Iskanje po repozitoriju

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Povzetek: The responses of the current and the coupled potential to rapid depassivation have been studied on a three-electrode system under open-circuit conditions. Passivated AISI 304 stainless steel in low- and high-conductivity solutions of NaSO has been depassivated with a single, rapid scratch over the small fraction of surface of the working electrode (WE). Single- and dual-WE configurations have been implemented. Once the surface is scratched, the current and potential transients exhibit a delayed maximum and minimum, respectively, in contrast to the outcome of more common potentiostatic scratching experiments. A simple model based on the equivalent circuit has been developed to predict the observed transients and provides clear relations between the features of the transient and the parameters of the electrolyte and the electrodes. The interfacial capacitance of the electrodes’ passive surfaces proves crucial for the shapes of the observed potential and current transients. It is shown that this capacitance temporarily provides the majority of the charge for repassivation under open-circuit conditions. Possible sources of specific discrepancies between the model and the measured transients are indicated.
Ključne besede: repassivation, open circuit conditions, transient, modelling, interfacial capacitance
Objavljeno v DiRROS: 21.06.2023; Ogledov: 324; Prenosov: 150
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Povzetek: When bronze or artificially patinated bronze is exposed to an outdoor environment that contains aggressive ions such as sulphates, nitrates, and carbonates, the surface of the bronze changes its appearance due to the formation of corrosion products on the surface. Research is being conducted on versatile protective measures that can be used to protect the surface from these changes. A recently synthesised fluoropolymer-based coating with mercaptopropyl groups, i.e. a 3-component fluoropolymer coating FA-MS-SH (silane-modified poly methylmethacrylate (MS) with added mercaptopropyltrimethoxy silane (SH) and a fluoroacrylate (FA)) was explored in detail in this work where its protective mechanism on sulphide patinated bronze was investigated. Electrochemical tests were conducted on the sulphide patinated bronze with and without the 3-component coating FA-MS-SH. Furthermore, FA, MS and SH alone and various combinations and concentrations of FA-MS were studied in order to determine the protective effect and properties of each component. Colour change and contact angle measurements were also defined. FIB-SEM measurements and GCIB-XPS depth profiles were carried out to study surface bonding with the sulphide patina in detail. A mechanism for the protection of sulphide patinated bronze was presented through the use of a multianalytical tool approach. It was shown that FA physisorbed on the patinated surface, while MS and blends of the components chemisorbed on the layer of sulphide patinated bronze, also resulting in the surface being efficiently protected from corrosion processes.
Ključne besede: bronze, protection, brown patina, fluoropolymer coating
Objavljeno v DiRROS: 31.05.2023; Ogledov: 333; Prenosov: 195
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Povzetek: The high temperature corrosion at 650°C in the presence of NaCl at atmospheric pressure of AISI 304L, AISI 309, AISI 310S, AISI 314 and AISI 321 austenitic stainless steel was studied. The specimens were cyclically heated in the furnace and immersed in a 3.5% aqueous NaCl solution after cooling for 15 min. After each cycle, the change in mass of the samples was measured. The corroded samples were analysed by SEM /EDX, and the corrosion products were analysed by XRD. The chloride ions react with the steel surface to form porous and poorly adherent oxides and metal chlorides. After the mass increase during the first exposure cycles, spalling of the oxides occurred. The high temperature austenitic stainless steels (AISI 309, AISI 310S, AISI 314) showed less mass loss than conventional austenitic steels (AISI 304L). Surprisingly, the stainless steel AISI 321 showed a similar low weight loss after the cyclic test as AISI 309, but a detailed analysis of the exposed surfaces after the test showed a similar corrosion attack as for AISI 304. After the cyclic test at high temperature in the presence of NaCl, a higher concentration of Cr and Ni definitely improves the corrosion resistance under the present conditions, but a certain addition of Si is even more obvious.
Ključne besede: austenitic stainless steel, high temperature corrosion, NaCl, exhaust systems, open access
Objavljeno v DiRROS: 31.05.2023; Ogledov: 273; Prenosov: 175
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Povzetek: Various coatings have been developed and explored to protect bronze surfaces against the uncontrolled formation of different corrosion products when exposed to outdoor environments. In this research, the surfaces of artificially-formed oxidized bronze patinas (OB), consisting of Cu2O, were covered with either a single-component (fluoroacrylate, FA or methacryloxypropyl-trimethoxysilane, MS) or multi-component (a mixture of FA and MS, FA-MS) fluoropolymer coating and investigated. Variations in the concentration of each component in the coating were studied. Electrochemical tests were performed to determine the corrosion protection efficiency, followed by detailed surface analyses of the OBs, both uncoated and covered with single and multi-component coatings. A variety of investigative methods were used, including focused ion beam scanning electron microscopy (FIB-SEM), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The coating made from a combination of FA and MS resulted in a very high protection efficiency. Despite the increased hydrophilicity of the single MS component, however, it was shown to efficiently protect the oxidized bronze surface. The FA-MS systems showed high hydrophobicity, but no improvement was measured in the efficiency of the corrosion protection when it was compared to the coating that contained 10% MS. According to XPS and ToF-SIMS imaging, the FA component of the FA-MS coating was not present only on the uppermost surface of the coating but throughout the whole coating, which could affect its corrosion protection efficiency.
Ključne besede: bronze, Cu2O layer on bronze, fluoropolymer coating, protection efficiency, surface spectroscopy
Objavljeno v DiRROS: 30.05.2023; Ogledov: 335; Prenosov: 180
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Povzetek: The aim of this study was to compare corrosion resistance and ion release in CoCr dental alloys with identical chemical compositions produced using different technologies (SLM – selective laser melting and milling from cast blocks) and heat treatment (SLM parts only). The corrosion properties were tested in artificial saliva, artificial saliva with fluoride ions, and artificial saliva with added lactic acid to simulate inflammations. The study included electrochemical tests, microstructural investigation and ion release tests in the three different environments for a total of 42 days. The best performance of CoCr as a result of potentiodynamic polarization was observed in the artificial saliva with added lactic acid, which is in contradiction with the highest ion release measured from all the materials tested and electrochemical impedance spectroscopy that showed a deterioration of the passive layer in an acidic environment. Microstructural investigation revealed that different phases precipitated by heat treatment trigger increased release of Mo and W ions. The printing method does not raise critically ion release from CoCr alloy, while the state of the surface greatly impacts the extent of the ion release. This study demonstrates the importance of an interdisciplinary approach to the study of corrosion and biocompatibility in dental alloys.
Ključne besede: CoCr dental alloy, selective laser melting, corrosion, ion release, artificial saliva
Objavljeno v DiRROS: 29.05.2023; Ogledov: 339; Prenosov: 287
Celotno besedilo (9,28 MB)
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