T melting. Melting temperature, properties and self-smelting of cast iron

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 in the periodic table are 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 low-melting 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 whose simple substances 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.

At which the crystal lattice of the metal is destroyed and it passes from the solid state to the liquid state.

The melting point of metals is an indicator of the temperature of the heated metal, upon reaching which the process (melting) begins. The process itself is the reverse of crystallization and is inextricably linked with it. To melt metal? it must be heated using an external heat source to the melting temperature, and then continue to supply heat to overcome the energy of the phase transition. The fact is that the very value of the melting point of metals indicates the temperature at which the material will be in phase equilibrium, at the boundary between the liquid and the solid. At this temperature, a pure metal can exist simultaneously in both solid and liquid states. To carry out the melting process, it is necessary to overheat the metal slightly above the equilibrium temperature in order to provide a positive thermodynamic potential. Give a boost to the process.

The melting point of metals is constant only for pure substances. The presence of impurities will shift the equilibrium potential in one direction or another. This is because the metal with impurities forms a different crystal lattice, and the interaction forces of atoms in them will differ from those present in pure materials. Depending on the melting point, metals are divided into fusible (up to 600 ° C, such as gallium , mercury), medium-melting (600-1600°С, copper, aluminum) and refractory (>1600°С, tungsten, molybdenum).

In the modern world, pure metals are rarely used due to the fact that they have a limited range of physical properties. The industry has long and densely used various combinations of metals - alloys, the varieties and characteristics of which are much larger. The melting point of the metals that make up the various alloys will also differ from the melting point of their alloy. Different concentrations of substances determine the order of their melting or crystallization. But there are equilibrium concentrations at which the metals that make up the alloy solidify or melt simultaneously, that is, they behave like a homogeneous material. Such alloys are called eutectic.

Knowing the melting temperature is very important when working with metal, this value is necessary both in production, for calculating the parameters of alloys, and in the operation of metal products, when the phase transition temperature of the material from which the product is made determines the limitations in its use. For convenience, these data are summarized in a single melting of metals - a summary result of physical studies of the characteristics of various metals. There are also similar tables for alloys. The melting point of metals also significantly depends on pressure, so the data in the table are relevant for a specific pressure value (usually these are normal conditions when the pressure is 101.325 kPa). The higher the pressure, the higher the melting point, and vice versa.

Already in ancient times, people mined and smelted copper. This metal was widely used in everyday life and served as a material for the manufacture of various items. They learned how to make bronze about 3 thousand years ago. Good weapons were made from this alloy. The popularity of bronze quickly spread, as the metal was distinguished by its beautiful appearance and strength. Jewelry, hunting and labor tools, dishes were made from it. Due to the low melting point of copper, man quickly mastered its production.

Being in nature

The metal received its Latin name Cuprum from the name of the island of Cyprus, where it was mined in the third millennium BC. e. In the Mendeleev system, Cu received number 29, and is located in the 11th group of the fourth period.

In the earth's crust, the element is in 23rd place in terms of distribution and occurs more often in the form of sulfide ores. The most common are copper luster and pyrites. Today, copper is mined from ore in several ways, but any technology implies a phased approach to achieve the result.

Physical properties

The metal is ductile and covered with an oxide film in the open air in a short time. Thanks to this film, copper also has its yellowish-red hue; in the film gap, the color can be greenish-blue. In terms of thermal and electrical conductivity, Cuprum is in second place after silver.

• Density - 8.94×103 kg/m3.
• Specific heat at T=20°C - 390 J/kg x K.
• Electrical specific at 20−100 ° C - 1.78×10−8 Ohm/m.
• Boiling point - 2595 ° C.
• Specific electrical conductivity at 20 ° C - 55.5−58 MS/m.

At what temperature does copper melt

Melting occurs when a metal changes from a solid state to a liquid state. Each element has its own melting point. Much depends on the impurities in the metal. The normal melting point of copper is 1083°C. When tin is added, the temperature drops to 930-1140°C. The melting point here depends on the content of tin in the alloy. In an alloy of cuprum with zinc, melting occurs at 900-1050 ° C.

