Glass - What is and how is it? Glass properties. Quartz sand - Classification and operational properties

Please tell me what melting point of sand?

1. Melting temperature
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   Temperature # 769; RA Floating # 769; and hardening # 769; The temperature at which the solid crystal body makes the transition to a liquid state and vice versa. At melting point, the substance may be both in the liquid and in the firm state. When submitting additional heat, the substance is transferred to a liquid state, and the temperature will not change until the Sun substance in the system under consideration is not melted. When the excess heat (cooling) is allotted (cooling), the substance will switch to the firm state (wing) and, until it freezes completely, the temperature will not change.

   Melting / hardening temperature and boiling / condensation temperature are considered important. physical properties Substances. The hardened temperature coincides with the melting point only for pure substance. Special thermometer calibrators are based on this property for high temperatures. Since the temperature of pouring a clean matter, for example, tin, is stable, it is enough to melted and wait until the melt is not crystallized. At this time, under the condition of good thermal insulation, the temperature of the frozen ingot does not change and exactly coincides with the reference temperature specified in reference books. Mixtures of substances do not have a melting / hardening temperature at all, and make a transition in some temperature range (the temperature of the liquid phase is called a solidus point, the temperature of full melting point of the liquidus). Since accurate to measure the melting point of this kind of substances cannot be used, special methods (GOST 20287 and ASTM D 97) are used. But some mixtures (eutectic composition) have a certain melting point, as pure substances.
   Amorphous (non-crystalline) substances, as a rule, do not have an overweight melting point, with increasing temperature decreases the viscosity of such substances, and the lower viscosity, the more liquid material becomes.
   For example, conventional window glass is a converted liquid. In a few centuries it becomes clear that at room temperature, the glass on the window slides down under the action of gravity and becomes thicker below. At a temperature of 500-600, the same effect can be observed for several days.

   Since when melting the volume of the body changes slightly, the pressure has little effect on the melting point. The dependence of the temperature of the phase transition (including melting, and boiling) on \u200b\u200bthe pressure for one-component system is given by the Klapairone-Clausius equation. The melting point at a normal atmospheric pressure (1013.25 GPa, or 760 mm mercury pillar) is called melting point.

   Melting temperatures of some important substances:

   sand (melting temperature (TPL) \u003d 1710 C), clay (TPL from 1150 to 1787 s),
   melting point C.
   hydrogen # 8722; 259.2
   oxygen # 8722; 218.8
   nitrogen # 8722; 210.0
   ethyl alcohol # 8722; 114.5
   ammonia # 8722; 77.7
   mercury # 8722; 38.87
   ice (water) +0
   benzene +5,53
   cezia +28,64.
   sugarozes +185
   sakharin +225
   owl +231,93
   lead +327,5
   aluminum +660,1
   silver +960.8.
   gold +1063.
   iron +1535
   platinum +1769,3
   corunda +2050
   tungsten +3410

2. 17131728C if the sand consists of pure quartz
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Fulgurites (English. Fulgrite) - Hollow tubes in sands consisting of composhable silica, and melted surfaces on the outcrops of rocks formed under the influence of the discharge of lightning. The inner surface is smooth and melted, and the outer form is formed by the substitresses to the melted mass and outsiders. The diameter of tubular fulgarity is not more than a few centimeters, the length can reach up to several meters, there were separate finds of flagistic 5-6 meters long.

When the lightning is discharged 10 9 -10 10 joule energy. Lightning can warm up the channel, along which it moves, to 30.000 ° C, five times higher than the temperature on the surface of the Sun. The temperature inside the zipper is much larger than the melting point of sand (1600-2000 ° C), but the sand melts or not, depends on the duration of lightning, which can be from tens of microseconds to tenths of a second. The impulse amplitude of the lightning current is usually equal to several tens of kiloampers, but sometimes can exceed 100 ka. The most powerful zippers and cause the birth of Fulgurites - hollow cylinders From melted sand.

