Malleable silver-white metal with high chemical reactivity: iron corrodes quickly at high temperatures or high humidity in air. In pure oxygen, iron burns, and in a finely dispersed state, it ignites spontaneously in air. It is designated by the symbol Fe (lat. Ferrum). One of the most common metals in the earth's crust (second place after).
See also:
STRUCTURE
For iron, several polymorphic modifications have been established, of which the high-temperature modification - γ-Fe (above 906 °) forms a face-centered cube lattice of the Cu type (a 0 \u003d 3.63), and the low-temperature modification - α-Fe-lattice of a centered cube of the α-Fe type ( a 0 = 2.86).
Depending on the heating temperature, iron can be in three modifications, characterized by a different structure of the crystal lattice:
- In the temperature range from the lowest to 910 ° C - a-ferrite (alpha-ferrite), having a crystal lattice structure in the form of a centered cube;
- In the temperature range from 910 to 1390°C - austenite, the crystal lattice of which has the structure of a face-centered cube;
- In the temperature range from 1390 to 1535 ° C (melting point) - d-ferrite (delta-ferrite). The crystal lattice of d-ferrite is the same as that of a-ferrite. The difference between them is only in other (large for d-ferrite) distances between atoms.
When liquid iron is cooled, primary crystals (crystallization centers) appear simultaneously at many points of the cooled volume. During subsequent cooling, new crystalline cells are built around each center until the entire supply of liquid metal is exhausted.
The result is a granular structure of the metal. Each grain has a crystal lattice with a certain direction of its axes.
Upon subsequent cooling of solid iron, during the transitions of d-ferrite to austenite and austenite to α-ferrite, new crystallization centers can appear with a corresponding change in grain size
PROPERTIES
In its pure form under normal conditions, it is a solid. It has a silvery-gray color and a pronounced metallic sheen. The mechanical properties of iron include the level of hardness on the Mohs scale. It is equal to four (medium). Iron has good electrical and thermal conductivity. The last feature can be felt by touching an iron object in a cold room. Since this material conducts heat quickly, it takes a lot of it out of your skin in a short amount of time, which is why you feel cold.
Touching, for example, a tree, it can be noted that its thermal conductivity is much lower. The physical properties of iron are its melting and boiling points. The first is 1539 degrees Celsius, the second is 2860 degrees Celsius. It can be concluded that the characteristic properties of iron are good ductility and fusibility. But that's not all. The physical properties of iron also include its ferromagnetism. What it is? Iron, whose magnetic properties we can observe in practical examples every day, is the only metal that has such a unique hallmark. This is due to the fact that this material is able to be magnetized under the influence of a magnetic field. And after the termination of the action of the latter, iron, the magnetic properties of which have just been formed, remains a magnet for a long time. This phenomenon can be explained by the fact that in the structure of this metal there are many free electrons that are able to move.
RESERVES AND PRODUCTION
Iron is one of the most common elements in the solar system, especially on the terrestrial planets, in particular on Earth. A significant part of the iron of the terrestrial planets is located in the cores of the planets, where its content is estimated to be about 90%. The content of iron in the earth's crust is 5%, and in the mantle about 12%.
In the earth's crust, iron is widely distributed - it accounts for about 4.1% of the mass of the earth's crust (4th place among all elements, 2nd among metals). In the mantle and the earth's crust, iron is concentrated mainly in silicates, while its content is significant in basic and ultrabasic rocks, and low in acidic and intermediate rocks.
A large number of ores and minerals containing iron are known. Of the greatest practical importance are red iron ore (hematite, Fe2O3; contains up to 70% Fe), magnetic iron ore (magnetite, FeFe 2 O 4 , Fe 3 O 4 ; contains 72.4% Fe), brown iron ore or limonite (goethite and hydrogoethite, FeOOH and FeOOH nH 2 O, respectively). Goethite and hydrogoethite are most often found in weathering crusts, forming the so-called "iron hats", whose thickness reaches several hundred meters. They can also be of sedimentary origin, falling out of colloidal solutions in lakes or coastal areas of the seas. In this case, oolitic, or legume, iron ores are formed. They often contain vivianite Fe 3 (PO 4) 2 8H 2 O, which forms black elongated crystals and radially radiant aggregates.
The content of iron in sea water is 1 10 -5 -1 10 -8%
In industry, iron is obtained from iron ore, mainly from hematite (Fe 2 O 3) and magnetite (FeO·Fe 2 O 3).
