Zinc oxide is an
inorganic compoundTraditionally, inorganic compounds are considered to be of a mineral, not biological, origin. Complementarily, most organic compounds are traditionally viewed as being of biological origin...
with the
formulaA chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....
ZnO. It usually appears as a white powder, nearly 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 tyres), lubricants, paints, ointments, adhesives, sealants, pigments, foods (source of Zn
nutrientA 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. Nutrients are the substances that enrich the body. They build and repair tissues, give heat and energy, and regulate body processes...
), batteries, ferrites, fire retardants, first aid tapes, etc. ZnO is present in the Earth crust as a mineral
zinciteZincite is the mineral form of zinc oxide . In nature its crystal form is rare, with the exception of 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 color that depends on impurities...
; however, most ZnO used commercially is produced synthetically.
In
materials scienceMaterials science or materials engineering is an interdisciplinary field involving the properties of matter and its applications to various areas of science and engineering. This science investigates the relationship between the structure of materials at atomic or molecular scales and their...
, ZnO is often called a II-VI semiconductor because
zincZinc , also known as 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
oxygenOxygen Oxygen Oxygen (acid, literally "sharp", from the taste of acids) and -γενής (-genēs) (producer, literally begetter) is the element with atomic number 8 and represented by the symbol O...
belong to the 2nd and 6th groups of the
periodic tableThe periodiс table of the chemical elements is a tabular display of the chemical elements...
, respectively. This semiconductor has several favorable properties: good transparency, high
electron mobilityIn physics, electron mobility , is a quantity relating the drift velocity of electrons to the applied electric field across a material, according to the formula:where...
, wide bandgap, strong room-temperature
luminescenceLuminescence is light that usually occurs at low temperatures, and 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 generated by high...
, etc. Those properties are already used in emerging applications for transparent
electrodeAn electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit...
s in
liquid crystal displayA liquid crystal display is a thin, flat panel used for electronically displaying information such as text, images, and moving pictures...
s and in energy-saving or heat-protecting windows, and electronic applications of ZnO as thin-film
transistorA transistor is a semiconductor device commonly used to amplify or switch electronic signals. A transistor is made of a solid piece 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...
and
light-emitting diodeA light-emitting diode , is an electronic light source. The first LED was built in the 1920s by Oleg Vladimirovich Losev, a radio technician who noticed that diodes used in radio receivers emitted light when current was passed through them...
are forthcoming as of 2009.
Chemical properties
ZnO occurs as white powder known as zinc white or as the mineral
zinciteZincite is the mineral form of zinc oxide . In nature its crystal form is rare, with the exception of 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 color that depends on impurities...
. The mineral usually contains a certain amount of manganese and other elements and is of yellow to red color. Crystalline zinc oxide is
thermochromicThermochromism 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. Thermochromism is one of several types of chromism....
, 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 Zn
1+xO, where at 800 °C, x= 0.00007.
Zinc oxide is an amphoteric oxide. It is nearly
insolubleSolubility is the property of a solid, liquid, or gaseous chemical substance called solute to dissolve in a liquid solvent to form a homogeneous solution. The solubility of a substance strongly depends on the used solvent as well as on temperature and pressure...
in water and alcohol, but it is soluble in (degraded by) most
acidAn acid is traditionally considered any chemical compound that, when dissolved in water, gives a solution with a hydrogen ion activity greater than in pure water, i.e. a pH less than 7.0...
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
stearateStearateis the anion form of stearic acid.Formula is C17H35COO−.-Examples:* Sodium stearate, Na* Calcium stearate, Ca2...
. ZnO forms cement-like products when mixed with a strong aqueous solution of
zinc chlorideZinc chloride is the name of chemical compound with the formula ZnCl
2 and its hydrates. Zinc chlorides, of which nine crystalline forms are known, are colorless or white and highly soluble in water. ZnCl
2 itself is hygroscopic and even deliquescent. Samples should therefore...
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 acidPhosphoric 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...
