There is nothing more practical than a good theory. V. I. Lenin.
At the dawn of the last century, Niels Bohr predicted that the last rare-earth metal is element number 72, similar to zirconium. In 1923 D. Koster, and D. de Hevesy opened this item with the predicted Boron properties in the Nordic zircons. And today, the source of hafnium in zirconium ore remain. The name hafnium received from the ancient name of Copenhagen — Hafnia… IN the twenty-first century, annual world production of hafnium is greater than 70 tons, is proportional to the production of zirconium. Most of hafnium is mined in Australia and South Africa. The price of hafnium in 99% purity of about $ 780 per kilogram.
Hafnium (symbol Hf) is a heat-resistant steel silver color metal. Its crystal lattice has a hexagonal structure, a density greater than 13 g/cm3. The melting point of 2150 °C. the capture cross Section for thermal neutrons is about 100 barn, five hundred times more than zirconium. Therefore, zirconium is used for nuclear energy must be free of hafnium. Natural isotope 174 Hf α-active, its half-life is about 2×1015 years.
|Atomic number||Atomic (molar) mass, g/mol||The degree of oxidation||Density [g/cm3]||The melting temperature t°C||The boiling point of t°C||The heat of fusion kJ/kg|
|No. 72||178,5||4||For 13, 31||2150°C||5400°C||25,1|
Nuclear energy. Ability to capture of neutrons leads to the use of hafnium in control rods Fuel elements spectrasite and glass (oxide, boride, oxicarbide, carbide, garrat lithium garret dysprosium). The alloy Ta-W-Hf — best fuel in the gas-phase nuclear engines.
Optics. Due to the heat resistance and a very high degree of refractive index of HfO2 and HfF4 used in the fiber optics, and astronomical multilayer x-ray mirrors, and night vision devices.
Electronics. Low work function of electrons (3,53 eV), allows for cathodes of Hf powerful radio tubes and electron guns, and efficient thermionic generator.
Electrical engineering. Along with heat resistance, small electron work function allows you to use Hf in the manufacture of electrodes for welding in argon, especially for welding of low carbon steel in the atmosphere CO2, where the electrodes were almost 4 times more resistant than tungsten. Note also the large economic benefit of the use of alloy hafnium-tantalum for electrodes-oxygen flame and air-plasma cutting of metals. The alloy Hf — 77% Ta — 20% W — 2%, Ag — 0,5%, Cs — 0,1%, Cr — 0.4% of a nine-time resource of work in comparison with pure hafnium.
Alloys. Supplement 1% Hf to aluminum significantly hardens the alloy increases the tensile strength of tensile, shear and torsion, improves resistance to vibration and shock loads Hafnium dramatically hardens the alloys of cobalt, so necessary in modern processing industries. The carbide and boride of hafnium (t° PL. 3250°C) used in the composition of superhard alloys in the construction of nuclear boilers gas-phase and in the production of rocket nozzles, and as a wear resistant coating. Alloy HfB2+ Ni as relevant as exceptionally wear-resistant composite coating. Alloy of hafnium carbide and 20% of tantalum carbide and 80% is considered the most heat resistant of known materials (t° PL 4216 °C).
Mechanical engineering. Titanium alloys doped with hafnium, which is the basis of parts of marine engines. The addition of hafnium to Nickel hardens the alloy, improves corrosion resistance, easier welding and seals the weld. Additive of hafnium in the tantalum leads to the formation of the surface protective film of complex oxides, which increase the oxidation resistance to teploobmenu (thermal shock). On the basis of alloys of these two metals was created materials for jet engines and gas rudders, nozzles, etc.
Other fields of application. Hafnium alloyed with rare earth elements such as terbium and samarium when creating a powerful permanent magnets. The dielectrics on the basis of the HfO2 with a high dielectric constant is successfully replace silicon oxide in computers, allowing you to achieve a much greater density of filling chips. Dielectric silicide of hafnium also have a significant dielectric constant. Alloys of hafnium and scandium are known in microelectronics as the basis of the resistive films.
Standards controlled admixtures, %, not more
Prospective application of
Hf-178m2 is a byproduct of nuclear power (waste absorbing hafnium rods in nuclear power plants). This isotope (half-life 31) contains an excess of energy that can be release by irradiation of the nucleus. Energy contained in 1 gr. Hf-178m2, equivalent to 50 kg of TNT. This can be used to «pump» the compact combat lasers and as an adjustable source of gamma rays, for example, in defectoscopy and as a capacious source of energy for transport.
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