Tantalum designation. Properties of simple substances and compounds

Story

Tantalum was discovered in 1802 by the Swedish chemist A. G. Ekeberg in two minerals found in Finland and Sweden. However, it was not possible to isolate it in its pure form. Due to the difficulty of obtaining this element, it was named after the hero of ancient Greek mythology, Tantalus.

Subsequently, tantalum and "columbium" (niobium) were considered identical. Only in 1844, the German chemist Heinrich Rose proved that the mineral columbite-tantalite contains two different elements - niobium and tantalum.

About 20 native minerals of tantalum are known - a series of columbite-tantalite, vojinite, loparite, manganotantalite and others, as well as more than 60 minerals containing tantalum. All of them are associated with endogenous mineral formation. In minerals, tantalum is always found together with niobium due to the similarity of their physical and chemical properties. Tantalum is a typically dispersed element, as it is isomorphic with many chemical elements. Deposits of tantalum are confined to granitic pegmatites, carbonatites and alkaline layered intrusions.

Place of Birth

The largest deposits of tantalum ores are located in France, Egypt, Thailand, and China. There are also deposits of tantalum ores in Mozambique, Australia, Nigeria, Canada, Brazil, CIS, DRC, Malaysia.

The world's largest deposit of tantalum ores, Greenbushes, is located in Australia in the state of Western Australia, 250 km south of Perth.

Physical properties

At temperatures below 4.45 K, it goes into the superconducting state.

Chemical properties

Under normal conditions, tantalum is inactive; it oxidizes in air only at temperatures above 280 ° C, becoming covered with an oxide film of Ta 2 O 5; reacts with halogens at temperatures above 250 °C. When heated, it reacts with C, B, Si, P, Se, Te, H 2 O, CO, CO 2, NO, HCl, H 2 S.

Chemically pure tantalum is exceptionally resistant to liquid alkali metals, most inorganic and organic acids, and many other aggressive media (with the exception of molten alkalis).

In terms of chemical resistance to reagents, tantalum is similar to glass. Tantalum is insoluble in acids and their mixtures, except for a mixture of hydrofluoric and nitric acids; even aqua regia does not dissolve it. The reaction with hydrofluoric acid occurs only with metal dust and is accompanied by an explosion. Very resistant to sulfuric acid of any concentration and temperature (at 200 ° C, the metal corrodes in acid by only 0.006 millimeters per year), stable in deoxygenated molten alkali metals and their superheated vapors (lithium, sodium, potassium, rubidium, cesium).

Toxicology

Prevalence

Receipt

The main raw materials for the production of tantalum and its alloys are tantalite and loparite concentrates containing about 8% Ta 2 O 5 , as well as 60% or more Nb 2 O 5 . Concentrates are decomposed by acids or alkalis, loparite concentrates are chlorinated. The separation of Ta and Nb is carried out by extraction. Tantalum metal 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.

To obtain 1 ton of tantalum concentrate, it is necessary to process up to 3,000 tons of ore.

Price

Application

It was originally used to make wire for incandescent lamps. Today, tantalum and its alloys are used to make:

• heat-resistant and corrosion-resistant alloys;
• corrosion-resistant equipment for the chemical industry, spinnerets, laboratory glassware and crucibles for obtaining, melting, and casting rare earth elements, as well as yttrium and scandium;
• heat exchangers for nuclear power systems (tantalum is the most stable of all metals in superheated melts and cesium vapor);
• in surgery, tantalum sheets, foil and wire are used to fasten tissues, nerves, suturing, making prostheses that replace damaged parts of bones (due to biological compatibility);
• tantalum wire is used in cryotrons - superconducting elements installed in computer technology;
• in the production of ammunition, tantalum is used to make metal lining of advanced shaped charges, which improves armor penetration;
• tantalum and niobium are used to make electrolytic capacitors (higher quality than aluminum electrolytic capacitors, but designed for lower voltage);
• tantalum has been used in recent years as a jewelry metal, due to its ability to form durable oxide films of beautiful rainbow colors on the surface;
• the nuclear isomer tantalum-180m2, which accumulates in the structural materials of nuclear reactors, can, along with hafnium-178m2, serve as a source of gamma rays and energy in the development of weapons and special vehicles.
• The US Bureau of Standards and the International Bureau of Weights and Measures of France use tantalum instead of platinum to make high precision standard analytical weights;
• Tantalum beryllide is extremely hard and resistant to oxidation in air up to 1650 ° C, used in aerospace technology;
• tantalum carbide (melting point 3880 ° C, hardness close to that of diamond) is used in the production of hard alloys - a mixture of tungsten and tantalum carbides (TT index grades), for the most difficult conditions of metalworking and percussive rotary drilling of the strongest materials (stone, composites), and also applied to nozzles, nozzles of rockets;
• Tantalum(V) oxide is used in nuclear technology to melt glass that absorbs gamma radiation. One of the most widely used compositions of such glass: silicon dioxide - 2%, lead monoxide (litharge) - 82%, boron oxide - 14%, tantalum pentoxide - 2%;
• in numismatics. Since 2006

The gods punished the Phrygian king Tantalus for unjustified cruelty. They doomed Tantalus to eternal torments of thirst, hunger and fear. Since then, he stands in the underworld up to his throat in clear water. Under the weight of ripened fruits, the branches of trees lean towards him. When the thirsty Tantalum tries to get drunk, the water goes down. As soon as he stretches out his hand to the juicy fruits, the wind lifts the branch, and the sinner, exhausted from hunger, cannot reach it. And right above his head hung a rock, threatening to collapse at any moment.

