Mullite/cordierite laminates with β→α cristobalite transformation weakened interphases

Laminates of β-cristobalite and mullite/cordierite mixtures in 60:40 wt% respectively were tape cast and hot pressed. The β-cristobalite form, chemically stabilized with Ca²⁺ and Al³⁺ stuffing cations, was prepared by the solution-polymerization route employing PVA solution as the polymeric carrier. The critical grain size of β-cristobalite for transformation and fracture behavior was investigated with laminates densified by hot-pressing at different thickness ratios between mullite/cordierite and β-cristobalite. The grain size was controlled by annealing at 1300 °C. A load-deflection curve for hot pressed samples annealed for 10 h showed a significant work of fracture (2.38 kJ/m²) with a strength of 131 MPa at the thickness ratio of cristobalite to the mullite/cordierite layer of 1:5. A low strength in spite of increasing work of fracture above a critical grain size of 4 μm was attributed to the crack deflection by microcracks in the transformation weakened cristobalite layer.