M. Schmaicker et al. Journal of the European Ceramic Society 20(2000)2491-2497 76 74 Matrix mullite crystal composition 8芝E°d式 Matrix bulk composition 67 1200 1300 1400 1600 1700 Annealing temperature [ oc] Fig. 6. Matrix bulk composition (i.e. mullite plus vitreous phase) and matrix mullite composition of alumino silicate fibre/porous mullite matrix composite plotted as a function of temperature Rhombs: matrix composition as determined by SEM-EDX Squares: mullite composition on basis of lattice constant data. Open circles: mullite composition analyzed by TEM-EDX. crystal composition was determined via mullite lattice 1600oC, however, causes a drastic change of the matrix constants by X-ray methods using fibre-free reference composition mullite crystals and matrix display vir matrix material and was checked in composite samples tually the same composition with about 72 wt. Al2O by EDX analyses in combination with transmission Fig. 7 shows the fibre/matrix interface area of a sam- electron microscopy. The matrix mullite crystals of the ple heat-treated at 1300@C for 1000 h. A reaction zone, as-prepared material are relatively alumina-rich (74.5 free in a-Al2O3, becomes visible in this material though wt% Al2O3) with respect to stoichiometric mullite(72 the zone's extension is smaller than oberved in the sam- wt% Al2O3). Treatment at higher temperatures leads to ple heat-treated at 1600C, 2 h. Load/deflection curves a gradual development towards the Al2O3/SiO2 ratio of of the porous mullite composites heat-treated at various stoichiometric mullite. On the other hand, the matrix temperatures are plotted in Fig 8. Bending tests signal bulk composition of samples fired below 1500C, is non-brittle(damage-tolerant) fracture behavior of the relatively poor in Al_O3(ca 68 wt. Al2O3). Firing at composites up to 1500C though the maximum strength values slightly decrease with increasing temperature Firing at 1600 C, on the other hand, leads to brittle A 200 MPa Fig. 7. Fibre /matrix interface area of alumino silicate fibre/porous Fig 8. Load/ deflection curves of alumino silicate fibre/porous mullite mullite matrix composite heat-treated at 1300oC for 1000 h. Note the matrix composites fired at various temperatures(2 h)(A) as-prepared ormation of an a-Al,O3 free fibre rim (B)1400°C;(C)1500°C;(D1600°C.crystal composition was determined via mullite lattice constants by X-ray methods using ®bre-free reference matrix material and was checked in composite samples by EDX analyses in combination with transmission electron microscopy. The matrix mullite crystals of the as-prepared material are relatively alumina-rich (74.5 wt.% Al2O3) with respect to stoichiometric mullite (72 wt.% Al2O3). Treatment at higher temperatures leads to a gradual development towards the Al2O3/SiO2 ratio of stoichiometric mullite. On the other hand, the matrix bulk composition of samples ®red below 1500C, is relatively poor in Al2O3 (ca. 68 wt.% Al2O3). Firing at 1600C, however, causes a drastic change of the matrix composition: mullite crystals and matrix display vir￾tually the same composition with about 72 wt.% Al2O3. Fig. 7 shows the ®bre/matrix interface area of a sam￾ple heat-treated at 1300C for 1000 h. A reaction zone, free in a-Al2O3, becomes visible in this material though the zone's extension is smaller than oberved in the sam￾ple heat-treated at 1600C, 2 h. Load/de¯ection curves of the porous mullite composites heat-treated at various temperatures are plotted in Fig. 8. Bending tests signal non-brittle (damage-tolerant) fracture behavior of the composites up to 1500C though the maximum strength values slightly decrease with increasing temperature. Firing at 1600C, on the other hand, leads to brittle Fig. 6. Matrix bulk composition (i.e. mullite plus vitreous phase) and matrix mullite composition of alumino silicate ®bre/porous mullite matrix composite plotted as a function of temperature. Rhombs: matrix composition as determined by SEM-EDX. Squares: mullite composition on basis of lattice constant data. Open circles: mullite composition analyzed by TEM-EDX. Fig. 7. Fibre/matrix interface area of alumino silicate ®bre/porous mullite matrix composite heat-treated at 1300C for 1000 h. Note the formation of an a-Al2O3 free ®bre rim. Fig. 8. Load/de¯ection curves of alumino silicate ®bre/porous mullite matrix composites ®red at various temperatures (2 h) (A) as-prepared; (B) 1400C; (C) 1500C; (D) 1600C. 2494 M. SchmuÈcker et al. / Journal of the European Ceramic Society 20 (2000) 2491±2497