High temperature heat content and heat capacity of silicate glasses; experimental determination and a model for calculation

The high temperature heat contents, HT -H 298 , ~f two FeO-rich synthetic silicate glasses and five glasses and three supercooled I iquids prepared from igneous rocks ranging from basalt to rhyolite have been measured by drop calorimetry. Data for the two synthetic glasses are combined with published heat content determinations on simple si I icate glasses to yield the partial molar heat contents and heat capacities of of necessity that there is Si0 2 , AJ 2 o 3 , FeO, MgO, CaO, Na 2 o and K 2 0 in si I icate glass, assuming/no compositional dependence over the range in question. The partial molar heat content of Si0 2 is essentially equal to that of pure Si0 2 glass. Experimental heat contents of the five natural compositions are reproduced by calculation from the partial molar heat contents. Experimental glass transition temperatures for the glasses studied range from 700 to 1080K and bear no simple relation to liquidus temperature, calculated liquid thermal expansion or activation energy for viscous flow. The heat capacity of silicate glass generally approximates 3R cal the glass transformation temperature.