Physical properties of metals table 9. Physical properties of metals

Density. This is one of the the most important characteristics metals and alloys. According to their density, metals are divided into the following groups:

lungs(density not more than 5 g/cm 3) - magnesium, aluminum, titanium, etc.:

heavy- (density from 5 to 10 g/cm 3) - iron, nickel, copper, zinc, tin, etc. (this is the most extensive group);

very heavy(density more than 10 g/cm3) - molybdenum, tungsten, gold, lead, etc.

Table 2 shows the density values ​​of metals. (This and the following tables characterize the properties of those metals that form the basis of alloys for artistic casting).

Table 2. Metal density.

Melting point. Depending on the melting point, the metal is divided into the following groups:

fusible(melting point does not exceed 600 o C) - zinc, tin, lead, bismuth, etc.;

medium-melting(from 600 o C to 1600 o C) - these include almost half of the metals, including magnesium, aluminum, iron, nickel, copper, gold;

refractory(more than 1600 o C) - tungsten, molybdenum, titanium, chromium, etc.

Mercury is a liquid.

When making artistic castings, the melting point of the metal or alloy determines the choice of melting unit and refractory molding material. When additives are introduced into a metal, the melting point, as a rule, decreases.

Table 3. Melting and boiling points of metals.

Specific heat. This is the amount of energy required to raise the temperature of a unit mass by one degree. Specific heat capacity decreases with increasing serial number element in the periodic table. The dependence of the specific heat capacity of an element in the solid state on atomic mass is described approximately by the Dulong and Petit law:

m a c m = 6.

Where, m a - atomic mass; c m- specific heat capacity (J/kg * o C).

Table 4 shows the specific heat capacity of some metals.

Table 4. Specific heat capacity of metals.

Latent heat of fusion of metals. This characteristic (Table 5), along with the specific heat capacity of the metals, largely determines the required power of the melting unit. Melting a low-melting metal sometimes requires more thermal energy than a refractory metal. For example, heating copper from 20 to 1133 o C will require one and a half times less thermal energy than heating the same amount of aluminum from 20 to 710 o C.

Table 5. Latent heat of metal

Heat capacity. Heat capacity characterizes the transfer of thermal energy from one part of the body to another, or more precisely, the molecular transfer of heat in a continuous medium due to the presence of a temperature gradient. (Table 6)

Table 6. Thermal conductivity coefficient of metals at 20 o C

The quality of artistic casting is closely related to the thermal conductivity of the metal. During the smelting process, it is important not only to ensure a sufficiently high temperature of the metal, but also to achieve a uniform temperature distribution throughout the entire volume of the liquid bath. The higher the thermal conductivity, the more uniformly the temperature is distributed. During electric arc melting, despite the high thermal conductivity of most metals, the temperature difference across the cross section of the bath reaches 70-80 o C, and for a metal with low thermal conductivity this difference can reach 200 o C or more.

Favorable conditions for temperature equalization are created during induction melting.

Thermal expansion coefficient. This value, which characterizes the change in the dimensions of a 1 m long sample when heated by 1 o C, is important for enamel work (Table 7)

The thermal expansion coefficients of the metal base and enamel should be as close as possible so that the enamel does not crack after firing. Most enamels representing a solid coefficient of silicon oxides and other elements have a low coefficient of thermal expansion. As practice has shown, enamels adhere very well to iron and gold, and less firmly to copper and silver. It can be assumed that titanium is a very suitable material for enameling.

Table 7. Thermal expansion coefficient of metals.

Reflectivity. This is the ability of a metal to reflect light waves of a certain length, which is perceived by the human eye as color (Table 8). Metal colors are shown in Table 9.

Table 8. Correspondence between color and wavelength.

Table 9. Metal colors.

Pure metals are practically not used in decorative and applied arts. For the manufacture of various products, alloys are used, the color characteristics of which differ significantly from the color of the base metal.

Over the course of a long time, vast experience has been accumulated in the use of various casting alloys for the manufacture of jewelry, household items, sculptures and many other types of artistic casting. However, the relationship between the structure of the alloy and its reflectivity has not yet been revealed.

Last year you already have an idea about nature chemical bond, existing in metal crystals, - metal connection. Let us recall that at the nodes of metal crystal lattices there are atoms and positive ions of metals, connected through shared external electrons that belong to the entire crystal. These electrons compensate for the electrostatic repulsion forces between the positive ions and thereby bind them, ensuring the stability of the metal lattice.

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1. Name the most fusible metal.

