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Iskalni niz: "avtor" (Miha Hren) .

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Monitoring the galvanic corrosion of copper–steel coupling in bentonite slurry during the early oxic phase using coupled multielectrode arrays
Tadeja Kosec, Miha Hren, Klara Prijatelj, Bojan Zajec, Nina Gartner, Andraž Legat, 2023, izvirni znanstveni članek

Povzetek: In the case of a two-part container for spent nuclear fuel, consisting of an iron-based inner structure with a copper coating, the potential perforation of copper through minor damage may result in intensive galvanic corrosion between copper and steel. The present work focuses on the corrosion of steel galvanically coupled to copper and exposed to a slightly saline environment under oxic conditions. The electrochemical processes on individual electrodes were monitored by coupled multielectrode arrays (CMEAs). The CMEAs were either in contact with groundwater saturated with bentonite or immersed in groundwater only. Very high galvanic corrosion currents were detected between carbon steel and pure copper in the early oxic phase. Additionally, the use of CMEAs further made it possible to monitor the distribution of cathodic currents around the steel electrode, which behaved anodically. Various microscopy and spectroscopy techniques were applied to identify the modes of corrosion and the type of corrosion products present at the end of the period of exposure.
Ključne besede: copper, steel, bentonite, Aspö groundwater, coupled multi electrode array, electrochemical properties, Raman analysis, corrosion
Objavljeno v DiRROS: 16.11.2023; Ogledov: 75; Prenosov: 9
.pdf Celotno besedilo (1,66 MB)
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Corrosion performance of steel in blended cement pore solutions
Miha Hren, Tadeja Kosec, Andraž Legat, Violeta Bokan-Bosiljkov, 2019, izvirni znanstveni članek

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: 135; Prenosov: 55
.pdf Celotno besedilo (1,80 MB)
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Corrosion behavior of steel in pore solutions extracted from different blended cements
Miha Hren, Tadeja Kosec, Andraž Legat, 2020, izvirni znanstveni članek

Povzetek: Mortar specimens made from four different types of cement, CEM I, CEM II, CEM III, and CEM IV, were prepared and pore solutions extracted. Three different types of exposure were studied: noncarbonated without chlorides, noncarbonated with chlorides, and carbonated with chlorides. Various electrochemical methods (linear polarization, potentiodynamic polarization measurements) were implemented to characterize the processes of corrosion on steel in these solutions. The type and extent of corrosion products were evaluated by means of various spectroscopic techniques. Specific differences in the type and extent of corrosion damage were determined and compared for each of the extracted pore solutions from the different blended cements. An attempt was made to classify these differences in comparison with the reference cement (CEM I) and in relation to the different types of exposure.
Ključne besede: corrosion, steel in pore water, blended cements, Raman Spectroscopy
Objavljeno v DiRROS: 22.08.2023; Ogledov: 135; Prenosov: 68
.pdf Celotno besedilo (1,25 MB)
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Sensor development for corrosion monitoring of stainless steels in H2SO4 solutions
Miha Hren, Tadeja Kosec, Mari Lindgren, Elina Huttunen-Saarivirta, Andraž Legat, 2021, izvirni znanstveni članek

Povzetek: Equipment made of different stainless steels is often used in the hydrometallurgical processing industry. In this study, an electrical resistance sensor was developed for monitoring corrosion in acidic solutions at high temperature. Two types of stainless steel were used as the electrode materials, namely grade 316L stainless steel (EN 1.4404) and grade 2507 duplex stainless steel (EN 1.4410). The materials and sensors were exposed to a 10% H2SO4 solution containing 5000 mg/L of NaCl at various temperatures. Results from the sensors were verified using electrochemical techniques and postexposure examination. Results showed that the microstructure played an important role in the interpretation of corrosion rates, highlighting the importance of using an appropriate stainless steel for the production of sensors. Electrochemical tests and postexposure examination both showed that the grade 2507 had a significantly lower corrosion rate compared to the grade 316L. Under industrial‑process conditions, the results for the grade 2507 sensor were promising with respect to sensor durability and performance, despite the extremely harsh operating environment.
Ključne besede: stainless steel, hydrometallurgical industry, sulphuric acid, electrical resistance sensor, corrosion
Objavljeno v DiRROS: 05.07.2023; Ogledov: 186; Prenosov: 127
.pdf Celotno besedilo (5,12 MB)
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Characterizing steel corrosion in different alkali-activated mortars
Nina Gartner, Miha Hren, Tadeja Kosec, Andraž Legat, 2021, izvirni znanstveni članek

