Direct synthesis of diamond from low purity carbon nanotubes

摘要

The transformation of graphite 1, fullerenes 2-4, and carbon nanotubes (CNTs) 5 to diamond, a valuable engineering material, is of great technological importance, and therefore has become the subject of intensive research. Generally, pressures above several GPa and high temperature are needed, catalysts such as Ni, Co, other metals or alloys are necessary for a considerable diamond yield. Spark plasma sintering (SPS) is a newly developed, plasma assisted sintering method, which is characterized by a spark plasma created by on-off pulse direct current during heat treatment of powders in a graphite die. We first demonstrated the conversion of CNTs to diamond during SPS, where high purity (95 percent) multi-walled CNTs were used as the starting material 6. However, high purity CNTs are expensive due to their complicated purification procedure and low yield 7.