The appearance of a glass tubule in the sand when the lightning is discharged due to the fact that air and moisture are always located between the sands. Electric lightning current for the fraction of seconds splits air and water vapors to huge temperatures, causing an explosive increase in air pressure between the sands and its expansion. The expanding air forms a cylindrical cavity inside the molten sand, and the subsequent rapid cooling fixes the fuligurite - the glass tube in the sand.

Often neatly dug from the sand fuligurite in shape resembles a root of a tree or a branch with numerous processes. Such branchy fulguits are formed when the discharge of lightning falls into wet sand, which is known to have a good electrical conductivity than dry. In these cases, the lightning current, entering the soil, immediately begins to spread to the sides, forming a structure similar to the root of the tree, and the fuligurite is born only repeats this form. Fuligurite is very fragile, and attempts to clean from sticking sand often lead to its destruction. This applies to branchy fulguits formed in wet sand.

Fulgurites sometimes also refer to solid mountain breeds, marble, lav, etc. ( petrophurgurti) formed by a lightning strike; Such refurbish sometimes in large quantities are found on the rocky vertices of some mountains. For example, the Andesit, forming the top of the Small Ararat, is permeated with numerous futgulti in the form of green glass windows, why he received from Abikha's name of Fulguirite Andesita.

The longest of the excavated Fulgurites went underground to the depth of more than five meters. Fulgurites also refer to the melted solid rock formation formed by a lightning strike; They are sometimes found in large numbers on the rocky vertices of the mountains. Fulgurites consisting of composhable silica are usually cone-shaped tubes thick with a pencil or a finger. Their inner surface is smooth and melted, and the outer surface is formed by the substincams to the melted mass. Fuligurite color depends on the impurities of minerals in sandy soil. Most of them have reddish brown, gray or black, however, there are greenish, white or even translucent fulgurites.

"A strong thunderstorm passed, and the sky had already cleared over us. I went through the field that our house separates from my companion's house. I gone yards ten along the path, how suddenly my daughter Margaret called me. I stopped for ten seconds and barely moved on, how suddenly the sky cut the bright blue line, with the roar of the twelve-yard gun, hitting the three-step to me in front of the twenty steps and raising a huge paragraph of a couple. I went on to see what a lightning left. In the place where Zipper hit, there was a stain of the burned clover inch in five diameters, with a hole in the middle of half a .... I returned to the laboratory, melted eight pounds of tin and flooded in a hole ... What I Delivered when Tin harded, it was like a huge, slightly curved dog arapist, heavy, as it should be, in the handle and gradually moving towards an end. It was a little longer than three feet "(cited by V. Sibruk. Robert Wood. - M.: Science, 1985, p. 285).

Employees of the Autonomous University of Mexico University revealed new details of the history of the appearance of the Sahara desert. According to their data, 15 thousand years ago, sugar (at least she is part of it in the south-west of Egypt) was located in the field of moderate climate and could delight the eye not with sand dunes, but a variety of vegetation. For his research, the team of chemists under the leadership of Drofael Navarro-Gonzalez found "frozen" lightning, or Fuligurite.

Fulguits (in the photo) - it is hung from the shock of lightning sand. Sand melting temperature - about 1700 ° C, power electric charge Enough to melt it. Therefore, hollow branchy glass tubes are in the thicker. Their inner surface is smooth, but the outer - rough, since it is formed by the prefects to the melted mass. In addition, such lightning in the sand is fixed and many other natural inclusions characteristic of one or another stage of geological history.

Fuligurite discovered by Navarro-Gonzalez was distinguished from ordinary tracks of lightning. Egyptian Fuligurite contained small bubbles.
With the help of a laser, scientists opened bubbles and discovered a gas mixture of carbon oxides in them, carbon monoxide and nitrogen oxides. As the chemist noted, these substances could be formed as a result of oxidation of organic substances when heated.

