Chemical properties of zinc and its compounds

Zinc is a typical representative of the group of metallic elements and has the full range of their characteristics: metallic luster, ductility, electrical and thermal conductivity. However, the chemical properties of zinc differ somewhat from the basic reactions inherent in most metals. An element can behave like a nonmetal under certain conditions, for example, react with alkalis. This phenomenon is called amphotericity. In our article we will study the physical properties of zinc, and also consider typical reactions characteristic of the metal and its compounds.

Position of the element in the periodic table and distribution in nature

The metal is located in a secondary subgroup of the second group of the periodic table. In addition to zinc, it contains cadmium and mercury. Zinc belongs to the d-elements and is in the fourth period. In chemical reactions, its atoms always give up electrons of the last energy level, therefore, in such compounds of the element as oxide, intermediate salts and hydroxide, the metal exhibits an oxidation state of +2. The structure of the atom explains all the physical and chemical properties of zinc and its compounds. The total metal content in the soil is approximately 0.01 wt. %. It is found in minerals such as galmea and zinc blende. Since the zinc content in them is low, the rocks are first subjected to enrichment, which is carried out in shaft furnaces. Most zinc-containing minerals are sulfides, carbonates and sulfates. These are zinc salts, the chemical properties of which underlie their processing processes, such as roasting.

What are amphoteric metals?

The list of amphoteric metals includes many items. Some of them can be confidently called amphoteric, some - presumably, others - conditionally. If we consider the issue on a large scale, then for brevity we can simply name the serial numbers of the above mentioned metals. These numbers are: 4.13, from 22 to 32, from 40 to 51, from 72 to 84, from 104 to 109. But there are metals that can be called basic. These include chromium, iron, aluminum and zinc. Strontium and beryllium complete the main group. The most common of all listed at the moment is aluminum. Its alloys have been used for many centuries in a wide variety of fields and applications. The metal has excellent anti-corrosion resistance and is easy to cast and various types of machining. In addition, the popularity of aluminum is complemented by such advantages as high thermal conductivity and good electrical conductivity.

Aluminum is an amphoteric metal that tends to exhibit chemical activity. The durability of this metal is determined by a strong oxide film and, under normal environmental conditions, during chemical reactions, aluminum acts as a reducing element. Such an amphoteric substance is capable of interacting with oxygen in the event of fragmentation of the metal into small particles. Such interaction requires the influence of high temperature conditions. A chemical reaction upon contact with an oxygen mass is accompanied by a huge release of thermal energy. At temperatures above 200 degrees, the interaction of reactions when combined with a substance such as sulfur forms aluminum sulfide. Amphoteric aluminum is not able to directly interact with hydrogen, and when this metal is mixed with other metal components, various alloys containing intermetallic compounds arise.

Iron is an amphoteric metal, which is one of the side subgroups of group 4 of the period in the system of elements of the chemical type. This element stands out as the most common component of the group of metallic substances in the components of the earth's crust. Iron is classified as a simple substance, among the distinctive properties of which are its malleability and silvery-white color. Such a metal has the ability to provoke an increased chemical reaction and quickly goes into the stage of corrosion when exposed to high temperatures. Iron placed in pure oxygen burns out completely, and when brought to a finely dispersed state it can spontaneously ignite in plain air. When exposed to air, a metallic substance quickly oxidizes due to excessive humidity, that is, it rusts. When burning in an oxygen mass, a kind of scale is formed, which is called iron oxide.

Metal production

The severe oxidation reaction of zinc carbonate or sulfide produces its oxide. The process takes place in a fluidized bed. This is a special method based on close contact of finely ground mineral and a stream of hot air moving at high speed. Next, zinc oxide ZnO is reduced with coke and the resulting metal vapors are removed from the reaction sphere. Another method of producing metal, based on the chemical properties of zinc and its compounds, is electrolysis of a solution of zinc sulfate. It is a redox reaction that occurs under the influence of electric current. High purity metal is deposited on the electrode.

Production

As stated, zinc is not found in nature in its pure form. It is mainly obtained from polymer ores. In these ores, zinc is present in the form of sulfide. It always comes with the accompanying metals listed above.

The selective flotation beneficiation process produces zinc concentrate. In parallel with this process, other substance concentrates are released from polymetallic ores. For example, lead and copper.

The resulting zinc concentrates are fired in a furnace. As a result of high temperatures, zinc changes from the sulfide state to the oxide state. During the production process, sulfur dioxide is released, which is used to produce sulfuric acid. Pure zinc is obtained from zinc oxide by two methods: pyrometallurgical and electrolytic.

The pyrometallurgical method has a very long history. The concentrate is fired and subjected to a sintering process. The zinc is then reduced using coal or coke. The zinc obtained by this method is brought to a pure state by settling.
In the electrolytic method, zinc concentrate is treated with sulfuric acid. The result is a solution that is subjected to the process of electrolysis. Here the zinc is deposited and melted in special furnaces.

