Zinc oxide
Overview
 
Zinc oxide is an inorganic compound
Inorganic compound
Inorganic compounds have traditionally been considered to be of inanimate, non-biological origin. In contrast, organic compounds have an explicit biological origin. However, over the past century, the classification of inorganic vs organic compounds has become less important to scientists,...

 with the formula
Chemical formula
A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....

 ZnO. It is a white powder that is insoluble in water. The powder is widely used as an additive into numerous materials and products including plastics, ceramics, glass, cement, rubber (e.g., car tires), lubricants, paints, ointments, adhesives, sealants, pigments, foods (source of Zn nutrient
Nutrient
A nutrient is a chemical that an organism needs to live and grow or a substance used in an organism's metabolism which must be taken in from its environment. They are used to build and repair tissues, regulate body processes and are converted to and used as energy...

), batteries, ferrites, fire retardants, first aid tapes, etc. ZnO is present in the Earth's crust as the mineral zincite
Zincite
Zincite is the mineral form of zinc oxide . Its crystal form is rare in nature; a notable exception to this is at the Franklin and Sterling Hill Mines in New Jersey, an area also famed for its many fluorescent minerals. It has a hexagonal crystal structure and a color that depends on the presence...

, however, most ZnO used commercially is synthetic.

In materials science
Materials science
Materials science is an interdisciplinary field applying the properties of matter to various areas of science and engineering. This scientific field investigates the relationship between the structure of materials at atomic or molecular scales and their macroscopic properties. It incorporates...

, ZnO is a wide-bandgap semiconductor of the II-VI semiconductor group (since zinc
Zinc
Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...

 and oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

 belong to the 2nd and 6th groups of the periodic table
Periodic table
The periodic table of the chemical elements is a tabular display of the 118 known chemical elements organized by selected properties of their atomic structures. Elements are presented by increasing atomic number, the number of protons in an atom's atomic nucleus...

, respectively).
Encyclopedia
Zinc oxide is an inorganic compound
Inorganic compound
Inorganic compounds have traditionally been considered to be of inanimate, non-biological origin. In contrast, organic compounds have an explicit biological origin. However, over the past century, the classification of inorganic vs organic compounds has become less important to scientists,...

 with the formula
Chemical formula
A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....

 ZnO. It is a white powder that is insoluble in water. The powder is widely used as an additive into numerous materials and products including plastics, ceramics, glass, cement, rubber (e.g., car tires), lubricants, paints, ointments, adhesives, sealants, pigments, foods (source of Zn nutrient
Nutrient
A nutrient is a chemical that an organism needs to live and grow or a substance used in an organism's metabolism which must be taken in from its environment. They are used to build and repair tissues, regulate body processes and are converted to and used as energy...

), batteries, ferrites, fire retardants, first aid tapes, etc. ZnO is present in the Earth's crust as the mineral zincite
Zincite
Zincite is the mineral form of zinc oxide . Its crystal form is rare in nature; a notable exception to this is at the Franklin and Sterling Hill Mines in New Jersey, an area also famed for its many fluorescent minerals. It has a hexagonal crystal structure and a color that depends on the presence...

, however, most ZnO used commercially is synthetic.

In materials science
Materials science
Materials science is an interdisciplinary field applying the properties of matter to various areas of science and engineering. This scientific field investigates the relationship between the structure of materials at atomic or molecular scales and their macroscopic properties. It incorporates...

, ZnO is a wide-bandgap semiconductor of the II-VI semiconductor group (since zinc
Zinc
Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...

 and oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

 belong to the 2nd and 6th groups of the periodic table
Periodic table
The periodic table of the chemical elements is a tabular display of the 118 known chemical elements organized by selected properties of their atomic structures. Elements are presented by increasing atomic number, the number of protons in an atom's atomic nucleus...

, respectively). The native doping of the semiconductor (due to oxygen vacancies) is n-type. This semiconductor has several favorable properties: good transparency, high electron mobility
Electron mobility
In solid-state physics, the electron mobility characterizes how quickly an electron can move through a metal or semiconductor, when pulled by an electric field. In semiconductors, there is an analogous quantity for holes, called hole mobility...

, wide bandgap, strong room-temperature luminescence
Luminescence
Luminescence is emission of light by a substance not resulting from heat; it is thus a form of cold body radiation. It can be caused by chemical reactions, electrical energy, subatomic motions, or stress on a crystal. This distinguishes luminescence from incandescence, which is light emitted by a...

, etc. Those properties are already used in emerging applications for transparent electrode
Electrode
An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit...

s in liquid crystal display
Liquid crystal display
A liquid crystal display is a flat panel display, electronic visual display, or video display that uses the light modulating properties of liquid crystals . LCs do not emit light directly....

s and in energy-saving or heat-protecting windows, and electronic applications of ZnO as thin-film transistor
Transistor
A transistor is a semiconductor device used to amplify and switch electronic signals and power. It is composed of a semiconductor material with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals changes the current...

s and light-emitting diode
Light-emitting diode
A light-emitting diode is a semiconductor light source. LEDs are used as indicator lamps in many devices and are increasingly used for other lighting...

s are forthcoming as of 2009.

Chemical properties

ZnO occurs as white powder known as zinc white or as the mineral zincite
Zincite
Zincite is the mineral form of zinc oxide . Its crystal form is rare in nature; a notable exception to this is at the Franklin and Sterling Hill Mines in New Jersey, an area also famed for its many fluorescent minerals. It has a hexagonal crystal structure and a color that depends on the presence...

. The mineral usually contains a certain amount of manganese and other elements that confer yellow to red color. Crystalline zinc oxide is thermochromic
Thermochromism
Thermochromism is the ability of substance to change color due to a change in temperature. A mood ring is an excellent example of this, but it has many other uses such as baby bottles and kettles. Thermochromism is one of several types of chromism.The two basic approaches are based on liquid...

, changing from white to yellow when heated and in air reverting to white on cooling. This color change is caused by a very small loss of oxygen at high temperatures to form the non-stoichiometric Zn1+xO, where at 800 °C, x = 0.00007.

Zinc oxide is an amphoteric oxide. It is nearly insoluble
Solubility
Solubility is the property of a solid, liquid, or gaseous chemical substance called solute to dissolve in a solid, liquid, or gaseous solvent to form a homogeneous solution of the solute in the solvent. The solubility of a substance fundamentally depends on the used solvent as well as on...

 in water and alcohol, but it is soluble in (degraded by) most acid
Acid
An acid is a substance which reacts with a base. Commonly, acids can be identified as tasting sour, reacting with metals such as calcium, and bases like sodium carbonate. Aqueous acids have a pH of less than 7, where an acid of lower pH is typically stronger, and turn blue litmus paper red...

s, such as hydrochloric acid:
ZnO + 2 HCl → ZnCl2 + H2O


Bases also degrade the solid to give soluble zincates:
ZnO + 2 NaOH + H2O → Na2[Zn(OH)4]


ZnO reacts slowly with fatty acids in oils to produce the corresponding carboxylates, such as oleate or stearate
Stearate
Stearateis the anion form of stearic acid.Formula is C17H35COO−.-Examples:* Sodium stearate, Na* Calcium stearate, Ca2* Magnesium stearate, Mg2...

