Study On Corrosion Behavior Of The Typical Metals In Rain/Acid Rain

The atmospheric corrosion behavior for metals could be influenced apparently by acid rain and rain precipitation. It had been proved that the acid rain can accelerate atmospheric corrosion rate of metals, however, the mechanism that effects of acid rain or rain on atmospheric corrosion process of metals was not still clear. In this dissertation, the study was focused on the corrosion behavior of the typical metals: A3 steel, LY12 aluminum alloy, Cu, Zn under simulated acid rain or rain environment, which was studied with different experiment method according the prosperities of the metals. The goal of this dissertation was to supply fundamental experiment data for clearing mechanism that the effects of acid rain or rain on the atmospheric corrosion of these metals.1. A global system to simulate rain precipitation was set up, which could control the rain intensity, rain droplet size and relative humidity, temperature, pollutant gas level of simulated rain precipitation room etc. 2. With the system to simulate rain precipitation, combined ACM (Atmosphere Corrosion Monitor), AAS( Atom Adsorption Spectrum) and SEM, the corrosion and runoff behavior for A3 steel were studied under the environment to simulate rain precipitation. The results proved that rain precipitation could corrode and erode A3 steel, the action of corrosion and erosion were intensified with pH of rainwater and rain intensity increasing. The contrast of galvanic current determined by ACM to corrosion rate of A3 steel showed that it was practicable to monitor corrosion of rain with ACM. 3. In the simulated rainwater, the corrosion rate of LY12aluminum alloy increased with pH of water decreasing. In the rainwater of pH lower than 3.4, the corrosion of LY12 aluminum alloy was controlled by the dissolution of oxide film. With dissolution of oxide film and the thickness of film decreasing, the transmit resistance for ions and electrons across the film decreased, the corrosion rate of LY12aluminum increased with pH of rainwater decreasing and immersion time increasing. The dissolution of oxide film intensified pit corrosion of aluminum alloy, and made more Cu, Fe alloy elements precipitated on surface, which accelerated enlargement of pit. In the rainwater of pH3.8, the corrosion of LY12 aluminum alloy was mainly influenced by the corrosion product formed on the surface of aluminum alloy, the corrosion was inhibited by the sulfate of aluminum formed on the surface. With immersion time increasing, the thickness of oxide film was almost constant, however, the transmit resistance increased, thus the corrosion rate decreased. The chloride and sulfate ions dissolved in rainwater accelerated pit corrosion apparently, but nitrate ions inhibited corrosion of LY12 alloy. 4. With EIS, polarization curve, SKP(San Kelvin Probe), XPS, FITR, the effects of corrosion product on the corrosion kinetic of Cu in simulated rainwater was studied. In the rainwater, the corrosion products formed on the surface of Cu were mainly Cu2O, which will transform to Cu (Ⅱ) compounds with time slowly. The local deposit of corrosion product made the difference of corrosion potential for the surface of copper, therefore galvanic corrosion occurred between the area with corrosion product and without corrosion product. The difference of potential on the surface made the transmit resistance decrease with time, which showed deposition of corrosion product facilitated electrochemical corrosion process of Cu and promoted dissolution of Cu。 The area with corrosion product or more quantity and more dense had noble potential so which play a cathode role, the area without corrosion product had lower potential and play an anode role. 5. With an electrochemical occluded cell which can control thickness of liquid film, the corrosion behavior of Zn in bulk solution and under liquid film formed by simulated rainwater was investigated. In the solutions with pH 2.4~3.8, the corrosion of Zn was controlled by transmission process of electron, corrosion rate and potential of Zn increased with...