Tin dioxide

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Tin dioxide
SnO2powder.jpg
Rutile-unit-cell-3D-balls.png
Identifiers
CAS number 18282-10-5 YesY
13472-47-4 (hydrate)
PubChem 29011
EC number 242-159-0
RTECS number XQ4000000
Jmol-3D images Image 1
Properties
Molecular formula SnO2
Molar mass 150.709 g/mol
Appearance white powder
Density 6.95 g/cm3
Melting point 1,630 °C (2,970 °F; 1,900 K)
Boiling point 1,800 to 1,900 °C (3,270 to 3,450 °F; 2,070 to 2,170 K) sublimes
Solubility in water insoluble
Refractive index (nD) 2.006
Structure
Crystal structure Rutile (tetragonal), tP6
Space group P42/mnm, No. 136
Coordination
geometry
Octahedral (SnIV); trigonal planar (O2–)
Thermochemistry
Std molar
entropy
So298
52 J·mol−1·K−1[2]
Std enthalpy of
formation
ΔfHo298
−581 kJ·mol−1[2]
Hazards
MSDS ICSC 0954
EU Index Not listed
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g., chloroform Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
Flash point Non-flammable
Related compounds
Other anions Tin disulfide
Other cations Carbon dioxide
Silicon dioxide
Titanium dioxide
Germanium dioxide
Zirconium dioxide
Hafnium dioxide
Lead dioxide
Related tin oxides Tin(II) oxide
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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Infobox references

Tin dioxide, also known by the systematic name tin(IV) oxide and stannic oxide in the older notation, is the inorganic compound with the formula SnO2. The mineral form of SnO2 is called cassiterite, and this is the main ore of tin.[3] With many other names (see infobox), this oxide of tin is the most important raw material in tin chemistry. This colourless, diamagnetic solid is amphoteric.

Structure[edit]

It crystallises with the rutile structure, wherein the tin atoms are six coordinate and the oxygen atoms three coordinate.[3] SnO2 is usually regarded as an oxygen-deficient n-type semiconductor.[4] 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.[5]

Preparation[edit]

Tin dioxide occurs naturally but is purified by reduction to the metal followed by burning tin in air.[5] Annual production is in the range of 10 kilotons.[5] SnO2 is reduced industrially to the metal with carbon in a reverbatory furnace at 1200-1300 °C.[6]

Amphoterism[edit]

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.[7] "Stannic acid" refers to hydrated tin dioxide, SnO2, which is also called "stannic hydroxide."

Tin oxides dissolve in acids. Halogen acids attack SnO2 to give hexahalostannates,[8] such as [SnI6]2-. One report describes reacting a sample in refluxing HI for many hours.[9]

SnO2 + 6 HI → H2SnI6 + 2 H2O

Similarly, SnO2 dissolves in sulfuric acid to give the sulfate:[5]

SnO2 + 2 H2SO4 → Sn(SO4)2 + 2 H2O

SnO2 dissolves in strong base to give "stannates," with the nominal formula Na2SnO3.[5] Dissolving the solidified SnO2/NaOH melt in water gives Na2[Sn(OH)6]2, "preparing salt," which is used in the dye industry.[5]

Uses[edit]

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.[3]

Ceramic glazes[edit]

Tin dioxide has long been used as an opacifier and as a white colorant in ceramic glazes.[10] Its use has been particularly common in glazes for earthenware, sanitaryware and wall tiles; see the articles tin-glazing and Tin-glazed pottery. Tin oxide remains in suspension in vitreous matrix of the fired glazes, and, with its high refractive index being sufficiently different from the matrix, light is scattered, and hence increases the opacity of the glaze. The degree of dissolution increases with the firing temperature, and hence the extent of opacity diminishes.[11] Although dependent on the other constituents the solubility of tin oxide in glaze melts is generally low. Its solubility is increased by Na2O, K2O and B2O3, and reduced by CaO, BaO, ZnO, Al2O3, and to a limited extent PbO.[12]

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.[5]

Polishing[edit]

Tin dioxide can be used as a polishing powder,[5] sometimes in mixtures also with lead oxide, for polishing glass, jewelery, marble and silver.[1] Tin dioxide for this use is sometimes called as "putty powder"[7] or "jeweler's putty".[1]

Glass coatings[edit]

SnO2 coatings can be applied using chemical vapor deposition, vapour deposition techniques that employ SnCl4[3] or organotin trihalides[13] 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.[3]

Thicker layers doped with Sb or F ions are electrically conducting and used in electroluminescent devices.[3]

Gas sensing[edit]

SnO2 wires are commonly used as the detecting element in carbon monoxide detectors.

SnO2 is used in sensors of combustible gases. In these the sensor area is heated to a constant temperature (few hundred °C) and in the presence of a combustible gas the electrical resistivity drops.[14] Doping with various compounds has been investigated (e.g. with CuO [15]). Doping with cobalt and manganese, gives a material that can be used in e.g. high voltage varistors.[16] Tin dioxide can be doped into the oxides of iron or manganese.[17]

References[edit]

  1. ^ a b c "Material Name: stannic oxide". Museum of Fine Arts, Boston. 2007-02-10. Retrieved 2013-03-29. 
  2. ^ a b Zumdahl, Steven S. (2009). Chemical Principles 6th Ed. Houghton Mifflin Company. p. A23. ISBN 0-618-94690-X. 
  3. ^ a b c d e f Greenwood, Norman N.; Earnshaw, Alan (1984). Chemistry of the Elements. Oxford: Pergamon Press. pp. 447–48. ISBN 0-08-022057-6. 
  4. ^ Solid State Chemistry: An Introduction Lesley Smart, Elaine A. Moore (2005) CRC Press ISBN 0-7487-7516-1
  5. ^ a b c d e f g h Holleman, A. F.; Wiberg, E. (2001), Inorganic Chemistry, San Diego: Academic Press, ISBN 0-12-352651-5 
  6. ^ Tin: Inorganic chemistry,J L Wardell, Encyclopedia of Inorganic Chemistry ed R. Bruce King, John Wiley & Son Ltd., (1995) ISBN 0-471-93620-0
  7. ^ a b Inorganic & Theoretical chemistry, F. Sherwood Taylor, Heineman, 6th Edition (1942)
  8. ^ Donaldson & Grimes in Chemistry of tin ed. P.G. Harrison Blackie (1989)
  9. ^ Earle R. Caley (1932). "The Action Of Hydriodic Acid On Stannic Oxide". J. Am. Chem. Soc. 54 (8): 3240–3243. doi:10.1021/ja01347a028. 
  10. ^ ’The Glazer’s Book’ – 2nd edition. A.B.Searle.The Technical Press Limited. London. 1935.
  11. ^ ’A Treatise On Ceramic Industries.’ E.Bourry. Fourth edition. Scott, Greenwood & son. London. 1926.
  12. ^ ’Ceramic Glazes’ Third edition. C.W.Parmelee & C.G.Harman. Cahners Books, Boston, Massachusetts. 1973.
  13. ^ US 4130673 
  14. ^ 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 0-8493-7346-8
  15. ^ 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:10.1111/j.1551-2916.2006.01076.x. [1]
  16. ^ 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:10.1590/S1516-14392006000300015. 
  17. ^ 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:10.1103/PhysRevB.72.054402. 

Further reading[edit]