. ZnO forms cement-like products when mixed with a strong aqueous solution of zinc chloride
Zinc chloride
Zinc chloride is the name of chemical compound with the formula ZnCl2 and its hydrates. Zinc chlorides, of which nine crystalline forms are known, are colorless or white, and are highly soluble in water. ZnCl2 itself is hygroscopic and even deliquescent. Samples should therefore be protected from...

 and these are best described as zinc hydroxy chlorides. This cement was used in dentistry.
ZnO also forms cement-like products when treated with phosphoric acid
Phosphoric acid
Phosphoric acid, also known as orthophosphoric acid or phosphoric acid, is a mineral acid having the chemical formula H3PO4. Orthophosphoric acid molecules can combine with themselves to form a variety of compounds which are also referred to as phosphoric acids, but in a more general way...

; related materials are used in dentistry. A major component of zinc phosphate cement produced by this reaction is hopeite
Hopeite
Hopeite is a hydrated zinc phosphate with formula: Zn32·4H2O. It is a rare mineral used mainly as a collectors specimen.Hopeite crystallizes in the orthorhombic system with prismatic, vitreous white to yellow crystals...

, Zn3(PO4)2·4H2O.

ZnO decomposes into zinc vapor and oxygen only at around 1975 °C, reflecting its considerable stability. Heating with carbon converts the oxide into the metal, which is more volatile than the oxide.
ZnO + C → Zn + CO


Zinc oxide can react violently with aluminium
Aluminium
Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....

 and magnesium
Magnesium
Magnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...

 powders, with chlorinated rubber and linseed oil
Linseed oil
Linseed oil, also known as flaxseed oil, is a clear to yellowish oil obtained from the dried ripe seeds of the flax plant . The oil is obtained by cold pressing, sometimes followed by solvent extraction...

 on heating causing fire and explosion hazard.

It reacts with hydrogen sulfide
Hydrogen sulfide
Hydrogen sulfide is the chemical compound with the formula . It is a colorless, very poisonous, flammable gas with the characteristic foul odor of expired eggs perceptible at concentrations as low as 0.00047 parts per million...

 to give the sulfide
Zinc sulfide
Zinc sulfide is a inorganic compound with the formula ZnS. ZnS is the main form of zinc in nature, where it mainly occurs as the mineral sphalerite...

: this reaction is used commercially in removing H2S using ZnO powder (e.g., as deodorant).
ZnO + H2S → ZnS + H2O


When ointments containing ZnO and water are melted and exposed to ultraviolet
Ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...

 light, hydrogen peroxide
Hydrogen peroxide
Hydrogen peroxide is the simplest peroxide and an oxidizer. Hydrogen peroxide is a clear liquid, slightly more viscous than water. In dilute solution, it appears colorless. With its oxidizing properties, hydrogen peroxide is often used as a bleach or cleaning agent...

 is produced.

Physical properties

Structure

Zinc oxide crystallizes in two main forms
Polymorphism (materials science)
Polymorphism in materials science is the ability of a solid material to exist in more than one form or crystal structure. Polymorphism can potentially be found in any crystalline material including polymers, minerals, and metals, and is related to allotropy, which refers to chemical elements...

, hexagonal wurtzite 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
Tetrahedral molecular geometry
In a tetrahedral molecular geometry a central atom is located at the center with four substituents that are located at the corners of a tetrahedron. The bond angles are cos−1 ≈ 109.5° when all four substituents are the same, as in CH4. This molecular geometry is common throughout the first...

, the most characteristic geometry for Zn(II).

In addition to the wurtzite and zincblende polymorphs, ZnO can be crystallises in the rocksalt
Sodium chloride
Sodium chloride, also known as salt, common salt, table salt or halite, is an inorganic compound with the formula NaCl. Sodium chloride is the salt most responsible for the salinity of the ocean and of the extracellular fluid of many multicellular organisms...

 motif at relatively high pressures about 10 GPa.

Hexagonal and zincblende polymorphs have no inversion symmetry
Reflection symmetry
Reflection symmetry, reflectional symmetry, line symmetry, mirror symmetry, mirror-image symmetry, or bilateral symmetry is symmetry with respect to reflection. That is, a figure which does not change upon undergoing a reflection has reflectional symmetry.In 2D there is a line of symmetry, in 3D a...

 (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
Piezoelectricity is the charge which accumulates in certain solid materials in response to applied mechanical stress. The word piezoelectricity means electricity resulting from pressure...

 of the hexagonal and zincblende ZnO, and pyroelectricity
Pyroelectricity
Pyroelectricity is the ability of certain materials to generate a temporary voltage when they are heated or cooled. The change in temperature modifies the positions of the atoms slightly within the crystal structure, such that the polarization of the material changes. This polarization change...

 of hexagonal ZnO.

The hexagonal structure has a point group 6 mm (Hermann-Mauguin notation
Hermann-Mauguin notation
Hermann–Mauguin notation is used to represent the symmetry elements in point groups, plane groups and space groups. It is named after the German crystallographer Carl Hermann and the French mineralogist Charles-Victor Mauguin...

) or C6v (Schoenflies notation
Schoenflies notation
The Schoenflies notation or Schönflies notation, named after the German mathematician Arthur Moritz Schoenflies, is one of two conventions commonly used to describe Point groups. This notation is used in spectroscopy. The other convention is the Hermann–Mauguin notation, also known as the...

), and the space group
Space group
In mathematics and geometry, a space group is a symmetry group, usually for three dimensions, that divides space into discrete repeatable domains.In three dimensions, there are 219 unique types, or counted as 230 if chiral copies are considered distinct...

 is P63mc or C6v4. 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
Ionic bond
An ionic bond is a type of chemical bond formed through an electrostatic attraction between two oppositely charged ions. Ionic bonds are formed between a cation, which is usually a metal, and an anion, which is usually a nonmetal. Pure ionic bonding cannot exist: all ionic compounds have some...

, which explains its strong piezoelectricity
Piezoelectricity
Piezoelectricity is the charge which accumulates in certain solid materials in response to applied mechanical stress. The word piezoelectricity means electricity resulting from pressure...

. Due to the polar Zn-O bonds, zinc and oxygen planes bear electric charge (positive and negative, respectively). Therefore, 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. This anomaly of ZnO is not fully explained yet.

