Zinc is a chemical element with symbol Zn
and atomic number 30. It is the first element
in group 12 of the periodic table. In some
respects zinc is chemically similar to magnesium:
both elements exhibit only one normal oxidation
state (+2), and the Zn2+ and Mg2+ ions are
of similar size. Zinc is the 24th most abundant
element in Earth's crust and has five stable
isotopes. The most common zinc ore is sphalerite
(zinc blende), a zinc sulfide mineral. The
largest workable lodes are in Australia, Asia,
and the United States. Zinc is refined by
froth flotation of the ore, roasting, and
final extraction using electricity (electrowinning).
Brass, an alloy of copper and zinc in various
proportions, was used as early as the third
millennium BC in the Aegean, Iraq, the United
Arab Emirates, Kalmykia, Turkmenistan and
Georgia, and the second millennium BC in West
India, Uzbekistan, Iran, Syria, Iraq, and
Israel (Judea). Zinc metal was not produced
on a large scale until the 12th century in
India, though it was known to the ancient
Romans and Greeks. The mines of Rajasthan
have given definite evidence of zinc production
going back to the 6th century BC. To date,
the oldest evidence of pure zinc comes from
Zawar, in Rajasthan, as early as the 9th century
AD when a distillation process was employed
to make pure zinc. Alchemists burned zinc
in air to form what they called "philosopher's
wool" or "white snow".
The element was probably named by the alchemist
Paracelsus after the German word Zinke (prong,
tooth). German chemist Andreas Sigismund Marggraf
is credited with discovering pure metallic
zinc in 1746. Work by Luigi Galvani and Alessandro
Volta uncovered the electrochemical properties
of zinc by 1800. Corrosion-resistant zinc
plating of iron (hot-dip galvanizing) is the
major application for zinc. Other applications
are in electrical batteries, small non-structural
castings, and alloys such as brass. A variety
of zinc compounds are commonly used, such
as zinc carbonate and zinc gluconate (as dietary
supplements), zinc chloride (in deodorants),
zinc pyrithione (anti-dandruff shampoos),
zinc sulfide (in luminescent paints), and
zinc methyl or zinc diethyl in the organic
laboratory.
Zinc is an essential mineral, including to
prenatal and postnatal development. Zinc deficiency
affects about two billion people in the developing
world and is associated with many diseases.
In children, deficiency causes growth retardation,
delayed sexual maturation, infection susceptibility,
and diarrhea. Enzymes with a zinc atom in
the reactive center are widespread in biochemistry,
such as alcohol dehydrogenase in humans. Consumption
of excess zinc can cause ataxia, lethargy,
and copper deficiency.
== Characteristics ==
=== Physical properties ===
Zinc is a bluish-white, lustrous, diamagnetic
metal, though most common commercial grades
of the metal have a dull finish. It is somewhat
less dense than iron and has a hexagonal crystal
structure, with a distorted form of hexagonal
close packing, in which each atom has six
nearest neighbors (at 265.9 pm) in its own
plane and six others at a greater distance
of 290.6 pm. The metal is hard and brittle
at most temperatures but becomes malleable
between 100 and 150 °C. Above 210 °C, the
metal becomes brittle again and can be pulverized
by beating. Zinc is a fair conductor of electricity.
For a metal, zinc has relatively low melting
(419.5 °C) and boiling points (907 °C).
The melting point is the lowest of all the
d-block metals aside from mercury and cadmium;
for this, among other reasons, zinc, cadmium,
and mercury are often not considered to be
transition metals like the rest of the d-block
metals are.Many alloys contain zinc, including
brass. Other metals long known to form binary
alloys with zinc are aluminium, antimony,
bismuth, gold, iron, lead, mercury, silver,
tin, magnesium, cobalt, nickel, tellurium,
and sodium. Although neither zinc nor zirconium
are ferromagnetic, their alloy ZrZn2 exhibits
ferromagnetism below 35 K.A bar of zinc generates
a characteristic sound when bent, similar
to tin cry.
=== Occurrence ===
Zinc makes up about 75 ppm (0.0075%) of Earth's
crust, making it the 24th most abundant element.
Soil contains zinc in 5–770 ppm with an
average 64 ppm. Seawater has only 30 ppb and
the atmosphere, 0.1–4 µg/m3. The element
is normally found in association with other
base metals such as copper and lead in ores.
Zinc is a chalcophile, meaning the element
is more likely to be found in minerals together
with sulfur and other heavy chalcogens, rather
than with the light chalcogen oxygen or with
non-chalcogen electronegative elements such
as the halogens. Sulfides formed as the crust
solidified under the reducing conditions of
the early Earth's atmosphere. Sphalerite,
which is a form of zinc sulfide, is the most
heavily mined zinc-containing ore because
its concentrate contains 60–62% zinc.Other
source minerals for zinc include smithsonite
(zinc carbonate), hemimorphite (zinc silicate),
wurtzite (another zinc sulfide), and sometimes
hydrozincite (basic zinc carbonate). With
the exception of wurtzite, all these other
minerals were formed by weathering of the
primordial zinc sulfides.Identified world
zinc resources total about 1.9–2.8 billion
tonnes. Large deposits are in Australia, Canada
and the United States, with the largest reserves
in Iran. The most recent estimate of reserve
base for zinc (meets specified minimum physical
criteria related to current mining and production
practices) was made in 2009 and calculated
to be roughly 480 Mt. Zinc reserves, on the
other hand, are geologically identified ore
bodies whose suitability for recovery is economically
based (location, grade, quality, and quantity)
at the time of determination. Since exploration
and mine development is an ongoing process,
the amount of zinc reserves is not a fixed
number and sustainability of zinc ore supplies
cannot be judged by simply extrapolating the
combined mine life of today's zinc mines.
This concept is well supported by data from
the United States Geological Survey (USGS),
which illustrates that although refined zinc
production increased 80% between 1990 and
2010, the reserve lifetime for zinc has remained
unchanged. About 346 million tonnes have been
extracted throughout history to 2002, and
scholars have estimated that about 109–305
million tonnes are in use.
=== Isotopes ===
Five isotopes of zinc occur in nature. 64Zn
is the most abundant isotope (48.63% natural
abundance). That isotope has such a long half-life,
at 4.3×1018 years, that its radioactivity
can be ignored. Similarly, 70Zn (0.6%), with
a half-life of 1.3×1016 years is not usually
considered to be radioactive. The other isotopes
found in nature are 66Zn (28%), 67Zn (4%)
and 68Zn (19%).
