Boron trioxide

From Wikipedia, the free encyclopedia
  (Redirected from Boron(III) oxide)
Jump to: navigation, search
Boron trioxide
B2O3powder.JPG
Kristallstruktur Bortrioxid.png
Identifiers
CAS number 1303-86-2 YesY
PubChem 518682
ChemSpider 452485 YesY
ChEBI CHEBI:30163 YesY
RTECS number ED7900000
Jmol-3D images Image 1
Properties
Molecular formula B2O3
Molar mass 69.6182 g/mol
Appearance white, glassy solid
Density 2.460 g/cm3, liquid;

2.55 g/cm3, trigonal;
3.11–3.146 g/cm3, monoclinic

Melting point 450 °C (trigonal)
510 °C (tetrahedral)
Boiling point 1860 °C,[1] sublimates at 1500 °C[2]
Solubility in water 1.1 g/100mL (10 °C)
3.3 g/100mL (20 °C)
15.7 100 g/100mL (100 °C)
Solubility partially soluble in methanol
Acidity (pKa) ~ 4
Thermochemistry
Specific
heat capacity
C
66.9 J/mol K
Std molar
entropy
So298
80.8 J/mol K
Std enthalpy of
formation
ΔfHo298
-1254 kJ/mol
Gibbs free energy ΔG -832 kJ/mol
Hazards
MSDS External MSDS
EU classification Repr. Cat. 2
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 1: Normally stable, but can become unstable at elevated temperatures and pressures. E.g., calcium Special hazards (white): no codeNFPA 704 four-colored diamond
LD50 3163 mg/kg (oral, rat)
Supplementary data page
Structure and
properties
n, εr, etc.
Thermodynamic
data
Phase behaviour
Solid, liquid, gas
Spectral data UV, IR, NMR, MS
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 YesY (verify) (what is: YesY/N?)
Infobox references

Boron trioxide (or diboron trioxide) is one of the oxides of boron. It is a white, glassy solid with the formula B2O3. It is almost always found as the vitreous (amorphous) form; however, it can be crystallized after extensive annealing (that is, under prolonged heat). It is known as one of the most difficult compounds to crystallize.[clarification needed]

Glassy boron oxide (g-B2O3) is thought to be composed of boroxol rings which are six-membered rings composed of alternating 3-coordinate boron and 2-coordinate oxygen. This view is controversial, however, because no model has ever been made of glassy boron oxide of the correct density containing a large number of six-membered rings. The rings are thought to make a few BO3 triangles, but mostly link (polymerize) into ribbons and sheets.[3][4] The crystalline form (α-B2O3) (see structure in the infobox[5]) is exclusively composed of BO3 triangles. This trigonal, quartz-like network undergoes a coesite-like transformation to monoclinic β-B2O3 at several gigapascals (9.5 GPa).[6]

Preparation[edit]

Boron trioxide is produced by treating borax with sulfuric acid in a fusion furnace. At temperatures above 750 °C, the molten boron oxide layer separates out from sodium sulfate. It is then decanted, cooled and obtained in 96–97% purity.[2]

Another method is heating boric acid above ~300 °C. Boric acid will initially decompose into water steam and metaboric acid (HBO2) at around 170 °C, and further heating above 300 °C will produce more steam and boron trioxide. The reactions are:

H3BO3 → HBO2 + H2O
2 HBO2 → B2O3 + H2O

Boric acid goes to anhydrous microcrystalline B2O3 in a heated fluidized bed.[7] Carefully controlled heating rate avoids gumming as water evolves. Molten boron oxide attacks silicates. Internally graphitized tubes via acetylene thermal decomposition are passivated.[8]

Crystallization of molten α-B2O3 at ambient pressure is strongly kinetically disfavored (compare liquid and crystal densities). Threshold conditions for crystallization of the amorphous solid are 10 kbar and ~200 °C.[9] Its proposed crystal structure in enantiomorphic space groups P31(#144); P32(#145)[10][11] (e.g., γ-glycine) has been revised to enantiomorphic space groups P3121(#152); P3221(#154)[12](e.g., α-quartz).

