Explore chapters and articles related to this topic
Galvanic protection of piles in a marine environment
Published in Hiroshi Yokota, Dan M. Frangopol, Bridge Maintenance, Safety, Management, Life-Cycle Sustainability and Innovations, 2021
Galvanic protection is achieved when two dissimilar metals are connected. The metal with the higher potential for corrosion (generally a zinc-based system in concrete applications) will corrode in preference to the more noble metal. With respect to a copper-copper sulfate electrode, the potential of zinc is about -1.1V and the potential of reinforcing steel in concrete is typically in the range of -0.2 to -0.5V. As the sacrificial metal corrodes, it generates electrical current to protect the reinforcing steel. Galvanic protection systems are the most commonly utilized cathodic protection technology to protect concrete piles in the corrosive marine environment. The limitation on applied voltage by zinc-based galvanic systems allows for their use to safely protect high strength prestressing steel.x
Protection Mechanisms of Organic Coatings
Published in Ole Øystein Knudsen, Amy Forsgren, Corrosion Control Through Organic Coatings, 2017
Ole Øystein Knudsen, Amy Forsgren
Steel that is immersed in an electrolyte may be protected by sacrificial anodes mounted on the structure. This will not work in atmosphere, since there is no electrolytic contact between the anode and the steel. To overcome this limitation, the sacrificial material must be applied to the steel as a coating, which is in electric contact with the steel on the entire surface. There are many ways of applying a sacrificial metal on a steel surface, the most important being hot-dip galvanizing, thermal spraying, and electroplating. Cathodic protection by painting is achieved with zinc-rich paints, whose zinc pigment acts as a sacrificial anode, corroding preferentially to the steel substrate. In order for the zinc to provide cathodic protection, the zinc must be in electric contact with the steel substrate, which means that the zinc-rich paint must be the first coat applied. They are therefore referred to as zinc-rich primers. The binder in zinc-rich primers is based on organic polymers, typically epoxies, or inorganic silicates. More information on the formulation of zinc-rich coatings and the protection mechanism is given in Chapter 4.
Advanced Micro/Nanocapsules for Self-healing Smart Anticorrosion Coatings
Published in Hatem M.A. Amin, Ahmed Galal, Corrosion Protection of Metals and Alloys Using Graphene and Biopolymer Based Nanocomposites, 2021
Kayla Lee, Cynthia G. Cavazos, Jacob Rouse, Xin Wei, Mei Li, Suying Wei
There are well developed mature strategies for preventing corrosion. In summary, cathodic protection is the conventional method to slow down the corrosion process. A sacrificial metal is used to convert all of the anodic sites, which is more easily corroded, on the protected metal surface to cathodic sites. The sacrificial metal is a more electronegative metal based on the galvanic series, e.g., iron materials are usually coated with a layer of zinc. However, the cathodic protection method requires a regular replacement of sacrificial metals. Another way to prevent corrosion is coating protection method. Different types of coatings have been well developed and widely used to protect corrosion. For this method, a multi-layered chemical barrier is employed to protect the underlying metal. The most important three layers are the pretreatment layer, the primer, and the topcoat [1]. The pre-treatment layer plays an important role to enhance the adhesion between the primer and the protected metal. The primer is the layer where the corrosion inhibitor is incorporated which could be galvanization metal elements or polymerizing agent. The top coat is applied to isolate the protected metal and other layers from the environmental factors, such as ultraviolet radiation, high external temperature, water, hot corrosive liquids, air pollution, acid rain, micro-organisms, etc. [3] However, the toxicity of the chemicals used in the multi-layered barrier, such as chromated pigments, epoxy resin, and polyurethane, is harmful to both the environment and human health [4]. Recently, graphene and its derivatives have been tested in replacement partially of the hazardous species in the coating layer, and showed promising corrosion protection results and potentially the alternative “greener” choices of coating materials [5].
