Boron trioxide

Boron trioxide
Other names	Boron oxide, diboron trioxide, boron sesquioxide, boric oxide, boria, anhydric boric acid
Identifiers
CAS number	1303-86-2
Properties
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 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, 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).

Applications

• 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

• boron suboxide
• boric acid
• sassolite

References

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).

External links

• National Pollutant Inventory: Boron and compounds
• Australian Government information
• [1] US NIH hazard information

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