Melting and boiling points of pure chemical elements at atmospheric pressure

Steel is an alloy of iron mixed with carbon. Its main benefit in construction is strength, because this substance retains its volume and shape for a long time. The whole point is that the particles of the body are in a position of equilibrium. In this case, the attractive and repulsive forces between the particles are equal. The particles are in a clearly defined order.

There are four types of this material: regular, alloy, low-alloy, high-alloy steel. They differ in the number of additives in their composition. The usual one contains a small amount, and then increases. The following additives are used:

Melting temperatures of steel

Under certain conditions, solids melt, that is, they turn into a liquid state. Each substance does this at a certain temperature.

• Melting is the process of transition of a substance from a solid to a liquid state.
• Melting point is the temperature at which a crystalline solid melts into a liquid state. Denoted by t.

Physicists use a specific table of melting and crystallization, which is given below:

Based on the table, we can safely say that the melting point of steel is 1400 °C.

Boiling temperature

If evaporation occurs at any temperature, then boiling occurs at a certain temperature. Wherein:

• different liquids boil at different temperatures
• boiling occurs at a constant temperature from start to finish

Boiling point is the temperature at which a liquid boils.

During boiling, the temperature of the liquid does not change.

Remember, when preparing the same soup, after boiling the water, reduce the heat. Now it simply maintains this very boiling temperature. This saves fuel.

The boiling point depends on the pressure on the surface of the liquid. The saturated vapor pressure in bubbles during boiling is always greater than the external pressure.

Accordingly, if we increase the external pressure, the boiling point increases. If we reduce it, the boiling point will also decrease.

Air pressure depends on altitude. As it increases above sea level, the air pressure gradually decreases. This means that the boiling point of the liquid decreases. If at normal atmospheric pressure water boils at $100 \degree C$, then in the mountains it will boil at a temperature of $90 \degree C$.

Will it be possible to boil an ordinary chicken egg under such conditions? No. The protein will never be able to coagulate - this is impossible at temperatures below $100 \degree C$.

Stainless steel

Stainless steel is one of the many iron alloys found in steel. It contains Chromium from 15 to 30%, which makes it rust-resistant, creating a protective layer of oxide on the surface, and carbon. The most popular brands of this type are foreign. These are the 300th and 400th series. They are distinguished by their strength, resistance to adverse conditions and ductility. The 200 series is of lower quality, but cheaper. This is a beneficial factor for the manufacturer. Its composition was first noticed in 1913 by Harry Brearley, who conducted many different experiments on steel.

At the moment, stainless steel is divided into three groups:

• Heat-resistant - at high temperatures it has high mechanical strength and stability. The parts that are made from it are used in the pharmaceutical, rocketry, and textile industries.
• Rust-resistant - has great resistance to rusting processes. It is used in household and medical devices, as well as in mechanical engineering for the manufacture of parts.
• Heat-resistant - resistant to corrosion at high temperatures, suitable for use in chemical plants.

The melting point of stainless steel varies depending on its grade and the number of alloys from approximately 1300 °C to 1400 °C.

Content

In order to turn a liquid into steam, there are two ways: evaporation and boiling. In previous lessons we discussed in detail how the evaporation process occurs. During its course, steam is formed, which, depending on conditions, can be saturated or unsaturated.

We often observe the phenomenon of boiling in everyday life. To make tea or coffee, we first bring water to a boil. To cook the soup, we wait for the water in the pan to boil.

In this lesson we will look at how physics describes this process, study the changes that occur during boiling and establish dependencies on other quantities.

Cast iron and steel

Cast iron is an alloy of carbon and iron, it contains impurities of manganese, silicon, sulfur and phosphorus. Withstands low voltages and loads. One of its many advantages is its low cost for consumers. There are four types of cast iron:

• White - has high strength and poor ability to be processed with a knife. Types of alloy according to the increase in the amount of carbon in the composition: hypoeutectic, eutectic, hypereutectic. It was called white due to the fact that it has a white color in the fault. White cast iron also has a special structure of the metal mass and great wear resistance. Useful in making mechanical parts that will operate in a non-lubricated environment. It is used to make the following types of cast iron.
• Gray cast iron - contains carbon, silicon, manganese, phosphorus and some sulfur. It can be easily obtained and has poor mechanical properties. Used for the manufacture of parts that are not exposed to shock loads. There is a gray color in the fracture; the darker it is, the softer the material. The properties of gray cast iron depend on the temperature of the environment in which it is located and the amount of various impurities.
• Malleable cast iron is obtained from white cast iron as a result of simmering (prolonged heating and holding). The substance contains: carbon, silicon, manganese, phosphorus, and a small amount of sulfur. It is more durable and ductile, easier to process.
• Ductile iron is the strongest of all types of cast iron. Contains carbon, manganese, sulfur, phosphorus, silicon. Has high impact strength. This important metal is used to make pistons, crankshafts and pipes.