Several dozen radioisotopes have been characterized.
65Zn, which has a half-life of 243.66 days,
is the least active radioisotope, followed
by 72Zn with a half-life of 46.5 hours. Zinc
has 10 nuclear isomers. 69mZn has the longest
half-life, 13.76 h. The superscript m indicates
a metastable isotope. The nucleus of a metastable
isotope is in an excited state and will return
to the ground state by emitting a photon in
the form of a gamma ray. 61Zn has three excited
metastable states and 73Zn has two. The isotopes
65Zn, 71Zn, 77Zn and 78Zn each have only one
excited metastable state.The most common decay
mode of a radioisotope of zinc with a mass
number lower than 66 is electron capture.
The decay product resulting from electron
capture is an isotope of copper.
n30Zn + e− → n29CuThe most common decay
mode of a radioisotope of zinc with mass number
higher than 66 is beta decay (β−), which
produces an isotope of gallium.
n30Zn → n31Ga + e− + νe
== Compounds and chemistry ==
=== 
Reactivity ===
Zinc has an electron configuration of [Ar]3d104s2
and is a member of the group 12 of the periodic
table. It is a moderately reactive metal and
strong reducing agent. The surface of the
pure metal tarnishes quickly, eventually forming
a protective passivating layer of the basic
zinc carbonate, Zn5(OH)6(CO3)2, by reaction
with atmospheric carbon dioxide. This layer
helps prevent further reaction with air and
water.
Zinc burns in air with a bright bluish-green
flame, giving off fumes of zinc oxide. Zinc
reacts readily with acids, alkalis and other
non-metals. Extremely pure zinc reacts only
slowly at room temperature with acids. Strong
acids, such as hydrochloric or sulfuric acid,
can remove the passivating layer and subsequent
reaction with water releases hydrogen gas.The
chemistry of zinc is dominated by the +2 oxidation
state. When compounds in this oxidation state
are formed, the outer shell s electrons are
lost, yielding a bare zinc ion with the electronic
configuration [Ar]3d10. In aqueous solution
an octahedral complex, [Zn(H2O)6]2+ is the
predominant species. The volatilization of
zinc in combination with zinc chloride at
temperatures above 285 °C indicates the formation
of Zn2Cl2, a zinc compound with a +1 oxidation
state. No compounds of zinc in oxidation states
other than +1 or +2 are known. Calculations
indicate that a zinc compound with the oxidation
state of +4 is unlikely to exist.Zinc chemistry
is similar to the chemistry of the late first-row
transition metals, nickel and copper, though
it has a filled d-shell and compounds are
diamagnetic and mostly colorless. The ionic
radii of zinc and magnesium happen to be nearly
identical. Because of this some of the equivalent
salts have the same crystal structure, and
in other circumstances where ionic radius
is a determining factor, the chemistry of
zinc has much in common with that of magnesium.
In other respects, there is little similarity
with the late first-row transition metals.
Zinc tends to form bonds with a greater degree
of covalency and much more stable complexes
with N- and S- donors. Complexes of zinc are
mostly 4- or 6- coordinate although 5-coordinate
complexes are known.
=== Zinc(I) compounds ===
Zinc(I) compounds are rare and need bulky
ligands to stabilize the low oxidation state.
Most zinc(I) compounds contain formally the
[Zn2]2+ core, which is analogous to the [Hg2]2+
dimeric cation present in mercury(I) compounds.
The diamagnetic nature of the ion confirms
its dimeric structure. The first zinc(I) compound
containing the Zn–Zn bond, (η5-C5Me5)2Zn2,
is also the first dimetallocene. The [Zn2]2+
ion rapidly disproportionates into zinc metal
and zinc(II), and has been obtained only a
yellow glass only by cooling a solution of
metallic zinc in molten ZnCl2.
=== Zinc(II) compounds ===
Binary compounds of zinc are known for most
of the metalloids and all the nonmetals except
the noble gases. The oxide ZnO is a white
powder that is nearly insoluble in neutral
aqueous solutions, but is amphoteric, dissolving
in both strong basic and acidic solutions.
The other chalcogenides (ZnS, ZnSe, and ZnTe)
have varied applications in electronics and
optics. Pnictogenides (Zn3N2, Zn3P2, Zn3As2
and Zn3Sb2), the peroxide (ZnO2), the hydride
(ZnH2), and the carbide (ZnC2) are also known.
Of the four halides, ZnF2 has the most ionic
character, while the others (ZnCl2, ZnBr2,
and ZnI2) have relatively low melting points
and are considered to have more covalent character.In
weak basic solutions containing Zn2+ ions,
the hydroxide Zn(OH)2 forms as a white precipitate.
In stronger alkaline solutions, this hydroxide
is dissolved to form zincates ([Zn(OH)4]2−).
The nitrate Zn(NO3)2, chlorate Zn(ClO3)2,
sulfate ZnSO4, phosphate Zn3(PO4)2, molybdate
ZnMoO4, cyanide Zn(CN)2, arsenite Zn(AsO2)2,
arsenate Zn(AsO4)2·8H2O and the chromate
ZnCrO4 (one of the few colored zinc compounds)
are a few examples of other common inorganic
compounds of zinc. One of the simplest examples
of an organic compound of zinc is the acetate
(Zn(O2CCH3)2).
Organozinc compounds are those that contain
zinc–carbon covalent bonds. Diethylzinc
((C2H5)2Zn) is a reagent in synthetic chemistry.
It was first reported in 1848 from the reaction
of zinc and ethyl iodide, and was the first
compound known to contain a metal–carbon
sigma bond.
=== Test for zinc ===
Cobalticyanide paper (Rinnmann's test for
Zn) can be used as a chemical indicator for
zinc. 4 g of K3Co(CN)6 and 1 g of KClO3 is
dissolved on 100 ml of water. Paper is dipped
in the solution and dried at 100 °C. One
drop of the sample is dropped onto the dry
paper and heated. A green disc indicates the
presence of zinc.
== History ==
=== 
Ancient use ===
Various isolated examples of the use of impure
zinc in ancient times have been discovered.
