Microstructural development of SrAl12O19 in alumina–strontia composites

Boehmite sol was prepared by hot water hydrolysis of aluminium iso-propoxide using nitric acid as catalyst. Strontium nitrate was added to the boehmite sol to yield 0-20 vol.% strontia. The boehmite with additives was dried at 120 °C. The powder samples were calcined at 1600 °C for 3 h and the formation of strontium hexa-aluminate is discussed using phase diagram, transmission electron microscope and energy dispersive spectra. The powder samples calcined at 500 °C were milled for 6 h, compacted into cylindrical pellets using uni-axial press at 180 MPa and sintered at 1600 °C for 6 h. A microstructural model was proposed for the formation of strontium hexa-aluminate. The sintered pellets were ground and phases determined using XRD. The formation of hexa-aluminate (plate-like) grains was confirmed using optical microscope and scanning electron micronscope.