Properties and applications of pure refractory metals. The value of pure metals in the great Soviet encyclopedia, bse I
If we draw a diagonal from beryllium to astatine in the periodic table of elements of D.I. Mendeleev, then there will be metal elements on the diagonal at the bottom left (they also include elements of secondary subgroups, highlighted in blue), and non-metal elements at the top right (highlighted in yellow). Elements located near the diagonal - semimetals or metalloids (B, Si, Ge, Sb, etc.) have a dual character (highlighted in pink).
As can be seen from the figure, the vast majority of elements are metals.
By their chemical nature, metals are chemical elements whose atoms donate electrons from the outer or pre-outer energy levels, thus forming positively charged ions.
Almost all metals have relatively large radii and a small number of electrons (from 1 to 3) at the external energy level. Metals are characterized by low electronegativity values and reducing properties.
The most typical metals are located at the beginning of periods (starting from the second), further from left to right, the metallic properties weaken. In a group from top to bottom, metallic properties are enhanced, because the radius of atoms increases (due to an increase in the number of energy levels). This leads to a decrease in the electronegativity (the ability to attract electrons) of the elements and an increase in the reducing properties (the ability to donate electrons to other atoms in chemical reactions).
typical metals are s-elements (elements of the IA group from Li to Fr. elements of the PA group from Mg to Ra). The general electronic formula of their atoms is ns 1-2. They are characterized by oxidation states + I and + II, respectively.
The small number of electrons (1-2) in the outer energy level of typical metal atoms suggests that these electrons are easily lost and exhibit strong reducing properties, which reflect low electronegativity values. This implies the limited chemical properties and methods for obtaining typical metals.
A characteristic feature of typical metals is the tendency of their atoms to form cations and ionic chemical bonds with non-metal atoms. Compounds of typical metals with non-metals are ionic crystals "metal cation anion of non-metal", for example, K + Br -, Ca 2+ O 2-. Typical metal cations are also included in compounds with complex anions - hydroxides and salts, for example, Mg 2+ (OH -) 2, (Li +) 2CO 3 2-.
The A-group metals forming the amphoteric diagonal in the Be-Al-Ge-Sb-Po Periodic Table, as well as the metals adjacent to them (Ga, In, Tl, Sn, Pb, Bi) do not exhibit typically metallic properties. The general electronic formula of their atoms ns 2 np 0-4 implies a greater variety of oxidation states, a greater ability to retain their own electrons, a gradual decrease in their reducing ability and the appearance of an oxidizing ability, especially in high oxidation states (typical examples are compounds Tl III, Pb IV, Bi v). Similar chemical behavior is also characteristic of most (d-elements, i.e., elements of the B-groups of the Periodic system ( typical examples- amphoteric elements Cr and Zn).
This manifestation of duality (amphoteric) properties, both metallic (basic) and non-metallic, is due to the nature of the chemical bond. In the solid state, compounds of atypical metals with non-metals contain predominantly covalent bonds (but less strong than bonds between non-metals). In solution, these bonds are easily broken, and the compounds dissociate into ions (completely or partially). For example, gallium metal consists of Ga 2 molecules, in the solid state aluminum and mercury (II) chlorides AlCl 3 and HgCl 2 contain strongly covalent bonds, but in a solution AlCl 3 dissociates almost completely, and HgCl 2 - to a very small extent (and then into HgCl + and Cl - ions).
General physical properties of metals
Due to the presence of free electrons ("electron gas") in the crystal lattice, all metals exhibit the following characteristic general properties:
1) Plastic- the ability to easily change shape, stretch into a wire, roll into thin sheets.
2) metallic luster and opacity. This is due to the interaction of free electrons with light incident on the metal.
3) Electrical conductivity. It is explained by the directed movement of free electrons from the negative to the positive pole under the influence of a small potential difference. When heated, the electrical conductivity decreases, because. as the temperature rises, vibrations of atoms and ions in the nodes of the crystal lattice increase, which makes it difficult for the directed movement of the "electron gas".
4) Thermal conductivity. It is due to the high mobility of free electrons, due to which the temperature is quickly equalized by the mass of the metal. The highest thermal conductivity is in bismuth and mercury.
