Zinc oxide
From Wikipedia, the free encyclopedia
| Zinc oxide | |
|---|---|
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| General | |
| Other names | Zinc white, calamine |
| Molecular formula | ZnO |
| Molar mass | 81.4084 g/mol |
| Appearance | White solid |
| Crystal Structure | wurtzite (hexagonal) |
| CAS number | [] |
| Properties | |
| Density and phase | 5.606 g/cm3, solid |
| Solubility in water | Insoluble |
| Melting point | 1975°C (decomposes) |
| Boiling point | |
| Mohs hardness | 5 |
| a, c Lattice constants | 3.249Å, 5.201Å |
| Thermodynamic data | |
| Standard enthalpy of formation ΔfH°solid |
−348.0 kJ/mol |
| Standard molar entropy S°solid |
43.9 J.K−1.mol−1 |
| Hazards | |
| EU classification | Dangerous for the environment (N) |
| R-phrases | R20, R36, R37. |
| S-phrases | S60, S61. |
| NFPA 704 |    |
| Supplementary data page | |
| Structure and properties |
n, εr, etc. |
| Thermodynamic data |
Phase behaviour Solid, liquid, gas |
| Spectral data | UV, IR, NMR, MS |
| Regulatory data | Flash point, RTECS number, etc. |
| Related compounds | |
| Other anions | Zinc sulfide Zinc selenide Zinc telluride |
| Other cations | Cadmium oxide Mercury oxide |
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references |
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Zinc oxide is a chemical compound with formula ZnO. It is nearly insoluble in water but soluble in acids or alkalis. It occurs as white hexagonal crystals or a white powder commonly known as zinc white. It remains white when exposed to hydrogen sulfide or ultraviolet light. Crystalline zinc oxide exhibits the piezoelectric effect and is thermochromic (it will change colour from white to yellow when heated, and back again when cooled down). Zinc oxide decomposes into zinc vapor and oxygen at around 1975°C. High-quality single-crystalline ZnO is almost transparent. Fumes of zinc oxide are generated when melting brass, because the melting point of brass is close to the boiling point of zinc.[2] Exposure to zinc oxide in the air (also while welding) can result in a nervous malady called metal fume fever[3].
Zinc oxide occurs in nature as the mineral zincite.
Zincum Oxydatum is the latin name for Zinc Oxide commonly listed on homeopathic medicines.
Contents |
[edit] Applications
Zinc oxide in a mixture with about 0.5% iron(III) oxide (Fe2O3) is called calamine and is used in calamine lotion. There are also two minerals, smithsonite and hemimorphite, which have been called calamine historically (see: calamine (mineral).
Zinc peroxide, ZnO2 .½ H2O, is a white to yellow powder that is used in antiseptic ointments.
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. Because it reflects both UVA and UVB rays of ultraviolet light, 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).
Zinc oxide and stearic acid are important ingredients in the commercial manufacture of rubber goods. A proper mixture of these two compounds allows a quicker and more controllable rubber cure. Zinc oxide can also be used as a filler in some rubber mixtures.
Zinc oxide is a semiconductor with a direct band gap of 3.37 eV (368 nm at room temperature, deep violet/borderline UV). A common application is in gas sensors. As of 2003, it has been utilized in recent research to build blue LEDs and transparent TFTs.
n-type doped films are often used in thin film technology, where zinc oxide serves as a TCO (transparent conducting oxide). n-type doping is possible by introduction of aluminum, indium, or excess zinc [1]. Oxygen vacancies generate states in the band gap and hence also cause an increase in conductivity.[2] p-type doping is difficult and is currently an active area of research, with arsenic as the leading candidate dopant[3]. Thin-film solar cells, LCD and flat panel displays are typical applications of this material. Appropriately doped Zinc oxide may be transparent and conductive, and can therefore be used as a transparent electrode. Indium tin oxide (ITO) is another transparent conducting oxide often used in microelectronics.
ZnO has also been considered for spintronics applications because of theoretical predictions of room temperature ferromagnetism. Unsubstantiated reports of ferromagnetism have been made, but presence of dilute magnetic semiconductors remains a large unanswered question in physics.
ZnO layers are mainly deposited by sputter deposition and chemical vapor deposition (CVD). The latter method allows the growth of a rough layer, which can diffuse the incoming light by scattering, increasing the efficiency of solar cells.
Recently, ZnO has been observed to act as a chemical reagent for Friedel-Craft Acylation Reaction.
Zinc oxide – recognized as a mild antimicrobial, wound healing and sunscreen agent. Primarily absorbs UVA light rather than scattering or reflecting, non-irritating, non-comedogenic, and micronized by forming many small micro particles for cosmetic use.
Zinc oxide has been studied as a treatment for cold sores and appears to shorten their duration.[4]
When mixed with eugenol, zinc oxide eugenol forms which has restorative and prosthodontic applications in dentistry.
[edit] Pyroelectric coefficient
- Primary pyroelectric coefficient: -6.8 μC/m2·K
- Secondary pyroelectric coefficient: -2.5 μC/m2·K
- Total pyroelectric coefficient: -9.4 μC/m2·K
[edit] Production Methods
Zinc oxide is produced by oxidation of metallic zinc vapor at elevated temperatures. There are two methods. Direct method and indirect method.
[edit] Indirect method
Metallic zinc is vaporized in suitable containers. Zinc vapor reacts with oxygen that is in the air to form zinc oxide.
[edit] Direct method
Zinc ores or roasted sulfide concentrates are mixed with coal. In a reduction furnace, ore is reduced to metallic zinc and vaporized zinc reacts with oxygen to form zinc oxide.
For more information and specifications
[edit] Use in pop culture
Zinc Oxide and You is a spoof of a high school science film, in Kentucky Fried Movie. The plot is straightforward - as the announcer intones "without zinc oxide, you would not have ...", then there is a "ding" and the noted object disappears, with successively more disastrous results. The results can be guessed at from the title of the next film (introduced but not shown), which is "Rebuilding your Home". An online version of this sketch can be found at the Frankin-Sterling Hill web site.
In one episode of SpongeBob SquarePants, SpongeBob rubs Zinc Oxide on his nose to achieve the "life guard look".
[edit] External links
- International Chemical Safety Card 0208.
- NIOSH Pocket Guide to Chemical Hazards.
- Nav Bharat Metallic Oxide Industries. (uses of zinc oxide)
- External MSDS.
[edit] References
- ^ Acc. Chem. Res. 1985, 18, pp. 228-234, Zinc Oxide: An Outstanding Example of a Binary Compound Semiconductor, Hirschwald, Wolfgang H.
- ^ "Oxygen Vacancies in ZnO", A. Janotti and C. G. Van de Walle, Appl. Phys. Lett. 87, 122102 (2005).
- ^ Phys. Lett. 87, 192103 (2005) p type doping of zinc oxide by arsenic ion implantation by G. Braunstein, A. Muraviev, H. Saxena, N. Dhere, V. Richter and R. Kalish
- ^ [1]
- Physics Today, volume 58, No. 8, p.33, August 2005.
- "Introduction and recovery of point defects in electron-irradiated ZnO", Tuomisto, F., Saarinen, K., Look, D.C., and Farlow, G.C., Physical Review B 72, 085206 (2005).
