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Experimental study and modeling of swelling and bubble growth in carbon nanofiber filled mesophase pitch during carbonization.

机译：碳纳米纤维填充中间相沥青碳化过程中溶胀和气泡生长的实验研究和建模。

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摘要

Graphite and all carbon bipolar plates show corrosion resistance in fuel cells and provide good electrical conductivity. These materials typically need to be individually machined, a time consuming and costly process. Mesophase pitch is used to manufacture carbon fibers and carbon-carbon composites. This material provides a good starting point for the production of a moldable, all carbon bipolar plate. However, processing of mesophase pitch to produce all carbon materials requires a time intensive oxidation step to prevent swelling during carbonization.;In this work, carbon nanofibers were used to reduce swelling in mesophase pitch. It was found that the increase in viscosity with the addition of carbon nanofibers was responsible for the reduction in swelling. The influence of the filler became apparent above the percolation threshold. At loadings below the percolation threshold, the swelling of the mesophase pitch was not reduced after carbonization. The swelling of the mesophase pitch at a given carbon nanofiber loading was also dependent on the length of the carbon nanofibers. Longer carbon nanofibers led to greater increases in the viscosity of the melt and thus led to greater reduction in swelling.;The final carbon product was evaluated for use as a low temperature fuel cell bipolar plate material. Constraining the mesophase pitch during carbonization led to a final product with strength and electrical conductivity comparable to current composite bipolar plate materials. The addition of micron size chopped glass fibers with a softening point near 850 °C and carbon nanofibers led to a final product with air permeability less than that of graphite.;A spherically symmetric, single bubble growth model was also developed. The model included temperature dependence, liquid to bubble mass transfer and reactions in the system. Results from simulations showed that that the increase in viscosity due to the addition of carbon nanofibers slows the growth of bubbles, but that the time scale of single bubble growth is much shorter than the time over which the foam grows. The single bubble growth model was deemed to be applicable to low loadings of carbon nanofiber, where the bubble size distribution in the final foam is narrow.
机译：石墨和所有碳双极板在燃料电池中均表现出耐腐蚀性，并具有良好的导电性。这些材料通常需要单独加工，既耗时又昂贵。中间相沥青用于制造碳纤维和碳-碳复合材料。这种材料为可模制的全碳双极板的生产提供了良好的起点。然而，加工中间相沥青以生产所有碳材料需要耗时的氧化步骤，以防止碳化过程中的溶胀。在这项工作中，碳纳米纤维被用来减少中间相沥青的溶胀。发现添加碳纳米纤维引起的粘度增加是溶胀减少的原因。在渗透阈值以上，填料的影响变得明显。在低于渗滤阈值的载荷下，碳化后中间相沥青的溶胀没有降低。在给定的碳纳米纤维负载下，中间相沥青的膨胀还取决于碳纳米纤维的长度。较长的碳纳米纤维导致熔体的粘度更大地增加，从而导致溶胀的更大降低。评估了最终的碳产品用作低温燃料电池双极板材料。在碳化过程中限制中间相沥青可得到具有与目前的复合双极板材料相当的强度和导电率的最终产品。添加了软化点接近850°C的微米级切碎的玻璃纤维和碳纳米纤维，最终产品的透气性小于石墨。并建立了球对称的单气泡生长模型。该模型包括温度依赖性，液体到气泡的传质以及系统中的反应。模拟的结果表明，由于添加了碳纳米纤维而导致的粘度增加减慢了气泡的生长，但是单气泡生长的时间尺度比泡沫增长的时间短得多。单个气泡增长模型被认为适用于低负荷的碳纳米纤维，其中最终泡沫中的气泡尺寸分布较窄。

著录项

  • 作者

    Calebrese, Christopher.;

  • 作者单位

    Rensselaer Polytechnic Institute.;

  • 授予单位 Rensselaer Polytechnic Institute.;
  • 学科 Engineering Materials Science.
  • 学位 Ph.D.
  • 年度 2009
  • 页码 239 p.
  • 总页数 239
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 工程材料学;
  • 关键词

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