Hafnium is a heavy refractory silvery-white metal, 72nd element of the periodic system.

The history of the discovery of hafnium

D. I. Mendeleev foresaw the future discovery of an element with serial number 72. But Mendeleev could not describe its properties with the same thoroughness as the properties of scandium, germanium and gallium, which had not yet been discovered. The harmony of the periodic system was inexplicably violated by lanthanum and the elements following it. Later, Boguslav Brauner, an outstanding Czech chemist, friend and associate of Mendeleev, proposed to isolate 14 lanthanides in an independent series, and in the main “text” of the table, place them all in the lanthanum cell. In 1907, the heaviest lanthanide, lutetium, was discovered. However, most chemists did not have confidence that lutetium is the last and heaviest of the rare earth elements.

Systematic searches for element No. 72 began only in the 20th century.

In 1911, Georges Urbain announced the discovery of a new element in ores of rare earths. In honor of the ancient tribes of the Celts who once inhabited the territory of France, he named the new element Celtium. In 1922, Deauvilliers, also a Frenchman, applied improved methods of X-ray analysis while investigating a mixture of rare earths. Noticing two new lines in the spectrum, Deauvillier decided that these lines belonged to an element with serial number 72, and Celtium was recognized as the fifteenth lanthanide.

But the joy of discovery was short-lived.

By this time electronic model The theory of the atom was already developed to such an extent that, on its basis, Niels Bohr was able to explain the periodicity of the structure of atoms, to explain the features and order of placement of elements in the periodic system. Based on his calculations, Bohr concluded that the last rare earth element should be element No. 71 - lutetium, and element No. 72, in his opinion, should be an analogue of zirconium.

The employees of the Institute for Theoretical Physics in Copenhagen Koster and Hevesy undertook to test Bohr's conclusions experimentally. To this end, they examined several samples of zirconium minerals. The remains obtained after leaching Norwegian and Greenland zircons with boiling acids were subjected to X-ray spectral analysis. The x-ray lines coincided with the characteristic lines calculated for element No. 72 according to Moseley's law. Based on this, Koster and Hevesy announced the discovery of element No. 72 in 1923 and named it hafnium in honor of the city where this discovery was made (Hafnia is the Latin name Copenhagen). In the same article, they noted that the substance obtained by Urbain and Deauville could not be an element with the atomic number 72, since the wavelengths of the X-ray lines indicated by them differed from the theoretical values ​​much more than is permissible for the experimental error. And soon employees of the same institute, Werner and Hansen, showed that the spectral lines discovered by Urbain corresponded not to lines of hafnium, but to lutetium; in the spectrum of samples containing 90% hafnium, not a single spectral line of Urbain was found.

In 1924, the report of the Commission on Atomic Weights clearly stated that the element with atomic number 72 should be called hafnium, as suggested by Coster and Hevesy. Since then, the name "hafnium" has been preferred by all scientists of the world, except for French scientists, who until 1949 used the name "Celtium".

Obtaining hafnium

The average content of hafnium in the earth's crust is about 4 g/t. Due to the absence of hafnium of its own minerals and its constant association with zirconium, it is obtained by processing zirconium ores, where it is contained in an amount of 2.5% by weight of zirconium (zircon contains 4% HfO 2, baddeleyite 4 - 6% HfO 2).

Hafnium accompanies zirconium not only in natural ores and minerals, but also in all artificial preparations of the element, including metallic zirconium. This was established shortly after the discovery of element 72.

Zirconium separated from hafnium was first obtained in 1923 by Koster and Hevesy. And together with Jantsen, Hevesy received the first sample of metallic hafnium of 99% purity.

In subsequent years, many methods were found for separating zirconium and hafnium, but all of them were complex and laborious, and, moreover, the problem of separating zirconium and hafnium was of no practical interest. It was developed mainly for scientific purposes, since in any of the then known areas of application of zirconium and its compounds, the constant presence of an impurity of hafnium did not affect at all. The independent use of hafnium and its compounds did not promise anything particularly new. Therefore, the chemistry of hafnium developed slowly, and the new metal and its compounds were isolated in negligible quantities: until 1930, only about 70 g of pure hafnium dioxide was obtained in Europe.

Our age is called atomic. Not zirconium or hafnium is the reason for this, but they turned out to be involved in atomic affairs. And if from the point of view of chemistry zirconium and hafnium are analogues, then from the point of view of nuclear technology they are antipodes.

The probability of neutron absorption (in physics, we recall, it is called the capture cross section) is measured in barns. Pure zirconium has a capture cross section of 0.18 barn, while pure hafnium has a capture cross section of 120 barn. An admixture of 2% hafnium increases the capture cross section of zirconium by a factor of 20, which is why zirconium intended for reactors should contain no more than 0.01% hafnium. In natural zirconium compounds, the content of hafnium is usually more than 0.5%. The separation of these elements became necessary, if only for the sake of zirconium...

In 1949, a fairly efficient process for the separation of zirconium and hafnium by liquid extraction was developed in the United States. In 1950, this process was introduced at the plant, and since January 1951, the systematic smelting of "reactor-grade" zirconium was established. Hafnium in the form of hydroxide, obtained in the separation process, was initially a waste by-product. But soon the technology needed hafnium itself.

Each of the six natural hafnium isotopes has its own "neutron appetite", the size of which can be judged from the data on the nuclear-physical properties of hafnium isotopes:

Technology for obtaining hafnium

The most common technological process for obtaining hafnium is as follows.

Crushed zircon is mixed with graphite (or other carbonaceous material) and heated to 1800°C in an airless arc furnace. In this case, zirconium and hafnium are bound by carbon, forming ZrC and HfC carbides, and silicon volatilizes in the form of SiO monoxide. If the same mixture is heated in the presence of air, the reaction products will contain nitrogen along with carbon and are called carbonitrides.

Carbides and carbonitrides are cooled, broken into pieces and loaded into a shaft furnace. There, at a temperature of about 500°C, these products react with chlorine gas to form zirconium and hafnium tetrachlorides.

Zirconium and hafnium are separated using minimal differences in the properties of the compounds of these elements. So far, two methods have found industrial application: extraction, based on the different solubility of zirconium and hafnium compounds in methyl isobutyl ketone or tributyl phosphate, and the method of fractional crystallization of complex fluorides, based on different solubility of K 2 and K 2 in water.

Let's talk a little more about chemically more interesting first method.

A mixture of tetrachlorides is dissolved in water and ammonium thiocyanate NH 4 CNS is added to the solution. This solution is then mixed with methyl isobutyl ketone (MIBK) saturated with HCNS thiocyanate. Under these conditions, the hafnium compounds dissolve better in MIBC than the corresponding zirconium compounds, and the hafnium is concentrated in the organic phase. The process is repeated many times and an aqueous solution of zirconium compounds and a solution of hafnium salt in an organic solvent are obtained. But in the latter there is an admixture of zirconium. To extract it, the organic 1st phase is washed with a hydrochloric acid solution and then the hafnium is extracted with a sulfuric acid solution. Hafnium is precipitated from a sulfuric acid solution in the form of hydroxide, which is converted to hafnium dioxide by calcination. The latter is again chlorinated and hafnium tetrachloride is obtained, which is again purified by sublimation.

Metallic hafnium is reduced from purified tetrachloride with magnesium or magnesium-sodium alloy. The process takes place in a hermetically sealed furnace in a helium atmosphere. The sponge hafnium obtained in this way is melted down into ingots. This is done in vacuum electric arc or electron beam furnaces.

To prepare hafnium of the highest purity, a common metal is converted into tetraiodide, which is then decomposed at high temperature.

All hafnium obtained in our time is a by-product of the production of reactor zirconium. If it were necessary to obtain hafnium in independent production, it would be several times more expensive. And he is already one of the most expensive metals. According to American data, in 1969 hafnium was two and a half times more expensive than silver.