Analysis of the ratio of carbon isotopes in the compounds showed VVOVO-Gonzalez and his colleagues, which, at the time of the lightning strike, the grass, shrubs and other vegetation, characteristic of half-circular terrain, should be located in the damage zone. It is worth noting that now in this area of \u200b\u200bthe Sahara desert such plants in no case can grow. And scientists decided to calculate the time to understand when the grass grew in the place of Sugara.

To establish the date of the electric discharge, a member of the researcher team, Geochronologist Shannon Megen, from the Geological Research Center in Denver (USA) used the thermolumine system - heated Fuligurite to 500 ° C and estimated the energy of the "heated" natural radiation of electrons, which during heat treatment was separated in the form of light. Its quantity directly indicates at the time of the last heating. In this case, it happened at the time of the lightning strike, which occurred 15 thousand years ago.
The analysis of Fulgurita once again confirmed the theory according to which sugar not so long ago was quite suitable for living area with a temperate climate.
According to Steve Forman, a geochronologist from the University of Illinois to Chicago, scientists from Mexico demonstrated new approach To study the environmental situation of the period and drew the attention of other researchers to previously not studied facilities of Fulgurites.

As for the comments of representatives russian science, as noted in a conversation with the correspondent "Gazeta.Ru" KFMN, an employee of the Institute of Foreign Physics of the Land of the Russian Academy of Medical Sciences noted, from the point of view of physics, the team of Navarro-Gonzalez acted competently: "Everything that has been done by scientists is included in the classical model of determining the composition and The age of the substance, "he said. Accordingly, no falsifications and mystulations during this analysis of isotopes cannot be noted - rather, it is quite traditional way Research.
The staff of the Institute of Physics of the Atmosphere of the Russian Academy of Sciences also confirmed "Gazeta.Ru" the legitimacy of the theory of the international team of scientists. According to the Senior Researcher, the Laboratory of the Theory of Climate Sergey Demchenko, 15 thousand years ago, vegetation could have been completely in the south-western Egypt.

Moreover, even in the period of Holocene (about 6 thousand years ago) this area could be within a moderate climatic belt.
As clarified Demchenko's colleague, KFMN Alexey Eliseev, vegetation in various areas of the Sahara desert was present in different time, for example, at the Arabian Peninsula, the vegetation remained up to the era of Alexander Macedon.

As for the figures of 15 thousand years, here scientists noted that about this time the completion of the last glacial period. What indirectly confirms the theory of Navarro-Gonzalez, so that, in general, the discovery of Mexican scientists can be attributed to the discharge verified.
Details of the study of the team of Dr. Navarro-Gonzalez can be found in the journal of American Geological Society (Geological Society of America).

Apparently, the first description of Fulgurites and their connection with lightning strikes was made in 1706 by Pastor D. Germanic ( David Hermann.). Subsequently, many found fulguits near people affected by the discharge of lightning. Charles Darwin during around the world travel on the ship "Beagle" discovered on sandwaking Near Maldonado (Uruguay), several glass tubes flowing into the sand vertically down on more than a meter. He described their size and tied their formation with lightning discharges. Famous American physicist Robert Wood received an "autograph" of lightning, which almost killed him

Each of us has ever met glass. What is this fragile and transparent material, any schoolboy knows. We see it every day in the mirrors, windows, in dishes and furniture elements, but are we good familiar with him? How is it produced, what is the properties of glass?

What does this word mean

There is a lot reference materialswhich can help in this matter. What is the meaning of the word "glass" according to one of the most popular sources? Dictionary of Ozhegova characterizes this substance as solid materialobtained from quartz sand mixed with oxides of some metals. Even the definition gives some idea of \u200b\u200bthe production method. this material. But we will go to this topic later.

Surely everyone is accustomed that glass is a transparent material. But pay attention - Ozhegov's dictionary does not give such clarification. Glass can be not only transparent, but also color or matte. But the composition of the material is distinguished insignificant.