; related materials are used in dentistry. A major component of zinc phosphate cement produced by this reaction is
hopeiteHopeite is a hydrated zinc phosphate with formula: Zn32·4H2O. It is a rare mineral used mainly as a collectors specimen....
, Zn
3(PO
4)
2·4H
2O.
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 aluminum and
magnesiumMagnesium 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 by mass, although ninth in the Universe as a whole...
powders, with chlorinated rubber and
linseed oilLinseed oil, also known as "flax seed 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 sulfideHydrogen sulfide is the chemical compound with the formula H
2S. This colorless, toxic and flammable gas is partially responsible for the foul odor of rotten eggs and flatulence....
to give the sulfide: this reaction is used commercially in removing H
2S using ZnO powder (e.g., as deodorant).
- ZnO + H2S → ZnS + H2O
When ointments containing ZnO and water are melted and exposed to
ultravioletUltraviolet 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 peroxideHydrogen peroxide is a very pale blue liquid, slightly more viscous than water, that appears colorless in dilute solution. It is a weak acid, has strong oxidizing properties, and is a powerful bleaching agent. It is used as a disinfectant, antiseptic, oxidizer, and in rocketry as a propellant...
is produced.
Physical properties
Crystal structure
Zinc oxide crystallizes in three
formsPolymorphism 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 elemental solids...
: hexagonal wurtzite, cubic zincblende, and the rarely observed cubic
rocksaltSodium chloride, also known as salt, common salt, table salt, or halite, is an ionic 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...
). 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
tetrahedralIn 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...
. The rocksalt (NaCl-type) structure is only observed at relatively high pressures about 10 GPa.
Hexagonal and zincblende polymorphs have no
inversion symmetryReflection symmetry, line symmetry, mirror symmetry, mirror-image symmetry, or bilateral symmetry is symmetry with respect to reflection....
(reflection of a crystal relatively any given point does not transform it into itself). This and other lattice symmetry properties result in
piezoelectricityPiezoelectricity is the ability of some materials to generate an electric field or electric potential in response to applied mechanical stress. The effect is closely related to a change of polarization density within the material's volume...
of the hexagonal and zincblende ZnO, and in
pyroelectricityPyroelectricity is the ability of certain materials to generate a temporary electrical potential when they are heated or cooled. The change in temperature slightly modifies the positions of the atoms within the crystal structure, such that the polarization of the material changes...
of hexagonal ZnO.
The hexagonal structure has a point group 6 mm (
Hermann-Mauguin notationHermann-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 minerologist Charles-Victor Mauguin...
) or C
6v (
Schoenflies notationThe Schoenflies notation or Schönflies notation, is one of two conventions commonly used to describe crystallographic point groups. This notation is used in spectroscopy. The other convention is the Hermann-Mauguin notation, also known as the International notation...
), and the
space groupIn crystallography, the space group of a crystal is a description of the symmetry of the crystal, and can have one of 230 types...
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 II-VI materials, the bonding in ZnO is largely
ionicAn ionic bond is a type of chemical bond that involves a metal and a nonmetal ion through electrostatic attraction. In short, it is a bond formed by the attraction between two oppositely charged ions....
, which explains its strong
piezoelectricityPiezoelectricity is the ability of some materials to generate an electric field or electric potential in response to applied mechanical stress. The effect is closely related to a change of polarization density within the material's volume...
. 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
GaNGan 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 - Fictions :...
. The high heat capacity and heat conductivity, low thermal expansion and high melting temperature of ZnO are beneficial for ceramics.
Among the tetrahedrally bonded semiconductors, it has been stated that ZnO has the highest piezoelectric tensor or at least one comparable to that of
GaNGan 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 - Fictions :...
and
AlNALN, AlN or Aln may refer to:* Ação Libertadora Nacional* Africa Liberal Network* Alianza Liberal Nicaragüense, a political party in Nicaragua* Aluminium nitride* Althorne railway station, from its National Rail code...
. This property makes it a technologically important material for many
piezoelectricalPiezoelectricity is the ability of some materials to generate an electric field or electric potential in response to applied mechanical stress. The effect is closely related to a change of polarization density within the material's volume...
applications, which require a large electromechanical coupling.
