Papers by Author: Xiao Dong Li

Abstract: A melt-spinnable precursor for SiC based fibers was prepared from blend polymers of polycarbosilane (PCS) and modified polymethylsilane (M-PMS). The blend polymers cured at 320°C are different from M-PMS and PCS. The ceramic yield of these blend polymers is about 83%. The C/Si ratio of M-PMS/PCS derived ceramics (pyrolyzed at 1250°C) is linear to the content of MPMS in M-PMS/PCS. After melt spinning, thermal oxidation curing, and pyrolysis, Si-C-O fibers were obtained. The diameter and the tensile strength of the resulted fibers are 16.5μm and 1.62GPa, respectively.

Abstract: Ultra-high-temperature resistant Si-Al-C fibers derived from polyaluminocarbosilane were prepared by the procedures of melt-spinning, air curing and heated at 1800°C. It was found that oxygen content in the cured fibers has great influences on the chemical composition of the Si-Al-C fibers and its crystalline behavior during sintering. When oxygen content of cured fibers was too high, crystallite grains in the fiber would grow up. Oxygen evolvement in the fiber during the preparation was studied in detail by chemical analysis. It was found that oxygen is liberated mainly as CO gas from 1300°C to1600°C.

Abstract: In this paper, effect of heat treatment on the SSA of Si-C-O fibers was investigated and morphologies of the treated fibers were studied using SEM. The results revealed that weight loss was proportional to the treatment time at 1573K and the specific surface area (SSA) increased sharply when the weight loss reached above 6wt%. A rough and porous ceramic fiber with SSA of 23.76m2/g could be obtained at the weight loss of 9.1wt%, as a result of the treatment at 1573K for 32h.

Abstract: Silicon carbide coatings on graphite were prepared through polymer vapor pyrolysis deposition process (PVPD) under N2 atmosphere. During this process, some low molecular weight substances that polycarbosilane (PCS) pyrolyzed can be deposited on graphite, and they can convert into SiC in high temperature. The results of XRD showed that amorphous SiC coatings were formed on graphite when the pyrolysis temperature was 1000°C, andβ-SiC phase formed in the coatings when the temperature up to 1250°C. Effects of the coatings on the microstructure and properties were investigated. It was shown that the uniform dense SiC coatings could be obtained by carefully controlling the pyrolysis temperature and ramping rate when the number molecular weight of PCS was in the range of 1,000~1,500.

Abstract: A novel SiC precursor antimony-substituted polymethylsilane (APS) is present in this paper. First, pre-APS was synthesized from polymethylsilane (PMS) and SbCl3 at room temperature. Pre-APS was a liquid mixture and could be used in PIP process without solvent. After the elemination of HCl and the crosslinking of pre-APS, the novel precursor APS with the ceramic yield 91% was prepared.

Abstract: Hollow nanostructures have important applications in the field of gas adsorption, separation and storage due to their large specific surface areas. Silicon carbide nanotubes (SiCNTs) are one kind of such materials. In this paper, SiCNTs were synthesized from multiwalled carbon nanotubes (MWCNTs) via chemical vapor reaction (CVR) and purification. The SiCNTs were characterized by XRD, SEM and TEM. The results revealed that C-SiC nanotubes were obtained after CVR and most carbon were removed after purification with some traces retained inside SiCNTs. Hydrogen storage capacities measurements indicated that SiCNTs are superior to MWCNTs.