INFLUENCE OF MICROSTRUCTURAL PARAMETERS ON THERMAL-DIFFUSIVITY OF ALUMINUM NITRIDE-BASED CERAMICS

Thermal diffusivity of various AIN-based ceramics obtained by hotpressing or hot isostatic pressing has been measured at room temperature using the laser-flash technique. It is shown that diffusivity: (i) depends on nature and oxygen contents of the starting powders; (ii) decreases with porosity of the materials, especially near to theoretical density; (iii) is strongly influenced by the nature and amount of sintering aids (BeO, MgO, CaO, Y2O3...) used for densification, as a result of microstructural effects. For a given additive, the best performances are expected when using firing temperatures which allow the formation of a fairly viscous liquid phase and its subsequent location at triple points of the grain boundaries.