ZINC OXIDE

ZINC OXIDE

Zinc oxide is an inorganic compound with the formula ZnO. ZnO is a white powder that is insoluble in water. Zinc oxide is used as an additive in numerous materials and products including cosmetics, food supplements, rubbers, plastics, ceramics, glass, cement, lubricants, paints, ointments, adhesives, sealants, pigments, foods, batteries, ferrites, fire retardants, and first-aid tapes. Although Zinc oxide occurs naturally as the mineral zincite, most zinc oxide is produced synthetically.

CAS No. : 1314-13-2
EC No. : 215-222-5

Zinc Oxide

Zinc Oxide is a wide-band gap semiconductor of the II-VI semiconductor group. The native doping of the semiconductor due to oxygen vacancies or zinc interstitials is n-type. Other favorable properties include good transparency, high electron mobility, wide band gap, and strong room-temperature luminescence. Those properties make ZnO valuable for a variety of emerging applications: transparent electrodes in liquid crystal displays, energy-saving or heat-protecting windows, and electronics as thin-film transistors and light-emitting diodes.

Chemical properties of Zinc Oxide
Pure Zinc oxide is a white powder, but in nature Zinc oxide occurs as the rare mineral zincite, which usually contains manganese and other impurities that confer a yellow to red color.

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

Zinc oxide is an amphoteric oxide. It is nearly insoluble in water, but it will dissolve in most acids, such as hydrochloric acid:
Zinc oxide + 2 HCl → ZnCl2 + H2O

Solid zinc oxide will also dissolve in alkalis to give soluble zincates:

Zinc oxide + 2 NaOH + H2O → Na2[Zn(OH)4]
Zinc oxide reacts slowly with fatty acids in oils to produce the corresponding carboxylates, such as oleate or stearate. Zinc oxide forms cement-like products when mixed with a strong aqueous solution of zinc chloride and these are best described as zinc hydroxy chlorides. This cement was used in dentistry.

Hopeite
Zinc oxide also forms cement-like material when treated with phosphoric acid; related materials are used in dentistry. A major component of zinc phosphate cement produced by this reaction is hopeite, Zn3(PO4)2·4H2O.

Zinc oxide decomposes into zinc vapor and oxygen at around 1975 °C with a standard oxygen pressure. In a carbothermic reaction, heating with carbon converts the oxide into zinc vapor at a much lower temperature (around 950 °C).
Zinc oxide + C → Zn(Vapor) + CO

Physical properties of Zinc oxide

Zinc oxide crystallizes in two main forms, 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 Zinc oxide on substrates with cubic lattice structure. In both cases, the zinc and oxide centers are tetrahedral, the most characteristic geometry for Zn(II). Zinc oxide converts to the rocksalt motif at relatively high pressures about 10 GPa. The many remarkable medical properties of creams containing Zinc oxide can be explained by its elastic softness, which is characteristic of tetrahedral coordinated binary compounds close to the transition to octahedral structures.

Hexagonal and zincblende polymorphs have no inversion symmetry (reflection of a crystal relative to any given point does not transform it into itself). This and other lattice symmetry properties result in piezoelectricity of the hexagonal and zincblende Zinc oxide, and pyroelectricity of hexagonal Zinc oxide.

The hexagonal structure has a point group 6 mm (Hermann-Mauguin notation) or C6v (Schoenflies notation), and the space group 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 Zinc oxide is largely ionic (Zn2+–O2−) with the corresponding radii of 0.074 nm for Zn2+ and 0.140 nm for O2−. This property accounts for the preferential formation of wurtzite rather than zinc blende structure, as well as the strong piezoelectricity of Zinc oxide. Because of the polar Zn-O bonds, zinc and oxygen planes are electrically charged. To maintain electrical neutrality, those planes reconstruct at atomic level in most relative materials, but not in Zinc oxide – its surfaces are atomically flat, stable and exhibit no reconstruction. However, studies using wurtzoid structures explained the origin of surface flatness and the absence of reconstruction at Zinc oxide wurtzite surfaces in addition to the origin of charges on Zinc oxide planes.

Mechanical properties of Zinc oxide
Zinc oxide 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. The high heat capacity and heat conductivity, low thermal expansion and high melting temperature of Zinc oxide are beneficial for ceramics. The E2 optical phonon in Zinc oxide exhibits an unusually long lifetime of 133 ps at 10 K.

Among the tetrahedrally bonded semiconductors, it has been stated that Zinc oxide has the highest piezoelectric tensor, or at least one comparable to that of GaN and AlN. This property makes it a technologically important material for many piezoelectrical applications, which require a large electromechanical coupling. Therefore Zinc oxide has been in forms of thin film one of the most studied resonator material for thin-film bulk acoustic resonators.

