Antimony is a metalloid between metal and nonmetal, density 6.697 g/cm³, melting point 631 °C. Brittle and silvery, it cannot serve as a structural material on its own, yet holds an irreplaceable niche in flame retardancy, batteries and type metals. Its largest use is as a flame-retardant synergist paired with halogen systems in plastics, rubber and coatings: Sb2O3 itself does not burn, but at high temperature it reacts with halogens to release antimony oxides that capture free radicals and slow polymer ignition, so it is ubiquitous in wire and cable jackets, appliance housings, furniture and textiles. In lead-acid batteries, a small antimony addition hardens the grid, improves castability and suppresses gassing, making starting and backup batteries more cycle-resistant. For printing and bearings, antimony's slight expansion on solidification matters: tin-lead-antimony type alloys cast sharp, clean letterforms and were the heart of movable-type printing; tin-based babbitt alloys containing antimony serve as main and connecting-vehicle bearings. Antimony also appears in military detonators, pyrotechnic colorants and glass fining.
Antimony trioxide (Sb2O3), known as antimony white, is the most important compound, a white crystalline powder with limited flame retardancy on its own but strong synergy with halogenated retardants in plastics and textiles, and is the workhorse system in cables, TV casings, toys and polyurethane foam. Antimony trisulfide (Sb2S3), stibnite, is the main ore for smelting; historically used in match heads and military primer compositions for its friction-ignition property, it now also goes into black glass and infrared windows. Antimony trichloride (SbCl3), once called butter of antimony, was used for antiqued gilding and as an emetic, and now serves mainly as a chlorination catalyst in organic synthesis. Indium antimonide (InSb) and gallium antimonide (GaSb) are important semiconductors used in infrared detectors, Hall sensors and terahertz devices. Antimony pentoxide (Sb2O5) is used as a flame retardant and polyester polymerization catalyst.
