Solids. Crystalline bodies. Amorphous bodies. Amorphous bodies – Knowledge Hypermarket

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.

MINISTRY OF EDUCATION

PHYSICS 8TH GRADE

Report on the topic:

“Amorphous bodies. Melting of amorphous bodies.”

8th grade student:

2009

Amorphous bodies.

Let's do an experiment. We will need a piece of plasticine, a stearine candle and an electric fireplace. Let's place plasticine and a candle at equal distances from the fireplace. After some time, part of the stearin will melt (become liquid), and part will remain in the form of a solid piece. During the same time, the plasticine will soften only a little. After some time, all the stearin will melt, and the plasticine will gradually “corrode” along the surface of the table, softening more and more.

So, there are bodies that do not soften when melted, but turn from a solid state immediately into a liquid. During the melting of such bodies, it is always possible to separate the liquid from the not yet melted (solid) part of the body. These bodies are crystalline. There are also solids that, when heated, gradually soften and become more and more fluid. For such bodies it is impossible to indicate the temperature at which they turn into liquid (melt). These bodies are called amorphous.

Let's do the following experiment. Throw a piece of resin or wax into a glass funnel and leave it in a warm room. After about a month, it will turn out that the wax has taken the shape of a funnel and even began to flow out of it in the form of a “stream” (Fig. 1). In contrast to crystals, which retain their own shape almost forever, amorphous bodies exhibit fluidity even at low temperatures. Therefore, they can be considered as very thick and viscous liquids.

The structure of amorphous bodies. Studies using an electron microscope, as well as using X-rays, indicate that in amorphous bodies there is no strict order in the arrangement of their particles. Take a look, figure 2 shows the arrangement of particles in crystalline quartz, and the one on the right shows the arrangement of particles in amorphous quartz. These substances consist of the same particles - molecules of silicon oxide SiO 2.

The crystalline state of quartz is obtained if molten quartz is cooled slowly. If the cooling of the melt is rapid, then the molecules will not have time to “line up” in orderly rows, and the result will be amorphous quartz.

Particles of amorphous bodies oscillate continuously and randomly. They can jump from place to place more often than crystal particles. This is also facilitated by the fact that the particles of amorphous bodies are located unequally densely: there are voids between them.

Crystallization of amorphous bodies. Over time (several months, years), amorphous substances spontaneously transform into a crystalline state. For example, sugar candies or fresh honey left alone in a warm place will become opaque after a few months. They say that honey and candy are “candied.” By breaking a candy cane or scooping up honey with a spoon, we will actually see the sugar crystals that have formed.

Spontaneous crystallization of amorphous bodies indicates that the crystalline state of a substance is more stable than the amorphous one. The intermolecular theory explains it this way. Intermolecular forces of attraction and repulsion cause particles of an amorphous body to jump preferentially to where there are voids. As a result, a more ordered arrangement of particles appears than before, that is, a polycrystal is formed.

Melting of amorphous bodies.

As the temperature increases, the energy of the vibrational motion of atoms in a solid increases and, finally, a moment comes when the bonds between atoms begin to break. In this case, the solid turns into a liquid state. This transition is called melting. At a fixed pressure, melting occurs at a strictly defined temperature.

The amount of heat required to convert a unit mass of a substance into a liquid at its melting point is called the specific heat of fusion λ .

To melt a substance of mass m it is necessary to expend an amount of heat equal to:

Q = λ m .

The process of melting amorphous bodies differs from the melting of crystalline bodies. As the temperature increases, amorphous bodies gradually soften and become viscous until they turn into liquid. Amorphous bodies, unlike crystals, do not have a specific melting point. The temperature of amorphous bodies changes continuously. This happens because in amorphous solids, as in liquids, molecules can move relative to each other. When heated, their speed increases, and the distance between them increases. As a result, the body becomes softer and softer until it turns into liquid. When amorphous bodies solidify, their temperature also decreases continuously.

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.

In the previous paragraph, we learned that some solids (for example, salt, quartz, metals and others) are mono- or polycrystals. Let's get acquainted now with amorphous bodies. They occupy an intermediate position between crystals and liquids, so they cannot be unambiguously called solid.

Let's do an experiment. We will need: a piece of plasticine, a stearin candle and an electric heater. Let's place the plasticine and the candle at equal distances from the heater. Soon part of the candle will melt, part will remain in the form of a solid, and the plasticine will “go limp.” After some time, all the stearin will melt, and the plasticine will gradually “dissolve”, becoming completely soft.

Like stearin, there are others crystalline substances, which do not soften when heated, and during melting you can always see both the liquid and the part of the body that has not yet melted. This, for example, is all metals. But there are also amorphous substances, which when heated gradually soften and become more and more fluid, so it is impossible to indicate the temperature at which the body turns into liquid (melts).

Amorphous bodies at any temperature have fluidity. Let us confirm this with experience. Let's throw a piece of an amorphous substance into a glass funnel and leave it in a warm room (in the picture - tar resin; asphalt is made from it). After a few weeks, it turns out that the resin took the shape of a funnel and even began to flow out of it like a “jet.” That is an amorphous body behaves like a very thick and viscous liquid.

The structure of amorphous bodies. Electron microscope and X-ray studies show 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, only close order– a certain ordering of the arrangement of particles is preserved only near each individual particle(see picture). The top shows the arrangement of particles in crystalline quartz, the bottom shows the amorphous form of quartz. These substances consist of the same particles - molecules of silicon oxide SiO 2.

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 places creating relatively large gaps. However, this is not the same as “vacancies” in crystals (see § 7th).

Crystallization of amorphous bodies. Over time (weeks, months), amorphous substances 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 such a candy or scooping up such honey with a spoon, we will see the formation of sugar crystals 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 forces of attraction and repulsion of “neighbors” move particles of an amorphous body to positions where potential energy is minimal(see § 7-d). In this case, a more ordered arrangement of particles appears, which means that independent crystallization occurs.

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.