Osmium
Osmium (symbol Os, atomic number 76) is a hard, brittle, bluish-white transition metal in the platinum group. It is one of the densest naturally occurring elements, rivaled only by iridium. Osmium occurs as a trace element in alloys, mostly in platinum ores.
Properties
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Physical Properties: Osmium has an extremely high density (approximately 22.59 g/cm³), a high melting point (over 3000 °C), and a high boiling point (over 5000 °C). It is very hard and brittle, making it difficult to machine or work.
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Chemical Properties: Osmium is relatively inert, but at elevated temperatures it reacts with oxygen to form osmium tetroxide (OsO4). Osmium tetroxide is a highly toxic and volatile compound with a characteristic acrid odor. Finely divided osmium metal reacts slowly with oxygen at room temperature to also form OsO4. Osmium is resistant to attack by acids and alkalis.
Occurrence and Production
Osmium is found in trace amounts in platinum-bearing ores, primarily in Russia, North and South America. It is obtained as a byproduct of nickel and copper refining. Osmium is separated from the other platinum group metals through a complex series of chemical processes.
Applications
Due to its hardness and resistance to wear, osmium is used in:
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Alloys: Osmium is alloyed with other platinum group metals, especially platinum and iridium, to create extremely hard and durable alloys. These alloys are used in electrical contacts, fountain pen tips, and instrument pivots.
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Hardening Agents: Osmium is used as a hardening agent for platinum.
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Microscopy: Osmium tetroxide is used as a stain in microscopy to provide contrast in biological specimens. However, due to its toxicity, its use has decreased.
Toxicity
Osmium tetroxide (OsO4) is highly toxic. It is a strong oxidizing agent and irritates the eyes, skin, and respiratory system. Exposure to osmium tetroxide can cause lung damage, skin burns, and corneal damage. Proper ventilation and handling procedures are essential when working with osmium compounds. Metallic osmium, in bulk form, is generally considered less hazardous than its compounds.