The nitrogen solubility and nitride capacity of the BaO-B2O3 and CaO-B2O3 systems were measured at 1698 and 1773 K, respectively, using a gas-liquid equilibration technique. These systems were chosen because they have wide liquidus regions at the temperature of interest and were expected to show two types of nitride solution behavior. The nitride capacities of both systems showed minimum values with changing composition. This was explained by considering that nitrogen can dissolve into slag as "free nitride" at high basicities and as "nitride incorporated" with the network for acidic slags. The change of the nitride capacity with optical basicity and the activity of the basic component followed the predicted behavior for the proposed solution mechanism. The nitride capacity of the BaO-B2O3 system is considerably greater than for the CaO-B2O3 system because BaO is a more basic oxide than CaO. The activity of BaO in the BaO-B2O3 system was also measured by equilibration with liquid silver, at known oxygen potentials, and the activities show large negative deviations from ideal behavior.
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