Abstract
Hydrogen-based direct reduction (H₂-DR) of iron ore pellets is a promising route toward low-emission ironmaking. The reduction performance of H₂-DR pellets is strongly influenced by the evolution of their internal pore and crack networks, which control gas transport, access to reaction sites, and mechanical integrity during reduction. X-ray computed tomography (XCT) offers three-dimensional characterization of these networks, yet its quantitative limits across relevant microstructural length scales remain insufficiently defined. In this work, we evaluate the ability of XCT to quantify porosity and cracking in industrial hematite pellets reduced in pure H2 at 800 and 1000 °C, representing two distinct reduced microstructures. Whole-pellet XCT was combined with deep-learning-based segmentation to quantify porosity, crack fraction, and pore size distributions. In addition, a high-resolution XCT scan was performed on the 800 °C pellet to assess the resolution limits of pellet-scale imaging. Overall, this study delineates the range of pore/crack sizes and fractions that can be quantified with confidence by typical laboratory XCT configurations in hydrogen-reduced iron ore pellets. It also clarifies the conditions under which whole-pellet XCT alone is sufficient and when complementary high-resolution XCT or SEM is required.