Bismuth

When bismuth liquid cools slowly, the edges of the crystal grow faster than the central faces, forming striking stepped pyramid-shaped bulges. When it is taken out into the hot air, the metal immediately oxidises creating a thin transparent film. Light reflects between the oxide surface and the metal, producing optical interferences with vivid yellow, purple and blue reflections.

In the treatment of peptic ulcer and gastritis, subsalicylate of bismuth acts by a triple mechanism: it covers the eroded gastric mucosa with a protective film against digestive acids, stimulates the secretion of endogenous prostaglandins and exerts a direct bactericidal action. Bismuth ions penetrate the Helicobacter pylori bacterium and inhibit key respiratory enzymes and adhesions, destroying the bacterial cell wall and eradicating the infection in combined therapies.

Peltier cooling cells use bismuth telluride semiconductors (Bi₂Te₃) doped p and n type joined in series electrically. When a direct current crosses the semiconductor junctions, electrons absorb thermal energy on one side and transfer it to the opposite side by Peltier effect. This allows computer processors, astronomical cameras and portable fridges to be cooled silently without mechanical motors, refrigerant liquids or greenhouse gases.

Bismuth-213 is an alpha radionuclide with short half-life (46 minutes) produced in actinium-225 generators. In nuclear medicine it is chemically bound to monoclonal antibodies designed to anchor exclusively on the surface of leukaemic cells or micrometastases. Upon decay, it emits a high-energy alpha particle that destroys the DNA of the cancer cell in a microscopic path of a few healthy cells' distance, minimising damage to neighbouring tissues.

For more than a century it was believed that bismuth-209 was the heaviest stable element in nature. In 2003, French scientists enclosed pure bismuth germanate crystals in cryogenic thermal detectors at just twenty-thousandths of a degree above absolute zero in a underground laboratory. After weeks of environmental silence, they detected the minuscule alpha decay signal with a half-life of nineteen trillion years, confirming that technically all bismuth is radioactive.

Almost all metals contract and occupy less space when they cool and pass from liquid to solid. Bismuth is one of the few exceptions of nature, behaving like water when it freezes: when solidifying, its atoms reorganise into a more open and spacious crystal lattice, increasing its volume by more than three percent. This property is ideal for melting intricate pieces and printing types.

Diamagnetism is the property by which a material induces an opposite magnetic field inside it to the applied external field, experiencing a repulsive force. Bismuth has delocalised electrons with a very small effective mass that circulate with great freedom, giving it the greatest diamagnetic susceptibility of all metals. If a bismuth sheet is placed between strong neodymium magnets, the repulsive force overcomes gravity, making it levitate in the air.