Rhodium (Rh) - Properties, Applications

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.

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