Antimony

Antimony is a hard, brittle, blue-white metalloid that has been known since antiquity, ancient Egyptians used it as eyeliner and physicians used it as a medicine for centuries, often with fatal results. Today it is inside the flame retardants in your furniture, the lead plates in car batteries, and the diodes in power electronics.

• Atomic Number5151 protons, 51 electrons
• Atomic Mass121.760 u51× heavier than hydrogen
• State at Room TempSolidSolid
• Density6.685 g/cm³
• Melting / Boiling630.6°C / 1586.8°C
• DiscoveredAncient

What is Antimony?

Antimony is a metalloid in Group 15 of the periodic table, sitting below arsenic. With 51 protons, antimony has a metallic appearance but is brittle and a poor electrical conductor. Its most common oxidation states are +3 and +5. Like arsenic and bismuth, it expands when it solidifies, a rare property that makes it useful in type metal alloys. It is toxic to humans, though less acutely so than arsenic.

The chemical symbol Sb comes from the Latin stibium, which in turn derives from the Greek stibi: the black powder of stibnite used as eyeliner in antiquity. The English name antimony comes from the Medieval Latin antimonium. The origin of this word is disputed, it may derive from Arabic al-ithmid (the kohl powder) or from Greek words meaning "not alone" (never found as the pure element in antiquity).

Fact In the 18th century, antimony compounds were a popular but extremely dangerous medicine. "Emetic wine", wine stored in antimony cups, was prescribed for almost everything from constipation to fever. The resulting sickness was seen as the body purging its illness. Many patients were actually being repeatedly poisoned.

Where you find Antimony

In space

Antimony is produced in stars and found in the Sun.

On Earth

Antimony is moderately rare at approx. 0.2 parts per million in the Earth's crust.

• Stibnite (Sb₂S₃). The main antimony ore, a lead-grey mineral with metallic lustre. China produces approx. 75% of world supply, with Russia and Bolivia also significant.
• Gudmundite and other sulfosalts. Various antimony sulfide minerals are found in hydrothermal vein deposits worldwide.

How we use Antimony

• Flame retardants.. Antimony trioxide is added to plastics, textiles and rubber as a flame retardant, working synergistically with halogenated flame retardants. Found in car seats, aircraft interiors and electronics casings.
• Lead-acid batteries.. Adding antimony to the lead plates in car batteries makes them harder, stronger and more resistant to corrosion, extending battery life.
• Semiconductor electronics.. Antimony is used to dope n-type germanium and silicon semiconductors. Indium antimonide is a narrow-bandgap semiconductor used in infrared detectors.

Did you know? The famous Gutenberg Bible, printed around 1455, was set in type made from an alloy of lead, tin and antimony. Antimony was crucial because it expands slightly on solidifying, ensuring the molten metal filled every corner of the type mould precisely, producing crisp, sharp type. This property of antimony made the printing revolution possible.

How it was discovered

Antimony has been known since antiquity, kohl eyeliner from ancient Egypt contained antimony sulfide. The pure metal was produced and described by the Italian monk Basil Valentine in the early 15th century and later discussed in Vannoccio Biringuccio's Pirotechnia (1540). Jöns Jacob Berzelius established its status as a true chemical element in the early 19th century.

Deeper dive: antimony chemistry and applications

The synergistic flame-retardant action of antimony trioxide with halogenated compounds is an important industrial mechanism. Antimony trioxide alone is a modest flame retardant. But mixed with brominated or chlorinated compounds in plastics, it reacts in the gas phase during burning to form antimony trihalides, volatile compounds that interrupt the radical chain reactions of combustion, smothering the flame. The combination is far more effective than either component alone, allowing lower total additive levels.

Moving to 52 protons on the periodic table brings us to Tellurium.