Tantalum metal properties. Tantalum
Sulfur dioxide can add oxygen, turning into sulfur trioxide (trioxide). Under normal conditions, this reaction proceeds extremely slowly. It passes much faster and easier at elevated temperatures in the presence of catalysts.
Sulfur trioxide is a colorless, mobile liquid with a density that boils at and crystallizes at . During storage, especially in the presence of traces of moisture, this substance is modified, turning into long silky crystals.
Free molecules (in the gaseous state) are built in the form of a regular triangle, in the center of which there is a sulfur atom, and at the vertices - oxygen atoms. As in the molecule, the sulfur atom is here in the state of -hybridization; in accordance with this, the nuclei of all four atoms that make up the molecule are located in the same plane, and the bond angles are equal:
The sulfur atom in the molecule is bound to the oxygen atoms by three two-center o-bonds and one four-center bond (cf. with the structure of the molecule § 129). In addition, due to lone -electron pairs of oxygen atoms and free -orbitals of the sulfur atom, the formation of additional covalent bonds is possible here, just as it takes place in a molecule (p. 341).
Sulfur trioxide - anhydride of sulfuric acid; The latter is formed by interaction with water:
The structure of sulfuric acid molecules corresponds to the formula:
Anhydrous, colorless oily liquid that crystallizes at .
When heated, anhydrous sulfuric acid (called "monohydrate") splits off, which volatilizes. Cleavage continues until an azeotropic solution is obtained. It contains (mass) and (mass) water. This solution boils and distills without changing the composition at . An azeotropic solution is eventually obtained by distillation of dilute sulfuric acid. In this case, predominantly water is distilled off until the acid concentration reaches .
When sulfuric acid is dissolved in water, hydrates are formed and a very large amount of heat is released. Therefore, concentrated sulfuric acid should be mixed with water with caution. In order to avoid splashing of the heated surface layer of the solution, it is necessary to pour sulfuric acid (as a heavier one) into water in small portions or in a thin stream; Under no circumstances should water be added to acid.
Sulfuric acid greedily absorbs water vapor and is therefore often used to dry gases. The ability to absorb water also explains the charring of many organic substances, especially those belonging to the class of carbohydrates (fiber, sugar, etc.), when exposed to concentrated sulfuric acid. Hydrogen and oxygen are present in carbohydrates in the same ratio as they are in water. Sulfuric acid removes hydrogen and oxygen from carbohydrates, which forms water, and carbon is released in the form of coal.
Concentrated sulfuric acid, especially hot, is a vigorous oxidizing agent. It oxidizes HI and (but not) to free halogens, coal to , sulfur to . These reactions are expressed by the equations:
The interaction of sulfuric acid with metals is different depending on its concentration. Dilute sulfuric acid oxidizes with its hydrogen ion. Therefore, it interacts only with those metals that are in the series of voltages up to hydrogen, for example:
However, lead does not dissolve in dilute acid because the resulting salt is insoluble.
Concentrated sulfuric acid is an oxidizing agent due to. It oxidizes metals in the voltage series up to and including silver. The products of its reduction may be different depending on the activity of the metal and on the conditions (acid concentration, temperature). When interacting with inactive metals, such as copper, the acid is reduced to:
When interacting with more active metals, reduction products can be both free sulfur and hydrogen sulfide. For example, when interacting with zinc, reactions can occur:
On the action of sulfuric acid on iron, see § 242.
Sulfuric acid is a strong dibasic acid. In the first stage, in solutions of low concentrations, it dissociates almost completely:
Dissociation on the second stage
proceeds to a lesser extent. Dissociation constant of sulfuric acid in the second stage, expressed in terms of ion activities, .
As a dibasic acid, sulfuric acid forms two series of salts: medium and acidic. Medium salts of sulfuric acid are called sulfates, and acid salts are called hydrosulfates.
Most salts of sulfuric acid are quite soluble in water. Barium, strontium and lead sulfates are practically insoluble. Slightly soluble calcium sulfate. The solubility product is .