There are various ways to extract iron from ores. The most common is the domain process.
The first stage of production is the reduction of iron with carbon in a blast furnace at a temperature of 2000 °C. In a blast furnace, carbon in the form of coke, iron ore in the form of sinter or pellets, and flux (eg limestone) are fed from above and are met by a stream of injected hot air from below.
In addition to the blast furnace process, the process of direct production of iron is common. In this case, pre-crushed ore is mixed with special clay to form pellets. The pellets are roasted and treated in a shaft furnace with hot methane conversion products that contain hydrogen. Hydrogen easily reduces iron without contaminating the iron with impurities such as sulfur and phosphorus, which are common impurities in coal. Iron is obtained in solid form, and then melted down in electric furnaces. Chemically pure iron is obtained by electrolysis of solutions of its salts.
ORIGIN
The origin of telluric (terrestrial) iron is rarely found in basaltic lavas (Wifaq, Disko Island, off the western coast of Greenland, near the city of Kassel, Germany). Pyrrhotite (Fe 1-x S) and cohenite (Fe 3 C) are associated with it at both points, which explains both reduction by carbon (including from host rocks) and decomposition of carbonyl complexes of the Fe(CO) n type. In microscopic grains, it has been established more than once in altered (serpentinized) ultrabasic rocks, also in paragenesis with pyrrhotite, sometimes with magnetite, due to which it arises during reduction reactions. It is very rare in the zone of oxidation of ore deposits, during the formation of swamp ores. Findings in sedimentary rocks associated with the reduction of iron compounds by hydrogen and hydrocarbons have been registered.
Almost pure iron has been found in the lunar soil, which is associated with both meteorite falls and magmatic processes. Finally, two classes of meteorites - stony-iron and iron - contain natural iron alloys as a rock-forming component.
APPLICATION
Iron is one of the most used metals, accounting for up to 95% of the world's metallurgical production.
Iron is the main component of steels and cast irons - the most important structural materials.
Iron can be part of alloys based on other metals - for example, nickel.
Magnetic iron oxide (magnetite) is an important material in the manufacture of long-term computer memory devices: hard drives, floppy disks, etc.
Ultrafine magnetite powder is used in many black and white laser printers mixed with polymer granules as a toner. It uses both the black color of magnetite and its ability to adhere to a magnetized transfer roller.
The unique ferromagnetic properties of a number of iron-based alloys contribute to their widespread use in electrical engineering for the magnetic cores of transformers and electric motors.
Iron(III) chloride (ferric chloride) is used in amateur radio practice for etching printed circuit boards.
Ferrous sulfate (iron sulfate) mixed with copper sulphate is used to control harmful fungi in gardening and construction.
Iron is used as an anode in iron-nickel batteries, iron-air batteries.
Aqueous solutions of ferrous and ferric chlorides, as well as its sulfates, are used as coagulants in the purification of natural and Wastewater in the water treatment of industrial enterprises.
Iron (English Iron) - Fe
CLASSIFICATION
Hey's CIM Ref1.57
| Strunz (8th edition) | 1/A.07-10 |
| Nickel-Strunz (10th edition) | 1.AE.05 |
| Dana (7th edition) | 1.1.17.1 |
Almost all metals are solids under normal conditions. But at certain temperatures, they can change their state of aggregation and become liquid. Let's find out what is the highest melting point of metal? What is the lowest?
Melting point of metals
Most of the elements periodic table refers to metals. Currently, there are approximately 96 of them. They all need different conditions to turn into a liquid.
The threshold of heating solid crystalline substances, exceeding which they become liquid, is called the melting point. In metals, it fluctuates within a few thousand degrees. Many of them pass into a liquid with relatively high heating. Because of this, they are a common material for the production of pots, pans and other kitchen appliances.
Silver (962 °C), aluminum (660.32 °C), gold (1064.18 °C), nickel (1455 °C), platinum (1772 °C), etc. have average melting points. There is also a group of refractory and fusible metals. The first one needs more than 2000 degrees Celsius to turn into a liquid, the second one needs less than 500 degrees.
Low-melting metals usually include tin (232 °C), zinc (419 °C), lead (327 °C). However, some of them may have even lower temperatures. For example, francium and gallium melt already in the hand, and cesium can only be heated in an ampoule, because it ignites from oxygen.