Electronic properties
ZnO has a relatively large direct
band gapIn solid state physics, a band gap, also called an energy gap or bandgap, is an energy range in a solid where no electron states exist...
of ~3.3 eV at room temperature; therefore, pure ZnO is colorless and transparent. Advantages associated with a large band gap include higher breakdown voltages, ability to sustain large electric fields, lower
electronic noiseElectronic noise is a random signal characteristic of all electronic circuits. Depending on the circuit, the noise generated by electronic devices can vary greatly. Noise can be produced by several different effects. Thermal noise and shot noise are inherent to all devices...
, and high-temperature and high-power operation. The bandgap of ZnO can further be tuned from ~3–4 eV by its alloying with
magnesium oxideMagnesium oxide, or magnesia, is a white solid mineral that occurs naturally as periclase and is a source of magnesium . It has an empirical formula of . It is formed by an ionic bond between one magnesium and one oxygen atom. Magnesium oxide is hygroscopic in nature and care must be taken to...
or
cadmium oxideCadmium 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 rarely occurs naturally as the mineral monteponite. Cadmium oxide...
.
Most ZnO has
n-type character, even in the absence of intentional
dopingIn semiconductor production, doping is the process of intentionally introducing impurities into an extremely pure semiconductor to change 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
chlorineChlorine Chlorine Chlorine ( , from the Greek word 'χλωρóς' (khlôros, meaning 'pale green'), is the chemical element with atomic number 17 and symbol Cl. It is a halogen, found in the periodic table in group 17 (formerly VII, VIIa, or VIIb). As the chloride ion, which is part of common salt and...
or
iodineIodine , is a chemical element that has the symbol I and atomic number 53. Naturally-occurring iodine is a single isotope with 74 neutrons....
.
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
GaNGan 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 - Fictions :...
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 mobilityIn physics, electron mobility , is a quantity relating the drift velocity of electrons to the applied electric field across a material, according to the formula:where...
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).
Production
For industrial use, ZnO is produced at levels of 10
5 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 instantaneously 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. Major applications involve industries related to
rubberNatural rubber is an elastomer that was originally derived from a milky colloidal suspension, or latex, found in the sap of some plants. The purified form of natural rubber is the chemical polyisoprene, which can also be produced synthetically...
, varistors, sunscreens, paints, healthcare, and poultry nutrients. Recent developments involve acicular nanostructures (rods, wires, tripods, tetrapods, plates) synthesized using a modified French process known as catalyst-free combust-oxidized mesh (CFCOM) process. Acicular nanostructures usually have micrometre-length nanorods with nanometric diameters (below 100 nm).
Direct (American) process
In the direct process, the starting material is various contaminated zinc composites, such as
zinc oresCalamine 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 smeleter by-products. It is reduced by heating with a carbon additive (e.g. antracite) 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
Wet chemical processes start with purified zinc solutions, from which zinc carbonate or
zinc hydroxideZinc hydroxide Zn2 is an inorganic chemical compound. It also occurs naturally as 3 rare minerals: wülfingite , ashoverite and sweetite .It is unusual in that, like zinc oxide, it is amphoteric...
is precipitated. It is then filtered, washed, dried and calcined at temperatures ~800 °C.
Laboratory synthesis
A large number of ZnO production methods exist for producing ZnO for scientific studies and electronic applications. These methods can be classified by the resulting ZnO form (bulk, thin film,
nanowireA 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 synthesisHydrothermal 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 pressureVapor pressure or equilibrium vapor pressure is the pressure of a vapor in thermodynamic equilibrium with its condensed phases in a closed container. All liquids and solids have a tendency to evaporate into a gaseous form, and all gases have a tendency to condense back to their liquid or solid...
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 depositionChemical 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 epitaxyMetalorganic vapour phase epitaxy is a chemical vapour deposition method of epitaxial growth of materials, especially compound semiconductors from the surface reaction of organic compounds or metalorganics and metal hydrides containing the required chemical elements...
,
electrodepositionElectrophoretic 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 depositionPulsed 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...
