What are refractory metals?

Refractory metals - description, products made from refractory metals

The definition of “refractory metals” does not require additional explanation due to the exhaustive information content of the term itself. The only nuance remains the threshold melting temperature, after which the substance can be considered refractory.

Disagreement on a Critical Parameter

Some sources set the threshold value as 4000 F. Translated to the usual scale, this gives 2204 0C. According to this criterion, only five elements are considered heat-resistant: tungsten, niobium, rhenium, tantalum and molybdenum. For example, the melting point of tungsten is 3422 0C.

melting tungsten with a hydrogen torch

Another statement allows us to expand the class of temperature-resistant materials, since it takes the melting point of iron as the starting point - 1539 0C. This allows the list to be expanded by nine more elements to include titanium, vanadium, chromium, iridium, zirconium, hafnium, rhodium, ruthenium and osmium.

There are several other temperature thresholds, but they are not widely used.

Comparative table of the degree of refractoriness of pure metals

It should be noted that refractory materials are not limited solely to metals. This category includes a number of compounds - alloys and alloy metals - designed to improve certain characteristics of the original material.

Regarding pure elements, we can give a visual table of the degree of their temperature stability. It is headed by the most refractory metal known today - tungsten with a melting point of 3422 0C. This cautious formulation is associated with attempts to isolate metals that have a melt threshold that exceeds tungsten.

Therefore, the question of which metal is the most refractory may in the future receive a completely different definition.

The threshold values ​​for the remaining compounds are given below:

• rhenium 3186;
• osmium 3027;
• tantalum 3014;
• molybdenum 2623;
• niobium 2477;
• iridium 2446;
• ruthenium 2334;
• hafnium 2233;
• rhodium 1964;
• vanadium 1910;
• chrome 1907;
• zirconium 1855;
• titanium 1668.

It remains to add one more interesting fact concerning the physical properties of heat-resistant elements. The melting point of some of them is sensitive to the purity of the material. A striking example of this is chromium, the melting point of which can vary from 1513 to 1920 0C, depending on the chemical composition of the impurities. Therefore, these Internet spaces often differ in exact numbers, but the quality component does not suffer from this.

Pure chrome

General properties of heat-resistant materials

The relative similarity of the physicochemical characteristics of these elements is due to the common atomic structure and the fact that they turn out to be transition metals. On the contrary, differences in properties are associated with their belonging to a wide range of groups of the Periodic Table: IV – VII.

The basic general characteristic of refractory materials is strong interatomic bonds. Their rupture requires high energy, which determines the melting temperature of thousands of degrees Celsius. Additionally, this property affects the high values ​​of such parameters of refractory metals as: hardness, mechanical strength, electrical resistance.

The next characteristic that unites these elements is high chemical activity. It is associated with the general tendency of refractory metals to form chemical bonds through a free p- and partially filled d-orbital, donating electrons from the outer s and d levels. This property makes it difficult to obtain pure refractory metals, dividing the technological production into several stages.

The structure of the heat-resistant elements is also identical; they are all characterized by a body-centered cubic crystal lattice. This structure is characterized by “brittleness.” The exception is rhenium, which has a hexagonal cell. The transition to a brittle state for each metal occurs at a certain temperature, the regulation of which is achieved through alloying.

Every refractory metal is, by definition, heat-resistant, but not all of them are heat-resistant. Most refractory metals are resistant to oxidation and aggressive environments: acids, alkalis; under normal conditions.

However, with an increase in temperature to 400 0C, their activity increases abnormally. This requires the creation of certain operating conditions.

Therefore, products made of refractory metals, at elevated temperatures of use, are often placed in an atmosphere of inert gases or the air is rarefied to vacuum conditions.

Obtaining refractory materials

As noted earlier, the main obstacle to the production of heat-resistant metals is their high chemical activity, which prevents the release of elements in their pure form.

