Papers by Author: Xiao Dong Li

Abstract: Crystallization behavior of ZrO2-ZnO-Al2O3-SiO2 glass has been studied by differential thermal analysis, X-ray diffraction analysis and scanning electronic microscope. ZrO2 doped in the glass induces the phase separation effectively. The crystal phases obtained are gahnite (ZnAl2O4) and a small amount of ZrO2 phase. SEM photographs show that the crystal phases distribute uniformly in the glass ceramics and the grain sizes of glass ceramics after different heat treatment are less than 60nm.

Abstract: In the preparation of polymer-derived SiC fibers, nanochannels are believed to be formed in the early pyrolysis stages due to loss of large volumes of pyrolysis gases. In this paper, small angle X-ray scattering (SAXS) was applied to the characterization and calculation of nanochannels in partiallypyrolyzed SiC fibers. The SAXS measurements showed that nanochannels with a radius of 1.0-20 nm were formed for fibers heat-treated at 973K and 1173K. But their distributions were not continuous and at lower part of the distribution, a peak value was observed at about 1.2nm. This means if the nanochannels are finely controlled, the partially-pyrolyzed SiC fibers have great potential application in the fields of hydrogen storage, gas separation, and so on.

Abstract: Due to the introduction of oxygen that works to keep the shape of the fibers and enhance the ceramic yield during high temperature pyrolysis, air-curing is a critical step during the preparation of the polymer-derived Si-Al-C-O fibers (KD-A). In this work, to investigate the evolvement of oxygen in the fibers and the influence of oxygen on the mechanical properties of the resulted KD-A fibers, FT-IR, TGA, XRD, SEM and element analysis were performed on the air-curing process of polyaluminocarbosilane (PACS) fibers and the pyrolysis process of the cured PACS fibers. The results showed that the oxygen in the cured PACS fibers was originated from aluminum aletylacetanate (Al(AcAc)3) and the air-curing process, which could be regarded as a constant mass during the pyrolysis. In addition, it was found that the mechanical properties of the achieved KD-A fibers were greatly effected by the amount of oxygen in the fibers due to its inhabiting the crystallization of silicon carbide. And the oxygen content which leaded to the KD-A fibers with the highest tensile strength was found to be 8~10%.

Abstract: The thin-film of silicon deposited by RTCVD on pressureless sintered SiC substrate with the size of 30mm×20mm, which is cleaned by ultrasonic method and chemical treatment. The crystal size of silicon columnar grain can reach 190 µm and its preferred orientation is [111] after ZMR process.

Abstract: ZnO-Al2O3-SiO2 glasses with different surface conditions were surface crystallized by different heat treatment process. Differential thermal analysis (DTA), X-ray diffraction analysis (XRD) and scanning electronic microscope (SEM) were used to investigate the crystallization behavior of glasses, the crystalline components and microstructure of the as-got glass-ceramics. According to the DTA results, different heat treatment processes of surface crystallization on the glass were adopted. The SEM results show that surface conditions of glasses are important for the surface crystallization, and the thickness of surface crystalline layer increases with heat treatment time.