Barium sulfate is insoluble not only in water, but also in dilute acids. Therefore, the formation of a white precipitate insoluble in acids when exposed to a solution with a barium salt indicates the presence of ions in this solution:
Thus, soluble barium salts serve as a reagent for sulfation.
The most important salts of sulfuric acid include the following.
Sodium sulfate . It crystallizes from aqueous solutions with ten water molecules and in this form is called Glauber's salt named after the German physician and chemist I.R. Glauber, who was the first to obtain it by the action of sulfuric sodium chloride. Anhydrous salt is used in the manufacture of glass.
Potassium sulfate. Colorless crystals, highly soluble in water. Forms a number of double salts, in particular alum (see below).
Magnesium sulfate . Found in sea water. It crystallizes from solutions as a hydrate.
calcium sulfate. It occurs naturally in large quantities as the mineral gypsum. When heated to gypsum, it loses the water of crystallization contained in it and turns into the so-called burnt gypsum, or alabaster. Being mixed with water into batter, burnt gypsum hardens rather quickly, turning back into. Due to this property, gypsum is used to make casting molds and casts from various objects, as well as a binder for plastering walls and ceilings. In surgery for fractures, plaster bandages are used.
When you find an error on the page, select it and press Ctrl + Enter
|
|||||||
Tantalum
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 columbium 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 zirconium? No, he answered, I dissolve in soda, which zircon earth does not. 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 am sending 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 also failed to clarify the relationship between tantalum and columbia. 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 columbium, 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 daughter of Tantalus).
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, is easily stamped, 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. Only in 1922 could it 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 - more than 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 potassium fluorotantalate and potassium fluoroniobate 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 isobutyl ketone and cyclohexanone have the best extraction properties.
Nowadays, the main method for the production of metallic tantalum is the electrolysis of molten potassium fluorotantalate 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 fluorotantalate 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 methods of powder processing have also been used - arc or induction melting in a vacuum 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 inferior only to noble metals, and even then not always.
Tantalum does not dissolve even in such a chemically aggressive medium as aqua regia, which easily dissolves gold, platinum, and other noble 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; it is possible to manufacture thin-walled products and products of complex shape 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. Rarely entire devices.
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 shortcoming, 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 at all.
"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 the share of the metal, named after the mythological martyr, that fell to the humane mission to alleviate human suffering...
Main customer 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 - superstrong, 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 into 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 a very thin (only a few microns!) Oxide film, it will go only in 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. Tantalum is also used to make hot fittings for lamps - 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 cryotrons - superconducting elements needed, for example, in computer technology.
Side "specialties" of tantalum
Tantalum is a fairly frequent visitor to jewelers' workshops, in many cases they replace 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 tantalum pentoxide 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 allow coating 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, aluminum oxide, graphite, quartz, glass, porcelain and others. It is characteristic that 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 granites. 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 is the smart choice for all applications where high corrosion resistance is required. Although tantalum is not a noble metal, it is comparable to them in its chemical stability. In addition, tantalum is easy to form even at temperatures below room temperature due to its body-centered cubic crystal structure. The high corrosion resistance of tantalum makes it a valuable material for use in a wide variety of chemical environments. We use our "hard" material, for example, for heat exchangers for the instrumentation sector, feed trays for furnace construction, implants for medical technology and capacitor components for the electronics industry.
Guaranteed Purity
You can be sure of the quality of our products. We manufacture our tantalum products ourselves - from metal powder to finished product. We use only the purest tantalum powder as raw material. In this way, we guarantee you an extremely high purity of the material.
We guarantee quality purity of sintered tantalum - 99,95 % (purity of metal without niobium). According to chemical analyses, the residual content consists of the following elements:
| Element | Standard max. value [µg/g] | Guaranteed max. meaning [µg/g] |
|---|---|---|
| Fe | 17 | 50 |
| Mo | 10 | 50 |
| Nb | 10 | 100 |
| Ni | 5 | 50 |
| Si | 10 | 50 |
| Ti | 1 | 10 |
| W | 20 | 50 |
| C | 11 | 50 |
| H | 2 | 15 |
| N | 5 | 50 |
| O | 81 | 150 |
| CD | 5 | 10 |
| Hg* | -- | 1 |
| Pb | 5 | 10 |
We guarantee tantalum purity quality obtained by melting - 99,95 % (metal purity without niobium) According to chemical analysis, the residual content consists of the following elements:
| Element | Typical value max. [µg/g] | Guaranteed value [µg/g] |
|---|---|---|
| Fe | 5 | 100 |
| Mo | 10 | 100 |
| Nb | 19 | 400 |
| Ni | 5 | 50 |
| Si | 10 | 50 |
| Ti | 1 | 50 |
| W | 20 | 100 |
| C | 10 | 30 |
| H | 4 | 15 |
| N | 5 | 50 |
| O | 13 | 100 |
| CD | -- | 10 |
| Hg* | -- | 1 |
| Pb | -- | 10 |
The presence of Cr(VI) and organic impurities is excluded by the production process (repeated heat treatment at temperatures above 1000 °C in a high vacuum atmosphere). * Initial value.
material with special talents
As unique as the properties of our tantalum are, so are its industrial applications. We will briefly introduce two of them below:
Individually selected chemical and electrical properties.
Due to its extremely fine microstructure, tantalum is an ideal material for producing ultra-fine wires with a flawless, exceptionally clean surface for use in tantalum capacitors. We can determine the chemical, electrical and mechanical properties of such wire with a high degree of accuracy. Thus, we provide our customers with individually selected and stable properties of the components, which we constantly develop and improve.
Excellent tool life and high cold ductility
Excellent durability combined with excellent formability and weldability make tantalum an ideal material for heat exchangers. Our tantalum heat exchangers are exceptionally stable and resistant to a wide range of harsh environments. With years of experience in tantalum processing, we are also able to manufacture complex geometries to meet your exact requirements.
Pure tantalum or is it an alloy?
We prepare our tantalum in the optimum way for any application. With the help of various alloying elements, we can change the following properties of tungsten:
- physical properties(e.g. melting point, vapor pressure, density, electrical conductivity, thermal conductivity, thermal expansion, heat capacity)
- mechanical properties(e.g. strength, fracture mechanism, ductility)
- Chemical properties(e.g. corrosion resistance, etchability)
- machinability(e.g. machining, formability, weldability)
- structure and characteristics of recrystallization(e.g. recrystallization temperature, embrittlement tendency, aging effect, grain size)
And that's not all: using our special manufacturing techniques, we can change various other properties of tantalum over a wide range. The result: two different tantalum production technologies and alloys with different properties, precisely tailored to the requirements of a particular application.
Sintered Tantalum (TaS).
Pure sintered tantalum and pure smelted tantalum have the following common characteristics:
- high melting point of 2996 °C
- excellent cold ductility
- recrystallization at temperatures from 900 to 1450 °C (depending on the degree of deformation and purity)
- excellent resistance in aqueous solutions and metal melts
- superconductivity
- high level of biocompatibility
When extremely hard work lies ahead, our sintered tantalum comes to the rescue: thanks to our powder metallurgy method sintered tantalum, (TaS) has an extremely fine grain structure and high purity. As a result, the material is different. highest surface quality and good mechanical properties.
For use in capacitors we recommend one of our tantalum varieties with extremely high surface quality ( TaK). Such tantalum is used in the form of wire in tantalum capacitors. High capacitance, low leakage current and low resistance can only be guaranteed when a wire that is free from defects and impurities is used.
Tantalum smelted (TaM)
The best of the best is not always required. Tantalum obtained by smelting, (TaM), as a rule, more economical in production than sintered tantalum, and its quality is sufficient for many applications. However, this material is not as fine-grained and uniform as sintered tantalum. Just contact us. We will be happy to advise you.
Stabilized tantalum (TaKS)
We doping our sintered stabilized tantalum with silicon which prevents grain growth even at high temperatures. This makes our tantalum usable even at extremely high temperatures. The fine-grained microstructure remains stable even after annealing at temperatures up to 2000 °C. This process preserves the excellent mechanical properties of the material, such as its ductility and strength. Stabilized tantalum in wire or sheet form is ideal for the production of tantalum anodes by sintering or for use in the furnace building sector.
