Shear viscosities of galliosilicate liquids

Donald B. Dingwell
1990
Ansrrucr The shear viscosities of 19 galliosilicate and related liquids have been measured using the concentric cylinder method. Nine of the liquid compositions lie in the NarO-GarOr-SiO, system, eight liquids correspond in composition to XltlGaSi'O' (where X: Cs, Rb, K, Na, Li, Ba, Sr, and Ca), and five liquids are Li silicates related by the exchange of Al, Ga, and Fe. The measurements were performed at 1 atm of air pressure in the temperature range of 1700-900'C and a viscosity range of
more » ... osity range of 10"3-105 dPaS. The rotation rates ranged from 0.5 to 100 rpm. All melts exhibited Newtonian viscosities. The viscosities of the Xi;iGaSirO' liquids decrease in the orderCs > Rb > K > Na > Li and Ba > Sr > Ca. IncreasingSiO, content in liquids on the SiOr-NaGaO, join (NaGaSiOo, NaGaSi'Ou, NaGaSirOr) results in increasing viscosity. The exchange of GarO, for NarO along the 75 molVo SiO, isopleth (NarSirOr, Na,rGa"rSirOrr, NaGaSirOr, Na"rGa,5Si3Ors, GarSirOn) yields a viscosity maximum at NaGaSirO.. Comparison with viscosity data for aluminosilicate, ferrosilicate, and borosilicate liquids indicates that viscosities decrease in the order aluminosilicate > galliosilicate > ferrosilicate > borosilicate. Recent heat of solution measurements on NaXSi3O8 glasses (where X: Al, Fe, Ga, and B), in molten PbrB2O5 at973K indicate that the degree to which glasses are stabilized increases in the order Al > Ga > Fe > B (DeYoreo et al., 1990) . Thus a correlation can be made between liquid viscosity and glassy heat of solution that is similar to that previously noted for the alkali exchange in aluminosilicate melts of the formula XAlSi3O8 (where X : alkali). Galliosilicate liquids have been used as structural analogues of the aluminosilicates. The composition-dependence of their viscosities is analogous to the aluminosilicates with the diference that the glass transition occurs at much lower temperatures in galliosilicate liquids. These results confirm galliosilicate liquids as useful analogues for aluminosilicate liquids in studies where the high viscosities of the latter may prevent experimental determination of certain relaxed liquid properties. INrnooucrroN Viscosity is possibly the most diagnostic property of a liquid. It has been demonstrated recently that the time scale of relaxation associated with viscous flow closely matches the mean lifetime of individual Si-O bonds in silicate liquids (Liu et al., 1988) . Farnan and Stebbins (1990) have recently calculated viscosity from "Si NMR relaxation time data. The relaxation behavior of silicate Iiquids can be approximated from the ratio of viscosity to elastic modulus, i.e., the Maxwell relation (e.g., Angell and Torrell, 1983). The relative composition and temperature invariance of the elastic modulus yields the approximation that viscosity is a linear measure of the time scale of bond exchange that dominates high-temperature melt kinetics and defines the glass transition (Dingwell and Webb, 1989). Fundamentally then, viscosity is a measure of melt dynamics, but the dynamics themselves must correlate with the strength of bonds and distribution of cations in silicate melts. One source of information on the static structure of silicate melts is the relative enthalpies of silicate glasses. Relative enthalpies ofsilicate glasses are available for a wide range of compositions from the systematic studies of Nawotsky and coworkers using lead borate solution studies (e.g., Roy and Navrotsky, 1984). A recent comparison of relative heats of solution of Na alumino-, gallio-, ferro-, and borosilicate glasses (DeYoreo et al., 1990) provides data that enable comparison with the present shear viscosity data. Gallium has been used as a structural analogue for Al in several studies of the properties and structure of silicate liquid and glass (e.g., Fleet et al., 19841' Henderson et al., 1985; Matson and Sharma, 1985; Dickenson and Hess, 1986; Sherritrand Fleet, 1990). The present study illustrates some of the similarities in properties of galliosilicates and aluminosilicates. However, one important difference is the lower viscosities ofthe galliosilicates that reduce the temperatures required for several types of experimental investigations of melt properties. Expr,mvrnr.mAl METHoD Eight of the compositions used in this study are based on a stoichiometry given by the general formula 0003-o04x/90/1 I I 2-123 1 $02.00 t23r
doi:10.5282/ubm/epub.6015 fatcat:ywaeh6k2pngmtfxsv5o77yil7m