Are nanotubes and carbon nanostructures the precursors of coexisting graphite and micro-diamonds in UHP rocks?
详细信息 查看全文
- 作者：Maria D. Ruiz Cruz
- 关键词：Carbon nanotubes ; Carbon nanoparticles ; Diamond ; Ultrahigh pressure metamorphism
- 刊名：Diamond and Related Materials
- 出版年：November, 2013
- 年：2013
- 卷：40
- 期：Complete
- 页码：24-31
- 全文大小：2750 K
文摘
A transmission electron microscopy study of garnet from diamond-grade gneisses of the Betic Cordillera (Spain) has revealed the presence of abundant, previously unrecognized, nanosized carbonaceous grains, coexisting with micrometer-sized graphite and diamond. The nanosized particles occur as multiwall nanotubes, and as polyhedral and quasi-spherical graphite + diamond nanoparticles, whereas larger graphite particles appear as rods and as tabular crystals. The topotactic relationships between graphite in nanoparticles and in micrometer-sized particles and the host garnet suggest that carbon nano- and microparticles precipitated from an originally homogeneous solid solution of carbon in the garnet. Based on orientation relationships and on experimental data it is suggested that the three main types of nanosized particles (nanospheres, polyhedral particles and nanotubes) were the precursor of the three main types of larger carbon phases (diamond, tabular and rod-shaped graphite particles, respectively). It is interpreted, as in the case of diamond-graphite nanocomposites, that diamond formation in the core of the nanoparticles is due to an increase of the cross-links between the layers, and then, to the collapse, at a certain point, of the whole graphite structure into diamond. This finding opens a new door for explaining the origin of some metamorphic diamonds and of coexisting graphite and diamond in ultrahigh pressure rocks.