Zinc ores were used to make the zinc–copper
alloy brass thousands of years prior to the
discovery of zinc as a separate element. Judean
brass from the 14th to 10th centuries BC contains
23% zinc.Knowledge of how to produce brass
spread to Ancient Greece by the 7th century
BC, but few varieties were made. Ornaments
made of alloys containing 80–90% zinc, with
lead, iron, antimony, and other metals making
up the remainder, have been found that are
2,500 years old. A possibly prehistoric statuette
containing 87.5% zinc was found in a Dacian
archaeological site.The oldest known pills
were made of the zinc carbonates hydrozincite
and smithsonite. The pills were used for sore
eyes and were found aboard the Roman ship
Relitto del Pozzino, wrecked in 140 BC.The
manufacture of brass was known to the Romans
by about 30 BC. They made brass by heating
powdered calamine (zinc silicate or carbonate),
charcoal and copper together in a crucible.
The resulting calamine brass was then either
cast or hammered into shape for use in weaponry.
Some coins struck by Romans in the Christian
era are made of what is probably calamine
brass.Strabo writing in the 1st century BC
(but quoting a now lost work of the 4th century
BC historian Theopompus) mentions "drops of
false silver" which when mixed with copper
make brass. This may refer to small quantities
of zinc that is a by-product of smelting sulfide
ores. Zinc in such remnants in smelting ovens
was usually discarded as it was thought to
be worthless.The Berne zinc tablet is a votive
plaque dating to Roman Gaul made of an alloy
that is mostly zinc.The Charaka Samhita, thought
to have been written between 300 and 500 AD,
mentions a metal which, when oxidized, produces
pushpanjan, thought to be zinc oxide. Zinc
mines at Zawar, near Udaipur in India, have
been active since the Mauryan period (c. 
322 and 187 BCE). The smelting of metallic
zinc here, however, appears to have begun
around the 12th century AD. One estimate is
that this location produced an estimated million
tonnes of metallic zinc and zinc oxide from
the 12th to 16th centuries. Another estimate
gives a total production of 60,000 tonnes
of metallic zinc over this period. The Rasaratna
Samuccaya, written in approximately the 13th
century AD, mentions two types of zinc-containing
ores: one used for metal extraction and another
used for medicinal purposes.
=== Early studies and naming ===
Zinc was distinctly recognized as a metal
under the designation of Yasada or Jasada
in the medical Lexicon ascribed to the Hindu
king Madanapala (of Taka dynasty) and written
about the year 1374. Smelting and extraction
of impure zinc by reducing calamine with wool
and other organic substances was accomplished
in the 13th century in India. The Chinese
did not learn of the technique until the 17th
century.
Alchemists burned zinc metal in air and collected
the resulting zinc oxide on a condenser. Some
alchemists called this zinc oxide lana philosophica,
Latin for "philosopher's wool", because it
collected in wooly tufts, whereas others thought
it looked like white snow and named it nix
album.The name of the metal was probably first
documented by Paracelsus, a Swiss-born German
alchemist, who referred to the metal as "zincum"
or "zinken" in his book Liber Mineralium II,
in the 16th century. The word is probably
derived from the German zinke, and supposedly
meant "tooth-like, pointed or jagged" (metallic
zinc crystals have a needle-like appearance).
Zink could also imply "tin-like" because of
its relation to German zinn meaning tin. Yet
another possibility is that the word is derived
from the Persian word سنگ seng meaning
stone. The metal was also called Indian tin,
tutanego, calamine, and spinter.German metallurgist
Andreas Libavius received a quantity of what
he called "calay" of Malabar from a cargo
ship captured from the Portuguese in 1596.
Libavius described the properties of the sample,
which may have been zinc. Zinc was regularly
imported to Europe from the Orient in the
17th and early 18th centuries, but was at
times very expensive.
=== Isolation ===
Metallic zinc was isolated in India by 1300
AD, much earlier than in the West. Before
it was isolated in Europe, it was imported
from India in about 1600 CE. Postlewayt's
Universal Dictionary, a contemporary source
giving technological information in Europe,
did not mention zinc before 1751 but the element
was studied before then.Flemish metallurgist
and alchemist P. M. de Respour reported that
he had extracted metallic zinc from zinc oxide
in 1668. By the start of the 18th century,
Étienne François Geoffroy described how
zinc oxide condenses as yellow crystals on
bars of iron placed above zinc ore that is
being smelted. In Britain, John Lane is said
to have carried out experiments to smelt zinc,
probably at Landore, prior to his bankruptcy
in 1726.In 1738 in Great Britain, William
Champion patented a process to extract zinc
from calamine in a vertical retort style smelter.
His technique resembled that used at Zawar
zinc mines in Rajasthan, but no evidence suggests
he visited the Orient. Champion's process
was used through 1851.German chemist Andreas
Marggraf normally gets credit for discovering
pure metallic zinc, even though Swedish chemist
Anton von Swab had distilled zinc from calamine
four years previously. In his 1746 experiment,
Marggraf heated a mixture of calamine and
charcoal in a closed vessel without copper
to obtain a metal. This procedure became commercially
practical by 1752.
=== Later work ===
William Champion's brother, John, patented
a process in 1758 for calcining zinc sulfide
into an oxide usable in the retort process.
Prior to this, only calamine could be used
to produce zinc. In 1798, Johann Christian
Ruberg improved on the smelting process by
building the first horizontal retort smelter.
Jean-Jacques Daniel Dony built a different
kind of horizontal zinc smelter in Belgium
that processed even more zinc.
Italian doctor Luigi Galvani discovered in
1780 that connecting the spinal cord of a
freshly dissected frog to an iron rail attached
by a brass hook caused the frog's leg to twitch.
He incorrectly thought he had discovered an
ability of nerves and muscles to create electricity
and called the effect "animal electricity".
The galvanic cell and the process of galvanization
were both named for Luigi Galvani, and his
discoveries paved the way for electrical batteries,
galvanization, and cathodic protection.Galvani's
friend, Alessandro Volta, continued researching
the effect and invented the Voltaic pile in
1800. The basic unit of Volta's pile was a
simplified galvanic cell, made of plates of
copper and zinc separated by an electrolyte
and connected by a conductor externally. The
units were stacked in series to make the Voltaic
cell, which produced electricity by directing
electrons from the zinc to the copper and
allowing the zinc to corrode.The non-magnetic
character of zinc and its lack of color in
solution delayed discovery of its importance
to biochemistry and nutrition. This changed
in 1940 when carbonic anhydrase, an enzyme
that scrubs carbon dioxide from blood, was
shown to have zinc in its active site. The
digestive enzyme carboxypeptidase became the
second known zinc-containing enzyme in 1955.
