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Open-Circuit Metal Dissolution Processes
Published in Madhav Datta, Electrodissolution Processes, 2020
Cathodic protection is an electrochemical method that converts the anodic (active) sites on a metallic surface to cathodic (passive) sites through the application of opposing current. This can be done by two different means. The first is the introduction of a galvanic anode which in the corrosive electrolytic environment sacrifices itself by corroding to protect the cathode. Sacrificial anodes are generally made of zinc, aluminum, or magnesium, metals that have the most negative electro-potential. The sacrificial anodes are required to be regularly replaced. Impressed current protection is another method of cathodic protection in which the negative terminal of a current source is connected to the metal, while the positive terminal is attached to an auxiliary anode, thus forming an electrical circuit through which a precalculated current is applied. Unlike in the sacrificial anode system, the auxiliary anode is not sacrificed in the cathodic protection system. This method is often used to protect buried pipelines and ship hulls.
Durable consolidation by cathodic protection of steel elements in historical concrete and masonry buildings
Published in Koen Van Balen, Els Verstrynge, Structural Analysis of Historical Constructions: Anamnesis, Diagnosis, Therapy, Controls, 2016
Kris Brosens, Dionys Van Gemert, Kristof Verreydt
The galvanic cathodic protection technique consists in electrically connecting a metal with lower electric chemical potential to the metal element, which has to be protected. That metal element will then serve as cathode. Also in this technique an electrical current will flow from the anode to the cathode. The extra added elements will act as anodes, and will gradually dissolve in the pore fluid. Therefore, these anodes are also called `self-sacrificing' anodes. Zinc is mostly used as sacrificing metal in the galvanic anodes. When both metals are put in contact, the cathodic steel will not be attacked or eroded. But at the zinc anode, zinc will dissolve and oxidize, to keep the electron current going. The protection will continue until the sacrificing anode is completely consumed. This also means that the system has a limited life span, depending on the zinc content and the environmental and exposure conditions. An advantage of this system is that no further control is needed, nor an external current source. Various application types are available. Fig. 10 shows a concrete beam, externally covered with zinc
EUROCORR 2017 in combination with the 20th International Corrosion Congress and the Process Safety Congress 2017: Corrosion Control for safer living part 3
Published in Corrosion Engineering, Science and Technology, 2018
E. Lyublinski (Corrosion Science, LLC, Solon, USA) addressed ‘Formation of the basic properties of galvanic anodes during the industrial production’. Aluminium, magnesium and zinc alloys in the form of cast galvanic anodes (GA) are commonly used in C.P. Any deviations arising from melting and casting may be deleterious, for example impurity elements (dissolved hydrogen, oxide inclusions, etc.) and lack of structural homogeneity. It was concluded that for standard sacrificial anodic compositions, MAl (Mg–Al–Zn), ZA1 (Zn–Al) and AA1 (Al–Zn), stable electrochemical characteristics are achieved by forming a homogeneous, fine-grained structure with a uniform distribution of structural components. The best conditions for obtaining such a structure would be achieved using a casting temperature 10–15% above the liquidus. This is also applied to water-cooled moulds.
A case study on corrosion conditions and guidelines for repair of a reinforced concrete chimney in industrial environment
Published in Structure and Infrastructure Engineering, 2022
Maddalena Carsana, Matteo Gastaldi, Elena Redaelli
Moreover, the protection of reinforcement from corrosion can be prolonged – always on the South region – by the use of embedded galvanic anodes (Bertolini et al., 2013). Galvanic anodes are small elements of zinc embedded in a conductive material that exhibit a mechanism of cathodic protection to the steel reinforcement, hence reducing the corrosion rate on active rebars and inhibiting the effect of possible macrocells between rebars in different conditions of corrosion. The type, shape and number of anodes need to be determined in the framework of a dedicated design.