Boron oxide will also form when Diborane (B2H6) reacts with oxygen in the air or trace amounts of moisture:

2B2H6(g) + 3O2(g) → 2B2O3(s) + 6H2(g)
B2H6(g) + 3H2O(v) → B2O3(s) + 6H2(g)[13]

Applications[edit]

See also[edit]

References[edit]

  1. ^ High temperature corrosion and materials chemistry: proceedings of the Per Kofstad Memorial Symposium. Proceedings of the Electrochemical Society. The Electrochemical Society. 2000. p. 496. ISBN 1-56677-261-3. 
  2. ^ a b Patnaik, P. (2003). Handbook of Inorganic Chemical Compounds. McGraw-Hill. p. 119. ISBN 0-07-049439-8. Retrieved 2009-06-06. 
  3. ^ Eckert, H. (1992). "Structural characterization of noncrystalline solids and glasses using solid state NMR". Progress in Nuclear Magnetic Resonance Spectroscopy 24 (3): 159–293. doi:10.1016/0079-6565(92)80001-V. 
  4. ^ Hwang, S.-J.; Fernandez, C.; Amoureux, J. P.; Cho, J.; Martin, S. W.; Pruski, M. (1997). "Quantitative study of the short range order in B2O3 and B2S3 by MAS and two-dimensional triple-quantum MAS 11B NMR". Solid State Nuclear Magnetic Resonance 8 (2): 109–121. doi:10.1016/S0926-2040(96)01280-5. PMID 9203284. 
  5. ^ Gurr, G. E.; Montgomery, P. W.; Knutson, C. D.; Gorres, B. T. (1970). "The Crystal Structure of Trigonal Diboron Trioxide". Acta Crystallographica B 26 (7): 906–915. doi:10.1107/S0567740870003369. 
  6. ^ Brazhkin, V. V.; Katayama, Y.; Inamura, Y.; Kondrin, M. V.; Lyapin, A. G.; Popova, S. V.; Voloshin, R. N. (2003). "Structural transformations in liquid, crystalline and glassy B2O3 under high pressure". JETP Letters 78 (6): 393–397. doi:10.1134/1.1630134. 
  7. ^ Kocakuşak, S.; Akçay, K.; Ayok, T.; Koöroğlu, H. J.; Koral, M.; Savaşçi, Ö. T.; Tolun, R. (1996). "Production of anhydrous, crystalline boron oxide in fluidized bed reactor". Chemical Engineering and Processing 35 (4): 311–317. doi:10.1016/0255-2701(95)04142-7. 
  8. ^ Morelock, C. R. (1961). Research Laboratory Report #61-RL-2672M. General Electric. 
  9. ^ Aziz, M. J.; Nygren, E.; Hays, J. F.; Turnbull, D. (1985). "Crystal Growth Kinetics of Boron Oxide Under Pressure". Journal of Applied Physics 57 (6): 2233. doi:10.1063/1.334368. 
  10. ^ Gurr, G. E.; Montgomery, P. W.; Knutson, C. D.; Gorres, B. T. (1970). "The crystal structure of trigonal diboron trioxide". Acta Crystallographica B 26 (7): 906–915. doi:10.1107/S0567740870003369. 
  11. ^ Strong, S. L.; Wells, A. F.; Kaplow, R. (1971). "On the crystal structure of B2O3". Acta Crystallographica B 27 (8): 1662–1663. doi:10.1107/S0567740871004515. 
  12. ^ Effenberger, H.; Lengauer, C. L.; Parthé, E. (2001). "Trigonal B2O3 with Higher Space-Group Symmetry: Results of a Reevaluation". Monatshefte für Chemie 132 (12): 1515–1517. doi:10.1007/s007060170008. 
  13. ^ AirProducts (2011). Diborane Storage & Delivery. 

External links[edit]