Galvanization or galvanisation refers to any of several electrochemical processes named after the Italian scientist Luigi Galvani. Electrochemistry is a branch of Chemistry that studies Chemical reactions which take place in a Solution at the interface of an electron conductor Luigi Galvani was an Italian Physician and Physicist who lived and died in Bologna.

Old meanings: ref. electricity

Originally, galvanization was the administration of electric shocks (in the 19th century also termed Faradism, after Michael Faraday). Michael Faraday, FRS ( September 22 1791 – August 25 1867) was an English It stemmed from Galvani's induction of twitches in severed frogs' legs, by his accidental generation of electricity. This article is about the block cipher algorithm For the ultrafast laser pulse measurement technique see Frequency-resolved optical gating. This archaic sense is the origin of the meaning of galvanic when meaning "affected/affecting, as if by a shock of electricity; startled". In Language, an archaism is the use of a form of speech or writing that is no longer current ^[1] Its claims to health benefits have largely been disproven, except for some limited uses in psychiatry in the form of electroconvulsive therapy (ECT). Psychiatry is a medical specialty which exists to study, prevent, and treat Mental disorders in Humans Psychiatric Electroconvulsive therapy ( ECT) also known as electroshock, is a controversial psychiatric treatment in which Seizures are electrically induced Later the word was used for processes of electrodeposition. This remains a useful and broadly applied technology, but the term "galvanization" has largely come to be associated with zinc coatings, to the exclusion of other metals. Zinc (ˈzɪŋk from Zink is a Metallic Chemical element with the symbol Zn and Atomic number 30

Modern meaning: dipping in molten zinc

In current use, it typically means hot-dip galvanizing, a metallurgical process that is used to coat steel or iron with zinc. Hot-dip galvanizing is a form of Galvanization. It is the process of coating Iron or Steel with a thin Zinc layer by passing the steel Steel is an Alloy consisting mostly of Iron, with a Carbon content between 0 Iron (ˈаɪɚn is a Chemical element with the symbol Fe (ferrum and Atomic number 26 This is done to prevent galvanic corrosion (specifically rusting) of the ferrous item; while it is accomplished by non-electrochemical means, it serves an electrochemical purpose. Galvanic corrosion is an Electrochemical process in which one Metal Corrodes preferentially when in electrical contact with a different type of metal Iron (ˈаɪɚn is a Chemical element with the symbol Fe (ferrum and Atomic number 26

Hot-dip galvanized steel has been effectively used for more than 150 years. The value of hot-dip galvanizing stems from the relative corrosion resistance of zinc, which, under most service conditions, is considerably better than iron and steel. In addition to forming a physical barrier against corrosion, zinc, applied as a hot-dip galvanized coating, cathodically protects exposed steel. Furthermore, galvanizing for protection of iron and steel is favored because of its low cost, the ease of application, and the extended maintenance-free service that it provides.

Zinc coatings

Zinc coatings prevent corrosion of the protected metal by forming a physical barrier, and by acting as a sacrificial anode if this barrier is damaged. A sacrificial anode, or sacrificial rod, is a metallic Anode used in Cathodic protection where it is intended to be dissolved to protect other metallic When exposed to the atmosphere, zinc reacts with oxygen to form zinc oxide, which further reacts with water molecules in the air to form zinc hydroxide. Zinc oxide is a Chemical compound with the formula ZnO It is nearly insoluble in water but soluble in Acids and Bases It occurs Finally zinc hydroxide reacts with carbon dioxide in the atmosphere to yield a thin, impermeable, tenacious and quite insoluble dull grey layer of zinc carbonate which adheres extremely well to the underlying zinc, so protecting it from further corrosion, in a way similar to the protection afforded to aluminium and stainless steels by their oxide layers. Smithsonite, or zinc spar, is Zinc Carbonate Zn[[carbon C]] O 3 a mineral ore of zinc Passivation is the process of making a material "passive" in relation to another material prior to using the materials together WikipediaNaming In Metallurgy, stainless steel is defined as a Steel Alloy with a minimum of 11

Hot dip galvanizing deposits a thick robust layer that may be more than is necessary for the protection of the underlying metal in some applications. This is the case in automobile bodies, where additional rust proofing paint will be applied. Here, a thinner form of galvanizing is applied by electroplating, called "electrogalvanization". Electroplating is the process of using electrical current to reduce Cations of a desired material from a solution and coat a conductive object Electrogalvanization is the process of bonding a layer of Zinc to Steel in order to protect against Corrosion. However, the protection this process provides is insufficient for products that will be constantly exposed to corrosive materials such as salt water. Nevertheless, most nails made today are electro-galvanized. In Engineering, Woodworking and Construction, a nail is a pin -shaped sharp object of hard Metal, typically Steel,

