Zinc oxide is an
inorganic compound
An inorganic compound is typically a chemical compound that lacks carbon–hydrogen bondsthat is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as ''inorganic chemistry''.
Inorgan ...
with the
formula
In science, a formula is a concise way of expressing information symbolically, as in a mathematical formula or a ''chemical formula''. The informal use of the term ''formula'' in science refers to the general construct of a relationship betwe ...
. It is a white powder which is insoluble in water. ZnO is used as an additive in numerous materials and products including cosmetics,
food supplements, rubbers, plastics, ceramics, glass, cement, lubricants,
paints, sunscreens, ointments, adhesives, sealants, pigments, foods, batteries, ferrites, fire retardants, semi conductors,
and first-aid tapes. Although it occurs naturally as the mineral
zincite, most zinc oxide is produced synthetically.
History
Early humans probably used zinc compounds in processed
and unprocessed forms, as paint or medicinal ointment; however, their composition is uncertain. The use of ''pushpanjan'', probably zinc oxide, as a salve for eyes and open wounds is mentioned in the Indian medical text the
Charaka Samhita
The ''Charaka Samhita'' () is a Sanskrit text on Ayurveda (Indian traditional medicine). Along with the '' Sushruta Samhita'', it is one of the two foundational texts of this field that have survived from ancient India. It is one of the three w ...
, thought to date from 500 BC or before. Zinc oxide ointment is also mentioned by the Greek physician
Dioscorides
Pedanius Dioscorides (, ; 40–90 AD), "the father of pharmacognosy", was a Greek physician, pharmacologist, botanist, and author of (in the original , , both meaning "On Materia medica, Medical Material") , a 5-volume Greek encyclopedic phar ...
(1st century AD).
Galen
Aelius Galenus or Claudius Galenus (; September 129 – AD), often Anglicization, anglicized as Galen () or Galen of Pergamon, was a Ancient Rome, Roman and Greeks, Greek physician, surgeon, and Philosophy, philosopher. Considered to be one o ...
suggested treating ulcerating cancers with zinc oxide, as did
Avicenna
Ibn Sina ( – 22 June 1037), commonly known in the West as Avicenna ( ), was a preeminent philosopher and physician of the Muslim world, flourishing during the Islamic Golden Age, serving in the courts of various Iranian peoples, Iranian ...
in his ''
The Canon of Medicine
''The Canon of Medicine'' () is an encyclopedia of medicine in five books compiled by Avicenna (, ibn Sina) and completed in 1025. It is among the most influential works of its time. It presents an overview of the contemporary medical knowle ...
''. It is used as an ingredient in products such as
baby powder
Baby powder is an astringent powder (substance), powder used for preventing diaper rash and for Cosmetics, cosmetic uses. It may be composed of talc (in which case it is also called talcum powder), corn starch or potato starch. It may contain a ...
and creams against
diaper rashes,
calamine
Calamine, also known as calamine lotion, is a medication made from powdered calamine (mineral), calamine mineral that is used to treat mild itchiness. Conditions treated include sunburn, insect bites, Toxicodendron radicans, poison ivy, poiso ...
cream, anti-
dandruff shampoos, and
antiseptic
An antiseptic ( and ) is an antimicrobial substance or compound that is applied to living tissue to reduce the possibility of sepsis, infection, or putrefaction. Antiseptics are generally distinguished from ''antibiotics'' by the latter's abil ...
ointments.
The Romans produced considerable quantities of
brass
Brass is an alloy of copper and zinc, in proportions which can be varied to achieve different colours and mechanical, electrical, acoustic and chemical properties, but copper typically has the larger proportion, generally copper and zinc. I ...
(an alloy of
zinc
Zinc is a chemical element; it has symbol Zn and atomic number 30. It is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodic tabl ...
and
copper
Copper is a chemical element; it has symbol Cu (from Latin ) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish-orang ...
) as early as 200 BC by a cementation process where copper was reacted with zinc oxide. The zinc oxide is thought to have been produced by heating zinc ore in a shaft furnace. This liberated metallic zinc as a vapor, which then ascended the flue and condensed as the oxide. This process was described by
Dioscorides
Pedanius Dioscorides (, ; 40–90 AD), "the father of pharmacognosy", was a Greek physician, pharmacologist, botanist, and author of (in the original , , both meaning "On Materia medica, Medical Material") , a 5-volume Greek encyclopedic phar ...
in the 1st century AD. Zinc oxide has also been recovered from zinc mines at Zawar in
India
India, officially the Republic of India, is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area; the List of countries by population (United Nations), most populous country since ...
, dating from the second half of the first millennium BC.
From the 12th to the 16th century, zinc and zinc oxide were recognized and produced in India using a primitive form of the direct synthesis process. From India, zinc manufacturing moved to China in the 17th century. In 1743, the first European zinc smelter was established in
Bristol
Bristol () is a City status in the United Kingdom, cathedral city, unitary authority area and ceremonial county in South West England, the most populous city in the region. Built around the River Avon, Bristol, River Avon, it is bordered by t ...
, United Kingdom. Around 1782,
Louis-Bernard Guyton de Morveau proposed replacing
lead white pigment with zinc oxide.
The main usage of zinc oxide (zinc white) was in paints and as an additive to ointments. Zinc white was accepted as a pigment in oil paintings by 1834 but it did not mix well with oil. This problem was solved by optimizing the synthesis of ZnO. In 1845,
Edme-Jean Leclaire in Paris was producing the oil paint on a large scale; by 1850, zinc white was being manufactured throughout Europe. The success of zinc white paint was due to its advantages over the traditional
white lead: zinc white is essentially permanent in sunlight, it is not blackened by sulfur-bearing air, it is non-toxic and more economical. Because zinc white is so "clean" it is valuable for making tints with other colors, but it makes a rather brittle dry film when unmixed with other colors. For example, during the late 1890s and early 1900s, some artists used zinc white as a ground for their oil paintings. These paintings developed cracks over time.
In recent times, most zinc oxide has been used in the
rubber
Rubber, also called India rubber, latex, Amazonian rubber, ''caucho'', or ''caoutchouc'', as initially produced, consists of polymers of the organic compound isoprene, with minor impurities of other organic compounds.
Types of polyisoprene ...
industry to resist
corrosion
Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engine ...
. In the 1970s, the second largest application of ZnO was
photocopying
A photocopier (also called copier or copy machine, and formerly Xerox machine, the generic trademark) is a machine that makes copies of documents and other visual images onto paper or plastic film quickly and cheaply. Most modern photocopiers ...
