charge Storage Layer

    NASA Astrophysics Data System (ADS)

    Nakata, Shunji; Saito, Kunio; Shimada, Masaru

    2006-04-01

    This article describes the fabrication process and capacitance-voltage (C-V) characteristics of a new non-volatile Al2O3 memory with nanoscale thin film deposited by electron-cyclotron-resonance sputtering. Al-rich Al2O3 shows characteristics somewhere between Al and Al2O3 in the refractive index and wet etching rate. C-V characteristics of Al-rich Al2O3 memory show a large hysteresis window due to the Al-rich structure, while there is no hysteresis window in the case of stoichiometric Al2O3. This memory is expected to stay non-volatile for several years or more because the capacitance value after writing and erasing operation remained almost unchanged after 4 h at T=85 °C. Also, another new memory structure comprising SiO2/Al2O3 and the Al-rich Al2O3 structure is proposed, which features increased mobility due to the reduction of electron scattering at the Si/Al2O3 interface.

  13. Al-Al2O3-Pd junction hydrogen sensor

    NASA Astrophysics Data System (ADS)

    Okuyama, K.; Takinami, N.; Chiba, Y.; Ohshima, S.; Kambe, S.

    1994-07-01

    Al-Al2O3-Pd MIM (metal insulator metal) junctions fabricated on a glass substrate were tested as hydrogen sensors. The I-V (current versus voltage) characteristics of the junctions were measured at room temperature in a vacuum of 10-5 Torr and in H2 gas of 10-2-100 Torr. A significant increase in the current was observed upon introduction of H2 gas. This phenomenon is believed to occur due to the work function lowering of the hydrogen-absorbed Pd top electrode. The rise time was on the order of minutes, while the recovery time when hydrogen was purged was more than 20 h. However, when the junction was placed in an oxidizing ambient such as air, the recovery time was drastically reduced to the order of minutes, indicating that the device is operative as a hydrogen sensor in the atmospheric ambient. Hydrogen adsorption and desorption behavior of the Pd film was also investigated using a Pd coated quartz microbalance, and the results explained the current response of the Pd MIM junction to hydrogen in the presence of oxygen.

  14. The thermodynamic properties of hydrated -Al2O3 nanoparticles

    SciTech Connect

    Spencer, Elinor; Huang, Baiyu; Parker, Stewart F.; Kolesnikov, Alexander I; Ross, Dr. Nancy; Woodfield, Brian

    2013-01-01

    In this paper we report a combined calorimetric and inelastic neutron scattering (INS) study of hydrated -Al2O3 ( -alumina) nanoparticles. These complementary techniques have enabled a comprehensive evaluation of the thermodynamic properties of this technological and industrially important metal oxide to be achieved. The isobaric heat capacity (Cp) data presented herein provide further critical insights into the much-debated chemical composition of -alumina nanoparticles. Furthermore, the isochoric heat capacity (Cv) of the surface water, which is so essential to the stability of all metal-oxides at the nanoscale, has been extracted from the high-resolution INS data and differs significantly from that of ice Ih due to the dominating influence of strong surface-water interactions. This study also encompassed the analysis of four -alumina samples with differing pore diameters [4.5 (1), 13.8 (2), 17.9 (3), and 27.2 nm (4)], and the results obtained allow us to unambiguously conclude that the water content and pore size have no influence on the thermodynamic behaviour of hydrated -alumina nanoparticles.

  15. Hydrogen induced passivation of Si interfaces by Al2O3 films and SiO2/Al2O3 stacks

    NASA Astrophysics Data System (ADS)

    Dingemans, G.; Beyer, W.; van de Sanden, M. C. M.; Kessels, W. M. M.

    2010-10-01

    The role of hydrogen in Si surface passivation is experimentally identified for Al2O3 (capping) films synthesized by atomic layer deposition. By using stacks of SiO2 and deuterated Al2O3, we demonstrate that hydrogen is transported from Al2O3 to the underlying SiO2 already at relatively low annealing temperatures of 400 °C. This leads to a high level of chemical passivation of the interface. Moreover, the thermal stability of the passivation up to 800 °C was significantly improved by applying a thin Al2O3 capping film on the SiO2. The hydrogen released from the Al2O3 film favorably influences the passivation of Si interface defects.

  16. Porous α-Al2O3 thermal barrier coatings with dispersed Pt particles prepared by cathode plasma electrolytic deposition

    NASA Astrophysics Data System (ADS)

    Wang, Peng; He, Ye-dong; Deng, Shun-jie; Zhang, Jin

    2016-01-01

    Porous α-Al2O3 thermal barrier coatings (TBCs) containing dispersed Pt particles were prepared by cathode plasma electrolytic deposition (CPED). The influence of the Pt particles on the microstructure of the coatings and the CPED process were studied. The prepared coatings were mainly composed of α-Al2O3. The average thickness of the coatings was approximately 100 μm. Such single-layer TBCs exhibited not only excellent high-temperature cyclic oxidation and spallation resistance, but also good thermal insulation properties. Porous α-Al2O3 TBCs inhibit further oxidation of alloy substrates because of their extremely low oxygen diffusion rate, provide good thermal insulation because of their porous structure, and exhibit excellent mechanical properties because of the toughening effect of the Pt particles and because of stress relaxation induced by deformation of the porous structure.

  17. Study on catalytic incineration of methane using Cr2O3/gamma-Al2O3 as the catalyst.

    PubMed

    Wang, Ching-Huei; Lin, Shiow-Shyung

    2004-01-01

    A fixed bed reactor was employed to investigate the catalytic incineration of CH4 by various supported transition metal oxide catalysts, with a view of finding the optimal one. Results indicated that the active species, the support, the metal content, the weight hourly space velocity (WHSV), and the inlet CH4 concentration were all important factors affecting CH4 oxidation. Cr2O3/gamma-Al2O3 was found to be the most active catalyst among the seven gamma-Al2O3-supported metal oxide catalysts tested. With Cr2O3 as the active species, gamma-Al2O3 was the most suitable of six supports tested. Furthermore, the optimal Cr content of Cr2O3/ gamma-Al2O3 was 9 wt.%. X-ray diffraction (XRD) patterns showed that it was formation of CrO3 crystals that caused a decline in catalyst activity at Cr content above 9wt.%. Using the optimal Cr2O3/gamma-Al2O3 catalyst, CH4 was completely oxidized at about 390 degrees C. much lower than the temperature required by noble metal catalysts for the same outcome. The stability of Cr2O3/gamma-Al2O3 was good and was not affected by the reaction temperature, demonstrated by a nearly constant conversion rate of CH4 of 57% at 350 degrees C and 97% at 380 degrees C during a 20 h on-stream test. However, WHSV and inlet concentration of CH4 did affect CH4 conversion noticeably. For complete oxidation of CH4, the reaction temperature required increased with WHSV and inlet CH4 concentration.

  18. Trapped charge densities in Al2O3-based silicon surface passivation layers

    NASA Astrophysics Data System (ADS)

    Jordan, Paul M.; Simon, Daniel K.; Mikolajick, Thomas; Dirnstorfer, Ingo

    2016-06-01

    In Al2O3-based passivation layers, the formation of fixed charges and trap sites can be strongly influenced by small modifications in the stack layout. Fixed and trapped charge densities are characterized with capacitance voltage profiling and trap spectroscopy by charge injection and sensing, respectively. Al2O3 layers are grown by atomic layer deposition with very thin (˜1 nm) SiO2 or HfO2 interlayers or interface layers. In SiO2/Al2O3 and HfO2/Al2O3 stacks, both fixed charges and trap sites are reduced by at least a factor of 5 compared with the value measured in pure Al2O3. In Al2O3/SiO2/Al2O3 or Al2O3/HfO2/Al2O3 stacks, very high total charge densities of up to 9 × 1012 cm-2 are achieved. These charge densities are described as functions of electrical stress voltage, time, and the Al2O3 layer thickness between silicon and the HfO2 or the SiO2 interlayer. Despite the strong variation of trap sites, all stacks reach very good effective carrier lifetimes of up to 8 and 20 ms on p- and n-type silicon substrates, respectively. Controlling the trap sites in Al2O3 layers opens the possibility to engineer the field-effect passivation in the solar cells.

  19. Epitaxial growth and electric properties of γ-Al2O3(110) films on β-Ga2O3(010) substrates

    NASA Astrophysics Data System (ADS)

    Hattori, Mai; Oshima, Takayoshi; Wakabayashi, Ryo; Yoshimatsu, Kohei; Sasaki, Kohei; Masui, Takekazu; Kuramata, Akito; Yamakoshi, Shigenobu; Horiba, Koji; Kumigashira, Hiroshi; Ohtomo, Akira

    2016-12-01

    Epitaxial growth and electrical properties of γ-Al2O3 films on β-Ga2O3(010) substrates were investigated regarding the prospect of a gate oxide in a β-Ga2O3-based MOSFET. The γ-Al2O3 films grew along the [110] direction and inherited the oxygen sublattice from β-Ga2O3 resulting in the unique in-plane epitaxial relationship of γ-Al2O3 [\\bar{1}10] ∥ β-Ga2O3[001]. We found that the γ-Al2O3 layer had a band gap of 7.0 eV and a type-I band alignment with β-Ga2O3 with conduction- and valence-band offsets of 1.9 and 0.5 eV, respectively. A relatively high trap density (≅ 2 × 1012 cm-2 eV-1) was found from the voltage shift of photoassisted capacitance-voltage curves measured for a Au/γ-Al2O3/β-Ga2O3 MOS capacitor. These results indicate good structural and electric properties and some limitations hindering the better understanding of the role of the gate dielectrics (a γ-Al2O3 interface layer naturally crystallized from amorphous Al2O3) in the β-Ga2O3 MOSFET.

  20. The MgO-Al2O3-SiO2 system - Free energy of pyrope and Al2O3-enstatite. [in earth mantle formation

    NASA Technical Reports Server (NTRS)

    Saxena, S. K.

    1981-01-01

    The model of fictive ideal components is used to determine Gibbs free energies of formation of pyrope and Al2O3-enstatite from the experimental data on coexisting garnet and orthopyroxene and orthopyroxene and spinel in the temperature range 1200-1600 K. It is noted that Al2O3 forms an ideal solution with MgSiO3. These thermochemical data are found to be consistent with the Al2O3 isopleths that could be drawn using most recent experimental data and with the reversed experimental data on the garnet-spinel field boundary.

  1. Bulk Crystallization in a SiO2/Al2O3/Y2O3/AlF3/B2O3/Na2O Glass: Fivefold Pseudo Symmetry due to Monoclinic Growth in a Glassy Matrix Containing Growth Barriers

    PubMed Central

    Wisniewski, Wolfgang; Seyring, Martin; Patzig, Christian; Höche, Thomas; Keshavarzi, Ashkan; Rüssel, Christian

    2016-01-01

    A glass with the mol% composition 17 Y2O3·33 Al2O3·40 SiO2·2 AlF3·3 Na2O·2 CeF3·3 B2O3 is heat treated at 1000 °C for 6–24 h. This results in the surface nucleation and growth of YAG. Nucleation and growth of star-shaped alumina and later of monoclinic β-Y2Si2O7 and orthorhombic δ-Y2Si2O7 are additionally observed in the bulk. Phase identification and localization are performed by electron backscatter diffraction (EBSD) as well as TEM analysis. The monoclinic β-Y2Si2O7 observed in the bulk occurs in the form of large, crystal agglomerates which range from 50 to 120 μm in size. The individual crystals are aligned along the c-axis which is the fastest growing axis. Ten probability maxima are observed in the pole-figures illustrating the rotation of orientations around the c-axes indicating a fivefold symmetry. This symmetry is caused by multiple twinning which results in a high probability of specific orientation relationships with rotation angles of ~36°, ~108° (also referred to as the pentagon angle) and ~144° around the c-axis. All these rotation angles are close to the multiples of 36° which are required for an ideal fivefold symmetry. This is the first report of a fivefold symmetry triggered by the presence of barriers hindering crystal growth. PMID:26813152

  2. Catalytic sterilization of Escherichia coli K 12 on Ag/Al2O3 surface.

    PubMed

    Chen, Meixue; Yan, Lizhu; He, Hong; Chang, Qingyun; Yu, Yunbo; Qu, Jiuhui

    2007-05-01

    Bactericidal action of Al(2)O(3), Ag/Al(2)O(3) and AgCl/Al(2)O(3) on pure culture of Escherichia coli K 12 was studied. Ag/Al(2)O(3) and AgCl/Al(2)O(3) demonstrated a stronger bactericidal activity than Al(2)O(3). The colony-forming ability of E. coli was completely lost in 0.5 min on both of Ag/Al(2)O(3) and AgCl/Al(2)O(3) at room temperature in air. The configuration of the bacteria on the catalyst surface was observed using scanning electron microscopy (SEM). Reactive oxygen species (ROS) play an important role in the expression of the bactericidal activity on the surface of catalysts by assay with O(2)/N(2) bubbling and scavenger for ROS. Furthermore, the formation of CO(2) as an oxidation product could be detected by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and be deduced by total carbon analysis. These results strongly support that the bactericidal process on the surface of Ag/Al(2)O(3) and AgCl/Al(2)O(3) was caused by the catalytic oxidation.

  3. Tape-cast and sintered β-tricalcium phosphate laminates for biomedical applications: Effect of milled Al2O3 fiber additives on microstructural and mechanical properties.

    PubMed

    Tanimoto, Yasuhiro; Teshima, Masahiro; Nishiyama, Norihiro; Yamaguchi, Masaru; Hirayama, Satoshi; Shibata, Yo; Miyazaki, Takashi

    2012-11-01

    The aim of this study was to develop the tape-cast, laminated, and sintered β-tricalcium phosphate (β-TCP) with milled Al(2)O(3) fibers for biomedical applications. Moreover, the effects of Al(2)O(3)-fiber content on the microstructural and mechanical properties of the sintered β-TCP laminates were investigated. The milled Al(2)O(3) fibers were added at four different contents, namely 0, 5, 10, or 15 mass%, to the initial β-TCP slurry. Next, β-TCP green sheets were fabricated from the β-TCP slurry containing the milled Al(2)O(3) fibers by a tape-casting method. Finally, six plies of β-TCP monolayer sheet were laminated and sintered at a maximum temperature of 1100°C in a furnace. The results showed that there were large differences between the apparent porosities, dynamic hardness, and flexural properties of the sintered β-TCP laminates with Al(2)O(3)-fiber contents of 0 and 5 mass%, but few differences among laminates with fiber contents of 5, 10, and 15 mass%. This indicates that the addition of only 5 mass% of Al(2)O(3) fibers strongly affects the degree of sintering, corresponding to crystallization of the β-TCP matrix phase. Furthermore, the flexural moduli of our materials ranged from 10.7 to 16.0 GPa when the Al(2)O(3)-fiber content changed from 5 to 15 mass% and were the almost same as those of human bones reported by other researchers. In conclusion, sintered β-TCP laminates with Al(2)O(3) fibers have potential uses in a wide range of biomedical applications because the microstructural and mechanical properties of the sintered β-TCP laminates can be controlled by adding Al(2)O(3) fibers to the β-TCP.

  4. Preparation and characterization of Al2O3 coating by MOD method on CLF-1 RAFM steel

    NASA Astrophysics Data System (ADS)

    Wang, L.; Yang, J. J.; Feng, Y. J.; Li, F. Z.; Liao, J. L.; Yang, Y. Y.; Feng, K. M.; Liu, N.

    2017-04-01

    Metal organic decomposition (MOD) method was proposed to prepare Al2O3 TPB coatings on CLF-1 RAFM steel. A comprehensive characterization of SEM, XPS, and XRD demonstrated the formation of Al2O3 coatings. The effect of the preparation parameters, including annealing temperature Ta, withdrawal speed Vw and immersion time ti on the microstructure and properties of the coatings was investigated. It showed that amorphous aluminum oxide coating began to transform to γ-Al2O3 at temperature of Ta = 600 °C. The Al2O3 coating with Ta = 700 °C and Tb = 500 °C performed the best crystallization feature. The hardness of the coatings gradually increased with increasing Vw, while the corrosion resistance exhibited a reverse trend. Meanwhile, the nanohardness and corrosion resistance of the coating with ti = 300 s was improved as compared to the coating with ti = 0 s. Moreover, the effect of particle size and substrate oxidation on the mechanical property and corrosion resistance of the coatings was discussed.

  5. Thermo-mechanical and Microstructural Characterization of Geopolymers with α-Al2O3 Particle Filler

    NASA Astrophysics Data System (ADS)

    Lin, T. S.; Jia, D. C.; He, P. G.; Wang, M. R.

    2009-10-01

    Geopolymers with different content of α-Al2O3 particle filler were prepared. The thermo-mechanical and microstructural characterization of the obtained geopolymers were systematically studied by flexural strength and thermal shrinkage measurements, TG-DTA (thermogravimetry and differential thermal analysis), XRD (X-ray diffractometry), and SEM (scanning electron microscopy). The results show that the addition of α-Al2O3 particle filler not only increases the onset crystalline temperature but also reduces the crystalline velocity of the geopolymers. The thermal shrinkage of the geopolymers increases with increasing heat treatment temperatures due to the water loss and densification. The flexural strength of the geopolymers increases with the increase of heat treatment temperatures from RT to 1200 °C, and shows a sharp increase in the range from 600 °C to 800 °C due to crystallization and solidification. The increase in content of α-Al2O3 particle filler can clearly reduce the thermal shrinkage and maintain a higher porosity at high temperatures. However, it has no distinct influence on the flexural strength after heat treatment. This is mainly attributed to the higher thermal resistance and strength of α-Al2O3.

  6. Nucleation and growth mechanisms of Al2O3 atomic layerdeposition on synthetic polycrystalline MoS2.

    PubMed

    Zhang, H; Chiappe, D; Meersschaut, J; Conard, T; Franquet, A; Nuytten, T; Mannarino, M; Radu, I; Vandervorst, W; Delabie, A

    2017-02-07

    Two-dimensional (2D) semiconducting transition metal dichalcogenides (TMDs) are of great interest for applications in nano-electronic devices. Their incorporation requires the deposition of nm-thin and continuous high-k dielectric layers on the 2D TMDs. Atomic layer deposition (ALD) of high-k dielectric layers is well established on Si surfaces: the importance of a high nucleation density for rapid layer closure is well known and the nucleation mechanisms have been thoroughly investigated. In contrast, the nucleation of ALD on 2D TMD surfaces is less well understood and a quantitative analysis of the deposition process is lacking. Therefore, in this work, we investigate the growth of Al2O3 (using Al(CH3)3/H2O ALD) on MoS2 whereby we attempt to provide a complete insight into the use of several complementary characterization techniques, including X-ray photo-electron spectroscopy, elastic recoil detection analysis, scanning electron microscopy, and time-of-flight secondary ion mass spectrometry. To reveal the inherent reactivity of MoS2, we exclude the impact of surface contamination from a transfer process by direct Al2O3 deposition on synthetic MoS2 layers obtained by a high temperature sulfurization process. It is shown that Al2O3 ALD on the MoS2 surface is strongly inhibited at temperatures between 125°C and 300°C, with no growth occurring on MoS2 crystal basal planes and selective nucleation only at line defects or grain boundaries at MoS2 top surface. During further deposition, the as-formed Al2O3 nano-ribbons grow in both vertical and lateral directions. Eventually, a continuous Al2O3 film is obtained by lateral growth over the MoS2 crystal basal plane, with the point of layer closure determined by the grain size at the MoS2 top surface and the lateral growth rate. The created Al2O3/MoS2 interface consists mainly of van der Waals interactions. The nucleation is improved by contributions of reversible adsorption on the MoS2 basal planes by using low

  7. Nucleation and growth mechanisms of Al2O3 atomic layer deposition on synthetic polycrystalline MoS2

    NASA Astrophysics Data System (ADS)

    Zhang, H.; Chiappe, D.; Meersschaut, J.; Conard, T.; Franquet, A.; Nuytten, T.; Mannarino, M.; Radu, I.; Vandervorst, W.; Delabie, A.

    2017-02-01

    Two-dimensional (2D) semiconducting transition metal dichalcogenides (TMDs) are of great interest for applications in nano-electronic devices. Their incorporation requires the deposition of nm-thin and continuous high-k dielectric layers on the 2D TMDs. Atomic layer deposition (ALD) of high-k dielectric layers is well established on Si surfaces: the importance of a high nucleation density for rapid layer closure is well known and the nucleation mechanisms have been thoroughly investigated. In contrast, the nucleation of ALD on 2D TMD surfaces is less well understood and a quantitative analysis of the deposition process is lacking. Therefore, in this work, we investigate the growth of Al2O3 (using Al(CH3)3/H2O ALD) on MoS2 whereby we attempt to provide a complete insight into the use of several complementary characterization techniques, including X-ray photo-electron spectroscopy, elastic recoil detection analysis, scanning electron microscopy, and time-of-flight secondary ion mass spectrometry. To reveal the inherent reactivity of MoS2, we exclude the impact of surface contamination from a transfer process by direct Al2O3 deposition on synthetic MoS2 layers obtained by a high temperature sulfurization process. It is shown that Al2O3 ALD on the MoS2 surface is strongly inhibited at temperatures between 125°C and 300°C, with no growth occurring on MoS2 crystal basal planes and selective nucleation only at line defects or grain boundaries at MoS2 top surface. During further deposition, the as-formed Al2O3 nano-ribbons grow in both vertical and lateral directions. Eventually, a continuous Al2O3 film is obtained by lateral growth over the MoS2 crystal basal plane, with the point of layer closure determined by the grain size at the MoS2 top surface and the lateral growth rate. The created Al2O3/MoS2 interface consists mainly of van der Waals interactions. The nucleation is improved by contributions of reversible adsorption on the MoS2 basal planes by using low

  8. Stability of Al2O3 and Al2O3/a-SiNx:H stacks for surface passivation of crystalline silicon

    NASA Astrophysics Data System (ADS)

    Dingemans, G.; Engelhart, P.; Seguin, R.; Einsele, F.; Hoex, B.; van de Sanden, M. C. M.; Kessels, W. M. M.

    2009-12-01

    The thermal and ultraviolet (UV) stability of crystalline silicon (c-Si) surface passivation provided by atomic layer deposited Al2O3 was compared with results for thermal SiO2. For Al2O3 and Al2O3/a-SiNx:H stacks on 2 Ω cm n-type c-Si, ultralow surface recombination velocities of Seff<3 cm/s were obtained and the passivation proved sufficiently stable (Seff<14 cm/s) against a high temperature "firing" process (>800 °C) used for screen printed c-Si solar cells. Effusion measurements revealed the loss of hydrogen and oxygen during firing through the detection of H2 and H2O. Al2O3 also demonstrated UV stability with the surface passivation improving during UV irradiation.

  9. Preparation of γ-Al2O3 films by laser chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Gao, Ming; Ito, Akihiko; Goto, Takashi

    2015-06-01

    γ- and α-Al2O3 films were prepared by chemical vapor deposition using CO2, Nd:YAG, and InGaAs lasers to investigate the effects of varying the laser wavelength and deposition conditions on the phase composition and microstructure. The CO2 laser was found to mostly produce α-Al2O3 films, whereas the Nd:YAG and InGaAs lasers produced γ-Al2O3 films when used at a high total pressure. γ-Al2O3 films had a cauliflower-like structure, while the α-Al2O3 films had a dense and columnar structure. Of the three lasers, it was the Nd:YAG laser that interacted most with intermediate gas species. This promoted γ-Al2O3 nucleation in the gas phase at high total pressure, which explains the cauliflower-like structure of nanoparticles observed.

  10. Stacked Graphene-Al2O3 Nanopore Sensors for Sensitive Detection of DNA and DNA-Protein Complexes

    PubMed Central

    Venkatesan, Bala Murali; Estrada, David; Banerjee, Shouvik; Jin, Xiaozhong; Dorgan, Vincent E.; Bae, Myung-Ho; Aluru, Narayana R.; Pop, Eric; Bashir, Rashid

    2012-01-01

    We report the development of a multilayered graphene-Al2O3 nanopore platform for the sensitive detection of DNA and DNA-protein complexes. Graphene-Al2O3 nanolaminate membranes are formed by sequentially depositing layers of graphene and Al2O3 with nanopores being formed in these membranes using an electron-beam sculpting process. The resulting nanopores are highly robust, exhibit low electrical noise (significantly lower than nanopores in pure graphene), are highly sensitive to electrolyte pH at low KCl concentrations (attributed to the high buffer capacity of Al2O3) and permit the electrical biasing of the embedded graphene electrode, thereby allowing for three terminal nanopore measurements. In proof-of-principle biomolecule sensing experiments, the folded and unfolded transport of single DNA molecules and RecA coated DNA complexes could be discerned with high temporal resolution. The process described here also enables nanopore integration with new graphene based structures, including nanoribbons and nanogaps, for single molecule DNA sequencing and medical diagnostic applications. PMID:22165962

  11. Effect of Ultrasonic Vibration on the Behavior of Antifriction and Wear Resistance of Al2O3/Al2O3 Ceramic Friction Pairs Under Oil Lubrication

    NASA Astrophysics Data System (ADS)

    Dong, X. Y.; Qiao, Y. L.; Zang, Y.; Cui, Q. S.

    The behavior of antifriction and wear resistance of Al2O3/Al2O3 ceramic friction pairs lubricated by four different lubrication oils under ultrasonic vibration was studied. The surface morphologies of wear scare was analyzed by metallographic microscope. The effect mechanism of ultrasonic vibration on frictional pairs under different lubrication oils was discussed. The studied results showed that, ultrasonic vibration would improve the behavior of antifriction and wear resistance of the Al2O3/Al2O3 ceramic friction pairs under various lubrication oils.The improving would be dramaticer when the viscosity of lubrication oil was low. Ultrasonic vibration decreased the friction coefficient and wear volume 12.9% and 38.7% respectively, when the lubrication oil was 6#,the viscosity of which is 39.77 mm2/s. When the lubrication oil was 150BS, the viscosity of which is 549.69 mm2/s, ultrasonic vibration made friction coefficient and wear volume decreased 4.6% and 11.6% respectively.The effect of ultrasonic vibration on the behavior of antifriction and wear resistance of Al2O3/Al2O3 ceramic friction pairs was determined by the formation and the destruction of oil film on the friction surface and the upward floatage created by ultrasonic vibration.

  12. Study on the Mechanical Properties of Heat-Treated Electroless NiP Coatings Reinforced with Al2O3 Nano Particles

    NASA Astrophysics Data System (ADS)

    Karthikeyan, S.; Vijayaraghavan, L.; Madhavan, S.; Almeida, A.

    2016-05-01

    This work reports the effects of electroless co-deposition of Al2O3 nanoparticles and NiP to obtain a NiP-Al2O3 coating on the structure and mechanical properties of the composite coatings. The effects of annealing heat treatments at 373 K, 473 K, 573 K, and 673 K (100 °C, 200 °C, 300 °C, and 400 °C) on the structure and properties of the coatings were evaluated. The as-deposited coatings are a mixture of crystalline and amorphous phases that tend to crystallize during heat treatment. Heat treatment at higher temperatures causes the precipitation of the Ni3P phase. The mechanical properties of as-deposited and heat-treated NiP-Al2O3 coatings were evaluated using depth-sensing indentation tests performed at loads of 200 mN. The incorporation of Al2O3 nanoparticles induces strengthening of the NiP coating by dispersion. Heat treatment of the NiP-Al2O3 coatings induced crystallization of the amorphous phase with the formation of nanosized grains and the precipitation of Ni3P. Consequently, there is an increase in the hardness and Young's modulus of the coatings to 15.4 ± 0.5 and 227 ± 2.8 GPa, respectively, in a combined hardening effect induced by dispersion of the Al2O3 nanoparticles and crystallization and precipitation during heat treatment.

  13. DNA Sensing using Nano-crystalline Surface Enhanced Al2O3 Nanopore Sensors

    PubMed Central

    Venkatesan, B. M.; Shah, A.B.; Zuo, J.M.; Bashir, R.

    2013-01-01

    A new solid-state, Al2O3 nanopore sensor with enhanced surface properties for the real-time detection and analysis of individual DNA molecules is reported. Nanopore formation using electron beam based decomposition transformed the local nanostructure and morphology of the pore from an amorphous, stoichiometric structure (O to Al ratio of 1.5) to a hetero-phase crystalline network, deficient in O (O to Al ratio of ~0.6). Direct metallization of the pore region was observed during irradiation, thereby permitting the potential fabrication of nano-scale metallic contacts in the pore region with potential application to nanopore-based DNA sequencing. Dose dependent phase transformations to purely γ and/or α-phase nanocrystallites were also observed during pore formation allowing for surface charge engineering at the nanopore/fluid interface. DNA transport studies revealed an order of magnitude reduction in translocation velocities relative to alternate solid-state architectures, accredited to high surface charge density and the nucleation of charged nanocrystalline domains. The unique surface properties of Al2O3 nanopore sensors makes them ideal for the detection and analysis of ssDNA, dsDNA, RNA secondary structures and small proteins. These nano-scale sensors may also serve as a useful tool in studying the mechanisms driving biological processes including DNA-protein interactions and enzyme activity at the single molecule level. PMID:23335871

  14. XPS and NMR analysis on 12CaO•7Al2O3

    NASA Astrophysics Data System (ADS)

    Pan, R. K.; Feng, S.; Tao, H. Z.

    2017-01-01

    12CaO·7Al2O3 (C12A7) glass was prepared by the melt quenching method. The glass transition temperature (T g) and the crystallization temperature (T c) of C12A7 glass are about 1050 K and 1194 K, respectively, measured by the differential scanning calorimetry (DSC). The structure of C12A7 glass was investigated by X-ray photoelectron spectroscopy (XPS) as well as magic angle spinning-nuclear magnetic resonance spectroscopy (MAS-NMR). Analysis shows that Al coordination number is about four in C12A7 glass, in which AlO4 tetrahedrons and bridging oxygens (BO) constitute the glass network. Ca2+ produces a few of non-bridging oxygens (NBO), which become neighbours of Al.

  15. The resistance to wear and corrosion of laser-cladding Al 2O 3 ceramic coating on Mg alloy

    NASA Astrophysics Data System (ADS)

    Gao, Ya-li; Wang, Cun-shan; Yao, Man; Liu, Hong-bin

    2007-04-01

    The paper presents a study on the preparation of Al 2O 3 ceramic coating on AZ91HP Mg alloy by laser remelting plasma-sprayed coating. It was found that after laser remelting, the coating exhibited obvious layer-like characteristics due to influence of temperature distribution, thermophysical parameters and layer thickness. According to the microstructural difference, the coating can be divided into the melted zone with the α-Al 2O 3 column-like crystal, the sintered zone with flock-like structure, the residual plasma-sprayed zone with loosened structure. Because of the dense column-like crystal, the hardness, wear and corrosion resistance of the laser remelted coating are much higher than those of the plasma-sprayed coating and as-received Mg alloy.

  16. Sonochemical asymmetric hydrogenation of isophorone on proline modified Pd/Al2O3 catalysts.

    PubMed

    Mhadgut, Shilpa C; Bucsi, Imre; Török, Marianna; Török, Béla

    2004-04-21

    The sonochemical asymmetric hydrogenation of isophorone (3,3,5-trimethyl-2-cyclohexenone) by proline-modified Pd/Al2O3 catalysts is described; presonication of a commercial Pd/Al2O3-proline catalytic system resulted in highly enhanced enantioselectivities (up to 85% ee).

  17. Process Optimization for Suppressing Cracks in Laser Engineered Net Shaping of Al2O3 Ceramics

    NASA Astrophysics Data System (ADS)

    Niu, F. Y.; Wu, D. J.; Yan, S.; Ma, G. Y.; Zhang, B.

    2017-03-01

    Direct additive manufacturing of ceramics (DAMC) without binders is a promising technique for rapidly fabricating high-purity components with good performance. Nevertheless, cracks are easily generated during fabrication as a result of the high intrinsic brittleness of ceramics and the great temperature gradients. Therefore, optimizing the DAMC process is a challenge. In this study, direct fabrication of Al2O3 single-bead wall structures are conducted with a laser engineered net shaping (LENS) system. A new process optimization method for suppressing cracks is proposed based on analytical models, and then the influence of process parameters on crack number is discussed experimentally. The results indicate that the crack number decreases obviously with the increase of scanning speed. Single-bead wall specimens without cracks are successfully fabricated by the optimized process.

  18. Influence of Al2O3 sol concentration on the microstructure and mechanical properties of Cu-Al2O3 composite coatings

    NASA Astrophysics Data System (ADS)

    Wei, Xiaojin; Yang, Zhendi; Tang, Ying; Gao, Wei

    2015-03-01

    Copper (Cu) is widely used as electrical conducting and contacting material. However, Cu is soft and does not have good mechanical properties. In order to improve the hardness and wear resistance of Cu, sol-enhanced Cu-Al2O3 nanocomposite coatings were electroplated by adding a transparent Al oxide (Al2O3) sol into the traditional electroplating Cu solution. It was found that the microstructure and mechanical properties of the nanocomposite coatings were largely influenced by the Al2O3 sol concentration. The results show that the Al2O3 nanoparticle reinforced the composite coatings, resulting in significantly improved hardness and wear resistance in comparison with the pure Cu coatings. The coating prepared at the sol concentration of 3.93 mol/L had the best microhardness and wear resistance. The microhardness has been improved by 20% from 145.5 HV (Vickers hardness number) of pure Cu coating to 173.3 HV of Cu-Al2O3 composite coatings. The wear resistance was also improved by 84%, with the wear volume loss dropped from 3.2 × 10-3 mm3 of Cu coating to 0.52 × 10-3 mm3 of composite coatings. Adding excessive sol to the electrolyte deteriorated the properties.

  19. Effect of Al2O3 Concentration on Density and Structure of (CaO-SiO2)-xAl2O3 Slag

    NASA Astrophysics Data System (ADS)

    Rajavaram, Ramaraghavulu; Kim, Hyelim; Lee, Chi-Hoon; Cho, Won-Seung; Lee, Chi-Hwan; Lee, Joonho

    2017-03-01

    The effect of Al2O3 concentration on the density and structure of CaO-SiO2-Al2O3 slag was investigated at multiple Al2O3 mole percentages and at a fixed CaO/SiO2 ratio of 1. The experiments were conducted in the temperature range of 2154 K to 2423 K (1881 °C to 2150 °C) using the aerodynamic levitation technique. In order to understand the relationship between density and structure, structural analysis of the silicate melts was carried out using Raman spectroscopy. The density of each slag sample investigated in this study decreased linearly with increasing temperature. When the Al2O3 content was less than 15 mole pct, density decreased with increasing Al2O3 content due to the coupling of Si (Al), whereas above 20 mole pct density of the slag increased due to the role of Al3+ ion as a network modifier.

  20. Formation of gamma(sup prime)-Ni3Al via the Peritectoid Reaction: gamma + beta (+ Al2O3)=gamma(sup prime)(+ Al2O3)

    NASA Technical Reports Server (NTRS)

    Copeland, Evan

    2008-01-01

    The activities of Al and Ni were measured using multi-cell Knudsen effusion-cell mass spectrometry (multi-cell KEMS), over the composition range 8-32 at.%Al and temperature range T=1400-1750 K in the Ni-Al-O system. These measurements establish that equilibrium solidification of gamma(sup prime)-Ni3Al-containing alloys occurs by the eutectic reaction, L (+ Al2O3)=gamma + Beta(+ Al2O3), at 1640 +/- 1 K and a liquid composition of 24.8 +/- 0.2 at.%al (at an unknown oxygen content). The {gamma + Beta (+Al2O3} phase field is stable over the temperature range 1633-1640 K, and gamma(sup prime)-Ni3Al forms via the peritectoid, gamma + Beta (+ Al2O3)=gamma(sup prime) (+ Al2O3), at 1633 +/- 1 K. This behavior is consistent with the current Ni-Al phase diagram and a new diagram is proposed. This new Ni-Al phase diagram explains a number of unusual steady-state solidification structures reported previously and provides a much simpler reaction scheme in the vicinity of the gamma(sup prime)-Ni2Al phase field.

  1. Formation of gamma'-Ni3Al via the Peritectoid Reaction: gamma plus beta (+Al2O3) equals gamma'(+Al2O3)

    NASA Technical Reports Server (NTRS)

    Copland, Evan

    2008-01-01

    The activities of Al and Ni were measured using multi-cell Knudsen effusion-cell mass spectrometry (multi-cell KEMS), over the composition range 8 - 32 at.%Al and temperature range T = 1400 - 1750 K in the Ni-Al-O system. These measurements establish that equilibrium solidification of gamma'-Ni3Al-containing alloys occurs by the eutectic reaction, L (+ Al2O3) = gamma + beta (+ Al2O3), at 1640 plus or minus 1 K and a liquid composition of 24.8 plus or minus 0.2 at.%Al (at an unknown oxygen content). The {gamma + beta + Al2O3} phase field is stable over the temperature range 1633 - 1640 K, and gamma'-Ni3Al forms via the peritectiod, gamma + beta (+ Al2O3) = gamma'(+ Al2O3), at 1633 plus or minus 1 K. This behavior is inconsistent with the current Ni-Al phase diagram and a new diagram is proposed. This new Ni-Al phase diagram explains a number of unusual steady state solidification structures reported previously and provides a much simpler reaction scheme in the vicinity of the gamma'-Ni3Al phase field.

  2. Interface behavior of Al2O3/Ti joints produced by liquid state bonding.

    PubMed

    Lemus-Ruiz, J; Guevara-Laureano, A O; Zarate-Medina, J; Arellano-Lara, A; Ceja-Cárdenas, L

    2015-04-01

    In this work we study brazing of Al2O3 to Ti with biocompatibility properties, using a Au-foil as joining element. Al2O3 was produced by sintering of powder at 1550°C. Al2O3 samples were coated with a 2 and 4μm thick of Mo layer and then stacked with Ti. Al2O3-Mo/Au/Ti combinations were joined at 1100°C in vacuum. Successful joining of Mo-Al2O3 to Ti was observed. Interface shows the formation of a homogeneous diffusion zone. Mo diffused inside Au forming a concentration line. Ti3Au and TiAu phases were observed.

  3. Epitaxial Growth of Mo Single Crystal on Sapphire by H2 Reduction of MoO3 and Characterization by Reflection High-Energy Electron Diffraction

    NASA Astrophysics Data System (ADS)

    Igarashi, Osamu

    1995-05-01

    Mo depositions on sapphire ( Al2O3) were effected by H2 reduction of MoO3, and the crystallinity of the films was characterized by reflection high-energy electron diffraction (RHEED). In the case of growth on the (1\\=102) Al2O3 substrates, single-crystal epitaxial growth of (001) Mo was realized. On (0001) Al2O3, single-crystal Mo was not obtained; Mo deposited on (0001) Al2O3 was composed of three sets of (110)-oriented crystallites. To obtain Debye-Scherrer ring-free Mo films whose RHEED patterns did not include arcs, growth temperatures of 890 and 920° C were required in growths on (1\\=102) and (0001) Al2O3 substrates, respectively.

  4. Characterization and prevention of humidity related degradation of atomic layer deposited Al2O3

    NASA Astrophysics Data System (ADS)

    Rückerl, Andreas; Zeisel, Roland; Mandl, Martin; Costina, Ioan; Schroeder, Thomas; Zoellner, Marvin H.

    2017-01-01

    Atomic layer deposited aluminum oxide (ALD-Al2O3) is a dielectric material, which is widely used in organic light emitting diodes in order to prevent their organic layers from humidity related degradation. Unfortunately, there are strong hints that in some cases, ALD-Al2O3 itself is suffering from humidity related degradation. Especially, high temperature and high humidity seem to enhance ALD-Al2O3 degradation strongly. For this reason, the degradation behavior of ALD-Al2O3 films at high temperature and high humidity was investigated in detail and a way to prevent it from degradation was searched. The degradation behavior is analyzed in the first part of this paper. Using infrared absorbance measurements and X-ray diffraction, boehmite (γ-AlOOH) was identified as a degradation product. In the second part of the paper, it is shown that ALD-Al2O3 films can be effectively protected from degradation using a silicon oxide capping. The deposition of very small amounts of silicon in a molecular beam epitaxy system and an X-ray photoelectron spectroscopy investigation of the chemical bonding between the silicon and the ALD-Al2O3 surface led to the conclusion that a silicon termination of the ALD-Al2O3 surface (Al*-O-SiOx) is able to stop humidity related degradation of the underlying ALD-Al2O3 films. The third part of the paper shows that the protection mechanism of the silicon termination is probably due to the strong tendency of silicic acid to resilificate exposed ALD-Al2O3 surfaces. The protective effect of a simple silicon source on an ALD-Al2O3 surface is shown exemplary and the related chemical reactions are presented.

  5. Protection of Polymer from Atomic-Oxygen Erosion using Al2O3 Atomic Layer Deposition Coatings

    DTIC Science & Technology

    2008-01-01

    coatings other than Al2O3 . Multilayer ALD films of Al2O3 / TiO2 or Al2O3 / ZnO could protect against both O atoms and... Al2O3 growth. The steady-state Al2O3 ALD growth rate after nucleation is ∼1.2 Å per AB cycle [19,26]. The polyimide substrates were coated with Al2O3 ALD ...apparatus is shown in Fig. 1. This apparatus has Fig. 2. Mass change of polyimide substrates coated with varying numbers of Al2O3 ALD AB cycles

  6. ALD of Al2O3 for Highly Improved Performance in Li-Ion Batteries

    SciTech Connect

    Dillon, A.; Jung, Y. S.; Ban, C.; Riley, L.; Cavanagh, A.; Yan, Y.; George, S.; Lee, S. H.

    2012-01-01

    Significant advances in energy density, rate capability and safety will be required for the implementation of Li-ion batteries in next generation electric vehicles. We have demonstrated atomic layer deposition (ALD) as a promising method to enable superior cycling performance for a vast variety of battery electrodes. The electrodes range from already demonstrated commercial technologies (cycled under extreme conditions) to new materials that could eventually lead to batteries with higher energy densities. For example, an Al2O3 ALD coating with a thickness of ~ 8 A was able to stabilize the cycling of unexplored MoO3 nanoparticle anodes with a high volume expansion. The ALD coating enabled stable cycling at C/2 with a capacity of ~ 900 mAh/g. Furthermore, rate capability studies showed the ALD-coated electrode maintained a capacity of 600 mAh/g at 5C. For uncoated electrodes it was only possible to observe stable cycling at C/10. Also, we recently reported that a thin ALD Al2O3 coating with a thickness of ~5 A can enable natural graphite (NG) electrodes to exhibit remarkably durable cycling at 50 degrees C. The ALD-coated NG electrodes displayed a 98% capacity retention after 200 charge-discharge cycles. In contrast, bare NG showed a rapid decay. Additionally, Al2O3 ALD films with a thickness of 2 to 4 A have been shown to allow LiCoO2 to exhibit 89% capacity retention after 120 charge-discharge cycles performed up to 4.5 V vs Li/Li+. Bare LiCoO2 rapidly deteriorated in the first few cycles. The capacity fade is likely caused by oxidative decomposition of the electrolyte at higher potentials or perhaps cobalt dissolution. Interestingly, we have recently fabricated full cells of NG and LiCoO2 where we coated both electrodes, one or the other electrode as well as neither electrode. In creating these full cells, we observed some surprising results that lead us to obtain a greater understanding of the ALD coatings. We have also recently coated a binder free LiNi0.04Mn0

  7. Pinhole Effect on the Melting Behavior of Ag@Al2O3 SERS Substrates.

    PubMed

    Ma, Lingwei; Huang, Yu; Hou, Mengjing; Li, Jianghao; Zhang, Zhengjun

    2016-12-01

    High-temperature surface-enhanced Raman scattering (SERS) sensing is significant for practical detections, and pinhole-containing (PC) metal@oxide structures possessing both enhanced thermal stability and superior SERS sensitivity are served as promising SERS sensors at extreme sensing conditions. Through tuning the Al2O3 precursors' exposure time during atomic layer deposition (ALD), Al2O3 shells with different amount of pinholes were covered over Ag nanorods (Ag NRs). By virtue of these unique PC Ag@Al2O3 nanostructures, herein we provide an excellent platform to investigate the relationship between the pinhole rate of Al2O3 shells and the melting behavior, high-temperature SERS performances of these core-shell nanostructures. Pinhole effect on the melting procedures of PC Ag@Al2O3 substrates was characterized in situ via their reflectivity variations during heating, and the specific melting point was quantitatively estimated. It is found that the melting point of PC Ag@Al2O3 raised along with the decrement of pinhole rate, and substrates with less pinholes exhibited better thermal stability but sacrificed SERS efficiency. This work achieved highly reliable and precise control of the pinholes over Al2O3 shells, offering sensitive SERS substrates with intensified thermal stability and superior SERS performances at extreme sensing conditions.

  8. Al2O3 on Black Phosphorus by Atomic Layer Deposition: An in Situ Interface Study.

    PubMed

    Zhu, Hui; McDonnell, Stephen; Qin, Xiaoye; Azcatl, Angelica; Cheng, Lanxia; Addou, Rafik; Kim, Jiyoung; Ye, Peide D; Wallace, Robert M

    2015-06-17

    In situ "half cycle" atomic layer deposition (ALD) of Al2O3 was carried out on black phosphorus ("black-P") surfaces with modified phosphorus oxide concentrations. X-ray photoelectron spectroscopy is employed to investigate the interfacial chemistry and the nucleation of the Al2O3 on black-P surfaces. This work suggests that exposing a sample that is initially free of phosphorus oxide to the ALD precursors does not result in detectable oxidation. However, when the phosphorus oxide is formed on the surface prior to deposition, the black-P can react with both the surface adventitious oxygen contamination and the H2O precursor at a deposition temperature of 200 °C. As a result, the concentration of the phosphorus oxide increases after both annealing and the atomic layer deposition process. The nucleation rate of Al2O3 on black-P is correlated with the amount of oxygen on samples prior to the deposition. The growth of Al2O3 follows a "substrate inhibited growth" behavior where an incubation period is required. Ex situ atomic force microscopy is also used to investigate the deposited Al2O3 morphologies on black-P where the Al2O3 tends to form islands on the exfoliated black-P samples. Therefore, surface functionalization may be needed to get a conformal coverage of Al2O3 on the phosphorus oxide free samples.

  9. Pinhole Effect on the Melting Behavior of Ag@Al2O3 SERS Substrates

    NASA Astrophysics Data System (ADS)

    Ma, Lingwei; Huang, Yu; Hou, Mengjing; Li, Jianghao; Zhang, Zhengjun

    2016-03-01

    High-temperature surface-enhanced Raman scattering (SERS) sensing is significant for practical detections, and pinhole-containing (PC) metal@oxide structures possessing both enhanced thermal stability and superior SERS sensitivity are served as promising SERS sensors at extreme sensing conditions. Through tuning the Al2O3 precursors' exposure time during atomic layer deposition (ALD), Al2O3 shells with different amount of pinholes were covered over Ag nanorods (Ag NRs). By virtue of these unique PC Ag@Al2O3 nanostructures, herein we provide an excellent platform to investigate the relationship between the pinhole rate of Al2O3 shells and the melting behavior, high-temperature SERS performances of these core-shell nanostructures. Pinhole effect on the melting procedures of PC Ag@Al2O3 substrates was characterized in situ via their reflectivity variations during heating, and the specific melting point was quantitatively estimated. It is found that the melting point of PC Ag@Al2O3 raised along with the decrement of pinhole rate, and substrates with less pinholes exhibited better thermal stability but sacrificed SERS efficiency. This work achieved highly reliable and precise control of the pinholes over Al2O3 shells, offering sensitive SERS substrates with intensified thermal stability and superior SERS performances at extreme sensing conditions.

  10. Thermoluminescence studies of γ-irradiated Al2O3:Ce3+ phosphor

    NASA Astrophysics Data System (ADS)

    Reddy, S. Satyanarayana; Nagabhushana, K. R.; Singh, Fouran

    2016-07-01

    Pure and Ce3+ doped Al2O3 phosphors were synthesized by solution combustion method. The synthesized samples were characterized by X-ray diffraction (XRD) and its shows α-phase of Al2O3. Crystallite size was estimated by Williamson-Hall (W-H) method and found to be 49, 59 and 84 nm for pure, 0.1 mol% and 1 mol% Ce3+ doped Al2O3 respectively. Trace elemental analysis of undoped Al2O3 shows impurities viz. Fe, Cr, Mn, Mg, Ti, etc. Photoluminescence (PL) spectra of Al2O3:Ce3+ shows emission at 367 nm and excitation peak at 273 nm, which are corresponding to 5D → 4F and 4F → 5D transitions respectively. PL intensity decreases with concentration up to 0.4 mol%, beyond this mol% PL intensity increases with doping concentration up to 2 mol%. Thermoluminescence (TL) studies of γ-rayed pure and Ce3+ doped Al2O3 have been studied. Two well resolved TL glow peaks at 457.5 K and 622 K were observed in pure Al2O3. Additional glow peak at 566 K was observed in Al2O3:Ce3+. Maximum TL intensity was observed for Al2O3:Ce3+ (0.1 mol%) beyond this TL intensity decreases with increasing Ce3+ concentration. Computerized glow curve deconvolution (CGCD) method was used to resolve the multiple peaks and to calculate TL kinetic parameters. Thermoluminescence emission (TLE) spectra of pure Al2O3 glow peaks (457.5 K and 622 K) shows sharp emission at 694 nm and two small humps at 672 nm and 709 nm. The sharp peak at 696 nm corresponds to Cr3+ impurity of 2Eg → 4A2g transition of R lines and 713 nm hump is undoubtedly belongs to Cr3+ emission of near neighbor pairs. The emission at 672 nm is characteristic of Mn4+ impurity ions of 2E → 4A2 transition. TLE of Al2O3:Ce3+ (0.1 mol%) shows additional broad emission at 412 nm corresponds to F-centers. Linearity is observed in the dose range 20-500 Gy in Al2O3:Ce3+ (1 mol%).

  11. Investigation on thermal stability of Ta2O5, TiO2 and Al2O3 coatings for application at high temperature

    NASA Astrophysics Data System (ADS)

    Shang, Peng; Xiong, Shengming; Li, Linghui; Tian, Dong; Ai, Wanjun

    2013-11-01

    In this paper, tantalum pentoxide (Ta2O5), titanium dioxide (TiO2) and aluminum oxide (Al2O3) coatings are deposited on silicon substrates by ion beam sputtering (IBS). The influences of the thermal exposure at high temperature in air on the surface morphology, roughness, and the structure were investigated. The results indicate that the chemical composition of the as-deposited TiO2 and Ta2O5 coatings are apparently close to the stoichiometry ratios and both of them are amorphous structures. The peaks corresponding to anatase TiO2 appear at 400 °C while the anatase-to-rutile transformation is not observed after 800 °C and 1000 °C bake. Ta2O5 coating crystallizes at 800 °C and 1000 °C to form the hexagonal structure and orthorhombic structure, respectively. TiO2 and Al2O3 single layers all develop catastrophic damage at 400 °C in the form of noted spallation or blisters, whereas there is no visible damage for the Ta2O5 coating even at 1000 °C. To understand possible damage mechanisms, the thermal stress distributions through the thickness of Ta2O5 and TiO2 coatings and the influence of the microstructure transformation are discussed. Finally, some possible approaches to improve the thermal stability are also proposed.

