Size-related stabilization of diamond nanoparticles

Boundaries of stability regions (of particles sizes) of diamond and graphite at low pressure and various temperatures have been established by modeling and computation of free energies of the crystal phases. The results indicate that diamond is the stable modification of carbon, and graphite is the metastable one at small particle sizes. The diamond charge lattice is presented by ion-electron lattice of negative bond charges and positive ions. The graphite charge lattice consists of hexagonal ion-electron nets and collectivized conduction electrons located between the nets. The consideration of conduction electrons in the graphite model provides the stable graphite structure, since the attraction between the conduction electrons and hexagonal nets compensates the repulsive forces acting between the nets. The intersection of size dependencies of free energies of diamond and graphite indicates the size-related stabilization of small diamond particles. The established boundaries of stability regions of diamond and graphite are: 10.2 nm at room temperature, 6.1 nm at 525 degrees C, 4.8 nm at 800 degrees C and 4.3 nm at 1100 degrees C.