The concept of metallurgy: general methods for producing metals

The concept of metallurgy: general methods for producing metals

Metallurgy is the science of industrial methods for producing metals. There are ferrous and non-ferrous metallurgy.

Ferrous metallurgy is the production of iron and its alloys (steel, cast iron, etc.).

Non-ferrous metallurgy is the production of other metals and their alloys.

Metal alloys are widely used. The most common iron alloys are cast iron and steel.

Cast iron is an iron alloy containing 2-4 wt. % carbon, as well as silicon, manganese and small amounts of sulfur and phosphorus.

Steel is an iron alloy containing 0.3-2 wt. % carbon and small impurities of other elements.

Alloy steels are alloys of iron with chromium, nickel, manganese, cobalt, vanadium, titanium and other metals. The addition of metals gives steel additional properties. Thus, the addition of chromium gives the alloy strength, and the addition of nickel gives the steel ductility.

Main stages of metallurgical processes:

1. Enrichment of natural ore (purification, removal of impurities)
2. Production of metal or its alloy.
3. Metal machining

Most metals occur in nature in the form of compounds. The most common metal in the earth's crust is aluminum. Then iron, calcium, sodium and other metals.

Active metals (alkali and alkaline earth) cannot be obtained from compounds using classical “chemical” methods. Such metals in the form of ions are very weak oxidizing agents, and in their simple form they are very strong reducing agents, so it is very difficult to reduce them from cations to simple substances. The more active the metal, the more difficult it is to obtain it in its pure form - because it tends to react with other substances.

Such metals can be obtained, as a rule, by electrolysis of molten salts , or by displacement of other metals from salts under harsh conditions.

Sodium is produced industrially by electrolysis of molten sodium chloride with calcium chloride additives:

2NaCl = 2Na + Cl2

Potassium is obtained by passing sodium vapor through a melt of potassium chloride at 800°C:

KCl + Na = K↑ + NaCl

Lithium can be obtained by electrolysis of molten lithium chloride in a mixture with KCl or BaCl2 (these salts serve to lower the melting point of the mixture):

2LiCl = 2Li + Cl2

Cesium can be obtained by heating a mixture of cesium chloride and specially prepared calcium:

Ca + 2CsCl = 2Cs + CaCl2

Magnesium is obtained by electrolysis of molten carnallite or magnesium chloride with additions of sodium chloride at 720–750°C:

MgCl2 → Mg + Cl2

Calcium is obtained by electrolysis of molten calcium chloride with calcium fluoride additives:

CaCl2 → Ca + Cl2

Barium is obtained from the oxide by reduction with aluminum in vacuum at 1200 °C:

4BaO+ 2Al = 3Ba + Ba(AlO2)2

Aluminum is produced by electrolysis of a solution of aluminum oxide Al2O3 in cryolite Na3AlF6:

2Al2O3 → 4Al + 3O2

Low-active and inactive metals are reduced from oxides with carbon, carbon monoxide (II) CO or a more active metal. Metal sulfides are first fired.

3.2. Reduction of metals with coal

Pure metals can be obtained by reduction from oxides with carbon. In this case, only metal oxides located in the series of electrochemical activity after aluminum .

For example , iron is obtained by reduction from oxide with carbon:

2Fe2O3 + 6C → 2Fe + 6CO

ZnO + C → Zn + CO

Metal oxides, located in the series of electrochemical activity up to aluminum , react with coal to form metal carbides:

CaO + 3C → CaC2 + CO

Types of raw materials

The very name “colored” means the color of the metal. Some types, such as copper, have a distinct color tint. Such substances are important because of their properties and qualities, which are much different from ordinary iron.

Therefore, the production of non-ferrous metals and alloys is necessary to obtain qualitatively new compounds used in all industries.

An alloy is a mixture of metals. When two or more metals in a molten state are combined, a new material is formed that has almost the full range of properties possessed by the constituents of the alloy.

Non-ferrous metals are divided into several large groups:

• Heavy - this group includes copper, zinc, lead, tin.
• Lungs - this group is represented by magnesium, titanium, beryllium, calcium, strontium, aluminum, sodium, potassium, cesium.
• Noble - are the most expensive of non-ferrous metals, which are scarce in nature: platinum, gold, silver, osmium, ruthenium, rhodium, palladium.
• Minor substances are a group of substances that are also rare in nature. These include cobalt, cadmium, antimony, bismuth, and mercury.
• Refractory: manganese, tungsten, chromium, vanadium, tantalum.
• Rare earths.
• Absent-minded.
• Radioactive.

