Osmium (Os) - Properties, Applications

Topics Covered

Introduction
Chemical Properties
Physical Properties
Mechanical Properties
Thermal Properties
Applications

Introduction

Osmium is a hard, brittle, bluish-white chemical element in Group 8 of the periodic table, with an atomic number 76. It is the densest of all naturally occuring elements, and it is found in platinum ores as well as iridomine and nickel-bearing ores. It was discovered in 1803 in London, by an English chemist Smithson Tennant.

Powdered osmium in air tends to form pungent, highly toxic osmium tetroxide that causes damage to eye, lung and skin.

Commercially, osmium is recovered as a by-product of nickel refining. It is unworkable as a metal, and hence it has very few applications.

Chemical Properties

The chemical properties of osmium are provided in the table below.

Chemical Data
CAS number 4/2/7440
Thermal neutron cross section 15 barns/atom
Electrode potential 0.70 V
Ionic radius (crystal ionic radius for valence +6) 0.690 Å
Electronegativity 2.2
X-ray absorption edge (K) 0.1678 Å

Physical Properties

The following table discusses the physical properties of osmium.

Properties Metric Imperial
Density 22.5 g/cm3 0.813 lb/in3
Melting point 3050 °C 5520°F
Boiling point 5012°C 9054°F

Mechanical Properties

The mechanical properties of osmium are tabulated below.

Properties Metric Imperial
Tensile strength 1000 MPa 145000 psi
Poisson’s ratio 0.25 0.25
Modulus of elasticity 560 GPa 81200 ksi
Bulk modulus 462 GPa 67007 ksi
Rigidity modulus 222 GPa 32198.4 ksi
Hardness, Brinell 293 293
Hardness, Vickers 300 300
Hardness, Rockwell A 66 66
Hardness, Rockwell C 30 30

Thermal Properties

The thermal properties of manganese are tabulated below.

Properties Metric Imperial
Thermal expansion co-efficient (@20-100°C/68-212°F) 6.60 µm/m°C 3.67 µin/in°F
Thermal conductivity 91.67 W/mK 636.2 BTU in/hr.ft².°F

Applications

Due to volatility and toxicity of its oxide, osmium is rarely used in its pure form for high-wear applications. Its alloys with platinum and iridium are used in fountain pen tips, electrical contacts and instrument pivots.

Osmium tetraoxide has been used in fingerprint detection and staining fatty tissues using electron and optical microscopy.

An alloy of 90% platinum and 10% osmium is used in surgical implants such as pacemakers and replacement heart valves. Finely divided osmium metal is also used as a catalyst.

The high reflectivity of osmium in the UV range is desirable for use in space-based UV spectrometers having reduced mirror sizes due to space limitations.

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