S. Bueno et al. /Journal of the European Ceramic Society 25(2005)847-850 Fig.2. Scanning electron micrographs of fracture surfaces of the monoliths (prepared with heating and cooling rates of 2Cmin-l, with 4-h dwell at 200C and 3-h dwell at the maximum temperature, 1550C). Alumina grains appear with dark grey colour, aluminium titanate of an intermediate grey shade and titania, which would appear white, is not observed. Tensile surfaces are located at the lower part of the micrographs (a)AlO(A-+T);(b) A30(A+T);(c)A40(A+T. had viscosities of 40-50 mPas at a shear rate of 500s-I containing 30 and 40 vol. of aluminium titanate(Fig 2b (Table 1). The optimised colloidal processing led to high and c), green density composites (62.5% of theoretical density, Characteristic nominal stress-apparent strain relations for the small (25 mm x 2 mm x 2.5 mm) monolithic In Fig. I, dynamic sintering curves for alumina and the samples are shown in Fig 3a and the thermal expanse shrinkage levels are coincident at 1240C(Fig. la)and the Table 2. The curves corresponding to the monolith with sintering rates are coincident at 1150 C(Fig. 1b). These the lowest aluminium titanate content, AlO(A+T),were three curves exhibit a change of slope at temperatures of practically linear up to fracture and this material pproximately I380°C sented the highest strength, Youngs modulus and ther In Fig. 2, characteristic fracture surfaces of the com- mal expansion values and the lowest strains to fracture posite monoliths sintered at 1550C are observed. Alu- Increasing proportions of aluminium titanate decrease minium titanate is homogeneously distributed and mainly strength, Youngs modulus and thermal expansion and located at alumina triple points and grain boundaries, and increase the non-linear behaviour, with high strains to no titania is detected, according to XRD. In the samples acture with 10 vol. of aluminium titanate( Fig. 2a)the grain size 1g. 4 shows characteristic fracture surfaces of the of alumina( 5 um)is much larger than in the samples three monoliths at low magnification. Those of AlO(A+T)850 S. Bueno et al. / Journal of the European Ceramic Society 25 (2005) 847–856 Fig. 2. Scanning electron micrographs of fracture surfaces of the monoliths (prepared with heating and cooling rates of 2 ◦C min−1, with 4-h dwell at 1200 ◦C and 3-h dwell at the maximum temperature, 1550 ◦C). Alumina grains appear with dark grey colour, aluminium titanate of an intermediate grey shade and titania, which would appear white, is not observed. Tensile surfaces are located at the lower part of the micrographs. (a) A10(A+T); (b) A30(A+T); (c) A40(A+T). had viscosities of ≈40–50 mPa s at a shear rate of 500 s−1 (Table 1). The optimised colloidal processing led to high green density composites (>62.5% of theoretical density, Table 1). In Fig. 1, dynamic sintering curves for alumina and the three studied composites are plotted. For the composites, the shrinkage levels are coincident at 1240 ◦C (Fig. 1a) and the sintering rates are coincident at 1150 ◦C (Fig. 1b). These three curves exhibit a change of slope at temperatures of approximately 1380 ◦C. In Fig. 2, characteristic fracture surfaces of the com￾posite monoliths sintered at 1550 ◦C are observed. Alu￾minium titanate is homogeneously distributed and mainly located at alumina triple points and grain boundaries, and no titania is detected, according to XRD. In the samples with 10 vol.% of aluminium titanate (Fig. 2a) the grain size of alumina (≈5
m) is much larger than in the samples containing 30 and 40 vol.% of aluminium titanate (Fig. 2b and c), Characteristic nominal stress–apparent strain relations for the small (25 mm × 2 mm × 2.5 mm) monolithic samples are shown in Fig. 3a and the thermal expansion coefficient and mechanical properties are summarised in Table 2. The curves corresponding to the monolith with the lowest aluminium titanate content, A10(A+T), were practically linear up to fracture and this material pre￾sented the highest strength, Young’s modulus and ther￾mal expansion values and the lowest strains to fracture. Increasing proportions of aluminium titanate decrease strength, Young’s modulus and thermal expansion and increase the non-linear behaviour, with high strains to fracture. Fig. 4 shows characteristic fracture surfaces of the three monoliths at low magnification. Those of A10(A+T)