WI&7037/86fi3.00 +.oO Viscosity-temperature lationships in the system Na2Si205-N&Al205

Abstract-The viscosity-temperature relationships of five melts on the join Na&C&-N&A120 ~ (5, 10, 20, 30 and 40 mole percent N&A120s) have been measured in air, at 1 atm and lOOO- 1350°C with a concentric cylinder viscometer. Ail the melts on this join of constant bulk polymerization behave as Newtonian thuds. in the range of shear rates investigated, and the melts exhibit Arrhenian viscosity-temperature relationships. Isothermal viscosities on this join initially decrease and then increase with increasing mole percent Na.&O ~. The minimum viscosity occurs near 20 mole percent N%AlrOs at 1000°C and moves to higher N&A120j content with increasing temperature. The observation of a viscosity minimum along the join Na2Si2-0,-N~AlzO ~ is not predicted based on earlier viscosity data for the system Na@-A1203-SiOt (RIEBLING, 1966) or based on calculation methods derived from this and other data (BOI-IINGA and WEILL, 1972). This unexpected behavior in melt vixosity-temperature r lations emphasizes the need for a more complete data set in simple silicate systems. Previous spectroscopic nvestigation of melts on the join NazSi&Na,A1201, offer a structural explanation for the observed viscosity data in terms of a disproportionation reaction involving polyanionic units. Mac-roscooicallv. the viscositv data mav he aualitativelv reconciled with t e configurational entropy model for viscous flow (RICHET, 1484)...