. High-quality ZnO produced by the "French process" was added to photocopying paper as a filler. This application was soon displaced by
titanium
Titanium is a chemical element; it has symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resistant to corrosion in ...
.
Chemical properties
Pure ZnO is a white powder. However, in nature, it occurs as the rare mineral
zincite, which usually contains
manganese
Manganese is a chemical element; it has Symbol (chemistry), symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese was first isolated in the 1770s. It is a transition m ...
and other impurities that confer a yellow to red color.
Crystalline zinc oxide is
thermochromic, changing from white to yellow when heated in air and reverting to white on cooling.
This color change is caused by a small loss of oxygen to the environment at high temperatures to form the
non-stoichiometric
Non-stoichiometric compounds are chemical compounds, almost always solid inorganic compounds, having chemical element, elemental composition whose proportions cannot be represented by a ratio of small natural numbers (i.e. an empirical formula); ...
Zn
1+xO, where at 800 °C, x = 0.00007.
Zinc oxide is an
amphoteric oxide. It is nearly
insoluble in water, but it will dissolve in most
acid
An acid is a molecule or ion capable of either donating a proton (i.e. Hydron, hydrogen cation, H+), known as a Brønsted–Lowry acid–base theory, Brønsted–Lowry acid, or forming a covalent bond with an electron pair, known as a Lewis ...
s, such as
hydrochloric acid:
:ZnO + 2 HCl → ZnCl
2 + H
2O
Solid zinc oxide will also dissolve in alkalis to give soluble zincates:
:ZnO + 2 NaOH + H
2O → Na
2 4">n(OH)4
ZnO reacts slowly with fatty acids in oils to produce the corresponding
carboxylates, such as
oleate or
stearate. When mixed with a strong aqueous solution of
zinc chloride
Zinc chloride is an Inorganic chemistry, inorganic chemical compound with the chemical formula, formula ZnCl2·''n''H2O, with ''n'' ranging from 0 to 4.5, forming water of hydration, hydrates. Zinc chloride, anhydrous and its hydrates, are colo ...
, ZnO forms cement-like products best described as zinc hydroxy chlorides. This cement was used in dentistry.

ZnO also forms cement-like material when treated with
phosphoric acid
Phosphoric acid (orthophosphoric acid, monophosphoric acid or phosphoric(V) acid) is a colorless, odorless phosphorus-containing solid, and inorganic compound with the chemical formula . It is commonly encountered as an 85% aqueous solution, ...
; related materials are used in dentistry.
A major component of zinc phosphate cement produced by this reaction is
hopeite, Zn
3(PO
4)
2·4H
2O.
ZnO decomposes into zinc vapor and oxygen at around 1975 °C with a standard oxygen pressure. In a
carbothermic reaction, heating with carbon converts the oxide into zinc vapor at a much lower temperature (around 950 °C).
:ZnO + C → Zn
(Vapor) + CO
Physical properties
Structure
Zinc oxide crystallizes in two main
forms, hexagonal
wurtzite
Wurtzite is a zinc and iron sulfide mineral with the chemical formula , a less frequently encountered Polymorphism (materials science), structural polymorph form of sphalerite. The iron content is variable up to eight percent.Palache, Charles, H ...
and cubic
zincblende. The wurtzite structure is most stable at ambient conditions and thus most common. The zincblende form can be stabilized by growing ZnO on substrates with cubic lattice structure. In both cases, the zinc and oxide centers are
tetrahedral, the most characteristic geometry for Zn(II). ZnO converts to the
rocksalt motif at relatively high pressures about 10 GPa.
Hexagonal
and zincblende polymorphs have no
inversion symmetry (reflection of a crystal relative to any given point does not transform it into itself).
This and other lattice symmetry properties result in
piezoelectricity
Piezoelectricity (, ) is the electric charge that accumulates in certain solid materials—such as crystals, certain ceramics, and biological matter such as bone, DNA, and various proteins—in response to applied mechanical stress.
The piezoel ...
of the hexagonal
and zincblende
ZnO, and
pyroelectricity of hexagonal ZnO.
The hexagonal structure has a point group 6 mm (
Hermann–Mauguin notation) or C
6v (
Schoenflies notation), and the
space group
In mathematics, physics and chemistry, a space group is the symmetry group of a repeating pattern in space, usually in three dimensions. The elements of a space group (its symmetry operations) are the rigid transformations of the pattern that ...
is P6
3mc or C
6v4. The lattice constants are ''a'' = 3.25 Å and ''c'' = 5.2 Å; their ratio ''c/a'' ~ 1.60 is close to the ideal value for hexagonal cell ''c/a'' = 1.633. As in most
group II-VI materials, the bonding in ZnO is largely
ionic (Zn
2+O
2−) with the corresponding radii of 0.074 nm for Zn
2+ and 0.140 nm for O
2−. This property accounts for the preferential formation of wurtzite rather than zinc blende structure, as well as the strong
piezoelectricity
Piezoelectricity (, ) is the electric charge that accumulates in certain solid materials—such as crystals, certain ceramics, and biological matter such as bone, DNA, and various proteins—in response to applied mechanical stress.
The piezoel ...
of ZnO. Because of the polar Zn−O bonds, zinc and oxygen planes are electrically charged. To maintain electrical neutrality, those planes reconstruct at atomic level in most relative materials, but not in ZnO – its surfaces are atomically flat, stable and exhibit no reconstruction.
However, studies using wurtzoid structures explained the origin of surface flatness and the absence of reconstruction at ZnO wurtzite surfaces in addition to the origin of charges on ZnO planes.
Mechanical properties
ZnO is a wide-band gap semiconductor of the
II-VI semiconductor group. The native
doping of the semiconductor due to oxygen vacancies or zinc interstitials is n-type.
ZnO is a relatively soft material with approximate hardness of 4.5 on the
Mohs scale
The Mohs scale ( ) of mineral hardness is a qualitative ordinal scale, from 1 to 10, characterizing scratch resistance of minerals through the ability of harder material to scratch softer material.
The scale was introduced in 1812 by the Ger ...
.
Its elastic constants are smaller than those of relevant III-V semiconductors, such as
GaN. The high heat capacity and heat conductivity, low thermal expansion and high melting temperature of ZnO are beneficial for ceramics.
The E2
optical phonon in ZnO exhibits an unusually long lifetime of 133 ps at 10 K.
Among the tetrahedrally bonded semiconductors, it has been stated that ZnO has the highest piezoelectric tensor, or at least one comparable to that of
GaN and
AlN
Aln, ALN, or AlN may refer to:
Organizations
Paramilitary
* Ação Libertadora Nacional, a Brazilian Marxist–Leninist guerrilla movement
* Armée de Libération Nationale, the armed wing of the nationalist National Liberation Front of Alge ...