== Production ==
=== 
Mining and processing ===
Zinc is the fourth most common metal in use,
trailing only iron, aluminium, and copper
with an annual production of about 13 million
tonnes. The world's largest zinc producer
is Nyrstar, a merger of the Australian OZ
Minerals and the Belgian Umicore. About 70%
of the world's zinc originates from mining,
while the remaining 30% comes from recycling
secondary zinc. Commercially pure zinc is
known as Special High Grade, often abbreviated
SHG, and is 99.995% pure.Worldwide, 95% of
new zinc is mined from sulfidic ore deposits,
in which sphalerite (ZnS) is nearly always
mixed with the sulfides of copper, lead and
iron. Zinc mines are scattered throughout
the world, with the main areas being China,
Australia, and Peru. China produced 38% of
the global zinc output in 2014.Zinc metal
is produced using extractive metallurgy. The
ore is finely ground, then put through froth
flotation to separate minerals from gangue
(on the property of hydrophobicity), to get
a zinc sulfide ore concentrate consisting
of about 50% zinc, 32% sulfur, 13% iron, and
5% SiO2.Roasting converts the zinc sulfide
concentrate to zinc oxide:
2 ZnS + 3 O2 → 2 ZnO + 2 SO2The sulfur dioxide
is used for the production of sulfuric acid,
which is necessary for the leaching process.
If deposits of zinc carbonate, zinc silicate,
or zinc spinel (like the Skorpion Deposit
in Namibia) are used for zinc production,
the roasting can be omitted.For further processing
two basic methods are used: pyrometallurgy
or electrowinning. Pyrometallurgy reduces
zinc oxide with carbon or carbon monoxide
at 950 °C (1,740 °F) into the metal, which
is distilled as zinc vapor to separate it
from other metals, which are not volatile
at those temperatures. The zinc vapor is collected
in a condenser. The equations below describe
this process:
2 ZnO + C → 2 Zn + CO2
ZnO + CO → Zn + CO2In electrowinning, zinc
is leached from the ore concentrate by sulfuric
acid:
ZnO + H2SO4 → ZnSO4 + H2OFinally, the zinc
is reduced by electrolysis.
2 ZnSO4 + 2 H2O → 2 Zn + 2 H2SO4 + O2The
sulfuric acid is regenerated and recycled
to the leaching step.
When galvanised feedstock is fed to an electric
arc furnace, the zinc is recovered from the
dust by a number of processes, predominately
the Waelz process (90% as of 2014).
=== Environmental impact ===
Refinement of sulfidic zinc ores produces
large volumes of sulfur dioxide and cadmium
vapor. Smelter slag and other residues contain
significant quantities of metals. About 1.1
million tonnes of metallic zinc and 130 thousand
tonnes of lead were mined and smelted in the
Belgian towns of La Calamine and Plombières
between 1806 and 1882. The dumps of the past
mining operations leach zinc and cadmium,
and the sediments of the Geul River contain
non-trivial amounts of metals. About two thousand
years ago, emissions of zinc from mining and
smelting totaled 10 thousand tonnes a year.
After increasing 10-fold from 1850, zinc emissions
peaked at 3.4 million tonnes per year in the
1980s and declined to 2.7 million tonnes in
the 1990s, although a 2005 study of the Arctic
troposphere found that the concentrations
there did not reflect the decline. Anthropogenic
and natural emissions occur at a ratio of
20 to 1.Zinc in rivers flowing through industrial
and mining areas can be as high as 20 ppm.
Effective sewage treatment greatly reduces
this; treatment along the Rhine, for example,
has decreased zinc levels to 50 ppb. Concentrations
of zinc as low as 2 ppm adversely affects
the amount of oxygen that fish can carry in
their blood.
Soils contaminated with zinc from mining,
refining, or fertilizing with zinc-bearing
sludge can contain several grams of zinc per
kilogram of dry soil. Levels of zinc in excess
of 500 ppm in soil interfere with the ability
of plants to absorb other essential metals,
such as iron and manganese. Zinc levels of
2000 ppm to 180,000 ppm (18%) have been recorded
in some soil samples.
== Applications ==
Major applications of zinc include (numbers
are given for the US)
Galvanizing (55%)
Brass and bronze (16%)
Other alloys (21%)
Miscellaneous (8%)
=== Anti-corrosion and batteries ===
Zinc is most commonly used as an anti-corrosion
agent, and galvanization (coating of iron
or steel) is the most familiar form. In 2009
in the United States, 55% or 893,000 tons
of the zinc metal was used for galvanization.Zinc
is more reactive than iron or steel and thus
will attract almost all local oxidation until
it completely corrodes away. A protective
surface layer of oxide and carbonate (Zn5(OH)6(CO3)2)
forms as the zinc corrodes. This protection
lasts even after the zinc layer is scratched
but degrades through time as the zinc corrodes
away. The zinc is applied electrochemically
or as molten zinc by hot-dip galvanizing or
spraying. Galvanization is used on chain-link
fencing, guard rails, suspension bridges,
lightposts, metal roofs, heat exchangers,
and car bodies.The relative reactivity of
zinc and its ability to attract oxidation
to itself makes it an efficient sacrificial
anode in cathodic protection (CP). For example,
cathodic protection of a buried pipeline can
be achieved by connecting anodes made from
zinc to the pipe. Zinc acts as the anode (negative
terminus) by slowly corroding away as it passes
electric current to the steel pipeline. Zinc
is also used to cathodically protect metals
that are exposed to sea water. A zinc disc
attached to a ship's iron rudder will slowly
corrode while the rudder stays intact. Similarly,
a zinc plug attached to a propeller or the
metal protective guard for the keel of the
ship provides temporary protection.
With a standard electrode potential (SEP)
of −0.76 volts, zinc is used as an anode
material for batteries. (More reactive lithium
(SEP −3.04 V) is used for anodes in lithium
batteries ). Powdered zinc is used in this
way in alkaline batteries and the case (which
also serves as the anode) of zinc–carbon
batteries is formed from sheet zinc. Zinc
is used as the anode or fuel of the zinc-air
battery/fuel cell. The zinc-cerium redox flow
battery also relies on a zinc-based negative
half-cell.
