Metals. The most ductile metal? What are the most malleable metals

Metals (from Latin metallum - mine, mine) are a group of elements in the form of simple substances with characteristic metallic properties, such as high thermal and electrical conductivity, positive temperature coefficient of resistance, high ductility and metallic luster.

Of the 118 chemical elements discovered so far (not all of them are officially recognized), metals include:

6 elements in the alkali metal group,
6 in the group of alkaline earth metals,
38 in the group of transition metals,
11 in the group of light metals,
7 in the group of semimetals,
14 in the group lanthanides + lanthanum,
14 in the group actinides (the physical properties of not all elements have been studied) + actinium,
outside of certain groups beryllium and magnesium.

Thus, 96 of all discovered elements may be metals.

In astrophysics, the term "metal" can have a different meaning and denote all chemical elements heavier than helium

Characteristic properties of metals

Metallic luster (characteristic not only of metals: non-metals iodine and carbon in the form of graphite also have it)
Good electrical conductivity
Possibility of easy machining
High density (usually metals are heavier than non-metals)
High melting point (exceptions: mercury, gallium and alkali metals)
Great thermal conductivity
They are most often reducing agents in reactions.

Physical properties of metals

All metals (except mercury and, conditionally, francium) are in a solid state under normal conditions, but have different hardnesses. Below is the hardness of some metals on the Mohs scale.

Melting points pure metals range from −39 °C (mercury) to 3410 °C (tungsten). Most metals (except alkalis) have a high melting point, but some "normal" metals, such as tin and lead, can be melted on a regular electric or gas stove.

Depending on the density, metals are divided into light (density 0.53 ÷ 5 g/cm³) and heavy (5 ÷ 22.5 g/cm³). The lightest metal is lithium (density 0.53 g/cm³). It is currently impossible to name the heaviest metal, since the densities of osmium and iridium - the two heaviest metals - are almost equal (about 22.6 g/cm³ - exactly twice the density of lead), and calculating their exact density is extremely difficult: for this you need completely clean the metals, because any impurities reduce their density.

Most metals plastic, that is, the metal wire can be bent without breaking. This occurs due to the displacement of layers of metal atoms without breaking the bond between them. The most ductile are gold, silver and copper. Gold can be used to make foil 0.003 mm thick, which is used for gilding products. However, not all metals are ductile. Wire made of zinc or tin crunches when bent; When deformed, manganese and bismuth hardly bend at all, but immediately break. Plasticity also depends on the purity of the metal; Thus, very pure chromium is very ductile, but, contaminated with even minor impurities, it becomes brittle and harder. Some metals such as gold, silver, lead, aluminum, osmium can grow together, but this can take decades.

All metals are good conduct electric current; this is due to the presence in their crystal lattices of mobile electrons moving under the influence of an electric field. Silver, copper and aluminum have the highest electrical conductivity; for this reason, the latter two metals are most often used as wire materials. Sodium also has very high electrical conductivity; in experimental equipment, attempts are known to use sodium conductors in the form of thin-walled stainless steel pipes filled with sodium. Due to the low specific gravity of sodium, with equal resistance, sodium “wires” are much lighter than copper and even somewhat lighter than aluminum.

The high thermal conductivity of metals also depends on the mobility of free electrons. Therefore, the series of thermal conductivities is similar to the series of electrical conductivities, and the best conductor of heat, as well as electricity, is silver. Sodium also finds use as a good conductor of heat; It is widely known, for example, that sodium is used in valves of automobile engines to improve their cooling.

Color Most metals are approximately the same - light gray with a bluish tint. Gold, copper and cesium are yellow, red and light yellow, respectively.

Chemical properties of metals

At the external electronic level, most metals have a small number of electrons (1-3), so in most reactions they act as reducing agents (that is, they “donate” their electrons)

Reactions with simple substances

All metals except gold and platinum react with oxygen. The reaction with silver occurs at high temperatures, but silver(II) oxide is practically not formed, since it is thermally unstable. Depending on the metal, the output may include oxides, peroxides, and superoxides:

lithium oxide

sodium peroxide

potassium superoxide

To obtain an oxide from peroxide, the peroxide is reduced with a metal:

With medium and low-active metals, the reaction occurs when heated:

Only the most active metals react with nitrogen; at room temperature only lithium reacts, forming nitrides:

When heated:

All metals except gold and platinum react with sulfur:

Iron reacts with sulfur when heated, forming sulfide:

Only the most active metals, that is, metals of groups IA and IIA except Be, react with hydrogen. Reactions occur when heated, and hydrides are formed. In reactions, the metal acts as a reducing agent, the oxidation state of hydrogen is −1:

Only the most active metals react with carbon. In this case, acetylenides or methanides are formed. When reacting with water, acetylenides give acetylene, methanides give methane.

