Zirconium (Zr)
Zirconium is a refractory metal best known for its critical role in nuclear reactor fuel rod cladding, where its low neutron absorption cross-section is unmatched. It also offers exceptional corrosion resistance to many acids and alkalis, driving applications in chemical processing. Zirconia (ZrO₂) ceramic is widely used in dental crowns and technical ceramics.
Properties
- Density
- 6,506 kg/m³
- Melting Point
- 1,855 °C
- Boiling Point
- 4,409 °C
- Thermal Conductivity
- 22.6 W/(m·K)
- Electrical Resistivity
- 4.21 × 10⁻⁷ Ω·m
- Tensile Strength
- 330–550 MPa
- Yield Strength
- 230–380 MPa
- Hardness
- 120–200 HB
- Elongation
- 16–32%
- Crystal Structure
- HCP (α) / BCC (β)
Common Grades
- Zr 702 (R60702): Commercially pure zirconium. Chemical processing — heat exchangers, reactor vessels, piping.
- Zr 705 (R60705): Zr-Nb alloy, higher strength. Pressure vessels, valves, pumps in corrosive service.
- Zircaloy-4 (Zr-Sn-Fe-Cr): Nuclear-grade alloy. Fuel rod cladding, fuel assembly components in PWR/BWR reactors.
- ZrO₂ (Zirconia): Zirconium oxide ceramic. Dental crowns, oxygen sensors, thermal barrier coatings.
Applications
- Nuclear: Fuel rod cladding, fuel assembly spacers, calandria tubes, pressure tubes
- Chemical Processing: HCl and H₂SO₄ resistant piping, heat exchangers, reactor vessels, valves
- Medical/Dental: Zirconia dental crowns and bridges, femoral heads for hip replacements
- Ceramics: Oxygen sensors (lambda probes), thermal barrier coatings in jet engines, cutting tools
FAQ
Why is zirconium used in nuclear reactors?
Zirconium has an extremely low thermal neutron absorption cross-section (0.18 barns vs. 2.56 for stainless steel), allowing neutrons to pass through fuel cladding efficiently. Combined with good corrosion resistance in high-temperature water (300°C+) and adequate mechanical strength, it is the only practical fuel cladding material for light-water reactors.
What is the difference between zirconium and zirconia?
Zirconium (Zr) is the metallic element used for chemical processing and nuclear applications. Zirconia (ZrO₂) is zirconium oxide, an extremely hard ceramic used for dental crowns, oxygen sensors, and thermal barrier coatings. They have completely different properties — zirconia has no metallic character and melts at 2,715°C.
Why must hafnium be removed from nuclear-grade zirconium?
Hafnium (Hf) naturally occurs with zirconium in ore but has a neutron absorption cross-section 600× higher than Zr (105 vs 0.18 barns). Nuclear-grade zirconium (Zircaloy) must contain <100 ppm Hf to maintain neutron economy. This expensive separation process (liquid-liquid extraction) is a major contributor to nuclear-grade zirconium's cost.