Chemical compatibility of fuming nitric acid, fuming sulfuric acid, and their mixtures with metals

Abstract Fuming nitric acid and fuming sulfuric acid, as critical industrial chemicals, can exhibit high reactivity with metals, posing significant thermal safety risks. This study systematically evaluated the thermal stability of fuming nitric acid, fuming sulfuric acid, and their mixed acid, alongside their chemical compatibility with common structural metals. Utilizing differential scanning calorimetry with custom glass crucibles effectively prevented side reactions with the container, allowing for precise characterization of thermal behavior. Findings revealed that while none of the three acids exhibited exothermic decomposition, their thermal stability varied. Metal compatibility results were distinct: gold was inert across all systems; titanium demonstrated good compatibility only with fuming nitric acid, reacting exothermically with the others; both aluminum and copper triggered vigorous exothermic reactions in all acids, indicating a high thermal runaway risk—the copper/mixed acid system further displayed autocatalytic behavior; the stainless steels showed complex, composition‐dependent reactivity.