3.4. Reduction of metals with more active metals

More active metals displace less active metals from their oxides. The activity of metals can be roughly estimated from the electrochemical series of metals:

The reduction of metals from oxides by other metals is a common method for obtaining metals. Aluminum and magnesium are often used to restore metals. But alkali metals are not very suitable for this - they are too chemically active, which creates difficulties when working with them.

For example , cesium explodes in air.

Aluminothermy is the reduction of metals from oxides with aluminum.

For example : aluminum reduces copper (II) oxide from the oxide:

3CuO + 2Al = Al2O3 + 3Cu

Magneothermy is the reduction of metals from oxides with magnesium.

CuO + Mg = Cu + MgO

Iron can be displaced from the oxide using aluminum:

2Fe2O3 + 4Al → 4Fe + 2Al2O3

Aluminothermy produces a very pure metal, free of carbon impurities.

Active metals displace less active metals from solutions of their salts.

For example , when copper (Cu) is added to a solution of a salt of a less active metal - silver (AgNO3), a chemical reaction will occur:

2 AgNO 3 + Cu = Cu ( NO 3 )2 + 2 Ag

The copper will be covered with white silver crystals.

When adding iron (Fe) to a solution of copper salt (CuSO4), a pink coating of copper metal appeared on the iron nail:

CuSO 4 + Fe = FeSO 4 + Cu

When zinc is added to a solution of lead(II) nitrate, a layer of metallic lead forms on the zinc:

Pb(NO3)2 + Zn = Pb + Zn (NO3)2

Materials scientist

The concept of alloys and methods for their production

An alloy is a substance obtained by fusing two or more elements. Other methods of preparing alloys are possible: sintering, electrolysis, sublimation. In this case, the substances are called pseudoalloys.

An alloy made primarily from metallic elements and having metallic properties is called a metal alloy. Alloys have a more diverse set of properties, which vary depending on the composition and processing method.

Basic concepts in the theory of alloys.

System – a group of bodies allocated for observation and study.

In metallurgy, systems are metals and metal alloys. A pure metal is a simple one-component system, an alloy is a complex system consisting of two or more components.

Components are substances that form a system. Pure substances and chemical compounds act as components if they do not dissociate into their constituent parts in the temperature range under study.

A phase is a homogeneous part of a system, separated from other parts of the system by an interface, upon passage through which the structure and properties change sharply.

Variation © (number of degrees of freedom) is the number of internal and external factors (temperature, pressure, concentration) that can be changed without changing the number of phases in the system.

If variation C ═ 1 (monovariant system), then it is possible to change one of the factors within certain limits, without changing the number of phases.

If variation C ═ 0 (invariant system), then external factors cannot be changed without changing the number of phases in the system.

There is a mathematical relationship between the number of components (K), the number of phases (F) and the system variability (C). This is the phase rule or Gibbs law:

If we assume that all transformations occur at constant pressure, then the number of variables will decrease:

where C is the number of degrees of freedom, K is the number of components, F is the number of phases, 1 takes into account the possibility of temperature changes.

Features of the structure, crystallization and properties of alloys: mechanical mixtures,

solid solutions, chemical compounds

The structure of a metal alloy depends on the interactions between the components that make up the alloy. Almost all metals in the liquid state dissolve in each other in any ratio. When alloys are formed during their solidification, various interactions between the components are possible.

Depending on the nature of the interaction of the components, alloys are distinguished:

1) mechanical mixtures;

2) chemical compounds;

3) solid solutions.

Alloys are mechanical mixtures formed when the components are not capable of mutual dissolution in the solid state and do not enter into a chemical reaction to form a compound. They are formed between elements that differ significantly in structure and properties, when the force of interaction between homogeneous atoms is greater than between dissimilar ones. The alloy consists of crystals of its constituent components (Fig. 4.1). In alloys, the crystal lattices of the components are preserved.

Rice. 4.1. Scheme of the microstructure of a mechanical mixture

Alloys are chemical compounds formed by elements that differ significantly in structure and properties if the force of interaction between dissimilar atoms is greater than between homogeneous ones.

Features of these alloys:

1. Constancy of composition, that is, the alloy is formed at a certain ratio of components, the chemical compound is designated An Bm/

2. A specific crystal lattice with a regular ordered arrangement of atoms is formed, different from the lattices of the elements that make up the chemical compound (Fig. 4.2)

3. Pronounced individual properties

4.Consistency of crystallization temperature, like pure components

Rice. 4.2. Crystal lattice of a chemical compound

Solid solution alloys are solid phases in which the ratios between components can change. They are crystalline substances.

