Papers by Keyword: SiBCN

Abstract: Si₃N₄/SiBCN composite ceramics were prepared by infiltrating and pyrolyzing liquid polyborosilazane in porous Si₃N₄ ceramics. To increase their wave-absorbing ability, SiC nanoparticles and SiC film obtained by chemical vapor infiltration were separately introduced into the composite ceramics. The surface morphology, element and phase composition of ceramics were analyzed by means of scanning electron microscopy, energy dispersive spectrometer and X-ray diffraction. Dielectric and electromagnetic wave absorbing property researches show that the permittivity and dielectric loss of the ceramics were effectively improved and the electromagnetic reflection coefficient was visibly decreased when SiC was loaded. It is indicated that SiC is an effective dielectric lossy absorbent, and the Si₃N₄/SiBCN composite ceramics containing SiC possess the great potential in the application of wave-absorbing material.

Abstract: Amorphous Si-B-C-N ceramics obtained by high energy ball milling and hot pressing using hexagonal boron nitride (h-BN), graphite (C) and amorphous Si as starting materials have been studied. The mechanical milling with high energy resulted in the generation of large amounts of amorphous composites only milled for 5 h. Si-B-C-N powders were consolidation by hot pressing at 1850 °C. X-ray diffraction (XRD) and transmission electron microscopy (TEM) show that small amount of BN and SiC crystal lies in the amorphous matrix. The flexural strength reached the maximal value of 137.2 MPa at a mole ratio of BN/(Si+C) being 0.6.

Abstract: Amorphous nano-sized silicoboron carbonitride (Si-B-C-N) powders with average grain size <50 nm were fabricated by high energy shaker mill using hexagonal boron nitride, graphite and amorphous silicon powders as starting materials. The powders were consolidated by spark plasma sintering at 1900° and 1950°C. Amorphous phase were partially retained in ceramic sintered at 1900°C. For ceramic sintered at 1950°C, amorphous Si-B-C-N ceramic transferred to hexagonal BN and cubic SiC.

Abstract: Boron-modified polyvinylsilazanes have been studied for suitability as fiber precursor. A melt-tractable polymer displaying Si- and N-bonded methyl groups was successfully processed into green fibers ~18μm in diameter via a melt-spinning process. After the shaping process, the use of an ammonia curing atmosphere at 200°C allowed to increase the ceramic yield of the polymer, then avoid inter-fiber fusion during the further increase of the temperature. As-cured fibers were annealed in the temperature range 1000-1800°C in a nitrogen atmosphere to provide SiBCN ceramic fibers black colored, of flexible form and ~12μm in diameter in different crystallinity states going from totally amorphous below 1600°C to well-crystallized at 1800°C. The excellent strength retention after heat-treatment at 1600°C (1.3-1.5GPa) is clearly related to the high amorphous stability of fibers. Elemental compositions of such amorphous fibers showed a typical chemical formula of Si3.0B1.0C5.0N2.4. Between 1600°C and 1700°C, the fiber strength decreased to 0.9GPa then dropped to about one-quarter the original value at 1800°C while structural changes were evident by XRD analysis.