Hafnium was discovered in 1923 as a novel metal by Hevesy and Coster. In nature, it exists in combination with zirconium and its alloys have high refractory properties.
History and Discovery
Hafnium was discovered as a novel element by Georg von Hevesy and Dirk Coster in 1923. They analyzed the mineral zircon through X-ray spectroscopic analysis and found the novel element Hafnium. However, its presence was predicted by Dmitri Mendeleev (1869). The name hafnium has been derived from Latin word Hafnia, that was the name of Copenhagen, the home town of Niels Bohr and the discoverers of hafnium. Bohr’s theory predicted that a novel element was associated with zirconium [1].
Hafnium
| Periodic Table Classification | Group 4 Period 6 |
|---|---|
| State at 20C | Solid |
| Color | Steel gray |
| Electron Configuration | [Xe] 4f14 5d2 6s2 |
| Electron Number | 72 |
| Proton Number | 72 |
| Electron Shell | 2, 8, 18, 32, 10, 2 |
| Density | 13.31 g.cm-3 at 20°C |
| Atomic number | 72 |
| Atomic Mass | 178.49 g.mol -1 |
| Electronegativity according to Pauling | 1.3 |
Occurrence
Hafnium is not very abundant element and is found in a concentration of about 5.8 ppm in the Earth’s crust. Hafnium does not exist in free metallic form in nature. It is found in combined mineral with zirconium, including thortveitite, alvite [(Hf, Th, Zr) SiO4 H2O] and zircon (ZrSiO4). Hafnium is obtained as byproduct during the refinement of zirconium. However, the separation of hafnium and zirconium is extremely difficult as the two elements closely resemble reach other. Large mineral deposits of hafnium and zirconium have been found in Malawi and Brazil and Australia [2].
Physical Characteristics
Hafnium is a greyish-silver lustrous metal. It is a transition metal and resembles zirconium in its chemical properties, as both have equal number of valence electrons. It is ductile and is resistant to corrosion. Hafnium is denser than zirconium.
Chemical Characteristics
Hafnium is resistant to attacks by concentrated alkalis. It reacts with halogens to form hafnium tetrahalides. When exposed to air, hafnium forms a protective layer on its surface that is prves to be protective against corrosion. Hafnium also react with carbon, oxygen, sulfur and nitrogen, at elevated temperatures. Hafnium nitride is characterized as the most refractory of all nitrides of metals, and it has melting point of as high as 3310°C. So, it can withstand high temperatures. It has significant nuclear properties as it can absorb high thermal neutrons, whereas, zirconium is transparent to neutrons. The common oxidation state of hafnium is +4. Compounds of hafnium and zirconium have similar attributes.
Significance and Uses
- Hafnium is widely used to make neutron absorbing rods (control rods) in nuclear reactors.
- Hafnium is used in incandescent lamps, as it can scavenge nitrogen and oxygen.
- Hafnium dioxide is being considered as an ideal candidate for use as insulators in High-K gates used in integrated circuits.
- Hafnium nuclear isomer, Hf-178-ms has potential for use in nuclear energy generation projects and nuclear war heads.
- Hafnium is used to make electrodes and filaments.
- Hafnium is used to make various superalloys, with tungsten, niobium and titanium that are used in various significant applications.
- Hafnium and its carbides are widely used as construction materials that are exposed to very high temperature.
- Hafnium alloys are used in making simulation of supercomputer that can withstand temperatures as high as 4400 K [3].
Health Hazards
Hafnium metal is non-toxic. However, exposure of various compounds and salts of hafnium are considered potentially dangerous. Hafnium in powdered or fine divided form is considered hazardous and needs to be handled with care. As powdered hafnium can spontaneously ignite when exposed to air (pyrophoric).
Isotopes of Hafnium
Hafnium has 34 isotopes, with mass number ranging from 153 to 186 [3]. There are five stable isotopes of hafnium, hafnium-176 to 180. The most stable radioactive isotope is hafnium-174, that has a half-life of 1015 years [4].
REFERENCES
[1]. Bob Weintraub, George De Hevesy (1885 1966) (pdf document)
[2]. Dubbo Zirconia Project Fact Sheet” (PDF). Alkane Resources Limited. June 2007. Archived from the original (PDF) on 2008-02-28. Retrieved 2008-09-10.
[3]. Georges, Audi; Bersillon, O.; Blachot, J.; Wapstra, A. H. (2003). “The NUBASE Evaluation of Nuclear and Decay Properties”. Nuclear Physics A. Atomic Mass Data Center. 729: 3–128. Bibcode:2003NuPhA.729….3A. doi:10.1016/j.nuclphysa.2003.11.001.
[4]. EnvironmentalChemistry.com. “Hafnium Nuclides / Isotopes”. Periodic Table of Elements. J.K. Barbalace. Retrieved 2008-09-10.