As the temperature decreases, a substance can change from a liquid state to a solid state.

This process is called solidification or crystallization.
During the solidification of a substance, the same amount of heat is released, which is absorbed during its melting.

The calculation formulas for the amount of heat during melting and crystallization are the same.

The melting and solidification temperatures of the same substance, if the pressure does not change, are the same.
Throughout the process of crystallization, the temperature of the substance does not change, and it can simultaneously exist in both liquid and solid states.

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INTERESTING ABOUT CRYSTALLIZATION

Colored ice?

If you add a little paint or tea leaves to a plastic glass with water, stir it and, having received a colored solution, wrap the glass on top and expose it to frost, then a layer of ice will begin to form from the bottom to the surface. However, don't expect to get colored ice!

Where the freezing of water began, there will be an absolutely transparent layer of ice. Its upper part will be colored, and even stronger than the original solution. If the concentration of paint was very high, then a puddle of its solution may remain on the surface of the ice.
The fact is that transparent fresh ice is formed in solutions of paint and salts. growing crystals displace any foreign atoms and impurity molecules, trying to build a perfect lattice while it is possible. Only when the impurities have nowhere to go does the ice begin to build them into its structure or leave them in the form of capsules with a concentrated liquid. Therefore, sea ice is fresh, and even the dirtiest puddles are covered with transparent and clean ice.

At what temperature does water freeze?

Is it always at zero degrees?
But if boiled water is poured into an absolutely clean and dry glass and placed outside the window in frost at a temperature of minus 2-5 degrees C, covered with clean glass and protected from direct sunlight, then in a few hours the contents of the glass will cool below zero, but remain liquid.
If you then open a glass and throw a piece of ice or snow or even just dust into the water, then literally before your eyes the water will instantly freeze, sprouting throughout the volume with long crystals.

Why?
The transformation of a liquid into a crystal occurs primarily on impurities and inhomogeneities - dust particles, air bubbles, irregularities on the walls of the vessel. Pure water has no centers of crystallization and can be supercooled while remaining liquid. In this way, it was possible to bring the water temperature to minus 70°C.

How does it happen in nature?

In late autumn, very clean rivers and streams begin to freeze from the bottom. Through a layer of clear water it is clearly visible that algae and driftwood at the bottom are overgrown with a loose ice coat. At some point, this bottom ice emerges, and the surface of the water instantly turns out to be bound by an ice crust.

The temperature of the upper layers of water is lower than the deep ones, and freezing seems to start from the surface. However, pure water freezes reluctantly, and ice first of all forms where there is a suspension of silt and a solid surface - near the bottom.

Downstream of waterfalls and dam spillways, there is often a spongy mass of in-water ice growing in churning water. Rising to the surface, it sometimes clogs the entire channel, forming the so-called zazhory, which can even dam the river.

Why is ice lighter than water?

Inside the ice there are many pores and gaps filled with air, but this is not the reason that can explain the fact that ice is lighter than water. Ice and without microscopic pores
still has a density less than that of water. It's all about the features of the internal structure of ice. In an ice crystal, water molecules are located at the nodes of the crystal lattice so that each has four "neighbors".

Water, on the other hand, does not have a crystalline structure, and molecules in a liquid are located closer than in a crystal, i.e. water is denser than ice.
First, when ice melts, the released molecules still retain the structure of the crystal lattice, and the density of water remains low, but gradually the crystal lattice is destroyed, and the density of water increases.
At a temperature of + 4°C, the density of water reaches a maximum, and then, with an increase in temperature, it begins to decrease due to an increase in the rate of thermal motion of molecules.

How does a puddle freeze?

When cooled, the upper layers of water become denser and sink down. Their place is taken by denser water. Such mixing occurs until the water temperature drops to +4 degrees Celsius. At this temperature, the density of water is maximum.
With a further decrease in temperature, the upper layers of water can already shrink more, and gradually cooling down to 0 degrees, the water begins to freeze.

In autumn, the air temperature at night and day is very different, so the ice freezes in layers.
The bottom surface of ice on a freezing puddle is very similar to a cross section of a tree trunk:
concentric rings are visible. The width of the ice rings can be used to judge the weather. Usually the puddle starts to freeze from the edges, because. there is less depth. The area of ​​the formed rings decreases with approach to the center.