What makes glass

The standard composition of the glass is a mixture of pure lime and soda. Various additives can be used to change the material properties. Still, the main component is pure river sand. Its amount is approximately 75% of the entire mixture. Soda reduces sand almost 2 times. Lime protects the glass from the effects of most chemicals, and also adds strength and gloss.

Additional impurities:

• Manganese. It is added to the glass to obtain a specific green shade. Nickel or chrome can be used to get other colors.
• Lead gives glass extra shine and characteristic ringing. The material is colder to the touch. Glass with admixture of lead is called a crystal.
• Oxide boric acid Also gives the material an additional shine and transparency, while lowering the coefficient of thermal expansion of products.

History of glass production

Another 6000 years ago, people knew how to create this beautiful and fragile material. Of course Him appearance somewhat different from modern glass because Ancient Egypt And Mesopotamia did not have equipment for high-quality sand purification and other tools. Nevertheless, glass production began there. Due to resistance to influences ambient This material gave historians an idea of \u200b\u200bculture and technical capabilities Ancient peoples.

In Russia, the first glass production plant appeared in 1636. It was located not far from Moscow. There were created dishes and a large development of this industry was obtained under Peter I.

Only in 1859 the invention of the pump high pressure allowed to create glass without the participation of glass fiber. This has significantly simplified production. And in the early 19th century it was discovered interesting property material - if ready product warm up to a certain temperature mechanical properties Glasses will rise by 400%.

Modern production

Technology stepped far forward, which made it possible to create any materials in huge quantities and S. the least costs human strength. Currently, there are many factories on which glass is created by standard technology. What modern materialobtained from molten quartzite sand, learn by reading the technology. As an example, take a sheet material.

Glass production in stages:

1. All the necessary ingredients are loaded into the furnace and heated until the liquid homogeneous mass is formed.
2. In a special homogenizer, this alloy is stirred to a homogeneous state.
3. The resulting mass is poured into a flat container, at the bottom of which there is a molten tin. There, the glass is distributed, forming a uniform thin layer.
4. The cooled and hardened material goes to the conveyor. There are control of glass thickness and cutting. Material, N. past check, as well as defective parts are sent to the smelting.
5. The latest quality check is performed, after which the glass enters the finished product warehouse.

Types of glass

Currently, this material is one of the most common. Not surprisingly that exist different types Glasses, characterized in both appearance and physical properties. Here is some of them:

1. Crystal glass. This material containing lead in its composition. We talked about him above.
2. Contains the purest sand due to which it is different high strength. Able to withstand temperatures, so used to create optical devices, laboratory dishes and windows.
3. Foamglass. Easy building material that can be used for both finishing and masonry walls and floors. Contains a large amount of voids, thereby having high heat and sound insulation properties.
4. Glasswater. Volume air Materialconsisting of thin and very durable threads. Fire resistant, therefore used not only in construction, but also when sewing the clothes of firefighters and welders.

Glass use

Depending on the properties and appearance, this material can be found almost any application. The main consumer is manufactured in our time glass - the construction industry. It uses more than half of the material being manufactured. His appointment may be the most diverse - wall cladding, glazing windows, the construction of walls from hollow bricks, thermal insulation, etc. TO construction region You can attribute and what is the Gothic window, everyone knows everything. As a rule, it is posted from large number Color glass. Nowadays, stained-glass windows have not lost their relevance and are used both in construction and furniture manufacturing.

In second place in popularity go glass vessels various destination. Dishes are made slightly less. It is worth noting that in the chemical industry, the glass is an indispensable material, since it is steady to most reagents.

Physical properties

Like any other material, glass has a number of qualities that need to know before using it in a particular area.

1. Density. It may vary depending on the composition of the mixture and the method of manufacture. The density value of glass can range from 220 to 650 kg / m 3.
2. Fragility. This characteristic is a distinctive feature Glass and limits its use in the construction area. Currently, scientists create more complex alloys, the most increasing material strength.
3. Heat resistance. Normal glass Withstand temperatures up to 90 o C. After processing, the thermal properties of the material are significantly increased. For example, industrial glass can withstand the temperature of more than 200 o C.