. This property makes it a technologically important material for many
piezoelectrical applications, which require a large electromechanical coupling. Therefore, ZnO in the form of
thin film
A thin film is a layer of materials ranging from fractions of a nanometer ( monolayer) to several micrometers in thickness. The controlled synthesis of materials as thin films (a process referred to as deposition) is a fundamental step in many ...
has been one of the most studied and used resonator materials for
thin-film bulk acoustic resonators.
Electrical and optical properties
Favourable properties of zinc oxide include good transparency, high
electron mobility
In solid-state physics, the electron mobility characterizes how quickly an electron can move through a metal or semiconductor when pushed or pulled by an electric field. There is an analogous quantity for Electron hole, holes, called hole mobilit ...
, wide
band gap
In solid-state physics and solid-state chemistry, a band gap, also called a bandgap or energy gap, is an energy range in a solid where no electronic states exist. In graphs of the electronic band structure of solids, the band gap refers to t ...
, and strong room-temperature
luminescence
Luminescence is a spontaneous emission of radiation from an electronically or vibrationally excited species not in thermal equilibrium with its environment. A luminescent object emits ''cold light'' in contrast to incandescence, where an obje ...
. Those properties make ZnO valuable for a variety of emerging applications: transparent
electrode
An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or a gas). In electrochemical cells, electrodes are essential parts that can consist of a varie ...
s in
liquid crystal display
A liquid-crystal display (LCD) is a flat-panel display or other Electro-optic modulator, electronically modulated optical device that uses the light-modulating properties of liquid crystals combined with polarizers to display information. Liq ...
s,
energy-saving or heat-protecting windows,
and electronics as thin-film
transistor
A transistor is a semiconductor device used to Electronic amplifier, amplify or electronic switch, switch electrical signals and electric power, power. It is one of the basic building blocks of modern electronics. It is composed of semicondu ...
s and
light-emitting diode
A light-emitting diode (LED) is a semiconductor device that emits light when current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy in the form of photons. The color of the light (corre ...
s.
ZnO has a relatively wide
direct
Direct may refer to:
Mathematics
* Directed set, in order theory
* Direct limit of (pre), sheaves
* Direct sum of modules, a construction in abstract algebra which combines several vector spaces
Computing
* Direct access (disambiguation), ...
band gap
In solid-state physics and solid-state chemistry, a band gap, also called a bandgap or energy gap, is an energy range in a solid where no electronic states exist. In graphs of the electronic band structure of solids, the band gap refers to t ...
of ~3.3 eV at room temperature. Advantages associated with a wide band gap include higher
breakdown voltages, ability to sustain large electric fields, lower
electronic noise, and high-temperature and high-power operation. The band gap of ZnO can further be tuned to ~3–4 eV by its alloying with
magnesium oxide
Magnesium oxide (MgO), or magnesia, is a white hygroscopic solid mineral that occurs naturally as periclase and is a source of magnesium (see also oxide). It has an empirical formula of MgO and consists of a lattice of Mg2+ ions and O2− ions ...
or
cadmium oxide.
Due to this large band gap, there have been efforts to create visibly transparent solar cells utilising ZnO as a light absorbing layer. However, these solar cells have so far proven highly inefficient.
Most ZnO has
''n''-type character, even in the absence of intentional
doping.
Nonstoichiometry is typically the origin of n-type character, but the subject remains controversial.
An alternative explanation has been proposed, based on theoretical calculations, that unintentional substitutional hydrogen impurities are responsible.
Controllable n-type doping is easily achieved by substituting Zn with group-III elements such as Al, Ga, In or by substituting oxygen with group-VII elements
chlorine
Chlorine is a chemical element; it has Symbol (chemistry), symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between ...
or
iodine
Iodine is a chemical element; it has symbol I and atomic number 53. The heaviest of the stable halogens, it exists at standard conditions as a semi-lustrous, non-metallic solid that melts to form a deep violet liquid at , and boils to a vi ...
.
Reliable
p-type doping of ZnO remains difficult. This problem originates from low solubility of p-type dopants and their compensation by abundant n-type impurities. This problem is observed with
GaN and
ZnSe. Measurement of p-type in "intrinsically" n-type material is complicated by the inhomogeneity of samples.
Current limitations to p-doping limit electronic and optoelectronic applications of ZnO, which usually require junctions of n-type and p-type material. Known p-type dopants include group-I elements Li, Na, K; group-V elements N, P and As; as well as copper and silver. However, many of these form deep acceptors and do not produce significant p-type conduction at room temperature.
Electron mobility
In solid-state physics, the electron mobility characterizes how quickly an electron can move through a metal or semiconductor when pushed or pulled by an electric field. There is an analogous quantity for Electron hole, holes, called hole mobilit ...
of ZnO strongly varies with temperature and has a maximum of ~2000 cm
2/(V·s) at 80 K. Data on hole mobility are scarce with values in the range 5–30 cm
2/(V·s).
ZnO discs, acting as a
varistor, are the active material in most
surge arresters.
Zinc oxide is noted for its strongly
nonlinear optical
Nonlinear optics (NLO) is the branch of optics that describes the behaviour of light in nonlinear media, that is, media in which the polarization density P responds non-linearly to the electric field E of the light. The non-linearity is typicall ...
properties, especially in bulk. The nonlinearity of ZnO nanoparticles can be fine-tuned according to their size.
Production
For industrial use, ZnO is produced at levels of 10
5 tons per year
by three main processes:
Indirect process
In the indirect or French process, metallic zinc is melted in a graphite crucible and vaporized at temperatures above 907 °C (typically around 1000 °C). Zinc vapor reacts with the oxygen in the air to give ZnO,
[ accompanied by a drop in its temperature and bright luminescence. Zinc oxide particles are transported into a cooling duct and collected in a bag house. This indirect method was popularized by Edme Jean LeClaire of Paris in 1844 and therefore is commonly known as the French process. Its product normally consists of agglomerated zinc oxide particles with an average size of 0.1 to a few micrometers. By weight, most of the world's zinc oxide is manufactured via French process.
]
Direct process
The direct or American process starts with diverse contaminated zinc composites, such as zinc ores or smelter by-products. The zinc precursors are reduced ( carbothermal reduction) by heating with a source of carbon such as anthracite to produce zinc vapor, which is then oxidized as in the indirect process. Because of the lower purity of the source material, the final product is also of lower quality in the direct process as compared to the indirect one.