Mechanical properties

ZnO is a relatively soft material with approximate hardness of 4.5 on the Mohs scale. Its elastic constants are smaller than those of relevant III-V semiconductors, such as GaN
Gan
Gan may refer to:-Computing and telecommunications:*.gan, the file extension for documents created by GanttProject*Generic Access Network formerly known as Unlicensed Mobile Access *Global Area Network- Mythology :...

. The high heat capacity and heat conductivity, low thermal expansion and high melting temperature of ZnO are beneficial for ceramics.
ZnO's most stable phase being wurtzite, ZnO exhibits a very long lived optical phonon E2(low) with a lifetime as high as 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
Gan
Gan may refer to:-Computing and telecommunications:*.gan, the file extension for documents created by GanttProject*Generic Access Network formerly known as Unlicensed Mobile Access *Global Area Network- Mythology :...

 and AlN
ALN
ALN, AlN or Aln may refer to:* Ação Libertadora Nacional* Africa Liberal Network* Alianza Liberal Nicaragüense, a political party in Nicaragua* Aln, a pre-metric Swedish measurement of length* Aluminium nitride...

. This property makes it a technologically important material for many piezoelectrical
Piezoelectricity
Piezoelectricity is the charge which accumulates in certain solid materials in response to applied mechanical stress. The word piezoelectricity means electricity resulting from pressure...

 applications, which require a large electromechanical coupling.

Electrical properties

ZnO has a relatively large direct band gap
Band gap
In solid state physics, a band gap, also called an energy gap or bandgap, is an energy range in a solid where no electron states can exist. In graphs of the electronic band structure of solids, the band gap generally refers to the energy difference between the top of the valence band and the...

 of ~3.3 eV at room temperature. Advantages associated with a large band gap include higher breakdown voltages, ability to sustain large electric fields, lower electronic noise
Electronic noise
Electronic noise is a random fluctuation in an electrical signal, a characteristic of all electronic circuits. Noise generated by electronic devices varies greatly, as it can be produced by several different effects...

, and high-temperature and high-power operation. The bandgap of ZnO can further be tuned to ~3–4 eV by its alloying with magnesium oxide
Magnesium oxide
Magnesium oxide , or magnesia, is a white hygroscopic solid mineral that occurs naturally as periclase and is a source of magnesium . It has an empirical formula of and consists of a lattice of Mg2+ ions and O2– ions held together by ionic bonds...

 or cadmium oxide
Cadmium oxide
Cadmium oxide is an inorganic compound with the formula CdO. It is one of the main precursors to other cadmium compounds. It crystallizes in a cubic rocksalt lattice like sodium chloride, with octahedral cation and anion centers. It occurs naturally as the rare mineral monteponite. Cadmium oxide...

.

Most ZnO has n-type
N-type semiconductor
N-type semiconductors are a type of extrinsic semiconductor where the dopant atoms are capable of providing extra conduction electrons to the host material . This creates an excess of negative electron charge carriers....

 character, even in the absence of intentional doping
Doping (semiconductor)
In semiconductor production, doping intentionally introduces impurities into an extremely pure semiconductor for the purpose of modulating its electrical properties. The impurities are dependent upon the type of semiconductor. Lightly and moderately doped semiconductors are referred to as extrinsic...

. 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
Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...

 or iodine
Iodine
Iodine is a chemical element with the symbol I and atomic number 53. The name is pronounced , , or . The name is from the , meaning violet or purple, due to the color of elemental iodine vapor....

.

Reliable p-type
P-type semiconductor
A P-type semiconductor is obtained by carrying out a process of doping: that is, adding a certain type of atoms to the semiconductor in order to increase the number of free charge carriers ....

 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
Gan
Gan may refer to:-Computing and telecommunications:*.gan, the file extension for documents created by GanttProject*Generic Access Network formerly known as Unlicensed Mobile Access *Global Area Network- Mythology :...

 and ZnSe. Measurement of p-type in "intrinsically" n-type material is complicated by the inhomogeneity of samples.

Current limitations to p-doping does not 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
Electron mobility
In solid-state physics, the electron mobility characterizes how quickly an electron can move through a metal or semiconductor, when pulled by an electric field. In semiconductors, there is an analogous quantity for holes, called hole mobility...

 of ZnO strongly varies with temperature and has a maximum of ~2000 cm2/(V·s) at 80 K. Data on hole mobility are scarce with values in the range 5–30 cm2/(V·s).

Production

For industrial use, ZnO is produced at levels of 105 tons per year by three main processes:

Indirect (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 LeClaire (France) 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 (American) process

The direct process starts with diverse contaminated zinc composites, such as zinc ores
Calamine (mineral)
Calamine is a historic name for an ore of zinc. The name calamine was derived from the Belgian town of Kelmis, whose French name is "La Calamine", which is home to a zinc mine...

 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 purified zinc salts, from which zinc carbonate or zinc hydroxide
Zinc hydroxide
Zinc hydroxide Zn2 is an inorganic chemical compound. It also occurs naturally as 3 rare minerals: wülfingite , ashoverite and sweetite ....

 is precipitated. The precipitate is then filtered, washed, dried and calcined at temperatures around 800 °C.

Laboratory synthesis

A large number of 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
Nanowire
A nanowire is a nanostructure, with the diameter of the order of a nanometer . Alternatively, nanowires can be defined as structures that have a thickness or diameter constrained to tens of nanometers or less and an unconstrained length. At these scales, quantum mechanical effects are important —...

), 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) are usually grown by the gas transport (vapor-phase deposition), hydrothermal synthesis
Hydrothermal synthesis
Hydrothermal synthesis includes the various techniques of crystallizing substances from high-temperature aqueous solutions at high vapor pressures; also termed "hydrothermal method". The term "hydrothermal" is of geologic origin. Geochemists and mineralogists have studied hydrothermal phase...

, or melt growth. However, because of high vapor pressure
Vapor pressure
Vapor pressure or equilibrium vapor pressure is the pressure of a vapor in thermodynamic equilibrium with its condensed phases in a closed system. All liquids have a tendency to evaporate, and some solids can sublimate into a gaseous form...

 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 chemical vapor deposition
Chemical vapor deposition
Chemical vapor deposition is a chemical process used to produce high-purity, high-performance solid materials. The process is often used in the semiconductor industry to produce thin films. In a typical CVD process, the wafer is exposed to one or more volatile precursors, which react and/or...

, metalorganic vapour phase epitaxy
Metalorganic vapour phase epitaxy
Metalorganic vapour phase epitaxy , also known as organometallic vapour phase epitaxy or metalorganic chemical vapour deposition , is a chemical vapour deposition method of epitaxial growth of materials, especially compound semiconductors, from the surface reaction of organic compounds or...

, electrodeposition
Electrophoretic deposition
Electrophoretic deposition , is a term for a broad range of industrial processes which includes electrocoating, e-coating, cathodic electrodeposition, and electrophoretic coating, or electrophoretic painting...

