Phase-field modeling of porosity formation and evolution during hydrogen-based iron oxide reduction
4 affiliations
- 1Circular Metallurgy and Alloy Design, Max Planck Institute for Sustainable Materials GmbH, Max-Planck-Straße 1,, Düsseldorf, Germany, 40237
- 2School of Advanced Engineering
- 3Great Bay University
- 4Material Mechanics, RWTH Aachen University, Schinkelstr. 2, Aachen, Germany, 52062
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.
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BibTeX
@misc{umate2026phasefield,
title = {{Phase-field modeling of porosity formation and evolution during hydrogen-based iron oxide reduction}},
author = {Kartik Sunil Umate and Yang Bai and Bob Svendsen and Dierk Raabe},
howpublished = {ChemRxiv},
year = {2026},
month = sep,
doi = {10.26434/chemrxiv.15009406/v1},
url = {https://chemrxiv.org/doi/full/10.26434/chemrxiv.15009406/v1},
note = {CC BY},
}
RIS
TY - UNPB
TI - Phase-field modeling of porosity formation and evolution during hydrogen-based iron oxide reduction
AU - Kartik Sunil Umate
AU - Yang Bai
AU - Bob Svendsen
AU - Dierk Raabe
PY - 2026
DA - 2026/09/24
PB - ChemRxiv
DO - 10.26434/chemrxiv.15009406/v1
UR - https://chemrxiv.org/doi/full/10.26434/chemrxiv.15009406/v1
AB - 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.
ER -