Molybdenum - useful properties and prospects of the metal

Being in nature

The occurrence of free molybdenum in nature has not been recorded. But two dozen minerals based on it have been identified. The most notable: molybdenite, molybdite, wulfenite.

Molybdenite from Australia

In the earth's crust the element is distributed evenly. Also found in rivers, seas, fossils of organic origin (plant ash, coal, oil). However, the total mass content of the metal is hundredths of a percent.

World reserves of molybdenum are estimated at 11.5 million tons.

Australia and both Americas (USA, Canada, Mexico, Chile) have large deposits. In Europe – Russia and Norway.

Mining is carried out using closed or open-pit methods.

Metal discovered in space. Its concentrations are off the charts in systems with a central star - a red (super) giant and a neutron star inside it.

What is barium

• What is barium? Characteristics of the element
• Barium is
• Receipt and use

(Barium; from Greek heavy), Ba - chemical. element of group II of the periodic system of elements; at. n. 56, at. m. 137.34. Silver-white metal. In compounds it exhibits an oxidation state of +2. Natural barium consists of seven stable isotopes, among which the 138Ba isotope predominates (71.66%). Barium in the form of oxide was discovered in 1774 by the Swede, chemist K. Scheele. Metallic barium was obtained in 1808 by the English. chemist G. Davy. The content of barium in the earth's crust is 5 X 10% It does not occur in nature in a free state. From industrial minerals Barite and the less common witherite are important. The most important inorganic compounds: BaO oxide, BaO2 peroxide, Ba(OH)2 hydroxide, BaCO3 carbonate, BaS04 sulfate and BaCl2 chloride. Barium crystal lattice is cubic body-centered with a period a = 5.019 A; density 3.76 g/cm3; melting point 710° C; bp 1637 -1640° C; temperature coefficient of linear expansion (temperature 0 - 100° C) 1.9 · 10 degrees; specific heat capacity 0.068 cal/g deg; electrical resistivity 6 · 10-5 ohm · cm, Brinell hardness 4.2, Mohs hardness 2. According to chemistry. St. is similar to calcium, strontium and radium. In air it oxidizes quickly. When heated in air, it ignites and burns easily. Vigorously decomposes water. With hydrogen it forms the hydride BaH2. When heated, it combines directly with nitrogen, sulfur and halogens. The main raw material for the production of barium and its compounds is barite, which is reduced with coal in fiery furnaces. The resulting soluble barium sulfide is processed into other metal salts. Metal barium is obtained by thermal reduction of its oxide with aluminum powder at a temperature of 1100-1200 ° C. The process is carried out in periodic electric vacuum apparatus, where the reduction, distillation, condensation and casting of the metal into an ingot take place successively. The technical product contains 96-98% metal. By double distillation in vacuum at a temperature of 900° C, the impurity content is reduced to 1 X 10-4%. Barium alloys are produced by electrolysis of a molten mixture of chlorides. The practical use of barium metal is limited. Barium and its alloys with magnesium and aluminum are used to absorb residual gases in high vacuum technology (see Getters). B. is introduced into some antifriction materials. Lead-barium alloys are replacing lead-antimony printing alloys. Barium-nickel alloys are used to make electrodes for spark plugs in engines and in radio tubes. BaS04 sulfate is used as a white pigment, as well as in the production of linoleum and paper. Titanate BaTi03 is one of the most important ferroelectric materials. BaO oxide is used in the manufacture of glass, enamels and thermal catalysts. Ba02 peroxide is used to produce hydrogen peroxide, for bleaching fabrics, it is also used as a catalyst for the cracking process, as one of the components of ignition mixtures in aluminothermy and pyrotechnics. BaF2 fluoride is used in the manufacture of enamels and optical glasses. Zirconate BaZr03 is a high-quality refractory material. X-ray and radioactive radiation excites the yellow-green fluorescence of the Ba complex salt, on which the use of special is based. screens coated with this salt. B. compounds absorb X-rays and gamma radiation, as a result of which they are included in protective materials in X-ray installations and nuclear reactors. Colored salts of B. are pigments: BaCrO4 chromate is yellow, BaMnO4 manganate is green. Soluble barium salts are poisonous.

How it was opened

The history of the discovery of the element begins in the second half of the 18th century.

Shiny silver-white metal

It was written by three scientists:

• Swedish chemist Karl Scheele obtained the oxide.
• The Frenchman Pierre Guelm isolated the metal. But its purity was symbolic.
• The production of metal almost without “dirt” is the merit of the patriarch of European chemists, Swede Jens Berzelius. This happened at the dawn of the 19th century.