, pulsed laser deposition
Pulsed laser deposition
Pulsed laser deposition is a thin film deposition technique where a high power pulsed laser beam is focused inside a vacuum chamber to strike a target of the material that is to be deposited...

, sputtering
Sputtering
Sputtering is a process whereby atoms are ejected from a solid target material due to bombardment of the target by energetic particles. It is commonly used for thin-film deposition, etching and analytical techniques .-Physics of sputtering:...

, sol-gel synthesis, atomic layer deposition
Atomic layer deposition
Atomic layer deposition is a thin film deposition technique that is based on the sequential use of a gas phase chemical process. The majority of ALD reactions use two chemicals, typically called precursors. These precursors react with a surface one-at-a-time in a sequential manner...

, spray pyrolysis, etc.

Ordinary white powdered zinc oxide can be produced in the laboratory by electrolyzing a solution of sodium bicarbonate with a zinc anode. Zinc hydroxide and hydrogen gas are produced. The zinc hydroxide upon heating decomposes to zinc oxide.
Zn + 2 H2O → Zn(OH)2 + H2

Zn(OH)2 → ZnO + H2O

Nanophase ZnO

Nanophase 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
Vapor-liquid-solid method
The vapor–liquid–solid method is a mechanism for the growth of one-dimensional structures, such as nanowires, from chemical vapor deposition. The growth of a crystal through direct adsorption of a gas phase on to a solid surface is generally very slow...

.

Rodlike nanostructures of ZnO can be produced via aqueous methods. They are attractive because of relatively low synthesis temperatures (<300 °C) and absence of complex vacuum setup. The synthesis is typically carried out at temperatures of about 90 °C, in an equimolar aqueous solution of zinc nitrate and hexamine
Hexamine
Hexamethylenetetramine is a heterocyclic organic compound with the formula 6N4. This white crystalline compound is highly soluble in water and polar organic solvents. It has a cage-like structure similar to adamantane. It is useful in the synthesis of other chemical compounds, e.g. plastics,...

, 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
Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...

, glass
Glass
Glass is an amorphous solid material. Glasses are typically brittle and optically transparent.The most familiar type of glass, used for centuries in windows and drinking vessels, is soda-lime glass, composed of about 75% silica plus Na2O, CaO, and several minor additives...

 and gallium nitride substrates have been grown in aqueous solutions using aqueous zinc salts such as Zinc nitrate
Zinc nitrate
Zinc nitrate is a highly deliquescent substance which is usually prepared by dissolving zinc in nitric acid. It can be used as a mordant in dyeing...

 and Zinc acetate
Zinc acetate
Zinc acetate is the chemical compound with the formula Zn2, which commonly occurs as a dihydrate Zn22. Both the hydrate and the anhydrous forms are colorless solids that are commonly used in chemical synthesis and as dietary supplements. Zinc acetates are prepared by the action of acetic acid on...

 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
Zinc acetate
Zinc acetate is the chemical compound with the formula Zn2, which commonly occurs as a dihydrate Zn22. Both the hydrate and the anhydrous forms are colorless solids that are commonly used in chemical synthesis and as dietary supplements. Zinc acetates are prepared by the action of acetic acid on...

 crystallites, spincoating of ZnO nanoparticles and the use of various physical vapor deposition
Physical vapor deposition
Physical vapor deposition is a variety of vacuum deposition and is a general term used to describe any of a variety of methods to deposit thin films by the condensation of a vaporized form of the desired film material onto various workpiece surfaces...

 methods to deposit ZnO thin films. Pre-seeding can be performed in conjunction with top down patterning methods such as electron beam lithography
Electron beam lithography
Electron beam lithography is the practice of emitting a beam of electrons in a patterned fashion across a surface covered with a film , and of selectively removing either exposed or non-exposed regions of the resist...

 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
Refractive index
In optics the refractive index or index of refraction of a substance or medium is a measure of the speed of light in that medium. It is expressed as a ratio of the speed of light in vacuum relative to that in the considered medium....

, high thermal conductivity, binding, antibacterial and UV-protection properties. Consequently, it is added into various materials and products, including plastics, ceramics, glass, cement, rubber, lubricants, paints, ointments, adhesive, sealants, pigments, foods, batteries, ferrites, fire retardants, etc.

Rubber manufacture

About 50% of ZnO use is in the rubber industry. Zinc oxide along with stearic acid
Stearic acid
Stearic acid is the saturated fatty acid with an 18 carbon chain and has the IUPAC name octadecanoic acid. It is a waxy solid, and its chemical formula is CH316CO2H. Its name comes from the Greek word στέαρ "stéatos", which means tallow. The salts and esters of stearic acid are called stearates...

 is used in the vulcanization
Vulcanization
Vulcanization or vulcanisation is a chemical process for converting rubber or related polymers into more durable materials via the addition of sulfur or other equivalent "curatives." These additives modify the polymer by forming crosslinks between individual polymer chains. Vulcanized material is...

 of rubber ZnO additive also protect rubber from fungi (see medical applications) and UV light.

Concrete industry

Zinc oxide is widely used for concrete
Concrete
Concrete is a composite construction material, composed of cement and other cementitious materials such as fly ash and slag cement, aggregate , water and chemical admixtures.The word concrete comes from the Latin word...

 manufacturing. Addition of ZnO improves the processing time and the resistance of concrete against water.

Medical

Zinc oxide as a mixture with about 0.5% iron(III) oxide
Iron(III) oxide
Iron oxide or ferric oxide is the inorganic compound with the formula Fe2O3. It is one of the three main oxides of iron, the other two being iron oxide , which is rare, and iron oxide , which also occurs naturally as the mineral magnetite. As the mineral known as hematite, Fe2O3 is the main...

 (Fe2O3) is called calamine
Calamine
Calamine is a mixture of zinc oxide with about 0.5% ferric oxide . It is the main ingredient in calamine lotion and is used as an antipruritic to treat mild pruritic conditions such as sunburn, eczema, rashes, poison ivy, chickenpox, and insect bites and stings...

 and is used in calamine lotion. There are also two minerals, zincite
Zincite
Zincite is the mineral form of zinc oxide . Its crystal form is rare in nature; a notable exception to this is at the Franklin and Sterling Hill Mines in New Jersey, an area also famed for its many fluorescent minerals. It has a hexagonal crystal structure and a color that depends on the presence...

 and hemimorphite
Hemimorphite
Hemimorphite, is a sorosilicate mineral which has been mined from days of old from the upper parts of zinc and lead ores, chiefly associated with smithsonite. It was often assumed to be the same mineral and both were classed under the same name of calamine...

, which have been historically called calamine
Calamine (mineral)
Calamine is a historic name for an ore of zinc. The name calamine was derived from the Belgian town of Kelmis, whose French name is "La Calamine", which is home to a zinc mine...

