Scandium fluoride

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Scandium fluoride
ScF3structure.jpg
Identifiers
CAS number 13709-47-2 N
PubChem 83678
EC number 237-555-4
RTECS number VQ8930000
Jmol-3D images Image 1
Properties
Molecular formula ScF3
Molar mass 101.95112 g/mol
Appearance bright white powder
Density 2.53 g/cm3
Melting point 1552 °C[1]
Boiling point 1607 °C[1]
Structure
Crystal structure Rhombohedral, R32
Space group hR12, No. 155
Hazards
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
Related compounds
Related compounds Scandium(III) chloride
Scandium(III) nitrate
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

Scandium(III) fluoride, ScF3, is an ionic compound. It is slightly soluble in water but dissolves in the presence of excess fluoride to form ScF63−.[1] ScF3 can be produced by reacting scandium and fluorine.[2] It is also formed during the extraction from the ore thortveitite by the reaction of Sc2O3 with ammonium bifluoride at high temperature:[3]

Sc2O3 + NH4HF2 → 2 ScF3 + 6 NH4F + 3 H2O

The resulting mixture contains a number of metal fluorides and this is reduced by reaction with calcium metal at high temperature.[3] Further purification steps are required to produce usable metallic scandium.[3]

Scandium trifluoride exhibits the unusual property of negative thermal expansion, meaning it shrinks when heated. This phenomenon is explained by the quartic oscillation of the fluoride ions. The energy stored in the bending strain of the fluoride ion is proportional to the fourth power of the displacement angle, unlike most other materials where it is proportional to the square of the displacement. A fluorine atom is bound to two scandium atoms, and as temperature increases the fluorine oscillates more perpendicularly to its bonds. This motion draws the scandium atoms together throughout the bulk material, which contracts.[4] ScF3 exhibits this property from at least 10 K to 1100 K above which it shows the normal positive thermal expansion; furthermore, the material has cubic symmetry over this entire temperature range, and up to at least 1600 K at ambient pressure. The negative thermal expansion at very low temperatures is quite strong (coefficient of thermal expansion around -14 ppm/K between 60 and 110 K).[5]

References[edit]

  1. ^ a b c Egon Wiberg, Arnold Frederick Holleman (2001) Inorganic Chemistry, Elsevier, ISBN 0-12-352651-5.
  2. ^ S.A.Cotton, Scandium, Yttrium and the Lanthanides: Inorganic and Coordination Chemistry, Encyclopedia of Inorganic Chemistry, 1994, John Wiley & Sons, ISBN 0-471-93620-0.
  3. ^ a b c Pradyot Patnaik, 2003, Handbook of Inorganic Chemicals, McGraw-Hill Professional, ISBN 0-07-049439-8.
  4. ^ Woo, Marcus (7 November 2011). "An incredible shrinking material: Engineers reveal how scandium trifluoride contracts with heat". Physorg. Retrieved 8 November 2011. 
  5. ^ Greve, Benjamin K.; Kenneth L. Martin; Peter L. Lee; Peter J. Chupas; Karena W. Chapman; Angus P. Wilkinson (19 October 2010). "Pronounced Negative Thermal Expansion from a Simple Structure: Cubic ScF3". Journal of the American Chemical Society 132 (44): 15496–15498. doi:10.1021/ja106711v. PMID 20958035.