A century later, the era of the heyday of metal began.

Molybdenum steel was smelted in tons for the needs of the armies that fought on the fronts of the First World War.

Later they developed a technology for producing metal using powder metallurgy.

The name of the element is of ancient Greek origin: μόλυβδος means “lead”.

It was molybdenite that caused the confusion. It was obtained first, but the shine of the substance copied lead.

For the same reason, until the 18th century, molybdenum was called graphite.

Types of bronze

Tin

copper-tin alloy

Tin bronze is difficult to forge, roll, cut, sharpen, and stamp and is generally only suitable for solid casting. A small draft (no more than 1%) allows the material to be used when creating particularly precise products in artistic casting.

Other metals can be added to the alloy if desired.

1. Zinc (no more than 10%) increases the corrosion resistance of the alloy and is used to create elements of ships and vessels that will often come into contact with sea water.
2. Thanks to the addition of lead and phosphorus, the antifriction properties of bronze can be significantly improved, and the alloy is also easier to process by pressure and cutting.

Tinless

In some cases, the use of tin is unacceptable. In this case, other metals come to the rescue, the addition of which allows you to obtain the necessary characteristics. And although tin bronze is the standard and most in demand, tin-free bronzes are not inferior to it.

Leaded or leaded

Lead bronze is an excellent anti-friction alloy, it resists pressure well, has increased strength and refractoriness. It is used for the manufacture of bearings that are subject to the greatest pressure during operation.

Kremnetzinc

Bronze is used in the manufacture of springs, bearings, grilles, guide bushings, evaporators and networks.

Beryllium

Beryllium bronze is the hardest of all types. It has increased anti-corrosion properties and heat resistance, is stable at low temperatures, does not produce sparks on impacts and is not magnetic. The metal is hardened at 750Co - 790Co, aged at 300Co - 325Co. Nickel, iron or cobalt are sometimes added to beryllium bronze to facilitate the hardening technology. In addition, beryllium can be replaced with nickel.

The material is used to create springs and spring parts, membranes, and for watch parts.

Aluminum

Aluminum bronze consists of copper (95%) and aluminum (5%). It has a pleasant golden color and shine, and can withstand prolonged exposure to aggressive environments, such as acids. The alloy has a higher casting density, heat resistance and increased strength, and tolerates low temperatures well. Among the disadvantages, it is worth noting weaker corrosion resistance, stronger shrinkage, as well as strong gas absorption in the liquid state.

Bronze is used to make car parts and in gunpowder production; gears, bushings, coins and medals are smelted.

Other metals

In addition to those mentioned above, bronze may also contain other elements. Nickel and iron increase the recrystallization temperature and promote grain refinement. Chromium and zirconium reduce electrical conductivity and increase the heat resistance of bronze.

Physico-chemical characteristics

Molybdenum has many advantages:

• Elasticity, almost zero expansion when heated, resistance to heat and corrosion.
• Electrical conductivity is higher than iron.
• Only tungsten has higher mechanical strength. But under pressure, molybdenum is processed more easily.
• The main chemical property of the metal is its resistance to almost all alkaline solutions and aggressive acids, regardless of their concentration and temperature.

Disadvantages of metal: fragility when welding, insignificant ductility.

The negative characteristics of molybdenum appear only at ultra-low temperatures or incorrect use.

Advantages/disadvantages

Advantages:

has a high melting point, and therefore heat resistance; because the density of this metal (10,200 kg/m³) is almost two times less than the density of tungsten (19,300 kg/m³), then molybdenum-based alloys have significantly greater specific strength (at temperatures below 1370°C); has a high elastic modulus; low temperature coefficient of expansion; has good heat resistance; small cross section for thermal neutron capture; Molybdenum is characterized by high corrosion resistance. This metal is stable in most alkaline solutions, as well as in sulfuric, hydrochloric and hydrofluoric acids at different temperatures and concentrations.

Flaws:

has little scale; high fragility of welds; low plasticity at low temperatures; work hardening can be used only up to 700-800°C; at higher temperatures, softening occurs due to return.

Grades and alloys

Industry uses molybdenum as a pure metal, with additives and alloys.

The range of brands includes dozens of items. There are several most common ones:

Additions of Mo (less than a percent) to structural steels multiply their toughness, strength, and corrosion resistance.

To increase the hardness of the metal, cobalt-chromium alloys are used.

Alloys “molybdenum + nickel + cobalt + chromium” increase resistance to acids and heat.

