The use of molybdenum and its properties. Density of molybdenum, its physical and mechanical properties, compounds, applications
Molybdenum lead wires in incandescent lamps appeared in the early days of the 20th century.
Molybdenum was chosen for this for its stability and strength at elevated temperatures.
Since this first application, scientists and engineers have discovered that other properties of molybdenum make it an indispensable material for many technical solutions. Molybdenum and its alloys are widely used in industry and electronics, especially in ferrous metallurgy for high-temperature alloys.
Many of them use molybdenum's strength and stability at high temperatures, much like the first conductive wire in an incandescent lamp. However, molybdenum has many other properties that make it attractive for industrial use and manufacturing, including as a traditional component of high temperature industrial alloys. You can buy a molybdenum crucible here at a very attractive price.
The main properties of molybdenum:
High thermal conductivity;
. High electrical conductivity;
. Low coefficient of thermal expansion;
. Resistant to molten metal;
. Compatible with most glass compositions;
. Thermal resistance;
. High rigidity and strong adhesion to glass is used in lamps and electronic devices;
Since many of its properties are attractive to engineers and designers, molybdenum metal and its alloys are used in:
Lighting;
. Electrical and electronic appliances;
. Medical equipment;
. Material handling equipment;
. High-temperature furnaces and related equipment for thermal spraying of coatings;
. Aerospace and defense components;
Applications in all of these areas require unique combinations of several properties. Molybdenum and its alloys, as well as composite materials that use molybdenum metal, provide unique combinations of thermal and electrical conductivity, thermal expansion, high temperature strength and creep resistance, vapor pressure, environmental stability,
abrasion and wear resistance that make them ideal.
This article intends to help the reader understand why this unique material finds application in such diverse fields. It also provides some information on the application and manufacture of machinery from molybdenum and its alloys.
How molybdenum metal products are made
Because pure molybdenum melts at a very high temperature, and because it oxidizes at relatively low temperatures, traditional smelting processes cannot extract the metal from the ore. Instead, the ore is processed through a series of grinding and separation steps to isolate the MoS (molybdenum disulphide) from other components. This isolated material, containing up to about 90% MoS, is "roasted" in air to produce MoO (Molybdenum Oxide) and (Sulphur Dioxide). Sulfur dioxide is converted to sulfuric acid and can be sold for chemical applications.
Technical oxide contains about 57% Mo and less than 0.1% S, but this is not a problem for the vast majority of production technologies that use oxide, including the production of molybdenum steel alloy.
However, the technical oxide must be chemically purified in order to be used in the production of molybdenum metal. The oxide is first dissolved in sodium or ammonium hydroxide, and then this
the solution is treated by precipitation and filtration, subjected to solvent extraction, or a combination of both methods together to remove impurities.
Properties and Applications of Molybdenum
There is an inextricable link between the properties of a material and its application.
In some cases, the application of a particular property (such as electrical conductivity) is
of paramount importance. In other countries, a combination of properties allows you to make the best choice.
Optimum is an important word in this context. This means that while other materials may
have an advantage in one or the other property, the combination of properties provides the best solution to engineering design problems.
Sometimes the best solution is not to use a single material, but to use a combination of materials, or a composite material, which allows the designer to tailor the properties of interest to a particular problem.
In all cases, cost-effective solutions are those that ultimately win the competition. This means that molybdenum metal materials, which are very costly as construction materials compared to conventional design office standards, should demonstrate a significant advantage over competitors. For example, molybdenum alloys provide greater strength than pure molybdenum and help maintain that strength at temperatures higher than pure molybdenum can tolerate.
Electrical and electronic appliances and manufacturing
In electronics, molybdenum alloys are widely used by manufacturers in vacuum vacuum tubes, using molybdenum for filament and grid poles due to its high temperature
strength and mechanical stability.
Solid-state device designers have discovered properties other than heat resistance that have made molybdenum compounds indispensable in the manufacture of electronic devices.
Molybdenum in its properties is close to silicon, has excellent thermal and electrical conductivity properties. These properties make it ideal as a substrate for fragile belt devices. Molybdenum provides a strong, rigid base that conducts electricity to and from the device and conducts heat efficiently. Its low CTE minimizes differential expansion stresses.
Semiconductor manufacturing
Semiconductor manufacturing equipment has long used molybdenum components, requiring temperature strength and compatibility with aggressive process environments. The ion implantation process is used to dope silicon wafers with atoms to create semiconductor devices.
Use in metallurgy
High temperature processing
Hot working, heat resistance and deformation resistance are important properties
for hot working equipment. Molybdenum alloy allows the formation of a temperature regime above
1100°C. Molybdenum alloys are ideal for brass extrusion, metal casting, liquid metal processing and even plastic injection molding.
Not many people know that molybdenum is a chemical element of the sixth group of the periodic table, related to transition metals. In the classification structure, it is next to chromium and tungsten. It is distinguished by rich grey colour and specific metallic luster. This refractory element has found wide application in the metallurgical industry.
Brief history of discovery
Not much information has survived to this day about the discovery of molybdenum. This is because the element is not very common. However, the first mention of it was made in 1778, when analytical chemistry had not yet reached its maturity. First, the substance was isolated in the form of an oxide.
Despite the discovery of the chemical element in 1778, the name currently used is much earlier. It was often mentioned for minerals dating back to the Middle Ages.
Presence in the environment
Although molybdenum is not a very common element, in earth's crust it is relatively evenly distributed. It does not occur in free form. The smallest amount of this metal includes carbonate and ultramafic rocks. A certain proportion of the substance is contained in river and sea water. There is much less metal in the upper layers than at depth.
There are two forms of occurrence:
- sulfide;
- molybdate.
