Zinc oxide CAS#1314-13-2
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Chemical Name: zinc oxide
CAS No.: 1314-13-2
Molecular Fomula: OZn
Molecular weight: 81.39
Appearance: White to pale yellow nanopowder
Zinc oxide: The Complete Guide
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It has numerous applicaltions. It is widely used as an additive in many materials and products including plastics, ceramics, glass, cement, lubricants, etc.
ZINC HYDROXIDE;Zinc oxide;Zinc dihydroxide;
UN 3077 9/PG 3
P210; P273; P280; P337 + P313; P391; P403 + P235
H225; H319; H410
GHS02, GHS07, GHS09
Appearance & Physical State
1.6 mg/L (29 ºC)
Stable. Incompatible with magnesium, strong acids.
Store in a tightly closed container. Store in a cool, dry, well-ventilated area away from incompatible substances.
- Zinc oxide crystallizes in two main forms, hexagonal sillimanite, and cubic sphalerite. The sphalerite structure is the most stable under environmental conditions and is, therefore, the most common. The sphalerite form can be stabilized by growing ZnO on a substrate with a cubic lattice structure. In both cases, the zinc and oxide centers are tetrahedral, which is the most characteristic geometry of Zn(II). ZnO is converted to rock salt sequences at relatively high pressures of about 10 GPa. [Many of the remarkable medical properties of ZnO-containing creams can be explained by their elastic softness, which is characteristic of tetrahedral coordination dimers approaching the transition to octahedral structures.
- Hexagonal and sphalerite polymorphs have no inversion symmetry (the reflection of the crystal relative to any given point does not convert it into itself). This and other lattice symmetry properties lead to the piezoelectricity of hexagonal and sphalerite ZnO and the thermoelectricity of hexagonal ZnO.
- The hexagonal structure has a point group of 6 mm (Hermann-Mauguin notation) or C6v (Schoenflies notation) and a space group of 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 of c/a = 1.633 for hexagonal units. As with most II -This property explains the preferential formation of sillimanite rather than sphalerite structures, and the strong piezoelectricity of ZnO. Zn and oxygen planes are electrically charged due to the polar Zn-O bond. To remain electrically neutral, these planes are reconstructed at the atomic level in most related materials, but not in ZnO – its surface is atomically flat, stable, and not reconstructed. However, studies using fibrillated zincite structures explain the origin of surface flatness and the reconstruction of ZnO fibrillated zincite surfaces  in addition to the origin of charge on the ZnO planes.
- ZnO is a relatively soft material with a Mohs hardness of about 4.5. Its elastic constants are smaller than those of related group III-V semiconductors, such as GaN. The high heat capacity and thermal conductivity, low thermal expansion, and high melting temperature of ZnO favor ceramics. The E2 optical phonon in ZnO has an unusually long lifetime of 133 ps at 10 K .
- Among tetrahedrally bonded semiconductors, ZnO is said to have the highest piezoelectric tensor, or at least comparable to GaN and AlN. This property makes it a technically important material for many piezoelectric applications, which require large electromechanical coupling. Therefore, ZnO has been one of the most studied resonator materials for thin-film bulk acoustic wave resonators in the form of thin films.
Electrical and optical properties
- ZnO has a relatively large direct band gap at room temperature of ~3.3 eV. Advantages associated with a large band gap include higher breakdown voltages, the ability to sustain large electric fields, lower electronic noise, and high temperature and high power operation. The band gap of ZnO can be further tuned to ~3-4 eV by alloying with magnesium oxide or cadmium oxide.
- Most ZnO has n-type properties, even in the absence of intentional doping. Non-chemometrics is usually the origin of n-type features, but the subject remains controversial. An alternative explanation based on theoretical calculations has been proposed that unintentional substitution of hydrogen impurities is the culprit. Controlled n-type doping is easily achieved by replacing Zn with group III elements such as aluminum, gallium, and indium or by replacing oxygen with group VII elements chlorine or iodine.
- Reliable p-type doping of ZnO is still difficult. This problem arises from the low solubility of p-type dopants and their compensation by a large number of n-type impurities. This problem can be observed using GaN and ZnSe. The measurement of p-type in “essentially” n-type materials is complicated by the inhomogeneity of the sample.
- The current limitation of p-doping limits the electronic and optoelectronic applications of ZnO, which usually requires junctions of n-type and p-type materials. Known p-type dopants include the group I elements Li, Na, and K; the group V elements N, P, and As; and copper and silver. However, many of them form deep bodies and do not produce significant p-type conduction at room temperature.
- The electron mobility of ZnO varies greatly with temperature, with a maximum of about 2000 cm2/(V-s) at 80 K Very few data are available on the hole mobility, with values in the range of 5-30 cm2/(V-s).
