ALUMINUM TITANATE CERAMIC WITH MULLITE ADDITION

The relation between the size of the thermal expansion hysteresis curves area and grain-boundary cracks presence of aluminum titanate ceramic with mullite addition were established. Ceramic samples from Al2TiO5 and mullite were obtained by a two-stage technology. To the sintered by solid state reaction at 1500 degrees C aluminum titanate 5; 7,5; 10; 12,5; 15; 20; 25 and 30 wt.% mullite were added and then the compositions were wet milled in a ball mill. The samples with sizes 20 x 10 x 105 mm(3) were cold isostatically pressed at 100 MPa and then fired at 1515 degrees C in a chamber gas furnace with holding time 2 h at maximum temperature. The physico-mechanical and thermal properties as mechanical bending strength, water absorption, apparent density, porosity, thermal expansion coefficient (TEC) and thermal hysteresis curves of the ceramic samples with pure Al2TiO5 and of the Al2TiO5 ceramic with mullite addition were measured. With the increasing of the mullite quantity, the density is not significantly changed and the water absorption slightly decreases. The mechanical strength increases from 30 for pure AT up to 38.5 MPa in the sample with 30 wt.% mullite. The thermal expansion coefficient increases from 0.74 x 10(-6)K(-1) for AT up to 2.45 x 10(-6)K(-1) for ATM30. Simultaneously, mullite addition decreased the hysteresis curves area and the micro-crackcing of the tialite ceramic. The calculated hysteresis areas with increase of mullite content decreases from 82.13 cm(2) for pure AT to 52.74 cm(2) for ATM30. It is proved that the mullite, acts as a barrier against microcracks growth, as is in higher quantity, because part of him is dissolved in the lattice of aluminum titanate and form solid solution with him. The presence of mullite as second phase to Al2TiO5 limited the grain growth of aluminum titanate and effectively prevented microcracking and increased the bending strength and thermal expansion coefficient.