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

Most substances in the Earth's temperate climate are in a solid state. Solids retain not only their shape, but also their volume.

Based on the nature of the relative arrangement of particles, solids are divided into three types: crystalline, amorphous and composites.

Amorphous bodies. Examples of amorphous bodies include glass, various hardened resins (amber), plastics, etc. If an amorphous body is heated, it gradually softens, and the transition to a liquid state takes a significant temperature range.

The similarity with liquids is explained by the fact that atoms and molecules of amorphous bodies, like liquid molecules, have a “settled life” time. There is no specific melting point, so amorphous bodies can be considered as supercooled liquids with very high viscosity. The absence of long-range order in the arrangement of atoms of amorphous bodies leads to the fact that a substance in an amorphous state has a lower density than in a crystalline state.

The disorder in the arrangement of atoms of amorphous bodies leads to the fact that the average distance between atoms in different directions is the same, therefore they are isotropic, that is, all physical properties (mechanical, optical, etc.) do not depend on the direction of external influence. A sign of an amorphous body is the irregular shape of the surface when fractured. Amorphous bodies after a long period of time still change their shape under the influence of gravity. This makes them look like liquids. As the temperature increases, this change in shape occurs faster. The amorphous state is unstable; a transition from the amorphous state to the crystalline state occurs. (The glass becomes cloudy.)

Crystalline bodies. If there is periodicity in the arrangement of atoms (long-range order), the solid is crystalline.

If you examine grains of salt with a magnifying glass or microscope, you will notice that they are limited by flat edges. The presence of such faces is a sign of being in a crystalline state.

A body that is one crystal is called a single crystal. Most crystalline bodies consist of many randomly located small crystals that have grown together. Such bodies are called polycrystals. A piece of sugar is a polycrystalline body. Crystals of different substances have different shapes. The sizes of the crystals are also varied. The sizes of polycrystalline crystals can change over time. Small iron crystals turn into large ones, this process is accelerated by impacts and shocks, it occurs in steel bridges, railway rails, etc., as a result of which the strength of the structure decreases over time.

Very many bodies of the same chemical composition in the crystalline state, depending on conditions, can exist in two or more varieties. This property is called polymorphism. Ice has up to ten modifications known. Carbon polymorphism - graphite and diamond.

An essential property of a single crystal is anisotropy - the dissimilarity of its properties (electrical, mechanical, etc.) in different directions.

Polycrystalline bodies are isotropic, that is, they exhibit the same properties in all directions. This is explained by the fact that the crystals that make up the polycrystalline body are randomly oriented relative to each other. As a result, none of the directions is different from the others.

Composite materials have been created whose mechanical properties are superior to natural materials. Composite materials (composites) consist of a matrix and fillers. Polymer, metal, carbon or ceramic materials are used as a matrix. Fillers may consist of whiskers, fibers or wires. In particular, composite materials include reinforced concrete and ferrographite.

Reinforced concrete is one of the main types of building materials. It is a combination of concrete and steel reinforcement.

Iron graphite is a metal-ceramic material consisting of iron (95-98%) and graphite (2-5%). Bearings and bushings for various machine components and mechanisms are made from it.

Fiberglass is also a composite material, which is a mixture of glass fibers and hardened resin.

Human and animal bones are a composite material consisting of two completely different components: collagen and mineral matter.

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.

