Grain-growth kinetics of ferropericlase at high-pressure

Grain-growth kinetics Of (Mg0.85Fe0.15)O ferropericlase was investigated at pressures of 5 and 10GPa and temperatures of 1673-1873 K using a Kawai-type multi-anvil apparatus. Presintered ferropericlase aggregate with an average grain size of 4.0 mu m was used as starting material of grain-growth annealing experiments. The grain-growth kinetics of ferropericlase is described by G(n) - G(0)(n) = k(0) t exp[-(E* + PV*)/RT], where G is the average grain size at annealing time t, Go the initial average grain size, P the pressure, R the gas constant and T is the absolute temperature, with n = 2.6 +/- 0.4, log(10) k(0) = -7.5 +/- 1.7 m(2.6)/s. E* = 262 +/- 30 kJ/mol, V* = 4.7 +/- 0.7 cm(3)/mol. Compared at same pressure and temperature, grain-growth rate of ferropericlase is similar to olivine and faster than those of wadsleyite and ringwoodite. The present results show that, at the top of the lower mantle (P = 25 GPa and T = 1773 10 grain size of ferropericlase in single phase system evolves to similar to 2 x 10(-2) m after significant geological time (10 My) while a previous study predicts that grain size of MgO in two-phase system is as small as similar to 8 x 10(-6) in at same condition. (C) 2008 Elsevier B.V. All rights reserved