5) Hardness. The hardest is chrome (cuts glass); softest - alkali metals- potassium, sodium, rubidium and cesium - cut with a knife.
6) Density. It is the smaller, the smaller the atomic mass of the metal and the larger the radius of the atom. The lightest is lithium (ρ=0.53 g/cm3); the heaviest is osmium (ρ=22.6 g/cm3). Metals having a density less than 5 g/cm3 are considered "light metals".
7) Melting and boiling points. The most fusible metal is mercury (m.p. = -39°C), the most refractory metal is tungsten (t°m. = 3390°C). Metals with t°pl. above 1000°C are considered refractory, below - low melting point.
General chemical properties of metals
Strong reducing agents: Me 0 – nē → Me n +
A number of stresses characterize the comparative activity of metals in redox reactions in aqueous solutions. 
I. Reactions of metals with non-metals
1) With oxygen:
2Mg + O 2 → 2MgO
2) With sulfur:
Hg + S → HgS
3) With halogens:
Ni + Cl 2 – t° → NiCl 2
4) With nitrogen:
3Ca + N 2 – t° → Ca 3 N 2
5) With phosphorus:
3Ca + 2P – t° → Ca 3 P 2
6) With hydrogen (only alkali and alkaline earth metals react):
2Li + H 2 → 2LiH
Ca + H 2 → CaH 2
II. Reactions of metals with acids
1) Metals standing in the electrochemical series of voltages up to H reduce non-oxidizing acids to hydrogen:
Mg + 2HCl → MgCl 2 + H 2
2Al+ 6HCl → 2AlCl 3 + 3H 2
6Na + 2H 3 PO 4 → 2Na 3 PO 4 + 3H 2
2) With oxidizing acids:
In the interaction of nitric acid of any concentration and concentrated sulfuric acid with metals hydrogen is never released! 
Zn + 2H 2 SO 4 (K) → ZnSO 4 + SO 2 + 2H 2 O
4Zn + 5H 2 SO 4(K) → 4ZnSO 4 + H 2 S + 4H 2 O
3Zn + 4H 2 SO 4(K) → 3ZnSO 4 + S + 4H 2 O
2H 2 SO 4 (c) + Cu → Cu SO 4 + SO 2 + 2H 2 O
10HNO 3 + 4Mg → 4Mg(NO 3) 2 + NH 4 NO 3 + 3H 2 O
4HNO 3 (c) + Сu → Сu (NO 3) 2 + 2NO 2 + 2H 2 O
III. Interaction of metals with water
1) Active (alkali and alkaline earth metals) form a soluble base (alkali) and hydrogen:
2Na + 2H 2 O → 2NaOH + H 2
Ca+ 2H 2 O → Ca(OH) 2 + H 2
2) Metals of medium activity are oxidized by water when heated to oxide:
Zn + H 2 O – t° → ZnO + H 2
3) Inactive (Au, Ag, Pt) - do not react.
IV. Displacement by more active metals of less active metals from solutions of their salts:
Cu + HgCl 2 → Hg + CuCl 2
Fe+ CuSO 4 → Cu+ FeSO 4
In industry, not pure metals are often used, but their mixtures - alloys in which the beneficial properties of one metal are complemented by the beneficial properties of another. So, copper has a low hardness and is of little use for the manufacture of machine parts, while alloys of copper with zinc ( brass) are already quite hard and are widely used in mechanical engineering. Aluminum has high ductility and sufficient lightness (low density), but is too soft. On its basis, an alloy with magnesium, copper and manganese is prepared - duralumin (duralumin), which, without losing useful properties aluminum, acquires high hardness and becomes suitable in the aircraft industry. Alloys of iron with carbon (and additions of other metals) are widely known cast iron And steel.
Metals in free form are reducing agents. However, the reactivity of some metals is low due to the fact that they are covered with surface oxide film, to varying degrees resistant to the action of such chemicals like water, solutions of acids and alkalis.
