Controllable reduction mechanism of rust via thermal-field-modulated plasma strategy

Abstract

Rust removal via glow-discharge plasma has attracted considerable attention owing to its dry environment with little contaminant, environmental-friendliness and treatment rapidity. The plasma-rust interaction process has been studied over the years, but a crucial influencing factor, the surface temperature of the iron substrate, remains inadequately controlled during plasma processing, leading to suboptimal rust removal performance and an ambiguous mechanism. Here, we innovatively modulate the rust-reducing performance on iron (Fe) surface via controlling surface thermal field during plasma processing along with the elucidation of rust reduction mechanism. Coupled with operando plasma diagnostics along with numerical simulation, it is confirmed that plasma processing with the cooling component introduction causes the insufficient surface thermal field on Fe substrate and hence results in partial Fe₂O₃ reduction towards porous Fe₃O₄ with little metallic phase formation. Comparatively, excessive thermal field results in exorbitant surface kinetic and thereby resulting in compact layer formation with inner FeO on Fe surface. Such phenomenon is ascribed to the initially achieved H₂O vapor constraint within oxide to achieve FeO. We found that appropriate thermal field, where the Fe surface temperature is neither too high or too low, can remove rust effectively owing to synergistic effect of thermal field and porous structure formation. Our work is to provide a novel plasma-based pathway to effectively modulate surface oxide reduction.