Bismuth (symbol Bi, atomic number 83) is a chemical element belonging to Group VA of the periodic table. It is a slightly reddish, silvery-white metal. Bismuth forms an uneven oxide film (Bi₂O₃) in air, displaying iridescent colors under light, usually a light red.
Its melting point is relatively low (271 ℃), while its boiling point is relatively high (1560 ℃). Its most unique physical property is that it expands in volume upon solidification. It is chemically stable and not easily corroded by non-oxidizing acids at room temperature. Common oxidation states are 0, +3, and +5. Previously, bismuth was considered the most stable element in terms of relative atomic mass. However, in 2003, it was discovered that naturally occurring bismuth has weak radioactivity and undergoes alpha decay, slowly transforming into thallium.
Simultaneously, the half-life of 20⁹Bi was determined to be 1.9 × 10¹⁹ years, thus making lead the heaviest stable element. Bismuth is typically found in nature in hydrothermal veins, often associated with quartz and minerals formed from metals such as cobalt, silver, iron, and lead, or in the contact zone between granite intrusions and limestone. Bismuth is rarely found in its free state, and bismuth crystals are quite rare. Common compounds include bismuthite (Bi₂S₃) and bismuth oxide (Bi₂O₃).
In industry, bismuth is primarily used to manufacture low-melting-point alloys and is widely used in fire protection and electrical safety devices. In the pharmaceutical field, bismuth compounds are important components of gastrointestinal drugs. It is also used in lead-free pigments, electronic ceramics, semiconductor components, and chemical catalysts. Bismuth exists in nature mainly as sulfide or oxide ores, and is primarily extracted through pyrometallurgy. High-purity bismuth (99.999%) is used in the nuclear industry as a heat transfer fluid or coolant in reactors and also in radiation protection structures. Bismuth is also used in the manufacture of lead-free glass, high-refractive-index glass, nuclear industry glass, as well as as a filler and mold material in metal processing, offering advantages such as reusability and rapid molding.
