Side specialties of tantalum. Tantalum. Description and properties of tantalum metal Side “specialties” of tantalum

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

Receipt:

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

Physical properties:

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

Chemical properties:

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

The most important connections:

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

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

Application:

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

E. Rosenberg.

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

Metal Tantalum opened quite recently, namely in 1802. The Swedish chemist A.G. was lucky enough to discover this metal. Ekeberg. When studying two new minerals that were found in the Scandinavian countries, it turned out that in addition to the known elements, they also contained previously unstudied ones. The scientist was never able to isolate the metal from the mineral in its pure form, as great difficulties arose with this.

In this regard, the unexplored metal was named after a hero from the mythology of Ancient Greece, and after which it was written myth of Tantalus. After this, for more than 40 years, it was believed that tantalum and niobium- these are the same metal. However, one German chemist proved the difference between the 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 is given the name “smart metal”, since rapidly developing electronics cannot do without it.

Description and properties of tantalum

Tantalum is a metal with high hardness and atomic density. In the periodic chemical elements, tantalum is located at position 73. In world practice, it is customary to denote this metal by a combination of two letters, namely Ta. At atmospheric pressure and room temperature, tantalum has a characteristic silvery-metallic color. The oxide film that forms on the surface of the metal will give it a leaden tint.

Tantalum element inactive at room temperature. Oxidation of the surface of this metal by air is possible only at temperatures above 280 degrees. Tantalum reacts with halogens at a temperature 30 degrees lower than with air. In this case, a protective film is formed on the surface, which prevents further penetration of oxidizing elements throughout 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/cm3) and hardness, it is quite plastic. In terms of ductility, tantalum can be compared with. Pure metal is very easy and convenient to work with.

It is easy to machine, for example, it can be rolled out to a thickness of 1-10 microns. It should also be noted that tantalum is paramagnetic. An interesting feature of this metal begins to appear at a temperature of 800 degrees: tantalum absorbs 740 of its gas volumes.

There are already a number of facts in world practice that indicate the excellent durability 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 corrosive destruction, but already at 200 degrees the metal will begin to dissolve at a rate of 0.006 mm/year.

Some production facts also indicate that tantalum is much more resistant than austenitic stainless steels. Therefore, there is a 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, onto which the noble metal is in turn 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.

Applications of tantalum

Long ago, this metal was used to produce filaments in incandescent lamps. Today tantalum and tantalum alloys used in the following industries and products:

— when smelting 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;

— during 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 penetrating power of ammunition;

- more efficient low voltage capacitors are made from tantalum;

- Recently, tantalum has become firmly established in 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 one (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 resistance. The tool is obtained by sintering a mixture of carbide powders. These tools are used in very difficult conditions, for example, during percussion drilling;

- pentavalent tantalum oxide necessary for welding glass in nuclear technology.

Tantalum deposits and mining

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 occurs in the form of its own compounds and is part of many minerals. If tantalum is included in a mineral, it will always be together with niobium.

Deposits of tantalum compounds and minerals are found in many countries. The largest deposit of this element in Europe is located in France. On the African continent, Egypt has the most tantalum. 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 for this metal are located in the USA and Germany. It is worth noting that the international community is declaring the need to increase the production of this rare metal. Such statements are primarily related to the increase in the production of electronics, in which this element is intensively used.

Thus, the number of developed fields increases every year. For example, to the main world developing fields, more places were added in Brazil, the USA and South Africa. However, it is worth noting that in the last 10 years there has been an intense reduction in tantalum production. The lowest production figure in the 21st century occurred in 2010.

Tantalum price

The cost of tantalum has fluctuated greatly over the past 15 years. So, in 2002-2003 buy tantalum it was possible at the lowest price. This year tantalum price ranged from 340 to 375 dollars per kilogram. In Russia today you can buy tantalum, price which is 2950 rubles per kilogram.

The Popular Chemical Elements Library contains information about all the elements known to mankind. Today there are 107 of them, some of them obtained artificially.