The main production technology remains powder metallurgy. This technique makes it possible to obtain powders of refractory metals in various ways:

1. Reduction with hydrogen trioxide. The process is carried out in several stages, inside multi-tube furnaces at 750 – 950 °C. The technology is applicable for powders of refractory metals: tungsten and molybdenum.
2. Reduction of perrhenate with hydrogen. The scheme is implemented in the production of rhenium metal. Operating temperatures are around 500 °C. The final stage involves washing the powder from the alkali. To do this, hot water and a solution of hydrochloric acid are used sequentially.
3. Use of metal salts. Technology has been developed to isolate molybdenum. The main raw materials are the ammonium salt of the metal and its metal powder, introduced into the mixture at a level of 5 - 15% by weight. The composition undergoes heat treatment at 500 – 850 °C in flowing inert gas. The reduction of the metal takes place in a hydrogen atmosphere at temperatures of 800 – 1000 °C.

Production of refractory metals - powder metallurgy

Excursion to production

Methods for producing heat-resistant metals continue to be improved, as does the chemical technology of refractory non-metallic and silicate materials, which is associated with the development of nuclear energy, aircraft construction, and the emergence of new models of rocket engines.

One of the largest tungsten production enterprises in the Russian Federation is the Unech Refractory Metals Plant. This enterprise is relatively young; its construction began in 2007 on the territory of the settlement of Unecha. The plant's production focus is on powders of refractory metals, more precisely tungsten and its carbides.

Subsequently, to obtain ingots, the crumbly mass is sintered or compressed with a press. In a similar way, refractory metal powders are processed to produce heat-resistant products.

Application of refractory materials

The use of pure heat-resistant metals has priorities in a number of areas:

• production of spacecraft;

• production of guided missiles, missiles;

• electronic and vacuum technology.

Space industry

The last point concerns the electrodes of vacuum tubes. For example, high-purity niobium is used to produce meshes and tubes for electronic parts. It is also used to make electrodes - anodes of electric vacuum devices.

Electrovacuum radio tubes

Similar applications are typical for molybdenum and tungsten. These metals in their pure form are used not only as filaments, but also for electrodes of radio tubes, hooks, and pendants of electric vacuum equipment. Tungsten single crystals, on the contrary, are used as heaters for electrodes, in particular cathodes, and also in the manufacture of electrical contacts and fuses.

Pure vanadium and niobium are used in nuclear energy, where they are used to make pipes for nuclear reactors and shells of fuel elements. The area of ​​application of high-purity tantalum is chemistry (ware and equipment), since the metal is highly resistant to corrosion.

Refractory solder should be considered separately, since it does not include metals with high melting points. For example, refractory tin does not contain refractory metal powders. Copper, silver, nickel or magnesium are used as additives here.

Refractory metals and alloys are in demand both in rolled products and in other areas. In particular, the use of alloys is due to the ability to modify certain properties of the metal: lower the embrittlement temperature, improve heat-resistant characteristics.

Rolled products from refractory metals are quite wide in range and include:

• regular and deep-drawing strips;

Tungsten-rhenium thermoelectrode wire

The largest domestic manufacturer of this type of product is an experimental plant for refractory metals and hard alloys.

refractory metals

Source: http://xlom.ru/spravochnik/tugoplavkie-metally-opisanie-izdeliya-iz-tugoplavkix-me/

The most refractory metal in the world - Metalist's Handbook

Since ancient times, man has learned to process and use metals in his life.

Some of them are suitable for making dishes and other consumer goods, while others, such as stainless steel, are used to make weapons and medical instruments.

And some metals and alloys are used to build complex technical mechanisms, such as a spaceship or an airplane. One of the characteristics that people pay attention to when choosing a particular material is its refractoriness.

The most refractory metal is tungsten

Refractoriness of metals

All engineers and designers working in mechanical engineering pay attention to this characteristic. Depending on the value of this characteristic, a person can calculate and determine in which design certain refractory materials can be used.

Materials whose melting point is higher than the melting point of iron, equal to 1539 ° C, are called refractory. The most refractory materials:

• tantalum;
• niobium;
• molybdenum;
• rhenium;
• tungsten.

TantalumMolybdenum

The full list contains more chemical elements, but not all of them are widely used in production and some have lower melting points or are radioactive.

Tungsten is the most refractory metal. It looks light gray in color and is quite hard and heavy. However, it becomes brittle at low temperatures and is easy to break (cold brittleness). If you heat tungsten above 400 °C, it will become ductile. Tungsten does not combine well with other substances. It is extracted from complex and rare ore minerals, such as:

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

Ore processing is a very complex and expensive process. The extracted material is formed into bars or finished parts.

Huebnerite

Tungsten was discovered in the 18th century, but for a long time there were no furnaces capable of heating to the melting point of this refractory metal. Scientists have conducted many studies and confirmed that tungsten is the most refractory metal. It is worth noting that according to one of the theories, seaborgium has a high melting point, but it is not possible to conduct a sufficient number of studies, because it is radioactive and unstable.

Adding tungsten to steel increases its hardness, so it began to be used in the manufacture of cutting tools, which increased cutting speed and thereby led to an increase in production.

The high cost and difficulty of processing this refractory metal affect its areas of application. It is used in cases where it is not possible to use another. Its advantages:

• resistant to high temperatures;
• increased hardness;
• durable or resilient at certain temperatures;

Metal ore processing

All these characteristics help tungsten find wide application in various fields, such as:

• metallurgy, for alloy steels;
• electrical engineering, for filaments, electrodes, etc.;
• mechanical engineering, in the manufacture of gear units and shafts, gearboxes and much more;
• aviation production, in the manufacture of engines;
• space industry, used in rocket nozzles and jet engines;
• military-industrial complex, for armor-piercing shells and cartridges, armor of military equipment, in the design of torpedoes and grenades;
• chemical industry, tungsten has good corrosion resistance to acids, which is why filter meshes are made from it. In addition, compounds with tungsten are used as fabric dyes, in the production of clothing for firefighters, and much more.

Such a list of industries where this refractory metal is used suggests that its importance for humanity is very great. Every year, tens of thousands of tons of pure tungsten are produced around the world, and every year the demand for it grows.

Refractory metals and their alloys

According to Wikipedia, refractory metals include metals that have a melting point of 2200 °C. Niobium, rhenium, molybdenum, tantalum and tungsten fall under this statement.

Name	Melting temperature
Niobium	2477°C
Molybdenum	2623 °C
Tantalum	3017 °C
Tungsten	3422 °C
Rhenium	3186 °C

Refractory metals are widely used in many industries and in everyday life. They are used in the manufacture of incandescent light bulbs, mobile phones, computers or, for example, nuclear reactors.

In a broader concept and practical application, refractory metals also include vanadium, hafnium, ruthenium, chromium, zirconium and osmium.

They are also used as alloying elements in alloys with metals from the first group to improve a set of operational or technological properties.

Pure metals themselves are of course used in production, for example, pure molybdenum and tungsten are used in the electronics industry, chemical engineering or in the production of heat treatment furnaces. But most of them are prone to brittle fracture at high temperatures, and they also have relatively low heat resistance. Much more interesting, from the point of view of increasing performance properties, is the use of alloys of these metals.

Refractory tungsten-based alloys

A representative of such alloys is the tungsten and niobium alloy BB2 with a heat resistance temperature of up to 1200°C. To increase corrosion resistance and refractoriness, tungsten alloys are alloyed with rhenium. And to increase wear resistance, thorium.

Molybdenum-based alloys

Molybdenum and its alloys are probably the most frequently used of all refractory materials. In industry, alloys alloyed with zirconium, boron, titanium, and niobium are often used: alloys TsM3, TsM6, TsM2A, VM3

Refractory niobium-based alloys

Niobium and its alloys, due to their high corrosion resistance, high heat resistance (up to 1300°C) and good performance under neutron irradiation, are widely used in the manufacture of nuclear industry products. As an example of niobium-based alloys, it is worth mentioning the alloys VN2, VN2A, VN3.

Methods for increasing the heat resistance and heat resistance of alloys

The heat resistance of refractory alloys, as mentioned above, is increased by alloying elements with a higher melting point, which form substitutional solid solutions in the alloy. Greater efficiency in increasing heat resistance and, in some cases, wear resistance can be achieved by dispersion hardening of the alloy with the formation of carbides (ZrC, NiC), nitrides (TiN) and oxides (ZrO2).