Obtaining molybdenum

The raw materials from which metallic molybdenum is produced are molybdenum concentrates. They contain about 50% of this element. They also contain: sulfur ~ 30%, silicon oxide (up to 9%) and about 20% of other impurities.

The concentrate is pre-fired for additional oxidation. The process is carried out in two types of furnaces: multi-hearth or fluidized bed. Firing temperature 570 °C - 600 °C. The result is cinder - MoO3 and impurities.

In the next step, impurities are removed to obtain pure molybdenum oxide. Two methods are used:

1. Sublimation at a temperature of 950 °C - 1100 °C.
2. Chemical leaching. The essence of the method is that when interacting with ammonia water, impurities of copper and iron are eliminated and molybdenum carbide is obtained, which is crystallized by evaporation or neutralization. Next, the carbide is heated and maintained at temperatures up to 500°C. The output is pure MoO3 oxide, in which the impurity content is only 0.05%.

Molybdenum production is based on the reduction of MoO3. The process is carried out in two stages:

1. In a tube furnace at a temperature of 550°C - 700°C, oxygen atoms are separated in a flow of dry hydrogen.
2. Then the temperature rises to 900°C - 1000°C and final recovery occurs. The resulting metal is in powder form.

To obtain a monolithic metal, powder is melted or sintered. Melting is used when producing workpieces weighing more than 500 kg. The process is carried out in arc furnaces with a cooled crucible, into which a consumable electrode is supplied from previously sintered rods.

Obtaining molybdenum

Powder sintering is pressing in a hydrogen atmosphere at high pressure (2000-3000 atmospheres) and temperature (1000°C - 1200°C). The resulting bars are subjected to sintering at high temperatures equal to 2200°C - 2400°C. Subsequently, molybdenum is given the required shape through pressure treatment - forging, rolling, broaching.

Ferromolybdenum, which contains up to 60-70% molybdenum and the rest is iron, is widely used in industry. It is obtained by introducing molybdenum additives into steel. The alloy is produced by reducing cinder with iron silicate with the addition of steel filings and ferrous ore.

Where is it used?

The refractoriness, variety and ease of processing of the metal, and other physical and chemical properties have determined the areas of use of products made from it.

Metallurgy

The main consumer of raw materials is metallurgy. Its products from molybdenum are wire, rods, powder, sheet, and rod.

Molybdenum powder

These are blanks for a range of products produced by almost all industries.

Other industries

The lion's share of products made from molybdenum and metal alloys is taken by manufacturers of radio and electric lamps, radio electronics.

There is enough material for other purposes:

• Molds, machine parts for injection molding of alloys.
• Electrovacuum production (X-ray tubes).
• Positive electrode of lithium-based current sources.
• Shells of nuclear reactor parts.
• Heaters for electric furnaces operating in harsh conditions.
• The outer layer of the “nose” segment of the body of supersonic aircraft.
• Electrodes for glass melting.
• Catalysis of chemical reactions.
• Varnishes, paints for porcelain, textiles, furs.

These products are created on the basis of natural compounds and metal alloys.

The newest area of ​​application of molybdenum is space technology.

Assortment: components of rocket (ion, plasma) engines; skin of descent vehicles; heat exchangers. Here, the properties of molybdenum are corrected by alloys with niobium and tantalum.

Pure crystalline Mo is used as a component of mirrors for special purpose lasers.

Microdoses of metal are added to agricultural fertilizers.

Physical properties

The use of molybdenum depends on its properties and characteristics. The inherent physical properties of molybdenum are given below:

• metal type - high temperature melting;
• molybdenum color – lead;
• molybdenum density - 10.2 g/cm3;
• melting at a temperature of 2615°C;
• boiling at a temperature of - 4700°C;
• thermal conductivity - 143 W/(m K);
• thermal capacity - 0.27 kJ/(kgK);
• energy for melting - 28000 J/mol;
• energy for evaporation - 590000 J/mol;
• linear expansion, coefficient - 6·10-6;
• electrical resistance - 5.70 μOhm cm;
• calculated volume - 9.4 cm3/mol;
• shear force - 122·10·6 Pa;
• hardness - 125 HB;
• magnetic permeability -90·10-6.

This metal is not often subjected to turning, but processing is carried out with a standardized tool.

Meaning for humans

The effect of molybdenum on living organisms was studied by the middle of the 20th century.

It turned out that this microelement:

1. Regulates the synthesis of amino acids.
2. Activates antioxidants, including ascorbic acid.
3. It is part of enzymes and the tissue respiration system.

