Along with crystalline solids, amorphous solids are also found. U amorphous bodies Unlike crystals, there is no 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 form of a lattice, but 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 the same in all directions. Amorphous bodies include glass, many plastics, resin, rosin, sugar candy, etc.
At 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 at very prolonged exposure amorphous bodies flow. For example, a piece of resin gradually spreads over a solid surface. Atoms or molecules of amorphous bodies, like liquid molecules, have certain time“sedentary life” is 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. No certain temperature Amorphous bodies, unlike crystalline ones, do not melt.
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 combined into large area 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 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?
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, crystal lattice They dont have. 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 is not stored in long distances like 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). At 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 cooling 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 in different substances passes with at different speeds. 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. Special interest cause 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.
« Physics - 10th grade"
In addition to solids that have crystal structure, which is characterized in strict order in the arrangement of atoms, amorphous solids exist.
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.
Theoretical research lead to the production 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, - shining example how understanding the structure of solids led to a revolution in all radio technology.
Obtaining materials with specified mechanical, magnetic, electrical and other properties is one of the main directions of modern solid state physics.
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 put plasticine and a candle on 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 from solid state turns immediately into 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 almost forever own form, amorphous bodies exhibit fluidity even at low temperatures. Therefore, they can be considered as very thick and viscous liquids.
The structure of amorphous bodies. Research 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 solid body 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 specific heat melting 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.
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 temperature increases, energy oscillatory 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 body goes into 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.