  12. Constraint density functional calculations for multiplets in ligand-fields: Applications to Fe-phthalocyanine and Al2O3:Cr^3+

    NASA Astrophysics Data System (ADS)

    Kitaoka, Y.; Nakamura, K.; Akiyama, T.; Ito, T.; Weinert, M.; Freeman, A. J.

    2012-02-01

    In transition-metal-based complexes and molecules, multiplet structures are essential in understanding the electronic structure. However, it is often difficult to evaluate a true ground state or the lowest state within a given ligand (or crystal) symmetry from first principles calculations based on density-functional theory (DFT). Here, we propose a simple DFT approach, implemented into the FLAPW methodootnotetextWimmer, Krakauer, Weinert, Freeman, PRB24, 864; Weinert, Wimmer, Freeman, PRB26, 4571, to treat multiplets in ligand-fields, by imposing a density matrix constraint on the d-orbital occupation numbers. We demonstrate the utility of this approach for the case of an isolated single Fe phthalocyanine (FePc) and a Cr impurity in a corundum Al2O3. For the FePc, results predict that there are three stationary states of ^3Eg, ^3B2, and ^3A2 in the Fe^2+ ion, and our total energy calculations clearly demonstrate that the ground state is ^3A2g. In the case of the Al2O3:Cr^3+, where an on-site Coulomb correlation correction (+U) is incorporated, the ground state is ^4A2 and the total energy difference between the ground state and the excited state ^4T2, 2.9 eV, roughly agrees with an experimental value of 2.23 eV.

  13. Twin symmetry texture of energetically condensed niobium thin films on sapphire substrate (a-plane Al2O3)

    NASA Astrophysics Data System (ADS)

    Zhao, X.; Phillips, L.; Reece, C. E.; Seo, Kang; Krishnan, M.; Valderrama, E.

    2011-08-01

    An energetic condensation technique, cathodic arc discharge deposition, is used to grow epitaxial Niobium (Nb) thin films on a-plane sapphire (hexagonal-closed-packed Al2O3) at moderate substrate heating temperature (<400 °C). The epitaxial Nb(110)/Al2O3(1,1,-2,0) thin films reached a maximum residual resistance ratio (RRR) value 214, despite using a reactor-grade Nb cathode source whose RRR was only 30. The measurements suggest that the film's density of impurities and structural defects are lower when compared to Nb films produced by other techniques, such as magnetron sputtering, e-beam evaporation or molecular-beam-epitaxy. At lower substrate temperature, textured polycrystalline Nb thin films were created, and the films might have twin symmetry grains with {110} orientations in-plane. The texture was revealed by x-ray diffraction pole figures. The twin symmetry might be caused by a combination effect of the Nb/Al2O3 three-dimensional epitaxial relationship ("3D-Registry" Claassen's nomenclature) and the "Volmer-Weber" (Island) growth model. However, pole figures obtained by electron backscattering diffraction (EBSD) found no twin symmetry on the thin films' topmost surface (˜50 nm in depth). The EBSD pole figures showed only one Nb{110} crystal plane orientation. A possible mechanism is suggested to explain the differences between the bulk (XRD) and surface (EBSD) pole figures.

  14. Traps in Al2O3 detected by tunneling

    NASA Technical Reports Server (NTRS)

    Skarlatos, Y.; Barker, R. C.; Yelon, A.

    1976-01-01

    A structure, quite different from inelastic tunneling peaks, has been observed in electron-tunneling spectra of MOM junctions. A capacitance peak is associated with this structure, which is attributed to traps in the oxide at energies smaller than those previously reported. The C-V characteristics calculated using a single-energy trap model agree with experimental results; however, no satisfactory explanation has yet been found to account for the strong temperature dependence of the trap energy levels.

  15. [Effects of SO2 on NO reduction with methanol over Ag/Al2O3 catalyst].

    PubMed

    Zhu, Tianle; Hao, Jiming; Fu, Lixin; Cui, Xiangyu; Wang, Yanji

    2002-07-01

    Ag/Al2O3 catalyst with 5% Ag loading was prepared by the single step sol-gel mixture method and the effects of adding SO2 to reaction feed on NO reduction by CH3OH over the catalyst was investigated in the presence of oxygen. The results showed that in the absence of SO2 and H2O the catalyst displayed lower activity temperature and higher N2O selectivity, which was attributed to the partial reduction of oxidized Ag into metallic Ag under reaction conditions. Selective catalytic reduction activity was not decreased but significantly increased, N2O formation was suppressed and most effective NO reduction temperature shifted to higher temperature by pre-sulfated Ag/Al2O3 or addition of SO2 to reaction mixture. XPS analysis showed that the sulfate-like species were formed by the effect of SO2.

  16. Microstructure and Optical Properties of SS/Mo/Al2O3 Spectrally Selective Solar Absorber Coating

    NASA Astrophysics Data System (ADS)

    Gao, Xiang-Hu; Guo, Zhi-Ming; Geng, Qing-Fen; Ma, Peng-Jun; Liu, Gang

    2017-01-01

    Surface-textured Mo thin film is fabricated by magnetron sputtering through the adjustment of deposition parameters, which exhibits a high absorptance of 0.80 and a low emittance of 0.09. The single-layer Mo deposited on stainless steel (SS) is characterized by x-ray diffraction (XRD), ultra-high resolution scanning electron microscope, atomic force microscope and optical measurement. The controlled surface roughness combined with larger aspect ratio contributes much to the high absorptance and low emittance. Based on the SS/Mo coating, a spectrally selective coating (SS/Mo/Al2O3) is designed and fabricated. The coating shows an amorphous structure and exhibits an absorptance of 0.90 and an emittance of 0.08. Tauc-Lorentz and Drude free-electron models are used to modeling the optical properties of Al2O3 and Mo layers by phase-modulated spectroscopic ellipsometry.

  17. Atomic layer deposited Al2O3 passivation of type II InAs/GaSb superlattice photodetectors

    NASA Astrophysics Data System (ADS)

    Salihoglu, Omer; Muti, Abdullah; Kutluer, Kutlu; Tansel, Tunay; Turan, Rasit; Kocabas, Coskun; Aydinli, Atilla

    2012-04-01

    Taking advantage of the favorable Gibbs free energies, atomic layer deposited (ALD) aluminum oxide (Al2O3) was used as a novel approach for passivation of type II InAs/GaSb superlattice (SL) midwave infrared (MWIR) single pixel photodetectors in a self cleaning process (λcut-off ˜ 5.1 μm). Al2O3 passivated and unpassivated diodes were compared for their electrical and optical performances. For passivated diodes, the dark current density was improved by an order of magnitude at 77 K. The zero bias responsivity and detectivity was 1.33 A/W and 1.9 × 1013 Jones, respectively at 4 μm and 77 K. Quantum efficiency (QE) was determined as %41 for these detectors. This conformal passivation technique is promising for focal plane array (FPA) applications.

  18. Microstructure and Optical Properties of SS/Mo/Al2O3 Spectrally Selective Solar Absorber Coating

    NASA Astrophysics Data System (ADS)

    Gao, Xiang-Hu; Guo, Zhi-Ming; Geng, Qing-Fen; Ma, Peng-Jun; Liu, Gang

    2016-11-01

    Surface-textured Mo thin film is fabricated by magnetron sputtering through the adjustment of deposition parameters, which exhibits a high absorptance of 0.80 and a low emittance of 0.09. The single-layer Mo deposited on stainless steel (SS) is characterized by x-ray diffraction (XRD), ultra-high resolution scanning electron microscope, atomic force microscope and optical measurement. The controlled surface roughness combined with larger aspect ratio contributes much to the high absorptance and low emittance. Based on the SS/Mo coating, a spectrally selective coating (SS/Mo/Al2O3) is designed and fabricated. The coating shows an amorphous structure and exhibits an absorptance of 0.90 and an emittance of 0.08. Tauc-Lorentz and Drude free-electron models are used to modeling the optical properties of Al2O3 and Mo layers by phase-modulated spectroscopic ellipsometry.

  19. Data of ALD Al2O3 rear surface passivation, Al2O3 PERC cell performance, and cell efficiency loss mechanisms of Al2O3 PERC cell.

    PubMed

    Huang, Haibing; Lv, Jun; Bao, Yameng; Xuan, Rongwei; Sun, Shenghua; Sneck, Sami; Li, Shuo; Modanese, Chiara; Savin, Hele; Wang, Aihua; Zhao, Jianhua

    2017-04-01

    This data article is related to the recently published article '20.8% industrial PERC solar cell: ALD Al2O3 rear surface passivation, efficiency loss mechanisms analysis and roadmap to 24%' (Huang et al., 2017) [1]. This paper is about passivated emitter and rear cell (PERC) structures and it describes the quality of the Al2O3 rear-surface passivation layer deposited by atomic layer deposition (ALD), in relation to the processing parameters (e.g. pre-clean treatment, deposition temperature, growth per cycle, and film thickness) and to the cell efficiency loss mechanisms. This dataset is made public in order to contribute to the limited available public data on industrial PERC cells, to be used by other researchers.

  20. Optical properties of the Al2O3/SiO2 and Al2O3/HfO2/SiO2 antireflective coatings

    NASA Astrophysics Data System (ADS)

    Marszałek, Konstanty; Winkowski, Paweł; Jaglarz, Janusz

    2014-01-01

    Investigations of bilayer and trilayer Al2O3/SiO2 and Al2O3/HfO2/SiO2 antireflective coatings are presented in this paper. The oxide films were deposited on a heated quartz glass by e-gun evaporation in a vacuum of 5 × 10-3 [Pa] in the presence of oxygen. Depositions were performed at three different temperatures of the substrates: 100 °C, 200 °C and 300 °C. The coatings were deposited onto optical quartz glass (Corning HPFS). The thickness and deposition rate were controlled with Inficon XTC/2 thickness measuring system. Deposition rate was equal to 0.6 nm/s for Al2O3, 0.6 nm - 0.8 nm/s for HfO2 and 0.6 nm/s for SiO2. Simulations leading to optimization of the thin film thickness and the experimental results of optical measurements, which were carried out during and after the deposition process, have been presented. The optical thickness values, obtained from the measurements performed during the deposition process were as follows: 78 nm/78 nm for Al2O3/SiO2 and 78 nm/156 nm/78 nm for Al2O3/HfO2/SiO2. The results were then checked by ellipsometric technique. Reflectance of the films depended on the substrate temperature during the deposition process. Starting from 240 nm to the beginning of visible region, the average reflectance of the trilayer system was below 1 % and for the bilayer, minima of the reflectance were equal to 1.6 %, 1.15 % and 0.8 % for deposition temperatures of 100 °C, 200 °C and 300 °C, respectively.

  1. Low-temperature thermal conductivity measurements of Al2O3 ceramic for use in bolometric particle detector

    NASA Astrophysics Data System (ADS)

    Drobizhev, Alexey

    2013-04-01

    Bolometric particle detectors for rare weak processes operate at temperatures as low as 10mK and are background-dependent, so radiopure structural materials such as alumina ceramic (Al2O3) are of interest, and their thermal properties in the very low temperature regime must be understood. Our experiments are conducted in a dilution refrigerator, with heaters being used to create temperature gradients across elongated alumina samples of different cross-sectional geometries mounted in copper clamps, with one end thermalized on the 10mK plate of the cryostat. Temperatures of both ends are measured with RuO2 resistance thermometers, and thermal conductivity k(T) can be determined using the relationship dQdt =Alk(T)dT, where dQdt is heating power, A is cross-sectional area of the sample, l is its length, and T is temperature. Absolute values and temperature dependence of thermal conductivity of the alumina samples were measured and compared to well-investigated single-crystal sapphire properties. Thermal conductivity of other materials of interest was also investigated; the results will be presented.

  2. Growth and magnetic anisotropy of thin W(110)/Co films on Al2O3(112¯0)

    NASA Astrophysics Data System (ADS)

    Sellmann, R.; Fritzsche, H.; Maletta, H.; Leiner, V.; Siebrecht, R.

    2001-06-01

    The growth and magnetism of thin W(110)/Co films deposited by molecular beam epitaxy on single-crystal sapphire Al2O3(112¯0) substrates is investigated. Low-energy electron diffraction analysis shows that the Co films grow on the epitaxial W(110) substrate layer with a constant lattice strain up to a Co thickness dCo=20 Å. Pseudomorphic growth is found for the W[11¯0] direction. The thickness-dependent magnetic anisotropy is studied in situ at T=300 K by means of magneto-optical Kerr-effect measurements on a Co wedge-shaped sample prior and after coverage with a Au overlayer. After the coverage the Co wedge reveals a perpendicular magnetic anisotropy for small Co film thickness followed by a spin-reorientation transition from out-of-plane to in-plane alignment of the magnetization vector in the thickness regime 7 Å<=dCo<=9 Å. Spin-dependent neutron reflectivity data provide evidence for a pronounced magnetic anisotropy within the film plane even for relatively thick Co films. The observed decrease of the splitting between spin-up and spin-down reflectivities for decreasing temperature indicates that the spin-reorientation transition of the system W(110)/Co/Au can also be induced thermally.

  3. Effects of annealing on properties of Al2O3 monolayer film at 355 nm

    NASA Astrophysics Data System (ADS)

    Tu, Feifei; Wang, Hu; Xing, Huanbin; Zheng, Ruxi; Zhang, Weili; Yi, Kui

    2015-07-01

    Al2O3 monolayer films were deposited on fused silica substrate and K9 glass substrate by electron-beam deposition. Annealing as a general post-treatment was used to enhance the quality of the Al2O3 coatings. The optical properties of the films were analyzed from the transmission spectra of the samples. The composition of the samples before and after annealing were measured by X-ray photoelectron spectroscopy (XPS). According to the analysis of the results, it can be found that the oxidation degree of the coatings increases after annealing in O2 inside coating chamber. The laser-induced damage thresholds of the Al2O3 films can be increased after the annealing process. Finally, the damage morphologies of the Al2O3 coatings were analyzed.

  4. Production of hydrogen by autothermal reforming of propane over Ni/delta-Al2O3.

    PubMed

    Lee, Hae Ri; Lee, Kwi Yeon; Park, Nam Cook; Shin, Jae Soon; Moon, Dong Ju; Lee, Byung Gwon; Kim, Young Chul

    2006-11-01

    The performance of Ni/delta-Al2O3 catalyst in propane autothermal reforming (ATR) for hydrogen production was investigated in the present study. The catalysts were characterized using XRD, TEM, and SEM. The activity of the Ni/delta-Al2O3 catalyst manufactured by the water-alcohol method was better than those of the catalysts manufactured by the impregnation and chemical reduction methods. The Ni/delta-Al2O3 catalysts were modified by the addition of promoters such as Mg, La, Ce, and Co, in order to improve their stability and yield. Hydrogen production was the largest for the Ni-Co-CeO2/Al2O3, catalyst.

  5. Oxidation of Al2O3 continuous fiber-reinforced/NiAl composites

    NASA Technical Reports Server (NTRS)

    Doychak, J.; Nesbitt, J. A.; Noebe, R. D.; Bowman, R. R.

    1992-01-01

    The 1200 C and 1300 C isothermal and cyclic oxidation behavior of Al2O3 continuous fiber-reinforced/NiAl composites were studied. Oxidation resulted in formation of Al2O3 external scales in a similar manner as scales formed on monolithic NiAl. The isothermal oxidation of an Al2O3/NiAl composite resulted in oxidation of the matrix along the fiber/matrix interface near the fiber ends. This oxide acted as a wedge between the fiber and the matrix, and, under cyclic oxidation conditions, led to further oxidation along the fiber lengths and eventual cracking of the composite. The oxidation behavior of composites in which the Al2O3 fibers were sputter coated with nickel prior to processing was much more severe. This was attributed to open channels around the fibers which formed during processing, most likely as a result of the diffusion of the nickel coating into the matrix.

  6. Microstructure and Mechanical Properties of Al2O3 / A336 Compsite by Low Pressure Infiltratrion

    DTIC Science & Technology

    2011-08-01

    clear and bonds directly with matrix and fiber. It is confirmed by the presence of the γ-Al2O3, MgO from diffraction peaks in the XRD pattern (Fig 4...and EDS (Fig. 3(b),(c)). It suggests that γ-Al2O3, MgO can be produced as results of the interfacial reaction between the Al liquid and the SiO2...results of the reaction between the α-Al2O3 and the MgO , i.e. α-Al2O3+ MgO →MgAl2O4, It was noticed that MgAl2O4 improve wettability, but decrease

  7. Al2O3 Scale Development on Iron Aluminides

    SciTech Connect

    Zhang, Xiao-Feng; Thaidigsmann, Katja; Ager, Joel; Hou, Peggy Y.

    2005-11-10

    The structure and phase of the Al{sub 2}O{sub 3} scale that forms on an Fe{sub 3}Al-based alloy (Fe-28Al-5Cr) (at %) was investigated by transmission electron microscopy (TEM) and photoluminescence spectroscopy (PL). Oxidation was performed at 900 C and 1000 C for up to 190 min. TEM revealed that single-layer scales were formed after short oxidation times. Electron diffraction was used to show that the scales are composed of nanoscale crystallites of the {theta}, {gamma}, and {alpha} phases of alumina. Band-like structure was observed extending along three 120{sup o}-separated directions within the surface plane. Textured {theta} and {gamma} grains were the main components of the bands, while mixed {alpha} and transient phases were found between the bands. Extended oxidation produced a double-layered scale structure, with a continuous {alpha} layer at the scale/alloy interface, and a {gamma}/{theta} layer at the gas surface. The mechanism for the formation of Al{sub 2}O{sub 3} scales on iron aluminide alloys is discussed and compared to that for nickel aluminide alloys.

  8. Preparation and characterization of Al2O3/Y3Al5O12/ZrO2 ternary hypoeutectic in situ composites by laser rapid solidification

    NASA Astrophysics Data System (ADS)

    Su, Haijun; Zhang, Jun; Tian, Junjie; Liu, Lin; Fu, Hengzhi

    2008-07-01

    The directionally solidified oxide eutectic in situ composite is one of the most promising high-temperature structural materials in oxidizing environments. Pore-free rods and plates of ternary Al2O3/Y3Al5O12 (YAG)/ZrO2 hypoeutectic in situ composites with hypoeutectic composition (71 mol % Al2O3, 17 mol % Y2O3, and 12 mol % ZrO2) are prepared rapidly by the laser zone remelting technique. The hypoeutectic growth and microstructure characteristic of grown crystals are studied using the scanning electron microscopy, x-ray diffraction, and energy dispersive spectroscopy, aiming to understand well the rapid solidification behavior of the ternary oxide system of Al2O3-Y2O3-ZrO2. The rapidly solidified Al2O3/YAG/ZrO2 hypoeutectic shows a refined, interpenetrating, and irregular lamellar structure with a reticular distribution of coarse Al2O3 and yttrium aluminum garnet (YAG) and smaller ZrO2 phases. The fine ZrO2 phases are partially embedded at the Al2O3/YAG interfaces. Moreover, the typical dendrite microstructure similar to the metallic solidification is also observed. The formation of two kinds of microstructures is mainly attributed to the rapid growth during the laser zone remelting and constitutional supercooling. The Al2O3 and YAG phases grow in a typical faceted manner, and the ZrO2 phase presents a weak-faceted growth. The size of the interphase spacing obtained decreases rapidly in increasing the laser scanning rate. The fundamental investigations on the irregular growth mechanisms of the hypoeutectic are suggestive to the comprehension of the complex solidification behavior of the ternary oxide systems.

  9. The formation of tungsten doped Al2O3/ZnO coatings on aluminum by plasma electrolytic oxidation and their application in photocatalysis

    NASA Astrophysics Data System (ADS)

    Stojadinović, Stevan; Vasilić, Rastko; Radić, Nenad; Tadić, Nenad; Stefanov, Plamen; Grbić, Boško

    2016-07-01

    Tungsten doped Al2O3/ZnO coatings are formed by plasma electrolytic oxidation of aluminum substrate in supporting electrolyte (0.1 M boric acid + 0.05 M borax + 2 g/L ZnO) with addition of different concentrations of Na2WO4·2H2O. The morphology, crystal structure, chemical composition, and light absorption characteristics of formed surface coatings are investigated. The X-ray diffraction and X-ray photoelectron spectroscopy results indicate that formed surface coatings consist of alpha and gamma phase of Al2O3, ZnO, metallic tungsten and WO3. Obtained results showed that incorporated tungsten does not have any influence on the absorption spectra of Al2O3/ZnO coatings, which showed invariable band edge at about 385 nm. The photocatalytic activity of undoped and tungsten doped Al2O3/ZnO coatings is estimated by the photodegradation of methyl orange. The photocatalytic activity of tungsten doped Al2O3/ZnO coatings is higher thanof undoped Al2O3/ZnO coatings; the best photocatalytic activity is ascribed to coatings formed in supporting electrolyte with addition of 0.3 g/L Na2WO4·2H2O. Tungsten in Al2O3/ZnO coatings acts as a charge trap, thus reducing the recombination rate of photogenerated electron-hole pairs. The results of PL measurements are in agreement with photocatalytic activity. Declining PL intensity corresponds to increasing photocatalytic activity of the coatings, indicating slower recombination of electron-hole pairs.

  10. Temperature dependence of the dielectric response of anodized Al-Al2O3-metal capacitors

    NASA Astrophysics Data System (ADS)

    Hickmott, T. W.

    2003-03-01

    The temperature dependence of capacitance, CM, and conductance, GM, of Al-Al2O3-metal capacitors with Cu, Ag, and Au electrodes has been measured between 100 and 340 K at seven frequencies between 10 kHz and 1 MHz. Al2O3 films between 15 and 64 nm thick were formed by anodizing evaporated Al films in borate-glycol or borate-H2O electrolyte. The interface capacitance at the Al2O3-metal interface, CI, which is in series with the capacitance CD due to the Al2O3 dielectric, is determined from plots of 1/CM versus insulator thickness. CI is not fixed for a given metal-insulator interface but depends on the vacuum system used to deposit the metal electrode. CI is nearly temperature independent. When CI is taken into account the dielectric constant of Al2O3 determined from capacitance measurements is ˜8.3 at 295 K. The dielectric constant does not depend on anodizing electrolyte, insulator thickness, metal electrode, deposition conditions for the metal electrode or measurement frequency. By contrast, GM of Al-Al2O3-metal capacitors depends on both the deposition conditions of the metal and on the metal. For Al-Al2O3-Cu capacitors, GM is larger for capacitors with large values of 1/CI that result when Cu is evaporated in an oil-pumped vacuum system. For Al-Al2O3-Ag capacitors, GM does not depend on the Ag deposition conditions.

  11. Al/Al2O3 Metal Matrix Composites (MMCs) and Macrocomposites for Armor Applications

    DTIC Science & Technology

    2013-09-01

    ceramics (high hardness, high stiffness, low thermal expansion). In this study , Al/Al2O3 MMCs with alumina particle contents ranging from 12% to 46% were...expansion). In this study , Al/Al2O3 MMCs with alumina particle contents ranging from 12% to 46% were fabricated by different processing approaches...the different MMCs. The matrix alloy, alumina volume fraction, densities, mechanical properties , and thermal properties are summarized in Table 2

  12. Tb3+ ion doping into Al2O3: Solubility limit and luminescence properties

    NASA Astrophysics Data System (ADS)

    Onishi, Yuya; Nakamura, Toshihiro; Adachi, Sadao

    2016-11-01

    Tb3+-activated Al2O3 phosphors with a molar ratio of \\text{Al}:\\text{Tb} = (1 - x):x are synthesized by metal organic decomposition (x = 0-0.15) and subsequent calcination at T c = 200-1200 °C for 1 h in air. The material properties of the synthesized phosphors are investigated by X-ray diffraction (XRD), photoluminescence (PL) analyses, PL excitation spectroscopy, and luminescence lifetime measurements. At x = 0.015, the metastable phase of γ-Al2O3 is obtained by calcination at T c ˜ 300-1050 °C and a mixture of γ, θ, and α phases at T c ˜ 1050-1150 °C. The high-temperature stable phase of α-Al2O3 is obtained only at T c ≥ 1150 °C. Below T c ˜ 300 °C, the XRD data suggest the formation of boehmite (AlOOH). The solubility limit of Tb3+ in α-Al2O3 is also clearly determined to be x ˜ 0.015 (1.5%). The PL decay time of the Tb3+ green emission in α-Al2O3 is ˜1.1 ms for x < 0.015 and slowly decreases with further increase in x (Tb3+). The schematic energy-level diagram of Tb3+ in α-Al2O3 is proposed for a better understanding of the present phosphor system. Finally, the temperature dependence of the PL intensity is examined between T = 20 and 450 K, yielding quenching energies of E q ˜ 0.28 eV (α-Al2O3 and γ-Al2O3).

  13. Single Crystal Structure Determination of Alumina to 1 Mbar

    NASA Astrophysics Data System (ADS)

    Dong, H.; Zhang, L.; Prakapenka, V.; Mao, H.

    2014-12-01

    Aluminum oxide (Al2O3) is an important ceramic material and a major oxide in the earth. Additionally, alumina is a widely used pressure standard in static high-pressure experiments (Cr3+-bearing corundum, ruby). The changes of its crystal structure with pressure (P) and temperature (T) are important for its applications and understanding its physical properties in the deep Earth. There have been numerous reports on the high P-T polymorphs of alumina. Previous theoretical calculations and experiments suggest that the crystal structure of Al2O3 evolves greatly at high P-T. In this study, we used the newly developed multigrain crystallography method combined with single-crystal x-ray diffraction analysis technique for the structure determination of alumina at high P-T to provide single-crystal structure refinement for high-pressure phases of Al2O3. Alumina powder was mixed with ~10% Pt and Ne was used as both pressure transmitting media and thermal insulating layers during laser-heating. Coarse-grained aggregates of Al2O3 were synthesized in a laser-heated diamond anvil cell. The structure change of Al2O3 was monitored by in situ x-ray diffraction at ~1 Mbar and 2700 K. The results allow us to distinguish the structural differences between the Rh2O3 (II) structure (space group Pbcn) and perovskite structure (space group Pbnm) for the first high-pressure phase of Al2O3. More detailed results will be discussed in the later work.

  14. Thermally assisted photo transfer OSL from deep traps in Al2O3:C grains exhibiting different TL peak shapes.

    PubMed

    Polymeris, George S; Kitis, George

    2012-10-01

    The present work studies the thermally assisted photo transfer OSL (TAPT OSL) signal in the case of Al(2)O(3):C samples showing double-structured main dosimetric TL peaks. The measurement signal provides indirect experimental evidence regarding the presence of deep traps along with one transfer mechanism extremely powerful and efficient. The experimental features of this signal are presented along with those yielded for samples with narrow TL peaks for the sake of comparison. In the framework of a dosimetric characterization, the straightforward relation observed between the TAPT OSL integrated intensity and the dose, even if non-linear, implies that this signal could be effectively used towards dosimetry purposes in the high dose region up to 250 Gy. Furthermore, the study on the influence of the annealing temperature on the TL glow curve shape on Al(2)O(3):C grains is attempted. The variety of glow curve shapes reported especially in the case of single grains is not affected by high temperature annealing, since its effect is dominant even after heating at 1085°C. Thus, this variety should not be correlated to the different deep trap occupancies, but rather be attributed to a possible structural defect. The main dosimetric TL peak af all grains is considered to be a composite of two unambiguously different traps of non-first-order kinetics. The low temperature part of these traps, reaching a maximum at ~190°C is an electron trap and the high temperature part with maximum at ~250°C is a hole trap. TL dose response of Al(2)O(3):C grains presenting double peak structures is presented for the first time in literature, suggesting the usefulness on the applicability of Al(2)O(3):C in the dose regime up to 100 Gy.

  15. The use of 99mTc-Al2O3 for detection of sentinel lymph nodes in breast cancer

    NASA Astrophysics Data System (ADS)

    Sinilkin, I.; Chernov, V.; Medvedeva, A.; Zeltchan, R.; Slonimskaya, E.; Doroshenko, A.; Varlamova, N.; Skuridin, V.

    2016-08-01

    Purpose: to study the feasibility of using the new radiopharmaceutical based on the technetium-99m-labeled gamma-alumina for identification of sentinel lymph nodes (SLNs) in breast cancer patients. The study included two groups of breast cancer patients who underwent single photon emission computed tomography (SPECT) and intraoperaive gamma probe identification of sentinel lymph nodes (SLNs). To identify SLNs, the day before surgery Group I patients (n = 34) were injected with radioactive 99mTc-Al2O3, and Group II patients (n = 30) received 99mTc-labeled phytate colloid. A total of 37 SLNs were detected in Group I patients. The number of identified SLNs per patient ranged from 1 to 2 (the average number of identified SLNs was 1.08). Axillary lymph nodes were the most common site of SLN localization. 18 hours after 99mTc-Al2O3 injection, the percentage of its accumulation in the SLN was 7-11% (of the counts in the injection site) by SPECT and 17-31% by gamma probe detection. In Group II SLNs were detected in 27 patients. 18 hours after injection of the phytate colloid the percentage of its accumulation in the SLN was 1.5-2% out of the counts in the injection site by SPECT and 4-7% by gamma probe. The new radiopharmaceutical based on the 99mTc-Al2O3 demonstrates high accumulation in SLNs without redistribution through the entire lymphatic basin. The sensitivity and specificity of 99mTc-Al2O3 were 100% for both SPECT and intraoperative gamma probe identification.

  16. Postperovskite phase equilibria in the MgSiO3-Al2O3 system.

    PubMed

    Tsuchiya, Jun; Tsuchiya, Taku

    2008-12-09

    We investigate high-P,T phase equilibria of the MgSiO(3)-Al(2)O(3) system by means of the density functional ab initio computation methods with multiconfiguration sampling. Being different from earlier studies based on the static substitution properties with no consideration of Rh(2)O(3)(II) phase, present calculations demonstrate that (i) dissolving Al(2)O(3) tends to decrease the postperovskite transition pressure of MgSiO(3) but the effect is not significant ( approximately -0.2 GPa/mol% Al(2)O(3)); (ii) Al(2)O(3) produces the narrow perovskite+postperovskite coexisting P,T area (approximately 1 GPa) for the pyrolitic concentration (x(Al2O3) approximately 6 mol%), which is sufficiently responsible to the deep-mantle D'' seismic discontinuity; (iii) the transition would be smeared (approximately 4 GPa) for the basaltic Al-rich composition (x(Al2O3) approximately 20 mol%), which is still seismically visible unless iron has significant effects; and last (iv) the perovskite structure spontaneously changes to the Rh(2)O(3)(II) with increasing the Al concentration involving small displacements of the Mg-site cations.

  17. Pressure drop and heat transfer of Al2O3-H2O nanofluids through silicon microchannels

    NASA Astrophysics Data System (ADS)

    Wu, Xinyu; Wu, Huiying; Cheng, Ping

    2009-10-01

    Experimental investigations were performed on the single-phase flow and heat transfer characteristics through the silicon-based trapezoidal microchannels with a hydraulic diameter of 194.5 µm using Al2O3-H2O nanofluids with particle volume fractions of 0, 0.15% and 0.26% as the working fluids. The effects of the Reynolds number, Prandtl number and nanoparticle concentration on the pressure drop and convective heat transfer were investigated. Experimental results show that the pressure drop and flow friction of the nanofluids increased slightly when compared with that of the pure water, while the Nusselt number increased considerably. At the same pumping power, using nanofluids instead of pure water caused a reduction in the thermal resistance. It was also found that the Nusselt number increased with the increase in the particle concentration, Reynolds number and Prandtl number. Based on the experimental data, the dimensionless correlations for the flow friction and heat transfer of Al2O3-H2O nanofluids through silicon microchannels were proposed for the first time. The agglomeration and deposition of nanoparticles in the silicon microchannels were also examined in this paper. It was found that the Al2O3 nanoparticles deposited on the inner wall of microchannels more easily with increasing wall temperature, and once boiling commenced, there is a severe deposition and adhesion of nanoparticles to the inner wall, which makes the boiling heat transfer of nanofluids in silicon microchannels questionable.

  18. H2 dissociation on γ-Al2O3 supported Cu/Pd atoms: A DFT investigation

    NASA Astrophysics Data System (ADS)

    Wang, Hongtao; Chen, Lijuan; Lv, Yongkang; Ren, Ruipeng

    2014-01-01

    The density functional theory (DFT) was applied to investigate the promotion effects of single Cu and Pd atoms deposition on γ-Al2O3 surface for the adsorption and dissociation of H2 molecule, which is of importance for many catalysis reactions. Due to its strong Lewis acidity, the tri-coordinated surface Al site was identified to be the most preferable site for both Cu and Pd location. The inner surface electrons rearrangement from O to Al of alumina was found to be a key factor to stabilize the Cu/Pd adsorption configurations, rather than the total electrons transfer between Cu/Pd and the surface. It was found that the supported Cu and Pd atoms are more active for H2 dissociation than the clean γ-Al2O3 surface. The supported Pd is more active than Cu for H2 dissociation. In addition, the metal-support interaction of the γ-Al2O3 supported Cu/Pd atoms are more favored than the metal-metal interaction of the metal clusters for the H2 dissociated adsorption.

  19. Internal photoemission in Ag-Al2O3-Al junctions

    NASA Technical Reports Server (NTRS)

    Guedes, J. M. P.; Slayman, C. W.; Gustafson, T. K.; Jain, R. K.

    1979-01-01

    The magnitude of the photon-induced current in Ag-Al2O3-Al metal-oxide-metal junctions has been studied as a function of photon energy and angle of incident radiation. Photocurrents were theoretically analyzed on the basis of a modified vacuum photoemission model (Jain, 1975; Slayman et al., to be published). Optical constants previously reported in the literature (Irani et al., 1971; Ehnrereich et al., 1963) were used to calculate the true spatial generation rate in Ag and Al as a function of the angle, polarization of incident radiation, and film thickness. Results were found to be in very good agreement with experimentally determined values for a tunable dye laser with a KDP doubling crystal pumped by a Q-switched Nd:YAG laser with a LiIO3 doubling crystal. The system provided risetimes of 50 ns or less and peak powers of 10 W. Under short circuit conditions, the photoresponse to incident power was linear up to available power densities of 10 kW/sq cm. Quantum efficiencies of about 0.1% at zero-bias, near 3.8 eV under P polarization, were typically observed.

  20. Image reconstruction algorithm for optically stimulated luminescence 2D dosimetry using laser-scanned Al2O3:C and Al2O3:C,Mg films

    NASA Astrophysics Data System (ADS)

    Ahmed, M. F.; Schnell, E.; Ahmad, S.; Yukihara, E. G.

    2016-10-01

    The objective of this work was to develop an image reconstruction algorithm for 2D dosimetry using Al2O3:C and Al2O3:C,Mg optically stimulated luminescence (OSL) films imaged using a laser scanning system. The algorithm takes into account parameters associated with detector properties and the readout system. Pieces of Al2O3:C films (~8 mm  ×  8 mm  ×  125 µm) were irradiated and used to simulate dose distributions with extreme dose gradients (zero and non-zero dose regions). The OSLD film pieces were scanned using a custom-built laser-scanning OSL reader and the data obtained were used to develop and demonstrate a dose reconstruction algorithm. The algorithm includes corrections for: (a) galvo hysteresis, (b) photomultiplier tube (PMT) linearity, (c) phosphorescence, (d) ‘pixel bleeding’ caused by the 35 ms luminescence lifetime of F-centers in Al2O3, (e) geometrical distortion inherent to Galvo scanning system, and (f) position dependence of the light collection efficiency. The algorithm was also applied to 6.0 cm  ×  6.0 cm  ×  125 μm or 10.0 cm  ×  10.0 cm  ×  125 µm Al2O3:C and Al2O3:C,Mg films exposed to megavoltage x-rays (6 MV) and 12C beams (430 MeV u-1). The results obtained using pieces of irradiated films show the ability of the image reconstruction algorithm to correct for pixel bleeding even in the presence of extremely sharp dose gradients. Corrections for geometric distortion and position dependence of light collection efficiency were shown to minimize characteristic limitations of this system design. We also exemplify the application of the algorithm to more clinically relevant 6 MV x-ray beam and a 12C pencil beam, demonstrating the potential for small field dosimetry. The image reconstruction algorithm described here provides the foundation for laser-scanned OSL applied to 2D dosimetry.

  1. Image reconstruction algorithm for optically stimulated luminescence 2D dosimetry using laser-scanned Al2O3:C and Al2O3:C,Mg films.

    PubMed

    Ahmed, M F; Schnell, E; Ahmad, S; Yukihara, E G

    2016-10-21

    The objective of this work was to develop an image reconstruction algorithm for 2D dosimetry using Al2O3:C and Al2O3:C,Mg optically stimulated luminescence (OSL) films imaged using a laser scanning system. The algorithm takes into account parameters associated with detector properties and the readout system. Pieces of Al2O3:C films (~8 mm  ×  8 mm  ×  125 µm) were irradiated and used to simulate dose distributions with extreme dose gradients (zero and non-zero dose regions). The OSLD film pieces were scanned using a custom-built laser-scanning OSL reader and the data obtained were used to develop and demonstrate a dose reconstruction algorithm. The algorithm includes corrections for: (a) galvo hysteresis, (b) photomultiplier tube (PMT) linearity, (c) phosphorescence, (d) 'pixel bleeding' caused by the 35 ms luminescence lifetime of F-centers in Al2O3, (e) geometrical distortion inherent to Galvo scanning system, and (f) position dependence of the light collection efficiency. The algorithm was also applied to 6.0 cm  ×  6.0 cm  ×  125 μm or 10.0 cm  ×  10.0 cm  ×  125 µm Al2O3:C and Al2O3:C,Mg films exposed to megavoltage x-rays (6 MV) and (12)C beams (430 MeV u(-1)). The results obtained using pieces of irradiated films show the ability of the image reconstruction algorithm to correct for pixel bleeding even in the presence of extremely sharp dose gradients. Corrections for geometric distortion and position dependence of light collection efficiency were shown to minimize characteristic limitations of this system design. We also exemplify the application of the algorithm to more clinically relevant 6 MV x-ray beam and a (12)C pencil beam, demonstrating the potential for small field dosimetry. The image reconstruction algorithm described here provides the foundation for laser-scanned OSL applied to 2D dosimetry.

  2. Nanocomposite YCrO3/Al2O3: characterization of the core-shell, magnetic properties, and enhancement of dielectric properties.

    PubMed

    Durán, A; Tiznado, H; Romo-Herrera, J M; Domínguez, D; Escudero, R; Siqueiros, J M

    2014-05-19

    Multifuncionality in polycrystalline multiferroic ceramics can be improved using an advanced synthesis process. In this work, core-shell design is being proposed to enhance the transport properties of biferroic YCrO3. The atomic layer deposition (ALD) thin-film growth technique was used for the YCrO3/Al2O3 (Y@Al) nanocomposite fabrication. A continuous, amorphous, and uniform Al2O3 shell, a few nanometers thick, was obtained and characterized by X-ray photoelectron spectroscopy, X-ray diffraction, and high-resolution transmission electron microscopy. The transport properties of biferroic YCrO3 coated with 50, 500, and 1000 ALD cycles of insulating Al2O3 were investigated using magnetization and AC conductivity measurements. It is observed that the values of the magnetic coercive field and the magnetization are affected by the amorphous and partially crystallized Al2O3 shell. Additionally, the Y@Al nanocomposite experiments show a notorious decreasing in the loss tangent and the electrical conductivity. Accordingly, hysteresis loops in the polarization versus electric energy data confirm the decrease of the leakage current as a consequence of the Al2O3 shell acting as a barrier layer. The results shown here confirm that the core-shell architecture is a promising alternative for improvement of the magnetic and ferroelectric properties in bulk multiferroics.

  3. The chemisorption of H2O, HCOOH and CH3COOH on thin amorphous films of Al2O3

    NASA Technical Reports Server (NTRS)

    Lewis, B. F.; Weinberg, W. H.; Mosesman, M.

    1974-01-01

    Investigation of the irreversible chemisorption of water, formic acid and acetic acid on a thin amorphous aluminum oxide film, using inelastic tunneling spectroscopy. All of the tunnel junctions employed were Al-Al2O3-Pb junctions with the adsorbate on the Al2O3 surface between the Al2O3 and the Pb electrode. The results obtained include the finding that all Al2O3 surfaces prepared by oxidation of Al have free CH groups present on them.

  4. Effect of annealing temperature on the structural reorganization of Eu3+ optical centers in Al2O3-Eu2O3-BiOF gel films

    NASA Astrophysics Data System (ADS)

    Malashkevich, G. E.; Kornienko, A. A.; Dunina, E. B.; Prusova, I. V.; Shevchenko, G. P.; Bokshits, Yu. V.

    2007-06-01

    The dependence of the structural reorganization of Eu3+ optical centers in Al2O3-Eu2O3-BiOF films on the annealing temperature has been investigated. It is shown by the methods of crystal field theory and computer simulation that the increase in the annealing temperature from 700 to 1100 °C leads to removal of bismuth from Eu-O-Bi complex centers with the C 3V symmetry in the Al2O3 structure and the change in symmetry from D 3 to O h for a large fraction of EuAlO3 centers.

  5. Synthesis of methanol and dimethyl ether from syngas over Pd/ZnO/Al2O3 catalysts

    SciTech Connect

    Lebarbier, Vanessa M.; Dagle, Robert A.; Kovarik, Libor; Lizarazo-Adarme, Jair A.; King, David L.; Palo, Daniel R.

    2012-01-01

    A Pd/ZnO/Al2O3 catalyst was developed for the synthesis of methanol and dimethyl ether (DME) from syngas. Studied were temperatures of operation ranging from 250°C to 380°C. High temperatures (e.g. 380°C) are necessary when combining methanol and DME synthesis with a methanol to gasoline (MTG) process in a single reactor bed. A commercial Cu/ZnO/Al2O3 catalyst, utilized industrially for the synthesis of methanol at 220-280°C, suffers from a rapid deactivation when the reaction is conducted at high temperature (>320°C). On the contrary, a Pd/ZnO/Al2O3 catalyst was found to be highly stable for methanol and DME synthesis at 380°C. The Pd/ZnO/Al2O3 catalyst was thus further investigated for methanol and DME synthesis at P=34-69 bars, T= 250-380°C, GHSV= 5 000-18 000 h-1, and molar feeds H2/CO= 1, 2, and 3. Selectivity to DME increased with decreasing operating temperature, and increasing operating pressure. Increased GHSV’s and H2/CO syngas feed ratios also enhanced DME selectivity. Undesirable CH4 formation was observed, however, can be minimized through choice of process conditions and by catalyst design. By studying the effect of the Pd loading and the Pd:Zn molar ratio the formulation of the Pd/ZnO/Al2O3 catalyst was optimized. A catalyst with 5% Pd and a Pd:Zn molar ratio of 0.25:1 has been identified as the preferred catalyst. Results indicate that PdZn particles are more active than Pdº particles for the synthesis of methanol and less active for CH4 formation. A correlation between DME selectivity and the concentration of acid sites of the catalysts has been established. Hence, two types of sites are required for the direct conversion of syngas to DME: 1) PdZn particles are active for the synthesis of methanol from syngas, and 2) acid sites which are active for the conversion of methanol to DME. Additionally, CO2 formation was problematic as PdZn was found to be active for the water-gas-shift (WGS) reaction, under all the conditions evaluated.

  6. The process of growing Cr2O3 thin films on α-Al2O3 substrates at low temperature by r.f. magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Gao, Yin; Leiste, Harald; Stueber, Michael; Ulrich, Sven

    2017-01-01

    Cr2O3 thin films with a thickness of 180 nm are grown on c-plane α-Al2O3 (0001) single crystal substrates at a substrate temperature of 320 °C by non-reactive radio frequency magnetron sputtering. Phase formation and composition are characterized by X-ray diffraction (XRD) and Raman spectroscopy analysis. Additional information such as in-plane and out-of-plane lattice parameters, strain relaxation and texture are obtained by reciprocal space mappings (RSMs) and pole figure measurements. Transmission electron microscopy (TEM) has been carried out in order to study the microstructure and further confirm the orientation and epitaxial relationship between films and substrates.

  7. Theoretical study of the coordination of the Cr3+ ion in α-Al2O3

    NASA Astrophysics Data System (ADS)

    Franco, R.; Recio, J. M.; Pendas, A. Martín; Francisco, E.; Luaña, V.; Pueyo, L.

    1995-12-01

    The local arrangement of a substitutional Cr3+ ion for an Al3+ ion in corundum is studied by means of first-principles pairwise simulations and quantum-mechanical ab initio Perturbed Ion calculations. Our investigation is organized in two steps. First, we determine the cohesive properties of the host lattice by calculating the set of four crystalline parameters that makes minimum the total energy of corundum. Secondly, we solve cluster models of increasing complexity centered at the Cr3+ site and embedded in the previously computed crystal potential. This is a consistent strategy that contributes to determine the local geometry of Cr3+ in α-Al2O3.

  8. A first-principles study of Hg adsorption on Pd(1 1 1) and Pd/γ-Al2O3(1 1 0) surfaces

    NASA Astrophysics Data System (ADS)

    Geng, Lu; Han, Lina; Cen, Wanglai; Wang, Jiancheng; Chang, Liping; Kong, Dejin; Feng, Gang

    2014-12-01

    Spin-polarized density functional theory calculations were carried out to investigate the adsorption of Hgn (n = 1-3) on the perfect, step and vacancy-defective Pd(1 1 1) surfaces as well as the Pd/γ-Al2O3(1 1 0) surface. It is found that Hg atoms prefer to adsorb on the hollow sites on Pd(1 1 1) surfaces. The adsorption of Hg on the step and vacancy-defective Pd(1 1 1) surfaces is stronger than on the perfect Pd(1 1 1) surface, which indicates that the existence of vacancy and step defects can enhance the mercury adsorption activity of Pd adsorbents. As indicated by the calculated adsorption energies, the mercury adsorption on γ-Al2O3 is weak. The γ-Al2O3 supported single Pd atom shows as good Hg adsorption activity as the perfect Pd(1 1 1) surface at low Hg coverage, while more coordination unsaturated active Pd atoms is needed to achieve high Hg adsorption capacity. In addition, it was also found that the Hg adsorption on Pd/γ-Al2O3 weakens the binding of Pd to the γ-Al2O3 surface.

  9. Design of Al2O3/SiO2 laminated stacks with multiple interface dipole layers to achieve large flatband voltage shifts of MOS capacitors

    NASA Astrophysics Data System (ADS)

    Kamata, Hironobu; Kita, Koji

    2017-03-01

    We studied the dipole induced flatband voltage (VFB) shifts of Si MOS capacitors with Al2O3/SiO2/Al2O3/SiO2/Si laminated stacks ((Al2O3/SiO2)n/Si, n = 2) designed for a large positive shift of VFB. The VFB shift caused by each dipole layer was determined from capacitance-voltage characteristics by excluding the effect of fixed charges. Due to the additivity of multiple dipole layers in the laminated stack, a large VFB shift (>1 V) was observed. In our experimental condition, the dipole layers at Al2O3-on-SiO2 interfaces were selectively formed, while those at SiO2-on-Al2O3 interfaces were effectively suppressed. The validity of such additivity of VFB shifts induced by selectively formed dipole layers was also experimentally demonstrated for n ≥ 3 laminated stacks. An introduction of multiple dipole layers is applicable for a threshold voltage tuning in a wider range than the tuning with a single dipole layer.

  10. A study on Si / Al 2 O 3 paramagnetic point defects

    NASA Astrophysics Data System (ADS)

    Kühnhold-Pospischil, S.; Saint-Cast, P.; Hofmann, M.; Weber, S.; Jakes, P.; Eichel, R.-A.; Granwehr, J.

    2016-11-01

    In this contribution, negative charges and electronic traps related to the Si / Al 2 O 3 interface were measured and related to paramagnetic point defects and molecular vibrations. To this end, contactless capacitance voltage measurements, X-band electron paramagnetic resonance (EPR), and infrared spectroscopy were carried out, and their results were compared. A change in the negative charge density and electron trap density at the Si / Al 2 O 3 interface was achieved by adding a thermally grown SiO 2 layer with varying thicknesses and conducting an additional temperature treatment. Using EPR, five paramagnetic moments were detected in Si / ( SiO 2 ) / Al 2 O 3 samples with g values of g 1 = 2.0081 ± 0.0002 , g 2 = 2.0054 ± 0.0002 , g 3 = 2.0003 ± 0.0002 , g 4 = 2.0026 ± 0.0002 , and g 5 = 2.0029 ± 0.0002 . Variation of the Al 2 O 3 layer thickness shows that paramagnetic species associated with g1, g2, and g3 are located at the Si / Al 2 O 3 interface, and those with g4 and g5 are located within the bulk Al 2 O 3 . Furthermore, g1, g2, and g3 were shown to originate from oxygen plasma exposure during Al 2 O 3 deposition. Comparing the g values and their location within the Si / Al 2 O 3 system, g1 and g3 can be attributed to P b 0 centers, g3 to Si dangling bonds (Si-dbs), and g4 and g5 to rotating methyl radicals. All paramagnetic moments observed in this contribution disappear after a 5-min temperature treatment at 450 ° C . The deposition of an additional thermal SiO 2 layer between the Si and the Al 2 O 3 decreases the negative fixed charge density and defect density by about one order of magnitude. In this contribution, these changes can be correlated with a decrease in amplitude of the Si-db signal. P b 0 and the methyl radical signals were less affected by this additional SiO 2 layer. Based on these observations, microscopic models for the negative fixed charge density ( Q tot ) and the interface trap density ( D it ) and the connection between these

  11. The impact of ultrathin Al2O3 films on the electrical response of p-Ge/Al2O3/HfO2/Au MOS structures

    NASA Astrophysics Data System (ADS)

    Botzakaki, M. A.; Skoulatakis, G.; Kennou, S.; Ladas, S.; Tsamis, C.; Georga, S. N.; Krontiras, C. A.

