On the Fe²⁺ –Mg²⁺‐Interdiffusion in Olivine (II)

Abstract

Abstract Interdiffusion experiments have been performed in the quasibinary system Fe 2 SiO 4 –Mg 2 SiO 4 . Interdiffusion coefficients D̄ have been evaluated for polycrystalline (Fe x Mg 1‐ x ) 2 SiO 4 between 1050°C < T < 1280°C and compositions x ranging from 0.9 to 0.1. It was found that D̄ , at given T and p o 2 , increases almost exponentially with composition x in (Fe x Mg 1‐ x ) 2 SiO 4 , in accordance with other oxide solid solutions. For x > 0.3, a p o 2 1/5 ‐dependence is found. For smaller x ‐values, D̄ is rather proportional to p o 2 1/5.5 . It is also found that the oxygen pressure dependence of D̄ , and of the vacancy concentration in the sublattice of the divalent cations, is the same. This means that indeed a vacancy mechanism is operative in the interdiffusion process. The strong composition dependence of D̄ is almost entirely due to the strong composition dependence of the vacancy concentration. Various other olivine solid solution systems (where Me 2+ = Ni 2+ , Co 2+ , Mn 2+ ) can be shown to behave similar to the iron‐olivine. It is also found that D Fe > D Mg . The meaning of D̄ is discussed in terms of the selfdiffusion coefficients D Fe and D Mg .