So the myths of Ancient Greece tell about the torments of Tantalus. The Swedish chemist Ekeberg must have had to remember more than once about tantalum flour when he unsuccessfully tried to dissolve the "earth" discovered by him in 1802 in acids and isolate a new element from it. How many times, it seemed, the scientist was close to the goal, but he failed to isolate a new metal in its pure form. Hence the “martyr” name of element No. 73.

Controversy and misconceptions

After some time, it turned out that tantalum has a twin, which was born a year earlier. This twin is element #41, discovered in 1801 and originally named Columbia. Later it was renamed to niobium. The similarity of niobium and tantalum has misled chemists. After much debate, they came to the conclusion that tantalum and Columbia are one and the same.

At first, the most famous chemist of that time, Jene Jakob Berzelius, adhered to the same opinion, but later he doubted this. In a letter to his student, the German chemist Friedrich Wöhler, Berzelius wrote:

“I am sending you back your X, whom I asked as best I could, but from whom I received evasive answers. Are you a titan? I asked. He answered: Wöhler told you that I am not a Titan.

I also installed this.

Are you a zircon? - No, - he answered, - I dissolve in soda, which zirconium earth does not do. - Are you a tin? “I do contain tin, but very little. Are you a tantalum? I am related to him, - he answered, - but I dissolve in caustic potash and precipitate yellow-brown from it. “Well, what kind of devilish thing are you then?” I asked. Then it seemed to me that he answered: they did not give me a name.

By the way, I'm not quite sure if I really heard it, because he was on my right, and I can't hear very well in my right ear. Since your hearing is better than mine, I send this tomboy back to you to inflict a new interrogation on him ... "

This letter was about an analogue of tantalum, an element discovered by the Englishman Charles Hatchet in 1801.

But Wöhler failed to clarify the relationship between tantalum and Colombia. Scientists were destined to err for more than forty years. It was only in 1844 that the German chemist Heinrich Rosa managed to resolve the confusing problem and prove that Colombia, like tantalum, has every right to "chemical sovereignty". And since there were family ties of these elements, Rose gave Columbia a new name - niobium, which emphasized their relationship (in ancient Greek mythology, Niobe - Tantalus' daughter).

First steps

For many decades, designers and technologists showed no interest in tantalum. Actually, tantalum, as such, simply did not exist: after all, scientists were able to obtain this metal in its pure compact form only in the 20th century. The first to do this was the German chemist von Bolton in 1903. Even earlier, attempts to isolate pure tantalum were made by many scientists, in particular Moissan. But the metal powder obtained by Moissan, who reduced tantalum pentoxide Ta 2 O 5 with carbon in an electric furnace, was not pure tantalum, the powder contained 0.5% carbon.

So, at the beginning of our century, pure tantalum fell into the hands of researchers, and now they could already study in detail the properties of this light gray metal with a slightly bluish tint.

What does he represent? First of all, it is a heavy metal: its density is 16.6 g / cm 3 (note that it would take six three-ton trucks to transport a cubic meter of tantalum).

High strength and hardness are combined in it with excellent plastic characteristics. Pure tantalum lends itself well to machining, easy stamping, processed into the thinnest sheets (about 0.04 mm thick) and wire. A characteristic feature of tantalum is its high thermal conductivity. But perhaps the most important physical property of tantalum is its refractoriness: it melts at almost 3000°C (more precisely, at 2996°C), second only to tungsten and rhenium in this.

When it became known that tantalum is very refractory, scientists had the idea to use it as a material for the filaments of electric lamps. However, a few years later, tantalum was forced to give way to this field even more refractory and not so expensive tungsten.

For several more years, tantalum did not find practical use. It was only in 1922 that it could be used in AC rectifiers (tantalum, coated with an oxide film, passes current in only one direction), and a year later, in radio tubes. At the same time, the development of industrial methods for obtaining this metal began. The first industrial sample of tantalum, obtained by one of the American firms in 1922, was the size of a match head. Twenty years later, the same company commissioned a specialized plant for the production of tantalum.

How tantalum is separated from niobium

The earth's crust contains only 0.0002% Ta, but many of its minerals are known - over 130. Tantalum in these minerals, as a rule, is inseparable from niobium, which is explained by the extreme chemical similarity of the elements and the almost identical sizes of their ions.

The difficulty of separating these metals for a long time hindered the development of the industry of tantalum and niobium. Until recently, they were isolated only by the method proposed as early as 1866 by the Swiss chemist Marignac, who took advantage of the different solubility of tantalate fluorine and potassium fluorine niobate in dilute hydrofluoric acid.

In recent years, extraction methods for separating tantalum, based on the different solubilities of tantalum and niobium salts in certain organic solvents, have also acquired great importance. Experience has shown that methyl ethyl ketone and cyclohexanone have the best extraction properties.

Nowadays, the main method for the production of metallic tantalum is the electrolysis of molten potassium fluorine tantalate in graphite, cast iron or nickel crucibles, which also serve as cathodes. Tantalum powder is deposited on the walls of the crucible. Extracted from the crucible, this powder is first pressed into rectangular plates (if the workpiece is intended for rolling into sheets) or square bars (for wire drawing), and then sintered.