Now more than 90% of hafnium consumes nuclear energy. Therefore, when talking about the possibilities of using hafnium in other areas, the epithet “potential” is usually added. Most likely, this situation will continue for a long time, because nuclear energy is developing very quickly, faster than the vast majority of industries... Apparently, it is destined to be a "nuclear" metal. And this is an element in which only one of the six natural isotopes is radioactive!

Physical properties of hafnium

Hafnium has a high thermal neutron capture cross section (about 10² barn), while its chemical counterpart, zirconium, has a capture cross section that is 2 orders of magnitude smaller, about 2 × 10 −1 barn. In this regard, zirconium used to create reactor fuel elements must be thoroughly purified from hafnium. One of the rare natural isotopes of hafnium, 174 Hf, exhibits weak alpha activity (half-life 2×10 15 years).

Hafnium is twice as heavy as zirconium and melts at a higher temperature (2230°C) than zirconium. No less interesting is such a series of melting points; hafnium oxide - 2912°C, hafnium boride - 3250°C, hafnium nitride - 3310°C, hafnium carbide - 3890°C; that is why the nitrides of refractory metals, including hafnium, are the basis of heat-resistant alloys, high-temperature refractories, hard materials, radio and electrical alloys (bolometers, resistors, hot cathodes).

At ordinary temperature, Hafnium has a hexagonal lattice with periods a = 3.1946Å and c = 5.0511Å. The density of Hafnium is 13.09 g/cm 3 (20 °C). Hafnium is refractory, its melting point is 2222 °C, bp t is 5400 °C. Atomic heat capacity 26.3 kJ/(kmol K) (25-100°C); electrical resistivity 32.4·10 -8 ohm·m (0°C). A feature of Hafnium is its high emissivity; electron work function 5.77 10 -19 J, or 3.60 eV (980-1550°C); Hafnium has a high thermal neutron capture cross section of 115·10 -28 m 2 , or 115 barn (zirconium has 0.18·10 -28 m 2 , or 0.18 barn). Pure hafnium is ductile, easily amenable to cold and hot working (rolling, forging, stamping).

Chemical properties of hafnium

By chemical properties Hafnium is very similar to zirconium due to the almost identical sizes of the ions of these elements and the complete similarity of the electronic structure. However, the chemical activity of Hafnium is somewhat less than that of Zr. The basic valency of Hafnium is 4. Compounds of 3-, 2- and 1-valent Hafnium are also known.

At room temperature compact Hafnium is completely resistant to atmospheric gases. However, when heated above 600 °C, it quickly oxidizes and interacts, like zirconium, with nitrogen and hydrogen. Hafnium is distinguished by corrosion resistance in pure water and water vapor up to temperatures of 400 °C. Powdered hafnium is pyrophoric. Hafnium oxide HfO 2 is a white refractory (t pl 2780 ° C) substance with high chemical resistance. Hafnium (IV) oxide and its corresponding hydroxides are amphoteric with a predominance of basic properties. When HfO 2 is heated with alkalis and oxides of alkaline earth metals, hafnates are formed, for example Me 2 HfO 3 , Me 4 HfO 4 , Me 2 Hf 2 O 3 .

Hafnium, like tantalum, is a fairly inert material due to the formation of a thin passive oxide film on the surface. In general, the chemical resistance of hafnium is much greater than that of its counterpart, zirconium.

The best solvent for hafnium is hydrofluoric acid (HF), or a mixture of hydrofluoric and nitric acids, as well as aqua regia.

At high temperatures (above 1000 K), hafnium oxidizes in air and burns in oxygen. Reacts with halogens. Similar to glass in resistance to acids. Like zirconium, it has hydrophobic properties (not wetted by water).

Elements of the periodic system with very similar chemical properties are called analogues. The most striking example of the chemical analogy of the elements is the similarity between zirconium and hafnium. Until now, no reaction has been found in which one of them would enter and the other would not enter. This is explained by the fact that hafnium and zirconium have the same external structures. electron shells. And besides, the sizes of their atoms and ions are almost the same. Zirconium was discovered back in the 18th century, and hafnium was so successfully disguised as zirconium that for a century and a half, scientists who studied zirconium minerals and their processed products did not even suspect that they were actually dealing with two elements. Indeed, in the 19th century Several reports were published on the discovery of unknown elements in zirconium minerals: ostranium (Breithaupt, 1825), noria (Svanberg, 1845), jargonium (Sorbi, 1869), nigrium (Church, 1869), euxenium (Hoffman and Prandtl, 1901). However, none of these "claims" was confirmed by control experiments.

The most important chemical compounds

Divalent hafnium compounds

• HfBr 2 - solid black, self-igniting in air. Decomposes at 400 °C into hafnium and hafnium tetrabromide. Obtained by disproportionation of hafnium tribromide in vacuum with heating.

• Hf(HPO 4) 2- white precipitate, soluble in sulfuric and hydrofluoric acids. Obtained by treating solutions of hafnium (II) salts with phosphoric acid.

Trivalent hafnium compounds

• HfBr 3- black-blue solid. Disproportionates at 400 °C to dibromide and hafnium tetrabromide. Obtained by the reduction of hafnium tetrabromide by heating in a hydrogen atmosphere or with metallic aluminum.

Compounds of tetravalent hafnium

• HfO2- colorless monoclinic crystals (density - 9.98 g/cm³) or colorless tetragonal crystals (density - 10.47 g/cm³). The latter have a melting point of 2900 °C, are slightly soluble in water, are diamagnetic, have a more basic character than ZrO 2 and exhibit catalytic properties. Obtained by heating metallic hafnium in oxygen or by calcining hydroxide, dioxalate, hafnium disulfate.

• Hf(OH)4- a white precipitate that dissolves with the addition of alkalis and hydrogen peroxide with the formation of peroxo-hafniates. It is obtained by deep hydrolysis of salts of tetravalent hafnium when heated or by treating solutions of hafnium (IV) salts with alkalis.

• HFF 4- colorless crystals. t pl 1025 ° C, density - 7.13 g / cm³. Soluble in water. Obtained by thermal decomposition of the compound (NH 4) 2 in a stream of nitrogen at 300 °C.

• HfCl 4- white powder sublimating at 317 °C. t pl 432 °C. Obtained by the action of chlorine on metallic hafnium, hafnium carbide or a mixture of hafnium (II) oxide with coal.

• HfBr 4- colorless crystals. Sublimated at 322°C. t pl 420 °C. Obtained by the action of bromine vapor on a mixture of hafnium oxide heated to 500 ° C (II) with coal.

• HFI 4- yellow crystals. Sublimates at 427°C and thermally dissociates at 1400°C. Obtained by the interaction of hafnium with iodine at 300 °C.

Application of hafnium

The main areas of application of metallic hafnium are the production of alloys for aerospace technology, the nuclear industry, and special optics.

• Nuclear technology uses the ability of hafnium to capture neutrons, and its use in the nuclear industry is the production of control rods, special ceramics and glass (oxide, carbide, boride, oxocarbide, dysprosium hafnate, lithium hafnate). A feature and advantage of hafnium diboride is a very small outgassing (helium, hydrogen) during the "burnout" of boron.
• Hafnium oxide is used in optics due to its temperature stability (mp 2780 °C) and very high refractive index. A significant area of ​​hafnium consumption is the production of special grades of glass for fiber optic products, as well as for obtaining especially high-quality optical products, mirror coatings, including for night vision devices, thermal imagers. Hafnium fluoride has a similar scope.
• Hafnium carbide and boride (mp. 3250 °C) are used as extremely wear-resistant coatings and in the production of superhard alloys. In addition, hafnium carbide is one of the most refractory compounds (mp 3890 °C) and is used for the production of nozzles space rockets and some structural elements of gas-phase nuclear jet engines.
• Hafnium distinguishes relatively low work electron output (3.53 eV), and therefore it is used for the manufacture of cathodes for high-power radio tubes and electron guns. At the same time, this quality, along with its high melting point, makes it possible to use hafnium for the production of electrodes for welding metals in argon, and especially electrodes (cathodes) for welding low-carbon steel in carbon dioxide. The stability of such electrodes in carbon dioxide is more than 3.7 times higher than that of tungsten ones. Barium hafnate is also used as efficient cathodes with low work function.
• Hafnium carbide in the form of a finely porous ceramic product can serve as an extremely efficient electron collector, provided that cesium-133 vapor evaporates from its surface in a vacuum, in this case the electron work function decreases to less than 0.1–0.12 eV, and this effect can be used to creation of highly efficient thermionic electric generators and parts of powerful ion engines.
• Based on hafnium and nickel diboride, a highly wear-resistant and hard composite coating has been developed and has long been used.
• Tantalum-tungsten-hafnium alloys are the best alloys for fuel supply in gas-phase nuclear rocket engines.
• Titanium alloys alloyed with hafnium are used in shipbuilding (manufacturing of marine engine parts), and alloying nickel with hafnium not only increases its strength and corrosion resistance, but also dramatically improves the weldability and strength of welds.
• The addition of hafnium to tantalum dramatically increases its resistance to air oxidation (heat resistance) by forming a dense and impermeable film of complex oxides on the surface, and, above all, this oxide film is very resistant to heat cycles (thermal shock). These properties made it possible to create very important alloys for rocket technology (nozzles, gas rudders). One of the best alloys of hafnium and tantalum for rocket nozzles contains up to 20% hafnium. It should also be noted that there is a great economic effect when using the hafnium-tantalum alloy for the production of electrodes for air-plasma and oxygen-flame cutting of metals. The experience of using such an alloy (hafnium - 77%, tantalum - 20%, tungsten - 2%, silver - 0.5%, cesium - 0.1%, chromium - 0.4%) showed a 9 times longer service life compared to with pure hafnium.
• Alloying with hafnium sharply strengthens many cobalt alloys, which are very important in turbine construction, oil, chemical and food industries.
• Hafnium is used in some alloys for heavy-duty permanent magnets based on rare earths (in particular, based on terbium and samarium).
• An alloy of hafnium carbide (HfC, 20%) and tantalum carbide (TaC, 80%) is the most refractory alloy (mp. 4216 °C). In addition, there are separate indications that when alloying this alloy with a small amount of titanium carbide, the melting point can be increased by another 180 degrees.
• By adding 1% hafnium to aluminum, heavy-duty aluminum alloys with a metal grain size of 40-50 nm are obtained. This not only strengthens the alloy, but also achieves a significant relative elongation and increases the ultimate strength in shear and torsion, as well as improves vibration resistance.
• Dielectrics with high permittivity based on hafnium oxide over the next decade will replace traditional silicon oxide in microelectronics, which will allow to achieve much higher element densities in chips. Since 2007, hafnium dioxide has been used in 45 nm Intel Penryn processors. Hafnium silicide is also used as a dielectric with a high permittivity in electronics. Alloys of hafnium and scandium are used in microelectronics to obtain resistive films with special properties.
• Hafnium is used to produce high quality multilayer X-ray mirrors.

earlier this month, the Semiconductor Research Corporation (SRC) did not announce a "groundbreaking" success in making insulators containing this metal. Intel and IBM are reportedly planning to use hafnium to build faster and more energy efficient microprocessors.

Hafnium oxide will replace the silicon oxide currently in use. Thus, the element, which occupies position 72 in the periodic table, should provide a breakthrough into the future generation of semiconductor devices. Manufacturers expect to use it in chips that are very common - from cell phones to servers.

If a rare element is so massively used, will it be enough for everyone?

Experts believe that there is no cause for concern. Mainly because the amount of hafnium used in a single chip is negligible.

Jim McGregor, an analyst at In-Stat, says, "Even if you take all the hafnium needed for a 300mm wafer, it will be impossible to see with the naked eye."

Bernard Meyerson, chief technologist at IBM, put it even more eloquently: if you take one cubic centimeter of hafnium and spread it over a surface with a layer as thick as a chip would cover an area equal to 10 football fields. Moreover, this estimate is taken with a margin for the worse - firstly, not pure hafnium is used, but its oxide, and secondly, the layer thickness will constantly decrease as the technology improves.

World resources and production of hafnium

Prices for hafnium 99% in 2007 averaged $780 per kilogram

Every year, all countries of the world, taken together, produce about 50 tons of this substance. It does not occur in the form of veins, like gold or other metals, but is obtained as a by-product during the extraction of zirconium dioxide (zirconium is a metal that is quite widespread in the United States, Brazil, Australia, Russia and China).

World resources of hafnium in terms of hafnium dioxide slightly exceed 1 million tons. The distribution structure of these resources is approximately as follows:

• Australia - more than 630 thousand tons,
• South Africa - almost 287 thousand tons,
• USA - just over 105 thousand tons,
• India - about 70 thousand tons,
• Brazil - 9.88 thousand tons.

The vast majority of the raw material base of hafnium in foreign countries is represented by zircon from coastal sea placers.

Hafnium reserves in Russia and the CIS, according to independent experts, are very large, and in this regard, with the development of the hafnium industry, Russia is able to become the undisputed leader in the world hafnium market. It is also worth mentioning, in this connection, the very significant resources of hafnium in the Ukraine. The main hafnium-containing minerals in Russia and the CIS are represented by loparite, zircon, baddeleyite, and rare-metal alkaline granites.

The proximity of the atomic structures of hafnium and zirconium makes the separation process expensive. About 60-70% of the resulting hafnium goes to the production of the so-called "graphite rods" used to control the reaction in a nuclear reactor. Most of the rest of the hafnium is used to make alloys used in aircraft engines. The question of the lack of hafnium has not yet arisen, and its production can be increased if necessary.

Effect of hafnium on living organisms

The toxic effect of hafnium was studied in experiments on animals. LD50 (dose causing 50% mortality) for rats when administered intragastrically was about 400 mg/kg body weight. Necrotic changes developed in the stomach, and when inhaled, such changes on the bronchial mucosa were noted, and pulmonary edema was also noted. Chronic poisoning developed in animals with daily administration for 5 hours of hafnium carbide and nitride at a concentration of 10.8 mg/m3 for 6 and 9 months.

J/(K mol)

Molar volume The crystal lattice of a simple substance Lattice structure

hexagonal

Lattice parameters

a=3.196 nm; c=5.051 nm

Attitude c/a Other characteristics Thermal conductivity

(300 K) 23.0 W/(m K)

72
4f 14 5d 2 6s 2

Hafnium - chemical element 4th group of the long-period form of the periodic system of D. I. Mendeleev (according to the short form of the periodic system - a side subgroup of group IV), the sixth period, with atomic number 72. It is denoted by the symbol Hf (lat. Hafnium). A simple substance is a heavy refractory silvery-white metal.

History of discovery and origin of the name

Hafnium was searched among the rare earth elements, since the structure of the 6th period of the D. I. Mendeleev system was not clarified. In 1911, the French chemist J. Urbain announced the discovery of a new element, which he called Celtium. In reality, he obtained a mixture consisting of ytterbium, lutetium and a small amount of hafnium. And only after N. Bohr, on the basis of quantum mechanical calculations, showed that the last rare earth element is element number 71, it became clear that hafnium is an analogue of zirconium.

Based on the findings of Bohr, who predicted its properties and valency, in 1923 Dirk Coster and György de Hevesy systematically analyzed Norwegian and Greenland zircons by X-ray spectroscopy. The coincidence of the X-ray lines of the remains after leaching of zircon with boiling acid solutions with those calculated according to the Moseley law for the 72nd element allowed the researchers to announce the discovery of the element, which they called hafnium in honor of the city where the discovery was made (lat. hafnia Latin name for Copenhagen. The dispute about priority between J. Urbain, N. Coster and D. Hevesy, which began after that, continued for a long time. In 1949, the name of the element "hafnium" was approved by the International Commission and accepted everywhere.

Receipt

The average content of hafnium in the earth's crust is about 4 g/t. Due to the absence of its own minerals in hafnium and its constant association with zirconium, it is obtained by processing zirconium ores, where it is contained in an amount of 2.5% by weight of zirconium (zircon contains 4% HfO 2, baddeleyite - 4-6% HfO 2). In the world, about 70 tons of hafnium are mined per year on average, and the volume of its production is proportional to the volume of zirconium production. An interesting feature of the scandium mineral is tortveitite: it contains much more hafnium than zirconium, and this circumstance is very important when processing tortveitite into scandium and concentrating hafnium from it.

World resources of hafnium

Prices for hafnium 99% in 2007 averaged $780 per kilogram (according to infogeo.ru)

World resources of hafnium in terms of hafnium dioxide slightly exceed 1 million tons. The distribution structure of these resources is approximately as follows:

• Australia - more than 630 thousand tons,
• South Africa - almost 287 thousand tons,
• USA - just over 105 thousand tons,
• India - about 70 thousand tons,
• Brazil - 9.88 thousand tons.

The vast majority of the raw material base of hafnium in foreign countries is represented by zircon from coastal sea placers.

Physical properties

Hafnium is a lustrous, silvery-white metal, hard and refractory. In a finely dispersed state, it has a dark gray, almost black color; matt . Density under normal conditions - 13.31 g / cm 3. Melting point is 2506 (2233 °C), boils at 4876 (4603 °C).

Chemical properties

The best solvent for hafnium is hydrofluoric acid (HF) or a mixture of hydrofluoric and nitric acids, and aqua regia.

At high temperatures (over 1000) hafnium oxidizes in air, and burns out in oxygen. Reacts with halogens. Similar to glass in resistance to acids. Just like zirconium, it has hydrophobic properties (not wetted by water).

The most important chemical compounds

Divalent hafnium compounds

• HfBr 2, hafnium dibromide is a black solid that ignites spontaneously in air. Decomposes at 400 °C into hafnium and hafnium tetrabromide. Obtained by disproportionation of hafnium tribromide in vacuum with heating.

Trivalent hafnium compounds

• HfBr 3 , hafnium tribromide is a black-blue solid. Disproportionates at 400 °C to dibromide and hafnium tetrabromide. Obtained by the reduction of hafnium tetrabromide by heating in a hydrogen atmosphere or with aluminum metal.

Compounds of tetravalent hafnium

• HfO 2 , hafnium dioxide - colorless monoclinic crystals (density - 9.98 g / cm³) or colorless tetragonal crystals (density - 10.47 g / cm³). The latter have T mp 2900 °C, slightly soluble in water, diamagnetic, more basic than ZrO 2 and show catalytic properties. Obtained by heating metallic hafnium in oxygen or by calcining hafnium hydroxide, dioxalate, hafnium disulfate.
• Hf (OH) 4, hafnium hydroxide - a white precipitate that dissolves with the addition of alkalis and hydrogen peroxide to form peroxo-hafniates. It is obtained by deep hydrolysis of salts of tetravalent hafnium when heated or by treating solutions of hafnium (IV) salts with alkalis.
• HfF 4 , hafnium tetrafluoride - colorless crystals. T pl 1025 ° C, density - 7.13 g / cm³. Soluble in water. Obtained by thermal decomposition of the compound (NH 4) 2 in a stream of nitrogen at 300 °C.
• HfCl 4 , hafnium tetrachloride - white powder sublimating at 317 °C. T pl 432 °C. Obtained by the action of chlorine on metallic hafnium, hafnium carbide, or a mixture of hafnium(II) oxide with charcoal.
• HfBr 4 , hafnium tetrabromide - colorless crystals. Sublimated at 322°C. T pl 420 °C. Obtained by the action of bromine vapor on a mixture of hafnium(II) oxide and coal heated to 500 ° C.
• HfI 4 , hafnium tetraiodide - yellow crystals. Sublimates at 427°C and thermally dissociates at 1400°C. Obtained by the interaction of hafnium with iodine at 300 °C.
• Hf (HPO 4) 2, hafnium hydrogen phosphate - a white precipitate, soluble in sulfuric and hydrofluoric acids. Obtained by treating solutions of hafnium(IV) salts with phosphoric acid.

Application

The main areas of application of metallic hafnium are the production of alloys for aerospace technology, the nuclear industry, and special optics.

• Nuclear engineering exploits the ability of hafnium to capture neutrons, and its applications in the nuclear industry are the production of control rods, special ceramics, and glass (oxide, carbide, boride, oxocarbide, dysprosium hafnate, lithium hafnate). A feature and advantage of hafnium diboride is a very small outgassing (helium, hydrogen) during the "burnout" of boron.
• Hafnium oxide is used in optics due to its thermal stability (mp 2780 °C) and very high refractive index. A significant area of ​​hafnium consumption is the production of special grades of glass for fiber optic products, as well as for obtaining especially high-quality optical products, mirror coatings, including for night vision devices, thermal imagers. Hafnium fluoride has a similar scope.
• Hafnium carbide and boride (mp. 3250 °C) are used as extremely wear-resistant coatings and in the production of superhard alloys. In addition, hafnium carbide is one of the most refractory compounds (mp. 3960 ° C) and is used to manufacture nozzles for space rockets and some structural elements of gas-phase nuclear jet engines.
• Hafnium is distinguished by a relatively low electron work function (3.53 eV), and therefore it is used to make cathodes for high-power radio tubes and electron guns. At the same time, this quality, along with its high melting point, makes it possible to use hafnium for the production of electrodes for welding metals in argon, and especially electrodes (cathodes) for welding mild steel in carbon dioxide. The stability of such electrodes in carbon dioxide is more than 3.7 times higher than that of tungsten electrodes. Barium hafnate is also used as efficient cathodes with low work function.
• Hafnium carbide in the form of a finely porous ceramic product can serve as an extremely efficient electron collector, provided that cesium-133 vapor evaporates from its surface in a vacuum, in this case the work function of electrons decreases to less than 0.1-0.12 eV, and this effect can be used to create highly efficient thermionic electric generators and parts of powerful ion engines.
• Based on hafnium and nickel diboride, a highly wear-resistant and hard composite coating has been developed and has long been used.
• Tantalum-tungsten-hafnium alloys are the best alloys for fuel delivery in gas-phase nuclear rocket engines.
• Titanium alloys alloyed with hafnium are used in shipbuilding (manufacturing of marine engine parts), and alloying nickel with hafnium not only increases its strength and corrosion resistance, but also dramatically improves the weldability and strength of welds.
• Tantalum hafnium carbide. The addition of hafnium to tantalum sharply increases its resistance to air oxidation (heat resistance) due to the formation of a dense and impermeable film of complex oxides on the surface, and, above all, this oxide film is very resistant to heat changes (thermal shock). These properties made it possible to create very important alloys for rocket technology (nozzles, gas rudders). One of the best alloys of hafnium and tantalum for rocket nozzles contains up to 20% hafnium. It should also be noted that there is a great economic effect when using the hafnium-tantalum alloy for the production of electrodes for air-plasma and oxygen-flame cutting of metals. The experience of using such an alloy (hafnium - 77%, tantalum - 20%, tungsten - 2%, silver - 0.5%, cesium - 0.1%, chromium - 0.4%) showed a 9 times longer service life compared to with pure hafnium.
• Alloying with hafnium sharply strengthens many cobalt alloys, which are very important in turbine construction, oil, chemical and food industries.
• Hafnium is used in some alloys for heavy-duty permanent magnets based on rare earths (in particular, based on terbium and samarium).
• An alloy of hafnium carbide (HfC, 20%) and tantalum carbide (TaC, 80%) is the most refractory alloy (mp. 4216 °C). In addition, there are separate indications that when alloying this alloy with a small amount of titanium carbide, the melting point can be increased by another 180 degrees.
• By adding 1% hafnium to aluminum, heavy-duty aluminum alloys are obtained with a metal grain size of 40-50 nm. This not only strengthens the alloy, but also achieves a significant relative elongation and increases the ultimate strength in shear and torsion, as well as improves vibration resistance.
• High permittivity dielectrics based on hafnium oxide will replace traditional silicon oxide in microelectronics over the next decade, allowing much higher element densities to be achieved in chips. Since 2007, hafnium dioxide has been used in 45 nm Intel Penryn processors. Also hafnium silicide is used as a high permittivity dielectric in electronics. Alloys of hafnium and scandium are used in microelectronics to obtain resistive films with special properties.
• Hafnium is used to produce high quality multilayer X-ray mirrors.