Just as the properties of each of the “bricks of the universe” are different, their histories and destinies are also different. Some elements, such as copper, iron, sulfur, carbon, have been known since prehistoric times. The age of others is measured only by centuries, despite the fact that they, not yet discovered, were used by humanity in time immemorial. It is enough to recall oxygen, which was discovered only in the 18th century. Still others were discovered 100 - 200 years ago, but only in our time acquired paramount importance. These are uranium, aluminum, boron, lithium beryllium. For others, such as europium and scandium, their working history is just beginning. The fifth ones were obtained artificially by methods of nuclear physical synthesis: technetium, plutonium, mendelevium, kurchatovium... In a word, so many elements, so many individuals, so many stories, so many unique combinations of properties.

The first book included materials about the first 46 elements, in order of atomic numbers, the second about all the rest

Book:

Side specialties of tantalum

Tantalum is a fairly frequent guest in jewelers' workshops; in many cases it is used to replace platinum. Tantalum is used to make watch cases, bracelets and other jewelry. And in one more area, element No. 73 competes with platinum: standard analytical balances made of this metal are not inferior in quality to platinum ones. In the production of nibs for automatic pens, tantalum is replaced by the more expensive iridium. But tantalum’s track record does not end there. Experts in military technology believe that it is advisable to make some parts of guided projectiles 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 when producing butadiene from ethyl alcohol.

Tantalum oxide is sometimes used in glassmaking - for the production of glasses with a high refractive index. A mixture of tantalum pentoxide Ta 2 O 5 with a small amount of iron trioxide has been 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 chrome. Attractive not only in appearance. Methods have been developed that make it possible to coat large-sized products (crucibles, pipes, sheets, rocket nozzles) with a tantalum layer of varying thickness, 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 tantalum coating, according to Brinell, is 180–200 kg/mm ​​2, while the hardness of technical tantalum in the form of annealed rods or sheets ranges from 50–80 kg/mm ​​2.

CHEAPER PLATINUM, MORE EXPENSIVE SILVER. Replacing platinum with tantalum, as a rule, is very profitable - it is several times cheaper. Nevertheless, tantalum cannot be called cheap. The relative high cost of tantalum is explained by the high price of the 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 today. 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 obtain tantalum from such unusual raw materials.

ONLY ONE OXIDATE. It was previously believed that, like many other transition metals, tantalum, when interacting with oxygen, can form several oxides of different compositions. However, later studies showed 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 in a vacuum. The formation of solid solutions of oxygen greatly affects the physical properties of tantalum. Its strength, hardness, and electrical resistance increase, but its magnetic susceptibility and corrosion resistance decrease.

TANTALUM COATING. Cladding (this term is of French origin) is the application of thin layers of another metal to metal products by thermomechanical methods. The reader already knows about the outstanding chemical resistance of tantalum. The fact that this metal is expensive and not very accessible is also true. Naturally, tantalum plating of less resistant metal surfaces would be very beneficial, but applying these coatings by electrolytic methods is difficult for many reasons. That's why they resort to cladding. It is believed that steel clad with tantalum by explosion will eventually become more important for the chemical industry than steel clad with glass, although, of course, the prices of glass and tantalum are incommensurable. Such steel is already used in the production of nuclear reactors.

Tantalum is the smart choice for all applications where high corrosion resistance is required. Although tantalum is not a noble metal, it is comparable in its chemical stability. Additionally, tantalum can be easily formed even at temperatures below room temperature due to its body-centered cubic crystal structure. Tantalum's high corrosion resistance makes it a valuable material for use in a wide variety of chemical environments. We use our “unyielding” material, for example, for heat exchangers for the instrumentation sector, charging trays for furnace construction, implants for medical technology and capacitor components for the electronics industry.

Guaranteed purity

You can be confident in the quality of our products. We make our tantalum products ourselves - from metal powder to finished product. We use only the purest tantalum powder as the starting material. This way we guarantee you extremely high purity of the material.

We guarantee quality purity of sintered tantalum - 99,95 % (metal purity without niobium). According to chemical analyses, the residual content consists of the following elements:

We guarantee tantalum purity quality obtained by smelting - 99,95 % (metal purity without niobium) According to chemical analysis, the residual content consists of the following elements:

The presence of Cr(VI) and organic impurities is eliminated by the production process (multiple 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, the scope of its application in industry is just as specific. Below we will briefly introduce two of them:

Individually selected chemical and electrical properties.

Due to its extremely fine microstructure, tantalum is an ideal material for producing ultra-thin 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 components, which we constantly develop and improve.

