Atmospheric Corrosion of Aluminum in the Presence of Ammonium Sulfate Particles

Abstract

The effect of (NH4)2S04 particles on the atmospheric corrosion of aluminum has been investigated at 300 and 373 K at various relative humidity (RH) levels. Aluminum reacts with (NH4)2S04 particles only at or above the critical relative humidity (CRH) of (NH4)2S04 at either temperature. The corrosion rate increases with increasing RH and temperature. Above the CRH of (NH4)2S04, droplets are formed on the particles at both temperatures, making electrochemical reactions possible. The (NH4)2504 decomposes and ammonia evaporates from the droplets. At 373 K mixed ammonium-metal-sulfates are formed, followed by basic metal sulfates; oxide formation is enhanced at 373 K compared to 300 K. At 300 K no solid corrosion products containing Al are found, but it was shown that Al dissolves in the droplets. A corrosion mechanism has been proposed that explains the experimental observations, including pH and corrosion potential changes with time. InfroductionCompared to other metals, aluminum corrodes rather slowly under atmospheric conditions, because it forms an insulating, amorphous oxide film of low solubility in air and aqueous solutions over the pH range from 4 to 8.6. However, enhanced corrosion occurs in marine environments and in some urban areas.' Common corrosion prod ucts found under these conditions are basic aluminum sul-. fates and amorphous aluminum sulfate hydrate.1'2 Indoors, sulfate is the most abundant anion found on aluminum surfaces.3 The presence of SO42 on these surfaces may be due to SO2 induced corrosion or sulfates associated with particle deposition, The accumulation of inorganic ionic substances is primarily due to particle deposition.4Because of their high ionic content and high indoor coneentration, fine particles (<2 m) play a major role in the corrosion of electronic materials.45 Ammonium and sulfate ions are the most abundant ions in fine dust particles commonly found in urban environments, and may, therefore, play. a dominant role in the corrosion process. The effect of (NH4)2S04 on copper, another metal common1y used in the electronic industry, has been reported previously.6-9 * Electrochemical Society Active Member. * *Electrochemical Society Fellow.start to absorb water vapor from the atmosphere, cannot be simulated.Patterson and Wilkinson10 investigated the effect of NaC1 and NH4C1 particles on the corrosion of aluminum at 293 K and 80% relative humidity (RH). The weight increase due to NaC1 particles was linear with time and was small compared to the weight increase due to NH4C1 particles. With NH4C1, Al showed an initial phase of slow weight increase, and after 5 days, a sudden rapid weight gain. Also the appearance of the specimen changed after

Effect of varying conditions of exposure to an aggressive medium on the corrosion behavior of the 2050 Al–Cu–Li alloy

“…The rate of the OCP drop was calculated for four different tests; this rate decreased by a factor of ten between the two steps (5.6 Â 10 À3 mV/h for the first 24 h of immersion compared with 5.6 Â 10 À4 mV/h during the second step). The OCP drop at the beginning of the test could be linked to the dissolution of the protective oxide [27]. Importantly, Hagyard et al showed that the potential rose to a peak at the beginning of the immersion and that this increase was attributed to the dissolution of aluminum and to the formation of the protective oxide [28,29].…”

Use of thermally sprayed aluminium (TSA) coatings to protect offshore structures in submerged and splash zones

“…EDX analysis confirmed the presence of sulphur in felsobanyaite and sodium in dawsonite. Aluminium sulphate hydrates are common corrosion products on aluminium exposed to marine atmosphere [13] [14] [15]. Sulphates present in the solution are adsorbed on aluminium oxide layer [16] and converted into corrosion products.…”

Characterization of Patinas that Formed on Copper Exposed in Different Environments for One Month

“…When the cupric, sulfate, and hydroxyl ion concentrations are high enough to form posnjakite, this phase starts to precipitate on the cuprite surface. 8 As described above, there are two roles of oxidized sulfur species, including SO 2 and (NH 4 ) 2 SO 4 , in the early stage of copper patination. One is lowering the pH of the surface electrolyte, which accelerates the dissolution of the initially formed cuprite.…”

“…29) As shown in Fig 10(b), posnjakite formed on cuprite. A posnjakite formation mechanism was proposed by Lobnig et al 8) and Odnevall et al 18) Odnevall et al showed that posnjakite forms on cuprite and that the existence of intermediate non-crystalline compounds composed of copper and sulfate are present before posnjakite formation. 18) Fig.…”

“…Cuprite is also formed by the process represented by the following equation in the presence of Cu(NH 3 ) 2 ions. 8) 2Cu(NH 3 ) 2 H 2 O Cu 2 O 2H 4NH 3 (16) As shown in Table 1, the average relative humidity during exposure was beyond 65 . Therefore, an electrochemical reaction is more likely to occur rather than a chemical one.…”