A percolating path to green iron

Subhechchha Paul^{1

2}, Brinthan Kanesalingam^{2

3}, Yan Ma^{4

5}, Julie Villanova⁶, Guillermo Requena^{7

8}, Stanley Chidubem Akpu⁹, Dierk Raabe⁵, Ilenia Battiato¹⁰, Leora Dresselhaus-Marais^{1

2

3}

Affiliations

¹ Department of Mechanical Engineering, Stanford University, Stanford, CA 94305, USA.
² SLAC National Accelerator Laboratory, Stanford, CA 94025, USA.
³ Department of Materials Science and Engineering, Stanford University, Stanford, CA 94305, USA.
⁴ Department of Materials Science and Engineering, Delft University of Technology, Delft 2628 CD, the Netherlands.
⁵ Max Planck Institute for Sustainable Materials, 40237 Düsseldorf, Germany.
⁶ European Synchrotron Radiation Facility (ESRF), 38043 Grenoble, France.
⁷ Institute for Frontier Materials on Earth and in Space, German Aerospace Center (DLR), 51147 Cologne, Germany.
⁸ Department of Metallic Structures and Materials Systems for Aerospace, RWTH Aachen University, 52062 Aachen, Germany.
⁹ Department of Chemical Engineering, Nnamdi Azikiwe University, Awka 420007, Nigeria.
¹⁰ Department of Energy Science and Engineering, Stanford University, Stanford, CA 94305, USA.

PMID: 40861821
PMCID: PMC12374072
DOI: 10.1016/j.xcrp.2025.102729

A percolating path to green iron

Subhechchha Paul et al. Cell Rep Phys Sci. 2025.

. 2025 Aug 20;6(8):102729.

doi: 10.1016/j.xcrp.2025.102729.

Authors

Affiliations

¹ Department of Mechanical Engineering, Stanford University, Stanford, CA 94305, USA.
² SLAC National Accelerator Laboratory, Stanford, CA 94025, USA.
³ Department of Materials Science and Engineering, Stanford University, Stanford, CA 94305, USA.
⁴ Department of Materials Science and Engineering, Delft University of Technology, Delft 2628 CD, the Netherlands.
⁵ Max Planck Institute for Sustainable Materials, 40237 Düsseldorf, Germany.
⁶ European Synchrotron Radiation Facility (ESRF), 38043 Grenoble, France.
⁷ Institute for Frontier Materials on Earth and in Space, German Aerospace Center (DLR), 51147 Cologne, Germany.
⁸ Department of Metallic Structures and Materials Systems for Aerospace, RWTH Aachen University, 52062 Aachen, Germany.
⁹ Department of Chemical Engineering, Nnamdi Azikiwe University, Awka 420007, Nigeria.
¹⁰ Department of Energy Science and Engineering, Stanford University, Stanford, CA 94305, USA.

PMID: 40861821
PMCID: PMC12374072
DOI: 10.1016/j.xcrp.2025.102729

Abstract

About 1.9 gigatons of steel is produced every year, emitting 8% (3.6 gigatons) of global CO₂ in the process. More than 50% of the CO₂ emissions come from a single step of steel production, known as ironmaking. Hydrogen-based direct reduction (HyDR) of iron oxide to iron has emerged as an emission-free ironmaking alternative. However, multiple physical and chemical phenomena ranging from nanometers to meters inside HyDR reactors alter the microstructure and pore networks in iron oxide pellets, in ways that resist gaseous transport of H₂/H₂O, slow reaction rates, and disrupt continuous reactor operation. Using synchrotron nano X-ray computed tomography and percolation theory, we quantify the evolution of pores in iron oxide pellets and demonstrate how nanoscale pore connectivity influences micro- and macroscale flow properties such as permeability, diffusivity, and tortuosity. Our modeling framework connects disparate scales and offers opportunities to accelerate HyDR.

Keywords: hydrogen; ironmaking; percolation; pores.

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