Mo deficiency in the body is signaled by weakened immunity (fatigue, frequent illness).

Molybdenum dust is toxic. Its prolonged inhalation provokes blood diseases and irreversible destruction of the lungs.

Heat resistant

To create heat-resistant properties, titanium, aluminum, molybdenum, tungsten, niobium, rhenium, ruthenium and strontium are added to the nickel solution. This alloy is characterized by long-term strength, excellent manufacturability and resistance to high temperatures. The characteristics of alloy grades depend on the percentage of a certain metal in the composition.

For example, Inconel 600 alloy is used to create parts for gas turbines. They can withstand temperatures up to 750°C and have a high degree of resistance to oxidation and metal fatigue. And Inconel 718 is suitable for creating rotor blades in gas turbine engines that operate at temperatures of 800-850°C. After heat treatment, the alloy is not notch sensitive.

Copper-nickel alloys are classified into two subgroups:

• Structural – this type includes cupronickel and nickel silver. Most often, iron and manganese are taken as alloying elements. The most common ratio is ~5-30% Ni, the rest is Cu.;
• Electrical - one of the representatives of this category are Copel or Constantan. Distinctive features are high electrical resistance and thermoelectromotive force. Most often, the alloy consists of ~60% copper, with the rest provided by nickel and other alloying parts.

Modern classification of stainless steel

Stainless steel is a type of alloy steel that is resistant to corrosion due to its chromium content. In the presence of oxygen, chromium oxide is formed, which creates an inert film on the surface of the steel, protecting the entire product from adverse influences.

Not every grade of stainless steel demonstrates the resistance of chromium oxide film to mechanical and chemical damage. Although the film recovers when exposed to oxygen, special grades of stainless steel have been developed for use in aggressive environments.

The first conditional type of division into groups:

• Food
• Heat resistant steel
• Acid resistant steel

The second type of classification is by microstructure:

• Austenitic
  - non-magnetic steel with the main components of 15-20% chromium and 5-15% nickel which increases corrosion resistance. It is well suited to heat treatment and welding. It is the austenitic group of steels that is most widely used in industry and in the production of fasteners.
• Martensitic steels
  are significantly harder than austenitic steels and can be magnetic. They are hardened by quenching and tempering like simple carbon steels, and are used mainly in the manufacture of cutlery, cutting tools and general engineering. More susceptible to corrosion.
• Ferritic steels
  are much softer than martensitic steels due to their low carbon content. They also have magnetic properties.

Production

Molybdenum deposits and its production by country

Genetic groups and industrial types of deposits

1. Contact-metasomatic (skarns).

2. Hydrothermal.

A. High temperature (greisen). B. Medium temperature. A. quartz-molybdenite. b. quartz-sphalerite-galena-molybdenite. V. quartz-chalcopyrite-molybdenite (porphyry copper ores). pitchblende-molybdenite.

Story

The history of metal begins with the Ancient East. Two thousand years BC, Egyptian fashionistas and fashionistas inked their eyebrows with crushed antimony and lined their eyelids.

The origin of the Russian term “antimony” is twofold:

1. In the Ottoman Empire, this was the name given to galena metal powder, which Turkish women used to ink their eyebrows.
2. The Persians used the word “surme” to designate any metal.

The Latin name of the substance goes back to the ancient Greek στίμμι. During the Middle Ages, the term antimonium was in use. By the end of the 18th century, it was introduced into scientific circulation and the list of known chemical elements by the “luminary” of European science Antoine Lavoisier.

The term Stibium comes from “stibnite,” the name given to natural antimony sulfide.

Stainless steel markings

In Russia and the CIS countries, an alphanumeric system has been adopted, according to which numbers indicate the content of steel elements, and letters indicate the name of the elements. The designations common to all are the letter designations of alloying elements: H - nickel, X - chromium, K - cobalt, M - molybdenum, B - tungsten, T - titanium, D - copper, G - manganese, C - silicon.

Standard stainless steel, according to GOST 5632-72, is marked with letters and numbers (for example, 08Х18Н10Т). In the United States, there are several systems for naming metals and their alloys. This is due to the presence of several standardization organizations, these include AMS, ASME, ASTM, AWS, SAE, ACJ, ANSI, AJS. It is quite clear that such marking requires additional clarification and knowledge when trading metal, placing orders, etc.

Europe (EN)

Germany (DIN)

USA (AISI)

Japan (JIS)

CIS (GOST)

Of the variety of brands, we use three main ones in our production - AISI 304, AISI 316 and AISI 430.