    2016-09-01

    It is well known that the most critical issue in Ge CMOS technology is the successful growth of high-k gate dielectrics on Ge substrates. The high interface quality of Ge/high-k dielectric is connected with advanced electrical responses of Ge based MOS devices. Following this trend, atomic layer deposition deposited ultrathin Al2O3 and HfO2 films were grown on p-Ge. Al2O3 acts as a passivation layer between p-Ge and high-k HfO2 films. An extensive set of p-Ge/Al2O3/HfO2 structures were fabricated with Al2O3 thickness ranging from 0.5 nm to 1.5 nm and HfO2 thickness varying from 2.0 nm to 3.0 nm. All structures were characterized by x-ray photoelectron spectroscopy (XPS) and AFM. XPS analysis revealed the stoichiometric growth of both films in the absence of Ge sub-oxides between p-Ge and Al2O3 films. AFM analysis revealed the growth of smooth and cohesive films, which exhibited minimal roughness (~0.2 nm) comparable to that of clean bare p-Ge surfaces. The electrical response of all structures was analyzed by C-V, G-V, C-f, G-f and J-V characteristics, from 80 K to 300 K. It is found that the incorporation of ultrathin Al2O3 passivation layers between p-Ge and HfO2 films leads to superior electrical responses of the structures. All structures exhibit well defined C-V curves with parasitic effects, gradually diminishing and becoming absent below 170 K. D it values were calculated at each temperature, using both Hill-Coleman and Conductance methods. Structures of p-Ge/0.5 nm Al2O3/2.0 nm HfO2/Au, with an equivalent oxide thickness (EOT) equal to 1.3 nm, exhibit D it values as low as ~7.4  ×  1010 eV-1 cm-2. To our knowledge, these values are among the lowest reported. J-V measurements reveal leakage currents in the order of 10-1 A cm-2, which are comparable to previously published results for structures with the same EOT. A complete mapping of the energy distribution of D its into the energy bandgap of p-Ge, from the valence band

  12. Mechanical and morphological properties of polypropylene/nano α-Al2O3 composites.

    PubMed

    Mirjalili, F; Chuah, L; Salahi, E

    2014-01-01

    A nanocomposite containing polypropylene (PP) and nano α-Al2O3 particles was prepared using a Haake internal mixer. Mechanical tests, such as tensile and flexural tests, showed that mechanical properties of the composite were enhanced by addition of nano α-Al2O3 particles and dispersant agent to the polymer. Tensile strength was approximately ∼ 16% higher than pure PP by increasing the nano α-Al2O3 loading from 1 to 4 wt% into the PP matrix. The results of flexural analysis indicated that the maximum values of flexural strength and flexural modulus for nanocomposite without dispersant were 50.5 and 1954 MPa and for nanocomposite with dispersant were 55.88 MPa and 2818 MPa, respectively. However, higher concentration of nano α-Al2O3 loading resulted in reduction of those mechanical properties that could be due to agglomeration of nano α-Al2O3 particles. Transmission and scanning electron microscopic observations of the nanocomposites also showed that fracture surface became rougher by increasing the content of filler loading from 1 to 4% wt.

  13. Photochemistry of the α-Al2O3-PETN interface

    DOE PAGES

    Tsyshevsky, Roman V.; Zverev, Anton; Mitrofanov, Anatoly; ...

    2016-02-29

    Optical absorption measurements are combined with electronic structure calculations to explore photochemistry of an α-Al2O3-PETN interface formed by a nitroester (pentaerythritol tetranitrate, PETN, C5H8N4O12) and a wide band gap aluminum oxide (α-Al2O3) substrate. The first principles modeling is used to deconstruct and interpret the α-Al2O3-PETN absorption spectrum that has distinct peaks attributed to surface F0-centers and surfacePETN transitions. We predict the low energy α-Al2O3 F0-centerPETN transition, producing the excited triplet state, and α-Al2O3 F-0-centerPETN charge transfer, generating the PETN anion radical. This implies that irradiation by commonly used lasers can easily initiate photodecomposition of both excited and charged PETN atmore » the interface. As a result, the feasible mechanism of the photodecomposition is proposed.« less

  14. Interface of atomic layer deposited Al2O3 on H-terminated silicon

    NASA Astrophysics Data System (ADS)

    Gao, K. Y.; Speck, F.; Emtsev, K.; Seyller, Th.; Ley, L.; Oswald, M.; Hansch, W.

    2006-07-01

    Al2O3 films 1 to 20 nm thick were deposited as alternative high- gate dielectric on hydrogen-terminated silicon by Atomic Layer Deposition (ALD) and characterized by Synchrotron X-ray Photoelectron Spec-troscopy (SXPS), Fourier Transform Infrared (FTIR) absorption spectroscopy and admittance measure-ments. The SXPS results indicate that about 60% of the original Si-H surface bonds are preserved at the Al2O3/Si interface and this is confirmed by monitoring the Si-H stretching modes by FTIR spectroscopy in the Attenuated Total Reflection (ATR) mode both before and after ALD of Al2O3. The remaining 40% of Si-H bonds are replaced by Si-O bonds as verified by SXPS. In addition, a fraction of a monolayer of SiO2 forms on top of the Al2O3 dielectric during deposition. The presence of OH-groups at a level of 3% of the total oxygen content was detected throughout the Al2O3 layer through a chemically shifted O 1s component in SXPS. Admittance measurements give a dielectric constant of 9.12, but a relatively high density of interface traps between 1011 and 1012 cm-2 eV-1.

  15. Mechanical and Morphological Properties of Polypropylene/Nano α-Al2O3 Composites

    PubMed Central

    Mirjalili, F.; Chuah, L.; Salahi, E.

    2014-01-01

    A nanocomposite containing polypropylene (PP) and nano α-Al2O3 particles was prepared using a Haake internal mixer. Mechanical tests, such as tensile and flexural tests, showed that mechanical properties of the composite were enhanced by addition of nano α-Al2O3 particles and dispersant agent to the polymer. Tensile strength was approximately ∼16% higher than pure PP by increasing the nano α-Al2O3 loading from 1 to 4 wt% into the PP matrix. The results of flexural analysis indicated that the maximum values of flexural strength and flexural modulus for nanocomposite without dispersant were 50.5 and 1954 MPa and for nanocomposite with dispersant were 55.88 MPa and 2818 MPa, respectively. However, higher concentration of nano α-Al2O3 loading resulted in reduction of those mechanical properties that could be due to agglomeration of nano α-Al2O3 particles. Transmission and scanning electron microscopic observations of the nanocomposites also showed that fracture surface became rougher by increasing the content of filler loading from 1 to 4% wt. PMID:24688421

  16. Wet foams hydrophobized by amphiphiles to give Al2O3 porous ceramics

    NASA Astrophysics Data System (ADS)

    Pokhrel, Ashish; Park, Jung Gyu; Kim, Ik Jin

    2012-05-01

    Wet chemical method to prepare ceramic foams with antecedent stability using inorganic particles (Al2O3,SiO2 etc.) which are in situ hydrophobized upon adsorption of short-chain amphiphilic molecules in the wet state and heightened mechanical property in the sintered state was developed. These wet foams are stable over several days and show no bubble coarsening nor drainage or creaming. This long-term stability is achieved through the irreversible adsorption of partially hydrophobized colloidal particles to the air-water interface using short-chain amphiphiles to in situ modify the wetting behavior of the particle surface based on the observations of Pickering emulsions. As a result, the suspension is foamed homogeneously throughout its entire volume and porous bulk materials can be produced upon drying and sintering. Wet foams featuring average bubble sizes between 30 and 300μm and sintered foams with porosity from 50 to 85% were obtained by adjusting the amphiphile - particle concentration, and additives in the initial suspension. Cells were mostly closed with an average size of approximately 150 μm. Single cells were separated by walls with minimum thicknesses of 1-3 μm.

  17. Mixed Matrix Carbon Molecular Sieve and Alumina (CMS-Al2O3) Membranes

    PubMed Central

    Song, Yingjun; Wang, David K.; Birkett, Greg; Martens, Wayde; Duke, Mikel C.; Smart, Simon; Diniz da Costa, João C.

    2016-01-01

    This work shows mixed matrix inorganic membranes prepared by the vacuum-assisted impregnation method, where phenolic resin precursors filled the pore of α-alumina substrates. Upon carbonisation, the phenolic resin decomposed into several fragments derived from the backbone of the resin matrix. The final stages of decomposition (>650 °C) led to a formation of carbon molecular sieve (CMS) structures, reaching the lowest average pore sizes of ~5 Å at carbonisation temperatures of 700 °C. The combination of vacuum-assisted impregnation and carbonisation led to the formation of mixed matrix of CMS and α-alumina particles (CMS-Al2O3) in a single membrane. These membranes were tested for pervaporative desalination and gave very high water fluxes of up to 25 kg m−2 h−1 for seawater (NaCl 3.5 wt%) at 75 °C. Salt rejection was also very high varying between 93–99% depending on temperature and feed salt concentration. Interestingly, the water fluxes remained almost constant and were not affected as feed salt concentration increased from 0.3, 1 and 3.5 wt%. PMID:27469389

  18. Supermagnetism in discontinuous CoFe/Al2O3 multilayers

    NASA Astrophysics Data System (ADS)

    Bedanta, Subhankar; Kleemann, Wolfgang

    2012-06-01

    An ensemble of nanoparticles in which the interparticle magnetic interactions are sufficiently weak shows superparamagnetic (SPM) behavior as described by the Néel-Brown model. On the contrary, when inter-particle interactions are non-negligible, the system eventually shows collective behavior, which overcomes the individual anisotropy properties of the particles. At sufficiently strong interactions a magnetic nanoparticle ensemble can show superspin glass (SSG) properties similar to those of atomic spin glass systems in bulk. With further increase in concentration, but still below physical percolation, sufficiently strong interactions can be experienced to form a superferromagnetic (SFM) state. SFM domains in a non-percolated nanoparticle assembly are expected to be similar to conventional FM domains in a continuous film, with the decisive difference that the atomic spins are replaced by the superspins of the single-domain nanoparticles. In this article, we show that by varying the nominal thickness tn of the magnetic component in granular multilayers [Co80Fe20(tn)/Al2O3(3nm)]10 different types of "supermagnetism", such as superparamagnetism, superspin glass and superferromagnetism can be observed.

  19. Mixed Matrix Carbon Molecular Sieve and Alumina (CMS-Al2O3) Membranes.

    PubMed

    Song, Yingjun; Wang, David K; Birkett, Greg; Martens, Wayde; Duke, Mikel C; Smart, Simon; Diniz da Costa, João C

    2016-07-29

    This work shows mixed matrix inorganic membranes prepared by the vacuum-assisted impregnation method, where phenolic resin precursors filled the pore of α-alumina substrates. Upon carbonisation, the phenolic resin decomposed into several fragments derived from the backbone of the resin matrix. The final stages of decomposition (>650 °C) led to a formation of carbon molecular sieve (CMS) structures, reaching the lowest average pore sizes of ~5 Å at carbonisation temperatures of 700 °C. The combination of vacuum-assisted impregnation and carbonisation led to the formation of mixed matrix of CMS and α-alumina particles (CMS-Al2O3) in a single membrane. These membranes were tested for pervaporative desalination and gave very high water fluxes of up to 25 kg m(-2) h(-1) for seawater (NaCl 3.5 wt%) at 75 °C. Salt rejection was also very high varying between 93-99% depending on temperature and feed salt concentration. Interestingly, the water fluxes remained almost constant and were not affected as feed salt concentration increased from 0.3, 1 and 3.5 wt%.

  20. Mixed Matrix Carbon Molecular Sieve and Alumina (CMS-Al2O3) Membranes

    NASA Astrophysics Data System (ADS)

    Song, Yingjun; Wang, David K.; Birkett, Greg; Martens, Wayde; Duke, Mikel C.; Smart, Simon; Diniz da Costa, João C.

    2016-07-01

    This work shows mixed matrix inorganic membranes prepared by the vacuum-assisted impregnation method, where phenolic resin precursors filled the pore of α-alumina substrates. Upon carbonisation, the phenolic resin decomposed into several fragments derived from the backbone of the resin matrix. The final stages of decomposition (>650 °C) led to a formation of carbon molecular sieve (CMS) structures, reaching the lowest average pore sizes of ~5 Å at carbonisation temperatures of 700 °C. The combination of vacuum-assisted impregnation and carbonisation led to the formation of mixed matrix of CMS and α-alumina particles (CMS-Al2O3) in a single membrane. These membranes were tested for pervaporative desalination and gave very high water fluxes of up to 25 kg m‑2 h‑1 for seawater (NaCl 3.5 wt%) at 75 °C. Salt rejection was also very high varying between 93–99% depending on temperature and feed salt concentration. Interestingly, the water fluxes remained almost constant and were not affected as feed salt concentration increased from 0.3, 1 and 3.5 wt%.

  1. Glycerol Steam Reforming Over Ni-Fe-Ce/Al2O3 Catalyst: Effect of Cerium.

    PubMed

    Go, Gwang-Sub; Go, Yoo-Jin; Lee, Hong-Joo; Moon, Dong-Ju; Park, Nam-Cook; Kim, Young-Chul

    2016-02-01

    In this work, hydrogen production from glycerol by steam reforming was studied using Ni-metal oxide catalysts. Ni-based catalyst becomes deactivated during steam reforming reactions because of coke deposits and sintering. Therefore, the aim of this study was to reduce carbon deposits and sintering on the catalyst surface by adding a promoter. Ni-metal oxide catalysts supported on Al2O3 were prepared via impregnation method, and the calcined catalyst was reduced under H2 flow for 2 h prior to the reaction. The characteristics of the catalysts were examined by XRD, TPR, TGA, and SEM. The Ni-Fe-Ce/Al2O3 catalyst, which contained less than 2 wt% Ce, showed the highest hydrogen selectivity and glycerol conversion. Further analysis of the catalysts revealed that the Ni-Fe-Ce/Al2O3 catalyst required a lower reduction temperature and produced minimum carbon deposit.

  2. Anchorage of γ-Al2O3 nanoparticles on nitrogen-doped multiwalled carbon nanotubes

    DOE PAGES

    Rodríguez-Pulido, A.; Martínez-Gutiérrez, H.; Calderon-Polania, G. A.; ...

    2016-06-07

    Nitrogen-doped multiwalled carbon nanotubes (CNx-MWNTs) have been decorated with γ-Al2O3 nanoparticles by a novel method. This process involved a wet chemical approach in conjunction with thermal treatment. During the particle anchoring process, individual CNx-MWNT nanotubes agglomerated into bundles, resulting in arrays of aligned CNx-MWNT coated with γ-Al2O3. Extensive characterization of the resulting γ-Al2O3/CNx-MWNT bundles was performed using a range of electron microscopy imaging and microanalytical techniques. In conclusion, a possible mechanism explaining the nanobundle alignment is described, and possible applications of these materials for the fabrication of ceramic composites using CNx-MWNTs are briefly discussed.

  3. Electrical Double Layer Capacitance in a Graphene-embedded Al2O3 Gate Dielectric

    PubMed Central

    Ki Min, Bok; Kim, Seong K.; Jun Kim, Seong; Ho Kim, Sung; Kang, Min-A; Park, Chong-Yun; Song, Wooseok; Myung, Sung; Lim, Jongsun; An, Ki-Seok

    2015-01-01

    Graphene heterostructures are of considerable interest as a new class of electronic devices with exceptional performance in a broad range of applications has been realized. Here, we propose a graphene-embedded Al2O3 gate dielectric with a relatively high dielectric constant of 15.5, which is about 2 times that of Al2O3, having a low leakage current with insertion of tri-layer graphene. In this system, the enhanced capacitance of the hybrid structure can be understood by the formation of a space charge layer at the graphene/Al2O3 interface. The electrical properties of the interface can be further explained by the electrical double layer (EDL) model dominated by the diffuse layer. PMID:26530817

  4. Electrowetting properties of atomic layer deposited Al2O3 decorated silicon nanowires

    NASA Astrophysics Data System (ADS)

    Rajkumar, K.; Rajavel, K.; Cameron, D. C.; Mangalaraj, D.; Rajendrakumar, R. T.

    2015-06-01

    This paper reports the electrowetting properties of liquid droplet on superhydrophobic silicon nanowires with Atomic layer deposited (ALD) Al2O3 as dielectric layer. Silicon wafer were etched by metal assisted wet chemical etching with silver as catalyst. ALD Al2O3 films of 10nm thickness were conformally deposited over silicon nanowires. Al2O3 dielectric film coated silicon nanowires was chemically modified with Trichloro (1H, 1H, 2H, 2H-perfluorooctyl) silane to make it superhydrophobic(SHP). The contact angle was measured and all the samples exhibited superhydrophobic nature with maximum contact angles of 163° and a minimum contact angle hysteresis of 6°. Electrowetting induced a maximum reversible decrease of the contact angle of 20°at 150V in air.

  5. Electrical Double Layer Capacitance in a Graphene-embedded Al2O3 Gate Dielectric.

    PubMed

    Ki Min, Bok; Kim, Seong K; Jun Kim, Seong; Ho Kim, Sung; Kang, Min-A; Park, Chong-Yun; Song, Wooseok; Myung, Sung; Lim, Jongsun; An, Ki-Seok

    2015-11-04

    Graphene heterostructures are of considerable interest as a new class of electronic devices with exceptional performance in a broad range of applications has been realized. Here, we propose a graphene-embedded Al2O3 gate dielectric with a relatively high dielectric constant of 15.5, which is about 2 times that of Al2O3, having a low leakage current with insertion of tri-layer graphene. In this system, the enhanced capacitance of the hybrid structure can be understood by the formation of a space charge layer at the graphene/Al2O3 interface. The electrical properties of the interface can be further explained by the electrical double layer (EDL) model dominated by the diffuse layer.

  6. Hard α-Al2O3 Film Coating on Industrial Roller Using Aerosol Deposition Method

    NASA Astrophysics Data System (ADS)

    Seto, Naoki; Endo, Kazuteru; Sakamoto, Nobuo; Hirose, Shingo; Akedo, Jun

    2014-12-01

    It is well known that α-Al2O3 forms very hard, highly insulating, smooth films. There is demand for the use of such films instead of conventional hard, smooth films; For example, industrial rollers such as calendering rollers etc. are always required to have a harder and smoother surface than conventional rollers. Therefore, this work investigated the specification of α-Al2O3 films, e.g., their wear resistance and chemical stability, using various tests. This paper also discusses whether α-Al2O3 film can take the place of Cr plating film as a hard, smooth film by comparing their wear resistance and chemical stability.

  7. Process Capability Analysis of Vacuum Moulding for Development of Al-Al2O3 MMC

    NASA Astrophysics Data System (ADS)

    Singh, R.

    2013-01-01

    The purpose of the present study is to investigate process capability of vacuum moulding (VM) for development of Al-Al2O3 metal matrix composite (MMC). Starting from the identification of component, prototypes were prepared (with three different input parameters namely: vacuum pressure; component volume and sand grit size to give output in form of dimensional accuracy). Measurements on the coordinate measuring machine helped in calculating the dimensional tolerances of the Al-Al2O3 MMC prepared. Some important mechanical properties were also compared to verify the suitability of the components. Final components produced are acceptable as per ISO standard UNI EN 20286-I (1995). The results of study suggest that VM process lies in ±4.5 sigma (σ) limit as regard to dimensional accuracy of Al-Al2O3 MMC is concerned. This process ensures rapid production of pre-series technological prototypes and proof of concept at less production cost and time.

  8. Ionic conductivity and thermoelectric power of pure and Al2O3-dispersed AgI

    NASA Technical Reports Server (NTRS)

    Shahi, K.; Wagner, J. B., Jr.

    1981-01-01

    Ionic and electronic conductivities, and thermoelectric power have been measured for AgI and AgI containing a dispersion of submicron size Al2O3 particles. While the dispersion of Al2O3 enhances the ionic conductivity significantly, it does not affect the electronic properties of the matrix. The enhancement is a strong function of the size and concentration of the dispersoid. Various models have been tested to account for the enhanced conduction. However, the complex behavior of the present results points out the need for more sophisticated theoretical models. Ionic conduction and thermoelectric power data suggest that the dispersed Al2O3 generates an excess of cation vacancies and thereby enhances the conductivity and suppresses the thermoelectric power of the matrix. The individual heats of transport of cation interstitials and vacancies have been estimated and compared to their respective migration energies.

  9. Solubility of corundum and quartz in the system Al2O3-SiO2-NaCl-H2O at deep-crustal metamorphic conditions: 800 ° C and 10 kbar

    NASA Astrophysics Data System (ADS)

    Newton, R. C.; Manning, C. E.

    2004-12-01

    The solubility of corundum in H2O-NaCl-SiO2 fluids has been measured at 800 ° C and 10 kbar. Solubility was determined by weight loss after equilibration of polished single crystals of synthetic corundum with fluids in welded Pt envelopes. Fluid compositions were XNaCl=0 to 0.5 and SiO2 up to quartz saturation at a given XNaCl. The experiments were 1 to 7 days duration in 1.91-cm-diameter piston-cylinder apparatus with NaCl pressure medium. Kyanite and sillimanite are slightly more stable than quartz + corundum at these P-T conditions, but did not appear. The solubility in initially pure H2O is very small: mAl2O3 (mol Al2O3/kg H2O) = 0.00135, but increases rapidly as the fourth root of XNaCl to 0.01 at XNaCl=0.1 and 0.015 at halite saturation (XNaCl\\sim0.6). Quenched solutions were pH neutral. The data were modeled with simple mixing models involving NaAl(OH)_{4}, Al(OH)_{3}, and any of their several dehydration and dissociation products, as well as Na^{+}, Cl^{-}, and H_{2}O. The best-fit reactions are: X_{NaCl}$<0.3: Al2O3(cr) + Na+ + H2O = NaAlO(OH)2 + AlO+ XNaCl>0.3: Al2O3(cr) + Na+ = NaAlO2 + AlO+ Silica in solution further amplifies NaCl-enhancement of corundum solubility. Al2O3 molality at metastable quartz saturation rises rapidly from 0.006 at XNaCl=0, to 0.038 at XNaCl=0.1, and then more gradually to 0.045 at XNaCl=0.3. Quenched solutions from SiO2- and NaCl-rich compositions are acid (pH ˜1). The dissolution reaction, assuming a neutral NaAlSi species, must therefore be similar to: Al2O3(cr) + 2Na+ + xSi(OH)4 = 2NaAl Six/2Ox/2+y(OH)x-2y+4) + (x+2y-5)H2O + 2H+. Simple-mixing modeling suggests that the average Si/Al ratio (x/2) and number of non-bridging O2- (y) of the dominant Al solute species at 0.03≤XNaCl≤0.6 and quartz saturation are given by the formula: NaAlSi2.75O6.38(OH)2.24, close to the NaAlSi3O8-H2O join. Small amounts of spherical globules of aluminosilicate glass appeared close to quartz saturation at XNaCl≥0.1 It was not proven in

  10. Impacts of Annealing Conditions on the Flat Band Voltage of Alternate La2O3/Al2O3 Multilayer Stack Structures

    NASA Astrophysics Data System (ADS)

    Feng, Xing-Yao; Liu, Hong-Xia; Wang, Xing; Zhao, Lu; Fei, Chen-Xi; Liu, He-Lei

    2016-09-01

    The mechanism of flat band voltage (VFB) shift for alternate La2O3/Al2O3 multilayer stack structures in different annealing condition is investigated. The samples were prepared for alternate multilayer structures, which were annealed in different conditions. The capacitance-voltage (C-V) measuring results indicate that the VFB of samples shift negatively for thinner bottom Al2O3 layer, increasing annealing temperature or longer annealing duration. Simultaneously, the diffusion of high- k material to interfaces in different multilayer structures and annealing conditions is observed by X-ray photoelectron spectroscopy (XPS). Based on the dipole theory, a correlation between the diffusion effect of La towards bottom Al2O3/Si interface and VFB shift is found. Without changing the dielectric constant k of films, VFB shift can be manipulated by controlling the single-layer cycles and annealing conditions of alternate high- k multilayer stack.

  11. Nb2O5-γ-Al2O3 nanofibers as heterogeneous catalysts for efficient conversion of glucose to 5-hydroxymethylfurfural

    PubMed Central

    Jiao, Huanfeng; Zhao, Xiaoliang; Lv, Chunxiao; Wang, Yijun; Yang, Dongjiang; Li, Zhenhuan; Yao, Xiangdong

    2016-01-01

    One-dimensional γ-Al2O3 nanofibers were modified with Nb2O5 to be used as an efficient heterogeneous catalyst to catalyze biomass into 5-hydroxymethylfurfural (5-HMF). At low Nb2O5 loading, the niobia species were well dispersed on γ-Al2O3 nanofiber through Nb–O–Al bridge bonds. The interaction between Nb2O5 precursor and γ-Al2O3 nanofiber results in the niobia species with strong Lewis acid sites and intensive Brønsted acid sites, which made 5-HMF yield from glucose to reach the maximum 55.9~59.0% over Nb2O5-γ-Al2O3 nanofiber with a loading of 0.5~1 wt% Nb2O5 at 150 °C for 4 h in dimethyl sulfoxide. However, increasing Nb2O5 loading could lead to the formation of two-dimensional polymerized niobia species, three-dimensional polymerized niobia species and crystallization, which significantly influenced the distribution and quantity of the Lewis acid sites and Brönst acid sites over Nb2O5-γ-Al2O3 nanofiber. Lewis acid site Nbδ+ played a key role on the isomerization of glucose to fructose, while Brønsted acid sites are more active for the dehydration of generated fructose to 5-HMF. In addition, the heterogeneous Nb2O5-γ-Al2O3 nanofiber catalyst with suitable ratio of Lewis acid to Brönsted sites should display an more excellent catalytic performance in the conversion of glucose to 5-HMF. PMID:27666867

  12. Nb2O5-γ-Al2O3 nanofibers as heterogeneous catalysts for efficient conversion of glucose to 5-hydroxymethylfurfural

    NASA Astrophysics Data System (ADS)

    Jiao, Huanfeng; Zhao, Xiaoliang; Lv, Chunxiao; Wang, Yijun; Yang, Dongjiang; Li, Zhenhuan; Yao, Xiangdong

    2016-09-01

    One-dimensional γ-Al2O3 nanofibers were modified with Nb2O5 to be used as an efficient heterogeneous catalyst to catalyze biomass into 5-hydroxymethylfurfural (5-HMF). At low Nb2O5 loading, the niobia species were well dispersed on γ-Al2O3 nanofiber through Nb–O–Al bridge bonds. The interaction between Nb2O5 precursor and γ-Al2O3 nanofiber results in the niobia species with strong Lewis acid sites and intensive Brønsted acid sites, which made 5-HMF yield from glucose to reach the maximum 55.9~59.0% over Nb2O5-γ-Al2O3 nanofiber with a loading of 0.5~1 wt% Nb2O5 at 150 °C for 4 h in dimethyl sulfoxide. However, increasing Nb2O5 loading could lead to the formation of two-dimensional polymerized niobia species, three-dimensional polymerized niobia species and crystallization, which significantly influenced the distribution and quantity of the Lewis acid sites and Brönst acid sites over Nb2O5-γ-Al2O3 nanofiber. Lewis acid site Nbδ+ played a key role on the isomerization of glucose to fructose, while Brønsted acid sites are more active for the dehydration of generated fructose to 5-HMF. In addition, the heterogeneous Nb2O5-γ-Al2O3 nanofiber catalyst with suitable ratio of Lewis acid to Brönsted sites should display an more excellent catalytic performance in the conversion of glucose to 5-HMF.

  13. Mechanism for converting Al2O3-containing borate glass to hydroxyapatite in aqueous phosphate solution.

    PubMed

    Zhao, Di; Huang, Wenhai; Rahaman, Mohamed N; Day, Delbert E; Wang, Deping

    2009-05-01

    The effect of replacing varying amounts (0-2.5 mol.%) of B2O3 with Al2O3 in a borate glass on (1) the conversion of the glass to HA in an aqueous phosphate solution and (2) the compressive strength of the as-formed HA product was investigated. Samples of each glass (10 x 10 x 8 mm) were placed in 0.25 M K2HPO4 solution at 60 degrees C, and the conversion kinetics to HA were determined from the weight loss of the glass and the pH of the solution. The structure and composition of the solid reaction products were characterized using X-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy. While the conversion rate of the glass to HA decreased considerably with increasing Al2O3 content, the microstructure of the HA product became denser and the compressive strength of the HA product increased. The addition of SiO2 to the Al2O3-containing borate glass reversed the deterioration of the conversion rate, and produced a further improvement in the strength of the HA product. The compressive strength of the HA formed from the borate glass with 2.5 mol.% Al2O3 and 5 mol.% SiO2 was 11.1 +/- 0.2 MPa, which is equal to the highest strengths reported for trabecular bone. The results indicated that simultaneous additions of Al2O3 and SiO2 could be used to control the bioactivity of the borate glass and to enhance the mechanical strength of the HA product. Furthermore, the HA product formed from the glass containing both SiO2 and Al2O3 could be applied to bone repair.

  14. Rapid fabrication of Al2O3 encapsulations for organic electronic devices

    NASA Astrophysics Data System (ADS)

    Ali, Kamran; Ali, Junaid; Mehdi, Syed Murtuza; Choi, Kyung-Hyun; An, Young Jin

    2015-10-01

    Organic electronics have earned great reputation in electronic industry yet they suffer technical challenges such as short lifetimes and low reliability because of their susceptibility to water vapor and oxygen which causes their fast degradation. This paper report on the rapid fabrication of Al2O3 encapsulations through a unique roll-to-roll atmospheric atomic layer deposition technology (R2R-AALD) for the life time enhancement of organic poly (4-vinylphenol) (PVP) memristor devices. The devices were then categorized into two sets. One was processed with R2R-AALD Al2O3 encapsulations at 50 °C and the other one was kept as un-encapsulated. The field-emission scanning electron microscopy (FESEM) results revealed that pin holes and other irregularities in PVP films with average arithmetic roughness (Ra) of 9.66 nm have been effectively covered by Al2O3 encapsulation having Ra of 0.92 nm. The X-ray photoelectron spectroscopy XPS spectrum for PVP film showed peaks of C 1s and O 1s at the binding energies of 285 eV and 531 eV, respectively. The respective appearance of Al 2p, Al 2s, and O 1s peaks at the binding energies of 74 eV, 119 eV, and 531 eV, confirms the fabrication of Al2O3 films. Electrical current-voltage (I-V) measurements confirmed that the Al2O3 encapsulation has a huge influence on the performance, robustness and life time of memristor devices. The Al2O3 encapsulated memristor performed with superior stability for four weeks whereas the un-encapsulated devices could only last for one week. The performance of encapsulated device had been promising after being subjected to bending test for 100 cycles and the variations in its stability were of minor concern confirming the mechanical robustness and flexibility of the devices.

  15. Effect of AL2O3 and TiO2 nanoparticles on aquatic organisms

    NASA Astrophysics Data System (ADS)

    Gosteva, I.; Morgalev, Yu; Morgaleva, T.; Morgalev, S.

    2015-11-01

    Environmental toxicity of aqueous disperse systems of nanoparticles of binary compounds of titanium dioxides (with particle size Δ50=5 nm, Δ50=50 nm, Δ50=90 nm), aluminum oxide alpha-forms (Δ50=7 nm and Δ50=70 nm) and macro forms (TiO2 Δ50=350 nm, Al2O3 A50=4000 nm) were studied using biological testing methods. The bioassay was performed using a set of test organisms representing the major trophic levels. We found the dependence of the toxic effect concentration degree of nTiO2 and nAl2O3 on the fluorescence of the bacterial biosensor "Ekolyum", the chemotactic response of ciliates Paramecium caudatum, the growth of unicellular algae Chlorella vulgaris Beijer and mortality of entomostracans Daphnia magna Straus. We revealed the selective dependence of nTiO2 and nAl2O3 toxicity on the size, concentration and chemical nature of nanoparticles. The minimal concentration causing an organism's response on nTiO2 and nAl2O3 effect depends on the type of the test- organism and the test reaction under study. We specified L(E)C50 and acute toxicity categories for all the studied nanoparticles. We determined that nTiO2 (Δ50=5 nm) belong to the category «Acute toxicity 1», nTiO2 (A50=90 nm) and nAl2O3 (Δ50=70 nm) - to the category «Acute toxicity 2», nAl2O3 (Δ50=7 nm) - to the category «Acute toxicity 3». No acute toxicity was registered for nTiO2 (Δ50=50 nm) and macro form TiO2.

  16. Study of LDPE/Al2O3 composite material as substrate for microstrip antenna

    NASA Astrophysics Data System (ADS)

    Sarmah, Debashis; Bhattacharyya, N. S.; Bhattacharyya, S.; Gogoi, J. P.

    2013-01-01

    Low density polyethylene (LDPE)/Alumina (Al2O3) composite systems have been studied as an alternate substrate for microstrip patch antennas (MPA). Morphological, thermal and microwave characterizations of the composites are carried out for different volume fractions of Al2O3 in the LDPE matrix. The size and the distribution of alumina particles are quite uniform in the composite. Enhancement of thermal and microwave properties of the composite over the parent polymer is observed. Simple rectangular MPA in X-band is fabricated on the composite material to verify its applicability as substrates for MPA. A return loss of ~ -26dB is observed at the design frequency.

  17. Study of the KNO3-Al2O3 system by differential scanning calorimetry

    NASA Astrophysics Data System (ADS)

    Amirov, A. M.; Gafurov, M. M.; Rabadanov, K. Sh.

    2016-09-01

    The structural and the thermodynamic properties of potassium nitrate KNO3 and its composites with nanosized aluminum oxide Al2O3 have been studied by differential scanning calorimetry. It has been found that an amorphous phase forms in composites (1- x)KNO3- x Al2O3. The thermal effect corresponding to this phase has been observed at 316°C. It has been found that the phase transition heats of potassium nitrate decreased as the aluminum oxide fraction increased.

  18. Epitaxial Graphene Surface Preparation for Atomic Layer Deposition of Al2O3

    DTIC Science & Technology

    2011-06-01

    j dielectrics such as Al2O3 , HfO2, Ta2O5, and TiO2 , are important for the realization of graphene-based top-gated electronic devices including field... ALD pulse sequencing of NO2-trimethylaluminum (TMA); 16 oxidation of electron beam evaporated metallic Al, Hf, Ti, Ta;17,18 and spin- coating of a... ALD of Al2O3 films in promoting uni- form, high quality oxide deposition. Initial treatments resulted in partial coverage, while the optimized treatment

  19. Surface passivation of gallium nitride by ultrathin RF-magnetron sputtered Al2O3 gate.

    PubMed

    Quah, Hock Jin; Cheong, Kuan Yew

    2013-08-14

    An ultrathin RF-magnetron sputtered Al2O3 gate on GaN subjected to postdeposition annealing at 800 °C in O2 ambient was systematically investigated. A cross-sectional energy-filtered transmission electron microscopy revealed formation of crystalline Al2O3 gate, which was supported by X-ray diffraction analysis. Various current conduction mechanisms contributing to leakage current of the investigated sample were discussed and correlated with metal-oxide-semiconductor characteristics of this sample.

  20. The Influence of Al2O3 Powder Morphology on the Properties of Cu-Al2O3 Composites Designed for Functionally Graded Materials (FGM)

    NASA Astrophysics Data System (ADS)

    Strojny-Nędza, Agata; Pietrzak, Katarzyna; Węglewski, Witold

    2016-08-01

    In order to meet the requirements of an increased efficiency applying to modern devices and in more general terms science and technology, it is necessary to develop new materials. Combining various types of materials (such as metals and ceramics) and developing composite materials seem to be suitable solutions. One of the most interesting materials includes Cu-Al2O3 composite and gradient materials (FGMs). Due to their potential properties, copper-alumina composites could be used in aerospace industry as rocket thrusters and components in aircraft engines. The main challenge posed by copper matrix composites reinforced by aluminum oxide particles is obtaining the uniform structure with no residual porosity (existing within the area of the ceramic phase). In the present paper, Cu-Al2O3 composites (also in a gradient form) with 1, 3, and 5 vol.% of aluminum oxide were fabricated by the hot pressing and spark plasma sintering methods. Two forms of aluminum oxide (αAl2O3 powder and electrocorundum) were used as a reinforcement. Microstructural investigations revealed that near fully dense materials with low porosity and a clear interface between the metal matrix and ceramics were obtained in the case of the SPS method. In this paper, the properties (mechanical, thermal, and tribological) of composite materials were also collected and compared. Technological tests were preceded by finite element method analyses of thermal stresses generated in the gradient structure, and additionally, the role of porosity in the formation process of composite properties was modeled. Based on the said modeling, technological conditions for obtaining FGMs were proposed.

  1. Atomic layer deposition of highly-doped Er:Al2O3 and Tm:Al2O3 for silicon-based waveguide amplifiers (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Roenn, John; Karvonen, Lasse; Pyymäki-Perros, Alexander; Peyghambarian, Nasser; Lipsanen, Harri; Säynätjoki, Antti; Sun, Zhipei

    2016-05-01

    Recently, rare-earth doped waveguide amplifiers (REDWAs) have drawn significant attention as a promising solution to on-chip amplification of light in silicon photonics and integrated optics by virtue of their high excited state lifetime (up to 10 ms) and broad emission spectrum (up to 200 nm) at infrared wavelengths. In the family of rare-earths, at least erbium, holmium, thulium, neodymium and ytterbium have been demonstrated to be good candidates for amplifier operation at moderate concentrations (< 0.1 %). However, efficient amplifier operation in REDWAs is a very challenging task because high concentration of ions (<0.1%) is required in order to produce reasonable amplification over short device length. Inevitably, high concentration of ions leads to energy-transfer between neighboring ions, which results as decreased gain and increased noise in the amplifier system. It has been shown that these energy-transfer mechanisms in highly-doped gain media are inversely proportional to the sixth power of the distance between the ions. Therefore, novel fabrication techniques with the ability to control the distribution of the rare-earth ions within the gain medium are urgently needed in order to fabricate REDWAs with high efficiency and low noise. Here, we show that atomic layer deposition (ALD) is an excellent technique to fabricate highly-doped (<1%) RE:Al2O3 gain materials by using its nanoscale engineering ability to delicately control the incorporation of RE ions during the deposition. In our experiment, we fabricated Er:Al2O3 and Tm:Al2O3 thin films with ALD by varying the concentration of RE ions from 1% to 7%. By measuring the photoluminescence response of the fabricated samples, we demonstrate that it is possible to incorporate up to 5% of either Er- or Tm-ions in Al2O3 host before severe quenching occurs. We believe that this technique can be extended to other RE ions as well. Therefore, our results show the exceptionality of ALD as a deposition technique for

  2. Optical spectroscopy of RE3 ions in sol-gel prepared α-Al2O3

    NASA Astrophysics Data System (ADS)

    Feofilov, S. P.; Kaplyanskii, A. A.; Kulinkin, A. B.; Kutsenko, A. B.; Vasilevskaya, T. N.; Zakharchenya, R. I.

    The monolithic polycrystalline small-grain corundum α-Al2O3 doped with trivalent rare earth ions RE3+ (Eu3+, Er3+, Pr3+) was produced for the first time using the sol-gel technology. The fluorescence and absorption spectra of these materials were studied which exhibit the sets of narrow lines belonging to f-f transitions between RE3+ states. It was shown that Eu3+ and Er3+ ions form in corundum lattice the single dominating type of regular centers. The energy scheme of Stark sublevels for ground and excited states of dominating Eu3+ and Er3+ centers in corundum was determined.

  3. Atomic layer deposition (ALD) of TiO2 and Al2O3 thin films on silicon

    NASA Astrophysics Data System (ADS)

    Mitchell, David R. G.; Triani, Gerry; Attard, Darren J.; Finnie, Kim S.; Evans, Peter J.; Barbe, Christophe J.; Bartlett, John R.

    2004-04-01

    The essential features of the ALD process involve sequentially saturating a surface with a (sub)monolayer of reactive species, such as a metal halide, then reacting it with a second species to form the required phase in-situ. Repetition of the reaction sequence allows the desired thickness to be deposited. The self-limiting nature of the reactions ensures excellent conformality, and sequential processing results in exquisite control over film thickness, albeit at rather slow deposition rates, typically <200nm/hr. We have been developing our capability with ALD deposition, to understand the influence of deposition parameters on the nature of TiO2 and Al2O3 films (high and low refractive index respectively), and multilayer stacks thereof. These stacks have potential applications as anti-reflection coatings and optical filters. This paper will explore the evolution of structure in our films as a function of deposition parameters including temperature and substrate surface chemistry. A broad range of techniques have been applied to the study of these films, including cross sectional transmission electron microscopy, spectroscopic ellipsometry, secondary ion mass spectrometry etc. These have enabled a wealth of microstructural and compositional information on the films to be acquired, such as accurate film thickness, composition, crystallization sequence and orientation with respect to the substrate. The ALD method is shown to produce single layer films and multilayer stacks with exceptional uniformity and flatness, and in the case of stacks, chemically abrupt interfaces. We are currently extending this technology to the coating of polymeric substrates.

  4. Modifying γ-Al2O3 surface with Y2Sn2O7 pyrochlore: on monolayer dispersion behaviour of composite oxides.

    PubMed

    Xu, Xianglan; Liu, Fang; Tian, Jinshu; Peng, Honggen; Liu, Wenming; Fang, Xiuzhong; Zhang, Ning; Wang, Xiang

    2017-03-21

    To investigate the dispersion behaviours of composite oxides onto the supports, and to achieve better supports for Pd for CO oxidation, a series of Y2Sn2O7/Al2O3 composite oxides with different Y2Sn2O7 loadings were prepared via deposition-precipitation method. Using XRD and XPS extrapolation methods, it is revealed that similar to single component metal oxides, composite oxides can also disperse spantaneously onto the support surfaces to form a monlayer with a certain capacity. The monolayer dispersion capacity/threshhold for Y2Sn2O7 on γ-Al2O3 surface is 0.109 mmol*100 m-2 γ-Al2O3, equalling to 7.2% Y2Sn2O7 weight loading. It is deserved to mention here that this is the first work to demonstrate the monolayer dispersion phenomenon of a composite oxide on a support. After the combination of Y2Sn2O7 with γ-Al2O3, active oxygen species can be introduced onto the catalyst surfaces. Therefore, the interaction between Pd and the supports can be strengthened, thus improving the Pd dispersion in comparison with the individual Y2Sn2O7 support and inducing synergistic effect between Pd and the composite supports, which is beneficial to the activity of the catalysts. By tuning the γ-Al2O3 surface with different amount of pyrochlore Y2Sn2O7 compound, the CO oxidation activity on the 1%Pd/Y2Sn2O7/Al2O3 has been improved. These findings may put new insights for people to design and prepare competitve supported noble metal catalysts with less amount of noble metals.

  5. Synthesis of MgO nanoparticle loaded mesoporous Al2O3 and its defluoridation study

    NASA Astrophysics Data System (ADS)

    Dayananda, Desagani; Sarva, Venkateswara R.; Prasad, Sivankutty V.; Arunachalam, Jayaraman; Parameswaran, Padmanabhan; Ghosh, Narendra N.

    2015-02-01

    MgO nanoparticle loaded mesoporous alumina has been synthesized using a simple aqueous solution based cost effective method for removal of fluoride from water. Wide angle powder X-ray diffraction, nitrogen adsorption desorption analysis, transmission electron microscopy techniques and energy dispersive X-ray spectroscopy were used to characterize the synthesized adsorbents. Synthesized adsorbents possess high surface area with mesoporous structure. The adsorbents have been thoroughly investigated for the adsorption of F- using batch adsorption method. MgO nanoparticle loading on mesoporous Al2O3 enhances the F- adsorption capacity of Al2O3 from 56% to 90% (initial F- concentration = 10 mg L-1). Kinetic study revealed that adsorption kinetics follows the pseudo-second order model, suggesting the chemisorption mechanism. The F- adsorption isotherm data was explained by both Langmuir and Freundlich model. The maximum adsorption capacity of 40MgO@Al2O3 was 37.35 mg g-1. It was also observed that, when the solutions having F- concentration of 5 mg L-1 and 10 mg L-1 was treated with 40MgO@Al2O3, the F- concentration in treated water became <1 mg L-1, which is well below the recommendation of WHO.

  6. Effect of Heat Treatment on the Microstructure and Microhardness of Nanostructural Al2O3 Coatings

    NASA Astrophysics Data System (ADS)

    Kovaleva, M.; Tyurin, Yu.; Vasilik, N.; Kolisnichenko, O.; Prozorova, M.; Arseenko, M.; Sirota, V.; Pavlenko, I.

    2014-10-01

    Nanostructural Al2O3 coatings were formed on a steel substrate surface using a multichamber detonation sprayer. The Al2O3 coatings were characterized by a dense microstructure with porosity below 1% and hardness of 1300 ± 25 HV0.3. The transition layer between the coating and substrate was up to 15 μm thick, containing Fe-Al-type intermetallic compounds (FeAl3, Fe2Al5). Postdeposition heat treatment of the samples at 850 °C for 3 h was carried out in air and argon environments. The effect of heat treatment on the microstructure and microhardness of the Al2O3 coatings was investigated by optical microscopy, scanning and transmission electron microscopy, scanning probe microscopy, x-ray phase analysis, and Vickers hardness testing. A positive impact of postcoating heat treatment on the coating microstructure and microhardness was observed. Heat treatment resulted in an increase in the coating hardness from 1300, to 1350 ± 25 HV0.3 and 1600 ± 25 HV0.3 after annealing in air and argon, respectively. Heat treatment in argon led to a more significant increase in the α-Al2O3 phase from 47 to 81%.

  7. Crack-resistant Al2O3–SiO2 glasses

    NASA Astrophysics Data System (ADS)

    Rosales-Sosa, Gustavo A.; Masuno, Atsunobu; Higo, Yuji; Inoue, Hiroyuki

    2016-04-01

    Obtaining “hard” and “crack-resistant” glasses have always been of great important in glass science and glass technology. However, in most commercial glasses both properties are not compatible. In this work, colorless and transparent xAl2O3–(100–x)SiO2 glasses (30 ≤ x ≤ 60) were fabricated by the aerodynamic levitation technique. The elastic moduli and Vickers hardness monotonically increased with an increase in the atomic packing density as the Al2O3 content increased. Although a higher atomic packing density generally enhances crack formation in conventional oxide glasses, the indentation cracking resistance increased by approximately seven times with an increase in atomic packing density in binary Al2O3–SiO2 glasses. In particular, the composition of 60Al2O3•40SiO2 glass, which is identical to that of mullite, has extraordinary high cracking resistance with high elastic moduli and Vickers hardness. The results indicate that there exist aluminosilicate compositions that can produce hard and damage-tolerant glasses.

  8. Reduction of nitrotoluenes in supercritical isopropanol over Al2O3 in a flow reactor

    NASA Astrophysics Data System (ADS)

    Sivcev, V. P.; Korchagina, D. V.; Volcho, K. P.; Salakhutdinov, N. F.; Anikeev, V. I.

    2015-02-01

    The reduction of o-, m-, and p-nitrotoluenes in supercritical isopropanol over Al2O3 in a flow reactor is studied. It is shown that corresponding toluidines are major reaction products. Aromatic ring alkoxylation and N-alkylation products make a considerable contribution to the composition of reaction mixtures.

  9. Uniform Atomic Layer Deposition of Al2O3 on Graphene by Reversible Hydrogen Plasma Functionalization

    PubMed Central

    2017-01-01

    A novel method to form ultrathin, uniform Al2O3 layers on graphene using reversible hydrogen plasma functionalization followed by atomic layer deposition (ALD) is presented. ALD on pristine graphene is known to be a challenge due to the absence of dangling bonds, leading to nonuniform film coverage. We show that hydrogen plasma functionalization of graphene leads to uniform ALD of closed Al2O3 films down to 8 nm in thickness. Hall measurements and Raman spectroscopy reveal that the hydrogen plasma functionalization is reversible upon Al2O3 ALD and subsequent annealing at 400 °C and in this way does not deteriorate the graphene’s charge carrier mobility. This is in contrast with oxygen plasma functionalization, which can lead to a uniform 5 nm thick closed film, but which is not reversible and leads to a reduction of the charge carrier mobility. Density functional theory (DFT) calculations attribute the uniform growth on both H2 and O2 plasma functionalized graphene to the enhanced adsorption of trimethylaluminum (TMA) on these surfaces. A DFT analysis of the possible reaction pathways for TMA precursor adsorption on hydrogenated graphene predicts a binding mechanism that cleans off the hydrogen functionalities from the surface, which explains the observed reversibility of the hydrogen plasma functionalization upon Al2O3 ALD.

  10. Complete oxidation of volatile organic compounds over Ce/Cu/gamma-AL2O3 catalyst.

    PubMed

    Kim, S C; Shim, W G

    2008-05-01

    The effect of cerium (Ce) addition into Cu (5, 10 or 15 wt%)/gamma-Al2O3 catalysts on the catalyst properties and catalytic activity was investigated for the complete oxidation of volatile organic compounds (VOCs). X-ray diffraction (XRD), the Brunauer Emmett Teller method (BET), temperature programmed reduction (TPR) by H2, and N2O pulse titration were used to characterize a series of supported copper catalysts modified with cerium. Cerium was observed to be an inhibitor for 5 wt% and promoter for 10 or 15 wt% Cu/gamma-Al2O3 catalyst. The results of TPR, average crystallite size and dispersion indicated that even though Ce loadings on 10 and 15 wt% Cu/gamma-Al2O3 caused a reduction in BET surface area of the catalysts, the loaded amounts of Ce enhanced the catalytic activity through the formation of highly dispersed copper clusters. Kinetic parameters were developed for individual benzene, toluene and o-xylene (BTX) for 5 wt% Ce/10 wt% Cu/gamma-Al2O3 catalyst at temperatures ranging from 210 to 240 degrees C. The Mars and Van Krevelen model was found to be an adequate description of the catalytic oxidation of BTX for this study. The activity sequence with respect to the BTX molecules was found to be benzene > toluene > o-xylene under the surface-reaction-controlled region.

  11. Al2O3 half-wave films for long-life CW lasers

    NASA Technical Reports Server (NTRS)

    Ladany, I.; Ettenberg, M.; Lockwood, H. F.; Kressel, H.

    1977-01-01

    Long-term operating-life data are reported for (AlGa)As CW laser diodes. The use of half-wave Al2O3 facet coatings is shown to eliminate facet erosion, allowing stable diode operation at constant current for periods in excess of 10,000 h.

  12. Crack-resistant Al2O3–SiO2 glasses

    PubMed Central

    Rosales-Sosa, Gustavo A.; Masuno, Atsunobu; Higo, Yuji; Inoue, Hiroyuki

    2016-01-01

    Obtaining “hard” and “crack-resistant” glasses have always been of great important in glass science and glass technology. However, in most commercial glasses both properties are not compatible. In this work, colorless and transparent xAl2O3–(100–x)SiO2 glasses (30 ≤ x ≤ 60) were fabricated by the aerodynamic levitation technique. The elastic moduli and Vickers hardness monotonically increased with an increase in the atomic packing density as the Al2O3 content increased. Although a higher atomic packing density generally enhances crack formation in conventional oxide glasses, the indentation cracking resistance increased by approximately seven times with an increase in atomic packing density in binary Al2O3–SiO2 glasses. In particular, the composition of 60Al2O3•40SiO2 glass, which is identical to that of mullite, has extraordinary high cracking resistance with high elastic moduli and Vickers hardness. The results indicate that there exist aluminosilicate compositions that can produce hard and damage-tolerant glasses. PMID:27053006

  13. Electrochemical Impedance Studies on Tribocorrosion Behavior of Plasma-Sprayed Al2O3 Coatings

    NASA Astrophysics Data System (ADS)

    Liu, Zhe; Chu, Zhenhua; Chen, Xueguang; Dong, Yanchun; Yang, Yong; Li, Yingzhen; Yan, Dianran

    2015-06-01

    In this paper, the tribocorrosion of plasma-sprayed Al2O3 coatings in simulated seawater was investigated by electrochemical impedance spectroscopy (EIS) technique, complemented by scanning electron microscopy to observe the morphology of the tribocorrosion attack. Base on EIS of plasma-sprayed Al2O3 coatings undergoing long-time immersion in simulated seawater, the corrosion process of Al2O3 coatings can be divided into the earlier stage of immersion (up to 20 h) and the later stage (beyond 20 h). Then, the wear tests were carried out on the surface of Al2O3 coating undergoing different times of immersion to investigate the influence of wear on corrosion at different stages. The coexistence of wear and corrosion condition had been created by a boron nitride grinding head rotating on the surface of coatings corroded in simulated seawater. The measured EIS and the values of the fitting circuit elements showed that wear accelerated corrosion at the later stage, meanwhile, corrosion accelerated wear with the immersion time increasing.

