1,721,086 research outputs found
Effect of a Nitrate-Based Corrosion Inhibitor on Carbonation-Induced Corrosion
No full textCorrosion inhibitors are additives that can work both as a preventative technique to delay the onset of corrosion or as a protection system to reduce corrosion rate, once corrosion is initiated. Several substances have been evaluated as possible candidates, both organic and inorganic in nature. Recently, a nitrate-based compound has been proposed as a corrosion inhibitor, as nitrates are still used in concrete as set accelerators. Nitrates inhibiting mechanism is similar to nitrites, the latter being the most efficient compound nowadays available. This work evaluates the effect of a nitrate-based corrosion inhibitor on carbonated-induced corrosion in concrete. Results show that the addition of calcium nitrate (4% vs. cement weight) can delay the carbonation penetration rate: the carbonation coefficient is reduced by about 30% with respect to the noninhibited specimens. Once corrosion is initiated, nitrate-based inhibitor, even at a high dosage (4% vs. cement weight), is not effective in reducing the corrosion rate: values as high as 10 μm/y were measured after about 2 y of external exposure
Recent advances in the use of inhibitors to prevent chloride-induced corrosion in reinforced concrete
Full text linkRebar corrosion is one of the most important phenomena affecting durability of reinforced concrete structures. Corrosion inhibitors are considered an effective preventative technique to delay the onset of corrosion and/reduce the corrosion rare. Substances can be both organic and inorganic in nature. Besides the well-known effectiveness of nitrite-based inhibitor, new organic and inorganic substances have been investigated as alternative to face safety and environmental issues related to sodium or potassium nitrites. From the ‘90s, a wide number of organic substances were studied, including amines, alkanolamines, carboxylates and mixtures of esters. The present literature review is focused on the effectiveness of the most commonly used inhibitors as nitrites and amines. The use of nitrates, new organic and green compounds, i.e., natural substances typically extracted from plants, are investigated as potential corrosion inhibitors
Big milestones in the study of steel corrosion in concrete
No full textRebar corrosion in concrete has been neglected for a long time in the scientific and technical literature, as reinforced concrete was considered an "eternal" material. Only during the 60s, and more during the 70s and the 80s, several research groups and many corrosion schools gave important contributions. An important impact was also achieved by Italian researchers thanks to the Universities of Roma, Napoli, Ancona, Ferrara, Bergamo, and Politecnico di Milano, where professor Pietro Pedeferri and his school contributed to the study of stainless steel reinforcement, corrosion inhibitors, service life modeling, cathodic protection and cathodic prevention, the latter proposed by Pedeferri in the early 90s. The paper is dedicated to the memory of Pietro Pedeferri (1938-2008) and Luca Bertolini (1966-2017)
Chemical oxidation as repairing technique to restore corrosion resistance on damaged anodized titanium
Full text linkAnodized titanium shows an excellent resistance to pitting corrosion. However, it could be subject to failure in case of local removal of the oxide film due, for example, to incorrect handling during transport, installation, or use. Depending on part size and usage, an electrochemical anodizing treatment could be not feasible. In this case, localized chemical oxidation treatment could be used to recover damaged film and restore corrosion resistance. Chemical oxidation was performed on titanium by immersion in NaOH 10 M and H 2 O 2 10 M at temperature from room to 90 °C with duration ranging between 1 h and 72 h. Potentiodynamic tests in bromides 0.5 M were used to determine the effectiveness of the treatment in relation with the one obtained with anodic oxidation. Higher bath temperature led to faster growth of the film, however it has no effect on the final corrosion resistance. Breakdown potential in bromides increased with treatment duration. The establishment of a plateau occurs at earlier stage, as temperature is increased. Titanium samples anodized and then scratched, to simulate film mechanical removal, were recovered using chemical oxidation and initial corrosion resistance was restored. The suggested treatments for in-situ recovery are 72 h of exposure to NaOH or 6 h at H 2 O 2 at room temperature
Effect of binary mixtures on chloride induced corrosion of rebars in concrete
Full text linkRebar corrosion is one of the most important phenomena affecting the durability of reinforced concrete structures. Corrosion inhibitors can be used as a preventative method, able to delay corrosion, or as repair method, to reduce corrosion rate. During more than 15 years in our laboratories an intense experimental research was carried out: the aim of the research was to identify new organic substances or mixtures thereof that might have inhibiting effectiveness. In the paper the effect of binary mixtures on chloride induced corrosion of rebars in concrete is studied; the mixtures are based on two amines, dimethylethanolamine (DMEA) and triethylenetetramine (TETA), and a carboxylate (benzoate); the tests were carried out for comparison purpose also in concrete containing nitrite, acknowledged to be the most effective product. The best results among the binary mixtures were shown by the benzoate-TETA, while the mixtures based on DMEA-TETA were not satisfactory. The performance of the mixtures is not comparable to nitrites
Hydrogen charging of carbon and low alloy steel by electrochemical methods
Full text linkAtomic hydrogen can be the result of different processes like electroplating, chemical and electrochemical pickling treatments, in welding or by cathodic processes in corrosive fluids. Moreover, adsorption of atomic hydrogen can affect materials in contact with high pressure gaseous hydrogen. Once entered the material, atomic hydrogen interacts with the metal structure and may produce a "damage" of various forms, such as Hydrogen Induced Cracking (HIC), delayed fracture, blistering and hydrogen embrittlement. In particular, when H2S is present ("sour service"), metallic materials, such as carbon and low alloy steels, may suffer hydrogen damage and hydrogen embrittlement. Sour service materials must be used in compliance with international accepted standards, used worldwide in oil and gas activities, when fluids are classified as sour. The present study has been carried out in order to set up an electrochemical method to charge with hydrogen two typical pipeline materials, carbon and low alloy steels. The reason of the use of an electrochemical method is to avoid any critical conditions from the point of view of preparation, safety and disposal. Hydrogen content in the specimens was measured by two different methods: hot glycerol bath and Inert Gas Fusion (IGF) analysis. Hydrogen content in the specimens is about 0.6-2 ppm; mechanical performances were assessed by means of J integral tests: a pronounced decrease of fracture toughness was observed for H charged specimens.{GRAPHIACAL ABSTRACT
La realcalinización y la extracción electroquímica de los cloruros en las construcciones de hormigón armado
No full textRealkalisation and electrochemical chloride removal techniques, developed for rehabiliting carbonated and chloride-containing structures, are presented. Electrolysis and electromigration mechanisms and consequences as well as electrochemical conditions at the reinforcement surface are discussed and compared with cathodic protection ones. Furthermore, possible side effects are commented
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