Novel glass formation in the Ca-Si-Al-O-N-F system

Ca-Si-Al-O-N-F glass formation regions have been mapped on 6Ca ²⁺-3Si⁴⁺-4Al³⁺ ternary diagrams at fixed O:N:F of 79:20:1 and 75:20:5 (in eq%). For both fluorine contents, glass formation regions extend toward more Ca-rich compositions at 1650°C compared with the Ca-Si-Al-O-N system at 1700°C. Ca-Si-Al-O-N-F melting temperatures are 150°-800°C lower than equivalent Ca-Si-Al-O compositions due to fluorine incorporation into the melt. Si-rich compositions, with both 1 and 5 eq% F, form porous glasses due to loss of SiF₄. Reaction mechanisms were studied by firing two compositions (0 or 5 eq% F) with identical cation ratios in the range of 900°-1650°C at 100°C intervals and following phase development using X-ray diffraction. For Ca-Si-Al-O-N compositions, initial liquid formation occurs at >1200°C with complete dissolution of Si ₃N₄ at 1300°C. For Ca-Si-Al-O-N-F compositions, reactions occur at lower temperatures with Si₃N₄ dissolution at 1200°C. At 20 eq% N, glasses with maximum fluorine content of ∼7 eq% were obtained. At 5 eq% F, the solubility limit for N is ∼25 eq%. At 1 eq% F, the maximum nitrogen content can be substantially increased to 40 eq% N. Incorporation of both nitrogen and fluorine in Ca-Si-Al-O glasses extends glass formation regions through combinations of lower melting temperatures (fluorine) and higher viscosities (nitrogen).