Galvanic protection (also known as sacrificial-anode or cathodic protection) can be achieved by connecting zinc both electronically (often by direct bonding to the protected metal) and ionically (by submerging both into the same body of electrolyte, such as a drop of rain). A sacrificial anode, or sacrificial rod, is a metallic Anode used in Cathodic protection where it is intended to be dissolved to protect other metallic Cathodic protection ( CP) is a technique to control the Corrosion of a metal surface by making it work as a Cathode of an Electrochemical In such a configuration the zinc is absorbed into the electrolyte in preference to the metal that it protects, and maintains that metal's structure by inducing an electric current. An electrolyte is any substance containing free Ions that behaves as an electrically conductive medium In the usual example, ingots of zinc are used to protect a boat's hull and propellers, with the ocean as the common electrolyte.

As noted previously, both mechanisms are often at work in practical applications. For example, the traditional measure of a coating's effectiveness is resistance to a salt spray. Sea spray is a Spray of Water that forms when Ocean waves crash Thin coatings cannot remain intact indefinitely when subject to surface abrasion, and the galvanic protection offered by zinc can be sharply contrasted to more noble metals. As an example, a scratched or incomplete coating of chromium actually exacerbates corrosion of the underlying steel, since it is less electrochemically active than the substrate. Chromium (ˈkroʊmiəm is a Chemical element which has the symbol Cr and Atomic number 24

Galvanized surface with visible spangle

The size of crystallites in galvanized coatings is an aesthetic feature, known as spangle. A crystallite is a domain of solid-state matter that has the same structure as a single Crystal. By varying the number of particles added for heterogeneous nucleation and the rate of cooling in a hot-dip process, the spangle can be adjusted from an apparently uniform surface (crystallites too small to see with the naked eye) to grains several centimeters wide. Nucleation is the onset of a Phase transition in a small region Visible crystallites are rare in other engineering materials. Protective coatings for steel constitute the largest use of zinc and rely upon the galvanic or sacrificial property of zinc relative to steel.

Thermal diffusion galvanizing is a new "green" process which creates a zinc coating metallurgically similar to hot dip galvanizing. Instead of dipping parts in molten zinc, zinc is applied in a powder form with accelerator chemicals. The parts and the zinc compound are sealed in a drum which is rotated in an oven. Due to accelerator chemicals added to the zinc powder, the zinc/iron diffusion (alloying) takes place at a lower temperature than hot dip galvanizing, and results in a more uniform and wear resistant coating. The process also eliminates the need for hazardous caustic, acid, and flux baths required to prepare parts for hot dip galvanizing. The unique crystal structure formed by the process provides a strong bond with paint, powder coating, and rubber overmolding processes.

Corrosion

Rusted corrugated steel roof

Although galvanizing will inhibit attack of the underlying steel, rusting will be inevitable, especially if the local rainfall is at all acidic in nature. So for example, corrugated iron sheet roofing will start to degrade within a few years despite the protective action of the zinc coating. Corrugated galvanised iron (colloquially corrugated iron, commonly abbreviated CGI is a Building material composed of sheets of hot-dip galvanised Marine environments also lower the lifetime of galvanized iron roofs and similar products, because the high electrical conductivity of sea water encourages and increases the rate of corrosion. Electrical conductivity or specific conductivity is a measure of a material's ability to conduct an Electric current. Seawater is Water from a Sea or Ocean. On average seawater in the world's oceans has a Salinity of about 3 Corrugated steel roofs can last for many years if further protected by a paint layer. Paint is any Liquid, liquifiable or mastic composition which after application to a substrate in a thin layer is converted to an opaque Solid Galvanized car frames may also be at risk, especially where road salting is used extensively.

Variations

Sometimes one can hear the expression in Maltese which is "kullux galvaniz", which would mean that everything is in tip-top shape. One can also use "kullux huwa stylis" which would mean the same thing.

See also

• Sherardising
• Hot-dip galvanizing
• Corrugated galvanised iron
• Galvanism

References

External links

• Life Program regarding liquid waste management in galvanic processes.
• Americam Galvanizers Association