- ZnO discs as varistors are the active material in most lightning arresters.
- Zinc oxide is known for its strong nonlinear optical properties, especially in bulk. The nonlinearity of ZnO nanoparticles can be fine-tuned depending on their size.
- Indirect process
- In the indirect or French process, zinc metal is melted in a graphite crucible and evaporates at temperatures above 907 °C (usually around 1000 °C). The zinc vapor reacts with oxygen in the air to form ZnO, accompanied by a drop in temperature and a bright glow. The zinc oxide particles are transported to a cooling duct and collected in a baghouse. This indirect method was popularized by LeClaire (France) in 1844, hence the common name French process. The product usually consists of agglomerated zinc oxide particles with an average size of 0.1 to a few microns. By weight, most of the world’s zinc oxide is manufactured by the French process.
- Direct Process
- The direct or U.S. process starts with various contaminated zinc composites such as zinc ore or smelter by-products. The zinc precursor is reduced (carbothermic reduction) by heating with a carbon source such as anthracite to produce zinc vapor, which is then oxidized as in the indirect process. Due to the lower purity of the feedstock, the final product quality is also lower in the direct process compared to the indirect process.
- Wet chemical processes
- A small amount of industrial production involves a wet chemical process that starts with an aqueous solution of zinc salts from which zinc carbonate or zinc hydroxide is precipitated. The solid precipitate is then calcined at a temperature of about 800 °C.
- Laboratory synthesis
- The red and green colors of these synthetic zinc oxide crystals are caused by different concentrations of oxygen vacancies.
There are many specialized methods to produce ZnO for scientific research and niche applications, depending on the resulting ZnO form (bulk, thin-film, nanowire), temperature (“low”, i.e., near room temperature or “high”, i.e., T ~ 1000 °C) ), the type of process (vapor deposition or growth from solution) and other parameters.
- Large single crystals (many cubic centimeters) can be grown by gas transport (vapor deposition), hydrothermal synthesis, or melt growth. However, growth from the melt is problematic due to the high vapor pressure of ZnO Growth by gas transport is difficult to control, so hydrothermal methods are preferred. Thin films can be prepared by chemical vapor deposition, metal-organic vapor phase epitaxy, electrodeposition, pulsed laser deposition, sputtering, sol-gel synthesis, atomic layer deposition, spray pyrolysis, etc.
- Plain white powdered zinc oxide can be produced in the laboratory by electrolysis of sodium bicarbonate solution with a zinc anode. Zinc hydroxide and hydrogen gas are produced. When heated, zinc hydroxide decomposes into zinc oxide.
- Zn + 2 H2O → Zn(OH)2 + H2
Zn(OH)2 → ZnO + H2O
Zinc oxide nanostructures
Nanostructures of ZnO can be synthesized in a variety of forms, including nanowires, nanorods, tetrapods, nanoribbons, nanoflowers, nanoparticles, etc. Nanostructures can be obtained by most of the above techniques under certain conditions and also by gas-liquid-solid methods. The synthesis is usually carried out at a temperature 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 polyethyleneimine, can improve the aspect ratio of ZnO nanowires. Doping of ZnO nanowires is achieved by adding other metal nitrates to the growth solution. The morphology of the resulting nanostructures can be tuned by changing parameters related to precursor composition (e.g., Zn concentration and pH) or thermal treatment (e.g., temperature and heating rate).
- ZnO nanowires arranged on pre-inoculated silicon, glass, and GaN substrates have been grown using aqueous zinc salts (e.g., zinc nitrate and zinc acetate). During synthesis, pre-inoculation of the substrate with ZnO creates a location for uniform nucleation of ZnO crystals. Common pre-inoculation methods include in situ thermal decompositions of zinc acetate microcrystals, spin coating of ZnO nanoparticles, and deposition of ZnO films using physical vapor deposition methods. Pre-inoculation can be performed in conjunction with top-down patterning methods such as electron beam lithography and nanosphere lithography to specify nucleation sites prior to growth. Aligned ZnO nanowires can be used for dye-sensitized solar cells and field emission devices.
What is Zinc oxide?
With the progress of science and technology and the development of society, chemical products have invariably permeated our daily lives, in medicine, food, cosmetics, electronics, industry, and other areas, becoming an essential part of our lives. One such product is zinc oxide which has developed particularly rapidly in recent years. Do you know about zinc oxide?
The official answer:It is an inorganic substance with the chemical formula ZnO, an oxide of zinc.
It also known as zinc white, is a pure white coloured powder consisting of small, indefinite or needle-like particles. As a basic chemical raw material, it has a wide range of applications in industries such as rubber electronics, pharmaceuticals and coatings
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