Wet chemical process
A small amount of industrial production involves wet chemical processes, which start with aqueous solutions of zinc salts, from which zinc carbonate
Zinc carbonate is the inorganic compound with the formula ZnCO3. It is a white solid that is insoluble in water. It exists in nature as the mineral smithsonite. It is prepared by treating cold solutions of zinc sulfate with potassium bicarbonat ...
or zinc hydroxide is precipitated. The solid precipitate is then calcined at temperatures around 800 °C.
Laboratory synthesis
Numerous specialised methods exist for producing ZnO for scientific studies and niche applications. These methods can be classified by the resulting ZnO form (bulk, thin film, nanowire
file:[email protected], upright=1.2, Crystalline 2×2-atom tin selenide nanowire grown inside a single-wall carbon nanotube (tube diameter ≈1 nm).
A nanowire is a nanostructure in the form of a wire with the diameter of the order of a nanometre ( ...
), temperature ("low", that is close to room temperature or "high", that is T ~ 1000 °C), process type (vapor deposition or growth from solution) and other parameters.
Large single crystals (many cubic centimeters) can be grown by the gas transport (vapor-phase deposition), hydrothermal synthesis, or melt growth. However, because of the high vapor pressure
Vapor pressure or equilibrium vapor pressure is the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phases (solid or liquid) at a given temperature in a closed system. The equilibrium vapor pressure is an indicat ...
of ZnO, growth from the melt is problematic. Growth by gas transport is difficult to control, leaving the hydrothermal method as a preference.[ Thin films can be produced by a variety of methods including ]chemical vapor deposition
Chemical vapor deposition (CVD) is a vacuum deposition method used to produce high-quality, and high-performance, solid materials. The process is often used in the semiconductor industry to produce thin films.
In typical CVD, the wafer (electro ...
, metalorganic vapour phase epitaxy, electrodeposition, sputtering, spray pyrolysis, thermal oxidation, sol–gel synthesis, atomic layer deposition
Atomic layer deposition (ALD) is a thin-film deposition technique based on the sequential use of a gas-phase chemical process; it is a subclass of chemical vapour deposition. The majority of ALD reactions use two chemicals called wiktionary:precu ...
, and pulsed laser deposition.
Zinc oxide can be produced in bulk by precipitation
In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls from clouds due to gravitational pull. The main forms of precipitation include drizzle, rain, rain and snow mixed ("sleet" in Commonwe ...
from zinc compounds, mainly zinc acetate, in various solutions, such as aqueous sodium hydroxide
Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula . It is a white solid ionic compound consisting of sodium cations and hydroxide anions .
Sodium hydroxide is a highly corrosive base (chemistry), ...
or aqueous ammonium carbonate. Synthetic methods characterized in literature since the year 2000 aim to produce ZnO particles with high surface area and minimal size distribution, including precipitation, mechanochemical, sol-gel, microwave
Microwave is a form of electromagnetic radiation with wavelengths shorter than other radio waves but longer than infrared waves. Its wavelength ranges from about one meter to one millimeter, corresponding to frequency, frequencies between 300&n ...
, and emulsion
An emulsion is a mixture of two or more liquids that are normally Miscibility, immiscible (unmixable or unblendable) owing to liquid-liquid phase separation. Emulsions are part of a more general class of two-phase systems of matter called colloi ...
methods.
ZnO nanostructures
Nanostructures of ZnO can be synthesized into a variety of morphologies, including nanowires, nanorods, tetrapods, nanobelts, nanoflowers, nanoparticles, etc. Nanostructures can be obtained with most above-mentioned techniques, at certain conditions, and also with the vapor–liquid–solid method. The synthesis is typically carried out at temperatures of about 90 °C, in an equimolar aqueous solution of zinc nitrate and hexamine, the latter providing the basic environment. Certain additives, such as polyethylene glycol or polyethylenimine, can improve the aspect ratio of the ZnO nanowires. Doping of the ZnO nanowires has been achieved by adding other metal nitrates to the growth solution. The morphology of the resulting nanostructures can be tuned by changing the parameters relating to the precursor composition (such as the zinc concentration and pH) or to the thermal treatment (such as the temperature and heating rate).
Aligned ZnO nanowires on pre-seeded silicon
Silicon is a chemical element; it has symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic lustre, and is a tetravalent metalloid (sometimes considered a non-metal) and semiconductor. It is a membe ...
, glass
Glass is an amorphous (non-crystalline solid, non-crystalline) solid. Because it is often transparency and translucency, transparent and chemically inert, glass has found widespread practical, technological, and decorative use in window pane ...
, and gallium nitride substrates have been grown using aqueous zinc salts such as zinc nitrate and zinc acetate in basic environments. Pre-seeding substrates with ZnO creates sites for homogeneous nucleation of ZnO crystal during the synthesis. Common pre-seeding methods include in-situ thermal decomposition of zinc acetate crystallites, spin coating of ZnO nanoparticles, and the use of physical vapor deposition
Physical vapor deposition (PVD), sometimes called physical vapor transport (PVT), describes a variety of vacuum deposition methods which can be used to produce thin films and coatings on substrates including metals, ceramics, glass, and polym ...
methods to deposit ZnO thin films. Pre-seeding can be performed in conjunction with top down patterning methods such as electron beam lithography and nanosphere lithography to designate nucleation sites prior to growth. Aligned ZnO nanowires can be used in dye-sensitized solar cells and field emission devices.
Applications
The applications of zinc oxide powder are numerous, and the principal ones are summarized below. Most applications exploit the reactivity of the oxide as a precursor to other zinc compounds. For material science applications, zinc oxide has high refractive index
In optics, the refractive index (or refraction index) of an optical medium is the ratio of the apparent speed of light in the air or vacuum to the speed in the medium. The refractive index determines how much the path of light is bent, or refrac ...
, high thermal conductivity, binding, antibacterial and UV-protection properties. Consequently, it is added into materials and products including plastics, ceramics, glass, cement, rubber, lubricants, paints, ointments, adhesive, sealants, concrete
Concrete is a composite material composed of aggregate bound together with a fluid cement that cures to a solid over time. It is the second-most-used substance (after water), the most–widely used building material, and the most-manufactur ...
manufacturing, pigments, foods, batteries, ferrites Ferrite may refer to:
* Ferrite (iron), one of the allotropes of iron that is stable at room temperature and pressure, α-Fe
* Ferrite (magnet), a ferromagnetic ceramic material
See also
*
* Ferrite bead, a component placed on the end of a data c ...
, and fire retardants.[Ambica Dhatu Private Limited]
Applications of ZnO.