Some application is also found by the sodium-thermal method for the production of tantalum. Potassium fluorine tantalate and sodium metal interact in this process:

K 2 TaF 7 + 5Na → Ta + 2KF + 5NaF.

The end product of the reaction is powdered tantalum, which is then sintered. In the last two decades, other powder processing methods have also been used - vacuum arc or induction melting and electron beam melting.

In the service of chemistry

Undoubtedly, the most valuable property of tantalum is its exceptional chemical resistance: in this respect it is second only to noble metals, and even then not always.

Tantalum does not dissolve even in such a chemically aggressive environment as aqua regia, which easily dissolves gold, platinum, and other precious metals. The following facts testify to the highest corrosion resistance of tantalum. At 200°C, it is not susceptible to corrosion in 70% nitric acid, in sulfuric acid at 150°C, tantalum corrosion is also not observed, and at 200°C, the metal corrodes, but only by 0.006 mm per year.

In addition, tantalum is a ductile metal; thin-walled products and products of complex shape can be made from it. Not surprisingly, it 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), bromine, chlorine, hydrogen peroxide. At one facility using hydrogen chloride gas, stainless steel parts failed after two months. But, 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.

Of all the acids, only hydrofluoric acid is capable of dissolving tantalum (especially at high temperatures). Coils, distillers, valves, mixers, aerators and many other parts of chemical apparatus are made from it. Less often - devices entirely.

Many structural materials quickly lose their thermal conductivity: a poorly heat-conducting oxide or salt film forms on their surface. Tantalum equipment is free from this drawback, or rather, an oxide film can form on it, but it is thin and conducts heat well. By the way, it is high thermal conductivity combined with plasticity that made tantalum an excellent material for heat exchangers.

Tantalum cathodes are used in the electrolytic separation of gold and silver. The advantage of these cathodes is that the deposit of gold and silver can be washed off them with aqua regia, which does not harm the tantalum.

Tantalum is important not only for the chemical industry. Many research chemists also meet with him in their daily laboratory practice. Tantalum crucibles, cups, spatulas are not uncommon.

“You need to have tantalum nerves…”

The unique quality of tantalum is its high biological compatibility, i.e. the ability to take root in the body without causing irritation of surrounding tissues. This property is the basis for the widespread use of tantalum in medicine, mainly in reconstructive surgery - for the repair of the human body. Plates of this metal are used, for example, in case of damage to the skull - they close the fractures of the skull. The literature describes a case when an artificial ear was made from a tantalum plate, and the skin transplanted from the thigh took root so well that it was soon difficult to distinguish the tantalum ear from the real one.

Tantalum yarn is sometimes used to compensate for the loss of muscle tissue. With the help of thin tantalum plates, surgeons strengthen the walls of the abdominal cavity after surgery. Tantalum staples, similar to those used to sew notebooks, securely connect blood vessels. Nets made of tantalum are used in the manufacture of ocular prostheses. Tendons are replaced with threads of this metal and even nerve fibers are sewn together. And if we usually use the expression "iron nerves" in a figurative sense, then you may have met people with tantalum nerves.

Indeed, there is something symbolic in the fact that it was on the share of the metal, named after the mythological martyr, that the humane mission fell - to alleviate human suffering ...

The main customer is metallurgy

However, only 5% of the tantalum produced in the world is spent on medical needs, about 20% is consumed by the chemical industry. The main part of tantalum - over 45% - goes to metallurgy. In recent years, tantalum has been increasingly used as an alloying element in special steels - heavy-duty, corrosion-resistant, heat-resistant. The effect exerted on steel by tantalum is similar to that of niobium. The addition of these elements to conventional chromium steels increases their strength and reduces brittleness after hardening and annealing.

A very important field of application of tantalum is the production of heat-resistant alloys, which are increasingly needed by rocket and space technology. An alloy consisting of 90% tantalum and 10% tungsten has remarkable properties. In the form of sheets, such an alloy is efficient at temperatures up to 2500°C, and more massive parts can withstand over 3300°C! Abroad, this alloy is considered quite reliable for the manufacture of nozzles, exhaust pipes, parts of gas control and regulation systems, and many other critical components of spacecraft. In cases where rocket nozzles are cooled by a liquid metal that can cause corrosion (lithium or sodium), it is simply impossible to do without an alloy of tantalum and tungsten.

Even greater heat resistance of parts made of tantalum-tungsten alloy is obtained if a layer of tantalum carbide is deposited on them (the melting point of this coating is over 4000 ° C). During experimental rocket launches, such nozzles withstood enormous temperatures, at which the alloy itself quickly corrodes and collapses.

Another advantage of tantalum carbide - its hardness, close to that of diamond - led this material to the production of carbide tools for high-speed metal cutting.

Working under stress

Approximately a quarter of the world's tantalum production goes to the electrical and vacuum industry. 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 reaches 12 years, and sometimes more. Miniature tantalum capacitors are used in radio transmitters, radar installations and other electronic systems. It is curious that these capacitors can repair themselves: suppose a spark that occurred at high voltage destroyed the insulation - immediately an insulating oxide film forms again at the breakdown site, and the capacitor continues to work as if nothing had happened.

