|
|
| General |
| Name, Symbol, Number | Hafnium, Hf, 72 |
| Chemical series | Transition metals |
| Group, Period, Block | 4 (IVB)[?], 6 , d |
| Density, Hardness | 13310 kg/m3, 5.5 |
| Appearance | grey steel |
| Atomic Properties |
| Atomic weight | 178.49 amu |
| Atomic radius (calc.) | 155 (208) pm |
| Covalent radius | 150 pm |
| van der Waals radius | no data |
| Electron configuration | [Xe]4f14 5d2 6s2 |
| e- 's per energy level | 2, 8, 18, 32, 10, 2 |
| Oxidation state (Oxide) | 4 (amphoteric) |
| Crystal structure | Hexagonal |
| Physical Properties |
| State of matter | solid |
| Melting point | 2506 K (4051 °F) |
| Boiling point | 4876 K (8317 °F) |
| Molar volume | 13.44 ×10-3 m3/mol |
| Heat of vaporization | 575 kJ/mol |
| Heat of fusion | 24.06 kJ/mol |
| Vapor pressure | 0.00112Pa at 2500K |
| Speed of sound | 3010 m/s at 293.15 K |
| Miscellaneous |
| Electronegativity | 1.3 (Pauling scale) |
| Specific heat capacity | 140 J/(kg*K) |
| Electrical conductivity | 3.12 106/m ohm |
| Thermal conductivity | 23 W/(m*K) |
| 1st ionization potential | 658.5 kJ/mol |
| 2nd ionization potential | 1440 kJ/mol |
| Most Stable Isotopes |
| iso | NA | half-life | DM | DE MeV | DP |
| 172Hf | {syn.} | 1.87 y | ε | 0.350 | 172Lu |
| 174Hf | 0.162% | 2 E15 y | α | 2.495 | 170Yb
|
| 176Hf | 5.206% | Hf is stable with 104 neutrons |
| 177Hf | 18.606% | Hf is stable with 105 neutrons |
| 178Hf | 27.297% | Hf is stable with 106 neutrons |
| 179Hf | 13.629% | Hf is stable with 107 neutrons |
| 180Hf | 35.1% | Hf is stable with 108 neutrons |
| 182Hf | {syn} | 9 E6 y | β | 0.373 | 182Ta
|
|
| SI units & STP are used except where noted. |
Hafnium is a
chemical element in the
periodic table that has the symbol Hf and
atomic number 72. A lustrous, silvery gray tetravalent
transition metal, hafnium resembles
zirconium chemically and is found in zirconium
minerals. Hafnium is used in
tungsten alloys in filaments and
electrodes and also acts as a
neutron absorber in nuclear control rods.
This is a shiny silvery, ductile
metal that is
corrosion resistant and chemically similar to
zirconium. The properties of hafnium are markedly affected by zirconium impurities and these two elements are amongst the most difficult to separate. The only notable difference between them is their density (zirconium is about half as dense as hafnium).
Hafnium carbide is the most refractory binary compound known and hafnium nitride is the most refractory of all known metal nitrides with a melting point of 3310 °C).
This metal is resistant to concentrated alkalis, but halogens react with it to form hafnium tetrahalides. At higher temperatures hafnium reacts with oxygen, nitrogen, carbon, boron, sulfur, and silicon.
The nuclear isomer Hf-178-2m is also a source of energetic gamma rays, and is being studied as a possible power source for gamma ray lasers.
Hafnium is used to make nuclear control rods, such as those found in
nuclear submarines because of its ability to absorb
neutrons (its thermal neutron absorption cross section is nearly 600 times that of zirconium), excellent mechanical properties and exceptional corrosion-resistance properties. Other uses;
Hafnium (
Latin Hafnia for "
Copenhagen") was discovered by
Dirk Coster[?] and
Georg von Hevesy[?] in
1923 in Copenhagen,
Denmark. Soon after, the new element was predicted to be associated with
zirconium by using the Bohr theory and was finally found in zircon through
X-ray spectroscope analysis in
Norway.
It was separated from zirconium through repeated recrystallization of double ammonium or potassium fluorides by Jantzen and von Hevesey. Metallic hafnium was first prepared by Anton Eduard van Arkel[?] and Jan Hendrik deBoer[?] by passing the tetraiodide vapor over a heated tungsten filament.
Hafnium is found combined in natural
zirconium compounds but it is never found as a free element in nature.
Minerals that contain zirconium, such as
alvite[?] [(Hf,
Th,
Zr)
SiO4 H2O],
thortveitite and
zircon (ZrSiO
4), usually contain 1 and 5 percent hafnium. Hafnium and zirconium have nearly identical chemistry, which makes the two difficult to separate. About half of all hafnium metal manufactured is produced by a by-product of zirconium refinement. This is done through reducing hafnium tetrachloride with
magnesium or
sodium in the
Kroll Process[?].
Care needs to be taken when machining hafnium because when it is divided into fine particles, it is
pyrophoric and can ignite spontaneously in air. Compounds that contain this metal are rarely encountered by most people and the pure metal is not normally toxic but all its compounds should be handled as if they are toxic (although there appears to be limited danger to exposed individuals).