Access date January 25, 2009.
Rubber industry
Between 50% and 60% of ZnO use is in the rubber industry. Zinc oxide along with stearic acid
Stearic acid ( , ) is a saturated fatty acid with an 18-carbon chain. The IUPAC name is octadecanoic acid. It is a soft waxy solid with the formula . The triglyceride derived from three molecules of stearic acid is called stearin. Stearic acid ...
is used in the sulfur vulcanization
Sulfur vulcanization is a chemical process for converting natural rubber or related polymers into materials of varying hardness, elasticity, and mechanical durability by heating them with sulfur or sulfur-containing compounds. Sulfur forms cros ...
of rubber. ZnO additives in the form of nanoparticles are used in rubber as a pigment and to enhance its durability, and have been used in composite rubber materials such as those based on montmorillonite
Montmorillonite is a very soft phyllosilicate group of minerals that form when they precipitate from water solution as microscopic crystals, known as clay. It is named after Montmorillon in France. Montmorillonite, a member of the smectite grou ...
to impart germicidal properties.
Ceramic industry
Ceramic industry consumes a significant amount of zinc oxide, in particular in ceramic glaze and frit compositions. The relatively high heat capacity, thermal conductivity and high temperature stability of ZnO coupled with a comparatively low coefficient of expansion are desirable properties in the production of ceramics. ZnO affects the melting point and optical properties of the glazes, enamels, and ceramic formulations. Zinc oxide as a low expansion, secondary flux improves the elasticity of glazes by reducing the change in viscosity as a function of temperature and helps prevent crazing and shivering. By substituting ZnO for BaO and PbO, the heat capacity is decreased and the thermal conductivity is increased. Zinc in small amounts improves the development of glossy and brilliant surfaces. However, in moderate to high amounts, it produces matte and crystalline surfaces. With regard to color, zinc has a complicated influence.
Medicine
Skin treatment
Zinc oxide as a mixture with about 0.5% iron(III) oxide
Iron(III) oxide or ferric oxide is the inorganic compound with the formula . It occurs in nature as the mineral hematite, which serves as the primary source of iron for the steel industry. It is also known as red iron oxide, especially when use ...
(Fe2O3) is called calamine and is used in calamine lotion, a topical skin treatment. Historically, the name calamine
Calamine, also known as calamine lotion, is a medication made from powdered calamine (mineral), calamine mineral that is used to treat mild itchiness. Conditions treated include sunburn, insect bites, Toxicodendron radicans, poison ivy, poiso ...
was ascribed to a mineral that contained zinc used in powdered form as medicine, but it was determined in 1803 that ore described as calamine was actually a mixture of the zinc minerals smithsonite
Smithsonite, also known as zinc spar, is the mineral form of zinc carbonate ( Zn CO3). Historically, smithsonite was identified with hemimorphite before it was realized that they were two different minerals. The two minerals are very similar in a ...
and hemimorphite.
Zinc oxide is widely used to treat a variety of skin conditions, including atopic dermatitis
Atopic dermatitis (AD), also known as atopic eczema, is a long-term type of inflammation of the skin. Atopic dermatitis is also often called simply eczema but the same term is also used to refer to dermatitis, the larger group of skin conditi ...
, contact dermatitis
Contact dermatitis is a type of acute or chronic inflammation of the skin caused by exposure to chemical or physical agents. Symptoms of contact dermatitis can include itchy or dry skin, a red rash, bumps, blisters, or swelling. These rashes ...
, itching due to eczema
Dermatitis is a term used for different types of skin inflammation, typically characterized by itchiness, redness and a rash. In cases of short duration, there may be small blisters, while in long-term cases the skin may become thickened ...
, diaper rash and acne
Acne ( ), also known as ''acne vulgaris'', is a long-term Cutaneous condition, skin condition that occurs when Keratinocyte, dead skin cells and Sebum, oil from the skin clog hair follicles. Typical features of the condition include comedo, ...
. It is used in products such as baby powder
Baby powder is an astringent powder (substance), powder used for preventing diaper rash and for Cosmetics, cosmetic uses. It may be composed of talc (in which case it is also called talcum powder), corn starch or potato starch. It may contain a ...
and barrier cream
A barrier cream is a Topical medication, topical formulation used in industrial applications and as a cosmetic to place a physical barrier between the skin and contaminants that may irritate the skin (contact dermatitis or occupational dermatitis ...
s to treat diaper rashes, calamine
Calamine, also known as calamine lotion, is a medication made from powdered calamine (mineral), calamine mineral that is used to treat mild itchiness. Conditions treated include sunburn, insect bites, Toxicodendron radicans, poison ivy, poiso ...
cream, anti- dandruff shampoos, and antiseptic
An antiseptic ( and ) is an antimicrobial substance or compound that is applied to living tissue to reduce the possibility of sepsis, infection, or putrefaction. Antiseptics are generally distinguished from ''antibiotics'' by the latter's abil ...
ointments.[ It is often combined with castor oil to form an emollient and astringent, zinc and castor oil cream, commonly used to treat infants.
It is also a component in tape (called "zinc oxide tape") used by athletes as a bandage to prevent soft tissue damage during workouts.
]
Antibacterial
Zinc oxide is used in mouthwash products and toothpaste
Toothpaste is a paste or gel dentifrice that is used with a toothbrush to clean and maintain the aesthetics of Human tooth, teeth. Toothpaste is used to promote oral hygiene: it is an abrasive that aids in removing dental plaque and food from th ...
s as an anti-bacterial agent proposed to prevent plaque and tartar formation, and to control bad breath by reducing the volatile gases and volatile sulfur compounds (VSC) in the mouth. Along with zinc oxide or zinc salts, these products also commonly contain other active ingredients, such as cetylpyridinium chloride
Cetylpyridinium chloride (CPC) is a cationic quaternary ammonium compound used in some types of mouthwashes, toothpastes, lozenges, throat sprays, breath sprays, and nasal sprays. It is an antiseptic that kills bacteria and other microor ...
, xylitol
Xylitol is a chemical compound with the formula , or HO(CH2)(CHOH)3(CH2)OH; specifically, one particular Stereoisomerism, stereoisomer with that structural formula. It is a colorless or white crystalline solid. It is classified as a polyalcoho ...
, hinokitiol, essential oils and plant
Plants are the eukaryotes that form the Kingdom (biology), kingdom Plantae; they are predominantly Photosynthesis, photosynthetic. This means that they obtain their energy from sunlight, using chloroplasts derived from endosymbiosis with c ...
extract
An extract (essence) is a substance made by extracting a part of a raw material, often by using a solvent such as ethanol, oil or water. Extracts may be sold as tinctures or absolutes or dried and powdered.