Plasticity is the ability of a metal to deform plastically without collapsing under the influence of external forces. This is one of the important mechanical properties of metal, which, combined with high strength, makes it the main structural material. No samples or equipment are required to determine ductility. Indicators (characteristics) of plasticity - relative elongation (delta) and narrowing
(xi).

Relative elongation is called the ratio of absolute elongation, i.e. the increment in the calculated length of the sample after rupture
, to its original design length , mm, expressed as a percentage:

%, (2)

Where – sample length after rupture, mm.

Relative narrowing
is called the absolute contraction ratio, i.e. the reduction in the cross-sectional area of the sample after rupture
, to its original cross-sectional area mm 2, expressed as a percentage:

%, (3)

Where – cross-sectional area of the sample after rupture, mm 2 .

Hardness of metals

Hardness is the property of a metal to resist the penetration of another harder body into it. To determine hardness, the manufacture of special samples is not required; tests are carried out without destroying the metal.

The hardness of the metal is determined by direct and indirect methods: indentation, scratching, elastic recoil, magnetic.

In direct methods, a hard tip (indenter) of various shapes (ball, cone, pyramid) made of hardened steel, diamond or hard alloy is pressed into the metal. After removing the load on the indenter, an imprint remains in the metal, which characterizes hardness.

Brinell method. A hardened steel ball with a diameter of 10 mm is pressed into the flat surface of the metal (Figure 2). After removing the load, an imprint (hole) remains in the metal. The diameter of the print d is measured with a special microscope with an accuracy of 0.05 mm. In practice, a special table is used, in which the diameter of the indentation d corresponds to a certain hardness number HB.

Ball diameter D and load P set depending on the hardness and thickness of the metal being tested. For example, for steel and cast iron the load R= 3000 kg; D= 10 mm. The hardness of technically pure iron according to Brinell is 80 - 90 units.

a – according to Brinell; b – according to Rockwell

Figure 2 - Hardness test scheme

The Brinell method is not recommended for metals with a hardness greater than HB 450, since the ball may deform and result in a distorted result. This method is mainly used to measure the hardness of workpieces and semi-finished products made of unhardened metal.

Rockwell method. Hardness is determined by the depth of the indentation. The indenter is a hardened steel ball with a diameter of 1.58 mm for soft metals or a diamond cone with an apex angle of 120º for hard and superhard (more than HRC 70) metals (Figure 2, b).

The ball and cone are pressed into the metal under the action of two loads - preliminary and main. The total load is equal to their sum. The preload is assumed to be the same for all metals (10 kg). Before starting the test, the large arrow of the hardness meter is set to “0” on the indicator scale, and then the main load is turned on - the large arrow moves along the indicator scale and shows the hardness value.

When pressing a steel ball, the load is 100 kg, the hardness is measured using the internal (red) scale of the indicator, the hardness is designated HRB. When pressing the diamond cone, the hardness is determined by the arrow reading on the outer (black) scale of the indicator. For hard metals the main load is 150 kg. This is the main method for measuring the hardness of hardened steels. Hardness designation - HRC.

For very hard and thin materials, the load is assumed to be 60 kg. Hardness designation – HRA.

The Rockwell hardness method allows you to test soft and hard metals, while the marks from the ball or cone are very small, so this method can also measure the hardness of finished parts. The test surface must be polished. Measurements are carried out quickly (within 30 - 60 s); no calculations are required, since the hardness value is read on the scale of the hardness tester indicator.

Vickers method. A tetrahedral diamond pyramid is pressed into the test surface (ground or polished) under a load of 5, 10, 20, 30, 50 or 100 kg. A square imprint is left in the metal. Using a special hardness tester microscope, the diagonal of the print is measured (Figure 3).

Figure 3 - Vickers hardness test scheme

Knowing the load on the pyramid and the diagonal of the imprint, the hardness of the metal HV is determined from the tables.

The method is universal. It can be used to determine the hardness of parts of small thickness and thin surface layers of high hardness (after nitriding, nitrocimentation, etc.). The thinner the metal, the less the load on the pyramid should be, but with a large load the result is more accurate.

Before you find out which element from the periodic table is awarded the title of “the most ductile metal,” you need to clearly understand what ductility is. This is one of the physical properties associated with the structure of the metal.

