Galvanization

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Galvanized surface with visible spangle Feuerverzinktes Gelander.jpg
Galvanized surface with visible spangle

Galvanization or galvanizing (also spelled galvanisation or galvanising) [1] is the process of applying a protective zinc coating to steel or iron, to prevent rusting. The most common method is hot-dip galvanizing, in which the parts are submerged in a bath of hot, molten zinc. [2]

Contents

Protective action

The zinc coating, when intact, prevents corrosive substances from reaching the underlying iron. [3] Additional electroplating such as a chromate conversion coating may be applied to provide further surface passivation to the substrate material. [4]

History and etymology

Galvanized nails NailsCloseup.jpg
Galvanized nails

The earliest known example of galvanized iron was encountered by Europeans on 17th-century Indian armour in the Royal Armouries Museum collection. [5]

The term "galvanized" continues to be used metaphorically of any stimulus which results in activity by a person or group of people. [6]

In modern usage, the term "galvanizing" has largely come to be associated with zinc coatings, to the exclusion of other metals. Galvanic paint, a precursor to hot-dip galvanizing, was patented by Stanislas Sorel, of Paris, on June 10, 1837, as an adoption of a term from a highly fashionable field of contemporary science, despite having no evident relation to it. [7]

Methods

Hot-dip galvanizing deposits a thick, robust layer of zinc iron alloys on the surface of a steel item. In the case of automobile bodies, where additional decorative coatings of paint will be applied, a thinner form of galvanizing is applied by electrogalvanizing. The hot-dip process generally does not reduce strength to a measurable degree, with the exception of high-strength steels where hydrogen embrittlement can become a problem. [8]

Thermal diffusion galvanizing, or Sherardizing, provides a zinc diffusion coating on iron- or copper-based materials. [9] [10]

Eventual corrosion

Rusted corrugated steel roof Rust 1.jpeg
Rusted corrugated steel roof

Galvanized steel can last for many decades if other supplementary measures are maintained, such as paint coatings and additional sacrificial anodes. The rate of corrosion in non-salty environments is caused mainly by levels of sulfur dioxide in the air. [11]

Galvanized construction steel

This is the most common use for galvanized metal, and hundreds of thousands of tons of steel products are galvanized annually worldwide. In developed countries most larger cities have several galvanizing factories, and many items of steel manufacture are galvanized for protection. Typically these include: street furniture, building frameworks, balconies, verandahs, staircases, ladders, walkways, and more. Hot dip galvanized steel is also used for making steel frames as a basic construction material for steel frame buildings. [12]

Galvanized piping

In the early 20th century, galvanized piping replaced previously-used cast iron and lead in cold-water plumbing. Typically, galvanized piping rusts from the inside out, building up layers of plaque on the inside of the piping, causing both water pressure problems and eventual pipe failure. These plaques can flake off, leading to visible impurities in water and a slight metallic taste. The life expectancy of galvanized piping is about 40–50 years, [13] but it may vary on how well the pipes were built and installed. Pipe longevity also depends on the thickness of zinc in the original galvanizing, which ranges on a scale from G01 to G360. [14]

See also

Related Research Articles

<span class="mw-page-title-main">Rust</span> Type of iron oxide

Rust is an iron oxide, a usually reddish-brown oxide formed by the reaction of iron and oxygen in the catalytic presence of water or air moisture. Rust consists of hydrous iron(III) oxides (Fe2O3·nH2O) and iron(III) oxide-hydroxide (FeO(OH), Fe(OH)3), and is typically associated with the corrosion of refined iron.

<span class="mw-page-title-main">Corrosion</span> Gradual destruction of materials by chemical reaction with its environment

Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials by chemical or electrochemical reaction with their environment. Corrosion engineering is the field dedicated to controlling and preventing corrosion.

<span class="mw-page-title-main">Galvanic anode</span> Main component of cathodic protection

A galvanic anode, or sacrificial anode, is the main component of a galvanic cathodic protection (CP) system used to protect buried or submerged metal structures from corrosion.

<span class="mw-page-title-main">Hot-dip galvanization</span> Process of coating iron or steel with molten zinc

Hot-dip galvanization is a form of galvanization. It is the process of coating iron and steel with zinc, which alloys with the surface of the base metal when immersing the metal in a bath of molten zinc at a temperature of around 450 °C (842 °F). When exposed to the atmosphere, the pure zinc (Zn) reacts with oxygen (O2) to form zinc oxide (ZnO), which further reacts with carbon dioxide (CO2) to form zinc carbonate (ZnCO3), a usually dull grey, fairly strong material that protects the steel underneath from further corrosion in many circumstances. Galvanized steel is widely used in applications where corrosion resistance is needed without the cost of stainless steel, and is considered superior in terms of cost and life-cycle. It can be identified by the crystallization patterning on the surface (often called a "spangle").

<span class="mw-page-title-main">Cathodic protection</span> Corrosion prevention technique

Cathodic protection is a technique used to control the corrosion of a metal surface by making it the cathode of an electrochemical cell. 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 instead of the protected metal. For structures such as long pipelines, where passive galvanic cathodic protection is not adequate, an external DC electrical power source is used to provide sufficient current.

PPGI is pre-painted galvanised iron, also known as pre-coated steel, coil coated steel, color coated steel etc., typically with a hot dip zinc coated steel substrate.

<span class="mw-page-title-main">Chromate conversion coating</span> Chemical treatment of metals

Chromate conversion coating or alodine coating is a type of conversion coating used to passivate steel, aluminium, zinc, cadmium, copper, silver, titanium, magnesium, and tin alloys. The coating serves as a corrosion inhibitor, as a primer to improve the adherence of paints and adhesives, as a decorative finish, or to preserve electrical conductivity. It also provides some resistance to abrasion and light chemical attack on soft metals.

A conversion coating is a chemical or electro-chemical treatment applied to manufactured parts that superficially converts the material into a thin adhering coating of an insoluble compound. These coatings are commonly applied to protect the part against corrosion, to improve the adherence of other coatings, for lubrication, or for aesthetic purposes.

Sherardising is a process of galvanization of ferrous metal surfaces, also called vapour galvanising and dry galvanizing. The process is named after British metallurgist Sherard Osborn Cowper-Coles who invented and patented the method c. 1900. This process involves heating the steel parts up to c. 500 °C in a closed rotating drum that contains metallic zinc dust and possibly an inert filler, such as sand. At temperatures above 300 °C, zinc evaporates and diffuses into the steel substrate forming diffusion bonded Zn-Fe-phases.

The salt spray test is a standardized and popular corrosion test method, used to check corrosion resistance of materials and surface coatings. Usually, the materials to be tested are metallic and finished with a surface coating which is intended to provide a degree of corrosion protection to the underlying metal.

Phosphate conversion coating is a chemical treatment applied to steel parts that creates a thin adhering layer of iron, zinc, or manganese phosphates, to achieve corrosion resistance, lubrication, or as a foundation for subsequent coatings or painting. It is one of the most common types of conversion coating. The process is also called phosphate coating, phosphatization, phosphatizing, or phosphating. It is also known by the trade name Parkerizing, especially when applied to firearms and other military equipment.

<span class="mw-page-title-main">Aluminized steel</span> Steel coated with aluminum or aluminum-silicon combination

Aluminized steel is steel that has been plated with aluminium or aluminium-silicon alloy, in a process analogous to hot-dip galvanizing. The steel workpiece is immersed in molten aluminum to produce a tight metallic bond between the steel and coating. The product has a unique combination of properties possessed by neither steel alone nor aluminium alone. Aluminized steel is more resistant to corrosion than bare steel while retaining properties of steel, at temperature lower than the melting point of aluminum, 800 °C (1,470 °F). Common applications include heat exchangers in residential furnaces, commercial rooftop HVAC units, automotive mufflers, ovens, kitchen ranges, water heaters, fireplaces, barbecue burners, and baking pans. Aluminized steel transfers heat more effectively than bare steel. It often serves where galvanized steel might have been used historically, without galvanized steel's drawbacks.

Electrogalvanizing is a process in which a layer of zinc is bonded to steel in order to protect against corrosion. The process involves electroplating, running a current of electricity through a saline/zinc solution with a zinc anode and steel conductor. Such Zinc electroplating or Zinc alloy electroplating maintains a dominant position among other electroplating process options, based upon electroplated tonnage per annum. According to the International Zinc Association, more than 5 million tons are used yearly for both hot dip galvanizing and electroplating. The plating of zinc was developed at the beginning of the 20th century. At that time, the electrolyte was cyanide based. A significant innovation occurred in the 1960s, with the introduction of the first acid chloride based electrolyte. The 1980s saw a return to alkaline electrolytes, only this time, without the use of cyanide. The most commonly used electrogalvanized cold rolled steel is SECC, acronym of "Steel, Electrogalvanized, Cold-rolled, Commercial quality". Compared to hot dip galvanizing, electroplated zinc offers these significant advantages:

Galvannealed or galvanneal is the result from the processes of galvanizing followed by annealing of sheet steel.

