Antimony (Sb), a metalloid element with the atomic number 51, was historically used in cosmetics and early medicine. Today, its applications are entirely industrial, leveraging its unique properties to enhance the performance and safety of modern materials. This silvery-gray, brittle solid is valuable across diverse manufacturing sectors due to its ability to modify the physical and chemical behavior of other substances.
Use in Lead-Acid Batteries and Alloys
One of the largest applications for antimony is as a hardening agent in metal alloys, primarily with lead. Pure lead is soft and malleable, making it unsuitable for structural components in demanding applications like lead-acid batteries. Introducing antimony significantly improves the lead’s tensile strength and mechanical rigidity.
This “antimonial lead” is used to cast the internal grids and plates of batteries found in vehicles and backup power systems. Antimony, typically added in concentrations of 3% to 6%, provides the necessary strength to withstand manufacturing and operational stresses. It also offers corrosion resistance against the sulfuric acid electrolyte, ensuring long-term durability. Antimony-lead alloys are also utilized beyond batteries in products requiring strength and density, such as cable sheathing, specialized ammunition, and babbitt metals used in plain bearings.
Role as a Synergistic Flame Retardant
Another major application involves the compound Antimony Trioxide (\(\text{Sb}_2\text{O}_3\)) as a synergistic flame retardant. Antimony Trioxide is not effective as a fire suppressant by itself, but it dramatically enhances the performance of other halogen-containing flame retardants. This partnership is activated when the material is subjected to the heat of a flame.
During combustion, the halogenated compound decomposes, releasing hydrogen halides. The Antimony Trioxide then reacts with these gases to form volatile antimony halides, such as antimony trichloride or tribromide. These antimony halides vaporize and enter the gas phase of the flame, where they act as radical scavengers.
The antimony halides effectively “quench” the flame by trapping highly reactive free radicals, interrupting the chemical chain reaction that sustains combustion. This dual-component system is widely incorporated into materials like plastics (including PVC), textiles, coatings, and rubber to meet fire safety standards for consumer and industrial products.
Specialized Industrial and Catalytic Functions
Antimony compounds also serve unique roles across the chemical and manufacturing industries, often acting as powerful catalysts. The most prominent is the use of Antimony Glycolate in the production of polyethylene terephthalate (PET) plastic, which is used for plastic bottles and polyester fibers.
Antimony-based catalysts, such as Antimony Glycolate, account for over 90% of the catalysts used in PET synthesis globally. The antimony compound facilitates the polycondensation reaction between terephthalic acid and ethylene glycol, accelerating the polymerization process. This enables the efficient mass production of high-quality, recyclable PET.
Other applications utilize the element’s distinct properties. Antimony compounds are used in the glass industry to remove tiny bubbles, improving the clarity of the finished product. They also act as pigments, such as antimony yellow, and are incorporated into friction materials like brake pads.