Tantalum tungsten (TaW) has good mechanical properties and excellent corrosion resistance. We add 2.5 to 10 weight percent tungsten to pure tantalum. Although the resulting alloy 1.4 times stronger pure tantalum, it is easy to work at temperatures up to 1600 °C. Therefore, our TaW alloy is particularly well suited for heat exchangers and heating elements used in the chemical industry.
Good in every way. Characteristics of tantalum.
Tantalum belongs to the group refractory metals. Refractory metals have a melting point higher than that of platinum (1772 °C). The energy that binds individual atoms is extremely high. The high melting point of refractory metals is combined with low vapor pressure. Refractory metals are also characterized by high density and low coefficient of thermal expansion.
In the periodic table, tantalum is in the same period as tungsten. Like tungsten, tantalum has a very high density - 16.6 g / cm 3. However, unlike tungsten, tantalum becomes brittle during manufacturing operations involving a hydrogen atmosphere. Therefore, the material is produced in a high vacuum.
Tantalum is definitely the most stable of the refractory metals. It is stable in all acids and bases and has very specific properties:
| Properties | |||
|---|---|---|---|
| Atomic number | 73 | ||
| Atomic mass | 180,95 | ||
| Melting temperature | 2996°C/3269°K | ||
| Boiling temperature | 5458°C/5731°K | ||
| Atomic volume | 1.80 10 -29 [m 3 ] | ||
| Steam pressure | at 1800 °C at 2200 °C | 5 10 -8 [Pa] 7 10 -5 [Pa] |
|
| Density at 20 °C (293 °K) | 16.65 [g/cm3] | ||
| Crystal structure | body-centered cubic | ||
| Lattice constant | 330 [pm] | ||
| Hardness at 20 °C (293 °K) | deformed recrystallized | 120–220 80–125 |
|
| Modulus of elasticity at 20 °C (293 °K) | 186 [GPa] | ||
| Poisson's ratio | 0,35 | ||
| Coefficient of linear thermal expansion at 20 °C (293 °K) | 6.4 10 -6 [m/(m K)] | ||
| Thermal conductivity at 20 °C (293 °K) | 57.5 [W/(m K)] | ||
| Specific heat at 20 °C (293 °K) | 0.14 [J/(g K)] | ||
| Electrical conductivity at 20 °C (293 °K) | 8 10 6 | ||
| Electrical resistivity at 20 °C (293 °K) | 0.125 [(Ohm mm2)/m] | ||
| Sound speed at 20 °C (293 °K) | Longitudinal wave transverse wave | 4100 [m/s] 2900 [m/s] |
|
| Work function of an electron | 4.3 [eV] | ||
| Thermal neutron capture cross section | 2.13 10 -27 [m 2] | ||
| Recrystallization temperature (annealing time: 1 hour) | 900–1450°C | ||
| Superconductive (junction temperature) | < -268,65 °C / < 4,5 °K | ||
Thermophysical properties
Refractory metals usually have low coefficient of thermal expansion and relatively high density. This also applies to tantalum. Although the thermal conductivity of tantalum is lower than that of tungsten and molybdenum, the material has a higher coefficient of thermal expansion than many other metals.
The thermophysical properties of tantalum change with temperature. The graphs below show the curves of the most important variables:
Mechanical properties
Even small amounts of interstitial solid solution elements such as oxygen, nitrogen, hydrogen, and carbon can change the mechanical properties of tantalum. In addition, factors such as the purity of the metal powder, the production technology (sintering or melting), the degree of cold working, and the type of heat treatment are used to change its mechanical properties.
Like tungsten and molybdenum, tantalum has body-centered cubic crystal lattice. The brittle-ductile transition temperature of tantalum is -200°C, which is well below room temperature. Because of this, the metal extremely easy to mold. In the process of cold working, the tensile strength and hardness of the metal increase, but at the same time the elongation at break decreases. Although the material loses its ductility, it does not become brittle.
Heat resistance material is lower than that of tungsten, but comparable to heat resistance pure molybdenum. To increase the heat resistance, we add refractory metals such as tungsten to our tantalum.
The elastic modulus of tantalum is lower than that of tungsten and molybdenum and is comparable to that of pure iron. The modulus of elasticity decreases with increasing temperature.
Mechanical properties
Due to its high ductility, tantalum is ideally suited for molding processes such as bending, punching, pressing or deep drawing. Tantalum is hard to come by machine processing. The chip does not separate well. For this reason, we recommend the use of chip removal steps. Tantalum is different excellent weldability compared to tungsten and molybdenum.
Do you have questions about the machining of refractory metals? We will be happy to help you with our many years of experience.
Chemical properties
Because tantalum is resistant to all types of chemicals, it is often compared to precious metals. However, thermodynamically, tantalum is a base metal that can nevertheless form stable compounds with a wide range of elements. When exposed to air, tantalum forms a very dense oxide layer(Ta 2 O 5), which protects the base material from aggressive attack. This oxide layer makes tantalum corrosion resistant.
At room temperature, tantalum is not stable only in the following inorganic substances: concentrated sulfuric acid, fluorine, hydrogen fluoride, hydrofluoric acid, and acid solutions containing fluorine ions. Alkaline solutions, molten sodium hydroxide and potassium hydroxide also have a chemical attack on tantalum. At the same time, the material is stable in an aqueous solution of ammonia. If tantalum is exposed to chemical attack, hydrogen enters its crystal lattice and the material becomes brittle. The corrosion resistance of tantalum gradually decreases with increasing temperature.
Tantalum is inert to many solutions. However, if tantalum is exposed to a mixed solution, then its corrosion resistance may be reduced even if it is stable in the individual components of such a solution. Do you have difficult corrosion questions? We will be happy to assist you with our experience and our own corrosion laboratory.
| Corrosion resistance in water, aqueous solutions and non-metal media | ||
|---|---|---|
| Water | Hot water< 150 °C | persistent |
| inorganic acids | Hydrochloric acid< 30 % до 190 °C Sulphuric acid< 98 % до 190 °C Nitric acid< 65 % до 190 °C Hydrofluoric acid< 60 % Phosphoric acid< 85 % до 150 °C | persistent persistent persistent unstable persistent |
| organic acids | Acetic acid< 100 % до 150 °C Oxalic acid< 10 % до 100 °C Lactic acid< 85 % до 150 °C Wine acid< 20 % до 150 °C | persistent persistent persistent persistent |
| Alkaline solutions | Sodium hydroxide< 5 % до 100 °C Potassium hydroxide< 5 % до 100 °C Ammonia solutions< 17 % до 50 °C Sodium carbonate< 20 % до 100 °C | persistent persistent persistent persistent |
| Salt solutions | ammonium chloride< 150 °C Calcium chloride< 150 °C Ferric chloride< 150 °C potassium chlorate< 150 °C biological fluids< 150 °C Magnesium sulfate< 150 °C sodium nitrate< 150 °C Tin chloride< 150 °C | persistent persistent persistent persistent persistent persistent persistent persistent |
| non-metals | Fluorine Chlorine< 150 °C Bromine< 150 °C Iodine< 150 °C Sulfur< 150 °C Phosphorus< 150 °C Bor< 1000 °C | not persistent persistent persistent persistent persistent persistent persistent |
Tantalum is stable in some metal melts such as Ag, Bi, Cd, Cs, Cu, Ga, Hg, °K, Li, Mg, Na and Pb, provided that these melts contain a small amount of oxygen. However, this material is attacked by Al, Fe, Be, Ni and Co.
| Corrosion resistance in metal melts | |||
|---|---|---|---|
| Aluminum | unstable | Lithium | resistant at < 1000 °C |
| Beryllium | unstable | Magnesium | temperature resistant< 1150 °C |
| Lead | resistant at < 1000 °C | Sodium | resistant at < 1000 °C |
| Cadmium | resistant at < 500 °C | Nickel | unstable |
| Cesium | temperature resistant< 980 °C | Mercury | temperature resistant< 600 °C |
| Iron | unstable | Silver | resistant at < 1200 °C |
| Gallium | temperature resistant< 450 °C | Bismuth | temperature resistant< 900 °C |
| Potassium | resistant at < 1000 °C | Zinc | resistant at < 500 °C |
| Copper | temperature resistant< 1300 °C | Tin | temperature resistant< 260 °C |
| Cobalt | unstable | ||
When a base metal, such as tantalum, comes into contact with noble metals, such as platinum, a chemical reaction occurs very quickly. In this regard, it is necessary to take into account the reaction of tantalum with other materials present in the system, especially at high temperature.
