Neutron diffraction study of the reduction of NiAl₂O₄

The reduction of a solid NiAl₂O₄ cylinder to a metal-ceramic composite consisting of Ni particles in an Al₂O₃ matrix was monitored in situ at 1220°C with neutron powder diffraction. The reaction kinetics was determined with a time resolution of 30 min. The reduction is associated with a volume shrinkage. A comparison of finite element calculations and the changes in the measured lattice parameters suggests that creep has relaxed the residual strains that would otherwise result from the volume shrinkage. The data also indicate that structural evolution in unreduced NiAl₂O₄ via a change in the cationic sublattice towards inverse spinel occurred and that led to a variation in lattice parameters.