- ▸ Flame-retardant synergist: synergist with halogenated systems in plastics and textiles
- ▸ Polyester catalyst: polycondensation catalyst for PET
- ▸ Opacifier: glass, ceramic, and enamel opacification
- ▸ Stabilizer / pigment: plastics stabilizer and pigment
A grade-specific Safety Data Sheet (SDS) — with the complete hazard classification, handling precautions, and transport information — is supplied with every shipment and available on request. Confirm all safety and regulatory details against the SDS for your specific grade.
Request SDS →⚠ WARNING: This product can expose you to Antimony Trioxide, which is known to the State of California to cause cancer. For more information go to www.P65Warnings.ca.gov.
Antimony trioxide (ATO) is the classic flame-retardant synergist — it has little effect on its own but sharply boosts the efficiency of halogenated flame retardants, letting formulators use less of them. It is used together with a halogen source, not as a halogen-free solution. Identity: CAS 1309-64-4.
What it is
Antimony trioxide (CAS 1309-64-4, Sb2O3) is a white powder. In flame retardancy it is a synergist for brominated and chlorinated systems; it is also used as a catalyst (e.g. in PET) and as a pigment/opacifier. Confirm regulatory status for your market and end use.
How it performs in fire
It works in the gas phase: with a halogen source it forms antimony halides and oxyhalides that scavenge the radicals feeding the flame, multiplying the effectiveness of the halogenated flame retardant so a lower total loading reaches the fire rating. Alone it does little, so it is always paired with a halogen donor.
Applications
ATO is used as a synergist in halogenated flame-retardant plastics, PVC, textiles, rubber and coatings, dosed with a brominated or chlorinated flame retardant. For halogen-free routes, see the mineral and intumescent options in the flame retardants guide; zinc borate is used as a partial antimony replacement.
Forms, grades and handling
ATO is supplied as a white powder in a range of particle sizes in bags and bulk. Properties are typical reference values; the Certificate of Analysis (CoA) for the lot you buy governs. Handle per the current Safety Data Sheet (SDS), and confirm regulatory status and restrictions for your market and end use. Each lot ships with CoA, TDS and SDS.
Bulk supply and RFQ
RawSource sources Antimony Trioxide direct from producers in bulk, with CoA, TDS and SDS per lot. Tell us your polymer or system, the fire test you must pass, your maximum loading, and any particle-size or grade requirement, and we will quote the right grade. See the full range and selection logic in the flame retardants guide.
Typical Properties
Typical reference values, not a specification; the Certificate of Analysis (CoA) for the lot governs.
| Property | Typical Value |
|---|---|
| Chemical / class | Flame-retardant synergist (antimony oxide) |
| Flame-retardant type | Gas-phase synergist |
| Role in fire performance | Boosts halogenated flame retardants |
| CAS Number | 1309-64-4 |
| Molecular Formula | Sb2O3 |
| Molecular Weight | 291.5 g/mol |
| Handling | Refer to the current SDS |
Regulatory & registration requirements
- TSCA (US):
- REACH (EU):
- EC number: 215-175-0
Source: EPA TSCA Inventory (July 2025 release) · ECHA CHEM — retrieved 2026-07-12
Regulatory restriction status
Antimony Trioxide (Antimony(III) Oxide, ATO) (CAS 1309-64-4) appears on the regulatory list(s) below. This is public regulatory information about the substance — not a statement about any specific supplier’s material, and not a safety claim. Confirm the current status for your jurisdiction and intended use.
- California Proposition 65: listed for cancer, listed 1 Oct 1990. A California Proposition 65 warning applies (see the warning above).
Sources: ECHA Candidate List / Annex XIV / Annex XVII (echa.europa.eu); U.S. EPA TSCA; UN Stockholm Convention / EU POPs Regulation; California OEHHA Proposition 65 list. Retrieved 2026-07-13.
Solutions Using This Product
Process-solution guides on this site that specify this chemistry:
- Flame Retardants for Plastics & Polymers (Plastics & Polymers)
- Flame Retardants for Textiles: APP, Mineral & N-P Systems (Textiles)
Frequently Asked Questions
What is antimony trioxide used for in flame retardancy?
Antimony trioxide (ATO, CAS 1309-64-4) is a gas-phase synergist that greatly boosts halogenated flame retardants, so less total flame retardant is needed to reach a fire rating. It is used with a brominated or chlorinated flame retardant, not as a standalone or halogen-free solution. It is also used as a PET catalyst and pigment.
Is antimony trioxide halogen-free?
No — antimony trioxide is a synergist that only works together with a halogen source, so it is part of halogenated systems. For halogen-free flame retardancy use mineral hydroxides, intumescent or nitrogen systems.
Can zinc borate replace antimony trioxide?
Zinc borate is often used as a partial replacement for or synergist with antimony trioxide, reducing antimony use while adding smoke and afterglow suppression; the right ratio depends on the system.
How is bulk antimony trioxide supplied and quoted?
RawSource supplies antimony trioxide in bulk with CoA, TDS and SDS per lot. Pricing is quote-based on grade, particle size and volume; submit an RFQ with your polymer/system and the fire test you must pass.
What is the REACH and TSCA regulatory status of Antimony Trioxide (Antimony(III) Oxide, ATO)?
Antimony Trioxide (Antimony(III) Oxide, ATO) (CAS 1309-64-4) is subject to U.S. TSCA Inventory requirements; supplying it into the EU requires valid REACH registration ((EC) No 1907/2006). RawSource cannot verify a third-party supplier's registrations — buyers should require documented TSCA and REACH compliance for their jurisdiction and volume (EC 215-175-0).