  14. Transport mechanisms of leakage current in Al2O3/InAlAs MOS capacitors

    NASA Astrophysics Data System (ADS)

    Jin, Chengji; Lu, Hongliang; Zhang, Yimen; Zhang, Yuming; Guan, He; Wu, Lifan; Lu, Bin; Liu, Chen

    2016-09-01

    An Al2O3 layer is inserted between the InAlAs layer and the metal gate in InAs/AlSb HEMTs to suppress the leakage current. The transport mechanisms of leakage current in Al2O3/InAlAs metal-oxide-semiconductor (MOS) capacitors at both positive and negative biases at different temperatures ranging from 10 °C to 70 °C are investigated. For positive bias, the leakage current is dominated by Schottky emission. Based on the fitted straight lines, the relative dielectric constant of Al2O3 and the barrier height between Al2O3 and InAlAs are extracted. However, for negative bias, the leakage current is dominated by Frenkel-Poole (F-P) emission and the depth of the trap energy level from the conduction band (ϕt) is extracted. Furthermore, authors explain the reason why the dominating mechanisms at positive and negative biases are different.

  15. Plasma etching behavior of Y2O3 ceramics: Comparative study with Al2O3

    NASA Astrophysics Data System (ADS)

    Cao, Yu-Chao; Zhao, Lei; Luo, Jin; Wang, Ke; Zhang, Bo-Ping; Yokota, Hiroki; Ito, Yoshiyasu; Li, Jing-Feng

    2016-03-01

    The plasma etching behavior of Y2O3 coating was investigated and compared with that of Al2O3 coating under various conditions, including chemical etching, mixing etching and physical etching. The etching rate of Al2O3 coating declined with decreasing CF4 content under mixing etching, while that of Y2O3 coating first increased and then decreased. In addition, the Y2O3 coating demonstrated higher erosion-resistance than Al2O3 coating after exposing to fluorocarbon plasma. X-ray photoelectron spectroscopy (XPS) analysis confirmed the formations of YF3 and AlF3 on the Y2O3 and Al2O3 coatings, respectively, which acted as the protective layer to prevent the surface from further erosion with fluorocarbon plasma. It was revealed that the etching behavior of Y2O3 depended not only on the surface fluorination but also on the removal of fluoride layer. To analyze the effect of porosity, Y2O3 bulk samples with high density were prepared by spark plasma sintering, and they demonstrated higher erosion-resistances compared with Y2O3 coating.

  16. Hydrothermal extraction and gasification of low rank coal with catalyst Al2O3 and Pd/Al2O3

    NASA Astrophysics Data System (ADS)

    Fachruzzaki, Handayani, Ismi; Mursito, Anggoro Tri

    2017-01-01

    Increasing coal quality is very important in order to utilize low-rank coal. This research is attempted to increase the quality of low-rank coal using hydrothermal process with hot compressed water (HCW) at 200 °C and 3 MPa. The product from this process were solid residue and liquid filtrate with organic component. Product from gasification of the filtrate was synthetic gas. The result showed that higher water flow rate could increase organic component in the filtrate. When a catalyst was used, the extraction process was faster, the organic component in the filtrate was increased while its content was decreased in the residue. Fourier transform infrared spectroscopy (FTIR) analysis indicated that coal extraction using HCW was more effective with catalyst Pd/Al2O3. Increasing the process temperature will increase the amounts CO and H2 gas. In this research, highest net heating value at 800°C using K2CO3 solution and Pd/Al2O3 catalyst was 17,774.36 kJ/kg. The highest cold gas efficiency was 91.29% and the best carbon conversion was 34.78%.

  17. High-k ZrO2/Al2O3 bilayer on hydrogenated diamond: Band configuration, breakdown field, and electrical properties of field-effect transistors

    NASA Astrophysics Data System (ADS)

    Liu, J. W.; Liao, M. Y.; Imura, M.; Koide, Y.

    2016-09-01

    A band configuration of a high-k ZrO2/Al2O3 bilayer on hydrogenated diamond (H-diamond), a breakdown field (EB) of the ZrO2/Al2O3 bilayer, and an effect of gate-drain distance (dG-D) on electrical properties of ZrO2/Al2O3/H-diamond metal-insulator-semiconductor field-effect transistors (MISFETs) have been investigated. The Al2O3 and ZrO2 layers are successively deposited on H-diamond by atomic layer deposition (ALD) and sputtering-deposition (SD) techniques, respectively. The thin ALD-Al2O3 buffer layer with 4.0 nm thickness plays a role in protecting the H-diamond surface from being damaged by the plasma discharge during SD-ZrO2 deposition. The ZrO2/Al2O3 heterojunction has a type I band structure with valence and conduction band offsets of 0.6 ± 0.2 and 1.0 ± 0.2 eV, respectively. The valence band offset between ZrO2 and H-diamond is deduced to be 2.3 ± 0.2 eV. The EB of the ZrO2/Al2O3 bilayer is measured to be 5.2 MV cm-1, which is larger than that of the single ZrO2 layer due to the existence of the ALD-Al2O3 buffer layer. The dependence of dG-D on drain-source current maximum (IDS,max), on-resistance (RON), threshold voltage (VTH), and extrinsic transconductance maximum (gm,max) of the MISFETs has been investigated. With increasing dG-D from 4 to 18 μm, the absolute IDS,max decreases from 72.7 to 40.1 mA mm-1, and the RON increases linearly from 83.3 ± 5 to 158.7 ± 5 Ω mm. Variation of VTH values of around 1.0 V is observed, and the gm,max is in the range between 8.0 ± 0.1 and 13.1 ± 0.1 mS mm-1.

  18. Copper pillar and memory characteristics using Al2O3 switching material for 3D architecture

    PubMed Central

    2014-01-01

    A novel idea by using copper (Cu) pillar is proposed in this study, which can replace the through-silicon-vias (TSV) technique in future three-dimensional (3D) architecture. The Cu pillar formation under external bias in an Al/Cu/Al2O3/TiN structure is simple and low cost. The Cu pillar is formed in the Al2O3 film under a small operation voltage of <5 V and a high-current-carrying conductor of >70 mA is obtained. More than 100 devices have shown tight distribution of the Cu pillars in Al2O3 film for high current compliance (CC) of 70 mA. Robust read pulse endurances of >106 cycles are observed with read voltages of −1, 1, and 4 V. However, read endurance is failed with read voltages of −1.5, −2, and −4 V. By decreasing negative read voltage, the read endurance is getting worst, which is owing to ruptured Cu pillar. Surface roughness and TiO x N y on TiN bottom electrode are observed by atomic force microscope and transmission electron microscope, respectively. The Al/Cu/Al2O3/TiN memory device shows good bipolar resistive switching behavior at a CC of 500 μA under small operating voltage of ±1 V and good data retention characteristics of >103 s with acceptable resistance ratio of >10 is also obtained. This suggests that high-current operation will help to form Cu pillar and lower-current operation will have bipolar resistive switching memory. Therefore, this new Cu/Al2O3/TiN structure will be benefited for 3D architecture in the future. PMID:25136279

  19. Structural optical correlated properties of SnO2/Al2O3 core@ shell heterostructure

    NASA Astrophysics Data System (ADS)

    Heiba, Zein K.; Imam, N. G.; Bakr Mohamed, Mohamed

    2016-07-01

    Nano size polycrystalline samples of the core@shell heterostructure of SnO2 @ xAl2O3 (x = 0, 25, 50, 75 wt.%) were synthesized by sol-gel technique. The resulting samples were characterized with fourier transform infrared spectroscopy (FT-IR), photoluminescence (PL) and X-ray powder diffraction (XRD). The XRD patterns manifest diffraction peaks of SnO2 as main phase with weak peaks corresponding to Al2O3 phase. The formation of core@ shell structure is confirmed by TEM images and Rietveld quantitative phase analysis which revealed that small part of Al2O3 is incorporated into the SnO2 lattice while the main part (shell) remains as a separate phase segregated on the grain boundary surface of SnO2 (core). It is found that the grain size of the mixed oxides SnO2 @ xAl2O3 is below 10 nm while for pure SnO2 it is over 41 nm, indicating that alumina can effectively prevent SnO2 from further growing up in the process of calcination. This is confirmed by the large increase in the specific surface area for mixed oxide samples. The PL emission showed great dependence on the structure properties analyzed by XRD and FTIR. The PL results recommend Al2O3@SnO2 core@shell heterostructure to be a promising short-wavelength luminescent optoelectronic devices for blue, UV, and laser light-emitting diodes.

  20. Vanadium oxides on aluminum oxide supports. 2. Structure, vibrational properties, and reducibility of V2O5 clusters on alpha-Al2O3(0001).

    PubMed

    Brázdová, Veronika; Ganduglia-Pirovano, M Verónica; Sauer, Joachim

    2005-12-15

    The structure, stability, and vibrational properties of isolated V2O5 clusters on the Al2O3(0001) surface have been studied by density functional theory and statistical thermodynamics. The most stable structure does not possess vanadyl oxygen atoms. The positions of the oxygen atoms are in registry with those of the alumina support, and both vanadium atoms occupy octahedral sites. Another structure with one vanadyl oxygen atom is only 0.12 eV less stable. Infrared spectra are calculated for the two structures. The highest frequency at 922 cm(-1) belongs to a V-O stretch in the V-O-Al interface bonds, which supports the assignment of such a mode to the band observed around 941 cm(-1) for vanadia particles on alumina. Removal of a bridging oxygen atom from the most stable cluster at the V-O-Al interface bond costs 2.79 eV. Removal of a (vanadyl) oxygen atom from a thin vanadia film on alpha-Al2O3 costs 1.3 eV more, but removal from a V2O5(001) single-crystal surface costs 0.9 eV less. Similar to the V2O5(001) surface, the facile reduction is due to substantial structure relaxations that involve formation of an additional V-O-V bond and yield a pair of V(IV)(d1) sites instead of a V(III)(d2)/V(V)(d0) pair.

  1. Ab Initio Density Funcitonal Calculations of Adsorption of Transiton Metal Atoms on theta-Al2O3 (010) Surface

    SciTech Connect

    Narula, Chaitanya Kumar; Stocks, George Malcolm

    2012-01-01

    The catalytic properties of metal clusters and particles depend on their environment, however, little is known so far about the subnanometer metal particles, smallest being single atoms, supported on metal oxide substrates, especially, the systems that can be experimentally synthesized. Employing first principles density functional theory approach, we have studied single metal atoms, Ni, Pt, Pd, Cu, Au, and Ag, adsorbed on a -Al2O3 (010) surface. We find that metal adsorption on a dry alumina surface follows the binding strength order of Pd>Pt>Ni>Cu>Au>Ag. Interestingly, Ni, Pt, and Pd atoms, supported on alumina, exhibit no magnetization whereas Cu, Ag, and Au exhibit unpaired electrons. The bonding picture that emerges from this study shows that Ni, Pt, and Pd, are d10 species with d-s hybrid character that are able to interact with the 2p orbital of surface oxygen. The interaction of Group 11 (Cu, Ag, Au) atoms with 010 surface of -Al2O3 is superficially similar to that of Group 10 metals. Group 11 metals with filled d orbitals have low tendency for d-s hybridization due to larger energy gaps than Group 10 metals. As a result of the overlap with O 2p, the d orbital shifts to lower energy. The magnetization of Group 11 metals is primarily due to single electrons in s orbitals.

  2. Effect of CeO2 doping on catalytic activity of Fe2O3/gamma-Al2O(3) catalyst for catalytic wet peroxide oxidation of azo dyes.

    PubMed

    Liu, Yan; Sun, Dezhi

    2007-05-08

    In order to find a catalyst with high activity and stability for catalytic wet peroxide oxidation (CWPO) process under normal condition, with Fe(2)O(3)/gamma-Al(2)O(3) and Fe(2)O(3)-CeO(2)/gamma-Al(2)O(3) catalysts prepared by impregnation method, the effect of CeO(2) doping on the structure and catalytic activity of Fe(2)O(3)/gamma-Al(2)O(3) for catalytic wet peroxide oxidation of azo dyes at 25 degrees C and atmospheric pressure is evaluated using BET, SEM, XRF, XRD, XPS and chemical analysis techniques, and test results show that, better dispersion and smaller size of Fe(2)O(3) crystal can be achieved by adding CeO(2), and the content of chemisorbed oxygen can also be increased on the surface of catalyst. CWPO experimental results indicate that azo dyes in simulated wastewater can be efficiently mineralized and the catalytic activity of Fe(2)O(3)-CeO(2)/gamma-Al(2)O(3) can be increased by about 10% compared with that of Fe(2)O(3)/gamma-Al(2)O(3) because of the promotion of the structural and redox properties of the ferric oxide by ceria doped. Leaching tests indicate that Fe(2)O(3)/gamma-Al(2)O(3) and Fe(2)O(3)-CeO(2)/gamma-Al(2)O(3) are stable with a negligible amount of irons found in the aqueous solution after reaction for 2h. It can therefore be concluded from results and discussion that in comparison with Fe(2)O(3)/gamma-Al(2)O(3), Fe(2)O(3)-CeO(2)/gamma-Al(2)O(3) is a suitable catalyst, which can effectively degrade contaminants at normal temperature and atmospheric pressure.

  3. Single Crystal Surfaces

    NASA Astrophysics Data System (ADS)

    Aguilar-Santillan, Joaquin

    2014-06-01

    The present work studies (0001) Al2O3 and (111) Al2MgO4 wetting with pure molten Al by the sessile drop technique from 1073 K to 1473 K (800 °C to 1200 °C) under Ar at PO2 10-15 Pa. Al pure liquid wets a smooth and chemically homogeneous surface of an inert solid, the wetting driving force ( t, T) can be readily studied when surface solid roughness increases in the system. Both crystals planes (0001) Al2O3 and (111) Al2MgO4 have crystallographic surfaces with identical O-2 crystalline positions however considering Mg2+ content in Al2MgO4 structure may influence a reactive mode. Kinetic models results under similar experimental conditions show that Al wetting on (0001) Al2O3 is less reactive than (111) Al2MgO4, however at >1273 K (1000 °C) (0001) Al2O3 transformation occurs and a transition of wetting improves. The (111) Al2MgO4 and Al system promotes interface formations that slow its wetting process.

  4. Structural Determination of (Al2O3)(n) (n = 1-15) Clusters Based on Graphic Processing Unit.

    PubMed

    Zhang, Qiyao; Cheng, Longjiu

    2015-05-26

    Global optimization algorithms have been widely used in the field of chemistry to search the global minimum structures of molecular and atomic clusters, which is a nondeterministic polynomial problem with the increasing sizes of clusters. Considering that the computational ability of a graphic processing unit (GPU) is much better than that of a central processing unit (CPU), we developed a GPU-based genetic algorithm for structural prediction of clusters and achieved a high acceleration ratio compared to a CPU. On the one-dimensional (1D) operation of a GPU, taking (Al2O3)n clusters as test cases, the peak acceleration ratio in the GPU is about 220 times that in a CPU in single precision and the value is 103 for double precision in calculation of the analytical interatomic potential. The peak acceleration ratio is about 240 and 107 on the block operation, and it is about 77 and 35 on the 2D operation compared to a CPU in single precision and double precision, respectively. And the peak acceleration ratio of the whole genetic algorithm program is about 35 compared to CPU at double precision. Structures of (Al2O3)n clusters at n = 1-10 reported in previous works are successfully located, and their low-lying structures at n = 11-15 are predicted.

  5. Adsorption of Pd atoms on γ-Al 2O 3: a density functional study of metal-support interactions

    NASA Astrophysics Data System (ADS)

    Márquez, Antonio M.; Sanz, Javier Fernández

    2004-11-01

    The Pd/γ-Al2O3 interface at low coverage has been theoretically studied by means of periodic-supercell density functional calculations. The most stable (1 1 0) γ-Al2O3 clean surface plane has been modelled by using a six layers slab stoichiometric model of 40 atoms. A single Pd atom has been deposited on top of the surface in different positions, first freezing the surface structure and later allowing the surface to relax. The results indicate that the metal-support interaction is dominated by the strong Lewis acid properties of the tetrahedral cationic sites. It is also shown that in the octahedral cationic sites, adsorption of single Pd atoms induces a significant relaxation of the substrate. While the interaction energy with the preferred site is strong (∼3.8 eV), small differences are found for nearby sites, indicating a high mobility of Pd atoms on the surface, at least on the channels.

  6. Mechanical Properties and Microstructural Evolution of Bimetal 1050/Al2O3/5083 Composites Fabricated by Warm Accumulative Roll Bonding

    NASA Astrophysics Data System (ADS)

    Sedighi, M.; Farhadipour, P.; Heydari Vini, M.

    2016-12-01

    In this study, a warm accumulative roll bonding process was used to produce a 1050 /5% Al2O3/5083 composite from AA1050 and AA5083 sheets. Firstly, the raw materials were roll-bonded and then rolled up to five accumulative rolling cycles by preheating for 5 min at 280°C before each cycle. The mechanical properties of the ARBed bimetals were evaluated in comparison with 1050/5% Al2O3 and 5083 /5% Al2O3 roll-bonded single-metal metal matrix composites (MMCs). It was found that two different layers of the bimetal sheet (1050/5% Al2O3/5083 composite) were deformed in a nearly identical way during the first three cycles. After that, the 5083 layers started necking. The strength of the bimetal samples was superior to the average of these two single-metal MMCs. Furthermore, the strength and ductility of the ARBed bimetal improved by ARB cycles. Finally, the fracture surfaces of the bimetal composite were studied at all ARB cycles by scanning electron microscopy.

  7. Electrical Discharge Machining of Al/7.5% Al2O3 MMCs Using Rotary Tool and Al2O3 Powder

    NASA Astrophysics Data System (ADS)

    Daneshmand, Saeed; Masoudi, Behnam; Monfared, Vahid

    Nowadays, composites are used in different parts of industries and it is one of the most important subjects. The most widely used reinforcements in metal matrix composites are Al2O3 and SiC fibers and particles which may be used in cutting-edge functional and structural applications of aerospace, defense, and automobile industries. Depending on the type of powder used, composite materials are difficult to machine by conventional cutting tools and methods. The most appropriate way for machining of these composites is electro discharge. For the reason of improving the surface quality, tool wear rate and material removal rate and reducing the cracks on the surface, Al2O3 powder was used. In this study, the effect of input parameters of EDM such as voltage, pulse current, pulse on-time and pulse off-time on output parameters like material removal rate, tool wear rate and surface roughness in both conditions of the rotary tool with powder mixed dielectric EDM and the stationary tool excluding powder mixed dielectric were investigated. The critical parameters were identified by variance analysis, while the optimum machining parameter settings were achieved via Taguchi method. Results show that using of powder mixed dielectric and rotary tool reduce the tool wear rate, surface roughness and the cracks on the surface significantly. It is found also that using of powder mixed dielectric and rotary tool improve the material removal rate due to improved flushing action and sparking efficiency. The analysis of variance showed that the pulse current and pulse on-time affected highly the MRR, TWR, surface roughness and surface cracks.

  8. Effect of Nano-Al2O3 on the Toxicity and Oxidative Stress of Copper towards Scenedesmus obliquus

    PubMed Central

    Li, Xiaomin; Zhou, Suyang; Fan, Wenhong

    2016-01-01

    Nano-Al2O3 has been widely used in various industries; unfortunately, it can be released into the aquatic environment. Although nano-Al2O3 is believed to be of low toxicity, it can interact with other pollutants in water, such as heavy metals. However, the interactions between nano-Al2O3 and heavy metals as well as the effect of nano-Al2O3 on the toxicity of the metals have been rarely investigated. The current study investigated copper toxicity in the presence of nano-Al2O3 towards Scenedesmus obliquus. Superoxide dismutase activity and concentration of glutathione and malondialdehyde in cells were determined in order to quantify oxidative stress in this study. Results showed that the presence of nano-Al2O3 reduced the toxicity of Cu towards S. obliquus. The existence of nano-Al2O3 decreased the growth inhibition of S. obliquus. The accumulation of copper and the level of oxidative stress in algae were reduced in the presence of nano-Al2O3. Furthermore, lower copper accumulation was the main factor that mitigated copper toxicity with the addition of nano-Al2O3. The decreased copper uptake could be attributed to the adsorption of copper onto nanoparticles and the subsequent decrease of available copper in water. PMID:27294942

  9. Effect of catalyst preparation conditions on the hydrodesulfurization of thiophene over Co-Mo/gamma-Al2O3.

    PubMed

    Chen, Chun-Liang; Lin, Shiow-Shyung; Liu, Tuan-Chi

    2002-01-01

    The purpose of this research was to study the effects of preparation conditions on the catalytic properties of the Co-Mo/gamma-Al2O3 catalyst. The work included catalyst preparations and reactions. In the preparations, cobalt-impregnated Mo/gamma-Al2O3 (designated as IcIM) was found to have a promoting effect on the hydrodesulfurization (HDS) of thiophene. Activity and stability of IcIM was higher than that of Mo/gamma-Al2O3. Conversely, when cobalt was added onto Mo/gamma-Al2O3 by the mechanical mixing method, no promoting effect was observed. Mo/gamma-Al2O3 was also prepared using the two different methods (incipient impregnation or mechanical mixing). The differently prepared Mo/gamma-Al203 resulted in no obvious difference in activity of IcIM. It was further found that Co-Mo/gamma-Al2O3 activity initially increased appreciably with Mo content and leveled off at Mo contents above 9 wt.%. The catalyst exhibited a maximum activity at Co/Mo ratio 0.3. The order in which metal species were added had a great influence on the activity of the Co-Mo/gamma-Al2O3 catalyst. Higher activity was obtained when Co was added into Mo/gamma-Al2O3 as opposed to Mo added into Co/gamma-Al2O3.

  10. Millimeter distance effects of surface plasmon polaritons in electroformed Al-Al2O3-Ag diodes

    NASA Astrophysics Data System (ADS)

    Hickmott, T. W.

    2017-02-01

    Electroforming of metal-insulator-metal diodes is a soft dielectric breakdown that changes the high resistance of as-prepared diodes to a low resistance state. Electroforming of Al-Al2O3-metal diodes with anodic Al2O3 results in voltage-controlled negative resistance in the current-voltage (I-V) characteristics, electroluminescence (EL), and electron emission into vacuum (EM). EL is due to electrons injected at the Al-Al2O3 interface combining with radiative defects in Al2O3. Surface plasmon polaritons (SPPs) are electromagnetic waves that can be excited by photons or electrons. SPPs are confined to a metal-dielectric interface, cause large electric fields in the metal and dielectric, and have ranges of micrometers. The temperature dependence of I-V curves, EL, and EM of a group of electroformed Al-Al2O3-Ag diodes with Al2O3 thicknesses between 12 nm and 20 nm, group A, was measured between 200 K and 300 K. After a sequence of temperature measurements, the Al-Al2O3-Ag diodes, the Al-Al2O3 regions between diodes, and portions of the Ag on the glass region that provides contacts to the diodes are darkened. The range of darkening is >7 mm in a diode with 12 nm of Al2O3 and 2.0-3.5 mm in diodes with Al2O3 thicknesses between 14 nm and 20 nm. Darkening is attributed to the occurrence of SPPs generated by EL photons at the Ag-Al2O3 and Al-Al2O3 interfaces. The results are compared to a second group of Al-Al2O3-Ag diodes with identical Al2O3 thicknesses, group B, that were prepared in the same way as the diodes of group A except for a difference in the deposition of Al films for the two groups. Al-Al2O3-Ag diodes of group B exhibit enhanced EL, which is attributed to spontaneous emission of recombination centers in Al2O3 being enhanced by large electromagnetic fields that are due to SPPs that are generated by EL photons.

  11. Diffusion processes in Al2O3 scales - Void growth, grain growth, and scale growth

    NASA Technical Reports Server (NTRS)

    Smialek, J. L.; Gibala, R.

    1983-01-01

    The internal microstructure and growth kinetics of Al2O3 scales on Ni-15Cr-13Al (wt percent) are investigated by TEM and analyzed in relation to models of diffusivity. Polished arc-melted specimens were oxidized in 1-atm air at 1100 C for 0.1, 1.0, and 20 hours and ion-thinned for TEM at 100 kV. The frequency distribution of void size and grain size is determined for different oxidation times and scale depths. The kinetics of microvoid growth and of grain and scale growth are plotted and related via simplified models to lattice and grain-boundary oxygen diffusivity, respectively. Good agreement is found between model predictions and data obtained by Oishi and Kingery (1960) on oxygen diffusion in bulk Al2O3. The further implications and limitations of these findings are discssed.

  12. Adherent Al2O3 scales produced on undoped NiCrAl alloys

    NASA Technical Reports Server (NTRS)

    Smialek, James L.

    1986-01-01

    Repeated oxidation and polishing of high purity Ni-15Cr-13Al has dramatically changed its cyclic oxidation behavior from nonadherent to adherent. No apparent change in scale phase, morphology or interface structure occurred during this transition, dismissing any mechanism based on pegging, vacancy sink, or growth stress. The principle change that did occur was a reduction in the sulfur content from 10 ppmw to 3 ppmw after 25 cycles at 1120 C. These observations are used to support the model of Al2O3 scale adherence put forth by Smeggil et al. which claims that Al2O3 scale spallation occurs due to sulfur segregation and bond deterioration at the oxide-metal interface.

  13. Anormalous Optical Absorption in Porous Al_2O3 Host Matrix---Nano-Oxide Particle Nanocomposites

    NASA Astrophysics Data System (ADS)

    Zhang, Lide; Zhang, Biao; Mo, Chimei

    1996-03-01

    Porous Al_2O3 host matrix---nano-γ-Fe_2O3 particle composites (porous nanocomposite) were prepared by pyrolysis of Fe(NO_3)_39H_2O in porous nano- Al_2O3 matrix at 250^0C. Comparing with simple nanocomposites formed by mixing nano-γ-Fe_2O3 and compacting at room temperature, followed by annealing at 250^0C, the following anomalous optical behaviors were observed: for porous nanocomposite containing 5% Fe_2O_3, the aborption edge shifts obviously from 827nm to 543nm, and with increasing dopping amount of Fe_2O3 from 5% to 70%, blue shift phenomina decreases. Namely, the absorption edge moves from 543nm to 710nm. The mechanism of shift of the absorption edge is discussed.

  14. Fabrication of SiC/Al2O3 CMCs & their physical properties

    NASA Astrophysics Data System (ADS)

    Kumar, S. Santhosh; Devaiah, M.; Rajasekharan, T.

    2012-06-01

    SiC particulate reinforced Al2O3 matrix composites were fabricated using Directed Metal Oxidation (DIMOX) process. Continuous oxidation of an Al-8.5Si-1.5Mg-9Zn alloy in presence SiC perform with suitable dopants has led to the formation of the Al2O3 matrix. Ceramic composites with SiC volume fraction in the range of 0.35 - 0.43 were evaluated for effective co-efficient of linear thermal expansion (CTE) and elastic properties. The composites with high volume fraction of SiC showed a minimum dilatation with temperature (5.0 × 10-6 /K) and also enhancement in elastic properties (E: 262 GPa; G: 87 GPa; K: 189 GPa). Also, the elastic properties of the ceramic composites increased with SiC volume fraction.

  15. Interdiffusion in the MgO-Al2O3 spinel with or without some dopants

    NASA Astrophysics Data System (ADS)

    Zhang, P.; Debroy, T.; Seetharaman, S.

    1996-08-01

    With a view to seek an improved understanding of the DIMOX process, interdiffusion of polycrystalline MgO and Al2O3 in the temperature range 1473 to 1873 K was studied by diffusion couple experiments. The interdiffusivities in the spinel layer were calculated as functions of composition and temperature. The spinel portion of the phase diagram in the system MgO-Al2O3 was determined from carefully measured compositions at the phase boundaries, and the low temperature spinel region of the phase diagram was confirmed from the present results. For Zn2+ as dopant in alumina, the growth rate of spinel thickness seems to increase when compared with that of the diffusion couples without dopant. The samples containing Si4+ as dopant reveal the formation of a glass phase, and the effect of Si4+ on the diffusion process appears to be negligible.

  16. Mechanical properties of Al2O3 inverse opals by means of nanoindentation

    NASA Astrophysics Data System (ADS)

    Roa, J. J.; Coll, A.; Bermejo, S.; Jiménez-Piqué, E.; Alcubilla, R.; Castañer, L.; Llanes, L.

    2016-11-01

    In order to understand the mechanical behaviour of Al2O3 inverse opals, nanoindentation techniques have been implemented in material layers with three different microstructures, in terms of hollow or polystyrene spheres, with Al2O3 shells of distinct wall thickness. Different indenter tip geometries as well as contact loading conditions have been used, in order to induce different stress field and fracture events to the layers. Field emission scanning electron microscopy and focused ion beam have been employed to understand accommodation of plastic deformation induced during the indentation process. Results show that materials with polystyrene spheres exhibit higher hardness and modulus under sharp indentation, and cracking resistance under spherical indentation. Furthermore, deformation is discerned to be mainly governed by the rotation of the microspheres. In the case of the inverse opals made of hollow spheres, the main deformation mechanisms activated under indentation are the rearrangement and densification of them.

  17. Geant4 calculations for space radiation shielding material Al2O3

    NASA Astrophysics Data System (ADS)

    Capali, Veli; Acar Yesil, Tolga; Kaya, Gokhan; Kaplan, Abdullah; Yavuz, Mustafa; Tilki, Tahir

    2015-07-01

    Aluminium Oxide, Al2O3 is the most widely used material in the engineering applications. It is significant aluminium metal, because of its hardness and as a refractory material owing to its high melting point. This material has several engineering applications in diverse fields such as, ballistic armour systems, wear components, electrical and electronic substrates, automotive parts, components for electric industry and aero-engine. As well, it is used as a dosimeter for radiation protection and therapy applications for its optically stimulated luminescence properties. In this study, stopping powers and penetrating distances have been calculated for the alpha, proton, electron and gamma particles in space radiation shielding material Al2O3 for incident energies 1 keV - 1 GeV using GEANT4 calculation code.

  18. High brightness, narrow-band, Ti:Al2O3 oscillator

    NASA Astrophysics Data System (ADS)

    Brown, A. J. W.; Kangas, K. W.; Fisher, C. H.

    The injection-seeding of a short (about 30 cm) Ti:Al2O3 power oscillator with the output from a short-pulse, narrow-band, tunable, Ti:Al2O3 oscillator is reported. The frequency-doubled output from a Continuum YG681C Nd:YAG laser was used as the common pump source for both the seed laser and power oscillator. Good injection-seeding was observed with more than 20 ns delay; less delay than this resulted in poorer seeding. Minimizing the seed laser turn on time allowed harder pumping of the power oscillator, hence higher output energy, while maining good seeding. The spectral output from the power oscillator was analyzed using both an etalon and a 1-m MacPherson spectrometer. The seeded power oscillator is shown to closely replicate the seed laser output, operating on 2 or 3 longitudinal modes.

  19. Effect of sulfur removal on Al2O3 scale adhesion

    NASA Technical Reports Server (NTRS)

    Smialek, James L.

    1991-01-01

    The effect of removing sulfur impurity on the adhesion of Al2O3 scale to NiCrAl was investigated in four experiments. It was found that removing sulfur to concentration less than 1 ppm per weight is sufficient to produce a very significant degree of alpha-Al2O3 scale adhesion to undoped NiCrAl alloys. Results of experiments show that repeated oxidation, and polishing after each oxidation cycle, of pure NiCrAl alloy lowered sulfur content from 10 to 2 ppm by weight (presumably by removing the segregated interfacial layer after each cycle); thinner samples became adherent after fewer oxidation-polishing cycles because of more limited supply of sulfur. It was found that spalling in subsequent cyclic oxidation tests was a direct function of the initial sulfur content. The transition between the adherent and nonadherent behavior was modeled in terms of sulfur flux, sulfur content, and sulfur segregation.

  20. Visible luminescence of Al2O3 nanoparticles embedded in silica glass host matrix

    NASA Astrophysics Data System (ADS)

    El Mir, L.; Amlouk, A.; Barthou, C.

    2006-11-01

    This paper deals with the sol gel elaboration and defects photoluminescence (PL) examination of Al2O3 nanocrystallites (size ˜30 nm) confined in glass based on silica aerogel. Aluminium oxide aerogels were synthesized using esterification reaction for hydrolysis of the precursor and supercritical conditions of ethyl alcohol for drying. The obtained nanopowder was incorporated in SiO2 host matrix. After heating under natural atmosphere at 1150 °C for 2 h, the composite Al2O3/SiO2 (AS) exhibited a strong PL bands at 400 600 and 700 900 nm in 78 300 K temperature range. PL excitation (PLE) measurements show different origins of the emission. It was suggested that OH-related radiative centres and non-bridging oxygen hole centres (NBOHCs) were responsible for the bands at 400 600 and 700 900 nm, respectively.

  1. Modification of Fluorinated Al2O3 Surface by Irradiating H2 and O2 Plasmas

    NASA Astrophysics Data System (ADS)

    Miwa, Kazuhiro; Usami, Kenji; Takada, Noriharu; Sasaki, Koichi

    2009-12-01

    We irradiated H2 and O2 plasmas onto fluorinated Al2O3, which was prepared by exposing a virgin Al2O3 sample to an SF6/O2 plasma. The effects of the H2 plasma irradiation were the reduction of the AlOxFy (x + y = 1.5) and AlFx (x < 3) bonding components and the realization of smooth sample surface. It was observed that the irradiation of the H2 plasma induced Al-OH bonding. The Al-OH bonding was removed by the sequential irradiation of the O2 plasma after the H2 plasma irradiation. The O2 plasma irradiation also resulted in peroxidation and an increase in surface roughness.

  2. Theory of the clean and hydrogenated Al2O3(0001)-(1×1) surfaces

    NASA Astrophysics Data System (ADS)

    Felice, Rosa Di; Northrup, John E.

    1999-12-01

    We present the results of a first principles investigation of the equilibrium properties of c-plane α-Al2O3 surfaces. The stable structure for the 1×1 clean surface is Al terminated with a stoichiometric composition, while other terminations are unstable independent of surface preparation conditions. We discuss the implications of our results in the frame of possible extended reconstructions. For 1 monolayer of H coverage, we find that the preferred structure has OH dimers both perpendicular and nearly parallel to the surface. H-terminated surfaces may form in suitable preparation conditions. We discuss our results in terms of water adsorption and atomic layer epitaxy of α-Al2O3(0001).

  3. Effect of hydrogen on Al2O3/Cu interfacial structure and adhesion

    NASA Astrophysics Data System (ADS)

    Wang, Xiao-Gang; Smith, John R.; Scheffler, Matthias

    2002-08-01

    We have carried out an ab initio investigation of the effect of hydrogen on the Al2O3/Cu interface. H on the Al2O3 surface can play a bridging role in the formation of the interface. The interfacial OH bond is stable in the presence of two atomic layers of Cu. In contrast, an Al monolayer would dissociate the surface OH bond. For thicker Cu, one-third of a monolayer of H remains stable in the interface, lowering the work of separation by 2.3 J/m2. The interfacial work of separation remains larger than that of bulk Cu, however. These results are consistent with available experimental data.

  4. Luminescence study of nanosized Al2O3:Tb3+ obtained by gas-dispersed synthesis

    NASA Astrophysics Data System (ADS)

    Berezovskaya, I. V.; Poletaev, N. I.; Khlebnikova, M. E.; Zatovsky, I. V.; Bychkov, K. L.; Efryushina, N. P.; Khomenko, O. V.; Dotsenko, V. P.

    2016-09-01

    Terbium-doped Al2O3 samples were obtained by gas-dispersed synthesis. It was shown that the resulting powders, with particle sizes of 10-70 nm, consist of a mixture of transition aluminas, among which the δ *-polymorph is dominant. The luminescence properties of Al2O3:Tb3+ have been studied upon excitation in the UV-visible range of the spectrum. It was found that Tb3+ ions cause several groups of inhomogeneously broadened emission bands in the range of 470-640 nm, which are characteristic for disordered materials. In addition, the emission spectra contain a broad band at about 450 nm and several narrower ones in the 680-720 nm region. These features are attributed to surface defects and impurity Cr3+ ions occupying Al3+ octahedral positions, respectively.

  5. Space-charge-controlled field emission model of current conduction through Al2O3 films

    NASA Astrophysics Data System (ADS)

    Hiraiwa, Atsushi; Matsumura, Daisuke; Kawarada, Hiroshi

    2016-02-01

    This study proposes a model for current conduction in metal-insulator-semiconductor (MIS) capacitors, assuming the presence of two sheets of charge in the insulator, and derives analytical formulae of field emission (FE) currents under both negative and positive bias. Since it is affected by the space charge in the insulator, this particular FE differs from the conventional FE and is accordingly named the space-charge-controlled (SCC) FE. The gate insulator of this study was a stack of atomic-layer-deposition Al2O3 and underlying chemical SiO2 formed on Si substrates. The current-voltage (I-V) characteristics simulated using the SCC-FE formulae quantitatively reproduced the experimental results obtained by measuring Au- and Al-gated Al2O3/SiO2 MIS capacitors under both biases. The two sheets of charge in the Al2O3 films were estimated to be positive and located at a depth of greater than 4 nm from the Al2O3/SiO2 interface and less than 2 nm from the gate. The density of the former is approximately 1 × 1013 cm-2 in units of electronic charge, regardless of the type of capacitor. The latter forms a sheet of dipoles together with image charges in the gate and hence causes potential jumps of 0.4 V and 1.1 V in the Au- and Al-gated capacitors, respectively. Within a margin of error, this sheet of dipoles is ideally located at the gate/Al2O3 interface and effectively reduces the work function of the gate by the magnitude of the potential jumps mentioned above. These facts indicate that the currents in the Al2O3/SiO2 MIS capacitors are enhanced as compared to those in ideal capacitors and that the currents in the Al-gated capacitors under negative bias (electron emission from the gate) are more markedly enhanced than those in the Au-gated capacitors. The larger number of gate-side dipoles in the Al-gated capacitors is possibly caused by the reaction between the Al and Al2O3, and therefore gate materials that do not react with underlying gate insulators should be chosen

  6. Protective Al2O3 scale formation on NbAl3-base alloys

    NASA Technical Reports Server (NTRS)

    Doychak, J.; Hebsur, M. G.

    1991-01-01

    The oxidation of NbAl3 with additions of Cr and Y was studied to determine the mechanisms of the beneficial effects of these elements upon oxidation. Cr additions to the binary NbAl3 alloy of up to 6.8 at. percent reduced the scale growth rates and promoted alpha-Al2O3 formation over much longer times relative to binary NbAl3. A major effect of Cr is to form a layer of AlNbCr at the metal/scale interface, which is inherently more oxidation-resistant than the matrix alloy in the long term. Yttrium additions to a Cr-containing alloy improved the scale growth rate and adherence and changed the scale microstructure to mimic that of a typical protective Al2O3 scale.

  7. Pressure sintering of Si3N4-Al2O3 /Sialon/

    NASA Technical Reports Server (NTRS)

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

    1977-01-01

    Essentially pore-free Sialon bodies were obtained by pressure sintering for three blends (mol ratios of 4:1, 2:3, and 3:2) of Si3N4 and Al2O3 powders under the conditions of 27.6 MN/sq m and a temperature of 1700 C for 2 h. These dense bodies consist mainly of a Sialon solid solution with a minor amount of a particular second phase. The higher the Al2O3 content (20 to 60 mol% range) in Sialon, the higher the densification rate. Fully dense bodies can be obtained at temperatures as low as 1500 C at 27.6 MN/sq m for 2 h with no second phase detectable by X-ray diffraction. A 100% dense body can be obtained by heating at 1700 C at 27.6 MN/sq m without a holding time.

  8. Versatile sputtering technology for Al2O3 gate insulators on graphene.

    PubMed

    Friedemann, Miriam; Woszczyna, Mirosław; Müller, André; Wundrack, Stefan; Dziomba, Thorsten; Weimann, Thomas; Ahlers, Franz J

    2012-04-01

    We report a novel, sputtering-based fabrication method of Al2O3 gate insulators on graphene. Electrical performance of dual-gated mono- and bilayer exfoliated graphene devices is presented. Sputtered Al2O3 layers possess comparable quality to oxides obtained by atomic layer deposition with respect to a high relative dielectric constant of about 8, as well as low-hysteresis performance and high breakdown voltage. We observe a moderate carrier mobility of about 1000 cm(2) V(-1) s(-1) in monolayer graphene and 350 cm(2) V(-1) s(-1) in bilayer graphene, respectively. The mobility decrease can be attributed to the resonant scattering on atomic-scale defects, likely originating from the Al precursor layer evaporated prior to sputtering.

  9. Frustration of Negative Capacitance in Al2O3/BaTiO3 Bilayer Structure

    NASA Astrophysics Data System (ADS)

    Kim, Yu Jin; Park, Min Hyuk; Lee, Young Hwan; Kim, Han Joon; Jeon, Woojin; Moon, Taehwan; Do Kim, Keum; Jeong, Doo Seok; Yamada, Hiroyuki; Hwang, Cheol Seong

    2016-01-01

    Enhancement of capacitance by negative capacitance (NC) effect in a dielectric/ferroelectric (DE/FE) stacked film is gaining a greater interest. While the previous theory on NC effect was based on the Landau-Ginzburg-Devonshire theory, this work adopted a modified formalism to incorporate the depolarization effect to describe the energy of the general DE/FE system. The model predicted that the SrTiO3/BaTiO3 system will show a capacitance boost effect. It was also predicted that the 5 nm-thick Al2O3/150 nm-thick BaTiO3 system shows the capacitance boost effect with no FE-like hysteresis behavior, which was inconsistent with the experimental results; the amorphous-Al2O3/epitaxial-BaTiO3 system showed a typical FE-like hysteresis loop in the polarization – voltage test. This was due to the involvement of the trapped charges at the DE/FE interface, originating from the very high field across the thin Al2O3 layer when the BaTiO3 layer played a role as the NC layer. Therefore, the NC effect in the Al2O3/BaTiO3 system was frustrated by the involvement of reversible interface charge; the highly stored charge by the NC effect of the BaTiO3 during the charging period could not be retrieved during the discharging process because integral part of the polarization charge was retained within the system as a remanent polarization.

  10. Frustration of Negative Capacitance in Al2O3/BaTiO3 Bilayer Structure.

    PubMed

    Kim, Yu Jin; Park, Min Hyuk; Lee, Young Hwan; Kim, Han Joon; Jeon, Woojin; Moon, Taehwan; Kim, Keum Do; Jeong, Doo Seok; Yamada, Hiroyuki; Hwang, Cheol Seong

    2016-01-08

    Enhancement of capacitance by negative capacitance (NC) effect in a dielectric/ferroelectric (DE/FE) stacked film is gaining a greater interest. While the previous theory on NC effect was based on the Landau-Ginzburg-Devonshire theory, this work adopted a modified formalism to incorporate the depolarization effect to describe the energy of the general DE/FE system. The model predicted that the SrTiO3/BaTiO3 system will show a capacitance boost effect. It was also predicted that the 5 nm-thick Al2O3/150 nm-thick BaTiO3 system shows the capacitance boost effect with no FE-like hysteresis behavior, which was inconsistent with the experimental results; the amorphous-Al2O3/epitaxial-BaTiO3 system showed a typical FE-like hysteresis loop in the polarization - voltage test. This was due to the involvement of the trapped charges at the DE/FE interface, originating from the very high field across the thin Al2O3 layer when the BaTiO3 layer played a role as the NC layer. Therefore, the NC effect in the Al2O3/BaTiO3 system was frustrated by the involvement of reversible interface charge; the highly stored charge by the NC effect of the BaTiO3 during the charging period could not be retrieved during the discharging process because integral part of the polarization charge was retained within the system as a remanent polarization.

  11. Electrical characteristics of SrTiO3/Al2O3 laminated film capacitors

    NASA Astrophysics Data System (ADS)

    Peng, Yong; Yao, Manwen; Chen, Jianwen; Xu, Kaien; Yao, Xi

    2016-07-01

    The electrical characteristics of SrTiO3/Al2O3 (160 nm up/90 nm down) laminated film capacitors using the sol-gel process have been investigated. SrTiO3 is a promising and extensively studied high-K dielectric material, but its leakage current property is poor. SrTiO3/Al2O3 laminated films can effectively suppress the demerits of pure SrTiO3 films under low electric field, but the leakage current value reaches to 0.1 A/cm2 at higher electric field (>160 MV/m). In this study, a new approach was applied to reduce the leakage current and improve the dielectric strength of SrTiO3/Al2O3 laminated films. Compared to laminated films with Au top electrodes, dielectric strength of laminated films with Al top electrodes improves from 205 MV/m to 322 MV/m, simultaneously the leakage current maintains the same order of magnitude (10-4 A/cm2) until the breakdown occurs. The above electrical characteristics are attributed to the anodic oxidation reaction in origin, which can repair the defects of laminated films at higher electric field. The anodic oxidation reactions have been confirmed by the corresponding XPS measurement and the cross sectional HRTEM analysis. This work provides a new approach to fabricate dielectrics with high dielectric strength and low leakage current.

  12. Al2O3 Nanoparticle Addition to Commercial Magnesium Alloys: Multiple Beneficial Effects

    PubMed Central

    Paramsothy, Muralidharan; Chan, Jimmy; Kwok, Richard; Gupta, Manoj

    2012-01-01

    The multiple beneficial effects of Al2O3 nanoparticle addition to cast magnesium based systems (followed by extrusion) were investigated, constituting either: (a) enhanced strength; or (b) simultaneously enhanced strength and ductility of the corresponding magnesium alloys. AZ31 and ZK60A nanocomposites containing Al2O3 nanoparticle reinforcement were each fabricated using solidification processing followed by hot extrusion. Compared to monolithic AZ31 (tension levels), the corresponding nanocomposite exhibited higher yield strength (0.2% tensile yield strength (TYS)), ultimate strength (UTS), failure strain and work of fracture (WOF) (+19%, +21%, +113% and +162%, respectively). Compared to monolithic AZ31 (compression levels), the corresponding nanocomposite exhibited higher yield strength (0.2% compressive yield strength (CYS)) and ultimate strength (UCS), lower failure strain and higher WOF (+5%, +5%, −4% and +11%, respectively). Compared to monolithic ZK60A (tension levels), the corresponding nanocomposite exhibited lower 0.2% TYS and higher UTS, failure strain and WOF (−4%, +13%, +170% and +200%, respectively). Compared to monolithic ZK60A (compression levels), the corresponding nanocomposite exhibited lower 0.2% CYS and higher UCS, failure strain and WOF (−10%, +7%, +15% and +26%, respectively). The capability of Al2O3 nanoparticles to enhance the properties of cast magnesium alloys in a way never seen before with micron length scale reinforcements is clearly demonstrated.

  13. Exploring metalorganic chemical vapor deposition of Si-alloyed Al2O3 dielectrics using disilane

    NASA Astrophysics Data System (ADS)

    Chan, Silvia H.; Keller, Stacia; Koksaldi, Onur S.; Gupta, Chirag; DenBaars, Steven P.; Mishra, Umesh K.

    2017-04-01

    The alloying of Al2O3 films with Si is a promising route to improve gate dielectric properties in Si- and wide-bandgap- based MOS devices. Here we present a comprehensive investigation of alloyed film growth by metalorganic chemical vapor deposition (MOCVD) using trimethylaluminum, disilane, and oxygen precursors over a variety of temperature and flow conditions. Binary growth rates of Al2O3 and SiO2 were evaluated to explain the aggregate growth kinetics of Si-alloyed Al2O3 films, and refractive indices were used to monitor Si incorporation efficiencies. The temperature dependence of the reaction rate of disilane with oxygen was found to be similar to that of trimethylaluminum and oxygen, leading to well-behaved deposition behavior in the kinetic and mass-transport controlled growth regimes. Compositional predictability and stability was achieved over a wider growth space with disilane-based growths as compared to previous work, which used silane as the Si precursor instead. In situ (Al,Si)O/n-GaN MOS gate stacks were grown and showed increasing reduction of net positive fixed charges with higher Si composition.

  14. Tribological Behavior of A356/Al2O3 Surface Nanocomposite Prepared by Friction Stir Processing

    NASA Astrophysics Data System (ADS)

    Mazaheri, Y.; Karimzadeh, F.; Enayati, M. H.

    2014-04-01

    Surface A356 aluminum alloy matrix composites containing micro and nanosized Al2O3 are prepared by a new approach utilizing high-velocity oxy-fuel spraying and friction stir processing (FSP). Optical and scanning electron microscopy, microhardness, and wear tests were used to characterize the surface composites. Results indicated that, the presence of Al2O3 in matrix can improve the mechanical properties of specimens. The microhardness of surface composites containing micro and nanosized Al2O3 were 89.8 ± 2.6 HV and 109.7 ± 2.5 HV, respectively, which were higher than those for the as-received (79.6 ± 1.1 HV) and the FSPed A356-T6 with no alumina powder (66.8 ± 0.9 HV). Surface composites revealed low friction coefficients and wear rates, which were significantly lower than those obtained for substrate. The wear mass losses of the as-received, the FSPed, and surface micro and nanocomposite specimens after 500-m sliding distance were 50.5, 55.6, 31, and 17.2 mg, respectively. Scanning electron microscopy tests revealed different wear mechanisms on the surface of the wear test specimens.

  15. Paramagnetic Spins on -Al2O3 with Varied Surface Termination

    NASA Astrophysics Data System (ADS)

    Ray, Keith; Lee, Donghwa; Adelstein, Nicole; Dubois, Jonathan; Lordi, Vincenzo

    Superconducting qubits (SQs) are promising building blocks for a quantum computer, however, coherence in SQs is reduced by unintended coupling to magnetic noise sources. The microscopic origins of the magnetic noise have not been satisfactorily characterized. Building on previous computational studies of magnetic spins induced by molecules adsorbed on bare Al terminated Al2O3, we present a density functional theory investigation of magnetic noise associated with other Al2O3 surfaces likely to be encountered in experiment. We calculate the exchange interaction between native defects and adsorbed molecules, as well as the magnetic states energy splitting and anisotropy, on fully hydroxylated Al2O3, with and without a water over-layer. We also present simulated x-ray adsorption and x-ray magnetic circular dichroism spectra of these systems with the aim of aiding experimental surface characterization. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344.