A characteristic feature of solid solutions is the presence of dissimilar atoms in their crystal lattice, while maintaining the type of solvent lattice.

The solid solution consists of homogeneous grains (Fig. 4.3).

Fig.4.3. Scheme of the microstructure of a solid solution

Classification of solid solution alloys

Based on the degree of solubility of the components, solid solutions are distinguished:

– with unlimited solubility of components;

– with limited solubility of components.

With unlimited solubility of the components, the crystal lattice of the solvent component, as the concentration of the dissolved component increases, smoothly transforms into the crystal lattice of the dissolved component.

To form solutions with unlimited solubility, you need:

1.isomorphy (same type) of the crystal lattices of the components;

2. proximity of the atomic radii of the components, which should not differ by more than 8...13%.

3. the similarity of the physicochemical properties of the valence shells of atoms with similar structures.

With limited solubility of the components, the concentration of the dissolved substance is possible up to a certain limit. With a further increase in the concentration, the homogeneous solid solution decomposes to form a two-phase mixture.

Based on the nature of the distribution of atoms of the solute in the crystal lattice of the solvent, solid solutions are distinguished:

– substitutions;

– implementation;

– subtraction.

In substitution solutions in the crystal lattice of the solvent, some of its atoms are replaced by atoms of the dissolved element (Fig. 4.4a). Substitution occurs at random locations, which is why such solutions are called disordered solid solutions.

Fig.4.4. Crystal lattice of solid solutions of substitution (a), interstitial (b)

When substitution solutions are formed, the lattice periods change depending on the difference in the atomic diameters of the dissolved element and the solvent. If the atom of the dissolved element is larger than the atom of the solvent, then the unit cells increase; if less, they contract. To a first approximation, this change is proportional to the concentration of the dissolved component. The change in lattice parameters during the formation of solid solutions is an important point that determines the change in properties. Decreasing the parameter leads to greater hardening than increasing it.

Interstitial solid solutions are formed by the introduction of atoms of the dissolved component into the pores of the crystal lattice of the solvent (Fig. 4.4, b).

The formation of such solutions is possible if the atoms of the dissolved element are small in size. These are the elements found at the beginning of Mendeleev’s periodic table, carbon, hydrogen, nitrogen, boron. The dimensions of the atoms exceed the dimensions of the interatomic gaps in the crystal lattice of the metal, this causes distortion of the lattice and stresses arise in it. The concentration of such solutions does not exceed 2-2.5%

Subtraction solid solutions or solutions with a defective lattice. are formed on the basis of chemical compounds, and it is possible not only to replace some atoms in the nodes of the crystal lattice with others, but also to form empty nodes in the lattice not occupied by atoms.

One of the elements included in the formula is added to a chemical compound, its atoms occupy a normal position in the lattice of the compound, and the places of the atoms of the other element remain unoccupied.

Crystallization of alloys

The crystallization of alloys follows the same laws as the crystallization of pure metals. A necessary condition is the tendency of the system to a state with a minimum of free energy.

The main difference is the large role of diffusion processes between the liquid and the crystallizing phase. These processes are necessary for the redistribution of dissimilar atoms uniformly distributed in the liquid phase.

In alloys in the solid state, recrystallization processes take place due to

allotropic transformations of alloy components, decomposition of solid solutions, separation of secondary phases from solid solutions, when the solubility of the components in the solid state changes with temperature.

These transformations are called phase transformations in the solid state.

During recrystallization in the solid state, crystallization centers are formed and their growth occurs...

Typically, crystallization centers appear along the grain boundaries of the old phase, where the lattice has the most defective structure and where there are impurities that can become centers of new crystals. The old and new phases have common planes for some time. Such a connection of lattices is called a coherent connection. If the structure of the old and new phases differs, the transformation proceeds with the formation of intermediate phases.

A violation of the coherence and isolation of crystals occurs when they acquire a certain size.

The processes of crystallization of alloys are studied using phase diagrams.

State diagram

The phase diagram is a graphical representation of the state of any alloy of the system under study depending on concentration and temperature (Fig. 4.5)

.

Rice. 4.5. State diagram

State diagrams show stable states, i.e. states that, under given conditions, have a minimum free energy, and therefore they are also called equilibrium diagrams, since they show which equilibrium phases exist under given conditions.

The construction of phase diagrams is most often carried out using thermal analysis.

As a result, a series of cooling curves is obtained, in which inflection points and temperature stops are observed at phase transformation temperatures.

Temperatures corresponding to phase transformations are called critical points. Some critical points have names, for example, the points corresponding to the beginning of crystallization are called liquidus points, and the end of crystallization are called solidus points.

