Rhodium

History

(Gr. rhodon: rose) Wollaston discovered rhodium between 1803 and 1804 in crude platinum ore he presumably obtained from South America.[1]

Sources

Rhodium occurs natively with other platinum metals in river sands of the Urals and in North and South America. It is also found with other platinum metals in the copper-nickel sulfide area of the Sudbury, Ontario region. Although the quantity occurring there is very small, the large tonnages of nickel processed make the recovery commercially feasible. The annual world production of rhodium is only 7 or 8 tons.[1]

Properties

General
Name : rhodium
Symbol : Rh
Atomic Number : 45
Chemical Series : Transition Metal
Block, Period : 9, 5
Appearance : silvery white metallic
Atomic Properties
Atomic Weight : 102.90550
Covalent Radius (pm) : 135
Physical Properties
Matter : solid (paramagnetic)
Density (kg/) : 12450
Hardness (Mohs): 6
Melting Point (K) : 2237
Boiling Point (K) : 3968
Evaporation Heat (kJ/mol) : 493
Fusion Heat (kJ/mol) : 21.5
Specific Heat (J/(kg*K) ) : 0.242
Miscellaneous
Electrical Conductivity (/m ohm) : 21.1
Thermal Conductivity (W/(m*K) ) : 150

The metal is silvery white and at red heat slowly changes in air to the resquioxide. At higher temperatures it converts back to the element. Rhodium has a higher melting point and lower density than platinum. It is highly reflective, hard, and durable.[1]

Uses

Rhodium's primary use is as an alloying agent to harden platinum and palladium. Such alloys are used for furnace windings, thermocoupling elements, bushings for glass fiber production, electrodes for aircraft spark plugs, and laboratory crucibles. It is useful as an electrical contact material as it has a low electrical resistance, a low and stable contact resistance, and is highly resistant to corrosion. Plated rhodium, produced by electroplating or evaporation, is exceptionally hard and is used for optical instruments. Rhodium is also used for jewelry, for decoration, and as a catalyst.[1]

Handling

Exposure to rhodium (metal fume and dust, as Rh) should not exceed 1 mg/m^3 (8-hour time-weighted average, 40-hour week).[1]

Notes

[1] From Los Alamos National Laboratory's Chemistry Division Website