INTERESTING

That in the pipes of the underground part of buildings, water often freezes not in frost, but in thaw!
This is due to the poor thermal conductivity of the soil. Heat passes through the earth so slowly that the minimum temperature in the soil occurs later than on the surface of the earth. The deeper, the more late. Often, during frosts, the soil does not have time to cool, and only when a thaw sets in on the ground does frost reach the ground.

That, freezing in a corked bottle, water breaks it. What happens to a glass if you freeze water in it? Water, freezing, will expand not only upwards, but also to the sides, and the glass will shrink. This will still lead to the destruction of the glass!

DID YOU KNOW

There is a known case when the contents of a bottle of narzan well chilled in the freezer, opened on a hot summer day, instantly turned into a piece of ice.

The metal "cast iron" behaves interestingly, which expands during crystallization. This allows it to be used as a material for artistic casting of thin lace lattices and small table sculptures. Indeed, when solidifying, expanding, cast iron fills everything, even the most delicate details of the form.

In the Kuban, strong drinks are prepared in winter - “freezes”. To do this, the wine is exposed to frost. First of all, water freezes, and a concentrated solution of alcohol remains. It is drained and the operation is repeated until the desired strength is achieved. The higher the concentration of alcohol, the lower the freezing point.

The largest hailstone recorded by people fell in Kansas, USA. Its weight was almost 700 grams.

Oxygen in a gaseous state at a temperature of minus 183 degrees C turns into a liquid, and at a temperature of minus 218.6 degrees C, solid oxygen is obtained from liquid

In the old days, people used ice to store food. Carl von Linde created the first home refrigerator powered by a steam engine that pumped freon gas through pipes. Behind the refrigerator, the gas in the pipes condensed and turned into a liquid. Inside the refrigerator, liquid freon evaporated and its temperature dropped sharply, cooling the refrigerator compartment. Only in 1923, Swedish inventors Balzen von Platen and Carl Muntens created the first electric refrigerator, in which freon turns from liquid into gas and takes heat from the air in the refrigerator.

THIS IS YES

Several pieces of dry ice thrown into burning gasoline extinguish the fire.
There is ice that would burn fingers if it could be touched. It is obtained under very high pressure, at which water turns into a solid state at a temperature well above 0 degrees Celsius.

Almost all types of polymers that are found on the market of industrial and building materials and products can also be produced in the form liquid two-component mixtures, enamels and solutions. These materials are a semi-finished product for further production of hard coatings, parts and elements of complex structures. Semi-finished products have a wide range of uses, from large-scale industrial production to individual household needs.

Types and purposes of liquid plastics

The term "liquid plastics" is a code name for a whole group of products produced in the form of an initial fluid mass, which, after being poured into molds or coated on surfaces, acquires the qualities of a solid synthetic material.

Chemical reactions that start the process of hardening of the material proceed under the influence of air. Depending on the type of mixture, the process can proceed at normal ambient temperature or at elevated temperatures. The main types are as follows:

• Liquid plastic paints are a universal coating for all types of surfaces that reliably protect products, parts and containers from the effects of chemically aggressive liquids, mechanical shocks, corrosion and give decorative and aesthetic qualities to structures. Paints are mixtures of polyurethane, acrylic or alkyds with coloring and plasticizing additives. As a solvent, as a rule, organic compounds are used.
• Polymer compounds for sealing joints, filling gaps and holes are significantly superior in their technical characteristics to the commonly used silicone sealants. The starting material has the consistency of a paste, and after hardening acquires the strength and elasticity of a solid polymer.
• Cold-cured injection molded plastics are fluid two-component formulations that, when mixed, cure in the open air. The composition polymerizes at normal ambient temperature for a short period of time. The material is ideal for casting various complex shapes, as it repeats even the smallest details of the matrix.
• Liquid plastic for a car is applied to the body to preserve the paintwork, prevent the formation of microcracks, protect the metal from rust and mechanical damage. The polymer coating prevents the "native" color of the car from fading, enhances the effect of shine and novelty of the body.

