Alumina precipitate along dislocations in rutile single crystal of diffusion couple during cooling from 1200 to 1400C

Diffusion couples of rutile and corundum single crystals were prepared and examined for the solid solution and precipitation of corundum in rutile during cooling. Alumina dissolves in rutile according to the following equation, Al2O3 -> 2AlTi '+3OO+V-o(center dot center dot). In the sample air-quenched from 1200 degrees C, the supersaturated oxide ion vacancies, V-o(center dot center dot), reacted with the edge component of screw dislocation parallel to c axis to form helical dislocations, along which corundum was precipitated. When air-quenched from 1300 degrees C and 1400 degrees C, corundum was precipitated in the form of stacked rectangular loops. Corundum grains with eight lobes extending in the < 101 > directions were precipitated in the samples cooled at 10 degrees C/min from 1300 degrees C and 1400 degrees C. The solid solution reaction increased the volume of rutile single crystals and caused voids outside the reaction region at the interface. Both the corundum and rutile components of the voids also contributed to the solid solution reaction.