Phase-field modeling of porosity formation and evolution during hydrogen-based iron oxide reduction
Year: 2026
Type: preprint
Abstract: Hydrogen-based direct reduction of iron oxides (HyDRI) offers a low-emission route to solid-state ironmaking by replacing carbon-based reductants with hydrogen. The mass loss associated with oxygen removal generates porosity. The evolving pore network influences reduction kinetics through changes in transport pathways and internal reaction surfaces. Here, we develop a phase-field framework that couples solid-state oxygen transport, the wüstite–ferrite transformation, and pore evolution during the rate-controlling step of HyDRI. Pore generation follows the local transformation rate at the advancing reaction front, whereas surface diffusion redistributes existing porosity. The newly formed solid–pore interfaces provide additional oxygen-removal sites, coupling pore evolution back to front propagation. The simulations show that increasing reduction-generated porosity drives a transition from isolated pores to connected channels, raising the fraction of pore space connected to the external surface from approximately 7% to 97%. Additional internal reaction surfaces shorten the time to 90% reduction by approximately 15%, demonstrating how pore formation accelerates further reduction. Faster front propagation preserves fine, tortuous pores, whereas faster surface diffusion promotes smoothing and coarsening. The resulting structures differ by more than a factor of two in the solid–pore interfacial length available for oxygen removal, even at the same reduction-generated porosity. Pore connectivity and the internal surface available for reaction therefore depend on reduction history and cannot be inferred from porosity alone. These findings provide a physical basis for linking local pore evolution to gas access and overall reduction kinetics at larger scales.
Source: ChemRxiv
Language: English
Subfield: Metals and Alloys
Field: Materials Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7214188734