For example, lead is always covered with an oxide film; its transition into solution requires not only exposure to a reagent (for example, dilute nitric acid), but also heating. The oxide film on aluminum prevents its reaction with water, but is destroyed under the action of acids and alkalis. Loose oxide film (rust), formed on the surface of iron in moist air, does not interfere with the further oxidation of iron.
Under the influence concentrated acids are formed on metals sustainable oxide film. This phenomenon is called passivation. So, in concentrated sulfuric acid passivated (and then do not react with acid) such metals as Be, Bi, Co, Fe, Mg and Nb, and in concentrated nitric acid - metals A1, Be, Bi, Co, Cr, Fe, Nb, Ni, Pb , Th and U.
When interacting with oxidizing agents in acidic solutions, most metals turn into cations, the charge of which is determined by the stable oxidation state of a given element in compounds (Na +, Ca 2+, A1 3+, Fe 2+ and Fe 3+)
The reducing activity of metals in an acidic solution is transmitted by a series of stresses. Most metals are converted into a solution of hydrochloric and dilute sulfuric acids, but Cu, Ag and Hg - only sulfuric (concentrated) and nitric acids, and Pt and Au - "aqua regia".
Corrosion of metals
unwanted chemical property metals is theirs, i.e. active destruction (oxidation) upon contact with water and under the influence of oxygen dissolved in it (oxygen corrosion). For example, the corrosion of iron products in water is widely known, as a result of which rust is formed, and the products crumble into powder.
Corrosion of metals proceeds in water also due to the presence of dissolved CO 2 and SO 2 gases; an acidic environment is created, and H + cations are displaced by active metals in the form of hydrogen H 2 ( hydrogen corrosion).
The point of contact between two dissimilar metals can be especially corrosive ( contact corrosion). Between one metal, such as Fe, and another metal, such as Sn or Cu, placed in water, a galvanic couple occurs. The flow of electrons goes from the more active metal, which is to the left in the series of voltages (Re), to the less active metal (Sn, Cu), and the more active metal is destroyed (corrodes).
It is because of this that the tinned surface of cans (tin-plated iron) rusts when stored in a humid atmosphere and carelessly handled (iron quickly collapses after even a small scratch appears, allowing contact of iron with moisture). On the contrary, the galvanized surface of an iron bucket does not rust for a long time, because even if there are scratches, it is not iron that corrodes, but zinc (a more active metal than iron).
Corrosion resistance for a given metal is enhanced when it is coated with a more active metal or when they are fused; for example, coating iron with chromium or making an alloy of iron with chromium eliminates the corrosion of iron. Chrome-plated iron and steel containing chromium ( stainless steel) have high corrosion resistance.
electrometallurgy, i.e., obtaining metals by electrolysis of melts (for the most active metals) or salt solutions;
pyrometallurgy, i.e., the recovery of metals from ores at high temperature (for example, the production of iron in the blast furnace process);
hydrometallurgy, i.e., the isolation of metals from solutions of their salts by more active metals (for example, the production of copper from a CuSO 4 solution by the action of zinc, iron or aluminum).
Native metals are sometimes found in nature (typical examples are Ag, Au, Pt, Hg), but more often metals are in the form of compounds ( metal ores). By prevalence in the earth's crust, metals are different: from the most common - Al, Na, Ca, Fe, Mg, K, Ti) to the rarest - Bi, In, Ag, Au, Pt, Re.
For a very long time, some other metals were also considered brittle - chromium, molybdenum, tungsten, tantalum, bismuth, zirconium, etc. However, this was until they learned how to obtain them in a sufficiently pure form. Once this was done, it turned out that these metals are very ductile even at low temperatures. In addition, they do not rust and have a number of other valuable properties. Now these metals are widely used in various industries.
But what is a pure metal? It turns out that there is no definitive answer to this either. Conventionally, according to purity, metals are divided into three groups - technically pure, chemically pure and extra pure. If the alloy contains at least 99.9 percent of the base metal, this is technical purity. From 99.9 to 99.99 percent - chemical purity. If 99.999 or more, this is an especially pure metal. In everyday life, scientists also use another definition of purity - by the number of nines after the decimal point. They say: “the purity of three nines”, “the purity of five nines”, etc.
At first, the industry was quite satisfied with chemically, and often even technically pure metals. But the scientific and technological revolution made much more stringent demands. The first orders for ultra-pure metals came from the nuclear industry. Ten-thousandths, and sometimes even millionths of a percent of some impurities made uranium, thorium, beryllium, and graphite unusable. Obtaining ultra-pure uranium was perhaps the main difficulty in creating an atomic bomb.
Then jet technology presented its requirements. Ultra-pure metals were required to obtain particularly heat-resistant and heat-resistant alloys that were supposed to work in the combustion chambers of jet aircraft and rockets. Before the metallurgists had time to cope with this task, a new "application" was received - for semiconductors. This task was more difficult - in many semiconductor materials the amount of impurities should not exceed a millionth of a percent! Don't let this meager amount confuse you. Even with such purity, where one impurity atom falls on 100,000,000,000 atoms of the main substance, each gram of it still contains more than 100,000,000,000 “foreign” atoms. So it's far from perfect. However, absolute purity does not exist. This is an ideal to strive for, but it is impossible to achieve at this level of technological development. Even if by a miracle it is possible to obtain an absolutely pure metal, then atoms of other substances contained in the air will immediately penetrate into it.
Indicative in this respect is a curious incident that happened to the famous German physicist Werner Heisenberg. He worked with a mass spectrograph in his laboratory. And suddenly the device showed the presence of gold atoms in the experimental substance. The scientist was amazed, because this could not be. But the device stubbornly “stands on its own”. The misunderstanding was clarified only when the scientist removed and hid his gold-rimmed glasses. Separate gold atoms, "escaping" from the crystal lattice of the frame, fell into the substance under study and "confused" the extremely sensitive device.
But this happened in the laboratory, where the air is clean. What can we say about modern industrial regions, the air of which is more and more polluted by industrial waste?
We began this chapter by talking about the fact that in one case the presence of impurities in the metal is good, and in the other it is bad. Moreover, at first we said that alloys have better strength and heat resistance than pure metals, and now it turns out that pure metals have the highest properties. There is no contradiction. In many cases, the alloy is stronger, more heat resistant, etc., than any of the metals in its composition. But these qualities are enhanced many times over when all the components of the alloy perform a certain task necessary for a person. When there is nothing "extra" in it. And this means that the components themselves must be as pure as possible, contain a minimum number of "foreign" atoms. Therefore, now the question of the purity of the obtained metallurgical products is becoming more and more acute. How do they solve this problem?
In metallurgical plants, which produce a large amount of metal that goes into ordinary products, vacuum is increasingly being used. In a vacuum, the metal is melted and poured, and this makes it possible to protect it from the ingress of harmful gases and molecules of other substances from the surrounding air. And in some cases, melting is carried out in an atmosphere of neutral gas, which further protects the metal from unwanted "penetration".
PURE METALS
metals, metals with a low content of impurities. Depending on the degree of purity, there are metals of high purity (99.90-99.99%), metals high purity, or chemically pure (99.99-99.999%), high purity metals, or spectrally pure, ultrapure metals (over 99.999%).
