Volume changes during solid state reactions: Stress accommodation mechanisms and their influence on product scale microstructure

Partial reduction of mixed oxides with diffusion-controlled formation of metal precipitates inside the oxide matrix is accompanied by important volume changes at the reaction front. Therefore, large stresses are expected to build up. At high temperatures these stresses are relaxed by plastic deformation of the matrix. In the present work, internal reduction of eloped magnesia and alumina is investigated. In the case of doped magnesia, formation and climb of free matrix dislocations allow the relaxation of the stresses generated by the reaction. For doped alumina, less stress is generated due to the contribution of different species to the diffusional transport and to Aux coupling under stress.