Thermodynamic and transport properties of iron-bearing silicate melts.

The heat capacities of 29 glasses and supercooled liquids in the Na$\sb2$O-SiO$\sb2$, Na$\sb2$O-Al$\sb2$O$\sb3$-SiO$\sb2$, Na$\sb2$O-(FeO)-Fe$\sb2$O$\sb3$-SiO$\sb2$, and Na$\sb2$O-TiO$\sb2$-SiO$\sb2$ systems were measured in air from 328 to 998 K with a differential scanning calorimeter. Within the resolution of the data, the heat capacities of sodium silicate and sodium aluminosilicate liquids are temperature independent. The heat capacities of the Fe$\sb2$O$\sb3$- and TiO$\sb2$-bearing sodium silicate melts decrease with temperature. Using heat capacity data on glasses in the Na$\sb2$O-Al$\sb2$O$\sb3$-SiO$\sb2$ system and on two mixed alkali silicate glasses, the limiting fictive temperatures (T$\sb{\rm f}\sp\prime$) for these samples were determined. The T$\sb{\rm f}\sp\prime$ values for the eight silicate glasses were compared to the glass transition temperatures (T$\sb{\rm g}$) estimated from dilatometry curves and found to vary by 10$\sp\circ$ on average. Configurational C$\sb{\rm P}$ data and low and high temperature viscosity data were combined and fit to the configurational entropy equation for viscosity for the samples in the Na$\sb2$O-FeO-Fe$\sb2$O$\sb3$-SiO$\sb2$ system. A non-linear least squares regression was used to derive fitted values for A$\sb{\rm e}$, B$\sb{\rm e}$, and S$\sp{\rm conf}$(T$\sb{\rm g}$) for each melt composition. Values of S$\sp{\rm conf}$(T$\sb{\rm g}$) for nine samples range from 1.8 to 2.3 J/g$\sp{\cdot}$atom$\sp{\cdot}$K, whereas the configurational entropy of the sample liquid corresponding to a crystalline phase (acmite: NaFeSi$\sb2$O$\sb6$) is 1.2 J/g$\sp{\cdot}$atom$\sp{\cdot}$K. The rheologically-defined T$\sb{\rm g}$ (temperature at which the viscosity is 13 log$\sb{10}$ poise) is within 11$\sp\circ$ of the calorimetrically defined glass transition (the onset of the C$\sb{\rm P}$ peak) for all ten samples. A thermodynamic model was calibrated which describes ferric-ferrous equilibria in K$\sb2$O-FeO-Fe$\sb2$O$\sb3$-SiO$\sb2$ liquids as a function of temperature and composition at one bar. The compositions (wt %) of the sample liquids range from 34.7-85.3 SiO$\sb2$, 3.1-40.5 Fe$\sb2$O$\sb3$, 0-4.8 FeO, and 11.2-33.6 K$\sb2$O. Data on the 75 peralkaline liquids were used to derive a symmetric, regular solution model for ferric-ferrous equilibria in K$\sb2$O-FeO-Fe$\sb2$O$\sb3$-SiO$\sb2$ liquids. The model has a standard error of 0.18 wt % in the prediction of FeO. Two principal conclusions are drawn from the experimental results: (1) substituting K$\sp+$ for Na$\sp+$ or Ca$\sp{2+}$ causes an increase in the ferric-ferrous ratio in simple, four-component silicate liquids, and (2) increasing K$\sb2$O concentration in peralkaline K$\sb2$O-FeO-Fe$\sb2$O$\sb3$-SiO$\sb2$ liquids causes a decrease in their ferric-ferrous ratios.Ph.D.Earth SciencesGeologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/131103/2/9825351.pd