S. Bueno et al. /Journal of the European Ceramic Society 25 (2005)847-850 a t [min Fig. 5. Square wall thickness, F, vs. casting time for alumina and alumina-titania aqueous suspensions Al2O3 and TiO to form Al2TiOs and sufficient grain growth as to originate microcracking and, consequently non-linear stress-strain behaviour in the compositions with high Al2TiOs contents were also to be achieved. To satisfy these two latter requirements rather high final sintering temperatures(1450C), whereas are needed, in order to allow co-sintering of the different compositions in the laminates, similar shrinkage levels as well as shrinkage rates through the temperature range are preferred In Fig. l, the change of slope in the dynamic sinter ing curves for the composites at approximately 1380C is in agreement with the reported temperature for the expan sive reaction between AlO3 and TiO2 to form aluminium titanate> From these curves, a two-step sintering treatment, with a rather low heating rate 2C min-, was designed.An initial dwell of 4 h at 1200C was chosen for homogeneous shrinkage before reaction, this temperature being a com- mise between those for coincident levels of shrinkage 40C, and of shrinkage rate, 1150C. In this temperat ange, the alumina compacts have similar levels of shrinkage and shrinkage rate as those of the composite with the low est titania contents. a 3-h dwell at 1550oC was selected for final reaction and grain growth, as this was the temperature at which shrinkage was arrested in the three composites Using this sintering schedule, dense (Table 1)and re- acted. at least at the Xrd level. materials were obtained The second phase, Al2TiO5, was homogeneously distributed as small particles located mostly at triple points of the alumina matrix(Fig. 2) As shown in Fig. 2. extreme differences are found be- tween grain sizes of alumina in the AlO(A+T) composite urfaces of monolith x 2 mm x 2.5 mm). The tensile and in those containing larger quantities of aluminium ti- surfaces of the micrographs (a)AIO(A+T anate, which are much smaller. This is due to the inhibiting b)A30+1);(c)A40(A+T effect of the second phase in matrix grain growth, and indi- cate that most alumina grain growth occurs after the for tion of aluminium titanate Compositional differences originate highly different thermal expansion values and deformation and fracture852 S. Bueno et al. / Journal of the European Ceramic Society 25 (2005) 847–856 Fig. 4. Low magnification scanning electron micrographs of fracture surfaces of monolith samples (25 mm × 2 mm × 2.5 mm). The tensile surfaces are located at the lower part of the micrographs. (a) A10(A+T); (b) A30(A+T); (c) A40(A+T). Fig. 5. Square wall thickness, l 2, vs. casting time for alumina and alumina–titania aqueous suspensions. Al2O3 and TiO2 to form Al2TiO5 and sufficient grain growth as to originate microcracking and, consequently, non-linear stress–strain behaviour in the compositions with high Al2TiO5 contents were also to be achieved. To satisfy these two latter requirements rather high final sintering temperatures (>1450 ◦C)11,12 whereas are needed, in order to allow co-sintering of the different compositions in the laminates, similar shrinkage levels as well as shrinkage rates through the temperature range are preferred. In Fig. 1, the change of slope in the dynamic sinter￾ing curves for the composites at approximately 1380 ◦C is in agreement with the reported temperature for the expan￾sive reaction between Al2O3 and TiO2 to form aluminium titanate.15 From these curves, a two-step sintering treatment, with a rather low heating rate 2 ◦C min−1, was designed. An initial dwell of 4 h at 1200 ◦C was chosen for homogeneous shrinkage before reaction, this temperature being a com￾promise between those for coincident levels of shrinkage, 1240 ◦C, and of shrinkage rate, 1150 ◦C. In this temperature range, the alumina compacts have similar levels of shrinkage and shrinkage rate as those of the composite with the low￾est titania contents. A 3-h dwell at 1550 ◦C was selected for final reaction and grain growth, as this was the temperature at which shrinkage was arrested in the three composites. Using this sintering schedule, dense (Table 1) and re￾acted, at least at the XRD level, materials were obtained. The second phase, Al2TiO5, was homogeneously distributed as small particles located mostly at triple points of the alumina matrix (Fig. 2). As shown in Fig. 2, extreme differences are found be￾tween grain sizes of alumina in the A10(A+T) composite and in those containing larger quantities of aluminium ti￾tanate, which are much smaller. This is due to the inhibiting effect of the second phase in matrix grain growth, and indi￾cate that most alumina grain growth occurs after the forma￾tion of aluminium titanate. Compositional differences originate highly different thermal expansion values and deformation and fracture