=== 
Alloys ===
A widely used zinc alloy is brass, in which
copper is alloyed with anywhere from 3% to
45% zinc, depending upon the type of brass.
Brass is generally more ductile and stronger
than copper, and has superior corrosion resistance.
These properties make it useful in communication
equipment, hardware, musical instruments,
and water valves.
Other widely used zinc alloys include nickel
silver, typewriter metal, soft and aluminium
solder, and commercial bronze. Zinc is also
used in contemporary pipe organs as a substitute
for the traditional lead/tin alloy in pipes.
Alloys of 85–88% zinc, 4–10% copper, and
2–8% aluminium find limited use in certain
types of machine bearings. Zinc is the primary
metal in American one cent coins (pennies)
since 1982. The zinc core is coated with a
thin layer of copper to give the appearance
of a copper coin. In 1994, 33,200 tonnes (36,600
short tons) of zinc were used to produce 13.6
billion pennies in the United States.Alloys
of zinc with small amounts of copper, aluminium,
and magnesium are useful in die casting as
well as spin casting, especially in the automotive,
electrical, and hardware industries. These
alloys are marketed under the name Zamak.
An example of this is zinc aluminium. The
low melting point together with the low viscosity
of the alloy makes possible the production
of small and intricate shapes. The low working
temperature leads to rapid cooling of the
cast products and fast production for assembly.
Another alloy, marketed under the brand name
Prestal, contains 78% zinc and 22% aluminium,
and is reported to be nearly as strong as
steel but as malleable as plastic. This superplasticity
of the alloy allows it to be molded using
die casts made of ceramics and cement.Similar
alloys with the addition of a small amount
of lead can be cold-rolled into sheets. An
alloy of 96% zinc and 4% aluminium is used
to make stamping dies for low production run
applications for which ferrous metal dies
would be too expensive. For building facades,
roofing, and other applications for sheet
metal formed by deep drawing, roll forming,
or bending, zinc alloys with titanium and
copper are used. Unalloyed zinc is too brittle
for these manufacturing processes.As a dense,
inexpensive, easily worked material, zinc
is used as a lead replacement. In the wake
of lead concerns, zinc appears in weights
for various applications ranging from fishing
to tire balances and flywheels.Cadmium zinc
telluride (CZT) is a semiconductive alloy
that can be divided into an array of small
sensing devices. These devices are similar
to an integrated circuit and can detect the
energy of incoming gamma ray photons. When
behind an absorbing mask, the CZT sensor array
can determine the direction of the rays.
=== Other industrial uses ===
Roughly one quarter of all zinc output in
the United States in 2009 was consumed in
zinc compounds; a variety of which are used
industrially. Zinc oxide is widely used as
a white pigment in paints and as a catalyst
in the manufacture of rubber to disburse heat.
Zinc oxide is used to protect rubber polymers
and plastics from ultraviolet radiation (UV).
The semiconductor properties of zinc oxide
make it useful in varistors and photocopying
products. The zinc zinc-oxide cycle is a two
step thermochemical process based on zinc
and zinc oxide for hydrogen production.Zinc
chloride is often added to lumber as a fire
retardant and sometimes as a wood preservative.
It is used in the manufacture of other chemicals.
Zinc methyl (Zn(CH3)2) is used in a number
of organic syntheses. Zinc sulfide (ZnS) is
used in luminescent pigments such as on the
hands of clocks, X-ray and television screens,
and luminous paints. Crystals of ZnS are used
in lasers that operate in the mid-infrared
part of the spectrum. Zinc sulfate is a chemical
in dyes and pigments. Zinc pyrithione is used
in antifouling paints.Zinc powder is sometimes
used as a propellant in model rockets. When
a compressed mixture of 70% zinc and 30% sulfur
powder is ignited there is a violent chemical
reaction. This produces zinc sulfide, together
with large amounts of hot gas, heat, and light.Zinc
sheet metal is used to make zinc bars.64Zn,
the most abundant isotope of zinc, is very
susceptible to neutron activation, being transmuted
into the highly radioactive 65Zn, which has
a half-life of 244 days and produces intense
gamma radiation. Because of this, zinc oxide
used in nuclear reactors as an anti-corrosion
agent is depleted of 64Zn before use, this
is called depleted zinc oxide. For the same
reason, zinc has been proposed as a salting
material for nuclear weapons (cobalt is another,
better-known salting material). A jacket of
isotopically enriched 64Zn would be irradiated
by the intense high-energy neutron flux from
an exploding thermonuclear weapon, forming
a large amount of 65Zn significantly increasing
the radioactivity of the weapon's fallout.
Such a weapon is not known to have ever been
built, tested, or used.65Zn is used as a tracer
to study how alloys that contain zinc wear
out, or the path and the role of zinc in organisms.Zinc
dithiocarbamate complexes are used as agricultural
fungicides; these include Zineb, Metiram,
Propineb and Ziram. Zinc naphthenate is used
as wood preservative. Zinc in the form of
ZDDP, is used as an anti-wear additive for
metal parts in engine oil.
=== Organic chemistry ===
Organozinc chemistry is the science of compounds
that contain carbon-zinc bonds, describing
the physical properties, synthesis, and chemical
reactions.Many organozinc compounds are important.
Among important applications are
The Frankland-Duppa Reaction in which an oxalate
ester (ROCOCOOR) reacts with an alkyl halide
R'X, zinc and hydrochloric acid to form the
α-hydroxycarboxylic esters RR'COHCOOR
The Reformatskii reaction in which α-halo-esters
and aldehydes are converted to β-hydroxy-esters
The Simmons–Smith reaction in which the
carbenoid (iodomethyl)zinc iodide reacts with
alkene(or alkyne) and converts them to cyclopropane
The Addition reaction of organozinc compounds
to form carbonyl compounds
The Barbier reaction (1899), which is the
zinc equivalent of the magnesium Grignard
reaction and is the better of the two. In
presence of water, formation of the organomagnesium
halide will fail, whereas the Barbier reaction
can take place in water.
