Self-diffusion in crystalline adamantane

Abstract

Abstract Measurements of lattice (D 1) said, sub-grain boundary (Dp) self-diffusion coefficients in the high temperature face-centred cubic phase of adamantane (C10H16) yield expressions for the temperature dependence of the two processes of the form D 1= 1·6 exp (-138·5 kJ mol−1/RT) m2 s−1 D Pδ = 1·7 × 10−13 exp (−49 kJ mol−1/RT) m2 g−1 where δ is the grain-boundary width. The grain-boundary diffusion data are used to test the reliability of the present and previous lattice self-diffusion studies in this possibly highly defective material, and to establish reasonable experimental conditions for studies of the influence of isotope-mass and hydrostatic pressure on lattice self-diffusion. Isotope-mass studies yield a value for the mass factor E ab in the range 0·70–0·80 (±0·08), and the pressure variation, an activation volume of V+ = 1·2 ω (ω is the molar volume). The results are consistent with lattice self-diffusion by a vacancy migration mechanism.