Electrical properties of Zinc oxide
Zinc oxide has a relatively large direct band gap 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, and high-temperature and high-power operation. The band gap of Zinc oxide can further be tuned to ~3–4 eV by its alloying with magnesium oxide or cadmium oxide.

Most Zinc oxide has n-type character, even in the absence of intentional doping. Nonstoichiometry is typically the origin of n-type character, but the subject remains controversial. An alternative explanation has been proposed, based on theoretical calculations, that unintentional substitutional hydrogen impurities are responsible. Controllable n-type doping is easily achieved by substituting Zn with group-III elements such as Al, Ga, In or by substituting oxygen with group-VII elements chlorine or iodine.

Reliable p-type doping of Zinc oxide remains difficult. This problem originates from low solubility of p-type dopants and their compensation by abundant n-type impurities. This problem is observed with GaN and ZnSe. Measurement of p-type in "intrinsically" n-type material is complicated by the inhomogeneity of samples.

Current limitations to p-doping limit electronic and optoelectronic applications of Zinc oxide, 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 of Zinc oxide 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).

Zinc oxide discs, acting as a varistor, are the active material in most surge arresters.

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

Indirect process of Zinc oxide
In the indirect or French process, metallic zinc is melted in a graphite crucible and vaporized at temperatures above 907 °C (typically around 1000 °C). Zinc vapor reacts with the oxygen in the air to give Zinc oxide, 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 process of Zinc oxide
The direct or American process starts with diverse contaminated zinc composites, such as zinc ores or smelter by-products. The zinc precursors are reduced (carbothermal reduction) by heating with a source of carbon such as anthracite to produce zinc vapor, which is then oxidized as in the indirect process. Because of the lower purity of the source material, the final product is also of lower quality in the direct process as compared to the indirect one.

Wet chemical process
A small amount of industrial production involves wet chemical processes, which start with aqueous solutions of zinc salts, from which zinc carbonate or zinc hydroxide is precipitated. The solid precipitate is then calcined at temperatures around 800 °C.

Laboratory synthesis

The red and green colors of these synthetic Zinc oxide crystals result from different concentrations of oxygen vacancies.
Numerous specialised methods exist for producing Zinc oxide for scientific studies and niche applications. These methods can be classified by the resulting Zinc oxide form (bulk, thin film, nanowire), temperature ("low", that is close to room temperature or "high", that is T ~ 1000 °C), process type (vapor deposition or growth from solution) and other parameters.

Large single crystals (many cubic centimeters) can be grown by the gas transport (vapor-phase deposition), hydrothermal synthesis, or melt growth. However, because of high vapor pressure of Zinc oxide, 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, metalorganic vapour phase epitaxy, electrodeposition, pulsed laser deposition, sputtering, sol-gel synthesis, atomic layer deposition, 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 → Zinc oxide + H2O

Zinc oxide nanostructures
Nanostructures of Zinc oxide can be synthesized into a variety of morphologies including nanowires, nanorods, tetrapods, nanobelts, nanoflowers, nanoparticles etc. Nanostructures can be obtained with most above-mentioned techniques, at certain conditions, and also with the vapor-liquid-solid method. The synthesis is typically carried out at temperatures of about 90 °C, in an equimolar aqueous solution of zinc nitrate and hexamine, the latter providing the basic environment. Certain additives, such as polyethylene glycol or polyethylenimine, can improve the aspect ratio of the Zinc oxide nanowires. Doping of the Zinc oxide 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 Zinc oxide nanowires on pre-seeded silicon, glass, and gallium nitride substrates have been grown using aqueous zinc salts such as zinc nitrate and zinc acetate in basic environments. Pre-seeding substrates with Zinc oxide creates sites for homogeneous nucleation of Zinc oxide crystal during the synthesis. Common pre-seeding methods include in-situ thermal decomposition of zinc acetate crystallites, spincoating of Zinc oxide nanoparticles and the use of physical vapor deposition methods to deposit Zinc oxide thin films. Pre-seeding can be performed in conjunction with top down patterning methods such as electron beam lithography and nanosphere lithography to designate nucleation sites prior to growth. Aligned Zinc oxide nanowires can be used in dye-sensitized solar cells and field emission devices.

