Numerical simulations of coarsening of eutectoid structures: Implications for grain size in the lower mantle

Abstract

Since it has been realized that the viscosity of the lower mantle depends on the grain size, several studies have been conducted to constrain grain size in the lower mantle. One of the problems is that the initial structure generated by spinel-perovskite phase transformation is characterized by lamellae of alternating perovskite and magnesioüstite. It is not clear how long it takes for such structures to reach the asymptotic regime of conventional Ostwald ripening and whether this can happen on typical time scales of laboratory experiments. We performed numerical simulations of coarsening of lamellar structures using Monte Carlo Potts model. We find that at high temperatures, an isotropic lamellar structure degenerates into nearly equiaxed grains with the diameter which is 2 to 3 times larger that the original lamellar spacing. The duration of this process is comparable with that expected for conventional Ostwald …