Supplier Data - Rhodium (Rh) (Goodfellow)

Rhodium (Rh) was discovered in 1803 by W.H. Woolaston in London.

One of the rarest metals on earth (abundance of 2 x 10-4 ppm), Rhodium does not appear naturally, tending to be found with other platinum group metals.

It is a hard, lustrous, silvery coloured metal which is stable in air. Rhodium is inert to all acids but is attacked by fused alkalis.

The metal has high thermal and electrical conductivities and is alloyed with platinum to form the positive wire of a Pt/Rh - Pt thermocouple.

Other applications of Rhodium include its use as a plating material (to provide a hard and bright surface which is resistant to oxidation), as a catalyst and also as an alloying element, where it improves the hardness of the resulting alloy.

Typical Properties

The key properties of Rhodium are tabulated below.

Table 1. Key properties

Atomic Properties
Atomic number 45
Atomic radius - Goldschmidt ( nm ) 0.134
Atomic weight ( amu ) 102.9055
Crystal structure Face centred cubic
Electronic structure Kr 4d8 5s1
Ionisation potential No. eV
1 7.46
2 18.1
3 31.1
Natural isotope distribution Mass No. %
103 100
Photo-electric work function ( eV ) 4.6
Thermal neutron absorption cross-section ( Barns ) 150
Valences shown 2, 3, 4, 5, 6
Electrical Properties
Electrical resistivity @ 20 C ( µOhm.cm ) 4.7
Temperature coefficient @ 0-100 C ( K-1 ) 0.0044
Thermal emf against Pt (cold 0 °C - hot 100 °C) ( mV ) +0.70
Mechanical Properties
Material condition Soft Hard Polycrystalline
Bulk modulus ( GPa ) 276
Hardness – Vickers 120 300
Poisson's ratio 0.26
Tensile modulus ( GPa ) 379
Tensile strength ( MPa ) 690-760 1380-2070
Yield strength ( MPa ) 69-275
Physical Properties
Boiling point (°C ) 3727
Density @ 20 C ( g.cm-3 ) 12.4
Melting point (°C ) 1965
Thermal Properties
Coefficient of thermal expansion @ 0-100 C ( x10-6 K-1 ) 8.5
Latent heat of evaporation ( J.g-1 ) 4800
Latent heat of fusion ( J.g-1 ) 210
Specific heat @ 25 C ( J.K-1.kg-1 ) 244
Thermal conductivity @ 0-100 C ( W.m-1.K-1 ) 150

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