The melting points of steel and cast iron are different, as stated in the table above. Steel has higher strength and resistance to high temperatures than cast iron, temperatures differ by as much as 200 degrees. For cast iron, this number ranges from approximately 1100 to 1200 degrees, depending on the impurities it contains.

Non-metals. Physical and chemical properties

Position of non-metals in the periodic table

How can one determine whether a substance is a metal or a non-metal?
If you look closely at the Periodic Table of D.I. Mendeleev (we get acquainted with the classification of elements in detail in paragraph 42 of the chemistry textbook for the 8th grade, edited by V.V. Eremin) and draw a conditional diagonal from hydrogen through boron to astatine and the yet undiscovered element No. 118, the table of non-metals will occupy the upper right corner.

Each horizontal period of the table ends with an element with a completed external energy level. This group of elements is called noble gases

and has special properties, which can be found in paragraph 18 of the textbook “Chemistry” for grade 8, edited by Eremin V.V.

When considering the electronic structure of nonmetals, you can notice that the energy levels of an atom are filled with electrons by more than 50% (the exception is boron), and for elements located in the table from right to left, the number of electrons at the outer level increases. Therefore, in chemical reactions, this group of substances can be both an electron acceptor with oxidizing properties and an electron donor with reducing properties.

The substances that form the boron-silicon-germanium-arsenic-tellurium diagonal are unique and, depending on the reaction and reagent, can exhibit both metallic and non-metallic properties. They are called metalloids. In chemical reactions they exhibit predominantly reducing properties.

Chemistry. A basic level of. Grade 10. Textbook.

The textbook was written by teachers of the Faculty of Chemistry of Moscow State University. M. V. Lomonosov. The simplicity and accessibility of the presentation of the organic chemistry course, a large number of illustrations, as well as a variety of questions, exercises and tasks contribute to the successful assimilation of the educational material. The textbook complies with the Federal State Educational Standard of Secondary General Education.

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Physical properties of nonmetals. Allotropy

If you look at metals, then with the naked eye you can notice general properties - metallic luster, solid state of aggregation (with the exception of liquid mercury), thermal and electrical conductivity.

With non-metals everything is much more complicated. They may have molecular

and
non-molecular
structure. Due to differences in structure, simple nonmetal substances exist in three states of aggregation:

1. Molecular:
   Volatile, gaseous, colorless oxygen, hydrogen.
2. Gaseous, colored chlorine, nitrogen, fluorine.
3. The only liquid representative is dark red bromine.
4. Solid but brittle substances with a low melting point - crystals of iodine, sulfur, white phosphorus.
5. Non-molecular:
   Solids with a high melting point are silicon, graphite, diamond and red phosphorus.

Most non-metallic substances are poor conductors of electricity and heat.

The exception is graphite, a type of carbon.

Allotropy is the unique ability of a nonmetallic element to form several simple substances. In the natural environment, there are allotropic modifications of elements that differ in physical and chemical properties. These include ozone and oxygen, graphite and diamond. You can learn more about the physical properties of nonmetals in the textbook “Chemistry. 9th grade."

Chemical properties of non-metals

As we discussed above, the group of nonmetals is quite polymorphic and, depending on the type of reactions in which they participate, they can exhibit both oxidizing and reducing properties. Fluorine is an exception in this series. It is always an oxidizing agent.

In the series F, O, N, CL, Br, I, S, C, Se, P, As, Si, H, the oxidizing properties decrease. Oxygen can exhibit reducing properties only in relation to fluorine.

1. Reactions with metals.

In this type of reaction, oxidizing properties occur and nonmetals accept electrons to form negatively charged species.