Physical characteristics

A bluish-silver, brittle metal under normal conditions. In the temperature range from 100° to 150°, zinc becomes flexible and can be rolled into sheets. When heated above 200°, the metal becomes unusually brittle. Under the influence of atmospheric oxygen, pieces of zinc are covered with a thin layer of oxide, and upon further oxidation it turns into hydroxycarbonate, which plays the role of a protector and prevents further interaction of the metal with atmospheric oxygen. The physical and chemical properties of zinc are interrelated. Let's consider this using the example of the interaction of a metal with water and oxygen.

In food

The element is found in meat, cheese, sesame seeds, oysters, chocolate, legumes, oatmeal, sunflower and pumpkin seeds, and is often present in mineral water. The highest percentage of zinc is found in the following products (per 100 grams):

Oysters (up to 40 mg), anchovies (1.72 mg), octopus (1.68 mg), carp (1.48 mg), caviar (up to 1 mg), herring (about 1 mg).
Pumpkin seeds (10 mg), sesame seeds (7 mg), sunflower seeds (5.3 mg), peanuts (4 mg), walnuts (3 mg), almonds (3 mg).
Beef (up to 8.4 mg), lamb (up to 6 mg), beef liver (4 mg), pork (up to 3.5 mg), chicken (up to 3.5 mg).
Cocoa powder without sugar and sweeteners (6.81 mg), pure dark chocolate (2.3 mg), chocolate candies (up to 2 mg depending on the amount and type of chocolate).
Lentils (4.78 mg), oats (3.97 mg), wheat (3.46 mg), soybeans (3 mg), rye (2.65 mg), bread (up to 1.5 mg), green peas (1.24 mg), peas (1.2 mg), bamboo shoots (1.1 mg), rice (1 mg), cereal cookies (up to 1 mg).
Hard cheese (up to 4 mg).

Redox reactions involving zinc

Since the element comes before hydrogen in the activity series of metals, it is able to displace it from acid molecules.

The reaction products between zinc and acids will depend on two factors:

type of acid
its concentration

Dilute sulfuric acid, which does not exhibit pronounced oxidizing properties, reacts with the metal according to the following scheme:

H₂SO₄ + Zn = ZnSO₄ + H₂↑

Reactions of the element with phosphoric and dilute sulfuric acids proceed in the same way. The chemical properties and reactions of zinc with nitrate acid have their own characteristics. A dilute solution of nitric acid of average concentration and zinc interact with each other to form nitrogen oxide (II), water and an average salt - zinc nitrate. Concentrated nitrate acid reacts with the metal in such a way that nitric oxide (IV), average salt and water can be detected in the products.

A very dilute solution of nitric acid and zinc as a reducing agent react to form zinc nitrate, water, and several possible products: ammonia, free nitrogen, or nitric oxide.

Features of smelting

The temperature required to melt zinc should be less than 419 C o, but not more than 480 C o. Otherwise, metal waste will increase and wear on the walls of the bath, which is usually made from iron, will increase. In the molten state, no more than 0.05% iron admixture is allowed, otherwise the temperature required for melting will begin to rise. If the percentage of iron content exceeds 0.2%, zinc cannot be rolled.

Zinc is obtained from polymetallic ores, which can contain up to 4% of the element . If the ores have been enriched by selective flotation, up to 60% of zinc concentrates can be obtained from them, the rest will be occupied by concentrates of other metals. Zinc concentrates are fired in furnaces in a fluidized bed, after which zinc sulfide turns into oxide and sulfur dioxide is released. The latter is consumed: sulfuric acid is obtained from it.

To convert zinc oxide into the metal itself, two methods are used.

Distillation or pyrometallurgical. The concentrate is fired, then sintered to impart gas permeability and granularity and reduced with coke or coal at temperatures of 1200-1300 C o. During the reaction, metal vapors are formed, which are condensed and poured into molds. The purity of zinc reaches 98.7%, after which it can be increased to 99.995% using rectification, but the latter method is quite expensive and complex.
Electrolytic or hydrometallurgical. The fired concentrates are treated with sulfuric acid, the solution is cleaned of impurities using zinc dust and subjected to electrolysis in bathtubs lined with lead or vinyl plastic. Zinc is deposited on aluminum cathodes, from where it is collected and melted in induction furnaces. The purity of the metal obtained by this method reaches 99.95%.

Chemical properties of zinc

The reaction equations for the interaction of a metal with alkali solutions confirm its amphoteric properties. Complex salts - tetrahydroxycinates and hydrogen - are found in the products.

Zn + 2NaOH + 2H2O = Na2 [Zn(OH)4] + H2

By fusing solid alkali and metal, they obtain salts of another type - zincates. A by-product of such a process will also be hydrogen gas.

Zn + 2KOH = K2ZnO2 + H2

The metal actively interacts with halogens, for example, chlorine, bromine or iodine, as well as with nitrogen, sulfur and carbon. As a result, intermediate salts are formed - nitrides, sulfides or carbides.

