High-temperature corrosion behavior and mechanism of AISI 304 stainless steel exposed to KAl(OH) ₂ CO ₃ powder

This study investigates the high-temperature corrosion behavior of AISI 304 stainless steel (0Cr18Ni9) exposed to a novel hydrophobic and oleophobic KAl(OH) 2 CO 3 ultrafine dry powder fire-extinguishing agent, aiming to assess its corrosion characteristics and application safety in extreme high-temperature environments such as aircraft and ship engine compartments. Cyclic corrosion experiments were performed at 850°C for five cycles. SEM, XRD, and XPS were used to analyze surface morphology, phase composition, and elemental valence. Under pure oxidation, a composite Cr 2 O 3 and Mn-enriched (Mn,Fe)Cr 2 O 4 spinel film formed, with initial rapid growth followed by diffusion-controlled kinetics. In contrast, alkaline molten salts from KAl(OH) 2 CO 3 accelerated corrosion, disrupting the protective oxide layer and producing Fe 2 O 3 , Fe 3 O 4 , and FeCr 2 O 4 . Continued cycling partially converted Cr 3+ to Cr 6+ (e.g., K 2 CrO 4 ), and the film evolved from dense to porous. The overall corrosion process included an initial rapid corrosion stage and a subsequent corrosion deceleration stage, marked by protective film failure and multilayered corrosion products. These results clarify the relationship between the chemical properties of the powder and high-temperature material degradation, providing guidance for material protection strategies and the safe application of KAl(OH) 2 CO 3 -based fire-extinguishing agents in extreme environments.