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Povzetek: Blended cements might change the chemistry of the pore solution and subsequently affect the corrosion of steel in concrete. Pore solutions were extracted, analyzed and compared from mortars made of CEM I, CEM II, CEM III and CEM IV cements. Three combinations of carbonation and chloride states were studied, i.e., non-carbonated without chlorides, non-carbonated with chlorides and carbonated with chlorides. Different electrochemical and spectroscopic techniques were used to study the electrochemical properties, the type and the extent of the corrosion products, as well as the type and the extent of the corrosion damage. It was confirmed that the most corrosive environments were pore solutions extracted from the carbonated mortars with chlorides. In this environment the highest corrosion rate was observed for the CEM III pore solution, and the lowest for the CEM I. The extent and the type of corrosion products and the corrosion damage varied according to the environment.
Ključne besede: corrosion, blended cements, pore solution, mortar
Objavljeno v DiRROS: 14.09.2023; Ogledov: 294; Prenosov: 111
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Povzetek: The surface, corrosion and wear properties of new and in vivo exposed nickel titanium (NiTi) and stainless steel (SS) archwires used in orthodontic treatment were investigated. Electrochemical and tribo-electrochemical tests in artificial saliva were performed in order to define corrosion properties and to estimate wear rate of new and in vivo exposed NiTi and SS archwires. The surface chemical analysis of the passive film on the NiTi and SS archwires before and after tribocorrosion tests was performed by Auger Electron Spectroscopy (AES). In vivo exposed NiTi and SS archwires had better electrochemical properties than new archwires due to the protective nature of oral deposits. Total wear and coefficients of friction were higher among in vivo exposed archwires and higher in NiTi archwires in comparison to SS archwires. The estimated thickness of the TiO2 passive film on as-received NiTi is 8 nm, while the passive Cr2O3 film on as-received SS is just 1–2 nm. On in vivo exposed NiTi archwire, a 60–80 nm thick organic film/dental plaque was observed, and on SS, it was thinner, at about 60 nm. This research shows the importance of combining AES with electrochemical testing, to characterize tribocorrosive properties of NiTi and SS orthodontic archwires.
Ključne besede: archwires, NiTi, stainless steel, wear
Objavljeno v DiRROS: 24.08.2023; Ogledov: 265; Prenosov: 114
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Povzetek: Reinforced concrete structures require continuous monitoring and maintenance to prevent corrosion of the carbon steel reinforcement. In this work, concrete columns with carbon and stainless steel reinforcements were exposed to a real marine environment. In order to monitor the corrosion processes, two types of corrosion probes were embedded in these columns at different height levels. The results from the monitoring of the probes were compared to the actual corrosion damage in the different exposure zones. Electrical resistance (ER) probes and coupled multi-electrodes (CMEs) were shown to be promising methods for long-term corrosion monitoring in concrete. Correlations between the different exposure zones and the corrosion processes of the steel in the concrete were found. Macrocell corrosion properties and the distribution of the separated anodic/cathodic places on the steel in chloride-contaminated concrete were addressed as two of the key issues for understanding the corrosion mechanisms in such environments. The specific advantages and limitations of the tested measuring techniques for long-term corrosion monitoring were also indicated. The results of the measurements and the corrosion damage evaluation clearly confirmed that the tested stainless steels (AISI 304 and AISI 304L) in a chloride-contaminated environment behave significantly better than ordinary carbon steel, with corrosion rates from 110% to 9500% lower in the most severe (tidal) exposure conditions.
Ključne besede: corrosion in concrete, steel reinforcement, long-term exposure, field exposure, electrical resistance (ER) probes, coupled multi-electrodes
Objavljeno v DiRROS: 21.08.2023; Ogledov: 248; Prenosov: 156
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Povzetek: The aim of the study was to define the influence of microstructural properties on the electrochemical properties of copper in four different forms: copper in sheet form, copper doped with phosphorus, electroplated copper and copper wire. Open circuit potential and polarization resistance measurements were carried out in order to determine the electrochemical properties and corrosion rates of copper in 0.1 M NaCl solution in oxic conditions at ambient temperature. Statistical evaluation of the electrochemical data was performed in order to differentiate between the various forms of copper samples. Microstructural and electrochemical investigations were combined with electron microscopy and Raman analysis of the corrosion products after immersion of the copper samples in a 0.1 M NaCl solution for 30 days. The various morphologies of copper corrosion products were identified and analyzed by Raman spectroscopy for the various forms of copper.
Ključne besede: copper, microstructura, corrosion, Raman
Objavljeno v DiRROS: 19.07.2023; Ogledov: 301; Prenosov: 144
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Povzetek: Stainless steels are widely used in industrial assets and equipment. Despite their good corrosion resistance under a wide range of operating conditions, there is the possibility of pitting corrosion in the presence of chlorides. However, very few studies have identified the safe operating conditions for various high-alloyed stainless steel grades by comparing their pitting susceptibility. In this research, the susceptibility to pitting attack of five stainless steels with austenitic and duplex microstructures was examined in dilute sulphuric acid solution with varying amounts of NaCl at the temperatures of 50, 90 and 130◦C. Based on potentiodynamic polarization scans, none of the test materials underwent pitting corrosion at 50◦C, but differences in susceptibility to pitting attack were clear between the test materials and NaCl concentrations at the temperature of 90◦C, and further tem- perature increase facilitated uniform corrosion. 28-day immersion tests at 90◦ C confirmed the pitting suscepti- bility of duplex grades 1.4662 (PREN 33) and 1.4462 (PREN 35) in the presence of at least 2000 mg/L NaCl, but not the susceptibility of a corresponding austenitic grade 1.4539 (PREN 34). The grades 1.4547 (PREN 43) and 1.4410 (PREN 44) were not susceptible to pitting corrosion under any of the studied conditions. The results from materials microstructural and electrochemical characterization are presented and discussed in this paper.
Ključne besede: stainless steel, austenitic stainless steel, duplex stainless steel, pitting atttack
Objavljeno v DiRROS: 12.07.2023; Ogledov: 304; Prenosov: 381
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