Zn–Ni compositionally modulated multilayered alloy coatings for improved corrosion resistance
Published in Surface Engineering, 2021
Ramesh S. Bhat, P. Nagaraj, Sharada Priyadarshini
Electrodeposition, also known as electroplating or simply plating, is an inexpensive technique for protective and improving the functionality of parts used in a wide range of industries, including home appliances, jewellery, automobile, aircraft/aerospace and electronics, electrical and tools for machinery items [1]. Metal coatings have been widely used in surface protection or for decorative applications. Zinc and its alloy coatings find numerous applications as sacrificial metal coatings [2]. For several years, thick Zn coatings have been used to provide economic protection for metal parts. Slowly zinc alloys replaced the conventional zinc coatings, because of their improved efficiency at elevated temperature [3]. Iron group metals like nickel, cobalt, etc. alloyed with zinc provides better protection efficiency than zinc coating [2–5]. Zinc–Nickel alloy coatings can be obtained by an electroplating process in an acidic or alkaline bath. The Zn–Ni alloy coating, where the wt-%Ni content is 12–16, shows the highest corrosion resistance [6]. For a range of parameters, it has been observed that the process takes place anomalously, since zinc being less noble metal is preferentially deposited. This may be explained by ‘hydroxide suppression mechanism’, where zinc hydroxy compounds inhibit the nickel deposition [7–10]. Vasilache et al. described the mechanism of electrochemical deposition of nickel and zinc–nickel alloy [11,12].
A future application of pulse plating – silver recovery from hydrometallurgical bottom ash leachant
Published in Transactions of the IMF, 2018
H. Elomaa, P. Halli, T. Sirviö, K. Yliniemi, M. Lundström
The enrichment factors were calculated based on the values in Table 3 in order to evaluate the silver enrichment on the Pt surface. The observed Ag/(Cu + Zn) ratio (0.3) indicated remarkable enrichment of silver on the surface, when compared to the ratio of these elements (Ag/(Cu + Zn)) in the solution (6.8 × 10−5). Ag vs. base metal (Cu + Zn) ratio can be increased to ca. 4500 fold on the cathode surface compared to the original leaching solution. The highest enrichment of silver compared to Cu and Zn was achieved with a deposition time of 10 s (Figure 5). This deposition time (10 s) was shown to provide the most favourable level for Cu deposition, replaced by Ag in the parameter range studied. Owing to the fact that the redox replacement reaction takes place only at the deposit/solution interface, it is favourable to create a thin layer of sacrificial metal with a certain level of defects to gain a higher Ag enrichment. The thickness of the deposited Cu layer increases with a higher deposition time (15 s), affecting the purity of deposited surface.22
Defluoridation of drinking water by magnesium and aluminum electrocoagulation in continuous flow-rate: a response surface design
Published in Environmental Technology, 2022
Ana Gabriela Sierra-Sánchez, Verónica Martínez-Miranda, Elia Alejandra Teutli-Sequeira, Ivonne Linares-Hernández, Guadalupe Vázquez-Mejía, Monserrat Castañeda-Juárez
To reduce the F− of water, different techniques have been used, such as electrodialysis (C0 = 1.8 mg L−1 F−, 95% E1) [16], adsorption (C0 = 5 mg L−1 F−, 99% E) [17]; nanofiltration (C0 = 20 mg L−1 F−, 98% E) [18]; freezing concentration (C0 = 4 mg L−1 F−, 85% E) [19]; flue gas desulfurisation gypsum (C0 = 10.9 mg L−1 F−, 93.31% E) [20], and electrocoagulation (EC). The EC process operates according to the principle of a standard electrochemical cell. The sacrificial metal anode dissolves in the aqueous medium and generates a hydrolysis product (hydrometal species) that adequately destabilises the polluting particles that are suspended, emulsified or dissolved in an aqueous medium, inducing an electrical current in the water through various materials, with Fe and Al being the most commonly used [21]. The main advantages of the EC process are the low cost of investment, the zero addition of chemical compounds, ease of operation and, most importantly, very low sludge production [13]. The EC is a process that can be carried out in batch or in continuous flow operations. Several continuous flow EC studies have been conducted that have shown good removal rates. Emamjomeh and Sivakumar [22] obtained 99% removal by using Al electrodes (C0 = 10 mg L−1 F−, HRT = 53 min, flow-rate = 150 mL min−1). When using real water samples, the removal percentages decrease as a result of the nature of the samples. Sinha et al. [23] obtained 68% removal by using Al electrodes (C0 = 11.6 mg L−1 F−, HRT = 14 min, flow-rate = 150 mL min−1). On the other hand, Apshankar and Goel [24] obtained 46.7% removal by using steel electrodes (C0 = 14 mg L−1 F−, HRT = 6 h, flow-rate = 1 L h−1).