,
sputteringSputtering is a process whereby atoms are ejected from a solid target material due to bombardment of the target by energetic ions. It is commonly used for thin-film deposition, etching and analytical techniques .- Physics of sputtering :...
, sol-gel synthesis, spray pyrolysis, etc. Nanostructures can be obtained with most above-mentioned techniques, at certain conditions, and also with the
vapor-liquid-solid methodThe vapor-liquid-solid method is a mechanism for the growth of one-dimensional structures, such as nanowires, from chemical vapor deposition. Growth of a crystal through direct adsorption of a gas phase on to a solid surface is generally very slow...
.
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 indexThe refractive index of a medium is a measure of how much the speed of light is reduced inside the medium. For example, typical soda-lime glass has a refractive index close to 1.5, which means that in glass, light travels at 1 / 1.5 = 2/3 the speed of light in a vacuum...
, good thermal, 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 rubber industry. Zinc oxide along with stearic acid activates vulcanization, which otherwise may not occur at all. Zinc oxide and
stearic acidStearic acid or 18:0 is a saturated fatty acid. It is a waxy solid, and its chemical formula is C
18H
36O
2, or CH
316COOH. Its name comes from the Greek word stéar , which means tallow...
are ingredients in the commercial manufacture of
rubberNatural rubber is an elastomer that was originally derived from a milky colloidal suspension, or latex, found in the sap of some plants. The purified form of natural rubber is the chemical polyisoprene, which can also be produced synthetically...
goods. A mixture of these two compounds allows a quicker and more controllable rubber cure. ZnO is also an important additive to the rubber of car tyres.
VulcanizationVulcanization or vulcanisation refers to a specific curing process of rubber involving high heat and the addition of sulfur or other equivalent curatives. It is a chemical process in which polymer molecules are linked to other polymer molecules by atomic bridges composed of sulfur atoms or carbon...
catalysts are derived from zinc oxide, and it considerably improves the
thermal conductivityIn physics, thermal conductivity, , is the property of a material that indicates its ability to conduct heat. It appears primarily in Fourier's Law for heat conduction.-Measurement:...
, which is crucial to dissipate the heat produced by the deformation when the tyre rolls. ZnO additive also protect rubber from fungi (see medical applications) and UV light.
Concrete industry
Zinc oxide is widely used for
concreteConcrete is a construction material composed of cement as well as other cementitious materials such as fly ash and slag cement, aggregate , water, and chemical admixtures...
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) oxideIron oxide—also known as ferric oxide, ferric iron, hematite, red iron oxide, synthetic maghemite, colcothar, or simply rust—is one of the several oxide compounds of iron, and has paramagnetic properties...
(Fe
2O
3) is called
calamineCalamine is a mixture of zinc oxide with about 0.5% iron 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, insect bites and stings...
and is used in calamine lotion. There are also two minerals,
zinciteZincite is the mineral form of zinc oxide . In nature its crystal form is rare, with the exception of 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 color that depends on impurities...
and
hemimorphiteHemimorphite, 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 called calamine historically (see:
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
eugenolEugenol , is 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, and bay leaf . It is slightly soluble in water and...
, a chelate,
zinc oxide eugenolZinc oxide eugenol is a material created by the combination of zinc oxide and eugenol which can be used as a filling or cement material in dentistry. It is often used in dentistry when the decay is very deep or very close to the nerve or pulp chamber. Because the tissue inside the tooth, i. e...
is formed which has
restorativeA 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
prosthodonticProsthodontics 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...
applications in
dentistryDentistry is the known evaluation, diagnosis, prevention, and treatment of diseases, disorders and conditions of the soft and hard tissues of the jaw , the oral cavity, maxillofacial area and the adjacent and associated structures and their impact on the human body. Dentistry is a part of stomatology...
.
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
silverSilver is a 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 powderBaby 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...
and
barrier creamA 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 rashDiaper rash or nappy rash , is a generic term applied to skin rashes in the diaper area that are caused by various skin disorders and/or irritants....
es,
calamineCalamine is a mixture of zinc oxide with about 0.5% iron 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, insect bites and stings...
cream, anti-
dandruffDandruff is the excessive shedding of dead skin cells from the scalp. Dandruff can also be 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 in fact quite common...
shampooShampoo 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
antisepticAntiseptics 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.
