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 amorphous bodies glass, various hardened resins (amber), plastics, etc. can serve. 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.
Disorder in the arrangement of atoms of amorphous bodies leads to the fact that the average distance between atoms is different directions the same, so they are isotropic, i.e. all physical properties(mechanical, optical, etc.) do not depend on the direction of external influence. Signs of an amorphous body are irregular shape fractured surfaces. 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. Majority crystalline bodies consists of many randomly located small crystals that have grown together. Such bodies are called polycrystals. A piece of sugar is a polycrystalline body. Crystals various substances have a variety of 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.
So many bodies are the same chemical composition in the crystalline state, depending on conditions, they 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, i.e. they exhibit identical 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 mechanical properties which are superior to natural materials. Composite materials (composites) consist of a matrix and fillers. Polymer, metal, carbon or ceramic materials. 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 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 are made from it different nodes machines and mechanisms.
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.
Let's do an experiment. We will need a piece of plasticine, a stearin 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 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.
Have you ever wondered what these mysterious amorphous substances are? They differ in structure from both solids and liquids. The fact is that such bodies are in a special condensed state, which has only short-range order. Examples amorphous substances- resin, glass, amber, rubber, polyethylene, polyvinyl chloride (our favorite plastic windows), various polymers and others. These are solids that do not have a crystal lattice. These also include sealing wax, various adhesives, ebonite and plastics.
During cleavage, no edges are formed in amorphous solids. The particles are completely random and are located at close distances from each other. They can be either very thick or viscous. How are they affected by external influences? Influenced different temperatures bodies become fluid, like liquids, and at the same time quite elastic. In case external influence does not last long, substances of an amorphous structure can break into pieces with a powerful blow. Long-term influence from outside leads to the fact that they simply flow.
Try a little resin experiment at home. Put it on hard surface, and you will notice that it begins to spread smoothly. That's right, it's substance! The speed depends on the temperature readings. If it is very high, the resin will begin to spread noticeably faster.
What else is characteristic of such bodies? They can take any form. If amorphous substances in the form of small particles are placed in a vessel, for example, in a jug, then they will also take the shape of the vessel. They are also isotropic, that is, they exhibit the same physical properties in all directions.
The amorphous state of a substance does not imply the maintenance of any specific temperature. At low values the bodies freeze, at high values they melt. By the way, the degree of viscosity of such substances also depends on this. Low temperature promotes reduced viscosity, high temperature, on the contrary, increases it.
For substances of the amorphous type, one more feature can be distinguished - the transition to a crystalline state, and a spontaneous one. Why is this happening? The internal energy in a crystalline body is much less than in an amorphous one. We can notice this in the example of glass products - over time, the glass becomes cloudy.
Metallic glass - what is it? The metal can be removed from the crystal lattice during melting, that is, a substance with an amorphous structure can be made glassy. During solidification during artificial cooling, the crystal lattice is formed again. Amorphous metal has amazing resistance to corrosion. For example, a car body made from it would not need various coatings, since it would not be subject to spontaneous destruction. An amorphous substance is a body whose atomic structure has unprecedented strength, which means that an amorphous metal could be used in absolutely any industrial sector.
In order to have a good understanding of the characteristics of metals and be able to work with them, you need to have knowledge of the crystalline structure of certain substances. The production of metal products and the field of metallurgy could not have developed so much if people did not have certain knowledge about changes in the structure of alloys, technological techniques and operational characteristics.
It is well known that there are four states of aggregation: solid, liquid, gaseous, plasma. Amorphous solids can also be crystalline. With this structure, spatial periodicity in the arrangement of particles can be observed. These particles in crystals can perform periodic motion. In all bodies that we observe in a gaseous or liquid state, we can notice the movement of particles in the form of a chaotic disorder. Amorphous solids (for example, metals in a condensed state: hard rubber, glass products, resins) can be called frozen liquids, because when they change shape, you can notice such characteristic feature, like viscosity.
