Electrochemical corrosion tests on steel in alkali-activated materials

One of the potential alternatives to Ordinary Portland Cement (OPC) are Alkali-Activated Materials (AAMs). The service life of reinforced concrete structures greatly depends on the corrosion resistance of embedded steel reinforcement. Due to the wide range of AAMs and their diverse properties, corrosion processes of steel in these materials are relatively unknown. Corrosion monitoring methods or their interpretations in certain cases cannot be directly transferred from the ones for OPC materials. The chemical compositions of pore solution in different AAMs influence the results of electrochemical measurements and their interpretations. Within this research, three different alkali-activated mortar mixes were prepared, based on fly ash, slag or metakaolin. Pore solutions were extracted from each mortar andchemical analysis was acquired. Different electrochemical corrosion measurements were performed on steel submerged to synthetic pore solutions. In parallel, ordinary carbon steel reinforcing bar was installed in the same types of alkali-activated mortar mixes. Specimens were exposed to wet/dry cycles with saline solution and periodic measurements of electrochemical impedance spectroscopy (EIS) were performed. Measured parameters in both systems were analysedand compared. It was concluded that electrochemical measurements in pore solutions can provide basic overview on corrosion behaviour in different AAMs environments. Periodic EIS measurements enabled monitoring of corrosion initiation and propagation on steel reinforcement in AAMs, although the information on the corrosion type is missing. Interpretation of results depends on visual analysis of corrosion damages after the end of exposure, providing information on corrosion type and intensity. The continuation of research on corrosion monitoring techniques will be performed by using Electrical Resistance (ER) sensors and Coupled Multi-Electrode Array (CMEA) sensors

Sensor development for corrosion monitoring of stainless steels in H₂SO₄ solutions

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

Steel corrosion in different alkali-activated mortars

One of the potential alternatives to Ordinary Portland Cement (OPC) are Alkali-Activated Materials (AAMs) [1]. The service life of reinforced concrete structures greatly depends on the corrosion resistance of embedded steel reinforcement. Due to the wide range of AAMs with their diverse properties, corrosion processes of steel in these materials are relatively unknown. Corrosion monitoring methods or their interpretations in certain cases cannot be directly transferred from the ones for OPC materials, and therefore results of different corrosion studies are sometimes contradictory [2]. The chemical composition of pore solution in different AAMs are influencing the results of electrochemical measurements and their interpretation, e.g. the presence of sulphides reduces the redox potential of the pore solution, but enables the steel to remain in an apparently passive state [3]. The aim of this paper is to compare electrochemical parameters measured on steel reinforcement in different alkali-activated and OPC mortars. Ordinary carbon steel reinforcing bar was installed in three different alkali-activated mortar mixtures, based on fly ash, slag or metakaolin. Specimens were exposed to wet/dry cycles with saline solution and periodic measurements of electrochemical impedance spectroscopy (EIS). Measured parameters were analyzed and compared to the ones measured in reference OPC mortar. The propagation of corrosion damages on embedded steel bars was also followed using x-ray computed microtomography (MicroCT). In addition to corrosion tests, information on pore water chemistry was obtained, as well as general mechanical and physical properties of tested AAMs. In certain specimens also Electrical Resistance (ER) probes were implemented, which can successfully detect corrosion initiation and monitor general corrosion rate [4]. It was concluded that EIS method can follow the evolution of corrosion processes on steel reinforcement in AAMs, although the caution is needed when interpreting the results. The additional use of the MicroCT can provide verification of ongoing results obtained by electrochemical methods, and deeper insight in corrosion processes in AAMs. [1] J.L. Provis, Cem. Concr. Res. (2017). [2] M. Criado, C. Monticelli, S. Fajardo, D. Gelli, V. Grassi, J.M. Bastidas, Constr. Build. Mater. 35 (2012) 30–37. [3] M. Criado, S.A. Bernal, P. Garcia-Triñanes, J.L. Provis, J. Mater. Sci. (2017) 1–20. [4] A. Česen, T. Kosec, A. Legat, Corros. Sci. 75 (2013) 47–57

Development of multi-component fluoropolymer based coating on simulated outdoor patina on quaternary bronze