Cigarette filters
Zinc oxide is a constituent of cigarette filters for removal of selected components from tobacco smoke. A filter consisting of charcoal impregnated with zinc oxide and iron oxide removes significant amounts of
HCNHydrogen cyanide is a chemical compound with chemical formula HCN. A solution of hydrogen cyanide in water is called hydrocyanic acid. Hydrogen cyanide is a colorless, extremely poisonous, and highly volatile liquid that boils slightly above room temperature at 26 °C...
and
H2SHydrogen sulfide is the chemical compound with the formula H
2S. This colorless, toxic and flammable gas is partially responsible for the foul odor of rotten eggs and flatulence....
from tobacco smoke without affecting its flavor.
Food additive
Zinc oxide is added to many food products, e.g.,
breakfast cerealA breakfast cereal is a packaged breakfast food. It is eaten cold, usually mixed with milk or water, but sometimes eaten dry. Some cereals, such as oatmeal, may be served hot as porridge. Some companies promote their products for the health benefits from eating oat-based and high-fiber cereals....
s, as a source of zinc, a necessary
nutrientA 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. Nutrients are the substances that enrich the body. They build and repair tissues, give heat and energy, and regulate body processes...
. (Other cereals may contain
zinc sulfateZinc sulfate is a colorless crystalline, water-soluble chemical compound. The hydrated form, ZnSO4·7H2O, the mineral goslarite, was historically known as "white vitriol" and can be prepared by reacting zinc with aqueous sulfuric acid...
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
paintPaint is any liquid, liquifiable, or mastic composition which after application to a substrate in a thin layer is converted to an opaque solid film.-History:...
s and is more opaque than
lithoponeLithopone is a white pigment, a mixture of barium sulfate and zinc sulfide. It is used in interior paints and in some enamels.Wooden artifacts are treated with zinc sulfate and barium sulfide, which undergo ion exchange reaction to form the aforementioned precipitates, which render a marble-like...
, but less opaque than
titanium dioxideTitanium dioxide, also known as titanium oxide or titania, is the naturally occurring oxide of titanium, chemical formula TiO
2. When used as a pigment, it is called titanium white, Pigment White 6, or CI 77891...
. It is also used in coatings for paper. Chinese white is a special grade of zinc white used in artists'
pigmentA 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. Because it reflects both UVA and UVB rays of ultraviolet light, zinc oxide can be used in ointments, creams, and
lotionA lotion is a low- to medium-viscosity, topical preparation intended for application to unbroken skin; creams and gels have a higher viscosity. Most lotions are oil-in-water emulsions using a substance such as Cetearyl alcohol to keep the emulsion together, but water-in-oil lotions are also...
s to protect against
sunburnA sunburn is a burn to living tissue such as skin produced by overexposure to ultraviolet radiation, commonly from the sun's rays.Usual mild symptoms in humans and animals are red or reddish skin that is hot to the touch, general fatigue, and mild dizziness. An excess of UV-radiation can be...
and other damage to the skin caused by ultraviolet light (see
sunscreenSunscreen 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 absorber that is approved for use as a sunscreen by the FDA, and is completely photostable. 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 nitrogen is transparent and conductive (transparency ~90%, lowest
resistivityElectrical 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 electrical charge...
~10
−4 Ωcm).
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 poly(ethylene-naphthalate) (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 (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 isotopeNaturally occurring zinc is composed of the 5 stable isotopes 64Zn, 66Zn, 67Zn, 68Zn, and 70Zn with 64Zn being the most abundant...
with the
atomic massThe atomic mass is the mass of an atom, most often expressed in unified atomic mass units. The atomic mass may be considered to be the total mass of protons, neutrons and electrons in a single atom...