The lowest and highest melting points of metals are presented in the table:
Tungsten
The highest melting point is tungsten metal. Above it in this indicator is only non-metal carbon. Tungsten is a light gray lustrous substance, very dense and heavy. It boils at 5555 °C, which is almost equal to the temperature of the Sun's photosphere.
Under room conditions, it reacts weakly with oxygen and does not corrode. Despite its refractoriness, it is quite ductile and can be forged even when heated to 1600 °C. These properties of tungsten are used for filaments in lamps and kinescopes of electrodes for welding. Most of the mined metal is alloyed with steel to increase its strength and hardness.
Tungsten is widely used in the military sphere and technology. It is indispensable for the manufacture of ammunition, armor, engines and the most important parts of military vehicles and aircraft. It is also used to make surgical instruments, boxes for storing radioactive substances.
Mercury
Mercury is the only metal whose melting point is minus. In addition, it is one of two chemical elements, simple substances which, under normal conditions, exist in the form of liquids. Interestingly, the metal boils when heated to 356.73 ° C, which is much higher than its melting point.
It has a silvery-white color and a pronounced luster. It evaporates already at room conditions, condensing into small balls. The metal is highly toxic. It is able to accumulate in the internal organs of a person, causing diseases of the brain, spleen, kidneys and liver.
Mercury is one of the seven first metals known to man. In the Middle Ages, it was considered the main alchemical element. Despite its toxicity, it was once used in medicine as part of dental fillings, and also as a cure for syphilis. Now mercury has been almost completely excluded from medicines, but it is widely used in measuring instruments (barometers, pressure gauges), for the manufacture of lamps, switches, and doorbells.
Alloys
To change the properties of a metal, it is alloyed with other substances. So, it can not only acquire greater density, strength, but also lower or increase the melting point.
An alloy can consist of two or more chemical elements, but at least one of them must be a metal. Such "mixtures" are very often used in industry, because they allow you to get exactly the qualities of the materials that are needed.
The melting point of metals and alloys depends on the purity of the former, as well as on the proportions and composition of the latter. To obtain fusible alloys, lead, mercury, thallium, tin, cadmium, and indium are most often used. Those containing mercury are called amalgams. A compound of sodium, potassium and cesium in a ratio of 12%/47%/41% becomes a liquid already at minus 78 °C, amalgam of mercury and thallium at minus 61 °C. The most refractory material is an alloy of tantalum and hafnium carbides in proportions of 1:1 with a melting point of 4115 °C.
The melting point of iron is important indicator technologies for the production of metal and its alloys. When smelting raw materials, the physical and chemical properties of the ore and metal are taken into account.
The most common chemical element on Earth.
Physical and chemical properties of iron
- Chemical element number 26 is the most abundant in the solar system. According to studies, the iron content in the Earth's core is 79–85.5%. In terms of prevalence in the planet's crust, it is second only to aluminum.
- The metal in its pure form has a white color with a silvery tint, it is plastic. The presence of impurities determines its physical parameters. Iron tends to react to a magnet.
- This chemical element is characterized by polymorphism, which occurs when heated. An increased concentration of metal is observed in the places of rock eruption. Industrial deposits are formed as a result of external and internal processes occurring in the earth's crust.
- River water contains approximately 2 mg/l of metal, while the indicator for sea water is 100–1000 times less.
- Iron has several degrees of oxidation, which determine its geochemical feature in a particular environment. In its neutral form, the metal is found in the Earth's core.
- Iron oxide is the main form of occurrence in nature, and oxide iron is located in the uppermost part of the earth's crust as part of sedimentary formations.
- The content of chemical element No. 26 in minerals with an unstable composition increases with a decrease in the temperature gradient. Boiling occurs when heated to + 2861 °C. Specific heat melting is 247.1 kJ/kg.
Metal mining
Among the ores containing iron, the raw material for industrial production are:
- hematite;
- goethite;
- magnetite.
Goethite and hydrogoethite form formations in the weathering crust hundreds of meters in size. In the shelf zone and lakes, colloidal solutions of minerals form oolites (bean iron ores) as a result of precipitation.
Pyrite and pyrrhotite, both naturally occurring iron minerals, are used as raw materials for the production of sulfuric acid.
Common iron minerals also include:
- siderite;
- lellingite;
- marcasite;
- ilmenite;
- jarosite
The mineral melanterite, which is a brittle green crystal with a vitreous luster, is used in pharmaceutical industry for the production of iron-containing preparations.