Ca + Cl2 = CaCl2

Ca + O2 = CaO2

Na + Cl2 = Na+Cl2

1. Reactions with hydrogen

Almost all non-metals react with hydrogen. Only noble gases are an exception for reactions of this type. The reaction product is volatile hydrogen compounds:

Cl2 + H2 = 2HCl

C + 2H2 = CH4

1. Reactions with oxygen.

Nonmetals form acidic or non-salt-forming oxides.
S + O2 = SO2 P + 5O2 = 2P2O5 4. Interaction with water and acids is not typical for non-metals.

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History of the discovery of nonmetals

Copper utensils, iron tools, gold jewelry - people have long noticed that all these substances have certain common properties:

• they conduct heat and electricity;
• they are characterized by a metallic luster;
• due to their plasticity and malleability, they can be given any shape;
• All substances are characterized by a metallic crystal lattice.

In contrast to metals, there were other substances that did not have metallic properties, and were accordingly called nonmetals. Almost until the end of the 17th century, alchemical scientists knew only two non-metallic substances - carbon and sulfur.

In 1669, Brand, in search of the “philosopher’s stone,” discovered white phosphorus. And in a short period from 1748 to 1798, about 15 new metals and 5 non-metals were discovered.

Attempts to discover fluorine cost researchers not only their health, but also their lives. Devi, the Knox brothers, Gay-Lussac - this is an incomplete list of victims of science who lost their health in attempts to isolate fluorine from fluorspar. It was only in 1886 that Moissan solved a difficult problem using electrolysis. And he received the first halogen, and also poisonous chlorine. During the First World War it was used as a weapon of mass destruction.

Currently, 22 non-metallic elements have been discovered.

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Density, melting and boiling points of simple substances: tables for elements

The table shows the basic physical properties of simple substances: density at a temperature of 20 ° C (if the density is measured at another temperature, the latter is indicated in parentheses), melting point and boiling point of substances in degrees Celsius.

The density and melting and boiling points of the following simple substances are indicated: nitrogen N2, actinium Ac, aluminum Al, americium Am, argon Ar, astatine At, barium Ba, beryllium Be, boron B, bromine Br, vanadium V, bismuth Bi, hydrogen h3, tungsten W, gadolinium Gd, gallium Ga, hafnium Hf, helium He, germanium Ge, holmium Ho, dysprosium Dy, europium Eu, iron Fe, gold Au, indium In, iodine (iodine) J, iridium Ir, ytterbium Yb, yttrium Y , cadmium Cd, potassium K, calcium Ca, oxygen O2, ozone O3, cobalt Co, silicon Si, krypton Kr, xenon Xe, curium Cm, lanthanum La, lithium Li, lutetium Lu, magnesium Mg, manganese Mn, copper Cu, molybdenum Mo, arsenic As, sodium Na, neodymium Nd, neon Ne, neptunium Np, nickel Ni, niobium Nb, tin Sn, osmium Os, palladium Pd, platinum Pt, plutonium Pu, polonium Po, praseodymium Pr, promethium Pm, protactinium Pa, radium Ra, radon Rn, rhenium Re, rhodium Rh, mercury Hg, rubidium Rb, ruthenium Ru, samarium Sm, lead Pb, selenium Se, sulfur S, silver Ag, scandium Sc, strontium Sr, antimony Sb, thallium Tl, tantalum Ta , tellurium Te, terbium Tb, technetium Tc, titanium Ti, thorium Th, thulium Tu, carbon C (diamond, graphite), uranium U, phosphorus P (white, red), francium Fr, fluorine F, chlorine Cl, chromium Cr, cesium Cs, cerium Ce, zinc Zn, zirconium Zr, erbium Er.

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It should be noted that the density of substances in the table is expressed in units of kg/m3. In the table you can highlight substances (chemical elements) with minimum and maximum densities. Gases have the lowest density of chemical elements - for example, the density of hydrogen is only 0.08987 kg/m3 - this is the lightest gas on the planet. Of the heavy elements, tungsten, uranium, neptunium, osmium and other metals are distinguished by high density.

The numbers in brackets mean that the substance decomposes at a given temperature. Abbreviations: g. - gas, l. - liquid, tv. - solid, sublime — sublimates, rhombus. - rhombic structure.

According to the table, it is possible to identify substances with minimum and maximum melting and boiling points. The chemical element helium has the lowest melting point - its melting point is minus 272.2 °C. Helium also has the lowest boiling point.

The chemical element carbon in the form of graphite has the highest melting point among simple substances. It begins to melt at a temperature of 3600°C. Another modification of carbon, diamond, is also a refractory substance with a melting point of 3500°C.

The element cadmium has the highest boiling point; it boils at a temperature not lower than 7670°C, although it begins to melt at only 321°C.

Atomic mass and density of simple substances

The table shows the atomic mass and density of the following chemical elements: nitrogen, actinium, aluminum, americium, argon, astatine, barium, beryllium, berkelium, boron, bromine, vanadium, bismuth, hydrogen, tungsten, gadolinium, gallium, hafnium, helium, germanium , holmium, dysprosium, europium, iron, gold, indium, iodine, iridium, ytterbium, yttrium, cadmium, potassium, californium, calcium, oxygen, cobalt, silicon, krypton, xenon, curium, lanthanum, lithium, lutetium, magnesium, manganese , copper, mendelevium, molybdenum, arsenic, sodium, neodymium, neon, neptunium, nickel, niobium, tin, osmium, palladium, platinum, plutonium, polonium, praseodymium, promethium, protactinium, radium, radon, rhenium, rhodium, mercury, rubidium , ruthenium, samarium, lead, selenium, sulfur, silver, scandium, strontium, antimony, thallium, tantalum, tellurium, terbium, technetium, titanium, thorium, thulium, carbon (graphite, diamond), uranium, fermium, phosphorus, francium, fluorine, chlorine, chromium, cesium, cerium, zinc, zirconium, einsteinium, erbium.

The densities indicated correspond to the densities of substances at a temperature of 20°C and atmospheric pressure, except in cases where a different temperature is indicated in parentheses.

The density of elements is given in the dimension of ton per cubic meter. For example, the density of liquid nitrogen at a temperature of -195.8°C is 0.808 t/m3 or 808 kg/m3; The density of chlorine in the gaseous state is 3.214 kg/m3, and that of liquid chlorine is 1557 kg/m3. The density values ​​of substances are given for their natural molecular and aggregate states at the indicated temperature.

Sources:1. Pisarenko V.V. Handbook of laboratory chemist. Ref. manual for professional technical textbook establishments. M., “Higher School”, 1970. - 192 pages with illustration 2. Physical quantities. Directory. A.P. Babichev, N.A. Babushkina, A.M. Bratkovsky and others; Ed. I.S. Grigorieva, E.Z. Meilikhova. - M.: Energoatomizdat, 1991. - 1232 p.

Table 3.3.7

Boiling or sublimation points (°C) of inorganic substances at vapor pressure from 13.3 Pa to 101.3 kPa

*1 Below 233 °C - orthorhombic modification, from 233 to 313 °C - monoclinic modification. *2 In BeBr2 + Be2Br4 vapors. *3 In BeCl2 + Be2Cl4 vapors. *4 In BeI2 + Be2I4 pairs. *5 For other methane halogen derivatives, see table. 3.3.9. *6 Triple point. *7 See also table. 3.3.15 and 3.3.16. *8 Steam consists of GaBr3 + GaBr4 + Br2. *9 See also table. 3.3.19–3.3.22. *10 Below 386 °C - red modification, above 386 °C - black modification. *11 In vapors it is disproportionate to HgBr2 and Hg. *12 In vapors it disproportionates into HgCl2 and Hg. *13 Partially disproportionate between InCl and InCl3. *14 See also table. 3.3.17. *15 Steam consists of NH3 and the corresponding hydrogen halide. *16 In NO2 + N2O4 vapors; at T ≤ –50 °C the NO2 pressure can be neglected. *17 Above 420 °C unstable. *18 Below 569 °C - cubic modification, from 569 to 655 °C - orthorhombic modification. *19 In vapors it dissociates into SeCl2 and Cl2. *20 Above 194 °C it is disproportionate. *21 In TiCl3 + Ti2Cl6 vapors. *22 Below 226.9 °C - α-modification, from 226.9 to 284 °C - β-modification.

PHYSICAL PROPERTIES OF METALS MELTING POINT

The particles of any body - atoms or molecules - are in constant random motion. In solids, this movement is practically limited to the vibration of atoms around a certain equilibrium position. The higher the body temperature, the more animated the movement. At a certain temperature, a solid melts and turns into a liquid.