64 is used in corrosion prevention in nuclear
pressurized water reactorPressurized water reactors comprise a majority of all western nuclear power plants and are one of two types of light water reactor , the other type being boiling water reactors . In a PWR the primary coolant is pumped under high pressure to the reactor core, then the heated water transfers...
s. The depletion is necessary, because
64Zn is
transformedNeutron 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 diodesLEd 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
GaNGan 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 - Fictions :...
, 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. 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.
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
electrodeAn 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 oxideIndium 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. 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 displayA liquid crystal display is a thin, flat panel used for electronically displaying information such as text, images, and moving pictures...
s.
Transparent thin-film
transistorA transistor is a semiconductor device commonly used to amplify or switch electronic signals. A transistor is made of a solid piece 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...
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 sensorA 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
nanowireA 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
adsorptionAdsorption is the accumulation of atoms or molecules on the surface of a material. This process creates a film of the adsorbate on the adsorbent's surface. It is different from absorption, in which a substance diffuses into a liquid or solid to form a solution...
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
spintronicsSpintronics , also known as magnetoelectronics, is an emerging technology that exploits the intrinsic spin of the electron and its associated magnetic moment, in addition to its fundamental electronic charge, in solid-state devices.-History:The research field of Spintronics emerged from experiments...
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
ferromagnetismFerromagnetism is the basic mechanism by which certain materials form permanent magnets and/or exhibit strong interactions with magnets; it is responsible for most phenomena of magnetism encountered in everyday life...
in ZnO:Mn has been observed, but it is not clear yet whether it originates from the matrix itself or from Mn-containing precipitates.
Piezoelectricity
The
piezoelectricityPiezoelectricity is the ability of some materials to generate an electric field or electric potential in response to applied mechanical stress. The effect is closely related to a change of polarization density within the material's volume...
in
textileA textile is a flexible material consisting of a network of natural or artificial fibres often referred to as thread or yarn. Yarn is produced by spinning raw wool fibres, linen, cotton, or other material on a spinning wheel to produce long strands...
fibers coated in ZnO have been shown capable of "self-powering nanosystems" with everyday mechanical stress generated by wind or body movements.
In 2008 the
Center for Nanostructure Characterization at the
Georgia Institute of TechnologyThe Georgia Institute of Technology, commonly called Georgia Tech, Tech, and GT, is a public, coeducational 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 wires. 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 nanometer size.
Biosensor
ZnO has high biocompatibility and fast electron transfer kinetics. Such features advocate the use of this material as a biomimic membrane to immobilize and modify biomolecules.
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
IndiaIndia, 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, and the most populous democracy in the world. Bounded by the Indian Ocean on the south, the Arabian Sea on the west, and the Bay of Bengal...
n medical text the
Charaka SamhitaThe ' is an ancient Indian Ayurvedic text on internal medicine written by Caraka. It is believed to be the oldest of the three ancient treatises of Ayurveda. It is central to the modern-day practice of Ayurvedic medicine; and, along with the it is now identified worldwide as an important early...
, thought to date from 500 BC or before. Zinc oxide ointment is also mentioned by the
GreekThe Greeks , also known as Hellenes, are a nation and ethnic group native to Greece, Cyprus and neighbouring regions, who can also be found in diaspora communities around the world....
physician Dioscorides (1st century AD.)
Avicenna, known as Abū Alī Sīnā or Ibn Sīnā , and commonly known in English by his Latinized name Avicenna , was a Persian polymath and the foremost physician and philosopher of his time...
mentions zinc oxide in
The Canon of MedicineThe Canon of Medicine is a 14-volume medical encyclopedia written by Islamic scientist and physician Ibn Sīnā...
(1025 AD), which mentioned it as a preferred treatment for a variety of skin conditions, including
skin cancerSkin cancer is a malignant growth on the skin which can have many causes. The most common skin cancers are basal cell cancer, squamous cell cancer, and melanoma. Skin cancer generally develops in the epidermis , so a tumor is usually clearly visible. This makes most skin cancers detectable in the...