Excellent durability 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 aggressive environments. With many years of experience in tantalum processing, we can also produce complex geometries to suit your exact requirements.

Pure tantalum or an alloy?

We optimally prepare our tantalum for any application. Using 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, failure mechanism, ductility)
• Chemical properties(e.g. corrosion resistance, etchability)
• machinability(e.g. machinability, formability, weldability)
• structure and recrystallization characteristics(e.g. recrystallization temperature, brittleness, aging effect, grain size)

And that's not all: using our special production technologies, we can change various other properties of tantalum over a wide range. The result: two different tantalum production technologies and alloys with different properties to precisely meet the requirements of a particular application.

Tantalum produced by sintering (TaS).

Pure sintered tantalum and pure smelting tantalum have the following general 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 molten metals
• superconductivity
• high level of biological compatibility

When the job is extremely tough, our sintered tantalum will help: thanks to our powder metallurgy process sintered tantalum, (TaS) has an extremely fine grain structure and high purity. In this regard, 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). This tantalum is used in the form of wire in tantalum capacitors. High capacitance, low leakage current and low resistance can only be guaranteed when wire that is free from defects and impurities is used.

Melted tantalum (TaM)

You don't always need the best of the best. 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 we alloy our sintered stabilized tantalum with silicon, which prevents grain growth even at high temperatures. This makes our tantalum suitable for use even at extremely high temperatures. The fine-grained microstructure remains stable even after annealing at temperatures up to 2000 °C. This process allows the material to retain its excellent mechanical properties, such as its ductility and strength. Stabilized tantalum in the form of wire or sheets is ideal for the production of tantalum anodes by sintering or for use in the furnace construction sector.

Tantalum-tungsten (TaW) has good mechanical properties and excellent corrosion resistance. We add 2.5 to 10 percent by weight of tungsten to pure tantalum. Although the resulting alloy 1.4 times stronger pure tantalum, it is easy to process at temperatures up to 1600 °C. Our TaW alloy is therefore particularly suitable 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 the melting point of platinum (1772 °C). The energy binding individual atoms together 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 high vacuum.

Tantalum is undoubtedly the most stable of the refractory metals. It is stable in all acids and bases and has extremely specific properties:

Thermophysical properties

Refractory metals usually have low coefficient of thermal expansion And relatively high density. This also applies to tantalum. Although tantalum's thermal conductivity 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 changes. The graphs below show the change curves of the most important variables:

Mechanical properties

Even small amounts of interstitial 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, production technology (sintering or smelting), degree of cold working, and 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 significantly lower than room temperature. Thanks to this metal extremely easy to mold. During cold working, the tensile strength and hardness of the metal increases, 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 heat resistance, we add refractory metals to our tantalum, such as tungsten.

The modulus of elasticity of tantalum is lower than that of tungsten and molybdenum, and is comparable to that of pure iron. The elastic modulus decreases with increasing temperature.

Mechanical properties

Due to its high ductility, tantalum is optimally suited for molding processes such as bending, stamping, pressing or deep drawing. Tantalum is difficult to yield machining. The chips are difficult to separate. For this reason, we recommend the use of chip evacuation steps. Tantalum is different excellent weldability compared to tungsten and molybdenum.

Do you have questions about machining refractory metals? We will be happy to help you using our many years of experience.

Chemical properties

Because tantalum is resistant to all types of chemicals, the material 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 very dense oxide layer(Ta 2 O 5), which protects the base material from aggressive influences. 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 effect on tantalum. At the same time, the material is stable in an aqueous ammonia solution. If tantalum is chemically attacked, hydrogen enters its crystal lattice and the material becomes brittle. The corrosion resistance of tantalum gradually decreases with increasing temperature.

Tantalum is inert towards many solutions. However, if tantalum is exposed to a mixed solution, its corrosion resistance may be reduced, even if it is stable in the individual components of the solution. Do you have complex questions about corrosion? We will be happy to assist you using our experience and our in-house corrosion laboratory.

Tantalum is stable in some metal melts such as Ag, Bi, Cd, Cs, Cu, Ga, Hg, °K, Li, Mg, Na and Pb, provided these melts contain a small amount of oxygen. However, this material is susceptible to Al, Fe, Be, Ni and Co.

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 temperatures.