We learned a lot about the glass - what it is made and what properties has. It's time to distract a little and get acquainted with the most interesting facts This is a very common material. Few people know that:

• The speed of the flow rate of software is 4828 km / h.
• The decomposition time of this material is approximately a million years.
• Glass can be repeatedly reproof almost without loss of quality. In this regard, he has almost no analogues.
• Being an amorphous material, the molten glass does not harde it with rapid cooling. This requires special conditions.

The glass is not in vain is so actively used in construction and other areas of human life. Surely it will remain one of the most popular Materials. In favor of this statement, strength, durability and relative simplicity of glass manufacturing are related to the fact that the components for its creation are present on the ground in large quantities.

The basis of the majority building materials make up natural components that possess necessary properties And are in sufficient quantity for industrial production. Quartz sand refers to one of the most common natural minerals and is applied in all areas of construction activities.

What is the chemical properties of the material

The main component of quartz sand is silicon dioxide (quartz). His formula is SiO2. It may also contain organic impurities, clay, iron oxides and a number of other metals. The content of quartz in the source mineral is usually at least 93-95%.

The principle of construction mixtures used to obtain construction blocks and plates is based on the chemical interaction of components. The inorganic chains formed in the result ensure the required parameters of the material.

Silicon dioxide is acidic oxide, therefore, it reacts with calcium and aluminum compounds contained in limestone and clay. The interaction can occur both when drying the wet mixture and in thermal baked.

Varieties of quartz sand and its prey

Highlight natural I. artificial species Sand, differing in the production method.

Natural natural

This type of sand is widespread in nature and is located at the bottom of the water pools and as part of the soil thickness. The dimensions of most of its grains range from 0.2 to 1 mm.

There are several quartz sand mining paths:

• career development - It is the main way. If mining is carried out above sea level, the sand gained is called mountain. Varieties of soil sand are extracted in the development of soil on the plains. Appearance career sand It is characterized by pointed forms and often - rough surface, which makes this valuable building material. The extracted sand can be subject to additional processing - sifting, washing and dried. The striking the requirements for the properties of sand in any industry, the more carefully the preparation is required. In the construction of small sand structures, it is usually not exposed to no effect and deliver directly from its prey;
• development of water basins - The sand is washed out with dredge and characterized by a high purity provided by natural flushing. Mining is conducted in the river river, lakes, as well as marine waters. Sea sand somewhat less valuable due to greater content of mineral impurities. River sand is distinguished by a smooth form - under the increase in the sand microscope resemble sea pebbles. The use of smooth (retoticered) sands is distributed in self-leveling mixtures - the grains are not cling to each other.

So the photo looks like natural quartz sand

Artificial sand

Despite the name, the mineral has a natural origin, but is initially in the form of large crystals. To convert quartz crystals in the sand, a mechanical impact (explosion) is used, after which the fragments are exposed to crushing.

Quartz sand classification methods

The starting point in the classification system is the properties of the material and the ways to prepare it. Select the following areas of quartz sand classification:

By size (fractional composition)

The numerical expression is the average value of the particle size or the range of their size (fraction):

1. pull quartz represents a fraction of less than 0.1 mm (sifted to a sieve with a pore diameter of 0.1 mm) and is usually found when crushing quartz crystals;
2. small grade sand - fraction 0.1-0.25 mm;
3. middle sand - fraction 0.25-0.5 mm;
4. coarse sand - fraction 0.5-1 (rare up to 3) mm.

For enrichment

Quartz sand is divided into uneducated and enriched sand:

• sad sand is the source mineral that was not processed to increase the content of silica;
• enriched sand contains a few percent quartz content obtained by removing most impurities. So, white quartz sand is cleared of organic compounds, iron oxides and clay impurities by sieving, washing and drying.

Due to the peculiarities of production differ and the main specifications The material obtained. This in turn affects the possibility of further .