Plasticity is the ability to take on a new shape without causing ionic bonds to break. In practice, the result of plasticity is good malleability, due to which metals can be used in industry, medicine, electrical engineering and households. Of the 126 elements in the periodic table, gold is recognized as the most ductile metal. Thanks to today's technologies, it can be pulled out into the thinnest thread, which will not be visible to the human eye.

Metal properties

Why do jewelry makers and repairers put gold first? First of all, this is due to its excellent ductility: from 1 gram of metal, a wire up to 3 kilometers long can be drawn, gold ingots are forged into sheets, the thickness of which is measured in ten thousandths of a millimeter. The domes of temples are covered with this gold; it is called leaf. It looks quite interesting: when exposed to light it gives a blue-green tint.

Pure gold can dissolve in aqua regia. This is the name given to a mixture of two concentrated acids: nitric and hydrochloric. The most ductile metal in the table is number 79, melting point is 1064 ° C, density is 19.32 g/cm3. In terms of thermal conductivity and electrical resistance, gold is second only to silver and copper.

Gold in its pure form is too soft, so jewelry is usually made from alloys. Most often, silver or copper is added to gold. Have you ever wondered what “test” means on jewelry? This is the pure gold content in parts per thousand. 999 purity is considered pure gold.

Application

Gold has long been used as an investment object; in addition, it has found active use in the jewelry industry.

In many countries, gold coins were used as money. Despite this, it was recognized as a world currency only in the 19th century. In 1922, bank notes with gold content, called “chervonets”, appeared in circulation in Russia. One bank note was equivalent to 10 gold rubles of the old coinage.

Gold is the most common material used in jewelry making. The higher the gold purity, the better resistance to corrosion the material will have; silver and copper give the product strength and different shades of color.

Ductility is a measure of a metal's ability to withstand tensile stress—any force that pulls two ends of a material away from each other. The game of tug of war serves as a good example of tensile strength applied to a rope. Plasticity is the plastic deformation resulting from such deformations. The term "ductile" literally means that a metallic substance is capable of being stretched into a thin wire and it does not become weaker or brittle in the process.

Metals with high or low ductility

Metals with high ductility, such as copper, can be drawn into long, thin wires without breaking. Copper has historically been an excellent conductor of electricity, but the metal can conduct almost anything. Metals with low ductility, such as bismuth, instead rupture when they are subjected to tensile stress.

Strength and bendability

In contrast, malleability is a measure of a metal's ability to withstand compression such as impact, rolling, or extrusion. Although the two concepts may seem similar on the surface, metals that are ductile are not necessarily malleable. A common example of the difference between these two properties is lead, which is highly malleable but not very ductile due to its crystalline structure. The crystal structure of metals dictates how they will deform under stress.

The atomic particles that matting metals can deform under stress either slide over each other or are pulled apart from each other.

The crystal structure of more ductile metals allows the metal atoms to stretch further, a process called "twinning." More ductile metals are those that are more easily close, and they also deform more easily in other directions.

Effect of temperature

Plasticity in metals is also related to temperature.

When metals are heated, they typically become less brittle, resulting in plastic deformation. In other words, most metals become more ductile when heated and are easier to pull into wires without breaking. Certificate is an exception to this rule as it becomes more brittle as it heats up.

What are the most malleable metals?

While it is difficult to compare ductility between metals, gold and platinum are considered the most ductile. It is said that gold can be drawn into wires so beautifully that one ounce of the metal can reach up to fifty miles.

most ductile metal?

Indium
aluminum
Alkali metals are the most ductile.
Sodium. You can cut it off with a knife and roll it into foil with a bottle.
The one from which the nose fairing of rockets is made.
Gold.
And also bobbit and lead (after gold). Gold is listed in the Guinness Book of Records as one of the most ductile metals.
Gold from 1g of the substance can be used to make a dart 2.4 km long
everything depends on the temperature.
Mercury, although it is under normal conditions
liquid, can hardly be called plastic due to the extremely high
surface tension coefficient)) but this is closer to a joke.
A plastic material is not one that does not spring, but one that
which does not undergo ruptures and has irreversible fluidity. Therefore, gold, which can be rolled out into a transparent leaf, is one of the most ductile, and its chemical neutrality allows it to remain intact for a long time.
The plasticity of gold is also manifested in the fact that it can diffuse in solid form along with lead. Two plates placed one on top of the other under pressure for a long time penetrate one another and grow together.