Jianbao Hu

In situ growth behavior of boron nitride nanotubes on the surface of silicon carbide fibers as hierarchical reinforcements

BNNTs grown in situ on the surface of silicon carbide fibers via a simplified ball milling, impregnation and annealing method using boron powder as the raw material were synthesized. The morphology, microstructure and chemical composition of as-grown BNNTs were well characterized by field-emission scanning electron microscopy, field emission transmission electron microscopy, electron energy loss spectroscopy and Raman spectroscopy. The analysis results indicate that the nanostructures are BNNTs with the diameter of 50–130 nm, exhibiting a multi-walled and bamboo-like structure and possessing two distinct morphologies of the tube walls: flat walls and bubble-chain walls, respectively. Based on the experimental characterization of BNNTs and as-milled powders, the possible growth process of BNNTs has been described and the formation mechanisms of two types of bamboo-like BNNTs have been proposed, including the tip growth mode and the base growth mode.

Oxidation behavior of Al2O3 added reaction-sintered SiC ceramics in wet oxygen environment at 1300°C

ABSTRACT The oxidation behavior of reaction-bonded SiC ceramics with Al2O3 was investigated at 1300°C for exposure duration up to 100 h under water vapor environment. Results show that Al2O3 is enriched on the oxidation surface, reducing the volatilization of the oxide layer and preventing the reduction of macroscopic size. Raman spectra results further testified that Al2O3 obviously improves the stability of glass structure and reduces the generation of non-bridged oxygen atoms (Si–O–H), which results in a lower reaction activity with steam of the aluminosilicate melt, therefore, significantly improving the oxidation resistance of SiC in O2/H2O atmosphere.

Fabrication and microstructure of ZrB2–ZrC–SiC coatings on C/C composites by reactive melt infiltration using ZrSi2 alloy

ZrB2–ZrC–SiC ternary coatings on C/C composites are investigated by reactive melt infiltration of ZrSi2 alloy into pre-coatings. Two different pre-coating structures, including porous B4C–C and dense C/B, are designed by slurry dip and chemical vapor deposition (CVD) process respectively. The coating prepared by reactive melt infiltration (RMI) into B4C–C presents a flat and smooth surface with a three-layer cross-sectional structure, namely interior SiC transition layer, gradient ZrB2–ZrC–SiC layer, and ZrB2–ZrC exterior layer. In comparison, the coating prepared by RMI into C/B shows a more granular surface with a different three-layer cross-sectional structure, interior unreacted B–C pre-coating layer, middle SiC layer, and exterior ZrB2–ZrC–ZrSi2 layer. The forming mechanisms of the specific microstructures in two coatings are also investigated and discussed in detail.