A solid is one of the four fundamental states of matter, besides liquid, gas and plasma. It is characterized by structural rigidity and resistance to changes in shape or volume. Unlike a liquid, a solid object does not flow or take the shape of the container in which it is placed. A solid does not expand to fill the entire available volume as a gas does.
Atoms in a solid are closely connected to each other, are in an ordered state at the nodes of the crystal lattice (these are metals, ordinary ice, sugar, salt, diamond), or are arranged irregularly, do not have strict repeatability in the structure of the crystal lattice (these are amorphous bodies, such How window glass, rosin, mica or plastic).
Crystalline solids or crystals have a distinctive internal feature- a structure in the form of a crystal lattice in which atoms, molecules or ions of a substance occupy a certain position.
The crystal lattice leads to the existence of special flat faces in crystals, which distinguish one substance from another. When exposed to X-rays, each crystal lattice emits a characteristic pattern that can be used to identify the substance. The edges of crystals intersect at certain angles that distinguish one substance from another. If the crystal is split, the new faces will intersect at the same angles as the original.
For example, galena - galena, pyrite - pyrite, quartz - quartz. The crystal faces intersect at right angles in galena (PbS) and pyrite (FeS 2), and at other angles in quartz.
Examples of amorphous bodies that do not have a strict structure and repeatability of crystal lattice cells are: glass, resin, Teflon, polyurethane, naphthalene, polyvinyl chloride.
They have two characteristic properties: isotropy and lack of a specific melting point.
Isotropy of amorphous bodies is understood as the sameness physical properties substances in all directions.
In an amorphous solid, the distance to neighboring nodes of the crystal lattice and the number of neighboring nodes varies throughout the material. Therefore, different amounts of thermal energy are required to break intermolecular interactions. Consequently, amorphous substances soften slowly in wide range temperatures and do not have a clear melting point.
A feature of amorphous solids is that at low temperatures they have the properties of solids, and when the temperature rises, they have the properties of liquids.
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 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 in contrast to crystals, they 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.
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 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 environment, and their properties are constant. Such substances are called isotropic.
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.
As mentioned above, amorphous bodies do not have a crystal lattice. Their atoms and molecules have a short order of placement, which will be the first distinctive feature of these substances.
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.
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.
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.
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.
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.
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.
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 about which we're talking about, 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 are better known to an ordinary person called 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. Special attention it did not cause 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, quite high level strength and corrosion resistance.
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 is not stored in long distances, like crystalline bodies.
Examples of amorphous bodies are glass, amber, artificial resins, wax, paraffin, plasticine, etc.
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 solids behave when heated? crystalline bodies? 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.
Let's put a piece of plasticine nearby 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 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 occurs in different substances with at different speeds. We see candy canes becoming covered in sugar crystals. This does not take very 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.
In crystalline solids, physical properties vary according to 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.
Properties amorphous substances 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.
Amorphous bodies
Amorphous substances (bodies)(from ancient Greek. ἀ "not-" and μορφή "type, form") - a condensed state of a substance, the atomic structure of which has short-range order and does not have long-range order, characteristic of crystal structures. Unlike crystals, stable amorphous substances do not solidify with the formation of crystalline faces, and (unless they were under a strong anisotropic influence - compression or electric field, for example) they have isotropic properties, that is, they do not exhibit different properties in different directions. And they do not have a specific melting point: with increasing temperature, stable amorphous substances gradually soften and above the glass transition temperature (T g) they turn into a liquid state. Substances with a high crystallization rate, usually having a (poly-)crystalline structure, but strongly supercooled during solidification 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 substances.
They are obtained at a high rate of solidification (cooling) of a liquid melt or by condensation of vapors onto a substrate (any object) cooled noticeably below the MELTING temperature (not boiling!). The ratio of the actual cooling rate (dT/dt) and the characteristic crystallization rate determines the proportion of polycrystals in the amorphous volume. The rate of crystallization is a parameter of a substance that weakly depends on pressure and temperature (strongly around the melting point). And it strongly depends on the complexity of the composition - for metals it is on the order of fractions to tens of milliseconds; and for glass at room temperature- hundreds and thousands of years (old glass and mirrors become cloudy).
Electrical and mechanical properties amorphous substances are closer to those for single crystals than for polycrystals due to the absence of sharp and heavily contaminated intercrystalline transitions (boundaries) with often a 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.
At external influences amorphous substances exhibit both elastic properties, like crystalline solids, and fluidity, like liquids. Thus, under short-term impacts (impacts), they behave like solid substances and, with a strong impact, break into pieces. But with very prolonged exposure (for example, stretching), amorphous substances flow. For example, resin (or tar, bitumen) is also an amorphous substance. If you break it into small parts and fill the vessel with the resulting mass, then after some time the resin will merge into a single whole and take the shape of the vessel.
Depending on the electrical properties, separate amorphous metals, amorphous nonmetals, and amorphous semiconductors.
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