The most fusible metal is mercury. Already at room temperature it is a liquid. Melting point -39C.

2. What physical properties of metals are used in technology?

In technology, such properties of metals as electrical conductivity, hardness, and heat resistance are used.

3. The photoelectric effect, i.e. the property of metals to emit electrons under the influence of light rays, is characteristic of alkali metals, for example for cesium. Why? Where is this property used?

Alkali metals have the lowest ionization energy, i.e. they easily donate an electron from the last layer. In order to take this electron away from the metal, even the energy of light (photon) is enough.

The effect of photoelectric devices is based on the phenomenon of the photoelectric effect, which have received various applications in various fields of science and technology - photocells operating on the basis of the photoelectric effect convert radiation energy into electrical energy.

4. What physical properties of tungsten underlie its use in incandescent lamps?

Its use in incandescent lamps is based on the refractoriness of tungsten. Melting point 3422C.

5. What properties of metals underlie figurative literary expressions: “silver frost”, “golden dawn”, “lead clouds”?

The literary expressions “silver frost”, “golden dawn”, “lead clouds” contain the property of metals to reflect light rays, as a result of which they acquire a characteristic color and metallic luster.

All metals and metal alloys have certain properties. Properties metals and alloys divided into four groups: physical, chemical, mechanical and technological.

Physical properties . To physical properties metals and alloys include: density, melting point, thermal conductivity, thermal expansion, specific heat, electrical conductivity and magnetizability. The physical properties of some metals are given in the table:

Physical properties of metals

Name	Specific weight, g 1cm 3	Melting point, °C	Linear expansion coefficient, α 10 -6	Specific heat capacity C, cal/g-deg	Thermal conductivity λ, Cal/cm sec-deg	Electrical resistivity at 20°, Ohm mm / m
Aluminum
Tungsten
Manganese
Molybdenum

Density. The amount of substance contained in a unit volume is called density. The density of the metal can vary depending on the method of its production and the nature of processing.

Temperaturemelting. The temperature at which the metal completely changes from solid state into liquid, called melting point. Each metal or alloy has its own melting point. Knowing the melting point of metals helps to correctly conduct thermal processes during heat treatment of metals.

Thermal conductivity. The ability of bodies to transfer heat from more heated particles to less heated ones is called thermal conductivity . The thermal conductivity of a metal is determined by the amount of heat that passes through a metal rod with a cross section of 1 cm 2 , 1cm long within 1 sec. at a temperature difference of 1°C.

Thermalextension. Heating a metal to a certain temperature causes it to expand.

The amount of elongation of a metal when heated is easy to determine if the coefficient of linear expansion of the metal α is known. The coefficient of volumetric expansion of the metal ß is equal to 3α.

Specificheat capacity. Amount of heat required to raise temperature 1 G substances per 1°C is called specific heat capacity. Metals have a lower heat capacity compared to other substances, so they are heated without much heat.

Electrical conductivity. Ability of metals to conduct electric current called electrical conductivity. The main quantity characterizing the electrical properties of a metal is the electrical resistivity ρ, i.e. the resistance that a wire of a given metal 1 m long has to current and section 1 mm 2. It is defined in ohms. The reciprocal of electrical resistivity is called elecconductivity.

Most metals are highly conductive, such as silver, copper and aluminum. With increasing temperature, electrical conductivity decreases, and with decreasing temperature it increases.

Magnetic properties. The magnetic properties of metals are characterized by the following quantities: remanent induction, coercive force and magnetic permeability.

Residual induction (INr) is the magnetic induction that remains in a sample after it is magnetized and the magnetic field is removed. Residual induction is measured in Gauss.

Coercive force (NS) is the magnetic field strength that must be applied to the sample in order to reduce the residual induction to zero, i.e., demagnetize the sample. Coercive force is measured in oersteds.

Magnetic permeability μ characterizes the ability of a metal to be magnetized under determined by the formula

Iron, nickel, cobalt and gadolinium are attracted to the outside magnetic field much stronger than other metals, and constantly retain the ability to be magnetized. These metals are called ferromagnetic (from Latin word ferrum - iron), and their magnetic properties- ferromagnetism. When heated to a temperature of 768°C (Curie temperature), ferromagnetism disappears and the metal becomes non-magnetic.

Chemical properties. Chemical properties of metals and metal alloys name the properties that determine their relationship to the chemical effects of various active media. Each metal or metal alloy has a certain ability to resist the effects of these environments.

