Boron trioxide

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Boron trioxide
B2O3.JPG
Names
IUPAC name
Boron trioxide
Other names
Boria
Boric anhydride
Boric oxide
Boron sesquioxide
Diboron trioxide
Properties
B2O3
Molar mass 69.6182 g/mol
Appearance Hard glassy solid or white powder.
Odor Odorless
Density 2.460 g/cm3 (liquid)
2.55 g/cm3 (trigonal)
3.11–3.146 g/cm3 (monoclinic)
Melting point 450–510 °C (842–950 °F; 723–783 K) (trigonal)
510 °C (950 °F; 783 K) (tetrahedral)
Boiling point 1,860 °C (3,380 °F; 2,130 K)
1.1 g/100 ml (10 °C)
2.77 g/100 ml (20 °C)
3.6 g/100 ml (25 °C)
15.7 100 g/100 ml (100 °C)
Solubility Soluble in ethanol, glycerol, methanol
Vapor pressure ~0 mmHg
Acidity (pKa) ~ 4
Thermochemistry
80.8 J·mol-1·K-1
-1254 kJ/mol
Hazards
Safety data sheet Sigma-Aldrich
Flash point Non-flammable
Lethal dose or concentration (LD, LC):
3,163 mg/kg (mouse, oral)
Related compounds
Related compounds
Boric acid
Borax
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Boron trioxide is a glass like solid or white powder with the chemical formula B2O3.

Properties

Chemical

Boron trioxide is very unreactive towards most common reagents. While an anhydride oxide, it does not react with water visibly.

It can however be reduced to elemental boron with magnesium powder in a thermite reaction. Magnesium boride is produces as side product. A similar effect occurs when powdered aluminium is used, though aluminium not not give a good yield.

Physical

When produced from boric acid, it forms as a non crystaline mass that is very hard and difficuilt to grind, forming a very fine powder when ground very similar to a solid plane of glass.

Availability

It is used in glassmaking, whether as a boron additive for making borosilicate glass or as a fluxing agent so this may be a source, however it is easy to produce from the starting materials boric acid or borax.

Preparation

Boric acid can be dehydrated above 300 degrees to form boron trioxide. Boron trioxide prepared at up to 800 degrees is a desiccant but it is slow acting if not finely powdered. Made at higher temperature it has an induction period.

Projects

  • Producing boron
  • Making the ester trimethyl borate
  • Fluxing agent for glass and enamels
  • Acid catalyst in organic synthesis

Handling

Safety

Boron trioxide has low toxicity, though it is irritant to skin, mouth, nose and eyes.

Storage

No special storage is required, storing it in closed bottles is fairly enough.

Disposal

Can be dumped in trash.

References

Relevant Sciencemadness threads