Xinhai He

Preparation, dielectric property and microwave absorption property of Cu doped SiC nanopowder by combustion synthesis

Abstract Cu doped SiC nanopowders have been prepared via combustion synthesis, using silicon powder and carbon black as the raw materials, copper powder as the doping source and polytetrafluoroethylene as the chemical activator respectively. The microstructure of prepared nanopowders has been characterised by X-ray diffraction and scanning electronic microscope. The electric permittivities of prepared SiC nanopowders in the frequency range of 8·2–12·4 GHz have been determined. Results show that prepared β-SiC nanopowders have fine spherical particles and narrow particle size distribution, and a quantity of SiC whisker increases with increasing Cu doping content. The Cu3Si impurity has been generated when Cu content is up to 10%. The β-SiC doped with 10% Cu has the highest real part ϵ′ and dielectric loss tanδ values. The 5% Cu doped SiC nanopowder with matching thickness of 2 or 2·5 mm exhibits the best microwave absorption properties in the frequency range of 8·2–12·4 GHz.

A Method to Adjust Dielectric Property of SiC Powder in the GHz Range

The SiC powders by AI or N doping have been synthesized by combustion synthesis, using AI powder and NH 4 CI powder as the dopants and polytetrafluoroethylene as the chemical activator. Characterization by X-ray diffraction, Raman spectrometer, scanning electron microscopy and energy dispersive spectrometer demonstrates the formation of AI doped SiC, N doped SiC and the AI and N co-doped SiC solid solution powders, respectively. The electric permittivities of prepared powders have been determined in the frequency range of 8.2–12.4 GHz. It indicates that the electric permittivities of the prepared SiC powders have been improved by the pure AI or N doping and decrease by the AI and N co-doping. The paper presents a method to adjust dielectric property of SiC powders in the GHz range.

Synthesis of biomorphic SiC fabric ceramic from pre-processed ramie fibres

ABSTRACT Biomorphic SiC fabric ceramic was synthesised by in situ reactive molten silicon infiltration process using artificial ramie fibres’ template, phenolic resin, and silicon. The phase compositions, microstructure, and physical characteristics of the biomorphic fabric ceramic were characterised and tested. The results show that the final ceramic retains the ramie fabric structure, and presents duplex microstructure including biomorphic SiC fibres and network SiC ceramic around the biomorphic fibres. This biomorphic SiC fabric ceramic is constituted by 95.8% of SiC, has a low density of 1.02 g cm−3 and a high porosity of 63.7%, and shows low linear shrinkages and better electrical resistivity along the fibre axis. The uniform and fine SiC particles with the size of ∼4 µm indicate that the reaction–formation mechanism is the dissolution of carbon and the precipitation of SiC, without a second precipitation.

EFFECT OF REACTION TIME ON MICROSTRUCTURE, DIELECTRIC PROPERTY AND MICROWAVE ABSORPTION PROPERTY OF Cu-DOPED SiC NANOPOWDER

Cu-doped SiC nanopowders have been prepared via combustion synthesis of the silicon and carbon system in a 0.1 MPa nitrogen atmosphere under different reaction time, using copper as the dopant and PTFE as the chemical activator, respectively. X-ray diffraction, scanning electronic microscope and Raman spectra have been used to characterize the phase and morphology of prepared nanopowders. Results indicate that the lattice constant of prepared Cu-doped SiC nanopowder decreases with extending reaction time. The prepared nanopowders have fine spherical particles and narrow particle size distribution and the particle size increases with increasing reaction time. The electric permittivities of prepared Cu-doped SiC nanopowders in the frequency range of 8.2–12.4 GHz have been determined. The real part e′, imaginary part e′′ and dielectric loss tgδ of complex permittivity decrease with increasing reaction time. All prepared Cu-doped SiC nanopowder exhibits good microwave absorption property in the frequency range of 8.2–12.4 GHz.