The main deposit of this metal is in Brazil. Recently, attention has been focused on the exploitation of nodules present on the seafloor, which contain iron and manganese.
melting iron
What determines the melting point of iron?
Metal production provides for various technologies for its extraction from ore raw materials. The most common smelting of iron is the blast-furnace method.
Before the metal is smelted, it is reduced in a furnace at a temperature of +2000 °C. To extract impurities, flux is added, which decomposes when heated to oxide, followed by combination with silicon dioxide and the formation of slag.
In addition to the blast-furnace method, iron is smelted by roasting crushed ore with clay. The mixture is formed into pellets and processed in a hydrogen reduction furnace. Further smelting of iron is carried out in electric furnaces.
Production of alloys in furnaces.
The properties of a metal depend on the purity of the material. For commercially pure iron, the melting point is +1539 °C. Sulfur is a harmful impurity. It can only be extracted from a liquid solution. Chemically pure material is obtained by electrolysis of metal salts.
metal alloys
In its pure form, this material is soft, so carbon is added to the composition to increase strength.
In metallurgy, iron alloys are called ferrous metals.
Depending on the components of the ligature, the properties of the materials change. The melting point of iron also changes in the presence of ligature components.
The specific heat of fusion of steel is 84 kJ. This indicator means that at the melting temperature of steel, 84 kJ of energy is needed to transfer 1 kg of an alloy from a crystalline to a liquid state.
Compounds of various metals form alloys. Specific heat of fusion cast iron is 96–140 kJ. Cast iron contains up to 4% carbon, 1.5% manganese, up to 4.5% silicon and impurities in the form of sulfur and phosphorus. There are white and gray alloys.
In white, some of the carbon is in the iron carbide compound. This alloy is brittle and hard. It is intended for the manufacture of structures and parts.
The gray alloy containing carbon in the form of graphite is easy to machine. Cast iron is smelted from iron ore in blast furnaces. The melting of the ore is accompanied by a reduction reaction of iron from oxides with carbon.
Most substances can melt with an increase in volume when heated. For cast iron with a volume of 1000 cm³, this figure is 988–994 cm³.
Cast iron is a raw material for the production of steel, characterized by a carbon content (not higher than 2.14%).
According to the chemical composition, steel is distinguished:
- alloyed;
- carbon.
Carbon steel contains impurities of sulfur, phosphorus and silicon. It is distinguished by low electrical properties, low strength, and is easily susceptible to corrosion.
The presence of ligature additives gives the steel new technical properties. As additional components use:
- molybdenum;
- nickel;
- tungsten;
- chromium;
- vanadium.
The composition of high-alloy steel includes no more than 10% of additives. The alloy is durable. The technology for the production of steel from cast iron makes it possible to obtain high-quality material for the production of:
Steel is used as a raw material in various industries. Without it, it is impossible to imagine the aircraft industry, shipbuilding, the automotive industry and many other production areas.
Each metal and alloy has its own unique set of physical and chemical properties, not least of which is the melting point. The process itself means the transition of the body from one state of aggregation to another, in this case, from a solid crystalline state to a liquid one. To melt a metal, it is necessary to supply heat to it until the melting point is reached. With it, it can still remain in a solid state, but with further exposure and an increase in heat, the metal begins to melt. If the temperature is lowered, that is, part of the heat is removed, the element will harden.
Highest melting point among metals belongs to tungsten: it is 3422C o, the lowest is for mercury: the element melts already at - 39C o. As a rule, it is not possible to determine the exact value for alloys: it can vary significantly depending on the percentage of components. They are usually written as a number span.
How is it happening
The melting of all metals occurs in approximately the same way - with the help of external or internal heating. The first is carried out in a thermal furnace, for the second, resistive heating is used with the passage of an electric current or induction heating in a high-frequency electromagnetic field. Both options affect the metal in about the same way.
As the temperature increases, so does amplitude of thermal vibrations of molecules, structural lattice defects appear, which are expressed in the growth of dislocations, hopping of atoms, and other disturbances. This is accompanied by the breaking of interatomic bonds and requires a certain amount of energy. At the same time, a quasi-liquid layer is formed on the surface of the body. The period of destruction of the lattice and the accumulation of defects is called melting.
Depending on the melting point, metals are divided into:
Depending on the melting temperature choose and melting apparatus. The higher the score, the stronger it should be. You can find out the temperature of the element you need from the table.
