SIZE-RELATED STABILIZATION OF DIAMOND NANOPARTICLES

Boundaries of stability regions (of particles sizes) of diamond and gr aphite at low pressure and various temperatures have been established by modeling and computation of free energies of the crystal phases. Th e results indicate that diamond is the stable modification of carbon, and graphite is the metastable one at small particle sizes. The diamon d charge lattice is presented by ion-electron lattice of negative bond charges and positive ions. The graphite charge lattice consists of he xagonal ion-electron nets and collectivized conduction electrons locat ed between the nets. The consideration of conduction electrons in the graphite model provides the stable graphite structure, since the attra ction 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 s ize-related stabilization of small diamond particles. The established boundaries of stability regions of diamond and graphite are: 10.2 nm a t room temperature, 6.1 nm at 525 degrees C, 4.8 nm at 800 degrees C a nd 4.3 nm at 1100 degrees C.