Corrosion Behaviors Of Copper In The Atmospheres Polluted By Drywall And Elemental Sulphur

Because of Hurricane Katrina in the period of2004～2005, a large number of houses were terribly destroyed in numerous U.S. states. As a result of lacking building materials, lots of drywalls were imported from China to rebuild residential homestead. Within a few years, the Consumer Product Safety Commission (CPSC) received a lot of complaints from the locals, focused on some issues related to health and household metal-corrosion phenomena (especially copper). Primary investigations from U.S.A led to the conclusion that the Chinese drywalls could release sulfur-based corrosive gas, all the imported Chinese drywalls were called as "problem dry wall" correspondingly. Thus, lawsuit was caused between the U.S. consumers and Chinese drywall manufacturers.Up to now, it is lack of data on the corrosion of copper by drywalls before the occurrence of "problem drywall", and the mechanism of the corrosion of copper by elemental sulphur is not clear, either. In this thesis, with the aim to determine the corrosivity of drywalls and elemental sulphur, the effects of drywalls and elemental sulphur on the corrosion behavior of copper under various temperatures and humidity were studied. And what’s more, the corrosion mechanism of copper in the atmospheres polluted by drywalls and elemental sulphur was discussed. The following experiments were carried out:(1) The weight gain per unit area of copper samples due to the drywalls was obtained to determine the corrosivity of sixteen drywalls made in China and U.S.A. The corrosion tests for30to90days were performed under the conditons of constant temperature and humidity in sealed vessels. At the same time, the effect of sterilization treatment of drywalls at high temperature on their corrosivity to copper was compared.(2) In the same way as mentioned above, the effect of elemental sulphur on the corrosion behavior of copper was investigated. Elemental sulphur was obtained either by superficial application by organic agent containing sulphur or by sublimation with various sublimating areas.(3) The corrosion products were characterized and analysised by means of Scanning Electronic Microscope (SEM), Energy Dispersive Spectrometer (EDS), X-ray Diffraction (XRD) and X-ray Photoelectron Spectrometer (XPS).(4) According to the characterization of corrosion products and the analysis of corrosion kinetics, the corrosion mechanism of copper due to the drywalls and elemental sulphur was concluded.The following conclusions were drawn:Under the condition of constant temperature and humidity, the drywalls are corrosive to copper, but annual corrosion rate of copper due to the drywalls was much lower, so that the corrosivity of all the tested drywalls to copper was negligible. The annual corrosion rate of copper in the case of two Chinese drywalls was0.001-0.005mm/a, and for the rest of the drywalls, the annual corrosion rate of copper was less than0.001mm/a. Especially, no local corrosion, such as pitting corrosion was found, which was potentially dangerous to the saftety of metallic structure. Sterilization treatment of the drywalls at high temperature had no obvious effect on corrosion behavior of copper, which means that there were no microbes or bacteria significantly promoting the corrosion of copper in the initial drywalls. The main corrosion product was Cu2O, the corrosion product of Cu2S was detected in the case of three Chinese drywalls. The sublimation of elemental sulphur could promote corrosion of copper. It was revealed that corrosion rate of copper samples due to elemental sulphur increased as four times as that of those without sulphur. The reason is that elemental sulphur promotes the cathodic reaction process of total electrochemical process.