In the activity series of metals, zinc is placed before hydrogen and is therefore an active metal. However, it is inferior in its properties to alkali and alkaline earth metals.

Properties of the metals Al and Zn as simple substances

Zinc is a fairly dense metal. It retains its qualities in a small temperature range: at low temperatures (up to -30) it becomes brittle, at temperatures above 1000 C it is very plastic. This is used in metallurgy by rolling zinc sheets a few millimeters thick (zinc foil). Some impurities dramatically increase the fragility of the metal, so purified material is used.

Al is a highly ductile light metal with a low melting point. It has high malleability and electrical conductivity.

In air it is covered with an oxide film and therefore practically does not corrode. Due to this, it is used in the manufacture of wires and machinery housings.

Use of zinc in galvanic cells

The chemical properties of zinc underlie the operating principle of various types of galvanic devices. The manganese-zinc element is the most common in technology. It works by undergoing a redox reaction between the metal and manganese dioxide. Both electrodes are made from them and placed inside the device. The active substance - ammonium chloride - has the form of a paste, or porous plates inserted between the cathode and anode are impregnated with it. The zinc air element is represented by a negative zinc electrode - cathode. The anode is a carbon-graphite rod filled with air. Solutions of ammonium chloride or sodium hydroxide are used as an electrolyte.

Interaction with simple substances

with oxygen

Without heating, beryllium and magnesium do not react with either atmospheric oxygen or pure oxygen due to the fact that they are covered with thin protective films consisting of BeO and MgO oxides, respectively. Their storage does not require any special methods of protection from air and moisture, unlike alkaline earth metals, which are stored under a layer of liquid inert to them, most often kerosene.

Be, Mg, Ca, Sr, when burned in oxygen, form oxides of the composition MeO, and Ba - a mixture of barium oxide (BaO) and barium peroxide (BaO2):

2Mg + O2 = 2MgO

2Ca + O2 = 2CaO

2Ba + O2 = 2BaO

Ba + O2 = BaO2

It should be noted that during the combustion of alkaline earth metals and magnesium in air, a side reaction of these metals with air nitrogen also occurs, as a result of which, in addition to metal compounds with oxygen, nitrides with the general formula Me3N2 are also formed.

with halogens

Beryllium reacts with halogens only at high temperatures, and the rest of the Group IIA metals - already at room temperature:

Mg + I2 = MgI2 – magnesium iodide

Ca + Br2 = CaBr2 – calcium bromide

Ba + Cl2 = BaCl2 – barium chloride

with non-metals of groups IV–VI

All metals of group IIA react when heated with all nonmetals of groups IV–VI, but depending on the position of the metal in the group, as well as the activity of the nonmetals, varying degrees of heating are required. Since beryllium is the most chemically inert among all Group IIA metals, its reactions with non-metals require a significantly higher temperature.

It should be noted that the reaction of metals with carbon can form carbides of different natures. There are carbides that belong to methanides and are conventionally considered derivatives of methane, in which all hydrogen atoms are replaced by metal. They, like methane, contain carbon in the -4 oxidation state, and when they are hydrolyzed or interact with non-oxidizing acids, one of the products is methane. There is also another type of carbides - acetylenides, which contain the C22- ion, which is actually a fragment of the acetylene molecule. Carbides such as acetylenides, upon hydrolysis or interaction with non-oxidizing acids, form acetylene as one of the reaction products. The type of carbide - methanide or acetylenide - obtained when a particular metal reacts with carbon depends on the size of the metal cation. Metal ions with a small radius usually form metanides, and larger ions form acetylenides. In the case of metals of the second group, methanide is obtained by the interaction of beryllium with carbon:

The remaining metals of group II A form acetylenides with carbon:

With silicon, group IIA metals form silicides - compounds of the Me2Si type, with nitrogen - nitrides (Me3N2), with phosphorus - phosphides (Me3P2):

with hydrogen

All alkaline earth metals react with hydrogen when heated. In order for magnesium to react with hydrogen, heating alone, as in the case of alkaline earth metals, is not enough; in addition to high temperature, increased hydrogen pressure is also required. Beryllium does not react with hydrogen under any conditions.

Zinc oxide

A white porous powder that turns yellow when heated and returns to its original color when cooled is a metal oxide. The chemical properties of zinc oxide and the reaction equations for its interaction with acids and alkalis confirm the amphoteric nature of the compound. Thus, the substance cannot react with water, but interacts with both acids and alkalis. The reaction products will be medium salts (in case of interaction with acids) or complex compounds - tetrahydroxocinates.

Zinc oxide is used in the production of white paint, which is called zinc white. In dermatology, the substance is included in ointments, powders and pastes that have an anti-inflammatory and drying effect on the skin. Most of the zinc oxide produced is used as a filler for rubber. Continuing to study the chemical properties of zinc and its compounds, let's consider Zn(OH)2 hydroxide.

Where are amphoteric metals used?

