Jindong Su

Morphology of α-Si3N4 in Fe–Si3N4 prepared via flash combustion

The state and formation mechanism of α-Si3N4 in Fe–Si3N4 prepared by flash combustion were investigated by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The results indicate that α-Si3N4 crystals exist only in the Fe–Si3N4 dense areas. When FeSi75 particles react with N2, which generates substantial heat, a large number of Si solid particles evaporate. The product between Si gas and N2 is a mixture of α-Si3N4 and β-Si3N4. At the later stage of the flash combustion process, α-Si3N4 crystals dissolve and reprecipitate as β-Si3N4 and the β-Si3N4 crystals grow outward from the dense areas in the product pool. As the temperature decreases, the α-Si3N4 crystals cool before transforming into β-Si3N4 crystals in the dense areas of Fe–Si3N4. The phase composition of flash-combustion-synthesized Fe–Si3N4 is controllable through manipulation of the gas-phase reaction in the early stage and the α→β transformation in the later stage.

Morphology characterization of periclase–hercynite refractories by reaction sintering

A periclase-hercynite brick was prepared via reaction sintering at 1600°C for 6 h in air using magnesia and reaction-sintered hercynite as raw materials. The microstructure development of the periclase-hercynite brick during sintering was investigated using X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy in combination with energy-dispersive X-ray spectroscopy. The results show that during sintering, Fe2+, Fe3+ and Al3+ ions in hercynite crystals migrate and react with periclase to form (Mg1-xFex)(Fe2-yAly)O4 spinel with a high Fe/Al ratio. Meanwhile, Mg2+ in periclase crystals migrates into hercynite crystals and occupies the oxygen tetrahedron vacancies. This Mg2+ migration leads to the formation of (Mg1-uFeu)(Fe2-vAlv)O4 spinel with a lower Fe/Al ratio and results in Al3+ remaining in hercynite crystals. Cation diffusion between periclase and hercynite crystals promotes the sintering process and results in the formation of a microporous structure.

A Three-Dimensional Porous Conducting Polymer Composite with Ultralow Density and Highly Sensitive Pressure Sensing Properties

An ultralight conducting polyaniline/SiC/polyacrylonitrile PANI/SiC/PAN composite was fabricated by in situ polymerization of aniline monomer on the surface of fibers in SiC/PAN aerogel. The SiC/PAN aerogel was obtained by electrospinning, freeze-drying, and heat treatment. The ingredient, morphology, structure, and electrical properties of the aerogel before and after in situ polymerization were investigated by X-ray powder diffraction XRD, Fourier transform infrared spectroscopy FT-IR, scanning electron microscope SEM, and voltage-current characteristic measurement. The thermostability of PANI/SiC/PAN composite was investigated by thermogravimetric analysis TGA and electrical resistance measured at different temperatures. The density of the PANI/SiC/PAN composite was approximately 0.211 g cm−3, the porosity was 76.44%, and the conductivity was 0.013 S m−1. The pressure sensing properties were evaluated at room temperature. The electrical resistance of as-prepared sample decreased gradually with the increase of pressure. Furthermore, the pressure sensing process was reversible and the response time was short about 1 s. This composite may have application in pressure sensor field.