Through entrustment by the New Energy and Industrial Technology Development Organization (NEDO), and in cooperation with the Japan Fine Ceramics Center (JFCC), the Research Center for Advanced Carbon Materials of the National Institute of Advanced Industrial Science and Technology (AIST) has been carrying out “Research and Development of Frontier Carbon Technology,” and has succeeded in the development of a new super-hard phase of nanotubes.

Diamond is considered to be the hardest insulator material, and it is well known that graphite transforms into diamond under conditions of high temperature and high pressure. Using monolayered nanotubes, we have succeeded in the synthesis of a new super-hard phase with electric conductivity under conditions of high pressure at room temperature.

Bundles of monolayered nanotubes 1.2 to 1.3 nm in diameter were used as samples. Pressure up to 54 GPa was applied using a diamond anvil cell, which can induce shear deformation. In the range of pressure from 14 to 19 GPa, a transition phase was observed, and the new super-high phase appeared when pressure exceeded 24 GPa. Hardness was evaluated by comparing results from hardness measurements of other high-pressure specimens. The results show that high pressurization of monolayered nanotubes induces transformation of these nanotubes into a new super-hard material (highly pressurized nanotube material) with a maximum hardness comparable to the hardness of diamond.

The bulk modulus of the highly pressurized nanotube material is in the order of 462 to 546 GPa, surpassing the value of 420 GPa for diamond.

High expectation is set on the thermal conductivity characteristics of this highly pressurized nanotube material, and the fields of application could extend to boards for SAW devices, processing chips, tools, tribological materials, heat sinks, etc.

Future Trends

It has been demonstrated that application of high pressure (over 240,000 atmospheres) at room temperature to monolayered nanotubes results in an ultra-hard phase. The next step will be to further advance the research on crystallization, and, after accurate measurements of hardness, x-ray diffraction analysis of the crystal, the electron energy loss spectroscopy (EELS), measurements of electric conductivity, etc., to identify the structure and characteristics of this phase. Finally, we aim to develop processing methods that allow mass production and widen the field of application of this material.