  16. Theoretical insight into Cobalt subnano-clusters adsorption on α-Al2O3 (0001)

    NASA Astrophysics Data System (ADS)

    Gao, Fen-e.; Ren, Jun; Wang, Qiang; Li, Debao; Hou, Bo; Jia, Litao; Cao, Duanlin

    2017-02-01

    The investigation on the structural stability, nucleation, growth and interaction of cobalt cluster Con(n=2-7) on the α-Al2O3(0001) surface by using density functional theory methods has been reported. Energetically, the most favorable adsorption sites were identified and the strongest adsorption energy cluster is the tetrahedral Co4 cluster. On the other hand, the nucleation of Con(n=2-7) clusters on the surface is exothermic and thermodynamically favorable. Moreover, even-odd alternation was found with respect to clusters nucleation as a function of the number of cobalt atoms (for n=1-7). Meanwhile, the Con clusters can be adsorbed on the surface stably owing to the charge transfer from Co atoms to Al and O atoms of the Al2O3 substrate. In addition, we establish the crucial importance of monomer, dimer and trimer diffusion on the surface. The diffusion of the monomer cobalt from Al(3) to O(5) or O(5) to Al(4) site is quite easy on the Al2O3(0001) surface, whereas the diffusion of the Co2 dimer is thermodynamically unfavorable by compared with that of the Co adatom and Co3 trimer.

  17. Effect of adsorbed films on friction of Al2O3-metal systems

    NASA Technical Reports Server (NTRS)

    Pepper, S. V.

    1976-01-01

    The kinetic friction of polycrystalline Al2O3 sliding on Cu, Ni, and Fe in ultrahigh vacuum was studied as a function of the surface chemistry of the metal. Clean metal surfaces were exposed to O2, Cl2, C2H4, and C2H3Cl, and the change in friction due to the adsorbed species was observed. Auger electron spectroscopy assessed the elemental composition of the metal surface. It was found that the systems exposed to Cl2 exhibited low friction, interpreted as the van der Waals force between the Al2O3 and metal chloride. The generation of metal oxide by oxygen exposures resulted in an increase in friction, interpreted as due to strong interfacial bonds established by reaction of metal oxide with Al2O3 to form the complex oxide (spinel). The only effect of C2H4 was to increase the friction of the Fe system, but C2H3Cl exposures decreases friction in both Ni and Fe systems, indicating the dominance of the chlorine over the ethylene complex on the surface

  18. Insight into the effects of different ageing protocols on Rh/Al2O3 catalyst

    NASA Astrophysics Data System (ADS)

    Zhao, Baohuai; Ran, Rui; Cao, Yidan; Wu, Xiaodong; Weng, Duan; Fan, Jun; Wu, Xueyuan

    2014-07-01

    In this work, a catalyst of Rh loaded on Al2O3 was prepared by impregnating method with rhodium nitrate aqueous solution as the Rh precursor. The catalyst was aged under different protocols (lean, rich, inert and cyclic) to obtain several aged samples. All the Rh/Al2O3 samples were characterized by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) method, CO-chemisorption, H2-temperature programmed reduction (H2-TPR), transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS). It was found that a specific ageing treatment could strongly affect the catalytic activity. The N2 aged and the H2 aged samples had a better catalytic activity for CO + NO reaction than the fresh sample while the air aged and the cyclic aged samples exhibited much worse activity. More surface Rh content and better reducibility were obtained in the N2 and the H2 aged samples and the Rh particles existed with an appropriate size, which were all favorable to the catalytic reaction. However, the air and the cyclic ageing protocols induced a strong interaction between Rh species and the Al2O3 support, which resulted in a severe sintering of particles of Rh species and the loss of active sites. The structure evolution scheme of the catalysts aged in different protocols was also established in this paper.

  19. Room Temperature Radiolytic Synthesized Cu@CuAlO2-Al2O3 Nanoparticles

    PubMed Central

    Abedini, Alam; Saion, Elias; Larki, Farhad; Zakaria, Azmi; Noroozi, Monir; Soltani, Nayereh

    2012-01-01

    Colloidal Cu@CuAlO2-Al2O3 bimetallic nanoparticles were prepared by a gamma irradiation method in an aqueous system in the presence of polyvinyl pyrrolidone (PVP) and isopropanol respectively as a colloidal stabilizer and scavenger of hydrogen and hydroxyl radicals. The gamma irradiation was carried out in a 60Co gamma source chamber with different doses up to 120 kGy. The formation of Cu@CuAlO2-Al2O3 nanoparticles was observed initially by the change in color of the colloidal samples from colorless to brown. Fourier transform infrared spectroscopy (FTIR) confirmed the presence of bonds between polymer chains and the metal surface at all radiation doses. Results of transmission electron microscopy (TEM), energy dispersive X-ray spectrometry (EDX), and X-ray diffraction (XRD) showed that Cu@CuAlO2-Al2O3 nanoparticles are in a core-shell structure. By controlling the absorbed dose and precursor concentration, nanoclusters with different particle sizes were obtained. The average particle diameter increased with increased precursor concentration and decreased with increased dose. This is due to the competition between nucleation, growth, and aggregation processes in the formation of nanoclusters during irradiation. PMID:23109893

  20. A short-time fading study of Al2O3:C

    NASA Astrophysics Data System (ADS)

    Nascimento, L. F.; Vanhavere, F.; Silva, E. H.; Deene, Y. De

    2015-01-01

    This paper studies the short-time fading from Al2O3:C by measuring optically stimulated luminescence (OSL) signals (Total OSL: TOSL, and Peak OSL: POSL) from droplets and Luxel™ pellets. The influence of various bleaching regimes (blue, green and white) and light power is compared. The fading effect is the decay of the OSL signal in the dark at room temperature. Al2O3:C detectors were submitted to various bleaching regimes, irradiated with a reference dose and read out after different time spans. Investigations were carried out using 2 mm size droplet detectors, made of thin Al2O3:C powder mixed with a photocured polymer. Tests were compared to Luxel™-type detectors (Landauer Inc.). Short-time post-irradiation fading is present in OSL results (TOSL and POSL) droplets for time spans up to 200 s. The effect of short-time fading can be lowered/removed when treating the detectors with high-power and/or long time bleaching regimes; this result was observed in both TOSL and POSL from droplets and Luxel™.

  1. Atomic layer deposition of Al2O3 on NF3-pre-treated graphene

    NASA Astrophysics Data System (ADS)

    Junige, Marcel; Oddoy, Tim; Yakimova, Rositsa; Darakchieva, Vanya; Wenger, Christian; Lupina, Grzegorz; Kitzmann, Julia; Albert, Matthias; Bartha, Johann W.

    2015-06-01

    Graphene has been considered for a variety of applications including novel nanoelectronic device concepts. However, the deposition of ultra-thin high-k dielectrics on top of graphene has still been challenging due to graphene's lack of dangling bonds. The formation of large islands and leaky films has been observed resulting from a much delayed growth initiation. In order to address this issue, we tested a pre-treatment with NF3 instead of XeF2 on CVD graphene as well as epitaxial graphene monolayers prior to the Atomic Layer Deposition (ALD) of Al2O3. All experiments were conducted in vacuo; i. e. the pristine graphene samples were exposed to NF3 in the same reactor immediately before applying 30 (TMA-H2O) ALD cycles and the samples were transferred between the ALD reactor and a surface analysis unit under high vacuum conditions. The ALD growth initiation was observed by in-situ real-time Spectroscopic Ellipsometry (irtSE) with a sampling rate above 1 Hz. The total amount of Al2O3 material deposited by the applied 30 ALD cycles was cross-checked by in-vacuo X-ray Photoelectron Spectroscopy (XPS). The Al2O3 morphology was determined by Atomic Force Microscopy (AFM). The presence of graphene and its defect status was examined by in-vacuo XPS and Raman Spectroscopy before and after the coating procedure, respectively.

  2. Simulation of pressure-induced phase transition in liquid and amorphous Al2 O3

    NASA Astrophysics Data System (ADS)

    Hoang, Vo Van; Oh, Suhk Kun

    2005-08-01

    We investigated the pressure-induced structural transformation in liquid and amorphous Al2O3 by the molecular dynamics (MD) method. Simulations were done in the basic cube under periodic boundary conditions containing 3000 ions with Born-Mayer type pair potentials. The structure of the amorphous Al2O3 model with real density at ambient pressure is in good agreement with Lamparter’s experiment. In order to study the amorphous-amorphous phase transition, 23 models of amorphous alumina at the temperature of 350K and at densities ranging from 2.83to5.0gcm-3 had been built. The microstructure of the Al2O3 systems had been analyzed through pair radial distribution functions, coordination number distributions, interatomic distances, and bond-angle distributions. Here we found clear evidence of a structural transition in amorphous alumina from a tetrahedral to an octahedral network upon compression. According to our results, this transformation occurred at densities ranging from 3.6to4.05gcm-3 . We also presented the amorphous-amorphous phase transition from an octahedral to a tetrahedral network structure upon decompression at densities ranging from 5.00to2.83gcm-3 . Also, the same study was carried out for the liquid state of the system at the temperature of 3500K , and the liquid-liquid phase transition had been discussed.

  3. Solid state reduction of chromium (VI) pollution for Al2O3-Cr metal ceramics application

    NASA Astrophysics Data System (ADS)

    Zhu, Hekai; Fang, Minghao; Huang, Zhaohui; Liu, Yangai; Tang, Hao; Min, Xin; Wu, Xiaowen

    2016-04-01

    Reduction of chromium (VI) from Na2CrO4 through aluminothermic reaction and fabrication of metal-ceramic materials from the reduction products have been investigated in this study. Na2CrO4 could be successfully reduced into micrometer-sized Cr particles in a flowing Ar atmosphere in presence of Al powder. The conversion ratio of Na2CrO4 to metallic Cr attained 96.16% efficiency. Al2O3-Cr metal-ceramic with different Cr content (5 wt%, 10 wt%, 15 wt%, 20 wt%) were further prepared from the reduction product Al2O3-Cr composite powder, and aluminum oxide nanopowder via pressure-less sintering. The phase composition, microstructure and mechanical properties of metal-ceramic composites were characterized to ensure the potential of the Al2O3-Cr composite powder to form ceramic materials. The highest relative density and bending strength can reach 93.4% and 205 MP, respectively. The results indicated that aluminothermic reduction of chromium (VI) for metal-ceramics application is a potential approach to remove chromium (VI) pollutant from the environment.

  4. Impact of Al2O3 on the aggregation and deposition of graphene oxide.

    PubMed

    Ren, Xuemei; Li, Jiaxing; Tan, Xiaoli; Shi, Weiqun; Chen, Changlun; Shao, Dadong; Wen, Tao; Wang, Longfei; Zhao, Guixia; Sheng, Guoping; Wang, Xiangke

    2014-05-20

    To assess the environmental behavior and impact of graphene oxide (GO) on living organisms more accurately, the aggregation of GO and its deposition on Al2O3 particles were systematically investigated using batch experiments across a wide range of solution chemistries. The results indicated that the aggregation of GO and its deposition on Al2O3 depended on the solution pH and the types and concentrations of electrolytes. MgCl2 and CaCl2 destabilized GO because of their effective charge screening and neutralization, and the presence of NaH2PO4 and poly(acrylic acid) (PAA) improved the stability of GO with the increase in pH values as a result of electrostatic interactions and steric repulsion. Specifically, the dissolution of Al2O3 contributed to GO aggregation at relatively low pH or high pH values. Results from this study provide critical information for predicting the fate of GO in aquatic-terrestrial transition zones, where aluminum (hydro)oxides are present.

  5. Thermodynamic simulation on mineralogical composition of CaO-SiO2-Al2O3-MgO quaternary slag system.

    PubMed

    Liu, Chao; Zhang, Yu-Zhu; Li, Jie; Li, Jun-Guo; Kang, Yue

    2016-01-01

    It is necessary to elucidate the crystallization thermodynamic of mineralogical phases during the cooling process of the molten BFS with different chemical composition, because the high-melting point mineral phase maybe crystallized during the fiber forming and thereafter cooling process. Thermodynamic calculation software FactSage6.4 and the hot remelting experiments were performed to explore the influence of basicity, Al2O3 content and MgO content on the crystallization of mineralogical components and their transformation. The results showed that the main mineralography of the CaO-SiO2-Al2O3-MgO quaternary slag system was melilite, and a certain amount of anorthite and calcium metasilicate. The crystallographic temperature of melilite is increased with the increasing of basicity, MgO and Al2O3 content, which has a significant impact on the utilization performance of the mineral wool prepared with the hot blast furnace slag directly. With the increasing of basicity, there was a tendency that crystallographic amount of melilite increased to the summit and then declined, while the amount of anorthite and calcium metasilicate decreased consistently. Finally, these two mineralogical components could be replaced by magnesium rhodonite and spinel with the increasing of basicity. When the basicity and MgO content were 1.0 and 9 %, the crystallographic mass ratio of melilite and anorthite increased, while that of calcium silicate declined, and replaced by spinel finally with the increasing of Al2O3 content. When the basicity and Al2O3 content were 1.0 and 13 %, the crystallographic mass ratio of melilite increased, while that of anorthite and calcium silicate declined, and replaced by pyroxene and spinel with the increasing of MgO content. To decline fiberization temperature of the melt BFS, the basicity, MgO and Al2O3 content should be decreased during the modification process of chemical composition, because the crystallization temperature of the primary crystalline

  6. Optically stimulated luminescence (OSL) response of Al2O3:C, BaFCl:Eu and K2Ca2(SO4)3:Eu phosphors.

    PubMed

    Kumar, Pratik; Bahl, Shaila; Sahare, P D; Kumar, Surender; Singh, Manveer

    2015-12-01

    This paper investigates the optically stimulated luminescence (OSL) response of BaFCl:Eu and K2Ca2(SO4)3:Eu phosphors for different doses and bleaching durations. The results have also been compared with the commercially available Landauer Al2O3:C (Luxel®) dosemeter. Nanocrystalline K2Ca2(SO4)3:Eu is known to be a sensitive thermoluminescent phosphor, but its OSL response is hardly reported. At first, pellets of nanocrystalline K2Ca2(SO4)3:Eu powder were prepared by adding Teflon as a binder. Their OSL signal was compared with that of the material in pure form, i.e. without adding the binder (in 100:1 ratio). It was observed that adding the binder does not appreciably affect the OSL intensity. On comparison with the commercially available Al2O3:C from Landauer, it was found that K2Ca2(SO4)3:Eu is around 15 times less sensitive than Al2O3:C. 'Homemade' BaFCl:Eu phosphor has also been studied. The intensity of BaFCl:Eu was ∼20 times more than the standard Al2O3:C dosemeter and ∼200 times more sensitive than K2Ca2(SO4)3:Eu in the dose range of 13-200 cGy. OSL dosemeters are believed to give luminescence signal even if they are read before, i.e. multiple reading may be possible under suitable conditions after single exposure. This was also checked for all the prepared dosemeters and it was found that Al2O3:C showed the least decrease of <2 %, followed by BaFCl:Eu of 15 % and K2Ca2(SO4)3:Eu with 20 %. Finally, Al2O3:C and BaFCl:Eu phosphors were also studied for their optical bleaching durations to which the respective signals get completely removed so that the phosphor can be re-used. It was observed that BaFCl:Eu is bleached faster and more easily than Al2O3:C.

  7. Microstructure and High-Temperature Mechanical Properties of ZrO2-Al2O3-SiC Ceramics

    NASA Astrophysics Data System (ADS)

    Zhang, Xiu-Ping; Ouyang, Jia-Hu; Wang, Yu-Jin; Liu, Zhan-Guo; Wang, Ya-Ming

    2015-09-01

    In the present work, ZrO2-Al2O3 ceramics incorporated with and without β-SiC were prepared by hot pressing. ZrO2-Al2O3 ceramic powder used in this study is a mixture of 71 vol.% YSZ (3 mol.% Y2O3 partially stabilized zirconia) and 29 vol.% α-Al2O3. β-SiC powders with different volume fractions are added into the ZrO2-Al2O3 powder to form the composite powder. The microstructure and high-temperature mechanical properties of ZrO2-Al2O3-SiC ceramics were investigated by tailoring the compositions and sintering parameters to optimize the strengthening mechanisms. For a comparative study, the TZ3Y20A powder was also hot-pressed under identical sintering condition to form dense bulk ceramic. ZrO2-Al2O3-SiC ceramics consist mainly of t-ZrO2, α-Al2O3, and β-SiC phases. SiC particles in the ZrO2-Al2O3 ceramic restrain the grain growth of the oxide matrix. The incorporation of SiC into ZrO2-Al2O3 ceramic enhances high-temperature flexural strength at 1273 K. ZrO2-Al2O3 ceramic incorporated with 15 vol.% SiC has a flexural strength of 518 MPa at 1273 K, much higher than that (201 MPa) of unmodified ZrO2-Al2O3 ceramic.

  8. Hydrogen defects in α-Al2O3 and water weakening of sapphire and alumina ceramics between 600°C and 1000°C: II. Mechanical properties

    USGS Publications Warehouse

    Castaing, J.; Kronenberg, A.K.; Kirby, S.H.; Mitchell, T.E.

    2000-01-01

    Hydrogen impurities in alumina have been introduced by hydrothermal annealing (see part I). In this paper, we report on reductions in the flow strength of α-Al2O3 single crystals and polycrystals associated with hydrogen incorporation. Prior to deformation, α-Al2O3 single crystal and ceramic specimens were annealed in the presence of supercritical water at 850° or 900°C, under 1500 MPa pressure. Sapphire and alumina ceramics were plastically deformed between 600° and 1000°C under 1500 MPa pressure, by the addition of a uniaxial stress. Flow stresses are reduced by a factor of two, due to the presence of water, for sapphire and large grain (30–50 μm) polycrystals, as a result of enhanced dislocation mobility. Flow stresses of fine-grained (3–5 μm) polycrystals are reduced by water by a factor of six. This large reduction in strength is attributed to a change in mechanism from dislocation glide under dry conditions to grain boundary sliding under hydrothermal conditions.

  9. A nanoplate-like α-Al2O3 out-layered Al2O3-ZrO2 coating fabricated by micro-arc oxidation for hip joint prosthesis

    NASA Astrophysics Data System (ADS)

    Zhang, Lan; Zhang, Wenting; Han, Yong; Tang, Wu

    2016-01-01

    A nanoplate-like α-Al2O3 out-layered Al2O3-ZrO2 coating was fabricated on Zr substrate by micro-arc oxidation (MAO). The structure, formation mechanism, anti-wear property and aging behavior of the coating were explored. The obtained results show that the coating is composed of Al2O3 and ZrO2; the amount and crystallinity of Al2O3 increase gradually from inner layer to the coating surface; monoclinic ZrO2 (m-ZrO2) and tetragonal ZrO2 (t-ZrO2) are both present in the coating, and the ratio of t-ZrO2/m-ZrO2 increases with closing to the coating surface by a "constraint" mechanism of Al2O3; the coating surface mainly consists of nanoplate-like α-Al2O3, and a small amount of nanocrystallized m- and t-ZrO2. The superimposition of α-Al2O3 growth unit on {0 0 0 1} face should be prohibited by PO43- during the MAO process, resulting in the formation of nanoplate-like α-Al2O3 on the coating surface. Compared with pure Zr, the coating shows noticeable improvement in wear-resistance. For aging behavior, although more t-ZrO2 in the coating is transformed to m-ZrO2 with increasing aging time, wear loss increases slightly. It indicates that the nanoplate-like α-Al2O3 out-layered Al2O3-ZrO2 is a potential coating for articular head replacement.

  10. Generation of 13-fs pulses from a mode-locked Ti:Al2O3 laser with reduced third-order dispersion

    NASA Astrophysics Data System (ADS)

    Proctor, Bob; Wise, Frank

    1993-02-01

    The third-order dispersion of a mode-locked Ti:Al2O3 laser has been reduced by replacing a pair of flint glass prisms with a sequence of four quartz prisms. This allows transform-limited 13-fs pulses to be generated with a gain crystal 20 mm long. To date, these are the shortest pulses generated directly from a laser.

  11. Structure, optical properties and thermal stability of Al2O3-WC nanocomposite ceramic spectrally selective solar absorbers

    NASA Astrophysics Data System (ADS)

    Gao, Xiang-Hu; Wang, Cheng-Bing; Guo, Zhi-Ming; Geng, Qing-Fen; Theiss, Wolfgang; Liu, Gang

    2016-08-01

    Traditional metal-dielectric composite coating has found important application in spectrally selective solar absorbers. However, fine metal particles can easily diffuse, congregate, or be oxidized at high temperature, which causes deterioration in the optical properties. In this work, we report a new spectrally selective solar absorber coating, composed of low Al2O3 ceramic volume fraction (Al2O3(L)-WC) layer, high Al2O3 ceramic volume fraction (Al2O3(H)-WC layer) and Al2O3 antireflection layer. The features of our work are: 1) compared with the metal-dielectric composites concept, Al2O3-WC nanocomposite ceramic successfully achieves the all-ceramic concept, which exhibits a high solar absorptance of 0.94 and a low thermal emittance of 0.08, 2) Al2O3 and WC act as filler material and host material, respectively, which are different from traditional concept, 3) Al2O3-WC nanocomposite ceramic solar absorber coating exhibits good thermal stability at 600 °C. In addition, the solar absorber coating is successfully modelled by a commercial optical simulation programme, the result of which agrees with the experimental results.

  12. Electrochemical synthesis of polypyrrole-Al2O3 composite coating on 316 stainless steel for corrosion protection

    NASA Astrophysics Data System (ADS)

    Yan, Qun; Li, Chuanxian; Huang, Tingting; Yang, Fei

    2017-03-01

    Polypyrrole (PPy)-Al2O3 composite coating was electrochemically deposited on 316 stainless steel (316 SS) by cyclic voltammetry technique. Scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR) were employed to understand the morphology and composition of the PPy-Al2O3 coated SS. The corrosion protection ability of the PPy-Al2O3 coating was studied using open circuit potential (Eocp)-time measurements, polarization curves, and electrochemical impedance spectroscopy (EIS) after the electrodes had been immersed in a 3.5 wt% NaCl solution as the corrosive media. The results showed that PPy-Al2O3 composite coatings have a homogeneous and smooth surface without detectable cracks. Anodic polarization analysis revealed that the hybrid films provided an exceptional barrier and corrosion protection in comparison with PPy coating. The EIS studies indicated that the charge transfer resistance increases with the presence of PPy-Al2O3. PPy-Al2O3 composite coating provides better corrosion protection and can be considered as a coating material to protect 316SS. With increase in Al2O3/Py mole ratio, PPy-Al2O3 coatings tend to exhibit a better corrosion resistance ability.

  13. Characterization of Al2O3 in High-Strength Mo Alloy Sheets by High-Resolution Transmission Electron Microscopy.

    PubMed

    Zhou, Yucheng; Gao, Yimin; Wei, Shizhong; Hu, Yajie

    2016-02-01

    A novel type of alumina (Al2O3)-doped molybdenum (Mo) alloy sheet was prepared by a hydrothermal method and a subsequent powder metallurgy process. Then the characterization of α-Al2O3 was investigated using high-resolution transmission electron microscopy as the research focus. The tensile strength of the Al2O3-doped Mo sheet is 43-85% higher than that of the pure Mo sheet, a very obvious reinforcement effect. The sub-micron and nanometer-scale Al2O3 particles can increase the recrystallization temperature by hindering grain boundary migration and improve the tensile strength by effectively blocking the motion of the dislocations. The Al2O3 particles have a good bond with the Mo matrix and there exists an amorphous transition layer at the interface between Al2O3 particles and the Mo matrix in the as-rolled sheet. The sub-structure of α-Al2O3 is characterized by a number of nanograins in the $\\left[ {2\\bar{2}1} \\right]$ direction. Lastly, a new computer-based method for indexing diffraction patterns of the hexagonal system is introduced, with 16 types of diffraction patterns of α-Al2O3 indexed.

  14. NMR Spectroscopy of the Hydrated Layer of Composite Particles Based on Nanosized Al2O3 and Vitreous Humor

    NASA Astrophysics Data System (ADS)

    Turov, V. V.; Gerashchenko, I. I.; Markina, A. I.

    2013-11-01

    The hydrated layer of composite particles prepared using Al2O3 and cattle vitreous humor was investigated using NMR spectroscopy. It was found that water bound to Al2O3 nanoparticles was present in the form of clusters with different degrees of association and energies of interaction with the surface. Water bound to the surface of the Al2O3/vitreous humor composite became more uniform upon immobilization of vitreous humor components on the surface of the Al2O3. With this, the clusters of adsorbed water had characteristics that were close to those found in air and weakly polar CHCl3 media. Addition of polar CH3CN led to the formation of very small water clusters. PMR spectra of the surface of the Al2O3/vitreous humor composite in the presence of trifluoroacetic acid differentiated four types of hydrated structures that differed in the degree of water association.

  15. Au/n-InP Schottky diodes using an Al2O3 interfacial layer grown by atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Kim, Hogyoung; Kim, Min Soo; Yoon, Seung Yu; Choi, Byung Joon

    2017-02-01

    We investigated the effect of an Al2O3 interfacial layer grown by atomic layer deposition on the electrical properties of Au Schottky contacts to n-type InP. Considering barrier inhomogeneity, modified Richardson plots yielded a Richardson constant of 8.4 and 7.5 Acm-2K-2, respectively, for the sample with and without the Al2O3 interlayer (theoretical value of 9.4 Acm-2K-2 for n-type InP). The dominant reverse current flow for the sample with an Al2O3 interlayer was found to be Poole-Frenkel emission. From capacitance-voltage measurements, it was observed that the capacitance for the sample without the Al2O3 interlayer was frequency dependent. Sputter-induced defects as well as structural defects were passivated effectively with an Al2O3 interlayer.

  16. Behavior of Al2O3 and SiO2 with heating in a Cl2 + CO stream

    NASA Technical Reports Server (NTRS)

    Shchetinin, L. K.

    1984-01-01

    Differential thermal analysis (DTA) and Thermogravimetric analysis (TGA) were used to study the chlorination of alpha-Al2O3, gamma-Al2O3 and amorphous SiO2 in a Cl + CO stream, for the preparation of AlCl3 and SiCl4. The chlorination starting temperatures were 235 deg for Al2O3 and 680 deg for SiO2. The chlorination of alpha- and gamma-Al2O3 takes place via the formation of AlOCl as an intermediate product, and its subsequent dissociation at 480 to 560 deg, according to 3AlOCl yields AlCl3 + Al2O3. The chlorination activation energies are given for the three oxides.

  17. Structural properties of Y2O3–Al2O3 liquids and glasses: An overview

    SciTech Connect

    Wilding, Martin C.; Wilson, Mark; McMillan, Paul F.; Benmore, Chris J.; Weber, J. K.R.; Deschamps, Thierry; Champagnon, Bernard

    2015-01-01

    Liquids in the system Y2O3- Al2O3 have been the subject of considerable study because of the reported occurrence of a first-order density and entropy-driven liquid-liquid phase transition (LLPT) in the supercooled liquid state. The observations have become controversial because of the presence of crystalline material that can be formed simultaneously and that can mask the nucleation and growth of the lower density liquid. The previous work is summarized here along with arguments for and against the different viewpoints. Also two studies have been undertaken to investigate the LLPT in this refractory system with emphasis on determining the structure of unequivocally amorphous materials. These include the in situ high energy X-ray diffraction (HEXRD) of supercooled Y2O3 - Al2O3 liquids and the low frequency vibrational dynamics of recovered glasses. Manybody molecular dynamics simulations are also used to interpret the results of both studies. The HEXRD measurements, combined with aerodynamic levitation and rapid data acquisition techniques, show that for the 20 mol% Y2O3 (i.e. AlY20) liquid there is a shift in the position of the first peak in the diffraction pattern over a narrow temperature range (2100-1800 K) prior to crystallization. Microbeam Raman spectroscopy measurements made on AlY20 glasses clearly show contrasting spectra in the low frequency part of the spectrum for low(LDA) and high-density (HDA) glassy regions. The molecular dynamics simulations identify contrasting coordination environments around oxygen anions for the high- (HDL) and low-density (LDL) liquids. (C) 2014 Elsevier B.V. All rights reserved.

  18. Time/Temperature Dependent Tensile Strength of SiC and Al2O3-Based Fibers

    NASA Technical Reports Server (NTRS)

    Yun, Hee Mann; DiCarlo, James A.

    1997-01-01

    In order to understand and model the thermomechanical behavior of fiber-reinforced composites, stress-rupture, fast-fracture, and warm-up rupture studies were conducted on various advanced SiC and Al2O3-based fibers in the,temperature range from 20 to 1400 C in air as well as in inert environments. The measured stress-rupture, fast fracture, and warm-up rupture strengths were correlated into a single master time/temperature-dependent strength plot for each fiber type using thermal activation and slow crack growth theories. It is shown that these plots are useful for comparing and selecting fibers for CMC and MMC reinforcement and that, in comparison to stress rupture tests, the fast-fracture and warm-up tests can be used for rapid generation of these plots.

  19. Aggregation and Colloidal Stability of Commercially Available Al2O3 Nanoparticles in Aqueous Environments

    PubMed Central

    Mui, Julie; Ngo, Jennifer; Kim, Bojeong

    2016-01-01

    The aggregation and colloidal stability of three, commercially-available, gamma-aluminum oxide nanoparticles (γ-Al2O3 NPs) (nominally 5, 10, and 20–30 nm) were systematically examined as a function of pH, ionic strength, humic acid (HA) or clay minerals (e.g., montmorillonite) concentration using dynamic light scattering and transmission electron microscopy techniques. NPs possess pH-dependent surface charges, with a point of zero charge (PZC) of pH 7.5 to 8. When pH < PZC, γ-Al2O3 NPs are colloidally stable up to 100 mM NaCl and 30 mM CaCl2. However, significant aggregation of NPs is pronounced in both electrolytes at high ionic strength. In mixed systems, both HA and montmorillonite enhance NP colloidal stability through electrostatic interactions and steric hindrance when pH ≤ PZC, whereas their surface interactions are quite limited when pH > PZC. Even when pH approximates PZC, NPs became stable at a HA concentration of 1 mg·L−1. The magnitude of interactions and dominant sites of interaction (basal planes versus edge sites) are significantly dependent on pH because both NPs and montmorillonite have pH-dependent (conditional) surface charges. Thus, solution pH, ionic strength, and the presence of natural colloids greatly modify the surface conditions of commercial γ-Al2O3 NPs, affecting aggregation and colloidal stability significantly in the aqueous environment. PMID:28335218

  20. Sulfation and Desulfation Behavior of Pt-BaO/MgO-Al2O3 NOx Storage Reduction Catalyst.

    PubMed

    Jeong, Soyeon; Kim, Do Heui

    2016-05-01

    The comparative study between Pt-BaO/Al2O3 and Pt-BaO/MgO-Al2O3 gives the information about the effect of MgO addition to Al2O3 support on the sulfation and desulfation behavior of Pt-BaO/MgO-Al2O3 NOx storage reduction catalyst. The sulfated two samples were analyzed by using element analysis (EA), X-ray diffraction (XRD), H2 temperature programmed reaction (H2 TPRX) and NOx uptake measurement. The amount of sulfur uptake on 2 wt% Pt-20 wt% BaO/Al2O3 and 2 wt% Pt-20 wt% BaO/MgO-Al2O3 are almost identical as 0.45 and 0.40 of S/Ba, respectively, which yields the drastic decrease in NOx uptake for both sulfated samples. However, after desulfa- tion with H2 at 600 degrees C, the residual sulfur amount on MgO-Al2O3 supported catalyst is three times larger than that on Al2O3 supported one, indicating that sulfur species formed on the former are more stable than those on the latter. It is also well corresponding to the H2 TPRX results where the main H2S peak from MgO-Al2O3 supported sample is observed at higher temperature than Al2O3 supported one, resulting in the lower NOx uptake activity of former sample than the latter one. Meanwhile, after desulfation of MgO-Al2O3 supported sample at 700 degrees C and 800 degrees C, the activity is recovered more significantly due to the removal of the large amount of sulfur while Al2O3 supported one decreases monotonically due to the sintering of Pt crystallite and the formation of BaAl2O4 phase. It is summarized that MgO-Al2O3 supported catalyst enhances the thermal stability of the catalyst, however, forms the stable sulfate species, which needs to be improved to develop the more sulfur resistant NSR catalyst system.

  1. Ultrasonic Al2O3 Ceramic Thermometry in High-Temperature Oxidation Environment

    PubMed Central

    Wei, Yanlong; Gao, Yubin; Xiao, Zhaoqian; Wang, Gao; Tian, Miao; Liang, Haijian

    2016-01-01

    In this study, an ultrasonic temperature measurement system was designed with Al2O3 high-temperature ceramic as an acoustic waveguide sensor and preliminarily tested in a high-temperature oxidation environment. The test results indicated that the system can indeed work stably in high-temperature environments. The relationship between the temperature and delay time of 26 °C–1600 °C ceramic materials was also determined in order to fully elucidate the high-temperature oxidation of the proposed waveguide sensor and to lay a foundation for the further application of this system in temperatures as high as 2000 °C. PMID:27845726

  2. Superconductivity of Al/Al2O3 interface formed by shock-wave pressure

    NASA Astrophysics Data System (ADS)

    Palnichenko, A. V.; Shakhrai, D. V.; Avdonin, V. V.; Vyaselev, O. M.; Khasanov, S. S.

    2015-05-01

    A mixture of Al and α -Al2O3 has been subjected to a shock-wave pressure of ≃ 170 kbar, followed by vacuum-encapsulating and quenching of the product to liquid nitrogen. The ac magnetic susceptibility measurements of the samples have revealed metastable superconductivity with Tc ≈ 37 K, characterized by glassy dynamics of the shielding currents below Tc . Comparison of the ac susceptibility and the dc magnetization measurements infers that the superconductivity arises within the interfacial granular layer formed between metallic Al and its oxide due to the shock-wave treatment.

  3. Hydrogen and Carbon Effects on Al2O3 Surface Phases and Metal Deposition

    NASA Astrophysics Data System (ADS)

    Wang, Xiao-Gang; Smith, John

    2005-03-01

    Effects of H and C impurities on α-Al2O3 (0001) surface stability and metal wetting behavior are determined from first principles[1]. The ab initio surface phase diagram for H and C on the alumina surface reveals six distinct surface phases. These different surface phases exhibit a variety of adhesion strengths with Cu and Co, and correspondingly different wetting behaviors. These results are consistent with the varied wetting characteristics observed experimentally. [1] Xiao-Gang Wang and John R. Smith, Phys. Rev. B70, Rapid communications, 081401 (2004).

  4. Superconductivity of Al/Al2O3 interface formed under shock-wave conditions

    NASA Astrophysics Data System (ADS)

    Shakhray, D. V.; Avdonin, V. V.; Palnichenko, A. V.; Vyaselev, O. M.

    2015-11-01

    A mixture of powdered Al and Al2O3 has been subjected to a shock-wave pressure of ≈ 170 kbar, followed by vacuum-encapsulating and quenching of the product to liquid nitrogen. The ac magnetic susceptibility measurements of the samples have revealed metastable superconductivity with Tc ≈ 37 K, characterized by glassy dynamics of the shielding currents below Tc. Comparison of the ac susceptibility and the dc magnetization measurements infers that the superconductivity arises within the interfacial granular layer formed between metallic Al and its oxide due to the shock-wave treatment.

  5. Understanding the clean interface between covalent Si and ionic Al2O3.

    PubMed

    Xiang, H J; Da Silva, Juarez L F; Branz, Howard M; Wei, Su-Huai

    2009-09-11

    The atomic and electronic structures of the (001)-Si/(001)-gamma-Al(2)O(3) heterointerface are investigated by first principles total energy calculations combined with a newly developed "modified basin-hopping" method. It is found that all interface Si atoms are fourfold coordinated due to the formation of Si-O and unexpected covalent Si-Al bonds in the new abrupt interface model. And the interface has perfect electronic properties in that the unpassivated interface has a large LDA band gap and no gap levels. These results show that it is possible to have clean semiconductor-oxide interfaces.

  6. Viscosity affected by nanoparticle aggregation in Al2O3-water nanofluids.

    PubMed

    Duan, Fei; Kwek, Dingtian; Crivoi, Alexandru

    2011-03-22

    An investigation on viscosity was conducted 2 weeks after the Al2O3-water nanofluids having dispersants were prepared at the volume concentration of 1-5%. The shear stress was observed with a non-Newtonian behavior. On further ultrasonic agitation treatment, the nanofluids resumed as a Newtonian fluids. The relative viscosity increases as the volume concentrations increases. At 5% volume concentration, an increment was about 60% in the re-ultrasonication nanofluids in comparison with the base fluid. The microstructure analysis indicates that a higher nanoparticle aggregation had been observed in the nanofluids before re-ultrasonication.

  7. Head-up display using an inclined Al2O3 column array.

    PubMed

    Cho, Wen-Hao; Lee, Chao-Te; Kei, Chi-Chung; Liao, Bo-Huei; Chiang, Donyau; Lee, Cheng-Chung

    2014-02-01

    An orderly inclined Al2O3 column array was fabricated by atomic layer deposition and sequential electron beam evaporation using a hollow nanosphere template. The transmittance spectra at various angles of incidence were obtained through the use of a Perkin-Elmer Lambda 900 UV/VIS/NIR spectrometer. The inclined column array could display the image information through a scattering mechanism and was transparent at high viewing angles along the deposition plane. This characteristic of the inclined column array gives it potential for applications in head-up displays in the automotive industry.

  8. Ultra-low thermal conductivity in W/Al2O3 nanolaminates.

    PubMed

    Costescu, R M; Cahill, D G; Fabreguette, F H; Sechrist, Z A; George, S M

    2004-02-13

    Atomic layer deposition and magnetron sputter deposition were used to synthesize thin-film multilayers of W/Al(2)O(3). With individual layers only a few nanometers thick, the high interface density produced a strong impediment to heat transfer, giving rise to a thermal conductivity of approximately 0.6 watts per meter per kelvin. This result suggests that high densities of interfaces between dissimilar materials may provide a route for the production of thermal barriers with ultra-low thermal conductivity.

  9. Nitridation of Al2O3 surfaces: chemical and structural change triggered by oxygen desorption.

    PubMed

    Akiyama, Toru; Saito, Yasutaka; Nakamura, Kohji; Ito, Tomonori

    2013-01-11

    We present theoretical investigations that clarify elemental nitridation processes of corundum Al2O3(0001) and (1102) surfaces. The calculations within the density functional theory framework reveal that the structures with substitutional N atoms beneath the surface are stabilized under nitridation conditions. We also find that the desorption of O atoms at the topmost layer induces outward diffusion of O atoms as well as inward diffusion of N atoms, leading to the transformation into AlN films. The kinetic Monte Carlo simulations in conjunction with density functional theory results indeed observe a dependence of these chemical and structural changes on temperature and pressure.

  10. Influences of annealing on structural and compositional properties of Al2O3 thin films grown on 4H-SiC by atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Tian, Li-Xin; Zhang, Feng; Shen, Zhan-Wei; Yan, Guo-Guo; Liu, Xing-Fang; Zhao, Wan-Shun; Wang, Lei; Sun, Guo-Sheng; Zeng, Yi-Ping

    2016-12-01

    Annealing effects on structural and compositional performances of Al2O3 thin films on 4H-SiC substrates are studied comprehensively. The Al2O3 films are grown by atomic layer deposition through using trimethylaluminum and H2O as precursors at 300 °C, and annealed at various temperatures in ambient N2 for 1 min. The Al2O3 film transits from amorphous phase to crystalline phase as annealing temperature increases from 750 °C to 768 °C. The refractive index increases with annealing temperature rising, which indicates that densification occurs during annealing. The densification and grain formation of the film upon annealing are due to crystallization which is relative with second-nearest-neighbor coordination variation according to the x-ray photoelectron spectroscopy (XPS). Although the binding energies of Al 2p and O 1s increase together during crystallization, separations between Al 2p and O 1s are identical between as-deposited and annealed sample, which suggests that the nearest-neighbour coordination is similar. Project supported by the National Basic Research Program of China (Grant No. 2015CB759600), the National Natural Science Foundation of China (Grant Nos. 61474113, 61574140, and 61274007), and the Beijing Nova Program, China (Grant No. xx2016071), and the CAEP Microsystem and THz Science and Technology Foundation (Grant No. CAEPMT201502).

  11. Anisotropic temperature-dependent thermal conductivity by an Al2O3 interlayer in Al2O3/ZnO superlattice films

    NASA Astrophysics Data System (ADS)

    Lee, Won-Yong; Lee, Jung-Hoon; Ahn, Jae-Young; Park, Tae-Hyun; Park, No-Won; Kim, Gil-Sung; Park, Jin-Seong; Lee, Sang-Kwon

    2017-03-01

    The thermal conductivity of superlattice films is generally anisotropic and should be studied separately in the in-plane and cross-plane directions of the films. However, previous works have mostly focused on the cross-plane thermal conductivity because the electrons and phonons in the cross-plane direction of superlattice films may result in much stronger interface scattering than that in the in-plane direction. Nevertheless, it is highly desirable to perform systematic studies on the effect of interface formation in semiconducting superlattice films on both in-plane and cross-plane thermal conductivities. In this study, we determine both the in-plane and cross-plane thermal conductivities of Al2O3 (AO)/ZnO superlattice films grown by atomic layer deposition (ALD) on SiO2/Si substrates in the temperature range of 50–300 K by the four-point-probe 3-ω method. Our experimental results indicate that the formation of an atomic AO layer (0.82 nm) significantly contributes to the decrease of the cross-plane thermal conductivity of the AO/ZnO superlattice films compared with that of AO/ZnO thin films. The cross-plane thermal conductivity (0.26–0.63 W m‑1 K‑1 of the AO/ZnO superlattice films (with an AO layer of ∼0.82 nm thickness) is approximately ∼150%–370% less than the in-plane thermal conductivity (0.96–1.19 W m‑1 K‑1) of the corresponding film, implying significant anisotropy. This indicates that the suppression of the cross-plane thermal conductivity is mainly attributed to the superlattice, rather than the nanograin columnar structure in the films. In addition, we theoretically analyzed strong anisotropic behavior of the in-plane and cross-plane thermal conductivities of the AO/ZnO superlattice films in terms of temperature dependence.

  12. Anisotropic temperature-dependent thermal conductivity by an Al2O3 interlayer in Al2O3/ZnO superlattice films.

    PubMed

    Lee, Won-Yong; Lee, Jung-Hoon; Ahn, Jae-Young; Park, Tae-Hyun; Park, No-Won; Kim, Gil-Sung; Park, Jin-Seong; Lee, Sang-Kwon

    2017-03-10

    The thermal conductivity of superlattice films is generally anisotropic and should be studied separately in the in-plane and cross-plane directions of the films. However, previous works have mostly focused on the cross-plane thermal conductivity because the electrons and phonons in the cross-plane direction of superlattice films may result in much stronger interface scattering than that in the in-plane direction. Nevertheless, it is highly desirable to perform systematic studies on the effect of interface formation in semiconducting superlattice films on both in-plane and cross-plane thermal conductivities. In this study, we determine both the in-plane and cross-plane thermal conductivities of Al2O3 (AO)/ZnO superlattice films grown by atomic layer deposition (ALD) on SiO2/Si substrates in the temperature range of 50-300 K by the four-point-probe 3-ω method. Our experimental results indicate that the formation of an atomic AO layer (0.82 nm) significantly contributes to the decrease of the cross-plane thermal conductivity of the AO/ZnO superlattice films compared with that of AO/ZnO thin films. The cross-plane thermal conductivity (0.26-0.63 W m(-1) K(-1) of the AO/ZnO superlattice films (with an AO layer of ∼0.82 nm thickness) is approximately ∼150%-370% less than the in-plane thermal conductivity (0.96-1.19 W m(-1) K(-1)) of the corresponding film, implying significant anisotropy. This indicates that the suppression of the cross-plane thermal conductivity is mainly attributed to the superlattice, rather than the nanograin columnar structure in the films. In addition, we theoretically analyzed strong anisotropic behavior of the in-plane and cross-plane thermal conductivities of the AO/ZnO superlattice films in terms of temperature dependence.

  13. Characteristics of nanocomposite ZrO2/Al2O3 films deposited by plasma-enhanced atomic layer deposition.

    PubMed

    Yun, Sun Jin; Lim, Jung Wook; Kim, Hyun-Tak

    2007-11-01

    Nanocomposite ZrO2/Al2O3 (ZAO) films were deposited on Si by plasma-enhanced atomic layer deposition and the film characteristics including interfacial oxide formation, dielectric constant (k), and electrical breakdown strength were investigated without post-annealing process. In both the mixed and nano-laminated ZAO films, the thickness of the interfacial oxide layer (T(IL)) was considerably reduced compared to ZrO2 and Al2O3 films. The T(IL) was 0.8 nm in nano-composite films prepared at a mixing ratio (ZrO2:Al2O3) of 1:1. The breakdown strength and the leakage current level were greatly improved by adding Al2O3 as little as 7.9% compared to that of ZrO2 and were enhanced more with increasing content of Al2O3. The k of ZrO2 and mixed ZAO (Al2O3 7.9%) films were 20.0 and 16.5, respectively. These results indicate that the addition of Al2O3 to ZrO2 greatly improves the electrical properties with less cost of k compared to the addition of SiO2.

  14. Enhanced Dielectric Properties and High-Temperature Microwave Absorption Performance of Zn-Doped Al2O3 Ceramic

    NASA Astrophysics Data System (ADS)

    Wang, Yuan; Luo, Fa; Wei, Ping; Zhou, Wancheng; Zhu, Dongmei

    2015-07-01

    To improve the dielectric and microwave absorption properties of Al2O3 ceramic, Zn-doped Al2O3 ceramic was prepared by conventional ceramic processing. X-ray diffraction analysis confirmed that Zn atoms successfully entered the Al2O3 ceramic lattice and occupied Al sites. The complex permittivity increased with increasing Zn concentration, which is mainly attributed to the increase in charged vacancy defects and densification of the Al2O3 ceramic. In addition, the temperature-dependent complex permittivity of 3% Zn-doped Al2O3 ceramic was determined in the temperature range from 298 K to 873 K. Both the real and imaginary parts of the complex permittivity increased monotonically with increasing temperature, which can be ascribed to the shortened relaxation time and increasing electrical conductivity. The increased complex permittivity leads to a great improvement in microwave absorption. In particular, when the temperature is up to 873 K, the 3% Zn-doped Al2O3 ceramic exhibited the best absorption performance with a maximum peak (-12.1 dB) and broad effective absorption bandwidth (reflection loss less than -10 dB from 9.3 GHz to 12.3 GHz). These results reveal that Zn-doped Al2O3 ceramic is a promising candidate for use as a kind of high-temperature microwave absorption material.

  15. Hydrogen defects in α-Al2O3 and water weakening of sapphire and alumina ceramics between 600 and 1000°C: I. Infrared characterization of defects

    USGS Publications Warehouse

    Kronenberg, A.K.; Castaing, J.; Mitchell, T.E.; Kirby, S.H.

    2000-01-01

    Hydrogen impurities in materials influence their properties, including flow strength. α-Al2O3 single crystals and polycrystalline ceramics were annealed in supercritical water between 850 and 1025°C, under pressures in the range 1500–2000 MPa. A few specimens were further subjected to plastic deformation. Hydrogen penetration was examined using infrared absorption measurements of O–H bond vibrations, which revealed two kinds of hydrogen defects. In single crystals, defects are characterized by sharp O–H absorption bands assigned to interstitial protons. Hydrogen impurities of hydrothermally annealed ceramics and of all hydrothermally deformed specimens are characterized by broad O–H bands assigned to molecular water. The grain boundaries of hydrothermally annealed ceramics are severely damaged. The kinetics of hydrogen penetration is consistent with diffusion data.

  16. The transient oxidation of single crystal NiAl+Zr. M.S. Thesis. Final Report

    NASA Technical Reports Server (NTRS)

    Doychak, J. K.

    1983-01-01

    The 800 C oxidation of oriented single crystals of Zr doped beta-NiAl was studied using transmission electron microscopy. The oxide phases and metal-oxide orientation relationships were determined to characterize the transient stages of oxidation prior to the transformation to or formation of alpha-Al2O3. On (001) and (012) metal orientations, NiAl2O4 was the first oxide to form followed by delta-Al2O3 which becomes the predominant oxide phase. All oxides were highly epitaxially related to the metal; the orientation relationships being function of parallel cation close-packed directions in the meta and oxide. On (011) and (111) metal orientations, gamma-Al2O3 became the predominant oxide phase rather than delta-Al2O3, indicating a structural stability from the highly epitaxial oxides. The relative concentration of aluminum in the oxide scales increased with time indicating preferential gamma-or delta-Al2O3 growth. The striking feature common to the orientation relationships is the alignment of 100 m and 110 ox directions, believed to result from the minimal 3 percent mismatch between the corresponding (100)m and (110)ox planes.

  17. Some TEM observations of Al2O3 scales formed on NiCrAl alloys

    NASA Technical Reports Server (NTRS)

    Smialek, J.; Gibala, R.

    1979-01-01

    The microstructural development of Al2O3 scales on NiCrAl alloys has been examined by transmission electron microscopy. Voids were observed within grains in scales formed on a pure NiCrAl alloy. Both voids and oxide grains grew measurably with oxidation time at 1100 C. The size and amount of porosity decreased towards the oxide-metal growth interface. The voids resulted from an excess number of oxygen vacancies near the oxidemetal interface. Short-circuit diffusion paths were discussed in reference to current growth stress models for oxide scales. Transient oxidation of pure, Y-doped, and Zr-doped NiCrAl was also examined. Oriented alpha-(Al, Cr)2O3 and Ni(Al, Cr)2O4 scales often coexisted in layered structures on all three alloys. Close-packed oxygen planes and directions in the corundum and spinel layers were parallel. The close relationship between oxide layers provided a gradual transition from initial transient scales to steady state Al2O3 growth.

  18. Cyclic Oxidation of FeCrAlY/Al2O3 Composites

    NASA Technical Reports Server (NTRS)

    Nesbitt, James A.; Draper, Susan L.; Barrett, Charles A.

    1999-01-01

    Three-ply FeCrAlY/Al2O3 composites and FeCrAlY matrix-only samples were cyclically oxidized at 1000 C and 1100 C for up to 1000 1-hr cycles. Fiber ends were exposed at the ends of the composite samples. Following cyclic oxidation, cracks running parallel to and perpendicular to the fibers were observed on the large surface of the composite. In addition, there was evidence of increased scale damage and spallation around the exposed fiber ends, particularly around the middle ply fibers. This damage was more pronounced at the higher temperature. The exposed fiber ends showed cracking between fibers in the outer plies, occasionally with Fe and Cr-rich oxides growing out of the cracks. Large gaps developed at the fiber/matrix interface around many of the fibers, especially those in the outer plies. Oxygen penetrated many of these gaps resulting in significant oxide formation at the fiber/matrix interface far within the composite sample. Around several fibers, the matrix was also internally oxidized showing Al2O3 precipitates in a radial band around the fibers. The results show that these composites have poor cyclic oxidation resistance due to the CTE mismatch and inadequate fiber/matrix bond strength at temperatures of 1000 C and above.

  19. Some TEM observations of Al2O3 scales formed on NiCrAl alloys

    NASA Technical Reports Server (NTRS)

    Smialek, J.; Gibala, R.

