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 degrees 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. (C) 2000 American Institute of Physics. [S0003-6951(00)02806-0].