On the downside, organozincs are much less
nucleophilic than Grignards, and they are
expensive and difficult to handle. Commercially
available diorganozinc compounds are dimethylzinc,
diethylzinc and diphenylzinc. In one study,
the active organozinc compound is obtained
from much cheaper organobromine precursors
The Negishi coupling is also an important
reaction for the formation of new carbon-carbon
bonds between unsaturated carbon atoms in
alkenes, arenes and alkynes. The catalysts
are nickel and palladium. A key step in the
catalytic cycle is a transmetalation in which
a zinc halide exchanges its organic substituent
for another halogen with the palladium (nickel)
metal center.
The Fukuyama coupling is another coupling
reaction, but it uses a thioester as reactant
and produces a ketone.Zinc has found many
applications as catalyst in organic synthesis
including asymmetric synthesis, being cheap
and easily available alternative to precious
metal complexes. The results (yield and ee)
obtained with chiral zinc catalysts are comparable
to those achieved with palladium, ruthenium,
iridium and others, and zinc becomes metal
catalyst of choice.
=== Dietary supplement ===
In most single-tablet, over-the-counter, daily
vitamin and mineral supplements, zinc is included
in such forms as zinc oxide, zinc acetate,
or zinc gluconate. Zinc is generally considered
to be an antioxidant. However, it is redox
inert and thus can serve such a function only
indirectly. Generally, zinc supplement is
recommended where there is high risk of zinc
deficiency (such as low and middle income
countries) as a preventive measure.Zinc deficiency
has been associated with major depressive
disorder (MDD), and zinc supplements may be
an effective treatment.Zinc serves as a simple,
inexpensive, and critical tool for treating
diarrheal episodes among children in the developing
world. Zinc becomes depleted in the body during
diarrhea, but recent studies suggest that
replenishing zinc with a 10- to 14-day course
of treatment can reduce the duration and severity
of diarrheal episodes and may also prevent
future episodes for as long as three months.A
Cochrane review stated that people taking
zinc supplement may be less likely to progress
to age-related macular degeneration.Zinc supplement
is an effective treatment for acrodermatitis
enteropathica, a genetic disorder affecting
zinc absorption that was previously fatal
to affected infants.Gastroenteritis is strongly
attenuated by ingestion of zinc, possibly
by direct antimicrobial action of the ions
in the gastrointestinal tract, or by the absorption
of the zinc and re-release from immune cells
(all granulocytes secrete zinc), or both.In
2011, researchers reported that adding large
amounts of zinc to a urine sample masked detection
of drugs. The researchers did not test whether
orally consuming a zinc dietary supplement
could have the same effect.Zinc is a negative
allosteric modulator of the GABAA receptor.
==== Common cold ====
Zinc supplements (frequently zinc acetate
or zinc gluconate lozenges) are a group of
dietary supplements that are commonly used
for the treatment of the common cold. The
use of zinc supplements at doses in excess
of 75 mg/day within 24 hours of the onset
of symptoms has been shown to reduce the duration
of cold symptoms by about 1 day. Due to a
lack of data, there is insufficient evidence
to determine whether the preventative use
of zinc supplements reduces the likelihood
of contracting a cold. Adverse effects with
zinc supplements by mouth include bad taste
and nausea. The intranasal use of zinc-containing
nasal sprays has been associated with the
loss of the sense of smell; consequently,
in June 2009, the United States Food and Drug
Administration (USFDA) warned consumers to
stop using intranasal zinc products.The human
rhinovirus – the most common viral pathogen
in humans – is the predominant cause of
the common cold. The hypothesized mechanism
of action by which zinc reduces the severity
and/or duration of cold symptoms is the suppression
of nasal inflammation and the direct inhibition
of rhinoviral receptor binding and rhinoviral
replication in the nasal mucosa.
=== Topical use ===
Topical preparations of zinc include those
used on the skin, often in the form of zinc
oxide. Zinc preparations can protect against
sunburn in the summer and windburn in the
winter. Applied thinly to a baby's diaper
area (perineum) with each diaper change, it
can protect against diaper rash.Chelated zinc
is used in toothpastes and mouthwashes to
prevent bad breath.Zinc pyrithione is widely
included in shampoos to prevent dandruff.
== Biological role ==
Zinc is an essential trace element for humans
and other animals, for plants and for microorganisms.
Zinc is required for the function of over
300 enzymes and 1000 transcription factors,
and is stored and transferred in metallothioneins.
It is the second most abundant trace metal
in humans after iron and it is the only metal
which appears in all enzyme classes.In proteins,
zinc ions are often coordinated to the amino
acid side chains of aspartic acid, glutamic
acid, cysteine and histidine. The theoretical
and computational description of this zinc
binding in proteins (as well as that of other
transition metals) is difficult.Roughly 2–4
grams of zinc are distributed throughout the
human body. Most zinc is in the brain, muscle,
bones, kidney, and liver, with the highest
concentrations in the prostate and parts of
the eye. Semen is particularly rich in zinc,
a key factor in prostate gland function and
reproductive organ growth.In humans, the biological
roles of zinc are ubiquitous. It interacts
with "a wide range of organic ligands", and
has roles in the metabolism of RNA and DNA,
signal transduction, and gene expression.
It also regulates apoptosis. A 2006 study
estimated that about 10% of human proteins
(2800) potentially bind zinc, in addition
to hundreds more that transport and traffic
zinc; a similar in silico study in the plant
Arabidopsis thaliana found 2367 zinc-related
proteins.In the brain, zinc is stored in specific
synaptic vesicles by glutamatergic neurons
and can modulate neuronal excitability. It
plays a key role in synaptic plasticity and
so in learning. Zinc homeostasis also plays
a critical role in the functional regulation
of the central nervous system. Dysregulation
of zinc homeostasis in the central nervous
system that results in excessive synaptic
zinc concentrations is believed to induce
neurotoxicity through mitochondrial oxidative
stress (e.g., by disrupting certain enzymes
involved in the electron transport chain,
including complex I, complex III, and α-ketoglutarate
dehydrogenase), the dysregulation of calcium
homeostasis, glutamatergic neuronal excitotoxicity,
and interference with intraneuronal signal
transduction. L- and D-histidine facilitate
brain zinc uptake. SLC30A3 is the primary
zinc transporter involved in cerebral zinc
homeostasis.
=== Enzymes ===
Zinc is an efficient Lewis acid, making it
a useful catalytic agent in hydroxylation
and other enzymatic reactions. The metal also
has a flexible coordination geometry, which
allows proteins using it to rapidly shift
conformations to perform biological reactions.
