Jianqiang Bi

In situ synthesis of one-dimensional MWCNT/SiC porous nanocomposites with excellent microwave absorption properties

One-dimensional multiwalled carbon nanotube (MWCNT)/SiC porous nanocomposites were prepared via an in situ reaction between Si and MWCNTs induced by the reaction between Na and I2. The as-prepared nanocomposites exhibit outstanding microwave absorbing performances with an absorber thickness of about 2 mm. The absorbing bandwidth for the nanocomposites increases by raising the reaction temperature from 200 to 400 °C. The dielectric polarizations, which originate from the synergistic effect of the defects, porous structures and nanoparticles in the nanocomposites, are responsible for the excellent microwave absorbing performances.

Microwave absorption properties of MWCNT-SiC composites synthesized via a low temperature induced reaction

The composites containing SiC and multiwalled carbon nanotubes (MWCNTs) were synthesized via the reaction of Si powders and MWCNTs induced by that of Na and sulfur. The MWCNT-SiC composites prepared at 600 °C exhibit excellent microwave absorbing properties, which reach a minimum reflection loss of -38.7 dB at a frequency around 12.9 GHz. The absorbing properties are bound up with the high yield of porous SiC spheres comprised of nanocrystals. The porous structure, high density of stacking faults in SiC crystallites, interfaces between MWCNTs and SiC spheres, grain boundaries between SiC nanocrystals, as well as the interfacial polarizations aroused therefrom, are responsible for the excellent microwave absorbing properties.

Microstructure, hardness, and bending strength of carbon nanotube-iron aluminide composites

Iron aluminide (Fe3Al) composites reinforced with ~3 wt% of carbon nanotube (CNT) were fabricated by hot press consolidation. Ambient-temperature mechanical properties of the iron aluminide—CNT composites were determined. The hardness, compressive yield strength, and bending strength hardness of composites were higher by 63%, 1%, and 5%, respectively. Microscopic examination of the composite showed the added CNTs still keep their tubular structure. The preliminary results on the processing and improvement in mechanical properties of CNT-reinforced iron aluminide matrix composites are being reported here for the first time.

Synthesis of hollow carbon sphere/ZnO @ C composite as a light-weight microwave absorber

Hollow carbon spheres (HCSs) and HCS/ZnO@C composite are synthesized by the reaction of zinc with sucrose and glycerol, respectively. The electromagnetic parameters of the HCSs and HCS/ZnO@C composite are measured by a coaxial line method. Both the real and imaginary complex permittivities and the loss tangent for the HCS/ZnO@C composite are larger than those for the HCSs. The electromagnetic absorption properties of the HCS/ZnO@C composite are advantageous over those of the HCSs, not only in band width but also in absorber thickness.

VALENCE ELECTRON STRUCTURE ANALYSIS OF INTERFACE OF FeAl/TiN COMPOSITES

Based on Paulings nature of chemical bond, the valence electron structures of TiN and FeAl have been constructed, and the relative electron density differences (REDD) between the low index plane of TiN and FeAl, respectively, have been calculated. [110] FeAl//[110]TiN crystallography orientation has been set up from the minimization of the electron density difference across the interface. From the viewpoint of improving the mechanical properties of composites, the formation of such structures must been engineered in the fabrication processing.

Effect of diatomite additive on the mechanical and dielectric properties of porous SiO2-Si3N4 composite ceramics

Porous SiO2-Si3N4 composite ceramics with high porosity and excellent mechanical properties were fabricated by pressureless-sintering at relatively low temperature of 1 500 °C using diatomite as pore forming agent. The effects of diatomite on flexural strength, fracture toughness, shrinkage, porosity and phase transformation of the porous ceramics were investigated in detail. Compared with that of the ceramic without adding diatomite, the porosity of the ceramic with 10% diatomite is increased by about 27.4%, the flexural strength and fracture toughness reaches 78.04 MPa and 1.25 MPa·m1/2, respectively. As the porosity increases, the dielectric constant of porous SiO2-Si3N4 ceramic decreases obviously from 3.65 to 2.95.