Zirconium
Atomic Data
| Atomic Number | 40 |
| Symbol | Zr |
| Atomic Weight | 91.224 u |
| Density (STP) | 6.52 g/cm³ |
| Melting Point | 1854.85 °C (2128 K) |
| Boiling Point | 4408.85 °C (4682 K) |
| Electronegativity | 1.33 (Pauling) |
| Electron Config. | 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d2 5s2 |
| Oxidation States | +4 |
| Phase at STP | Solid |
| Category | Transition Metal |
| Period / Group | 5 / 4 |
| CAS Number | 7440-67-7 |
Electron Configuration
[Kr] 4d2 5s2
| Shell | n | Subshell | Electrons | Cumulative |
|---|---|---|---|---|
| K | 1 | 1s | 2 | 2 |
| L | 2 | 2s | 2 | 4 |
| L | 2 | 2p | 6 | 10 |
| M | 3 | 3s | 2 | 12 |
| M | 3 | 3p | 6 | 18 |
| M | 3 | 3d | 10 | 28 |
| N | 4 | 4s | 2 | 30 |
| N | 4 | 4p | 6 | 36 |
| N | 4 | 4d | 2 | 38 |
| O | 5 | 5s | 2 | 40 |
| Total | 40 | 40 | ||
Isotopes of Zirconium
Zirconium has five naturally occurring stable isotopes. The most abundant is ⁹⁰Zr, comprising 51.45% of all naturally occurring Zirconium.
| Isotope | Symbol | Protons | Neutrons | Abundance | Stability |
|---|---|---|---|---|---|
| Zirconium-90 | ⁹⁰Zr | 40 | 50 | 51.45 | Stable |
| Zirconium-91 | ⁹¹Zr | 40 | 51 | 11.22 | Stable |
| Zirconium-92 | ⁹²Zr | 40 | 52 | 17.15 | Stable |
| Zirconium-94 | ⁹⁴Zr | 40 | 54 | 17.38 | Stable |
| Zirconium-96 | ⁹⁶Zr | 40 | 56 | 2.8 | Stable |
Abundance & Occurrence
Zirconium is present in Earth's crust at approximately 165 ppm by mass and at approximately 4 ppm by mass throughout the universe.
Earth's Crust (ppm by mass)
Universe (ppm by mass)
Discovery & History
Read more about the discovery of the periodic table of elements →
Safety & Handling
- Zirconium powder fire hazard: Finely divided zirconium powder is highly pyrophoric: it can ignite spontaneously in air and burns intensely; it is classified as a dangerous explosive dust and must be handled under inert gas or water.
- Zirconium tetrachloride: ZrCl4 reacts violently with water, producing HCl; it is corrosive to skin, eyes, and respiratory tract and must be handled in dry conditions.
- Bulk metal: low toxicity: Bulk zirconium metal has low systemic toxicity and good biocompatibility (used in medical and dental implants); primary hazards are physical (fire/dust) rather than toxic.
- Radiation: natural isotopes: Natural zirconium contains trace Zr-96, a very long-lived beta emitter; at natural abundance levels, the radioactivity is negligible for practical handling purposes.
Zirconium in the Real World
Real-World Uses
- Nuclear reactor fuel cladding: Zircaloy (a zirconium alloy) has extremely low neutron absorption and excellent corrosion resistance in hot water, making it the standard cladding material for uranium dioxide fuel pellets in light-water nuclear reactors.
- Zirconia ceramics: Yttria-stabilised zirconia (YSZ) is used in dental crowns and bridges (tooth-white colour, high fracture toughness), thermal barrier coatings on turbine blades, and ceramic knife blades.
- Refractory materials: Zirconium dioxide withstands temperatures above 2700 °C and resists attack by molten metals and slags, used in crucibles, furnace linings, glass tank blocks, and investment casting moulds for superalloys.
- Optical coatings: Zirconium dioxide thin films are used as hard, wear-resistant anti-reflection coatings on optical lenses and as dielectric layers in multilayer interference filters for laser optics.
- Foundry applications: Zircon sand (ZrSiO₄) is a premium foundry moulding sand for casting metals because its high melting point and low thermal expansion prevent burn-on defects and dimensional errors in steel and aluminium castings.
Downloadable Resources
Free periodic table reference sheets for classrooms, study sessions, and laboratory use.
Frequently Asked Questions
What is zirconium used for?
Zirconium's most important use is in nuclear reactors: it is used as cladding for uranium fuel rods because it has a very low neutron-absorption cross-section, excellent corrosion resistance in hot water, and adequate mechanical strength. Zirconium is also used in chemical plant equipment for corrosive environments, in heat exchangers, and zirconium dioxide (zirconia) is used in high-performance ceramics and as a diamond simulant.
Is zirconium safe?
Zirconium metal and most of its compounds have low toxicity and are generally considered safe. Zirconium compounds are used in deodorant sticks (zirconium chlorohydrate) and have been used in some medical applications. It is not considered to be a cumulative toxin or carcinogen. The main hazard is from fine zirconium powder, which is flammable.
How was zirconium discovered?
Zirconium was identified as a new element in 1789 by German chemist Martin Heinrich Klaproth in the mineral jargon (a type of zircon). The metal was first isolated in impure form in 1824 by Swedish chemist Jöns Jacob Berzelius. Pure zirconium metal was not produced until 1925, when Anton Eduard van Arkel and Jan Hendrik de Boer developed the crystal bar process. The name comes from 'zircon', from the Arabic 'zarqun' meaning gold-coloured.
Why is zirconium crucial for nuclear reactors?
In a nuclear reactor, the fuel cladding must allow neutrons to pass through freely to sustain the chain reaction, while containing the radioactive fuel and fission products. Zirconium absorbs very few neutrons (its thermal neutron absorption cross-section is about 0.18 barns), far less than most structural metals. Combined with its excellent corrosion resistance in pressurised hot water and adequate strength, this makes zirconium alloys (Zircaloys) the standard choice for light-water reactor fuel cladding.