Amorphous bodies. Melting of amorphous bodies. Amorphous substances. Crystalline and amorphous state of matter. Application of amorphous substances

Solids are characterized by constant shape and volume and are divided into crystalline and amorphous.

Crystal bodies

Each chemical substance in a crystalline state corresponds to a specific crystal lattice, which determines the physical properties of the crystal.

Did you know?
Many years ago in St. Petersburg, in one of the unheated warehouses, there were large stocks of white tin shiny buttons. And suddenly they began to darken, lose their shine and crumble into powder. Within a few days, the mountains of buttons turned into a pile of gray powder. "Tin Plague"- this is how this “disease” of white tin was called.
And this was just a rearrangement of the order of atoms in tin crystals. Tin, passing from a white variety to a gray one, crumbles into powder.
Both white and gray tin are crystals of tin, but at low temperatures their crystal structure changes, and as a result the physical properties of the substance change.

Crystals can have different shapes and are limited to flat edges.

In nature there are:
A) single crystals- these are single homogeneous crystals that have the shape of regular polygons and have a continuous crystal lattice

Single crystals of table salt:

b) polycrystals- these are crystalline bodies fused from small, chaotically located crystals.
Most solids have a polycrystalline structure (metals, stones, sand, sugar).

Bismuth polycrystals:

Anisotropy of crystals

In crystals it is observed anisotropy- dependence of physical properties (mechanical strength, electrical conductivity, thermal conductivity, refraction and absorption of light, diffraction, etc.) on the direction inside the crystal.

Anisotropy is observed mainly in single crystals.

In polycrystals (for example, in a large piece of metal), anisotropy does not appear in the normal state.
Polycrystals consist of a large number of small crystal grains. Although each of them has anisotropy, due to the disorder of their arrangement, the polycrystalline body as a whole loses its anisotropy.

Any crystalline substance melts and crystallizes at a strictly defined melting point: iron - at 1530°, tin - at 232°, quartz - at 1713°, mercury - at minus 38°.

Particles can disrupt the order of arrangement in a crystal only if it begins to melt.

As long as there is an order of particles, there is a crystal lattice, a crystal exists. If the structure of the particles is disrupted, it means that the crystal has melted - turned into liquid, or evaporated - turned into steam.

Amorphous bodies

Amorphous bodies do not have a strict order in the arrangement of atoms and molecules (glass, resin, amber, rosin).

In amorphous bodies it is observed isotropy- their physical properties are the same in all directions.

Under external influences, amorphous bodies exhibit simultaneously elastic properties (when impacted, they break into pieces like solids) and fluidity (with prolonged exposure, they flow like liquids).

At low temperatures, amorphous bodies resemble solids in their properties, and at high temperatures they are similar to very viscous liquids.

Amorphous bodies do not have a specific melting point, and hence the crystallization temperature.
When heated, they gradually soften.

Amorphous bodies occupy intermediate position between crystalline solids and liquids.

Same substance can occur in both crystalline and non-crystalline forms.

In a liquid melt of a substance, particles move completely randomly.
If, for example, you melt sugar, then:

1. if the melt solidifies slowly, calmly, then the particles gather in even rows and crystals form. This is how granulated sugar or lump sugar is obtained;

2. if cooling occurs very quickly, then the particles do not have time to line up in regular rows and the melt solidifies non-crystalline. So, if you pour melted sugar into cold water or onto a very cold saucer, sugar candy, non-crystalline sugar, is formed.

Marvelous!

Over time, a non-crystalline substance can “degenerate”, or, more precisely, crystallize; the particles in them gather in regular rows.

Only the period is different for different substances: for sugar it is several months, and for stone it is millions of years.

Let the candy lie quietly for two or three months. It will become covered with a loose crust. Look at it with a magnifying glass: these are small crystals of sugar. Crystal growth has begun in non-crystalline sugar. Wait a few more months - and not only the crust, but the entire candy will crystallize.

Even our ordinary window glass can crystallize. Very old glass sometimes becomes completely cloudy because a mass of small opaque crystals forms in it.

