Quick Facts
| Property | Value |
|---|---|
| Symbol | Zr |
| Atomic Number | 40 |
| Atomic Mass | 91.224 u |
| Category | Transition Metal |
| Period | 5 |
| Group | 4 |
| Block | d |
| Electron Configuration | [Kr] 4d² 5s² |
Physical Properties
| Property | Value |
|---|---|
| State at 20°C | Solid |
| Density | 6.52 g/cm³ |
| Melting Point | 1855°C (2128 K) |
| Boiling Point | 4409°C (4682 K) |
| Appearance | Silvery-gray, lustrous metal |
Atomic Properties
| Property | Value |
|---|---|
| Electron Configuration | [Kr] 4d² 5s² |
| Electronegativity | 1.33 (Pauling scale) |
| First Ionization Energy | 640.1 kJ/mol |
| Atomic Radius | 160 pm |
| Covalent Radius | 175 pm |
| Van der Waals Radius | 186 pm |
History and Discovery
Discovered by: Martin Heinrich Klaproth Year of Discovery: 1789 Location: Berlin, Germany
Etymology
Named from "zircon," the mineral in which it was discovered, which comes from Arabic "zarqun" (vermilion) or Persian "zargun" (gold-colored).
Discovery Story
Martin Heinrich Klaproth discovered zirconium in 1789 while analyzing the gemstone jargon (zircon). He produced zirconium oxide but could not isolate the metal. Jöns Jacob Berzelius produced impure zirconium in 1824. Pure zirconium metal was not obtained until 1914.
Isotopes
| Isotope | Natural Abundance | Half-life | Decay Mode |
|---|---|---|---|
| ⁹⁰Zr | 51.45% | Stable | - |
| ⁹¹Zr | 11.22% | Stable | - |
| ⁹²Zr | 17.15% | Stable | - |
| ⁹⁴Zr | 17.38% | Stable | - |
| ⁹⁶Zr | 2.80% | 2.0 × 10¹⁹ years | β⁻β⁻ |
Occurrence
Natural Abundance
Zirconium is the 19th most abundant element in Earth's crust (about 165 ppm). Main ores are zircon (ZrSiO₄) and baddeleyite (ZrO₂). Major producers are Australia, South Africa, and China. Zircon is also a common heavy mineral in beach sands.
Extraction and Production
- Kroll Process: Reduction of zirconium tetrachloride with magnesium
- Van Arkel-de Boer Process: For high-purity metal
- Sources: Zircon sand mining
- Global production: about 1.4 million tons of zircon annually
Applications and Uses
Nuclear Industry
- Nuclear reactor fuel rod cladding (zircaloy)
- Low neutron absorption cross-section
- High-temperature corrosion resistance
Ceramics and Refractories
- Zirconia ceramics (extremely hard)
- Dental crowns and implants
- Crucibles and furnace linings
- Foundry sands
Chemical Industry
- Corrosion-resistant equipment
- Chemical process vessels
- Heat exchangers
Other Uses
- Cubic zirconia gemstones
- Surgical instruments
- Explosive primers
- White pigments (zirconium silicate)
Biological Role
Zirconium has no known biological role and is not essential for any organism.
In the Human Body
Zirconium is not normally present in significant amounts. It has low toxicity due to poor absorption.
Medical Uses
Zirconia ceramics are used in dental implants and prosthetics due to their biocompatibility and strength.
Safety and Hazards
Toxicity
Zirconium and most of its compounds have low toxicity. It is poorly absorbed by the body.
Handling Precautions
- Zirconium powder is highly flammable and can explode
- Use in well-ventilated areas
- Store away from oxidizers
- Metal dust requires careful handling
Environmental Impact
Zirconium mining (heavy mineral sands) can affect coastal environments. The metal itself is non-toxic and environmentally benign.
Interesting Facts
- Zirconium is nearly transparent to neutrons, making it ideal for nuclear reactor cladding
- Cubic zirconia is a popular diamond simulant
- The Fukushima accident involved zirconium cladding failures
- Zirconium and hafnium are so chemically similar that separation is difficult
- Ancient zircon crystals (4.4 billion years old) are the oldest known minerals on Earth