What is pure osmium used for?

Osmium is a group VIII element of the periodic table. One of the platinum group (ruthenium, rhodium, palladium, osmium, iridium, platinum) elements. The element symbol is Os, the atomic number is 76, and the atomic weight is 190.2. In 1804, British Tennant et al. separated osmium from the residue after dissolving crude platinum with aqua regia. 

The content in the crust is 1×10-7% (mass), and it is often symbiotic with other elements of the platinum series, such as original platinum ore, nickel pyrite, nickel sulfide ore, gray-iridium osmium ore, osmium-iridium alloy, etc. Osmium is a gray-blue metal with a melting point of 2700°C, a boiling point higher than 5300°C, and a density of 22.48 g/cm3. Hard and brittle. The bulk metal osmium is chemically inactive and stable in air and humid environments. Spongy or powdered osmium will gradually be oxidized to osmium tetroxide at room temperature.

Osmium is mainly used as a hardener for platinum group metal alloys to manufacture various wear-resistant and corrosion-resistant cemented carbides. Alloys made of osmium and iridium, rhodium, ruthenium, platinum, etc. can be used to make contacts and plugs of instruments and electrical appliances. Osmium-iridium alloys can be used as pen tips, record player needles, compasses, pivots for instruments, etc. In the valve industry, the ability of the cathode to emit electrons is enhanced by condensing osmium vapor onto the filament of the valve. Osmium tetroxide can be reduced to black osmium dioxide by certain biological substances, so it is sometimes used as a tissue stain in electron microscopy. Osmium tetroxide is also used in organic synthesis. Osmium metal is non-toxic. Osmium tetroxide is highly irritating and toxic, and has serious effects on skin, eyes and upper respiratory tract.

Chemical properties of pure osmium

CAS Number: 7440-04-2

EINECS Number: 231-114-0

UN Number: 3089

Melting point: 3045 ℃

Boiling point: 5027 ℃

Water solubility: not easily soluble in water

Density: 22.59 g/cm³

Appearance: gray-blue metal, osmium powder is blue-black

Source of osmium metal 

The crustal abundance of osmium is 1×10-7%. It is mainly produced in chromite, cuprite and placer related to basic and ultrabasic rocks, and a few are produced in molybdenum ore. The main minerals are intermetallic compounds formed with iridium, and contain a small amount of ruthenium and platinum. Such as: iridium osmium ore contains Ir65.4%~79.1%, Os13.4%~31.2%, and a small amount of ruthenium; platinum osmium ruthenium ore contains Pt46.6%~72.6%, Os18%~49.3%, Ru7.6%; ruthenium Osmium-iridium ore contains Ir43.1%～51.4%, Os33.1%～38.5%, Ru10.7%～14.7%; osmium-iridium ore contains Os41.8%～Chemicalbook86.5%, Ir12.3%～18.9%, Ru0%～8.9%; osmium iridium ruthenium ore contains Os41.4%～49.5%, Ir19.6%～41.0%, Ru10.9%～18.6%. 

In addition, the highest content of osmium in iron meteorites with high platinum group metals can reach 17g/t. Osmium has mass numbers of 184, 186, 187, 188, 189, 190, and 1927 natural isotopes, and their abundances (mass fraction ω/%) are 0.018, 1.59, 1.64, 13.3, 16.1, 26.4 and 41.0, respectively. Osmium is mainly produced in the former Soviet Union and South Africa.

Isotopes of pure osmium

There are 41 isotopes of osmium, five of which are stable and two are naturally occurring radioactive isotopes with long half-lives. The following are the naturally occurring abundances of stable isotopes in the earth's crust: Os-187=1.6%, Os-188=13.29%, Os-189=16.21%, OsChemicalbook-190=26.36% and Os-192=40.93%. The abundance of the remaining two natural radioisotopes on Earth: Os-184=0.02% and Os-186=1.59%. All other isotopes of osmium that are artificially produced in nuclear reactors and particle accelerators are radioactive.

Osmium toxicity

Most osmium oxides are harmless but toxic if inhaled or ingested. This compound is highly toxic. It is a strong oxidant, soluble in water, and can oxidize all layers of skin tissue, causing severe burns.

Uses of osmium metal

Due to the hard and brittle nature of metallic osmium, it is of little use. However, powdered powders, while toxic and malodorous, can be sintered at high pressure and temperature to form some useful products. Its main use is as an alloy for manufacturing equipment, which is wear-resistant and durable.

As an alloy, osmium has no odor or toxicity. Some products are nibs for ballpoint pens and fountain pens, needles for record players, pivots for compasses. Osmium alloys are also used for contact points on special switches and other devices that require reduced friction and wear. Another use is to stain animal tissue for microscopic examination to improve the contrast of the specimen.