Reseach On Two New Types Of Ganlvanic Effects

Ganlvanic effect is a common phenomenon which will exist when two different metals contact together in solution:when two different metals contact with each other in the solution, the electron will transport from the metal with low potential to the metal with high potential. In the meanwhile, the oxidation reaction will take place on the surface of the anodic metal with low potential and the reduction reaction will take place on the surface of the cathodic metal with high potential. Focused on the corrosion field, on one hand, the galvanic effect can cause important influence to the corrosion of the metal; on the other hand, it can be also applied to provide corrosion protection to the metal. Therefore, in this work, which is supported by the national science foundation of China and US Environmental Agency, the galvanic effect between the lead pipe and copper pipe in US drinking water distribution system and the galvanic anodic protection of the stainless steel by conductive polymer were systematically studied respectively.In the research on the galvanic effect between the lead pipe and copper pipe in US drinking water distribution system, the experiment plan was well deisned. The galvanic corrosion of the lead pipe and the deposition corrosion caused by the Cu2+in the drinking water were studied by directly measuring the lead concentration in the water combined with the electrochemical measurement. The main work and results are as follows:(1) When the new lead pipe was galvanically connected with copper pipe, the lead amount in the drinking water increased which was resulted from the galvanic corrosion of the lead pipe; when the old pipe was galvanically connected with copper pipe, at the start of the connection, the lead amount in the drinking water decreased becaue the connection made the lead oxidate film on the lead pipe more stable. However, as the connection continued, the galvanic corrosion of the lead pipe became the main resource of the lead in the drinking water and caused the in creased of the lead amount in the drinking water.(2) The CSMR of the drinking water is an important factor which can influence the galvanic corrosion of the lead pipe:the higher the CSMR is, the higher the corrosion rate of the lead pipe is. The disinfectant choice can also influence the galvanic corrosion of the lead pipe. When NH4Cl is chosen as the disinfectant, the corrosion rate of the lead pipe is faster. However, compared with CSMR, the influence of the disinfectan is not so obvious.(3) The "partial replacement" of the lead pipe in the US drinking water system can not solve the "lead crisis" caused by the disinfectant swith from free chlorine to chloramine. Furthermore, it will make the problem even worse because of the galvanic corrosion of the lead pipe.(4) In the stagnant condition, the Cu2+ in the drinking water caused deposition corrosion to the lead pipe. The deposition corrosion resulted in the increase of the lead concentration in the drinking water in a certain period. In the flowing condition, the Cu2+ in the drinking water caused deposition corrosion to the lead pipe and resulted in the increase of the lead concentration in the drinking water. Furthermore, in the flowing condition, the rate of the deposition corrosion was faster.(5) In the stagnant condition, the drinking water with a low Cu2+concentration still caused deposition corrosion to the lead pipe and resulted in the increase of the lead concentration in the drinking water. This point is very important to the actual deposition corrosion control in the drinking distribution pipe systemIn the research on the galvanic anodic protection of the stainless steel by conductive polymer, based on our formal research, the separate PPy powder-pressed electrodes have been prepared and the electrochemical properties of the PPy electrode were studied. The galvanic anodic protection of the stainless steel was studied by the means of galvanically coupling the PPy electrode and stainless steel. The galvanic anodic protection provided by PPy and PANi were compared. The results are as follows: (1) The influences of many factors on PPy’s electro-synthesis were studied, such as the kind and concentration of oxidant in the synthesis solution, the mol ratio of oxidant to aniline monomer, reaction temperature and reaction time. The best synthesized conditions were as follows:the FeCl3 was adopted as the oxidant, the solution is 0.5M pyrrole and 2M HClO4, the mol ratio of FeCl3 to pyrrole is 1:1, the reaction temperature is 0～4℃, and the reaction time is 3h.(2) PPy powder-pressed electrode can provide efficient galvanic anodic protection to 410 stainless steel under different conditions. The protection is influenced by many factors such as the area ratio of PPy to 410 stainless steel, the concentration of the acid and the solution acidity. The larger the area ratio of PPy to 410 stainless steel is, the more stable the passivity of the stainless steel is. More PPy will be needed when the acid concentration is higher and the solution aicidity is higher.(3) Besides 410 stainless steel, PPy powder-pressed electrode can also provide galvanic anodic protection to other ferrous metals, such as 304 stainless steel,316 stainless steel,321 stainless steel, carbon steel and so on.(4) For the galvanic anodic protection of stainless steel, PPy is better than PANi. It is more efficient and can protect the stainless steel for a longer time and in a stronger acid solution. However, for the pitting corrosion protection of stainless steel, PANi is better than PPy.