Galvanization
Galvanization or galvanisation refers to any of several
electrochemical processes named after the Italian scientist
Luigi Galvani.
# Originally, galvanization was the administration of electric shocks . It stemmed from Galvani's induction of twitches in severed
frogs' legs, by his accidental generation of
electricity. This archaic sense is the origin of the meaning of galvanized when meaning 'stirred to sudden action'. Its claims to health benefits have largely been disproven, except for some limited uses in psychiatry. See also:
Galvanism, Violet wand
Encyclopedia
Galvanization or
galvanisation refers to any of several
electrochemical processes named after the Italian scientist
Luigi Galvani.
- Originally, galvanization was the administration of electric shocks . It stemmed from Galvani's induction of twitches in severed frogs' legs, by his accidental generation of electricity. This archaic sense is the origin of the meaning of galvanized when meaning 'stirred to sudden action'. Its claims to health benefits have largely been disproven, except for some limited uses in psychiatry. See also: Galvanism
[i] ...
, Violet wand
- 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.
- In current use, it typically means hot-dip galvanizing, a chemical process that is used to coat steel or iron with zinc. This is done to reduce corrosion of the ferrous item; while it is accomplished by non-electrochemical means, it serves an electrochemical purpose.
The remainder of the article is about zinc anti-corrosion coatings.Zinc coatings prevent oxidation of the protected metal by forming a barrier, and by acting as a sacrificial anode if this barrier is damaged.
Zinc oxide is a fine white dust that does not cause a breakdown of the substrate's surface integrity as it is formed. Indeed the zinc oxide, if undisturbed, can act as a barrier to further
oxidation, in a way similar to the protection afforded to
aluminium and
stainless steels by their oxide layers.
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 "electro-galvanization". 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.
Galvanic protection can be achieved by connecting zinc both electronically and ionically . 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. 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. 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.
The size of
crystallites in galvanized coatings is an aesthetic feature, known as
spangle. 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 to grains several centimeters wide. Visible crystallites are rare in other engineering materials.
See also
