The effect of mechanical activation on the properties of β-sialon precursors

Nanostructured β-sialon precursors were produced from the relevant mixtures of Si3N4, AlN and Al2O3 by mechanical milling in a new planetary mill with a centrifugal factor of 28 g, at milling times <60 min. Zirconia balls were used in order to avoid the effect of the susceptibility of the separate components to deform under mechanical activation. Several milling regimes were studied and only planetary milling with a high acceleration affected the particles structure. Under these conditions, AlN and Al2O3 crystallites were formed with new boundaries and dislocations, but the α-Si3N4 particles were more resistant to deformation. Milling at the higher acceleration conditions produces only a small increase in the crystal lattice parameters of the precursor components, but FTIR and 27Al and 29Si solid-state MAS NMR spectroscopy indicates the formation of new tetrahedral AlO4 units and Si–O–Al bonds, possibly in solid solution or partially reacted hybrid particles of Al2O3 and β-Si3N4. The total oxygen content in the activated sialon precursor mixture can be limited by replacement of alumina by AlN.