热解碳沉积温度对增强石墨力学性能的影响

采用化学气相沉积增密技术制备热解碳增强普通石墨材料。研究沉积温度对增强石墨力学性能的影响,并探讨热解碳增强普通石墨材料的沉积机理。结果表明:随沉积温度升高,增强石墨的抗弯强度提高,在1 600℃沉积时达到最大值39.33 MPa,比石墨基体提高21.7%。其主要原因是随沉积温度升高,热解沉积由CVI过程变为CVD过程。当温度低于1 600℃时,化学气相渗透过程占主导;温度高于1 600℃后热解碳极易沉积在基体表面,形成热解碳膜,化学气相沉积过程占主导。在1 600℃温度下,其抗弯强度随沉积时间的变化不大,这证明高温下(1 600℃)化学气相沉积主要发生在石墨块体表面。     

Absorption-enhanced steam gasification of biomass for hydrogen production: Effect of calcium oxide addition on steam gasification of pyrolytic volatiles

The effect mechanism of calcium oxide (CaO) addition on gasification of pyrolytic volatiles as a key sub-process in the absorption-enhanced steam gasification of biomass (AESGB) for H₂ production at different conditions was investigated using a two-stage fixed-bed pyrolysis–gasification system. The results indicate that CaO functions as a CO₂ absorbent and a catalyst in the volatiles gasification process. CaO triggers the chemical equilibrium shift to produce more H₂ and accelerates volatile cracking and gasification reactions to obtain high volatile conversion rates. Increasing the gasification temperature could improve the reaction rate of cracking and gasification of volatiles as well as the catalytic effect of CaO, which continuously increase H₂ yield. When the gasification temperature exceeds 700 °C, the sharp decrease in CO₂ absorption capability of CaO drastically increases the CO₂ concentration and yield, which significantly decrease H₂ concentration. The appropriate temperature for the absorption-enhanced gasification process should be selected between 600 °C and 700 °C in atmospheric pressure. Increasing the water injection rate (represented as the mass ratio of steam to biomass) could also improve H₂ yield. The type of biomasses is closely associated with H₂ yield, which is closely related to the volatile content of biomass materials.     

Pyrolytic carbon layers—an electron spin resonance analysis

Chemical vapour infiltration is simulated by deposition of pyrolytic carbon on planar boron nitride substrates and carbon fibers in a hot-wall tubular reactor at about 1100 °C for varied pressure and flow-velocity of methane. The degree of orientation of the deposited graphite-like domains can be monitored via orientation and temperature dependence of the electron spin resonance parameters (g-tensor, linewidth). The electronic structure of the localized defects and conduction electrons is accessible by a quantitative modelling of these parameters. The interaction of the built-in hydrogen atoms with the unpaired electron spins is analysed by electron-proton spin double resonance technique (Overhauser shift)     

Investigation of porosity of carbon materials and related effects on gas separation properties

Carbon molecular sieving membranes are chemically robust materials with tailorable gas transport properties for O₂/N₂, CO₂/CH₄ and C₃H₆/C₃H₈ separations. Such carbon materials were formed in this study by the pyrolysis of polyimide precursors. The final pyrolysis temperature was varied to alter the carbon structure, which changed the average pore size. Characterization of the porosity of these materials and how this feature changes when pyrolysis conditions are varied could guide the systematic control of these materials. However, the carbon is an amorphous, microporous material, which makes it difficult to characterize compared to crystalline materials. From separation studies of penetrants on these materials it appears that these materials have both ultramicropores (<7 Å) and larger micropores. The ultramicropores are believed to be mainly responsible for molecular sieving while the micropores provide negligible resistance to diffusion but provide high capacity sorption sites for penetrants. Techniques such as wide angle X-ray diffraction and the analysis of carbon dioxide adsorption isotherms using density functional theory were employed to characterize the microporosity of the material. The small dimensions of the key ultramicropores make accurate determination of their pore size distribution difficult. Therefore, to effectively discuss the differences in transport properties when different pyrolysis temperatures are used as well as penetrants with different dimensions, a hypothetical ultramicropore size distribution was used as a tool to discuss and interpret a combination of parameter effects and trends of separation properties.     