. When mixed with eugenol
Eugenol
Eugenol is a phenylpropene, an allyl chain-substituted guaiacol. Eugenol is a member of the phenylpropanoids class of chemical compounds. It is a clear to pale yellow oily liquid extracted from certain essential oils especially from clove oil, nutmeg, cinnamon, basil and bay leaf. It is slightly...

, a ligand
Ligand
In coordination chemistry, a ligand is an ion or molecule that binds to a central metal atom to form a coordination complex. The bonding between metal and ligand generally involves formal donation of one or more of the ligand's electron pairs. The nature of metal-ligand bonding can range from...

, zinc oxide eugenol
Zinc Oxide Eugenol
Zinc oxide eugenol is a material created by the combination of zinc oxide and eugenol contained in oil of cloves. An acid-base reaction takes place with the formation of zinc eugenolate chelate. The reaction is catalysed by water and is accelerated by the presence metal salts. ZOE can be used as...

 is formed, which has applications as restorative
Dental restoration
A dental restoration or dental filling is a dental restorative material used to restore the function, integrity and morphology of missing tooth structure. The structural loss typically results from caries or external trauma. It is also lost intentionally during tooth preparation to improve the...

 and prosthodontic
Prosthodontics
Prosthodontics, also known as dental prosthetics or prosthetic dentistry, is one of nine dental specialties recognized by the American Dental Association, Royal College of Dentists of Canada, and Royal Australasian College of Dental Surgeons...

 in dentistry
Dentistry
Dentistry is the branch of medicine that is involved in the study, diagnosis, prevention, and treatment of diseases, disorders and conditions of the oral cavity, maxillofacial area and the adjacent and associated structures and their impact on the human body. Dentistry is widely considered...

.

Reflecting the basic properties of ZnO, fine particles of the oxide have deodorizing and antibacterial action and for that reason are added into various materials including cotton fabric, rubber, food packaging, etc. Enhanced antibacterial action of fine particles compared to bulk material is not intrinsic to ZnO and is observed for other materials, such as silver
Silver
Silver is a metallic chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal...

.

Zinc oxide is widely used to treat a variety of other skin conditions, in products such as baby powder
Baby powder
Baby powder is an astringent powder used for preventing diaper rash, as a deodorant, and for other cosmetic uses. It may be composed of talc or corn starch. Talcum powder is harmful if inhaled since it may cause aspiration pneumonia or granuloma. Drugs such as cocaine are sometimes cut with...

 and barrier cream
Barrier cream
A barrier cream is a topical formulation used in industrial and medical environments to place a physical barrier between the skin and contaminants which may irritate the skin and cause contact dermatitis or occupational dermatitis.- Medical application :...

s to treat diaper rash
Diaper rash
Irritant diaper dermatitis is a generic term applied to skin rashes in the diaper area that are caused by various skin disorders and/or irritants.Generic rash or irritant diaper dermatitis is characterized by joined patches of erythema and...

es, calamine
Calamine
Calamine is a mixture of zinc oxide with about 0.5% ferric oxide . It is the main ingredient in calamine lotion and is used as an antipruritic to treat mild pruritic conditions such as sunburn, eczema, rashes, poison ivy, chickenpox, and insect bites and stings...

 cream, anti-dandruff
Dandruff
Dandruff is the shedding of dead skin cells from the scalp . Dandruff is sometimes caused by frequent exposure to extreme heat and cold. As it is normal for skin cells to die and flake off, a small amount of flaking is normal and common; about 487,000 cells/cm2 get released normally after...

 shampoo
Shampoo
Shampoo is a hair care product used for the removal of oils, dirt, skin particles, dandruff, environmental pollutants and other contaminant particles that gradually build up in hair...

s, and antiseptic
Antiseptic
Antiseptics are antimicrobial substances that are applied to living tissue/skin to reduce the possibility of infection, sepsis, or putrefaction...

 ointments. It is also a component in tape (called "zinc oxide tape") used by athletes as a bandage to prevent soft tissue damage during workouts.

Zinc oxide can be used in ointments, creams, and lotion
Lotion
A lotion is a low- to medium-viscosity, topical preparation intended for application to unbroken skin. By contrast, creams and gels have higher viscosity.Lotions are usually applied to external skin with bare hands, a clean cloth, cotton wool or gauze...

s to protect against sunburn
Sunburn
A sunburn is a burn to living tissue, such as skin, which is produced by overexposure to ultraviolet radiation, commonly from the sun's rays. Usual mild symptoms in humans and other animals include red or reddish skin that is hot to the touch, general fatigue, and mild dizziness. An excess of UV...

 and other damage to the skin caused by ultraviolet light (see sunscreen
Sunscreen
Sunblock is a lotion, spray, gel or other topical product that absorbs or reflects some of the sun's ultraviolet radiation on the skin exposed to sunlight and thus helps protect against sunburn...

). It is the broadest spectrum UVA and UVB reflector that is approved for use as a sunscreen by the FDA, and is completely photostable. When used as an ingredient in sunscreen
Sunscreen
Sunblock is a lotion, spray, gel or other topical product that absorbs or reflects some of the sun's ultraviolet radiation on the skin exposed to sunlight and thus helps protect against sunburn...

, zinc oxide sits on the skin’s surface i.e. is not absorbed into the skin, and blocks both UVA (320–400 nm) and UVB (280–320 nm) rays of ultraviolet light. Because zinc oxide (and the other most common physical sunscreen
Sunscreen
Sunblock is a lotion, spray, gel or other topical product that absorbs or reflects some of the sun's ultraviolet radiation on the skin exposed to sunlight and thus helps protect against sunburn...

, titanium dioxide
Titanium dioxide
Titanium dioxide, also known as titanium oxide or titania, is the naturally occurring oxide of titanium, chemical formula . When used as a pigment, it is called titanium white, Pigment White 6, or CI 77891. Generally it comes in two different forms, rutile and anatase. It has a wide range of...

) are not absorbed into the skin, they are nonirritating and nonallergenic.

Many sunscreens use nano-sized zinc oxide (along with nano titanium dioxide) because such small particles do not scatter light and therefore do not appear white. Although there has been concern that they might be absorbed into the skin, comprehensive reviews of the medical literature have not uncovered any risk.

Cigarette filters

Zinc oxide is a constituent of cigarette filter
Cigarette filter
A cigarette filter has the purpose of reducing the amount of smoke, tar, and fine particles inhaled during the combustion of a cigarette. Filters also reduce the harshness of the smoke and keep tobacco flakes out of the smoker's mouth.-History:...

s for removal of selected components from tobacco smoke. A filter consisting of charcoal impregnated with zinc oxide and iron oxide removes significant amounts of HCN and H2S
Hydrogen sulfide
Hydrogen sulfide is the chemical compound with the formula . It is a colorless, very poisonous, flammable gas with the characteristic foul odor of expired eggs perceptible at concentrations as low as 0.00047 parts per million...

 from tobacco smoke without affecting its flavor.