They appear as microscopic secretions. Crystallization of molybdenite occurs with increased acidity and the presence of a reducing environment. Oxygen compounds are usually formed on the surface. As for the primary ores, molybdenite can be found in them together with the minerals of copper, bismuthine, and wolframite. In large volumes, the metal is found in sedimentary deposits.
Large deposits in Russia
In the Russian Federation, the use of molybdenum is carried out in many areas of activity. The country has one of the largest the globe mineral resource base for the extraction of this metal. The main share of enterprises is concentrated in the southern part of Siberia.
In terms of reserves, Russia is second only to three countries - the United States, China and Chile. The main part of the mineral resource base is represented by stockwork deposits containing more than 87% of explored resources. However, Russian deposits are characterized not very well. high quality ores
The table shows the largest deposits.
Practical use
IN pure form the use of molybdenum is carried out in the production of wires or tapes designed to withstand high temperatures. Such products can act as heating elements for electric ovens, electronic lamps or
The presented metal significantly improves the characteristics of steels. After its introduction into the composition, their strength qualities and resistance to corrosion increase, which is necessary in the manufacture important details. Often, with the addition of molybdenum, they are also distinguished by acid resistance.
Compounds with this metal are actively used in the manufacture of the front skin of aircraft and missiles. On the basis of alloys, honeycomb panels of aircraft are produced and resistance to high temperatures allows the use of products with the introduction of molybdenum for the processing of steels. Many compounds act as catalysts for chemical reactions.
Physical and chemical properties
Molybdenum is a light gray metal with a volume centered cubic lattice. Its mechanical properties are determined by the purity of the material itself, as well as pre-treatment and heat treatment. In details physical properties are discussed in the table below.
Under normal conditions, a component of the periodic table is resistant to many substances. The oxidation process begins to proceed at temperatures above 400 degrees. Alkaline solutions have a slow effect on molybdenum. Moisture resistance without aeration is quite high.
Compounds with other metals
The quality of the resulting molybdenum alloys largely depends on the proportion, as well as the ability of the impurities used and the base component to interact with the substance. Doping technology plays an important role. However, certain types of connections raise doubts among experts in terms of suitability for further operation.
Molybdenum does not mix well with tungsten. With its introduction, the heat resistance of the material significantly increases, but at the same time, the resistance to deformation worsens. Similar problems also arise in combinations with other metals, so these types of alloying have ceased to be carried out.
Despite the existing difficulties, it was still possible to find some compounds that can increase the thermal threshold for the use of molybdenum. At the same time, plasticity, resistance to deformation and other characteristics are at the same level.
Brands in industry
The production process involves the use of the material not only in its pure form, but also with the addition of impurities. Below are the grades of molybdenum that are common in the industry.
Receipt process
For the production of molybdenum, ore is prepared, which includes up to 50 percent of the main substance, a significant amount of sulfur, a small concentration of silicon and other components. It is fired at a temperature of 570 to 600 degrees in special furnaces. After thermal exposure, a concentrate is formed containing molybdenum oxide with impurities.
There are two ways to get a mass without foreign substances:
- By the method of successive effects of a chemical nature. When using ammonia water, the resulting cinder turns into a liquid state. Foreign impurities are removed from the resulting solution. After processing, their number should not exceed 0.05 percent.
- By sublimation, which is the process of converting a solid compound into a gaseous state. In this case, the liquid phase is bypassed.
Purified from impurities, molybdenum oxide is processed in tube furnaces by means of hydrogen. As a result, a powder is obtained, which, by melting and introducing special substances, is converted directly into metal. The shape of the blanks will depend on the production technology used.
Manufactured products from molybdenum
The most common type of products are rods. They can not only be used independently, but also serve as the basis for the production of wire. Molybdenum rods with a square section of not more than 40 mm act as the feedstock for the manufacture of products.
In the process of obtaining bars, rotational forging is carried out, which takes place in several stages. At each stage, bars with a specific cross section are produced. The forging conditions vary according to the diameter of the incoming billet. The disadvantages of the technology include the complexity of the production process.
Molybdenum is also used to make special wire. Manufacturers form it from properly prepared rods, the diameter of which does not exceed 3 mm. With this section, the products are easily wound on a coil for further production of wire.
In the manufacturing process, a broach method is used, which includes four main stages. The wire eventually gets the final diameter, which was set in advance. Temperature regime during the production process can vary from 300 to 700 degrees.
After drawing, the wire is cleaned by annealing in a hydrogen environment. In this case, the temperature reaches 1300-1400 degrees. Sometimes cleaning is carried out by electrolytic etching using nitrogen.
Molybdenum can be made into solid sheets and strips. They can be obtained by forging and rolling. In production, pneumatic hammers and two-roll mills are used. The thickness of the resulting strip after hot rolling depends on the cross section of the original plate.
After manufacturing, the molybdenum strips are chemical treatment. They are placed in a special environment from active substances. Next, cold rolling is carried out at normal temperature. At the final stage, the tapes are again cleaned and, if necessary, polished.
There are manufacturing standards for molybdenum metal products. GOST 18905-73 establishes requirements for the manufacture of wire. It reflects the permissible deviations of mass and diameter.
Molybdenum producers in Russia
On the territory of the Russian Federation, skarn, stockwork and vein deposits are mainly developed. In terms of quality, the mined ore is not much inferior to foreign raw materials, but it still has certain features associated with the structure.
In Russia, the largest producers of molybdenum are two companies:
- LLC "Sorsky GOK"
- OJSC Zhirekensky GOK.
The listed enterprises provide up to 95 percent of domestic metal production.
In conclusion about the role of the element for the human body
Molybdenum acts as an important substance necessary for the normal functioning of people. It is found in many organs and bones. The daily requirement for a chemical element is on average 70-300 mcg. With its deficiency, these indicators increase.
