The Stability of Metals in the Atmosphere: New Chemical Insights to Old Problems

Abstract

ABSTRACTThe stability of metals (or lack thereof) upon exposure to the indoor or outdoor atmosphere places strong constraints upon many of their uses, including uses in advanced technologies. Two recent developments permit increased understanding of the processes that occur: a detailed knowledge of the chemical constitution of indoor and outdoor atmospheres and of precipitation, and extensive analytical studies of the corrosion layers of degraded metals. Among the insights revealed from these perspectives are (1) the participation in materials degradation of the sulfuric and nitric acids in small aerosol particles and in precipitation; (2) the presence of organic acid anions within corrosion films, revealing interactions with atmospheric formic, acetic, and oxalic acids; (3) the participation of dissolved hydrogen peroxide in the passivation or dissolution of the surface layers of metals; and (4) the frequent occurrence of insoluble mixed salts of hydroxide and either sulfate, chloride, or carbonate anions in the corrosion layers of many metals, suggesting that the rates of formation and dissolution of such minerals may be limiting steps in many stabilization or degradation processes.