When heating any metal its crystal lattice is destroyed. The melting point rises as it is heated, but then levels off when a certain temperature limit is reached. At this point, the metal melts. It melts completely and the temperature rises again.

When the metal is cooled, the temperature decreases, at a certain point it remains at the same level until the metal solidifies completely. After complete hardening, the temperature decreases again. This is demonstrated by the phase diagram, which shows the temperature process from the beginning of melting to solidification. When heated, heated copper at 2560 ° C begins to boil. Boiling is similar to the boiling of liquid substances, when gas is released and bubbles appear on the surface. At the moment of boiling at the highest possible temperatures, the release of carbon formed during oxidation begins.

Melting at home

Due to the low melting point ancient people could melt cuprum on a fire and use the metal to make various products.

To melt copper at home you will need:

The process proceeds in stages, the metal is placed in the crucible and then placed in the muffle furnace. The desired temperature is set, and the process is monitored through a glass window. In the process, an oxide film will appear in the container with Cu, which must be removed - open the window and move it aside with a steel hook.

In the absence of a muffle furnace, copper can be melted with autogenous. Melting will go if there is a normal air supply. A blowtorch melts brass and low-melting bronze. The flame must cover the entire crucible.

If none of the listed products is at hand, you can use a hearth mounted on a layer of charcoal. To increase T, you can use a vacuum cleaner switched on in blowing mode, but the hose must have a metal tip, it’s good if it has a narrower end, so the air stream will be thinner.

The melting point of bronze and brass, as well as the melting point of copper and aluminum, are low.

Today, pure Cu is not used in industrial conditions. It contains many impurities: nickel, iron, arsenic, antimony, and other elements. The quality of the product is determined by the percentage of impurities in the alloy (not more than 1%). Important indicators are thermal and electrical conductivity. Due to its ductility, low melting point and flexibility, copper is widely used in many industries.

Density and melting point of some metals.

Metal	Atomic weight of metal	Density of metal, g/cm3	Melting point, С
Light metals
Aluminum
Heavy metals
Manganese
Tungsten

For metals, the following properties are most characteristic:
*metallic sheen
*hardness,
*plastic,
*ductility,
*good conductivity of heat and electricity.

All metals have a metallic crystal lattice:
positively charged ions are located at its nodes, and electrons move freely between them.
The presence of free electrons explains the high electrical and thermal conductivity, as well as the ability to be machined.

Thermal conductivity and electrical conductivity decrease in the series of metals:
Ag Cu Au Al Mg Zn Fe Pb Hg

All metals are divided into two large groups:

Black metals
They have a dark gray color, high density, high melting point and relatively high hardness.
Iron is a typical representative of ferrous metals.

Non-ferrous metals
They have a characteristic color: red, yellow, white; have high plasticity, low hardness, relatively low melting point.
A typical representative of non-ferrous metals is copper.

According to their density, metals are divided into:
*Lungs(density not more than 5 g/cm)
Light metals include: lithium, sodium, potassium, magnesium, calcium, cesium, aluminum, barium.
The lightest metal is lithium 1l, density 0.534 g/cm3.
*Heavy(density greater than 5 g/cm3).
Heavy metals include: zinc, copper, iron, tin, lead, silver, gold, mercury, etc.
The heaviest metal is osmium, density 22.5 g/cm3.

Metals vary in their hardness:
*Soft: cut even with a knife (sodium, potassium, indium);
*Solid: metals are compared in hardness with diamond, whose hardness is 10. Chrome is the hardest metal, it cuts glass.

Depending on the melting point, metals are conditionally divided into :
*fusible(melting point up to 1539°C).
Low-melting metals include: mercury - melting point -38.9°C; gallium - melting point 29.78°C; cesium - melting point 28.5°C; and other metals.
*Refractory(melting point above 1539 C).
Refractory metals include: chromium - melting point 1890°C; molybdenum - melting point 2620°C; vanadium - melting point 1900°C; tantalum - melting point 3015°C; and many other metals.
The most refractory metal is tungsten - melting point 3420°C.

