Carbon Deposition Behavior Catalyzed by Porous Iron Whiskers in a CO-CO₂-H₂ Atmosphere

Abstract

This study investigates carbon deposition behavior of porous iron whiskers in a CO–CO₂–H₂ gas atmosphere, aiming to enhance carbon recycling strategies for the Carbon Recycling Ironmaking Process using Deposited carbon iron ore composite (CRIP-D), a fossil-free alternative to traditional blast furnace ironmaking. The porous iron whisker, characterized by high porosity (~95%) and obtained from carbon-iron oxide composites, serves as a carbon deposition catalyst. Experiments revealed a two-stage carbon deposition process: the initial stage involves the formation of cementite (Fe₃C), while the later stage involves the metastable iron carbide Fe₅C₂, whose decomposition yields nano-sized iron particles that catalyze the growth of carbon filaments.

The analyses of carbonization degree trends, sample morphology, and SEM/XRD indicate that Fe₅C₂ plays a crucial role in facilitating the second-stage carbon filament formation. In-situ high-temperature XRD experiment confirmed this transformation and correlated the decline in Fe₅C₂ peak intensity with carbon filament growth. The sulfur content in porous iron, higher than that in electrolytic iron, stabilized iron carbide formation and suppressed premature free carbon deposition.

These findings highlight the significance of controlling carbide phase evolution for efficient carbon deposition. Understanding this relationship supports the development of effective carbon recycling within the CRIP-D framework, reducing CO₂ emissions while enabling the use of non-fossil carbon sources in large-scale ironmaking.