Tantalum does not react with inert gases. For this reason, high purity inert gases can be used as shield gases. However, as the temperature rises, tantalum actively reacts with oxygen or air and can absorb large amounts of hydrogen and nitrogen. This makes the material brittle. These impurities can be eliminated by annealing tantalum in high vacuum. Hydrogen disappears at 800°C and nitrogen disappears at 1700°C.
In high temperature furnaces, tantalum can react with structural components made of refractory oxides or graphite. Even very stable oxides such as alumina, magnesium oxide or zirconium oxide can be reduced at high temperature if they come into contact with tantalum. Upon contact with graphite, tantalum carbide can be formed, which leads to an increase in the brittleness of tantalum. Although tantalum can usually be easily combined with other refractory metals such as molybdenum or tungsten, it can react with hexagonal boron nitride and silicon nitride.
The table below shows the corrosion resistance of the material in relation to heat resistant materials used in the construction of industrial furnaces. The specified limit temperatures apply to vacuum. These temperatures are approx. 100–200 °C lower when shielding gas is used.
| Corrosion resistance against heat-resistant materials used in the construction of industrial furnaces | |||
|---|---|---|---|
| Aluminium oxide | temperature resistant< 1900 °C | Molybdenum | persistent |
| beryllium oxide | temperature resistant< 1600 °C | silicon nitride | resistant at < 700 °C |
| Hexagonal. boron nitride | resistant at < 700 °C | Thorium oxide | temperature resistant< 1900 °C |
| Graphite | resistant at < 1000 °C | Tungsten | persistent |
| magnesium oxide | temperature resistant< 1800 °C | zirconium oxide | temperature resistant< 1600 °C |
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 integrity of the insulation 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 gave Colombia a new name, Niobium - 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 rather late - at the beginning of the 20th century it was used as a material for the incandescent 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 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 - 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 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 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; in this case, refractory tantalum carbides are formed, 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).
Metal Tantalum opened quite recently, namely in 1802. The Swedish chemist A.G. was lucky to discover this metal. Ekeberg. In the study of two new minerals that were found in the Scandinavian countries, it turned out that in addition to the known elements, there is also a previously unexplored one. The scientist did not succeed in isolating the metal from the mineral in its pure form, since great difficulties arose with this.
In this regard, the unexplored metal was named after the hero from the mythology of Ancient Greece, and according to which the myth of tantalum. After that, for more than 40 years, it was believed that tantalum and niobium are the same metal. However, one German chemist proved the difference between metals, and after that another German isolated tantalum in its pure form, and this happened only in 1903.
Serial production of rolled products and tantalum products began only during the Second World War. Today, this element has been given the name of “smart metal”, since intensively developing electronics cannot do without it.
Description and properties of tantalum
Tantalum It is a metal with high hardness and atomic density. In the periodic chemical elements, tantalum is located at 73 positions. In world practice, it is customary to designate this metal with a combination of two letters, namely Ta. At atmospheric pressure and room temperature, tantalum has a characteristic silvery metallic color. The oxide film formed on the surface on the metal will give it a lead tint.
Tantalum element inactive at room temperature. Air oxidation of the surface of this metal is possible only at temperatures above 280 degrees. Tantalum reacts with halogens at a temperature 30 degrees lower than with air. At the same time, a protective film is formed on the surface, which prevents further penetration of oxidizing elements along the depth of the metal.
Tantalum chemical element with a fairly high melting point. So, it is 3290 K, and the boiling point reaches 5731 K. Despite the high density (16.7 g / cm 3) and hardness, it is quite plastic. In terms of plasticity, tantalum can be compared with. It is very easy and convenient to work with pure metal.