History of Zinc oxide
Zinc compounds were probably used by early humans, in processed and unprocessed forms, as a paint or medicinal ointment, but their composition is uncertain. The use of pushpanjan, probably zinc oxide, as a salve for eyes and open wounds, is mentioned in the Indian medical text the Charaka Samhita, thought to date from 500 BC or before. Zinc oxide ointment is also mentioned by the Greek physician Dioscorides (1st century AD). Galen suggested treating ulcerating cancers with zinc oxide, as did Avicenna in his The Canon of Medicine. Zinc oxide is no longer used for treating skin cancer, though it is still used as an ingredient in products such as baby powder and creams against diaper rashes, calamine cream, anti-dandruff shampoos, and antiseptic ointments.

The Romans produced considerable quantities of brass (an alloy of zinc and copper) 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, dating from the second half of the first millennium BC.

From the 12th to the 16th century zinc and zinc oxide were recognized and produced in India using a primitive form of the direct synthesis process. From India, zinc manufacture moved to China in the 17th century. In 1743, the first European zinc smelter was established in Bristol, United Kingdom. Around 1782 Louis-Bernard Guyton de Morveau proposed replacing lead white with zinc oxide.

The main usage of zinc oxide (zinc white) was in paints and as an additive to ointments. Zinc white was accepted as a pigment in oil paintings by 1834 but it did not mix well with oil. This problem was solved by optimizing the synthesis of Zinc oxide. 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 valuable for making tints with other colors, but it makes a rather brittle dry film when unmixed with other colors. For example, during the late 1890s and early 1900s, some artists used zinc white as a ground for their oil paintings. All those paintings developed cracks over the years.

In recent times, most zinc oxide was used in the rubber industry to resist corrosion. In the 1970s, the second largest application of Zinc oxide was photocopying. High-quality Zinc oxide produced by the "French process" was added to photocopying paper as a filler. This application was soon displaced by titanium.

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

Rubber manufacture of Zinc oxide
Between 50% and 60% of Zinc oxide use is in the rubber industry. Zinc oxide along with stearic acid is used in the vulcanization of rubber Zinc oxide additive also protect rubber from fungi (see medical applications) and UV light.

Ceramic industry
Ceramic industry consumes a significant amount of zinc oxide, in particular in ceramic glaze and frit compositions. The relatively high heat capacity, thermal conductivity and high temperature stability of Zinc oxide coupled with a comparatively low coefficient of expansion are desirable properties in the production of ceramics. Zinc oxide affects the melting point and optical properties of the glazes, enamels, and ceramic formulations. Zinc oxide as a low expansion, secondary flux improves the elasticity of glazes by reducing the change in viscosity as a function of temperature and helps prevent crazing and shivering. By substituting Zinc oxide for BaO and PbO, the heat capacity is decreased and the thermal conductivity is increased. Zinc in small amounts improves the development of glossy and brilliant surfaces. However, in moderate to high amounts, it produces matte and crystalline surfaces. With regard to color, zinc has a complicated influence.

Medicine
Zinc oxide as a mixture with about 0.5% iron(III) oxide (Fe2O3) is called calamine and is used in calamine lotion. Two minerals, zincite and hemimorphite, have been historically called calamine. When mixed with eugenol, a ligand, zinc oxide eugenol is formed, which has applications as a restorative and prosthodontic in dentistry.

Reflecting the basic properties of Zinc oxide, fine particles of the oxide have deodorizing and antibacterial properties and for that reason are added into materials including cotton fabric, rubber, oral care products, and food packaging. Enhanced antibacterial action of fine particles compared to bulk material is not exclusive to Zinc oxide and is observed for other materials, such as silver. This property results from the increased surface area of the fine particles.

Zinc oxide is used in mouthwash products and toothpastes as an anti-bacterial agent proposed to prevent plaque and tartar formation, and to control bad breath by reducing the volatile gases and volatile sulphur compounds (VSC) in the mouth. Along with zinc oxide or zinc salts, these products also commonly contain other active ingredients, such as cetylpyridinium chloride, xylitol, hinokitiol, essential oils and plant extracts.

Zinc oxide is widely used to treat a variety of skin conditions, including atopic dermatitis, contact dermatitis, itching due to eczema, diaper rash and acne. Zinc oxide is also often added into sunscreens.

It is used in products such as baby powder and barrier creams to treat diaper rashes, calamine cream, anti-dandruff shampoos, and antiseptic 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 lotions to protect against sunburn and other damage to the skin caused by ultraviolet light (see sunscreen). It is the broadest spectrum UVA and UVB absorber that is approved for use as a sunscreen by the U.S. Food and Drug Administration (FDA), and is completely photostable. When used as an ingredient in sunscreen, zinc oxide blocks both UVA (320–400 nm) and UVB (280–320 nm) rays of ultraviolet light. Zinc oxide and the other most common physical sunscreen, titanium dioxide, are considered to be nonirritating, nonallergenic, and non-comedogenic. Zinc from zinc oxide is, however, slightly absorbed into the skin.

