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

Abstract

Nanostructured β-sialon precursors were produced from the relevant mixtures of Si 3N 4, AlN and Al 2O 3 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 Al 2O 3 crystallites were formed with new boundaries and dislocations, but the α-Si 3N 4 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 AlO 4 units and Si–O–Al bonds, possibly in solid solution or partially reacted hybrid particles of Al 2O 3 and β-Si 3N 4. The total oxygen content in the activated sialon precursor mixture can be limited by replacement of alumina by AlN.