Two examples of zinc-containing enzymes are
carbonic anhydrase and carboxypeptidase, which
are vital to the processes of carbon dioxide
(CO2) regulation and digestion of proteins,
respectively.In vertebrate blood, carbonic
anhydrase converts CO2 into bicarbonate and
the same enzyme transforms the bicarbonate
back into CO2 for exhalation through the lungs.
Without this enzyme, this conversion would
occur about one million times slower at the
normal blood pH of 7 or would require a pH
of 10 or more. The non-related β-carbonic
anhydrase is required in plants for leaf formation,
the synthesis of indole acetic acid (auxin)
and alcoholic fermentation.Carboxypeptidase
cleaves peptide linkages during digestion
of proteins. A coordinate covalent bond is
formed between the terminal peptide and a
C=O group attached to zinc, which gives the
carbon a positive charge. This helps to create
a hydrophobic pocket on the enzyme near the
zinc, which attracts the non-polar part of
the protein being digested.
=== Signalling ===
Zinc has been recognized as a messenger, able
to activate signalling pathways. Many of these
pathways provide the driving force in aberrant
cancer growth. They can be targeted through
ZIP transporters.
=== Other proteins ===
Zinc serves a purely structural role in zinc
fingers, twists and clusters. Zinc fingers
form parts of some transcription factors,
which are proteins that recognize DNA base
sequences during the replication and transcription
of DNA. Each of the nine or ten Zn2+ ions
in a zinc finger helps maintain the finger's
structure by coordinately binding to four
amino acids in the transcription factor. The
transcription factor wraps around the DNA
helix and uses its fingers to accurately bind
to the DNA sequence.
In blood plasma, zinc is bound to and transported
by albumin (60%, low-affinity) and transferrin
(10%). Because transferrin also transports
iron, excessive iron reduces zinc absorption,
and vice versa. A similar antagonism exists
with copper. The concentration of zinc in
blood plasma stays relatively constant regardless
of zinc intake. Cells in the salivary gland,
prostate, immune system, and intestine use
zinc signaling to communicate with other cells.Zinc
may be held in metallothionein reserves within
microorganisms or in the intestines or liver
of animals. Metallothionein in intestinal
cells is capable of adjusting absorption of
zinc by 15–40%. However, inadequate or excessive
zinc intake can be harmful; excess zinc particularly
impairs copper absorption because metallothionein
absorbs both metals.The human dopamine transporter
contains a high affinity extracellular zinc
binding site which, upon zinc binding, inhibits
dopamine reuptake and amplifies amphetamine-induced
dopamine efflux in vitro. The human serotonin
transporter and norepinephrine transporter
do not contain zinc binding sites.
=== Dietary recommendations ===
The U.S. Institute of Medicine (IOM) updated
Estimated Average Requirements (EARs) and
Recommended Dietary Allowances (RDAs) for
zinc in 2001. The current EARs for zinc for
women and men ages 14 and up is 6.8 and 9.4
mg/day, respectively. The RDAs are 8 and 11
mg/day. RDAs are higher than EARs so as to
identify amounts that will cover people with
higher than average requirements. RDA for
pregnancy is 11 mg/day. RDA for lactation
is 12 mg/day. For infants up to 12 months
the RDA is 3 mg/day. For children ages 1–13
years the RDA increases with age from 3 to
8 mg/day. As for safety, the IOM sets Tolerable
upper intake levels (ULs) for vitamins and
minerals when evidence is sufficient. In the
case of zinc the adult UL is 40 mg/day (lower
for children). Collectively the EARs, RDAs,
AIs and ULs are referred to as Dietary Reference
Intakes (DRIs).The European Food Safety Authority
(EFSA) refers to the collective set of information
as Dietary Reference Values, with Population
Reference Intake (PRI) instead of RDA, and
Average Requirement instead of EAR. AI and
UL are defined the same as in United States.
For people ages 18 and older the PRI calculations
are complex, as the EFSA has set higher and
higher values as the phytate content of the
diet increases. For women, PRIs increase from
7.5 to 12.7 mg/day as phytate intake increases
from 300 to 1200 mg/day; for men the range
is 9.4 to 16.3 mg/day. These PRIs are higher
than the U.S. RDAs. The EFSA reviewed the
same safety question and set its UL at 25
mg/day, which is much lower than the U.S.
value.For U.S. food and dietary supplement
labeling purposes the amount in a serving
is expressed as a percent of Daily Value (%DV).
For zinc labeling purposes 100% of the Daily
Value was 15 mg, but as of May 27, 2016 it
has been revised to 11 mg. A table of the
old and new adult Daily Values is provided
at Reference Daily Intake. Food and supplement
companies have until January 1, 2020 to comply
with the change.
=== Dietary intake ===
Animal products such as meat, fish, shellfish,
fowl, eggs, and dairy contain zinc. The concentration
of zinc in plants varies with the level in
the soil. With adequate zinc in the soil,
the food plants that contain the most zinc
are wheat (germ and bran) and various seeds,
including sesame, poppy, alfalfa, celery,
and mustard. Zinc is also found in beans,
nuts, almonds, whole grains, pumpkin seeds,
sunflower seeds, and blackcurrant. Plant phytates
are particularly found in pulses and cereals
and interfere with zinc absorption.
Other sources include fortified food and dietary
supplements in various forms. A 1998 review
concluded that zinc oxide, one of the most
common supplements in the United States, and
zinc carbonate are nearly insoluble and poorly
absorbed in the body. This review cited studies
that found lower plasma zinc concentrations
in the subjects who consumed zinc oxide and
zinc carbonate than in those who took zinc
acetate and sulfate salts. For fortification,
however, a 2003 review recommended cereals
(containing zinc oxide) as a cheap, stable
source that is as easily absorbed as the more
expensive forms. A 2005 study found that various
compounds of zinc, including oxide and sulfate,
did not show statistically significant differences
in absorption when added as fortificants to
maize tortillas.
=== Deficiency ===
Zinc deficiency is usually due to insufficient
dietary intake, but can be associated with
malabsorption, acrodermatitis enteropathica,
chronic liver disease, chronic renal disease,
sickle cell disease, diabetes, malignancy,
and other chronic illnesses. Groups at risk
of zinc deficiency include the elderly, children
in developing countries, and those with renal
dysfunction.