Many sunscreens use nanoparticles of zinc oxide (along with nanoparticles of titanium dioxide) because such small particles do not scatter light and therefore do not appear white. The nanoparticles are not absorbed into the skin more than regular-sized zinc oxide particles are, and are only absorbed into the outermost layer of the skin but not into the body.

Zinc oxide nanoparticles can enhance the antibacterial activity of ciprofloxacin. It has been shown that nano Zinc oxide that has an average size between 20 nm and 45 nm can enhance the antibacterial activity of ciprofloxacin against Staphylococcus aureus and Escherichia coli in vitro. The enhancing effect of this nanomaterial is concentration dependent against all test strains. This effect may be due to two reasons. First, zinc oxide nanoparticles can interfere with NorA protein, which is developed for conferring resistance in bacteria and has pumping activity that mediate the effluxing of hydrophilic fluoroquinolones from a cell. Second, zinc oxide nanoparticles can interfere with Omf protein, which is responsible for the permeation of quinolone antibiotics into the cell.

Cigarette filters
Zinc oxide is a component of cigarette filters. A filter consisting of charcoal impregnated with zinc oxide and iron oxide removes significant amounts of hydrogen cyanide (HCN) and hydrogen sulfide (H2S) from tobacco smoke without affecting its flavor.

Food additive
Zinc oxide is added to many food products, including breakfast cereals, as a source of zinc, a necessary nutrient. (Zinc sulfate is also used for the same purpose.) Some prepackaged foods also include trace amounts of Zinc oxide even if it is not intended as a nutrient.

Zinc oxide was linked to dioxin contamination in pork exports in the 2008 Chilean pork crisis. The contamination was found to be due to dioxin contaminated zinc oxide used in pig feed.

Pigment
Zinc white is used as a pigment in paints and is more opaque than lithopone, but less opaque than titanium dioxide. It is also used in coatings for paper. Chinese white is a special grade of zinc white used in artists' pigments. The use of zinc white (zinc oxide) as a pigment in oil painting started in the middle of 18th century. It has partly replaced the poisonous lead white and was used by painters such as Böcklin, Van Gogh, Manet, Munch and others. It is also a main ingredient of mineral makeup (CI 77947).

UV absorber
Micronized and nano-scale zinc oxide and titanium dioxide provide strong protection against UVA and UVB ultraviolet radiation, and are used in suntan lotion, and also in UV-blocking sunglasses for use in space and for protection when welding, following research by scientists at Jet Propulsion Laboratory (JPL).

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

Zinc oxide highly n-type doped with aluminium, gallium, or indium is transparent and conductive (transparency ~90%, lowest resistivity ~10−4 Ω·cm). Zinc oxide:Al coatings are used for energy-saving or heat-protecting windows. The coating lets the visible part of the spectrum in but either reflects the infrared (IR) radiation back into the room (energy saving) or does not let the IR radiation into the room (heat protection), depending on which side of the window has the coating.

Plastics, such as polyethylene naphthalate (PEN), can be protected by applying zinc oxide coating. The coating reduces the diffusion of oxygen with PEN. Zinc oxide layers can also be used on polycarbonate in outdoor applications. The coating protects polycarbonate from solar radiation, and decreases its oxidation rate and photo-yellowing.

Corrosion prevention in nuclear reactors
Zinc oxide depleted in 64Zn (the zinc isotope with atomic mass 64) is used in corrosion prevention in nuclear pressurized water reactors. The depletion is necessary, because 64Zn is transformed into radioactive 65Zn under irradiation by the reactor neutrons.

Methane reforming
Zinc oxide (ZnO) is used as a pretreatment step to remove hydrogen sulfide (H2S) from natural gas following hydrogenation of any sulfur compounds prior to a methane reformer, which can poison the catalyst. At temperatures between about 230–430 °C (446–806 °F), H2S is converted to water by the following reaction:

H2S + Zinc oxide → H2O + ZnS
The zinc sulfide (ZnS) is replaced with fresh zinc oxide when the zinc oxide has been consumed.