. 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 powderBaby 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...
and creams against
diaper rashDiaper rash or nappy rash , is a generic term applied to skin rashes in the diaper area that are caused by various skin disorders and/or irritants....
es,
calamineCalamine is a mixture of zinc oxide with about 0.5% iron 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, insect bites and stings...
cream, anti-
dandruffDandruff is the excessive shedding of dead skin cells from the scalp. Dandruff can also be 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 in fact quite common...
shampooShampoo 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
antisepticAntiseptics 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
brassBrass is any 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. Despite this distinction, some types of brasses are called bronzes. Brass is a...
(an alloy of
zincZinc , also known as 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
copperCopper 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 rather soft and malleable and a freshly-exposed surface has a pinkish or peachy color...
) as early as 200 BCE 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 CE. Zinc oxide has also been recovered from zinc mines at Zawar in
IndiaIndia, 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, and the most populous democracy in the world. Bounded by the Indian Ocean on the south, the Arabian Sea on the west, and the Bay of Bengal...
, dating from the second half of the first millennium BCE. 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
IndiaIndia, 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, and the most populous democracy in the world. Bounded by the Indian Ocean on the south, the Arabian Sea on the west, and the Bay of Bengal...
using a primitive form of the direct synthesis process. From India, zinc manufacture moved to
ChinaChina is a cultural region, an ancient civilization, and, depending on perspective, a national or multinational entity extending over a large area in East Asia....
in the 17th century. In 1743, the first European zinc smelter was established in
BristolBristol is a city, unitary authority area and ceremonial county in South West England, west of London, and east of Cardiff.With an estimated population of 416,400 for the unitary authority in mid-2007, and a surrounding urban area with an estimated 561,500 residents, it is England's sixth, and...
,
United KingdomThe United Kingdom of Great Britain and Northern Ireland is a sovereign state located off the northwestern coast of continental Europe. It is an island country, spanning an archipelago including Great Britain, the northeastern part of Ireland, and many small islands...
.
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 safeGenerally 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.GRAS exemptions are granted...
, or GRAS, substances.
Zinc oxide itself is non-toxic; however it is hazardous to breathe zinc oxide fumes, as generated when zinc or zinc alloys are melted and oxidized at high temperature. This problem occurs while melting
brassBrass is any 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. Despite this distinction, some types of brasses are called bronzes. Brass is a...
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)
steelSteel is an alloy consisting mostly of iron, with a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most cost-effective 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 feverMetal fume fever also known as brass founders' ague, brass shakes, zinc shakes, Galvie Flu, or Monday morning fever
. For this reason, typically galvanized steel is not welded, or the zinc is removed first.
See also
- Zinc
Zinc , also known as 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
The zinc-zinc oxide cycle or Zn/ZnO cycle is a two step thermochemical process based on zinc and zinc oxide for hydrogen production with a typical efficiency around 40%.-Process description:...
- 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 ZnO
2 is additive to antiseptic ointments...
- Gallium(III) nitride
Gallium nitride is a very hard material commonly used in bright LEDs since the 1990s.The compound is a direct-bandgap semiconductor material of wurtzite crystal structure, with a wide band gap, used in optoelectronic, high-power and high-frequency devices. It is a binary group III/group V direct...
- 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 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 is a material created by the combination of zinc oxide and eugenol which can be used as a filling or cement material in dentistry. It is often used in dentistry when the decay is very deep or very close to the nerve or pulp chamber. Because the tissue inside the tooth, i. e...
- Zinc-air battery
Zinc-air batteries , and zinc-air fuel cells, are electro-chemical batteries powered by the oxidation of zinc with oxygen from the air. These batteries have high energy densities and are relatively inexpensive to produce. They are used in hearing aids and in experimental electric vehicles...
Reviews
- U. Ozgur et al. "A comprehensive review of ZnO materials and devices" (103 pages) J. Appl. Phys. 98 (2005) 041301 - a very highly cited article (~800 citations in the period 2005-2008 according to Web of Science
ISI Web of Knowledge is an online academic database provided by Thomson Scientific's Institute for Scientific Information. It provides access to many databases and other resources: Web of Science ISI Web of Knowledge is an online academic database provided by Thomson Scientific's Institute for...
)
- 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