It is easy to machine, for example, it can be rolled into rolls with a thickness of 1-10 microns. It should also be noted that tantalum is a paramagnet. An interesting feature of this metal begins to appear at a temperature of 800 degrees: tantalum absorbs 740 of its volumes of gas.
In world practice, there are already a number of facts that speak of the excellent resistance of this metal in very aggressive environments. For example, it is known that tantalum is not damaged even by 70% nitric acid. Sulfuric acid up to 150 degrees also does not lead to corrosion damage, but already at 200 degrees the metal will begin to dissolve at a rate of 0.006 mm / year.
Some manufacturing facts also suggest that tantalum is much more resistant than austenitic grade stainless steels. Therefore, there is a well-known case in which tantalum parts lasted 20 years longer than stainless steel parts.
Another interesting fact is that tantalum is used for catalytic separation of gold. Cathodes are made from it, on which, in turn, a noble metal is deposited, and then washed off with aqua regia. At the same time, the cathode and tantalum, due to its excellent resistance to acids, remain intact.
Application of tantalum
Once upon a time this metal was used for the production of filaments in incandescent lamps. Today, tantalum and tantalum alloys used in the following industries and products:
- in the smelting of heat-resistant and corrosion-resistant alloys (for example, aircraft engine parts);
- in the chemical industry to create corrosion-resistant equipment;
— in metallurgical production for the production of rare earth metals;
- in the construction of nuclear reactors (tantalum is the most resistant metal to cesium vapor);
— due to its high biocompatibility, tantalum is used for the manufacture of medical implants and prostheses;
- for the production of superconductors - cryotrons (these are elements of computer technology);
- used in the military industry for the manufacture of shells. The use of this metal increases the penetration of ammunition;
- more efficient low-voltage capacitors are made from tantalum;
- Recently, tantalum has firmly entered the business. This is due to the ability of the metal to form strong oxide films on the surface, which can be of various colors and shades;
- a large number of modifications of tantalum accumulates in nuclear reactors. For laboratory or military purposes, this modification of the metal can be used as a source of gamma radiation;
- this metal is used as the main (after platinum) for the manufacture of mass standards, which have increased accuracy;
- some intermetallic tantalum compounds have very high hardness and strength, as well as increased resistance to oxidation. These compounds are used in the aviation and space industries;
— tantalum carbides are used for the manufacture of cutting tools with increased red hardness. The tool is obtained by sintering a mixture of carbide powders. These tools are used in very difficult conditions, such as percussive drilling;
- pentavalent tantalum oxide necessary for welding glass nuclear technology.
Deposits and mining of tantalum
Tantalum is a rare metal. Its amount in the earth's crust is only 0.0002%. This amount includes two modifications of the metal: stable and radioactive. This rare metal is found in the form of its own compounds and is part of many minerals. If tantalum is included in the mineral, then it will always be together with niobium.
Deposits of tantalum compounds and minerals are available in many countries. The largest deposit of this element in Europe is in France. On the African continent, the most tantalum is in Egypt. China and Thailand also have high reserves of this metal. Smaller deposits are located in the CIS, Nigeria, Canada, Australia and other countries. However, the largest deposits discovered to date are in Australia.
About 420 tons of tantalum are mined annually in the world. The main processing plants of this metal are located in the USA and Germany. It is worth noting that the world community declares the need to increase the production of this rare metal. Such statements are primarily associated with an increase in the production of electronics, in which this element is intensively used.
Thus, the number of developed fields is increasing every year. So, for example, to the main world, developed deposits, more places were added in Brazil, the USA and South Africa. However, it is worth noting that in the last 10 years you have been flying, there has been an intense decline in tantalum production. The lowest production rate in the 21st century was in 2010.
Tantalum price
The cost of tantalum has fluctuated greatly over the past 15 years. So, in 2002-2003 buy tantalum possible at the lowest possible cost. In the current year tantalum price fluctuated from 340 to 375 dollars per kilogram. In Russia today you can buy tantalum, price which is 2950 rubles per kilogram.
