Antimony Oxide Overview

Antimony trioxide is an inorganic compound with the chemical formula Sb2O3. It is a white, odorless and crystalline (sand-like) powder. ATO is an amphoteric oxide, which can dissolve both in alkaline and acidic solutions. ATO gives antimonites when dissolved in alkaline solution and gives polyantimonous acids when dissolved in acid solution. ATO can easily be oxidized or reduced; it can be oxidized to antimony pentoxide and various other antimony compounds. ATO is toxic, it is presumed to have carcinogenic potential on humans.

It is manufactured by a sublimation reaction of antimony (that is found in the Earth’s crust as stibnite ores) with Oxygen. The stibnite ores are first smelted and oxidized to crude antimony trioxide. This crude antimony trioxide is subsequently sublimated to separate the antimony trioxide from the more volatile arsenic trioxide. This reaction results in the formation of a cubic crystalline lattice. Antimony trioxide is the most important commercial compound of Antimony. It’s most important use is as a flame retardant.

The General properties of Antimony trioxide are:
  • It is an amphoteric oxide
  • It has very low solubility in water
  • It diminishes the Izod impact strength (specifies the impact resistance of materials) and translucency because of its particle size and pigmentation strength, respectively.

Production of Antimony Trioxide:

The commercial production of Antimony Trioxide involves two main steps. The first step involves the oxidisation of crude stibnite to crude antimony trioxide, in a furnace operating at 850 – 1000⁰C.

The chemical reaction is as follows:
2 Sb2S3 + 9 O2 → 2 Sb2O3 + 6 SO2

The second step involves the vaporisation of the crude antimony trioxide, followed by condensation. Apart from the above method, there is another commercial method available. This method involves the oxidation of antimony metal to antimony trioxide, in a furnace. This method involves an exothermic reaction. The oxidation is followed by sublimation of the antimony trioxide, and the obtained antimony trioxide can be recovered using filters. The chemical reaction is as follows:
4 Sb + 3 O2 → 2 Sb2O3

As a catalyst in the polymerization of PET:
Antimony trioxide is used as a catalyst in the production of Polyethylene Terephthalate (PET plastic). It is the most preferred poly-condensation catalyst because it offers the high catalytic activity, does not give rise to undesirable colours, has a low tendency to catalyse side reactions, and most of all, the price is low for such good performance.

As a flame retardant:
Flame retardants are those substances that can be chemically inserted into polymer molecules, or be physically blended in polymers after polymerization, to retard the propagation of a flame, through plastic materials. Antimony trioxide is used as a synergist to enhance the efficiency of halogenated flame retardants, by releasing the halogen radicals stepwise, while retarding the gas phase chain reaction of the spreading flame. Without Antimony trioxide, twice as much the amount of halogen compound would be needed to achieve the same level of retarding, as with Antimony trioxide.

The degradation products of the flame retardants, stop the radical mechanism of the combustion process that takes place in the gas phase. Thus the exothermic processes that occur in the flame are stopped and the system cools down, leading to the reduction in the supply of flammable gases, and eventually the flame is completely suppressed.

When Antimony trioxide is present in the flame retardant, it allows the formation of volatile antimony species (antimony halides or antimonyoxyhalide) that are capable of interrupting the combustion process. It increases the efficiency by trapping free radicals that need to reach the flame in the gas phase.

Thus, the use of Antimony trioxide not only economizes the process, but also enhances the physical properties of the flame retardants.

Other Applications:

It is used as clarifying agent for glasses, opacifier for ceramics and enamels, catalyst in the vulcanization of rubber, flocculant in titanium dioxide production and as stabilizer in pigments and ceramic frites.

  Specification Typical
Antimony Oxide Minimum 99.5% 99.5%
Antimony (Sb) Minimum 83.3% 83.3%
Arsenic (As) Maximum 0.2% 0.075%
Lead (Pb) Maximum 0.1% 0.050%
Iron (Fe) Maximum 0.002% < 0.0004%
Selenium Maximum 50 ppm < 50ppm
Specific Gravity Maximum 5.2-5.6 5.2-5.6
Average Particle Size FSSS   1.1-1.8 1.2-1.6
Color   Excellent White  
Residue on 325 mesh (% max/min)   0.5% < 0.1%
Weight per cubic ft. (approx)   44 to 55 lbs  
ACR_App_file_documentPDF Specification ACR_App_file_documentPDF MSDS

Antimony Oxide Safety Data Sheet
product identification
CAS No. 1309-64-4
Mol wt. 291.52
EINECS 2151750
Synonyms Antimonious oxide, antimony(III) oxide
DENSITY 5.2.-5.7 g/cm3
0.406 mmHg at 550°C
VAPOR DENSITY (Air = 1) Not available.
SOLUBILITY IN H2O .001g/100ml @25°C
APPEARANCE AND ODOR White, crystalline powder; odorless.
Thermal Decomposition: None expected.
Conditions Contributing To Instability: None expected
Incompatibility: Avoid contact with acids, bases, reducing agents; toxic products of reaction may be generated.
Hazardous Decomposition Products: None expected.None expected.