Chemical properties of alkaline earth metals.
list of alkaline earth metals Areas of application:

Manufacturing of parts for seismic and speed sensors, clock mechanisms, torque.
Production of parts for equipment that will interact with aggressive factors.
Reinforcement of high pressure pipes.
Shipbuilding, aircraft construction.
Production of household appliances and tools. These include cutlery, tape measures, razor blades, and kitchen utensils.
Assembly of video recording equipment.

Every year more and more chemical compounds appear. Thanks to this, new amphoteric metals are discovered. They are called materials of the future, but their popularity is growing slowly. This is due to the high cost and small size of finished products.

https://youtube.com/watch?v=BZIhw3pQFQs

Amphoteric nature of zinc hydroxide

The white precipitate that precipitates under the action of alkali on solutions of metal salts is the base of zinc. The compound dissolves quickly when exposed to acids or alkalis. The first type of reaction ends with the formation of medium salts, the second - zincates. Complex salts—hydroxycinates—are isolated in solid form. A special feature of zinc hydroxide is its ability to dissolve in an aqueous solution of ammonia to form tetraamminium zinc hydroxide and water. Zinc base is a weak electrolyte, therefore both its average salts and zincates in aqueous solutions are hydrolyzable, that is, their ions react with water and form zinc hydroxide molecules. Solutions of metal salts such as chloride or nitrate will be acidic due to the accumulation of excess hydrogen ions.

History of discovery.

Also on topic:
CHEMICAL ELEMENTS

Zinc (like gold, silver, copper, mercury, lead, tin and iron) belongs to the metals of antiquity, the date of discovery of which is lost in the centuries.

The reduction of zinc oxide with charcoal requires a temperature of at least 1000 ° C. Since the metal at this temperature is in a vapor state and is easily oxidized, the isolation of zinc requires the ability to condense metal vapor, and this must be done in the absence of air, otherwise the metal will turn into oxide.

Also on topic:

CHEMICAL ELEMENTS IN NATURE – CYCLE AND MIGRATION

The production of zinc alloys from mixed ores does not require the isolation of zinc itself and is easier to achieve. The small amounts of zinc present in ancient Egyptian copper samples reflect the composition of local ores, but for the smelting of Palestinian brass dating from 1400–1000 BC. and containing about 23% zinc, copper ore must have been deliberately mixed with zinc ore. Brass was also obtained in Cyprus and, later, in the Cologne area (Germany). Chinese craftsmen mastered the art of zinc smelting in the Middle Ages. Zinc coins were used during the Ming Dynasty (1368–1644).

There was no dedicated production of zinc in medieval Europe, although small quantities were obtained in the production of lead, silver and brass. Beginning around 1605, it was imported from China by the East India Company. The English zinc industry emerged in the Bristol area in the early 18th century, and its products quickly spread to Silesia and Belgium.

The origin of the element's name is unclear, but it seems plausible that it is derived from Zinke (German for "point" or "tooth"), due to the appearance of the metal.

Distribution of zinc in nature and its industrial extraction. The zinc content in the earth's crust is 7.6 10–3%, it is approximately the same as rubidium (7.8 10–3%) and slightly more abundant than copper (6.8 10–3%) .

The main zinc minerals are zinc sulfide ZnS (known as zincblende or sphalerite) and zinc carbonate ZnCO3 (calamine in Europe, smithsonite in the US). This mineral received its name in honor of James Smithson, founder of the Smithsonian Institution in Washington. Less important minerals are hemimorphite Zn4Si2O7(OH)2·H2O and franklinite (Zn,Fe)O·Fe2O3.

Canada ranks first in the world in terms of production (16.5% of world production, 1113 thousand tons, 1995) and reserves of zinc. In addition, rich zinc deposits are concentrated in China (13.5%), Australia (13%), Peru (10%), USA (10%), Ireland (about 3%).

Zinc mining is carried out in 50 countries. In Russia, zinc is extracted from copper pyrite deposits in the Urals, as well as from polymetallic deposits in the mountains of Southern Siberia and Primorye. Large zinc reserves are concentrated in Rudny Altai (Eastern Kazakhstan), which accounts for more than 50% of zinc production in the CIS countries. Zinc is also mined in Azerbaijan, Uzbekistan (Almalyk deposit) and Tajikistan.

Characteristics of simple substances and industrial production of metallic zinc. Metallic zinc has a characteristic bluish luster on a fresh surface, which it quickly loses in humid air. Melting point 419.58° C, boiling point 906.2° C, density 7.133 g/cm3. At room temperature, zinc is brittle, at 100–150° C it becomes ductile and is easily rolled into thin sheets and wire, and at 200–250° C it again becomes very brittle and can be crushed into powder.

