【作者】 李志强；

【导师】 吕永根；

【作者基本信息】 东华大学 ， 材料物理与化学， 2010， 硕士

【摘要】 沥青基泡沫炭具备密度低、耐腐蚀、热膨胀系数小、高强度、高导热导电等优点,在航空航天以及民用领域有着广泛的应用前景。超临界溶剂法制备的中间相沥青基泡沫炭,由于具有发达的三维网络结构和高度的可石墨化性,成为一种优异的轻型导热碳材料。针对如何提高泡沫炭中泡孔的尺寸均一性,改善泡孔的分布均匀性,该研究选取了合适的溶剂,并对影响发泡过程中气泡成核以及气泡生长的各个因素进行了系统的研究。本论文主要考虑发泡压力,发泡温度,释压速率（或释压时间）和溶剂配比对气泡密度和气泡平均孔径的影响,并分别在高压反应釜中进行了实验,得出了各自的变化关系。为了从理论上对成核过程进行分析,该研究借鉴Colton和Suh的经典成核理论,参考Kim的气体分子团簇模型,对中间相沥青超临界溶剂发泡均相成核过程进行了数学模拟,通过数据回归得出了适合超临界溶剂发泡的均相成核理论模型。该研究采用自制的易冷却微型发泡装置进行了中间相沥青的超临界溶剂发泡实验,并通过实验数据进行了公式参数的回归,最终得到了适合于中间相沥青超临界溶剂发泡工艺的数学模型。针对模型准确性的问题,在模型的指导下,该研究进行了有效的实验验证。结果显示:当分别控制饱和压力小于5.0MPa,释压速率大于1.0MPa/s时,实验得出的数据基本符合该均相成核模型,但是由于理论模型只考察了均相成核过程,忽略了实验中存在的非均相成核过程,从而使得实验得到的气泡密度值要稍高于模拟气核密度值。当饱和压力很大或者释压速率很小时,由于不可避免的融并现象,使得泡沫样品中的气泡密度要普遍小于模拟气核密度值。通过对影响发泡过程中气泡成核以及气泡生长的各个因素的系统研究,文章得出了各个因素的最佳发泡条件范围,并在此基础上,通过条件的综合设定进行了最佳发泡工艺的探索。研究得出:当控制发泡温度为588～593K,初始压力为2.0～3.0MPa,释压速率为1.0～1.5MPa/s,溶剂配比为30wt%时,可以制备出气泡平均孔径400～800μm,气泡密度10～16×10³cm^-3,泡孔形状规则、泡孔分布均匀的中间相沥青基泡沫炭。更多还原

【Abstract】 Due to low density, corrosion resistance, low thermal expansion coefficient, high tensile strength, high thermal conductivity, pitch-based carbon foams have a broad application prospect in the field of aviation and aerospace as well as civilian. Mesophase pitch-based carbon foams prepared by supercritical solvent, become an excellent light thermal conductive carbon material as a developed three dimensional net-like and highly graphitized structure. This study focused on choosing the proper solvent to improve the size uniformity and distributing uniformity of bubbles, and had done a systemic research of various factors influencing foaming process. This paper mainly studied the effects of initial pressure, foaming temperature, depressurization rate, and solvent proportion on bubble density and average bubble size. The experiments were carried out in a high pressure reactor, and various curves were made based on the experiments.In order to analyze the nucleation process by supercritical solvent theoretically, we have made the mathematical simulation of homogeneous nucleation process, referring to Colton and Suh’s classical nucleation theory and Kim’s cluster model of gas molecule. And we got the theory model of homogeneous nucleation by supercritical solvent through regression of parameters. A self- made micro foaming equipment that could be cooled easily was applied for carrying out accurate experiments, and a mathematical model was established based on received data. This study gave the validation to the simulated model under instructions. Comparison between theory and experimental results showed that the variability of the bubble density following saturation pressure and depressurization time agreed well with the mathematical model when the saturation pressure was less than 5.0MPa and depressurization time was less than 5.0s, but real bubble densities were smaller than that simulated nucleus densities due to unavoidable coalescence. When saturation pressure was much high or depressurization time was very long, the bubble densities of foams were much smaller than the simulated nucleus densities due to strong coalescence for bubbles’ excessive growth.Through the systematic study of all effective factors, we obtained the range of best foaming conditions. The results showed that supercritical fluid （ SCF ） was suitable for preparing mesophase pitch foams with cell size in the range of 200～800μm, either communicating or closed, and different cell density. Carbon foams with hexagon cell shape, cell diameter of 400～800μm, cell density of 10～16×10³cm^-3 and a ligament-mesh structure were prepared at a temperature of 588～593K, initial pressure of 2.0～3.0MPa, depressurization rate of 1.0～1.5MPa/s and solvent proportion of 30%.更多还原