School encyclopedia. Amorphous bodies Amorphous state of matter and its properties

It must be remembered that not all bodies that exist on planet Earth have a crystalline structure. Exceptions to the rule are called “amorphous bodies.” How are they different? Based on the translation of this term - amorphous - it can be assumed that such substances differ from others in their shape or appearance. We are talking about the absence of the so-called crystal lattice. The splitting process that produces edges does not occur. Amorphous bodies are also distinguished by the fact that they do not depend on the environment and their properties are constant. Such substances are called isotropic.

A short description of amorphous bodies

From a school physics course, you can remember that amorphous substances have a structure in which the atoms in them are arranged in a chaotic order. Only neighboring structures where such an arrangement is forced can have a specific location. But still, drawing an analogy with crystals, amorphous bodies do not have a strict ordering of molecules and atoms (in physics this property is called “long-range order”). As a result of research, it was found that these substances are similar in structure to liquids.

Some bodies (for example, we can take silicon dioxide, whose formula is SiO 2) can simultaneously be in an amorphous state and have a crystalline structure. Quartz in the first version has the structure of an irregular lattice, in the second - a regular hexagon.

Property No. 1

As mentioned above, amorphous bodies do not have a crystal lattice. Their atoms and molecules have a short order of arrangement, which will be the first distinctive property of these substances.

Property No. 2

These bodies are deprived of fluidity. In order to better explain the second property of substances, we can do this using the example of wax. It's no secret that if you pour water into a funnel, it will simply pour out of it. The same will happen with any other fluid substances. But the properties of amorphous bodies do not allow them to perform such “tricks”. If the wax is placed in a funnel, it will first spread over the surface and only then begin to drain from it. This is due to the fact that molecules in a substance jump from one equilibrium position to a completely different one, without having a primary location.

Property No. 3

It's time to talk about the melting process. It should be remembered that amorphous substances do not have a specific temperature at which melting begins. As the temperature rises, the body gradually becomes softer and then turns into liquid. Physicists always focus not on the temperature at which a given process began to occur, but on the corresponding melting temperature range.

Property No. 4

It has already been mentioned above. Amorphous bodies are isotropic. That is, their properties in any direction are unchanged, even if the conditions of stay in places are different.

Property No. 5

At least once, every person has observed that over a certain period of time the glass began to become cloudy. This property of amorphous bodies is associated with increased internal energy (it is several times greater than that of crystals). Because of this, these substances can easily go into a crystalline state.

Transition to the crystalline state

After a certain period of time, any amorphous body transforms into a crystalline state. This can be observed in a person’s everyday life. For example, if you leave candy or honey for several months, you may notice that they both have lost their transparency. The average person will say that they are simply sugar-coated. Indeed, if you break the body, you will notice the presence of sugar crystals.

So, speaking about this, it is necessary to clarify that spontaneous transformation into another state is due to the fact that amorphous substances are unstable. Comparing them with crystals, you can understand that the latter are many times more “powerful”. This fact can be explained using the intermolecular theory. According to it, molecules constantly jump from one place to another, thereby filling the voids. Over time, a stable crystal lattice is formed.

Melting of amorphous bodies

The process of melting of amorphous bodies is the moment when, with an increase in temperature, all bonds between atoms are destroyed. This is when the substance turns into a liquid. If the melting conditions are such that the pressure is the same throughout the entire period, then the temperature must also be fixed.

Liquid crystals

In nature, there are bodies that have a liquid crystalline structure. As a rule, they are included in the list of organic substances, and their molecules have a thread-like shape. The bodies in question have the properties of liquids and crystals, namely fluidity and anisotropy.

In such substances, the molecules are located parallel to each other, however, there is no fixed distance between them. They move constantly, but are unwilling to change orientation, so they are constantly in one position.

Amorphous metals

Amorphous metals are better known to the average person as metallic glasses.

Back in 1940, scientists started talking about the existence of these bodies. Even then it became known that metals specially produced by vacuum deposition did not have crystal lattices. And only 20 years later the first glass of this type was produced. It did not attract much attention from scientists; and only after another 10 years did American and Japanese professionals, and then Korean and European ones, start talking about him.

Amorphous metals are characterized by viscosity, a fairly high level of strength and resistance to corrosion.

There are several states of aggregation in which all bodies and substances are found. This:

• liquid;
• plasma;
• solid.

If we consider the totality of the planet and space, then most of the substances and bodies are still in the state of gas and plasma. However, on the Earth itself the content of solid particles is also significant. So we’ll talk about them, finding out what crystalline and amorphous solids are.

Crystalline and amorphous bodies: general concept

All solid substances, bodies, objects are conventionally divided into:

• crystalline;
• amorphous.

The difference between them is huge, because the division is based on the signs of structure and manifested properties. In short, solid crystalline substances are those substances and bodies that have a certain type of spatial crystal lattice, that is, they have the ability to change in a certain direction, but not in all (anisotropy).

If we characterize amorphous compounds, then their first feature is the ability to change physical characteristics in all directions simultaneously. This is called isotropy.

The structure and properties of crystalline and amorphous bodies are completely different. If the former have a clearly limited structure, consisting of orderly located particles in space, then the latter lack any order.

Properties of Solids

Crystalline and amorphous bodies, however, belong to a single group of solids, which means they have all the characteristics of a given state of aggregation. That is, the common properties for them will be the following:

1. Mechanical - elasticity, hardness, ability to deform.
2. Thermal - boiling and melting points, coefficient of thermal expansion.
3. Electrical and magnetic - thermal and electrical conductivity.

Thus, the states we are considering have all these characteristics. Only they will manifest themselves in amorphous bodies somewhat differently than in crystalline ones.

Important properties for industrial purposes are mechanical and electrical. The ability to recover from deformation or, on the contrary, to crumble and grind is an important feature. Also important is the fact whether a substance can conduct electric current or is not capable of this.

Crystal structure

If we describe the structure of crystalline and amorphous bodies, then first of all we should indicate the type of particles that compose them. In the case of crystals, these can be ions, atoms, atom-ions (in metals), molecules (rarely).

In general, these structures are characterized by the presence of a strictly ordered spatial lattice, which is formed as a result of the arrangement of particles forming the substance. If you imagine the structure of a crystal figuratively, you will get something like this: atoms (or other particles) are located at certain distances from each other so that the result is an ideal elementary cell of the future crystal lattice. Then this cell is repeated many times, and this is how the overall structure develops.

The main feature is that the physical properties in such structures vary in parallel, but not in all directions. This phenomenon is called anisotropy. That is, if you influence one part of the crystal, the second side may not react to it. So, you can chop half a piece of table salt, but the second will remain intact.

Types of Crystals

It is customary to designate two types of crystals. The first is monocrystalline structures, that is, when the lattice itself is 1. Crystalline and amorphous bodies in this case are completely different in properties. After all, a single crystal is characterized by pure anisotropy. It represents the smallest structure, elementary.

If single crystals are repeated many times and combined into one whole, then we are talking about a polycrystal. Then we are not talking about anisotropy, since the orientation of the unit cells violates the overall ordered structure. In this regard, polycrystals and amorphous bodies are close to each other in their physical properties.

Metals and their alloys

Crystalline and amorphous bodies are very close to each other. This is easy to verify by taking metals and their alloys as an example. They themselves are solid substances under normal conditions. However, at a certain temperature they begin to melt and, until complete crystallization occurs, they will remain in a state of stretchy, thick, viscous mass. And this is already an amorphous state of the body.

Therefore, strictly speaking, almost every crystalline substance can, under certain conditions, become amorphous. Just like the latter, upon crystallization it becomes a solid with an ordered spatial structure.

Metals can have different types of spatial structures, the most famous and studied of which are the following:

1. Simple cubic.
2. Face-centered.
3. Volume-centered.

The crystal structure can be based on a prism or pyramid, and its main part is represented by:

• triangle;
• parallelogram;
• square;
• hexagon.

A substance having a simple regular cubic lattice has ideal isotropic properties.

The concept of amorphism

Crystalline and amorphous bodies are quite easy to distinguish externally. After all, the latter can often be confused with viscous liquids. The structure of an amorphous substance is also based on ions, atoms, and molecules. However, they do not form an ordered, strict structure, and therefore their properties change in all directions. That is, they are isotropic.

The particles are arranged chaotically, randomly. Only sometimes they can form small loci, which still does not affect the overall properties exhibited.

Properties of similar bodies

They are identical to those of crystals. The differences are only in the indicators for each specific body. For example, we can distinguish the following characteristic parameters of amorphous bodies:

• elasticity;
• density;
• viscosity;
• ductility;
• conductivity and semiconductivity.

You can often find boundary states of connections. Crystalline and amorphous bodies can become semi-amorphous.

Also interesting is that feature of the condition under consideration, which manifests itself under a sharp external influence. Thus, if an amorphous body is subjected to a sharp impact or deformation, it can behave like a polycrystal and break into small pieces. However, if you give these parts time, they will soon join together again and turn into a viscous fluid state.

A given state of compounds does not have a specific temperature at which a phase transition occurs. This process is greatly extended, sometimes even for decades (for example, the decomposition of low-density polyethylene).

Examples of amorphous substances

There are many examples of such substances. Let's outline a few of the most obvious and frequently encountered ones.

1. Chocolate is a typical amorphous substance.
2. Resins, including phenol-formaldehyde, all plastics.
3. Amber.
4. Glass of any composition.
5. Bitumen.
6. Tar.
7. Wax and others.

An amorphous body is formed as a result of very slow crystallization, that is, an increase in the viscosity of the solution with a decrease in temperature. It is often difficult to call such substances solids; they are more likely to be classified as viscous, thick liquids.

Those compounds that do not crystallize at all during solidification have a special state. They are called glasses, and the state is glassy.

Glassy substances

The properties of crystalline and amorphous bodies are similar, as we have found out, due to a common origin and a single internal nature. But sometimes a special state of substances called glassy is considered separately from them. This is a homogeneous mineral solution that crystallizes and hardens without forming spatial lattices. That is, it always remains isotropic in terms of changes in properties.

For example, ordinary window glass does not have an exact melting point. It’s just that when this indicator increases, it slowly melts, softens and turns into a liquid state. If the impact is stopped, the process will reverse and solidification will begin, but without crystallization.

Such substances are highly valued; glass today is one of the most common and sought-after building materials throughout the world.

What is an "AMORPHOUS STATE"? How to spell this word correctly. Concept and interpretation.

