Viscosity-temperature relationships in the system Na2Si2O5-Na4Al2O5
The viscosity-temperature relationships of five melts on the join Na2Si2O2-Na4Al2O5 (5, 10, 20, 30 and 40 mole percent Na4Al2O5) have been measured in air, at 1 atm and 1000\u20131350\xb0C with a concentric cylinder viscometer. All the melts on this join of constant bulk polymerization behave as Newtonian fluids, in the range of shear rates investigated, and the melts exhibit Arrhenian viscosity-temperature relationships.\n\nIsothermal viscosities on this join initially decrease and then increase with increasing mole percent Na4Al2O5. The minimum viscosity occurs near 20 mole percent Na4Al2O5 at 1000\xb0C and moves to higher Na4Al2O5 content with increasing temperature.\n\nThe observation of a viscosity minimum along the join Na2Si2-O5-Na4Al2O5 is not predicted based on earlier viscosity data for the system Na2O-Al2O3-SiO2 (RlEBLlNG, 1966) or based on calculation methods derived from this and other data (Bottinga and Weill, 1972). This unexpected behavior in melt viscosity-temperature relations emphasizes the need for a more complete data set in simple silicate systems.\n\nPrevious spectroscopic investigation of melts on the join Na22Si2O5-Na4Al2O5 offer a structural explanation for the observed viscosity data in terms of a disproportionation reaction involving polyanionic units. Macroscopically, the viscosity data may be qualitatively reconciled with the configurational entropy model for viscous flow (Richet, 1984).