Meeting room "Glova", 4 floor, Integrated Research Building
Abstract
Nano-polycrystalline diamond (NPD) synthesized directly from graphite under high pressure and high temperature consists of diamond grains of several tens of nanometers in size and has extremely high hardness without mechanical anisotropy. Because of these features NPD has outstanding potential for applications to high pressure anvils. I have developed experimental techniques to synthesize NPD with dimension of up to 1cm using a newly introduced large-volume Kawai-type multianvil apparatus operated in a 6000 tonf hydraulic ram (BOTCHAN-6000). Pressure calibrations were performed at room temperature with various OEL/TEL (Octahedron edge length/Truncated edge length) ratios of 25/15, 29/18, 30/18, 34/20 and 38/22, using press load up to 5000 tonf. All of these assemblies could generate pressure up to 15.6 GPa within the applied press loads. In this study, 25/15, 30/18 and 38/22 were mainly used for synthesis of NPD. Re foil heater and LaCrO3 thermal insulator were used for furnace assembly, and temperatures up to 2500 ?C, which are needed to form pure NPD, were produced. However, some major cracks were found to occur in the samples, due to the possible uniaxial decompression. An attempt was made to fully supress these cracks by maintaining high temperature during decompression. When temperatures were maintained at 800-1000?C, flawless NPDs could be synthesized. Consequently, flawless NPD rods with dimensions of 6.5mm, 8mm and 1cm in both diameter and length were successfully synthesized in the cells with 25/15, 30/18 and 38/22, respectively. Details of these experimental results will be described in the seminar.
For inquiry：Taku Tsuchiya TEL:（089）927-8198
E-mail takut@sci.ehime-u.ac.jp
