Properties and Structure of Bismuth

Bismuth is a chemical element with the symbol Bi and atomic number 83. It is a post-transition metal and one of the pnictogens with lead. Bismuth has a rhombohedral crystal structure and in its elemental form is a brittle metal with a white to off-white coloring. Some key physical properties of bismuth include its low melting point of 271.4°C, high boiling point of 1564°C, and low thermal conductivity of only 8.0 W·m−1·K−1. Bismuth also has the unusual property of expanding as it cools below its melting point, making it one of the few substances with a negative volumetric thermal expansion coefficient. In this article, we will explore the interesting world of bismuth - its distinctive physical and chemical characteristics, major uses, production methods and the global Bismuth   outlook.

Discovery and Production

Bismuth was first coined by the famous 18th-century German chemist Georg Brandt, who discovered the element in 1753. It is obtained during refining of lead from its ores. The ores contain only 0.2-5% of bismuth. Commercially, bismuth is obtained as a by-product in refining of lead. The most important ore of bismuth is bismite Bi2O3. Other bismuth minerals are bismuthinite Bi2S3 and bismutite PbBiOPO4. Promising new sources of bismuth include polymetallic deposits from which it is recovered as a byproduct and residues from copper production. Global bismuth production is around 8,000 tonnes per year. China accounts for over 60% of world bismuth mining.

Uses and Compounds

Much of the bismuth produced is used in alloys, primarily lead-bismuth and tin-bismuth alloys. Lead-bismuth alloys have moderate toxicity and find applications as radiation shielding in nuclear reactors. Many bismuth compounds have also found important industrial uses. Bismuth subcarbonate, also known as bismuth oxychloride, is widely used as a pigment in cosmetics and paints for its high refractive index. Bismuth citrate is used in some pharmaceutical drugs as an antacid. Bismuth subnitrate and bismuth subgallate are used to treat gastrointestinal disorders by inhibiting H. pylori bacteria. Bismuth vanadate gives a uranium green phosphorescence in TV screens and CRT monitors.

Alloys and Metallurgy

Due to its low melting point and toxicity, pure bismuth metal sees limited commercial applications. It primarily finds use in alloys where it improves certain properties. Bismuth acts as a galling preventative in machinery applications. The bismuth-tin alloy bismuth telluride is a widely used thermoelectric material. Lead-bismuth alloy has favorable nuclear properties and high resistance to radiation damage. It demonstrates good heat transfer characteristics and low neutron absorption cross-section for fast neutrons. This allows lead-bismuth to serve as a coolant in some innovative nuclear reactor designs. The metallurgy of bismuth is intricate due to its unusual solidification behavior and formation of different crystalline structures with different alloys and temperatures.

Emerging Applications

Scientists are exploring new and emerging applications of bismuth and its compounds. Bismuth vanadate has shown promise as a low-cost yellow pigment and is being studied for photovoltaic applications. Its luminescent properties could be relevant in the development of new display technologies. Nanoparticles of bismuth telluride are being investigated for thermoelectric devices and Peltier coolers. Their efficiency at converting heat to electricity is far superior to existing materials. The exceptionally low toxicity of metallic bismuth makes it an eco-friendly substitute for lead in applications such as free-machining alloys, fusible alloys and dental amalgams. Bismuth compounds also continue yielding new pharmaceutical usages. Areas likemedicinal imaging and radioactive isotopes harness unique properties of bismuth and its daughter isotopes.

Environmental and Health Considerations

Despite its many industrial uses, elemental bismuth and most bismuth compounds pose minimal risks to human health or the environment. The primary hazards are from inhalation of dusts or fumes containing bismuth and its compounds. Skin contact is not absorbed to any significant degree. Bismuth itself is poorly absorbed from the gastrointestinal tract. Even large oral doses of water-soluble bismuth salts cause no systemic effects but may discolor the tongue, teeth or stool. Bismuth is almost universally categorized as having low oral and dermal toxicity. It is neither bioaccumulative nor toxic in aquatic systems. Though non-radioactive, bismuth isotopes have half-lives suitable for use as gamma-ray tracers. This opens up opportunities in medical imaging with little associated radiation hazards. Overall, bismuth poses minimal pollution threats during mining, production or disposal for its current industrial scale uses.

Market Outlook

The unique physical properties of bismuth offering distinct advantages compared to alternatives have fueled steady growth in its industrial applications. For more details on factors driving global Bismuth   trends and analysis of dominant regional markets, please refer to the comprehensive market research report published on the topic on Coherent Market Insights website.

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