Food additive

Zinc oxide is added to many food products, e.g., breakfast cereal
Breakfast cereal
A breakfast cereal is a food made from processed grains that is often, but not always, eaten with the first meal of the day. It is often eaten cold, usually mixed with milk , water, or yogurt, and sometimes fruit but sometimes eaten dry. Some cereals, such as oatmeal, may be served hot as porridge...

s, as a source of zinc, a necessary nutrient
Nutrient
A nutrient is a chemical that an organism needs to live and grow or a substance used in an organism's metabolism which must be taken in from its environment. They are used to build and repair tissues, regulate body processes and are converted to and used as energy...

. (Other cereals may contain zinc sulfate
Zinc sulfate
Zinc sulfate is the inorganic compound with the formula ZnSO4 as well as any of three hydrates. It was historically known as "white vitriol". It is a colorless solid that is a common source of soluble zinc ions.-Production and reactivity:...

 for the same purpose.) Some prepackaged foods also include trace amounts of ZnO even if it is not intended as a nutrient.

Pigment

Zinc white is used as a pigment in paint
Paint
Paint is any liquid, liquefiable, or mastic composition which after application to a substrate in a thin layer is converted to an opaque solid film. One may also consider the digital mimicry thereof...

s and is more opaque than lithopone
Lithopone
Lithophone is a white pigment consisting of a mixture of barium sulfate and zinc sulfide. It is used in interior paints and in some enamels. It is widely used for white paint.-History:...

, but less opaque than titanium dioxide
Titanium dioxide
Titanium dioxide, also known as titanium oxide or titania, is the naturally occurring oxide of titanium, chemical formula . When used as a pigment, it is called titanium white, Pigment White 6, or CI 77891. Generally it comes in two different forms, rutile and anatase. It has a wide range of...

. It is also used in coatings for paper. Chinese white is a special grade of zinc white used in artists' pigment
Pigment
A pigment is a material that changes the color of reflected or transmitted light as the result of wavelength-selective absorption. This physical process differs from fluorescence, phosphorescence, and other forms of luminescence, in which a material emits light.Many materials selectively absorb...

s.
It is also a main ingredient of mineral makeup.

Coatings

Paints containing zinc oxide powder have long been utilized as anticorrosive coatings for various metals. They are especially effective for galvanised Iron. The latter is difficult to protect because its reactivity with organic coatings leads to brittleness and lack of adhesion. Zinc oxide paints however, retain their flexibility and adherence on such surfaces for many years.

ZnO highly n-type doped with Al, Ga or In is transparent and conductive (transparency ~90%, lowest resistivity
Resistivity
Electrical resistivity is a measure of how strongly a material opposes the flow of electric current. A low resistivity indicates a material that readily allows the movement of electric charge. The SI unit of electrical resistivity is the ohm metre...

 ~10−4 Ω·cm). ZnO:Al coatings are being 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.

Various plastics, such as polyethylene naphthalate
Polyethylene naphthalate
Polyethylene naphthalate Polyethylene naphthalate (PEN) Polyethylene naphthalate (PEN) (Poly(ethylene 2,6-naphthalate) is a polyester with good barrier properties (even better than Polyethylene terephthalate). Because it provides a very good oxygen barrier, it is particularly well-suited for...

 (PEN), can be protected by applying zinc oxide coating. The coating reduces the diffusion of oxygen with PEN. Zinc oxide layers can also be used on polycarbonate
Polycarbonate
PolycarbonatePhysical PropertiesDensity 1.20–1.22 g/cm3Abbe number 34.0Refractive index 1.584–1.586FlammabilityV0-V2Limiting oxygen index25–27%Water absorption – Equilibrium0.16–0.35%Water absorption – over 24 hours0.1%...

 (PC) in outdoor applications. The coating protects PC form solar radiation and decreases the oxidation rate and photo-yellowing of PC.

Corrosion prevention in nuclear reactors

Zinc oxide depleted in the zinc isotope
Isotopes of zinc
Naturally occurring zinc is composed of the 5 stable isotopes 64Zn, 66Zn, 67Zn, 68Zn, and 70Zn with 64Zn being the most abundant . Twenty-five radioisotopes have been characterised with the most abundant and stable being 65Zn with a half-life of 244.26 days, and 72Zn with a half-life of 46.5 hours...

 with the atomic mass
Atomic mass
The atomic mass is the mass of a specific isotope, most often expressed in unified atomic mass units. The atomic mass is the total mass of protons, neutrons and electrons in a single atom....

 64 is used in corrosion prevention in nuclear pressurized water reactor
Pressurized water reactor
Pressurized water reactors constitute a large majority of all western nuclear power plants and are one of three types of light water reactor , the other types being boiling water reactors and supercritical water reactors...

s. The depletion is necessary, because 64Zn is transformed
Neutron activation
Neutron activation is the process in which neutron radiation induces radioactivity in materials, and occurs when atomic nuclei capture free neutrons, becoming heavier and entering excited states. The excited nucleus often decays immediately by emitting particles such as neutrons, protons, or alpha...

 into radioactive 65Zn under irradiation by the reactor neutrons.

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
LEd
LEd is a TeX/LaTeX editing software working under Microsoft Windows. It is a freeware product....

 (LEDs). Some optoelectronic applications of ZnO overlap with that of GaN
Gan
Gan may refer to:-Computing and telecommunications:*.gan, the file extension for documents created by GanttProject*Generic Access Network formerly known as Unlicensed Mobile Access *Global Area Network- Mythology :...

, which has a similar bandgap (~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 as TCO layer and ZnO nanostructures provide better light outcoupling. Other properties of ZnO favorable for electronic applications include its stability to high-energy radiation and to wet chemical etching. Radiation resistance makes ZnO a suitable candidate for space applications. ZnO is currently the most promising candidate in the field of random laser
Random laser
A random laser is a laser that uses a highly disordered gain medium. A random laser uses no optical cavity but the remaining principles of operation remain the same as for a conventional laser...

s to produce an electronically pumped UV laser source.

The pointed tips of ZnO nanorods result in a strong enhancement of an electric field. Therefore, they can be used as field emitters.

Aluminium-doped ZnO layers are used as a transparent electrode
Electrode
An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit...

s. The constituents Zn and Al are much cheaper and less poisonous compared to the generally used indium tin oxide
Indium tin oxide
Indium tin oxide is a solid solution of indium oxide and tin oxide , typically 90% In2O3, 10% SnO2 by weight. It is transparent and colorless in thin layers while in bulk form it is yellowish to grey...

 (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
Liquid crystal display
A liquid crystal display is a flat panel display, electronic visual display, or video display that uses the light modulating properties of liquid crystals . LCs do not emit light directly....

s.