Molybdenum takes part in metabolism, as well as in the process of cleansing the body of aldehydes, acids and other compounds. It promotes the utilization of iron, allowing you to quickly eliminate the consequences of various types poisoning. The trace element effectively cleanses the body of toxic substances.
Studies have shown that molybdenum relieves pain in arthritis and other diseases, has a positive effect in the presence of asthma, and reduces the risk of cancerous tumors in the intestines and stomach. Most of the substance is found in leafy vegetables, buckwheat, barley, liver, eggs, milk, gooseberries and black currants.
In the article “Molybdenum. Properties, application, production, products” discusses in detail the refractory metal molybdenum. The properties of molybdenum are described, the areas of its application are indicated. Various grades of molybdenum are also listed with their features.The article covers the process of molybdenum production from the stage of ore enrichment to the stage of obtaining blanks in the form of bars and ingots. Characteristic features of each stage are noted.
Special attention the article focuses on products (wire, rods, sheets, strips, powder, etc.). The processes of manufacturing one or another product from molybdenum, its characteristic features and areas of application are described.
Chapter 1. Molybdenum. Properties and applications of molybdenum
Molybdenum (denoted by Mo) is a chemical element of group VI of the 5th period of the D.I. table. Mendeleev, has number 42; light gray transition metal. It belongs to the category of refractory metals, has a melting point t pl = 2620 °C. Considering the various applications of molybdenum as a metal, the most important properties should be considered density, melting point, electrical resistance, coefficient of linear expansion.§1. Properties of molybdenum
The main physical and mechanical properties of molybdenum are presented in the table. It is also worth noting that the electrical conductivity of molybdenum is higher compared to the electrical conductivity of iron and lower than the analogous property of copper. In terms of mechanical strength, molybdenum is slightly inferior to tungsten, but, at the same time, it is easier to process by pressure.| Property | Meaning |
|---|---|
| Physical Properties | |
| atomic number | 42 |
| Atomic mass, a.m.u. (g/mol) | 95,94 |
| Atomic diameter, nm | 0,273 |
| Density, g / cm 3 | 10,2 |
| Melting point, °С | 2620 |
| Boiling point, °C | 4830 |
| Specific heat capacity, J/(g K) | 0,248 |
| Thermal conductivity, W/(m K) | 138 |
| Electrical resistance, µOhm cm | 5,7 |
| Coefficient of linear thermal expansion, 10 -6 m/mK | 4,9 |
| Mechanical properties | |
| Young's modulus, GPa | 329,3 |
| Shear modulus, GPa | 122,0 |
| Poisson's ratio | 0,30 |
| Ultimate strength σ B , MPa | 800-900 |
| Relative elongation δ, % | 0-15 |
§2. Molybdenum grades
| Molybdenum brand | Brand characteristic |
|---|---|
| MCH | Molybdenum pure without additives |
| MCHVP | Molybdenum pure without additives obtained by vacuum melting |
| MRN | Molybdenum without additives. Molybdenum for various purposes. The recrystallization temperature of molybdenum of this grade may be somewhat higher than that of molybdenum of the MCH grade due to the higher content of impurities. |
| MK | Molybdenum with silicon alkali additive. It is characterized by a significantly higher recrystallization temperature compared to molybdenum of the MCh grade and higher bending strength in the annealed state |
| MR | Alloys of molybdenum and rhenium |
| CM | Molybdenum doped with zirconium and/or titanium |
| MV | Alloys of molybdenum and tungsten |
High-temperature materials based on molybdenum can be divided into four groups:
- practically pure molybdenum;
- low-alloy low-carbon alloys;
- low-alloy high-carbon alloys;
- high alloys.
The second group includes such molybdenum alloys as TsM5, TsM6, TsM-2A, VM-1, TSM4 with a typical carbon content (by mass) of 0.004-0.05% C, as well as TsM10 and TSM-7 alloys with a reduced carbon content. Alloys TsM5 and TsM6 belong to the molybdenum-zirconium (Mo-Zr) system, and alloys TsM-2A, VM-1 are alloyed simultaneously with small additions of titanium and zirconium. The TCM4 alloy, in addition to zirconium, contains small concentrations of nickel and carbon; it is an alloy of the molybdenum-zirconium-nickel-carbon (Mo-Zr-Ni-C) system. Among the alloys of the second group, the most widely used is the low-alloy alloy TsM-2A, which is characterized by sufficient manufacturability and higher heat resistance compared to pure molybdenum. Alloy TsM-2A is the least prone to cold brittleness after deformation. Recrystallization increases its tendency to brittleness. Alloy VM-1 is similar in composition and properties to alloy TsM-2A. Alloy TsM5 is more heat resistant than TsM-2A. The TsM6 alloy with a lower content of zirconium and carbon is inferior to the TsM5 alloy in terms of heat resistance, but is more technologically advanced, less prone to cold brittleness in the recrystallized state, and welds well.
The third group (low-alloyed high-carbon alloys) includes VM-3 with a high carbon content, reaching (by weight) up to 0.25-0.50%. To bind all the carbon into carbides, this alloy is alloyed with large amounts of titanium and zirconium; additional hardening is provided by niobium. Titanium (TiC) and zirconium (ZrC) carbides improve the heat resistance of the alloy. At the same time, molybdenum carbide (Mo 2 C) has Negative influence on the technological properties of alloys. Its presence reduces ductility at both room and high temperatures. To exclude the formation of Mo 2 C, titanium, zirconium and carbon are introduced into the alloys in certain proportions.
The fourth group (high alloys) includes TsMV30, TsMV50 and MP47VP. TsMV30 and TsMV50 alloys are characterized by high heat resistance due to their alloying with large amounts of tungsten, and the MP47VP alloy of the molybdenum-rhenium (Mo-Re) system is distinguished by high strength properties at moderate temperatures and high manufacturability. The heat resistance of the latter alloy can be substantially increased by introducing ZrC and TiC carbides.