Abstract Bronze reacts with oxygen, humidity, and pollutants in the atmosphere so that a patina forms. Natural exposure to an outdoor atmosphere can be simulated and accelerated in order to achieve a patina that mimics outdoor ancient patina. In order to avoid the uncontrolled dissolving of either the natural or artificially formed patina, protection of the patina is needed. In this study, a multi-component fluoropolymer based coating for the protection of bronze patina was developed. In order to provide various functionalities of the coating (such as the hydrophobicity of the coating surface, obtaining interactions within the coating itself as well as a bronze substrate and inhibiting the corrosion processes), a fluoroacrylate coating with appropriate adhesion promoter was suggested, with and without a silane modified benzotriazole inhibitor. The protective efficiency and durability of the applied coatings were investigated electrochemically using potentiodynamic tests and electrochemical impedance spectroscopy in a simulated acid rain solution. All of the developed coatings showed a significant decrease in the corrosion current density. The self-assembled single layer coating (FA-MS) also showed 100% inhibition efficiency. After ageing the coating remained transparent and did not change by UV exposure and/or thermal cycling. The patina and coating investigations using FIB-SEM and EDX showed that the latter coating (FA-MS) successfully covered the surface of the patinated bronze. The mechanism of the bonding was proposed and supported with the spectroscopic observation of a thin and even coating

Construction of a new class of tetracycline lead structures with potent antibacterial activity through biosynthetic engineering

Antimicrobial resistance and the shortage of novel antibiotics have led to an urgent need for new antibacterial drug leads. Several existing natural product scaffolds (including chelocardins) have not been developed because their suboptimal pharmacological properties could not be addressed at the time. It is demonstrated here that reviving such compounds through the application of biosynthetic engineering can deliver novel drug candidates. Through a rational approach, the carboxamido moiety of tetracyclines (an important structural feature for their bioactivity) was introduced into the chelocardins, which are atypical tetracyclines with an unknown mode of action. A broad-spectrum antibiotic lead was generated with significantly improved activity, including against all Gram-negative pathogens of the ESKAPE panel. Since the lead structure is also amenable to further chemical modification, it is a platform for further development through medicinal chemistry and genetic engineering

B-IMPACT project: eco-friendly and non-hazardous coatings for the protection of outdoor bronzes

Application of protective coatings is the most widely used conservation treatment for outdoor bronzes. Eco-friendly and non-hazardous coatings are currently needed for conservation of outdoor bronze monuments. To fulfil this need, the M-ERA.NET European research project B-IMPACT (Bronze-IMproved non-hazardous PAtina CoaTings) aimed at assessing the protectiveness of innovative coatings for historical and modern bronze monuments exposed outdoors.In this project, two bronze substrates (historical Cu-Sn-Zn-Pb and modern Cu-Si-Mn alloys) were artificially patinated, by acid rain solution using dropping test and by “liver of sulphur” procedure (K2S aqueous solution)to obtain black patina, respectively. Subsequently, the application of several newly developedprotective coatings was carried out and their performance was investigated by preliminary electrochemical tests. In the following stepsof the work, the assessment of the best-performing coatings was carried out and their performance was compared to Incralac, one of the most widely used protective coatings in conservation practice. A multi-analytical approach was adopted,considering artificial ageing (carried out in representative conditions, including exposure to rain runoff, stagnant rain and UV radiation)and metal release, as well as visual aspect (so as to include aesthetical impact among the coating selection parameters) and morphological and structural evolution of the coated surfaces due to simulated outdoor exposure. Lastly, also the health impact of selected coatings was assessed by occupational hazard tests. The removability and re-applicability of the best-performing coatings were also assessed.The best alternatives to the conventional Incralac exhibited were: (i) fluoroacrylate blended with methacryloxy-propyl-trimethoxy-silane (FA-MS) applied on patinated Cu-Sn-Zn-Pb bronze and (ii) 3-mercapto-propyl-trimethoxysilane (PropS-SH) applied on patinated Cu-Si-Mn bronz