Transparent thin-film transistor
Transistor
A transistor is a semiconductor device used to amplify and switch electronic signals and power. It is composed of a semiconductor material with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals changes the current...

s (TTFT) can be produced with ZnO. As field-effect transistors, they even may 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.

Zinc oxide nanorod sensor

Zinc oxide nanorod sensor
Zinc oxide nanorod sensor
A zinc oxide nanorod sensor or ZnO nanorod sensor is an electronic device detecting presence of certain gas or liquid molecules in the ambient atmosphere. The sensor exploits enhanced surface area intrinsic to all nano-sized materials, including ZnO nanorods...

s are devices detecting changes in electrical current passing through zinc oxide nanowire
Nanowire
A nanowire is a nanostructure, with the diameter of the order of a nanometer . Alternatively, nanowires can be defined as structures that have a thickness or diameter constrained to tens of nanometers or less and an unconstrained length. At these scales, quantum mechanical effects are important —...

s due to adsorption
Adsorption
Adsorption is the adhesion of atoms, ions, biomolecules or molecules of gas, liquid, or dissolved solids to a surface. This process creates a film of the adsorbate on the surface of the adsorbent. It differs from absorption, in which a fluid permeates or is dissolved by a liquid or solid...

 of gas molecules. Selectivity to hydrogen gas was achieved by sputtering Pd clusters on the nanorod surface. The addition of Pd appears to be effective in the catalytic dissociation of hydrogen molecules into atomic hydrogen, increasing the sensitivity of the sensor device. The sensor detects hydrogen concentrations down to 10 parts per million at room temperature, whereas there is no response to oxygen.

Spintronics

ZnO has also been considered for spintronics
Spintronics
Spintronics , also known as magnetoelectronics, is an emerging technology that exploits both the intrinsic spin of the electron and its associated magnetic moment, in addition to its fundamental electronic charge, in solid-state devices.An additional effect occurs when a spin-polarized current is...

 applications: if doped with 1–10% of magnetic ions (Mn, Fe, Co, V, etc.), ZnO could become ferromagnetic, even at room temperature. Such room temperature ferromagnetism
Ferromagnetism
Ferromagnetism is the basic mechanism by which certain materials form permanent magnets, or are attracted to magnets. In physics, several different types of magnetism are distinguished...

 in ZnO:Mn has been observed, but it is not clear yet whether it originates from the matrix itself or from secondary oxide phases.

Piezoelectricity

The piezoelectricity
Piezoelectricity
Piezoelectricity is the charge which accumulates in certain solid materials in response to applied mechanical stress. The word piezoelectricity means electricity resulting from pressure...

 in textile
Textile
A textile or cloth is a flexible woven material consisting of a network of natural or artificial fibres often referred to as thread or yarn. Yarn is produced by spinning raw fibres of wool, flax, cotton, or other material to produce long strands...

 fibers coated in ZnO have been shown capable of fabricating "self-powered nanosystems" with everyday mechanical stress from wind or body movements.

In 2008 the Center for Nanostructure Characterization at the Georgia Institute of Technology
Georgia Institute of Technology
The Georgia Institute of Technology is a public research university in Atlanta, Georgia, in the United States...

 reported producing an electricity generating device (called flexible charge pump generator) delivering alternating current by stretching and releasing zinc oxide nanowires. This mini-generator creates an oscillating voltage up to 45 millivolts, converting close to seven percent of the applied mechanical energy into electricity. Researchers used wires with lengths of 0.2–0.3 mm and diameters of three to five micrometers, but the device could be scaled down to smaller size.

History

It is hardly possible to trace the first usage of zinc oxide – various zinc compounds were widely used by early humans, in various processed and unprocessed forms, as a paint or medicinal ointment, but their exact composition is uncertain.

The use of pushpanjan, probably zinc oxide, as a salve for eyes and open wounds, is mentioned in the India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...

n medical text the Charaka Samhita
Charaka Samhita
The ' is an early Ayurvedic text on internal medicine. It is believed to be the oldest of the three ancient treatises of Ayurveda...

, thought to date from 500 BC or before. Zinc oxide ointment is also mentioned by the Greek
Greeks
The Greeks, also known as the Hellenes , are a nation and ethnic group native to Greece, Cyprus and neighboring regions. They also form a significant diaspora, with Greek communities established around the world....

 physician Dioscorides (1st century AD.) Avicenna
Avicenna
Abū ʿAlī al-Ḥusayn ibn ʿAbd Allāh ibn Sīnā , commonly known as Ibn Sīnā or by his Latinized name Avicenna, was a Persian polymath, who wrote almost 450 treatises on a wide range of subjects, of which around 240 have survived...

 mentions zinc oxide in The Canon of Medicine
The Canon of Medicine
The Canon of Medicine is an encyclopedia of Galenic medicine in five books compiled by Ibn Sīnā and completed in 1025. It presents a clear and organized summary of all the medical knowledge of the time...

(1025 AD), which mentioned it as a preferred treatment for a variety of skin conditions, including skin cancer
Skin cancer
Skin neoplasms are skin growths with differing causes and varying degrees of malignancy. The three most common malignant skin cancers are basal cell cancer, squamous cell cancer, and melanoma, each of which is named after the type of skin cell from which it arises...

. Though it is no longer used for treating skin cancer, it is still widely used to treat a variety of other skin conditions, in products such as baby powder
Baby powder
Baby powder is an astringent powder used for preventing diaper rash, as a deodorant, and for other cosmetic uses. It may be composed of talc or corn starch. Talcum powder is harmful if inhaled since it may cause aspiration pneumonia or granuloma. Drugs such as cocaine are sometimes cut with...

 and creams against diaper rash
Diaper rash
Irritant diaper dermatitis is a generic term applied to skin rashes in the diaper area that are caused by various skin disorders and/or irritants.Generic rash or irritant diaper dermatitis is characterized by joined patches of erythema and...

es, calamine
Calamine
Calamine is a mixture of zinc oxide with about 0.5% ferric oxide . It is the main ingredient in calamine lotion and is used as an antipruritic to treat mild pruritic conditions such as sunburn, eczema, rashes, poison ivy, chickenpox, and insect bites and stings...

 cream, anti-dandruff
Dandruff
Dandruff is the shedding of dead skin cells from the scalp . Dandruff is sometimes caused by frequent exposure to extreme heat and cold. As it is normal for skin cells to die and flake off, a small amount of flaking is normal and common; about 487,000 cells/cm2 get released normally after...

 shampoo
Shampoo
Shampoo is a hair care product used for the removal of oils, dirt, skin particles, dandruff, environmental pollutants and other contaminant particles that gradually build up in hair...

s, and antiseptic
Antiseptic
Antiseptics are antimicrobial substances that are applied to living tissue/skin to reduce the possibility of infection, sepsis, or putrefaction...

 ointments.

