M. Schmaicker et al. Journal of the European Ceramic Society 20(2000)2491-2497 3. Results of the matrix. Moreover, small glassy pockets become visible between the mullite crystals. Microstructural Fig. I gives an overview of the as-prepared Nextel 720 details of heat-treated samples are given in Fig 3 and 4 lumino silicate fibre/porous mullite matrix composite. With increasing temperature, gradual coarsening of the Fig 2 shows the mullite matrix in higher magnification: fibre compounds, a-Al2O3 and mullite, occurs. Beside it clearly demonstrates a very high porosity(a50 vol % coarsening, dissapearance of a-Al2O3 in the fibre rim area can be observed in the 1600C sample. These a Al2O3-free zones are formed only when fibres and matrix are in direct contact (Fig. 4). For comparison Nextel 720 fibres alone were fired at 1600C(Fig. 5).N depletion of a-Al,O, occurs in the fibre rim area Fig. 6 provides information on the temperature- dependent development of the chemical composition of the matrix in its entirety and of the matrix mullite crys tals, respectively. The bulk composition was determined by EDX analyses of relatively large(5 um diameter or more) matrix agglomerates, each of them containing numerous mullite crystals and glassy areas. The mullite 的以好 25 龙 Fig. 4. Alumino silicate fibre/porous mullite matrix composite heat treated at 1600C( h). Note that the aAlO3 free fibre rims are formed only in areas of fibre/matrix contact. Fig 3. Microstructural changes of alumino silicate fibre/porous mul lite matrix composite caused by thermal treatment. (a) as-prepared 1500.C, 2 h;(c)1600 C,2 h. Note that with increasing temperature, Fig. 5. Nextel 720 fibres fired without matrix at 1600 C. Embedding gradual coarsening of the fibre compounds occurs. At 1600.C, a the fibres in epoxy allows the preparation of a polished cross-section depletion of a-Al2O3 in the fibre rim area is observed No a-Al2O3 free fibre rims occur in contrast to Fig 33. Results Fig. 1 gives an overview of the as-prepared Nextel 720 alumino silicate ®bre/porous mullite matrix composite. Fig. 2 shows the mullite matrix in higher magni®cation: it clearly demonstrates a very high porosity (50 vol.%) of the matrix. Moreover, small glassy pockets become visible between the mullite crystals. Microstructural details of heat-treated samples are given in Fig. 3 and 4. With increasing temperature, gradual coarsening of the ®bre compounds, a-Al2O3 and mullite, occurs. Beside coarsening, dissapearance of a-Al2O3 in the ®bre rim area can be observed in the 1600C sample. These a￾Al2O3-free zones are formed only when ®bres and matrix are in direct contact (Fig. 4). For comparison, Nextel 720 ®bres alone were ®red at 1600C (Fig. 5). No depletion of a-Al2O3 occurs in the ®bre rim area. Fig. 6 provides information on the temperature￾dependent development of the chemical composition of the matrix in its entirety and of the matrix mullite crys￾tals, respectively. The bulk composition was determined by EDX analyses of relatively large (5 mm diameter or more) matrix agglomerates, each of them containing numerous mullite crystals and glassy areas. The mullite Fig. 3. Microstructural changes of alumino silicate ®bre/porous mul￾lite matrix composite caused by thermal treatment. (a) as-prepared; (b) 1500C, 2 h; (c) 1600C, 2 h. Note that with increasing temperature, gradual coarsening of the ®bre compounds occurs. At 1600C, a depletion of a-Al2O3 in the ®bre rim area is observed. Fig. 4. Alumino silicate ®bre/porous mullite matrix composite heat￾treated at 1600C (2 h). Note that the a-Al2O3 free ®bre rims are formed only in areas of ®bre/matrix contact. Fig. 5. Nextel 720 ®bres ®red without matrix at 1600C. Embedding the ®bres in epoxy allows the preparation of a polished cross-section. No a-Al2O3 free ®bre rims occur in contrast to Fig. 3. M. SchmuÈcker et al. / Journal of the European Ceramic Society 20 (2000) 2491±2497 2493