Spark plasma sintering assisted diamond formation from carbon nanotubes at very low pressure

The thermal stability of multi-walled carbon nanotubes (MWCNTs) was assessed under various spark plasma sintering (SPS) conditions. Our experimental results show that the MWCNTs transform into micrometre-sized diamonds at 1500 °C and only 80 MPa during SPS. The resulting diamonds are single or agglomerated crystalline particles, with diameters up to 100 µm, and are sheathed with an amorphous carbon layer and a residue of a few CNT layers. The SPS-assisted transition from MWCNTs to diamond was investigated, and a model for CNT breakage is proposed to describe the initial diamond growth. Taking into account the rapid and simple operating features of SPS, we believe that this process exhibits great potential for diamond synthesis on a large scale.