There are several aggregative states in which all bodies and substances are located. It:
If we consider the total population of the planet and space, then most of the substances and bodies are still in a state of gas and plasma. However, on the Earth itself, the content of solid particles is also significant. Here we will talk about them, finding out what crystalline and amorphous solids are.
Crystalline and amorphous bodies: a general concept
All solids, bodies, objects are conditionally divided into:
The difference between them is huge, because the basis of the unit are the signs of the structure and manifested properties. Briefly, solid substances are those substances and bodies that have a certain type of spatial crystal lattice, that is, they have the ability to change in a certain direction, but not in all (anisotropy).
If, however, amorphous compounds are characterized, then their first sign is the ability to change the physical characteristics in all directions simultaneously. This is called isotropy.
The structure, properties of crystalline and amorphous bodies are completely different. If the former have a clearly limited structure consisting of orderly particles in space, then the latter has no order.
Properties of solids
Crystalline and amorphous bodies nevertheless belong to a single group of solids, and therefore, have all the characteristics of this aggregative state. That is, the general properties for them will be the following:
- Mechanical - elasticity, hardness, ability to deform.
- Heat - boiling and melting points, coefficient of thermal expansion.
- Electrical and magnetic - thermal and electrical conductivity.
Thus, the states under consideration possess all these characteristics. Only appear in amorphous bodies, they will be slightly different than the crystalline ones.
Important properties for industrial purposes are mechanical and electrical. The ability to recover from deformation or, on the contrary, to crumble and grind is an important feature. Also a big role is played by the fact that a substance can conduct an electric current or is not capable of it.
If we describe the structure of crystalline and amorphous bodies, then first of all it is necessary to indicate the type of particles that compose them. In the case of crystals, these can be ions, atoms, atom ions (in metals), molecules (rarely).
In general, these structures are characterized by the presence of a strictly ordered spatial lattice, which is formed as a result of the arrangement of the particles forming the substance. If you imagine the structure of a crystal figuratively, you will get something like this: atoms (or other particles) are spaced at certain distances from each other, so that the ideal unit cell of the future crystal lattice is obtained. Then this cell is repeated many times, and so the overall structure is formed.
The main feature is that the physical properties in such structures vary in parallel, but not in all directions. This phenomenon is called anisotropy. That is, if you act on one part of the crystal, the second side may not respond to it. So, you can grind half a piece of salt, but the second will remain intact.
Types of crystals
It is customary to designate two variants of crystals. The first is single-crystal structures, that is, when the lattice itself is 1. The crystalline and amorphous bodies in this case are completely different in properties. After all, a single crystal is characterized by anisotropy in its pure form. It is the smallest elementary structure.
If single crystals are repeated many times and are combined into one, then we are talking about a polycrystal. Then there is no talk about anisotropy, since the orientation of the unit cells violates the general ordered structure. In this respect, polycrystals and amorphous bodies are close to each other in their physical properties.
Metals and alloys
Crystalline and amorphous bodies are very close to each other. It is easy to verify this by taking metals and their alloys as an example. By themselves, they are under normal conditions solids. However, at a certain temperature, they begin to melt and, until complete crystallization occurs, they will remain in a state of stretching, thick, viscous mass. And this is already the amorphous state of the body.
Therefore, strictly speaking, almost every crystalline substance can, under certain conditions, become amorphous. Just as the latter during solidification, it becomes a solid with an ordered spatial structure.
Metals may have different types of spatial structures, the most famous and studied of which are the following:
- Simple cubic.
The structure of the crystal may be based on a prism or a pyramid, and its main part is represented by:
- a triangle;
- by square;
A substance having a simple regular cubic lattice possesses ideal isotropic properties.
The concept of amorphous
Crystalline and amorphous bodies outwardly simple enough to distinguish. After all, the latter can often be confused with viscous liquids. The structure of an amorphous substance is also based on ions, atoms, molecules. However, they do not form an ordered strict structure, and therefore their properties change in all directions. That is, they are isotropic.
Particles are arranged randomly, randomly. Only sometimes they can form small loci, which still does not affect the general properties shown.
Properties of similar bodies
They are identical to those of crystals. The differences are only in indicators for each particular body. So, for example, we can distinguish such characteristic parameters of amorphous bodies:
- conductivity and semiconductivity.
Often you can meet the boundary conditions of the compounds. Crystalline and amorphous bodies can become semi-amorphous.
Also interesting is the feature of the state under consideration, which manifests itself with a sharp external influence. So, if an amorphous body is subjected to a sharp blow or deformation, then it is capable of behaving like a polycrystal and splitting into small pieces. However, if we give these parts time, they will soon be connected together again and will turn into a viscous fluid state.
This state of the compounds does not have a specific temperature at which a phase transition occurs. This process is greatly extended, sometimes even for decades (for example, decomposition of low-pressure polyethylene).
Examples of amorphous substances
Many examples of such substances can be cited. Let's designate some most evident and often met.
- Chocolate is a typical amorphous substance.
- Resins, including phenol-formaldehyde, all plastics.
- Glass of any composition.
- Wax and others.
An amorphous body is formed as a result of very slow crystallization, that is, an increase in the viscosity of the solution with a decrease in temperature. It is often difficult to call such substances solid, rather they are referred to viscous thick liquids.
Compounds that do not crystallize at all upon solidification have a special state. They are called glasses, and the state - glassy.
The properties of crystalline and amorphous bodies are similar, as we found out, due to their common origin and a single internal nature. But sometimes they are separately considered a special state of substances, called vitreous. It is a homogeneous mineral solution that crystallizes and hardens without the formation of spatial lattices. That is, it remains isotropic in terms of changing properties always.
For example, a conventional window glass does not have the exact value of the melting point. It just with the increase of this indicator slowly melts, softens and turns into a liquid state. If the effect is stopped, then the reverse process will begin and solidification will begin, but without crystallization.
Such substances are very much appreciated, glass today is one of the most common and sought-after building materials worldwide.