Material with a high melting point. The most refractory metal. Characteristics of metals. The most refractory metal is tungsten

As is known, the most fusible metal is mercury, which was classified as a metal immediately after it was confirmed that it has electrical conductivity, both in liquid and solid form.

Francium could “compete” for the title of the most fusible of metals, but it is a rare metal, which, moreover, cannot be studied well due to its high radioactivity. We know about the most fusible material, but which metal is the most refractory? This is tungsten.

How was this metal discovered?

The most refractory metal in the world was discovered by the Swedish scientist K.V. Scheele (in 1781). He managed to synthesize tungsten trioxide (this is what the lightest of metals was called) by dissolving the ore in nitric acid. A couple of years later, the purest metal was obtained by chemists from Spain - F. Fermin and J. José de Eluard, who isolated it from wolframite. However, at that time, this discovery did not particularly impress humanity, and all because the necessary technologies did not exist to process the resulting metal.

Where is tungsten used?

Tungsten compounds are widely used. They are used in the engineering and mining industries, for drilling wells. Due to its high strength and hardness, this metal is used to make parts of aircraft engines, filaments, artillery shells, high-speed gyroscope rotors, bullets, etc. Tungsten is also successfully used as an electrode in argon-arc welding. Such industries cannot do without tungsten compounds - textile, paint and varnish.

Production technology

Since “pure” tungsten cannot be found in nature (it is a component of rocks), a procedure is necessary to isolate this metal. Moreover, scientists estimate its content in the Earth’s crust as follows: per 1000 kg of rock there is only 1.3 grams of tungsten. It can be noted that the most refractory metal is a rather rare element if we compare it with known types of metals.

When ore is mined from the depths of the Earth, the amount of tungsten in it is only up to two percent. For this reason, the extracted raw materials go to processing plants, where the mass fraction of metal is reduced to sixty percent using special methods. When obtaining “pure” tungsten, the process is divided into several technological stages. The first is to isolate pure trioxide from the mined raw material. For this purpose, thermal decomposition is used, when the highest melting point of the metal is from 500 to 800 degrees. At this temperature, excess elements melt, and tungsten oxide is collected from the molten mass.

Next, the resulting compound undergoes a thorough grinding stage, and then a reduction reaction takes place. To do this, hydrogen is added and a temperature of 700 degrees is used. The result is pure metal that has a powdery appearance. Then comes the process of compacting the powder, for which high pressure is used, and sintering in a hydrogen environment, where the temperature is 1200-1300 degrees.

The resulting mass is sent to a special melting furnace, where the mass is heated by electric current to more than 3000 degrees. That is, tungsten turns out to be liquid after melting. Then the mass is cleared of impurities and its monocrystalline lattice is created. To do this, they use the zone melting method - its essence is that only part of the metal is molten over a certain period of time. This method allows for the process of redistribution of impurities, which accumulate in one area, from where they can be easily removed from the overall structure of the alloy. The required tungsten comes in the form of ingots, which are used to produce the necessary types of products in various industries.

Tungsten metal

The most refractory metal, tungsten (wolframium), was obtained in 1783. Spanish chemists the d'Eluyar brothers isolated it from the mineral wolframite and reduced it with carbon. Currently, the raw materials for the production of tungsten are wolframite and scheelite concentrates - WO3. Tungsten powder is produced in electric furnaces at a temperature of 700-850 °C. The metal itself is produced from powder by pressing in steel molds under pressure and further heat treatment of the workpieces. The final point is that heating to approximately 3000 °C occurs by passing an electric current.

Industrial Application

Tungsten did not find industrial application for a long time. Only in the 19th century did they begin to study the influence of tungsten on the properties of steel of a different nature. At the beginning of the twentieth century, tungsten began to be used in light bulbs: a filament made from it heats up to 2200 °C. In this capacity, tungsten is indispensable in our time.

Tungsten steels are also used in the defense industry - for the production of tank armor, torpedoes and shells, the thinnest parts of aircraft, etc. The tool, made of tungsten steel, can withstand the most intense metalworking processes.

Tungsten differs from all other metal brethren in its special refractoriness, heaviness and hardness. Pure tungsten melts at 3380 °C, but boils only at 5900 °C, which coincides with the temperature on the surface of the Sun.

From one kilogram of tungsten you can make a wire 3.5 km long. This length is enough to produce filaments for 23,000 60-watt light bulbs.

There is still no consensus on which metals are considered refractory. Most often, metals that melt at temperatures above the melting point of iron (1536°C) are conventionally classified as refractory. Of all the refractory metals in their pure form and as the basis of alloys, titanium, zirconium, molybdenum, tungsten and, to a much lesser extent, niobium, tantalum, and vanadium have found widespread use in technology.

Until recently, refractory metals were produced by powder metallurgy methods and were used mainly for alloying steels and some alloys. Due to the fact that to meet the growing needs of aviation and rocket technology, increasingly heat-resistant materials are needed, refractory metals and alloys based on them are increasingly used as heat-resistant structural materials. In this case, they are subject to increased requirements for cleanliness, since refractory metals contaminated with impurities, especially gases, are fragile and difficult to process by pressure and welding.

Titanium and its alloys

Titanium - an element of the 4th group of D.I. Mendeleev's periodic table - is a transition metal. It has a relatively low density (4.51 g/cm3). In terms of specific strength, titanium alloys are superior to alloy steels and high-strength aluminum alloys, which makes them indispensable structural materials for aviation and rocketry. The main disadvantage of titanium and its alloys as a structural material is its small elastic modulus (see § 5), approximately half that of iron and its alloys. Titanium melts at 1670°C, and in the solid state it has two allotropic modifications. The low-temperature α-modification, existing up to 882°C, has a hexagonal close-packed lattice. The high-temperature β-modification has a body-centered cubic lattice. Titanium is characterized by high corrosion resistance in fresh and sea water and in various aggressive environments. This property is explained by the formation of a protective oxide film on the surface, so titanium is especially resistant in environments that do not destroy the oxide film or promote its formation (in dilute sulfuric acid, aqua regia, nitric acid).

In air at temperatures up to 500°C, titanium is practically resistant. Above 500°C, it actively interacts with atmospheric gases (oxygen, nitrogen), as well as with hydrogen, carbon monoxide, and water vapor. Nitrogen and oxygen, dissolving in titanium in significant quantities, reduce its plastic properties. Carbon with a content of more than 0.1 - 0.2%, deposited in the form of titanium carbide along the grain boundaries, also greatly reduces the ductility of titanium. A particularly harmful impurity is hydrogen, which even when present in thousandths of a percent leads to the appearance of very brittle hydrides and thereby causes cold brittleness of titanium. All these impurities impair the corrosion resistance and weldability of titanium. Due to their strong reactivity, titanium and its alloys are melted in vacuum arc electric furnaces in water-cooled copper crystallizers.

It is advisable to evaluate the influence of alloying elements introduced into titanium by their effect on the temperature of the polymorphic transformation. A large group of metals increases the range of existence of the β-phase and makes it stable up to room temperature. Such elements, which are called β-stabilizers, include transition metals V, Cr, Mn, Mo, Nb, Fe. Other elements are active β-stabilizers, expanding the range of existence of the α-modification of titanium. These include A1, O, N, C. Neutral elements (Sn, Zr, Hf) are also known, which practically do not affect the temperature of the polymorphic transformation.

Thus, when titanium is doped with one or more elements at room temperature, a different structure consisting of an α-, α+β-, or β-phase can be obtained. It is these three groups that all modern titanium alloys are divided into.

Almost all titanium alloys are alloyed with aluminum. This is explained by the fact that aluminum effectively strengthens both the α- and β-phases while maintaining satisfactory ductility, increases the heat resistance of alloys, and reduces the tendency to hydrogen embrittlement.

A typical wrought titanium α-alloy is BT5 double alloy containing 5% Al. Mechanical properties of this alloy at room temperature: σ in = 750÷950 MPa, δ = 12÷25%. To increase creep resistance, dual titanium-aluminum alloys are alloyed with neutral hardeners - tin and zirconium. Such alloys are BT5-1, containing 5% Al and 2.5% Sn, and alloy BT20, containing 6.5% Al, 2% Zr and small additions (1% each) of molybdenum and vanadium. At room temperature, the first alloy has σ in = 850÷950 MPa, the second - σ in = 950÷1000 MPa. Alloys of this class are characterized by increased heat resistance. They are not hardened by heat treatment and can operate at temperatures up to 450 - 500°C. Most α-titanium alloys are used in the annealed state, the annealing temperature is 700 - 850°C.