In glass factories, sometimes a “goat” is formed in the furnace, that is, a block of crystalline glass. This crystal glass is very durable. It is easier to destroy a furnace than to knock out a stubborn “goat” from it.
Having studied it, scientists created a new, very durable glass material - ceramic glass. This is a glass-crystalline material obtained as a result of volumetric crystallization of glass.

Curious!

Different crystal forms may exist the same substance.
For example, carbon.

Graphite is crystalline carbon. Pencil leads are made from graphite, which leaves a mark on paper when pressed lightly. The structure of graphite is layered. The layers of graphite shift easily, so the graphite flakes stick to the paper when writing.

But there is another form of crystalline carbon - diamond.

AMORPHOUS BODIES(Greek amorphos - formless) - bodies in which elementary constituent particles (atoms, ions, molecules, their complexes) are randomly located in space. To distinguish amorphous bodies from crystalline ones (see Crystals), X-ray diffraction analysis is used (see). Crystalline bodies on X-ray diffraction patterns give a clear, defined diffraction pattern in the form of rings, lines, spots, while amorphous bodies give a blurred, irregular image.

Amorphous bodies have the following features: 1) under normal conditions they are isotropic, that is, their properties (mechanical, electrical, chemical, thermal, and so on) are the same in all directions; 2) do not have a certain melting point, and with increasing temperature, most amorphous bodies, gradually softening, turn into a liquid state. Therefore, amorphous bodies can be considered as supercooled liquids that have not had time to crystallize due to a sharp increase in viscosity (see) due to an increase in the interaction forces between individual molecules. Many substances, depending on the production methods, can be in amorphous, intermediate or crystalline states (proteins, sulfur, silica, and so on). However, there are substances that exist almost exclusively in one of these states. Thus, most metals and salts are in a crystalline state.

Amorphous bodies are widespread (glass, natural and artificial resins, rubber, and so on). Artificial polymer materials, which are also amorphous bodies, have become indispensable in technology, everyday life, and medicine (varnishes, paints, plastics for prosthetics, various polymer films).

In living nature, amorphous bodies include the cytoplasm and most of the structural elements of cells and tissues, consisting of biopolymers - long-chain macromolecules: proteins, nucleic acids, lipids, carbohydrates. Molecules of biopolymers easily interact with each other, giving aggregates (see Aggregation) or swarm-coacervates (see Coacervation). Amorphous bodies are also found in cells in the form of inclusions and reserve substances (starch, lipids).

A feature of polymers that make up the amorphous bodies of biological objects is the presence of narrow limits of physicochemical zones of reversible state, for example. When the temperature rises above the critical temperature, their structure and properties irreversibly change (protein coagulation).

Amorphous bodies formed by a number of artificial polymers, depending on temperature, can be in three states: glassy, ​​highly elastic and liquid (viscous-fluid).

The cells of a living organism are characterized by transitions from a liquid to a highly elastic state at a constant temperature, for example, retraction of a blood clot, muscle contraction (see). In biological systems, amorphous bodies play a crucial role in maintaining the cytoplasm in a stationary state. The role of amorphous bodies in maintaining the shape and strength of biological objects is important: the cellulose membrane of plant cells, the membranes of spores and bacteria, animal skin, and so on.

Bibliography: Bresler S. E. and Yerusalimsky B. L. Physics and chemistry of macromolecules, M.-L., 1965; Kitaygorodsky A.I. X-ray structural analysis of fine-crystalline and amorphous bodies, M.-L., 1952; aka. Order and disorder in the world of atoms, M., 1966; Kobeko P. P. Amorphous substances, M.-L., 1952; Setlow R. and Pollard E. Molecular biophysics, trans. from English, M., 1964.

A solid is one of the four fundamental states of matter, besides liquid, gas and plasma. It is characterized by structural rigidity and resistance to changes in shape or volume. Unlike a liquid, a solid object does not flow or take the shape of the container in which it is placed. A solid does not expand to fill the entire available volume as a gas does.
Atoms in a solid are closely connected to each other, are in an ordered state at the nodes of the crystal lattice (these are metals, ordinary ice, sugar, salt, diamond), or are arranged irregularly, do not have strict repeatability in the structure of the crystal lattice (these are amorphous bodies, such such as window glass, rosin, mica or plastic).