    1979-01-01

    The microstructural development of Al2O3 scales on NiCrAl alloys has been examined by transmission electron microscopy. Voids have been observed within grains in scales formed on a pure NiCrAl alloy. Both voids and oxide grains grew measurably with oxidation time at 1100 C. The size and amount of porosity decreased towards the oxide-metal growth interface. It was postulated that the voids resulted from an excess number of oxygen vacancies near the oxide-metal interface. Short-circuit diffusion paths were discussed in reference to current growth stress models for oxide scales. Transient oxidations of pure, Y-doped, and Zr-doped NiCrAl was also examined. Oriented alpha-(Al,Cr)2O3 and Ni(Al,Cr)2O4 scales often coexisted in layered structures on all three alloys. Close-packed oxygen planes and directions in the corundum and spinel layers were parallel. The close relationships between oxide layers provided a gradual transition from initial transient scales to steady state Al2O3 growth.

  20. Texture Analyses of Ti/Al2O3 Nanocomposite Produced Using Friction Stir Processing

    NASA Astrophysics Data System (ADS)

    Shafiei-Zarghani, Aziz; Kashani-Bozorg, Seyed Farshid; Gerlich, Adrian P.

    2016-11-01

    The texture evolution of Ti/Al2O3 nanocomposite fabricated using friction stir processing (FSP) was investigated at both macroscopic and microscopic levels employing X-ray diffraction and electron backscattering diffraction techniques. The developed textures were compared with ideal shear textures of hexagonal close-packed (hcp) structure, revealing that the fabricated nanocomposite is dominated by the P 1 hcp (fiber { 10bar{1}1} < 1bar{2}10rangle (and relatively weak B (fiber { 10bar{1}1} < bar{1}bar{1}23rangle ) textures. The analyses of macro- and microtextures showed that the presence of nanosized Al2O3 particles activated the pyramidal { 10bar{1}1} < bar{1}bar{1}23rangle slip system in addition to dominant { 10bar{1}0} < 1bar{2}10rangle prism, basal { {0002} }< 1bar{2}10rangle, and pyramidal { 10bar{1}1} < 1bar{2}10rangle slip systems which normally govern plastic deformation during FSP of commercially pure titanium alloy. Moreover, the presence of nanoparticles promoted the occurrence of continuous dynamic recrystallization as well as increasing the fraction of high-angle grain boundaries within the developed microstructure.

  1. Separation of Fine Al2O3 Inclusion from Liquid Steel with Super Gravity

    NASA Astrophysics Data System (ADS)

    Li, Chong; Gao, Jintao; Wang, Zhe; Guo, Zhancheng

    2017-01-01

    An innovative approach of super gravity was proposed to separate fine Al2O3 inclusions from liquid steel in this study. To investigate the removal behaviors of inclusions, the effects of different gravity coefficients and time on separating the inclusions were studied. The results show that a large amount of Al2O3 inclusions gathered at the top of the sample obtained by super gravity, whereas there were almost no inclusions appearing at the bottom. The volume fraction and number density of inclusions presented a gradient distribution along the direction of the super gravity, which became steeper with increasing gravity coefficient and separating time. As a result of the collision between inclusions, a large amount of inclusions aggregated and grew during the moving process, which further decreased the removal time. The experimental required removal time of inclusions is close to the theoretical values calculated by Stokes law under gravity coefficient G ≤ 80, t ≤ 15 minutes, and the small deviation may be because the inclusion particles are not truly spherical. Under the condition of gravity coefficient G = 80, t = 15 minutes, the total oxygen content at the bottom of the sample (position of 5 cm) is only 8.4 ppm, and the removal rate is up to 95.6 pct compared with that under normal gravity.

  2. Plasma-Assisted ALD of an Al2O3 Permeation Barrier Layer on Plastic

    NASA Astrophysics Data System (ADS)

    Lei, Wenwen; Li, Xingcun; Chen, Qiang; Wang, Zhengduo

    2012-02-01

    Atomic layer deposition (ALD) technique is used in the preparation of organic/inorganic layers, which requires uniform surfaces with their thickness down to several nanometers. For film with such thickness, the growth mode defined as the arrangement of clusters on the surface during the growth is of significance. In this work, Al2O3 thin film was deposited on various interfacial species of pre-treated polyethylene terephthalate (PET, 12 μm) by plasma assisted atomic layer deposition (PA-ALD), where trimethyl aluminium was used as the Al precursor and O2 as the oxygen source. The interfacial species, -NH3, -OH, and -COOH as well as SiCHO (derived from monomer of HMDSO plasma), were grafted previously by plasma and chemical treatments. The growth mode of PA-ALD Al2O3 was then investigated in detail by combining results from in-situ diagnosis of spectroscopic ellipsometry (SE) and ex-situ characterization of as-deposited layers from the morphologies scanned by atomic force microscopy (AFM). In addition, the oxygen transmission rates (OTR) of the original and treated plastic films were measured. The possible reasons for the dependence of the OTR values on the surface species were explored.

  3. Cold-Sprayed Ni-Al2O3 Coatings for Applications in Power Generation Industry

    NASA Astrophysics Data System (ADS)

    Sevillano, F.; Poza, P.; Múnez, C. J.; Vezzù, S.; Rech, S.; Trentin, A.

    2013-06-01

    Cermets coatings are extensively used in energy applications both because of their high wear resistance as required, for example, in components like gas turbine sealants, and because of their specific functionality as required in solar absorbers. So far, high-temperature thermal spraying and physical vapor deposition have traditionally been used to deposit this kind of coatings. In this study, Ni-Al2O3 coatings have been deposited using a Kinetic®3000 cold-spray system starting from Ni and Al2O3 powders blend; five blends have been prepared setting the alumina content in the feedstock to 10, 25, 50, 75, and 90 wt.%. The embedded alumina ranges between a few percent weight up to 16 and 31 wt.%, while the microhardness shows a deep increase from 175 Vickers in the case of pure Ni coatings up to 338 Vickers. The spray and coating growth mechanism have been discussed, with special attention to the fragmentation of the ceramic particles during the impact. Finally, the coating behavior at high temperature was analyzed by oxidation tests performed in air at 520 °C emphasizing a good oxidation resistance that could represent a very promising basis for application in power generation systems.

  4. Crystalline gamma-Al2O3 physical vapour deposition-coating for steel thixoforging tools.

    PubMed

    Bobzin, K; Hirt, G; Bagcivan, N; Khizhnyakova, L; Ewering, M

    2011-10-01

    The process of thixoforming, which has been part of many researches during the last decades, combines the advantages of forging and casting for the shaping of metallic components. But due to the high temperatures of semi-solid steel alloys high demands on the tools are requested. To resists the thermal and mechanical loads (wear, friction, thermal and thermomechanical fatigue) protecting thin films are necessary. In this regard crystalline gamma-Al2O3 deposited via Physical Vapour Deposition (PVD) is a promising candidate: It exhibits high thermal stability, high oxidation resistance and high hot hardness. In the present work the application of a (Ti, Al)N/gamma-Al2O3 coating deposited by means of Magnetron Sputter Ion Plating in an industrial coating unit is presented. The coating was analysed by means of Rockwell test, nanoindentation, and Scanning Electron Microscopy (SEM). The coated tool was tested in thixoforging experiments with steel grade X210CrW12 (AlSI D6). The surface of the coated dies was examined with Scanning Electron Microscope (SEM) after 22, 42, 90 and 170 forging cycles.

  5. Tribological performance of Graphene/Carbon nanotube hybrid reinforced Al2O3 composites

    PubMed Central

    Yazdani, Bahareh; Xu, Fang; Ahmad, Iftikhar; Hou, Xianghui; Xia, Yongde; Zhu, Yanqiu

    2015-01-01

    Tribological performance of the hot-pressed pure Al2O3 and its composites containing various hybrid contents of graphene nanoplatelets (GNPs) and carbon nanotubes (CNTs) were investigated under different loading conditions using the ball-on-disc method. Benchmarked against the pure Al2O3, the composite reinforced with a 0.5 wt% GNP exhibited a 23% reduction in the friction coefficient along with a promising 70% wear rate reduction, and a hybrid reinforcement consisting of 0.3 wt.% GNPs + 1 wt.% CNTs resulted in even better performance, with a 86% reduction in the wear rate. The extent of damage to the reinforcement phases caused during wear was studied using Raman spectroscopy. The wear mechanisms for the composites were analysed based on the mechanical properties, brittleness index and microstructural characterizations. The excellent coordination between GNPs and CNTs contributed to the excellent wear resistance property in the hybrid GNT-reinforced composites. GNPs played the important role in the formation of a tribofilm on the worn surface by exfoliation; whereas CNTs contributed to the improvement in fracture toughness and prevented the grains from being pulled out during the tribological test. PMID:26100097

  6. Fabrication of Al2O3-W Functionally Graded Materials by Slipcasting Method

    NASA Astrophysics Data System (ADS)

    Katayama, Tomoyuki; Sukenaga, Sohei; Saito, Noritaka; Kagata, Hajime; Nakashima, Kunihiko

    2011-10-01

    We have successfully fabricated a functionally graded material (FGM) from tungsten and alumina powders by a slip-casting method. This FGM has applications as a sealing and conducting component for high-intensity discharge lamps (HiDLs) that have a translucent alumina envelope. Two types of W powder, with different oxidizing properties, were used as the raw powders for the Al2O3-W FGM. "Oxidized W" was prepared by heat-treatment at 200 °C for 180 min in air. Alumina and each of the W powders were mixed in ultrapure water by ultrasonic stirring. The slurry was then cast into a cylindrical acrylic mold, which had a base of porous alumina, under controlled pressure. The green compacts were subsequently dried, and then sintered using a vacuum furnace at 1600 °C for a fixed time. The microstructures of the FGMs were observed by scanning electron microscopy (SEM) of the polished section. The Al2O3-W FGM with the "oxidized W" powder resulted in a microscopic compositional gradient. However, the FGM with "as-received W" showed no compositional gradient. This result was mainly attributed to the difference between the ζ-potentials of the W powders with the different oxidizing conditions; basically "oxidized W" powder tends to disperse because of the larger ζ-potential of the oxide layer coated on the W powder core.

  7. Separation of Fine Al2O3 Inclusion from Liquid Steel with Super Gravity

    NASA Astrophysics Data System (ADS)

    Li, Chong; Gao, Jintao; Wang, Zhe; Guo, Zhancheng

    2017-04-01

    An innovative approach of super gravity was proposed to separate fine Al2O3 inclusions from liquid steel in this study. To investigate the removal behaviors of inclusions, the effects of different gravity coefficients and time on separating the inclusions were studied. The results show that a large amount of Al2O3 inclusions gathered at the top of the sample obtained by super gravity, whereas there were almost no inclusions appearing at the bottom. The volume fraction and number density of inclusions presented a gradient distribution along the direction of the super gravity, which became steeper with increasing gravity coefficient and separating time. As a result of the collision between inclusions, a large amount of inclusions aggregated and grew during the moving process, which further decreased the removal time. The experimental required removal time of inclusions is close to the theoretical values calculated by Stokes law under gravity coefficient G ≤ 80, t ≤ 15 minutes, and the small deviation may be because the inclusion particles are not truly spherical. Under the condition of gravity coefficient G = 80, t = 15 minutes, the total oxygen content at the bottom of the sample (position of 5 cm) is only 8.4 ppm, and the removal rate is up to 95.6 pct compared with that under normal gravity.

  8. Sulfuric acid baking and leaching of spent Co-Mo/Al2O3 catalyst.

    PubMed

    Kim, Hong-In; Park, Kyung-Ho; Mishra, Devabrata

    2009-07-30

    Dissolution of metals from a pre-oxidized refinery plant spent Co-Mo/Al(2)O(3) catalyst have been tried through low temperature (200-450 degrees C) sulfuric acid baking followed by mild leaching process. Direct sulfuric acid leaching of the same sample, resulted poor Al and Mo recoveries, whereas leaching after sulfuric acid baking significantly improved the recoveries of above two metals. The pre-oxidized spent catalyst, obtained from a Korean refinery plant found to contain 40% Al, 9.92% Mo, 2.28% Co, 2.5% C and trace amount of other elements such as Fe, Ni, S and P. XRD results indicated the host matrix to be poorly crystalline gamma- Al(2)O(3). The effect of various baking parameters such as catalyst-to-acid ratio, baking temperature and baking time on percentage dissolutions of metals has been studied. It was observed that, metals dissolution increases with increase in the baking temperature up to 300 degrees C, then decreases with further increase in the baking temperature. Under optimum baking condition more than 90% Co and Mo, and 93% Al could be dissolved from the spent catalyst with the following leaching condition: H(2)SO(4)=2% (v/v), temperature=95 degrees C, time=60 min and Pulp density=5%.

  9. Revisiting the Al/Al2O3 Interface: Coherent Interfaces and Misfit Accommodation

    DOE PAGES

    Pilania, Ghanshyam; Thijsse, Barend J.; Hoagland, Richard G.; ...

    2014-03-27

    We report the coherent and semi-coherent Al/α-Al2O3 interfaces using molecular dynamics simulations with a mixed, metallic-ionic atomistic model. For the coherent interfaces, both Al-terminated and O-terminated nonstoichiometric interfaces have been studied and their relative stability has been established. To understand the misfit accommodation at the semi-coherent interface, a 1-dimensional (1D) misfit dislocation model and a 2-dimensional (2D) dislocation network model have been studied. For the latter case, our analysis reveals an interface dislocation structure with a network of three sets of parallel dislocations, each with pure-edge character, giving rise to a pattern of coherent and stacking-fault-like regions at the interface.more » Structural relaxation at elevated temperatures leads to a further change of the dislocation pattern, which can be understood in terms of a competition between the stacking fault energy and the dislocation interaction energy at the interface. In conclusion, our results are expected to serve as an input for the subsequent dislocation dynamics models to understand and predict the macroscopic mechanical behavior of Al/α-Al2O3 composite heterostructures.« less

  10. Electrodeposition of Ni-Al2O3 nano composite coating and evaluation of wear characteristics

    NASA Astrophysics Data System (ADS)

    Raghavendra, C. R.; Basavarajappa, S.; Sogalad, Irappa

    2016-09-01

    Electrodeposition is one of the most technologically feasible and economically superior technique for producing metallic coating. The advancement in the application of nano particles has grabbed the attention in all fields of engineering. In this present study an attempt has been made on the nano particle composite coating on aluminium substrate by electrodeposition process. The aluminium surface requires a specific pre-treatment for better adherence of coating. In light of this a thin zinc layer is coated on the aluminium substrate by electroless process. This layer offers protection against oxidation thus prevents the formation of a native oxide layer. In this work Ni-Al2O3 composite coating were successfully coated by varying the process parameters such as bath temperature, current density and particle loading. The experimentation was performed using central composite design based 20 trials of experiments. The effect of process parameters on surface morphology and wear behavior was studied. The results shown a better wear resistance of Ni-Al2O3 composite electrodeposited coating compared to Ni coating. The particle loading and interaction effect of current density with temperature has greater significant effect on wear rate followed by the bath temperature. The decrease in wear rate was observed with the increased current density and temperature.

  11. Revisiting the Al/Al2O3 Interface: Coherent Interfaces and Misfit Accommodation

    PubMed Central

    Pilania, Ghanshyam; Thijsse, Barend J.; Hoagland, Richard G.; Lazić, Ivan; Valone, Steven M.; Liu, Xiang-Yang

    2014-01-01

    We study the coherent and semi-coherent Al/α-Al2O3 interfaces using molecular dynamics simulations with a mixed, metallic-ionic atomistic model. For the coherent interfaces, both Al-terminated and O-terminated nonstoichiometric interfaces have been studied and their relative stability has been established. To understand the misfit accommodation at the semi-coherent interface, a 1-dimensional (1D) misfit dislocation model and a 2-dimensional (2D) dislocation network model have been studied. For the latter case, our analysis reveals an interface dislocation structure with a network of three sets of parallel dislocations, each with pure-edge character, giving rise to a pattern of coherent and stacking-fault-like regions at the interface. Structural relaxation at elevated temperatures leads to a further change of the dislocation pattern, which can be understood in terms of a competition between the stacking fault energy and the dislocation interaction energy at the interface. Our results are expected to serve as an input for the subsequent dislocation dynamics models to understand and predict the macroscopic mechanical behavior of Al/α-Al2O3 composite heterostructures. PMID:24670940

  12. Cooling Rate Effects on Dynamics in Supercooled Al2O3

    NASA Astrophysics Data System (ADS)

    Hoang, Vo Van; Oh, Suhk Kun

    The cooling rate effects in supercooled Al2O3 have been investigated by Molecular Dynamics (MD) method. Simulations were done in the basic cube under periodic boundary conditions containing 3000 ions with Born-Mayer type pair potentials. The temperature of the system was decreased linearly in time as T(t)=T0-γt, where γ is the cooling rate. The cooling rate dependence of density, thermal expansion coefficient and enthalpy of the system was found. Structure of amorphous Al2O3 model at the temperature of 0 K was in good agreement with Lamparter's experimental data. The cooling rate dependence of the dynamical heterogeneities in supercooled states has been studied through the comparison of the partial radial distribution functions (PRDFs) for the 10% most mobile or immobile particles with the corresponding mean PRDFs in the models. Also, cooling rate effects on the cluster size distributions of the most mobile or immobile particles have been obtained. Calculations show that the cooling rate effects on the dynamical heterogeneities are pronounced. Finally, the evolution of structural defects and cluster size distributions of the most mobile or immobile particles in the system upon cooling has been studied and presented.

  13. Structure and magnetism of granular Fe-Al 2O 3

    NASA Astrophysics Data System (ADS)

    Santos, A.; Ardisson, J. D.; Viegas, A. D. C.; Schmidt, J. E.; Persiano, A. I. C.; Macedo, W. A. A.

    2001-05-01

    The structural and magnetic properties of granular Fe-Al 2O 3 nanocomposite obtained starting from sol-gel processing are presented. Samples with nominal Fe content ranging from 20% to 62% in volume were prepared. The conversion of Fe oxides into metallic Fe was obtained by calcination at 800°C followed by reduction at 600°C for 2 h in H 2 atmosphere. After reduction, our results indicated up to 78% α-Fe, preserving the mean diameter of the metallic nanoparticles between 50 and 80 nm, ˜16% Fe oxides and ˜7% interstitial Fe 2+ and substitutional Fe 3+ cations in the Al 2O 3 lattice. Vibrating sample magnetometry at 300 K resulted in coercivity between 400 and 630 Oe and saturation magnetization between 40 and 134 emu/g. From transport measurements, the highest magnetoresistance, close to 2% at room temperature, was observed for samples with 25% α-Fe and 51 vol% total Fe.

  14. Activation energy of negative fixed charges in thermal ALD Al2O3

    NASA Astrophysics Data System (ADS)

    Kühnhold-Pospischil, S.; Saint-Cast, P.; Richter, A.; Hofmann, M.

    2016-08-01

    A study of the thermally activated negative fixed charges Qtot and the interface trap densities Dit at the interface between Si and thermal atomic-layer-deposited amorphous Al2O3 layers is presented. The thermal activation of Qtot and Dit was conducted at annealing temperatures between 220 °C and 500 °C for durations between 3 s and 38 h. The temperature-induced differences in Qtot and Dit were measured using the characterization method called corona oxide characterization of semiconductors. Their time dependency were fitted using stretched exponential functions, yielding activation energies of EA = (2.2 ± 0.2) eV and EA = (2.3 ± 0.7) eV for Qtot and Dit, respectively. For annealing temperatures from 350 °C to 500 °C, the changes in Qtot and Dit were similar for both p- and n-type doped Si samples. In contrast, at 220 °C the charging process was enhanced for p-type samples. Based on the observations described in this contribution, a charging model leading to Qtot based on an electron hopping process between the silicon and Al2O3 through defects is proposed.

  15. Growth and characterization of Al2O3 films on fluorine functionalized epitaxial graphene

    NASA Astrophysics Data System (ADS)

    Robinson, Zachary R.; Jernigan, Glenn G.; Wheeler, Virginia D.; Hernández, Sandra C.; Eddy, Charles R.; Mowll, Tyler R.; Ong, Eng Wen; Ventrice, Carl A.; Geisler, Heike; Pletikosic, Ivo; Yang, Hongbo; Valla, Tonica

    2016-08-01

    Intelligent engineering of graphene-based electronic devices on SiC(0001) requires a better understanding of processes used to deposit gate-dielectric materials on graphene. Recently, Al2O3 dielectrics have been shown to form conformal, pinhole-free thin films by functionalizing the top surface of the graphene with fluorine prior to atomic layer deposition (ALD) of the Al2O3 using a trimethylaluminum (TMA) precursor. In this work, the functionalization and ALD-precursor adsorption processes have been studied with angle-resolved photoelectron spectroscopy, low energy electron diffraction, and X-ray photoelectron spectroscopy. It has been found that the functionalization process has a negligible effect on the electronic structure of the graphene, and that it results in a twofold increase in the adsorption of the ALD-precursor. In situ TMA-dosing and XPS studies were also performed on three different Si(100) substrates that were terminated with H, OH, or dangling Si-bonds. This dosing experiment revealed that OH is required for TMA adsorption. Based on those data along with supportive in situ measurements that showed F-functionalization increases the amount of oxygen (in the form of adsorbed H2O) on the surface of the graphene, a model for TMA-adsorption on graphene is proposed that is based on a reaction of a TMA molecule with OH.

  16. Effect of interface geometry on electron tunnelling in Al/Al2O3/Al junctions

    NASA Astrophysics Data System (ADS)

    Koberidze, M.; Feshchenko, A. V.; Puska, M. J.; Nieminen, R. M.; Pekola, J. P.

    2016-04-01

    We investigate how different interface geometries of an Al/Al2O3 junction, a common component of modern tunnel devices, affect electron transport through the tunnel barrier. We study six distinct Al/Al2O3 interfaces which differ in stacking sequences of the metal and the oxide surface atoms and the oxide termination. To construct model potential barrier profiles for each examined geometry, we rely on first-principles density-functional theory (DFT) calculations for the barrier heights and the shapes of the interface regions as well as on experimental data for the barrier widths. We show that even tiny variations in the atomic arrangement at the interface cause significant changes in the tunnel barrier parameters and, consequently, in electron transport properties. Especially, we find that variations in the crucial barrier heights and widths can be as large as 2 eV and 5 Å, respectively. Finally, to gain information about the average properties of the measured junction, we fit the conductance calculated within the Wentzel-Kramers-Brillouin approximation to the experimental data and interpret the fit parameters with the help of the DFT results.

  17. The effect of particle size on the electrical conductivity of CuCl (Al2O3) composites

    NASA Technical Reports Server (NTRS)

    Chang, M. R.-W.; Shahi, K.; Wagner, J. B., Jr.

    1984-01-01

    The conductivity of CuCl containing Al2O3 of 0.06, 0.3, 1, 3, 8, and 15 micron sized particles was measured between 25 and 390 C. Conductivity was enhanced for the 0.06 and 0.3 sized Al2O3 particles for temperatures below approximately 250 C. The maximum enhancement occurred at 10 m/o of 0.06 micron Al2O3 at 25 C. Uncertain degrees of agglomeration as well as the grain size of the matrix were found to be significant.

  18. The synthesis, activity, stability and the charge transfer identification of Ag:AgBr/γ-Al2O3 photocatalyst for organic pollutant decomposition in water

    NASA Astrophysics Data System (ADS)

    Huang, Shan; Si, Zhichun; Weng, Duan

    2015-12-01

    Highly stable Ag:AgBr/γ-Al2O3 photo-catalyst was obtained by dispersing AgBr sol on hollow γ-Al2O3 microsphere. Metallic Ag nanoparticles were in situ generated on AgBr crystals by a photo-reduction method. The activity of catalyst was characterized by MO and phenol decomposition. The light irradiation response, the life times of the photo-induced charges, and the charge separation and transition were determined by the UV-vis diffuse reflection spectra, open circuit voltage decay spectra and transient photocurrent responses. The as-prepared Ag:AgBr/γ-Al2O3 catalyst can response to visible light irradiation. Charge separation was clarified to correlate with electrons transferring from Ag to AgBr surface and the consequent reaction with ads-O2 to generate rad O2- species. It was found that the rad O2- rather than rad OH played a dominant role in the photocatalytic oxidation of MO and phenol in water. However, the electrons trended to transfer from AgBr to Ag intrinsically without light irradiation. Therefore, the electron transfer between Ag and AgBr reaching the dynamic equilibrium was the key factor for obtaining a high stable Ag/AgBr catalyst which can be obtained by optimizing the Ag:AgBr ratio. Loading amount of Ag:AgBr on γ-Al2O3 was optimized to 30 wt.% and the metallic Ag content was stabilized at 9 wt.% of Ag:AgBr catalyst.

  19. Improved memory characteristics of charge trap memory by employing double layered ZrO2 nanocrystals and inserted Al2O3

    NASA Astrophysics Data System (ADS)

    Tang, Z. J.; Li, R.; Zhang, X. W.; Hu, D.; Zhao, Y. G.

    2016-07-01

    The charge trap memory capacitors incorporating a stacked charge trapping layer consisting of double layered ZrO2 nanocrystals (NCs) and inserted Al2O3 have been fabricated and investigated. It is observed that the memory capacitor with stacked trapping layer exhibits a hysteresis window as large as 14.3 V for ±10 V sweeping gate voltage range, faster program/erase speed, improved endurance performance, and good data retention characteristics with smaller extrapolated ten years charge loss at room temperature and 125 °C compared to single layered NCs. The special energy band alignment and the introduced additional traps of double layered ZrO2 NCs and inserted Al2O3 change the trapping and loss behavior of charges, and jointly contribute to the remarkable memory characteristics. Therefore, the memory capacitor with a stacked charge trapping layer is a promising candidate in future nonvolatile charge trap memory device design and application.

  20. Effect of Al2O3 on the Viscosity and Structure of CaO-SiO2-MgO-Al2O3-FetO Slags

    NASA Astrophysics Data System (ADS)

    Wang, Zhanjun; Sun, Yongqi; Sridhar, Seetharaman; Zhang, Mei; Guo, Min; Zhang, Zuotai

    2015-04-01

    The present paper provided a fundamental investigation on the effect of Al2O3 on the viscosity and structure of CaO-SiO2-MgO-Al2O3-FetO slags for the purpose of efficiently recycling the valuable elements from the steelmaking slags. The results show that the viscosity of CaO-SiO2-Al2O3-MgO-FetO slags slightly increases with increasing Al2O3 content. The degree of the polymerization (DOP) of quenched slags, determined from Raman spectra and magic angle spinning-nuclear magnetic resonance, is also found to increase with increasing Al2O3 content. It can be deduced that the increasing DOP can promote the formation of gehlenite phase (Ca2Al2SiO7), thus facilitating the formation of higher phosphorous (or vanadium) contained solid solution ( n'Ca2SiO4·Ca3((P or V)O4)2). As Al2O3 content increases up to a specific value, the charge compensating ions which present near [AlO4]-tetrahedra and [FeO4]-tetrahedra are not fully supplied due to the scarcity of Ca2+. In this case, the existing Fe3+ in the melt cannot completely form [FeO4]-tetrahedra and part of Fe3+ would form [FeO6]-octahedra to substitute Ca2+ to modify the slags.

  1. The role of scattering and absorption on the optical properties of birefringent polycrystalline ceramics: Modeling and experiments on ruby (Cr:Al2O3)

    NASA Astrophysics Data System (ADS)

    Penilla, E. H.; Hardin, C. L.; Kodera, Y.; Basun, S. A.; Evans, D. R.; Garay, J. E.

    2016-01-01

    Light scattering due to birefringence has prevented the use of polycrystalline ceramics with anisotropic optical properties in applications such as laser gain media. However, continued development of processing technology has allowed for very low porosity and fine grains, significantly improving transparency and is paving the way for polycrystalline ceramics to be used in demanding optical applications. We present a method for producing highly transparent Cr3+ doped Al2O3 (ruby) using current activated pressure assisted densification. The one-step doping/densification process produces fine grained ceramics with well integrated (doped) Cr, resulting in good absorption and emission. In order to explain the light transmission properties, we extend the analytical model based on the Rayleigh-Gans-Debye approximation that has been previously used for undoped alumina to include absorption. The model presented captures reflection, scattering, and absorption phenomena in the ceramics. Comparison with measured transmission confirms that the model adequately describes the properties of polycrystalline ruby. In addition the measured emission spectra and emission lifetime are found to be similar to single crystals, confirming the high optical quality of the ceramics.

  2. Mathematical formulation of Tmax-Tstop method for LM-OSL and its experimental validation on α-Al2O3:C

    NASA Astrophysics Data System (ADS)

    Soni, Anuj; Mishra, D. R.

    2016-05-01

    A mathematical formulation and its experimental validation on α-Al2O3:C for evaluating the number of OSL components has been described. The method consists of various partial bleaching steps of LM-OSL curve and as a result, the peak position (Tmax) of the resultant curve shifts if the system contains multiple components. However, for single component system the peak position of the resultant curve doesn't change on partial bleaching for a phosphor obeying first order kinetics. The method has been theoretically formulated for single and multiple component system with different order of kinetics and validated experimentally on the commercial α-Al2O3:C OSL phosphor. The slope of the curve between shift in Tmax and bleaching time gives the number of the OSL components and measure of their closeness in terms of photoionization cross-section. Based on this result, the photoionization cross-section of the two embedded peaks in the LM-OSL curve of α-Al2O3:C were found to be 1.51 × 10-18 cm2 and 5.02 × 10-19 cm2 using CW-OSL and NL-OSL method.

  3. Structure Evolution and Electric Properties of TaN Films Deposited on Al2O3-BASED Ceramic and Glass Substrates by Magnetron Reactive Sputtering

    NASA Astrophysics Data System (ADS)

    Zhou, Yan Ming; Ma, Yang Zhao; Xie, Zhong; He, Ming Zhi

    2014-03-01

    Structure evolution and electric properties of tantalum nitride (TaN) films deposited on Al2O3-based ceramic and glass substrates by magnetron reactive sputtering were carried out as a function of the N2-to-Ar flow ratio. The TaN thin films on Al2O3-based ceramic substrates grow with micronclusters composed of numerous nanocrystallites, contains from single-phase of Ta2N grains to TaN, and exhibits high defect density, sheet resistance and negative TCR as the N2-to-Ar flow ratio continuously increases. However, the films on the glass substrates grow in the way of sandwich close-stack, contains from single-phase of Ta2N grains to TaN and Ta3N5 phases with the increase of N2-to-Ar flow ratio. These results indicate that the N2-to-Ar flow ratio and surface characteristic difference of substrates play a dominant effect on the structure and composition of the TaN films, resulting in different electrical properties for the films on Al2O3-based ceramic and the samples on glass substrates.

  4. Effects of plasma-enhanced chemical vapor deposition (PECVD) on the carrier lifetime of Al2O3 passivation stack

    NASA Astrophysics Data System (ADS)

    Cho, Kuk-Hyun; Cho, Young Joon; Chang, Hyo Sik; Kim, Kyung-Joong; Song, Hee Eun

    2015-09-01

    We investigated the effect on the minority carrier lifetime of atomic layer deposition (ALD) Al2O3 passivation by a plasma-enhanced chemical vapor deposition (PECVD) SiON layer in Si/Al2O3/SiON-passivated structure. The lifetime variation of the Al2O3/SiON stack layer was found to depend on both the plasma power and the deposition temperature during the PECVD SiON process and to show better thermal stability than the Al2O3/SiNx:H stack under the same deposition conditions. The lifetime after a high-temperature firing process was improved dramatically at the PECVD deposition temperature of 200 °C. Our results provide a significant clue to reason for the improvement of the passivation performance for passivated emitter and rear contact (PERC) silicon solar cells.

  5. Synthesis of CoFe/Al2O3 composite nanoparticles as the impedance matching layer of wideband multilayer absorber

    NASA Astrophysics Data System (ADS)

    Zhen, L.; Gong, Y. X.; Jiang, J. T.; Xu, C. Y.; Shao, W. Z.; Liu, P.; Tang, J.

    2011-04-01

    CoFe/Al2O3 composite nanoparticles were successfully prepared by hydrogen-thermally reducing cobalt aluminum ferrite. Compared with CoFe alloy nanoparticles, the permeability of CoFe/Al2O3 composite nanoparticles was remarkably enhanced and an improved impedance characteristic was achieved due to the introduction of insulated Al2O3. A multilayer absorber with CoFe/Al2O3 composite nanoparticles as the impedance matching layer and CoFe nanoflake as the dissipation layer was designed by using genetic algorithm, in which an ultrawide operation frequency bandwidth over 2.5-18 GHz was obtained. The microwave absorption performance in both normal and oblique incident case was evaluated by using electromagnetic simulator. The backward radar cross-section (RCS) was decreased at least 10 dB over a wide frequency range by covering the multilayer absorber on the surface of perfect electrical conductive plate.

  6. Epitaxial growth and electrochemical transfer of graphene on Ir(111)/α-Al2O3(0001) substrates

    NASA Astrophysics Data System (ADS)

    Koh, Shinji; Saito, Yuta; Kodama, Hideyuki; Sawabe, Atsuhito

    2016-07-01

    Low-pressure chemical vapor deposition growth of graphene on Iridium (Ir) layers epitaxially deposited on α-Al2O3 (0001) substrates was investigated. The X-ray diffraction, Raman and reflection high energy electron diffraction characterizations revealed that graphene films were epitaxially grown on Ir(111) layers, and the in-plane epitaxial relationship between graphene, Ir(111), and α-Al2O3(0001) was graphene ⟨ 1 1 ¯ 00 ⟩//Ir⟨ 11 2 ¯ ⟩//α-Al2O3⟨ 11 2 ¯ 0 ⟩. The graphene on Ir(111) was electrochemically transferred onto SiO2/Si substrates. We also demonstrated the reuse of the Ir(111)/α-Al2O3(0001) substrates in multiple growth and transfer cycles.

  7. Critical tensile and compressive strains for cracking of Al2O3 films grown by atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Jen, Shih-Hui; Bertrand, Jacob A.; George, Steven M.

    2011-04-01

    Al2O3 atomic layer deposition (ALD) is a model ALD system and Al2O3 ALD films are excellent gas diffusion barrier on polymers. However, little is known about the response of Al2O3 ALD films to strain and the potential film cracking that would restrict the utility of gas diffusion barrier films. To understand the mechanical limitations of Al2O3 ALD films, the critical strains at which the Al2O3 ALD films will crack were determined for both tensile and compressive strains. The tensile strain measurements were obtained using a fluorescent tagging technique to image the cracks. The results showed that the critical tensile strain is higher for thinner thicknesses of the Al2O3 ALD film on heat-stabilized polyethylene naphthalate (HSPEN) substrates. A low critical tensile strain of 0.52% was measured for a film thickness of 80 nm. The critical tensile strain increased to 2.4% at a film thickness of 5 nm. In accordance with fracture mechanics modeling, the critical tensile strains and the saturation crack densities scaled as (1/h)1/2 where h is the Al2O3 ALD film thickness. The fracture toughness for cracking, KIC, of the Al2O3 ALD film was also determined to be KIC = 2.30 MPa m1/2. Thinner Al2O3 ALD film thicknesses also had higher critical strains for cracking from compressive strains. Field-emission scanning electron microscopy (FE-SEM) images revealed that Al2O3 ALD films with thicknesses of 30-50 nm on Teflon fluorinated ethylene propylene (FEP) substrates cracked at a critical compressive strain of ˜1.0%. The critical compressive strain increased to ˜2.0% at a film thickness of ˜20 nm. A comparison of the critical tensile strains on HSPEN substrates and critical compressive strains on Teflon FEP substrates revealed some similarities. The critical strain was ˜1.0% for film thicknesses of 30-50 nm for both tensile and compressive strains. The critical compressive strain then increased more rapidly than the critical tensile strain for thinner films with thicknesses

  8. Effect of Al2O3 on the friction performance of P/M composite materials for friction applications

    NASA Astrophysics Data System (ADS)

    Ivǎnuş, R. C.; ǎnuş, D., IV; Cǎlmuc, F.

    2010-06-01

    Bronze bearings are one of most used friction materials. In those applications where higher mechanical properties are needed, iron base bearings can be an alternative to bronze base materials, or other alloying elements added to bronze. The paper presents the results obtained in metal matrix composites field with friction characteristics, for automotive brakes, by P/M. The scope of these researches was the improvement of wear resistance and friction properties of metal matrix composites. Friction-wear properties of the Al2O3 reinforced samples were measured and compared with those of plain bronze based ones. For this purpose, density, hardness, friction coefficient wear behaviour of the samples were tested.Microstructures of samples before and after sintering and worn surfaces were also investigated by scanning electron microscopy (SEM), and the wear types were determined. The optimum friction-wear behaviour was obtained in the sample compacted at 500 MPa and sintered at 820°C. Density of the final samples decreased with increasing the amount of reinforcing elements (Al2O3) before presintering. However after sintering, there is no change in density of the samples including reinforcing elements (Al2O3). With increasing friction surface temperature, a reduction in the friction coefficient of the samples was observed. However, the highest reductions in the friction coefficients were observed in the as-received samples containing 0,5% reinforced Al2O3. The SEM images of the sample indicated that while bronze-based break lining material without Al2O3 showed abrasive wear behaviour, increasing the amount of Al2O3 resulted in a change of abrasive to adhesive wear mechanism. With increasing the amount of reinforcing Al2O3, wear resistance of the samples was increased. However samples reinforced with 5% and 6% Al2O3 showed the best results.

  9. Al2O3 e-Beam Evaporated onto Silicon (100)/SiO2, by XPS

    SciTech Connect

    Madaan, Nitesh; Kanyal, Supriya S.; Jensen, David S.; Vail, Michael A.; Dadson, Andrew; Engelhard, Mark H.; Samha, Hussein; Linford, Matthew R.

    2013-09-25

    We report the XPS characterization of a thin film of Al2O3 (35 nm) deposited via e-beam evaporation onto silicon (100). The film was characterized with monochromatic Al Ka radiation. An XPS survey scan, an Al 2p narrow scan, and the valence band spectrum were collected. The Al2O3 thin film is used as a diffusion barrier layer for templated carbon nanotube (CNT) growth in the preparation of microfabricated thin layer chromatography plates.

  10. Probing defect emissions in bulk, micro- and nano-sized α-Al2O3 via X-ray excited optical luminescence.

    PubMed

    Wang, Zhiqiang; Li, Chunlei; Liu, Lijia; Sham, Tsun-Kong

    2013-02-28

    The electronic structure and optical properties of bulk, micro-sized, and nano-sized α-Al2O3 (wafer, microparticles (MPs), nanowires (NWs), and nanotubes (NTs)) have been investigated using X-ray absorption near-edge structures (XANES) and X-ray excited optical luminescence (XEOL). XANES results show that the wafer, MPs, and NTs have characteristic features of α-Al2O3. The NWs have a core∕shell structure with a single crystalline α-Al2O3 core surrounded by an amorphous shell, which is consistent with transmission electron microscopy result. It is found that some Al(3+) in the shell and core∕shell interface of the NWs as well as the surface of the NTs were reduced to Al(2+) or Al(1+) during the growth process. XEOL results show that the wafer and MPs have a broad emission at 325 nm and a sharp emission at 694 nm, which are attributed to F(+) center and Cr(3+) impurities, respectively. The NWs exhibit an intense emission at 404 nm that comes from F center, while the NTs show relatively weak luminescence at 325, 433, and 694 nm, which are attributed to F(+) center, F center, and Cr(3+) impurities, respectively. The O K-edge XEOL confirms that the emissions of α-Al2O3 in the range of 250-550 nm are related to the oxygen site. Furthermore, on the basis of XEOL and photoluminescence yield, the strong luminescence of the NWs (404 nm) is related to the Al(2+) or Al(1+) in the shell and core∕shell interface, while the luminescence of the NTs at 325 and 433 nm are related to the bulk and the Al(2+) or Al(1+) on the surface, respectively.

  11. Memristive behavior of Al2O3 film with bottom electrode surface modified by Ag nanoparticles

    NASA Astrophysics Data System (ADS)

    Qin, Shu-Chao; Dong, Rui-Xin; Yan, Xun-Ling

    2014-09-01

    The memristive behavior of Al2O3-based device is significantly improved by introducing Ag nanoparticles (NPs). Inserting Ag NPs can effectively reduce the switching voltages, increase the resistance ratio (about 104) and enhance the sweep endurance (300 cycles). In particular, the stable switching properties are obtained by inserting an Ag NPs layer with an average diameter of 14 nm on the surface of bottom electrode, and the devices show a long retention time (more than 106 s) compared with the devices without Ag NPs. The switching mechanism is related to the oxygen-vacancy-based conducting filaments and the interfacial effect. The local enhancement and nonuniform distribution of electric field have the benefits to promote, induce and modulate the growth of conducting filaments, such as shape, location and orientation, which are responsible for the improvement performance of the devices.

  12. Memristive behavior of Al2O3 film with bottom electrode surface modified by Ag nanoparticles

    NASA Astrophysics Data System (ADS)

    Qin, Shu-Chao; Dong, Rui-Xin; Yan, Xun-Ling

    2015-02-01

    The memristive behavior of Al2O3-based device is significantly improved by introducing Ag nanoparticles (NPs). Inserting Ag NPs can effectively reduce the switching voltages, increase the resistance ratio (about 104) and enhance the sweep endurance (300 cycles). In particular, the stable switching properties are obtained by inserting an Ag NPs layer with an average diameter of 14 nm on the surface of bottom electrode, and the devices show a long retention time (more than 106 s) compared with the devices without Ag NPs. The switching mechanism is related to the oxygen-vacancy-based conducting filaments and the interfacial effect. The local enhancement and nonuniform distribution of electric field have the benefits to promote, induce and modulate the growth of conducting filaments, such as shape, location and orientation, which are responsible for the improvement performance of the devices.

  13. An impedance study of complex Al/Cu-Al2O3 electrode

    NASA Astrophysics Data System (ADS)

    Denisova, J.; Katkevics, J.; Erts, D.; Viksna, A.

    2011-06-01

    Electrochemical impedance spectroscopy (EIS) was used to investigate different Cu deposition regimes on Al surface obtained by internal electrolysis and to characterize properties of fabricated electrodes. EIS experimental data confirmed that Cu deposition by internal electrolysis is realized and the complex electrode system is obtained. The main difficulty in preparation of Al/Cu electrodes is to prevent aluminium oxidation before and during electrochemical deposition of Cu particles. In this work NaCl, CH3COONa, K2SO4, mono- and diammonium citrate electrolytes were examined to determine their suitability for impedance measurements. Al/Cu-Al2O3 electrode composition was approved by equivalent circuit analysis, optical and scanning electron microscope methods. The most optimal Cu deposition mode using internal electrolysis was determined. The obtained results are promising for future electrochemical fabrication of nanostructures directly on Al surfaces by internal electrolysis.

  14. Investigation of etching techniques for superconductive Nb/Al-Al2O3/Nb fabrication processes

    NASA Technical Reports Server (NTRS)

    Lichtenberger, A. W.; Lea, D. M.; Lloyd, F. L.

    1993-01-01

    Wet etching, CF4 and SF6 reactive ion etching (RIE), RIE/wet hybrid etching, Cl-based RIE, ion milling, and liftoff techniques have been investigated for use in superconductive Nb/Al-Al2O3/Nb fabrication processes. High-quality superconductor-insulator-superconductor (SIS) junctions have been fabricated using a variety of these etching methods; however, each technique offers distinct tradeoffs for a given process an wafer design. In particular, it was shown that SF6 provides an excellent RIE chemistry for low-voltage anisotropic etching of Nb with high selectivity to Al. The SF6 tool has greatly improved the trilevel resist junction insulation process. Excellent repeatability, selectivity with respect to quartz, and submicron resolution make Cl2 + BCl3 + CHCl3 RIE a very attractive process for trilayer patterning.

  15. Fundamental Influence of C on Adhesion of the Al2O3/Al Interface

    NASA Astrophysics Data System (ADS)

    Wang, Xiao-Gang; Smith, John R.; Evans, Anthony

    2002-12-01

    Our first-principles computations indicate that the clean Al2O3/Al interface is relatively weak—weaker than bulk Al. Fracture experiments reveal that the interface is relatively strong with observed failure in bulk Al, however. This paradox is resolved via doping effects of the common impurity C. We have found that only 1/3 of a monolayer of carbon segregated to the interface can increase the work of separation by a factor of 3. The resulting strong interface is consistent with fracture experiments. It arises due to void formation in the interface, which provides low-strain sites for the carbon to segregate to. The degree of void formation is consistent with the relatively high heat of oxide formation of Al.

  16. CoFe2/Al2O3/PMNPT multiferroic heterostructures by atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Zhou, Ziyao; Grocke, Garrett; Yanguas-Gil, Angel; Wang, Xinjun; Gao, Yuan; Sun, Nianxiang; Howe, Brandon; Chen, Xing

    2016-05-01

    Multiferroic materials and applications allow electric bias control of magnetism or magnetic bias control of polarization, enabling fast, compact, energy-efficient devices in RF/microwave communication systems such as filters, shifters, and antennas; electronics devices such as inductors and capacitors; and other magnetic material related applications including sensors and memories. In this manuscript, we utilize atomic layer deposition technology to grow magnetic CoFe metallic thin films onto PMNPT, with a ˜110 Oe electric field induced ferromagnetic resonance field shift in the CoFe/Al2O3/PMNPT multiferroic heterostructure. Our work demonstrates an atomic layer deposition fabricated multiferroic heterostructure with significant tunability and shows that the unique thin film growth mechanism will benefit integrated multiferroic application in near future.

  17. CVD Fiber Coatings for Al2O3/NiAl Composites

    NASA Technical Reports Server (NTRS)

    Boss, Daniel E.

    1995-01-01

    While sapphire-fiber-reinforced nickel aluminide (Al2O3/NiAl) composites are an attractive candidate for high-temperature structures, the significant difference in the coefficient of thermal expansion between the NiAl matrix and the sapphire fiber creates substantial residual stresses in the composite. This study seeks to produce two fiber-coating systems with the potential to reduce the residual stresses in the sapphire/NiAl composite system. Chemical vapor deposition (CVD) was used to produce both the compensating and compliant-fiber coatings for use in sapphire/NiAl composites. A special reactor was designed and built to produce the FGM and to handle the toxic nickel precursors. This process was successfully used to produce 500-foot lengths of fiber with coating thicknesses of approximately 3 microns, 5 microns, and 10 microns.

  18. Acoustic phonon dynamics in strained cubic and hexagonal GaN/Al2O3 superlattices

    NASA Astrophysics Data System (ADS)

    Sesion, P. D., Jr.; Albuquerque, E. L.; Vasconcelos, M. S.; Mauriz, P. W.; Freire, V. N.

    2006-06-01

    We study the acoustic-phonon spectra in periodic and quasiperiodic (Fibonacci type) superlattices made up from III V nitride materials (GaN) intercalated by sapphire (Al2O3). Due to the misalignments between the sapphire and the GaN layers that can lead to threading dislocation densities as high as 108-1010 cm-1, and a significant lattice mismatch (~14%), the phonon dynamics is described beyond the continuum elastic model using coupled elastic and electromagnetic equations, stressing the importance of the piezoelectric polarization field in a strained condition. We use a transfer-matrix treatment to simplify the algebra, which would be otherwise quite complicated, allowing a neat analytical expressions for the phonon dispersion relation. Furthermore, a quantitative analysis of the localization and magnitude of the allowed band widths in the phonon's spectra, as well as their scale law and the parametric spectrum of singularities f(α), are presented and discussed.

  19. 12CaO-7Al2O3 Electride Hollow Cathode

    NASA Technical Reports Server (NTRS)

    Rand, Lauren P. (Inventor); Williams, John D. (Inventor); Martinez, Rafael A. (Inventor)

    2017-01-01

    The use of the electride form of 12CaO-7Al2O3, or C12A7, as a low work function electron emitter in a hollow cathode discharge apparatus is described. No heater is required to initiate operation of the present cathode, as is necessary for traditional hollow cathode devices. Because C12A7 has a fully oxidized lattice structure, exposure to oxygen does not degrade the electride. The electride was surrounded by a graphite liner since it was found that the C12A7 electride converts to it's eutectic (CA+C3A) form when heated (through natural hollow cathode operation) in a metal tube.

  20. Wear Resistance of Aluminum Matrix Composites Reinforced with Al2O3 Particles After Multiple Remelting

    NASA Astrophysics Data System (ADS)

    Klasik, Adam; Pietrzak, Krystyna; Makowska, Katarzyna; Sobczak, Jerzy; Rudnik, Dariusz; Wojciechowski, Andrzej

    2016-08-01

    Based on previous results, the commercial composites of A359 (AlSi9Mg) alloy reinforced with 22 vol.% Al2O3 particles were submitted to multiple remelting by means of gravity casting and squeeze-casting procedures. The studies were focused on tribological tests, x-ray phase analyses, and microstructural examinations. More promising results were obtained for squeeze-casting method mainly because of the reduction of the negative microstructural effects such as shrinkage porosity or other microstructural defects and discontinuities. The results showed that direct remelting may be treated as economically well-founded and alternative way compared to other recycling processes. It was underlined that the multiple remelting method must be analyzed for any material separately.

  1. Synthesis and characterisation of YSZ-Al2O3 nanostructured materials.

    PubMed

    Santoyo-Salazar, J; González, G; Schabes-Retchkiman, P S; Ascencio, J A; Tartaj-Salvador, J; Chávez-Carvayar, J A

    2006-07-01

    In this work a co-precipitation route was used to synthesise two yttria-stabilised-zirconia (YSZ) phases with different concentrations of alumina (Al2O3). A tetragonal, with 3 mol% yttria, and a cubic, with 8 mol% yttria, phases were added with alumina in different weight proportions, 90/10, 80/20, 70/30, and 60/40, respectively. After synthesised, products were sintered in a range 800-1100 degrees C for different intervals of time. Compounds were characterised by X-ray diffraction, transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), and atomic force microscopy (AFM). Rietveld refinements, using FULPROF-Suite software, were carried out to obtain the cell parameters and structural characterisation of products.

