OXYGEN SELF-DIFFUSION IN RUTILE UNDER HYDROTHERMAL CONDITIONS

Oxygen self-diffusion coefficients have been determined for synthetic and natural rutile single crystals under hydrothermal conditions at 1 00 M Pa total pressure and in the temperature range 873-1 373 K. The d iffusion coefficients are lower than the results from dry gas exchange studies would predict. Between 973 and 1 373 K the results can be cha racterized by two linear Arrhenius relationships. D = 1.14 x 10(-11) e xp (-168.8 k J mol-1 /RT) m-2 s-1 for the natural rutile, and D = 2.41 x 10(-12) exp (-172.5 kJ mol-1 /RT) M2S-1 for the synthetic crystal. The results have been interpreted in terms of a defect model involving the dissolution of water in rutile as substitutional hydroxyl defects on oxygen lattice sites, with a solution enthalpy in the range 81-106 kJ mol-1.