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No description available.

No description available.

This thesis mainly concerns the application of electrochemical impedance spectroscopy (EIS) and electrochemical noise analysis (ENA) to the study of CO(subscript)2 corrosion of mild steel and its inhibition. The primary focus is on the use of EIS and ENA to monitor inhibitor film performance and to evaluate inhibitor film persistency.EIS was shown to be a suitable technique to study CO(subscript)2 corrosion product scale, and inhibitor films. The formation and deterioration of protective scales and inhibitor films is found to be accompanied by characteristic spectral changes and a rapid change in electrode impedance. EIS data were used to calculate corrosion related parameters such as the resistances and capacitances of inhibitor layers, and the charge transfer resistance and double layer capacitance. These parameters were used to analyse inhibitor mechanisms, determine corrosion rates and the persistence of inhibitor films.ENA is also a suitable technique to monitor the formation and deterioration of inhibitor films. It has the advantage of being able to monitor rapid processes which occur within one second. Several technical and theoretical developments were made in this thesis including the development of a new method of instantaneous corrosion rate measurement to study fast corrosion processes (the continuous noise resistance calculation method). Experimentally, the noise resistance was confirmed to be similar to linear polarisation resistance in the systems studies. The theoretical background and the advantages and disadvantages of the ENA technique are also discussed.Corrosion product scales formed under different conditions were investigated using EIS and surface analysis techniques. Temperature, pressure and exposure time were confirmed to be the important factors influencing the degree of protection given by the scale. The morphology of corrosion scales ++ / showed an obvious correlation to their protective ability. Electron microscopy revealed two types of crystal structures on corroded steel coupons. The smaller crystals associated with one of these structures was found to contribute most to corrosion protection.Several typical CO(subscript)2 corrosion inhibitors, including an imidazoline and a quaternised amine, were studied by EIS. A multi-layer model was employed to explain the EIS characteristics and self-repairing ability of imidazoline films. A quaternised amine film is most probably a physically or electrostatically adsorbed molecular layer which forms rapidly and desorbs easily.The deterioration of films, formed by commercial batch treatment inhibitors, was found to occur in three stages which were indicated or characterised by Bode phase-angle plots. A method to determine inhibitor film persistency was developed. This method is based on determining the three stages of inhibitor film deterioration, and the continuous measurement of corrosion rate, which is accessible at the second and third stages of film deterioration.

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This work, within EPSRC LATEST2 (Light Alloys Towards Environmentally Sustainable Transport 2) Programme Grant, is focused on the development of environmentally-friendly corrosion inhibitors, nanocontainers loaded with inhibitors and epoxy coatings for corrosion protection of the aerospace alloy AA 2024-T3. More specifically, the electrochemical techniques of image assisted electrochemical noise, electrochemical impedance spectroscopy, split-cell technique and potentiodynamic polarization were used for the qualitative and quantitative evaluation and characterization of environmentally-friendly corrosion inhibitors on AA 2024-T3. Scanning electron microscopy observations complemented the electrochemical measurements. It was found that the organic inhibitor 2-mercaptobenzothiazole provides excellent corrosion inhibition properties to AA 2024-T3 in 3.5% sodium chloride solution. Among the tested nitrates, cerium nitrate provides the best inhibition performance. The concentration of the nitrate salt is critical in determining the corrosion protection. An excessive concentration of nitrate ions results in the dissolution of copper-containing oxides, increasing the corrosion rate. Different types of core-shell structured nanocontainers were synthesised with the methods of distillation precipitation polymerization, emulsion polymerization and sol-gel. The nanocontainers were characterized by scanning electron and transmission electron microscopy observations. The corrosion inhibitor 2-mercaptobenzothiazole was encapsulated into the nanocontainers. The encapsulation of 2-mercaptobenzothiazole was evaluated with energy dispersive X-ray analysis mapping micrographs from transmission electron microscopy measurements. Epoxy coatings with nanocontainers loaded with 2-mercaptobenzothiazole were applied on AA 2024-T3 for protection against corrosion. The corrosion protection properties of the coatings were evaluated with electrochemical impedance spectroscopy. The results indicated that epoxy coatings provide excellent barrier properties to AA 2024-T3 in the demanding environment of 3.5% sodium chloride solution with low frequency impedance values more than 1 GOhm cm2 for over 4000 hours of testing. Coatings containing nanocontainers loaded with 2-mercaptobenzothiazole tested with an artificial scribe revealed protection of the AA 2024-T3 substrate in the scribed area, decrease of the anodic delamination in the early hours and decrease number of cathodic dark areas after long immersion time. Overall, epoxy coatings with encapsulated inhibitors can be considered as a promising system for potential replacement of hexavalent chromium treatments on aerospace alloy AA 2024-T3.

Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / O cromato à amplamente utilizado como inibidor de corrosÃo. No entanto, à altamente tÃxico e carcinogÃnico, o que tem levado pesquisadores a buscarem alternativas ecologicamente amigÃveis a este inibidor. Dentre estes, molibdato, tungstato, silicato e fosfato surgem como potenciais candidatos por apresentarem propriedades inibidoras e serem atÃxicos. Assim, este trabalho tem por objetivo desenvolver um estudo sistemÃtico dos Ãons como inibidores da corrosÃo do Zn. Foram utilizadas soluÃÃes aquosas de NaCl 10-1 mol dm-3 com concentraÃÃes dos inibidores variando de 10-4 a 10-1 mol dm-3 . A eficiÃncia destes com relaÃÃo à corrosÃo do Zn foi avaliada empregando-se medidas do potencial a circuito aberto, curvas de polarizaÃÃo potenciodinÃmica e espectroscopia de impedÃncia eletroquÃmica. As tÃcnicas de Microscopia EletrÃnica de Varredura (MEV), Energia Dispersiva de Raios-X (EDX), DifraÃÃo de Raios-X (DRX) e Espectroscopia FotoeletrÃnica de Raios-X (XPS) foram usadas para caracterizar o Zn apÃs os ensaios de corrosÃo. Todos os Ãnions estudados inibiram a corrosÃo do Zn. Com as tÃcnicas de caracterizaÃÃo foi possÃvel identificar a presenÃa de filmes superficiais de silicato, tungstato, molibdato e fosfato na superfÃcie do Zn apÃs os ensaios de corrosÃo nas respectivas soluÃÃes contendo os inibidores / The chromate is widely used as a corrosion inhibitor. However, it is highly toxic and carcinogenic, which has done researchers to study environmentally friendly alternatives to this inhibitor. Among these, molybdate, tungstate, silicate and phosphate anions appear as potential candidates because they are non toxic. Thus, this work aims to develop a systematic study to investigate molybdate, tungstate, silicate and phosphate as corrosion inhibitors of zinc. Aqueous solutions of 10-1 mol dm-3 NaCl were used and the concentrations of the inhibitors ranging from 10-4 to 10-1 mol dm-3. The corrosion studies were carried out by open circuit potential measurements, potentiodynamic linear polarization and electrochemical impedance spectroscopy. The Scanning Electron Microscopy (SEM), X-Ray Dispersive Energy (XDE), X-Ray diffraction (XRD) and X-Ray Photoelectronic Spectroscopy (XPS) techniques were used to characterize the Zn after the corrosion tests. All the studied anions inhibited the zinc corrosion. The characterization techniques made possible to detect the presence of molybdate, silicate, tungstate and phosphate on the zn surface after the corrosion tests in the solution containing the corresponding inhibitors

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Skystosios trąšos yra laikomos, gaminamos ir transportuojamos plieninėse talpose, kurios visiškai surūdytų, jei nebūtų pridedama korozijos inhibitorių. Korozijos inhibitoriai yra sudaryti iš cheminių junginių, kurie apsaugo plieno paviršių formuodami apsauginį sluoksnį. Šis sluoksnis apsaugo plieno paviršių nuo reakcijos su skystųjų trąšų komponentėmis ir taip galima sutaupyti milijonines lėšas, nesant būtinybės keisti ar taisyti plienines talpas. Lietuvoje AB „Achema“ per metus pagamina apie 1 milijoną tonų skystųjų trąšų. Dažniausiai korozijos inhibitorius sudaro riebiosios rūgštys, aminai, paviršiaus aktyvios medžiagos, glikoliai ir kt. Korozijos inhibitoriai plačiai analizuojami dujų ir skysčių chromatografijos - masių spektrometrijos metodais. Šiame darbe bus pristatyti dujų chromatografijos - masių spektrometrijos, efektyviosios skysčių chromatografijos - elektropurkštuvinės jonizacijos - skrydžio laiko masių spektrometrijos ir matrica skatinamos lazeriu sužadinamos - skrydžio laiko masių spektrometrijos metodai komercinių korozijos inhibitorių sudėties nustatymui ir indentifikavimui. Šio darbo tikslas buvo optimizuoti chromatografijos ir masių spektrometrijos metodikas skirtas korozijos inhibitorių analizei ir nustatyti komercinių korozijos inhibitorių kiekybinę ir kokybinę sudėtį. Darbo rezultatai. Ištirti trys skirtingų gamintojų komerciniai korozijos inhibitoriai: Cordon 99, Galoryl Ic 22, Ixonol-5. Dujų chromatografijos - masių spektrometrijos metodu nustatyta... [toliau žr. visą tekstą] / Liquid fertilizers are stored, manufactured, and transported in metallic tanks which can completely corrode if corrosion inhibitor will not be added. Corrosion inhibitors are chemical compounds which protect metallic surface by forming a protection layer. This layer protects metallic surface from reaction with liquid fertilizers compounds and can save millions of dollars, since there are no need to replace or repair the tanks. In Lithuania Achema corporation is producing about 1 million tons of liquid fertilizers in the year. Usual ingredients of corrosion inhibitors are fatty acids, amines, surfactants, glycols etc. Corrosion inhibitors are widely analyzed by gas and liquid chromatographic mass spectrometry methods. In this work will be presented gas chromatography- mass spectrometry, high performance liquid chromatography - electrospray ionization – time-of-flight - mass spectrometry and matrix assisted laser desorption ionization time-of-flight mass spectrometry, methods for commercial corrosion inhibitors determination and identification. The aim of this work is optimize chromatographic and mass spectrometry methods for corrosion inhibitors analysis and determinate quantitative and qualitative composition of commercial corrosion inhibitors. Results. Analyses of corrosion inhibitors: Cordon 99, Galoryl Ic 22, Ixonol-5 from three different manufacturers were performed. The main compound determined in all the corrosion inhibitors samples by gas chromatography mass... [to full text]