When heated, zinc reacts with non-metals (except hydrogen, carbon and nitrogen). Reacts actively with acids:

Zn + H2SO4(dil.) = ZnSO4 + H2

Zinc is the only element of the group that dissolves in aqueous solutions of alkalis to form [Zn(OH)4]2– ions (hydroxycinates):

Zn + 2OH– + 2H2O = [Zn(OH)4]2– + H2

When metallic zinc is dissolved in an ammonia solution, an ammonia complex is formed:

Zn + 4NH3 H2O = [Zn(NH3)4](OH)2 + 2H2O + H2

The initial raw materials for the production of metallic zinc are zinc sulfide and polymetallic ores. Isolation of zinc begins with the concentration of ore using sedimentation or flotation methods, then it is roasted to form oxides:

2ZnS + 3O2 = 2ZnO + SO2

The resulting sulfur dioxide is used in the production of sulfuric acid, and zinc oxide is processed electrolytically or smelted with coke.

In the first case, zinc is leached from the crude oxide with a dilute solution of sulfuric acid. In this case, cadmium is deposited with zinc dust:

Zn + Cd2+ = Zn2+ + Cd

The zinc sulfate solution is then subjected to electrolysis. Metal of 99.95% purity is deposited on aluminum cathodes.

The reduction of zinc oxide by coke is described by the equation:

2ZnO + C = 2Zn + CO2

Zinc smelting previously used rows of highly heated horizontal retorts intermittently, then these were replaced by continuously operating vertical retorts (in some cases, electrically heated). These processes were not as thermally efficient as the blast furnace process, in which the combustion of heating fuel is carried out in the same chamber as the oxide reduction, however the inevitable problem in the case of zinc is that the reduction of zinc oxide by carbon does not proceed below the boiling point of zinc ( This problem does not exist for iron, copper or lead), so subsequent cooling is necessary to condense the vapors. In addition, in the presence of combustion products, the metal is re-oxidized.

This problem can be solved by spraying the zinc vapors coming out of the furnace with molten lead. This results in rapid cooling and dissolution of the zinc, so that re-oxidation of the zinc is minimized. The nearly 99% pure zinc is then isolated as a liquid and further purified by vacuum distillation to 99.99% pure. All cadmium present is recovered during distillation. The advantage of the blast furnace is that the composition of the charge is not critical, so mixed ores of zinc and lead (ZnS and PbS are often found together) can be used to continuously produce both metals. Lead is released from the bottom of the furnace.

According to experts, in 2004 zinc production amounted to 9.9 million tons, and its consumption was about 10.2 million tons. Thus, the zinc deficit on the world market is 250–300 thousand tons.

In 2004, the production of refined zinc in China reached 2.46 million tons. Canada and Australia produce approximately 1 million tons each. The price of zinc at the end of 2004 was more than $1,100 per ton.

Demand for the metal remains high, thanks to rapid growth in the production of anti-corrosion coatings. To obtain such coatings, various methods are used: immersion in molten zinc (hot galvanizing), electrolytic deposition, liquid metal spraying, heating with zinc powder and the use of paints containing zinc powder. Galvanized sheet is widely used as roofing material. Metallic zinc in the form of bars is used to protect steel products in contact with sea water from corrosion. Zinc alloys - brass (copper plus 20–50% zinc) are of great practical importance. In addition to brass, a rapidly growing number of special zinc alloys are used for die casting. Another application is in the production of dry cell batteries, although this has declined significantly in recent years.

Approximately half of all zinc produced is used to produce galvanized steel, one third is used in hot-dip galvanizing of finished products, and the rest is used for strip and wire. Over the past 20 years, the global market for these products has more than doubled, increasing on average by 3.7% per year, and in Western countries, metal production is increasing annually by 4.8%. Currently, galvanizing 1 ton of steel sheet requires an average of 35 kg of zinc.

According to preliminary estimates, in 2005, zinc consumption in Russia may amount to about 168.5 thousand tons per year, including 90 thousand tons will be used for galvanizing, 24 thousand tons - for semi-finished products (brass, rolled zinc, etc.), 29 thousand tons - for the chemical industry (paints and varnishes, rubber products), 24.2 thousand tons - for foundry zinc alloys.

Characteristics of zinc sulfate

The chemical properties of zinc that we examined earlier, in particular, its reactions with dilute sulfate acid, confirm the formation of an average salt - zinc sulfate. These are colorless crystals, which, when heated to 600° and above, can produce oxosulfates and sulfur trioxide. With further heating, zinc sulfate is converted to zinc oxide. The salt is soluble in water and glycerin. The substance is isolated from solution at temperatures up to 39°C in the form of crystalline hydrate, the formula of which is ZnSO4 × 7H2O. In this form it is called zinc sulfate.

In the temperature range 39°-70°, a hexahydrate salt is obtained, and above 70° only one molecule of water remains in the crystalline hydrate. The physicochemical properties of zinc sulfate make it possible to use it as a bleach in paper production, as a mineral fertilizer in crop production, and as a fertilizer in the diet of domestic animals and poultry. In the textile industry, the compound is used in the production of viscose fabric and in the dyeing of chintz.