Crystal bodies

Crystalline solids or crystals have a distinctive internal feature - a structure in the form of a crystal lattice, in which atoms, molecules or ions of a substance occupy a certain position.
The crystal lattice leads to the existence of special flat faces in crystals, which distinguish one substance from another. When exposed to X-rays, each crystal lattice emits a characteristic pattern that can be used to identify the substance. The edges of crystals intersect at certain angles that distinguish one substance from another. If the crystal is split, the new faces will intersect at the same angles as the original.

For example, galena - galena, pyrite - pyrite, quartz - quartz. The crystal faces intersect at right angles in galena (PbS) and pyrite (FeS 2), and at other angles in quartz.

Properties of crystals

• constant volume;
• correct geometric shape;
• anisotropy - the difference in mechanical, light, electrical and thermal properties from the direction in the crystal;
• a well-defined melting point, since it depends on the regularity of the crystal lattice. The intermolecular forces holding a solid together are uniform, and it takes the same amount of thermal energy to break each force simultaneously.

Amorphous bodies

Examples of amorphous bodies that do not have a strict structure and repeatability of crystal lattice cells are: glass, resin, Teflon, polyurethane, naphthalene, polyvinyl chloride.

They have two characteristic properties: isotropy and the absence of a specific melting point.
Isotropy of amorphous bodies is understood as the same physical properties of a substance in all directions.
In an amorphous solid, the distance to neighboring nodes of the crystal lattice and the number of neighboring nodes varies throughout the material. Therefore, different amounts of thermal energy are required to break intermolecular interactions. Consequently, amorphous substances soften slowly over a wide range of temperatures and do not have a clear melting point.
A feature of amorphous solids is that at low temperatures they have the properties of solids, and when the temperature rises, they have the properties of liquids.

Unlike crystalline solids, there is no strict order in the arrangement of particles in an amorphous solid.

Although amorphous solids are capable of maintaining their shape, they do not have a crystal lattice. A certain pattern is observed only for molecules and atoms located in the vicinity. This order is called close order . It is not repeated in all directions and does not persist over long distances, as with crystalline bodies.

Examples of amorphous bodies are glass, amber, artificial resins, wax, paraffin, plasticine, etc.

Features of amorphous bodies

Atoms in amorphous bodies vibrate around points that are randomly located. Therefore, the structure of these bodies resembles the structure of liquids. But the particles in them are less mobile. The time they oscillate around the equilibrium position is longer than in liquids. Jumps of atoms to another position also occur much less frequently.

How do crystalline solids behave when heated? They begin to melt at a certain melting point. And for some time they are simultaneously in a solid and liquid state, until the entire substance melts.

Amorphous solids do not have a specific melting point . When heated, they do not melt, but gradually soften.

Place a piece of plasticine near the heating device. After some time it will become soft. This does not happen instantly, but over a certain period of time.

Since the properties of amorphous bodies are similar to the properties of liquids, they are considered as supercooled liquids with very high viscosity (frozen liquids). Under normal conditions they cannot flow. But when heated, jumps of atoms in them occur more often, viscosity decreases, and amorphous bodies gradually soften. The higher the temperature, the lower the viscosity, and gradually the amorphous body becomes liquid.

Ordinary glass is a solid amorphous body. It is obtained by melting silicon oxide, soda and lime. By heating the mixture to 1400 o C, a liquid glassy mass is obtained. When cooled, liquid glass does not solidify like crystalline bodies, but remains a liquid, the viscosity of which increases and the fluidity decreases. Under normal conditions, it appears to us as a solid body. But in fact it is a liquid that has enormous viscosity and fluidity, so low that it can barely be distinguished by the most ultrasensitive instruments.

The amorphous state of a substance is unstable. Over time, it gradually turns from an amorphous state into a crystalline state. This process occurs at different rates in different substances. We see candy canes becoming covered in sugar crystals. This does not take very much time.

