Unlike crystalline solids, there is no strict order in the arrangement of particles in an amorphous body.
Although amorphous solids are able to retain their shape, they do not have a crystal lattice. Some regularity is observed only for molecules and atoms located in the neighborhood. This order is called short-range order . It is not repeated in all directions and is not preserved over long distances, as in crystalline bodies.
Examples of amorphous bodies are glass, amber, artificial resins, wax, paraffin, plasticine, etc.
Features of amorphous bodies
Atoms in amorphous bodies oscillate 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 of their oscillation 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 all the substance is melted.
Amorphous bodies do not have a specific melting point. . When heated, they do not melt, but gradually soften.
Put a piece of plasticine near the heating device. After a while it will become soft. This does not happen instantly, but over a period of time.
Since the properties of amorphous bodies are similar to those of liquids, they are considered as supercooled liquids with a very high viscosity (solidified 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. Heating the mixture to 1400 about C, get a liquid vitreous mass. When cooled, liquid glass does not solidify, like crystalline bodies, but remains a liquid, the viscosity of which increases, and the fluidity decreases. Under ordinary conditions, it appears to us as a solid body. But in fact it is a liquid that has an enormous viscosity and fluidity, so small that it can hardly be distinguished by the most ultra-sensitive instruments.
The amorphous state of matter is unstable. Over time, from an amorphous state, it gradually turns into a crystalline one. This process in different substances takes place at different speeds. We see how sugar crystals cover sugar candies. This does not take much time.
And in order 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, the physical properties differ in different directions. And in amorphous bodies they are the same in all directions. This phenomenon is called isotropy .
An amorphous body equally conducts electricity and heat in all directions, and refracts light equally. Sound also propagates 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 are amorphous solids. They are called metal glasses . Their physical, mechanical, electrical and other properties differ from similar properties of conventional metals for the better.
So, in medicine, amorphous alloys are used, the strength of which 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 by bone material over time.
High-strength alloys are used in the manufacture of metal-cutting tools, fittings, springs, and parts of mechanisms.
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 a factor of 20.
Amorphous metals have unique properties. They are called the material of the future.
Amorphous bodies
Amorphous substances (bodies)(from other Greek. ἀ "not-" and μορφή "type, form") - a condensed state of matter, the atomic structure of which has a short-range order and does not have a long-range order, characteristic of crystalline structures. Unlike crystals, stably amorphous substances do not solidify with the formation of crystalline faces, and (if they were not under the strongest anisotropic influence - compression or an electric field, for example) have isotropy of properties, that is, they do not exhibit different properties in different directions. And they do not have a specific melting point: with increasing temperature, stably amorphous substances gradually soften and above the glass transition temperature (T g) they pass into a liquid state. Substances with a high crystallization rate, usually having a (poly-)crystalline structure, but strongly supercooled when solidifying into an amorphous state, upon subsequent heating, shortly before melting, recrystallize (in the solid state with little heat release), and then melt as ordinary polycrystalline.
They are obtained at a high rate of solidification (cooling) of a liquid melt or by condensation of vapors on a substrate cooled noticeably below the MELTING temperature (not boiling!) (any object). The ratio of the real cooling rate (dT/dt) and the characteristic crystallization rate determines the proportion of polycrystals in the amorphous volume. The crystallization rate is a parameter of a substance that weakly depends on pressure and temperature (strongly near the melting point). And strongly dependent on the complexity of the composition - for metals of the order of fractions or tens of milliseconds; and for glasses at room temperature - hundreds and thousands of years (old glasses and mirrors become cloudy).
The electrical and mechanical properties of amorphous substances are closer to those for single crystals than for polycrystals due to the absence of sharp and heavily contaminated with impurities intercrystalline transitions (boundaries) with often completely different chemical composition.
The non-mechanical properties of semi-amorphous states are usually intermediate between amorphous and crystalline, and are isotropic. However, the absence of sharp intercrystalline transitions noticeably affects the electrical and mechanical properties, making them similar to amorphous ones.
Under external influences, amorphous substances exhibit both elastic properties, like crystalline solids, and fluidity, like a liquid. So, with short-term impacts (impacts), they behave like solid substances and, with a strong impact, break into pieces. But with a very long exposure (for example, stretching), amorphous substances flow. For example, resin (or tar, bitumen) is also an amorphous substance. If you crush it into small parts and fill the vessel with the resulting mass, then after a while the resin will merge into a single whole and take the form of a vessel.
Depending on the electrical properties, amorphous metals, amorphous non-metals, and amorphous semiconductors are divided.
see also
(obsolete term)Wikimedia Foundation. 2010 .
See what "Amorphous bodies" are in other dictionaries:
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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 are close order. This means that a certain order 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 arrangement of particles in the amorphous form of the existence of quartz. These substances consist of the same particles - molecules of silicon oxide SiO2.
Like the particles of any body, particles of amorphous bodies vibrate 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 not equally dense - in some places there are relatively large gaps between their particles. However, this is not the same as "vacancies" in crystals (see § 7-e).
Crystallization of amorphous bodies. Over time (weeks, months), some amorphous bodies spontaneously go into a crystalline state. For example, sugar candy or honey, left alone for several months, becomes opaque. In this case, they say that honey and candies are "candied". Breaking a sugared candy or scooping up honey with a spoon, we really see the formed sugar crystals, which previously existed in an amorphous state.
Spontaneous crystallization of amorphous bodies indicates that the crystalline state of matter is more stable than the amorphous state. MKT explains it this way. The repulsive forces of the "neighbors" cause the particles of the amorphous body to move mainly to where there are large gaps. As a result, a more ordered arrangement of particles occurs, that is, crystallization occurs.
Test yourself:
- The purpose of this section is to introduce...