Korozija in zaščita nepatiniranega, sulfidno- inkloridno-patiniranega brona

The surface of bronze undergoes changes when it is exposed to a polluted atmosphere, and bronze should therefore be protected from this natural deterioration. The most common protective coating currently in use is Incralac, which includes toxic components and is reported to dissolve a few months after application. This work therefore investigates a fluoropolymer-based coating (FA-MS), and compares it to the protection offered by Incralac. Bronze samples (non-patinated, sulphide-patinated or chloride-patinated) were exposed to simulated urban rain for four months. The corrosion products formed were characterised using SEM/EDS and Raman analyses. To study the protection efficiency of the newly developed fluoropolymer coating (FA-MS) and Incralac protection, various electrochemical methods were used: measurements of open circuit potential linear polarisation and potentiodynamic measurements. Findings show that the FA-MS coating provides a protection efficiency of 71 % for chloride-patinated bronze and 99.5 % for sulphide-patinated bronze. Contact angles of the FA-MS samples were higher than those of the unprotected samples or the samples protected by Incralac, indicating better hydrophobic properties of the FA-MS coating.Povšina brona se z izpostavljenostjo onesnaženemu okolju spreminja, zato mora biti pred naravnim propadanjem zaščitena. Trenutno je najbolj pogosto uporabljen zaščitni premaz Incralac, ki vsebuje okolju škodljive snovi, hkrati pa poročajo, da po nanosu razpade že po nekaj mesecih. Na podlagi tega je bil v tej študiji raziskan zaščitni premaz na osnovi fluoropolimera (FA-MS), ter primerjava z Incralac premazom. Vzorci brona (ne-patiniran, rjavo-patiniran in kloridno-patiniran) so bili za štiri mesece izpostavljeni simulaciji deževnice v urbanem okolju. Tvorjeni korozijski produkti so bili nato označeni s pomočjo SEM/EDS in ramanske analize. Za študij učinkovitosti zaščite novo razvitega fluoropolimernega premaza (FA-MS) in Incralac zaščite smo uporabili različne elektrokemijske metode: meritve potenciala odprtega kroga, linearno polarizacijo in potenciodinamske meritve. Prav tako smo določili hidrofobnost z meritvami kontaktnih kotov in izmerili spremembe v barvi pred in po nanosu zaščite. Ugotovitve preiskav so, da FA-MS premaz nudi učinkovitost zaščite v vrednosti 71 % za kloridno patiniran bron in 99,5 % za sulfidno patiniran bron. Izmerjene vrednosti kontaktnih kotov vzorcev, zaščitenih s FA-MS prevleko, so bili višje kot pri nezaščitenih vzorcih in vzorcih, zaščitenih z Incralacom, kar kaže na izboljšane hidrofobne lastnosti FA-MS zaščite

Efficiency of a corrosion inhibitor on bare, oxidized and real archeological bronze in indoor polluted atmosphere - digital image correlation approach

A corrosion inhibitor, tolyl methyl imidazole (TMI), was tested in practice and verified in a polluted in-door atmosphere. Special attention was given to its behavior in indoor storage conditions, where volatileorganic pollutants may cause damage to metal artefacts. Prepared samples of bronze and oxidized bronzewere exposed to acetic acid vapors. Raman analysis showed copper acetate and copper nitrate forma-tion. Suppression of corrosion development following the application of tolyl methyl imidazole (TMI) wasobserved. A simple method based on image analysis for corrosion evaluation was specifically developed.The TMI inhibition action was tested on a Roman archeological object and evaluated after exposure toindoor pollutants

A critical appraisal of the use and properties of nickel–titanium dental alloys

Nickel–titanium (NiTi) archwires are used in dentistry for orthodontic treatment. NiTi alloys have favourable mechanical characteristics, such as superelasticity and shape memory, and are also known as a corrosion-resistant alloy. In specific cases, an archwire could be attacked by certain types of corrosion or wear degradation, which can cause the leaching of metal ions and a hypersensitive response due to increased concentrations of Ni in the human body. A systematic search of the literature retrieved 102 relevant studies. The review paper focuses on three main fields: (i) electrochemical properties of NiTi wires and the effect of different environments on the properties of NiTi wires (fluoride and low pH)(ii) tribocorrosion, a combination of chemical and mechanical wear of the material, and (iii) the biocompatibility of NiTi alloy and its subsequent effect on the human body. The review showed that corrosion properties are affected by microstructure, pH of saliva and the presence of fluorides. A high variation in published results should be, therefore, interpreted with care. The release of nickel ions was assessed using the same unit, showing that the vast majority of metal ions were released in the first few days of exposure, then a stable, steady state was reached. In tribocorrosion studies, the increased concentrations of Ni ions were reported