Phillips Jonathan, Shiina Toshi, Nemer Martin, Lester Kelvin
Los Alamos National Laboratory, MS-E549, Los Alamos, New Mexico 87545, USA.
Langmuir. 2006 Nov 7;22(23):9694-703. doi: 10.1021/la060915c.
It is shown that self-supporting graphitic structures of specific shape can be grown in a variety of forms, from nanoscale to macroscale, on metal templates, in a fuel-rich mixture of ethylene and oxygen at temperatures between 750 and 900 K. The evidence presented suggests graphite can be grown in any shape created from catalytic metals (e.g., Ni) under the proper conditions of temperature and gas composition. Structures produced include macroscale bodies, centimeters in dimension, composed of micrometer-scale graphite elements such as graphite "foam" and regular graphite "lattices". Nanoscale hollow graphite spheres were also produced. The production rate in the apparatus employed was roughly shown to be 1 layer/s and was steady with time over several hours. The process of producing self-supporting bodies generally produces hollow graphite structures, as the underlying metal template must be removed by acid following the completion of graphite growth. The process is believed to be possible only in an environment, such as combustion, in which a high concentration of particular radical species is present in the vicinity of the template surface. The following process is postulated: (i) a single layer of graphite is formed from gas-phase radicals by the catalytic action of the metal template, (ii) additional graphite growth is "autocatalytic" and occurs via the decomposition of radicals on the surface and the incorporation of "free" carbon atoms, or other radical fragments, into "edge sites" on the graphite surface.
结果表明，在750至900K的温度下，在金属模板上，于富含燃料的乙烯和氧气混合物中，可以生长出从纳米级到宏观尺度的各种特定形状的自支撑石墨结构。所提供的证据表明，在适当的温度和气体组成条件下，石墨可以在由催化金属（例如镍）形成的任何形状中生长。所产生的结构包括尺寸为厘米级的宏观物体，其由微米级的石墨元素组成，如石墨“泡沫”和规则的石墨“晶格”。还制备出了纳米级空心石墨球。在所使用的装置中，生成速率大致显示为1层/秒，并且在数小时内随时间保持稳定。由于在石墨生长完成后，必须通过酸去除底层金属模板，所以制备自支撑物体的过程通常会产生空心石墨结构。据信，该过程仅在诸如燃烧的环境中才有可能发生，在这种环境中，模板表面附近存在高浓度的特定自由基物种。推测的过程如下：（i）通过金属模板的催化作用，由气相自由基形成单层石墨；（ii）额外石墨的生长是“自催化的”，并且通过表面上自由基的分解以及“游离”碳原子或其他自由基片段并入石墨表面的“边缘位点”而发生。
