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

Abstract

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+VO∙∙. In the sample air-quenched from 1200 °C, the supersaturated oxide ion vacancies, VO⋅⋅, 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 °C and 1400 °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 °C/min from 1300 °C and 1400 °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.