<span class="mw-page-title-main">Architectural metals</span>

Metals used for architectural purposes include lead, for water pipes, roofing, and windows; tin, formed into tinplate; zinc, copper and aluminium, in a range of applications including roofing and decoration; and iron, which has structural and other uses in the form of cast iron or wrought iron, or made into steel. Metal alloys used in building include bronze ; brass ; monel metal and nickel silver, mainly consisting of nickel and copper; and stainless steel, with important components of nickel and chromium.

Stanislas Sorel was a French civil engineer, inventor, and chemist, raised the son of a poor clock-maker.

Corrosion engineering is an engineering specialty that applies scientific, technical, engineering skills, and knowledge of natural laws and physical resources to design and implement materials, structures, devices, systems, and procedures to manage corrosion. From a holistic perspective, corrosion is the phenomenon of metals returning to the state they are found in nature. The driving force that causes metals to corrode is a consequence of their temporary existence in metallic form. To produce metals starting from naturally occurring minerals and ores, it is necessary to provide a certain amount of energy, e.g. Iron ore in a blast furnace. It is therefore thermodynamically inevitable that these metals when exposed to various environments would revert to their state found in nature. Corrosion and corrosion engineering thus involves a study of chemical kinetics, thermodynamics, electrochemistry and materials science.

A sacrificial metal is a metal used as a sacrificial anode in cathodic protection that corrodes to prevent a primary metal from corrosion or rusting. It may also be used for galvanization.

Zinc flake coatings are non-electrolytically applied coatings, which provide good protection against corrosion. These coatings consist of a mixture of zinc and aluminium flakes, which are bonded together by an inorganic matrix.

<span class="mw-page-title-main">Galvanic corrosion</span> Electrochemical process

Galvanic corrosion is an electrochemical process in which one metal corrodes preferentially when it is in electrical contact with another, in the presence of an electrolyte. A similar galvanic reaction is exploited in primary cells to generate a useful electrical voltage to power portable devices.

References

  1. "Galvanize". Cambridge English Dictionary . Retrieved 10 November 2019.
  2. "Galvanizing - an overview | ScienceDirect Topics". www.sciencedirect.com. Retrieved 2022-10-17.
  3. "How to Galvanize Metal to Protect Pipes". www.appmfg.com. Retrieved 3 February 2022.
  4. Magalhães, A. A. O; Margarit, I. C. P; Mattos, O. R (1999-07-31). "Electrochemical characterization of chromate coatings on galvanized steel". Electrochimica Acta. 44 (24): 4281–4287. doi:10.1016/S0013-4686(99)00143-7. ISSN   0013-4686.
  5. ZINC COATINGS OF INDIAN PLATE AND MAIL ARMOUR. Summary of XRF analysis conducted in September 1999 by the Royal Armouries Museum in Leeds and written up as part of a thesis by Helen Bowstead Stallybrass at the Department of Archaeological Sciences, Bradford University.
  6. Murray, James A. H.; et al., eds. (1989). The Oxford English Dictionary . Vol. VI (2 ed.). Oxford University Press. p. 340. ISBN   0 19 861218-4.
  7. Sorel, M. (1838). "Specification of a Patent for a process for protecting articles made of Iron or Steel from oxidation". Journal of the Franklin Institute (Philadelphia, Pa.). Pergamon Press.
  8. "Steel Selection". American Galvanizers Association. Archived from the original on 21 August 2013. Retrieved 3 April 2015.
  9. Porter, Frank C. (1991). Zinc Handbook. CRC Press. ISBN   978-0-8247-8340-2.
  10. Natrup, F.; Graf, W. (21 November 2014). "20 – Sherardizing: corrosion protection of steels by zinc diffusion coatings". In Mittemeijer, Eric J.; Somers, Marcel A. J. (eds.). Thermochemical Surface Engineering of Steels: Improving Materials Performance. Elsevier Science. p. 737. ISBN   978-0-85709-652-4.
  11. "Atmospheric Resistance". Galvanising Association (UK). Archived from the original on 2014-02-22.
  12. marshall (2019-10-11). "Galvanized Steel: Types, Uses, Benefits". National Material Company – Steel Processing Facilities. Retrieved 2021-02-06.
  13. Biard & Crockett (2016-05-16). "How Long Will My Galvanized Pipes Last?". Biard & Crockett. Retrieved 2021-02-06.
  14. American Galvanizers Association. "Zinc Coatings" (PDF). courtgalvanizinginc.com.{{cite web}}: CS1 maint: url-status (link)