Novel Glass Formation in the Ca-Si-Al-O-N-F System

摘要

Ca-Si-Al-O-N-F glass formation regions have been mapped on 6Ca~(2+)-3Si~(4+)-4Al~(3+) 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℃ compared with the Ca-Si-Al-O-N system at 1700℃. Ca-Si-Al-O-N-F melting temperatures are 150°-800℃ 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 SiF_4.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_3N_4 at 1300℃. For Ca-Si-Al-O-N-F compositions, reactions occur at lower temperatures with Si_3N_4 dissolution at 1200℃. 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).