Ultrahigh-pressure synthesis and applications of nano-polycrystalline diamond

Brief history and the current status of synthesis and applications of nano-polycrystalline diamond (NPD) have been reviewed, as an example of serendipity in basic science, which led to a novel material useful in both scientific and industrial applications. NPD was first witnessed as a tiny piece of glassy transparent material in the wreckage product of an unsuccessful high-pressure experiment, when the author was studying phase transitions of a basaltic composition in a graphite capsule in the mid-1980s. Since then, a number of trial-and-error experiments were made over 15 years, and the author found it was well-sintered polycrystalline material made of nano-crystalline diamond directly converted from graphite under very high pressure and temperature. The NPD was also found to be extremely hard, even harder than natural single crystal diamond. Efforts were made to produce the NPD samples with higher quality and larger sizes, and those with dimensions up to 1 cm in both diameter and length became available by using a large-volume Kawai-type multianvil apparatus (KMA) in the early 2010s. Since then, successful applications of this novel ultra-hard material have been made in high-pressure geoscience, physics, chemistry, and materials science. NPD has also been used for some industrial applications, and known as the very first material successfully commercialized using ultrahigh-pressure synthesis method with the KMA technology. Some novel materials such as Transparent Nano-Ceramics have been synthesized using the similar technique of ultrahigh-pressure synthesis, leading to the development of a new research field “ultra-high pressure materials science”.