Viscosity model for fully liquid silicate melt

A model for estimating the viscosity of silicate melt as derived in our previous paper is extended to the system containing MgO, CaO, SrO, BaO, Li2O, Na2O, K2O, which can express the nonlinear variation of activation energy of viscosity with the composition. It is found that the optimized parameters of model which characterize the deforming ability of bonds around non-bridging oxygen decrease with increasing the bond strength of M-O bond expressed by I=2Q/RMz+ + rO2-)2 (where Q is the valence of cation M; r is the radius). It is pointed out that viscosity is not only determined by the bond strength, but also by the radius of cation which is defined as the size effect. The radius of cation plays paradox roles in the two factors: smaller radius leads to a stronger bond, thus a higher viscosity; while cations with smaller radius are easier to diffuse when neglecting the interaction force, thus a lower viscosity will be.