Application of liquid polymers

Due to the highest technical characteristics, convenience and manufacturability of work injection molded plastic is often used instead of a wide variety of structural materials of artificial and natural origin. Some applications of liquid polymers are worth considering in detail.

Polyurethane flooring

Traditionally, floors in industrial buildings have a concrete or mosaic pavement cut into 6x6 m cards. Depending on the type of technological processes, floors in workshops can also be tiled, have reinforced waterproofing and other technical features.

Recently, polyurethane self-leveling floors are gaining more and more popularity. Polymeric flooring has the following distinctive properties:

• high wear resistance and strength, allowing the operation of the coating as a surface for the passage of forklifts, cars and even trucks;
• high maintainability, providing the possibility of quick and high-quality restoration of damaged areas. For this, cold-curing liquid plastics are used;
• excellent waterproofing characteristics, which make it possible to use this floor design in rooms with wet technological processes;
• resistance to ultraviolet radiation;
• the possibility of operation in the presence of chemically aggressive environments;
• resistance to spills of technical liquids, such as solvents, fuels and lubricants and others;
• the possibility of laying the polymer composition on almost any surface - concrete, cement, wood, stone base, metal plates;
• polyurethane-coated floors are easy to use, easy to hand and mechanized washing and cleaning;
• floors can be used both in heated and unheated rooms, as well as in rooms with high humidity and sudden changes in temperature;
• Polyurethane concrete floor coating has high aesthetic qualities and gives the room a neat and modern look.

Molded polymer coatings can be installed both indoors and outdoors (open warehouses for raw materials and finished products, parking lots, tennis courts, roller skating, go-karting and other technical and sports facilities). Liquid plastic can be used for application to asphalt pavements as road markings.

In addition to polyurethane coatings for finishing street building structures, steps, stairs, fences, various small architectural forms, polymer-alkyd-based paints can also be used.

The application of such compositions does not require careful surface preparation and reliably protects structures from corrosion, the effects of mechanical loads, impacts and shocks. The coating is easily cleaned from dust and dirt and has a beautiful and attractive appearance.

Liquid plastics for windows

One of the relatively new areas of application of liquid plastics is the sealing of plastic window and door mounting assemblies. The use of polyvinyl chloride adhesives for these purposes is gradually replacing traditional silicone sealants and mastics.

Unlike silicone, liquid polyvinyl chloride, filling the gaps, enters into a chemical bond with plastic window structures, starting the process of chemical welding of parts. At the end of the polymerization process, a strong homogeneous plastic structure is formed, which does not have pronounced joint boundaries.

Flowable polymer mixtures for windows can have a variety of colors and shades. Available in transparent materials. The cured material will not fade or shrink over time, making the seal better and more durable than silicone fill.

Injection molded two-component plastics

One of the most popular applications for liquid polymer blends is production of various parts by pouring the material into the appropriate molds. Liquid plastic for casting is a two-component mixture consisting of a base and a hardener, which, interacting with each other, form. The material is widely used for the manufacture of such products:

• building blocks;
• facade structures;
• relief decorative elements;
• sculptures, masks and other volumetric art products;
• rollers, rollers, wheels;
• plates for lining metal structures;
• chemically resistant lining elements of tanks and containers;
• medical prostheses;
• anti-vibration bushings, gaskets and nozzles.

After pouring into molds, the two-component liquid plastic polymerizes and hardens, exactly repeating the smallest details of the matrix. After extraction from the mold, the surface of the product can be further refined mechanically or manually.

Ease of processing makes this material popular among workers in creative specialties.

Types and grades of cast polymers differ from each other in the rate of hardening, the degree of density, plasticity, strength, hardness, as well as color solutions and the level of transparency. Products obtained by pouring liquid plastic are superior in performance to products made from rubber, rubber, gypsum and concrete mixes.

Any element can be in several different states, subject to some external conditions. Melting and solidification of crystalline bodies are the main changes in the structure of materials. A good example is water, which can be in liquid, gaseous, and solid states. These different forms are called aggregate (from the Greek. “I bind”) states. The state of aggregation is the forms of one element, which differ in the nature of the arrangement of particles (atoms), which do not change their structure.