All refractory metals have low heat resistance, so intermetallic and ceramic coatings are used to protect them at temperatures above 400°C. For molybdenum and tungsten, silicon-based coatings (MoSi2, WSi2) are used. [1]

Literature:

1. Yu.M. Lakhtin, V.P. Leontiev., Materials Science, 1990

Source: https://HeatTreatment.ru/tugoplavkie-metally-i-ih-splavy.html

Which metal is considered the most refractory?

Metal has been used by humans in various fields of activity since ancient times. To obtain a high-quality metal product, it is important to choose a good material, while assessing its characteristics. An important parameter is refractoriness. For the manufacture of some products, only the most refractory metals are suitable.

Historical information

Before studying the characteristics of the most refractory metals in the world, you should familiarize yourself with their discovery history. Metalworking has been known to man for several thousand years. However, active production of refractory metals began only in the second half of the 19th century.

Initially they were used only in electrical engineering. With the advent of new technologies in the construction of airplanes, cars, trains and rockets, parts with a high melting rate began to be used more actively. The peak popularity of blanks that can withstand temperatures of more than 1000 degrees occurred in the mid-20th century.

Definition

Refractory metal is a separate class that includes metal blanks that can withstand exposure to critically high temperatures. Typically, members of this class have a melting point of more than 1600 degrees, which is considered the melting point of iron. These include noble alloys. They are also called representatives of the platinum group.

Kinds

Types of metals and alloys that are resistant to elevated temperatures:

1. Tungsten. They first learned about it in 1781. To melt it, it needed to be heated to 3380 degrees. Tungsten is considered the most refractory. It is made from powder, which is processed chemically. First, the mixture is heated and then subjected to pressure. The output is compressed blanks.
2. Niobium. Melts at 2500 degrees. It has high thermal conductivity and is not as difficult to process as tungsten. It is made from powder that is baked and processed using high pressure. Niobium is used to make wire, pipes and tape.
3. Molybdenum. Visually, it can be confused with tungsten. It is made from powder by baking and applying pressure. Like tungsten, it has paramagnetic properties. Used in radio electronics, manufacturing of industrial equipment, furnaces and electrodes.
4. Tantalum. Melts at 3000 degrees. To make tantalum wire or harden the material, it does not need to be heated to critical temperatures. Used for the manufacture of elements in radio electronics (capacitors, film resistors). Popular in the nuclear industry.
5. Rhenium. Material that scientists discovered later than others. You can find it in copper and platinum ore. Used in industrial production as an alloying additive.

Chromium is also a material with high melting points. Due to its unique characteristics, it is used in various industries. It has increased resistance to critical temperatures and corrosive processes. However, it is worth considering its fragility.

Properties

To understand where it is best to use a material, you need to know the properties of refractory metals. They are used to make parts for industrial equipment, machinery and electronics. The characteristics of heavy refractory metals will be described below.

Physical properties

Characteristics:

1. Density - up to 10000 kg/m3. For tungsten this figure reaches 19,000 kg/m3.
2. The average melting point is 2500 degrees Celsius. Tungsten has the highest metal melting point - 3390 degrees.
3. Specific heat capacity - 400 J.

Refractory objects cannot withstand impacts and falls.

Chemical properties

Chemical properties:

1. These are solid substances with high chemical activity.
2. Strong interatomic structure.
3. Resistance to long-term exposure to acids and alkalis.
4. High paramagnetic index.

These materials have some disadvantages. The main one is the difficult process of processing and manufacturing products from it.

Application

Initially, refractory metals were used in the manufacture of capacitors and transistors for radio electronics. The number of their areas of application increased only by the middle of the 20th century. The industrial complex expanded to produce parts for machine tools, cars, airplanes and missiles.

Alloys that can withstand exposure to critical temperatures began to be used to make tableware. Refractory metals are used in the production of building and connecting materials. They are used to make parts for household appliances and electronics.

Tungsten is considered the most refractory. Its melting point of 3390 degrees exceeds other materials. However, we must not forget that if a tungsten part falls from a height, it will crack or break into separate parts.

Tungsten is the most refractory metal on earth!
Other materials with a high melting index are little different from tungsten. They are used in mechanical engineering, shipbuilding, nuclear energy, and the manufacture of industrial equipment.

Their development and research continues to this day.

Which metal is considered the most refractory? Link to main publication

Source: https://metalloy.ru/obrabotka/termo/samyj-tugoplavkij-metall

Refractory metals - characteristics, properties and applications

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
• Chromium
• 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.

In addition, niobium has established itself as a metal with a relatively low density, increased manufacturability and fairly high refractoriness. Molybdenum is valuable, first of all, for its specific strength and heat resistance.

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.

Source: https://prompriem.ru/metally/tugoplavkie-metally.html

What is the most refractory metal: name and properties:

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.

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'Eluyard 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.

Tungsten-containing steels are resistant to abrasion, do not crack, and always remain hard. Cutting tools not only increase the speed of metal processing, but also have a long service life.

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.

Source: https://www.syl.ru/article/362939/kakoy-samyiy-tugoplavkiy-metall-nazvanie-i-svoystva

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.

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-fusibility ones are those that are capable of changing their state of aggregation at temperatures below 1000 °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 °C is presented below. This is where the most refractory representatives are located.

Metal name	Melting point, oC	Boiling point, oC
Gold, Au	1064.18	2856
Beryllium, Be	1287	2471
Cobalt, Co

Source: https://FB.ru/article/182368/naibolee-tugoplavkiy-metall-harakteristika-metallov

Refractory metals

Refractory metals were allocated into a separate class due to the property that unites them - a high melting point. It is higher than that of iron, which is 1539 °C. Therefore, the metals of this group received such a name. They belong to the so-called rare earth elements. For example, in terms of abundance in the earth’s crust, niobium and tantalum account for 3%, and zirconium only 2%.

Refractory metals

According to the melting temperature indicator, in addition to those listed, these include metals of the so-called platinum group. They are also called noble or precious.

A certain similarity in the structure of the atom determined the similarity of their properties. Based on this, it is possible to summarize some of the features of the manifestation of such metals in the earth’s crust and determine the technology for their extraction, production and processing.

Properties of refractory metals

Due to the fact that they are located in adjacent groups of the periodic table, the physical properties of refractory metals are quite similar:

• The density of the metal ranges from 6100 to 10000 kg/m3. In terms of this indicator, only tungsten stands out. For him it is equal to 19000 kg/m3.
• Melting temperature. It exceeds the melting point of iron and ranges from 1950 °C for vanadium to 3395 °C for tungsten.
• Their specific heat capacity differs slightly from each other and ranges from 200 to 400 J/(kg-deg).
• The thermal conductivity coefficient varies greatly from element to element. If for vanadium it is 31 W/(m-deg), then for tungsten it reaches a value of 188 W/(m-deg).

Physical properties of refractory metals

The chemical properties are also quite similar:

• Very similar atomic structure.
• They have high chemical activity. This property determines the main difficulties in maintaining the stability of their compounds.
• The strength of interatomic bonds determines the high melting point. This circumstance explains the high mechanical strength, hardness and electrical characteristics (in particular resistance).
• Show good resistance to various acids.

The main disadvantages of refractory metals include:

• Low corrosion resistance. The oxidation process occurs quite quickly. It is divided into two successive stages. Direct interaction of the metal with oxygen in the surrounding air, which leads to the formation of an oxide film. At the second stage, the process of diffusion (penetration) of oxygen atoms through the formed oxide film occurs.
• Difficulties with weldability of refractory metals. This is caused by high chemical reactivity to the surrounding air at high temperatures, fragility when saturated with various impurities. In addition, it is difficult to determine the overheating point and almost impossible to control the increase in yield strength.
• Difficulties in obtaining them for use in their pure form without impurities.
• The need to use special coatings to prevent rapid oxidation. Silicide coatings have been developed for alloys based on tungsten and molybdenum.
• Difficulties associated with machining. For high-quality processing, they must first be heated.

