Antimony Trioxide
Properties
| State | Solid |
| Color | White to pale cream |
| Solubility | Insoluble in water; slightly soluble in acids and alkali (amphoteric) |
| Melting Point | 656 °C |
| Boiling Point | 1425 °C |
About Antimony Trioxide
Antimony trioxide is the most important commercial antimony compound by volume, and almost all of the roughly 150,000 tonnes produced each year ends up as a flame-retardant synergist combined with brominated organics in plastics, textiles, and electronics housings. The synergy chemistry is unusual enough to be worth describing in detail. Sb2O3 alone is not a flame retardant — sprinkle it on burning wood and nothing happens. But combine it with a brominated organic compound (decabromodiphenyl ethane, tetrabromobisphenol A, etc.) in a plastic, and the combination becomes one of the most efficient flame-retardant systems known. Under combustion conditions, the brominated organic decomposes and releases HBr; Sb2O3 reacts with HBr to form volatile SbBr3 and SbOBr; those antimony-bromine species rise into the gas-phase flame zone, where they catalytically scavenge the H• and OH• radicals that propagate combustion's branching chain reaction. Cutting the radical concentration extinguishes the flame from above, while the condensed phase below char-forms and stops feeding fuel. The structure of Sb2O3 itself is interesting: the cubic polymorph (senarmontite) consists of discrete Sb4O6 cage molecules with the same connectivity as As4O6, P4O6, and the white phosphorus core — molecular oxides assembled into ionic-looking lattices. The other commercial uses are smaller in volume but real: PET bottle and fiber polycondensation catalyst (about 90% of global PET uses Sb catalysts), opacifier in ceramic glazes and fiberglass, and decolorizing agent in optical glass.
Where you'll encounter it
If you've handled a TV cabinet, computer monitor housing, child car seat, or upholstered office chair, the Sb/Br flame-retardant system is probably what kept the case from being acutely flammable. Standards like UL-94 V-0 (vertical burn rating used for electronics enclosures) are routinely met by adding 5–15% brominated retardant plus 2–5% Sb2O3 to the resin during compounding. The PET-bottle catalysis is the other place Sb2O3 shows up at consumer scale — antimony trace residue (typically 200–300 ppb) in bottled water has been studied extensively and is consistently below the EPA 6 ppb drinking-water limit, but consumer pressure and sustainability concerns have pushed some premium brands to titanium- or germanium-based catalysts that leave no antimony behind.
Common Uses
- Sb-Br flame-retardant synergist in plastics, textiles, and electronics
- Polyethylene terephthalate (PET) polycondensation catalyst
- Opacifier in ceramic glazes, enamels, and fiberglass
- Decolorizing fining agent in optical-glass production
- Precursor for Sb-Sn solders and battery-grid alloys
Safety Information
IARC Group 2B (possibly carcinogenic to humans) — chronic inhalation of fine dust over years has been associated with lung tumors in animal studies, and the OSHA PEL is 0.5 mg/m³ as antimony. Acute toxicity is moderate; the major concern is dust exposure during compounding or grinding operations, where N95 dust respirators and local exhaust ventilation are required. The white powder is otherwise fairly inert and not water-soluble enough to produce significant aqueous-toxicity issues. GHS H351, H372.
This safety summary is for educational reference only and may not be complete. It is not a substitute for Safety Data Sheets (SDS), medical advice, or professional chemical safety guidance. Always consult appropriate SDS and qualified professionals before handling chemicals.