Nickel is a chemical element
with the chemical symbol Ni and atomic number 28. It is a
silvery-white lustrous metal with a slight golden tinge.
Nickel belongs to the transition metals and is hard and
ductile. Pure nickel shows a significant chemical activity
that can be observed when nickel is powdered to maximize the
exposed surface area on which reactions can occur, but
larger pieces of the metal are slow to react with air at
ambient conditions due to the formation of a protective
oxide surface. Even then, nickel is reactive enough with
oxygen so that native nickel is rarely found on Earth's
surface, being mostly confined to the interiors of larger
nickel–iron meteorites that were protected from oxidation
during their time in space. On Earth, such native nickel is
always found in combination with iron, a reflection of those
elements' origin as major end products of supernova
nucleosynthesis. An iron–nickel mixture is thought to
compose Earth's inner core.
The use of nickel (as a natural meteoric nickel–iron alloy)
has been traced as far back as 3500 BC. Nickel was first
isolated and classified as a chemical element in 1751 by
Axel Fredrik Cronstedt, who initially mistook its ore for a
copper mineral. The element name comes from a mischievous
sprite of German miner's mythology, Nickel (similar to Old
Nick), that personified the fact that copper-nickel ores
resisted refinement into copper. Nickel's most important
modern ore minerals are laterites, including limonite,
garnierite, and pentlandite. Major production sites include
Sudbury region in Canada (which is thought to be of meteoric
origin), New Caledonia in the Pacific and Norilsk in Russia.
Because of nickel's slow rate of oxidation at room
temperature, it is considered corrosion-resistant.
Historically this has led to its use for plating metals such
as iron and brass, to its use for chemical apparatus, and
its use in certain alloys that will retain a high silvery
polish, such as German silver. About 6% of world nickel
production is still used for corrosion-resistant pure-nickel
plating. Nickel was once a common component of coins, but
has largely been replaced by cheaper iron for this purpose,
especially since the metal has proven to be a skin allergen
for some people.
Nickel is one of the four elements that are ferromagnetic
around room temperature. Alnico permanent magnets based
partly on nickel are of intermediate strength between
iron-based permanent magnets and rare-earth magnets. The
metal is chiefly valuable in the modern world for the alloys
it forms; about 60% of world production is used in
nickel-steels (particularly stainless steel). Other common
alloys, as well as some new superalloys, make up most of the
remainder of world nickel use, with chemical uses for nickel
compounds consuming less than 3% of production. As a
compound, nickel has a number of niche chemical
manufacturing uses, such as a catalyst for hydrogenation.
Enzymes of some microorganisms and plants contain nickel as
an active center, which makes the metal an essential
nutrient for them.