Tantalum oxide has the most valuable property for electrical engineering: if an alternating electric current is passed through a solution in which tantalum is immersed, covered with the thinnest (only a few microns!) Oxide film, it will go in only one direction - from the solution to the metal. Tantalum rectifiers are based on this principle, which are used, for example, in the signal service of railways, telephone switches, fire alarm systems.

Tantalum serves as a material for various parts of electrovacuum devices. Like niobium, it does an excellent job as a getter, i.e. getter. So, at 800°C, tantalum is able to absorb an amount of gas that is 740 times its own volume. And they also make hot fittings for lamps from tantalum - anodes, grids, indirectly heated cathodes and other heated parts. Tantalum is especially needed for lamps that, operating at high temperatures and voltages, must maintain accurate characteristics for a long time. Tantalum wire is used in kenotrons - superconducting elements needed, for example, in computer technology.

Side "specialties" of tantalum

Tantalum is a fairly frequent guest in jewelers' workshops; in many cases, it is replaced by platinum. Tantalum is used to make watch cases, bracelets and other jewelry. And in another area, element No. 73 competes with platinum: standard analytical weights made of this metal are not inferior in quality to platinum ones. Tantalum is used as a replacement for the more expensive iridium in the production of nibs for automatic pens. But this track record of tantalum is not exhausted. Specialists in military technology believe that it is expedient to manufacture some parts of guided missiles and jet engines from tantalum.

Tantalum compounds are also widely used. Thus, potassium fluorotantalate is used as a catalyst in the production of synthetic rubber. Tantalum pentoxide also plays the same role in the production of butadiene from ethyl alcohol.

Tantalum oxide is sometimes also used in glassmaking - for the manufacture of glasses with a high refractive index. A mixture of five oxides of tantalum Ta 2 O 5 with a small amount of iron trioxide is proposed to be used to accelerate blood clotting. Tantalum hydrides are successfully used for soldering contacts on silicon semiconductors.

The demand for tantalum is constantly growing, and therefore there is no doubt that in the coming years the production of this wonderful metal will increase faster than now.

Tantalum is harder… tantalum

Tantalum coatings are no less attractive than, say, nickel and chromium coatings. Attractive not only externally. Methods have been developed that make it possible to cover large-sized products (crucibles, pipes, sheets, rocket nozzles) with a tantalum layer of various thicknesses, and the coating can be applied to a wide variety of materials - steel, iron, copper, nickel, molybdenum, alumina, graphite, quartz, glass, porcelain and others. Characteristically, the hardness of the tantalum coating, according to Brinell, is 180...200 kg/mm ​​2 , while the hardness of technical tantalum in the form of annealed bars or sheets ranges from 50...80 kg/mm ​​2 .

Cheaper than platinum, more expensive than silver

Replacing platinum with tantalum, as a rule, is very profitable - it is several times cheaper than it. Nevertheless, tantalum cannot be called cheap. The relative high cost of tantalum is explained by the high price of materials used in its production and the complexity of the technology for obtaining element No. 73: to obtain a ton of tantalum concentrate, it is necessary to process up to 3 thousand tons of ore.

Granite metal

The search for tantalum raw materials continues to this day. Valuable elements, including tantalum, are found in ordinary granite. In Brazil, they have already tried to extract tantalum from granites. True, this process of obtaining tantalum and other elements does not yet have industrial significance - it is very complicated and expensive, but they managed to get tantalum from such unusual raw materials.

Only one oxide

It was previously thought that, like many other transition metals, tantalum, when reacting with oxygen, can form several oxides of different composition. However, later studies have shown that oxygen always oxidizes tantalum to Ta 2 O 5 pentoxide. The existing confusion is explained by the formation of solid solutions of oxygen in tantalum. Dissolved oxygen is removed by heating above 2200°C under vacuum. The formation of solid solutions of oxygen strongly affects the physical properties of tantalum. Its strength, hardness, electrical resistance increase, but magnetic susceptibility and corrosion resistance decrease.

Tantalum- light gray metal with a slightly bluish tint. In terms of refractoriness (melting point about 3000 ° C), it is second only to tungsten and rhenium. High strength and hardness are combined in it with excellent plastic characteristics. Pure tantalum lends itself well to various mechanical processing, is easily stamped, processed into the thinnest sheets (about 0.04 mm thick) and wire.

Tantalum has a cubic body-centered lattice (a = 3.296 Å); atomic radius 1.46 Å, ionic radii Ta 2+ 0.88 Å, Ta 5+ 0.66 Å; density 16.6 g/cm 3 at 20 °C; t pl 2996 °C; Tbp 5300 °C; specific heat at 0-100°C 0.142 kJ/(kg K); thermal conductivity at 20-100 ° C 54.47 W / (m K) . Temperature coefficient of linear expansion 8.0 10 -6 (20-1500 °C); electrical resistivity at 0 °C 13.2 10 -8 ohm m, at 2000 °C 87 10 -8 ohm m.

At 4.38 K it becomes a superconductor. Tantalum is paramagnetic, specific magnetic susceptibility is 0.849 10 -6 (18 °C). Pure tantalum is a ductile metal, processed by pressure in the cold without significant work hardening. It can be deformed to a reduction ratio of 99% without intermediate annealing. The transition of Tantalum from the ductile to the brittle state upon cooling to -196 °C was not detected.