Production of refractory metals

All methods for producing refractory metals are based on the methods of so-called powder metallurgy. The process itself occurs in several stages:

1. At the initial stage, metal powder is obtained.
2. The required metal is then isolated by chemical reduction methods (usually ammonium salts or oxides). This release occurs as a result of exposure of the powder to hydrogen.
3. At the final stage, a chemical compound called hexafluoride of the corresponding metal is obtained, and from it the metal itself is obtained.

Application of refractory metals

Starting from the second half of the twentieth century, refractory metals began to be used in many branches of industrial production. Powders of refractory metals are used for the production of primary products. Refractory metals are produced in the form of wire, ingots, fittings, rolled metal and foil.

Such metals occupy a special place in the technology of growing leucosapphires. They belong to the class of single crystals and are called artificial rubies.

Products made of refractory metals are included in household and industrial electrical appliances, fire-resistant structures, and parts for engines of aviation and space technology. Refractory metals occupy a special place in the production of parts with complex configurations.

This metal was discovered back in 1781. Its melting point is 3380 °C. Therefore, it is by far the most refractory metal. Tungsten is obtained from a special powder by subjecting it to chemical treatment. This process is based on pressing followed by sintering at high temperatures. Next, it is subjected to forging and drawing on machines. This is due to its greatest refractoriness.

This is how a fibrous structure (wire) is obtained. It is quite durable and practically does not break. At the final stage, it is rolled out into thin threads or flexible tape. To carry out mechanical treatment, it is necessary to create a protective environment of inert gas. In this environment the temperature must exceed 400 °C. At ambient temperatures it acquires paramagnetic properties.

It has the following disadvantages:

• difficulty in creating conditions for mechanical processing;
• rapid formation of oxide films on the surface. If there are sulfur-containing substances in contact, sulfide films are formed;
• creating good electrical contact between several parts is only possible when creating high pressure.

Tungsten

To improve the properties of tungsten (refractoriness, corrosion resistance, wear resistance), alloying metals are added to it. For example, rhenium and thorium.

The metal is used to produce filaments for lighting and drying lamps. It is added to welding electrodes, elements of electron lamps and X-ray tubes. It is also used in the production of rocket elements, jet engines, and artillery shells.

In appearance and characteristics it is very similar to tungsten. The main difference is that its specific gravity is almost two times less. It is obtained in a similar way. It is widely used in the electronics industry, for the manufacture of various evaporators in vacuum technology, and breaking electrical contacts. Like tungsten, it is paramagnetic. It is simply irreplaceable for the manufacture of electrodes for glass melting furnaces.

Niobium

The melting point of niobium is 2741 °C. In its chemical, physical and mechanical properties it is very similar to tantalum. It is quite flexible. It has good weldability and high thermal conductivity even without additional heating. Like all other metals, it is obtained from powder. Final niobium workpieces - wire, tape, pipe.

Niobium

The metal itself and its alloys demonstrate the effect of superconductivity. It is widely used for the manufacture of anodes, screen and anti-dynatron grids in electric vacuum devices. Due to its good porosity, it is successfully used as a gas absorbent. In microelectronics, it is used to make resistors in microcircuits.

Niobium has proven itself well as an alloying additive. It is used to create various heat-resistant structures and units operating in aggressive and radioactive environments. Some elements of jet engines are made from an alloy of steel and niobium. Due to its property of not interacting with radioactive substances at high temperatures, for example, uranium, it is used in the manufacture of shells for uranium elements that remove heat in reactors.

Tantalum

Externally it has a light gray color with a slight bluish tint. The melting point is close to 3000 °C. Amenable to basic types of processing. It can be forged, rolled, and drawn to make wire.

These operations do not require significant heating. For ease of further use, tantalum is produced in the form of foil and thin sheets.

An increase in temperature causes active interaction with all gases, except inert ones - no reactions are observed with them.

Tantalum

Tantalum is used to produce the internal elements of generator tubes (magnetrons and klystrons). It is actively used in the production of plates in electrolytic capacitors. Very convenient for making film resistors. It is actively used for the manufacture of so-called boats in evaporators, in which thermal spraying of various materials is carried out on thin films.

Due to a number of its unique qualities, it is considered indispensable in the nuclear, aerospace and radio-electronic industries.