§3. Applications of molybdenum
Refractory metal molybdenum has found wide application in modern industry as a dopant to various alloys, and as structural material.The main areas of application of molybdenum
1. Alloying element in various steels and non-ferrous metal alloys
As an alloying additive, molybdenum is actively used in ferrous metallurgy in the production of steels and cast irons. Structural steels contain up to 0.5% of this refractory metal. Thanks to molybdenum, the structure of structural steel is significantly improved. It becomes more uniform and fine-grained. The addition of molybdenum makes it possible to improve the mechanical properties of steels and alloys, namely: elastic limit, wear and impact resistance. One of the valuable properties of molybdenum is its ability to eliminate the temper brittleness of austenitic steel.
Molybdenum is actively used in the production of various tool steels. The steels from which the dies are made usually contain 1-1.5% of this refractory metal, high-speed steels - 5-8.5%. Molybdenum increases the red hardness of tool steels, their hardness, strength, resistance to hardening cracks, and wear.
Chrome and chromium-nickel steels also contain molybdenum. It reduces brittleness and increases the heat resistance of these steels under long-term operation. The introduction of 2-4% molybdenum into stainless chromium-nickel steels improves their corrosion resistance.
The refractory metal molybdenum is also included in the composition of cast irons. The introduction of 0.2-0.5% molybdenum into cast iron increases viscosity, wear resistance and improves properties at high temperatures, and also reduces the tendency to grain growth.
2. Anti-corrosion and heat-resistant alloys
Very often, molybdenum is a part of heat-resistant and acid-resistant alloys. Metals cobalt and nickel, as a rule, are the basis of heat-resistant alloys (50-60%), such alloys also contain chromium (20-28%) and molybdenum (3-10%). An example is a heat-resistant alloy used for the manufacture of blades and disks of gas turbine rotors: Ni - 37%, Co - 20%, Cr - 18%, Fe - 17%, Mo - 3%, Ti - 2.8%
Acid-resistant alloys containing 17-28% molybdenum, as well as chromium, tungsten and iron, are resistant to all mineral acids (for example, sulfuric acid, hydrochloric acid and others), except hydrofluoric acid.
3. Structural material in aerospace and nuclear technology
Due to its properties, molybdenum is used as a structural material in aerospace and nuclear engineering. Structural metals and alloys used in the aerospace industry must have good heat resistance and scale resistance. Refractory metals tungsten, molybdenum, niobium and others have these properties, however, niobium and molybdenum have a higher specific strength at temperatures up to 1370 ° C compared to tungsten, therefore they are more preferable as structural materials operating at the indicated and lower temperatures.
Molybdenum is used for the manufacture of skin and frame elements of supersonic aircraft and rockets, as well as heat exchangers, shells for rockets and capsules returning to the ground, heat shields, rocket leading edges, rocket nose cones, and supersonic aircraft wing edge skins.
Molybdenum with additives of niobium, vanadium, titanium and other metals that increase heat resistance is used for the manufacture of critical parts of rocket engines and gas turbines: gas turbine nozzle and rotor blades, exhaust nozzles and combustion chambers of ramjet engines.
The molybdenum metal is refractory and quite well resistant to liquid metal coolants such as lithium and lead-bismuth alloy. These properties of molybdenum make it possible to use it as a structural material in nuclear power reactors at temperatures up to 800 °C. Containers, shells, pipes and other elements of the reactor core are made from the refractory metal molybdenum.
4. Material for the manufacture of metal forming equipment
The heat resistance of molybdenum, its refractoriness, high thermal conductivity and low coefficient of expansion make it possible to use this metal for the manufacture of equipment elements intended for hot forming of metals. So mandrels for piercing mills, dies, press dies are made from molybdenum. It is worth noting that, according to the experimental data, piercing punches for piercing stainless steel workpieces, made of an alloy of molybdenum with 0.5% titanium, pierce 100 times more workpieces before failure compared to punches made of other materials. Molybdenum is also used to produce molds and cores for injection molding of copper, zinc and aluminum alloys from the refractory metal.
5. Material for the manufacture of heaters for high-temperature furnaces
Molybdenum wire, strip and rods are used as heaters in high-temperature electric furnaces. The temperature in such furnaces can reach 1700 - 2000 °C. It is worth noting that molybdenum heaters should only work in a protective atmosphere (usually hydrogen, argon) or in a vacuum.
Molybdenum rods are also used as electrodes in glass melting furnaces. As a rule, rods with a diameter of 25 to 150 mm and a length of up to 1.8 m are used for these purposes. Melting furnaces with electrodes in the form of molybdenum plates are also found. It is worth noting that molybdenum practically does not react with molten glass. This allows the use of this metal for the manufacture of parts for glass melting furnaces.
6. Material for the production of electric lamps and vacuum technology
Properties such as heat resistance, high electrical conductivity, high melting point, make it possible to use molybdenum in the production of electric lamps and vacuum devices. Molybdenum wire is used to make hooks that support a tungsten filament in an incandescent lamp. Molybdenum is also used as a core for winding tungsten wire.
Molybdenum rods are used to input current into various vacuum devices and flasks of powerful light sources. Molybdenum sheets are used for the production of generator lamp anodes. Also, grids of receiving-amplifying lamps, auxiliary electrodes of generator lamps, cathodes of gas discharge tubes are made from this metal.
Molybdenum has also found application in X-ray technology. For example, focusing electrodes, cathode inputs are produced from it.
