Neutron diffraction study of the reduction of NiAl2O4

The reduction of a solid NiAl2O4 cylinder to a metal-ceramic composite cons isting of Ni particles in an Al2O3 matrix was monitored in situ at 1220 deg rees C with neutron powder diffraction. The reaction kinetics was determine d with a time resolution of 30 min. The reduction is associated with a volu me shrinkage. A comparison of finite element calculations and the changes i n the measured lattice parameters suggests that creep has relaxed the resid ual 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].