Rhenium

It was discovered later than all of the previously listed metals. It fully lives up to its name "rare earth metal" because it is found in small quantities in the ore of other metals such as platinum or copper.

It is mainly used as an alloying additive. The resulting alloys acquire good strength and ductility characteristics. This is one of the most expensive metals, so its use leads to a sharp increase in the price of all equipment.

However, it is used as a catalyst.

Chromium

Chrome is a unique metal. It is widely used in industry due to its remarkable properties: strength, resistance to external influences (heat and corrosion), ductility. A fairly hard but brittle metal. It has a steel-gray color. All the chromium needed is extracted from the ore of two types of iron chromite or chromium oxide.

Its main properties are:

• Even at normal temperature it has almost perfect antiferromagnetic ordering. This gives it excellent magnetic properties.
• Reacts differently to exposure to hydrogen and nitrogen. In the first case, it retains its strength. In the second, it becomes brittle and completely loses all its plastic properties.
• It is highly resistant to corrosion. This happens due to the fact that when interacting with oxygen, a thin protective film is formed on the surface. It serves to protect against further corrosion.

Chromium crystals

It is used in the metallurgical, chemical, and construction industries. Chromium, as an alloying additive, is necessarily used for the production of various grades of stainless steel. It occupies a special place in the manufacture of such material as nichrome.

This material can withstand very high temperatures. Therefore, it is used in various heating elements. Chrome is actively used to cover the surfaces of various parts (metal, wood, leather). This process is carried out using electroplating.

The toxicity of some chromium salts is used to preserve wood from damage and the harmful effects of fungi and mold. They are also good at repelling ants, termites, and insects that destroy wooden structures. Chromium salts are used to treat the skin. Chromium is used in the manufacture of various dyes.

Due to its high heat resistance, it is used as a refractory material for blast furnaces. The catalytic properties of chromium compounds are successfully used in the processing of hydrocarbons. It is added when producing the highest quality magnetic tapes. It provides low noise figure and wide bandwidth.

Source: https://stankiexpert.ru/spravochnik/materialovedenie/tugoplavkie-metally.html

Refractory metals list

• 1 Refractory metals - characteristics, properties and applications
• 2 Refractory metals - description, products made from refractory metals
• 3 Encyclopedia of Technology - the meaning of the word Refractory Metals
• 4 The most refractory metal on earth
  • 4.1 Which metal is the most refractory?
  • 4.2 How is tungsten obtained?
• 5 Refractory metals. Niobium, Molybdenum, Tantalum, Tungsten and Rhenium. Titanium, vanadium, chromium, zirconium, hafnium, ruthenium, osmium and iridium.

  Price, delivery, warehouse, buy

• 6 Refractory metals and their alloys

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. 

Properties of refractory metals and alloys

Metals that are difficult to melt are called refractory. Technically, this group includes five main and 9 additional elements of the periodic table. The main refractory metals are those that have a melt temperature of more than 2 thousand degrees Celsius.

These are niobium, rhenium, tantalum, molybdenum and tungsten. Additional refractory metal elements are usually classified as those whose melting point is about 1700-1850 degrees Celsius.

These are three elements of the fourth period (titanium, vanadium, chromium), three elements of the fifth period (zirconium, ruthenium, rhodium) and three elements of the sixth period (hafnium, osmium, iridium).

Such a high refractoriness of metals is achieved due to the structure of their atoms. They contain two types of electrons: ordinary s-electrons and special d-electrons. The latter, due to their close location, make the bonds between atoms very strong. So strong that the metal needs to be heated a couple of thousand degrees to break these bonds.

From a chemical point of view, these metals are similar. They easily form natural chemicals. compounds, therefore it is not possible to find them in their pure form. In the open air they react with oxygen, but at normal temperatures the reaction is sluggish, and a protective film forms on the surface of the metal.

But if the infusible metal is heated, the reaction will accelerate many times, and the material will be susceptible to corrosion, become brittle and lose some of its natural properties. Carbon, hydrogen and nitrogen act in a similar way on some infusible metals.

That is why they prefer to use refractory materials in a vacuum, protecting them from the influence of “hazardous” substances.