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How change happens

There are several processes that characterize shape changing various substances:

• hardening;
• boiling;
• (from a solid form immediately to a gaseous one);
• evaporation;
• fuse;
• condensation;
• desublimation (reverse transition from sublimation).

Each transformation is characterized by certain conditions that must be met for a successful transition.

Formulas

What process is called thermal? Any, in which there is a change in the aggregate states of materials, since temperature plays an important role in them. Any thermal change has its opposite: from liquid to solid and vice versa, from solid to vapor and vice versa.

Important! Almost all thermal processes are reversible.

There are formulas by which you can determine what the specific heat will be, that is, the heat required to change 1 kg of solid.

For example, the solidification and melting formula is: Q=λm, where λ is the specific heat.

But the formula for displaying the cooling and heating process is Q \u003d cmt, where c is the specific heat capacity - the amount of heat to heat 1 kg of material by one degree, m is the mass, and t is the temperature difference.

Formula for condensation and vaporization: Q=Lm, where specific heat is -L and m is mass.

Description of processes

Melting is one of the methods of deformation of the structure, change from solid to liquid. It proceeds in almost the same way in all cases, but in two different ways:

• the element is heated externally;
• heating comes from within.

These two methods differ in tools: in the first case, the substances are heated in a special furnace, and in the second, they pass current through the object or inductively heat it, placing it in an electromagnetic field with high frequencies.

Important! The destruction of the crystalline structure of the material and the occurrence of changes in it leads to the liquid state of the element.

Using different tools, you can achieve the same process:

• the temperature rises;
• the crystal lattice changes;
• particles move away from each other;
• other violations of the crystal lattice appear;
• interatomic bonds are broken;
• a quasi-liquid layer is formed.

As it has already become clear, temperature is the main factor due to which element state changes. The melting point is divided into:

• lungs - no more than 600 ° C;
• medium - 600-1600 ° C;
• tight - over 1600 ° С.

The tool for this work is chosen according to belonging to one or another group: the more it is necessary to heat the material, the more powerful the mechanism should be.

However, you should be careful and compare the data with the coordinate system, for example, the critical temperature of solid mercury is -39 ° C, and solid alcohol - -114 ° C, but the largest of them will be -39 ° C, since this number is closer to zero.

An equally important indicator is the boiling point, at which the liquid boils. This value is equal to the heat of vapors formed above the surface. This indicator is directly proportional to pressure: with an increase in pressure, the melting point rises and vice versa.

Auxiliary materials

Each material has its own temperature indicators at which its shape changes, and for each of them it is possible to draw up its own melting and solidification schedule. Depending on the crystal lattice, the indicators will change. For example, ice melt chart shows that it needs very little heat, as shown below:

The graph shows the ratio of the amount of heat (vertically) and time (horizontally) needed to melt ice.

The table shows how much is needed to melt the most common metals.

The melting chart and other auxiliary materials are essential during the experiments in order to follow the changes in the position of the particles and to notice the beginning of the change in the shape of the elements.

solidification of bodies

Hardening is changing the liquid form of an element into a solid form. The prerequisite is that the temperature drops below the freezing point. During this procedure, a crystal structure of molecules can form, and then the change of state is called crystallization. In this case, the element in liquid form must cool to the solidification or crystallization temperature.

Melting and solidification of crystalline bodies is carried out under the same environmental conditions: it crystallizes at 0 ° C, and ice melts at the same indicator.

And in the case of metals: iron required 1539°С for melting and crystallization.

Experience proves that for solidification a substance must release an equal amount of heat, as in the reverse transformation.

At the same time, the molecules are attracted to each other, forming a crystal lattice, unable to resist, as they lose their energy. Thus, specific heat determines how much energy is needed to turn a body into a liquid state and how much is released during solidification.

Curing formula - this is Q = λ*m. During crystallization, a minus sign is added to the Q sign, since the body in this case releases or loses energy.

We study physics - graphs of melting and solidification of substances

Processes of melting and solidification of crystals

Conclusion

All these indicators of thermal processes must be known for a deep understanding of physics and understanding of primitive natural processes. It is necessary to explain them to students as early as possible, using improvised means as examples.