Each metal or alloy has unique properties, including its melting point. In this case, the object passes from one state to another, in a particular case, it becomes from a solid to a liquid. To melt it, it is necessary to bring heat to it and heat it until the desired temperature is reached. At the moment when the desired temperature point of a given alloy is reached, it can still remain in a solid state. With continued exposure, it begins to melt.

In contact with

Mercury has the lowest melting point - it melts even at -39 ° C, tungsten has the highest - 3422 ° C. For alloys (steel and others), it is extremely difficult to determine the exact figure. It all depends on the ratio of the components in them. For alloys, it is written as a numerical interval.

How is the process

Elements, whatever they are: gold, iron, cast iron, steel, or any other - melt about the same. This happens with external or internal heating. External heating is carried out in a thermal furnace. For internal, resistive heating is used, passing an electric current or induction heating in high frequency electromagnetic field. The impact is about the same.

When heating occurs, the amplitude of thermal vibrations of molecules increases. Appear lattice structural defects accompanied by the breaking of interatomic bonds. The period of lattice destruction and accumulation of defects is called melting.

Depending on the degree at which metals are melted, they are divided into:

1. fusible - up to 600 ° C: lead, zinc, tin;
2. medium-melting - from 600 ° C to 1600 ° C: gold, copper, aluminum, cast iron, iron and most of all elements and compounds;
3. refractory - from 1600 ° C: chromium, tungsten, molybdenum, titanium.

Depending on what the maximum degree is, the melting apparatus is also selected. It should be the stronger, the stronger the heating.

The second important value is the degree of boiling. This is the parameter at which liquids begin to boil. As a rule, it is twice the degree of melting. These values ​​are directly proportional to each other and are usually given at normal pressure.

If the pressure increases, the amount of melting also increases. If the pressure decreases, then it decreases.

Characteristic table

Metals and alloys - indispensable basis for forging, foundry, jewelry and many other areas of production. Whatever the master does ( gold jewelry, cast iron fences, knives made of steel or copper bracelets), for proper operation, he needs to know the temperatures at which this or that element melts.

To find out this parameter, you need to refer to the table. In the table you can also find the degree of boiling.

Among the most commonly used elements in everyday life, the melting point indicators are as follows:

1. aluminum - 660 °C;
2. melting point of copper - 1083 °C;
3. melting point of gold - 1063 ° C;
4. silver - 960 °C;
5. tin - 232 °C. Tin is often used for soldering, since the temperature of a working soldering iron is just 250–400 degrees;
6. lead - 327 °C;
7. melting point of iron - 1539 ° C;
8. melting temperature of steel (an alloy of iron and carbon) - from 1300 °C to 1500 °C. It fluctuates depending on the saturation of steel components;
9. melting point of cast iron (also an alloy of iron and carbon) - from 1100 ° C to 1300 ° C;
10. mercury - -38.9 ° C.

As is clear from this part of the table, the most fusible metal is mercury, which is already in a liquid state at positive temperatures.

The degree of boiling of all these elements is almost twice, and sometimes even higher than the degree of melting. For example, for gold it is 2660 ° C, for aluminum - 2519°C, for iron - 2900 ° C, for copper - 2580 ° C, for mercury - 356.73 ° C.

For alloys such as steel, cast iron and other metals, the calculation is approximately the same and depends on the ratio of components in the alloy.

The maximum boiling point for metals is rhenium - 5596°C. The highest boiling point is in the most refractory materials.

There are tables that also indicate density of metals. The lightest metal is lithium, the heaviest is osmium. Osmium has a higher density than uranium and plutonium when viewed at room temperature. Light metals include: magnesium, aluminum, titanium. Heavy metals include most common metals: iron, copper, zinc, tin and many others. The last group is very heavy metals, these include: tungsten, gold, lead and others.

Another indicator found in the tables is thermal conductivity of metals. Worst of all, neptunium conducts heat, and silver is the best thermal conductor. Gold, steel, iron, cast iron and other elements are in the middle between these two extremes. Clear characteristics for each can be found in the desired table.