Another important value is the boiling point. This is the value at which the process of boiling liquids begins, it corresponds to the temperature of saturated steam that forms above the flat surface of the boiling liquid. Usually it is almost twice as high as the melting point.
Both values are given at normal pressure. Among themselves they directly proportional.
- The pressure increases - the amount of melting will increase.
- The pressure decreases - the amount of melting decreases.
Table of fusible metals and alloys (up to 600C o)
| Element name | Latin designation | Temperatures | |
| Melting | boiling | ||
| Tin | sn | 232 C o | 2600 C o |
| Lead | Pb | 327 C o | 1750 C o |
| Zinc | Zn | 420 C o | 907 S o |
| Potassium | K | 63.6 C o | 759 S o |
| Sodium | Na | 97.8 C o | 883 C o |
| Mercury | hg | - 38.9 C o | 356.73 C o |
| Cesium | Cs | 28.4 C o | 667.5 C o |
| Bismuth | Bi | 271.4 C o | 1564 S o |
| Palladium | Pd | 327.5 C o | 1749 S o |
| Polonium | Po | 254 C o | 962 S o |
| Cadmium | CD | 321.07 C o | 767 S o |
| Rubidium | Rb | 39.3 C o | 688 S o |
| Gallium | Ga | 29.76 C o | 2204 C o |
| Indium | In | 156.6 C o | 2072 S o |
| Thallium | Tl | 304 C o | 1473 S o |
| Lithium | Li | 18.05 C o | 1342 S o |
Table of medium-melting metals and alloys (from 600С o to 1600С o)
| Element name | Latin designation | Temperatures | |
| Melting | boiling | ||
| Aluminum | Al | 660 C o | 2519 S o |
| Germanium | Ge | 937 S o | 2830 C o |
| Magnesium | mg | 650 C o | 1100 C o |
| Silver | Ag | 960 C o | 2180 S o |
| Gold | Au | 1063 C o | 2660 S o |
| Copper | Cu | 1083 C o | 2580 S o |
| Iron | Fe | 1539 S o | 2900 C o |
| Silicon | Si | 1415 S o | 2350 S o |
| Nickel | Ni | 1455 S o | 2913 C o |
| Barium | Ba | 727 S o | 1897 C o |
| Beryllium | Be | 1287 S o | 2471 S o |
| Neptunium | Np | 644 C o | 3901.85 C o |
| Protactinium | Pa | 1572 S o | 4027 S o |
| Plutonium | Pu | 640 C o | 3228 S o |
| Actinium | AC | 1051 C o | 3198 S o |
| Calcium | Ca | 842 C o | 1484 S o |
| Radium | Ra | 700 C o | 1736.85 C o |
| Cobalt | co | 1495 S o | 2927 C o |
| Antimony | Sb | 630.63 C o | 1587 S o |
| Strontium | Sr | 777 S o | 1382 S o |
| Uranus | U | 1135 C o | 4131 C o |
| Manganese | Mn | 1246 S o | 2061 S o |
| Konstantin | 1260 S o | ||
| Duralumin | Alloy of aluminum, magnesium, copper and manganese | 650 C o | |
| Invar | Nickel-iron alloy | 1425 C o | |
| Brass | Alloy of copper and zinc | 1000 C o | |
| Nickel silver | Alloy of copper, zinc and nickel | 1100 C o | |
| Nichrome | An alloy of nickel, chromium, silicon, iron, manganese and aluminum | 1400 C o | |
| Steel | Alloy of iron and carbon | 1300 C o - 1500 C o | |
| Fechral | An alloy of chromium, iron, aluminum, manganese and silicon | 1460 S o | |
| Cast iron | Alloy of iron and carbon | 1100 C o - 1300 C o | |
Table of refractory metals and alloys (over 1600C o)
| Element name | Latin designation | Temperatures | |
| Melting | boiling | ||
| Tungsten | W | 3420 S o | 5555 C o |
| Titanium | Ti | 1680 C o | 3300 S o |
| Iridium | Ir | 2447 S o | 4428 S o |
| Osmium | Os | 3054 C o | 5012 C o |
| Platinum | Pt | 1769.3 C o | 3825 C o |
| Rhenium | Re | 3186 S o | 5596 S o |
| Chromium | Cr | 1907 S o | 2671 S o |
| Rhodium | Rh | 1964 S o | 3695 S o |
| Ruthenium | Ru | 2334 S o | 4150 C o |
| Hafnium | hf | 2233 S o | 4603 C o |
| Tantalum | Ta | 3017 S o | 5458 S o |
| Technetium | Tc | 2157 S o | 4265 S o |
| Thorium | Th | 1750 C o | 4788 S o |
| Vanadium | V | 1910 C o | 3407 C o |
| Zirconium | Zr | 1855 S o | 4409 S o |
| Niobium | Nb | 2477 S o | 4744 S o |
| Molybdenum | Mo | 2623 C o | 4639 s o |
| hafnium carbides | 3890 C o | ||
| Niobium carbides | 3760 S o | ||
| Titanium carbides | 3150 S o | ||
| Zirconium carbides | 3530 S o | ||
Metals have a number of original properties that are unique to these materials. There is a melting point of metals at which the crystal lattice is destroyed. The substance retains volume, but it is no longer possible to speak of the constancy of form.