>>Physics: Amorphous bodies

Not all solids are crystals. There are many amorphous bodies. How are they different from crystals?
Amorphous bodies do not have a strict order in the arrangement of atoms. Only the nearest neighbor atoms are arranged in some order. But there is no strict repeatability in all directions of the same structural element, which is characteristic of crystals, in amorphous bodies.
In terms of the arrangement of atoms and their behavior, amorphous bodies are similar to liquids.
Often the same substance can be found in both crystalline and amorphous states. For example, quartz SiO 2 can be in either crystalline or amorphous form (silica). The crystalline form of quartz can be schematically represented as a lattice of regular hexagons ( Fig. 12.6, a). The amorphous structure of quartz also has the appearance of a lattice, but of irregular shape. Along with hexagons, it contains pentagons and heptagons ( Fig. 12.6, b).
Properties of amorphous bodies. All amorphous bodies are isotropic, that is, their physical properties are the same in all directions. Amorphous bodies include glass, resin, rosin, sugar candy, etc.
Under external influences, amorphous bodies exhibit both elastic properties, like solids, and fluidity, like liquids. Thus, under short-term impacts (impacts), they behave like solid bodies and, under a strong impact, break into pieces. But with very long exposure, amorphous bodies flow. You can see this for yourself if you are patient. Follow the piece of resin that is lying on a hard surface. Gradually the resin spreads over it, and the higher the temperature of the resin, the faster this happens.
Atoms or molecules of amorphous bodies, like molecules of a liquid, have a certain time of “settled life” - the time of oscillations around the equilibrium position. But unlike liquids, this time is very long.
So, for var at t= 20°C “settled life” time is approximately 0.1 s. In this respect, amorphous bodies are close to crystalline ones, since jumps of atoms from one equilibrium position to another occur relatively rarely.
Amorphous bodies at low temperatures resemble solid bodies in their properties. They have almost no fluidity, but as the temperature rises they gradually soften and their properties become closer and closer to the properties of liquids. This happens because with increasing temperature, jumps of atoms from one equilibrium position to another gradually become more frequent. Certain melting point Amorphous bodies, unlike crystalline ones, do not.
Liquid crystals. In nature, there are substances that simultaneously possess the basic properties of a crystal and a liquid, namely anisotropy and fluidity. This state of matter is called liquid crystal. Liquid crystals are mainly organic substances whose molecules have a long thread-like or flat plate shape.
Let us consider the simplest case, when a liquid crystal is formed by thread-like molecules. These molecules are located parallel to each other, but are randomly shifted, i.e., order, unlike ordinary crystals, exists only in one direction.
During thermal motion, the centers of these molecules move randomly, but the orientation of the molecules does not change, and they remain parallel to themselves. Strict molecular orientation does not exist throughout the entire volume of the crystal, but in small regions called domains. Refraction and reflection of light occurs at the domain boundaries, which is why liquid crystals are opaque. However, in a layer of liquid crystal placed between two thin plates, the distance between which is 0.01-0.1 mm, with parallel depressions of 10-100 nm, all the molecules will be parallel and the crystal will become transparent. If electrical voltage is applied to some areas of the liquid crystal, the liquid crystal state is disrupted. These areas become opaque and begin to glow, while the areas without tension remain dark. This phenomenon is used in the creation of liquid crystal television screens. It should be noted that the screen itself consists of a huge number of elements and the electronic control circuit for such a screen is extremely complex.
Solid state physics. Humanity has always used and will continue to use solids. But if previously solid state physics lagged behind the development of technology based on direct experience, now the situation has changed. Theoretical research leads to the creation of solids whose properties are completely unusual.
It would be impossible to obtain such bodies by trial and error. The creation of transistors, which will be discussed later, is a striking example of how understanding the structure of solids led to a revolution in all radio engineering.
Obtaining materials with specified mechanical, magnetic, electrical and other properties is one of the main directions of modern solid state physics. Approximately half of the world's physicists now work in this area of ​​physics.
Amorphous solids occupy an intermediate position between crystalline solids and liquids. Their atoms or molecules are arranged in relative order. Understanding the structure of solids (crystalline and amorphous) allows you to create materials with desired properties.

???
1. How do amorphous bodies differ from crystalline bodies?
2. Give examples of amorphous bodies.
3. Would the glassblowing profession have arisen if glass had been a crystalline solid rather than an amorphous one?

G.Ya.Myakishev, B.B.Bukhovtsev, N.N.Sotsky, Physics 10th grade

If you have corrections or suggestions for this lesson,

Solids are divided into amorphous and crystalline, depending on their molecular structure and physical properties.

Unlike crystals, the molecules and atoms of amorphous solids do not form a lattice, and the distance between them fluctuates within a certain range of possible distances. In other words, in crystals, atoms or molecules are mutually arranged in such a way that the formed structure can be repeated throughout the entire volume of the body, which is called long-range order. In the case of amorphous bodies, the structure of molecules is preserved only relative to each one such molecule, a pattern is observed in the distribution of only neighboring molecules - short-range order. An illustrative example is presented below.

Amorphous bodies include glass and other substances in a glassy state, rosin, resins, amber, sealing wax, bitumen, wax, as well as organic substances: rubber, leather, cellulose, polyethylene, etc.