The aromatic principles of ma ...
s.
Powdered zinc oxide has deodorizing and antibacterial properties.
ZnO is added to cotton fabric, rubber, oral care products, and food packaging. Enhanced antibacterial action of fine particles compared to bulk material is not exclusive to ZnO and is observed for other materials, such as silver
Silver is a chemical element; it has Symbol (chemistry), symbol Ag () and atomic number 47. A soft, whitish-gray, lustrous transition metal, it exhibits the highest electrical conductivity, thermal conductivity, and reflectivity of any metal. ...
. The mechanism of ZnO's antibacterial effect has been variously described as the generation of reactive oxygen species, the release of Zn2+ ions, and a general disturbance of the bacterial cell membrane by nanoparticles.
Sunscreen
Zinc oxide is used in sunscreen
Sunscreen, also known as sunblock, sun lotion or sun cream, is a photoprotection, photoprotective topical product for the Human skin, skin that helps protect against sunburn and prevent skin cancer. Sunscreens come as lotions, sprays, gels, fo ...
to absorb ultraviolet light. It is the broadest spectrum UVA and UVB absorber that is approved for use as a sunscreen by the U.S. Food and Drug Administration
The United States Food and Drug Administration (FDA or US FDA) is a List of United States federal agencies, federal agency of the United States Department of Health and Human Services, Department of Health and Human Services. The FDA is respo ...
(FDA), and is completely photostable. When used as an ingredient in sunscreen, zinc oxide blocks both UVA (320–400 nm) and UVB (280–320 nm) rays of ultraviolet light. Zinc oxide and the other most common physical sunscreen, titanium dioxide
Titanium dioxide, also known as titanium(IV) oxide or titania , is the inorganic compound derived from titanium with the chemical formula . When used as a pigment, it is called titanium white, Pigment White 6 (PW6), or Colour Index Internationa ...
, are considered to be nonirritating, nonallergenic, and non- comedogenic. Zinc from zinc oxide is, however, slightly absorbed into the skin.
Many sunscreens use nanoparticles of zinc oxide (along with nanoparticles of titanium dioxide) because such small particles do not scatter light and therefore do not appear white. The nanoparticles are not absorbed into the skin more than regular-sized zinc oxide particles are and are only absorbed into the outermost layer of the skin but not into the body.
Dental restoration
When mixed with eugenol
Eugenol is an allyl chain-substituted guaiacol, a member of the allylbenzene class of chemical compounds. It is a colorless to pale yellow, aromatic oily liquid extracted from certain essential oils especially from clove, nutmeg, cinnamon, ...
, zinc oxide eugenol is formed, which has applications as a restorative and prosthodontic in dentistry
Dentistry, also known as dental medicine and oral medicine, is the branch of medicine focused on the Human tooth, teeth, gums, and Human mouth, mouth. It consists of the study, diagnosis, prevention, management, and treatment of diseases, dis ...
.
Food additive
Zinc oxide is added to many food products, including breakfast cereal
Breakfast cereal is a category of food, including food products, made from food processing, processed cereal, cereal grains, that are eaten as part of breakfast or as a snack food, primarily in Western societies.
Although warm, cooked cereals li ...
s, as a source of zinc, a necessary nutrient
A nutrient is a substance used by an organism to survive, grow and reproduce. The requirement for dietary nutrient intake applies to animals, plants, fungi and protists. Nutrients can be incorporated into cells for metabolic purposes or excret ...
. Zinc may be added to food in the form of zinc oxide nanoparticle
A nanoparticle or ultrafine particle is a particle of matter 1 to 100 nanometres (nm) in diameter. The term is sometimes used for larger particles, up to 500 nm, or fibers and tubes that are less than 100 nm in only two directions. At ...
s, or as zinc sulfate
Zinc sulfate is an inorganic compound with the formula ZnSO4. It forms hydrates ZnSO4·''n''H2O, where ''n'' can range from 0 to 7. All are colorless solids. The most common form includes water of crystallization as the heptahydrate, with the che ...
, zinc gluconate, zinc acetate, or zinc citrate. Some foods also include trace amounts of ZnO even if it is not intended as a nutrient.
Pigment
Zinc oxide (zinc white) is used as a pigment
A pigment is a powder used to add or alter color or change visual appearance. Pigments are completely or nearly solubility, insoluble and reactivity (chemistry), chemically unreactive in water or another medium; in contrast, dyes are colored sub ...
in paint
Paint is a material or mixture that, when applied to a solid material and allowed to dry, adds a film-like layer. As art, this is used to create an image or images known as a painting. Paint can be made in many colors and types. Most paints are ...
s and is more opaque than lithopone, but less opaque than titanium dioxide
Titanium dioxide, also known as titanium(IV) oxide or titania , is the inorganic compound derived from titanium with the chemical formula . When used as a pigment, it is called titanium white, Pigment White 6 (PW6), or Colour Index Internationa ...
.[ It is also used in coatings for paper. Chinese white is a special grade of zinc white used in artists' pigments. The use of zinc white as a pigment in oil painting started in the middle of 18th century. It has partly replaced the poisonous lead white and was used by painters such as Böcklin, Van Gogh, Manet, Munch and others. It is also a main ingredient of mineral makeup (CI 77947).
]
UV absorber
Micronized and nano-scale zinc oxide provides strong protection against UVA and UVB ultraviolet radiation
Ultraviolet radiation, also known as simply UV, is electromagnetic radiation of wavelengths of 10–400 nanometers, shorter than that of visible light, but longer than X-rays. UV radiation is present in sunlight and constitutes about 10% of t ...
, and are consequently used in sunscreen
Sunscreen, also known as sunblock, sun lotion or sun cream, is a photoprotection, photoprotective topical product for the Human skin, skin that helps protect against sunburn and prevent skin cancer. Sunscreens come as lotions, sprays, gels, fo ...
s, and also in UV-blocking sunglasses for use in space and for protection when welding
Welding is a fabrication (metal), fabrication process that joins materials, usually metals or thermoplastics, primarily by using high temperature to melting, melt the parts together and allow them to cool, causing Fusion welding, fusion. Co ...
, following research by scientists at Jet Propulsion Laboratory ( JPL).
Coatings
Paints containing zinc oxide powder have long been utilized as anticorrosive coatings for metals. They are especially effective for galvanized iron. Iron is difficult to protect because its reactivity with organic coatings leads to brittleness and lack of adhesion. Zinc oxide paints retain their flexibility and adherence on such surfaces for many years.