Potential applications of Zinc oxide
Electronics

Zinc oxide has wide direct band gap (3.37 eV or 375 nm at room temperature). Therefore, its most common potential applications are in laser diodes and light emitting diodes (LEDs). Some optoelectronic applications of Zinc oxide overlap with that of GaN, which has a similar band gap (~3.4 eV at room temperature). Compared to GaN, Zinc oxide 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 Zinc oxide. Zinc oxide can be combined with GaN for LED-applications. For instance as transparent conducting oxide layer and Zinc oxide nanostructures provide better light outcoupling. Other properties of Zinc oxide favorable for electronic applications include its stability to high-energy radiation and its possibility to be patterned by wet chemical etching. Radiation resistance makes Zinc oxide a suitable candidate for space applications. Zinc oxide is the most promising candidate in the field of random lasers to produce an electronically pumped UV laser source.

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

Aluminium-doped Zinc oxide layers are used as transparent electrodes. The components Zn and Al are much cheaper and less toxic compared to the generally used indium tin oxide (ITO). One application which has begun to be commercially available is the use of Zinc oxide as the front contact for solar cells or of liquid crystal displays.

Transparent thin-film transistors (TTFT) can be produced with Zinc oxide. As field-effect transistors, they even may not need a p–n junction, thus avoiding the p-type doping problem of Zinc oxide. Some of the field-effect transistors even use Zinc oxide nanorods as conducting channels.

Zinc oxide nanorod sensor
Zinc oxide nanorod sensors are devices detecting changes in electric current passing through zinc oxide nanowires due to adsorption 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. Zinc oxide have been used as immobilization layers in imunosensors enabling the distribution of antibodies across the entire region probed by the measuring electric field applied to the microelectrodes.

Spintronics
Zinc oxide has also been considered for spintronics applications: if doped with 1–10% of magnetic ions (Mn, Fe, Co, V, etc.), Zinc oxide could become ferromagnetic, even at room temperature. Such room temperature ferromagnetism in Zinc oxide: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 in textile fibers coated in Zinc oxide 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 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.

Zinc oxide as anode of Li-ion battery
In form of a thin film Zinc oxide has been demonstrated in miniaturised high frequency thin film resonators, sensors and filters.

Li-ion battery
Zinc oxide is a promising anode material for lithium-ion battery because it is cheap, biocompatible, and environmentally friendly. Zinc oxide has a higher theoretical capacity (978 mAh g−1) than many other transition metal oxides such as CoO (715 mAh g−1), NiO (718 mAh g−1) and CuO (674 mAh g−1).

Safety of Zinc oxide
As a food additive, zinc oxide is on the U.S. FDA's list of generally recognized as safe, or GRAS, substances.

Zinc oxide itself is non-toxic; it is hazardous, however, to inhale zinc oxide fumes, such as generated when zinc or zinc alloys are melted and oxidized at high temperature. This problem occurs while melting alloys containing brass 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, can result in a malady called metal fume fever. For this reason, typically galvanized steel is not welded, or the zinc is removed first.

Zinc oxide is an inorganic compound used in a number of manufacturing processes. It can be found in rubbers, plastics, ceramics, glass, cement, lubricants, paints, ointments, adhesives, sealants, pigments, foods, batteries, ferrites, fire retardants, and first-aid tapes. It occurs naturally as the mineral zincite, but most zinc oxide is produced synthetically. It is also widely used to treat a variety of other skin conditions, in products such as baby powder and barrier creams to treat diaper rashes, calamine cream, anti-dandruff shampoos, and antiseptic ointments.

Zinc oxide is mildly astringent and is used topically as a soothing and protective application in eczema and slight excoriations, in wounds, and for hemorrhoids. It is also used with coal tar or ichthammol in the treatment eczema.

Zinc oxide is used as the basis for the production of a number of dental cements. Mixed with phosphoric acid it forms a hard material composed largely of zinc phosphate; mixed with clove oil or eugenol, it is used as temporary dental filling.

Pharmacologic levels of zinc as zinc oxide have consistently been found to increase pig performance during the postweaning period. In some instances, high levels of zinc oxide have been reported to reduce the incidence and severity of postweaning diarrhea. Responses to zinc oxide and antibiotics seem to be additive in nature, much like the responses to high copper and antibiotics; however, there is no advantage in including high copper and high zinc in the same diet.

Zinc oxide accounts for the largest use of zinc compounds, and is used primarily by the rubber industry as a vulcanization activator and accelerator and to slow rubber aging by neutralizing sulfur and organic acids formed by oxidation. It also acts in rubber as a reinforcing agent, a heat conductor, a white pigment, and an absorber of UV light. In paints, zinc oxide serves as a mildewstat, acid buffer, and a pigment. It is used in animal feed as a zinc supplement and as a fertilizer additive for zinc-deficient soils. Zinc oxide is used in cosmetics and drugs primarily for its fungicide properties, and in dentistry in dental cements. It is also used in ceramics, in glass manufacture, as a catalyst in organic synthesis, and in coated photocopy paper.