Manifestations of plasticity, elasticity, and hardening during deformation are characteristic of many bodies. Crystalline and amorphous substances exhibit these characteristics to a greater extent, while liquids and gases do not have such properties. But you can notice that they contribute to an elastic change in volume.
What are crystalline and amorphous substances? As mentioned above, those bodies that have a huge viscosity coefficient can be called amorphous, and their fluidity is impossible at ordinary temperatures. And here heat, on the contrary, allows them to be fluid, like a liquid.
Substances of the crystalline type appear to be completely different. These solids can have their own melting point, depending on external pressure. Obtaining crystals is possible if the liquid is cooled. If you do not take certain measures, you will notice that various crystallization centers begin to appear in the liquid state. In the area surrounding these centers, formation occurs solid. Very small crystals begin to connect with each other in a random order, and a so-called polycrystal is obtained. Such a body is isotropic.
What determines physical and mechanical characteristics tel? Atomic bonds are important, as well as the type crystal structure. Ionic crystals are characterized by ionic bonds, which means a smooth transition from one atom to another. In this case, the formation of positively and negatively charged particles occurs. Ionic bond we can watch on simple example- such characteristics are characteristic of various oxides and salts. Another feature of ionic crystals is low thermal conductivity, but its performance can increase noticeably when heated. At the nodes of the crystal lattice you can see various molecules that are distinguished by strong atomic bonds.
Many minerals that we find throughout nature have a crystalline structure. And the amorphous state of matter is also nature in pure form. Only in this case the body is something shapeless, but crystals can take the form of beautiful polyhedrons with flat edges, and also form new solid bodies of amazing beauty and purity.
The shape of such bodies is constant for a particular compound. For example, beryl always looks like a hexagonal prism. Try a little experiment. Take a small crystal table salt cubic shape (ball) and put it in a special solution as saturated as possible with the same table salt. Over time, you will notice that this body has remained unchanged - it has again acquired the shape of a cube or ball, which is characteristic of table salt crystals.
3. - polyvinyl chloride, or the well-known plastic PVC windows. It is resistant to fires, as it is considered low-flammable, has an increased mechanical strength and electrical insulating properties.
4. Polyamide is a substance with very high strength and wear resistance. It is characterized by high dielectric characteristics.
5. Plexiglas, or polymethyl methacrylate. We can use it in the field of electrical engineering or use it as a material for structures.
6. Fluoroplastic, or polytetrafluoroethylene, is a well-known dielectric that does not exhibit dissolution properties in solvents of organic origin. A wide temperature range and good dielectric properties allow it to be used as a hydrophobic or anti-friction material.
7. Polystyrene. This material is not affected by acids. It, like fluoroplastic and polyamide, can be considered a dielectric. Very durable against mechanical impact. Polystyrene is used everywhere. For example, it has proven itself well as a structural and electrical insulating material. Used in electrical and radio engineering.
8. Probably the most famous polymer for us is polyethylene. The material is resistant to exposure to aggressive environments; it is absolutely impermeable to moisture. If the packaging is made of polyethylene, there is no fear that the contents will deteriorate when exposed to heavy rain. Polyethylene is also a dielectric. Its application is extensive. It is used to make pipe structures, various electrical products, insulating film, sheaths for telephone and power line cables, parts for radio and other equipment.
9. Polyvinyl chloride is a high-polymer substance. It is synthetic and thermoplastic. It has a molecular structure that is asymmetrical. It is almost impervious to water and is made by pressing, stamping and molding. Polyvinyl chloride is most often used in the electrical industry. Based on it, various heat-insulating hoses and hoses for chemical protection, battery banks, insulating sleeves and gaskets, wires and cables are created. PVC is also an excellent replacement for harmful lead. It cannot be used as a high-frequency circuit in the form of a dielectric. And all because in this case the dielectric losses will be high. Has high conductivity.
Let's do an experiment. We will need a piece of plasticine, a stearin 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.
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 - between their particles there are relatively large gaps. 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.
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