The most numerous and having the greatest practical application is the group of α+β-deformable alloys. This group includes alloys alloyed with aluminum and β-stabilizers. These alloys have a good range of strength and plastic properties and can operate at temperatures up to 350 - 400°C. By varying the relative amounts of α- and β-phases, alloys with a wide range of properties can be obtained. In addition, α+β-alloys are thermally hardened, which also makes it possible to significantly change their properties. Typical α+β alloys are BT6 (6% Al; 4% V) and BT14 (4% Al; 3% Mo; 1% V). Alloy VT14 is one of the most durable titanium alloys. Thus, after quenching from 860 - 880°C, the tensile strength of this alloy is 950 MPa, and after aging at 480 - 550°C for 12 - 16 hours it increases to 1200 - 1300 MPa while maintaining high plastic properties. Products made from these alloys are used in an annealed and thermally strengthened state; they can operate at temperatures up to 350 - 400°C. Of the β-alloys, the most widely used is the VT15 alloy (3 - 4% A1; 7 - 8% Mo; 10 - 11% Cr), which, after hardening and aging, has a tensile strength of 1300 - 1500 MPa with an elongation of about 6%. However, due to the low stability of the supersaturated β-phase, this alloy can operate at temperatures up to 350°C.

Cast titanium alloys are characterized by high fluidity and produce dense castings, but compared to wrought alloys they have lower strength and ductility. The most widely used alloy VT5L, containing 5% Al, has σ in = 700÷900 MPa, δ = 6÷13%. The alloy is intended for producing shaped castings that operate for a long time at temperatures up to 400°C. Additional alloying of the VT5L alloy with chromium and molybdenum (VT3-11 alloy) leads to an increase in strength (σ in = 1050 MPa) and heat resistance (up to 450°C), but to a decrease in ductility and fluidity.

Titanium alloys are used mainly in aviation, rocketry, shipbuilding, and chemical engineering.

Zirconium and its alloys

Zirconium has a melting point of 1855°C, density at room temperature is 6.49 g/cm 3 . Like titanium, it exists in two modifications. The low-temperature α-modification, stable up to 865°C, has a hexagonal close-packed lattice. The high-temperature β-modification has a body-centered cubic lattice.

Zirconium is resistant in solutions of acids and alkalis, in water and water vapor; actively interacts with gases: with oxygen above 150 - 200°C, hydrogen in the temperature range 300 - 1000°C, nitrogen and carbon dioxide above 450°C with the formation of oxides, nitrides, hydrides, carbides. Thanks to this ability, zirconium is widely used as a getter - a gas absorption material. Contamination of pure zirconium with interstitial impurities, which form, in addition to the indicated compounds, solid solutions in zirconium, leads to a decrease in the ductility and corrosion resistance of the metal. Due to the high chemical activity of zirconium, the processes of its production and processing are carried out in a vacuum or in a protective atmosphere.

Another distinctive feature of zirconium is its small thermal neutron capture cross-section and high resistance to nuclear irradiation. These qualities, combined with resistance in water and superheated steam up to 300 - 350°C, make zirconium one of the main structural materials of nuclear water-cooled reactors. However, pure zirconium has relatively low mechanical properties: σ in = 200÷400 MPa, δ = 30÷20%, HB (70 - 90). Therefore, zirconium alloys are used as structural materials. Zirconium is doped with small additions (up to 1 - 2%) of tin, iron, nickel, chromium, molybdenum, niobium. These alloying elements, strengthening zirconium, increase its corrosion resistance. In addition, they have a relatively small thermal neutron capture cross section, which is important when operating under nuclear irradiation.

Niobium increases the corrosion resistance of zirconium in water and superheated steam. Binary alloys Zr-1% Nb and Zr - 2.5% Nb are widely used for the manufacture of claddings of fuel elements (fuel elements) in water-cooled reactors, where solid fuel is used as fuel. Small additions of tin suppress the harmful effects of interstitial impurities, especially nitrogen, on the corrosion resistance of zirconium. An even greater effect is achieved with complex alloying with tin, iron, chromium, and nickel. Currently, alloys of the zircalloy-2 type are used on an industrial scale (1.2 - 1.7% Sn; 0.07 - 0.2% Fe; 0.05 - 0.15% Cr; 0.03 - 0.08 % Ni), as well as the Ozhenit-0.5 alloy, alloyed with tin, iron, niobium, nickel with a total content of 0.5%. In terms of mechanical properties, alloys of the Zircalloy-2 type (σ in = 480÷500 MPa, δ = 30%) are close to stainless steels, the Ojenite alloy has lower strength (σ in = 300 MPa, δ = 35%).

Using heat treatment (quenching, tempering, annealing) it is possible to change the mechanical properties of zirconium alloys, but usually they are only subjected to annealing in the α-region (800 - 850°C) to relieve stress. This is due to the fact that quenching and tempering, as a rule, lead to a decrease in the main performance characteristic of zirconium alloys - corrosion resistance due to the formation of metastable phases.

Tungsten and its alloys

Tungsten is the most refractory metal. Its melting point is 3400°C. The density of tungsten at room temperature is 19.3 g/m 3, the crystal lattice is body-centered cubic. The bulk of this metal is spent on alloying steels and producing so-called hard alloys. As an independent material, tungsten is used in the vacuum and electrical industries. It is used to make filaments of incandescent lamps, parts of radio lamps, heaters, various parts of vacuum furnaces, etc. These products are obtained by plastic deformation of bars sintered from workpiece powders and are used in a cold-worked state or after annealing to relieve stress (1000°C, 1 h). The main disadvantage of commercial grade tungsten is its brittleness at room temperature, caused by contamination with interstitial impurities, primarily oxygen and carbon. The tensile strength of such a metal at room temperature is 500 - 1400 MPa with practically zero elongation. Tungsten of technical purity becomes plastic at temperatures above 300 - 400°C. This temperature is called the brittleness threshold. Recrystallized tungsten (recrystallization temperature 1400 - 1500°C) is even more fragile, its brittleness threshold is 450 - 500°C. This is caused by the movement of interstitial impurities to the grain boundaries and the formation of brittle interlayers. By deep cleaning of tungsten the threshold of brittleness, bones can be reduced to sub-zero temperatures.

In the electric vacuum industry, in addition to technically pure tungsten of the HF grade, special grades with oxide additives are used - A1 2 O 3, SiO 2, K 2 O (grade BA). Fine particles of these additives, located along the boundaries of tungsten grains, increase its recrystallization temperature. Therefore, products made from such metal are capable of maintaining their shape when heated and not sagging. Thoriated tungsten (with 1 - 2% ThO 2) has high heat resistance, as well as high and stable thermionic properties, however, due to the danger to human health (radioactivity), it has recently been successfully replaced by tungsten with additives of lanthanum oxide (L) and oxide yttrium (VI). Products made from fused tungsten and its alloys have so far found limited use, mainly in new technology.

When alloying tungsten, one strives to increase its strength, heat resistance, reduce fragility and improve manufacturability. Single-phase alloys of tungsten with niobium (up to 2% Nb), with molybdenum (up to 15% Mo), with rhenium (up to 30% Re) have been developed. Rhenium has a particularly effective effect on the properties of tungsten. The alloy with 27% Re is ductile at room temperature and has σ in = 1400 MPa and δ = 15% in the cast state. However, the possibilities of using these alloys are limited by the scarcity of rhenium.

Heterophase tungsten alloys strengthened with dispersed carbide particles are also promising. The introduction of small additions of tantalum (up to 0.2 - 0.4%) and carbon (up to 0.1%) causes an increase in strength and ductility. Tungsten alloys at temperatures up to 1600 - 1900°C are more heat resistant than tungsten, but above these temperatures they lose their advantage in heat resistance.

Molybdenum and its alloys

Molybdenum has a body-centered cubic lattice. Its melting point is 2620°C. Molybdenum is less brittle compared to tungsten. The temperature threshold of its fragility, depending on purity, lies in the range of 70 - 300°C. The brittleness of molybdenum is also caused by the accumulation of interstitial impurities or interstitial phases near grain boundaries. When heated, molybdenum is strongly oxidized, and at temperatures above 680 - 700 ° C its oxides sublimate. The bulk of molybdenum is spent on alloying steels. As an independent material, molybdenum is used in the form of wire, rods, tape, sheets made from billet bars, which are produced by powder metallurgy. In this form, it is used in electronic vacuum devices (anodes, grids, supports) as heating elements and screens for vacuum furnaces. The tensile strength of molybdenum of different purities at room temperature is 450 - 800 MPa with an elongation of 25 - 1%. Since the density of molybdenum (10.2 g/cm3) is almost two times lower than the density of tungsten, molybdenum is superior to tungsten and its alloys in terms of specific strength at temperatures up to 1300 - 1400°C.

Recently, purer molybdenum subjected to vacuum arc or electron beam remelting, as well as molybdenum alloys, have been increasingly used. Alloying molybdenum with certain elements leads to its strengthening and increased ductility. Rhenium has a particularly effective effect on molybdenum, as well as on tungsten, which forms a wide range of solid solutions with it. Rhenium significantly strengthens molybdenum, at the same time reduces its sensitivity to interstitial impurities and cold brittleness, and increases the recrystallization temperature. Alloying molybdenum with small amounts of titanium and zirconium (up to 1%) leads to significant strengthening at room and elevated temperatures. These alloying elements form dispersed particles of carbides with carbon, which is always present in molybdenum.

Niobium, tantalum, vanadium and their alloys

Niobium has about. c. lattice, has a melting point of 2470°C, density 8.57 g/cm 3 . Unlike tungsten and molybdenum, niobium is capable of dissolving oxygen, nitrogen, and carbon in fairly significant quantities. Therefore, it and its alloys have significantly higher ductility, do not become embrittled during recrystallization, and are capable of good welding. Niobium alloys of the solid solution type with tungsten (up to 15%) and molybdenum (up to 5%) have been developed. Alloys with additions of zirconium (up to 1%) and carbon (up to 0.1%) have also been created, in which hardening is achieved as a result of the occurrence of precipitation of zirconium carbides. The alloys are designed to operate at 900 - 1200°C. Significant amounts of niobium are used for alloying steels.

Tantalum has about. c. with a lattice, melts at 3996°C, its density is 16.6 g/cm 3 . This metal is characterized by high ductility and chemical resistance in aggressive environments. Resistance is explained by the formation of a dense and durable oxide film. Tantalum is used in powder form for the manufacture of electrolytic capacitor anodes using powder metallurgy methods. In this case, the main importance is the high dielectric properties of the oxide film, specially created on the inner surface of porous anodes. Tape, rods, wire, and pipes for parts of electric vacuum devices and chemical equipment are made from tantalum.

Vanadium has a melting point of 1900°C, has about. c. k. lattice, its density is 6.1 g/cm 3. The main amount of vanadium is consumed for alloying steels. Pure vanadium and alloys based on it have not yet found widespread industrial use.

Hard alloys

Hard alloys are metal materials consisting of tungsten carbide and a small amount of cobalt (2 - 20%). Products from hard alloys are produced only by powder metallurgy. First, compacts are made from a mixture of tungsten carbide and cobalt powders. Then they are sintered at 1350 - 1480°C. At approximately 1200°C, a liquid of eutectic composition (65 - 70% Co, 35 - 30% WC) appears in the mixture of powders. Thus, sintering occurs in the presence of a large amount of liquid phase. When cooled after sintering, the liquid solidifies and tungsten carbide is released from it, which attaches to the unmelted grains, and cobalt, which forms layers between the tungsten carbide grains and provides the mechanical strength of carbide products. The particle size of tungsten carbide in the finished hard alloy is usually 1 - 2 microns. The main purpose of hard alloys is metal-cutting and drilling tools. Ribs, cutters, and drills made of hard alloys can be used to process steel, cast iron, and non-ferrous alloys under conditions where the heating of the cutting edge reaches 1000°C and higher. Carbide drilling tools (bits, cutters) last several times longer than steel ones. Hard alloys are also used to make tools for metal forming - dies, dies, dies.

In addition to hard alloys based on tungsten carbide, there are hard alloys based on double tungsten and titanium carbide, as well as triple tungsten carbide, titanium and tantalum.

Hard alloys based on complex carbides have higher resistance when processing steel.

Tungsten-cobalt carbide alloys are designated BK2, BK6, BK15, etc. The last number corresponds to the percentage of cobalt. Hard alloys based on tungsten and titanium carbides are designated T15K6, T30K4, etc. The number after the letter T indicates the titanium carbide content, the number after the letter K indicates the cobalt content. For alloys based on ternary carbide, the designation TT7K12, etc. is accepted. The number after the letters TT corresponds to the total content of titanium and tantalum carbides. Hard alloys are characterized by bending strength and Rockwell hardness. The bending strength is 1000 - 2000 MPa, and the hardness is HRC (85 - 90). Alloys with a higher cobalt content have greater strength and lower hardness.

Surfacing alloys based on cast tungsten carbide, the so-called relit, are close to hard alloys in structure and nature of use. Tungsten carbide obtained by melting in a graphite crucible is crushed to particles no larger than 0.6 mm and then applied to the working surfaces of mining equipment by melting. The structure of the surface layer consists of unmelted grains of relit in a melted steel base.

Almost all metals are solids under normal conditions. But at certain temperatures they can change their state of aggregation and become liquid. Let's find out what is the highest melting point of metal? Which is the lowest?

Melting point of metals

Most of the elements in the periodic table are metals. There are currently approximately 96 of them. They all require different conditions to turn into liquid.

The heating threshold of solid crystalline substances, above which they become liquid, is called the melting point. For metals it varies within several thousand degrees. Many of them turn into liquid with relatively high heat. This makes them a common material for making pots, pans and other kitchen utensils.

Silver (962 °C), aluminum (660.32 °C), gold (1064.18 °C), nickel (1455 °C), platinum (1772 °C), etc. have average melting points. There is also a group of refractory and low-melting metals. The first need more than 2000 degrees Celsius to turn into liquid, the second need less than 500 degrees.

Low-melting metals usually include tin (232 °C), zinc (419 °C), and lead (327 °C). However, some of them may have even lower temperatures. For example, francium and gallium melt in the hand, but cesium can only be heated in an ampoule, because it ignites with oxygen.

The lowest and highest melting temperatures of metals are presented in the table:

Tungsten

Tungsten metal has the highest melting point. Only the nonmetal carbon ranks higher in this indicator. Tungsten is a light gray shiny substance, very dense and heavy. It boils at 5555 °C, which is almost equal to the temperature of the Sun's photosphere.

At room conditions, it reacts weakly with oxygen and does not corrode. Despite its refractoriness, it is quite ductile and can be forged even when heated to 1600 °C. These properties of tungsten are used for incandescent filaments in lamps and picture tubes and electrodes for welding. Most of the mined metal is alloyed with steel to increase its strength and hardness.

Tungsten is widely used in the military sphere and technology. It is indispensable for the manufacture of ammunition, armor, engines and the most important parts of military vehicles and aircraft. It is also used to make surgical instruments and boxes for storing radioactive substances.

Mercury

Mercury is the only metal whose melting point is minus. In addition, it is one of two chemical elements whose simple substances, under normal conditions, exist in the form of liquids. Interestingly, the metal boils when heated to 356.73 °C, and this is much higher than its melting point.

It has a silvery-white color and a pronounced shine. It evaporates already at room conditions, condensing into small balls. The metal is very toxic. It can accumulate in human internal organs, causing diseases of the brain, spleen, kidneys and liver.

Mercury is one of the seven first metals that man learned about. In the Middle Ages it was considered the main alchemical element. Despite its toxicity, it was once used in medicine as part of dental fillings, and also as a cure for syphilis. Now mercury has been almost completely eliminated from medical preparations, but it is widely used in measuring instruments (barometers, pressure gauges), for the manufacture of lamps, switches, and doorbells.

Alloys

To change the properties of a particular metal, it is alloyed with other substances. Thus, it can not only acquire greater density and strength, but also reduce or increase the melting point.

An alloy can consist of two or more chemical elements, but at least one of them must be a metal. Such “mixtures” are very often used in industry, because they make it possible to obtain exactly the qualities of materials that are needed.

The melting point of metals and alloys depends on the purity of the former, as well as on the proportions and composition of the latter. To obtain low-melting alloys, lead, mercury, thallium, tin, cadmium, and indium are most often used. Those containing mercury are called amalgams. A compound of sodium, potassium and cesium in a ratio of 12%/47%/41% becomes a liquid already at minus 78 °C, an amalgam of mercury and thallium - at minus 61°C. The most refractory material is an alloy of tantalum and hafnium carbides in 1:1 proportions with a melting point of 4115 °C.

www.syl.ru

The most refractory metal. Characteristics of metals

Metals are the most common material (along with plastics and glass) that has been used by people since ancient times. Even then, man knew the characteristics of metals; he profitably used all their properties to create beautiful works of art, dishes, household items, and structures.

One of the main features when considering these substances is their hardness and refractoriness. It is these qualities that make it possible to determine the area of ​​​​use of a particular metal. Therefore, we will consider all the physical properties and pay special attention to the issues of fusibility.

Physical properties of metals

The characteristics of metals by physical properties can be expressed in the form of four main points.

1. Metallic luster - all have approximately the same silvery-white beautiful characteristic luster, except for copper and gold. They have a reddish and yellow tint, respectively. Calcium is silvery blue.
2. State of aggregation - all are solid under ordinary conditions, except for mercury, which is in the form of a liquid.
3. Electrical and thermal conductivity is characteristic of all metals, but is expressed to varying degrees.
4. Malleability and ductility are also parameters common to all metals, which can vary depending on the specific representative.
5. Melting and boiling points determine which metal is refractory and which is fusible. This parameter is different for all elements.

All physical properties are explained by the special structure of the metal crystal lattice. Its spatial arrangement, shape and strength.

Low-melting and refractory metals

This parameter is very important when it comes to the areas of application of the substances in question. Refractory metals and alloys are the basis of machine and shipbuilding, smelting and casting of many important products, and obtaining high-quality working tools. Therefore, knowledge of melting and boiling points plays a fundamental role.

Characterizing metals by strength, we can divide them into hard and brittle. If we talk about refractoriness, then there are two main groups:

1. Low-melting materials are those that are capable of changing their state of aggregation at temperatures below 1000 o C. Examples include: tin, lead, mercury, sodium, cesium, manganese, zinc, aluminum and others.
2. Refractory are those whose melting point is higher than the indicated value. There are not many of them, and even fewer are used in practice.

A table of metals with a melting point above 1000 o C is presented below. This is where the most refractory representatives are located.

Metal name	Melting point, o C	Boiling point, o C
Gold, Au	1064.18	2856
Beryllium, Be	1287	2471
Cobalt, Co	1495	2927
Chromium, Cr	1907	2671
Copper, Cu	1084,62	2562
Iron, Fe	1538	2861
Hafnium, Hf	2233	4603
Iridium, Ir	2446	4428
Manganese, Mn	1246	2061
Molybdenum, Mo	2623	4639
Niobium, Nb	2477	4744
Nickel, Ni	1455	2913
Palladium, Pd	1554,9	2963
Platinum, Pt	1768.4	3825
Rhenium, Re	3186	5596
Rhodium, Rh	1964	3695
Ruthenium, Ru	2334	4150
Tantalus, Ta	3017	5458
Technetium, Ts	2157	4265
Thorium, Th	1750	4788
Titanium, Ti	1668	3287
Vanadium, V	1910	3407
Tungsten, W	3422	5555
Zirconium, Zr	1855	4409

This table of metals includes all representatives whose melting point is above 1000 o C. However, in practice, many of them are not used for various reasons. For example, due to economic benefits or due to radioactivity, too high a degree of fragility, susceptibility to corrosive effects.

It is also obvious from the table data that the most refractory metal in the world is tungsten. Gold has the lowest rate. When working with metals, softness is important. Therefore, many of the above are also not used for technical purposes.

The most refractory metal is tungsten

In the periodic table it is located at serial number 74. It was named after the famous physicist Stephen Wolfram. Under normal conditions, it is a hard, refractory metal with a silvery-white color. Has a pronounced metallic luster. Chemically practically inert, it reacts reluctantly.

Found in nature in the form of minerals:

• wolframite;
• scheelitis;
• hübnerite;
• ferberite

Scientists have proven that tungsten is the most refractory metal of all existing ones. However, there are suggestions that seaborgium is theoretically capable of breaking the record of this metal. But it is a radioactive element with a very short lifetime. Therefore, it is not yet possible to prove this.

At a certain temperature (over 1500 o C), tungsten becomes malleable and ductile. Therefore, it is possible to produce thin wire based on it. This property is used to make filaments in ordinary household light bulbs.

As the most refractory metal that can withstand temperatures above 3400 o C, tungsten is used in the following areas of technology:

• as an electrode for argon welding;
• for producing acid-resistant, wear-resistant and heat-resistant alloys;
• as a heating element;
• in vacuum tubes as filament and so on.

In addition to metal tungsten, its compounds are widely used in technology, science and electronics. As the most refractory metal in the world, it forms compounds with very high-quality characteristics: strong, resistant to almost all types of chemical influences, non-corrosive, and can withstand low and high temperatures (tungsten sulfide, its single crystals and other substances will win).

Niobium and its alloys

Nb, or niobium, is a silvery-white shiny metal under normal conditions. It is also refractory, since the temperature of transition to the liquid state for it is 2477 o C. It is this quality, as well as the combination of low chemical activity and superconductivity, that allows niobium to become more and more popular in human practice every year. Today this metal is used in industries such as:

• rocket science;
• aviation and space industry;
• nuclear power;
• chemical apparatus engineering;
• radio engineering.

This metal retains its physical properties even at very low temperatures. Products based on it are characterized by corrosion resistance, heat resistance, strength, and excellent conductivity.

This metal is added to aluminum materials to improve chemical resistance. Cathodes and anodes are made from it, and non-ferrous alloys are alloyed with it. Even coins in some countries are made with niobium content.

Tantalum

Metal, in its free form and under normal conditions, covered with an oxide film. It has a set of physical properties that allow it to be widespread and very important for humans. Its main characteristics are as follows:

1. At temperatures above 1000 o C it becomes a superconductor.
2. It is the most refractory metal after tungsten and rhenium. The melting point is 3017 o C.
3. Absorbs gases perfectly.
4. It is easy to work with as it can be rolled into sheets, foil and wire without much difficulty.
5. It has good hardness and is not brittle, retains ductility.
6. Very resistant to chemical agents (does not dissolve even in aqua regia).

Thanks to these characteristics, it has managed to gain popularity as the basis for many heat-resistant and acid-resistant, anti-corrosion alloys. Its numerous compounds are used in nuclear physics, electronics, and computational devices. Used as superconductors. Previously, tantalum was used as an element in incandescent lamps. Now tungsten has taken its place.

Chrome and its alloys

One of the hardest metals, naturally bluish-white in color. Its melting point is lower than that of the elements considered so far, and amounts to 1907 o C. However, it is still used in technology and industry everywhere, since it lends itself well to mechanical influences, is processed and molded.

Chromium is especially valuable as a coating. It is applied to products to give them a beautiful shine, protect against corrosion and increase wear resistance. The process is called chrome plating.

Chromium alloys are very popular. After all, even a small amount of this metal in the alloy significantly increases the hardness and resistance of the latter to impacts.

Zirconium

It is one of the most expensive metals, so its use for technical purposes is difficult. However, its physical characteristics make it simply indispensable in many other industries.

Under normal conditions it is a beautiful silvery-white metal. It has a fairly high melting point - 1855 o C. It has good hardness and resistance to corrosion, since it is not chemically active. It also has excellent biological compatibility with human skin and the entire body as a whole. This makes it a valuable metal for medical use (instruments, prosthetics, etc.).

The main areas of application of zirconium and its compounds, including alloys, are as follows:

• nuclear energy;
• pyrotechnics;
• metal alloying;
• medicine;
• production of bioware;
• construction material;
• like a superconductor.

Even jewelry that can influence the improvement of human health is made from zirconium and alloys based on it.

Molybdenum

If you find out which metal is the most refractory, then, in addition to the indicated tungsten, you can also name molybdenum. Its melting point is 2623 o C. At the same time, it is quite hard, plastic and amenable to processing.

It is mainly used not in its pure form, but as an integral component of alloys. They, thanks to the presence of molybdenum, are significantly strengthened in wear resistance, heat resistance and anti-corrosion.

Some molybdenum compounds are used as technical lubricants. This metal is also an alloying material that simultaneously affects both strength and corrosion resistance, which is very rare.

Vanadium

Gray metal with a silvery sheen. It has a fairly high fusibility index (1920 o C). It is used mainly as a catalyst in many processes due to its inertness. It is used in the energy sector as a chemical current source, in the production of inorganic acids. It is not the pure metal that is of primary importance, but rather some of its compounds.

Rhenium and alloys based on it

Which metal is the most refractory after tungsten? This is rhenium. Its fusibility index is 3186 o C. It is superior in strength to both tungsten and molybdenum. Its plasticity is not too high. The demand for rhenium is very high, but production is difficult. As a result, it is the most expensive metal existing today.

Used for making:

• jet engines;
• thermocouples;
• filaments for spectrometers and other devices;
• as a catalyst in oil refining.

All areas of application are expensive, so it is used only in cases of extreme necessity, when there is no possibility of replacing it with anything else.

Titanium alloys

Titanium is a very light silver-white metal that is widely used in the metallurgical industry and metalworking. It can explode when in a finely dispersed state, therefore it is a fire hazard.

It is used in aircraft and rocket engineering, and in the production of ships. Widely used in medicine due to its biological compatibility with the body (prostheses, piercings, implants, etc.).

fb.ru

name and properties:: SYL.ru

Metals are among the most common materials, along with glass and plastics. They have been used by people since ancient times. In practice, people learned the properties of metals and used them profitably to make dishes, household items, various structures and works of art. The main characteristics of these materials are their refractoriness and hardness. Actually, their application in a particular area depends on these qualities.

