Mechanical properties of textured ceramics from muscovite–kaolinite alternate layers

An organized network of mullite anisotropic crystals embedded in a silico-aluminate matrix material is obtained at interfaces of sintered alternate layers of muscovite and kaolinite minerals. The nucleation and growth of mullite anisotropic crystals occur preferentially along the muscovite basal planes through topotactic reaction with the high temperature form of muscovite.Simultaneously to structural transformations, dehydroxylation of muscovite induces an exfoliation process, which is temperature and time dependent. The kinetics of this process was controlled using an appropriate thermal cycle and uniaxial load. During sintering, the control of mullite size mainly depends in temperature and the addition of a small quantity of low-temperature liquid phase also favors the growth of mullite. But liquid induces the weakening of the organization degree of the mullite network. Quantitative texture analysis (QTA) and SEM were used to characterize microstructural characteristics.Flexural strength, Young modulus and fracture toughness are closely related to size and organization degree of the mullite network. In general, mullite length favors the increase of strength and fracture toughness. But a high organization degree of the mullite network favors the occurrence of interconnected crystals and increases mechanical properties.