SiO -formation and -condensation with hydrogen in carbon free conditions

Abstract There is a growing need to replace carbon with hydrogen in silicon production to eliminate CO₂ emissions. Understanding how H₂ influences both the forward Si + SiO₂ → 2SiO reaction and the back reaction is therefore essential. In this work, the reaction was studied in a carbon‑free atmosphere using 0.25 L/min H₂ for varying reaction times, with Ar used as a reference under identical conditions. Reaction products were analysed using SEM, EPMA, and LECO. While the gas atmosphere did not significantly change the overall Si/SiO₂ product composition, it affected the morphology and distribution of condensed material. Kinetic evaluation using the 1‑D diffusion‑controlled (D1) model showed that the reaction proceeds faster in H₂, with a diffusion rate constant of k = 0.010 min⁻¹, compared to k = 0.006 min⁻¹ in Ar. This demonstrates that hydrogen enhances diffusion through the interfacial SiOₓ layer and accelerates SiO formation. H₂ also produced finer, well‑dispersed condensates with reduced wall fouling, whereas Ar led to coarser deposits and greater wall accumulation. These differences are attributed to the higher diffusivity of hydrogen, which accelerates SiO formation and modifies the condensation behaviour.