AMORPHOUS STATE (from the Greek amorphos - formless), a condensed state of a substance, the main feature of which is the absence of an atomic or molecular lattice, i.e., the three-dimensional periodicity of the structure characteristic of the crystalline state. Amorphous bodies are isotropic, that is, their properties (mechanical, optical, electrical, etc.) do not depend on direction. A. s. usually established, firstly, by a small number of maxima in the diffraction pattern (usually 2-4) against the background of a diffuse halo, which are characterized by a large half-width and a rapid decrease in intensity with increasing diffraction angle; secondly, by the absence in the vibrational or electronic spectrum of splitting bands associated with the symmetry of the structure (see Diffraction methods, Molecular spectra). Melts of all substances above their melting temperature T pl are usually in a thermodynamically equilibrium state, in which any thermodynamic. The function of the state (specific volume, enthalpy, entropy) is uniquely determined by temperature, pressure and other parameters. At T pl the substance goes into an equilibrium solid state and crystallizes (see figure). However, under certain conditions, at temperatures below T pp m. a nonequilibrium state of the supercooled liquid is obtained, and upon further cooling below the glass transition temperature Tst, a nonequilibrium solid state is obtained. (See Glassy state). In this state, in-in m.b. stable over a long period of time. time; known, for example, volcanic. glass (obsidian, etc.), whose age is estimated at millions of years. Thermodynamic functions of glassy A. s. are determined not only by temperature and pressure, but also depend on the history of the sample (for example, cooling rate). Phys. and chem. saints in the glassy A. s. usually close to the holy crystalline. modifications of the same item, but they may differ significantly. Thus, glassy GeO2 sol. in water and alkali solutions, reacts with hydrofluoric and hydrochloric acids, while the GeO2 modification is practically insoluble in water, dissolving very slowly. in solutions of alkalis when heated, does not react with the indicated compounds. Temperature intervals for the existence of amorphous and crystalline states of the substance: solid line - equilibrium state, dash-dotted - nonequilibrium. Transition from supercooled liquid to glassy a.s. usually occurs in a narrow temperature range and is accompanied by a sharp change in the properties, in particular viscosity (by 10-15 orders of magnitude), temperature coefficient. expansion (10-100 times), elastic moduli (10-1000 times), heat capacity, density, etc., which formally resembles a second-order phase transition. However, the formation of glassy A. s. is not accompanied by the appearance of embryos of a new phase and physical. phase boundaries. T st is not thermodynamic. characteristic of the item and, depending on the measurement conditions, may vary by several. tens of degrees. This is due to the fact that in the glass transition temperature range the restructuring of the short-range order structure of the liquid (structural relaxation) sharply slows down, i.e. kinetic. nature of glass transition. Below Tst, structural transformations in matter stop completely (at a finite observation time), particles (atoms, molecules, fragments of molecules) are capable of only vibrational and small-scale rotation. movements, the translational mobility characteristic of the liquid state is lost. T. arr., the difference in the properties of liquid and solid A. s. determined by the nature of the thermal motion of particles. There are substances that cannot be obtained into crystalline form. condition. These include statistics. copolymers and atactic polymers, in macromolecules of which the sequence of monomer units is irregular in the direction of the chain axis. It is believed that due to the lack of periodicity in the structure of macromolecules, three-dimensional periodicity cannot arise under any circumstances. structure and, therefore, these things exist only in A. s. Question about thermodynamics. nature of equilibrium solid a.s. remains open for now (see Third Law of Thermodynamics). A number of rigid-chain polymers with high Tst exist only in a glassy state, because when heated. above Tst they decompose. Attempts to create physical models of A. s. have not yet led to success. Lit.: Tarasov V.V., Problems of glass physics, ed. G. M. Barteneva, 2nd ed., M., 1979; Phillips J., Physics of glass, in: Physics abroad, M., 1983, p. 154-78; ZallenR., The physics of amorphous solid, N.Y., 1983. E.F. Oleinik. G. Z. Pinsker.

Amorphous state(amorphous - shapeless, from the Greek o! - negative prefix and tsorsrt] - form) - the state of solids in which they

have, in contrast to crystals, isotropy, i.e. they have the same physical properties in all directions (cf. Crystals, Anisotropy). Gases and liquids can also be considered amorphous in this sense.

Amorphous bodies are natural (opal, volcanic glass - obsidian, amber, resins, bitumen) and artificial (regular glass, fused quartz, bakelite); a number of oxides and salts can be obtained in amorphous form. Some of the amorphous bodies are very complex in composition (ordinary glass), while others are simple chemical compounds, for example, glassy quartz, borax, boric anhydride, etc. Ordinary glass is the most typical example of an amorphous body, therefore a solid body is currently accepted as A. s. call it glassy. The isotropy of an amorphous substance is manifested, for example, in the fact that it does not give a flat cleavage surface, like a crystal with cleavage, but gives an irregular “conchoidal” fracture. Physical properties of matter in A. s. - compressibility, electrical and thermal conductivity, optical. properties, etc. are the same in all directions. There is no birefringence in an amorphous substance unless the substance is under stress. By rapid cooling, the amorphous substance can be obtained in a hardened form (see Batavian tears); then there are significant internal stresses in it, which give rise to very sharp interference fringes in the polarization device. Slow annealing completely destroys the hardening. This is of great importance in glass production. Currently, the nolarization-optical method of studying stresses in machine parts on models made of amorphous plastics is widely used.

The properties of amorphous bodies are determined by their structure. In crystals, atoms or ions are arranged in a crystal lattice with a certain periodic pattern; In an amorphous body, atoms and molecules are arranged chaotically. The isotropy of an amorphous substance is explained by the random distribution of its particles. A sharp difference in the behavior of crystals and amorphous substances is revealed during the transition of a solid into a liquid state and back. The melting curve of a crystal has a more or less abrupt stop in temperature at the melting point, where latent heat is absorbed (see) and a discontinuous change in all properties is detected (figure!). In an amorphous body, the transition occurs gradually, without breaking continuity, and a “softening interval” is observed (an interval of very large - 1,000°), in which

Time t Fig. 1.

