3D diagrams of equations of viscous flow of silicate glass-forming melts

Vogel–Fulcher–Tammann (VFT) equation and Mauro, Yue, Ellison, Gupta and Allan (MYEGA) equation for the viscous flow are here expressed using the parameters characteristic for Avramov and Milchev model. This enabled us to represent these functions through 3D diagrams and compare them directly. The 3D diagrams of these functions were compared as functions of the two variables for different temperature (or ratio T/T_r) and in a wide range of x. T_r is referential temperature at which η_Tr = 10¹³ d Pa s.The 3D diagrams were also used to present the differences of these functions. It followed from the 3D diagrams that for x ~ 0.5 and x > 0.8 the most significant differences occur in the values of logη. For that reason equations are additionally tested on concrete silicate systems with such composition of x. The VFT and the MYEGA functions are then modified so that through T_r they include lubricant coefficient k. We show that the 3D diagrams of the so modified VFT and MYEGA functions can predict the behavior of viscosity of silicate systems, both when a component with large k and when a component with small k is present. With these some more frequent anomalies at certain parts of the 3D diagram were observed with the VFT function. The MYEGA function proved to be just as successful as the AM function in predicting the lubricant effect and showed good agreement with the experimental results.