Antimony trioxide has the chemical formula Sb2O3 and CAS number 1309-64-4. It is generally a white, odorless crystalline powder with a melting point of approximately 656°C, a boiling point of approximately 1,550°C, and a Mohs hardness of 2.5-3. It is slightly soluble in water, insoluble in ethanol and diethyl ether, and readily soluble in concentrated hydrochloric acid, sulfuric acid, and strong alkali solutions. It is chemically stable, does not readily oxidize at ambient temperature, and can be reduced to metallic antimony at high temperatures. It provides a strong synergistic flame-retardant effect when used with halogen compounds. It is mainly used as an inorganic flame retardant in plastics, rubber, and textiles and as an opacifier in enamels and glass. It is also used as a colorant and flux in ceramics, in electronic materials for its photoelectric properties, in the production of antimonates and organoantimony stabilizers, as a pharmaceutical intermediate, and as a catalyst for certain oxidation reactions.