Enrichment technology

The high purity of the quartz mix is \u200b\u200ba necessary requirement in a number technological processes. The initial stage of enrichment includes fractionation and flushing - with their help the coarse impurities are removed.

The next step is to use special technologies, such as:

• gravitational enrichment - The main method, the essence of which consists in the separation of the components of the mixture by density. Lighter particles are carried away with water flow, while heavy settles on the bottom of the apparatus. The gravitational impact can be enhanced by centrifugation or addition of chemical reagents changing the wettability of sand components;
• electric and magnetic separation - is an impact electric shock and magnetic fieldleading to the separation of some impurities. Thus, the magnetic effect is particularly effective when cleaning from particles of iron with magnetic properties.

The parameters of the enriched sand fundamentally affect the quality of the work performed. The best sandy mixtures produce only certified enterprises using standard technologies.

By coloring

It happens natural and painted. Natural quartz sand has a color from pale yellow to brownish yellow. Artificial painting is carried out by resistant paints based on synthetic binders, allowing you to create original multicolor ornaments from the sand. Such sand can be colored and white.

According to the degree of training

Depending on the technological requirements, sand can be produced in the following varieties:

1. fractional - represents a specific sand fraction, the dimensions of which are limited to the technical regulations;
2. dry - dried to air-dry state. Together with fractionated sand can be used as a working fluid of sandblasting machines;
3. curved sand - Fully dehydrated by calcination. Heating significantly above 100 ° C provides desorption of moisture even from deep pores quartz. Such sand is used in ready-made construction mixesstored for a long time - even a minor moisture content can be in disrepair the whole mixture;
4. retranged quartz sand - has less abrasive properties, therefore suitable for delicate use, for example, sandboxes in playgrounds;
5. forming quartz sand - It is used to obtain cast quartz products and is characterized by a high degree of enrichment.

Production and mining of quartz sand

There is a significant number of large quartz sand deposits in Russia. The most famous includes Chulkovsky (Moscow region), Kozlovskoye (Bryansk region), Elshanskoye (Volgograd region), Berezichkoye (Kaluga region) of the deposit and a number of others.

Differences quartz construction sand, mined from these places, is initially high quality parameters and greater cost. It is important to understand that the properties of sand from the nearest career will be quite sufficient for the construction of small dual facilities, Therefore, you should not overpay. If the goal is to build a major mansion, then the savings on the quality of sand can negatively affect the durability of the house.

This is the mining of quartz sand on a special production line:

What normalizes the characteristics of the sand

The main regulatory document is GOST 2138-91, there are also other regulations (gOST 22551 77, GOST 51641 2000, 8736 93). They reflect the requirements for the basic parameters of quality and properties, namely:

1. the content of the clay component. 5 groups with mounted clay quantities of 0.2 to 2.0% are isolated;
2. the content of silica - from 99% to 93%, corresponding to groups from K1 to K5;
3. the coefficient of homogeneity reflecting the variation of particles relative to the average (in%). The greater the value, the time is sand mix. There are only five groups (from O1 to O5), characterized by the coefficient of homogeneity (from 80 to 50%);
4. fractional composition. This parameter reflects the average size of quartz sand particles: up to 0.14 mm; 0.14-0.18 mm, 0.19-0.23 mm, 0.24-0.28 mm, more than 0.28 mm;
5. humidity. Dry sands contain no more than 0.5% moisture, wet - no more than 4.0%, raw - no more than 6.0%;
6. the composition of the sand is also normalized by the content of metal oxides, the surface area of \u200b\u200bgrains, their shape, gas permeability, as well as weight loss during calcination.

High-quality sand must necessarily have a certificate of compliance with these standards.

