Boron trioxide


Boron trioxide
Boron trioxide
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 22 g/L
Solubility partially soluble in methanol
Acidity (pKa) ~ 4
Hazards
MSDS External MSDS
EU classification Repr. Cat. 2
NFPA 704
NFPA 704.svg
0
1
0
LD50 3150 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
 YesY trioxide (verify) (what is: YesY/N?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
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 (amorphic) form; however, it can be crystallized after extensive annealing. It is one of the most difficult compounds known to crystallize.

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 and is 9.5 GPa.[6]

Contents

Preparation

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).

Hardness

The bulk modulus of β-B2O3 is rather high (K = 180 GPa). The Vickers hardness of g-B2O3 is 1.5 GPa and of β-B2O3 is 16 GPa.[13]

Applications

See also

References

  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 1566772613. http://books.google.com/?id=ZrxSWmueNMQC&pg=PA496. 
  2. ^ a b Patnaik, Pradyot (2003). Handbook of Inorganic Chemical Compounds. McGraw-Hill. p. 119. ISBN 0070494398. http://books.google.com/?id=Xqj-TTzkvTEC&pg=PA119. Retrieved 2009-06-06. 
  3. ^ Eckert, H. (1992). "Structural characterization of noncrystalline solids and glasses using solid state NMR". Prog. NMR Spectrosc. 24 (3): 159. doi:10.1016/0079-6565(92)80001-V. 
  4. ^ S.-J. Hwang, C. Femandez, J.P. Amoureux, J. Cho, S.W. Martin & M. Pruski. (1997). "Quantitative study of the short range order in B,O, and B,S, 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. ^ G.E. Gurr, P.W. Montgomery, C.D. Knutson, B.T.Gorres (1970). "The Crystal Structure of Trigonal Diboron Trioxide". Acta Cryst. B 26 (7): 906–915. doi:10.1107/S0567740870003369. 
  6. ^ V. V. Brazhkin et al. (2003). "Structural transformations in liquid, crystalline and glassy B2O3 under high pressure". JETPh Lett. 78 (6): 845. doi:10.1134/1.1630134. http://www.jetpletters.ac.ru/ps/47/article_679.shtml. 
  7. ^ Kocakusak, S; Akcay, K; Ayok, T; Kooroglu, H; Koral, M; Savasci, O; 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. ^ C.R. Morelock, General Electric Research Laboratory Report #61-RL-2672M(1961)
  9. ^ "Crystal Growth Kinetics of Boron Oxide Under Pressure". J. Appl. Phys. 57 (6): 2233. 1985. doi:10.1063/1.334368. http://dash.harvard.edu/handle/1/3645198. 
  10. ^ Gurr, G. E.; Montgomery, P. W.; Knutson, C. D.; Gorres, B. T. (1970). "The crystal structure of trigonal diboron trioxide". Acta Crystallographica Section B Structural Crystallography and Crystal Chemistry 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 Section B Structural Crystallography and Crystal Chemistry 27 (8): 1662–1663. doi:10.1107/S0567740871004515. 
  12. ^ Effenberger, Herta; Lengauer, Christian L.; Parthé, Erwin (2001). "Trigonal B2O3 with Higher Space-Group Symmetry: Results of a Reevaluation". Monatshefte für Chemie/Chemical Monthly 132 (12): 1515–1517. doi:10.1007/s007060170008. 
  13. ^ V. A. Mukhanov, O. O. Kurakevich, and V. L. Solozhenko (2008). "On the Hardness of Boron (III) Oxide". Journal of Superhard Materials 30: 71. doi:10.3103/S1063457608010097. 

External links


Wikimedia Foundation. 2010.

Look at other dictionaries:

  • boron trioxide — noun A white solid, of empirical formula BO, that is an inorganic polymer, and is used in making glass and enamel and for synthesizing other boron compounds. Syn: boric oxide …   Wiktionary

  • boron trioxide — /ˌbɔrɒn traɪˈɒksaɪd/ (say .bawron truy oksuyd) noun a colourless crystalline solid, B2O3, which forms boric acid on hydration. Also, boron oxide …   Australian English dictionary

  • Boron trioxide (data page) — This page provides supplementary chemical data on boron trioxide. Material Safety Data Sheet The handling of this chemical may incur notable safety precautions. It is highly recommend that you seek the Material Safety Datasheet (MSDS) for this… …   Wikipedia

  • Boron nitride — IUPAC name Boron nitride Identifiers …   Wikipedia

  • Boron tribromide — Chembox new Name = Boron tribromide ImageFile = Boron tribromide 3D vdW.png ImageSize = 200px ImageName = Boron tribromide IUPACName = Boron tribromide Section1 = Chembox Identifiers CASNo = 10294 33 4 Section2 = Chembox Properties Formula = BBr3 …   Wikipedia

  • boron oxide — noun The compound boron trioxide …   Wiktionary

  • boron trifluoride — /ˌbɔrɒn traɪˈfluraɪd/ (say .bawron truy floohruyd) noun a pungent colourless gas, BF3, which fumes in moist air, formed by the action of fluorine on boron trioxide …   Australian English dictionary

  • Boric acid — Boric acid …   Wikipedia

  • Water-fuelled car — A water fuelled car is an automobile that is claimed to use water as its fuel or produces fuel from water onboard, with no other energy input. Water fuelled cars have been mentioned in newspapers, popular science magazines, local news coverage,… …   Wikipedia

  • boric oxide — noun A white solid, of empirical formula BO; it is an inorganic polymer used in making glass and enamel and for synthesizing other boron compounds. Syn: boron trioxide …   Wiktionary