Two processes are used to produce metallic zinc from the ore concentrates that are not subjected to caustic soda leaching. In one process, the ore concentrate containing zinc sulfide is roasted in the presence of air to produce zinc oxide, which is combined with coke or coal and retorted to approximately 1,100 °C to produce metallic zinc. In the other process, the roasted zinc oxide is leached with sulfuric acid, and the solution is electrolyzed to produce zinc of >99.9% purity.

Zinc oxide is also produced industrially from purified solutions of zinc sulfate or chloride by precipitating the basic carbonate, which is then washed, filtered, and finally calcined. This method produces a grade of zinc oxide with a high specific surface area. Products of this type are also obtained from waste hydroxides which are purified by a chemical route and then calcined.

Residues of zinc oxide are exempted from the requirement of a tolerance when used as a coating agent in accordance with good agricultural practice as inert (or occasionally active) ingredients in pesticide formulations applied to growing crops or to raw agricultural commodities after harvest.

Zinc oxide effectively reduces visual cell loss in rats exposed to intense visible light and is known to slow the rate of disease progression in advanced stages of age-related macular degeneration. Our goal was to determine the efficacy of zinc oxide in combination with novel and well-established antioxidants in an animal model of light-induced oxidative retinal damage. One group of male Sprague-Dawley rats was pretreated with zinc oxide with or without a detergent extract of rosemary powder and then exposed to intense visible light for 4-24 hr. Another group of animals received zinc oxide combined with rosemary oil diluted with a mixture of polyunsaturated fatty acids (ROPUFA) and a third group was given an antioxidant mineral mix containing zinc oxide, as recommended by the Age Related Eye Disease Study group's first clinical trial (AREDS1). Visual cell survival was determined 2 weeks after intense light treatment by measuring rhodopsin and photoreceptor cell DNA levels and confirmed by retinal histology and agarose gel electrophoresis of DNA. Western analysis was used to determine the effects of zinc and antioxidants on the oxidative stress markers, glial fibrillary acidic protein (GFAP), heme-oxygenase-1 (HO-1), and carboxyethylpyrrole (CEP). Rod and cone opsin and arrestin levels were used as markers of photoreceptor cell function. Dark-reared rats treated with 1.3 mg/kg zinc oxide and 17 mg/kg rosemary extract, or with one-half those doses, and exposed to moderate intensity green light retained 75%-85% of the rhodopsin and retinal DNA measured in unexposed rats. These levels were significantly higher than found for zinc oxide or rosemary treatment alone. Rosemary oil was also effective when combined with zinc oxide, but ROPUFA alone was no more effective than the detergent vehicle. Prolonged intense green light led to increases in retinal GFAP and HO-1 levels and to decreases in cone cell opsin and rod and cone arrestins. Rosemary plus zinc treatment reduced the expression of oxidative stress protein markers and enhanced visual cell survival, as shown by improved photoreceptor cell morphology and by decreased retinal DNA degradation. Using higher intensity white light for exposures in cyclic light-reared rats, treatment with an AREDS antioxidant/mineral mixture was found to be ineffective, whereas rosemary extract plus an equivalent dose of zinc oxide was significantly more effective in preserving visual cells. CEP protein adduct formation was reduced by all antioxidant treatments, but rosemary plus zinc oxide also prevented the loss of cone cell opsin and arrestin more effectively than AREDS. In the rat model of acute retinal light damage, zinc oxide combined with a detergent extract of rosemary powder or rosemary oil is more effective than treatment with either component alone and significantly more effective than an AREDS mixture containing a comparable dose of zinc oxide. Light-induced oxidative stress in animal models of retinal degeneration can be a useful preclinical paradigm for screening novel antioxidants and for testing potential therapeutics designed to slow the progression of age-related ocular disease.

Uses
This medication is used to treat and prevent diaper rash and other minor skin irritations (e.g., burns, cuts, scrapes). It works by forming a barrier on the skin to protect it from irritants/moisture.

How to use Zinc Oxide Ointment
Use this medication on the skin only. Follow all directions on the product package or use as directed by your doctor. If you have any questions, ask your doctor or pharmacist.

Avoid getting this medication in the eyes. If you do get the medication in the eyes, flush with plenty of water.

If you are using the spray, shake the container well before each use.