Properties of amorphous bodies

The structural features of amorphous solids give them individual properties:

1. Weak fluidity is one of the most well-known properties of such bodies. An example would be glass drips that have been sitting in a window frame for a long time.
2. Amorphous solids do not have a specific melting point, since the transition to a liquid state during heating occurs gradually, through softening of the body. For this reason, the so-called softening temperature range is applied to such bodies.

1. Due to their structure, such bodies are isotropic, that is, their physical properties do not depend on the choice of direction.
2. A substance in an amorphous state has greater internal energy than in a crystalline state. For this reason, amorphous bodies are able to independently transform into a crystalline state. This phenomenon can be observed as a result of glass becoming cloudy over time.

Glassy state

In nature, there are liquids that are practically impossible to transform into a crystalline state by cooling, since the complexity of the molecules of these substances does not allow them to form a regular crystal lattice. Such liquids include molecules of some organic polymers.

However, with the help of deep and rapid cooling, almost any substance can transform into a glassy state. This is an amorphous state that does not have a clear crystal lattice, but can partially crystallize on the scale of small clusters. This state of matter is metastable, that is, it persists under certain required thermodynamic conditions.

Using cooling technology at a certain speed, the substance will not have time to crystallize and will be converted into glass. That is, the higher the cooling rate of the material, the less likely it is to crystallize. For example, to produce metal glasses, a cooling rate of 100,000 - 1,000,000 Kelvin per second will be required.

In nature, the substance exists in a glassy state and arises from liquid volcanic magma, which, interacting with cold water or air, quickly cools. In this case, the substance is called volcanic glass. You can also observe glass formed as a result of the melting of a falling meteorite interacting with the atmosphere - meteorite glass or moldavite.

Along with crystalline solids, amorphous solids are also found. Amorphous bodies, unlike crystals, do not have a strict order in the arrangement of atoms. Only the closest atoms - neighbors - are arranged in some order. But

There is no strict repeatability in all directions of the same structural element, which is characteristic of crystals, in amorphous bodies.

Often the same substance can be found in both crystalline and amorphous states. For example, quartz can be in either crystalline or amorphous form (silica). The crystalline form of quartz can be schematically represented as a lattice of regular hexagons (Fig. 77, a). The amorphous structure of quartz also has the appearance of a lattice, but of irregular shape. Along with hexagons, it contains pentagons and heptagons (Fig. 77, b).

Properties of amorphous bodies. All amorphous bodies are isotropic: their physical properties are the same in all directions. Amorphous bodies include glass, many plastics, resin, rosin, sugar candy, etc.

Under external influences, amorphous bodies exhibit both elastic properties, like solids, and fluidity, like liquids. Under short-term impacts (impacts), they behave like a solid body and, with a strong impact, break into pieces. But with very long exposure, amorphous bodies flow. For example, a piece of resin gradually spreads over a solid surface. Atoms or molecules of amorphous bodies, like molecules of a liquid, have a certain “settled life” time, the time of oscillations around the equilibrium position. But unlike liquids, this time is very long. In this respect, amorphous bodies are close to crystalline ones, since jumps of atoms from one equilibrium position to another rarely occur.

At low temperatures, amorphous bodies resemble solids in their properties. They have almost no fluidity, but as the temperature rises they gradually soften and their properties become closer and closer to the properties of liquids. This happens because with increasing temperature, jumps of atoms from one position gradually become more frequent.

balance to another. There is no specific melting point for amorphous bodies, unlike crystalline ones.

Solid state physics. All properties of solids (crystalline and amorphous) can be explained on the basis of knowledge of their atomic-molecular structure and the laws of motion of molecules, atoms, ions and electrons that make up solids. Studies of the properties of solids are united in a large field of modern physics - solid state physics. The development of solid state physics is stimulated mainly by the needs of technology. Approximately half of the world's physicists work in the field of solid state physics. Of course, achievements in this area are unthinkable without deep knowledge of all other branches of physics.

1. How do crystalline bodies differ from amorphous ones? 2. What is anisotropy? 3. Give examples of monocrystalline, polycrystalline and amorphous bodies. 4. How do edge dislocations differ from screw dislocations?