Nitride capacities of CaO-Al2O3-CaF2 melts at 1 773 K

Abstract

The nitrogen solubility of CaO-Al2O3-CaF2 was studied at 1 773 K. It was found that nitride capacity increased with increasing CaO content for a given CaF2/Al2O3 ratio, decreased with increasing Al2O3 content for a given CaO/CaF2 ratio, and increases with increasing CaF2 content when the CaO/Al2O3 molar ratio was less than about 2, but became unaffected by CaF2 content when the ratio exceeded about 2. These observations were interpreted that CaO depolymerized the Al2O3 network, allowing for nitrogen to exist as both free and non-bridging nitrides, and that CaF, assisted in depolymerization and hence increased nitrogen solubility, provided that there was a sufficient amount of network to be depolymerized. A diagram of iso-nitride capacity was drawn for the CaO-Al2O3-CaF2 ternary system at 1 773 K, and the nitride capacity was related to the optical basicity of the melt to obtain the following correlation equation: