Tantalum (Ta) is an element with atomic number 73 and atomic weight 180.948. It is an element of a secondary subgroup of the fifth group, the sixth period of the periodic table of Dmitry Ivanovich Mendeleev. Tantalum in the free state under normal conditions is a platinum-gray metal with a slightly leaden tint, which is a consequence of the formation of an oxide film (Ta 2 O 5). Tantalum is a heavy, refractory, fairly hard, but not brittle metal, at the same time it is very malleable, easily machined, especially in its pure form.

In nature, tantalum is found in the form of two isotopes: stable 181 Ta (99.99%) and radioactive 180 Ta (0.012%) with a half-life of 10 12 years. Of the artificially obtained radioactive 182 Ta (half-life 115.1 days) is used as an isotope indicator.

The element was discovered in 1802 by the Swedish chemist A. G. Ekeberg in two minerals found in Finland and Sweden. It was named after the hero of ancient Greek myths Tantalus due to the difficulty of isolating him. For a long time, the minerals columbite, which contains columbium (niobium), and tantalite, which contains tantalum, were considered to be one and the same. After all, these two elements are frequent companions of each other and are similar in many ways. This opinion was considered correct for a long time among chemists of all countries, only in 1844 the German chemist Heinrich Rose again studied columbites and tantalites from various places and found in them a new metal, similar in properties to tantalum. It was niobium. Plastic pure metal tantalum was first obtained by the German scientist W. von Bolton in 1903.

The main deposits of tantalum minerals are located in Finland, Scandinavian countries, North America, Brazil, Australia, France, China and a number of other countries.

Due to the fact that tantalum has a number of valuable properties - good ductility, high strength, weldability, corrosion resistance at moderate temperatures, refractoriness and a number of other important qualities - the use of the seventy-third element is very wide. The most important areas of application of tantalum are electronics and mechanical engineering. Approximately a quarter of the world's tantalum production goes to the electrical and vacuum industries. In electronics, it is used for the manufacture of electrolytic capacitors, anodes of high-power lamps, and grids. In the chemical industry, tantalum is used to make machine parts used in the production of acids, because this element has exceptional chemical resistance. Tantalum does not dissolve even in such a chemically aggressive environment as aqua regia! Metals, such as rare earths, are melted in tantalum crucibles. Heaters for high-temperature furnaces are made from it. Due to the fact that tantalum does not interact with living tissues of the human body and does not harm them, it is used in surgery to hold bones together during fractures. However, the main consumer of such a valuable metal is metallurgy (over 45%). In recent years, tantalum is increasingly used as an alloying element in special steels - ultra-strong, corrosion-resistant, heat-resistant. In addition, many structural materials quickly lose thermal conductivity: an oxide or salt film that conducts heat poorly is formed on their surface. Structures made of tantalum and its alloys do not face such problems. The oxide film formed on them is thin and conducts heat well, and also has protective anti-corrosion properties.

Not only pure tantalum is valuable, but also its compounds. Thus, the high hardness of tantalum carbide is used in the manufacture of carbide tools for high-speed cutting of metal. Tantalum-tungsten alloys impart heat resistance to parts made from them.

Biological properties

Due to its high biological compatibility - the ability to get along with living tissues without causing irritation or rejection by the body - tantalum has found wide use in medicine, mainly in reconstructive surgery - to restore the human body. Thin plates of tantalum are used for damage to the skull - they close breaks in the skull. Medicine knows of a case where an artificial ear was made from a tantalum plate, and the skin transplanted from the thigh took root so well and quickly that soon the artificial organ could not be distinguished from the real one. Tantalum threads are used to restore damaged muscle tissue. Surgeons use tantalum plates to fasten the walls of the abdominal cavity after operations. Even blood vessels can be connected using tantalum clips. Networks made from this unique material are used in the manufacture of eye prostheses. Threads made of this metal are used to replace tendons and even sew together nerve fibers.

No less widespread is the use of tantalum pentoxide Ta 2 O 5 - its mixture with a small amount of iron trioxide is proposed to be used to accelerate blood clotting.

Over the past decade, a new branch of medicine has been developing, based on the use of short-range static electric fields to stimulate positive biological processes in the human body. Moreover, electric fields are formed not due to traditional electrical energy sources with network or battery power supply, but due to autonomously functioning electret coatings (a dielectric that retains an uncompensated electric charge for a long time), applied to implants for various purposes, widely used in medicine.

Currently, positive results from the use of electret films of tantalum pentoxide have been obtained in the following areas of medicine: maxillofacial surgery (the use of implants coated with Ta 2 O 5 eliminates the occurrence of inflammatory processes and reduces the time of implant healing); orthopedic dentistry (coating dentures made of acrylic plastics with a film of tantalum pentoxide eliminates all possible pathological manifestations caused by intolerance to acrylates); surgery (use of an electret applicator in the treatment of defects of the skin and connective tissue in long-term non-healing wound processes, bedsores, neurotrophic ulcers, thermal injuries); traumatology and orthopedics (acceleration of bone tissue development in the treatment of fractures and diseases of the human musculoskeletal system under the influence of a static field created by an electret coating film).

All these unique scientific developments became possible thanks to the scientific work of specialists from the St. Petersburg State Electrotechnical University (LETI).

In addition to the areas listed above where unique tantalum pentoxide coatings are already being used or are being introduced, there are developments that are in the very early stages. These include developments for the following areas of medicine: cosmetology (production of a material based on tantalum pentoxide coatings, which will replace “golden threads”); cardiac surgery (applying electret films to the inner surface of artificial blood vessels, preventing the formation of blood clots); endoprosthetics (reducing the risk of rejection of prostheses that are in constant interaction with bone tissue). In addition, a surgical instrument coated with tantle pentoxide film is being created.

It is known that tantalum is very resistant to aggressive environments, as evidenced by a number of facts. So at a temperature of 200 °C this metal is not affected by seventy percent nitric acid! In sulfuric acid at a temperature of 150 °C, tantalum corrosion is also not observed, and at 200 °C the metal corrodes, but only by 0.006 mm per year!

There is a known case where at one enterprise that used hydrogen chloride gas, stainless steel parts failed after just a couple of months. However, as soon as steel was replaced by tantalum, even the thinnest parts (0.3...0.5 mm thick) turned out to be practically indefinite - their service life increased to 20 years!

Tantalum, along with nickel and chromium, is widely used as an anti-corrosion coating. It covers parts of a wide variety of shapes and sizes: crucibles, pipes, sheets, rocket nozzles and much more. Moreover, the material on which tantalum coating is applied can be very diverse: iron, copper, graphite, quartz, glass and others. What is most interesting is that the hardness of the tantalum coating is three to four times higher than the hardness of technical tantalum in annealed form!

Due to the fact that tantalum is a very valuable metal, the search for its raw materials continues today. Mineralogists have discovered that ordinary granites, in addition to other valuable elements, also contain tantalum. An attempt to extract tantalum from granite rocks was made in Brazil, the metal was obtained, but such extraction did not reach an industrial scale - the process turned out to be extremely expensive and complex.

Modern electrolytic tantalum capacitors are stable, reliable and durable. Miniature capacitors made from this material, used in various electronic systems, in addition to the above advantages, have one unique quality: they can carry out their own repairs on their own! How does this happen? Suppose that the integrity of the insulation is damaged due to a voltage drop or for another reason - instantly an insulating oxide film is formed again at the site of the breakdown, and the capacitor continues to work as if nothing had happened!

Undoubtedly, the term “smart metal”, which appeared in the middle of the 20th century, that is, a metal that helps smart machines operate, can rightfully be assigned to tantalum.

In some areas, tantalum replaces and sometimes even competes with platinum! Thus, in jewelry work, tantalum often replaces a more expensive noble metal in the manufacture of bracelets, watch cases and other jewelry. In another area, tantalum successfully competes with platinum - standard analytical balances made from this metal are not inferior in quality to platinum ones.

In addition, tantalum is replacing the more expensive iridium in the production of nibs for automatic pens.

Due to its unique chemical properties, tantalum has found application as a material for cathodes. Thus, tantalum cathodes are used in the electrolytic separation of gold and silver. Their value lies in the fact that the sediment of noble metals can be washed off with aqua regia, which does not harm tantalum.

One can definitely talk about the fact that there is something symbolic, if not mystical, in the fact that the Swedish chemist Ekeberg, trying to saturate a new substance with acids, was struck by its “thirst” and gave the new element a name in honor of the mythical villain who killed his own son and betrayed the gods. And two hundred years later it turned out that this element is capable of literally “sewing” a person and even “replacing” his tendons and nerves! It turns out that the martyr, languishing in the underworld, atones for his guilt by helping man, tries to beg forgiveness from the gods...

Story

Tantalus is a hero of ancient Greek myths, a Lydian or Phrygian king, the son of Zeus. He divulged the secrets of the Olympian gods, stole ambrosia from their feast and treated the Olympians to a dish prepared from the body of his own son Pelops, whom he killed. For his atrocities, Tantalus was sentenced by the gods to eternal torment of hunger, thirst and fear in the underworld of Hades. Since then, he has been standing up to his neck in transparent crystal clear water, branches bending towards his head under the weight of ripe fruits. Only he cannot quench his thirst or hunger - the water goes down as soon as he tries to drink, and the branches are lifted by the wind, from the hands of a hungry killer. A rock hangs over Tantalus's head, which could collapse at any moment, forcing the unfortunate sinner to forever suffer from fear. Thanks to this myth, the expression “Tantalum’s torment” arose, denoting unbearable suffering, ethereal attempts to free oneself from torment. Apparently, during the unsuccessful attempts of the Swedish chemist Ekeberg to dissolve the “earth” he discovered in 1802 in acids and isolate a new element from it, it was this expression that came to his mind. More than once the scientist thought that he was close to his goal, but he was never able to isolate the new metal in its pure form. This is how the “martyrdom” name of the new element appeared.

The discovery of tantalum is closely related to the discovery of another element - niobium, which was born a year earlier and was originally named Columbia, which was given to it by its discoverer Hatchet. This element is a twin of tantalum and is close to it in a number of properties. It was this proximity that misled chemists, who, after much debate, came to the erroneous conclusion that tantalum and columbium were the same element. This misconception lasted for more than forty years, until in 1844 the famous German chemist Heinrich Rose, during a repeated study of columbites and tantalites from various deposits, proved that columbium is an independent element. The Columbia studied by Gatchet was niobium with a high tantalum content, which misled the scientific world. In honor of such a close relationship between the two elements, Rose gave Colombia the new name Niobium - in honor of the daughter of the Phrygian king Tantalus Niobia. Although Rose also made the mistake of allegedly discovering another new element, which he named Pelopius (after Tantalus's son Pelops), his work became the basis for a strict distinction between niobium (Columbium) and tantalum. Only, even after Rose’s evidence, tantalum and niobium were confused for a long time. So tantalum was called columbium, in Russia columbus. Hess, in his "Principles of Pure Chemistry" up to its sixth edition (1845), speaks only of tantalum, without mentioning Columbia; Dvigubsky (1824) mentions the name tantalium. Such errors and reservations are understandable - the method for separating tantalum and niobium was developed only in 1866 by the Swiss chemist Marignac, and as such pure elemental tantalum did not yet exist: after all, scientists were able to obtain this metal in its pure compact form only in the 20th century. The first who was able to obtain tantalum metal was the German chemist von Bolton, and this happened only in 1903. Previously, of course, attempts were made to obtain pure tantalum metal, but all the efforts of chemists were unsuccessful. For example, the French chemist Moissan obtained a metal powder, which he claimed was pure tantalum. However, this powder, obtained by reducing tantalum pentoxide Ta 2 O 5 with carbon in an electric furnace, was not pure tantalum; the powder contained 0.5% carbon.

As a result, a detailed study of the physicochemical properties of the seventy-third element became possible only at the beginning of the twentieth century. For several more years, tantalum did not find practical use. Only in 1922 could it be used in AC rectifiers.

Being in nature

The average content of the seventy-third element in the earth's crust (clarke) is 2.5∙10 -4% by mass. Tantalum is a characteristic element of acidic rocks - granite and sedimentary shells, in which its average content reaches 3.5∙10 -4%, as for ultrabasic and basic rocks - the upper parts of the mantle and the deep parts of the earth's crust, the concentration of tantalum there is much lower: 1 .8∙10 -6%. Tantalum is scattered in rocks of igneous origin, as well as in the biosphere, since it is isomorphic with many chemical elements.

Despite the low content of tantalum in the earth's crust, its minerals are very widespread - there are more than a hundred of them, both tantalum minerals themselves and tantalum-containing ores, all of them formed in connection with magmatic activity (tantalite, columbite, loparite, pyrochlore and others). In all minerals, tantalum's companion is niobium, which is explained by the extreme chemical similarity of the elements and the almost identical sizes of their ions.

Tantalum ores themselves have a ratio of Ta 2 O 5: Nb 2 O 5 ≥1. The main minerals of tantalum ores are columbite-tantalite (Ta 2 O 5 content 30-45%), tantalite and manganotantalit (Ta 2 O 5 45-80%), wodginite (Ta, Mn, Sn) 3 O 6 (Ta 2 O 5 60-85%), microlite Ca 2 (Ta, Nb) 2 O 6 (F, OH) (Ta 2 O 5 50-80%) and others. Tantalite (Fe, Mn)(Ta, Nb) 2 O 6 has several varieties: ferrotantalite (FeO>MnO), manganotantalit (MnO>FeO). Tantalite comes in different shades from black to red-brown. The main minerals of tantalum-niobium ores, from which, along with niobium, much more expensive tantalum is extracted, are columbite (Ta 2 O 5 5-30%), tantalum-containing pyrochlore (Ta 2 O 5 1-4%), loparite (Ta 2 O 5 0.4-0.8%), gatchettolite (Ca, Tr, U) 2 (Nb, Ta) 2 O 6 (F, OH)∙nH 2 O (Ta 2 O 5 8-28%), ixiolite (Nb , Ta, Sn, W, Sc) 3 O 6 and some others. Tantalum-niobates containing U, Th, TR are metamict, highly radioactive and contain variable amounts of water; polymorphic modifications are common. Tantalum-niobates form small disseminations, large allocations are rare (crystals are typical mainly for loparite, pyrochlore and columbite-tantalite). Color black, dark brown, brownish-yellow. Usually translucent or slightly translucent.

There are several main industrial and genetic types of tantalum ore deposits. Rare-metal pegmatites of the natro-lithium type are represented by zoned vein bodies consisting of albite, microcline, quartz, and, to a lesser extent, spodumene or petalite. Rare-metal tantalum-bearing granites (apogranites) are represented by small stocks and domes of microcline-quartz-albite granites, often enriched in topaz and lithium micas containing thin dissemination of columbite-tantalite and microlite. Weathering crusts, deluvial-alluvial and alluvial placers arising in connection with the destruction of pegmatites contain cassiterite and minerals of the columbite-tantalite group. Loparite-bearing nepheline syenites of lujavrite and foyalite composition.

In addition, deposits of complex tantalum-niobium ores, represented by carbonatites and associated forsterite-apatite-magnetite rocks, are involved in industrial use; microcline-albite riebeckite alkaline granites and granosyenites and others. Some tantalum is extracted from wolframites of greisen deposits.

The largest deposits of titanium ores are located in Canada (Manitoba, Bernick Lake), Australia (Greenbushes, Pilbara), Malaysia and Thailand (tantalum-bearing tin placers), Brazil (Paraiba, Rio Grande do Norte), and a number of African states (Zaire, Nigeria, Southern Rhodesia).

Application

Tantalum found its technical application quite late - at the beginning of the 20th century it was used as a material for incandescent filaments of electric lamps, which was due to the quality of this metal, such as refractoriness. However, it soon lost its importance in this area, replaced by the less expensive and more refractory tungsten. Tantalum again became “technically unsuitable” until the twenties of the 20th century, when it began to be used in alternating current rectifiers (tantalum, coated with an oxide film, passes current in only one direction), and a year later - in radio tubes. After which the metal gained recognition and soon began to conquer more and more new areas of industry.

Nowadays, due to its unique properties, tantalum is used in electronics (production of capacitors with high specific capacitance). About a quarter of the world's tantalum production goes to the electrical and vacuum industries. Due to the high chemical inertness of both tantalum itself and its oxide film, electrolytic tantalum capacitors are very stable in operation, reliable and durable: their service life can reach more than twelve years. In radio engineering, tantalum is used in radar equipment. Tantalum mini capacitors are used in radio transmitters, radar installations and other electronic systems.

The main consumer of tantalum is metallurgy, which uses over 45% of the metal produced. Tantalum is actively used as an alloying element in special steels - ultra-strong, corrosion-resistant, heat-resistant. The addition of this element to conventional chromium steels increases their strength and reduces brittleness after hardening and annealing. The production of heat-resistant alloys is a great need for rocket and space technology. In cases where rocket nozzles are cooled by liquid metal that can cause corrosion (lithium or sodium), it is simply impossible to do without a tantalum-tungsten alloy. In addition, heaters for high-temperature vacuum furnaces, heaters, and mixers are made from heat-resistant steels. Tantalum carbide (melting point 3,880 °C) is used in the production of hard alloys (mixtures of tungsten and tantalum carbides - grades with the TT index, for the most difficult conditions of metalworking and rotary impact drilling of the strongest materials (stone, composites).

Steels alloyed with tantalum are widely used, for example in chemical engineering. After all, such alloys have exceptional chemical resistance, they are ductile, heat-resistant and heat-resistant; it is thanks to these properties that tantalum has become an indispensable structural material for the chemical industry. Tantalum equipment is used in the production of many acids: hydrochloric, sulfuric, nitric, phosphoric, acetic, as well as bromine, chlorine and hydrogen peroxide. Coils, distillers, valves, mixers, aerators and many other parts of chemical apparatus are made from it. Sometimes - entire devices. Tantalum cathodes are used in the electrolytic separation of gold and silver. The advantage of these cathodes is that gold and silver deposits can be washed off with aqua regia, which does not harm tantalum.

In addition, tantalum is used in instrument making (X-ray equipment, control instruments, diaphragms); in medicine (material for reconstructive surgery); in nuclear energy - as a heat exchanger for nuclear energy systems (tantalum is the most stable of all metals in superheated melts and cesium-133 vapors). The high ability of tantalum to absorb gases is used to maintain high vacuum (electric vacuum devices).

In recent years, tantalum has been used as a jewelry material due to its ability to form durable oxide films of any color on the surface.

Tantalum compounds are also widely used. Tantalum pentoxide is used in nuclear technology to melt glass that absorbs gamma radiation. Potassium fluorotantalate is used as a catalyst in the production of synthetic rubber. Tantalum pentoxide also plays the same role when producing butadiene from ethyl alcohol.

Production

It is known that ores containing tantalum are rare and poor in this element. The main raw materials for the production of tantalum and its alloys are tantalite and loparite concentrates containing only 8% Ta 2 O 5 and more than 60% Nb 2 O 5. In addition, even those ores that contain only hundredths of a percent (Ta, Nb) 2 O 5 are processed!

The tantalum production technology is quite complex and is carried out in three stages: opening or decomposition; separation of tantalum from niobium and obtaining their pure chemical compounds; recovery and refining of tantalum.

The opening of tantalum concentrate, in other words, the extraction of tantalum from ores is carried out using alkalis (fusion) or using hydrofluoric acid (decomposition) or a mixture of hydrofluoric and sulfuric acids. After which they move on to the second stage of production - extraction extraction and separation of tantalum and niobium. The last task is very difficult due to the similarity of the chemical properties of these metals and the almost identical size of their ions. Until recently, metals were separated only by the method proposed back in 1866 by the Swiss chemist Marignac, who took advantage of the different solubility of potassium fluorotantalate and potassium fluoroniobate in dilute hydrofluoric acid. Modern industry uses several methods for separating tantalum and niobium: extraction with organic solvents, selective reduction of niobium pentachloride, fractional crystallization of complex fluoride salts, separation using ion exchange resins, rectification of chlorides. Currently, the most commonly used separation method (it is also the most advanced) is extraction from solutions of tantalum and niobium fluoride compounds containing hydrofluoric and sulfuric acids. At the same time, tantalum and niobium are also purified from impurities of other elements: silicon, titanium, iron, manganese and other related elements. As for loparite ores, their concentrates are processed using the chlorine method to produce a condensate of tantalum and niobium chlorides, which are further separated by rectification. The separation of a mixture of chlorides consists of the following stages: preliminary rectification (separation of tantalum and niobium chlorides from accompanying impurities occurs), main rectification (to obtain pure NbCl 5 and TaCl 5 concentrate) and final rectification of the tantalum fraction (to obtain pure TaCl 5). Following the separation of related metals, the tantalum phase is precipitated and purified to produce potassium fluorotantalate of increased purity (using KCl).

Tantalum metal is obtained by reducing its high-purity compounds, for which several methods can be used. This is either the reduction of tantalum from pentoxide with soot at a temperature of 1800-2000 ° C (carbothermic method), or the reduction of potassium fluorotantalate with sodium when heated (sodium thermal method), or electrochemical reduction from a melt containing potassium fluorotantalate and tantalum oxide (electrolytic method). One way or another, the metal is obtained in powder form with a purity of 98-99%. In order to obtain metal in ingots, it is sintered in the form of pre-compressed billets from powder. Sintering occurs by passing current at a temperature of 2,500–2,700 °C or by heating in a vacuum at 2,200–2,500 °C. After which the purity of the metal increases significantly, becoming equal to 99.9-99.95%.

For further refining and production of tantalum ingots, electric vacuum melting is used in arc furnaces with a consumable electrode, and for deeper refining, electron beam melting is used, which significantly reduces the content of impurities in tantalum, increases its ductility and reduces the temperature of transition to a brittle state. Tantalum of such purity retains high ductility at temperatures close to absolute zero! The surface of a tantalum ingot is melted (to give the required characteristics to the surface of the ingot) or processed on a lathe.

Physical properties

Only at the beginning of the 20th century did scientists get their hands on pure tantalum metal and were able to study in detail the properties of this light gray metal with a slightly bluish lead tint. What qualities does this element have? Definitely, tantalum is a heavy metal: its density is 16.6 g/cm 3 at 20 ° C (for comparison, iron has a density of 7.87 g/cm 3, the density of lead is 11.34 g/cm 3) and for transporting one cubic meter This element would require six three-ton trucks. High strength and hardness are combined with excellent plastic characteristics. Pure tantalum lends itself well to mechanical processing, is easily stamped, processed into the thinnest sheets (about 0.04 mm thick) and wire (elastic modulus of tantalum 190 Hn/m2 or 190·102 kgf/mm2 at 25 °C). In the cold, the metal can be processed without significant work hardening and is subject to deformation with a compression ratio of 99% without intermediate firing. The transition of tantalum from a plastic to a brittle state is not observed even when it is cooled to -196 °C. The tensile strength of annealed high purity tantalum is 206 MN/m2 (20.6 kgf/mm2) at 27 °C and 190 MN/m2 (19 kgf/mm2) at 490 °C; relative elongation 36% (at 27 °C) and 20% (at 490 °C). Tantalum has a body-centered cubic lattice (a = 3.296 A); atomic radius 1.46 A, ionic radii Ta 2+ 0.88 A, Ta 5+ 0.66 A.

As mentioned earlier, tantalum is a very hard metal (the Brinell hardness of tantalum sheets in the annealed state is 450-1250 MPa, in the deformed state 1250-3500 MPa). Moreover, it is possible to increase the hardness of the metal by adding a number of impurities to it, for example carbon or nitrogen (the Brinell hardness of a tantalum sheet after absorbing gases during heating increases to 6000 MPa). As a result, interstitial impurities contribute to an increase in Brinell hardness, tensile strength, and yield strength, but they reduce the plasticity characteristics and increase cold brittleness; in other words, they make the metal brittle. Other characteristic features of the seventy-third element are its high thermal conductivity, at 20–100 °C this value is 54.47 W/(m∙K) or 0.13 cal/(cm·sec·°С) and refractoriness (perhaps the most an important physical property of tantalum) - it melts at almost 3,000 °C (more precisely, at 2,996 °C), second only to tungsten and rhenium. The boiling point of tantalum is also extremely high: 5,300 °C.

As for other physical properties of tantalum, its specific heat at temperatures from 0 to 100 °C is 0.142 kJ/(kg K) or 0.034 cal/(g °C); the temperature coefficient of linear expansion of tantalum is 8.0·10 -6 (at temperatures of 20–1,500 °C). The electrical resistivity of the seventy-third element at 0 °C is 13.2 10 -8 ohm m, at 2000 °C 87 10 -8 ohm m. At 4.38 K the metal becomes a superconductor. Tantalum is paramagnetic, specific magnetic susceptibility 0.849·10 -6 (at 18 °C).

So, tantalum has a unique set of physical properties: high heat transfer coefficient, high ability to absorb gases, heat resistance, refractoriness, hardness, and plasticity. In addition, it is distinguished by high strength - it lends itself well to pressure treatment using all existing methods: forging, stamping, rolling, drawing, twisting. Tantalum is characterized by good weldability (welding and soldering in argon, helium, or in vacuum). In addition, tantalum has exceptional chemical and corrosion resistance (with the formation of an anodic film), low vapor pressure and low electron work function, and, in addition, it gets along well with living tissue of the body.

Chemical properties

Definitely, one of the most valuable properties of tantalum is its exceptional chemical resistance: in this respect it is second only to noble metals, and even then not always. It is resistant to hydrochloric, sulfuric, nitric, phosphoric and organic acids of all concentrations (up to a temperature of 150 ° C). In terms of its chemical stability, tantalum is similar to glass - it is insoluble in acids and their mixtures, even aqua regia does not dissolve it, against which gold and platinum and a number of other valuable metals are powerless. The seventy-third element is soluble only in a mixture of hydrofluoric and nitric acids. Moreover, the reaction with hydrofluoric acid occurs only with metal dust and is accompanied by an explosion. Even in hot hydrochloric and sulfuric acids, tantalum is more resistant than its twin brother niobium. However, tantalum is less resistant to alkalis - hot solutions of caustic alkalis corrode the metal. Salts of tantalic acids (tantalates) are expressed by the general formula: xMe 2 O yTa 2 O 5 H 2 O, these include metatantalates MeTaO 3, orthotantalates Me 3 TaO 4, salts like Me 5 TaO 5, where Me is an alkali metal; in the presence of hydrogen peroxide, pertantalates are also formed. The most important alkali metal tantalates are KTaO 3 and NaTaO 3; these salts are ferroelectrics.

The high corrosion resistance of tantalum is also indicated by its interaction with atmospheric oxygen, or rather, its high resistance to this influence. The metal begins to oxidize only at 280 °C, becoming covered with a protective film of Ta 2 O 5 (tantalum pentoxide is the only stable metal oxide), which protects the metal from the action of chemical reagents and prevents the flow of electric current from the metal to the electrolyte. However, with an increase in temperature to 500 ° C, the oxide film gradually becomes porous, delaminates and separates from the metal, depriving the surface of the protective layer against corrosion. Therefore, it is advisable to carry out hot pressure treatment in a vacuum, since in air the metal oxidizes to a significant depth. The presence of nitrogen and oxygen increases the hardness and strength of tantalum, while simultaneously reducing its ductility and making the metal brittle, and, as mentioned earlier, tantalum forms a solid solution and oxide Ta 2 O 5 with oxygen (with an increase in the O 2 content in tantalum, a sharp increase in strength properties occurs and a strong decrease in ductility and corrosion resistance). Tantalum reacts with nitrogen to form three phases - a solid solution of nitrogen in tantalum, tantalum nitrides: Ta 2 N and TaN - in the temperature range from 300 to 1,100 ° C. It is possible to get rid of nitrogen and oxygen in tantalum under high vacuum conditions (at temperatures above 2,000 °C).

Tantalum reacts weakly with hydrogen until heated to 350 °C; the reaction rate increases significantly only from 450 °C (tantalum hydride is formed and tantalum becomes brittle). The same heating in a vacuum (over 800 °C) helps to get rid of hydrogen, during which the mechanical properties of tantalum are restored and the hydrogen is completely removed.

Fluorine acts on tantalum already at room temperature, and hydrogen fluoride also reacts with the metal. Dry chlorine, bromine and iodine have a chemical effect on tantalum at temperatures of 150 °C and above. Chlorine begins to actively interact with the metal at a temperature of 250 °C, bromine and iodine at a temperature of 300 °C. Tantalum begins to interact with carbon at very high temperatures: 1,200–1,400 °C, and the formation of refractory tantalum carbides, which are very resistant to acids, occurs. Tantalum combines with boron to form borides - solid, refractory compounds that are resistant to the effects of aqua regia. Tantalum forms continuous solid solutions with many metals (molybdenum, niobium, titanium, tungsten, vanadium and others). Tantalum forms limited solid solutions with gold, aluminum, nickel, beryllium and silicon. Tantalum does not form any compounds with magnesium, lithium, potassium, sodium and some other elements. Pure tantalum is resistant to many liquid metals (Na, K, Li, Pb, U-Mg and Pu-Mg alloys).

The discovery of tantalum is closely related to the discovery of niobium. For several decades, chemists considered the element columbium, discovered by the English chemist Hatchett in 1802, and tantalum, discovered in 1802 by the Swede Ekeberg, as one element. Only in 1844 did the German chemist Rose finally prove that these are two different elements, very similar in their properties. And since tantalum was named after the hero of ancient Greek myths Tantalus, he proposed calling “Columbium” niobium after Tantalus’ daughter Niobe. Tantalum itself got its name from the expression “torment of Tantalum”, due to the futility of Ekeberg’s attempts to dissolve the oxide of this element he obtained in acids.

Receipt:

Tantalum almost always accompanies niobium in tantalites and niobites. The main deposits of tantalite are located in Finland, Scandinavia and North America.
The decomposition of tantalum ores in technology is carried out by heating them with potassium hydrogen sulfate in iron vessels, leaching the alloy with hot water and dissolving the remaining powdery tantalum acid residue with contaminated niobic acid. Then tantalum oxide is reduced with coal at 1000°C and the resulting metal is separated in the form of a black powder containing a small amount of oxide. Also, metal powder can be obtained by reducing TaCl 5 with hydrogen or magnesium, as well as potassium fluorotantalate with sodium: K 2 TaF 7 + 5Na = Ta + 2KF + 5NaF.
Metal powder is processed into compact metal using powder metallurgy methods, pressing into “stacks”, followed by plasma or electrobeam melting.

Physical properties:

Tantalum is a heavy, platinum-gray shiny metal with a bluish tint, quite hard, but extremely malleable and ductile; its ductility increases as it is cleaned. Melt = 3027°C (second only to tungsten and rhenium). Heavy, density 16.65 g/cm 3

Chemical properties:

At room temperature it has exceptional chemical resistance. Apart from hydrofluoric acid, tantalum is not affected by any other acids, not even aqua regia. It interacts with a mixture of hydrofluoric and nitric acids, sulfuric anhydride, solutions and melts of alkalis, when heated to 300-400°C with halogens, hydrogen, oxygen, nitrogen, above 1000°C - with carbon.
In compounds it exhibits an oxidation state of +5. However, tantalum compounds with lower oxidation states are also known: TaCl 4, TaCl 3, TaCl 2.

The most important connections:

Tantalum(V) oxide Ta 2 O 5 in a pure state is most conveniently obtained by calcination of pure tantalum metal in a stream of oxygen or by decomposition of Ta (OH) 5 hydroxide. Tantalum(V) oxide is a white, insoluble in water and acids (except for hydrofluoric acid) powder with a specific gravity of 8.02. It does not change when calcined in air, in an atmosphere of hydrogen sulfide or in sulfur vapor. However, at temperatures above 1000°C, the oxide reacts with chlorine and hydrogen chloride. Tantalum(V) oxide is dimorphic. At ordinary temperatures, its rhombic modification is stable.

Tantalates and tantalic acid. By fusing tantalum(V) oxide with alkalis or alkali metal carbonates, tantalates are obtained - salts of metatantalum HTaO 3 and orthotantalic acids H 3 TaO 4 . There are also salts with the composition M 5 TaO 5 . Crystalline substances. used as ferroelectrics.
Tantalic acids are white gelatinous precipitates with variable water content; even freshly prepared ones do not dissolve in hydrochloric and nitric acids. They dissolve well in HF and alkali solutions. In technology, tantalic acid is usually obtained by decomposing double fluoride of tantalum and potassium (potassium heptafluorotantalate) with sulfuric acid.
Tantalum(V) chloride, crystals, hygroscopic, hydrolyzed by water, soluble in CS 2 and CCl 4. It is used in tantalum production and coating.
Tantalum pentafluoride. Can be obtained by reacting pentachloride with liquid hydrogen fluoride. It forms colorless prisms and is hydrolyzed by water. Melt=96.8°С, boil=229°С. Used for applying tantalum coatings.
Potassium heptafluorotantalate- K 2 TaF 7 is a complex compound that can be obtained by reacting tantalum pentafluoride with potassium fluoride. White crystals, stable in air. Hydrolyzed by water: K 2 TaF 7 + H 2 O -> Ta 2 O 5 *nH 2 O + KF + HF

Application:

Since tantalum combines excellent metallic properties with exceptional chemical resistance, it has proven highly suitable for the manufacture of surgical and dental instruments such as tweezer tips, injection needles, needles, etc. In some cases it can replace platinum.
They are also used for the manufacture of capacitors, cathodes of electron tubes, equipment in the chemical industry and nuclear energy, and dies for the production of artificial fibers. Carbide, silicide, tantalum nitride - heat-resistant materials, components of hard and heat-resistant alloys.
Heat-resistant alloys of tantalum with niobium and tungsten are used in rocket and space technology.

E. Rosenberg.

Sources: Tantalum // Popular library of chemical elements Publishing house "Science", 1977.
Tantalum // Wikipedia. Update date: 12/12/2017. (access date: 05/20/2018).
// S. I. Levchenkov. A brief outline of the history of chemistry/ SFU.

TANTALUM, Ta (named after the hero of ancient Greek mythology Tantalus; lat. Tantalum * a. tantalum; n. Tantal; f. tantale; i. tantalo), is a chemical element of group V of the periodic system of Mendeleev, atomic number 73, atomic mass 180 ,9479. It occurs in nature in the form of two isotopes: 181 Ta (99.9877%) and 180 Ta (0.0123%). There are 13 known artificial radioactive isotopes of tantalum with mass numbers from 172 to 186. Tantalum was discovered in 1802 by the Swedish chemist A. G. Ekeberg. Plastic metal tantalum was first obtained by the German scientist W. Bolten in 1903.

Application and use

The main raw materials for the production of tantalum and its alloys are tantalite and loparite concentrates containing about 8% Ta 2 O 5, 60% or more Nb 2 O 5. Concentrates are decomposed by acids or alkalis, while loparite concentrates are chlorinated. The separation of Ta and Nb is carried out using extraction. Metallic tantalum is usually obtained by reduction of Ta 2 O 5 with carbon, or electrochemically from melts.

Compact metal is produced by vacuum arc, plasma melting or powder metallurgy. Corrosion-resistant equipment for the chemical industry, dies, laboratory glassware and crucibles are made from tantalum and its alloys; heat exchangers for nuclear energy systems. In surgery, sheets, foil and wire made of tantalum are used to fasten tissues, nerves, apply sutures, and make prostheses that replace damaged parts of bones (due to biological compatibility). Tantalum carbide is used in the production of hard alloys.

Tantalum has a high melting point -- 3290 K (3017 °C); boils at 5731 K (5458 °C).

Tantalum density is 16.65 g/cm. Despite its hardness, it is as flexible as gold. Pure tantalum lends itself well to machining, is easily stamped, rolled into wire and thin sheets a hundredths of a millimeter thick. Tantalum is an excellent getter (gas absorber); at 800 °C it is capable of absorbing 740 volumes of gas. Tantalum has a body-centered cubic lattice. Has paramagnetic properties. At 4.38 K it becomes a superconductor. Pure tantalum is a ductile metal that can be processed by pressure in the cold without significant hardening. It can be deformed with a reduction rate of 99% without intermediate annealing. The transition of tantalum from a ductile to a brittle state upon cooling to -196 °C was not detected. The properties of tantalum depend largely on its purity; impurities of hydrogen, nitrogen, oxygen and carbon make the metal brittle.

Electronic structure of the atom.

1s 22s 22p 63s 23p64s 23d104p65s24d105p66s24f145d3

serial number-73

Belonging to group - A

d-element

Tantalum (V) oxide is a white powder, insoluble in either water or acids (except H2F2). Very refractory (tmelt = 1875°C). The acidic nature of the oxide is rather weakly expressed and mainly manifests itself during the reaction with alkali melts: tantalum atom oxidation of niobium

Ta2O5 + 2NaOH = 2NaTaO3 + H2O

or carbonates:

Ta2O5 + 3Na2CO3 = 2Na3TaO4 + 3CO2

Salts containing tantalum in the -4, -5 oxidation state can be of several types: metatantalates NaTaO3, orthotantalates Na3TaO4, but there are polyions penta- and hexa-, crystallizing together with water molecules, 7- and 8-. Five-charged tantalum forms the TaO3+ cation and salts TaO(NO3)3 or Nb2O5(SO4)3 in reactions with acids, continuing the “tradition” of the side subgroup introduced by the vanadium ion VO2+.

At 1000°C Ta2O5 reacts with chlorine and hydrogen chloride:

Ta2O5+ 10HC1==2ТаС15+5Н2О

Consequently, it can be argued that tantalum (V) oxide is also characterized by amphotericity with superior acidic properties over the properties of a base.

The hydroxide corresponding to tantalum (V) oxide is obtained by neutralizing acidic solutions of tantalum tetrachloride. This reaction also confirms the instability of the +4 oxidation state.

At low oxidation states, the most stable compounds are halides (see Fig. 3). The easiest way to obtain them is through pyridine complexes. Pentahalides TaX5 (where X is C1, Br, I) are easily reduced by pyridine (denoted by Py) to form complexes of the composition MX4(Py)2.

Tantalum salts. Salts of the sixth subgroup are predominantly colorless crystals or white powders. Many of them are very hygroscopic and diffuse in air. The oxides of these metals have amphoteric properties, so most of their salts are easily hydrolyzed, turning into basic salts that are slightly or completely insoluble in water. Salts are also known where these metals are part of the anions (for example, niobates and tantalates) Hydration and dehydration. All catalysts of this class have a strong affinity for water. The main representative of the b class is alumina. Phosphoric acid or its acid salts are also used on carriers such as aluminosilicate gel and silica gel with tantalum, zirconium or hafnium oxides. In the first works on the separation of tantalum and niobium by fractionated extraction, the systems hydrochloric acid-xylene-methyldioctylamine (1952), as well as hydrochloric acid-hydrofluoric acid-diisopropyl ketone (1953) were proposed. Both metals are dissolved in aqueous acid solutions as salts, and then tantalum is extracted with an organic solvent. In the system 6/W sulfuric acid--9 Ai hydrofluoric acid

7. Tantalum is used to make dies for drawing threads in the production of artificial fibers. Previously, such dies were made of platinum and gold. The hardest alloys are made from tantalum carbide with nickel as a cementitious additive. They are so hard that they leave scratches even on diamond, which is considered the standard of hardness.

The first place in terms of the critical temperature of transition to the superconducting state was given to niobium germanide Nb3Ge. Its critical temperature is 23.2K (about -250 °C). Another compound, niobium stannide, becomes a superconductor at a slightly lower temperature of -255 °C. To more fully appreciate this fact, we point out that most superconductors are known only for temperatures of liquid helium (2.172 K). Superconductors made from niobium materials make it possible to produce magnetic coils that create extremely powerful magnetic fields. A magnet with a diameter of 16 cm and a height of 11 cm, where the winding is a tape made of such material, is capable of creating a field of colossal intensity. It is only necessary to transfer the magnet to a superconducting state, that is, to cool it, and cooling to a lower temperature is, of course, easier to do.

The role of niobium in welding is important. While ordinary steel was being welded, this process did not present any particular difficulties and did not create any difficulties. However, when they began to weld structures made of special steels of complex chemical composition, the welds began to lose many valuable qualities of the metal being welded. Neither changes in the composition of the electrodes, nor improvements in the designs of welding machines, nor welding in an atmosphere of inert gases had any effect. This is where niobium comes to the rescue. Steel into which niobium is introduced as a small additive can be welded without fear for the quality of the weld (Fig. 4). The fragility of the weld is caused by the carbides formed during welding, but the ability of niobium to combine with carbon and prevent the formation of carbides of other metals that violate the properties of the alloys saved the situation. Carbides of niobium itself, like tantalum, have sufficient viscosity. This is especially valuable when welding boilers and gas turbines operating under pressure and in aggressive environments.

Niobium and tantalum are capable of absorbing significant quantities of gases such as hydrogen, oxygen and nitrogen. At room temperature, 1 g of niobium is capable of absorbing 100 cm3 of hydrogen. But even with strong heating, this property practically does not weaken. At 500°C, niobium can still absorb 75 cm3 of hydrogen, and tantalum 10 times more. This property is used to create high vacuums or in electronic devices where it is necessary to maintain precise characteristics at high temperatures. Niobium and tantalum, deposited on the surface of parts like a sponge, absorb gases, ensuring stable operation of devices. Reconstructive surgery has achieved great success with the help of these metals. Medical practice included not only plates of tantalum, but also threads of tantalum and niobium. Surgeons have successfully used such threads to stitch together torn tendons, blood vessels and nerves. Tantalum “yarn” serves to compensate for muscular strength. With its help, surgeons strengthen the walls of the abdominal cavity after surgery. Tantalum has extremely strong bonds between atoms. This causes its extremely high melting and boiling points. Mechanical qualities and chemical resistance bring tantalum closer to platinum. The chemical industry uses this favorable combination of tantalum qualities. It is used to prepare parts for acid-resistant equipment of chemical plants, heating and cooling devices that come into contact with aggressive environments.

Two properties of niobium are being used in the rapidly developing nuclear energy industry. Niobium has amazing “transparency” for thermal neutrons, that is, it is able to pass them through a layer of metal without practically reacting with neutrons. The artificial radioactivity of niobium (produced by contact with radioactive materials) is low. Therefore, it can be used to make containers for storing radioactive waste and installations for their processing. Another equally valuable (for a nuclear reactor) property of niobium is the absence of noticeable interaction with uranium and other metals even at a temperature of 1000 °C. Molten sodium and potassium, used as coolants in some types of nuclear reactors, can circulate freely through niobium pipes without causing any harm to them.

The rapid development of modern technologies today is certainly associated with the use of effective materials and substances that have quite practical and very useful properties and features.

From this perspective, it is worth paying attention to such a unique chemical element as tantalum. And this is not surprising, because thanks to its strength characteristics, today the use of tantalum is becoming quite relevant in many areas of industry.

To broaden the horizons of the average person on this topic, we will describe in detail the physical and chemical properties of tantalum and talk about where this metal is very successfully used today.

Technical features of tantalum

First of all, it is worth understanding that tantalum is a gray metal with a shiny tint that can be easily processed mechanically.

Among the features of the metal, it is worth noting a number of the following important aspects:

• serial number in the periodic table - 73;
• atomic weight - 180;
• the density of the substance is 60 g/cm3;
• melting point - 3015 0 C;
• The boiling point of the substance is 5300 0 C.

Metal properties

Due to these characteristics, tantalum undoubtedly has the following advantageous properties:

1. Tantalum is a refractory metal, and, as a result, the element has the following properties:

• small linear expansion rate;
• good level of thermal conductivity;
• high mechanical strength and ductility.

1. Has excellent anti-corrosion qualities. It is worth noting that tantalum under normal conditions is practically inert to sea water, but if it is saturated with oxygen, then the metal in this case only tarnishes.
2. Tantalum has good resistance to the following types of salts:

• iron and copper chlorides;
• nitrates;
• sulfates;
• salts of organic acids, however, provided that they do not contain fluorine or fluorides.

1. Tantalum begins to lose its strength characteristics when it reacts with fluorine. It is also worth considering the fact that tantalum does not react chemically with bromine, iodine and liquid chlorine unless a temperature of 150 0 C is reached.
2. Tantalum is quite resistant to the effects of liquid metals with a low melting point.
3. Tantalum has excellent stability characteristics in air at temperatures up to 400 0 C, while a protective oxide film appears during storage or processing.
4. Tantalum melted by the electron beam method has an increased plasticity property, which, when the metal is deformed, allows for a greater degree of compression.
5. It converts well into sheet metal, which lends itself well to forging.
6. It lends itself well to processing during cold deformation. However, you need to understand that this metal should not be deformed in a hot state, since when heated, tantalum begins to absorb nitrogen, carbon dioxide, oxygen, and, as a result, the material becomes quite brittle.
7. One of the main operations in tantalum processing is cutting the material on high-speed equipment.

As for the connection of tantalum parts, it can be done in the following ways:

• welding;
• soldering;
• connection using rivets.

Here it is worth taking into account the fact that the last two methods are used quite rarely, so the quality of tantalum welded joints always remains at a high level.

Areas of application of tantalum

These properties make it possible to widely use it in various fields of industry. Let us note in detail the main directions of use of such a unique material as tantalum.

Metallurgical industry

Metallurgy is the main consumer of this metal. The metallurgical industry accounts for 45% of tantalum production.

The main use of tantalum lies in a number of the following important aspects:

• metal is the main alloying element in the manufacture of heat-resistant and anti-corrosion steel grades;
• Tantalum carbide is a reliable protection for steel molds in foundries.

Electrical industry

First of all, it is worth noting the fact that a quarter of the tantalum produced in the world is used in the electrical industry. And this is not surprising, because the following types of electrical products are produced using this metal:

• electrolytic tantalum capacitors are characterized by stable operation;
• widely used in the manufacture of structural elements of lamps such as anodes, indirectly heated cathodes and grids;
• tantalum wire is used in the production of cryotron parts, which are integral elements of computer technology;
• Heaters for furnaces with high-temperature operating conditions are very successfully made from this metal.

Interesting fact! Tantalum capacitors tend to self-repair. For example, when a high voltage suddenly appeared, a spark destroyed the insulating layer. In this case, an insulating oxide film is instantly formed at the site of the defect, while the capacitor will continue to function in normal operating mode!

Chemical industry

It is necessary, first of all, to note the fact that 20% of the tantalum used goes to the needs of the chemical industry. In particular, this metal is used in the following cases:

• production of the following types of acids:

1. nitrogen;
2. Olyanaya;
3. sulfuric;
4. phosphorus;
5. vinegar

• production of hydrogen peroxide, bromine and chlorine;
• production of chemical equipment of the following types:

1. aerators;
2. distillation plants;
3. coils of different types;
4. stirrers;
5. valve

IN medical industry no more than 5% of the tantalum mined in the world is used. In medicine, this metal is very successfully used in plastic and bone surgery, so tantalum elements are made from it for fastening bones, suturing, etc. This is achieved due to the fact that tantalum does not harm the vital functions of the body and does not irritate living tissue.