Zinc oxide is an essential ingredient of many enzymes, sun screens, and ointments for pain and itch relief. Its microcrystals are very efficient light absorbers in the UVA and UVB region of spectra due to wide bandgap. Impact of zinc oxide on biological functions depends on its morphology, particle size, exposure time, concentration, pH, and biocompatibility. They are more effective against microorganisms such as Bacillus subtilis, Bacillus megaterium, Staphylococcus aureus, Sarcina lutea, Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumonia, Pseudomonas vulgaris, Candida albicans, and Aspergillus niger. Mechanism of action has been ascribed to the activation of zinc oxide nanoparticles by light, which penetrate the bacterial cell wall via diffusion. It has been confirmed from SEM and TEM images of the bacterial cells that zinc oxide nanoparticles disintegrate the cell membrane and accumulate in the cytoplasm where they interact with biomolecules causing cell apoptosis leading to cell death.

Zinc oxide nanoparticle is one such inorganic metal oxide which fulfills all the above requirements, and hence, it can safely be used as medicine, preservative in packaging, and an antimicrobial agent. It easily diffuses into the food material, kill the microbes, and prevent human being from falling ill. In accordance with the regulations 1935/2004/EC and 450/2009/EC of the European Union, active packaging is defined as active material in contact with food with ability to change the composition of the food or the atmosphere around it. Therefore, it is commonly used as preservative and incorporated in polymeric packaging material to prevent food material from damage by microbes. Zinc oxide nanoparticles have been used as an antibacterial substance against Salmonella typhi and S. aureus in vitro. Of all the metal oxide nanoparticles studied thus far, zinc oxide nanoparticles exhibited the highest toxicity against microorganisms. It has also been demonstrated from SEM and TEM images that zinc oxide nanoparticles first damage the bacterial cell wall, then penetrate, and finally accumulate in the cell membrane. They interfere with metabolic functions of the microbes causing their death. All the characteristics of the zinc oxide nanoparticles depend on their particle size, shape, concentration, and exposure time to the bacterial cell. Further, biodistribution studies of zinc oxide nanoparticles have also been examined. For instance, Wang et al. have investigated the effect of long-term exposure of zinc oxide nanoparticle on biodistribution and zinc metabolism in mice over 3 to 35 weeks. Their results showed minimum toxicity to mice when they were exposed to 50 and 500 mg/kg zinc oxide nanoparticle in diet. At higher dose of 5000 mg/kg, zinc oxide nanoparticle decreased body weight but increased the weight of the pancreas, brain, and lung. Also, it increased the serum glutamic-pyruvic transaminase activity and mRNA expression of zinc metabolism-related genes such as metallothionein. Biodistribution studies showed the accumulation of sufficient quantity of zinc in the liver, pancreas, kidney, and bones. Absorption and distribution of zinc oxide nanoparticle/zinc oxide microparticles are largely dependent on the particle size. Li et al. have studied biodistribution of zinc oxide nanoparticles fed orally or through intraperitoneal injection to 6 weeks old mice. No obvious adverse effect was detected in zinc oxide nanoparticles orally treated mice in 14 days study. However, intraperitoneal injection of 2.5 g/kg body weight given to mice showed accumulation of zinc in the heart, liver, spleen, lung, kidney, and testes. Nearly ninefold increase in zinc oxide nanoparticle in the liver was observed after 72 h. Zinc oxide nanoparticles have been shown to have better efficiency in liver, spleen, and kidney biodistribution than in orally fed mice. Since zinc oxide nanoparticles are innocuous in low concentrations, they stimulate certain enzymes in man and plants and suppress diseases. Singh et al. have also been recently reviewed the biosynthesis of zinc oxide nanoparticle, their uptake, translocation, and biotransformation in plant system.

