Tin dioxide

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IUPACName = Tin(IV) oxide
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OtherNames = stannic oxide, tin(IV) oxide, stannic oxide, stannic anhydride, flowers of tin
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CASNo = 18282-10-5
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Formula = SnO₂
MolarMass = 150.708 g/mol
Appearance = white powder
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CrystalStruct = tetragonal, tP6
SpaceGroup = P4₂/mnm, #136
Coordination = Sn, 6, octahedral
O,3, trigonal planar
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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. 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.

tructure

It crystallises with the rutile structure, wherein the tin atoms are 6 coordinate and the oxygen atoms three coordinate. SnO₂ is usually regarded as an oxygen-deficient n-type semiconductor. [Solid State Chemistry: An Introduction Lesley Smart, Elaine A. Moore (2005) CRC Press ISBN 0748775161 ] . 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."Inorganic Chemistry", Egon Wiberg, Arnold Frederick Holleman Elsevier 2001 ISBN 0123526515]

Preparation

Tin dioxide occurs naturally but is purified by reduction to the metal followed by by burning tin in air. Annual production is in the range of 10 kilotons. SnO₂ is reduced industrially to the metal with carbon in a reverbatory furnace at 1200-1300 °C. ["Tin: Inorganic chemistry",J L Wardell, Encyclopedia of Inorganic Chemistry ed R. Bruce King, John wiley & Son Ltd., (1995) ISBN 0471936200]

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. "Inorganic & Theoretical chemistry", F. Sherwood Taylor Heineman, 6th Edition (1942)] "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, [Donaldson & Grimes in Chemistry of tin ed. P.G. Harrison Blackie (1989)] e.g. [SnI₆] ²⁻. One report describes reacting a sample in refluxing HI for many hours. [cite journal
title = The Action Of Hydriodic Acid On Stannic Oxide
author = Earle R. Caley
journal = J. Am. Chem. Soc.
year = 1932
volume =54
issue = 8
pages = 3240–3243
doi = 10.1021/ja01347a028] :$mathrm\{SnO\_2\; +\; 6\; HI\; longrightarrow\; H\_2\; [SnI]\; \_6\; +\; 2\; H\_2O\}$Similarly, SnO₂ dissolves in sulfuric acid to give the sulfate::$mathrm\{SnO\_2\; +\; 2\; H\_2SO\_4\; longrightarrow\; Sn(SO\_4)\_2\; +\; 2\; H\_2O\}$

SnO₂ dissolves in strong base to give "stannates," with the nominal formula Na₂SnO₃. Dissolving the solidified SnO₂/NaOH melt in water gives Na₂ [Sn(OH)₆] ₂, "preparing salt," which is used in the dyeing industry.

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.

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 SnCl₄ Greenwood&Earnshaw] or organotin trihalides [Cite patent
US|4130673] 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. Thicker layers doped with Sb or F ions are electrically conducting and used in electroluminescent devices.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.SnO₂ has been used as a polishing powder and is sometimes known as "putty powder", 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. [ 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]
Doping with various compounds has been investigated (e.g. with CuO [cite journal
title = Microstructural Morphology and Electrical Properties of Copper- and Niobium-Doped Tin Dioxide Polycrystalline Varistors
author = Wang, Chun-Ming; Wang, Jin-Feng; Su, Wen-Bin
journal = Journal of the American Ceramic Society
year = 2006
volume =89
issue = 8
pages = 2502–2508
doi = 10.1111/j.1551-2916.2006.01076.x [http://www.scielo.br/pdf/mr/v9n3/31795.pdf] ] ). Doping with Cobalt + Manganese, gives a material that can be used in e.g. high voltage varistors. [cite journal
title = Evaluation of Rare Earth Oxides doping SnO₂.(Co_0.25,Mn_0.75)O-based Varistor System
author = Dibb A., Cilense M, Bueno P.R, Maniette Y., Varela J.A., Longo E.
journal = Materials Research
year = 2006
volume =9
issue = 3
pages = 339–343
doi =10.1590/S1516-14392006000300015 ] Tin dioxide can be doped into the oxides of iron or manganese. [cite journal
title = Development of high-temperature ferromagnetism in SnO2 and paramagnetism in SnO by Fe doping
author = A. Punnoose, J. Hays, A. Thurber, M. H. Engelhard, R. K. Kukkadapu, C. Wang, V. Shutthanandan, and S. Thevuthasan
journal = Phys. Rev. B
year = 2005
volume = 72
issue = 8
pages = 054402
doi = 10.1103/PhysRevB.72.054402]

References

[http://ceramic-materials.com/cermat/material/1642.html CeramicMaterials.Info]