SEM (Scanning Electron Microscope) micrographs showing the morphological changes at the granular scale in CVRD-DR pellets; (a) to (d): grains in different stages of a reduction at 800 °C; (d) to (g): iron grains after reduction at different temperatures; (h): polished cross-section at a conversion degree of 65% of a sample reduced at 900 °C, the red arrow points to shrinking wüstite cores (dark gray) surrounded with a spreading layer of iron (light gray), indicated by the blue arrow. All images by SE (secondary electrons), except (h) BSE (backscattered electrons). Reducing gas used: 2 L/min H₂–He (60–40 vol.%) in a thermobalance.