含油污泥资源化技术研究进展

含油污泥是由水包油(o/w)、油包水(w/o)以及悬浮固体组成的稳定的悬浮体系,属于危险废物。主要介绍了溶剂萃取法、热解处理法、破乳法、调剖、焚烧技术在含油污泥处理中的应用研究,并对各种油泥资源技术进行了评述。     

利用XRD研究呋喃树脂制备玻璃炭过程中的结构变化

根据热失重曲线和运用Ｘ射线衍射（ＸＲＤ）所测得的实验结果，讨论了聚糠醇（ＰＦＡ）和聚糠酮（ＰＦＫ）两种呋喃树脂在氮气气氛中热解过程中的结构变化。结果表明，两种试样在４５０℃以前，随着炭化温度的升高，聚合物分子的原有序态结构逐渐被破坏；４５０℃以后，随着炭化温度的升高，六角碳网新的序态结构形成并逐渐增长     

300kt／a乙烯装置危险性分析与防灾对策

针对裂解炉的高温、高压、可燃性物料的泄漏、设备管线的腐蚀、工艺控制指标繁多等因素所导致乙烯装置发生爆燃的危险性,从工艺操作维护方面提出了6条措施。     

Performance of a proton exchange membrane fuel cell stack with thermally conductive pyrolytic graphite sheets for thermal management

This work experimentally investigates the effects of the pyrolytic graphite sheets (PGS) on the performance and thermal management of a proton exchange membrane fuel cell (PEMFC) stack. These PGS with the features of light weight and high thermal conductivity serve as heat spreaders in the fuel cell stack for the first time to reduce the volume and weight of cooling systems, and homogenizes the temperature in the reaction areas. A PEMFC stack with an active area of 100 cm² and 10 cells in series is constructed and used in this research. Five PGS of thickness 0.1 mm are cut into the shape of flow channels and bound to the central five cathode gas channel plates. Four thermocouples are embedded on the cathode gas channel plates to estimate the temperature variation in the stack. It is shown that the maximum power of the stack increase more than 15% with PGS attached. PGS improve the stack performance and alleviate the flooding problem at low cathode flow rates significantly. Results of this study demonstrate the feasibility of application of PGS to the thermal management of a small-to-medium-sized fuel cell stack.     

Quantitative structural and textural assessment of laminar pyrocarbons through Raman spectroscopy, electron diffraction and few other techniques

In pyrocarbon materials, the width of the Raman D band (FWHM_D) is very sensitive to low energy structural defects (e.g., disorientations of the graphene layers). The correlation between the two parameters, FWHM_D and OA (as derived from selected area electron diffraction: SAED), has allowed to differentiate various pyrocarbons unambiguously. Furthermore, the optical properties of pyrocarbons, i.e., the extinction angle, the optical phase shift and the ordinary and extraordinary reflectance, have been accurately determined at 550 nm by means of the extinction curves method. These results are completed by in-plane and out-of-plane dielectric constant measurements by angular resolved EELS. Moreover, the hybridization degree of the carbon atoms has been assessed by the same technique. About 80% of the carbon atoms of the pyrocarbons have a sp² hybridization. The lack of pure sp² carbon atoms, as compared to graphite, might be explained by the presence of sp³-like line defects.     

Influence of the matrix microstructure on the mechanical properties of CVI-infiltrated carbon fiber felts

The correlation between the matrix microstructure and the mechanical properties of CVI-infiltrated carbon fiber felts was studied by optical microscopy, scanning electron microscopy, and three-point bending tests. The results of these investigations show a correlation between (a) the content of highly textured pyrocarbon in the matrix and the quasi-ductile fracture behavior of the samples and (b) the thickness of the low textured pyrocarbon layers beneath the fibers and the measured flexural strengths. Fractographic investigations using SEM showed that toughness increase results from multiple crack deflections at the interface between numerous ‘sublayers’ forming the highly textured pyrocarbon. The increase of flexural strength could be explained by a thicker, so called ‘virtual’ fiber.