Promising areas of application

Periodic system of chemical elements of D. I. Mendeleev
																		hf
															Uut

An excerpt characterizing Hafnium

She was the same as he knew her almost as a child and then the bride of Prince Andrei. A cheerful, inquiring gleam shone in her eyes; there was an affectionate and strangely mischievous expression on his face.
Pierre dined and would have sat out all evening; but Princess Mary was on her way to Vespers, and Pierre left with them.
The next day, Pierre arrived early, dined and sat out the whole evening. Despite the fact that Princess Mary and Natasha were obviously glad to have a guest; despite the fact that all the interest in Pierre's life was now concentrated in this house, by evening they had talked everything over, and the conversation moved incessantly from one insignificant subject to another and was often interrupted. Pierre sat up so late that evening that Princess Mary and Natasha looked at each other, obviously expecting him to leave soon. Pierre saw this and could not leave. It became difficult for him, awkward, but he kept sitting, because he could not get up and leave.
Princess Mary, not foreseeing the end of this, was the first to get up and, complaining of a migraine, began to say goodbye.
- So you are going to Petersburg tomorrow? Oka said.
“No, I’m not going,” Pierre said hastily, with surprise and as if offended. - No, to Petersburg? Tomorrow; I just don't say goodbye. I’ll call for commissions, ”he said, standing in front of Princess Marya, blushing and not leaving.
Natasha gave him her hand and left. Princess Mary, on the contrary, instead of leaving, sank into an armchair and, with her radiant, deep gaze, looked sternly and attentively at Pierre. The weariness that she had obviously shown before was completely gone now. She sighed heavily and long, as if preparing herself for a long conversation.
All the embarrassment and awkwardness of Pierre, when Natasha was removed, instantly disappeared and was replaced by an excited animation. He quickly moved the chair very close to Princess Marya.
“Yes, I wanted to tell you,” he said, answering, as if in words, in her glance. “Princess, help me. What should I do? Can I hope? Princess, my friend, listen to me. I know everything. I know that I'm not worth it; I know it's impossible to talk about it now. But I want to be her brother. No, I don't want... I can't...
He stopped and rubbed his face and eyes with his hands.
“Well, here it is,” he continued, apparently making an effort on himself to speak coherently. I don't know since when I love her. But I have loved her alone, alone in my whole life, and I love her so much that I cannot imagine life without her. Now I do not dare to ask for her hand; but the thought that maybe she could be mine and that I would miss this opportunity ... opportunity ... is terrible. Tell me, can I hope? Tell me what should I do? Dear princess,” he said, after a pause and touching her hand, as she did not answer.
“I am thinking about what you told me,” Princess Mary answered. “I'll tell you what. You are right, what now to tell her about love ... - The princess stopped. She wanted to say: it is now impossible for her to talk about love; but she stopped, because for the third day she saw from the suddenly changed Natasha that not only Natasha would not be offended if Pierre expressed his love to her, but that she wanted only this.
“It’s impossible to tell her now,” Princess Marya said anyway.
“But what am I to do?
“Give it to me,” said Princess Mary. - I know…
Pierre looked into the eyes of Princess Mary.
“Well, well…” he said.
“I know that she loves ... she will love you,” Princess Mary corrected herself.
Before she had time to say these words, Pierre jumped up and, with a frightened face, grabbed Princess Mary by the hand.
- Why do you think? Do you think that I can hope? You think?!
“Yes, I think so,” said Princess Mary, smiling. - Write to your parents. And entrust me. I'll tell her when I can. I wish it. And my heart feels that it will be.
- No, it can't be! How happy I am! But it can't be... How happy I am! No, it can not be! - said Pierre, kissing the hands of Princess Mary.
- You go to St. Petersburg; it is better. I'll write to you, she said.
- To Petersburg? Drive? Okay, yes, let's go. But tomorrow I can come to you?
The next day, Pierre came to say goodbye. Natasha was less lively than in the old days; but on this day, sometimes looking into her eyes, Pierre felt that he was disappearing, that neither he nor she was anymore, but there was one feeling of happiness. “Really? No, it can’t be,” he said to himself at her every look, gesture, word that filled his soul with joy.
When, bidding her farewell, he took her thin, thin hand, he involuntarily held it a little longer in his.
“Is it possible that this hand, this face, these eyes, all this treasure of female charm, alien to me, will it all be forever mine, familiar, the same as I am for myself? No, It is Immpossible!.."
“Farewell, Count,” she said to him loudly. “I will be waiting for you very much,” she added in a whisper.
And these simple words, the look and facial expression that accompanied them, for two months, were the subject of Pierre's inexhaustible memories, explanations and happy dreams. “I will be waiting for you very much ... Yes, yes, as she said? Yes, I will be waiting for you. Ah, how happy I am! What is it, how happy I am!” Pierre said to himself.

In Pierre's soul now nothing similar happened to what happened in her in similar circumstances during his courtship with Helen.
He did not repeat, as then, with painful shame, the words he had spoken, he did not say to himself: “Ah, why didn’t I say this, and why, why did I say “je vous aime” then?” [I love you] Now, on the contrary, he repeated every word of hers, his own, in his imagination with all the details of her face, smile, and did not want to subtract or add anything: he only wanted to repeat. There was no doubt now whether what he had done was good or bad, there was no shadow now. Only one terrible doubt sometimes crossed his mind. Is it all in a dream? Was Princess Mary wrong? Am I too proud and arrogant? I believe; and suddenly, as it should happen, Princess Marya will tell her, and she will smile and answer: “How strange! He was right, wrong. Doesn't he know that he is a man, just a man, and I? .. I am completely different, higher.
Only this doubt often came to Pierre. He didn't make any plans either. It seemed to him so incredibly impending happiness that as soon as this happened, nothing could be further. Everything ended.
Joyful, unexpected madness, for which Pierre considered himself incapable, took possession of him. The whole meaning of life, not for him alone, but for the whole world, seemed to him to consist only in his love and in the possibility of her love for him. Sometimes all people seemed to him busy with only one thing - his future happiness. It sometimes seemed to him that they all rejoiced in the same way as he himself, and only tried to hide this joy, pretending to be occupied with other interests. In every word and movement he saw hints of his happiness. He often surprised people who met him with his significant, expressing secret consent, happy looks and smiles. But when he realized that people might not know about his happiness, he felt sorry for them with all his heart and felt a desire to somehow explain to them that everything they were doing was complete nonsense and trifles not worthy of attention.
When he was offered to serve, or when some general state affairs and war were discussed, assuming that the happiness of all people depended on such or such an outcome of such and such an event, he listened with a meek, condoling smile and surprised the people who spoke to him with his strange remarks. But both those people who seemed to Pierre to understand the real meaning of life, that is, his feeling, and those unfortunate people who obviously did not understand this - all people in this period of time seemed to him in such a bright light of the feeling shining in him that without the slightest effort, he immediately, meeting with any person, saw in him everything that was good and worthy of love.
Considering the affairs and papers of his late wife, he had no feeling for her memory, except for pity that she did not know the happiness that he knew now. Prince Vasily, now especially proud of having received a new place and a star, seemed to him a touching, kind and pitiful old man.
Pierre often later recalled this time of happy madness. All the judgments that he made for himself about people and circumstances during this period of time remained forever true for him. Not only did he not subsequently renounce these views on people and things, but, on the contrary, in internal doubts and contradictions, he resorted to the view that he had at that time of madness, and this view always turned out to be correct.
“Perhaps,” he thought, “I seemed then strange and ridiculous; but then I was not as mad as I seemed. On the contrary, I was then smarter and more perceptive than ever, and I understood everything that is worth understanding in life, because ... I was happy.
Pierre's madness consisted in the fact that he did not, as before, wait for personal reasons, which he called the virtues of people, in order to love them, and love overflowed his heart, and he, loving people for no reason, found undoubted reasons for which it was worth loving them.

From that first evening, when Natasha, after Pierre's departure, with a joyfully mocking smile, told Princess Marya that he was definitely, well, exactly from the bath, and a frock coat, and a short haircut, from that moment something hidden and unknown to her, but irresistible woke up in Natasha's soul
Everything: face, gait, look, voice - everything suddenly changed in her. Unexpected for herself - the power of life, hopes for happiness surfaced and demanded satisfaction. From the first evening, Natasha seemed to have forgotten everything that had happened to her. Since then, she has never complained about her situation, has not said a single word about the past and was not afraid to do fun plans for the future. She spoke little of Pierre, but when Princess Mary mentioned him, a long-extinct gleam lit up in her eyes and her lips puckered up in a strange smile.
The change that took place in Natasha surprised Princess Mary at first; but when she understood its meaning, this change upset her. “Is it possible that she loved her brother so little that she could forget him so soon,” thought Princess Mary, when she alone pondered the change that had taken place. But when she was with Natasha, she did not get angry with her and did not reproach her. The awakened power of life that seized Natasha was obviously so unstoppable, so unexpected for herself, that Princess Mary, in Natasha's presence, felt that she had no right to reproach her even in her soul.
Natasha surrendered herself to the new feeling with such fullness and sincerity that she did not try to hide the fact that she was now not sad, but joyful and cheerful.
When, after a nightly explanation with Pierre, Princess Mary returned to her room, Natasha met her on the threshold.
- He said? Yes? He said? she repeated. Both joyful and at the same time pathetic, asking for forgiveness for his joy, the expression stopped on Natasha's face.
“I wanted to listen at the door; but I knew what you would tell me.
No matter how understandable, no matter how touching was for Princess Marya the look with which Natasha looked at her; no matter how sorry she was to see her excitement; but Natasha's words in the first minute offended Princess Marya. She remembered her brother, his love.
“But what to do! she cannot do otherwise,” thought Princess Marya; and with a sad and somewhat stern face she conveyed to Natasha everything that Pierre had told her. On hearing that he was going to Petersburg, Natasha was amazed.
- To Petersburg? she repeated, as if not understanding. But, peering into the sad expression on Princess Mary's face, she guessed the reason for her sadness and suddenly burst into tears. “Marie,” she said, “teach me what to do.” I'm afraid to be stupid. What you say, I will do; teach me…
- You love him?
“Yes,” Natasha whispered.
- What are you crying about? I’m happy for you,” said Princess Marya, forgiving Natasha’s joy for those tears.
“It won't be anytime soon. Just think what happiness it will be when I will be his wife and you will marry Nicolas.
“Natasha, I asked you not to talk about it. We'll talk about you.
They were silent.
- But why go to Petersburg! - suddenly said Natasha, and she herself hastily answered herself: - No, no, it’s necessary ... Yes, Marie? So you need...

Seven years have passed since the 12th year. The agitated historical sea of ​​Europe has subsided to its shores. It seemed quiet; but the mysterious forces that move mankind (mysterious because the laws governing their movement are unknown to us) continued their action.
Despite the fact that the surface of the historical sea seemed motionless, humanity moved as continuously as the movement of time. Various groups of human clutches were formed and disintegrated; the reasons for the formation and disintegration of states, the movements of peoples were prepared.
The historical sea, unlike before, was directed by gusts from one coast to another: it seethed in the depths. Historical figures, not as before, were carried in waves from one coast to another; now they seemed to circle in one place. Historical figures, who previously at the head of the troops reflected the movement of the masses with the orders of wars, campaigns, battles, now reflected the seething movement with political and diplomatic considerations, laws, treatises ...
Historians call this activity of historical persons reaction.
Describing the activities of these historical figures, who, in their opinion, were the cause of what they call reaction, historians condemn them severely. All famous people of that time, from Alexander and Napoleon to m me Stael, Photius, Schelling, Fichte, Chateaubriand, etc., are put before their strict judgment and justified or condemned, according to whether they contributed to progress or reaction.
In Russia, according to their description, a reaction also took place during this period of time, and the main culprit of this reaction was Alexander I - the same Alexander I, who, according to their own descriptions, was the main culprit of the liberal undertakings of his reign and the salvation of Russia.
In real Russian literature, from a schoolboy to a learned historian, there is no person who would not throw his stone at Alexander I for his wrong actions during this period of his reign.
“He should have done this and that. In this case, he did well, in this badly. He behaved well at the beginning of his reign and during the 12th year; but he acted badly, giving a constitution to Poland, creating a Holy Alliance, giving power to Arakcheev, encouraging Golitsyn and mysticism, then encouraging Shishkov and Photius. He did badly, being engaged in the front part of the army; he acted badly, cashiering the Semyonovsky regiment, etc.”
It would be necessary to fill out ten sheets in order to list all the reproaches that historians make to him on the basis of the knowledge of the good of mankind that they possess.
What do these accusations mean?
The very actions for which historians approve of Alexander I - such as: the liberal undertakings of the reign, the struggle with Napoleon, the firmness shown by him in the 12th year, and the campaign of the 13th year, do not follow from the same sources - the conditions of blood , upbringing, life, which made the personality of Alexander what it was - from which those actions follow, for which historians blame him, such as: the Holy Alliance, the restoration of Poland, the reaction of the 20s?
What is the essence of these accusations?
In the fact that such a historical person as Alexander I, a person who stood at the highest possible level of human power, is, as it were, in the focus of the blinding light of all historical rays concentrating on him; a person who was subject to those strongest influences in the world of intrigue, deceit, flattery, self-delusion, which are inseparable from power; a person who felt on himself, every minute of his life, responsibility for everything that happened in Europe, and a person not invented, but living, like every person, with his personal habits, passions, aspirations for goodness, beauty, truth - that this person , fifty years ago, not only was it not virtuous (historians do not reproach for this), but did not have those views on the good of mankind that a professor now has, who is engaged in science from a young age, that is, reading books, lectures and copying these books and lectures in one notebook.
But even if we assume that Alexander I was mistaken fifty years ago in his view of what is the good of the peoples, we must involuntarily assume that the historian who judges Alexander, in the same way, after some time has passed, will turn out to be unfair in his view of the fact that which is the good of mankind. This assumption is all the more natural and necessary because, following the development of history, we see that every year, with every new writer, the view of what is the good of mankind changes; so that what seemed good ten years later seems to be evil; and vice versa. Moreover, at the same time we find in history completely opposite views on what was evil and what was good: some of the constitution and the Holy Alliance given to Poland are credited, others reproach Alexander.
It is impossible to say about the activity of Alexander and Napoleon that it was useful or harmful, because we cannot say for what it is useful and for what it is harmful. If someone does not like this activity, then he does not like it only because it does not coincide with his limited understanding of what is good. Whether the preservation of my father's house in Moscow in the 12th year, or the glory of the Russian troops, or the prosperity of St. Petersburg and other universities, or the freedom of Poland, or the power of Russia, or the balance of Europe, or a certain kind of European enlightenment - progress, I must admit that the activity of every historical person had, in addition to these goals, other goals that were more general and inaccessible to me.
But let us suppose that so-called science has the possibility of reconciling all contradictions and has an invariable measure of good and bad for historical persons and events.
Let us assume that Alexander could have done everything differently. Let us suppose that he could, at the behest of those who accuse him, those who profess the knowledge of the ultimate goal of the movement of mankind, dispose of according to the program of nationality, freedom, equality and progress (there seems to be no other) that the present accusers would give him. Let us assume that this program would have been possible and drawn up, and that Alexander would have acted according to it. What would have happened then to the activities of all those people who opposed the then direction of the government - to the activities that, according to historians, are good and useful? This activity would not exist; there would be no life; there would be nothing.
If we assume that human life can be controlled by reason, then the possibility of life will be destroyed.

If one assumes, as historians do, that great men lead mankind to certain goals, which are either the greatness of Russia or France, or the equilibrium of Europe, or the spreading of the ideas of the revolution, or general progress, or whatever it is, it is impossible to explain the phenomena of history without the concepts of chance and genius.

Hf - chem. element of group IV of the periodic system of elements; at. and. 72, at. m. 178.49. Silvery white metal. In compounds, it exhibits an oxidation state of +4. Natural hydrogen is composed of six stable isotopes with mass numbers 174, 176-180. Artificial radioactive materials with mass numbers 170-173.175, 179, 180, 181, 183 and half-lives respectively 1.87 h, 16 h, 5 years, 23.6 h, 70 days, 19 sec, 5.5 h, 46 days were obtained and 64 min.

Hafnium was discovered in 1922 by the Hungarians. chemist D. Khevesi and goll. physicist D. Coster. Metal G, received in 1925 by D. Hevesy. The beginning of the widespread use of hafnium is associated with its use in nuclear technology. G. is a scattered element, does not have its own minerals and in nature usually accompanies zirconium (1-7%). Its content in the earth's crust is 3.2 10-4%. G. exists in two polymorphic modifications. At ordinary temperature, a hexagonal close-packed lattice of the magnesium type is stable, with periods a = 3.1883 A, c = 5.0422 A, c/a = 1.5815 (with a content of 0.78% Zr). Above t-ry 1760 ± 35 ° C, a body-centered cubic lattice is stable (typeα -Fe) with a period a = 3.60 A (t-ra 2000 ° C). Density (t-ra 20 ° C) 13.31 g / cm3 tpl 2222 ± 30 ° C; tkap = 5400° s. Temperature coefficient linear expansion (with a content of 0.86-0.89% Zr) in interval t-r 0-1000°C is 5.9 10 -6 deg-1. The thermal conductivity coefficient (when wine contains 2% Zr) decreases from 0.0533 to 0.0490 cal / cm sec deg with an increase in temperature from 50 to 500 ° C. Specific heat(t-ra 25 ° C) 0.0342 cal / g deg. T-ra Debye for G. with a purity of 99.95-99.98% is 251.5-252.3 K. Specific electrical resistance(t-ra 20 ° C) 40 10-8 ohm m, temperature coefficient. electrical resistance in the range of t-r 0-800 ° C is 3.51 10-3 deg-1.

A feature of hafnium is its high emissivity. The electron work function is 3.53 eV. Thermal neutron capture cross section 105 ± 5 barn. G. is paramagnetic. Fur. Saint-va G. significantly depend on the purity and conditions of preparation of the sample. Pure metal grout can be cold and hot worked (milled, drilled, rolled). Iodide G. has HV = 152 (load 1.2 kg), H = 206 kg/mm2 (load 60 g). Coeff. compressibility at t-re 303 K is 0.901 10-6 cm2/kg. The Young's modulus of iodide hydrogen (0.72% Zr) after annealing in vacuum at a temperature of 1040 ° C is 14 105 kgf / cm 'Under normal conditions, hydrogen is resistant to action hot water, steam-air mixtures, liquid sodium, alkalis, dilute hydrochloric acid, nitrogen acid of any concentration, oxygen, nitrogen and hydrogen. In powder form, it is pyrophoric. It dissolves well in "royal vodka", concentrated sulfuric and hydrofluoric acids. At high temperatures, it noticeably reacts with hydrogen, water, oxygen, halogens (forming HfX4), forms refractory compounds with nitrogen and carbon: HfN nitride (tmelt 2982 ± 50 ° C) and HfC carbide (tmelt 3887 ± 50 ° C)

To separate the compounds of hydrogen and zirconium, fractional crystallization, fractionated precipitation (the fastest and most efficient method in laboratory practice), ion exchange, adsorption, electrolysis, liquid extraction (the most common in industrial production), fractional distillation, and selective reduction are used. (the most promising for the chlorine method of opening zircon). Metallic hydrogenation is obtained by metallothermic reduction of HfCl4 with magnesium, calcium, sodium, or mixtures thereof, thermal dissociation of low-valency halides or carbonyl, and electrolysis of molten media.

For additional purification, iodide (the most common) or electrolytic refining, disproportionation, electron beam and electric arc melting in high vacuum are used. G. metal, as well as its compounds (for example, HfO and HfO2) are used to make regulator rods nuclear reactors and protective devices. In addition, hydrogen in its pure form and in the form of alloys is used in electrical, radio, and X-ray technology (electric filaments and incandescent electrodes, covers for carbon and graphite anodes, getters, etc.). It is also used as an alloying additive that increases the heat resistance in special applications. steels and alloys with palladium (potentiometric wire), with copper (contact plates of welding electrodes), in heat-resistant alloys based on molybdenum, tantalum, tungsten and niobium for rocket and space technology.

Promising as a structural material for jet engines, chemical. devices, etc. G. oxide is used for the manufacture of refractory refractory materials, as constituent part specialist. optical glasses operated at high temperatures as a catalyst pl. organic reactions and etc.; promising as a binder in heat-resistant materials based on borides, carbides, silicides and other compounds of alkaline earth metals, thorium, uranium and for the manufacture of ceramic-metal materials in combination with niobium, tantalum, titanium and vanadium. Carbide G., the most refractory among simple carbides, is a highly refractory material.

Element characteristic

Hafnium and due to lanthanide compression have almost the same sizes of atoms and -ions, therefore the properties of the elements are as close as in any other subgroup. Their most important difference from titanium is that low oxidation states are extremely rare. Only a few compounds are reliably known where Hf does not exhibit the highest oxidation state. Such compounds are characterized by strong reducing properties. In aqueous solutions of salts

hydrolysis proceeds to a lesser extent than that of titanium salts, however, the existence of free Hf ions⁴ ⁺ seems unlikely. The coordination number in the complexes of this element is higher than that of titanium, and is equal to 7 and even 8.

Properties of simple substances and compounds

In the solid state, hafnium is a lustrous, silvery-white metal. Hafnium belongs to heavy metals, it is refractory and in its pure state has good metallic properties. When contaminated with oxygen, nitrogen, carbon, bromine,hydrogen, etc. lose their plasticity and become hard and brittle. Hafnium forms with iron, chromium, manganese, vanadium, aluminum copper, carbon, sulfur, nitrogen,phosphorus, boron, etc. In the powdered state, it is able to absorb large amounts of hydrogen. FROM chemical point Titanium subgroup vision is inactive, stable in air or in water under normal conditions. At elevated temperatures, they become very active with respect to oxygen, halogens, sulfur, nitrogen, carbon, boron, etc. Oxides are hardly soluble, and the basic properties of their hydrates are enhanced by Hf.

The element does not occur in nature in a free state and cannot be obtained by electrolysis of aqueous solutions. While titanium(IV) oxide is acidic, hafnium oxides are weakly basic. Hydroxides of the elements Hf(OH) 4 (or as hydrated MeO dioxides 2 -2H 2 O) are formed during the treatment of solutions of the corresponding tetrahalides with HfCl 4 and alkalis. They are gelatinous white sediments, poorly soluble in water; exhibit very mildly acidic properties, as a result of which they almost do not react with alkalis. The basic nature of the compound increases from zirconium to hafnium, which, for example, acquires the ability to dissolve in strong acids.

Obtaining and using hafnium

Hafnium is found in all zirconium minerals, where its content does not exceed a few percent of the zirconium content. Separating these elements is more difficult than the lanthanides. This is possible only with the help of ion exchange and extraction. Most often it is used as a material for the construction of nuclear reactors.

The earth's crust contains only four grams of hafnium. The only way to get it is by processing zirconium ore and some other minerals. Ordinary zircons contain up to 4 percent hafnium oxide. To extract this rare metal, zircons are dissolved in boiling acids.

Mining

The richest country in hafnium is Australia. More than 600 tons of this metal are concentrated here. The total reserves of hafnium on the planet are estimated at 1000 tons. There is also a lot of hafnium in Russia - it is found in minerals such as granite, baddeleyite, loparite, etc.

Properties

Outwardly, hafnium looks like a shiny metal with a silvery sheen. Hafnium is very refractory and has a high ability to capture thermal neutrons.

Hafnium is rather inert chemically. An oxide film forms on its surface, which protects it from the action of aggressive environments. Best of all, hafnium dissolves in strong acids - nitric, hydrofluoric and aqua regia.

Application

Hafnium is practically not used in household devices. It is very rare to find super-powerful permanent magnets based on hafnium alloys. But the owners of computers running on Intel Penryn series microprocessors have the opportunity to hold hafnium in their hands. Such processors, for example, include the Intel Core 2 Duo family. They use hafnium compounds as a dielectric.

Hafnium has found wide application in the production of high-power radio tubes, the manufacture of nozzles rocket engines and parts of nuclear reactors. Hafnium oxide has a very high melting point and a good refractive index - based on it, special grades of glass are made for night vision devices, fiber optic networks and thermal imagers.

If you fuse tantalum carbide with hafnium carbide, you get the most refractory alloy in the world. Its melting point is over 4200 degrees. Hafnium is used to make wear-resistant composite coatings, electrodes for argon welding, and reflective coatings for X-ray mirrors.

Let us dwell on another curious application of hafnium. An isotope of hafnium called 178m2 contains so much excess energy that when exposed to it x-rays able to release it explosively. At the same time, as much energy is released from one gram of hafnium-178m2 as is released in the explosion of 50 kilograms of TNT.

hafnium chemical element was opened relatively recently. At the beginning of the twentieth century, Dirk Coster and György Hevesy were busy searching for zirconium and related elements. It was they who discovered hafnium in 1923 and mined its first sample of high purity. What is this element and why is it needed?

Description and properties of hafnium

The element hafnium belongs to the VI group of the periodic system of Mendeleev and is located at number 72, has a mass number of 178. Based on this, we can say which hafnium has an atomic structure: 72 electrons, and the nucleus has the same number of protons and 106 neutrons.

There are six isotopes of hafnium in nature. mass numbers range from 174 to 180, one of them exhibits radioactive properties. Electronic formula of hafnium looks like 4f ​​14 5d 2 6s 2 . The main oxidation state is +4, but +3 and +2 are sometimes found. The electronegativity is 1.6.

In pure solid form, hafnium is a silver-white metal with a characteristic luster, in powder it is matte and gray, almost black. The thermal conductivity is 22 W / (m * K) at a temperature of 100 ° C. The metal is very hard and no less refractory.

Mechanical properties. They in hafnium have a strong dependence on purity and how it was processed. If the metal contains impurities of oxygen, carbon or nitrogen, it becomes brittle.

Firing helps to restore the original properties. Normally, the modulus of elasticity is 137 GPa, the compressibility coefficient is 1.18 GPa, and the hardness is 1.1-1.2 GPa.

Chemically zirconium and hafnium similar. The metal melted into a piece does not interact with water if the pressure does not exceed 25 MPa and the temperature does not exceed 400°C. At three hundred degrees, it begins to interact with water vapor.

hafnium oxide get the more difficult, given that it does not react with oxygen in the air. Oxidation will start only at a temperature of 500-600°C. The higher it is, the faster it will oxidize.

Hafnium dioxides look like crystals or gel. The typical formula for these compounds is HfO 2 * xH 2 O. The defining property is amphoteric, they are also poorly soluble in water and are subject to polycondensation over time.

In alkali solutions hafnium is also stable, at temperatures below one hundred degrees does not begin to react with hydrochloric, sulfuric and nitric acids. May react with:

Hydrofluoric acid;

Mixtures of mineral acids;

Boiling chamois;

A mixture of hydrofluoric and nitrogen;

Royal vodka.

The last two dissolve hafnium best of all. Resistance to mineral acids is reduced by ammonium and alkali metal fluorides.

Origin and production of hafnium

hafnium ore in the classical sense does not exist, this element is rare and scattered. These are those that have a clarke, that is, the content in the earth's crust is less than 0.01-0.001%.

Hafnium is found in nature only together with zirconium, it is even called "shadow", in this regard, it is present in all zirconium minerals. hafnium ore mineral in industry - zircon ZrSiO 4 due to the high degree of substitution of zirconium atoms by hafnium (0.5 ... 2%).

The difficulty of isolating hafnium is in its similarity to zirconium. The industrial method for isolating hafnium consists of several stages:

Zircon is crushed, mixed with graphite and placed in an arc furnace. Air does not enter there, and the temperature rises to 1800 ° C. Zirconium and hafnium carbides are formed, silicon volatilizes.

The carbides are broken into pieces and in a shaft furnace at 500° C. they react with chlorine gas. Tetrachlorides are formed.

Resources of hafnium all over the world, if converted into metal dioxide, are only a little over 1 million tons. The largest part of them is in Australia, about 630 thousand tons.

South Africa, the USA, India and Brazil also have large reserves. As a rule, industrial reserves are zircon from coastal marine placers.

The world's major companies involved in the production and sale of hafnium are Allegheny Technologies Incorporated, Western Zirconium and Cezus. The first two are located in the USA, the last - in.

Application of hafnium

The main scope of this metal is control rods for nuclear reactors. It was first tried in this area in the early 1950s.

main reason, according to which hafnium is used in the nuclear industry, the efficiency of rods made of it practically does not deteriorate over time. Also, a high resistance to corrosion in water at high temperatures plays an important role, even the radiation background does not affect it.

These properties, as well as strength with heat resistance, can be increased by alloying hafnium and, for example, zirconium. Other areas that use this metal get it in very small quantities. The nuclear industry takes more than 90% of hafnium, although only one of its isotopes is radioactive.

This metal is used in alloys and metallurgists, but not as a base material, but as an additive. Hafnium improves the physical and mechanical properties of other metals. Another important application of hafnium is the production of parts in rocket science.

In this area, it is valued for its high refractoriness and ability to quickly absorb and release heat. In tantalum, it does not oxidize unless the temperature exceeds 1650°C.

Due to the high resistance of hafnium to almost all substances, they cover apparatus for the chemical industry. It is also used in radio engineering, the manufacture of parts for electron guns and radio tubes.

Used in optics hafnium oxide because of its high refractive index, mirrors for thermal imagers and devices for seeing in the dark are plated with metal.

One of the areas of application is heavy-duty magnets, they are made from an alloy of hafnium with other rare earth metals. Another interesting area in which this rare metal is used is jewelry.

For attractive, its silvery white color and bright , which does not tarnish, true due to high price hafnium is replaced.

hafnium price

One of the disadvantages of metal hafnium - price. Hafnium necessarily includes production costs, which make up most of the cost due to the complex process of extracting and separating from.

In addition, it depends on the purity of the metal, the batch size and special requirements that may be placed on nuclear grade hafnium. The rental of this metal is traditionally even more expensive. Several magazines, such as Metal Bulletin, have calculated prices for different kinds hafnium for 2005.

So, even metal waste metal cost 176-198 dollars per kg. Various alloys were estimated at 50–150 dollars/kg, hafnium sponge 165–209 dollars/kg, oxide at 150, crystalline rods from 220.

Hafnium of the highest degree of purification cost up to $330 per kg. Now it is much higher, taking into account the elapsed time, inflation and increased consumption of the metal.

Summing up, we can say that hafnium metal quite rare and expensive. It is hard to find it in the public domain. This is due to rather specific areas of application. Despite all this, it is quite popular in less high-tech areas.