Tantalum does not react with inert gases. For this reason, high purity inert gases can be used as shielding gases. However, as the temperature rises, tantalum reacts actively 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 a high vacuum. Hydrogen disappears at a temperature of 800 °C, and nitrogen at 1700 °C.

In high temperature furnaces, tantalum can react with structural parts made from refractory oxides or graphite. Even very stable oxides such as aluminum, magnesium or zirconium oxide can undergo high temperature reduction if they come into contact with tantalum. Upon contact with graphite, tantalum carbide can form, which leads to increased brittleness of tantalum. Although tantalum can generally 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 temperature limits are valid for vacuum. When using shielding gas, these temperatures are approximately 100–200 °C lower.

Sulfur dioxide can add oxygen, turning into sulfur trioxide (trioxide). Under normal conditions, this reaction proceeds extremely slowly. It occurs much faster and easier at elevated temperatures in the presence of catalysts.

Sulfur trioxide is a colorless, highly mobile liquid with a density that boils at and crystallizes at. When stored, especially in the presence of traces of moisture, this substance changes, turning into long, silky crystals.

Free molecules (in the gaseous state) are built in the shape of a regular triangle, with a sulfur atom in the center and oxygen atoms at the vertices. As in the molecule, the sulfur atom is here in a 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 connected to the oxygen atoms by three two-center o-bonds and one four-center - bond (cf. the structure of the molecule § 129). In addition, due to the 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 occurs in a molecule (p. 341).

Sulfur trioxide - sulfuric acid anhydride; the latter is formed upon 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 (the so-called "monohydrate") splits off, which volatilizes. Elimination continues until an azeotropic solution is obtained. It contains (wt.) and (wt.) water. This solution boils and distills without changing its composition at . An azeotropic solution is ultimately obtained by distilling dilute sulfuric acid. In this case, predominantly water is distilled off until the acid concentration reaches .

When sulfuric acid dissolves in water, hydrates are formed and a very large amount of heat is released. Therefore, mixing concentrated sulfuric acid with water should be done with caution. To avoid splashing of the heated surface layer of the solution, it is necessary to pour sulfuric acid (as it is heavier) into the water in small portions or in a thin stream; Under no circumstances should you pour water into 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 , and sulfur to . These reactions are expressed by the equations:

The interaction of sulfuric acid with metals varies depending on its concentration. Dilute sulfuric acid oxidizes with its hydrogen ion. Therefore, it interacts only with those metals that are in the voltage series before 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 range up to and including silver. The products of its reduction may vary depending on the activity of the metal and the conditions (acid concentration, temperature). When interacting with low-active metals, such as copper, the acid is reduced to:

When interacting with more active metals, the reduction products can be both free sulfur and hydrogen sulfide. For example, when interacting with zinc, the following reactions can occur:

For the effect of sulfuric acid on iron, see § 242.

Sulfuric acid is a strong dibasic acid. In the first step, in solutions of low concentrations, it dissociates almost completely:

Second stage dissociation

occurs to a lesser extent. The dissociation constant of sulfuric acid in the second stage, expressed in terms of ion activity, .

As a dibasic acid, sulfuric acid forms two series of salts: medium and acidic. Average salts of sulfuric acid are called sulfates, and acid salts are called hydrosulfates.

Most sulfuric acid salts are quite soluble in water. The practically insoluble sulfates include barium, strontium and lead sulfates. Slightly soluble calcium sulfate. The product of solubility is .

Barium sulfate is insoluble not only in water, but also in dilute acids. Therefore, the formation of a white, acid-insoluble precipitate when a barium salt is applied to any solution serves as an indication of 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 sodium sulfuric chloride. Anhydrous salt is used in glass making.

Potassium sulfate. Colorless crystals, highly soluble in water. Forms a number of double salts, in particular alum (see below).

Magnesium sulfate . Contained in sea water. From solutions it crystallizes as a hydrate.

Calcium sulfate. Occurs naturally in large quantities as the mineral gypsum. When heated to gypsum, it loses the water of crystallization it contains and turns into the so-called burnt gypsum, or alabaster. When mixed with water into a batter, burnt plaster hardens quite quickly, turning back into . Thanks to this property, gypsum is used for making casting molds and impressions of various objects, as well as as a binding material for plastering walls and ceilings. In surgery for fractures, plaster casts are used.