And for crystals to form in ordinary glass, a lot of time must pass. During crystallization, glass loses its strength, transparency, becomes cloudy, and becomes brittle.

Isotropy of amorphous bodies

In crystalline solids, physical properties vary in different directions. But in amorphous bodies they are the same in all directions. This phenomenon is called isotropy .

An amorphous body conducts electricity and heat equally in all directions and refracts light equally. Sound also travels equally in amorphous bodies in all directions.

The properties of amorphous substances are used in modern technologies. Of particular interest are metal alloys that do not have a crystalline structure and belong to amorphous solids. They are called metal glasses . Their physical, mechanical, electrical and other properties differ from those of ordinary metals for the better.

Thus, in medicine they use amorphous alloys whose strength exceeds that of titanium. They are used to make screws or plates that connect broken bones. Unlike titanium fasteners, this material gradually disintegrates and is replaced over time by bone material.

High-strength alloys are used in the manufacture of metal-cutting tools, fittings, springs, and mechanism parts.

An amorphous alloy with high magnetic permeability has been developed in Japan. By using it in transformer cores instead of textured transformer steel sheets, eddy current losses can be reduced by 20 times.

Amorphous metals have unique properties. They are called the material of the future.

The structure of amorphous bodies. Studies using an electron microscope and X-rays indicate that in amorphous bodies there is no strict order in the arrangement of their particles. Unlike crystals, where there is long range order in the arrangement of particles, in the structure of amorphous bodies there is close order. This means that a certain orderliness in the arrangement of particles is preserved only near each individual particle (see figure).

The upper part of the figure shows the arrangement of particles in crystalline quartz, the lower part shows the amorphous form of existence of quartz. These substances consist of the same particles - molecules of silicon oxide SiO2.

Like particles of any bodies, particles of amorphous bodies fluctuate continuously and randomly and, more often than particles of crystals, can jump from place to place. This is facilitated by the fact that the particles of amorphous bodies are located unequally densely - in some places there are relatively large gaps between their particles. However, this is not the same as “vacancies” in crystals (see § 7th).

Crystallization of amorphous bodies. Over time (weeks, months), some amorphous bodies spontaneously transform into a crystalline state. For example, sugar candies or honey left alone for several months become opaque. In this case, the honey and candy are said to be “candied.” By breaking a candied candy or scooping up honey with a spoon, we will actually see the formation of crystals of sugar that previously existed in an amorphous state.

Spontaneous crystallization of amorphous bodies indicates that The crystalline state of a substance is more stable than the amorphous one. MKT explains it this way. The repulsive forces of the “neighbors” force the particles of the amorphous body to move preferentially to where there are large gaps. As a result, a more ordered arrangement of particles occurs, that is, crystallization occurs.

Check yourself:

1. The purpose of this paragraph is to introduce...
2. What comparative characteristics have we given to amorphous bodies?
3. For the experiment we use the following equipment and materials: ...
4. During preparation for the experiment, we...
5. What will we see during the experiment?
6. What is the result of the experiment with a stearin candle and a piece of plasticine?
7. Unlike amorphous bodies, crystalline bodies...
8. When a crystalline body melts...
9. Unlike crystalline bodies, amorphous...
10. Amorphous bodies include bodies for which...
11. What makes amorphous bodies look like liquids? They...
12. Describe the beginning of the experiment to confirm the fluidity of amorphous bodies.
13. Describe the result of the experiment to confirm the fluidity of amorphous bodies.
14. Formulate a conclusion from the experience.
15. How do we know that amorphous bodies do not have a strict order in the arrangement of their particles?
16. How do we understand the term “short-range order” in the arrangement of particles of an amorphous body?
17. The same molecules of silicon oxide are found in both crystalline and...
18. What is the nature of the movement of particles of an amorphous body?
19. What is the nature of the arrangement of particles of an amorphous body?
20. What can happen to amorphous bodies over time?
21. How can you be sure that there are polycrystals of sugar in candy or candied honey?
22. Why do we think that the crystalline state of a substance is more stable than the amorphous one?
23. How does MCT explain the independent crystallization of some amorphous bodies?