Spark plasma sintering (SPS) of carbon nanotubes based materials to diamond was conducted at a very low pressure in vacuum and argon atmospheres. The phases and microstructures of the sintered samples were analyzed by Synchrotron X-ray, Raman spectroscopy, and scanning electron microscopy. Diamond phases are created from carbon nanotubes/FeNi mixtures at pressure of 9.55 MPa in vacuum and argon atmospheres during SPS. At this pressure, carbon flowers, and perfect diamond crystals are obtained at 1200 °C only in the argon atmosphere. The consequences provide an indirect evidence for the existence of plasma during SPS. The argon atmosphere promotes the plasma generation and thus enhances the diamond transition.
Diamonds are obtained from carbon nanotubes/FeNi at 1200 °C and 9.55 MPa in argon atmosphere of SPS.