(for ordinary glasses this

a substance gradually changes from a solid state to a fluid state. When the process is reversed, hypothermia is often detected; the substance does not crystallize at the melting point, but upon further cooling it thickens in a liquid state, its viscosity (see) increases greatly, the molecules lose their mobility, and, finally,

solidification occurs in an amorphous form. The molecules of the substance in this case turn out to be arranged randomly, since they did not have time to form a regular crystal lattice due to enormous internal friction. In this case, latent heat is not released, and the energy reserve of an amorphous substance turns out to be greater than that of a crystalline one; therefore A. s. thermodynamically unstable and tends to transform into a stable crystalline form. Crystallization of a solid a.s. proceeds very slowly; Glass becomes cloudy during crystallization, turning into a porcelain-like mass. When producing glass, crystallization often produces large defects and is called solidification. When the rock solidifies in an amorphous state, the processes of association of molecules, polymerization and condensation (see) play an important role, which is of significant interest for the production of bakelite. other plastics.

Theory of A. s. developed based on the study of crystallization and supercooling processes. The ability of a substance to crystallize is determined by the number of crystallization centers n formed per unit time (Fig. 2 - general diagram), the linear rate of crystallization v and the increase in viscosity m) during supercooling. As can be seen from curve 2, during supercooling there is initially a maximum crystallization rate, however

at this time the number of centers is still small, since the maximum of this curve lies well below the melting point. With further cooling, the viscosity becomes too high, making the formation of centers difficult, and the crystallization rate becomes vanishingly low. Therefore, if the melt is quickly supercooled, it loses the ability to crystallize and solidifies into an amorphous glassy mass. Although a certain point of transition of a substance from A. s. in a liquid but exists, a number of physical properties in the softening range exhibit anomalous behavior, approximately at the point where the viscosity has an abs value. units (poises). Thus, when heated, the coefficient of expansion in the softening range increases very sharply, as well as heat capacity, electrical conductivity, and dielectric. permeability, refractive index. On this basis, it is sometimes believed that the glassy amorphous state is a special fourth state of matter.

With the widespread development of X-ray analysis, as well as electron diffraction, it became clear that many bodies previously considered amorphous actually have a fine-crystalline structure, that is, they are highly dispersed systems (see Disperse systems). It turned out that amorphous carbon consists of tiny crystals, as well as many oxides and hydrates of metal oxides and a number of colloids, that is, dispersed particles in colloidal solutions. X-ray studies have shown that in ordinary glass, in fused

Subcooling temperature Fig. 2.

quartz, in borax glass there are crystal nuclei measuring 10~6-10~7 cm. Confirmation of this fact by further research should smooth out the sharp edge in our ideas about the structure of amorphous glassy substances and ordinary polycrystalline bodies.

Lit.: K o beko P. P., Amorphous state. L.-M., ; And in g u s t i n i k A. I., Physical chemistry of silicates. L.-M., ; B o t v i i k i n O. K., Introduction to the physical chemistry of silicates, M.-L., ; B l yu m-berg B. Ya., Introduction to the physical chemistry of glass, Leningrad, ; Glass technology (Special course), ed. I. I. Kitaygorodsky, vol. 1, M.-L., ; The structure of glass. Sat. articles, ed. M. A. Bezborodova, M.-L., ; Glagolev S.P., Quartz glass, its properties, production and application, M.-L., ; Lewis W. K., Chemistry of colloidal and amorphous substances, trans. from English, M., ; Gatchek E., Viscosity of liquids, 2nd ed., with add. M. P. Volarovich and D. M. Tolstoy, M.-L.,

The structure of a solid is determined not only by the relative position of chemical particles inside, but also by the location of the particles themselves in space relative to each other and the distances between them. Depending on the location of particles in space, short-range and long-range order are distinguished.

Short-range order is that particles of matter are regularly located in space at certain distances and directions from each other. If such ordering is maintained or periodically repeated throughout the entire volume of a solid, then long-range order is formed. In other words, long-range and short-range orders are the presence of a correlation in the microstructure of a substance either within the entire macroscopic sample (long-range) or in a region with a limited radius (short-range). Depending on the cumulative (or suppressive) effect of the short-range or long-range order of particle placement, a solid can have a crystalline or amorphous state.

