  To reduce the emission of greenhouse gases by the steel industry,
particularly for ironmaking, the production of DRI (Direct Reduced Iron) using
hydrogen as the reducing gas instead of carbon monoxide is being considered. In
this context, the reduction of pure hematite by hydrogen was studied at the
laboratory scale, varying the experimental conditions and observing the rate
and the course of the reaction. All the reduction experiments were performed in
a thermobalance and supplementary characterization methods were used like
scanning and transmission electron microscopy, X-ray diffraction, and
M\"ossbauer spectrometry. The influence of rising temperature in the range
550-900 degrees C is to accelerate the reaction; no slowing down was observed,
contrary to some literature conclusions. A series of experiments consisted in
interrupting the runs before complete conversion, thus enabling the
characterization of partially reduced samples. Interpretation confirms the
occurrence of three successive and rather separate reduction steps, through
magnetite and wustite to iron, and illustrates a clear structural evolution of
the samples. Finally, the influence of the sample type was revealed comparing a
regular powder, a nanopowder and a sintered sample. The regular powder proved
to be the most reactive despite its larger grain size, due to a more porous
final structure.