Zinc sulfate is also included in the electrolyte solution used in the process of galvanic coating of iron or steel products with a layer of zinc using the diffuse method or hot-dip galvanizing method. A layer of zinc protects such structures from corrosion for a long time. Considering the chemical properties of zinc, it should be noted that in conditions of high salinity of water, significant fluctuations in temperature and air humidity, galvanizing does not give the desired effect. Therefore, metal alloys with copper, magnesium and aluminum are widely used in industry.

Historical reference

The name “zinc” itself was first mentioned in the book “Liber Mineralium” by Paracelsus. According to some sources, it meant “prong.” The alloy of zinc with copper or brass has been known for a long time. It was used in Ancient Greece, India and Ancient Egypt, and later the material became known in China.

The metal was obtained in its pure form only in the first half of the 18th century in 1738 in Great Britain using the distillation method. Its discoverer was William Champion. Industrial production began 5 years later, and in 1746 in Germany, the chemist Andreas Sigismund Marggraff developed and described in detail his own method for producing zinc . He proposed using the method of calcining a mixture of metal oxide and coal in fireproof clay retorts without air access. Subsequent condensation of the vapors had to take place in the refrigerator. Due to his detailed description and painstaking development, Marggraf is often called the discoverer of the substance.

Application of alloys containing zinc

Transporting many chemicals, such as ammonia, through pipelines requires special requirements for the composition of the metal from which the pipes are made. They are made on the basis of alloys of iron with magnesium, aluminum and zinc and have high anti-corrosion resistance to aggressive chemical environments. In addition, zinc improves the mechanical properties of alloys and neutralizes the harmful effects of impurities such as nickel and copper. Copper and zinc alloys are widely used in industrial electrolysis processes. Tankers are used to transport petroleum products. They are built from aluminum alloys containing, in addition to magnesium, chromium and manganese, a large proportion of zinc. Materials of this composition not only have high anti-corrosion properties and increased strength, but also cryogenic resistance.

Mixtures and alloys

To enhance strength and increase the melting point, the metal is mixed with copper, aluminum, tin, magnesium and lead.

The most famous and sought after alloy is brass. This is a mixture of copper with the addition of zinc, sometimes tin, nickel, manganese, iron, and lead are also found. The density of brass reaches 8700 kg/m3 . The temperature required for melting is kept at around 880 C o - 950 C o: the higher the zinc content in it, the lower it is. The alloy perfectly resists unfavorable external environments, although it turns black in air if not varnished, it is perfectly polished and welded by resistance welding.

There are two types of brass:

Alpha brass: more ductile, bends well in any condition, but wears out more.
Alpha+beta brass: deforms only when heated, but is more wear-resistant. Often alloyed with magnesium, aluminum, lead and iron. This increases strength, but reduces ductility.

Zamak or Zamac alloy is composed of zinc, aluminum, copper and magnesium . The name itself is formed from the first letters of the Latin names: Zink - Aluminum - Magnesium - Kupfer / Cuprum (Zinc-Aluminum-Magnesium-Copper). In the USSR, the alloy was known as TsAM: Zinc-Aluminum-Copper. Actively used in injection molding, melting begins at low temperatures (381 C o - 387 C o) and has a low coefficient of friction (0.07). It has increased strength, which makes it possible to produce products of complex shapes that are not afraid of breaking: door handles, golf clubs, firearms, construction fittings, fasteners of various types and fishing tackle.

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A small percentage of zinc (no more than 0.01%) is contained in hart alloys used in printing for casting typographic fonts and rulers, printing forms and typesetting. These are outdated mixtures, replaced by pure zinc with a small addition of impurities.

The low temperature required to melt zinc is often compensated for by alloys with other metals, but it also happens vice versa. If the temperature required to melt a “pure” metal is 419.5 C o , then the alloy with tin is reduced to 199 C o, and with tin and lead - to 150 C o. And although such alloys can be soldered and welded, most often mixtures with zinc are used only to seal existing defects due to their weak strength. For example, an alloy of tin, lead and zinc is recommended for use only on nickel-plated products.

Most often, zinc alloys are used to create carburetors, speedometer frames, radiator grilles, hydraulic brakes, pumps and decorative elements, parts for washing machines, mixers and kitchen equipment, watch cases, typewriters, cash registers and household appliances. These parts cannot be used in industrial production: when the temperature rises to 100 C, the strength of the product decreases by a third, and hardness by almost 40%. When the temperature drops to 0 C, zinc becomes too brittle, which can lead to breakage.

The role of zinc in the human body

The Zn content in cells is 0.0003%, so it is classified as a microelement. The chemical properties and reactions of zinc and its compounds play an important role in metabolism and maintaining a normal level of homeostasis, both at the level of the cell and the entire organism as a whole. Metal ions are part of important enzymes and other biologically active substances. For example, it is known that zinc has a serious effect on the formation and functions of the male reproductive system. It is part of the coenzyme of the hormone testosterone, which is responsible for the fertility of seminal fluid and the formation of secondary sexual characteristics. The non-protein part of another important hormone, insulin, produced by the beta cells of the islets of Langerhans in the pancreas, also contains a trace element. The immune status of the body is also directly related to the concentration of Zn+2 ions in cells, which are found in the thymus hormone - thymulin and thymopoietin. A high concentration of zinc is recorded in nuclear structures - chromosomes containing deoxyribonucleic acid and participating in the transmission of hereditary information of the cell.