Chapter 2. Production of molybdenum
§1. The process of obtaining refractory metal molybdenum
Molybdenum is usually referred to a wide group of rare metals. In addition to this metal, this group includes tungsten, vanadium and others. Rare metals are characterized by a relatively small scale of production and consumption, as well as a low prevalence in the earth's crust. For example, as a rule, the content of molybdenum in ores is hundredths and thousandths of a percent. Not a single rare metal is obtained by direct reduction from raw materials. First, raw materials are processed into chemical compounds. In addition, all rare metal ores undergo additional enrichment before processing.In the process of obtaining a rare metal, three main stages can be distinguished:
- The decomposition of ore material is the separation of the extracted metal from the bulk of the processed raw material and its concentration in solution or sediment.
- Obtaining pure chemical compounds - isolation and purification of a chemical compound.
- Isolation of the metal from the resulting compound - obtaining pure rare metals.
The process of obtaining molybdenum consists of several stages.
- Enrichment of molybdenum ore. It is produced by flotation. As a result of enrichment, molybdenite concentrates containing 90 - 95% MoS 2 are obtained. The industry produces concentrates of three grades: KM1 (contains at least 50% molybdenum), KM2 (contains at least 48% molybdenum) and KM3 (contains at least 47% molybdenum). In molybdenite concentrates, the content of impurities - phosphorus, arsenic, tin, copper and silica is controlled. If polymetallic molybdenum ores are enriched, then, as a rule, the content of molybdenum in concentrates is 15-20%.
- Obtaining molybdenum trioxide (anhydride) MoO 3 , which serves as a feedstock for the production of metallic molybdenum. First, a cinder (molybdenum oxide MoO 3 containing a large amount of impurities) is obtained from molybdenite concentrate (MoS 2) by oxidative roasting of the latter. Further, molybdenum anhydride (pure MoO 3) is obtained from the cinder. For this, processes such as sublimation or hydrometallurgical (chemical) processing of cinder can be used. As a result, pure molybdenum trioxide is obtained with a content of the latter of at least 99.975%
- Obtaining molybdenum powder. Molybdenum anhydride MoO 3 serves as the feedstock for obtaining pure metal. For the production of pure molybdenum powder, the anhydride reduction process is carried out with hydrogen. Recovery is carried out in three stages: reduction of MoO 3 to MoO 2 at a temperature of 450-600 °C; reduction of MoO 2 at a temperature of 950 ° C to a metal containing 0.5-1.5% oxygen; reduction of the oxygen content in the metal below 0.25-0.3% by reduction at a temperature of 1000-1100 °C. As a result, a pure molybdenum powder is obtained, having an average grain size of about 0.5-2 microns.
- Obtaining compact molybdenum. Compact molybdenum, usually in the form of rods or ingots, is a blank for the production of semi-finished products, such as wire, rod, strip, and so on.
§2. Obtaining compact molybdenum
There are two ways to obtain compact molybdenum. The first is the application of powder metallurgy methods. The second - with the help of melting in furnaces of various operating principles.Powder Metallurgy Methods
This method of obtaining malleable molybdenum is the most common, as it allows a more even distribution of additives that improve the physical and mechanical properties of molybdenum. Titanium (Ti), zirconium (Zr), vanadium (V) and other metals can be used as additives.
The process of obtaining compact molybdenum by powder metallurgy consists of several stages:
- pressing rods from metal powder - molding;
- low-temperature (preliminary) sintering of blanks;
- sintering (welding) of blanks;
- processing of blanks in order to obtain semi-finished products - molybdenum wire, rods and other semi-finished products; Usually blanks are processed under pressure (forging) or subjected to machining by cutting (for example, grinding, polishing).
Preliminary sintering of rods is usually carried out in muffle or tube furnaces at a temperature of 1110-1200 °C. Sintering (welding) is carried out at a temperature of 2200-2400 °C in special apparatus for high-temperature sintering. If the blanks are large, then it is preferable to use a furnace with indirect heating for their sintering. An example of such a furnace is a continuous vacuum furnace for high-temperature sintering of rods by indirect heating, where graphite rods are used as heaters. It should be noted that the pre-sintering of the rods is carried out in a hydrogen environment, which contributes to the hardening of the workpiece and an increase in electrical conductivity.
Fuse
Melting is used to obtain compact molybdenum in the form of large billets (from 200 to 2000 kg) intended for rolling, pipe drawing, and the production of products by casting. Melting is carried out in electric arc furnaces with a consumable electrode and/or electron beam melting. As a result of melting, molybdenum ingots are obtained.
In arc melting, packages of sintered molybdenum rods serve as electrodes, which, in turn, are obtained by welding (sintering) rods. Such rods, as a rule, have a length of 1-2.5 m and are combined into packages of 4-16 rods, and in some cases more.
After arc melting, molybdenum ingots contain the following impurities (approximately),%: O 2 - 1-3 ∙ 10-4, H 2 - 1-2 ∙ 10-5, N 2 - 10-3-10-4. As a result of electron beam melting, it is possible to get rid of a large number impurities, including oxygen, nitrogen, carbon, iron, copper, nickel, manganese, cobalt. It should be noted that upon receipt of molybdenum ingots by any of the above methods for deep purification of molybdenum from oxygen (the content in the metal
Chapter 3. Products from molybdenum. Rods, wire, sheets (strips), powder
The industry produces a large number of products from the refractory metal molybdenum. In this context, it is worth highlighting products with a round section - molybdenum rods and wires, flat products - molybdenum strips, sheets and strips, as well as powders.Sintered molybdenum rods (manufactured by powder metallurgy) or ingots (manufactured by casting) can serve as blanks for the production of the above products. Most molybdenum metal products are obtained by pressure treatment of workpieces. Depending on the type and size of workpieces technological processes production can vary greatly.
§1. Molybdenum bars
ProductionMolybdenum rods are one of the most common types of molybdenum refractory metal products. In addition to independent use, molybdenum rods can also serve as blanks for the manufacture of wire.
Starting materials for the production of bars are sintered molybdenum rods of square section with a side of 40 mm or less, as well as fused molybdenum ingots of various sizes.