Chemical influences environments manifest themselves in various forms: iron rusts, bronze is covered with a green layer of oxide, steel, when heated in quenching furnaces without a protective atmosphere, oxidizes, turning into scale, and dissolves in sulfuric acid, etc. Therefore, for the practical use of metals and alloys, it is necessary to know them chemical properties. These properties are determined by the change in the weight of the test samples per unit of time per unit of surface. For example, the resistance of steel to scale formation (heat resistance) is determined by increasing the weight of the samples by 1 in 1 hour. dm surface area in grams (gain is obtained due to the formation of oxides).

Mechanical properties. Mechanical properties determine performance metal alloys when exposed to external forces. These include strength, hardness, elasticity, ductility, impact strength, etc.

To determine mechanical properties metal alloys they are subjected to various tests.

Trialtensile(break). This is the main test method used to determine the proportional limit σ pts, the yield strength σ s, tensile strength σ b relative elongation σ and relative contraction ψ.

For tensile testing, special samples are made - cylindrical and flat. They can be of different sizes, depending on the type of tensile testing machine used to test the metal.

The tensile testing machine operates as follows: the test sample is secured in the head clamps and gradually stretched with increasing force R until the break.

At the beginning of the test, under small loads, the sample is deformed elastically, its elongation is proportional to the increase in load. The dependence of the elongation of a sample on the applied load is called law of proportionality.

The greatest load that a sample can withstand without deviating from the law of proportionality is called beforeproportionality crowbar:

σ pc = Рр/Fo

FO mm 2.

As the load increases, the curve deviates to the side, i.e., the law of proportionality is violated. To the point R r the deformation of the sample was elastic. The deformation is called elastic if it completely disappears after unloading the sample. In practice, the elastic limit for steel is taken to be equal to the proportionality limit.

With a further increase in load (above the point R e) the curve begins to deviate significantly. The lowest load at which the sample is deformed without a noticeable increase in load is called yield strength:

σ s=Ps/Fo

Where , kgf;

F o - initial cross-sectional area of ​​the sample, mm 2. After the yield point, the load increases to a point R e, where it reaches its maximum. By dividing the maximum load by the cross-sectional area of ​​the sample, the tensile strength:

σb=Pb/Fo,

F o - initial cross-sectional area of ​​the sample, mm 2. At the point R k the sample breaks. By the change in the sample after rupture, the plasticity of the metal is judged, which is characterized by relative elongation δ and narrowing ψ.

Relative elongation is understood as the ratio of the increment in the length of the sample after rupture to its initial length, expressed as a percentage:

δ= l 1 - l 0 / l 0 · 100%

Where l 1 - length of the sample after rupture, mm;

l 0 - initial sample length, mm.

Relative contraction is the ratio of the reduction in the cross-sectional area of ​​the sample after rupture to its initial cross-sectional area

φ= F o- F 1 / F 0 · 100%,

Where F o - initial cross-sectional area of ​​the sample, mm 2;

F 1 - cross-sectional area of ​​the sample at the rupture site (neck), mm 2.

Creep test. Creep is a property metal alloys slowly and continuously deform plastically under constant load and high temperatures. The main purpose of the creep test is to determine the creep limit - the magnitude of the stress acting for a long time at a certain temperature.

For parts working long time at elevated temperatures, take into account only the creep rate during a steady process and set boundary conditions, for example 1°/o per 1000 hours. or 1°/o per 10,000 hours.

Trialfor impact strength. The ability of metals to resist impact loads is called impact strength. Structural steels are mainly subjected to impact strength testing, since they must have not only high static strength, but also high impact toughness.

For testing, take a sample of standard shape and size. The sample is cut in the middle so that it breaks in this place during the test.

The sample is tested as follows. The test sample is placed on the supports of the pendulum pile driver notch to the bed . Pendulum weight G raised to a height h 1 . When falling from this height, the pendulum destroys the sample with the edge of a knife, after which it rises to a height h 2 .

The work expended is determined from the weight of the pendulum and the height of its rise before and after the destruction of the sample. A.

Knowing the work of destruction of the sample, we calculate the impact strength:

α To=A/F

Where A- work spent on destruction of the sample, kgsm;

F - cross-sectional area of ​​the sample at the incision site, cm 2.

WayBrinell. The essence of this method is , that, using a mechanical press, a hardened steel ball is pressed into the metal under test under a certain load and the hardness is determined by the diameter of the resulting imprint.