The elastic modulus of tantalum is 190 Gn / m 2 (190 10 2 kgf / mm 2) at 25 ° 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; elongation 36% (27°C) and 20% (490°C). The Brinell hardness of pure recrystallized Tantalum is 500 MN/m2 (50 kgf/mm2). The properties of tantalum depend to a large extent on its purity; impurities of hydrogen, nitrogen, oxygen and carbon make the metal brittle.

In the science-intensive and strategic industries of the leading countries of the world, there is a continuous growth. The dynamics of this growth is due to two interrelated reasons. The first is the need to improve the quality characteristics of high-tech products for civil and military purposes. The second is that tantalum is best suited for solving the first problem, since it has an impressive list of the most valuable properties, including:

• exceptional corrosion resistance;
• unique resistance to chemical attack by gases and acids;
• high density (16.6 g / cm 3) and specific electrical capacity;
• superhardness and plasticity;
• good manufacturability (machinability, weldability);
• heat resistance and heat resistance (melting point 3000°C);
• the ability to absorb gases (hundreds of times its own volume);
• high heat transfer coefficient;
• unique biological compatibility and much more.

Forms of release of tantalum

For the production of high-tech products, tantalum is used both in pure form and in the form of alloys. A wide range of its application is due to a large selection of tantalum and tantalum-containing semi-finished products. For further processing, tantalum rod and tape, plates, disks, ingots (grades ELP-1, ELP-2, ELP-3) are produced. The most demanded are tantalum wire and sheets, as well as foil (TVCh and TVCh-1 brands) and metal powder of capacitor qualification. The powder accounts for about 60% of the world production of tantalum, which is consumed by the radio-electronic industry to create the element base of modern "smart" technology. About 25% of the market is occupied by tantalum sheet and wire, plus foil.

Figure 1. Products from tantalum.

Applications for tantalum

• production of electrovacuum devices;
• electrical and Electronics;
• telecommunications and communication;
• aerospace industry;
• chemical engineering;
• nuclear industry;
• metallurgy of hard alloys;
• medicine, etc.

Tantalum in electrovacuum devices

The working space of electrovacuum devices is filled with a special gas or vacuum, in which there are two (anode and cathode) or more electrodes, which form an emission current in space. Such devices include electrovacuum microwave devices of the magnetron type, devices for radar, navigation and hydroacoustic stations, oscilloscopes, elementary particle counters, electrovacuum photocells, X-ray equipment, vacuum tubes and much more. In a number of electrovacuum devices, tantalum serves as a material for getters - getters that maintain a state of deep vacuum in the chambers. In some devices, the electrodes heat up very quickly and strongly, therefore, in them, as a “hot fitting”, a thin tantalum tape (T or HDTV brand) or wire (HDTV brand) is used, which can work for a long time (tens of thousands of hours) and work stably at high temperatures. voltages and fluctuating temperatures.

Tantalum in the metallurgy of hard alloys

In the metallurgical industry, tantalum is used to create superhard refractory alloys, the components of which are tantalum carbides (TT grade) and tungsten. From tantalum-tungsten alloys (brands TV-15, TV-10, TV-5) they produce metal-cutting and processing tools, heavy-duty "crowns" for drilling holes in stone and composites. Tantalum and nickel carbide alloys easily process the surface of diamonds, not inferior to them in hardness. Tantalum (Brinell hardness up to 1250–3500 MPa) is used to make parts for cryogenic installations, spinnerets and crucibles for melting and purifying rare earth metals, and vessels for cold pressing of metal powders.

Tantalum in chemical engineering

In chemical engineering, seamless cold-formed tantalum pipe (HFC brand) and sheet are used in the construction of corrosion-resistant equipment operating in a chemically aggressive environment. Tantalum is used to produce various acid-resistant structures (coils, stirrers, distillers, aerators, pipelines), laboratory equipment, heating and cooling devices that operate in contact with acids, including concentrated substances. Tantalum foil is used for cladding (thin thermomechanical coating) of the surface of parts and equipment on lines for the production of sulfuric acid, ammonia, etc.

Tantalum in medicine

Tantalum has a unique compatibility with living tissues and is not rejected by them. In medicine, tantalum wire is used in the form of threads and staples for fastening muscle tissues, tendons, nerve fibers, and blood vessels. Nets for eye prostheses are also made from it, and from the sheet - the body of cardiac pacemakers. In reconstructive surgery, tantalum rod and tape are considered to be non-alternative materials for bone prosthetics and replacement. Of exceptional importance is the tantalum sheet as a "repair" material for skull injuries.

Tantalum in the aerospace industry

As a high-temperature structural material, tantalum sheet is used in the aerospace industry for the production of critical components for rockets and aircraft. For example, tantalum is used to make the nose parts of rockets and heat-resistant blades of gas turbines of liquid-fuel turbojet engines. Nozzle parts, afterburners, etc. are produced from tantalum alloys.

Tantalum in the nuclear industry

Tantalum tubes (TVCh brand) are used to manufacture heat exchangers for nuclear power systems that are resistant to superheated melts and cesium vapor. Diffusion barriers for superconductors of thermonuclear reactors are produced from tantalum. The radioactive isotope tantalum-182 is used in radiation therapy. A thin tantalum wire (50-100 microns) coated with platinum is used as an interstitial source of gamma radiation, which has a point effect on cancer cells. At the beginning of 2018, information appeared in the media that Chinese scientists were conducting experiments with tantalum-182 for military purposes. The essence of the experiments was not disclosed, but, most likely, we can talk about the use of the tantalum isotope as a "propagating" agent for "dirty" bombs.

