Zirconium
Zirconium is a chemical element with symbol Zr and atomic number 40. The name of zirconium is taken from the name of the mineral zircon, the most important source of zirconium. The word zircon comes from the Persian word zargun زرگون, meaning "gold-colored".
Identity
- Atomic mass
- 91.224 u
- Category
- Transition metals
- Group
- 4
- Period
- 5
- Block
- d
- Oxidation States
- +4
- Phase (25 °C)
- Solid
- Appearance
- silvery white
Electronic Structure
- Electron configuration
- 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d2
- Short configuration
- [Kr] 4d2 5s2
- Electrons per shell
- 2, 8, 18, 10, 2
- Electronegativity (Pauling)
- 1.33
- Electron affinity
- 41.8 kJ/mol
- 1st ionization energy
- 640 kJ/mol
- Ionization energies
- 640 · 1270 · 2218 · 3313 · 7752… kJ/mol
Physical properties
- Melting point
- 1854.8 °C (2128 K)
- Boiling point
- 4376.9 °C (4650 K)
- Density
- 6.52 g/cm³
- Molar heat capacity
- 25.4 J/(mol·K)
Chemical behavior of zirconium
Zirconium is a group 4 transition metal with symbol Zr and atomic number 40. It is a soft silvery-gray metal, corrosion resistant and refractory. Its most stable oxidation state is +4, with +2 and +3 in specific phases. It resembles hafnium and behaves as a high-strength, heat-resistant metal.
Reactivity
Zr + 2 Cl2 -> ZrCl4
Zirconium reacts with chlorine forming zirconium tetrachloride, a colorless liquid that is the main precursor of zirconium compounds.
Zr + 2 H2O (hot) -> ZrO2 + 2 H2
Zirconium reacts with steam at high temperatures, forming zirconium dioxide and releasing hydrogen.
Notable compounds
| Compound | Formula | Use or importance |
|---|---|---|
| Zirconium dioxide | ZrO2 | White ceramic; used in dental prostheses, tools and technical components |
| Zirconium tetrachloride | ZrCl4 | Colorless liquid; precursor of compounds and chlorination reagent |
| Metallic zirconium | Zr (pura) | Structural material; used in nuclear reactors and chemical equipment |
Electron shell distribution
View in the atom builderIsotopes
Natural zirconium has five isotopes: zirconium-90 (51.5 %), zirconium-94 (17.4 %), zirconium-92 (17.2 %), zirconium-91 (11.2 %) and zirconium-96 (2.8 %). Zirconium-96 is slightly radioactive with an immense half-life, effectively stable for applications.
Occurrence and production
About 0.013 % of the crust (19th most abundant). Main minerals are zircon (ZrSiO4) and baddeleyite (ZrO2). Leading resources are in Australia, South Africa, India, Mozambique and the United States. Metal is made by the Kroll-type reduction of tetrachloride with magnesium.
History and origin of the name
Martin Heinrich Klaproth identified its oxide in zircon in 1789. Jons Jacob Berzelius isolated impure metal in 1824 from tetrachloride with potassium. The name comes from zircon, via Persian zargun (gold-colored). Pure ductile metal waited for 20th-century processes.
Applications and relevance of zirconium
Uses of the element
Its low neutron absorption makes Zircaloy cladding the standard for nuclear fuel rods. It also builds chemical equipment (vessels, heat exchangers, pumps), aerospace parts and high-end watch cases needing corrosion resistance.
Uses of its compounds
Zirconia dominates: dental crowns, cutting ceramics, oxygen sensors, fuel-cell electrolytes and cubic zirconia gems. Zircon sands serve foundries and refractories; salts catalyze and opacify.
Health, safety and environment
Biological role
Zirconium is not essential and is considered low toxicity; it does not accumulate in tissues. Fine dust can irritate airways and skin, but bulk metal and zirconia are biocompatible enough for dental and joint implants.
Safety
Compact metal is stable, but fine powder is flammable and can ignite. Chloride precursors are corrosive. Work needs ventilation, dust control and protection for eyes and airways.
Environment
Zircon mining is mostly sand mining with land and water impacts to manage. Zirconia products are inert and long-lived; recycling refractories and ceramics trims demand for fresh sand.
Frequently asked questions about Zirconium
Why is zirconium used in nuclear reactors?
Zirconium alloys absorb very few neutrons, so fuel cladding barely perturbs fission while resisting hot pressurized water. Zircaloys sheath uranium pellets for years. Hafnium must first be removed because, unlike zirconium, it strongly absorbs neutrons.
Why is zirconia used in dental crowns?
It combines strength, chemical stability and tooth-like looks with tunable translucency. Modern formulations balance aesthetics and toughness. Success still depends on design, milling and placement by the dentist.
Why is zirconium used in chemical equipment?
It forms a protective oxide film resisting many aggressive media. Selected grades suit vessels, exchangers and parts in acid and chloride duties. Choice must weigh temperature, concentration, exact chemistry, cost and fabrication.
Why is zirconium important in advanced ceramics?
Zirconia takes several crystal structures by temperature and additives. Stabilizing them yields tough, thermal-shock resistant or ion-conducting ceramics for industry, dentistry, sensors and fuel cells, depending on formulation.
What is the difference between zirconium metal and zirconia?
Zirconium is a corrosion-resistant metal for reactors and chemical plant; zirconia is its oxide ceramic, very hard and heat-stable, for crowns, tools and linings. Both contain zirconium but properties and uses differ completely.
How can zirconia be used in knives and cutting tools?
Zirconia technical ceramics are very hard and wear resistant, holding an edge long in suitable uses. But ceramics are more brittle under impact than steel, so they do not replace steel everywhere. Composition and microstructure decide performance.
What is cubic zirconia and why in jewelry?
A synthetic cubic form of zirconium dioxide made transparent, brilliant and colored, imitating diamond at low cost. Composition and physics differ from diamond. Do not confuse it with zircon, the natural silicate mineral.
Main sources consulted: PubChem, Royal Society of Chemistry, NIST, IUPAC. Last revision: November 2026.