N P Bansal /Journal of the European Ceramic Sociery 29(2009)525-535 wt%Al203 Tridymite A2O3:15% 1400° Mullite /8 BS- B2s YY￥ Wt Al2O3 Fig 13. Phase diagram of Bao-Al2O3-SiO2 system showing the presence of low-melting ternary eutectics. The silica formed reacts with celsian resulting in the formation SEM micrograph of Fig. 6. On cooling, celsian crystals pre- of a low-melting phase. The phase diagram of Ba0-Al2O3-SiOz cipitate from the melt leaving behind a glassy matrix which ternary system is given in Fig. 13. It does show the pres- is richer in SiO2 and poorer in BaO and Al2O3 than celsian ence of a ternary phase with a melting point of 1122 C. This SEM micrograph(Fig. 14) taken from the surface of 1200C phase is richer in SiOz but poorer in BaO and Al2O3 than cel- annealed CMC shows the presence of elongated crystals in some sian. Formation of gaseous by-products CO and CO2 during glassy matrix. From qualitative EDS analysis, these crystals are reaction(4)results in the evolution of bubbles as observed in seen to be celsian and the glassy matrix is found to be richer SEM Picture a EDS Area 2 EDS Area 1 g surface of Hi-Nicalon/ BN/SiC/BSAS composite annealed at 1200 C for 100 h in air. Also shown are the EDS analyses of two areas. labeled as 2. of the CMC surfaceN.P. Bansal / Journal of the European Ceramic Society 29 (2009) 525–535 533 Fig. 13. Phase diagram of BaO–Al2O3–SiO2 system showing the presence of low-melting ternary eutectics. The silica formed reacts with celsian resulting in the formation of a low-melting phase. The phase diagram of BaO–Al2O3–SiO2 ternary system30 is given in Fig. 13. It does show the pres￾ence of a ternary phase with a melting point of 1122 ◦C. This phase is richer in SiO2 but poorer in BaO and Al2O3 than cel￾sian. Formation of gaseous by-products CO and CO2 during reaction (4) results in the evolution of bubbles as observed in SEM micrograph of Fig. 6. On cooling, celsian crystals pre￾cipitate from the melt leaving behind a glassy matrix which is richer in SiO2 and poorer in BaO and Al2O3 than celsian. SEM micrograph (Fig. 14) taken from the surface of 1200 ◦C annealed CMC shows the presence of elongated crystals in some glassy matrix. From qualitative EDS analysis, these crystals are seen to be celsian and the glassy matrix is found to be richer Fig. 14. SEM micrograph showing surface of Hi-Nicalon/BN/SiC/BSAS composite annealed at 1200 ◦C for 100 h in air. Also shown are the EDS analyses of two different areas, labeled as 1 and 2, of the CMC surface