Based on the cooling curves, a state diagram is constructed in coordinates: the abscissa axis is the concentration of components, and the ordinate axis is temperature.

The concentration scale shows the content of component B. The main lines are liquidus 1 and solidus (2), as well as lines corresponding to phase transformations in the solid state 3, 4.

From the phase diagram, you can determine the temperatures of phase transformations, changes in phase composition, approximately the properties of the alloy, and the types of processing that can be used for the alloy.

Process Features

In industry, non-ferrous metals in their pure form are practically not used, but rather alloys are used, which makes it possible to achieve the required properties. During the production of non-ferrous metals, their chemical, physical and mechanical properties are modified, which is very important for the manufacture of both household and industrial items.

A special feature of non-ferrous metals is their ease of processing. Almost all of them are ground, forged, stamped, pressed, cut, welded or soldered.

During production from these substances it is possible to obtain not only finished products, but also a variety of semi-finished products:

• rods;
• wire;
• powder;
• foil.

Production of non-ferrous metal wire

Production of certain types

Copper production

This non-ferrous metal is obtained from copper ores. Its content in these compounds ranges from 1 to 6%. With a copper composition of less than 1%, its extraction at the current level of technology development does not seem to be profitable.

Copper is obtained in two ways:

• hydrometallurgical;
• pyrometallurgical.

The first method is less common, since when using it it is not possible to extract other elements from the ore.

The pyrometallurgical copper mining method consists of several successive stages:

• Preparing ore for smelting through beneficiation and further roasting. This allows you to obtain a copper concentrate.
• Subsequent roasting is required to reduce the amount of sulfur.
• Melting for matte. By smelting copper concentrates it is possible to obtain matte or sulfides of copper and iron.

Matte conversion is also carried out. This stage consists of blowing air inside a special copper smelting converter onto the resulting matte, which allows the iron to be separated into slag and obtain blister copper.

And finally - refining. Blister copper is subjected to fire melting and electrolytic refining, which ultimately results in a product whose purity is 99.97–99.99%.

Aluminum production

Aluminum is produced by the electrolysis of alumina. The process includes several stages.

Obtaining pure alumina or aluminum oxide. This process involves treating bauxite (ores containing metal) with alkaline solutions. The result is the precipitation of aluminum hydroxide.

Preparation of cryolite - its production consists of processing fluorspar to obtain hydrofluoric acid and further release of fluoroaluminum acid. By means of soda, cryolite is released in the form of sediment.

Electrolysis of alumina - the result of this process is the production of raw aluminum.

Refining – by blowing molten raw material with chlorine, pure aluminum is extracted.

Magnesium production

Magnesium is extracted through an electrolysis reaction. The raw materials are molten metal salts (carnallite, magnesite, dolomite, bischofite). The electrolyte is based on magnesium chloride. Additionally, sodium chloride, calcium and potassium are used.

After the reaction, a rough metal containing up to 5% impurities settles on the anode. Their removal occurs through a refining process using fluxes. All non-metallic components are converted into slag, and pure metal is poured into molds.

Titanium production

Titanium and its alloys are superior in quality to alloy steels. The titanium production process is hampered by its increased activity, especially as temperatures rise.

Its peculiarity is the ability to react with many metals, which requires compliance with certain conditions to obtain pure titanium.

The method used to obtain titanium is called magnetothermy. It consists of the following operations.

Isolation of titanium concentrate by beneficiation of ore containing such metal.

Slag production - at this stage, the separation of iron oxides from titanium oxides occurs.

Obtaining titanium tetrachloride - to obtain titanium metal, the use of titanium chloride is required, obtained by chlorinating slag.

Reduction through magnesium - the reduction process takes place at very high temperatures - close to 1 thousand degrees. A reactor where magnesium is melted and titanium vapor is supplied. During metallization, it settles on the walls, and molten magnesium is removed through a tap hole.

Separation of the mass in a vacuum - the titanium obtained as a result of the previous step in the form of a sponge mass must be heated using a vacuum, which will allow the separation of pure metal.

Features of raw materials

All non-ferrous metals have a number of characteristics that must be taken into account when processing or using them.

A number of elements have increased thermal conductivity and specific heat capacity:

• copper;
• magnesium;
• aluminum.

When welding, the joint quickly cools, which will require the use of powerful sources, especially heat during welding.

Some elements change their mechanical properties when suddenly heated. Their decline is observed. At the same time, the metal itself becomes easily destroyed by impacts or other mechanical impacts.

All non-ferrous metals easily interact with gases, except inert ones. This feature is typical for refractory non-ferrous metals.