A novel large-volume Kawai-type apparatus and its application to the synthesis of sintered bodies of nano-polycrystalline diamond

•New multi-anvil press is used for synthesis of sintered polycrystalline samples.•High-quality nano-polycrystalline diamond (NPD) rods of ∼1cm are synthesized.•NPD anvils are successfully used in high-pressure geoscience and physical science. A Kawai-type multianvil apparatus operated in a 60 MN press has been constructed for materials synthesis at high pressure and temperature. After having tested various tungsten carbide anvils and optimization of the cell assembly for this novel apparatus, we are now able to perform synthesis experiments of high-pressure phases at temperatures to ∼2500°C with relatively large sample volumes of about 2cm3 in a pressure range up to about 16GPa. Using this apparatus, synthesis of high-quality rods of sintered nano-polycrystalline diamond with dimensions to 1cm in both diameter and length has been routinely made, which should be important as new anvil material for high-pressure mineral physics studies, as well as for some industrial applications.