  2. Effect of Surface Treatment on Shear Bond Strength between Resin Cement and Ce-TZP/Al2O3

    PubMed Central

    Kim, Jong-Eun; Kim, Jee-Hwan; Shim, June-Sung; Roh, Byoung-Duck

    2016-01-01

    Purpose. Although several studies evaluating the mechanical properties of Ce-TZP/Al2O3 have been published, to date, no study has been published investigating the bonding protocol between Ce-TZP/Al2O3 and resin cement. The aim of this study was to evaluate the shear bond strength to air-abraded Ce-TZP/Al2O3 when primers and two different cement types were used. Materials and Methods. Two types of zirconia (Y-TZP and Ce-TZP/Al2O3) specimens were further divided into four subgroups according to primer application and the cement used. Shear bond strength was measured after water storage for 3 days or 5,000 times thermocycling for artificial aging. Results. The Y-TZP block showed significantly higher shear bond strength than the Ce-TZP/Al2O3 block generally. Primer application promoted high bond strength and less effect on bond strength reduction after thermocycling, regardless of the type of cement, zirconia block, or aging time. Conclusions. Depending on the type of the primer or resin cement used after air-abrasion, different wettability of the zirconia surface can be observed. Application of primer affected the values of shear bond strength after the thermocycling procedure. In the case of using the same bonding protocol, Y-TZP could obtain significantly higher bond strength compared with Ce-TZP/Al2O3. PMID:27382569

  3. Postperovskite phase equilibria in the MgSiO3–Al2O3 system

    PubMed Central

    Tsuchiya, Jun; Tsuchiya, Taku

    2008-01-01

    We investigate high-P,T phase equilibria of the MgSiO3–Al2O3 system by means of the density functional ab initio computation methods with multiconfiguration sampling. Being different from earlier studies based on the static substitution properties with no consideration of Rh2O3(II) phase, present calculations demonstrate that (i) dissolving Al2O3 tends to decrease the postperovskite transition pressure of MgSiO3 but the effect is not significant (≈-0.2 GPa/mol% Al2O3); (ii) Al2O3 produces the narrow perovskite+postperovskite coexisting P,T area (≈1 GPa) for the pyrolitic concentration (xAl2O3 ≈6 mol%), which is sufficiently responsible to the deep-mantle D″ seismic discontinuity; (iii) the transition would be smeared (≈4 GPa) for the basaltic Al-rich composition (xAl2O3 ≈20 mol%), which is still seismically visible unless iron has significant effects; and last (iv) the perovskite structure spontaneously changes to the Rh2O3(II) with increasing the Al concentration involving small displacements of the Mg-site cations. PMID:19036928

  4. Electroless Ni-P-PTFE-Al2O3 Dispersion Nanocomposite Coating for Corrosion and Wear Resistance

    NASA Astrophysics Data System (ADS)

    Sharma, Ankita; Singh, A. K.

    2014-01-01

    With the aim to produce a coating having good corrosion and wear resistance alongside hardness but lesser friction coefficient, Ni-P-PTFE-Al2O3 (NiPPA) dispersion coating was developed. This was achieved by introducing nanosized polytetrafluoroethylene (PTFE) and alumina (Al2O3) in the Ni-P matrix deposited on mild steel substrate. The coating was characterized using scanning electron microscopy, energy dispersive analysis of x-ray, and x-ray diffractrometry. Microhardness and wear resistance of the coating was measured using Vicker's hardness tester and Pin-on-Disc method, respectively. The corrosion behavior was measured using electrochemical polarization and immersion tests with and without exposure in 3.5% NaCl solution. It is observed that codeposition of Al2O3 and PTFE particles with Ni-P coating results in comparatively smooth surface with nodular grains. The NiPPA coating was observed to have moderate hardness between electroless Ni-P-PTFE and Ni-P-Al2O3 coating and good wear resistance with lubricating effect. Addition of both PTFE and Al2O3 is observed to enhance corrosion resistance of the Ni-P coating. However, improvement in corrosion resistance is more due to addition of Al2O3 than PTFE. Continuous exposure for 10-20 days in corrosive solution is found to deteriorate corrosion protection properties of the coating.

  5. Substrate-induced band structure and electronic properties in graphene/Al2O3(0001) interface

    NASA Astrophysics Data System (ADS)

    Ilyasov, V. V.; Ershov, I. V.; Ilyasov, A. V.; Popova, I. G.; Nguyen, Chuong V.

    2015-02-01

    Band structure investigation results of two-dimensional (2D) graphene (SLG) on Al2O3(0001) using the density functional theory (DFT) method as a possible element base for spintronics are presented. Regularities of a band structure change in the order three-dimensional (3D) Al2O3 → 2D Al2O3(0001) → 2D SLG/Al2O3(0001) as well as features of a chemical bond between SLG and sapphire on the basis of DFT calculations have been studied. Analysis of the band structure and interatomic spacing in the interface for both models allows speaking about physical SLG adsorption on the (0001)-surface sapphire constrained by aluminum atoms. Energy distribution features of surface states in 2D SLG/Al2O3(0001) interface are discussed. Analysis of effective atomic charge in the interface revealed surface charge fluctuations on the substrate in the presence of SLG, which can be explained by a decrease of the energy of occupied subsurface Al2O3 states relatively to the Fermi level.

  6. Electrical characteristics of multilayered HfO2-Al2O3 charge trapping stacks deposited by ALD

    NASA Astrophysics Data System (ADS)

    Spassov, D.; Paskaleva, A.; Guziewicz, E.; Luka, G.; AKrajewski, T.; Kopalko, K.; Wierzbicka, A.; Blagoev, B.

    2016-10-01

    Electrical and charge trapping properties of atomic layer deposited HfO2-Al2O3 multilayer stacks with two different Al2O3 sublayer thicknesses were investigated regarding their implementation in charge trapping non-volatile memories. The effect of post deposition annealing in oxygen at 600°C is also studied. The decreasing Al2O3 thickness increases the stack's dielectric constant and the density of the initial positive oxide charge. The initial oxide charge increases after annealing to ∼6×1012 cm-2 and changes its sign to negative for the stacks with thicker Al2O3. The annealing enhances the dielectric constant of the stacks and reduces their thickness preserving the amorphous status. Nevertheless the annealing is not beneficial for the stacks with thicker Al2O3 as it considerably increases leakage currents. Conduction mechanisms in stacks were considered in terms of hopping conduction at low electric fields, and Fowler- Nordheim tunnelling, Schottky emission and Poole-Frenkel effect at higher ones. Maximum memory windows of about 12 and 16V were obtained for the as-grown structures with higher and lower Al2O3 content, respectively. In latter case additional improvement (the memory window increase up to 23V) is achieved by the annealing.

  7. Methionine bound to Pd/γ-Al2O3 catalysts studied by solid-state (13)C NMR.

    PubMed

    Johnson, Robert L; Schwartz, Thomas J; Dumesic, James A; Schmidt-Rohr, Klaus

    2015-11-01

    The chemisorption and breakdown of methionine (Met) adsorbed on Pd/γ-Al2O3 catalysts were investigated by solid-state NMR. (13)C-enriched Met (ca. 0.4mg) impregnated onto γ-Al2O3 or Pd/γ-Al2O3 gives NMR spectra with characteristic features of binding to γ-Al2O3, to Pd nanoparticles, and oxidative or reductive breakdown of Met. The SCH3 groups of Met showed characteristic changes in chemical shift on γ-Al2O3 (13ppm) vs. Pd (19ppm), providing strong evidence for preferential binding to Pd, while the NC carbon generates a small resonance at 96ppm assigned to a distinct nonprotonated species bound to O or Pd. Additionally, NMR shows that the SCH3 groups of Met are mobile on γ-Al2O3 but immobilized by binding to Pd particles; on small Pd particles (ca. 4nm), the NCH groups undergo large-amplitude motions. In a reducing environment, Met breaks down by C-S bond cleavage followed by formation of C2-C4 organic acids. The SCH3 signal shifts to 22ppm, which is likely the signature of the principal species responsible for strong catalyst inhibition. These experiments demonstrate that solid-state magic-angle spinning NMR of (13)C-enriched Met can be a sensitive probe to investigate catalyst surfaces and characterize catalyst inhibition both before reaction and postmortem.

  8. Preparation and photocatalytic properties of core-shell nano-TiO2 @ α-Al2O3 microspheres.

    PubMed

    Jing, Mao-Xiang; Han, Chong; Wang, Zhou; Shen, Xiang-Qian

    2014-09-01

    Core-shell nano-TiO2@a-Al2O3 microspheres of 5-20 μm were prepared by the heterogeneous precipitation method combined with the hydro-thermal and calcination process using α-Al2O3 microspheres as substrate. Their morphologies, microstructure and crystalline phase were characterized by SEM and XRD respectively. The photocatalytic activity was evaluated by degradation of methyl orange. The as-prepared 10 wt.% nano-TiO2@α -Al2O3 microspheres possess α core-shell structure with a monolayer of nano-TiO2 particles less than 30 nm on the surface of α-Al2O3 microspheres. Their photocatalytic properties are largely influenced by the calcination temperature and the sample calcined at 800 degrees C for 2 h has the best photocatalytic activity. This high photocatalytic activity can be attributed to the synergetic effects of the unique structure of nano-TiO2 @α-Al2O3 microspheres, quantum size effect, composition of crystalline phase and crystallinity of nano-TiO2. These nano-TiO2@α-Al2O3 microspheres may be conveniently separable and useful in practical treatment of organic waste waters due to the large particle size and high photocatalytic properties.

  9. Size-dependent sorption of myo-inositol hexakisphosphate and orthophosphate on nano-γ-Al2O3.

    PubMed

    Yan, Yupeng; Koopal, Luuk K; Li, Wei; Zheng, Anmin; Yang, Jun; Liu, Fan; Feng, Xionghan

    2015-08-01

    The effects of particle size (5, 35 and 70nm) on the sorption of myo-inositol hexakisphosphate (IHP) and inorganic phosphate (KH2PO4, Pi) on γ-Al2O3 nanoparticles were investigated using batch sorption experiments, zeta potential measurements and solid-state nuclear magnetic resonance spectroscopy (NMR). The results show that the maximum sorption densities (μmolm(-2)) for IHP and Pi increase with decreasing γ-Al2O3 particle size. The sorption affinity of γ-Al2O3 for IHP and Pi generally increases with decreasing particle size, and the sorption affinity for IHP is approximately one order of magnitude greater than that for Pi. In our experimental time scale, surface complexation is the main mechanism for IHP and Pi sorption on large size γ-Al2O3. While an additional surface precipitation mechanism, indicated by solid-state (31)P and (27)Al NMR data, is partly responsible for the greater sorption density on very small size γ-Al2O3. Compared with Pi, the effect of particle size on the sorption of IHP is more pronounced. The results suggest a size-dependent surface reactivity of Al2O3 nanoparticles with Pi/IHP. The underlying mechanism will also be relevant for other small nanosize (hydr)oxide particles and is important for our understanding of the role of small nanoparticles in controlling the mobility and fate of organic and inorganic phosphates in the environment.

  10. Titanium distribution profiles obtained by luminescence and LIBS measurements on Ti: Al2O3 grown by Czochralski and Kyropoulos techniques

    NASA Astrophysics Data System (ADS)

    Alombert-Goget, Guillaume; Trichard, Florian; Li, Hui; Pezzani, Cyril; Silvestre, Maud; Barthalay, Nicolas; Motto-Ros, Vincent; Lebbou, Kheirreddine

    2017-03-01

    The titanium distributions in Ti-doped sapphires grown by Czochralski and Kyropoulos techniques were evaluated using Laser-Induced Breakdown Spectroscopy (LIBS) and luminescence characterizations. Distinctly different radial profiles of Ti4+ distribution were observed in the as grown Ti: Al2O3 crystals. The Ti4+ distribution in the crystal grown by Kyropoulos technique was analyzed as a function of the specific of the growth technique, the conclusion is significant for Ti: sapphire on laser application. Kyropoulos technique presents an advantage to reduce the proportion of Ti4+ in Ti: sapphire comparing to Czochralski technique.

  11. [Experimental study of catalytic reduction of SO2 on CeO2-La2O3/gamma-Al2O3 rare earth mixed compounds].

    PubMed

    Hu, Hui; Li, Jin; Zhang, Shun-xi; Li, Sheng-li

    2004-03-01

    Addition of rare earth oxide CeO2 with variable valences to La2O3 formed a mixture of rare earth oxides. This mixture can be used as the catalyst for the reduction of SO2 by CO. In a fixed-bed flow reactor, experimental were investigated for studying the activation process of this catalyst and effect factors such as temperature and concentration ratio of reactant on the activation reaction under the following conditions: composition of the gas mixture SO2:CO = 1:3, balancing with N2 and feed flow rate 1000 mL/min. The phase structure changes of this catalyst were expressed with XRD and XPS. The results demonstrated that the activation temperature of CeO2-La2O3/gamma-Al2O3 is 50-100 degrees C lower than that of a single component La2O3/gamma-Al2O3 or CeO2/gamma-Al2O3, and the mixture of rare earth oxides has higher activity on catalytic reduction of SO2 by CO. It's most likely that the result reveals on the synergism between CeO2 and La2O3.

  12. Composition Optimization of Al-DOPING Lithium Manganese Oxide from Al2O3-Li2CO3-MnO2 Ternary System

    NASA Astrophysics Data System (ADS)

    He, Gang; Sun, Xinyan; Hong, Jianhe; He, Mingzhong

    2013-07-01

    In order to synthesize eutectic compound of Al doping lithium manganese oxide which can be used as cathode material in lithium battery, using γ-Al2O3, Li2CO3 and MnO2 as starting raw materials, the composition optimization research work has been done by the solid state synthesis method. A limited composition range was found in Al2O3-Li2CO3-MnO2 ternary system, in which the synthesized Al doping lithium manganese oxides have single spinel structure and good electrochemical performance. The results showed that the LiAl0.04Mn1.96O4 material presented better charge-discharge cycling behavior than pure LiMn2O4, and showed the best electrochemistry property among the compounds in the Al2O3-Li2O-Mn2O3 ternary system. LiAl0.04Mn1.96O4 still kept perfect cubic structure, but LiMn2O4 kept the coexistence of the cubic and tetragonal phases after 50 charge-discharge cycles.

  13. EXAFS Characterization of Dendrimer-Derived Pt/γ-Al2O3

    NASA Astrophysics Data System (ADS)

    Siani, A.; Alexeev, O. S.; Williams, C. T.; Ploehn, H. J.; Amiridis, M. D.

    2007-02-01

    The various steps involved in the preparation of a Pt/γ-Al2O3 material using hydroxyl-terminated generation four (G4OH) PAMAM dendrimers as templates were monitored by EXAFS. The results indicate that Cl ligands in the Pt precursors (H2PtCl6 and K2PtCl4) were partially replaced by aquo ligands upon hydrolysis to form [PtCl3(H2O)3]+ and [PtCl2(H2O)2] species. After interaction of such species with G4OH, Cl ligands from the first coordination shell of Pt were further replaced by nitrogen atoms from the dendrimer interior, indicating the complexation of Pt with the dendrimer. This process was accompanied by a transfer of the electron density from the dendrimer to Pt, indicating that the former plays the role of a ligand. Following treatment of the H2PtCl6/G4OH and K2PtCl4/G4OH composites with NaBH4, no substantial changes were detecteded in the electronic or coordination environment of Pt, and no formation of metal nanoparticles was observed. However, when the reduction treatment was performed with H2, the formation of extremely small Pt clusters incorporating no more than 4 Pt atoms was observed. These Pt species remained strongly bonded to the dendrimer and their nuclearity depends on the length of the H2 treatment. Formation of Pt nanoparticles with an average diameter of approximately 10 Å was finally observed after the deposition of H2PtCl6/G4OH on γ-Al2O3 and drying, suggesting that their formation may be related to the collapse of the dendrimer structure. The Pt nanoparticles formed appear to have high mobility, since subsequent thermal treatment in O2/H2 led to further sintering.

  14. Optimization of Al2O3 and Li3BO3 Content as Sintering Additives of Li7- x La2.95Ca0.05ZrTaO12 at Low Temperature

    NASA Astrophysics Data System (ADS)

    Rosero-Navarro, Nataly Carolina; Miura, Akira; Higuchi, Mikio; Tadanaga, Kiyoharu

    2017-01-01

    Simultaneous effect of Al2O3 and Li3BO3 additions on sintering behavior and Li-ion conductivity of Li7- x La2.95Ca0.05ZrTaO12 (LLCZT) garnet electrolyte sintered at 900°C (10 h) is evaluated. The crystal phase and microstructure of the different composites were evaluated by x-ray diffraction and scanning electron microscopy (SEM), respectively. Electrical properties of the composites with high relative densities (95%) were examined by impedance spectroscopy. The cubic phase was formed for LLCZT sintered with 0-0.21 mol of Al2O3 and 0.70 mol-0.80 mol of Li3BO3. The excess of Al2O3 (0.22 mol) led to the formation of secondary phases. SEM observation revealed the good interconnection between LLCZT grains and the distribution of the glassy phase formed by Li3BO3 and Al2O3. Effective combination of 0.21 mol of Al2O3 and 0.80 mol of Li3BO3 produced denser material with high relative density of 95% and high Li-ion conduction of 1 × 10-4 S/cm at 32°C.

  15. Structural insights into M2O-Al2O3-WO3 (M = Na, K) system by electron diffraction tomography.

    PubMed

    Andrusenko, Iryna; Krysiak, Yaşar; Mugnaioli, Enrico; Gorelik, Tatiana E; Nihtianova, Diana; Kolb, Ute

    2015-06-01

    The M2O-Al2O3-WO3 (M = alkaline metals) system has attracted the attention of the scientific community because some of its members showed potential applications as single crystalline media for tunable solid-state lasers. These materials behave as promising laser host materials due to their high and continuous transparency in the wide range of the near-IR region. A systematic investigation of these phases is nonetheless hampered because it is impossible to produce large crystals and only in a few cases a pure synthetic product can be achieved. Despite substantial advances in X-ray powder diffraction methods, structure investigation on nanoscale is still challenging, especially when the sample is polycrystalline and the structures are affected by pseudo-symmetry. Electron diffraction has the advantage of collecting data from single nanoscopic crystals, but it is frequently limited by incompleteness and dynamical effects. Automated diffraction tomography (ADT) recently emerged as an alternative approach able to collect more complete three-dimensional electron diffraction data and at the same time to significantly reduce dynamical scattering. ADT data have been shown to be suitable for ab initio structure solution of phases with large cell parameters, and for detecting pseudo-symmetry that was undetected in X-ray powder data. In this work we present the structure investigation of two hitherto undetermined compounds, K5Al(W3O11)2 and NaAl(WO4)2, by a combination of electron diffraction tomography and precession electron diffraction. We also stress how electron diffraction tomography can be used to obtain direct information about symmetry and pseudo-symmetry for nanocrystalline phases, even when available only in polyphasic mixtures.

  16. Preparation of nanocomposite γ-Al2O3/polyethylene separator crosslinked by electron beam irradiation for lithium secondary battery

    NASA Astrophysics Data System (ADS)

    Nho, Young-Chang; Sohn, Joon-Yong; Shin, Junhwa; Park, Jong-Seok; Lim, Yoon-Mook; Kang, Phil-Hyun

    2017-03-01

    Although micro-porous membranes made of polyethylene (PE) offer excellent mechanical strength and chemical stability, they exhibit large thermal shrinkage at high temperature, which causes a short circuit between positive and negative electrodes in cases of unusual heat generation. We tried to develop a new technology to reduce the thermal shrinkage of PE separators by introducing γ-Al2O3 particles treated with coupling agent on PE separators. Nanocomposite γ-Al2O3/PE separators were prepared by the dip coating of polyethylene(PE) separators in γ-Al2O3/poly(vinylidenefluoride-hexafluoropropylene) (PVDF-HFP)/crosslinker (1,3,5-trially-1,3,5-triazine-2,4,6(1 H,3 H,5 H)-trione (TTT) solution with humidity control followed by electron beam irradiation. γ-Al2O3/PVDF-HFP/TTT (95/5/2)-coated PE separator showed the highest electrolyte uptake (157%) and ionic conductivity (1.3 mS/cm). On the basis of the thermal shrinkage test, the nanocomposite γ-Al2O3/PE separators containing TTT irradiated by electron beam exhibited a higher thermal resistance. Moreover, a linear sweep voltammetry test showed that the irradiated nanocomposite γ-Al2O3/PE separators have electrochemical stabilities of up to 5.0 V. In a battery performance test, the coin cell assembled with γ-Al2O3/PVDF-HFP/TTT-coated PE separator showed excellent discharge cycle performance.

  17. Antibacterial potential of Al2O3 nanoparticles against multidrug resistance strains of Staphylococcus aureus isolated from skin exudates

    NASA Astrophysics Data System (ADS)

    Ansari, Mohammad Azam; Khan, Haris M.; Khan, Aijaz A.; Pal, Ruchita; Cameotra, Swaranjit Singh

    2013-10-01

    To date very little studies are available in the literature on the interaction of Al2O3 nanoparticles with multidrug-resistant strains of Staphylococcus aureus. Considering the paucity of earlier reports the objective of present study was to investigate the antibacterial activity of Al2O3 NPs (<50 nm) against methicillin-resistant S. aureus and methicillin-resistant coagulase negative staphylococci by various methods. Al2O3 NPs were characterized by scanning electron microscopy, high-resolution transmission electron microscopy, and X-ray diffraction. The MIC was found to be in the range of 1,700-3,400 μg/ml. Almost no growth was observed at 2,000 μg/ml for up to 10 h. SEM micrograph revealed that the treated cells were significantly damaged, showed indentation on cell surface and clusters of NPs on bacterial cell wall. HR-TEM micrograph shows disruption and disorganization of cell membrane and cell wall. The cell membrane was extensively damaged and, most probably, the intracellular content has leaked out. Al2O3 NPs not only adhered at the surface of cell membrane, but also penetrated inside the bacterial cells, cause formation of irregular-shaped pits and perforation on their surfaces and may also interact with the cellular macromolecules causing adverse effect including cell death. The data presented here are novel in that Al2O3 NPs are effective bactericidal agents regardless of the drug resistance mechanisms that confer importance to these bacteria as an emergent pathogen. Therefore, in depth studies regarding the interaction of Al2O3 NPs with cells, tissues, and organs as well as the optimum dose required to produce therapeutic effects need to be ascertained before we can expect a more meaningful role of the Al2O3 NPs in medical application.

  18. Thermal stability of surface and interface structure of atomic layer deposited Al2O3 on H-terminated silicon

    NASA Astrophysics Data System (ADS)

    Gao, K. Y.; Speck, F.; Emtsev, K.; Seyller, Th.; Ley, L.

    2007-11-01

    Using the atomic layer deposition technique, 1.2nm Al2O3 films were deposited as high-k gate dielectric layer on hydrogen-terminated silicon and annealed in vacuum and pure hydrogen in order to elucidate the effects of growth and annealing on the structure of film, interface, and surface. As analytical tools, high resolution core level spectroscopy using synchrotron radiation as variable photon source and Fourier Transform Infrared absorption spectroscopy in the attenuated total refraction mode were employed. For Al2O3 on H-terminated Si(111) and (100) surfaces the Si-H bonds are preserved at the interface, while Si-O-Al bonds provide the atomically abrupt interface between Al2O3 and Si. The chemical and structural integrity of the interface is maintained upon annealing except for a gradual loss of Si-H bonds. Growth of a SiO2 layer is observed after annealing, that is unambiguously located at the Al2O3 surface and not at the interface. Stress-induced emission of Si atoms from the interface is identified as the source of SiO2 based on a substantial broadening of the Si 2p core lines. A thermally induced reaction between Si and Al2O3 to form volatile SiO and Al2O is suggested to be responsible for the significant thickness reduction of Al2O3 that accompanies annealing at temperatures of 750°C. Conclusions for the likely effects of forming gas anneals on Al2O3/Si are drawn from this work.

  19. Kinetics for Steam and CO2 Reforming of Methane Over Ni/La/Al2O3 Catalyst.

    PubMed

    Park, Myung Hee; Choi, Bong Kwan; Park, Yoon Hwa; Moon, Dong Ju; Park, Nam Cook; Kim, Young Chul

    2015-07-01

    Kinetic studies of mixed (steam and dry) reforming of methane on Ni/La/Al2O3 and Ni/La-Co (1, 3 wt%)/Al2O3 catalysts were performed in an atmospheric fixed-bed reactor. Kinetic parameters for the mixed reforming over these catalysts were obtained under reaction conditions free from heat and mass transfer limitations. Variables for the mixed reforming were the reaction temperature and partial pressure of reactants. The fitting of the experimental data for the rate of methane conversion, rCH4, using the power law rate equation rCH4 = k(PrCH4)α(PCO2)β(PH2O)γ showed that the reaction orders α, β, and γ are steady and obtained values equal to α = 1, β = 0, and γ = 0. In other words, among CH4, CO2, H2O, and H2, only CH4 reaction orders were not zero and they were affected by the promoters. The apparent activation energy on catalysts Ni/La/Al2O3, Ni/La-Co (1)/Al2O3 and Ni/La-Co (3)/Al2O3 is 85.2, 93.8, and 99.4 kJ/mol, respectively. The addition of Co to Ni/La/Al2O3 was increased the apparent activation energy of the mixed reforming reaction. And the Ni/La-Co (3 wt%)/Al2O3 catalyst showed the highest reforming activity and apparent activation energy. The Co promoters can increase the apparent activation energy of mixed reforming of methane.

  20. Processing of spent NiMo and CoMo/Al2O3 catalysts via fusion with KHSO4.

    PubMed

    Busnardo, Roberto Giovanini; Busnardo, Natália Giovanini; Salvato, Gustavo Nascimento; Afonso, Júlio Carlos

    2007-01-10

    This work describes a route for processing spent commercial hydrorefining (HDR) catalysts (CoMo and NiMo/Al2O3), containing support additives, for recovering active phase and support components. Samples were used as catalysts in diesel hydrotreaters. They had neither been submitted to mechanical stresses nor overheating while under operation. The route is based on fusion of samples with KHSO4. Four experimental parameters were optimized: reaction time, sample/flux mass ratio, temperature, and sample physical characteristics (ground/non-ground). After fusion, the solid was dissolved in water (90-100 degrees C); the insoluble matter presented low crystallization. Several phases were identified: silicates, spinel-like compounds and aluminosilicates. Cobalt, nickel, molybdenum and aluminum were recovered by conventional precipitation techniques or selective solvent-extraction procedures, with at least 85 wt.% yield. Final liquid colorless effluents are obtained as neutral solutions of alkali sulfates or chlorides and a water insoluble solid after fusion, which can be either sent to industrial dumps or co-processed. Fusion with KHSO4 was shown to be applicable to the catalysts of the present study, and the optimized experimental parameters are much less drastic than the conventional pyrometallurgical routes proposed in the literature.

  1. Electronic structure, mechanical, and optical properties of CaO·Al2O3 system: a first principles approach

    NASA Astrophysics Data System (ADS)

    Hussain, A.; Mehmood, S.; Rasool, M. N.; Aryal, S.; Rulis, P.; Ching, W. Y.

    2016-08-01

    A comprehensive study of the structure, bonding, mechanical and optical properties of five stable phases within the calcium aluminate (Ca-Al-O) series with different CaO to Al2O3 proportions has been carried out using the density functional theory based orthogonalized linear combination of atomic orbitals (OLCAO) method. The phases are C3A, C12A7-crystal, CA, CA2, and CA6 and the oxygen deficient C12A7-electride phase. These five stable phases are wide band gap insulators with energy gap values ranging from 3.85 to 4.62 eV. The charge neutral C12A7-crystal has localized defective states in the gap whereas the C12A7-electride phase has a region of metallic bands of about 2 eV wide in the gap. Effective charge and bond order calculations reveal intimate details of electronic structure and bonding in relation to the aluminate contents in the series. It is shown that Al-O bonds dominate the Ca-O bonds in determining the crystal strength with CA6 having the highest and C12A7 having the lowest bond order density. Calculations of elastic coefficients and mechanical properties in these crystals show a high degree of diversity and anisotropic behavior consistent with the bond order calculations. The refractive index values from optical properties calculations are in good agreement with available literature. Other results furnish more insights for the Ca-Al-O series and provide the opportunity for further investigations on similar or more complicated quaternary systems with potential novel properties.

  2. Generation of sub-20-femtosecond pulses from mode-locked Ti:Al2O3 lasers with reduced cubic phase

    NASA Astrophysics Data System (ADS)

    Proctor, Bob; Wise, Frank W.

    1993-06-01

    The third-order dispersion of a modelocked Ti:Al2O3 laser can be reduced by using quartz prisms for dispersion control. Two such lasers have been constructed, one which uses a novel sequence of four quartz prisms and a second which uses a pair of quartz prisms. The laser which incorporates four quartz prisms allows transform-limited 13-fs pulses to be generated with a gain crystal 20 mm long. The second laser has four times less third-order dispersion but does not produce pulses shorter than 15 fs. Evidence is presented to show that third-order dispersion is not limiting pulse duration.

  3. Ultrahigh-pressure acoustic wave velocities of SiO2-Al2O3 glasses up to 200 GPa

    NASA Astrophysics Data System (ADS)

    Ohira, Itaru; Murakami, Motohiko; Kohara, Shinji; Ohara, Koji; Ohtani, Eiji

    2016-12-01

    Extensive experimental studies on the structure and density of silicate glasses as laboratory analogs of natural silicate melts have attempted to address the nature of dense silicate melts that may be present at the base of the mantle. Previous ultrahigh-pressure experiments, however, have been performed on simple systems such as SiO2 or MgSiO3, and experiments in more complex system have been conducted under relatively low-pressure conditions below 60 GPa. The effect of other metal cations on structural changes that occur in dense silicate glasses under ultrahigh pressures has been poorly understood. Here, we used a Brillouin scattering spectroscopic method up to pressures of 196.9 GPa to conduct in situ high-pressure acoustic wave velocity measurements of SiO2-Al2O3 glasses in order to understand the effect of Al2O3 on pressure-induced structural changes in the glasses as analogs of aluminosilicate melts. From 10 to 40 GPa, the transverse acoustic wave velocity ( V S ) of Al2O3-rich glass (SiO2 + 20.5 mol% Al2O3) was greater than that of Al2O3-poor glass (SiO2 + 3.9 mol% Al2O3). This result suggests that SiO2-Al2O3 glasses with higher proportions of Al ions with large oxygen coordination numbers (5 and 6) become elastically stiffer up to 40 GPa, depending on the Al2O3 content, but then soften above 40 GPa. At pressures from 40 to ~100 GPa, the increase in V S with increasing pressure became less steep than below 40 GPa. Above ~100 GPa, there were abrupt increases in the P-V S gradients ( dV S /dP) at 130 GPa in Al2O3-poor glass and at 116 GPa in Al2O3-rich glass. These changes resemble previous experimental results on SiO2 glass and MgSiO3 glass. Given that changes of dV S / dP have commonly been related to changes in the Si-O coordination states in the glasses, our results, therefore, may indicate a drastic structural transformation in SiO2-Al2O3 glasses above 116 GPa, possibly associated with an average Si-O coordination number change to higher than 6. Compared

  4. Analysis of the co-deposition of Al2O3 particles with nickel by an electrolytic route: The influence of organic additives presence and Al2O3 concentration

    NASA Astrophysics Data System (ADS)

    Temam, H. B.; Temam, E. G.

    2016-04-01

    Alloy coatings were prepared by co-deposition of Al2O3 particles in Ni matrix on carbon steel substrate from nickel chloride bath in which metallic powders were held in suspension. The influence of metal powder amount in the bath on chemical composition, morphology, thickness, microhardness and corrosion behavior of obtained coatings, has been investigated. It was shown that the presence of Al2O3 particles in deposit greatly improves the hardness and the wear resistance of alloy coatings. Characterization by microanalysis (EDX) of the various deposits elaborated confirms that the rate of particles incorporated increases as the concentration of solid particles increasing. The results showed that the presence of organic additives in Ni-Al2O3 electrolyte deposition led to an increase in the hardness and corrosion resistance of the deposits.

  5. Glass structure and NIR emission of Er3+ at 1.5 μm in oxyfluoride BaF2-Al2O3-B2O3 glasses

    NASA Astrophysics Data System (ADS)

    Shinozaki, Kenji; Pisarski, Wojciech; Affatigato, Mario; Honma, Tsuyoshi; Komatsu, Takayuki

    2015-12-01

    The glass structure, photoluminescence properties of Eu3+, Judd-Ofelt analysis, and near infrared emissions of Er3+ at 1.5 μm in the oxyfluoride glasses and glass-ceramics of 1Eu2O3- or 1Er2O3-doped 50BaF2-xAl2O3-(50 - x)B2O3 (x = 0-25 mol%) were investigated. It was clarified on the ground of Raman scattering spectroscopy and F1s and O1s XPS measurements that the glass with no Al2O3 (1Er2O3-50BaF2-50B2O3) is composed of BO3, BO2F and BO3F units with F-Ba bonds. The glasses with 25Al2O3 (1Er2O3-50BaF2-25Al2O3-25B2O3) is mainly composed of BO3- and Al(O,F)x units. Existence of non-bridging oxygen was not detected by O1s-XPS spectra. It was proposed that these structures are largely affected on crystallization behavior, e.g., the glass with no Al2O3 forms BaF2 and β-BaB2O4 due to Ba-F bonds and the glass with 25Al2O3 forms BaAlBO3F2 because the glass structure composed of BO3 and Al(O,F) units is similar to the BaAlBO3F2 crystal structure. Judd-Ofelt parameters of Er3+ and Eu3+ in the glasses showed almost the same values in Ω4 and Ω6 for each glass, on the other hand Ω2 decreased with addition of Al2O3. The emission spectra of Er3+ at 1.5 μm in the glasses and glass-ceramics with BaAlBO3F2 crystals showed broad peaks. It is proposed that oxyfluoride glasses and glass-ceramics based on the BaF2-Al2O3-B2O3 system have a high potential for optical device applications such as broadband optical amplifiers.

  6. Effect of Al2O3 encapsulation on multilayer MoSe2 thin-film transistors

    NASA Astrophysics Data System (ADS)

    Lee, Hyun Ah; Yeoul Kim, Seong; Kim, Jiyoung; Choi, Woong

    2017-03-01

    We report the effect of Al2O3 encapsulation on the device performance of multilayer MoSe2 thin-film transistors based on statistical investigation of 29 devices with a SiO2 bottom-gate dielectric. On average, Al2O3 encapsulation by atomic layer deposition increased the field-effect mobility from 10.1 cm2 V‑1 s‑1 to 14.8 cm2 V‑1 s‑1, decreased the on/off-current ratio from 8.5  ×  105 to 2.3  ×  105 and negatively shifted the threshold voltage from  ‑1.1 V to  ‑8.1 V. Calculation based on the Y-function method indicated that the enhancement of intrinsic carrier mobility occurred independently of the reduction of contact resistance after Al2O3 encapsulation. Furthermore, contrary to previous reports in the literature, we observe a negligible effect of thermal annealing on contact resistance and carrier mobility during the atomic layer deposition of Al2O3. These results demonstrate that Al2O3 encapsulation is a useful method for improving the carrier mobility of multilayer MoSe2 transistors, providing important implications on the application of MoSe2 and other 2D materials into high-performance transistors.

  7. Temperature-dependent elastic stiffness constants of α- and θ-Al2O3 from first-principles calculations.

    PubMed

    Shang, Shun-Li; Zhang, Hui; Wang, Yi; Liu, Zi-Kui

    2010-09-22

    Temperature-dependent elastic stiffness constants (c(ij)s), including both the isothermal and isoentropic ones, have been predicted for rhombohedral α-Al(2)O(3) and monoclinic θ-Al(2)O(3) in terms of a quasistatic approach, i.e., a combination of volume-dependent c(ij)s determined by a first-principles strain versus stress method and direction-dependent thermal expansions obtained by first-principles phonon calculations. A good agreement is observed between the predictions and the available experiments for α-Al(2)O(3), especially for the off-diagonal elastic constants. In addition, the temperature-dependent c(ij)s predicted herein, in particular the ones for metastable θ-Al(2)O(3), enable the stress analysis at elevated temperatures in thermally grown oxides containing α- and θ-Al(2)O(3), which are crucial to understand the failure of thermal barrier coatings in gas-turbine engines.

  8. Development of Ni-Mo/Al2O3 catalyst for reverse water gas shift (RWGS) reaction.

    PubMed

    Kharaji, Abolfazl Gharibi; Shariati, Ahmad; Ostadi, Mohammad

    2014-09-01

    In the present study, Mo/Al2O3 catalyst was prepared using impregnation method. Then it was promoted with Ni ions to produce Ni-Mo/Al2O3 catalyst. The structures of the catalysts were studied using X-ray diffraction (XRD), Energy dispersive X-ray (EDAX), Brunauer-Emmett-Teller (BET), X-ray photoelectron spectroscopy (XPS), CO chemisorption, temperature programmed reduction of hydrogen (H2-TPR) and scanning electron microscope (SEM) techniques. Catalytic performances of the two catalysts were investigated in a fixed-bed reactor for RWGS reaction. The results indicated that addition of nickel promoter to Mo/Al2O3 catalyst enhances its activity. It is reasonable for the electron deficient state of the Ni species and existence of NiMoO4 phase to possess high activity in RWGS reaction. Stability test of Ni-Mo/Al2O3 catalyst was carried out in a fixed bed reactor and a high CO2 conversion for 60 h time on stream was demonstrated. This study introduces a new catalyst, Ni-Mo/Al2O3, with high activity and stability for RWGS reaction.

  9. Assimilation Behavior of Calcium Ferrite and Calcium Diferrite with Sintered Al2O3 and MgO

    NASA Astrophysics Data System (ADS)

    Long, Hongming; Wu, Xuejian; Chun, Tiejun; Di, Zhanxia; Yu, Bin

    2016-10-01

    In this study, the assimilation behaviors between calcium ferrite (CF), calcium diferrite (CF2) and sintered Al2O3, and MgO were explored by an improved sessile drop technique, and the interfacial microstructure was discussed. The results indicated that the apparent contact angles of CF slag on Al2O3 and MgO substrate were 15.7 and 5.5 deg, and the apparent contact angles of CF2 slag on Al2O3 and MgO substrate were 17.9 and 7.2 deg, respectively. Namely, CF and CF2 slag were wetting well with Al2O3 and MgO substrate. The dissolution of Al2O3 substrate into the CF and CF2 slag was found to be the driving force of the wetting process. For the CF-MgO and CF2-MgO substrate systems, CaO contrarily distributed with MgO after wetting. For the CF-MgO system, after wetting, the slag was composed of CF and C2F, and most of the Fe2O3 permeated into substrate and formed two permeating layers.

  10. Methanobactin-Mediated Synthesis of Gold Nanoparticles Supported over Al2O3 toward an Efficient Catalyst for Glucose Oxidation

    PubMed Central

    Xin, Jia-Ying; Lin, Kai; Wang, Yan; Xia, Chun-Gu

    2014-01-01

    Methanobactin (Mb) is a copper-binding peptide that appears to function as an agent for copper sequestration and uptake in methanotrophs. Mb can also bind and reduce Au(III) to Au(0). In this paper, Au/Al2O3 catalysts prepared by a novel incipient wetness-Mb-mediated bioreduction method were used for glucose oxidation. The catalysts were characterized, and the analysis revealed that very small gold nanoparticles with a particle size <4 nm were prepared by the incipient wetness-Mb-mediated bioreduction method, even at 1.0% Au loading (w/w). The influence of Au loading, calcination temperature and calcination time on the specific activity of Au/Al2O3 catalysts was systematically investigated. Experimental results showed that decomposing the Mb molecules properly by calcinations can enhance the specific activity of Au/Al2O3 catalysts, though they acted as reductant and protective agents during the catalyst preparation. Au/Al2O3 catalysts synthesized by the method exhibited optimum specific activity under operational synthesis conditions of Au loading of 1.0 wt % and calcined at 450 °C for 2 h. The catalysts were reused eight times, without a significant decrease in specific activity. To our knowledge, this is the first attempt at the preparation of Au/Al2O3 catalysts by Mb-mediated in situ synthesis of gold nanoparticles. PMID:25429424

  11. Microstructure Investigation of Cu-Ni Base Al2O3 Nanocomposites: From Nanoparticles Synthesis to Consolidation

    NASA Astrophysics Data System (ADS)

    Ramos, M. I.; Suguihiro, N. M.; Brocchi, E. A.; Navarro, R.; Solorzano, I. G.

    2017-02-01

    Different compositions of Cu-Ni/Al2O3 nanocomposites were prepared by a chemical-based synthesis of co-formed oxides (CuO-NiO-Al2O3) nanoparticles followed by selective hydrogen reduction of the Cu and Ni oxides and finally by consolidation into pellets. The synthesized composites with both phases (metallic and oxide) containing nanoparticles in the 5 to 60 nm range have been systematically produced. Micro- and nanoscale characterization techniques were extensively employed in all stages of the process. X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses have shown a heterogeneous distribution of chemical elements resulting in the formation of Cu- and Ni-rich nanoparticles containing Al2O3 phase in a controlled low volume fraction, which later mostly dispersed between the metallic particle and, to a lesser extent, within metallic particles. After consolidation, under uniaxial pressure followed by sintering, the compacted nanocomposite observed in the transmission electron microscope (TEM) revealed that the Al2O3 have been more homogeneously distributed as such: the majority of it at the newly formed grain boundaries of the consolidated pellet and a small part of it within the metallic Cu-Ni matrix. Microhardness measurements demonstrate that dispersion of Al2O3 was successfully achieved as reinforcement phase, yielding up to 100 pct increase in hardness.

  12. Comparing the Thermodynamic Behaviour of Al(1)+ZrO2(s) to Al(1)+Al2O3(s)

    NASA Technical Reports Server (NTRS)

    Copland, Evan

    2004-01-01

    In an effort to better determine the thermodynamic properties of Al(g) and Al2O(g). the vapor in equilibrium with Al(l)+ZrO2(s) was compared to the vapor in equilibrium with Al(l)+Al2O3(s) over temperature range 1197-to-1509K. The comparison was made directly by Knudsen effusion-cell mass spectrometry with an instrument configured for a multiple effusion-cell vapor source (multi-cell KEMS). Second law enthalpies of vaporization of Al(g) and Al2O(g) together with activity measurements show that Al(l)+ZrO2(s) is thermodynamically equivalent to Al(l)+Al2O3(s), indicating Al(l) remained pure and Al2O3(s) was present in the ZrO2-cell. Subsequent observation of the Al(l)/ZrO2 and vapor/ZrO2 interfaces revealed a thin Al2O3-layer had formed, separating the ZrO2-cell from Al(l) and Al(g)+Al2O(g), effectively transforming it into an Al2O3 effusion-cell. This behavior agrees with recent observations made for Beta-NiAl(Pt) alloys measured in ZrO2 effusion-cell.

  13. W:Al2O3 nanocomposite thin films with tunable optical properties prepared by atomic layer deposition

    DOE PAGES

    Babar, Shaista; Mane, Anil U.; Yanguas-Gil, Angel; ...

    2016-06-17

    Here, a systematic alteration in the optical properties of W:Al2O3 nanocomposite films is demonstrated by precisely varying the W cycle percentage (W%) from 0 to 100% in Al2O3 during atomic layer deposition. The direct and indirect band energies of the nanocomposite materials decrease from 5.2 to 4.2 eV and from 3.3 to 1.8 eV, respectively, by increasing the W% from 10 to 40. X-ray absorption spectroscopy reveals that, for W% < 50, W is present in both metallic and suboxide states, whereas, for W% ≥ 50, only metallic W is seen. This transition from dielectric to metallic character at W%more » ~ 50 is accompanied by an increase in the electrical and thermal conductivity and the disappearance of a clear band gap in the absorption spectrum. The density of the films increases monotonically from 3.1 g/cm3 for pure Al2O3 to 17.1 g/cm3 for pure W, whereas the surface roughness is greatest for the W% = 50 films. The W:Al2O3 nanocomposite films are thermally stable and show little change in optical properties upon annealing in air at 500 °C. These W:Al2O3 nanocomposite films show promise as selective solar absorption coatings for concentrated solar power applications.« less

  14. Passivation Effect of Atomic Layer Deposition of Al2O3 Film on HgCdTe Infrared Detectors

    NASA Astrophysics Data System (ADS)

    Zhang, Peng; Ye, Zhen-Hua; Sun, Chang-Hong; Chen, Yi-Yu; Zhang, Tian-Ning; Chen, Xin; Lin, Chun; Ding, Ring-Jun; He, Li

    2016-09-01

    The passivation effect of atomic layer deposition of (ALD) Al2O3 film on a HgCdTe infrared detector was investigated in this work. The passivation effect of Al2O3 film was evaluated by measuring the minority carrier lifetime, capacitance versus voltage ( C- V) characteristics of metal-insulator-semiconductor devices, and resistance versus voltage ( R- V) characteristics of variable-area photodiodes. The minority carrier lifetime, C- V characteristics, and R- V characteristics of HgCdTe devices passivated by ALD Al2O3 film was comparable to those of HgCdTe devices passivated by e-beam evaporation of ZnS/CdTe film. However, the baking stability of devices passivated by Al2O3 film is inferior to that of devices passivated by ZnS/CdTe film. In future work, by optimizing the ALD Al2O3 film growing process and annealing conditions, it may be feasible to achieve both excellent electrical properties and good baking stability.

  15. Enhancement of the photoluminescence in Er-doped Al2O3 fabricated by atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Rönn, John; Karvonen, Lasse; Pyymäki-Perros, Alexander; Peyghambarian, Nasser; Lipsanen, Harri; Säynätjoki, Antti; Sun, Zhipei

    2016-02-01

    We show the enhancement of the photoluminescence at λ = 1:5 μm in highly-doped (> 1021 cm-3) Er-Al2O3 samples by controlling the vertical distance between the Er-ions using atomic layer deposition (ALD) technique. Er2O3 and Al2O3 were deposited on top of silicon in an alternating fashion with ALD. Five Er2O3-Al2O3 samples were fabricated by keeping the amount of Er2O3 constant but changing the thickness of the Al2O3-layers between the Er2O3-layers. The PL spectra of the samples reveal that the PL signal enhances up to 90% when the vertical distance (the number of Al2O3-layers) between the Er-ions increases. The PL enhancement can be related to the reduction of up-conversion signal at 532 and 650 nm in the Er-ions. Our results demonstrate that ALD is an excellent technique to fabricate and to optimize Er-doped materials due to its unique depositions properties.

  16. Solubility and partitioning of water in synthetic forsterite and enstatite in the system MgO SiO2 H2O±Al2O3

    NASA Astrophysics Data System (ADS)

    Grant, Kevin J.; Kohn, Simon C.; Brooker, Richard A.

    2006-06-01

    The solubility of water in coexisting enstatite and forsterite was investigated by simultaneously synthesizing the two phases in a series of high pressure and temperature piston cylinder experiments. Experiments were performed at 1.0 and 2.0 GPa at temperatures between 1,100 and 1,420°C. Integrated OH absorbances were determined using polarized infrared spectroscopy on orientated single crystals of each phase. Phase water contents were estimated using the calibration of Libowitzky and Rossman (Am Mineral 82:1111 1115, 1997). Enstatite crystals, synthesized in equilibrium with forsterite and an aqueous phase at 1,350°C and 2.0 GPa, contain 114 ppm H2O. This is reduced to 59 ppm at 1,100°C, under otherwise identical conditions, suggesting a strong temperature dependence. At 1,350°C and 1.0 GPa water solubility in enstatite is 89 ppm, significantly lower than that at 2.0 GPa. In contrast water solubility in forsterite is essentially constant, being in the range 36 41 ppm for all conditions studied. These data give partition coefficients {text{D}}_{{{text{H}}2 {text{O}}}} ^{{{text{en}}/{text{fo}}}} in the range 2.28 3.31 for all experiments at 1,350°C and 1.34 for one experiment at 1,100°C. The incorporation of Al2O3 in enstatite modifies the OH stretching spectrum in a systematic way, and slightly increases the water solubility.

  17. ENERGY CONVERSION FOR THE TRANSITION FROM Al TO γ-Al2O3 NANOPARTICLES

    NASA Astrophysics Data System (ADS)

    Wang, Shulin; Li, Shengjuan; Xu, Bo; Jian, Dunliang; Zhu, Yufang

    2013-07-01

    We have successfully converted large volume Al particles into γ-Al2O3 nanostructures by vibration milling at room temperature and successive treatment. We show that there exist special relationships among stacking fault energy (SFE), strain energy (SRE), and surface energy (SE) of the materials, including interdependence, intercompetition, and interconversion during the phase transition. SFE and SRE perform the same changing tendency, while SE just does the opposite. However, it is not the particle size but the energy state that determines the reactivity of the materials. And it is the SE that can directly determine the physical chemical reaction and the conversion into the end product rather than SFE and SRE. When SE goes up, the material reactivity and the product yield will be enhanced; and when SE goes down, the reaction and the product yield will decay. However, the state of SE depends closely on the change tendency of the SFE and SRE. That is, when SFE and SRE goes up, SE will goes down; if SFE and SRE goes down, SE will goes up. It seems that energy conservation law may be followed in a sense in the particle system if the external input keeps constant. The work may be significant for energy conversion in nano-scale and mechanosynthesis of oxide nanoparticles.

  18. Improving protein resistance of α-Al 2O 3 membranes by modification with POEGMA brushes

    NASA Astrophysics Data System (ADS)

    He, Huating; Jing, Wenheng; Xing, Weihong; Fan, Yiqun

    2011-11-01

    A kind of protein-resistant ceramic membrane is prepared by grafting poly(oligo (ethylene glycol) methyl ether methacrylate) (POEGMA) brushes onto the surfaces and pore walls of α-Al2O3 membrane (AM) by surface-initiated atom-transfer radical polymerization (SI-ATRP). Contact-angle, Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and field-emission scanning electron microscopy (FESEM) were measured to confirm that the surfaces and pore walls of the ceramic porous membranes have been modified by the brushes with this method successfully. The protein interaction behavior with the POEGMA modified membranes (AM-POEGMA) was studied by the model protein of bovine serum albumin (BSA). A protein-resistant mechanism of AM-POEGMA was proposed to describe an interesting phenomenon discovered in the filtration experiment, in which the initial flux filtrating BSA solution is higher than the pure water flux. The fouling of AM-POEGMA was easier to remove than AM for the action of POEGMA brushes, indicated that the ceramic porous membranes modified with POEGMA brushes exhibit excellent protein resistance.

  19. HCOOH hydrogenation over lanthanide-oxide-promoted Rh/Al 2O 3 catalysts

    NASA Astrophysics Data System (ADS)

    Benitez, J. J.; Carrizosa, I.; Odriozola, J. A.

    1993-08-01

    In this report, data corresponding to the hydrogenation of HCOOH adsorbed over a series of lanthanide-oxide-promoted Rh/Al 2O 3 catalysts are presented (Ln xO y, Ln=La, Ce, Sm, Yb, Lu). By comparison to thermal decomposition, it can be observed that the supports are unable to carry out the hydrogenation. Under these conditions, adsorbed formate decomposes through a dehydration mechanism as observed for an inert atmosphere. When rhodium is added to the samples and in the presence of hydrogen, adsorbed formate is eliminated from the surface at a lower temperature and a higher rate than the thermal decomposition. Adsorbed formate hydrogenation produces methane and water in the range 470-510 K, depending on the support employed. The presence of a small amount of gaseous HCOOH during methane production points to a mechanism in which adsorbed formate is converted into formic acid on the support. Its transformation into formic acid allows the adsorbate to reach the metal more easily where it immediately decomposes. The products of this decomposition are further hydrogenated into water and methane. Lewis acidity of the catalyst surface and metal dispersion are essential factors for formic-acid development and both are strongly modified by the presence of lanthanide oxides.

  20. Enhanced TC in granular and thin film Al-Al2O3 nanostructures

    NASA Astrophysics Data System (ADS)

    Higgins, J. S.; Greene, R. L.

