An alternative experimental technique for the investigation of the reduction of dense synthetic NiO in H-2-N-2 and H-2-H2O gas mixtures at high temperature has been developed. This technique enables the nickel product pore structures to be accurately characterized and the intrinsic reaction rates to be measured. A number of distinctly different nickel product microstructures, originating at the Ni-NiO interface were observed. The formation of these microstructures was found to be a function of temperature, gas composition and reaction time. (c) 2007 Elsevier Ltd. All rights reserved.