In the process of obtaining molybdenum rods from rods, the latter are subjected to rotational forging. Molybdenum bars are forged in several stages. At each stage, bars of certain diameters are obtained, while the forging conditions change in a special way depending on the diameter of the incoming billet.
Device of rotary forging machine
1 - frame, 2 - shaft, 3 - rollers, 4 - steel cage, 5 - forging dies, 6 - sintered rod
At the first stage, the rods are heated to a temperature of 1350-1400 °C. Forging is carried out directly at a temperature of about 1300 °C. As a result of heat treatment, the density of porous rods increases, and the pores at the grain boundaries inside the crystals disappear. As a result, the tensile strength of the material increases sharply and exceeds the strength of the sintered rod by several times. As a rule, resistance furnaces with molybdenum heaters and a hydrogen atmosphere are used for heating. Muffle furnaces are sometimes used to heat large rods, in which, depending on the size of the muffle, several rods can be placed at the same time. The furnaces are placed near the forging machine to avoid excessive cooling of the rods during their removal from the furnace and insertion into the working channel of the machine. The workpieces are fed into the forging machine manually. At this stage, bars are obtained, the diameter of which is 20-25 mm. In the following steps, the forging temperature is gradually reduced as the diameter of the bars decreases. Forging bars having a diameter of 2.5-3 mm is carried out at a temperature of 950-1000 °C.
When the length of the bars increases significantly, they switch to continuous forging. This transition is carried out with a rod diameter of 3 mm, if the initial blanks were rods with a section of 10x10 or 12x12 mm. The bars are fed into the forging machine mechanically, and a gas furnace is used for heating. During continuous forging, the rods are coated with a lubricant - aquadag or hydrocollag (aqueous colloidal suspensions of graphite). Lubrication protects the bar from oxidation and reduces wear on the forging machine dies.
The disadvantages of rotational forging include the complexity of the process and the unevenness of the surface of the resulting bars. When billets are heated, significant losses of molybdenum occur due to its oxidation. To reduce losses and improve the plastic properties of molybdenum, forging processes in an inert gas atmosphere have been developed.
In addition to sintered rods, ingots can serve as blanks for the production of molybdenum rods. Fused molybdenum ingots have a coarse coarse grained structure and are much more difficult to work with pressure than sintered billets. Therefore, hot forging can only be used for ingots with a diameter of up to 100 mm. Forging is carried out at a temperature of 1400-1450 °C. Billets with a diameter of 150 mm or more are processed by pressing. Forging such workpieces can lead to the formation of cracks.
Before pressing, the ingot is heated to a temperature of 760 °C, coated with a special enamel, on which finely ground glass is then rolled. Glass in this case acts as a lubricant. Then the workpiece is heated to 1260 ° C and again covered with glass. Next comes the pressing. After pressing, the ingots are subjected to hot forging at a temperature of 1425 °C. The ends of the bar obtained as a result of forging are cut off. Then the bar is turned to a depth of 25 mm in order to remove glass and a layer of scale. In the future, the bars can be forged to obtain the required size.
It should be noted that products made from sintered and fused molybdenum blanks do not differ in properties.
Application
One of the areas of application of molybdenum products is the manufacture of heaters for high-temperature electric furnaces (see). Molybdenum rods can be used as such heaters. As a rule, molybdenum rod heaters are free-radiating, that is, heat is transferred from the heater directly to the heated product, thereby achieving more efficient use of the furnace power. The fastening of such heating elements must be very reliable in order to prevent them from sagging. Molybdenum rod heaters are highly durable. They are used in high-temperature electric furnaces with high power.
Molybdenum rods are used for the manufacture of inputs for electrovacuum devices. Molybdenum rods are widely used in this area due to the fact that this metal has a sufficiently high electrical conductivity and a low thermal expansion coefficient, which is in excellent agreement with the thermal expansion coefficient of refractory glass, from which the cases of electrovacuum devices are made. Molybdenum rods are used to make bushings designed for great power current, for example, for inputs of glass gates.
One of the most important areas of application for molybdenum rods is the production of wire, where molybdenum rods act as blanks (see).
Bibliography
- Agte K., Vacek I. "Tungsten and molybdenum".
- Zelikman A.N. "Molybdenum".
- Elagin V.I., Kolachev B.A., Livanov V.A. "Metal science and heat treatment of non-ferrous metals and alloys".
- Utkin N.I. “Metallurgy of non-ferrous metals”.
- http://en.wikipedia.org
- http://slovari.yandex.ru
- http://www.site
Molybdenum
MOLYBDENUM[de], -a; m.[lat. Molybdaenum] A chemical element (Mo), a hard, refractory metal with a silvery-white luster (used in the electrical industry and in the form of alloys in mechanical engineering). Molybdenum wire.
◁ Molybdenum, th, th. M-th ores. M-th steel. M wire.
molybdenum(lat. Molybdaenum), a chemical element of group VI of the periodic system. The name is from the Greek mólybdos - lead (according to the similarity of the minerals Mo and Pb). Light gray metal, density 10.2 g/cm3, t pl 2623°C. Chemically resistant (oxidized in air at temperatures above 400°C). The main mineral is molybdenite. More than 75% of molybdenum is used for alloying cast irons and steels used in the aircraft and automotive industries, in the manufacture of turbine blades, etc. Heat-resistant (for jet engines) and acid-resistant (chemical industry apparatus) alloys are very promising; thus, the Fe-Ni-Mo alloy is resistant to all acids (except HF) up to 100°C. An important structural material in the production of filaments for electric lamps and cathodes for vacuum devices. Oxides MoO 2 , MoO 3 - catalysts for petrochemical and other processes.