Great Soviet Encyclopedia, TSB. 2012
See also interpretations, synonyms, word meanings and what PURE METALS are in Russian in dictionaries, encyclopedias and reference books:
- CLEAN
PRIVATE DOMESTIC INVESTMENT - Gross domestic private investment net of depreciation … - CLEAN in the Dictionary of Economic Terms:
LOSS - losses economic entities associated with the creation of an artificial shortage by the monopolist, leading to the establishment of a price that does not coincide with the marginal ... - CLEAN in the Dictionary of Economic Terms:
TRANSFER PAYMENTS - personal and government transfer payments to residents of other countries minus personal and government transfer payments received from residents of other ... - CLEAN in the Dictionary of Economic Terms:
CURRENT ASSETS are current, readily marketable assets less the costs associated with their … - CLEAN in the Dictionary of Economic Terms:
PURCHASES - the total amount of purchases for a certain period, minus discounts, returns of originally purchased products and reductions in the normal price and ... - CLEAN in the Dictionary of Economic Terms:
TAXES ON PRODUCTS - the difference between taxes on products and subsidies allocated to them ... - CLEAN in the Dictionary of Economic Terms:
IMPORT TAXES - the difference between import taxes and subsidies on ... - CLEAN in the Dictionary of Economic Terms:
TAXES - taxes that are paid by the population to the state, minus transfer payments that the population receives from ... - CLEAN in the Dictionary of Economic Terms:
LIQUID ASSETS - the amount of cash Money, easily marketable securities, and so on. accounts receivable By … - CLEAN in the Dictionary of Economic Terms:
CAPITAL INVESTMENT - gross capital investment less … - CLEAN in the Dictionary of Economic Terms:
COSTS OF DISPOSAL - costs directly related to the process of buying and selling goods; include transport costs, costs for transshipment of cargo, its processing, ... - CLEAN in the Dictionary of Economic Terms:
ASSETS - an estimated value determined by subtracting from the amount of assets, which includes monetary and non-monetary property at book value, ... - METALS in the Dictionary of Economic Terms:
PRECIOUS - see PRECIOUS METALS ... - METALS in the Bible Encyclopedia of Nicephorus:
In the Holy The Scriptures are often mentioned from metals: iron, copper, tin, lead, zinc, silver, gold. see about each in his own ... - METALS in the Big Encyclopedic Dictionary:
(Greek) substances that under normal conditions have high electrical conductivity (106-107 Ohm-1 cm-1, decreases with increasing temperature) and thermal conductivity, malleability, "metallic" luster ... - METALS
simple substances that under normal conditions have characteristic properties: high electrical and thermal conductivity, negative temperature coefficient of electrical conductivity, the ability to reflect electromagnetic radiation well ... - METALS
I (and metalloids) (chem.) - M. is a group of simple bodies (see), with known characteristic properties, which are sharply in typical representatives ... - METALS in the Modern Encyclopedic Dictionary:
- METALS in the Encyclopedic Dictionary:
simple substances that under normal conditions have characteristic properties - high electrical conductivity (106-104 Ohm-1?cm-1), decreasing with increasing temperature, high thermal conductivity, brilliance, ... - CLEAN
"CLEAN BROTHERS" ("Brothers of Purity", Arab. Ikhvan as-safa), a group of philosophers of the 10th century, which included the thinkers of Iraq (ch. arr. from the city of ... - METALS in the Big Russian Encyclopedic Dictionary:
"METALS", scientific. journal of the Russian Academy of Sciences, since 1959, Moscow. Founder (1998) - Institute of Metallurgy im. A.A. Baikov. 6 rooms in … - METALS in the Big Russian Encyclopedic Dictionary:
METALS, substances that under normal conditions have high electrical conductivity (10 6 - 10 4 Ohm -1 cm -1, decreases with ... - CLEAN in the New explanatory and derivational dictionary of the Russian language Efremova:
- METALS in Modern explanatory dictionary, TSB:
(Greek), substances that under normal conditions have high electrical conductivity (106-107 Ohm-1 cm-1, decreases with increasing temperature) and thermal conductivity, malleability, "metallic" luster ... - CLEAN in the Explanatory Dictionary of Efremova:
clean pl. unfold The money left after deductions... - CLEAN in the New Dictionary of the Russian Language Efremova:
pl. unfold The money left after deductions... - CLEAN in the Big Modern Explanatory Dictionary of the Russian Language:
pl. unfold The money left after deductions... - NON-FERROUS METALS in big Soviet encyclopedia, TSB:
metals, the technical name of all metals and their alloys (except iron and its alloys, called ferrous metals). The term "C. m." V … - REFRACTORY METALS in the Great Soviet Encyclopedia, TSB:
metals, by technical classification- metals melting at temperatures above 1650-1700 | C; the number of T. m. (table) includes titanium ... - RARE METALS in the Great Soviet Encyclopedia, TSB:
metals, the conventional name of a group of metals (over 50), a list of which is given in the table. These are metals that are relatively new in technology or else ... - PRECIOUS METALS in the Great Soviet Encyclopedia, TSB:
metals, gold, silver, platinum and platinum group metals (iridium, osmium, palladium, rhodium, ruthenium), which got their name mainly due to their high ... - CASTING METALS: CASTING METALS in Collier's Dictionary:
To the article CASTING METALS All metals can be cast. But not all metals have the same casting properties, in particular fluidity - ... - IMPRESSIONISM in the Lexicon of non-classics, artistic and aesthetic culture of the XX century, Bychkov:
(from the French impression - impression) A trend in art that arose in France in the last third of the 19th century. The main representatives of I.: Claude ... - SOLID in the Great Soviet Encyclopedia, TSB.
