Chemical Properties
Bluish-white lustrous metal; brittle and fairly hard; close-packed hexago- nal crystal system; density 22.48 g/cm3; Moh’s hardness 7.0; melts at about 3,050°C; vaporizes above 5,300°C; electrical resistivity 8.12 microhms-cm at 0°C; Young’s modulus 4.0x104 tons/in2; magnetic susceptibility 0.052x10–6 cm3/g; thermal neutron absorption coefficient 15 barns; insoluble in water; insoluble in HCl and H2SO4; slightly soluble in nitric acid and aqua regia; insoluble in ammonia; solubilized by fusion with caustic soda and sodium peroxide or caustic soda and potassium chlorate and the mass dissolved in water.
Chemical Properties
Osmium is a blue－white metal. It is found in
platinum ores and in the naturally occurring alloy osmiridium.
Osmium when heated in air or when the finely
divided form is exposed to air at room temperature, oxidizes
to form the tetroxide (OsO4), osmic acid. Osmium
tetraoxide is a colorless, crystalline solid or pale-yellow
mass. Unpleasant, acrid, chlorine-like odor. A liquid above
41°C.
Potential Exposure
Osmium may be alloyed with platinum
metals, iron, cobalt, and nickel; and it forms compounds
withtin and zinc. The alloy with iridium is used in
the manufacture of fountain pen points, engraving tool;
record player needles; electrical contacts; compass needles;
fine machine bearings; and parts for watch and
lock mechanisms. The metal is a catalyst in the synthesis
of ammonia; and in the dehydrogenation of organic compounds. It is also used as a stain for histological
examination of tissues. Osmium tetroxide is used as an
oxidizing agent, catalyst, and as a fixative for tissues in
electron microscopy. Other osmium compounds find use
in photography. Osmium no longer is used in incandescent
lights or in fingerprinting.
First aid
Move victim to fresh air. Call 911 or emergency
medical service. Give artificial respiration if victim is not
breathing. Do not use mouth-to-mouth methods if victim
ingested or inhaled the substance; give artificial respiration
with the aid of a pocket mask equipped with a one-way valve
or other proper respiratory medical device? Administer oxygen
if breathing is difficult. Remove and isolate contaminated
clothing and shoes. In the case of contact with substance,
immediately flush skin or eyes with running water for at least
20 minutes. For minor skin contact, avoid spreading material
on unaffected skin. Keep victim warm and quiet. Effects of
exposure (inhalation, ingestion, or skin contact) to substance
may be delayed. Ensure that medical personnel are aware of
the material(s) involved and take precautions to protect themselves.
Medical observation is recommended for
2448 hours after breathing overexposure, as pulmonary
edema may be delayed. As first aid for pulmonary edema, a
doctor or authorized paramedic may consider administering a
drug or other inhalation therapy.
Incompatibilities
Osmium tetroxide is a strong oxidizer.
Reacts with combustibles and reducing materials. Reacts
with hydrochloric acid to form toxic chlorine gas. Forms
unstable compounds with alkalis.
Waste Disposal
Consult with environmental
regulatory agencies for guidance on acceptable disposal
practices. Generators of waste containing this contaminant
(≥100 kg/mo) must conform with EPA regulations
governing storage, transportation, treatment, and waste
disposal.
Physical properties
One of the important properties of osmium is the formation of gases when the metal isexposed to air. These fumes are extremely toxic, which limits osmium’s usefulness. Osmium is ahard, tough, brittle, bluish-white metal that is difficult to use except in a powder form that oxidizesinto osmium tetroxide (OsO4), which not only has objectionable odor but also is toxic.
Osmium has a relatively high melting point of 3,054°C and a boiling point of 5,500°C,with a density of 22.61 g/cm3.
Isotopes
Osmium has 41 isotopes, five of which are stable. Two are naturally radioactiveisotopes with very long half-lives. Following are the stable isotopes and their contributionto the element’s natural existence in the Earth’s crust: Os-187 = 1.6%, Os-188 =13.29%, Os-189 = 16.21%, Os-190 = 26.36%, and Os-192 = 40.93%. The remain ing percentage of the element on Earth is in the form of the two naturally radioactiveisotopes: Os-184 = 0.02% and Os-186 = 1.59%. All the other isotopes of osmium areradioactive and artificially produced in nuclear reactors and particle accelerators.
Origin of Name
Its name is derived from the Greek word osme, meaning “odor” or
“smell,” because of the element’s objectionable smell when it is first isolated from platinum
ores using aqua regia.
Occurrence
Osmium is the 80th most abundant element on Earth. As a metal, it is not found free innature and is considered a companion metal with iridium. It is also found mixed with platinum-and nickel-bearing ores. It is recovered by treating the concentrated residue of these oreswith aqua regia (a mixture of 75% HCl and 25% HNO). The high cost of refining osmium ismade economically feasible by also recovering marketable amounts of platinum and nickel.