Tantalum in electrical engineering and electronics

Tantalum powder (TU95.250-74) is used in the manufacture of modern capacitors for telecommunications, microelectronics and computer equipment. With their miniature size, they surpass most other electrolytic capacitors in terms of specific capacitance per unit volume, they are distinguished by a large operating temperature range, and high reliability. Tantalum capacitors retain their characteristics for up to 25 years in storage mode, and in operation mode they can work up to 150 thousand hours. Today, tantalum capacitors are present on the microcircuits of almost every smartphone, computer, game console, and also in military equipment. Tantalum is used in electric current rectifiers because it has the ability to pass it in only one direction.

Figure 2. Tantalum capacitor.

Conclusion

In addition to the above, tantalum rod and sheet, foil, wire, powder, are used to solve dozens and hundreds of other problems. In metallurgy, tantalum is used as an alloying stabilizing component in the production of heavy-duty, corrosion-resistant, heat-resistant steels and alloys. Tantalum compounds act as catalysts in chemical production processes, such as synthetic rubber. Tantalum has shown high efficiency in optics, because when added to glass, it increases its refractive index, which makes it possible to make lenses not spherical, but thinner and flatter, even at high diopters. In jewelry, tantalum is used along with platinum in the manufacture of bracelets, watches, and fountain pen nibs. There is no doubt that tantalum is one of the most sought-after and promising metals used in high-tech industries, and, as we can see, not only in them.

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 system of Dmitry Ivanovich Mendeleev. Tantalum in the free state under normal conditions is a platinum gray metal with a slightly lead tint, which is a consequence of the formation of an oxide film (Ta 2 O 5). Tantalum is a heavy, refractory, rather hard, but not brittle metal, at the same time it is very malleable, well machinable, 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 tracer.

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 identifying it. For a long time, the minerals columbite containing columbium (niobium) and tantalite containing tantalum were considered one and the same. After all, these two elements are frequent companions of each other and are similar in many respects. This opinion was considered true 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 metallic tantalum was first obtained by the German scientist W. von Bolton in 1903.

The main deposits of tantalum minerals are located in Finland, Scandinavia, 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 industry. In electronics, it is used to make electrolytic capacitors, anodes for 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! In tantalum crucibles, metals, such as rare earths, are melted. Heaters of 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 in case of fractures. However, the main consumer of such a valuable metal is metallurgy (over 45%). In recent years, tantalum has been increasingly used as an alloying element in special steels - heavy-duty, corrosion-resistant, heat-resistant. In addition, many structural materials quickly lose their thermal conductivity: a poorly heat-conducting oxide or salt film forms 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, moreover, it has protective anti-corrosion properties.

Not only pure tantalum is of value, but also its compounds. So the high hardness of tantalum carbide is used in the manufacture of carbide tools for high-speed metal cutting. Tantalum-tungsten alloys give 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 and rejection of the body - tantalum has found wide application in medicine, mainly in reconstructive surgery - to restore the human body. Thin plates of tantalum are used for damage to the cranium - they close the fractures in the skull. Medicine knows the case when an artificial ear was made from a tantalum plate, while 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 in the restoration of damaged muscle tissue. Surgeons fasten the walls of the abdominal cavity with tantalum plates after operations. Even blood vessels can be connected using tantalum staples. Networks of this unique material are used in the manufacture of ocular prostheses. Tendons are replaced with threads of this metal and even nerve fibers are sewn together.

Tantalum pentoxide Ta 2 O 5 is no less widely used - its mixture with a small amount of iron trioxide is proposed to be used to accelerate blood coagulation.

In the last 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 mains or battery power supply, but due to autonomously functioning electret coatings (a dielectric that retains an uncompensated electric charge for a long time) deposited on implants for various purposes, widely used in medicine.

At present, positive results of 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, reduces the time of engraftment of the implant); orthopedic dentistry (covering prostheses made of acrylic plastics with a film of tantalum pentoxide eliminates all possible pathological manifestations caused by intolerance to acrylates); surgery (the use of an electret applicator in the treatment of defects in the skin and connective tissue with long-term non-healing wound processes, bedsores, neurotrophic ulcers, thermal lesions); 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 above areas where unique coatings of tantalum pentoxide are already being applied or introduced, there are developments that are at the very initial stages. These include developments for the following areas of medicine: cosmetology (production of a material based on coatings of tantalum pentoxide, which will replace the "golden threads"); cardiac surgery (application of electret films on the inner surface of artificial blood vessels, prevents the formation of blood clots); arthroplasty (reducing the risk of rejection of prostheses that are in constant interaction with bone tissue). In addition, a surgical instrument coated with a film of tantalum pentoxide is being created.

It is known that tantalum is very resistant to aggressive media, a number of facts testify to this. 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!

A case is known when in one enterprise using gaseous hydrogen chloride, stainless steel parts failed after 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. They cover parts of a wide variety of shapes and sizes: crucibles, pipes, sheets, rocket nozzles and much more. Moreover, the material on which the 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 production did not reach an industrial scale - the process turned out to be extremely expensive and complicated.

Modern electrolytic tantalum capacitors are stable in operation, 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 make their own repairs themselves! How does this happen? Suppose that the insulation integrity is violated due to a voltage drop, or for another reason - instantly an insulating oxide film forms again at the breakdown site, 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 work, can rightfully be attributed to tantalum.

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

In addition, tantalum is used as a substitute for the more expensive iridium in the production of nib nibs for automatic pens.

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

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

Story

Tantalus is the hero of ancient Greek myths, the Lydian or Phrygian king, the son of Zeus. He divulged the secrets of the Olympic gods, stole ambrosia from their feast and treated the Olympians to a dish prepared from the body of his own son Pelops, whom he also 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 leaning towards his head under the weight of ripe fruits. Only he cannot quench either thirst or hunger - the water goes down as soon as he tries to get drunk, and the branches are lifted by the wind, at the hands of a hungry killer. A rock hangs over Tantalus's head, which can collapse at any moment, forcing the unfortunate sinner to suffer forever from fear. Thanks to this myth, the expression "tantalum torment" arose, denoting unbearable suffering, incorporeal attempts to free oneself from torment. Apparently, in the course of unsuccessful attempts by the Swedish chemist Ekeberg to dissolve the “earth” discovered by him in 1802 in acids and isolate a new element from it, it was this expression that came to his mind. More than once it seemed to the scientist that he was close to the goal, but he failed to isolate a new metal in its pure form. This is how the “martyr” name of the new element appeared.

The discovery of tantalum is closely related to the discovery of another element - niobium, which appeared a year earlier and was originally called Columbia, which was given to it by the discoverer Gatchet. This element is a twin of tantalum 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 one and the same element. This delusion lasted for more than forty years, until in 1844 the famous German chemist Heinrich Rose, in the course of re-studying columbites and tantalites from various deposits, proved that columbium is an independent element. The Columbia studied by Gatchet was niobium with a high content of tantalum, which led the scientific world astray. In honor of such a family proximity of the two elements, Rosa assigned the new name Niobium to Colombia - in honor of the daughter of the Phrygian king Tantalus Niobia. And although Rose also made the mistake of allegedly discovering another new element, which he named Pelopius (in honor of 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 columbum. Hess, in his Foundations of Pure Chemistry, up to their sixth edition (1845), speaks only of tantalum, without mentioning Columbia; Dvigubsky (1824) has a name - tantalium. Such errors and reservations are understandable - a 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 a pure compact form only in the 20th century. The first who was able to obtain metallic tantalum was the German chemist von Bolton, and this happened only in 1903. Earlier, of course, attempts were made to obtain pure metallic tantalum, but all the efforts of chemists were unsuccessful. For example, the French chemist Moissan received a metal powder, according to him - 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 weight. Tantalum is a characteristic element of acid 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 deep parts of the earth's crust, the concentration of tantalum there is much lower: 1 .8∙10 -6%. In rocks of igneous origin, tantalum is dispersed, 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 proper and tantalum-containing ores, all of them were formed in connection with magmatic activity (tantalite, columbite, loparite, pyrochlore and others). In all minerals, tantalum is accompanied by niobium, which is explained by the extreme chemical similarity of the elements and the almost identical sizes of their ions.

Actually tantalum ores 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 manganotantalite (Ta 2 O 5 45-80%), wojinite (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), manganotantalite (MnO>FeO). Tantalite comes in many 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%), hatchettolite (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. Tantalo-niobates containing U, Th, TR are metamict, highly radioactive, and contain variable amounts of water; polymorphic modifications are common. Tantalo-niobates form small disseminations, large segregations are rare (crystals are typical mainly for loparite, pyrochlore and columbite-tantalite). Coloration 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 fine 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 amount of 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), 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 the filaments of electric lamps, which was due to such a quality of this metal as refractoriness. However, it soon lost its importance in this area, supplanted by the less expensive and more refractory tungsten. Again, tantalum became “technically unsuitable” until the twenties of the 20th century, when it began to be used in AC rectifiers (tantalum, coated with an oxide film, passes current in only one direction), and a year later, in radio tubes. After that, the metal gained recognition and soon began to conquer more and more new areas of industry.

Nowadays, tantalum, due to its unique properties, is used in electronics (production of high specific capacitance capacitors). Approximately a quarter of the world production of tantalum goes to the electrical and vacuum industry. 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. Mini tantalum 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 - heavy-duty, corrosion-resistant, heat-resistant. The addition of this element to ordinary chromium steels increases their strength and reduces brittleness after hardening and annealing. The production of heat-resistant alloys is a great necessity for rocket and space technology. In cases where rocket nozzles are cooled by a liquid metal that can cause corrosion (lithium or sodium), it is simply impossible to do without an alloy of tantalum and tungsten. In addition, heat-resistant steels are used to manufacture heaters for high-temperature vacuum furnaces, heaters, and stirrers. 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 metalworking conditions and percussive rotary 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 plastic, 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 - the whole apparatus. Tantalum cathodes are used in the electrolytic separation of gold and silver. The advantage of these cathodes is that the deposit of gold and silver can be washed off them with aqua regia, which does not harm the tantalum.

In addition, tantalum is used in instrumentation (X-ray equipment, control instruments, diaphragms); in medicine (material for reconstructive surgery); in nuclear power - as a heat exchanger for nuclear power systems (tantalum is the most stable of all metals in superheated melts and cesium-133 vapor). The high ability of tantalum to absorb gases is used to maintain a deep vacuum (electrovacuum 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 for melting 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 in the production of butadiene from ethyl alcohol.

Production

It is known that ores containing tantalum are rare and poor in this particular 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 technology for the production of tantalum is quite complex and is carried out in three stages: opening or decomposition; separating 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 with the help of alkalis (fusion) or with the help of hydrofluoric acid (decomposition) or a mixture of hydrofluoric and sulfuric acids. Then they proceed to the second stage of production - extraction extraction and separation of tantalum and niobium. The latter 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 as early as 1866 by the Swiss chemist Marignac, who took advantage of the different solubility of potassium fluorotantalate and potassium fluoroniobate in dilute hydrofluoric acid. In modern industry, several methods are used for the separation of tantalum and niobium: extraction with organic solvents, selective reduction of niobium pentachloride, fractional crystallization of complex fluoride salts, separation using ion exchange resins, and rectification of chlorides. Currently, the most commonly used method of separation (it is also the most perfect) 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 by the chlorine method, with the production of a condensate of tantalum and niobium chlorides, which are further separated by the rectification method. Separation of a mixture of chlorides consists of the following stages: preliminary rectification (separation of tantalum and niobium chlorides from accompanying impurities), main rectification (to obtain pure NbCl 5 and TaCl 5 concentrate) and final rectification of the tantalum fraction (obtaining pure TaCl 5). Following the separation of related metals, the tantalum phase is precipitated and purified to obtain high purity potassium fluorotantalate (using KCl).

Tantalum metal is obtained by reducing its compounds of high purity, 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 (carbothermal 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 blanks pre-compressed 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 that, the purity of the metal increases significantly, becoming equal to 99.9-99.95%.

For further refining and obtaining 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 plasticity and reduces the transition temperature to a brittle state. Tantalum of such purity retains high ductility at temperatures close to absolute zero! The surface of the tantalum ingot is melted (to give the required indicators on 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 metallic tantalum and were able to study in detail the properties of this light gray metal with a slightly bluish lead tint. What are the qualities of this element? 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 in it with excellent plastic characteristics. Pure tantalum lends itself well to machining, is easily stamped, processed into the thinnest sheets (about 0.04 mm thick) and wire (tantalum's modulus of elasticity is 190 Gn/m 2 or 190 10 2 kgf/mm 2 at 25 °C). In the cold, the metal can be processed without significant work hardening, it is subjected to deformation with a compression ratio of 99% without intermediate firing. The transition of tantalum from a plastic state to a brittle state is not observed even when it is cooled to -196 °C. Tensile strength of high purity annealed tantalum is 206 MN/m2 (20.6 kgf/mm2) at 27°C and 190 MN/m2 (19 kgf/mm2) at 490°C; elongation 36% (at 27°C) and 20% (at 490°C). Tantalum has a cubic body-centered 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 sheet tantalum 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, such as carbon or nitrogen (the Brinell hardness of a tantalum sheet after the absorption of 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 reduce ductility characteristics and increase cold brittleness, in other words, 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 ° C) and refractoriness (perhaps the most an important physical property of tantalum) - it melts at almost 3,000 ° C (more precisely, at 2,996 ° C), yielding in this 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 capacity at temperatures from 0 to 100 ° C is 0.142 kJ / (kg K) or 0.034 cal / (g ° C); temperature coefficient of linear expansion of tantalum 8.0 10 -6 (at temperatures of 20-1500 °C). The specific electrical resistance 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 is 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, plasticity. In addition, it is distinguished by high strength - it lends itself well to pressure treatment by 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 anode 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 stable 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 MeTaO 3 metatantalates, Me 3 TaO 4 orthotantalates, salts of the Me 5 TaO 5 type, where Me is an alkali metal; in the presence of hydrogen peroxide, pertantalates are also formed. The most important are alkali metal tantalates - 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, high resistance to this effect. The metal begins to oxidize only at 280 ° C, being 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, as the temperature rises to 500 °C, the oxide film gradually becomes porous, stratifies 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 the metal is oxidized to a considerable depth in air. The presence of nitrogen and oxygen increases the hardness and strength of tantalum, 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 with the formation of three phases - a solid solution of nitrogen in tantalum, tantalum nitrides: Ta 2 N and TaN - in the temperature range from 300 to 1100 ° 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 up to heating to 350 °C, the reaction rate increases significantly only from 450 °C (tantalum hydride is formed and tantalum becomes brittle). The same heating in vacuum (over 800 °C) helps to get rid of hydrogen, during which the mechanical properties of tantalum are restored, and hydrogen is completely removed.

Fluorine acts on tantalum already at room temperature, hydrogen fluoride also reacts with the metal. Dry chlorine, bromine and iodine have a chemical effect on tantalum at a temperature 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, with the formation of refractory tantalum carbides, which are very resistant to acids. With boron, tantalum combines to form borides - solid refractory compounds resistant to aqua regia. With many metals, tantalum forms continuous solid solutions (molybdenum, niobium, titanium, tungsten, vanadium, and others). With gold, aluminum, nickel, beryllium and silicon, tantalum forms limited solid solutions. Does not form any compounds of tantalum 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).