Such chemically similar and physical properties of refractory metals are very different, which is due to the difference in the shapes of their crystal lattices. For some it is hexagonal, while for others it is cubic, volume-centered. Hence the differences in density, hardness and compression resistance.

Refractory metals and alloys

However, research does not stand still, and therefore now most of the properties of refractory elements can be corrected by alloying them, that is, producing alloys. Alloys based on infusible metals retain their unsurpassed resistance to high temperatures and resistance to deformation. At the same time, they also acquire such useful properties as greater or lesser ductility, corrosion resistance, heat resistance, elasticity, etc.

Two-thirds of all infusible metals are obtained from ore, or rather their so-called ore concentrates. This means that in addition to the main element, the ore contains many auxiliary elements.

Before you get even a gram of a refractory element, you need to “saw up” the concentrate, chemically clean it of everything unnecessary, and then restore it or, as they say, refine it. Depending on how pure the metal is needed, arc-shaped, electron-beam or plasma melting is used.

The latter produces metals of the best kind. Ready-made refractory metal elements are powder or granules, although sometimes they are immediately processed and refractory blanks are obtained - sheets, film, pipes, threads, etc. Factories of refractory metals and alloys produce both blanks and pure metals.

One of the oldest in Russia, OJSC Pilot Plant of Refractory Metals and Hard Alloys, has been working in this field since the 48th year of the 20th century. Another Soviet, and now Uzbek plant, OJSC UzKTZhM, has existed since 1956.

The use of refractory metals is based on the most efficient use of their natural properties.

Among the sectors of the national economy that resort to the help of refractory metal elements are the construction of machines, ships, spacecraft and their parts, nuclear energy, the nuclear industry and the chemical industry, electricity supply and metallurgy. At the same time, almost nowhere are refractory metal elements used “live”; usually, their various alloys are used for these purposes.

Properties of the most refractory metals

Thus, the most refractory metal in the world (tungsten) is usually alloyed with rhenium, thorium, nickel with the participation of copper and/or iron. The first makes the alloy more corrosion-resistant, the second - more reliable, and the third - gives unprecedented density. It should be noted that all tungsten alloys contain no more than 4/5.

Because tungsten is both hard and refractory, it is commonly used in power supply, instrument construction, and the manufacture of weapons, projectiles, warheads, and missiles. Denser alloys (nickel-based) are used to produce golf clubs. Tungsten also forms so-called pseudo-alloys. The fact is that the metal in them is not alloyed, but filled with liquid silver or copper.

Due to the difference in melt temperatures, better heat and electrical conductivity properties are obtained.

Molybdenum, unlike tungsten, can be alloyed with only a few hundredths of parts and obtain excellent properties. The main alloying elements of molybdenum are: titanium + zirconium and tungsten. With the latter, the alloy turns out to be extremely inert, with great resistance.

This makes it possible to use it for the manufacture of molds for casting zinc parts. A special use of molybdenum is as an alloying element in steel alloys. Steel+molybdenum alloys have good wear resistance and low friction values.

Steel + molybdenum is used in the manufacture of pipes, pipe structures, automobiles and mechanical engineering.

Niobium and tantalum are like brothers, always nearby. Both are used in the manufacture of electrolytic capacitors. Niobium is also sometimes doped with hafnium and titanium to prevent it from reacting with oxygen during heating.

Annealing niobium makes it possible to obtain metal with different elasticity and hardness coefficients. Niobium can be found in power supply, rocket and shipbuilding, nuclear industry, etc.

Tantalum, due to its inertness to acids, is used in medicine and the production of high-precision electronics.

The rarest and most expensive metal presented is rhenium. It is difficult to extract, so in alloys it acts not as the main element, but as an alloying element. It is often used with copper and platinum. Rhenium strengthens such formations and improves their ability to forge. Used in nuclear, chemical (catalyst) and electronics industries.

The use of the beneficial properties of refractory metals and alloys is considered by scientists around the world as a very promising area of ​​scientific research.

Source: https://promplace.ru/vidy-metallov-i-klassifikaciya-staty/tugoplavkii-metall-1526.htm