Effects of Exposure to Vapors of Saturated Salt Aqueous Solutions

Saturated salt aqueous solutions are used to produce controlled relative humidities in many laboratory tests. Components of the salt are shown to enter the gas phase and, in some instances, to alter surface film characteristics and chemisty. Coupons of Cu were exposed to the vapors of saturated salt aqueous solutions. NaNO3, (NH4)2SO4, and NaCI saturated solutions were kept at 85°C for three to six weeks with the coupons suspended above. After exposure, surface films were analyzed by Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). NaNO3 solution vapors yield Cu surface films enriched in N. Samples exposed to (NH4)2 SO4 and NaCl solution vapors have modified surface chemistry as seen by a surface film of CuO rather than the usual Cu2O.