【作者】 李万千；

【导师】 张红波；

【作者基本信息】 中南大学 ， 材料学， 2011， 博士

【摘要】 中间相沥青基泡沫炭具有低密度、热导率高、热稳定性好、耐腐蚀性能,热膨胀系数低等一系列优良特性,是一种极具发展潜力的新型炭材料。但泡沫炭的强度较低,限制了其应用。因此,如何提高其强度并保持其较高的热导率是当前亟待解决的问题。本文以日本三菱公司的萘基中间相沥青为原料,采用高温自发泡法制备泡沫炭。研究了不同压力下的恒压发泡工艺、中间相沥青预氧化处理对中间相沥青基泡沫炭的结构和性能的影响；在中间相沥青中分别添加聚丙烯腈基炭纤维、聚丙烯腈基预氧丝和碳纳米管,系统地考察了纤维种类、纤维长度、原料配比和不同石墨化温度对泡沫炭的微观结构、力学性能和导热性能的影响。主要研究结论如下：1.当恒压发泡压力较低时,泡沫炭的孔泡结构以开孔为主；随着发泡压力的升高,泡沫炭的开孔逐渐减少,炭泡沫和石墨泡沫的抗压强度均逐渐增加,而石墨泡沫的热导率和比热导率呈现了先增加后减小的趋势。当发泡压力为7MPa时,石墨泡沫的热导率和比热导率达到最大值,分别为61.0W/m K和93.1(W/m K)/(g/cm3),高于传统导热材料(铜和泡沫铝)的比热导率。2.随着预氧化时间的延长,炭泡沫和石墨泡沫的体积密度和抗压强度逐渐增加,当预氧化时间为6h时,炭泡沫和石墨泡沫的体积密度和抗压强度达到最大值,分别为1.07g/cm3、1.23g/cm3、12.07MPa和9.06MPa。3.添加炭纤维粉较添加短切炭纤维对泡沫炭的的抗压强度和热导率的改善更加明显。纤维与炭基体之间的应力石墨化作用能提高基体的微区石墨化度。使其微晶尺寸增大,热导率提高。当炭纤维粉含量为6wt%时,石墨泡沫的抗压强度和热导率分别为6.7MPa和83.OW/m K,较纯石墨泡沫的热导率(39.2W/m K)提高一倍。随着石墨化温度的提高(2000℃-2500℃),石墨泡沫的微晶尺寸进一步增大,热导率显著提高,抗压强度降低。4.添加预氧丝粉较添加短切预氧丝对泡沫炭的的抗压强度和热导率的改善程度更加明显。预氧丝粉与炭基体之间的应力石墨化作用有利于提高炭基体的石墨化度,明显改善石墨泡沫的热导率。预氧丝粉含量为2wt%时,石墨泡沫的抗压强度为7.7MPa。随着石墨化温度的提高(2000℃-2500℃),预氧丝粉含量为2wt%的石墨泡沫材料的抗压强度降低,石墨微晶尺寸La和Lc明显增加,体积密度和热导率增加。石墨化温度为2500℃时,石墨泡沫的热导率达到71.8W/m K。5.适量的碳纳米管能均匀分散在炭基体中,碳纳米管与基体之间的良好界面结合显著改善了炭泡沫的力学性能,碳纳米管的含量为2wt%时,炭泡沫抗压强度最大,为11.5MPa。碳纳米管能促进石墨微晶尺寸的生长,提高其热导率,2500℃高温热处理后,碳纳米管含量为1wt%的石墨泡沫材料的微晶尺寸La和Lc有较大增加,热导率提高,为78.2W/m K,但抗压强度下降。更多还原

【Abstract】 Mesophase pitch-based carbon foam possessed excellent properties such as low density, high thermal conductivity, excellent thermal stability, corrosion resistance, low coefficient of thermal expansion. It was a kind of promising carbon material. However, the strength of carbon foam is low, which limited its application. To enhance the strength without decreasing its high thermal conductivity was our aim. In this work carbon foam was fabricated by foaming at high temperature. Mesophase pitch was used as precursor. Investigations were carried out to determine the effects of constant autoclave pressure and preoxidation of pitch on the structure and properties of carbon foam. PAN-based carbon fiber, PAN-based preoxidized fiber and carbon nanotubes were respectively added into mesophase pitch. The influence of kinds of fiber, fiber length, mass ration between mesophase pitch and fiber, different graphite temperature on microstructure, strength properties and thermal conductivities was discussed. The results were summarized as follows.1.Carbon foam had high open porosity under low foaming pressure. The open porosity was decreased when the foaming pressure was increased. Both of the compressive strength of carbon foam and graphite foam was improved. The thermal conductivity and specific conductivity tend to decrease while they were increased at first. When the pressure was7MPa, the thermal conductivity and specific thermal conductivity reached61.0W/m K and93.1W/m K respecitvely. The specific thermal conductivity was higher than conventional radiater (copper and aluminum foam).2.The bulk density and compressive strength of carbon foam and graphite foam was increased with the extension of oxidation time. The maximal values reacehd1.07g/cm3,1.23g/cm3,12.07MPa and9.06MPa when the oxidation time was6h.3.The addition of carbon fiber powder could improve the compressive strength and thermal conductivity. While the addition of short carbon fiber had less effects in improving these properties.The stress-introduced graphitization between fiber and carbon matrix can improve the graphitization in micro-aera. The microcrystalline value was increased. The thermal conductivity was also improved. When the carbon fiber powder content was6wt%, the maximal value of compressive strength of graphite foam was6.7MPa. The thermal conductivity of graphite foam reached83W/m K, which was a times of that of graphite foam. The microcrystalline value was further increased with the increasing of temperature(2000℃～2500℃). The thermal conductvity was improved, while the compressive strength was decreased.4.The addition of PAN-based preoxidized fiber powder could improve the compressive strength and thermal conductivity. While the addition of short carbon fiber had less effects in improving these properties. The stress-introduced graphitization between fiber and carbon matrix can improve the graphitization degree and thermal conductivity.When the preoxidized fiber powder content was2wt%, the microcrystalline value was further increased with the increasing of temperature(2000℃～2500℃), and the compressive strength was decreased. Both of the bulk density and thermal conductivity were increased. The thermal conductivity reached71.8W/m K at2500℃5.Moderate amount of CNTs could be dispersed uniformly in carbon matrix. CNTs could form good interfaces with carbon matrix, and improve the mechanical properties.The compressive strength of carbon foam reached11.5MPa when the CNTs content was2wt%. CNTs could promote the increasing of microcrystalline of graphite, which inproved the thermal conductivity. La and Lc values were increased obviously when the graphite foam contain lwt%CNTs was heat treated at2500℃. The thermal conductivity reached78.2W/m K, while the compressive strength decreased.更多还原