Effect of Hydrogen Atmosphere on Pyrolysis of Cured Polycarbosilane Fibers
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SiC‐based fibers with various chemical compositions were synthesized using an irradiation‐curing process. Polycarbosilane (PCS) fibers were cured by irradiation with an electron beam in a helium atmosphere. The cured PCS fibers were pyrolyzed at 1300°C under controlled hydrogen or argon atmospheres, and SiC fibers with C/Si of 0.84 to 1.56 were obtained. The fibers consisted of <1.0 wt% O, <0.2 wt% N, <0.1 wt% H, with the balance being Si and C. The mechanism of pyrolytic transformation of cured PCS to SiC‐based ceramics was investigated using TG/DTA analysis. Greater mass losses were observed during pyrolysis in a hydrogen atmosphere than in argon. This result suggests that the hydrogen atmosphere suppresses H 2 evolution and helps to remove excess carbon as CH 4 during pyrolysis. The microstructure and mechanical properties of the resulting SiC‐based fibers were found to be very dependent on their C/Si chemical compositions.Keywords:
Pyrolytic carbon
Boron-doped isotropic pyrolytic carbons were prepared by chemical vapor deposition(CVD) with CH4、H2 and BCl3 as gaseous precursors.The effects of boron on the microstructure and oxidation properties of pyrolytic carbons were investigated.The results show that boron can be doped into pyrolytic carbon,and the concentration increases with the flow rate of BCl3.Boron doping does not change the isotropy of pyrolytic carbons,but remarkably changes the microstructure of pyrolytic carbons.Increasing the flow rate of BCl3,the microstructure of pyrolytic carbon changes gradually from spherical carbon structures to fine wrinkled graphitic sheet structures,while boron changes from substitutional boron into boron carbide.The results from oxidation show that boron can effectively inhibit the oxidation of pyrolytic carbon.
Pyrolytic carbon
Boron carbide
Carbon fibers
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Pyrolytic carbon
Sawdust
Characterization
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The rice husk fast pyrolysis was studied by using pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS), and the pyrolysis gases were online analyzed. The effects of pyrolytic temperature and time on the pyrolysis of biomass was focused. The results show that the number and yield of product species increase with temperature below 450 ℃. The less species at lower pyrolytic temperature is of benefit to the enrichment of high value products. However, the number of product species becomes constant and the yield only changes when the temperature is over 450 ℃. The yield reaches the maximum when the temperature is 550 ℃. As the temperature increases, the optimum pyrolytic time descends. The pyrolysis of biomass with a long pyrolysis time at lower temperature is more completely than that with a shot pyrolysis time at higher temperature.
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Husk
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Pine sawdust pyrolysis was carried out respectively using microwave and conventional electrical heating at different temperatures in order to understand the properties of pyrolytic products from microwave pyrolysis of biomass. Less char material was obtained by microwave pyrolysis compared to conventional heating at the same temperature. While comparing the components of the pyrolytic gases, it was revealed that the microwave pyrolysis gas usually had higher H2 and CO contents and lower CH4 and CO2 contents than those obtained by conventional pyrolysis at the same temperature. The texture analysis results of the microwave pyrolysis chars showed that the chars would melt and the pores would shrink at high temperatures, and hence, the specific surface areas of the chars decreased with increasing temperature. Similarly, the reactivity of the char was remarkably reduced when the microwave pyrolysis temperature exceeded 600°C.
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Sawdust
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Polymers' controlled pyrolysis is an economical and environmentally friendly solution to prepare activated carbon. However, due to the experimental difficulty in measuring the dependence between tissues and pyrolysis parameters at high temperatures, the unknown pyrolysis mechanism hinders access to the target products with desirable morphologies and performances. In this study, we investigate the pyrolysis process of polystyrene under different heating rates and temperatures employing reactive molecular dynamics (ReaxFF-MD) simulations. A clear profile of the generation of pyrolysis products determined by the temperature and heating rate is constructed. It is found that the heating rate affects the type and amount of pyrolysis intermediates and their timing, and low-rate heating helps yield more diverse pyrolysis intermediates. While the temperature affects the pyrolytic tissues of the final equilibrium products, either too low or too high a target temperature is detrimental to generating large areas of graphitized tissue. The established theoretical evolution process matches experiments well, thus contributing to preparing target activated carbons by referring to the regulatory mechanism of pyrolytic tissues.
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ReaxFF
Polystyrene
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快热分解是能把生物资源变换成液体的一种有希望的技术。简历油是一个如此的产品，不仅作为一个温室知道到石块上的还原剂信赖的气体中立的精力来源，而且一个机会造成。Pyrolytic 木质素，好同类的粉末，是简历油的水不可溶解的部分，它贡献简历油的不稳定性。另外， pyrolytic 木质素能在基于木头的面板工业在象粘合剂那样的商业材料被使用。这份报纸论述从在它的性质和年老的简历油的处理温度之间的年老的简历油和关系提取的 pyrolytic 木质素的结构的描述。Pyrolytic 木质素样品被 Fourier 变换描绘红外线的光谱学，胶化浸透层析，微分扫描热量测定， thermogravimetric 分析和质子原子磁性的回声光谱学。pyrolytic 木质素的平均分子的重量与增加老化温度从 700 ～ 1000 g/mol 增加了(650 ? 牰獥湥整 ? 瑳 'L 汩穩瑡潩 ? 諗珨?桴 ? 慧湩洠瑡楲? 景挠湯牴汯敬 ? 獩挠湯瑳畲瑣摥戠 ? 桴 ? 敷汬欭潮湷氠湩慥? 潣瑮潲 ? 整档楮畱 ? 潦 ? 敤慬? 牦敥猠獹整獭
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Thermogravimetric analysis
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The pyrolytic characteristics of rice husk and lignite were investigated by using the TG-DSC.Result demonstrated that the thermal weight loss of rice husk was more intense than lignite.The co-pyrolysis weight loss process was almost the summation of rice husk and lignite pyrolysis weight loss process respectively.The absorbing and releasing heat of pyrolysis prosess was analyzed through DSC curves.There needed more heat-absorption at high temperature pyrolytic process during co-pyrolysis.Gas products content of pyrolytic system were also determined by gas chromatography as the temperature changed.Variations of gas products were analyzed combining TG curves.The results showed that H2 and CH4 content had the similar trend with the temperature grew when pyrolysised separately.CO content was more in rice husk pyrolysis gas product than lignite.Overall,there were heat exchange and interactions between husk and lignite during co-pyrolysis though the co-pyrolysis products were just the summation of pyrolysis separately.
Husk
Pyrolytic carbon
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Samples of TetraPak cartons were processed by pyrolysis at temperatures up to 700 centigrade degrees. Char samples were analyzed by pyrolytic gas chromatography with mass spectrometric detection. Differences of pyrolytic carbon were characterized by specific organic compounds used as markers of pyrolytic conditions.
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Carton
Carbon fibers
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The effect of pyrolytic temperature on the microstructure changes, mass loss and H/C ratio of polyarylacetylene was studied by thermal gravity analysis, element analysis and X ray diffraction. The results show that polyarylacetylene gives 84% char yield when pyrolysis at 900 ℃;with the increase of pyrolytic temperature, the ratio of H/C decreases and the carbon content and the degree of graphilization of pyrolytic sample increases. At the temperature range of 350~600 ℃, with the increase of pyrolytic temperature, the initial structure of polymer was destructed gradually; and when the pyrolytic temperature higher than 600 ℃, with the increase of pyrolytic temperature, a new structure was formed gradually.
Pyrolytic carbon
Atmospheric temperature range
Carbon fibers
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