- REAGENTS CHEMICAL in the Great Soviet Encyclopedia, TSB:
chemical, chemical reagents, chemical preparations (substances) used in laboratories for analysis, scientific research (when studying methods of obtaining, properties and transformations ... - METALLURGY in the Great Soviet Encyclopedia, TSB:
(from Greek metallurgeo - I mine ore, process metals, from metallon - mine, metal and ergon - work), in the original, narrow ... - ADHESIVES in the Great Soviet Encyclopedia, TSB:
natural or synthetic substances used to join various materials due to the formation of an adhesive bond between the adhesive film and the surfaces of the materials to be bonded. … - COSTS OF DISPOSAL in the Great Soviet Encyclopedia, TSB:
circulation, a set of costs associated with the process of circulation of goods. By its economic nature, I. o. divided into pure and additional. Clean… - FLUORINE
- TURKISH V encyclopedic dictionary Brockhaus and Euphron:
(the exact meaning of the word is unknown) is a group of peoples who speak various dialects of the Turkic language (see Turkish languages) and according to physical characteristics ... - ALLOYS in the Encyclopedic Dictionary of Brockhaus and Euphron.
- PLANTINGS in the Encyclopedic Dictionary of Brockhaus and Euphron:
areas of the forest, naturally different from the neighboring ones in the nature of woody vegetation. The difference between N. can be determined by their origin, composition, age, degree ... - ORGANIC ARTIFICIAL PAINTS in the Encyclopedic Dictionary of Brockhaus and Euphron:
The development of the production and use of artificial organic tar is closely connected with the history of the scientific study of coal tar. Studying the composition of the latter, Runge in ... - FACTORIES in the Encyclopedic Dictionary of Brockhaus and Euphron:
In colloquial language, the concepts of Z. and factories are not distinguished, and, perhaps, there is still no particular need for that, ... - GERMANS PHYSICAL TYPE in the Encyclopedic Dictionary of Brockhaus and Euphron:
Rome. writers (Tacitus and others) described G. as a people of high stature, strong build, blond or red-haired and with fair, blue ... - RECOVERY in the Encyclopedic Dictionary of Brockhaus and Euphron:
The alchemists accepted that metals are complex bodies, consisting of spirit, soul and body, or mercury, sulfur and salt; under the spirit...
In connection with the development of new branches of technology, metals of very high purity are required. For example, in the germanium metal used as a semiconductor, only one atom of phosphorus, arsenic, or antimony is allowed per ten million germanium atoms. In heat-resistant alloys used in rocket science, even an insignificant admixture of lead or sulfur is completely unacceptable.
One of the best construction materials for nuclear reactors- zirconium becomes completely unusable if it contains even a slight impurity of hafnium, cadmium or boron, so the content of these elements in nuclear power materials should not exceed 10 -6. The electrical conductivity of copper decreases by 14% in the presence of an arsenic impurity of only 0.03%. Of particular importance is the purity of metals in electronic and computer technology, as well as nuclear power. For metal materials of thermonuclear reactors and semiconductor devices the content of impurities should not exceed 10 -10%. There are several methods for cleaning metals.
1. Vacuum distillation. This method is based on the difference between the volatility of the metal and the impurities present in it.
2. Thermal decomposition of volatile metal compounds. This method is based on chemical reactions in which a metal with one or another reagent forms gaseous products, which then decompose with the release of high-purity metal. Consider the principle of this method on the example of carbonyl and iodide methods.