In its pure form, individual metals are extremely rare. In practice, alloys are used. They have certain differences from pure substances. When complex compounds are formed, crystal lattices are combined with each other. Therefore, the properties of alloys can differ markedly from the constituent elements. The melting temperature no longer remains a constant value, it depends on the concentration of the ingredients included in the alloy.
The concept of the temperature scale
Some non-metal objects also have similar properties. The most common is water. Regarding the properties of the liquid that occupies a dominant position on Earth, a temperature scale has been developed. The reference points are the temperature of change in the aggregate states of water:
- The transformations from liquid to solid and vice versa are taken as zero degrees.
- Boiling (vaporization inside the liquid) at normal atmospheric pressure (760 mm Hg) is taken as 100 ⁰С.
Attention! In addition to the Celsius scale, in practice, temperature is measured in degrees Fahrenheit and on the absolute Kelvin scale. But when studying the properties of metal objects, other scales are used quite rarely.
Crystal lattices of metal
A solid is characterized by constancy:
- shape, the object retains linear dimensions in different conditions;
- volume, the object does not change the amount of substance occupied;
- masses, the amount of a substance expressed in grams (kilograms, tons);
- density, there is a constant mass per unit volume.
Upon transition to a liquid state, having reached a certain temperature, the crystal lattices are destroyed. Now you can not talk about the constancy of form. The liquid will take the form in which it is poured.
When evaporation occurs, only the mass of the substance remains constant. Gas will take up the entire volume that will be provided to it. Here it cannot be argued that the density is a constant value.
When liquids are combined, options are possible:
- Liquids completely dissolve one into another, this is how water and alcohol behave. Throughout the volume, the concentration of substances will be the same.
- Liquids are stratified in density, the connection occurs only at the interface. Only temporarily can you get a mechanical mixture. By mixing liquids of different properties. An example is oil and water.
Metals form alloys in the liquid state. To obtain an alloy, each of the components must be in a liquid state. In alloys, phenomena of complete dissolution of one into another are possible. Options are not excluded when the alloy will be obtained only as a result of intensive mixing. The quality of the alloy in this case is not guaranteed, therefore, they try not to mix components that do not allow obtaining stable alloys.
The resulting substances soluble in each other, when solidified, form crystal lattices of a new type. Determine:
- Heliocentered crystal lattices, they are also called body-centered. In the middle is a molecule of one substance, and around are four more molecules of another. It is customary to call such lattices loose, since in them the bond between metal molecules is weaker.
- Face-centered crystal lattices form compounds in which the component molecules are located on the faces. Metal scientists call such crystalline alloys dense. In reality, the density of the alloy may be higher than that of each of the components included in the composition (the alchemists of the Middle Ages were looking for alloys in which the density would correspond to the density of gold).
Melting point of metals
Different substances have different melting points. It is customary to divide metals into:
- Fusible - it is enough to heat them up to 600 ⁰С in order to obtain a substance in liquid form.
- Medium-melting metals are melted in the temperature range of 600…1600 ⁰С.
- Refractory are metals that can melt at temperatures above 1600 ⁰С.
The table shows low-melting metals in ascending order. Here you can see that the most unusual metal is mercury (Hg). Under normal conditions, it is in a liquid state. This metal has the lowest melting point.
Table 1, melting and boiling points of low-melting metals:
Table 2, melting and boiling points of medium melting metals:
Table 3, melting and boiling points of refractory metals:
To conduct the melting process, different devices are used. For example, blast furnaces are used to smelt pig iron. For melting non-ferrous metals, internal heating is carried out using currents high frequency.
