Properties and Overview of Bismuth

Overview:

Bismuth (Bi) is a dense, brittle metal with the atomic number 83 and Bi symbol on the periodic table. It is the heaviest element that is not radioactive. Known since ancient times, bismuth was often confused with lead and tin due to its similar appearance but was later recognized as a distinct element in the 18th century. Bismuth is characterized by its unique properties, including its low toxicity relative to other heavy metals, making it increasingly valuable in various applications, particularly as a safer alternative to lead. Physically, bismuth is notable for its lustrous, silver-white color with a slight pinkish hue due to the thin oxide layer that forms on its surface. It is a brittle metal with a relatively low melting point of approximately 270°C and a high boiling point of 1,560°C. Bismuth is diamagnetic, meaning magnetic fields repel it, and it has the highest Hall effect of any metal, which is the production of a voltage difference across an electrical conductor when placed in a magnetic field. Bismuth's low thermal conductivity and high electrical resistance distinguish it from other metals, making it useful in specific applications. Additionally, bismuth expands upon solidification, an unusual property for metals. This expansion can be beneficial in casting applications, where the expansion helps to fill molds more completely.
Chemically, bismuth is relatively stable and resistant to oxidation, though it does react with oxygen at elevated temperatures to form bismuth oxide (Bi₂O₃). Bismuth forms a variety of compounds, including bismuth chloride (BiCl₃), bismuth nitrate (Bi(NO₃)₃), and bismuth sulfide (Bi₂S₃). Bismuth oxide is vital industrially, as it is used to manufacture certain glasses and ceramics, giving them a distinctive yellow color and improving their optical properties. Bismuth compounds are also known for their antimicrobial properties, contributing to their use in medical applications.
Regarding safety, bismuth is considered one of the least toxic heavy metals, making it suitable for medical and cosmetic applications. Unlike lead and mercury, which pose significant health risks, bismuth compounds are generally non-toxic. They are even used in pharmaceuticals, such as bismuth subsalicylate, the active ingredient in popular over-the-counter antacids and anti-diarrheal medications. However, inhalation of bismuth dust or fumes can still cause respiratory irritation, and large doses of bismuth compounds can lead to bismuth poisoning, characterized by kidney damage and neurological symptoms. As with all chemicals, appropriate safety measures should be taken when handling bismuth, especially in industrial settings where exposure to dust and fumes is more likely.

Production:

Bismuth production primarily involves its extraction as a byproduct from mining and refining other metals, such as lead, copper, tin, and silver. Bismuth is typically found in the ores of these metals in small quantities, often in the form of bismuthinite (Bi₂S₃) and bismite (Bi₂O₃). The extraction process usually begins with smelting these ores, during which bismuth is separated from the primary metals through a series of chemical reactions and physical processes, such as electrolysis or distillation. Once isolated, bismuth can be further purified through zone refining. This technique removes impurities by melting a small metal region and allowing it to recrystallize as it moves along the ingot.

Applications:

Bismuth's physical properties make it a safe and valuable material in the production of alloys, especially as a non-toxic replacement for lead. Bismuth alloys are used in various applications, including low-melting-point solders, fire sprinkler systems, and fusible plugs. These safety devices melt at a specific temperature to release pressure or activate a system. These alloys are particularly important in fire detection and suppression systems, where the low melting point of bismuth alloys allows for rapid response in emergency situations. Additionally, bismuth is used in the manufacture of free-machining steels and aluminium, where its presence improves the machinability of these metals without compromising their structural integrity. The safety benefits of bismuth, as a non-toxic replacement for lead, provide reassurance and confidence in its use in various applications.
In more specialized applications, bismuth is used to produce bismuth telluride (Bi₂Te₃), a semiconductor material critical in thermoelectric devices. These devices can convert heat directly into electricity, making them useful in power generation, refrigeration, and temperature control systems. Bismuth's unique properties also make it a candidate for use in nuclear reactors or lead-bismuth eutectic alloys, which serve as a low-melting-point coolant in some fast reactors.
Bismuth's versatility is evident in its wide range of applications across various industries. In the pharmaceutical industry, bismuth compounds are commonly used in medications to treat gastrointestinal disorders, such as ulcers and diarrhea. Bismuth subsalicylate, for example, is the main ingredient in popular remedies like Pepto-Bismol, which provides relief from upset stomach and indigestion. In the cosmetics industry, bismuth oxychloride is used as a pigment in products like eyeshadows and nail polishes due to its pearlescent appearance. This versatility, from medicine to cosmetics, is a testament to the unique properties of bismuth and its ability to adapt to diverse applications.

Summary:

Bismuth is a versatile and important metal with a growing number of applications due to its unique combination of physical and chemical properties and relatively low toxicity. While it shares some similarities with other heavy metals, its lower health risks and specialized properties make it increasingly valuable in industries ranging from medicine to electronics. The development of bismuth-based materials continues to expand its role in modern technology, mainly as environmental and health regulations drive the search for safer alternatives to more toxic metals.

See a comprehensive list of atomic, electrical, mechanical, physical and thermal properties for bismuth below: