ZINC OXIDE
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(Redirected from ZnO)
'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.[1] Exposure to zinc oxide in the air (also while welding) can result in a nervous malady called metal fume fever[2].
Zinc oxide occurs in nature as the mineral zincite.
Zincum Oxydatum is the latin name for Zinc Oxide commonly listed on homeopathic medicines.
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 absorbs 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). It is the broadest spectrum UVA and UVB absorber that is approved for use as a sunscreen by FDA, and is completely photostable. Additionally, since zinc oxide has antimicrobial and antifungal activities, it is the number one active ingredient recommended by pediatricians for the treatment of diaper rash.
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.
ZnO is a semiconductor with a direct bandgap energy of 3.37 eV at room temperature. The most common applications are in laser diodes and light emitting diodes since it has a exciton and biexciton energies of 60 meV and 15 meV, respectively. It is expected that this exciton properties of ZnO will be improved further by epitaxy.
''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 has been 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.
★ Primary pyroelectric coefficient: -6.8 µC/m2·K
★ Secondary pyroelectric coefficient: -2.5 µC/m2·K
★ Total pyroelectric coefficient: -9.4 µC/m2·K
Zinc Oxide is produced by two main processes:-
1. French Process
In this process, metallic zinc (Zinc Dross) is heated to a vapour form, the metallic zinc vapour is allowed to auto oxidize to form Zinc Oxide.
Higher purity of Zinc Oxide (Up to 99.9%) can be obtained by this method.
2. American Process
In this process ore of zinc (Zinc Ash) is dissolved (as ZnCl2) then goes through a precipitation process using alkali. Then it is filtered off, dried and micronised to obtain the powdered form.
Zinc oxide made from this process is known as "Active Zinc Oxide"
Metallic zinc is melted at 419.5 deg C in a graphite crucible and vaporized above 907 deg C. Zinc vapor instantaneously reacts with the oxygen in the air to become zinc oxide accompanied by a sudden drop in its temperature and also bright luminescence. Zinc oxide particles are transported into a cooling duct and collected in a bag house. This indirect method is commonly known as the French process (FP) which was popularised by LeClaire (France) in 1844. A typical FP zinc oxide normally consists of agglomerated zinc oxide particles with an average size of 0.1 micron to a few microns. By tonnage, most of the world's zinc oxide is manufactured via French process and major applications involve industries related to rubber, varistors, suncreens, 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 micron-length nanorods with nanometric diameters (below 100 nm).
More details on new developments here NanoZnO
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.
''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 gets ice cream on his nose and Larry the lifeguard thinks that it is Zinc Oxide and believes Spongebob has the "lifeguard look" and makes him a lifeguard.
In the series Gundam SEED and Gundam SEED Destiny, there is a mass-produced unit called the ZnO which is an underwater type mobile suit.
★ International Chemical Safety Card 0208.
★ NIOSH Pocket Guide to Chemical Hazards.
★ Nav Bharat Metallic Oxide Industries. (describes industrial uses of zinc oxide)
★ External MSDS (Material Safety Data Sheet) on zinc oxide.
1. Acc. Chem. Res. 1985, 18, pp. 228-234, ''Zinc Oxide: An Outstanding Example of a Binary Compound Semiconductor'',
Hirschwald, Wolfgang H.
2. "Oxygen Vacancies in ZnO", A. Janotti and C. G. Van de Walle, Appl. Phys. Lett. 87, 122102 (2005).
3. 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
4. [3]
★ ''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).
★ "Nanostructure of ZnO fabricated via French Process and its correlation to electrical properties of semiconducting varistors", S.Mahmud, M.J.Abdullah, J.Chong, A.K.Mohamad, M.Z.Zakaria, J. Syn. React. Inorg., Met-org. and Nano-metal Chem., 36, pp155-159 (2006).
| Zinc Oxide | |
|---|---|
 Zinc oxide  | |
| 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 | 3.249Ã…, 5.201Ã… |
| Thermodynamic data | |
| Standard enthalpy offormation Δf''H''°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 | , , . |
| S-phrases | , . |
| 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) | |
'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.[1] Exposure to zinc oxide in the air (also while welding) can result in a nervous malady called metal fume fever[2].