MOLYBDENUMMOLYBDENUM (lat. Molibdaenum), Mo (read "molybdenum"), a chemical element with atomic number 42, atomic mass 95.94. Natural molybdenum consists of seven stable isotopes: 92 Mo (15.86% by mass), 94 Mo (9.12%), 95 Mo (15.70), 96 Mo (16.50%), 97 Mo (9.45%), 98 Mo (23.75) and 100 Mo (9.62% by mass). Configuration of two outer electron layers 4 s 2
p 6
d 5
5s 1
. The oxidation states from +2 (valence II) to +6 (VI) are the most typical. It is located in group VIB in the 5th period of the Periodic Table of the Elements.
The radius of the atom is 0.140 nm, the radius of the Mo 3+ ion is 0.083 nm, the Mo 4+ ion is 0.079 nm, the Mo 5+ ion is 0.075 nm, the Mo 6+ ion is from 0.055 nm (coordination number 4) to 0.087 (7). Sequential ionization energies 7.10, 16.15, 27.13, 40.53, 55.6 and 71.7 eV. The electron work function is 4.3 eV. Electronegativity according to Pauling (cm. PAULING Linus) 1,8.
Discovery history
Discovered in 1778 by the Swedish chemist K. Scheele (cm. SCHEELE Karl Wilhelm), which, by calcining molybdic acid, obtained MoO 3 oxide. Having restored it with coal, he received molybdenum. This metal was contaminated with coal and molybdenum carbide. Pure molybdenum was obtained in 1817 by J. Berzelius (cm. BERZELIUS Jens Jacob). The name of the element comes from the Greek. "molubdos" - lead, since the mineral - molybdenum luster - looks like lead and its mineral - lead luster
Being in nature
The content in the earth's crust is 3·10 -4% by weight. Molybdenum does not occur in free form. About 20 molybdenum minerals are known. The most important of them: molybdenite (cm. MOLYBDENITE) MoS 2, powellite (cm. POVELLIT) CaMoO 4, molybdite Fe(MoO 4) 3 .nH 2 O and wulfenite (cm. WULFENITE) PbMoO 4 .
Receipt
The industrial production of molybdenum begins with the enrichment of ores by the flotation method. The resulting concentrate is fired until the formation of oxide MoO 3:
2MoS 2 + 7O 2 \u003d 2MoO 3 + 4SO 2,
which is further purified. Next, MoO 3 restore H 2 . The resulting blanks are processed by pressure (forging, rolling, broaching).
Physical and chemical properties
Molybdenum is a light gray metal with a cubic body-centered lattice of the a-Fe type, A= 0.314 nm. Melting point 2623°C, boiling point 4800°C, density 10.2 kg/dm 3 . Paramagnetic. Mechanical properties are determined by the purity of the metal and the previous mechanical and heat treatment.
Mo is stable at room temperature in air. Begins to oxidize at 400°C. Above 600°C it rapidly oxidizes to MoO 3 trioxide. This oxide is also obtained by the oxidation of molybdenum disulfide MoS 2 and the thermolysis of ammonium molybdate (NH 4) 6 Mo 7 O 24 .4H 2 O.
Mo has molybdenum (IV) oxide MoO 2 and a number of oxides intermediate between MoO 3 and MoO 2 .
With halogens (cm. HALOGENS) Mo forms a number of compounds in different oxidation states. When powder of molybdenum or MoO 3 reacts with F 2, molybdenum hexafluoride MoF 6 is obtained, a colorless, low-boiling liquid.
Mo (+4 and +5) forms solid halides MoHal 4 and MoHal 5 (Hal = F, Cl, Br). With iodine, only molybdenum diiodide MoI 2 is known.
Mo forms oxyhalides: MoOF 4 , MoOCl 4 , MoO 2 F 2 , MoO 2 Cl 2 , MoO 2 Br 2 , MoOBr 3 and others.
When molybdenum is heated with sulfur (cm. SULFUR) molybdenum disulfide MoS 2 is formed, with selenium (cm. SELENIUM)- molybdenum diselenide composition MoSe 2 . Molybdenum carbides Mo 2 C and MoC are known - crystalline high-melting substances and molybdenum silicide MoSi 2 .
special group molybdenum compounds - molybdenum blue (cm. MOLYBDATES). Under the action of sulfur dioxide, zinc dust, aluminum or other reducing agents on slightly acidic (pH 4) suspensions of molybdenum oxide, bright blue substances of variable composition are formed: Mo 2 O 5 H 2 O, Mo 4 O 11 H 2 O and Mo 8 O 23 8H 2 O.
Mo forms molybdates, salts of weak molybdic acids not isolated in the free state, X H 2 O at MoO 3 (ammonium paramolybdate 3 (NH 4) 2 O 7MoO 3 z H2O; CaMoO 4, Fe 2 (MoO 4) 3 - occur in nature). Metal molybdates I and III groups contain tetrahedral groups [MoO 4 ].
When aqueous solutions of normal molybdates are acidified, MoO 3 OH - ions are formed, then polymolybdate ions: hepta-, (para-) Mo 7 O 26 6-, tetra- (meta-) Mo 4 O 13 2-, octa-Mo 8 O 26 4- and others. Anhydrous polymolybdates are synthesized by sintering MoO 3 with metal oxides.
There are double molybdates, which include two cations at once, for example, M +1 M +3 (MoO 4) 2, M +1 5 M +3 (MoO 4) 4. Oxide compounds containing molybdenum in lower oxidation states are molybdenum bronzes, for example, red K 0.26 MoO 3 and blue K 0.28 MoO 3. These compounds have metallic conductivity and semiconducting properties.
