科研之友
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摘要
The oxygen content of the SiAlCO fibers was a key for the transformation from SiAlCO fibers to dense stoichiometric SiC fibers after sintering at > 1700 degrees C, which was mainly introduced during curing process. The novel preoxidation-thermal curing method was applied to the conversion of polyaluminocarbosilane (PACS) fibers and the oxygen content of the SiAlCO fibers as-pyrolyzed was adjustable in 10%-13% (mass fraction). A minimal degree of preoxidation of the PACS green fibers, which performed at 190 degrees C for 4 h leading to 7. 87% (mass fraction) oxygen pick-up, is necessary for their further thermal-curing. Then, the preoxidation fibers formed crosslinking structure after thermal-curing at 450 degrees C under N-2 flow. The curing process was investigated by gel permeation chromatography (GPC), infrared spectrum(IR) and thermogravimetric analysis-mass spectra(TG-MS). The results show that the Si-OH bonds are formed after the Si-H bonds in the structure of PACS fibers reacting with oxygen molecular during preoxidation. Additionally, partial Si-OH bonds could react with each other continuously to form Si-O-Si structure, resulting in molecular increase. During the thermal-curing process, the residue of Si OH further react with each other at lower than 300 degrees C. The formation of Si-CH2-Si structure resulted from the reaction between Si-H bond and Si-CH3 bond happened in the range of 300-450 degrees C.
- 出版日期2015-6-10
- 单位中国人民解放军国防科学技术大学