Zinc oxide occurs in nature as the mineral zincite.
Zincum Oxydatum is the latin name for Zinc Oxide commonly listed on homeopathic medicines.
| Contents |
| Applications |
| Pyroelectric coefficient |
| Production Methods |
| Indirect method |
| Direct method |
| Use in pop culture |
| External links |
| References |
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 absorbs 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). It is the broadest spectrum UVA and UVB absorber that is approved for use as a sunscreen by FDA, and is completely photostable. Additionally, since zinc oxide has antimicrobial and antifungal activities, it is the number one active ingredient recommended by pediatricians for the treatment of diaper rash.
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.
ZnO is a semiconductor with a direct bandgap energy of 3.37 eV at room temperature. The most common applications are in laser diodes and light emitting diodes since it has a exciton and biexciton energies of 60 meV and 15 meV, respectively. It is expected that this exciton properties of ZnO will be improved further by epitaxy.
''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 has been 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.
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
Production Methods
Zinc Oxide is produced by two main processes:-
1. French Process
In this process, metallic zinc (Zinc Dross) is heated to a vapour form, the metallic zinc vapour is allowed to auto oxidize to form Zinc Oxide.
Higher purity of Zinc Oxide (Up to 99.9%) can be obtained by this method.
2. American Process
In this process ore of zinc (Zinc Ash) is dissolved (as ZnCl2) then goes through a precipitation process using alkali. Then it is filtered off, dried and micronised to obtain the powdered form.
Zinc oxide made from this process is known as "Active Zinc Oxide"
Indirect method
Metallic zinc is melted at 419.5 deg C in a graphite crucible and vaporized above 907 deg C. Zinc vapor instantaneously reacts with the oxygen in the air to become zinc oxide accompanied by a sudden drop in its temperature and also bright luminescence. Zinc oxide particles are transported into a cooling duct and collected in a bag house. This indirect method is commonly known as the French process (FP) which was popularised by LeClaire (France) in 1844. A typical FP zinc oxide normally consists of agglomerated zinc oxide particles with an average size of 0.1 micron to a few microns. By tonnage, most of the world's zinc oxide is manufactured via French process and major applications involve industries related to rubber, varistors, suncreens, 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 micron-length nanorods with nanometric diameters (below 100 nm).
More details on new developments here NanoZnO
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.
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 gets ice cream on his nose and Larry the lifeguard thinks that it is Zinc Oxide and believes Spongebob has the "lifeguard look" and makes him a lifeguard.
In the series Gundam SEED and Gundam SEED Destiny, there is a mass-produced unit called the ZnO which is an underwater type mobile suit.
External links
★ International Chemical Safety Card 0208.
★ NIOSH Pocket Guide to Chemical Hazards.
★ Nav Bharat Metallic Oxide Industries. (describes industrial uses of zinc oxide)
★ External MSDS (Material Safety Data Sheet) on zinc oxide.
References
1. Acc. Chem. Res. 1985, 18, pp. 228-234, ''Zinc Oxide: An Outstanding Example of a Binary Compound Semiconductor'',
Hirschwald, Wolfgang H.
2. "Oxygen Vacancies in ZnO", A. Janotti and C. G. Van de Walle, Appl. Phys. Lett. 87, 122102 (2005).
3. 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
4. [3]
★ ''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).
★ "Nanostructure of ZnO fabricated via French Process and its correlation to electrical properties of semiconducting varistors", S.Mahmud, M.J.Abdullah, J.Chong, A.K.Mohamad, M.Z.Zakaria, J. Syn. React. Inorg., Met-org. and Nano-metal Chem., 36, pp155-159 (2006).
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