Application
Molybdenum is used for alloying steels, as a component of heat-resistant and corrosion-resistant alloys. Molybdenum wire (tape) is used for the manufacture of heaters for high-temperature furnaces, electric current inputs in light bulbs. Molybdenum compounds - sulfide, oxides, molybdates - are catalysts for chemical reactions, dye pigments, glaze components. Molybdenum hexafluoride is used in the deposition of metallic Mo on various materials MoSi 2 is used as a solid high temperature lubricant. Mo is a part of microfertilizers. Radioactive isotopes 93 Mo (T 1/2 6.95 h) and 99 Mo (T 1/2 66 h) are isotope tracers.
Physiological significance
Microamounts of Mo are essential for the normal development of plants.
encyclopedic Dictionary. 2009 .
Synonyms:See what "molybdenum" is in other dictionaries:
- (Greek molibdaine, from molybdos lead). A whitish metal found in molybdenite combined with sulfur. Dictionary of foreign words included in the Russian language. Chudinov, A.N., 1910. MOLYBDENUM, a shiny brittle metal; beats V. = 9.01; solution... Dictionary of foreign words of the Russian language
MOLYBDENUM- MOLYBDENUM, chem. element, char. Mo, serial number 42, at. weight 96.0; stands in the 6th group of the periodic system. Natural compounds of M.: molybdenum shine MoS2 and yellow lead ore PbMo04. It turns out M. from MoS2 by firing and subsequent ... ... Big Medical Encyclopedia
- (symbol Mo), silvery white TRANSITION CHEMICAL ELEMENT, a metal first discovered in 1778. It is mined from ores containing MOLYBDENITE (MoS2). The concentrated mineral is fired to produce molybdenum trioxide, which is mixed with iron... Scientific and technical encyclopedic Dictionary
- (Latin Molybdaenum), Mo, a chemical element of group VI of the periodic system, atomic number 42, atomic mass 95.94; metal, mp 2623 shC. Molybdenum is used for alloying steels, as a component of heat-resistant alloys in aviation, rocket and ... ... Modern Encyclopedia
Mo (lat. Molybdaenum, from Greek molybdos lead * a. molybdenum; n. Molybdan; f. molybdene; i. molibdeno), chem. element VI group periodic. Mendeleev systems, at. n. 42, at. m. 95.94. Natural M. has seven stable isotopes; 92Mo (15.86%) ... Geological Encyclopedia
Molybdenum- (Latin Molybdaenum), Mo, a chemical element of group VI of the periodic system, atomic number 42, atomic mass 95.94; metal, mp 2623 °C. Molybdenum is used for alloying steels, as a component of heat-resistant alloys in aviation, rocket and ... ... Illustrated Encyclopedic Dictionary
- (Molybdenum), Mo, chem. element of a side subgroup of group VI non-periodic. systems of elements, at. number 42, at. weight 95.94. In nature, it is represented by 7 stable isotopes: 92Mo (14.84%), 94Mo (9.25%), 95Mo (15.92%), 96Mo (16.68%), 97Mo (9.55%), 98Mo ... ... Physical Encyclopedia
Exist., number of synonyms: 2 metal (86) element (159) ASIS synonym dictionary. V.N. Trishin. 2013 ... Synonym dictionary
History of molybdenum
The story of the discovery of molybdenum began in 1778, when the Swedish chemist Carl Scheele obtained the mineral molybdenite by calcining molybdic acid (calorizator). A few years later, in 1781, P. Gjelm received molybdenum in the form of a metal, while pure molybdenum was obtained only in 1817 by J. Berzelius.
Due to similarity appearance mineral molybdenum with a lead luster, at first they were called the same - from the ancient Greek μόλυβδος, which means lead.
Molybdenum is an element of group VI of period V of the periodic system chemical elements DI. Mendeleev, has an atomic number of 42 and an atomic mass of 95.94. The accepted designation is Mo(from Latin Molybdaenum).
Being in nature
Molybdenum is not found in free form in nature. It is available in the form of several dozen known minerals in the earth's crust, sea and river water, in oil, coal, a meager amount in the air. The main deposits of molybdenum are located in the United States, Mexico, Chile, Canada, Russia and Armenia.
Physical and chemical properties
Molybdenum is a transitional soft metal of light gray color with a characteristic metallic luster. Stable when exposed to air at room temperature, oxidation starts at temperatures above 400˚C.
The daily requirement for molybdenum varies depending on age, it is also influenced by physical activity and body weight. The norm for children from birth to 10 years of age is 15-150 mcg per day, for adults - 75-250 mcg, after 70 years the need for molybdenum decreases and should not exceed 200 mcg per day. Usually, a person receives the necessary amount of this trace element with food, so an additional intake is not required.
Useful properties of molybdenum and its effect on the body
Molybdenum is important for:
- Stimulation of the activity of enzymes that provide the synthesis of acids and tissue respiration;
- Maintaining a healthy state of teeth;
- Improving the qualitative composition of the blood, increasing the level of hemoglobin in the blood;
- Regulation of metabolic processes;
- Removal of uric acid, prevention of gout;
- Prevention of impotence and other disorders of the male genital area;
- Participation in the synthesis of vitamins,
- Prevention of diabetes.
Interaction with others
Molybdenum is an important part of the recycling enzyme. With an excess of molybdenum, the utilization and synthesis of the vitamin is disrupted.
The main suppliers of molybdenum to the human body are green leafy vegetables ( , ), cereals, cereals ( , ) and legumes ( , ). Molybdenum is present in fish, nuts and berries.
The use of molybdenum in life
The main use of molybdenum is the metallurgical industry, it is also used in the manufacture of incandescent lamps.
Signs of excess molybdenum
An excessive amount of molybdenum occurs in workers in the metallurgical industry, manifested by the so-called molybdenum gout, caused by an increase in uric acid in the blood.
An insufficient amount of molybdenum (deficiency) is extremely rare, usually in regions where soils lack the mineral or in people with a poor diet. Signs of a lack of molybdenum are: growth retardation, hair loss, edema, flabbiness of the skin and muscles, dermatitis and fungal infections of the skin.
