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Cathodic protection (CP; / k æ ˈ θ ɒ d ɪ k / ⓘ) is a technique used to control the corrosion of a metal surface by making it the cathode of an electrochemical cell. [1] A simple method of protection connects the metal to be protected to a more easily corroded "sacrificial metal" to act as the anode. The sacrificial metal then corrodes ...
Corrosion of an iron nail wrapped in bright copper wire, showing cathodic protection of copper; a ferroxyl indicator solution shows colored chemical indications of two types of ions diffusing through a moist agar medium.
Electrochemical coloring of metals is a process in which the surface color of metal is changed by electrochemical techniques, i.e. cathodic or anodic polarization. The first method of electrochemical coloring of metals are certainly Nobili's colored rings, discovered by Leopoldo Nobili , an Italian physicist in 1826.
In brief, corrosion is a chemical reaction occurring by an electrochemical mechanism (a redox reaction). [1] During corrosion of iron or steel there are two reactions, oxidation (equation 1), where electrons leave the metal (and the metal dissolves, i.e. actual loss of metal results) and reduction, where the electrons are used to convert oxygen and water to hydroxide ions (equation 2): [2]
Black oxide or blackening is a conversion coating for ferrous materials, stainless steel, copper and copper based alloys, zinc, powdered metals, and silver solder. [1] It is used to add mild corrosion resistance, for appearance, and to minimize light reflection. [ 2 ]
Another cathodic protection is used on the impressed current anode. [12] It is made from titanium and covered with mixed metal oxide. Unlike the sacrificial anode rod, the impressed current anode does not sacrifice its structure. This technology uses an external current provided by a DC source to create the cathodic protection. [13]
The copper–copper(II) sulfate electrode is a reference electrode of the first kind, [1] based on the redox reaction with participation of the metal and its salt, copper(II) sulfate. It is used for measuring electrode potential and is the most commonly used reference electrode for testing cathodic protection corrosion control systems. [2]
The galvanic series (or electropotential series) determines the nobility of metals and semi-metals.When two metals are submerged in an electrolyte, while also electrically connected by some external conductor, the less noble (base) will experience galvanic corrosion.