Using a hot isostatic pressing (HIP) technique, we synthesized diamond-SiC composites from diamond and Si powders. At an HIP condition of 1450°C and 100 MPa, a pressure much lower than that of the diamond stability field, diamond powders react with molten Si to form well-sintered diamond-SiC composites. Cubes of the composites were thereby fabricated, and an application to the second stage anvils in the Kawai-type multi-anvil high-pressure apparatus was attempted. Since the diamond-SiC composites are transparent to X rays, the present system is applicable not only to conventional energy dispersive X-ray diffraction studies but also to angle dispersive diffraction and radiographic studies that need a larger window for X-ray images. In this article, our recent advances were reviewed.
In this decade, attainable pressure range in a Kawai-type high-pressure apparatus equipped with sintered diamond as second stage anvil is significantly increased and we generated pressure to 97.2 GPa measured by in situ X-ray observation at SPring-8. By using this technique, we measured compressibility of (Fe0.08Mg0.92)SiO3 perovskite up to more than 90 GPa. The bulk modulus and its pressure derivative are determined to be 268 GPa and 3.8, respectively. These values are slightly different from previous results. However, we obtained consistent results with previous study of bulk modulus of 257 GPa and pressure derivative of 4.3 when we fitted the data in the pressure range less than 70 GPa. The change of compressibility may indicate the spin transition in Fe-bearing perovskite around 70 GPa as suggested by previous study, for example, electrical conductivity measurement, X-ray emission method and so on.
Since the first report of synthesis nano-polycrystalline diamond (NPD), efforts have been directed to synthesize larger bodies of NPD with higher quality, using Kawai-type multianvil apparatus. NPD has extraordinarily high hardness, peculiar nano-texture and high transparency, which has also been found to have very high elastic stiffness, high toughness, and high wear-resistance. These characteristics of NPD are important in applications as anvils for various types of high-pressure apparatus toward generation of higher pressures and temperatures with greater accuracies. Here, we review current status of synthesis of NPD, its physical properties, and some preliminary results in applications to high-pressure studies.
Nano-polycrystalline diamond (NPD), consisting of nano-sized diamond grains oriented in random directions without containing any secondary phases, can be produced by direct conversion sintering from graphite under high pressure and high temperature. NPD is characterized by high hardness surpassing that of single crystal diamond, and exhibits no cleavage features and has isotropy of mechanical properties. These characteristics of NPD suggest potential applications of this novel material as anvils for diamond anvil cells. In this article, some properties of NPD and results of high-pressure generation tests using NPD anvils are reviewed, and its potentiality as a new anvil material is discussed.
In this article, synthesis of cubic boron nitride (cBN) sintered bodies without any additive was reviewed. At pressures higher than 8 GPa, direct transformation from hexagonal BN (hBN) to cBN took place near 2000°C. The resultant binderless cBN sintered bodies exhibit superior properties as highly wear resistive materials. At 10 GPa region, reaction temperature required for the complete transformation from hBN to cBN can be suppressed to near 1700°C, resulting in suppression of grain growth during the sintering. Higher wear resistance properties of binderless cBN sintered bodies with finer grains as cutting tools were demonstrated by their superior cutting performance against ferrous materials. Further requirement for the fabrication of large scale binderless cBN sintered bodies by sintering of fine cBN grains was also discussed for future study.
Computed micro-tomography (CMT) allows us to visualize 3-dimensional sample image. Such unique capability has contributed to our society, especially in the filed of medical science. In this article, fundamentals of CMT are reviewed in order to encourage further application to other scientific field. Application to high pressure research, developed by the GeoSoilEnviroCARS, the University of Chicago, is given to present an idea about what to do and how to build the system. CMT in transmission electron microscopy is also described in comparison to synchrotron-based tomography.