- What comparative characteristic did we give to amorphous bodies?
- For the experiment we use the following equipment and materials: ...
- While preparing for the experience, we...
- What will we see in the course of the experiment?
- What is the result of the experiment with a stearin candle and a piece of plasticine?
- Unlike amorphous bodies, crystalline bodies...
- When a crystalline body melts...
- Unlike crystalline solids, amorphous...
- Amorphous bodies include bodies for which ...
- What makes amorphous bodies look like liquids? They...
- Describe the beginning of the experiment to confirm the fluidity of amorphous bodies.
- Describe the result of an experiment to confirm the fluidity of amorphous bodies.
- Formulate a conclusion from experience.
- How do we know that amorphous bodies do not have a strict order in the arrangement of their particles?
- How do we understand the term "short range order" in the arrangement of particles of an amorphous body?
- The same molecules of silicon oxide are available both in crystalline and ...
- What is the nature of the movement of particles of an amorphous body?
- What is the nature of the arrangement of particles of an amorphous body?
- What can happen to amorphous bodies over time?
- How can you be sure of the presence of polycrystals of sugar in a candy or in candied honey?
- Why do we believe that the crystalline state of matter is more stable than the amorphous state?
- How does MKT explain the independent crystallization of some amorphous bodies?
Solids are characterized by constancy of shape and volume and are divided into crystalline and amorphous.
Crystalline bodies
Crystalline bodies (crystals) are solids whose atoms or molecules occupy ordered positions in space.Particles of crystalline bodies form a regular pattern in space. crystal lattice.
Each chemical substance in the 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 shiny white pewter buttons. And suddenly they began to darken, lose their luster and crumble into powder. In a few days, the mountains of buttons turned into a pile of gray powder. "Tin Plague"- so they called this "disease" of white tin.
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 tin crystals, but at low temperatures their crystal structure changes, and as a result, the physical properties of the substance change.
Crystals can have various shapes and are limited to flat faces.
In nature there are:
a) single crystals- these are single homogeneous crystals having the shape of regular polygons and having a continuous crystal lattice
Salt monocrystals:
b) polycrystals- These are crystalline bodies fused from small, randomly arranged crystals.
Most solids have a polycrystalline structure (metals, stones, sand, sugar).
Bismuth polycrystals:
Anisotropy of crystals
In crystals, there is 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 usual state.
Polycrystals consist of a large number of small crystalline grains. Although each of them has anisotropy, but due to the randomness 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 disturb 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 - there is a crystal. The structure of the particles was disturbed - it means that the crystal melted - turned into a liquid, or evaporated - turned into vapor.
Amorphous bodies
Amorphous bodies do not have a strict order in the arrangement of atoms and molecules (glass, resin, amber, rosin).
In amphatic bodies, there is isotropy- their physical properties are the same in all directions.
Under external influences, amorphous bodies exhibit simultaneously elastic properties (on impact, 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.
The same substance It can be found in both crystalline and non-crystalline form.
In a liquid melt of a substance, particles move completely randomly.
If, for example, sugar is melted, then:
1. If the melt solidifies slowly, calmly, then the particles are collected in even rows and crystals are formed. This is how granulated sugar or lump sugar is obtained;
2. if the cooling occurs very quickly, then the particles do not have time to build up in regular rows and the melt solidifies non-crystalline. So, if melted sugar is poured into cold water or on a very cold saucer, sugar candy, non-crystalline sugar, is formed.
Marvelous!
Over time, a non-crystalline substance can "reborn", or, more precisely, crystallize, the particles in them gather in regular rows.
Only the period for different substances is different: for sugar it is several months, and for a stone it is millions of years.
Let the lollipop lie quietly for two or three months. It will be covered with a loose crust. Look at it through a magnifying glass: these are small sugar crystals. Crystals began to grow in non-crystalline sugar. Wait a few more months - and not only the crust, but the whole lollipop 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 the furnace than to knock out a stubborn "goat" from it.
Having studied it, scientists have created a new very durable glass material - glass-ceramic. This is a glass-ceramic material obtained as a result of bulk crystallization of glass.
Curious!
There may be different crystal forms the same substance.
For example, carbon.
Graphite is crystalline carbon. Graphite is used to make pencil stems that leave a mark on paper when lightly pressed. The structure of graphite is layered. The graphite layers slide easily, so the graphite flakes stick to the paper when writing.
But there is another form of crystalline carbon - diamond.
Along with crystalline solids, there are amorphous solids. Amorphous bodies, unlike crystals, do not have a strict order in the arrangement of atoms. Only the nearest atoms - neighbors - are arranged in some order. But
there is no strict repetition in all directions of the same structural element, which is characteristic of crystals, in amorphous bodies.
Often the same substance can be in both a crystalline and an amorphous state. For example, quartz can be in both crystalline and 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 of an 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. With short-term impacts (impacts), they behave like a solid body and, with a strong impact, break into pieces. But with a very long exposure, amorphous bodies flow. So, for example, a piece of resin gradually spreads over a solid surface. Atoms or molecules of amorphous bodies, like liquid molecules, have a certain time of "settled life" - the time of oscillations around the equilibrium position. But unlike liquids, they have a very long time. 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 solid bodies in their properties. They have almost no fluidity, but as the temperature rises, they gradually soften and their properties more and more approach those of liquids. This is because as the temperature rises, jumps of atoms from one position gradually become more frequent.
balance to another. Amorphous bodies, unlike crystalline ones, have no specific melting point.
Solid state physics. All properties of solids (crystalline and amorphous) can be explained on the basis of knowledge of their atomic and 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 area 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 single-crystal, polycrystalline and amorphous bodies. 4. How do edge dislocations differ from screw ones?