The most ordered arrangement of particles is in crystals (from the Greek “krystalos” - ice), in which atoms, molecules or ions are located only at certain points in space, called nodes.

The crystalline state is an ordered periodic structure, which is characterized by the presence of both short- and long-range order in the arrangement of particles of a solid substance.

A characteristic feature of crystalline substances compared to amorphous ones is anisotropy.

Anisotropy is the difference in the physical and chemical properties of a crystalline substance (electrical and thermal conductivity, strength, optical characteristics, etc.) depending on the chosen direction in the crystal.

Anisotropy is due to the internal structure of the crystals. In different directions, the distance between particles in a crystal is different, therefore the quantitative characteristics of a particular property for these directions will be different.

Anisotropy is especially pronounced in single crystals. The production of lasers, the processing of semiconductor single crystals, the manufacture of quartz resonators and ultrasonic generators are based on this property. A typical example of an anisotropic crystalline substance is graphite, the structure of which consists of parallel layers with different binding energies in the middle of the layers and between individual layers. Due to this, the thermal conductivity along the layers is five times higher than in the perpendicular direction, and the electrical conductivity in the direction of an individual layer is close to metallic and hundreds of times higher than the electrical conductivity in the perpendicular direction.

Structure of graphite (the length of the C-C bond inside the layer and the distance between individual layers in the crystal are indicated)

Sometimes the same substance can form crystals of different shapes. This phenomenon is called polymorphism, and different crystalline forms of one substance are called polymorphic modifications, for example, alotropes diamond and graphite; a-, b-, g- and d-iron; a- and b-quartz (note the difference between the concepts of “allotropy,” which refers exclusively to simple substances in any quartz, and “polymorphism,” which characterizes the structure of only crystalline compounds).

At the same time, substances with different compositions can form crystals of the same shape - this phenomenon is called isomorphism. Thus, isomorphic substances that have the same crystal lattices are Al and Cr and their oxides; Ag and Au; BaCl 2 and SrCl 2; KMnO 4 and BaSO 4 .

The vast majority of solids under ordinary conditions exist in a crystalline state.

Solids that do not have a periodic structure are classified as amorphous (from the Greek " amorphos"- shapeless). However, some order of structure is present in them. It manifests itself in the regular placement of its nearest “neighbors” around each particle, that is, amorphous substances have only short-range order and in this way resemble liquids, therefore, with some approximation, they can be considered as supercooled liquids with a very high viscosity. The difference between the liquid and solid amorphous state is determined by the nature of the thermal movement of particles: in the amorphous state they are only capable of vibrational and rotational movements, but cannot move through the thickness of the substance.

An amorphous state is a solid state of a substance, characterized by the presence of short-range order in the arrangement of particles, as well as isotropy - the same properties in any direction.

The amorphous state of substances is less stable compared to the crystalline state, so amorphous substances can transform into a crystalline state under the influence of mechanical loads or when temperature changes. However, some substances can remain in an amorphous state for a fairly long period. For example, volcanic glass (which is up to several million years old), ordinary glass, resins, waxes, most transition metal hydroxides, and the like. Under certain conditions, almost all substances can be in an amorphous state, except for metals and some ionic compounds. On the other hand, substances are known that can exist only in an amorphous state (organic polymers with an uneven sequence of elementary units).

The physical and chemical properties of a substance in the amorphous state can differ significantly from its properties in the crystalline state. The reactivity of substances in the amorphous state is much higher than in the crystalline state. For example, amorphous GeO 2 is much more chemically active than crystalline GeO 2.

The transition of solids into a liquid state, depending on the structure, has its own characteristics. For a crystalline substance, melting occurs at a certain value, which is fixed for a given substance, and is accompanied by an abrupt change in its properties (density, viscosity, etc.). Amorphous substances, on the contrary, transform into a liquid state gradually, over a certain temperature range (the so-called softening interval), during which a smooth, slow change in properties occurs.

Comparative characteristics of amorphous and crystalline substances: