Boron trioxide

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.

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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).