• 主题
高级搜索  >
历史搜索 清空历史
首页> 外文学位 >The structural and property evolution of cellulose during carbonization.
【24h】

The structural and property evolution of cellulose during carbonization.

机译：碳化过程中纤维素的结构和性能演变。

获取原文
获取原文并翻译 | 示例
页面导航
  • 摘要
  • 著录项
  • 相似文献
  • 相关主题

摘要

The understanding of the structure and related property evolution during carbonization is imperative in engineering carbon materials for specific functionalities. High purity cellulose was used as a model precursor to help understand the conversion of organic compounds to hard carbons. Several characterization techniques were employed to follow the structural, compositional and property changes during the thermal transformation of microcrystalline cellulose to carbon over the temperature range of 250°C to 2000°C.;These studies revealed several stages of composition and microstructure evolution during carbonization supported by the observation of five distinct regions of electrical and thermal properties. In Region I, from 250°C to 400°C, depolymerisation of cellulose molecules caused the evolution of volatile gases and decrease in dipole polarization. This also led to the reduction of overall AC electrical conductivity and specific heat. In Region II, from 450°C to 500°C, the formation and growth of conducting sp 2 carbon clusters resulted in increases in overall AC electrical conductivity and thermal diffusivity with rising temperature. For heat treatment temperatures of 550°C and 600°C, Region III, carbon clusters grew into aggregates of curved carbon layers leading to interfacial polarization and onset of percolation. AC electrical and thermal conductivities are enhanced due to electron hopping and improved phonon transport among carbon clusters. With temperatures rising from 650°C to 1000°C, Region IV, DC conductivity began to emerge and increased sharply along with thermal conductivity with further percolation of carbon clusters as lateral growth of carbon layers continued. Lastly, from 1200°C to 2000°C, Region V, DC electrical conductivity remained constant due to a fully percolated system.
机译：在工程碳材料中具有特定功能时，必须了解碳化过程中的结构和相关性能演变。高纯度纤维素用作模型前体，以帮助了解有机化合物向硬碳的转化。在250°C至2000°C的温度范围内，采用了几种表征技术来跟踪微晶纤维素向碳热转化过程中的结构，组成和性能变化;这些研究揭示了支持碳化过程中组成和微观结构演变的几个阶段通过观察五个不同的电和热特性区域。在区域I中，从250°C到400°C，纤维素分子的解聚导致挥发性气体的释放和偶极极化的降低。这也导致了总体交流电导率和比热的降低。在区域II中，从450°C到500°C，导电的sp 2碳簇的形成和增长导致总的AC电导率和热扩散率随温度升高而增加。对于550°C和600°C区域III的热处理温度，碳簇生长为弯曲碳层的聚集体，从而导致界面极化和渗流开始。由于电子跳变和碳簇之间的声子传输改善，交流电和导热性得到了提高。随着温度从650°C升高到1000°C（区域IV），DC传导率开始出现并急剧上升，同时随着碳层横向生长的继续，随着碳簇的进一步渗透，热导率也随之急剧上升。最后，在1200°C至2000°C的区域V中，由于完全渗透的系统，直流电导率保持恒定。

著录项

  • 作者

    Rhim, Yo-Rhin.;

  • 作者单位

    The Johns Hopkins University.;

  • 授予单位 The Johns Hopkins University.;
  • 学科 Engineering Mechanical.;Engineering Materials Science.
  • 学位 Ph.D.
  • 年度 2009
  • 页码 150 p.
  • 总页数 150
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 机械、仪表工业;工程材料学;
  • 关键词

  • 入库时间 2022-08-17 11:37:37

相似文献

  • 外文文献
  • 中文文献
  • 专利
获取原文

客服邮箱：kefu@zhangqiaokeyan.com

京公网安备：11010802029741号 ICP备案号：京ICP备15016152号-6 六维联合信息科技 (北京) 有限公司©版权所有

  • 客服微信

  • 服务号