Physical properties of metals

All metals have the following general properties:

1. Color – silver-gray with a characteristic shine. The exceptions are: copper and gold. They are respectively distinguished by a reddish and yellow tint.
2. The physical state is a solid, except for mercury, which is a liquid.
3. Thermal and electrical conductivity is expressed differently for each type of metal.
4. Plasticity and malleability are variable parameters depending on the specific metal.
5. Melting and boiling points - establishes refractoriness and fusibility, has different values ​​for all materials.

All physical properties of metals depend on the structure of the crystal lattice, its shape, strength and spatial arrangement.

Refractoriness of metals

This parameter becomes important when the question arises about the practical use of metals. For such important sectors of the national economy as aircraft construction, shipbuilding, and mechanical engineering, the basis is refractory metals and their alloys. In addition, they are used for the manufacture of high-strength working tools. Many important parts and products are produced by casting and smelting. Based on their strength, all metals are divided into brittle and hard, and based on their refractoriness they are divided into two groups.

Refractory and low-melting metals

1. Refractory - their melting point exceeds the melting point of iron (1539 °C). These include platinum, zirconium, tungsten, tantalum. There are only a few types of such metals. In practice, even fewer are used. Some are not used because they have high radioactivity, others are too fragile and do not have the necessary softness, others are susceptible to corrosion, and there are others that are not economically viable. Which metal is the most refractory? This is exactly what will be discussed in this article.
2. Low-melting metals are metals that, at a temperature less than or equal to the melting point of tin 231.9 °C, can change their state of aggregation. For example, sodium, manganese, tin, lead. Metals are used in radio and electrical engineering. They are often used for anti-corrosion coatings and as conductors.

Tungsten is the most refractory metal

It is a hard and heavy material with a metallic luster, light gray in color, and has high refractoriness. It is difficult to machine. At room temperature it is a brittle metal and breaks easily. This is caused by contamination with oxygen and carbon impurities. Technically pure tungsten becomes plastic at temperatures above 400 degrees Celsius. It exhibits chemical inertness and reacts poorly with other elements. In nature, tungsten occurs in the form of complex minerals, such as:

• scheelitis;
• wolframite;
• ferberite;
• hübnerite.

Tungsten is obtained from ore using complex chemical processing in powder form. Using pressing and sintering methods, simple shaped parts and bars are produced. Tungsten is a very temperature-resistant element. Therefore, they could not soften the metal for a hundred years. There were no furnaces that could heat up to several thousand degrees. Scientists have proven that tungsten is the most refractory metal. Although there is an opinion that seaborgium, according to theoretical data, has greater refractoriness, this cannot be stated firmly, since it is a radioactive element and has a short lifespan.

Historical information

The famous Swedish chemist Karl Scheele, who had the profession of a pharmacist, discovered manganese, barium, chlorine and oxygen in a small laboratory, conducting numerous experiments. And shortly before his death in 1781, he discovered that the mineral tungsten was a salt of an acid then unknown. After two years of work, his students, the two d'Eluyar brothers (Spanish chemists), isolated a new chemical element from the mineral and named it tungsten. Only a century later, tungsten - the most refractory metal - made a real revolution in industry.

Cutting properties of tungsten

In 1864, English scientist Robert Muschet used tungsten as an alloying additive to steel, which could withstand red heat and further increase hardness. The cutters, which were made from the resulting steel, increased the metal cutting speed by 1.5 times, and it became 7.5 meters per minute.

Working in this direction, scientists received new technologies, increasing the speed of metal processing using tungsten. In 1907, a new compound of tungsten with cobalt and chromium appeared, which became the founder of hard alloys capable of increasing cutting speed. Currently, it has increased to 2000 meters per minute, and all this is thanks to tungsten - the most refractory metal.

Applications of tungsten

This metal has a relatively high price and is difficult to process mechanically, so it is used where it is impossible to replace it with other materials of similar properties. Tungsten perfectly withstands high temperatures, has significant strength, is endowed with hardness, elasticity and refractoriness, therefore it is widely used in many areas of industry:

• Metallurgical. It is the main consumer of tungsten, which is used to produce high-quality alloy steels.
• Electrotechnical. The melting point of the most refractory metal is almost 3400 °C. The refractoriness of the metal allows it to be used for the production of incandescent filaments, hooks in lighting and electronic lamps, electrodes, X-ray tubes, and electrical contacts.

• Mechanical engineering. Due to the increased strength of steels containing tungsten, solid forged rotors, gears, crankshafts, and connecting rods are manufactured.
• Aviation. What is the most refractory metal used to produce hard and heat-resistant alloys, from which parts of aircraft engines, electric vacuum devices, and incandescent filaments are made? The answer is simple - it is tungsten.
• Space. Steel containing tungsten is used to produce jet nozzles and individual elements for jet engines.
• Military. The high density of the metal makes it possible to produce armor-piercing shells, bullets, armor protection for torpedoes, shells and tanks, and grenades.
• Chemical. Resistant tungsten wire against acids and alkalis is used for filter meshes. Tungsten is used to change the rate of chemical reactions.
• Textile. Tungstic acid is used as a dye for fabrics, and sodium tungstate is used to make leather, silk, water-resistant and fire-resistant fabrics.

The above list of uses of tungsten in various areas of industry indicates the high value of this metal.

Preparation of alloys with tungsten

Tungsten, the world's most refractory metal, is often used to make alloys with other elements to improve the properties of materials. Alloys that contain tungsten are usually produced using powder metallurgy technology, since the conventional method turns all metals into volatile liquids or gases at its melting point. The fusion process takes place in a vacuum or argon atmosphere to avoid oxidation. A mixture of metal powders is pressed, sintered and melted. In some cases, only tungsten powder is pressed and sintered, and then the porous workpiece is saturated with a melt of another metal. Alloys of tungsten with silver and copper are obtained in this way. Even small additions of the most refractory metal increase heat resistance, hardness and oxidation resistance in alloys with molybdenum, tantalum, chromium and niobium. The proportions in this case can be absolutely anything depending on the needs of the industry. More complex alloys, depending on the ratio of components with iron, cobalt and nickel, have the following properties:

• do not fade in air;
• have good chemical resistance;
• have excellent mechanical properties: hardness and wear resistance.

Tungsten forms rather complex compounds with beryllium, titanium and aluminum. They are distinguished by their resistance to oxidation at high temperatures, as well as heat resistance.

Properties of alloys

In practice, tungsten is often combined with a group of other metals. Tungsten compounds with chromium, cobalt and nickel, which have increased resistance to acids, are used for the manufacture of surgical instruments. And special heat-resistant alloys, in addition to tungsten - the most refractory metal, contain chromium, nickel, aluminum, and nickel. Tungsten, cobalt and iron are among the best grades of magnetic steel.

The most fusible and refractory metals

Low-melting metals include all metals whose melting point is lower than that of tin (231.9 °C). Elements of this group are used as anti-corrosion coatings, in electrical and radio engineering, and are part of anti-friction alloys. Mercury, whose melting point is -38.89 °C, is a liquid at room temperature and is widely used in scientific instruments, mercury lamps, rectifiers, switches, and chlorine production. Mercury has the lowest melting point compared to other metals included in the fusible group. Refractory metals include all metals whose melting point is higher than that of iron (1539 °C). They are most often used as additives in the manufacture of alloy steels, and they can also serve as the basis for some special alloys. Tungsten, which has a maximum melting point of 3420 °C, is used in its pure form mainly for filaments in electric lamps.

Quite often in crossword puzzles questions are asked: which metal is the most fusible or the most refractory? Now, without hesitation, you can answer: the most fusible is mercury, and the most refractory is tungsten.

Briefly about hardware

This metal is called the main structural material. Iron parts are found both on a spaceship or submarine, and at home in the kitchen in the form of cutlery and various decorations. This metal has a silver-gray color, has softness, ductility and magnetic properties. Iron is a very active element; an oxide film forms in air, which prevents the continuation of the reaction. Rust appears in a humid environment.

Melting point of iron

Iron has ductility, is easily forged and is difficult to cast. This durable metal is easily processed mechanically and is used for the manufacture of magnetic drives. Good malleability allows it to be used for decorative decorations. Is iron the most refractory metal? It should be noted that its melting point is 1539 °C. And by definition, refractory metals include metals whose melting point is higher than that of iron.

We can definitely say that iron is not the most refractory metal, and does not even belong to this group of elements. It belongs to medium-melting materials. What is the most refractory metal? Such a question will not take you by surprise now. You can safely answer – it’s tungsten.

Instead of a conclusion

Approximately thirty thousand tons per year of tungsten are produced worldwide. This metal is certainly included in the best grades of steel for making tools. Up to 95% of all tungsten produced is consumed for the needs of metallurgy. To reduce the cost of the process, they mainly use a cheaper alloy consisting of 80% tungsten and 20% iron. Using the properties of tungsten, its alloy with copper and nickel is used to produce containers used for storing radioactive substances. In radiotherapy, the same alloy is used to make screens, providing reliable protection.

www.syl.ru

Melting points of different metals in the table

Each metal and alloy has its own unique set of physical and chemical properties, not least of which is the melting point. The process itself means the transition of a body from one state of aggregation to another, in this case, from a solid crystalline state to a liquid one. To melt a metal, it is necessary to apply heat to it until the melting temperature is reached. With it, it can still remain in a solid state, but with further exposure and increased heat, the metal begins to melt. If the temperature is lowered, that is, some of the heat is removed, the element will harden.

Highest melting point of any metal belongs to tungsten: it is 3422C o, the lowest is for mercury: the element melts already at - 39C o. As a rule, it is not possible to determine the exact value for alloys: it can vary significantly depending on the percentage of components. They are usually written as a number interval.

How it happens

Melting of all metals occurs approximately the same way - using external or internal heating. The first is carried out in a thermal furnace; for the second, resistive heating is used by passing an electric current or induction heating in a high-frequency electromagnetic field. Both options affect the metal approximately equally.

As the temperature increases, the amplitude of thermal vibrations of molecules, structural defects in the lattice arise, expressed in the growth of dislocations, atomic jumps and other disturbances. This is accompanied by the rupture of interatomic bonds and requires a certain amount of energy. At the same time, a quasi-liquid layer forms on the surface of the body. The period of lattice destruction and defect accumulation is called melting.

Metal separation

Depending on their melting point, metals are divided into:

1. Low-melting: they need no more than 600C o. This is zinc, lead, hang, tin.
2. Medium melting: melting point ranges from 600C to 1600C. These are gold, copper, aluminum, magnesium, iron, nickel and more than half of all elements.
3. Refractory: temperatures above 1600C are required to make the metal liquid. These include chromium, tungsten, molybdenum, titanium.

Depending on melting point melting apparatus is also selected. The higher the indicator, the stronger it should be. You can find out the temperature of the element you need from the table.

Another important quantity is the boiling point. This is the value at which the process of boiling liquids begins; it corresponds to the temperature of saturated steam that forms above the flat surface of the boiling liquid. It is usually almost twice the melting point.

Both values ​​are usually given at normal pressure. Between themselves they directly proportional.

1. As the pressure increases, the amount of melting increases.
2. As the pressure decreases, the amount of melting decreases.

Table of low-melting metals and alloys (up to 600C o)

Table of medium-melting metals and alloys (from 600C o to 1600C o)

Table of refractory metals and alloys (over 1600C o)

stanok.guru

Refractory metals - list and scope

Refractory metals have been known since the end of the 19th century. There was no use for them then. The only industry where they were used was electrical engineering, and then in very limited quantities. But everything changed dramatically with the development of supersonic aviation and rocket technology in the 50s of the last century. The production required new materials that could withstand significant loads at temperatures above 1000 ºC.

List and characteristics of refractory metals

Refractoriness is characterized by an increased value of the transition temperature from the solid state to the liquid phase. Metals that melt at 1875 ºC and above are classified as refractory metals. In order of increasing melting temperature, these include the following types:

• Vanadium
• Rhodium
• Hafnium
• Ruthenium
• Tungsten
• Iridium
• Tantalum
• Molybdenum
• Osmium
• Rhenium
• Niobium.

Modern production in terms of the number of deposits and the level of production is satisfied only by tungsten, molybdenum, vanadium and chromium. Ruthenium, iridium, rhodium and osmium are quite rare in natural conditions. Their annual production does not exceed 1.6 tons.

Heat-resistant metals have the following main disadvantages:

• Increased cold brittleness. It is especially pronounced in tungsten, molybdenum and chromium. The transition temperature of a metal from a ductile to a brittle state is slightly above 100 ºC, which creates inconvenience when processing them under pressure.
• Instability to oxidation. Because of this, at temperatures above 1000 ºC, refractory metals are used only with preliminary application of galvanic coatings to their surface. Chromium is the most resistant to oxidation processes, but as a refractory metal it has the lowest melting point.

The most promising refractory metals include niobium and molybdenum. This is due to their prevalence in nature, and, consequently, low cost in comparison with other elements of this group.

The most refractory metal found in nature is tungsten. Its mechanical characteristics do not decrease at ambient temperatures above 1800 ºC. But the disadvantages listed above plus increased density limit its scope of use in production. As a pure metal, it is used less and less. But the value of tungsten as an alloying component increases.

Physical and mechanical properties

Metals with a high melting point (refractory) are transition elements. According to the periodic table, there are 2 types of them:

• Subgroup 5A – tantalum, vanadium and niobium.
• Subgroup 6A – tungsten, chromium and molybdenum.

Vanadium has the lowest density - 6100 kg/m3, tungsten has the highest density - 19300 kg/m3. The specific gravity of the remaining metals is within these values. These metals are characterized by a low coefficient of linear expansion, reduced elasticity and thermal conductivity.

These metals do not conduct electricity well, but have the quality of superconductivity. The temperature of the superconducting regime is 0.05-9 K based on the type of metal.

Absolutely all refractory metals are characterized by increased ductility under room conditions. Tungsten and molybdenum also stand out from other metals due to their higher heat resistance.

Corrosion resistance

Heat-resistant metals are characterized by high resistance to most types of aggressive environments. The corrosion resistance of elements of subgroups 5A increases from vanadium to tantalum. As an example, at 25 ºC vanadium dissolves in aqua regia, while niobium is completely inert towards this acid.

Tantalum, vanadium and niobium are resistant to molten alkali metals. Provided there is no oxygen in their composition, which significantly increases the intensity of the chemical reaction.

Molybdenum, chromium and tungsten have greater resistance to corrosion. Thus, nitric acid, which actively dissolves vanadium, has a much less effect on molybdenum. At a temperature of 20 ºC this reaction completely stops.

All refractory metals readily enter into chemical bonds with gases. The absorption of hydrogen from the environment by niobium occurs at 250 ºC. Tantalum at 500 ºC. The only way to stop these processes is to carry out vacuum annealing at 1000 ºC. It is worth noting that tungsten, chromium and molybdenum are much less prone to interact with gases.

As mentioned earlier, only chromium is resistant to oxidation. This property is due to its ability to form a solid film of chromium oxide on its surface. The dissolution of oxygen by chromium occurs only at 700 C. For other refractory metals, oxidation processes begin approximately at 550 ºC.

Cold brittleness

The spread of the use of heat-resistant metals in production is hampered by their increased tendency to cold brittleness. This means that when the temperature drops below a certain level, the brittleness of the metal sharply increases. For vanadium this temperature is -195 ºC, for niobium -120 ºC, and tungsten +330 ºC.

The presence of cold brittleness in heat-resistant metals is due to the content of impurities in their composition. Molybdenum of special purity (99.995%) retains increased plastic properties up to the temperature of liquid nitrogen. But the introduction of only 0.1% oxygen shifts the cold brittleness point to -20 C.

Areas of use

Until the mid-40s, refractory metals were used only as alloying elements to improve the mechanical characteristics of non-ferrous steel alloys based on copper and nickel in the electrical industry. Compounds of molybdenum and tungsten were also used in the production of hard alloys.

The technical revolution associated with the active development of aviation, the nuclear industry and rocket science has found new ways to use refractory metals. Here is a partial list of new applications:

• Production of heat shields for the head unit and rocket frames.
• Structural material for supersonic aircraft.
• Niobium serves as a material for the honeycomb panel of spacecraft. And in rocket science it is used as heat exchangers.
• Thermojet and rocket engine components: nozzles, tail skirts, turbine blades, nozzle flaps.
• Vanadium is the basis for the manufacture of thin-walled tubes of fusion reactor fuel elements in the nuclear industry.
• Tungsten is used as the filament of electric lamps.
• Molybdenum is increasingly used in the production of electrodes used for melting glass. In addition, molybdenum is a metal used to produce injection molds.
• Production of tools for hot processing of parts.

prompriem.ru

The most refractory metal on earth

Curious people are probably interested in the question, which metal is the most refractory? Before answering it, it is worth understanding the concept of refractoriness itself. All metals known to science have different melting points due to varying degrees of stability of bonds between atoms in the crystal lattice. The weaker the bond, the lower the temperature required to break it.

The world's most refractory metals are used in their pure form or in alloys to produce parts that operate under extreme thermal conditions. They can effectively withstand high temperatures and significantly extend the operating life of the units. But the resistance of metals of this group to thermal effects forces metallurgists to resort to non-standard methods of their production.

Which metal is the most refractory?

The most refractory metal on Earth was discovered in 1781 by the Swedish scientist Carl Wilhelm Scheele. The new material is called tungsten. Scheele was able to synthesize tungsten trioxide by dissolving the ore in nitric acid. The pure metal was isolated two years later by Spanish chemists Fausto Fermin and Juan José de Eluar. The new element did not immediately gain recognition and was adopted by industrialists. The fact is that the technology of that time did not allow processing such a refractory substance, so most contemporaries did not attach much importance to the scientific discovery.

Tungsten was appreciated much later. Today, its alloys are used in the production of heat-resistant parts for various industries. The filament in gas-discharge household lamps is also made of tungsten. It is also used in the aerospace industry for the production of rocket nozzles, and is used as reusable electrodes in gas arc welding. In addition to being refractory, tungsten also has a high density, which makes it suitable for making high-quality golf clubs.

Tungsten compounds with non-metals are also widely used in industry. So sulfide is used as a heat-resistant lubricant that can withstand temperatures up to 500 degrees Celsius, carbide is used to make cutters, abrasive discs and drills that can handle the hardest substances and withstand high heating temperatures. Let us finally consider the industrial production of tungsten. The most refractory metal has a melting point of 3422 degrees Celsius.

How is tungsten obtained?

Pure tungsten does not occur in nature. It is part of rocks in the form of trioxide, as well as wolframites of iron, manganese and calcium, less often copper or lead. According to scientists, the tungsten content in the earth's crust averages 1.3 grams per ton. This is a rather rare element compared to other types of metals. The tungsten content in ore after mining usually does not exceed 2%. Therefore, the extracted raw materials are sent to processing plants, where the mass fraction of metal is brought to 55-60% using magnetic or electrostatic separation.

The process of its production is divided into technological stages. In the first stage, pure trioxide is isolated from the mined ore. For this purpose, the thermal decomposition method is used. At temperatures from 500 to 800 degrees Celsius, all excess elements melt, and refractory tungsten in the form of oxide can be easily collected from the melt. The output is raw material with a hexavalent tungsten oxide content of 99%.

The resulting compound is thoroughly crushed and a reduction reaction is carried out in the presence of hydrogen at a temperature of 700 degrees Celsius. This allows you to isolate pure metal in powder form. Next, it is pressed under high pressure and sintered in a hydrogen environment at temperatures of 1200-1300 degrees Celsius. After this, the resulting mass is sent to an electric melting furnace, where, under the influence of current, it is heated to a temperature of over 3000 degrees. This is how tungsten turns into a molten state.

For final purification from impurities and obtaining a single-crystal structural lattice, the zone melting method is used. It implies that at a certain point in time only a certain zone of the total area of ​​the metal is molten. Gradually moving, this zone redistributes impurities, as a result of which they ultimately accumulate in one place and can be easily removed from the alloy structure.

Finished tungsten arrives at the warehouse in the form of bars or ingots, intended for the subsequent production of the desired products. To obtain tungsten alloys, all constituent elements are crushed and mixed in powder form in the required proportions. Next, sintering and melting are carried out in an electric furnace.

promplace.ru

Refractory metals are... What are refractory metals?

H																		He
Li	Be												B	C	N	O	F	Ne
Na	Mg												Al	Si	P	S	Cl	Ar
K	Ca	Sc	Ti	V	Cr	Mn	Fe	Co	Ni	Cu	Zn	Ga	Ge	As	Se	Br	Kr
Rb	Sr	Y	Zr	Nb	Mo	Tc	Ru	Rh	Pd	Ag	Cd	In	Sn	Sb	Te	I	Xe
Cs	Ba	La	*	Hf	Ta	W	Re	Os	Ir	Pt	Au	Hg	Tl	Pb	Bi	Po	At	Rn
Fr	Ra	Ac	**	Rf	Db	Sg	Bh	Hs	Mt	Ds	Rg
			*	Ce	Pr	Nd	Pm	Sm	Eu	Gd	Tb	Dy	Ho	Er	Tm	Yb	Lu
			**	Th	Pa	U	Np	Pu	Am	Cm	Bk	Cf	Es	Fm	MD	No	Lr

Refractory metals- a class of chemical elements (metals) that have a very high melting point and resistance to wear. The expression refractory metals is most often used in disciplines such as materials science, metallurgy and engineering sciences. The definition of refractory metals applies to each element of the group differently. The main representatives of this class of elements are the elements of the fifth period - niobium and molybdenum; sixth period - tantalum, tungsten and rhenium. All of them have a melting point above 2000 °C, are chemically relatively inert and have an increased density. Thanks to powder metallurgy, they can be used to produce parts for various industries.

Definition

Most definitions of the term refractory metals define them as metals having high melting points. By this definition, it is necessary that metals have a melting point above 2,200 °C. This is necessary for their definition as refractory metals. Five elements - niobium, molybdenum, tantalum, tungsten and rhenium are included in this list as the main ones, while a broader definition of these metals allows us to also include elements with a melting point of 2123K (1850 °C) - titanium, vanadium, chromium, zirconium, hafnium, ruthenium and osmium. Transuranium elements (all isotopes of which are unstable and very difficult to find on earth) will never be classified as refractory metals.

Properties

Physical properties

The melting point of these elements is the highest, excluding carbon and osmium. This property depends not only on their properties, but also on the properties of their alloys. Metals have a cubic system, with the exception of rhenium, in which it takes the form of a hexagonal close packing. Most of the physical properties of the elements in this group vary significantly because they are members of different groups.

Resistance to creep deformation ( English) is a defining property of refractory metals. In ordinary metals, deformation begins at the melting point of the metal, and hence creep deformation in aluminum alloys begins at 200 °C, while in refractory metals it begins at 1500 °C. This resistance to deformation and high melting point allows refractory metals to be used, for example, as jet engine parts or in the forging of various materials.

Chemical properties

In open air they undergo oxidation. This reaction slows down due to the formation of a passivated layer. Rhenium oxide is very unstable because when a dense flow of oxygen is passed through, its oxide film evaporates. All of them are relatively resistant to acids.

Application

Refractory metals are used as light sources, parts, lubricants, in the nuclear industry as ARC, and as a catalyst. Because they have high melting points, they are never used as an open smelting material. In powder form, the material is compacted using melting furnaces. Refractory metals can be processed into wire, ingot, rebar, tin or foil.

Tungsten and its alloys

Tungsten was discovered in 1781 by the Swedish chemist Carl Wilhelm Scheele. Tungsten has the highest melting point of all metals - 3422 °C.

Tungsten.

Rhenium is used in alloys with tungsten in concentrations up to 22%, which increases refractoriness and corrosion resistance. Thorium is used as an alloying component of tungsten. This increases the wear resistance of materials. In powder metallurgy, components can be used for sintering and subsequent application. To obtain heavy tungsten alloys, nickel and iron or nickel and copper are used. The tungsten content in these alloys is usually above 90%. The mixing of alloying material with it is low even during sintering.

Tungsten and its alloys are still used where high temperatures are present, but high hardness is required and where high density can be neglected. Filaments consisting of tungsten find their use in everyday life and in instrument making. Bulbs convert electricity into light more efficiently as temperatures increase. In tungsten gas arc welding ( English) the equipment is used continuously, without melting the electrode. Tungsten's high melting point allows it to be used in welding without cost. Tungsten's high density and hardness allow it to be used in artillery shells. Its high melting point is used in the construction of rocket nozzles, an example being the Polaris rocket. Sometimes it finds its use due to its density. For example, it finds its use in the production of golf clubs. In such parts, the use is not limited to tungsten, since the more expensive osmium can also be used.

Molybdenum alloys

Molybdenum.

Molybdenum alloys are widely used. The most commonly used alloy - titanium-zirconium-molybdenum - contains 0.5% titanium, 0.08% zirconium and the rest molybdenum. The alloy has increased strength at high temperatures. The operating temperature for the alloy is 1060 °C. The high resistance of tungsten-molybdenum alloy (Mo 70%, W 30%) makes it an ideal material for casting zinc parts such as valves.

Molybdenum is used in mercury reed relays because mercury does not form amalgams with molybdenum.

Molybdenum is the most commonly used refractory metal. Most important is its use as a strengthener for steel alloys. Used in the manufacture of pipelines together with stainless steel. Molybdenum's high melting point, wear resistance and low coefficient of friction make it a very useful alloying material. Its excellent friction properties lead it to be used as a lubricant where reliability and performance are required. Used in the production of CV joints in the automotive industry. Large deposits of molybdenum are found in China, the USA, Chile and Canada.