    It is known since the 1970s that the superconducting transition temperature of granular aluminum films can be as high as two to three times the transition temperature of bulk aluminum, depending on the grain size and how strongly the nanometer size grains are connected1,2. As the strength of the grain connectivity becomes increasingly weak, the enhanced TC is suppressed. The mechanism behind this enhancement is still under debate. Recently, work on larger aluminum nanoparticles (18nm) embedded in an insulating Al2O3 matrix showed an onset of the superconducting transition as high as three times that of bulk aluminum3. In this situation, the Al grains are electrically disconnected and in a regime far removed from that of the granular films. Here we compare the two situations through electronic and thermal measurements in order to help elucidate the mechanism behind the enhancements. 1S. Pracht, et al., arXiv:1508.04270v1 [cond-mat.supr-con] (2015). 2G. Deutscher, New Superconductors From Granular to High TC, New Jersey: World Scientific, 2006, p. 72-74. 3V. N. Smolyaninova, et al., Sci. Rep. 5, 15777 (2015). Funding by NSF DMR # 1410665.

  1. Laminar convective heat transfer characteristic of Al2O3/water nanofluid in a circular microchannel

    NASA Astrophysics Data System (ADS)

    Trinavee, K.; Gogoi, T. K.; Pandey, M.

    2016-10-01

    In this study, laminar convective heat transfer characteristics Al2O3/water nanofluid in a circular microchannel is investigated using a two-phase (discrete phase) model. The computational fluid dynamic code FLUENT (ANSYS) is employed to solve the coupled momentum and energy equations with the boundary conditions of uniform wall heat flux and velocity at channel inlet. Detail analysis is done showing variation of wall temperature, fluid bulk mean temperature, heat transfer coefficient, Nusselt number, shear stress, friction, pressure drop, entropy generation etc. along the microchannel at two particle volume concentrations (1% and 4%) of the nanofluid. Comparison of results is provided between base and nanofluid and also for two cases, one with constant property and the other with variable temperature thermal conductivity and viscosity. Results show that heat transfer is enhanced in case of the nanofluid with low entropy generation and the heat transfer parameters increase with increase in nanoparticle volume concentration and Reynolds number. However, use of nanofluid also causes increase in pressure drop and shear stress. A comparison of the constant and variable property model showed that heat transfer is further enhanced; entropy, shear stress and pressure drop further decrease when temperature dependent properties of the nanofluid are considered instead of constant properties.

  2. Numerical investigation of Al2O3/water nanofluid laminar convective heat transfer through triangular ducts.

    PubMed

    Zeinali Heris, Saeed; Noie, Seyyed Hossein; Talaii, Elham; Sargolzaei, Javad

    2011-02-28

    In this article, laminar flow-forced convective heat transfer of Al2O3/water nanofluid in a triangular duct under constant wall temperature condition is investigated numerically. In this investigation, the effects of parameters, such as nanoparticles diameter, concentration, and Reynolds number on the enhancement of nanofluids heat transfer is studied. Besides, the comparison between nanofluid and pure fluid heat transfer is achieved in this article. Sometimes, because of pressure drop limitations, the need for non-circular ducts arises in many heat transfer applications. The low heat transfer rate of non-circular ducts is one the limitations of these systems, and utilization of nanofluid instead of pure fluid because of its potential to increase heat transfer of system can compensate this problem. In this article, for considering the presence of nanoparticl: es, the dispersion model is used. Numerical results represent an enhancement of heat transfer of fluid associated with changing to the suspension of nanometer-sized particles in the triangular duct. The results of the present model indicate that the nanofluid Nusselt number increases with increasing concentration of nanoparticles and decreasing diameter. Also, the enhancement of the fluid heat transfer becomes better at high Re in laminar flow with the addition of nanoparticles.

  3. Residual Stress in Brazing of Submicron Al2O3 to WC-Co

    NASA Astrophysics Data System (ADS)

    Grunder, T.; Piquerez, A.; Bach, M.; Mille, P.

    2016-07-01

    This study evaluated the residual stresses induced by brazing and grinding submicron Al2O3, using different methods. Energy dispersive x-ray spectrometry analysis (EDX) of 72Ag-Cu filler and filler/WC-Co interface showed evidence of atomic diffusion and possible formation of titanium oxide layers between the joint and the bonding materials. An analytical model supported by the finite element method (FEM) based on strain determination due to the difference in variation of thermal expansion was used to assess the stress distribution at the coupling interface and in bulk materials. The model took into account the evolution of the Young's modulus and of the thermal expansion with temperature. The model could be used to follow strain and stress evolutions of the bonded materials during the cooling cycle. The maximum stress rose above -300 MPa at the center of the 100 × 100 × 3 mm ceramic plates. The residual stresses on the external surface of ceramic were investigated by x-ray diffraction (XRD) and indentation fracture method (IFM). After brazing and grinding the plate, the principal stresses were 128.1 and 94.9 MPa, and the shear stress was -20.1 MPa. Microscopic examination revealed grain pull-out promoted by the global residual stresses induced by the brazing and grinding processes. The surface stresses evaluated by the different methods were reasonably correlated.

  4. Numerical investigation of Al2O3/water nanofluid laminar convective heat transfer through triangular ducts

    PubMed Central

    2011-01-01

    In this article, laminar flow-forced convective heat transfer of Al2O3/water nanofluid in a triangular duct under constant wall temperature condition is investigated numerically. In this investigation, the effects of parameters, such as nanoparticles diameter, concentration, and Reynolds number on the enhancement of nanofluids heat transfer is studied. Besides, the comparison between nanofluid and pure fluid heat transfer is achieved in this article. Sometimes, because of pressure drop limitations, the need for non-circular ducts arises in many heat transfer applications. The low heat transfer rate of non-circular ducts is one the limitations of these systems, and utilization of nanofluid instead of pure fluid because of its potential to increase heat transfer of system can compensate this problem. In this article, for considering the presence of nanoparticl: es, the dispersion model is used. Numerical results represent an enhancement of heat transfer of fluid associated with changing to the suspension of nanometer-sized particles in the triangular duct. The results of the present model indicate that the nanofluid Nusselt number increases with increasing concentration of nanoparticles and decreasing diameter. Also, the enhancement of the fluid heat transfer becomes better at high Re in laminar flow with the addition of nanoparticles. PMID:21711694

  5. Structural, elastic, vibrational and electronic properties of amorphous Al2O3 from ab initio calculations.

    PubMed

    Davis, Sergio; Gutiérrez, Gonzalo

    2011-12-14

    First-principles molecular dynamics calculations of the structural, elastic, vibrational and electronic properties of amorphous Al(2)O(3), in a system consisting of a supercell of 80 atoms, are reported. A detailed analysis of the interatomic correlations allows us to conclude that the short-range order is mainly composed of AlO(4) tetrahedra, but, in contrast with previous results, also an important number of AlO(6) octahedra and AlO(5) units are present. The vibrational density of states presents two frequency bands, related to bond-bending and bond-stretching modes. It also shows other recognizable features present in similar amorphous oxides. We also present the calculation of elastic properties (bulk modulus and shear modulus). The calculated electronic structure of the material, including total and partial electronic density of states, charge distribution, electron localization function and the ionicity for each species, gives evidence of correlation between the ionicity and the coordination for each Al atom.

  6. Fuel purpose hydrotreating of sunflower oil on CoMo/Al2O3 catalyst.

    PubMed

    Krár, Márton; Kovács, Sándor; Kalló, Dénes; Hancsók, Jeno

    2010-12-01

    The importance of the economical production and usage of new generation biofuels, the so-called bio gas oil (paraffins from triglycerides) and the results of the investigation for their productability on the CoMo/Al(2)O(3) catalyst, which was activated by reduction, are presented. The conversion of triglycerides, the yield of total organic fractions and the target product, furthermore the type and ratio of deoxygenation reactions were determined as a function of process parameters. The advantageous process parameters were found (380 degrees C, 40-60 bar, 500-600 Nm(3)/m(3) H(2)/sunflower oil ratio, 1.0 h(-1)), where the conversion of triglycerides was 100% and the yield of the target fraction [high paraffin containing (>99%) gas oil boiling range product] was relatively high (73.7-73.9%). The deoxygenation of triglycerides the reduction as well as the decarboxylation/decarbonylation reactions took place. The yield of the target fractions did not achieve the theoretical values (81.4-86.5%). That is why it is necessary to separate the target fraction and recirculate the heavy fraction.

  7. New battery strategies with a polymer/Al2O3 separator

    NASA Astrophysics Data System (ADS)

    Park, Kyusung; Cho, Joon Hee; Shanmuganathan, Kadhiravan; Song, Jie; Peng, Jing; Gobet, Mallory; Greenbaum, Steven; Ellison, Christopher J.; Goodenough, John B.

    2014-10-01

    A low-cost, thin, flexible, and mechanically robust alkali-ion electrolyte separator is shown to allow fabrication of a safe rechargeable alkali-ion battery with alternative cathode strategies. A Na-ion battery with an insertion host as cathode and a Li-ion battery with a redox flow-through cathode are demonstrated to cycle without significant fade. The separator membrane is a composite of Al2O3 particles and cross-linked ethylene-oxide chains; it can be fabricated at low cost into a large-area thin membrane that blocks dendrites from an alkali-metal anode. To block a soluble ferrocene redox molecule from crossing from the cathode side to the anode in a Li-ion battery with a redox-flow cathode, a thin mixed Li+/electronic-conducting film has been added to the cathode side of the composite separator. An osmosis issue was minimized by balancing concentrations of solutes on the two sides of the separator where the cathode side contains a soluble redox molecule.

  8. Regimes of leakage current in ALD-processed Al2O3 thin-film layers

    NASA Astrophysics Data System (ADS)

    Spahr, Holger; Reinker, Johannes; Bülow, Tim; Nanova, Diana; Johannes, Hans-Hermann; Kowalsky, Wolfgang

    2013-04-01

    A recently known phenomenon of thin oxide layers with thicknesses below approximately 40 nm is the increase in their breakdown electric field, called disruptive strength, towards lower thicknesses. This offers the possibility of examining the current-electric field characteristics at higher electric field strengths without an early electric breakdown. In this paper, we report on the identification of a current regime of trap-free square law and the buildup of an S-shaped current-electric field characteristic curve. This observation for atomic layer deposition (ALD)-processed Al2O3 layers has not been mentioned in the literature so far. Additionally, a modern model of space charge limited current is used to fit the S-shaped characteristic and extract the associated parameters, such as mobility, density of states, and the energy band gap between the conduction band and the trap state. In this context, the Poole-Frenkel effect is neglected in the model to fit our measurements towards the current increase after the trap filled limit.

  9. Conduction mechanisms in thin atomic layer deposited Al2O3 layers

    NASA Astrophysics Data System (ADS)

    Spahr, Holger; Montzka, Sebastian; Reinker, Johannes; Hirschberg, Felix; Kowalsky, Wolfgang; Johannes, Hans-Hermann

    2013-11-01

    Thin Al2O3 layers of 2-135 nm thickness deposited by thermal atomic layer deposition at 80 °C were characterized regarding the current limiting mechanisms by increasing voltage ramp stress. By analyzing the j(U)-characteristics regarding ohmic injection, space charge limited current (SCLC), Schottky-emission, Fowler-Nordheim-tunneling, and Poole-Frenkel-emission, the limiting mechanisms were identified. This was performed by rearranging and plotting the data in a linear scale, such as Schottky-plot, Poole-Frenkel-plot, and Fowler-Nordheim-plot. Linear regression then was applied to the data to extract the values of relative permittivity from Schottky-plot slope and Poole-Frenkel-plot slope. From Fowler-Nordheim-plot slope, the Fowler-Nordheim-energy-barrier was extracted. Example measurements in addition to a statistical overview of the results of all investigated samples are provided. Linear regression was applied to the region of the data that matches the realistic values most. It is concluded that ohmic injection and therefore SCLC only occurs at thicknesses below 12 nm and that the Poole-Frenkel-effect is no significant current limiting process. The extracted Fowler-Nordheim-barriers vary in the range of up to approximately 4 eV but do not show a specific trend. It is discussed whether the negative slope in the Fowler-Nordheim-plot could in some cases be a misinterpreted trap filled limit in the case of space charge limited current.

  10. Formation, growth and dissociation of He bubbles in Al 2O 3

    NASA Astrophysics Data System (ADS)

    van Huis, M. A.; van Veen, A.; Labohm, F.; Fedorov, A. V.; Schut, H.; Kooi, B. J.; De Hosson, J. Th. M.

    2004-02-01

    The formation and dissociation of helium bubbles and helium desorption are investigated in sapphire Al 2O 3(0 0 0 1) implanted with 30 keV He ions to four different doses of 0.1, 0.3, 1.0 and 2.0 × 10 16 ions cm -2. The samples were annealed isochronally up to 1850 K in steps of 100 K. The techniques of Doppler broadening positron beam analysis (PBA) and neutron depth profiling (NDP) were used to investigate defect evolution and helium retention, respectively, during the annealing procedure. It was observed that the maximum bubble volume is found after 1250 K annealing, after which a process of bubble shrinkage sets in. Cross-sectional transmission electron microscopy (XTEM) was performed on the sample that was implanted with the highest-dose (2.0 × 10 16 He ions cm -2) after annealing at 1250 K. It was found that the bubbles are shaped as discs lying parallel with the surface and that the average bubble size is 5.5 nm. In all samples, helium is released mainly at a temperature of 1750 K. The desorption curves were analyzed by means of a permeation model. The activation energy for permeation was found as 4.0 eV.

  11. Thermal conductivity and viscosity measurements of ethylene glycol-based Al2O3 nanofluids

    PubMed Central

    2011-01-01

    The dispersion and stability of nanofluids obtained by dispersing Al2O3 nanoparticles in ethylene glycol have been analyzed at several concentrations up to 25% in mass fraction. The thermal conductivity and viscosity were experimentally determined at temperatures ranging from 283.15 K to 323.15 K using an apparatus based on the hot-wire method and a rotational viscometer, respectively. It has been found that both thermal conductivity and viscosity increase with the concentration of nanoparticles, whereas when the temperature increases the viscosity diminishes and the thermal conductivity rises. Measured enhancements on thermal conductivity (up to 19%) compare well with literature values when available. New viscosity experimental data yield values more than twice larger than the base fluid. The influence of particle size on viscosity has been also studied, finding large differences that must be taken into account for any practical application. These experimental results were compared with some theoretical models, as those of Maxwell-Hamilton and Crosser for thermal conductivity and Krieger and Dougherty for viscosity. PMID:21711737

  12. Surface reactions of dimethyl ether on γ-Al2O3

    NASA Astrophysics Data System (ADS)

    Bondarenko, G. N.; Volnina, E. A.; Kipnis, M. A.; Rodionov, A. S.; Samokhin, P. V.; Lin, G. I.

    2016-02-01

    The surface reactions of dimethyl ether (DME) on industrial alumina (γ-Al2O3) were studied by chromatographic analysis of the products at the outlet of the flow reactor and (independently) by diffuse reflectance IR spectroscopy. The major products of the reactions at 250°C were found to be methanol formed in the reaction of DME with hydroxyl groups (the 3720 and 3674 cm-1 bands in the diffuse reflectance spectrum) and various methoxy groups (the 1121, 1070, 695, and 670 cm-1 bands in the differential spectra). The presence of molecularly adsorbed methanol was confirmed by experiments with methanol fed in a high-temperature IR cell. The interaction of the resulting methanol molecule with the hydroxyl group led to the formation of a water molecule in the gas phase and a methoxy group on the oxide surface. Strong adsorption of molecular DME was revealed, which was favored by an increase in the temperature of the preliminary calcination of oxide from 250 to 450-500°C; treatment of alumina with water vapor after its preliminary contact with DME led to a recovery of the hydroxyl coating and a replacement of molecularly adsorbed DME with hydroxyl. The thermal effect recorded in a flow reactor was positive during the adsorption of DME and negative during the desorption of weakly bonded DME. Schemes of formation of methoxy groups in the interaction of DME and methanol with surface hydroxyls were suggested.

  13. Dynamic Friction Performance of a Pneumatic Cylinder with Al2O3 Film on Cylinder Surface.

    PubMed

    Chang, Ho; Lan, Chou-Wei; Wang, Hao-Xian

    2015-11-01

    A friction force system is proposed for accurately measuring friction force and motion properties produced by reciprocating motion of piston in a pneumatic cylinder. In this study, the proposed system is used to measure the effects of lubricating greases of different viscosities on the friction properties of pneumatic cylinder, and improvement of stick-slip motion for the cylinder bore by anodizing processes. A servo motor-driven ball screw is used to drive the pneumatic cylinder to be tested and to measure the change in friction force of the pneumatic cylinder. Experimental results show, that under similar test conditions, the lubricating grease with viscosity VG100 is best suited for measuring reciprocating motion of the piston of pneumatic cylinder. The wear experiment showed that, in the Al2O3 film obtained at a preset voltage 40 V in the anodic process, the friction coefficient and hardness decreased by 55% and increased by 274% respectively, thus achieving a good tribology and wear resistance. Additionally, the amplitude variation in the friction force of the pneumatic cylinder wall that received the anodizing treatment was substantially reduced. Additionally, the stick-slip motion of the pneumatic cylinder during low-speed motion was substantially improved.

  14. Interface considerations in Al2O3/NiAl composite

    NASA Technical Reports Server (NTRS)

    Misra, Ajay K.

    1993-01-01

    The fiber-matrix interface requirements in an Al2O3/NiAl composite were examined from theoretical considerations. Several factors that influence the interface bonding requirements were analyzed. These include: (1) residual stresses due to fiber-matrix coefficient of thermal expansion (CTE) mismatch; (2) matrix cracking stress at room temperature; (3) fracture toughness at room temperature; (4) load transfer from the matrix to the fiber and ultimate tensile strength at the use temperature; and (5) creep resistance at high temperature. A relatively weak fiber-matrix bond, with an interfacial shear strength of approximately 15-20 MPa, might be sufficient for attaining the desired mechanical properties in the fiber direction at the use temperature. A weak fiber-matrix bond is also beneficial for increasing the fracture toughness of the composite at room temperature. In contrast, a strong fiber-matrix bond is required to withstand some of the residual stresses resulting from the fiber-matrix CTE mismatch, which are not likely to be reduced significantly by interface coatings. A relatively strong bond is also beneficial in increasing the matrix cracking stress at room temperature. Various interface coating options to accommodate the conflicting bonding requirements were reviewed. One viable coating option is to incorporate a thick, ductile interface layer well bonded to both the fiber and the matrix.

  15. Al2O3/GdAlO3 fiber for dental porcelain reinforcement.

    PubMed

    Medeiros, Igor S; Luz, Luciana A; Yoshimura, Humberto N; Cesar, Paulo F; Hernandes, Antonio C

    2009-10-01

    The aim of this study was to test the hypothesis that the addition of continuous or milled GdAlO3/Al2O3 fibers to a dental porcelain increases its mechanical properties. Porcelain bars without reinforcement (control) were compared to those reinforced with long fibers (30 vol%). Also, disk specimens reinforced with milled fibers were produced by adding 0 (control), 5 or 10 vol% of particles. The reinforcement with continuous fibers resulted in significant increase in the uniaxial flexural strength from 91.5 to 217.4 MPa. The addition of varied amounts of milled fibers to the porcelain did not significantly affect its biaxial flexural strength compared to the control group. SEM analysis showed that the interface between the continuous fiber and the porcelain was free of defects. On the other hand, it was possible to note the presence of cracks surrounding the milled fiber/porcelain interface. In conclusion, the reinforcement of the porcelain with continuous fibers resulted in an efficient mechanism to increase its mechanical properties; however the addition of milled fibers had no significant effect on the material because the porcelain was not able to wet the ceramic particles during the firing cycle.

  16. The Influence of impact on Composite Armour System Kevlar-29/polyester-Al2O3

    NASA Astrophysics Data System (ADS)

    Ramadhan, A. A.; Abu Talib, A. R.; Mohd Rafie, A. S.; Zahari, R.

    2012-09-01

    An experimental investigation of high velocity impact responses of composite laminated plates using a helium gas gun has been presented in this paper. The aim of this study was to develop the novel composite structure that meets the specific requirements of ballistic resistance which used for body protections, vehicles and other applications. Thus the high velocity impact tests were performed on composite Kevlar-29 fiber/polyester resin with alumina powder (Al2O3). The impact test was conducted by using a cylindrical steel projectile of 7.62mm diameter at a velocity range of 160-400 m/s. The results (shown in this work) are in terms of varying plate thickness and the amount of energy absorbed by the laminated plates meanwhile we obtained that the 12mm thickness of composite plate suitable for impact loading up to 200m/s impact velocity. Therefore this composite structure (it is used to reduce the amount of Kevlar) considered most economical armoure products. We used the ANSYS AUTODYN 3D- v.12 software for our simulations. The results have been obtained a4.1% maximum errors with experimental work of energy absorption.

  17. Growth of Polarity-Controlled ZnO Films on (0001) Al2O3

    NASA Astrophysics Data System (ADS)

    Park, J. S.; Chang, J. H.; Minegishi, T.; Lee, H. J.; Park, S. H.; Im, I. H.; Hanada, T.; Hong, S. K.; Cho, M. W.; Yao, T.

    2008-05-01

    The polarity control of ZnO films grown on (0001) Al2O3 substrates by plasma-assisted molecular-beam epitaxy (P-MBE) was achieved by using a novel CrN buffer layer. Zn-polar ZnO films were obtained by using a Zn-terminated CrN buffer layer, while O-polar ZnO films were achieved by using a Cr2O3 layer formed by O-plasma exposure of a CrN layer. The mechanism of polarity control was proposed. Optical and structural quality of ZnO films was characterized by high-resolution X-ray diffraction and photoluminescence (PL) spectroscopy. Low-temperature PL spectra of Zn-polar and O-polar samples show dominant bound exciton (I8) and strong free exciton emissions. Finally, one-dimensional periodic structures consisting of Zn-polar and O-polar ZnO films were simultaneously grown on the same substrate. The periodic inversion of polarity was confirmed in terms of growth rate, surface morphology, and piezo response microscopy (PRM) measurement.

  18. Heat transfer performance of Al2O3/water nanofluids in a mini channel heat sink.

    PubMed

    Dominic, A; Sarangan, J; Suresh, S; Sai, Monica

    2014-03-01

    The high density heat removal in electronic packaging is a challenging task of modern days. Finding compact, energy efficient and cost effective methods of heat removal is being the interest of researchers. In the present work, mini channel with forced convective heat transfer in simultaneously developing regime is investigated as the heat transfer coefficient is inversely proportional to hydraulic diameter. Mini channel heat sink is made from the aluminium plate of 30 mm square with 8 mm thickness. It has 15 mini channel of 0.9 mm width, 1.3 mm height and 0.9 mm of pitch. DI water and water based 0.1% and 0.2% volume fractions of Al2O3/water nanofluids are used as coolant. The flow rates of the coolants are maintained in such a way that it is simultaneously developing. Reynolds number is varied from 400 to 1600 and heat input is varied from 40 W to 70 W. The results showed that heat transfer coefficient is more than the heat transfer coefficient of fully developed flow. Also the heat transfer is more for nanofluids compared to DI water.

  19. Atomic layer deposition of TiO2 / Al2O3 films for optical applications

    NASA Astrophysics Data System (ADS)

    Triani, Gerry; Evans, Peter J.; Mitchell, David R. G.; Attard, Darren J.; Finnie, Kim S.; James, Michael; Hanley, Tracey; Latella, Bruno; Prince, Kathryn E.; Bartlett, John

    2005-09-01

    Atomic layer deposition (ALD) is an important technology for depositing functional coatings on accessible, reactive surfaces with precise control of thickness and nanostructure. Unlike conventional chemical vapour deposition, where growth rate is dependent on reactant flux, ALD employs sequential surface chemical reactions to saturate a surface with a (sub-) monolayer of reactive compounds such as metal alkoxides or covalent halides, followed by reaction with a second compound such as water to deposit coatings layer-by-layer. A judicious choice of reactants and processing conditions ensures that the reactions are self-limiting, resulting in controlled film growth with excellent conformality to the substrate. This paper investigates the deposition and characterisation of multi-layer TiO2 /Al2O3 films on a range of substrates, including silicon <100>, soda glass and polycarbonate, using titanium tetrachloride/water and trimethylaluminium/water as precursor couples. Structure-property correlations were established using a suite of analytical tools, including transmission electron microscopy (TEM), secondary ion mass spectrometry (SIMS), X-ray reflectometry (XRR) and spectroscopic ellipsometry (SE). The evolution of nanostructure and composition of multi-layer high/low refractive index stacks are discussed as a function of deposition parameters.

  20. Investigation of vinyl phosphonic acid/hydroxylated α-Al 2O 3( 0 0 0 1 ) reaction enthalpies

    NASA Astrophysics Data System (ADS)

    Hector, L. G., Jr.; Opalka, S. M.; Nitowski, G. A.; Wieserman, L.; Siegel, D. J.; Yu, H.; Adams, J. B.

    2001-11-01

    The eleven ion vinyl phosphonic acid (VPA) molecule consists of a phosphorus ion that serves as a cationic anchor for two electron-rich functional groups, viz., a tripodal oxygen-rich base and vinyl hydrocarbon tail. Recent inelastic tunneling experiments have implied that VPA binds in a tridentate coordination though its base leaving the vinyl tail free to react with a resin in adhesive bonding applications. Using first-principles total energy calculations, the reaction enthalpies for bonding of a single VPA molecule to selected threefold sites on hydroxylated α-Al 2O 3(0 0 0 1) are investigated. Tridentate, bidentate and unidentate coordinations, both with and without liberated water molecules, are examined to determine if the tridentate coordination is favored over the others and the extent to which the VPA molecule is sensitive to surface site geometry. The electron localization function is used to examine the extent of covalent character between the P-O bonds that anchor the VPA fragment to the oxide surface. Some comments on the entropic contributions of the VPA and H 2O molecules to the binding energetics are offered, along with a discussion of the effects of H 2O placement on the oxide surface and aluminum alloying agents.

  1. Tensile Properties of Nano AL2O3 Particulate-Reinforced Aluminum Matrix Composites by Mechanical Alloying and Hot Extrusion

    NASA Astrophysics Data System (ADS)

    Mehdinia, M.; Jenabali Jahromi, S. A.

    The powder of the micro Al and variant volume fractions of nano Al2O3 were milled by a high energy planetary ball-mill. By milling, a homogenous distribution of nano Al2O3 particles in the metal matrix were developed. Then the milled powder was cold compressed and sintered at 545°C for one hr. The mold and the sintered sample hold in a furnace until the temperature reached 545°C. Then the hot 27mm diameter sample was extruded to 6mm diameter. From the extruded specimens, tensile, hardness and microstructure of the prepared specimens were determined. By these tests the effect of milling time, the percent of nano-particles and the microstructure were evaluated. The hardness and tensile behaviors of aluminum matrix composites reinforced with nano Al2O3 particulate have been found to increase remarkably with the volume fraction of the reinforcement.

  2. Hypereutectic Al2O3/YAG/ZrO2 In Situ Composite Prepared by Horizontal Laser Zone Melting

    NASA Astrophysics Data System (ADS)

    Song, Kan; Zhang, Jun; Liu, Lin

    2017-01-01

    Al2O3/YAG/ZrO2 eutectic in situ composite has now been considered as the new generation of high-temperature structural material due to its excellent performance even close to its melting point. In this work, hypereutectic Al2O3/YAG/ZrO2 in situ composite is manufactured by the horizontal laser zone melting technique. The relationship between the solidification microstructure and the solidification parameters is studied. The minimum lamellar spacing is as finer as 0.20 μm when the laser scanning rate is 800 μm/s. Compared with eutectic Al2O3/YAG/ZrO2, hypereutectic exhibits more regular and finer microstructure at the similar conditions. Meanwhile, it is found that the lamellar spacing remains almost as constant at a certain high solidification velocity. The maximum hardness and fracture toughness are 15.9 GPa and 4.2 MPa · m1/2, respectively.

  3. Use of Al 2O 3 as inter-poly dielectric in a production proven 130 nm embedded Flash technology

    NASA Astrophysics Data System (ADS)

    Kakoschke, R.; Pescini, L.; Power, J. R.; van der Zanden, K.; Andersen, E.-O.; Gong, Y.; Allinger, R.

    2008-04-01

    We have successfully integrated 2 Mb arrays with SiO 2/Al 2O 3 stacks as inter-poly dielectric (IPD) fabricated in a proven 130 nm embedded Flash technology. Gate stack write/erase high voltages (HV) can be reduced by 3 V. Write/erase distributions show evidence of bit pinning which can be explained by barrier lowering along Al 2O 3 grain boundaries. Reliability assessment of the 2 Mb array reveals promising data retention and cycle endurance, indicating the absence of charge trapping in the high- k IPD. Despite several integration issues, these results demonstrate the high potential of Al 2O 3 IPDs in embedded Flash technologies.

  4. CO2 gas detection properties of a TIO2/Al2O3 heterostructure under UV light irradiation

    NASA Astrophysics Data System (ADS)

    Karaduman, Irmak; Demir, Mehmet; Yıldız, Dilber Esra; Acar, Selim

    2015-05-01

    Al/TiO2/p-Si and Al/TİO2/Al2O3/p-Si samples were prepared using the atomic layer deposition method (ALD) and their gas sensing properties were investigated. The electrical properties of the samples were studied using a two probe method in the temperature range 25-230 °C and at room temperature UV conditions. The TiO2/Al2O3 heterojunction sample exhibited an excellent gas sensing response to CO2 gas at room temperature and improved the effect of UV light irradiation. The results showed that heterostructures helped to improve the gas sensor properties, affected the sensing at room temperature and thus guided the design of photocatalysts. The TiO2/Al2O3 heterojunction prepared using this method can be used as a material for semiconductor gas sensors detecting poisonous gases like CO2 at room temperature with high sensitivity and selectivity.

  5. Experimental and theoretical studies of surface nitrate species on Ag/Al2O3 using DRIFTS and DFT.

    PubMed

    Zhang, Xiuli; He, Hong; Gao, Hongwei; Yu, Yunbo

    2008-12-15

    Surface nitrate (NO3(-)) species on the Ag/Al2O3 play an important role in the selective catalytic reduction (SCR) of NOx. In this study, the formation and configuration of surface nitrate NO3(-)(ads) species on Ag/Al2O3 and Al2O3 in the oxidation of NO have been studied using in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and density functional theory (DFT) calculations. Different nitrates species (bridging, bidentate and monodentate) were observed by in situ DRIFTS and validated by DFT calculations results. Attention was especially focused on the proposal of two different bidentate nitrates species (a normal bidentate and an isolated bidentate). In addition, the thermal stability of different surface nitrate species was discussed based on the adsorption energies calculations, DRIFTS, and temperature-programmed desorption (TPD) results. It was suggested that the decomposition and desorption of the surface nitrate species could be controlled by kinetics.

  6. Inelastic electron tunneling spectroscopy study of ultrathin Al2O3-TiO2 dielectric stack on Si

    NASA Astrophysics Data System (ADS)

    Liu, Zuoguang; Cui, Sharon; Kornblum, Lior; Eizenberg, Moshe; Chang, Ming-Feng; Ma, T. P.

    2010-11-01

    We report the properties of an ultrathin Al2O3-TiO2 dielectric stack with the equivalent-oxide thickness =1.0 nm. The stack exhibits nondiscernable interfacial layer on Si, and absence of serious Al2O3-TiO2 intermixing. Inelastic electron tunneling spectroscopy (IETS) has been used to provide a wealth of information concerning the phonons, bonding vibration modes, and traps in the Al2O3-TiO2 gate dielectric stack as well as its interfaces in a metal-oxide-Si structure. The IETS spectra before and after forming gas annealing suggest that the reduction of traps is related to the formation of Si-H bonds at the oxide-Si interface.

  7. Combustion synthesis of ceramic-metal composite materials - The TiC-Al2O3-Al system

    NASA Technical Reports Server (NTRS)

    Feng, H. J.; Moore, John J.; Wirth, D. G.

    1992-01-01

    Combustion synthesis was applied for producing ceramic-metal composites with reduced levels of porosity, by allowing an excess amount of liquid metal, generated by the exothermic reaction during synthesis, to infiltrate the pores. It is shown that this method, when applied to TiC-Al2O3 system, led to a decreased level of porosity in the resulting TiC-Al2O3-Al product, as compared with that of TiC-Al2O3 system. This in situ procedure is more efficient than the two-stage conventional processes (i.e., sintering followed by liquid metal infiltration), although there are limitations with respect to total penetration of the liquid metal and maintaining a stable propagation of the combustion reaction.

  8. Effect of calcination time on NiAl-Al2O3 using gel combustion synthesis method

    NASA Astrophysics Data System (ADS)

    Afandi, N. F.; Manap, A.; Yusof, S. N. A.; Salim, M. A.; Azim, M. Al.; Othman, S. Z.; Pauzi, N. I. M.; Omar, Nooririnah; Misran, H.

    2015-07-01

    This study was conducted in order to investigate the effect of calcination time on phase and microstructural characteristics of intermetallic matric composite (IMC), NiAl-Al2O3 powder. This powder was synthesized using gel combustion method with octyl alcohol as fuel. Upon completion of the combustion process, the loose powder was calcined at 1050°C for 1, 2 and 4 hours and characterized using XRD, FESEM and TEM. The crystallite size was calculated to be in the range of 29-30 nm. It was found that NiAl-Al2O3 exhibits high crystalline structure after calcination for 4 hours. Furthermore, longer calcination time also cause growth of the particle size. Findings indicate that high crystalline nanostructured NiAl-Al2O3 powder consisting of submicron particles can be successfully produced using gel combustion synthesis with longer calcination time.

  9. Passivation of type II InAs/GaSb superlattice photodetectors with atomic layer deposited Al2O3

    NASA Astrophysics Data System (ADS)

    Salihoglu, Omer; Muti, Abdullah; Kutluer, Kutlu; Tansel, Tunay; Turan, Rasit; Kocabas, Coskun; Aydinli, Atilla

    2012-06-01

    We have achieved significant improvement in the electrical performance of the InAs/GaSb midwave infrared photodetector (MWIR) by using atomic layer deposited (ALD) aluminium oxide (Al2O3) as a passivation layer. Plasma free and low operation temperature with uniform coating of ALD technique leads to a conformal and defect free coverage on the side walls. This conformal coverage of rough surfaces also satisfies dangling bonds more efficiently while eliminating metal oxides in a self cleaning process of the Al2O3 layer. Al2O3 passivated and unpassivated diodes were compared for their electrical and optical performances. For passivated diodes the dark current density was improved by an order of magnitude at 77 K. The zero bias responsivity and detectivity was 1.33 A/W and 1.9 x 1013 Jones, respectively at 4 μm and 77 K. Quantum efficiency (QE) was determined as %41 for these detectors.

  10. The effect of SiO2/Al2O3 ratio on the structure and microstructure of the glazes from SiO2-Al2O3-CaO-MgO-Na2O-K2O system

    NASA Astrophysics Data System (ADS)

    Partyka, Janusz; Sitarz, Maciej; Leśniak, Magdalena; Gasek, Katarzyna; Jeleń, Piotr

    2015-01-01

    Ceramic glazes are commonly used to covering of the facing surface of ceramics ware. A well-chosen oxide composition and firing conditions of glazes causes significant improvement of technical parameters of ceramic products. Modern glazes are classified as glass-ceramic composites with different crystalline phases arising during firing. The presence of crystals in the glass matrix is influenced by many factors, especially by oxides molar composition. A crucial role is played by the molar ratio of SiO2/Al2O3. In this work the six composition of glazes from SiO2-Al2O3-CaO-MgO-Na2O-K2O system were examined. The only variable is the ratio of the silicon oxideto alumina at a constant content of other components: MgO, CaO, K2O, Na2O, ZnO. In order to determine the real phase composition of the obtained glazes research on fluorescence spectrometer (XRF) were done. For structural studies X-ray diffraction (XRD) and spectroscopic in the middle infrared (MIR) were performed. In order to determine the state of the surface (microstructure) research on the scanning electron microscope (SEM) with EDX. The research allowed to determine the influence of SiO2/Al2O3 ratio on the structure and phase composition of glazes and the nature, and type of formed crystalline phases.

  11. Synthesis and Characterization of Biodegradable Ultrasonicated Films made from Chitosan/al2o3 Polymer Nanocomposites

    NASA Astrophysics Data System (ADS)

    Prakash, B.; Jothirajan, M. A.; Umapathy, S.; Amala, Viji

    Chitosan is a biopolymer which is biodegradable, biocompatible, non toxic and cationic in nature. Due to these interesting properties, it finds advanced applications in sensors, drug delivery vehicle and gene therapy etc., In this present work, the biocompatible Al2O3 Nano particles were embedded into Chitosan Polymer matrix by ultrasonication route. XRD and FTIR studies confirm the presence of Al2O3 nanoparticle in the Chitosan polymer matrix. The morphological, optical, electrical properties of the polymer nano composite films are carried out by employing scanning electron microscopy (SEM), UV- Vis, LCR and Impedance studies.

  12. Elastic, dielectric, and piezoelectric properties of ceramic lead zirconate titanate/α-Al2O3 composites

    NASA Astrophysics Data System (ADS)

    Rybyanets, A. N.; Konstantinov, G. M.; Naumenko, A. A.; Shvetsova, N. A.; Makar'ev, D. I.; Lugovaya, M. A.

    2015-03-01

    The technology of producing ceramic lead zirconate titanate/α-Al2O3 composites has been developed. Elements of piezoactive composites containing from 0 to 60 vol % α-Al2O3 have been prepared. The elastic, dielectric, and piezoelectric parameters of the synthesized ceramic composites have been measured, and their microstructure has been studied. It has been found that the concentration dependences of the elastic and piezoelectric properties exhibit anomalies. The obtained data have been interpreted based on the percolation theory and the concept of microstructural constructing polycrystalline composition materials.

  13. A study on kinetics of Al2O3 inclusion absorbed by mold slag used for non-manganese steel

    NASA Astrophysics Data System (ADS)

    Li, Zhiyang; Zhou, Weican; Chen, Mindong

    2017-01-01

    Dissolution kinetics of alumina into a new type CaO-Al2O3 mold slag was investigated by employing the rotating cylinder method. The results shows that the alumina dissolution was controlled by the mass transfer in the molten slag; the diffusion coefficient D=4.2×10-5mm2/s under 1400°C the activation energy of dissolution process was 213.8 Kj/mo1, this energy was higher than that of traditional mold slag; the ability of the new mold slag to absorb Al2O3 was weaker than that of traditional mold slag.

  14. Partial Melt Processing of Solid-Solution Bi2Sr2CaCu2O8+delta Thick-Film Conductors with Nanophase Al2O3 Additions

    DTIC Science & Technology

    2006-04-01

    range of partial-melt temperatures. Results were compared to Al2O3-free films with compositions lying within the single-phase solid - solution 2212 region...Nanophase Al2O3 reacted with 2212-type precursors to form a composite of micron size or smaller particles of solid - solution (Sr,Ca)3Al2O6 in a solid ... solution 2212 superconducting matrix. The Ca content of the (Sr,Ca)3Al2O6 in a solid - solution 2212 superconducting matrix. The Ca content of the (Sr,Ca

  15. Kinetics of NiO and NiCl2 Hydrogen Reduction as Precursors and Properties of Produced Ni/Al2O3 and Ni-Pd/Al2O3 Catalysts

    PubMed Central

    Sokić, Miroslav; Kamberović, Željko; Nikolić, Vesna; Marković, Branislav; Korać, Marija; Anđić, Zoran; Gavrilovski, Milorad

    2015-01-01

    The objects of this investigation were the comparative kinetic analysis of the NiO and NiCl2 reduction by hydrogen during an induction period and elimination of the calcination during the synthesis of Ni/Al2O3 catalysts. The effect of temperature and time on NiO and NiCl2 reduction degrees was studied. Avrami I equation was selected as the most favorable kinetic model and used to determine activation energy of the NiO and NiCl2 reduction for the investigated temperature range (623–923 K) and time intervals (1–5 minutes). The investigation enabled reaching conclusions about the reaction ability and rate of the reduction processes. Afterward, Ni/Al2O3 catalysts were obtained by using oxide and chloride precursor for Ni. The catalysts were supported on alumina-based foam and prepared via aerosol route. Properties of the samples before and after low-temperature hydrogen reduction (633 K) were compared. Obtained results indicated that the synthesis of Ni/Al2O3 catalysts can be more efficient if chloride precursor for Ni is directly reduced by hydrogen during the synthesis process, without the calcination step. In addition, Ni-Pd/Al2O3 catalysts with different metal content were prepared by using chloride precursors. Lower reduction temperature was utilized and the chlorides were almost completely reduced at 533 K. PMID:25789335

  16. Kinetic studies of CO2 methanation over a Ni/γ-Al2O3 catalyst.

    PubMed

    Hubble, R A; Lim, J Y; Dennis, J S

    2016-10-20

    The production of methane by reacting CO2 with H2 (CO2 methanation) has the potential for producing synthetic natural gas, which could be exported using the existing infrastructure for the distribution of natural gas. The methanation of CO2 was investigated over a wide range of partial pressures of products and reactants using (i) a gradientless, spinning-basket reactor operated in batch mode and (ii) a laboratory-scale packed bed reactor operated continuously. The rate and selectivity of CO2 methanation, using a 12 wt% Ni/γ-Al2O3 catalyst, were explored at temperatures 445-497 K and pressures up to 20 bar. Research with the batch reactor showed that the rate increased with increasing partial pressures of H2 and CO2 when the partial pressures of these reactants were low; however, the rate of reaction was found to be insensitive to changes in the partial pressures of H2 and CO2 when their partial pressures were high. A convenient method of determining the effect of H2O on the rate of reaction was also developed using the batch reactor and the inhibitory effect of H2O on CO2 methanation was quantified. The kinetic measurements were compared with a mathematical model of the reactor, in which different kinetic expressions were explored. The kinetics of the reaction were found to be consistent with a mechanism in which adsorbed CO2 dissociated to adsorbed CO and O on the surface of the catalyst with the rate-limiting step being the subsequent dissociation of adsorbed CO. The ability of the kinetic expressions to predict the results from the continuous, packed-bed reactor was explored, with some discrepancies discussed.

  17. Toughness enhancement in graphene nanoplatelet/SiC reinforced Al2O3 ceramic hybrid nanocomposites

    NASA Astrophysics Data System (ADS)

    Ahmad, Iftikhar; Islam, Mohammad; Subhani, Tayyab; Zhu, Yanqiu

    2016-10-01

    This paper elucidates the effect of silicon carbide nanoparticles (SiCNP) and graphene nanoplatelets (GNPs), on their own and together, on the densification behavior and fracture toughness of alumina (Al2O3) ceramic matrix. This was investigated by using the high-frequency induction heat sintering (HFIHS) process. While the addition of each nanostructure caused varying degrees of grain refinement and enhancement of mechanical properties, the incorporation of as little as 0.5 wt.% GNPs along with 5.0 wt.% SiCNP promoted uniform dispersion of the latter due to the lateral surface area of the graphene nanosheets with their two-dimensional morphology. There was an associated reduction in grain size from 1500 to 300 nm upon the addition of both types of nanoscale reinforcements. Extensive electron microscopy of the as-produced nanocomposites indicated the presence of SiCNP within, as well as at, the grain boundary areas whereas the 2D GNPs anchored between neighboring grains. Fractography of the samples revealed a transition from a mixed intergranular/transgranular mode for SiCNP or GNP-reinforced nanocomposites to transgranular fracture mode for the hybrid nanocomposites with improvements in fracture toughness and microhardness by 160 and 27%, respectively, largely due to the synergic role of the nanostructured reinforcements and their distinctly different toughening mechanisms. A new toughening model is proposed for the hybrid nanocomposites by taking into consideration crack deflection and pull-out effects due to SiCNP and the atomic level slip-stick driven GNPs inter-layer slithering. It was found that the addition of GNPs facilitates SiCNP dispersion that subsequently develops dense, fine-grained microstructures after a short-cycle, pressure-assisted consolidation process.

  18. Up-conversion luminescence in Yb(3+)-Er(3+)/Tm(3+) co-doped Al2O3-TiO2 nano-composites.

    PubMed

    Mokoena, Teboho Patrick; Linganiso, Ella Cebisa; Kumar, Vinod; Swart, Hendrik C; Cho, So-Hye; Ntwaeaborwa, Odireleng Martin

    2017-06-15

    The sol gel method was used to prepare rare-earths (Yb(3+)-Er(3+) and Yb(3+)-Tm(3+)) co-doped Al2O3-TiO2 nano-composite powder phosphors and their up-conversion luminescence properties were investigated. Mixed oxides of titania (TiO2) rutile phase and an early stage crystallization of alumina (Al2O3) phase were confirmed from the X-ray diffraction data with the average crystallite size of ∼36nm. The rutile phase TiO2 was further confirmed by selected area diffraction analysis of the composites. Microscopy analysis showed interesting rod-like morphologies with rough surfaces indicating that a spherulitic growth process took place during the crystal growth. Photoluminescence characterization of the phosphors was carried out under near infra-red excitation at 980nm and the prominent emission bands were observed in the visible region at 523, 548 and 658nm for the Yb(3+)-Er(3+) co-doped systems. Emission in bands extending from the visible to near infra-red regions were observed at 480, 650, 693 and 800nm for the Yb(3+)-Tm(3+) co-doped systems. These upconverted emissions and energy transfer mechanisms taking place are discussed in detail.

  19. Improvement of performance in low temperature solid oxide fuel cells operated on ethanol and air mixtures using Cu-ZnO-Al2O3 catalyst layer

    NASA Astrophysics Data System (ADS)

    Morales, M.; Espiell, F.; Segarra, M.

    2015-10-01

    Anode-supported single-chamber solid oxide fuel cells with and without Cu-ZnO-Al2O3 catalyst layers deposited on the anode support have been operated on ethanol and air mixtures. The cells consist of gadolinia-doped ceria electrolyte, Ni-doped ceria anode, and La0.6Sr0.4CoO3-δ-doped ceria cathode. Catalyst layers with different Cu-ZnO-Al2O3 ratios are deposited and sintered at several temperatures. Since the performance of single-chamber fuel cells strongly depends on catalytic properties of electrodes for partial oxidation of ethanol, the cells are electrochemically characterized as a function of the temperature, ethanol-air molar ratio and gas flow rate. In addition, catalytic activities of supported anode, catalytic layer-supported anode and cathode for partial oxidation of ethanol are analysed. Afterwards, the effect of composition and sintering temperature of catalyst layer on the cell performance are determined. The results indicate that the cell performance can be significantly enhanced using catalyst layers of 30:35:35 and 40:30:30 wt.% Cu-ZnO-Al2O3 sintered at 1100 °C, achieving power densities above 50 mW cm-2 under 0.45 ethanol-air ratio at temperatures as low as 450 °C. After testing for 15 h, all cells present a gradual loss of power density, without carbon deposition, which is mainly attributed to the partial re-oxidation of Ni at the anode.

  20. High-density ordered Ag@Al2O3 nanobowl arrays in applications of surface-enhanced Raman spectroscopy

    NASA Astrophysics Data System (ADS)

    Kang, Mengyang; Zhang, Xiaoyan; Liu, Liwei; Zhou, Qingwei; Jin, Mingliang; Zhou, Guofu; Gao, Xingsen; Lu, Xubing; Zhang, Zhang; Liu, Junming

    2016-04-01

    In this paper, we demonstrate a high-performance surface-enhanced Raman scattering (SERS) substrate based on high-density ordered Ag@Al2O3 nanobowl arrays. By ion beam etching (IBE) the anodized aluminum oxide (AAO) and subsequent Ag coating, ordered Ag@Al2O3 nanobowl arrays were created on the Si substrate. Unlike the ‘hot spots’ generated between adjacent metallic nanostructures, the Ag@Al2O3 nanobowl introduced ‘hot spots’ on the metal boundary of its hemispherical cavity. Based on the analysis of SERS signals, the optimized SERS substrate of Ag@Al2O3 nanobowl arrays had both high sensitivity and large-area uniformity. A detection limit as low as 10-10 M was obtained using chemisorbed p-thiocresol (p-Tc) molecules, and the SERS signal was highly reproducible with a small standard deviation. The method opens up a new way to create highly sensitive SERS sensors with high-density ‘hot spots’, and it could play an important role in device design and corresponding biological and food safety monitoring applications.

  1. Al 2O 3 supported Ru catalysts prepared by thermolysis of Ru 3(CO) 12 for catalytic wet air oxidation

    NASA Astrophysics Data System (ADS)

    Yu, Chaoying; Zhao, Peiqing; Chen, Gexin; Hu, Bin

    2011-06-01

    Low loading catalysts Ru/γ-Al 2O 3 and Ru-Ce/γ-Al 2O 3 were prepared by thermolysis of Ru 3(CO) 12 on γ-Al 2O 3. The catalysts were characterized by XPS, XRD and SEM. Two new Ru species (Ru A and Ru B) were detected during the Ru 3(CO) 12 decomposition process due to chemical interaction with the active OH groups on the surface of Al 2O 3 support, and the reduction of them can lead to more dispersed metallic phases. The sample was completely decomposed at 673 K in H 2, and RuO 2 was formed with minor amounts of Ru 0. When the temperature was increased to 773 K to heat the sample, the ratio of Ru 0 to RuO 2 increased. However, after the addition of CeO 2, only RuO 2 was detected on surface. The catalysts exhibited high activities in Catalytic Wet Air Oxidation (CWAO) of different organic compounds at high concentration such as isopropyl alcohol, phenol, acetic acids and N,N-dimethylformamide, which is attributed to the better dispersion of Ru particles and the addition of CeO 2 further enhanced number of effectively active sites on the cluster-derived catalyst surface.

  2. Structural characterization and catalytic activity of Pt dendrimer encapsulated nanoparticles supported over Al2O3 for SCR of NOx.

    PubMed

    Bae, HyunSook; Rao, Komateedi N; Ha, HeonPhil

    2011-07-01

    Pt/Al2O3 and Pt-Mg/Al2O3 nano composites were successfully prepared by dendrimer templated synthesis route. The obtained dendritic nanoparticles were dispersed in alumina support and they were evaluated for SCR of NOx using methane as reductant. Thermal analysis results of uncalcined samples revealed that the oxygen can accelerate the rate of dendrimer shell decomposition. X-ray diffractograms of 500 degrees C calcined samples disclosed the amorphous nature of materials, whereas 1000 degrees C air calcined samples showed enhanced crystallinity as well as diffraction pattern corresponding to Pt and PtO. HRTEM images of Pt40-G4OH dendritic nanoparticles showed uniform particulate distribution with average particle size of 2.4 nm. The STEM results of 0.5 Pt/Al2O3 sample calcined at 500 degrees C exhibited a wide range of particles between 2 and 20 nm. This indicates the huge segregation of platinum metal particles during impregnation and subsequent calcination. Among the synthesized materials 0.5 wt% Pt/Al2O3 sample showed excellent conversion and selectivity for SCR of NOx.

  3. Enhanced permeability, selectivity, and antifouling ability of CNTs/Al2O3 membrane under electrochemical assistance.

    PubMed

    Fan, Xinfei; Zhao, Huimin; Liu, Yanming; Quan, Xie; Yu, Hongtao; Chen, Shuo

    2015-02-17

    Membrane filtration provides effective solutions for removing contaminants, but achieving high permeability, good selectivity, and antifouling ability remains a great challenge for existing membrane filtration technologies. In this work, membrane filtration coupled with electrochemistry has been developed to enhance the filtration performance of a CNTs/Al2O3 membrane. The as-prepared CNTs/Al2