Operating properties of quartz sand

The parameters of the material affecting the quality of work and the decisive scope include:

• bulk density is about 1300-1500 kg / m3;
• true density is in the range of 2600-2700 kg / m3. The value of the true density is used in calculating the volume of the cement or concrete solution obtained by mixing the components;
• the thermal conductivity of quartz sand is about 0.30 W / (m? ° С). A significant effect on heat insulating properties has a form and dimensions of sandy granules - the more denser their location and less gaps, the factory thermal conductivity above;
• melting temperature -maximum working temperature quartz sand is estimated at 1050 ° C, which is quite enough for any construction work. When casting quartz products, temperatures are 1700 ° C and higher.
• ordinary quartz sand in loose state has volume weight 1 500 kg / m3, and the bulkmower is 1600 kg / m3.

The advantages and disadvantages of the material - the overall rating

Quartz sand is a practically indispensable component in a variety of applications, and technology with its participation is worked out to perfection. For practicality, the material receives "5".

The appearance of the sand is familiar with childhood, and the sanding platforms are often associated with the beach and recreation - for the appearance also put a solid "5".

Despite the massive use of sand, its fine dust can lead to chronic diseases from builders. For environmental friendliness, the material receives "4".

The cost of sand is comparable with the cost of other building materials. Without possessing special advantages in the price, quartz sand perfectly deserves the estimates of "4".

The approximate cost of various quartz sand fractions is given in Table:

Along with clay and limestone, quartz sand is among the most important and necessary components for production and life. The variety of material properties provides wide spectrum Applications. Availability sand quarries Not far from the construction site significantly reduces the exercise costs.

The melting and hardening temperature is the temperature at which the solid crystal body makes the transition to a liquid state and vice versa. At the melting point, the substance may be both in liquid and in solid state. When submitting additional heat, the substance will switch to a liquid state, and the temperature will not change until the entire substance is melted in the system under consideration. When the excess heat (cooling) is allocated, the substance will switch to a solid state (wing) and until it freezes completely, the temperature will not change.

The melting / hardening temperature and boiling / condensation temperature are considered important physical properties of the substance. The hardened temperature coincides with the melting point only for pure substance. Special thermometer calibrators for high temperatures are based on this property. Since the temperature of pouring the pure substance, for example, tin, is stable, it is enough to melt and wait until the melt starts crystallize. At this time, under the condition of good thermal insulation, the temperature of the frozen ingot does not change and exactly coincides with the reference temperature specified in reference books. Mixtures of substances do not have a melting / hardening temperature at all, and make a transition in a certain temperature range (the temperature of the liquid phase is called a solid to the point, the temperature of full melting is a waterpoint). Since accurate to measure the melting point of this kind of substances cannot be used, special methods (GOST 20287 and ASTM D 97) are used. But some mixtures (eutectic composition) have a certain melting point, as pure substances.
Amorphous (non-crystalline) substances, as a rule, do not have a clear melting point, with increasing temperature, the viscosity of such substances is reduced, and the lower viscosity, the more liquid material becomes.
For example, ordinary window glass is a supercooled fluid. In a few centuries it becomes clear that at room temperature, the glass on the window slides down under the action of gravity and becomes thicker below. At a temperature of 500-600, the same effect can be observed for several days.

Since when melting the body volume changes insignificantly, the pressure has little effect on the melting point. The dependence of the temperature of the phase transition (including melting, and boiling) on \u200b\u200bthe pressure for one-component system is given by the Klapairone-Clausius equation. The melting point at a normal atmospheric pressure (1013.25 GPa, or 760 mm mercury pillar) is called melting point.

Melting temperatures of some important substances:

Sand (melting temperature (TPL) \u003d 1710 ° C), clay (TPL from 1150 to 1787 ° C),
Melting temperature ° C
hydrogen -259,2
oxygen -218.8.
Nitrogen -210,0
Ethyl alcohol -114,5
Ammonia -77,7
Mercury -38,87
Ice (water) +0
Benzene +5,53
Cezia +28,64.
Sugarozes +185
Sakharin +225
Owl +231,93
Lead +327,5
Aluminum +660,1
Silver +960.8.
Gold +1063.
Iron +1535
platinum +1769,3
Corunda +2050
Tungsten +3410