Osmium occurs along with iridium in nature as the mineral iridosmine. It is found inCanada, Russia, and parts of Africa.
Characteristics
Osmium is found in group 8 (VIII) of the periodic table and has some of the same chemical,physical, and historical characteristics as several other elements. This group of similarelements is classed as the platinum group, which includes Ru, Rh, and Pd of the second transitionseries and Os, Ir, and Pt of the third series of transition metals .
Uses
Because of its hard brittle nature, the metal osmium has few uses. However, the powderedform can be sintered under high pressure and temperatures to form some useful products,despite its toxicity and malodor. Its main use is as an alloy to manufacture devices that resistwear and stand up to constant use. As an alloy, osmium loses both its foul odor and toxicity.Some of these products are ballpoint and fountain pen tips, needles for record players, andpivot points for compass needles. Osmium alloys are also used for contact points on specialswitches and other devices that require reduced frictional wear.
Another use is as a stain for animal tissues that are to be examined with a microscope toimprove the contrast of the specimen.
Uses
Osmium, plasma standard solution is used as a standard solution in analytical chemistry and atomic absorption spectroscopy. It is also used as a single-element standard solution for plasma emission spectrometry.
Definition
A transition metal that is found associated with platinum. Osmium is the most dense of all metals. It has a characteristic smell resulting from the production of osmium(VIII) oxide (osmium tetroxide, OsO4). The metal is used in catalysts and in alloys for pen nibs, pivots, and electrical contacts. Symbol: Os; m.p. 3054°C; b.p. 5027°C; r.d. 22.59 (20°C); p.n. 76; r.a.m. 190.23.
Definition
osmium: Symbol Os. A hard bluewhitemetallic transition element;a.n. 76; r.a.m. 190.2; r.d. 22.57; m.p.3045°C; b.p. 5027°C. It is found associatedwith platinum and is used incertain alloys with platinum and iridium(see osmiridium). Osmium formsa number of complexes in a range ofoxidation states. It was discovered bySmithson Tennant (1761–1815) in1804.
Production Methods
Osmium is obtained in the reaction of osmium tetroxide
(OsO4) reduction with carbon at red heat temperature.
Osmium is also obtained from osmiridium. After separation
from other metals with aqua regia, osmiridium is distilled
in chlorine stream with formation of osmium tetrachloride
(OsCl4), from which the metal is recovered by
reduction.
Hazard
Most of the oxides of osmium are not noxious, but are toxic if inhaled or ingested. Thecompound OsO4 is extremely poisonous. It is a powerful oxidizing agent that is soluble inwater and will produce serious burns in skin as it oxidizes the various layers of tissues.
Industrial uses
A platinum-group metal, osmium is noted for its high hardness, about 400 Brinell. The heaviest known metal, it has a high specific gravity, 22.65, and a high melting point, 2698 C. The boiling point is about 5468 C. Osmium has a close-packed hexagonal crystal structure, and forms solid-solution alloys with platinum, having more than double the hardening power of iridium in platinum. However, it is seldom used to replace iridium as a hardener except for fountain-pen tips where the alloy is called osmiridium.
Osmium is not affected by the common acids, and is not dissolved by aqua regia. It is practically unworkable, and its chief use is as a catalyst.
Osmium tetraoxide, a commercially available yellow solid (melting point 40 C) is used commercially as a stain for tissue in microscopy. It is poisonous and attacks the eyes. Osmium metal is catalytically active, but it is not commonly used for this purpose because of its high price. Osmium and its alloys are hard and resistant to corrosion and wear (particularly to rubbing wear). Alloyed with other platinum metals, osmium has been used in needles for record players, fountain-pen tips, and mechanical parts.
storage
Color Code—Blue: Health Hazard/Poison(osmium tetroxide): Store in a secure poison location. Priorto working with this chemical you should be trained on itsproper handling and storage. Store refrigerated in tightlyclosed containers away from hydrochloric acid, reducingagents and easily oxidized materials. Where possible, automatically pump liquid from drums or other storage containers to process containers. Sources of ignition, such assmoking and open flames, are prohibited where this chemical is handled, used, or stored. Metal containers involvingthe transfer of 5 gallons or more of this chemical should begrounded and bonded. Drums must be equipped with selfclosing valves, pressure vacuum bungs, and flame arresters. Use only nonsparking tools and equipment, especially whenopening and closing containers of this chemical. Whereverthis chemical is used, handled, manufactured, or stored, useexplosion-proof electrical equipment and fittings. SeeOSHA Standard 1910.104 and NFPA 43A Code for theStorage of Liquid and Solid Oxidizers for detailed handlingand storage regulations.
Shipping
Osmium tetroxide requires a shipping label of“POISONOUS/TOXIC MATERIALS.” It falls in HazardClass 6.1 and Packing Group I.
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