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Fabrication Of Wire Beam Electrode And Solid Ph Electrode And The Detection Inlocalized Corrosion Of316Stainless Steel

Posted on:2014-01-29Degree:MasterType:Thesis
Country:ChinaCandidate:L L GaoFull Text:PDF
GTID:2251330401485350Subject:Applied Chemistry
Abstract/Summary:PDF Full Text Request
Metal materials suffer localized corrosion such as pitting or crevice corrosioneasily and cause accidents. Although the localized corrosion of metals had beenstudied extensively, it remains lack of direct and in situ detection techniques ofcorrosion sensitive segments. The distributions of potential and H+concentration insensitive area are the main crucial factors in occurrence and development oflocalized corrosion, which offer benefits for corrosion mechanism study.Generally the traditional electrochemical techniques can only get the totalinformation, although micro electrode technique can get the localized informationof metals, it can not get the localized information at the same time, which are alsounable to detect localized corrosion. In this work, we developed an array referenceelectrode of Ag/AgCl and Ir/IrOx pH electrode to in situ detect the localizedcorrosion of the weld and try to develop a new in situ online detection technique.The main results are as follows:1. A wire beam electrode of Ag/AgCl was developed and experiments werecarried out to characterize its property. The results indicate that the electrode waseasily made and the AgCl particle distributed evenly; Ag/AgCl reference electrodenot only had stable voltage remained between41and43mV(vs.SCE), but also hadgood parallelism; CV and potential response curve showed that the reversible abilityand Nernst response of this electrode was good, which met the needs of electrode.2. Ir/IrOx pH electrodes were prepared with a method of oxidization incarbonate melt at high temperature. Experiments were carried out to characterizetheir working performance. The results indicate that the best prepared condition is 850℃,5h. Ir/IrOx electrode made under this condition had stable voltage with anaging process, it showed good linear response to pH in buffer solution with a slope59mV/pH, which is close to Nernst slope. The intercept of E pH curve increased asfunction of time and remained580mV after15days eventually. In addition, it had agood reproducibility. Scanning electric micro scope (SEM) showed temperature hasa significant effect on the iridium oxide film thickness and density, the higher thetemperature is, the thicker and denser the iridium oxide film is. It was found thatNa2IrO3may be the main cause that led to the failure of the electrode by X raydiffraction. Ir/IrOx electrode can be applied to pH measurement and it basicallymeets the measurement requirements compared to glass electrode.3. The Ag/AgCl wire beam electrode was used to in situ determine the potentialdistribution of the welded316stainless steel in0.1mol/L NaCl solution to forecastits localized corrosion. It is shown that the local corrosion potential distribution onthe sample surface was obvious and the potential map could point out the possiblelocal corrosion sites. As function of time, the potential at welded area moved to thenegative direction and the localized corrosion was accelerated. It is proved that themanufactured Ag/AgCl wire beam electrode is promising to detect the locations ofcorrosion for weld corrosion evaluation.4. We used Electrochemical Noise technique combined with immersion methodto monitor and evaluate pitting corrosion process of316L stainless steel. TheInstability and Pitting parameters firstly increase then decrease, which prove thatcorrosion rate also increase then decrease and the passivation film is correspondinglyin the state from stable to damage to apparently localized corrosion. The corrosionresistance Rpdeclines while corrosion rate increases all the time and the trend is inaccordance with pitting depth. In a word Electrochemical Noise technique could getthe real time parameters of Instability and Pitting, the average corrosion rate toindicate the occurrence and development of localized corrosion and it is moreconvenient than the traditional immersion method and suitable for field monitoring.
Keywords/Search Tags:wire beam electrode, Ag/AgCl, Ir/IrOx pH electrode, localizedcorrosion, detect
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