In our article, we studied the chemical functions of zinc and its compounds, and also determined its role in the life of the human body.

Biocomplexes [edit]

Carbonic anhydrase: showing hydroxide group (red) attached to zinc (gray)

Zinc fingers. The zinc ion (green) is coordinated by two histidine residues and two cysteine residues.

A very large number of metalloenzymes contain zinc(II). Also, many proteins contain zinc for structural reasons. The zinc ion invariably has 4-coordinates with at least three ligands, which are amino acid side chains. The imidazole nitrogen in the histidine side chain is a common ligand. Below are typical examples of two types of zinc-protein complexes.

In the active site of resting carbonic anhydrase, the zinc ion is coordinated by three histidine residues. The fourth position is occupied by a water molecule, which, as in hydrolysis, is highly polarized (see above). When carbon dioxide enters the active site, it is subject to nucleophilic attack by an oxygen atom, which carries a partial negative charge, or indeed a total negative charge if the water molecule dissociates. CO 2 quickly turns into bicarbonate ion. [23]

[(-hys) 3 Zn (H 2 O)] 2+ + CO 2 → [(-hys) 3 Zn] 2+ + HCO 3 - + H +

Some peptidases, such as glutamate carboxypeptidase II, are thought to act in a similar manner, with the zinc ion promoting the formation of the nucleophilic reagent. [23]

A zinc finger motif is a rigid substructure in a protein that facilitates the binding of the protein to another molecule such as DNA. [24] In this case, all four coordination positions are occupied by histidine and cysteine residues. The tetrahedral geometry around the zinc ion constrains the α-helical moiety and the antiparallel β-sheet moiety to a specific orientation relative to each other.

Magnesium ion, which has a higher concentration in biological fluids, cannot perform these functions because its complexes are much weaker than those of zinc.

Galvanizing methods

Metallurgical plants are distinguished not only by their equipment, but also by the production methods used. It depends on the pricing policy, and location (natural resources used for the metallurgical industry). There are several galvanizing methods, which are discussed below.

Hot galvanizing method

This method involves dipping a metal part in a liquid solution. It happens like this:

The part or product is degreased, cleaned, washed and dried.
Next, the zinc is melted to a liquid state at temperatures up to 480 °C.
The prepared product is lowered into the liquid solution. At the same time, it is well wetted in the solution and a coating up to 450 microns thick is formed. This is 100% protection against the effects of external factors on the product (moisture, direct sunlight, water with chemical impurities).

Hot galvanizing of metal structures

But this method has a number of disadvantages:

The zinc film on the product results in an uneven layer.
This method cannot be used for parts that meet exact standards according to GOST. Where every millimeter is considered a defect.
After hot-dip galvanizing, not every part will remain strong and wear-resistant, since brittleness appears after passing through high temperatures.

This method is also not suitable for products coated with paints and varnishes.

Cold galvanizing

This method has 2 names: galvanic and electrolytic. The method of coating a product with corrosion protection is as follows:

The metal part, the product is prepared (degreased, cleaned).
After this, the “staining method” is carried out - a special composition is used, which has the main component - zinc.
The part is coated with this composition by spraying.

Cold galvanizing

Thanks to this method, parts with precise tolerances and products coated with paints and varnishes are protected. Increases resistance to external factors leading to corrosion.

Disadvantages of this method: thin protective layer - up to 35 microns. This results in less protection and shorter protection periods.

Thermal diffusion method

This method makes a coating that is an electrode with positive polarity, while the metal of the product (steel) becomes negative polarity. An electrochemical protective layer appears.

The method is applicable only if the parts are made of carbon steel, cast iron, or steel with impurities. Zinc is used in the following ways:

At temperatures from 290 °C to 450 °C in a powder medium, the surface of the part is saturated with Zn. Here, the marking of the steel, as well as the type of product, matter - the appropriate temperature is selected.
The thickness of the protective layer reaches 110 microns.
A product made of steel or cast iron is placed in a closed tank.
A special mixture is added there.
The last step is special treatment of the product to prevent the appearance of white efflorescence from salt water.

Thermal diffusion galvanizing

This method is mainly used when it is necessary to coat parts that have a complex shape: threads, small strokes. The formation of a uniform protective layer is important, since these parts undergo multiple exposures to external aggressive environments (constant moisture).

This method provides the highest percentage of product protection against corrosion.

Galvanized coating is wear-resistant and practically indelible, which is very important for parts that are rotated and disassembled from time to time

Galvanizing methods

Today, there are different technologies for applying zinc to the surface of products. It is necessary to consider each of them in detail.

