There are several aggregate states in which all bodies and substances are located. It:
If we consider the total set of the planet and the cosmos, then most of the substances and bodies are still in a state of gas and plasma. However, the content of solid particles is also significant on the Earth itself. 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 at the heart of the unit are signs of structure and manifested properties. In short, solid substances are those substances and bodies that have a certain type of spatial crystal lattice, that is, they have the ability to vary in a certain direction, but not all (anisotropy).
If we characterize amorphous compounds, then their first sign is the ability to change 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 well-defined structure consisting of ordered particles in space, then the second order is absent.
Properties of solids
Crystalline and amorphous bodies nevertheless belong to a single group of solid, and therefore possess all the characteristics of a given aggregate state. That is, the common properties for them will be the following:
- Mechanical - elasticity, hardness, ability to deformation.
- Thermal - the boiling point and melting point, the coefficient of thermal expansion.
- Electrical and magnetic - conductivity thermal and electrical.
Thus, the states considered by us have all these characteristics. Only in amorphous bodies they will appear somewhat differently than in crystalline bodies.
Important properties for industrial purposes are mechanical and electrical. The ability to recover after deformation or, on the contrary, to crumble and crush is an important feature. Also important is the fact that a substance can conduct an electric current or is incapable of it.
The structure of crystals
If we describe the structure of crystalline and amorphous bodies, then first of all we must specify the type of particles that make them up. 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 substance-forming particles. If we imagine the crystal structure in a figurative way, we get approximately the following picture: atoms (or other particles) are located at certain distances from each other so that the ideal unit cell of the future crystal lattice is obtained as a result. Then this cell is repeated many times, and so the general structure is formed.
The main feature is that physical properties in similar structures vary in parallels, but not in all directions. This phenomenon is called anisotropy. That is, if you act on one part of the crystal, then the second side may not react to it. So, you can grind half a piece of table salt, but the second will remain intact.
Types of crystals
It is customary to designate two variants of crystals. The first is a single-crystal structure, that is, when the lattice itself is 1. The crystalline and amorphous bodies in this case are quite different in properties. After all, an anisotropy in pure form is characteristic of a single crystal. It is the smallest structure, elementary.
If monocrystals are repeated many times and unite in a single whole, then we are talking about a polycrystal. Then there is no question of anisotropy, since the orientation of elementary cells breaks the general ordered structure. In this respect, polycrystals and amorphous bodies are close to one another according to the physical properties that are manifested.
Metals and their 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. In themselves, they are solid substances under normal conditions. However, at a certain temperature, they begin to melt and, until full crystallization occurs, will remain in a state of stretching, thick, viscous mass. And this is already an amorphous state of the body.
Therefore, strictly speaking, practically every crystalline substance can become amorphous under certain conditions. Just as the latter crystallizes into a solid with an ordered spatial structure.
Metals can have different types of spatial structures, the most famous and studied of which are the following:
- Simple cubic.
- The one-centered.
The structure of the crystal can be based on a prism or pyramid, and its main part is represented by:
Ideal properties of isotropy are possessed by a substance having a simple regular cubic lattice.
The notion of amorphism
Crystalline and amorphous bodies can be distinguished outwardly quite simply. After all, the latter can often be confused with viscous liquids. The structure of the 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.
The particles are randomly distributed. Only sometimes they can form small loci, which still does not affect the common manifest properties.
Properties of similar bodies
They are identical to those of crystals. Differences only in the indicators for each specific body. Thus, for example, one can single out such characteristic parameters of amorphous bodies:
- conductivity and semiconductivity.
It is often possible to find boundary states of compounds. Crystalline and amorphous bodies can become semi-amorphous.
Also of interest is the feature of the state under consideration, which manifests itself in a sharp external effect. So, if an amorphous body is subjected to a sharp shock or deformation, then it is capable of behaving like a polycrystal and split into small pieces. However, if we give these parts time, then they will soon reunite and go into a viscous fluid state.
This state of compounds does not have a definite temperature at which a phase transition occurs. This process is greatly stretched, sometimes even for tens of years (for example, decomposition of low-pressure polyethylene).
Examples of amorphous substances
There are many examples of such substances. Let us designate some of the most obvious and often encountered.
- 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 as the temperature is lowered. It is often difficult to call such substances solid, they are more likely to be viscous thick liquids.
Particular conditions have those compounds that, when solidified, do not crystallize at all. They are called glasses, and the state is glassy.
The properties of crystalline and amorphous bodies are similar, as we have explained, due to their common origin and unified inner nature. But sometimes a special state of substances called glassy is considered separately from them. It is a homogeneous mineral solution that crystallizes and solidifies without the formation of spatial gratings. That is, it remains isotropic in changing properties always.
For example, conventional window glass does not have an exact melting point value. It simply melts, softens and becomes liquid when the given index is raised. If the effect is stopped, then the reverse process will begin and solidification will start, but without crystallization.
Such substances are very much appreciated, glass today is one of the most common and sought-after building materials in the whole world.