Synonyms:
ZINC OXIDE; 1314-13-2; Zinc White; oxozinc; Amalox; ZnO; Chinese White; Snow white; Emanay zinc oxide; Felling zinc oxide; Zinc oxide (ZnO); Akro-zinc bar 85; Zinc monoxide; zink oxid; çinko oxid; Flowers of zinc; Azo-33; Outmine; Supertah; Zincite; Zincoid; Azodox; Ozide; Ozlo; Zincum Oxydatum; Zinci Oxicum; Zinci Oxydum; Flores de zinci; Hubbuck's White; Blanc de Zinc; Unichem ZO; Vandem VAC; Vandem VOC; çinko oksit; Vandem VPC; Green seal-8; Philosopher's wool; White seal-7; K-Zinc; Powder base 900; Protox type 166; Protox type 167; Protox type 168; Protox type 169; Protox type 267; Protox type 268; Akro-zinc bar 90; Azodox-55; Azodox-55TT; Red Seal 9; EMAR; CI Pigment white 4; Electrox 2500; Actox 14; Actox 16; Kadox 15; Kadox 72; Kadox-25; Zinc oxide [USAN]; Zinca 20; Protox 166; Protox 168; Protox 169; Caswell No. 920; Electox 2500; Cadox XX 78; Actox 216; Cynku tlenek [Polish]; Nogenol; C-Weiss 8 [German]; Azo-55TT; Azo-66TT; Azo-77TT; çinko oksit; Zinc gelatin; C.I. Pigment White 4; RVPaque; Azo 22; Azo-55; Azo-66; Azo-77; No-Genol; Pigment white 4; C.I. 77947; Dome Paste Bandage; A&D Medicated Ointment; XX 78; EINECS 215-222-5; XX 203; XX 601; EPA Pesticide Chemical Code 088502; ZN-0401 E 3/16''; Lassars Paste; Zinc oxide, ACS reagent; Lassar Paste; Zinc oxide, 99.5+%; ZNO; Desitin; zincum oxidatum; Cynku tlenek; oxyde de zinc; Zinc oxide fume; Zinc oxide substrate, 10x10x0.5mm, polished two sides, 0001 orientation; Zinc oxide, 99.99% trace metals basis; C-Weiss 8; Zinc oxide, 99.999%, (trace metal basis); Zinc oxide [USP:JAN]; Zinkoxid; oxido de cinc; Leaded zinc oxide; Zinc (as oxide); Zinc Oxide Powder; Zinc oxide (TN); Zine Oxide ,(S); Zinc (as zinc oxide); EC 215-222-5; Zinc oxide (JP17/USP); Zinc oxide, LR, >=99%; Zinc oxide, analytical standard; Zinc Oxide Nanopowder (Type I); Zinc oxide, p.a., 99.0%; Zinc Oxide Nanopowder (Type II); 9015AF; Zinc oxide, USP, 99-100.5%; Zinc Oxide Nanoparticles / Nanopowder; Zinc oxide, ACS reagent, >=99.0%; Zinc oxide, 30nm,20 wt.% isopropanol; Zinc oxide, tested according to Ph.Eur.; Zinc oxide, 99.999% trace metals basis; Zinc oxide, SAJ first grade, >=99.0%; Zinc oxide, JIS special grade, >=99.0%; Zinc oxide, nanopowder, <100 nm particle size; çinko oksit; Zinc Oxide Nanodispersion Type A-Nonionic (70nm); Zinc Oxide Nanodispersion Type B-Anionic (70nm); Zinc Oxide Nanodispersion Type C-Cationic (70nm); Zinc oxide, nanowires, diam. x L 90 nm x 1 mum; Zinc oxide, nanowires, diam. x L 50 nm x 300 nm; Zinc oxide, nanowires, diam. x L 300 nm x 4-5 mum; Zinc oxide, puriss. p.a., ACS reagent, >=99.0% (KT); Zinc oxide, nanopowder, <50 nm particle size (BET), >97%; Zinc oxide, ReagentPlus(R), powder, <5 mum particle size, 99.9%; Zinc oxide, United States Pharmacopeia (USP) Reference Standard; Zinc oxide substrate, 10x10x0.5mm, polished one side, 0001 orientation; Zinc oxide sputtering target, 76.2mm (3.0in) dia x 3.18mm (0.125in) thick; Zinc oxide sputtering target, 76.2mm (3.0in) dia x 6.35mm (0.250in) thick; Zinc oxide, dispersion, nanoparticles, <110 nm particle size, 40 wt. % in butyl acetate; Zinc oxide, dispersion, nanoparticles, 40 wt. % in ethanol, <130 nm particle size; Zinc oxide, dispersion, nanoparticles, <100 nm particle size (TEM), <=40 nm avg. part. size (APS), 20 wt. % in H2O; Zinc oxide, puriss., meets analytical specification of Ph. Eur., BP, USP, 99-100.5% (calc. for dried substance); Zinc oxide, sputtering target, diam. x thickness 3.00 in. x 0.125 in., 99.99% trace metals basis; ZINC OXIDE; 1314-13-2; Zinc White; oxozinc; Amalox; Chinese White; Snow white; Emanay zinc oxide; Felling zinc oxide; Zinc oxide (ZnO); Akro-zinc bar 85; Zinc monoxide; Flowers of zinc; Azo-33; Outmine; Supertah; Zincite; Zincoid; Azodox; Ozide; Ozl