Povzetek: Alkali-activated materials (AAMs) present a promising potential alternative to ordinary Portland cement (OPC). The service life of reinforced concrete structures depends greatly on the corrosion resistance of the steel used for reinforcement. Due to the wide range and diverse properties of AAMs, the corrosion processes of steel in these materials is still relatively unknown. Three different alkali-activated mortar mixes, based on fly ash, slag, or metakaolin, were prepared for this research. An ordinary carbon-steel reinforcing bar was installed in each of the mortar mixes. In order to study the corrosion properties of steel in the selected mortars, the specimens were exposed to a saline solution in wet/dry cycles for 17 weeks, and periodic electrochemical impedance spectroscopy (EIS) measurements were performed. The propagation of corrosion damage on the embedded steel bars was followed using X-ray computed microtomography (XCT). Periodic EIS measurements of the AAMs showed different impedance response in individual AAMs. Moreover, these impedance responses also changed over the time of exposure. Interpretation of the results was based on visual and numerical analysis of the corrosion damages obtained by XCT, which confirmed corrosion damage of varying type and extent on steel bars embedded in the tested AAMs.
Ključne besede: corrosion, alkali-activated mortars, steel reinforcement, electrochemical impedance spectroscopy, X-ray computed microtomography, visual analysis
Objavljeno v DiRROS: 05.07.2023; Ogledov: 204; Prenosov: 112
.pdf Celotno besedilo (7,00 MB)
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Characterization of steel corrosion processes in various blended cements by means of coupled multi-electrode arrays
Miha Hren, Tadeja Kosec, Andraž Legat, 2023, izvirni znanstveni članek

Povzetek: Supplementary cementitious materials can affect the porosity of concrete, pore solution pH and chloride binding, all of which influence the type and magnitude of corrosion damage. Advanced corrosion monitoring techniques are needed to follow the development of corrosion on steel embedded in concrete across space and over time. In this study, coupled multi-electrode arrays (CMEAs) were used to characterise corrosion processes in OPC and three blended cements. Cyclic wetting with chlorides was undertaken to initiate corrosion. The results showed three distinct types of corrosion: localised corrosion (CEM I), localised corrosion that expanded over time (CEM II), and a combination of localised and general corrosion (CEM III and CEM IV). Cathodic locations were also monitored successfully, and the corrosion behaviour was related to total porosity and pH of the pore solution. MicroCT was used to quantify the volume of corroded material, which agreed well with results calculated from the CMEA measurements.
Ključne besede: blended cements, coupled multi-electrode array, corrosion of steel in concrete, supplementary cementitious materials, open access
Objavljeno v DiRROS: 29.05.2023; Ogledov: 129; Prenosov: 113
.pdf Celotno besedilo (12,61 MB)
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Tribocorrosion susceptibility and mechanical characteristics of as-received and long-term in-vivo aged nickel-titanium and stainless-steel archwires
Jasmina Primožič, Miha Hren, Uroš Mezeg, Andraž Legat, 2022, izvirni znanstveni članek

Povzetek: To evaluate the effect of long-term in-vivo aging on orthodontic archwires, we aimed to assess the triboelectrochemical and mechanical characteristics of as-received and in-vivo aged nickel-titanium (NiTi) and stainless-steel (SS) orthodontic archwires. Four consecutive tribocorrosion cycles on six NiTi and six SS archwires, as-received and in-vivo aged, were performed on a reciprocal tribometer. Electrochemical noise and friction coefficient measurements, three-dimensional surface profiling, and hardness measurements were performed. Repassivation times of as-received archwires were longer than of the in-vivo aged; however, were shorter for NiTi. Friction coefficients were higher for NiTi than for SS archwires. Sudden major current drops concomitant with inverse potential shifts and friction coefficients’ fluctuations, were seen for as-received (last cycle) and in-vivo aged (last three cycles) NiTi archwires. More pronounced tribocorrosion damage was observed on in-vivo aged NiTi than on other archwires. Hardness was generally higher inside the wear track of archwires. Long-term in-vivo exposure decreases the corrosion susceptibility of archwires, more evidently for the NiTi ones. Sudden major fluctuations in electrochemical current, potential, and friction coefficient detected for NiTi archwires, might be related to localized residual parts of the oxide layer persisting due to increased surface roughness or to phase transformations of the alloy’s crystal structure.
Ključne besede: tribocorrosion, orthodontic archwires, electrochemical noise, open access
Objavljeno v DiRROS: 26.04.2023; Ogledov: 228; Prenosov: 83
.pdf Celotno besedilo (2,52 MB)
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