The Unique Strength of Diamond

Abstract

ABSTRACTThe features of diamond that make it unique are: 1] its efficient tetrahedral structure which is stabilized by resonance of the bonding electrons among adjacent bonds; 2] the exceptionallly high ratios of its shear moduli to its bulk modulus; 3] the large gap between the top of its valence band and the bottom of its conduction band which makes dislocation mobility very low in it; 4] its high surface energy. Although diamond is nearly elastically Isotropic, the ratio of its C44 shear constant to its bulk modulus is 1.3 which is the highest measured value for this ratio. It is quite unusual for it to be greater than unity. This high shear stiffness appears to be associated with the bimodal distribution of electrons along the lengths of the C-C bonds. Also, for centrally directed interatomic forces, the ratio C44/C12is expected to be unity. But In diamond it is 4.6, indicating that the behavior of diamond cannot be described even approximately by pair-potentials. Because of its unique strength diamond can perform exceptionally in mechanical devices such as: pressure vessels, ultracentrifuges, springs, flywheels, and cutting (or drawing) tools.