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| Tin dioxide | |
|---|---|
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| IUPAC name | Tin(IV) oxide |
| Other names | stannic oxide, tin(IV) oxide, stannic oxide, stannic anhydride, flowers of tin |
| Identifiers | |
| CAS number | 18282-10-5 |
| EINECS number | |
| Properties | |
| Molecular formula | SnO2 |
| Molar mass | 150.708 g/mol |
| Appearance | white powder |
| Melting point |
1127 °C |
| Structure | |
| Crystal structure | tetragonal, tP6 |
| Space group | P42/mnm, #136 |
| Coordination geometry |
Sn, 6, octahedral O,3, trigonal planar |
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox references |
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Tin dioxide is the inorganic compound with the formula SnO2. The mineral form of SnO2 is called cassiterite, and this is the main ore of tin.1 With many other names (see Table), this oxide of tin is the most important raw material in tin chemistry. This colourless, diamagnetic solid is amphoteric.
Contents |
Structure
It crystallises with the rutile structure, wherein the tin atoms are 6 coordinate and the oxygen atoms three coordinate.1 SnO2 is usually regarded as an oxygen-deficient n-type semiconductor.2. Hydrous forms of SnO2 have been described in the past as stannic acids, although such materials appear to be hydrated particles of SnO2 where the composition reflects the particle size.3
Preparation
Tin dioxide occurs naturally but is purified by reduction to the metal followed by burning tin in air.3 Annual production is in the range of 10 kilotons.3 SnO2 is reduced industrially to the metal with carbon in a reverbatory furnace at 1200-1300 °C.4
Amphoterism
Although SnO2 is insoluble in water, it is an amphoteric oxide, although cassiterite ore has been described as difficult to dissolve in acids and alkalis.5 "Stannic acid" (CAS RN 13472-47-4) refers to hydrated tin dioxide, SnO2, which is also called "stannic hydroxide."
Tin oxides dissolve in acids. Halogen acids attack SnO2 to give hexahalostannates,6 e.g. [SnI62−. One report describes reacting a sample in refluxing HI for many hours.7
![\mathrm{SnO_2 \ + \ 6 \ HI \ \longrightarrow \ \ H_2[SnI]_6 \ + \ 2 \ H_2O}](http://upload.wikimedia.org/math/c/c/a/cca912d87650d52c6a03ba3a34327521.png)
Similarly, SnO2 dissolves in sulfuric acid to give the sulfate:3
SnO2 dissolves in strong base to give "stannates," with the nominal formula Na2SnO3.3 Dissolving the solidified SnO2/NaOH melt in water gives Na2[Sn(OH)62, "preparing salt," which is used in the dyeing industry.3
Uses
In conjunction with vanadium oxide, it is used as a catalyst for the oxidation of aromatic compounds in the synthesis of carboxylic acids and acid anhydrides.1
Throughout history it has been used as an opacifier in the ceramic industry (where it is just known as tin oxide), especially in earthenware. Tin oxide does not go into solution in the glaze melt, generally amounts of 4-8% are needed. Zircon compounds are also used for this purpose.
SnO2 coatings can be applied using CVD, vapour deposition techniques that employ SnCl41 or organotin trihalides8 e.g. butyltin trichloride as the volatile agent. This technique is used to coat glass bottles with a thin (<0.1 μm) layer of SnO2, which helps to adhere a subsequent, protective polymer coating such as polyethylene to the glass.1 Thicker layers doped with Sb or F ions are electrically conducting and used in electroluminescent devices.1 SnO2 has been used as pigment in the manufacture of glasses, enamels and ceramic glazes. Pure SnO2 gives a milky white colour; other colours are achieved when mixed with other metallic oxides e.g. V2O5 yellow; Cr2O3 pink; and Sb2O5 grey blue.3 SnO2 has been used as a polishing powder3 and is sometimes known as "putty powder", 5 SnO2 is used in sensors of combustible gases. In these the sensor area is heated to a constant temperature (low 100s °C) and in the presence of a combustible gas the electrical resistivity drops.9 Doping with various compounds has been investigated (e.g. with CuO 10). Doping with Cobalt + Manganese, gives a material that can be used in e.g. high voltage varistors.11 Tin dioxide can be doped into the oxides of iron or manganese.12
References
- ^ a b c d e f Greenwood, Norman N.; Earnshaw, A. (1997). Chemistry of the Elements, 2nd Edition, Oxford: Butterworth-Heinemann. ISBN 0-7506-3365-4.
- ^ Solid State Chemistry: An Introduction Lesley Smart, Elaine A. Moore (2005) CRC Press ISBN 0748775161
- ^ a b c d e f g h Inorganic Chemistry, Egon Wiberg, Arnold Frederick Holleman Elsevier 2001 ISBN 0123526515
- ^ Tin: Inorganic chemistry,J L Wardell, Encyclopedia of Inorganic Chemistry ed R. Bruce King, John wiley & Son Ltd., (1995) ISBN 0471936200
- ^ a b Inorganic & Theoretical chemistry, F. Sherwood Taylor Heineman, 6th Edition (1942)
- ^ Donaldson & Grimes in Chemistry of tin ed. P.G. Harrison Blackie (1989)
- ^ Earle R. Caley (1932). "The Action Of Hydriodic Acid On Stannic Oxide". J. Am. Chem. Soc. 54 (8): 3240–3243. doi:.
- ^ US patent 4130673
- ^ Joseph Watson The stannic oxide semiconductor gas sensor in The Electrical engineering Handbook 3d Edition; Sensors Nanoscience Biomedical Engineering and Instruments ed R.C Dorf CRC Press Taylor and Francis ISBN 084937 34 68
- ^ Wang, Chun-Ming; Wang, Jin-Feng; Su, Wen-Bin (2006). "Microstructural Morphology and Electrical Properties of Copper- and Niobium-Doped Tin Dioxide Polycrystalline Varistors". Journal of the American Ceramic Society 89 (8): 2502–2508. doi:.[1]
- ^ Dibb A., Cilense M, Bueno P.R, Maniette Y., Varela J.A., Longo E. (2006). "Evaluation of Rare Earth Oxides doping SnO2.(Co0.25,Mn0.75)O-based Varistor System". Materials Research 9 (3): 339–343. doi:.
- ^ A. Punnoose, J. Hays, A. Thurber, M. H. Engelhard, R. K. Kukkadapu, C. Wang, V. Shutthanandan, and S. Thevuthasan (2005). "Development of high-temperature ferromagnetism in SnO2 and paramagnetism in SnO by Fe doping". Phys. Rev. B 72 (8): 054402. doi:.
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