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Boron trioxide

Boron trioxide
Other names Boron oxide, diboron trioxide, boron sesquioxide, boric oxide, boria, anhydric boric acid
CAS number 1303-86-2
Molecular formula B2O3
Molar mass 69.6182 g/mol
Appearance Colorless, glassy solid.
Density 1.85 g/cm3, glass;

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

Melting point

480 °C

Boiling point

1680 °C

Solubility in water 2.2 g/100 g
Related Compounds
Related compounds B2O2.5;
B2O3·H2O (metaborite)
Supplementary data page
Structure and
n, εr, etc.
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, 100 kPa)

Infobox disclaimer and references

Boron oxide is one of the oxides of boron. It is white, glassy, and solid, also known as diboron trioxide, formula B2O3. It is almost always found as the vitreose (amorphic) form; however, it can be crystallized after extensive annealing. It is one of the most difficult compounds known to crystallize.

Glassy boron oxide (α-B2O3) is thought to be composed of boroxol rings which are six-membered rings composed of alternating 3-coordinate boron and 2-coordinate oxygen. The rings make a few BO3 triangles, but mostly link (polymerize) into ribbons and sheets. (1,2) The crystalline form (B2O3) is exclusively composed of BO3 triangles and is almost half as hard as quartz, 4 GPa Vickers. This trigonal, quartz-like network undergoes a monoclinic, coesite-like transformation of BO4 tetrahedra at several gigapascals and is 9.5 GPa (3).


  • Fluxing agent for glass and enamels
  • Starting material for synthesizing other boron compounds such as boron carbide
  • An additive used in glass fibres (optical fibres)
  • It is used in the production of borosilicate glass

See also


  1. Eckert, H. Prog. NMR Spectrosc., 24 (1992) 159-293.
  2. "Quantitative study of the short range order in B,O, and B,S, by MAS and two-dimensional triple-quantum MAS 11B NMR". S.-J. Hwang, C. Femandez, J.P. Amoureux, J. Cho, S.W. Martin & M. Pruski. Solid State Nuclear Magnetic Resonance 8 (1997) 109-121.
  3. "Structural transformations in liquid, crystalline and glassy B2O3 under high pressure". Institute for High Pressure Physics RAS and Japan Atomic Energy Research Institute. (2003).
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Boron_trioxide". A list of authors is available in Wikipedia.
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