Antimony

Antimony occupies an unusual position in the history of chemistry: it was used extensively for thousands of years before it was recognized as an element. Ancient Egyptians and Mesopotamians ground the black sulfide mineral stibnite into kohl, the dark powder used to line eyes for cosmetic and ritual purposes. Alchemists of the medieval period were so fascinated by antimony's behavior — its brittle, crystalline structure, its tendency to purify gold and silver during smelting — that a text attributed to Basil Valentine called it the 'Triumphal Chariot of Antimony.' The chemical symbol Sb derives from the Latin stibium, reflecting that long tradition. Antimony sits on the border between metals and nonmetals: it conducts electricity but poorly, fractures rather than bends, and its properties shift dramatically depending on the compound it forms.

Flame retardants represent antimony's single largest application. Antimony trioxide is combined with halogenated compounds in plastics, textiles, and circuit boards; the two work synergistically, with antimony trioxide acting as a catalyst that increases the effectiveness of the halogen flame retardant far beyond what either achieves alone. Lead-acid batteries, the rechargeable batteries that start every conventional vehicle, rely on antimony to harden lead grid plates and reduce water loss during charging. Semiconductor applications include indium antimonide for infrared detectors and gallium antimonide for thermophotovoltaic cells. Antimony trioxide also serves as a white pigment and opacifier in glass and ceramics. Historically, antimony-lead-tin alloys were the foundation of movable type for printing presses, because the alloy expands slightly on solidification, filling the mold precisely and producing sharp letter edges.

The use of stibnite as eye cosmetic dates back at least 5,000 years in Egypt and the ancient Near East. Arabic physicians of the medieval period used antimony compounds medicinally, and the Arabic term 'al-ithmid' may be one etymology for the element's name, though this is disputed. European alchemists isolated the metal by reducing stibnite with iron in the 15th and 16th centuries. The influential 1604 treatise on antimony — 'Currus Triumphalis Antimonii' — spread knowledge of its properties across Europe. Nicolas Lémery's 1707 chemical analysis helped establish antimony as a distinct element rather than a compound. Jöns Jacob Berzelius confirmed its elemental nature in the early 19th century. The flame retardant applications that now dominate its use were developed in the mid-20th century as plastics proliferated in consumer goods.

Antimony is relatively rare, comprising roughly 0.2 parts per million of Earth's crust. The primary ore mineral is stibnite (Sb₂S₃), a lead-grey sulfide that forms in hydrothermal veins, often associated with gold and silver deposits. China accounts for roughly half to three-quarters of global antimony mine production, with significant reserves in Hunan Province. Other producing countries include Russia, Bolivia, Tajikistan, and Australia. Antimony also occurs as a byproduct in the smelting of lead, copper, and silver ores, where it must be removed as an impurity or recovered for sale. Secondary production from recycling, especially from lead-acid battery scrap, supplies a meaningful share of the market. The United States has no significant active antimony mines and depends heavily on imports.

Antimony trioxide (Sb₂O₃) is the most commercially important compound, used in flame retardants and as a catalyst in PET polyester production. Antimony trisulfide (Sb₂S₃, stibnite) is both the primary ore and a component in pyrotechnic compositions, where it burns with a bright white flame. Antimony pentoxide (Sb₂O₅) is used in flame retardants and as an ion-exchange material. Antimony trichloride (SbCl₃) is a Lewis acid catalyst in organic synthesis and appears in the production of antimony compounds generally. Potassium antimony tartrate, historically called tartar emetic, was used for centuries as a medicine and emetic; its toxicity is now well understood. Indium antimonide (InSb) and gallium antimonide (GaSb) are compound semiconductors with applications in infrared optics and high-speed electronics.

• Kohl, used to darken the eyes in ancient Egypt, was almost certainly powdered stibnite — meaning antimony was a cosmetic ingredient more than 5,000 years before its chemistry was understood.
• The lead alloy used for Gutenberg's movable type was roughly 83 percent lead, 12 percent antimony, and 5 percent tin; antimony's slight expansion on cooling filled mold cavities perfectly for sharp letter edges.
• Antimony has a remarkable property: when alloyed with lead and tin in certain proportions, the resulting metal expands very slightly as it solidifies, the opposite of most metals, which made it ideal for casting type that required precise dimensions.
• Some historians have argued that the word 'antimony' derives from anti-monos, Greek for 'not alone,' because the element was thought never to occur in pure form in nature — though the etymology remains debated.
• Antimony compounds were used as medicines and poisons in European history almost interchangeably; the same compound — potassium antimony tartrate — was prescribed to induce vomiting and was also a documented poison used in high-profile poisoning cases.