The Experts below are selected from a list of 9765 Experts worldwide ranked by ideXlab platform

Fritz Aldinger - One of the best experts on this subject based on the ideXlab platform.

  • si b c n al precursor derived Ceramics Synthesis high temperature behaviour and oxidation resistance
    Journal of The European Ceramic Society, 2004
    Co-Authors: Anita Muller, Peter Gerstel, E Butchereit, Klaus G Nickel, Fritz Aldinger
    Abstract:

    Abstract The Si/B/C/N/H polymer T2(1), [B(C2H4Si(CH3)NH)3]n, was reacted with different amounts of H3Al·NMe3 to produce three organometallic precursors for Si/B/C/N/Al Ceramics. These precursors were transformed into ceramic materials by thermolysis at 1400 °C. The ceramic yield varied from 63% for the Al-poor polymer (3.6 wt.% Al) to 71% for the Al-rich precursor (9.2 wt.% Al). The as-thermolysed Ceramics contained nano-sized SiC crystals. Heat treatment at 1800 °C led to the formation of a microstructure composed of crystalline SiC, Si3N4, AlN(+SiC) and a BNCx phase. At 2000 °C, nitrogen-containing phases (partly) decomposed in a nitrogen or argon atmosphere. The high temperature stability was not clearly related to the aluminium concentration within the samples. The oxidation behaviour was analysed at 1100, 1300, and 1500 °C. The addition of aluminium significantly improved the oxide scale quality with respect to adhesion, cracking and bubble formation compared to Al-free Si(/B)/C/N Ceramics. Scale growth rates on Si/B/C/N/Al Ceramics at 1500 °C were comparable with CVD–SiC and CVD–Si3N4, which makes these materials promising candidates for high-temperature applications in oxidizing environments.

D Vivien - One of the best experts on this subject based on the ideXlab platform.

  • rare earth doped oxyfluoride glass Ceramics and fluoride Ceramics Synthesis and optical properties
    Optical Materials, 2007
    Co-Authors: M Mortier, A Bensalah, Geraldine Dantelle, G Patriarche, D Vivien
    Abstract:

    Abstract Ultra-transparent glass-Ceramics are synthesized in the GeO2–PbO–PbF2 system by rare-earth heterogeneous nucleation of PbF2. The influence of YbF3 on the nucleation process is studied through differential thermal analysis (DTA) and the morphology is observed by transmission electron microscopy (TEM). The optical properties of the glass-Ceramics are compared to those of the starting glass as well as to those of a PbF2 single crystal. Thanks to the RE segregation inside the PbF2 crystallites, the optical characteristics of the glass-Ceramics are found to be equivalent to those of the single crystal. The Synthesis of rare-earth doped CaF2 nano-powders, as precursors for transparent Ceramics, by direct precipitation, microemulsion and mechanoSynthesis is described. The different obtained powders are characterized by X-ray diffraction (XRD) and TEM and their respective morphology and purity are compared. For the powder obtained by microemulsion, the effect of annealing at various temperatures is investigated showing an increase of the particles sizes and an enhancement of the optical properties.

Tong Zhao - One of the best experts on this subject based on the ideXlab platform.

  • polymer derived ta4hfc5 nanoscale ultrahigh temperature Ceramics Synthesis microstructure and properties
    Journal of The European Ceramic Society, 2019
    Co-Authors: Yanan Sun, Tuzi Zhang, Fenghua Chen, Tong Zhao
    Abstract:

    Abstract Nanoscale Ta4HfC5 Ceramics were synthesized from curing and pyrolysis of novel polymer precursors which were synthesized by cohydrolysis and polycondensation of acetyl acetone coordinated tantalum alkoxide and hafnium alkoxide followed by blending with phenolic resin as carbon source. Pyrolysis of the polymer precursor at 1600 °C in vacuum produced Ta4HfC5 nanocrystallites with an average grain size of 21 nm and well-distributed elements, encapsulated by an amorphous carbon shell. Near full dense Ta4HfC5 monoliths can be prepared by spark plasma sintering (SPS) at 1600 °C with 10 vol% MoSi2 as an additive, of which the Vicker micro-hardness and flexural strength achieved 17.58 GPa and 466 MPa, respectively. The polymer precursor method shed light on the fabrication of ceramic matrix composites. Besides, the high electrical conductivity of 1.5 × 104 S/m entitled the Ceramics to a prospective of utilization in microwave absorbing/shielding fields under harsh conditions.

M Mortier - One of the best experts on this subject based on the ideXlab platform.

  • rare earth doped oxyfluoride glass Ceramics and fluoride Ceramics Synthesis and optical properties
    Optical Materials, 2007
    Co-Authors: M Mortier, A Bensalah, Geraldine Dantelle, G Patriarche, D Vivien
    Abstract:

    Abstract Ultra-transparent glass-Ceramics are synthesized in the GeO2–PbO–PbF2 system by rare-earth heterogeneous nucleation of PbF2. The influence of YbF3 on the nucleation process is studied through differential thermal analysis (DTA) and the morphology is observed by transmission electron microscopy (TEM). The optical properties of the glass-Ceramics are compared to those of the starting glass as well as to those of a PbF2 single crystal. Thanks to the RE segregation inside the PbF2 crystallites, the optical characteristics of the glass-Ceramics are found to be equivalent to those of the single crystal. The Synthesis of rare-earth doped CaF2 nano-powders, as precursors for transparent Ceramics, by direct precipitation, microemulsion and mechanoSynthesis is described. The different obtained powders are characterized by X-ray diffraction (XRD) and TEM and their respective morphology and purity are compared. For the powder obtained by microemulsion, the effect of annealing at various temperatures is investigated showing an increase of the particles sizes and an enhancement of the optical properties.

Xiuli Chen - One of the best experts on this subject based on the ideXlab platform.

  • sol gel derived cacu3ti4o12 Ceramics Synthesis characterization and electrical properties
    Materials Research Bulletin, 2008
    Co-Authors: Laijun Liu, Huiqing Fan, Pinyang Fang, Xiuli Chen
    Abstract:

    Abstract The giant dielectric constant material CaCu 3 Ti 4 O 12 (CCTO) has been synthesized by sol–gel method, for the first time, using nitrate and alkoxide precursor. The electrical properties of CCTO Ceramics, showing an enormously large dielectric constant ɛ  ∼ 60,000 (100 Hz at RT), were investigated in the temperature range from 298 to 358 K at 0, 5, 10, 20, and 40 V dc. The phases, microstructures, and impedance properties of final samples were characterized by X-ray diffraction, scanning electron microscopy, and precision impedance analyzer. The dielectric permittivity of CCTO synthesized by sol–gel method is at least three times of magnitude larger than that synthesized by other low-temperature method and solid-state reaction method. Furthermore, the results support the internal barrier layer capacitor (IBLC) model of Schottky barriers at grain boundaries between semiconducting grains.