ZnO highly n-type doped with aluminium
Aluminium (or aluminum in North American English) is a chemical element; it has chemical symbol, symbol Al and atomic number 13. It has a density lower than that of other common metals, about one-third that of steel. Aluminium has ...
, gallium
Gallium is a chemical element; it has Chemical symbol, symbol Ga and atomic number 31. Discovered by the French chemist Paul-Émile Lecoq de Boisbaudran in 1875,
elemental gallium is a soft, silvery metal at standard temperature and pressure. ...
, or indium
Indium is a chemical element; it has Symbol (chemistry), symbol In and atomic number 49. It is a silvery-white post-transition metal and one of the softest elements. Chemically, indium is similar to gallium and thallium, and its properties are la ...
is transparent and conductive ( transparency ~90%, lowest resistivity
Electrical resistivity (also called volume resistivity or specific electrical resistance) is a fundamental specific property of a material that measures its electrical resistance or how strongly it resists electric current. A low resistivity i ...
~10−4 Ω·cm). ZnO:Al coatings are used for energy-saving or heat-protecting windows. The coating lets the visible part of the spectrum in but either reflects the infrared (IR) radiation back into the room (energy saving) or does not let the IR radiation into the room (heat protection), depending on which side of the window has the coating.
Plastics, such as polyethylene naphthalate (PEN), can be protected by applying zinc oxide coating. The coating reduces the diffusion of oxygen through PEN. Zinc oxide layers can also be used on polycarbonate
Polycarbonates (PC) are a group of thermoplastic polymers containing carbonate ester, carbonate groups in their chemical structures. Polycarbonates used in engineering are strong, toughness, tough materials, and some grades are optically transp ...
in outdoor applications. The coating protects polycarbonate from solar radiation, and decreases its oxidation rate and photo-yellowing.
Corrosion prevention in nuclear reactors
Zinc oxide depleted in 64Zn (the zinc isotope with atomic mass
Atomic mass ( or ) is the mass of a single atom. The atomic mass mostly comes from the combined mass of the protons and neutrons in the nucleus, with minor contributions from the electrons and nuclear binding energy. The atomic mass of atoms, ...
64) is used in corrosion prevention in nuclear pressurized water reactor
A pressurized water reactor (PWR) is a type of light-water nuclear reactor. PWRs constitute the large majority of the world's nuclear power plants (with notable exceptions being the UK, Japan, India and Canada).
In a PWR, water is used both as ...
s. The depletion is necessary, because 64Zn is transformed into radioactive 65Zn under irradiation by the reactor neutrons.
Methane reforming
Zinc oxide (ZnO) is used as a pretreatment step to remove hydrogen sulfide
Hydrogen sulfide is a chemical compound with the formula . It is a colorless chalcogen-hydride gas, and is toxic, corrosive, and flammable. Trace amounts in ambient atmosphere have a characteristic foul odor of rotten eggs. Swedish chemist ...
(H2S) from natural gas
Natural gas (also fossil gas, methane gas, and gas) is a naturally occurring compound of gaseous hydrocarbons, primarily methane (95%), small amounts of higher alkanes, and traces of carbon dioxide and nitrogen, hydrogen sulfide and helium ...
following hydrogenation
Hydrogenation is a chemical reaction between molecular hydrogen (H2) and another compound or element, usually in the presence of a catalyst such as nickel, palladium or platinum. The process is commonly employed to redox, reduce or Saturated ...
of any sulfur
Sulfur ( American spelling and the preferred IUPAC name) or sulphur ( Commonwealth spelling) is a chemical element; it has symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms ...
compounds prior to a methane reformer A methane reformer is a device based on steam reforming, autothermal reforming or partial oxidation and is a type of chemical synthesis which can produce pure hydrogen gas from methane using a catalyst. There are multiple types of reformers in devel ...
, which can poison the catalyst. At temperatures between about , H2S is converted to water
Water is an inorganic compound with the chemical formula . It is a transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance. It is the main constituent of Earth's hydrosphere and the fluids of all known liv ...
by the following reaction:
:H2S + ZnO → H2O + ZnS
Electronics
ZnO has wide direct band gap (3.37 eV or 375 nm at room temperature). Therefore, its most common potential applications are in laser diodes and light emitting diodes (LEDs). Moreover, ultrafast nonlinearities and photoconductive functions have been reported in ZnO. Some optoelectronic applications of ZnO overlap with that of GaN, which has a similar band gap (~3.4 eV at room temperature). Compared to GaN, ZnO has a larger exciton binding energy (~60 meV, 2.4 times of the room-temperature thermal energy), which results in bright room-temperature emission from ZnO. ZnO can be combined with GaN for LED-applications. For instance, a transparent conducting oxide layer and ZnO nanostructures provide better light outcoupling. Other properties of ZnO favorable for electronic applications include its stability to high-energy radiation and its ability to be patterned by wet chemical etching. Radiation resistance makes ZnO a suitable candidate for space applications. Nanostructured ZnO is an effective medium both in powder and polycrystalline forms in random lasers, due to its high refractive index
In optics, the refractive index (or refraction index) of an optical medium is the ratio of the apparent speed of light in the air or vacuum to the speed in the medium. The refractive index determines how much the path of light is bent, or refrac ...
and aforementioned light emission properties.
Gas sensors
Zinc oxide is used in semiconductor gas sensors for detecting airborne compounds such as hydrogen sulfide
Hydrogen sulfide is a chemical compound with the formula . It is a colorless chalcogen-hydride gas, and is toxic, corrosive, and flammable. Trace amounts in ambient atmosphere have a characteristic foul odor of rotten eggs. Swedish chemist ...
, nitrogen dioxide, and volatile organic compound
Volatile organic compounds (VOCs) are organic compounds that have a high vapor pressure at room temperature. They are common and exist in a variety of settings and products, not limited to Indoor mold, house mold, Upholstery, upholstered furnitur ...
s. ZnO is a semiconductor that becomes n-doped by adsorption of reducing compounds, which reduces the detected electrical resistance through the device, in a manner similar to the widely used tin oxide semiconductor gas sensors. It is formed into nanostructures such as thin films, nanoparticle
A nanoparticle or ultrafine particle is a particle of matter 1 to 100 nanometres (nm) in diameter. The term is sometimes used for larger particles, up to 500 nm, or fibers and tubes that are less than 100 nm in only two directions. At ...
s, nanopillars, or nanowire
file:[email protected], upright=1.2, Crystalline 2×2-atom tin selenide nanowire grown inside a single-wall carbon nanotube (tube diameter ≈1 nm).