A) carbonyl method. This method is used to obtain high-purity nickel and iron. To be cleaned technical metal heated with this method in the presence of carbon monoxide (II): Ni + 4CO \u003d Ni (CO) 4, Fe + 5CO \u003d Fe (CO) 5
The resulting volatile carbonyls Ni(CO) 4 (boiling point 43 °C) or Fe(CO) 5 (boiling point 105 °C) are distilled to remove impurities. Then the carbonyls decompose at temperatures above 180 ° C, resulting in the formation of pure metals and gaseous carbon monoxide (II): Ni (CO) 4 \u003d Ni + 4CO, Fe (CO) 5 \u003d Fe + 5CO
B) Iodide method. With this method, the metal being cleaned, for example titanium, is heated together with iodine to a temperature of 900 ° C: Ti + 2I 2 \u003d TI 4
The resulting volatile titanium tetraiodide enters the reactor, which contains a pure titanium wire heated by electric current to 1400 °C. At this temperature, titanium tetraiodide thermally dissociates: Til 4 = Ti + 2I 2
Pure titanium is deposited on the wire, and iodine is returned to the titanium purification process again. This method also produces pure zirconium, chromium and other refractory metals.
3. Zone melting. A remarkable cleaning method is the so-called zone melting. Zone melting consists in slowly pulling an ingot of the metal to be purified through an annular furnace. Zone melting is applied to metals that have undergone preliminary purification to an impurity concentration of approximately 1%. The method is based on different content of impurities in solid and molten metal. The process is carried out by slowly moving along a solid elongated sample (ingot) of a narrow molten zone created by a special heater (annular furnace) .
The area (zone) of the metal ingot, which is currently in the furnace, goes into a molten state.
There are two moving interphase boundaries: on one (metal entering the furnace) melting occurs, on the other (metal exiting the furnace) crystallization occurs.
Depending on the solubility of impurities, some are concentrated in the molten zone and move along with it to the end of the ingot, impurities of other metals are concentrated in the resulting crystals and remain behind the moving zone, with repeated repetition of the process, they move to the beginning of the ingot. As a result, the composition of the formed crystals differs from the composition of the melt.
To achieve a high degree of purification, several passes of the molten zone are usually made along the metal ingot. As a result, the middle part of the ingot is the cleanest, it is cut out and used.
The zone melting method makes it possible to obtain highly pure metals with an impurity content of 10 -7 -10 -9%. This method is used to obtain ultrapure germanium, bismuth, tellurium, etc.
Main advantage this method- high efficiency. The disadvantages of the method are low productivity, high cost, and a long process time.
4. electrochemical method of cleaning metals(refining of metals).
VACUUM DISTILLATION OF 4-TH PERIOD REFRACTORY METALS (Mn, Cr, Fe, Ni, Co)
The most refractory and hardly volatile metals that are currently subjected to distillation are manganese, chromium, iron, nickel and cobalt. All of these metals are part of the most important technical alloys.
Mechanical and physical properties alloys based on iron, nickel and other specified elements, especially the properties of various heat-resistant alloys, are largely determined by the purity of the starting materials. It is well known that non-metallic inclusions and a number of impurities that form low-melting eutectics sharply degrade many alloys: ductility, heat resistance, corrosion resistance, etc. Especially harmful impurities in all these metals are lead, bismuth, cadmium, sulfur, phosphorus, nitrogen and oxygen.In this regard, obtaining pure metals of the 4th period is an exceptional interest both from the point of view of studying their properties, and for studying the effect of alloying additives on changing the properties of alloys.Pure metals are necessary in vacuum technology for the manufacture of electrodes, for anodes of X-ray tubes and for the production of some parts of ion devices.Pure iron almost does not interact with mercury vapor It can be used in tubes with oxide cathodes, which are extremely sensitive to the slightest contamination. Pure iron has a high magnetic permeability, which allows it to be used for shielding magnetic fields. High purity nickel is essential for coating various refractory metals. A significant amount of pure metals of the 4th period is consumed by the chemical industry for the manufacture of various compounds. Detailed information on the effect of impurities on the properties of the metals under consideration can be found in monographs.
The most common method for cleaning refractory metals of the 4th period is the chemical binding of impurities as a result of redox processes (often by hydrogen treatment) followed by degassing and distillation of impurities during vacuum melting. Processing of molten metals in a vacuum has become widespread over the past 5-10 years. It is used not only for pure metals, but also for steels and other alloys. Not being able to elucidate in detail the relevant works, in which the range of issues considered is far beyond the scope of this topic, we will confine ourselves to a description of the work on the distillation of these metals and on the distillation of metallic impurities. Detailed information regarding the vacuum melting of metals and the removal of gaseous impurities can be found in a number of collections of articles and monographs.
Of the metals considered in this paragraph, iron, nickel and cobalt are included in the iron subgroup of group VIII of the periodic system. As the main impurities in these metals, in addition to related elements, there are copper, silicon, manganese, chromium, aluminum, carbon, phosphorus, sulfur and gases (N 2, 0 2, H 2). Due to the proximity of the properties of related elements, the degree of purification from them during distillation is low, but small additions of these metals have little effect on the properties of the main element. All pure metals of the iron subgroup are plastic at room and even lower temperatures, and nickel is plastic up to the temperature of liquid helium (4.2 °K). However, an increase in the content of gas and some metal impurities can lead to an increase in the transition temperature of metals from a ductile to a brittle state. Thus, iron containing >0.005% 0 2 becomes brittle at 20°C. Cobalt has a lower ductility than iron or nickel, which may be due to its insufficient purity. All three considered metals have similar vapor pressure values. Their distillation is usually carried out at temperatures 20-50 ° C above the melting point, although they all sublimate in vacuum at a temperature > 1100 ° C.
Unlike metals of the iron subgroup, chromium and high purity manganese are brittle at room temperature. Even small concentrations of impurities such as carbon, sulfur, nitrogen and oxygen sharply worsen them. mechanical properties. In the purest chromium, the transition temperature from the brittle to the ductile state is close to 50 ° C. There is, however, the possibility of lowering this temperature by further cleaning the metal.
At present, it is believed that the main reason for the brittleness of chromium at room temperature is the presence of nitrogen and oxygen in it in amounts of ~0.001%. The transition temperature of chromium to a plastic state increases sharply with the addition of aluminum, copper, nickel, manganese and cobalt. It is possible that a great effect of purifying chromium from nitrogen can be obtained by distilling it in an isolated volume.
Manganese is brittle over the entire range of existence of the α-phase (up to 700°C), while the high-temperature phases (β- and γ-Mπ) are quite plastic. The reasons for the brittleness of α-Mn have not been sufficiently studied.
Chromium and manganese have significant vapor pressures below their melting points. Chromium sublimates in a vacuum at a noticeable rate above 1200 ° C. Since the melting point of chromium is about 1900 ° C, it is not possible to melt it in a vacuum due to sublimation. Usually, the remelting of the original metal or condensate is carried out in an inert gas at a pressure of more than 700 mm Hg. Art. Manganese is distilled both by sublimation and from the liquid phase.
Usually, when distilling all the metals under consideration, it is possible to obtain condensates with a purity of ~ 99.99%. However, highly efficient purification is only possible with the use of temperature gradient condensers. The distillation of chromium and manganese has been studied in detail, mainly by Croll and in the authors' laboratory.
Vacuum distillation of manganese was first described by Thide and Birnbrauer. Geiler studied this process in detail and investigated a number of properties of the resulting high-purity manganese. Distillation was carried out in a quartz tube 600 mm long and 100 mm in diameter. Manganese evaporated from a magnesite crucible and condensed on another similar crucible. The metal was heated by high frequency currents. Evaporation was carried out at a temperature of ~ 1250 ° C in a vacuum of 1-2 mm Hg. Art. An aluminothermic metal with a purity of ~99% and commercial manganese (~96–98%) were used as the starting material. The results of a single distillation are shown in table. 48. The output of pure metal was -50% of the weight of the load. With the specified process parameters and a load of 2.7 kg, 0.76 kg of pure metal was obtained in 5 hours. In the Geyler installation, the possibility of metal interaction with the pipe material was not eliminated, and therefore, in a number of experiments, the distillate was contaminated with silicon.
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