Rockwell method. To determine hardness using the Rockwell method, a diamond cone with an apex angle of 120° is used, or steel ball with a diameter of 1.58 mm. With this method, it is not the diameter of the print that is measured, but the depth of indentation of a diamond cone or steel ball. The hardness is indicated by the indicator arrow immediately after the end of the test. When testing hardened parts with high hardness, a diamond cone and a load of 150 are used. kgf. In this case, hardness is measured on a scale WITH and denote H.R.C. If a steel ball and a load of 100 kgf are taken during testing, then the hardness is measured on a scale IN and denote HRB. When testing very hard materials or thin products, use a diamond cone and a load of 60 kgf. Hardness is measured on a scale A and denote HRA.

Parts for determining hardness on a Rockwell device must be well cleaned and not have deep marks. The Rockwell method allows you to accurately and quickly test metals.

Vickers method . When determining hardness using the Vickers method, a tetrahedral diamond pyramid with an interface angle of 136° is used as a tip pressed into the material. The resulting print is measured using a microscope included in the device. Then, using the table, find the hardness number H.V. When measuring hardness, one of the following loads is used: 5, 10, 20, 30, 50, 100 kgf. Small loads make it possible to determine the hardness of thin products and surface layers of nitrided and cyanidated parts. The Vickers instrument is commonly used in laboratories.

Method for determining microhardness . This method measures the hardness of very thin surface layers and some structural components. metal alloys.

Microhardness is determined using the PMT-3 device, which consists of a mechanism for indenting a diamond pyramid under a load of 0.005-0.5 kgf and metallographic microscope. As a result of the test, the length of the diagonal of the resulting print is determined, after which the hardness value is found from the table. Microsections with a polished surface are used as samples for determining microhardness.

Elastic recoil method. To determine hardness using the elastic recoil method, a Shore device is used, which operates as follows. On the well-cleaned surface of the test part from a height N the striker, equipped with a diamond tip, falls. Having struck the surface of the part, the striker rises to a height h. The hardness numbers are calculated based on the height of the striker's rebound. The harder the metal being tested, the greater the rebound height of the striker, and vice versa. Shore's device is used mainly to test the hardness of large crankshafts, connecting rod heads, cylinders and other large parts, the hardness of which is difficult to measure with other devices. Shore's device allows you to check ground parts without compromising the surface quality, however, the test results obtained are not always accurate.

Hardness conversion table

Imprint diameter (m m) according to Brinell, ball diameter 10 mm, load 3000 kgf	Hardness number according to
	Brinell NV	Rockwell scale				Vickers HV

Scratching method. This method, unlike those described, is characterized by the fact that during testing not only elastic and plastic deformation of the tested material occurs, but also its destruction.

Currently for testing hardness and quality heat treatment For steel blanks and finished parts without destruction, a device is used - an inductive flaw detector DI-4. This device operates on eddy currents excited by an alternating electromagnetic field, which is created by sensors in the controlled parts and the reference.

1. How are metals located in D.I. Mendeleev’s periodic table? How does the structure of metal atoms differ from the structure of non-metal atoms?
Metals are predominantly located on the left and bottom periodic table, i.e. mainly in groups I-III. And at the outer energy level, metals usually have from one to three electrons (although exceptions are possible: antimony and bismuth have 5 electrons, polonium has 6).

2. How do metal crystal lattices differ in structure and properties from ionic and atomic crystal lattices?
At the nodes of a metal crystal lattice there are positively charged ions and atoms, between which electrons move, and in the molecular and atomic crystal lattice Molecules and atoms are located at the nodes, respectively.

3. What are the general physical properties of metals? Explain these properties based on ideas about metallic bonding.

4. Why are some metals ductile (such as copper) and others brittle (such as antimony)?
Antimony has 5 electrons at the outer energy level, copper has 1. With an increase in the number of electrons, the strength of individual layers of ions is ensured, preventing their free sliding, reducing ductility.

5. When 12.9 g of an alloy consisting of copper and zinc was “dissolved” in hydrochloric acid, 2.24 liters of hydrogen (n.s.) were obtained. Calculate the mass fractions (in percent) of zinc and copper in this alloy.

6. Copper-aluminum alloy processed 60 g hydrochloric acid (mass fraction HCl – 10%). Calculate the mass and volume of the gas released (no.).

TEST TASKS

1. The most pronounced metallic properties are exhibited by simple substances whose atoms have the structure of an electron shell
1) 2e, 1e

2. The most pronounced metallic properties are exhibited by simple substances whose atoms have the structure of an electron shell
4) 2e, 8e, 18e, 8e, 2e

3. A solid substance having a crystal lattice conducts electricity well
3) metal