Amorphous bodies - wax, resin, amber, glass - when heated, gradually soften and then become liquid. The transition of wax from solid to liquid occurs smoothly, and we cannot say exactly what the melting point of wax is.

Crystalline substances are a different matter. When heated, the ions fixed at the nodes of the crystal lattice vibrate more and more energetically, but as long as the lattice is maintained, the crystal remains solid. Only when the vibrations of the ions increase so much that the lattice is destroyed do the first traces of liquid appear. That is why all crystalline substances, including metals, have a completely definite melting point.

Among the metals there are those for the melting of which special high-temperature electric furnaces are built; There are those that melt from the warmth of your hand, and there are those that melt at temperatures below zero.

The most fusible metals are mercury and cesium, and the most refractory are rhenium and tungsten. Below we provide a table of melting points of various metals:

Melting point in degrees Celsius

Melting point in degrees Celsius

The transfer of heat from one body to another is the transfer of energy of random motion from one molecules to another.

Water, glass, air, wood, brick transfer heat slowly, their thermal conductivity is low. Metals conduct heat very quickly. How can we explain this?

We already know that in the spatial lattice of metal crystals there are positively charged metal atoms - ions. They are more or less firmly held in place. Free electrons move randomly around the ions. They can be imagined as “electron gas” flowing around the crystal lattice. Free electrons easily move inside the lattice and serve as good carriers of heat energy from heated metal layers to cold ones.

The high thermal conductivity of a metal is always easy to detect. In cold weather, touch the wall of a wooden house and an iron fence with your hand: iron is always much colder to the touch than wood, since iron quickly removes heat from the hand, and wood is hundreds of times slower. Silver and gold conduct heat better than all other metals, followed by copper, aluminum, tungsten, magnesium, zinc and others. The worst metal conductors of heat are lead and mercury.

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Thermal conductivity is measured by the amount of heat that passes through a metal rod with a cross-section of

1 square centimeter in 1 minute. If the thermal conductivity of silver is conventionally taken as 100, then the thermal conductivity of copper will be 90, aluminum 27, iron 15, lead 12, mercury 2, and the thermal conductivity of wood is only 0.05.

The greater the thermal conductivity of the metal, the faster and more evenly it heats up.

Due to their high thermal conductivity, metals are widely used in applications where rapid heating or cooling is required. Steam boilers, devices in which various chemical processes take place at high temperatures, central heating radiators, car radiators - all this is made of metals. Devices that must give or absorb a lot of heat are most often made of good heat conductors - copper, aluminum.

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Melting point of metals

Melting of a metal is a certain thermodynamic process in which the crystal lattice of the metal is destroyed and it passes from the solid phase state to the liquid.

The melting point of metals is an indicator of the temperature of the heated metal, upon reaching which the process of phase transition (melting) begins. The process itself is the reverse of crystallization and is inextricably linked with it. To melt metal? it must be heated using an external heat source to the melting point, and then continue to supply heat to overcome the phase transition energy. The fact is that the very value of the melting point of metals indicates the temperature at which the material will be in phase equilibrium, at the boundary between a liquid and a solid. At this temperature, pure metal can exist simultaneously in both solid and liquid states. To carry out the melting process, it is necessary to overheat the metal slightly above the equilibrium temperature in order to provide a positive thermodynamic potential. Give a kind of impetus to the process.

The melting point of metals is constant only for pure substances. The presence of impurities will shift the equilibrium potential in one direction or another. This happens because a metal with impurities forms a different crystal lattice, and the forces of interaction between atoms in them will differ from those present in pure materials. Depending on the melting point, metals are divided into low-melting ones (up to 600 ° C, such as gallium , mercury), medium-melting (600-1600°C, copper, aluminum) and refractory (>1600°C, tungsten, molybdenum).

In the modern world, pure metals are rarely used due to the fact that they have a limited range of physical properties. Industry has long and extensively used various combinations of metals - alloys, the varieties and characteristics of which are much greater. The melting point of the metals that make up various alloys will also differ from the melting point of their alloy. Different concentrations of substances determine the order of their melting or crystallization. But there are equilibrium concentrations at which the metals that make up the alloy solidify or melt simultaneously, that is, they behave like a homogeneous material. Such alloys are called eutectic.

Knowing the melting point is very important when working with metal; this value is necessary both in production, for calculating the parameters of alloys, and during the operation of metal products, when the phase transition temperature of the material from which the product is made determines the restrictions on its use. For convenience, these data are summarized in a single table. The metal melting table is a summary result of physical studies of the characteristics of various metals. There are also similar tables for alloys. The melting point of metals also significantly depends on pressure, so these tables are relevant for a specific pressure value (usually these are normal conditions when the pressure is 101.325 kPa). The higher the pressure, the higher the melting point, and vice versa.

Metals have a number of original properties that are unique to these materials. There is a melting point for metals at which the crystal lattice is destroyed. The substance retains its volume, but it is no longer possible to talk about the constancy of its shape.

Individual metals are found extremely rarely in their pure form. In practice, alloys are used. They have certain differences from pure substances. When complex compounds are formed, the crystal lattices combine with each other. Therefore, the properties of alloys may differ markedly from those of their constituent elements. The melting point no longer remains constant; it depends on the concentration of the ingredients included in the alloy.

Concept of temperature scale

Some non-metallic objects also have similar properties. The most common is water. A temperature scale was developed regarding the properties of the liquid that occupies a dominant position on Earth. The reference points are the temperature of changes in the aggregative states of water:

1. Transformations from liquid to solid and vice versa are taken to be zero degrees.
2. Boiling (vapor formation inside a liquid) at normal atmospheric pressure (760 mm Hg) is taken to be 100 ⁰C.

Metal crystal lattices

In its ideal form, it is generally accepted that metals have a cubic lattice (real substances may have flaws). There are equal distances between molecules horizontally and vertically.

A solid substance is characterized by constancy:

• shapes, the object retains linear dimensions in different conditions;
• volume, the object does not change the amount of substance it occupies;
• mass, the amount of a substance expressed in grams (kilograms, tons);
• density, unit volume contains constant mass.

When transitioning into a liquid state, having reached a certain temperature, the crystal lattices are destroyed. Now we can’t talk about constancy of form. The liquid will take the form in which it is poured.

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When evaporation occurs, only the mass of the substance remains constant. Gas will take up the entire volume that will be provided to it. Here we cannot say that density is a constant value.

When liquids combine, the following options are possible:

1. Liquids completely dissolve in one another, as do water and alcohol. The concentration of substances will be the same throughout the entire volume.
2. Liquids are stratified by density, the connection occurs only at the interface. It is only temporarily possible to obtain a mechanical mixture. Mix liquids with different properties. An example is oil and water.

The resulting substances, soluble in each other, when solidified, form crystal lattices of a new type. Define:

• Heliocentered crystal lattices are also called body-centered. In the middle there is a molecule of one substance, and four more molecules of another are located around it. It is customary to call such lattices loose, since the bonds between metal molecules in them are weaker.
• Face-centered crystal lattices form compounds in which the component molecules are located on the faces. Metallurgists call such crystalline alloys dense. In reality, the density of the alloy can be higher than that of each of the components included in the composition (alchemists of the Middle Ages were looking for options for alloys in which the density would correspond to the density of gold).

Boiling process

Let's conduct an experiment: we will heat water in an open glass vessel and measure its temperature.

Note that before we start heating the water, evaporation occurs from the surface of the water. The steam is not visible to the eye, but nevertheless exists.

Let's start heating the water. We will notice that bubbles begin to appear in the water (Figure 1, a). As the temperature rises, they begin to increase in size.

Figure 1. Boiling water

There is always some air dissolved in water. As the temperature rises, this air is released from the water in the form of bubbles. Inside them there is air and water vapor . Water vapor is present because the surrounding water evaporates into these air bubbles.

As bubbles rise to the upper (colder) layers of the liquid, they decrease in size. This happens due to the condensation of steam inside the bubbles. Under the influence of gravity, they fall down into hotter water.

And they begin to rise to the surface again. The bubbles alternately increase and decrease as they move through the liquid. At the same time we hear noise. It precedes the boiling of water.

The water gradually warms up throughout the entire volume. The bubbles stop decreasing in size (Figure 1, b). Under the influence of Archimedean force, they float to the surface and burst. The saturated steam contained in them mixes with the surrounding air. The noise stops, only gurgling remains - the water has boiled . The water temperature is $100 \degree C$.

Boiling is an intense transition of liquid into vapor, which occurs with the formation of vapor bubbles throughout the entire volume of the liquid at a certain temperature.

