Antimony trioxide

Antimony trioxide (CAS 1309-64-4), also known as Flowers of Antimony, is a flame retardant synergist used in plastics, textiles, and industrial materials.

Where is Antimony trioxide used?

• Plastics and polymers: compounded with brominated or chlorinated flame retardants to meet UL 94 and other flammability standards in wire insulation, connectors, and housings
• Textile and fabric coatings: automotive interiors, upholstery, and protective workwear
• Construction materials: PVC profiles, roofing membranes, and wall panels where building codes mandate flame resistance
• Electronics: printed circuit board laminates and encapsulant compounds to control flame spread in high-density assemblies
• It amplifies the performance of halogenated flame retardant systems, allowing formulators to achieve target fire ratings at lower total additive loadings.
• In the absence of antimony trioxide, about twice as much halogenated compound would be needed to achieve the same level of flame retardancy.
• Used as a catalyst in PET production.
• Used as a clarifying aid in glasses.
• Used as an opacifier in cast iron and dip enameling baths.

Good to know: It does not act as a standalone flame retardant.

Formulation notes

• In PET preparation, the amount used may range from 100-300 mg/kg.
• Reacts violently with bromine trifluoride.
• Reacts with hydrogen under certain conditions to produce stibine, a very toxic gas.

Typical specification

• A wetted grade is available with plasticizers, typically 4% DIDP.
• Available in a Standard Grade with 99.5% purity.

Regulatory status

• Not regulated for transport under special provision SP45 unless it contains more than 0.5% arsenic.
• The harmonised classification and labelling index number under the EU CLP Regulation is 051-005-00-X.

Frequently asked questions about Antimony trioxide

In which applications is antimony trioxide used as a pigment?

Antimony trioxide is used as a paint pigment.

Technical content is compiled and updated by the SoleChem product team from public technical sources; the certificate of analysis (COA) governs product-specific specifications.