THE INFLUENCE OF ALKALINE-EARTH OXIDES (BEO, MGO, CAO, SRO, BAO) ON THE VISCOSITY OF A HAPLOGRANITIC MELT - SYSTEMATICS OF NON-ARRHENIAN BEHAVIOR

The effect of the addition of 5, 10 and 20 wt % of the alkaline-earth oxides on the viscosity of a haplogranitic melt composition has been i nvestigated at 1 atm pressure and in the temperature range of 640 to 1 675 degrees C. The high-temperature viscosity data were obtained with concentric-cylinder viscometry and the low-temperature viscosity data using micropenetration viscometry. The combined data sets for low and high temperature viscosities have been fit for each composition using the Tamann-Vogel-Fulcher (TVF) equation. The effect of alkaline-earth oxide on the viscosity of the present haplogranitic melt is extremely variable. The viscosity decreases with added alkaline-earth oxide cont ent in a nonlinear fashion. The first few mole % of alkaline-earth oxi de added decreases viscosity up to several orders of magnitude whereas subsequent addition of alkaline-earth oxide has a much smaller effect . The effects of each of the alkaline-earth oxides are quite distinct on a molar basis. The viscosity of the melts investigated here decreas es with the size of the added alkaline-earth cation in the order Ba < Sr < Ca < Mg < Be. This trend of viscosity versus cation size is the o pposite to that observed for the effects of alkali oxide additions on the melt viscosity. The alkaline-earth-bearing melts are significantly non-Arrhenian. The degree of ''fragility'' N or non-Arrhenian tempera ture-dependence of viscosity of these melts may be quantified using th e ratio of the c parameter in the TVF fit to the value of temperature at which the viscosity equals 10(12) Pa s, designated T-N. The paramet er N = c/T-N varies smoothly as a single function of the number of mol es of added cations for all melts of this study as well as all the alk ali-oxide-rich peralkaline melts.