DIPHASIC MULLITE GEL PRESSED AT 1.5 GPA - MECHANICAL PROPERTIES AND MICROSTRUCTURE OF CERAMICS

摘要

Mullite gels containing 72-85 wt% Al2O3 were prepared by mixing commercial boehmite a nd silica sols and gelled by heating. Powdered gels were either dried at 60 degrees C or calcined at 550 degrees C, and cold isostatically pressed under 0.5, 1.0 or 1.5 GPa. The effect of pressure is greater for the calcined gels than for the dried gels. The bulk density and room-temperature flexural strength of ceramics increased with increasing compacting pressure, while the fracture toughness is independent of the pressure. Mullite containing 75 wt% Al2O3 and sintered at 1500 degrees C for 3 h has a density which is about 99% of the theoretical density, a flexural strength of 523 +/- 40 MPa and a fracture toughness of 3.5 MPa m(1/2). [References: 24]