A nanowire is a nanostructure in the form of a wire with the diameter of the order of a nanometre ( ...
s to provide a large surface area for interaction with gasses. The sensors are made selective for specific gasses by doping or surface-attaching materials such as catalytic noble metals.
Aspirational applications
Transparent electrodes
Aluminium-doped ZnO layers are used as transparent electrode
An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or a gas). In electrochemical cells, electrodes are essential parts that can consist of a varie ...
s. The components Zn and Al are much cheaper and less toxic compared to the generally used indium tin oxide
Indium tin oxide (ITO) is a ternary composition of indium, tin and oxygen in varying proportions. Depending on the oxygen content, it can be described as either a ceramic or an alloy. Indium tin oxide is typically encountered as an oxygen-saturate ...
(ITO). One application which has begun to be commercially available is the use of ZnO as the front contact for solar cells or of liquid crystal display
A liquid-crystal display (LCD) is a flat-panel display or other Electro-optic modulator, electronically modulated optical device that uses the light-modulating properties of liquid crystals combined with polarizers to display information. Liq ...
s.
Transparent thin-film transistor
A transistor is a semiconductor device used to Electronic amplifier, amplify or electronic switch, switch electrical signals and electric power, power. It is one of the basic building blocks of modern electronics. It is composed of semicondu ...
s (TTFT) can be produced with ZnO. As field-effect transistors, they do not need a p–n junction, thus avoiding the p-type doping problem of ZnO. Some of the field-effect transistors even use ZnO nanorods as conducting channels.
Piezoelectricity
The piezoelectricity
Piezoelectricity (, ) is the electric charge that accumulates in certain solid materials—such as crystals, certain ceramics, and biological matter such as bone, DNA, and various proteins—in response to applied mechanical stress.
The piezoel ...
in textile
Textile is an Hyponymy and hypernymy, umbrella term that includes various Fiber, fiber-based materials, including fibers, yarns, Staple (textiles)#Filament fiber, filaments, Thread (yarn), threads, and different types of #Fabric, fabric. ...
fibers coated in ZnO have been shown capable of fabricating "self-powered nanosystems" with everyday mechanical stress from wind or body movements.
Photocatalysis
ZnO, both in macro- and nano- scales, could in principle be used as an electrode in photocatalysis, mainly as an anode
An anode usually is an electrode of a polarized electrical device through which conventional current enters the device. This contrasts with a cathode, which is usually an electrode of the device through which conventional current leaves the devic ...
in green chemistry
Green chemistry, similar to sustainable chemistry or circular chemistry, is an area of chemistry and chemical engineering focused on the design of products and processes that minimize or eliminate the use and generation of hazardous substances. Wh ...
applications. As a photocatalyst, ZnO reacts when exposed to UV radiation and is used in photodegradation reactions to remove organic pollutants from the environment. It is also used to replace catalysts used in photochemical reactions that would ordinarily require costly or inconvenient reaction conditions with low yields.
Other
The pointed tips of ZnO nanorods could be used as field emitters.
ZnO is a promising anode material for lithium-ion battery
A lithium-ion or Li-ion battery is a type of rechargeable battery that uses the reversible intercalation of Li+ ions into electronically conducting solids to store energy. Li-ion batteries are characterized by higher specific energy, energ ...
because it is cheap, biocompatible, and environmentally friendly. ZnO has a higher theoretical capacity (978 mAh g−1) than many other transition metal oxides such as CoO (715 mAh g−1), NiO (718 mAh g−1) and CuO (674 mAh g−1). ZnO is also used as an electrode in supercapacitors.
Safety
As a food additive
Food additives are substances added to food to preserve flavor or enhance taste, appearance, or other sensory qualities. Some additives, such as vinegar ( pickling), salt ( salting), smoke ( smoking) and sugar ( crystallization), have been used f ...
, zinc oxide is on the U.S. Food and Drug Administration
The United States Food and Drug Administration (FDA or US FDA) is a List of United States federal agencies, federal agency of the United States Department of Health and Human Services, Department of Health and Human Services. The FDA is respo ...
's list of generally recognized as safe
Generally recognized as safe (GRAS) is a United States Food and Drug Administration (FDA) designation that a chemical or substance added to food is considered safe by experts under the conditions of its intended use. An ingredient with a GRAS d ...
substances.
Zinc oxide itself is non-toxic; it is hazardous, however, to inhale high concentrations of zinc oxide fumes, such as those generated when zinc or zinc alloys are melted and oxidized at high temperature. This problem occurs while melting alloys containing brass
Brass is an alloy of copper and zinc, in proportions which can be varied to achieve different colours and mechanical, electrical, acoustic and chemical properties, but copper typically has the larger proportion, generally copper and zinc. I ...
because the melting point of brass is close to the boiling point of zinc. Inhalation of zinc oxide, which may occur when welding galvanized (zinc-plated) steel
Steel is an alloy of iron and carbon that demonstrates improved mechanical properties compared to the pure form of iron. Due to steel's high Young's modulus, elastic modulus, Yield (engineering), yield strength, Fracture, fracture strength a ...
, can result in a malady called metal fume fever.
In sunscreen formulations that combined zinc oxide with small-molecule UV absorbers, UV light caused photodegradation of the small-molecule absorbers and toxicity in embryonic zebrafish assays.
See also
* Depleted zinc oxide
* Zinc oxide nanoparticle
* Gallium(III) nitride
* List of inorganic pigments
The following list includes commercially or artistically important inorganic pigments of natural and synthetic origin..
Purple pigments
Aluminosilicate pigments
* Ultramarine violet (): a synthetic or naturally occurring sulfur containing silica ...
* Zinc
Zinc is a chemical element; it has symbol Zn and atomic number 30. It is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodic tabl ...
* Zinc oxide eugenol
* Zinc peroxide
* Zinc smelting
* Zinc–air battery
* Zinc–zinc oxide cycle
* ZnO nanostructures
References
Cited sources
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Reviews
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External links
Zincite properties
*
Zinc white pigment
at ColourLex
{{Authority control
Amphoteric compounds
Antipruritics
Ceramic materials
Corrosion inhibitors
II-VI semiconductors
Inorganic pigments
Nonlinear optical materials
Oxides
Piezoelectric materials
Sunscreening agents
Wurtzite structure type
oxide
An oxide () is a chemical compound containing at least one oxygen atom and one other element in its chemical formula. "Oxide" itself is the dianion (anion bearing a net charge of −2) of oxygen, an O2− ion with oxygen in the oxidation st ...