Preparation of vapor-phase-grown graphene using hot isostatic pressing and its formation mechanism

A method for mass-producing graphene without a substrate or catalyst has not yet been developed. Consequently, combined with the tendency of graphene to stack easily, there are currently no applications that effectively exploit its structure and functionality. We address these issues by investigating the preparation of graphene using hot isostatic pressing (HIP) and the mechanism of this process. We developed a method for mass-producing vapor-phase-grown graphene by first heating a resin material such as phenolic resin under conditions that control the amount of residual hydrogen and then treating the product with argon or nitrogen using HIP equipment. After heating, the resin powder changed to carbon powder containing small quantity of residual hydrogen and oxygen. In the HIP method, the carbonized powder generates hydrogen and hydrocarbons from inside the powder particles. These create a concentration gradient near the carbonized powder surface by hydrostatic pressure due to HIP, and a thermal chemical vapor deposition reaction occurs due to the heating, which results in the radial formation of flower-like graphene on the carbonized powder surface. The results show that in the formation of vapor-phase-grown carbon, when the HIP treatment temperature is 1300–1500 ℃, thin two-dimensional growth is preferred over three-dimensional growth, and graphene grows in the same manner as carbon nanotubes without a catalyst.