Encyclopedia > Hafnium

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Name, Symbol, NumberHafnium, Hf, 72
Chemical series Transition metals
Group, Period, Block4 (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 level2, 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
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
isoNAhalf-life DMDE MeVDP
172Hf{syn.}1.87 y ε0.350172Lu
174Hf0.162%2 E15 y α2.495170Yb
176Hf5.206%Hf is stable with 104 neutrons
177Hf18.606%Hf is stable with 105 neutrons
178Hf27.297%Hf is stable with 106 neutrons
179Hf13.629%Hf is stable with 107 neutrons
180Hf35.1%Hf is stable with 108 neutrons
182Hf{syn}9 E6 yβ0.373182Ta
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.

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Notable Characteristics 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.

Applications 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;

History 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. Occurrence 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 (ZrSiO4), 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[?]. Precautions 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).

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