The Romans produced considerable quantities of brass
Brass
Brass is an alloy of copper and zinc; the proportions of zinc and copper can be varied to create a range of brasses with varying properties.In comparison, bronze is principally an alloy of copper and tin...

 (an alloy of zinc
Zinc
Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...

 and copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...

) 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 in the 1st century AD. Zinc oxide has also been recovered from zinc mines at Zawar in India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...

, dating from the second half of the first millennium BC. This was presumably also made in the same way and used to produce brass.

From the 12th to the 16th century zinc and zinc oxide were recognized and produced in India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...

 using a primitive form of the direct synthesis process. From India, zinc manufacture moved to China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...

 in the 17th century. In 1743, the first European zinc smelter was established in Bristol
Bristol
Bristol is a city, unitary authority area and ceremonial county in South West England, with an estimated population of 433,100 for the unitary authority in 2009, and a surrounding Larger Urban Zone with an estimated 1,070,000 residents in 2007...

, United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

.

The main usage of zinc oxide (zinc white) was again paints and additive to ointments. Zinc white was accepted as a watercolor by 1834 but it did not mix well with oil. This problem was quickly solved by optimizing the synthesis of ZnO. In 1845, LeClaire in Paris was producing the oil paint on a large scale, and 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 very valuable for making tints with other colors; however, 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. All those paintings developed cracks over the years.

In the recent times, most zinc oxide was used in the rubber industry (see applications above). In the 1970s, the second largest application of ZnO was photocopying. High-quality ZnO produced by the "French process" was added into the photocopying paper as a filler. This application was however soon displaced.

Safety

As a food additive, zinc oxide is on the U.S. FDA's generally recognized as safe
Generally recognized as safe
Generally recognized as safe is an American Food and Drug Administration designation that a chemical or substance added to food is considered safe by experts, and so is exempted from the usual Federal Food, Drug, and Cosmetic Act food additive tolerance requirements.-History:On January 1, 1958,...

, or GRAS, substances.

Zinc oxide itself is non-toxic; however it is hazardous to inhale zinc oxide fumes, as generated when zinc or zinc alloys are melted and oxidized at high temperature. This problem occurs while melting brass
Brass
Brass is an alloy of copper and zinc; the proportions of zinc and copper can be varied to create a range of brasses with varying properties.In comparison, bronze is principally an alloy of copper and tin...

 because the melting point of brass is close to the boiling point of zinc. Exposure to zinc oxide in the air, which also occurs while welding galvanized (zinc plated) steel
Steel
Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...

, can result in a nervous malady called metal fume fever
Metal fume fever
Metal fume fever also known as brass founders' ague, brass shakes, zinc shakes, Galvie Flu, or Monday morning fever is an illness caused primarily by exposure to certain fumes...

. For this reason, typically galvanized steel is not welded, or the zinc is removed first.

In popular culture

Reflecting its many varied but relatively unobtrusive and unglamorous uses, zinc oxide was the theme of a spoof in The Kentucky Fried Movie
The Kentucky Fried Movie
The Kentucky Fried Movie is an American comedy film, released in 1977 and directed by John Landis. The film's writers were the team of David Zucker, Jim Abrahams and Jerry Zucker. This same team would go on to write and direct Airplane!, Top Secret! and the Police Squad! television series and its...

 as a short educational film Zinc Oxide and You.

See also

  • Zinc
    Zinc
    Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...

  • Zinc-zinc oxide cycle
    Zinc-zinc oxide cycle
    The zinc–zinc oxide cycle or Zn–ZnO cycle is a two step thermochemical cycle based on zinc and zinc oxide for hydrogen production with a typical efficiency around 40%.-Process description:...

  • Zinc peroxide
    Zinc peroxide
    Zinc peroxide is a chemical compound used as a bleaching and curing agent. It appears as white to yellow powder. Perhaps its most important use is to promote cross-linking in carboxylated nitrile rubber and other elastomers. Another application of ZnO2 is additive to antiseptic ointments...

  • Gallium(III) nitride
    Gallium(III) nitride
    Gallium nitride is a binary III/V direct bandgap semiconductor commonly used in bright light-emitting diodes since the 1990s. The compound is a very hard material that has a Wurtzite crystal structure. Its wide band gap of 3.4 eV affords it special properties for applications in optoelectronic,...

  • Depleted zinc oxide
    Depleted zinc oxide
    Depleted zinc oxide is a zinc oxide depleted in the zinc isotope with the atomic mass 64, and used in corrosion prevention in nuclear pressurized water reactors....

  • Zinc smelting
    Zinc smelting
    Zinc smelting is the process of converting zinc concentrates into pure zinc.The most common zinc concentrate processed is zinc sulfide, which is obtained by concentrating sphalerite using the froth flotation method. Secondary zinc material, such as zinc oxide, is also processed with the zinc...

  • Zinc oxide eugenol
    Zinc Oxide Eugenol
    Zinc oxide eugenol is a material created by the combination of zinc oxide and eugenol contained in oil of cloves. An acid-base reaction takes place with the formation of zinc eugenolate chelate. The reaction is catalysed by water and is accelerated by the presence metal salts. ZOE can be used as...

  • Zinc-air battery
    Zinc-air battery
    Zinc–air batteries , and zinc–air fuel cells, are electro-chemical batteries powered by oxidizing zinc with oxygen from the air. These batteries have high energy densities and are relatively inexpensive to produce...



Reviews

  • U. Ozgur et al. "A comprehensive review of ZnO materials and devices" (103 pages) J. Appl. Phys. 98 (2005) 041301
  • A. Bakin and A. Waag "ZnO Epitaxial Growth" (28 pages) Chapter in “Comprehensive Semiconductor Science and Technology“ 6 Volume Encyclopaedia, ELSEVIER, edited by Pallab Bhattacharya, Roberto Fornari and Hiroshi Kamimura, ISBN 978-0-444-53143-8
  • S. Baruah and J. Dutta "Hydrothermal growth of ZnO nanostructures" (18 pages) Sci. Technol. Adv. Mater. 10 (2009) 013001 free download
  • R. Janisch et al. "Transition metal-doped TiO2 and ZnO—present status of the field" (32 pages) J. Phys.: Condens. Matter 17 (2005) R657
  • Y.W. Heo et al. "ZnO nanowire growth and devices" (47 pages) Mater. Sci. Eng. R 47 (2004) 1
  • C. Klingshirn "ZnO: From basics towards applications" (46 pages) Phys. Stat. Solidi (b) 244 (2007) 3027
  • C. Klingshirn "ZnO: Material, Physics and Applications" (21 pages) ChemPhysChem 8 (2007) 782
  • J. G. Lu et al. "Quasi-one-dimensional metal oxide materials—Synthesis, properties and applications" (42 pages) Mater. Sci. Eng. R 52 (2006) 49

External links

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