In the United States, a federal survey of
food consumption determined that for women
and men over the age of 19, average consumption
was 9.7 and 14.2 mg/day, respectively. For
women, 17% consumed less than the EAR, for
men 11%. The percentages below EAR increased
with age. The most recent published update
of the survey (NHANES 2013–2014) reported
lower averages – 9.3 and 13.2 mg/day – again
with intake decreasing with age.Symptoms of
mild zinc deficiency are diverse. Clinical
outcomes include depressed growth, diarrhea,
impotence and delayed sexual maturation, alopecia,
eye and skin lesions, impaired appetite, altered
cognition, impaired host defense properties,
defects in carbohydrate utilization, and reproductive
teratogenesis. Mild zinc deficiency depresses
immunity, although excessive zinc does also.
Animals with a zinc deficiency require twice
as much food to attain the same weight gain
as animals with sufficient zinc.Despite some
concerns, western vegetarians and vegans do
not suffer any more from overt zinc deficiency
than meat-eaters. Major plant sources of zinc
include cooked dried beans, sea vegetables,
fortified cereals, soy foods, nuts, peas,
and seeds. However, phytates in many whole-grains
and fibers may interfere with zinc absorption
and marginal zinc intake has poorly understood
effects. The zinc chelator phytate, found
in seeds and cereal bran, can contribute to
zinc malabsorption. Some evidence suggests
that more than the US RDA (15 mg) of zinc
daily may be needed in those whose diet is
high in phytates, such as some vegetarians.
These considerations must be balanced against
the paucity of adequate zinc biomarkers, and
the most widely used indicator, plasma zinc,
has poor sensitivity and specificity. Diagnosing
zinc deficiency is a persistent challenge.Nearly
two billion people in the developing world
are deficient in zinc. In children, it causes
an increase in infection and diarrhea and
contributes to the death of about 800,000
children worldwide per year. The World Health
Organization advocates zinc supplementation
for severe malnutrition and diarrhea. Zinc
supplements help prevent disease and reduce
mortality, especially among children with
low birth weight or stunted growth. However,
zinc supplements should not be administered
alone, because many in the developing world
have several deficiencies, and zinc interacts
with other micronutrients.
=== Soil remediation ===
Species of Calluna, Erica and Vaccinium can
grow in zinc metalliferous soils, because
translocation of toxic ions is prevented by
the action of ericoid mycorrhizal fungi.
=== Agriculture ===
Zinc deficiency appears to be the most common
micronutrient deficiency in crop plants; it
is particularly common in high-pH soils. Zinc-deficient
soil is cultivated in the cropland of about
half of Turkey and India, a third of China,
and most of Western Australia. Substantial
responses to zinc fertilization have been
reported in these areas. Plants that grow
in soils that are zinc-deficient are more
susceptible to disease. Zinc is added to the
soil primarily through the weathering of rocks,
but humans have added zinc through fossil
fuel combustion, mine waste, phosphate fertilizers,
pesticide (zinc phosphide), limestone, manure,
sewage sludge, and particles from galvanized
surfaces. Excess zinc is toxic to plants,
although zinc toxicity is far less widespread.
== Precautions ==
=== 
Toxicity ===
Although zinc is an essential requirement
for good health, excess zinc can be harmful.
Excessive absorption of zinc suppresses copper
and iron absorption. The free zinc ion in
solution is highly toxic to plants, invertebrates,
and even vertebrate fish. The Free Ion Activity
Model is well-established in the literature,
and shows that just micromolar amounts of
the free ion kills some organisms. A recent
example showed 6 micromolar killing 93% of
all Daphnia in water.The free zinc ion is
a powerful Lewis acid up to the point of being
corrosive. Stomach acid contains hydrochloric
acid, in which metallic zinc dissolves readily
to give corrosive zinc chloride. Swallowing
a post-1982 American one cent piece (97.5%
zinc) can cause damage to the stomach lining
through the high solubility of the zinc ion
in the acidic stomach.Evidence shows that
people taking 100–300 mg of zinc daily may
suffer induced copper deficiency. A 2007 trial
observed that elderly men taking 80 mg daily
were hospitalized for urinary complications
more often than those taking a placebo. Levels
of 100–300 mg may interfere with the utilization
of copper and iron or adversely affect cholesterol.
Zinc in excess of 500 ppm in soil interferes
with the plant absorption of other essential
metals, such as iron and manganese. A condition
called the zinc shakes or "zinc chills" can
be induced by inhalation of zinc fumes while
brazing or welding galvanized materials. Zinc
is a common ingredient of denture cream which
may contain between 17 and 38 mg of zinc per
gram. Disability and even deaths from excessive
use of these products have been claimed.The
U.S. Food and Drug Administration (FDA) states
that zinc damages nerve receptors in the nose,
causing anosmia. Reports of anosmia were also
observed in the 1930s when zinc preparations
were used in a failed attempt to prevent polio
infections. On June 16, 2009, the FDA ordered
removal of zinc-based intranasal cold products
from store shelves. The FDA said the loss
of smell can be life-threatening because people
with impaired smell cannot detect leaking
gas or smoke, and cannot tell if food has
spoiled before they eat it.Recent research
suggests that the topical antimicrobial zinc
pyrithione is a potent heat shock response
inducer that may impair genomic integrity
with induction of PARP-dependent energy crisis
in cultured human keratinocytes and melanocytes.
=== Poisoning ===
In 1982, the US Mint began minting pennies
coated in copper but containing primarily
zinc. Zinc pennies pose a risk of zinc toxicosis,
which can be fatal. One reported case of chronic
ingestion of 425 pennies (over 1 kg of zinc)
resulted in death due to gastrointestinal
bacterial and fungal sepsis. Another patient
who ingested 12 grams of zinc showed only
lethargy and ataxia (gross lack of coordination
of muscle movements). Several other cases
have been reported of humans suffering zinc
intoxication by the ingestion of zinc coins.Pennies
and other small coins are sometimes ingested
by dogs, requiring veterinary removal of the
foreign objects. The zinc content of some
coins can cause zinc toxicity, commonly fatal
in dogs through severe hemolytic anemia and
liver or kidney damage; vomiting and diarrhea
are possible symptoms. Zinc is highly toxic
in parrots and poisoning can often be fatal.
The consumption of fruit juices stored in
galvanized cans has resulted in mass parrot
poisonings with zinc.
== See also ==
List of countries by zinc production
Spelter
Wet storage stain
Zinc alloy electroplating
== Notes