Melting point of metals

Different substances have different melting points. It is customary to divide metals into:

1. Low-melting - it is enough to heat them to 600 ⁰C to obtain the substance in liquid form.
2. Medium-melting metals melt in the temperature range 600…1600 ⁰С.
3. Refractory are metals that can melt at temperatures above 1600 ⁰C.

The table shows low-melting metals in ascending order. Here you can see that the most unusual metal is mercury (Hg). Under normal conditions it is in a liquid state. This metal has the lowest melting point.

Table 1, melting and boiling points of fusible metals:

Table 2, melting and boiling points of medium-melting metals:

Table 3, melting and boiling points of refractory metals:

Various devices are used to carry out the smelting process. For example, blast furnaces are used to smelt iron. For melting non-ferrous metals, internal heating is carried out using high-frequency currents.

Molds made of non-metallic materials contain non-ferrous metals in a solid state. An alternating microwave magnetic field is created around them. As a result, the crystal lattices begin to loosen. The molecules of the substance begin to move, which causes heating within the entire mass.

If it is necessary to melt a small amount of low-melting metals, muffle furnaces are used. In them, the temperature rises to 1000...1200 ⁰С, which is enough for melting non-ferrous metals.

Ferrous metals are melted in convectors, open hearths and induction furnaces. The process involves the addition of alloying components that improve the quality of the metal.

It is most difficult to work with refractory metals. The problem is that you need to use materials that have a temperature higher than the melting point of the metal itself. The aircraft industry is currently considering the use of Titanium (Ti) as a structural material. At high flight speeds in the atmosphere, the skin heats up. Therefore, a replacement for aluminum and its alloys (AL) is needed.

Strength of metals

In addition to the ability to transition from a solid to a liquid state, one of the important properties of a material is its strength - the ability of a solid body to resist destruction and irreversible changes in shape. The main indicator of strength is the resistance that occurs when a pre-annealed workpiece breaks. The concept of strength does not apply to mercury because it is in a liquid state. The designation of strength is accepted in MPa - Mega Pascals.

There are the following strength groups of metals:

• Fragile. Their resistance does not exceed 50MPa. These include tin, lead, soft-alkaline metals
• Durable, 50−500 MPa. Copper, aluminum, iron, titanium. Materials of this group are the basis of many structural alloys.
• High strength, over 500 MPa. For example, molybdenum and tungsten.

Metal strength table

Metal alloys

To design products from alloys, their properties are first studied. To study, the metals being studied are melted in small containers in different ratios to each other. Based on the results, graphs are built.

The lower axis represents the concentration of component A with component B. The vertical axis is temperature. Here the values ​​of the maximum temperature are noted when all the metal is in a molten state.

When cooled, one of the components begins to form crystals. In a liquid state, eutectic is an ideal compound of metals in an alloy.

Metallurgists identify a special ratio of components at which the melting point is minimal. When making alloys, they try to select the amount of substances used in order to obtain a eutectoid alloy. Its mechanical properties are the best possible. Crystal lattices form ideal face-centered positions of atoms.

The crystallization process is studied by studying the hardening of samples upon cooling. They build special graphs where they observe how the cooling rate changes. Ready-made diagrams are available for different alloys. By marking the start and end points of crystallization, the composition of the alloy is determined.

Soldering alloys

In practice, many people experience melting when soldering parts. If the surfaces of the materials to be joined are cleaned of contaminants and oxides, then they can be easily soldered with solders. It is customary to divide solders into hard and soft. Soft ones are most widespread:

• POS-15 - 278...282 °C;
• POS-25 - 258...262 °C;
• POS-33 - 245...249 °C;
• POS-40 - 236...241 °C;
• POS-61 - 181...185 °C;
• POS-90 - 217...222 °C.

They are produced for enterprises manufacturing various radio equipment.

Brazing alloys based on zinc, copper, silver and bismuth have a higher melting point:

• PSr-10 - 825...835 °C;
• PSr-12 - 780...790 °C;
• PSr-25 - 760...770 °C;
• PSr-45 - 715...721 °C;
• PSr-65 - 738...743 °C;
• PSr-70 - 778...783 °C;
• PMC-36 - 823...828 °C;
• PMC-42 - 830...837 °C;
• PMC-51 - 867...884 °C.

The use of hard solders allows you to obtain strong connections.

Attention! Wed means that silver is used in the solder. Such alloys have minimal electrical resistance.