ArXiv preprint maps 10,000 K thermal gradient in hydrogen plasma iron reduction, showing neutral atomic H as primary reductant

The study employed transferred-arc HPSR with simultaneous OES tracking Ar I, Ar II, hydrogen Balmer lines, and Fe I emissions as natural spatial filters, paired with infrared melt thermography and an LTE model benchmarked on free-burning argon arcs. This approach captured the non-uniform plasma-melt interface that uniform-heat-source models overlook. Sample size was a laboratory-scale reactor; measurements spanned multiple arc currents and hydrogen fractions.

Findings show positive hydrogen ions recombine before surface contact, delivering reductant flux primarily as atomic H and vibrationally excited H2(v) across a steep temperature drop to the 1,900-2,300 K melt. Electron density and excitation temperature measurements bound interfacial ionization below levels assumed in many kinetic models. This directly informs boundary conditions for plasma-based reduction simulations.

Hydrogen plasma smelting targets the 7-9% of global CO2 emissions from steelmaking, where mainstream coverage focuses on green hydrogen DRI but rarely resolves plasma chemistry. The diagnostics reveal why ion-driven mechanisms are overstated, aligning with earlier HPSR work at RWTH Aachen showing neutral species control kinetics yet lacking spatial resolution. The preprint flags itself as pre-peer-review.

Next steps include scaling the multi-species framework to pilot reactors and coupling results with CFD-kinetic models to test whether neutral-H dominance persists at higher throughputs, a threshold that would accelerate industrial adoption if reduction rates exceed 20% over current assumptions.