Hot galvanizing method

The metal product is degreased, washed and etched in advance. Zinc is melted at a temperature of 450–480 °C. The part is lowered into the liquid metal. The operating principle of this method is based on the fact that iron and its alloys are well wetted. As a result, a coating of significant thickness from 40 to 450 microns is formed, due to which the product is reliably protected from corrosion. However, the hot method also has disadvantages. These include:

uneven layer thickness;
it is impossible to use the method for parts with precise tolerances, and in cases where the characteristics of the fastener change under the influence of high temperature.

There is also a possibility that after hot-dip galvanizing, the strength of the fastening will decrease, the so-called embrittlement. To avoid such a situation, the product must be thermally treated after applying zinc, but even this does not provide a complete guarantee. The method under consideration is not suitable for parts coated with paints or powder paints. The reason is the low adhesion between them and hot zinc.

Hot zinc surface treatment

Cold galvanizing method

This method has 2 more names: galvanic and electrolytic. In this case, the technology resembles the process of dyeing a product, but instead of paints, a special composition containing zinc is used. As a result, the part is coated with an anti-corrosion layer. Unlike the previous method, fasteners of any size and painted products can be cold galvanized. Using this method, increased chemical resistance is achieved. The weak points of the method include the small thickness of the layer - 5–35 microns, which leads to a decrease in anti-corrosion properties. The method under consideration, like the previous one, does not exclude the occurrence of embrittlement.

Thermal diffusion galvanizing method

The coating obtained using this method is a positive electrode, while the steel is negative. This is how electrochemical protection occurs. Thermal diffusion galvanizing can only be used for products whose materials are carbon steel, cast iron and low-impurity steel. The galvanizing process occurs as follows. The surface of the product is saturated with zinc, and the medium should be powder and the temperature should be 290–450 °C. The steel grade and product type affect the choice of temperature. In this way, you can achieve any thickness of the protective layer from 6 to 110 microns. With this method, a part is placed in a closed container and a special saturated mixture is added. Final treatment is required to ensure that white corrosion products do not form on the products when they come into contact with salt water and condensate.

The described technology is applicable to workpieces with threads and complex geometric shapes. As a result, a uniform layer is formed over the entire surface; zinc does not accumulate in recesses or joints. Thanks to this advantage, there is no need to remove the coating on the internal threaded part, as is necessary after hot-dip galvanizing. There is also no embrittlement, meaning this technology is suitable for high-strength fasteners. The level of anti-corrosion resistance is 1.5–2 times higher than with galvanic galvanizing, and 3–5 times higher than with the hot method. Also, this technology is characterized by high adhesion of the zinc layer to paints and high accuracy, so the scope of application also extends to structures with precise tolerances. The applied anti-corrosion layer is very wear-resistant and therefore suitable for parts that are frequently assembled and disassembled.

Properties of zinc alloys

Of course, all compositions with this metal differ from each other in its percentage content. In general, zinc alloys have good casting and mechanical properties. The first and most important thing is corrosion resistance. It manifests itself most of all in an atmosphere of dry, clean air. Possible manifestations of corrosion can be seen in industrial cities. This is due to the presence of vapors of hydrochloric acid, chlorine and sulfur oxides in the air, which, condensing with moisture, make it difficult to form a protective film. Copper-tin-zinc is an alloy characterized by high protective properties. It is this composition that is least susceptible to corrosion, especially in an industrial atmosphere. If we talk about the casting properties of zinc, then, of course, they depend on the alloying elements in its alloys.

For example, aluminum makes their structure homogeneous, fine-grained, refines it, and reduces the negative influence of iron. Another important alloying element is copper. It increases strength characteristics and reduces intercrystalline corrosion. The copper-zinc alloy has high impact strength, but at the same time partially loses its casting properties.

Production and use of pure metal

Many types of everyday household items are galvanized. For example:

metal roofs of buildings,
building gutters,
water tanks, etc.

A fairly large proportion of zinc is used in the designs of disposable zinc-carbon non-rechargeable batteries. The brass manufacturing process also requires significant amounts of this substance.

A characteristic feature of zinc is the formation of a number of useful compounds:

Sulfide (phosphor of old TV screens, oscilloscopes, fluorescent lamps and luminous paints);
Sulfate (weed protectants, use in textile production);
Oxide (used to make rubber, helps improve the properties of plastics, paints, inks, concrete, cosmetics).

Many well-known alloys are formed on the zinc component. For example, brass, dental amalgam, bronze and some types of solders. Galvanizing not only prevents water tanks from rusting. Almost all types of cough and cold medicines, vitamin tablets and supplements cannot do without this substance.

Common dietary supplement tablets (capsules) include calcium supplements for strong teeth and bones, vitamin C, omega-3 for the eyes, and zinc for a stronger immune system.

Zinc deficiency in the body is accompanied by various problems in relation to the health of the body and leads to the development of diseases. True, this problem is mainly typical for developing countries, where there are factors of malnutrition in the population and a lack of balanced healthy nutrition.