In molds made of non-metallic materials, there are non-ferrous metals in the solid state. An alternating microwave magnetic field is created around them. As a result, the crystal lattices begin to loosen. The molecules of the substance begin to move, which causes heating inside the entire mass.
If it is necessary to melt a small amount of low-melting metals, muffle furnaces are used. In them, the temperature rises to 1000 ... 1200 ⁰С, which is sufficient for melting non-ferrous metals.
Ferrous metals are melted in convectors, open-hearth furnaces and induction furnaces. The process comes with the addition of alloying components that improve the quality of the metal.
The most difficult thing is to work with refractory metals. The problem is that you need to use materials that have a temperature higher than the melting point of the metal itself. Currently aviation industry considers the use of titanium (Ti) as a structural material. At high speed flight in the atmosphere, the skin is heated. Therefore, a replacement for aluminum and its alloys (AL) is needed.
The maximum melting point of this contented light metal attracts designers. Therefore, technologists develop technological processes and equipment to produce parts from titanium and its alloys.
metal alloys
To design products from alloys, their properties are first studied. To study in small containers, the studied metals are melted in different ratios to each other. As a result, graphs are built.
The lower axis represents the concentration of component A with component B. Temperature is considered vertically. Here, the values \u200b\u200bof the maximum temperature are noted when all the metal is in a molten state.
When cooled, one of the components begins to form crystals. The eutectic is in the liquid state - an ideal combination of metals in an alloy.
Metal scientists distinguish a special ratio of components at which the melting point is minimal. When alloys are made, they try to select the amount of substances used in order to obtain a eutectoid alloy. His mechanical properties the best possible. Crystal lattices form ideal face-centered positions of atoms.
The crystallization process is studied by studying the hardening of samples upon cooling. They build special graphs where they observe how the cooling rate changes. There are ready-made diagrams for different alloys. Marking the beginning and end points of crystallization, determine the composition of the alloy.
Wood's fusion
In 1860, an American dental technician, Barnabas Wood, was looking for optimal ratios of components to make teeth for clients at the lowest melting temperatures. He found an alloy that has a melting point of only 60.2 ... 68.5 ⁰С. Even in hot water, the metal melts easily. It includes:
- tin - 12.5 ... 12.7%;
- lead - 24.5 ... 25.0%;
- bismuth - 49.5 ... 50.3%;
- cadmium - 12.5 ... 12.7%.
The alloy is interesting for its low temperature, but has not found practical application. Attention! Cadmium and lead are heavy metals, contact with them is not recommended. Many people can become poisoned by contact with cadmium.
Alloys for soldering
In practice, many are faced with melting when soldering parts. If the surfaces of the materials to be joined are cleaned of impurities and oxides, then it is not difficult to solder them with solders. It is customary to divide solders into hard and soft solders. Soft are the most common:
- POS-15 - 278…282 °C;
- POS-25 - 258…262 °C;
- POS-33 - 245…249 °C;
- POS-40 - 236…241 °C;
- POS-61 - 181…185 °C;
- POS-90 - 217…222 °C.
They are produced for enterprises manufacturing various radio engineering devices.
Hard solders based on zinc, copper, silver and bismuth have a higher melting point:
- PSr-10 - 825…835 °С;
- PSr-12 - 780…790 °С;
- PSr-25 - 760…770 °С;
- PSr-45 - 715…721 °С;
- PSr-65 - 738…743 °С;
- PSr-70 - 778…783 °С;
- PMC-36 - 823…828 °С;
- PMTs-42 - 830…837 °С;
- ПМЦ-51 - 867…884 °С.
The use of hard solders allows you to get strong connections.
Attention! Cp means that silver is used in the composition of the solder. Such alloys have a minimum electrical resistance.
Melting point of non-metals
Non-metallic materials can be presented in solid and liquid form. Inorganic substances are presented in table. four.
Table 4, melting point of inorganic non-metals:
In practice, users are most interested in organic materials: polyethylene, polypropylene, wax, paraffin, and others. The melting point of some substances is shown in table. 5.
Table 5, melting point of polymeric materials:
Attention! The glass transition temperature is understood as the state when the material becomes brittle.
Video: melting point of known metals.
Conclusion
- The melting point depends on the nature of the substance itself. Most often it is a constant value.
- In practice, not pure metals are used, but their alloys. They usually have properties much better than pure metal.