Niobium alloys

The dark part of the Apollo CSM nozzle is made of titanium-niobium alloy.

Niobium is almost always found together with tantalum; niobium was named after Niobe, the daughter of Tantalus in Greek mythology. Niobium has many uses, some of which it shares with refractory metals. Its uniqueness lies in the fact that it can be developed by annealing to achieve a wide range of hardness and elasticity properties; its density index is the smallest compared to other metals in this group. It can be used in electrolytic capacitors and is the most common metal in superconducting alloys. Niobium can be used in aircraft gas turbines, vacuum tubes and nuclear reactors.

Niobium alloy C103, which consists of 89% niobium, 10% hafnium and 1% titanium, is used to create nozzles in liquid rocket engines, such as the Apollo CSM ( English) . The alloy used does not allow niobium to oxidize, since the reaction occurs at a temperature of 400 °C.

Tantalum

Tantalum is the most corrosion-resistant metal of all refractory metals.

An important property of tantalum was discovered through its use in medicine - it is able to withstand an acidic environment (of the body). It is sometimes used in electrolytic capacitors. Used in cell phone and computer capacitors.

Rhenium alloys

Rhenium is the most recently discovered refractory element of the entire group. It is found in low concentrations in the ores of other metals in this group - platinum or copper. It can be used as an alloying component with other metals and gives the alloys good characteristics - malleability and increases tensile strength. Rhenium alloys can be used in electronic components, gyroscopes and nuclear reactors. Its most important application is as a catalyst. Can be used in alkylation, dealkylation, hydrogenation and oxidation. Its rare presence in nature makes it the most expensive of all refractory metals.

General properties of refractory metals

Refractory metals and their alloys attract the attention of researchers due to their unusual properties and future prospects for application.

The physical properties of refractory metals such as molybdenum, tantalum and tungsten, their hardness and stability at high temperatures make them a material used for hot metal processing of materials both in vacuum and without it. Many parts are based on their unique properties: for example, tungsten filaments can withstand temperatures up to 3073K.

However, their resistance to oxidation up to 500 °C makes this one of the main disadvantages of this group. Contact with air can significantly affect their high temperature performance. That is why they are used in materials in which they are isolated from oxygen (for example, a light bulb).

Alloys of refractory metals - molybdenum, tantalum and tungsten - are used in parts of space nuclear technologies. These components have been specifically designed to withstand high temperatures (1350K to 1900K). As stated above, they should not come into contact with oxygen.

see also

Notes

1. H. Ortner International Journal of Refractory Metals and Hard Materials (English). Elsevier. Archived from the original on June 20, 2012. Retrieved September 26, 2010.
2. Michael Bauccio Refractory metals // ASM metals reference book / American Society for Metals. - ASM International, 1993. - pp. 120-122. - ISBN 19939780871704788
3. Wilson, J. W. General Behavior of Refractory Metals // Behavior and Properties of Refractory Metals. - Stanford University Press, 1965. - pp. 1-28. - 419 p. - ISBN 9780804701624
4. Joseph R. Davis Alloying: understanding the basics. - ASM International, 2001. - pp. 308-333. - 647 p. - ISBN 9780871707444
5. 1 2 Borisenko, V. A. Investigation of the temperature dependence of the hardness of molybdenum in the range of 20-2500 °C // Soviet Powder Metallurgy and Metal Ceramics Magazine. - 1963. - P. 182. - DOI:10.1007/BF00775076
6. Fathi, Habashi Historical Introduction to Refractory Metals // Journal of Mineral Processing and Extractive Metallurgy Review. - 2001. - P. 25-53. - DOI:10.1080/08827509808962488
7. Schmid, Kalpakjian Creep // Manufacturing engineering and technology. - Pearson Prentice Hall, 2006. - pp. 86-93. - 1326 p. - ISBN 9787302125358
8. Weroński, Andrzej; Hejwowski, Tadeusz Creep-Resisting Materials // Thermal fatigue of metals. - CRC Press, 1991. - pp. 81-93. - 366 s. - ISBN 9780824777265
9. 1 2 Erik Lassner, Wolf-Dieter Schubert Tungsten: properties, chemistry, technology of the element, alloys, and chemical compounds. - Springer, 1999. - pp. 255-282. - 422 s. - ISBN 9780306450532
10. National Research Council (U.S.), Panel on Tungsten, Committee on Technical Aspects of Critical and Strategic Material Trends in Usage of Tungsten: Report. - National Research Council, National Academy of Sciences-National Academy of Engineering, 1973. - pp. 1-3. - 90 s.
11. Michael K. Harris Welding Health and Safety // Welding health and safety: a field guide for OEHS professionals. - AIHA, 2002. - P. 28. - 222 p. - ISBN 9781931504287
12. William L. Galvery, Frank M. Marlow Welding essentials: questions & answers. - Industrial Press Inc., 2001. - P. 185. - 469 p. - ISBN 9780831131517
13. W. Lanz, W. Odermatt, G. Weihrauch (7-11 May 2001). “KINETIC ENERGY PROJECTILES: DEVELOPMENT HISTORY, STATE OF THE ART, TRENDS” in 19th International Symposium of Ballistics..
14. P. Ramakrishnan Powder metallurgy for Aerospace Applications // Powder metallurgy: processing for automotive, electrical/electronic and engineering industry. - New Age International, 2007. - P. 38. - 381 p. - ISBN 8122420303
15. Arora, Arran Tungsten Heavy Alloy For Defense Applications // Materials Technology Magazine. - 2004. - V. 19. - No. 4. - P. 210-216.
16. V. S. Moxson, F. H. Froes Fabricating sports equipment components via powder metallurgy // JOM Magazine. - 2001. - V. 53. - P. 39. - DOI:10.1007/s11837-001-0147-z
17. Robert E. Smallwood TZM Moly Alloy // ASTM special technical publication 849: Refractory metals and their industrial applications: a symposium. - ASTM International, 1984. - P. 9. - 120 p. - ISBN 19849780803102033
18. Kozbagarova, G. A.; Musina, A. S.; Mikhaleva, V. A. Corrosion Resistance of Molybdenum in Mercury // Protection of Metals Magazine. - 2003. - V. 39. - P. 374-376. - DOI:10.1023/A:1024903616630
19. Gupta, C. K. Electric and Electronic Industry // Extractive Metallurgy of Molybdenum. - CRC Press, 1992. - pp. 48-49. - 404 p. - ISBN 9780849347580
20. Michael J. Magyar Commodity Summary 2009: Molybdenum. United States Geological Survey. Archived from the original on June 20, 2012. Retrieved September 26, 2010.
21. D.R. Ervin, D. L. Bourell, C. Persad, L. Rabenberg Structure and properties of high energy, high rate consolidated molybdenum alloy TZM // Journal of Materials Science and Engineering: A. - 1988. - V. 102. - P. 25.
22. Neikov Oleg D. Properties of Molybdenum and Molybdenum Alloys powder // Handbook of Non-Ferrous Metal Powders: Technologies and Applications. - Elsevier, 2009. - pp. 464-466. - 621 p. - ISBN 9781856174220
23. Joseph R. Davis Refractory Metals and Alloys // ASM specialty handbook: Heat-resistant materials. - ASM International, 1997. - pp. 361-382. - 591 p. - ISBN 9780871705969
24. 1 2 John Hebda Niobium alloys and high Temperature Applications // Journal of Niobium Science & Technology: Proceedings of the International Symposium Niobium 2001 (Orlando, Florida, USA). - Companhia Brasileira de Metalurgia e Mineração, 2001.
25. J. W. Wilson Rhenium // Behavior and Properties of Refractory Metals. - Stanford University Press, 1965. - ISBN 9780804701624

Literature

• Levitin, Valim High Temperature Strain of Metals and Alloys: Physical Fundamentals. - WILEY-VCH, 2006. - ISBN 978-3-527-31338-9
• Brunner, T. Chemical and structural analyzes of aerosol and fly-ash particles from fixed-bed biomass combustion plants by electron microscopy, 1st World Conference on Biomass for Energy and Industry: proceedings of the conference held in Sevilla, Spain, 5-9 June 2000,London: James & James Ltd(2000). Retrieved September 26, 2010.
• Donald Spink Reactive Metals. Zirconium, Hafnium, and Titanium // . - 1961. - V. 53. - No. 2. - P. 97-104. - DOI:10.1021/ie50614a019
• Earl Hayes Chromium and Vanadium // Journal of Industrial & Engineering Chemistry. - 1961. - V. 53. - No. 2. - P. 105-107. - DOI:10.1021/ie50614a020