Aug 7 2013
Topics Covered
Introduction
Chemical Properties
Physical Properties
Mechanical Properties
Thermal Properties
Applications
Introduction
Rhodium is a rare, silvery-white, hard, and chemically inert metal that belongs to group 9 and period 5. It was first discovered in 1803 by William Hyde Wollaston. It is found as free element in nature and also as a chemical compound in minerals such as rhodplumsite and bowieite. It can be obtained as a by-product of mining and refining platinum.
When heated, the element becomes an oxide and turns back to its elemental form at high temperatures. It is resistant to corrosion and alloyed with platinum or palladium for high-temperature applications.
Chemical Properties
The chemical properties of rhodium are provided in the table below.
| Chemical Data |
| CAS number |
7440-16-6 |
| Thermal neutron cross section |
2.6 barns/atom |
| Electrode potential |
0.80 V |
| Ionic radius |
0.680 Å |
| Electronegativity |
2.28 |
| X-ray absorption edge |
0.533 Å |
Physical Properties
The following table discusses the physical properties of rhodium.
| Properties |
Metric |
Imperial |
| Density |
12.4 g/cm3 |
0.448 lb/in3 |
| Melting point |
1960°C |
3560°F |
| Boiling point |
3695°C |
6683°F |
Mechanical Properties
The mechanical properties of rhodium are tabulated below.
| Properties |
Metric |
Imperial |
| Tensile strength |
951 MPa |
138000 psi |
| Modulus of elasticity |
359 GPa |
52100 ksi |
| Shear modulus |
150 GPa |
21756 ksi |
| Bulk modulus |
380 GPa |
55114 ksi |
| Poisson’s ratio |
0.26 |
0.26 |
| Hardness, Brinell |
89 |
89 |
| Hardness, Vickers |
100 |
100 |
| Hardness, Rockwell A |
35 |
35 |
| Hardness, Rockwell B |
51 |
51 |
| Young Modulus |
275 GPa |
39885 ksi |
Thermal Properties
The thermal properties of rhodium are tabulated below.
| Properties |
Metric |
Imperial |
| Thermal expansion co-efficient (@20-100°C/68-212°F) |
8.50 µm/m°C |
4.72 µin/in°F |
| Thermal conductivity |
151 W/mK |
1050 BTU in/hr.ft².°F |
Applications
The primary use of rhodium is in automotives as a catalytic converter that converts harmful unburned hydrocarbons and nitrogen oxide emissions into less noxious gases. It is also used in the glass industry for the production of flat-panel glass and fiberglass.
Other major applications of rhodium include:
- Jewelry
- Furnace windings
- Electrodes for aircraft spark plugs
- Thermocouple elements
- Mammography systems
- Nuclear reactors.